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1

Charge transfer effects in molecule-negative ion complexes induced by core ionization  

NASA Astrophysics Data System (ADS)

A variety of charge transfer effects can take place as a result of core ionization of anion-molecule complexes. As specific examples we study the core ionization of Na-H2O and Cl-H2O clusters using an ab initio Green's function method. The site-localized character of the electron distribution in the ground state of these weakly bound clusters favors a transfer of an electron from the negative atomic ion to the H2O molecular unit upon ionization of the O1s core level. The charge transferred screens the created core hole giving rise to the appearance of low-lying satellites which are completely absent in the spectrum of the isolated H2O molecule. Energies and intensities of the charge-transfer satellites are found to depend strongly on the chemical type of the atomic anion. While the bandshape of the O1s-1 spectrum of Cl-H2O is very similar to that of isolated H2O, the spectrum of Na-H2O has virtually nothing to do with the core-ionization spectrum of the water molecule. Interestingly, the charge-transfer satellites seen in the O1s core-ionization spectrum of the Cl-H2O cluster can be well related to states in the O1s core-excitation spectrum of the isolated H2O molecule. The physics of core ionization of the clusters is discussed in detail.

Streltsov, A. I.; Dobrodey, N. V.; Cederbaum, L. S.

2003-08-01

2

Negative ions of polyatomic molecules.  

PubMed Central

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

Christophorou, L G

1980-01-01

3

Primitive Virtual Negative Charge  

E-print Network

Physical fields, such as gravity and electromagnetic field, are interpreted as results from rearrangement of vacuum particles to get the equilibrium of net charge density and net mass density in 4-dimensional complex space. Then, both fields should interact to each other in that physical interaction is considered as a field-to-field interaction. Hence, Mass-Charge interaction is introduced with primitive-virtual negative charge defined for the mass. With the concept of Mass-Charge interaction electric equilibrium of the earth is discussed, especially about the electric field and magnetic field of the earth. For unsettled phenomena related with the earth's gravity, such as antigravity phenomenon, gravity anomalies during the solar eclipses, the connection between geomagnetic storms and earthquakes, etc., possible explanations are discussed.

Kiyoung Kim

2008-11-04

4

Primitive Virtual Negative Charge  

E-print Network

Physical fields, such as gravity and electromagnetic field, are interpreted as results from rearrangement of vacuum particles to get the equilibrium of net charge density and net mass density in 4-dimensional complex space. Then, both fields should interact to each other in that physical interaction is considered as a field-to-field interaction. Hence, Mass-Charge interaction is introduced with primitive-virtual negative charge defined for the mass. With the concept of Mass-Charge interaction electric equilibrium of the earth is discussed, especially about the electric field and magnetic field of the earth. For unsettled phenomena related with the earth's gravity, such as antigravity phenomenon, gravity anomalies during the solar eclipses, the connection between geomagnetic storms and earthquakes, etc., possible explanations are discussed.

Kim, Kiyoung

2008-01-01

5

Emissions from nonconducting negatively charged dust grains  

Microsoft Academic Search

Dust grains immersed into a low-temperature plasma are charged negatively because the electron attachment dominates other charging processes. However, increasing energy of impinging electrons leads to the increase of the yield of secondary emission. When this yield exceeds unity, the grain becomes charged positively. Previous laboratory experiments with electron beams have shown that the surface potential of large grains follows

J. Pavlu; Z. Nemecek; J. Safrankova; I. Cermak

2004-01-01

6

Enhanced synthesis of cytokines by peripheral blood monocytes cultured in the presence of autoantibodies against U1-ribonucleoprotein and/or negatively charged molecules: implication in the pathogenesis of pulmonary hypertension in mixed connective tissue disease (MCTD).  

PubMed Central

An attempt was made to determine whether addition of purified autoantibodies against U1-ribonucleoprotein (RNP) and negatively charged molecules (cardiolipin and double-stranded (ds) DNA) to cultures of peripheral blood monocytes could enhance the synthesis of cytokines in patients with MCTD and normal healthy volunteers. It was found that: (i) at the baseline, levels of cytokines such as IL-1 alpha, IL-1 beta and IL-6 extracellularly released by or associated with monocytes were significantly higher in MCTD patients than in normal subjects; (ii) addition of antibodies against U1-RNP to cultures of MCTD monocytes resulted in a significant overall increase of the released and cell-associated IL-1 alpha, IL-1 beta and IL-6. On the other hand, addition of antibodies against cardiolipin or dsDNA to cultures of MCTD monocytes resulted in a significant increase of released and/or cell-associated IL-1 alpha and IL-1 beta; (iii) addition of these autoantibodies to cultures of normal monocytes resulted in a significant overall increase of released and cell-associated IL-1 alpha, IL-1 beta and IL-6. The extent of enhancement of cytokines released by or associated with monocytes was greater in normal subjects than in MCTD patients; (iv) a F(ab')2 preparation of autoantibodies against U1-RNP also enhanced the level of released and cell-associated IL-1 alpha. Our findings that both autoantibodies against U1-RNP and negatively charged molecules were able to enhance the synthesis of cytokines by monocytes suggest that these autoantibodies might cause derangement of endothelial cells and lead to proliferative vasculopathy, which is a characteristic of pulmonary hypertension in MCTD. PMID:7994907

Okawa-Takatsuji, M; Aotsuka, S; Uwatoko, S; Sumiya, M; Yokohari, R

1994-01-01

7

Membrane permeabilization induced by sphingosine: effect of negatively charged lipids.  

PubMed

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 in the release process. Fluorescence lifetime measurements and confocal fluorescence microscopy have been applied to observe 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

Jiménez-Rojo, Noemi; Sot, Jesús; Viguera, Ana R; Collado, M Isabel; Torrecillas, Alejandro; Gómez-Fernández, J C; Goñi, Félix M; Alonso, Alicia

2014-06-17

8

Positronium negative ion: Molecule or atom  

SciTech Connect

A highly accurate calculation is supplemented by an adiabatic approximation to explore the resonance spectrum of positronium Ps{sup {minus}}. Surprisingly, the spectrum can be understood and classified with H{sub 2}{sup +} quantum numbers by treating the interelectronic axis of Ps{sup {minus}} as an adiabatic parameter. We report and interpret the existence of {sup 1}{ital S} shape resonances, a phenomenon so far unknown in three-body Coulomb systems. The new results on Ps{sup {minus}} combined with previous results for H{sup {minus}} suggest the existence of a resonance spectrum and its similarity for all {ital ABA} Coulomb systems with charges {vert bar}{ital Z}{sub {ital A}}/{ital Z}{sub {ital B}}{vert bar}=1 and masses {ital m}{sub {ital A}}/{ital m}{sub {ital B}}{ge}1.

Rost, J.M.; Wintgen, D. (Department of Chemistry, University of Washington BG-10, Seattle, Washington 98195 (United States) Fakultaet fuer Physik der Universitat, Hermann-Herder-Strasse 3 7800 Freiburg (Germany))

1992-10-26

9

Probing charge transport through individual molecules on silicon surfaces  

NASA Astrophysics Data System (ADS)

The ultra-high vacuum (UHV) scanning tunneling microscope (STM) allows individual molecules to be imaged, addressed, and manipulated on semiconducting surfaces with atomic resolution. In particular, this paper considers three different molecules on the Si(100) surface: styrene, cyclopentene, and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). In all cases, room temperature STM current-voltage characteristics on individual molecules mounted on degenerately n-type Si(100) show multiple negative differential resistance (NDR) events at negative sample bias. On the other hand, at positive sample bias, the current-voltage characteristics do not show NDR, although a discontinuity in the differential conductance is observed. When the Si(100) substrate is changed to degenerate p-type doping, multiple NDR events are observed at positive sample bias while the discontinuity in the differential conductance occurs at negative sample bias. These empirical observations can be qualitatively explained by considering the energy band diagram for a semiconductor-molecule-metal junction [1]. More sophisticated nonequilibrium Green's function theoretical treatments also confirm the experimental data [2]. This paper will also describe recent efforts to characterize the temperature dependence of charge transport through molecule-semiconductor junctions using cryogenic UHV STM at temperatures between 10 K and 300 K [3]. In addition, using multi-step feedback controlled lithography [4], heteromolecular nanostructures consisting of both styrene and TEMPO molecules have been fabricated on hydrogen passivated Si(100). Atomic-scale characterization of these structures will be discussed in the context of silicon-based molecular electronics. [1] N. P. Guisinger, M. E. Greene, R. Basu, A. S. Baluch, and M. C. Hersam, Nano Letters, 4, 55 (2004). [2] T. Rakshit, G.-C. Liang, A. W. Ghosh, and S. Datta, Nano Letters, 4, 1803 (2004). [3] E. T. Foley, N. L. Yoder, N. P. Guisinger, and M. C. Hersam, Rev. Sci. Instrum., 75, 5280 (2004). [4] R. Basu, N. P. Guisinger, M. E. Greene, and M. C. Hersam, Appl. Phys. Lett., 85, 2619 (2004).

Hersam, Mark

2005-03-01

10

Double-negative acoustic metamaterial based on meta-molecule  

NASA Astrophysics Data System (ADS)

This work presents a double-negative acoustic metamaterial (AM) constructed using unitary meta-molecule structure. Analogy to electromagnetic metamaterials, transmission and reflection parameters are obtained by experiments in free space. The refractive index, effective mass density, and effective bulk modulus are found to be negative in a specific frequency region by retrieving the effective parameter from experimental data. In contrast to the reference acoustic field distribution through sponge substrate, the slab focusing phenomenon of the fabricated metamaterial lens is clearly displayed within the range of double-negative frequency at 5.7 kHz. The negative refraction is demonstrated in a triangular sample with refraction index of -0.78, which agrees well with the derived results. The proposed meta-molecule model is an effective approach to preparing integrative AMs, and the method of studying AMs is extended to completely free space.

Zhai, Shilong; Chen, Huaijun; Ding, Changlin; Zhao, Xiaopeng

2013-11-01

11

Negative Differential Resistance in Transport through Organic Molecules on Silicon  

NASA Astrophysics Data System (ADS)

Recent scanning tunneling microscopy studies of individual organic molecules on Si(001) reported negative differential resistance (NDR) above a critical applied field, observations explained by a resonant tunneling model proposed prior to the experiments. Here we use both density functional theory and a many-electron GW self-energy approach to quantitatively assess the viability of this mechanism in hybrid junctions with organic molecules on Si. For cyclopentene on p-type Si(001), the frontier energy levels are calculated to be independent of applied electric fields, ruling out the proposed mechanism for NDR. Guidelines for achieving NDR are developed and illustrated with two related molecules, aminocyclopentene and pyrroline.

Quek, Su Ying; Neaton, J. B.; Hybertsen, Mark S.; Kaxiras, Efthimios; Louie, Steven G.

2007-02-01

12

Large negative differential conductance in single-molecule break junctions  

NASA Astrophysics Data System (ADS)

Molecular electronics aims at exploiting the internal structure and electronic orbitals of molecules to construct functional building blocks. To date, however, the overwhelming majority of experimentally realized single-molecule junctions can be described as single quantum dots, where transport is mainly determined by the alignment of the molecular orbital levels with respect to the Fermi energies of the electrodes and the electronic coupling with those electrodes. Particularly appealing exceptions include molecules in which two moieties are twisted with respect to each other and molecules in which quantum interference effects are possible. Here, we report the experimental observation of pronounced negative differential conductance in the current–voltage characteristics of a single molecule in break junctions. The molecule of interest consists of two conjugated arms, connected by a non-conjugated segment, resulting in two coupled sites. A voltage applied across the molecule pulls the energy of the sites apart, suppressing resonant transport through the molecule and causing the current to decrease. A generic theoretical model based on a two-site molecular orbital structure captures the experimental findings well, as confirmed by density functional theory with non-equilibrium Green's functions calculations that include the effect of the bias. Our results point towards a conductance mechanism mediated by the intrinsic molecular orbitals alignment of the molecule.

Perrin, Mickael L.; Frisenda, Riccardo; Koole, Max; Seldenthuis, Johannes S.; Gil, Jose A. Celis; Valkenier, Hennie; Hummelen, Jan C.; Renaud, Nicolas; Grozema, Ferdinand C.; Thijssen, Joseph M.; Duli?, Diana; van der Zant, Herre S. J.

2014-10-01

13

Large negative differential conductance in single-molecule break junctions.  

PubMed

Molecular electronics aims at exploiting the internal structure and electronic orbitals of molecules to construct functional building blocks. To date, however, the overwhelming majority of experimentally realized single-molecule junctions can be described as single quantum dots, where transport is mainly determined by the alignment of the molecular orbital levels with respect to the Fermi energies of the electrodes and the electronic coupling with those electrodes. Particularly appealing exceptions include molecules in which two moieties are twisted with respect to each other and molecules in which quantum interference effects are possible. Here, we report the experimental observation of pronounced negative differential conductance in the current-voltage characteristics of a single molecule in break junctions. The molecule of interest consists of two conjugated arms, connected by a non-conjugated segment, resulting in two coupled sites. A voltage applied across the molecule pulls the energy of the sites apart, suppressing resonant transport through the molecule and causing the current to decrease. A generic theoretical model based on a two-site molecular orbital structure captures the experimental findings well, as confirmed by density functional theory with non-equilibrium Green's functions calculations that include the effect of the bias. Our results point towards a conductance mechanism mediated by the intrinsic molecular orbitals alignment of the molecule. PMID:25173832

Perrin, Mickael L; Frisenda, Riccardo; Koole, Max; Seldenthuis, Johannes S; Gil, Jose A Celis; Valkenier, Hennie; Hummelen, Jan C; Renaud, Nicolas; Grozema, Ferdinand C; Thijssen, Joseph M; Duli?, Diana; van der Zant, Herre S J

2014-10-01

14

Charging of dust particles in a negative ion plasma  

Microsoft Academic Search

Positively charges nanoparticles have been detected during sounding rocket flights in the nighttime polar mesosphere. Simultaneous measurements of the plasma densities indicated the presence of few electrons and significant numbers of heavy negative ions. Model calculations show that dust particles immersed in such a plasma can acquire a positive charge if the relative density of the heavy negative ions is

Robert Merlino

2008-01-01

15

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

16

Charge Exchange Processes for Highly Charged Ion -Atom, Molecule  

E-print Network

for Fusion Science H.A.Sakaue #12;Charge Exchange Processes Highly charged ions (HCI's) exist as an impurity ion in high temperature plasma. Charge exchange cross sections of HCI's are very large (~10-14cm2) Charge Exchange Processes of HCI's are very important for understanding the edge plasma behavior

Princeton Plasma Physics Laboratory

17

Pseudoparticle approach for charge-transferring molecule-surface collisions  

NASA Astrophysics Data System (ADS)

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(3?u+) 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(3?u+) molecule, the molecular ground state N2(1?g+), and the negative ion N2-(2?g) 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.

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

2012-09-01

18

Micro injector sample delivery system for charged molecules  

DOEpatents

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.

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

1999-11-09

19

Increased negatively charged nitrogen-vacancy centers in fluorinated diamond  

NASA Astrophysics Data System (ADS)

We investigated the effect of fluorine-terminated diamond surface on the charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is achieved with CF4 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-) population than oxygen-terminated surfaces. NV- population is estimated by the ratio of negative to neutral charged NV zero-phonon lines. Surface chemistry control of NV- density is an important step towards improving the optical and spin properties of NVs for quantum information processing and magnetic sensing.

Cui, Shanying; Hu, Evelyn L.

2013-07-01

20

Control of charge migration in molecules by ultrashort laser pulses  

E-print Network

Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme for control of the charge migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and an amine moieties that simple pulses can be used for stopping the charge-migration oscillations and localizing the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

Golubev, Nikolay V

2015-01-01

21

Control of charge migration in molecules by ultrashort laser pulses  

E-print Network

Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme for control of the charge migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and an amine moieties that simple pulses can be used for stopping the charge-migration oscillations and localizing the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.

Nikolay V. Golubev; Alexander I. Kuleff

2015-02-19

22

Mean field theory of charged dendrimer molecules.  

PubMed

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

Lewis, Thomas; Pryamitsyn, Victor; Ganesan, Venkat

2011-11-28

23

Contactless measurements of charge migration within single molecules  

SciTech Connect

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.

Nagaya, Kiyonobu; Iwayama, Hiroshi; Sugishima, Akinori; Ohmasa, Yoshinori; Yao, Makoto [Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Sakyo-Ku, Kyoto 606-8502 (Japan)

2010-06-07

24

Gram-Negative Bacterial Sensors for Eukaryotic Signal Molecules  

PubMed Central

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

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

2009-01-01

25

Electrostatic Power Generation from Negatively Charged, Simulated Lunar Regolith  

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

26

Molecular Rotation at Negatively Charged Surfactant/Aqueous Interfaces Kim T. Nguyen, Xiaoming Shang, and Kenneth B. Eisenthal*  

E-print Network

of the molecular probe coumarin 314 (C314) at air/water interfaces covered with the negatively charged surfactant in this laboratory have reported a signifi- cantly slower reorientation time of the dye molecule coumarin 314 (C314) at the air/water interface than the value of 100 ps in bulk water using a closely related coumarin molecule.7

Eisenthal, Kenneth B.

27

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

PubMed

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

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

2015-01-21

28

Space-charge-induced negative resistance in avalanche diodes  

Microsoft Academic Search

With a realistic and accurate model and the use of numerical techniques to solve the diode equations, it is shown that certain p+-n-n+diodes exhibit a static negative resistance that is due to space-charge effects. The magnitude of this resistance and the value of current density at which negative resistance appears depend on several device parameters. The dependence of the diode

H. C. Bowers

1968-01-01

29

SCREENING PLATELET – SURFACE INTERACTIONS USING NEGATIVE SURFACE CHARGE GRADIENTS  

PubMed Central

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 (-SO3-) 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

Corum, Lindsey E.; Hlady, Vladimir

2012-01-01

30

Negatively-charged helices in the gas phase.  

PubMed

A polyalanine-based peptide which forms a stable, negatively-charged ?-helix in the gas phase is reported. Addition of an N-terminal acidic residue forms a stabilizing hydrogen bond network and an electrostatic interaction with the helical dipole. Formation of this secondary structure was demonstrated using ion mobility-mass spectrometry and molecular modelling techniques. PMID:24901462

Johnson, Andrew R; Dilger, Jonathan M; Glover, Matthew S; Clemmer, David E; Carlson, Erin E

2014-08-18

31

The sheath structure around a negatively charged rocket payload  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

32

Increased negatively charged nitrogen-vacancy centers in fluorinated diamond  

SciTech Connect

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.

Cui, Shanying; Hu, Evelyn L. [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)] [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

2013-07-29

33

DNA compaction in a crowded environment with negatively charged proteins.  

PubMed

We studied the conformational properties of DNA in a salt solution of the strongly charged protein bovine serum albumin. DNA is compacted when a suitable amount of bovine serum albumin is added to the solution due to a crowding effect and strong electrostatic repulsion between DNA and bovine serum albumin, both of which carry negative charges. However, DNA undergoes an unfolding transition with an increase in the salt concentration. This observation contradicts the current understanding of polymer- and salt-induced condensation, ? condensation. We propose a simple theoretical model by taking into account the competition between the translational entropy of ions and electrostatic interaction. PMID:20867679

Krotova, M K; Vasilevskaya, V V; Makita, N; Yoshikawa, K; Khokhlov, A R

2010-09-17

34

DNA Compaction in a Crowded Environment with Negatively Charged Proteins  

NASA Astrophysics Data System (ADS)

We studied the conformational properties of DNA in a salt solution of the strongly charged protein bovine serum albumin. DNA is compacted when a suitable amount of bovine serum albumin is added to the solution due to a crowding effect and strong electrostatic repulsion between DNA and bovine serum albumin, both of which carry negative charges. However, DNA undergoes an unfolding transition with an increase in the salt concentration. This observation contradicts the current understanding of polymer- and salt-induced condensation, ? condensation. We propose a simple theoretical model by taking into account the competition between the translational entropy of ions and electrostatic interaction.

Krotova, M. K.; Vasilevskaya, V. V.; Makita, N.; Yoshikawa, K.; Khokhlov, A. R.

2010-09-01

35

Disappearance of Schwinger's string at the charge - monopole "molecule"  

E-print Network

An equivalence of total momentum operator of charge - monopole system to the momentum operator of a symmetrical quantum top is observed. This explicitly shows the string independence of Dirac's quantization condition leading to disappearance of Schwinger's string and reveals some properties of diatomic molecule for this system.

S. E. Korenblit; Kieun Lee

2010-03-07

36

Single molecule detection using charge-coupled device array technology  

SciTech Connect

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.

Denton, M.B.

1992-07-29

37

X-ray emission from charge exchange of highly-charged ions in atoms and molecules  

NASA Technical Reports Server (NTRS)

Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in their approach to the Sun. A new apparatus was constructed to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross sections for single and multiple charge exchange, and (b) normalized X-ray emission cross sections.

Greenwood, J. B.; Williams, I. D.; Smith, S. J.; Chutjian, A.

2000-01-01

38

Second bound state of negatively charged excitons in quantum dots  

NASA Astrophysics Data System (ADS)

By using the method of few-body physics, the binding energy spectra of the second bound state of a negatively charged exciton X - in a GaAs quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio and of the dot radius. In the case of L=1 and S12=1 our calculation predicts the existence of a second bound state of X - in QDs.

Xie, Wenfang

2001-05-01

39

Probing luminal negative charge in the type 3 ryanodine receptor  

Microsoft Academic Search

In this study, we have investigated block of potassium (K+) current by neomycin, a large polycation, from the luminal face of the type 3 ryanodine receptor (RyR3). Previous studies have shown that neomycin is an open channel blocker of RyR2 that interacts with negatively charged residues in the mouth of the conduction pathway to partially occlude it. In the current

Nicholas Pugh; Fiona C. Mead-Savery; W. John Coadwell; Daniela Rossi; Vincenzo Sorrentino; Alan J. Williams

2005-01-01

40

Enhancing biocompatibility of D-oligopeptide hydrogels by negative charges.  

PubMed

Oligopeptide hydrogels are emerging as useful matrices for cell culture with commercial products on the market, but L-oligopeptides are labile to proteases. An obvious solution is to create D-oligopeptide hydrogels, which lack enzymatic recognition. However, D-oligopeptide matrices do not support cell growth as well as L-oligopeptide matrices. In addition to chiral interactions, many cellular activities are strongly governed by charge-charge interactions. In this work, the effects of chirality and charge on human mesenchymal stem cell (hMSC) behavior were studied using hydrogels assembled from oppositely charged oligopeptides. It was found that negative charges significantly improved hMSC viability and proliferation in D-oligopeptide gels but had little effect on their interactions with L-oligopeptide gels. This result points to the possibility of using charge and other factors to engineer biomaterials whose chirality is distinct from that of natural biomaterials, but whose performance is close to that of natural biomaterials. PMID:23256640

Hyland, Laura L; Twomey, Julianne D; Vogel, Savannah; Hsieh, Adam H; Yu, Y Bruce

2013-02-11

41

Enhancing Biocompatibility of D-Oligopeptide Hydrogels by Negative Charges  

PubMed Central

Oligopeptide hydrogels are emerging as useful matrices for cell culture with commercial products on the market, but L-oligopeptides are labile to proteases. An obvious solution is to create D-oligopeptide hydrogels, which lack enzymatic recognition. However, D-oligopeptide matrices do not support cell growth as well as L-oligopeptide matrices. In addition to chiral interactions, many cellular activities are strongly governed by charge-charge interactions. In this work the effects of chirality and charge on human mesenchymal stem cell (hMSC) behavior were studied using hydrogels assembled from oppositely charged oligopeptides. It was found that negative charges significantly improved hMSC viability and proliferation in D-oligopeptide gels but had little effect on their interactions with L-oligopeptide gels. This result points to the possibility of using charge and other factors to engineer biomaterials whose chirality is distinct from that of natural biomaterials, but whose performance is close to that of natural biomaterials. PMID:23256640

Hyland, Laura L.; Twomey, Julianne D.; Vogel, Savannah; Hsieh, Adam H.; Yu, Y. Bruce

2013-01-01

42

Charge-sharing in fragmentation of nitrogen molecules in collision with highly charged ions  

NASA Astrophysics Data System (ADS)

An apparatus for low-energy collision of highly charged ions with molecules, comprising a position sensitive time-of-flight measurement devise for recoil ions and a charge state analyser for the scattered projectile, was newly constructed at a beam line of an electron cyclotron resonance ion source. Collision experiments of 120 keV Ar8+ with the target of nitrogen molecules were conducted as a test run of this apparatus. Focusing on the dissociation channels with asymmetric sharing of the charges by fragmentation, correlation between Auger electron emission of the projectile and Coulomb explosion of the target is discussed.

Matsumoto, J.; Tezuka, H.; Shiromaru, H.

2015-01-01

43

Mechanism of Charging and Supercharging Molecules in Electrospray Ionization  

PubMed Central

The origin of the extent of charging and the mechanism by which multiply charged ions are formed in electrospray ionization have been hotly debated for over a decade. Many factors can affect the number of charges on an analyte ion. Here, we investigate the extent of charging of poly(propyleneimine) dendrimers (generations 3.0 and 5.0), cytochrome c, poly(ethylene glycol)s, and 1,n-diaminoalkanes formed from solutions of different composition. We demonstrate that in the absence of other factors, the surface tension of the electrospray droplet late in the desolvation process is a significant factor in determining the overall analyte charge. For poly(ethylene glycol)s, 1,n-diaminoalkanes, and poly(propyleneimine) dendrimers electrosprayed from single-component solutions, there is a clear relationship between the analyte charge and the solvent surface tension. Addition of m-nitrobenzyl alcohol (m-NBA) into electrospray solutions increases the charging when the original solution has a lower surface tension than m-NBA, but the degree of charging decreases when this compound is added to water, which has a higher surface tension. Similarly, the charging of cytochrome c ions formed from acidified denaturing solutions generally increases with increasing surface tension of the least volatile solvent. For the dendrimers investigated, there is a strong correlation between the average charge state of the dendrimer and the Rayleigh limiting charge calculated for a droplet of the same size as the analyte molecule and with the surface tension of the electrospray solvent. A bimodal charge distribution is observed for larger dendrimers formed from water/m-NBA solutions, suggesting the presence of more than one conformation in solution. A similar correlation is found between the extent of charging for 1,n-diaminoalkanes and the calculated Rayleigh limiting charge. These results provide strong evidence that multiply charged organic ions are formed by the charged residue mechanism. A significantly smaller extent of charging for both dendrimers and 1,n-diaminoalkanes would be expected if the ion evaporation mechanism played a significant role. PMID:12590562

Iavarone, Anthony T.; Williams*, Evan R.

2005-01-01

44

Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery  

NASA Astrophysics Data System (ADS)

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 theo

2007-07-01

45

Space Charge Neutralization Using Negative Ions and Dust Particles in the Ion and Hall Thrusters  

Microsoft Academic Search

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

Yevgeny Raitses; Nathaniel J. Fisch

2005-01-01

46

Effect of charging on electronic structure of the Alq 3 molecule: the identification of carrier transport properties  

NASA Astrophysics Data System (ADS)

The effects of electrical charging on the electronic structure of tris(8-hydroxy-quinoline) aluminum (Alq 3) have been studied theoretically using density functional theory, and semi-empirical and ab initio molecular orbital theories. All three methods show that negatively charged Alq 3 molecules have rather delocalized electronic structures suitable for electron transport. On the other hand, the distribution of the highest occupied molecular orbital in the Alq 3 molecule becomes highly localized upon positive charging. This localization of the frontier molecular orbital restrains movement of the residing electrons and thus inhibits the electron transport. The success of the current approach in explaining the electron transport properties of the Alq 3 molecule suggests it may be useful for the design of organic molecules for electronic applications.

Zhang, R. Q.; Lee, C. S.; Lee, S. T.

2000-08-01

47

Formation and decay of negative ion resonances in gaseous and condensed molecules  

Microsoft Academic Search

Formation of negative ions under low energy electron impact (0-15 eV) is studied from C6F6 and C6F5Cl at different stages of aggregation: gas phase molecules, free molecular clusters and condensed molecules. The gas phase experiments (molecules, clusters) are performed in a crossed beam apparatus and the condensed phase experiments in a UHV apparatus where the molecules are deposited in definite

Oddur Ingólfsson; Fritz Weik; Eugen Illenberger

1996-01-01

48

Air Purification Effect of Positively and Negatively Charged Ions Generated by Discharge Plasma at Atmospheric Pressure  

Microsoft Academic Search

In this paper, the air purification effect of positively and negatively charged ions generated by discharge plasma at atmospheric pressure is reported. We have developed a novel ion generation device which consists of a cylindrical glass tube and attached inner and outer mesh electrodes. With the application of AC voltage between the electrodes, positively charged ions and negatively charged ions

Kazuo Nishikawa; Hideo Nojima

2001-01-01

49

Peptides 25 (2004) 14251440 Peptide signal molecules and bacteriocins in Gram-negative bacteria: a  

E-print Network

-negative bacteria: a genome-wide in silico screening for peptides containing a double-glycine leader sequence Abstract Quorum sensing (QS) in Gram-negative bacteria is generally assumed to be mediated by N-acyl-homoserine lactone molecules while Gram-positive bacteria make use of signaling peptides. We analyzed the occurrence

50

Quantum tunnelling and classical above-barrier transitions in electron detachment from negative ions by negatively charged projectiles  

Microsoft Academic Search

A simple model of electron detachment from negative ions by negatively charged projectile impact is developed as a combination of quantum tunnelling and classical field ionization. While the tunnelling theory has been discussed previously by Smirnov and Chibisov, we have substantially amended Solov'ev's classical model for above-barrier transition. As the most important modification we introduce the concept of decay rate

V. N. Ostrovsky; K. Taulbjerg

1996-01-01

51

What happens to negatively charged lipid vesicles upon interacting with polycation species?  

PubMed

Complexation of synthetic polycations with negative lipid vesicles as cell-mimetic species was studied. It was found that such interaction could be accompanied by lateral lipid segregation, highly accelerated transmembrane migration of lipid molecules (polycation-induced flip-flop), incorporation of adsorbed polycations into vesicular membrane as well as aggregation and disruption of vesicles. A polycation adsorbed on the surface of liquid vesicles due to electrostatic attraction could be completely removed from the membrane by increase in simple salt concentration or by recomplexation with polyanions. In contrast, adsorption of a polycation carrying pendant hydrophobic groups was irreversible apparently due to incorporation of these groups into the hydrophobic part of the vesicular membrane. The above mentioned phenomena were examined depending on the polycation structure, fraction of charged lipids in the membrane, vesicle phase state and ionic strength of solution. PMID:11772467

Kabanov, V A; Yaroslavov, A A

2002-01-17

52

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

53

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

PubMed Central

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

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

2015-01-01

54

The meteorology of negative cloud-to-ground lightning strokes with large charge moment changes: Implications  

E-print Network

The meteorology of negative cloud-to-ground lightning strokes with large charge moment changes-to-ground (CG) strokes (i.e., peak currents in excess of 100 kA and charge moment changes in excess of 800 C km­2011. Within 15 km of the negative sprite-parent/class stroke, the median characteristics for these systems

Rutledge, Steven

55

CRYSTALLINE SILICON SURFACE PASSIVATION BY THE NEGATIVE-CHARGE-DIELECTRIC Al2O3  

E-print Network

CRYSTALLINE SILICON SURFACE PASSIVATION BY THE NEGATIVE-CHARGE- DIELECTRIC Al2O3 B. Hoex 1 , J negative charge density on the surface passivation of both n- and p-type c-Si will be addressed it will be shown that the excellent surface passivation by Al2O3 can for a large part be attributed to a high fixed

56

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

E-print Network

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

Cummer, Steven A.

57

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)

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.

Fang, Yigang; Liu, Fangwei; Liu, Jianbo

2013-01-01

58

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

SciTech Connect

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.

Smirnov, A.; Raitses, Y.; Fisch, N.J. [Princeton University Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543 (United States)

2005-05-15

59

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

SciTech Connect

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.

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

2005-01-25

60

Dielectric solvation dynamics of molecules of arbitrary shape and charge distribution  

E-print Network

Dielectric solvation dynamics of molecules of arbitrary shape and charge distribution Xueyu Song and solvation dynamics with realistic models of solute molecular shape and charge distribution. The algo- rithm. Employing quantum chemical estimates of the chromophore's charge distribution, the Richards­Lee estimate

Song, Xueyu

61

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

SciTech Connect

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.

Sharma, Suresh C.; Walia, Ritu [Department of Physics, Maharaja Agrasen Institute of Technology, PSP Area Plot No.-1, Sector-22, Rohini, Delhi 110 086 (India); Sharma, Kavita [Department of Physics, Bhagwan Parshuram Institute of Technology, Sector-17, Rohini, New Delhi 110 089 (India)

2012-07-15

62

ORIGINAL PAPER Attachment of b2-glycoprotein I to negatively charged liposomes  

E-print Network

ORIGINAL PAPER Attachment of b2-glycoprotein I to negatively charged liposomes may prevent­cholesterol giant lipid vesicles in the presence of b2-glycoprotein I (b2-GPI) in the outer solution was studied

Iglic, Ales

63

A Charge Pump that Generates Negative High Voltage with Variable Voltage , Eugene Ivanova,  

E-print Network

A Charge Pump that Generates Negative High Voltage with Variable Voltage Gain Jun Zhaob, , Eugene@ece.neu.edu (Jun Zhao), eugene.Ivanov@analog.com (Eugene Ivanov), hjlee@ece.neu.edu (Ho Joon Lee), ybk

Ayers, Joseph

64

Minimum charge moment change in positive and negative cloud to ground lightning discharges producing sprites  

E-print Network

) positive cloud-to-ground lightning discharges (+CGs) in thunder- storms [Lyons, 1996]. In the theoryMinimum charge moment change in positive and negative cloud to ground lightning discharges that surprisingly small charge moment changes of $200 C km in positive cloud-to-ground lightning discharges (+CGs

Pasko, Victor

65

Charge moment change and lightning-driven electric fields associated with negative sprites and halos  

E-print Network

Charge moment change and lightning-driven electric fields associated with negative sprites optical emissions produced by lightning-driven electric fields. Both strong positive and negative cloud to detect lightning-driven transient luminous events (TLEs). At Duke University, two pairs of magnetic

Cummer, Steven A.

66

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 ...

67

Unstable, metastable, or stable halogen bonding interaction involving negatively charged donors? A statistical and computational chemistry study.  

PubMed

The noncovalent halogen bonding could be attributed to the attraction between the positively charged ?-hole and a nucleophile. Quantum mechanics (QM) calculation indicated that the negatively charged organohalogens have no positively charged ?-hole on their molecular surface, leading to a postulation of repulsion between negatively charged organohalogens and nucleophiles in vacuum. However, PDB survey revealed that 24% of the ligands with halogen bonding geometry could be negatively charged. Moreover, 36% of ionizable drugs in CMC (Comprehensive Medicinal Chemistry) are possibly negatively charged at pH 7.0. QM energy scan showed that the negatively charged halogen bonding is probably metastable in vacuum. However, the QM calculated bonding energy turned negative in various solvents, suggesting that halogen bonding with negatively charged donors should be stable in reality. Indeed, QM/MM calculation on three crystal structures with negatively charged ligands revealed that the negatively charged halogen bonding was stable. Hence, we concluded that halogen bonding with negatively charged donors is unstable or metastable in vacuum but stable in protein environment, and possesses similar geometric and energetic characteristics as conventional halogen bonding. Therefore, negatively charged organohalogens are still effective halogen bonding donors for medicinal chemistry and other applications. PMID:25390886

Yang, Zhuo; Xu, Zhijian; Liu, Yingtao; Wang, Jinan; Shi, Jiye; Chen, Kaixian; Zhu, Weiliang

2014-12-11

68

Inelastic scattering effects on single molecule spectroscopy: Consequences for Negative Differential Resistance  

NASA Astrophysics Data System (ADS)

The adsorption of styrene and cyclopentene on Si(100) has been studied with scanning tunneling microscopy and spectroscopy. Blinking of molecules in images and irregularities in current-voltage spectra and in current-time traces are analyzed. It is also shown that NDR-like features in IV spectra of both styrene and cyclopentene molecules are not consistently present. Such erratic behavior cannot be accounted for by voltage controlled resonant alignment of adsorbate and substrate energy levels but is consistent with random configuration change driven by inelastically scattered electrons. These random processes, which include molecular rearrangement, desorption and/or decomposition occur with increasing frequency at larger voltage and current settings. It is concluded that the molecules studied do not exhibit negative differential resistance due to a resonant tunneling mechanism. Conditions where resonant NDR may be observed are discussed.

Pitters, Jason; Wolkow, Robert

2006-03-01

69

Improving carrier injection in organic diodes by incorporating charge trapping molecules  

Microsoft Academic Search

We demonstrate improved charge injection in organic diodes by incorporating charge trapping molecules near the injecting electrode that dynamically alter the effective Schottky energy barrier to carrier injection between a metal electrode and the organic electronic material. Hole injection from Al and Cu anodes into the electroluminescent polymer poly[2-methoxy,5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] was improved by incorporating C60 molecules into the polymer near

I. H. Campbell; B. K. Crone

2006-01-01

70

Improving carrier injection in organic diodes by incorporating charge trapping molecules  

Microsoft Academic Search

We demonstrate improved charge injection in organic diodes by incorporating charge trapping molecules near the injecting electrode that dynamically alter the effective Schottky energy barrier to carrier injection between a metal electrode and the organic electronic material. Hole injection from Al and Cu anodes into the electroluminescent polymer poly[2-methoxy,5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] was improved by incorporating C60 molecules into the polymer near

I. H. Campbell; B. K. Crone

2006-01-01

71

Interactions of Cationic Peptides and Ions with Negatively Charged Lipid Bilayers  

NASA Astrophysics Data System (ADS)

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.

Taheri-Araghi, Sattar

72

Application of a novel analysis to measure the binding of the membrane-translocating peptide penetratin to negatively charged liposomes.  

