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Sample records for negatively charged molecules

  1. Astronomers Discover First Negatively-charged Molecule in Space

    NASA Astrophysics Data System (ADS)

    2006-12-01

    Cambridge, MA - Astronomers have discovered the first negatively charged molecule in space, identifying it from radio signals that were a mystery until now. While about 130 neutral and 14 positively charged molecules are known to exist in interstellar space, this is the first negative molecule, or anion, to be found. "We've spotted a rare and exotic species, like the white tiger of space," said astronomer Michael McCarthy of the Harvard-Smithsonian Center for Astrophysics (CfA). By learning more about the rich broth of chemicals found in interstellar space, astronomers hope to explain how the young Earth converted these basic ingredients into the essential chemicals for life. This new finding helps to advance scientists' understanding of the chemistry of the interstellar medium, and hence the birthplaces of planets. McCarthy worked with CfA colleagues Carl Gottlieb, Harshal Gupta (also from the Univ. of Texas), and Patrick Thaddeus to identify the molecular anion known as C6H-: a linear chain of six carbon atoms with one hydrogen atom at the end and an "extra" electron. Such molecules were thought to be extremely rare because ultraviolet light that suffuses space easily knocks electrons off molecules. The large size of C6H-, larger than most neutral and all positive molecules known in space, may increase its stability in the harsh cosmic environment. "The discovery of C6H- resolves a long-standing enigma in astrochemistry: the apparent lack of negatively charged molecules in space," stated Thaddeus. The team first conducted laboratory experiments to determine exactly what radio frequencies to use in their search. Then, they used the National Science Foundation's Robert C. Byrd Green Bank Telescope to hunt for C6H- in celestial objects. In particular, they targeted locations in which previous searches had spotted unidentified radio signals at the appropriate frequencies. They found C6H- in two very different locations-a shell of gas surrounding the evolved red giant star IRC +10216 in the constellation Leo, and the cold molecular cloud TMC-1 in Taurus. The presence of the anion in both regions shows that the chemical processes that form C6H- are ubiquitous. It also suggests that other molecular anions are present and will be found in the near future. "This finding is dramatic evidence that our understanding of interstellar chemistry is still quite rudimentary. It also implies that more molecular anions, perhaps many, may now be found in the laboratory and in space," said McCarthy. This research will appear in the December 1 issue of The Astrophysical Journal Letters. Note to editors: High-resolution photographs of the Green Bank Telescope are available at http://www.nrao.edu/imagegallery/php/level2a.php?class=Telescopes&subclass=GBT. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

  2. Characterization of bonds formed between platelet factor 4 and negatively charged drugs using single molecule force spectroscopy.

    PubMed

    Block, Stephan; Greinacher, Andreas; Helm, Christiane A; Delcea, Mihaela

    2014-04-28

    Immunogenicity (i.e., the ability to initiate immune reactions) is one of the major challenges for the development of new drugs, as it may turn the developed drug therapeutically ineffective or cause severe immune-related effects. Using single molecule force spectroscopy, we study rupture forces between the positively charged, endogenous protein platelet factor 4 (PF4; also known as CXC chemokine ligand 4, CXCL4) and the antithrombotic drug heparin and other negatively charged glycosaminoglycans (GAGs), which are known to form immunogenic PF4/GAG-complexes (e.g., heparin and dextran sulfate) as well as non-immunogenic complexes (e.g., chondroitin sulfate A). Our measurements suggest that the average number of sulfate groups per monosaccharide unit (i.e., the degree of sulfation DS) does not affect the unbinding characteristics of single PF4/GAG-bonds (reaction coordinate x0 = 2.2 0.2 , energy barrier ?G ? -1 kBT). However, the average number of GAG bonds formed to a single PF4 molecule increases with increasing DS as indicated by a rising frequency of unbinding events, suggesting a multivalent binding scheme between PF4 and GAGs. Our studies show that at least three GAG bonds have to be formed to each PF4 molecule to induce epitope formation on the PF4/GAG-complex to which PF4/GAG-complex specific antibodies bind. Hence, GAG-based drugs that form less than three bonds per PF4 molecule are unlikely to constitute PF4/drug-complexes that are of immunologic relevance. PMID:24667820

  3. Infrared Vibrational Fluorescence and Persistent Spectral Hole Burning from Negatively Charged Cyanogen Molecules in Alkali Halides.

    NASA Astrophysics Data System (ADS)

    Spitzer, Ronnie Claudette

    1988-12-01

    The union of IR semiconductor diode laser and Fourier transform interferometric methods has produced two new spectroscopic probes for investigating the dynamics of matrix isolated molecules: vibrational fluorescence and persistent spectral hole burning. In this thesis, we investigate a single system, CN^- doped ionic crystals, with both low power techniques. High resolution measurements of the IR vibrational fluorescence from CN^- molecules matrix isolated in alkali halide hosts at low temperatures reveal an up-the-ladder cascade of remarkable range. The CN^- fundamental absorption line is pumped with a CW tunable diode laser near 5 ?m and the vibrational fluorescence analyzed with the high resolution (0.04 cm^{ -1}) interferometer. We find high-lying vibrational levels of CN^- (up to v = 16) are populated at 1.7 K by an electric dipole mediated V-V energy transfer process. At our high resolution, new aspects of the system emerge. Emission features from defect centers composed of a CN^- molecule associated with another nearby impurity ion dominate the spectrum at high CN^- concentrations. The most important center is the CN^- pair defect. At elevated temperatures population of the CN^- pair defect vibrational levels in the ground electronic state have been observed at ultraviolet energies for all hosts. Our results show that energy preferentially accumulates at the pair defect because one member of the pair is always in the ground state ready to accept an excitation from a neighboring center. By using the diode laser as a high brightness probe, a new photophysical hole burning mechanism has been identified. Persistent spectral holes form during laser excitation of the Na^+:CN ^- defect's vibrational mode, when the CN ^- molecule occasionally reorients by 180^circ to an inequivalent lattice orientation generated by the nearby Na ^+ ion. A lattice barrier to reorientation blocks relaxation back to the original ground state at low temperatures. By combining persistent spectral hole burning with broadband FT spectroscopy, the CN ^- dynamics are identified. A solid state linear vibrational Stark effect, observed here for the first time, probes the local lattice configuration.

  4. Negative ions of polyatomic molecules.

    PubMed Central

    Christophorou, L G

    1980-01-01

    In this paper general concepts relating to, and recent advances in, the study of negative ions of polyatomic molecules area discussed with emphasis on halocarbons. The topics dealt with in the paper are as follows: basic electron attachment processes, modes of electron capture by molecules, short-lived transient negative ions, dissociative electron attachment to ground-state molecules and to "hot" molecules (effects of temperature on electron attachment), parent negative ions, effect of density, nature, and state of the medium on electron attachment, electron attachment to electronically excited molecules, the binding of attached electrons to molecules ("electron affinity"), and the basic and the applied significance of negative-ion studies. PMID:7428744

  5. Electrokinetic concentration of charged molecules

    DOEpatents

    Singh, Anup K. (Berkeley, CA); Neyer, David W. (Castro Valley, CA); Schoeniger, Joseph S. (Oakland, CA); Garguilo, Michael G. (Livermore, CA)

    2002-01-01

    A method for separating and concentrating charged species from uncharged or neutral species regardless of size differential. The method uses reversible electric field induced retention of charged species, that can include molecules and molecular aggregates such as dimers, polymers, multimers, colloids, micelles, and liposomes, in volumes and on surfaces of porous materials. The retained charged species are subsequently quantitatively removed from the porous material by a pressure driven flow that passes through the retention volume and is independent of direction thus, a multi-directional flow field is not required. Uncharged species pass through the system unimpeded thus effecting a complete separation of charged and uncharged species and making possible concentration factors greater than 1000-fold.

  6. Charging of dust grains in a plasma with negative ions

    SciTech Connect

    Kim, Su-Hyun; Merlino, Robert L.

    2006-05-15

    The effect of negative ions on the charging of dust particles in a plasma is investigated experimentally. A plasma containing a very low percentage of electrons is formed in a single-ended Q machine when SF{sub 6} is admitted into the vacuum system. The relatively cold Q machine electrons (T{sub e}{approx_equal}0.2 eV) readily attach to SF{sub 6} molecules to form SF{sub 6}{sup -} negative ions. Calculations of the dust charge indicate that for electrons, negative ions, and positive ions of comparable temperatures, the charge (or surface potential) of the dust can be positive if the positive ion mass is smaller than the negative ion mass and if {epsilon}, the ratio of the electron to positive ion density, is sufficiently small. The Q machine plasma is operated with K{sup +} positive ions (mass 39 amu) and SF{sub 6}{sup -} negative ions (mass 146 amu), and also utilizes a rotating cylinder to dispense dust into the plasma column. Analysis of the current-voltage characteristics of a Langmuir probe in the dusty plasma shows evidence for the reduction in the (magnitude) of the negative dust charge and the transition to positively charged dust as the relative concentration of the residual electrons is reduced. Some remarks are offered concerning experiments that could become possible in a dusty plasma with positive grains.

  7. Membrane Permeabilization Induced by Sphingosine: Effect of Negatively Charged Lipids

    PubMed Central

    Jimnez-Rojo, Noemi; Sot, Jess; Viguera, AnaR.; Collado, M. Isabel; Torrecillas, Alejandro; Gmez-Fernndez, J.C.; Goi, FlixM.; Alonso, Alicia

    2014-01-01

    Sphingosine [(2S, 3R, 4E)-2-amino-4-octadecen-1, 3-diol] is the most common sphingoid long chain base in sphingolipids. It is the precursor of important cell signaling molecules, such as ceramides. In the last decade it has been shown to act itself as a potent metabolic signaling molecule, by activating a number of protein kinases. Moreover, sphingosine has been found to permeabilize phospholipid bilayers, giving rise to vesicle leakage. The present contribution intends to analyze the mechanism by which this bioactive lipid induces vesicle contents release, and the effect of negatively charged bilayers inthe release process. Fluorescence lifetime measurements and confocal fluorescence microscopy have been applied toobserve the mechanism of sphingosine efflux from large and giant unilamellar vesicles; a graded-release efflux has been detected. Additionally, stopped-flow measurements have shown that the rate of vesicle permeabilization increases with sphingosine concentration. Because at the physiological pH sphingosine has a net positive charge, its interaction with negatively charged phospholipids (e.g., bilayers containing phosphatidic acid together with sphingomyelins, phosphatidylethanolamine, and cholesterol) gives rise to a release of vesicular contents, faster than with electrically neutral bilayers. Furthermore, phosphorous 31-NMR and x-ray data show the capacity of sphingosine to facilitate the formation of nonbilayer (cubic phase) intermediates in negatively charged membranes. The data might explain the pathogenesis of Niemann-Pick type C1 disease. PMID:24940775

  8. Interaction of yeast 3-phosphoglycerate kinase with negatively charged carriers.

    PubMed

    Roustan, C; Fattoum, A; Jeanneau, R; Pradel, L A; Schuhmann, D; Vanel, P

    1982-05-01

    The aim of this study was to investigate the possibility of an interaction of yeast 3-phosphoglycerate kinase with negatively charged carriers such as polyanionic agents or a polarized electrode. Various polyanions were found to promote enzyme aggregation as judged by ultracentrifugation measurements and chemical modification. The data obtained suggest that these interactions are mediated through the N-terminal domain of the protein. However, the most striking property of 3-phosphoglycerate kinase described here is concerned with its significant dipolar moment as evidenced by electrocapillary measurements, which allows an orientation of the macromolecule in an electric field. Further, the enzyme could be absorbed by a negatively charged surface, first by hydrophobic links and then oriented perpendicularly to the surface. Therefore, the intrinsic properties of yeast 3-phosphoglycerate kinase agree with the formation of an enzyme-membrane complex and afford the ability for a specific orientation of the molecule at the lipid bilayer surface or in the cytoplasm. PMID:6178443

  9. Laboratory infrared spectroscopy of gaseous negatively charged polyaromatic hydrocarbons

    SciTech Connect

    Gao, Juehan; Berden, Giel; Oomens, Jos

    2014-06-01

    Based largely on infrared spectroscopic evidence, polycyclic aromatic hydrocarbon (PAH) molecules are now widely accepted to occur abundantly in the interstellar medium. Laboratory infrared spectra have been obtained for a large variety of neutral and cationic PAHs, but data for anionic PAHs are scarce. Nonetheless, in regions with relatively high electron densities and low UV photon fluxes, PAHs have been suggested to occur predominantly as negatively charged ions (anions), having substantial influence on cloud chemistry. While some matrix spectra have been reported for radical anion PAHs, no data is available for even-electron anions, which are more stable against electron detachment. Here we present the first laboratory infrared spectra of deprotonated PAHs ([PAH-H]{sup }) in the wavelength ranges between 6 and 16 ?m and around 3 ?m. Wavelength-dependent infrared multiple-photon electron detachment is employed to obtain spectra for deprotonated naphthalene, anthracene, and pyrene in the gas phase. Spectra are compared with theoretical spectra computed at the density functional theory level. We show that the relative band intensities in different ranges of the IR spectrum deviate significantly from those of neutral and positively charged PAHs, and moreover from those of radical anion PAHs. These relative band intensities are, however, well reproduced by theory. An analysis of the frontier molecular orbitals of the even- and odd-electron anions reveals a high degree of charge localization in the deprotonated systems, qualitatively explaining the observed differences and suggesting unusually high electric dipole moments for this class of PAH molecules.

  10. Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Gao, Juehan; Berden, Giel; Oomens, Jos

    2014-06-01

    Based largely on infrared spectroscopic evidence, polycyclic aromatic hydrocarbon (PAH) molecules are now widely accepted to occur abundantly in the interstellar medium. Laboratory infrared spectra have been obtained for a large variety of neutral and cationic PAHs, but data for anionic PAHs are scarce. Nonetheless, in regions with relatively high electron densities and low UV photon fluxes, PAHs have been suggested to occur predominantly as negatively charged ions (anions), having substantial influence on cloud chemistry. While some matrix spectra have been reported for radical anion PAHs, no data is available for even-electron anions, which are more stable against electron detachment. Here we present the first laboratory infrared spectra of deprotonated PAHs ([PAH-H]-) in the wavelength ranges between 6 and 16 ?m and around 3 ?m. Wavelength-dependent infrared multiple-photon electron detachment is employed to obtain spectra for deprotonated naphthalene, anthracene, and pyrene in the gas phase. Spectra are compared with theoretical spectra computed at the density functional theory level. We show that the relative band intensities in different ranges of the IR spectrum deviate significantly from those of neutral and positively charged PAHs, and moreover from those of radical anion PAHs. These relative band intensities are, however, well reproduced by theory. An analysis of the frontier molecular orbitals of the even- and odd-electron anions reveals a high degree of charge localization in the deprotonated systems, qualitatively explaining the observed differences and suggesting unusually high electric dipole moments for this class of PAH molecules.

  11. Infrared Investigations of Negatively Charged Complexes and Clusters

    NASA Astrophysics Data System (ADS)

    Wild, D. A.; Bieske, E. J.

    The review describes recent progress in the characterization of size-selected negatively charged clusters in the gas phase using vibrational predissociation spectroscopy. Examples from the authors' laboratory are used to demonstrate the way in which spectra are obtained and interpreted to provide information on anion-neutral interactions. Infrared studies of simple dimer complexes consisting of hydrogen molecules attached to halide anions (Cl --H 2 , Br --H 2 , I --H 2 ) are described. From rotationally resolved spectra in the 2.5 μm H-H stretch region one can deduce that the complexes have linear equilibrium structures and can ascertain intermolecular separations. Corresponding spectra of the Cl --D 2 and Br --D 2 isotopomers display a series of clearly resolved doublets, highlighting the importance of hindered internal rotation of the D 2 subunit. Studies of Cl --(C 2 H 2 ) n , Br --(C 2 H 2 ) n and I --(C 2 H 2 ) n clusters containing up to nine C 2 H 2 molecules illustrate how infrared spectra can be used to explore the progressive 'solvation' of halide anions. The smaller clusters ( n ≤6) have morphologies in which equivalent acetylene molecules are hydrogen bonded to the interior halide anion. For n > 6 there is evidence for structures in which one or more acetylene molecules are situated in the second solvation shell and also for the existence of multiple isomeric forms. The article concludes by discussing prospects for extending spectroscopic studies to hitherto uncharacterized anion complexes.

  12. Pseudoparticle approach for charge-transferring molecule-surface collisions

    NASA Astrophysics Data System (ADS)

    Marbach, Johannes; Bronold, Franz Xaver; Fehske, Holger

    2012-09-01

    Based on a semiempirical generalized Anderson-Newns model, we construct a pseudoparticle description for electron emission due to deexcitation of metastable molecules at surfaces. The pseudoparticle approach allows us to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both channels are open. This is, for instance, the case when a metastable N2(3Σu+) molecule hits a diamond surface. Using nonequilibrium Green functions and physically motivated approximations to the self-energies of the Dyson equations, we derive a system of rate equations for the probabilities with which the metastable N2(3Σu+) molecule, the molecular ground state N2(1Σg+), and the negative ion N2-(2Πg) can be found in the course of the scattering event. From the rate equations, we also obtain the spectrum of the emitted electron and the secondary electron emission coefficient. Our numerical results indicate the resonant tunneling process undermining the source of the Auger channel, which therefore contributes only a few percent to the secondary electron emission.

  13. Micro injector sample delivery system for charged molecules

    DOEpatents

    Davidson, James C. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

    1999-11-09

    A micro injector sample delivery system for charged molecules. The injector is used for collecting and delivering controlled amounts of charged molecule samples for subsequent analysis. The injector delivery system can be scaled to large numbers (>96) for sample delivery to massively parallel high throughput analysis systems. The essence of the injector system is an electric field controllable loading tip including a section of porous material. By applying the appropriate polarity bias potential to the injector tip, charged molecules will migrate into porous material, and by reversing the polarity bias potential the molecules are ejected or forced away from the tip. The invention has application for uptake of charged biological molecules (e.g. proteins, nucleic acids, polymers, etc.) for delivery to analytical systems, and can be used in automated sample delivery systems.

  14. Recovery of small dye molecules from aqueous solutions using charged ultrafiltration membranes.

    PubMed

    Chen, Xiuwen; Zhao, Yiru; Moutinho, Jennifer; Shao, Jiahui; Zydney, Andrew L; He, Yiliang

    2015-03-01

    Recovery of reactive dyes from effluent streams is a growing environmental challenge. In this study, various charged regenerated cellulose (RC) ultrafiltration (UF) membranes were prepared and tested for removal of three model reactive dyes (reactive red ED-2B, reactive brilliant yellow K-6G, and reactive brilliant blue KN-R). Data were obtained with charged UF membranes having different spacer arm lengths between the base cellulose and the charge functionality. The effects of charge density of the dye molecules, ionic strength of the feed solution, spacer arm length of charged membranes and filtrate flux were studied. Results indicated that dye retention was greatest with the most negatively charged dye molecule. Higher rejection was also observed in low ionic strength solutions. Results were consistent with model calculations based on the partitioning of a charged sphere into a charged cylindrical pore. The membranes with longer spacer arm length had higher rejection coefficients, consistent with the greater negative charge on these membranes. This study confirms that charged UF membranes can effectively recover small reactive dye molecules at low pressures (below 100 kPa) under appropriate solution conditions due to the strong electrostatic repulsion from the membrane pores. PMID:25463218

  15. Mean field theory of charged dendrimer molecules.

    PubMed

    Lewis, Thomas; Pryamitsyn, Victor; Ganesan, Venkat

    2011-11-28

    Using self-consistent field theory (SCFT), we study the conformational properties of polyelectrolyte dendrimers. We compare results for three different models of charge distributions on the polyelectrolytes: (1) a smeared, quenched charge distribution characteristic of strong polyelectrolytes; (2) a smeared, annealed charge distribution characteristic of weak polyelectrolytes; and (3) an implicit counterion model with Debye-Huckel interactions between the charged groups. Our results indicate that an explicit treatment of counterions is crucial for the accurate characterization of the conformations of polyelectrolyte dendrimers. In comparing the quenched and annealed models of charge distributions, annealed dendrimers were observed to modulate their charges in response to the density of polymer monomers, counterions, and salt ions. Such phenomena is not accommodated within the quenched model of dendrimers and is shown to lead to significant differences between the predictions of quenched and annealed model of dendrimers. In this regard, our results indicate that the average dissociated charge ? inside the dendrimer serves as a useful parameter to map the effects of different parametric conditions and models onto each other. We also present comparisons to the scaling results proposed to explain the behavior of polyelectrolyte dendrimers. Inspired by the trends indicated by our results, we develop a strong segregation theory model whose predictions are shown to be in very good agreement with the numerical SCFT calculations. PMID:22128954

  16. Mean field theory of charged dendrimer molecules

    NASA Astrophysics Data System (ADS)

    Lewis, Thomas; Pryamitsyn, Victor; Ganesan, Venkat

    2011-11-01

    Using self-consistent field theory (SCFT), we study the conformational properties of polyelectrolyte dendrimers. We compare results for three different models of charge distributions on the polyelectrolytes: (1) a smeared, quenched charge distribution characteristic of strong polyelectrolytes; (2) a smeared, annealed charge distribution characteristic of weak polyelectrolytes; and (3) an implicit counterion model with Debye-Huckel interactions between the charged groups. Our results indicate that an explicit treatment of counterions is crucial for the accurate characterization of the conformations of polyelectrolyte dendrimers. In comparing the quenched and annealed models of charge distributions, annealed dendrimers were observed to modulate their charges in response to the density of polymer monomers, counterions, and salt ions. Such phenomena is not accommodated within the quenched model of dendrimers and is shown to lead to significant differences between the predictions of quenched and annealed model of dendrimers. In this regard, our results indicate that the average dissociated charge bar{α } inside the dendrimer serves as a useful parameter to map the effects of different parametric conditions and models onto each other. We also present comparisons to the scaling results proposed to explain the behavior of polyelectrolyte dendrimers. Inspired by the trends indicated by our results, we develop a strong segregation theory model whose predictions are shown to be in very good agreement with the numerical SCFT calculations.

  17. Is the negative glow plasma of a direct current glow discharge negatively charged?

    SciTech Connect

    Bogdanov, E. A.; Saifutdinov, A. I.; Demidov, V. I.; Kudryavtsev, A. A.

    2015-02-15

    A classic problem in gas discharge physics is discussed: what is the sign of charge density in the negative glow region of a glow discharge? It is shown that traditional interpretations in text-books on gas discharge physics that states a negative charge of the negative glow plasma are based on analogies with a simple one-dimensional model of discharge. Because the real glow discharges with a positive column are always two-dimensional, the transversal (radial) term in divergence with the electric field can provide a non-monotonic axial profile of charge density in the plasma, while maintaining a positive sign. The numerical calculation of glow discharge is presented, showing a positive space charge in the negative glow under conditions, where a one-dimensional model of the discharge would predict a negative space charge.

  18. CCMV capsid formation induced by a functional negatively charged polymer.

    PubMed

    Minten, Inge J; Ma, Yujie; Hempenius, Mark A; Vancso, G Julius; Nolte, Roeland J M; Cornelissen, Jeroen J L M

    2009-11-21

    A functional negatively charged polyelectrolyte, polyferrocenylsilane (PFS) was encapsulated in cowpea chlorotic mottle virus (CCMV) capsid proteins, yielding monodisperse particles of 18 nm in size with altered redox properties compared to the parent materials. PMID:19865705

  19. Contactless measurements of charge migration within single molecules

    NASA Astrophysics Data System (ADS)

    Nagaya, Kiyonobu; Iwayama, Hiroshi; Sugishima, Akinori; Ohmasa, Yoshinori; Yao, Makoto

    2010-06-01

    Contactless measurements of charge migration were carried out for three π-conjugated molecules in each of which a bromine atom and an oxygen atom are located on the opposite sides of the aromatic ring. A core hole was generated selectively in the Br atom by x-ray absorption, followed by the Auger cascade, and the subsequent charge migration within the molecule was examined by detecting an O+ ion by means of the coincidence momentum imaging measurements.

  20. Contactless measurements of charge migration within single molecules

    SciTech Connect

    Nagaya, Kiyonobu; Iwayama, Hiroshi; Sugishima, Akinori; Ohmasa, Yoshinori; Yao, Makoto

    2010-06-07

    Contactless measurements of charge migration were carried out for three pi-conjugated molecules in each of which a bromine atom and an oxygen atom are located on the opposite sides of the aromatic ring. A core hole was generated selectively in the Br atom by x-ray absorption, followed by the Auger cascade, and the subsequent charge migration within the molecule was examined by detecting an O{sup +} ion by means of the coincidence momentum imaging measurements.

  1. On charge transfer in the adsorbed molecules-graphene monolayer-SiC substrate system

    SciTech Connect

    Davydov, S. Yu.

    2011-05-15

    A step-by-step consideration of charge transfer in the molecule-single-layer graphene-SiC substrate system is presented. At the first step, a simple model of the density of states of a single graphene monolayer adsorbed on silicon carbide (the graphene-SiC system) is suggested, which allows the calculation of the corresponding occupation numbers of graphene atoms. It is shown that the graphene monolayer accumulates a negative charge. At the second step, the graphene-SiC system is considered as a substrate that adsorbs molecules with a high electron affinity. The charge of these molecules as a function of their surface concentration is calculated. It is shown that, in the case of a monolayer coating, the negative surface charge density of molecules in the molecule-graphene monolayer-SiC substrate system is considerably higher than the surface charge density transferring from the SiC substrate to the graphene layer. This suggests that it is possible to neutralize the excess charge in the graphene layer via adsorption of proper particles on the layer.

  2. Electrostatic plasma lens for focusing negatively charged particle beams

    SciTech Connect

    Goncharov, A. A.; Dobrovolskiy, A. M.; Dunets, S. M.; Litovko, I. V.; Gushenets, V. I.; Oks, E. M.

    2012-02-15

    We describe the current status of ongoing research and development of the electrostatic plasma lens for focusing and manipulating intense negatively charged particle beams, electrons, and negative ions. The physical principle of this kind of plasma lens is based on magnetic isolation electrons providing creation of a dynamical positive space charge cloud in shortly restricted volume propagating beam. Here, the new results of experimental investigations and computer simulations of wide-aperture, intense electron beam focusing by plasma lens with positive space charge cloud produced due to the cylindrical anode layer accelerator creating a positive ion stream towards an axis system is presented.

  3. Field Regulation of Single Molecule Conductivity by a Charged Atom

    NASA Astrophysics Data System (ADS)

    Wolkow, Robert

    2006-03-01

    A new concept for a single molecule transistor is demonstrated [1]. A single chargeable atom adjacent to a molecule shifts molecular energy levels into alignment with electrode levels, thereby gating current through the molecule. Seemingly paradoxically, the silicon substrate to which the molecule is covalently attached provides 2, not 1, effective contacts to the molecule. This is achieved because the single charged silicon atom is at a substantially different potential than the remainder of the substrate. Charge localization at one dangling bond is ensured by covalently capping all other surface atoms. Dopant level control and local Fermi level control can change the charge state of that atom. The same configuration is shown to be an effective transducer to an electrical signal of a single molecule detection event. Because the charged atom induced shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature. [1] Paul G. Piva1,Gino A. DiLabio, Jason L. Pitters, Janik Zikovsky, Moh'd Rezeq, Stanislav Dogel, Werner A. Hofer & Robert A. Wolkow, Field regulation of single-molecule conductivity by a charged surface atom, NATURE 435, 658-661 (2005)

  4. Negative Differential Resistance in Insulating Systems: From Molecules to Polymers

    NASA Astrophysics Data System (ADS)

    Pati, Swapan

    2007-03-01

    We have developed a microscopic theory to explain the negative differential resistance behavior in molecular bridges. This feature has been observed in many molecules with different on/off ratios, sharpness of the current peak and the critical bias. Our theory, based on simple dimer model (both Peierls and donor/acceptor) together with bias driven conformational/ electronic change, covers almost all the experimental characteristics for a large number of real molecular systems and encompasses all the theory that has been known till date. Similar argument is also extended to Mott insulator, where we find a large number of insulator/quasi-metal transitions in finite size chains and a thermodynamic insulator/metal transition in polymers due to the application of static electric field between two ends of the chain. The interplay between charge inhomogenities and electric field induced polarization will be discussed in a number of cases. We will also show that none of these transitions follow Landau-Zener mechanism. I shall also discuss our theoretical proposal for the experimental strategies to stabilize highly unstable and reactive metal clusters like Al4Li4 and their analogs. Reference: 1. S. Lakshmi and Swapan K. Pati, Phys. Rev. B 72, 193410 (2005). 2. S. Lakshmi, Ayan Datta and Swapan K. Pati, Phys. Rev. B 72, 045131 (2005). 3. S. Lakshmi and Swapan K. Pati, Spl on Nanosc and Tech, Pramana, 65, 593. (2005). 4. S. Sengupta, S. Lakshmi and Swapan K Pati, J. Phys. Cond. Mat. 18, 9189 (2006). 5. Swapan K. Pati and S. Ramasesha, J. Phys. Condens. Matter 16, 989 (2004). 6. S.Lakshmi and Swapan K. Pati, J. Chem. Phys. 121, 11998 (2004). 7. S. Dutta, S. Lakshmi and Swapan K Pati, Submitted (2006). 8. A. Datta and Swapan K. Pati, J. Am. Chem. Soc. 127, 3496 (2005). 9. Sairam S. M., A. Datta and Swapan K. Pati, J. Phys. Chem. B 110, 20098 (2006). 10. A. Datta, Sairam S. M. and Swapan K. Pati, Acc. Chem. Res. (to appear)

  5. Electrostatic Power Generation from Negatively Charged, Simulated Lunar Regolith

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; King, Glen C.; Kim, Hyun-Jung; Park, Yeonjoon

    2010-01-01

    Research was conducted to develop an electrostatic power generator for future lunar missions that facilitate the utilization of lunar resources. The lunar surface is known to be negatively charged from the constant bombardment of electrons and protons from the solar wind. The resulting negative electrostatic charge on the dust particles, in the lunar vacuum, causes them to repel each other minimizing the potential. The result is a layer of suspended dust about one meter above the lunar surface. This phenomenon was observed by both Clementine and Surveyor spacecrafts. During the Apollo 17 lunar landing, the charged dust was a major hindrance, as it was attracted to the astronauts' spacesuits, equipment, and the lunar buggies. The dust accumulated on the spacesuits caused reduced visibility for the astronauts, and was unavoidably transported inside the spacecraft where it caused breathing irritation [1]. In the lunar vacuum, the maximum charge on the particles can be extremely high. An article in the journal "Nature", titled "Moon too static for astronauts?" (Feb 2, 2007) estimates that the lunar surface is charged with up to several thousand volts [2]. The electrostatic power generator was devised to alleviate the hazardous effects of negatively charged lunar soil by neutralizing the charged particles through capacitive coupling and thereby simultaneously harnessing power through electric charging [3]. The amount of power generated or collected is dependent on the areal coverage of the device and hovering speed over the lunar soil surface. A thin-film array of capacitors can be continuously charged and sequentially discharged using a time-differentiated trigger discharge process to produce a pulse train of discharge for DC mode output. By controlling the pulse interval, the DC mode power can be modulated for powering devices and equipment. In conjunction with a power storage system, the electrostatic power generator can be a power source for a lunar rover or other systems. The negatively charged lunar soil would also be neutralized mitigating some of the adverse effects resulting from lunar dust.

  6. Gating capacitive field-effect sensors by the charge of nanoparticle/molecule hybrids.

    PubMed

    Poghossian, Arshak; Bäcker, Matthias; Mayer, Dirk; Schöning, Michael J

    2015-01-21

    The semiconductor field-effect platform is a powerful tool for chemical and biological sensing with direct electrical readout. In this work, the field-effect capacitive electrolyte-insulator-semiconductor (EIS) structure - the simplest field-effect (bio-)chemical sensor - modified with citrate-capped gold nanoparticles (AuNPs) has been applied for a label-free electrostatic detection of charged molecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in AuNP/molecule inorganic/organic hybrids induced by the molecular adsorption or binding events. The feasibility of the proposed detection scheme has been exemplarily demonstrated by realizing capacitive EIS sensors consisting of an Al-p-Si-SiO2-silane-AuNP structure for the label-free detection of positively charged cytochrome c and poly-d-lysine molecules as well as for monitoring the layer-by-layer formation of polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4-styrene sulfonate), representing typical model examples of detecting small proteins and macromolecules and the consecutive adsorption of positively/negatively charged polyelectrolytes, respectively. For comparison, EIS sensors without AuNPs have been investigated, too. The adsorption of molecules on the surface of AuNPs has been verified via the X-ray photoelectron spectroscopy method. In addition, a theoretical model of the functioning of the capacitive field-effect EIS sensor functionalized with AuNP/charged-molecule hybrids has been discussed. PMID:25470772

  7. Gram-Negative Bacterial Sensors for Eukaryotic Signal Molecules

    PubMed Central

    Lesouhaitier, Olivier; Veron, Wilfried; Chapalain, Annelise; Madi, Amar; Blier, Anne-Sophie; Dagorn, Audrey; Connil, Nathalie; Chevalier, Sylvie; Orange, Nicole; Feuilloley, Marc

    2009-01-01

    Ample evidence exists showing that eukaryotic signal molecules synthesized and released by the host can activate the virulence of opportunistic pathogens. The sensitivity of prokaryotes to host signal molecules requires the presence of bacterial sensors. These prokaryotic sensors, or receptors, have a double function: stereospecific recognition in a complex environment and transduction of the message in order to initiate bacterial physiological modifications. As messengers are generally unable to freely cross the bacterial membrane, they require either the presence of sensors anchored in the membrane or transporters allowing direct recognition inside the bacterial cytoplasm. Since the discovery of quorum sensing, it was established that the production of virulence factors by bacteria is tightly growth-phase regulated. It is now obvious that expression of bacterial virulence is also controlled by detection of the eukaryotic messengers released in the micro-environment as endocrine or neuro-endocrine modulators. In the presence of host physiological stress many eukaryotic factors are released and detected by Gram-negative bacteria which in return rapidly adapt their physiology. For instance, Pseudomonas aeruginosa can bind elements of the host immune system such as interferon-? and dynorphin and then through quorum sensing circuitry enhance its virulence. Escherichia coli sensitivity to the neurohormones of the catecholamines family appears relayed by a recently identified bacterial adrenergic receptor. In the present review, we will describe the mechanisms by which various eukaryotic signal molecules produced by host may activate Gram-negative bacteria virulence. Particular attention will be paid to Pseudomonas, a genus whose representative species, P. aeruginosa, is a common opportunistic pathogen. The discussion will be particularly focused on the pivotal role played by these new types of pathogen sensors from the sensing to the transduction mechanism involved in virulence factors regulation. Finally, we will discuss the consequence of the impact of host signal molecules on commensally or opportunistic pathogens associated with different human tissue. PMID:22399982

  8. Screening platelet-surface interactions using negative surface charge gradients.

    PubMed

    Corum, Lindsey E; Hlady, Vladimir

    2010-04-01

    Negative surface charge density gradients were prepared on fused silica slides using selective oxidation of a 3-mercaptopropyltrimethoxysilane (MTS) monolayer converting surface thiol groups (-SH) into negatively charged sulfonate (-SO(3)(-)) groups. The sulfonate-to-thiol gradient samples were characterized by water contact angle and electron spectroscopy for chemical analysis (ESCA). Gradients were pre-adsorbed with proteins from three different solutions: platelet free plasma (PFP), fibrinogen, or albumin in phosphate buffered saline (PBS). Washed platelets were perfused over gradient samples in a parallel plate flow chamber and platelet adhesion was measured across the gradients using differential interference contrast (DIC) microscopy. Gradients pre-adsorbed with PFP showed adhesion contrast inversely related to the negative surface charge density. The magnitude of the adhesion contrast along the gradient was also dependent on PFP concentration. Gradients pre-adsorbed with fibrinogen showed an adhesion maximum in the center of the gradient region. Albumin coating of the gradients resulted in low overall platelet adhesion with increased adhesion in regions of high negative charge density. The effect of gradient orientation with respect to the flow was also investigated. Gradients pre-adsorbed with 10% PFP showed different adhesion contrast when the platelets were perfused in opposite directions. This suggests that platelet adhesion is, in addition to responding to the local surface properties, also dependent on the upstream conditions. PMID:20149436

  9. The sheath structure around a negatively charged rocket payload

    NASA Technical Reports Server (NTRS)

    Neubert, T.; Gilchrist, B. E.; Banks, P. M.; Mandell, M. J.; Sasaki, S.

    1990-01-01

    The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. The experimental results come from the Charge 2 sounding rocket experiment in which the payload was split into two separate sections (mother and daughter) connected with a conducting, insulated tether. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. A floating probe array was mounted on the mother with probes located 25, 50, 75, and 100 cm from the rocket surface. The internal impedance of the array was smaller than the probe/plasma impedance, which influenced the potential measurements. The measurements contain signatures, resulting from the outward expansion of the ion sheath with increasing negative mother potential. This conclusion is substantiated by computer simulations of space charge limited flow.

  10. Space Charge Neutralization in the ITER Negative Ion Beams

    SciTech Connect

    Surrey, Elizabeth

    2007-08-10

    A model of the space charge neutralization of negative ion beams, developed from the model due to Holmes, is applied to the ITER heating and diagnostic beams. The Holmes model assumed that the plasma electron temperature was derived from the stripped electrons. This is shown to be incorrect for the ITER beams and the plasma electron temperature is obtained from the average creation energy upon ionization. The model shows that both ITER beams will be fully space charge compensated in the drift distance between the accelerator and the neutralizer. Inside the neutralizer, the plasma over compensates the space charge to the extent that a significant focusing force is predicted. At a certain position in the neutraliser this force balances the defocusing force due to the ions' transverse energy. Under these conditions the beam distribution function can change from Gaussian to Bennett and evidence of such a distribution observed in a multi-aperture, neutralized negative ion beam is presented.

  11. Increased negatively charged nitrogen-vacancy centers in fluorinated diamond

    SciTech Connect

    Cui, Shanying; Hu, Evelyn L.

    2013-07-29

    We investigated the effect of fluorine-terminated diamond surface on the charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is achieved with CF{sub 4} plasma, and the surface chemistry is confirmed with x-ray photoemission spectroscopy. Photoluminescence of these ensemble NVs reveals that fluorine-treated surfaces lead to a higher and more stable negatively charged nitrogen vacancy (NV{sup ?}) population than oxygen-terminated surfaces. NV{sup ?} population is estimated by the ratio of negative to neutral charged NV zero-phonon lines. Surface chemistry control of NV{sup ?} density is an important step towards improving the optical and spin properties of NVs for quantum information processing and magnetic sensing.

  12. Catalysis effects of water molecules and of charge on intramolecular proton transfer of uracil.

    PubMed

    Li, Dejie; Ai, Hongqi

    2009-08-27

    In this work, the three most stable uracil isomers (U1, U2, and U3) and their neutral, positive, and negative charged multihydrates are chosen as research objects to investigate the tautomeric process between the most stable uracil, U1, and its two minor stable isomers, U2 and U3. By the study, deeper insight can be obtained regarding point mutations induced by uracil deformation. Toward the target, the activation energies of the intramolecular proton transfer (tautomeric process) as well as the catalysis effects of water molecules and of charges attached are investigated using density functional theory (DFT) calculations by means of the B3LYP exchange and correlation functions. Results reveal that water molecules hold a stronger catalysis effect on the proton transfer in these negative charged uracil hydrates than in the neutral counterparts. The optimal number of water molecules needed to catalyze the proton transfer is determined as two in the neutral hydrated systems, whereas it is three in the negative charged systems. Positive charge attachment, however, hinders the intramolecualr proton transfer of uracil, and the charge and the proton of uracil will transfer to the water clusters if water molecules are attached. Then the positive charged hydrates look more like U1a/b+[(H2O)n+H+] species in structure. Analysis reveals that it is the acceptance process of the last proton to determine the impossibility of proton transfer and result in the failure of tautomeric processes from cat-U1a-nw to cat-U2-nw and from cat-U1b-nw to cat-U3-nw. Detailed structural parameters and energy changes are discussed for the above different processes. PMID:19645458

  13. Charge mobility in molecules: charge fluxes from second derivatives of the molecular dipole.

    PubMed

    Galimberti, Daria; Milani, Alberto; Castiglioni, Chiara

    2013-04-28

    On the basis of the analytical model previously suggested by Dinur, we discuss here a method for the calculation of vibrational charge fluxes in planar molecules, obtained as numerical second derivatives of the molecular dipole moment. This model is consistent with the partitioning of the atomic polar tensors into atomic charge and charge fluxes according to the Equilibrium Charges-Charge Fluxes model and it is directly related to experimentally measurable quantities such as IR intensities. On the basis of density functional theory calculations carried out for several small benchmark molecules, the complete set of charge fluxes is calculated for each molecule and compared with the approximated flux parameters previously derived and reported in the past literature. The degree of localization of charge fluxes is investigated and discussed; in addition, some approximations are analyzed in order to verify the applicability of the method to large and?or non-planar molecules, aimed at obtaining a description of the electron charge mobility in different molecular environments. PMID:23635119

  14. Single molecule detection using charge-coupled device array technology

    SciTech Connect

    Denton, M.B.

    1992-07-29

    A technique for the detection of single fluorescent chromophores in a flowing stream is under development. This capability is an integral facet of a rapid DNA sequencing scheme currently being developed by Los Alamos National Laboratory. In previous investigations, the detection sensitivity was limited by the background Raman emission from the water solvent. A detection scheme based on a novel mode of operating a Charge-Coupled Device (CCD) is being developed which should greatly enhance the discrimination between fluorescence from a single molecule and the background Raman scattering from the solvent. Register shifts between rows in the CCD are synchronized with the sample flow velocity so that fluorescence from a single molecule is collected in a single moving charge packet occupying an area approaching that of a single pixel while the background is spread evenly among a large number of pixels. Feasibility calculations indicate that single molecule detection should be achieved with an excellent signal-to-noise ratio.

  15. The free solution mobility of DNA and other analytes varies as the logarithm of the fractional negative charge.

    PubMed

    Stellwagen, Nancy C; Peters, Justin P; Dong, Qian; Maher, L James; Stellwagen, Earle

    2014-07-01

    The free solution mobilities of ssDNA and dsDNA molecules with variable charge densities have been measured by CE. DNA charge density was modified either by appending positively or negatively charged groups to the thymine residues in a 98 bp DNA molecule, or by replacing some of the negatively charged phosphate internucleoside linkers in small ssDNA or dsDNA oligomers with positively charged phosphoramidate linkers. Mobility ratios were calculated for each dataset by dividing the mobility of a charge variant by the mobility of its unmodified parent DNA. Mobility ratios essentially eliminate the effect of the BGE on the observed mobility, making it possible to compare analytes measured under different experimental conditions. Neutral moieties attached to the thymine residues in the 98-bp DNA molecule had little or no effect on the mobility ratios, indicating that bulky substituents in the DNA major groove do not affect the mobility significantly. The mobility ratios observed for the thymine-modified and linker-modified DNA charge variants increased approximately linearly with the logarithm of the fractional negative charge of the DNA. Mobility ratios calculated from previous studies of linker-modified DNA charge variants and small multicharged organic molecules also increased approximately linearly with the logarithm of the fractional negative charge of the analyte. The results do not agree with the Debye-Hückel-Onsager theory of electrophoresis, which predicts that the mobility of an analyte should depend linearly on analyte charge, not the logarithm of the charge, when the frictional coefficient is held constant. PMID:24648187

  16. Physical methods to quantify small antibiotic molecules uptake into Gram-negative bacteria.

    PubMed

    Winterhalter, Mathias; Ceccarelli, Matteo

    2015-09-01

    The development of antibiotics against Gram-negative bacteria is a challenge: any active compound must cross the outer cell envelope composed of a hydrophilic highly charged lipopolysaccharide layer followed by a tight hydrophobic layer containing water filled gates called porins to reach the hydrophilic periplasmic space and depending on the target with the further need to cross the hydrophobic inner membrane. In addition to a possible rapid enzymatic deactivation efflux pumps shuffle compounds back outside. The resulting low permeability of cell envelope requires high dose and leads therefore to toxicity problems. Despite its relevance the permeability barrier in Gram-negative bacteria is not well understood partially caused by the lack of appropriate direct assays. Here we give a brief introduction on current available techniques to quantify passive diffusion of small hydrophilic molecules into Gram-negative bacteria. PMID:26036449

  17. Capture of negative exotic particles by atoms, ions and molecules

    NASA Astrophysics Data System (ADS)

    Cohen, James S.

    2004-10-01

    This article describes the capture of heavy negative particles (mgr-, pgr-, K-, \\barp ) by normal atoms, ions and molecules to form exotic systems. Capture by even the hydrogen atom presents great challenges for theoretical treatment. The wide variety of methods used are reviewed, including perturbative, two-state adiabatic and diabatic, time-independent quantum mechanical, time-dependent semiclassical and quantum mechanical and quasi-classical treatments. A few of these methods, as well as the Fermi-Teller model, have also been applied to heavier atomic targets. Most of the methods, other than the quasi-classical formulations, are not yet up to treating the dynamical electron correlation and multiple ionization found to be important in capture by multi-electron atoms, or the vibronic coupling found to be important in capture by simple molecules. The essential elements of potentially more rigorous quantum mechanical theories are characterized. The experimental data on capture states and relative capture probabilities in mixtures are also discussed. The connection of this experimental data to the theoretical capture calculations is fairly tenuous, but forthcoming experiments with antiprotons promise direct tests of some of the recent theoretical findings.

  18. Positive/negative ion velocity mapping apparatus for electron-molecule reactions

    SciTech Connect

    Wu Bin; Xia Lei; Li Hongkai; Zeng Xianjin; Tian Shanxi

    2012-01-15

    In molecular dissociative ionization by electron collisions and dissociative electron attachment to molecule, the respective positively and negatively charged fragments are the important products. A compact ion velocity mapping apparatus is developed for the angular distribution measurements of the positive or negative fragments produced in the electron-molecule reactions. This apparatus consists of a pulsed electron gun, a set of ion velocity mapping optic lenses, a two-dimensional position detector including two pieces of micro-channel plates, and a phosphor screen, and a charge-coupled-device camera for data acquisition. The positive and negative ion detections can be simply realized by changing the voltage polarity of ion optics and detector. Velocity sliced images can be directly recorded using a narrow voltage pulse applied on the rear micro-channel plate. The efficient performance of this system is evaluated by measuring the angular distribution of O{sup -} from the electron attachments to NO at 7.3 and 8.3 eV and O{sup +} from the electron collision with CO at 40.0 eV.

  19. Study on space charge compensation in negative hydrogen ion beam

    NASA Astrophysics Data System (ADS)

    Zhang, A. L.; Peng, S. X.; Ren, H. T.; Zhang, T.; Zhang, J. F.; Xu, Y.; Guo, Z. Y.; Chen, J. E.

    2016-02-01

    Negative hydrogen ion beam can be compensated by the trapping of ions into the beam potential. When the beam propagates through a neutral gas, these ions arise due to gas ionization by the beam ions. However, the high neutral gas pressure may cause serious negative hydrogen ion beam loss, while low neutral gas pressure may lead to ion-ion instability and decompensation. To better understand the space charge compensation processes within a negative hydrogen beam, experimental study and numerical simulation were carried out at Peking University (PKU). The simulation code for negative hydrogen ion beam is improved from a 2D particle-in-cell-Monte Carlo collision code which has been successfully applied to H+ beam compensated with Ar gas. Impacts among ions, electrons, and neutral gases in negative hydrogen beam compensation processes are carefully treated. The results of the beam simulations were compared with current and emittance measurements of an H- beam from a 2.45 GHz microwave driven H- ion source in PKU. Compensation gas was injected directly into the beam transport region to modify the space charge compensation degree. The experimental results were in good agreement with the simulation results.

  20. Electron interactions with positively and negatively multiply charged biomolecular clusters

    NASA Astrophysics Data System (ADS)

    Feketeov, Linda

    2012-07-01

    Interactions of positively and negatively multiply charged biomolecular clusters with low-energy electrons, from ~ 0 up to 50 eV of electron energy, were investigated in a high resolution Fourier-Transform Ion Cyclotron Resonance mass spectrometer equipped with an electrospray ionisation source. Electron-induced dissociation reactions of these clusters depend on the energy of the electrons, the size and the charge state of the cluster. The positively charged clusters [Mn+2H]2+ of zwitterionic betaines, M = (CH3)2XCH2CO2 (X = NCH3 and S), do capture an electron in the low electron energy region (< 10 eV). At higher electron energies neutral evaporation from the cluster becomes competitive with Coulomb explosion. In addition, a series of singly charged fragments arise from bond cleavage reactions, including decarboxylation and CH3 group transfer, due to the access of electronic excited states of the precursor ions. These fragmentation reactions depend on the type of betaine (X = NCH3 or S). For the negative dianionic clusters of tryptophan [Trp9-2H]2-, the important channel at low electron energies is loss of a neutral. Coulomb explosion competes from 19.8 eV and dominates at high electron energies. A small amount of [Trp2-H-NH3]- is observed at 21.8 eV.

  1. Charge state reduction of oligonucleotide negative ions from electrospray ionization

    SciTech Connect

    Cheng, X.; Gale, D.C.; Udseth, H.R.; Smith, R.D. )

    1995-02-01

    We have investigated the feasibility of simplifying the electrospray ionization (ESI) mass spectra for mixture analyses through charge state reduction. Two methods for charge state reduction of gas phase oligonucleotide negative ions were evaluated: (1) the addition of acids to the oligonucleotide solution and (2) the formation of diamine adducts followed by dissociation in the interface region. In the first method, the efficiency of charge state reduction depends on the pK[sub a], the concentration, and the nature of the acids. Acetic and formic acids were found to be better reagents than HCl, CF[sub 3]CO[sub 2]H, and H[sub 3]PO[sub 4]. The second method has the advantage that the stability of oligonucleotides is not affected but requires the optimization of the interface dissociation conditions and the amounts of diamine added to the oligonucleotide solution. Both methods show promise for charge state reduction, and results are presented for two oligonucleotides: d(pT)[sub 12] and d(AGCT). Substantial reduction in spectral complexity upon charge state reduction was also observed for a four-component mixture of oligonucleotides. 54 refs., 8 figs.

  2. Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery

    NASA Astrophysics Data System (ADS)

    2007-07-01

    Astronomers using data from the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) have found the largest negatively-charged molecule yet seen in space. The discovery of the third negatively-charged molecule, called an anion, in less than a year and the size of the latest anion will force a drastic revision of theoretical models of interstellar chemistry, the astronomers say. Molecule formation Formation Process of Large, Negatively-Charged Molecule in Interstellar Space CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for page of graphics and detailed information "This discovery continues to add to the diversity and complexity that is already seen in the chemistry of interstellar space," said Anthony J. Remijan of the National Radio Astronomy Observatory (NRAO). "It also adds to the number of paths available for making the complex organic molecules and other large molecular species that may be precursors to life in the giant clouds from which stars and planets are formed," he added. Two teams of scientists found negatively-charged octatetraynyl, a chain of eight carbon atoms and one hydrogen atom, in the envelope of gas around an old, evolved star and in a cold, dark cloud of molecular gas. In both cases, the molecule had an extra electron, giving it a negative charge. About 130 neutral and about a dozen positively-charged molecules have been discovered in space, but the first negatively-charged molecule was not discovered until late last year. The largest previously-discovered negative ion found in space has six carbon atoms and one hydrogen atom. "Until recently, many theoretical models of how chemical reactions evolve in interstellar space have largely neglected the presence of anions. This can no longer be the case, and this means that there are many more ways to build large organic molecules in cosmic environments than have been explored," said Jan M. Hollis of NASA's Goddard Space Flight Center (GSFC). Ultraviolet light from stars can knock an electron off a molecule, creating a positively-charged ion. Astronomers had thought that molecules would not be able to retain an extra electron, and thus a negative charge, in interstellar space for a significant time. "That obviously is not the case," said Mike McCarthy of the Harvard-Smithsonian Center for Astrophysics. "Anions are surprisingly abundant in these regions." Remijan and his colleagues found the octatetraynyl anions in the envelope of the evolved giant star IRC +10 216, about 550 light-years from Earth in the constellation Leo. They found radio waves emitted at specific frequencies characteristic of the charged molecule by searching archival data from the GBT, the largest fully-steerable radio telescope in the world. Another team from the Harvard-Smithsonian Center for Astrophysics (CfA) found the same characteristic emission when they observed a cold cloud of molecular gas called TMC-1 in the constellation Taurus. These observations also were done with the GBT. In both cases, preceding laboratory experiments by the CfA team showed which radio frequencies actually are emitted by the molecule, and thus told the astronomers what to look for. "It is essential that likely interstellar molecule candidates are first studied in laboratory experiments so that the radio frequencies they can emit are known in advance of an astronomical observation," said Frank Lovas of the National Institute of Standards and Technology (NIST). Both teams announced their results in the July 20 edition of the Astrophysical Journal Letters. "With three negatively-charged molecules now found in a short period of time, and in very different environments, it appears that many more probably exist. We believe that we can discover more new species using very sensitive and advanced radio telescopes such as the GBT, once they have been characterized in the laboratory," said Sandra Bruenken of the CfA. "Further detailed studies of anions, including astronomical observations, laboratory studies, and theoretical calculations, will allow us to use them to reveal new information about the physical and chemical processes going on in interstellar space," said Martin Cordiner, of Queen's University in Belfast, Northern Ireland. "The GBT continues to take a leading role in discovering, identifying and mapping the distribution of the largest molecules ever found in astronomical environments and will continue to do so for the next several decades," said Phil Jewell of NRAO. In addition to Hollis, Lovas, Cordiner and Jewell, Remijan worked with Tom Millar of Queen's University in Belfast, Northern Ireland, and Andrew Markwick-Kemper of the University of Manchester in the UK. Bruenken worked with McCarthy, Harshal Gupta, Carl Gottlieb, and Patrick Thaddeus, all of the Harvard-Smithsonian Center for Astrophysics. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

  3. Gating capacitive field-effect sensors by the charge of nanoparticle/molecule hybrids

    NASA Astrophysics Data System (ADS)

    Poghossian, Arshak; Bäcker, Matthias; Mayer, Dirk; Schöning, Michael J.

    2014-12-01

    The semiconductor field-effect platform is a powerful tool for chemical and biological sensing with direct electrical readout. In this work, the field-effect capacitive electrolyte-insulator-semiconductor (EIS) structure - the simplest field-effect (bio-)chemical sensor - modified with citrate-capped gold nanoparticles (AuNPs) has been applied for a label-free electrostatic detection of charged molecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in AuNP/molecule inorganic/organic hybrids induced by the molecular adsorption or binding events. The feasibility of the proposed detection scheme has been exemplarily demonstrated by realizing capacitive EIS sensors consisting of an Al-p-Si-SiO2-silane-AuNP structure for the label-free detection of positively charged cytochrome c and poly-d-lysine molecules as well as for monitoring the layer-by-layer formation of polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4-styrene sulfonate), representing typical model examples of detecting small proteins and macromolecules and the consecutive adsorption of positively/negatively charged polyelectrolytes, respectively. For comparison, EIS sensors without AuNPs have been investigated, too. The adsorption of molecules on the surface of AuNPs has been verified via the X-ray photoelectron spectroscopy method. In addition, a theoretical model of the functioning of the capacitive field-effect EIS sensor functionalized with AuNP/charged-molecule hybrids has been discussed.The semiconductor field-effect platform is a powerful tool for chemical and biological sensing with direct electrical readout. In this work, the field-effect capacitive electrolyte-insulator-semiconductor (EIS) structure - the simplest field-effect (bio-)chemical sensor - modified with citrate-capped gold nanoparticles (AuNPs) has been applied for a label-free electrostatic detection of charged molecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in AuNP/molecule inorganic/organic hybrids induced by the molecular adsorption or binding events. The feasibility of the proposed detection scheme has been exemplarily demonstrated by realizing capacitive EIS sensors consisting of an Al-p-Si-SiO2-silane-AuNP structure for the label-free detection of positively charged cytochrome c and poly-d-lysine molecules as well as for monitoring the layer-by-layer formation of polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4-styrene sulfonate), representing typical model examples of detecting small proteins and macromolecules and the consecutive adsorption of positively/negatively charged polyelectrolytes, respectively. For comparison, EIS sensors without AuNPs have been investigated, too. The adsorption of molecules on the surface of AuNPs has been verified via the X-ray photoelectron spectroscopy method. In addition, a theoretical model of the functioning of the capacitive field-effect EIS sensor functionalized with AuNP/charged-molecule hybrids has been discussed. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05987e

  4. Formation of Negative Ions upon Dissociative Electron Attachment to the Astrochemically Relevant Molecule Aminoacetonitrile.

    PubMed

    Pelc, Andrzej; Huber, Stefan E; Matias, Carolina; Czupyt, Zbigniew; Denifl, Stephan

    2016-02-18

    Aminoacetonitrile (NH2CH2CN, AAN) is a molecule relevant for interstellar chemistry and the chemical evolution of life. It is a very important molecule in the Strecker diagram explaining the formation of amino acids. In the present investigation, dissociative electron attachment to NH2CN was studied in a crossed electron-molecular beams experiment in the electron energy range from about 0 to 17 eV. In this electron energy range, the following six anionic species were detected: C2H3N2(-), C2H2N2(-), C2H2N(-), C2HN(-), CN(-), and NH2(-). Possible reaction channels for all the measured negative ions are discussed, and the experimental results are compared with calculated thermochemical thresholds of the observed anions. Similar to other nitrile and aminonitrile compounds, the main anions detected were the negatively charged nitrile group, the dehydrogenated parent molecule, and the amino group. No parent anion was observed. Low anion yields were observed indicating that AAN is less prone to electron capture. Therefore, AAN can be considered to exhibit a relatively long lifetime under typical conditions in outer space. PMID:26810336

  5. Negative thermal expansion induced by intermetallic charge transfer

    NASA Astrophysics Data System (ADS)

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-06-01

    Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu3Fe4O12 and LaCu3Fe4-xMnxO12, as well as in Bi or Ni substituted BiNiO3. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding -70 10-6 K-1 near room temperature, in the temperature range which can be controlled by substitution.

  6. Electron-molecule chemistry and charging processes on organic ices and Titan's icy aerosol surrogates

    NASA Astrophysics Data System (ADS)

    Pirim, C.; Gann, R. D.; McLain, J. L.; Orlando, T. M.

    2015-09-01

    Electron-induced polymerization processes and charging events that can occur within Titan's atmosphere or on its surface were simulated using electron irradiation and dissociative electron attachment (DEA) studies of nitrogen-containing organic condensates. The DEA studies probe the desorption of H- from hydrogen cyanide (HCN), acetonitrile (CH3CN), and aminoacetonitrile (NH2CH2CN) ices, as well as from synthesized tholin materials condensed or deposited onto a graphite substrate maintained at low temperature (90-130 K). The peak cross sections for H- desorption during low-energy (3-15 eV) electron irradiation were measured and range from 3 × 10-21 to 2 × 10-18 cm2. Chemical and structural transformations of HCN ice upon 2 keV electron irradiation were investigated using X-ray photoelectron and Fourier-transform infrared spectroscopy techniques. The electron-beam processed materials displayed optical properties very similar to tholins produced by conventional discharge methods. Electron and negative ion trapping lead to 1011 charges cm-2 on a flat surface which, assuming a radius of 0.05 μm for Titan aerosols, is ∼628 charges/radius (in μm). The facile charge trapping indicates that electron interactions with nitriles and complex tholin-like molecules could affect the conductivity of Titan's atmosphere due to the formation of large negative ion complexes. These negatively charged complexes can also precipitate onto Titan's surface and possibly contribute to surface reactions and the formation of dunes.

  7. Charge transfer and charge localization in extended radical cations: Investigation of model molecules for peptides

    NASA Astrophysics Data System (ADS)

    Weinkauf, Rainer; Lehrer, Florian

    1998-12-01

    Molecules consisting of a flexible tail and an aromatic chromophore are used as model systems to understand the situation of a single chromophore in a small peptide. Their S0-S1 resonant multiphoton ionization (REMPI) spectra show, that in neutral molecules the tail-chromophore interaction is weak and electronic excitation is localized at the chromophore. For molecules, where the ionization energy of the tail is considerable higher than that of the chromophore, by high resolution REMPI photoelectron spectroscopy we find the charge to be localized on the aromatic chromophore. This scheme also in suitable peptides allows local ionization at the aromatic chromophore. An estimate for various charge positions in peptide chains, however, shows, that for most of the amino acids electron hole positions in the nitrogen and oxygen "lone pair" orbitals of the peptide bond are nearly degenerate. REMPI photoelectron spectra of phenylethylamine, which as a model system contains such two degenerate charge positions, show small energetic shift of the ionization energy but strong geometry changes upon electron removal. This result is interpreted as direct ionization into a mixed charge delocalized state. Consequences for the charge transfer mechanism in peptides are discussed.

  8. How Do Electric Charges Fix the Architecture of Diatomic Molecules?

    NASA Astrophysics Data System (ADS)

    Yarman, Tolga

    2002-03-01

    Previously, we had established an elegant relationship for the vibrational period T, of a diatomic molecule, in terms of its internuclear distance R, and its "clock mass", M_clock, which can be expressed as f_Mm_e, where me is the electron mass, and f_M= [M_red/m_e]^1/2; M_red is the nuclei reduced mass [1, 2]. Thus we had formerly discovered the relationship T_Mm_eR^2, for any diatomic molecule. More specifically we ended up with the relationship T=4?^2/[h(n_in_j)^1/2][gM_redm_e]^1/2R^2; here g is a dimensionless coefficient; ni and nj are the principal quantum numbers of the electrons making up the bond of the molecule of concern. In this work we relate T and R in terms of the electric charges of the molecule to arrive at T_MR/[(f_Zm_e)^(2)], where fZ is an appropriate coefficient, remaining nearly constant for diatomic molecules belonging to a given chemical family; e is the charge of the electron. One can derive an other interesting relationship for T, still based on the electrical charges; this is T_M/[(f_Ze^(2))^(2)m_e]. Note that the elimination of f_Ze^(2) from the last two period relationships leads to the original compact relationship T_Mm_eR^2, and that all of the relationships in question, are Lorentz invariant. In other terms, we can further state the following: Because matter is built as indicated by the above relationships that, the findings of the special theory of relativity occur, i.e. this is for instance how, say the vibrational frequency of a diatomic molecule, brought to a uniform, translational motion is retarded, just as much as an associated "light clock". Note furthermore that the occurances, such as "clock retardation" in a gravitational field, coming into play, within the frame of the general theory of relativity too, can be derived from the above relationships, without having to use the classical principle of equivalence [3, 4]. The proportionality coefficients in question are found to be around unity. Our approach can be extended to poliatomic molecules with no great difficulty. 1. T. Yarman, A Novel Systematic of Diatomic Molecules Via the Very Special Theory of Relativity, Chimica Acta Turcica, Vol 26, No 3, 1998. 2. N. Zaim, An Approach to The Systematization of Diatomic And Three Atomic Molecules, Ph. D. Thesis Directed by T. Yarman, Trakya University (Edirne, Turkey), September 2000. 3. A. Einstein, The Meaning of Relativity, Princeton University Press, 1953. 4. T. Yarman, A Novel Approach to The End Results of the General Theory of Relativity and to Bound Muon Decay Rate Retardation, DAMOP 2001 Meeting, APS, May 16 -19, 2001, London, Ontario, Canada.

  9. Stability of negatively charged dust grains in Saturn's ring plane

    NASA Technical Reports Server (NTRS)

    Northrop, T. G.; Hill, J. R.

    1982-01-01

    The boundary between the inner and outer parts of Saturn's B ring is located at the theoretical limit of stability of dust grains with large negative charge to mass ratio. A grain inside of this stability limit will move along magnetic field lines and strike Saturn if given a slight velocity component normal to the ring plane. Outside of this marginal stability radius, a perturbed grain merely oscillates back and forth through the ring plane. The theoretical location of the marginal stability radius is at 1.625 Saturn radius. Observations by Pioneer 11 and Voyager 2 in the infared see the boundary as a prominent change in ring brightness at this radius. The occultation of delta-Scorpii by the rings in the ultraviolet seen by Voyager 2 shows about a factor of two change in optical depth beginning very close to this radius.

  10. Symmetry breaking and structural distortions in charged XH{sub 4} (X=C, Si, Ge, Sn, and Pb) molecules

    SciTech Connect

    Balamurugan, D.; Harbola, Manoj K.; Prasad, R.

    2004-03-01

    We have investigated the ground-state structures of neutral and charged XH{sub 4}(X=C, Si, Ge, Sn, and Pb) molecules using the first-principles electronic structure methods. The structure of positively charged molecules for X=Si, Ge, Sn, and Pb is characterized by a severe distortion from tetrahedral structure and an unusual H-H bond while the negatively charged molecules get distorted by pushing two hydrogen atoms away from each other. However, CH{sub 4}{sup +} and CH{sub 4}{sup -} are exceptions to this behavior. We provide an insight into the symmetry breaking mechanism and unusual H-H bonding using simple electrostatic arguments based on the unequal charge distribution on H atoms. Those charged molecules having unequal charge distribution on H atoms get distorted due to different electrostatic forces between the atoms. We show that the directionality and occupation of the highest occupied molecular orbital play an important role in creating charge asymmetry in these molecules.

  11. Charged supramolecular assemblies of surfactant molecules in gas phase.

    PubMed

    Bongiorno, David; Ceraulo, Leopoldo; Indelicato, Sergio; Turco Liveri, Vincenzo; Indelicato, Serena

    2016-01-01

    The aim of this review is to critically analyze recent literature on charged supramolecular assemblies formed by surfactant molecules in gas phase. Apart our specific interest on this research area, the stimuli to undertake the task arise from the widespread theoretical and applicative benefits emerging from a comprehensive view of this topic. In fact, the study of the formation, stability, and physicochemical peculiarities of non-covalent assemblies of surfactant molecules in gas phase allows to unveil interesting aspects such as the role of attractive, repulsive, and steric intermolecular interactions as driving force of supramolecular organization in absence of interactions with surrounding medium and the size and charge state dependence of aggregate structural and dynamical properties. Other interesting aspects worth to be investigated are joined to the ability of these assemblies to incorporate selected solubilizates molecules as well as to give rise to chemical reactions within a single organized structure. In particular, the incorporation of large molecules such as proteins has been of recent interest with the objective to protect their structure and functionality during the transition from solution to gas phase. Exciting fall-out of the study of gas phase surfactant aggregates includes mass and energy transport in the atmosphere, origin of life and simulation of supramolecular aggregation in the interstellar space. Moreover, supramolecular assemblies of amphiphilic molecules in gas phase could find remarkable applications as atmospheric cleaning agents, nanosolvents and nanoreactors for specialized chemical processes in confined space. Mass spectrometry techniques have proven to be particularly suitable to generate these assemblies and to furnish useful information on their size, size polydispersity, stability, and structural organization. On the other hand molecular dynamics simulations have been very useful to rationalize many experimental findings and to furnish a vivid picture of the structural and dynamic features of these aggregates. Thus, in this review, we will focus on the most important achievements gained in recent years by both these investigative tools. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 35: 170-187, 2016. PMID:26113001

  12. Charge neutralization of dust particles in a plasma with negative ions

    SciTech Connect

    Merlino, Robert L.; Kim, Su-Hyun

    2006-08-28

    Charging of dust grains in a plasma with negative ions is studied experimentally. When the relatively mobile electrons are attached to heavy negative ions, their tendency to charge the grains negatively is reduced. In a plasma in which a substantial fraction of the electrons are eliminated (positive ion/negative ion plasma), the grain charge can be reduced in magnitude nearly to zero ('decharging' or charge neutralization). If the positive ions are lighter than the negative ions, dust grains having a small net positive charge can be produced.

  13. Negative differential mobility for negative carriers as revealed by space charge measurements on crosslinked polyethylene insulated model cables

    NASA Astrophysics Data System (ADS)

    Teyssedre, G.; Vu, T. T. N.; Laurent, C.

    2015-12-01

    Among features observed in polyethylene materials under relatively high field, space charge packets, consisting in a pulse of net charge that remains in the form of a pulse as it crosses the insulation, are repeatedly observed but without complete theory explaining their formation and propagation. Positive charge packets are more often reported, and the models based on negative differential mobility(NDM) for the transport of holes could account for some charge packets phenomenology. Conversely, NDM for electrons transport has never been reported so far. The present contribution reports space charge measurements by pulsed electroacoustic method on miniature cables that are model of HVDC cables. The measurements were realized at room temperature or with a temperature gradient of 10 °C through the insulation under DC fields on the order 30-60 kV/mm. Space charge results reveal systematic occurrence of a negative front of charges generated at the inner electrode that moves toward the outer electrode at the beginning of the polarization step. It is observed that the transit time of the front of negative charge increases, and therefore the mobility decreases, with the applied voltage. Further, the estimated mobility, in the range 10-14-10-13 m2 V-1 s-1 for the present results, increases when the temperature increases for the same condition of applied voltage. The features substantiate the hypothesis of negative differential mobility used for modelling space charge packets.

  14. Negatively Charged Hydrogen Production in a Multicusp Microwave Plasma

    NASA Astrophysics Data System (ADS)

    Trow, John Robert

    1985-06-01

    High energy neutral beams are necessary for the continued development of magnetically confined fusion plasma devices. Neutral beams based on positive ions are not efficient at beam energies of 100 keV or above, however negative ion based neutral beam systems are efficient, even at high beam energies. Volume production of H('-) has many advantages over the other methods, chiefly: simplicity of design and operation, and no need for alkalai metals. Since volume production requires a low electron temperature ((TURN)1 eV) but also requires molecular intermediates only formed by more energetic electrons (>20 eV), double plasma devices with a separate hot electron region are desirable. Therefore an experiment was undertaken to examine H('-) production by volume processes in a multicusp microwave discharge, part of the cusp field being enhanced to produce an ECR (electron cyclotron resonance), that would also isolate the hotter plasma formed there. This arrangement is analogous to the "magnetic filters" used in some other negative ion sources. This work describes the experiment set up and the results obtained, which are a survey of the behavior of this type of device. Also included is a discussion of the volume processes associated with H('-) production including numerical estimates, based on the experimental measurements, which indicate H('-) production is by dissociative attachment of cold electrons to vibrationally excited hydrogen molecules, and loss is by mutual neutralization with positive ions. The experimental observations are consistent with this model. These are also the same mechanisms used in the models of Bacal and Hiskes. Since magnetic fields generated by samarium cobalt permanent magnets were an important part of this experiment a set of field calculations was undertaken and is included here as a separate chapter. This device is shown to be a viable scheme of H('-) (or D('-)) produc- tion and is worthy of further development. There are several more. quantities which still need to be measured listed in the conclusion, along with suggested improvements. *This work was supported by the Director, Office of Energy Research, Office of Fusion Energy, Development & Technology Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

  15. Controllable transition from positive space charge to negative space charge in an inverted cylindrical magnetron

    NASA Astrophysics Data System (ADS)

    Rane, R.; Bandyopadhyay, M.; Ranjan, M.; Mukherjee, S.

    2016-01-01

    The combined effect of magnetic field (B), gas pressure (P), and the corresponding discharge voltage on the discharge properties of argon in inverted cylindrical magnetron has been investigated. In the experiment, anode is biased with continuous 10 ms sinusoidal half wave. It is observed that at a comparatively higher magnetic field (i.e., >200 gauss) and lower operating pressure (i.e., <1 × 10-3 mbar), the discharge extinguishes and demands a high voltage to reignite. Discharge current increases with increase in magnetic field and starts reducing at sufficiently higher magnetic field for a particular discharge voltage due to restricted electron diffusion towards the anode. It is observed that B/P ratio plays an important role in sustaining the discharge and is constant for a discharge voltage. The discharge is transformed to negative space charge regime from positive space charge regime at certain B/P ratio and this ratio varies linearly with the discharge voltage. The space charge reversal is indicated by the radial profile of the floating potential and plasma potential in between two electrodes for different magnetic fields. At a particular higher magnetic field (beyond 100 gauss), the floating potential increases gradually with the radial distance from cathode, whereas it remains almost constant at lower magnetic field.

