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1

Astronomers Discover First Negatively-charged Molecule in Space  

NASA Astrophysics Data System (ADS)

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

2006-12-01

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

Charged charmonium molecules  

SciTech Connect

We make use of a self-consistent quark-model based study of four-quark charmonium-like states to interpret recent charmonium experimental data. We conclude that there exists a D*D* meson-meson molecule with quantum numbers (I{sup G})J{sup PC}=(1{sup -})2{sup ++}. Our study confirms the presence of charged charmonium-like resonances on the excited charmonium spectrum. We find support from recent experimental data by the Belle Collaboration [R. Mizuk et al. (Belle Collaboration), Phys. Rev. D 78, 072004 (2008)]. Confirmation of the experimental data by the Belle Collaboration and the determination of the quantum numbers of the new structures would help in discriminating among different theoretical models and would give further support to the theoretical analysis of T. Fernandez-Carames, A. Valcarce, and J. Vijande [Phys. Rev. Lett. 103, 222001 (2009)].

Carames, T. F.; Valcarce, A.; Vijande, J. [Departamento de Fisica Fundamental, Universidad de Salamanca, E-37008 Salamanca (Spain); Departamento de Fisica Atomica, Molecular y Nuclear, Universidad de Valencia (UV) and IFIC (UV-CSIC), Valencia (Spain)

2010-09-01

6

Charge loss in gas-phase multiply negatively charged oligonucleotides.  

PubMed

In an attempt to shed light on the mechanism by which gaseous samples of negatively charged oligonucleotides undergo extremely slow (i.e., over 1-1000 s) charge loss, we have carried out molecular dynamics simulations on an oligonucleotide anion, T(5)(3-), containing five thymine, deoxyribose, and phosphate units in which the first, third, and fifth phosphates are negatively charged. The study is aimed at determining the rate at which an electron is detached from such a trianion by way of an internal Coulomb repulsion induced event. In this process, the intrinsic 5.0-5.1 eV electron binding strength of each phosphate site is reduced by the repulsive Coulomb potentials of the other two negative sites. As geometrical fluctuations cause the distances among the three negative phosphate sites to change, this causes the Coulomb repulsion energies at these sites to fluctuate. Once the Coulomb potential at any phosphate site exceeds ca. 5 eV, the electron on that site is able to undergo autodetachment. Although such an electron must tunnel through a barrier to escape, it is shown that the tunneling rate is not the rate-limiting step in electron loss; instead, it is the rate at which geometrical fluctuations cause the Coulomb potentials to exceed 5 eV that determines the rate of electron loss. Because these rates are extremely slow, special techniques had to be introduced to allow results of dynamics simulations on more flexible models of T(5)(3-) to be extrapolated to predict the behavior of the actual T(5)(3-). PMID:16839113

Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Czaplewski, Cezary; Sobczyk, Monika; Daranowski, Emma M; Skurski, Piotr; Simons, Jack

2005-01-13

7

Negatively charged hydrogen-bonded chains formed by tetrazole  

NASA Astrophysics Data System (ADS)

The complexes formed by tetrazole with MTBD, an N-base of guanidin-like character, were studied by FTIR spectroscopy. In the chloroform solution of 1:1 ratio, a -N⋯H +MTBD asymmetrical complex is formed and no dissociation of this complex is visible. With increasing tetrazole-MTBD ratio, the formation of chains of tetrazole molecules is observed. In acetonitrile solution of tetrazole with MTBD, the amount of protonated and dissociated H +MTBD species increases with increasing concentration of tetrazole. In these mixtures, negatively charged chains are observed to be formed with tetrazole molecules only; however, some amount of free tetrazole molecules is also detected in this case. All these chains show large proton polarizability

Brzezinski, B.; Wojciechowski, G.; Zundel, G.; Sobczyk, L.; Grech, E.

1999-09-01

8

The formation of negatively charged particles in thermoemission plasmas  

SciTech Connect

The results of measuring the charges of the magnesium oxide particles formed near a block of metallic magnesium burning in air are presented. It has been found that, apart from positively charged magnesium oxide particles, there are negatively charged particles in the thermoemission plasma of the burning products. It has been shown that within the framework of the model of neutralizing charges, the oxide particles can acquire unlike charges in the thermoemission plasma. The calculations agree with the experimental data.

Vishnyakov, V. I., E-mail: pipeaes@te.net.ua; Dragan, G. S.; Florko, A. V. [Mechnikov Odessa National University (Ukraine)

2008-01-15

9

The formation of negatively charged particles in thermoemission plasmas  

NASA Astrophysics Data System (ADS)

The results of measuring the charges of the magnesium oxide particles formed near a block of metallic magnesium burning in air are presented. It has been found that, apart from positively charged magnesium oxide particles, there are negatively charged particles in the thermoemission plasma of the burning products. It has been shown that within the framework of the model of neutralizing charges, the oxide particles can acquire unlike charges in the thermoemission plasma. The calculations agree with the experimental data.

Vishnyakov, V. I.; Dragan, G. S.; Florko, A. V.

2008-01-01

10

Static Electricity: Charging an Electroscope by Induction Using a Negatively-Charged Balloon  

NSDL National Science Digital Library

This item gives step-by-step animated explanations of charge interactions when a negatively-charged balloon is brought near a charge detecting device (the electroscope). It reinforces the concepts of induction, charge polarization, grounding, and charge distribution. This item is part of Multimedia Physics Studio, a set of animations within The Physics Classroom collection of tutorials for high school physics students.

Henderson, Tom

2006-03-15

11

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

12

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

13

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

14

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

15

An electrodiffusion model for the blood-brain barrier permeability to charged molecules.  

PubMed

The endothelial surface glycocalyx layer (SGL) and the basement membrane (BM) are two important components of the blood-brain barrier (BBB). They provide large resistance to solute transport across the BBB in addition to the tight junctions in the cleft between adjacent endothelial cells. Due to their glycosaminoglycan compositions, they carry negative charge under physiological conditions. To investigate the charge effect of the SGL and BM on the BBB permeability to charged solutes, we developed an electrodiffusion model for the transport of charged molecules across the BBB. In this model, constant charge densities were assumed in the SGL and in the BM. Both electrostatic and steric interaction and exclusion to charged molecules were considered within the SGL and the BM and at their interfaces with noncharged regions of the BBB. On the basis of permeability data for the positively charged ribonuclease (+4,radius=2.01?nm) and negatively charged ?-lactalbumin (-10,radius=2.08?nm) measured in intact rat mesenteric and pial microvessels, our model predicted that the charge density in both SGL and BM would be ?30?mEq/L, which is comparable to that in the SGL of mesenteric microvessels. Interestingly, our model also revealed that due to the largest concentration drop in the BM, there is a region with a higher concentration of negatively charged ?-lactalbumin in the uncharged inter-endothelial cleft, although the concentration of ?-lactalbumin is always lower than that of positively charged ribonuclease and that of a neutral solute in the charged SGL and BM. PMID:21280874

Li, Guanglei; Fu, Bingmei M

2011-02-01

16

Evidence for Leaflet-Dependent Redistribution of Charged Molecules in Fluid Supported Phospholipid Bilayers  

PubMed Central

The asymmetric distribution of charged molecules between the leaflets of solid-substrate-supported phospholipid bilayers is studied using imaging ellipsometry, fluorescence microscopy, and numerical solutions of the Poisson-Boltzmann equation. Experiments are facilitated by the use of patterned substrates that allow for side-by-side comparison of lipid monolayers and supported bilayers. On silica surfaces, negatively charged lipid components are shown to be enriched in the outer leaflet of a supported bilayer system at modest salt concentrations. The approaches developed provide a general means for determining asymmetries of charged components in supported lipid bilayers. PMID:19007257

Shreve, Andrew P.; Howland, Michael C.; Sapuri-Butti, Annapoorna R.; Allen, Toby W.; Parikh, Atul N.

2009-01-01

17

Charged vortices in the negative U Hubbard model  

Microsoft Academic Search

We have studied the negative U Hubbard model as a candidate generic model for high-Tc superconductivity with short coherence length. We show that in the strong coupling limit the structure of the vortex is qualitatively different from the usual picture. Charge is accumulated in the vortex and the core is insulating, while the size depends on the band filling.

L. F. Feiner; J. Zaanen

1989-01-01

18

Interfacial charge transfer events of BODIPY molecules: single molecule spectroelectrochemistry and substrate effects.  

PubMed

We present single molecule fluorescence and spectroelectrochemistry characteristics of 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) bearing two carboxylic acid groups at its 2 and 6 positions. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-tin oxide (ITO) surfaces. Single molecule stability tests show longer ON duration time and a stable fluorescence feature when dispersed in polystyrene thin film than molecules exposed to air. Shorter ON times are observed for molecules. In intimate contact with ITO in comparison to glass substrates. Such a decrease in their fluorescence stability or intensity is explained by charge transfer activities from the dye molecules to the metal oxide surface. Electron transfer and back transfer rates are calculated to illustrate the substrate effects by using a well-established model. PMID:25252244

Liu, Jia; Hill, Caleb M; Pan, Shanlin; Liu, Haiying

2014-10-01

19

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

20

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

NASA Astrophysics Data System (ADS)

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

Weinkauf, Rainer; Lehrer, Florian

1998-12-01

21

In pursuit of negative Fukui functions: molecules with very small band gaps.  

PubMed

A justification for the likely presence of negative Fukui functions in molecules with small band gaps is given, and a computational study performed to check whether molecules with small band gaps have negative Fukui functions to a chemically significant extent is reported. While regions with negative Fukui functions were observed, significantly negative values for the atom-condensed Fukui functions were not observed. PMID:24573501

Echegaray, Eleonora; Rabi, Sandra; Cárdenas, Carlos; Zadeh, Farnaz Heidar; Rabi, Nataly; Lee, Sungmin; Anderson, James S M; Toro-Labbe, Alejandro; Ayers, Paul W

2014-03-01

22

Partial Atomic Charge Derivation of small molecule Partial atomic charge is very crucial for computing physical, chemical and biological  

E-print Network

Partial Atomic Charge Derivation of small molecule Partial atomic charge is very crucial of the atomic charge in a given species, it is possible to predict the stability, solvation energetics atomic charges from experiment. Also, there is no universally agreed upon best procedure for computing

Jayaram, Bhyravabotla

23

Hair treatment composition comprising composite particles of clay and charged organic molecule  

US Patent & Trademark Office Database

A hair treatment composition comprising an aqueous dispersion of composite particles, said particles comprising: i) a clay with a net surface charge, and ii) a charged organic molecule comprising at least 6, preferably at least 11, more preferably at least 17 carbon atoms, wherein the charge on the charged organic molecule is opposite to the net surface charge of the clay, said hair treatment composition further comprising one or more suitable hair treatment ingredients.

2010-04-06

24

Influence of charge distribution on the thermophysical and dynamical properties of polar linear molecules  

NASA Astrophysics Data System (ADS)

Gibbs ensemble Monte Carlo and molecular dynamics simulations were used to study thermophysical and dynamical properties of Kihara fluids consisting of linear molecules with dipolar symmetry. Two models differing in the electrostatic part of the intermolecular potential have been considered. The first one is an ideal dipole (ID) model where electrostatic interactions are modeled as point dipoles placed on the molecular center of mass, and the second one is a discrete charge (DC) model with single positive and negative charges placed at opposite ends of the molecules. The magnitude of the charges and the distance between them were chosen to reproduce the dipole moment of the ID model. In addition, an effective ionic strength for the DC model has been defined. Simulations were performed at several densities and temperatures in a wide range of molecular lengths and at three dipole moments. For all the systems, vapor-liquid equilibrium, thermodynamic, and structural properties, autocorrelation functions, correlation times, and transport properties such as diffusion, shear viscosity, and thermal conductivity have been obtained and analyzed. The results of the present study are in agreement with those found in previous works and they confirm that, although differences between the DC model and the ID model are small for the lower molecular lengths, they become more pronounced at higher molecular lengths. Finally, the influence of the effective ionic strength on the different properties of the system is discussed.

Calero, Sofía; Garzón, Benito; Lago, Santiago

2003-06-01

25

Heparosan based negatively charged nanocarrier for rapid intracellular drug delivery.  

PubMed

In this study, a heparosan-DOX conjugate (HDC) was designed and prepared by covalently linking heparosan with anticancer drug doxorubicin (DOX) via "Schiff" base. Due to the amphiphilic nature, the HDC could self-assemble into nanoparticles in aqueous solution of pH 7.4. In spite of the surface charge of HDC nanoparticles was negative, HDC could achieve intracellular delivery of DOX efficiently. Cellular uptake study revealed the endocytosis pathway of heparosan based nanocarrier includes clathrin-mediated endocytosis and macropinocytosis, and the process of endocytosis is energy dependent. This meant the HDC would reach endosomes and behave pH-sensitive DOX release profile due to the inherent property of "Schiff" base. The cytotoxicity assay and flow cytometry analysis demonstrated the cellular uptake of HDC was faster than that of free DOX, showing improved efficacy within short co-incubation period. Furthermore, the HDC nanoparticles were stable in culture medium containing 10% FBS, indicating promising application for drug delivery. PMID:25089505

Chen, Jing-Xiao; Liu, Wen; Zhang, Miao; Chen, Jing-Hua

2014-10-01

26

Brownian dynamics simulations of simplified cytochrome c molecules in the presence of a charged surface  

NASA Astrophysics Data System (ADS)

Simulations were performed for up to 150 simplified spherical horse heart cytochrome c molecules in the presence of a charged surface, which serves as an approximate model for a lipid membrane. Screened electrostatic and short-ranged attractive as well as repulsive van der Waals forces for interparticle and particle-membrane interactions are utilized in the simulations. At a distance from the membrane, where particle-membrane interactions are negligible, the simulation is coupled to a noninteraction continuum analogous to a heat bath [Geyer et al., J. Chem. Phys. 120, 4573 (2004)]. From the particles' density profiles perpendicular to the planar surface binding isotherms are derived and compared to experimental results [Heimburg et al. (1999)]. Using a negatively charged structureless membrane surface a saturation effect was found for relatively large particle concentrations. Since biological membranes often contain membrane proteins, we also studied the influence of additional charges on our model membrane mimicking bacterial reaction centers. We find that the onset of the saturation occurs for much lower concentrations and is sensitive to the detailed implementation. Therefore we suggest that local distortion of membrane planarity (undulation), or lipid demixing, or the presence of charged integral membrane proteins create preferential binding sites on the membrane. Only then do we observe saturation at physiological concentrations.

Gorba, C.; Geyer, T.; Helms, V.

2004-07-01

27

Effect of charged and excited states on the decomposition of 1,1-diamino-2,2-dinitroethylene molecules  

SciTech Connect

The authors have calculated the electronic structure of individual 1,1-diamino-2,2-dinitroethylene molecules (FOX-7) in the gas phase by means of density functional theory with the hybrid B3LYP functional and 6-31+G(d,p) basis set and considered their dissociation pathways. Positively and negatively charged states as well as the lowest excited states of the molecule were simulated. They found that charging and excitation can not only reduce the activation barriers for decomposition reactions but also change the dominating chemistry from endo- to exothermic type. In particular, they found that there are two competing primary initiation mechanisms of FOX-7 decomposition: C-NO{sub 2} bond fission and C-NO{sub 2} to CONO isomerization. Electronic excitation or charging of FOX-7 disfavors CONO formation and, thus, terminates this channel of decomposition. However, if CONO is formed from the neutral FOX-7 molecule, charge trapping and/or excitation results in spontaneous splitting of an NO group accompanied by the energy release. Intramolecular hydrogen transfer is found to be a rare event in FOX-7 unless free electrons are available in the vicinity of the molecule, in which case HONO formation is a feasible exothermic reaction with a relatively low energy barrier. The effect of charged and excited states on other possible reactions is also studied. Implications of the obtained results to FOX-7 decomposition in condensed state are discussed.

Kimmel, Anna V.; Sushko, Peter V.; Shluger, Alexander L.; Kuklja, Maija M. [Department of Physics, University of Nevada, Las Vegas, Nevada 89154 and Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Department of Physics, University of Nevada, Las Vegas, Nevada 89154 (United States); Division of Materials Research, National Science Foundation, Arlington, Virginia 22203 (United States)

2007-06-21

28

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

29

Charge Transfer and Chemisorption of Fullerene Molecules on Metal Surfaces: Application to Dynamics of Nanocars  

E-print Network

Charge Transfer and Chemisorption of Fullerene Molecules on Metal Surfaces: Application to Dynamics Information ABSTRACT: It is widely believed that the dynamics of surface-bound fullerene molecules theoretical approach to describe charge transfer and chemisorption processes for fullerenes on gold surfaces

30

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.

31

Differing roles for B7 and intercellular adhesion molecule-1 in negative selection of thymocytes  

PubMed Central

To ensure self tolerance, immature thymocytes with high binding affinity for self peptides linked to major histocompatibility complex (MHC) molecules are eliminated in situ via apoptosis (negative selection). The roles of two costimulatory molecules, B7-1 and intercellular adhesion molecule-1 (ICAM-1), in negative selection was examined by studying apoptosis of T cell receptor transgenic CD4+8+ thymocytes cultured with specific peptides presented by MHC class I- transfected Drosophila cells. When coexpressed on these cells, B7-1 and ICAM-1 act synergistically and cause strong class 1-restricted negative selection of thymocytes. When expressed separately, however, B7-1 and ICAM-1 display opposite functions: negative selection is augmented by B7-1, but is inhibited by ICAM-1. It is notable that B7-1 is expressed selectively in the thymic medulla, whereas ICAM-1 is expressed throughout the thymus. Because of this distribution, the differing functions of B7-1 and ICAM-1 may dictate the sites of positive and negative selection. Thus, in the cortex, the presence of ICAM-1, but not B7-1, on the cortical epithelium may preclude or reduce negative selection and thereby promote positive selection. Conversely, the combined expression of B7-1 and ICAM-1 may define the medulla as the principal site of negative selection. PMID:8760806

1996-01-01

32

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

E-print Network

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

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

33

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

PubMed Central

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

Stace, T M; Damiano, E R

2001-01-01

34

Electromagnetic plane waves with negative phase velocity in charged black strings  

SciTech Connect

We investigate the propagation regions of electromagnetic plane waves with negative phase velocity in the ergosphere of static charged black strings. For such a propagation, some conditions for negative phase velocity are established that depend on the metric components and the choice of the octant. We conclude that these conditions remain unaffected by the negative values of the cosmological constant.

Sharif, M., E-mail: msharif.math@pu.edu.pk; Manzoor, R., E-mail: rubabmanzoor9@yahoo.com [University of the Punjab, Department of Mathematics (Pakistan)

2013-02-15

35

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

Microsoft Academic Search

Negative differential resistance (NDR) has been observed for individual 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) molecules on Si(111) 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(111) sample. At 77K no NDR effects were observed, but the I(V) curves were similar in shape to

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

2007-01-01

36

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

37

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

38

Surface sliding friction of negatively charged polyelectrolyte gels.  

PubMed

The friction between two polyelectrolyte gels carrying the same or opposite sign of charges has been investigated using a rheometer. It is found that the friction was strongly dependent on the interfacial interaction between two gel surfaces. In the repulsive interaction case, especially, the friction was extremely low. The friction behavior is attempted to be described in terms of the hydrodynamic lubrication of the solvent layer between two like-charged gel surfaces, which is formed due to the electrostatic repulsion of the two gel surfaces. From the theoretical analysis (hydrodynamic mechanism), the friction behaviors were explained qualitatively, all of the experimental results, nevertheless, could not be understood well. The viscoelastic feature of the gel and the non-Newtonian behavior of water at the friction interface are considered to be important to elucidate the gel friction. PMID:17137762

Kagata, Go; Gong, Jian Ping

2007-04-15

39

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

PubMed Central

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

Buchoux, Sebastien; Lai-Kee-Him, Josephine; Garnier, Marie; Tsan, Pascale; Besson, Francoise; Brisson, Alain; Dufourc, Erick J.

2008-01-01

40

Aberration of a negative ion beam caused by space charge effect  

SciTech Connect

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

Miyamoto, K. [Naruto University of Education, 748 Nakashima, Takashima, Naruto-cho, Naruto-shi, Tokushima 772-8502 (Japan); Wada, S.; Hatayama, A. [Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

2010-02-15

41

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

PubMed

Aberrations are inevitable when the charged particle beams are extracted, accelerated, transmitted, and focused with electrostatic and magnetic fields. In this study, we investigate the aberration of a negative ion accelerator for a neutral beam injector theoretically, especially the spherical aberration caused by the negative ion beam expansion due to the space charge effect. The negative ion current density profiles with the spherical aberration are compared with those without the spherical aberration. It is found that the negative ion current density profiles in a log scale are tailed due to the spherical aberration. PMID:20192393

Miyamoto, K; Wada, S; Hatayama, A

2010-02-01

42

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

43

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

NASA Astrophysics Data System (ADS)

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

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

1990-07-01

44

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

45

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

46

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

47

Negatively charged excitons and photoluminescence in asymmetric quantum wells  

SciTech Connect

We study photoluminescence (PL) of charged excitons (X{sup -}) in narrow asymmetric quantum wells in high magnetic fields B. The binding of all X{sup -} states strongly depends on the separation {delta} of electron and hole layers. The most sensitive is the ''bright'' singlet, whose binding energy decreases quickly with increasing {delta} even at relatively small B. As a result, the value of B at which the singlet-triplet crossing occurs in the X{sup -} spectrum also depends on {delta}, and decreases from 35 T in a symmetric 10 nm GaAs well to 16 T for {delta}=0.5 nm. Since the critical values of {delta} at which different X{sup -} states unbind are surprisingly small compared to the well width, the observation of strongly bound X{sup -} states in an experimental PL spectrum implies virtually no layer displacement in the sample. This casts doubt on the interpretation of PL spectra of heterojunctions in terms of X{sup -} recombination.

Szlufarska, Izabela; Wojs, Arkadiusz; Quinn, John J.

2001-02-15

48

Static Electricity: Charging an Electrophorus by Induction Using a Negatively Charged Object  

NSDL National Science Digital Library

This animation depicts the common physics demonstration of charging an aluminum pie plate by induction. The detailed text explanation helps students understand grounding and separation of charge. This item is part of Multimedia Physics Studio, a set of animations within The Physics Classroom collection of tutorials for high school physics students.

Henderson, Tom

2006-03-15

49

Photoelectron spectroscopy of negatively charged bismuth clusters: Big, Big, and Bi,-  

E-print Network

Photoelectron spectroscopy of negatively charged bismuth clusters: Big, Big, and Bi,- Mark L. Polak Institute of Standards and Technology and University of Colorado and Department of Chemistry of mass selectivity and high sensitivity, negative ion photoelectron spectroscopy is a particularly useful

Lineberger, W. Carl

50

New analytical potential energy function for doubly charged diatomic molecules  

NASA Astrophysics Data System (ADS)

A new analytical potential function for doubly charged diatomic ions is proposed as V(R) = (?n = 0kanRn-1)exp(-ak+1R)+C/R, where an, ak+1 and C are parameters and R is the nuclear distance. This function can be used to describe the potential curves for doubly charged diatomic ions with both potential minimum and maximum, or without any stationary point. As examples, potential functions of this form for ground states of BH2+, He22+ and HF2+ have been derived. The calculations using the theoretical method QCISD with basis set 6-311++Gast have shown that the potential minimum of BH2+is at Rmin=0.147nm, the maximum at Rmax=0.185nm and ?E = Emax-Emin=0.062 eV; for He22+ Rmin=0.0736nm, Rmax=0.105nm and ?E = Emax-Emin=0.71 eV. It is found that the potential curve for HF2+ is one with a singly repulsive branch. The force constants and spectroscopic data for BH2+ and He22+ have also been worked out.

Wang, Fan-Hou; Yang, Chuan-Lu; Zhu, Zheng-He; Jing, Fu-Qian

2005-02-01

51

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

52

New Model of Charged Molecule Redistribution Induced in Spherical Vesicles by Direct Current Electric Field  

PubMed Central

A new electrophoresis model of charged components in a spherical phospholipid vesicle is proposed. In the new model the effective local tangential electric field is a result of the uniform external electric field modified by the electric field of redistributed charges. The modification is calculated on the basis of the Gouy-Chapman surface potential theory. Numerical calculations of steady-state distribution of charged molecules and the transmembrane potential are performed. The results show significant difference from the old, simplified model that neglects modification of the external electric field caused by redistributed charges. PMID:9017190

Piasecki, Wojciech; Salwinski, Lukasz; Froncisz, Wojciech

1997-01-01

53

Water freezes differently on positively and negatively charged surfaces of pyroelectric materials.  

PubMed

Although ice melts and water freezes under equilibrium conditions at 0 degrees C, water can be supercooled under homogeneous conditions in a clean environment down to -40 degrees 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 degrees C freeze immediately when this surface is heated to -8 degrees 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. PMID:20133568

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

2010-02-01

54

Nanotribological Properties of Positively and Negatively charged nanodiamonds as additives to solutions  

NASA Astrophysics Data System (ADS)

Nano-diamond (ND) particles are known to be beneficial for wear and friction reduction when used as additives in liquids,[1] but the fundamental origins of the improvement in tribological properties has not been established. In order to explore this issue, we have investigated the nanotribological properties of ND coated with self-assembled monolayers (SAM) as additives to solutions, employing gold/chrome coated quartz crystal microbalances (QCM). Measurements were performed with the QCM initially immersed in deionized water. ND particles with positively and negatively charged SAM end groups were then added to the water, while the frequency and amplitude of the QCM were monitored. Negative shifts in both the QCM frequency and amplitude were observed when ND with positively charged SAM end groups were added, while positive shifts in both the QCM frequency and amplitude were observed when ND with negatively charged ND end groups were added . The results are consistent with a lubricating effect for the negatively charged ND, but were only observed for sufficiently small negative ND particle size. Experiments on QCM surfaces with differing textures and roughness are in progress, to determine the separate contributing effects of surface roughness charge-water interactions. 1. V. N. Mochalin, et al, Nat. Nanotech. 7, 11--23 (2012) doi:10.1038/nnano.2011.209

Liu, Zijian; Corley, Steven; Shenderova, Olga; Brenner, Donald; Krim, Jacqueline

2013-03-01

55

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

56

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

SciTech Connect

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

Wegner, P.C.

1986-02-11

57

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

58

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

59

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

60

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

61

Small-molecule suppression of ?-lactam resistance in multidrug-resistant gram-negative pathogens.  

PubMed

Recent efforts toward combating antibiotic resistance in bacteria have focused on Gram-positive bacteria; however, multidrug-resistant Gram-negative bacteria pose a significant risk to public health. An orthogonal approach to the development of new antibiotics is to develop adjuvant compounds that enhance the susceptibility of drug-resistant strains of bacteria to currently approved antibiotics. This paper describes the synthesis and biological activity of a library of aryl amide 2-aminoimidazoles based on a lead structure from an initial screen. A small molecule was identified from this library that is capable of lowering the minimum inhibitory concentration of ?-lactam antibiotics by up to 64-fold. PMID:25137478

Brackett, Christopher M; Melander, Roberta J; An, Il Hwan; Krishnamurthy, Aparna; Thompson, Richele J; Cavanagh, John; Melander, Christian

2014-09-11

62

Picosecond reorientational dynamics of oppositely charged dye molecules. Correlation with the dielectric friction  

Microsoft Academic Search

The rotational reorientation times (?rot) of charged dyes have been measured in polar protic and aprotic solvents, using difference frequency modulation picosecond pump-probe spectroscopy. The dielectric friction (DF) model has been shown to explain nonhydrodynamic behavior in alcohols and alcohol\\/water mixtures but is unsuccessful in predicting observed differences between the dye molecules in other solvent systems. These deviations are correlated

Eva F. Gudgin Templeton; G. A. Kenney-Wallace

1986-01-01

63

Picosecond reorientational dynamics of oppositely charged dye molecules. Correlation with the dielectric friction  

Microsoft Academic Search

The rotational reorientation times (taurot) of charged dyes have been measured in polar protic and aprotic solvents, using difference frequency modulation picosecond pump-probe spectroscopy. The dielectric friction (DF) model has been shown to explain nonhydrodynamic behavior in alcohols and alcohol\\/water mixtures but is unsuccessful in predicting observed differences between the dye molecules in other solvent systems. These deviations are correlated

Eva F. Gudgin Templeton; G. A. Kenney-Wallace

1986-01-01

64

Charge Manipulation in Molecules Encapsulated Inside Single-Wall Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

65

Synthesized negatively charged macromolecules (NCMs) for the surface modification of anticoagulant membrane biomaterials.  

PubMed

A series of negatively charged macromolecules (NCMs) including poly (sulfonated styrene-co-methyl methacrylate) (P(SS-co-MMA)), poly (acrylic acid-co-methyl methacrylate) (P(AA-co-MMA)) and poly (sulfonated styrene-co-acrylic acid-co-methyl methacrylate) (P(SS-co-AA-co-MMA)) are synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization using carboxyl-terminated trithiocarbonate as a RAFT agent. Activated partial thromboplastin time (APTT) tests indicate that the NCMs can retard blood clotting due to the negatively charged groups. The synthesized NCMs can be blended with polyethersulfone (PES) in dimethylacetamide (DMAC) to prepare membranes by means of a liquid-liquid phase separation technique. The prepared membranes were regular and smooth, except P(AA-co-MMA) modified membranes which were crude and rough due to the poor miscibility of AA segment and PES. The NCM modified PES membranes exhibited good anticoagulant ability due to the existence of the large density of the negative charges on the membrane surface, which induced a strong electrostatic repulsion with the negatively charged blood constituents. Therefore, the P(SS-co-AA-co-MMA) was designed and prepared with appropriate proportions of SS, AA and MMA for better membrane performance. The results indicated that the P(SS-co-AA-co-MMA) had potential to improve the anticoagulant property of biomaterials and to be applied in blood purification. PMID:23375800

Ran, Fen; Nie, Shengqiang; Yin, Zehua; Li, Jie; Su, Baihai; Sun, Shudong; Zhao, Changsheng

2013-04-01

66

Coherent population trapping of an electron spin in a single negatively charged  

E-print Network

,8 , slow light9 , quantum information storage10 and quantum repeaters11,12 . A critical condition proposed as a qubit for quantum computing owing to its long coherence time compared with fast opticalLETTERS Coherent population trapping of an electron spin in a single negatively charged quantum dot

Loss, Daniel

67

Static Electricity: Charging a Two-Sphere System by Induction Using a Negative Object  

NSDL National Science Digital Library

This animation depicts what happens when a negatively-charged balloon is brought near two neutral conducting spheres. A complete text explanation of the process accompanies the animation. This item is part of Multimedia Physics Studio, a set of animations within The Physics Classroom collection of tutorials for high school physics students.

Henderson, Tom

2006-03-15

68

Iron oxide/hydroxide nanoparticles with negatively charged shells show increased uptake in Caco-2 cells.  

PubMed

The absorption of commonly used ferrous iron salts from intestinal segments at neutral to slightly alkaline pH is low, mainly because soluble ferrous iron is easily oxidized to poorly soluble ferric iron and because ferrous iron, but not ferric iron, is carried by the divalent metal transporter DMT-1. Moreover, ferrous iron frequently causes gastrointestinal side effects. Iron hydroxide nanoparticles with neutral and hydrophilic carbohydrate shells are alternatively used to ferrous salts. In these formulations gastrointestinal side effects are rare because hundreds of ferric iron atoms are safely packed in nanoscaled cores surrounded by the solubilizing shell; nevertheless, iron bioavailability is even worse compared to ferrous salts. In this study the cell uptake of iron hydroxide and iron oxide nanoparticles (FeONP) with negatively charged shells of different chemical types and sizes was compared to the uptake of those with neutral hydrophilic shells, ferrous sulfate and ferric chloride. The nanoparticle uptake was measured in Caco-2 cells with the iron detecting ferrozine method and visualized by transmission electron microscopy. The toxicity was evaluated using the MTT assay. For nanoparticles with a negatively charged shell the iron uptake was about 40 times higher compared to those with neutral hydrophilic carbohydrate shell or ferric chloride and in the same range as ferrous sulfate. However, in contrast to ferrous sulfate, nanoparticles with negatively charged shells showed no toxicity. Two different uptake mechanisms were proposed: diffusion for hydroxide nanoparticles with neutral hydrophilic shell and adsorptive endocytosis for nanoparticles with negatively charged shells. It needs to be determined whether iron hydroxide nanoparticles with negatively charged shells also show improved bioavailability in iron-deficient patients compared to iron hydroxide nanoparticles with a neutral hydrophilic shell, which exist in the market today. PMID:22587679

Jahn, Markus R; Nawroth, Thomas; Fütterer, Sören; Wolfrum, Uwe; Kolb, Ute; Langguth, Peter

2012-06-01

69

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

70

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

SciTech Connect

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

Duha, S. S. [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)

2009-11-15

71

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 Grunberg, Hans Hennig

2002-01-01

72

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

73

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

74

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

75

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?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

76

Gating the Charge State of Single Molecules by Local Electric Fields  

NASA Astrophysics Data System (ADS)

The electron-acceptor molecule TCNQ is found in either of two distinct integer charge states when embedded into a monolayer of a charge transfer complex on a gold surface. Scanning tunneling spectroscopy measurements identify these states through the presence or absence of a zero-bias Kondo resonance. Increasing the (tip-induced) electric field allows us to reversibly induce the oxidation or reduction of TCNQ species from their anionic or neutral ground state, respectively. We show that the different ground states arise from slight variations in the underlying surface potential, pictured here as the gate of a three-terminal device.

Fernández-Torrente, I.; Kreikemeyer-Lorenzo, D.; Stró?ecka, A.; Franke, K. J.; Pascual, J. I.

2012-01-01

77

MIT Physics 8.02: Electrostatics - Electric Field of a Moving Negative Charge  

NSDL National Science Digital Library

This item is an animation depicting electric field of a moving negative charge when the speed of the charge is small compared to the speed of light. The item may be viewed as a video or in stepped motion. This item is part of a larger collection of visualizations developed by the MIT TEAL/Studio Physics Project to support an introductory course in electricity and magnetism. Lecture notes, labs, and presentations are also available as part of the MIT Open Courseware Repository: MIT Open Courseware: Electricity and Magnetism

Belcher, John

2010-04-11

78

Frequency-Dependent Capacitance of Hydrophobic Membranes Containing Fixed Negative Charges  

PubMed Central

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, Asher

1968-01-01

79

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

80

FAST TRACK COMMUNICATION: Silicon crystal for channelling of negatively charged particles  

NASA Astrophysics Data System (ADS)

Efficient channelling of negatively charged-particle beams in a bent crystal demands operation in axial mode, preferably along the lang1 1 1rang axis due to the strong confining potential generated along this direction. We propose a bent crystal suitable for steering negatively charged particle beams via axial channelling (AC) for operation at some gigaelectronvolt energy. The crystal is a quasi-mosaic crystal, relying on mechanical anisotropy of crystalline silicon. By use of high-resolution x-ray diffraction, we investigated the lattice bending of a crystal under the high-deformation regime. Anticlastic bending was found to weaken under a high deformation regime while anisotropic bending holds also under strong deformation. This circumstance envisages a versatile way to manage beams by AC.

Guidi, V.; Mazzolari, A.; De Salvador, D.; Carnera, A.

2009-09-01

81

Antiphospholipid syndrome and the relevance of antibodies to negatively charged phospholipids in diagnostic evaluation.  

PubMed

The presence of lupus anticoagulant, moderate-to-high levels of IgG and/or IgM antibodies to beta-2 glycoprotein I or cardiolipin in association with at least one of the two major clinical manifestations (thrombosis and/or pregnancy-related morbidity) are required for a diagnosis of definite antiphospholipid syndrome (APS). The realization that certain negatively charged phospholipid (PL) autoantibodies broadly react with antibodies directed against cardiolipin and may be more reliable and specific markers for APS has led to the search for diagnostic assays with greater predictability for disease evaluation and management. This review focuses on the state-of-the-art analytical and clinical performance of IgG and IgM antibodies directed against negatively charged PLs, specifically phosphatidic acid (aPA), phosphatidylinositol (aPI), and phosphatidylserine (aPS), as well as the APhL assay, which contains a proprietary mixture of phospholipid antigens. PMID:25228736

Tebo, Ae

2014-10-01

82

Surface Modification of Poly(ether sulfone) Membrane with a Synthesized Negatively Charged Copolymer.  