PubMed

The binding of penetratin, a peptide that has been found useful for cellular delivery of large hydrophilic molecules, to negatively charged vesicles was investigated. The surface charge density of the vesicles was varied by mixing zwitterionic dioleoylphosphatidylcholine (DOPC) and negatively charged dioleoylphosphatidylglycerol (DOPG) at various molar ratios. The extent of membrane association was quantified from tryptophan emission spectra recorded during titration of peptide solution with liposomes. A singular value decomposition of the spectral data demonstrated unambiguously that two species, assigned as peptide free in solution and membrane-bound peptide, respectively, account for the spectral data of the titration series. Binding isotherms were then constructed by least-squares projection of the titration spectra on reference spectra of free and membrane-bound peptide. A model based on the Gouy-Chapman theory in combination with a two-state surface partition equilibrium, separating the electrostatic and the hydrophobic contributions to the binding free energy, was found to be in excellent agreement with the experimental data. Using this model, a surface partition constant of approximately 80 M(-)(1) was obtained for the nonelectrostatic contribution to the binding of penetratin irrespective of the fraction of negatively charged lipids in the membrane, indicating that the hydrophobic interactions are independent of the surface charge density. In accordance with this, circular dichroism measurements showed that the secondary structure of membrane-associated penetratin is independent of the DOPC/DOPG ratio. Experiments using vesicles with entrapped carboxyfluorescein showed that penetratin does not form membrane pores. Studies of the cationic peptide penetratin are complicated by extensive adsorption to surfaces of quartz and plastics. By modification of the quartz cell walls with the cationic polymer poly(ethylenimine), the peptide adsorption was reduced to a tolerable level. The data analysis method used for construction of the binding isotherms eliminated errors emanating from the remaining peptide adsorption, which otherwise would prevent a proper quantification of the binding. PMID:12525169

Persson, Daniel; Thorén, Per E G; Herner, Mattias; Lincoln, Per; Nordén, Bengt

2003-01-21

73

Charge Transfer and Vibrational Excitation in Molecule-Surface Collisions: Trajectorized Quantum Theory  

Microsoft Academic Search

Vibrational excitation of diatomic molecules scattered from solid surfaces is considered. Emphasis is placed on a mechanism in which charge transfer between the molecule and surface creates a temporary molecular ion. A classical mechanics analysis of this effect has been presented previously. Here a mixed picture is offered in which the center-of-mass translational motion is treated classically with a trajectory

J. W. Gadzuk; S. Holloway

1985-01-01

74

Charge carrier trapping effect by luminescent dopant molecules in single-layer organic light emitting diodes  

Microsoft Academic Search

We investigated electroluminescent (EL) characteristics of single-layer organic light emitting diodes (SOLEDs). Our SOLED devices are composed of an inert polymer as a binder, in which hole transport molecules, emissive electron transport molecules (ETMs), and highly fluorescent dopants as luminescent centers are dispersed. We examined two typical dopants: rubrene and coumarin 6. These exhibited different charge carrier recombination and emission

Masahiro Uchida; Chihaya Adachi; Toshiki Koyama; Yoshio Taniguchi

1999-01-01

75

Interactions of PAMAM dendrimers with negatively charged model biomembranes.  

PubMed

We have investigated the interactions between cationic poly(amidoamine) (PAMAM) dendrimers of generation 4 (G4), a potential gene transfection vector, with net-anionic model biomembranes composed of different ratios of zwitterionic phosphocholine (PC) and anionic phospho-L-serine (PS) phospholipids. Two types of model membranes were used: solid-supported bilayers, prepared with lipids carrying palmitoyl-oleoyl (PO) and diphytanoyl (DPh) acyl chains, and free-standing bilayers, formed at the interface between two aqueous droplets in oil (droplet interface bilayers, DIBs) using the DPh-based lipids. G4 dendrimers were found to translocate through POPC:POPS bilayers deposited on silica surfaces. The charge density of the bilayer affects translocation, which is reduced when the ionic strength increases. This shows that the dendrimer-bilayer interactions are largely controlled by their electrostatic attraction. The structure of the solid-supported bilayers remains intact upon translocation of the dendrimer. However, the amount of lipids in the bilayer decreases and dendrimer/lipid aggregates are formed in bulk solution, which can be deposited on the interfacial layers upon dilution of the system with dendrimer-free solvent. Electrophysiology measurements on DIBs confirm that G4 dendrimers cross the lipid membranes containing PS, which then become more permeable to ions. The obtained results have implications for PAMAM dendrimers as delivery vehicles to cells. PMID:25310456

Yanez Arteta, Marianna; Ainalem, Marie-Louise; Porcar, Lionel; Martel, Anne; Coker, Helena; Lundberg, Dan; Chang, Debby P; Soltwedel, Olaf; Barker, Robert; Nylander, Tommy

2014-11-13

76

Electrostatic surface guiding of cold polar molecules with a single charged wire  

Microsoft Academic Search

This paper proposes a scheme to guide cold polar molecules by using a single charged wire half embanked in an insulating substrate and a homogeneous bias electric field, which is generated by a plate capacitor composed of two infinite parallel metal plates. The spatial distributions of the electrostatic field produced by the combination of the charged wire and the plate

Lian-Zhong Deng; Yong Xia; Jian-Ping Yin

2007-01-01

77

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

PubMed Central

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

2013-01-01

78

Water Freezes Differently on Positively and Negatively Charged Surfaces of Pyroelectric Materials  

NASA Astrophysics Data System (ADS)

Although ice melts and water freezes under equilibrium conditions at 0°C, water can be supercooled under homogeneous conditions in a clean environment down to -40°C without freezing. The influence of the electric field on the freezing temperature of supercooled water (electrofreezing) is of topical importance in the living and inanimate worlds. We report that positively charged surfaces of pyroelectric LiTaO3 crystals and SrTiO3 thin films promote ice nucleation, whereas the same surfaces when negatively charged reduce the freezing temperature. Accordingly, droplets of water cooled down on a negatively charged LiTaO3 surface and remaining liquid at -11°C freeze immediately when this surface is heated to -8°C, as a result of the replacement of the negative surface charge by a positive one. Furthermore, powder x-ray diffraction studies demonstrated that the freezing on the positively charged surface starts at the solid/water interface, whereas on a negatively charged surface, ice nucleation starts at the air/water interface.

Ehre, David; Lavert, Etay; Lahav, Meir; Lubomirsky, Igor

2010-02-01

79

Surface charging by large multivalent molecules. Extending the standard Gouy-Chapman treatment.  

PubMed Central

Traditionally, Gouy-Chapman theory has been used to calculate the distribution of ions in the diffuse layer next to a charged surface. In recent years, the same theory has found application to adsorption (incorporation, partitioning) of charged peptides, hormones, or drugs at the membrane-water interface. Empirically it has been found that an effective charge, smaller than the physical charge, must often be used in the Gouy-Chapman formula. In addition, the large size of these molecules can be expected to influence their adsorption isotherms. To improve evaluation techniques for such experiments, comparatively simple extensions of the standard Gouy-Chapman formalism have been studied which are based on a discrete charge virial expansion. The model allows for the mobility of charged groups at the interface. It accounts for finite size of the adsorbed macromolecules and for discrete charge effects arising from pair interactions in the interface plane. In contrast to previous discrete charge treatments this model nearly coincides with the Gouy-Chapman formalism in the case where the adsorbing molecules are univalent. Large discrepancies are found for multivalent molecules. This could explain the reduced effective charges needed in the standard Gouy-Chapman treatment. The reduction factor can be predicted. The model is mainly limited to low surface coverage, typical for the adsorption studies in question. PMID:1912277

Stankowski, S

1991-01-01

80

The chemical hardness of molecules and the band gap of solids within charge equilibration formalisms. Toward force field-based simulations of redox reactions  

NASA Astrophysics Data System (ADS)

This work finds that different charge equilibration methods lead to qualitatively different responses of molecules and solids to an excess charge. The investigated approaches are the regular charge equilibration (QE), the atom-atom-charge transfer (AACT), and the split-charge equilibration (SQE) method. In QE, the hardness of molecules and the band gap of solids approaches zero at large particle numbers, affirming the claim that QE induces metallic behavior. AACT suffers from producing negative values of the hardness; moreover valence and conduction bands of solids cross. In contrast to these methods, SQE can reproduce the generic behavior of dielectric molecules or solids. Moreover, first quantitative results for the NaCl molecule are promising. The results derived in this work may have beneficial implications for the modeling of redox reactions. They reveal that by introducing formal oxidation states into force field-based simulations it will become possible to simulate redox reactions including non-equilibrium contact electrification, voltage-driven charging of galvanic cells, and the formation of zwitterionic molecules.

Müser, M. H.

2012-04-01

81

The influence of negative charged centers on the hole transport in a typical molecularly doped polymer  

NASA Astrophysics Data System (ADS)

We have studied effects of the negative charged centers on the time of flight (TOF) curves measured in a typical hole-conducting molecularly doped polymer. The main effects are the unusual TOF (surface generation) current rise in the preflight region (be it a flat plateau or a cusp) due to the accumulated space charge and the current reduction at all times because of the monomolecular recombination. TOF-2 (bulk generation) transients are less sensitive to charged centers. Analysis of these effects has proved that charged centers do not change the carrier mobility provided that the space charge field and bimolecular recombination are properly accounted for in terms of the proposed two-layer MT model. We have shown that combination of TOF, TOF-1a and TOF-2 variants of the electron-gun based technique allows one to establish definitively the character of the charge carrier transport in MDPs.

Tyutnev, Andrey P.; Ikhsanov, Renat Sh.; Saenko, Vladimir S.; Pozhidaev, Evgenii D.

2014-03-01

82

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

SciTech Connect

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.

Ghosh, Samiran [Government College of Engineering and Textile Technology, 4, Cantonment Road, Berhampore, Murshidabad 742101 West Bengal (India)

2005-09-15

83

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

84

Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*– and He2*–  

PubMed Central

Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium. PMID:25068008

2014-01-01

85

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

PubMed

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. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 58-65, 2014. PMID:23640767

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

2014-01-01

86

Charged squashed black holes with negative cosmological constant in odd dimensions  

E-print Network

We construct new electrically charged solutions of the Einstein-Maxwell equations with negative cosmological constant in general odd dimensions $d=2n+3 \\geq 5$. They correspond to higher dimensional generalizations of the squashed black hole solutions, which were known so far only in five dimensions. We explore numerically the general properties of such classical solutions and, using a counterterm prescription, we compute their conserved charges and discuss their thermodynamics.

Yves Brihaye; Eugen Radu; Cristian Stelea

2012-01-25

87

Bionic design for surface optimization combining hydrophilic and negative charged biological macromolecules.  

PubMed

While polyethersulfone (PES) membrane represents a promising option for blood purification, the blood compatibility must be dramatically enhanced to meet today's ever-increasing demands for many emerging application. In this study, we report a bionic design for optimization and development of a modified PES membrane combining hydrophilic and negative charged biological macromolecules on its surface. The hydrophilic and ionic charged biological macromolecules sulfonated poly(styrene)-b-poly(methyl methacrylate)-b-poly-(styrene) (PSSMSS) and poly(vinyl pyrrolidone)-b-poly(methyl methacrylate)-b-poly-(vinyl pyrrolidone) were synthesized via reversible addition-fragmentation chain transfer polymerization and used together to modify PES membranes by blending method. A hydrophilic membrane surface with negative charged surface coating was obtained, imitating the hydrophilic and negatively charged structure feature of heparin. The modified PES membranes showed suppressed platelet adhesion, and a prolonged blood clotting time, and thereby improved blood compatibility. In addition, the blood clotting time of the modified membranes increased with the blended PSSMSS amounts increment, indicating that both the hydrophilic and negative charged groups play important roles in improving the blood compatibility of PES membranes. PMID:24680810

Ran, Fen; Song, Haiming; Niu, Xiaoqin; Yang, Aimei; Nie, Shengqiang; Wang, Lingren; Li, Jie; Sun, Shudong; Zhao, Changsheng

2014-06-01

88

The Resonance Scattering Phenomenon of Fast Negatively Charged Particles in a Single Crystal  

E-print Network

The energy spectrum of the extended attractive potential of a crystallographic row for negatively charged particles has quasi-bound states. It follows that a negatively charged particle with small transversal momentum component ($p_{\\bot} R <<1$) may undergo resonance scattering. Thus the resonance scattering phenomenon can be observed in a single crystal, when fast electrons move with a small glancing angle ($\\theta_0 << 1/pR$) to a crystallographic axis. The calculated results for the electrons and angular widths of resonance peaks are consistent with experimental data.

Gennady V. Kovalev

2014-12-12

89

The Resonance Scattering Phenomenon of Fast Negatively Charged Particles in a Single Crystal  

E-print Network

The energy spectrum of the extended attractive potential of a crystallographic row for negatively charged particles has quasi-bound states. It follows that a negatively charged particle with small transversal momentum component ($p_{\\bot} R <<1$) may undergo resonance scattering. Thus the resonance scattering phenomenon can be observed in a single crystal, when fast electrons move with a small glancing angle ($\\theta_0 << 1/pR$) to a crystallographic axis. The calculated results for the electrons and angular widths of resonance peaks are consistent with experimental data.

Kovalev, Gennady V

2015-01-01

90

Negative differential resistance of TEMPO molecules on Si(1 1 1)  

NASA Astrophysics Data System (ADS)

Negative differential resistance (NDR) has been observed for individual 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) molecules on Si(1 1 1) in ultra high vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) measurements at room temperature. NDR effects were observed exclusively at negative bias voltage using an n-type Si(1 1 1) sample. At 77 K no NDR effects were observed, but the I( V) curves were similar in shape to those recorded on bare Si(1 1 1) sites. TEMPO was observed to adsorb preferentially at corner adatom sites of the Si(1 1 1)-7 × 7 structure. Although the Si(1 1 1)-7 × 7 reconstruction was conserved, local defects were frequently observed in the vicinity of the TEMPO adsorbates.

Hallbäck, Ann-Sofie; Poelsema, Bene; Zandvliet, Harold J. W.

2007-02-01

91

Quantum tunnelling and classical above-barrier transitions in electron detachment from negative ions by negatively charged projectiles  

NASA Astrophysics Data System (ADS)

A simple model of electron detachment from negative ions by negatively charged projectile impact is developed as a combination of quantum tunnelling and classical field ionization. While the tunnelling theory has been discussed previously by Smirnov and Chibisov, we have substantially amended Solov'ev's classical model for above-barrier transition. As the most important modification we introduce the concept of decay rate for the classical ensemble related to the quantum state and evaluate the rate in terms of the simple free-fall atomic model. The present theory compares very well with recent experiments while the isolated application of the tunnelling model and of the classical model yields results that are a factor of two too large and too small, respectively.

Ostrovsky, V. N.; Taulbjerg, K.

1996-06-01

92

Ionization of water molecules by fast charged projectiles  

SciTech Connect

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.

Dubois, A.; Carniato, S. [UPMC Universite Paris 6, UMR 7614, Laboratoire de Chimie Physique-Matiere et Rayonnement, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05 (France); CNRS, UMR 7614, Laboratoire de Chimie Physique-Matiere et Rayonnement, 11 rue Pierre et Marie Curie, F-75005, Paris (France); Fainstein, P. D. [Centro Atomico Bariloche, Comision Nacional de Energia Atomica, Avda. E. Bustillo 9500, 8400 Bariloche (Argentina); Hansen, J. P. [Department of Physics and Technology, University of Bergen, N-5007 Bergen (Norway)

2011-07-15

93

Negative correlation between charge carrier density and mobility fluctuations in graphene  

NASA Astrophysics Data System (ADS)

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.

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

94

Space Charge Compensation in the Linac4 Low Energy Beam Transport Line with Negative Hydrogen Ions  

E-print Network

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 Tranport (LEBT) using the package IBSimu1, 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- 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.

Valerio-Lizarraga, C; Leon-Monzon, I; Lettry, J; Midttun, O; Scrivens, R

2013-01-01

95

Gram-Negative Bacterial Lipopolysaccharide Retention by a Positively Charged New-Generation Filter  

Microsoft Academic Search

Endotoxins are lipopolysaccharides (LPS) which constitute the main component of the outer membranes of gram-negative bacteria. Endotoxins at high doses are pathogenic molecules which act as potent activators of the immune system. Mono- cytes and macrophages, following LPS stimulation, release me- diators with powerful biological and pyrogenic activities. More- over, LPS interact with the vascular endothelium and stimulate the complement

Ilaria Bononi; Veronica Balatti; Soccorso Gaeta; Mauro Tognon

2008-01-01

96

The role of dipole interactions of molecules with charged particles in the polar stratosphere  

NASA Astrophysics Data System (ADS)

On the basis of the analysis of the reported balloon, airborne and ground based lidar experiments in the polar regions a new pathway explaining the photochemical processes in the polar stratosphere is considered. A close relationship of these processes with the electric phenomena in the stratosphere such as an accumulation of charged particles on the upper and lower boundaries of the polar stratospheric clouds as a result of the global electric circuit operation is shown. The dipole interaction of molecules with charged particles, mainly with ionic clusters, results in a sticking and decay of some molecules. The additional energy for molecules that becomes available on the surface of charged particles allows such reactions, which are not otherwise possible in space.

Belikov, Yury; Nikolayshvili, Sergey

97

Terminal supraparticle assemblies from similarly charged protein molecules and nanoparticles  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

98

Terminal Supraparticle Assemblies from Similarly Charged Protein Molecules and Nanoparticles  

PubMed Central

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

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

99

Negative Surface Charge Near Sodium Channels of Nerve: Divalent Ions, Monovalent Ions, and pH  

Microsoft Academic Search

Evidence is given for a high density of negative surface charge near the sodium channel of myelinated nerve fibres. The voltage dependence of peak sodium permeability is measured in a voltage clamp. The object is to measure voltage shifts in sodium activation as the following external variables are varied: divalent cation concentration and type, monovalent concentration, and pH. With equimolar

B. Hille; Ann M. Woodhull; B. I. Shapiro

1975-01-01

100

4.1.6 SINGLE MOLECULE RESONANT TUNNELING SPECTROSCOPY N. P. Guisinger, N. L. Yoder, M. C. Hersam, "Probing Charge Transport at the Single Molecule Level on  

E-print Network

20 4.1.6 SINGLE MOLECULE RESONANT TUNNELING SPECTROSCOPY N. P. Guisinger, N. L. Yoder, M. C. Hersam, "Probing Charge Transport at the Single Molecule Level on Silicon by Using Cryogenic Ultra-High Vacuum to image and probe individual organic molecules on silicon. At cryogenic temperatures, the precision

Shull, Kenneth R.

101

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

102

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

PubMed

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. PMID:25698329

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

2015-03-01

103

Phenomenological theory of a charged polymer molecule in a nanosized gap between two fluidic reservoirs  

NASA Astrophysics Data System (ADS)

We use a simple Born ion continuum model to analyse the effect of solvation energy change on the translocation of a charged linear polymer molecule through a nanosized vapor gap between two fluid reservoirs. As the effective radius of the discretely spaced charges increases, our model predicts a transition from trapping to diffusion of the molecule in the vapor gap. We discuss the applicability of our model to single-stranded DNA translocations in gaps, suggest experiments to validate our prediction and propose immediate applications of this new trapping mechanism for slowing down DNA motion for electronic DNA sequencing.

Polonsky, Stanislav; Balagurusamy, Venkat S. K.

2013-09-01

104

Phonon Effects on Charge Transport Through a Two State Molecule  

NASA Astrophysics Data System (ADS)

We study the effect of local and non-local phonon on the transport properties of a molecule model described by two- electronic states. The local phonon interaction is tackled by means of a Lang Firsov transformation [1,2]. The interaction with non-local phonons (phonon-assisted hopping) is considered perturbatively up to the first nonzero order in the self energy. The presence of different kinds of electron-phonon interaction open new transmission channels. In addition to the polaron shift and replicas due to local phonons, non-local phonons cause the appearance of new satellite states around the initial states. In the weak coupling regime of non-local phonon and electrons, states are shifted an amount proportional to square of the interaction. However, in the strong coupling regime, the non-linear effects emerge and display more interesting features on transport properties. Additional features on transport properties due to new transmission channel are shown to appear at finite temperatures. [1] G. D. Mahan, Many-particle physics, 3rd ed. (Plenum Publishers, New York, 2000). [2] R. Gutierrez et al., Phys. Rev. B. 74, 235105 (2006).

Ulloa, Sergio E.; Yudiarsah, Efta

2008-03-01

105

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

SciTech Connect

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.

Zanni, Martin T.

1999-12-17

106

Negative dispersion of birefringence of smectic liquid crystal-polymer composite: dependence on the constituent molecules and temperature.  

PubMed

We investigated the dependence of the negative dispersion of birefringence of smectic liquid crystal-polymer composites on the constituent molecules and temperature. The dispersion of birefringence was significantly varied from positive dispersion to negative dispersion by the change of the relative fraction of the constituent monomers. For the temperature dependence of the dispersion, a composite with more fraction of monomers located at the inter-layer space showed a wider temperature range of the negative dispersion of birefringence. PMID:25836114

Yang, Seungbin; Lee, Hyojin; Lee, Ji-Hoon

2015-02-01

107

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

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

108

Discharges on a negatively biased solar cell array in a charged-particle environment  

NASA Technical Reports Server (NTRS)

The charging behavior of a negatively biased solar cell array when subjected to a charged particle environment is studied in the ion density range from 200 to 12,000 ions/sq cm with the applied bias range of -500 to -1400 V. The profile of the surface potentials across the array is related to the presence of discharges. At the low end of the ion density range the solar cell cover slides charge to from 0 to +5 volts independent of the applied voltage. No discharges are seen at bias voltages as large as -1400 V. At the higher ion densities the cover slide potential begins to fluctuate, and becomes significantly negative. Under these conditions discharges can occur. The threshold bias voltage for discharges decreases with increasing ion density. A condition for discharges emerging from the experimental observations is that the average coverslide potential must be more negative than -4 V. The observations presented suggest that the plasma potential near the array becomes negative before a discharge occurs. This suggests that discharges are driven by an instability in the plasma.

Snyder, D. B.

1985-01-01

109

Glutamic acid 181 is negatively charged in the bathorhodopsin photointermediate of visual rhodopsin  

PubMed Central

Assignment of the protonation state of the residue Glu-181 is important to our understanding of the primary event, activation processes and wavelength selection in rhodopsin. Despite extensive study, there is no general agreement on the protonation state of this residue in the literature. Electronic assignment is complicated by the location of Glu-181 near the nodal point in the electrostatic charge shift that accompanies excitation of the chromophore into the low-lying, strongly allowed ??* state. Thus, the charge on this residue is effectively hidden from electronic spectroscopy. This situation is resolved in bathorhodopsin, because photoisomerization of the chromophore places Glu-181 well within the region of negative charge shift following excitation. We demonstrate that Glu-181 is negatively charged in bathorhodopsin based on the shift in the batho absorption maxima at 10K [?max band (native)= 544±2 nm, ?max band (E181Q)= 556±3 nm] and the decrease in the ?max band oscillator strength (0.069±0.004) of E181Q relative to the native protein. Because the primary event in rhodopsin does not include a proton translocation or disruption of the hydrogen-bonding network within the binding pocket, we may conclude that the Glu-181 residue in rhodopsin is also charged. PMID:21319741

Sandberg, Megan N.; Amora, Tabitha L.; Ramos, Lavoisier S.; Chen, Min-Hsuan; Knox, Barry E.; Birge, Robert R.

2011-01-01

110

Negative Ion CID Fragmentation of O-linked Oligosaccharide Aldoses—Charge Induced and Charge Remote Fragmentation  

NASA Astrophysics Data System (ADS)

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.

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

2011-06-01

111

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

NASA Astrophysics Data System (ADS)

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.

Yao, Yao

2015-01-01

112

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

SciTech Connect

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.

Denton, M.B.

1992-07-29

113

Frequency-dependent capacitance of hydrophobic membranes containing fixed negative charges.  

PubMed

Filters containing fixed negative charges were saturated with hydrophobic solvent and interposed between aqueous solutions. The capacitance of such membranes was measured in the frequency range of 0.05-30 kc. The capacitance increased with decrease in frequency. The frequency dependence of the capacitance was sensitive to nature of the cation present and to salt concentration in the aqueous solution. It is suggested that variation of membrane resistivity in the space charge region of the membrane is responsible for this phenomenon. Possible effects of the potential and counterion concentration profiles at the membrane-water interface are discussed. PMID:5699796

Ilani, A

1968-05-01

114

Adhesion, stretching, and electrical charge assessment of dermatan sulfate molecules by colloidal probes.  

PubMed

Electrical and mechanical properties of dermatan sulfate (DS) molecules are studied in an aqueous environment as a function of pH. DS molecules linked at various points distributed on the surface of mica previously silanizated along with a suitable functionalized microsphere, attached to the cantilever of an atomic force microscope (AFM), provided suitable surfaces for testing interactions through the colloidal probe methodology. The repulsive force between the surfaces indicated that the charge of DS increases with pH as a result of the gradual deprotonation of acidic groups. Pulling experiments revealed increasing adhesion of DS to the monolayer as a function of pH, presumably due both to the electrical nature of the interaction between these molecules and the progressive increase of the charge of DS with pH. Serrations exhibited by the force in pulling experiments indicate that more than a single DS molecule is stretched at the same time. In addition, pulling force remained significant even at extensions that went beyond the average contour length of a single DS molecule, which suggests the existence of a significant link between DS molecules. PMID:22607055

Gonzalez, Rodrigo; Caballero, Leonardo; Pavez, Jorge; Melo, Francisco

2012-06-26

115

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

PubMed Central

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

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

2002-01-01

116

Observation of negatively charged excitons (X^-) in ZnCdSe\\/ZnSe Quantum Wells  

Microsoft Academic Search

We have studied the photoluminescence spectra from a 100 ÅZnCdSe\\/ZnSe(Cl) quantum well in magnetic fields up to 30 Tesla. The band-edge luminescence spectra consist of two features separated by 5 meV. These are associated with the recombination of neutral (X) and negatively charged (X^-) confined excitons. The intensity of the X^- (X) feature decreases (increases) with magnetic field. The intensity

A. Petrou; M. S. Salib; G. Kioseoglou; B. T. Jonker; J. Warnock

1997-01-01

117

Negative oxygen vacancies in HfO$_2$ as charge traps in high-k stacks  

Microsoft Academic Search

We calculated the optical excitation and thermal ionization energies of\\u000aoxygen vacancies in m-HfO$_2$ using atomic basis sets, a non-local density\\u000afunctional and periodic supercell. The thermal ionization energies of\\u000anegatively charged V$^-$ and V$^{2-}$ centres are consistent with values\\u000aobtained by the electrical measurements. The results suggest that negative\\u000aoxygen vacancies are the likely candidates for intrinsic electron traps

J. L. Gavartin; D. Munoz Ramo; A. L. Shluger; G. Bersuker; B. H. Lee

2006-01-01

118

Monitoring FET flow control and wall adsorption of charged fluorescent dye molecules in nanochannels integrated into a multiple internal reflection  

E-print Network

Monitoring FET flow control and wall adsorption of charged fluorescent dye molecules can be used to monitor the FET flow control of charged, fluorescent dye molecules during fluorescence microscopy is simultaneously used to provide a comparison and verification of the IR analysis

New Mexico, University of

119

Potential Dependent Alignment and Hydrogen Bonding of Water Molecules at Charged Air/Water and CCl4/Water Interfaces  

E-print Network

Potential Dependent Alignment and Hydrogen Bonding of Water Molecules at Charged Air/Water and CCl4/Water Interfaces D. E. Gragson and G. L. Richmond* Contribution from the Department of Chemistry, Uni and hydrogen bonding of interfacial water molecules at a charged air/water and CCl4/water interface

Richmond, Geraldine L.

120

Positron-annihilation studies of neutral and negatively charged As vacancies in GaAs  

NASA Astrophysics Data System (ADS)

The electronic properties of native monovacancy defects were investigated using techniques based on positron annihilation in n-type Si-doped GaAs. The positron lifetime measurements as a function of temperature have shown the thermal ionization of native As vacancies from negative to neutral charge state: V-As-->V0As. By combining the results of positron lifetime and two-dimensional angular-correlation-of-annihilation-radiation (2D-ACAR) experiments, the 2D-ACAR distributions of neutral and negative arsenic vacancies were separated from the partial bulk contribution. We found that 2D-ACAR distributions of the As vacancies are different from those of the bulk, and we also observed differences between the distributions of V0As and V-As. When compared to the negative charge state V-As, the neutral charge state V0As is characterized by a narrower momentum distribution from valence electron annihilations and a lower high-momentum tail from core electrons. These findings lead us to conclude that the electronic and ionic structure of the As vacancies depend strongly on their ionization. We also infer that V-As has a smaller open volume than V0As. This conclusion is in agreement with previous positron lifetime results and molecular-dynamics calculations.

Ambigapathy, R.; Manuel, A. A.; Hautojärvi, P.; Saarinen, K.; Corbel, C.

1994-07-01

121

Theoretical Compton profile anisotropies in molecules and solids. III. Relationship of parallel–perpendicular anisotropies to charge distributions in alkali chloride molecules  

Microsoft Academic Search

Total Compton profiles and anisotropies associated with momentum distribution along vectors parallel and perpendicular to bond axes in alkali chloride molecules are calculated and related to changes in charge distributions accompanying bond formation.

R. L. Matcha; B. M. Pettitt; B. I. Ramirez; W. R. McIntire

1978-01-01

122

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

SciTech Connect

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.

Valerio-Lizarraga, Cristhian A., E-mail: cristhian.alfonso.valerio.lizarraga@cern.ch [CERN, Geneva (Switzerland); Departamento de Investigación en Física, Universidad de Sonora, Hermosillo (Mexico); Lallement, Jean-Baptiste; Lettry, Jacques; Scrivens, Richard [CERN, Geneva (Switzerland)] [CERN, Geneva (Switzerland); Leon-Monzon, Ildefonso [Facultad de Ciencias Fisico-Matematicas, Universidad Autónoma de Sinaloa, Culiacan (Mexico)] [Facultad de Ciencias Fisico-Matematicas, Universidad Autónoma de Sinaloa, Culiacan (Mexico); Midttun, Øystein [CERN, Geneva (Switzerland) [CERN, Geneva (Switzerland); University of Oslo, Oslo (Norway)

2014-02-15

123

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

PubMed Central

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

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

2014-01-01

124

Fragmentation of molecules under charge-changing collisions of a few MeV heavy ions  

NASA Astrophysics Data System (ADS)

We investigated molecular fragmentation of CO and C2H2 molecules by impact of various fast heavy ions. Fragment ions produced in electron capture and loss collisions of projectile ions were measured in coincidence with final projectile charge states. Data acquisition using position sensitive detection system allows us to obtain 3D momentum imaging of fragment ions and kinetic energy release (KER) in various charge-changing collisions. It was found that the KER spectra show strong dependence on the type of charge-changing collisions. This may be caused by the difference of impact parameters associated with individual charge-changing collisions. Moreover we revealed the different fragmentation pathway between ion impacts and photoionization.

Mizuno, T.; Itoh, A.

2014-04-01

125

Quantum interference and electron correlation in charge transport through triangular quantum dot molecules.  

PubMed

We study the charge transport properties of triangular quantum dot molecules (TQDMs) connected to metallic electrodes, taking into account all correlation functions and relevant charging states. The quantum interference (QI) effect of TQDMs resulting from electron coherent tunneling between quantum dots is revealed and well interpreted by the long distance coherent tunneling mechanism. The spectra of electrical conductance of TQDMs with charge filling from one to six electrons clearly depict the many-body and topological effects. The calculated charge stability diagram for conductance and total occupation numbers matches well with the recent experimental measurements. We also demonstrate that the destructive QI effect on the tunneling current of TQDMs is robust with respect to temperature variation, making the single electron QI transistor feasible at higher temperatures. PMID:25660124

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

2015-02-18

126

Atomistic theory of mesoscopic pattern formation induced by bimolecular surface reactions between oppositely charged molecules  

NASA Astrophysics Data System (ADS)

The kinetics of mesoscopic pattern formation is studied for a reversible A+B rightleftharpoons 0 reaction between mobile oppositely charged molecules at the interface. Using formalism of the joint correlation functions, non-equilibrium charge screening and reverse Monte Carlo methods, it is shown that labyrinth-like percolation structure induced by (even moderate-rate) reaction is principally non-steady-state one and is associated with permanently growing segregation of dissimilar reactants and aggregation of similar reactants into mesoscopic size domains. A role of short-range and long-range reactant interactions in pattern formation is discussed.

Kuzovkov, V. N.; Kotomin, E. A.; Zvejnieks, G.

2011-12-01

127

Enhanced charge photogeneration promoted by crystallinity in small-molecule donor-acceptor bulk heterojunctions  

NASA Astrophysics Data System (ADS)

We examined sub-nanosecond time-scale charge carrier dynamics in crystalline films of a functionalized anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene acceptor added at 7-10 wt. % concentrations, whereas a gradual decrease in peak photocurrent amplitude with acceptor concentration was observed with functionalized pentacene and indenofluorene acceptors. The results were directly correlated with the ADT-tri(ethylsilyl)ethynyl-F donor crystallinity. In the best-performing blends, the presence of crystalline acceptor domains was also established.

Paudel, Keshab; Johnson, Brian; Thieme, Mattson; Haley, Michael M.; Payne, Marcia M.; Anthony, John E.; Ostroverkhova, Oksana

2014-07-01

128

Solution, surface, and single molecule platforms for the study of DNA-mediated charge transport  

PubMed Central

The structural core of DNA, a continuous stack of aromatic heterocycles, the base pairs, which extends down the helical axis, gives rise to the fascinating electronic properties of this molecule that is so critical for life. Our laboratory and others have developed diverse experimental platforms to investigate the capacity of DNA to conduct charge, termed DNA-mediated charge transport (DNA CT). Here, we present an overview of DNA CT experiments in solution, on surfaces, and with single molecules that collectively provide a broad and consistent perspective on the essential characteristics of this chemistry. DNA CT can proceed over long molecular distances but is remarkably sensitive to perturbations in base pair stacking. We discuss how this foundation, built with data from diverse platforms, can be used both to inform a mechanistic description of DNA CT and to inspire the next platforms for its study: living organisms and molecular electronics. PMID:22850865

Muren, Natalie B.; Olmon, Eric D.; Barton, Jacqueline K.

2012-01-01

129

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

NASA Astrophysics Data System (ADS)

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.

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

130

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

131

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

PubMed

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) cm(2) 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 cm(2) 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. PMID:24658783

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

2014-05-01

132

'Tunable' positive and negative surface charges on a capillary wall: exploiting the Immobiline chemistry.  

PubMed

The Immobiline (weak acrylamido acids and bases) chemistry has been applied to the covalent attachment of a positively (or, if needed, negatively) charged layer onto the inner surface of the silica wall. In particular, the following basic Immobilines have been used: pK 6.2, pK 7.0, pK 8.5 and pK 9.3. In order to avoid pK changes, the charged Immobilines are mixed with neutral acrylamido derivatives (in particular the highly resistant and hydrophilic N-acryloyl aminoethoxyethanol) so as to form a co-polymer having a 1:5 molar ratio (charged to neutral). The mu(eo) vs. pH curves have a slope opposite to that of a naked capillary and fan out on the pH scale following the titration curves of the different weak bases. Such chemistry allows the covalent attachment of charged species having known pK values and offering controlled charged densities on the wall. However, with the atomic force microscope, it is found that such soft coatings (whether charged or neutral) do not seem to provide complete coverage of the surface: naked patches of fused silica are found interdispersed among the polymer-coated ones. A good solution is a hybrid bonded and dynamic coating, obtained by adding short chain linear polyacrylamides to the background electrolyte. Good separations of polycations [poly(L-histidine)] and of histones are reported up to pH 5.7. PMID:8796483

Capelli, L; Ermakov, S V; Righetti, P G

1996-05-14

133

Distance dependent rates of photoinduced charge separation and dark charge recombination in fixed distance porphyrin-quinone molecules  

SciTech Connect

Three zinc tetraphenylporphyrin-anthraquinone derivatives were prepared in which the edge-to-edge distances between the porphyrin and quinone ..pi.. systems are fixed by a rigid hydrocarbon spacer molecule. Triptycene, trans-1,2-diphenylcyclopentane, and adamantane were used to fix the porphyrin-anthraquinone distance at 2.5, 3.7, and 4.9 A, respectively. These molecules possess 1,2, and 3 saturated carbon atoms, respectively, between the porphyrin donor and the quinone acceptor. Rate constants for photoinduced electron transfer from the lowest excited singlet state of the zinc tetraphenylporphyrin donor to the anthraquinone acceptor were measured. In addition, the corresponding radical ion pair recombination rate constants for each of these molecules were also determined. The rate constants for both photoinduced charge separation and subsequent radical ion pair recombination decrease by approximately a factor of 10 for each saturated carbon atom intervening between the porphyrin donor and the quinone acceptor. These results are consistent with a model in which the rate of electron transfer is determined by weak mixing of the sigma orbitals of the saturated hydrocarbon spacer with the ..pi.. orbitals of the donor and acceptor. 22 refs., 5 figs.

Wasielewski, M.R.; Niemczyk, M.P.

1986-01-01

134

High-throughput ion exchange purification of positively charged recombinant protein in the presence of negatively charged dextran sulfate.  