  16. Space charge characteristics of an insulating thin film negatively charged by a low-energy electron beam.

    PubMed

    Zhang, Hai-Bo; Li, Wei-Qin; Cao, Meng

    2012-04-01

    In this study, based on a comprehensive numerical simulation of self-consistent charging, we investigate the formation, evolution and influencing factors of space charge distributions for a grounded insulating thin film of SiO(2) negatively charged by a keV non-penetrating focused electron beam. The simulated space charge presents first positive distributions and then negative ones along both the radial and depth directions because of the difference between electron and hole transports. The variations in distribution occur within a range of the minimum potential acting as a potential barrier for carrier transport. The negative space charge is distributed more widely and deeply, though its peak value in density is usually lower than that of the positive one. Electrons trapped outside the minimum potential range dominate the strength of negative charging. With the increase in potential barrier and the occurrence of leakage current, the space charge eventually reaches equilibrium and exhibits an approximately one-dimensional axial distribution outside the minimum potential range. Distribution features of the space charge density in the equilibrium state correlate with the film and beam parameters via transients of the leakage current. These results and analyses provide new insights into the negative charging effects involved in various electron-beam-based surface microscopic methods, analyses and fabrication techniques. PMID:22215798

  17. Experimental evidence on removing copper and light-induced degradation from silicon by negative charge

    NASA Astrophysics Data System (ADS)

    Boulfrad, Yacine; Lindroos, Jeanette; Wagner, Matthias; Wolny, Franziska; Yli-Koski, Marko; Savin, Hele

    2014-11-01

    In addition to boron and oxygen, copper is also known to cause light-induced degradation (LID) in silicon. We have demonstrated previously that LID can be prevented by depositing negative corona charge onto the wafer surfaces. Positively charged interstitial copper ions are proposed to diffuse to the negatively charged surface and consequently empty the bulk of copper. In this study, copper out-diffusion was confirmed by chemical analysis of the near surface region of negatively/positively charged silicon wafer. Furthermore, LID was permanently removed by etching the copper-rich surface layer after negative charge deposition. These results demonstrate that (i) copper can be effectively removed from the bulk by negative charge, (ii) under illumination copper forms a recombination active defect in the bulk of the wafer causing severe light induced degradation.

  18. Experimental evidence on removing copper and light-induced degradation from silicon by negative charge

    SciTech Connect

    Boulfrad, Yacine Lindroos, Jeanette; Yli-Koski, Marko; Savin, Hele; Wagner, Matthias; Wolny, Franziska

    2014-11-03

    In addition to boron and oxygen, copper is also known to cause light-induced degradation (LID) in silicon. We have demonstrated previously that LID can be prevented by depositing negative corona charge onto the wafer surfaces. Positively charged interstitial copper ions are proposed to diffuse to the negatively charged surface and consequently empty the bulk of copper. In this study, copper out-diffusion was confirmed by chemical analysis of the near surface region of negatively/positively charged silicon wafer. Furthermore, LID was permanently removed by etching the copper-rich surface layer after negative charge deposition. These results demonstrate that (i) copper can be effectively removed from the bulk by negative charge, (ii) under illumination copper forms a recombination active defect in the bulk of the wafer causing severe light induced degradation.

  19. An analysis of five negative sprite-parent discharges and their associated thunderstorm charge structures

    NASA Astrophysics Data System (ADS)

    Boggs, Levi D.; Liu, Ningyu; Splitt, Michael; Lazarus, Steven; Glenn, Chad; Rassoul, Hamid; Cummer, Steven A.

    2016-01-01

    In this study we analyze the discharge morphologies of five confirmed negative sprite-parent discharges and the associated charge structures of the thunderstorms that produced them. The negative sprite-parent lightning took place in two thunderstorms that were associated with a tropical disturbance in east central and south Florida. The first thunderstorm, which moved onshore in east central Florida, produced four of the five negative sprite-parent discharges within a period of 17 min, as it made landfall from the Atlantic Ocean. These negative sprite-parents were composed of bolt-from-the-blue (BFB), hybrid intracloud-negative cloud-to-ground (IC-NCG), and multicell IC-NCGs discharges. The second thunderstorm, which occurred inland over south Florida, produced a negative sprite-parent that was a probable hybrid IC-NCG discharge and two negative gigantic jets (GJs). Weakened upper positive charge with very large midlevel negative charge was inferred for both convective cells that initiated the negative-sprite-parent discharges. Our study suggests tall, intense convective systems with high wind shear at the middle to upper regions of the cloud accompanied by low cloud-to-ground (CG) flash rates promote these charge structures. The excess amount of midlevel negative charge results in these CG discharges transferring much more charge to ground than typical negative CG discharges. We find that BFB discharges prefer an asymmetrical charge structure that brings the negative leader exiting the upper positive charge region closer to the lateral positive screening charge layer. This may be the main factor in determining whether a negative leader exiting the upper positive region of the thundercloud forms a BFB or GJ.

  20. Transport of charge and energy in metal-molecule-metal junctions

    NASA Astrophysics Data System (ADS)

    Sangi Reddy, Pramod Reddy

    This dissertation presents the experimental study of the electrical conductance (G) and Seebeck coefficient (S) of metal-molecule-metal junctions. The dependence of the electrical conductance of metal-molecule-metal junctions on the molecule's structure is elucidated. The existence of a measurable Seebeck coefficient in metal-molecule-metal junctions is shown for the first time and the sign of the measured Seebeck coefficient is used to determine whether the charge transport in metal-molecule-metal junctions is dominated by positive (p-type) or negative (n-type) charge carriers. The electrical conductance of a series of thiol (-SH), amine (-NH 2) terminated aliphatic and aromatic molecules was measured using a modified scanning tunneling microscope break junction technique. A new method called the last-step analysis (LSA) was introduced to analyze data obtained in these measurements. This analysis in contrast to previous work does not require any data pre-selection, making the results less subjective and more reproducible. We first studied the electrical conductance of aliphatic molecular junctions. It was found that Au-hexanedithiol-Au, Au-octanedithiol-Au and Au-decanedithiol-Au junctions have an electrical conductance of 3.6 X 10 -4 Go, 4.4 X 10-5 Go and 5.7 X 10-6 Go, respectively, where Go is the fundamental quantum of electrical conductance. The electrical conductance decreases exponentially with the length of the alkane chains suggesting that the mechanism for electrical transport through these molecular junctions is quantum mechanical tunneling. On varying the end groups of aliphatic molecules 0rom thiols to amines we found that the electrical conductance was almost identical, suggesting that the end group had no significant effect on the electrical conductance in this case. We also measured the electrical conductance of aromatic molecular junctions: Au-1,4-benzenediamine-Au, Au-4,4'-dibenzenediamine-Au and Au-4.4''-tribenzenediamine-Au and they were found to have an electrical conductance of 1.05 X 10 -2 Go, 1.41 X 10-3 Go and 2.05 X 10-4 Go, respectively. Although, the electrical conductance decreases exponentially with the lengths of the molecules even in the case of aromatic molecules, the length dependence of the electrical conductance was much weaker than that of aliphatic molecular junctions. From the data it can be seen that for a given length aromatic molecular junctions have a larger conductance than aliphatic molecular junctions. The Seebeck coefficient (S) of molecular junctions was measured using a modified break junction technique by trapping molecules between two gold electrodes with a temperature difference across them. The junction Seebeck coefficient of Au-1,4-benzenedithiol-Au, Au-4,4'-dibenzenedithiol-Au and Au-4,4"-tribenzenedithiol-Au was measured at room temperature to be (+8.7 +/- 2.1) microvolts per Kelvin (muV/K), (+12.9 +/- 2.2) muV/K, and (+14.2 +/- 3.2) muV/K, respectively. The positive sign unambiguously indicates p-type (hole) conduction through these heterojunctions, and the Au Fermi level position for AuBDT-Au junctions was identified at 1.2 eV above the highest occupied molecular orbital (HOMO) level of BDT. Our study provides the first experimental answer to the question of whether charge transport through molecular junctions is dominated by p-type or n-type charge carriers. In perspective, the ability to study thermoelectricity in molecular junctions as demonstrated here allows us to address some of the fundamental transport problems in molecular electronics.

  1. Binding of monovalent alkali metal ions with negatively charged phospholipid membranes.

    PubMed

    Maity, Pabitra; Saha, Baishakhi; Kumar, Gopinatha Suresh; Karmakar, Sanat

    2016-04-01

    We have systematically investigated the effect of various alkali metal ions with negatively charged phospholipid membranes. Size distributions of large unilamellar vesicles have been confirmed using dynamic light scattering. Zeta potential and effective charges per vesicle in the presence of various alkali metal ions have been estimated from the measured electrophoretic mobility. We have determined the intrinsic binding constant from the zeta potential using electrostatic double layer theory. The reasonable and consistent value of the intrinsic binding constant of Na(+), found at moderate NaCl concentration (10-100mM), indicates that the Gouy-Chapman theory cannot be applied for very high (>100mM) and very low (<10mM) electrolyte concentrations. The isothermal titration calorimetry study has revealed that the net binding heat of interaction of the negatively charged vesicles with monovalent alkali metal ions is small and comparable to those obtained from neutral phosphatidylcholine vesicles. The overall endothermic response of binding heat suggests that interaction is primarily entropy driven. The entropy gain might arise due to the release of water molecules from the hydration layer vicinity of the membranes. Therefore, the partition model which does not include the electrostatic contribution suffices to describe the interaction. The binding constant of Na(+) (2.4±0.1M(-1)), obtained from the ITC, is in agreement with that estimated from the zeta potential (~2.0M(-1)) at moderate salt concentrations. Our results suggest that hydration dynamics may play a vital role in the membrane solution interface which strongly affects the ion-membrane interaction. PMID:26802251

  2. Positively and negatively surface-charged chondroitin sulfate-trimethylchitosan nanoparticles as protein carriers.

    PubMed

    Young, Jenn-Jong; Chen, Cheng-Cheung; Chen, Ying-Chuan; Cheng, Kuang-Ming; Yen, Hui-Ju; Huang, Yu-Chuan; Tsai, Tsung-Neng

    2016-02-10

    Positively and negatively surface-charged nanoparticles (NPs) were prepared with chondroitin sulfate (ChS) and trimethylchitosan (TMC). NP size, surface charge, formation yield, and water content were investigated as a function of weight ratio and concentration. Size and zeta potential were controlled by varying the ChS/TMC mass ratio. FTIR spectra revealed interactions among composite NP constituents. TEM images showed that the NPs were nearly spherical, with an average size of ∼300nm. Encapsulation efficiency increased in positively charged NPs with increases in fluorescein isothiocyanate-bovine serum albumin concentration. Negatively charged NPs had only 10-20% encapsulation efficiency. The release profile, release kinetics and mechanism of positively charged ChS-TMC NPs were studied in vitro. NP cytocompatibility and uptake were verified ex vivo. Both types of NPs were taken up and retained in cells. A549 cells took up more positively charged (49.4%) than negatively charged (35.5%) NPs. PMID:26686160

  3. Mass Spectrometry Study of Multiply Negatively Charged, Gas-Phase NaAOT Micelles: How Does Charge State Affect Micellar Structure and Encapsulation?

    NASA Astrophysics Data System (ADS)

    Fang, Yigang; Liu, Fangwei; Liu, Jianbo

    2013-01-01

    We report the formation and characterization of multiply negatively charged sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) aggregates in the gas phase, by electrospray ionization of methanol/water solution of NaAOT followed by detection using a guided-ion-beam tandem mass spectrometer. Singly and doubly charged aggregates dominate the mass spectra with the compositions of [Nan-zAOTn]z- ( n = 1-18 and z = 1-2). Solvation by water was detected only for small aggregates [Nan-1AOTnH2O]- of n = 3-9. Incorporation of glycine and tryptophan into [Nan-zAOTn]z- aggregates was achieved, aimed at identifying effects of guest molecule hydrophobicity on micellar solubilization. Only one glycine molecule could be incorporated into each [Nan-zAOTn]z- of n ? 7, and at most two glycine molecules could be hosted in that of n ? 13. In contrast to glycine, up to four tryptophan molecules could be accommodated within single aggregates of n ? 6. However, deprotonation of tryptophan significantly decrease its affinity towards aggregates. Collision-induced dissociation (CID) was carried out for mass-selected aggregate ions, including measurements of product ion mass spectra for both empty and amino acid-containing aggregates. CID results provide a probe for aggregate structures, surfactant-solute interactions, and incorporation sites of amino acids. The present data was compared with mass spectrometry results of positively charged [Nan+zAOTn]z+ aggregates. Contrary to their positive analogues, which form reverse micelles, negatively charged aggregates may adopt a direct micelle-like structure with AOT polar heads exposed and amino acids being adsorbed near the micellar outer surface.

  4. Lightning morphology and impulse charge moment change of high peak current negative strokes

    NASA Astrophysics Data System (ADS)

    Lu, Gaopeng; Cummer, Steven A.; Blakeslee, Richard J.; Weiss, Stephanie; Beasley, William H.

    2012-02-01

    We have analyzed very high frequency lightning mapping observations and remote magnetic field measurements to investigate connections between lightning morphology and impulse charge moment change (iCMC) of negative cloud-to-ground (CG) strokes with high estimated peak currents. Four lightning morphologies are identified for a total of 2126 strokes within optimum detection range of the North Alabama Lightning Mapping Array, and statistical iCMC distributions are given for each of these types. Almost all (>90%) of the largest impulse charge moments (greater than -200 C km in this data set) are not produced by strokes in ordinary negative CG flashes. Instead, negative strokes with the largest iCMCs are almost exclusively associated with two unusual flash types that both initially develop as positive (normal) intracloud lightning. In the first type the negative stroke with high iCMCs results from a negative leader that descends from the midlevel negative charge region after the upper level negative leader ceases propagating. In the second type, the upper level negative leader of the intracloud lightning progresses toward ground as a so-called bolt from the blue to generate the negative stroke. Measurements of strokes associated with four negative polarity sprites suggest that all four were most likely produced in the first unusual lightning type. Our results highlight that estimated peak current and impulse charge transfer are not always well correlated and that the in-cloud lightning structure strongly influences charge transfer on short time scales in negative CG strokes.

  5. Self-Optimized Biological Channels in Facilitating the Transmembrane Movement of Charged Molecules

    PubMed Central

    Huyen, V. T. N.; Lap, Vu Cong; Nguyen, V. Lien

    2016-01-01

    We consider an anisotropically two-dimensional diffusion of a charged molecule (particle) through a large biological channel under an external voltage. The channel is modeled as a cylinder of three structure parameters: radius, length, and surface density of negative charges located at the channel interior-lining. These charges induce inside the channel a potential that plays a key role in controlling the particle current through the channel. It was shown that to facilitate the transmembrane particle movement the channel should be reasonably self-optimized so that its potential coincides with the resonant one, resulting in a large particle current across the channel. Observed facilitation appears to be an intrinsic property of biological channels, regardless of the external voltage or the particle concentration gradient. This facilitation is very selective in the sense that a channel of definite structure parameters can facilitate the transmembrane movement of only particles of proper valence at corresponding temperatures. Calculations also show that the modeled channel is nonohmic with the ion conductance which exhibits a resonance at the same channel potential as that identified in the current.

  6. Negative differential conductance and super-Poissonian shot noise in single-molecule magnet junctions

    PubMed Central

    Xue, Hai-Bin; Liang, Jiu-Qing; Liu, Wu-Ming

    2015-01-01

    Molecular spintroinic device based on a single-molecule magnet is one of the ultimate goals of semiconductor nanofabrication technologies. It is thus necessary to understand the electron transport properties of a single-molecule magnet junction. Here we study the negative differential conductance and super-Poissonian shot noise properties of electron transport through a single-molecule magnet weakly coupled to two electrodes with either one or both of them being ferromagnetic. We predict that the negative differential conductance and super-Poissonian shot noise, which can be tuned by a gate voltage, depend sensitively on the spin polarization of the source and drain electrodes. In particular, the shot noise in the negative differential conductance region can be enhanced or decreased originating from the different formation mechanisms of negative differential conductance. The effective competition between fast and slow transport channels is responsible for the observed negative differential conductance and super-Poissonian shot noise. In addition, we further discuss the skewness and kurtosis properties of transport current in the super-Poissonian shot noise regions. Our findings suggest a tunable negative differential conductance molecular device, and the predicted properties of high-order current cumulants are very interesting for a better understanding of electron transport through single-molecule magnet junctions. PMID:25736094

  7. Maximizing Ion Current by Space Charge Neutralization using Negative Ions and Dust Particles

    SciTech Connect

    A. Smirnov; Y. Raitses; N.J. Fisch

    2005-01-25

    Ion current extracted from an ion source (ion thruster) can be increased above the Child-Langmuir limit if the ion space charge is neutralized. Similarly, the limiting kinetic energy density of the plasma flow in a Hall thruster might be exceeded if additional mechanisms of space charge neutralization are introduced. Space charge neutralization with high-mass negative ions or negatively charged dust particles seems, in principle, promising for the development of a high current or high energy density source of positive light ions. Several space charge neutralization schemes that employ heavy negatively charged particles are considered. It is shown that the proposed neutralization schemes can lead, at best, only to a moderate but nonetheless possibly important increase of the ion current in the ion thruster and the thrust density in the Hall thruster.

  8. Maximizing ion current by space-charge neutralization using negative ions and dust particles

    SciTech Connect

    Smirnov, A.; Raitses, Y.; Fisch, N.J.

    2005-05-15

    Ion current extracted from an ion source (ion thruster) can be increased above the Child-Langmuir limit if the ion space charge is neutralized. Similarly, the limiting kinetic energy density of the plasma flow in a Hall thruster might be exceeded if additional mechanisms of space-charge neutralization are introduced. Space-charge neutralization with high-mass negative ions or negatively charged dust particles seems, in principle, promising for the development of a high current or high energy density source of positive light ions. Several space-charge neutralization schemes that employ heavy negatively charged particles are considered. It is shown that the proposed neutralization schemes can lead, at best, only to a moderate but nonetheless possibly important increase of the ion current in the ion thruster and the thrust density in the Hall thruster.

  9. Ion beam driven ion-acoustic waves in a plasma cylinder with negatively charged dust grains

    SciTech Connect

    Sharma, Suresh C.; Walia, Ritu; Sharma, Kavita

    2012-07-15

    An ion beam propagating through a magnetized potassium plasma cylinder having negatively charged dust grains drives electrostatic ion-acoustic waves to instability via Cerenkov interaction. The phase velocity of sound wave increases with the relative density of negatively charged dust grains. The unstable wave frequencies and the growth rate increase, with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales as one-third power of the beam density. The real part of frequency of the unstable mode increases with the beam energy and scales as almost the one-half power of the beam energy.

  10. Ion beam driven ion-acoustic waves in a plasma cylinder with negatively charged dust grains

    NASA Astrophysics Data System (ADS)

    Sharma, Suresh C.; Sharma, Kavita; Walia, Ritu

    2012-07-01

    An ion beam propagating through a magnetized potassium plasma cylinder having negatively charged dust grains drives electrostatic ion-acoustic waves to instability via Cerenkov interaction. The phase velocity of sound wave increases with the relative density of negatively charged dust grains. The unstable wave frequencies and the growth rate increase, with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales as one-third power of the beam density. The real part of frequency of the unstable mode increases with the beam energy and scales as almost the one-half power of the beam energy.

  11. Charging-delay induced dust acoustic collisionless shock wave: Roles of negative ions

    SciTech Connect

    Ghosh, Samiran; Bharuthram, R.; Khan, Manoranjan; Gupta, M. R.

    2006-11-15

    The effects of charging-delay and negative ions on nonlinear dust acoustic waves are investigated. It has been found that the charging-delay induced anomalous dissipation causes generation of dust acoustic collisionless shock waves in an electronegative dusty plasma. The small but finite amplitude wave is governed by a Korteweg-de Vries Burger equation in which the Burger term arises due to the charging-delay. Numerical investigations reveal that the charging-delay induced dissipation and shock strength decreases (increases) with the increase of negative ion concentration (temperature)

  12. Electrical Detection of Negatively Charged Proteins Using n-Type Carbon Nanotube Field-Effect Transistor Biosensors

    NASA Astrophysics Data System (ADS)

    Yamamoto, Yasuki; Maehashi, Kenzo; Ohno, Yasuhide; Matsumoto, Kazuhiko

    2010-02-01

    We fabricated n-type carbon nanotube field-effect transistor (CNTFET) biosensors. To prevent the single-wall carbon nanotube (SWNT)/metal contacts from adsorption of ambient molecules, SiNx passivation films were deposited on CNTFETs by catalytic chemical vapor deposition. CNTFETs with SiNx passivation films on SWNT/metal contacts, but SWNT channels are exposed to environment for sensing, exhibit n-type behavior both in air and solution. Negatively charged bovine serum albumin is successfully detected using the fabricated n-type CNTFET biosensors with SiNx passivation films. Electrical detections of both negatively and positively charged proteins are achieved using n- and p-type CNTFET biosensors, respectively.

  13. An electrochemical model of the transport of charged molecules through the capillary glycocalyx.

    PubMed

    Stace, T M; Damiano, E R

    2001-04-01

    An electrochemical theory of the glycocalyx surface layer on capillary endothelial cells is developed as a model to study the electrochemical dynamics of anionic molecular transport within capillaries. Combining a constitutive relationship for electrochemical transport, derived from Fick's and Ohm's laws, with the conservation of mass and Gauss's law from electrostatics, a system of three nonlinear, coupled, second-order, partial, integro-differential equations is obtained for the concentrations of the diffusing anionic molecules and the cations and anions in the blood. With the exception of small departures from electroneutrality that arise locally near the apical region of the glycocalyx, the model assumes that cations in the blood counterbalance the fixed negative charges bound to the macromolecular matrix of the glycocalyx in equilibrium. In the presence of anionic molecular tracers injected into the capillary lumen, the model predicts the size- and charge-dependent electrophoretic mobility of ions and tracers within the layer. In particular, the model predicts that anionic molecules are excluded from the glycocalyx at equilibrium and that the extent of this exclusion, which increases with increasing tracer and/or glycocalyx electronegativity, is a fundamental determinant of anionic molecular transport through the layer. The model equations were integrated numerically using a Crank-Nicolson finite-difference scheme and Newton-Raphson iteration. When the concentration of the anionic molecular tracer is small compared with the concentration of ions in the blood, a linearized version of the model can be obtained and solved as an eigenvalue problem. The results of the linear and nonlinear models were found to be in good agreement for this physiologically important case. Furthermore, if the fixed-charge density of the glycocalyx is of the order of the concentration of ions in the blood, or larger, or if the magnitude of the anionic molecular valence is large, a closed-form asymptotic solution for the diffusion time can be obtained from the eigenvalue problem that compares favorably with the numerical solution. In either case, if leakage of anionic molecules out of the capillary occurs, diffusion time is seen to vary exponentially with anionic valence and in inverse proportion to the steady-state anionic tracer concentration in the layer relative to the lumen. These findings suggest several methods for obtaining an estimate of the glycocalyx fixed-charge density in vivo. PMID:11259282

  14. Calculating Henrys Constants of Charged Molecules Using SPARC

    EPA Science Inventory

    SPARC Performs Automated Reasoning in Chemistry is a computer program designed to model physical and chemical properties of molecules solely based on thier chemical structure. SPARC uses a toolbox of mechanistic perturbation models to model intermolecular interactions. SPARC has ...

  15. Calculating Henry’s Constants of Charged Molecules Using SPARC

    EPA Science Inventory

    SPARC Performs Automated Reasoning in Chemistry is a computer program designed to model physical and chemical properties of molecules solely based on thier chemical structure. SPARC uses a toolbox of mechanistic perturbation models to model intermolecular interactions. SPARC has ...

  16. Surfactin-Triggered Small Vesicle Formation of Negatively Charged Membranes: A Novel Membrane-Lysis Mechanism

    PubMed Central

    Buchoux, Sbastien; Lai-Kee-Him, Josphine; Garnier, Marie; Tsan, Pascale; Besson, Franoise; Brisson, Alain; Dufourc, Erick J.

    2008-01-01

    The molecular mode of action of the lipopeptide SF with zwitterionic and negatively charged model membranes has been investigated with solid-state NMR, light scattering, and electron microscopy. It has been found that this acidic lipopeptide (negatively charged) induces a strong destabilization of negatively charged micrometer-scale liposomes, leading to the formation of small unilamellar vesicles of a few 10s of nanometers. This transformation is detected for very low doses of SF (Ri = 200) and is complete for Ri = 50. The phenomenon has been observed for several membrane mixtures containing phosphatidylglycerol or phosphatidylserine. The vesicularization is not observed when the lipid negative charges are neutralized and a cholesterol-like effect is then evidenced, i.e., increase of gel membrane dynamics and decrease of fluid membrane microfluidity. The mechanism for small vesicle formation thus appears to be linked to severe changes in membrane curvature and could be described by a two-step action: 1), peptide insertion into membranes because of favorable van der Waals forces between the rather rigid cyclic and lipophilic part of SF and lipid chains and 2), electrostatic repulsion between like charges borne by lipid headgroups and the negatively charged SF amino acids. This might provide the basis for a novel mode of action of negatively charged lipopeptides. PMID:18515378

  17. Aberration of a negative ion beam caused by space charge effect

    SciTech Connect

    Miyamoto, K.; Wada, S.; Hatayama, A.

    2010-02-15

    Aberrations are inevitable when the charged particle beams are extracted, accelerated, transmitted, and focused with electrostatic and magnetic fields. In this study, we investigate the aberration of a negative ion accelerator for a neutral beam injector theoretically, especially the spherical aberration caused by the negative ion beam expansion due to the space charge effect. The negative ion current density profiles with the spherical aberration are compared with those without the spherical aberration. It is found that the negative ion current density profiles in a log scale are tailed due to the spherical aberration.

  18. Comment on "An experimental and theoretical study of the negatively charged helium dimer, He2-"

    NASA Astrophysics Data System (ADS)

    Michels, H. H.; Hobbs, R. H.; Bae, Y. K.; Peterson, J. R.

    1990-07-01

    It is shown that the study of the negatively charged helium dimer reported by Krishnamurthy and Mathur contains serious errors in both the theoretical interpretation and experimental analysis of this ion.

  19. Nonlinear charge transport in the helicoidal DNA molecule

    NASA Astrophysics Data System (ADS)

    Dang Koko, A.; Tabi, C. B.; Ekobena Fouda, H. P.; Mohamadou, A.; Kofan, T. C.

    2012-12-01

    Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schrdinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter ?, which measures hopping interaction correction. In so doing, increasing ? leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of ?. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study.

  20. Nonlinear charge transport in the helicoidal DNA molecule.

    PubMed

    Dang Koko, A; Tabi, C B; Ekobena Fouda, H P; Mohamadou, A; Kofan, T C

    2012-12-01

    Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schro?dinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter ?, which measures hopping interaction correction. In so doing, increasing ? leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of ?. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study. PMID:23278045

  1. Forth-back oscillated charge carrier motion in dynamically disordered hexathienocoronene molecules: a theoretical study.

    PubMed

    Navamani, K; Senthilkumar, K

    2015-07-21

    Electronic structure calculations were performed to investigate the charge transport properties of hexathienocoronene (HTC) based molecules. The effective displacement of the charge carrier along the ?-orbital of nearby molecules is calculated by monitoring the forth and back oscillations of the charge carrier through kinetic Monte Carlo simulation. The charge transport parameters such as charge transfer rate, mobility, hopping conductivity, localized charge density, time average effective mass and degeneracy pressure are calculated and used to study the charge transport mechanism in the studied molecules. The existence of degeneracy levels facilitates the charge transfer and is analyzed through degeneracy pressure. Theoretical results show that the site energy difference in the dynamically disordered system controls the forth-back oscillation of charge carrier and facilitates the unidirectional charge transport mechanism along the sequential localized sites. The ethyl substituted HTC has good hole and electron hopping conductivity of 415 and 894 S cm(-1), respectively, whereas unsubstituted HTC has the small hole mobility of 0.06 cm(2) V(-1) s(-1) which is due to large average effective mass of 1.42 10(-28) kg. PMID:26080732

  2. Vibrational States of Hydrogen Molecules in One Third LHD Negative Ion Source

    SciTech Connect

    Nishiura, M.; Tsumori, K.; Matsumoto, Y.; Wada, M.; Inoue, T.

    2011-09-26

    The effect of the cesium on hydrogen negative ions is discussed using the vacuum ultraviolet emissions (VUV) from vibrational states of hydrogen molecules. The VUV spectrum from 90 to 165 nm is related to the H{sup -} production from the dissociative attachment of electrons to hydrogen molecules. The VUV spectra in hydrogen plasmas are measured in the extraction region of a negative ion source for neutral beam injector. Under the pure hydrogen discharge, the cesium vapor is introduced into the ion source to enhance the hydrogen negative ion density. When the same arc power of {approx}99 kW is applied in both with and without cesium admixture cases, the ratio of the observed VUV spectrum without to with cesium is not changed clearly. Therefore the production process of H{sup -} related to the wall/electrode surface would be enhanced rather than the volume production process.

  3. Role of solvent dielectric properties on charge transfer from PbS nanocrystals to molecules.

    PubMed

    Hyun, Byung-Ryool; Bartnik, A C; Lee, Jin-Kyun; Imoto, Hiroaki; Sun, Liangfeng; Choi, Joshua J; Chujo, Yoshiki; Hanrath, Tobias; Ober, Christopher K; Wise, F W

    2010-01-01

    Transfer of photoexcited charge from PbS nanocrystals to ligand molecules is investigated in different solvents. We find that the charge transfer rate increases dramatically with solvent dielectric constant. This trend is accounted for by a modified Marcus theory that incorporates only static dielectric effects. The choice of solvent allows significant control of the charge transfer process. As an important example, we find that PbS nanocrystals dispersed in water exhibit charge transfer rates 1000 times higher than the same nanocrystals in organic solvent. Rapid charge extraction will be important to efficient nanocrystal-based photovoltaic and photodetector devices. PMID:19968265

  4. Polarized Protein-Specific Charges from Atoms-in-Molecule Electron Density Partitioning

    PubMed Central

    2013-01-01

    Atomic partial charges for use in traditional force fields for biomolecular simulation are often fit to the electrostatic potentials of small molecules and, hence, neglect large-scale electronic polarization. On the other hand, recent advances in atoms-in-molecule charge derivation schemes show promise for use in flexible force fields but are limited in size by the underlying quantum mechanical calculation of the electron density. Here, we implement the density derived electrostatic and chemical charges method in the linear-scaling density functional theory code ONETEP. Our implementation allows the straightforward derivation of partial atomic charges for systems comprising thousands of atoms, including entire proteins. We demonstrate that the derived charges are chemically intuitive, reproduce ab initio electrostatic potentials of proteins and are transferable between closely related systems. Simulated NMR data derived from molecular dynamics of three proteins using force fields based on the ONETEP charges are in good agreement with experiment. PMID:23894231

  5. Interactions of Cationic Peptides and Ions with Negatively Charged Lipid Bilayers

    NASA Astrophysics Data System (ADS)

    Taheri-Araghi, Sattar

    In this thesis we study the interactions of ions and cationic peptides with a negatively charged lipid bilayer in an ionic solution where the electrostatic interactions are screened. We first examine the problem of charge renormalization and inversion of a highly charged bilayer with low dielectric constant. To be specific, we consider an asymmetrically charged lipid bilayer, in which only one layer is negatively charged. In particular, we study how dielectric discontinuities and charge correlations among lipid charges and condensed counterions influence the effective charge of the surface. When counterions are monovalent, e. g. , Na+, our mean-field approach implies that dielectric discontinuities can enhance counterion condensation. A simple scaling picture shows how the effects of dielectric discontinuities and surface-charge distributions are intertwined: Dielectric discontinuities diminish condensation if the backbone charge is uniformly smeared out while counterions are localized in space; they can, however, enhance condensation when the backbone charge is discrete. In the presence of asymmetric salts such as CaCl2, we find that the correlation effect, treated at the Gaussian level, is more pronounced when the surface has a lower dielectric constant, inverting the sign of the charge at a smaller value of Ca2+ concentration. In the last chapter we study binding of cationic peptides onto a lipid-bilayer membrane. The peptide not only interacts electrostatically with anionic lipids, rearranging their spatial distributions, but it can also insert hydrophobically into the membrane, expanding the area of its binding layer (i. e. , the outer layer). We examine how peptide charges and peptide insertion (thus area expansion) are intertwined. Our results show that, depending on the bilayer's surface charge density and peptide hydrophobicity, there is an optimal peptide charge yielding the maximum peptide penetration. Our results shed light on the physics behind the activity and selective toxicity of antimicrobial peptides, i. e. , they selectively rupture bacterial membranes while leaving host cells intact.

  6. Energy distribution extraction of negative charges responsible for positive bias temperature instability

    NASA Astrophysics Data System (ADS)

    Ren, Shang-Qing; Yang, Hong; Wang, Wen-Wu; Tang, Bo; Tang, Zhao-Yun; Wang, Xiao-Lei; Xu, Hao; Luo, Wei-Chun; Zhao, Chao; Yan, Jiang; Chen, Da-Peng; Ye, Tian-Chun

    2015-07-01

    A new method is proposed to extract the energy distribution of negative charges, which results from electron trapping by traps in the gate stack of nMOSFET during positive bias temperature instability (PBTI) stress based on the recovery measurement. In our case, the extracted energy distribution of negative charges shows an obvious dependence on energy, and the energy level of the largest energy density of negative charges is 0.01 eV above the conduction band of silicon. The charge energy distribution below that energy level shows strong dependence on the stress voltage. Project supported by the National Science & Technology Major Projects of the Ministry of Science and Technology of China (Grant No. 2009ZX02035) and the National Natural Science Foundation of China (Grant Nos. 61176091 and 61306129).

  7. Ionization of water molecules by fast charged projectiles

    SciTech Connect

    Dubois, A.; Carniato, S.; Fainstein, P. D.; Hansen, J. P.

    2011-07-15

    Single-ionization cross sections of water molecules colliding with fast protons are calculated from lowest-order perturbation theory by taking all electrons and molecular orientations consistently into account. Explicit analytical formulas based on the peaking approximation are obtained for differential ionization cross sections with the partial contribution from the various electron orbitals accounted for. The results, which are in very good agreement with total and partial cross sections at high electron and projectile energies, display a strong variation on molecular orientation and molecular orbitals.

  8. Interfacial charge transfer dynamics in small molecule-modified TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Varaganti, Shankar; Mghangha, Edwin; Hasan, Jameel A.; Ramakrishna, Guda

    2010-08-01

    Direct molecule-semiconductor interfacial charge transfer interactions have received considerable research attention for their applications in various fields. In this study, the dynamics of molecule-TiO2 interfacial charge transfer complexes is monitored with femtosecond fluorescence upconversion and transient absorption. Small molecules (catechol, dopamine, benzhydroxamic acid, acetyl acetonate and salicylate)-modified TiO2 nanoparticles are prepared and the complexation is followed with optical absorption measurements. Although little visible luminescence is observed from these molecule- TiO2 nanoparticles, ultrafast emission in broad range of wavelengths is detected with fluorescence upconversion which is ascribed to the interfacial charge transfer emission. The charge transfer emission arose out of the radiative recombination of the electrons in the conduction band of TiO2 with holes in the molecule. Femtosecond fluorescence anisotropy measurements have shown that the interfacial charge-transfer excitation is mostly a localized one for catechol, dopamine and benzhydroxamate modified TiO2 nanoparticles. However, the possibility of delocalized charge-transfer excitations is observed for salicylate and acetyl acetonate-TiO2 nanoparticles. The decay of the charge transfer emission is ascribed to the relaxation of the localized states to delocalized states in the TiO2 conduction band. Transient absorption measurements have shown long-lived charge separation in the case of surface-modified TiO2 nanoparticles. Further measurements on the influence of charge-transfer excitations on the interfacial electron transfer in surface-modified TiO2 nanoparticles are being carried out.

  9. Terminal supraparticle assemblies from similarly charged protein molecules and nanoparticles

    NASA Astrophysics Data System (ADS)

    Park, Jai Il; Nguyen, Trung Dac; de Queirs Silveira, Gleiciani; Bahng, Joong Hwan; Srivastava, Sudhanshu; Zhao, Gongpu; Sun, Kai; Zhang, Peijun; Glotzer, Sharon C.; Kotov, Nicholas A.

    2014-05-01

    Self-assembly of proteins and inorganic nanoparticles into terminal assemblies makes possible a large family of uniformly sized hybrid colloids. These particles can be compared in terms of utility, versatility and multifunctionality to other known types of terminal assemblies. They are simple to make and offer theoretical tools for designing their structure and function. To demonstrate such assemblies, we combine cadmium telluride nanoparticles with cytochrome C protein and observe spontaneous formation of spherical supraparticles with a narrow size distribution. Such self-limiting behaviour originates from the competition between electrostatic repulsion and non-covalent attractive interactions. Experimental variation of supraparticle diameters for several assembly conditions matches predictions obtained in simulations. Similar to micelles, supraparticles can incorporate other biological components as exemplified by incorporation of nitrate reductase. Tight packing of nanoscale components enables effective charge and exciton transport in supraparticles and bionic combination of properties as demonstrated by enzymatic nitrate reduction initiated by light absorption in the nanoparticle.

  10. Terminal Supraparticle Assemblies from Similarly Charged Protein Molecules and Nanoparticles

    PubMed Central

    Park, Jai Il; Nguyen, Trung Dac; de Queirós Silveira, Gleiciani; Bahng, Joong Hwan; Srivastava, Sudhanshu; Sun, Kai; Zhao, Gongpu; Zhang, Peijun; Glotzer, Sharon C.; Kotov, Nicholas A.

    2015-01-01

    Self-assembly of proteins and inorganic nanoparticles into terminal assemblies makes possible a large family of uniformly sized hybrid colloids. These particles can be compared in terms of utility, versatility and multifunctionality to other known types of terminal assemblies. They are simple to make and offer theoretical tools for designing their structure and function. To demonstrate such assemblies, we combine cadmium telluride nanoparticles with cytochrome C protein and observe spontaneous formation of spherical supraparticles with a narrow size distribution. Such self-limiting behaviour originates from the competition between electrostatic repulsion and non-covalent attractive interactions. Experimental variation of supraparticle diameters for several assembly conditions matches predictions obtained in simulations. Similar to micelles, supraparticles can incorporate other biological components as exemplified by incorporation of nitrate reductase. Tight packing of nanoscale components enables effective charge and exciton transport in supraparticles as demonstrated by enzymatic nitrate reduction initiated by light absorption in the nanoparticle. PMID:24845400

  11. The Role of Negative Charge in the Delivery of Quantum Dots to Neurons

    PubMed Central

    Walters, Ryan; Medintz, Igor L.; Delehanty, James B.; Stewart, Michael H.; Susumu, Kimihiro; Huston, Alan L.; Dawson, Philip E.

    2015-01-01

    Despite our extensive knowledge of the structure of negatively charged cell surface proteoglycans and sialoglycoconjugates in the brain, we have little understanding of how their negative charge contributes to brain function. We have previously shown that intensely photoluminescent 9-nm diameter quantum dots (QDs) with a CdSe core, a ZnS shell, and a negatively charged compact molecular ligand coating (CL4) selectively target neurons rather than glia. We now provide an explanation for this selective neuronal delivery. In this study, we compared three zwitterionic QD coatings differing only in their regions of positive or negative charge, as well as a positively charged (NH2) polyethylene glycol (PEG) coat, for their ability to deliver the cell-membrane-penetrating chaperone lipopeptide JB577 (WG(Palmitoyl)VKIKKP9G2H6) to individual cells in neonatal rat hippocampal slices. We confirm both that preferential uptake in neurons, and the lack of uptake in glia, is strongly associated with having a region of greater negative charge on the QD coating. In addition, the role of negatively charged chondroitin sulfate of the extracellular matrix (ECM) in restricting uptake was further suggested by digesting neonatal rat hippocampal slices with chondroitinase ABC and showing increased uptake of QDs by oligodendrocytes. Treatment still did not affect uptake in astrocytes or microglia. Finally, the future potential of using QDs as vehicles for trafficking proteins into cells continues to show promise, as we show that by administering a histidine-tagged green fluorescent protein (eGFP-His6) to hippocampal slices, we can observe neuronal uptake of GFP. PMID:26243591

  12. Process for preparing negative plates for use in a dry charge battery

    SciTech Connect

    Wegner, P.C.

    1986-02-11

    This patent describes a process for the production of lead-containing negative plates for use in a dry charge battery. The process cnsists of drying wet negative plates while protecting them from oxidation. This improvement is accomplished by treating the wet negative plates prior to the drying operation with an aqueous soluton of an oxidation inhibiting agent selected from salicylic acid, and 2-naphtol. The plates are then protected against oxidation during drying; and dry negative plates are obtained which are resistant to the absorption of water from the atmosphere on storage but are wet immediately by battery acid in use.

  13. Comparison of charge models for fixed-charge force fields: small-molecule hydration free energies in explicit solvent.

    PubMed

    Mobley, David L; Dumont, Elise; Chodera, John D; Dill, Ken A

    2007-03-01

    In molecular simulations with fixed-charge force fields, the choice of partial atomic charges influences numerous computed physical properties, including binding free energies. Many molecular mechanics force fields specify how nonbonded parameters should be determined, but various choices are often available for how these charges are to be determined for arbitrary small molecules. Here, we compute hydration free energies for a set of 44 small, neutral molecules in two different explicit water models (TIP3P and TIP4P-Ew) to examine the influence of charge model on agreement with experiment. Using the AMBER GAFF force field for nonbonded parameters, we test several different methods for obtaining partial atomic charges, including two fast methods exploiting semiempirical quantum calculations and methods deriving charges from the electrostatic potentials computed with several different levels of ab initio quantum calculations with and without a continuum reaction field treatment of solvent. We find that the best charge sets give a root-mean-square error from experiment of roughly 1 kcal/mol. Surprisingly, agreement with experimental hydration free energies does not increase substantially with increasing level of quantum theory, even when the quantum calculations are performed with a reaction field treatment to better model the aqueous phase. We also find that the semiempirical AM1-BCC method for computing charges works almost as well as any of the more computationally expensive ab initio methods and that the root-mean-square error reported here is similar to that for implicit solvent models reported in the literature. Further, we find that the discrepancy with experimental hydration free energies grows substantially with the polarity of the compound, as does its variation across theory levels. PMID:17291029

  14. Dust acoustic solitary wave with variable dust charge: Role of negative ions

    SciTech Connect

    Ghosh, Samiran

    2005-09-15

    The role of negative ions on small but finite amplitude dust acoustic solitary wave including the effects of high and low charging rates of dust grains compared to the dust oscillation frequency in electronegative dusty plasma is investigated. In the case of high charging rate, the solitary wave is governed by Korteweg-de Vries (KdV) equation, but in the case of low charging rate, it is governed by KdV equation with a linear damping term. Numerical investigations reveal that in both cases dust acoustic soliton sharpens (flatens) and soliton width decreases (increases) with the increase of negative-ion number density (temperature). Also, the negative ions reduce the damping rate.

  15. Quantum mechanical investigations on the role of neutral and negatively charged enamine intermediates in organocatalyzed reactions

    NASA Astrophysics Data System (ADS)

    Hubin, Pierre O.; Jacquemin, Denis; Leherte, Laurence; Vercauteren, Daniel P.

    2014-04-01

    The proline-catalyzed aldol reaction is the seminal example of asymmetric organocatalysis. Previous theoretical and experimental studies aimed at identifying its mechanism in order to rationalize the outcome of this reaction. Here, we focus on key steps with modern first principle methods, i.e. the M06-2X hybrid exchange-correlation functional combined to the solvation density model to account for environmental effects. In particular, different pathways leading to the formation of neutral and negatively charged enamine intermediates are investigated, and their reactivity towards two electrophiles, i.e. an aldehyde and a benzhydrylium cation, are compared. Regarding the self-aldol reaction, our calculations confirm that the neutral enamine intermediate is more reactive than the negatively charged one. For the reaction with benzhydrylium cations however, the negatively charged enamine intermediate is more reactive.

  16. Cell proliferation and cell sheet detachment from the positively and negatively charged nanocomposite hydrogels.

    PubMed

    Liu, Dan; Wang, Tao; Liu, Xinxing; Tong, Zhen

    2014-01-01

    The charged nanocomposite hydrogels (NC gels) were synthesized by copolymerization of positively or negatively chargeable monomer with N-isopropylacrylamide (NIPAm) in the aqueous suspension of hectorite clay. The ionic NC gels preserved the thermo-responsibility with the phase-transition temperature below 37°C. The L929 cell proliferation was sensitive to charge polarity and charge density. As compared to the PNIPAm NC gel, the cationic NC gels with <5 mol % of 2-(dimethylamino)ethyl methacrylate (DMAEMA) showed improved cell proliferation, whereas the cells grew slowly on the gels with negatively charged 2-acrylamido-2-methylpropane sulfonic acid (AMPSNa). By lowering temperature, rapid cell sheet detachment was observed from the surface of ionic NC gels with 1 mol % of ionizable monomers. However, lager amount of AMPSNa or DMAEMA did not support rapid cell sheet detachment, probably owing to the adverse swelling effects and/or enhanced electrostatic attraction. PMID:23640767

  17. Negative correlation between charge carrier density and mobility fluctuations in graphene

    NASA Astrophysics Data System (ADS)

    Pan, Jie; Lu, Jianming; Sheng, Ping; Institute of Physics and Department of Electrophysics, National Chiao Tung University, Taiwan Collaboration

    2014-03-01

    By carrying out simultaneous longitudinal and Hall measurements in graphene, we find that the 1/f noise for the charge carrier density is negatively correlated to that of mobility, with a governing behavior that differs significantly from the relation between their mean values. The correlation in the noise data can be quantitatively explained by a single parameter theory whose underlying physics is the trapping and de-trapping of the fluctuating charge carriers by the oppositely charged Coulomb scattering centers. This can alter the effective density of long-range scattering centers in a transient manner, with the consequent fluctuating effect on the mobility. The longitudinal noise turns out to be dominated by the remaining component of the mobility fluctuations, and display no correlation to the Hall noise. Due to the negative correlation between charge carrier density and mobility fluctuations, the normalized PSD is smaller than that of the Hall noise. Research Grants Council of Hong Kong Grant HKUST9/CRF/08.

  18. Doping effect on photoabsorption and charge-separation dynamics in light-harvesting organic molecule

    NASA Astrophysics Data System (ADS)

    Ohmura, Satoshi; Tsuruta, Kenji; Shimojo, Fuyuki; Nakano, Aiichiro

    2016-01-01

    Using ab-initio theoretical methods, we demonstrate possible enhancement of photo-conversion efficiency of an organic solar cell via intentional doping in molecular graphene-fullerene heterojunction [the hexabenzocoronene (HBC)-triethylene glycol (TEG)-C60 molecule]. Photoabsorption analysis indicates oxygen substitution into HBC leads to an extension of the spectra up to an infrared regime. A quantum-mechanical molecular dynamics simulation incorporating nonadiabatic electronic transitions reveals that a dissociated charge state (D+ and A-) in the O-doped system is more stable than the pristine case due to the presence of an effective barrier by the TEG HOMO/LUMO level. We also find that oxygen doping in HBC enhances the intermolecular carrier mobility after charge separation. On the other hand, the pristine molecule undergoes rapid recombination between donor and acceptor charges at the interface. These analyses suggest that the graphene oxidation opens a new window in the application of organic super-molecules to solar cells.

  19. Negative space charge effects in photon-enhanced thermionic emission solar converters

    NASA Astrophysics Data System (ADS)

    Segev, G.; Weisman, D.; Rosenwaks, Y.; Kribus, A.

    2015-07-01

    In thermionic energy converters, electrons in the gap between electrodes form a negative space charge and inhibit the emission of additional electrons, causing a significant reduction in conversion efficiency. However, in Photon Enhanced Thermionic Emission (PETE) solar energy converters, electrons that are reflected by the electric field in the gap return to the cathode with energy above the conduction band minimum. These electrons first occupy the conduction band from which they can be reemitted. This form of electron recycling makes PETE converters less susceptible to negative space charge loss. While the negative space charge effect was studied extensively in thermionic converters, modeling its effect in PETE converters does not account for important issues such as this form of electron recycling, nor the cathode thermal energy balance. Here, we investigate the space charge effect in PETE solar converters accounting for electron recycling, with full coupling of the cathode and gap models, and addressing conservation of both electric and thermal energy. The analysis shows that the negative space charge loss is lower than previously reported, allowing somewhat larger gaps compared to previous predictions. For a converter with a specific gap, there is an optimal solar flux concentration. The optimal solar flux concentration, the cathode temperature, and the efficiency all increase with smaller gaps. For example, for a gap of 3 μm the maximum efficiency is 38% and the optimal flux concentration is 628, while for a gap of 5 μm the maximum efficiency is 31% and optimal flux concentration is 163.

  20. Bactericidal action mechanism of negatively charged food grade clove oil nanoemulsions.

    PubMed

    Majeed, Hamid; Liu, Fei; Hategekimana, Joseph; Sharif, Hafiz Rizwan; Qi, Jing; Ali, Barkat; Bian, Yuan-Yuan; Ma, Jianguo; Yokoyama, Wallace; Zhong, Fang

    2016-04-15

    Clove oil (CO) anionic nanoemulsions were prepared with varying ratios of CO to canola oil (CA), emulsified and stabilized with purity gum ultra (PGU), a newly developed succinylated waxy maize starch. Interfacial tension measurements showed that CO acted as a co-surfactant and there was a gradual decrease in interfacial tension which favored the formation of small droplet sizes on homogenization until a critical limit (5:5% v/v CO:CA) was reached. Antimicrobial activity of the negatively charged CO nanoemulsion was determined against Gram positive GPB (Listeria monocytogenes and Staphylococcus aureus) and Gram negative GNB (Escherichia coli) bacterial strains using minimum inhibitory concentration (MIC) and a time kill dynamic method. Negatively charged PGU emulsified CO nanoemulsion showed prolonged antibacterial activities against Gram positive bacterial strains. We concluded that negatively charged CO nanoemulsion droplets self-assemble with GPB cell membrane, and facilitated interaction with cellular components of bacteria. Moreover, no electrostatic interaction existed between negatively charged droplets and the GPB membrane. PMID:26616926

  1. Storage of charge carriers on emitter molecules in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Weichsel, Caroline; Burtone, Lorenzo; Reineke, Sebastian; Hintschich, Susanne I.; Gather, Malte C.; Leo, Karl; Lssem, Bjrn

    2012-08-01

    Organic light-emitting diodes (OLEDs) using the red phosphorescent emitter iridium(III)bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate) [Ir(MDQ)2(acac)] are studied by time-resolved electroluminescence measurements. A transient overshoot after voltage turn-off is found, which is attributed to electron accumulation on Ir(MDQ)2(acac) molecules. The mechanism is verified via impedance spectroscopy and by application of positive and negative off-voltages. We calculate the density of accumulated electrons and find that it scales linearly with the doping concentration of the emitter. Using thin quenching layers, we locate the position of the emission zone during normal OLED operation and after voltage turn-off. In addition, the transient overshoot is also observed in three-color white-emitting OLEDs. By time- and spectrally resolved measurements using a streak camera, we directly attribute the overshoot to electron accumulation on Ir(MDQ)2(acac). We propose that similar processes are present in many state-of-the-art OLEDs and believe that the quantification of charge carrier storage will help to improve the efficiency of OLEDs.

  2. Resonant charge transfer at dielectric surfaces. Electron capture and release due to impacting metastable nitrogen molecules

    NASA Astrophysics Data System (ADS)

    Marbach, J.; Bronold, F. X.; Fehske, H.

    2012-04-01

    We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable N2(3?+ u ) molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance N2 -(2? g ) and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green's function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for Al2O3, MgO, SiO2, and diamond at several kinetic energies of the projectile. With the exception of MgO the coefficients turn out to be of the order of 10-1 over the whole range of kinetic energies. This rather large value is a direct consequence of the shape resonance acting as a relay state for electron emission.

  3. Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes

    NASA Astrophysics Data System (ADS)

    Dell, Emma J.; Capozzi, Brian; Xia, Jianlong; Venkataraman, Latha; Campos, Luis M.

    2015-03-01

    To develop advanced materials for electronic devices, it is of utmost importance to design organic building blocks with tunable functionality and to study their properties at the molecular level. For organic electronic and photovoltaic applications, the ability to vary the nature of charge carriers and so create either electron donors or acceptors is critical. Here we demonstrate that charge carriers in single-molecule junctions can be tuned within a family of molecules that contain electron-deficient thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed to increase electron affinity and maintain delocalized frontier orbitals while significantly decreasing the transport gap. Through thermopower measurements we show that the dominant charge carriers change from holes to electrons as the number of TDO units is increased. This results in a unique system in which the charge carrier depends on the backbone length, and provides a new means to tune p- and n-type transport in organic materials.

  4. Sensing organic molecules by charge transfer through aptamer-target complexes: theory and simulation.

    PubMed

    Schill, Maria; Koslowski, Thorsten

    2013-01-17

    Aptamers, i.e., short sequences of RNA and single-stranded DNA, are capable of specificilly binding objects ranging from small molecules over proteins to entire cells. Here, we focus on the structure, stability, dynamics, and electronic properties of oligonucleotides that interact with aromatic or heterocyclic targets. Large-scale molecular dynamics simulations indicate that aromatic rings such as dyes, metabolites, or alkaloides form stable adducts with their oligonucleotide host molecules at least on the simulation time scale. From molecular dynamics snapshots, the energy parameters relevant to Marcus' theory of charge transfer are computed using a modified Su-Schrieffer-Heeger Hamiltonian, permitting an estimate of the charge transfer rates. In many cases, aptamer binding seriously influences the charge transfer kinetics and the charge carrier mobility within the complex, with conductivities up to the nanoampere range for a single complex. We discuss the conductivity properties with reference to potential applications as biosensors. PMID:23227783

  5. Negative correlation between charge carrier density and mobility fluctuations in graphene

    NASA Astrophysics Data System (ADS)

    Lu, Jianming; Pan, Jie; Yeh, Sheng-Shiuan; Zhang, Haijing; Zheng, Yuan; Chen, Qihong; Wang, Zhe; Zhang, Bing; Lin, Juhn-Jong; Sheng, Ping

    2014-08-01

    By carrying out simultaneous longitudinal and Hall measurements in graphene, we find that the 1/f noise for the charge carrier density is negatively correlated to that of mobility, with a governing behavior that differs significantly from the relation between their mean values. The correlation in the noise data can be quantitatively explained by a single-parameter theory whose underlying physics is the trapping and detrapping of the fluctuating charge carriers by the oppositely charged Coulomb scattering centers. This can alter the effective density of long-range scattering centers in a transient manner, with the consequent fluctuating effect on the mobility.

  6. Reversible Tuning of Interfacial and Intramolecular Charge Transfer in Individual MnPc Molecules.

    PubMed

    Zhong, Jian-Qiang; Wang, Zhunzhun; Zhang, Jia Lin; Wright, Christopher A; Yuan, Kaidi; Gu, Chengding; Tadich, Anton; Qi, Dongchen; Li, He Xing; Lai, Min; Wu, Kai; Xu, Guo Qin; Hu, Wenping; Li, Zhenyu; Chen, Wei

    2015-12-01

    The reversible selective hydrogenation and dehydrogenation of individual manganese phthalocyanine (MnPc) molecules has been investigated using photoelectron spectroscopy (PES), low-temperature scanning tunneling microscopy (LT-STM), synchrotron-based near edge X-ray absorption fine structure (NEXAFS) measurements, and supported by density functional theory (DFT) calculations. It is shown conclusively that interfacial and intramolecular charge transfer arises during the hydrogenation process. The electronic energetics upon hydrogenation is identified, enabling a greater understanding of interfacial and intramolecular charge transportation in the field of single-molecule electronics. PMID:26528623

  7. A Model of Ball Lightning as a Formation of Water Molecules Confining an Electric Charge and the Classical Theory of the Electron

    NASA Astrophysics Data System (ADS)

    Tennakone, K.

    2012-04-01

    Ball lightning or faintly luminous floating spheres with radii of the order of ten centimeters appearing transiently in air notably during stormy weather continue to remain an unresolved phenomenon. It is suggested that these objects are organized structures constituted of an electrically charged spherical thin shell of electro-frozen dipole oriented water molecules carrying an electric charge, balanced by the internal negative pressure and outward electrostatic stress. A model presented, resembling the classical theory of the electron with Poincare stresses explain almost all observed attributes of this phenomenon. The possibility of realizing macroscopic spherical surface charge distributions in the vacuum and their implication on the problem of electron are commented.

  8. Gating of single molecule junction conductance by charge transfer complex formation.

    PubMed

    Vezzoli, Andrea; Grace, Iain; Brooke, Carly; Wang, Kun; Lambert, Colin J; Xu, Bingqian; Nichols, Richard J; Higgins, Simon J

    2015-12-01

    The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference. PMID:26510687

  9. Selective charge asymmetric distribution in heteronuclear diatomic molecules in strong laser fields

    NASA Astrophysics Data System (ADS)

    Lai, Wei; Guo, Chunlei

    2015-07-01

    In this paper we study double-ionization-induced charge asymmetric dissociation (CAD) in heteronuclear diatomic molecules. In CO we find a selective charge distribution in two CAD channels, i.e., C2 ++O is abundantly produced but C +O2 + is nearly nonexistent. This cannot be explained by the ionization energy difference between the two channels alone. Our study shows that the C2 ++O channel is sequentially formed through an intermediate state C++O and the selective charge distribution is the result of electron distribution in CO when exposed to intense laser fields.

  10. Dok-3, a Novel Adapter Molecule Involved in the Negative Regulation of Immunoreceptor Signaling

    PubMed Central

    Lemay, Serge; Davidson, Dominique; Latour, Sylvain; Veillette, Andr

    2000-01-01

    Adapters are typically viewed as molecules coordinating the recruitment of positive effectors of cell signaling. Herein, we report the identification of Dok-3, a novel adapter molecule belonging to the Dok family. Our studies show that Dok-3 is highly expressed in several hemopoietic cell types, including B cells and macrophages. It undergoes rapid tyrosine phosphorylation in response to immunoreceptor-mediated cellular activation, seemingly as a result of the action of Src family kinases. This phosphorylation induces the binding of Dok-3 to at least two inhibitory molecules, the 5? inositol phosphatase SHIP and the protein tyrosine kinase Csk. We also demonstrate that augmented expression of wild-type Dok-3 in a B-cell line results in an inhibition of immunoreceptor-mediated nuclear factor of activated T-cells (NFAT) activation and cytokine release, while introduction of a Dok-3 mutant with impaired ability to associate with SHIP and Csk enhances B-cell responsiveness. Taken together, these results indicate that Dok-3 is an adapter involved in the recruitment of inhibitory molecules and that it may play a significant role in the negative regulation of immunoreceptor signaling in hemopoietic cells such as B cells and macrophages. PMID:10733577

  11. Small molecules for interference with cell-cell-communication systems in Gram-negative bacteria.

    PubMed

    Janssens, Joost C A; De Keersmaecker, Sigrid C J; De Vos, Dirk E; Vanderleyden, Jos

    2008-01-01

    Quorum sensing (QS) systems are bacterial cell-to-cell communication systems that use small molecules as signals. Since QS is involved in the regulation of virulence and biofilm formation in several pathogenic bacteria, it has been suggested as a new target for the development of novel antibacterial therapies. As such, interference with the signal receptors by using chemical compounds has been proposed as an alternative strategy for treatment of bacterial infections and has already shown promising results in combination with traditional antibiotic treatments. In Gram-negative bacteria, the best studied QS systems use N-acyl homoserine lactones (AHLs) as signal molecules. This review provides an overview of all new chemical structure types that inhibit AHL-mediated QS systems as reported during the last three years in scientific journals and in the patent literature. The compounds were classified into three main groups depending on their structure: AHL analogues, 2(5H)-furanones, and compounds that are not structurally related to AHLs. We discuss the biological assays used and the different strategies applied to discover these molecules, including new approaches such as molecular docking for in silico identification of lead structures and random high-throughput screening of large libraries of chemicals. Finally, we elaborate on structure-activity relationships and on the new insights in the mechanisms of action of the identified inhibitors, highlighting the potential of these small molecules in medicine. PMID:18781941

  12. Charged particle flows in the beam extraction region of a negative ion source for NBI

    NASA Astrophysics Data System (ADS)

    Geng, S.; Tsumori, K.; Nakano, H.; Kisaki, M.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Takeiri, Y.; Shibuya, M.; Kaneko, O.

    2016-02-01

    Experiments by a four-pin probe and photodetachment technique were carried out to investigate the charged particle flows in the beam extraction region of a negative hydrogen ion source for neutral beam injector. Electron and positive ion flows were obtained from the polar distribution of the probe saturation current. Negative hydrogen ion flow velocity and temperature were obtained by comparing the recovery times of the photodetachment signals at opposite probe tips. Electron and positive ions flows are dominated by crossed field drift and ambipolar diffusion. Negative hydrogen ion temperature is evaluated to be 0.12 eV.

  13. Bound state properties and photodetachment of the negatively charged hydrogen ions

    NASA Astrophysics Data System (ADS)

    Frolov, Alexei M.

    2015-05-01

    Absorption of infrared and visible radiation from stellar emission spectra by the negatively charged hydrogen ions H- is considered. The explicit formula for the photodetachment cross-section of the negatively charged hydrogen ion(s) is derived. Photodetachemnt cross-sections of the {?}H-, {3}H- (or T-), {2}H- (or D-) and {1}H- ions are determined to high accuracy and for a large number of photo-electron momenta/energies. We introduce criteria which can be used to evaluate the overall quality of highly accurate wave functions of the hydrogen ion(s). One of these criteria is based on highly accurate calculations of the lowest order QED corrections in the negatively charged hydrogen ions, including {1}H- (protium), {2}H- (deuterium), {3}H- (tritium) and model ion with the infinitely heavy nucleus {?}H-. An effective approach has been developed to calculate three-body integrals with the Bessel functions of different orders. Some preliminary evaluations of the phototdetachment cross-sections of the negatively charged hydrogen ions are performed. Inverse bremsstrahlung in the field of the neutral hydrogen atom is briefly discussed.

  14. Ion-exchange molecularly imprinted polymer for the extraction of negatively charged acesulfame from wastewater samples.

    PubMed

    Zarejousheghani, Mashaalah; Schrader, Steffi; Möder, Monika; Lorenz, Pierre; Borsdorf, Helko

    2015-09-11

    Acesulfame is a known indicator that is used to identify the introduction of domestic wastewater into water systems. It is negatively charged and highly water-soluble at environmental pH values. In this study, a molecularly imprinted polymer (MIP) was synthesized for negatively charged acesulfame and successfully applied for the selective solid phase extraction (SPE) of acesulfame from influent and effluent wastewater samples. (Vinylbenzyl)trimethylammonium chloride (VBTA) was used as a novel phase transfer reagent, which enhanced the solubility of negatively charged acesulfame in the organic solvent (porogen) and served as a functional monomer in MIP synthesis. Different molecularly imprinted polymers were synthesized to optimize the extraction capability of acesulfame. The different materials were evaluated using equilibrium rebinding experiments, selectivity experiments and scanning electron microscopy (SEM). The most efficient MIP was used in a molecularly imprinted-solid phase extraction (MISPE) protocol to extract acesulfame from wastewater samples. Using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) analysis, detection and quantification limits were achieved at 0.12μgL(-1) and 0.35μgL(-1), respectively. Certain cross selectivity for the chemical compounds containing negatively charged sulfonamide functional group was observed during selectivity experiments. PMID:26256920

  15. Dust charging processes with a Cairns-Tsallis distribution function with negative ions

    NASA Astrophysics Data System (ADS)

    Abid, A. A.; Khan, M. Z.; Yap, S. L.; Teras, H.; Mahmood, S.

    2016-01-01

    Dust grain charging processes are presented in a non-Maxwellian dusty plasma following the Cairns-Tsallis (q, ?)-distribution, whose constituents are the electrons, as well as the positive/negative ions and negatively charged dust grains. For this purpose, we have solved the current balance equation for a negatively charged dust grain to achieve an equilibrium state value (viz., qd = constant) in the presence of Cairns-Tsallis (q, ?)-distribution. In fact, the current balance equation becomes modified due to the Boltzmannian/streaming distributed negative ions. It is numerically found that the relevant plasma parameters, such as the spectral indexes q and ?, the positive ion-to-electron temperature ratio, and the negative ion streaming speed (U0) significantly affect the dust grain surface potential. It is also shown that in the limit q ? 1 the Cairns-Tsallis reduces to the Cairns distribution; for ? = 0 the Cairns-Tsallis distribution reduces to pure Tsallis distribution and the latter reduces to Maxwellian distribution for q ? 1 and ? = 0.

  16. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    SciTech Connect

    Zanni, Martin T.

    1999-12-17

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

  17. Luminescent systems based on the isolation of conjugated PI systems and edge charge compensation with polar molecules on a charged nanostructured surface

    DOEpatents

    Ivanov, Ilia N.; Puretzky, Alexander A.; Zhao, Bin; Geohegan, David B.; Styers-Barnett, David J.; Hu, Hui

    2014-07-15

    A photoluminescent or electroluminescent system and method of making a non-luminescent nanostructured material into such a luminescent system is presented. The method of preparing the luminescent system, generally, comprises the steps of modifying the surface of a nanostructured material to create isolated regions to act as luminescent centers and to create a charge imbalance on the surface; applying more than one polar molecule to the charged surface of the nanostructured material; and orienting the polar molecules to compensate for the charge imbalance on the surface of the nanostructured material. The compensation of the surface charge imbalance by the polar molecules allows the isolated regions to exhibit luminescence.

  18. Negative Ion CID Fragmentation of O-linked Oligosaccharide AldosesCharge Induced and Charge Remote Fragmentation

    NASA Astrophysics Data System (ADS)

    Doohan, Roisin A.; Hayes, Catherine A.; Harhen, Brendan; Karlsson, Niclas Gran

    2011-06-01

    Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M - H]- ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M - H]- ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M - 2H]2- ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the 0,2A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable ?/? pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.

  19. Charge Manipulation in Molecules Encapsulated Inside Single-Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Yanagi, Kazuhiro; Moriya, Rieko; Cuong, Nguyen Thanh; Otani, Minoru; Okada, Susumu

    2013-02-01

    We report clear experimental evidence for the charge manipulation of molecules encapsulated inside single-wall carbon nanotubes (SWCNTs) using electrochemical doping techniques. We encapsulated β-carotene (Car) inside SWCNTs and clarified electrochemical doping characteristics of their Raman spectra. C=C streching modes of encapsulated Car and a G band of SWCNTs showed clearly different doping behaviors as the electrochemical potentials were shifted. Electron extraction from encapsulated Car was clearly achieved. However, electrochemical characteristics of Car inside SWCNTs and doping mechanisms elucidated by calculations based on density-functional theory indicate the difficulty of charge manipulation of molecules inside SWCNTs due to the presence of strong on-site Coulomb repulsion energy at the molecules.

  20. Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces.

    PubMed

    Cappel, Ute B; Moia, Davide; Bruno, Annalisa; Vaissier, Valerie; Haque, Saif A; Barnes, Piers R F

    2016-01-01

    Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures. PMID:26891851

  1. Spin-boson theory for charge photogeneration in organic molecules: Role of quantum coherence

    NASA Astrophysics Data System (ADS)

    Yao, Yao

    2015-01-01

    The charge photogeneration process in organic molecules is investigated by a quantum heat engine model, in which two molecules are modeled by a two-spin system sandwiched between two bosonic baths. The two baths represent the high-temperature photon emission source and the low-temperature phonon environment, respectively. We utilize the time-dependent density matrix renormalization group algorithm to investigate the quantum dynamics of the model. It is found that the transient energy current flowing through the two molecules exhibits two stages. In the first stage the energy current is of a coherent feature and represents the ultrafast delocalization of the charge-transfer state, and in the second stage a steady incoherent current is established. The power conversion efficiency is significantly high and may reach the maximum value of 93 % with optimized model parameters. The long-lived quantum entanglement between the two spins is found to be primarily responsible for the hyperefficiency.

  2. Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces

    NASA Astrophysics Data System (ADS)

    Cappel, Ute B.; Moia, Davide; Bruno, Annalisa; Vaissier, Valerie; Haque, Saif A.; Barnes, Piers R. F.

    2016-02-01

    Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures.

  3. Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces

    PubMed Central

    Cappel, Ute B.; Moia, Davide; Bruno, Annalisa; Vaissier, Valerie; Haque, Saif A.; Barnes, Piers R. F.

    2016-01-01

    Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures. PMID:26891851

  4. Single molecule detection using charge-coupled device array technology. Technical progress report

    SciTech Connect

    Denton, M.B.

    1992-07-29

    A technique for the detection of single fluorescent chromophores in a flowing stream is under development. This capability is an integral facet of a rapid DNA sequencing scheme currently being developed by Los Alamos National Laboratory. In previous investigations, the detection sensitivity was limited by the background Raman emission from the water solvent. A detection scheme based on a novel mode of operating a Charge-Coupled Device (CCD) is being developed which should greatly enhance the discrimination between fluorescence from a single molecule and the background Raman scattering from the solvent. Register shifts between rows in the CCD are synchronized with the sample flow velocity so that fluorescence from a single molecule is collected in a single moving charge packet occupying an area approaching that of a single pixel while the background is spread evenly among a large number of pixels. Feasibility calculations indicate that single molecule detection should be achieved with an excellent signal-to-noise ratio.

  5. Simulation of space charge compensation in a multibeamlet negative ion beam

    NASA Astrophysics Data System (ADS)

    Sartori, E.; Maceina, T. J.; Veltri, P.; Cavenago, M.; Serianni, G.

    2016-02-01

    Ion beam space charge compensation occurs by cumulating in the beam potential well charges having opposite polarity, usually generated by collisional processes. In this paper we investigate the case of a H- ion beam drift, in a bi-dimensional approximation of the NIO1 (Negative Ion Optimization phase 1) negative ion source. H- beam ion transport and plasma formation are studied via particle-in-cell simulations. Differential cross sections are sampled to determine the velocity distribution of secondary particles generated by ionization of the residual gas (electrons and slow H2+ ions) or by stripping of the beam ions (electrons, H, and H+). The simulations include three beamlets of a horizontal section, so that multibeamlet space charge and secondary particle diffusion between separate generation regions are considered, and include a repeller grid biased at various potentials. Results show that after the beam space charge is effectively screened by the secondary plasma in about 3 μs (in agreement with theoretical expectations), a plasma grows across the beamlets with a characteristic time three times longer, and a slight overcompensation of the electric potential is verified as expected in the case of negative ions.

  6. Dust negative ion acoustic shock waves in a dusty multi-ion plasma with positive dust charging current

    SciTech Connect

    Duha, S. S.

    2009-11-15

    Recent analysis of Mamun et al.[ Phys. Lett. A 373, 2355 (2009)], who considered electrons, light positive ions, heavy negative ions, and extremely massive (few micron size) charge fluctuating dust, has been extended by positive dust charging current, i.e., considering the charging currents for positively charged dust grains. A dusty multi-ion plasma system consisting of electrons, light positive ions, negative ions, and extremely massive (few micron size) charge fluctuating stationary dust have been considered. The electrostatic shock waves associated with negative ion dynamics and dust charge fluctuation have been investigated by employing the reductive perturbation method. It has been shown that the dust charge fluctuation is a source of dissipation and is responsible for the formation of dust negative ion acoustic (DNIA) shock structures. The basic features of such DNIA shock structures have been identified. The findings of this investigation may be useful in understanding the laboratory phenomena and space dusty plasmas.

  7. Characteristics of EMI generated by negative metal-positive dielectric voltage stresses due to spacecraft charging

    NASA Technical Reports Server (NTRS)

    Chaky, R. C.; Inouye, G. T.

    1985-01-01

    Charging of spacecraft surfaces by the environmental plasma can result in differential potentials between metallic structure and adjacent dielectric surfaces in which the relative polarity of the voltage stress is either negative dielectric/positive metal or negative metal/positive dielectric. Negative metal/positive dielectric is a stress condition that may arise if relatively large areas of spacecraft surface metals are shadowed from solar UV and/or if the UV intensity is reduced as in the situation in which the spacecraft is entering into or leaving eclipse. The results of experimental studies of negative metal/positive dielectric systems are given. Information is given on: enhanced electron emission I-V curves; e(3) corona noise vs e(3) steady-state current; the localized nature of e(3) and negative metal arc discharge currents; negative metal arc discharges at stress thresholds below 1 kilovolt; negative metal arc discharge characteristics; dependence of blowoff arc discharge current on spacecraft capacitance to space (linear dimension); and damage to second surface mirrors due to negative metal arcs.