PubMed

In this study, we provide a new method to modify poly(ether sulfone) (PES) membrane with good biocompatibility, for which diazotized PES (PES-N2(+)) membrane is covalently coated by a negatively charged copolymer of sodium sulfonated poly(styrene-alt-maleic anhydride) (NaSPS-MA). First, aminated PES (PES-NH2) is synthesized by nitro reduction reaction of nitro-PES (PES-NO2), and then blends with pristine PES to prepare PES/PES-NH2 membrane; then the membrane is treated with NaNO2 aqueous solution at acid condition; after surface diazo reaction, surface positively charged PES/PES-N2(+) membrane is prepared. Second, poly(styrene-alt-maleic anhydride) (PS-alt-MA) is synthesized, then sulfonated and treated by sodium hydroxide solution to obtain sodium sulfonated (PS-alt-MA) (NaSPS-MA). Finally, the negatively charged NaSPS-MA copolymer is coated onto the surface positively charged PES/PES-N2(+) membrane via electrostatic interaction; after UV-cross-linking, the linkage between the PES-N2(+) and NaSPS-MA changes to a covalent bond. The surface-modified PES membrane is characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) analyses, and surface zeta potential analyses. The modified membrane exhibits good hemocompatibility and cytocompatibility, and the improved biocompatibility might have resulted from the existence of the hydrophilic groups (sodium carboxylate (-COONa) and sodium sulfonate (-SO3Na)). Moreover, the stability of the modified membrane is also investigated. The results indicated that the modified PES membrane using negatively charged copolymers had a lot of potential in blood purification fields and bioartificial liver supports for a long time. PMID:25347292

Zou, Wen; Qin, Hui; Shi, Wenbin; Sun, Shudong; Zhao, Changsheng

2014-11-18

83

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

84

Butyrylcholinesterase-catalysed hydrolysis of aspirin, a negatively charged ester, and aspirin-related neutral esters  

Microsoft Academic Search

Although aspirin (acetylsalicylic acid) is negatively charged, it is hydrolysed by butyrylcholinesterase (BuChE). Catalytic parameters were determined in 100 mM Tris buffer, pH 7.4, in the presence and absence of metal cations. The presence of Ca2+ or Mg2+ (<100 mM) in buffer did not change the Km, but accelerated the rate of hydrolysis of aspirin by wild-type or D70G mutant

Patrick Masson; Marie-Thérèse Froment; Pierre-Louis Fortier; Jean-Emmanuel Visicchio; Cynthia F. Bartels; Oksana Lockridge

1998-01-01

85

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

PubMed

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(-) 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. PMID:24593428

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

2014-02-01

86

Efflux pumps of gram-negative bacteria, a new target for new molecules.  

PubMed

Antibiotic resistance mechanisms reported in Gram-negative bacteria are a worldwide health problem. The continuous dissemination of multi-drug resistant (MDR) bacteria drastically reduces the efficacy of our antibiotic “arsenal” and consequently increases the frequency of therapeutic failure. In MDR bacteria the over-expression of efflux pumps expel structurally-unrelated antibiotics decreasing their intracellular concentration. It is necessary to clearly define the molecular and genetic bases of the efflux pump in order to combat this mechanism. The characterization of efflux pumps, from genetic to structural studies, allows the definition of a new, original antiresistance bullet, the efflux pump inhibitor (EPI). This new class of antibacterial molecules may act conjointly to the usual antibiotic in order to restore its activity. Several families of EPIs have been now reported and described. The use of these EPIs promotes a significant increase of susceptibility to one or more antibiotics in strains or clinical isolates which were initially resistant. These EPIs may target different efflux targets, (i) the expression of genes that induces MDR, the transporters that pump the antibiotic out of bacterium, (ii) the assembly of membrane transporter complex involved in drug efflux, (iii) the energy involved in this active transport, (iv) the inhibition of the flux of molecules inside the efflux channel by competition or blocking (via steric hindrances). With the recent thorough characterization of the efflux pump AcrB at its structural and physiological level including the identification of drug affinity sites and kinetic parameters for some antibiotics, it is now possible to rationally develop an improved new generation of EPIs. PMID:20615189

Pagès, Jean-Marie; Sandrine, Alibert-Franco; Mahamoud, Abdallah; Bolla, Jean-Michel; Davin-Regli, Anne; Chevalier, Jacqueline; Garnotel, Eric

2010-01-01

87

Localization accuracy in single molecule microscopy using electron-multiplying charge-coupled device cameras  

PubMed Central

The electron-multiplying charge-coupled device (EMCCD) is a popular technology for imaging under extremely low light conditions. It has become widely used, for example, in single molecule microscopy experiments where few photons can be detected from the individual molecules of interest. Despite its important role in low light microscopy, however, little has been done in the way of determining how accurately parameters of interest (e.g., location of a single molecule) can be estimated from an image that it produces. Here, we develop the theory for calculating the Fisher information matrix, and hence the Cramer-Rao lower bound-based limit of the accuracy, for estimating parameters from an EMCCD image. An EMCCD operates by amplifying a weak signal that would otherwise be drowned out by the detector’s readout noise as in the case of a conventional charge-coupled device (CCD). The signal amplification is a stochastic electron multiplication process, and is modeled here as a geometrically multiplied branching process. In developing our theory, we also introduce a “noise coefficient” which enables the comparison of the Fisher information of different data models via a scalar quantity. This coefficient importantly allows the selection of the best detector (e.g., EMCCD or CCD), based on factors such as the signal level, and regardless of the specific estimation problem at hand. We apply our theory to the problem of localizing a single molecule, and compare the calculated limits of the localization accuracy with the standard deviations of maximum likelihood location estimates obtained from simulated images of a single molecule. PMID:24379939

Chao, Jerry; Ward, E. Sally; Ober, Raimund J.

2012-01-01

88

Charge carrier dynamics of vapor-deposited small-molecule/fullerene organic solar cells.  

PubMed

Although small-molecule organic solar cells (SMOSCs) have shown increasingly promising prospects as a source of solar power, there have been few studies concerning the photophysics of these systems. Here, we report the time scale and efficiency of charge separation and recombination in a vapor-deposited SMOSC material that produces 5.81% power conversion efficiency. Transient absorption and time-resolved photoluminescence (trPL) studies of thin film blends comprising DTDCTB, a narrow-band gap electron donor, and either C60 or C70 as an electron acceptor show that charge separation occurs in ~100 fs, while charge recombination takes place over sub-ns and ns time scales. trPL indicates a donor electron-hole pair lifetime of ~33 ps in the neat film and reveals that ~20% of donors fail to charge separate in donor-acceptor mixed films, likely owing to some spatially extended donor-rich regions that interact poorly with acceptors. Our results suggest that morphological manipulations of this material could further improve device efficiency. PMID:23718234

Chang, Angela Y; Chen, Yi-Hong; Lin, Hao-Wu; Lin, Li-Yen; Wong, Ken-Tsung; Schaller, Richard D

2013-06-19

89

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

PubMed

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

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

2012-08-14

90

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 of interfacial water molecules. As the potential is increased at the air/water interface we observe a progression/Water Interfaces D. E. Gragson and G. L. Richmond* Contribution from the Department of Chemistry, Uni

Richmond, Geraldine L.

91

Dynamical coupling and negative differential resistance from interactions across the molecule-electrode interface in molecular junctions  

NASA Astrophysics Data System (ADS)

Negative differential resistance - a decrease in current with increasing bias voltage - is a counter-intuitive effect that is observed in various molecular junctions. Here, we present a novel mechanism that may be responsible for such an effect, based on strong Coulomb interaction between electrons in the molecule and electrons on the atoms closest to the molecule. The Coulomb interaction induces electron-hole binding across the molecule-electrode interface, resulting in a renormalized and enhanced molecule-electrode coupling. Using a self-consistent non-equilibrium Green's function approach, we show that the effective coupling is non-monotonic in bias voltage, leading to negative differential resistance. The model is in accord with recent experimental observations that showed a correlation between the negative differential resistance and the coupling strength. We provide detailed suggestions for experimental tests which may help to shed light on the origin of the negative differential resistance. Finally, we demonstrate that the interface Coulomb interaction affects not only the I-V curves but also the thermoelectric properties of molecular junctions.

Dubi, Yonatan

2013-10-01

92

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

93

Effect of carbon foams as negative current collectors on partial-state-of-charge performance of lead acid batteries  

Microsoft Academic Search

Flooded lead acid batteries were assembled by using a pitch-based carbon foam and a punched lead sheet as the negative current collectors, respectively. Comparative galvanostatic charge–discharge experiments were performed on the batteries to evaluate the effect of the carbon foam as a negative current collector material on the performance of lead acid batteries under partial-state-of-charge operation. The results indicate that

Ya Chen; Bai-Zhen Chen; Li-Wen Ma; Yan Yuan

2008-01-01

94

The Negatively Charged Regions of Lactoferrin Binding Protein B, an Adaptation against Anti-Microbial Peptides  

PubMed Central

Lactoferrin binding protein B (LbpB) is a bi-lobed membrane bound lipoprotein that is part of the lactoferrin receptor complex in a variety of Gram-negative pathogens. Despite high sequence diversity among LbpBs from various strains and species, a cluster of negatively charged amino acids is invariably present in the protein’s C-terminal lobe in all species except Moraxella bovis. The function of LbpB in iron acquisition has yet to be experimentally demonstrated, whereas in vitro studies have shown that LbpB confers protection against lactoferricin, a short cationic antimicrobial peptide released from the N- terminus of lactoferrin. In this study we demonstrate that the negatively charged regions can be removed from the Neisseria meningitidis LbpB without compromising stability, and this results in the inability of LbpB to protect against the bactericidal effects of lactoferricin. The release of LbpB from the cell surface by the autotransporter NalP reduces the protection against lactoferricin in the in vitro killing assay, attributed to removal of LbpB during washing steps, but is unlikely to have a similar impact in vivo. The protective effect of the negatively charged polysaccharide capsule in the killing assay was less than the protection conferred by LbpB, suggesting that LbpB plays a major role in protection against cationic antimicrobial peptides in vivo. The selective release of LbpB by NalP has been proposed to be a mechanism for evading the adaptive immune response, by reducing the antibody binding to the cell surface, but may also provide insights into the primary function of LbpB in vivo. Although TbpB and LbpB have been shown to be major targets of the human immune response, the selective release of LbpB suggests that unlike TbpB, LbpB may not be essential for iron acquisition, but important for protection against cationic antimicrobial peptides. PMID:24465982

Morgenthau, Ari; Beddek, Amanda; Schryvers, Anthony B.

2014-01-01

95

Surface patterns on co-assembled fibers from charged, amphiphilic molecules  

NASA Astrophysics Data System (ADS)

We analyze local segregation of species in charged multicomponent cylindrical micelles. In particular, we consider co-assemblies of cationic and anionic heterogeneous molecules such as lipids and peptide amphiphiles. Charge heterogeneities can develop at the surface of the fibers due to the competition between the short-range incompatibility of the co-assembled components and the electrostatic interactions. The system can be described by a line tension between domains ?, which favors growth of the domains of segregated components, and the electrostatic energy of the domains with charge density ?, which increases rapidly with the size of the segregated domain L. The competition results in the formation of domains with a characteristic size Lo=(??/2circ)^1/2. In stoichiometric mixtures the constraints of the geometry and the long range correlations lead to lamellar stripes of different pitch. We present results on the different orientations of the lamellar patterns as a function of the ratio between the lamellar size and the cylinder radius. We find the critical salt concentration, which is a function of radius and lamellar size, at which the patterns grow to macroscopic sizes due to the screening of the Coulomb interactions.

Kohlstedt, Kevin; Solis, Francisco; Olvera de La Cruz, Monica

2006-03-01

96

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

97

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

PubMed

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

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

2011-04-15

98

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

99

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

PubMed

Oligomers of the negatively-charged amino acids, glutamic acid, aspartic acid, and O-phospho-L-serine are adsorbed by hydroxylapatite and illite with affinities that increase with oligomer length. In the case of oligo-glutamic acids adsorbed on hydroxylapatite, addition of an extra residue results in an approximately four-fold increase in the strength of adsorption. Oligomers much longer than the 7-mer are retained tenaciously by the mineral. Repeated incubation of short oligo-glutamic acids adsorbed on hydroxylapatite or illite with activated monomer leads to the accumulation of oligomers at least 45 units long. The corresponding reactions of aspartic acid and O-phospho-L-serine on hydroxylapatite are less effective in generating long oligomers, while illite fails to accumulate substantial amounts of long oligomers of aspartic acid or of O-phospho-L-serine. PMID:9611764

Hill, A R; Böhler, C; Orgel, L E

1998-06-01

100

Photoinduced intramolecular charge-transfer state in thiophene-?-conjugated donor–acceptor molecules  

Microsoft Academic Search

Novel thiophene-?-conjugated donor–acceptor molecules, 5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thiophene-2-carbaldehyde (QTC) and (1-cyano-2-{5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thiophen-2-yl}-vinyl)-phosphonic acid diethyl ester (QTCP), were designed and synthesized. Combined experimental and theoretical methods were performed to investigate the photoinduced intramolecular charge-transfer (ICT) processes of these compounds. Steady-state absorption and fluorescence measurements in different solvents indicate the photoinduced ICT characters of QTC and QTCP. Solvent dependency of the large Stokes shifts and high

Ruikui Chen; Guangjiu Zhao; Xichuan Yang; Xiao Jiang; Jifeng Liu; Haining Tian; Yan Gao; Xien Liu; Keli Han; Mengtao Sun; Licheng Sun

2008-01-01

101

Photoelectron spectroscopy of color centers in negatively charged cesium iodide nanocrystals  

NASA Astrophysics Data System (ADS)

We present the photoelectron spectra of negatively charged cesium iodide nanocrystals recorded using 2.540 eV photons. The species examined were produced using an inert gas condensation cluster ion source, and they ranged in size from (CsI)-n=13 to nanocrystal anions comprised of 330 atoms. Nanocrystals showing two distinct types of photoemission behavior were observed. For (CsI)-n=13 and (CsI)-n=36-165, a plot of cluster anion photodetachment threshold energies vs n-1/3 gives a straight line extrapolating (at n-1/3=0, i.e., n=?) to 2.2 eV, the photoelectric threshold energy for F centers in bulk cesium iodide. The linear extrapolation of the cluster anion data to the corresponding bulk property implies that the electron localization in these gas-phase nanocrystals is qualitatively similar to that of F centers in extended alkali halide crystals. These negatively charged cesium iodide nanocrystals are thus shown to support embryonic forms of F centers, which mature with increasing cluster size toward condensed phase impurity centers. Under an alternative set of source conditions, nanocrystals were produced which showed significantly lower photodetachment thresholds than the aforementioned F-center cluster anions. For these species, containing 83-131 atoms, a plot of their cluster anion photodetachment threshold energies versus n-1/3 gives a straight line which extrapolates to 1.4 eV. This value is in accord with the expected photoelectric threshold energy for F' centers in bulk cesium iodide, i.e., color centers with two excess electrons in a single defect site. These nanocrystals are interpreted to be the embryonic F'-center containing species, Cs(CsI)-n=41-65.

Sarkas, Harry W.; Kidder, Linda H.; Bowen, Kit H.

1995-01-01

102

Electron molecule cross sections relevant to negative ion sources and divertor plasmas  

SciTech Connect

Electron-molecule cross sections for electronic transitions in H{sub 2} and D{sub 2} molecules vibrationally excited are presented, and a scaling law for the vibrational cross sections is discussed for the {ital X}{sup 1}{summation}{sup +}{sub {ital g}}{r_arrow}{ital B}{sup 1}{summation}{sup +}{sub {ital u}} electronic transition. {copyright} {ital 1996 American Institute of Physics.}

Celiberto, R.; Capitelli, M.; Lamanna, U.T. [Dipartimento di Chimica Universita` di Bari, and Centro di Studio per la Chimica dei Plasmi del C.N.R., Via Orabona, 4 70126 Bari (Italy); Janev, R.K. [International Atomic Energy Agency, Wagramerstrasse 5, P.O. Box 100, A-1400, Vienna (Austria)

1996-07-01

103

Characteristics of low energy atom and molecule beams generated by the charge exchange reaction  

SciTech Connect

A low energy NB source, which consisted of a surface wave plasma (SWP) source and two large diameter carbon electrodes, was developed for damageless etching of ultralarge-scale integrated devices. Ion beams were extracted from the SWP using two carbon electrodes, accelerated and injected to the process chamber, and then neutralized without energy loss by a charge exchange reaction. The energy distribution functions of an Ar ion beam and an Ar atom beam was observed using a quadrupole mass spectroscope equipped with an energy analyzer. The energy of the Ar ion beam and the Ar atom beam was controlled by the acceleration voltage. N{sub 2} ion and N ion beams were also extracted from a nitrogen plasma source. The intensity ratio of the N ion beam to the N{sub 2} ion beam was 5:9, indicating that N ions were efficiently generated in the nitrogen SWP. The N{sub 2} ion and N ion beams were changed to N{sub 2} molecule and N atom beams, respectively, through a charge exchange reaction without energy loss. The energy of these beams was controlled by the acceleration voltage and was in the region less of than 100 eV. When the acceleration voltage is higher than 40 V, not only the primary peaks due to the N{sub 2} ion beam or N ion beam were observed but also a low energy second peak was observed in the energy distribution. The energy of the low energy second peak was controlled by the acceleration voltage. It was concluded that the low energy second peak corresponds to the N{sub 2} molecule ion beam and the N ion beam, which is extracted from the second plasma generated in the space between the two carbon electrodes.

Hara, Yasuhiro; Takashima, Seigo; Toyoda, Hirotaka; Sekine, Makoto; Hori, Masaru [Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yamakawa, Koji; Den, Shoji [Katagiri Engineering Co., Ltd., Tsurumi-ku, Yokohama 230-0003 (Japan)

2008-03-01

104

Multielectron Effects in Charge Asymmetric Molecules Induced by Asymmetric Laser Fields  

NASA Astrophysics Data System (ADS)

Using a 45 fs pump pulse at 800 nm, a wave packet is created in a charge asymmetric dissociation channel of iodine, I22+?I2++I0+ (2,0). As the molecule dissociates, a two-color (1?2?) probe pulse is used to study the dynamics as a function of internuclear separation R. We find a critical region of R in which there is spatially asymmetric enhanced ionization of the (2,0) channel to a counterintuitive (1,2) channel. In this region the I0+ is ionized such that one electron is released to the continuum and another is transferred to the I2+ resulting in I0+?I2+ and I2+?I1+. At larger R, the ionization is consistent with simple one-electron ionization in a double well where I0+?I1+. We find qualitative agreement between simulations and experiment further highlighting the importance of multielectron effects in the strong-field ionization of molecules.

Tagliamonti, V.; Chen, H.; Gibson, G. N.

2013-02-01

105

Multielectron effects in charge asymmetric molecules induced by asymmetric laser fields.  

PubMed

Using a 45 fs pump pulse at 800 nm, a wave packet is created in a charge asymmetric dissociation channel of iodine, I(2)(2+)?I(2+)+I(0+) (2,0). As the molecule dissociates, a two-color (1?2?) probe pulse is used to study the dynamics as a function of internuclear separation R. We find a critical region of R in which there is spatially asymmetric enhanced ionization of the (2,0) channel to a counterintuitive (1,2) channel. In this region the I(0+) is ionized such that one electron is released to the continuum and another is transferred to the I(2+) resulting in I(0+)?I(2+) and I(2+)?I(1+). At larger R, the ionization is consistent with simple one-electron ionization in a double well where I(0+)?I(1+). We find qualitative agreement between simulations and experiment further highlighting the importance of multielectron effects in the strong-field ionization of molecules. PMID:25166372

Tagliamonti, V; Chen, H; Gibson, G N

2013-02-15

106

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

107

Charge transfer through single molecule contacts: How reliable are rate descriptions?  

PubMed Central

Summary Background: The trend for the fabrication of electrical circuits with nanoscale dimensions has led to impressive progress in the field of molecular electronics in the last decade. However, a theoretical description of molecular contacts as the building blocks of future devices is challenging, as it has to combine the properties of Fermi liquids in the leads with charge and phonon degrees of freedom on the molecule. Outside of ab initio schemes for specific set-ups, generic models reveal the characteristics of transport processes. Particularly appealing are descriptions based on transfer rates successfully used in other contexts such as mesoscopic physics and intramolecular electron transfer. However, a detailed analysis of this scheme in comparison with numerically exact solutions is still elusive. Results: We show that a formulation in terms of transfer rates provides a quantitatively accurate description even in domains of parameter space where strictly it is expected to fail, e.g., at lower temperatures. Typically, intramolecular phonons are distributed according to a voltage driven steady state that can only roughly be captured by a thermal distribution with an effective elevated temperature (heating). An extension of a master equation for the charge–phonon complex, to effectively include the impact of off-diagonal elements of the reduced density matrix, provides very accurate solutions even for stronger electron–phonon coupling. Conclusion: Rate descriptions and master equations offer a versatile model to describe and understand charge transfer processes through molecular junctions. Such methods are computationally orders of magnitude less expensive than elaborate numerical simulations that, however, provide exact solutions as benchmarks. Adjustable parameters obtained, e.g., from ab initio calculations allow for the treatment of various realizations. Even though not as rigorously formulated as, e.g., nonequilibrium Green’s function methods, they are conceptually simpler, more flexible for extensions, and from a practical point of view provide accurate results as long as strong quantum correlations do not modify the properties of the relevant subunits substantially. PMID:22003449

Kecke, L; Ankerhold, J

2011-01-01

108

Interaction of positively and negatively charged aromatic hydrocarbons with benzene and triphenylene: Towards a model of pure organic insulators  

NASA Astrophysics Data System (ADS)

A theoretical study of the complexes formed by two aromatic charged hydrocarbons, cyclopropenyl cation and phenalenyl anion, with benzene and triphenylene has been carried out. The binary complexes between the charged molecules and the neutral ones have been characterized as well as the ternary systems with the neutral systems acting as insulators of the charged ones. In the ternary complex a cooperative effect is observed both in the energy and in the geometry. In general, the interaction with ions reduces the aromaticity of the insulators.

Quiñonero, David; Frontera, Antonio; Deyà, Pere M.; Alkorta, Ibon; Elguero, José

2008-07-01

109

Quantum critical transition from charge-ordered to superconducting state in the triangular lattice negative-U extended Hubbard model  

Microsoft Academic Search

We demonstrate a robust frustration-driven charge-order to superconductivity\\u000atransition in the half-filled negative-U extended Hubbard model.\\u000aSuperconductivity extends over a broad region of the parameter space. We argue\\u000athat the model provides the correct insight to understanding unconventional\\u000asuperconductivity in the organic charge-transfer solids and other\\u000aquarter-filled systems.

S. Mazumdar; R. T. Clay

2008-01-01

110

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

111

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

2008-09-27

112

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

NASA Astrophysics Data System (ADS)

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-, C-, and O- are observed for the first time in deep-core-level excitation of DMSO.

Coutinho, L. H.; Gardenghi, D. J.; Schlachter, A. S.; de Souza, G. G. B.; Stolte, W. C.

2014-01-01

113

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

114

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

NASA Astrophysics Data System (ADS)

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

2014-10-01

115

Influence of charge on encapsulation and release behavior of small molecules in self-assembled layer-by-layer microcapsules.  

PubMed

Abstract The objective of this study is to investigate the influence of charge of model small molecules on their encapsulation and release behavior in layer-by-layer microcapsules (LbL-MC). Poly(styrene sulfonate) and poly(ethylene imine) were sequentially adsorbed on calcium carbonate sacrificial templates to prepare LbL-MC. Model molecules with varying charge, anionic - ascorbic acid, cationic - imatinib mesylate (IM) and neutral - 5-fluorouracil were encapsulated in LbL-MC. Free and encapsulated LbL-MC were characterized using zetasizer, FTIR spectroscope and differential scanning calorimeter. The influence of IM-loaded LbL-MC on cell viability was studied in B16F10 murine melanoma cells. Furthermore, biodistribution of IM-loaded LbL-MC with and without PEGylation was studied in BALB/c mice. Results showed spherical LbL-MC of 3.0?±?0.4??m diameter. Encapsulation efficiency of LbL-MC increased linearly (R(2?)=?0.89-0.99) with the increase in solute concentration. Increase in pH from 2 to 6 increased the encapsulation of charged molecules in LbL-MC. Charged molecules showed greater encapsulation efficiency in LbL-MC compared with neutral molecule. In vitro release kinetics showed Fickian and non-Fickian diffusion of small molecules, depending on the nature of molecular interactions with LbL-MC. At 50??M concentration, free IM showed significantly (p?molecules depending on their physical and chemical properties. PMID:24328418

Mandapalli, Praveen K; Labala, Suman; Vanamala, Deekshith; Koranglekar, Manali P; Sakimalla, Lakshmi A; Venuganti, Venkata Vamsi K

2014-12-01

116

Is the negative charge on RNHSO3-M+ an essential requirement for sulfamate sweetness?  

PubMed

Although many structure-taste studies have been carried out on sulfamate (cyclamate) sweeteners, there are still some unanswered questions-notably whether the sulfamate anion, -NHSO(3)(-), is essential for sweetness in this class of compounds. The literature is contradictory on this point; therefore, 14 sulfamate esters RNHSO(3)R', which contain the sulfamate moiety but without the negative charge, i.e., -NHSO(3)(-), have been synthesized and tasted under standard conditions. Almost all of the esters were found to possess strong sweetness accompanied by bitterness. Because the esters had to be heated in water to 60 degrees C to dissolve them, it was necessary to check for partial hydrolysis to the free sulfamic acids, RNHSO(3)H, since they would be sweet and would invalidate the tasting results if formed. This was done by monitoring (gas-liquid chromatography) the formation of alcohol after heating. Negligible or very low hydrolysis to acid was found for all 14 esters. This work, in addition to answering an important structure-taste question, points the way to the potential use of suitable sulfamate esters as additives in situations where the more usual sodium sulfamate salts are unsuitable, for example, in hydrophobic media. PMID:12720391

Spillane, William J; Hanniffy, Gary G

2003-05-01

117

New RGD-peptide amphiphile mixtures containing a negatively charged diluent.  

PubMed

Here, we studied the self-assembly of two peptide amphiphiles, C16-Gly-Gly-Gly-Arg-Gly-Asp (PA 1: C16-GGG-RGD) and C16-Gly-Gly-Gly-Arg-Gly-Asp-Ser (PA 2: C16-GGG-RGDS). We showed that PA 1 and PA 2 self-assemble into nanotapes with an internal bilayer structure. C16 chains were highly interdigitated within the nanotape cores, while the peptide blocks formed water-exposed 13-sheets too. PA 1 nanotapes were characterized by one spacing distribution, corresponding to a more regular internal structure than that of PA 2 nanotapes, which presented two different spacing distributions. We showed that it is possible to obtain homogeneous nanotapes in water by co-assembling PA 1 or PA 2 with the negatively charged diluent C,16-Glu-Thr-Thr-Glu-Ser (PA 3: C16-ETTES). The homogeneous tapes formed by PA 1-PA 3 or PA 2-PA 3 mixtures presented a structure similar to that observed for the corresponding pure PA 1 or PA 2 nanotapes. The mixed nanotapes, which were able to form a stabilized matrix containing homogeneously distributed cell adhesive RGD groups, represent promising materials for designing new cell adhesion substrates. PMID:24611289

Castelletto, Valeria; Gouveia, Ricardo M; Connon, Che J; Hamley, Ian W

2013-01-01

118

Negatively charged phospholipids trigger the interaction of a bacterial Tat substrate precursor protein with lipid monolayers.  

PubMed

Folded proteins can be translocated across biological membranes via the Tat machinery. It has been shown in vitro that these Tat substrates can interact with membranes prior to translocation. Here we report a monolayer and infrared reflection-absorption spectroscopic (IRRAS) study of the initial states of this membrane interaction, the binding to a lipid monolayer at the air/water interface serving as a model for half of a biological membrane. Using the model Tat substrate HiPIP (high potential iron-sulfur protein) from Allochromatium vinosum, we found that the precursor preferentially interacts with monolayers of negatively charged phospholipids. The signal peptide is essential for the interaction of the precursor protein with the monolayer because the mature HiPIP protein showed no interaction with the lipid monolayer. However, the individual signal peptide interacted differently with the monolayer compared to the complete precursor protein. IRRA spectroscopy indicated that the individual signal peptide forms mainly aggregated ?-sheet structures. This ?-sheet formation did not occur for the signal peptide when being part of the full length precursor. In this case it adopted an ?-helical structure upon membrane insertion. The importance of the signal peptide and the mature domain for the membrane interaction is discussed in terms of current ideas of Tat substrate-membrane interactions. PMID:22263701

Brehmer, Tina; Kerth, Andreas; Graubner, Wenke; Malesevic, Miroslav; Hou, Bo; Brüser, Thomas; Blume, Alfred

2012-02-21

119

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

120

Exact relations between charge-density functions determining the total Coulomb energy and the dielectric constant for a mixture of neutral and charged site-site molecules  

E-print Network

We extend results developed by Chandler [J. Chem. Phys. 65, 2925 (1976)] for the dielectric constant of neutral site-site molecular models to mixtures of both charged and uncharged molecules. This provides a unified derivation connecting the Stillinger-Lovett moment conditions for ions to standard results for the dielectric constant for polar species and yields exact expressions for the small-k expansion of the two-point intermolecular charge-density function used to determine the total Coulomb energy. The latter is useful in determining corrections to the thermodynamics of uniform site-site molecular models simulated with spherically truncated Coulomb interactions.

Jocelyn M. Rodgers; John D. Weeks

2009-07-16

121

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

SciTech Connect

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

Zhukov, A. A., E-mail: azhukov@issp.ac.ru [Russian Academy of Science, Institute of Solid State Physics (Russian Federation); Volk, Ch.; Winden, A.; Hardtdegen, H.; Schaepers, Th. [Peter Gruenberg Institut (PGI-9) (Germany)

2012-12-15

122

Evaluation of HA negatively charged membranes in the recovery of human adenoviruses and hepatitis A virus in different water matrices  

Microsoft Academic Search

Human adenoviruses (HAdV) and hepatitis A virus (HAV) are shed in the faeces and consequently may be pres- ent in environmental waters, resulting in an increase in pathogen concentration that can affect water quality and human health. The aim of this study was to evaluate an adsorption-elution method which utilizes negatively charged membrane HA to determine the efficient recovery of

C Rigotto; CK Kolesnikovas; V Moresco; CMO Simões; CRM Barardi

2009-01-01

123

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

SciTech Connect

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

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

2008-08-28

124

High-energy negative ion beam obtained from pulsed inductively coupled plasma for charge-free etching process  

SciTech Connect

Negative ions in conventional inductively coupled plasma are often more chemically active than positive ions (for example, in CF{sub 4} or SF{sub 6} plasmas), but inconveniently they are trapped inside the sheath and cannot be used for high-energy surface etching in sources with a grid-type acceleration system. In this work we describe a method of positive and negative ion extraction that allows the energy and flux of oppositely charged particles to be varied independently. Then by scattering the ions off from a metal surface, it is possible to form a high-energy beam of neutrals from the negative ions by using the low-energy positive component of the beam current for better charge compensation.

Vozniy, O. V.; Yeom, G. Y. [Sungkyunkwan Advanced Institute of Nano Technology, Sungkyunkwan University, Jangan-Gu Chunchun-Dong 300, Suwon, Kyunggi-Do 440-746 (Korea, Republic of)

2009-06-08

125

New results on catalyzed big bang nucleosynthesis with a long-lived negatively charged massive particle  

SciTech Connect

It has been proposed that the apparent discrepancies between the inferred primordial abundances of {sup 6}Li and {sup 7}Li and the predictions of big bang nucleosynthesis (BBN) can be resolved by the existence of a negatively charged massive unstable supersymmetric particle (X{sup -}) during the BBN epoch. Here, we present new BBN calculations with an X{sup -} particle utilizing an improved nuclear reaction network including captures of nuclei by the particle, nuclear reactions and {beta} decays of normal nuclei and nuclei bound to the X{sup -} particles (X nuclei), and new reaction rates derived from recent rigorous quantum many-body dynamical calculations. We find that this is still a viable model to explain the observed {sup 6}Li and {sup 7}Li abundances. We also show that with the new rates the production of heavier nuclei is suppressed and there is no signature on abundances of nuclei heavier than Be in the X{sup -}-particle catalyzed BBN model as has been previously proposed. We also consider the version of this model whereby the X{sup -} particle decays into the present cold dark matter. We analyze this paradigm in light of the recent constraints on the dark-matter mass deduced from the possible detected events in the CDMS-II experiment. We conclude that based upon the inferred range for the dark-matter mass, only X{sup -} decay via the weak interaction can achieve the desired {sup 7}Li destruction while also reproducing the observed {sup 6}Li abundance.

Kusakabe, Motohiko [Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582 (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); Yoshida, Takashi [Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Mathews, Grant J. [Department of Physics, Center for Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2010-04-15

126

Spatially Extended Kondo State in Magnetic Molecules Induced by Interfacial Charge Transfer  

E-print Network

An extensive redistribution of spin density in TBrPP-Co molecules adsorbed on a Cu(111) surface is investigated by monitoring Kondo resonances at different locations on single molecules. Remarkably, the width of the Kondo ...

Perera, U. G. E.

127

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

128

Atoms-in-molecules analysis for planewave DFT calculations--a numerical approach on a successively interpolated charge density grid.  

PubMed

We used a successive charge interpolation scheme and Ridders method for differentiation, to acquire accurate charge densities and their higher derivatives in electronic structure calculations. This enables us to search bond critical points using arbitrary charge density grids. We applied the planewave-DFT code, VASP, to generate the charge density of selected benchmark molecules. The properties of bond critical points are in good agreement with those obtained by complementary implementations. We validated our GRID implementation by performing electronic structure calculations using the Gaussian 03 program package and various tools for analysis of the charge density provided by the AIMPAC package. In particular, we carefully investigate the influence of effective core potentials on the location of bond critical points, especially for a short chemical bond, which is crucial in the present pseudopotential-based planewave DFT calculations. We expect our generic implementation will not only be useful for the analysis of chemical bonding in molecules, but will particularly provide a microscopic understanding of extended systems including periodic boundary conditions. PMID:18172841

Yim, Wai-Leung; Klüner, Thorsten

2008-06-01

129

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.

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

2014-01-01

130

Quantum effects in the capture of charged particles by dipolar polarizable symmetric top molecules. I. General axially nonadiabatic channel treatment  

NASA Astrophysics Data System (ADS)

The rate coefficients for capture of charged particles by dipolar polarizable symmetric top molecules in the quantum collision regime are calculated within an axially nonadiabatic channel approach. It uses the adiabatic approximation with respect to rotational transitions of the target within first-order charge-dipole interaction and takes into account the gyroscopic effect that decouples the intrinsic angular momentum from the collision axis. The results are valid for a wide range of collision energies (from single-wave capture to the classical limit) and dipole moments (from the Vogt-Wannier and fly-wheel to the adiabatic channel limit).

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

2013-08-01

131

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

PubMed

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

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

2014-09-01

132

Structure, Stability, and Fragmentation of Sodium bis(2-ethylhexyl)Sulfosuccinate Negatively Charged Aggregates In Vacuo by MD Simulations  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

133

Design and Implementation of a Charge Equalization Using Positive\\/Negative Pulse Charger  

Microsoft Academic Search

The power for an electric vehicle (EV) is usually supplied by a series-connected battery strings. The life expectancy of the batteries will affect the economical development of EV that leading to the public acceptance. Conventionally, the charging and discharging processes are conducted on the whole battery strings that will experience an unbalance charging due to the distinct characteristics of each

Wu-Shun Jwo; Wei-Liang Chien

2007-01-01

134

Why Charged Molecules Move Across a Temperature Gradient: The Role of Electric Fields  

NASA Astrophysics Data System (ADS)

Methods to move solvated molecules are rare. Apart from electric fields, only thermal gradients are effective enough to move molecules inside a fluid. This effect is termed thermophoresis, and the underlying mechanisms are still poorly understood. Nevertheless, it is successfully used to quantify biomolecule binding in complex liquids. Here we show experiments that reveal that thermophoresis in water is dominated by two electric fields, both established by the salt ions of the solution. A local field around the molecule drives molecules along an energy gradient, whereas a global field moves the molecules by a combined thermoelectrophoresis mechanism known as the Seebeck effect. Both mechanisms combined predict the thermophoresis of DNA and RNA polymers for a wide range of experimental parameters. For example, we correctly predict a complex, nonlinear size transition, a salt-species-dependent offset, a maximum of thermophoresis over temperature, and the dependence of thermophoresis on the molecule concentration.

Reichl, Maren; Herzog, Mario; Götz, Alexandra; Braun, Dieter

2014-05-01

135

Expansion dynamics of Pb-Pb collisions at 40 A GeV/c viewed by negatively charged hadrons  

E-print Network

In this paper we present results on transverse mass spectra and Hanbury-Brown and Twiss correlation functions of negatively charged hadrons, which are expected to be mostly negative pions, measured in Pb-Pb collisions at 40 A GeV/c beam momentum. Based on these data, the collision dynamics and the space-time extent of the system at the thermal freeze-out are studied over a centrality range corresponding to the most central 53% of the Pb--Pb inelastic cross section. Comparisons with freeze-out conditions of strange particles and HBT results from other experiments are discussed.

The NA57 Collaboration

2007-01-11

136

Pairing and charge-density correlations in the three-dimensional negative-U Hubbard model on the fcc lattice  

NASA Astrophysics Data System (ADS)

Using symmetry considerations and exact-diagonalization techniques, we examine s-wave pairing and charge-density correlations in the three-dimensional negative-U Hubbard model on the fcc lattice. The correlations as functions of band filling and hopping and interaction parameters are studied. Results are presented for general cases. Implications for properties of alkali-metal-intercalated C60 materials are discussed.