PubMed

Product quality analyses are critical for developing cell line and bioprocess producing therapeutic proteins with desired critical product quality attributes. To facilitate these analyses, a high-throughput small-scale protein purification (SSP) is required to quickly purify many samples in parallel. Here we develop an SSP using ion exchange resins to purify a positively charged recombinant growth factor P1 in the presence of negatively charged dextran sulfate supplemented to improve the cell culture performance. The major challenge in this work is that the strong ionic interaction between P1 and dextran sulfate disrupts interaction between P1 and chromatography resins. To solve this problem, we develop a two-step SSP using Q Sepharose Fast Flow (QFF) and SP Sepharose XL (SPXL) resins to purify P1. The overall yield of this two-step SSP is 78%. Moreover, the SSP does not affect the critical product quality attributes. The SSP was critical for developing the cell line and process producing P1. PMID:24449619

Markely, Lam Raga A; Kurt, Lutfiye; Lau, Janet; Mane, Sarthak; Guan, Bing; Ryll, Thomas; Estes, Scott; Prajapati, Shashi; Bakhshayeshi, Meisam; Pieracci, John

2014-01-01

135

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

NASA Astrophysics Data System (ADS)

Primordial 7Li 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 7Be destruction during the BBN epoch caused by a long-lived negatively charged massive particle, X-. The particle can bind to nuclei, and X-bound nuclei (X-nuclei) can experience new reactions. The radiative X- capture by 7Be nuclei followed by proton capture of the bound state of 7Be and X- (7Bex) is a possible 7Be destruction reaction. Since the primordial abundance of 7Li originates mainly from 7Li produced via the electron capture of 7Be after BBN, the 7Be destruction provides a solution to the 7Li problem. We suggest a new route of 7Bex formation, that is the 7Be charge exchange at the reaction of 7Be3+ ion and X-. The formation rate depends on the ionization fraction of 7Be3+ ion, the charge exchange cross section of 7Be3+, and the probability that excited states 7Bex* 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 7Be and X-. The effect of this new route is shown in a nuclear reaction network calculation.

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

2014-05-01

136

The role of negatively charged lipids in lysosomal phospholipase A2 function  

PubMed Central

Lysosomal phospholipase A2 (LPLA2) is characterized by increased activity toward zwitterionic phospholipid liposomes containing negatively charged lipids under acidic conditions. The effect of anionic lipids on LPLA2 activity was investigated. Mouse LPLA2 activity was assayed as C2-ceramide transacylation. Sulfatide incorporated into liposomes enhanced LPLA2 activity under acidic conditions and was weakened by NaCl or increased pH. Amiodarone, a cationic amphiphilic drug, reduced LPLA2 activity. LPLA2 exhibited esterase activity when p-nitro-phenylbutyrate (pNPB) was used as a substrate. Unlike the phospholipase A2 activity, the esterase activity was detected over wide pH range and not inhibited by NaCl or amiodarone. Presteady-state kinetics using pNPB were consistent with the formation of an acyl-enzyme intermediate. C2-ceramide was an acceptor for the acyl group of the acyl-enzyme but was not available as the acyl group acceptor when dispersed in liposomes containing amiodarone. Cosedimentation of LPLA2 with liposomes was enhanced in the presence of sulfatide and was reduced by raising NaCl, amiodarone, or pH in the reaction mixture. LPLA2 adsorption to negatively charged lipid membrane surfaces through an electrostatic attraction, therefore, enhances LPLA2 enzyme activity toward insoluble substrates. Thus, anionic lipids present within lipid membranes enhance the rate of phospholipid hydrolysis by LPLA2 at lipid-water interfaces.—Abe, A., and J. A. Shayman. The role of negatively charged lipids in lysosomal phospholipase A2 function. PMID:19321879

Abe, Akira; Shayman, James A.

2009-01-01

137

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

SciTech Connect

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.

Lee, C. M., E-mail: mesimon-hk@yahoo.com.hk, E-mail: apkschan@cityu.edu.hk; Chan, K. S., E-mail: mesimon-hk@yahoo.com.hk, E-mail: apkschan@cityu.edu.hk [Department of Physics and Materials Science and Center for Functional Photonics, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Shenzhen Research Institute, City University of Hong Kong, Shenzhen (China)

2014-07-28

138

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

NASA Astrophysics Data System (ADS)

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 D3d 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.

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

139

Negatively charged metallacarborane redox couples with both members stable to air.  

PubMed

The metallacarborane [3,3'-Co(1,2-closo-C2 B9 H11 )2 ](-) has been synthesized. This species allows the formation of redox couples in which both partners are negatively charged. The E1/2 potential can be tuned by adjusting the nature and number of substituents on B and C. The octaiodinated species [3,3'-Co(1,2-closo-C2 B9 H7 I4 )2 ](-) is the most favorable, as it is isolatable and stable in air. A DFT study on stability and redox potentials of complexes has been performed. PMID:25788451

Lupu, Marius; Zaulet, Adnana; Teixidor, Francesc; Ruiz, Eliseo; Viñas, Clara

2015-04-27

140

Negatively Charged Excitons (X^-) in GaAs/AlGaAs MQWs  

NASA Astrophysics Data System (ADS)

We report the observation of negatively charged excitons (X^-) in photoluminescence measurements on GaAs/Al_0.3Ga_0.7As Multiple-Quantum-Well (MQW) samples. Four samples of different structure and different doping but with the same nominal well width (200Åhave been investigated. In addition to heavy-hole free excitons (X) and D^0X, we have observed a feature (Y) only in samples 2 (doped both barriers and wells), 3 (nominally identical to sample 2, except for a higher barrier doping) and 4 (doped in the barriers only). We emphasize that feature Y is not due to donor impurities in the well because it is very strong in sample 4 but is not observed in sample 1 (doped in the wells only). Feature Y appears only when there are excess electrons in the well and becomes dominant in higher barrier doping density samples. Temperature dependence studies of these features show that feature Y is a bound state which has smaller binding energy than X or D^0X. Magneto-PL studies of the samples show that feature Y is excitonic. From these observations we identify feature Y as negatively charged exiton, X^-. Work Supported in part by ONR and the ONR/MFEL Program

Ryu, S. R.; Yu, W.-Y.; Fu, L. P.; Petrou, A.; McCombe, B. D.

1996-03-01

141

Disappearance of the negative charge in giant DNA with a folding transition.  

PubMed Central

In the present study we measure the electrophoretic mobility of giant T4 DNA (166 kbp) by electrophoretic light scattering for the elongated and folded compact states at different spermidine (trivalent cation) concentrations in 50 mM sodium maleate buffer (pH 6.0). It is found that the electrophoretic mobility of elongated DNA in the absence of the multivalent cation is seven times greater than that of fully folded compact DNA, where, with the increase of the concentration of spermidine, an abrupt transition is generated after a gradual decrease of the mobility. An analysis of the electrophoretic mobility suggests that the folded compact DNA chains almost completely lose their negative charges, by taking into account the difference of friction mechanism between an elongated and folded compact state. From the single chain observation by use of fluorescence microscopy, it is found that a phase-segregated structure is generated at intermediate concentrations of spermidine. The gradual decrease of the electrophoretic mobility in the transition region is, thus, attributed to the formation of the segregated state, exhibiting partial electroneutralization in the folded part. Disappearance of the negative charges in the completely folded compact DNAs is discussed in relation to the mechanism of transition, in terms of a first-order phase transition. PMID:11371456

Yamasaki, Y; Teramoto, Y; Yoshikawa, K

2001-01-01

142

Dust-ion acoustic shock waves in a dusty multi-ion plasma with negatively dust-charge fluctuation  

NASA Astrophysics Data System (ADS)

The nonlinear propagation of dust-ion acoustic shock waves in a collisionless, unmagnetized multi-ion dusty plasma contains Botlzemann-distributed electrons, negative and positive ions with extremely massive and stationary negative charge dust grains with dust charge fluctuations is investigated. By employing the reductive perturbation method, we obtain a Burgers equation that describes the two-ion fluid dynamics. The dust charge variation is found to play an important role in the formation of such dust-ion acoustic shock structures. The viscosity only affects the thickness of the shock waves. The dependences of the shock wave's velocity, height and thickness on the system parameters are investigated.

Wang, Hongyan; Zhang, Kaibiao

2015-01-01

143

Coherent electron emission from simple molecules by impact of energetic charged particles  

NASA Astrophysics Data System (ADS)

We review the theoretical and experimental progress in the field of coherent electron emission from simple molecules by the impact of energetic charged particles. We describe in detail the different theoretical approaches to tackle the single ionization of diatomic molecules by the impact of ions and electrons. Furthermore, we compare with experimental measurements, where available. The case of photon impact is also considered, in order to obtain a deeper understanding of the physics involved. An attempt is made to emphasize the phenomenology behind these molecular processes and to discuss the advantages and drawbacks of the different theoretical approaches. Additionally, we highlight the differences and similarities between the particular projectiles which initiate the process, namely ions, electrons or photons. This review is in memorial of Professor Uwe Becker (1947-2013), who inspired us during the writing of this work.

Ciappina, M. F.; Fojón, O. A.; Rivarola, R. D.

2014-02-01

144

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

SciTech Connect

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.

Kusakabe, Motohiko [School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791, Korea and Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Kim, K. S. [School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791 (Korea, Republic of); Cheoun, Myung-Ki [Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Kajino, Toshitaka [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan and Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kino, Yasushi [Department of Chemistry, Tohoku University, Sendai 980-8578 (Japan); Mathews, Grant J. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan and Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)

2014-05-02

145

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

NASA Astrophysics Data System (ADS)

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- 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.

Surrey, Elizabeth; Porton, Michael

2011-09-01

146

Charge transfer interactions of a Ru(II) dye complex and related ligand molecules adsorbed on Au(111)  

SciTech Connect

The interaction of the dye molecule, N3 (cis-bis(isothiocyanato)bis(2,2{sup '}-bipyridyl-4,4{sup '}-dicarboxylato) -ruthenium(II)), and related ligand molecules with a Au(111) surface has been studied using synchrotron radiation-based electron spectroscopy. Resonant photoemission spectroscopy (RPES) and autoionization of the adsorbed molecules have been used to probe the coupling between the molecules and the substrate. Evidence of charge transfer from the states near the Fermi level of the gold substrate into the lowest unoccupied molecular orbital (LUMO) of the molecules is found in the monolayer RPES spectra of both isonicotinic acid and bi-isonicotinic acid (a ligand of N3), but not for the N3 molecule itself. Calibrated x-ray absorption spectroscopy and valence band spectra of the monolayers reveals that the LUMO crosses the Fermi level of the surface in all cases, showing that charge transfer is energetically possible both from and to the molecule. A core-hole clock analysis of the resonant photoemission reveals a charge transfer time of around 4 fs from the LUMO of the N3 dye molecule to the surface. The lack of charge transfer in the opposite direction is understood in terms of the lack of spatial overlap between the {pi}*-orbitals in the aromatic rings of the bi-isonicotinic acid ligands of N3 and the gold surface.

Britton, Andrew J.; Weston, Matthew; O'Shea, James N. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Nottingham Nanotechnology and Nanoscience Centre (NNNC), University of Nottingham, Nottingham NG7 2RD (United Kingdom); Taylor, J. Ben; Rienzo, Anna; Mayor, Louise C. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2011-10-28

147

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

148

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

PubMed

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

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

2012-08-21

149

Quantum Theory of Atoms in Molecules/Charge-Charge Flux-Dipole Flux interpretation of fundamental vibrational intensity enhancements on H-bond formation of water trimer  

NASA Astrophysics Data System (ADS)

The Quantum Theory Atoms in Molecules/Charge-Charge Flux-Dipole Flux model was used to investigate electronic structure variations associated with intensity changes for water trimer vibrations. The total of 440 km mol-1 experimental intensity for the symmetric stretches amounts to an average contribution of 147 km mol-1 per hydrogen bond. The calculated QCISD/cc-pVTZ value is 274 km mol-1. The largest changes on complex formation occur for the charge, charge flux and their interaction. The hydrogen-bonded hydrogen atoms account for 99% of the total intensity of the two strongest symmetric stretches, mostly owing to mechanical vibration factors.

Silva, Arnaldo F.; Richter, Wagner E.; Bruns, Roy E.

2014-08-01

150

Black strings with negative cosmological constant: inclusion of electric charge and rotation  

E-print Network

We generalize the vacuum static black strings with negative cosmological constant recently discussed in literature, by including an electromagnetic field. These higher-dimensional configurations have no dependence on the `compact' extra dimension, and their boundary topology is the product of time and $S^{d-3}\\times S^1$ or $H^{d-3}\\times S^1$. Rotating generalizations of the even dimensional black string configurations are considered as well. Different from the static, neutral case, no regular limit is found for a vanishing event horizon radius. We explore numerically the general properties of such solutions and, using a counterterm prescription, we compute their conserved charges and discuss their thermodynamics. We find that the thermodynamics of the black strings follows the pattern of the corresponding black hole solutions in AdS backgrounds.

Yves Brihaye; Eugen Radu; Cristian Stelea

2007-08-21

151

Direct Single-Molecule Observations of Local Denaturation of a DNA Double Helix under a Negative Supercoil State.  

PubMed

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 ?DNA and ?DNA containing the SV40 origin of DNA replication (SV40ori-?DNA) 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 ?DNA and SV40ori-?DNA 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 ?DNA and 0, -0.047, and -0.1 for SV40ori-?DNA, single bright spots at the single-stranded regions were frequently induced under higher negative supercoil densities of -0.095 for ?DNA and -0.1 for SV40ori-?DNA. However, single bright spots of the single-stranded regions were rarely observed below a negative supercoil density of -0.045 and -0.047 for ?DNA and SV40ori-?DNA, respectively. The probability of occurrence of the local denaturation increased with negative superhelicity for both ?DNA and SV40ori-?DNA. PMID:25697222

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

152

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

NASA Astrophysics Data System (ADS)

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.

Rawson, Jeffrey Scott

153

A robust force field based method for calculating conformational energies of charged drug-like molecules.  

PubMed

The binding affinity of a drug-like molecule depends among other things on the availability of the bioactive conformation. If the bioactive conformation has a significantly higher energy than the global minimum energy conformation, then the molecule is unlikely to bind to its target. Determination of the global minimum energy conformation and calculation of conformational penalties of binding is a prerequisite for prediction of reliable binding affinities. Here, we present a simple and computationally efficient procedure to estimate the global energy minimum for a wide variety of structurally diverse molecules, including polar and charged compounds. Identifying global energy minimum conformations of such compounds with force field methods is problematic due to the exaggeration of intramolecular electrostatic interactions. We demonstrate that the global energy minimum conformations of zwitterionic compounds generated by conformational analysis with modified electrostatics are good approximations of the conformational distributions predicted by experimental data and with molecular dynamics performed in explicit solvent. Finally the method is used to calculate conformational penalties for zwitterionic GluA2 agonists and to filter false positives from a docking study. PMID:21985436

Poehlsgaard, Jacob; Harpsøe, Kasper; Jørgensen, Flemming Steen; Olsen, Lars

2012-02-27

154

Observation of a molecule–metal interface charge transfer related feature by resonant photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

We report the discovery of a charge transfer (CT) related low binding energy feature at a molecule–metal interface by the application of resonant photoelectron spectroscopy (RPES). This interface feature is neither present for molecular bulk samples nor for the clean substrate. A detailed analysis of the spectroscopic signature of the low binding energy feature shows characteristics of electronic interaction not found in other electron spectroscopic techniques. Within a cluster model description this feature is assigned to a particular eigenstate of the photoionized system that is invisible in direct photoelectron spectroscopy but revealed in RPES through a relative resonant enhancement. Interpretations based on considering only the predominant character of the eigenstates explain the low binding energy feature by an occupied lowest unoccupied molecular orbital, which is either realized through CT in the ground or in the intermediate state. This reveals that molecule–metal CT is responsible for this feature. Consequently, our study demonstrates the sensitivity of RPES to electronic interactions and constitutes a new way to investigate CT at molecule–metal interfaces.

Sauer, C.; Wießner, M.; Schöll, A.; Reinert, F.

2015-04-01

155

Effect of charge on negative-phase-velocity propagation of electromagnetic waves in the ergosphere of a rotating black hole  

E-print Network

The presence of charge promotes the propensity of a rotating black hole to support the propagation of electromagnetic plane waves with negative phase velocity (NPV) in its ergosphere, whether the Kerr-Newman or the Kerr-Sen metric descriptions of spacetime are considered. Striking differences in the NPV characteristics for the Kerr-Newman and Kerr-Sen metrics emerge from numerical studies, particularly close to the outer event horizon when the magnitude of the charge is large.

Benjamin M. Ross; Tom G. Mackay; Akhlesh Lakhtakia

2006-08-19

156

Cationic Cell-Penetrating Peptide Binds to Planar Lipid Bilayers Containing Negatively Charged Lipids but does not Induce Conductive Pores  

PubMed Central

Using a cation-selective gramicidin A channel as a sensor of the membrane surface charge, we studied interactions of oligoarginine peptide R9C, a prototype cationic cell-penetrating peptide (CPP), with planar lipid membranes. We have found that R9C sorption to the membrane depends strongly on its lipid composition from virtually nonexistent for membranes made of uncharged lipids to very pronounced for membranes containing negatively charged lipids, with charge overcompensation at R9C concentrations exceeding 1 ?M. The sorption was reversible as it was removed by addition of polyanionic dextran sulfate to the membrane bathing solution. No membrane poration activity of R9C (as would be manifested by increased bilayer conductance) was detected in the charged or neutral membranes, including those with asymmetric negative/neutral and negative/positive lipid leaflets. We conclude that interaction of R9C with planar lipid bilayers does not involve pore formation in all studied lipid combinations up to 20 ?M peptide concentration. However, R9C induces leakage of negatively charged but not neutral liposomes in a process that involves lipid mixing between liposomes. Our findings suggest that direct traversing of CPPs through the uncharged outer leaflet of the plasma membrane bilayer is unlikely and that permeabilization necessarily involves both anionic lipids and CPP-dependent fusion between opposing membranes. PMID:23663836

Gurnev, Philip A.; Yang, Sung-Tae; Melikov, Kamran C.; Chernomordik, Leonid V.; Bezrukov, Sergey M.

2013-01-01

157

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

SciTech Connect

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.

Sharma, Suresh C. [Department of Applied Physics, Delhi Technological University (DTU), Shahbad Daulatpur, Bawana Road, Delhi-42 (India); Kaur, Daljeet [Department of Physics, Guru Teg Bahadur Institute of Technology, Rajouri Garden, New Delhi (India); Gahlot, Ajay [Department of Physics, Maharaja Surajmal Institute of Technology, Janakpuri, New Delhi (India); Sharma, Jyotsna [Department of Physics, KIIT College of Engineering, Bhondsi Gurgaon 122102 (India)

2014-10-15

158

Big-Bang Nucleosynthesis Reactions Catalyzed by a Long-Lived Negatively Charged Leptonic Particle  

E-print Network

An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a long-lived negatively-charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau. The reactions studied here includes, i) 4He-transfer reactions such as (4He X)+d --> 6Li+X, ii) radiative capture reactions such as (7Be X)+ p --> (8B X) + gamma, iii) three-body breakup reactions such as (7Li X)+ p --> 4He+4He+X, iv) charge-exchange reactions such as (p X)+4He -->(4He X) +p, and v) neutron induced reactions such as (8Be X)+ n -->9Be+X, where (A X) denotes a Coulombic bound state of a nucleus A and X^-. In recent papers it has been claimed that some of the catalyzed BBN reactions have significantly large cross sections so as to markedly change the abundances of some elements, not only giving a solution to the 6Li-7Li problem (calculated underproduction of 6Li by a factor of 1000 and overproduction of 7Li+7Be by a factor of nearly 3) but also imposing strong restrictions on the lifetime and the primordial abundance of X^-. However, most of the calculations of these reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for the complicated low-energy nuclear reactions. We use a high-accuracy few-body calculational method developed by the authors, and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

Masayasu Kamimura; Yasushi Kino; Emiko Hiyama

2009-06-13

159

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

NASA Astrophysics Data System (ADS)

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.

Mishra, S. K.; Misra, Shikha

2015-02-01

160

Mapping charge to function relationships of the DNA mimic protein Ocr   

E-print Network

This thesis investigates the functional consequences of neutralising the negative charges on the bacteriophage T7 antirestriction protein ocr. The ocr molecule is a small highly negatively charged, protein homodimer that ...

Kanwar, Nisha

2014-06-28

161

Energy, Charge, and Spin Transport in Molecules and Self-Assembled Nanostructures Inspired by Photosynthesis  

SciTech Connect

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.

Wasielewski, Michael R. (NWU)

2008-10-03

162

Stability of negatively charged platelets in calcium-rich anionic copolymer solutions.  

PubMed

Controlling the stability of anisotropic particles is key to the development of advanced materials. Here, we report an investigation, by means of mesoscale molecular dynamics simulations, of the stability and structural change of calcium-rich dispersions containing negatively charged nanoplatelets, neutralized by calcium counterions, in the presence of either comb copolymers composed of anionic backbones with attached neutral side chains or anionic-neutral linear block copolymers. In agreement with experimental observations, small stacks of platelets (tactoids) are formed, which are greatly stabilized in the presence of copolymers. In the absence of polymers, tactoids will grow and aggregate strongly due to large attractive Ca(2+)-Ca(2+) correlation forces. Unlike comb copolymers which only adsorb on the external surfaces, block copolymers are found to intercalate between the platelets. The present results show that the stabilization is the result of a free energy barrier induced by the excluded volume of hydrophilic chains, while the intercalation is due to bridging forces. More generally, the results shed new light on the recent finding of the first hybrid cementitious mesocrystal. PMID:24850266

Turesson, Martin; Nonat, André; Labbez, Christophe

2014-06-17

163

Control of charge trapping in a novel photorefractive composite consisting of a bifunctional molecule based on TPD  

Microsoft Academic Search

A novel photorefractive polymer is presented, based on a bifunctional molecule which is a derivative of the well known charge transport molecule N,N'-diphenyl-N,N'-bis(3- methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD). In this material the low intrinsic tap density causes the rather low value for the gain coefficient as well as the 90 degree phase shift between the refractive index grating and the illumination pattern. The

Henk J. Bolink; C. Arts; Victor V. Krasnikov; George G. Malliaras; Georges Hadziioannou

1996-01-01

164

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

NASA Technical Reports Server (NTRS)

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.

Armstrong, T. W.

1972-01-01

165

Big-Bang Nucleosynthesis Reactions Catalyzed by a Long-Lived Negatively Charged Leptonic Particle  

NASA Astrophysics Data System (ADS)

An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X^- particle has a lifetime ?_X ? 10^3 s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state, for example, (^7Be X^-) at temperature T_9 ? 0.4 (in units of 10^9 K), (? X^-) at T_9 ? 0.1 and (p X^-) at T_9 ? 0.01. The bound state, an exotic atom, is expected to induce the following reactions in which X^- acts as a catalyst: i) ?-transfer reactions such as (? X^-)+d to ^6Li + X, ii) radiative capture reactions such as (^7Be X^-) + p to (^8B X^-) + ?, iii) three-body breakup reactions such as (^7Li X^-) + p to ? + ? + X^-, iv) charge-exchange reactions such as (p X^-) + ? to (? X^-) +p and v) neutron induced reactions such as (^8Be X^-) + n to ^9Be + X^-. In recent papers it has been claimed that some of these X^-catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements, giving not only a solution to the ^6Li-^7Li problem (the calculated underproduction of ^6Li by a factor of ˜ 1000 and overproduction of ^7Li+$^7Be by a factor of ˜ 3) but also a constraint on the lifetime and primordial abundance of the elementary particle X^-. However, most of these calculations of the reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for these complicated low-energy nuclear reactions. We use a high-accuracy few-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

Kamimura, M.; Kino, Y.; Hiyama, E.

2009-05-01

166

Molecules  

NSDL National Science Digital Library

The Switzerland-based society, Molecular Diversity Preservation International (MDPI) provides this free, online journal, Molecules. This journal of synthetic and natural product chemistry encourages chemists to publish their experimental detail, particularly synthetic procedures and characterization information. "Any scattered unassembled experimental data for individual compounds which is conventionally not publishable is particularly welcomed," says the site. The idea is to get information out as quickly as possible to the scientific community. To access Molecules, follow the instructions on how to request a username and password.

1995-01-01

167

Spectroscopic investigations on the binding of Methylene Blue and Nile Blue to negatively charged gold nanorods  

NASA Astrophysics Data System (ADS)

The effect of longitudinal surface plasmon (l-SP) electric field of gold nanorods (AuNRs) on the optical (absorption and fluorescence) properties of two dyes Methylene Blue (MB) and Nile Blue (NB) has been studied by tuning and detuning the l-SP band with the absorption maxima of the dyes. Binding between dyes and nanorods were established by electrostatic interaction by making the nanorods negatively charged after coating them with polystyrene sulfonate (PSS). The absorption spectra of the dye-nanorod complex showed two prominent absorption bands in the 550-700 nm regions. For the detuned condition these changes are attributed to the nanorod induced aggregation of the dyes. However for the tuned condition, with increasing dye concentration the energy gap between the bands were observed to increase and then saturate. This is attributed to resonance coupling between the l-SP of the nanorod with the dye absorption. Although the fluorescence intensity of the dyes in the presence of increasing amount of AuNRs were observed to be quenched their lifetimes were observed to increase. Both the radiative (kr) and nonradiative (knr) rates of the dyes decreases in the presence of AuNRs. The magnitude of decrease for kr is much higher than knr, which is attributed to the formation of the non-fluorescent dimeric species. The increase in the fluorescence lifetime is attributed to the suppression of the excited state nonradiative pathways of these dyes adsorbed on the surface of the AuNRs. In addition, the changes of kr and knr were observed to be greater for the tuned condition.

Shrivastava, R.; Jain, B.; Das, K.

2012-08-01

168

Design, synthesis and biological evaluation of negatively charged ¹¹¹In-DTPA-octreotide derivatives.  

PubMed

Our previous studies indicated that (111)In-diethylenetriaminepentaacetic acid ((111)In-DTPA)-octreotide derivatives with an additional negative charge by replacing N-terminal d-phenylalanine (d-Phe) with an acidic amino acid such as l-aspartic acid (Asp) or its derivative exhibited low renal radioactivity levels when compared with (111)In-DTPA-D-Phe(1)-octreotide. On the basis of the findings, we designed, synthesized and evaluated two Asp-modified (111)In-DTPA-conjugated octreotide derivatives, (111)In-DTPA-Asp(1)-octreotide and (111)In-DTPA-Asp(0)-D-Phe(1)-octreotide. While (111)In-DTPA-Asp(1)-octreotide showed negligible AR42J cell uptake, (111)In-DTPA-Asp(0)-D-Phe(1)-octreotide exhibited AR42J cell uptake similar to that of (111)In-DTPA-D-Phe(1)-octreotide. When administered to AR42J tumor-bearing mice, (111)In-DTPA-Asp(0)-D-Phe(1)-octreotide exhibited renal radioactivity levels significantly lower than did (111)In-DTPA-D-Phe(1)-octreotide at 1 and 3 h post-injection. No significant differences were observed in tumor accumulation between (111)In-DTPA-Asp(0)-D-Phe(1)-octreotide and (111)In-DTPA-D-Phe(1)-octreotide after 1 and 3h injection. The findings in this study suggested that an interposition of an Asp at an appropriate position in (111)In-DTPA-D-Phe(1)-octreotide would constitute a useful strategy to develop (111)In-DTPA-D-Phe(1)-octreotide derivatives of low renal radioactivity levels while preserving tumor accumulation. PMID:24457092

Oshima, Nobuhiro; Akizawa, Hiromichi; Zhao, Songji; Zhao, Yan; Nishijima, Ken-ichi; Kitamura, Yoji; Arano, Yasushi; Kuge, Yuji; Ohkura, Kazue

2014-02-15

169

?-? Interaction among violanthrone molecules: observation, enhancement, and resulting charge transport properties.  

PubMed

To investigate the relationship between ?-? stacking and charge transport property of organic semiconductors, a highly soluble violanthrone derivative, 16,17-bis(2-ethylhexyloxy)anthra[9,1,2-cde-]benzo[rst]pentaphene-5,10-dione (3), is designed and synthesized. The ?-? stacking behavior and the aggregation of compound 3 in both solution and thin film were studied in detail by (1)H nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-vis) absorption, X-ray diffraction (XRD), and atomic force microscopy (AFM). When (1)H NMR spectroscopy and theoretical modeling results were combined, the arrangements of compound 3 molecules in the aggregates are demonstrated, where the dipole moments of the two adjacent molecules are nearly reversed to achieve efficient intermolecular ?-? overlapping. Furthermore, it is interesting to find that the ?-? stacking of compound 3, in both solution and thin films, can be enhanced by introducing a poor solvent n-hexane into the dilute chloroform solution. The resulting film exhibits more red-shifted absorption and higher crystallinity than the film made from pure chloroform solvent, suggesting that ?-? interactions in the solid state are intensified by the poor solvent. Organic field-effect transistors (OFETs) with compound 3 film as the transportation layer were fabricated. It is disclosed that the compound 3 film obtained from the chloroform/n-hexane mixed solvents exhibits 1 order of magnitude higher hole mobility than that from the pure chloroform solvent because of the enhanced ?-? interactions and the higher crystallinity in the former film. This work provided us valuable information in the improvement of electronic and optoelectronic performances of organic semiconductors by tuning their aggregate structures. PMID:21142198

Shi, Min-Min; Chen, Yi; Nan, Ya-Xiong; Ling, Jun; Zuo, Li-Jian; Qiu, Wei-Ming; Wang, Mang; Chen, Hong-Zheng

2011-02-01

170

Enhanced antidepressant-like effects of the macromolecule trefoil factor 3 by loading into negatively charged liposomes  

PubMed Central

Immunocytes, mainly neutrophils and monocytes, exhibit an intrinsic homing property, enabling them to migrate to sites of injury and inflammation. They can thus act as Trojan horses carrying concealed drug cargoes while migrating across impermeable barriers to sites of disease, especially the blood–brain barrier (BBB). In this study, to target circulating phagocytic cells, we formulated negatively charged nanosize liposomes and loaded trefoil factor 3 (TFF3) into liposomes by the pH-gradient method. According to the optimized formulation (5:1.5 of lipid to cholesterol, 10:1 of lipid to drug, 10 mg/mL of lipid concentration, and 10 mmol/L of phosphate-buffered saline), 44.47% entrapment efficiency was obtained for TFF3 liposomes with 129.6 nm particle size and ?36.6 mV zeta potential. Compared with neutrally charged liposomes, the negatively charged liposomes showed a strong binding capacity with monocytes and were effectively carried by monocytes to cross the BBB in vitro. Furthermore, enhanced antidepressant-like effects were found in the tail-suspension and forced-swim tests in mice, as measured by decreased immobility time, as well as increased swimming time and reduced immobility in rats. These results suggested that negatively charged liposomes could improve the behavioral responses of TFF3, and our study opens up a new way for the development of effective therapies for brain disease by increasing the permeability of the BBB. PMID:25419129

Qin, Jing; Yang, Xu; Mi, Jia; Wang, Jianxin; Hou, Jia; Shen, Teng; Li, Yongji; Wang, Bin; Li, Xuri; Zhu, Weili

2014-01-01

171

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

PubMed Central

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

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

2010-01-01

172

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

PubMed

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

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

2015-03-15

173

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

PubMed

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 Li3PO4-xNx/LiCoO2 interface are negligible and demonstrates that it is possible to fabricate all-solid state batteries with faster charging/discharging properties. PMID:25710500

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

2015-03-11

174

Charge symmetric dissociation of doubly ionized N2 and CO molecules.  

PubMed

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

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

2014-01-21

175

Charge symmetric dissociation of doubly ionized N2 and CO molecules  

NASA Astrophysics Data System (ADS)

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 N_2^{++} 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.

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

2014-01-01

176

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

SciTech Connect

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.

Coutinho, L. H., E-mail: lucia@if.ufrj.br [Physics Institute, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21941-972 (Brazil); Gardenghi, D. J. [Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States)] [Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States); Schlachter, A. S. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Souza, G. G. B. de [Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21949-900 (Brazil); Stolte, W. C. [Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States) [Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154-4003 (United States); Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2014-01-14

177

Probing the Structure of Water Molecules at an Oil/Water Interface in the Presence of a Charged Soluble Surfactant through Isotopic Dilution Studies  

E-print Network

Soluble Surfactant through Isotopic Dilution Studies D. E. Gragson and G. L. Richmond* Department spectra of water molecules at an oil/water interface in the presence of a charged, soluble surfactant molecules in the bulk aqueous phase. The presence of a charged surfactant enhances the SF response in the OH

Richmond, Geraldine L.

178

Nearly Perfect Spin Filter, Spin Valve and Negative Differential Resistance Effects in a Fe4-based Single-molecule Junction  

NASA Astrophysics Data System (ADS)

The spin-polarized transport in a single-molecule magnet Fe4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices.

Zu, Fengxia; Liu, Zuli; Yao, Kailun; Gao, Guoying; Fu, Huahua; Zhu, Sicong; Ni, Yun; Peng, Li

2014-05-01

179

Nearly Perfect Spin Filter, Spin Valve and Negative Differential Resistance Effects in a Fe4-based Single-molecule Junction  

PubMed Central

The spin-polarized transport in a single-molecule magnet Fe4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices. PMID:24787446

Zu, Fengxia; Liu, Zuli; Yao, Kailun; Gao, Guoying; Fu, Huahua; Zhu, Sicong; Ni, Yun; Peng, Li

2014-01-01

180

Coherent population trapping in negatively charged self-assembled quantum dots using a train of femtosecond pulses  

NASA Astrophysics Data System (ADS)

We demonstrate the coherent population trapping in a single quantum dot and an ensemble of negatively charged quantum dots using a train of femtosecond pulses. Particularly in an ensemble of quantum dots, we show that the detrimental effects due to the inhomogeneous distribution of their properties can be minimized by appropriately choosing the pulse-train parameters and the magnetic-field strength in such a way that the electron-Zeeman splitting is an integer multiple of the pulse repetition rate.

Kumar, Parvendra; Nakajima, Takashi

2015-02-01

181

Negatively charged self-assembling DNA\\/poloxamine nanospheres for in vivo gene transfer  

Microsoft Academic Search

Over the past decade, numerous nonviral cationic vectors have been synthesized. They share a high density of positive charges and efficiency for gene transfer in vitro. However, their positively charged surface causes instability in body fluids and cytotoxi- city, thereby limiting their efficacy in vivo. Therefore, there is a need for developing alternative molecular structures. We have examined tetrabranched amphi-

Bruno Pitard; Mahajoub Bello-Roufai; Olivier Lambert; Peggy Richard; Lea Desigaux; Sarah Fernandes; Caroline Lanctin; Helene Pollard; Mehdi Zeghal; Pierre-Yves Rescan; Denis Escande

2004-01-01

182

A ring of eight conserved negatively charged amino acids doubles the conductance of BK channels and prevents inward rectification  

PubMed Central

Large-conductance Ca2+–voltage-activated K+ channels (BK channels) control many key physiological processes, such as neurotransmitter release and muscle contraction. A signature feature of BK channels is that they have the largest single channel conductance of all K+ channels. Here we examine the mechanism of this large conductance. Comparison of the sequence of BK channels to lower-conductance K+ channels and to a crystallized bacterial K+ channel (MthK) revealed that BK channels have a ring of eight negatively charged glutamate residues at the entrance to the intracellular vestibule. This ring of charge, which is absent in lower-conductance K+ channels, is shown to double the conductance of BK channels for outward currents by increasing the concentration of K+ in the vestibule through an electrostatic mechanism. Removing the ring of charge converts BK channels to inwardly rectifying channels. Thus, a simple electrostatic mechanism contributes to the large conductance of BK channels. PMID:12843404

Brelidze, Tinatin I.; Niu, Xiaowei; Magleby, Karl L.

2003-01-01

183

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...

184

Evidence of negative charge trapping in high temperature annealed thermal oxide  

Microsoft Academic Search

The effect of high temperature processing of Si\\/SiO2\\/Si sandwich structures has been studied on a thermal dry oxide, by considering charge trapping after irradiation. The radiation-induced charge trapping is shown to be very different in annealed and unannealed structures. The latter reveal interfacial trapping behavior, whereas annealed structures exhibit a large trapping of both holes and electrons in the bulk

P. Paillet; D. Herve; J. L. Leray; R. A. B. Devine

1994-01-01

185

Charge recombination in organic small-molecule solar cells by Jiye Lee.  

E-print Network

To enhance the power conversion efficiency in organic solar cells, charge recombination loss needs to be minimized. First, we perform transient absorption spectroscopy to study the charge recombination dynamics of thin ...

Lee, Jiye

2008-01-01

186

Calculation of escape currents of electrons emitted from negatively charged spacecraft surfaces in a magnetic field  

SciTech Connect

In low Earth orbit, the geomagnetic field B is strong enough that secondary electrons or photoelectrons emitted from spacecraft surfaces have an average gyroradius much smaller than typical dimensions of large spacecraft. This implies that escape of these electrons will be strongly inhibited on surfaces which are nearly parallel to B, even if a repelling electric field exists outside them. This effect is likely to make an important contribution to the current balance and hence the equilibrium potential of such surfaces, making high-voltage charging of them more likely. The authors presents numerically-calculated escaping electron fluxes for these conditions, based on the approximations of uniform fields and Maxwellian emission-velocity distributions. He also presents an analytic curve-fit to the results for the important case of normal electric field (uniformly-charged surfaces). For strong normal electric fields, escape is effectively suppressed only when a surface is parallel to B within a few degrees or less, and this leads to sensitivity effects in attempts to predict auroral-zone spacecraft charging. A nonzero tangential component in the surface electric field can greatly enlarge the range of surface orientations for which escape is suppressed, and can also produce large surface currents. He also proposes a simple approximate method for calculating the space-charge-density distribution of escaping electrons. His results imply that on a mostly dielectric large spacecraft such as Shuttle, local charging, especially on surfaces nearly parallel to B, may occur in ionospheric conditions which do not produce overall charging.

Laframboise, J.G. (York Univ., Toronto, Ontario (Canada))

1988-03-01

187

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

PubMed Central

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

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

1988-01-01

188

Polarization states of charged excitons in coupled InAs\\/GaAs quantum dot molecules  

Microsoft Academic Search

The polarization state of charged excitons in coupled InAs\\/GaAs dots can reveal useful information about the spin state of its charge carriers. In this study, we examine the complete polarization state through Stokes parameter measurements to relate the polarization parameters of the luminescence to the spin configurations of the various charged excitons they originate from. We demonstrate that this method

Ramana Thota; Swati Ramanathan; Kushal Wijesundara; Eric Stinaff; Allan Bracker; Dan Gammon

2011-01-01

189

On the Charge and Molecule Based Summations of Solvent Electrostatic Potentials and the Validity of Electrostatic Linear Response in Water  

Microsoft Academic Search

Solvent-induced electrostatic potentials and field components at thesolute sites of model Na+q–Cs-q molecules were computed bysumming over either solvent charges (q-summation) or solventmolecular centers (M-summation) from molecular dynamics simulations.These were compared with values obtained by solving Poisson equation withthe dielectric boundary defined by Reff = (Ratom+Rgmax )\\/2.q-summation using cut-offs that are = 10 Å generallyunderestimates or overestimates the magnitude of

C. Satheesan Babu; Pei-Kun Yang; Carmay Lim

2002-01-01

190

Characterization of a Novel Small Molecule That Potentiates ?-Lactam Activity against Gram-Positive and Gram-Negative Pathogens.  