  8. Probing Dynamics from Within in Negative Ions, Neutral Molecules and van der Waals Clusters

    NASA Astrophysics Data System (ADS)

    Berrah, Nora

    2006-05-01

    We have investigated with unprecedented levels of detail, processes and phenomena involving photodetachment of negative ions and photoionization of molecules and van der Waals clusters using the brightness, spectral resolution, tunability and polarization of the Advanced Light Source at Lawrence Berkeley National Laboratory. Photodetachment of negative ions exhibit structure and processes differing substantially from corresponding processes in neutral and positive ions, owing to the dominance of correlation in both the initial and final states. We will report on investigations carried out in inner-valence CN^- molecules giving rise to absolute double photodetachment cross sections as well as on fragmentation of negative ions clusters. We will also present absolute inner-shell photodetachment of atoms leading to multi-Auger decay [1] and discuss threshold laws [2] and PCI effects [3]. The measurements were conducted using collinear photon-ion spectroscopy. The evolution of inner-shell photoionization of clusters, as a function of photon energy, will be presented and compared to analogous measurements in atoms. The measurements were conducted using angle resolved two-dimensional photoelectron spectroscopy. Molecular fragmentation results using an ion imaging detector will briefly be presented. [1] R. C. Bilodeau, J. D. Bozek, G. D. Ackerman, N. D. Gibson, C. W.Walter, A. Aguilar, G. Turri, I. Dumitriu and N. Berrah, PRA 72, 050701(R), 2005. [2] R. C. Bilodeau, J. D. Bozek, N. D. Gibson, C. W. Walter, G. D. Ackerman, I. Dumitriu, and N. Berrah, Phys. Rev. Lett. 95, 083001 (2005). [3] R. C. Bilodeau, J. D. Bozek, A. Agular, G. D. Ackerman, and N. Berrah, (in press PRA brief report).

  9. Influence of charge mode on the capacity and cycle life of lead-acid battery negative plates

    NASA Astrophysics Data System (ADS)

    Petkova, G.; Pavlov, D.

    The effect of fast and three-step charge mode on the capacity and cycle life of lead-acid battery negative plates was investigated using a model mini electrode (ME). It has been found that the charge algorithm exerts a strong effect on the charge acceptance of the negative electrode. In the two-step charging mode I1, ?2 with increase of the current at the first step of charge, the capacity of the negative electrode decreases and the cycle life shortens. This phenomenon is reversible as it is probably due to the incomplete reduction of PbSO 4 to Pb. The phenomenon is explained based on the mechanism of the process of reduction of PbSO 4. At high initial charge currents, the concentration of H 2SO 4 in the pores of NAM increases, which decreases the solubility of PbSO 4 crystals and limits the charge acceptance of the negative plate. The higher initial charge current influences markedly the formation of smaller Pb crystals that build up the energetic structure of the negative active material. It is essential that a third step with a small constant current, I3 is added to the charge algorithm. The third step of charge in the I1, ?2, I3 charge mode decreases the Ohmic resistance and ensures complete charge of the lead electrode.

  10. Ensemble density functional theory, the atom-in-molecule problem, and reactive charge transfer

    NASA Astrophysics Data System (ADS)

    Atlas, Susan; Valone, Steven

    2008-03-01

    A major challenge in large-scale simulations of complex biomolecular and materials systems is the ability to accurately describe reactive dynamics. We have previously described a new multiscale formalism, based on density functional theory and the embedded-atom method, that enables the rigorous encoding of quantum mechanical excitation effects such as charge polarization and charge transfer within a classical potential. Here we describe a new formulation of a key element of the theory: the deconstruction of molecular densities into subsystem atom-in-molecule components via ensemble constrained-search density functional theory. The method is implemented via the self-consistent solution of coupled sets of Kohn-Sham equations in conjunction with chemical potential equalization across subsystems. This leads to a natural interpretation of dynamical charge transfer and charge polarization in terms of an electronic entropy, thus extending the seminal work of Gross, Oliveira, and Kohn (1988).

  11. Anomalous charge and negative-charge-transfer insulating state in cuprate chain compound KCuO2

    NASA Astrophysics Data System (ADS)

    Choudhury, D.; Rivero, P.; Meyers, D.; Liu, X.; Cao, Y.; Middey, S.; Whitaker, M. J.; Barraza-Lopez, S.; Freeland, J. W.; Greenblatt, M.; Chakhalian, J.

    2015-11-01

    Using a combination of x-ray absorption spectroscopy (XAS) experiments and first-principles calculations, we demonstrate that insulating KCuO2 contains Cu in an unusually high formal 3+ valence state, and the ligand-to-metal (O-to-Cu) charge-transfer energy is intriguingly negative (Δ ˜-1.5 eV) and has a dominant (˜60 % ) ligand-hole character in the ground state akin to the high Tc cuprate Zhang-Rice state. Unlike most other formal Cu3 + compounds, the Cu 2 p XAS spectra of KCuO2 exhibit pronounced 3 d8 (Cu3 +) multiplet structures, which account for ˜40 % of its ground state wave function. Ab initio calculations elucidate the origin of the band gap in KCuO2 as arising primarily from strong intracluster Cu 3 d -O 2 p hybridizations (tpd); the value of the band gap decreases with a reduced value of tpd. Further, unlike conventional negative-charge-transfer insulators, the band gap in KCuO2 persists even for vanishing values of Coulomb repulsion U , underscoring the importance of single-particle band-structure effects connected to the one-dimensional nature of the compound.

  12. Poisson-Boltzmann theory for membranes with mobile charged lipids and the pH-dependent interaction of a DNA molecule with a membrane.

    PubMed Central

    Fleck, Christian; Netz, Roland R; von Grnberg, Hans Hennig

    2002-01-01

    We consider a planar stiff model membrane consisting of mobile surface groups whose state of charge depends on the pH and the ionic composition of the adjacent electrolyte solution. To calculate the mean-field interaction potential between a charged object and such a model membrane, one needs to solve a Poisson-Boltzmann boundary value problem. We here derive and discuss the boundary condition at the membrane surface, a condition that is generally appropriate for biological membranes where two charge-regulating mechanisms are present at the same time: the pH-dependent chemical charge regulation and a regulation through the in-plane mobility of the surface groups. As an application of this general formalism, we consider the specific example of a single DNA molecule, approximated by a cylinder with smeared-out surface charges, interacting with such a model membrane. We study the effect that the two competing charge-regulating mechanisms have on the DNA/membrane interaction and the distribution of surface ions in the plane of the membrane. We find that, at short DNA-membrane distances, membrane fluidity can have a considerable impact on the DNA adsorption behavior and can lead to such counterintuitive phenomena as the adsorption of a negatively charged DNA onto a (on average) negatively charged membrane. PMID:11751297

  13. Protecting-Group-Free Synthesis of Well-Defined Glycopolymers Featuring Negatively Charged Oligosaccharides.

    PubMed

    Albertin, Luca

    2016-01-01

    Control of the macromolecular architecture is essential to enable sophisticated functions for glycopolymers and to allow a precise correlation between these functions and the polymer structure. A number of biologically important ligands are negatively charged oligosaccharides that are difficult to manipulate in organic solvent and that are hardly amenable to protection/deprotection strategies. RAFT polymerization is a simple and robust technique that enables the synthesis of well-defined glycopolymers directly in aqueous solution and starting from unprotected vinyl glycomonomers. Here I describe how RAFT polymerization can be combined with reductive amination to transform negatively charged oligosaccharides having 5-20 monosaccharide units into well-defined glycopolymers directly in water and without the need to resort to protecting-group chemistry. PMID:26537461

  14. Annihilation, bound state properties and photodetachment of the positronium negatively charged ion

    NASA Astrophysics Data System (ADS)

    Frolov, Alexei M.

    2015-04-01

    Bound state properties of the negatively charged Ps- ion (or e-e+e-) are discussed. The expectation values of operators which correspond to these properties have been determined with the use of the highly accurate wave functions constructed for this ion. Our best variational energy obtained for the Ps- ion is E = -0.2620050 7023298 0107770 40051 a.u. Annihilation of the electron-positron pair(s) in the negatively charged Ps- ion (or e-e+e-) is considered in detail. By using accurate values for a number annihilation rates ?n?, where n = 1, 2, 3, 4 and 5, we evaluated the half-life ?a of the Ps- ion against positron annihilation (?a = 1/? ? 4.793584140 10-10 s). Photodetachment of the Ps- ion is considered in the long-range, asymptotic approximation. The overall accuracy of our photodetachment cross-section of the Ps- ion is very good for such a simple approximation.

  15. Optimizing charge neutralization for a magnetic sector SIMS instrument in negative mode

    SciTech Connect

    Pivovarov, Alexander L.; Guryanov, Georgiy M.

    2012-07-15

    Successful self-adjusted charge compensation was demonstrated for a CAMECA magnetic-sector secondary ion mass spectrometer applied in negative mode. Operation with the normal-incidence electron gun (NEG) potential positively biased relative to a sample potential enables substantial broadening of the Cs primary-ion-current density range available for analysis of insulators. The decrease of the negative NEG potential by 30 V allows the highest value of primary current density used for the analysis of a silica sample to increase by a factor of more than 6. By applying the improved charge neutralization technique, accurate Na depth profiles for SiO{sub 2} samples were obtained within detection limits of {approx}3 Multiplication-Sign 10{sup 15} atoms/cm{sup 3}.

  16. Effect of Interlayer Coupling on Ultrafast Charge Transfer from Semiconducting Molecules to Mono- and Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Wang, Ti; Liu, Qingfeng; Caraiani, Claudiu; Zhang, Yupeng; Wu, Judy; Chan, Wai-Lun

    2015-07-01

    Graphene is used as flexible electrodes in various optoelectronic devices. In these applications, ultrafast charge transfer from semiconducting light absorbers to graphene can impact the overall device performance. Here, we propose a mechanism in which the charge-transfer rate can be controlled by varying the number of graphene layers and their stacking. Using an organic semiconducting molecule as a light absorber, the charge-transfer rate to graphene is measured by using time-resolved photoemission spectroscopy. Compared to graphite, the charge transfer to monolayer graphene is about 2 times slower. Surprisingly, the charge transfer to A -B -stacked bilayer graphene is slower than that to both monolayer graphene and graphite. This anomalous behavior disappears when the two graphene layers are randomly stacked. The observation is explained by a charge-transfer model that accounts for the band-structure difference in mono- and bilayer graphene, which predicts that the charge-transfer rate depends nonintuitively on both the layer number and stacking of graphene.

  17. Solvent-tuned intramolecular charge-recombination rates in a conjugated donor-acceptor molecule

    NASA Technical Reports Server (NTRS)

    Khundkar, Lutfur R.; Stiegman, A. E.; Perry, Joseph W.

    1990-01-01

    The nonradiative charge-recombination rates from the charge-transfer state of a new conjugated donor-acceptor molecule (p-cyano-p-prime-methylthiodiphenylacetylene) can be tuned over almost an order of magnitude by varying the polarity of the solvent. These measurements of intramolecular recombination show a turnover of rates as a function of emission energy, consistent with the 'normal' and 'inverted' behavior of Marcus theory. Steady-state spectra and time-resolved measurements make it possible to quantitatively compare thermal and optical electron-transfer rates as a function of driving force and demonstrate their correspondence.

  18. Ultrafast charge rearrangement and nuclear dynamics upon inner-shell multiple ionization of small polyatomic molecules.

    PubMed

    Erk, B; Rolles, D; Foucar, L; Rudek, B; Epp, S W; Cryle, M; Bostedt, C; Schorb, S; Bozek, J; Rouzee, A; Hundertmark, A; Marchenko, T; Simon, M; Filsinger, F; Christensen, L; De, S; Trippel, S; Kpper, J; Stapelfeldt, H; Wada, S; Ueda, K; Swiggers, M; Messerschmidt, M; Schrter, C D; Moshammer, R; Schlichting, I; Ullrich, J; Rudenko, A

    2013-02-01

    Ionization and fragmentation of methylselenol (CH(3)SeH) molecules by intense (>10(17) W/cm(2)) 5 fs x-ray pulses (??=2 keV) are studied by coincident ion momentum spectroscopy. We contrast the measured charge state distribution with data on atomic Kr, determine kinetic energies of resulting ionic fragments, and compare them to the outcome of a Coulomb explosion model. We find signatures of ultrafast charge redistribution from the inner-shell ionized Se atom to its molecular partners, and observe significant displacement of the atomic constituents in the course of multiple ionization. PMID:23414017

  19. Space charge compensation in the Linac4 low energy beam transport line with negative hydrogen ions

    SciTech Connect

    Valerio-Lizarraga, Cristhian A.; Lallement, Jean-Baptiste; Lettry, Jacques; Scrivens, Richard; Leon-Monzon, Ildefonso; Midttun, Øystein; University of Oslo, Oslo

    2014-02-15

    The space charge effect of low energy, unbunched ion beams can be compensated by the trapping of ions or electrons into the beam potential. This has been studied for the 45 keV negative hydrogen ion beam in the CERN Linac4 Low Energy Beam Transport using the package IBSimu [T. Kalvas et al., Rev. Sci. Instrum. 81, 02B703 (2010)], which allows the space charge calculation of the particle trajectories. The results of the beam simulations will be compared to emittance measurements of an H{sup −} beam at the CERN Linac4 3 MeV test stand, where the injection of hydrogen gas directly into the beam transport region has been used to modify the space charge compensation degree.

  20. Pure negatively charged state of the NV center in n -type diamond

    NASA Astrophysics Data System (ADS)

    Doi, Yuki; Fukui, Takahiro; Kato, Hiromitsu; Makino, Toshiharu; Yamasaki, Satoshi; Tashima, Toshiyuki; Morishita, Hiroki; Miwa, Shinji; Jelezko, Fedor; Suzuki, Yoshishige; Mizuochi, Norikazu

    2016-02-01

    Optical illumination on negatively charged nitrogen-vacancy (N V-) centers inevitably causes stochastic charge-state transitions between the N V- and the neutral charge state of the NV center. It limits the steady-state population of N V- to 5% at minimum (˜610 nm) and 80% (˜532 nm) at maximum in intrinsic diamond depending on the wavelength. Here, we show Fermi-level control by phosphorus doping generates 99.4 ± 0.1% N V- under 1-μW and 593-nm excitation which is close to maximum absorption of N V- . The pure N V- shows a fivefold increase in luminescence and a fourfold enhancement of an optically detected magnetic resonance under 593-nm excitation compared with those in intrinsic diamond.

  1. Is the unique negatively charged polypeptide of crayfish yolk HDL a component of crustacean vitellin?

    PubMed

    Abdu, U; Yehezkel, G; Weil, S; Ziv, T; Sagi, A

    2001-08-01

    The yolk protein of Cherax quadricarinatus contains six major high-density lipoprotein (HDL) subunits with the approximate molecular masses of 177, 155, 106, 95, 86, and 75 kDa, of which only the 106-kDa polypeptide is negatively charged. On the basis of their molecular weights, time of appearance and disappearance, their floating density and susceptibility to enzyme degradation (by a serine proteinase), these six HDL polypeptides were classified into two subgroups. One group comprises the higher-molecular-weight compounds above 106 kDa, and the other includes the lower-molecular-weight compounds up to 95 kDa. Other than being different from the lower-molecular-weight polypeptides, the negatively charged 106-kDa polypeptide was significantly different from members of its higher-molecular-weight group belonging to a different, less abundant, yolk protein as shown by HPLC separation. Immunological studies and peptide mapping in which the 106-kDa polypeptide did not show similarity to any of the other HDL components confirmed these differences. Moreover, the amino acid composition of the 106-kDa polypeptide was different from that of known vitellin from other crustacean species. This unique negatively charged polypeptide presents an enigma as it is known to be a secondary vitellogenic-related HDL polypeptide, immunolocalized in yolk globules; however, it is different to all the other HDL polypeptides, thus presenting the question whether it is indeed a component of "classical" crustacean vitellin. PMID:11479901

  2. The effect of charge mode transition on electrohydrodynamic flow in a multistage negative air corona discharge

    NASA Astrophysics Data System (ADS)

    Kim, C.; Hwang, J.

    2012-11-01

    We study the electrohydrodynamic (EHD) flow induced by a multistage negative air corona discharge with two main subjects: unipolar-to-bipolar charge mode transition, mechanism of EHD flow. Charge mode transition is identified through the maximum-current-based numerical analysis of a six-stage cylindrical ionic wind generator, and confirmed by the experimental data. After formulating the degree of charge mode transition ?, we discuss how ? affects the electric-to-kinetic energy conversion efficiency and the thrust performance of the EHD flow. We suggest 35 Td of reduced electric field on the collector surface as the occurrence criterion of charge mode transition. As an essential feature of the multistage EHD flow, the highest negative pressure is created in the intake. Accordingly, air is drawn into the intake and subsequent flow climbs up a positive static pressure slope, and exhausted into the atmosphere with a high linearity. We explain the physical mechanism of this interesting flow pattern using the first-principle based analysis.

  3. A Negatively Charged Residue Stabilizes the Tropoelastin N-terminal Region for Elastic Fiber Assembly*

    PubMed Central

    Yeo, Giselle C.; Baldock, Clair; Wise, Steven G.; Weiss, Anthony S.

    2014-01-01

    Tropoelastin is an extracellular matrix protein that assembles into elastic fibers that provide elasticity and strength to vertebrate tissues. Although the contributions of specific tropoelastin regions during each stage of elastogenesis are still not fully understood, studies predominantly recognize the central hinge/bridge and C-terminal foot as the major participants in tropoelastin assembly, with a number of interactions mediated by the abundant positively charged residues within these regions. However, much less is known about the importance of the rarely occurring negatively charged residues and the N-terminal coil region in tropoelastin assembly. The sole negatively charged residue in the first half of human tropoelastin is aspartate 72. In contrast, the same region comprises 17 positively charged residues. We mutated this aspartate residue to alanine and assessed the elastogenic capacity of this novel construct. We found that D72A tropoelastin has a decreased propensity for initial self-association, and it cross-links aberrantly into denser, less porous hydrogels with reduced swelling properties. Although the mutant can bind cells normally, it does not form elastic fibers with human dermal fibroblasts and forms fewer atypical fibers with human retinal pigmented epithelial cells. This impaired functionality is associated with conformational changes in the N-terminal region. Our results strongly point to the role of the Asp-72 site in stabilizing the N-terminal segment of human tropoelastin and the importance of this region in facilitating elastic fiber assembly. PMID:25342751

  4. Properties of clusters in the gas phase. V - Complexes of neutral molecules onto negative ions

    NASA Technical Reports Server (NTRS)

    Keesee, R. G.; Lee, N.; Castleman, A. W., Jr.

    1980-01-01

    Ion-molecules association reactions of the form A(-)(B)n-1 + B = A(-)(B)n were studied over a range of temperatures in the gas phase using high pressure mass spectrometry. Enthalpy and entropy changes were determined for the stepwise clustering reactions of (1) sulfur dioxide onto Cl(-), I(-), and NO2(-) with n ranging from one to three or four, and onto SO2(-) and SO3(-) with n equal to one; and (2) carbon dioxide onto Cl(-), I(-), NO2(-), CO3(-), and SO3(-) with n equal to one. From these data and earlier hydration results, the order of the magnitude of the enthalpy changes on the association of the first neutral for a series of negative ions was found to parallel the gas-phase basicity of those anions.

  5. Spin-dependent negative differential conductance in transport through single-molecule magnets

    NASA Astrophysics Data System (ADS)

    Luo, Wei; Wang, Rui-Qiang; Hu, Liang-Bin; Yang, Mou

    2013-04-01

    Transport properties are theoretically studied through an anisotropy single-molecule magnet symmetrically connected to two identical ferromagnetic leads. It is found that even though in parallel configuration of leads' magnetizations, the total current still greatly depends on the spin polarization of leads at certain particular bias region, and thus for large polarization a prominent negative differential conductance (NDC) emerges. This originates from the joint effect of single-direction transitions and spin polarization, which removes the symmetry between spin-up and spin-down transitions. The present mechanism of NDC is remarkably different from the previously reported mechanisms. To clarify the physics of the NDC, we further monitored the shot noise spectroscopy and found that the appearance of the NDC is accompanied by the rapid decrease of Fano factor.

  6. Gating of single molecule junction conductance by charge transfer complex formation

    NASA Astrophysics Data System (ADS)

    Vezzoli, Andrea; Grace, Iain; Brooke, Carly; Wang, Kun; Lambert, Colin J.; Xu, Bingqian; Nichols, Richard J.; Higgins, Simon J.

    2015-11-01

    The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference.The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference. Electronic supplementary information (ESI) available: Synthesis of 1c; experimental details of conductance measurements, formation of charge transfer complexes of 1c and 2 in solution; further details of theoretical methods. See DOI: 10.1039/c5nr04420k

  7. Nanoscale charge transport in cytochrome c3/DNA network: Comparative studies between redox-active molecules

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Harumasa; Che, Dock-Chil; Hirano, Yoshiaki; Suzuki, Masayuki; Higuchi, Yoshiki; Matsumoto, Takuya

    2015-09-01

    The redox-active molecule of a cytochrome c3/DNA network exhibits nonlinear current-voltage (I-V) characteristics with a threshold bias voltage at low temperature and zero-bias conductance at room temperature. I-V curves for the cytochrome c3/DNA network are well matched with the Coulomb blockade network model. Comparative studies of the Mn12 cluster, cytochrome c, and cytochrome c3, which have a wide variety of redox potentials, indicate no difference in charge transport, which suggests that the conduction mechanism is not directly related to the redox states. The charge transport mechanism has been discussed in terms of the newly-formed electronic energy states near the Fermi level, induced by the ionic interaction between redox-active molecules with the DNA network.

  8. Excited states and valley effects in a negatively charged impurity in a silicon FinFET.

    SciTech Connect

    Hollenberg, Lloyd; Klimeck, Gerhard; Carroll, Malcolm S.; Rahman, Rajib; Muller, Richard Partain; Rogge, Sven; Verduijn, Arjan; Lansbergen, Gabriel

    2010-07-01

    The observation and characterization of a single atom system in silicon is a significant landmark in half a century of device miniaturization, and presents an important new laboratory for fundamental quantum and atomic physics. We compare with multi-million atom tight binding (TB) calculations the measurements of the spectrum of a single two-electron (2e) atom system in silicon - a negatively charged (D-) gated Arsenic donor in a FinFET. The TB method captures accurate single electron eigenstates of the device taking into account device geometry, donor potentials, applied fields, interfaces, and the full host bandstructure. In a previous work, the depths and fields of As donors in six device samples were established through excited state spectroscopy of the D0 electron and comparison with TB calculations. Using self-consistent field (SCF) TB, we computed the charging energies of the D- electron for the same six device samples, and found good agreement with the measurements. Although a bulk donor has only a bound singlet ground state and a charging energy of about 40 meV, calculations show that a gated donor near an interface can have a reduced charging energy and bound excited states in the D- spectrum. Measurements indeed reveal reduced charging energies and bound 2e excited states, at least one of which is a triplet. The calculations also show the influence of the host valley physics in the two-electron spectrum of the donor.

  9. Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctions.

    PubMed

    Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Egler-Lucas, Carolina; Semenov, Sergey N; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

    2016-02-01

    Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios. PMID:26571004

  10. Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Egler-Lucas, Carolina; Semenov, Sergey N.; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

    2016-02-01

    Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.

  11. Negative regulation of NEDD8 conjugation pathway by novel molecules and agents for anticancer therapy.

    PubMed

    Tanaka, Tomoaki; Nakatani, Tatsuya; Kamitani, Tetsu

    2013-01-01

    Tumor cells frequently promote the dysregulation of the cell cycle and escape from apoptotic cell death triggered by a number of cellular stresses. Programmed proteolytic degradation of regulatory proteins via the ubiquitin-proteasome pathway is crucial for homeostasis of numerous biological processes. Disruption of this system is one of the factors that promote aberrant cell-proliferation. The small ubiquitin-like protein, NEDD8, has been identified as a fundamental regulator of the activity of the E3 ubiquitin ligases called the SCF complex (consisting of Skp-1, cullin, and F-box protein) or CRL (cullin-RING ubiquitin ligase) which control a final step in ubiquitination of diverse substrates associated with cancer biology. The ubiquitin ligase activity of the SCF complex requires NEDD8 to covalently bind to cullins. To a large extent, exploring the negative regulation system of the NEDD8 pathway is expected to lead to the development of novel anticancer targets. This review focuses on the NEDD8 negative regulation system including chemical compounds such as MLN4924 and protein molecules (e.g. COP9 signalosome, CAND1, inactive mutant of Ubc12 and NUB1/NUB1L) and clarifies possible strategies for targeting the NEDD8 cascade in cancer cells. PMID:23181574

  12. Microscopic approach to the kinetics of pattern formation of charged molecules on surfaces

    SciTech Connect

    Kuzovkov, V. N.; Zvejnieks, G.; Kotomin, E. A.; Olvera de la Cruz, Monica

    2010-08-09

    A microscopic formalism based on computing many-particle densities is applied to the analysis of the diffusion-controlled kinetics of pattern formation in oppositely charged molecules on surfaces or adsorbed at interfaces with competing long-range Coulomb and short-range Lennard-Jones interactions. Particular attention is paid to the proper molecular treatment of energetic interactions driving pattern formation in inhomogeneous systems. The reverse Monte Carlo method is used to visualize the spatial molecular distribution based on the calculated radial distribution functions (joint correlation functions). We show the formation of charge domains for certain combinations of temperature and dynamical interaction parameters. The charge segregation evolves into quasicrystalline clusters of charges, due to the competing long- and short-range interactions. The clusters initially co-exist with a gas phase of charges that eventually add to the clusters, generating fingers or line of charges of the same sign, very different than the nanopatterns expected by molecular dynamics in systems with competing interactions in two dimensions, such as strain or dipolar versus van der Waals interactions.

  13. Double electron transfer in slow, highly charged ion-molecule collisions

    NASA Astrophysics Data System (ADS)

    Krok, F.; Tawara, H.; Tolstikhina, I. Yu; Sakaue, H. A.; Yamada, I.; Hosaka, K.; Kimura, M.; Matsumoto, A.; Nakamura, N.; Ohtani, S.; Sakurai, M.; Watanabe, H.; Yoshino, M.

    1997-01-01

    During collisions between slow highly charged ions and neutral atoms or molecules, a lot of electrons can be transferred into multiply excited levels of the highly charged ions, and finally the product ions are stabilized by ejection of electrons (autoionization decay) or photons (radiative decay). The ratios of the radiative decay to the autoionization decay after double-electron transfer processes in slow Iq+ (q = 8 23) + CO collisions have been measured by using the coincidence method. It was found that these ratios increase (from 2% up to about 10%) as the charge of the projectile ions increases. A model which explains such a feature is proposed. Based upon the model we have calculated the theoretical rediative/autoionization decay ratios, using the Cowan code, and compared them with the measured results.

  14. Two-Dimensional Heterodyne-Detected VSFG Spectroscopy of Water Molecules at Charged Interfaces

    NASA Astrophysics Data System (ADS)

    Nihonyanagi, S.; Singh, P. C.; Yamaguchi, S.; Tahara, T.

    2013-03-01

    Two-dimensional heterodyne-detected vibrational sum-frequency generation (2D-HD-VSFG) spectroscopy of water at interfaces has been realized for the first time. In the present study, 2D-HD-VSFG spectra were measured at a charged monolayer / isotopically diluted water interface. In contrast to the 2D-IR spectrum of bulk isotopically diluted water, the 2D-HD- VSFG of the charged interface shows a narrower bleach band in the higher frequency region immediately after the photoexcitation. The results clearly show that the dynamics of the water at the charged interface is different from that in the bulk, reflecting the different environment where water molecules are located.

  15. Anisotropic charge transport in large single crystals of ?-conjugated organic molecules

    NASA Astrophysics Data System (ADS)

    Hourani, Wael; Rahimi, Khosrow; Botiz, Ioan; Vinzenz Koch, Felix Peter; Reiter, Gnter; Lienerth, Peter; Heiser, Thomas; Bubendorff, Jean-Luc; Simon, Laurent

    2014-04-01

    The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of ?-? stacking (along the long axis of the single crystal) with a mobility value in the order of 10-3 cm2 V-1 s-1, and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm2 V-1 s-1. The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the ?-? stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.

  16. Long-range charge transport in single G-quadruplex DNA molecules

    NASA Astrophysics Data System (ADS)

    Livshits, Gideon I.; Stern, Avigail; Rotem, Dvir; Borovok, Natalia; Eidelshtein, Gennady; Migliore, Agostino; Penzo, Erika; Wind, Shalom J.; di Felice, Rosa; Skourtis, Spiros S.; Cuevas, Juan Carlos; Gurevich, Leonid; Kotlyar, Alexander B.; Porath, Danny

    2014-12-01

    DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100?pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100?nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits.

  17. Preparation and characterization of negatively charged poly(lactic-co-glycolic acid) microspheres.

    PubMed

    Xu, Qingguo; Crossley, Alison; Czernuszka, Jan

    2009-07-01

    Negatively charged poly(lactic-co-glycolic acid) (PLGA) microspheres encapsulated with hydrophilic drugs have been successfully prepared by a solid-in-oil-in-water (s/o/w) solvent evaporation method in the presence of anionic surfactants, sodium dodecyl sulfate (SDS), and dioctyl sodium sulfosuccinate (DSS), and nonionic surfactant polyvinyl alcohol (PVA). The effects of microencapsulation methods, surfactants types, and surfactant concentrations on the properties of microspheres were studied. Amoxicillin (AMX) was chosen as a hydrophilic model drug, and its encapsulation efficiency (EE) and in vitro release profiles were measured. The s/o/w method achieved higher EE of 40% in PLGA microspheres using surfactant SDS compared with the conventional water-in-oil-in-water (w/o/w) method (about 2%). Triphasic release profiles were observed for all PLGA microspheres (s/o/w) with slight drug burst, a slow diffusion-controlled release within the period of about 7 days and followed by the degradation-controlled sustained release for further 30 days. Smaller particle size and surface charge were achieved for s/o/w method than w/o/w method using the same anionic surfactants, and smooth surface and less porous interior matrix. The s/o/w method effectively encapsulated AMX into anionic PLGA microspheres using anionic surfactants, and these negatively charged PLGA microspheres represented an attractive approach for the controlled release of hydrophilic drugs. PMID:19009589

  18. Ferrocenylundecanethiol self-assembled monolayer charging correlates with negative differential resistance measured by conducting probe atomic force microscopy.

    PubMed

    Tivanski, Alexei V; Walker, Gilbert C

    2005-05-25

    Electrical and mechanical properties of metal-molecule-metal junctions formed between Au-supported self-assembled monolayers (SAMs) of electroactive 11-ferrocenylundecanethiol (FcC(11)SH) and a Pt-coated atomic force microscope (AFM) tip have been measured using a conducting probe (CP) AFM in insulating alkane solution. Simultaneous and independent measurements of currents and bias-dependent adhesion forces under different applied tip biases between the conductive AFM probe and the FcC(11)SH SAMs revealed reversible peak-shaped current-voltage (I-V) characteristics and correlated maxima in the potential-dependent adhesion force. Trapped positive charges in the molecular junction correlate with high conduction in a feature showing negative differential resistance. Similar measurements on an electropassive 1-octanethiol SAM did not show any peaks in either adhesion force or I-V curves. A mechanism involving two-step resonant hole transfer through the occupied molecular orbitals (MOs) of ferrocene end groups via sequential oxidation and subsequent reduction, where a hole is trapped by the phonon relaxation, is proposed to explain the observed current-force correlation. These results suggest a new approach to probe charge-transfer involving electroactive groups on the nanoscale by measuring the adhesion forces as a function of applied bias in an electrolyte-free environment. PMID:15898817

  19. Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer

    PubMed Central

    Azuma, Masaki; Chen, Wei-tin; Seki, Hayato; Czapski, Michal; Olga, Smirnova; Oka, Kengo; Mizumaki, Masaichiro; Watanuki, Tetsu; Ishimatsu, Naoki; Kawamura, Naomi; Ishiwata, Shintaro; Tucker, Matthew G.; Shimakawa, Yuichi; Attfield, J. Paul

    2011-01-01

    The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion <−10−4 K−1 over a temperature range ~100 K) is accessible in perovskite oxides showing charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi0.95La0.05NiO3 is −137×10−6 K−1 and a value of −82×10−6 K−1 is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders. PMID:21673668

  20. Effects of Surfactants and Polyelectrolytes on the Interaction between a Negatively Charged Surface and a Hydrophobic Polymer Surface.

    PubMed

    Rapp, Michael V; Donaldson, Stephen H; Gebbie, Matthew A; Gizaw, Yonas; Koenig, Peter; Roiter, Yuri; Israelachvili, Jacob N

    2015-07-28

    We have measured and characterized how three classes of surface-active molecules self-assemble at, and modulate the interfacial forces between, a negatively charged mica surface and a hydrophobic end-grafted polydimethylsiloxane (PDMS) polymer surface in solution. We provide a broad overview of how chemical and structural properties of surfactant molecules result in different self-assembled structures at polymer and mineral surfaces, by studying three characteristic surfactants: (1) an anionic aliphatic surfactant, sodium dodecyl sulfate (SDS), (2) a cationic aliphatic surfactant, myristyltrimethylammonium bromide (MTAB), and (3) a silicone polyelectrolyte with a long-chain PDMS midblock and multiple cationic end groups. Through surface forces apparatus measurements, we show that the separate addition of three surfactants can result in interaction energies ranging from fully attractive to fully repulsive. Specifically, SDS adsorbs at the PDMS surface as a monolayer and modifies the monotonic electrostatic repulsion to a mica surface. MTAB adsorbs at both the PDMS (as a monolayer) and the mica surface (as a monolayer or bilayer), resulting in concentration-dependent interactions, including a long-range electrostatic repulsion, a short-range steric hydration repulsion, and a short-range hydrophobic attraction. The cationic polyelectrolyte adsorbs as a monolayer on the PDMS and causes a long-range electrostatic attraction to mica, which can be modulated to a monotonic repulsion upon further addition of SDS. Therefore, through judicious selection of surfactants, we show how to modify the magnitude and sign of the interaction energy at different separation distances between hydrophobic and hydrophilic surfaces, which govern the static and kinetic stability of colloidal dispersions. Additionally, we demonstrate how the charge density of silicone polyelectrolytes modifies both their self-assembly at polymer interfaces and the robust adhesion of thin PDMS films to target surfaces. PMID:26135325

  1. Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

    SciTech Connect

    Pan, Shanlin

    2014-11-16

    Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an electrochemical cell. For example, we are able to use this technique to track electroluminescence of single Au NPs, and the electrodeposition of individual Ag NPs in-situ. These metallic NPs are useful to enhance light harvesting in organic photovoltaic systems. The scattering at the surface of an indium tin oxide (ITO) working electrode was measured during a potential sweep. Utilizing Mie scattering theory and high resolution scanning electron microscopy (SEM), the scattering data were used to calculate current-potential curves depicting the electrodeposition of individual Ag NPs. The oxidation of individual presynthesized and electrodeposited Ag NPs was also investigated using fluorescence and DFS microscopies. Our work has produced 1 US provisional patent, 15 published manuscripts, 1 submitted and two additional in-writing manuscripts. 5 graduate students, 1 postdoctoral student, 1 visiting professor, and two undergraduate students have received research training in the area of electrochemistry and optical spectroscopy under support of this award.

  2. Self-organization and oscillation of negatively charged dust particles in a 2-dimensional dusty plasma

    NASA Astrophysics Data System (ADS)

    Song, Y. L.; Huang, F.; Chen, Z. Y.; Liu, Y. H.; Yu, M. Y.

    2016-02-01

    Negatively charged dust particles immersed in 2-dimensional dusty plasma system are investigated by molecular dynamics simulations. The effects of the confinement potential and attraction interaction potential on dust particle self-organization are studied in detail and two typical dust particle distributions are obtained when the system reaches equilibrium. The average radial velocity (ARV), average radial force (ARF) and radial mean square displacement are employed to analyze the dust particles' dynamics. Both ARVs and ARFs exhibit oscillation behaviors when the simulation system reaches equilibrium state. The relationships between the oscillation and confinement potential and attraction potential are studied in this paper. The simulation results are qualitatively similar to experimental results.

  3. Electronic structure of the negatively charged silicon-vacancy center in diamond

    NASA Astrophysics Data System (ADS)

    Rogers, Lachlan J.; Jahnke, Kay D.; Doherty, Marcus W.; Dietrich, Andreas; McGuinness, Liam P.; Müller, Christoph; Teraji, Tokuyuki; Sumiya, Hitoshi; Isoya, Junichi; Manson, Neil B.; Jelezko, Fedor

    2014-06-01

    The negatively charged silicon-vacancy (SiV-) center in diamond is a promising single-photon source for quantum communications and information processing. However, the center's implementation in such quantum technologies is hindered by contention surrounding its fundamental properties. Here we present optical polarization measurements of single centers in bulk diamond that resolve this state of contention and establish that the center has a <111 > aligned split-vacancy structure with D3 d symmetry. Furthermore, we identify an additional electronic level and evidence for the presence of dynamic Jahn-Teller effects in the center's 738-nm optical resonance.

  4. Optical spectra and intensities of graphene magnetic dot bound to a negatively charged Coulomb impurity

    SciTech Connect

    Lee, C. M. E-mail: apkschan@cityu.edu.hk; Chan, K. S. E-mail: apkschan@cityu.edu.hk

    2014-07-28

    Employing numerical diagonalization, we study the optical properties of an electron in a monolayer-graphene magnetic dot bound to an off-center negatively charged Coulomb impurity based on the massless Dirac-Weyl model. Numerical results show that, since the electron-hole symmetry is broken by the Coulomb potential, the optical absorption spectra of the magnetic dot in the presence of a Coulomb impurity are different between the electron states and the hole states. Effects of both the magnetic field and the dot size on the absorption coefficient are presented as functions of the incident photon energies.

  5. Reversible switching of charge states of single TCNE molecules on Cu(111)

    NASA Astrophysics Data System (ADS)

    Choi, Taeyoung; Gupta, Jay

    2009-03-01

    The interplay of electronic structure and magnetic properties is of interest in various organic materials. TCNE (TCNE = tetracyanoethylene) is one component of well-known organic magnets with ferromagnetism up to room temperature. TCNE has a strong electron affinity that facilitates chemical bond formation and charge transfer with metals. We use scanning tunneling microscopy and spectroscopy to study single TCNE molecules on Cu(111) and Cu(100) surfaces. On Cu(111), we find that TCNE can be reversibly switched among three configurations via a controlled voltage pulse. We determine the adsorption sites for these configurations by co-adsorbing CO molecules, which are well known to adsorb atop Cu atoms. We believe these states represent different adsorption configurations and charge states. One of the configurations shows a strong Kondo resonance at low temperature; spectroscopic imaging indicates that this state is strongly localized at the corners of the TCNE molecule. Several features symmetric about V=0 suggest a convolution of the Kondo density of states with inelastic electron tunneling spectroscopy of vibrational modes. http://www.physics.ohio-state.edu/jgupta

  6. Transient performance estimation of charge plasma based negative capacitance junctionless tunnel FET

    NASA Astrophysics Data System (ADS)

    Singh, Sangeeta; Kondekar, P. N.; Pal, Pawan

    2016-02-01

    We investigate the transient behavior of an n-type double gate negative capacitance junctionless tunnel field effect transistor (NC-JLTFET). The structure is realized by using the work-function engineering of metal electrodes over a heavily doped n+ silicon channel and a ferroelectric gate stack to get negative capacitance behavior. The positive feedback in the electric dipoles of ferroelectric materials results in applied gate bias boosting. Various device transient parameters viz. transconductance, output resistance, output conductance, intrinsic gain, intrinsic gate delay, transconductance generation factor and unity gain frequency are analyzed using ac analysis of the device. To study the impact of the work-function variation of control and source gate on device performance, sensitivity analysis of the device has been carried out by varying these parameters. Simulation study reveals that it preserves inherent advantages of charge-plasma junctionless structure and exhibits improved transient behavior as well.

  7. Characterization of oil-free and oil-loaded liquid-crystalline particles stabilized by negatively charged stabilizer citrem.

    PubMed

    Nilsson, Christa; Edwards, Katarina; Eriksson, Jonny; Larsen, Susan Weng; stergaard, Jesper; Larsen, Claus; Urtti, Arto; Yaghmur, Anan

    2012-08-14

    The present study was designed to evaluate the effect of the negatively charged food-grade emulsifier citrem on the internal nanostructures of oil-free and oil-loaded aqueous dispersions of phytantriol (PHYT) and glyceryl monooleate (GMO). To our knowledge, this is the first report in the literature on the utilization of this charged stabilizing agent in the formation of aqueous dispersions consisting of well-ordered interiors (either inverted-type hexagonal (H(2)) phases or inverted-type microemulsion systems). Synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were used to characterize the dispersed and the corresponding nondispersed phases of inverted-type nonlamellar liquid-crystalline phases and microemulsions. The results suggest a transition between different internal nanostructures of the aqueous dispersions after the addition of the stabilizer. In addition to the main function of citrem as a stabilizer that adheres to the surface of the dispersed particles, it has a significant impact on the internal nanostructures, which is governed by the following factors: (1) its penetration between the hydrophobic tails of the lipid molecules and (2) its degree of incorporation into the lipid-water interfacial area. In the presence of citrem, the formation of aqueous dispersions with functionalized hydrophilic domains by the enlargement of the hydrophilic nanochannels of the internal H(2) phase in hexosomes and the hydrophilic core of the L(2) phase in emulsified microemulsions (EMEs) could be particularly attractive for solubilizing and controlling the release of positively charged drugs. PMID:22831645

  8. Charge localization on a redox-active single-molecule junction and its influence on coherent electron transport

    NASA Astrophysics Data System (ADS)

    Kastlunger, Georg; Stadler, Robert

    2013-07-01

    To adjust the charging state of a molecular metal complex in the context of a density functional theory description of coherent electron transport through single-molecule junctions, we correct for self-interaction effects by fixing the charge on a counterion, which in our calculations mimics the effect of the gate in an electrochemical scanning tunneling microscope setup, with two competing methods, namely, the generalized ?self consistent field (?SCF) technique and screening with solvation shells. One would expect a transmission peak to be pinned at the Fermi energy for a nominal charge of +1 on the molecule in the junction, but we find a more complex situation in this multicomponent system defined by the complex, the leads, the counterion, and the solvent. In particular the equilibrium charge transfer between the molecule and the leads plays an important role, which we investigate in relation to the total external charge in the context of electronegativity theory.

  9. Comprehensive approach to intrinsic charge carrier mobility in conjugated organic molecules, macromolecules, and supramolecular architectures.

    PubMed

    Saeki, Akinori; Koizumi, Yoshiko; Aida, Takuzo; Seki, Shu

    2012-08-21

    Si-based inorganic electronics have long dominated the semiconductor industry. However, in recent years conjugated polymers have attracted increasing attention because such systems are flexible and offer the potential for low-cost, large-area production via roll-to-roll processing. The state-of-the-art organic conjugated molecular crystals can exhibit charge carrier mobilities (?) that nearly match or even exceed that of amorphous silicon (1-10 cm(2) V(-1) s(-1)). The mean free path of the charge carriers estimated from these mobilities corresponds to the typical intersite (intermolecular) hopping distances in conjugated organic materials, which strongly suggests that the conduction model for the electronic band structure only applies to ? > 1 cm(2) V(-1) s(-1) for the translational motion of the charge carriers. However, to analyze the transport mechanism in organic electronics, researchers conventionally use a disorder formalism, where ? is usually less than 1 cm(2) V(-1) s(-1) and dominated by impurities, disorders, or defects that disturb the long-range translational motion. In this Account, we discuss the relationship between the alternating-current and direct-current mobilities of charge carriers, using time-resolved microwave conductivity (TRMC) and other techniques including field-effect transistor, time-of-flight, and space-charge limited current. TRMC measures the nanometer-scale mobility of charge carriers under an oscillating microwave electric field with no contact between the semiconductors and the metals. This separation allows us to evaluate the intrinsic charge carrier mobility with minimal trapping effects. We review a wide variety of organic electronics in terms of their charge carrier mobilities, and we describe recent studies of macromolecules, molecular crystals, and supramolecular architecture. For example, a rigid poly(phenylene-co-ethynylene) included in permethylated cyclodextrin shows a high intramolecular hole mobility of 0.5 cm(2) V(-1) s(-1), based on a combination of flash-photolysis TRMC and transient absorption spectroscopy (TAS) measurements. Single-crystal rubrene showed an ambipolarity with anisotropic charge carrier transport along each crystal axis on the nanometer scale. Finally, we describe the charge carrier mobility of a self-assembled nanotube consisting of a large ?-plane of hexabenzocoronene (HBC) partially appended with an electron acceptor. The local (intratubular) charge carrier mobility reached 3 cm(2) V(-1) s(-1) for the nanotubes that possessed well-ordered ?-stacking, but it dropped to 0.7 cm(2) V(-1) s(-1) in regions that contained greater amounts of the electron acceptor because those molecules reduced the structural integrity of ?-stacked HBC arrays. Interestingly, the long-range (intertubular) charge carrier mobility was on the order of 10(-4) cm(2) V(-1) s(-1) and monotonically decreased when the acceptor content was increased. These results suggest the importance of investigating charge carrier mobilities by frequency-dependent charge carrier motion for the development of more efficient organic electronic devices. PMID:22676381

  10. Excitation of Kelvin Helmholtz instability by an ion beam in a plasma with negatively charged dust grains

    SciTech Connect

    Rani, Kavita; Sharma, Suresh C.

    2015-02-15

    An ion beam propagating through a magnetized dusty plasma drives Kelvin Helmholtz Instability (KHI) via Cerenkov interaction. The frequency of the unstable wave increases with the relative density of negatively charged dust grains. It is observed that the beam has stabilizing effect on the growth rate of KHI for low shear parameter, but for high shear parameter, the instability is destabilized with relative density of negatively charged dust grains.

  11. A Hypersweet Protein: Removal of The Specific Negative Charge at Asp21 Enhances Thaumatin Sweetness

    PubMed Central

    Masuda, Tetsuya; Ohta, Keisuke; Ojiro, Naoko; Murata, Kazuki; Mikami, Bunzo; Tani, Fumito; Temussi, Piero Andrea; Kitabatake, Naofumi

    2016-01-01

    Thaumatin is an intensely sweet-tasting protein that elicits sweet taste at a concentration of 50 nM, a value 100,000 times larger than that of sucrose on a molar basis. Here we attempted to produce a protein with enhanced sweetness by removing negative charges on the interacting side of thaumatin with the taste receptor. We obtained a D21N mutant which, with a threshold value 31 nM is much sweeter than wild type thaumatin and, together with the Y65R mutant of single chain monellin, one of the two sweetest proteins known so far. The complex model between the T1R2-T1R3 sweet receptor and thaumatin, derived from tethered docking in the framework of the wedge model, confirmed that each of the positively charged residues critical for sweetness is close to a receptor residue of opposite charge to yield optimal electrostatic interaction. Furthermore, the distance between D21 and its possible counterpart D433 (located on the T1R2 protomer of the receptor) is safely large to avoid electrostatic repulsion but, at the same time, amenable to a closer approach if D21 is mutated into the corresponding asparagine. These findings clearly confirm the importance of electrostatic potentials in the interaction of thaumatin with the sweet receptor. PMID:26837600

  12. A Hypersweet Protein: Removal of The Specific Negative Charge at Asp21 Enhances Thaumatin Sweetness.

    PubMed

    Masuda, Tetsuya; Ohta, Keisuke; Ojiro, Naoko; Murata, Kazuki; Mikami, Bunzo; Tani, Fumito; Temussi, Piero Andrea; Kitabatake, Naofumi

    2016-01-01

    Thaumatin is an intensely sweet-tasting protein that elicits sweet taste at a concentration of 50?nM, a value 100,000 times larger than that of sucrose on a molar basis. Here we attempted to produce a protein with enhanced sweetness by removing negative charges on the interacting side of thaumatin with the taste receptor. We obtained a D21N mutant which, with a threshold value 31?nM is much sweeter than wild type thaumatin and, together with the Y65R mutant of single chain monellin, one of the two sweetest proteins known so far. The complex model between the T1R2-T1R3 sweet receptor and thaumatin, derived from tethered docking in the framework of the wedge model, confirmed that each of the positively charged residues critical for sweetness is close to a receptor residue of opposite charge to yield optimal electrostatic interaction. Furthermore, the distance between D21 and its possible counterpart D433 (located on the T1R2 protomer of the receptor) is safely large to avoid electrostatic repulsion but, at the same time, amenable to a closer approach if D21 is mutated into the corresponding asparagine. These findings clearly confirm the importance of electrostatic potentials in the interaction of thaumatin with the sweet receptor. PMID:26837600

  13. Manipulating the charge state and conductance of a single molecule on a semiconductor surface by electrostatic gating

    NASA Astrophysics Data System (ADS)

    Martinez-Blanco, Jesus; Nacci, Christophe; Erwin, Steven C.; Kanisawa, Kiyoshi; Locane, Elina; Thomas, Mark; von Oppen, Felix; Brouwer, Piet; Foelsch, Stefan

    2015-03-01

    We studied the charge state and tunneling conductance of single phthalocyanine molecules adsorbed on InAs(111)A using scanning tunneling microscopy (STM) at 5 K. On the InAs(111)A surface, native +1 charged indium adatoms can be repositioned by the STM tip using atom manipulation. This allows us to electrostatically gate an individual adsorbed molecule by placing charged adatoms nearby or, alternatively, by repositioning the molecule within the electrostatic potential landscape created by an STM-engineered adatom corral. By stepwise increasing the gating potential, the molecular charge state can be tuned from neutral to -1, as well as to bistable intermediate states. We find that the molecule changes its orientational conformation when the charge state is switched. Scanning tunneling spectroscopy measurements reveal that the conductance gap of the single-molecule tunneling junction can be precisely controlled by the electrostatic gating. We discuss the observed gating-dependent single-molecule tunneling conductance in terms of charge transport through a gated quantum dot. Granted by the German Research Foundation (FO 362/4-1; SFB 658).

  14. Charged Molecules Modulate the Volume Exclusion Effects Exerted by Crowders on FtsZ Polymerization

    PubMed Central

    Monterroso, Begoña; Reija, Belén; Jiménez, Mercedes; Zorrilla, Silvia; Rivas, Germán

    2016-01-01

    We have studied the influence of protein crowders, either combined or individually, on the GTP-induced FtsZ cooperative assembly, crucial for the formation of the dynamic septal ring and, hence, for bacterial division. It was earlier demonstrated that high concentrations of inert polymers like Ficoll 70, used to mimic the crowded cellular interior, favor the assembly of FtsZ into bundles with slow depolymerization. We have found, by fluorescence anisotropy together with light scattering measurements, that the presence of protein crowders increases the tendency of FtsZ to polymerize at micromolar magnesium concentration, being the effect larger with ovomucoid, a negatively charged protein. Neutral polymers and a positively charged protein also diminished the critical concentration of assembly, the extent of the effect being compatible with that expected according to pure volume exclusion models. FtsZ polymerization was also observed to be strongly promoted by a negatively charged polymer, DNA, and by some unrelated polymers like PEGs at concentrations below the crowding regime. The influence of mixed crowders mimicking the heterogeneity of the intracellular environment on the tendency of FtsZ to assemble was also studied and nonadditive effects were found to prevail. Far from exactly reproducing the bacterial cytoplasm environment, this approach serves as a simplified model illustrating how its intrinsically crowded and heterogeneous nature may modulate FtsZ assembly into a functional Z-ring. PMID:26870947

  15. Thin films of molecule-based charge transfer complex cobalt tetracyanoethylene: In situ X-ray photoemission study

    NASA Astrophysics Data System (ADS)

    Bhatt, Pramod; Yusuf, S. M.

    2011-10-01

    Thin films of molecule-based charge transfer magnet, cobalt tetracyanoethylene [Co(TCNE)x, x ~ 2] consisting of the transition metal Co, and an organic molecule viz. tetracyanoethylene (TCNE) have been deposited by using physical vapor deposition method under ultra-high vacuum conditions at room temperature. X-ray photoelectron spectroscopy (XPS) technique has been used extensively to investigate the electronic properties of the Co(TCNE)x thin films. The XPS measurements show that the prepared Co(TCNE)x films are clean, and oxygen free. The stoichiometries of the films, based on atomic sensitive factors, are obtained, and yields a ~ 1:2 ratio between metal Co and TCNE for all films. Interestingly, the positive shift of binding energy position for Co(2p), and negative shifts for C(1s) and N(1s) peaks suggest a charge-transfer from Co to TCNE, and cobalt is assigned to its Co(II) valence state. In the valence band investigation, the highest occupied molecular orbital (HOMO) of Co(TCNE)x is found to be at ~ 2.4 eV with respect to the Fermi level, and it is derived either from the TCNE- singly occupied molecular orbital (SOMO) or Co(3d) states. The peaks located at ~ 6.8 eV and ~ 8.8 eV are due to TCNE derived electronic states. The obtained core level and valence band results of Co(TCNE)x, films are compared with those of V(TCNE)x thin film magnet: a well known system of M(TCNE)x type of organic magnet, and important points regarding their electronic properties have been brought out.

  16. New effects of a long-lived negatively charged massive particle on big bang nucleosynthesis

    SciTech Connect

    Kusakabe, Motohiko; Kim, K. S.; Cheoun, Myung-Ki; Kajino, Toshitaka; Kino, Yasushi; Mathews, Grant J.

    2014-05-02

    Primordial {sup 7}Li abundance inferred from observations of metal-poor stars is a factor of about 3 lower than the theoretical value of standard big bang nucleosynthesis (BBN) model. One of the solutions to the Li problem is {sup 7}Be destruction during the BBN epoch caused by a long-lived negatively charged massive particle, X{sup −}. The particle can bind to nuclei, and X-bound nuclei (X-nuclei) can experience new reactions. The radiative X{sup −} capture by {sup 7}Be nuclei followed by proton capture of the bound state of {sup 7}Be and X{sup −} ({sup 7}Be{sub x}) is a possible {sup 7}Be destruction reaction. Since the primordial abundance of {sup 7}Li originates mainly from {sup 7}Li produced via the electron capture of {sup 7}Be after BBN, the {sup 7}Be destruction provides a solution to the {sup 7}Li problem. We suggest a new route of {sup 7}Be{sub x} formation, that is the {sup 7}Be charge exchange at the reaction of {sup 7}Be{sup 3+} ion and X{sup −}. The formation rate depends on the ionization fraction of {sup 7}Be{sup 3+} ion, the charge exchange cross section of {sup 7}Be{sup 3+}, and the probability that excited states {sup 7}Be{sub x}* produced at the charge exchange are converted to the ground state. We find that this reaction can be equally important as or more important than ordinary radiative recombination of {sup 7}Be and X{sup −}. The effect of this new route is shown in a nuclear reaction network calculation.

  17. Space Charge Neutralization of DEMO Relevant Negative Ion Beams at Low Gas Density

    SciTech Connect

    Surrey, Elizabeth; Porton, Michael

    2011-09-26

    The application of neutral beams to future power plant devices (DEMO) is dependent on achieving significantly improved electrical efficiency and the most promising route to achieving this is by implementing a photoneutralizer in place of the traditional gas neutralizer. A corollary of this innovation would be a significant reduction in the background gas density through which the beam is transported between the accelerator and the neutralizer. This background gas is responsible for the space charge neutralization of the beam, enabling distances of several metres to be traversed without significant beam expansion. This work investigates the sensitivity of a D{sup -} beam to reduced levels of space charge compensation for energies from 100 keV to 1.5 MeV, representative of a scaled prototype experiment, commissioning and full energy operation. A beam transport code, following the evolution of the phase space ellipse, is employed to investigate the effect of space charge on the beam optics. This shows that the higher energy beams are insensitive to large degrees of under compensation, unlike the lower energies. The probable degree of compensation at low gas density is then investigated through a simple, two component beam-plasma model that allows the potential to be negative. The degree of under-compensation is dependent on the positive plasma ion energy, one source of which is dissociation of the gas by the beam. The subsequent space charge state of the beam is shown to depend upon the relative times for equilibration of the dissociation energy and ionization by the beam ions.

  18. Charge transport through single alkanedithiol molecules on an ultrathin insulating film: Influence on an atomic Kondo resonance

    NASA Astrophysics Data System (ADS)

    Choi, Taeyoung; Gupta, Jay

    2011-03-01

    Studies of charge/spin transport through single molecules are important for understanding organic-based electronic and memory devices. We have realized a single molecule wire comprising an alkanedithiol molecule and a single Co atom contact using a low temperature scanning tunneling microscope. This wire is formed on an ultrathin insulating layer (Cu2N on Cu(100)). A Kondo resonance observed on isolated Co atoms on Cu2N indicates minimal contact to the Cu substrate. However, increased contact to Cu is achieved by connecting the Co atom via the alkanedithiol molecule. A change in the Kondo lineshape on the Co atom indicates an open conduction channel through the molecule. ~This result provides an opportunity to study charge/spin transport through single molecules with atomically precise contacts. We acknowledge financial support from NSF CAREER Award No. DMR-0645451 and NSF MRSEC-0820414. http://www.physics.ohio-state.edu/ ~ jgupta.

  19. A charge-charge flux-dipole flux decomposition of the dipole moment derivatives and infrared intensities of the AB 3 (A = N, P; B = H, F) molecules

    NASA Astrophysics Data System (ADS)

    Csar, Paulo H.; Faria, Srgio H. D. M.; da Silva, Joo V.; Haiduke, R. L. A.; Bruns, Roy E.

    2005-10-01

    The quantum theory of atoms in molecules (AIM) has been used to decompose dipole moment derivatives and fundamental infrared intensities of the AB 3 (A = N,P; B = H,F) molecules into charge-charge flux-dipole flux (CCFDF) contributions. Calculations were carried out at the MP2(FC)/6-311++G(3d,3p) level. Infrared intensities calculated from the AIM atomic charges and atomic dipoles are within 13.8 km mol -1 of the experimental values not considering the NH 3 and PH 3 stretching vibrations for which the experimental bands are severely overlapped. Group V atomic dipoles are very important in determining the molecular dipole moments of NF 3, PH 3 and PF 3 although the atomic charges account for almost all of the NH 3 molecular moment. Dipole fluxes on the Group V atom are important in determining the stretching band intensities of all molecules whereas they make small contributions to the bending mode intensities. Consideration of dipole flux contributions from the terminal atoms must also be made for accurately describing the intensities of all these molecules. As expected from a simple bond moment model, charge contributions dominate for most of the NH 3, NF 3, and PF 3 dipole moment derivatives and intensities. Charge flux and dipole flux contributions are very substantial for all the PH 3 vibrations, cancelling each other for the stretching modes and reinforcing one another for the bending modes.

  20. Probing charge transport of ruthenium-complex-based molecular wires at the single-molecule level.

    PubMed

    Liu, Ke; Wang, Xianhong; Wang, Fosong

    2008-11-25

    A ruthenium(II) bis(sigma-arylacetylide)-complex-based molecular wire functionalized with thiolacetyl alligator clips at both ends (OPERu) was used to fabricate gold substrate-molecular wire-conductive tip junctions. To elucidate the ruthenium-complex-enhanced charge transport, we conducted a single-molecule level investigation using the technique-combination method, where electronic decay constant, single-molecular conductance, and barrier height were obtained by scanning tunneling microscopy (STM) apparent height measurements, STM break junction measurements, and conductive probe-atomic force microscopy (CP-AFM) measurements, respectively. A quantitative comparison of OPERu with the well-studied pi-conjugated molecular wire oligo(1,4-phenylene ethynylene) (OPE) indicated that the lower electronic decay constant as well as the higher conductance of OPERu resulted from its lower band gap between the highest occupied molecular orbital (HOMO) and the gold Fermi level. The small offset of 0.25 eV was expected to be beneficial for the long-range charge transport of molecular wires. Moreover, the observed cross-platform agreement proved that this technique-combination method could serve as a benchmark for the detailed description of charge transport through molecular wires. PMID:19206398

  1. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2.

    PubMed

    Zhou, Changjie; Yang, Weihuang; Zhu, Huili

    2015-06-01

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides. PMID:26049513

  2. Long-range charge transport in single G-quadruplex DNA molecules.

    PubMed

    Livshits, Gideon I; Stern, Avigail; Rotem, Dvir; Borovok, Natalia; Eidelshtein, Gennady; Migliore, Agostino; Penzo, Erika; Wind, Shalom J; Di Felice, Rosa; Skourtis, Spiros S; Cuevas, Juan Carlos; Gurevich, Leonid; Kotlyar, Alexander B; Porath, Danny

    2014-12-01

    DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100 pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100 nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits. PMID:25344689

  3. Mitigation of charged impurity effects in graphene field-effect transistors with polar organic molecules (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Worley, Barrett C.; Kim, Seohee; Akinwande, Deji; Rossky, Peter J.; Dodabalapur, Ananth

    2015-09-01

    Recent developments in monolayer graphene production allow its use as the active layer in field-effect transistor technology. Favorable electrical characteristics of monolayer graphene include high mobility, operating frequency, and good stability. These characteristics are governed by such key transport physical phenomena as electron-hole transport symmetry, Dirac point voltage, and charged impurity effects. Doping of graphene occurs during device fabrication, and is largely due to charged impurities located at or near the graphene/substrate interface. These impurities cause scattering of charge carriers, which lowers mobility. Such scattering is detrimental to graphene transistor performance, but our group has shown that coating with fluoropolymer thin films or exposure to polar organic vapors can restore favorable electrical characteristics to monolayer graphene. By partially neutralizing charged impurities and defects, we can improve the mobility by approximately a factor of 2, change the Dirac voltage by fairly large amounts, and reduce the residual carrier density significantly. We hypothesize that this phenomena results from screening of charged impurities by the polar molecules. To better understand such screening interactions, we performed computational chemistry experiments to observe interactions between polar organic molecules and monolayer graphene. The molecules interacted more strongly with defective graphene than with pristine graphene, and the electronic environment of graphene was altered. These computational observations correlate well with our experimental results to support our hypothesis that polar molecules can act to screen charged impurities on or near monolayer graphene. Such screening favorably mitigates charge scattering, improving graphene transistor performance.

  4. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    NASA Astrophysics Data System (ADS)

    Rfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  5. Dynamic Jahn-Teller Effect in Negatively Charged Nitrogen-Vacancy Center in Diamond

    NASA Astrophysics Data System (ADS)

    Abtew, Tesfaye; Zhang, Peihong

    2011-03-01

    The negatively charged nitrogen-vacancy (NV) center in diamond has attracted much research interest recently owing to its desirable optical properties and long spin coherent lifetime. The ground state of NV- center has a 3 A2 symmetry, which can be optically excited, to a 3 E state. The excited state is orbitally degenerate therefore should experience either static or dynamic Jahn-Teller (JT) effects. We use accurate first-principles methods to study structural and electronic properties of the NV- center in diamond both in the ground and excited states. Our results indicate that the excited state of the NV- center is indeed a dynamic JT system. We acknowledge the Center for Computational Research at the University at Buffalo, SUNY. This work is supported by the National Science Foundation under Grant No. DMR-0946404 and by the Department of Energy under GrantNo. DE-SC0002623.

  6. Polymerization on the rocks: negatively-charged alpha-amino acids

    NASA Technical Reports Server (NTRS)

    Hill, A. R. Jr; Bohler, C.; Orgel, L. E.; Bada, J. L. (Principal Investigator)

    1998-01-01

    Oligomers of the negatively-charged amino acids, glutamic acid, aspartic acid, and O-phospho-L-serine are adsorbed by hydroxylapatite and illite with affinities that increase with oligomer length. In the case of oligo-glutamic acids adsorbed on hydroxylapatite, addition of an extra residue results in an approximately four-fold increase in the strength of adsorption. Oligomers much longer than the 7-mer are retained tenaciously by the mineral. Repeated incubation of short oligo-glutamic acids adsorbed on hydroxylapatite or illite with activated monomer leads to the accumulation of oligomers at least 45 units long. The corresponding reactions of aspartic acid and O-phospho-L-serine on hydroxylapatite are less effective in generating long oligomers, while illite fails to accumulate substantial amounts of long oligomers of aspartic acid or of O-phospho-L-serine.

  7. Higher stabilities of positive and negative charge on tetrafluoroethylene-hexafluoropropylene copolymer (FEP) electrets treated with titanium-tetrachloride vapor

    NASA Astrophysics Data System (ADS)

    Rychkov, D.; Rychkov, A.; Efimov, N.; Malygin, A.; Gerhard, R.

    2013-08-01

    Tetrafluoroethylene-hexafluoropropylene copolymer (FEP) films were treated with titanium-tetrachloride vapor in a molecular-layer deposition process. As a result of the surface treatment, significant improvements of the thermal and temporal charge stability were observed. Charge-decay measurements revealed enhancements of the half-value temperatures and the relaxation times of positively charged FEP electrets by at least 120 C and two orders of magnitude, respectively. Beyond previous publications on fluoropolymer electrets with surface modification, we here report enhanced charge stabilities of the FEP films charged in negative as well as in positive corona discharges. Even though the improvement for negatively charged FEP films is moderate (half-value temperature about 20 C higher), our experiments show that the asymmetry in positive and negative charge stability that is typical for FEP electrets can be overcome by means of chemical surface treatments. The results are discussed in the context of the formation of modified surface layers with enhanced charge-trapping properties.

  8. A fast empirical GAFF compatible partial atomic charge assignment scheme for modeling interactions of small molecules with biomolecular targets.

    PubMed

    Mukherjee, Goutam; Patra, Niladri; Barua, Poranjyoti; Jayaram, B

    2011-04-15

    We report here a new and fast approach [Transferable Partial Atomic Charge Model (TPACM4)-upto four bonds] for deriving the partial atomic charges of small molecules for use in protein/DNA-ligand docking and scoring. We have created a look-up table of 5302 atom types to cover the chemical space of C, H, O, N, S, P, F, Cl, and Br atoms in small molecules together with their quantum mechanical RESP fit charges. The atom types defined span diverse plausible chemical environments of each atom in a molecule. The partial charge on any atom in a given molecule is then assigned by a reference to the look-up table. We tested the sensitivity of the TPACM4 partial charges in estimates of hydrogen bond dimers energies, solvation free energies and protein-ligand binding free energies. An average error 1.11 kcal/mol and a correlation coefficient of 0.90 is obtained in the calculated protein-ligand binding free energies vis--vis an RMS error of 1.02 kcal/mol and a correlation coefficient of 0.92 obtained with RESP fit charges in comparison to experiment. Similar accuracies are realized in predictions of hydrogen bond energies and solvation free energies of small molecules. For a molecule containing 50-55 atoms, the method takes on the order of milliseconds on a single processor machine to assign partial atomic charges. The TPACM4 programme has been web-enabled and made freely accessible at http://www.scfbio-iitd.res.in/software/drugdesign/charge.jsp. PMID:21341292

  9. Linear free energy relationships for metal-ligand complexation: Bidentate binding to negatively-charged oxygen donor atoms

    NASA Astrophysics Data System (ADS)

    Carbonaro, Richard F.; Atalay, Yasemin B.; Di Toro, Dominic M.

    2011-05-01

    Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = ?OO( ?O log KHL,1 + ?O log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand p Ka values), and ?O is the Irving-Rossotti slope. The parameter ?OO is metal specific and has slightly different values for five and six membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, ?-hydroxycarboxylic acids, and ?-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of ?OO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems.

  10. Negatively Charged Carbon Nanohorn Supported Cationic Liposome Nanoparticles: A Novel Delivery Vehicle for Anti-Nicotine Vaccine.

    PubMed

    Zheng, Hong; Hu, Yun; Huang, Wei; de Villiers, Sabina; Pentel, Paul; Zhang, Jianfei; Dorn, Harry; Ehrich, Marion; Zhang, Chenming

    2015-12-01

    Tobacco addiction is the second-leading cause of death in the world. Due to the nature of nicotine (a small molecule), finding ways to combat nicotine's deleterious effects has been a constant challenge to the society and the medical field. In the present work, a novel anti-nicotine vaccine based on nanohorn supported liposome nanoparticles (NsL NPs) was developed. The nano-vaccine was constructed by using negatively charged carbon nanohorns as a scaffold for the assembly of cationic liposomes, which allow the conjugation of hapten conjugated carrier proteins. The assembled bio-nanoparticles are stable. Mice were immunized subcutaneously with the nano-vaccine, which induced high titer and high affinity of nicotine specific antibodies in mice. Furthermore, no evidence of clinical signs or systemic toxicity followed multiple administrations of NsL-based anti-nicotine vaccine. These results suggest that NsL-based anti-nicotine vaccine is a promising candidate in treating nicotine dependence and could have potential to significantly contribute to smoking cessation. PMID:26510313

  11. Synthesis of positively and negatively charged silver nanoparticles and their deposition on the surface of titanium

    NASA Astrophysics Data System (ADS)

    Sharonova, A.; Loza, K.; Surmeneva, M.; Surmenev, R.; Prymak, O.; Epple, M.

    2016-02-01

    Bacterial infections related to dental implants are currently a significant complication. A good way to overcome this challenge is functionalization of implant surface with Ag nanoparticles (NPs) as antibacterial agent. This article aims at review the synthesis routes, size and electrical properties of AgNPs. Polyvinyl pyrrolidone (PVP) and polyethyleneimine (PEI) were used as stabilizers. Dynamic Light Scattering, Nanoparticle Tracking Analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDX) have been used to characterize the prepared AgNPs. Two types of NPs were synthesized in aqueous solutions: PVP-stabilized NPs with a diameter of the metallic core of 70 ± 20 nm, and negative charge of -20 mV, PEI-stabilized NPs with the size of the metallic core of 50 ± 20 nm and positive charge of +55 mV. According to SEM results, all the NPs have a spherical shape. Functionalization of the titanium substrate surface with PVP and PEI-stabilized AgNPs was carried out by dropping method. XRD patterns revealed that the AgNPs are crystalline with the crystallite size of 14 nm.

  12. Segregation of negatively charged phospholipids by the polycationic and farnesylated membrane anchor of Kras.

    PubMed

    Janosi, Lorant; Gorfe, Alemayehu A

    2010-12-01

    The Kras protein, a member of the Ras family of bio-switches that are frequently mutated in cancer and developmental disorders, becomes functional when anchored to the inner surface of the plasma membrane. It is well known that membrane attachment involves the farnesylated and poylcationic C-terminus of the protein. However, little is known about the structure of the complex and the specific protein-lipid interactions that are responsible for the binding. On the basis of data from extensive (>0.55 ?s) molecular dynamics simulations of multiple Kras anchors in bilayers of POPC/POPG lipids (4:1 ratio), we show that, as expected, Kras is tethered to the bilayer surface by specific lysine-POPG salt bridges and by nonspecific farnesyl-phospholipid van der Waals interactions. Unexpectedly, however, only the C-terminal five of the eight Kras Lys side chains were found to directly interact with the bilayer, with the N-terminal ones staying in water. Furthermore, the positively charged Kras anchors pull the negatively charged POPG lipids together, leading to the clustering of the POPG lipids around the proteins. This selective Kras-POPG interaction is directly related to the specific geometry of the backbone, which exists in two major conformational states: 1), a stable native-like ensemble of structures characterized by an extended geometry with a pseudohelical turn; and 2), less stable nonnative ensembles of conformers characterized by severely bent geometries. Finally, although the interface-bound anchor has little effect on the overall structure of the bilayer, it induces local thinning within a persistence length of ?12. Our results thus go beyond documenting how Kras attaches to a mixed bilayer of charged and neutral lipids; they highlight a fascinating process of protein-induced lipid sorting coupled with the (re)shaping of a surface-bound protein by the host lipids. PMID:21112291

  13. Negatively charged hyperbranched polyglycerol grafted membranes for osmotic power generation from municipal wastewater.

    PubMed

    Li, Xue; Cai, Tao; Chen, Chunyan; Chung, Tai-Shung

    2016-02-01

    Osmotic power holds great promise as a clean, sustainable and largely unexploited energy resource. Recent membrane development for pressure-retarded osmosis (PRO) is making the osmotic power generation more and more realistic. However, severe performance declines have been observed because the porous layer of PRO membranes is fouled by the feed stream. To overcome it, a negatively charged antifouling PRO hollow fiber membrane has been designed and studied in this work. An antifouling polymer, derived from hyperbranched polyglycerol and functionalized by α-lipoic acid and succinic anhydride, was synthesized and grafted onto the polydopamine (PDA) modified poly(ether sulfone) (PES) hollow fiber membranes. In comparison to unmodified membranes, the charged hyperbranched polyglycerol (CHPG) grafted membrane is much less affected by organic deposition, such as bovine serum albumin (BSA) adsorption, and highly resistant to microbial growths, demonstrated by Escherichia coli adhesion and Staphylococcus aureus attachment. CHPG-g-TFC was also examined in PRO tests using a concentrated wastewater as the feed. Comparing to the plain PES-TFC and non-charged HPG-g-TFC, the newly developed membrane exhibits not only the smallest decline in water flux but also the highest recovery rate. When using 0.81 M NaCl and wastewater as the feed pair in PRO tests at 15 bar, the average power density remains at 5.6 W/m(2) in comparison to an average value of 3.6 W/m(2) for unmodified membranes after four PRO runs. In summary, osmotic power generation may be sustained by properly designing and anchoring the functional polymers to PRO membranes. PMID:26630043

  14. Ultrastructural, physico-chemical and conformational study of the interactions of gentamicin and bis(beta-diethylaminoethylether) hexestrol with negatively-charged phospholipid layers.