Chen, Changfeng

1993-02-01

137

Pairing and charge-density correlations in the three-dimensional negative-U Hubbard model on the fcc lattice  

Microsoft Academic Search

Using symmetry considerations and exact-diagonalization techniques, we examine s-wave pairing and charge-density correlations in the three-dimensional negative-U Hubbard model on the fcc lattice. The correlations as functions of band filling and hopping and interaction parameters are studied. Results are presented for general cases. Implications for properties of alkali-metal-intercalated C60 materials are discussed.

Changfeng Chen

1993-01-01

138

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

139

Negative magnetoresistance due to charge fluctuation in mono-layer graphene at the minimum conductivity point  

NASA Astrophysics Data System (ADS)

We have measured magnetotransport of monolayer graphene at the minimum conductivity point in detail to study negative magnetoresistance that often appears in moderately high magnetic field. By studying several samples with different qualities, we found that negative magnetoresistance originated from potential fluctuation that leads to the residual carriers at the minimum conductivity point.

Yagi, Ryuta; Fukada, Seiya; Kobara, Hiroaki; Ogita, Norio; Udagawa, Masayuki

2010-02-01

140

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

141

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

E-print Network

. Charged particle track-structure calculations utilizing this principle of superposition are thereby neglecting to account for approximately 30% of the molecular variation within the nucleus. To truly understand what happens when biological matter...

Madsen, Jonathan R

2013-08-13

142

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

PubMed

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

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

2014-10-01

143

Positively and Negatively Charged Residues Have Different Effects on the Position in the Membrane of a  

E-print Network

of single charged residues on the position of a model transmembrane helix in the endoplasmic reticulum interactions that control the precise position- ing of an isolated TMH in the bilayer. This is due both- plasmic reticulum (ER) membrane. This so-called glycosylation mapping technique, in principle, allows any

Nielsen, Steven O.

144

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

145

Layer-by-layer self-assembly and disassembly of single charged inorganic small molecules: towards surface patterning.  

PubMed

The patterning of layer-by-layer (LbL) polyelectrolyte multilayers with metal ions is important for the facile fabrication of circuits or selective catalysis. The strategy includes two issues: the incorporation of metal ions and their controlled assembly-disassembly, which require a good understanding of the assembly mechanism. Therefore, we explored the LbL assembly between a polycation, poly-(diallyldimethylammonium chloride) (PDDA) and an inorganic single charged molecule, [AuCl4](-), which could assemble at pH = 3.7 and disassemble at lower pH values. Moreover, we have demonstrated that the driving force in the assembly is a ligand-to-metal charge transfer interaction. Combining the controlled assembly-disassembly of PDDA-[AuCl4](-) multilayers and photolithography, we obtained a surface pattern of PDDA-[AuCl4](-) multilayers. PMID:23925457

Cheng, Mengjiao; Jiang, Chao; Ding, Zhiyi; Zhang, Yajun; Fu, Yu; Shi, Feng

2013-09-28

146

Polarised single crystal infra-red spectra and optical indicatrix rotation in an organic charge transfer molecule  

NASA Astrophysics Data System (ADS)

Polarised infrared reflectance spectra have been obtained for oriented single crystals of the polar organic nonlinear optical material 2-(?-methylbenzylamino)-5-nitropyridine (MBANP). The strong charge transfer electronic absorption was measured in several solvents and as a thin solid film. DFT calculations of vibrational frequencies and eigenvectors were used to assign relevant vibrational features and to derive useful information about the molecular structure. The intensities of the bands associated with the donor and acceptor groups are increased by electron phonon coupling with the strong charge transfer transition. This results in unusually strong NO2 and N-H stretching vibrations. The spectra are consistent with a large rotation of the optical indicatrix with increasing wavelength due to the bent shape and strong electron-phonon coupling in the molecule.

Bailey, R. T.; Bourhill, G. H.; Cruickshank, F. R.; Sherwood, J. N.; Tedford, M. C.

2013-09-01

147

The binding energy and the charged gaps in the negative- U Hubbard model: some rigorous results  

Microsoft Academic Search

By applying Lieb's spin-reflection-positivity method and exploiting a commutation relation satisfied by the negative-U Hubbard Hamiltonian, we prove two rigorous theorems on the binding energy of fermions, the one-particle and the two-particle gaps for the model on an arbitrary finite lattice.

Guang-Shan Tian

1997-01-01

148

The binding energy and the charged gaps in the negative- U Hubbard model: some rigorous results  

NASA Astrophysics Data System (ADS)

By applying Lieb's spin-reflection-positivity method and exploiting a commutation relation satisfied by the negative-U Hubbard Hamiltonian, we prove two rigorous theorems on the binding energy of fermions, the one-particle and the two-particle gaps for the model on an arbitrary finite lattice.

Tian, Guang-Shan

1997-08-01

149

Effects of superthermal electrons and negatively (positively) charged dust grains on dust-ion acoustic wave modulation  

NASA Astrophysics Data System (ADS)

The modulational instability of dust-ion acoustic (DIA) waves is studied in an unmagnetized dusty plasma comprising arbitrarily charged dust particles, adiabatic fluid ions, and electrons satisfying a kappa ( ?) distribution. By using the multiple space and time scales perturbation, a nonlinear Schrödinger (NLS) equation is derived, and then the existence along with the stability of wave packets are discussed in the parameter space of two oppositely charged dust and ion temperature over a range of values of electron superthermality. It is found that the transition from stable dark solitons to unstable bright ones shifts to the smaller wavelength regions in a way that depends on the increase of superthermality index ?. In this case, a narrower range (in spatial extension) of the envelope solitons is observed. It is also found that the instability growth rate reduces, due to the electron superthemality. Furthermore, positive dust concentration enhances the instability region, whereas more populations of negative dust grains may control or suppress one.

Ainejad, H.; Mahdavi, M.; Shahmansouri, M.

2014-05-01

150

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

Microsoft Academic Search

A short review of theoretical models previously used to study single and multiple electron ionization in collisions of bare fast highly charged ions with atomic and diatomic molecular targets is given. Electron emission with simultaneous electron capture by the projectile is also considered. The principal mechanisms producing the different reactions are revisited. It is emphasized that two-center descriptions are necessary

R. D. Rivarola; P. D. Fainstein

2003-01-01

151

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

152

Effect of charge on the interaction of two C 60 molecules from MNDO and ab initio UHF methods: stability and HOMO–LUMO gaps  

Microsoft Academic Search

We have investigated the interaction between two C60 molecules with overall charge on the system n between +1 and ?4 from infinite separation to a distance of 8.5Å, using the MNDO and ab initio unrestricted Hartree–Fock methods. We have determined the dependence of the interaction energy, charge distribution, |HOMO–LUMO| gap and charge transfer, on distance. The system is found to

J. D. Santos; E. Longo; C. A. Taft

2003-01-01

153

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

154

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

155

Interplay of charge state, lability, and magnetism in the molecule-like Au25(SR)18 cluster.  

PubMed

Au25(SR)18 (R = -CH2-CH2-Ph) is a molecule-like nanocluster displaying distinct electrochemical and optical features. Although it is often taken as an example of a particularly well-understood cluster, very recent literature has provided a quite unclear or even a controversial description of its properties. We prepared monodisperse Au25(SR)18(0) and studied by cyclic voltammetry, under particularly controlled conditions, the kinetics of its reduction or oxidation to a series of charge states, -2, -1, +1, +2, and +3. For each electrode process, we determined the standard heterogeneous electron-transfer (ET) rate constants and the reorganization energies. The latter points to a relatively large inner reorganization. Reduction to form Au25(SR)18(2-) and oxidation to form Au25(SR)18(2+) and Au25(SR)18(3+) are chemically irreversible. The corresponding decay rate constants and lifetimes are incompatible with interpretations of very recent literature reports. The problem of how ET affects the Au25 magnetism was addressed by comparing the continuous-wave electron paramagnetic resonance (cw-EPR) behaviors of radical Au25(SR)18(0) and its oxidation product, Au25(SR)18(+). As opposed to recent experimental and computational results, our study provides compelling evidence that the latter is a diamagnetic species. The DFT-computed optical absorption spectra and density of states of the -1, 0, and +1 charge states nicely reproduced the experimentally estimated dependence of the HOMO-LUMO energy gap on the actual charge carried by the cluster. The conclusions about the magnetism of the 0 and +1 charge states were also reproduced, stressing that the three HOMOs are not virtually degenerate as routinely assumed: In particular, the splitting of the HOMO manifold in the cation species is severe, suggesting that the usefulness of the superatom interpretation is limited. The electrochemical, EPR, and computational results thus provide a self-consistent picture of the properties of Au25(SR)18 as a function of its charge state and may furnish a methodology blueprint for understanding the redox and magnetic behaviors of similar molecule-like gold nanoclusters. PMID:24087848

Antonello, Sabrina; Perera, Neranjan V; Ruzzi, Marco; Gascón, José A; Maran, Flavio

2013-10-16

156

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

157

Determination of the ?-Charge Distribution of the DMe-DCNQI Molecule in (DMe-DCNQI) 2 M, M=Li, Ag, and Cu  

NASA Astrophysics Data System (ADS)

Solid state high-resolution NMR of 1H and 13C along with 15N is analyzed to investigate the electronic states of the charge transfer salts (DMe-DCNQI)2M, (M=Li, Ag, and Cu). We determined the spin/charge distribution in a DMe-DCNQI molecule of the Li-salt from the Knight shifts at each atom on the molecule. It is found that the obtained charge distribution is similar to the theoretical prediction. The charge density on the DCNQI molecules of the Ag-salt is found to be smaller by 20% than the Li-salt, which could be an origin of differences from the Li-salt. This result is consistent with the first principle calculations (Miyazaki and Terakura, Phys. Rev. B 54, 10452, 1996).

Mizoguchi, Kenji; Shinohara, Yukie; Kazama, Shigeo; Hiraoka, Maki; Sakamoto, Hirokazu; Kato, Reizo; Hiraki, Koichi; Takahashi, Toshihiro

2006-02-01

158

Quantum critical transition from charge-ordered to superconducting state in the negative- U extended Hubbard model on a triangular lattice  

Microsoft Academic Search

We demonstrate a robust frustration-driven charge order to superconductivity transition in the half-filled negative- U extended Hubbard model. Superconductivity extends over a broad region of the parameter space. We argue that the model provides the correct insight to understanding unconventional superconductivity in the organic charge-transfer solids and other quarter-filled systems.

S. Mazumdar; R. T. Clay

2008-01-01

159

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

160

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

PubMed Central

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. PMID:23162692

Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

2012-01-01

161

Exchange-Induced Negative-U Charge Order in N-Doped WO3: A Spin-Peierls-Like System  

SciTech Connect

An unconventional spin-Peierls-type distortion was found in a nonmagnetic atom N doped pseudo-one-dimensional WO{sub 3} system. The periodicity of the initial ferromagnetic WO{sub 3}:N is doubled in one direction, and the band gap opens up due to this distortion. The magnetic moment at the N site is asymmetric in the distorted system, and the interaction between the localized spin is very weak. We show that the large exchange interaction of the nitrogen 2p atomic orbital and the pseudo-one-dimensional W-O-W chain in monoclinic WO{sub 3} structure is the origin of this spin-Peierls-like transition that leads to the stabilization of an unusual negative-U charge-ordered system.

Huda, M. N.; Yan, Y.; Wei, S.-H.; Al-Jassim, M. M.

2009-01-01

162

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

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

163

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

164

Matrix interference-free method for the analysis of small molecules by using negative ion laser desorption/ionization on graphene flakes.  

PubMed

This work presents a new approach for the analysis of small molecules with direct negative ion laser desorption/ionization (LDI) on graphene flakes. A series of matrix interference-free mass spectra were obtained for the analysis of a wide range of small molecules including peptides, amino acids, fatty acids, as well as nucleosides and nucleotides. The mixture of analytes and graphene flakes suspension were directly pipetted onto a sample plate for LDI-time-of-flight mass spectrometry (TOFMS) analysis. Deprotonated monomeric species [M-H](-) ions were homogeneously obtained on uniform graphene flakes film when negative ion mode was applied. In positive ion mode, the analytes were detected in form of multiple adduct ions such as sodium adduct [M+Na](+), potassium adduct [M+K](+), double sodium adduct [M+2Na-H](+), double potassium adduct [M+2K-H](+), as well as sodium and potassium mixed adduct [M+Na+K-H](+). Better sensitivity and reproducibility were achieved in negative ion mode compared to positive ion mode. It is believed that the new method of matrix interference-free negative ion LDI on graphene flakes may be expanded for LDI-MS analysis of various small molecules. PMID:21428301

Lu, Minghua; Lai, Yongquan; Chen, Guonan; Cai, Zongwei

2011-04-15

165

Hapticity-Dependent Charge Transport through Carbodithioate-Terminated [5,15-Bis(phenylethynyl)porphinato]zinc(II) Complexes in Metal-Molecule-Metal Junctions.  

PubMed

Single molecule break junction experiments and nonequilibrium Green's function calculations using density functional theory (NEGF-DFT) of carbodithioate- and thiol-terminated [5,15-bis(phenylethynyl)-10,20-diarylporphinato]zinc(II) complexes reveal the impact of the electrode-linker coordination mode on charge transport at the single-molecule level. Replacement of thiolate (-S(-)) by the carbodithioate (-CS2(-)) anchoring motif leads to an order of magnitude increase of single molecule conductance. In contrast to thiolate-terminated structures, metal-molecule-metal junctions that exploit the carbodithioate linker manifest three distinct conductance values. We hypothesize that the magnitudes of these conductances depend upon carbodithoate linker hapticity with measured conductances across Au-[5,15-bis(4'-(dithiocarboxylate)phenylethynyl)-10,20-diarylporphinato]zinc(II)-Au junctions the greatest when both anchoring groups attach to the metal surface in a bidentate fashion. We support this hypothesis with NEGF-DFT calculations, which consider the electron transport properties for specific binding geometries. These results provide new insights into the origin of molecule-to-molecule conductance heterogeneity in molecular charge transport measurements and the factors that optimize electrode-molecule-electrode electronic coupling and maximize the conductance for charge transport. PMID:25255444

Li, Zhihai; Smeu, Manuel; Park, Tae-Hong; Rawson, Jeff; Xing, Yangjun; Therien, Michael J; Ratner, Mark A; Borguet, Eric

2014-10-01

166

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

167

Quantum effects in electron emission from and accretion on negatively charged spherical particles in a complex plasma  

SciTech Connect

The authors have investigated the electron emissions (thermionic, electric field, photoelectric, and light induced field) from and electron accretion on a charged particle in a complex plasma, on the basis of a three region electrical potential model in and around a charged spherical particle in a complex plasma, characterized by Debye shielding. A continuous variation of the transmission coefficient across the surface of a particle (corresponding to emission and accretion) with the radial electron energy {epsilon}{sub r} has been obtained. It is seen that the numerical values of the emission and accretion transmission coefficients [D({epsilon}{sub r})] are almost the same. This is the necessary and sufficient condition for the validity of Saha's equation for thermal equilibrium of a system of dust and electrons. This is in contrast to the earlier condition, which limited the range of validity of Saha's equation to the range of the applicability of Born approximation. It is seen that D({epsilon}{sub r}) increases with increasing {epsilon}{sub r}, increasing negative electric potential on the surface, decreasing radius, and deceasing Debye length. The electron currents, corresponding to thermionic, electric field, photoelectric and light induced field emission increase with increasing surface potential; this fact may have significant repercussions in complex plasma kinetics. Since numerically D({epsilon}{sub r}) is significantly different from unity in the range of {epsilon}{sub r} of interest, it is necessary to take into account the D({epsilon}{sub r})-{epsilon}{sub r} dependence in complex plasma theory.

Mishra, S. K. [Institute for Plasma Research, Gandhinagar (India); Sodha, M. S.; Misra, Shikha [DST Project, Department of Education Building, University of Lucknow, Lucknow-226007 (India)

2012-07-15

168

Specific negative charges in cysteine protease isoforms of Leishmaniamexicana are highly influential on the substrate binding and hydrolysis.  

PubMed

We focused on the importance of the electrostatic environment on the catalytic properties of the Leishmania mexicana CPB recombinant isoenzymes (rCPB2.8, rCPB3 and its mutant rH84Y), by investigating the influence of pH and NaCl on their hydrolytic activities. rCPB2.8 contains the residues Asn60, Asp61 and Asp64; rCPB3 presents the three variant residues Asp60, Asn61 and Ser64 and the mutant of the latter isoform, rH84Y, has a mutation on the outer loop residue (His84 to Tyr). Synthetic fluorescence resonance energy transfer (FRET) peptides, which contain different positive charge distribution in their sequences were used as substrates. The results show that hydrolytic efficiency is dependent of the positive charge distribution in the substrates and that NaCl activated rCPB2.8 and rCPB3 in acidic pH but inhibited them at pH higher than 5. The rate constants of substrate diffusion (k1), substrate dissociation (k-1), acylation (k2) and deacylation (k3) and the corresponding activation energies and entropies were derived. Significant differences in the kinetic rate constants (k) and entropies were found between the CPB isoforms, and the diffusion process seems to be the limiting step. The activation energy of denaturation (Ea-Den) and entropy of denaturation (DeltaSDen) of rCPB3 were higher than those for rCPB2.8, suggesting higher salvation and protein structure for rCPB3. Thus the findings suggest that the two CPB isoenzymes with a few negative charge modifications provide the parasite with an array of hydrolytic activity and enzymatic adaptation to pH, salinity and temperature that may be needed for its interaction with the mammalian host. PMID:16125801

Judice, Wagner A S; Mottram, Jeremy C; Coombs, Graham H; Juliano, Maria A; Juliano, Luiz

2005-11-01

169

Charge competition with oxygen molecules determines the growth of gold particles on doped CaO films.  

PubMed

The influence of gas-phase oxygen on the growth of Au nanoparticles on Mo-doped CaO films has been investigated by means of low temperature scanning tunnelling microscopy and X-ray photoelectron spectroscopy. Whereas at ideal vacuum conditions, only 2D Au islands develop on the oxide surface, the fraction of 3D deposits increases with increasing O2 pressure until they become the dominant species in 106 mbar oxygen. The morphology crossover arises from changes in the interfacial electron flow between Mo donors in the CaO lattice and different ad-species on the oxide surface. In the absence of 02 molecules, the donor electrons are predominately transferred to the Au ad-atoms, which consequently experience enhanced binding to the oxide surface and agglomerate into 2D islands. In an oxygen atmosphere, on the other hand, a substantial fraction of the excess electrons is trapped by adsorbed O2 molecules, while the Au atoms remain neutral and assemble into tall 3D particles that are typical for non-doped oxides. Our experiments demonstrate how the competition for charge between different adsorbates governs the physical and chemical properties of doped oxides, so widely used in heterogeneous catalysis. PMID:24015581

Cui, Yi; Huang, Kai; Nilius, Niklas; Freund, Hans-Joachim

2013-01-01

170

Interactions of neutral and singly charged keV atomic particles with gas-phase adenine molecules  

SciTech Connect

KeV atomic particles traversing biological matter are subject to charge exchange and screening effects which dynamically change this particle's effective charge. The understanding of the collision cascade along the track thus requires a detailed knowledge of the interaction dynamics of radiobiologically relevant molecules, such as DNA building blocks or water, not only with ionic but also with neutral species. We have studied collisions of keV H{sup +}, He{sup +}, and C{sup +} ions and H{sup 0}, He{sup 0}, and C{sup 0} atoms with the DNA base adenine by means of high resolution time-of-flight spectrometry. For H{sup 0} and H{sup +} we find qualitatively very similar fragmentation patterns, while for carbon, strong differences are observed when comparing C{sup 0} and C{sup +} impact. For collisions with He{sup 0} and He{sup +} projectiles, a pronounced delayed fragmentation channel is observed, which has not been reported before.

Alvarado, Fresia; Bari, Sadia; Hoekstra, Ronnie; Schlathoelter, Thomas [KVI Atomic Physics, University of Groningen, Zernikelaan 25, NL-9747AA Groningen (Netherlands)

2007-07-21

171

Consequences of including carbon in the negative plates of Valve-regulated Lead–Acid batteries exposed to high-rate partial-state-of-charge operation  

Microsoft Academic Search

In power-assist hybrid electric vehicles (HEVs) batteries are required to operate from a partial-state-of-charge baseline and to provide, and to accept, charge, for short periods, at very high rates. Under this regime conventional lead–acid batteries accumulate lead sulfate on the negative plate and fail quickly. This failure mode can be effectively countered by the inclusion of certain forms of carbon

P. T. Moseley

2009-01-01

172

Density functional study of the charge on Aun clusters (n=1-7) supported on a partially reduced rutile TiO2(110): Are all clusters negatively charged?  

NASA Astrophysics Data System (ADS)

It is widely believed that small gold clusters supported on an oxide surface and adsorbed at the site of an oxygen vacancy are negatively charged. It has been suggested that this negative charge helps a gold cluster adsorb oxygen and weakens the O-O bond to make oxidation reactions more efficient. Given the fact that an oxygen vacancy is electron rich and that Au is a very electronegative element, the assumption that the Au cluster will take electron density from the vacancy is plausible. However, the density functional calculations presented here show that the situation is more complicated. The authors have used the Bader method to examine the charge redistribution when a Aun cluster (n=1-7) binds next to or at an oxygen vacancy on rutile TiO2(110). For the lowest energy isomers they find that Au1 and Au3 are negatively charged, Au5 and Au7 are positively charged, and Au2, Au4, and Au6 exchange practically no charge. The behavior of the Aun isomers having the second-lowest energy is also unexpected. Au2, Au3, Au5, and Au7 are negatively charged upon adsorption and very little charge is transferred when Au4 and Au6 are adsorbed. These observations can be explained in terms of the overlap between the frontier molecular orbitals of the gold cluster and the eigenstates of the support. Aun with even n becomes negatively charged when the lowest unoccupied molecular orbital has a lobe pointing in the direction of the oxygen vacancy or towards a fivefold coordinated Ti (5c-Ti) located in the surface layer; otherwise it stays neutral. Aun with odd n becomes negatively charged when the singly occupied molecular orbital has a lobe pointing in the direction of a 5c-Ti located at the vacancy site or in the surface layer, otherwise it donates electron density into the conduction band of rutile TiO2(110) becoming positively charged.

Chrétien, Steeve; Metiu, Horia

2007-03-01

173

Non-adiabatic processes in the charge transfer reaction of O2 molecules with potassium surfaces without dissociation  

NASA Astrophysics Data System (ADS)

Thin potassium films grown on Si(001) substrates are used to measure internal chemicurrents and the external emission of exoelectrons simultaneously during adsorption of molecular oxygen on K surfaces at 120 K. The experiments clarify the dynamics of electronic excitations at a simple metal with a narrow valence band. X-ray photoemission reveals that for exposures below 5 L almost exclusively peroxide K2O2 is formed, i.e., no dissociation of the molecule occurs during interaction. Still a significant chemicurrent and a delayed exoelectron emission are detected due to a rapid injection of unoccupied molecular levels below the Fermi level. Since the valence band width of potassium is approximately equal to the potassium work function (2.4 eV) the underlying mechanism of exoemission is an Auger relaxation whereas chemicurrents are detected after resonant charge transfer from the metal valence band into the injected level. The change of the chemicurrent and exoemission efficiencies with oxygen coverage can be deduced from the kinetics of the reaction and the recorded internal and external emission currents traces. It is shown that the non-adiabaticity of the reaction increases with coverage due to a reduction of the electronic density of states at the surface while the work function does not vary significantly. Therefore, the peroxide formation is one of the first reaction systems which exhibits varying non-adiabaticity and efficiencies during the reaction. Non-adiabatic calculations based on model Hamiltonians and density functional theory support the picture of chemicurrent generation and explain the rapid injection of hot hole states by an intramolecular motion, i.e., the expansion of the oxygen molecule on the timescale of a quarter of a vibrational period.

Krix, David; Nienhaus, Hermann

2014-08-01

174

Vibrational relaxation in H/sub 2/ molecules by wall collisions: applications to negative ion source processes  

SciTech Connect

In the volume of a hydrogen discharge, H/sub 2/ molecules, excited to high vibrational levels (v'' > 6), are formed either by fast-electron collisions or from H/sub 2//sup +/ ions that are accelerated across the discharge-wall potential that undergo Auger neutralization prior to impact with the discharge chamber wall. We have used computer molecular dynamics to study the de-excitation and re-excitation of vibrationally-excited H/sub 2/ molecules undergoing repeated wall collisions. The initial translational energies range from thermal to 100 eV and the initial vibrational states range from v'' = 2 to v'' = 12. The average loss or gain of vibrational, rotational, translational, and total molecular energies and the survival rates of the molecules have been evaluated. At thermal energies vibrational de-excitation is the predominant process, and a consistent picture emerges of rapid energy redistribution into all the molecular degrees of freedom and a slower rate of loss of total molecular energy to the wall. At higher translational energies (1 to 100 eV) a substantial fraction of the molecules survive with large (v'' > 6) vibrational energy. This vibrational population provides a contribution to the total excited vibrational population comparable to that from the fast-electron collision process.

Karo, A.M.; Hiskes, J.R.; Hardy, R.J.

1984-10-01

175

Atomic charge transfer-counter polarization effects determine infrared CH intensities of hydrocarbons: a quantum theory of atoms in molecules model.  

PubMed

Atomic charge transfer-counter polarization effects determine most of the infrared fundamental CH intensities of simple hydrocarbons, methane, ethylene, ethane, propyne, cyclopropane and allene. The quantum theory of atoms in molecules/charge-charge flux-dipole flux model predicted the values of 30 CH intensities ranging from 0 to 123 km mol(-1) with a root mean square (rms) error of only 4.2 km mol(-1) without including a specific equilibrium atomic charge term. Sums of the contributions from terms involving charge flux and/or dipole flux averaged 20.3 km mol(-1), about ten times larger than the average charge contribution of 2.0 km mol(-1). The only notable exceptions are the CH stretching and bending intensities of acetylene and two of the propyne vibrations for hydrogens bound to sp hybridized carbon atoms. Calculations were carried out at four quantum levels, MP2/6-311++G(3d,3p), MP2/cc-pVTZ, QCISD/6-311++G(3d,3p) and QCISD/cc-pVTZ. The results calculated at the QCISD level are the most accurate among the four with root mean square errors of 4.7 and 5.0 km mol(-1) for the 6-311++G(3d,3p) and cc-pVTZ basis sets. These values are close to the estimated aggregate experimental error of the hydrocarbon intensities, 4.0 km mol(-1). The atomic charge transfer-counter polarization effect is much larger than the charge effect for the results of all four quantum levels. Charge transfer-counter polarization effects are expected to also be important in vibrations of more polar molecules for which equilibrium charge contributions can be large. PMID:25254435

Silva, Arnaldo F; Richter, Wagner E; Meneses, Helen G C; Bruns, Roy E

2014-10-01

176

Unique helical conformation of the fourth cytoplasmic loop of the CB1 cannabinoid receptor in a negatively charged environment†  

PubMed Central

The proximal portion of the C-terminus of the CB1 cannabinoid receptor is a primary determinant for G-protein activation. A seventeen residue proximal C-terminal peptide (rodent CB1401–417), the intracellular loop 4 (IL4) peptide, mimicked the receptor’s G-protein activation domain. Because of the importance of the cationic amino acids to G-protein activation, the three-dimensional structure of the IL4 peptide in a negatively charged sodium dodecylsulfate (SDS) micellar environment has been studied by two-dimensional proton nuclear magnetic resonance (2D 1H-NMR) spectroscopy and distance geometry calculations. Unambiguous proton NMR assignments were carried out with the aid of correlation spectroscopy (DQF-COSY and TOCSY) and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The distance constraints were used in torsion angle dynamics algorithm for NMR applications (DYANA) to generate a family of structures which were refined using restrained energy minimization and dynamics. In water, the IL4 peptide prefers an extended conformation, whereas in SDS micelles, 310-helical conformation is induced. The predominance of 310-helical domain structure in SDS represents a unique difference compared with structure in alternative environments, which can significantly impact global electrostatic surface potential on the cytoplasmic surface of the CB1 receptor and might influence the signal to the G-proteins. PMID:17524664

Grace, Christy R. R.; Cowsik, Sudha M.; Shim, Joong-Youn; Welsh, William J.; Howlett, Allyn C.

2007-01-01

177

Optimization of an Adsorption-Elution Method with a Negatively Charged Membrane to Recover Norovirus from Lettuce.  

PubMed

Viral pathogens, such as norovirus (NoV), are frequently associated with foodborne gastroenteritis worldwide, and the detection of NoV in food requires appropriate methods and the use of process controls. In this study, an adsorption-elution concentration method using negatively charged membranes was optimized to recover NoV from lettuce, using murine norovirus 1 (MNV-1) as a human NoV (HuNoV) surrogate. Initially, three elution buffers were evaluated by direct elution using a Stomacher(®) apparatus with a filter bag and different concentrations of MNV-1 genomic copies. The eluates were filtered in a Stericup(®) and concentrated by a Centriprep Concentrator(®), and the viral RNA was quantified by real-time PCR that was preceded by reverse transcription. The MNV-1 recovery efficiency varied based on the buffers used, ranging from 5.2 to 9.8 % for PBS pH 7.2, 0.2-18 % for glycine NaCl pH 9.5 and 10.8-33.3 % for glycine Tris-HCl pH 9.5. Further analysis of the glycine Tris-HCl pH 9.5 buffer revealed that gentle-shaking, direct elution could replace the use of a Stomacher(®), with recovery rates reaching 66 and 32 % for MNV-1 and HuNoV, respectively, all of which suggested that this procedure is a quick and efficient method for recovering NoV from lettuce. PMID:23649411

de Abreu Corrêa, Adriana; Miagostovich, Marize Pereira

2013-05-01

178

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

179

Polyethylenimine-capped Ag nanoparticle film as a platform for detecting charged dye molecules by surface-enhanced Raman scattering and metal-enhanced fluorescence.  

PubMed

Many drugs are charged molecules and are weak bases or acids having counterions. Their binding to biological surfaces is generally difficult to assess by vibrational spectroscopy. In this work, we demonstrated the potential of surface-enhanced Raman scattering (SERS) conducted using a polyethylenimine (PEI)-capped Ag nanoparticle film for the quantification of an electrostatic adsorption process of charged drug molecules, by using charged dye molecules such as sulforhodamine B (SRB) and rhodamine-123 (R123) as model drugs. It was possible to detect small-sized anions such as SCN(-) at 1 × 10(-9) M by SERS because of the cationic property of PEI. We were subsequently able to detect a prototype anionic dye molecule, SRB, by SERS at a subnanomolar concentration. On the other hand, it was difficult to detect cationic dyes such as R123 because of the electrostatically repulsive interaction with PEI. Nonetheless, we found that even R123 could be detected at subnanomolar concentrations by SERS by depositing an anionic polyelectrolyte such as poly(sodium 4-styrenesulfonate) (PSS) and poly(acrylic acid) (PAA) onto the PEI-capped Ag nanoparticles. Another noteworthy point is that a subnanomolar detection limit can also be achieved by carefully monitoring the fluorescence background in the measured SERS spectra. This was possible because charged dyes were not in contact with Ag but formed ion pairs with either PEI or PSS (PAA), allowing metal-enhanced fluorescence (MEF). The PEI-capped Ag nanoparticle film can thus serve as a useful indicator to detect charged drug molecules by SERS and MEF. PMID:23043369

Kim, Kwan; Lee, Ji Won; Shin, Kuan Soo

2012-10-24

180

Dissociative electron attachment to the highly reactive difluoromethylene molecule-importance of CF2 for negative ion formation in fluorocarbon plasmas  

NASA Astrophysics Data System (ADS)

Dissociative electron attachment to the highly reactive difluoromethylene molecule, CF2, produced in a C3F6/He microwave plasma and stepwise via the fast atom reaction CF3I+H?CF3+HI and CF3+H?CF2+HF, has been investigated. The upper limit for the cross section of formation of F- via dissociative electron attachment to CF2 is estimated to be 5×10-4 Å2. This value is four orders of magnitude smaller than the cross section previously predicted from scattering calculations. It is concluded that difluoromethylene plays a negligible role in negative ion formation in fluorocarbon plasmas.

Graupner, K.; Field, T. A.; Mayhew, C. A.

2010-08-01

181

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

182

First study of the negative binomial distribution applied to higher moments of net-charge and net-proton multiplicity distributions  

NASA Astrophysics Data System (ADS)

A study of the first four moments (mean, variance, skewness, and kurtosis) and their products (??2 and S?) of the net-charge and net-proton distributions in Au + Au collisions at ?{sNN}=7.7-200 GeV from HIJING simulations has been carried out. The skewness and kurtosis and the collision volume independent products ??2 and S? have been proposed as sensitive probes for identifying the presence of a QCD critical point. A discrete probability distribution that effectively describes the separate positively and negatively charged particle (or proton and anti-proton) multiplicity distributions is the negative binomial (or binomial) distribution (NBD/BD). The NBD/BD has been used to characterize particle production in high-energy particle and nuclear physics. Their application to the higher moments of the net-charge and net-proton distributions is examined. Differences between ??2 and a statistical Poisson assumption of a factor of four (for net-charge) and 40% (for net-protons) can be accounted for by the NBD/BD. This is the first application of the properties of the NBD/BD to describe the behavior of the higher moments of net-charge and net-proton distributions in nucleus-nucleus collisions.

Tarnowsky, Terence J.; Westfall, Gary D.

2013-07-01

183

Bright white-light emission from a novel donor-acceptor organic molecule in the solid state via intermolecular charge transfer.  

PubMed

Bright white-light emission was obtained from a novel pyridinium molecule by aggregation. Photophysical, single-crystal structural, and computational studies demonstrated that an additional low-energy emission was generated by the excitation of a new intermolecular charge-transfer (CT) band at the ground state that cooperates with the non-quenched high-energy monomer emission to produce white light. PMID:25376300

Jin, Xu-Hui; Chen, Cheng; Ren, Cai-Xia; Cai, Li-Xuan; Zhang, Jie

2014-11-20

184

Development of additives in negative active-material to suppress sulfation during high-rate partial-state-of-charge operation of lead–acid batteries  

Microsoft Academic Search

Additives in the negative active-material of lead–acid batteries were examined to determine whether they could prevent progressive accumulation of lead sulfate (PbSO4) in negative plates during high-rate partial-state-of-charge (HRPSoC) operation. This phenomenon is caused by progressive growth of PbSO4 particles and a lack of conductive paths near these PbSO4 particles.Barium sulfate (BaSO4) particles in various sizes and synthetic lignin were

Ken Sawai; Takayuki Funato; Masashi Watanabe; Hidetoshi Wada; Kenji Nakamura; Masaaki Shiomi; Shigeharu Osumi

2006-01-01

185

A New Class of Quorum Quenching Molecules from Staphylococcus Species Affects Communication and Growth of Gram-Negative Bacteria  

PubMed Central

The knowledge that many pathogens rely on cell-to-cell communication mechanisms known as quorum sensing, opens a new disease control strategy: quorum quenching. Here we report on one of the rare examples where Gram-positive bacteria, the ‘Staphylococcus intermedius group’ of zoonotic pathogens, excrete two compounds in millimolar concentrations that suppress the quorum sensing signaling and inhibit the growth of a broad spectrum of Gram-negative beta- and gamma-proteobacteria. These compounds were isolated from Staphylococcus delphini. They represent a new class of quorum quenchers with the chemical formula N-[2-(1H-indol-3-yl)ethyl]-urea and N-(2-phenethyl)-urea, which we named yayurea A and B, respectively. In vitro studies with the N-acyl homoserine lactone (AHL) responding receptor LuxN of V. harveyi indicated that both compounds caused opposite effects on phosphorylation to those caused by AHL. This explains the quorum quenching activity. Staphylococcal strains producing yayurea A and B clearly benefit from an increased competitiveness in a mixed community. PMID:24098134

Chu, Ya-Yun; Nega, Mulugeta; Wölfle, Martina; Plener, Laure; Grond, Stephanie; Jung, Kirsten; Götz, Friedrich

2013-01-01

186

Electron and Hole Injection via Charge Transfer at the Topological-Insulator $Bi_{2-x}Sb_xTe_{3-y}Se_y$/Organic-Molecule Interface  

E-print Network

As a methodology for controlling the carrier transport of topological insulators (TI's), a flexible tuning in carrier number on the surface states (SS's) of three dimensional TI's by surface modifications using organic molecules is described. The principle of the carrier tuning and its type conversion of TI's presented in this research are based on the charge transfer of holes or electrons at the TI/organic molecule interface. By employing 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) as an electron acceptor or tetracyanoquinodimethane (TCNQ) as a donor for n- and p- Bi2-xSbxTe3-ySey (BSTS) single crystals, successful carrier conversion from n to p and its reverse mode is demonstrated depending on the electron affinities of the molecules. The present method provides a nondestructive and efficient method for local tuning in carrier density of TI's, and is useful for future applications.

