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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

Ion-based materials derived from positively and negatively charged chloride complexes of ?-conjugated molecules.  

PubMed

Oriented salts from planar charged species were prepared by combining positively and negatively charged receptor-anion complexes with similar geometries using dicationic and electronically neutral ?-conjugated receptors. Phenylene- or pyrimidine-bridged bis(imidazolium) dicationic anion receptors formed monocationic receptor-Cl(-) complexes that were accompanied by a free Cl(-). This free Cl(-) was subsequently captured by pyrrole-based neutral anion receptors to form negatively charged receptor-Cl(-) complexes. The ion pair of the resulting positively and negatively charged planar receptor-Cl(-) complexes could produce a supramolecular octane gel, adopting a lamellar self-organized structure in its xerogel state. On the other hand, the solid-state ion pairs had hexagonal columnar mesophases, which formed via alternate stacking of the positively and negatively charged planar receptor-Cl(-) complexes. By use of the flash-photolysis time-resolved microwave conductivity technique, the one-dimensional charge-carrier transporting property, with a mobility of 0.05 cm(2) V(-1) s(-1), was determined for the newly prepared solid-state ion pairs. PMID:24053173

Dong, Bin; Sakurai, Tsuneaki; Bando, Yuya; Seki, Shu; Takaishi, Kazuto; Uchiyama, Masanobu; Muranaka, Atsuya; Maeda, Hiromitsu

2013-10-01

3

Negative ions of polyatomic molecules.  

PubMed

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

1980-06-01

4

Electrokinetic concentration of charged molecules  

DOEpatents

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

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

2002-01-01

5

Positive and negative cluster ions and multiply charged ions produced from frozen nitrogen, carbon monoxide and oxygen molecules under energetic, heavy-ion impact  

NASA Astrophysics Data System (ADS)

Positive and negative cluster ions have been observed in nitrogen, carbon monoxide and oxygen targets frozen at 15 K under 1.5 MeV u-1 Ar13+ projectile ion impact. For positive cluster ions obtained from frozen nitrogen targets, even-number cluster series ions N+2n for n > 2 predominate over odd-number cluster series N+2n+1. This is in sharp contrast to the fact that odd-number cluster series N-2n+1 are dominant in negative nitrogen cluster ions. Anions of N-2, etc., which do not exist in the gas phase, have been observed. Various positive cluster ions from frozen carbon monoxide targets have been observed, although pure carbon clusters C-n are dominant in the negative cluster ions. Clusters ions from frozen oxygen targets are formed with clustering element O3; the O+3n+2 series are the dominant positive cluster ions, whereas the O-3n+3 series are much stronger than either O-3n+2 as regards the negative cluster ions. In addition multiply charged atomic ions have been observed from all the frozen targets investigated; these can be explained qualitatively as being due to Coloumbic explosion of multiply charged molecular ions originally produced in primary energetic ion collisions.

Tonuma, Tadao; Kumagai, Hidekazu; Matsuo, Takashi; Shibata, Hiromi; Tawara, Hiroyuki

1994-08-01

6

Atomic scale control of single molecule charging.  

PubMed

A scanning tunneling microscope was used to study charging of single copper phthalocyanine molecules adsorbed on an ultrathin Al(2)O(3) film grown on a NiAl(110) surface. A double-barrier tunnel junction is formed by a vacuum barrier between the tip and the molecule and an oxide barrier between the molecule and the NiAl. In this geometry the molecule can be charged by the tunneling electrons. This charging was found to be strongly dependent on the position of the tip above the molecule and the applied bias voltage. PMID:16613439

Mikaelian, G; Ogawa, N; Tu, X W; Ho, W

2006-04-01

7

Charging Model and Dust Atoms & Molecules  

NASA Astrophysics Data System (ADS)

The condition for the validity of the orbital motion limited (OML) theory is reviewed with reference to the calculation of the floating potential attained by a spherical body immersed in a plasma. It is shown that the OML theory is never satisfied for some cases. Then a new approach of obtaining floating potential which in a way answers the questions raised is presented. Further assuming conservation of entropy, an important relation is obtained between the maximum potential and therefore the charge of the dust grain and the temperature of the electrons. The Thomas-Fermi equation is derived for the potential of a dust grain in a nondegenerate plasma suggesting the existence of dust atom with a well defined atomic radius. Furthermore, based on the Born-Oppenheimer approximation, the notion of a dust-grain molecule is introduced in which the protons act like a kind of "glue" which binds two negatively charged dust grains together, and the motion of the grains have little influence on that binding force. Finally, considering the weak interaction between the proton clouds of two dust grains, an expression of exchange energy is obtained.You are responsible for and will need to convert your document to PDF. Check the final version (including content, special characters, fonts etc.) to ensure that everything is correct before accepting the final submission.

Ehsan, Zahida; Tsintsadze, Nodar; Poedts, Stefaan

2010-05-01

8

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

PubMed

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

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

2014-06-17

9

Controlling charge transport in single molecules using electrochemical gate.  

PubMed

We have studied charge transport through single molecules covalently bound to two gold electrodes in electrolytes by applying a voltage between the two electrodes and a reference electrode (gate). This electrochemical gating can effectively control the current through the molecules, depending on the electronic properties of the molecules. For electrochemically inactive molecules, such as 4,4'-bipyridine and 1,4'-benzenedithiol, the gate voltage influences the transport current only slightly (less than 30%). This lack of significant gate effect is attributed to the large LUMO-HOMO gaps of the molecules and the screening of the gate field by the two electrodes. For nitro-oligo(phenylene ethynylene) (OPE-NO2), which undergoes multiple irreversible reductions at negative gate voltages, the current through the molecules can be modulated several folds by the gate. This gate effect is irreversible and associated with the reduction of the NO2 group to different products that have different electron withdrawing capabilities from the conjugate backbone of the molecule. The most interesting molecules are perylene tetracarboxylic diimide compounds (PTCDI), which exhibit fully reversible redox reactions. The current through PTCDI can be reversibly varied and controlled over three orders of magnitude with the gate. Such a large gate effect is related to a redox state-mediated electron transport process. PMID:16512367

Li, Xiulan; Xu, Bingqian; Xiao, Xiaoyin; Yang, Xiaomei; Zang, Ling; Tao, Nongjian

2006-01-01

10

Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons  

NASA Astrophysics Data System (ADS)

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

Gao, Juehan; Berden, Giel; Oomens, Jos

2014-06-01

11

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

12

Large negative differential conductance in single-molecule break junctions  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

13

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

14

Positively Charged Polyethylenimines Enhance Nasal Absorption of the Negatively Charged Drug, Low Molecular Weight Heparin  