    PubMed

    Mingeot-Leclercq, M P; Schanck, A; Ronveaux-Dupal, M F; Deleers, M; Brasseur, R; Ruysschaert, J M; Laurent, G; Tulkens, P M

    1989-03-01

    Aminoglycoside antibiotics such as gentamicin, which are fully hydrophilic, and cationic amphiphilic drugs such as bis(beta-diethylaminoethylether)hexestrol (DEH), are both known to inhibit lysosomal phospholipases and induce phospholipidosis. This enzymatic inhibition is probably related to the neutralization of the surface negative charges on which the lysosomal phospholipases A1 and A2 are dependent to express fully their activities (Mingeot-Leclerq et al., Biochem Pharmacol 37: 591-599, 1988). Using negatively charged liposomes, we show by 31P NMR spectroscopy that both gentamicin and DEH cause a significant restriction in the phosphate head mobility and, in sonicated vesicles, the appearance of larger bilayer structures. Both DEH and gentamicin increased the apparent size of sonicated negatively charged liposomes (but not of neutral liposomes) as measured by quasi-elastic light scattering spectroscopy. Examination of replicas from freeze-etched samples, however, revealed that gentamicin caused aggregation of liposomes, whereas DEH induced their fusion and the formation of intramembranous roundly shaped structures. Only DEH caused a significant decrease of the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, a fluorescent lipid-soluble probe. In addition, DEH, but not gentamicin, interfered with the bilayer to hexagonal phase transition occurring in dioleoyl- and dielaidoylphosphatidylethanolamine liposomes upon warming, and caused the appearance of an isotropic signal suggestive of the formation of inverted micelles. In computer-aided conformational analysis of the molecules at a simulated air-water interface, gentamicin was shown to display a largely-open crescent shape. When surrounded by phosphatidylinositol molecules, it remained as such at the interface which it locally mis-shaped, establishing close contact with the negatively charged phospho groups. In contrast, DEH could be oriented perpendicularly to the interface, with its two cationic groups associated with the phospho groups, and its phenyl- and diethylethandiyl moieties deeply inserted between and interacting with the aliphatic chains. Thus, although both agents cause lysosomal phospholipases inhibition, the differences in their interactions with negatively-charged bilayers is likely to result in a different organization of the phospholipids accumulated in vivo, which could lead to different toxicities. PMID:2539158

  15. Graphene field effect transistor as a probe of electronic structure and charge transfer at organic molecule-graphene interfaces.

    PubMed

    Cervenka, Jiri; Budi, Akin; Dontschuk, Nikolai; Stacey, Alastair; Tadich, Anton; Rietwyk, Kevin J; Schenk, Alex; Edmonds, Mark T; Yin, Yuefeng; Medhekar, Nikhil; Kalbac, Martin; Pakes, Chris I

    2015-01-28

    The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by the molecules and local molecular electric fields. Our results show that adsorbed molecules containing polar functional groups on graphene exhibit different coverage behaviour to nonpolar molecules. These effects open up a range of new opportunities for recognition of different molecules on graphene-based sensor devices. PMID:25502349

  16. Cluster ions and multiply charged ions formed in frozen CO sub 2 molecules under heavy ion impact

    SciTech Connect

    Tawara, H. ); Tonuma, T.; Kumagai, H. , Wako-shi 351-01, ); Matsuo, T. ); Shibata, H. )

    1991-02-15

    A variety of cluster ions, positive or negative, as well as multiply charged atomic ions have been observed from the frozen CO{sub 2} targets under (MeV/amu) energetic, highly charged projectile ion impact. Their spectra are found to be quite different from those produced in the cooled expanding CO{sub 2} gas targets.

  17. Negative Electron Binding Energies Observed in a Triply Charged Anion: Photoelectron Spectroscopy of 1-Hydroxy-3, 6, 8-Pyrene-Trisulfonate

    SciTech Connect

    Yang, Jie; Xing, Xiaopeng; Wang, Xue B.; Wang, Lai S.; Sergeeva, Alina P.; Boldyrev, Alexander I.

    2008-03-07

    We report the observation of negative electron binding energies in a triply charged anion, 1-hydroxy-3,6,8-pyrene-trisulfonate (HPTS3). Low-temperature photoelectron spectra were obtained for HPTS3 at several photon energies, revealing three detachment features below 0 electron binding energy. The HPTS3 trianion was measured to possess a negative electron binding of -0.66 eV. Despite the relatively high excess energy stored in HPTS3, it was observed to be a long-lived anion due to its high repulsive Coulomb barrier (~3.3 eV), which prevents spontaneous electron emission. Theoretical calculations were carried out, which confirmed the negative electron binding energies observed. The calculations further showed that the highest occupied molecular orbital in HPTS3 is an anti-bonding ? orbital on the pyrene rings, followed by lone pair electrons in the peripheral SO3 groups. Negative electron binding energy is a unique feature of multiply-charged anions due to the presence of the repulsive Coulomb barrier. Such metastable species may be good models to study electron-electron and vibronic interactions in complex molecules.

  18. Exploration of Porphyrin-based Semiconductors for Negative Charge Transport Applications Using Synthetic, Spectroscopic, Potentiometric, Magnetic Resonance, and Computational Methods

    NASA Astrophysics Data System (ADS)

    Rawson, Jeffrey Scott

    Organic pi-conjugated materials are emerging as commercially relevant components in electronic applications that include transistors, light-emitting diodes, and solar cells. One requirement common to all of these functions is an aptitude for accepting and transmitting charges. It is generally agreed that the development of organic semiconductors that favor electrons as the majority carriers (n-type) lags behind the advances in hole transporting (p-type) materials. This shortcoming suggests that the design space for n-type materials is not yet well explored, presenting researchers with the opportunity to develop unconventional architectures. In this regard, it is worth noting that discrete molecular materials are demonstrating the potential to usurp the preeminent positions that pi-conjugated polymers have held in these areas of organic electronics research. This dissertation describes how an extraordinary class of molecules, meso-to-meso ethyne-bridged porphyrin arrays, has been bent to these new uses. Chapter one describes vis-NIR spectroscopic and magnetic resonance measurements revealing that these porphyrin arrays possess a remarkable aptitude for the delocalization of negative charge. In fact, the miniscule electron-lattice interactions exhibited in these rigid molecules allow them to host the most vast electron-polarons ever observed in a pi-conjugated material. Chapter two describes the development of an ethyne-bridged porphyrin-isoindigo hybrid chromophore that can take the place of fullerene derivatives in the conventional thin film solar cell architecture. Particularly noteworthy is the key role played by the 5,15-bis(heptafluoropropyl)porphyrin building block in the engineering of a chromophore that, gram for gram, is twice as absorptive as poly(3-hexyl)thiophene, exhibits a lower energy absorption onset than this polymer, and yet possesses a photoexcited singlet state sufficiently energetic to transfer a hole to this polymer. Chapter three describes synthetic efforts that expand the repertoire of readily available meso-heptafluoropropyl porphyrin building blocks. The findings suggest that the remaining challenges to the exploitation of these pigments will be overcome by a sufficiently firm grasp of their subtle electronic structures, and a willingness to eschew the customary strategies of chromophore assembly.

  19. Many-body calculation for charge transport through triangular quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Chieh; Chang, Yia-Chung; Kuo, David M. T.

    2015-03-01

    We study the many-body effect of electron tunneling through the coupled quantum dots systems in the Coulomb blockade regime. Using the equation of motion method for the non-equilibrium Green's function, we calculate the charge current and conductance of junctions consisting of metallic electrodes and a few quantum dots. Many-particle correlation functions are explicitly solved numerically. Quantum phenomena like quantum interference, Coulomb blockade and spin blockade for the triangular quantum dot molecules are discussed. Our work suggests a new method for the modeling of the mesoscopic transport. This work was supported in part by the Ministry of Science and Technology, Taiwan under Contract Nos. NSC 101-2112-M-001-024-MY3 and NSC 103-2112-M-008-009-MY3.

  20. Effect of Charge Recombination on the Fill Factor of Small Molecule Bulk Heterojunction Solar Cells

    SciTech Connect

    Zhang, Yuan; Dang, Xuan-Dung; Kim, Chunki; Nguyen, Thuc-Quyen

    2011-06-09

    Solution-processed organic BHJ solar cells based on 3,6-bis[5-(benzofuran-2-yl)thiophen-2-yl]-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP(TBFu)₂) or poly(3-hexylthiophene) blended with [6,6]-phenyl-C60(70)-butyric acid methyl ester (PC60(70)BM) behave differently under various irradiation intensities. Small molecule-based DPP(TBFu)₂:PC₆₀ BM solar cells show up to 5.2% power conversion efficiency and a high fill factor at low light intensity. At 100 mW cm-2 illumination, the efficiency and fill factor decrease, resulting in stronger power losses. Impedance spectroscopy at various light intensities reveals that high charge recombination is the cause of the low fill factor in DPP(TBFu)₂:PC₆₀ BM.

  1. Single charge exchange in collision of fast protons with hydrogen molecules

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim; Sattarpour, Seyedeh Hedyeh

    2015-11-01

    Single charge transfer process in collision of energetic protons with molecular hydrogens is theoretically studied using a first-order two-effective-center Born approximation. The correct boundary conditions are incorporated in the formalism and the Hartree-Fock molecular wave function for molecular targets and the residual ions are used to calculate the transition amplitude. The interference patterns in the capture differential cross-sections (DCSs) for a given fixed orientation of the molecule, due to the scattering from the two-atomic centers in the molecular targets, are examined. The dependence of the DCSs upon the angle between the molecular axis and the direction of the incident velocity is theoretically investigated. Both average differential and integral cross-sections are calculated. The obtained results are compared with the available experimental data.

  2. Long-lived charge carrier generation in ordered films of a covalent perylenediimide–diketopyrrolopyrrole–perylenediimide molecule

    DOE PAGESBeta

    Hartnett, Patrick E.; Dyar, Scott M.; Margulies, Eric A.; Shoer, Leah E.; Cook, Andrew W.; Eaton, Samuel W.; Marks, Tobin J.; Wasielewski, Michael R.

    2015-07-31

    The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ~6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, uponmore » CH₂Cl₂ vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ~4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems.« less

  3. Long-lived charge carrier generation in ordered films of a covalent perylenediimide–diketopyrrolopyrrole–perylenediimide molecule

    SciTech Connect

    Hartnett, Patrick E.; Dyar, Scott M.; Margulies, Eric A.; Shoer, Leah E.; Cook, Andrew W.; Eaton, Samuel W.; Marks, Tobin J.; Wasielewski, Michael R.

    2015-07-31

    The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ~6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, upon CH₂Cl₂ vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ~4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems.

  4. Molecule/Surface Interactions and the Control of Electronic Structure In Epitaxial Charge Transfer Salts

    NASA Astrophysics Data System (ADS)

    Rojas, Geoffrey; Ganesh, P.; Kelly, Simon; Sumpter, Bobby; Schlueter, John; Maksymovych, Petro; CenterNanophase Materials; Sciences Team; Chemistry and Materials Science Division Team

    2013-03-01

    The two-dimensionality of the fulvalene-based superconducting charge transfer salts has lead to an increasing interest in the epitaxial growth and local probe analysis of monolayer CTS films. Curiously, these studies have shown remarkable differences in both the electronic structure and topography of the monolayers grown on metals, suggesting that the organic/metal interactions introduced by epitaxial growth strongly influence the resulting structures. Through recent experiments on monolayer films of the CTS (ET)2SF5CH2CF2SO3 and the bare fulvalene ET grown on Ag(111), we illustrate what effect the metal-molecule interaction has on the electronic structure and 2D charge transport of epitaxial CTS and how this differs from the bare fulvalene. Through a comparative analysis of the differences in stoichiometry and topography of these and heretofore published systems, the relative roles of ionic bonding, surface chemisorption, and hybridization for the preparation of this and future compounds are explored. Research was conducted at the Center for Nanophase Materials Sciences and sponsored by the Division of Scientific User Facilities, U.S. Department of Energy.

  5. Energy, charge, and spin transport in molecules and self-assembled nanostructures inspired by photosynthesis.

    PubMed

    Wasielewski, Michael R

    2006-07-01

    Electron transfer in biological molecules provides both insight and inspiration for developing chemical systems having similar functionality. Photosynthesis is an example of an integrated system in which light harvesting, photoinduced charge separation, and catalysis combine to carry out two thermodynamically demanding processes, the oxidation of water and the reduction of carbon dioxide. The development of artificial photosynthetic systems for solar energy conversion requires a fundamental understanding of electron-transfer reactions between organic molecules. Since these reactions most often involve single-electron transfers, the spin dynamics of photogenerated radical ion pairs provide important information on how the rates and efficiencies of these reactions depend on molecular structure. Given this knowledge, the design and synthesis of large integrated structures to carry out artificial photosynthesis is moving forward. An important approach to achieving this goal is the development of small, functional building blocks, having a minimum number of covalent bonds, which also have the appropriate molecular recognition sites to facilitate self-assembly into a complete, functional artificial photosynthetic system. PMID:16808492

  6. Dispersion interactions with linear scaling DFT: a study of planar molecules on charged polar surfaces

    NASA Astrophysics Data System (ADS)

    Andrinopoulos, Lampros; Hine, Nicholas; Haynes, Peter; Mostofi, Arash

    2010-03-01

    The placement of organic molecules such as CuPc (copper phthalocyanine) on wurtzite ZnO (zinc oxide) charged surfaces has been proposed as a way of creating photovoltaic solar cellsfootnotetextG.D. Sharma et al., Solar Energy Materials & Solar Cells 90, 933 (2006) ; optimising their performance may be aided by computational simulation. Electronic structure calculations provide high accuracy at modest computational cost but two challenges are encountered for such layered systems. First, the system size is at or beyond the limit of traditional cubic-scaling Density Functional Theory (DFT). Second, traditional exchange-correlation functionals do not account for van der Waals (vdW) interactions, crucial for determining the structure of weakly bonded systems. We present an implementation of recently developed approachesfootnotetextP.L. Silvestrelli, P.R.L. 100, 102 (2008) to include vdW in DFT within ONETEPfootnotetextC.-K. Skylaris, P.D. Haynes, A.A. Mostofi and M.C. Payne, J.C.P. 122, 084119 (2005) , a linear-scaling package for performing DFT calculations using a basis of localised functions. We have applied this methodology to simple planar organic molecules, such as benzene and pentacene, on ZnO surfaces.

  7. Positively-charged, porous, polysaccharide nanoparticles loaded with anionic molecules behave as 'stealth' cationic nanocarriers

    PubMed Central

    Paillard, Archibald; Passirani, Catherine; Saulnier, Patrick; Kroubi, Maya; Garcion, Emmanuel; Benot, Jean-Pierre; Betbeder, Didier

    2010-01-01

    PURPOSE Stealth nanoparticles are generally obtained after modifying their surface with hydrophilic polymers such as PEG. In this study we analysed the effect of a phospholipid (DG) or protein (BSA) inclusion in porous cationic polysaccharide (NP+) on their physico-chemical structure and the effect on complement activation. METHODS NP+s were characterised in terms of size, zeta potential (?) and static light-scattering (SLS). Complement consumption was assessed in normal human serum (NHS) by measuring the residual haemolytic capacity of the complement system. RESULTS DG-loading did not change their size or ? whereas progressive BSA loading decreased lightly their ?. An electrophoretic mobility analysis study showed the presence of 2 differently-charged sublayers at the NP+ surface which are not affected by DG-loading. Complement system activation, studied via a CH50 test, was suppressed by DG- or BSA-loading. We also demonstrated that NP+s could be loaded by a polyanionic molecule such as BSA, after their preliminary filling by a hydrophobic molecule such as DG. CONCLUSION These nanoparticles are able to absorb large amounts of phospholipids or proteins without change in their size or zeta potential. Complement studies showed that stealth behaviour is observed when they are loaded and saturated either with anionic phospholipid or proteins. PMID:19851846

  8. Highly efficient bioinspired molecular Ru water oxidation catalysts with negatively charged backbone ligands.

    PubMed

    Duan, Lele; Wang, Lei; Li, Fusheng; Li, Fei; Sun, Licheng

    2015-07-21

    The oxygen evolving complex (OEC) of the natural photosynthesis system II (PSII) oxidizes water to produce oxygen and reducing equivalents (protons and electrons). The oxygen released from PSII provides the oxygen source of our atmosphere; the reducing equivalents are used to reduce carbon dioxide to organic products, which support almost all organisms on the Earth planet. The first photosynthetic organisms able to split water were proposed to be cyanobacteria-like ones appearing ca. 2.5 billion years ago. Since then, nature has chosen a sustainable way by using solar energy to develop itself. Inspired by nature, human beings started to mimic the functions of the natural photosynthesis system and proposed the concept of artificial photosynthesis (AP) with the view to creating energy-sustainable societies and reducing the impact on the Earth environments. Water oxidation is a highly energy demanding reaction and essential to produce reducing equivalents for fuel production, and thereby effective water oxidation catalysts (WOCs) are required to catalyze water oxidation and reduce the energy loss. X-ray crystallographic studies on PSII have revealed that the OEC consists of a Mn4CaO5 cluster surrounded by oxygen rich ligands, such as oxyl, oxo, and carboxylate ligands. These negatively charged, oxygen rich ligands strongly stabilize the high valent states of the Mn cluster and play vital roles in effective water oxidation catalysis with low overpotential. This Account describes our endeavors to design effective Ru WOCs with low overpotential, large turnover number, and high turnover frequency by introducing negatively charged ligands, such as carboxylate. Negatively charged ligands stabilized the high valent states of Ru catalysts, as evidenced by the low oxidation potentials. Meanwhile, the oxygen production rates of our Ru catalysts were improved dramatically as well. Thanks to the strong electron donation ability of carboxylate containing ligands, a seven-coordinate Ru(IV) species was isolated as a reaction intermediate, shedding light on the reaction mechanisms of Ru-catalyzed water oxidation chemistry. Auxiliary ligands have dramatic effects on the water oxidation catalysis in terms of the reactivity and the reaction mechanism. For instance, Ru-bda (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water oxidation catalysts catalyze Ce(IV)-driven water oxidation extremely fast via the radical coupling of two Ru(V)?O species, while Ru-pda (H2pda = 1,10-phenanthroline-2,9-dicarboxylic acid) water oxidation catalysts catalyze the same reaction slowly via water nucleophilic attack on a Ru(V)?O species. With a number of active Ru catalysts in hands, light driven water oxidation was accomplished using catalysts with low catalytic onset potentials. The structures of molecular catalysts could be readily tailored to introduce additional functional groups, which favors the fabrication of state-of-the-art Ru-based water oxidation devices, such as electrochemical water oxidation anodes and photo-electrochemical anodes. The development of efficient water oxidation catalysts has led to a step forward in the sustainable energy system. PMID:26131964

  9. Molecular-scale quantitative charge density measurement of biological molecule by frequency modulation atomic force microscopy in aqueous solutions.

    PubMed

    Umeda, Kenichi; Kobayashi, Kei; Oyabu, Noriaki; Matsushige, Kazumi; Yamada, Hirofumi

    2015-07-17

    Surface charge distributions on biological molecules in aqueous solutions are essential for the interactions between biomolecules, such as DNA condensation, antibody-antigen interactions, and enzyme reactions. There has been a significant demand for a molecular-scale charge density measurement technique for better understanding such interactions. In this paper, we present the local electric double layer (EDL) force measurements on DNA molecules in aqueous solutions using frequency modulation atomic force microscopy (FM-AFM) with a three-dimensional force mapping technique. The EDL forces measured in a 100 mM KCl solution well agreed with the theoretical EDL forces calculated using reasonable parameters, suggesting that FM-AFM can be used for molecular-scale quantitative charge density measurements on biological molecules especially in a highly concentrated electrolyte. PMID:26120025

  10. Molecular-scale quantitative charge density measurement of biological molecule by frequency modulation atomic force microscopy in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Umeda, Kenichi; Kobayashi, Kei; Oyabu, Noriaki; Matsushige, Kazumi; Yamada, Hirofumi

    2015-07-01

    Surface charge distributions on biological molecules in aqueous solutions are essential for the interactions between biomolecules, such as DNA condensation, antibody-antigen interactions, and enzyme reactions. There has been a significant demand for a molecular-scale charge density measurement technique for better understanding such interactions. In this paper, we present the local electric double layer (EDL) force measurements on DNA molecules in aqueous solutions using frequency modulation atomic force microscopy (FM-AFM) with a three-dimensional force mapping technique. The EDL forces measured in a 100 mM KCl solution well agreed with the theoretical EDL forces calculated using reasonable parameters, suggesting that FM-AFM can be used for molecular-scale quantitative charge density measurements on biological molecules especially in a highly concentrated electrolyte.

  11. Excitation of dust acoustic waves by an ion beam in a plasma cylinder with negatively charged dust grains

    SciTech Connect

    Sharma, Suresh C.; Kaur, Daljeet; Gahlot, Ajay; Sharma, Jyotsna

    2014-10-15

    An ion beam propagating through a plasma cylinder having negatively charged dust grains drives a low frequency electrostatic dust acoustic wave (DAW) to instability via Cerenkov interaction. The unstable wave frequencies and the growth rate increase with the relative density of negatively charged dust grains. The growth rate of the unstable mode scales to the one-third power of the beam density. The real part of the frequency of the unstable mode increases with the beam energy and scales to almost one-half power of the beam energy. The phase velocity, frequency, and wavelength results of the unstable mode are in compliance with the experimental observations.

  12. Statistical mechanics of dust charging in a multi-ion plasma with negative and positive ionic species

    SciTech Connect

    Mishra, S. K.; Misra, Shikha

    2015-02-15

    On the basis of statistical mechanics and charging kinetics, the charge distribution over uniform size spherical dust particles in a multi-ion plasma comprising of multiple charged negative and positive ions is investigated. Two specific situations where the complex plasma is viz., (i) dark (no emission from dust) and (ii) irradiated by laser light (causing photoemission from dust) have been taken into account. The analytical formulation includes the population balance equation for the charged dust particles along with number and energy balance of the complex plasma constituents. The departure of the results for multi-ion plasma from that in case of usual singly charged positive ion plasma is graphically illustrated and discussed. In contrast to electron-ion plasma, significant number of particles is seen to acquire opposite charge in case of pure positive-negative ion plasma, even in the absence of electron emission from the dust grains. The effects of various plasma parameters viz., number density, particle size, and work function of dust on charge distribution have also been examined.

  13. Photoluminescence Studies of Both the Neutral and Negatively Charged Nitrogen-Vacancy Center in Diamond.

    PubMed

    Wang, Kaiyue; Steeds, John W; Li, Zhihong; Tian, Yuming

    2016-02-01

    In this study low temperature micro-photoluminescence technology was employed to investigate effects of the irradiation and nitrogen concentration on nitrogen-vacancy (NV) luminescence, with the photochromic and vibronic properties of the NV defects. Results showed that the NV luminescence was weakened due to recombination of self-interstitials created by electron irradiation in diamond and the vacancies within the structure of NV centers. For very pure diamond, the vacancies migrated the long distance to get trapped by N atoms only after sufficient high temperature annealing. As with the increase in nitrogen content, the migration distance of vacancies got smaller. The nitrogen also favored the formation of negatively charged NV centers with the donating electrons. Under the high-energy ultraviolet laser excitation, the photochromic property of the NV- center was also observed, though it was not stable. Besides, the NV centers showed very strong broad sidebands, and the vibrations involved one phonon with energy of ~42 meV and another with ~67 meV energy. PMID:26758647

  14. Negatively charged nano-grains at 67P/Churyumov-Gerasimenko

    NASA Astrophysics Data System (ADS)

    Gombosi, T. I.; Burch, J. L.; Hornyi, M.

    2015-11-01

    Shortly after the Rosetta mission's rendezvous with 67P/Churyumov-Gerasimenko the RPC/IES instrument intermittently detected negative particles that were identified as singly charged nano-dust grains. These grains were recorded as a nearly mono-energetic beam of particles in the 200-500 eV range arriving from the direction of the comet. Occasionally, another population of particles in the energy range of 1-20 keV were also noticed arriving from the approximate direction of the Sun. In this paper we review the processes that can explain the energization and the directionality of the observed nano-dust populations. We show that the observations are consistent with gas-drag acceleration of the outflowing particles with radii of 3-4 nm, and with the returning fragments of bigger particles accelerated by radiation pressure with approximate radii of 30-80 nm. In addition to gas drag and radiation pressure, we also examine the role of the solar wind induced motional electric field, and its possible role in explaining the intermittency of the detection of a nano-grain population arriving from the solar direction.

  15. The negatively charged nitrogen-vacancy centre in diamond: the electronic solution

    NASA Astrophysics Data System (ADS)

    Doherty, M. W.; Manson, N. B.; Delaney, P.; Hollenberg, L. C. L.

    2011-02-01

    The negatively charged nitrogen-vacancy centre is a unique defect in diamond that possesses properties highly suited to many applications, including quantum information processing, quantum metrology and biolabelling. Although the unique properties of the centre have been extensively documented and utilized, a detailed understanding of the physics of the centre has not yet been achieved. Indeed, there persist a number of points of contention regarding the electronic structure of the centre, such as the ordering of the dark intermediate singlet states. Without a detailed model of the centre's electronic structure, the understanding of the system's unique dynamical properties cannot effectively progress. In this work, the molecular model of the defect centre is fully developed to provide a self-consistent model of the complete electronic structure of the centre. The application of the model to describe the effects of electric, magnetic and strain interactions, as well as the variation of the centre's fine structure with temperature, provides an invaluable tool to those studying the centre and a means of designing future empirical and ab initio studies of this important defect.

  16. Promiscuous Activation of Transient Receptor Potential Vanilloid 1 (TRPV1) Channels by Negatively Charged Intracellular Lipids

    PubMed Central

    Lukacs, Viktor; Rives, Jan-Michael; Sun, Xiaohui; Zakharian, Eleonora; Rohacs, Tibor

    2013-01-01

    The regulation of the heat- and capsaicin-activated transient receptor potential vanilloid 1 (TRPV1) channels by phosphoinositides is controversial. Data in cellular systems support the dependence of TRPV1 activity on phosphoinositides. The purified TRPV1, however, was recently shown to be fully functional in artificial liposomes in the absence of phosphoinositides. Here, we show that several other negatively charged phospholipids, including phosphatidylglycerol, can also support TRPV1 activity in excised patches at high concentrations. When we incorporated TRPV1 into planar lipid bilayers consisting of neutral lipids, capsaicin-induced activity depended on phosphatidylinositol 4,5-bisphosphate. We also found that TRPV1 activity in excised patches ran down and that MgATP reactivated the channel. Inhibition of phosphatidylinositol 4-kinases or enzymatic removal of phosphatidylinositol abolished this effect of MgATP, suggesting that it activated TRPV1 by generating endogenous phosphoinositides. We conclude that endogenous phosphoinositides are positive cofactors for TRPV1 activity. Our data highlight the importance of specificity in lipid regulation of ion channels and may reconcile discordant data obtained in various experimental settings. PMID:24158445

  17. Protein PEGylation attenuates adsorption and aggregation on a negatively charged and moderately hydrophobic polymer surface.

    PubMed

    Pai, Sheetal S; Przybycien, Todd M; Tilton, Robert D

    2010-12-01

    Covalent grafting of poly(ethylene glycol) chains to proteins ("PEGylation") is emerging as an effective technique to increase the in vivo circulation time and efficacy of protein drugs. PEGylated protein adsorption at a variety of solid/aqueous interfaces is a critical aspect of their manufacture, storage, and delivery. A special category of block copolymer, PEGylated proteins have one or more water-soluble linear polymer (PEG) blocks and a single globular protein block that each exert distinct intermolecular and surface interaction forces. We report the impact of PEGylation on protein adsorption at the interface between aqueous solutions and solid films of poly(lactide-co-glycolide) (PLG), a moderately hydrophobic and negatively charged polymer. Using the model protein lysozyme with controlled degrees of PEGylation, we employ total internal reflection fluorescence techniques to measure adsorption isotherms, adsorption reversibility, and the extent of surface-induced aggregation. Lysozyme PEGylation reduces the extent of protein adsorption and surface-induced aggregation and increases the reversibility of adsorption compared to the unconjugated protein. Results are interpreted in terms of steric forces among grafted PEG chains and their effects on protein-protein interactions and protein orientation on the surface. PMID:21067142

  18. Both Positive and Negative Effects on Immune Responses by Expression of a Second Class II MHC Molecule

    PubMed Central

    Ni, Peggy P.; Wang, Yaming; Allen, Paul M.

    2014-01-01

    It is perplexing why vertebrates express a limited number of Major Histocompatibility Complex (MHC) molecules when theoretically, having a greater repertoire of MHC molecules would increase the number of epitopes presented, thereby enhancing thymic selection and T cell response to pathogens. It is possible that any positive effects would either be neutralized or outweighed by negative selection restricting the T cell repertoire. We hypothesize that the limit on MHC number is due to negative consequences arising from expressing additional MHC. We compared T cell responses between B6 mice (I-A+) and B6.E+ mice (I-A+, I-E+), the latter expressing a second class II MHC molecule, I-Eb, due to a monomorphic Eαk transgene that pairs with the endogenous I-Eβb chain. First, the naive T cell Vβ repertoire was altered in B6.E+ thymi and spleens, potentially mediating different outcomes in T cell reactivity. Although the B6 and B6.E+ responses to hen egg-white lysozyme (HEL) protein immunization remained similar, other immune models yielded differences. For viral infection, the quality of the T cell response was subtly altered, with diminished production of certain cytokines by B6.E+ CD4+ T cells. In alloreactivity, the B6.E+ T cell response was significantly dampened. Finally, we observed markedly enhanced susceptibility to experimental autoimmune encephalomyelitis (EAE) in B6.E+ mice. This correlated with decreased percentages of nTreg cells, supporting the concept of Tregs exhibiting differential susceptibility to negative selection. Altogether, our data suggest that expressing an additional class II MHC can produce diverse effects, with more severe autoimmunity providing a compelling explanation for limiting the expression of MHC molecules. PMID:25016574

  19. Linear Free Energy Relationships for Metal-Ligand Complexation: Bidentate Binding to Negatively-Charged Oxygen Donor Atoms

    PubMed Central

    Carbonaro, Richard F.; Atalay, Yasemin B.; Di Toro, Dominic M.

    2011-01-01

    Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = χOO(αO log KHL,1 + αO log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand pKa values), and αO is the Irving-Rossotti slope. The parameter χOO is metal specific and has slightly different values for 5 and 6 membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, α-hydroxycarboxylic acids, and α-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of χOO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems. PMID:21833149

  20. Negative differential conductance in InAs wire based double quantum dot induced by a charged AFM tip

    NASA Astrophysics Data System (ADS)

    Zhukov, A. A.; Volk, Ch.; Winden, A.; Hardtdegen, H.; Schpers, Th.

    2012-12-01

    We investigate the conductance of an InAs nanowire in the nonlinear regime in the case of low electron density where the wire is split into quantum dots connected in series. The negative differential conductance in the wire is initiated by means of a charged atomic force microscope tip adjusting the transparency of the tunneling barrier between two adjoining quantum dots. We confirm that the negative differential conductance arises due to the resonant tunneling between these two adjoining quantum dots. The influence of the transparency of the blocking barriers and the relative position of energy states in the adjoining dots on a decrease of the negative differential conductance is investigated in detail.

  1. Radiation transport codes for potential applications related to radiobiology and radiotherapy using protons, neutrons, and negatively charged pions

    NASA Technical Reports Server (NTRS)

    Armstrong, T. W.

    1972-01-01

    Several Monte Carlo radiation transport computer codes are used to predict quantities of interest in the fields of radiotherapy and radiobiology. The calculational methods are described and comparisions of calculated and experimental results are presented for dose distributions produced by protons, neutrons, and negatively charged pions. Comparisons of calculated and experimental cell survival probabilities are also presented.

  2. Spectroscopic and calorimetric investigations on the influence of calcium ions on the polyamine negatively charged phospholipid molecular interactions

    NASA Astrophysics Data System (ADS)

    Bertoluzza, Alessandro; Bonora, S.; Fini, G.; Morelli, M. A.

    1993-06-01

    Polyamines do not interact with neutral phospholipids (phosphatidylcholines) but they do interact in the presence of bivalent and trivalent cations. The effect of polyvalent cations is explained in terms of dehydration of the bilayer surface. Polyamines interact strongly with negatively charged phospholipids; the presence of bivalent and trivalent cations do not change sensitively the type of interaction between polyamines and phosphatidic acids.

  3. Room-Temperature Current Oscillation Based on Negative Differential Resistance in a One-Dimensional Organic Charge-Transfer Complex

    NASA Astrophysics Data System (ADS)

    Kishida, Hideo; Ito, Takafumi; Ito, Atsuya; Nakamura, Arao

    2011-03-01

    The one-dimensional organic charge-transfer complex potassium-tetracyanoquinodimethane shows negative differential resistance and a switching behavior between high- and low-resistance states. By controlling this switching behavior through the use of external circuit components, we achieved current oscillation at room temperature. Microscopic Raman measurements in the current oscillation indicate that the nonlinear conducting current flows throughout the crystal.

  4. Charge symmetric dissociation of doubly ionized N2 and CO molecules.

    PubMed

    Pandey, A; Bapat, B; Shamasundar, K R

    2014-01-21

    We report a comparative study of the features in dissociative double ionization by high energy electron impact of N2 and CO molecules. The ratio of cross-section of charge symmetric dissociative ionization to non-dissociative ionization (CSD-to-ND ratio) and the kinetic energy release (KER) spectra of dissociation are experimentally measured and carefully corrected for various ion transmission losses and detector inefficiencies. Given that the double ionization cross sections of these iso-electronic diatomics are very similar, the large difference in the CSD-to-ND ratios must be attributable to the differences in the evolution dynamics of the dications. To understand these differences, potential energy curves (PECs) of dications have been computed using multi-reference configuration interaction method. The Franck-Condon factors and tunneling life times of vibrational levels of dications have also been computed. While the KER spectrum of N2 (++) can be readily explained by considering dissociation via repulsive states and tunneling of meta-stable states, indirect dissociation processes such as predissociation and autoionization have to be taken into account to understand the major features of the KER spectrum of CO(++). Direct and indirect processes identified on the basis of the PECs and experimental KER spectra also provide insights into the differences in the CSD-to-ND ratios. PMID:25669391

  5. Charge symmetric dissociation of doubly ionized N{sub 2} and CO molecules

    SciTech Connect

    Pandey, A. Bapat, B.; Shamasundar, K. R.

    2014-01-21

    We report a comparative study of the features in dissociative double ionization by high energy electron impact of N{sub 2} and CO molecules. The ratio of cross-section of charge symmetric dissociative ionization to non-dissociative ionization (CSD-to-ND ratio) and the kinetic energy release (KER) spectra of dissociation are experimentally measured and carefully corrected for various ion transmission losses and detector inefficiencies. Given that the double ionization cross sections of these iso-electronic diatomics are very similar, the large difference in the CSD-to-ND ratios must be attributable to the differences in the evolution dynamics of the dications. To understand these differences, potential energy curves (PECs) of dications have been computed using multi-reference configuration interaction method. The Franck-Condon factors and tunneling life times of vibrational levels of dications have also been computed. While the KER spectrum of N{sub 2}{sup ++} can be readily explained by considering dissociation via repulsive states and tunneling of meta-stable states, indirect dissociation processes such as predissociation and autoionization have to be taken into account to understand the major features of the KER spectrum of CO{sup ++}. Direct and indirect processes identified on the basis of the PECs and experimental KER spectra also provide insights into the differences in the CSD-to-ND ratios.

  6. Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

    SciTech Connect

    Wan, Yimao Bullock, James; Cuevas, Andres

    2015-05-18

    This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta{sub 2}O{sub 5}) underneath plasma enhanced chemical vapour deposited silicon nitride (SiN{sub x}). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta{sub 2}O{sub 5} and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω·cm and n-type 1.0 Ω·cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm{sup 2} and 68 fA/cm{sup 2} are measured on 150 Ω/sq boron-diffused p{sup +} and 120 Ω/sq phosphorus-diffused n{sup +} c-Si, respectively. Capacitance–voltage measurements reveal a negative fixed insulator charge density of −1.8 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5} film and −1.0 × 10{sup 12 }cm{sup −2} for the Ta{sub 2}O{sub 5}/SiN{sub x} stack. The Ta{sub 2}O{sub 5}/SiN{sub x} stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

  7. Calcium diffusion enhanced after cleavage of negatively charged components of brain extracellular matrix by chondroitinase ABC

    PubMed Central

    Hrab?tov, Sabina; Masri, Daniel; Tao, Lian; Xiao, Fanrong; Nicholson, Charles

    2009-01-01

    The concentration of extracellular calcium plays a critical role in synaptic transmission and neuronal excitability as well as other physiological processes. The time course and extent of local fluctuations in the concentration of this ion largely depend on its effective diffusion coefficient (D*) and it has been speculated that fixed negative charges on chondroitin sulphate proteoglycans (CSPGs) and other components of the extracellular matrix may influence calcium diffusion because it is a divalent cation. In this study we used ion-selective microelectrodes combined with pressure ejection or iontophoresis of ions from a micropipette to quantify diffusion characteristics of neocortex and hippocampus in rat brain slices. We show that D* for calcium is less than the value predicted from the behaviour of the monovalent cation tetramethylammonium (TMA), a commonly used diffusion probe, but D* for calcium increases in both brain regions after the slices are treated with chondroitinase ABC, an enzyme that predominantly cleaves chondroitin sulphate glycans. These results suggest that CSPGs do play a role in determining the local diffusion properties of calcium in brain tissue, most likely through electrostatic interactions mediating rapid equilibrium binding. In contrast, chondroitinase ABC does not affect either the TMA diffusion or the extracellular volume fraction, indicating that the enzyme does not alter the structure of the extracellular space and that the diffusion of small monovalent cations is not affected by CSPGs in the normal brain ionic milieu. Both calcium and CSPGs are known to have many distinct roles in brain physiology, including brain repair, and our study suggests they may be functionally coupled through calcium diffusion properties. PMID:19546165

  8. Negatively Charged Lipid Membranes Promote a Disorder-Order Transition in the Yersinia YscU Protein

    PubMed Central

    Weise, ChristophF.; Login, FrdricH.; Ho, Oanh; Grbner, Gerhard; Wolf-Watz, Hans; Wolf-Watz, Magnus

    2014-01-01

    The inner membrane of Gram-negative bacteria is negatively charged, rendering positively charged cytoplasmic proteins in close proximity likely candidates for protein-membrane interactions. YscU is a Yersinia pseudotuberculosis type III secretion system protein crucial for bacterial pathogenesis. The protein contains a highly conserved positively charged linker sequence that separates membrane-spanning and cytoplasmic (YscUC) domains. Although disordered in solution, inspection of the primary sequence of the linker reveals that positively charged residues are separated with a typical helical periodicity. Here, we demonstrate that the linker sequence of YscU undergoes a largely electrostatically driven coil-to-helix transition upon binding to negatively charged membrane interfaces. Using membrane-mimicking sodium dodecyl sulfate micelles, an NMR derived structural model reveals the induction of three helical segments in the linker. The overall linker placement in sodium dodecyl sulfate micelles was identified by NMR experiments including paramagnetic relaxation enhancements. Partitioning of individual residues agrees with their hydrophobicity and supports an interfacial positioning of the helices. Replacement of positively charged linker residues with alanine resulted in YscUC variants displaying attenuated membrane-binding affinities, suggesting that the membrane interaction depends on positive charges within the linker. In vivo experiments with bacteria expressing these YscU replacements resulted in phenotypes displaying significantly reduced effector protein secretion levels. Taken together, our data identify a previously unknown membrane-interacting surface of YscUC that, when perturbed by mutations, disrupts the function of the pathogenic machinery in Yersinia. PMID:25418176

  9. STUDIES OF X-RAY PRODUCTION FOLLOWING CHARGE EXCHANGE RECOMBINATION BETWEEN HIGHLY CHARGED IONS AND NEUTRAL ATOMS AND MOLECULES

    SciTech Connect

    Brown, G V; Beiersdorfer, P; Chen, H; Clementson, J; Frankel, M; Gu, M F; Kelley, R L; Kilbourne, C A; Porter, F S; Thorn, D B; Wargelin, B J

    2008-08-28

    We have used microcalorimeters built by the NASA/Goddard Space Flight Center and the Lawrence Livermore National Laboratory Electron Beam Ion Trap to measure X-ray emission produced by charge exchange reactions between highly charged ions colliding with neutral helium, hydrogen, and nitrogen gas. Our measurements show the spectral dependence on neutral species and also show the distinct differences between spectra produced by charge exchange reactions and those produced by direct impact excitation. These results are part of an ongoing experimental investigation at the LLNL EBIT facility of charge exchange spectral signatures and can be used to interpret X-ray spectra produced by a variety of laboratory and celestial sources including cometary and planetary atmospheres, the Earth's magnetosheath, the heliosphere, and tokamaks.

  10. Charge Enhancement of Single-Stranded DNA in Negative Electrospray Ionization Using the Supercharging Reagent Meta-nitrobenzyl Alcohol

    NASA Astrophysics Data System (ADS)

    Brahim, Bessem; Alves, Sandra; Cole, Richard B.; Tabet, Jean-Claude

    2013-12-01

    Charge enhancement of single-stranded oligonucleotide ions in negative ESI mode is investigated. The employed reagent, meta-nitrobenzyl alcohol (m-NBA), was found to improve total signal intensity (Itot), increase the highest observed charge states (zhigh), and raise the average charge states (zavg) of all tested oligonucleotides analyzed in negative ESI. To quantify these increases, signal enhancement ratios (SER1%) and charge enhancement coefficients (CEC1%) were introduced. The SER1%, (defined as the quotient of total oligonucleotide ion abundances with 1 % m-NBA divided by total oligonucleotide abundance without m-NBA) was found to be greater than unity for every oligonucleotide tested. The CEC1% values (defined as the average charge state in the presence of 1 % m-NBA minus the average charge state in the absence of m-NBA) were found to be uniformly positive. Upon close inspection, the degree of charge enhancement for longer oligonucleotides was found to be dependent upon thymine density (i.e., the number and the location of phospho-thymidine units). A correlation between the charge enhancement induced by the presence of m-NBA and the apparent gas-phase acidity (largely determined by the sequence of thymine units but also by the presence of protons on other nucleobases) of multiply deprotonated oligonucleotide species, was thus established. Ammonium cations appeared to be directly involved in the m-NBA supercharging mechanism, and their role seems to be consistent with previously postulated ESI mechanisms describing desorption/ionization of single-stranded DNA into the gas phase.

  11. Direct single-molecule observations of local denaturation of a DNA double helix under a negative supercoil state.

    PubMed

    Takahashi, Shunsuke; Motooka, Shinya; Usui, Tomohiro; Kawasaki, Shohei; Miyata, Hidefumi; Kurita, Hirofumi; Mizuno, Takeshi; Matsuura, Shun-ichi; Mizuno, Akira; Oshige, Masahiko; Katsura, Shinji

    2015-03-17

    Effects of a negative supercoil on the local denaturation of the DNA double helix were studied at the single-molecule level. The local denaturation in λDNA and λDNA containing the SV40 origin of DNA replication (SV40ori-λDNA) was directly observed by staining single-stranded DNA regions with a fusion protein comprising the ssDNA binding domain of a 70-kDa subunit of replication protein A and an enhanced yellow fluorescent protein (RPA-YFP) followed by staining the double-stranded DNA regions with YOYO-1. The local denaturation of λDNA and SV40ori-λDNA under a negative supercoil state was observed as single bright spots at the single-stranded regions. When negative supercoil densities were gradually increased to 0, -0.045, and -0.095 for λDNA and 0, -0.047, and -0.1 for SV40ori-λDNA, single bright spots at the single-stranded regions were frequently induced under higher negative supercoil densities of -0.095 for λDNA and -0.1 for SV40ori-λDNA. However, single bright spots of the single-stranded regions were rarely observed below a negative supercoil density of -0.045 and -0.047 for λDNA and SV40ori-λDNA, respectively. The probability of occurrence of the local denaturation increased with negative superhelicity for both λDNA and SV40ori-λDNA. PMID:25697222

  12. Structure, stability, and fragmentation of sodium bis(2-ethylhexyl)sulfosuccinate negatively charged aggregates in vacuo by MD simulations.

    PubMed

    Longhi, Giovanna; Abbate, Sergio; Ceselli, Alberto; Ceraulo, Leopoldo; Fornili, Sandro L; Turco Liveri, Vincenzo

    2014-09-01

    Negatively charged supramolecular aggregates formed in vacuo by n bis(2-ethylhexyl)sulfosuccinate (AOT(-)) anions and n + n(c) sodium counterions (i.e., [AOT(n) Na(n+nc)](nc)) have been investigated by molecular dynamics (MD) simulations for n = 1 to 20 and n(c) = -1 to -5. By comparing the maximum excess charge values of negatively and positively charged AOTNa aggregates, it is found that the charge storage capability is higher for the latter systems, the difference decreasing as the aggregation number increases. Statistical analysis of physical properties like gyration radii and moment of inertia tensors of aggregates provides detailed information on their structural properties. Even for n(c) = -5, all stable aggregates show a reverse micelle-like structure with an internal core, including sodium counterions and surfactant polar heads, surrounded by an external layer consisting of the surfactant alkyl chains. Interestingly, the reverse micelle-like structure is retained also in proximity of fragmentation. Moreover, the aggregate shapes may be approximated by elongated ellipsoids whose longer axis increases with n and |n(c)|. The fragmentation patterns of a number of these aggregates have also been examined and have been found to markedly depend on the aggregate charge state. The simulated fragmentation patterns of a representative aggregate show good agreement with experimental data obtained using low collision voltages. PMID:24969925

  13. Negligible "negative space-charge layer effects" at oxide-electrolyte/electrode interfaces of thin-film batteries.

    PubMed

    Haruta, Masakazu; Shiraki, Susumu; Suzuki, Tohru; Kumatani, Akichika; Ohsawa, Takeo; Takagi, Yoshitaka; Shimizu, Ryota; Hitosugi, Taro

    2015-03-11

    In this paper, we report the surprisingly low electrolyte/electrode interface resistance of 8.6 ? cm(2) observed in thin-film batteries. This value is an order of magnitude smaller than that presented in previous reports on all-solid-state lithium batteries. The value is also smaller than that found in a liquid electrolyte-based batteries. The low interface resistance indicates that the negative space-charge layer effects at the Li3PO(4-x)N(x)/LiCoO2 interface are negligible and demonstrates that it is possible to fabricate all-solid state batteries with faster charging/discharging properties. PMID:25710500

  14. Validity of Saha's equation of thermal ionization for negatively charged spherical particles in complex plasmas in thermal equilibrium

    SciTech Connect

    Sodha, M. S.; Mishra, S. K.

    2011-04-15

    The authors have discussed the validity of Saha's equation for the charging of negatively charged spherical particles in a complex plasma in thermal equilibrium, even when the tunneling of the electrons, through the potential energy barrier surrounding the particle is considered. It is seen that the validity requires the probability of tunneling of an electron through the potential energy barrier surrounding the particle to be independent of the direction (inside to outside and vice versa) or in other words the Born's approximation should be valid.

  15. Negative-U carbon vacancy in 4H-SiC: Assessment of charge correction schemes and identification of the negative carbon vacancy at the quasicubic site

    NASA Astrophysics Data System (ADS)

    Trinh, X. T.; Szsz, K.; Hornos, T.; Kawahara, K.; Suda, J.; Kimoto, T.; Gali, A.; Janzn, E.; Son, N. T.

    2013-12-01

    The carbon vacancy (VC) has been suggested by different studies to be involved in the Z1/Z2 defect-a carrier lifetime killer in SiC. However, the correlation between the Z1/Z2 deep level with VC is not possible since only the negative carbon vacancy (VC-) at the hexagonal site, VC-(h), with unclear negative-U behaviors was identified by electron paramagnetic resonance (EPR). Using freestanding n-type 4H-SiC epilayers irradiated with low energy (250 keV) electrons at room temperature to introduce mainly VC and defects in the C sublattice, we observed the strong EPR signals of VC-(h) and another S = 1/2 center. Electron paramagnetic resonance experiments show a negative-U behavior of the two centers and their similar symmetry lowering from C3v to C1h at low temperatures. Comparing the 29Si and 13C ligand hyperfine constants observed by EPR and first principles calculations, the new center is identified as VC-(k). The negative-U behavior is further confirmed by large scale density functional theory supercell calculations using different charge correction schemes. The results support the identification of the lifetime limiting Z1/Z2 defect to be related to acceptor states of the carbon vacancy.

  16. Fixed negative charge and the Donnan effect: a description of the driving forces associated with brain tissue swelling and oedema

    PubMed Central

    Elkin, Benjamin S.; Shaik, Mohammed A.; Morrison, Barclay

    2010-01-01

    Cerebral oedema or brain tissue swelling is a significant complication following traumatic brain injury or stroke that can increase the intracranial pressure (ICP) and impair blood flow. Here, we have identified a potential driver of oedema: the negatively charged molecules fixed within cells. This fixed charge density (FCD), once exposed, could increase ICP through the Donnan effect. We have shown that metabolic processes and membrane integrity are required for concealing this FCD as slices of rat cortex swelled immediately (within 30 min) following dissection if treated with 2 deoxyglucose + cyanide (2DG+CN) or Triton X-100. Slices given ample oxygen and glucose, however, did not swell significantly. We also found that dead brain tissue swells and shrinks in response to changes in ionic strength of the bathing medium, which suggests that the Donnan effect is capable of pressurizing and swelling brain tissue. As predicted, a non-ionic osmolyte, 1,2 propanediol, elicited no volume change at 2000×10−3 osmoles l−1 (Osm). Swelling data were well described by triphasic mixture theory with the calculated reference state FCD similar to that measured with a 1,9 dimethylmethylene blue assay. Taken together, these data suggest that intracellular fixed charges may contribute to the driving forces responsible for brain swelling. PMID:20047940

  17. Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

    PubMed Central

    Fleming, Paul R.; MacCormack, Kathleen; McLaughlin, Robert E.; Whiteaker, James D.; Narita, Shin-ichiro; Mori, Makiko; Tokuda, Hajime; Miller, Alita A.

    2015-01-01

    In Gram-negative bacteria, lipoproteins are transported to the outer membrane by the Lol system. In this process, lipoproteins are released from the inner membrane by the ABC transporter LolCDE and passed to LolA, a diffusible periplasmic molecular chaperone. Lipoproteins are then transferred to the outer membrane receptor protein, LolB, for insertion in the outer membrane. Here we describe the discovery and characterization of novel pyridineimidazole compounds that inhibit this process. Escherichia coli mutants resistant to the pyridineimidazoles show no cross-resistance to other classes of antibiotics and map to either the LolC or LolE protein of the LolCDE transporter complex. The pyridineimidazoles were shown to inhibit the LolA-dependent release of the lipoprotein Lpp from E. coli spheroplasts. These results combined with bacterial cytological profiling are consistent with LolCDE-mediated disruption of lipoprotein targeting to the outer membrane as the mode of action of these pyridineimidazoles. The pyridineimidazoles are the first reported inhibitors of the LolCDE complex, a target which has never been exploited for therapeutic intervention. These compounds open the door to further interrogation of the outer membrane lipoprotein transport pathway as a target for antimicrobial therapy. PMID:25583975

  18. Small-molecule inhibitors of gram-negative lipoprotein trafficking discovered by phenotypic screening.

    PubMed

    McLeod, Sarah M; Fleming, Paul R; MacCormack, Kathleen; McLaughlin, Robert E; Whiteaker, James D; Narita, Shin-Ichiro; Mori, Makiko; Tokuda, Hajime; Miller, Alita A

    2015-03-01

    In Gram-negative bacteria, lipoproteins are transported to the outer membrane by the Lol system. In this process, lipoproteins are released from the inner membrane by the ABC transporter LolCDE and passed to LolA, a diffusible periplasmic molecular chaperone. Lipoproteins are then transferred to the outer membrane receptor protein, LolB, for insertion in the outer membrane. Here we describe the discovery and characterization of novel pyridineimidazole compounds that inhibit this process. Escherichia coli mutants resistant to the pyridineimidazoles show no cross-resistance to other classes of antibiotics and map to either the LolC or LolE protein of the LolCDE transporter complex. The pyridineimidazoles were shown to inhibit the LolA-dependent release of the lipoprotein Lpp from E. coli spheroplasts. These results combined with bacterial cytological profiling are consistent with LolCDE-mediated disruption of lipoprotein targeting to the outer membrane as the mode of action of these pyridineimidazoles. The pyridineimidazoles are the first reported inhibitors of the LolCDE complex, a target which has never been exploited for therapeutic intervention. These compounds open the door to further interrogation of the outer membrane lipoprotein transport pathway as a target for antimicrobial therapy. PMID:25583975

  19. Positive and negative singly charged ion production of a laser induced plasma using a capillary graphite target

    NASA Astrophysics Data System (ADS)

    Saquilayan, G. Q.; Wada, M.

    2016-02-01

    A new type of laser ion source is being developed aiming at the production of positive and negative singly charged ions using a capillary graphite target structure. The initial results of the laser plasma produced inside of the 10 mm diameter conduit indicated the formation of the secondary charged particle production inside the target. A high speed camera clearly recorded the plasma plume expansion inside the target. The time-of-flight spectrum of the laser produced plasma in vacuum showed that the signal of the positive ions formed two peaks as the laser power density exceeded 10 GW/cm2. The addition of neutral gas to the system produced a signal corresponding to negative ions after the positive signal.

  20. CHARGE MEASUREMENTS ON INDIVIDUAL PARTICLES EXITING LABORATORY PRECIPITATORS WITH POSITIVE AND NEGATIVE CORONA AT VARIOUS TEMPERATURES

    EPA Science Inventory

    The paper reports measurements of charge values on individual particles exiting three different laboratory electrostatic precipitators (ESPs) in an experimental apparatus containing a Millikan cell. Dioctylphthalate (DOP) droplets and fly ash particles were measured at temperatur...

  1. Energy straggling of low-energy ion beam in a charge exchange cell for negative ion production

    SciTech Connect

    Takeuchi, S.; Sasao, M.; Sugawara, H.; Tanaka, N.; Kisaki, M.; Okamoto, A.; Shinto, K.; Kitajima, S.; Nishiura, M.; Wada, M.

    2008-02-15

    Energy straggling in a charge exchange cell, which is frequently used for negative ion production, was studied experimentally and compared with the results of theoretical evaluation. The change of the energy spectrum of a He{sup +} beam due to charge exchange processes in argon gas was measured in the energy range of 2-6 keV. Energy straggling by multiple collisions is expressed by the energy loss formula due to inelastic and elastic processes. The impact parameter is related to the elastic scattering angle, and the geometry of the charge exchange cell and other components of the beam transportation system determines the maximum acceptable scattering angle. The energy spread was evaluated taking the integral limit over the impact parameter into consideration. The theoretical results showed good agreement with those of actual measurement.

  2. Spatial distribution of the charged particles and potentials during beam extraction in a negative-ion source.

    PubMed

    Tsumori, K; Nakano, H; Kisaki, M; Ikeda, K; Nagaoka, K; Osakabe, M; Takeiri, Y; Kaneko, O; Shibuya, M; Asano, E; Kondo, T; Sato, M; Komada, S; Sekiguchi, H; Kameyama, N; Fukuyama, T; Wada, S; Hatayama, A

    2012-02-01

    We report on the characteristics of the electronegative plasma in a large-scale hydrogen negative ion (H(-)) source. The measurement has been made with a time-resolved Langmuir probe installed in the beam extraction region. The H(-) density is monitored with a cavity ring-down system to identify the electrons in the negative charges. The electron-saturation current decreases rapidly after starting to seed Cs, and ion-ion plasma is observed in the extraction region. The H(-) density steps down during the beam extraction and the electron density jumps up correspondingly. The time integral of the decreasing H(-) charge density agrees well with the electron charge collected with the probe. The agreement of the charges is interpreted to indicate that the H(-) density decreasing at the beam extraction is compensated by the electrons diffusing from the driver region. In the plasmas with very low electron density, the pre-sheath of the extraction field penetrates deeply inside the plasmas. That is because the shielding length in those plasmas is longer than that in the usual electron-ion plasmas, and furthermore the electrons are suppressed to diffuse to the extraction region due to the strong magnetic field. PMID:22380273

  3. A graphene-based affinity nanosensor for detection of low-charge and low-molecular-weight molecules

    NASA Astrophysics Data System (ADS)

    Zhu, Yibo; Hao, Yufeng; Adogla, Enoch A.; Yan, Jing; Li, Dachao; Xu, Kexin; Wang, Qian; Hone, James; Lin, Qiao

    2016-03-01

    This paper presents a graphene nanosensor for affinity-based detection of low-charge, low-molecular-weight molecules, using glucose as a representative. The sensor is capable of measuring glucose concentration in a practically relevant range of 2 μM to 25 mM, and can potentially be used in noninvasive glucose monitoring.This paper presents a graphene nanosensor for affinity-based detection of low-charge, low-molecular-weight molecules, using glucose as a representative. The sensor is capable of measuring glucose concentration in a practically relevant range of 2 μM to 25 mM, and can potentially be used in noninvasive glucose monitoring. Electronic supplementary information (ESI) available: Further details on experiments, materials, fabrication, and data analysis. See DOI: 10.1039/c5nr08866f

  4. Positive and negative ion formation in deep-core excited molecules: S 1s excitation in dimethyl sulfoxide

    SciTech Connect

    Coutinho, L. H.; Gardenghi, D. J.; Schlachter, A. S.; Souza, G. G. B. de; Stolte, W. C.; Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720

    2014-01-14

    The photo-fragmentation of the dimethyl sulfoxide (DMSO) molecule was studied using synchrotron radiation and a magnetic mass spectrometer. The total cationic yield spectrum was recorded in the photon energy region around the sulfur K edge. The sulfur composition of the highest occupied molecular orbital's and lowest unoccupied molecular orbital's in the DMSO molecule has been obtained using both ab initio and density functional theory methods. Partial cation and anion-yield measurements were obtained in the same energy range. An intense resonance is observed at 2475.4 eV. Sulfur atomic ions present a richer structure around this resonant feature, as compared to other fragment ions. The yield curves are similar for most of the other ionic species, which we interpret as due to cascade Auger processes leading to multiply charged species which then undergo Coulomb explosion. The anions S{sup ?}, C{sup ?}, and O{sup ?} are observed for the first time in deep-core-level excitation of DMSO.

  5. Understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells.

    PubMed

    Ran, Niva A; Kuik, Martijn; Love, John A; Proctor, Christopher M; Nagao, Ikuhiro; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    Electroluminescence (EL) from the charge-transfer state and singlet excitons is observed at low applied voltages from high-performing small-molecule bulk-heterojunction solar cells. Singlet emission from the blends emerges upon altering the processing conditions, such as thermal annealing and processing with a solvent additive, and correlates with improved photovoltaic performance. Low-temperature EL measurements are utilized to access the physics behind the singlet emission. PMID:25212949

  6. Influence of coulomb corrections in the self-consistent charge extended Hckel (SCCEH) procedure on hyperfine properties of biological molecules

    NASA Astrophysics Data System (ADS)

    Roy, J. N.; Mishra, S. K.; Mishra, K. C.; Das, T. P.

    1987-04-01

    For the sake of simplicity, the Coulomb interaction between electrons of an atom with the cores and valence electrons belonging to neighbouring atoms is not completely incorporated in the SCCEH procedure often used for the study of electronic structures and hyperfine properties of biological systems. In the present work, the influence of this neglected interaction on the charge distribution in both small molecules and the large biologically important system, hemin, as well as on the hyperfine properties of the latter is analysed.

  7. Consecutive Charging of a Molecule-on-Insulator Ensemble Using Single Electron Tunnelling Methods.

    PubMed

    Rahe, Philipp; Steele, Ryan P; Williams, Clayton C

    2016-02-10

    We present the local charge state modification at room temperature of small insulator-supported molecular ensembles formed by 1,1'-ferrocenedicarboxylic acid on calcite. Single electron tunnelling between the conducting tip of a noncontact atomic force microscope (NC-AFM) and the molecular islands is observed. By joining NC-AFM with Kelvin probe force microscopy, successive charge build-up in the sample is observed from consecutive experiments. Charge transfer within the islands and structural relaxation of the adsorbate/surface system is suggested by the experimental data. PMID:26713686

  8. Analysis of negatively charged dye-binding antibodies reactive with double-stranded DNA and heparan sulfate in serum from patients with rheumatic diseases.

    PubMed Central

    Aotsuka, S; Okawa-Takatsuji, M; Kinoshita, M; Yokohari, R

    1988-01-01

    Antibodies to double-stranded (ds) DNA are characteristically present in serum from patients with systemic lupus erythematosus (SLE). Recently, anti-dsDNA antibodies have been shown to have the capacity to react with a diversity of molecules with repeating negative charges. Using the anionic dye Cibacron blue F3GA, bound to crosslinked agarose, we analysed the nature of antibodies capable of reacting with this dye in serum samples from patients with various rheumatic diseases. The dye-antibody complex could easily be split by eluting with solutions of increasing ionic strength, suggesting that the interaction is ionic in nature. Pepsin-digested F(ab')2 antibodies retained the capacity to bind Cibacron blue, confirming that the binding occurred via antigen-binding sites on the antibody molecule. The eluates obtained from dye-ligand chromatography of active SLE sera contained antibodies to both dsDNA and heparan sulfate, while those of sera from patients with other non-SLE rheumatic diseases contained antibodies only against heparan sulfate. Furthermore, the dye-ligand eluates of sera from patients with active SLE and other non-SLE rheumatic diseases were found to contain increased amounts of IgG. In one patient with SLE, levels of antibodies to dsDNA and heparan sulfate, and the amounts of total IgG in dye-ligand eluates, were shown to be correlated with disease activity. PMID:2974766

  9. Enhancement of charge transport in DNA molecules induced by the next nearest-neighbor effects

    NASA Astrophysics Data System (ADS)

    Malakooti, Sadeq; Hedin, Eric R.; Kim, Young D.; Joe, Yong S.

    2012-11-01

    An advanced two-dimensional tight-binding model including the next nearest-neighbor effects for quantum mechanical electron transport through double-stranded DNA molecules is proposed. Considering the next nearest-neighbor hopping strengths between sites gives a more rational and realistic model for the electron path-way through DNA molecules. We show higher overall transmission and enhanced current for a 30 base-pair poly(G)-poly(C) DNA molecule with the inclusion of diagonal electron hopping between the sites. In addition, an optimum condition of the contact hopping strength and Fermi energy to obtain the maximum current for the system is demonstrated. Finally, we present the current-voltage characteristics showing a transition from a semiconductor-like to a metal-like DNA molecule with the variation of the Fermi energy.

  10. Strong Intramolecular Electron-Phonon Coupling in the Negatively Charged Aromatic Superconductor Picene

    NASA Astrophysics Data System (ADS)

    Kato, Takashi; Kambe, Takashi; Kubozono, Yoshihiro

    2011-08-01

    Superconductivity was recently discovered in solid potassium-intercalated picene (K322ph), in which the picene molecule becomes trianionic (22ph3-). In this Letter, we conduct a theory-based study of the superconductivity of 22ph3- within the framework of BCS theory. We estimate the density of states N(?F) on the Fermi level to be 2.2 states per (eV molecule spin) by using the theoretical intramolecular electron-phonon coupling lx and the experimental superconducting transition temperature Tc of 18 K. The theoretical value is consistent with the 1.2 states per (eV molecule spin) determined experimentally for K322ph with Tc=18K, indicating the validity of our theoretical treatment and the electron-phonon mechanism for superconductivity. The predicted lx, 0.206 eV, for 22ph3- is larger than any value reported for organic superconductors, so picene may have the largest lx among the superconductors reported so far.

  11. Computational modeling of chemical reactions and interstitial growth and remodeling involving charged solutes and solid-bound molecules

    PubMed Central

    Nims, Robert J.; Maas, Steve; Weiss, Jeffrey A.

    2014-01-01

    Mechanobiological processes are rooted in mechanics and chemistry, and such processes may be modeled in a framework that couples their governing equations starting from fundamental principles. In many biological applications, the reactants and products of chemical reactions may be electrically charged, and these charge effects may produce driving forces and constraints that significantly influence outcomes. In this study, a novel formulation and computational implementation are presented for modeling chemical reactions in biological tissues that involve charged solutes and solid-bound molecules within a deformable porous hydrated solid matrix, coupling mechanics with chemistry while accounting for electric charges. The deposition or removal of solid-bound molecules contributes to the growth and remodeling of the solid matrix; in particular, volumetric growth may be driven by Donnan osmotic swelling, resulting from charged molecular species fixed to the solid matrix. This formulation incorporates the state of strain as a state variable in the production rate of chemical reactions, explicitly tying chemistry with mechanics for the purpose of modeling mechanobiology. To achieve these objectives, this treatment identifies the specific theoretical and computational challenges faced in modeling complex systems of interacting neutral and charged constituents while accommodating any number of simultaneous reactions where reactants and products may be modeled explicitly or implicitly. Several finite element verification problems are shown to agree with closed-form analytical solutions. An illustrative tissue engineering analysis demonstrates tissue growth and swelling resulting from the deposition of chondroitin sulfate, a charged solid-bound molecular species. This implementation is released in the open-source program FEBio (www.febio.org). The availability of this framework may be particularly beneficial to optimizing tissue engineering culture systems by examining the influence of nutrient availability on the evolution of inhomogeneous tissue composition and mechanical properties, the evolution of construct dimensions with growth, the influence of solute and solid matrix electric charge on the transport of cytokines, the influence of binding kinetics on transport, the influence of loading on binding kinetics, and the differential growth response to dynamically loaded versus free-swelling culture conditions. PMID:24558059

  12. Computational modeling of chemical reactions and interstitial growth and remodeling involving charged solutes and solid-bound molecules.

    PubMed

    Ateshian, Gerard A; Nims, Robert J; Maas, Steve; Weiss, Jeffrey A

    2014-10-01

    Mechanobiological processes are rooted in mechanics and chemistry, and such processes may be modeled in a framework that couples their governing equations starting from fundamental principles. In many biological applications, the reactants and products of chemical reactions may be electrically charged, and these charge effects may produce driving forces and constraints that significantly influence outcomes. In this study, a novel formulation and computational implementation are presented for modeling chemical reactions in biological tissues that involve charged solutes and solid-bound molecules within a deformable porous hydrated solid matrix, coupling mechanics with chemistry while accounting for electric charges. The deposition or removal of solid-bound molecules contributes to the growth and remodeling of the solid matrix; in particular, volumetric growth may be driven by Donnan osmotic swelling, resulting from charged molecular species fixed to the solid matrix. This formulation incorporates the state of strain as a state variable in the production rate of chemical reactions, explicitly tying chemistry with mechanics for the purpose of modeling mechanobiology. To achieve these objectives, this treatment identifies the specific theoretical and computational challenges faced in modeling complex systems of interacting neutral and charged constituents while accommodating any number of simultaneous reactions where reactants and products may be modeled explicitly or implicitly. Several finite element verification problems are shown to agree with closed-form analytical solutions. An illustrative tissue engineering analysis demonstrates tissue growth and swelling resulting from the deposition of chondroitin sulfate, a charged solid-bound molecular species. This implementation is released in the open-source program FEBio ( www.febio.org ). The availability of this framework may be particularly beneficial to optimizing tissue engineering culture systems by examining the influence of nutrient availability on the evolution of inhomogeneous tissue composition and mechanical properties, the evolution of construct dimensions with growth, the influence of solute and solid matrix electric charge on the transport of cytokines, the influence of binding kinetics on transport, the influence of loading on binding kinetics, and the differential growth response to dynamically loaded versus free-swelling culture conditions. PMID:24558059

  13. Percolation, tie-molecules, and microstructural origins of charge transport in semicrystalline conjugated polymers (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Mollinger, Sonya A.; Krajina, Brad; Noriega-Manez, Rodrigo J.; Salleo, Alberto; Spakowitz, Andrew J.

    2015-10-01

    Semiconducting polymers play an important role in a wide range of optical and electronic material applications. Polymer thin films that result in the highest performance typically have a complex semicrystalline morphology, indicating that considerable device improvement can be achieved through optimization of microstructural properties. However, the connection between molecular ordering and device performance is difficult to predict due to the current need for a mathematical theory of the physics that dictates charge transport in semiconducting polymers. It is experimentally suggested that efficient transport in such films occurs via connected networks of crystallites. We present an analytical and computational description of semicrystalline conjugated polymer materials that captures the impact of polymer conformation on charge transport in heterogeneous thin films. We first develop an analytical theory for the statistical behavior of a polymer emanating from a crystallite and predict the average distance to the first kink in the chain that traps a charge. We use this analysis to define the conditions for percolation and the consequent efficient transport through a semicrystalline material. We then establish a charge transport model using Monte Carlo simulations that predicts the multi-scale charge transport and crystallite connections. We approximate the thin film as a two-dimensional grid of crystallites embedded in amorphous polymer. The chain conformations in the amorphous region are determined by the wormlike chain model, and the crystallites are assigned fixed mobilities. We use this model to identify limits of charge transport at various time scales for varying fraction of crystallinity.

  14. Preparation and chromatographic evaluation of zwitterionic stationary phases with controllable ratio of positively and negatively charged groups.

    PubMed

    Cheng, Xiao-Dong; Hao, Yan-Hong; Peng, Xi-Tian; Yuan, Bi-Feng; Shi, Zhi-Guo; Feng, Yu-Qi

    2015-08-15

    The present study described the preparation and application of zwitterionic stationary phases (ACS) with controllable ratio of positively charged tertiary amine groups and negatively charged carboxyl groups. Various parameters, including water content, pH values and ionic strength of the mobile phase, were investigated to study the chromatographic characteristics of ACS columns. The prepared ACS columns demonstrated a mix-mode retention mechanism composed of surface adsorption, partitioning and electrostatic interactions. The elemental analysis of different batches of the ACS phases demonstrated good reproducibility of the preparation strategy. Additionally, various categories of compounds, including nucleosides, water-soluble vitamins, benzoic acid derivatives and basic compounds were successively employed to evaluate the separation selectivity of the prepared ACS stationary phases. These ACS phases exhibited entirely different selectivity and retention behavior from each other for various polar analytes, demonstrating the excellent application potential in the analysis of polar compounds in HILIC. PMID:25966373

  15. Zwitterionic i-motif structures are preserved in DNA negatively charged ions produced by electrospray mass spectrometry.

    PubMed

    Rosu, Frederic; Gabelica, Valrie; Joly, Laure; Grgoire, Gilles; De Pauw, Edwin

    2010-11-01

    DNA cytosine-rich strands can fold into an intercalated motif (i-motif) structure. The i-motif is formed by mutually intercalated duplexes containing proton-mediated C-H(+)-C (cytosine-proton-cytosine) base pairs. Negatively charged ions of DNA i-motifs produced by electrospray mass spectrometry are therefore zwitterionic if the base pairing motif is preserved in the gas phase. Here we used IRMPD spectroscopy and ion mobility spectrometry to assess whether i-motif structures were preserved in the gas phase. We first investigated the IRMPD spectral signature of the tetramer [dC(6)](4), which can only be formed via C-H(+)-C base pairing, compared to the single strand dC(6). The IR signature of i-motif formation is an apparent broadening of the band at 1650 cm(-1). DFT calculations show this apparent broadening is actually due to blue-shifts of the NH(2) scissoring modes and red shifts of C[double bond, length as m-dash]O stretching modes. We then investigated the gas-phase conformations of the telomeric sequence d(CCCAAT)(3)CCC, that can form an intramolecular i-motif, by performing IRMPD spectroscopy and ion mobility spectrometry as a function of the charge state. We show that the negative ions of the lowest charge states correspond to a preserved i-motif structure. This is the first demonstration of the native extraction of solution-phase zwitterionic nucleic acids using negative electrospray ionization. PMID:20838693

  16. Characterization of a novel small molecule that potentiates ?-lactam activity against gram-positive and gram-negative pathogens.