Tanabe, Yoichi; Nouchi, Ryo; Heguri, Satoshi; Mu, Gang; Xu, Jingtao; Shimotani, Hidekazu; Tanigaki, Katsumi

2014-01-01

187

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

188

Changes in Negative Charge at the Luminal Mouth of the Pore Alter Ion Handling and Gating in the Cardiac Ryanodine-Receptor  

Microsoft Academic Search

We have tested the hypothesis that a high density of negative charge at the luminal mouth of the RyR2 pore plays a pivotal role in the high cation conductance and limited selectivity observed in this channel by introducing into each monomer a double point mutation to neutralize acidic residues in this region of the mouse RyR2 channel. The resultant channel,

Fiona C. Mead-Savery; Ruiwu Wang; Bhavna Tanna-Topan; S. R. Wayne Chen; William Welch; Alan J. Williams

2009-01-01

189

Photon-Particle Coincidence Measurement of Charge-Transfer Excitation of the N2+ First Negative 3914-Å Band by Protons  

Microsoft Academic Search

The cross section for charge-transfer excitation of the N2+ first negative 3914-Å band by protons (5-65 keV) has been measured using a photon-particle coincidence technique. The target N2 is collisionally excited to the N2+ (B 2Sigma+u) state and emits a 3914-Å photon in the (0,0) transition. This photon is detected in coincidence with the scattered particle, a proton or hydrogen

P. J. Wehrenberg; K. C. Clark

1973-01-01

190

Direct indication of lateral nonuniformities of MOS capacitors from the negative equivalent interface trap density based on charge-temperature technique  

NASA Astrophysics Data System (ADS)

The charge-temperature technique was used to investigate the oxide properties of silicon MOS capacitors fabricated on a wafer with an oxide thickness of 660 Å. The stretchout of high frequency C — V curve of the capacitor after a positive charge-temperature aging was proved to be due to the lateral nonuniformities of mobile charges and the increase of interface traps. The effect of lateral nonuniformitites was found to be successfully described by a model consisting of two parallelly connected nonuniform capacitors. The only parameter of importance is their area ratio, which can be easily determined by theoretical fitting. The appearance of a negative equivalent interface trap density was proposed as a new method to directly identify the existence of lateral nonuniformities.

Hwu, J. G.; Wang, W. S.

1986-05-01

191

Influence of expander components on the processes at the negative plates of lead-acid cells on high-rate partial-state-of-charge cycling. Part II. Effect of carbon additives on the processes of charge and discharge of negative plates  

Microsoft Academic Search

Lead-acid batteries operated in the high-rate partial-state-of-charge (HRPSoC) duty rapidly lose capacity on cycling, because of sulfation of the negative plates. As the battery operates from a partially discharged state, the small PbSO4 crystals dissolve and precipitate onto the bigger crystals. The latter have low solubility and hence PbSO4 accumulates progressively in the negative plates causing capacity loss. In order

D. Pavlov; P. Nikolov; T. Rogachev

2010-01-01

192

Charge-controlled fixation of DNA molecules on silicon surface and electro-physical properties of Au-DNA-Si interface  

NASA Astrophysics Data System (ADS)

Light-induced fixation of DNA molecules on silicon surface was done and electro-physical properties of Schottky diodes with DNA on interfaces were investigated. Thymus DNA molecules were deposited on silicon from a water solution. Fixed molecular structures were observed with helium ionic microscopy and atomic force microscopy and then they were covered with thermal sputtered gold film. Obtained structures Au-DNA-(n-Si) were examined with current-voltage and frequency dependent admittance measurements. In darkness immobilizing of molecules leaded to form DNA ropes with thickness up to 10 nm and distances between them about 1 mkm. Fixation under illumination resulted in forming of single DNA mesh with thickness about 1 nm and cell size about 100 nm. Presence of molecular mesh on interface leaded to increasing of charge density controlled by metal Fermi level and improved diode quality. Presence of molecular ropes resulted in increasing of charge density controlled by semiconductor. From the estimation of interface state density values the origin of the states at the interface between DNA and silicon substrate is suggested to be DNA phosphate groups contacting or being close to the substrate surface.

Bazlov, N. V.; Vyvenko, O. F.; Sokolov, P. A.; Kas'yanenko, N. A.; Petrov, Yu V.

2013-02-01

193

Mechanism by which a single water molecule affects primary charge separation kinetics in a bacterial photosynthetic reaction center of Rhodobacter sphaeroides  

NASA Astrophysics Data System (ADS)

Using quantum-chemical methods, we have studied the role played by water molecules W-A and W-B that are bound by hydrogen bonds to accessory bacteriochlorophyll molecules B A and B B in the process of primary charge separation in the reaction center of Rhodobacter Sphaeroides. We have found that the occurrence of a rotational mode of the W-A molecule at 32 cm-1 and/or its harmonics in stimulated emission of an electron donor P* and the dynamics of population of the states P+B{/A -} and P+H{/A -} may be related to the structural heterogeneity of the reaction center and the existence of a conformation in which the W-A molecule is predominantly involved in one hydrogen bond (with B A). Based on the calculated redox potentials B A and P, it has been shown that the appearance of the W-A molecule in the reaction center reduces the energy of the P+B{/A -} state by ˜600 cm-1. This is somewhat smaller than the influence of the amino-acid residue TyrM210 (˜870 cm-1) and correlates well with a substantial decrease in the electron transfer rate in mutant forms of reaction centers GM203L (which do not contain W-A molecules) and YM210F (in which TyrM210 is replaced with Phe). The data obtained allow us to suggest that rotation of the water molecule with a fixed position of its H atom that is involved in a hydrogen bond with the keto carbonyl group of B A is initiated due to the charge separation between the halves of special pair P and the formation of the state P{/A +}P{/B -}. The large effect of this rotation on the kinetics of population of the states P+B{/A -} and P+H{/A -} after the excitation of P is quite consistent with its influence on the energy of the state P+B{/A -}.

Ivashin, N. V.; Shchupak, E. E.

2012-11-01

194

Negative electrospray ionization on porous supporting tips for mass spectrometric analysis: electrostatic charging effect on detection sensitivity and its application to explosive detection.  

PubMed

The simplicity and easy manipulation of a porous substrate-based ESI-MS technique have been widely applied to the direct analysis of different types of samples in positive ion mode. However, the study and application of this technique in negative ion mode are sparse. A key challenge could be due to the ease of electrical discharge on supporting tips upon the application of negative voltage. The aim of this study is to investigate the effect of supporting materials, including polyester, polyethylene and wood, on the detection sensitivity of a porous substrate-based negative ESI-MS technique. By using nitrobenzene derivatives and nitrophenol derivatives as the target analytes, it was found that the hydrophobic materials (i.e., polyethylene and polyester) with a higher tendency to accumulate negative charge could enhance the detection sensitivity towards nitrobenzene derivatives via electron-capture ionization; whereas, compounds with electron affinities lower than the cut-off value (1.13 eV) were not detected. Nitrophenol derivatives with pKa smaller than 9.0 could be detected in the form of deprotonated ions; whereas polar materials (i.e., wood), which might undergo competitive deprotonation with the analytes, could suppress the detection sensitivity. With the investigation of the material effects on the detection sensitivity, the porous substrate-based negative ESI-MS method was developed and applied to the direct detection of two commonly encountered explosives in complex samples. PMID:24492411

Wong, Melody Yee-Man; Man, Sin-Heng; Che, Chi-Ming; Lau, Kai-Chung; Ng, Kwan-Ming

2014-03-21

195

Solar cells: understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells (adv. Mater. 43/2014).  

PubMed

World-record-performing bulk-heterojunction (BHJ) small molecule solar cells are realized by careful optimization of their solid-state morphology. These BHJ films are transformed from an intimate mixture of the donor and acceptor phases to films with well-defined donor crystallites. In addition to correlating with a high photovoltaic response, the donor crystallites also appear to be linked with the emergence of donor singlet electroluminescence at low applied biases, where only charge-transfer-state emission is expected. On page 7405, T.-Q. Nguyen and co-workers study three blends of high-performing small-molecule solar-cell systems that show the same trend of emerging singlet emission upon an optimized photovoltaic response. PMID:25393444

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

2014-11-01

196

Predictive DFT-Based Approaches to Charge and Spin Transport in Single-Molecule Junctions and Two-Dimensional Materials: Successes and Challenges.  

PubMed

Conspectus The emerging field of flexible electronics based on organics and two-dimensional (2D) materials relies on a fundamental understanding of charge and spin transport at the molecular and nanoscale. It is desirable to make predictions and shine light on unexplained experimental phenomena independently of experimentally derived parameters. Indeed, density functional theory (DFT), the workhorse of first-principles approaches, has been used extensively to model charge/spin transport at the nanoscale. However, DFT is essentially a ground state theory that simply guarantees correct total energies given the correct charge density, while charge/spin transport is a nonequilibrium phenomenon involving the scattering of quasiparticles. In this Account, we critically assess the validity and applicability of DFT to predict charge/spin transport at the nanoscale. We also describe a DFT-based approach, DFT+?, which incorporates corrections to Kohn-Sham energy levels based on many-electron calculations. We focus on single-molecule junctions and then discuss how the important considerations for DFT descriptions of transport can differ in 2D materials. We conclude that when used appropriately, DFT and DFT-based approaches can play an important role in making predictions and gaining insight into transport in these materials. Specifically, we shall focus on the low-bias quasi-equilibrium regime, which is also experimentally most relevant for single-molecule junctions. The next question is how well can the scattering of DFT Kohn-Sham particles approximate the scattering of true quasiparticles in the junction? Quasiparticles are electrons (holes) that are surrounded by a constantly changing cloud of holes (electrons), but Kohn-Sham particles have no physical significance. However, Kohn-Sham particles can often be used as a qualitative approximation to quasiparticles. The errors in standard DFT descriptions of transport arise primarily from errors in the Kohn-Sham energy levels (self-energy errors). These errors are small in the strong-coupling regime where the molecular levels are significantly broadened at the Fermi level but are large in the coherent off-resonant tunneling regime where DFT overestimates conductance by orders of magnitude. The DFT+? approach uses a physically motivated, parameter free estimate of the self-energy corrections to correct the energy levels in DFT, giving conductance in quantitative agreement with experiment for a large but nonexhaustive class of single-molecule junctions. In 2D materials, the self-energy error is relatively small, and critical issues stem instead from the large length scales in experiments, which make it necessary to consider band-bending within the 2D material, as well as scattering due to electron-phonon interactions, spin-flip interactions, defects, etc. PMID:24933289

Quek, Su Ying; Khoo, Khoong Hong

2014-11-18

197

Crystal structure of Jararacussin-I: The highly negatively charged catalytic interface contributes to macromolecular selectivity in snake venom thrombin-like enzymes  

PubMed Central

Snake venom serine proteinases (SVSPs) are hemostatically active toxins that perturb the maintenance and regulation of both the blood coagulation cascade and fibrinolytic feedback system at specific points, and hence, are widely used as tools in pharmacological and clinical diagnosis. The crystal structure of a thrombin-like enzyme (TLE) from Bothrops jararacussu venom (Jararacussin-I) was determined at 2.48 Å resolution. This is the first crystal structure of a TLE and allows structural comparisons with both the Agkistrodon contortrix contortrix Protein C Activator and the Trimeresurus stejnegeri plasminogen activator. Despite the highly conserved overall fold, significant differences in the amino acid compositions and three-dimensional conformations of the loops surrounding the active site significantly alter the molecular topography and charge distribution profile of the catalytic interface. In contrast to other SVSPs, the catalytic interface of Jararacussin-I is highly negatively charged, which contributes to its unique macromolecular selectivity. PMID:23139169

Ullah, A; Souza, T A C B; Zanphorlin, L M; Mariutti, R B; Santana, V S; Murakami, M T; Arni, R K

2013-01-01

198

Crystal structure of Jararacussin-I: the highly negatively charged catalytic interface contributes to macromolecular selectivity in snake venom thrombin-like enzymes.  

PubMed

Snake venom serine proteinases (SVSPs) are hemostatically active toxins that perturb the maintenance and regulation of both the blood coagulation cascade and fibrinolytic feedback system at specific points, and hence, are widely used as tools in pharmacological and clinical diagnosis. The crystal structure of a thrombin-like enzyme (TLE) from Bothrops jararacussu venom (Jararacussin-I) was determined at 2.48 Å resolution. This is the first crystal structure of a TLE and allows structural comparisons with both the Agkistrodon contortrix contortrix Protein C Activator and the Trimeresurus stejnegeri plasminogen activator. Despite the highly conserved overall fold, significant differences in the amino acid compositions and three-dimensional conformations of the loops surrounding the active site significantly alter the molecular topography and charge distribution profile of the catalytic interface. In contrast to other SVSPs, the catalytic interface of Jararacussin-I is highly negatively charged, which contributes to its unique macromolecular selectivity. PMID:23139169

Ullah, A; Souza, T A C B; Zanphorlin, L M; Mariutti, R B; Santana, V S; Murakami, M T; Arni, R K

2013-01-01

199

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

200

Enantiomeric separations of primary amino compounds by capillary electrochromatography with monolithic chiral stationary phases of chiral crown ether-bonded negatively charged polyacrylamide gels.  

PubMed

A novel enantiomeric separation method by capillary electrochromatography with chiral crown ether-bonded negatively charged polyacrylamide gels is presented. Two kinds of chiral crown ether derivatives, (+)-tetraallyl 18-crown-6 carboxylate and (+)-18-crown-6 tetracarboxylic acid 2-allyl ester were synthesized and allowed to covalently bind to a negatively charged polyacrylamide gel, a so-called monolithic stationary phase, respectively. The gel was placed in fused-silica tubing, the walls of which had been activated with a bifunctional reagent to make the resulting gel bind covalently to the inner surface. Enantiomeric separations of 12 primary amino compounds were achieved using these columns and mobile phases of 200 mM triethanolamine-300 mM boric acid buffers with high efficiencies of up to 135000 plates m(-1). Both the within- and between-run reproducibilities of retention time and separation factor were good. The reproducibilities of retention time and separation factor for three different columns prepared from a different batch of monomers were acceptable. The gel-filled capillaries were stable for at least 13 months with intermittent use for 3 months followed by storage at room temperature for 10 months. The result of the optical purity test of alanine-2-naphthylamide is also described. PMID:11269530

Koide, T; Ueno, K

2001-02-16

201

The reduction rates of DEPC-modified mutant Thermus thermophilus Rieske proteins differ when there is a negative charge proximal to the cluster.  

PubMed

Rieske and Rieske-type proteins are electron transport proteins involved in key biological processes such as respiration, photosynthesis, and detoxification. They have a [2Fe-2S] cluster ligated by two cysteines and two histidines. A series of mutations, L135E, L135R, L135A, and Y158F, of the Rieske protein from Thermus thermophilus has been produced which probe the effects of the neighboring residues, in the second sphere, on the dynamics of cluster reduction and the reactivity of the ligating histidines. These properties were probed using titrations and modifications with diethyl pyrocarbonate (DEPC) at various pH values monitored using UV-Visible and circular dichroism spectrophotometry. These results, along with results from EPR studies, provide information on ligating histidine modification and rate of reduction of each of the mutant proteins. L135R, L135A, and Y158F react with DEPC similarly to wild type, resulting in modified protein with a reduced [2Fe-2S] cluster in <90 min, whereas L135E requires >15 h under the same conditions. Thus, the negative charge slows down the rate of reduction and provides an explanation as to why negatively charged residues are rarely, if ever, found in the equivalent position of other Rieske and Rieske-type proteins. PMID:24916128

Karagas, Nicholas E; Jones, Christie N; Osborn, Deborah J; Dzierlenga, Anika L; Oyala, Paul; Konkle, Mary E; Whitney, Emily M; David Britt, R; Hunsicker-Wang, Laura M

2014-10-01

202

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

203

Negative and positive ion trapping by isotopic molecules in cryocrystals in case of solid parahydrogen containing electrons and H{sub 6}{sup +} radical cations  

SciTech Connect

We performed electron spin resonance studies of trapped electrons and H{sub 6}{sup +} radical cations produced by radiolysis of solid parahydrogen (p-H{sub 2}), p-H{sub 2}-ortho-D{sub 2} (o-D{sub 2}), and p-H{sub 2}-HD mixtures. Yields of trapped electrons, H{sub 6}{sup +} radical cations, and its isotopic analogs H{sub 6-n}D{sub n}{sup +} (4{>=}n{>=}1) increased with increasing o-D{sub 2} and HD concentrations in solid p-H{sub 2}. Electrons were found trapped near an o-D{sub 2} or an HD in solid p-H{sub 2} due to the long-range charge-induced dipole and quadrupole interactions between electrons and isotopic hydrogen molecules. H{sub 6}{sup +} radical cations diffuse in solid p-H{sub 2} by repetition of H{sub 6}{sup +}+H{sub 2}{yields}H{sub 2}+H{sub 6}{sup +} and are trapped by ortho-D{sub 2} or HD to form H{sub 6-n}D{sub n}{sup +} (4{>=}n{>=}1) as isotope condensation reactions. Decay behaviors of these cations by the repetition, isotope condensation, and geminate recombination between electrons and H{sub 6-n}D{sub n}{sup +} (4{>=}n{>=}0) were reproduced by determining the corresponding reaction rate constants k{sub 1}, k{sub 2}, and k{sub 3}. Values of 0.045 and 0.0015 L mol{sup -1} min{sup -1} were obtained for k{sub 1} (H{sub 6}{sup +}+D{sub 2}{yields}H{sub 2}+H{sub 4}D{sub 2}{sup +}) and k{sub 2} (H{sub 4}D{sub 2}{sup +}+D{sub 2}{yields}H{sub 2}+H{sub 2}D{sub 4}{sup +}), respectively, and the value was quasinull for k{sub 3} (H{sub 2}D{sub 4}{sup +}+D{sub 2}{yields}H{sub 2}+D{sub 6}{sup +}). These rate constants suggest that hole mobility drastically decreased in the repetition reaction when H{sub 6}{sup +} radical cations acting as hole carriers formed H{sub 4}D{sub 2}{sup +} or H{sub 2}D{sub 4}{sup +}. HD and D{sub 2} molecules, therefore, act as electron and hole acceptors in irradiated solid p-H{sub 2}-o-D{sub 2} and p-H{sub 2}-HD mixtures.

Shimizu, Yuta; Inagaki, Makoto; Kumagai, Jun [Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Kumada, Takayuki [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)

2010-06-28

204

Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters  

NASA Astrophysics Data System (ADS)

We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the ?⋯HO interactions in the neutral Bz(H2O)n (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the ? system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (?*) of the Bz ring, and the ?⋯HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak ?⋯HO interaction plays an important role as the driving force in conversion of the two states.

Zhang, Meng; Zhao, Jing; Liu, Jinxiang; Zhou, Lianwen; Bu, Yuxiang

2013-01-01

205

Kinetic instability of the dust acoustic mode in inhomogeneous, partially magnetized plasma with both positively and negatively charged grains  

SciTech Connect

A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In the presence of a magnetic field, electrons and ions may be magnetized while at the same time dust grains may remain unmagnetized. Although the dynamics of the light species is strongly affected by the magnetic field, the dust acoustic mode may still propagate in practically any direction. The inhomogeneity implies a source of free energy for an instability that develops through the diamagnetic drift effects of the magnetized species. It is shown that this may be a powerful mechanism for the excitation of dust acoustic waves. The analysis presented in the work is also directly applicable to plasmas containing both positive and negative ions and electrons, provided that at least one of the two ion species is unmagnetized.

Vranjes, J.; Poedts, S. [Centre for Plasma Astrophysics, Celestijnenlaan 200B, 3001 Leuven (Belgium) and Leuven Mathematical Modeling and Computational Science Research Centre (LMCC), Celestijnenlaan 200B, 3001 Leuven (Belgium)

2010-08-15

206

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

207

Pair Tunneling through Single Molecules  

NASA Astrophysics Data System (ADS)

Coupling to molecular vibrations induces a polaronic shift, and can lead to a negative charging energy, U. For negative U, the occupation of the ground state of the molecule is even. In this situation, virtual pair transitions between the molecule and the leads can dominate electron transport. At low temperature, T, these transitions give rise to the charge-Kondo effect [1]. We developed the electron transport theory through the negative-U molecule [2] at relatively high T, when the Kondo correlations are suppressed. Two physical ingredients distinguish our theory from the transport through a superconducting grain coupled to the normal leads [3]: (i) in parallel with sequential pair-tunneling processes, single-particle cotunneling processes take place; (ii) the electron pair on the molecule can be created (or annihilated) by two electrons tunneling in from (or out to) opposite leads. We found that, even within the rate-equation description, the behavior of differential conductance through the negative-U molecule as function of the gate voltage is quite peculiar: the height of the peak near the degeneracy point is independent of temperature, while its width is proportional to T. This is in contrast to the ordinary Coulomb-blockade conductance peak, whose integral strength is T-independent. At finite source-drain bias, V>>T, the width of the conductance peak is ˜V, whereas the conventional Coulomb-blockade peak at finite V splits into two sharp peaks at detunings V/2, and -V/2. Possible applications to the gate-controlled current rectification and switching will be discussed. [1] A. Taraphder and P. Coleman, Phys. Rev. Lett. 66, 2814 (1991). [2] J. Koch, M. E. Raikh, and F. von Oppen, Phys. Rev. Lett. 96, 056803 (2006). [3] F. W. J. Hekking, L. I. Glazman, K. A. Matveev, and R. I. Shekhter, Phys. Rev. Lett. 70, 4138 (1993).

Raikh, Mikhail

2007-03-01

208

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

209

Sry HMG box protein 9-positive (Sox9+) epithelial cell adhesion molecule-negative (EpCAM-) biphenotypic cells derived from hepatocytes are involved in mouse liver regeneration.  

PubMed

It has been shown that mature hepatocytes compensate tissue damages not only by proliferation and/or hypertrophy but also by conversion into cholangiocyte-like cells. We found that Sry HMG box protein 9-positive (Sox9(+)) epithelial cell adhesion molecule-negative (EpCAM(-)) hepatocyte nuclear factor 4?-positive (HNF4?(+)) biphenotypic cells showing hepatocytic morphology appeared near EpCAM(+) ductular structures in the livers of mice fed 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diet. When Mx1-Cre:ROSA mice, which were injected with poly(I:C) to label mature hepatocytes, were fed with the DDC diet, we found LacZ(+)Sox9(+) cells near ductular structures. Although Sox9(+)EpCAM(-) cells adjacent to expanding ducts likely further converted into ductular cells, the incidence was rare. To know the cellular characteristics of Sox9(+)EpCAM(-) cells, we isolated them as GFP(+)EpCAM(-) cells from DDC-injured livers of Sox9-EGFP mice. Sox9(+)EpCAM(-) cells proliferated and could differentiate to functional hepatocytes in vitro. In addition, Sox9(+)EpCAM(-) cells formed cysts with a small central lumen in collagen gels containing Matrigel® without expressing EpCAM. These results suggest that Sox9(+)EpCAM(-) cells maintaining biphenotypic status can establish cholangiocyte-type polarity. Interestingly, we found that some of the Sox9(+) cells surrounded luminal spaces in DDC-injured liver while they expressed HNF4?. Taken together, we consider that in addition to converting to cholangiocyte-like cells, Sox9(+)EpCAM(-) cells provide luminal space near expanded ductular structures to prevent deterioration of the injuries and potentially supply new hepatocytes to repair damaged tissues. PMID:24482234

Tanimizu, Naoki; Nishikawa, Yuji; Ichinohe, Norihisa; Akiyama, Haruhiko; Mitaka, Toshihiro

2014-03-14

210

Novel negatively charged hybrids. 3. Removal of Pb2+ from aqueous solution using zwitterionic hybrid polymers as adsorbent.  

PubMed

Using zwitterionic hybrid polymers as adsorbent, the adsorption kinetics and isotherm, thermodynamic parameters of Delta G, Delta H and DeltaS for the removal of Pb(2+) from aqueous solution were investigated. It is indicated that the adsorption of Pb(2+) ions on these zwitterionic hybrid polymers followed the Lagergren second-order kinetic model and Freundlich isotherm model, demonstrating that the adsorption process might be Langmuir monolayer adsorption. The negative values of Delta G and the positive values of Delta H evidence that Pb(2+) adsorption on these zwitterionic hybrid polymers is spontaneous and endothermic process in nature. Moreover, the zwitterionic hybrid polymers produced reveal relatively higher desorption efficiency in 2 mol dm(-3) aqueous HNO(3) solution, indicating that they can be recycled in industrial processes. These findings suggest that these zwitterionic hybrid polymers are the promising adsorbents for Pb(2+) removal and can be potentially applied in the separation and recovery of Pb(2+) ions from the waste chemicals and contaminated water of lead-acid rechargeable battery. PMID:19744785

Liu, Junsheng; Ma, Yue; Zhang, Yaping; Shao, Guoquan

2010-01-15

211

PEG-b-PCL Copolymer Micelles with the Ability of pH-Controlled Negative-to-Positive Charge Reversal for Intracellular Delivery of Doxorubicin.  

PubMed

The application of PEG-b-PCL micelles was dampened by their inherent low drug-loading capability and relatively poor cell uptake efficiency. In this study, a series of novel PEG-b-PCL copolymers methoxy poly(ethylene glycol)-b-poly(?-caprolactone-co-?-dimethyl maleamidic acid -?-caprolactone) (mPEG-b-P(CL-co-DCL)) bearing different amounts of acid-labile ?-carboxylic amides on the polyester moiety were synthesized. The chain structure and chemical composition of copolymers were characterized by (1)H NMR, Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). mPEG-b-P(CL-co-DCL) with critical micellar concentrations (CMCs) of 3.2-6.3 ?g/mL could self-assemble into stable micelles in water with diameters of 100 to 150 nm. Doxorubicin (DOX), a cationic hydrophobic drug, was successfully encapsulated into the polymer micelles, achieving a very high loading content due to electrostatic interaction. Then the stability, charge-conversional behavior, loading and release profiles, cellular uptake and in vitro cytotoxicity of free drug and drug-loaded micelles were evaluated. The ?-carboxylic amides functionalized polymer micelles are negatively charged and stable in neutral solution but quickly become positively charged at pH 6.0, due to the hydrolysis of ?-carboxylic amides in acidic conditions. The pH-triggered negative-to-positive charge reversal not only resulted in a very fast drug release in acidic conditions, but also effectively enhanced the cellular uptake by electrostatic absorptive endocytosis. The MTT assay demonstrated that mPEG-b-P(CL-co-DCL) micelles were biocompatible to HepG2 cells while DOX-loaded micelles showed significant cytotoxicity. In sum, the introduction of acid-labile ?-carboxylic amides on the polyester block in mPEG-b-P(CL-co-DCL) exhibited great potentials for the modifications in the stability in blood circulation, drug solubilization, and release properties, as well as cell internalization and intracellular drug release. PMID:25325531

Deng, Hongzhang; Liu, Jinjian; Zhao, Xuefei; Zhang, Yuming; Liu, Jianfeng; Xu, Shuxin; Deng, Liandong; Dong, Anjie; Zhang, Jianhua

2014-11-10

212

Simultaneous solution to the {sup 6}Li and {sup 7}Li big bang nucleosynthesis problems from a long-lived negatively charged leptonic particle  

SciTech Connect

The {sup 6}Li abundance observed in metal-poor halo stars exhibits a plateau similar to that for {sup 7}Li suggesting a primordial origin. However, the observed abundance of {sup 6}Li is a factor of 10{sup 3} larger and that of {sup 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 Wilkinson microwave anisotropy probe. 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.

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, The 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, University of California, Livermore, California 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, Indiana 46556 (United States)

2007-12-15

213

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

214

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

215

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

216

Phase-transfer energetics of small-molecule alcohols across the water-hexane interface: molecular dynamics simulations using charge equilibration models.  

PubMed

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 and 0.6378±0.0001 g/cm(3), 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±0.13 and 198.7±0.01 mV, 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

2011-04-01

217

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

218

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

219

Class I negative CD8 T cells reveal the confounding role of peptide-transfer onto CD8 T cells stimulated with soluble H2-Kb molecules  

PubMed Central

Crosslinking of the T cell receptor has been proposed to be a prerequisite for T cell activation. Although the evidence supports this notion for CD4 T cells, the situation for CD8 T cells is less clear. Soluble class I monomers have been used to determine activation requirements in vitro with contradictory results. The possibility of transfer of peptide from soluble class I molecules onto class I molecules present on the surface of CD8 T cells, with ensuing presentation to other CD8 T cells, has been widely ignored. We show that monomeric and tetrameric class I molecules as well as free peptide can stimulate naïve CD8 T cells in vitro. We generate and characterize CD8 T cells that express the OT-I T cell receptor (for Kb/SIINFEKL) yet lack Kb and Db molecules, and show that their activation requirements differ from their class I positive counterparts when stimulated with soluble Kb molecules. By eliminating the confounding effect of peptide transfer, we unmask the true activation requirements for naïve CD8 T cells and show that multivalent engagement of T cell receptors, as well as costimulation, is required for optimal stimulation. PMID:12374858

Schott, Eckart; Bertho, Nicolas; Ge, Qing; Maurice, Madelon M.; Ploegh, Hidde L.

2002-01-01

220

Optimization studies of carbon additives to negative active material for the purpose of extending the life of VRLA batteries in high-rate partial-state-of-charge operation  

Microsoft Academic Search

The negative plates of lead-acid batteries subjected to partial-state-of-charge (PSOC) operation fail because of the development of an electrically inert film of lead sulfate on their surfaces. It has been found that carbon additives to the negative active material can significantly increase their cycle life in this type of operation. In this paper we show that various types of carbon,

D. P. Boden; D. V. Loosemore; M. A. Spence; T. D. Wojcinski

2010-01-01

221

Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: A path to ambipolar organic-based materials?  

NASA Astrophysics Data System (ADS)

We have carefully investigated the structural and electronic properties of coronene and some of its fluorinated and chlorinated derivatives, including full periphery substitution, as well as the preferred orientation of the non-covalent dimer structures subsequently formed. We have paid particular attention to a set of methodological details, to first obtain single-molecule magnitudes as accurately as possible, including next the use of modern dispersion-corrected methods to tackle the corresponding non-covalently bound dimers. Generally speaking, this class of compounds is expected to self-assembly in neighboring ?-stacks with dimer stabilization energies ranging from -20 to -30 kcal mol-1 at close distances around 3.0-3.3 Å. Then, in a further step, we have also calculated hole and electron transfer rates of some suitable candidates for ambipolar materials, and corresponding charge mobility values, which are known to critically depend on the supramolecular organization of the samples. For coronene and per-fluorinated coronene, we have found high values for their hopping rates, although slightly smaller for the latter due to an increase (decrease) of the reorganization energies (electronic couplings).

Sancho-García, J. C.; Pérez-Jiménez, A. J.

2014-10-01

222

Optimal white light control of the negative to neutral to positive charge transition (NeNePo) in the electronic manifold of the silver trimer.  

PubMed

Control over the electronic state of the Ag(3) cluster is approached via a progression of ultrafast photoinduced transitions within the full electronic manifold of the negative to the neutral and finally the cationic state of the system. High-bandwidth supercontinuum laser pulses ranging from 500 to 950 nm are employed for addressing the wide range of electronic resonance conditions associated with the ladder climbing process of a tandem photoelectron detachment and a resonance enhanced multiphoton ionization (REMPI). With the control of the phase over the full spectral envelope of the supercontinuum in a pulse shaper arrangement, pulse forms are generated with the aim of synchronizing ultrashort subpulse sequences to the characteristic dynamics of the system during charge reversal. Pulse forms ranging over several hundred femtoseconds in total duration and subpulse structures down to 15 fs duration with a variable spectral composition can be obtained for this purpose. A free optimization based on a closed-loop genetic algorithm is employed for ordering the subpulse sequences to match the structural evolution of the system. The effective control attainable in this scenario is evaluated in view of maintaining a defined sequence of electronic transitions within the complex dynamic response of the system during the photoexcitation. Further emphasis is made on analyzing the degree of control attainable in the nonlinear regime of multiphoton excitation at supercontinuum bandwidths. PMID:22954161

Schmidt, B E; Gause, O; Hagemann, F; Li, S; Unrau, W; Wöste, L; Siebert, T

2012-11-26

223

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

2013-10-09

224

Production of Multimeric Prostate-Specific Membrane Antigen Small-Molecule Radiotracers Using a SolidPhase 99mTc Preloading Strategy  

Microsoft Academic Search

Small-molecule ligands specific for prostate-specific membrane antigen (PSMA) have the potential to improve prostate cancer imaging. However, highly charged ligands are difficult to label with 99mTc and to purify. In this study, we present an adamantane- trimerized small molecule that has nanomolar binding to PSMA and also has 12 negative charges. Methods: To convert this molecule into a clinically viable

Preeti Misra; Valerie Humblet; Nadine Pannier; Wolfgang Maison; John V. Frangioni

225

IONIZATION OF NITROGEN MOLECULES BY NITROGEN MOLECULES  

Microsoft Academic Search

The ionization cross section for Nâ molecules on impact with N\\/sub ; 2\\/ molecules was measured over the laboratory energy range from 30 to 1000 ev. ; The incident molecular beam was produced by the technique of ionization by ; electron impact, electrostatic acceleration and neutralization by charge transfer. ; The measurements were carried out in a low-pressure parallel plate

Nyle Utterback; Glenn Miller

1961-01-01

226

ENTHALPIES OF FORMATION OF NEGATIVE IONS MnO , MnO , AND MnO AS DETERMINED BY ION-MOLECULE EQUILIBRIA METHOD  

E-print Network

/molecule equilibria. A platinum effusion chamber (diameter 12 mm, height 12 mm) was used with (0.5 to 1.2 mm) effusion into the effusion chamber. In the first case, decomposition of MnO with 2 formation of Mn O was performed in the effusion chamber itself 3 4 o in vacuum for two hours at temperature 750 C before beginning

Rudnyi, Evgenii B.

227

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

228

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

229

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

230

Elastic, Adhesive, and Charge Transport Properties of a Metal-molecule-metal Junction: the Role of Molecular Orientation, Order, and Coverage  

SciTech Connect

The elastic, adhesive, and charge transport properties of a metal-molecule-metal junction were studied via conducting-probe atomic force microscopy (AFM) and correlated with molecular structure by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The junctions consisted of Co-Cr-coated AFM tips in contact with methyl-terminated alkanethiols (CH{sub 3}(CH{sub 2}){sub n-1}SH, denoted by Cn, where n is the number of carbons in the molecular chain) on Au substrates. AFM contact data were analyzed with the Derjaguin-Muller-Toporov contact model, modified by a first-order elastic perturbation method to account for substrate effects, and a parabolic tunneling model, appropriate for a metal-insulator-metal junction in which the thickness of the insulator is comparable to the Fermi wavelength of the conducting electrons. NEXAFS carbon K-edge spectra were used to compute the dichroic ratio RI for each film, which provided a quantitative measure of the molecular structure as a function of n. As n decreased from 18 to 5, there was a change in the molecular phase from crystalline to amorphous (R{sub I} {yields} 0) and loss of surface coverage, and as a result, the work of adhesion w increased from 82.8 mJ m{sup -2} to 168.3 mJ m{sup -2}, the Young's modulus of the film E{sub film} decreased from 1.0 to 0.15 GPa, and the tunneling barrier height {psi}{sub 0} - E{sub F} decreased from 2.4 to 2.1 eV. For all n, the barrier thickness t decreased for small applied loads F and remained constant at {approx}2.2 nm for large F. The change in behavior was explained by the presence of two insulating layers: an oxide layer on the Co-Cr tip, and the alkanethiol monolayer on the Au surface. X-ray photoelectron spectroscopy confirmed the presence of an oxide layer on the Co-Cr tip, and by performing high-resolution region scans through the film, the thickness of the oxide layer t{sub oxide} was found to be between 1.9 and 3.9 nm. Finally, it was shown that {psi}{sub 0} - E{sub F} is strain-dependent, and the strain at which the film is completely displaced from under the tip is -0.17 for all values of n.

DelRio, F.; Steffens, K; Jaye, C; Fischer, D; Cook, R

2010-01-01

231

I - Matter, antimatter and geometry II - The twin universe model : a solution to the problem of negative energy particles III - The twin universe model plus electric charges and matter-antimatter symmetry  

E-print Network

We introduce a new dynamical group whose coadjoint action on its momentum space takes account of matter-antimatter symmetry on pure geometrical grounds. According to this description the energy and the spin are unchanged under matter-antimatter symmetry. We recall that the antichron components of the Poincar\\'{e} group, ruling relativistic motions of a mass-point particle, generate negative energy particles. The model with two twin universes, inspired by Sakharov's one, solves the stability issue. Positive and negative energy particles motions hold in two distinct folds. The model is extended to charged particles. As a result, the matter-antimatter duality holds in both universes.