PubMed Central

This study tests the hypothesis that positively charged polyethylenimines (PEIs) enhance nasal absorption of low molecular weight heparin (LMWH) by reducing the negative surface charge of the drug molecule. Physical interactions between PEIs and LMWH were studied by Fourier transform infrared (FTIR) spectroscopy, particle size analysis, conductivity measurements, zeta potential analysis, and azure A assay. The efficacy of PEIs in enhancing nasal absorption of LMWH was studied by administering LMWH formulated with PEI into the nose of anesthetized rats and monitoring drug absorption by measuring plasma anti-factor Xa activity. The metabolic stability of LMWH was evaluated by incubating the drug in rat nasal mucosal homogenates. FTIR spectra of the LMWH-PEI formulation showed a shift in peak position compared to LMWH or PEI alone. Decreases in conductivity, zeta potential and the amount of free LMWH in the PEI-LMWH formulation, as revealed by azure A assay, suggest that PEIs possibly neutralize the negative surface charge of LMWH. The efficacy of PEI in enhancing the bioavailability of nasally administered LMWH can be ranked as PEI-1000 KDa ? PEI-750 KDa > PEI-25 KDa. When PEI-1000 KDa was used at a concentration of 0.25%, there was a 4-fold increase in both the absolute and relative bioavailabilities of LMWH compared to the control formulation. Overall, these results indicate that polyethylenimines can be used as potential carriers for nasally administered LMWHs. PMID:17023085

Yang, Tianzhi; Hussain, Alamdar; Bai, Shuhua; Khalil, Ikramy A.; Harashima, Hideyoshi; Ahsan, Fakhrul

2007-01-01

15

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

PubMed

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

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

2015-03-01

16

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

17

Negative Differential Resistance in Insulating Systems: From Molecules to Polymers  

NASA Astrophysics Data System (ADS)

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

Pati, Swapan

2007-03-01

18

Mean field theory of charged dendrimer molecules.  

PubMed

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

Lewis, Thomas; Pryamitsyn, Victor; Ganesan, Venkat

2011-11-28

19

Contactless measurements of charge migration within single molecules  

SciTech Connect

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

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

2010-06-07

20

Charge Loss in Gas-Phase Multiply Negatively Charged Oligonucleotides Iwona Anusiewicz,,, Joanna Berdys-Kochanska,, Cezary Czaplewski, Monika Sobczyk,,  

E-print Network

Charge Loss in Gas-Phase Multiply Negatively Charged Oligonucleotides Iwona Anusiewicz,,,§ Joanna gaseous samples of negatively charged oligonucleotides undergo extremely slow (i.e., over 1-1000 s) charge are negatively charged. The study is aimed at determining the rate at which an electron is detached from

Simons, Jack

21

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

PubMed

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

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

2015-01-21

22

Charge Exchange Processes for Highly Charged Ion -Atom, Molecule  

E-print Network

) Charge Exchange Processes of HCI's are very important for understanding the edge plasma behavior process are greatly concerned with the cooling of the plasma. We paid attention to the following thing of Chemistry and Physics #12;The detail of electron transfer process by HCI's-Atom collision has been made

Princeton Plasma Physics Laboratory

23

Increased negatively charged nitrogen-vacancy centers in fluorinated diamond  

SciTech Connect

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

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

2013-07-29

24

Imaging the charge distribution within a single molecule.  

PubMed

Scanning tunnelling microscopy and atomic force microscopy can be used to study the electronic and structural properties of surfaces, as well as molecules and nanostructures adsorbed on surfaces, with atomic precision, but they cannot directly probe the distribution of charge in these systems. However, another form of scanning probe microscopy, Kelvin probe force microscopy, can be used to measure the local contact potential difference between the scanning probe tip and the surface, a quantity that is closely related to the charge distribution on the surface. Here, we use a combination of scanning tunnelling microscopy, atomic force microscopy and Kelvin probe force microscopy to examine naphthalocyanine molecules (which have been used as molecular switches) on a thin insulating layer of NaCl on Cu(111). We show that Kelvin probe force microscopy can map the local contact potential difference of this system with submolecular resolution, and we use density functional theory calculations to verify that these maps reflect the intramolecular distribution of charge. This approach could help to provide fundamental insights into single-molecule switching and bond formation, processes that are usually accompanied by the redistribution of charge within or between molecules. PMID:22367099

Mohn, Fabian; Gross, Leo; Moll, Nikolaj; Meyer, Gerhard

2012-04-01

25

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

E-print Network

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

S. E. Korenblit; Kieun Lee

2010-03-07

26

Colloidal stability of negatively charged cellulose nanocrystalline in aqueous systems.  

PubMed

Colloidal stability of negatively charged cellulose nanocrystalline (CNC) in the presence of inorganic and organic electrolytes was investigated by means of dynamic light scattering and atomic force microscopy. CNC could be well dispersed in distilled water due to the electrostatic repulsion among negatively charged sulfate ester groups. Increasing the concentration of inorganic cation ions (Na(+) and Ca(2+)) resulted in CNC aggregation. CNC in divalent cation ion Ca(2+) solution exhibited less stability than that in monovalent cation ion Na(+) solution. Organic low-molecular-weight electrolyte sodium dodecyl sulfate (SDS) favored the stability of CNC suspension, whereas organic high-molecular-weight electrolyte sodium carboxymethyl cellulose (CMC) induced CNC particle aggregation due to intermolecular bridging interaction or entanglement. Cationic polyacrylamide (CPAM) caused a serious aggregation of CNC particles even at low concentration of CPAM. At low ionic strength (Na(+), 1 mM), CNC were stable in aqueous solution at the pH range of 2-11. PMID:24751088

Zhong, Linxin; Fu, Shiyu; Peng, Xinwen; Zhan, Huaiyu; Sun, Runcang

2012-09-01

27

Polynucleotide Adsorption to Negatively Charged Surfaces in Divalent Salt Solutions  

PubMed Central

Polynucleotide adsorption to negatively charged surfaces via divalent ions is extensively used in the study of biological systems. We analyze here the adsorption mechanism via a self-consistent mean-field model that includes the pH effect on the surface-charge density and the interactions between divalent ions and surface groups. The adsorption is driven by the cooperative effect of divalent metal ion condensation along polynucleotides and their reaction with the surface groups. Although the apparent reaction constants are enhanced by the presence of polynucleotides, the difference between reaction constants of different divalent ions at the ideal condition explains why not all divalent cations mediate DNA adsorption onto anionic surfaces. Calculated divalent salt concentration and pH value variations on polynucleotide adsorption are consistent with atomic force microscope results. Here we use long-period x-ray standing waves to study the adsorption of mercurated-polyuridylic acid in a ZnCl2 aqueous solution onto a negatively charged hydroxyl-terminated silica surface. These in situ x-ray measurements, which simultaneously reveal the Hg and Zn distribution profiles along the surface normal direction, are in good agreement with our model. The model also provides the effects of polyelectrolyte line-charge density and monovalent salt on adsorption. PMID:16449197

Cheng, Hao; Zhang, Kai; Libera, Joseph A.; Olvera de la Cruz, Monica; Bedzyk, Michael J.