PubMed

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

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

2015-04-01

191

Propagation of charge-neutral beams in space - Modifications when negative ions are present  

NASA Technical Reports Server (NTRS)

Two-dimensional (three velocity component) electrostatic simulations are used to investigate the properties of a charge-neutral beam consisting of H(+), H(-), and electrons which will be used in the Beams on Rockets (BEAR) experiment to be launched in late 1987 or early 1988. For cross-field injection and beam densities much greater than the ambient plasma density, the beam splits into two approximately charge-neutral beams: a H(+)-e(-) beam that propagates down the field lines and a H(+)-H(-) beam that propagates at nearly the initial beam velocity on time scales less than the ion gyroperiod. Because of this splitting, space-charge oscillations are induced in the H(+)-H(-) component, which lead to its breakup. At lower beam densities, particularly when the beam electron density is less than about the density of the ambient plasma, the ambient plasma response reduces the space-charge fields as the beam splits and the space-charge oscillations are suppressed.

Winglee, R. M.; Pritchett, P. L.

1987-01-01

192

Spin dynamics in the negatively charged terbium (III) bis-phthalocyaninato complex.  

PubMed

The experimental and theoretical study of the electron spin dynamics in the anionic form of a single-ion molecule magnet (SIMM), the bis-phthalocyaninato terbium (III) molecule [Pc(2)Tb](-)[TBA](+), has been addressed by means of solid state (1)H NMR spectroscopy. The magnetic properties of the caged Tb(3+) metal center were investigated in a series of diamagnetically diluted preparations, where the excess of tetrabutylamonium bromide ([TBA]Br)(n) salt was used as diamagnetic matrix complement. We found that a high temperature activated spin dynamics characterizes the systems, which involved phonon-assisted transitions among the crystal field levels in qualitative agreements with literature results. However, the activation barriers in these processes range from 641 cm(-1) for the diamagnetically diluted samples to 584 cm(-1) for those undiluted; thus, they exhibit barriers 2-3 times larger than witnessed in earlier (230 cm(-1)) reports (e.g., Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694-8695). At cryogenic temperatures, fluctuations are driven by tunneling processes between the m = +6 and -6 low-energy levels. We found that the barrier Delta and the tunneling rates change from sample to sample and especially the diamagnetically diluted [Pc(2)Tb](-) molecules appear affected by the sample's magneto/thermal history. These observations emphasize that matrix arrangements around [Pc(2)Tb](-) can appreciably alter the splitting of the crystal field levels, its symmetry, and hence, the spin dynamics. Therefore, understanding how small differences in molecular surroundings (as for instance occurring by depositing on surfaces) can trigger substantial modifications in the SIMM property is of utmost importance for the effective operation of such molecules for single-molecule data storage, for example. PMID:19275145

Branzoli, Francesca; Carretta, Pietro; Filibian, Marta; Zoppellaro, Giorgio; Graf, Michael J; Galan-Mascaros, Jose R; Fuhr, Olaf; Brink, Susan; Ruben, Mario

2009-04-01

193

Negatively Charged Nitrogen-Vacancy Centers in a 5 nm Thin 12 Diamond Film  

E-print Network

, isotopically enriched ([12 C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NVNegatively Charged Nitrogen-Vacancy Centers in a 5 nm Thin 12 C Diamond Film K. Ohashi, T. Rosskopf # Diamond Research Group, Research Institute for Ubiquitous Energy Devices, National Institute of Advanced

Leonardo, Degiorgi

194

The Production of Negative Lithium Beams by Charge Exchange in Cesium Vapours  

Microsoft Academic Search

These measurements were carried out at the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory (ORNL-HRIBF) by researchers from the Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud (INFN-LNS), Catania, Italy and local staff. The Charge Exchange Cell (CEC) consisted of a vacuum chamber containing cesium vapours at a variable temperature T, in which positive

M. Re; M. Menna; F. Chines; G. Cuttone; E. Messina; D. W. Stracener; J. C. Bilheux

2005-01-01

195

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

E-print Network

in a Hall thruster might be exceeded if additional mechanisms of space-charge neutralization are introduced in the Hall thruster. © 2005 American Institute of Physics. DOI: 10.1063/1.1897715 I. INTRODUCTION The maximum current extracted from an ion source ion thruster can be increased above the Child­Langmuir limit

196

Adhesion of Aspergillus Species to Extracellular Matrix Proteins: Evidence for Involvement of Negatively Charged Carbohydrates on the Conidial Surface  

PubMed Central

Invasive lung disease caused by Aspergillus species is a potentially fatal infection in immunocompromised patients. The adhesion of Aspergillus fumigatus conidia to proteins in the basal lamina is thought to be an initial step in the development of invasive aspergillosis. The purpose of this study was to determine the mechanism of adhesion of A. fumigatus conidiospores to basal-lamina proteins and to determine whether conidia possess unique adhesins which allow them to colonize the host. We compared conidia from different Aspergillus species for the ability to bind to purified fibronectin and intact basal lamina. Adhesion assays using immobilized fibronectin or type II pneumocyte-derived basal lamina showed that A. fumigatus conidia bound significantly better than those of other Aspergillus species to both fibronectin and intact basal lamina. Neither desialylation nor complete deglycosylation of fibronectin decreased the binding of A. fumigatus conidia to fibronectin, suggesting that oligosaccharides on fibronectin were not involved in conidiospore binding. Further evidence for this hypothesis came from experiments using purified fragments of fibronectin; A. fumigatus conidia preferentially bound to the nonglycosylated 40-kDa fragment which contains the glycosaminoglycan (GAG) binding domain. Negatively charged carbohydrates, including dextran sulfate and heparin, as well as high-ionic-strength buffers, inhibited binding of A. fumigatus conidia to both fibronectin and intact basal lamina, suggesting that negatively charged carbohydrates on the surface of the conidium may bind to the GAG binding domain of fibronectin and other basal-lamina proteins. These data provide evidence for a novel mechanism of conidial attachment whereby adherence to fibronectin and other basal-lamina proteins is mediated via negatively charged carbohydrates on the conidial surface. PMID:10816488

Wasylnka, Julie A.; Moore, Margo M.

2000-01-01

197

Low temperature studies of the excited-state structure of negatively charged nitrogen-vacancy color centers in diamond.  

PubMed

We report a study of the 3E excited-state structure of single negatively charged nitrogen-vacancy (NV) defects in diamond, combining resonant excitation at cryogenic temperatures and optically detected magnetic resonance. A theoretical model is developed and shows excellent agreement with experimental observations. In addition, we show that the two orbital branches associated with the 3E excited state are averaged when operating at room temperature. This study leads to an improved physical understanding of the NV defect electronic structure, which is invaluable for the development of diamond-based quantum information processing. PMID:19518973

Batalov, A; Jacques, V; Kaiser, F; Siyushev, P; Neumann, P; Rogers, L J; McMurtrie, R L; Manson, N B; Jelezko, F; Wrachtrup, J

2009-05-15

198

Short Hydrogen Bonds and Negative Charge in Photoactive Yellow Protein Promote Fast Isomerization but not High Quantum Yield.  

PubMed

Biological signal transduction by photoactive yellow protein (PYP) in halophilic purple sulfur bacteria is initiated by trans-to-cis isomerization of the p-coumaric acid chromophore (pCa) of PYP. pCa is engaged in two short hydrogen bonds with protein residues E46 and Y42, and it is negatively charged at the phenolate oxygen. We investigated the role in the isomerization process of the E46 short hydrogen bond and that of the negative charge on the anionic phenolate moiety of the chromophore. We used wild-type PYP and the mutant E46A, in protonated and deprotonated states (referred to as pE46A and dpE46A, respectively), to reduce the number of hydrogen bond interactions between the pCa phenolate oxygen and the protein and to vary the negative charge density in the chromophore-binding pocket. Their effects on the yield and rate of chromophore isomerization were determined by ultrafast spectroscopy. Molecular dynamics simulations were used to relate these results to structural changes in the mutant protein. We found that deprotonated pCa in E46A has a slower isomerization rate as the main part of this reaction was associated with time constants of 1 and 6 ps, significantly slower than the 0.6 ps time constant in wild-type PYP. The quantum yield of isomerization in dpE46A was estimated to be 30 ± 2%, and that of pE46A was 32 ± 3%, very close to the value determined for wtPYP of 32 ± 2%. Relaxation of the isomerized product state I0 to I1 was faster in dpE46A. We conclude that the negative charge on pCa stabilized by the short hydrogen bonds with E46 and Y42 affects the rate of isomerization but not the quantum yield of isomerization. With this information, we propose a scheme for the potential energy surfaces involved in the isomerization and suggest protein motions near the pCa backbone as key events in successful isomerization. PMID:25144816

Zhu, Jingyi; Vreede, Jocelyne; Hospes, Marijke; Arents, Jos; Kennis, John T M; van Stokkum, Ivo H M; Hellingwerf, Klaas J; Groot, Marie Louise

2015-02-12

199

Charge Transport in C60-Based Dumbbell-type Molecules: Mechanically Induced Switching between Two Distinct Conductance States.  

PubMed

Single molecule charge transport characteristics of buckminsterfullerene-capped symmetric fluorene-based dumbbell-type compound 1 were investigated by scanning tunneling microscopy break junction (STM-BJ), current sensing atomic force microscopy break junction (CS-AFM-BJ), and mechanically controlled break junction (MCBJ) techniques, under ambient conditions. We also show that compound 1 is able to form highly organized defect-free surface adlayers, allowing the molecules on the surface to be addressed specifically. Two distinct single molecule conductance states (called high GH(1) and low GL(1)) were observed, depending on the pressure exerted by the probe on the junction, thus allowing molecule 1 to function as a mechanically driven molecular switch. These two distinct conductance states were attributed to the electron tunneling through the buckminsterfullerene anchoring group and fully extended molecule 1, respectively. The assignment of conductance features to these configurations was further confirmed by control experiments with asymmetrically designed buckminsterfullerene derivative 2 as well as pristine buckminsterfullerene 3, both lacking the GL feature. PMID:25651069

Moreno-García, Pavel; La Rosa, Andrea; Kolivoška, Viliam; Bermejo, Daniel; Hong, Wenjing; Yoshida, Koji; Baghernejad, Masoud; Filippone, Salvatore; Broekmann, Peter; Wandlowski, Thomas; Martín, Nazario

2015-02-18

200

Fluctuating charge force fields: recent developments and applications from small molecules to macromolecular biological systems  

Microsoft Academic Search

The past decade has seen intense development of what are anticipated to be the next generation of classical force fields to be used in computational statistical mechanical approaches to studying a broad class of physical and biological systems. Among the several approaches being actively pursued currently is the fluctuating charge (or equivalently charge equilibration or electronegativity equalization) method. Within this

Sandeep Patel; Charles L. Brooks III

2006-01-01

201

Conserved N-Terminal Negative Charges Support Optimally Efficient N-type Inactivation of Kv1 Channels  

PubMed Central

N-type inactivation is produced by the binding of a potassium channel's N-terminus within the open pore, blocking conductance. Previous studies have found that introduction of negative charges into N-terminal inactivation domains disrupts inactivation; however, the Aplysia AKv1 N-type inactivation domain contains two negatively charged residues, E2 and E9. Rather than being unusual, sequence analysis shows that this N-terminal motif is highly conserved among Kv1 sequences across many phyla. Conservation analysis shows some tolerance at position 9 for other charged residues, like D9 and K9, whereas position 2 is highly conserved as E2. To examine the functional importance of these residues, site directed mutagenesis was performed and effects on inactivation were recorded by two electrode voltage clamp in Xenopus oocytes. We find that inclusion of charged residues at positions 2 and 9 prevents interactions with non-polar sites along the inactivation pathway increasing the efficiency of pore block. In addition, E2 appears to have additional specific electrostatic interactions that stabilize the inactivated state likely explaining its high level of conservation. One possible explanation for E2's unique importance, consistent with our data, is that E2 interacts electrostatically with a positive charge on the N-terminal amino group to stabilize the inactivation domain at the block site deep within the pore. Simple electrostatic modeling suggests that due to the non-polar environment in the pore in the blocked state, even a 1 Å larger separation between these charges, produced by the E2D substitution, would be sufficient to explain the 65× reduced affinity of the E2D N-terminus for the pore. Finally, our studies support a multi-step, multi-site N-type inactivation model where the N-terminus interacts deep within the pore in an extended like structure placing the most N-terminal residues 35% of the way across the electric field in the pore blocked state. PMID:23638135

Prince, Alison; Pfaffinger, Paul J.

2013-01-01

202

Charge transfer between a CdSe/CdS quantum rod and an attached ferrocene molecule: a first principle study  

NASA Astrophysics Data System (ADS)

Semiconductor quantum dot (QD) shows interesting opto-electrical properties, very different from bulk semiconductors. However, one major challenge for opto-electrical application is to get the charge carrier out of the QD. One approach is to use an attached molecule to extract the photon generated carrier from the QD. Ferrocene has a potential to change its electron transition level either by adjusting the Ferrocene and Ferrocene+ ratio in a solvent, or by adding other functional groups. However, proper understanding of the interactions between QD and molecule is limited, which is extremely useful for further design of such system. One of the main difficult is that there are thousands of atoms contained in the system, a first principle study of which is beyond the limit of existing computational power using direct density functional theory method. In this work we used a novel technique called charge-patching method [1], and combined that with Marcus model to study the electron and hole transfer between ferrocene and CdS/CdSe core-shell quantum dot. This study allows us to gain insights into the molecule dot interactions and underlying photoluminescence quenching process.[4pt] [1] L-W Wang, Phys. Rev. B 65, 153410(2002)

Tarafder, Kartick; Wang, Lin-Wang

2013-03-01

203

The promotion effect of surface negative electrostatic field on the photogenerated charge separation of BiVO4 and its contribution to the enhanced PEC water oxidation.  

PubMed

The increased surface-carried negative charge of BiVO4 after phosphate modification prolongs the photogenerated charge carrier lifetime and improves the separation by inducing the holes to transfer to the surface, leading to the obvious enhancement of visible light activities for PEC water oxidation. PMID:25579796

Xie, Mingzheng; Bian, Ji; Humayun, Muhammad; Qu, Yang; Feng, Yujie; Jing, Liqiang

2015-02-18

204

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

PubMed

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

Kanikovski?, V B

2001-01-01

205

4.1.6 POLYNUCLEOTIDE ADSORPTION AT A NEGATIVELY CHARGED SURFACE J. A. Libera, H. Cheng, M. Olvera de la Cruz, M. J. Bedzyk, "Direct Observation of Cations and  

E-print Network

4.1.6 POLYNUCLEOTIDE ADSORPTION AT A NEGATIVELY CHARGED SURFACE J. A. Libera, H. Cheng, M. Olvera Adsorption to Like-Charged Surfaces," submitted to Nature. This research studied negatively charged polynucleotide adsorption on a like-charged surface in divalent salt solution using a two-state model

Shull, Kenneth R.

206

Calculation of the Response of Field-Effect Transistors to Charged Biological Molecules  

Microsoft Academic Search

Robust approximations are presented that allow for the simple calculation of the total charge and potential drop psi0 across the region of electrolyte containing charged biological macromolecules that are attached to the gate area of a field-effect transistor (FET). The attached macromolecules are modeled as an ion-permeable membrane in contact with the insulator surface, exchanging protons with the electrolyte as

Dolf Landheer; W. Ross McKinnon; Geof Aers; Weihong Jiang; M. Jamal Deen; M. Waleed Shinwari

2007-01-01

207

Ion-molecule clusters involving doubly charged metal ions (M2+)  

NASA Astrophysics Data System (ADS)

Doubly charged metal ion-ligand L clusters, M2+ (L)n, where M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, can be produced in the gas phase by electrospray of solutions of chloride, bromide or nitrate salts of M2+ in methanol-water. L may be added to the solution or to the gas phase. The ions produced by electrospray at atmospheric pressure are transferred to an interface chamber containing pure N2. When known amounts of ligand vapour are added, the equilibria M2+ (L)n-1 + L = M2+ (L)n can be determined by sampling the ions escaping from an orifice in the interface chamber with a quadrupole mass spectrometry. Equilibria for Ni2+ (H2O)n are determined. The clusters are with n [approximate] 10 and the binding energies are in the 15 kcal mol-1 range. Bonding of the ligands at n < 6 is much stronger. It can be studied with collision-induced dissociation (CID) in a triple quadrupole mass spectrometer. The binding energies in the inner shell, n = 0-6, are in the 60 kcal mol-1 range. At low n, charge reduction to M+ may occur. The water clusters undergo the charge reduction Different ligands may accelerate (NH3, pyridine) or retard (DMF, DMSO) the onset of charge reduction. Charge reduction with DMF and DMSO occurs by simple charge transfer Polydentate cage-type ligands protect ions from charge reduction. Thus the only triply charged ion, M3+, so far observed was Co3+ sepulchrate where the ion is coordinated to six nitrogens.

Blades, Arthur T.; Jayaweera, Palitha; Ikonomou, Michael G.; Kebarle, Paul

1990-12-01

208

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

209

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

PubMed Central

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

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

2013-01-01

210

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

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

211

Trap assisted creation of giant molecules and Rydberg-mediated coherent charge transfer in a Penning trap  

E-print Network

We study two ions confined in a Penning trap. We show that electronically highly excited states exist in which an electron is delocalized among the two ions forming a giant molecule of several micrometer size. At energies close to the top of the Coulomb barrier these molecular states can be regarded as superpositions of Rydberg states of individual ions. We illuminate the possibility to observe coherent charge transfer between the ions. Beyond a critical principal quantum number the electron can coherently tunnel through the Coulomb barrier to an adjacent doubly charged ion. The tunneling occurs on timescales on which the dynamics of the nuclei can be considered frozen and radiative decay can be neglected.

I. Lesanovsky; M. Mueller; P. Zoller

2008-09-18

212

Generation of macroscopic entangled coherent states for distant ensembles of polar molecules via effective coupling to a superconducting charge qubit  

NASA Astrophysics Data System (ADS)

We propose a potentially practical scheme for creating macroscopic entangled coherent states (ECSs) between two distant ensembles of polar molecules (PMs) placed, respectively, in separate transmission-line resonators (TLRs) interconnected by a superconducting charge qubit. The ECS between two PM ensembles can be generated in the dispersive regime through control of the superconducting qubit under classical strong-driving conditions, during which the TLRs are only virtually excited. The tunable coupling of the TLR hybrid system provides us the potential of extending the ECS generation to multimode cases. The experimental feasibility of the scheme is discussed briefly based on currently available techniques.

Chen, Qiong; Yang, Wanli; Feng, Mang

2012-10-01

213

Recent advances in negative ion mass spectrometry.  

PubMed Central

The paper describes theoretical and applied applications of negative ion chemistry carried out at Adelaide during the past five years. kinetic energy release in negative metastable ion decompositions is described, with particular reference to simple cleavage reactions, rearrangement reactions, and reactions which proceed by dual mechanisms. The application of deuterium isotope effects as a mechanistic probe is illustrated by reference to the elimination of ketene from quinone acetate negative ions. Charge stripping of a negative ion yields a decomposing positive ion, which produces a dissociative charge inversion spectrum of the negative ion. This technique allows the study of positive ions not available by conventional ionization; it provides a fingerprint for the parent positive ion produced in the collision process, and it may be used to determine the structure of the precursor negative ion. Finally, a combination of a negative ion spectrum and a charge inversion spectrum may be used as an analytical technique for the structure determination of unknown molecules. PMID:7428749

Bowie, J H

1980-01-01

214

Negatively Charged Ions on Mg(0001) Surfaces: Appearance and Origin of Attractive Adsorbate-Adsorbate Interactions  

NASA Astrophysics Data System (ADS)

Adsorption of electronegative elements on a metal surface usually leads to an increase in the work function and decrease in the binding energy as the adsorbate coverage rises. Using density-functional theory calculations, we show that Cl adsorbed on a Mg(0001) surface complies with these expectations, but adsorption of {N,O,F} causes a decrease in the work function and an increase in the binding energy. Analyzing the electronic structure, we show that the presence of a highly polarizable electron spill-out in front of Mg(0001) causes this unusual adsorption behavior and is responsible for the appearance of a hitherto unknown net-attractive lateral electrostatic interaction between same charged adsorbates.

Cheng, Su-Ting; Todorova, Mira; Freysoldt, Christoph; Neugebauer, Jörg

2014-09-01

215

Aggregation of negatively charged colloidal particles in the presence of multivalent cations.  

PubMed

The aggregation and charging behavior of sulfate and carboxyl latex particles in the presence of different multivalent salts was studied. Time-resolved light scattering and electrophoresis are the main experimental techniques used. In particular, the influence of the type of counterion is investigated. The main conclusion is that the valence of the counterion is highly relevant in determining the aggregation behavior, whereas its chemical nature is rather unimportant. Multivalent ions of higher valence destabilize the suspensions more effectively, in particular, by shifting the critical coagulation concentration (CCC) to lower values. This behavior reflects the classical Schulze-Hardy rule. Comparison with literature data reveals that the presently investigated systems behave similarly to the ones described earlier, but the observed dependence on valence is weaker than in some other systems. Moreover, we observe a slowdown of the aggregation at high electrolyte concentrations. This slowdown can be explained by the greater viscosity of the electrolyte solutions under these conditions. PMID:24400954

Oncsik, Tamas; Trefalt, Gregor; Csendes, Zita; Szilagyi, Istvan; Borkovec, Michal

2014-01-28

216

Charge-ice dynamics in the negative thermal expansion material Cd(CN)2  

NASA Astrophysics Data System (ADS)

We use variable-temperature (150-300 K) single-crystal x-ray diffraction to reexamine the interplay between structure and dynamics in the ambient phase of the isotropic negative thermal expansion (NTE) material Cd(CN)2. We find strong experimental evidence for the existence of low-energy vibrational modes that involve off-centering of Cd2+ ions. These modes have the effect of increasing network packing density, suggesting a mechanism for NTE in this material. Strong local correlations in the displacement directions of neighboring cadmium centers are evident in the existence of highly structured diffuse scattering in the experimental x-ray diffraction patterns. Monte Carlo simulations suggest that these patterns might be interpreted in terms of a basic set of “ice rules” that establish a mapping between the dynamics of Cd(CN)2 and proton ordering in cubic ice VII.

Fairbank, Vanessa E.; Thompson, Amber L.; Cooper, Richard I.; Goodwin, Andrew L.

2012-09-01

217

Westward cross-field motion of negative charge filament activated by gradient-curvature proton drift: A cause of the westward traveling surge  

SciTech Connect

The cross-field interactive dynamics of two azimuthally elongated filaments of negative and positive charge excess which are close to each other is numerically studied. The negative charge filament is assumed to exist in the premidnight sector the plasmasheet, causing a discrete aurora at high latitude in the ionosphere. The positive charge filament responsible for a diffuse aurora is assumed to be caused by injection of the ring current energetic protons and located equatorward of the negative charge filament. In our simulation model using two-fluid approximation, the energetic protons execute the gradient and curvature (westward) drifts in the addition to the E x B drift and the electron motion is approximated by the E x B drift. The spatial and temporal development of the charge filaments is numerically followed in a perpendicular plane to the magnetic field. The simulation results show that the gradient and curvature drift of the positive charge carriers (energetic protons) can significantly increase the westward front-velocity of the negative charge filament is found to be on the order of a kilometer per second as geomagnetically projected on the ionosphere. It is then suggested that this physical process can be a cause of the westward traveling surge. copyright American Geophysical Union 1988

Yamamoto, T.

1988-07-01

218

Gate-induced switching and negative differential resistance in a single-molecule transistor: emergence of fixed and shifting states with molecular length.  

PubMed

The quantum transport of a gated polythiophene nanodevice is analyzed using density functional theory and nonequilibrium Green's function approach. For this typical molecular field effect transistor, we prove the existence of two main features of electronic components, i.e., negative differential resistance and good switching. Ab initio based explanations of these features are provided by distinguishing fixed and shifting conducting states, which are shown to arise from the interface and functional molecule, respectively. The results show that proper functional molecules can be used in conjunction with metallic electrodes to achieve basic electronics functionality at molecular length scales. PMID:17640145

Farajian, A A; Belosludov, R V; Mizuseki, H; Kawazoe, Y; Hashizume, T; Yakobson, B I

2007-07-14

219

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

NASA Technical Reports Server (NTRS)

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.

Tosh, R. E.; Johnsen, R.

1993-01-01

220

Monte Carlo Electromagnetic Cross Section Production Method for Low Energy Charged Particle Transport Through Single Molecules  

E-print Network

for predicting molecule-specific ionization, excitation, and scattering cross sections in the very low energy regime that can be applied in a condensed history Monte Carlo track-structure code. The present methodology begins with the calculation of a solution...

Madsen, Jonathan R

2013-08-13

221

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

222

PHYSICAL REVIEW B 86, 115417 (2012) Pseudoparticle approach for charge-transferring molecule-surface collisions  

E-print Network

to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both percent to the secondary electron emission. DOI: 10.1103/PhysRevB.86.115417 PACS number(s): 34.35.+a, 34 of surface reactions is of fundamental interest. It represents a quantum impurity problem where a finite many

Fehske, Holger

223

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

DOE PAGESBeta

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.

Rébola, Alejandro; Fong, Dillon D.; Eastman, Jeffrey A.; Ö?üt, Serdar; Zapol, Peter

2013-06-01

224

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

NASA Astrophysics Data System (ADS)

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.

Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

2012-11-01

225

Expression of a Broad Array of Negative Costimulatory Molecules and Blimp-1 in T Cells following Priming by HIV-1 Pulsed Dendritic Cells  

PubMed Central

Accumulating evidence indicates that immune impairment in persistent viral infections could lead to T-cell exhaustion. To evaluate the potential contribution of induction of negative costimulatory molecules to impaired T-cell responses, we primed naïve T cells with mature monocyte-derived dendritic cells (MDDCs) pulsed with HIV-1 in vitro. We used quantitative real-time polymerase chain reaction and flow cytometry, respectively, to compare the gene and surface-protein expression profiles of naïve T cells primed with HIV-pulsed or mock-pulsed DCs. We detected elevated expressions of negative costimulatory molecules, including lymphocyte activation gene-3 (LAG-3), CD160, cytolytic T-lymphocyte antigen-4 (CTLA-4), T-cell immunoglobulin mucin-containing domain-3 (TIM-3), programmed death-1 (PD-1) and TRAIL (tumor necrosis-factor–related apoptosis-inducing ligand) in T cells primed by HIV-pulsed DCs. The PD-1+ T-cell population also coexpressed TIM-3, LAG-3, and CTLA-4. Interestingly, we also found an increase in gene expression of the transcriptional repressors Blimp-1 (B-lymphocyte–induced maturation protein-1) and Foxp3 (forkhead transcription factor) in T-cells primed by HIV-pulsed DCs; Blimp-1 expression was directly proportional to the expression of the negative costimulatory molecules. Furthermore, levels of the effector cytokines interleukin-2, tumor necrosis factor-? and interferon-?, and perforin and granzyme B were decreased in T-cell populations primed by HIV-pulsed DCs. In conclusion, in vitro priming of naïve T-cells with HIV-pulsed DC leads to expansion of T cells with coexpression of a broad array of negative costimulatory molecules and Blimp-1, with potential deleterious consequences for T-cell responses. PMID:21103670

Shankar, Esaki Muthu; Che, Karlhans Fru; Messmer, Davorka; Lifson, Jeffrey D; Larsson, Marie

2011-01-01

226

Estimating collision cross sections of negatively charged N-glycans using traveling wave ion mobility-mass spectrometry.  

PubMed

Glycosylation is one of the most common post-translational modifications occurring in proteins. A detailed structural characterization of the involved carbohydrates, however, is still one of the greatest challenges in modern glycoproteomics, since multiple regio- and stereoisomers with an identical monosaccharide composition may exist. Recently, ion mobility-mass spectrometry (IM-MS), a technique in which ions are separated according to their mass, charge, and shape, has evolved as a promising technique for the separation and structural analysis of complex carbohydrates. This growing interest is based on the fact that the measured drift times can be converted into collision cross sections (CCSs), which can be compared, implemented into databases, and used as additional search criteria for structural identification. However, most of the currently used commercial IM-MS instruments utilize a nonuniform traveling wave field to propel the ions through the IM cell. As a result, CCS measurements cannot be performed directly and require calibration. Here, we present a calibration data set consisting of over 500 reference CCSs for negatively charged N-glycans and their fragments. Moreover, we show that dextran, already widely used as a calibrant in high performance liquid chromatography, is also a suitable calibrant for CCS estimations. Our data also indicate that a considerably increased error has to be taken into account when reference CCSs acquired in a different drift gas are used for calibration. PMID:25268221

Hofmann, Johanna; Struwe, Weston B; Scarff, Charlotte A; Scrivens, James H; Harvey, David J; Pagel, Kevin

2014-11-01

227

Comparison of positively and negatively charged achiral co-monomers added to cyclodextrin monolith: improved chiral separations in capillary electrochromatography.  

PubMed

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 ?-cyclodextrin (GMA/?-CD) can affect the enantioselective separations in monolithic CEC. To achieve this goal, polymeric monoliths columns were prepared by co-polymerizing GMA/?-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/?-CD, GMA/?-CD-VBTA and GMA/?-CD-AMPS monolithic columns. PMID:24108813

Lu, Yang; Shamsi, Shahab A

2014-10-01

228

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

PubMed

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

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

2014-12-14

229

N-doped graphene: an alternative carbon-based matrix for highly efficient detection of small molecules by negative ion MALDI-TOF MS.  

PubMed

Gas-phase N-doped graphene (gNG) was synthesized by a modified thermal annealing method using gaseous melamine as nitrogen source and then for the first time applied as a matrix in negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for small molecule analysis. Unlike the complicated adducts produced in positive ion mode, MS spectra obtained on gNG matrix in negative ion mode was only featured by deprotonated molecule ion peaks without matrix interference. By the gNG assisted desorption/ionization (D/I) process, some applications were carried out on a wide range of low-molecular weight (MW) analytes including amino acids, fatty acids, peptides, anabolic androgenic steroids as well as anticancer drugs, with an extraordinary laser desorption/ionization (LDI) efficiency over traditional ?-cyano-4-hydroxycinnamic acid (CHCA) and other carbon-based materials in the negative ion detection mode. By comparison of a series of graphene-based matrixes, two main factors of matrix gNG were unveiled to play a decisive role in assisting negative ion D/I process: a well-ordered ?-conjugated system for laser absorption and energy transfer; pyridinic-doped nitrogen species functioning as deprotonation sites for proton capture on negative ionization. The good salt tolerance and high sensitivity allowed further therapeutic monitoring of anticancer drug nilotinib in the spiked human serum, a real case of biology. Signal response was definitely obtained between 1 mM and 1 ?M, meeting the demand of assessing drug level in the patient serum. This work creates a new application branch for nitrogen-doped graphene and provides an alternative solution for small molecule analysis. PMID:25137626

Min, Qianhao; Zhang, Xiaoxia; Chen, Xueqin; Li, Siyuan; Zhu, Jun-Jie

2014-09-16

230

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

231

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

SciTech Connect

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.

Wang, Zhiping, E-mail: wang-zhiping@aist.go.jp; Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji [Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan); Miyadera, Tetsuhiko, E-mail: tetsuhiko-miyadera@aist.go.jp [Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan); JST-PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, 332-0012 Saitama (Japan); Saeki, Akinori; Seki, Shu [Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, 565-0871 Suita, Osaka (Japan); Zhou, Ying [Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan)

2014-07-07

232

Spin-selective charge transport pathways through p-oligophenylene-linked donor-bridge-acceptor molecules.  

PubMed

A series of donor-bridge-acceptor (D-B-A) triads have been synthesized in which the donor, 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An), and the acceptor, naphthalene-1,8:4,5-bis(dicarboximide) (NI), are linked by p-oligophenylene (Ph(n)) bridging units (n = 1-5). Photoexcitation of DMJ-An produces DMJ(+*)-An(-*) quantitatively, so that An(-*) acts as a high potential electron donor, which rapidly transfers an electron to NI yielding a long-lived spin-coherent radical ion pair (DMJ(+*)-An-Ph(n)-NI(-*)). The charge transfer properties of 1-5 have been studied using transient absorption spectroscopy, magnetic field effects (MFEs) on radical pair and triplet yields, and time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The charge separation (CS) and recombination (CR) reactions exhibit exponential distance dependencies with damping coefficients of beta = 0.35 A(-1) and 0.34 A(-1), respectively. Based on these data, a change in mechanism from superexchange to hopping was not observed for either process in this system. However, the CR reaction is spin-selective and produces the singlet ground state and both (3*)An and (3*)NI. A kinetic analysis of the MFE data shows that superexchange dominates both pathways with beta = 0.48 A(-1) for the singlet CR pathway and beta = 0.35 A(-1) for the triplet CR pathway. MFEs and TREPR experiments were used to measure the spin-spin exchange interaction, 2J, which is directly related to the electronic coupling matrix element for CR, V(CR)(2). The magnitude of 2J also shows an exponential distance dependence with a damping coefficient alpha = 0.36 A(-1), which agrees with the beta values obtained from the distance dependence for triplet CR. These results were analyzed in terms of the bridge molecular orbitals that participate in the charge transport mechanism. PMID:19904984

Scott, Amy M; Miura, Tomoaki; Ricks, Annie Butler; Dance, Zachary E X; Giacobbe, Emilie M; Colvin, Michael T; Wasielewski, Michael R

2009-12-01

233

Role of the N-terminal negative charges of actin in force generation and cross-bridge kinetics in reconstituted bovine cardiac muscle fibres  

PubMed Central

Mutant yeast actins were used to determine the role of actin's N-terminal negative charges in force generation. The thin filament was selectively removed from bovine cardiac skinned muscle fibres by gelsolin, and the actin filament was reconstituted from purified G-actin. In this reconstitution, yeast wild-type actin (2Ac: two N-terminal negative charges), yeast mutant actins (3Ac and 4Ac), and rabbit skeletal muscle actin (MAc) were used. The effects of phosphate, ATP and ADP on force development were studied at 25°C. With MAc, isometric tension was 77% of the initial tension owing to the lack of a regulatory system. With 2Ac, isometric tension was 10% of the initial tension; with 3Ac, isometric tension was 23%; and with 4Ac, isometric tension was 44%. Stiffness followed a similar pattern (2Ac < 3Ac < 4Ac < MAc). A similar trend was observed during rigor induction and relaxation. Sinusoidal analysis was performed to obtain the kinetic constants of the cross-bridge cycle. The results showed that the variability of the kinetic constants was ? 2.5-fold among the 2Ac, 4Ac and MAc muscle models. When the cross-bridge distribution was examined, there was no significant reapportionment among these three models examined. These results indicate that force supported by each cross-bridge is modified by the N-terminal negative charges of actin, presumably via the actomyosin interface. We conclude that two N-terminal negative charges are not adequate, three negative charges are intermediate, and four negative charges are necessary to generate force. PMID:15649975

Lu, Xiaoying; Bryant, Mary K; Bryan, Keith E; Rubenstein, Peter A; Kawai, Masataka

2005-01-01

234

Intense X-ray FEL-molecule physics: Highly charged ions  

SciTech Connect

We report on sequential multiphoton ionization of N{sub 2}, H{sub 2}S and SF{sub 6} by intense, femtosecond duration pulses of x-rays from the LCLS free electron laser. Following either K- or L-shell excitation, we observe ionization and fragmentation of the molecule by Auger electron, photoelectron, and ion time-of-flight spectroscopy. Intense excitation of the K-shell leads to depletion and double core hole effects, observed in N{sub 2}. For L-shell excitation, additional relaxation channels suppress depletion, allowing ionization to continue until energetically forbidden. The investigation of multiphoton ionization has produced a better understanding of molecular plasmas created by intense ultrafast x-ray exposure.

Murphy, B. F.; Fang, L.; Osipov, T. Y.; Hoener, M.; Berrah, N. [Western Michigan University, Physics Department, 1903 W. Michigan Avenue, Kalamazoo, MI, 49008 (United States)

2012-05-25

235

First results from a double Vlasov model for negative ion extraction from volume sources - the possibility of an enhanced transverse space charge limit  

SciTech Connect

A new negative ion source extraction model has been formulated and implemented which explicitly considers the motion of positive ions and the volume generation of negative ions. It is found that (1) for high-beam currents, the beam current is limited by a transverse space charge limit, meaning that an increase in negative ion density at the extraction sheath will result in a lower beam current (this result is universally observed at high beam currents); (2) there is a saddle point with a potential barrier preventing the most volume produced negative ions from being extracted (the combination of 1 and 2 indicates that most of the negative ions being created do not find their way into the beam); (3) introduction of cesium may cause, most importantly, an increase in the transverse space charge limit (there is an abundance of experimental data supporting this effect); (4) cesium may also result in an increase in the fraction of volume produced negative ions which are extracted; (5) cesium may also result in a reduction of extracted electrons by dint of a less negative bias on the plasma electrode with respect to the adjacent plasma, thus allowing the transverse space charge limit budget to be taken up wholly by the ions. (The combination of 3-5 represents the way an actual increase in the beam current can be achieved); (6) a strong ion time scale sheath instability due to violation of Bohm criteria produces an anomalous ion temperature that increases with beam current routinely seen in experiments; and (7) introduction of cesium may result in a reduction in this instability. These insights may lead to improvements in volume negative ion sources, and the most important finding of an increased space charge limit has apparently been verified experimentally by reinterpretation of the findings of Bacal, Allison and Leung.

Whealton, J.H.; Olsen, D.K.; Raridon, R.J.