    PubMed

    Nair, Dhanalakshmi R; Monteiro, Joo M; Memmi, Guido; Thanassi, Jane; Pucci, Michael; Schwartzman, Joseph; Pinho, Mariana G; Cheung, Ambrose L

    2015-04-01

    In a loss-of-viability screen using small molecules against methicillin-resistant Staphylococcus aureus (MRSA) strain USA300 with a sub-MIC of a ?-lactam, we found a small molecule, designated DNAC-1, which potentiated the effect of oxacillin (i.e., the MIC of oxacillin decreased from 64 to 0.25 ?g/ml). Fluorescence microscopy indicated a disruption in the membrane structures within 15 min of exposure to DNAC-1 at 2 MIC. This permeabilization was accompanied by a rapid loss of membrane potential, as monitored by use of the DiOC2 (3,3'-diethyloxacarbocyanine iodide) dye. Macromolecular analysis showed the inhibition of staphylococcal cell wall synthesis by DNAC-1. Transmission electron microscopy of treated MRSA USA300 cells revealed a slightly thicker cell wall, together with mesosome-like projections into the cytosol. The exposure of USA300 cells to DNAC-1 was associated with the mislocalization of FtsZ accompanied by the localization of penicillin-binding protein 2 (PBP2) and PBP4 away from the septum, as well as mild activation of the vraRS-mediated cell wall stress response. However, DNAC-1 does not have any generalized toxicity toward mammalian host cells. DNAC-1 in combination with ceftriaxone is also effective against an assortment of Gram-negative pathogens. Using a murine subcutaneous coinjection model with 10(8) CFU of USA300 as a challenge inoculum, DNAC-1 alone or DNAC-1 with a sub-MIC of oxacillin resulted in a 6-log reduction in bacterial load and decreased abscess formation compared to the untreated control. We propose that DNAC-1, by exerting a bimodal effect on the cell membrane and cell wall, is a viable candidate in the development of combination therapy against many common bacterial pathogens. PMID:25583731

  17. [X-ray tubes with ionic indemnification of negative space electronic charge].

    PubMed

    Kanikovski?, V B

    2001-01-01

    How to increase anode current in the fine-focus diagnostic X-ray tubes (XTs) is analyzed. It has been found that there are new three-class XTs that have advantages of both ionic and electronic tubes. The specific feature of the new class XTs is the gaseous atmosphere available in the working volume. Ionizing the gaseous atmosphere with a emission electron flow in the path from the cathode to the anode yields a dot volumetric positively charged ion grid that closely approaches the cathode and can pay a big bonus in anode current output. PMID:11534285

  18. Charge and Nuclear Dynamics Induced by Deep Inner-Shell Multiphoton Ionization of CH3I Molecules by Intense X-ray Free-Electron Laser Pulses.

    PubMed

    Motomura, Koji; Kukk, Edwin; Fukuzawa, Hironobu; Wada, Shin-ichi; Nagaya, Kiyonobu; Ohmura, Satoshi; Mondal, Subhendu; Tachibana, Tetsuya; Ito, Yuta; Koga, Ryosuke; Sakai, Tsukasa; Matsunami, Kenji; Rudenko, Artem; Nicolas, Christophe; Liu, Xiao-Jing; Miron, Catalin; Zhang, Yizhu; Jiang, Yuhai; Chen, Jianhui; Anand, Mailam; Kim, Dong Eon; Tono, Kensuke; Yabashi, Makina; Yao, Makoto; Ueda, Kiyoshi

    2015-08-01

    In recent years, free-electron lasers operating in the true X-ray regime have opened up access to the femtosecond-scale dynamics induced by deep inner-shell ionization. We have investigated charge creation and transfer dynamics in the context of molecular Coulomb explosion of a single molecule, exposed to sequential deep inner-shell ionization within an ultrashort (10 fs) X-ray pulse. The target molecule was CH3I, methane sensitized to X-rays by halogenization with a heavy element, iodine. Time-of-flight ion spectroscopy and coincident ion analysis was employed to investigate, via the properties of the atomic fragments, single-molecule charge states of up to +22. Experimental findings have been compared with a parametric model of simultaneous Coulomb explosion and charge transfer in the molecule. The study demonstrates that including realistic charge dynamics is imperative when molecular Coulomb explosion experiments using short-pulse facilities are performed. PMID:26267186

  19. Mechanism of How Salt-Gradient-Induced Charges Affect the Translocation of DNA Molecules through a Nanopore

    PubMed Central

    He, Yuhui; Tsutsui, Makusu; Scheicher, RalphH.; Fan, Chun; Taniguchi, Masateru; Kawai, Tomoji

    2013-01-01

    Experiments using nanopores demonstrated that a salt gradient enhances the capture rate of DNA and reduces its translocation speed. These two effects can help to enable electrical DNA sequencing with nanopores. Here, we provide a quantitative theoretical evaluation that shows the positive net charges, which accumulate around the pore entrance due to the salt gradient, are responsible for the two observed effects: they reinforce the electric capture field, resulting in promoted molecule capture rate; and they induce cationic electroosmotic flow through the nanopore, thus significantly retarding the motion of the anionic DNA through the nanopore. Our multiphysical simulation results show that, during the polymer trapping stage, the former effect plays the major role, thus resulting in promoted DNA capture rate, while during the nanopore-penetrating stage the latter effect dominates and consequently reduces the DNA translocation speed significantly. Quantitative agreement with experimental results has been reached by further taking nanopore wall surface charges into account. PMID:23931325

  20. Image-charge-induced localization of molecular orbitals at metal-molecule interfaces: Self-consistent GW calculations

    NASA Astrophysics Data System (ADS)

    Strange, M.; Thygesen, K. S.

    2012-11-01

    Quasiparticle (QP) wave functions, also known as Dyson orbitals, extend the concept of single-particle states to interacting electron systems. Here we employ many-body perturbation theory in the GW approximation to calculate the QP wave functions for a semiempirical model describing a ?-conjugated molecular wire in contact with a metal surface. We find that image charge effects pull the frontier molecular orbitals toward the metal surface, while orbitals with higher or lower energy are pushed away. This affects both the size of the energetic image charge shifts and the coupling of the individual orbitals to the metal substrate. Full diagonalization of the QP equation and, to some extent, self-consistency in the GW self-energy, is important to describe the effect, which is not captured by standard density functional theory or Hartree-Fock. These results should be important for the understanding and theoretical modeling of electron transport across metal-molecule interfaces.

  1. Dissociative charge transfer of H/+/ ions with H2 and D2 molecules from 78 to 330 K

    NASA Technical Reports Server (NTRS)

    Johnsen, R.; Chen, A.; Biondi, M. A.

    1980-01-01

    The dissociative charge transfer of He(+) ions with H2 and D2 molecules has been studied using a temperature-variable drift-tube mass-spectrometer apparatus over the temperature range 78 to 330 K. The binary rate coefficients are small at 300 K, approximately 10 to the -13th to 10 to the -14th cu cm/sec, and only slightly larger at 78 K. Termolecular contributions to the binary rate coefficients are found to be small at 330 K but increase substantially with decreasing temperature. Two-body charge transfer with D2 is found to be slower than with H2 by a factor of 10, in good agreement with recent theoretical predictions, although the measured values of the rate coefficients are larger by a factor of about 4 than the predicted values.

  2. Femtosecond transient studies of photoinduced charge transfer in polymers doped with strong acceptor molecules; applications for organic solar cells

    NASA Astrophysics Data System (ADS)

    Holt, Josh; Drori, Tomer; Sheng, Chuanxiang; Valy Vardeny, Z.

    2007-03-01

    Current developments in organic solar cells (5% efficiency nowadays) require understanding and control of photoinduced charge carrier transfer and electronic state dynamics of donor-acceptor pairs. One current drawback to organic solar cell efficiency is negligible absorption in the near infrared region of the solar spectrum. We provide and compare evidence that poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (MEH-PPV) and regio-regular poly-3-hexyl thiophene (RR-P3HT) doped with 2,7-dinitrofluorenone (DNF) or 2,4,7-trinitrofluorenone (TNF) form below-gap charge transfer complex state that can extend absorption into the near infrared. Using fs transient and CW spectroscopies we found that the photoluminescence and mid-ir photoinduced absorption (PA) band of excitons are simultaneously quenched, when excited in the visible/uv or near ir. We compare our results to those of comparable systems using C60 as acceptor molecules.

  3. Single and double charge transfer of He(2+) ions with molecules at near-thermal energies

    NASA Technical Reports Server (NTRS)

    Tosh, R. E.; Johnsen, R.

    1993-01-01

    Rate coefficients were measured for charge-transfer reactions of He(2+) ions with H2, N2, O2, CO, CO2, and H2O. The experiments were carried out using a selected-ion drift-tube mass spectrometer. Total rate coefficients are found to be very large and are generally close to the limiting Langevin capture rate coefficients or the corresponding ADO-model (Su and Bowers, 1973) coefficients. The product-ion spectra indicate that both single and double charge transfer and possibly transfer ionization occur in these reactions.

  4. Influence of backbone on the charge transport properties of G4-DNA molecules: a model-based calculation

    NASA Astrophysics Data System (ADS)

    Guo, Ai-Min; Yang, Zhi; Zhu, Hong-Jun; Xiong, Shi-Jie

    2010-02-01

    We put forward a model Hamiltonian to describe the influence of backbone energetics on charge transport through guanine-quadruplex DNA (G4-DNA) molecules. Our analytical results show that an energy gap can be produced in the energy spectrum of G4-DNA by hybridization effects between the backbone and the base and by on-site energy difference of the backbone from the base. The environmental effects are investigated by introducing different types of disorder into the backbone sites. Our numerical results suggest that the localization length of G4-DNA can be significantly enhanced by increasing the backbone disorder degree when the environment-induced disorder is sufficiently large. There exists a backbone disorder-induced semiconducting-metallic transition in short G4-DNA molecules, where G4-DNA behaves as a semiconductor if the backbone disorder is weak and behaves as a conductor if the backbone disorder degree surpasses a critical value.

  5. Bianthrone at a metal surface: Conductance switching with a bistable molecule made feasible by image charge effects

    SciTech Connect

    Geskin, Victor; Bouzakraoui, Saïd; Cornil, Jérôme; Lara-Avila, Samuel; Danilov, Andrey; Kubatkin, Sergey; Bjornholm, Thomas

    2015-01-22

    Bianthrone is a sterically hindered compound that exists in the form of two non-planar isomers. Our experimental study of single-molecule junctions with bianthrone reveals persistent switching of electric conductance at low temperatures, which can be reasonably associated to molecular isomerization events. Temperature dependence of the switching rate allows for an estimate of the activation energy of the process, on the order of 35–90 meV. Quantum-chemical calculations of the potential surface of neutral bianthrone and its anion, including identification of transition states, yields the isolated molecule isomerization barriers too high vs. the previous estimate, though in perfect agreement with previous experimental studies in solution. Nevertheless, we show that the attraction of the anion in the vicinity of the metal surface by its image charge can significantly alter the energetic landscape, in particular, by reducing the barrier to the values compatible with the observed switching behavior.

  6. Fully numerical soluti ons of molecular Dirac equations for highly charged one-electron homonuclear diatomic molecules

    NASA Astrophysics Data System (ADS)

    Sundholm, Dage

    1994-07-01

    The two-centre four-component Dirac equations for the homonuclear one-electron systems H 2+, Ne 219+, Ca 239+, Zn 259+, Zr 279+, Sn 299+, Nd 2119+, Yb 2139+, Hg 2159+, Th 2179+, and Fm 2199+ are solved numerically by a finite-difference approach. Accurate values for the non-relativistic and relativistic orbital energies are given as benchmarks for these molecules. The assumed bond lengths are 2/ Z au where Z is the nuclear charge. For the lowest ? g orbital of the Th 2179+ molecule, the orbital energy is 14.6 au above the global basis-set result while for the lowest orbital of ? u symmetry the present orbital energy is 19.1 au below the global basis-set results. The relativistic corrections to the quadrupole moment of the ? g orbital are given.

  7. Comparison of chiral separation of basic drugs in capillary electrophoresis and liquid chromatography using neutral and negatively charged cyclodextrins.

    PubMed

    Kwaterczak, Arkadiusz; Duszczyk, Kazimiera; Bielejewska, Anna

    2009-07-10

    Liquid chromatography (LC) and capillary electrophoresis (CE) are very widely used as chiral separation methods. In this publication we try to find if the results obtained in CE and LC with the chiral selector added to the electrolyte and the mobile phase, respectively, can be used as tools for studying weak stereoselective interactions, and how this information can be useful for optimizing chiral separation processes. The manuscript presents a systematic comparison of chiral discrimination of model compounds in HPLC and CE using neutral and negatively charged cyclodextrins. The enantiomeric separation of basic chiral pharmaceuticals such as pheniramine, brompheniramine, metoxyphenamine, cyclopentolate, doxylamine and ketamine was investigated in capillary electrophoresis (CE) and liquid chromatography (HPLC) using negatively charged sulfated-beta-cyclodextrin (S-beta-CD) and neutral cyclodextrins (CDs). The apparent stability constants between the model compounds and cyclodextrins were estimated in both techniques. We discuss the influence of the stability constant and K1/K2 ratio of the investigated complexes on chiral separation obtained in both techniques. PMID:19481637

  8. The effect of negative electron affinity emitter materials on space charge mitigation of vacuum thermionic energy conversion devices

    NASA Astrophysics Data System (ADS)

    Smith, Joshua; Bilbro, Griff; Nemanich, Robert

    2006-03-01

    Vacuum thermionic energy conversion (TEC) devices provide a way to convert heat directly into electrical work. The negative space charge effect has been an effect that significantly degrades the performance of these devices, requiring small interelectrode spacings for reasonable performance. Recently, Nitrogen doped, Hydrogen terminated, ultra-nanocrystalline diamond films have been investigated as possible candidates for low operating temperature, low work function emitter materials. Furthermore, these materials exhibit a so-called negative electron affinity (NEA) where the vacuum level lies below the conduction band minimum of the material. As a result of this NEA property, the distribution of thermionically emitted electrons will have some nonzero minimum initial velocity. A model was developed to determine the effect that the NEA property of these types of emitters have on mitigation of the space charge effect. The model shows that a TEC with an NEA emitter material will have comparable performance with a non-NEA emitter TEC with a smaller gap. Thus, it is possible to use NEA emitters to relax the requirement of a small gap distance.

  9. The role of multiparticle correlations and Cooper pairing in the formation of molecules in an ultracold gas of Fermi atoms with a negative scattering length

    SciTech Connect

    Babichenko, V. S. Kagan, Yu.

    2012-11-15

    The influence of multiparticle correlation effects and Cooper pairing in an ultracold Fermi gas with a negative scattering length on the formation rate of molecules is investigated. Cooper pairing is shown to cause the formation rate of molecules to increase, as distinct from the influence of Bose-Einstein condensation in a Bose gas on this rate. This trend is retained in the entire range of temperatures below the critical one.

  10. Basis generator method study of electron removal from water molecules by multiply-charged ion impact

    NASA Astrophysics Data System (ADS)

    Pausz, T.; Ldde, H. J.; Murakami, M.; Horbatsch, M.; Kirchner, T.

    2014-04-01

    We apply the basis generator method for ion-molecule collisions to study He2+ and C6+ impact on H2O in the energy range of 20-5000 keV/amu. Results are compared with experimental data and previous calculations where available.

  11. Controllable electrostatic surface guide for cold molecules with a single charged wire

    NASA Astrophysics Data System (ADS)

    Gu, Zhenxing; Guo, Chaoxiu; Hou, Shunyong; Li, Shengqiang; Deng, Lianzhong; Yin, Jianping

    2013-05-01

    We demonstrate a controllable highly efficient electrostatic surface guide for ND3 molecules in the weak-field-seeking states on a ceramic substrate over a distance of 840 mm, and study the dependences of the relative molecule number (or the overall transmission efficiency) of our single-wire guide and the guiding-center positions on the guiding voltages, both experimentally and theoretically. Our study shows that the guiding-center position and the number of the guided molecules can be easily controlled by adjusting the guiding voltages, and find that an overall transmission efficiency of higher than 50% in a single quantum state can be obtained. Our experimental results are consistent with ones of Monte Carlo simulations. Also, we discuss the transverse velocity filtering effect and the acceptance of the guided molecules in four-dimensional phase space. Both the transmission efficiency and the acceptance in two-dimensional position space are higher than that in our previous two-wire guide [Y. Xia, Y. Yin, H. Chen, L. Deng, and J. Yin, Phys. Rev. Lett.0031-900710.1103/PhysRevLett.100.043003 100, 043003 (2008)].

  12. Light emission spectra of molecules in negative and positive back discharges in nitrogen with carbon dioxide mixture at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Czech, Tadeusz; Sobczyk, Arkadiusz Tomasz; Jaworek, Anatol

    2015-10-01

    Results of spectroscopic investigations and current-voltage characteristics of back discharge generated in point-plane electrode geometry with plate covered fly ash layer in a mixture of N2 + CO2 at atmospheric pressure, for positive and negative polarity of the discharge electrode are presented in this paper. Point-plane electrode configuration was chosen in these studies in order to simulate the physical processes occurring in electrostatic precipitator. Three forms of back discharge for both polarities were investigated: glow, streamers and low-current back-arc. Diatomic reactions and dissociation products of N2 and CO2 (OH, NO, CN), atoms from fly ash layer (N, Ti, Na), free radicals, molecules or ions, which have unpaired valence electrons, and other active species, e.g., N2 (in C,B,A-state), N 2 + (B) were identified in the discharges by the method of optical emission spectroscopy (OES). The measurements shown that atomic and molecular optical emission spectral lines from back discharge depend on the forms of discharge and the discharge current. In normal electrical discharges, the emission spectra are dominated by gaseous components, but in the case of back discharge, atomic lines belonging to chemical compounds of fly ash were also recorded and identified.

  13. Base-dependent electron photodetachment from negatively charged DNA strands upon 260-nm laser irradiation.

    PubMed

    Gabelica, Valrie; Rosu, Frdric; Tabarin, Thibault; Kinet, Catherine; Antoine, Rodolphe; Broyer, Michel; De Pauw, Edwin; Dugourd, Philippe

    2007-04-18

    DNA multiply charged anions stored in a quadrupole ion trap undergo one-photon electron ejection (oxidation) when subjected to laser irradiation at 260 nm (4.77 eV). Electron photodetachment is likely a fast process, given that photodetachment is able to compete with internal conversion or radiative relaxation to the ground state. The DNA [6-mer]3- ions studied here show a marked sequence dependence of electron photodetachment yield. Remarkably, the photodetachment yield (dG6 > dA6 > dC6 > dT6) is inversely correlated with the base ionization potentials (G < A < C < T). Sequences with guanine runs show increased photodetachment yield as the number of guanine increases, in line with the fact that positive holes are the most stable in guanine runs. This correlation between photodetachment yield and the stability of the base radical may be explained by tunneling of the electron through the repulsive Coulomb barrier. Theoretical calculations on dinucleotide monophosphates show that the HOMO and HOMO-1 orbitals are localized on the bases. The wavelength dependence of electron detachment yield was studied for dG63-. Maximum electron photodetachment is observed in the wavelength range corresponding to base absorption (260-270 nm). This demonstrates the feasibility of gas-phase UV spectroscopy on large DNA anions. The calculations and the wavelength dependence suggest that the electron photodetachment is initiated at the bases and not at the phosphates. This also indicates that, although direct photodetachment could also occur, autodetachment from excited states, presumably corresponding to base excitation, is the dominant process at 260 nm. Excited-state dynamics of large DNA strands still remains largely unexplored, and photo-oxidation studies on trapped DNA multiply charged anions can help in bridging the gap between gas-phase studies on isolated bases or base pairs and solution-phase studies on full DNA strands. PMID:17378565

  14. Charge recombination mechanism to explain the negative capacitance in dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Lie-Feng, Feng; Kun, Zhao; Hai-Tao, Dai; Shu-Guo, Wang; Xiao-Wei, Sun

    2016-03-01

    Negative capacitance (NC) in dye-sensitized solar cells (DSCs) has been confirmed experimentally. In this work, the recombination behavior of carriers in DSC with semiconductor interface as a carrier’s transport layer is explored theoretically in detail. Analytical results indicate that the recombination behavior of carriers could contribute to the NC of DSCs under small signal perturbation. Using this recombination capacitance we propose a novel equivalent circuit to completely explain the negative terminal capacitance. Further analysis based on the recombination complex impedance show that the NC is inversely proportional to frequency. In addition, analytical recombination resistance is composed by the alternating current (AC) recombination resistance (Rrac) and the direct current (DC) recombination resistance (Rrdc), which are caused by small-signal perturbation and the DC bias voltage, respectively. Both of two parts will decrease with increasing bias voltage. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204209 and 60876035) and the Natural Science Foundation of Tianjin City, China (Grant No. 13JCZDJC32800).

  15. Bias changing molecule-lead couple and inducing low bias negative differential resistance for electrons acceptor predicted by first-principles study

    NASA Astrophysics Data System (ADS)

    Min, Y.; Fang, J. H.; Zhong, C. G.; Dong, Z. C.; Zhao, Z. Y.; Zhou, P. X.; Yao, K. L.

    2015-10-01

    A first-principles study of the transport properties of 3,13-dimercaptononacene-6,21-dione molecule sandwiched between two gold leads is reported. The strong effect of negative differential resistance with large peak-to-valley ratio of 710% is present under low bias. We found that bias can change molecule-lead couple and induce low bias negative differential resistance for electrons acceptor, which may promise the potential applications in molecular devices with low-power dissipation in the future.

  16. The effect of polymer size and charge of molecules on permeation through synovial membrane and accumulation in hyaline articular cartilage.

    PubMed

    Sterner, B; Harms, M; Wöll, S; Weigandt, M; Windbergs, M; Lehr, C M

    2016-04-01

    The treatment of joint related diseases often involves direct intra-articular injections. For rational development of novel delivery systems with extended residence time in the joint, detailed understanding of transport and retention phenomena within the joint is mandatory. This work presents a systematic study on the in vitro permeation, penetration and accumulation of model polymers with differing charges and molecular weights in bovine joint tissue. Permeation experiments with bovine synovial membrane were performed with PEG polymers (6-200kDa) and methylene blue in customized diffusion chambers. For polyethylene glycol, 2-fold (PEG 6kDa), 3-fold (PEG 10kDa) and 13-fold (PEG 35kDa) retention by the synovial membrane in reference to the small molecule methylene blue was demonstrated. No PEG 200kDa was found in the acceptor in detectable amounts after 48h. This showed the potential for a distinct extension of joint residence times by increasing molecular weights. In addition, experiments with bovine cartilage tissue were conducted. The ability for positively charged, high molecular weight chitosans and HEMA-Co-TMAP (HCT) polymers (up to 233kDa) to distribute throughout the entire cartilage matrix was demonstrated. In contrast, a distribution into cartilage was not observed for neutral PEG polymers (6-200kDa). Furthermore, the positive charge density of different compounds (chitosan, HEMA-Co-TMAP, methylene blue, MSC C1 (neutral NCE) and MSC D1 (positively charged NCE) was found to correlate with their accumulation in bovine cartilage tissue. In summary, the results offer pre-clinical in vitro data, indicating that the modification of molecular size and charge of a substance has the potential to decelerate its clearance through the synovial membrane and to promote accumulation inside the cartilage matrix. PMID:26876928

  17. A time of flight mass spectrometer with field free interaction region for low energy charged particle-molecule collision studies

    SciTech Connect

    Rao, K. C.; Prabhudesai, V. S.; Kumar, S. V. K.

    2011-11-15

    A new design of a linear time of flight mass spectrometer (ToFMS) is implemented that gives nearly field-free interaction region without compromising on the mass resolution. The design addresses problems that would arise in a conventional Wiley-McLaren type of ToFMS: (i) field leakages into the charged particle-molecule interaction region from various components of the mass spectrometer, including that through the high transparency mesh used to obtain evenly distributed electric fields; (ii) complete collection and transportation of the ions produced in the interaction region to the detector, which is essential for high sensitivity and cross section measurements. This ToFMS works over a wide range of masses from H{sup +} to a few hundred Daltons and would be the most suitable for low energy charged particle-molecule interaction studies. Performance of the ToFMS has been tested by measuring the partial ionization cross sections for electron impact on CF{sub 4}.

  18. A time of flight mass spectrometer with field free interaction region for low energy charged particle-molecule collision studies.

    PubMed

    Rao, K C; Prabhudesai, V S; Kumar, S V K

    2011-11-01

    A new design of a linear time of flight mass spectrometer (ToFMS) is implemented that gives nearly field-free interaction region without compromising on the mass resolution. The design addresses problems that would arise in a conventional Wiley-McLaren type of ToFMS: (i) field leakages into the charged particle-molecule interaction region from various components of the mass spectrometer, including that through the high transparency mesh used to obtain evenly distributed electric fields; (ii) complete collection and transportation of the ions produced in the interaction region to the detector, which is essential for high sensitivity and cross section measurements. This ToFMS works over a wide range of masses from H(+) to a few hundred Daltons and would be the most suitable for low energy charged particle-molecule interaction studies. Performance of the ToFMS has been tested by measuring the partial ionization cross sections for electron impact on CF(4). PMID:22128960

  19. Exciton formation as a rate limiting step for charge recombination in disordered organic molecules or polymers

    SciTech Connect

    Preezant, Yevgeni; Tessler, Nir

    2011-01-01

    The exciton formation (direct charge recombination) is studied and quantified as a function of material physical-properties such as the exciton binding energy, the exciton lifetime, and the mechanism causing the electronic disorder. By using a model that is an extension of a charge transport model [Y. Preezant and N. Tessler, Phys. Rev. B 74, 235202 (2006)] we are able to compare the direct exciton formation rate with the one predicted by the Langevin model. Using reasonable material parameters we find that in many cases the overall balance between free charge carrier and excitons is significantly affected by the exciton formation rate with its values being significantly low compared to the Langevin rate. We also find that in order to describe the complete recombination process it is important to introduce an intermediate state which we term exciton-precursor. This is in contrast to the common practice of using the Langevin model which embeds the assumption that the exciton formation rate is negligibly fast. The relations found between the physical-properties and the recombination rate can explain why certain materials exhibit Langevin rate while others exhibit significantly suppressed rates. This would eventually lead to the design of new materials better suited for either photocells or light-emitting diodes.

  20. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    SciTech Connect

    Wang, Zhiping Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji; Miyadera, Tetsuhiko; Saeki, Akinori; Seki, Shu; Zhou, Ying

    2014-07-07

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C{sub 60}) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C{sub 60} bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C{sub 60} heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  1. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Miyadera, Tetsuhiko; Saeki, Akinori; Zhou, Ying; Seki, Shu; Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji

    2014-07-01

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C60) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C60 bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C60 heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  2. Interfacial charge transfer between CdTe quantum dots and Gram negative vs. Gram positive bacteria.

    SciTech Connect

    Dumas, E.; Gao, C.; Suffern, D.; Bradforth, S. E.; Dimitrejevic, N. M.; Nadeau, J. L.; McGill Univ.; Univ. of Southern California

    2010-01-01

    Oxidative toxicity of semiconductor and metal nanomaterials to cells has been well established. However, it may result from many different mechanisms, some requiring direct cell contact and others resulting from the diffusion of reactive species in solution. Published results are contradictory due to differences in particle preparation, bacterial strain, and experimental conditions. It has been recently found that C{sub 60} nanoparticles can cause direct oxidative damage to bacterial proteins and membranes, including causing a loss of cell membrane potential (depolarization). However, this did not correlate with toxicity. In this study we perform a similar analysis using fluorescent CdTe quantum dots, adapting our tools to make use of the particles fluorescence. We find that two Gram positive strains show direct electron transfer to CdTe, resulting in changes in CdTe fluorescence lifetimes. These two strains also show changes in membrane potential upon nanoparticle binding. Two Gram negative strains do not show these effects - nevertheless, they are over 10-fold more sensitive to CdTe than the Gram positives. We find subtoxic levels of Cd{sup 2+} release from the particles upon irradiation of the particles, but significant production of hydroxyl radicals, suggesting that the latter is a major source of toxicity. These results help establish mechanisms of toxicity and also provide caveats for use of certain reporter dyes with fluorescent nanoparticles which will be of use to anyone performing these assays. The findings also suggest future avenues of inquiry into electron transfer processes between nanomaterials and bacteria.

  3. The HIV-1 Nucleocapsid Protein Recruits Negatively Charged Lipids To Ensure Its Optimal Binding to Lipid Membranes

    PubMed Central

    Kempf, Nomie; Postupalenko, Viktoriia; Bora, Saurabh; Didier, Pascal; Arntz, Youri; de Rocquigny, Hugues

    2014-01-01

    ABSTRACT The HIV-1 Gag polyprotein precursor composed of the matrix (MA), capsid (CA), nucleocapsid (NC), and p6 domains orchestrates virus assembly via interactions between MA and the cell plasma membrane (PM) on one hand and NC and the genomic RNA on the other hand. As the Gag precursor can adopt a bent conformation, a potential interaction of the NC domain with the PM cannot be excluded during Gag assembly at the PM. To investigate the possible interaction of NC with lipid membranes in the absence of any interference from the other domains of Gag, we quantitatively characterized by fluorescence spectroscopy the binding of the mature NC protein to large unilamellar vesicles (LUVs) used as membrane models. We found that NC, either in its free form or bound to an oligonucleotide, was binding with high affinity (?107 M?1) to negatively charged LUVs. The number of NC binding sites, but not the binding constant, was observed to decrease with the percentage of negatively charged lipids in the LUV composition, suggesting that NC and NC/oligonucleotide complexes were able to recruit negatively charged lipids to ensure optimal binding. However, in contrast to MA, NC did not exhibit a preference for phosphatidylinositol-(4,5)-bisphosphate. These results lead us to propose a modified Gag assembly model where the NC domain contributes to the initial binding of the bent form of Gag to the PM. IMPORTANCE The NC protein is a highly conserved nucleic acid binding protein that plays numerous key roles in HIV-1 replication. While accumulating evidence shows that NC either as a mature protein or as a domain of the Gag precursor also interacts with host proteins, only a few data are available on the possible interaction of NC with lipid membranes. Interestingly, during HIV-1 assembly, the Gag precursor is thought to adopt a bent conformation where the NC domain may interact with the plasma membrane. In this context, we quantitatively characterized the binding of NC, as a free protein or as a complex with nucleic acids, to lipid membranes and showed that the latter constitute a binding platform for NC. Taken together, our data suggest that the NC domain may play a role in the initial binding events of Gag to the plasma membrane during HIV-1 assembly. PMID:25410868

  4. Regulation of K+ Flow by a Ring of Negative Charges in the Outer Pore of BKCa Channels. Part I

    PubMed Central

    Haug, Trude; Sigg, Daniel; Ciani, Sergio; Toro, Ligia; Stefani, Enrico; Olcese, Riccardo

    2004-01-01

    The pore region of the majority of K+ channels contains the highly conserved GYGD sequence, known as the K+ channel signature sequence, where the GYG is critical for K+ selectivity (Heginbotham, L., T. Abramson, and R. MacKinnon. 1992. Science. 258:11521155). Exchanging the aspartate residue with asparagine in this sequence abolishes ionic conductance of the Shaker K+ channel (D447N) (Hurst, R.S., L. Toro, and E. Stefani. 1996. FEBS Lett. 388:5965). In contrast, we found that the corresponding mutation (D292N) in the pore forming ? subunit (hSlo) of the voltage- and Ca2+-activated K+ channel (BKCa, MaxiK) did not prevent conduction but reduced single channel conductance. We have investigated the role of outer pore negative charges in ion conduction (this paper) and channel gating (Haug, T., R. Olcese, T. Ligia, and E. Stefani. 2004. J. Gen Physiol. 124:185197). In symmetrical 120 mM [K+], the D292N mutation reduced the outward single channel conductance by ?40% and nearly abolished inward K+ flow (outward rectification). This rectification was partially relieved by increasing the external K+ concentration to 700 mM. Small inward currents were resolved by introducing an additional mutation (R207Q) that greatly increases the open probability of the channel. A four-state multi-ion pore model that incorporates the effects of surface charge was used to simulate the essential properties of channel conduction. The conduction properties of the mutant channel (D292N) could be predicted by a simple ?8.5-fold reduction of the surface charge density without altering any other parameter. These results indicate that the aspartate residue in the BKCa pore plays a key role in conduction and suggest that the pore structure is not affected by the mutation. We speculate that the negative charge strongly accumulates K+ in the outer vestibule close to the selectivity filter, thus increasing the rate of ion entry into the pore. PMID:15277578

  5. One-step solvothermal synthesis of highly water-soluble, negatively charged superparamagnetic Fe3O4 colloidal nanocrystal clusters

    NASA Astrophysics Data System (ADS)

    Gao, Jining; Ran, Xinze; Shi, Chunmeng; Cheng, Humin; Cheng, Tianmin; Su, Yongping

    2013-07-01

    Highly charged hydrophilic superparamagnetic Fe3O4 colloidal nanocrystal clusters with an average diameter of 195 nm have been successfully synthesized using a modified one-step solvothermal method. Anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt containing both sulfonate and carboxylate groups was used as the stabilizer. The clusters synthesized under different experimental conditions were characterized with transmission electron microscopy and dynamic light scattering; it was found that the size distribution and water dispersity were significantly affected by the concentration of the polyelectrolyte stabilizer and iron sources in the reaction mixtures. A possible mechanism involving novel gel-like large molecular networks that confined the nucleation and aggregation process was proposed and discussed. The colloidal nanocrystal clusters remained negatively charged in the experimental pH ranges from 2 to 11, and also showed high colloidal stability in phosphate buffered saline (PBS) and ethanol. These highly colloidal stable superparamagnetic Fe3O4 clusters could find potential applications in bioseparation, targeted drug delivery, and photonics.Highly charged hydrophilic superparamagnetic Fe3O4 colloidal nanocrystal clusters with an average diameter of 195 nm have been successfully synthesized using a modified one-step solvothermal method. Anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt containing both sulfonate and carboxylate groups was used as the stabilizer. The clusters synthesized under different experimental conditions were characterized with transmission electron microscopy and dynamic light scattering; it was found that the size distribution and water dispersity were significantly affected by the concentration of the polyelectrolyte stabilizer and iron sources in the reaction mixtures. A possible mechanism involving novel gel-like large molecular networks that confined the nucleation and aggregation process was proposed and discussed. The colloidal nanocrystal clusters remained negatively charged in the experimental pH ranges from 2 to 11, and also showed high colloidal stability in phosphate buffered saline (PBS) and ethanol. These highly colloidal stable superparamagnetic Fe3O4 clusters could find potential applications in bioseparation, targeted drug delivery, and photonics. Electronic supplementary information (ESI) available: Fitted XPS results, Raman spectra, XRD patterns, typical intensity particle size distribution and TEM images of Fe3O4 MCNCs synthesized under different conditions, and digital photograph of the reaction mixtures with different reaction times. See DOI: 10.1039/c3nr00931a

  6. Modeling light-induced charge transfer dynamics across a metal-molecule-metal junction: Bridging classical electrodynamics and quantum dynamics

    NASA Astrophysics Data System (ADS)

    Hu, Zixuan; Ratner, Mark A.; Seideman, Tamar

    2014-12-01

    We develop a numerical approach for simulating light-induced charge transport dynamics across a metal-molecule-metal conductance junction. The finite-difference time-domain method is used to simulate the plasmonic response of the metal structures. The Huygens subgridding technique, as adapted to Lorentz media, is used to bridge the vastly disparate length scales of the plasmonic metal electrodes and the molecular system, maintaining accuracy. The charge and current densities calculated with classical electrodynamics are transformed to an electronic wavefunction, which is then propagated through the molecular linker via the Heisenberg equations of motion. We focus mainly on development of the theory and exemplify our approach by a numerical illustration of a simple system consisting of two silver cylinders bridged by a three-site molecular linker. The electronic subsystem exhibits fascinating light driven dynamics, wherein the charge density oscillates at the driving optical frequency, exhibiting also the natural system timescales, and a resonance phenomenon leads to strong conductance enhancement.

  7. Modeling light-induced charge transfer dynamics across a metal-molecule-metal junction: bridging classical electrodynamics and quantum dynamics.

    PubMed

    Hu, Zixuan; Ratner, Mark A; Seideman, Tamar

    2014-12-14

    We develop a numerical approach for simulating light-induced charge transport dynamics across a metal-molecule-metal conductance junction. The finite-difference time-domain method is used to simulate the plasmonic response of the metal structures. The Huygens subgridding technique, as adapted to Lorentz media, is used to bridge the vastly disparate length scales of the plasmonic metal electrodes and the molecular system, maintaining accuracy. The charge and current densities calculated with classical electrodynamics are transformed to an electronic wavefunction, which is then propagated through the molecular linker via the Heisenberg equations of motion. We focus mainly on development of the theory and exemplify our approach by a numerical illustration of a simple system consisting of two silver cylinders bridged by a three-site molecular linker. The electronic subsystem exhibits fascinating light driven dynamics, wherein the charge density oscillates at the driving optical frequency, exhibiting also the natural system timescales, and a resonance phenomenon leads to strong conductance enhancement. PMID:25494729

  8. On the role of charge transfer in the stabilization of weakly bound complexes involving water and hydrogen sulphide molecules

    NASA Astrophysics Data System (ADS)

    Pirani, F.; Candori, P.; Pedrosa Mundim, M. S.; Belpassi, L.; Tarantelli, F.; Cappelletti, D.

    2012-04-01

    Integral cross section data for collisions of water and hydrogen sulphide molecules with noble gas atoms, measured with the same apparatus under identical conditions and analyzed by exploiting the same potential model, provided a set of internally consistent potential parameters. Their critical comparison is exploited not only to identify those systems where the intermolecular bond is not simply due to the balancing of size repulsion with dispersion and induction attraction, but also to establish the amount of bond stabilization by charge-transfer effects. Such experimental findings are analyzed through extensive and accurate ab initio calculations, addressed at discovering the relevant differences in the basic features of the potential energy surfaces. In particular, we have analyzed in detail the prototype H2S, H2O-Kr systems and found pronounced differences in the dependence of the interaction nature and energy on the relative orientation of the colliding systems. Using the recently proposed charge-displacement analysis we have been able to quantitatively assess charge-transfer effects, which differ significantly in the two systems and exhibit different stereoselectivity. This casts further light on the specificity of water interactions.

  9. Modeling light-induced charge transfer dynamics across a metal-molecule-metal junction: Bridging classical electrodynamics and quantum dynamics

    SciTech Connect

    Hu, Zixuan; Ratner, Mark A.; Seideman, Tamar

    2014-12-14

    We develop a numerical approach for simulating light-induced charge transport dynamics across a metal-molecule-metal conductance junction. The finite-difference time-domain method is used to simulate the plasmonic response of the metal structures. The Huygens subgridding technique, as adapted to Lorentz media, is used to bridge the vastly disparate length scales of the plasmonic metal electrodes and the molecular system, maintaining accuracy. The charge and current densities calculated with classical electrodynamics are transformed to an electronic wavefunction, which is then propagated through the molecular linker via the Heisenberg equations of motion. We focus mainly on development of the theory and exemplify our approach by a numerical illustration of a simple system consisting of two silver cylinders bridged by a three-site molecular linker. The electronic subsystem exhibits fascinating light driven dynamics, wherein the charge density oscillates at the driving optical frequency, exhibiting also the natural system timescales, and a resonance phenomenon leads to strong conductance enhancement.

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

    SciTech Connect

    Zhou, Changjie; Zhu, Huili; Yang, Weihuang

    2015-06-07

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

  11. Electron emission in collisions of highly charged ions with atoms and diatomic molecules

    NASA Astrophysics Data System (ADS)

    Rivarola, R. D.; Fainstein, P. D.

    2003-05-01

    A short review of theoretical models previously used to study single and multiple electron ionization in collisions of bare fast highly charged ions with atomic and diatomic molecular targets is given. Electron emission with simultaneous electron capture by the projectile is also considered. The principal mechanisms producing the different reactions are revisited. It is emphasized that two-center descriptions are necessary for an adequate description of the existing experimental data. The role of electron correlation in the initial bound state and during the collision process is analyzed as well as the presence of effects associated with the two-center character of diatomic molecular targets.

  12. Voltage-induced conformational changes and current control in charge transfer through molecules

    NASA Astrophysics Data System (ADS)

    Kecke, Lars; Ankerhold, Joachim

    2012-06-01

    Transport through molecular contacts with a sluggish intramolecular vibrational mode strongly coupled to excess charges is studied far from equilibrium. A Born-Oppenheimer approximation in steady state reveals voltage-dependent energy surfaces, which cause abrupt conformational changes of the molecular backbone. These are directly related to transitions between current plateaus, which are relatively robust against thermal fluctuations. In a regime accessible in experiments this allows the operation of a molecular junction as a current switch or as a molecular machine in form of a valve controlled by time-dependent bias and gate voltages.

  13. [A molecular dynamics study of the interaction between domain I-BAR of the IRSp53 protein and negatively charged membranes].

    PubMed

    Levtsova, O V; Davletov, I D; Sokolova, O S; Sha?tan, K V

    2011-01-01

    The methods of computer simulation in full-atomic and large-grain approximations have been used to study specific interactions of the isolated domain I-BAR of the actin-binding protein IRSp53 and model membranes containing neutral phospholipids, as well as membranes containing high amounts of negatively charged PI(4,5)P2 phospholipids. It has been shown that the I-BAR domain does not interact with neutral lipids but induces the bending of the synthetic membrane rich in negatively charged phospholipids. A clusterization of charged lipids on the surface of the membrane at the sites of its interaction with the protein has been observed. This indicates that the interaction of the I-BAR protein with negatively charged lipids is of electrostatic and hydrophobic nature. PMID:21542353

  14. Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations.

    PubMed

    List, Nanna Holmgaard; Zaleśny, Robert; Murugan, N Arul; Kongsted, Jacob; Bartkowiak, Wojciech; Ågren, Hans

    2015-09-01

    We establish the relationships between the metric of charge transfer excitation (Δr) for the bright ππ* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push-pull π-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), Δr is a measure for the average hole-electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push-pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through Δr; if β ∼ (Δr)(k), then roughly, δ(TPA) ∼ (Δr)(k+1). Second, a simple power relation between Δr and the molecular hyperpolarizabilities of push-pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull π-conjugated systems through the metric of charge transfer. PMID:26575913

  15. Charge Exchange and Fragmentation in Slow Collisions of He2+ with Water Molecules

    NASA Astrophysics Data System (ADS)

    Stolterfoht, N.; Cabrera-Trujillo, R.; Hellhammer, R.; Pesic, Z.; Deumens, E.; hrn, Y.; Sabin, J. R.

    Cross sections for charge exchange and fragmentation in the collision system He2+ + H2O are investigated experimentally and theoretically at projectile energies of a few keV. Different experimental methods analyzing scattered projectiles, fragment ions and ejected photons are reviewed. Scattered and fragment ions were measured in the angular range from 25 to 135 with respect to the incident beam direction. The spectra provide evidence for the fragmentation mechanisms of Coulomb explosion and binary collisions. Emphasis is given to protons originating from collisions at large impact parameters involving the Coulomb explosion mechanism. Cross sections for proton ejections, differential in the observation angle d[sigma]/d[Omega], are found to be anisotropic with a maximum near 90. The theoretical investigation is carried out within the Electron-Nuclear Dynamics approach to take into account the coupling of the electrons and nuclei. The method is based on the evolution of a coherent state representation of the supermolecule wavefunction within the time-dependent variational principle. We calculate differential and total cross sections for the scattering of the projectile, charge transfer, and fragmentation of the system products. We find good agreement with the experimental data. In particular, we find that double electron capture occurs for impact parameters below 3.0 a.u. and produces full fragmentation of H2O independent of the target orientation.

  16. Cell Type-Specific Activation of AKT and ERK Signaling Pathways by Small Negatively-Charged Magnetic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

    2012-11-01

    The interaction of nanoparticles (NPs) with living organisms has become a focus of public and scientific debate due to their potential wide applications in biomedicine, but also because of unwanted side effects. Here, we show that superparamagnetic iron oxide NPs (SPIONs) with different surface coatings can differentially affect signal transduction pathways. Using isogenic pairs of breast and colon derived cell lines we found that the stimulation of ERK and AKT signaling pathways by SPIONs is selectively dependent on the cell type and SPION type. In general, cells with Ras mutations respond better than their non-mutant counterparts. Small negatively charged SPIONs (snSPIONs) activated ERK to a similar extent as epidermal growth factor (EGF), and used the same upstream signaling components including activation of the EGF receptor. Importantly, snSPIONs stimulated the proliferation of Ras transformed breast epithelial cells as efficiently as EGF suggesting that NPs can mimic physiological growth factors.

  17. Constitutive MHC class I molecules negatively regulate TLR-triggered inflammatory responses via the Fps-SHP-2 pathway.

    PubMed

    Xu, Sheng; Liu, Xingguang; Bao, Yan; Zhu, Xuhui; Han, Chaofeng; Zhang, Peng; Zhang, Xuemin; Li, Weihua; Cao, Xuetao

    2012-06-01

    The molecular mechanisms that fine-tune Toll-like receptor (TLR)-triggered innate inflammatory responses remain to be fully elucidated. Major histocompatibility complex (MHC) molecules can mediate reverse signaling and have nonclassical functions. Here we found that constitutively expressed membrane MHC class I molecules attenuated TLR-triggered innate inflammatory responses via reverse signaling, which protected mice from sepsis. The intracellular domain of MHC class I molecules was phosphorylated by the kinase Src after TLR activation, then the tyrosine kinase Fps was recruited via its Src homology 2 domain to phosphorylated MHC class I molecules. This led to enhanced Fps activity and recruitment of the phosphatase SHP-2, which interfered with TLR signaling mediated by the signaling molecule TRAF6. Thus, constitutive MHC class I molecules engage in crosstalk with TLR signaling via the Fps-SHP-2 pathway and control TLR-triggered innate inflammatory responses. PMID:22522491

  18. Integrating high electrical conductivity and photocatalytic activity in cotton fabric by cationizing for enriched coating of negatively charged graphene oxide.

    PubMed

    Sahito, Iftikhar Ali; Sun, Kyung Chul; Arbab, Alvira Ayoub; Qadir, Muhammad Bilal; Jeong, Sung Hoon

    2015-10-01

    Electroconductive textiles have attended tremendous focus recently and researchers are making efforts to increase conductivity of e-textiles, in order to increase the use of such flexible and low cost textile materials. In this study, surface conductivity and photo catalytic activity of standard cotton fabric (SCF) was enhanced by modifying its surface charge, from negative to positive, using Bovine Serum Albumin (BSA) as a cationic agent, to convert it into cationised cotton fabric (CCF). Then, both types of fabrics were dip coated with a simple dip and dry technique for the adsorption of negatively charged graphene oxide (GO) sheets onto its surface. This resulted in 67.74% higher loading amount of GO on the CCF making self-assembly. Finally, this coating was chemically converted by vapor reduction using hydrazine hydrate to reduced graphene oxide (rGO) for restoration of a high electrical conductivity at the fabric surface. Our results revealed that with such high loading of GO, the surface resistance of CCF was only 40Ω/sq as compared to 510Ω/sq of the SCF and a 66% higher photo catalytic activity was also achieved through cationization for improved GO coating. Graphene coated SCF and CCF were characterized using FE-SEM, FTIR, Raman, UV-vis, WAXD, EDX and XPS spectroscopy to ascertain successful reduction of GO to rGO. The effect of BSA treatment on adsorption of cotton fabric was studied using drop shape analyzer to measure contact angle and for thermal and mechanical resistance, the fabric was tested for TGA and tensile strength, respectively. rGO coated fabric also showed slightly improved thermal stability yet a minor loss of strength was observed. The high flexibility, photocatalytic activity and excellent conductivity of this fabric suggests that it can be used as an electrode material for various applications. PMID:26076630

  19. Exposure to negatively charged-particle dominant air-conditions on human lymphocytes in vitro activates immunological responses.

    PubMed

    Nishimura, Yasumitsu; Takahashi, Kazuaki; Mase, Akinori; Kotani, Muneo; Ami, Kazuhisa; Maeda, Megumi; Shirahama, Takashi; Lee, Suni; Matsuzaki, Hidenori; Kumagai-Takei, Naoko; Yoshitome, Kei; Otsuki, Takemi

    2015-12-01

    Indoor air-conditions may play an important role in human health. Investigation of house conditions that promote health revealed that negatively charged-particle dominant indoor air-conditions (NAC) induced immune stimulation. NAC was established using fine charcoal powder on walls and ceilings and utilizing forced negatively charged particles (approximate diameter: 20 nm) dominant in indoor air-conditions created by applying an electric voltage (72 V) between the backside of the walls and the ground. We reported previously that these conditions induced a slight and significant increase of interleukin-2 during 2.5 h stay, and an increase of natural killer (NK) cell cytotoxicity, when examining human subjects after a two-week night stay under these conditions. In the present study, we investigated whether exposure to NAC in vitro affects immune conditions. Although the concentrations of particles were different, an incubator for cell culture with NAC was set and cellular compositions and functions of various freshly isolated human lymphocytes derived from healthy donors were assayed in the NAC incubator and compared with those of cultures in a standard (STD) incubator. Results showed that NAC cultivation caused an increase of CD25 and PD-1 expressing cells in the CD4 positive fraction, enhancement of NK cell cytotoxicity, production of interferon-y (IFNγ), and slight enhancement of regulatory T cell function. In addition, the formula designated as the "immune-index" clearly differed between STD and NAC culture conditions. Thus, NAC conditions may promote human health through slight activation of the immune system against cancer cells and virus infection as shown by this in vitro study and our previously reported human studies. PMID:26213096

  20. Targeted delivery of chemically modified anti-miR-221 to hepatocellular carcinoma with negatively charged liposomes

    PubMed Central

    Zhang, Wendian; Peng, Fangqi; Zhou, Taotao; Huang, Yifei; Zhang, Li; Ye, Peng; Lu, Miao; Yang, Guang; Gai, Yongkang; Yang, Tan; Ma, Xiang; Xiang, Guangya

    2015-01-01

    Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death. Gene therapy was established as a new strategy for treating HCC. To explore the potential delivery system to support the gene therapy of HCC, negatively charged liposomal delivery system was used to deliver miR-221 antisense oligonucleotide (anti-miR-221) to the transferrin (Tf) receptor over expressed HepG2 cells. The liposome exhibited a mean particle size of 122.5 nm, zeta potential of ?15.74 mV, anti-miR-221 encapsulation efficiency of 70%, and excellent colloidal stability at 4C. Anti-miR-221-encapsulated Tf-targeted liposome demonstrated a 15-fold higher delivery efficiency compared to nontargeted liposome in HepG2 cells in vitro. Anti-miR-221 Tf-targeted liposome effectively delivered anti-miR-221 to HepG2 cells, upregulated miR-221 target genes PTEN, P27kip1, and TIMP3, and exhibited greater silencing efficiency over nontargeted anti-miR-221 liposome. After intravenous injection into HepG2 tumor-bearing xenografted mice with Cy3-labeled anti-miR-221 Tf-targeted liposome, Cy3-anti-miR-221 was successfully delivered to the tumor site and increased the expressions of PTEN, P27kip1, and TIMP3. Our results demonstrate that the Tf-targeted negatively charged liposome could be a potential therapeutic modality in the gene therapy of human HCC. PMID:26251599

  1. First-principles study of compensation mechanisms in negatively charged LaGaO3/MgAl2O4 interfaces

    NASA Astrophysics Data System (ADS)

    Rbola, Alejandro; Fong, Dillon D.; Eastman, Jeffrey A.; ?t, Serdar; Zapol, Peter

    2013-06-01

    Thin film oxide heterostructures with a bound charge at the interface require electrical compensation, which can involve redistribution of mobile charge carriers. We explore a model LaGaO3(001)//MgAl2O4(001) heterostructure with nominally negatively charged interfaces using first-principles methods and a Poisson-Boltzmann equation. We find that charge compensation by oxygen vacancies with quadratically decaying concentration away from the interface is more favorable than electronic redistribution. These vacancies have a potential to enhance ionic conductivity along the interfaces.

  2. Negatively charged silver nanoparticles cause retinal vascular permeability by activating plasma contact system and disrupting adherens junction.

    PubMed

    Long, Yan-Min; Zhao, Xing-Chen; Clermont, Allen C; Zhou, Qun-Fang; Liu, Qian; Feener, Edward P; Yan, Bing; Jiang, Gui-Bin

    2016-05-01

    Silver nanoparticles (AgNPs) have been extensively used as antibacterial component in numerous healthcare, biomedical and consumer products. Therefore, their adverse effects to biological systems have become a major concern. AgNPs have been shown to be absorbed into circulation and redistributed into various organs. It is thus of great importance to understand how these nanoparticles affect vascular permeability and uncover the underlying molecular mechanisms. A negatively charged mecaptoundeonic acid-capped silver nanoparticle (MUA@AgNP) was investigated in this work. Ex vivo experiments in mouse plasma revealed that MUA@AgNPs caused plasma prekallikrein cleavage, while positively charged or neutral AgNPs, as well as Ag ions had no effect. In vitro tests revealed that MUA@AgNPs activated the plasma kallikrein-kinin system (KKS) by triggering Hageman factor autoactivation. By using specific inhibitors aprotinin and HOE 140, we demonstrated that KKS activation caused the release of bradykinin, which activated B2 receptors and induced the shedding of adherens junction protein, VE-cadherin. These biological perturbations eventually resulted in endothelial paracellular permeability in mouse retina after intravitreal injection of MUA@AgNPs. The findings from this work provided key insights for toxicity modulation and biomedical applications of AgNPs. PMID:26399585

  3. Positive/negative surface charge of chitosan based nanogels and its potential influence on oral insulin delivery.

    PubMed

    Wang, Juan; Xu, Mengxue; Cheng, Xiaojie; Kong, Ming; Liu, Ya; Feng, Chao; Chen, Xiguang

    2016-01-20

    To develop insulin delivery system for the treatment of diabetes, two insulin-loaded nanogels with opposite zeta potential (-15.94 ± 0.449 mV for insulin:CMCS/CS-NGs(-) and +17.15 ± 0.492 mV for insulin:CMCS/CS-NGs(+)) were obtained. Ex vivo results showed that the nanogels with opposite surface charge exhibited different adhesion and permeation in specific intestinal segments. There was no significant differences in adhesion and permeation in rat duodenum, but in rat jejunum, insulin:CMCS/CS-NGs(-) exhibited enhanced adhesion and permeation, which were about 3 folds (adhesion) and 1.7 folds (permeation) higher than insulin:CMCS/CS-NGs(+). These results demonstrated that the surface charge property of nanogels determined the absorption sites of CMCS/CS-NGs in small intestine. In vivo study, the blood glucose level in insulin:CMCS/CS-NGs(-) group had 3 mmol/L lower than insulin:CMCS/CS-NGs(+) group during 1h to 11h after the oral administration, which demonstrated that negative insulin:CMCS/CS-NGs had a better management of blood glucose than positive ones. PMID:26572423

  4. Isomer-selected photoelectron spectroscopy of isolated DNA oligonucleotides: phosphate and nucleobase deprotonation at high negative charge states.

    PubMed

    Vonderach, Matthias; Ehrler, Oli T; Matheis, Katerina; Weis, Patrick; Kappes, Manfred M

    2012-05-01

    Fractionation according to ion mobility and mass-to-charge ratio has been used to select individual isomers of deprotonated DNA oligonucleotide multianions for subsequent isomer-resolved photoelectron spectroscopy (PES) in the gas phase. Isomer-resolved PE spectra have been recorded for tetranucleotides, pentanucleotides, and hexanucleotides. These were studied primarily in their highest accessible negative charge states (3-, 4-, and 5-, respectively), as provided by electrospraying from room temperature solutions. In particular, the PE spectra obtained for pentanucleotide tetraanions show evidence for two coexisting classes of gas-phase isomeric structures. We suggest that these two classes comprise: (i) species with excess electrons localized exclusively at deprotonated phosphate backbone sites and (ii) species with at least one deprotonated base (in addition to several deprotonated phosphates). By permuting the sequence of bases in various [A(5-x)T(x)](4-) and [GT(4)](4-) pentanucleotides, we have established that the second type of isomer is most likely to occur if the deprotonated base is located at the first or last position in the sequence. We have used a combination of molecular mechanics and semiempirical calculations together with a simple electrostatic model to explore the photodetachment mechanism underlying our photoelectron spectra. Comparison of predicted to measured photoelectron spectra suggests that a significant fraction of the detected electrons originates from the DNA bases (both deprotonated and neutral). PMID:22524691

  5. Quantum effects in electron emission from and accretion on negatively charged spherical particles in a complex plasma

    SciTech Connect

    Mishra, S. K.; Sodha, M. S.; Misra, Shikha

    2012-07-15

    The authors have investigated the electron emissions (thermionic, electric field, photoelectric, and light induced field) from and electron accretion on a charged particle in a complex plasma, on the basis of a three region electrical potential model in and around a charged spherical particle in a complex plasma, characterized by Debye shielding. A continuous variation of the transmission coefficient across the surface of a particle (corresponding to emission and accretion) with the radial electron energy {epsilon}{sub r} has been obtained. It is seen that the numerical values of the emission and accretion transmission coefficients [D({epsilon}{sub r})] are almost the same. This is the necessary and sufficient condition for the validity of Saha's equation for thermal equilibrium of a system of dust and electrons. This is in contrast to the earlier condition, which limited the range of validity of Saha's equation to the range of the applicability of Born approximation. It is seen that D({epsilon}{sub r}) increases with increasing {epsilon}{sub r}, increasing negative electric potential on the surface, decreasing radius, and deceasing Debye length. The electron currents, corresponding to thermionic, electric field, photoelectric and light induced field emission increase with increasing surface potential; this fact may have significant repercussions in complex plasma kinetics. Since numerically D({epsilon}{sub r}) is significantly different from unity in the range of {epsilon}{sub r} of interest, it is necessary to take into account the D({epsilon}{sub r})-{epsilon}{sub r} dependence in complex plasma theory.

  6. Comparison of Positively and Negatively Charged Achiral Co-Monomers Added to Cyclodextrin Monolith: Improved Chiral Separations in Capillary Electrochromatography

    PubMed Central

    Lu, Yang; Shamsi, Shahab A.

    2014-01-01

    Cyclodextrins (CDs) and their derivatives have been one of the most popular and successful chiral additives used in electrokinetic chromatography because of the presence of multiple chiral centers, which leads to multiple chiral interactions. However, there has been relatively less published work on the use of CDs as monolithic media for capillary electrochromatography (CEC). The goal of this study was to show how the addition of achiral co-monomer to a polymerizable CD such as glycidyl methacrylate β-cyclodextrin (GMA/β-CD) can affect the enantioselective separations in monolithic CEC. To achieve this goal, polymeric monoliths columns were prepared by co-polymerizing GMA/β-CD with cationic or anionic achiral co-monomers [(2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and vinyl benzyltrimethyl-ammonium (VBTA)] in the presence of conventional crosslinker (ethylene dimethacrylate) and ternary porogen system including butanediol, propanol and water. A total of 34 negatively charged compounds, 30 positively charged compounds and 33 neutral compounds were screened to compare the enantioresolution capability on the GMA/β-CD, GMA/β-CD-VBTA and GMA/β-CD-AMPS monolithic columns. PMID:24108813

  7. Comparison of positively and negatively charged achiral co-monomers added to cyclodextrin monolith: improved chiral separations in capillary electrochromatography.

    PubMed

    Lu, Yang; Shamsi, Shahab A

    2014-10-01

    Cyclodextrins (CDs) and their derivatives have been one of the most popular and successful chiral additives used in electrokinetic chromatography because of the presence of multiple chiral centers, which leads to multiple chiral interactions. However, there has been relatively less published work on the use of CDs as monolithic media for capillary electrochromatography (CEC). The goal of this study was to show how the addition of achiral co-monomer to a polymerizable CD such as glycidyl methacrylate β-cyclodextrin (GMA/β-CD) can affect the enantioselective separations in monolithic CEC. To achieve this goal, polymeric monoliths columns were prepared by co-polymerizing GMA/β-CD with cationic or anionic achiral co-monomers [(2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and vinyl benzyltrimethyl-ammonium (VBTA)] in the presence of conventional crosslinker (ethylene dimethacrylate) and ternary porogen system including butanediol, propanol and water. A total of 34 negatively charged compounds, 30 positively charged compounds and 33 neutral compounds were screened to compare the enantioresolution capability on the GMA/β-CD, GMA/β-CD-VBTA and GMA/β-CD-AMPS monolithic columns. PMID:24108813

  8. One-step solvothermal synthesis of highly water-soluble, negatively charged superparamagnetic Fe3O4 colloidal nanocrystal clusters.

    PubMed

    Gao, Jining; Ran, Xinze; Shi, Chunmeng; Cheng, Humin; Cheng, Tianmin; Su, Yongping

    2013-08-01

    Highly charged hydrophilic superparamagnetic Fe3O4 colloidal nanocrystal clusters with an average diameter of 195 nm have been successfully synthesized using a modified one-step solvothermal method. Anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt containing both sulfonate and carboxylate groups was used as the stabilizer. The clusters synthesized under different experimental conditions were characterized with transmission electron microscopy and dynamic light scattering; it was found that the size distribution and water dispersity were significantly affected by the concentration of the polyelectrolyte stabilizer and iron sources in the reaction mixtures. A possible mechanism involving novel gel-like large molecular networks that confined the nucleation and aggregation process was proposed and discussed. The colloidal nanocrystal clusters remained negatively charged in the experimental pH ranges from 2 to 11, and also showed high colloidal stability in phosphate buffered saline (PBS) and ethanol. These highly colloidal stable superparamagnetic Fe3O4 clusters could find potential applications in bioseparation, targeted drug delivery, and photonics. PMID:23803791

  9. Charge transfer states appear in the π-conjugated pure hydrocarbon molecule on Cu(111)

    NASA Astrophysics Data System (ADS)

    Yonezawa, Keiichirou; Suda, Yosuke; Yanagisawa, Susumu; Hosokai, Takuya; Kato, Kengo; Yamaguchi, Takuma; Yoshida, Hiroyuki; Ueno, Nobuo; Kera, Satoshi

    2016-04-01

    We report on the results of experimental and theoretical studies on the electronic structure of gas-phase diindenoperylene (DIP) and DIP-monolayer (ML) on Cu(111). Vapor-phase ultraviolet photoelectron spectroscopy (UPS) was realized for 11.3 mg of DIP, giving reference orbital energies of isolated DIP, and UPS and inverse photoemission spectroscopy of DIP-ML/graphite were performed to obtain DIP-ML electronic states at a weak interfacial interaction. Furthermore, first-principles calculation clearly demonstrates the interfacial rearrangement. These results provide evidence that the rearrangement of orbital energies, which is realized in HOMO–LUMO and HOMO–HOMO‑1 gaps, brings partially occupied LUMO through the surface-induced aromatic stabilization of DIP, a pure hydrocarbon molecule, on Cu(111).

  10. Associating a negatively charged GdDOTA-derivative to the Pittsburgh compound B for targeting Aβ amyloid aggregates.

    PubMed

    Martins, André F; Oliveira, Alexandre C; Morfin, Jean-François; Laurents, Douglas V; Tóth, Éva; Geraldes, Carlos F G C

    2016-03-01

    We have conjugated the tetraazacyclododecane-tetraacetate (DOTA) chelator to Pittsburgh compound B (PiB) forming negatively charged lanthanide complexes, Ln(L4), with targeting capabilities towards aggregated amyloid peptides. The amphiphilic Gd(L4) chelate undergoes micellar aggregation in aqueous solution, with a critical micellar concentration of 0.68 mM, lower than those for the neutral complexes of similar structure. A variable temperature (17)O NMR and NMRD study allowed the assessment of the water exchange rate, k ex (298)  = 9.7 × 10(6) s(-1), about the double of GdDOTA, and for the description of the rotational dynamics for both the monomeric and the micellar forms of Gd(L4). With respect to the analogous neutral complexes, the negative charge induces a significant rigidity of the micelles formed, which is reflected by slower and more restricted local motion of the Gd(3+) centers as evidenced by higher relaxivities at 20-60 MHz. Surface Plasmon Resonance results indicate that the charge does not affect significantly the binding strength to Aβ1-40 [K d = 194 ± 11 μM for La(L4)], but it does enhance the affinity constant to human serum albumin [K a = 6530 ± 68 M(-1) for Gd(L4)], as compared to neutral counterparts. Protein-based NMR points to interaction of Gd(L4) with Aβ1-40 in the monomer state as well, in contrast to neutral complexes interacting only with the aggregated form. Circular dichroism spectroscopy monitored time- and temperature-dependent changes of the Aβ1-40 secondary structure, indicating that Gd(L4) stabilizes the random coil relative to the α-helix and β-sheet. TEM images confirm that the Gd(L4) complex reduces the formation of aggregated fibrils. PMID:26613605

  11. Ion Accelerator With Negatively Biased Decelerator Grid

    NASA Technical Reports Server (NTRS)

    Brophy, John R.

    1994-01-01

    Three-grid ion accelerator in which accelerator grid is biased at negative potential and decelerator grid downstream of accelerator grid biased at smaller negative potential. This grid and bias arrangement reduces frequency of impacts, upon accelerator grid, of charge-exchange ions produced downstream in collisions between accelerated ions and atoms and molecules of background gas. Sputter erosion of accelerator grid reduced.

  12. Antitumor potential of a synthetic interferon-alpha/PLGF-2 positive charge peptide hybrid molecule in pancreatic cancer cells

    PubMed Central

    Yin, Hongmei; Chen, Naifei; Guo, Rui; Wang, Hong; Li, Wei; Wang, Guanjun; Cui, Jiuwei; Jin, Haofan; Hu, Ji-Fan

    2015-01-01

    Pancreatic cancer is the most aggressive malignant disease, ranking as the fourth leading cause of cancer-related death among men and women in the United States. Interferon alpha (IFNα) has been used to treat pancreatic cancer, but its clinical application has been significantly hindered due to the low antitumor activity. We used a “cDNA in-frame fragment library” screening approach to identify short peptides that potentiate the antitumor activity of interferons. A short positively charged peptide derived from the C-terminus of placental growth factor-2 (PLGF-2) was selected to enhance the activity of IFNα. For this, we constructed a synthetic interferon hybrid molecule (SIFα) by fusing the positively charged PLGF-2 peptide to the C-terminus of the human IFNα. Using human pancreatic cell lines (ASPC and CFPAC1) as a model system, we found that SIFα exhibited a significantly higher activity than did the wild-type IFNα in inhibiting the tumor cell growth. The enhanced activity of the synthetic SIFα was associated with the activation of interferon pathway target genes and the increased binding of cell membrane receptor. This study demonstrates the potential of a synthetic SIFα as a novel antitumor agent. PMID:26584517

  13. Basis-generator-method study of ionization and fragmentation of water molecules by multiply-charged ion impact

    NASA Astrophysics Data System (ADS)

    Kirchner, Tom; Horbatsch, M.; Murakami, M.; Pausz, T.; Ldde, H. J.

    2013-09-01

    In a recent series of publications we have described the adaptation of the basis generator method (BGM), originally developed for ion-atom collisions, to molecular targets and have reported on results for proton and He+-ion impact on H2O molecules. The microscopic collision calculations were complemented with a semi-phenomenological fragmentation model, which in contrast to previous models takes multiple electron removal processes into account. This turned out to be crucial for obtaining reasonable agreement with experimental data for the production of singly charged fragment ions. In this contribution, we report on results obtained from using the same methodology for bare helium, lithium, and carbon ion impact on H2O in the 20-5000 keV/amu regime and compare them with experimental data and previous calculations where available. In addition, we will discuss the usefulness of ternary plots to provide a somewhat more general view on fragmentation in ion-water-molecule collisions. This work is supported in part by NSERC Canada.

  14. Charge competition with oxygen molecules determines the growth of gold particles on doped CaO films.

    PubMed

    Cui, Yi; Huang, Kai; Nilius, Niklas; Freund, Hans-Joachim

    2013-01-01

    The influence of gas-phase oxygen on the growth of Au nanoparticles on Mo-doped CaO films has been investigated by means of low temperature scanning tunnelling microscopy and X-ray photoelectron spectroscopy. Whereas at ideal vacuum conditions, only 2D Au islands develop on the oxide surface, the fraction of 3D deposits increases with increasing O2 pressure until they become the dominant species in 106 mbar oxygen. The morphology crossover arises from changes in the interfacial electron flow between Mo donors in the CaO lattice and different ad-species on the oxide surface. In the absence of 02 molecules, the donor electrons are predominately transferred to the Au ad-atoms, which consequently experience enhanced binding to the oxide surface and agglomerate into 2D islands. In an oxygen atmosphere, on the other hand, a substantial fraction of the excess electrons is trapped by adsorbed O2 molecules, while the Au atoms remain neutral and assemble into tall 3D particles that are typical for non-doped oxides. Our experiments demonstrate how the competition for charge between different adsorbates governs the physical and chemical properties of doped oxides, so widely used in heterogeneous catalysis. PMID:24015581

  15. Enhancement of three-photon absorption cross-sections in a novel class of symmetrical charge transfer fluorene-based molecules

    NASA Astrophysics Data System (ADS)

    Ma, Wenbo; Wu, Yiqun; Han, Junhe; Gu, Donghong; Gan, Fuxi

    2005-07-01

    The three-photon absorption effect (3PA) of two novel symmetrical charge transfer fluorene-based molecules (abbreviated as BASF and BMOSF) has been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 84 10 -78 and 114 10 -78 cm 6 s 2, respectively. The geometries and electronic excitations of these two molecules are systematically studied by PM3 and ZINDO/S methods. The relationships between 3PA cross-sections and intramolecular charge transfer are discussed micromechanically. The experimental and theoretical results have shown that the larger intramolecular charge transfer, which was characterized by the charge density difference between the ground state (S 0) and the first excited state (S 1), the greater enhancement of the 3PA cross-sections.

  16. The reactions of the molecular nitrogen doubly charged ion with neutral molecules of relevance to planetary ionospheres

    NASA Astrophysics Data System (ADS)

    Ricketts, Claire Louise

    Diatomic dications (e.g. C02+) have been known to exist for several decades and are believed to be important components of energised media. Molecular dications possess significant internal energy due to the Coulombic repulsion of their two positive charges, meaning that many possible reaction channels are available to dications in a collision with a neutral molecule. Modellers have recently predicted that N22+ is present in the ionosphere of Earth and Titan as well as the dications C>22+ and 02+ in the ionosphere of Earth and CC>22+ in the ionosphere of Mars. These recent predictions, of dications in planetary ionospheres, imply that dications, and processes involving dication-neutral collisions, may have more significance than previously thought in the upper atmospheres of planets. Therefore this thesis describes a study of the reactions between N2 dications and neutrals, potentially of relevance to the ionosphere of Earth and Titan. A position sensitive coincidence (PSCO) time-of flight (TOF) mass spectrometer is used to probe the reactivity, energetics and dynamics of the bimolecular reactions of N22 . Dication-neutrals reactions often result in a pair of singly charged ions. The PSCO experiment is used to collect these pairs of singly-charged ions in coincidence. From the position-sensitive data we extract the velocity vectors of the product ions, and if the reaction of interest involves the formation of a third, undetected, neutral species, its velocity can be determined via conservation of momentum. The electron transfer reactions between dications and neutrals have been well rationalized 2+ previously, so only the electron transfer reactions of N2 with Ne and NO are discussed in this thesis. This thesis concentrates on probing the less well rationalized, bond- forming reactions between dications and neutrals. The bond-forming reactions of N22+ with O2, CO2, H2O, C2H2, CH4, H2 and Ar have been investigated and discussed. Several new bond-forming reactions mechanisms are derived for example, the bond-forming reactions of N22+ with O2 proceed via a 'long' lived complex which dissociates via loss of a neutral and then charge separation, a mechanism which is also operating for one of the bond-forming reactions of N2 with CO2 and N2 with H2O. Additional bond-forming reactions are detected for N22+ with CO2 and H2O, which proceed via shorter lived collision complexes. The reactions of N22+ with C2H2, CH4, H2 and Ar all proceed via a variety of mechanisms involving short-lived collision complexes or H and electron stripping.

  17. Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ.

    PubMed

    García, Raúl; Herranz, M Ángeles; Leary, Edmund; González, M Teresa; Bollinger, Gabino Rubio; Bürkle, Marius; Zotti, Linda A; Asai, Yoshihiro; Pauly, Fabian; Cuevas, Juan Carlos; Agraït, Nicolás; Martín, Nazario

    2015-01-01

    We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a π-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10(-7) G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species. PMID:26199662

  18. Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ

    PubMed Central

    García, Raúl; Herranz, M Ángeles; González, M Teresa; Bollinger, Gabino Rubio; Bürkle, Marius; Zotti, Linda A; Asai, Yoshihiro; Pauly, Fabian; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-01-01

    Summary We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a π-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10−7 G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species. PMID:26199662

  19. Manufacturing and characterization of bent silicon crystals for studies of coherent interactions with negatively charged particles beams

    NASA Astrophysics Data System (ADS)

    Germogli, G.; Mazzolari, A.; Bandiera, L.; Bagli, E.; Guidi, V.

    2015-07-01

    Efficient steering of GeV-energy negatively charged particle beams was demonstrated to be possible with a new generation of thin bent silicon crystals. Suitable crystals were produced at the Sensor Semiconductor Laboratory of Ferrara starting from Silicon On Insulator wafers, adopting proper revisitation of silicon micromachining techniques such as Low Pressure Chemical Vapor Deposition, photolithography and anisotropic chemical etching. Mechanical holders, which allow to properly bend the crystal and to reduce unwanted torsions, were employed. Crystallographic directions and crystal holder design were optimized in order to excite quasi-mosaic effect along (1 1 1) planes. Prior to exposing the crystal to particle beams, a full set of characterizations were performed. Infrared interferometry was used to measure crystal thickness with high accuracy. White-light interferometry was employed to characterize surface deformational state and its torsion. High-resolution X-rays diffraction was used to precisely measure crystal bending angle along the beam. Manufactured crystals were installed and tested at the MAMI MAinz MIcrotron to steer sub-GeV electrons, and at SLAC to deflect an electron beam in the 1 to 10 GeV energy range.