2006-01-01

28

Electron interactions with positively and negatively multiply charged biomolecular clusters  

NASA Astrophysics Data System (ADS)

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

Feketeová, Linda

2012-07-01

29

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

30

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

31

Complexes of Negatively Charged Polypeptides with Cationic Lipids  

NASA Astrophysics Data System (ADS)

Complexes of cationic lipids with oppositely charged proteins are promising candidates for new biomolecular materials. In addition to being used as a direct vehicle for protein transfection, they also find applications as templates for synthesis of molecular sieves. In spite of these wide ranging applications, the structure and interactions in these complexes have largely remained unclear. Here we report on the study of complexes formed between the cationic lipid didodecyldimethylammonium bromide (DDAB) with negatively charged polypeptide poly glutamic acid (PGA) both in the presence and absence of the neutral lipid dilauroylglycerophosphocholine (DLPC). X-ray diffraction of the complexes indicates a condensed lamellar lipid structure with the polypeptide intercalated between the layers. We present a comprehensive phase diagram on this system based on X-ray diffraction data. This work is supported in part by grants NSF DMR-9624091, PRF-31352 AC7, and CU LAR STP/UC 96-118.

Subramanian, G.; Li, Youli; Safinya, Cyrus R.

1997-03-01

32

Attractive Interactions Between Negatively Charged Dust Particles in a Plasma  

NASA Astrophysics Data System (ADS)

Plasma dust particle interactions, charges, and screening lengths are derived from measurements of time-dependent particle positions in a simplified geometry. The magnitude and structure of the ion wakefield potential below a negatively-charged dust particle levitated in the plasma sheath region were measured as functions of the pressure and interparticle spacing. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy dust collisions between different mass particles in a well-defined electrostatic potential that constrained the dynamics of the collisions to be one dimensional. Typical peak attractions varied between 60 and 230 fN while the peak particle-particle repulsion was on the order of 60 fN. Random thermal motion of the particles contributed to observable rates for transitions between different equilibrium configurations of vertically separated particles. We also observed a slight potential barrier that impeded the formation of vertically aligned pairs. The influence of nearest- and non-nearest-neighbor interactions on calculated particle parameters are examined using several methods. Implications for plasma / surface interactions and plasma dielectric charging will be discussed. This work was supported by the Division of Material Sciences, BES, Office of Science, U. S. Department of Energy and Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Hebner, Greg; Riley, Merle

2003-10-01

33

Enhanced Single Molecule Mass Spectrometry via Charged Metallic Clusters.  

PubMed

Nanopore sensing is a label-free method for characterizing water-soluble molecules. The ability to accurately identify and characterize an analyte depends on the residence time of the molecule within the pore. It is shown here that when a Au25(SG)18 metallic cluster is bound to an ?-hemolysin (?HL) nanopore, the mean residence time of polyethylene glycol (PEG) within the pore is increased by over 1 order of magnitude. This leads to an increase in the range of detectable PEG sizes and improves the peak resolution within the PEG-induced current blockade distribution. A model describing the relationship between the analyte residence time and the width of the peaks in the current blockade distribution is included. Finally, evidence is presented that shows the Coulombic interaction between the charged analyte and cluster plays an important role in the residence time enhancement, which suggests the cluster-based approach could be used to increase the residence time of a wide variety of charged analyte molecules. PMID:25343748

Angevine, Christopher E; Chavis, Amy E; Kothalawala, Nuwan; Dass, Amala; Reiner, Joseph E

2014-11-18

34

Adiabatic Charge Dynamics in Molecules Dissolved in A Polar Solvent. Application to Charge Migration in DNA  

NASA Astrophysics Data System (ADS)

We develop an adiabatic hopping model for charge migration through molecules dissolved in a polar liquid (water), based on an analytical approach [1]. The charge hopping between donor and acceptor states is due to a rare fluctuation of the solvent polarization forming a deeper well at the target places. The results are applied to the photoexcited hole migration in DNA [2] using the model parameters, obtained from the first principles studies. Theory can explain the length dependence of the transfer rate, becoming distant independent at long distances where correlations in fluctuations are weak, and one sees low absolute value of charge hopping rate, defined entirely by the slow kinetics of the solvent. Strong energy and weak temperature dependence of the transfer rate, observed experimentally can be due to the entropy control of water fluctuations at room temperature. Clarifying experiments are suggested. 1.A. L. Burin, et al, Phys. Rev. Lett. 86, 5616, 2001. 2.F. D. Lewis, et al, Nature 406, 51, 2000

Burin, A. L.; Berlin, Yu. A.; Kurnikov, I.; Ratner, M. A.

2002-03-01

35

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

36

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.

37

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

E-print Network

The meteorology of negative cloud-to-ground lightning strokes with large charge moment changes. [1] This study examined the meteorological characteristics of precipitation systems that produced 38, and W. A. Lyons (2013), The meteorology of negative cloud-to- ground lightning strokes with large charge

Cummer, Steven A.

38

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

NASA Astrophysics Data System (ADS)

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

Sangi Reddy, Pramod Reddy

39

Simple Bond-Charge Model for Potential-Energy Curves of Heteronuclear Diatomic Molecules  

Microsoft Academic Search

A model for the vibrational potential-energy functions of diatomic molecules, previously applied to homonuclear molecules only, is extended to 54 heteronuclear diatomic molecules in 93 different electronic states. Experimental Re and ke values are used to determine for each species the empirical bond-charge and bond-length parameters, q and ?, in the homopolar model potential W = W0 + (e2 ?

Raymond F. Borkman; Gary Simons; Robert G. Parr

1969-01-01

40

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

41

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

SciTech Connect

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

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

2012-07-15

42

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

SciTech Connect

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

Ghosh, Samiran; Bharuthram, R.; Khan, Manoranjan; Gupta, M. R. [University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg (South Africa); Centre for Plasma Studies, Faculty of Science, Jadavpur University, Kolkata-700 032 (India)

2006-11-15

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

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

45

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

46

Controlling single-molecule negative differential resistance in a double-barrier tunnel junction.  