1997-12-01

236

Negative regulation of TLR9-mediated IFN  induction by a small-molecule, synthetic TLR7 ligand  

Microsoft Academic Search

Toll-like receptors (TLRs) are a family of molecules that function as sensors for the detec- tion of foreign pathogens through the recognition of nonvariable microbial motifs. Although numer- ous studies have focused on singular TLRs, less attention has been focused on how simultaneous signaling of multiple TLRs may result in counter- regulation of the effects of each. Here, we examine

Jason D. Marshall; Darren S. Heeke; Marianne L. Gesner; Brian Livingston; Gary Van Nest

2007-01-01

237

Adsorption and transport of charged vs. neutral hydrophobic molecules at the membrane of murine erythroleukemia (MEL) cells.  

PubMed

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 (<600Da) 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)?m(-2) on the surface of undifferentiated MEL cells, and (1.8±0.5)×10(7)?m(-2) on differentiated MEL cells, while the deduced adsorption free energies are effectively identical (ca. -10.9±0.1 and -10.8±0.1kcalmol(-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

Zeng, Jia; Eckenrode, Heather M; Dai, Hai-Lung; Wilhelm, Michael J

2015-03-01

238

Using light-switching molecules to modulate charge mobility in a quantum dot array  

NASA Astrophysics Data System (ADS)

We have studied the electron hopping in a two-CdSe quantum dot (QD) system linked by an azobenzene-derived light-switching molecule. This system can be considered as a prototype of a QD supercrystal. Following the computational strategies given in our recent work [I.-H. Chu et al., J. Phys. Chem. C 115, 21409 (2011), 10.1021/jp206526s], we have investigated the effects of molecular attachment, molecular isomer (trans and cis), and QD size on the electron hopping rate using Marcus theory. Our results indicate that molecular attachment has a large impact on the system for both isomers. In the most energetically favorable attachment, the cis isomer provides significantly greater coupling between the two QDs and hence the electron hopping rate is greater compared to the trans isomer. As a result, the carrier mobility of the QD array in the low carrier density, weak external electric-field regime is several orders of magnitude higher in the cis compared to the trans configuration. This demonstration of mobility modulation using QDs and azobenzene could lead to an alternative type of switching device.

Chu, Iek-Heng; Trinastic, Jonathan; Wang, Lin-Wang; Cheng, Hai-Ping

2014-03-01

239

Unconventional charge distribution in the planar wheel-type M©B6H6(-/0/+) (M = Mn, Fe and Co): central M with negative charges and peripheral boron ring with positive charges.  

PubMed

Planar wheel-type D6h M©B6H6(-/0/+) (M = Mn, Fe and Co for anion, neutral and cation, respectively.) clusters with a planar hexacoordinate transition-metal at the center of the boron ring were designed and investigated by density functional theory. These planar clusters are chemically stable as a result of their large binding energy, vertical ionization potential, and vertical electron affinity. The detailed natural population and molecular orbital analyses suggest that not only does the M atom donate electrons to the boron ring for participation in the ?-delocalized bonding, but also the boron ring donates electrons back to the M atom for the formation of the ?-delocalized bonding, which leads to a strong aromaticity and unconventional charge distribution, i.e., the M atom is negatively charged, while the boron ring is positively charged. This study may open a new area in coordination chemistry for planar hexacoordinate transition metals and we expect further experimental exploration of their synthesis and potential applications. PMID:25830384

Hou, Jianhua; Duan, Qian; Qin, Jieming; Shen, Xiande; Zhao, Jianxun; Liang, Qingcheng; Jiang, Dayong; Gao, Shang

2015-04-01

240

New insight into the spin-conserving excitation of the negatively charged nitrogen-vacancy center in diamond  

NASA Astrophysics Data System (ADS)

The negatively charged nitrogen-vacancy (N-V-) color center in diamond is an important solid-state single photon source for applications to quantum communication and distributed quantum computation. Its full usefulness relies on sufficient radiative emission of the optical photons which requires realizable control to enhance emission into the zero-phonon line (ZPL) but until now is still a challenge. Detailed understanding of the associated excitation process would be of essential importance for such objective. Here we report a theoretical work that probes the spin-conserving optical excitation of the N-V- center. Using density-functional-theory (DFT) calculations, we find that the ZPL and the phonon-side band (PSB) depend sensitively on the axial strain of the system. Besides, we find a relatively small PSB appearing at about 100 GPa in the emission spectrum at low temperatures, which provides a means to enhance the coherent emission of the N-V- center in quantum optical networks.

Deng, Bei; Zhang, R. Q.; Shi, X. Q.

2014-06-01

241

New insight into the spin-conserving excitation of the negatively charged nitrogen-vacancy center in diamond  

PubMed Central

The negatively charged nitrogen-vacancy (N-V?) color center in diamond is an important solid-state single photon source for applications to quantum communication and distributed quantum computation. Its full usefulness relies on sufficient radiative emission of the optical photons which requires realizable control to enhance emission into the zero-phonon line (ZPL) but until now is still a challenge. Detailed understanding of the associated excitation process would be of essential importance for such objective. Here we report a theoretical work that probes the spin-conserving optical excitation of the N-V? center. Using density-functional-theory (DFT) calculations, we find that the ZPL and the phonon-side band (PSB) depend sensitively on the axial strain of the system. Besides, we find a relatively small PSB appearing at about 100?GPa in the emission spectrum at low temperatures, which provides a means to enhance the coherent emission of the N-V? center in quantum optical networks. PMID:24888367

Deng, Bei; Zhang, R. Q.; Shi, X. Q.

2014-01-01

242

Laser heating of solid hydrogen for production of vibrationally excited molecules for use in negative hydrogen ion sources  

Microsoft Academic Search

An experiment has been performed in which laser light was used to heat hydrogen pellets on a metallic substrate. The purpose of heating the hydrogen is to create a vibrationally excited population of hydrogen for use in negative hydrogen ion sources. The desired heating temperature is 3000-6000 K. A dye laser with an energy of 1-3 J with a pulse

1982-01-01

243

The Net Charge of the First 18 Residues of the Mature Sequence Affects Protein Translocation across the Cytoplasmic Membrane of Gram-Negative Bacteria  

PubMed Central

This statistical study shows that in proteins of gram-negative bacteria exported by the Sec-dependent pathway, the first 14 to 18 residues of the mature sequences have the highest deviation between the observed and expected net charge distributions. Moreover, almost all sequences have either neutral or negative net charge in this region. This rule is restricted to gram-negative bacteria, since neither eukaryotic nor gram-positive bacterial exported proteins have this charge bias. Subsequent experiments performed with a series of Escherichia coli alkaline phosphatase mutants confirmed that this charge bias is associated with protein translocation across the cytoplasmic membrane. Two consecutive basic residues inhibit translocation effectively when placed within the first 14 residues of the mature protein but not when placed in positions 19 and 20. The sensitivity to arginine partially reappeared again 30 residues away from the signal sequence. These data provide new insight into the mechanism of protein export in gram-negative bacteria and lead to practical recommendations for successful secretion of hybrid proteins. PMID:10735858

Kajava, Andrey V.; Zolov, Sergey N.; Kalinin, Andrey E.; Nesmeyanova, Marina A.

2000-01-01

244

The highly conserved negatively charged Glu141 and Asp145 of the G-protein-coupled receptor RXFP3 interact with the highly conserved positively charged arginine residues of relaxin-3.  

PubMed

Relaxin-3 is a newly identified insulin/relaxin superfamily peptide that plays a putative role in the regulation of food intake and stress response by activating its cognate G-protein-coupled receptor RXFP3. Relaxin-3 has three highly conserved arginine residues, B12Arg, B16Arg and B26Arg. We speculated that these positively charged arginines may interact with certain negatively charged residues of RXFP3. To test this hypothesis, we first replaced the negatively charged residues in the extracellular domain of RXFP3 with arginine, respectively. Receptor activation assays showed that arginine replacement of Glu141 or Asp145, especially Glu141, significantly decreased the sensitivity of RXFP3 to wild-type relaxin-3. In contrast, arginine replacement of other negatively charged extracellular residues had little effect. Thus, we deduced that Glu141 and Asp145, locating at the extracellular end of the second transmembrane domain, played a critical role in the interaction of RXFP3 with relaxin-3. To identify the ligand residues interacting with the negatively charged EXXXD motif of RXFP3, we replaced the three conserved arginines of relaxin-3 with negatively charged glutamate or aspartate, respectively. The mutant relaxin-3s retained the native structure, but their binding and activation potencies towards wild-type RXFP3 were decreased significantly. The compensatory effects of the mutant relaxin-3s towards mutant RXFP3s suggested two probable interaction pairs during ligand-receptor interaction: Glu141 of RXFP3 interacted with B26Arg of relaxin-3, meanwhile Asp145 of RXFP3 interacted with both B12Arg and B16Arg of relaxin-3. Based on these results, we proposed a relaxin-3/RXFP3 interaction model that shed new light on the interaction mechanism of the relaxin family peptides with their receptors. PMID:24615237

Zhang, Wei-Jie; Wang, Xin-Yi; Guo, Yu-Qi; Luo, Xiao; Gao, Xue-Juan; Shao, Xiao-Xia; Liu, Ya-Li; Xu, Zeng-Guang; Guo, Zhan-Yun

2014-05-01

245

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)

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 -3.4•1028 Gs•cm3 and 1.9•1028 Gs•cm3 respectively (use new rotate speed measured by Voyager 2). The P measured by Voyager 2 in 1986 and 1989 are about -1.9 •1028 Gs•cm3 and 1.5•1028 Gs•cm3 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

Chen, Shao-Guang

246

A 90-day study of subchronic oral toxicity of 20 nm, negatively charged zinc oxide nanoparticles in Sprague Dawley rats  

PubMed Central

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

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

247

Chemical bonding in hypervalent molecules. The dominance of ionic bonding and negative hyperconjugation over d-orbital participation  

SciTech Connect

Does sulfur form six covalent bonds in CH{sub 3}SO{sub 2}Cl, F{sub 3}S{triple bond}N or carbon or phosphorus five bonds in F{sub 3}C=O{sup {minus}}, F{sub 3}P=O After a brief history of the viewpoints on hypervalent bonding and a comparison of analysis methods (with CH{sub 3}SO{sub 2}Cl as example), natural population and natural bond orbital analysis is applied to a series of 32-valence-electron species of X{sub 3}XY type (CF{sub 4}, F{sub 3}NO, O{sub 3}ClF, O{sub 3}PS{sup 3{minus}}, F{sub 3}SN, etc.). The {sigma}-bonding in these systems is found to be significantly ionic, and the strongly polar {sigma}*{sub AX} orbitals are found to be more effective electron acceptors than the extra-valence d{sub {pi}} (A) orbitals. By generalizing our discussion to n-coordinate 8n-valence-electron species (HF{sub 2}{sup {minus}}, BF{sub 3}, ClO{sub 4}{sup {minus}}, F{sub 4}SO, F{sub 5}TeO{sup {minus}}, IF{sub 6}{sup +}, OXeF{sub 6}, etc.) and their reduced analogues that have one or more lone pairs on the central atom (SF{sub 4}, IF{sub 6}{sup {minus}}, ClF{sub 3}, etc.), we provide a classification of hypervalent (and many nonhypervalent) molecules. The simple, qualitative bonding concepts for hypervalent molecules developed here supercede the inaccurate and misleading dsp{sup 3} and d{sup 2}sp{sup 3} models that are still in widespread use.

Reed, A.E.; von Rague Schleyer, P. (Universitaet Erlangen-Nuernberg (Germany, F.R.))

1990-02-14

248

Excitation of atoms and molecules in collisions with highly charged ions. Progress report, January 1, 1990--December 1, 1992  

SciTech Connect

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.

Watson, R.L.

1993-01-01

249

Excitation of atoms and molecules in collisions with highly charged ions. [Cyclotron Inst. , Texas A M Univ. , College Station, Texas  

SciTech Connect

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.

Watson, R.L.

1993-01-01

250

Structural requirements for charged lipid molecules to directly increase or suppress K+ channel activity in smooth muscle cells. Effects of fatty acids, lysophosphatidate, acyl coenzyme A and sphingosine  

PubMed Central

We determined the structural features necessary for fatty acids to exert their action on K+ channels of gastric smooth muscle cells. Examination of the effects of a variety of synthetic and naturally occurring lipid compounds on K+ channel activity in cell-attached and excised membrane patches revealed that negatively charged analogs of medium to long chain fatty acids (but not short chain analogs) as well as certain other negatively charged lipids activate the channels. In contrast, positively charged, medium to long chain analogs suppress activity, and neutral analogs are without effect. The key requirements for effective compounds seem to be a sufficiently hydrophobic domain and the presence of a charged group. Furthermore, those negatively charged compounds unable to "flip" across the bilayer are effective only when applied at the cytosolic surface of the membrane, suggesting that the site of fatty acid action is also located there. Finally, because some of the effective compounds, for example, the fatty acids themselves, lysophosphatidate, acyl Coenzyme A, and sphingosine, are naturally occurring substances and can be liberated by agonist- activated or metabolic enzymes, they may act as second messengers targeting ion channels. PMID:8195783

1994-01-01

251

The Negative Charge of the Membrane Has Opposite Effects on the Membrane Entry and Exit of pH-Low Insertion Peptide.  

PubMed

The pH-low insertion peptide (pHLIP) targets acidic diseases such as cancer. The acidity of the environment causes key aspartic acids in pHLIP to become protonated, causing the peptide to insert into membranes. Here we investigate how the negative charge of the membrane influences how pHLIP enters and exits the lipid bilayer. We found that electrostatic repulsion affected differently the membrane entry and exit of pHLIP for negatively charged membranes. As a consequence, a large hysteresis was observed. We propose this is not a consequence of structural changes but results from local changes in the environment of aspartic acids, shifting their pK values. PMID:25692747

Scott, Haden L; Nguyen, Vanessa P; Alves, Daiane S; Davis, Forrest L; Booth, Kristen R; Bryner, Jordan; Barrera, Francisco N

2015-03-10

252

Negative surface ionization mass spectrometry for real-time monitoring of iodine molecules in process off-gas  

SciTech Connect

Negative surface ionization mass spectrometry is being developed for continuous measurement of iodine found in the atmospheric environment as a result of nuclear fuel reprocessing. Studies have been made on a series of low work function surface materials (CaCO[sub 3]-SrCO[sub 3]-CaCO[sub 3], BaCO[sub 3]-SrCO[sub 3], LaB[sub 6]) with the intent of developing improved methods for iodine analysis, particularly at the environmental level (ppb concentration range). The results demonstrate the feasibility of performing real-time measurements of the trace amount of iodine encountered in process off-gas by use of a CaCO[sub 3]-SrCO[sub 3]-CaCO[sub 3]-coated rhenium filament emitter. This emitter surface with thermoelectronic work function [phi] at 2.0 eV gives 37.5 times greater sensitivity than the established LaB[sub 6] emitter for iodine analysis. 22 refs., 6 figs., 1 tab.

Kishi, Hiroshi (Oyama National College of Technology (Japan)); Fujii, Toshihiro (National Inst. for Environmental Studies, Tsukuba (Japan))

1994-12-15

253

Nanosized films based on multicharged small molecules and oppositely charged polyelectrolytes obtained by simultaneous spray coating of interacting species.  

PubMed

Simultaneous spraying of polyelectrolytes and small multicharged molecules of opposite charges onto a vertical substrate leads to continuous buildups of organic films. Here, we investigate the rules governing the buildup of two such systems: poly(allylamine hydrochloride)/sodium citrate (PAH/citrate) and PAH/sulfated ?-cyclodextrin (PAH/CD-S). Special attention is paid to the film growth rate as a function of the spraying rate ratio of the two constituents. This parameter was varied by increasing the spraying rate of one of the constituents while maintaining constant that of the other. For PAH/CD-S systems, whatever the constituent (PAH or CD-S) whose spraying rate was kept fixed, the film growth rate first increases and passes through a maximum before decreasing when the spraying rate of the other constituent is increased. For PAH/citrate, the film growth rate reaches a plateau value when the spraying rate of citrate is increased while that of PAH is maintained constant, whereas when the spraying rate of citrate is maintained constant and that of PAH is increased, a behavior similar to that of PAH/CD-S is observed. The composition of PAH/CD-S sprayed films determined by X-ray photoelectron spectroscopy is independent of the spraying rate ratio of the two constituents and corresponds to one allylamine for one sulfate group. For PAH/citrate, by increasing the PAH/citrate spraying rate ratio, the carboxylic/nitrogen ratio in the film increases and tends to 1. There is thus always a deficit of carboxylic groups (COO(-) + COOH) with respect to amines (NH2 + NH3(+)). Yet, the ratio (COO(-)/NH3(+)) is always close to 1, ensuring exact charge compensation. The film morphology determined by atomic force microscopy is granular for PAH/CD-S and is smooth and liquid-like for PAH/citrate. A model based on strong (respectively weak) interactions between PAH and CD-S (respectively citrate) is proposed to explain these features. PMID:24171660

Lefort, Mathias; Jierry, Loïc; Boulmedais, Fouzia; Benmlih, Karim; Lavalle, Philippe; Senger, Bernard; Voegel, Jean-Claude; Hemmerlé, Joseph; Ponche, Arnaud; Schaaf, Pierre

2013-11-26

254

Buffer system for the separation of neutral and charged small molecules using micellar electrokinetic chromatography with mass spectrometric detection.  

PubMed

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

Goetzinger, Wolfgang K; Cai, Hong

2005-06-24

255

Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy.  

PubMed

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)-2x1 surface at a temperature of 80 K. Current-voltage 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 current-voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip-molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip-molecule 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

Guisinger, Nathan P; Yoder, Nathan L; Hersam, Mark C

2005-06-21

256

Development of 4? detector to clarify fragmentation dynamics of molecule in collisions with highly charged ions in ultra low energy region  

NASA Astrophysics Data System (ADS)

We have developed a new detector to study collision dynamics between highly charged ion and molecule in ultra low energy region (<= 1 keV/u). The outline of this detector is a recoil momentum spectroscopy in semi-spherical energy analyzer. At the conference, we will present progress report of the developments of this detector including TOF spectra of recoil ions in coincidence with HCI after collisions.

Okano, M.; Ishii, K.; Ogawa, H.

2012-11-01

257

Binding of ?-Amyloid (1–42) Peptide to Negatively Charged Phospholipid Membranes in the Liquid-Ordered State: Modeling and Experimental Studies  

PubMed Central

To explore the initial stages of amyloid ? peptide (A?42) deposition on membranes, we have studied the interaction of A?42 in the monomeric form with lipid monolayers and with bilayers in either the liquid-disordered or the liquid-ordered (Lo) state, containing negatively charged phospholipids. Molecular dynamics (MD) simulations of the system have been performed, as well as experimental measurements. For bilayers in the Lo state, in the absence of the negatively charged lipids, interaction is weak and it cannot be detected by isothermal calorimetry. However, in the presence of phosphatidic acid, or of cardiolipin, interaction is detected by different methods and in all cases interaction is strongest with lower (2.5–5 mol %) than higher (10–20 mol %) proportions of negatively charged phospholipids. Liquid-disordered bilayers consistently allowed a higher A?42 binding than Lo ones. Thioflavin T assays and infrared spectroscopy confirmed a higher proportion of ?-sheet formation under conditions when higher peptide binding was measured. The experimental results were supported by MD simulations. We used 100 ns MD to examine interactions between A?42 and three different 512 lipid bilayers consisting of palmitoylsphingomyelin, dimyristoyl phosphatidic acid, and cholesterol in three different proportions. MD pictures are different for the low- and high-charge bilayers, in the former case the peptide is bound through many contact points to the bilayer, whereas for the bilayer containing 20 mol % anionic phospholipid only a small fragment of the peptide appears to be bound. The MD results indicate that the binding and fibril formation on the membrane surface depends on the composition of the bilayer, and is the result of a subtle balance of many inter- and intramolecular interactions between the A?42 and membrane. PMID:22947861

Ahyayauch, Hasna; Raab, Michal; Busto, Jon V.; Andraka, Nagore; Arrondo, José-Luis R.; Masserini, Massimo; Tvaroska, Igor; Goñi, Félix M.

2012-01-01

258

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

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.

Silva, Arnaldo F.; Richter, Wagner E.; Bruns, Roy E., E-mail: bruns@iqm.unicamp.br [Instituto de Química, Universidade Estadual de Campinas, CP 6154, Campinas, CEP 13083-970, SP (Brazil); Terrabuio, Luiz A.; Haiduke, Roberto L. A. [Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, CP 780, 13560-970 São Carlos, SP (Brazil)] [Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São-carlense, 400, CP 780, 13560-970 São Carlos, SP (Brazil)

2014-02-28

259

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.  

PubMed

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(-1) on H-bond formation compared with the experimental values of 141 and 53 km mol(-1). The symmetric stretching of the proton donor water in the dimer has intensity contributions parallel and perpendicular to its C2v axis. The largest calculated increase of 107 km mol(-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(-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(-1) on HF dimerization and 592 km mol(-1) on HF:H2O 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(-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(-1), respectively. PMID:24588168

Silva, Arnaldo F; Richter, Wagner E; Terrabuio, Luiz A; Haiduke, Roberto L A; Bruns, Roy E

2014-02-28

260

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  

NASA Astrophysics Data System (ADS)

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-1 on H-bond formation compared with the experimental values of 141 and 53 km mol-1. The symmetric stretching of the proton donor water in the dimer has intensity contributions parallel and perpendicular to its C2v axis. The largest calculated increase of 107 km mol-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-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-1 on HF dimerization and 592 km mol-1 on HF:H2O 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-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-1, respectively.

Silva, Arnaldo F.; Richter, Wagner E.; Terrabuio, Luiz A.; Haiduke, Roberto L. A.; Bruns, Roy E.

2014-02-01

261

Simultaneous four-color imaging of single molecule fluorophores using dichroic mirrors and four charge-coupled devices  

NASA Astrophysics Data System (ADS)

We developed a total-internal-reflection (TIR) fluorescence microscopy using three dichroic mirrors and four charge-coupled devices (CCDs) to detect simultaneously four colors of single-molecule (SM) fluorophores. Four spectrally distinct species of fluorophores (Alexa 488, Cy3, Cy5, or Cy5.5) were each immobilized on a different fused silica slide. A species of fluorophores on the slide was irradiated simultaneously, by two excitation beams from an Ar ion laser (488 and 514.5 nm) and a diode laser (642 nm) through TIR on the slide surface. Fluorescence emitted from the fluorophores was spectrally resolved into four components by the dichroic mirrors, and four images were generated from them simultaneously and continuously, with the four CCDs at a rate of 10 Hz. A series of images was thus obtained with each CCD. Fluorescence spots for a species were observed mainly in the series of images recorded by its respective-color CCD. In the first image in the series, we picked out the spots as continuous pixel regions that had the values greater than a threshold. Then we selected only those spots that exhibited single-step photobleaching and regarded them as SM fluorescence spots. Pixel values of SM fluorescence spots widely differed. Some SM fluorophores had pixel values smaller than the threshold, and were left unpicked. Assuming the pixel values of SM fluorescence spots differed with a Gaussian profile, we estimated the ratios of unpicked fluorophores to be less than 20% for all the species. Because of the spectral overlaps between species, we also observed cross-talk spots into CCDs other than the respective-color CCDs. These cross-talk SM fluorescence spots can be mistaken for correct species. We thus introduced the classification method and classified SM fluorescence spots into correct species in accordance with two kinds of four-dimensional signal vectors. The error rates of fluorophore classification were estimated to be less than 3.2% for all the species. Our system is suitable for the biological studies that desire to simultaneously monitor the four colors of SM fluorophores.

Haga, Takanobu; Sonehara, Tsuyoshi; Sakai, Tomoyuki; Anazawa, Takashi; Fujita, Takeshi; Takahashi, Satoshi

2011-02-01

262

Apport de la microscopie a effet tunnel a la caracterisation d'interfaces molecule-metal a fort transfert de charge  

NASA Astrophysics Data System (ADS)

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

Bedwani, Stephane

263

Molecular motion, dielectric response, and phase transition of charge-transfer crystals: acquired dynamic and dielectric properties of polar molecules in crystals.  

PubMed

Molecules in crystals often suffer from severe limitations on their dynamic processes, especially on those involving large structural changes. Crystalline compounds, therefore, usually fail to realize their potential as dielectric materials even when they have large dipole moments. To enable polar molecules to undergo dynamic processes and to provide their crystals with dielectric properties, weakly bound charge-transfer (CT) complex crystals have been exploited as a molecular architecture where the constituent polar molecules have some freedom of dynamic processes, which contribute to the dielectric properties of the crystals. Several CT crystals of polar tetrabromophthalic anhydride (TBPA) molecules were prepared using TBPA as an electron acceptor and aromatic hydrocarbons, such as coronene and perylene, as electron donors. The crystal structures and dielectric properties of the CT crystals as well as the single-component crystal of TBPA were investigated at various temperatures. Molecular reorientation of TBPA molecules did not occur in the single-component crystal, and the crystal did not show a dielectric response due to orientational polarization. We have found that the CT crystal formation provides a simple and versatile method to develop molecular dielectrics, revealing that the molecular dynamics of the TBPA molecules and the dielectric property of their crystals were greatly changed in CT crystals. The TBPA molecules underwent rapid in-plane reorientations in their CT crystals, which exhibited marked dielectric responses arising from the molecular motion. An order-disorder phase transition was observed for one of the CT crystals, which resulted in an abrupt change in the dielectric constant at the transition temperature. PMID:25781627

Harada, Jun; Ohtani, Masaki; Takahashi, Yukihiro; Inabe, Tamotsu

2015-04-01

264

Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy  

NASA Astrophysics Data System (ADS)

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)-2×1 surface at a temperature of 80 K. Current-voltage 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 current-voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip-molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip-molecule 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. Author contributions: N.P.G., N.L.Y., and M.C.H. designed research; N.P.G. and N.L.Y. performed research; N.P.G., N.L.Y., and M.C.H. analyzed data; and N.P.G. and M.C.H. wrote the paper.This paper was submitted directly (Track II) to the PNAS office.Abbreviations: UHV, ultra-high vacuum; STM, scanning tunneling microscope; NDR, negative differential resistance; HOMO, highest occupied molecular orbital.

Guisinger, Nathan P.; Yoder, Nathan L.; Hersam, Mark C.

2005-06-01

265

Impact of negative affectively charged stimuli and response style on cognitive-control-related neural activation: an ERP study.  

PubMed

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

Lamm, C; Pine, D S; Fox, N A

2013-11-01

266

Comparing Coulomb explosion dynamics of multiply charged triatomic molecules after ionization by highly charged ion impact and few cycle femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Recent experiments using highly charged ions (HCI) at Tokyo Metropolitan University and few cycle laser pulses at the advanced laser light source have centered on multiply ionizing carbonyl sulfide to form charge states from 3 + to 7 + . By measuring the kinetic energy release during subsequent break up and comparing with previous results from HCI impact on CO2 we can see a pattern emerging which implies that shorter laser pulses than the current sub 7 fs standard could lead to higher kinetic energy release than expected from Coulomb explosion.

Wales, B.; Karimi, R.; Bisson, E.; Beaulieu, S.; Giguère, M.; Motojima, T.; Anderson, R.; Matsumoto, J.; Kieffer, J.-C.; Légaré, F.; Shiromaru, H.; Sanderson, J.

2013-09-01

267

6162 J. Phys. Chem. 1987, 91, 6162-6167 Stepwise Solvation of the Intramolecular-Charge-Transfer Molecule  

E-print Network

, and the spectroscopyof the stoichiometriccomplex with water, methanol, ammonia, and acetonitrile in the beam is reported). In polar solvents, an excited DMABN molecule undergoes a rotation of the dimethylamino group about

Eisenthal, Kenneth B.

268

Effects of energy offsets and molecular packing on exciton and charge carrier dynamics in small-molecule donor-acceptor composites  

NASA Astrophysics Data System (ADS)

We present a study of optical, photoluminescent (PL), and photoconductive properties of small-molecule D/A bulk heterojunctions of functionalized fluorinated anthradithiophene (ADT-R-F) and pentacene (Pn-R-F8) derivatives. We chose one of the ADT derivatives, ADT-TES-F, which exhibits a 2D "brick-work" .?-stacking, as the donor, and ADT-TIPS-F (2D "brick-work"), ADT-TSBS-F (1D "sandwich-herringbone"), Pn-TIPS-F8 (2D "brick-work"), or Pn-TCHS-F8 (1D "sandwich-herringbone"), as acceptors. We measured PL and photoconductivity at time scales from sub-nanoseconds to many seconds after photoexcitation, at various acceptor concentrations, under various experimental conditions. The choice of acceptors enabled us to distinguish between effects of the LUMO energy offsets between the donor and acceptor molecules and those of the molecular packing in the acceptor domains on exciton and charge carrier dynamics.

Paudel, Keshab; Johnson, Brian; Neunzert, Afina; Thieme, Mattson; Anthony, John; Ostroverkhova, Oksana

2013-09-01

269

Observation of negative charge trapping and investigation of its physicochemical origin in newly synthesized poly(tetraphenyl)silole siloxane thin films.  

PubMed

A new kind of organic-inorganic hybrid polymer, poly(tetraphenyl)silole siloxane, was invented and synthesized for realization of its unique charge trap properties. The organic portions consisting of (tetraphenyl)silole rings were responsible for negative charge trapping, while the Si-O-Si inorganic linkages provided the intrachain energy barrier for controlling electron transport. The polysilole siloxane dielectric thin films were fabricated by spin-coating and curing of the polymers, followed by characterization with spectroscopic ellipsometry (SE), near edge X-ray absorption fine structure spectroscopy (NEXAFS), and photoemission spectroscopy (PES). The abrupt increase in density and decrease in thickness of the thin film at a curing temperature of 100 °C was attributed to a thermodynamically preferred state in the nanoscopic arrangement of the polymer chains; this was due to cofacial ?-? interactions in a skewed manner between peripheral phenyl groups of the (tetraphenyl)silole rings of the adjacent polymer chains. Using the NEXAFS spectrum to assess high electron affinity, the LUMO energy level of the dielectric thin film cured at 150 °C was positioned 1 eV above the Fermi energy level (E(F)). The electron trapping of the dielectric thin films was confirmed from the positive flat band shift (?V(FB)) in the capacitance-voltage (C-V) measurements performed within the metal-insulator-semiconductor (MIS) device structure, which strongly verified the polymer design concept. From the simple kinetics model of the electron transport, it was proposed that the flat band shift (?V(FB)) or trap density of the negative charges (|?|) was logarithmically proportional to the decay constant (?) for the electron-tunneling process. When a phenyl group of a silole ring in a polymer chain was inserted into the two available phenyl groups of another silole ring in another polymer chain, the electron transfer between the groups was enhanced, decreasing the trap density of the negative charges (|?|). For the thermodynamically preferred state generating the high refractive index, the distance between the two phenyl groups of the adjacent polymer chains was estimated to be in the range of 0.27-0.36 nm. PMID:21542608

Choi, Jin-Kyu; Jang, Seunghyun; Kim, Ki-Jeong; Sohn, Honglae; Jeong, Hyun-Dam

2011-05-25

270

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)

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.

Yang, Jin-Hua; Rawashdeh, Abdel Monem M.; Oh, Woon Su; Sotiriou-Leventis, Chariklia; Leventis, Nicholas

2003-01-01

271

Charge localization and charge transfer in the Bebq2 monomer and dimer.  

PubMed

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

Safonov, Andrei A; Bagaturyants, Alexander A

2014-08-01

272

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

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.

Du Yuzhe; Song Weizhong [Department of Entomology, Neuroscience Program and Genetics Program, Michigan State University, East Lansing, MI 48824 (United States); Groome, James R. [Department of Biological Sciences, Idaho State University, Pocatello, ID 83209 (United States); Nomura, Yoshiko; Luo Ningguang [Department of Entomology, Neuroscience Program and Genetics Program, Michigan State University, East Lansing, MI 48824 (United States); Dong Ke, E-mail: dongk@msu.ed [Department of Entomology, Neuroscience Program and Genetics Program, Michigan State University, East Lansing, MI 48824 (United States)

2010-08-15

273

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.  

PubMed

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. PMID:20561903

Du, Yuzhe; Song, Weizhong; Groome, James R; Nomura, Yoshiko; Luo, Ningguang; Dong, Ke

2010-08-15

274

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

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

Vanquelef, Enguerran; Simon, Sabrina; Marquant, Gaelle; Garcia, Elodie; Klimerak, Geoffroy; Delepine, Jean Charles; Cieplak, Piotr; Dupradeau, François-Yves

2011-07-01

275

Basic Vapor Exposure for Tuning the Charge State Distribution of Proteins in Negative Electrospray Ionization: Elucidation of Mechanisms by Fluorescence Spectroscopy  

NASA Astrophysics Data System (ADS)

Manipulation for simplifying or increasing the observed charge state distributions of proteins can be highly desirable in mass spectrometry experiments. In the present work, we implemented a vapor introduction technique to an Agilent Jet Stream ESI (Agilent Technologies, Santa Clara, CA, USA) source. An apparatus was designed to allow for the enrichment of the nitrogen sheath gas with basic vapors. An optical setup, using laser-induced fluorescence and a pH-chromic dye, permits the pH profiling of the droplets as they evaporate in the electrospray plume. Mechanisms of pH droplet modification and its effect on the protein charging phenomenon are elucidated. An important finding is that the enrichment with basic vapors of the nitrogen sheath gas, which surrounds the nebulizer spray, leads to an increase in the spray current. This is attributed to an increase in the electrical conductivity of water-amine enriched solvent at the tip exit. Here, the increased current results in a generation of additional electrolytically produced OH- ions and a corresponding increase in the pH at the tip exit. Along the electrospray plume, the pH of the droplets increases due to both droplet evaporation and exposure to basic vapors from the seeded sheath gas. The pH evolution in the ESI plume obtained using pure and basic seeded sheath gas was correlated with the evolution of the charge state distribution observed in mass spectra of proteins, in the negative ion mode. Taking advantage of the Agilent Jet Stream source geometry, similar protein charge state distributions and ion intensities obtained with basic initial solutions, can be obtained using native solution conditions by seeding the heated sheath gas with basic vapors.

Girod, Marion; Antoine, Rodolphe; Dugourd, Philippe; Love, Craig; Mordehai, Alex; Stafford, George

2012-07-01

276

Charge density threshold for LbL self-assembly and small molecule diffusion in polyelectrolyte multilayer films  

Microsoft Academic Search

Polyelectrolyte multilayer films were prepared via the layer-by-layer self-assembly using poly(diallydimethylammonium chloride) (PDADMAC) and pyrene labeled polyanions of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and N,N-dimethylacrylamide copolymers with different charge densities (AMPS mole fraction) FAMPS=0.20–0.999. Multilayer growth with alternating deposition from salt-free polyelectrolyte solutions was monitored by fluorescence intensity and film thickness, showing a charge density threshold between 0.574 and 0.711 for our

Qilong Sun; Zhen Tong; Chaoyang Wang; Biye Ren; Xinxing Liu; Fang Zeng

2005-01-01

277

Electrical charging changes the composition of sulfuric acid-ammonia/dimethylamine clusters  

NASA Astrophysics Data System (ADS)

Sulfuric acid clusters stabilized by base molecules are likely to have a significant role in atmospheric new particle formation. Recent advances in mass spectrometry techniques have permitted the detection of electrically charged clusters. However, direct measurement of electrically neutral clusters is not possible. Mass spectrometry instruments can be combined with a charger, but the possible effect of charging on the composition of neutral clusters must be addressed before the measured data can be linked to properties of neutral clusters. In the present work we have used formation free energies from quantum chemical methods to calculate the evaporation rates of electrically charged (both positive and negative) sulfuric acid-ammonia/dimethylamine clusters. To understand how charging will affect the composition of these clusters, we have compared the evaporation rates of charged clusters with those of the corresponding neutral clusters. We found that the only cluster studied in this paper which will retain its composition is H2SO4 · NH3 when charged positively; all other clusters will be altered by both positive and negative charging. In the case of charging clusters negatively, base molecules will completely evaporate from clusters with 1 to 3 sulfuric acid molecules in the case of ammonia, and from clusters with 1 or 2 sulfuric acid molecules in the case of dimethylamine. Larger clusters will maintain some base molecules, but the H2SO4 : base ratio will increase. In the case of positive charging, some of the acid molecules will evaporate, decreasing the H2SO4 : base ratio.

Ortega, I. K.; Olenius, T.; Kupiainen-Määttä, O.; Loukonen, V.; Kurtén, T.; Vehkamäki, H.

2014-01-01

278

Nanoscale charge localization induced by random orientations of organic molecules in hybrid perovskite CH3NH3PbI3.  

PubMed

Perovskite-based solar cells have achieved high solar-energy conversion efficiencies and attracted wide attentions nowadays. Despite the rapid progress in solar-cell devices, many fundamental issues of the hybrid perovskites have not been fully understood. Experimentally, it is well-known that in CH3NH3PbI3 the organic molecules CH3NH3 are randomly orientated at the room temperature, but the impact of the random molecular orientation has not been investigated. Because of the dipole moment of the organic molecule, the random orientation creates a novel system with long-range potential fluctuations unlike alloys or other conventional disordered systems. Using linear scaling ab initio methods, we find that the charge densities of the conduction band minimum and the valence band maximum are localized in nanoscales due to the potential fluctuations. The charge localization causes electron-hole separation and reduces carrier recombination rates, which may contribute to the long carrier lifetime observed in experiments. PMID:25493911

Ma, Jie; Wang, Lin-Wang

2015-01-14

279

High brilliance negative ion and neutral beam source  

DOEpatents

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.

Compton, Robert N. (Oak Ridge, TN)

1991-01-01

280

Negatively Charged Metal Oxide Nanoparticles Interact with the 20S Proteasome and Differentially Modulate Its Biologic Functional Effects  

PubMed Central

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

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

281

A negatively charged residue in place of histone H3K56 supports chromatin assembly factor association but not genotoxic stress resistance.  