  20. Bid binding to negatively charged phospholipids may not be required for its pro-apoptotic activity in vivo.

    PubMed

    Manara, Anna; Lindsay, Jennefer; Marchioretto, Marta; Astegno, Alessandra; Gilmore, Andrew P; Esposti, Mauro Degli; Crimi, Massimo

    2009-10-01

    Bid is a ubiquitous pro-apoptotic member of the Bcl-2 family that has been involved in a variety of pathways of cell death. Unique among pro-apoptotic proteins, Bid is activated after cleavage by the apical caspases of the extrinsic pathway; subsequently it moves to mitochondria, where it promotes the release of apoptogenic proteins in concert with other Bcl-2 family proteins like Bak. Diverse factors appear to modulate the pro-apoptotic action of Bid, from its avid binding to mitochondrial lipids (in particular, cardiolipin) to multiple phosphorylations at sites that can modulate its caspase cleavage. This work addresses the question of how the lipid interactions of Bid that are evident in vitro actually impact on its pro-apoptotic action within cells. Using site-directed mutagenesis, we identified mutations that reduced mouse Bid lipid binding in vitro. Mutation of the conserved residue Lys157 specifically decreased the binding to negatively charged lipids related to cardiolipin and additionally affected the rate of caspase cleavage. However, this lipid-binding mutant had no discernable effect on Bid pro-apoptotic function in vivo. The results are interpreted in relation to an underlying interaction of Bid with lysophosphatidylcholine, which is not disrupted in any mutant retaining pro-apoptotic function both in vitro and in vivo. PMID:19463967

  1. Bid binding to negatively charged phospholipids may not be required for its pro-apoptotic activity in vivo

    PubMed Central

    Manara, Anna; Lindsay, Jennefer; Marchioretto, Marta; Astegno, Alessandra; Gilmore, Andrew P.; Esposti, Mauro Degli; Crimi, Massimo

    2010-01-01

    Bid is a ubiquitous pro-apoptotic member of the Bcl-2 family that has been involved in a variety of pathways of cell death. Unique among pro-apoptotic proteins, Bid is activated after cleavage by the apical caspases of the extrinsic pathway; subsequently it moves to mitochondria, where it promotes the release of apoptogenic proteins in concert with other Bcl-2 family proteins like Bak. Diverse factors appear to modulate the pro-apoptotic action of Bid, from its avid binding to mitochondrial lipids (in particular, cardiolipin) to multiple phosphorylations at sites that can modulate its caspase cleavage. This work addresses the question of how the lipid interactions of Bid that are evident in vitro actually impact on its pro-apoptotic action within cells. Using site-directed mutagenesis, we identified mutations that reduced mouse Bid lipid binding in vitro. Mutation of the conserved residue Lys157 specifically decreased the binding to negatively charged lipids related to cardiolipin and additionally affected the rate of caspase cleavage. However, this lipid-binding mutant had no discernable effect on Bid pro-apoptotic function in vivo. The results are interpreted in relation to an underlying interaction of Bid with lysophosphatidylcholine, which is not disrupted in any mutant retaining pro-apoptotic function both in vitro and in vivo. PMID:19463967

  2. The association of defensin HNP-2 with negatively charged membranes: A combined fluorescence and linear dichroism study.

    PubMed

    Pridmore, Catherine J; Rodger, Alison; Sanderson, John M

    2016-04-01

    The association of defensin HNP-2 with negatively charged membranes has been studied using a new approach that combines fluorescence and linear dichroism (LD) spectroscopies with simulated LD spectra in order to characterise the binding kinetics and bound configurations of the peptide. Binding to membranes composed of mixtures of diacylglycerophosphocholines (PC) with either diacylglycerophosphoglycerol (PG) or diacylglycerophosphoserine (PS) was conducted at lipid:peptide ratios that yielded binding, but not membrane fusion. HNP-2 association with membranes under these conditions was a 2 stage-process, with both stages exhibiting first order kinetics. The fast initial step, with a half-life of <1min, was followed by a slower step with a half-life of >3min. Conversion between the states was estimated to have an enthalpy of activation of approximately 10kJmol(-1) and an entropy of activation of -0.2kJKmol(-1). LD spectra corresponding to each of the membrane bound states were generated by non-linear regression using a standard kinetic model. These spectra are interpreted in comparison with spectra calculated using the program Dichrocalc and reveal that the peptide associates with membranes in a small number of stable configurations. All of these configurations have a significant proportion of β-sheet structure residing in the plane of the membrane. Two configurations support structures previously proposed for defensins in membranes. PMID:26801370

  3. Orally Administered Nano-curcumin to Attenuate Morphine Tolerance: Comparison between Negatively Charged PLGA and Partially and Fully PEGylated Nanoparticles

    PubMed Central

    Shen, Hao; Hu, Xiaoyu; Szymusiak, Magdalena; Wang, Zaijie Jim; Liu, Ying

    2014-01-01

    We have formulated hydrophobic curcurmin [1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] into stable nanoparticle suspensions (nano-curcumin) to overcome its relatively low bioavailability, high rate of metabolism and rapid elimination and clearance from the body. Employing the curcumin nanoformulations as the platform, we discovered that curcumin has the potential to alleviate morphine tolerance. The two types of stable polymeric nanoparticles - poly(lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) - and the hybrid of the two were generated using flash nanoprecipitation integrated with spray drying. The optimized formulations have high drug loading (>45%), small particles size with narrow distribution, and controlled surface properties. Mice behavioral studies (tail-flick and hot-plate tests) were conducted to verify the effects of nano-curcumin on attenuating morphine tolerance. Significant analgesia was observed in mice during both tail-flick and hot-plate tests using orally administrated nano-curcumin following subcutaneous injections of morphine. However, unformulated curcumin at the same dose showed no effect. Compared with PEGylated nano-curcumin, negatively charged PLGA nanoparticles showed better functionality. PMID:24195658

  4. Non-adiabatic processes in the charge transfer reaction of O2 molecules with potassium surfaces without dissociation

    NASA Astrophysics Data System (ADS)

    Krix, David; Nienhaus, Hermann

    2014-08-01

    Thin potassium films grown on Si(001) substrates are used to measure internal chemicurrents and the external emission of exoelectrons simultaneously during adsorption of molecular oxygen on K surfaces at 120 K. The experiments clarify the dynamics of electronic excitations at a simple metal with a narrow valence band. X-ray photoemission reveals that for exposures below 5 L almost exclusively peroxide K2O2 is formed, i.e., no dissociation of the molecule occurs during interaction. Still a significant chemicurrent and a delayed exoelectron emission are detected due to a rapid injection of unoccupied molecular levels below the Fermi level. Since the valence band width of potassium is approximately equal to the potassium work function (2.4 eV) the underlying mechanism of exoemission is an Auger relaxation whereas chemicurrents are detected after resonant charge transfer from the metal valence band into the injected level. The change of the chemicurrent and exoemission efficiencies with oxygen coverage can be deduced from the kinetics of the reaction and the recorded internal and external emission currents traces. It is shown that the non-adiabaticity of the reaction increases with coverage due to a reduction of the electronic density of states at the surface while the work function does not vary significantly. Therefore, the peroxide formation is one of the first reaction systems which exhibits varying non-adiabaticity and efficiencies during the reaction. Non-adiabatic calculations based on model Hamiltonians and density functional theory support the picture of chemicurrent generation and explain the rapid injection of hot hole states by an intramolecular motion, i.e., the expansion of the oxygen molecule on the timescale of a quarter of a vibrational period.

  5. Adsorption and transport of charged vs. neutral hydrophobic molecules at the membrane of murine erythroleukemia (MEL) cells.

    PubMed

    Zeng, Jia; Eckenrode, Heather M; Dai, Hai-Lung; Wilhelm, Michael J

    2015-03-01

    The adsorption and transport of hydrophobic molecules at the membrane surface of pre- and post-DMSO induced differentiated murine erythroleukemia (MEL) cells were examined by time- and wavelength-resolved second harmonic light scattering. Two medium (<600 Da) hydrophobic molecules, cationic malachite green (MG) and neutral bromocresol purple (BCP), were investigated. While it was observed that the MG cation adsorbs onto the surface of the MEL cell, neutral BCP does not. It is suggested that an electrostatic interaction between the opposite charges of the cation and the MEL cell surface is the primary driving force for adsorption. Comparisons of adsorption density and free energy, measured at different pH and cell morphology, indicate that the interaction is predominantly through sialic acid carboxyl groups. MG cation adsorption densities have been determined as (0.6±0.3)×10(6) μm(-2) on the surface of undifferentiated MEL cells, and (1.8±0.5)×10(7) μm(-2) on differentiated MEL cells, while the deduced adsorption free energies are effectively identical (ca. -10.9±0.1 and -10.8±0.1 kcal mol(-1), respectively). The measured MG densities indicate that the total number of surface carboxyl groups is largely conserved following differentiation, and therefore the density of carboxylic groups is much larger on the differentiated cell surface than the undifferentiated one. Finally, in contrast to synthetic liposomes and bacterial membranes, surface adsorbed MG cations are unable to traverse the MEL cell membrane. PMID:25660095

  6. Non-adiabatic processes in the charge transfer reaction of O{sub 2} molecules with potassium surfaces without dissociation

    SciTech Connect

    Krix, David; Nienhaus, Hermann

    2014-08-21

    Thin potassium films grown on Si(001) substrates are used to measure internal chemicurrents and the external emission of exoelectrons simultaneously during adsorption of molecular oxygen on K surfaces at 120 K. The experiments clarify the dynamics of electronic excitations at a simple metal with a narrow valence band. X-ray photoemission reveals that for exposures below 5 L almost exclusively peroxide K{sub 2}O{sub 2} is formed, i.e., no dissociation of the molecule occurs during interaction. Still a significant chemicurrent and a delayed exoelectron emission are detected due to a rapid injection of unoccupied molecular levels below the Fermi level. Since the valence band width of potassium is approximately equal to the potassium work function (2.4 eV) the underlying mechanism of exoemission is an Auger relaxation whereas chemicurrents are detected after resonant charge transfer from the metal valence band into the injected level. The change of the chemicurrent and exoemission efficiencies with oxygen coverage can be deduced from the kinetics of the reaction and the recorded internal and external emission currents traces. It is shown that the non-adiabaticity of the reaction increases with coverage due to a reduction of the electronic density of states at the surface while the work function does not vary significantly. Therefore, the peroxide formation is one of the first reaction systems which exhibits varying non-adiabaticity and efficiencies during the reaction. Non-adiabatic calculations based on model Hamiltonians and density functional theory support the picture of chemicurrent generation and explain the rapid injection of hot hole states by an intramolecular motion, i.e., the expansion of the oxygen molecule on the timescale of a quarter of a vibrational period.

  7. Theoretical study of the BeLi, BeNa, MgLi, MgNa, and AlBe molecules and their negative ions

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry

    1992-01-01

    The alkaline earth-alkali diatomics are found to have weak bonds, because the diffuse alkali valence s orbitals cannot form a bond of sufficient strength to pay the promotion energy of the alkaline-earth atoms. This leads to van der Waals bonding in the neutrals as well as the negative ions. In fact, the negative ions have larger binding energies than the neutrals as a result of the much larger polarizability of the negative ion. The binding energy of AlBe is significantly larger than the Be-alkali molecules, due to a covalent contribution to the bonding. The binding energy in AlBe(-) is considerably larger than AlBe; the binding energy of the X 3Sigma(-) state of AlBe(-) is computed to be 1.36 eV, as compared with 0.57 eV for the X 2Pi state of AlBe.

  8. The interplay of thermally activated delayed fluorescence (TADF) and room temperature organic phosphorescence in sterically-constrained donor-acceptor charge-transfer molecules.

    PubMed

    Ward, Jonathan S; Nobuyasu, Roberto S; Batsanov, Andrei S; Data, Przemyslaw; Monkman, Andrew P; Dias, Fernando B; Bryce, Martin R

    2016-02-11

    A series of phenothiazine-dibenzothiophene-S,S-dioxide charge-transfer molecules have been synthesized. Increasing steric restriction around the donor-acceptor bond significantly alters contributions from TADF and phosphorescence. Bulky substituents on the 1-(and 9) position(s) of the phenothiazine result in no TADF in the solid state; instead strong phosphorescence is observed at ambient temperature. PMID:26750426

  9. Excitation of atoms and molecules in collisions with highly charged ions. [Cyclotron Inst. , Texas A M Univ. , College Station, Texas

    SciTech Connect

    Watson, R.L.

    1993-01-01

    A study of the double ionization of He by high-energy N[sup 7+] ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N[sub 2], O[sub 2], and CO molecular ions produced in collisions with 97-MeV Ar[sup 14+] ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO[sup 2+] and CO[sup 3+] from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO[sup 1+] and CO[sup 2+] molecular ions, and the branching ratios for the most prominent charge division channels of CO[sup 2+] through CO[sup 7+] were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

  10. Excitation of atoms and molecules in collisions with highly charged ions. Progress report, January 1, 1990--December 1, 1992

    SciTech Connect

    Watson, R.L.

    1993-01-01

    A study of the double ionization of He by high-energy N{sup 7+} ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N{sub 2}, O{sub 2}, and CO molecular ions produced in collisions with 97-MeV Ar{sup 14+} ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO{sup 2+} and CO{sup 3+} from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO{sup 1+} and CO{sup 2+} molecular ions, and the branching ratios for the most prominent charge division channels of CO{sup 2+} through CO{sup 7+} were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

  11. Circumambulatory movement of negative charge ("ring walk") during gas-phase dissociation of 2,3,4-trimethoxybenzoate anion.

    PubMed

    Herath, Kithsiri B; Weisbecker, Carl S; Singh, Sheo B; Attygalle, Athula B

    2014-05-16

    A dramatic "ortho effect" was observed during gas-phase dissociation of ortho-, meta-, and para-methoxybenzoate anions. Upon activation under mass spectrometric collisional activation conditions, anions generated from all three isomers undergo a CO2 loss. Of the m/z 107 ions generated in this way, only the 1-dehydro-2-methoxybenzene anion from the ortho isomer underwent an exclusive formaldehyde loss. A peak for a formaldehyde loss in the spectra of 2,4-, 2,5-, and 2,6-dimethoxybenzoates and the absence of an analogous peak from 3,4- and 3,5-dimethoxy derivatives confirmed that this is a diagnostically useful ortho-isomer-specific phenomenon. Moreover, the spectrum from 2,3-dimethoxybenzoic acid showed peaks for two consecutive formaldehyde losses. The 1-dehydro-2,3,4-trimethoxybenzene anion (m/z 167) generated from 2,3,4-trimethoxybenzoate in this way endures three consecutive eliminations of formaldehyde units. For this, the negative charge, initially located on position 1, circumambulates to position 2, then to position 3, and finally to position 4 to form the final phenyl anion. The proposed stepwise fragmentation pathway, which resembles the well-known E1cB-elimination mechanism, is supported by tandem mass spectrometric observations made with 2-[(13)C(2)H3]methoxy-3-[(13)C]methoxy-4-methoxybenzoic acid, and ab initio calculations. In addition, the spectra of ions such as 1-dehydro-3,4-dimethoxybenzene anion show peaks for consecutive methyl radical losses, a feature that establishes the 1,2-relationship between the two methoxy groups. PMID:24749904

  12. A 90-day study of subchronic oral toxicity of 20 nm, negatively charged zinc oxide nanoparticles in Sprague Dawley rats

    PubMed Central

    Park, Hark-Soo; Shin, Sung-Sup; Meang, Eun Ho; Hong, Jeong-sup; Park, Jong-Il; Kim, Su-Hyon; Koh, Sang-Bum; Lee, Seung-Young; Jang, Dong-Hyouk; Lee, Jong-Yun; Sun, Yle-Shik; Kang, Jin Seok; Kim, Yu-Ri; Kim, Meyoung-Kon; Jeong, Jayoung; Lee, Jong-Kwon; Son, Woo-Chan; Park, Jae-Hak

    2014-01-01

    Purpose The widespread use of nanoparticles (NPs) in industrial and biomedical applications has prompted growing concern regarding their potential toxicity and impact on human health. This study therefore investigated the subchronic, systemic oral toxicity and no-observed-adverse-effect level (NOAEL) of 20 nm, negatively charged zinc oxide (ZnOSM20(?)) NPs in Sprague Dawley rats for 90 days. Methods The high-dose NP level was set at 500 mg/kg of bodyweight, and the mid- and low-dose levels were set at 250 and 125 mg/kg, respectively. The rats were observed during a 14-day recovery period after the last NP administration for the persistence or reduction of any adverse effects. Toxicokinetic and distribution studies were also conducted to determine the systemic distribution of the NPs. Results No rats died during the test period. However, ZnOSM20(?) NPs (500 mg/kg) induced changes in the levels of anemia-related factors, prompted acinar cell apoptosis and ductular hyperplasia, stimulated periductular lymphoid cell infiltration and excessive salivation, and increased the numbers of regenerative acinar cells in the pancreas. In addition, stomach lesions were seen at 125, 250, and 500 mg/kg, and retinal atrophy was observed at 250 and 500 mg/kg. The Zn concentration was dose-dependently increased in the liver, kidney, intestines, and plasma, but not in other organs investigated. Conclusion A ZnOSM20(?) NP NOAEL could not be established from the current results, but the lowest-observed-adverse-effect level was 125 mg/kg. Furthermore, the NPs were associated with a number of undesirable systemic actions. Thus, their use in humans must be approached with caution. PMID:25565828

  13. Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy

    PubMed Central

    Guisinger, Nathan P.; Yoder, Nathan L.; Hersam, Mark C.

    2005-01-01

    A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-21 surface at a temperature of 80 K. Currentvoltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope at cryogenic temperatures, repeated measurements can be routinely taken over the same molecule. Taking advantage of this improved stability, we show that currentvoltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tipmolecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tipmolecule distance. By using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single-molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices. PMID:15956214

  14. Negative Ion Laser Desorption/Ionization Time-of-Flight Mass Spectrometric Analysis of Small Molecules Using Graphitic Carbon Nitride Nanosheet Matrix.

    PubMed

    Lin, Zian; Zheng, Jiangnan; Lin, Guo; Tang, Zhi; Yang, Xueqing; Cai, Zongwei

    2015-08-01

    Ultrathin graphitic carbon nitride (g-C3N4) nanosheets served as a novel matrix for the detection of small molecules by negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was described for the first time. In comparison with conventional organic matrices and graphene matrix, the use of g-C3N4 nanosheet matrix showed free matrix background interference and increased signal intensity in the analysis of amino acids, nucleobases, peptides, bisphenols (BPs), and nitropolycyclic aromatic hydrocarbons (nitro-PAHs). A systematic comparison of g-C3N4 nanosheets with positive and negative ion modes revealed that mass spectra produced by g-C3N4 nanosheets in negative ion mode were featured by singly deprotonated ion without matrix interference, which was rather different from the complicated alkali metal complexes in positive ion mode. Good salt tolerance and reproducibility allowed the determination of 1-nitropyrene (1-NP) in sewage, and its corresponding detection limit was lowered to 1 pmol. In addition, the ionization mechanism of the g-C3N4 nanosheets as matrix was also discussed. The work expands its application scope of g-C3N4 nanosheets and provides an alternative approach for small molecules. PMID:26171593

  15. Basal electric and magnetic fields of celestial bodies come from positive-negative charge separation caused by gravitation of quasi-Casimir pressure in weak interaction

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Guang

    According to f =d(mv)/dt=m(dv/dt)+ v(dm/dt), a same gravitational formula had been de-duced from the variance in physical mass of QFT and from the variance in mass of inductive energy-transfer of GR respectively: f QF T = f GR = -G (mM/r2 )((r/r)+(v/c)) when their interaction-constants are all taken the experimental values (H05-0029-08, E15-0039-08). f QF T is the quasi-Casimir pressure. f GR is equivalent to Einstein's equation, then more easy to solve it. The hypothesis of the equivalent principle is not used in f QF T , but required by f GR . The predictions of f QF T and f GR are identical except that f QF T has quantum effects but f GR has not and f GR has Lense-Thirring effect but f QF T has not. The quantum effects of gravitation had been verified by Nesvizhevsky et al with the ultracold neutrons falling in the earth's gravitational field in 2002. Yet Lense-Thirring effect had not been measured by GP-B. It shows that f QF T is essential but f GR is phenomenological. The macro-f QF T is the statistic average pressure collided by net virtual neutrinos ? 0 flux (after self-offset in opposite directions) and in direct proportion to the mass. But micro-f QF T is in direct proportion to the scattering section. The electric mass (in inverse proportion to de Broglie wavelength ?) far less than nucleonic mass and the electric scattering section (in direct proportion to ?2 ) far large than that of nucleon, then the net ? 0 flux pressure exerted to electron far large than that to nucleon and the electric displacement far large than that of nucleon, it causes the gravitational polarization of positive-negative charge center separation. Because the gravity far less than the electromagnetic binding force, in atoms the gravitational polarization only produces a little separation. But the net ? 0 flux can press a part freedom electrons in plasma of ionosphere into the earth's surface, the static electric force of redundant positive ions prevents electrons from further falling and till reach the equilibrium of stable spatial charge distribution, which is just the cause of the geomagnetic field and the geo-electric field (the observational value on the earth surface is about 120 V/m downward equivalent to 500000 Coulomb negative charges in the earth surface). All celestial bodies are gravitation sources and attract the molecules and ions in space to its circumference by the gravitation of own and other celestial bodies, e.g., all planets in the solar system have their own atmospheres. Therefore, the origin mechanism of geo-electric and geomagnetic fields caused by gravitation is very universal, at least it is appli-cable to all the planets in the solar system. For planets, the joint result of the gravitations of the planets and the sun makes the negative charges and dipolar charges distributed in the surfaces of the celestial bodies. The quicker the rotation is, the larger the angular momentum U is, then larger the accompanying current and magnetic moment P, it accord a experiential law found by subsistent observational data of all celestial bodies in solar system: P = -G 1/2 U cos ? / c (1), ? is the angle between the net ? 0 flux direction (mark by CMB) and the rotational axis of celestial body (Chen Shao-Guang, Chinese Science Bulletin, 26,233,1981). Uranian and Neptunian P predicted with Eq.(1) in 1981 are about -3.41028 Gscm3 and 1.91028 Gscm3 respectively (use new rotate speed measured by Voyager 2). The P measured by Voyager 2 in 1986 and 1989 are about -1.9 1028 Gscm3 and 1.51028 Gscm3 respectively (the contribution of quadrupole P is converted into the contribution of dipole P alone). The neutron star pos-sesses much high density and rotational speed because of the conservation of the mass and the angular momentum during the course of the formation, then has strong gravity and largerU. From Eq.(1) there is a larger P and extremely strong surface magnetic field in neutron star. The origin mechanism of basal electric and magnetic fields of celestial bodies will affect directly all fields refer

  16. Pair Tunneling through Single Molecules.

    PubMed

    Koch, Jens; Raikh, M E; von Oppen, Felix

    2006-02-10

    By a polaronic energy shift, the effective charging energy of molecules can become negative, favoring ground states with even numbers of electrons. Here we show that charge transport through such molecules near ground-state degeneracies is dominated by tunneling of electron pairs which coexists with (featureless) single-electron cotunneling. Because of the restricted phase space for pair tunneling, the current-voltage characteristics exhibit striking differences from the conventional Coulomb blockade. In asymmetric junctions, pair tunneling can be used for gate-controlled current rectification and switching. PMID:16486970

  17. Charge-coupled device operated in a time-delayed integration mode as an approach to high-throughput flow-based single molecule analysis.

    PubMed

    Emory, Jason M; Soper, Steven A

    2008-05-15

    Single molecule detection (SMD) readouts are particularly attractive for assays geared toward high-throughput processing, because they can potentially reduce assay time by eliminating various processing steps. Unfortunately, most flow-based SMD experiments have generated low throughputs due primarily to the fact that they are configured in single assay formats. The use of a charge-coupled device (CCD) with flow-based SMD can image multiple single molecule assays simultaneously to realize high-throughput processing capabilities. We present, for the first time, the ability to simultaneously track and detect single molecules in multiple microfluidic channels by employing a CCD camera operated in time-delayed integration (TDI) mode as a means for increasing the throughput of any single molecule measurement. As an example of the technology, we have configured a CCD to operate in a TDI mode to detect single double-stranded DNA molecules (lambda and pBR322) labeled with an intercalating dye (TOTO-3) in a series of microfluidic channels poised on a poly(methyl methacrylate), PMMA, chip. A laser beam was launched into the side of the chip, which irradiated a series of fluidic channels (eight) with the resulting fluorescence imaged onto a CCD. Using this system, we were able to identify single DNA molecules based on the fluorescence burst intensity arising from differences in the extent of dye labeling associated with the DNA molecule length. The CCD/TDI approach allowed increasing sample throughput by a factor of 8 compared to a single-assay SMD experiment. A sampling throughput of 276 molecules s (-1) per channel and 2208 molecules s (-1) for an eight channel microfluidic system was demonstrated. Operated in its full capacity, this multichannel format was projected to yield a sample throughput of 1.7 x 10 (7) molecules s (-1), which represents a 170-fold improvement over previously reported single molecule sampling rates. PMID:18412372

  18. Tuning the opto-electronic properties of MoS2 layer using charge transfer interactions: effect of different donor molecules

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Arkamita; Pati, Swapan K.

    2015-08-01

    We have performed density functional theory calculations to study the effect of adsorption of a set of organic electron donor molecules on single layer MoS2 to find the optimum condition to tune the charge transfer, as well as to find how it changes the electronic properties of single layer MoS2. We have performed our calculations for three sets of organic Lewis bases. We have found that all the molecules are physisorbed on MoS2. Our calculations show that the charge transfer from the molecules to the MoS2 layer is highly dependent upon the inductive effect and HOMO-LUMO gap of the molecules. Furthermore, we show that the charge transfer interaction tunes the electronic and optical property of MoS2 to a significant amount: for example, the band-gap of the system can be changed from 1.8 eV to even a low value of 0.2 eV, making it interesting for different optoelectronic device applications.

  19. A self-consistent phase-field approach to implicit solvation of charged molecules with Poisson-Boltzmann electrostatics.

    PubMed

    Sun, Hui; Wen, Jiayi; Zhao, Yanxiang; Li, Bo; McCammon, J Andrew

    2015-12-28

    Dielectric boundary based implicit-solvent models provide efficient descriptions of coarse-grained effects, particularly the electrostatic effect, of aqueous solvent. Recent years have seen the initial success of a new such model, variational implicit-solvent model (VISM) [Dzubiella, Swanson, and McCammon Phys. Rev. Lett. 96, 087802 (2006) and J. Chem. Phys. 124, 084905 (2006)], in capturing multiple dry and wet hydration states, describing the subtle electrostatic effect in hydrophobic interactions, and providing qualitatively good estimates of solvation free energies. Here, we develop a phase-field VISM to the solvation of charged molecules in aqueous solvent to include more flexibility. In this approach, a stable equilibrium molecular system is described by a phase field that takes one constant value in the solute region and a different constant value in the solvent region, and smoothly changes its value on a thin transition layer representing a smeared solute-solvent interface or dielectric boundary. Such a phase field minimizes an effective solvation free-energy functional that consists of the solute-solvent interfacial energy, solute-solvent van der Waals interaction energy, and electrostatic free energy described by the Poisson-Boltzmann theory. We apply our model and methods to the solvation of single ions, two parallel plates, and protein complexes BphC and p53/MDM2 to demonstrate the capability and efficiency of our approach at different levels. With a diffuse dielectric boundary, our new approach can describe the dielectric asymmetry in the solute-solvent interfacial region. Our theory is developed based on rigorous mathematical studies and is also connected to the Lum-Chandler-Weeks theory (1999). We discuss these connections and possible extensions of our theory and methods. PMID:26723595

  20. A self-consistent phase-field approach to implicit solvation of charged molecules with Poisson-Boltzmann electrostatics

    NASA Astrophysics Data System (ADS)

    Sun, Hui; Wen, Jiayi; Zhao, Yanxiang; Li, Bo; McCammon, J. Andrew

    2015-12-01

    Dielectric boundary based implicit-solvent models provide efficient descriptions of coarse-grained effects, particularly the electrostatic effect, of aqueous solvent. Recent years have seen the initial success of a new such model, variational implicit-solvent model (VISM) [Dzubiella, Swanson, and McCammon Phys. Rev. Lett. 96, 087802 (2006) and J. Chem. Phys. 124, 084905 (2006)], in capturing multiple dry and wet hydration states, describing the subtle electrostatic effect in hydrophobic interactions, and providing qualitatively good estimates of solvation free energies. Here, we develop a phase-field VISM to the solvation of charged molecules in aqueous solvent to include more flexibility. In this approach, a stable equilibrium molecular system is described by a phase field that takes one constant value in the solute region and a different constant value in the solvent region, and smoothly changes its value on a thin transition layer representing a smeared solute-solvent interface or dielectric boundary. Such a phase field minimizes an effective solvation free-energy functional that consists of the solute-solvent interfacial energy, solute-solvent van der Waals interaction energy, and electrostatic free energy described by the Poisson-Boltzmann theory. We apply our model and methods to the solvation of single ions, two parallel plates, and protein complexes BphC and p53/MDM2 to demonstrate the capability and efficiency of our approach at different levels. With a diffuse dielectric boundary, our new approach can describe the dielectric asymmetry in the solute-solvent interfacial region. Our theory is developed based on rigorous mathematical studies and is also connected to the Lum-Chandler-Weeks theory (1999). We discuss these connections and possible extensions of our theory and methods.

  1. Buffer system for the separation of neutral and charged small molecules using micellar electrokinetic chromatography with mass spectrometric detection.

    PubMed

    Goetzinger, Wolfgang K; Cai, Hong

    2005-06-24

    An organic buffer system will be discussed that is suitable for the separation of neutral as well as charged molecules be means of micellar electrokinetic chromatography (MEKC). The buffers are based on the combination of a long chain alkyl acid, such as lauric acid with ammonium hydroxide or an organic base such as tris-hydroxymethylaminomethane (Tris). The resulting buffer system is able to separate neutral compounds based on its micellar properties. These buffers exhibit much reduced conductivity compared to traditional MEKC buffers, such as sodium dodecylsulfate (SDS), which contain inorganic salts. They also have inherent buffer capacity at high pH resulting from the basic buffer component, which in our studies had pK values from about 8-11. The separations that were observed showed high efficiency with plate counts in many cases above 500,000 plates per meter. The reduced conductivity allowed for the application of much higher electric fields, resulting in very fast analysis times. Alternatively, an increase in detection sensitivity could be achieved, as the reduced conductivity allowed for the use of capillaries with lager internal diameters. Combinations of different alkyl acids and organic bases provided for significant flexibility in selectivity tuning. Finally, the fact that the organic micellar buffer systems discussed here do not contain inorganic ions, allows for coupling with mass spectrometric (MS) detection. The possibility of MS detection combined with the high speed in analysis that can be obtained using these organic buffer systems, could make this approach an interesting option for high throughput analysis of combinatorial libraries. PMID:16038325

  2. Dependence of radiative stabilization on the projectile charge state after double-electron-transfer processes in slow, highly charged ion-molecule collisions

    NASA Astrophysics Data System (ADS)

    Krok, Franciszek; Tolstikhina, Inga Yu.; Sakaue, Hiroyuki A.; Yamada, Ichihiro; Hosaka, Kazumoto; Kimura, Masahiro; Nakamura, Nobuyuki; Ohtani, Shunsuke; Tawara, Hiroyuki

    1997-12-01

    We have measured the radiative stabilization probabilities after double-electron-transfer processes in slow (1.5q keV) Iq++CO collisions in the charge-state regime 8<=q<=26 by using the charge-selected-projectile-recoil-ion-coincidence method. It was found that the radiative stabilization probabilities Prad, defined as Prad=TDC/(TDC+ADC) (TDC is true double capture, and ADC autoionizing double capture), increases from about 1% at the lowest charge up to about 10% at the highest charge as the charge state of the projectile increases. A model is proposed which can explain such a feature, by incorporating a slight modification of the initial population of the transferred levels in the projectile predicted in the extended classical over-barrier model. Based upon the present model, theoretical radiative and autoionization decay rates have been calculated, using the Cowan code. Fairly good agreement between the measured and calculated results has been obtained.

  3. Charge steering of laser plasma accelerated fast ions in a liquid spray creation of MeV negative ion and neutral atom beams

    SciTech Connect

    Schnrer, M.; Abicht, F.; Priebe, G.; Braenzel, J.; Prasad, R.; Borghesi, M.; ELIBeamlines, Institute of Physics, Czech Academy of Science, 18221 Prague ; Andreev, A.; Vavilov State Optical Institute, 119034 St. Petersburg ; Nickles, P. V.; Jequier, S.; Tikhonchuk, V.; Ter-Avetisyan, S.

    2013-11-15

    The scenario of electron capture and loss has been recently proposed for the formation of negative ion and neutral atom beams with up to MeV kinetic energy [S. Ter-Avetisyan, et al., Appl. Phys. Lett. 99, 051501 (2011)]. Validation of these processes and of their generic nature is here provided in experiments where the ion source and the interaction medium have been spatially separated. Fast positive ions accelerated from a laser plasma source are sent through a cold spray where their charge is changed. Such formed neutral atom or negative ion has nearly the same momentum as the original positive ion. Experiments are released for protons, carbon, and oxygen ions and corresponding beams of negative ions and neutral atoms have been obtained. The electron capture and loss phenomenon is confirmed to be the origin of the negative ion and neutral atom beams. The equilibrium ratios of different charge components and cross sections have been measured. Our method is general and allows the creation of beams of neutral atoms and negative ions for different species which inherit the characteristics of the positive ion source.

  4. Charged clusters in liquid helium

    NASA Astrophysics Data System (ADS)

    Dyugaev, A. M.; Grigor'ev, P. D.; Lebedeva, E. V.

    2010-03-01

    The appropriateness of the experimental study of charged clusters in liquid helium has been supported. The interaction potential of negative ions (electron bubbles) with inert clusters formed by Ne, Ar, Kr, and Xe atoms or H2 and N2 molecules has been found. Small clusters levitate at a distance of 13-16 above the negative ion. The scalings laws for the properties of charged inert clusters have been discovered and grounded; the number of quantum levels and states of such clusters has been determined. The mobility measurement of charged clusters may provide a new technique of probing the properties of impurity nanoparticles in helium.

  5. Magnetic molecularly imprinted polymer nanoparticles based electrochemical sensor for the measurement of Gram-negative bacterial quorum signaling molecules (N-acyl-homoserine-lactones).

    PubMed

    Jiang, Hui; Jiang, Donglei; Shao, Jingdong; Sun, Xiulan

    2016-01-15

    We have developed a novel and economical electrochemical sensor to measure Gram-negative bacterial quorum signaling molecules (AHLs) using magnetic nanoparticles and molecularly imprinted polymer (MIP) technology. Magnetic molecularly imprinted polymers (MMIPs) capable of selectively absorbing AHLs were successfully synthesized by surface polymerization. The particles were deposited onto a magnetic carbon paste electrode (MGCE) surface, and characterized by electrochemical measurements. Differential Pulse Voltammetry (DPV) was utilized to record the oxidative current signal that is characteristic of AHL. The detection limit of this assay was determined to be 810(-10)molL(-1) with a linear detection range of 2.510(-9)molL(-1) to 1.010(-7)molL(-1). This Fe3O4@SiO2-MIP-based electrochemical sensor is a valuable new tool that allows quantitative measurement of Gram-negative bacterial quorum signaling molecules. It has potential applications in the fields of clinical diagnosis or food analysis with real-time detection capability, high specificity, excellent reproducibility, and good stability. PMID:26344904

  6. Quantum theory of atoms in molecules/charge-charge flux-dipole flux models for fundamental vibrational intensity changes on H-bond formation of water and hydrogen fluoride

    SciTech Connect

    Silva, Arnaldo F.; Richter, Wagner E.; Bruns, Roy E.; Terrabuio, Luiz A.; Haiduke, Roberto L. A.

    2014-02-28

    The Quantum Theory of Atoms In Molecules/Charge-Charge Flux-Dipole Flux (QTAIM/CCFDF) model has been used to investigate the electronic structure variations associated with intensity changes on dimerization for the vibrations of the water and hydrogen fluoride dimers as well as in the water-hydrogen fluoride complex. QCISD/cc-pVTZ wave functions applied in the QTAIM/CCFDF model accurately provide the fundamental band intensities of water and its dimer predicting symmetric and antisymmetric stretching intensity increases for the donor unit of 159 and 47 km mol{sup ?1} on H-bond formation compared with the experimental values of 141 and 53 km mol{sup ?1}. The symmetric stretching of the proton donor water in the dimer has intensity contributions parallel and perpendicular to its C{sub 2v} axis. The largest calculated increase of 107 km mol{sup ?1} is perpendicular to this axis and owes to equilibrium atomic charge displacements on vibration. Charge flux decreases occurring parallel and perpendicular to this axis result in 42 and 40 km mol{sup ?1} total intensity increases for the symmetric and antisymmetric stretches, respectively. These decreases in charge flux result in intensity enhancements because of the interaction contributions to the intensities between charge flux and the other quantities. Even though dipole flux contributions are much smaller than the charge and charge flux ones in both monomer and dimer water they are important for calculating the total intensity values for their stretching vibrations since the charge-charge flux interaction term cancels the charge and charge flux contributions. The QTAIM/CCFDF hydrogen-bonded stretching intensity strengthening of 321 km mol{sup ?1} on HF dimerization and 592 km mol{sup ?1} on HF:H{sub 2}O complexation can essentially be explained by charge, charge flux and their interaction cross term. Atomic contributions to the intensities are also calculated. The bridge hydrogen atomic contributions alone explain 145, 237, and 574 km mol{sup ?1} of the H-bond stretching intensity enhancements for the water and HF dimers and their heterodimer compared with total increments of 149, 321, and 592 km mol{sup ?1}, respectively.

  7. Sialidase NEU4 hydrolyzes polysialic acids of neural cell adhesion molecules and negatively regulates neurite formation by hippocampal neurons.

    PubMed

    Takahashi, Kohta; Mitoma, Junya; Hosono, Masahiro; Shiozaki, Kazuhiro; Sato, Chihiro; Yamaguchi, Kazunori; Kitajima, Ken; Higashi, Hideyoshi; Nitta, Kazuo; Shima, Hiroshi; Miyagi, Taeko

    2012-04-27

    Modulation of levels of polysialic acid (polySia), a sialic acid polymer, predominantly associated with the neural cell adhesion molecule (NCAM), influences neural functions, including synaptic plasticity, neurite growth, and cell migration. Biosynthesis of polySia depends on two polysialyltransferases ST8SiaII and ST8SiaIV in vertebrate. However, the enzyme involved in degradation of polySia in its physiological turnover remains uncertain. In the present study, we identified and characterized a murine sialidase NEU4 that catalytically degrades polySia. Murine NEU4, dominantly expressed in the brain, was found to efficiently hydrolyze oligoSia and polySia chains as substrates in sialidase in vitro assays, and also NCAM-Fc chimera as well as endogenous NCAM in tissue homogenates of postnatal mouse brain as assessed by immunoblotting with anti-polySia antibodies. Degradation of polySia by NEU4 was also evident in neuroblastoma Neuro2a cells that were co-transfected with Neu4 and ST8SiaIV genes. Furthermore, in mouse embryonic hippocampal primary neurons, the endogenously expressed NEU4 was found to decrease during the neuronal differentiation. Interestingly, GFP- or FLAG-tagged NEU4 was partially co-localized with polySia in neurites and significantly suppressed their outgrowth, whereas silencing of NEU4 showed the acceleration together with an increase in polySia expression. These results suggest that NEU4 is involved in regulation of neuronal function by polySia degradation in mammals. PMID:22393058

  8. Sialidase NEU4 Hydrolyzes Polysialic Acids of Neural Cell Adhesion Molecules and Negatively Regulates Neurite Formation by Hippocampal Neurons

    PubMed Central

    Takahashi, Kohta; Mitoma, Junya; Hosono, Masahiro; Shiozaki, Kazuhiro; Sato, Chihiro; Yamaguchi, Kazunori; Kitajima, Ken; Higashi, Hideyoshi; Nitta, Kazuo; Shima, Hiroshi; Miyagi, Taeko

    2012-01-01

    Modulation of levels of polysialic acid (polySia), a sialic acid polymer, predominantly associated with the neural cell adhesion molecule (NCAM), influences neural functions, including synaptic plasticity, neurite growth, and cell migration. Biosynthesis of polySia depends on two polysialyltransferases ST8SiaII and ST8SiaIV in vertebrate. However, the enzyme involved in degradation of polySia in its physiological turnover remains uncertain. In the present study, we identified and characterized a murine sialidase NEU4 that catalytically degrades polySia. Murine NEU4, dominantly expressed in the brain, was found to efficiently hydrolyze oligoSia and polySia chains as substrates in sialidase in vitro assays, and also NCAM-Fc chimera as well as endogenous NCAM in tissue homogenates of postnatal mouse brain as assessed by immunoblotting with anti-polySia antibodies. Degradation of polySia by NEU4 was also evident in neuroblastoma Neuro2a cells that were co-transfected with Neu4 and ST8SiaIV genes. Furthermore, in mouse embryonic hippocampal primary neurons, the endogenously expressed NEU4 was found to decrease during the neuronal differentiation. Interestingly, GFP- or FLAG-tagged NEU4 was partially co-localized with polySia in neurites and significantly suppressed their outgrowth, whereas silencing of NEU4 showed the acceleration together with an increase in polySia expression. These results suggest that NEU4 is involved in regulation of neuronal function by polySia degradation in mammals. PMID:22393058

  9. A New Class of Quorum Quenching Molecules from Staphylococcus Species Affects Communication and Growth of Gram-Negative Bacteria

    PubMed Central

    Chu, Ya-Yun; Nega, Mulugeta; Wölfle, Martina; Plener, Laure; Grond, Stephanie; Jung, Kirsten; Götz, Friedrich

    2013-01-01

    The knowledge that many pathogens rely on cell-to-cell communication mechanisms known as quorum sensing, opens a new disease control strategy: quorum quenching. Here we report on one of the rare examples where Gram-positive bacteria, the ‘Staphylococcus intermedius group’ of zoonotic pathogens, excrete two compounds in millimolar concentrations that suppress the quorum sensing signaling and inhibit the growth of a broad spectrum of Gram-negative beta- and gamma-proteobacteria. These compounds were isolated from Staphylococcus delphini. They represent a new class of quorum quenchers with the chemical formula N-[2-(1H-indol-3-yl)ethyl]-urea and N-(2-phenethyl)-urea, which we named yayurea A and B, respectively. In vitro studies with the N-acyl homoserine lactone (AHL) responding receptor LuxN of V. harveyi indicated that both compounds caused opposite effects on phosphorylation to those caused by AHL. This explains the quorum quenching activity. Staphylococcal strains producing yayurea A and B clearly benefit from an increased competitiveness in a mixed community. PMID:24098134

  10. Ultrafast Bidirectional Charge Transport and Electron Decoherence at Molecule/Surface Interfaces: A Comparison of Gold, Graphene, and Graphene Nanoribbon Surfaces.

    PubMed

    Adak, Olgun; Kladnik, Gregor; Bavdek, Gregor; Cossaro, Albano; Morgante, Alberto; Cvetko, Dean; Venkataraman, Latha

    2015-12-01

    We investigate bidirectional femtosecond charge transfer dynamics using the core-hole clock implementation of resonant photoemission spectroscopy from 4,4'-bipyridine molecular layers on three different surfaces: Au(111), epitaxial graphene on Ni(111), and graphene nanoribbons. We show that the lowest unoccupied molecular orbital (LUMO) of the molecule drops partially below the Fermi level upon core-hole creation in all systems, opening an additional decay channel for the core-hole, involving electron donation from substrate to the molecule. Furthermore, using the core-hole clock method, we find that the bidirectional charge transfer time between the substrate and the molecule is fastest on Au(111), with a 2 fs time, then around 4 fs for epitaxial graphene and slowest with graphene nanoribbon surface, taking around 10 fs. Finally, we provide evidence for fast phase decoherence of the core-excited LUMO* electron through an interaction with the substrate providing the first observation of such a fast bidirectional charge transfer across an organic/graphene interface. PMID:26574713

  11. An Explicit Consideration of Desolvation is Critical to Binding Free Energy Calculations of Charged Molecules at Ionic Surfaces.

    PubMed

    Mori, Toshifumi; Hamers, Robert J; Pedersen, Joel A; Cui, Qiang

    2013-11-12

    Identifying factors that control the strength and specificity of interactions between peptides and nanoparticles is essential for understanding the potential beneficial and deleterious effects of nanoparticles on biological systems. Computer simulations are valuable in this context, although the reliability of such calculations depends on the force field and sampling algorithm, as well as how the binding constant and binding free energy are defined; the latter must be carefully defined with a clear connection to microscopic models based on statistical mechanics. Using the example of formate binding to the rutile titanium dioxide (TiO2) (110) surface, we demonstrate that a reliable description of the binding process requires an explicit consideration of changes in the solvation state of the binding site. Specifically, we carry out metadynamics simulations in which the solvent coordination number of the binding site, s, is introduced as a collective variable in addition to the vertical distance of the adsorbate to the surface (z). The resulting two-dimensional potential of mean force (2D-PMF) clearly shows that explicitly including the local desolvation of the binding site on the TiO2 surface strongly impacts the convergence and result of the binding free energy calculations. Projecting the 2D-PMF into a one-dimensional PMF along either z or s leads to large errors in the free energy barriers. Results from metadynamics simulations are quantitatively supported by independent alchemical free energy simulations, in which the solvation state of the binding site is also carefully considered by explicitly introducing water molecules to the binding site as the adsorbate is decoupled from the system. On the other hand, preliminary committor analysis for the approximate transition state ensemble constructed based on the 2D-PMF suggests that to properly describe the binding/unbinding kinetics, variables beyond s and z, such as those describing the hydrogen bonding pattern of the adsorbate and surface water, need to be included. We expect that the insights and computational methodologies established in this work will be generally applicable to the analysis of binding interactions between highly charged adsorbates and ionic surfaces in solution, such as those implicated in peptide/nanoparticle binding and biomineralization processes. PMID:26583420

  12. Apport de la microscopie a effet tunnel a la caracterisation d'interfaces molecule-metal a fort transfert de charge

    NASA Astrophysics Data System (ADS)

    Bedwani, Stephane

    To assess the importance of charge-transfer on the interface properties, we studied the interaction of the tetracyanoethylene (TCNE) molecule with various copper surfaces. TCNE, a highly electrophilic molecule, appears as an ideal candidate to study the influence of high charge-transfer on the electronic and structural properties of molecule-surface interfaces. Indeed, various TCNE-transition metal complexes exhibit magnetism at room temperature, which is in agreement with a very significant change of the residual charge on the TCNE molecule. The adsorption of TCNE molecules on Cu(100) and Cu(111) surfaces was studied by scanning tunneling microscopy (STM) and by density functional theory (DFT) calculations with a local density approximation (LDA). DFT-LDA calculations were performed to determine the geometric and electronic structure of the studied interfaces. Mulliken analysis was used to evaluate the partial net charge on the adsorbed species. The density of states (DOS) diagrams provided informations on the nature of the frontier orbitals involved in the charge-transfer at molecule-metal interfaces. To validate the theoretical observations, a comparative study was conducted between our simulated STM images and experimental STM images provided by our collaborators. The theoretical STM images were obtained with the SPAGS-STM software using the Landauer-Buttiker formalism with a semi-empirical Hamiltonian based on the extended Huckel theory (EHT) and parameterized using DFT calculations. During the development of the SPAGS-STM software, we have created a discretization module allowing rapid generation of STM images. This module is based on an adaptive Delaunay meshing scheme to minimize the amount of tunneling current to be computed. The general idea consists into refining the mesh, and therefore the calculations, near large contrast zones rather than over the entire image. The adapted mesh provides an STM image resolution equivalent to that obtained with a conventional Cartesian grid but with a significantly smaller number of calculated pixels. This module is independent of the solver used to compute the tunneling current and can be transposed to different imaging techniques. Our work on the adsorption of TCNE molecules on Cu(100) surfaces revealed that the molecules assemble into a 1D chain, thereby buckling excessively a few Cu atoms from the surface. The large deformations observed at the molecule-metal interface show that the Cu atoms close to the TCNE nitrile groups assist the molecular assembly and show a distinct behavior compared with other Cu atoms. A strong charge-transfer is observed at the interface leading to an almost complete occupation of the state ascribed to the lowest unoccupied molecular orbital (LUMO) of TCNE in gas phase. In addition, a back-donation of charge from the molecule to the metal via the states associated with the highest occupied molecular orbitals (HOMO) of TCNE in gas phase may be seen. The magnitude of the charge-transfer between a TCNE molecule and Cu atoms is of the same order on the Cu(111) surface but causes much less buckling than that on the Cu(100) surface. However, experimental STM images of single TCNE molecules adsorbed on Cu(111) surfaces reveal a surprising electronic multistability. In addition, scanning tunneling spectroscopy (STS) reveals that one of these states has a magnetic nature and shows a Kondo resonance. STM simulations identified the source of two non-magnetic states. DFT-LDA calculations were able to ascribe the magnetic state to the partial occupation of a state corresponding to the LUMO+2 of TCNE. Moreover, the calculations showed that additional molecular deformations to those of TCNE in adsorbed phase, such the elongation of the C=C central bond and the bend of nitrile groups toward the surface, favor this charge-transfer to the LUMO+2. This suggested the presence of a Kondo state through the vibrational excitation of the stretching mode of the C=C central bond. The main results of this thesis led to the conclusion that strong charge-transfer between ad

  13. Positively and Negatively Charged Ionic Modifications to Cellulose Assessed as Cotton-Based Protease-Lowering and Haemostatic Wound Agents

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent developments in cellulose wound dressings targeted to different stages of wound healing have been based on structural and charge modifications that function to modulate events in the complex inflammatory and hemostatic phases of wound healing. Hemostasis and inflammation comprise two overlapp...

  14. Comment on ''Existence of H/sup 2 -/, a relatively long-lived doubly charged negative atomic hydrogen ion''

    SciTech Connect

    Odom, R.W.; Anbar, M.

    1980-11-01

    In connection with the production of H/sup 2 -/ ion, the author reports new experimental evidence which demonstrate that the fast H/sup -/ ions are in fact produced by charge transfer processes rather than by autoionization of H/sup 2 -/. (AIP)

  15. Role of GCR positive and negative particles in charging the LISA-PF test masses in 2015

    NASA Astrophysics Data System (ADS)

    Grimani, C.; Fabi, M.; Lobo, A. J.; Mateos, I.; Telloni, D.

    2015-05-01

    The LISA Pathfinder (LISA-PF) mission launch is scheduled during the second half of 2015. Galactic and solar ions with energies larger than 100 MeV/n and electrons above 10 MeV penetrate the spacecraft material and charge the gold-platinum test masses. This charging process generates spurious forces that, in some cases, may mimic the effects of genuine gravitational wave signals. A study of the test-mass charging due to galactic cosmic rays (GCRs) down to 1% in composition is reported here. The reliability of the results of this work is mainly limited by our capability to predict the energy spectra of GCRs in 2015. To this purpose, our model is applied to the expected PAMELA experiment proton data for the period January- March 2014 characterized by a positive polarity period and a level of solar modulation similar to those expected at the time of LISA-PF. The PAMELA observations will be available in the next few months. The comparison between our projections and measurements will provide valuable clues on the test-mass charging estimate uncertainty.

  16. Positronium ions and molecules

    NASA Technical Reports Server (NTRS)

    Ho, Y. K.

    1990-01-01

    Recent theoretical studies on positronium ions and molecules are discussed. A positronium ion is a three particle system consisting of two electrons in singlet spin state, and a positron. Recent studies include calculations of its binding energy, positron annihilation rate, and investigations of its doubly excited resonant states. A positronium molecule is a four body system consisting of two positrons and two electrons in an overall singlet spin state. The recent calculations of its binding energy against the dissociation into two positronium atoms, and studies of auto-detaching states in positronium molecules are discussed. These auto-dissociating states, which are believed to be part of the Rydberg series as a result of a positron attaching to a negatively charged positronium ion, Ps-, would appear as resonances in Ps-Ps scattering.

  17. Geoengineering with Charged Droplets

    NASA Astrophysics Data System (ADS)

    Gokturk, H.

    2011-12-01

    Water molecules in a droplet are held together by intermolecular forces generated by hydrogen bonding which has a bonding energy of only about 0.2 eV. One can create a more rugged droplet by using an ion as a condensation nucleus. In that case, water molecules are held together by the interaction between the ion and the dipole moments of the water molecules surrounding the ion, in addition to any hydrogen bonding. In this research, properties of such charged droplets were investigated using first principle quantum mechanical calculations. A molecule which exhibits positive electron affinity is a good candidate to serve as the ionic condensation nucleus, because addition of an electron to such a molecule creates an energetically more stable state than the neutral molecule. A good example is the oxygen molecule (O2) where energy of O2 negative (O2-) ion is lower than that of the neutral O2 by about 0.5 eV. Examples of other molecules which have positive electron affinity include ozone (O3), nitrogen dioxide (NO2) and sulfur oxides (SOx, x=1-3). Atomic models used in the calculations consisted of a negative ion of one of the molecules mentioned above surrounded by water molecules. Calculations were performed using the DFT method with B3LYP hybrid functional and Pople type basis sets with polarization and diffuse functions. Energy of interaction between O2- ion and the water molecule was found to be ~0.7 eV. This energy is an order of magnitude greater than the thermal energy of even the highest temperatures encountered in the atmosphere. Once created, charged rugged droplets can survive in hot and dry climates where they can be utilized to create humidity and precipitation. The ion which serves as the nucleus of the droplet can attract not only water molecules but also other dipolar gases in the atmosphere. Such dipolar gases include industrial pollutants, for example nitrogen dioxide (NO2) or sulfur dioxide (SO2). Energy of interaction between O2- ion and pollutant molecules was calculated to be ~0.5 eV for NO2 and ~0.9 eV for SO2. These values are comparable to that of water, hence charged droplets have the potential to serve as scavengers of pollutants in the atmosphere. The charged droplet can also interact with quadrupolar gases depending on the charge distribution of the gas. A quadrupole of interest is carbon dioxide (CO2) where oxygens are slightly negative and carbon is slightly positive in a neutral molecule. When CO2 is in the vicinity of a negative ion, the carbon atom gets attracted to the ion, whereas oxygens are repelled from it. This interaction distorts the linear geometry of CO2, turning it into a small dipole. Energy of interaction between O2- ion and CO2 was calculated to be ~0.3 eV which is smaller than those of the above mentioned dipoles, but still significantly greater than the typical thermal energy at 25 C (~0.03 eV). One can expect the diffusion of atmospheric CO2 into the droplets to be enhanced due to the charge. Hence such droplets can help capture the CO2 in the atmosphere and sequester it simply as rain. Charged droplets can be created using electrical,optical, thermal or other means. A method which utilizes solar energy will be described in the presentation.

  18. Effect of the electrostatic interaction on the redox reaction of positively charged cytochrome C adsorbed on the negatively charged surfaces of acid-terminated alkanethiol monolayers on a Au(111) electrode.

    PubMed

    Imabayashi, Shin-ichiro; Mita, Takahiro; Kakiuchi, Takashi

    2005-02-15

    The electrochemical properties of cytochrome c (cyt c) adsorbed on mixed self-assembled monolayers (SAMs) of 2-mercaptoethanesulfonate (MES)/2-mercaptoethanol (MEL) are compared with those on single-component SAMs of MES, MEL, and mercaptopropionic acid (MPA), using cyclic voltammetry and potential-modulated UV-vis reflectance spectroscopy. The rate constant of electron transfer (ET), k(et), of cyt c adsorbed on the SAM of MPA decreases from 1450 +/- 210 s(-1) at pH 7 to 890 +/- 100 s(-1) at pH 9. In contrast, the value of k(et) of cyt c on the SAM of MES is pH-independent at 100 +/- 15 s(-1). Those facts suggest that a large negative charge density on the SAM surface slows down the ET between cyt c and the electrode. The surface charge density of the SAM affects also the amount of electroactive cyt c, Gamma(e), which decreases from 10.0 +/- 1.0 to 5.3 +/- 1.1 pmol cm(-2) with increasing pH from 7 to 9 on the SAM of MPA. Similarly, the k(et) of cyt c adsorbed on the mixed SAMs of MES/MEL sharply decreases from 900 +/- 300 s(-1) to 110 s(-1) as the surface mole fraction of MES increases beyond 0.5, suggesting the presence of a negative surface charge threshold beyond which the rate of ET of cyt c is dramatically lowered. The decrease in the k(et) on the SAMs at high negative charge densities probably results from the confinement of adsorbed cyt c by the strong electrostatic force to an orientation that is not optimal for the ET reaction. PMID:15697296

  19. Effective production of Xe2I excimer molecules by high-energy charged particles in Xe containing a small amount of C3F7I

    NASA Astrophysics Data System (ADS)

    Mis'kevich, A. I.

    2015-09-01

    An anomalously high efficiency of generating Xe2I* excimer molecules in dense Xe-C3F7I gaseous mixtures with a small amount of C3F7I that are excited by a pulsed beam of fast electrons is discovered. The electron energy is 150 keV, and the beam current amplitude and duration are, respectively, 5 A and 5 ns. The temporal-spectral characteristics of spontaneous radiation from XeI* and Xe2I* excimer molecules are measured. Also, the luminescence times of the upper level for the B- X transition in the XeI* molecule (?max = 253 nm) and the upper level for the 42?-12? transition in the Xe2I* molecule (? = 352 nm), as well as the rate constants of quenching these levels by the gaseous mixture components, are determined. Based on the characteristics of the track structure of a high-energy plasma produced by charged particles in the dense gaseous medium, a model of plasma-chemical processes leading to the formation of XeI* (?max = 253 nm) and Xe2I* (? = 352 nmnm) excimer molecules in a Xe-C3F7I mixture with a small amount of an iodine atom donor is suggested.

  20. Negatively charged subnanometer-sized silicon clusters and their reversible migration into AFI zeolite pores studied with X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Choo, Cheow-keong; Sakamoto, Takashi; Tanaka, Katsumi; Nakata, Ryouhei; Asakawa, Tetsuo

    1999-02-01

    Subnanometer sized silicon clusters were deposited on AFI zeolite (AlPO 4-5: one-dimensional channel diameter <0.73 nm) by pulsed laser ablation of silicon wafer. Their electronic structures were elucidated in situ by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Core level Si 2p spectra were analyzed into five components, Si(I) to Si(V). Si(I) and Si(II) species selectively increased with a constant ratio during pulsed laser silicon ablation. Their binding energies (BEs) were below 99.5 eV implying negatively charged states. Charge transfer occurred between silicon clusters and framework oxygen and phosphor ions. It was interpreted that the stability of negative charge is due to large electron affinity of silicon clusters. The intensity of XPS signals decreased as a function of time and at the same time the channels were blocked. These results were interpreted due to migration of silicon clusters into zeolite pores. The estimated activation energy (57 kJ/mol) suggests that rate-determining step of the migration is reflected by a weak adsorbed state of silicon clusters similar to physisorbed state. The silicon clusters were partially oxidized at 573 K, which was interpreted as a driving force of backward migration from zeolite pores to the external surface. The composition of silicon cluster was discussed based on homogeneous dispersion of single species.

  1. Negative electrospray ionization on porous supporting tips for mass spectrometric analysis: electrostatic charging effect on detection sensitivity and its application to explosive detection.

    PubMed

    Wong, Melody Yee-Man; Man, Sin-Heng; Che, Chi-Ming; Lau, Kai-Chung; Ng, Kwan-Ming

    2014-03-21

    The simplicity and easy manipulation of a porous substrate-based ESI-MS technique have been widely applied to the direct analysis of different types of samples in positive ion mode. However, the study and application of this technique in negative ion mode are sparse. A key challenge could be due to the ease of electrical discharge on supporting tips upon the application of negative voltage. The aim of this study is to investigate the effect of supporting materials, including polyester, polyethylene and wood, on the detection sensitivity of a porous substrate-based negative ESI-MS technique. By using nitrobenzene derivatives and nitrophenol derivatives as the target analytes, it was found that the hydrophobic materials (i.e., polyethylene and polyester) with a higher tendency to accumulate negative charge could enhance the detection sensitivity towards nitrobenzene derivatives via electron-capture ionization; whereas, compounds with electron affinities lower than the cut-off value (1.13 eV) were not detected. Nitrophenol derivatives with pKa smaller than 9.0 could be detected in the form of deprotonated ions; whereas polar materials (i.e., wood), which might undergo competitive deprotonation with the analytes, could suppress the detection sensitivity. With the investigation of the material effects on the detection sensitivity, the porous substrate-based negative ESI-MS method was developed and applied to the direct detection of two commonly encountered explosives in complex samples. PMID:24492411

  2. Charge-transfer complexes of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone with amino molecules in polar solvents

    NASA Astrophysics Data System (ADS)

    Berto, Silvia; Chiavazza, Enrico; Ribotta, Valentina; Daniele, Pier Giuseppe; Barolo, Claudia; Giacomino, Agnese; Vione, Davide; Malandrino, Mery

    2015-10-01

    The charge-transfer complexes have scientific relevance because this type of molecular interaction is at the basis of the activity of pharmacological compounds and because the absorption bands of the complexes can be used for the quantification of electron donor molecules. This work aims to assess the stability of the charge-transfer complexes between the electron acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and two drugs, procaine and atenolol, in acetonitrile and ethanol. The stability of DDQ in solution and the time required to obtain the maximum complex formation were evaluated. The stoichiometry and the stability of the complexes were determined, respectively, by Job's plot method and by the elaboration of UV-vis titrations data. The latter task was carried out by using the non-linear global analysis approach to determine the equilibrium constants. This approach to data elaboration allowed us to overcome the disadvantages of the classical linear-regression method, to obtain reliable values of the association constants and to calculate the entire spectra of the complexes. NMR spectra were recorded to identify the portion of the donor molecule that was involved in the interaction. The data support the participation of the aliphatic amino groups in complex formation and exclude the involvement of the aromatic amine present in the procaine molecule.

  3. Charge-controlled fixation of DNA molecules on silicon surface and electro-physical properties of Au-DNA-Si interface

    NASA Astrophysics Data System (ADS)

    Bazlov, N. V.; Vyvenko, O. F.; Sokolov, P. A.; Kas'yanenko, N. A.; Petrov, Yu V.

    2013-02-01

    Light-induced fixation of DNA molecules on silicon surface was done and electro-physical properties of Schottky diodes with DNA on interfaces were investigated. Thymus DNA molecules were deposited on silicon from a water solution. Fixed molecular structures were observed with helium ionic microscopy and atomic force microscopy and then they were covered with thermal sputtered gold film. Obtained structures Au-DNA-(n-Si) were examined with current-voltage and frequency dependent admittance measurements. In darkness immobilizing of molecules leaded to form DNA ropes with thickness up to 10 nm and distances between them about 1 mkm. Fixation under illumination resulted in forming of single DNA mesh with thickness about 1 nm and cell size about 100 nm. Presence of molecular mesh on interface leaded to increasing of charge density controlled by metal Fermi level and improved diode quality. Presence of molecular ropes resulted in increasing of charge density controlled by semiconductor. From the estimation of interface state density values the origin of the states at the interface between DNA and silicon substrate is suggested to be DNA phosphate groups contacting or being close to the substrate surface.

  4. Charge-transfer complexes of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone with amino molecules in polar solvents.

    PubMed

    Berto, Silvia; Chiavazza, Enrico; Ribotta, Valentina; Daniele, Pier Giuseppe; Barolo, Claudia; Giacomino, Agnese; Vione, Davide; Malandrino, Mery

    2015-10-01

    The charge-transfer complexes have scientific relevance because this type of molecular interaction is at the basis of the activity of pharmacological compounds and because the absorption bands of the complexes can be used for the quantification of electron donor molecules. This work aims to assess the stability of the charge-transfer complexes between the electron acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and two drugs, procaine and atenolol, in acetonitrile and ethanol. The stability of DDQ in solution and the time required to obtain the maximum complex formation were evaluated. The stoichiometry and the stability of the complexes were determined, respectively, by Job's plot method and by the elaboration of UV-vis titrations data. The latter task was carried out by using the non-linear global analysis approach to determine the equilibrium constants. This approach to data elaboration allowed us to overcome the disadvantages of the classical linear-regression method, to obtain reliable values of the association constants and to calculate the entire spectra of the complexes. NMR spectra were recorded to identify the portion of the donor molecule that was involved in the interaction. The data support the participation of the aliphatic amino groups in complex formation and exclude the involvement of the aromatic amine present in the procaine molecule. PMID:25942088

  5. Impact of negative affectively charged stimuli and response style on cognitive-control-related neural activation: An ERP study

    PubMed Central

    Lamm, C.; Pine, D. S.; Fox, N. A.

    2013-01-01

    The canonical AX-CPT task measures two forms of cognitive control: sustained goal-oriented control (proactive control) and transient changes in cognitive control following unexpected events (reactive control). We modified this task by adding negative and neutral International Affective Picture System (IAPS) pictures to assess the effects of negative emotion on these two forms of cognitive control. Proactive and reactive control styles were assessed based on measures of behavior and electrophysiology, including the N2 event-related potential component and source space activation (Low Resolution Tomography [LORETA]). We found slower reaction-times and greater DLPFC activation for negative relative to neutral stimuli. Additionally, we found that a proactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during actively maintained previously cued information and that a reactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during just-in-time environmentally triggered information. This pattern of results was evident in relatively neutral contexts, but in the face of negative emotion, these associations were not found, suggesting potential response style-by-emotion interaction effects on prefrontal neural activation PMID:24021156

  6. Is ionized oxygen negatively or positively charged more effective for carboxyhemoglobin reduction compare to medical oxygen at atmospheric pressure?

    PubMed

    Pere?insk, S; Kron, I; Engler, I; Murnov, L; Doni?, V; Varga, M; Marossy, A; Legth, ?

    2015-12-29

    Carbon monoxide (CO) reversibly binds to hemoglobin forming carboxyhemoglobin (COHb). CO competes with O(2) for binding place in hemoglobin leading to tissue hypoxia. Already 30 % saturation of COHb can be deadly. Medical oxygen at atmospheric pressure as a therapy is not enough effective. Therefore hyperbaric oxygen O(2) inhalation is recommended. There was a question if partially ionized oxygen can be a better treatment at atmospheric pressure. In present study we evaluated effect of partially ionized oxygen produced by device Oxygen Ion 3000 by Dr. Engler in elimination of COHb in vitro experiments and in smokers. Diluted blood with different content of CO was purged with 5 l/min of either medicinal oxygen O(2), negatively ionized O(2) or positively ionized O(2) for 15 min, then the COHb content was checked. In vivo study, 15 smokers inhaled of either medicinal oxygen O(2) or negatively ionized O(2), than we compared CO levels in expired air before and after inhalation. In both studies we found the highest elimination of CO when we used negatively ionized O(2). These results confirmed the benefit of short inhalation of negatively ionized O(2), in frame of Ionized Oxygen Therapy (I O(2)Th/Engler) which could be used in smokers for decreasing of COHb in blood. PMID:26047377

  7. Crystal structure of Jararacussin-I: the highly negatively charged catalytic interface contributes to macromolecular selectivity in snake venom thrombin-like enzymes.

    PubMed

    Ullah, A; Souza, T A C B; Zanphorlin, L M; Mariutti, R B; Santana, V S; Murakami, M T; Arni, R K

    2013-01-01

    Snake venom serine proteinases (SVSPs) are hemostatically active toxins that perturb the maintenance and regulation of both the blood coagulation cascade and fibrinolytic feedback system at specific points, and hence, are widely used as tools in pharmacological and clinical diagnosis. The crystal structure of a thrombin-like enzyme (TLE) from Bothrops jararacussu venom (Jararacussin-I) was determined at 2.48 resolution. This is the first crystal structure of a TLE and allows structural comparisons with both the Agkistrodon contortrix contortrix Protein C Activator and the Trimeresurus stejnegeri plasminogen activator. Despite the highly conserved overall fold, significant differences in the amino acid compositions and three-dimensional conformations of the loops surrounding the active site significantly alter the molecular topography and charge distribution profile of the catalytic interface. In contrast to other SVSPs, the catalytic interface of Jararacussin-I is highly negatively charged, which contributes to its unique macromolecular selectivity. PMID:23139169

  8. Matrix assisted ionization: new aromatic and nonaromatic matrix compounds producing multiply charged lipid, peptide, and protein ions in the positive and negative mode observed directly from surfaces.

    PubMed

    Li, Jing; Inutan, Ellen D; Wang, Beixi; Lietz, Christopher B; Green, Daniel R; Manly, Cory D; Richards, Alicia L; Marshall, Darrell D; Lingenfelter, Steven; Ren, Yue; Trimpin, Sarah

    2012-10-01

    Matrix assisted inlet ionization (MAII) is a method in which a matrix:analyte mixture produces mass spectra nearly identical to electrospray ionization without the application of a voltage or the use of a laser as is required in laserspray ionization (LSI), a subset of MAII. In MAII, the sample is introduced by, for example, tapping particles of dried matrix:analyte into the inlet of the mass spectrometer and, therefore, permits the study of conditions pertinent to the formation of multiply charged ions without the need of absorption at a laser wavelength. Crucial for the production of highly charged ions are desolvation conditions to remove matrix molecules from charged matrix:analyte clusters. Important factors affecting desolvation include heat, vacuum, collisions with gases and surfaces, and even radio frequency fields. Other parameters affecting multiply charged ion production is sample preparation, including pH and solvent composition. Here, findings from over 100 compounds found to produce multiply charged analyte ions using MAII with the inlet tube set at 450 °C are presented. Of the compounds tested, many have -OH or -NH(2) functionality, but several have neither (e.g., anthracene), nor aromaticity or conjugation. Binary matrices are shown to be applicable for LSI and solvent-free sample preparation can be applied to solubility restricted compounds, and matrix compounds too volatile to allow drying from common solvents. Our findings suggest that the physical properties of the matrix such as its morphology after evaporation of the solvent, its propensity to evaporate/sublime, and its acidity are more important than its structure and functional groups. PMID:22895857

  9. Enhancement of NK Cell Cytotoxicity Induced by Long-Term Living in Negatively Charged-Particle Dominant Indoor Air-Conditions

    PubMed Central

    Nishimura, Yasumitsu; Takahashi, Kazuaki; Mase, Akinori; Kotani, Muneo; Ami, Kazuhisa; Maeda, Megumi; Shirahama, Takashi; Lee, Suni; Matsuzaki, Hidenori; Kumagai-Takei, Naoko; Yoshitome, Kei; Otsuki, Takemi

    2015-01-01

    Investigation of house conditions that promote health revealed that negatively charged-particle dominant indoor air-conditions (NCPDIAC) induced immune stimulation. Negatively charged air-conditions were established using a fine charcoal powder on walls and ceilings and utilizing forced negatively charged particles (approximate diameter: 20 nm) dominant in indoor air-conditions created by applying an electric voltage (72 V) between the backside of the walls and the ground. We reported previously that these conditions induced a slight and significant increase of interleukin-2 during a 2.5-h stay and an increase of NK cell cytotoxicity when examining human subjects after a two-week night stay under these conditions. In the present study, seven healthy volunteers had a device installed to create NCPDIAC in the living or sleeping rooms of their own homes. Every three months the volunteers then turned the NCPDIAC device on or off. A total of 16 ON and 13 OFF trials were conducted and their biological effects were analyzed. NK activity increased during ON trials and decreased during OFF trials, although no other adverse effects were found. In addition, there were slight increases of epidermal growth factor (EGF) during ON trials. Furthermore, a comparison of the cytokine status between ON and OFF trials showed that basic immune status was stimulated slightly during ON trials under NCPIADC. Our overall findings indicate that the NCPDIAC device caused activation of NK activity and stimulated immune status, particularly only on NK activity, and therefore could be set in the home or office buildings. PMID:26173062

  10. Enhancement of NK Cell Cytotoxicity Induced by Long-Term Living in Negatively Charged-Particle Dominant Indoor Air-Conditions.