PubMed

We observed the transition from negative differential resistance (NDR) to the absence of NDR in the differential conductance (dI/dV) spectra of single copper-phthalocyanine (CuPc) molecules adsorbed on one, two, and three atomic layers of NaBr grown on a NiAl(110) substrate. Through numerical simulation, this transition is attributed to two phenomena in the double-barrier tunnel junction: (i) the opposite bias dependence of the vacuum and NaBr barrier heights, and (ii) the changing barrier widths for CuPc molecules adsorbed on different layers of NaBr. PMID:18517901

Tu, X W; Mikaelian, G; Ho, W

2008-03-28

47

Calculating Henry?s Constants of Charged Molecules Using SPARC  

EPA Science Inventory

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

48

Negative-ion contribution to threshold peaks observed in vibrational excitation spectra of molecules by electron impact  

Microsoft Academic Search

The contribution of negative ions, formed by dissociative attachment, to threshold peaks reported in the vibrational excitation spectra of some molecules is discussed. It is concluded that negative ions formed in the energy range of the vibrational levels of a neutral molecule with no kinetic energy and a large cross section contribute significantly to threshold peaks or simulate threshold peaks

R. Azria; Y. LeCoat; J. P. Guillotin

1980-01-01

49

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

PubMed

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

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

2014-12-11

50

Interactions of Cationic Peptides and Ions with Negatively Charged Lipid Bilayers  

NASA Astrophysics Data System (ADS)

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

Taheri-Araghi, Sattar

51

Charge state control of molecules reveals modification of the tunneling barrier with intramolecular contrast.  

PubMed

From scanning tunneling microscopy and spectroscopy experiments it is shown that control over the charge-state of individual molecules adsorbed on surfaces can be obtained by choosing a substrate system with an appropriate workfunction. The distribution of the additional charge is studied using difference images. These images show marked intramolecular contrast. PMID:21428431

Swart, Ingmar; Sonnleitner, Tobias; Repp, Jascha

2011-04-13

52

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

53

Spatially ordered surfactant assemblies in the gas phase: negatively charged bis(2-ethylhexyl)sulfosuccinate-alkaline metal ion aggregates.  

PubMed

The formation and structural features of negatively charged aggregates of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) surfactant molecules in the gas phase have been investigated by electrospray ionization mass spectrometry (ESI-MS) and density functional theory calculations. Mainly driven by the interactions of alkali metal ions both with the oxygen atoms of the sulfonate group and with the succinate moiety of the AOT- anion, spatially ordered supramolecular assemblies, characterized by an internal core composed of surfactant counterions and hydrophilic head groups surrounded by the surfactant alkyl chains pointing outwards, are formed. Calculations have shown that surfactant self-organization in the gas phase is energetically favoured, the energy of formation of negatively charged aggregates from isolated AOTNa and AOT- being linearly related to the aggregation number. Information on the chelating properties of AOTNa towards clusters of inorganic salts was achieved by infusion of solutions at various AOTNa/metal salt (NaCl, NaBr, NaI, LiI, KCl, CsI, RbI) ratios in the ESI source of a mass spectrometer. A wide variety of negatively charged AOT-metal aggregates, some of them also incorporating halide (X-) ions, has been observed. Calculations have shown that the capture of a halide anion to give the AOTMX- species is favoured but the energetics of the process depends on the alkali metal and halide types. The use of energy-resolved mass spectrometry has allowed us to evaluate the stability of different complexes and to evaluate the role played by the metal ion. Overall, the present investigation supports the idea that, in the gas phase, mainly driven by electrostatic interactions, surfactant molecules are present as molecular aggregates characterized by a reverse micelle-like organization with an internal core formed by the surfactant counterions and head groups surrounded by the surfactant alkyl chains. These peculiar aggregates are able to incorporate ionic clusters in their hydrophilic core. PMID:19530148

Giorgi, Gianluca; Giocaliere, Elisa; Ceraulo, Leopoldo; Ruggirello, Angela; Liveri, Vincenzo Turco

2009-07-01

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

Nonlinear charge transport in the helicoidal DNA molecule.  

PubMed

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

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

2012-12-01

56

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

57

Interfacial charge transfer dynamics in small molecule-modified TiO2 nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

58

The involvement of the electrical double layer in the quenching of 9-aminoacridine fluorescence by negatively charged surfaces.  

PubMed

The addition of 9-aminoacridine monohydrochloride to carboxymethyl-cellulose particles or azolectin liposomes suspended in a low cation medium results in a quenching of its fluorescence. This quenching can be released on the addition of cations. The effectiveness of cations is related only to their valency in the series of salts tested, being monovalent less than divalent less than trivalent, and is independent of the associated anions. These results indicate an electrical rather than a chemical effect, and the relative effectiveness of the various cations can be predicted by the application of classical electrical double layer theory. Fluorescence quenching can also be released on protonation of the fixed negatively charged ionisable groups, and the quenching release curve follows the ionisation curve of these groups. We postulate that when 9-aminoacridine molecules are in the electrical diffuse layer adjacent to the charged surface their fluorescence is quenched, probably due to aggregate formation. As cations are added the 9-aminoacridine concentration at the surface falls as it is displaced into the bulk solution, where it shows a high fluorescence yield with a fluorescence lifetime of 16.3 ns. The fluorescence quenching is associated with an absorbance decrease, which is pronounced with carboxymethyl-cellulose particles and can probably be attributed to self-shielding. The negative charges carried by lipoprotein membranes are primarily due to carboxyl and phosphate groups. Therefore these results with carboxymethyl-cellulose (carboxyl) and azolectin (phosphate) support our earlier suggestion that 9-aminoacridine may be used to probe the electrical double layer associated with negatively charged biological membranes. PMID:26393

Searle, G F; Barber, J

1978-05-10

59

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

PubMed Central

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

2014-01-01

60

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

61

Entropic attraction condenses like-charged interfaces composed of self-assembled molecules.  