Frederic Henry-Couannier; Gilles D'Agostini; Jean-Pierre Petit

2005-02-20

232

Molecular Modeling of Geometries, Charge Distributions, and Binding Energies of Small, Drug-Like Molecules Containing Nitrogen Heterocycles and Exocyclic Amino Groups in the Gas Phase and Aqueous Solution  

PubMed Central

We have tested a variety of approximate methods for modeling 30 systems containing mixtures of nitrogen heterocycles and exocyclic amines, each of which is studied with up to 31 methods in one or two phases (gaseous and aqueous). Fifteen of the systems are protonated, and 15 are not. We consider a data set consisting of geometric parameters, partial atomic charges, and water binding energies for the methotrexate fragments 2-(aminomethyl)pyrazine and 2,4-diaminopyrimidine, as well as their cationic forms 1H-2-(aminomethyl)pyrazine and 1H-2,4-diaminopyrimidine. We first evaluated the suitability of several density functionals with the 6-31+G(d,p) basis set to serve as a benchmark by comparing calculated molecular geometries to results obtained from coupled-cluster [CCSD/6-31+G(d,p)] wave function theory (WFT). We found that the M05-2X density functional can be used to obtain reliable geometries for our data set. To accurately model partial charges in our molecules, we elected to utilize the well-validated Charge Model 4 (CM4). In the process of establishing benchmark values, we consider gas-phase coupled cluster and density functional theory (DFT) calculations followed by aqueous-phase DFT calculations, where the effect of solvent is treated by the SM6 quantum mechanical implicit solvation model. The resulting benchmarks were used to test several widely available and economical semiempirical molecular orbital (SE-MO) methods and molecular mechanical (MM) force fields for their ability to accurately predict the partial charges, binding energies to a water molecule, and molecular geometries of representative fragments of methotrexate in the gaseous and aqueous phases, where effects of water were simulated by the SM5.4 and SM5.42 quantum mechanical implicit solvation models for SE-MO and explicit solvation used for MM. In addition, we substituted CM4 charges into the MM force fields tested to observe the effect of improved charge assignment on geometric and energetic modeling. The most accurate MM force fields (with or without CM4 charges substituted) were validated against gas-phase and aqueous-phase geometries and charge distributions of a larger set of 16 drug-like ligands, both neutral and cationic. This process showed that the Merck Molecular Force Field (MMFF94) with or without CM4 charges substituted, is, on average, the most accurate force field for geometries of molecules containing nitrogen heterocycles and exocyclic amino groups, both protonated and unprotonated. This force field was then applied to the complete methotrexate molecule, in an effort to systematically explore its accuracy for trends in geometries and charge distributions. The most accurate force fields for the binding energies of nitrogen heterocycles to a water molecule are OPLS2005 and AMBER. PMID:23700392

White, Brian R.; Wagner, Carston R.; Truhlar, Donald G.; Amin, Elizabeth A.

2013-01-01

233

Analytical modeling and simulation of electrochemical charge/discharge behavior of Si thin film negative electrodes in Li-ion cells  

NASA Astrophysics Data System (ADS)

Physically-based analytical models that provide insights into the diffusion and/or interface charge transfer effects in bulk (lithiating/delithiating) electrodes are needed to truly assess the performance/limitations of electrode materials for Li-ion batteries. In this context, an analytical modeling framework is constructed here to predict the electrochemical charge-discharge characteristics during lithiation and delithiation of solid amorphous Si (a-Si) thin film electrodes. The framework includes analytical expressions that satisfy Fick's second law for Li transport and the requisite flux boundary conditions of lithiation and delithiation steps. The expressions are derived here by the method of separation of variables. They enable the determination of transient Li concentration profiles in the thin film electrode as a function of state of charge/discharge. The time-dependent electrode surface concentrations (at the electrode-electrolyte interface) obtained from these profiles were used to determine the activation overpotentials and thus, the non-equilibrium cell potentials, as a function of state of charge/discharge using Butler-Volmer kinetics. The simulated charge/discharge characteristics agreed well with the experimental data of a-Si thin film electrodes obtained at different C-rates. The model offers insights into how the charge-discharge behavior is controlled by diffusion limitation within electrode and/or the activation overpotentials at the interface. The analytical framework is also shown to predict successfully the hysteretic behavior of lithiation/delithiation voltage curves.

Jagannathan, M.; Chandran, K. S. Ravi

2014-02-01

234

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.

Kansas, University O.

2006-01-01

235

Phase behavior of mixtures of oppositely charged protein nanoparticles at asymmetric charge ratios.  

PubMed

We present experimental and theoretical results for the phase behavior of mixtures of oppositely charged globular protein molecules in aqueous solutions containing monovalent salt. These colloidal mixtures are interesting model systems, on the one hand for electrolyte solutions ("colloidal ionic liquids"), and on the other for mixtures of oppositely charged (bio)macromolecules, colloids, micelles, etc., with the range of the electrostatic interactions (Debye length) easily tunable from much smaller to much larger than the particle size, simply by adding different amounts of monovalent salt. In this paper we investigate the phase behavior of such mixtures in the case that equally sized colloids have a large difference in charge magnitude. This is possible at any mixing ratio because small ions compensate any colloidal charge asymmetry. Our experimental system is based on lysozyme, a positively charged "hard" globular protein molecule, and succinylated lysozyme, a chemical modification of lysozyme which is negatively charged. By changing the solution pH we can adjust the ratio of charge between the two molecules. To describe phase separation into a dilute phase and a dense "complex" phase, a thermodynamic model is set up in which we combine the Carnahan-Starling-van der Waals equation of state with a heterogeneous Poisson-Boltzmann cell model and include the possibility that protein molecules adjust their charge when they move from one phase to the other (charge regulation). The theory uses the nonelectrostatic attraction strength as the only adjustable parameter and reasonably well reproduces the data in that complexation is only possible at intermediate , not too asymmetric mixing ratios, and low enough ionic strength and temperature. PMID:16711801

Biesheuvel, P Maarten; Lindhoud, Saskia; Cohen Stuart, Martien A; de Vries, Renko

2006-04-01

236

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).

Muller, Eric

1995-01-01

237

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

238

Understanding the site selectivity in small-sized neutral and charged Al(n) (4 ? N ? 7) clusters using density functional theory based reactivity descriptors: a validation study on water molecule adsorption.  

PubMed

Aluminum clusters are now technologically important due to their high catalytic activity. Our present study on the small-sized aluminum clusters applies density functional theory (DFT)-based reactivity descriptors to identify potential sites for adsorption and eventual chemical reaction. Depending on symmetry, susceptibility of various type of reactive sites within a cluster toward an impending electrophilic and/or nucleophilic attack is predicted using the reactivity descriptors. In addition, the study devises general rules as to how the size, shape, and charge of the cluster influences the number of available sites for an electrophilic and/or nucleophilic attack. The predictions by reactivity descriptors are validated by performing an explicit adsorption of water molecule on Al clusters with four atoms. The adsorption studies demonstrate that the most stable water-cluster complex is obtained when the molecule is adsorbed through an oxygen atom on the site with the highest relative electrophilicity. PMID:23672406

Das, Susanta; Pal, Sourav; Krishnamurty, Sailaja

2013-09-12

239

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

at approximately 3460 cm-1. Introduction Water structure and ordering resulting from intermolecular hydrogen water molecules at liquid/air, liquid/solid, and liquid/liquid interfaces.3,5-7 Experimental in commercial products such as motor oils, lubricants, detergents, and soaps. Despite the abundant use

Richmond, Geraldine L.

240

Observation of gas molecules adsorbed in the nanochannels of porous coordination polymers by the in situ synchrotron powder diffraction experiment and the MEM\\/Rietveld charge density analysis  

Microsoft Academic Search

Microporous coordination polymers have attracted attention for their numerous nanotechnology and engineering applications. Nano-coordination space provides some unique properties and functions that could never be realized in conventional porous materials. For the strategy of rational designs and the syntheses of novel porous coordination polymers, the structural information of adsorbed guest molecules inside the nanopores and the host framework is very

Yoshiki Kubota; Masaki Takata; Tatsuo C. Kobayashi; S. Kitagawa

2007-01-01

241

Formation of hexagonal fullerene layers from neutral and negatively charged fullerenes in {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 containing gold cations with the C3v symmetry.  

PubMed

Fullerene salt {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 (1) containing (Ph3P)3Au(+) cations with the C3v symmetry has been obtained as single crystals. Hexagonal corrugated fullerene layers formed in 1 alternate with the layers consisting of (Ph3P)3Au(+) and C6H4Cl2 along the c axis. According to IR spectra and peculiarities of the crystal structure, the charge on fullerenes in the layers is evaluated to be -1 for two and close to zero for one C60. These fullerenes have different cationic surroundings, and positively charged gold atoms approach closer to C60(•-). Charged and neutral fullerenes are closely packed within hexagonal layers with an interfullerene center-to-center distance of 10.02 Å and multiple short van der Waals C···C contacts. The distances between C60(•-) are essentially longer with an interfullerene center-to-center distance of 10.37 Å due to corrugation of the layers, and no van der Waals contacts are formed in this case. As a result, each C60(•-) has only three negatively charged fullerene neighbors with rather long interfullerene distances providing only weak antiferromagnetic interaction of spins in the fullerene layers with a Weiss temperature of -5 K. PMID:24945795

Konarev, Dmitri V; Khasanov, Salavat S; Otsuka, Akihiro; Ishikawa, Manabu; Yamochi, Hideki; Saito, Gunzi; Lyubovskaya, Rimma N

2014-07-01

242

Multiplicity Distribution and Spectra of Negatively Charged Hadrons in Au+Au Collisions at (sNN) = 130 GeV  

Microsoft Academic Search

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h-) in Au+Au interactions at (sNN) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dNh-\\/deta\\\\|eta = 0 = 280+\\/-1(stat)+\\/-20(syst), an increase per participant of 38% relative to ppbar collisions at the same

C. Adler; Z. Ahammed; C. Allgower; J. Amonett; B. D. Anderson; M. Anderson; G. S. Averichev; J. Balewski; O. Barannikova; L. S. Barnby; J. Baudot; S. Bekele; V. V. Belaga; R. Bellwied; J. Berger; H. Bichsel; L. C. Bland; C. O. Blyth; B. E. Bonner; R. Bossingham; A. Boucham; A. Brandin; H. Caines; M. Calderón de La Barca Sánchez; A. Cardenas; J. Carroll; J. Castillo; M. Castro; D. Cebra; S. Chattopadhyay; M. L. Chen; Y. Chen; S. P. Chernenko; M. Cherney; A. Chikanian; B. Choi; W. Christie; J. P. Coffin; L. Conin; T. M. Cormier; J. G. Cramer; H. J. Crawford; M. Demello; W. S. Deng; A. A. Derevschikov; L. Didenko; J. E. Draper; V. B. Dunin; J. C. Dunlop; V. Eckardt; L. G. Efimov; V. Emelianov; J. Engelage; G. Eppley; B. Erazmus; P. Fachini; E. Finch; Y. Fisyak; D. Flierl; K. J. Foley; J. Fu; N. Gagunashvili; J. Gans; L. Gaudichet; M. Germain; F. Geurts; V. Ghazikhanian; J. Grabski; O. Grachov; D. Greiner; V. Grigoriev; M. Guedon; E. Gushin; T. J. Hallman; D. Hardtke; J. W. Harris; M. Heffner; S. Heppelmann; T. Herston; B. Hippolyte; A. Hirsch; E. Hjort; G. W. Hoffmann; M. Horsley; H. Z. Huang; T. J. Humanic; H. Hümmler; G. Igo; A. Ishihara; Yu. I. Ivanshin; P. Jacobs; W. W. Jacobs; M. Janik; I. Johnson; P. G. Jones; E. Judd; M. Kaneta; M. Kaplan; D. Keane; A. Kisiel; J. Klay; S. R. Klein; A. Klyachko; A. S. Konstantinov; L. Kotchenda; A. D. Kovalenko; M. Kramer; P. Kravtsov; K. Krueger; C. Kuhn; A. I. Kulikov; G. J. Kunde; C. L. Kunz; R. Kh. Kutuev; A. A. Kuznetsov; L. Lakehal-Ayat; J. Lamas-Valverde; M. A. Lamont; J. M. Landgraf; S. Lange; C. P. Lansdell; B. Lasiuk; F. Laue; A. Lebedev; T. Lecompte; R. Lednický; V. M. Leontiev; P. Leszczynski; M. J. Levine; Q. Li; S. J. Lindenbaum; M. A. Lisa; T. Ljubicic; W. J. Llope; G. Locurto; H. Long; R. S. Longacre; M. Lopez-Noriega; W. A. Love; D. Lynn; R. Majka; A. Maliszewski; S. Margetis; L. Martin; J. Marx; H. S. Matis; Yu. A. Matulenko; T. S. McShane; F. Meissner; Yu. Melnick; A. Meschanin; M. Messer; M. L. Miller; Z. Milosevich; N. G. Minaev; J. Mitchell; V. A. Moiseenko; D. Moltz; C. F. Moore; V. Morozov; M. M. de Moura; M. G. Munhoz; G. S. Mutchler; J. M. Nelson; P. Nevski; V. A. Nikitin; L. V. Nogach; B. Norman; S. B. Nurushev; G. Odyniec; A. Ogawa; V. Okorokov; M. Oldenburg; D. Olson; G. Paic; S. U. Pandey; Y. Panebratsev; S. Y. Panitkin; A. I. Pavlinov; T. Pawlak; V. Perevoztchikov; W. Peryt; V. A. Petrov; W. Pinganaud; E. Platner; J. Pluta; N. Porile; J. Porter; A. M. Poskanzer; E. Potrebenikova; D. Prindle; C. Pruneau; S. Radomski; G. Rai; O. Ravel; R. L. Ray; S. V. Razin; D. Reichhold; J. G. Reid; F. Retiere; A. Ridiger; H. G. Ritter; J. B. Roberts; O. V. Rogachevski; J. L. Romero; C. Roy; D. Russ; V. Rykov; I. Sakrejda; J. Sandweiss; A. C. Saulys; I. Savin; J. Schambach; R. P. Scharenberg; K. Schweda; N. Schmitz; L. S. Schroeder; A. Schüttauf; J. Seger; D. Seliverstov; P. Seyboth; E. Shahaliev; K. E. Shestermanov; S. S. Shimanskii; V. S. Shvetcov; G. Skoro; N. Smirnov; R. Snellings; J. Sowinski; H. M. Spinka; B. Srivastava; E. J. Stephenson; R. Stock; A. Stolpovsky; M. Strikhanov; B. Stringfellow; H. Stroebele; C. Struck; A. A. Suaide; E. Sugarbaker; C. Suire; M. Sumbera; T. J. Symons; A. Szanto de Toledo; P. Szarwas; J. Takahashi; A. H. Tang; J. H. Thomas; V. Tikhomirov; T. A. Trainor; S. Trentalange; M. Tokarev; M. B. Tonjes; V. Trofimov; O. Tsai; K. Turner; T. Ullrich; D. G. Underwood; G. van Buren; A. M. Vandermolen; A. Vanyashin; I. M. Vasilevski; A. N. Vasiliev; S. E. Vigdor; S. A. Voloshin; F. Wang; H. Ward; J. W. Watson; R. Wells; T. Wenaus; G. D. Westfall; C. Whitten; H. Wieman; R. Willson; S. W. Wissink; R. Witt; N. Xu; Z. Xu; A. E. Yakutin; E. Yamamoto; J. Yang; P. Yepes; A. Yokosawa; V. I. Yurevich; Y. V. Zanevski; I. Zborovský; W. M. Zhang; R. Zoulkarneev; A. N. Zubarev

2001-01-01

243

The Negativity of the Overlap-Based Topological Charge Density Correlator in Pure-Glue QCD and the Non-Integrable Nature of its Contact Part  

E-print Network

We calculate the lattice two-point function of topological charge density in pure-glue QCD using the discretization of the operator based on the overlap Dirac matrix. Utilizing data at three lattice spacings it is shown that the continuum limit of the correlator complies with the requirement of non-positivity at non-zero distances. For our choice of the overlap operator and the Iwasaki gauge action we find that the size of the positive core is ~2a (with a being the lattice spacing) sufficiently close to the continuum limit. This result confirms that the overlap-based topological charge density is a valid local operator over realistic backgrounds contributing to the QCD path integral, and is important for the consistency of recent results indicating the existence of a low-dimensional global brane-like topological structure in the QCD vacuum. We also confirm the divergent short-distance behavior of the correlator, and the non-integrable nature of the associated contact part.

I. Horvath; A. Alexandru; J. B. Zhang; Y. Chen; S. J. Dong; T. Draper; K. F. Liu; N. Mathur; S. Tamhankar; H. B. Thacker

2005-04-07

244

Solvation thermodynamics and heat capacity of polar and charged solutes in water  

SciTech Connect

The solvation thermodynamics and in particular the solvation heat capacity of polar and charged solutes in water is studied using atomistic molecular dynamics simulations. As ionic solutes we consider a F{sup -} and a Na{sup +} ion, as an example for a polar molecule with vanishing net charge we take a SPC/E water molecule. The partial charges of all three solutes are varied in a wide range by a scaling factor. Using a recently introduced method for the accurate determination of the solvation free energy of polar solutes, we determine the free energy, entropy, enthalpy, and heat capacity of the three different solutes as a function of temperature and partial solute charge. We find that the sum of the solvation heat capacities of the Na{sup +} and F{sup -} ions is negative, in agreement with experimental observations, but our results uncover a pronounced difference in the heat capacity between positively and negatively charged groups. While the solvation heat capacity {Delta}C{sub p} stays positive and even increases slightly upon charging the Na{sup +} ion, it decreases upon charging the F{sup -} ion and becomes negative beyond an ion charge of q=-0.3e. On the other hand, the heat capacity of the overall charge-neutral polar solute derived from a SPC/E water molecule is positive for all charge scaling factors considered by us. This means that the heat capacity of a wide class of polar solutes with vanishing net charge is positive. The common ascription of negative heat capacities to polar chemical groups might arise from the neglect of non-additive interaction effects between polar and apolar groups. The reason behind this non-additivity is suggested to be related to the second solvation shell that significantly affects the solvation thermodynamics and due to its large spatial extent induces quite long-ranged interactions between solvated molecular parts and groups.

Sedlmeier, Felix; Netz, Roland R. [Fachbereich Physik, Freie Universitaet Berlin, 14195 Berlin (Germany)

2013-03-21

245

An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster-configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices.  

PubMed

Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2(')-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy. PMID:25338878

Fukuda, Ryoichi; Ehara, Masahiro

2014-10-21

246

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

247

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.

Robertson, William C.

2005-01-01

248

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.

Little, Carlyn; Lahart, David; Meyers, Ted; Weisblat, Brooks

1997-01-01

249

Improvement of intramolecular charge transfer within a donor-acceptor blend by doping novel synthesized benzothiadiazole small molecules in solid state  

NASA Astrophysics Data System (ADS)

Three electron-deficient small molecules based on 2,1,3-benzothiadiazole (BTD) units namely, 4,7-bis(3-methoxyphenyl)-2,1,3-benzothiadiazole (BT1), (3-{7-[3-(dimethylamino)phenyl]-2,1,3-benzothiadiazole-4-yl}phenyl)dimethylamine (BT2) and 3,3?-(2,1,3-benzothiadiazole-4,7-dyl)dianiline (BT3) were synthesized and their photophysical properties were investigated systematically to understand their potential usage in ternary organic solar cells (OSCs) as additive material to enhance the cell efficiency. All these molecules show broad absorption bands in 350-750 nm on glass substrate and their optical band gaps were calculated to be around 2.50-2.80 eV. BTD fluorescence dynamics were measured in polymer:BT1:fullerene blends with varying emission wavelengths of active layer. Fluorescence emission and time resolved measurements indicated photoinduced energy shift from BT1 dye to fullerene and also from polymer to BT1 dye upon excitation of the active layer.

Dinçalp, Haluk; Murat, Gözde; ?çli, S?dd?k

2014-07-01

250

Activation of a water molecule using a mononuclear Mn complex: from Mn-aquo, to Mn-hydroxo, to Mn-oxyl via charge compensation†  

PubMed Central

Activation of a water molecule by the electrochemical oxidation of a Mn-aquo complex accompanied by the loss of protons is reported. The sequential (2 × 1 electron/1 proton) and direct (2 electron/2 proton) proton-coupled electrochemical oxidation of a non-porphyrinic six-coordinated Mn(II)OH2 complex into a mononuclear Mn(O) complex is described. The intermediate Mn(III)OH2 and Mn(III)OH complexes are electrochemically prepared and analysed. Complete deprotonation of the coordinated water molecule in the Mn(O) complex is confirmed by electrochemical data while the analysis of EXAFS data reveals a gradual shortening of an Mn–O bond upon oxidation from Mn(II)OH2 to Mn(III)OH and Mn(O). Reactivity experiments, DFT calculations and XANES pre-edge features provide strong evidence that the bonding in Mn(O) is best characterized by a Mn(III)-oxyl description. Such oxyl species could play a crucial role in natural and artificial water splitting reactions. We provide here a synthetic example for such species, obtained by electrochemical activation of a water ligand. PMID:24772190

Lassalle-Kaiser, Benedikt; Hureau, Christelle; Pantazis, Dimitrios A.; Pushkar, Yulia; Guillot, Regis; Yachandra, Vittal K.; Yano, Junko; Neese, Frank; Anxolabehere-Mallart, Elodie

2014-01-01

251

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV.  

PubMed

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1. PMID:11531517

Adler, C; Ahammed, Z; Allgower, C; Amonett, J; Anderson, B D; Anderson, M; Averichev, G S; Balewski, J; Barannikova, O; Barnby, L S; Baudot, J; Bekele, S; Belaga, V V; Bellwied, R; Berger, J; Bichsel, H; Bland, L C; Blyth, C O; Bonner, B E; Bossingham, R; Boucham, A; Brandin, A; Caines, H; Calderón De La Barca Sánchez, M; Cardenas, A; Carroll, J; Castillo, J; Castro, M; Cebra, D; Chattopadhyay, S; Chen, M L; Chen, Y; Chernenko, S P; Cherney, M; Chikanian, A; Choi, B; Christie, W; Coffin, J P; Conin, L; Cormier, T M; Cramer, J G; Crawford, H J; DeMello, M; Deng, W S; Derevschikov, A A; Didenko, L; Draper, J E; Dunin, V B; Dunlop, J C; Eckardt, V; Efimov, L G; Emelianov, V; Engelage, J; Eppley, G; Erazmus, B; Fachini, P; Finch, E; Fisyak, Y; Flierl, D; Foley, K J; Fu, J; Gagunashvili, N; Gans, J; Gaudichet, L; Germain, M; Geurts, F; Ghazikhanian, V; Grabski, J; Grachov, O; Greiner, D; Grigoriev, V; Guedon, M; Gushin, E; Hallman, T J; Hardtke, D; Harris, J W; Heffner, M; Heppelmann, S; Herston, T; Hippolyte, B; Hirsch, A; Hjort, E; Hoffmann, G W; Horsley, M; Huang, H Z; Humanic, T J; Hümmler, H; Igo, G; Ishihara, A; Ivanshin, Y I; Jacobs, P; Jacobs, W W; Janik, M; Johnson, I; Jones, P G; Judd, E; Kaneta, M; Kaplan, M; Keane, D; Kisiel, A; Klay, J; Klein, S R; Klyachko, A; Konstantinov, A S; Kotchenda, L; Kovalenko, A D; Kramer, M; Kravtsov, P; Krueger, K; Kuhn, C; Kulikov, A I; Kunde, G J; Kunz, C L; Kutuev, R K; Kuznetsov, A A; Lakehal-Ayat, L; Lamas-Valverde, J; Lamont, M A; Landgraf, J M; Lange, S; Lansdell, C P; Lasiuk, B; Laue, F; Lebedev, A; LeCompte, T; Lednický, R; Leontiev, V M; Leszczynski, P; LeVine, M J; Li, Q; Li, Q; Lindenbaum, S J; Lisa, M A; Ljubicic, T; Llope, W J; LoCurto, G; Long, H; Longacre, R S; Lopez-Noriega, M; Love, W A; Lynn, D; Majka, R; Maliszewski, A; Margetis, S; Martin, L; Marx, J; Matis, H S; Matulenko, Y A; McShane, T S; Meissner, F; Melnick, Y; Meschanin, A; Messer, M; Miller, M L; Milosevich, Z; Minaev, N G; Mitchell, J; Moiseenko, V A; Moltz, D; Moore, C F; Morozov, V; de Moura, M M; Munhoz, M G; Mutchler, G S; Nelson, J M; Nevski, P; Nikitin, V A; Nogach, L V; Norman, B; Nurushev, S B; Odyniec, G; Ogawa, A; Okorokov, V; Oldenburg, M; Olson, D; Paic, G; Pandey, S U; Panebratsev, Y; Panitkin, S Y; Pavlinov, A I; Pawlak, T; Perevoztchikov, V; Peryt, W; Petrov, V A; Pinganaud, W; Platner, E; Pluta, J; Porile, N; Porter, J; Poskanzer, A M; Potrebenikova, E; Prindle, D; Pruneau, C; Radomski, S; Rai, G; Ravel, O; Ray, R L; Razin, S V; Reichhold, D; Reid, J G; Retiere, F; Ridiger, A; Ritter, H G; Roberts, J B; Rogachevski, O V; Romero, J L; Roy, C; Russ, D; Rykov, V; Sakrejda, I; Sandweiss, J; Saulys, A C; Savin, I; Schambach, J; Scharenberg, R P; Schweda, K; Schmitz, N; Schroeder, L S; Schüttauf, A; Seger, J; Seliverstov, D; Seyboth, P; Shahaliev, E; Shestermanov, K E; Shimanskii, S S; Shvetcov, V S; Skoro, G; Smirnov, N; Snellings, R; Sowinski, J; Spinka, H M; Srivastava, B; Stephenson, E J; Stock, R; Stolpovsky, A; Strikhanov, M; Stringfellow, B; Stroebele, H; Struck, C; Suaide, A A; Sugarbaker, E; Suire, C; Sumbera, M; Symons, T J; Szanto De Toledo, A; Szarwas, P; Takahashi, J; Tang, A H; Thomas, J H; Tikhomirov, V; Trainor, T A; Trentalange, S; Tokarev, M; Tonjes, M B; Trofimov, V; Tsai, O; Turner, K; Ullrich, T; Underwood, D G; Van Buren, G; VanderMolen, A M; Vanyashin, A; Vasilevski, I M; Vasiliev, A N; Vigdor, S E; Voloshin, S A; Wang, F; Ward, H; Watson, J W; Wells, R; Wenaus, T; Westfall, G D; Whitten, C; Wieman, H; Willson, R; Wissink, S W; Witt, R; Xu, N; Xu, Z; Yakutin, A E; Yamamoto, E; Yang, J; Yepes, P; Yokosawa, A; Yurevich, V I; Zanevski, Y V; Zborovský, I; Zhang, W M; Zoulkarneev, R; Zubarev, A N

2001-09-10

252

Negative differential resistance behaviors in OPE derivatives combined C60 molecular junctions modulated with side groups  

NASA Astrophysics Data System (ADS)

By applying non-equilibrium Green's functions (NEGF) in combination with the density functional theory (DFT), we investigate the electronic transport properties of molecular junctions constructed by OPE derivatives with different side groups combined C60 molecules. The results show that the side groups play an important role in the properties of electron transport. Negative differential resistance (NDR) is observed in such devices. Especially for the molecule with electron-donating group (-OCH3), two NDR appear at different bias voltage regions. And the mechanism is proposed for the NDR behavior, owing to the shift of the molecular orbitals caused by the change in molecule charge.

Ma, JiaSai; Dong, HaiMing; Li, DongMei; Liu, DeSheng

2012-08-01

253

Organization and intramolecular charge-transfer enhancement in tripodal tris[(pyridine-4-yl)phenyl]amine push-pull molecules by intercalation into layered materials bearing acidic functionalities.  

PubMed

Two new intercalates of tris[4-(pyridin-4-yl)phenyl]amine (TPPA) with zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate having formulae Zr(HPO4)2·0.21(C33H24N4)·2.5H2O and Zr(HO3SC6H4PO3)(1.3)(C6H5PO3)(0.7)·0.35(C33H24N4)·2.5H2O were prepared and characterized by thermogravimetry, IR spectroscopy, and powder X-ray diffraction. The TPPA molecule has been selected as a model tripodal push-pull system with three peripheral basic centers that may undergo protonation. Their protonation/quaternization afforded HTPPA/MeTPPA molecules with enhanced intramolecular charge-transfer (ICT), which has been documented by electrochemical measurements, UV-Vis spectra and calculated properties such as the HOMO/LUMO levels and the first and second hyperpolarizabilities. Intercalation of TPPA into layered zirconium hydrogen phosphate and zirconium 4-sulfophenylphosphonate led to its significant organization and protonation as shown by the IR spectra. From the powder X-ray data we can deduce that the TPPA molecules are placed in the interlayer space of both hosts by anchoring two peripheral nitrogen atoms to one host layer and the opposite pyridine-4-yl terminus to the other neighboring host layer. In zirconium 4-sulfophenylphosphonate, the TPPA molecules are oriented perpendicularly, while in zirconium phosphate these molecules are slanted with respect to the layers of the host. On dehydration by heating, the interlayer distance of the intercalate decreases, which indicates a further slanting of the TPPA molecules. It follows from the UV-Vis spectra that TPPA is present in both intercalates in an equilibrium of protonated and non-protonated forms. The described materials represent the first case when a tripodal push-pull system was incorporated into a system with restricted geometry with the aim to influence its optical properties. PMID:24626407

Melánová, Klára; Cvejn, Daniel; Bureš, Filip; Zima, Vít?zslav; Svoboda, Jan; Beneš, Ludvík; Mikysek, Tomáš; Pytela, Old?ich; Knotek, Petr

2014-07-21

254

Ion adsorption and equilibrium distribution of charges in a cell of finite thickness  

E-print Network

charges adsorbées, on s'attend à trouver un caractère non local à la partie anisotrope de l'énergie d to consider the effect of the double layer forces, connected to selective surface adsorption of ions dissolved of the liquid molecules themselves (the intrinsic contribution). The positive and negative ions can have

Boyer, Edmond

255

Charge Pairing of Headgroups in Phosphatidylcholine Membranes: A Molecular Dynamics Simulation Study  

Microsoft Academic Search

Molecular dynamics simulation of the hydrated dimyristoylphosphatidylcholine (DMPC) bilayer membrane in the liquid-crystalline phase was carried out for 5ns to study the interaction among DMPC headgroups in the membrane\\/water interface region. The phosphatidylcholine headgroup contains a positively charged choline group and negatively charged phosphate and carbonyl groups, although it is a neutral molecule as a whole. Our previous study (Pasenkiewicz-Gierula,

Marta Pasenkiewicz-Gierula; Yuji Takaoka; Hiroo Miyagawa; Kunihiro Kitamura; Akihiro Kusumi

1999-01-01

256

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

257

Quantifying charge transfer energies at donor-acceptor interfaces in small-molecule solar cells with constrained DFTB and spectroscopic methods  

NASA Astrophysics Data System (ADS)

Charge transfer states around the donor-acceptor interface in an organic solar cell determine the device performance in terms of the open circuit voltage. In the present work, we propose a computational scheme based on constrained density functional tight binding theory (c-DFTB) to assess the energy of the lowest charge transfer (CT) state in such systems. A comparison of the c-DFTB scheme with Hartree-Fock based configuration interaction of singles (CIS) and with time-dependent density functional theory (TD-DFT) using the hybrid functional B3LYP reveals that CIS and c-DFTB reproduce the correct Coulomb asymptotics between cationic donor and anionic acceptor configurations, whereas TD-DFT gives a qualitatively wrong excitation energy. Together with an embedding scheme accounting for the polarizable medium, this c-DFTB scheme is applied to several donor-acceptor combinations used in molecular solar cells. The external quantum efficiency of photovoltaic cells based on zinc phthalocyanine-C60 blends reveals a CT band remaining much narrower than the density of states of acceptor HOMO and donor LUMO, an observation which can be interpreted in a natural way in terms of Marcus transfer theory. A detailed comparison with c-DFTB calculations reveals an energy difference of 0.32 eV between calculated and observed absorption from the electronic ground state into the CT state. In a blend of a functionalized thiophene and C60, the photoluminescence spectra differ significantly from neat films, allowing again an assignment to CT states. The proposed computational scheme reproduces the observed trends of the observed open circuit voltages in photovoltaic devices relying on several donor-acceptor blends, finding an offset of 1.16 eV on average. This value is similar as in polymer-fullerene photovoltaic systems where it amounts to about 0.9 eV, indicating that the photophysics of CT states in molecular donor-acceptor blends and in polymer-fullerene blends are governed by the same mechanisms.

Scholz, Reinhard; Luschtinetz, Regina; Seifert, Gotthard; Jägeler-Hoheisel, Till; Körner, Christian; Leo, Karl; Rapacioli, Mathias

2013-11-01

258

Molecule nanoweaver  

SciTech Connect

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

259

Negative Leadership.  

National Technical Information Service (NTIS)

Senior leaders must have the moral courage to modify the behavior or eliminate negative leadership in the Army. If action is not taken immediately, negative leaders and their toxic leadership style will be taught to their subordinates, the future leaders ...

D. M. Oberlander

2013-01-01

260

Roles of the negatively charged N-terminal extension of Saccharomyces cerevisiae ribosomal protein S5 revealed by characterization of a yeast strain containing human ribosomal protein S5.  

PubMed

Ribosomal protein (rp) S5 belongs to a family of ribosomal proteins that includes bacterial rpS7. rpS5 forms part of the exit (E) site on the 40S ribosomal subunit and is essential for yeast viability. Human rpS5 is 67% identical and 79% similar to Saccharomyces cerevisiae rpS5 but lacks a negatively charged (pI approximately 3.27) 21 amino acid long N-terminal extension that is present in fungi. Here we report that replacement of yeast rpS5 with its human homolog yielded a viable yeast strain with a 20%-25% decrease in growth rate. This replacement also resulted in a moderate increase in the heavy polyribosomal components in the mutant strain, suggesting either translation elongation or termination defects, and in a reduction in the polyribosomal association of the elongation factors eEF3 and eEF1A. In addition, the mutant strain was characterized by moderate increases in +1 and -1 programmed frameshifting and hyperaccurate recognition of the UAA stop codon. The activities of the cricket paralysis virus (CrPV) IRES and two mammalian cellular IRESs (CAT-1 and SNAT-2) were also increased in the mutant strain. Consistently, the rpS5 replacement led to enhanced direct interaction between the CrPV IRES and the mutant yeast ribosomes. Taken together, these data indicate that rpS5 plays an important role in maintaining the accuracy of translation in eukaryotes and suggest that the negatively charged N-terminal extension of yeast rpS5 might affect the ribosomal recruitment of specific mRNAs. PMID:17901157

Galkin, Oleksandr; Bentley, Amber A; Gupta, Sujatha; Compton, Beth-Ann; Mazumder, Barsanjit; Kinzy, Terri Goss; Merrick, William C; Hatzoglou, Maria; Pestova, Tatyana V; Hellen, Christopher U T; Komar, Anton A

2007-12-01

261

Charge separation in CO oxidation involving supported gold clusters  

SciTech Connect

The character of the catalytic oxidation of CO by supported gold cluster catalysts is analyzed with emphasis on the unique characteristics of this process. The scheme of this process used here has the reagent CO molecule captured in the interface between the cluster and support, with oxygen molecules or atoms located on the support surface to react with the CO. (Other models have also been presented.) The experimental data indicate that, together with configurational transitions that lead to the CO molecule joining an oxygen atom to form the CO{sub 2} molecule, the charge separation due to capture of the CO molecule by the supported gold cluster is important. The process of release of the CO{sub 2} molecule results in charge exchange; the time for this process is relatively long because of the large distance separating positive and negative charges, a distance exceeding the cluster radius. This provides a high efficiency of the oxidation of CO with this catalyst despite the relatively high activation energy for the configurational transition.

Berry, R. S. [University of Chicago, Department of Chemistry (United States); Smirnov, B. M., E-mail: bmsmirnov@gmail.com [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2011-12-15

262

Metallic behavior and negative differential resistance properties of (InAs)n (n = 2 - 4) molecule cluster junctions via a combined non-equilibrium Green's function and density functional theory study  

NASA Astrophysics Data System (ADS)

In this present work, the geometric structures and electronic transport properties of (InAs)n (n = 2, 3, 4) molecule cluster junctions are comparatively investigated using NEGF combined with DFT. Results indicate that all (InAs)n molecule cluster junctions present metallic behavior at the low applied biases ([-2V, 2V]), while NDR appears at a certain high bias range. Our calculation shows that the current of (InAs)4 molecule cluster-based junction is almost the largest at any bias. The mechanisms of the current-voltage characteristics of all the three molecule cluster junctions are proposed.

Wang, Qi; Zhang, Jianbing; Li, Rong; Xu, Yuanlan; Miao, Xiangshui; Zhang, Daoli

2014-06-01

263

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

264

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

265

Molecule matters  

Microsoft Academic Search

Carbon dioxide is a fascinating molecule; its gaseous, liquid, solid and even supercritical fluid states have unique properties\\u000a and applications. The linear triatomic structure of carbon dioxide molecule with two carbon-oxygen double bonds is all too\\u000a familiar. However a whole new world has been opened up by high pressure-high temperature experiments that effected the polymerization\\u000a of this small molecule into

T. P. Radhakrishnan

2006-01-01

266

Solvation of intrinsic positive charge in superfluid helium.  