    PubMed

    Nishimura, Yasumitsu; Takahashi, Kazuaki; Mase, Akinori; Kotani, Muneo; Ami, Kazuhisa; Maeda, Megumi; Shirahama, Takashi; Lee, Suni; Matsuzaki, Hidenori; Kumagai-Takei, Naoko; Yoshitome, Kei; Otsuki, Takemi

    2015-01-01

    Investigation of house conditions that promote health revealed that negatively charged-particle dominant indoor air-conditions (NCPDIAC) induced immune stimulation. Negatively charged air-conditions were established using a fine charcoal powder on walls and ceilings and utilizing forced negatively charged particles (approximate diameter: 20 nm) dominant in indoor air-conditions created by applying an electric voltage (72 V) between the backside of the walls and the ground. We reported previously that these conditions induced a slight and significant increase of interleukin-2 during a 2.5-h stay and an increase of NK cell cytotoxicity when examining human subjects after a two-week night stay under these conditions. In the present study, seven healthy volunteers had a device installed to create NCPDIAC in the living or sleeping rooms of their own homes. Every three months the volunteers then turned the NCPDIAC device on or off. A total of 16 ON and 13 OFF trials were conducted and their biological effects were analyzed. NK activity increased during ON trials and decreased during OFF trials, although no other adverse effects were found. In addition, there were slight increases of epidermal growth factor (EGF) during ON trials. Furthermore, a comparison of the cytokine status between ON and OFF trials showed that basic immune status was stimulated slightly during ON trials under NCPIADC. Our overall findings indicate that the NCPDIAC device caused activation of NK activity and stimulated immune status, particularly only on NK activity, and therefore could be set in the home or office buildings. PMID:26173062

  11. Femtosecond transient studies of charge transfer in polymers doped with acceptor molecules; applications for organic solar cells

    NASA Astrophysics Data System (ADS)

    Holt, Josh; Sheng, Chuanxiang; Drori, Tomer; Valy Vardeny, Z.

    2006-10-01

    Current developments in organic solar cells (5% efficiency nowadays) require understanding and control of charge carrier transfer and electronic state dynamics of donor-acceptor pairs. One current drawback to organic solar cell efficiency is negligible absorption in the near infrared region of the solar spectrum. We provide evidence that poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (MEH-PPV) doped with 2,7-dinitrofluoronone (DNF) forms a charge transfer complex state that can extend absorption into the near infrared. We found that photoluminescence and the photoinduced absorption (PA) band of excitons are simultaneously quenched. Ultrafast spectroscopic measurements with spectral range from 0.2 to 1.2 eV provide insights into polaron and exciton band dynamics for these complexes. We also suggest a mechanism for bimolecular charge transfer in this system.

  12. Inserting Thienyl Linkers into Conjugated Molecules for Efficient Multilevel Electronic Memory: A New Understanding of Charge-Trapping in Organic Materials.

    PubMed

    Li, Yang; Li, Hua; He, Jinghui; Xu, Qingfeng; Li, Najun; Chen, Dongyun; Lu, Jianmei

    2016-03-18

    The practical application of organic memory devices requires low power consumption and reliable device quality. Herein, we report that inserting thienyl units into D-π-A molecules can improve these parameters by tuning the texture of the film. Theoretical calculations revealed that introducing thienyl π bridges increased the planarity of the molecular backbone and extended the D-A conjugation. Thus, molecules with more thienyl spacers showed improved stacking and orientation in the film state relative to the substrates. The corresponding sandwiched memory devices showed enhanced ternary memory behavior, with lower threshold voltages and better repeatability. The conductive switching and variation in the performance of the memory devices were interpreted by using an extended-charge-trapping mechanism. Our study suggests that judicious molecular engineering can facilitate control of the orientation of the crystallite in the solid state to achieve superior multilevel memory performance. PMID:26812155

  13. R.E.D. Server: a web service for deriving RESP and ESP charges and building force field libraries for new molecules and molecular fragments.

    PubMed

    Vanquelef, Enguerran; Simon, Sabrina; Marquant, Gaelle; Garcia, Elodie; Klimerak, Geoffroy; Delepine, Jean Charles; Cieplak, Piotr; Dupradeau, François-Yves

    2011-07-01

    R.E.D. Server is a unique, open web service, designed to derive non-polarizable RESP and ESP charges and to build force field libraries for new molecules/molecular fragments. It provides to computational biologists the means to derive rigorously molecular electrostatic potential-based charges embedded in force field libraries that are ready to be used in force field development, charge validation and molecular dynamics simulations. R.E.D. Server interfaces quantum mechanics programs, the RESP program and the latest version of the R.E.D. tools. A two step approach has been developed. The first one consists of preparing P2N file(s) to rigorously define key elements such as atom names, topology and chemical equivalencing needed when building a force field library. Then, P2N files are used to derive RESP or ESP charges embedded in force field libraries in the Tripos mol2 format. In complex cases an entire set of force field libraries or force field topology database is generated. Other features developed in R.E.D. Server include help services, a demonstration, tutorials, frequently asked questions, Jmol-based tools useful to construct PDB input files and parse R.E.D. Server outputs as well as a graphical queuing system allowing any user to check the status of R.E.D. Server jobs. PMID:21609950

  14. R.E.D. Server: a web service for deriving RESP and ESP charges and building force field libraries for new molecules and molecular fragments

    PubMed Central

    Vanquelef, Enguerran; Simon, Sabrina; Marquant, Gaelle; Garcia, Elodie; Klimerak, Geoffroy; Delepine, Jean Charles; Cieplak, Piotr; Dupradeau, François-Yves

    2011-01-01

    R.E.D. Server is a unique, open web service, designed to derive non-polarizable RESP and ESP charges and to build force field libraries for new molecules/molecular fragments. It provides to computational biologists the means to derive rigorously molecular electrostatic potential-based charges embedded in force field libraries that are ready to be used in force field development, charge validation and molecular dynamics simulations. R.E.D. Server interfaces quantum mechanics programs, the RESP program and the latest version of the R.E.D. tools. A two step approach has been developed. The first one consists of preparing P2N file(s) to rigorously define key elements such as atom names, topology and chemical equivalencing needed when building a force field library. Then, P2N files are used to derive RESP or ESP charges embedded in force field libraries in the Tripos mol2 format. In complex cases an entire set of force field libraries or force field topology database is generated. Other features developed in R.E.D. Server include help services, a demonstration, tutorials, frequently asked questions, Jmol-based tools useful to construct PDB input files and parse R.E.D. Server outputs as well as a graphical queuing system allowing any user to check the status of R.E.D. Server jobs. PMID:21609950

  15. Redox-Active Star Molecules Incorporating the 4-Benzolypyridinium Cation: Implications for the Charge Transfer Efficiency Along Branches versus Across the Perimeter in Dendrimers

    NASA Technical Reports Server (NTRS)

    Yang, Jin-Hua; Rawashdeh, Abdel Monem M.; Oh, Woon Su; Sotiriou-Leventis, Chariklia; Leventis, Nicholas

    2003-01-01

    We report the redox properties of four star systems incorporating the 4-benzoyl-N-alkylpyridinium cation; the redox potential varies along the branches, but remains constant at fixed radii. Voltammetric analysis (cyclic voltammetry and differential pulse voltammetry) shows that only two of the three redox-active centers in the perimeter are electrochemically accessible during potential sweeps as slow as 20 mV/s and as fast as 10 V/s. On the contrary, both redox centers of a branch are accessible electrochemically within the same time frame. These results are discussed in terms of slow through-space charge transfer and the globular 3-D folding of the molecules.

  16. Predictive DFT-based approaches to charge and spin transport in single-molecule junctions and two-dimensional materials: successes and challenges.

    PubMed

    Quek, Su Ying; Khoo, Khoong Hong

    2014-11-18

    CONSPECTUS: The emerging field of flexible electronics based on organics and two-dimensional (2D) materials relies on a fundamental understanding of charge and spin transport at the molecular and nanoscale. It is desirable to make predictions and shine light on unexplained experimental phenomena independently of experimentally derived parameters. Indeed, density functional theory (DFT), the workhorse of first-principles approaches, has been used extensively to model charge/spin transport at the nanoscale. However, DFT is essentially a ground state theory that simply guarantees correct total energies given the correct charge density, while charge/spin transport is a nonequilibrium phenomenon involving the scattering of quasiparticles. In this Account, we critically assess the validity and applicability of DFT to predict charge/spin transport at the nanoscale. We also describe a DFT-based approach, DFT+?, which incorporates corrections to Kohn-Sham energy levels based on many-electron calculations. We focus on single-molecule junctions and then discuss how the important considerations for DFT descriptions of transport can differ in 2D materials. We conclude that when used appropriately, DFT and DFT-based approaches can play an important role in making predictions and gaining insight into transport in these materials. Specifically, we shall focus on the low-bias quasi-equilibrium regime, which is also experimentally most relevant for single-molecule junctions. The next question is how well can the scattering of DFT Kohn-Sham particles approximate the scattering of true quasiparticles in the junction? Quasiparticles are electrons (holes) that are surrounded by a constantly changing cloud of holes (electrons), but Kohn-Sham particles have no physical significance. However, Kohn-Sham particles can often be used as a qualitative approximation to quasiparticles. The errors in standard DFT descriptions of transport arise primarily from errors in the Kohn-Sham energy levels (self-energy errors). These errors are small in the strong-coupling regime where the molecular levels are significantly broadened at the Fermi level but are large in the coherent off-resonant tunneling regime where DFT overestimates conductance by orders of magnitude. The DFT+? approach uses a physically motivated, parameter free estimate of the self-energy corrections to correct the energy levels in DFT, giving conductance in quantitative agreement with experiment for a large but nonexhaustive class of single-molecule junctions. In 2D materials, the self-energy error is relatively small, and critical issues stem instead from the large length scales in experiments, which make it necessary to consider band-bending within the 2D material, as well as scattering due to electron-phonon interactions, spin-flip interactions, defects, etc. PMID:24933289

  17. A Fourier transform infrared spectroscopic study of the interaction of alkaline earth cations with the negatively charged phospholipid 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol.

    PubMed

    Garidel, P; Blume, A; Hbner, W

    2000-06-01

    The interaction of aqueous phospholipid dispersions of negatively charged 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol, sodium salt (DMPG) with the divalent cations Mg(2+), Ca(2+) and Sr(2+) at equimolar ratios in 100 mM NaCl at pH 7 was investigated by Fourier transform infrared spectroscopy. The binding of the three cations induces a crystalline-like gel phase with highly ordered and rigid all-trans acyl chains. These features are observed after storage below room temperature for 24 h. When the gel phase is heated after prolonged incubation at low temperature phase transitions into the liquid crystalline phase are observed at 58 degrees C for the DMPG:Sr(2+), 65 degrees C for the DMPG:Mg(2+), and 80 degrees C for the DMPG:Ca(2+) complex. By subsequent cooling from temperatures above T(m) these complexes retain the features of a liquid crystalline phase with disordered acyl chains until a metastable gel phase is formed at temperatures between 38 and 32 degrees C. This phase is characterized by predominantly all-trans acyl chains, arranged in a loosely packed hexagonal or distorted hexagonal subcell lattice. Reheating the DMPG:Sr(2+) samples after a storage time of 2 h at 4 degrees C results in the transition of the metastable gel to the liquid crystalline phase at 35 degrees C. This phase transition into the liquid crystalline state at 35 degrees C is also observed for the Mg(2+) complex. However, for DMPG:Mg(2+) at higher temperatures, a partial recrystallization of the acyl chains occurs and the high temperature phase transition at 65 degrees C is also detected. In contrast, DMPG:Ca(2+) exhibits only the phase transition at 80 degrees C from the crystalline gel into the fluid state upon reheating. Below 20 degrees C, the rate of conversion from the metastable gel to a thermodynamically stable, crystalline-like gel phase decreases in the order Ca(2+)&z. Gt;Mg(2+)>Sr(2+). This conversion into the crystalline gel phase is accompanied by a complete dehydration of the phosphate groups in DMPG:Mg(2+) and by a reorientation of the polar lipid head groups in DMPG:Ca(2+) and in DMPG:Sr(2+). The primary binding sites of the cations are the PO(2)(-) groups of the phosphodiester moiety. Our infrared spectroscopic results suggest a deep penetration of the divalent cations into the polar head group region of DMPG bilayers, whereby the ester carbonyl groups, located in the interfacial region of the bilayers, are indirectly affected by strong hydrogen bonding of immobilized water molecules. In the liquid crystalline phase, the interaction of all three cations with DMPG is weak, but still observable in the infrared spectra of the DMPG:Ca(2+) complex by a slight ordering effect induced in the acyl chains, when compared to pure DMPG liposomes. PMID:10825446

  18. Quasi-ohmic single molecule charge transport through highly conjugated meso-to-meso ethyne-bridged porphyrin wires.

    PubMed

    Li, Zhihai; Park, Tae-Hong; Rawson, Jeff; Therien, Michael J; Borguet, Eric

    2012-06-13

    Understanding and controlling electron transport through functional molecules are of primary importance to the development of molecular scale devices. In this work, the single molecule resistances of meso-to-meso ethyne-bridged (porphinato)zinc(II) structures (PZn(n) compounds), connected to gold electrodes via (4'-thiophenyl)ethynyl termini, are determined using scanning tunneling microscopy-based break junction methods. These experiments show that each α,ω-di[(4'-thiophenyl)ethynyl]-terminated PZn(n) compound (dithiol-PZn(n)) manifests a dual molecular conductance. In both the high and low conductance regimes, the measured resistance across these metal-dithiol-PZn(n)-metal junctions increases in a near linear fashion with molecule length. These results signal that meso-to-meso ethyne-bridged porphyrin wires afford the lowest β value (β = 0.034 Å(-1)) yet determined for thiol-terminated single molecules that manifest a quasi-ohmic resistance dependence across metal-dithiol-PZn(n)-metal junctions. PMID:22500812

  19. Characterization of a Novel Small Molecule That Potentiates β-Lactam Activity against Gram-Positive and Gram-Negative Pathogens

    PubMed Central

    Nair, Dhanalakshmi R.; Monteiro, João M.; Memmi, Guido; Thanassi, Jane; Pucci, Michael; Schwartzman, Joseph; Pinho, Mariana G.

    2015-01-01

    In a loss-of-viability screen using small molecules against methicillin-resistant Staphylococcus aureus (MRSA) strain USA300 with a sub-MIC of a β-lactam, we found a small molecule, designated DNAC-1, which potentiated the effect of oxacillin (i.e., the MIC of oxacillin decreased from 64 to 0.25 μg/ml). Fluorescence microscopy indicated a disruption in the membrane structures within 15 min of exposure to DNAC-1 at 2× MIC. This permeabilization was accompanied by a rapid loss of membrane potential, as monitored by use of the DiOC2 (3,3′-diethyloxacarbocyanine iodide) dye. Macromolecular analysis showed the inhibition of staphylococcal cell wall synthesis by DNAC-1. Transmission electron microscopy of treated MRSA USA300 cells revealed a slightly thicker cell wall, together with mesosome-like projections into the cytosol. The exposure of USA300 cells to DNAC-1 was associated with the mislocalization of FtsZ accompanied by the localization of penicillin-binding protein 2 (PBP2) and PBP4 away from the septum, as well as mild activation of the vraRS-mediated cell wall stress response. However, DNAC-1 does not have any generalized toxicity toward mammalian host cells. DNAC-1 in combination with ceftriaxone is also effective against an assortment of Gram-negative pathogens. Using a murine subcutaneous coinjection model with 108 CFU of USA300 as a challenge inoculum, DNAC-1 alone or DNAC-1 with a sub-MIC of oxacillin resulted in a 6-log reduction in bacterial load and decreased abscess formation compared to the untreated control. We propose that DNAC-1, by exerting a bimodal effect on the cell membrane and cell wall, is a viable candidate in the development of combination therapy against many common bacterial pathogens. PMID:25583731

  20. Femtochemistry of mass-selected negative-ion clusters of dioxygen: Charge-transfer and solvation dynamics

    NASA Astrophysics Data System (ADS)

    Paik, D. Hern; Bernhardt, Thorsten M.; Kim, Nam Joon; Zewail, Ahmed H.

    2001-07-01

    Femtosecond, time-resolved photoelectron spectroscopy is used to investigate the dissociation dynamics of mass-selected anionic molecular-oxygen clusters. The observed transient photoelectron signal for the clusters (O2)n- (n=3-5) shows the O2- production; for n=1 and 2, we observe no time-dependence at this wavelength of 800 nm. The observed transients are bi-exponential in form with two distinct time constants, but with clear trends, for all investigated cluster sizes. These striking observations describe the reaction pathways of the solvated core and we elucidate two primary processes: Charge transfer with concomitant nuclear motion, and direct dissociation of the O4- core-ion via electron recombination; the former takes 700-2700 fs, while the latter is on a shorter time scale, 110-420 fs. Both rates decrease differently upon increasing cluster size, indicating the critical role of step-wise solvation.

  1. A negative charge in transmembrane segment 1 of domain II of the cockroach sodium channel is critical for channel gating and action of pyrethroid insecticides

    SciTech Connect

    Du Yuzhe; Song Weizhong; Groome, James R.; Nomura, Yoshiko; Luo Ningguang; Dong Ke

    2010-08-15

    Voltage-gated sodium channels are the primary target of pyrethroids, an important class of synthetic insecticides. Pyrethroids bind to a distinct receptor site on sodium channels and prolong the open state by inhibiting channel deactivation and inactivation. Recent studies have begun to reveal sodium channel residues important for pyrethroid binding. However, how pyrethroid binding leads to inhibition of sodium channel deactivation and inactivation remains elusive. In this study, we show that a negatively charged aspartic acid residue at position 802 (D802) located in the extracellular end of transmembrane segment 1 of domain II (IIS1) is critical for both the action of pyrethroids and the voltage dependence of channel activation. Charge-reversing or -neutralizing substitutions (K, G, or A) of D802 shifted the voltage dependence of activation in the depolarizing direction and reduced channel sensitivity to deltamethrin, a pyrethroid insecticide. The charge-reversing mutation D802K also accelerated open-state deactivation, which may have counteracted the inhibition of sodium channel deactivation by deltamethrin. In contrast, the D802G substitution slowed open-state deactivation, suggesting an additional mechanism for neutralizing the action of deltamethrin. Importantly, Schild analysis showed that D802 is not involved in pyrethroid binding. Thus, we have identified a sodium channel residue that is critical for regulating the action of pyrethroids on the sodium channel without affecting the receptor site of pyrethroids.

  2. Binding of cationic pentapeptides with modified side chain lengths to negatively charged lipid membranes: Complex interplay of electrostatic and hydrophobic interactions.

    PubMed

    Hoernke, Maria; Schwieger, Christian; Kerth, Andreas; Blume, Alfred

    2012-07-01

    Basic amino acids play a key role in the binding of membrane associated proteins to negatively charged membranes. However, side chains of basic amino acids like lysine do not only provide a positive charge, but also a flexible hydrocarbon spacer that enables hydrophobic interactions. We studied the influence of hydrophobic contributions to the binding by varying the side chain length of pentapeptides with ammonium groups starting with lysine to lysine analogs with shorter side chains, namely omithine (Orn), alpha, gamma-diaminobutyric acid (Dab) and alpha, beta-diaminopropionic acid (Dap). The binding to negatively charged phosphatidylglycerol (PG) membranes was investigated by calorimetry, FT-infrared spectroscopy (FT-IR) and monolayer techniques. The binding was influenced by counteracting and sometimes compensating contributions. The influence of the bound peptides on the lipid phase behavior depends on the length of the peptide side chains. Isothermal titration calorimetry (ITC) experiments showed exothermic and endothermic effects compensating to a different extent as a function of side chain length. The increase in lipid phase transition temperature was more significant for peptides with shorter side chains. FTIR-spectroscopy revealed changes in hydration of the lipid bilayer interface after peptide binding. Using monolayer techniques, the contributions of electrostatic and hydrophobic effects could clearly be observed. Peptides with short side chains induced a pronounced decrease in surface pressure of PG monolayers whereas peptides with additional hydrophobic interactions decreased the surface pressure much less or even lead to an increase, indicating insertion of the hydrophobic part of the side chain into the lipid monolayer. PMID:22433675

  3. Effect of donor-acceptor orientation on ultrafast photoinduced electron transfer and dark charge recombination in porphyrin-quinone molecules

    SciTech Connect

    Sakata, Yoshiteru; Tsue, Hirohito ); O'Neil, M.P.; Wiederrecht, G.P.; Wasielewski, M.R. )

    1994-07-27

    A series of four zinc porphyrin-spacer-benzoquinone molecules were studied in which the spacer is either spiro[4,4]nonane or trans-decalin. The benzoquinone is attached to the porphyrin at two fixed distances each possessing two fixed orientations of the porphyrin relative to the quinone. The rate constants for photoinduced electron transfer from the lowest excited singlet state of the porphyrin to the quinone to form the Zn porphyrin[sup +]-quinone[sup [minus

  4. Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Meng; Zhao, Jing; Liu, Jinxiang; Zhou, Lianwen; Bu, Yuxiang

    2013-01-01

    We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the ?⋯HO interactions in the neutral Bz(H2O)n (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the ? system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (?*) of the Bz ring, and the ?⋯HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak ?⋯HO interaction plays an important role as the driving force in conversion of the two states.

  5. Charge state distribution studies of SrF 3, MnF 3 and CaF 3 molecules using single and double stripping in a Tandem accelerator

    NASA Astrophysics Data System (ADS)

    Kumar, Pankaj; Korschinek, G.; Chopra, S.; Faestermann, T.; Ludwig, P.; Rugel, G.; Seiler, D.; Wallner, A.; Ojha, S.; Gargari, S.; Joshi, R.; Kanjilal, D.

    2011-09-01

    High energy beams of high ion currents from a Tandem accelerator are a common requirement in nuclear physics, materials science and Accelerator Mass Spectrometry (AMS) research. In many cases, molecular beams are chosen from the ion source to achieve a high ion source yield for the negative ions, or, as for AMS, to suppress isobaric interference. For this reason we have studied the use of consecutive stripper foils, double stripping, to increase the ion yield in conjunction with increased energy of injected molecular beams through a Tandem accelerator. By this method we could achieve a shift in the yield towards higher charge states.

  6. REVISED BIG BANG NUCLEOSYNTHESIS WITH LONG-LIVED, NEGATIVELY CHARGED MASSIVE PARTICLES: UPDATED RECOMBINATION RATES, PRIMORDIAL {sup 9}Be NUCLEOSYNTHESIS, AND IMPACT OF NEW {sup 6}Li LIMITS

    SciTech Connect

    Kusakabe, Motohiko; Kim, K. S.; Cheoun, Myung-Ki; Kajino, Toshitaka; Kino, Yasushi; Mathews, Grant J. E-mail: kyungsik@kau.ac.kr E-mail: kajino@nao.ac.jp E-mail: gmathews@nd.edu

    2014-09-01

    We extensively reanalyze the effects of a long-lived, negatively charged massive particle, X {sup –}, on big bang nucleosynthesis (BBN). The BBN model with an X {sup –} particle was originally motivated by the discrepancy between the {sup 6,} {sup 7}Li abundances predicted in the standard BBN model and those inferred from observations of metal-poor stars. In this model, {sup 7}Be is destroyed via the recombination with an X {sup –} particle followed by radiative proton capture. We calculate precise rates for the radiative recombinations of {sup 7}Be, {sup 7}Li, {sup 9}Be, and {sup 4}He with X {sup –}. In nonresonant rates, we take into account respective partial waves of scattering states and respective bound states. The finite sizes of nuclear charge distributions cause deviations in wave functions from those of point-charge nuclei. For a heavy X {sup –} mass, m{sub X} ≳ 100 GeV, the d-wave → 2P transition is most important for {sup 7}Li and {sup 7,} {sup 9}Be, unlike recombination with electrons. Our new nonresonant rate of the {sup 7}Be recombination for m{sub X} = 1000 GeV is more than six times larger than the existing rate. Moreover, we suggest a new important reaction for {sup 9}Be production: the recombination of {sup 7}Li and X {sup –} followed by deuteron capture. We derive binding energies of X nuclei along with reaction rates and Q values. We then calculate BBN and find that the amount of {sup 7}Be destruction depends significantly on the charge distribution of {sup 7}Be. Finally, updated constraints on the initial abundance and the lifetime of the X {sup –} are derived in the context of revised upper limits to the primordial {sup 6}Li abundance. Parameter regions for the solution to the {sup 7}Li problem and the primordial {sup 9}Be abundances are revised.

  7. Negatively Charged Metal Oxide Nanoparticles Interact with the 20S Proteasome and Differentially Modulate Its Biologic Functional Effects

    PubMed Central

    Falaschetti, Christine A.; Paunesku, Tatjana; Kurepa, Jasmina; Nanavati, Dhaval; Chou, Stanley S.; De, Mrinmoy; Song, MinHa; Jang, Jung-tak; Wu, Aiguo; Dravid, Vinayak P.; Cheon, Jinwoo; Smalle, Jan; Woloschak, Gayle E.

    2013-01-01

    The multicatalytic ubiquitin-proteasome system (UPS) carries out proteolysis in a highly orchestrated way and regulates a large number of cellular processes. Deregulation of the UPS in many disorders has been documented. In some cases, e.g. carcinogenesis, elevated proteasome activity has been implicated in disease development, while the etiology of other diseases, e.g. neurodegeneration, includes decreased UPS activity. Therefore, agents that alter proteasome activity could suppress as well as enhance a multitude of diseases. Metal oxide nanoparticles, often developed as diagnostic tools, have not previously been tested as modulators of proteasome activity. Here, several types of metal oxide nanoparticles were found to adsorb to the proteasome and show variable preferential binding for particular proteasome subunits with several peptide binding hotspots possible. These interactions depend on the size, charge, and concentration of the nanoparticles and affect proteasome activity in a time-dependent manner. Should metal oxide nanoparticles increase proteasome activity in cells, as they do in vitro, unintended effects related to changes in proteasome function can be expected. PMID:23930940

  8. Charge density of the biologically active molecule (2-oxo-1,3-benzoxazol-3(2H)-yl)acetic acid.

    PubMed

    Wang, Ai; Ashurov, Jamshid; Ibragimov, Aziz; Wang, Ruimin; Mouhib, Halima; Mukhamedov, Nasir; Englert, Ulli

    2016-02-01

    (2-Oxo-1,3-benzoxazol-3(2H)-yl)acetic acid is a member of a biologically active class of compounds. Its molecular structure in the crystal has been determined by X-ray diffraction, and its gas phase structure was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory. In order to understand the dynamics of the molecule, two presumably soft degrees of freedom associated with the relative orientation of the planar benzoxazolone system and its substituent at the N atom were varied systematically. Five conformers have been identified as local minima on the resulting two-dimensional potential energy surface within an energy window of 27 kJ mol(-1). The energetically most favourable minimum closely matches the conformation observed in the crystal. Based on high-resolution diffraction data collected at low temperature, the experimental electron density of the compound was determined. Comparison with the electron density established by theory for the isolated molecule allowed the effect of intermolecular interactions to be addressed, in particular a moderately strong O-H...O hydrogen bond with a donor...acceptor distance of 2.6177 (9) Å: the oxygen acceptor is clearly polarized in the extended solid. The hydrogen bond connects consecutive molecules to chains, and the pronounced charge separation leads to stacking between neighburs with antiparallel dipole moments perpendicular to the chain direction. PMID:26830806

  9. Redox-Active Star Molecules Incorporating the 4-Benzoylpyridinium Cation - Implications for the Charge Transfer Along Branches vs. Across the Perimeter in Dendrimer

    NASA Technical Reports Server (NTRS)

    Leventis, Nicholas; Yang, Jinua; Fabrizio,Even F.; Rawashdeh, Abdel-Monem M.; Oh, Woon Su; Sotiriou-Leventis, Chariklia

    2004-01-01

    Dendrimers are self-repeating globular branched star molecules, whose fractal structure continues to fascinate, challenge, and inspire. Functional dendrimers may incorporate redox centers, and potential applications include antennae molecules for light harvesting, sensors, mediators, and artificial biomolecules. We report the synthesis and redox properties of four star systems incorporating the 4-benzoyl-N-alkylpyridinium cation; the redox potential varies along the branches but remains constant at fixed radii. Bulk electrolysis shows that at a semi-infinite time scale all redox centers are electrochemically accessible. However, voltammetric analysis (cyclic voltammetry and differential pulse voltammetry) shows that on1y two of the three redox-active centers in the perimeter are electrochemically accessible during potential sweeps as slow as 20 mV/s and as fast as 10 V/s. On the contrary, both redox centers along branches are accessible electrochemically within the same time frame. These results are explained in terms of slow through-space charge transfer and the globular 3-D folding of the molecules and are discussed in terms of their implications on the design of efficient redox functional dendrimers.

  10. Charge localization and charge transfer in the Bebq2 monomer and dimer.

    PubMed

    Safonov, Andrei A; Bagaturyants, Alexander A

    2014-08-01

    The geometrical structure and electronic properties of bis(10-hydroxybenzo[h]quinolinato)beryllium (Bebq2) molecule and its dimer both in the neutral and in the positively and negatively charged states were studied using quantum-chemical calculations. It is found that the excess charge in the charged systems is localized on one of the hydroxybenzoquinoline ligands. Structural changes in charged Bebq2 are pronounced in the charged ligand and nearly negligible in the neutral ligand. Charge transfer from the charged ligand to a neutral one can proceed either within a single Bebq2 monomer molecule or between the different monomers in the Bebq2 dimer. The corresponding hopping integrals were estimated as half the excitation energy from the ground to the first excited state of either the monomer or the dimer calculated at the avoided crossing point. PMID:25107360

  11. Hydration free energy of polar and charged molecules and amino acids: From water structure to hydration thermodynamics

    NASA Astrophysics Data System (ADS)

    Garde, Shekhar; Hummer, Gerhard; Paulaitis, Michael E.; Garcia, Angel E.

    1998-03-01

    The structure of water in the vicinity of molecular solutes or protein surfaces plays an important role in their hydration thermodynamics. For cases in which the electrostatic contributions to the free energy of hydration are dominant, calculation of the electrostatic potentials at charge sites resulting from the molecular structure of water is a crucial step. We present a method that uses local water-oxygen and hydrogen densities to calculate the electrostatic potentials and the free energies of hydration. These densities are obtained either from computer simulations or are predicted using theoretical approaches. Applications to the hydration of amino acids as well as proteins will be presented.

  12. Ab initio treatment of charge transfer in ion-molecule collisions based on one-electron wave functions

    NASA Astrophysics Data System (ADS)

    Gabs, P. M. M.; Errea, L. F.; Mndez, L.; Rabadn, I.

    2012-01-01

    Two simple ab initio methods based on one-electron wave functions are employed to calculate the single-electron capture and single ionization of H2O and CO molecules by ion impact. The anisotropy of the molecular targets is taken into account by using multicenter pseudopotentials to represent the interaction of the active electron with the ionic molecular core. These two methods are applied to the study of three collisional systems: H++H2O, He2++H2O, and C2++CO. Comparison with experiments and other theoretical works is presented when available.

  13. PEG-b-PCL copolymer micelles with the ability of pH-controlled negative-to-positive charge reversal for intracellular delivery of doxorubicin.

    PubMed

    Deng, Hongzhang; Liu, Jinjian; Zhao, Xuefei; Zhang, Yuming; Liu, Jianfeng; Xu, Shuxin; Deng, Liandong; Dong, Anjie; Zhang, Jianhua

    2014-11-10

    The application of PEG-b-PCL micelles was dampened by their inherent low drug-loading capability and relatively poor cell uptake efficiency. In this study, a series of novel PEG-b-PCL copolymers methoxy poly(ethylene glycol)-b-poly(ε-caprolactone-co-γ-dimethyl maleamidic acid -ε-caprolactone) (mPEG-b-P(CL-co-DCL)) bearing different amounts of acid-labile β-carboxylic amides on the polyester moiety were synthesized. The chain structure and chemical composition of copolymers were characterized by (1)H NMR, Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). mPEG-b-P(CL-co-DCL) with critical micellar concentrations (CMCs) of 3.2-6.3 μg/mL could self-assemble into stable micelles in water with diameters of 100 to 150 nm. Doxorubicin (DOX), a cationic hydrophobic drug, was successfully encapsulated into the polymer micelles, achieving a very high loading content due to electrostatic interaction. Then the stability, charge-conversional behavior, loading and release profiles, cellular uptake and in vitro cytotoxicity of free drug and drug-loaded micelles were evaluated. The β-carboxylic amides functionalized polymer micelles are negatively charged and stable in neutral solution but quickly become positively charged at pH 6.0, due to the hydrolysis of β-carboxylic amides in acidic conditions. The pH-triggered negative-to-positive charge reversal not only resulted in a very fast drug release in acidic conditions, but also effectively enhanced the cellular uptake by electrostatic absorptive endocytosis. The MTT assay demonstrated that mPEG-b-P(CL-co-DCL) micelles were biocompatible to HepG2 cells while DOX-loaded micelles showed significant cytotoxicity. In sum, the introduction of acid-labile β-carboxylic amides on the polyester block in mPEG-b-P(CL-co-DCL) exhibited great potentials for the modifications in the stability in blood circulation, drug solubilization, and release properties, as well as cell internalization and intracellular drug release. PMID:25325531

  14. Bias tuning charge-releasing leading to negative differential resistance in amorphous gallium oxide/Nb:SrTiO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Wang, P. C.; Li, P. G.; Zhi, Y. S.; Guo, D. Y.; Pan, A. Q.; Zhan, J. M.; Liu, H.; Shen, J. Q.; Tang, W. H.

    2015-12-01

    Negative differential resistance (NDR) and bipolar resistive switching (RS) phenomena were observed in Au/Ga2O3-x/Nb:SrTiO3/Au heterostructures fabricated by growing amorphous gallium oxide thin films on 0.7%Nb-doped SrTiO3 substrates using pulsed laser deposition technique. The RS behavior is reproducible and stable without the forming process. The NDR phenomenon happened during the course of RS from low resistance state to high resistance state and was dependent much on the applied forward bias. The bias dependent charge releasing from oxygen vacancies was considered to contribute to the NDR behavior. The results show that there is a very close relationship between NDR and RS.

  15. Time-dependent approach to three-body rearrangement collisions: Application to the capture of heavy negatively charged particles by hydrogen atoms

    SciTech Connect

    Tong, X. M.; Hino, K.; Shirahama, T.; Toshima, N.

    2007-05-15

    We present a theoretical method for Coulomb three-body rearrangement collisions solving a Chew-Goldberger-type integral equation directly. The scattering boundary condition is automatically satisfied by adiabatically switching on the interaction between the projectile and hydrogen atom. Hence the outgoing wave function is obtained without the tedious procedure of adjusting the total wave function in the asymptotic region. All the dynamical information can be derived from the outgoing wave function obtained on pseudospectral grids numerically. Taking {mu}{sup -}+H(1s) and p+H(1s) collisions as examples, we demonstrate the usefulness and powerfulness of the method and present the state-specified capture cross sections of heavy negatively charged particles by hydrogen atoms. The convergence and accuracy of the numerical procedure are examined with sufficient care.

  16. Extension of the spectral responsivity of the photocurrent in solution-processed small molecule composite via a charge transfer excitation

    NASA Astrophysics Data System (ADS)

    Hernandez-Sosa, Gerardo; Tong, Minghong; Coates, Nelson E.; Valouch, Sebastian; Moses, Daniel

    2011-10-01

    Incorporating [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in solution-processed composites comprising the two small molecular semiconductors 9,10-Diphenylanthracene (DPA) and 5,6,11,12-tetraphenylnaphthacene (Rubrene) extends significantly the onset wavelength of the steady-state photoconductivity from 610 nm in the pristine DPA:Rubrene composite to 900 nm in the DPA:Rubrene:PCBM composite. The experimental data indicate carrier generation in the near IR spectral region arising from inter-molecular charge transfer (IMCT) excitation that potentially could be useful for extending solar radiation light harvesting. Pump/probe photoinduced absorption (PIA) measurements indicate instantaneous carrier generation at sub-band-gap photon energies, confirming the viability of IMCT excitations as the underlying carrier generation mechanism at the near IR spectral region.

  17. In-111 chimeric negative-charged-Z2D3 PL-F(ab`){sub 2} imaging of proliferating smooth muscle cell in atherosclerotic lesions

    SciTech Connect

    Carrio, I.; Pieri, P.L.; Narula, J.

    1996-05-01

    Metabolically active plaques have proliferating smooth muscle cells. In-111-labeled negative-charged modified Z2-D3 PL-F(ab`){sub 2} (NC-Z2D3) specific for an antigen in proliferating smooth muscle cells has been shown to accumulate in rabbit atherosclerotic plaques. The safety, biodistribution and accumulation of NC-Z2D3 were assessed in 11 patients with angiographically confirmed carotid atheromas eligible for endarterectomy. NC-Z2D3 (250 mcg) labeled with 5 mCi of In-11 was administered by slow i.v. inj.. Planar and SPECT images were obtained 4, 24, 48 and 72 hrs later. Endarterectomy was then performed and the specimens were analyzed. Focal uptake of In-111-NCZ2D3 at the site of the carotid plaques was seen at 4 hrs. Target to control ratio at 4 hrs was 2.20 {plus_minus} 0.3, 1.98 {plus_minus} 0.03 at 24 hrs, 1.60 {plus_minus} 0.2 at 48 hrs and 1.45 {plus_minus} 0.2 at 72 hrs. The pattern of uptake was frequently more extended than the stenotic regions as delineated by the angiograms. Avidin-Biotin-Peroxidase immunostaining of the specimens revealed staining of proliferating smooth muscle cells at the site of the plaque. Percent of the injected dose per gram localization in the specimens was 0.0475 {plus_minus} 0.007. Blood clearance followed a biexponential curve with a mean t{1/2} of 920 minutes. Nonspecific localization of the antibody was observed in the liver, bone-marrow and kidneys. Adverse reactions were not seen. This study demonstrates the feasibility of targeting active atherosclerotic lesions with negatively charge-modified antibody.

  18. Identification of the SLAM Adapter Molecule EAT-2 as a Lupus-Susceptibility Gene That Acts through Impaired Negative Regulation of Dendritic Cell Signaling.

    PubMed

    Talaei, Nafiseh; Yu, Tao; Manion, Kieran; Bremner, Rod; Wither, Joan E

    2015-11-15

    We showed previously that C57BL/6 congenic mice with an introgressed homozygous 70 cM (125.6 Mb) to 100 cM (179.8 Mb) interval on c1 from the lupus-prone New Zealand Black (NZB) mouse develop high titers of antinuclear Abs and severe glomerulonephritis. Using subcongenic mice, we found that a genetic locus in the 88-96 cM region was associated with altered dendritic cell (DC) function and synergized with T cell functional defects to promote expansion of pathogenic proinflammatory T cell subsets. In this article, we show that the promoter region of the NZB gene encoding the SLAM signaling pathway adapter molecule EWS-activated transcript 2 (EAT-2) is polymorphic, which results in an ? 70% reduction in EAT-2 in DC. Silencing of the EAT-2 gene in DC that lacked this polymorphism led to increased production of IL-12 and enhanced differentiation of T cells to a Th1 phenotype in T cell-DC cocultures, reproducing the phenotype observed for DC from congenic mice with the NZB c1 70-100 cM interval. SLAM signaling was shown to inhibit production of IL-12 by CD40L-activated DCs. Consistent with a role for EAT-2 in this inhibition, knockdown of EAT-2 resulted in increased production of IL-12 by CD40-stimulated DC. Assessment of downstream signaling following CD40 cross-linking in the presence or absence of SLAM cross-linking revealed that SLAM coengagement blocked activation of p38 MAPK and JNK signaling pathways in DC, which was reversed in DC with the NZB EAT-2 allele. We conclude that EAT-2 negatively regulates cytokine production in DC downstream of SLAM engagement and that a genetic polymorphism that disturbs this process promotes the development of lupus. PMID:26432891

  19. Sry HMG Box Protein 9-positive (Sox9+) Epithelial Cell Adhesion Molecule-negative (EpCAM−) Biphenotypic Cells Derived from Hepatocytes Are Involved in Mouse Liver Regeneration*

    PubMed Central

    Tanimizu, Naoki; Nishikawa, Yuji; Ichinohe, Norihisa; Akiyama, Haruhiko; Mitaka, Toshihiro

    2014-01-01

    It has been shown that mature hepatocytes compensate tissue damages not only by proliferation and/or hypertrophy but also by conversion into cholangiocyte-like cells. We found that Sry HMG box protein 9-positive (Sox9+) epithelial cell adhesion molecule-negative (EpCAM−) hepatocyte nuclear factor 4α-positive (HNF4α+) biphenotypic cells showing hepatocytic morphology appeared near EpCAM+ ductular structures in the livers of mice fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diet. When Mx1-Cre:ROSA mice, which were injected with poly(I:C) to label mature hepatocytes, were fed with the DDC diet, we found LacZ+Sox9+ cells near ductular structures. Although Sox9+EpCAM− cells adjacent to expanding ducts likely further converted into ductular cells, the incidence was rare. To know the cellular characteristics of Sox9+EpCAM− cells, we isolated them as GFP+EpCAM− cells from DDC-injured livers of Sox9-EGFP mice. Sox9+EpCAM− cells proliferated and could differentiate to functional hepatocytes in vitro. In addition, Sox9+EpCAM− cells formed cysts with a small central lumen in collagen gels containing Matrigel® without expressing EpCAM. These results suggest that Sox9+EpCAM− cells maintaining biphenotypic status can establish cholangiocyte-type polarity. Interestingly, we found that some of the Sox9+ cells surrounded luminal spaces in DDC-injured liver while they expressed HNF4α. Taken together, we consider that in addition to converting to cholangiocyte-like cells, Sox9+EpCAM− cells provide luminal space near expanded ductular structures to prevent deterioration of the injuries and potentially supply new hepatocytes to repair damaged tissues. PMID:24482234

  20. A disparate subset of double-negative T cells contributes to the outcome of murine fulminant viral hepatitis via effector molecule fibrinogen-like protein 2.

    PubMed

    Wu, Di; Wang, Hongwu; Yan, Weiming; Chen, Tao; Wang, Ming; Han, Meifang; Wu, Zeguang; Wang, Xiaojing; Ai, Guo; Xi, Dong; Shen, Guanxin; Luo, Xiaoping; Ning, Qin

    2016-04-01

    The underlying immune-mediated mechanisms involved in virus-induced severe hepatitis have not been well elucidated. In this study, we investigated the role of CD3(+)CD4(-)CD8(-) double-negative T (DN T) cells in the pathogenesis of fulminant viral hepatitis (FVH) induced by murine hepatitis virus strain 3 (MHV-3). After MHV-3 infection, the proportions of DN T cells increased significantly in BALB/cJ mice, and splenic DN T cells expressing high levels of CD69 were recruited by MHV-3-infected hepatocytes to the liver. Serum levels of alanine aminotransferase, aspartate aminotransferase and total bilirubin increased, accompanied by massive hepatocyte necrosis. These DN T cells were predominantly consisted of a TCR??(+) subset expressing high levels of CD44 and did not produce cytokine except IL-2. Adoptive transfer of this subset of DN T cells to the MHV-3-infected mice resulted in an increase in murine fibrinogen-like protein 2 (mfgl2) expressions in association with massive fibrin deposition in the liver. Following MHV-3 infection, membrane mfgl2 expression and functional procoagulant activity increased remarkably in the DN T cells. Introduction of a recombinant adenovirus which encoded a microRNA specifically targeting mfgl2 gene (Ad-mfgl2-miRNA) in vivo significantly inhibited the hepatic expression of mfgl2 and improved survival in mice. However, under this condition, adoptive transfer of the DN T cells accelerated the disease progression and reversed the benefit from mfgl2 gene silence, leading to a 100% death rate. Our results demonstrate that DN T cells contribute to the outcome of MHV-3-induced FVH via an important effector molecule mfgl2. PMID:26482053

  1. ZRBA1, a Mixed EGFR/DNA Targeting Molecule, Potentiates Radiation Response Through Delayed DNA Damage Repair Process in a Triple Negative Breast Cancer Model

    SciTech Connect

    Heravi, Mitra; Kumala, Slawomir; Rachid, Zakaria; Jean-Claude, Bertrand J.; Radzioch, Danuta; Muanza, Thierry M.

    2015-06-01

    Purpose: ZRBA1 is a combi-molecule designed to induce DNA alkylating lesions and to block epidermal growth factor receptor (EGFR) TK domain. Inasmuch as ZRBA1 downregulates the EGFR TK-mediated antisurvival signaling and induces DNA damage, we postulated that it might be a radiosensitizer. The aim of this study was to further investigate the potentiating effect of ZRBA1 in combination with radiation and to elucidate the possible mechanisms of interaction between these 2 treatment modalities. Methods and Materials: The triple negative human breast MDA-MB-468 cancer cell line and mouse mammary cancer 4T1 cell line were used in this study. Clonogenic assay, Western blot analysis, and DNA damage analysis were performed at multiple time points after treatment. To confirm our in vitro findings, in vivo tumor growth delay assay was performed. Results: Our results show that a combination of ZRBA1 and radiation increases the radiation sensitivity of both cell lines significantly with a dose enhancement factor of 1.56, induces significant numbers of DNA strand breaks, prolongs higher DNA damage up to 24 hours after treatment, and significantly increases tumor growth delay in a syngeneic mouse model. Conclusions: Our data suggest that the higher efficacy of this combination could be partially due to increased DNA damage and delayed DNA repair process and to the inhibition of EGFR. The encouraging results of this combination demonstrated a significant improvement in treatment efficiency and therefore could be applicable in early clinical trial settings.

  2. Magnetic metal-organic framework nanocomposites for enrichment and direct detection of small molecules by negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

    PubMed

    Lin, Zian; Bian, Wei; Zheng, Jiangnan; Cai, Zongwei

    2015-05-25

    Zeolitic imidazolate framework-8 coated magnetic nanocomposites (Fe3O4@ZIF-8 MNCs) served as an absorbent and a matrix for negative-ion MALDI-TOF MS. The host-guest property and interference-free background made them an ideal dual platform for the sensitive analysis of small molecules. PMID:25915018

  3. Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

    NASA Astrophysics Data System (ADS)

    Ye, ChuanXiang; Zhao, Yi; Liang, WanZhen

    2015-10-01

    The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT.

  4. Strong anisotropy in the proton emission following fragmentation of H2O molecules by impact with slow, highly charged Xenon ions

    NASA Astrophysics Data System (ADS)

    Pei?, Z. D.; Hellhammer, R.; Sulik, B.; Stolterfoht, N.

    2009-12-01

    We measured the energy and angular distribution of ionic fragments produced by the interaction of 1-220 keV Xe22+ ions with water molecules. The measured distributions strongly depend on the projectile charge state and energy, as seen from the comparison of the results with previously published data for 5 keV He2+, and 2 and 90 keV Ne(3-9)+ ions. A significant forward-backward asymmetry of the energy and intensity of the H+ fragments is observed. The interpretation of the experimental results is guided by means of classical trajectory simulations based on a Coulomb explosion model. The experimental finding of a strong enhancement of the H+ yield at 90 is attributed to an alignment of the molecular axis during the collision and the momentum transfer from the slow projectile.

  5. Adsorption of carbon monoxide on small aluminum oxide clusters: Role of the local atomic environment and charge state on the oxidation of the CO molecule.

    PubMed

    Ornelas-Lizcano, J C; Guirado-Lpez, R A

    2015-03-28

    We present extensive density functional theory (DFT) calculations dedicated to analyze the adsorption behavior of CO molecules on small AlxOy () clusters. Following the experimental results of Johnson et al. [J. Phys. Chem. A 112, 4732 (2008)], we consider structures having the bulk composition Al2O3, as well as smaller Al2O2 and Al2O units. Our electron affinity and total energy calculations are consistent with aluminum oxide clusters having two-dimensional rhombus-like structures. In addition, interconversion energy barriers between two- and one-dimensional atomic arrays are of the order of 1 eV, thus clearly defining the preferred isomers. Single CO adsorption on our charged AlxOy () clusters exhibits, in general, spontaneous oxygen transfer events leading to the production of CO2 in line with the experimental data. However, CO can also bind to both Al and O atoms of the clusters forming aluminum oxide complexes with a CO2 subunit. The vibrational spectra of AlxOy + CO2 provides well defined finger prints that may allow the identification of specific isomers. The AlxOy (+) clusters are more reactive than the anionic species and the final Al2O(+) + CO reaction can result in the production of atomic Al and carbon dioxide as observed from experiments. We underline the crucial role played by the local atomic environment, charge density distribution, and spin-multiplicity on the oxidation behavior of CO molecules. Finally, we analyze the importance of coadsorption and finite temperature effects by performing DFT Born-Oppenheimer molecular dynamics. Our calculations show that CO oxidation on AlxOy (+) clusters can be also promoted by the binding of additional CO species at 300 K, revealing the existence of fragmentation processes in line with the ones experimentally inferred. PMID:25833583

  6. Predicting the stability of atom-like and molecule-like unit-charge Coulomb three-particle systems

    SciTech Connect

    King, Andrew W.; Herlihy, Patrick E.; Cox, Hazel

    2014-07-28

    Non-relativistic quantum chemical calculations of the particle mass, m{sub 2}{sup }, corresponding to the dissociation threshold in a range of Coulomb three-particle systems of the form (m{sub 1}{sup }m{sub 2}{sup }m{sub 3}{sup ?}), are performed variationally using a series solution method with a Laguerre-based wavefunction. These masses are used to calculate an accurate stability boundary, i.e., the line that separates the stability domain from the instability domains, in a reciprocal mass fraction ternary diagram. This result is compared to a lower bound to the stability domain derived from symmetric systems and reveals the importance of the asymmetric (mass-symmetry breaking) terms in the Hamiltonian at dissociation. A functional fit to the stability boundary data provides a simple analytical expression for calculating the minimum mass of a third particle required for stable binding to a two-particle system, i.e., for predicting the bound state stability of any unit-charge three-particle system.

  7. A fixed-charge model for alcohol polarization in the condensed phase, and its role in small molecule hydration.

    PubMed

    Fennell, Christopher J; Wymer, Karisa L; Mobley, David L

    2014-06-19

    We present a simple optimization strategy for incorporating experimental dielectric response information on neat liquids in classical molecular models of alcohol. Using this strategy, we determine simple and transferable hydroxyl modulation rules that, when applied to an existing molecular parameter set, result in a newly dielectric corrected (DC) parameter set. We applied these rules to the general Amber force field (GAFF) to form an initial set of GAFF-DC parameters, and we found this to lead to significant improvement in the calculated dielectric constant and hydration free energy values for a wide variety of small molecule alcohol models. Tests of the GAFF-DC parameters in the SAMPL4 blind prediction event for hydration show these changes improve agreement with experiment. Surprisingly, these simple modifications also outperform detailed quantum mechanical electric field calculations using a self-consistent reaction field environment coupling term. This work provides a potential benchmark for future developments in methods for representing condensed-phase environments in electronic structure calculations. PMID:24702668

  8. Ground state initialization in a doubly-charged, vertically-stacked InAs quantum dot molecule

    NASA Astrophysics Data System (ADS)

    Ross, Aaron; Chow, Colin; Sham, Lu; Bracker, Allan; Gammon, Daniel; Steel, Duncan

    2015-03-01

    We report on the rapid optical initialization of a subset of the two-electron ground states of a self-assembled, vertically stacked InAs quantum dot molecule, where the states of the electron are approximately localized to separate quantum dots with very little spatial overlap. Four eigenstates, a singlet and three triplets (S,T0,T+, T-) , arise from the exchange coupling and are identified via bias-dependent photoluminescence measurements. The degeneracy of the triplet states is lifted using an in-plane magnetic field (Voigt geometry). This allows for the determination of the in-plane electron and hole g-factors using differential transmission measurements in the co-tunneling regime (to avoid optical pumping). Three of the four eigenstates (S,T+, T-) can then be initialized with high fidelity using continuous wave (CW) optical pumping. Optical transition degeneracies prohibit simple CW initialization of the T0 state. Efforts towards near-unity initialization of the T0 state via two-photon Raman transitions will be presented. This work represents the first step in demonstrating a two-qubit quantum register based on electron spins in self-assembled quantum dots. This work is supported by NSF, ARO, AFSOR, DARPA, and ONR.

  9. Molecule-Like {CdSe} Nanoclusters Passivated with Strongly Interacting Ligands: Energy Level Alignment and Photoinduced Ultrafast Charge Transfer Processes

    NASA Astrophysics Data System (ADS)

    Xie, Yizhou; Teunis, Meghan B.; Pandit, Bill; Sardar, Rajesh; Liu, Jinjun

    2015-06-01

    Semiconductor nanoclusters (SCNCs) are promising electronic materials for use in solid-state device fabrication, where device efficiency is strongly controlled by charge generation and transfer from SCNCs to their surroundings. In this paper we report the excited-state dynamics of molecule-like 1.6 nm diameter CdSe SCNCs, which are passivated with the highly conjugated ligand phenyldithiocarbamate (PDTC) or para-substituted PDTCs. Femtosecond transient absorption studies reveal sub-picosecond hole transfer (? ? 0.9 ps) from a SCNC to its ligand shell based on strong electronic interaction and hole delocalization, and hot electron transfer (? ? 0.2 ps) to interfacial states created by charge separation. A series of control experiments were performed by varying SCNC size (1.6 nm v.s. 2.9 nm) and photon energy of the pump laser (388 nm v.s. 490 nm), as well as addition of electron quencher (benzoquinone) and hole quencher (pyridine), which rules out alternative mechanisms and confirms the critical role of energy level alignment between the SCNC and its passivating ligands.

  10. Charge transfer excitations in water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C60

    NASA Astrophysics Data System (ADS)

    Zope, Rajendra; Basurto, Luis; Olguin, Marco; Baruah, Tunna

    2013-03-01

    We present a study of charge transfer (CT) excited states for a recently synthesized group of water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C60. The ZnPcS donors (ZnPcS2, ZnPcS3, and ZnPcS4) are promising materials for achieving solar cell device production with the photoactive area prepared from aqueous solution. Experimentally, decreasing the number of sulfonate substituent groups for ZnPc increased the photocurrent and lowered the open circuit voltage VOC. Measurements show that the VOC is largest for ZnPc-S4/C60 and lowest for ZnPc-S3/C60. The degree of sulfonation and the measured device VOC does not result in the expected pattern of values based on donor-acceptor HOMO/LUMO energy differences. Variations in film morphology may account for the unexpected pattern of VOC values. Our charge transfer excited state calculations show that the lowest CT excitation energy among the group of ZnPcS/C60 donor-acceptor pairs corresponds to the disulfonated ZnPc/C60 system. The largest CT excited state energies belong to the tetrasulfonated ZnPc/C60 complex. We also examine the effect of geometrical orientation on the CT energies for the ZnPcS donor-acceptor pairs.

  11. Impact of Multiple Negative Charges on Blood Clearance and Biodistribution Characteristics of 99mTc-Labeled Dimeric Cyclic RGD Peptides

    PubMed Central

    2015-01-01

    This study sought to evaluate the impact of multiple negative charges on blood clearance kinetics and biodistribution properties of 99mTc-labeled RGD peptide dimers. Bioconjugates HYNIC-P6G-RGD2 and HYNIC-P6D-RGD2 were prepared by reacting P6G-RGD2 and P6D-RGD2, respectively, with excess HYNIC-OSu in the presence of diisopropylethylamine. Their IC50 values were determined to be 31 5 and 41 6 nM, respectively, against 125I-echistatin bound to U87MG glioma cells in a whole-cell displacement assay. Complexes [99mTc(HYNIC-P6G-RGD2)(tricine)(TPPTS)] (99mTc-P6G-RGD2) and [99mTc(HYNIC-P6D-RGD2)(tricine)(TPPTS)] (99mTc-P6D-RGD2) were prepared in high radiochemical purity (RCP > 95%) and specific activity (37110 GBq/?mol). They were evaluated in athymic nude mice bearing U87MG glioma xenografts for their biodistribution. The most significant difference between 99mTc-P6D-RGD2 and 99mTc-P6G-RGD2 was their blood radioactivity levels and tumor uptake. The initial blood radioactivity level for 99mTc-P6D-RGD2 (4.71 1.00%ID/g) was ?5 higher than that of 99mTc-P6G-RGD2 (0.88 0.05%ID/g), but this difference disappeared at 60 min p.i. 99mTc-P6D-RGD2 had much lower tumor uptake (2.203.11%ID/g) than 99mTc-P6G-RGD2 (7.829.27%ID/g) over a 2 h period. Since HYNIC-P6D-RGD2 and HYNIC-P6G-RGD2 shared a similar integrin ?v?3 binding affinity (41 6 nM versus 31 5 nM), the difference in their blood activity and tumor uptake is most likely related to the nine negative charges and high protein binding of 99mTc-P6D-RGD2. Despite its low uptake in U87MG tumors, the tumor uptake of 99mTc-P6D-RGD2 was integrin ?v?3-specific. SPECT/CT studies were performed using 99mTc-P6G-RGD2 in athymic nude mice bearing U87MG glioma and MDA-MB-231 breast cancer xenografts. The SPECT/CT data demonstrated the tumor-targeting capability of 99mTc-P6G-RGD2, and its tumor uptake depends on the integrin ?v?3 expression levels on tumor cells and neovasculature. It was concluded that the multiple negative charges have a significant impact on the blood clearance kinetics and tumor uptake of 99mTc-labeled dimeric cyclic RGD peptides. PMID:25144854

  12. Charge transfer in TATB and HMX under extreme conditions.

    PubMed

    Zhang, Chaoyang; Ma, Yu; Jiang, Daojian

    2012-11-01

    Charge transfer is usually accompanied by structural changes in materials under different conditions. However, the charge transfer in energetic materials that are subjected to extreme conditions has seldom been explored by researchers. In the work described here, the charge transfer in single molecules and unit cells of the explosives TATB and HMX under high temperatures and high pressures was investigated by performing static and dynamic calculations using three DFT methods, including the PWC functional of LDA, and the BLYP and PBE functionals of GGA. The results showed that negative charge is transferred from the nitro groups of molecular or crystalline TATB and HMX when they are heated. All DFT calculations for the compressed TATB unit cell indicate that, generally, negative charge transfer occurs to its nitro groups as the compression increases. PWC and PBE calculations for crystalline HMX show that negative charge is first transferred to the nitro groups but, as the compression increases, the negative charge is transferred from the nitro groups. However, the BLYP calculations indicated that there was gradual negative charge transfer to the nitro groups of HMX, similar to the case for TATB. The unrelaxed state of the uniformly compressed TATB causes negative charge to be transferred from its nitro groups, in contrast to what is seen in the relaxed state. Charge transfer in TATB is predicted to occur much more easily than in HMX. PMID:22707279

  13. Disinfection of Escherichia coli Gram negative bacteria using surface modified TiO2: optimization of Ag metallization and depiction of charge transfer mechanism.

    PubMed

    Gomathi Devi, LakshmipathiNaik; Nagaraj, Basavalingaiah

    2014-01-01

    The antibacterial activity of silver deposited TiO2 (Ag-TiO2 ) against Gram negative Escherichia coli bacteria was investigated by varying the Ag metal content from 0.10 to 0.50% on the surface of TiO2 . Ag depositions by the photoreduction method were found to be stable. Surface silver metallization was confirmed by EDAX and XPS studies. Photoluminescence studies show that the charge carrier recombination is less for 0.1% Ag-TiO2 and this catalyst shows superior bactericidal activity under solar light irradiation compared to Sol gel TiO2 (SG-TiO2 ) due to the surface plasmon effect. The energy levels of deposited Ag are dependent on the Ag content and it varies from -4.64 eV to -1.30 eV with respect to the vacuum energy level based on atomic silver to bulk silver deposits. The ability of electron transfer from Ag deposit to O2 depends on the position of the energy levels. The 0.25% and 0.50% Ag depositions showed detrimental effect on bactericidal activity due to the mismatch of energy levels. The effect of the EROS (External generation of the Reactive Oxygen Species by 0.1% Ag-TiO2 ) and IROS (Interior generation of Reactive Oxygen Species within the bacteria) on the bactericidal inactivation is discussed in detail. PMID:24995499

  14. Neutralization of a unique, negatively-charged residue in the voltage sensor of K V 7.2 subunits in a sporadic case of benign familial neonatal seizures.

    PubMed

    Miceli, Francesco; Soldovieri, Maria Virginia; Lugli, Licia; Bellini, Giulia; Ambrosino, Paolo; Migliore, Michele; del Giudice, Emanuele Miraglia; Ferrari, Fabrizio; Pascotto, Antonio; Taglialatela, Maurizio

    2009-06-01

    Benign Familial Neonatal Seizures (BFNS) is a rare, autosomal-dominant epilepsy of the newborn caused by mutations in K(v)7.2 (KCNQ2) or K(v)7.3 (KCNQ3) genes encoding for neuronal potassium (K(+)) channel subunits. In this study, we describe a sporadic case of BFNS; the affected child carried heterozygous missense mutations in both K(v)7.2 (D212G) and K(v)7.3 (P574S) alleles. Electrophysiological experiments revealed that the K(v)7.2 D212G substitution, neutralizing a unique negatively-charged residue in the voltage sensor of K(v)7.2 subunits, altered channel gating, leading to a marked destabilization of the open state, a result consistent with structural analysis of the K(v)7.2 subunit, suggesting a possible pathogenetic role for BFNS of this K(v)7.2 mutation. By contrast, no significant functional changes appeared to be prompted by the K(v)7.3 P574S substitution. Computational modelling experiments in CA1 pyramidal cells revealed that the gating changes introduced by the K(v)7.2 D212G increased cell firing frequency, thereby triggering the neuronal hyperexcitability which underlies the observed neonatal epileptic condition. PMID:19344764

  15. Measurement of negatively charged pion spectra in inelastic p+p interactions at 20, 31, 40, 80 and 158 GeV/c

    NASA Astrophysics Data System (ADS)

    Abgrall, N.; Aduszkiewicz, A.; Ali, Y.; Anticic, T.; Antoniou, N.; Baatar, B.; Bay, F.; Blondel, A.; Blumer, J.; Bogomilov, M.; Bravar, A.; Brzychczyk, J.; Bunyatov, S. A.; Busygina, O.; Christakoglou, P.; Czopowicz, T.; Davis, N.; Debieux, S.; Dembinski, H.; Diakonos, F.; Luise, S. Di; Dominik, W.; Drozhzhova, T.; Dumarchez, J.; Dynowski, K.; Engel, R.; Ereditato, A.; Feofilov, G. A.; Fodor, Z.; Fulop, A.; Ga?dzicki, M.; Golubeva, M.; Grebieszkow, K.; Grzeszczuk, A.; Guber, F.; Haesler, A.; Hasegawa, T.; Hierholzer, M.; Idczak, R.; Igolkin, S.; Ivashkin, A.; Jokovi?, D.; Kadija, K.; Kapoyannis, A.; Kaptur, E.; Kie?czewska, D.; Kirejczyk, M.; Kisiel, J.; Kiss, T.; Kleinfelder, S.; Kobayashi, T.; Kolesnikov, V. I.; Kolev, D.; Kondratiev, V. P.; Korzenev, A.; Kovesarki, P.; Kowalski, S.; Krasnoperov, A.; Kurepin, A.; Larsen, D.; Lszl, A.; Lyubushkin, V. V.; Ma?kowiak-Paw?owska, M.; Majka, Z.; Maksiak, B.; Malakhov, A. I.; Mani?, D.; Marcinek, A.; Marin, V.; Marton, K.; Mathes, H.-J.; Matulewicz, T.; Matveev, V.; Melkumov, G. L.; Mrwczy?ski, St.; Murphy, S.; Nakadaira, T.; Nirkko, M.; Nishikawa, K.; Palczewski, T.; Palla, G.; Panagiotou, A. D.; Paul, T.; Pistillo, C.; Peryt, W.; Petukhov, O.; P?aneta, R.; Pluta, J.; Popov, B. A.; Posiada?a, M.; Pu?awski, S.; Puzovi?, J.; Rauch, W.; Ravonel, M.; Redij, A.; Renfordt, R.; Robert, A.; Rhrich, D.; Rondio, E.; Roth, M.; Rubbia, A.; Rustamov, A.; Rybczy?ski, M.; Sadovsky, A.; Sakashita, K.; Savi?, M.; Schmidt, K.; Sekiguchi, T.; Seyboth, P.; Sgalaberna, D.; Shibata, M.; Sipos, R.; Skrzypczak, E.; S?odkowski, M.; Staszel, P.; Stefanek, G.; Stepaniak, J.; Strbele, H.; ua, T.; Szuba, M.; Tada, M.; Tereshchenko, V.; Tolyhi, T.; Tsenov, R.; Turko, L.; Ulrich, R.; Unger, M.; Vassiliou, M.; Veberi?, D.; Vechernin, V. V.; Vesztergombi, G.; Vinogradov, L.; Wilczek, A.; W?odarczyk, Z.; Wojtaszek-Szwarc, A.; Wyszy?ski, O.; Zambelli, L.; Zipper, W.

    2014-03-01

    We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/ c ( 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN super proton synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus-nucleus and proton-nucleus collisions.

  16. Adsorption of carbon monoxide on small aluminum oxide clusters: Role of the local atomic environment and charge state on the oxidation of the CO molecule

    SciTech Connect

    Ornelas-Lizcano, J. C.; Guirado-Lpez, R. A.

    2015-03-28

    We present extensive density functional theory (DFT) calculations dedicated to analyze the adsorption behavior of CO molecules on small Al{sub x}O{sub y}{sup } clusters. Following the experimental results of Johnson et al. [J. Phys. Chem. A 112, 4732 (2008)], we consider structures having the bulk composition Al{sub 2}O{sub 3}, as well as smaller Al{sub 2}O{sub 2} and Al{sub 2}O units. Our electron affinity and total energy calculations are consistent with aluminum oxide clusters having two-dimensional rhombus-like structures. In addition, interconversion energy barriers between two- and one-dimensional atomic arrays are of the order of 1 eV, thus clearly defining the preferred isomers. Single CO adsorption on our charged Al{sub x}O{sub y}{sup } clusters exhibits, in general, spontaneous oxygen transfer events leading to the production of CO{sub 2} in line with the experimental data. However, CO can also bind to both Al and O atoms of the clusters forming aluminum oxide complexes with a CO{sub 2} subunit. The vibrational spectra of Al{sub x}O{sub y} + CO{sub 2} provides well defined finger prints that may allow the identification of specific isomers. The Al{sub x}O{sub y}{sup +} clusters are more reactive than the anionic species and the final Al{sub 2}O{sup +} + CO reaction can result in the production of atomic Al and carbon dioxide as observed from experiments. We underline the crucial role played by the local atomic environment, charge density distribution, and spin-multiplicity on the oxidation behavior of CO molecules. Finally, we analyze the importance of coadsorption and finite temperature effects by performing DFT Born-Oppenheimer molecular dynamics. Our calculations show that CO oxidation on Al{sub x}O{sub y}{sup +} clusters can be also promoted by the binding of additional CO species at 300 K, revealing the existence of fragmentation processes in line with the ones experimentally inferred.

  17. Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering

    NASA Astrophysics Data System (ADS)

    Wodtke, Alec M.

    2013-06-01

    Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

  18. High brilliance negative ion and neutral beam source

    DOEpatents

    Compton, Robert N. (Oak Ridge, TN)

    1991-01-01

    A high brilliance mass selected (Z-selected) negative ion and neutral beam source having good energy resolution. The source is based upon laser resonance ionization of atoms or molecules in a small gaseous medium followed by charge exchange through an alkali oven. The source is capable of producing microampere beams of an extremely wide variety of negative ions, and milliampere beams when operated in the pulsed mode.

  19. Dynamics of ion-molecule reactions from beam experiments: A historical survey

    SciTech Connect

    Herman, Z.; Futrell, Jean H.

    2015-02-01

    A historical survey of beam scattering studies of ion-molecule reactions from the sixties up to the present time is presented. The centers of research that developed key instrumentation for these studies and early achievements in characterizing basic collisional mechanisms in scattering experiments are reviewed. Important classes of cation-molecule reaction dynamics, impulsive atom-transfer, reaction complexes, electron transfer (charge transfer) dynamics and the dynamics of negative ion-molecule reactions are described. Selected specific examples of ion-molecule reaction dynamics, including multiply-charged and ion-surface collisions, are briefly presented. (C) 2014 Elsevier B.V. All rights reserved.

  20. Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: A path to ambipolar organic-based materials?

    NASA Astrophysics Data System (ADS)

    Sancho-García, J. C.; Pérez-Jiménez, A. J.

    2014-10-01

    We have carefully investigated the structural and electronic properties of coronene and some of its fluorinated and chlorinated derivatives, including full periphery substitution, as well as the preferred orientation of the non-covalent dimer structures subsequently formed. We have paid particular attention to a set of methodological details, to first obtain single-molecule magnitudes as accurately as possible, including next the use of modern dispersion-corrected methods to tackle the corresponding non-covalently bound dimers. Generally speaking, this class of compounds is expected to self-assembly in neighboring π-stacks with dimer stabilization energies ranging from -20 to -30 kcal mol-1 at close distances around 3.0-3.3 Å. Then, in a further step, we have also calculated hole and electron transfer rates of some suitable candidates for ambipolar materials, and corresponding charge mobility values, which are known to critically depend on the supramolecular organization of the samples. For coronene and per-fluorinated coronene, we have found high values for their hopping rates, although slightly smaller for the latter due to an increase (decrease) of the reorganization energies (electronic couplings).

  1. Imaging ion-molecule reactions: Charge transfer and C-N bond formation in the C{sup +}+ NH{sub 3} system

    SciTech Connect

    Pei, Linsen; Farrar, James M.

    2012-05-28

    The velocity mapping ion imaging method is applied to the ion-molecule reactions occurring between C{sup +} and NH{sub 3}. The velocity space images are collected over the relative collision energy range from 1.5 to 3.3 eV, allowing both product kinetic energy distributions and angular distributions to be obtained from the data. The charge transfer process appears to be direct, dominated by long-range electron transfer that results in minimal deflection of the products. The product kinetic energy distributions are consistent with a process dominated by energy resonance. The kinetic energy distributions for C-N bond formation appear to scale with the total available energy, providing strong evidence that energy in the [CNH{sub 3}]{sup +} precursor to products is distributed statistically. The angular distributions for C-N bond formation show pronounced forward-backward symmetry, as expected for a complex that resembles a prolate symmetric top decaying along its symmetry axis.

  2. Charge transport in HoxLu1 -xB12 : Separating positive and negative magnetoresistance in metals with magnetic ions

    NASA Astrophysics Data System (ADS)

    Sluchanko, N. E.; Khoroshilov, A. L.; Anisimov, M. A.; Azarevich, A. N.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Krasnorussky, V. N.; Samarin, N. A.; Shitsevalova, N. Yu.; Filippov, V. B.; Levchenko, A. V.; Pristas, G.; Gabani, S.; Flachbart, K.

    2015-06-01

    The magnetoresistance (MR) ? ? /? of the cage-glass compound HoxLu1 -xB12 with various concentrations of magnetic holmium ions (x ?0.5 ) has been studied in detail concurrently with magnetization M (T ) and Hall effect investigations on high-quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of ? ? /? allows us to conclude that the large negative magnetoresistance (nMR) observed in the vicinity of the Nel temperature is caused by scattering of charge carriers on magnetic clusters of Ho3 + ions, and that these nanosize regions with antiferromagnetic (AF) exchange inside may be considered as short-range-order AF domains. It was shown that the Yosida relation -? ? /? M2 provides an adequate description of the nMR effect for the case of Langevin-type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9 ?B was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution ? ? /? ?D2H2 which dominates in HoxLu1 -xB12 in the intermediate temperature range 20-120 K allows us to estimate the drift mobility exponential changes ?DT-? with ? =1.3 -1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of HoxLu1 -xB12 where an additional linear positive component was observed and attributed to charge-carrier scattering on the spin density wave (SDW). High-precision measurements of ? ? /? =f (H ,T ) have allowed us also to reconstruct the magnetic H-T phase diagram of Ho0.5Lu0.5B12 and to resolve its magnetic structure as a superposition of 4 f (based on localized moments) and 5 d (based on SDW) components.

  3. Nonlinear Optical Properties of X(C6H5)4 (X = B(-), C, N(+), P(+)): A New Class of Molecules with a Negative Third-Order Polarizability.