PubMed

Like-charged solid interfaces repel and separate from one another as much as possible. Charged interfaces composed of self-assembled charged-molecules such as lipids or proteins are ubiquitous. The present study shows that although charged lipid-membranes are sufficiently rigid, in order to swell as much as possible, they deviate markedly from the behavior of typical like-charged solids when diluted below a critical concentration (ca. 15 wt %). Unexpectedly, they swell into lamellar structures with spacing that is up to four times shorter than the layers should assume (if filling the entire available space). This process is reversible with respect to changing the lipid concentration. Additionally, the research shows that, although the repulsion between charged interfaces increases with temperature, like-charged membranes, remarkably, condense with increasing temperature. This effect is also shown to be reversible. Our findings hold for a wide range of conditions including varying membrane charge density, bending rigidity, salt concentration, and conditions of typical living systems. We attribute the limited swelling and condensation of the net repulsive interfaces to their self-assembled character. Unlike solids, membranes can rearrange to gain an effective entropic attraction, which increases with temperature and compensates for the work required for condensing the bilayers. Our findings provide new insight into the thermodynamics and self-organization of like-charged interfaces composed of self-assembled molecules such as charged biomaterials and supramolecular assemblies that are widely found in synthetic and natural constructs. PMID:22191627

Steiner, Ariel; Szekely, Pablo; Szekely, Or; Dvir, Tom; Asor, Roi; Yuval-Naeh, Naomi; Keren, Nir; Kesselman, Ellina; Danino, Dganit; Resh, Roy; Ginsburg, Avi; Guralnik, Vicky; Feldblum, Esther; Tamburu, Carmen; Peres, Menachem; Raviv, Uri

2012-02-01

62

The influence of negatively charged heavy ions on the kinetic Alfven wave in a cometary environment  

NASA Astrophysics Data System (ADS)

Kinetic Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of the kinetic Alfven wave in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species was modeled by drifting ring distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution was simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies ?^{*} < ?_{cH^{ +}} ( ? ? and ?_{cH^{ +}} being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the growth rate increases with increasing negatively charged oxygen ion densities while decreasing with increasing propagation angles, negative ion temperatures and negative ion mass.

Chandu, Venugopal; Savithri Devi, E.; Jayapal, R.; Samuel, George; Antony, S.; Renuka, G.

2012-05-01

63

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

E-print Network

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

Kovalev, Gennady V

2015-01-01

64

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

65

Giant negative magnetoresistance in semiconductors doped by multiply charged deep impurities S. D. Ganichev,* H. Ketterl, and W. Prettl  

E-print Network

Giant negative magnetoresistance in semiconductors doped by multiply charged deep impurities S. D negative magnetoresistance has been observed in bulk germanium doped with multiply charged deep impurities on a giant negative magnetoresistance in Ge which shows sizable ef- fects already at very small magnetic

Ganichev, Sergey

66

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

67

Keynote FIELD REGULATION OF SINGLE MOLECULE CONDUCTIVITY BY A CHARGED ATOM  

E-print Network

A new concept for a single molecule transistor is demonstrated (1). A single chargeable atom adjacent to a molecule shifts molecular energy levels into alignment with electrode levels, thereby gating current through the molecule. Seemingly paradoxically, the silicon substrate to which the molecule is covalently attached provides 2, not 1, effective contacts to the molecule. This is achieved because the single charged silicon atom is at a substantially different potential than the remainder of the substrate. Charge localization at one dangling bond is ensured by covalently capping all other surface atoms. Dopant level control and local Fermi level control can change the charge state of that atom. The same configuration is shown to be an effective transducer to an electrical signal of a single molecule detection event. Because the charged atom induced shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature. One electron is sufficient to achieve gating because high gate efficiency is achieved. Because one electron achieves gating, compared to ~10^5 in a modern transistor, enormous speed, and minimal power consumption are implied.

Robert A. Wolkow

68

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

NASA Astrophysics Data System (ADS)

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

Tennakone, K.

2012-04-01

69

Mechanism of the Interaction of 2-Glycoprotein I with Negatively Charged Phospholipid Membranes  

E-print Network

role in the blood coagulation cascade (3), in platelet aggregation (4-7), and in the course of interaction based on the crystal structure of 2GPI. The data suggest that 2GPI anchors to the membrane surface of thrombolytic diseases (3, 8). 2GPI preferentially binds to surfaces carrying negative charges. Prominent

Hammel, Michal - School of Biological Sciences, University of Missouri

70

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

E-print Network

Maximizing ion current by space-charge neutralization using negative ions and dust particles A, Princeton, New Jersey 08543 Received 11 January 2005; accepted 3 March 2005; published online 2 May 2005 Ion current extracted from an ion source ion thruster can be increased above the Child­Langmuir limit

71

The Controlled Introduction of Multiple Negative Charge at Single Amino Acid Sites in Subtilisin Bacillus lentus  

E-print Network

as a means of tailoring enzyme activity and speci®city, we have adopted this approach for the controlled and 217 in the S1 H site. Kinetic parameters for these chemically modi®ed mutant (CMM) enzymes were of the transition state of the hydrolytic reactions catalyzed. Each unit increase in negative charge resulted

Davis, Ben G.

72

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

E-print Network

CRYSTALLINE SILICON SURFACE PASSIVATION BY THE NEGATIVE-CHARGE- DIELECTRIC Al2O3 B. Hoex 1 , J, 31860 Emmerthal, Germany ABSTRACT In this contribution it will demonstrated that Al2O3 films synthesized it will be shown that the excellent surface passivation by Al2O3 can for a large part be attributed to a high fixed

73

Expression analysis of multiple myeloma CD138 negative progenitor cells using single molecule microarray readout  

PubMed Central

We present a highly sensitive bioanalytical microarray assay that enables the analysis of small genomic sample material. By combining an optimized cDNA purification step with single molecule cDNA detection on the microarray, the platform has improved sensitivity compared to conventional systems, allowing amplification-free determination of expression profiles with as little as 600 ng total RNA. Total RNA from cells was reverse transcribed into fluorescently labeled cDNA and purified employing a precipitation method that minimizes loss of cDNA material. The microarray was scanned on a fluorescence chip-reader with single molecule sensitivity. Using the newly developed platform we were able to analyze the RNA expression profile of a subpopulation of rare multiple myeloma CD138 negative progenitor (MM CD138neg) cells. The high-sensitivity microarray approach led to the identification of a set of 20 genes differentially expressed in MM CD138neg cells. Our work demonstrates the applicability of a straight-forward single-molecule DNA array technology to current topics of molecular and cellular cancer research, which are otherwise difficult to address due to the limited amount of sample material. PMID:23416329

Jacak, Jaroslaw; Schnidar, Harald; Muresan, Leila; Regl, Gerhard; Frischauf, Annemarie; Aberger, Fritz; Schütz, Gerhard J.; Hesse, Jan

2013-01-01

74

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

PubMed

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

Schill, Maria; Koslowski, Thorsten

2013-01-17

75

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

76

Evolution of structure and properties of neutral and negatively charged transition metal-coronene complexes: a comprehensive analysis.  