PubMed

On the basis of electronic structure calculations, the structure of intrinsic positive charge solvated in superfluid helium is identified as triatomic He3(+) ion, which is bound to the surrounding ground state helium atoms through the charge–charge induced dipole interaction in a pairwise additive manner. Bosonic density functional theory calculations show that this ion forms the well-known Atkins’ snowball solvation structure where the first rigid helium shell is effectively disconnected from the rest of the liquid. Evaluation of the total energy vs helium droplet size N shows distinct regions related to the completion of solvent shells near N = 16 and N = 47. These regions can be assigned to magic numbers observed in positively charged helium droplets appearing at N = 15 and in the range between 20 and 50 helium atoms. The calculated added mass for the positive ion in bulk superfluid helium (18 mHe) is much smaller than the previous experiments suggest (30–40 mHe), indicating that there may be yet some unidentified additional factor contributing to the measured effective mass. Both previous experiments and the present calculations agree on the effective mass of the negative charge (240–250 mHe). The main difference between the solvated negative and positive charges in liquid helium is that the latter forms a chemically bound triatomic molecule surrounded by highly inhomogeneous liquid structure whereas the former remains as a separated charge with a smoothly varying liquid density around it. PMID:24654777

Mateo, David; Eloranta, Jussi

2014-08-21

267

Detection of nucleotides in positive-mode electrospray ionization mass spectrometry using multiply-charged cationic ion-pairing reagents  

Microsoft Academic Search

Nucleotides are a class of molecules that play an essential role in biological systems. A new method has been developed in\\u000a the detection of nucleotides. These molecules can exist as monomers or constituents of oligomers and polymers. As such, they\\u000a carry from one to several negative charges. In this study, different cationic ion-pairing reagents were used to complex with\\u000a each

Edra Dodbiba; Zachary S. Breitbach; Eranda Wanigasekara; Tharanga Payagala; Xiaotong Zhang; Daniel W. Armstrong

2010-01-01

268

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

269

Nanoparticle coagulation in fractionally charged and charge fluctuating dusty plasmas  

SciTech Connect

The kinetics of nanoparticle coagulation has been studied in fractionally charged and charge fluctuating dusty plasmas. The coagulation occurs when the mutual collision frequency among nanoparticles exceeds their charging and decharging/neutralization frequency. Interestingly, the coagulation is suppressed while a fraction (several percent) of nanoparticles are negatively charged in a plasma, in which stochastic charging plays an important role. A model is developed to predict a phase diagram of the coagulation and its suppression.

Nunomura, Shota; Kondo, Michio [Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568 (Japan); Shiratani, Masaharu; Koga, Kazunori; Watanabe, Yukio [Department of Electronics, Graduate School of Information Science and Electrical Engineering, Kyushu University, Fukuoka 819-0395 (Japan)

2008-08-15

270

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 SrTiO 3 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 SrTiO 3 (001) surface is presented as an active reduction and oxidation site. It shows that Ag prefers to mediate the charge transfer from electronically excited SrTiO 3 to target species. It illustrates that electron initially transfers from electron-doped SrTiO 3 to Ag, i.e., Ag is negatively charged. Interfacial charge transfer induces dipole moment and changes the surface work function. SrO-termination of SrTiO 3 (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

271

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

272

Probing Molecular Docking in a Charged Model Binding Site  

PubMed Central

A model binding site was used to investigate charge–charge interactions in molecular docking. This simple site, a small (180 Å3) engineered cavity in cyctochrome c peroxidase (CCP), is negatively charged and completely buried from solvent, allowing us to explore the balance between electrostatic energy and ligand desolvation energy in a system where many of the common approximations in docking do not apply. A database with about 5300 molecules was docked into this cavity. Retrospective testing with known ligands and decoys showed that overall the balance between electrostatic interaction and desolvation energy was captured. More interesting were prospective docking scre”ens that looked for novel ligands, especially those that might reveal problems with the docking and energy methods. Based on screens of the 5300 compound database, both high-scoring and low-scoring molecules were acquired and tested for binding. Out of 16 new, high-scoring compounds tested, 15 were observed to bind. All of these were small heterocyclic cations. Binding constants were measured for a few of these, they ranged between 20 ?M and 60 ?M. Crystal structures were determined for ten of these ligands in complex with the protein. The observed ligand geometry corresponded closely to that predicted by docking. Several low-scoring alkyl amino cations were also tested and found to bind. The low docking score of these molecules owed to the relatively high charge density of the charged amino group and the corresponding high desolvation penalty. When the complex structures of those ligands were determined, a bound water molecule was observed interacting with the amino group and a backbone carbonyl group of the cavity. This water molecule mitigates the desolvation penalty and improves the interaction energy relative to that of the “naked” site used in the docking screen. Finally, six low-scoring neutral molecules were also tested, with a view to looking for false negative predictions. Whereas most of these did not bind, two did (phenol and 3-fluorocatechol). Crystal structures for these two ligands in complex with the cavity site suggest reasons for their binding. That these neutral molecules do, in fact bind, contradicts previous results in this site and, along with the alkyl amines, provides instructive false negatives that help identify weaknesses in our scoring functions. Several improvements of these are considered. PMID:16490206

Brenk, Ruth; Vetter, Stefan W.; Boyce, Sarah E.; Goodin, David B.; Shoichet, Brian K.

2011-01-01

273

Charge transport in disordered materials  

NASA Astrophysics Data System (ADS)

This thesis is focused on on using Monte Carlo simulation to extract device relevant properties, such as the current voltage behavior of transistors and the efficiency of photovoltaics, from the hopping transport of molecules. Specifically, simulation is used to study organic field-effect transistors (OFETs) and organic photo-voltaics (OPVs). For OFETs, the current was found to decrease with increasing concentration of traps and barriers in the system. As the barrier/trap concentration approaches 100%, the current recovers as carrier begin to travel through the manifold of connected trap states. Coulomb interactions between like charges are found to play a role in removing carriers from trap states. The equilibrium current in OFETs was found to be independent of charge injection method, however, the finite size of devices leads to an oscillatory current. Fourier transforms of the electrical current show peaks that vary non-linearly with device length, while being independent of device width. This has implications for the mobility of carriers in finite sized devices. Lastly, the presence of defects and high barriers (> 0.4 eV) was found to produce negative differential resistance in the saturation region of OFET curves, unlike traps. While defects and barriers prohibit carriers from reaching the drain at high voltages, the repulsive interaction between like charged carriers pushes charges around the defects. For OPVs, the effects of device morphology and charge delocalization were studied. Fill factors increased with domain size in monolayer isotropic morphologies, but decreased for band morphologies. In single-phase systems without Coulomb interactions, astonishingly high fill factors (. 70%) were found. In multilayer OPVs,a complex interplay of domain size, connectivity, tortuosity, interface trapping, and delocalization determined efficiency.

Gagorik, Adam Gerald

274

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

275

New insight in the structural features of haloadaptation in ?-amylases from halophilic Archaea following homology modeling strategy: folded and stable conformation maintained through low hydrophobicity and highly negative charged surface.  

PubMed

Proteins from halophilic archaea, which live in extreme saline conditions, have evolved to remain folded, active and stable at very high ionic strengths. Understanding the mechanism of haloadaptation is the first step toward engineering of halostable biomolecules. Amylases are one of the main enzymes used in industry. Yet, no three-dimensional structure has been experimentally resolved for ?-amylases from halophilic archaea. In this study, homology structure modeling of ?-amylases from the halophilic archaea Haloarcula marismortui, Haloarcula hispanica, and Halalkalicoccus jeotgali were performed. The resulting models were subjected to energy minimization, evaluation, and structural analysis. Calculations of the amino acid composition, salt bridges and hydrophobic interactions were also performed and compared to a set of non-halophilic counterparts. It clearly appeared that haloarchaeal ?-amylases exhibited lower propensities for helix formation and higher propensities for coil-forming regions. Furthermore, they could maintain a folded and stable conformation in high salt concentration through highly negative charged surface with over representation of acidic residues, especially Asp, and low hydrophobicity with increase of salt bridges and decrease in hydrophobic interactions on the protein surface. This study sheds some light on the stability of ?-amylases from halophilic archaea and provides strong basis not only to understand haloadaptation mechanisms of proteins in microorganisms from hypersalines environments but also for biotechnological applications. PMID:24865847

Zorgani, Mohamed Amine; Patron, Kevin; Desvaux, Mickaël

2014-07-01

276

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 page features section on: the exhibit, activities, molecules and the New York Science homepage. Within the activities page, the site currently features three main lessons focusing on molecules, DNA and infra-red technology. The exhibit page displays pictures and additional information on the learning objectives of the display. The site features contact information for those interesting in more information on the exhibit.

2009-04-30

277

Modeling Molecules  

NASA Technical Reports Server (NTRS)

The molecule modeling method known as Multibody Order (N) Dynamics, or MBO(N)D, was developed by Moldyn, Inc. at Goddard Space Flight Center through funding provided by the SBIR program. The software can model the dynamics of molecules through technology which stimulates low-frequency molecular motions and properties, such as movements among a molecule's constituent parts. With MBO(N)D, a molecule is substructured into a set of interconnected rigid and flexible bodies. These bodies replace the computation burden of mapping individual atoms. Moldyn's technology cuts computation time while increasing accuracy. The MBO(N)D technology is available as Insight II 97.0 from Molecular Simulations, Inc. Currently the technology is used to account for forces on spacecraft parts and to perform molecular analyses for pharmaceutical purposes. It permits the solution of molecular dynamics problems on a moderate workstation, as opposed to on a supercomputer.

2000-01-01

278

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

279

Photoabsorption spectra in the continuum of molecules and atomic clusters  

E-print Network

We present linear response theories in the continuum capable of describing photoionization spectra and dynamic polarizabilities of finite systems with no spatial symmetry. Our formulations are based on the time-dependent local density approximation with uniform grid representation in the three-dimensional Cartesian coordinate. Effects of the continuum are taken into account either with a Green's function method or with a complex absorbing potential in a real-time method. The two methods are applied to a negatively charged cluster in the spherical jellium model and to some small molecules (silane, acetylene and ethylene).

Takashi Nakatsukasa; Kazuhiro Yabana

2000-10-09

280

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

PubMed

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. PMID:25355705

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

2014-11-21

281

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

282

Negative necrotaxis.  

PubMed

We studied necrotaxis in several strains of protists and compared the reaction of living cells in the vicinity of cells killed by a ruby laser. Negative necrotaxis was observed for the unicellular green alga Euglena gracilis, whereas Chlamydomonas was shown to exhibit positive necrotaxis. The cellular colony Pandorina morum exhibited no reaction to the killing of nearby colonies. Both the colorless cryptomonad Chilomonas paramecium and the ciliate Tetrahymena pyriformis exhibited negative necrotaxis following the lysis of vitally stained specimens of their own species. They also exhibited negative necrotaxis following the lysis of Euglena cells. It was also demonstrated that the cellular content of Euglena cells lysed by heat or by a mechanical procedure acts as a repellent to intact Euglena cells. These results suggest that the negative necrotaxis provoked in Euglena by the laser irradiation is probably due to the chemotactic effect produced by the release of cell content in the extracellular medium. This cell content could, according to its chemical composition, act either as a repellent, an attractant, or be inactive. The sensitivity of cells (specific or nonspecific ion channels or chemoreceptors) are also of prime importance in the process. PMID:8400315

Ragot, R

1993-01-01

283

Cumulation of de broglie waves of electrons, endoions and endoelectrons of fullerenes, and resonances in the properties of nanocomposite materials with spatial charge layers  

Microsoft Academic Search

The cumulation of de Broglie waves of electrons in hollow molecules (for example, C60) has been investigated. The existence of negatively charged endoions of fullerenes with trapped electrons in the inner cavity\\u000a (endoelectrons) is proved. The Schrodinger (Helmholtz) stationary equation for hollow polarized molecules is solved analytically.\\u000a An endoelectron has a positive total energy, but, because of the polarization forces,

Ph. I. Vysikaylo

2010-01-01

284

Nanopore detection of DNA molecules in magnesium chloride solutions  

PubMed Central

High translocation speed of a DNA strand through a nanopore is a major bottleneck for nanopore detection of DNA molecules. Here, we choose MgCl2 electrolyte as salt solution to control DNA mobility. Experimental results demonstrate that the duration time for straight state translocation events in 1 M MgCl2 solution is about 1.3 ms which is about three times longer than that for the same DNA in 1 M KCl solution. This is because Mg2+ ions can effectively reduce the surface charge density of the negative DNA strands and then lead to the decrease of the DNA electrophoretic speed. It is also found that the Mg2+ ions can induce the DNA molecules binding together and reduce the probability of straight DNA translocation events. The nanopore with small diameter can break off the bound DNA strands and increase the occurrence probability of straight DNA translocation events. PMID:23688283

2013-01-01

285

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.

Twin Cities Public Television, Inc.

2008-01-01

286

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.  

PubMed

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 N(2)(+)(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 N(2)(+)(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 N(2)(+) PFI-PI beam can be formed with a laboratory kinetic energy resolution of ?E(lab) = ± 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (E(cm)'s) down to thermal energies. Absolute total rovibrationally selected cross sections ?(v(+) = 0-2, N(+) = 0-9) for the N(2)(+)(X (2)?(g)(+); v(+) = 0-2, N(+) = 0-9) + Ar CT reaction have been measured in the E(cm) range of 0.04-10.0 eV, revealing strong vibrational enhancements and E(cm)-dependencies of ?(v(+) = 0-2, N(+) = 0-9). The thermochemical threshold at E(cm) = 0.179 eV for the formation of Ar(+) from N(2)(+)(X; v(+) = 0, N(+)) + Ar was observed by the measured ?(v(+) = 0), confirming the narrow ?E(cm) 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-Stu?ckelberg 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 E(cm) = 0.04-10.0 eV are found to be independent of N(+). PMID:22979852

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

2012-09-14

287

Atomic dipole polarization in charge-transfer complexes with halogen bonding.  

PubMed

The polarization effects associated with halogen bonding for the series of charge-transfer complexes D(m)···X-Y, where donor molecules D(m) = NH(3), H(2)O, H(2)S, C(2)H(4), CO and X-Y = Cl(2), ClF, Br(2), BrCl, ICl, I(2), are characterized in terms of the quantum theory of atoms in molecules using the B3LYP/6-311** Kohn-Sham wave functions. We study the electrostatic potential features of separate donor and acceptor molecules, the change in atomic charges as well as the atomic electric dipole moments and their components, and the intra-atomic electron density dipole polarization and the bonding dipole moments resulting from the electron density redistribution between the molecules in the charge-transfer complexes. The equation linking the most negative electrostatic potential values in the donor molecules and the most positive values in dihalogen molecules with the stretching force constants was found using two-factor regression. It is demonstrated that the dipole polarization of the acceptor atom mirrors the strength of halogen bonding in complexes in a series of different donors and acceptors. An exponential relationship between the magnitude of the total atomic electric dipole moment of the acceptor atom and the intermolecular stretching force constant is established for weakly bounded complexes. PMID:23322002

Bartashevich, E V; Tsirelson, V G

2013-02-21

288

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.

Center, Arizona S.

2012-01-01

289

Dissociation of alkane ionized molecules  

NASA Astrophysics Data System (ADS)

The subject of investigation is the fragmentation of variously charged molecular ions arising in col-lisions of several kiloelectronvolt H+, He2+, and Ar6+ ions with molecules of the simplest alkanes (from methane to butane). Using the method of time-of-flight mass spectrometry, the formation cross sections of dissociation-induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1-25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spatial arrangement of corresponding atoms in a parent molecule.

Afrosimov, V. V.; Baranova, L. A.; Basalaev, A. A.; Panov, M. N.; Smirnov, O. V.; Tulub, A. V.

2010-03-01

290

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

291

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

2006-02-03

292

Evaluation of Different Virtual Screening Programs for Docking in a Charged Binding Pocket  

PubMed Central

Virtual screening of small molecules against a protein target often identifies the correct pose, but the ranking in terms of binding energy remains a difficult problem, resulting in unacceptable numbers of false positives and negatives. To investigate this problem, the performance of three docking programs, FRED, QXP/FLO, and GLIDE, along with their five different scoring functions, was evaluated with the engineered cavity in cyctochrome c peroxidase (CCP). This small cavity is negatively charged and completely buried from solvent. A test set of 60 molecules, experimentally identified as 43 “binders” and 17 “non-binders”, were tested with the CCP binding site. The docking methods’ performance is quantified by the ROC curve and their reproduction of crystal poses. The effects from generation of different ligand tautomers and inclusion of water molecule in the cavity are also discussed. PMID:18821750

Deng, Wei; Verlinde, Christophe L. M. J.

2009-01-01

293

Negative Mass Propulsion  

NASA Astrophysics Data System (ADS)

Schrödinger's analysis of the Dirac equation gives a hint for the existence of negative masses hidden behind positive masses. But their use for propulsion by reducing the inertia of matter for example, in the limit of macroscopic bodied with zero rest mass, depends on a technical solution to free them from their imprisonment by positive masses. It appears that there are basically two ways this might be achieved: 1. By the application of strong electromagnetic or gravitational fields or by high particle energies. 2. By searching for places in the universe where nature has already done this separation, and from where the negative masses can be mined. The first of these two possibilities is for all practical means excluded, because if possible at all, it would depend on electromagnetic or gravitational fields with strength beyond what is technically attainable, or on extremely large likewise not attainable particle energies. With regard to the 2nd possibility, it has been observed that non-baryonic cold dark matter tends to accumulate near the center of galaxies, or places in the universe which have a large gravitational potential well. Because of the equivalence principle of general relativity, the attraction towards the center of a gravitational potential well, produced by a positive mass, is for negative masses the same as for positive masses, and large amounts of negative masses might have over billions of years been trapped in these gravitational potential wells. Now it just happens that the center of the moon is a potential well, not too deep that it cannot be reached by making a tunnel through the moon, not possible for the deeper potential well of the earth, where the temperature and pressure are too high. Making a tunnel through the moon, provided there is a good supply of negative mass, could revolutionize interstellar space flight. A sequence of thermonuclear shape charges would make such tunnel technically feasible.

Winterberg, F.

294

A model for negative ion extraction and comparison of negative ion optics calculations to experimental results  

Microsoft Academic Search

Negative ion extraction is described by a model that includes electron diffusion across transverse magnetic fields in the sheath. This model allows a two-dimensional approximation of the problem. It is used to introduce electron space charge effects in a 2-D particle trajectory code, designed for negative ion optics calculations. Another physical effect, the stripping of negative ions on neutral gas

1991-01-01

295

Charge density-dependent strength of hydration and biological structure.  

PubMed Central

Small ions of high charge density (kosmotropes) bind water molecules strongly, whereas large monovalent ions of low charge density (chaotropes) bind water molecules weakly relative to the strength of water-water interactions in bulk solution. The standard heat of solution of a crystalline alkali halide is shown here to be negative (exothermic) only when one ion is a kosmotrope and the ion of opposite charge is a chaotrope; this standard heat of solution is known to become proportionally more positive as the difference between the absolute heats of hydration of the corresponding gaseous anion and cation decreases. This suggests that inner sphere ion pairs are preferentially formed between oppositely charged ions with matching absolute enthalpies of hydration, and that biological organization arises from the noncovalent association of moieties with matching absolute free energies of solution, except where free energy is expended to keep them apart. The major intracellular anions (phosphates and carboxylates) are kosmotropes, whereas the major intracellular monovalent cations (K+; arg, his, and lys side chains) are chaotropes; together they form highly soluble, solvent-separated ion pairs that keep the contents of the cell in solution. PMID:8994593

Collins, K D

1997-01-01

296

Negativity Bias, Negativity Dominance, and Contagion  

Microsoft Academic Search

We hypothesize that there is a general bias, based on both innate predispositions and experience, in animals and humans, to give greater weight to negative entities (e.g., events, objects, personal traits). This is manifested in 4 ways: (a) negative potency (negative entities are stronger than the equivalent positive entities), (b) steeper nega - tive gradients (the negativity of negative events

Paul Rozin; Edward B. Royzman

2001-01-01

297

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

298

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

PubMed

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

299

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

300

Human fibrinogen adsorption on positively charged latex particles.  

PubMed

Fibrinogen (Fb) adsorption on positively charged latex particles (average diameter of 800 nm) was studied using the microelectrophoretic and the concentration depletion methods based on AFM imaging. Monolayers on latex were adsorbed from diluted bulk solutions at pH 7.4 and an ionic strength in the range of 10(-3) to 0.15 M where fibrinogen molecules exhibited an average negative charge. The electrophoretic mobility of the latex after controlled fibrinogen adsorption was systematically measured. A monotonic decrease in the electrophoretic mobility of fibrinogen-covered latex was observed for all ionic strengths. The results of these experiments were interpreted according to the three-dimensional electrokinetic model. It was also determined using the concentration depletion method that fibrinogen adsorption was irreversible and the maximum coverage was equal to 0.6 mg m(-2) for ionic strength 10(-3) M and 1.3 mg m(-2) for ionic strength 0.15 M. The increase of the maximum coverage was confirmed by theoretical modeling based on the random sequential adsorption approach. Paradoxically, the maximum coverage of fibrinogen on positively charged latex particles was more than two times lower than the maximum coverage obtained for negative latex particles (3.2 mg m(-2)) at pH 7.4 and ionic strength of 0.15 M. This was interpreted as a result of the side-on adsorption of fibrinogen molecules with their negatively charged core attached to the positively charged latex surface. The stability and acid base properties of fibrinogen monolayers on latex were also determined in pH cycling experiments where it was observed that there were no irreversible conformational changes in the fibrinogen monolayers. Additionally, the zeta potential of monolayers was more positive than the zeta potential of fibrinogen in the bulk, which proves a heterogeneous charge distribution. These experimental data reveal a new, side-on adsorption mechanism of fibrinogen on positively charged surfaces and confirmed the decisive role of electrostatic interactions in this process. PMID:25157934

Zeliszewska, Paulina; Bratek-Skicki, Anna; Adamczyk, Zbigniew; Cie?la, Micha?

2014-09-23

301

The dark side of hydrogen bonds in the design of optical materials: a charge-density perspective.  

PubMed

A combined investigation of the structural, electronic, and optical properties of three crystalline nonaaqualanthanoid(III) triflates, [Ln(H2 O)9 (CF3 SO3 )3 ], has provided unambiguous experimental evidence for charge redistribution in the first coordination sphere of a lanthanide ion as a result of hydrogen bonds with outer-sphere anions. As well as resulting in charge transfer from the noncoordinated anions to the coordinated water molecules, these hydrogen bonds give rise to a new excited state, an hydrogen-bond-induced charge-transfer state, which is observed experimentally for the first time. This state was shown to be responsible for the previously unknown negative aspect of hydrogen bonds with a lanthanide-bound water molecule: rather than increasing the luminescence efficiency of the complex, they can lead to additional quenching that is unfavorable for the task-specific design of optical materials. PMID:24488449

Nelyubina, Yulia V; Puntus, Lada N; Lyssenko, Konstantin A

2014-03-01

302

Single-Molecule Electronic Measurements with Metal Electrodes  

ERIC Educational Resources Information Center

A review of concepts like tunneling through a metal-molecule-metal-junction, contrast with electrochemical and optical-charge injection, strong-coupling limit, calculations of tunnel transport, electron transfer through Redox-active molecules is presented. This is followed by a discussion of experimental approaches for single-molecule measurements.

Lindsay, Stuart

2005-01-01

303

Development and surface characterization of positively charged filters  

Microsoft Academic Search

Filter media, which have been surface charge modified by modifiers with positive functional groups, are termed positively charged filters. The main aim of the present work was to manufacture positively charged filters for capturing negatively charged particles, mainly bacteria and virus from water. Filters were manufactured with varying ratios of base materials, processing conditions and charge modifiers. Experimental parameters were

N. Kattamuri; J. H. Shin; B. Kang; C. G. Lee; J. K. Lee; C. Sung

2005-01-01

304

Carbon nanodots as a matrix for the analysis of low-molecular-weight molecules in both positive- and negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and quantification of glucose and uric acid in real samples.  

PubMed

Carbon nanodots were applied for the first time as a new matrix for the analysis of low-molecular-weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in both positive- and negative-ion modes. A wide range of small molecules including amino acids, peptides, fatty acids, as well as ?-agonists and neutral oligosaccharides were analyzed by MALDI MS with carbon nanodots as the matrix, and the lowest 0.2 fmol limits-of-detection were obtained for octadecanoic acid. Clear sodium and potassium adducts and deprotonated signals were produced in positive- and negative-ion modes. Furthermore, the glucose and uric acid in real samples were quantitatively determined by the internal standard method with the linear range of 0.5-9 mM and 0.1-1.8 mM (R(2) > 0.999), respectively. This work gives new insight into the application of carbon nanodots and provides a general approach for rapid analysis of low-molecular-weight compounds. PMID:23796018

Chen, Suming; Zheng, Huzhi; Wang, Jianing; Hou, Jian; He, Qing; Liu, Huihui; Xiong, Caiqiao; Kong, Xianglei; Nie, Zongxiu

2013-07-16

305

The Local-Density Theory: Application to Atoms and Molecules  

NASA Astrophysics Data System (ADS)

The generalized local-spin-density functional (G-LSD) theory is proposed which avoids (a) the physical restriction used in the generalized exchange local-spin -density functional (GX-LSD) theory; (b) the homogeneous electron-density approximation in the Hartree-Fock-Slater (HFS) theory and in the Gaspar-Kohn-Sham (GKS) theory; and (c) the time-consuming step to search the optimal exchange parameter for each atom or ion in the Xalpha and Xia theories. Theoretically, the G-LSD theory is more rigorous than the GX-LSD, HFS, GKS, and Xia theories. Numerically, the statistical total energies for atoms are better in the G-LSD theory than in the GKS theory. Ionization potentials and electron affinities of atoms, the stability of singly and doubly charged negative ions, and the electronegativities, and hardnesses of the fractional charged atoms with Z < 37 are calculated by the SIC-GX-LSD theory with the GWB Fermi -hole parameters and electron-correlation correction. The self-interaction correction (SIC) is introduced into the multiple-Scattering Xalpha (MS-Xalpha) method and used to calculate some molecules and molecular anions. The results show that the ionization potentials from the negative of the one-electron eigenvalues are as good as those obtained in the transition state calculation and in very good agreement with experiment.

Guo, Yufei

1990-01-01

306

Charged Condensation  

E-print Network

We consider Bose-Einstein condensation of massive electrically charged scalars in a uniform background of charged fermions. We focus on the case when the scalar condensate screens the background charge, while the net charge of the system resides on its boundary surface. A distinctive signature of this substance is that the photon acquires a Lorentz-violating mass in the bulk of the condensate. Due to this mass, the transverse and longitudinal gauge modes propagate with different group velocities. We give qualitative arguments that at high enough densities and low temperatures a charged system of electrons and helium-4 nuclei, if held together by laboratory devices or by force of gravity, can form such a substance. We briefly discuss possible manifestations of the charged condensate in compact astrophysical objects.

Gregory Gabadadze; Rachel A. Rosen

2007-06-15

307

Electronic structure of Fe- vs. Ru-based dye molecules.  

PubMed

In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octahedral N cage, such as tris(bipyridines) and tris(phenanthrolines), exhibit a systematic downward shift of the N 1s-to-?* transition when Ru is replaced by Fe. This shift is explained by an extra transfer of negative charge from the metal to the N ligands in the case of Fe, which reduces the binding energy of the N 1s core level. The C 1s-to-?* transitions show the opposite trend, with an increase in the transition energy when replacing Ru by Fe. Molecules with the metal in a fourfold, planar N cage (porphyrins) exhibit a more complex behavior due to a subtle competition between the crystal field, axial ligands, and the 2+ vs. 3+ oxidation states. PMID:23387617

Johnson, Phillip S; Cook, Peter L; Zegkinoglou, Ioannis; García-Lastra, J M; Rubio, Angel; Ruther, Rose E; Hamers, Robert J; Himpsel, F J

2013-01-28

308

Electronic structure of Fe- vs. Ru-based dye molecules  

SciTech Connect

In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octahedral N cage, such as tris(bipyridines) and tris(phenanthrolines), exhibit a systematic downward shift of the N 1s-to-{pi}* transition when Ru is replaced by Fe. This shift is explained by an extra transfer of negative charge from the metal to the N ligands in the case of Fe, which reduces the binding energy of the N 1s core level. The C 1s-to-{pi}* transitions show the opposite trend, with an increase in the transition energy when replacing Ru by Fe. Molecules with the metal in a fourfold, planar N cage (porphyrins) exhibit a more complex behavior due to a subtle competition between the crystal field, axial ligands, and the 2+ vs. 3+ oxidation states.

Johnson, Phillip S.; Himpsel, F. J. [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States); Cook, Peter L. [Natural Sciences Department, University of Wisconsin-Superior, Belknap and Catlin, Superior, Wisconsin 54880 (United States); Zegkinoglou, Ioannis [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States); Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Garcia-Lastra, J. M. [Dpto. Fisica de Materiales, Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Centro de Fisica de Materiales CSIC-UPV-MPC and DIPC, Universidad del Pais Vasco, Av. Tolosa 72, E-20018 San Sebastian (Spain); Department of Physics, Center for Atomic-scale Materials Design, DTU, DK-2800 Kongens Lyngby (Denmark); Rubio, Angel [Dpto. Fisica de Materiales, Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Centro de Fisica de Materiales CSIC-UPV-MPC and DIPC, Universidad del Pais Vasco, Av. Tolosa 72, E-20018 San Sebastian (Spain); Ruther, Rose E. [NSF Center for Sustainable Materials Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA and University of Oregon, Eugene, Oregon 97403-1253 (United States); Hamers, Robert J. [Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706 (United States)

2013-01-28

309

Electric charge acquired by airplanes penetrating thunderstorms  

Microsoft Academic Search

Three airplanes-a sailplane, a piston powered sailplane, and a twin turboprop-have been instrumented to measure electric fields inside electrified clouds and the net electric charge on the airplanes. In unelectrified clouds the powered airplanes become negatively charged during collisions with liquid cloud water droplets whereas the sailplane does not. In thunderstorm clouds, several airplane charging mechanisms are found to operate.

J. J. Jones

1990-01-01

310

Internet access charge and economic activity  

Microsoft Academic Search

This article investigates empirically the impacts of the internet access charge on economic activity using a cross-country analysis based on data from 76 countries for the year 1998–2001. The results show that the level of the Internet access charge has a significantly negative effect on the level of economic activity. In other words, a low Internet access charge of a

Seung-Hoon Yoo

2007-01-01

311

Unconventional molecule-resolved current rectification in diamondoid-fullerene hybrids.  

PubMed

The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p-n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane-C60 conjugate. By linking both sp(3) (diamondoid) and sp(2) (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane-C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism. PMID:25202942

Randel, Jason C; Niestemski, Francis C; Botello-Mendez, Andrés R; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E P; Carlson, Robert M K; Butova, Ekaterina D; Fokin, Andrey A; Schreiner, Peter R; Charlier, Jean-Christophe; Manoharan, Hari C

2014-01-01

312

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids  

NASA Astrophysics Data System (ADS)

The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p–n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane–C60 conjugate. By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane–C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism.

Randel, Jason C.; Niestemski, Francis C.; Botello-Mendez, Andrés R.; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Butova, Ekaterina D.; Fokin, Andrey A.; Schreiner, Peter R.; Charlier, Jean-Christophe; Manoharan, Hari C.

2014-09-01

313

Self-organization of disc-like molecules: chemical aspects.  

PubMed

The hierarchical self-assembly of disc-shaped molecules leads to the formation of discotic liquid crystals. These materials are of fundamental importance not only as models for the study of energy and charge migration in self-organized systems but also as functional materials for device applications such as, one-dimensional conductors, photoconductors, light emitting diodes, photovoltaic solar cells, field-effect transistors and gas sensors. The negative birefringence films formed by polymerized nematic discotic liquid crystals have been commercialized as compensation foils to enlarge the viewing angle of commonly used twisted nematic liquid crystal displays. To date the number of discotic liquid crystals derived from more than 50 different cores comes to about 3000. This critical review describes, after an in-depth introduction, recent advances in basic design principles and synthetic approaches towards the preparation of most frequently encountered discotic liquid crystals. PMID:16365644

Kumar, Sandeep

2006-01-01

314

'Bootstrap' charging of surfaces composed of multiple materials  

NASA Technical Reports Server (NTRS)

The paper examines the charging of a checkerboard array of two materials, only one of which tends to acquire a negative potential alone, using the NASA Charging Analyzer Program (NASCAP). The influence of the charging material's field causes the otherwise 'non-charging' material to acquire a negative potential due to the suppression of its secondary emission ('bootstrap' charging). The NASCAP predictions for the equilibrium potential difference between the two materials are compared to results based on an analytical model.

Stannard, P. R.; Katz, I.; Parks, D. E.

1981-01-01

315

Single-molecule probes in organic field-effect transistors  

Microsoft Academic Search

The goal of this thesis is to study charge transport phenomena in organic materials. This is done optically by means of single-molecule\\u000aspectroscopy in a field-effect transistor based on a molecular crystal.\\u000a\\u000aWe present (in Chapter 2) a fundamental requirement for single-molecule\\u000aspectroscopy concerning the energy levels of the guest molecule with\\u000arespect to the ones of the host molecule.

Aurélien Armel Louis Nicolet

2007-01-01

316

Recovery of tritium from tritiated molecules  

DOEpatents

This invention relates to the recovery of tritium from various tritiated molecules by reaction with uranium. More particularly, the invention relates to the recovery of tritium from tritiated molecules by reaction with uranium wherein the reaction is conducted in a reactor which permits the reaction to occur as a moving front reaction from the point where the tritium enters the reactor charged with uranium down the reactor until the uranium is exhausted.

Swansiger, W.A.

1984-10-17

317

Point Charge Electric Potential Model  

NSDL National Science Digital Library

The Point Charge Electric Potential model shows the electric potential produced by N point charges. Charges can be arranged in a ring, a line, or in parallel lines and the charge Q can alternate in sign. Custom configurations can be created by dragging particles or by entering xy and Q values into a data table. Blue (red) indicates a region of negative (positive) electric potential. The value of this potential V(x,y) is displayed in a textbox near the bottom of the view when the mouse is pressed. The Point Charge Electric Potential model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double click the ejs_em_PointChargeElectricPotential.jar file to run the program if Java is installed.

Christian, Wolfgang

2011-09-05

318

The effect of phenylglyoxal on contraction and intramembrane charge movement in frog skeletal muscle.  

PubMed Central

1. The effects of the arginine-specific protein-modifying reagent, phenylglyoxal, on contraction and intramembrane charge movement were studied in cut single fibres from frog skeletal muscle, using the double-Vaseline-gap voltage clamp technique. 2. The strength-duration curve for pulses which produced microscopically just-detectable contractions was shifted to more positive potentials and longer durations following treatment of fibres with phenylglyoxal. Caffeine-induced contractures were not blocked. 3. The amount of charge moved by large depolarizing pulses from -100 mV holding potential (charge 1) declined during the phenylglyoxal treatment with a single-exponential time course (tau = 7 min). Linear capacitance did not change significantly over the entire experiment. Inhibition of charge movement was predominantly irreversible. 4. Slow bumps (Q gamma) observed in charge movement current transients recorded before phenylglyoxal treatment, using either large test pulses or small steps superimposed on test pulses, were absent from currents recorded after treatment. The current removed by phenylglyoxal contained the bump (Q gamma) and a small fast transient (Q beta). 5. The amount of charge moved by large depolarizing pulses from -100 mV was reduced 20-50% following phenylglyoxal treatment. Charge moved by pulses to potentials more negative than -40 mV was relatively unaffected. The magnitude and voltage range of this inhibitory effect were the same whether the reagent was applied at -100 mV or at 0 mV holding potential. 6. A phenylglyoxal-sensitive component of charge was isolated which had a much steeper voltage dependence than the total charge movement or the charge remaining after treatment. 7. Charge recorded during hyperpolarizing pulses from 0 mV holding potential (charge 2) was reduced very little (less than 5%) at any potential by phenylglyoxal treatments at either 0 or -100 mV. 8. The phenylglyoxal reaction with charge 2 was kinetically different from the reaction with charge 1. 9. The effects of phenylglyoxal on charge 1 and charge 2 both measured in the same fibre were compared. Whether phenylglyoxal was applied at -100 mV, or at 0 mV the results were the same: charge 1 was inhibited much more (25-60%) than charge 2(2-12%). 10. The results presented here indicate that arginyl residues have a functional role in the voltage-sensing mechanism of excitation-contraction coupling and support the hypothesis that the dihydropyridine receptor is the voltage sensor molecule. PMID:2348398

Etter, E F

1990-01-01

319

Improved negative ion source  

DOEpatents

A method and apparatus for providing a negative ion source accelerates electrons away from a hot filament electron emitter into a region of crossed electric and magnetic fields arranged in a magnetron configuration. During a portion of the resulting cycloidal path, the electron velocity is reduced below its initial value. The electron accelerates as it leaves the surface at a rate of only slightly less than if there were no magnetic field, thereby preventing a charge buildup at the surface of the emitter. As the electron traverses the cycloid, it is decelerated during the second, third, and fourth quadrants, then reaccelerated as it approaches the end of the fourth quadrant to regain its original velocity. The minimum velocity occurs during the fourth quadrant, and corresponds to an electron temperature of 200 to 500/sup 0/C for the electric and magnetic fields commonly encountered in the ion sources of magnetic sector mass spectrometers. An ion source using the above-described thermalized electrons is also disclosed.