    PubMed

    Gieseking, Rebecca L; Ensley, Trenton R; Hu, Honghua; Hagan, David J; Risko, Chad; Van Stryland, Eric W; Brédas, Jean-Luc

    2015-08-01

    Organic π-conjugated materials have been widely used for a variety of nonlinear optical (NLO) applications. Molecules with negative real components Re(γ) of the third-order polarizability, which leads to nonlinear refraction in macroscopic systems, have important benefits for several NLO applications. However, few organic systems studied to date have negative Re(γ) in the long wavelength limit, and all inorganic materials show positive nonlinear refraction in this limit. Here, we introduce a new class of molecules of the form X(C6H5)4, where X = B(-), C, N(+), and P(+), that have negative Re(γ). The molecular mechanism for the NLO properties in these systems is very different from those in typical linear conjugated systems: These systems have a band of excited states involving single-electron excitations within the π-system, several of which have significant coupling to the ground state. Thus, Re(γ) cannot be understood in terms of a simplified essential-state model and must be analyzed in the context of the full sum-over-states expression. Although Re(γ) is significantly smaller than that of other commonly studied NLO chromophores, the introduction of a new molecular architecture offering the potential for a negative Re(γ) introduces new avenues of molecular design for NLO applications. PMID:26098179

  4. Alteration of negatively charged residues in the 89 to 99 domain of apoA-I affects lipid homeostasis and maturation of HDL[S

    PubMed Central

    Kateifides, Andreas K.; Gorshkova, Irina N.; Duka, Adelina; Chroni, Angeliki; Kardassis, Dimitris; Zannis, Vassilis I.

    2011-01-01

    Abstract?In this study, we investigated the role of positively and negatively charged amino acids within the 89-99 region of apolipoprotein A-I (apoA-I), which are highly conserved in mammals, on plasma lipid homeostasis and the biogenesis of HDL. We previously showed that deletion of the 89-99 region of apoA-I increased plasma cholesterol and phospholipids, but it did not affect plasma triglycerides. Functional studies using adenovirus-mediated gene transfer of two apoA-I mutants in apoA-I-deficient mice showed that apoA-I[D89A/E91A/E92A] increased plasma cholesterol and caused severe hypertriglyceridemia. HDL levels were reduced, and approximately 40% of the apoA-I was distributed in VLDL/IDL. The HDL consisted of mostly spherical and a few discoidal particles and contained pre?1 and ?4-HDL subpopulations. The lipid, lipoprotein, and HDL profiles generated by the apoA-I[K94A/K96A] mutant were similar to those of wild-type (WT) apoA-I. Coexpression of apoA-I[D89A/E91A/E92A] and human lipoprotein lipase abolished hypertriglyceridemia, restored in part the ?1,2,3,4 HDL subpopulations, and redistributed apoA-I in the HDL2/HDL3 regions, but it did not prevent the formation of discoidal HDL particles. Physicochemical studies showed that the apoA-I[D89A/E91A/E92A] mutant had reduced ?-helical content and effective enthalpy of thermal denaturation, increased exposure of hydrophobic surfaces, and increased affinity for triglyceride-rich emulsions. We conclude that residues D89, E91, and E92 of apoA-I are important for plasma cholesterol and triglyceride homeostasis as well as for the maturation of HDL. PMID:21504968

  5. Glucosylceramide, a neutral glycosphingolipid anticoagulant cofactor, enhances the interaction of human- and bovine-activated protein C with negatively charged phospholipid vesicles.

    PubMed

    Yegneswaran, Subramanian; Deguchi, Hiroshi; Griffin, John H

    2003-04-25

    The effect of glucosylceramide (GlcCer) on activated protein C (APC)-phospholipid interactions was examined using fluorescence resonance energy transfer. Human APC, labeled with either fluorescein (Fl-APC) or dansyl (DEGR-APC) donor, bound to phosphatidylcholine/phosphatidylserine (PC/PS, 9:1 w/w) vesicles containing octadecylrhodamine (OR) acceptor with a K(d) (app) = 16 micro g/ml, whereas Fl-APC (or DEGR-APC) bound to PC/PS/GlcCer(OR) (8:1:1) vesicles with a K(d) (app) = 3 micro g/ml. This 5-fold increase in apparent affinity was not species-specific since bovine DEGR-APC also showed a similar GlcCer-dependent enhancement of binding of APC to PC/PS vesicles. From the efficiency of fluorescence resonance energy transfer, distances of closest approach of approximately 63 and approximately 64 A were estimated between the dansyl on DEGR-APC and rhodamine in PC/PS/GlcCer(OR) and PC/PS(OR), respectively, assuming kappa(2) = 2/3. DEGR-APC bound to short chain C8-GlcCer with an apparent K(d) of 460 nm. The presence of C8-GlcCer selectively enhanced the binding of C16,6-NBD-phosphatidylserine but not C16,6-7-nitrobenz-2-oxa-1,3-diazole (NBD)-phosphatidylcholine to coumarin-labeled APC. These data suggest that APC binds to GlcCer, that PC/PS/GlcCer vesicles like PC/PS vesicles bind to the N-terminal gamma-carboxyglutamic acid domain of APC, and that one mechanism by which GlcCer enhances the activity of APC is by increasing its affinity for membrane surfaces containing negatively charged phospholipids. PMID:12560338

  6. Triggered Upward Negative Lightning Leaders

    NASA Astrophysics Data System (ADS)

    Trueblood, J.; Eack, K.; Winn, W. P.; Edens, H. E.; Aulich, G. D.; Eastvedt, E. M.; Petersen, D.; Stock, M.; Lapierre, J. L.; Sonnenfeld, R. G.

    2013-12-01

    Lightning flashes with upward negative-leaders were triggered at Langmuir Laboratory using small rockets during the 2008 and 2012 storm seasons. The flashes were observed by the Laboratory's Lightning Mapping Array (LMA), a high speed video camera, electric-field-change sensors, current viewing resistors, electric-field mills, and a broadband interferometer. Both the current and the electric-field indicated that an upward negative leader was initiated, which transferred positive charge from the cloud to ground. LMA observations show that in all cases the thunderstorms had a normal polarity charge structure, with upper positive charge over mid-level negative charge. The triggered upward leaders provided an indication that there was also a lower positive charge layer under the the mid-level negative charge. The flashes were observed to propagate into lower positive charge and, in one case, continue upward to near the boundary of the main negative charge region.

  7. Investigations of correlation between nitro group charges and C-nitro bond strength, and amino group effects on C-nitro bonds in planar conjugated molecules

    NASA Astrophysics Data System (ADS)

    Zhang, Chaoyang

    2006-05-01

    The correlation between the nitro group charges ( QNitro) and the C-Nitro bond length ( RC-Nitro), and the positional effects of amino groups on C-nitro bond strength in planar conjugated molecules such as the amino-nitro derivatives of benzene, naphthalene, anthracene, phenanthrene, alkene, and minor heterocyclic nitrogen compounds are computationally investigated. All calculations are performed using density functional theory (DFT) and the general gradient approximation (GGA) method with the Beck-LYP hybrid functional and the DNP basis set in Acceryls' code Dmol 3. The results are: (1) QNitro can be used as a structural parameter to estimate the strength of the C-Nitro bond, and further the stability of the nitro compound for 15 fitted lines show there is a good linear QNitro- RC-Nitro relationship in any group of derivatives. In addition, QNitro is more sensitive to structural changes and more effective to assess the C-Nitro bond strength than RC-Nitro; (2) the nitrating reaction of aromatic hydrocarbon can be qualitatively predicted and compared by QNitro: the more QNitro, the easier the nitrating condition, and the higher occurrence ratio of the corresponding nitrating product and (3) the amino groups on even positions can significantly strengthen C-Nitro bonds, other than those on odd positions. Therefore, in synthesizing insensitive explosives, it should be recommendable to introduce amino groups on even positions, particularly on 2-position due to the combination of the hydrogen bond, the induction effect and the mesomeric effect, which can obviously increase the molecular stability.

  8. Dissociative electron attachment to molecules and unstable species relevant in plasma processing

    NASA Astrophysics Data System (ADS)

    Graupner, Karola; Field, Thomas

    2007-10-01

    Collisions between low energy electrons (0 to 10 eV) and molecules can lead to formation of negatively charged fragment ions by dissociative electron attachment. Electron attachment to plasma species, such as unstable molecules, formed in 2.45 GHz microwave discharges of CS2/He [1], C3F6/He, SF6/He, CH4/He and CCl4/He has been investigated with ERIC (Electron Radical Interaction Chamber), which includes a trochoidal electron monochromator and time-of-flight mass spectrometer. Knowledge of the spectra of negative ions formed as a function of electron energy for unstable molecules may be useful for understanding chemical processes and negative ion formation in plasmas. It may also be possible to identify unstable molecules in gas sampled from plasmas with these characteristic negative ion spectra. [1] Dissociative electron attachment to the unstable carbon monosulfide molecule CS, K. Graupner, T. A. Field and L. Feketeova, New J. Phys, 8 (2006) 314.

  9. CuFe2O4 magnetic nanocrystal clusters as a matrix for the analysis of small molecules by negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

    PubMed

    Lin, Zian; Zheng, Jiangnan; Bian, Wei; Cai, Zongwei

    2015-08-01

    CuFe2O4 magnetic nanocrystal clusters (CuFe2O4 MNCs) were proposed as a new matrix for small molecule analysis by negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the first time. We demonstrated its advantages over conventional organic matrices in the detection of small molecules such as amino acids, peptides, nucleobases, fatty acids, and steroid hormones. A systematic comparison of CuFe2O4 MNCs with different ionization modes revealed that MS spectra obtained for the CuFe2O4 MNC matrix in the negative ion mode was only featured by deprotonated ion peaks with a free matrix background, which was different from the complicated alkali metal adducts produced in the positive ion mode. The developed method was found relatively tolerant to salt contamination and exhibited good reproducibility. A detection limit down to the subpicomolar level was achieved when testosterone was analyzed. In addition, by comparison of the MS spectra obtained from bare Fe3O4 and MFe2O4 MNC (M = Co, Ni, Cu, Zn) matrices, two main factors of MFe2O4 MNC matrices were revealed to play a vital role in assisting the negative ion desorption/ionization (D/I) process: doping transition metals into ferrite nanocrystals favoring laser absorption and energy transfer and a good match between the UV absorption of MFe2O4 MNCs and the excitation of nitrogen laser source facilitating LDI efficiency. This work creates a new branch of application for MFe2O4 MNCs and provides an alternative solution for small molecule analysis. PMID:26086699

  10. Charge-exchange processes in collisions of H+,H2+,H3+,He+ , and He2+ ions with CO and CO2 molecules at energies below 1000 eV

    NASA Astrophysics Data System (ADS)

    Werbowy, S.; Pranszke, B.

    2016-02-01

    Absolute measurements of charge-exchange cross sections of H+,H2+,H3+,He+, and He2+ ions in CO and CO2 have been made for energies below 1000 eV, an equivalent of the energy of ionized particles at typical solar-wind conditions. An attenuation method for the case of complex ions of a molecule, taking into account the influence on the ion beam composition of the processes of disintegration of the primary ions into secondary ones with different charge-exchange cross sections, is described. Also the secondary effects, like three-body collisions and re-ionization processes that could emerge at higher pressures of the gas layer, are discussed. Dependence of the cross sections on the number of atomic centers in the projectile have been explained on the basis of the energy defect of the reactions and asymmetric near-resonant charge-exchange process between the ion and target molecule including the Doppler broadening in the interaction of the monoenergetic ion beam and target molecules having an isotropic Maxwellian velocity distribution corresponding to room temperature. Using the semiempirical approach based on the parametrized numerical coupled-channel two-state calculations, we have extrapolated the cross sections to a broader range of velocities.

  11. Analytical modeling and simulation of electrochemical charge/discharge behavior of Si thin film negative electrodes in Li-ion cells

    NASA Astrophysics Data System (ADS)

    Jagannathan, M.; Chandran, K. S. Ravi

    2014-02-01

    Physically-based analytical models that provide insights into the diffusion and/or interface charge transfer effects in bulk (lithiating/delithiating) electrodes are needed to truly assess the performance/limitations of electrode materials for Li-ion batteries. In this context, an analytical modeling framework is constructed here to predict the electrochemical charge-discharge characteristics during lithiation and delithiation of solid amorphous Si (a-Si) thin film electrodes. The framework includes analytical expressions that satisfy Fick's second law for Li transport and the requisite flux boundary conditions of lithiation and delithiation steps. The expressions are derived here by the method of separation of variables. They enable the determination of transient Li concentration profiles in the thin film electrode as a function of state of charge/discharge. The time-dependent electrode surface concentrations (at the electrode-electrolyte interface) obtained from these profiles were used to determine the activation overpotentials and thus, the non-equilibrium cell potentials, as a function of state of charge/discharge using Butler-Volmer kinetics. The simulated charge/discharge characteristics agreed well with the experimental data of a-Si thin film electrodes obtained at different C-rates. The model offers insights into how the charge-discharge behavior is controlled by diffusion limitation within electrode and/or the activation overpotentials at the interface. The analytical framework is also shown to predict successfully the hysteretic behavior of lithiation/delithiation voltage curves.

  12. Elastic, Adhesive, and Charge Transport Properties of a Metal-molecule-metal Junction: the Role of Molecular Orientation, Order, and Coverage

    SciTech Connect

    DelRio, F.; Steffens, K; Jaye, C; Fischer, D; Cook, R

    2010-01-01

    The elastic, adhesive, and charge transport properties of a metal-molecule-metal junction were studied via conducting-probe atomic force microscopy (AFM) and correlated with molecular structure by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The junctions consisted of Co-Cr-coated AFM tips in contact with methyl-terminated alkanethiols (CH{sub 3}(CH{sub 2}){sub n-1}SH, denoted by Cn, where n is the number of carbons in the molecular chain) on Au substrates. AFM contact data were analyzed with the Derjaguin-Muller-Toporov contact model, modified by a first-order elastic perturbation method to account for substrate effects, and a parabolic tunneling model, appropriate for a metal-insulator-metal junction in which the thickness of the insulator is comparable to the Fermi wavelength of the conducting electrons. NEXAFS carbon K-edge spectra were used to compute the dichroic ratio RI for each film, which provided a quantitative measure of the molecular structure as a function of n. As n decreased from 18 to 5, there was a change in the molecular phase from crystalline to amorphous (R{sub I} {yields} 0) and loss of surface coverage, and as a result, the work of adhesion w increased from 82.8 mJ m{sup -2} to 168.3 mJ m{sup -2}, the Young's modulus of the film E{sub film} decreased from 1.0 to 0.15 GPa, and the tunneling barrier height {psi}{sub 0} - E{sub F} decreased from 2.4 to 2.1 eV. For all n, the barrier thickness t decreased for small applied loads F and remained constant at {approx}2.2 nm for large F. The change in behavior was explained by the presence of two insulating layers: an oxide layer on the Co-Cr tip, and the alkanethiol monolayer on the Au surface. X-ray photoelectron spectroscopy confirmed the presence of an oxide layer on the Co-Cr tip, and by performing high-resolution region scans through the film, the thickness of the oxide layer t{sub oxide} was found to be between 1.9 and 3.9 nm. Finally, it was shown that {psi}{sub 0} - E{sub F} is strain-dependent, and the strain at which the film is completely displaced from under the tip is -0.17 for all values of n.

  13. The Orphan G Protein-coupled Receptor GPR17 Negatively Regulates Oligodendrocyte Differentiation via G?i/o and Its Downstream Effector Molecules.

    PubMed

    Simon, Katharina; Hennen, Stephanie; Merten, Nicole; Blttermann, Stefanie; Gillard, Michel; Kostenis, Evi; Gomeza, Jesus

    2016-01-01

    Recent studies have recognized G protein-coupled receptors as important regulators of oligodendrocyte development. GPR17, in particular, is an orphan G protein-coupled receptor that has been identified as oligodendroglial maturation inhibitor because its stimulation arrests primary mouse oligodendrocytes at a less differentiated stage. However, the intracellular signaling effectors transducing its activation remain poorly understood. Here, we use Oli-neu cells, an immortalized cell line derived from primary murine oligodendrocytes, and primary rat oligodendrocyte cultures as model systems to identify molecular targets that link cell surface GPR17 to oligodendrocyte maturation blockade. We demonstrate that stimulation of GPR17 by the small molecule agonist MDL29,951 (2-carboxy-4,6-dichloro-1H-indole-3-propionic acid) decreases myelin basic protein expression levels mainly by triggering the G?i/o signaling pathway, which in turn leads to reduced activity of the downstream cascade adenylyl cyclase-cAMP-PKA-cAMP response element-binding protein (CREB). In addition, we show that GPR17 activation also diminishes myelin basic protein abundance by lessening stimulation of the exchange protein directly activated by cAMP (EPAC), thus uncovering a previously unrecognized role for EPAC to regulate oligodendrocyte differentiation. Together, our data establish PKA and EPAC as key downstream effectors of GPR17 that inhibit oligodendrocyte maturation. We envisage that treatments augmenting PKA and/or EPAC activity represent a beneficial approach for therapeutic enhancement of remyelination in those demyelinating diseases where GPR17 is highly expressed, such as multiple sclerosis. PMID:26620557

  14. Combinatorial effects of charge characteristics and hydrophobicity of silk fibroin on the sorption and release of charged dyes.

    PubMed

    Wongpanit, Panya; Rujiravanit, Ratana

    2012-01-01

    The present study was designed to examine the influence of the charge characteristics of silk fibroin on the sorption and release of charged dyes by varying the pH values of the sorption and release media as well as types of charged dyes. Negatively charged dyes (phenol red and chromotrope 2R) and positively charged dyes (crystal violet and indoine blue) were used as the model compounds. Silk fibroin films were prepared by using a solution casting technique. The prepared films were then treated with an aqueous methanol solution or annealed with water to control their conformation. The sorption behavior of the model compounds made by the methanol-treated and water-annealed silk fibroin films was investigated. Compared to the water- annealed silk fibroin films, a higher hydrophobicity of the methanol-treated silk fibroin films caused a higher sorption of the hydrophobic dyes. The dye molecules had a fairly high affinity to the silk fibroin film, even though the dye and the matrix possessed the same charge. However, in the presence of two charged groups in a single dye molecule, the electrostatic repulsion become more dominant. Stronger interaction was observed when the charges of the film and the dye were opposite. The results of dye sorption and release experiments showed that the degree of synergism or competition between electrostatic and hydrophobic interactions directly depended on the charges and chemical structure of the dye molecules and the environmental pH conditions of the existing silk fibroin film. PMID:21639994

  15. Submolecular Resolution Imaging of Molecules by Atomic Force Microscopy: The Influence of the Electrostatic Force

    NASA Astrophysics Data System (ADS)

    van der Lit, Joost; Di Cicco, Francesca; Hapala, Prokop; Jelinek, Pavel; Swart, Ingmar

    2016-03-01

    The forces governing the contrast in submolecular resolution imaging of molecules with atomic force microscopy (AFM) have recently become a topic of intense debate. Here, we show that the electrostatic force is essential to understand the contrast in atomically resolved AFM images of polar molecules. Specifically, we image strongly polarized molecules with negatively and positively charged tips. A contrast inversion is observed above the polar groups. By taking into account the electrostatic forces between tip and molecule, the observed contrast differences can be reproduced using a molecular mechanics model. In addition, we analyze the height dependence of the various force components contributing to the high-resolution AFM contrast.

  16. Crucial roles of charged saccharide moieties in survival of gram negative bacteria against protamine revealed by combination of grazing incidence x-ray structural characterizations and Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Oliveira, Rafael G.; Schneck, Emanuel; Quinn, Bonnie E.; Konovalov, Oleg V.; Brandenburg, Klaus; Gutsmann, Thomas; Gill, Tom; Hanna, Charles B.; Pink, David A.; Tanaka, Motomu

    2010-04-01

    Grazing incidence x-ray scattering techniques and Monte Carlo (MC) simulations are combined to reveal the influence of molecular structure (genetic mutation) and divalent cations on the survival of gram negative bacteria against cationic peptides such as protamine. The former yields detailed structures of bacterial lipopolysaccharide (LPS) membranes with minimized radiation damages, while the minimal computer model based on the linearized Poisson-Boltzmann theory allows for the simulation of conformational changes of macromolecules (LPSs and peptides) that occur in the time scale of ms. The complementary combination of the structural characterizations and MC simulation demonstrates that the condensations of divalent ions ( Ca2+ or Mg2+ ) in the negatively charged core saccharides are crucial for bacterial survival.

  17. Fragmentation of multiply charged hydrocarbon molecules C{sub n}H{sup q+} (n{<=} 4, q{<=} 9) produced in high-velocity collisions: Branching ratios and kinetic energy release of the H{sup +} fragment

    SciTech Connect

    Beroff, K.; Pino, T.; Carpentier, Y.; Van-Oanh, N. T.; Chabot, M.; Tuna, T.; Martinet, G.; Le Padellec, A.; Lavergne, L.

    2011-09-15

    Fragmentation branching ratios for channels involving H{sup +} emission and associated kinetic energy release of the H{sup +} fragment [KER(H{sup +})] have been measured for multicharged C{sub n}H{sup q+} molecules produced in high velocity (3.6 a.u.) collisions between C{sub n}H{sup +} projectiles and helium atoms. For CH{sup q+} (q{<=} 4) molecules, measured KER(H{sup +}) were found well below predictions of the simple point charge Coulomb model (PCCM) for all q values. Multireference configuration interaction (MRCI) calculations for ground as well as electronic excited states were performed which allowed a perfect interpretation of the CH{sup q+} experimental results for low charges (q = 2-3) as well as for the highest charge (q = 4). In this last case we could show, on the basis of ionization cross sections calculations and experimental measurements performed on the same systems at slightly higher velocity (4.5 a.u.), the prominent role played by inner-shell ionization followed by Auger relaxation and could extract the lifetime of this Auger relaxation giving rise to the best agreement between the experiment and the calculations. For dissociation of C{sub 2}H{sup q+} and C{sub 3}H{sup q+} with the highest charges (q{>=} 5), inner-shell ionization contributed in a prominent way to the ion production. In these two cases it was shown that measured KER(H{sup +}) were in good agreement with PCCM predictions when those were corrected for Auger relaxation with the same Auger lifetime value as in CH{sup 3+}.

  18. The empirical dependence of radiation-induced charge neutralization on negative bias in dosimeters based on the metal-oxide-semiconductor field-effect transistor

    SciTech Connect

    Benson, Chris; Albadri, Abdulrahman; Joyce, Malcolm J.; Price, Robert A.

    2006-08-15

    The dependence of radiation-induced charge neutralization (RICN) has been studied in metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters. These devices were first exposed to x rays under positive bias and then to further dose increments at a selection of reverse bias levels. A nonlinear empirical trend has been established that is consistent with that identified in the data obtained in this work. Estimates for the reverse bias level corresponding to the maximum rate of RICN have been extracted from the data. These optimum bias levels appear to be independent of the level of initial absorbed dose under positive bias. The established models for threshold voltage change have been considered and indicate a related nonlinear trend for neutralization cross section {sigma}{sub N} as a function of oxide field. These data are discussed in the context of dose measurement with MOSFETs and within the framework of statistical mechanics associated with neutral traps and their field dependence.

  19. Detection of heavy-metal ions using liquid crystal droplet patterns modulated by interaction between negatively charged carboxylate and heavy-metal cations.

    PubMed

    Han, Gyeo-Re; Jang, Chang-Hyun

    2014-10-01

    Herein, we demonstrated a simple, sensitive, and rapid label-free detection method for heavy-metal (HM) ions using liquid crystal (LC) droplet patterns on a solid surface. Stearic-acid-doped LC droplet patterns were spontaneously generated on an n-octyltrichlorosilane (OTS)-treated glass substrate by evaporating a solution of the nematic LC, 4-cyano-4'-pentylbiphenyl (5CB), dissolved in heptane. The optical appearance of the droplet patterns was a dark crossed texture when in contact with air, which represents the homeotropic orientation of the LC. This was caused by the steric interaction between the LC molecules and the alkyl chains of the OTS-treated surface. The dark crossed appearance of the acid-doped LC patterns was maintained after the addition of phosphate buffered saline (PBS) solution (pH 8.1 at 25C). The deprotonated stearic-acid molecules self-assembled through the LC/aqueous interface, thereby supporting the homeotropic anchoring of 5CB. However, the optical image of the acid-doped LC droplet patterns incubated with PBS containing HM ions appeared bright, indicating a planar orientation of 5CB at the aqueous/LC droplet interface. This dark to bright transition of the LC patterns was caused by HM ions attached to the deprotonated carboxylate moiety, followed by the sequential interruption of the self-assembly of the stearic acid at the LC/aqueous interface. The results showed that the acid-doped LC pattern system not only enabled the highly sensitive detection of HM ions at a sub-nanomolar concentration but it also facilitated rapid detection (<10 min) with simple procedures. PMID:25059128

  20. Models for Cometary Comae Containing Negative Ions

    NASA Technical Reports Server (NTRS)

    Cordiner, M. A.; Charnley, S. B.

    2012-01-01

    The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of IP/Halley. The anions O(-), OH(-), C(-), CH(-) and CN(-) have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu [I]. Organic molecular anions such as C4H(-) and C6H(-) are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been fully explored. We present details of our new models for the chemistry of cometary comae that include atomic and molecular anions. We calculate the impact of these anions on the charge balance and examine their importance for cometary coma chemistry.

  1. Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV.

    PubMed

    Adler, C; Ahammed, Z; Allgower, C; Amonett, J; Anderson, B D; Anderson, M; Averichev, G S; Balewski, J; Barannikova, O; Barnby, L S; Baudot, J; Bekele, S; Belaga, V V; Bellwied, R; Berger, J; Bichsel, H; Bland, L C; Blyth, C O; Bonner, B E; Bossingham, R; Boucham, A; Brandin, A; Caines, H; Calderón De La Barca Sánchez, M; Cardenas, A; Carroll, J; Castillo, J; Castro, M; Cebra, D; Chattopadhyay, S; Chen, M L; Chen, Y; Chernenko, S P; Cherney, M; Chikanian, A; Choi, B; Christie, W; Coffin, J P; Conin, L; Cormier, T M; Cramer, J G; Crawford, H J; DeMello, M; Deng, W S; Derevschikov, A A; Didenko, L; Draper, J E; Dunin, V B; Dunlop, J C; Eckardt, V; Efimov, L G; Emelianov, V; Engelage, J; Eppley, G; Erazmus, B; Fachini, P; Finch, E; Fisyak, Y; Flierl, D; Foley, K J; Fu, J; Gagunashvili, N; Gans, J; Gaudichet, L; Germain, M; Geurts, F; Ghazikhanian, V; Grabski, J; Grachov, O; Greiner, D; Grigoriev, V; Guedon, M; Gushin, E; Hallman, T J; Hardtke, D; Harris, J W; Heffner, M; Heppelmann, S; Herston, T; Hippolyte, B; Hirsch, A; Hjort, E; Hoffmann, G W; Horsley, M; Huang, H Z; Humanic, T J; Hümmler, H; Igo, G; Ishihara, A; Ivanshin, Y I; Jacobs, P; Jacobs, W W; Janik, M; Johnson, I; Jones, P G; Judd, E; Kaneta, M; Kaplan, M; Keane, D; Kisiel, A; Klay, J; Klein, S R; Klyachko, A; Konstantinov, A S; Kotchenda, L; Kovalenko, A D; Kramer, M; Kravtsov, P; Krueger, K; Kuhn, C; Kulikov, A I; Kunde, G J; Kunz, C L; Kutuev, R K; Kuznetsov, A A; Lakehal-Ayat, L; Lamas-Valverde, J; Lamont, M A; Landgraf, J M; Lange, S; Lansdell, C P; Lasiuk, B; Laue, F; Lebedev, A; LeCompte, T; Lednický, R; Leontiev, V M; Leszczynski, P; LeVine, M J; Li, Q; Li, Q; Lindenbaum, S J; Lisa, M A; Ljubicic, T; Llope, W J; LoCurto, G; Long, H; Longacre, R S; Lopez-Noriega, M; Love, W A; Lynn, D; Majka, R; Maliszewski, A; Margetis, S; Martin, L; Marx, J; Matis, H S; Matulenko, Y A; McShane, T S; Meissner, F; Melnick, Y; Meschanin, A; Messer, M; Miller, M L; Milosevich, Z; Minaev, N G; Mitchell, J; Moiseenko, V A; Moltz, D; Moore, C F; Morozov, V; de Moura, M M; Munhoz, M G; Mutchler, G S; Nelson, J M; Nevski, P; Nikitin, V A; Nogach, L V; Norman, B; Nurushev, S B; Odyniec, G; Ogawa, A; Okorokov, V; Oldenburg, M; Olson, D; Paic, G; Pandey, S U; Panebratsev, Y; Panitkin, S Y; Pavlinov, A I; Pawlak, T; Perevoztchikov, V; Peryt, W; Petrov, V A; Pinganaud, W; Platner, E; Pluta, J; Porile, N; Porter, J; Poskanzer, A M; Potrebenikova, E; Prindle, D; Pruneau, C; Radomski, S; Rai, G; Ravel, O; Ray, R L; Razin, S V; Reichhold, D; Reid, J G; Retiere, F; Ridiger, A; Ritter, H G; Roberts, J B; Rogachevski, O V; Romero, J L; Roy, C; Russ, D; Rykov, V; Sakrejda, I; Sandweiss, J; Saulys, A C; Savin, I; Schambach, J; Scharenberg, R P; Schweda, K; Schmitz, N; Schroeder, L S; Schüttauf, A; Seger, J; Seliverstov, D; Seyboth, P; Shahaliev, E; Shestermanov, K E; Shimanskii, S S; Shvetcov, V S; Skoro, G; Smirnov, N; Snellings, R; Sowinski, J; Spinka, H M; Srivastava, B; Stephenson, E J; Stock, R; Stolpovsky, A; Strikhanov, M; Stringfellow, B; Stroebele, H; Struck, C; Suaide, A A; Sugarbaker, E; Suire, C; Sumbera, M; Symons, T J; Szanto De Toledo, A; Szarwas, P; Takahashi, J; Tang, A H; Thomas, J H; Tikhomirov, V; Trainor, T A; Trentalange, S; Tokarev, M; Tonjes, M B; Trofimov, V; Tsai, O; Turner, K; Ullrich, T; Underwood, D G; Van Buren, G; VanderMolen, A M; Vanyashin, A; Vasilevski, I M; Vasiliev, A N; Vigdor, S E; Voloshin, S A; Wang, F; Ward, H; Watson, J W; Wells, R; Wenaus, T; Westfall, G D; Whitten, C; Wieman, H; Willson, R; Wissink, S W; Witt, R; Xu, N; Xu, Z; Yakutin, A E; Yamamoto, E; Yang, J; Yepes, P; Yokosawa, A; Yurevich, V I; Zanevski, Y V; Zborovský, I; Zhang, W M; Zoulkarneev, R; Zubarev, A N

    2001-09-10

    The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1. PMID:11531517

  2. Charge and aggregation pattern govern the interaction of plasticins with LPS monolayers mimicking the external leaflet of the outer membrane of Gram-negative bacteria.

    PubMed

    Michel, J P; Wang, Y X; Dé, E; Fontaine, P; Goldmann, M; Rosilio, V

    2015-11-01

    Bacterial resistance to antibiotics has become today a major public health issue. In the development of new anti-infectious therapies, antimicrobial peptides appear as promising candidates. However, their mechanisms of action against bacterial membranes are still poorly understood. We describe for the first time the interaction and penetration of plasticins into lipid monolayers and bilayers modeling the two leaflets of the asymmetrical outer membrane of Gram-negative bacteria. The lipid composition of these monolayers mimics that of each leaflet: mixtures of LPS Re 595 mutant and wild type S-form from Salmonella enterica for the external leaflet, and SOPE/SOPG/cardiolipin (80/15/5) for the inner one. The analysis of the interfacial behavior of native (PTCDA1) and modified (PTCDA1-KF) antimicrobial plasticins showed that PTCDA1-KF exhibited better surface properties than its unmodified counterpart. Both peptides could penetrate into the model monolayers at concentrations higher than 0.1 μM. The penetration was particularly enhanced for PTCDA1-KF into the mixed LPS monolayer, due to attractive electrostatic interactions. Grazing X-ray diffraction and atomic force microscopy studies revealed the changes in LPS monolayers organization upon peptide insertion. The interaction of plasticins with liposomes was also monitored by light scattering and circular dichroism techniques. Only the cationic plasticin achieved full disaggregation and structuration in α helices, whereas the native one remained aggregated and unstructured. The main steps of the penetration mechanism of the two plasticins into lipid models of the external leaflet of the outer membrane of Gram-negative bacteria have been established. PMID:26343162

  3. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster-configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

    NASA Astrophysics Data System (ADS)

    Fukuda, Ryoichi; Ehara, Masahiro

    2014-10-01

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2'-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.

  4. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster-configuration interaction method: the accuracy of excitation energies and intuitive charge-transfer indices.

    PubMed

    Fukuda, Ryoichi; Ehara, Masahiro

    2014-10-21

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2'-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy. PMID:25338878

  5. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster–configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

    SciTech Connect

    Fukuda, Ryoichi Ehara, Masahiro

    2014-10-21

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2{sup ′}-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.

  6. Charge transfer doping of silicon.

    PubMed

    Rietwyk, K J; Smets, Y; Bashouti, M; Christiansen, S H; Schenk, A; Tadich, A; Edmonds, M T; Ristein, J; Ley, L; Pakes, C I

    2014-04-18

    We demonstrate a novel doping mechanism of silicon, namely n-type transfer doping by adsorbed organic cobaltocene (CoCp2*) molecules. The amount of transferred charge as a function of coverage is monitored by following the ensuing band bending via surface sensitive core-level photoelectron spectroscopy. The concomitant loss of electrons in the CoCp2* adlayer is quantified by the relative intensities of chemically shifted Co2p components in core-level photoelectron spectroscopy which correspond to charged and neutral molecules. Using a previously developed model for transfer doping, the evolution in relative intensities of the two components as a function of coverage has been reproduced successfully. A single, molecule-specific parameter, the negative donor energy of -(0.500.15)??eV suffices to describe the self-limiting doping process with a maximum areal density of transferred electrons of 21013??cm-2 in agreement with the measured downward band bending. The advantage of this doping mechanism over conventional doping for nanostructures is addressed. PMID:24785050

  7. Charge Transfer Doping of Silicon

    NASA Astrophysics Data System (ADS)

    Rietwyk, K. J.; Smets, Y.; Bashouti, M.; Christiansen, S. H.; Schenk, A.; Tadich, A.; Edmonds, M. T.; Ristein, J.; Ley, L.; Pakes, C. I.

    2014-04-01

    We demonstrate a novel doping mechanism of silicon, namely n-type transfer doping by adsorbed organic cobaltocene (CoCp2*) molecules. The amount of transferred charge as a function of coverage is monitored by following the ensuing band bending via surface sensitive core-level photoelectron spectroscopy. The concomitant loss of electrons in the CoCp2* adlayer is quantified by the relative intensities of chemically shifted Co2p components in core-level photoelectron spectroscopy which correspond to charged and neutral molecules. Using a previously developed model for transfer doping, the evolution in relative intensities of the two components as a function of coverage has been reproduced successfully. A single, molecule-specific parameter, the negative donor energy of -(0.500.15) eV suffices to describe the self-limiting doping process with a maximum areal density of transferred electrons of 21013 cm-2 in agreement with the measured downward band bending. The advantage of this doping mechanism over conventional doping for nanostructures is addressed.

  8. Electrostatic Properties of Molecules from the X-Ray Charge Density. Application to Deuterated Benzene, 1-Alanine and d,l-Histidine

    NASA Astrophysics Data System (ADS)

    Su, Zhengwei; Coppens, Philip

    1993-02-01

    It has been shown (Z. Su and P. Coppens, Acta Cryst. A 48, 188 (1992)) that the electrostatic potential, the electric field, and the electric field gradient (EFG) can be expressed in closed forms in terms of the positions and the charge-density parameters of individual atoms, whose aspherical density is described by a pseudoatom model (e.g., N. Hansen and P. Coppens, Acta Cryst. A 34, 909 (1978)). A F o r t r a n program Molprop91 based on this method has been written (Z. Su, State Univ. of New York at Buffalo 1991). The method has been applied to the title compounds. Low-temperature X-ray diffraction data of fully deuterated benzene (G. A. Jeffrey, J. R. Ruble, Y. Yeon, and C. Lemann, private communication, 1991), /-alanine (R. Destro, R. E. Marsh, and R. Bianchi, J. Phys. Chem. 92, 966 (1988) and d,/-histidine (N. Li, Ph.D. thesis, State University of New York at Buffalo 1989) were analyzed using the least-squares deformation density refinement program Lsmol90 (a modified version of M o l l y ) . Molprop91 was subsequently used to calculate the electrostatic-potential maps in selected sections, and at the nuclear positions. For the latter, the EFGs were also evaluated. The electrostatic potentials were used to fit net atomic charges and estimate the molecular energies. Errors in the derived quantities are given.

  9. Dynamics of low-energy electrons in liquid water with consideration of Coulomb interaction with positively charged water molecules induced by electron collision

    NASA Astrophysics Data System (ADS)

    Kai, Takeshi; Yokoya, Akinari; Ukai, Masatoshi; Fujii, Kentaro; Higuchi, Mariko; Watanabe, Ritsuko

    2014-09-01

    To explain the electron energy relaxation process in water, we performed dynamical calculations of electrons in water using a simulation code developed in this study to calculate mean diffusion distances and mean energies of incident and secondary electrons released by the impact of the incident electron, as well as spatial probability-distribution of the secondary electrons. In addition to the following molecular processes of water: ionization: electronic, vibrational, and rotational excitation by electron impact; dissociative electron attachment; and elastic electron scattering, which were basic parameters used by Monte Carlo simulation, we newly took into account Coulomb interactions between electrons and positively ionized water molecules to calculate classical electron trajectories. We found that the Coulomb interactions enhance the number of collisions for the vibrational and rotational excitation processes at the incident 500 eV electron energy. The secondary electrons diffuse to an average of 3 nm from their original position, resulting much different spatial probability-distribution of those electrons in comparison to those previously reported. We also found that approximately 20% of the secondary electrons were returned to the parent ions within 100 fs. By the electron re-capturing to either bonding or antibionding orbital, the molecules might be converted to some electronic excitation states. We suggest that the spatial probability-distribution of electrons, taken into account the re-capturing process, should be essential for detailed analysis of following chemical process arising in nanometer scales, such as biomolecular damage caused by radiation.

  10. Activation of a water molecule using a mononuclear Mn complex: from Mn-aquo, to Mn-hydroxo, to Mn-oxyl via charge compensation

    PubMed Central

    Lassalle-Kaiser, Benedikt; Hureau, Christelle; Pantazis, Dimitrios A.; Pushkar, Yulia; Guillot, Rgis; Yachandra, Vittal K.; Yano, Junko; Neese, Frank; Anxolabhre-Mallart, Elodie

    2014-01-01

    Activation of a water molecule by the electrochemical oxidation of a Mn-aquo complex accompanied by the loss of protons is reported. The sequential (2 1 electron/1 proton) and direct (2 electron/2 proton) proton-coupled electrochemical oxidation of a non-porphyrinic six-coordinated Mn(II)OH2 complex into a mononuclear Mn(O) complex is described. The intermediate Mn(III)OH2 and Mn(III)OH complexes are electrochemically prepared and analysed. Complete deprotonation of the coordinated water molecule in the Mn(O) complex is confirmed by electrochemical data while the analysis of EXAFS data reveals a gradual shortening of an MnO bond upon oxidation from Mn(II)OH2 to Mn(III)OH and Mn(O). Reactivity experiments, DFT calculations and XANES pre-edge features provide strong evidence that the bonding in Mn(O) is best characterized by a Mn(III)-oxyl description. Such oxyl species could play a crucial role in natural and artificial water splitting reactions. We provide here a synthetic example for such species, obtained by electrochemical activation of a water ligand. PMID:24772190

  11. Organization and intramolecular charge-transfer enhancement in tripodal tris[(pyridine-4-yl)phenyl]amine push-pull molecules by intercalation into layered materials bearing acidic functionalities.

    PubMed

    Melánová, Klára; Cvejn, Daniel; Bureš, Filip; Zima, Vítězslav; Svoboda, Jan; Beneš, Ludvík; Mikysek, Tomáš; Pytela, Oldřich; Knotek, Petr

    2014-07-21

    Two new intercalates of tris[4-(pyridin-4-yl)phenyl]amine (TPPA) with zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate having formulae Zr(HPO4)2·0.21(C33H24N4)·2.5H2O and Zr(HO3SC6H4PO3)(1.3)(C6H5PO3)(0.7)·0.35(C33H24N4)·2.5H2O were prepared and characterized by thermogravimetry, IR spectroscopy, and powder X-ray diffraction. The TPPA molecule has been selected as a model tripodal push-pull system with three peripheral basic centers that may undergo protonation. Their protonation/quaternization afforded HTPPA/MeTPPA molecules with enhanced intramolecular charge-transfer (ICT), which has been documented by electrochemical measurements, UV-Vis spectra and calculated properties such as the HOMO/LUMO levels and the first and second hyperpolarizabilities. Intercalation of TPPA into layered zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate led to its significant organization and protonation as shown by the IR spectra. From the powder X-ray data we can deduce that the TPPA molecules are placed in the interlayer space of both hosts by anchoring two peripheral nitrogen atoms to one host layer and the opposite pyridine-4-yl terminus to the other neighboring host layer. In zirconium 4-sulfophenylphosphonate, the TPPA molecules are oriented perpendicularly, while in zirconium phosphate these molecules are slanted with respect to the layers of the host. On dehydration by heating, the interlayer distance of the intercalate decreases, which indicates a further slanting of the TPPA molecules. It follows from the UV-Vis spectra that TPPA is present in both intercalates in an equilibrium of protonated and non-protonated forms. The described materials represent the first case when a tripodal push-pull system was incorporated into a system with restricted geometry with the aim to influence its optical properties. PMID:24626407

  12. Fragmentation of doubly charged HDO, H2O, and D2O molecules induced by proton and monocharged fluorine beam impact at 3 keV.

    PubMed

    Martin, S; Chen, L; Brdy, R; Bernard, J; Cassimi, A

    2015-03-01

    Doubly charged ions HDO(2+), H2O(2+), and D2O(2+) were prepared selectively to triplet or singlet excited states in collisions with F(+) or H(+) projectiles at 3 keV. Excitation energies of dications following two-body or three-body dissociation channels were measured and compared with recent calculations using ab initio multi-reference configuration interaction method [Gervais et al., J. Chem. Phys. 131, 024302 (2009)]. For HDO(2+), preferential cleavage of O-H rather than O-D bond has been observed and the ratio between the populations of the fragmentation channels OD(+)_H(+) and OH(+)_D(+) were measured. The kinetic energy release has been measured and compared with previous experiments. PMID:25747080

  13. Visualizing the Positive-Negative Interface of Molecular Electrostatic Potentials as an Educational Tool for Assigning Chemical Polarity

    ERIC Educational Resources Information Center

    Schonborn, Konrad; Host, Gunnar; Palmerius, Karljohan

    2010-01-01

    To help in interpreting the polarity of a molecule, charge separation can be visualized by mapping the electrostatic potential at the van der Waals surface using a color gradient or by indicating positive and negative regions of the electrostatic potential using different colored isosurfaces. Although these visualizations capture the molecular…

  14. Visualizing the Positive-Negative Interface of Molecular Electrostatic Potentials as an Educational Tool for Assigning Chemical Polarity

    ERIC Educational Resources Information Center

    Schonborn, Konrad; Host, Gunnar; Palmerius, Karljohan

    2010-01-01

    To help in interpreting the polarity of a molecule, charge separation can be visualized by mapping the electrostatic potential at the van der Waals surface using a color gradient or by indicating positive and negative regions of the electrostatic potential using different colored isosurfaces. Although these visualizations capture the molecular

  15. Negative mass

    NASA Astrophysics Data System (ADS)

    Hammond, Richard T.

    2015-03-01

    Some physical aspects of negative mass are examined. Several unusual properties, such as the ability of negative mass to penetrate any armor, are analysed. Other surprising effects include the bizarre system of negative mass chasing positive mass, naked singularities and the violation of cosmic censorship, wormholes, and quantum mechanical results as well. In addition, a brief look into the implications for strings is given.

  16. Thai Negation.

    ERIC Educational Resources Information Center

    Alam, Samsul

    A study analyzed the structure of negative sentences in the Thai language, based on data gathered from two native speakers. It is shown that the Thai negative marker generally occurs between the noun phrase (subject) and the verb phrase in simple active sentences and in passive sentences. Negation of noun phrases is also allowed in Thai, with a

  17. Molecule nanoweaver

    DOEpatents

    Gerald, II; Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2009-03-10

    A method, apparatus, and system for constructing uniform macroscopic films with tailored geometric assemblies of molecules on the nanometer scale. The method, apparatus, and system include providing starting molecules of selected character, applying one or more force fields to the molecules to cause them to order and condense with NMR spectra and images being used to monitor progress in creating the desired geometrical assembly and functionality of molecules that comprise the films.

  18. Metallic behavior and negative differential resistance properties of (InAs){sub n} (n = 2 − 4) molecule cluster junctions via a combined non–equilibrium Green's function and density functional theory study

    SciTech Connect

    Wang, Qi; Li, Rong; Xu, Yuanlan; Zhang, Jianbing; Miao, Xiangshui; Zhang, Daoli

    2014-06-21

    In this present work, the geometric structures and electronic transport properties of (InAs){sub n} (n = 2, 3, 4) molecule cluster junctions are comparatively investigated using NEGF combined with DFT. Results indicate that all (InAs){sub n} molecule cluster junctions present metallic behavior at the low applied biases ([−2V, 2V]), while NDR appears at a certain high bias range. Our calculation shows that the current of (InAs){sub 4} molecule cluster–based junction is almost the largest at any bias. The mechanisms of the current–voltage characteristics of all the three molecule cluster junctions are proposed.

  19. Charge transport in nanoscale junctions.

    PubMed

    Albrecht, Tim; Kornyshev, Alexei; Bjrnholm, Thomas

    2008-09-01

    Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for

  20. Negative ions at Titan and Enceladus: recent results.

    PubMed

    Coates, Andrew J; Wellbrock, Anne; Lewis, Gethyn R; Jones, Geraint H; Young, David T; Crary, Frank J; Waite, J Hunter; Johnson, Robert E; Hille, Thomas W; Sittler, Edward C

    2010-01-01

    The detection of heavy negative ions (up to 13 800 amu) in Titan's ionosphere is one of the tantalizing new results from the Cassini mission. These heavy ions indicate for the first time the existence of heavy hydrocarbon and nitrile molecules in this primitive Earth-like atmosphere. These ions were suggested to be precursors of aerosols in Titan's atmosphere and may precipitate to the surface as tholins. We present the evidence for and the analysis of these heavy negative ions at Titan. In addition we examine the variation of the maximum mass of the Titan negative ions with altitude and latitude for the relevant encounters so far, and we discuss the implications for the negative ion formation process. We present data from a recent set of encounters where the latitude was varied between encounters, with other parameters fixed. Models are beginning to explain the low mass negative ions, but the formation process for the higher mass ions is still not understood. It is possible that the structures may be chains, rings or even fullerenes. Negative ions, mainly water clusters in this case, were seen during Cassini's recent close flybys of Enceladus. We present mass spectra from the Enceladus plume, showing water clusters and additional species. As at Titan, the negative ions indicate chemical complexities which were unknown before the Cassini encounters, and are indicative of a complex balance between neutrals and positively and negatively charged ions. PMID:21302552

  1. Neutralization of a negative charge in the S1-S2 region of the KV7.2 (KCNQ2) channel affects voltage-dependent activation in neonatal epilepsy.

    PubMed

    Wuttke, Thomas V; Penzien, Johann; Fauler, Michael; Seebohm, Guiscard; Lehmann-Horn, Frank; Lerche, Holger; Jurkat-Rott, Karin

    2008-01-15

    The voltage-gated potassium channels KV7.2 and KV7.3 (genes KCNQ2 and KCNQ3) constitute a major component of the M-current controlling the firing rate in many neurons. Mutations within these two channel subunits cause benign familial neonatal convulsions (BFNC). Here we identified a novel BFNC-causing mutation (E119G) in the S1-S2 region of KV7.2. Electrophysiological investigations in Xenopus oocytes using two-microelectrode voltage clamping revealed that the steady-state activation curves for E119G alone and its coexpressions with KV7.2 and/or KV7.3 wild-type (WT) channels were significantly shifted in the depolarizing direction compared to KV7.2 or KV7.2/KV7.3. These shifts reduced the relative current amplitudes for mutant channels particularly in the subthreshold range of an action potential (about 45% reduction at --50 mV for E119G compared to KV7.2, and 33% for E119G/KV7.3 compared to KV7.2/KV7.3 channels). Activation kinetics were significantly slowed for mutant channels. Our results indicate that small changes in channel gating at subthreshold voltages are sufficient to cause neonatal seizures and demonstrate the importance of the M-current for this voltage range. This was confirmed by a computer model predicting an increased burst duration for the mutation. On a molecular level, these results reveal a critical role in voltage sensing of the negatively charged E119 in S1-S2 of KV7.2, a region that-- according to molecular modelling - might interact with a positive charge in the S4 segment. PMID:18006581

  2. Contact de-electrification of electrostatically charged polymers.

    PubMed

    Soh, Siowling; Kwok, Sen Wai; Liu, Helena; Whitesides, George M

    2012-12-12

    The contact electrification of insulating organic polymers is still incompletely understood, in part because multiple fundamental mechanisms may contribute to the movement of charge. This study describes a mechanism previously unreported in the context of contact electrification: that is, "contact de-electrification", a process in which polymers charged to the same polarity discharge on contact. Both positively charged polymeric beads, e.g., polyamide 6/6 (Nylon) and polyoxymethylene (Delrin), and negatively charged polymeric beads, e.g., polytetrafluoroethylene (Teflon) and polyamide-imide (Torlon), discharge when the like-charged beads are brought into contact. The beads (both with charges of ?20 ?C/m(2), or ?100 charges/?m(2)) discharge on contact regardless of whether they are made of the same material, or of different materials. Discharge is rapid: discharge of flat slabs of like-charged Nylon and Teflon pieces is completed on a single contact (?3 s). The charge lost from the polymers during contact de-electrification transfers onto molecules of gas in the atmosphere. When like-charged polymers are brought into contact, the increase in electric field at the point of contact exceeds the dielectric breakdown strength of the atmosphere and ionizes molecules of the gas; this ionization thus leads to discharge of the polymers. The detection (using a Faraday cup) of charges transferred to the cup by the ionized gas is compatible with the mechanism. Contact de-electrification occurs for different polymers and in atmospheres with different values of dielectric breakdown strength (helium, argon, oxygen, carbon dioxide, nitrogen, and sulfur hexafluoride): the mechanism thus appears to be general. PMID:23153329

  3. Nanoparticle coagulation in fractionally charged and charge fluctuating dusty plasmas

    SciTech Connect

    Nunomura, Shota; Kondo, Michio; Shiratani, Masaharu; Koga, Kazunori; Watanabe, Yukio

    2008-08-15

    The kinetics of nanoparticle coagulation has been studied in fractionally charged and charge fluctuating dusty plasmas. The coagulation occurs when the mutual collision frequency among nanoparticles exceeds their charging and decharging/neutralization frequency. Interestingly, the coagulation is suppressed while a fraction (several percent) of nanoparticles are negatively charged in a plasma, in which stochastic charging plays an important role. A model is developed to predict a phase diagram of the coagulation and its suppression.

  4. Rational Design of ?-Helical Antimicrobial Peptides to Target Gram-negative Pathogens, Acinetobacter baumannii and Pseudomonas aeruginosa: Utilization of Charge, Specificity Determinants, Total Hydrophobicity, Hydrophobe Type and Location as Design Parameters to Improve the Therapeutic Ratio

    PubMed Central

    Jiang, Ziqing; Vasil, Adriana I.; Gera, Lajos; Vasil, Michael L.; Hodges, Robert S.

    2011-01-01

    The rapidly growing problem of increased resistance to classical antibiotics makes the development of new classes of antimicrobial agents with lower rates of resistance urgent. Amphipathic cationic ?-helical antimicrobial peptides have been proposed as a potential new class of antimicrobial agents. The goal of this study was to take a broad-spectrum, 26-residue, antimicrobial peptide in the all-D conformation, peptide D1 (K13) with excellent biologic properties and address the question of whether a rational design approach could be used to enhance the biologic properties if the focus was on Gram-negative pathogens only. To test this hypothesis, we used 11 and 6 diverse strains of Acinetobacter baumannii and Pseudo-monas aeruginosa, respectively. We optimized the number and location of positively charged residues on the polar face, the number, location, and type of hydrophobe on the non-polar face and varied the number of specificity determinants in the center of the non-polar face from 1 to 2 to develop four new antimicrobial peptides. We demonstrated not only improvements in antimicrobial activity, but also dramatic reductions in hemolytic activity and unprecedented improvements in therapeutic indices. Compared to our original starting peptide D1 (V13), peptide D16 had a 746-fold improvement in hemolytic activity (i.e. decrease), maintained antimicrobial activity, and improved the therapeutic indices by 1305-fold and 895-fold against A. baumannii and P. aeruginosa, respectively. The resulting therapeutic indices for D16 were 3355 and 895 for A. baumannii and P. aeruginosa, respectively. D16 is an ideal candidate for commercialization as a clinical therapeutic to treat Gram-negative bacterial infections. PMID:21219588

  5. Rational design of ?-helical antimicrobial peptides to target Gram-negative pathogens, Acinetobacter baumannii and Pseudomonas aeruginosa: utilization of charge, 'specificity determinants,' total hydrophobicity, hydrophobe type and location as design parameters to improve the therapeutic ratio.

    PubMed

    Jiang, Ziqing; Vasil, Adriana I; Gera, Lajos; Vasil, Michael L; Hodges, Robert S

    2011-04-01

    The rapidly growing problem of increased resistance to classical antibiotics makes the development of new classes of antimicrobial agents with lower rates of resistance urgent. Amphipathic cationic ?-helical antimicrobial peptides have been proposed as a potential new class of antimicrobial agents. The goal of this study was to take a broad-spectrum, 26-residue, antimicrobial peptide in the all-D conformation, peptide D1 (K13) with excellent biologic properties and address the question of whether a rational design approach could be used to enhance the biologic properties if the focus was on Gram-negative pathogens only. To test this hypothesis, we used 11 and 6 diverse strains of Acinetobacter baumannii and Pseudomonas aeruginosa, respectively. We optimized the number and location of positively charged residues on the polar face, the number, location, and type of hydrophobe on the non-polar face and varied the number of 'specificity determinants' in the center of the non-polar face from 1 to 2 to develop four new antimicrobial peptides. We demonstrated not only improvements in antimicrobial activity, but also dramatic reductions in hemolytic activity and unprecedented improvements in therapeutic indices. Compared to our original starting peptide D1 (V13), peptide D16 had a 746-fold improvement in hemolytic activity (i.e. decrease), maintained antimicrobial activity, and improved the therapeutic indices by 1305-fold and 895-fold against A.baumannii and P.aeruginosa, respectively. The resulting therapeutic indices for D16 were 3355 and 895 for A.baumannii and P.aeruginosa, respectively. D16 is an ideal candidate for commercialization as a clinical therapeutic to treat Gram-negative bacterial infections. PMID:21219588

  6. Weakly Charged Cationic Nanoparticles Induce DNA Bending and Strand Separation

    SciTech Connect

    Railsback, Justin; Singh, Abhishek; Pearce, Ryan; McKnight, Timothy E; Collazo, Ramon; Sitar, Zlatko; Yingling, Yaroslava; Melechko, Anatoli Vasilievich

    2012-01-01

    The understanding of interactions between double stranded (ds) DNA and charged nanoparticles will have a broad bearing on many important applications from drug delivery [ 1 4 ] to DNAtemplated metallization. [ 5 , 6 ] Cationic nanoparticles (NPs) can bind to DNA, a negatively charged molecule, through a combination of electrostatic attraction, groove binding, and intercalation. Such binding events induce changes in the conformation of a DNA strand. In nature, DNA wraps around a cylindrical protein assembly (diameter and height of 6 nm) [ 7 ] with an 220 positive charge, [ 8 ] creating the complex known as chromatin. Wrapping and bending of DNA has also been achieved in the laboratory through the binding of highly charged species such as molecular assemblies, [ 9 , 10 ] cationic dendrimers, [ 11 , 12 ] and nanoparticles. [ 13 15 ] The charge of a nanoparticle plays a crucial role in its ability to induce DNA structural changes. If a nanoparticle has a highly positive surface charge density, the DNA is likely to wrap and bend upon binding to the nanoparticle [ 13 ] (as in the case of chromatin). On the other hand, if a nanoparticle is weakly charged it will not induce dsDNA compaction. [ 9 , 10 , 15 ] Consequently, there is a transition zone from extended to compact DNA conformations which depends on the chemical nature of the nanoparticle and occurs for polycations with charges between 5 and 10. [ 9 ] While the interactions between highly charged NPs and DNA have been extensively studied, the processes that occur within the transition zone are less explored.

  7. Tunable magnetoresistance in an asymmetrically coupled single-molecule junction.

    PubMed

    Warner, Ben; El Hallak, Fadi; Prser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J; Hirjibehedin, Cyrus F

    2015-03-01

    Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single-molecule level may enable novel spintronic devices. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications. PMID:25622229

  8. Interface trap and oxide charge generation under negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin plasma-nitrided SiON gate dielectrics

    SciTech Connect

    Zhu Shiyang; Nakajima, Anri; Ohashi, Takuo; Miyake, Hideharu

    2005-12-01

    The interface trap generation ({delta}N{sub it}) and fixed oxide charge buildup ({delta}N{sub ot}) under negative bias temperature instability (NBTI) of p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with ultrathin (2 nm) plasma-nitrided SiON gate dielectrics were studied using a modified direct-current-current-voltage method and a conventional subthreshold characteristic measurement. Different stress time dependences were shown for {delta}N{sub it} and {delta}N{sub ot}. At the earlier stress times, {delta}N{sub it} dominates the threshold voltage shift ({delta}V{sub th}) and {delta}N{sub ot} is negligible. With increasing stress time, the rate of increase of {delta}N{sub it} decreases continuously, showing a saturating trend for longer stress times, while {delta}N{sub ot} still has a power-law dependence on stress time so that the relative contribution of {delta}N{sub ot} increases. The thermal activation energy of {delta}N{sub it} and the NBTI lifetime of pMOSFETs, compared at a given stress voltage, are independent of the peak nitrogen concentration of the SiON film. This indicates that plasma nitridation is a more reliable method for incorporating nitrogen in the gate oxide.

  9. Interface trap and oxide charge generation under negative bias temperature instability of p-channel metal-oxide-semiconductor field-effect transistors with ultrathin plasma-nitrided SiON gate dielectrics

    NASA Astrophysics Data System (ADS)

    Zhu, Shiyang; Nakajima, Anri; Ohashi, Takuo; Miyake, Hideharu

    2005-12-01

    The interface trap generation (ΔNit) and fixed oxide charge buildup (ΔNot) under negative bias temperature instability (NBTI) of p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) with ultrathin (2 nm) plasma-nitrided SiON gate dielectrics were studied using a modified direct-current-current-voltage method and a conventional subthreshold characteristic measurement. Different stress time dependences were shown for ΔNit and ΔNot. At the earlier stress times, ΔNit dominates the threshold voltage shift (ΔVth) and ΔNot is negligible. With increasing stress time, the rate of increase of ΔNit decreases continuously, showing a saturating trend for longer stress times, while ΔNot still has a power-law dependence on stress time so that the relative contribution of ΔNot increases. The thermal activation energy of ΔNit and the NBTI lifetime of pMOSFETs, compared at a given stress voltage, are independent of the peak nitrogen concentration of the SiON film. This indicates that plasma nitridation is a more reliable method for incorporating nitrogen in the gate oxide.

  10. A comparative study on the effect of Curcumin and Chlorin-p6 on the diffusion of two organic cations across a negatively charged lipid bilayer probed by second harmonic spectroscopy

    NASA Astrophysics Data System (ADS)

    Saini, R. K.; Varshney, G. K.; Dube, A.; Gupta, P. K.; Das, K.

    2014-09-01

    The influence of Curcumin and Chlorin-p6 (Cp6) on the real time diffusion kinetics of two organic cations, LDS (LDS-698) and Malachite Green (MG) across a negatively charged phospholipid bilayer is investigated by Second Harmonic (SH) spectroscopy. The diffusion time constant of LDS at neutral pH in liposomes containing either Curcumin or Cp6 is significantly reduced, the effect being more pronounced with Curcumin. At acidic pH, the quantum of reduction in the diffusion time constant of MG by both the drugs was observed to be similar. The relative changes in the average diffusion time constants of the cations with increasing drug concentration at pH 5.0 and 7.4 shows a substantial pH effect for Curcumin induced membrane permeability, while a modest pH effect was observed for Cp6 induced membrane permeability. Based on available evidence this can be attributed to the increased interaction between the drug and the polar head groups of the lipid at pH 7.4 where the drug resides closer to the lipid-water interface.

  11. EPR studies of the isolated negatively charged silicon vacancies in n-type 4H- and 6H-SiC: Identification of C3v symmetry and silicon sites

    NASA Astrophysics Data System (ADS)

    Mizuochi, N.; Yamasaki, S.; Takizawa, H.; Morishita, N.; Ohshima, T.; Itoh, H.; Isoya, J.

    2003-10-01

    The isolated negatively charged silicon vacancy (V-Si) in the hexagonal lattices of 4H- and 6H-SiC has been studied by electron paramagnetic resonance (EPR). The local structure was suggested to have Td symmetry from the isotropic g value within the resolution of the conventional X-band measurements, from the isotropic 29Si hyperfine interaction of the next-nearest-neighbor silicon atoms and from the absence of the zero-field splitting with the high spin state of S=3/2. From the 13C hyperfine spectrum of the nearest-neighbor carbon atoms, the two kinds of V-Si, denoted V-Si(I) and V-Si(II), respectively have been distinguished. V-Si(I) and V-Si(II) are assigned to be arising from hexagonal site (h) and quasicubic sites (k in 4H-SiC, k1 and k2 in 6H-SiC), respectively. In both V-Si(I) and V-Si(II), from the 13C hyperfine interactions, the symmetry has been revealed to be C3v with the arrangement of the four nearest-neighbor carbon atoms slightly distorted from a regular tetrahedron.

  12. Fragmentation of biomolecules using slow highly charged ions

    SciTech Connect

    Ruehlicke, C.; Schneider, D.; Balhorn, R.; DuBois, R.

    1996-11-01

    We present first results of biomolecular fragmentation studies with slow highly charged ions (HCI). A layer of the tripeptide RVA was deposited on gold targets and irradiated with slow (few 100 keV) ions, e.g. Xe{sup 50+} and Xe{sup 15+}, extracted from the LLNL EBIT (electron beam ion trap). The secondary ions released upon ion impact were mass analyzed via Time-Of-Flight Secondary-Ion-Mass-Spectrometry (TOF-SIMS). The results show a strong dependence of the positive and negative ion yields on the charge state of the incident ion. We also found that incident ions with high charge states cause the ejection of fragments with a wide mass range as well as the intact molecule (345 amu). The underlying mechanisms are not yet understood but electron depletion of the target due to the high incident charge is likely to cause a variety of fragmentation processes. 6 refs., 2 figs.

  13. Charge transport in disordered materials

    NASA Astrophysics Data System (ADS)

    Gagorik, Adam Gerald

    This thesis is focused on on using Monte Carlo simulation to extract device relevant properties, such as the current voltage behavior of transistors and the efficiency of photovoltaics, from the hopping transport of molecules. Specifically, simulation is used to study organic field-effect transistors (OFETs) and organic photo-voltaics (OPVs). For OFETs, the current was found to decrease with increasing concentration of traps and barriers in the system. As the barrier/trap concentration approaches 100%, the current recovers as carrier begin to travel through the manifold of connected trap states. Coulomb interactions between like charges are found to play a role in removing carriers from trap states. The equilibrium current in OFETs was found to be independent of charge injection method, however, the finite size of devices leads to an oscillatory current. Fourier transforms of the electrical current show peaks that vary non-linearly with device length, while being independent of device width. This has implications for the mobility of carriers in finite sized devices. Lastly, the presence of defects and high barriers (> 0.4 eV) was found to produce negative differential resistance in the saturation region of OFET curves, unlike traps. While defects and barriers prohibit carriers from reaching the drain at high voltages, the repulsive interaction between like charged carriers pushes charges around the defects. For OPVs, the effects of device morphology and charge delocalization were studied. Fill factors increased with domain size in monolayer isotropic morphologies, but decreased for band morphologies. In single-phase systems without Coulomb interactions, astonishingly high fill factors (. 70%) were found. In multilayer OPVs,a complex interplay of domain size, connectivity, tortuosity, interface trapping, and delocalization determined efficiency.

  14. Process for increasing ionic charge in mass spectrometry

    SciTech Connect

    McLuckey, Scott A; He, Min

    2009-06-23

    Processes and apparatus are described for the analysis of molecules or fragments thereof, which are capable of carrying multiple charges, by reacting the multiply charged molecules or fragments thereof with other ions using mass spectrometry.

  15. Negative differential conductance and hysteretic current switching of benzene molecular junction in a transverse electric field

    NASA Astrophysics Data System (ADS)

    Zhu, Wen-Huan; Ding, Guo-Hui; Dong, Bing

    2014-11-01

    We study charge transport through single benzene molecular junction (BMJ) directly sandwiched between two platinum electrodes by using a tight-binding model and the non-equilibrium Green's function approach. Pronounced negative differential conductance is observed at finite bias voltage, resulting from charge redistribution in BMJ and a Coulomb blockade effect at the interface of molecule-electrode contacts. In the presence of a transverse electric field, hysteretic switching behavior and large spin-polarization of current are obtained, indicating the potential application of BMJ for acting as a nanoscale current modulator or spintronic molecular device.

  16. Charged particles interacting with a mixed supported lipid bilayer as a biomimetic pulmonary surfactant.

    PubMed

    Munteanu, B; Harb, F; Rieu, J P; Berthier, Y; Tinland, B; Trunfio-Sfarghiu, A-M

    2014-08-01

    This study shows the interactions of charged particles with mixed supported lipid bilayers (SLB) as biomimetic pulmonary surfactants. We tested two types of charged particles: positively charged and negatively charged particles. Two parameters were measured: adsorption density of particles on the SLB and the diffusion coefficient of lipids by FRAPP techniques as a measure of interaction strength between particles and lipids. We found that positively charged particles do not adsorb on the bilayer, probably due to the electrostatic repulsion between positively charged parts of the lipid head and the positive groups on the particle surface, therefore no variation in diffusion coefficient of lipid molecules was observed. On the contrary, the negatively charged particles, driven by electrostatic interactions are adsorbed onto the supported bilayer. The adsorption of negatively charged particles increases with the zeta-potential of the particle. Consecutively, the diffusion coefficient of lipids is reduced probably due to binding onto the lipid heads which slows down their Brownian motion. The results are directly relevant for understanding the interactions of particulate matter with pulmonary structures which could lead to pulmonary surfactant inhibition or deficiency causing severe respiratory distress or pathologies. PMID:25149067

  17. Mobius Molecules

    ERIC Educational Resources Information Center

    Eckert, J. M.

    1973-01-01

    Discusses formation of chemical molecules via Mobius strip intermediates, and concludes that many special physics-chemical properties of the fully closed circular form (1) of polyoma DNA are explainable by this topological feature. (CC)

  18. Interstellar Molecules

    ERIC Educational Resources Information Center

    Solomon, Philip M.

    1973-01-01

    Radioastronomy reveals that clouds between the stars, once believed to consist of simple atoms, contain molecules as complex as seven atoms and may be the most massive objects in our Galaxy. (Author/DF)

  19. Three chamber negative ion source

    DOEpatents

    Leung, Ka-Ngo (Hercules, CA); Ehlers, Kenneth W. (Alamo, CA); Hiskes, John R. (Livermore, CA)

    1985-01-01

    A negative ion vessel is divided into an excitation chamber, a negative ionization chamber and an extraction chamber by two magnetic filters. Input means introduces neutral molecules into a first chamber where a first electron discharge means vibrationally excites the molecules which migrate to a second chamber. In the second chamber a second electron discharge means ionizes the molecules, producing negative ions which are extracted into or by a third chamber. A first magnetic filter prevents high energy electrons from entering the negative ionization chamber from the excitation chamber. A second magnetic filter prevents high energy electrons from entering the extraction chamber from the negative ionizing chamber. An extraction grid at the end of the negative ion vessel attracts negative ions into the third chamber and accelerates them. Another grid, located adjacent to the extraction grid, carries a small positive voltage in order to inhibit positive ions from migrating into the extraction chamber and contour the plasma potential. Additional electrons can be suppressed from the output flux using ExB forces provided by magnetic field means and the extractor grid electric potential.

  20. Molecule-hugging graphene nanopores

    PubMed Central

    Garaj, Slaven; Liu, Song; Golovchenko, Jene A.; Branton, Daniel

    2013-01-01

    It has recently been recognized that solid-state nanopores in single-atomic-layer graphene membranes can be used to electronically detect and characterize single long charged polymer molecules. We have now fabricated nanopores in single-layer graphene that are closely matched to the diameter of a double-stranded DNA molecule. Ionic current signals during electrophoretically driven translocation of DNA through these nanopores were experimentally explored and theoretically modeled. Our experiments show that these nanopores have unusually high sensitivity (0.65 nA/) to extremely small changes in the translocating molecules outer diameter. Such atomically short graphene nanopores can also resolve nanoscale-spaced molecular structures along the length of a polymer, but do so with greatest sensitivity only when the pore and molecule diameters are closely matched. Modeling confirms that our most closely matched pores have an inherent resolution of ?0.6 nm along the length of the molecule. PMID:23836648

  1. Infrared spectra of monosubstituted toluene derivatives in cyclodextrin: Orientation of guest molecules in included complexes

    NASA Astrophysics Data System (ADS)

    Nagao, Akemi; Kan-no, Akira; Takayanagi, Masao

    2009-07-01

    Infrared spectroscopy was applied to determine the orientations of guest molecules ( m- and p-chlorotoluene, m- and p-tolunitrile, and m- and p-toluidine) in cyclodextrin (?-, ?-, or ?-cyclodextrin (CD)). Some bands of the guest molecules were found to shift by several wavenumbers upon formation of inclusion complexes or upon variation of the diameters of CD. The shifts could be explained by the steric hindrance imparted on the guest molecules in the CD cavities. Moreover, the bands were thought to be due to the vibrations of the moieties of guest molecules in the cavity of CD. The bands were assigned with the aid of quantum chemical calculations, which revealed that chlorotoluene, tolunitrile, and p-toluidine were able to enter the CD cavity, respectively, from the Cl, CN, and CH 3 sides. On the other hand, both the CH 3 and NH 2 groups of m-toluidine direct to the outside of the CD ring. The orientation of a guest molecule in a CD cavity was found to be determined by the charge distribution in the guest molecule; the negatively charged moiety of a guest molecule is attracted to the inside of CD.

  2. The experimental charge density in crystals

    NASA Astrophysics Data System (ADS)

    Yang, Huan-Wang

    1997-12-01

    The experimental charge density distribution in single crystals has been determined through the analysis of X- ray and neutron diffraction data. The crystal structure of 2-pyridone (C5H5NO) has been redetermined from high resolution X-ray data collected at 123K. The molecule is in the lactam form. Bond lengths and bond angles have been determined with e.s.d.'s of 0.001A and 0.1A. The hydrogen-bonded cyclic dimers that occur in vapor and in solution are absent in the crystal where molecules are linked by H-H ... O interaction (H ..., 2.57A) and weak C-H ... ? or van der Waals interactions occurring on both sides of the pyridone ring. The electronic charge density distribution in the crystal and its Laplacian have been calculated for atoms at rest. The total electrostatic potential has been mapped for an isolated molecule and the molecular dipole moment has been determined (8.8(19) Debyes). Critical points in the electron density have been located for the bonds within the molecule and for the molecular interactions cited above. For the C-H ... ? interactions, only the spherical components of the valence density for the pryridone ring atoms contribute effectively at the critical points. Hence these interactions may be described better as van der Waals. New X-ray diffraction data for adenosine (C10H13N5O4) have been collected at high resolution (sin/theta //lambda /le 1.38A-1) at 123K. The multipole model refinement, based on F2 and including 10,083 reflections, give R(F2) = 0.046 and Rw(F2) = 0.077 with goodness of fit gof = 1.64. The electrostatic potential, the total charge density and the Laplacian of the total charge density have been mapped for pseudoatoms at rest in crystal. The topological properties have been analyzed at the (3, - 1) bond critical points. The deformation charge density determines the trajectory of the bonding path. The charge density in the L-shell of an atom shows significant local maxima on the covalent bonding direction and non-bonding direction. At the bond critical points, ?b is consistently greater in the adenine base than in the ribose sugar. The Laplacian at all H-bond critical points is positive, indication a lack of covalent bonding. A weak H-bond C2-H2 ... O2' is observed at the critical point. High resolution X-ray data (sin?/lambda/le 1.22A-1) have been collected at 123K for the structure of dimethyl oxalate. The crystal packing involves 10 short intermolecular interactions including at least one weak H bond. The critical points