PubMed

The geometries, electronic and magnetic properties of neutral and negatively charged Mn(coronene)m (M = V and Ti; n, m = 1, 2) complexes were investigated using density functional theory. The results show that one V or Ti atom prefers to occupy the ?(6)-site in M(coronene)(0/-) complexes and to be sandwiched between the two coronene molecules in M(coronene)2(0/-) complexes. Two metal atoms always form a dimer and interact with one coronene molecule. The calculated vertical electron affinities and transition energies are in good agreement with experimental values. This lends considerable credence to the obtained ground state structure and validates the chosen computational method. The bond formation between metal atom and coronene is accounted for by 3d/4s-? bonds, as revealed by the molecular orbitals plots. The reason why the peripheral ring site binds metal most effectively has been analyzed systematically by ? electron content, aromaticity and average charge on carbon atoms. The electron localization function shows that there is perfect electron delocalization in these complexes. Furthermore, the magnetic moments of V(coronene)(0/-) and Ti(coronene)(-) are found to be substantially enhanced over the corresponding free metal atom; the magnetic moment of the neutral Ti(coronene) remains unchanged; while the larger size clusters experience a reduction. PMID:23632443

Ding, Li-Ping; Kuang, Xiao-Yu; Shao, Peng; Zhong, Ming-Min

2013-06-28

77

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

78

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

NASA Technical Reports Server (NTRS)

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

Snyder, D. B.

1983-01-01

79

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

SciTech Connect

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

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

2014-07-15

80

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

81

Beam Characteristics of Positively and Negatively Charged Droplets Generated by Vacuum Electrospray of an Ionic Liquid  

NASA Astrophysics Data System (ADS)

To develop a vacuum-electrospray beam source for secondary ion mass spectrometry (SIMS), beam characteristics of charged droplets electrosprayed in vacuum were investigated in the negative-ion mode as well as the positive-ion mode. A quaternary ammonium ionic liquid was tested. Experimental results showed that there are differences as well as similarities between the positive-ion mode and the negative-ion mode. Beam current changed greatly with capillary voltage and the flow rate of the ionic liquid. Transient response analysis showed that the vacuum electrospray generated a mixed beam consisting of charged particles of smaller m/z values (m/z?103) and charged droplets of larger m/z values (m/z?105 to 106). It turned out that the m/z values of the charged droplets diminished with increasing capillary voltage. Using a three-dimensional positioning stage, the capillary position dependence on the beam characteristics was measured. It proved to be of great importance to align the central axis of a capillary with those of apertures in order to maximize the current component of the charged droplets of the larger m/z values and minimize the ratio of the current component of the smaller m/z values. A high alignment accuracy proved to be required at small gap lengths between a capillary tip and a counter electrode.

Fujiwara, Yukio; Saito, Naoaki; Nonaka, Hidehiko; Ichimura, Shingo

2012-03-01

82

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

NASA Astrophysics Data System (ADS)

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

Yao, Yao

2015-01-01

83

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

84

Temperature dependence of positronium reactivities with charge transfer molecules in bilayer membranes  

NASA Astrophysics Data System (ADS)

Rate constants for positronium atoms reacting chemically with charge-transfer molecules such as p-benzoquinone, nitrobenzene, and coenzyme Q-10 in a model bilayer membrane, dipalmitoylphosphatidylcholine (DPPC), have been measured at temperatures between 23 and 65 °C. A strong variation of the positronium chemical reactivities, kPs was observed in these systems: kPs increases with increasing temperature until the pretransition temperature of the membrane reaches a maximum value near the main transition temperature and decreases at temperatures higher than the main transition temperature. This variation is interpreted in terms of fluidity and permeability changes associated with the phase transitions of membranes and in terms of charge-transfer-complex formation between the solubilized molecules and the polar head of the membrane. These results demonstrate that positronium and its annihilation characteristics can be employed to investigate charge transport phenomena and microstructural changes of real biological membranes.

Jean, Y. C.; Yu, C.; Wang, Y. Y.; Yeh, Y. Y.

1984-02-01

85

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

NASA Astrophysics Data System (ADS)

Sprites are structured high altitude optical emissions produced by lightning-driven electric fields. Both strong positive and negative cloud to ground flashes (CGs) are capable of initiating sprites. However, reported sprites are almost exclusively produced by +CGs. The very limited number of negative polarity sprites makes it difficult to reveal their morphologies and mechanisms. Since 2008, we have operated low light cameras at 5 locations in the United States to detect lightning-driven transient luminous events (TLEs). At Duke University, two pairs of magnetic sensors simultaneously record lightning-radiated magnetic fields. During 4 years of observations, the low light cameras collectively captured 1651 sprite events. Among them, 6 were produced by -CG lightning, which was confirmed by both the National Lightning Detection Network (NLDN) and magnetic field measurements. All of these negative sprites show similar features in their morphology, lightning source current, and lightning-driven ambient electric fields. They all initiate within a few ms from their parent lightning discharges and always are accompanied by sprite halos. Compared to positive sprites, the downward streamers in negative sprites terminate at higher altitudes, about 55-60 km. The extracted source current of their parent lightning discharges is very impulsive and produces at least 450 C km charge moment change in 0.5 ms or less. Unlike most +CG strokes, essentially no continuing current follows these -CGs. Thus the uniformity of negative sprite morphology appears to reflect the uniformity of the characteristics of high charge transfer negative strokes. Numerical simulation shows these impulsive source currents produce very high (>2 Ek, where Ek is the local air breakdown field) but short-lived electric fields at halo altitudes between 70 km and 90 km. At streamer termination altitudes, the inferred background electric field is 0.2-0.3 Ek, which is close to but below the critical field (0.4 Ek) for negative streamer propagation. The simulations also show that the timescale of the lightning source current has a significant impact on the high altitude electric fields and thus the sprite initiation and morphology. With the same amount of charge transfer, a more impulsive current source produces a higher electric field of shorter duration at halo and sprite altitudes. The short timescales may explain why a larger threshold of total charge moment change is required to initiate negative sprites than short-delayed positive sprites, whose parent lightning source current is usually less impulsive.

Li, Jingbo; Cummer, Steven; Lu, Gaopeng; Zigoneanu, Lucian

2012-09-01

86

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

87

Pion-nucleus single charge exchange induced by stopped negative pions  

NASA Astrophysics Data System (ADS)

The branching ratio (BR) for stopped negative pion induced single charge exchange was experimentally determined for CH2, 27Al, 31P, 32S, 45Sc, and 115In. The BR for CH2 agrees with a previous determination; the others can be understood in terms of the shell model structure of the targets. These results will facilitate studies of the effective pion-nucleon isovector interaction in nuclei at threshold energies.