Delmore, J.E.

1984-05-01

320

Taming Highly Charged Radioisotopes  

NASA Astrophysics Data System (ADS)

The precise and accurate mass of short-lived radioisotopes is a very important parameter in physics. Contribution to the improvement of nuclear models, metrological standard fixing and tests of the unitarity of the Caibbibo-Kobayashi-Maskawa (CKM) matrix are a few examples where the mass value plays a major role. TRIUMF's ion trap for atomic and nuclear physics (TITAN) is a unique facility of three online ion traps that enables the mass measurement of short-lived isotopes with high precision (˜10-8). At present TITAN's electron beam ion trap (EBIT) increases the charge state to increase the precision, but there is no facility to significantly reduce the energy spread introduced by the charge breeding process. The precision of the measured mass of radioisotopes is linearly dependent on the charge state while the energy spread of the charged radioisotopes affects the precision adversely. To boost the precision level of mass measurement at TITAN without loosing too many ions, a cooler Penning trap (CPET) is being developed. CPET is designed to use either positively (proton) or negatively (electron) charged particles to reduce the energy spread via sympathetic cooling. Off-line setup of CPET is complete. Details of the working principles and updates are presented

Chowdhury, Usman; Eberhardt, Benjamin; Jang, Fuluni; Schultz, Brad; Simon, Vanessa; Delheij, Paul; Dilling, Jens; Gwinner, Gerald

2012-10-01

321

Dipole-bound anions of carbonyl, nitrile, and sulfoxide containing molecules  

NASA Astrophysics Data System (ADS)

Dipole-bound anions of 27 molecules containing either a carbonyl, nitrile, or sulfoxide group were studied using Rydberg electron transfer (RET) reactions with rubidium atoms excited to ns 2S and nd 2D excited states. The electron affinity of each molecule was obtained from the Rydberg state, nmax*, that gave the largest negative ion yield using the empirical relationship electron affinity=23/nmax*2.8 eV as well as from fitting the charge exchange profile to a theoretical curve crossing model. Electron affinities for the low dipole moment molecules (carbonyls) were also deduced from measurements of the electric field required to detach the electron from the anion. Calculations of the electron affinities for some of the nitriles at the coupled-cluster level of theory were performed. The dependencies of the electron affinity upon dipole moment, polarizability, dispersion interaction, conformation, and geometry of the molecules were investigated. It was found that a higher dipole moment generally results in a higher electron affinity. However, for molecules with similar dipole moments, other factors such as polarizability and the dispersion interaction play an important role. The effect of collision velocity on the creation of these anions is also studied through the use of different carrier gases (H2, He, Ne, Ar, Kr, Xe) in the nozzle jet expansion. Competition between RET and collisional detachment is observed and discussed qualitatively.

Hammer, Nathan I.; Diri, Kadir; Jordan, Kenneth D.; Desfrançois, Charles; Compton, Robert N.

2003-08-01

322

Enhancement of IR and VCD intensities due to charge transfer.  

PubMed

Donor-acceptor interactions such as the one between the Cl(-) base and the N-H sigma* acceptor orbitals encountered in the complexation of Cl(-) counterions to the [Co(en)(3)](3+) transition metal complex, have been shown to cause huge enhancement (between 1 and 2 orders of magnitude) of the VCD intensities of N-H stretching modes. This effect has been fully analyzed, and could be attributed to increased charge flow from the Cl(-) donors when the N-H bonds become stretched. The transfer of charge counteracts the movement of negative electronic charge that happens along with the motion of the H nuclei, effectively reversing the electronic part of the electric dipole transition moment (EDTM) in the direction of the charge flow (z, say), and of the magnetic transition dipole moment (MDTM) in the perpendicular direction. The consequences for the IR and VCD intensity follow: IR intensity is strongly increased if the EDTM is polarized in the z direction, e.g. in A(2) modes, but not so much if it is polarized in the xy plane (E modes), the VCD is strongly enhanced if the EDTM and MTDM are polarized in the xy plane (in E modes), but less so when they are polarized in the z direction (in A(2) modes). The explanation holds generally for complexation phenomena of this sort, including the donor-acceptor part of hydrogen bonding interactions, e.g. with solvent molecules. PMID:19240930

Nicu, Valentin Paul; Autschbach, Jochen; Baerends, Evert Jan

2009-03-14

323

CHARGE syndrome  

Microsoft Academic Search

CHARGE syndrome was initially defined as a non-random association of anomalies (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, Ear anomalies\\/deafness). In 1998, an expert group defined the major (the classical 4C's: Choanal atresia, Coloboma, Characteristic ears and Cranial nerve anomalies) and minor criteria of CHARGE syndrome. Individuals with all four major characteristics or three major and

Kim D Blake; Chitra Prasad

2006-01-01

324

Charged Leptons  

E-print Network

This is the report of the Intensity Frontier Charged Lepton Working Group of the 2013 Community Summer Study "Snowmass on the Mississippi", summarizing the current status and future experimental opportunities in muon and tau lepton studies and their sensitivity to new physics. These include searches for charged lepton flavor violation, measurements of magnetic and electric dipole moments, and precision measurements of the decay spectrum and parity-violating asymmetries.

J. Albrecht; M. Artuso; K. Babu; R. H. Bernstein; T. Blum; D. N. Brown; B. C. K. Casey; C. -h. Cheng; V. Cirigliano; A. Cohen; A. Deshpande; E. C. Dukes; B. Echenard; A. Gaponenko; D. Glenzinski; M. Gonzalez-Alonso; F. Grancagnolo; Y. Grossman; R. C. Group; R. Harnik; D. G. Hitlin; B. Kiburg; K. Knoepfe; K. Kumar; G. Lim; Z. -T. Lu; D. McKeen; J. P. Miller; M. Ramsey-Musolf; R. Ray; B. L. Roberts; M. Rominsky; Y. Semertzidis; D. Stoeckinger; R. Talman; R. Van De Water; P. Winter

2013-11-21

325

Critical analysis and extension of the Hirshfeld atoms in molecules.  

PubMed

The computational approach to the Hirshfeld [Theor. Chim. Acta 44, 129 (1977)] atom in a molecule is critically investigated, and several difficulties are highlighted. It is shown that these difficulties are mitigated by an alternative, iterative version, of the Hirshfeld partitioning procedure. The iterative scheme ensures that the Hirshfeld definition represents a mathematically proper information entropy, allows the Hirshfeld approach to be used for charged molecules, eliminates arbitrariness in the choice of the promolecule, and increases the magnitudes of the charges. The resulting "Hirshfeld-I charges" correlate well with electrostatic potential derived atomic charges. PMID:17444705

Bultinck, Patrick; Van Alsenoy, Christian; Ayers, Paul W; Carbó-Dorca, Ramon

2007-04-14

326

Molecule of the Month  

NSDL National Science Digital Library

From the University of Bristol's School of Chemistry, this site features a new molecule each month. For example, the molecule for April is Melatonin. Each molecule comes with a link to a Webpage from a university or commercial site containing further information. (Links may require Chime, VRML, or Java.) Contributors may submit molecule pages to be considered in future months. Monthly molecules date back to January 1996.

327

Increasing binding density of yeast cells by control of surface charge with allylamine grafting to ion modified polymer surfaces.  

PubMed

Plasma immersion ion implantation (PIII) treatment of polymers creates a biointerface capable of direct covalent immobilization of biomolecules. The immobilization of protein molecules is achieved by covalent bonds formed between embedded radicals on the treated surface and amino acid side chains and cells can be immobilized through cell-wall proteins. The attachment density of negatively charged entities on a PIII treated surface is inhibited by its negative surface charge at neutral pH. To reduce the negative charge of PIII treated surfaces in phosphate buffer (pH 7.4, 11mM), we develop an effective approach of grafting allylamine monomers onto the treated surface. The results reveal reactions between allylamine and radicals on the PIII treated surface. One of these triggers polymerization, increasing the number of amine groups grafted. As a consequence, the PIII treated polystyrene surface after allylamine exposure becomes more hydrophobic and less negatively charged in phosphate buffer. Using yeast cells as an example, we have shown a significant improvement (6-15 times) of cell density immobilized on the PIII treated surface after exposure to allylamine. PMID:25092587

Tran, Clara T H; Kondyurin, Alexey; Chrzanowski, Wojciech; Bilek, Marcela M M; McKenzie, David R

2014-10-01

328

Surface Potential of Charged Liposomes Determined by Second Harmonic Generation  

E-print Network

Articles Surface Potential of Charged Liposomes Determined by Second Harmonic Generation Yan Liu that the surface potential of charged liposomes can be determined by second harmonic generation. The Gouy charge density and the surface potential of liposomes consisting of the negatively charged phospholipid

Eisenthal, Kenneth B.

329

Drug-induced ion channel opening tuned by the voltage sensor charge profile  

PubMed Central

Polyunsaturated fatty acids modulate the voltage dependence of several voltage-gated ion channels, thereby being potent modifiers of cellular excitability. Detailed knowledge of this molecular mechanism can be used in designing a new class of small-molecule compounds against hyperexcitability diseases. Here, we show that arginines on one side of the helical K-channel voltage sensor S4 increased the sensitivity to docosahexaenoic acid (DHA), whereas arginines on the opposing side decreased this sensitivity. Glutamates had opposite effects. In addition, a positively charged DHA-like molecule, arachidonyl amine, had opposite effects to the negatively charged DHA. This suggests that S4 rotates to open the channel and that DHA electrostatically affects this rotation. A channel with arginines in positions 356, 359, and 362 was extremely sensitive to DHA: 70 µM DHA at pH 9.0 increased the current >500 times at negative voltages compared with wild type (WT). The small-molecule compound pimaric acid, a novel Shaker channel opener, opened the WT channel. The 356R/359R/362R channel drastically increased this effect, suggesting it to be instrumental in future drug screening. PMID:24420769

Ottosson, Nina E.; Liin, Sara I.

2014-01-01

330

Swarm studies on elementary processes and ion-molecule reactions in low-temperature plasmas  

NASA Astrophysics Data System (ADS)

This paper deals with the presentation and discussion of some recent measurements on the interaction of electron and ion swarms in gases, with particular emphasis on flourinated gases. The processes to be discussed are related to electron impact ionization and attachment, including Penning ionization and electron detachment. Electron transport is discussed in mixtures of SF6 and fluorocarbon gases, where interesting regions of negative differential conductivity have been observed in C2F4, and apparent pressure dependences of the drift velocity in C4F8. Ion transport is discussed in terms of recent measurements on positive and negative ions in SF6 and Ar. Finally, the subject of ion-molecule reactions is illustrated with the dissociation and charge transfer processes of daughter ions in nitrogen. Throughout the paper, the advantages and limitations of both the pulsed Townsend technique and the drift tube-mass spectrometer are highlighted.

de Urquijo, J.

2002-08-01

331

Correlation of charge, hydrophobicity, and structure with antimicrobial activity of S1 and MIRIAM peptides.  

PubMed

Antimicrobial peptides are key elements of the innate immune system. Many of them interact with membranes of bacteria leading to perturbation of the lipid bilayer and eventually to inactivation of the pathogen. The emergence of multidrug-resistant bacteria has necessitated innovations of new and more powerful classes of antimicrobials. Here we present the in-depth study of an antimicrobial peptide, MIRIAM, derived from Sushi1 (S1), a well-characterized peptide from the horseshoe crab. MIRIAM interacts strongly with negatively charged lipids, forming an ?-helical structure. MIRIAM was found to neutralize LPS and kill Gram-negative bacteria with high efficiency, while not releasing LPS. The promising therapeutic potential of MIRIAM is shown by hemolytic assays, which demonstrate that eukaryotic membranes are unaffected at bactericidal concentrations. Nanoparticle-conjugated MIRIAM used in single-molecule fluorescence and electron microscopy experiments showed that MIRIAM targets bacterial membranes to kill bacteria similarly to parental S1. Furthermore, fragments derived from MIRIAM and S1 provided insights on their molecular mechanisms of action, in particular, the relationships of functional motifs comprised by charge, hydrophobicity, and structure within each peptide. We conclude that the combination of charge, hydrophobicity, and length of the peptide is important. A close interaction of amino acids in a single molecule in a carefully balanced ensemble of sequence position and secondary structure is crucial. PMID:20873868

Leptihn, Sebastian; Har, Jia Yi; Wohland, Thorsten; Ding, Jeak Ling

2010-11-01

332

Beams of fast neutral atoms and molecules in low-pressure gas-discharge plasma  

SciTech Connect

Fast neutral atom and molecule beams have been studied, the beams being produced in a vacuum chamber at nitrogen, argon, or helium pressure of 0.1-10 Pa due to charge-exchange collisions of ions accelerated in the sheath between the glow discharge plasma and a negative grid immersed therein. From a flat grid, two broad beams of molecules with continuous distribution of their energy from zero up to e(U + U{sub c}) (where U is voltage between the grid and the vacuum chamber and U{sub c} is cathode fall of the discharge) are propagating in opposite directions. The beam propagating from the concave surface of a 0.2-m-diameter grid is focused within a 10-mm-diameter spot on the target surface. When a 0.2-m-diameter 0.2-m-high cylindrical grid covered by end disks and composed of parallel 1.5-mm-diameter knitting needles spaced by 4.5 mm is immersed in the plasma, the accelerated ions pass through the gaps between the needles, turn inside the grid into fast atoms or molecules, and escape from the grid through the gaps on its opposite side. The Doppler shift of spectral lines allows for measuring the fast atom energy, which corresponds to the potential difference between the plasma inside the chamber and the plasma produced as a result of charge-exchange collisions inside the cylindrical grid.

Metel, A. S., E-mail: ametel@stankin.ru [Moscow State University of Technology 'Stankin,' (Russian Federation)

2012-03-15

333

Beams of fast neutral atoms and molecules in low-pressure gas-discharge plasma  

NASA Astrophysics Data System (ADS)

Fast neutral atom and molecule beams have been studied, the beams being produced in a vacuum chamber at nitrogen, argon, or helium pressure of 0.1-10 Pa due to charge-exchange collisions of ions accelerated in the sheath between the glow discharge plasma and a negative grid immersed therein. From a flat grid, two broad beams of molecules with continuous distribution of their energy from zero up to e( U + U c ) (where U is voltage between the grid and the vacuum chamber and U c is cathode fall of the discharge) are propagating in opposite directions. The beam propagating from the concave surface of a 0.2-m-diameter grid is focused within a 10-mm-diameter spot on the target surface. When a 0.2-m-diameter 0.2-m-high cylindrical grid covered by end disks and composed of parallel 1.5-mm-diameter knitting needles spaced by 4.5 mm is immersed in the plasma, the accelerated ions pass through the gaps between the needles, turn inside the grid into fast atoms or molecules, and escape from the grid through the gaps on its opposite side. The Doppler shift of spectral lines allows for measuring the fast atom energy, which corresponds to the potential difference between the plasma inside the chamber and the plasma produced as a result of charge-exchange collisions inside the cylindrical grid.

Metel, A. S.

2012-03-01

334

Grains charges in interstellar clouds  

NASA Technical Reports Server (NTRS)

The charge of cosmic grains could play an important role in many astrophysical phenomena. It probably has an influence on the coagulation of grains and more generally on grain-grain collisions, and on interaction between charged particles and grains which could lead to the formation of large grains or large molecules. The electrostatic charge of grains depends mainly on the nature of constitutive material of the grain and on the physical properties of its environment: it results from a delicate balance between the plasma particle collection and the photoelectron emission, both of them depending on each other. The charge of the grain is obtained in two steps: (1) using the numerical model the characteristics of the environment of the grain are computed; (2) the charge of a grain which is embedded in this environment is determined. The profile of the equilibrium charge of some typical grains through different types of interstellar clouds is obtained as a function of the depth of the cloud. It is shown that the grain charge can reach high values not only in hot diffuse clouds, but also in clouds with higher densities. The results are very sensitive to the mean UV interstellar radiation field. Three parameters appear to be essential but with different levels of sensitivity of the charge: the gas density, the temperature, and the total thickness of the cloud.

Bel, N.; Lafon, J. P.; Viala, Y. P.

1989-01-01

335

Charge Storage, Conductivity and Charge Profiles of Insulators as Related to Spacecraft Charging  

NASA Technical Reports Server (NTRS)

Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination. Conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping centers; and radiation-induced conductivity. Our experiments also show that "Malter" electron emission occurs for hours after turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects Program.

Dennison, J. R.; Swaminathan, Prasanna; Frederickson, A. R.

2004-01-01

336

Interaction between hydrogen molecules and metallofullerenes.  

SciTech Connect

Within first-principles density functional theory, we explore the feasibility of using metallofullerenes as efficient hydrogen storage media. In particular, we systematically investigate the interaction between hydrogen molecules and La encapsulated all-carbon fullerenes, Cn (20?n?82), focusing on the role of transferred charges between the metal atoms and fullerenes on the affinity of hydrogen molecules to the metallofullerenes. Our calculations show that three electrons are transferred from La atom to fullerene cages, while the induced charges are mostly screened by the fullerene cages. We find the local enhancement of molecular hydrogen affinity to the fullerenes to be sensitively dependent on the local bonding properties, rather than on the global charging effects.

Yoon, Mina [ORNL; Yang, Shenyuan [ORNL; Zhang, Zhenyu [ORNL

2009-01-01

337

Ion-Molecule Reactions and Ion Kinetics in DC Townsend Discharges in Dielectric Gases  

NASA Technical Reports Server (NTRS)

In gas discharges the identify, transport, relative intensities, and kinetic energy distributions (KEDs) of ions may be dominated by ion-molecule reactions. In order to understand these discharges, there is a need for cross section data for various ion-molecule reactions, including symmetric and asymmetric charge-transfer, collisional detachment, and ion conversion reactions, especially for low to intermediate ion-impact energies. In view of the importance of dielectric gases, we have recently measured the KEDs of various positive and negative ions produced in DC Townsend discharges in SF6, CF4, CHF3, O2, and CO2. The relative abundance and mean energies of ions are obtained from the measured KEDs. The effective cross sections (Qeff) describing the KEDs of various ions can be derived by using the mean ion energies and the electric field-to-gas density ratios (E/N). In the case of SF6 and O2 discharges, the determined cross sections (Qeff) for the negative-ion molecule reactions are consistent with previously measured cross section data obtained by crossed-beam experiment. The availability of these cross section values enabled us to understand the ion data reasonably well. However, the lack of adequate cross section data for positive ions in all of the above gases is a major obstacle in understanding ion transport in these gas discharges.

Rao, M. V. V. S.; Arnold, James O. (Technical Monitor)

1998-01-01

338

Coalescence and Breakup of Oppositely Charged Droplets  

PubMed Central

The coalescence process of oppositely charged drops for different electrical conductivities of liquids is presented. When the electrical conductivity was relatively low, oppositely charged drops failed to coalesce under sufficiently high electrical fields and capillary ripples were formed on the surfaces of droplets after rebound. For a high electrically conductive liquid, it was found that a crown profile of drop fission always appeared on the top surface of negatively charged drops after the two charged drops contacted and bounced off. Furthermore, we report here, for the first time, the newly found phenomenon and argue that the break up might be caused by Rayleigh instability, a form of Coulomb fission. The different mobility of positive and negative ions is the underlying mechanism that explains why the break up always happened on the negative side of charged drops. PMID:25410022

Wang, Junfeng; Wang, Bin; Qiu, Huihe

2014-01-01

339

Effects of induced charge in the kinestatic charge detector.  

PubMed

The principle of the kinestatic charge detector (KCD) for digital radiography depends on the synchronization of the scan velocity of a parallel plate drift chamber with the cation drift velocity. Compared with line-beam scanners, this motion-compensated imaging technique makes better use of the x-ray tube output. A Frisch grid traditionally has been used within the KCD to minimize unwanted signal contributions from both cations and negative charge carriers during irradiation. In this work the charge induction process in a parallel plate geometry was investigated for the special case of the KCD. In the limit of infinite plates, the cathode charge density due to both cations and negative charge carriers increases quadratically in time for a kinestatically scanned narrow slit. In the KCD the cathode is segmented into an array of narrow electrodes, each aligned with the incident x-ray beam. Our conformal mapping computation determined that the shape of the induced charge signal depends critically on delta x/w, the ratio of electrode width to drift gap. Our conclusion introduces the possibility of eliminating the Frisch grid from the KCD design because the value of delta x/w required for transverse sampling in the KCD is sufficiently low as to allow "self-gridding" to take effect. PMID:7643803

Wagenaar, D J; Terwilliger, R A

1995-05-01

340

Charge Transport in Molecular Catalysis in a Heterogeneous Phase  

Microsoft Academic Search

This chapter focuses on the fundamental aspects in controlling charge transport (CT) processes through molecules in energy\\u000a conversion systems. The central reactions involved in the energy conversion are the charge separation and charge transfer\\u000a processes along the reaction coordinates from reactant molecules, assisted by the catalyst active sites. In some cases the\\u000a polymer medium plays an important role in the

M. Kaneko; T. Okada

341

Vibrational excitation of a molecule by a resonance current  

SciTech Connect

Correct expressions are obtained for calculating a tunnel-resonance current through molecules. The participation of molecular vibrations in the resonance charge transfer through a molecule and vibrational excitation of the molecule are determined by the reorganization energy E{sub r} of the vibrational system depending on the displacement of the equilibrium position of vibrational modes in passing from the neutral molecule to the resonance state of a molecular ion. The mean excitation energy of the molecule during the propagation of an elementary charge changes from E{sub r} at the voltage across electrodes close to the threshold up to 2E{sub r} at voltages considerably exceeding the threshold voltage. An expression is obtained for the stationary vibrational temperature of the molecule, which is proportional to the resonance current.

Kozhushner, M. A., E-mail: kozhushner@gmail.com [Russian Academy of Sciences, Institute of Chemical Physics (Russian Federation); Oleinik, I. I. [University of South Florida (United States)

2012-11-15

342

Metal-organic and supramolecular architectures based on mechanically interlocked molecules  

NASA Astrophysics Data System (ADS)

The focus of this work is on mechanically interlocked molecules (MIMs), which have unusual physicochemical and mechanical properties with potential applications in nano-scale/molecular devices and high strength materials. Rotaxanes, for example, consist of an axle-like molecule threaded through a wheel-like molecule, with bulky groups at the two ends of the axle preventing the wheel from dissociating. The position of the wheel along the axle can be switched in a controllable and reversible manner by applying external stimuli, a feature that might lead to the next generation of computers. Molecularly woven materials (MWMs), another example of molecules with mechanically interlocked features, are predicted to be unprecedentedly strong while being lightweight and flexible. With the ultimate goal of achieving control over the functioning of molecular devices in the solid state, a variety of pseudorotaxane building blocks were prepared and characterized, including a novel, rare blue-colored motif. The temperature-dependent assembly/disassembly of pseudorotaxanes was exploited for the construction of single-wavelength colorimetric temperature sensors over a 100 °C window. Pseudorotaxanes based on aromatic crown ether wheels and disubstituted 4,4'-bipyridinium axles were converted into rotaxanes upon binding to metal complexes (zinc, cadmium, mercury, copper, cobalt), and the formation of ordered crystalline arrays was studied in the solid state. The columnar organization of pseudorotaxanes by Hg2X6 2-- complexes (X = Cl, Br, I), leading to unprecedented dichroic (blue/red) rotaxane crystals, was demonstrated for the first time. From the crystal structures studied it became apparent that negatively charged metal complexes are needed for successful assembly with the positively charged pseudorotaxane units. To be able to use the more common, positively charged metal ions for rotaxane framework construction, neutral and negatively charged pseudorotaxanes were synthesized, by attaching anionic substituents (carboxylates, sulfonates) to either the wheel or the axle component. It was found that pseudorotaxane formation also enabled resolution of two sulfonated crown ether isomers, which were inseparable by conventional methods. Organic ligands for MWM precursors were designed and synthesized according to multi-step schemes. Helical metal-complexes based on these ligands were prepared and characterized. Chromatography, Nuclear Magnetic Resonance and UV-Visible spectroscopy, Mass spectrometry, Electrochemistry, Thermogravimetric Analysis and X-ray crystallography were used in identification, purification and characterization of the compounds involved.

Fernando, Isurika Rosini

343

Random walk algorithms for estimating electrostatic properties of large molecules  

E-print Network

of a molecule as a cavity with point charges and constant inside. The exterior is considered as a dielectric) = M m=1 qm(x - xm). Here, the dielectric permittivity, = i, is constant. Assume first constant permittivity, e. The distri- bution of dissolved ions determines the charge density outside G

Simonov, Nikolai Aleksandrovich

344

Localization and delocalization of charges injected in DNA  

NASA Astrophysics Data System (ADS)

The electrical properties of DNA molecules are investigated by charge injection and electric force microscopy experiments. Prior to injection, DNA molecules exhibit a weak positively charged state. We probe the electrical behavior of DNA by measuring the localized or delocalized character of the DNA charge states upon injection of excess charges. We show that injected charges do not delocalize for overstretched DNA prepared by a receding meniscus technique, while the adjunction of spermidine during the deposition leads to relaxed DNA molecules exhibiting a charge delocalization over microns. The interplay between charge localization/delocalization and deposition techniques may explain that transport behaviors ranging from insulating to conductive have been reported for DNA deposited on surfaces.

Heim, T.; Mélin, T.; Deresmes, D.; Vuillaume, D.

2004-09-01

345

Negative ion generator  

DOEpatents

A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions. 8 figs.

Stinnett, R.W.

1984-05-08

346

Sentential Negation in English  

ERIC Educational Resources Information Center

This paper undertakes a detailed analysis of sentential negation in the English language with Chomsky's Government-Binding theory of Transformational Grammar as theoretical model. It distinguishes between constituent and sentential negation in English. The essay identifies the exact position of Negation phrase in an English clause structure. It…

Mowarin, Macaulay

2009-01-01

347

Grain charging in protoplanetary discs  

NASA Astrophysics Data System (ADS)

Context. Recent work identified a growth barrier for dust coagulation that originates in the electric repulsion between colliding particles. Depending on its charge state, dust material may have the potential to control key processes towards planet formation such as magnetohydrodynamic (MHD) turbulence and grain growth, which are coupled in a two-way process. Aims: We quantify the grain charging at different stages of disc evolution and differentiate between two very extreme cases: compact spherical grains and aggregates with fractal dimension Df = 2. Methods: Applying a simple chemical network that accounts for collisional charging of grains, we provide a semi-analytical solution. This allowed us to calculate the equilibrium population of grain charges and the ionisation fraction efficiently. The grain charging was evaluated for different dynamical environments ranging from static to non-stationary disc configurations. Results: The results show that the adsorption/desorption of neutral gas-phase heavy metals, such as magnesium, effects the charging state of grains. The greater the difference between the thermal velocities of the metal and the dominant molecular ion, the greater the change in the mean grain charge. Agglomerates have more negative excess charge on average than compact spherical particles of the same mass. The rise in the mean grain charge is proportional to N1/6 in the ion-dust limit. We find that grain charging in a non-stationary disc environment is expected to lead to similar results. Conclusions: The results indicate that the dust growth and settling in regions where the dust growth is limited by the so-called "electro-static barrier" do not prevent the dust material from remaining the dominant charge carrier.

Ilgner, M.

2012-02-01

348

Directly Observing the Motion of DNA Molecules near Solid-State Nanopores  

PubMed Central

We investigate the diffusion and the drift motion of ? DNA molecules near solid-state nanopores prior to their translocation though the nanopores using fluorescence microscopy. The radial dependence of the electric field near a nanopore generated by an applied voltage in ionic solution can be estimated quantitatively in 3D by analyzing the motion of negatively charged DNA molecules. We find that the electric field is approximately spherically symmetric around the nanopore under the conditions investigated. In addition, DNA clogging at the nanopore was directly observed. Surprisingly, the probability of the clogging event increases with increasing external bias voltage. We also find that DNA molecules clogging the nanopore reduce the electric field amplitude at the nanopore membrane surface. To better understand these experimental results, analytical method with Ohm’s law and computer simulation with Poisson and Nernst-Planck (PNP) equations are used to calculate the electric field near the nanopore. These results are of great interest in both experimental and theoretical considerations of the motion of DNA molecules near voltage-biased nanopores. These findings will also contribute to the development of solid-state nanopore based DNA sensing devices. PMID:23046052

Ando, Genki; Hyun, Changbae; Li, Jiali; Mitsui, Toshiyuki

2012-01-01

349

Biological Contexts for DNA Charge Transport Chemistry  

E-print Network

The double helical structure adopted by B-form DNA, where a negatively charged sugar phosphate backbone surrounds a ?-stacked array of heterocyclic aromatic basepairs, allows it to serve as an efficient medium for long-range charge transport (CT) (1). This chemistry has now been well established as a property of DNA. DNA CT can be

unknown authors

350

Physical basis of charge pairing in mitochondria.  

PubMed Central

The postulate of charge pairing in the mitochondrial inner membrane is justified by applying a formula due to Fuoss to calculate the probability density for the distance between a positive and a negative charge. For dielectric constants 10 or less pairing is absolute, for 20 there is some tendency towards pairing, and at 78 it is nonexistent. Pairing, partner exchange or charge substitution, inhibition, and antiport uncoupling can be rationalized within this framework. PMID:1056011

Kemeny, G; Singer, P

1975-01-01

351

Negative-U extended Hubbard model in intermediate correlation regime  

NASA Astrophysics Data System (ADS)

The phase boundary between the charge-ordered and the non-ordered states is derived for the negative- U extended Hubbard model with the high-temperature expansion method. The thermodynamic and the magnetic properties are then investigated.

Micnas, R.; Robaszkiewicz, S.; Chao, K. A.

1983-02-01

352

Negative-U extended Hubbard model in intermediate correlation regime  

Microsoft Academic Search

The phase boundary between the charge-ordered and the non-ordered states is derived for the negative-U extended Hubbard model with the high-temperature expansion method. The thermodynamic and the magnetic properties are then investigated.

R. Micnas; S. Robaszkiewicz; K. A. Chao

1983-01-01

353

The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules  

SciTech Connect

This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O{sub 2}. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO{sub 2} + Na and NaO + NaO. NaO{sub 2} products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O{sub 2}, which is likely a result of a charge transfer from Na{sub 2} to the excited state orbital of O{sub 2}{sup {minus}}. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH{sub 3} and Na(CH{sub 3}OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.

Hou, H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1995-12-01

354

Sensing small molecule interactions with lipid membranes by local pH modulation.  

PubMed

Herein, we utilized a label-free sensing platform based on pH modulation to detect the interactions between tetracaine, a positively charged small molecule used as a local anesthetic, and planar supported lipid bilayers (SLBs). The SLBs were patterned inside a flow cell, allowing for various concentrations of tetracaine to be introduced over the surface in a buffer solution. Studies with membranes containing POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) yielded an equilibrium dissociation constant value of Kd = 180 ± 47 ?m for this small molecule-membrane interaction. Adding cholesterol to the SLBs decreased the affinity between tetracaine and the bilayers, while this interaction tightened when POPE (1-hexadecanoyl-2-(9-Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine) was added. Studies were also conducted with three negatively charged membrane lipids, POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt)), POPS (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (sodium salt)), and ganglioside GM1. All three measurements gave rise to a similar tightening of the apparent Kd value compared with pure POPC membranes. The lack of chemical specificity with the identity of the negatively charged lipid indicated that the tightening was largely electrostatic. Through a direct comparison with ITC measurements, it was found that the pH modulation sensor platform offers a facile, inexpensive, highly sensitive, and rapid method for the detection of interactions between putative drug candidates and lipid bilayers. As such, this technique may potentially be exploited as a screen for drug development and analysis. PMID:24152205

Huang, Da; Zhao, Tao; Xu, Wei; Yang, Tinglu; Cremer, Paul S

2013-11-01

355

Oligomerization of Negatively-Charged Amino Acids by Carbonyldiimidazole  

NASA Technical Reports Server (NTRS)

The carbonyldiimidazole-induced oligomerizations of aspartic acid, glutamic acid and 0-phospho-serine are amongst the most efficient reported syntheses of biopolymers in aqueous solution. The dependence of the yields of products on the concentrations of reagents, the temperature and the enantiomeric composition of the substrate amino acids are reported. Catalysis by metal ions, particularly by Mg(2+), is described. These reactions do not generate significant amounts of material in the size-range of several tens of residues that are thought to be needed for a polymer to function as a genetic material.

Hill, Aubrey R., Jr.; Orgel, Leslie E.

1996-01-01

356

Ferric Iron Nanoparticle Formation Mediated By Negatively Charged Polypeptides  

Microsoft Academic Search

The creation of magnetite particles by magnetotactic bacteria has been of great interest for a number of years. Previous studies have shown that magnetite nanocrystals have been synthesized in the presence of recombinant Mms6 protein. Mms6 plays a vital role in the biomineralization of bacterial magnetite nanocrystals. The objective of this research is to determine the effect of functional group

Vamsi Krishna Aluru

2010-01-01

357

To Charge or Not to Charge.  

ERIC Educational Resources Information Center

Ways to fund a publications office and the merits of charge-back systems are discussed. Every charge-back system differs. Some offices try to cover costs; others bill for overhead. Some alternatives to charging are described. (MLW)

Hay, Tina M.

1989-01-01

358

Nanophotonics and Single Molecules  

Microsoft Academic Search

Single emitting molecules are currently providing a new window into nanoscale systems ranging from biology to materials science.\\u000a The amount of information that can be extracted from each single molecule depends upon the specific photophysical properties\\u000a of the fluorophore and how these properties are affected by the nearby environment. For this reason, it is necessary to develop\\u000a single-molecule emitters with

W. E. Moerner; P. James Schuck; David P. Fromm; Anika Kinkhabwala; Samuel J. Lord; Stefanie Y. Nishimura; Katherine A. Willets; Arvind Sundaramurthy; Gordon Kino; Meng He; Zhikuan Lu; Robert J. Twieg

359

Modular Battery Charge Controller  

NASA Technical Reports Server (NTRS)

A new approach to masterless, distributed, digital-charge control for batteries requiring charge control has been developed and implemented. This approach is required in battery chemistries that need cell-level charge control for safety and is characterized by the use of one controller per cell, resulting in redundant sensors for critical components, such as voltage, temperature, and current. The charge controllers in a given battery interact in a masterless fashion for the purpose of cell balancing, charge control, and state-of-charge estimation. This makes the battery system invariably fault-tolerant. The solution to the single-fault failure, due to the use of a single charge controller (CC), was solved by implementing one CC per cell and linking them via an isolated communication bus [e.g., controller area network (CAN)] in a masterless fashion so that the failure of one or more CCs will not impact the remaining functional CCs. Each micro-controller-based CC digitizes the cell voltage (V(sub cell)), two cell temperatures, and the voltage across the switch (V); the latter variable is used in conjunction with V(sub cell) to estimate the bypass current for a given bypass resistor. Furthermore, CC1 digitizes the battery current (I1) and battery voltage (V(sub batt) and CC5 digitizes a second battery current (I2). As a result, redundant readings are taken for temperature, battery current, and battery voltage through the summation of the individual cell voltages given that each CC knows the voltage of the other cells. For the purpose of cell balancing, each CC periodically and independently transmits its cell voltage and stores the received cell voltage of the other cells in an array. The position in the array depends on the identifier (ID) of the transmitting CC. After eight cell voltage receptions, the array is checked to see if one or more cells did not transmit. If one or more transmissions are missing, the missing cell(s) is (are) eliminated from cell-balancing calculations. The cell-balancing algorithm is based on the error between the cell s voltage and the other cells and is categorized into four zones of operation. The algorithm is executed every second and, if cell balancing is activated, the error variable is set to a negative low value. The largest error between the cell and the other cells is found and the zone of operation determined. If the error is zero or negative, then the cell is at the lowest voltage and no balancing action is needed. If the error is less than a predetermined negative value, a Cell Bad Flag is set. If the error is positive, then cell balancing is needed, but a hysteretic zone is added to prevent the bypass circuit from triggering repeatedly near zero error. This approach keeps the cells within a predetermined voltage range.

Button, Robert; Gonzalez, Marcelo

2009-01-01

360

Charged membranes.  

PubMed

This Teaching Resource provides three animated lessons that describe the storage and utilization of energy across plasma membranes. The "Na,K ATPase" animation explains how these pumps establish the electrochemical gradient that stores energy across plasma membranes. The "ATP synthesizing complexes" animation shows how these complexes transfer energy from the inner mitochondrial membrane to adenosine triphosphate (ATP). The "action potential" lesson explains how charged membranes are used to propagate signals along the axons of neurons. These animations serve as valuable resources for any collegiate-level course that describes these important factors. Courses that might employ them include introductory biology, biochemistry, biophysics, cell biology, pharmacology, and physiology. PMID:23592845

Thatcher, Jack D

2013-01-01

361

Charge Equilibrium  

NASA Astrophysics Data System (ADS)

The mean equililibrium charge of a penetrating ion can be estimated on the basis of Bohr's velocity criterion or Lamb's energy criterion. Qualitative and quantitative results are derived on the basis of the Thomas-Fermi model of the atom, which is discussed explicitly. This includes a brief introduction to the Thomas-Fermi-Dirac model. Special attention is paid to trial function approaches by Lenz and Jensen as well as Brandt and Kitagawa. The chapter also offers a preliminary discussion of the role of the stopping medium, gas-solid differences, and a survey of data compilations.