PubMed

In fungal species, lysine 56 of newly synthesized histone H3 molecules is modified by the acetyltransferase Rtt109, which promotes resistance to genotoxic agents. To further explore how H3 K56ac contributes to genome stability, we conducted screens for suppressors of the DNA damage sensitivity of budding yeast rtt109 Delta mutants. We recovered a single extragenic suppressor mutation that efficiently restored damage resistance. The suppressor is a point mutation in the histone H3 gene HHT2, and converts lysine 56 to glutamic acid. In some ways, K56E mimics K56ac, because it suppresses other mutations that interfere with the production of H3 K56ac and restores histone binding to chromatin assembly proteins CAF-1 and Rtt106. Therefore, we demonstrate that enhanced association with chromatin assembly factors can be accomplished not only by acetylation-mediated charge neutralization of H3K56 but also by the replacement of the positively charged lysine with an acidic residue. These data suggest that removal of the positive charge on lysine 56 is the functionally important consequence of H3K56 acetylation. Additionally, the suppressive function of K56E requires the presence of a second H3 allele, because K56E impairs growth when it is the sole source of histones, even more so than does constitutive H3K56 acetylation. Our studies therefore emphasize how H3 K56ac not only promotes chromatin assembly but also leads to chromosomal malfunction if not removed following histone deposition. PMID:19796999

Erkmann, Judith A; Kaufman, Paul D

2009-12-01

282

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)

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.

Leventis, Nicholas; Yang, Jinua; Fabrizio,Even F.; Rawashdeh, Abdel-Monem M.; Oh, Woon Su; Sotiriou-Leventis, Chariklia

2004-01-01

283

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

SciTech Connect

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.

Rébola, Alejandro; Fong, Dillon D.; Eastman, Jeffrey A.; Ö?üt, Serdar; Zapol, Peter

2013-06-01

284

Transverse momentum of ionized atoms and diatomic molecules acquired in collisions with fast highly charged heavy ions  

NASA Astrophysics Data System (ADS)

Using a recoil-ion momentum spectrometer (RIMS), transverse momenta (q?) of recoil atomic and molecular ions emerging from collisions between 2.5-MeV/u Xe34+ projectiles and neutral Ne, Ar, CO, N2, and O2 gases were measured as a function of the degree of target ionization. For the molecular targets the resulting distributions of q? corresponding to different dissociation channels were separated. Measurements with all the targets were performed under virtually identical conditions so that the results could be directly compared in detail. It was found that the shapes of the q? distributions are characterized by single asymmetric peaks and that, at least in the vicinity of their maximum values, they are well described by Weibull functions. Except for the Ar target, the velocities corresponding to the maxima of the q? distributions were found to follow (within the uncertainties of the results) a universal function of the target charge-to-mass number ratio for values up to 0.33. For larger charge-to-mass number ratios the results for the molecular targets appear to remain universal, but are slightly lower than the results for the Ne target. A more elaborate scaling was required to obtain a universal function that describes the low-charge-state results for Ne and Ar targets in a similar way. For different dissociation channels of the same parent molecular ion with charge states exceeding 6+, significant differences were found between the measured q? distributions. These differences were ascribed to increases in the ionization potential and to more prominent contributions from target-to-projectile electron transfer for the more asymmetric dissociation channels. For symmetric and nearly symmetric molecular dissociation channels the fragments with combined charge number Q exceeding 9 for N2 and 10 for O2 were found to be distributed with a reduced probability at angles close to 90° relative to the beam direction. The magnitude of this effect was found to depend on the number of electrons removed in addition to one half of the number of available electrons (Q-Z). On the other hand, for highly asymmetric dissociation channels the angular distributions seem to indicate that the fragments of highly charged molecular ions may be distributed with an enhanced probability at angles close to 90° relative to the beam direction. A slight dependence of the q? distribution on molecular orientation was found to be present for the symmetric and nearly symmetric dissociation channels having Q-Z?0. The magnitude of this effect also seems to be determined by the value of Q-Z.

Horvat, V.; Watson, R. L.

2013-08-01

285

A Simultaneous Solution to the ^6Li and ^7Li Big Bang Nucleosynthesis Problems from a Long-Lived Negatively-Charged Leptonic Particle  

E-print Network

The $^6$Li abundance observed in metal poor halo stars exhibits a plateau similar to that for $^7$Li suggesting a primordial origin. However, the observed abundance of $^6$Li is a factor of $10^3$ larger and that of $^7$Li is a factor of 3 lower than the abundances predicted in the standard big bang when the baryon-to-photon ratio is fixed by WMAP. Here we show that both of these abundance anomalies can be explained by the existence of a long-lived massive, negatively-charged leptonic particle during nucleosynthesis. Such particles would capture onto the synthesized nuclei thereby reducing the reaction Coulomb barriers and opening new transfer reaction possibilities, and catalyzing a second round of big bang nucleosynthesis. This novel solution to both of the Li problems can be achieved with or without the additional effects of stellar destruction.

Motohiko Kusakabe; Toshitaka Kajino; Richard N. Boyd; Takashi Yoshida; Grant J. Mathews

2007-11-24

286

Big-Bang Nucleosynthesis with Negatively-Charged Massive Particles as a Cosmological Solution to the {sup 6}Li and {sup 7}Li Problems  

SciTech Connect

Observations of metal poor halo stars exhibit a possible plateau of {sup 6}Li abundance as a function of metallicity similar to that for {sup 7}Li, suggesting a big bang origin. However, the inferred primordial abundance of {sup 6}Li is {approx}1000 times larger than that predicted by standard big bang nucleosynthesis (BBN) for the baryon-to-photon ratio inferred from the WMAP data. On the other hand, the inferred {sup 7}Li primordial abundance is about 3 times smaller than the prediction. We study a possible simultaneous solution to both the problems of underproduction of {sup 6}Li and overproduction of {sup 7}Li in BBN. This solution involves a hypothetical massive, negatively-charged leptonic particle that would bind to the light nuclei produced in BBN, but would decay long before it could be detected. Because the particle gets bound to the existing nuclei after the cessation of the usual big bang nuclear reactions, a second longer epoch of nucleosynthesis can occur among X-nuclei which have reduced Coulomb barriers. We numerically carry out a fully dynamical BBN calculation, simultaneously solving the recombination and ionization processes of negatively-charged particles by normal and X-nuclei as well as many possible nuclear reactions among them. We confirm that a reaction in which the hypothetical particle is transferred can occur that greatly enhance the production of {sup 6}Li while a reaction through an atomic excited state of X-nucleus depletes {sup 7}Li. It is confirmed that BBN in the presence of these hypothetical particles, together with or without an event of stellar burning process, can simultaneously solve the two Li abundance problems.

Kusakabe, Motohiko [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Kajino, Toshitaka [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Department of Astronomical Science, Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan); Boyd, Richard N. [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Yoshida, Takashi [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Mathews, Grant J. [Department of Physics and Center for Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States)

2008-05-21

287

Beneficial effects of activated carbon additives on the performance of negative lead-acid battery electrode for high-rate partial-state-of-charge operation  

NASA Astrophysics Data System (ADS)

Experiments are made with negative electrode of 2 V cell and 12 V lead-acid battery doped with typical activated carbon additives. It turns out that the negative electrode containing tens-of-micron-sized carbon particles in NAM exhibits markedly increased HRPSoC cycle life than the one containing carbon particles with much smaller size of several microns or the one containing no activated carbon. The improved performance is mainly attributed to the optimized NAM microstructure and the enhanced electrode reaction kinetics by introducing appropriate activated carbon. The beneficial effects can be briefly summarized from three aspects. First, activated carbon acts as new porous-skeleton builder to increase the porosity and active surface of NAM, and thus facilitates the electrolyte diffusion from surface to inner and provides more sites for crystallization/dissolution of lead sulfate; second, activated carbon plays the role of electrolyte supplier to provide sufficient H2SO4 in the inner of plate when the diffusion of H2SO4 from plate surface cannot keep pace of the electrode reaction; Third, activated carbon acts as capacitive buffer to absorb excess charge current which would otherwise lead to insufficient NAM conversion and hydrogen evolution.

Xiang, Jiayuan; Ding, Ping; Zhang, Hao; Wu, Xianzhang; Chen, Jian; Yang, Yusheng

2013-11-01

288

Charge-transfer processes in collisions of He{sup 2+} ions with H{sub 2}, N{sub 2}, O{sub 2}, CO, and CO{sub 2} molecules below 4 keV/u  

SciTech Connect

Single- and double-charge-transfer cross sections of {sup 3}He{sup 2+} ions in collisions with N{sub 2}, O{sub 2}, CO, and CO{sub 2} molecules have been measured in the energy range of 0.20 to 2.7 keV/u. In addition, the same type of measurements for H{sub 2} molecules has been also carried out again for energies in the range from 0.13 to 0.40 keV/u. For all molecules except for CO{sub 2}, the present single-charge-transfer cross sections are found to be generally larger than, or at least comparable to, double-charge-transfer cross sections in the energy region studied. This is a marked difference in comparison to experimental results reported earlier where a sharp increase for double charge transfer was observed below 0.3 keV/u. The double-charge-transfer cross sections are found to be apparently larger than single-charge-transfer cross sections only for CO{sub 2} molecules at energies below 0.8 keV/u. A theoretical analysis based on a close-coupling method within a molecular representation has also been carried out for H{sub 2} and CO targets to provide some insights.

Kusakabe, Toshio; Miyamoto, Yoshiharu; Kimura, Mineo; Tawara, Hiroyuki [Department of Science, Kinki University, Higashi-osaka, Osaka 577-8502 (Japan); Department of Nuclear Engineering, Kinki University, Higashi-osaka, Osaka 577-8502 (Japan); Graduate School of Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Max Planck Institute fuer Kernphysik, Saupferchechweg 1, D-69029 Heidelberg (Germany)

2006-02-15

289

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  

NASA Astrophysics Data System (ADS)

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.

Ornelas-Lizcano, J. C.; Guirado-López, R. A.

2015-03-01

290

Adapting SAFT-? perturbation theory to site-based molecular dynamics simulation. III. Molecules with partial charges at bulk phases, confined geometries and interfaces  

NASA Astrophysics Data System (ADS)

In Paper I [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 139(23), 234104 (2013)], we showed that how a third-order Weeks-Chandler-Anderson (WCA) Thermodynamic Perturbation Theory and molecular simulation can be integrated to characterize the repulsive and dispersive contributions to the Helmholtz free energy for realistic molecular conformations. To this end, we focused on n-alkanes to develop a theory for fused and soft chains. In Paper II [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 141(2), 024708 (2014)], we adapted the classical Density Functional Theory and studied the microstructure of the realistic molecular fluids in confined geometries and vapor-liquid interfaces. We demonstrated that a detailed consistency between molecular simulation and theory can be achieved for both bulk and inhomogeneous phases. In this paper, we extend the methodology to molecules with partial charges such as carbon dioxide, water, 1-alkanols, nitriles, and ethers. We show that the electrostatic interactions can be captured via an effective association potential in the framework of Statistical Associating Fluid Theory (SAFT). Implementation of the resulting association contribution in assessing the properties of these molecules at confined geometries and interfaces presents satisfactory agreement with molecular simulation and experimental data. For example, the predicted surface tension deviates less than 4% comparing to full potential simulations. Also, the theory, referred to as SAFT-? WCA, is able to reproduce the specific orientation of hydrophilic head and hydrophobic tail of 1-alkanols at the vapor-liquid interface of water.

Ghobadi, Ahmadreza F.; Elliott, J. Richard

2014-09-01

291

A Fixed-Charge Model for Alcohol Polarization in the Condensed Phase, and Its Role in Small Molecule Hydration  

PubMed Central

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

2015-01-01

292

Phase-Transfer Energetics of Small-Molecule Alcohols Across the Water-Hexane Interface: Molecular Dynamics Simulation Using Charge Equilibration Models  

PubMed Central

We study the water-hexane interface using molecular dynamics (MD) and polarizable charge equilibration (CHEQ) force fields. Bulk densities for TIP4P-FQ water and hexane, 1.0086±0.0002 g/cm3 and 0.6378±0.0001 g/cm3, demonstrate excellent agreement with experiment. Interfacial width and interfacial tension are consistent with previously reported values. The in-plane component of the dielectric permittivity (??) for water is shown to decrease from 81.7±0.04 to unity, transitioning longitudinally from bulk water to bulk hexane. ?? for hexane reaches a maximum in the interface, but this term represents only a small contribution to the total dielectric constant (as expected for a non-polar species). Structurally, net orientations of the molecules arise in the interfacial region such that hexane lies slightly parallel to the interface and water reorients to maximize hydrogen bonding. Interfacial potentials due to contributions of the water and hexane are calculated to be -567.9±0.13mV and 198.7±0.01mV, respectively, giving rise to a total potential in agreement with the range of values reported from previous simulations of similar systems. Potentials of mean force (PMF) calculated for methanol, ethanol, and 1-propanol for the transfer from water to hexane indicate an interfacial free energy minimum, corresponding to the amphiphilic nature of the molecules. The magnitudes of transfer free energies were further characterized from the solvation free energies of alcohols in water and hexane using thermodynamic integration. This analysis shows that solvation free energies for alcohols in hexane are 0.2-0.3 kcal/mol too unfavorable, whereas solvation of alcohols in water is approximately 1 kcal/mol too favorable. For the pure hexane-water interfacial simulations, we observe a monotonic decrease of the water dipole moment to near-vacuum values. This suggests that the electrostatic component of the desolvation free energy is not as severe for polarizable models than for fixed-charge force fields. The implications of such behavior pertain to the modeling of polar and charged solutes in lipidic environments. PMID:21414823

Bauer, Brad A.; Zhong, Yang; Meninger, David J.; Davis, Joseph E.; Patel, Sandeep

2010-01-01

293

Evidence for excited state intramolecular charge transfer reaction in donor–acceptor molecule 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester: Experimental and quantum chemical approach  

Microsoft Academic Search

Intramolecular charge transfer (ICT) reaction has been investigated in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) using spectroscopic techniques. The molecule DPDAME shows local emission in non-polar solvent and dual emission in polar solvents. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the charge transfer character of the excited state. Quantum chemical calculations have been performed at Hartree–Fock (HF) and

Bijan Kumar Paul; Anuva Samanta; Samiran Kar; Nikhil Guchhait

2010-01-01

294

Predicting the stability of atom-like and molecule-like unit-charge Coulomb three-particle systems.  

PubMed

Non-relativistic quantum chemical calculations of the particle mass, m±2, corresponding to the dissociation threshold in a range of Coulomb three-particle systems of the form m±1m±2m±3, 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. PMID:25084894

King, Andrew W; Herlihy, Patrick E; Cox, Hazel

2014-07-28

295

Ion internal energy distributions validate the charge residue model for small molecule ion formation by spray methods.  

PubMed

This paper reports a detailed study of the internal energy distribution of ions formed by four electrospray ionization (ESI)-related ionization methods, with particular emphasis on electrosonic spray ionization (ESSI). Substituted benzylpyridinium ions were used as thermometer ions to probe the internal energy distribution. The influence of different instrumental parameters was studied. Cone and skimmer voltages as well as the collision energy were found to strongly affect the ion internal energy distribution, whereas the distance between the emitter and the inlet of the mass spectrometer, the nebulizing gas pressure or the flow rate showed no influence. The internal energy distribution obtained with an ESSI source was compared with those obtained for electrospray (ESI), nanoelectrospray (nanoESI) and sonic spray ionization (SSI) on the same mass spectrometer with the same instrumental parameters. No clear differences were observed. As the charge residue model is the only ion formation mechanism possible for SSI, we conclude that benzylpyridinium ions are formed by the pathway suggested by this model. PMID:18327854

Touboul, David; Jecklin, Matthias Conradin; Zenobi, Renato

2008-04-01

296

Effects of graphene coating and charge injection on water adsorption of solid surfaces  

NASA Astrophysics Data System (ADS)

The adhesion and cohesion of water molecules on graphene-coated and bare copper and mica substrates under charge injection have been extensively studied by first-principles calculations. Water adsorption on graphene-coated copper surface is weakened by injecting negative charges into the substrate, while enhanced by positive charges. Both negatively and positively charge injecting on graphene-coated mica strengthen the adsorption between water and the surface. While the adhesive and cohesive energies of water adsorption on charged bare copper and mica exhibit similar trends and much stronger response to charge injection. The charge sensitivity of water adsorbing on positively charged surfaces is significantly weakened by the graphene coating layer, mainly due to lower interfacial charge exchange. Our results suggest a viable way to modify water adsorption on a graphene-coated surface and unveil the role of graphene as a passivation layer for the wetting of a charged substrate.The adhesion and cohesion of water molecules on graphene-coated and bare copper and mica substrates under charge injection have been extensively studied by first-principles calculations. Water adsorption on graphene-coated copper surface is weakened by injecting negative charges into the substrate, while enhanced by positive charges. Both negatively and positively charge injecting on graphene-coated mica strengthen the adsorption between water and the surface. While the adhesive and cohesive energies of water adsorption on charged bare copper and mica exhibit similar trends and much stronger response to charge injection. The charge sensitivity of water adsorbing on positively charged surfaces is significantly weakened by the graphene coating layer, mainly due to lower interfacial charge exchange. Our results suggest a viable way to modify water adsorption on a graphene-coated surface and unveil the role of graphene as a passivation layer for the wetting of a charged substrate. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02867d

Guo, Yufeng; Guo, Wanlin

2013-10-01

297

Atmospheric reactions on electrically charged surfaces.  

PubMed

It is proposed that tropospheric NO2 at concentrations in the parts-per-billion range can be efficiently converted to HONO in a dust storm, by a process that is initiated by electron capture by NO2 from a negatively-charged dust particle. The electron capture is visualized as a harpoon-type process that does not require the NO2 to be adsorbed on the particle. The resulting electronically excited [NO2(-)]* ion reacts with water to form an HONO molecule plus an OH(-)·(H2O)n cluster ion. It is suggested that analogous processes can occur on other atmospheric aerosol particles with both positive and negative charges, with other molecules of high electron affinity such as SO2, and also, because the earth's surface is effectively the negative plate of a planet-sized capacitor, at the surfaces of terrestrial solids, lakes and oceans. PMID:23689618

Phillips, Leon F

2013-07-14

298

Measurement of negatively charged pion spectra in inelastic p+p interactions at $p_{lab}$ = 20, 31, 40, 80 and 158 GeV/c  

E-print Network

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 ($\\sqrt{s} = $ 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.

NA61/SHINE Collaboration; :; N. Abgrall; A. Aduszkiewicz; Y. Ali; T. Anticic; N. Antoniou; B. Baatar; F. Bay; A. Blondel; J. Blumer; M. Bogomilov; A. Bravar; J. Brzychczyk; S. A. Bunyatov; O. Busygina; P. Christakoglou; T. Czopowicz; N. Davis; S. Debieux; H. Dembinski; F. Diakonos; S. Di Luise; W. Dominik; T. Drozhzhova; J. Dumarchez; K. Dynowski; R. Engel; A. Ereditato; G. A. Feofilov; Z. Fodor; A. Fulop; M. Ga?dzicki; M. Golubeva; K. Grebieszkow; A. Grzeszczuk; F. Guber; A. Haesler; T. Hasegawa; M. Hierholzer; R. Idczak; S. Igolkin; A. Ivashkin; D. Jokovi?; K. Kadija; A. Kapoyannis; E. Kaptur; D. Kie?czewska; M. Kirejczyk; J. Kisiel; T. Kiss; S. Kleinfelder; T. Kobayashi; V. I. Kolesnikov; D. Kolev; V. P. Kondratiev; A. Korzenev; P. Kovesarki; S. Kowalski; A. Krasnoperov; A. Kurepin; D. Larsen; A. László; V. V. Lyubushkin; M. Ma?kowiak-Paw?owska; Z. Majka; B. Maksiak; A. I. Malakhov; D. Mani?; A. Marcinek; V. Marin; K. Marton; H. -J. Mathes; T. Matulewicz; V. Matveev; G. L. Melkumov; St. Mrówczy?ski; S. Murphy; T. Nakadaira; M. Nirkko; K. Nishikawa; T. Palczewski; G. Palla; A. D. Panagiotou; T. Paul; C. Pistillo; W. Peryt; O. Petukhov; R. P?aneta; J. Pluta; B. A. Popov; M. Posiada?a; S. Pu?awski; J. Puzovi?; W. Rauch; M. Ravonel; A. Redij; R. Renfordt; A. Robert; D. Röhrich; E. Rondio; M. Roth; A. Rubbia; A. Rustamov; M. Rybczynski; A. Sadovsky; K. Sakashita; M. Savi?; K. Schmidt; T. Sekiguchi; P. Seyboth; D. Sgalaberna; M. Shibata; R. Sipos; E. Skrzypczak; M. S?odkowski; P. Staszel; G. Stefanek; J. Stepaniak; H. Ströbele; T. Šuša; M. Szuba; M. Tada; V. Tereshchenko; T. Tolyhi; R. Tsenov; L. Turko; R. Ulrich; M. Unger; M. Vassiliou; D. Veberi?; V. V. Vechernin; G. Vesztergombi; L. Vinogradov; A. Wilczek; Z. W?odarczyk; A. Wojtaszek-Szwarc; O. Wyszy?ski; L. Zambelli; W. Zipper

2014-02-26

299

Crossing behavior of the singlet and triplet State of the negatively charged magneto-exciton in a GaAs/AlGaAs quantum well  

SciTech Connect

Polarized magneto-photoluminescence (MPL) measurements on a high mobility {delta}-doped GaAs/AlGaAs single quantum well from 0--60 T at temperatures between 0.37--2.1 K are reported. In addition to the neutral heavy hole magneto-exciton (X{sup 0}), the singlet (X {sub s}{sup {minus}}) and triplet (X {sub t}{sup {minus}}) states of the negatively charged magneto-exciton are observed in both polarizations. The energy dispersive and time-resolved MPL data suggest that their development is fundamentally related to the formation of the neutral magneto-exciton. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher energy subbands in their energetic evolution, confirming theoretical predictions. The authors also observed the formation of two higher energy peaks. One of them is completely right circularly polarized and its appearance can be considered a result of the electron-hole exchange interaction enhancement with an associated electron g-factor of 3.7 times the bulk value. The other peak completely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previous anomalies observed in the integer and fractional quantum Hall regimes.

MUNTEANU,F.M.; KIM,YONGMIN; PERRY,C.H.; RICKEL,D.G.; SIMMONS,JERRY A.; RENO,JOHN L.

2000-01-27

300

Impact of negatively charged patches on the surface of MHC class II antigen-presenting proteins on risk of chronic beryllium disease.  

PubMed

Chronic beryllium disease (CBD) is a granulomatous lung disease that occurs primarily in workers who are exposed to beryllium dust or fumes. Although exposure to beryllium is a necessary factor in the pathobiology of CBD, alleles that code for a glutamic acid residue at the 69th position of the HLA-DPbeta1 gene have previously been found to be associated with CBD. To date, 43 HLA-DPbeta1 alleles that code for glutamic acid 69 (E69) have been described. Whether all of these E69 coding alleles convey equal risk of CBD is unknown. The present study demonstrates that, on the one hand, E69 alleloforms of major histocompatibility complex class II antigen-presenting proteins with the greatest negative surface charge convey the highest risk of CBD, and on the other hand, irrespective of allele, they convey equal risk of beryllium sensitization (BeS). In addition, the data suggest that the same alleles that cause the greatest risk of CBD are also important for the progression from BeS to CBD. Alleles convey the highest risk code for E26 in a constant region and for E69, aspartic acid 55 (D55), E56, D84 and E85 in hypervariable regions of the HLA-DPbeta1 chain. Together with the calculated high binding affinities for beryllium, these results suggest that an adverse immune response, leading to CBD, is triggered by chemically specific metal-protein interactions. PMID:17956852

Snyder, James A; Demchuk, Eugene; McCanlies, Erin C; Schuler, Christine R; Kreiss, Kathleen; Andrew, Michael E; Frye, Bonnie L; Ensey, James S; Stanton, Marcia L; Weston, Ainsley

2008-07-01

301

[Fusion of negatively-charged liposomes under the effect of peptides from the N-terminal fragment of the HIV-1 transmembrane protein].  

PubMed

The effect of a series of synthetic peptides mimicking the N-terminus of HIV transmembrane glycoprotein (gp41) on fusion of negatively charged liposomes consisting of phosphatidylcholine, phosphatidylethanolamine and cardiolipin at a 2:3:5 molar ratio, respectively, has been studied. Peptides P514 and P385 (residue 517-538), lysine and arginine at the C-terminus, respectively, with the amino acid sequence completely corresponding to the N-terminus of gp41 displayed the highest fusogenic activity. The extent of fusion was significantly increased at mild acidic pH (6.0). Acidification particularly influenced the fusogenic activity of P514. Modification of the N- and C-termini of fusion-active peptides by proteins and synthetic polymers blocked the fusion activity. The fusogenic properties of peptides depended on the chain length: P411 consisting of nine hydrophobic amino acid residues had no fusogenic activity, while P415, an 11-member peptide, effectively fused liposomes. The fluorescent probe ANS was used to monitor the hydrophobicity of these peptides. The hydrophobicity of P514 increased appreciably with a change in pH from 6.0 to 7.5. Peptides P514 and P385 induced the leakage of the aqueous contents from liposomes at neutral pH and caused a small, but detectable leakage at acidic pH. Structural and molecular factors influencing the peptide-induced liposome fusion are discussed. PMID:8555367

Terletskaia, Ia T; Trikash, I O; Serdiuk, E S; Andreev, S M

1995-10-01

302

Electrical charging changes the composition of sulfuric acid-ammonia/dimethylamine clusters  

NASA Astrophysics Data System (ADS)

Sulfuric acid clusters stabilized by base molecules are likely to have a significant role in atmospheric new-particle formation. Recent advances in mass spectrometry techniques have permitted the detection of electrically charged clusters. However, direct measurement of electrically neutral clusters is not possible. Mass spectrometry instruments can be combined with a charger, but the possible effect of charging on the composition of neutral clusters must be addressed in order to interpret and understand the measured data. In the present work we have used formation free energies from quantum chemical methods to calculate the evaporation rates of electrically charged (both positive and negative) sulfuric acid-ammonia/dimethylamine clusters. To understand how charging will affect the composition of electrically neutral clusters, we have compared the evaporation rates of the most stable neutral clusters with those of the corresponding charged clusters. Based on the evaporation rates of different molecules from the charged clusters, we determined the most likely resulting cluster composition when a stable neutral cluster is charged and the molecules with the highest evaporation rates are lost from it. We found that all of the most stable neutral clusters will be altered by both positive and negative charging. In the case of charging clusters negatively, base molecules will completely evaporate from clusters with 1 to 3 sulfuric acid molecules in the case of ammonia, and from clusters with 1 or 2 sulfuric acid molecules in the case of dimethylamine. Larger clusters will maintain some base molecules, but the H2SO4 : base ratio will increase. In the case of positive charging, some of the acid molecules will evaporate, decreasing the H2SO4 : base ratio.

Ortega, I. K.; Olenius, T.; Kupiainen-Määttä, O.; Loukonen, V.; Kurtén, T.; Vehkamäki, H.

2014-08-01

303

Influence of negatively charged plume grains and hemisphere coupling currents on the structure of Enceladus' Alfvén wings: Analytical modeling of Cassini magnetometer observations  

NASA Astrophysics Data System (ADS)

We present an analytical model of the Alfvén wing system that is generated by the interaction between the plume of Enceladus and the corotating plasma in Saturn's inner magnetosphere. Our primary purpose is to explain the orientation of the magnetic field perturbations detected in Enceladus' Alfvén wings by the Cassini magnetometer (MAG) instrument. Observational data from numerous close Enceladus flybys show both the Bx and By components (in Enceladus interaction coordinates: Bx, along corotation direction; By, toward or away from Saturn) in the center of the northern wing tube to possess a negative sign, whereas the opposite case of Bx and By being positive was observed within the southern wing. So far, none of the available models of Enceladus' magnetospheric interaction is able to reproduce this correlation between the directions of Bx and By. On the basis of the analytical calculations of Neubauer (1980, 1998) and Saur et al. (1999, 2007), we demonstrate that the observed orientation of the magnetic field may arise from the presence of negatively charged dust grains in the plume of Enceladus, serving as a sink for “free” magnetospheric electrons. Although the current carried by these particles does not make a noteworthy contribution to the magnetic field distortions in the interaction region, the negative charge accumulated by them needs to be accounted for in the quasi-neutrality condition of the plasma. The depletion of magnetospheric electrons within the plume is therefore far from causing only some localized perturbations of the magnetic field, but it drastically alters the nature of the interaction: we show that this process yields a reversal in the sign of the Hall conductivity, thereby giving rise to the observed field signatures. By applying a modified version of the Alfvén wing model developed by Saur et al. (2007), we demonstrate that the magnetic field observations from Cassini's targeted Enceladus flybys can be understood by taking into account the influence of electron-absorbing dust grains. In contrast to what is claimed in recent literature, we therefore propose that magnetic field observations near Enceladus can be completely understood in terms of a local interaction model, i.e., that it is not necessary to consider the large-scale dynamics of the flux tubes in Saturn's magnetosphere. In addition, we provide first in situ evidence that the hemisphere coupling current system predicted by Saur et al. (2007) and the associated magnetic field discontinuities are indeed present at Enceladus. The field perturbations caused by these hemisphere coupling currents arise from the partial blockage of the Alfvén wing at the nonconducting icy crust of Enceladus. This effect needs to be taken into account when interpreting Cassini MAG data from flybys that intersected the Enceladus flux tube and can only be reproduced by models that apply adequate boundary conditions to the surface of the icy moon.

Simon, Sven; Saur, Joachim; Kriegel, Hendrik; Neubauer, Fritz M.; Motschmann, Uwe; Dougherty, Michele K.

2011-04-01

304

Study of electrochemically active carbon, Ga2O3 and Bi2O3 as negative additives for valve-regulated lead-acid batteries working under high-rate, partial-state-of-charge conditions  

NASA Astrophysics Data System (ADS)

Electrochemically active carbon (EAC), Gallium (III) oxide (Ga2O3) and Bismuth (III) oxide (Bi2O3) are used as the negative additives of valve-regulated lead-acid (VRLA) batteries to prolong the cycle life of VRLA batteries under high-rate partial-state-of-charge (HRPSoC) conditions, and their effects on the cycle life of VRLA batteries are investigated. It is found that the addition of EAC in negative active material can restrain the sulfation of the negative plates and prolong the cycle performance of VRLA batteries under HRPSoC conditions. It is also observed that the addition of Ga2O3 or Bi2O3 in EAC can effectively increase the overpotential of hydrogen evolution on EAC electrodes, and decrease the evolution rate of hydrogen. An appropriate addition amount of Ga2O3 or Bi2O3 in the negative plates of VRLA batteries can decrease the cut-off charging voltage, increase the cut-off discharging voltage, and prolong the cycle life of VRLA batteries under HRPSoC conditions. The battery added with 0.5% EAC and 0.01% Ga2O3 in negative active material shows a lowest cut-off charging voltage and a highest cut-off discharging voltage under HRPSoC conditions, and its' cycle life reaches about 8100 cycles which is at least three times longer than that without Ga2O3.

Zhao, Li; Chen, Baishuang; Wu, Jinzhu; Wang, Dianlong

2014-02-01

305

Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering  

NASA Astrophysics Data System (ADS)

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).

Wodtke, Alec M.

2013-06-01

306

Adapting SAFT-? perturbation theory to site-based molecular dynamics simulation. III. Molecules with partial charges at bulk phases, confined geometries and interfaces.  

PubMed

In Paper I [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 139(23), 234104 (2013)], we showed that how a third-order Weeks-Chandler-Anderson (WCA) Thermodynamic Perturbation Theory and molecular simulation can be integrated to characterize the repulsive and dispersive contributions to the Helmholtz free energy for realistic molecular conformations. To this end, we focused on n-alkanes to develop a theory for fused and soft chains. In Paper II [A. F. Ghobadi and J. R. Elliott, J. Chem. Phys. 141(2), 024708 (2014)], we adapted the classical Density Functional Theory and studied the microstructure of the realistic molecular fluids in confined geometries and vapor-liquid interfaces. We demonstrated that a detailed consistency between molecular simulation and theory can be achieved for both bulk and inhomogeneous phases. In this paper, we extend the methodology to molecules with partial charges such as carbon dioxide, water, 1-alkanols, nitriles, and ethers. We show that the electrostatic interactions can be captured via an effective association potential in the framework of Statistical Associating Fluid Theory (SAFT). Implementation of the resulting association contribution in assessing the properties of these molecules at confined geometries and interfaces presents satisfactory agreement with molecular simulation and experimental data. For example, the predicted surface tension deviates less than 4% comparing to full potential simulations. Also, the theory, referred to as SAFT-? WCA, is able to reproduce the specific orientation of hydrophilic head and hydrophobic tail of 1-alkanols at the vapor-liquid interface of water. PMID:25194387

Ghobadi, Ahmadreza F; Elliott, J Richard

2014-09-01

307

On negative inertial defect  

Microsoft Academic Search

Morino's general formula for inertial defect has been applied to planar molecules with very low out-of-plane vibrations in order to explain negative inertial defects reported for such molecules. The obtained simple formula is combined with an empirical proportionality relation between zero point inertial defect ?0 and ?Icc for ordinary molecules to give semi-empirical relations between the inertial defect ?0, the

Takeshi Oka

1995-01-01

308

A Dominant-negative Clathrin Mutant Differentially Affects Trafficking of Molecules with Distinct Sorting Motifs in the Class II Major Histocompatibility Complex (MHC) Pathway  

Microsoft Academic Search

The role of clathrin in intracellular sorting was investigated by expression of a dominant-negative mutant form of clathrin, termed the hub fragment. Hub inhibition of clathrin-mediated membrane transport was established by demonstrating a block of transferrin internalization and an alteration in the intracellular dis- tribution of the cation-independent mannose-6-phos- phate receptor. Hubs had no effect on uptake of FITC- dextran,

Shu-Hui Liu; Michael S. Marks; Frances M. Brodsky

1998-01-01

309

A small radius hydrogen discharge: An effective source of volume produced negative ions  

Microsoft Academic Search

Free-fall regime maintenance of hydrogen discharges is analyzed based on numerical solutions of a set of equations involving the balance equations of the charged particles [electrons, the three types of the positive ions (H+, H2+, and H3+), and negative H- ions] and of the neutral species (hydrogen atoms H and vibrationally excited molecules), the momentum equations of the positive ions,

Ts. Paunska; A. Shivarova; Kh. Tarnev

2010-01-01

310

Observed suppression of room temperature negative differential resistance in organic monolayers on Si(100)  

NASA Astrophysics Data System (ADS)

The ultrahigh vacuum scanning tunnelling microscope was used to probe charge transport through two different organic monolayers adsorbed on the Si(100) substrate at room temperature. I-V measurements were taken on monolayers of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and cyclopentene for degenerately doped n-type and p-type substrates. Initial I-V measurements for transport through the TEMPO monolayer exhibited a suppression of negative differential resistance (NDR) relative to previously reported charge transport through isolated molecules. I-V measurements were also performed on isolated cyclopentene molecules and cyclopentene monolayers. Similarly to TEMPO monolayers, the cyclopentene monolayers exhibited attenuated NDR behaviour relative to isolated molecules. The observed NDR suppression suggests that the high packing density of organic monolayers influences charge transport through molecule-semiconductor junctions.

Guisinger, N. P.; Basu, R.; Greene, M. E.; Baluch, A. S.; Hersam, M. C.

2004-07-01

311

Hydrolytic cleavage of an RNA-model phosphodiester catalyzed by a highly negatively charged polyoxomolybdate [Mo7O24]6- cluster.  

PubMed

Hydrolysis of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNP), a commonly used RNA model substrate, was examined in molybdate solutions by means of (1)H, (31)P, and (95)Mo NMR, Raman, and Mo K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. (1)H and (31)P NMR spectroscopy indicate that at 50 degrees C and pD 5.9 the cleavage of the phosphodiester bond in HPNP proceeds with a rate constant of 6.62 x 10(-6) s(-1), giving a cyclic phosphate ester and p-nitrophenol as the only products of hydrolysis. The NMR spectra did not show evidence of any paramagnetic species, excluding the possibility of Mo(VI) reduction to Mo(V), and indicating that the cleavage of the phosphodiester bond is purely hydrolytic. The Mo K-edge XANES region also did not show any sign of Mo(VI) to Mo(V) reduction during the hydrolytic reaction. The pD dependence of k(obs) exhibits a bell-shaped profile, with the fastest cleavage observed at pD 5.9. Comparison of the rate profile with the concentration profile of polyoxomolybdates shows a striking overlap of the k(obs) profile with the concentration of heptamolybdate, suggesting that the highly negatively charged [Mo(7)O(24)](6-) is the hydrolytically active species. Kinetic experiments at pD 5.9 using a fixed amount of [Mo(7)O(24)](6-) and increasing amounts of HPNP revealed slight signs of curvature at 25 molar excess of HPNP. The data fit the general Michaelis-Menten reaction scheme, permitting the calculation of the catalytic rate constant k(2) (3.02 x 10(-4) s(-1)) and K(m) (1.06 M). Variable temperature (31)P NMR spectra of a reaction mixture revealed broadening of the HPNP (31)P resonance upon increase of temperature, implying the dynamic exchange process between free and bound HPNP at higher temperatures. Addition of salts resulted in the inhibition of HPNP hydrolysis, as well as addition of dimethyl phosphate, suggesting competition for the binding to [Mo(7)O(24)](6-). The hydrolysis of 10 equiv of HPNP could be achieved in the presence of 1 equiv of [Mo(7)O(24)](6-), and the multiple turnovers demonstrate that the reaction is catalytic. (31)P NMR and Mo K-edge EXAFS spectra measured during different stages of the hydrolysis indicated that under catalytic conditions a partial conversion of [Mo(7)O(24)](6-) into [P(2)Mo(5)O(23)](6-) occurs. PMID:19053457

Absillis, Gregory; Cartuyvels, Els; Van Deun, Rik; Parac-Vogt, Tatjana N

2008-12-24

312

Proposal for high-speed and high-fidelity electron-spin initialization in a negatively charged quantum dot coupled to a microcavity in a weak external magnetic field  

SciTech Connect

We describe a proposal for fast electron-spin initialization in a negatively charged quantum dot coupled to a microcavity without the need for a strong magnetic field. We employ two-photon excitation to access trion states that are spin forbidden by one-photon excitation. Our simulation shows a maximum initialization speed of 1.3 GHz and maximum fidelity of 99.7% with realistic system parameters.