Nair, R.; Plendl, H. S.; Gavathas, E. P.; Liu, L.-C.; Estep, R. J.; Dropesky, B. J.; Bowman, J. D.; Knudson, J. N.; Lieb, B. J.; Stronach, C. E.; Funsten, H. O.; MacKenzie, J.

1996-02-01

88

Space-charge waves in partially depleted negative-mobility media  

Microsoft Academic Search

Space-charge waves in a two-dimensional negative-mobility medium are described by a relatively simple and easy-touse expression for the complex propagation constant. Attention is focused on the dominant mode in the most important limit of low growth rate. Diffusion is included in the analysis. Whereas most previous workers imposed a stiff lateral-motion constraint at the surfaces of the drifting electron stream,

R. H. Dean; B. B. Robinson

1974-01-01

89

Transformation of Ultrafine Titanium Dioxide Particles from Rutile to Anatase at Negatively Charged Colloid Surfaces  

NASA Astrophysics Data System (ADS)

The phase transition of TiO 2from rutile to anatase has not been reported below the transition temperature from anatase to rutile. This work reports the new observation that ultrafine rutile-type particles are transformed into anatase by contacting the strongly negatively charged colloid particles such as V 2O 5· nH 2O, MoO 3, and H 2WO 4· nH 2O. The weakly negatively charged particles of silica and montmorillonite did not change the structure. More active Nb 2O 5· nH 2O and Ta 2O 5· nH 2O reacted chemically with TiO 2to produce new compounds. Conversely, anatase-type TiO 2was changed into rutile by contacting with HCl solution. From these facts it is concluded that chloride ions at the interface affect to form the rutile-type TiO 2, although anatase is thermodynamically stable at low temperatures. It is concluded that the surface field of the strongly negatively charged crystalline particles in an acidic condition eases the TiO 2article to crystallize into a thermodynamically stable one.

Kittaka, Shigeharu; Matsuno, Kohsaku; Takahara, Shuichi

1997-09-01

90

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

SciTech Connect

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

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

2014-02-15

91

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

92

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

NASA Astrophysics Data System (ADS)

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

Kim, C.; Hwang, J.

2012-11-01

93

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

PubMed Central

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

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

2014-01-01

94

Permeation of permanently positive charged molecules through artificial membranes--influence of physico-chemical properties.  

PubMed

The aim of this study was to investigate the permeation properties of 20 permanently positive charged molecules in the parallel artificial membrane permeability assay (PAMPA). Eight of them were derivatives of the N-alkyl-isoquinolinium salt and 12 were congeners of the dye rhodamine 110. Five out of 12 molecules from the rhodamine 110 series have one additional carboxylic group and two have two carboxylic acids. The experimentally derived effective permeability values (P(e)) cover a range of 3-4 log units. Ten compounds showed low permeabilities (P(e)<0.1x10(-6)cm/s), four medium permeabilities (0.1x10(-6)< or =P(e)<1x10(-6)cm/s) and six were highly permeable (P(e)> or =1x10(-6)cm/s). In addition, computational models were built with a number of calculated molecular descriptors and evaluated for their ability to predict membrane permeability. It turned out that the experimental P(e) values can be explained by electronic properties and parameters describing the shape of molecules. This work provides evidence that permanently charged molecules can have high passive membrane permeabilities provided that the charge can be spread over several aromatic ring systems. PMID:17416489

Fischer, Holger; Kansy, Manfred; Avdeef, Alex; Senner, Frank

2007-05-01

95

Polypeptide multilayer film co-delivers oppositely-charged drug molecules in sustained manners.  

PubMed

The current state-of-the-art for drug-carrying biomedical devices is mostly limited to those that release a single drug. Yet there are many situations in which more than one therapeutic agent is needed. Also, most polyelectrolyte multilayer films intended for drug delivery are loaded with active molecules only during multilayer film preparation. In this paper, we present the integration of capsules as vehicles within polypeptide multilayer films for sustained release of multiple oppositely charged drug molecules using layer-by-layer nanoassembly technology. Calcium carbonate (CaCO(3)) particles were impregnated with polyelectrolytes, shelled with polyelectrolyte multilayers, and then assembled onto polypeptide multilayer films using glutaraldehyde. Capsule-integrated polypeptide multilayer films were obtained after decomposition of CaCO(3) templates. Two oppositely charged drugs were loaded into capsules within polypeptide multilayer films postpreparation based on electrostatic interactions between the drugs and the polyelectrolytes impregnated within capsules. We determined that the developed innovative capsule-integrated polypeptide multilayer films could be used to load multiple drugs of very different properties (e.g., opposite charges) any time postpreparation (e.g., minutes before surgical implantation inside an operating room), and such capsule-integrated films allowed simultaneous delivery of two oppositely charged drug molecules and a sustained (up to two weeks or longer) and sequential release was achieved. PMID:21058719

Jiang, Bingbing; Defusco, Elizabeth; Li, Bingyun

2010-12-13

96

Coulomb excitation of highly charged projectile ions in relativistic collisions with diatomic molecules  

SciTech Connect

We investigate the Coulomb excitation of highly charged ions colliding with diatomic molecules. In this process, the coherent interaction between the projectile electron and two molecular centers may cause clear interference patterns in the (collision) energy dependencies of the total cross sections and alignment parameters. We discuss such a Young-type interference for the particular case of the K{yields}L excitation of hydrogen- and helium-like projectile ions. Calculations, performed for the scattering of these ions on nitrogen molecules, indicate that the interference effects are extremely sensitive to the collisional geometry and are pronounced only if the molecular axis is aligned almost parallel to the incident beam trajectory.

Artemyev, A. N.; McConnell, S. R.; Surzhykov, A.; Najjari, B.; Voitkiv, A. B. [Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, D-69120 Heidelberg, Germany and GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, D-64291 Darmstadt (Germany); Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)

2011-10-15

97

Fragmentation of CO2 molecules in slow charge exchange collisions with Ar8+  

NASA Astrophysics Data System (ADS)

Charge exchange collisions between multiply charged ions and CO2 have been studied at low collision velocities (E=400 eV/amu). The stability of the ion, produced in different charge states, is analyzed by means of a time-of-flight spectrometer. Recoil ions and fragments are measured in coincidence with projectile ions, which are selected with respect to their charge state and the scattering angle. For large impact parameters the production of singly and doubly charged CO2 ions turns out to be the major process. The opening of one out of two molecular bindings is found to be more likely than the total fragmentation of the molecule. The formation of O+ and CO+ fragments with very small kinetic energies is explained by single electron capture forming CO2+ in the excited (C˜ 2?g+) state. Collisions with smaller impact parameters and multi-electron capture processes always lead to a total fragmentation of the molecule characterized by a symmetric Coulomb explosion.