Sigmund, Peter

362

Structural and Functional Studies of trans-Encoded HLA-DQ2.3 (DQA1*03:01/DQB1*02:01) Protein Molecule*  

PubMed Central

MHC class II molecules are composed of one ?-chain and one ?-chain whose membrane distal interface forms the peptide binding groove. Most of the existing knowledge on MHC class II molecules comes from the cis-encoded variants where the ?- and ?-chain are encoded on the same chromosome. However, trans-encoded class II MHC molecules, where the ?- and ?-chain are encoded on opposite chromosomes, can also be expressed. We have studied the trans-encoded class II HLA molecule DQ2.3 (DQA1*03:01/DQB1*02:01) that has received particular attention as it may explain the increased risk of certain individuals to type 1 diabetes. We report the x-ray crystal structure of this HLA molecule complexed with a gluten epitope at 3.05 ? resolution. The gluten epitope, which is the only known HLA-DQ2.3-restricted epitope, is preferentially recognized in the context of the DQ2.3 molecule by T-cell clones of a DQ8/DQ2.5 heterozygous celiac disease patient. This preferential recognition can be explained by improved HLA binding as the epitope combines the peptide-binding motif of DQ2.5 (negative charge at P4) and DQ8 (negative charge at P1). The analysis of the structure of DQ2.3 together with all other available DQ crystal structures and sequences led us to categorize DQA1 and DQB1 genes into two groups where any ?-chain and ?-chain belonging to the same group are expected to form a stable heterodimer. PMID:22362761

Tollefsen, Stig; Hotta, Kinya; Chen, Xi; Simonsen, Bj?rg; Swaminathan, Kunchithapadam; Mathews, Irimpan I.; Sollid, Ludvig M.; Kim, Chu-Young

2012-01-01

363

Point Charges Optimally Placed to Represent the Multipole Expansion of Charge Distributions  

PubMed Central

We propose an approach for approximating electrostatic charge distributions with a small number of point charges to optimally represent the original charge distribution. By construction, the proposed optimal point charge approximation (OPCA) retains many of the useful properties of point multipole expansion, including the same far-field asymptotic behavior of the approximate potential. A general framework for numerically computing OPCA, for any given number of approximating charges, is described. We then derive a 2-charge practical point charge approximation, PPCA, which approximates the 2-charge OPCA via closed form analytical expressions, and test the PPCA on a set of charge distributions relevant to biomolecular modeling. We measure the accuracy of the new approximations as the RMS error in the electrostatic potential relative to that produced by the original charge distribution, at a distance the extent of the charge distribution–the mid-field. The error for the 2-charge PPCA is found to be on average 23% smaller than that of optimally placed point dipole approximation, and comparable to that of the point quadrupole approximation. The standard deviation in RMS error for the 2-charge PPCA is 53% lower than that of the optimal point dipole approximation, and comparable to that of the point quadrupole approximation. We also calculate the 3-charge OPCA for representing the gas phase quantum mechanical charge distribution of a water molecule. The electrostatic potential calculated by the 3-charge OPCA for water, in the mid-field (2.8 Å from the oxygen atom), is on average 33.3% more accurate than the potential due to the point multipole expansion up to the octupole order. Compared to a 3 point charge approximation in which the charges are placed on the atom centers, the 3-charge OPCA is seven times more accurate, by RMS error. The maximum error at the oxygen-Na distance (2.23 Å ) is half that of the point multipole expansion up to the octupole order. PMID:23861790

Onufriev, Alexey V.

2013-01-01

364

Physics Aspects of Charge Migration Through DNA  

NASA Astrophysics Data System (ADS)

In Chap. 5, Apalkov, Wang and Chakraborty have explored the geometry effects on charge transfer in a DNA molecule where they view the molecule as two strands of nucleotide bases with interstrand coupling. For a charge to migrate from one end of the molecule to the other, there exists several dominant channels in this two-strand model, as opposed to the standard assumption that only one such channel exists, according to the single-chain model. In this duplex-geometry picture, a weak distance dependence of the charge transfer was found to occur for pure quantum transport through DNA because there are many more available tunneling channels in DNA. The observed crossover between the strong and weak distance dependence may therefore be attributed to a crossover from unichannel to multichannel tunneling transport.

Apalkov, Vadim; Wang, Xue-Feng; Chakraborty, Tapash

365

Negative ions in the Enceladus plume  

NASA Astrophysics Data System (ADS)

During Cassini's Enceladus encounter on 12th March 2008, the Cassini Electron Spectrometer, part of the CAPS instrument, detected fluxes of negative ions in the plumes from Enceladus. It is thought that these ions include negatively charged water group cluster ions associated with the plume and forming part of the 'plume ionosphere'. In this paper we present our observations, argue that these are negative ions, and present preliminary mass identifications. We also suggest mechanisms for production and loss of the ions as constrained by the observations. Due to their short lifetime, we suggest that the ions are produced in or near the water vapour plume, or from the extended source of ice grains in the plume. We suggest that Enceladus now joins the Earth, Comet Halley and Titan as locations in the Solar System where negative ions have been directly observed although the ions observed in each case have distinctly different characteristics.

Coates, A. J.; Jones, G. H.; Lewis, G. R.; Wellbrock, A.; Young, D. T.; Crary, F. J.; Johnson, R. E.; Cassidy, T. A.; Hill, T. W.

2010-04-01

366

Negative Ions in the Enceladus Plume (Invited)  

NASA Astrophysics Data System (ADS)

During recent Enceladus encounters by Cassini, the Cassini Electron Spectrometer, part of the CAPS instrument, detected fluxes of negative ions in the plumes from Enceladus (Coates et al, Icarus in press, 2009). It is thought that these ions include negatively charged water group cluster ions associated with the plume and forming part of the ‘plume ionosphere’. Here we present our observations, show that these are negative ions, and present preliminary mass identifications. We also suggest mechanisms for production and loss of the ions as constrained by the observations. Due to their short lifetime, we suggest that the ions are produced in or near the water vapour plume, or from the extended source of ice grains in the plume. Enceladus now joins the Earth, comet Halley and Titan as locations in the solar system where negative ions have been directly observed, although the ions observed in each case have distinctly different characteristics.

Coates, A. J.; Jones, G. H.; Lewis, G.; Wellbrock, A.; Young, D. T.; Crary, F. J.; Johnson, R. E.; Hill, T. W.

2009-12-01

367

Negative Differential Resistance in C60 Diodes  

NASA Astrophysics Data System (ADS)

Morphology studies and current-voltage (IV) measurements of C60 thin film diodes in the temperature range of 300-4.2 K are presented. For defined evaporation parameters orientation domains along the growth direction are demonstrated by cross section transmission electron microscopy. From the electrical characterization the fullerene diodes exhibit space charge limited currents which follow a power law dependency. At current densities above 100 mA cm-2 and temperatures below 200 K reversible voltage instabilities (S-shape IV characteristics, negative differential resistance) arise. The instabilities are similar to charge transport effects in amorphous inorganic semiconductors.

Stadler, Philipp; Fuchsbauer, Anita; Hesser, Günther; Fromherz, Thomas; Matt, Gebhard J.; Neugebauer, Helmut; Sariciftci, Serdar N.

368

Characterization of protein and peptide binding to nanogels formed by differently charged chitosan derivatives.  

PubMed

Chitosan (Chi) is a natural biodegradable cationic polymer with remarkable potency as a vehicle for drug or vaccine delivery. Chi possesses multiple groups, which can be used both for Chi derivatization and for particle formation. The aim of this work was to produce stable nanosized range Chi gels (nanogels, NGs) with different charge and to study the driving forces of complex formation between Chi NGs and proteins or peptides. Positively charged NGs of 150 nm in diameter were prepared from hexanoyl chitosan (HC) by the ionotropic gelation method while negatively charged NGs of 190 nm were obtained from succinoyl Chi (SC) by a Ca²? coacervation approach. NGs were loaded with a panel of proteins or peptides with different weights and charges. We show that NGs preferentially formed complexes with oppositely charged molecules, especially peptides, as was demonstrated by gel-electrophoresis, confocal microscopy and HPLC. Complex formation was accompanied by a change in zeta-potential and decrease in size. We concluded that complex formation between Chi NGs and peptide/proteins is mediated mostly by electrostatic interactions. PMID:23823877

Zubareva, Anastasia; Ily'ina, Alla; Prokhorov, Aleksander; Kurek, Denis; Efremov, Mikhail; Varlamov, Valery; Senel, Sevda; Ignatyev, Pavel; Svirshchevskaya, ?lena

2013-01-01

369

Novel electromagnetic radiation in a semi-infinite space filled with a double-negative metamaterial  

E-print Network

We have theoretically investigated the electromagnetic radiation excited by a charged particle moving along a semi-infinite space filled with a double-negative metamaterial (DNM). Cherenkov radiation in the double-negative ...

Duan, Zhaoyun

370

Negative-ion formation in the explosives RDX, PETN, and TNT using the Reversal Electron Attachment Detection (READ) technique  

NASA Technical Reports Server (NTRS)

In the search for high sensitivity and direct atmospheric sampling of trace species, techniques have been developed such as atmospheric-sampling, glow-discharge ionization (ASGDI), corona discharge, atmospheric pressure ionization (API), electron-capture detection (ECD), and negative-ion chemical ionization (NICI) that are capable of detecting parts-per-billion to parts-per-trillion concentrations of trace species. These techniques are based on positive- or negative-ion formation via charge-transfer to the target, or electron capture under multiple-collision conditions in a Maxwellian distribution of electron energies at the source temperature. One drawback of the high-pressure, corona- or glow-discharge devices is that they are susceptible to interferences either through indistinguishable product masses, or through undesired ion-molecule reactions. The ASGDI technique is relatively immune from such interferences, since at target concentrations of less than 1 ppm the majority of negative ions arises via electron capture rather than through ion-molecule chemistry. A drawback of the conventional ECD, and possibly of the ASGDI, is that they exhibit vanishingly small densities of electrons with energies in the range 0-10 millielectron volts (meV), as can be seen from a typical Maxwellian electron energy distribution function at T = 300 K. Slowing the electrons to these subthermal (less than 10 meV) energies is crucial, since the cross section for attachment of several large classes of molecules is known to increase to values larger than 10(exp -12) sq cm at near-zero electron energies. In the limit of zero energy these cross sections are predicted to diverge as epsilon(exp -1/2), where epsilon is the electron energy. In order to provide a better 'match' between the electron energy distribution function and attachment cross section, a new concept of attachment in an electrostatic mirror was developed. In this scheme, electrons are brought to a momentary halt by reversing their direction with electrostatic fields. At this turning point the electrons have zero or near-zero energy. A beam of target molecules is introduced, and the resultant negative ions extracted. This basic idea has been recently improved to allow for better reversal geometry, higher electron currents, lower backgrounds, and increased negative-ion extraction efficiency. We present herein application of the so-called reversal electron attachment detector (READ) to the study of negative-ion formation in the explosives molecules RDX, PETN, and TNT under single-collision conditions.

Chutijian, Ara; Boumsellek, S.; Alajajian, S. H.

1992-01-01

371

Molecules in Living Systems  

NSDL National Science Digital Library

This lesson explains the difference between molecules in living systems and inanimate objects. In living systems, atoms and molecules are organized to a much greater degree and provide the structure of the organism. Lipids, carbohydrates, proteins, and nucleic acids are also discussed.

2012-06-19

372

Discovering Interstellar Molecules  

Microsoft Academic Search

This paper describes how high resolution spectroscopy has been the key for discovering interstellar molecules and for studying the interstellar medium. The development of radioastronomy in the 1950's has led to the detection of many interstellar molecules in the 1960s and 1970s, and the construction of a new field of research, astrochemistry. The discovery of molecular ions has confirmed the

M. Gerin

2006-01-01

373

Enzymatic DNA molecules  

NASA Technical Reports Server (NTRS)

The present invention discloses deoxyribonucleic acid enzymes--catalytic or enzymatic DNA molecules--capable of cleaving nucleic acid sequences or molecules, particularly RNA, in a site-specific manner, as well as compositions including same. Methods of making and using the disclosed enzymes and compositions are also disclosed.

Joyce, Gerald F. (Inventor); Breaker, Ronald R. (Inventor)

1998-01-01

374

What is a Molecule?  

NSDL National Science Digital Library

This video/animation shows that a molecule of water is made up of oxygen and hydrogen atoms. When oxygen and hydrogen atoms exist alone, their properties are different from the properties they have when they are chemically combined to form a water molecule

Wpsu

2007-04-09

375

Enhancing SERS by Means of Supramolecular Charge Transfer  

NASA Technical Reports Server (NTRS)

In a proposed method of sensing small quantities of molecules of interest, surface enhanced Raman scattering (SERS) spectroscopy would be further enhanced by means of intermolecular or supramolecular charge transfer. There is a very large potential market for sensors based on this method for rapid detection of chemical and biological hazards. In SERS, the Raman signals (vibrational spectra) of target molecules become enhanced by factors of the order of 108 when those molecules are in the vicinities of nanostructured substrate surfaces that have been engineered to have plasmon resonances that enhance local electric fields. SERS, as reported in several prior NASA Tech Briefs articles and elsewhere, has remained a research tool and has not yet been developed into a practical technique for sensing of target molecules: this is because the short range (5 to 20 nm) of the field enhancement necessitates engineering of receptor molecules to attract target molecules to the nanostructured substrate surfaces and to enable reliable identification of the target molecules in the presence of interferants. Intermolecular charge-transfer complexes have been used in fluorescence-, photoluminescence-, and electrochemistry-based techniques for sensing target molecules, but, until now, have not been considered for use in SERS-based sensing. The basic idea of the proposed method is to engineer receptor molecules that would be attached to nanostructured SERS substrates and that would interact with the target molecules to form receptor-target supramolecular charge-transfer complexes wherein the charge transfer could be photoexcited.

Wong, Eric; Flood, Amar; Morales, Alfredo

2009-01-01

376

Au adsorption and Au-mediated charge transfer on the SrO-termination of SrTiO 3 (0 0 1) surface  

NASA Astrophysics Data System (ADS)

Atomic Au adsorption on the SrO-termination of SrTiO 3 (0 0 1) surface has been studied by means of the first-principles calculations based on the density functional theory (DFT). It indicates that charge polarization dominantly contributes to the bonding between Au and SrO-termination. Interfacial charge transfer induces dipole moment and changes work function. The mediating role Au played in charge transfer from electron-doped SrTiO 3:Nb to NO has been simulated. Charge transfer from SrTiO 3:Nb to Au is ascertained indicating that Au plays as an electron trapping center. SrO-termination has weak activity to NO while the molecule can be strongly adsorbed on negatively charged Au atom. It has been represented that Au mediates the charge transfer from SrTiO 3:Nb to NO. Antibonding orbital (? 2p*) of NO accommodates the charge and thus molecular bond is weakened (activated). Fukui functions demonstrate the role Au played in transiting the charge transfer from electronically excited SrTiO 3 to target species. Evidence that metal deposited on photocatalyst surface effectively separates the electron-hole pairs and improves the photocatalytic activity is presented in the current work.

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

2011-05-01

377

Osmosis at constant volume. Negative pressure  

E-print Network

A thermodynamic state of solvent and solution separated with an elastic semipermeable membrane, in the box with a fixed volume, is considered. It is shown that the minimum of the free energy is accompanied by the compression of the solution and tension of the solvent caused by the transfer of solvent molecules into compartment with solution. The tensile state of the solvent is described in terms of negative pressure. It is found that the negative pressure as well as compression pressure is of the order of osmotic pressure given by van't Hoff equation. It is proposed that this mechanism could be responsible for the water uptake in tall trees.

Zupanovic, Pasko; Brumen, Milan; Fajmut, Ales; Juretic, Davor

2009-01-01

378

Positive and negative perfectionism  

Microsoft Academic Search

Previous research into perfectionism has focused on clinical populations resulting in a bias towards a negativistic, pathologically inclined conceptualization. The present study investigated the possibility of distinguishing aspects of perfectionism on the basis of perceived consequences, mirroring a behavioural distinction between positive and negative reinforcement. A 40-item questionnaire, designed to measure perfectionism defined in terms of both positive and negative

L. A. Terry-Short; R. Glynn Owens; P. D. Slade; M. E. Dewey

1995-01-01

379

Charged Membranes  

NSDL National Science Digital Library

This Teaching Resource provides three animated lessons that describe the storage and utilization of energy across plasma membranes. The “Na,K ATPase” animation explains how these pumps establish the electrochemical gradient that stores energy across plasma membranes. The “ATP synthesizing complexes” animation shows how these complexes transfer energy from the inner mitochondrial membrane to adenosine triphosphate (ATP). The “action potential” lesson explains how charged membranes are used to propagate signals along the axons of neurons. These animations serve as valuable resources for any collegiate-level course that describes these important factors. Courses that might employ them include introductory biology, biochemistry, biophysics, cell biology, pharmacology, and physiology.

Jack D. Thatcher (Lewisburg;West Virginia School of Osteopathic Medicine REV)

2013-04-16

380

On Negative Mass  

NASA Astrophysics Data System (ADS)

The Schwarzschild solution to the matter free, spherically symmetric Einstein equations has one free parameter, the mass. But the mass can be of any sign. What is the meaning of the negative mass solutions? The answer to this question for the case of a pure Schwarzschild negative mass black solution is still elusive, however, in this essay, we will consider negative mass solutions within a Schwarzschild-de Sitter geometry. We show that there exist reasonable configurations of matter, bubbles of distributions of matter, that satisfy the dominant energy condition everywhere, that are nonsingular and well behaved everywhere, but correspond to the negative mass Schwarzschild-de Sitter geometry outside the matter distribution. These negative mass bubbles could occur as the end state of a quantum tunneling transition.

Belletête, Jonathan; Paranjape, M. B.

2013-06-01

381

A spherical aberration corrector using space charge  

NASA Astrophysics Data System (ADS)

The use of space charge for the correction of spherical aberration in focused ion beam systems has been investigated. A negative space charge cloud can be formed to reduce the spherical aberration of a lens for ions or for electrons, depending on the details of the space charge distribution. Spherical aberration is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents used for milling or deposition, because it results in large tails on the current density distribution. A space charge distribution (cloud) can be produced with a small electron gun inside an electrostatic lens that can reduce this problem.

Chao, Liang-Chiun

1998-12-01

382

CHARGE Association  

PubMed Central

We present here a case of 17-year-old boy from Kolkata presenting with obesity, bilateral gynecomastia, mental retardation, and hypogonadotrophic hypogonadism. The patient weighed 70 kg and was of 153 cm height. Facial asymmetry (unilateral facial palsy), gynecomastia, decreased pubic and axillary hair, small penis, decreased right testicular volume, non-palpable left testis, and right-sided congenital inguinal hernia was present. The patient also had disc coloboma, convergent squint, microcornea, microphthalmia, pseudohypertelorism, low set ears, short neck, and choanalatresia. He had h/o VSD repaired with patch. Laboratory examination revealed haemoglobin 9.9 mg/dl, urea 24 mg/dl, creatinine 0.68 mg/dl. IGF1 77.80 ng/ml (decreased for age), GH <0.05 ng/ml, testosterone 0.25 ng/ml, FSH-0.95 ?IU/ml, LH 0.60 ?IU/ml. ACTH, 8:00 A.M cortisol, FT3, FT4, TSH, estradiol, DHEA-S, lipid profile, and LFT was within normal limits. Prolactin was elevated at 38.50 ng/ml. The patient's karyotype was 46XY. Echocardiography revealed ventricularseptal defect closed with patch, grade 1 aortic regurgitation, and ejection fraction 67%. Ultrasound testis showed small right testis within scrotal sac and undescended left testis within left inguinal canal. CT scan paranasal sinuses revealed choanalatresia and deviation of nasal septum to the right. Sonomammography revealed bilateral proliferation of fibroglandular elements predominantly in subareoalar region of breasts. MRI of brain and pituitary region revealed markedly atrophic pituitary gland parenchyma with preserved infundibulum and hypothalamus and widened suprasellar cistern. The CHARGE association is an increasingly recognized non-random pattern of congenital anomalies comprising of coloboma, heart defect, choanal atresia, retarded growth and development, genital hypoplasia, ear abnormalities, and/or deafness.[1] These anomalies have a higher probability of occurring together. In this report, we have described a boy with CHARGE association. PMID:23565479

Chakraborty, Semanti; Chakraborty, Jayanta

2012-01-01

383

Extracted current saturation in negative ion sources  

SciTech Connect

The extraction of negatively charged particles from a negative ion source is one of the crucial issues in the development of the neutral beam injector system for future experimental reactor ITER. Full 3D electrostatic particle-in-cell Monte Carlo collision code - ONIX [S. Mochalskyy et al., Nucl. Fusion 50, 105011 (2010)] - is used to simulate the hydrogen plasma behaviour and the extracted particle features in the vicinity of the plasma grid, both sides of the aperture. It is found that the contribution to the extracted negative ion current of ions born in the volume is small compared with that of ions created at the plasma grid walls. The parametric study with respect to the rate of negative ions released from the walls shows an optimum rate. Beyond this optimum, a double layer builds-up by the negative ion charge density close to the grid aperture surface reducing thus extraction probability, and therefore the extracted current. The effect of the extraction potential and magnetic field magnitudes on the extraction is also discussed. Results are in good agreement with available experimental data.

Mochalskyy, S.; Lifschitz, A. F.; Minea, T. [LPGP, University Paris-Sud 11, bat 210, 15 rue G. Clemenceau-Orsay, F91405 (France)

2012-06-01

384

Structure of the Dominant Negative S17N Mutant of Ras  

SciTech Connect

The use of the dominant negative mutant of Ras has been crucial in elucidating the cellular signaling of Ras in response to the activation of various membrane-bound receptors. Although several point mutants of Ras exhibit a dominant negative effect, the asparagine to serine mutation at position 17 (S17N) remains the most popular and the most effective at inhibiting the activation of endogenous Ras. It is now widely accepted that the dominant negative effect is due to the ability of the mutant to sequester upstream activators and its inability to activate downstream effectors. Here, we present the crystal structure of RasS17N in the GDP-bound form. In the three molecules that populate the asymmetric unit, the Mg{sup 2+} ion that normally coordinates the {beta}-phosphate is absent because of steric hindrance from the Asn17 side chain. Instead, a Ca{sup 2+} ion is coordinating the {alpha}-phosphate. Also absent from one molecule is electron density for Phe28, a conserved residue that normally stabilizes the nucleotide's guanine base. Except for Phe28, the nucleotide makes conserved interactions with Ras. Combined, the inability of Phe28 to stabilize the guanine base and the absence of a Mg{sup 2+} ion to neutralize the negative charges on the phosphates explain the weaker affinity of GDP for Ras. Our data suggest that the absence of the Mg{sup 2+} should also dramatically affect GTP binding to Ras and the proper positioning of Thr35 necessary for the activation of switch 1 and the binding to downstream effectors, a prerequisite for the triggering of signaling pathways.

Nassar, N.; Singh, K; Garcia-Diaz, M

2010-01-01

385

On-demand electrostatic droplet charging and sorting  

PubMed Central

This study reports a droplet-based microfluidic device for on-demand electrostatic droplet charging and sorting. This device combines two independent modules: one is a hydrodynamic flow focusing structure to generate water-in-oil droplets, and the other is the two paired-electrodes for charging and sorting of the droplets. Depending on the polarity on charging electrodes, water-in-oil droplets can be electrostatically charged positively or negatively, followed by automatic real-time electric sorting. This approach will be useful when preformed droplets, with a positive, a negative, or with no charge, need to be manipulated for further on-chip droplet manipulation. PMID:21772936

Ahn, Byungwook; Lee, Kangsun; Panchapakesan, Rajagopal; Oh, Kwang W.

2011-01-01

386

Effect of Absorbed Water on Space Charge Properties of Polyimide  

Microsoft Academic Search

Space charge distributions in polyimide (PI) films strongly depend upon electric field, temperature, water content and so on. When a dc field was applied to as-received PI films kept in the atmosphere, whose water contents were ca. 0.9 wt.%, four kinds of space charges were observed, i.e., positive- and negative-homo space charges in the vicinity of the electrodes and negative-

Kazue Kaneko; Takashi Ozaki; Emi Nakane; Yasuo Suzuoki; Teruyoshi Mizutani

2007-01-01

387

Stepwise oscillatory circuits of a DNA molecule.  

PubMed

A DNA molecule is characterized by a stepwise oscillatory circuit where every base pair is a capacitor, every phosphate bridge is an inductance, and every deoxyribose is a charge router. The circuitry accounts for DNA conductivity through both short and long distances in good agreement with experimental evidence that has led to the identification of the so-called super-exchange and multiple-step hopping mechanisms. However, in contrast to the haphazard hopping and super-exchanging events, the circuitry is a well-defined charge transport mechanism reflecting the great reliability of the genetic substance in delivering electrons. Stepwise oscillatory charge transport through a nucleotide sequence that directly modulates the oscillation frequency may have significant biological implications. PMID:19669574

Xu, Kunming

2009-08-01

388

Tuning cluster reactivity by charge state and composition: experimental and theoretical investigation of CO binding energies to Ag(n)Au(m)(+/-) (n + m = 3).  

PubMed

Temperature-dependent gas-phase reaction kinetics measurements and equilibrium thermodynamics under multicollision conditions in conjunction with ab initio DFT calculations were employed to determine the binding energies of carbon monoxide to triatomic silver-gold binary cluster cations and anions. The binding energies of the first CO molecule to the trimer clusters increase with increasing gold content and with changing charge from negative to positive. Thus, the reactivity of the binary clusters can be sensitively tuned by varying charge state and composition. Also, multiple CO adsorption on the clusters was investigated. The maximum number of adsorbed CO molecules was found to strongly depend on cluster charge and composition as well. Most interestingly, the cationic carbonyl complex Au(3)(CO)(4)(+) is formed at cryogenic temperature, whereas for the anion, only two CO molecules are adsorbed, leading to Au(3)(CO)(2)(-). All other trimer clusters adsorb three CO molecules in the case of the cations and are completely inert to CO in our experiment in the case of the anions. PMID:21214279

Popolan, Denisia M; Nössler, Melanie; Mitri?, Roland; Bernhardt, Thorsten M; Bonaci?-Koutecký, Vlasta

2011-02-17

389

Kriging without negative weights  

SciTech Connect

Under a constant drift, the linear kriging estimator is considered as a weighted average of n available sample values. Kriging weights are determined such that the estimator is unbiased and optimal. To meet these requirements, negative kriging weights are sometimes found. Use of negative weights can produce negative block grades, which makes no practical sense. In some applications, all kriging weights may be required to be nonnegative. In this paper, a derivation of a set of nonlinear equations with the nonnegative constraint is presented. A numerical algorithm also is developed for the solution of the new set of kriging equations.

Szidarovszky, F.; Baafi, E.Y.; Kim, Y.C.

1987-08-01

390

Ion-Ion Reactions with Fixed-Charge Modified Proteins to Produce Ions in a Single, Very High Charge State  

PubMed Central

Electrospray ionization (ESI) of denatured proteins produces a mass spectrum with a broad distribution of multiply charged ions. Attaching fixed positive charges, specifically quaternary ammonium groups, to proteins at their carboxylic acid groups generates substantially higher charge states compared to the corresponding unmodified proteins in positive-mode ESI. Ion-ion reactions of these modified proteins with reagent anions leads to charge reduction by proton transfer. These proton transfer reactions cannot remove charge from the quaternary ammonium groups, which do not have a proton to transfer to the anion. Thus, one might expect charge reduction to stop at a single charge state equal to the number of fixed charges on the modified protein. However, ion-ion reactions yield charge states lower than this number of fixed charges due to anion attachment (adduction) to the proteins. Charge reduction via ion-molecule reactions involving gas-phase bases also give adducts on the modified protein ions in low charge states. Such adducts are avoided by keeping the ions in charge states well above the number of fixed charges. In the present work protein ions were selectively “parked” within an ion trap mass spectrometer in a high charge state by mild radiofrequency excitation that dramatically slows their ion-ion reaction rate—a technique termed “ion parking”. The combination of ion parking with the fixed-charge modified proteins permits generation of a large population of ions in a single, very high charge state. PMID:19802328

Frey, Brian L.; Krusemark, Casey J.; Ledvina, Aaron R.; Coon, Joshua J.; Belshaw, Peter J.

2008-01-01

391

Deciphering the "chemical" nature of the exotic isotopes of hydrogen by the MC-QTAIM analysis: the positively charged muon and the muonic helium as new members of the periodic table.  

PubMed

This report is a primarily survey on the chemical nature of some exotic species containing the positively charged muon and the muonic helium, i.e., the negatively charged muon plus helium nucleus, as exotic isotopes of hydrogen, using the newly developed multi-component quantum theory of atoms in molecules (MC-QTAIM) analysis, employing ab initio non-Born-Oppenhiemer wavefunctions. Accordingly, the "atoms in molecules" analysis performed on various asymmetric exotic isotopomers of the hydrogen molecule, recently detected experimentally [Science, 2011, 331, 448], demonstrates that both the exotic isotopes are capable of forming atoms in molecules and retaining the identity of hydrogen atoms. Various derived properties of atomic basins containing the muonic helium cast no doubt that apart from its short life time, it is a heavier isotope of hydrogen while the properties of basins containing the positively charged muon are more remote from those of the orthodox hydrogen basins, capable of appreciable donation of electrons as well as large charge polarization. However, with some tolerance, they may also be categorized as hydrogen basins though with a smaller electronegativity. All in all, the present study also clearly demonstrates that the MC-QTAIM analysis is an efficient approach to decipher the chemical nature of species containing exotic constituents, which are difficult to elucidate by experimental and/or alternative theoretical schemes. PMID:24569859

Goli, Mohammad; Shahbazian, Shant

2014-04-14

392

Testing for Life's Molecules  

NSDL National Science Digital Library

In this activity, learners conduct tests for proteins, glucose, and starch. At the beginning of the activity, learners choose three items to test: one known to be ânever alive," one known to be âonce was alive,â and one mystery item. In addition, each station includes a positive control. By the end of the experiment, learners should be familiar with some of the major organic molecules and should recognize that living things, and substances derived from them, are made of organic molecules. Use this activity to bring in topics surrounding nutrition, health, and digestion--since our bodies are made up of organic molecules, we need each of these molecules as nutrients in our food.

Salter, Irene

2012-09-28

393

Of Molecules and Models.  

ERIC Educational Resources Information Center

Presents an activity in which models help students visualize both the DNA process and transcription. After constructing DNA, RNA messenger, and RNA transfer molecules; students model cells, protein synthesis, codons, and RNA movement. (MDH)

Brinner, Bonnie

1992-01-01

394

No to negative data  

SciTech Connect

A frequent criticism in biology is that we don’t publish our negative data. As a result, the literature has become biased towards papers that favor specific hypotheses1. Some scientists have become so concerned about this trend that they have created journals dedicated to publishing negative results (e.g. the Journal of Negative Results in Biomedicine). Personally, I don’t think they should bother. I say this because I believe negative results are not worth publishing. Rest assured that I do not include drug studies that show a lack of effectiveness towards a specific disease or condition. This type of finding is significant in a societal context, not a scientific one, and thus we all have a vested interest in seeing this type of result published. I am talking about a set of experimental results that fail to support a particular hypothesis. The problem with these types of negative results is that they don’t actually advance science. Science is a set of ideas that can be supported by observations. A negative result does not support any specific idea, but only tells you what isn’t right. Well, there are only a small number of potential hypotheses that are correct, but essentially an infinite number of ideas are not correct. I don’t want to waste my time reading a paper about what doesn’t happen, just about those things that do. I can remember a positive result because I can associate it with a specific concept. What do I do with a negative one? It is hard enough to following the current literature. A flood of negative results would make that task all but impossible

Wiley, H. S.

2008-04-01

395

Electronic spectroscopy of diatomic molecules  

NASA Technical Reports Server (NTRS)

This article provides an overview of the principal computational approaches and their accuracy for the study of electronic spectroscopy of diatomic molecules. We include a number of examples from our work that illustrate the range of application. We show how full configuration interaction benchmark calculations were instrumental in improving the understanding of the computational requirements for obtaining accurate results for diatomic spectroscopy. With this understanding it is now possible to compute radiative lifetimes accurate to within 10% for systems involving first- and second-row atoms. We consider the determination of the infrared vibrational transition probabilities for the ground states of SiO and NO, based on a globally accurate dipole moment function. We show how we were able to assign the a(sup "5)II state of CO as the upper state in the recently observed emission bands of CO in an Ar matrix. We next discuss the assignment of the photoelectron detachment spectra of NO and the alkali oxide negative ions. We then present several examples illustrating the state-of-the-art in determining radiative lifetimes for valence-valence and valence-Rydberg transitions. We next compare the molecular spectroscopy of the valence isoelectronic B2, Al2, and AlB molecules. The final examples consider systems involving transition metal atoms, which illustrate the difficulty in describing states with different numbers of d electrons.

Partridge, Harry; Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.

1994-01-01

396

Photoinduced Interfacial Charging and "Explosion" of Monolayer Pentacene  

E-print Network

Photoinduced Interfacial Charging and "Explosion" of Monolayer Pentacene Islands Liwei Chen interacting, -bonded molecules to construct inexpensive thin-film transistors (TFTs), typically is critical; for example, hydroxyl groups at the gate interface introduce electron trap states in polymer TFTs

397

Fabrication and characterization of controllable grain boundary arrays in solution-processed small molecule organic semiconductor films  

NASA Astrophysics Data System (ADS)

We have produced solution-processed thin films of 6,13-bis(tri-isopropyl-silylethynyl) pentacene with grain sizes from a few micrometers up to millimeter scale by lateral crystallization from a rectangular stylus. Grains are oriented along the crystallization direction, and the grain size transverse to the crystallization direction depends inversely on the writing speed, hence forming a regular array of oriented grain boundaries with controllable spacing. We utilize these controllable arrays to systematically study the role of large-angle grain boundaries in carrier transport and charge trapping in thin film transistors. The effective mobility scales with the grain size, leading to an estimate of the potential drop at individual large-angle grain boundaries of more than 1 volt. This result indicates that the structure of grain boundaries is not molecularly abrupt, which may be a general feature of solution-processed small molecule organic semiconductor thin films, where relatively high energy grain boundaries are typically formed. Transient measurements after switching from positive to negative gate bias or between large and small negative gate bias reveal reversible charge trapping, with time constants on the order of 10 s and trap densities that are correlated with grain boundary density. We suggest that charge diffusion along grain boundaries and other defects is the rate-determining mechanism of the reversible trapping.

Wo, Songtao; Headrick, Randall L.; Anthony, John E.

2012-04-01

398

Ultracold Giant Polyatomic Rydberg Molecules: Coherent Control of Molecular Orientation  

NASA Astrophysics Data System (ADS)

We predict the existence of a class of ultracold giant molecules formed from trapped ultracold Rydberg atoms and polar molecules. The interaction which leads to the formation of such molecules is the anisotropic, long-range charge-dipole interaction. We show that prominent candidate molecules such as deuterated hydroxyl (OD) and KRb should bind to Rydberg rubidium atoms, with energies Eb?5-25GHz at distances R?0.1-1?m. These molecules form in double wells, mimicking chiral molecules, with each well containing a particular dipole orientation. We prepare a set of correlated dressed electron-dipole eigenstates which are used in an on-resonance Raman scheme to coherently control the molecular dipole orientation.

Rittenhouse, Seth T.; Sadeghpour, H. R.

2010-06-01

399

Communication: Tailoring the optical gap in light-harvesting molecules.  

PubMed

Systematically varying the optical gap that is associated with charge-transfer excitations is an important step in the design of light-harvesting molecules. So far the guidance that time-dependent density functional theory could give in this process was limited by the traditional functionals' inability to describe charge-transfer excitations. We show that a nonempirical range-separated hybrid approach allows to reliably predict charge-transfer excitations for molecules of practically relevant complexity. Calculated absorption energies agree with measured ones. We predict from theory that by varying the number of thiophenes in donor-acceptor-donor molecules, the energy of the lowest optical absorption can be tuned to the lower end of the visible spectrum. Saturation sets in at about five thiophene rings. PMID:21513368

Karolewski, A; Stein, T; Baer, R; Kümmel, S

2011-04-21

400

Single-molecule studies of the effect of spermidine on DNA mechanics and viral DNA packaging  

NASA Astrophysics Data System (ADS)

Polyamine ions such as spermidine3+, along with monovalent and divalent salt ions, screen the negatively charged backbone of dsDNA and thereby facilitate processes in which DNA is confined in small spaces, such as viral DNA packaging. We use optical tweezers to directly manipulate single DNA molecules and have made preliminary measurements of the effect of spermidine on DNA elasticity, condensation, and viral packaging. We determine the concentration of spermidine3+ at which dsDNA condenses in the presence of Mg2+ and Na+ and report a monotonic increase in stretch modulus and decrease in persistence length at incremental spermidine concentrations up to the concentration at which dsDNA condenses. We also discuss the effect of spermidine on DNA packaging in bacteriophage phi29.

Keller, Nicholas; Smith, Douglas E.

2012-10-01