Majumdar, Arka; Lin Ziliang; Faraon, Andrei; Vuckovic, Jelena [E. L. Ginzton Laboratory, Stanford University, Stanford, California 94305 (United States)

2010-08-15

313

Isotope effect in charge-transfer collisions of slow H{sup +} and D{sup +} ions with H{sub 2}, HD, and D{sub 2} molecules  

SciTech Connect

Marked characteristics in charge-transfer cross sections between collisions of H{sup +} and D{sup +} ions with H{sub 2}, HD, and D{sub 2} molecules, the so-called isotope effect, are observed in the energy range from 0.18 to 1.0 keV/u. The observed cross-section ratios {sigma}(D{sup +}+D{sub 2})/{sigma}(H{sup +}+H{sub 2}) of charge transfer in D{sup +}+D{sub 2} and in H{sup +}+H{sub 2} collisions are found to be 0.665 at 0.18 keV/u and gradually increases, finally approaching unity at higher energies. Similar behavior and magnitude within the error bars of the cross-section ratios {sigma}(H{sup +}+HD)/{sigma}(H{sup +}+H{sub 2}) and {sigma}(D{sup +}+HD)/{sigma}(H{sup +}+H{sub 2}) have been observed, although the present calculation predicts a sizable difference for heteronuclear molecules. The cross section differences due to the target isotope effect are pronounced even in the high-eV to low-keV region. On the other hand, charge-transfer cross-section ratios for the same target but different projectile isotopes, e.g., {sigma}(H{sup +}+HD)/{sigma}(D{sup +}+HD) and {sigma}(D{sup +}+D{sub 2})/{sigma}(H{sup +}+D{sub 2}), are constant near unity, which indicates a minor role of collision-induced vibrations as compared to the target vibrational spacing. It is understood that the isotope effect in the charge transfer of ion-molecule collisions originates from the combination of a small offset in binding and vibrational energies and the different spaces occupied by the wave functions of the target H{sub 2}, HD, and D{sub 2} molecules.

Kusakabe, Toshio; Pichl, Lukas; Buenker, Robert J.; Kimura, Mineo; Tawara, Hiroyuki [Department of Science, Kinki University, Higashi-Osaka, Osaka, 577-8502 (Japan); Foundation of Computer Science Laboratory, University of Aizu, Ikki, Aizu-Wakamatsu, 965-8580 (Japan); Theoretische Chemie, Bergische Universitaet Wuppertal, D-42097 Wuppertal (Germany); Graduate School of Sciences, Kyushu University, Hakozaki, Fukuoka 812-8581 (Japan); Department of Pure and Applied Physics, The Queen's University, Belfast BT7 1NN, United Kingdom, and Max Planck Institute for Nuclear Physics, Saupfercheckweg 1, Heidelberg D-69117 (Germany)

2004-11-01

314

Relation between surface properties, pore structure and first-cycle charge loss of graphite as negative electrode in lithium-ion batteries  

Microsoft Academic Search

Cycling of graphite in lithium-ion batteries is reversible except for the first-cycle, where some charge is “lost” due to irreversible side reactions. The irreversible charge loss of different TIMREX® graphites was found to be a linear function, both of their specific BET surface areas and of the double-layer capacitance of electrodes manufactured from these graphites. Nitrogen-adsorption measurements and differential-porosity calculations

Felix Joho; Beat Rykart; Andreas Blome; Petr Novák; Henri Wilhelm; Michael E. Spahr

2001-01-01

315

Charge Challenge  

NSDL National Science Digital Library

In this activity, learners explore how objects can have positive, negative, or neutral charges, which attract, repel and move between objects. Learners charge various materials and observe their interactions. Winter is an ideal time to perform these experiments (because there is less water vapor in the air); if it is humid, use a hair dryer to dry the objects, surfaces, and air around the work area.

2012-06-26

316

Visualizing the Positive-Negative Interface of Molecular Electrostatic Potentials as an Educational Tool for Assigning Chemical Polarity  

ERIC Educational Resources Information Center

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…

Schonborn, Konrad; Host, Gunnar; Palmerius, Karljohan

2010-01-01

317

Vibrational effect on charge-transfer processes in collisions of H{sup +} and O{sup +} ions with C{sub 2}H{sub 4} molecules at energies below 10 keV/u  

SciTech Connect

Charge-transfer processes in collisions of H{sup +} and O{sup +} ions with C{sub 2}H{sub 4} molecules have been studied in joint theoretical and experimental approaches for collision energies below 10 keV/u. Since H and O atoms possess nearly identical ionization potentials, these two ions are expected to share similar dynamics and hence to have similar cross-section values for charge transfer, at least for the energy region above 100 eV. In the present experiments, these cross sections of H{sup +} and O{sup +} ions have been derived by the initial growth rate method in the energy range of 0.20 to 3.6 keV, while the present theoretical study has been carried out for H{sup +} impact only. We have examined the vibrational effect on charge transfer, especially the 'temperature effect' of the initial vibrational states of the C{sub 2}H{sub 4} molecule as well as the final vibrational states of the product C{sub 2}H{sub 4}{sup +} molecular ion. Indeed, a strong influence of the initial vibrational states on charge transfer has been observed since these vibrationally excited initial and final states force the process to be more nearly resonant, thus making charge transfer more efficient. This vibrational effect, and perhaps rotational effect as well, that makes the collision process more nearly resonant has not been well investigated previously, and thus the present study is expected to shed much light on this effect in general.

Kusakabe, Toshio; Gotanda, Kazushi; Kimura, Mineo; Rai, Sachchida N.; Liebermann, Heinz-Peter; Buenker, Robert J. [Department of Science, Kinki University, Higashi-osaka, Osaka 577-8502 (Japan); Graduate School of Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Computer Centre, Bijni Complex, North-Eastern Hill University, Shillong-793003, Meghalaya (India); Fachbereich C-Mathematik und Naturwissenschaften, Bergische Universitaet Wuppertal, D-42119 Wuppertal (Germany)

2007-10-15

318

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)

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.

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

319

A negatively charged residue in place of histone H3K56 supports chromatin assembly factor association but not genotoxic stress resistance  

Microsoft Academic Search

In fungal species, lysine 56 of newly synthesized histone H3 molecules is modified by the acetyltransferase Rtt109, which promotes resistance to genotoxic agents. To further explore how H3 K56ac contributes to genome stability, we conducted screens for suppressors of the DNA damage sensitivity of budding yeast rtt109? mutants. We recovered a single extragenic suppressor mutation that efficiently restored damage resistance.

Judith A. Erkmann; Paul D. Kaufman

2009-01-01

320

Holding Charge  

NSDL National Science Digital Library

In this trick, learners discover how to stick a straw to the palm of their hand, window door, or anywhere using static electricity. This activity introduces learners to negative and positive charges and shows how opposites attract. Note: this trick works best in low humidity (dry air).

Eric Muller

1995-01-01

321

Measurement of the Charge Number Per Adsorbed Molecule and Packing Densities of Self-Assembled Long-Chain Monolayers of Thiols  

E-print Network

and scanning probe microscopy.8,9 ElectrochemicalcharacterizationofSAMscomposedofthiolate- Au linkages the Faraday Law: where F is Faraday's constant. It is widely believed that the value of charge, Q, measured

Dutcher, John

322

Negative tandem mirror  

SciTech Connect

A tandem mirror configuration can be created by combining hot electron end cell plasmas with neutral beam pumping. A region of large negative potential formed in each end cell confines electrons in the central cell. The requirement of charge neutrality causes the central cell potential to become negative with respect to ground in order to confine ions as well as electrons. We discuss the method of producing and calculating the desired axial potential profile, and show the calculated axial potential profile and plasma parameters for a negative configuration of TMX-Upgrade.

Poulsen, P.; Allen, S.L.; Casper, T.A.; Grubb, D.P.; Jong, R.A.; Nexsen, W.E.; Porter, G.D.; Simonen, T.C.

1981-11-30

323

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

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+}.

Beroff, K.; Pino, T.; Carpentier, Y. [Institut des Sciences Moleculaires d'Orsay (ISMO), UMR CNRS 8214, Universite Paris Sud 11, bat.210, F-91405 Orsay Cedex (France); Van-Oanh, N. T. [Laboratoire de Chimie Physique (LCP), UMR CNRS 8000, Universite Paris Sud 11, Bat.349, F-91405 Orsay Cedex (France); Chabot, M.; Tuna, T.; Martinet, G. [Institut de Physique Nucleaire d'Orsay (IPNO), IN2P3- CNRS, Universite Paris Sud 11, F-91406 Orsay Cedex (France); Le Padellec, A. [Institut de Recherche en Astrophysique et Planetologie (IRAP), UMR CNRS 5187, Universite de Toulouse, 9 avenue du Colonel Roche, F-31028 Toulouse Cedex 9 (France); Lavergne, L. [Laboratoire de Physique Nucleaire et de Hautes Energies (LPNHE) UPMC, UPD, CNRS-IN2P3, 4 Place Jussieu, F-75005 Paris (France)

2011-09-15

324

Improvement of charge injection efficiency in organic-inorganic hybrid solar cells by chemical modification of metal oxides with organic molecules  

SciTech Connect

The effect of chemical modification of metal oxide surface with dye molecules in organic-inorganic hybrid solid solar cells was studied by using double layered cells consisting of poly(3-hexylthiophene) (P3HT) and a flat layer of dense TiO{sub 2}. The external quantum efficiency of the chemically modified cell was nearly double that expected from the photosensitizing effect of the dye molecules. The additional increase shows that the chemical modification with dye molecules can serve not only as a photosensitizer but mainly as an energy funnel and/or an electronic mediator to significantly improve the electron injection efficiency from P3HT to TiO{sub 2}.

Kudo, Naomi; Honda, Satoshi; Shimazaki, Yuta; Ohkita, Hideo; Ito, Shinzaburo; Benten, Hiroaki [Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510 (Japan); International Innovation Center, Kyoto University, Katsura, Nishikyo, Kyoto 615-8520 (Japan)

2007-04-30

325

Negative mass  

NASA Astrophysics Data System (ADS)

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.

Hammond, Richard T.

2015-03-01

326

Energetics of adsorption of neutral and charged molecules at the air\\/water interface by second harmonic generation: Hydrophobic and solvation effects  

Microsoft Academic Search

Surface second harmonic generation has been used to study the adsorption of alkyl phenols and anilines and their respective ions to the air\\/water interface. The free energies of adsorption of the neutral molecules were obtained using a simple Langmuir model. The quantitative effects of the opposing hydrophobic and solvations forces on molecular adsorption were investigated by varying the chain length

Alonso Castro; Kankan Bhattacharyya; Kenneth B. Eisenthal

1991-01-01

327

The empirical dependence of radiation-induced charge neutralization on negative bias in dosimeters based on the metal-oxide-semiconductor field-effect transistor  

SciTech Connect

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.

Benson, Chris; Albadri, Abdulrahman; Joyce, Malcolm J.; Price, Robert A. [Engineering Department, Lancaster University, Bailrigg, Lancaster, Lancashire LA1 4YR (United Kingdom); Department of Radiography, School of Allied Health Sciences, City University, Northampton Square, London EC1V 0HB (United Kingdom)

2006-08-15

328

More about Charging Things  

NSDL National Science Digital Library

In the first chapter, you charged things up with excess electrons and saw what could happen as a result. Now we're going to get an idea of how to measure how much charge something has, figure out whether an object is positively or negatively charged, and make up a new concept called the electric field.

William C. Robertson, Ph.D.

2005-01-01

329

Quantum effects in the capture of charged particles by dipolar polarizable symmetric top molecules. II. Interplay between electrostatic and gyroscopic interactions.  

PubMed

Within the general axially nonadiabatic channel approach described in Paper I of this series [M. Auzinsh, E. I. Dashevskaya, I. Litvin, E. E. Nikitin, and J. Troe, J. Chem. Phys. 139, 084311 (2013)], the present article analyzes the simultaneous manifestation of electrostatic and gyroscopic interactions in the quantum capture of dipolar polarizable symmetric top molecules by ions. As a demonstration, the rate coefficients for capture of CH3D and CD3H by H(+), D(+), and H3(+) are calculated. PMID:24116627

Auzinsh, M; Dashevskaya, E I; Litvin, I; Nikitin, E E; Troe, J

2013-10-14

330

Mighty Molecules  

NSDL National Science Digital Library

In this activity, learners use marshmallows and gum drops to construct seven models of molecules. Learners classify (solid, liquid or gas) and draw diagrams of the molecules. Learners can also create a table showing the chemical formula for each molecule and identify a common use for each chemical. Use this activity to introduce learners to molecules, compounds, and bonds.

Carlyn Little

1997-01-01

331

Charge-resonance excitations in symmetric molecules - Comparison of linear response DFT with CC3 for the excited states of a model dimer  

NASA Astrophysics Data System (ADS)

We present a study on the excited states of an ethylene dimer as to investigate the presence of and perturbation from low-lying charge-resonance states calculated by linear response density functional theory (DFT) using the B3LYP and CAM-B3LYP functionals. The calculations are compared to a reference CC3 calculation revealing a better description of the excited states by CAM-B3LYP than that of B3LYP. The ? parameter introduced by Peach et al. [M.J.G. Peach, P. Benfield, T. Helgaker, D.J. Tozer, J. Chem. Phys. 128 (2008) 044118] does not always reveal the problematic charge-resonance states obtained with B3LYP. The generality of the problem is addressed by taking pentacene as an example.

Kuhlman, Thomas S.; Mikkelsen, Kurt V.; Møller, Klaus B.; Sølling, Theis I.

2009-08-01

332

Negative Influence  

NSDL National Science Digital Library

This chapter is all about negative numbers, and how to deal with them. They're not all that difficult to understand, but for some reason people get just a little uptight when they see computations involving negative numbers. I'm guessing that the apprehension results from the view that negative numbers mean there are more rules to follow--rules you don't necessarily understand. Well, we'll try and correct that.

William C. Robertson, Ph.D.

2006-01-01

333

Total Cross Sections for Inelastic Scattering of Charged Particles by Atoms and Molecules. III. Accurate Bethe Cross Section for Ionization of Helium  

Microsoft Academic Search

The Bethe cross section sigmai for ionization of He by fast charged particles is accurately evaluated by a subtraction sigmai=sigmatot-sigmaex, where sigmatot is the total inelastic scattering cross section and sigmaex is the sum of all discrete-excitation cross sections. Our earlier work has given a highly precise value of sigmatot, and recent results on discrete excitations enables one to determine

Mitio Inokuti; Young-Ki Kim

1969-01-01

334

Comparison of all atom, continuum, and linear fitting empirical models for charge screening effect of aqueous medium surrounding a protein molecule  

NASA Astrophysics Data System (ADS)

To investigate the role hydration plays in the electrostatic interactions of proteins, the time-averaged electrostatic potential of the B1 domain of protein G in an aqueous solution was calculated with full atomic molecular dynamics simulations that explicitly considers every atom (i.e., an all atom model). This all atom calculated potential was compared with the potential obtained from an electrostatic continuum model calculation. In both cases, the charge-screening effect was fairly well formulated with an effective relative dielectric constant which increased linearly with increasing charge-charge distance. This simulated linear dependence agrees with the experimentally determined linear relation proposed by Pickersgill. Cut-off approximations for Coulomb interactions failed to reproduce this linear relation. Correlation between the all atom model and the continuum models was found to be better than the respective correlation calculated for linear fitting to the two models. This confirms that the continuum model is better at treating the complicated shapes of protein conformations than the simple linear fitting empirical model. We have tried a sigmoid fitting empirical model in addition to the linear one. When weights of all data were treated equally, the sigmoid model, which requires two fitting parameters, fits results of both the all atom and the continuum models less accurately than the linear model which requires only one fitting parameter. When potential values are chosen as weighting factors, the fitting error of the sigmoid model became smaller, and the slope of both linear fitting curves became smaller. This suggests the screening effect of an aqueous medium within a short range, where potential values are relatively large, is smaller than that expected from the linear fitting curve whose slope is almost 4. To investigate the linear increase of the effective relative dielectric constant, the Poisson equation of a low-dielectric sphere in a high-dielectric medium was solved and charges distributed near the molecular surface were indicated as leading to the apparent linearity.

Takahashi, Takuya; Sugiura, Junnnosuke; Nagayama, Kuniaki

2002-05-01

335

Charge-scaling effect in ionic liquids from the charge-density analysis of N,N'-dimethylimidazolium methylsulfate.  

PubMed

The charge scaling effect in ionic liquids was explored on the basis of experimental and theoretical chargedensity analyses of [C1MIM][C1SO4] employing the quantum theory of atoms in molecules (QTAIM) approach. Integrated QTAIM charges of the experimental (calculated) charge density of the cation and anion resulted in non-integer values of ±0.90 (±0.87) e. Efficient charge transfer along the bond paths of the hydrogen bonds between the imidazolium ring and the anion was considered as the origin of these reduced charges. In addition, a detailed QTAIM analysis of the bonding situation in the [C1SO4]- anion revealed the presence of negative ?O??*S-O hyperconjugation. PMID:24677323

Beichel, Witali; Trapp, Nils; Hauf, Christoph; Kohler, Oliver; Eickerling, Georg; Scherer, Wolfgang; Krossing, Ingo

2014-03-17

336

Single-molecule DNA detection with an engineered MspA protein nanopore  

PubMed Central

Nanopores hold great promise as single-molecule analytical devices and biophysical model systems because the ionic current blockades they produce contain information about the identity, concentration, structure, and dynamics of target molecules. The porin MspA of Mycobacterium smegmatis has remarkable stability against environmental stresses and can be rationally modified based on its crystal structure. Further, MspA has a short and narrow channel constriction that is promising for DNA sequencing because it may enable improved characterization of short segments of a ssDNA molecule that is threaded through the pore. By eliminating the negative charge in the channel constriction, we designed and constructed an MspA mutant capable of electronically detecting and characterizing single molecules of ssDNA as they are electrophoretically driven through the pore. A second mutant with additional exchanges of negatively-charged residues for positively-charged residues in the vestibule region exhibited a factor of ?20 higher interaction rates, required only half as much voltage to observe interaction, and allowed ssDNA to reside in the vestibule ?100 times longer than the first mutant. Our results introduce MspA as a nanopore for nucleic acid analysis and highlight its potential as an engineerable platform for single-molecule detection and characterization applications. PMID:19098105

Butler, Tom Z.; Pavlenok, Mikhail; Derrington, Ian M.; Niederweis, Michael; Gundlach, Jens H.

2008-01-01

337

Tunable magnetoresistance in an asymmetrically coupled single-molecule junction  

NASA Astrophysics Data System (ADS)

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.

Warner, Ben; El Hallak, Fadi; Prüser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J.; Hirjibehedin, Cyrus F.

2015-03-01

338

Tunable magnetoresistance in an asymmetrically coupled single-molecule junction.  

PubMed

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

Warner, Ben; El Hallak, Fadi; Prüser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J; Hirjibehedin, Cyrus F

2015-03-01

339

Glomerular permselectivity: barrier function based on discrimination of molecular size and charge.  

PubMed

The formation of glomerular ultrafiltrate is dependent on the interplay of glomerular pressures and flows as well as the intrinsic permselectivity properties of the glomerular capillary wall. These intrinsic permeability properties serve to exclude macromolecules from the urinary space, based on size as well as net molecular charge discrimination. Neutral dextrans with molecular radii less than 20 A cross the glomerular wall without measurable restriction, whereas dextrans with radii greater than 42 A are almost completely barred. For any given size, negatively charged macromolecules are restricted to a greater extent than neutral molecules. Additionally, positively charged molecules are enhanced in their ability to cross the glomerular wall compared to similarly sized neutral polymers. The concept of a charge barrier, due to fixed negative charges within the glomerular wall, is also supported by morphological studies. Glomerular injury, leading to proteinuria, has been associated with loss of the charge-selective properties of these capillaries. Loss of glomerular fixed negative charges may also result in the foot process fusion and mesangial cell dysfunction often observed in proteinuric states. PMID:665772

Brenner, B M; Hostetter, T H; Humes, H D

1978-06-01

340

Negative Refraction Induced by Möbius Topology  

E-print Network

We theoretically show the negative refraction existing in M\\"{o}bius molecules. The negative refractive index is induced by the non-trivial topology of the molecules. With the M\\"{o}bius boundary condition, the effective electromagnetic fields felt by the electron in a M\\"{o}bius ring is spatially inhomogeneous. In this regard, the $D_{N}$ symmetry is broken in M\\"{o}bius molecules and thus the magnetic response is induced through the effective magnetic field. Our findings open up a new architecture for negative refractive index materials based on the non-trivial topology of M\\"{o}bius molecules.

Y. N. Fang; Yao Shen; Qing Ai; C. P. Sun

2015-01-23

341

Raindrop charges, electric field and space charge measurements at a mountain station covered with monsoon clouds  

Microsoft Academic Search

Raindrop charges, electric field, space charge and rainfall intensity have been measured at a mountain station, Mahabaleshwar, during the southwest monsoon season when it is almost always covered with stratus and strato-cumulus clouds. Negative potential gradients of less than ?300 V\\/m, small fluctuating space charges and negative charges on 71% of the total number of the charged raindrops have been

A. K. Kamra; A. B. Sathe

1983-01-01

342

Ab initio NMR chemical shieldings in the neutral and charged 7-phosphabicyclo[2.2.1]heptane, -heptene, and -heptadiene systems; the largest predicted downfield shift for a conventional organophosphorus molecule  

NASA Astrophysics Data System (ADS)

Ab initio quantum mechanical calculations of phosphorus NMR chemical shieldings have been performed at the MP2 level of theory on the neutral and singly charged 7-phosphabicyclo[2.2.1]heptane, -heptene, and -heptadiene neutral, cationic, and anionic molecules using a P:tz2p/C:tzp/H:dz locally dense basis set. Inclusion of correlation at the MP2 level is quantitatively important for the dienes and all the anionic species. The presence of two lone pairs in the anions leads to drastically reduced HOMO-LUMO energy gaps and corresponding large deshielding effects. The absolute isotropic shielding of -756.6 ppm (? + 1085.0) calculated for the anionic diene is by far the largest downfield shielding predicted for phosphorus in a conventional organophosphorus compound.

Chesnut, D. B.

1997-12-01

343

Molecule nanoweaver  

DOEpatents

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.

Gerald, II; Rex E. (Brookfield, IL); Klingler, Robert J. (Glenview, IL); Rathke, Jerome W. (Homer Glen, IL); Diaz, Rocio (Chicago, IL); Vukovic, Lela (Westchester, IL)

2009-03-10

344

Ag-mediated charge transfer from electron-doped SrTiO 3 to CO and NO: A first-principles study  

NASA Astrophysics Data System (ADS)

Ag-mediated charge transfer from electron-doped SrTiO3 to molecules CO and NO has been studied through the first-principles calculations based on density functional theory (DFT). Evaluation of Fukui functions indicates that Ag atom on SrTiO3 (001) surface is presented as an active reduction and oxidation site. It shows that Ag prefers to mediate the charge transfer from electronically excited SrTiO3 to target species. It illustrates that electron initially transfers from electron-doped SrTiO3 to Ag, i.e., Ag is negatively charged. Interfacial charge transfer induces dipole moment and changes the surface work function. SrO-termination of SrTiO3 (001) surface has weak activity to CO and NO while CO and NO can be strongly adsorbed on the negatively charged Ag atom. Negatively charged Ag donates its charge to the molecules. Charge occupies the molecule ?2p* orbital, which is responsible for the activation of the molecular bonds. Evidence that deposited metals on photocatalyst surface can efficiently separate the photogenerated electron-hole pairs has been addressed in this study.

Wei, Wei; Dai, Ying; Guo, Meng; Niu, Chengwang; Huang, Baibiao

2011-07-01

345

Fragmentation of doubly charged HDO, H2O, and D2O molecules induced by proton and monocharged fluorine beam impact at 3 keV  

NASA Astrophysics Data System (ADS)

Doubly charged ions HDO2+, H2O2+, and D2O2+ 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 HDO2+, 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.

Martin, S.; Chen, L.; Brédy, R.; Bernard, J.; Cassimi, A.

2015-03-01

346

Fragmentation of doubly charged HDO, H2O, and D2O molecules induced by proton and monocharged fluorine beam impact at 3 keV.  

PubMed

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

Martin, S; Chen, L; Brédy, R; Bernard, J; Cassimi, A

2015-03-01

347

PHYS 242 Problem set 4 1. A simple example of a molecule with an electric dipole moment is HCl, which has  

E-print Network

, will hold a permanent electric polarization. 4. The space between the plates of a parallel-plate capacitor circular cylinder, of radius R and length L, carries a "frozen in" uniform polarization P, parallel to its "centre of gravity" of the negative charge distribution be located in the real molecule? What does

Lovejoy, Shaun

348

Negative differential conductance and hysteretic current switching of benzene molecular junction in a transverse electric field  

NASA Astrophysics Data System (ADS)

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.

Zhu, Wen-Huan; Ding, Guo-Hui; Dong, Bing

2014-11-01

349

Charged particles in Titan's ionosphere  

NASA Astrophysics Data System (ADS)

Charged particles in Titan's ionosphere Marykutty Michael1, Sachchida Nand Tripathi1,2,3, Pratima Arya1 1Indian Institute of Technology Kanpur 2Oak Ridge Associated Universities 3NASA Goddard Space Flight Center Observations by two instruments onboard the Cassini spacecraft, Ion Neutral Mass Spectrometer (INMS) and CAssini Plasma Spectrometer (CAPS), revealed the existence of heavy hydrocarbon and nitrile species with masses of several thousand atomic mass units at altitudes of 950 - 1400 km in the atmosphere of Titan (Waite et al., 2007; Crary et al., 2009). Though these particles were believed to be molecules, they are most likely aerosols formed by the clumping of smaller molecules (Waite et al., 2009). These particles were estimated to have a density of 10-3 kg m-3 and a size of up to 256 nm. The existence of very heavy ions has also been observed by the CAPS components with a mass by charge ratio of up to 10000 (Coates et al., 2007, 2009; Sittler et al., 2009). The goal of this paper is to find out whether the so called heavy ions (or charged particles) are generated by the charge transfer of ions and electrons to the particles. The charging of these particles has been studied by using the charge balance equations that include positive ions, negative ions, electrons, neutral and charged particles. Information on the most abundant ion clusters are obtained from Vuitton et al., (2009) and Wilson and Atreya, (2004). Mass by charge ratio thus calculated will be compared with those observed by Coates et al. (2007). References: Coates AJ, et al., Discovery of heavy negative ions in Titan's ionosphere, Geophys. Res. Lett., 34:L22103, 2007. Coates AJ, et al., Heavy negative ions in titan's ionosphere: altitude and latitude dependence. Planet. Space Sci., doi:10.1016/j.pss.2009.05.009, 2009. Crary F.J., et al., Heavy ions, temperatures and winds in titan's ionosphere: Combined cassini caps and inms observations. Planet. Space Sci., doi:10.1016/j.pss.2009.09.006, 2009. Sittler,E.C. et al., Heavy ion formation in Titan's ionosphere: Magnetospheric introduction of free oxygen and a source of Titan's aerosols? Planet. Space Sci., doi:10.1016/j.pss.2009.07.017, 2009. Vuitton, V., Negative ion chemistry in Titan's upper atmosphere, Planet. Space Sci., doi:10.1016/j.pss.2009.04.004, 2009. Waite J.H, et al., The process of tholin formation in Titan's upper atmosphere. Science, doi: 10.1126/science.1139727, 316, 870, 2007. Waite JH, et al., High altitude production of Titan's aerosols, In Titan from Cassini-Huygens, edited by RH. Brown, J.P Lebreton, JH Waite, Springer, 2009. Wilson, E.H. and S. Atreya, Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere, J. Geophys. Res., 109, E06002, doi:10.1029/2003JE002181, 2004.

Tripathi, Sachchida

2010-05-01

350

Charge transport in nanoscale junctions.  

PubMed

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

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

351

Single-Photon Multiple Detachment in Fullerene Negative Ions: Absolute Ionization Cross Sections and the Role of the Extra Electron  

NASA Astrophysics Data System (ADS)

We have obtained experimental photo-double- and photo-triple-detachment cross sections for the fullerene negative ion using Advanced Light Source photons of 17-90 eV. The cross sections are 2 and 2.5 times larger than those for C60 and appear to be compressed and shifted in photon energy as compared to C60. Our analysis reveals that the additional electron in C60- primarily produces screening which is responsible for the modification of the spectrum. Both screening effects, the shift and the compression, can be quantitatively accounted for by a linear transformation of the energy axis. Applying the transformation allows us to map the neutral and negative ion cross sections onto each other, pointing out the close relationship of correlated few-electron dynamics in neutral and negatively charged extended systems. In contrast, dynamics of neutral and negatively charged atoms or small molecules are typically not closely related.

Bilodeau, R. C.; Gibson, N. D.; Walter, C. W.; Esteves-Macaluso, D. A.; Schippers, S.; Müller, A.; Phaneuf, R. A.; Aguilar, A.; Hoener, M.; Rost, J. M.; Berrah, N.

2013-07-01

352

Contact de-electrification of electrostatically charged polymers.  

PubMed

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

Soh, Siowling; Kwok, Sen Wai; Liu, Helena; Whitesides, George M

2012-12-12

353

Three chamber negative ion source  

DOEpatents

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.

Leung, Ka-Ngo (Hercules, CA); Ehlers, Kenneth W. (Alamo, CA); Hiskes, John R. (Livermore, CA)

1985-01-01

354

Weakly Charged Cationic Nanoparticles Induce DNA Bending and Strand Separation  

SciTech Connect

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.

Railsback, Justin [North Carolina State University; Singh, Abhishek [North Carolina State University; Pearce, Ryan [North Carolina State University; McKnight, Timothy E [ORNL; Collazo, Ramon [North Carolina State University; Sitar, Zlatko [ORNL; Yingling, Yaroslava [North Carolina State University; Melechko, Anatoli Vasilievich [ORNL

2012-01-01

355

Fragmentation of biomolecules using slow highly charged ions  

SciTech Connect

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.

Ruehlicke, C.; Schneider, D.; Balhorn, R. [Lawrence Livermore National Lab., CA (United States); DuBois, R. [Missouri Univ., Rolla, MO (United States). Dept. of Physics

1996-11-01

356

Antibacterial activity of highly negative charged polyoxotungstates, K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural polyoxotungstates against Helicobacter pylori.  

PubMed

The antibacterial activity of polyoxometalates (PMs) against Helicobacter pylori was investigated based on determinations of minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC), time-killing of the bacteria, bacterial morphology and PM-uptake into the bacteria cell. The result of MIC values revealed that, of 13 PMs used in this study, highly negative-charged polyoxotungstates, such as K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural polyoxotungstates exhibited a potent antibacterial activity with the MIC values of less than 256 microg/ml. The former was the most active, and superior to metronidazole (MTZ) against MTZ-susceptible and resistant strains and also to clarithromycin (CLR) against CLR-resistant strains. In contrast, most of polyoxomolybdates showed little antibacterial activity with the MIC values of more than 256 microg/ml. The result of FIC index values indicated that the antibacterial polyoxotungstates had partially synergistic effect in combination with MTZ and CLR but indifferent effect in combination with amoxicillin (AMX). From the results of the time-killing and scanning electron microscope images, K27[KAs4W40O140] and K18[KSb9W21O86] proved the concentration-dependent bactericidal activity with the morphological change from bacillary form to coccoid form, while Keggin-structural K5[SiV(V)W11O40] showed the bacteriostatic activity with small change of morphology to coccoid form. The fluorescent X-ray analysis demonstrated that these polyoxotungstates were taken into the bacteria cell. It is pointed out that the Keggin-structure and/or high negativity polyoxotungstates are an important factor for the antibacterial activity against H. pylori. PMID:15833325

Inoue, Miyao; Segawa, Keiko; Matsunaga, Sae; Matsumoto, Nobuhiro; Oda, Mayumi; Yamase, Toshihiro

2005-05-01

357

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

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

Jiang, Ziqing; Vasil, Adriana I; Gera, Lajos; Vasil, Michael L; Hodges, Robert S

2011-04-01

358

SOI nanowires as sensors for charge detection  

NASA Astrophysics Data System (ADS)

The properties of silicon-on-insulator nanowires (SOI NWs) fabricated by means of electron lithography and gas etching of SOI in XeF2 or SF6:CFCl3 have been investigated. The method used to fabricate the nanowires was found to require no additional anneal to be given to the final structure for defect removal after nanostructuring. The sensitivity of SOI NWs to negative protein BSA molecules in the pH 7.4 buffer solution was shown to be as high as 1 femtomoles. The gate characteristics of SOI NWs were used to determine the charge density of particles adsorbed on the NW surface. A charge density of 4.6 × 1011 cm-2 was estimated for a 1 femtomole protein concentration. The combined use of open-channel structures with top gates was employed for determining the charge state of structure surfaces after different chemical treatments. Chemical treatments giving rise to a density of the negative charges on the surface of NWs ranging in the interval (7-23) × 1011 cm-2 were examined. Treatments in methanol (after removal of the native oxide) were found to provide stabilization of the SOI surface over a 3-h interval after the treatments.

Naumova, O. V.; Fomin, B. I.; Nasimov, D. A.; Dudchenko, N. V.; Devyatova, S. F.; Zhanaev, E. D.; Popov, V. P.; Latyshev, A. V.; Aseev, A. L.; Ivanov, Yu D.; Archakov, A. I.

2010-05-01

359

Marvelous Molecules  

NSDL National Science Digital Library

Presented by the New York Hall of Science, the Marvelous Molecules Web site accompanies its physical museum's exhibit by offering descriptions and additional online activities. The first page "About the Exhibit" shows what is available at the museum and gives interesting facts about molecules. The next page "All About Molecules" explains what a molecule is and gives eight examples (e.g., aspirin and carbon dioxide). The next page called "Marvelous Activities" contains several activities, one of which is the "How Many Molecules Are You?" interactive exercise. Here, users input their weight to see how many molecules their bodies contain and how that compares to other living things. Geared mainly towards kids, the Web site should give all people a fun way to learn.

1969-12-31

360

Interstellar molecules  

NASA Technical Reports Server (NTRS)

Progress in the discovery and study of interstellar molecules is summarized. The 36 molecular species thus far identified in interstellar space are listed in several groups which include simple hydrides, oxides, and sulfides, various derivatives of ammonia, molecules involving linear carbon chains, cyanides, and molecules related in structure to formaldehyde, alcohols, or ethers. Several free radicals are described, the discovery of molecules in external galaxies is discussed, and possible mechanisms for molecular formation are noted. Methods for examining relative isotopic abundances by measuring molecules in interstellar clouds are outlined, mechanisms for the excitation of interstellar molecules are reviewed, and values are presented for the C-12/C-13 abundance ratio in a number of interstellar clouds. The detection of interstellar masers is discussed along with pumping mechanisms and masing transitions in H2CO, CH, OH, and SiO. The nature of dense interstellar clouds is examined in terms of several simple and complex cloud models, with emphasis on multiple condensation models.

Townes, C. H.

1976-01-01

361

RICE UNIVERSITY Transport in Single Molecule Transistors  

E-print Network

RICE UNIVERSITY Transport in Single Molecule Transistors by Lam H. Yu A Thesis Submitted in Partial Houston, Texas January, 2006 #12;Abstract Transport in Single Molecule Transistors by Lam H. Yu molecule transistors (SMTs), nanometer-scale transistors in which charge transport occurs through

Natelson, Douglas

362

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)

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.

Saini, R. K.; Varshney, G. K.; Dube, A.; Gupta, P. K.; Das, K.

2014-09-01

363

Structural changes of water molecules during the photoactivation processes in bovine rhodopsin.  

PubMed

Internal water molecules of rhodopsins play an important role in stabilizing the crucial ion pair comprised by the protonated retinal Schiff base and its counterion. Previous low-temperature FTIR spectroscopy of archaeal rhodopsins observed water O-D stretching vibrations at 2400-2100 cm(-1) in D(2)O, corresponding to strong hydrogen bonds. Since a water molecule bridges the protonated Schiff base and an aspartate in archaeal rhodopsins, the observed water molecules presumably hydrate the negative charges in the Schiff base region. In contrast, the FTIR spectroscopy data of bovine rhodopsin presented here revealed that there are no spectral changes of water molecules under strongly hydrogen-bonding conditions (in the range <2400 cm(-1) for O-D stretch) during the photoactivation processes. The only observed water bands were located in the >2500 cm(-1) region that corresponds to weak hydrogen bonding. These results imply that the ion pair state in vertebrate visual rhodopsins is stabilized in a manner different from that in archaeal rhodopsins. In addition, the internal water molecules that hydrate the negative charges do not play important role in the photoactivation processes of rhodopsin that involve proton transfer from the Schiff base to Glu113 upon formation of Meta II. Structural changes of the H-D exchangeable peptide amide of a beta-sheet are observed upon formation of metarhodopsin II, suggesting that motion of a beta-sheet is coupled to the proton transfer reaction from the Schiff base to its counterion. PMID:12911303

Furutani, Yuji; Shichida, Yoshinori; Kandori, Hideki

2003-08-19

364

Surface charges and subsurface space-charge distribution in magnesium oxides containing dissolved traces of water  

Microsoft Academic Search

MgO crystals which contain dissolved traces of H2O eventually acquire an excess oxygen content, MgO1+delta, because OH- pairs, associated with cation vacancies, convert in part into molecular H2 and peroxy anions, O2-2. While H2 molecules are lost from the crystal, the vacancy-bound O2-2 remain as spin-paired, self-trapped positive holes. Probably at this stage the MgO surface is negatively charged. Around

Bruce V. King; Friedemann Freund

1984-01-01

365

Single Molecules  

NSDL National Science Digital Library

A new molecular science journal, Single Molecules, from Wiley Interscience, "will provide researchers with a broad overview of current methods and techniques, recent applications and shortcomings of present techniques in the field of single molecules." With temporary free access, the journal's latest issue contains a few full-text articles, with more articles being regularly added. This journal is currently calling for papers.

366

Charge-controlled switchable CO2 capture on boron nitride nanomaterials.  

PubMed

Increasing concerns about the atmospheric CO2 concentration and its impact on the environment are motivating researchers to discover new materials and technologies for efficient CO2 capture and conversion. Here, we report a study of the adsorption of CO2, CH4, and H2 on boron nitride (BN) nanosheets and nanotubes (NTs) with different charge states. The results show that the process of CO2 capture/release can be simply controlled by switching on/off the charges carried by BN nanomaterials. CO2 molecules form weak interactions with uncharged BN nanomaterials and are weakly adsorbed. When extra electrons are introduced to these nanomaterials (i.e., when they are negatively charged), CO2 molecules become tightly bound and strongly adsorbed. Once the electrons are removed, CO2 molecules spontaneously desorb from BN absorbents. In addition, these negatively charged BN nanosorbents show high selectivity for separating CO2 from its mixtures with CH4 and/or H2. Our study demonstrates that BN nanomaterials are excellent absorbents for controllable, highly selective, and reversible capture and release of CO2. In addition, the charge density applied in this study is of the order of 10(13) cm(-2) of BN nanomaterials and can be easily realized experimentally. PMID:23678978

Sun, Qiao; Li, Zhen; Searles, Debra J; Chen, Ying; Lu, Gaoqing Max; Du, Aijun

2013-06-01

367

Controlled and reversible binding of positively charged quantum dots to lambda DNA.  

PubMed

Biomacromolecules/Nanomaterials bioconjugate complexes have many applications in the interdisciplinary research fields. Accessible and easy synthesis methods of these complexes are the key roles for these applications. High quality water-soluble surface-charged quantum dots (QDs) were successfully prepared via surface modification by amphiphilic surfactants. The positively charged QDs can interact with deoxyribonucleic acid (DNA) molecules to form QDs/DNA bioconjugates via self-targeting electrostatic force. The stability of these QDs/DNA bioconjugates is influenced by ionic strength and concentration of negative or neutral surfactants in the solution. High ionic concentration or ca. 10(-3) mol/L surfactants can break the interaction between the QDs and DNA molecules (Lambda DNA/Hind III Marker segments) and controllably release DNA molecules from these bioconjugates. The conformation of DNA molecules has little change during the binding and releasing process. The condensation of lambda DNA molecules can be induced by positively charged QDs. High resolution transmission electron microscopy experiments have revealed the different stages of DNA condensation process, showing the fine structures of QDs/DNA bioconjugates at biomolecular scale. A long chain DNA molecule starts to self-enwind and condense to a porous globule when it is exposing to positively charged QDs but there is no direct interaction between QDs and DNA at early stages of condensation. After the DNA molecule becomes a compact globule, QDs stick onto its surface via electrostatic force. The coil conformation of the DNA molecules can be recovered from globule structure after DNA molecules are controllably released from bioconjugate complexes. These QDs/DNA bioconjugates have great potential applications for gene delivery and at the same time the fluorescence of QDs can be utilized to monitor the DNA releasing process. PMID:17981600

Liu, Yi; Zhang, Ming-Xi; Zhang, Zhi-Ling; Xie, Hai-Yan; Tian, Zhi-Quan; Wong, Kwok-Yin; Pang, Dai-Wen

2008-01-01

368

Mobius Molecules  

ERIC Educational Resources Information Center

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)

Eckert, J. M.

1973-01-01

369

Interstellar Molecules  

ERIC Educational Resources Information Center

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)

Solomon, Philip M.

1973-01-01

370

Ion-Molecule Reactions  

NASA Astrophysics Data System (ADS)

The observation of ion-molecule reactions has a history that goes back to the beginning of the twentieth century, when J. J. Thomson discovered that operating his positive ray parabola apparatus in a hydrogen atmosphere produced signals at a mass to charge ratio of 3, which he correctly attributed to the species H3 [67.1]. Later studies showed that this species was produced by a reaction between the primary ionization product H2 + and molecular hydrogen. Most ion-molecule reactions proceed without an activation barrier and their cross sections are governed by the long range attractive potential of the approaching reactants (Sect. 64.2.4). Reaction rates based on long range potential capture models [67.2] predict rates in excess of 10-9 cm3molecule-1s-1, corresponding to thermal energy cross sections (Sect. 47.1.7) of 10-16-10-15 cm2. The importance of ion-molecule reactions in such widely diverse areas as planetary atmospheres, (Sect. 84.1), electrical discharges and plasmas (Sect. 87.1.4), particularly in semiconductor processing, in the formation of molecules in interstellar space (Chapt. 82), and in flames and combustion systems (Sect. 88.1), has borne out that prediction. This chapter discusses applications of single-collision scattering methods to the study of reactive collision dynamics of ionic species with neutral partners.

Farrar, James

371

Conformational Transitions and Stop-and-Go Nanopore Transport of Single Stranded DNA on Charged Graphene  

PubMed Central

Control over interactions with biomolecules holds the key to applications of graphene in biotechnology. One such application is nanopore sequencing, where a DNA molecule is electrophoretically driven through a graphene nanopore. Here, we investigate how interactions of single-stranded DNA and a graphene membrane can be controlled by electrically biasing the membrane. The results of our molecular dynamics simulations suggest that electric charge on graphene can force a DNA homopolymer to adopt a range of strikingly different conformations. The conformational response is sensitive to even very subtle nucleotide modifications, such as DNA methylation. The speed of DNA motion through a graphene nanopore is strongly affected by the graphene charge: a positive charge accelerates the motion whereas a negative charge arrests it. As a possible application of the effect, we demonstrate stop-and-go transport of DNA controlled by the charge of graphene. Such on-demand transport of DNA is essential for realizing nanopore sequencing. PMID:25296960

Shankla, Manish; Aksimentiev, Aleksei

2014-01-01

372

Direct visualization of molecule deprotonation on an insulating surface.  

PubMed

Elucidating molecular-scale details of basic reaction steps on surfaces is decisive for a fundamental understanding of molecular reactivity within many fields, including catalysis and on-surface synthesis. Here, the deprotonation of 2,5-dihydroxybenzoic acid (DHBA) deposited onto calcite (101;4) held at room temperature is followed in situ by noncontact atomic force microscopy. After deposition, the molecules form two coexisting phases, a transient striped phase and a stable dense phase. A detailed analysis of high-resolution noncontact atomic force microscopy images indicates the transient striped phase being a bulk-like phase, which requires hydrogen bonds between the carboxylic acid moieties to be formed. With time, the striped phase transforms into the dense phase, which is explained by the deprotonation of the molecules. In the deprotonated state, the molecules can no longer form hydrogen bonds, but anchor to the surface calcium cations with their negatively charged carboxylate group. The deprotonation step is directly confirmed by Kelvin probe force microscopy images that unravel the change in the molecular charge. PMID:22838491

Kittelmann, Markus; Rahe, Philipp; Gourdon, André; Kühnle, Angelika

2012-08-28

373

Influence of surface charge distributions and particle size distributions on particle attachment in granular media filtration.  

PubMed

Filtration experiments were performed with a laboratory-scale filter using spherical glass beads with 0.55 mm diameter as collectors. Suspensions were made with Min-U-Sil 5 particles, and two different methods (pH control and polymer dosing) were used for destabilization. In the pH control experiments, all particles had negative surface charge, and those with lower (absolute value) charge were selectively attached to the collectors, especially during the early stage of filtration. This selective attachment of the lower charged particles caused the zeta potential distribution (ZPD) of the effluent to move to a more negative range. However, the ZPD of the effluent did not continue moving to more negative values during the later stages of filtration, and this result was attributed to two reasons: ripening effects and detachment of flocs. In the polymer experiments, substantial differences were found between experiments performed with negatively charged particles (underdosing) and those with positively charged particles (overdosing). With under-dosing, the results were similar to the pH control experiments (which also had negatively charged particles), but with overdosing, the effluent's ZPDs in the early stages did not overlap with those of the influent and more highly charged particles were removed more efficiently than lesser-charged particles. It is hypothesized that, despite a substantial period of pre-equilibration of media and coagulant, this equilibrium shifted when particles were also added. It was assumed that coagulant molecules previously adsorbed to the particles desorbed and subsequently attached to the filter media because of surface area differences in the particle and filter media. PMID:18504996

Kim, Jinkeun; Nason, Jeffrey A; Lawler, Desmond F

2008-04-01

374

Negative ion formation processes: A general review  

SciTech Connect

The principal negative ion formation processes will be briefly reviewed. Primary emphasis will be placed on the more efficient and universal processes of charge transfer and secondary ion formation through non-thermodynamic surface ionization. 86 refs., 20 figs.

Alton, G.D.

1990-01-01

375

'Escentric' molecules.  

PubMed

Can a fragrance be revolutionary? In this commentary, the creation of two unusual, extravagant fine fragrances, 'escentric01' and 'molecule01', is described. In response to the fantasy components found in release notes of many recent perfume launches, both center around a single real fragrance raw material, the transparent woody aroma chemical 'Iso E Super' (1+2). The perfume 'escentric01' contains 65% of it, accompanied by Trisamber (3), red pepper, lime oil, incense and musks, while 'molecule01' consists exclusively of 'Iso E Super' (1+2). The elegant woody note lives here its own eccentric life--the revolution starts. PMID:18618401

Schön, Geza

2008-06-01

376

Physics aspects of negative ion sources  

Microsoft Academic Search

The physical phenomena important in volume and surface production negative hydrogen ion sources are reviewed. The phenomenon, designated volume production, was attributed to dissociative electron attachment of low energy electrons to rovibrationally excited molecules. The experimental verification in 2005 of the reality of this mechanism is reported. Recent results obtained by measuring the negative ion temperature in a filament discharge

M. Bacal

2006-01-01

377

Enhanced electron attachment to vibrationally and electronically excited molecules  

NASA Astrophysics Data System (ADS)

Electron attachment studies on vibrationally and electronically excited states have been measured. The attachment of electrons to vibrationally excited states of the ground electronic state populated via temperature increase was measured in the mean electron energy range, (?), 0.04 to 4.8 eV, over the temperature range, T, 300 to 700 K and over the total gas number density, Nt, 2.25 to 15.5 × 1019 molecules/cm3. These studies are presented in Part 1 for three technologically important molecules: Methylene Chloride (C2H2Cl2), Boron Trichloride (BCl3), and Trichlorotrifluoroethane (1,1,2-C 2Cl3F3). Electron attachment rate constants, k a((?),T), was measured as a function of mean electron energy in Ar and N2 gases at different temperatures. Using swarm unfolding technique, electron attachment cross sections, ?a(?,T), was measured as a function of electron energy by unfolding ka((?),T) at each temperature. The results of these measurements show that the dissociative electron attachment cross sections increase with the increase of vibrational energies. In the studies an electronically-excited states, the attaching electrons and the excited states of molecules were produced with a single excimer-laser pulse. The excitation of molecules to energies above the ionization potential (IP) caused the population of core-excited Rydberg states (HR). The electrons produced via photoionization were attached to the concomitantly produced highly-excited molecules leading to negative ion formation under the high-pressure environment provided by Ar or N2 gases. In these experiments two different experimental techniques were used: two- electrode arrangement and three-electrode arrangement. The two-electrode arrangement techniques provided information on the lifetimes of the excited molecules as well as estimates of various experimental parameters including the electron attachment rate constant of excited molecules. The other technique, the three- electrode arrangement, provided information about the density of charged species including electrons and negative ions and the estimation of electron attachment rate constant. These results are presented in Part II for three molecules: Benzene (C6H 6), Oxygen (O2), and Dichlorodifluoromethane (CCl2,F2). It was shown that the electron attachment to highly-excited molecules was extremely efficient process leading to enormous electron attachment cross sections, ?a, ~ 10-10 cm2, which were many orders of magnitude larger compared to the cross sections for corresponding ground electronic states.

Tav, Cumali

378

Biological Molecules  

NSDL National Science Digital Library

Paul Anderson describes the four major biological molecules found in living things. He begins with a brief discussion of polymerization. Dehydration synthesis is used to connect monomers into polymers and hydrolysis breaks them down again. The major characteristics of nucleic acids are described as well as there directionality from 3' to 5' end.

Paul Anderson

2013-03-12

379

Examining the Contributions of Lipid Shape and Headgroup Charge on Bilayer Behavior  

Microsoft Academic Search

To better understand bilayer property dependency on lipid electrostatics and headgroup size, we use atomistic molecular dynamics simulations to study negatively charged and neutral lipid membranes. We compare the negatively charged phosphatidic acid (PA), which at physiological pH and salt concentration has a negative spontaneous curvature, with the negatively charged phosphatidylglycerol (PG) and neutrally charged phosphatidylcholine (PC), both of which

Allison Dickey; Roland Faller

2008-01-01

380

Critical Points of the Electric Field from a Collection of Point Charges  

SciTech Connect

The electric field around a molecule is generated by the charge distribution of its constituents: positively charged atomic nuclei, which are well approximated by point charges, and negatively charged electrons, whose probability density distribution can be computed from quantum mechanics. For the purposes of molecular mechanics or dynamics, the charge distribution is often approximated by a collection of point charges, with either a single partial charge at each atomic nucleus position, representing both the nucleus and the electrons near it, or as several different point charges per atom. The critical points in the electric field are useful in visualizing its geometrical and topological structure, and can help in understanding the forces and motion it induces on a charged ion or neutral dipole. Most visualization tools for vector fields use only samples of the field on the vertices of a regular grid, and some sort of interpolation, for example, trilinear, on the grid cells. There is less risk of missing or misinterpreting topological features if they can be derived directly from the analytic formula for the field, rather than from its samples. This work presents a method which is guaranteed to find all the critical points of the electric field from a finite set of point charges. To visualize the field topology, we have modified the saddle connector method to use the analytic formula for the field.

Max, N; Weinkauf, T

2007-02-16

381

Configuration effects on satellite charging response  

NASA Technical Reports Server (NTRS)

The response of various spacecraft configurations to a charging environment in sunlight was studied using the NASA Charging Analyzer Program code. The configuration features geometry, type of stabilization, and overall size. Results indicate that sunlight charging response is dominated by differential charging effects. Shaded insulation charges negatively result in the formation of potential barriers which suppress photoelectron emission from sunlit surfaces. Sunlight charging occurs relatively slowly: with 30 minutes of charging simulations, in none of the configurations modeled did the most negative surface cell reach half its equilibrium potential in eclipse.

Purvis, C. K.

1980-01-01

382

Triboelectric charging of lunar regolith simulant  

Microsoft Academic Search

We present an experimental investigation of the triboelectric charging behavior of lunar simulant (JSC-1). Our experimental approach ensures that the JSC-1 particles only make contact to other JSC-1 particles during the charging process (and no other surfaces). The results show that charge segregation occurs such that smaller particles tend to charge negatively and larger particles charge positively. This particle-size-dependent charging

Keith M. Forward; Daniel J. Lacks; R. Mohan Sankaran

2009-01-01

383

Triboelectric charging of lunar regolith simulant  

NASA Astrophysics Data System (ADS)

We present an experimental investigation of the triboelectric charging behavior of lunar simulant (JSC-1). Our experimental approach ensures that the JSC-1 particles only make contact to other JSC-1 particles during the charging process (and no other surfaces). The results show that charge segregation occurs such that smaller particles tend to charge negatively and larger particles charge positively. This particle-size-dependent charging follows behavior observed for other single-component granular systems and appears to be universal.

Forward, Keith M.; Lacks, Daniel J.; Sankaran, R. Mohan

2009-10-01

384

Negative ions in Trichel corona in air  

Microsoft Academic Search

The negative ions formed in Trichel corona in air (10-30 Torr pressure) have been identified and their times of flight in the corona gap measured. It is confirmed that the Trichel pulse frequency, at or near threshold, involves a full transit of the negative-ion space-charge layer.

P. S. Gardiner; J. D. Craggs

1977-01-01

385

Shake and Make: Charge Recognition  

NSDL National Science Digital Library

In this activity, learners explore how molecules self-assemble according to forces of attraction and repulsion. Learners investigate how the placement of charge determines the possible structures that molecules can make when they come together. This activity can be performed as a demonstration if purchasing the magnetic pieces is cost prohibitive.

Arizona Science Center

2012-01-01

386

Moving Molecules!  

NSDL National Science Digital Library

In this activity about molecular diffusion (located on page 2 of the PDF), learners will make predictions and move molecules of iodine through a seemingly solid plastic sandwich bag. The process of diffusion will be visually indicated by a color change when the iodine reacts with starch inside the bag. Information in the resource explains how this activity relates to nanoparticles and research. Related to linked video, DragonflyTV Nano: Nanosilver.

2014-06-24

387

Excited State Processes in Photosynthesis Molecules  

Microsoft Academic Search

A study of electronic processes in the chlorophyll and carothenoid molecules of the photo-reaction center II is presented with the focus on the electronic excitations and charge transfer in the photosynthetic process. Several novel ideas are mentioned especially concerning the electron replenishment and nuclear vibrational excitations. The study is build mainly on numerical quantum calculations of electronic structures of molecules

Henrik Bohr; Per Greisen; Barry Malic

2008-01-01

388

Excited State Processes in Photosynthesis Molecules  

Microsoft Academic Search

A study of electronic processes in the chlorophyll and carothenoid molecules of the photoreaction center II is presented with the focus on the electronic excitations and charge transfer in the photosynthetic process. Several novel ideas are mentioned especially concerning the electron replenishment and nuclear vibrational excitations. The study is build mainly on numerical quantum calculations of electronic structures of molecules

Henrik Bohr; Per Greisen; Barry Malic

2009-01-01

389

Negative ions of ethylene sulfite  

Microsoft Academic Search

The formation of negative ions in molecular beams of ethylene sulfite (ES, alternately called glycol sulfite or ethylene glycol, C2H4SO3) molecules has been studied using both Rydberg electron transfer (RET) and free electron attachment methods. RET experiments with jet-cooled ES show an unexpected broad profile of anion formation as a function of the effective quantum number (n*) of the excited

W. D. Robertson; N. I. Hammer; J. E. Bartmess; R. N. Compton; K. Diri; K. D. Jordan

2005-01-01

390

Preface: Charge transport in nanoscale junctions  

NASA Astrophysics Data System (ADS)

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

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

391

Charge-transfer-based Gas Sensing Using Atomic-layer MoS2  

PubMed Central

Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

2015-01-01

392

Charge-transfer-based gas sensing using atomic-layer MoS2.  

PubMed

Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M; Kim, Dong-Ho

2015-01-01

393

Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: Charge transfer reaction of N2+(X 2?g+; v+ = 0-2; N+ = 0-9) + Ar  

NASA Astrophysics Data System (ADS)

We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N2+(v+, N+) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N2+(X 2?g+, v+ = 0-2, N+ = 0-9) PFI-PIs with high quantum state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N2+ PFI-PI beam can be formed with a laboratory kinetic energy resolution of ?Elab = ± 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (Ecm's) down to thermal energies. Absolute total rovibrationally selected cross sections ?(v+ = 0-2, N+ = 0-9) for the N2+(X 2?g+; v+ = 0-2, N+ = 0-9) + Ar CT reaction have been measured in the Ecm range of 0.04-10.0 eV, revealing strong vibrational enhancements and Ecm-dependencies of ?(v+ = 0-2, N+ = 0-9). The thermochemical threshold at Ecm = 0.179 eV for the formation of Ar+ from N2+(X; v+ = 0, N+) + Ar was observed by the measured ?(v+ = 0), confirming the narrow ?Ecm spread achieved in the present study. The ?(v+ = 0-2; N+) values obtained here are compared with previous experimental and theoretical results. The theoretical predictions calculated based on the Landau-Zener-Stückelberg formulism are found to be in fair agreement with the present measured ?(v+ = 1 or 2; N+). Taking into account of the experimental uncertainties, the measured ?(v+ = 1 or 2, N+) for N+ = 0-9 at Ecm = 0.04-10.0 eV are found to be independent of N+.

Chang, Yih Chung; Xu, Yuntao; Lu, Zhou; Xu, Hong; Ng, C. Y.

2012-09-01

394

Photon: history, mass, charge  

E-print Network

The talk consists of three parts. ``History'' briefly describes the emergence and evolution of the concept of photon during the first two decades of the 20th century. ``Mass'' gives a short review of the literature on the upper limit of the photon's mass. ``Charge'' is a critical discussion of the existing interpretation of searches for photon charge. Schemes, in which all photons are charged, are grossly inconsistent. A model with three kinds of photons (positive, negative and neutral) seems at first sight to be more consistent, but turns out to have its own serious problems.

L. B. Okun

2006-02-13

395

Negative Refraction Induced by M\\"{o}bius Topology  

E-print Network

We theoretically show the negative refraction existing in M\\"{o}bius molecules. The negative refractive index is induced by the non-trivial topology of the molecules. With the M\\"{o}bius boundary condition, the effective electromagnetic fields felt by the electron in a M\\"{o}bius ring is spatially inhomogeneous. In this regard, the $D_{N}$ symmetry is broken in M\\"{o}bius molecules and thus the magnetic response is induced through the effective magnetic field. Our findings open up a new architecture for negative refractive index materials based on the non-trivial topology of M\\"{o}bius molecules.

Fang, Y N; Ai, Qing; Sun, C P

2015-01-01

396

Single molecule spectroscopy of tetrahedral oligophenylenevinylene molecules  

E-print Network

Single molecule spectroscopy of tetrahedral oligophenylenevinylene molecules Melissa A. Summers form 17 July 2002 Abstract We probe the fluorescence from single molecules of a new class of tetrahedral oligo(phenylenevinylene) (OPV) molecules. Our results show that the tetrahedral molecules contain

Buratto, Steve

397

Negative ion density distribution in a volume negative ion source-its dependence on plasma parameters  

Microsoft Academic Search

In a volume negative ion source, H- ions are formed in hydrogen plasmas by dissociative attachment of slow plasma electrons to highly vibrationally excited hydrogen molecules, and these vibrational molecules are produced by energetic electron impact. Production of D- ions is believed to be the same as that of H- ions. To develop efficient D- ion sources, it is important

S. Mori; Y. Tauchi; O. Fukumasa; M. Hamabe; Y. Takeiri

2003-01-01

398

Building Molecules  

NSDL National Science Digital Library

This online interactive has three activities in the NanoLab (press the upper right button): Build, Zoom, and Transform. In Build, learners build increasingly complex molecules out of carbon, oxygen, and hydrogen, and is useful for connecting subscripts and the number of atoms, and for introducing 3D molecular structures which are automatically built. Zoom is a "powers of 10" zoom-in ranging from 10,000 kilometers to 1 nanometer. Transform is a simulation of water changing phase from solid to liquid to gas. Through exploration of the site learners form a better understanding of the composition of matter.

Rensselaer Polytechnic Institute

2005-01-01

399

Charge-Tunable Silk-Tropoelastin Protein Alloys That Control Neuron Cell Responses  

PubMed Central

Tunable protein composites are important for constructing extracellular matrix mimics of human tissues with control of biochemical, structural, and mechanical properties. Molecular interaction mechanisms between silk fibroin protein and recombinant human tropoelastin, based on charge, are utilized to generate a new group of multifunctional protein alloys (mixtures of silk and tropoelastin) with different net charges. These new biomaterials are then utilized as a biomaterial platform to control neuron cell response. With a +38 net charge in water, tropoelastin molecules provide extraordinary elasticity and selective interactions with cell surface integrins. In contrast, negatively charged silk fibroin protein (net charge ?36) provides remarkable toughness and stiffness with morphologic stability in material formats via autoclaving-induced beta-sheet crystal physical crosslinks. The combination of these properties in alloy format extends the versatility of both structural proteins, providing a new biomaterial platform. The alloys with weak positive charges (silk/tropoelastin mass ratio 75/25, net charge around +16) significantly improved the formation of neuronal networks and maintained cell viability of rat cortical neurons after 10 days in vitro. The data point to these protein alloys as an alternative to commonly used poly-L-lysine (PLL) coatings or other charged synthetic polymers, particularly with regard to the versatility of material formats (e.g., gels, sponges, films, fibers). The results also provide a practical example of physically designed protein materials with control of net charge to direct biological outcomes, in this case for neuronal tissue engineering. PMID:25093018

Hu, Xiao; Tang-Schomer, Min D.; Huang, Wenwen; Xia, Xiao-Xia; Weiss, Anthony S.

2014-01-01

400

Conformational transitions and stop-and-go nanopore transport of single-stranded DNA on charged graphene  

NASA Astrophysics Data System (ADS)

Control over interactions with biomolecules holds the key to applications of graphene in biotechnology. One such application is nanopore sequencing, where a DNA molecule is electrophoretically driven through a graphene nanopore. Here we investigate how interactions of single-stranded DNA and a graphene membrane can be controlled by electrically biasing the membrane. The results of our molecular dynamics simulations suggest that electric charge on graphene can force a DNA homopolymer to adopt a range of strikingly different conformations. The conformational response is sensitive to even very subtle nucleotide modifications, such as DNA methylation. The speed of DNA motion through a graphene nanopore is strongly affected by the graphene charge: a positive charge accelerates the motion, whereas a negative charge arrests it. As a possible application of the effect, we demonstrate stop-and-go transport of DNA controlled by the charge of graphene. Such on-demand transport of DNA is essential for realizing nanopore sequencing.

Shankla, Manish; Aksimentiev, Aleksei

2014-10-01

401

Analysis of the kinetics of P+ HA- recombination in membrane-embedded wild-type and mutant Rhodobacter sphaeroides reaction centers between 298 and 77 K indicates that the adjacent negatively charged QA ubiquinone modulates the free energy of P+ HA- and may influence the rate of the protein dielectric response.  

PubMed

Time-resolved spectroscopic studies of recombination of the P(+)HA(-) radical pair in photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides give an opportunity to study protein dynamics triggered by light and occurring over the lifetime of P(+)HA(-). The state P(+)HA(-) is formed after the ultrafast light-induced electron transfer from the primary donor pair of bacteriochlorophylls (P) to the acceptor bacteriopheophytin (HA). In order to increase the lifetime of this state, and thus increase the temporal window for the examination of protein dynamics, it is possible to block forward electron transfer from HA(-) to the secondary electron acceptor QA. In this contribution, the dynamics of P(+)HA(-) recombination were compared at a range of temperatures from 77 K to room temperature, electron transfer from HA(-) to QA being blocked either by prereduction of QA or by genetic removal of QA. The observed P(+)HA(-) charge recombination was significantly slower in the QA-deficient RCs, and in both types of complexes, lowering the temperature from RT to 77 K led to a slowing of charge recombination. The effects are explained in the frame of a model in which charge recombination occurs via competing pathways, one of which is thermally activated and includes transient formation of a higher-energy state, P(+)BA(-). An internal electrostatic field supplied by the negative charge on QA increases the free energy levels of the state P(+)HA(-), thus decreasing its energetic distance to the state P(+)BA(-). In addition, the dielectric response of the protein environment to the appearance of the state P(+)HA(-) is accelerated from ?50-100 ns in the QA-deficient mutant RCs to ?1-16 ns in WT RCs with a negatively charged QA(-). In both cases, the temperature dependence of the protein dynamics is weak. PMID:23477295

Gibasiewicz, Krzysztof; Pajzderska, Maria; Dobek, Andrzej; Brettel, Klaus; Jones, Michael R

2013-09-26

402

Ionization phenomena and sources of negative ions  

SciTech Connect

Negative ion source technology has rapidly advanced during the past several years as a direct consequence of the discovery of Krohn that negative ion yields can be greatly enhanced by sputtering in the presence of Group IA elements. Today, most negative ion sources use this discovery directly or the principles implied to effect negative ion formation through surface ionization. As a consequence, the more traditional direct extraction plasma and charge exchange sources are being used less frequently. However, the charge exchange generation mechanism appears to be as universal, is very competitive in terms of efficiency and has the advantage in terms of metastable ion formation. In this review, an attempt has been made to briefly describe the principal processes involved in negative ion formation and sources which are representative of a particular principle. The reader is referred to the literature for specific details concerning the operational characteristics, emittances, brightnesses, species and intensity capabilities of particular sources. 100 references.

Alton, G.D.

1983-01-01

403

Orbital molecules in electronic materials  

NASA Astrophysics Data System (ADS)

Orbital molecules are made up of coupled orbital states on several metal ions within an orbitally ordered (and sometimes also charge-ordered) solid such as a transition metal oxide. Spin-singlet dimers are known in many materials, but recent discoveries of more exotic species such as 18-electron heptamers in AlV2O4 and magnetic 3-atom trimerons in magnetite (Fe3O4) have shown that orbital molecules constitute a general new class of quantum electronic states in solids.

Attfield, J. Paul

2015-04-01

404

Single molecule study of a processivity clamp sliding on DNA  

SciTech Connect

Using solution based single molecule spectroscopy, we study the motion of the polIII {beta}-subunit DNA sliding clamp ('{beta}-clamp') on DNA. Present in all cellular (and some viral) forms of life, DNA sliding clamps attach to polymerases and allow rapid, processive replication of DNA. In the absence of other proteins, the DNA sliding clamps are thought to 'freely slide' along the DNA; however, the abundance of positively charged residues along the inner surface may create favorable electrostatic contact with the highly negatively charged DNA. We have performed single-molecule measurements on a fluorescently labeled {beta}-clamp loaded onto freely diffusing plasmids annealed with fluorescently labeled primers of up to 90 bases. We find that the diffusion constant for 1D diffusion of the {beta}-clamp on DNA satisfies D {le} 10{sup -14} cm{sup 2}/s, much slower than the frictionless limit of D = 10{sup -10} cm{sup 2}/s. We find that the {beta} clamp remains at the 3-foot end in the presence of E. coli single-stranded binding protein (SSB), which would allow for a sliding clamp to wait for binding of the DNA polymerase. Replacement of SSB with Human RP-A eliminates this interaction; free movement of sliding clamp and poor binding of clamp loader to the junction allows sliding clamp to accumulate on DNA. This result implies that the clamp not only acts as a tether, but also a placeholder.

Laurence, T A; Kwon, Y; Johnson, A; Hollars, C; O?Donnell, M; Camarero, J A; Barsky, D

2007-07-05

405

Progress of Negative Ions in Fusion Research  

SciTech Connect

Negative ion beams are assuming increasing significance in the field of controlled fusion research. The first generation of large high current negative ion sources has now operated successfully on the JT-60U tokamak for some years, producing negative ions of hydrogen or deuterium at energies up to 400 keV for conversion to several megawatts of neutrals which are used for plasma heating and current drive. We report an unexpected intensification phenomenon, and some of the improvements made or planned. In the realm of inertial confinement fusion, interest has grown in the use of heavy negative ion driver beams formed from halogens such as bromine, iodine, or chlorine. We discuss the advantages of negative ions as heavy ion fusion drivers, and assess the technical feasibility of a halogen negative beam system. We also discuss the potential for photodetaching the negative ions to produce atomically neutral beams and reduce beam space charge effects within the target chamber.

Grisham, L.R. [Princeton Univ. Plasma Physics Lab., P.O. Box 451, Princeton, N. J. 08543 (United States); Umeda, N.; Kawai, M.; Kuriyama, M.; Ohga, T.; Yamamoto, T. [Japan Atomic Energy Research Institute, Naka-Machi, Ibaraki 311-0193 (Japan)

2003-08-26

406

High-Efficiency Low Energy Neutral Beam Generation Using Negative Ions in Pulsed Plasma  

NASA Astrophysics Data System (ADS)

To prevent several kinds of radiation damage caused by charge build-up and by ultraviolet and X-ray photons during etching processes, we have developed a high-performance, neutral-beam etching system. The neutral-beam source consists of an inductively coupled plasma (ICP) source and top and bottom carbon parallel plates. The bottom carbon plate includes many apertures for extracting neutral beams from the plasma. By supplying a positive or negative direct current (DC) bias to the top and bottom carbon plates in the pulsed SF6 plasma, the generated positive or negative ions are respectively accelerated towards the bottom plate. The negative ions are more efficiently converted into neutral atoms in comparison with the positive ions, either by neutralization in charge-transfer collisions with gas molecules during the ion transport or with aperture sidewalls in the bottom plate. The neutralization efficiency of negative ions was more than 98% and the neutral flux density was equivalent to 4 mA/cm2.

Samukawa, Seiji; Sakamoto, Keisuke; Ichiki, Katsunori

2001-10-01

407

Water organization between oppositely charged surfaces: Implications for protein sliding along DNA a)  

NASA Astrophysics Data System (ADS)

Water molecules are abundant in protein-DNA interfaces, especially in their nonspecific complexes. In this study, we investigated the organization and energetics of the interfacial water by simplifying the geometries of the proteins and the DNA to represent them as two equally and oppositely charged planar surfaces immersed in water. We found that the potential of mean force for bringing the two parallel surfaces into close proximity comprises energetic barriers whose properties strongly depend on the charge density of the surfaces. We demonstrated how the organization of the water molecules into discretized layers and the corresponding energetic barriers to dehydration can be modulated by the charge density on the surfaces, salt, and the structure of the surfaces. The 1-2 layers of ordered water are tightly bound to the charged surfaces representing the nonspecific protein-DNA complex. This suggests that water might mediate one-dimensional diffusion of proteins along DNA (sliding) by screening attractive electrostatic interactions between the positively charged molecular surface on the protein and the negatively charged DNA backbone and, in doing so, reduce intermolecular friction in a manner that smoothens the energetic landscape for sliding, and facilitates the 1D diffusion of the protein.

Marcovitz, Amir; Naftaly, Aviv; Levy, Yaakov

2015-02-01

408

Water organization between oppositely charged surfaces: Implications for protein sliding along DNA.  

PubMed

Water molecules are abundant in protein-DNA interfaces, especially in their nonspecific complexes. In this study, we investigated the organization and energetics of the interfacial water by simplifying the geometries of the proteins and the DNA to represent them as two equally and oppositely charged planar surfaces immersed in water. We found that the potential of mean force for bringing the two parallel surfaces into close proximity comprises energetic barriers whose properties strongly depend on the charge density of the surfaces. We demonstrated how the organization of the water molecules into discretized layers and the corresponding energetic barriers to dehydration can be modulated by the charge density on the surfaces, salt, and the structure of the surfaces. The 1-2 layers of ordered water are tightly bound to the charged surfaces representing the nonspecific protein-DNA complex. This suggests that water might mediate one-dimensional diffusion of proteins along DNA (sliding) by screening attractive electrostatic interactions between the positively charged molecular surface on the protein and the negatively charged DNA backbone and, in doing so, reduce intermolecular friction in a manner that smoothens the energetic landscape for sliding, and facilitates the 1D diffusion of the protein. PMID:25725757

Marcovitz, Amir; Naftaly, Aviv; Levy, Yaakov

2015-02-28

409

Photoelectric Charging of Dust Particles  

NASA Technical Reports Server (NTRS)

Laboratory experiments have been performed on the photoelectric charging of dust particles which are either isolated or adjacent to a surface that is also a photoemitter. We find that zinc dust charges to a positive potential of a few volts when isolated in vacuum and that it charges to a negative potential of a few volts when passed by a photoemitting surface. The illumination is an arc lamp emitting wavelengths longer than 200 nm and the emitting surface is a zirconium foil.

Sickafoose, A.; Colwell, J.; Horanyi, M.; Robertson, S.; Walch, B.

1999-01-01

410

Methods and applications in single molecule electronics  

NASA Astrophysics Data System (ADS)

In recent years it has become possible to measure charge transport in a single molecule contacted to two metal electrodes. However, a thorough understanding of how a molecule behaves while contacted to two electrodes and how it interacts with its environment is still lacking. This thesis demonstrates various experimental methods for understanding and controlling charge transport in a single molecule junction and the application of these methods to various molecular systems to help elucidate the conduction mechanisms invoked. First, the conductance of DNA is examined in a controlled environment while varying the length, sequence, base-pair matching, bias, temperature, and electrochemical gate of the molecule. These studies show that the conductance of DNA is extremely sensitive to changes in length, sequence, and base-matching, but not as sensitive to temperature and electrochemical gate. Despite the variety of experimental methods applied, the subtleties of the conduction mechanism remain uncertain, and as such necessitate the development of additional tools for understanding the behavior of a single molecule junction. Next, the Conductance Screening Tool for Molecules (CSTM) is described. This is a new tool capable of creating 1000's of single molecules junctions in a matter of minutes. This tool has been used to study the conductance of alkanedithiols, molecules in an array, and single amino acid residues. This system allows for greater speed and flexibility in determining the conductance of a single molecule junction, and provides a capability for performing large-scale systematic studies of molecular systems to determine the conduction mechanism. Finally, an additional experimental method capable of extracting information about the interaction between a molecule and its environment is developed. Here, electron-phonon interactions in a single molecule contacted to two electrodes are studied. This method allows one to obtain a specific, chemical signature of a single molecule, to extract information about changes in the configuration of a single molecule junction during an experiment, and to correlate these changes with changes in the conductance of the molecule.

Hihath, Joshua

411

Modulation of emulsion rheology through electrostatic heteroaggregation of oppositely charged lipid droplets: influence of particle size and emulsifier content.  

PubMed

The influence of electrostatically-induced heteroaggregation of oppositely charged lipid droplets on the rheology and stability of emulsions has been studied. 20 wt.% oil-in-water emulsions (pH 6) containing oppositely charged droplets were fabricated by mixing cationic lactoferrin-coated lipid droplets with anionic ?-lactoglobulin-coated lipid droplets. Emulsions containing mixtures of droplets with different charges (positive or negative) and sizes (large or small) were prepared, and then their overall particle characteristics (?-potential and size) and rheology were measured. Emulsions formed by mixing positive droplets and negative droplets that were both relatively small (d(43) ? 0.3 ?m) exhibited extensive flocculation and had paste-like properties at intermediate positive-to-negative particle ratios. On the other hand, emulsions formed by mixing positive droplets and negative droplets that were both relatively large (d(43) ? 3 ?m) exhibited little aggregation and had relatively low viscosities at all particle ratios. Emulsions with small negative droplets and large positive droplets (or vice versa), exhibited some aggregation and viscosity enhancement at intermediate particle ratios. The presence of relatively high levels of protein in the aqueous phase of mixed emulsions reduced the level of droplet aggregation and viscosity enhancem