Lebius, H.; Huber, B. A.

1993-06-01

98

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

99

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

PubMed

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

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

2013-02-01

100

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

SciTech Connect

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

Hollenberg, Lloyd (University of Melbourne, Australia); Klimeck, Gerhard (Purdue University, West Lafayette, IN); Carroll, Malcolm S.; Rahman, Rajib; Muller, Richard Partain; Rogge, Sven (Delft University of Technology Delft, The Netherlands); Verduijn, Arjan (Delft University of Technology Delft, The Netherlands); Lansbergen, Gabriel (Delft University of Technology Delft, The Netherlands)

2010-07-01

101

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

102

Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer  

PubMed Central

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

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

2011-01-01

103

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

104

Photoinduced charge separation in an organic donor-acceptor hybrid molecule.  

PubMed

Photoinduced charge separation in blends of organic materials of different electronic affinity and in organic donor-acceptor hybrids is a process of increasing importance for biological and artificial energy conversion and photovoltaics. Organic polymer solar cells are composed of an electron donor and an electron acceptor between which an electron transfer occurs after excitation by sunlight. Charge separation results in the formation of donor cation radicals and acceptor anion radicals. Here, we present our studies on a donor-acceptor hybrid molecule composed of a phenylene-bithiophene macrocycle used as a donor and a perylene bisimide acceptor. Using continuous wave EPR and modern pulsed EPR methodology in combination with light excitation, intermolecular as well as intramolecular charge separation has been observed. Light-induced charge separation observed upon selective excitation of either one of the chromophores indicates that both LUMO-based and HOMO-based electron transfer from donor to acceptor takes place. These experimental findings are corroborated by DFT calculations in which the HOMO of the donor-acceptor hybrid molecule is found at the phenylene-bithiophene macrocycle and the LUMO at the perylene bisimide. PMID:22004191

Marchanka, Aliaksandr; Maier, Stefan K; Höger, Sigurd; van Gastel, Maurice

2011-11-24

105

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

PubMed

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

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

1996-05-14

106

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

NASA Astrophysics Data System (ADS)

Primordial 7Li abundance inferred from observations of metal-poor stars is a factor of about 3 lower than the theoretical value of standard big bang nucleosynthesis (BBN) model. One of the solutions to the Li problem is 7Be destruction during the BBN epoch caused by a long-lived negatively charged massive particle, X-. The particle can bind to nuclei, and X-bound nuclei (X-nuclei) can experience new reactions. The radiative X- capture by 7Be nuclei followed by proton capture of the bound state of 7Be and X- (7Bex) is a possible 7Be destruction reaction. Since the primordial abundance of 7Li originates mainly from 7Li produced via the electron capture of 7Be after BBN, the 7Be destruction provides a solution to the 7Li problem. We suggest a new route of 7Bex formation, that is the 7Be charge exchange at the reaction of 7Be3+ ion and X-. The formation rate depends on the ionization fraction of 7Be3+ ion, the charge exchange cross section of 7Be3+, and the probability that excited states 7Bex* produced at the charge exchange are converted to the ground state. We find that this reaction can be equally important as or more important than ordinary radiative recombination of 7Be and X-. The effect of this new route is shown in a nuclear reaction network calculation.

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

2014-05-01

107

Negative isotope effect for charge transport in acenes and derivatives - a theoretical conclusion.  

PubMed

The isotope effect (IE) on charge transport in polyacenes was proposed in 1970 to judge the transport mechanism. However, there had not been a definitive answer for more than 40 years as to whether such an IE is positive or negative, both theoretically and experimentally, because either theory was too approximate or the experimental estimate was too rough to make a judgment. Employing the quantum nuclear tunneling model for organic semiconductors, we investigate the IE on both hole and electron transport for acenes and their derivatives. We show that both (13)C-substitution and deuteration lead to a negative IE. By introducing phenyl, chlorine, or alkyl side-chains into acenes, the IE becomes more remarkable, especially for hole transport. The vibrational relaxation processes involving in-plane bending of ring or alkyl side-chain motions are found to be responsible for the IE. PMID:25521587

Jiang, Yuqian; Peng, Qian; Geng, Hua; Ma, He; Shuai, Zhigang

2015-01-21

108

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

NASA Astrophysics Data System (ADS)

The negatively charged silicon-vacancy (SiV-) center in diamond is a promising single-photon source for quantum communications and information processing. However, the center's implementation in such quantum technologies is hindered by contention surrounding its fundamental properties. Here we present optical polarization measurements of single centers in bulk diamond that resolve this state of contention and establish that the center has a <111> aligned split-vacancy structure with D3d symmetry. Furthermore, we identify an additional electronic level and evidence for the presence of dynamic Jahn-Teller effects in the center's 738-nm optical resonance.

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

2014-06-01

109

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

110

A renormalization approach to describe charge transport in quasiperiodic dangling backbone ladder (DBL)-DNA molecules  

NASA Astrophysics Data System (ADS)

We study the charge transport properties of a dangling backbone ladder (DBL)-DNA molecule focusing on a quasiperiodic arrangement of its constituent nucleotides forming a Rudin-Shapiro (RS) and Fibonacci (FB) Poly (CG) sequences, as well as a natural DNA sequence (Ch22) for the sake of comparison. Making use of a one-step renormalization process, the DBL-DNA molecule is modeled in terms of a one-dimensional tight-binding Hamiltonian to investigate its transmissivity and current-voltage (I-V) profiles. Beyond the semiconductor I-V characteristics, a striking similarity between the electronic transport properties of the RS quasiperiodic structure and the natural DNA sequence was found.

Sarmento, R. G.; Fulco, U. L.; Albuquerque, E. L.; Caetano, E. W. S.; Freire, V. N.

2011-10-01

111

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

SciTech Connect

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

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

2014-05-02

112

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

NASA Astrophysics Data System (ADS)

The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by the molecules and local molecular electric fields. Our results show that adsorbed molecules containing polar functional groups on graphene exhibit different coverage behaviour to nonpolar molecules. These effects open up a range of new opportunities for recognition of different molecules on graphene-based sensor devices.The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by the molecules and local molecular electric fields. Our results show that adsorbed molecules containing polar functional groups on graphene exhibit different coverage behaviour to nonpolar molecules. These effects open up a range of new opportunities for recognition of different molecules on graphene-based sensor devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05390g

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

2015-01-01

113

Role of negatively charged ions in plasma on the growth and field emission properties of spherical carbon nanotube tip  

NASA Astrophysics Data System (ADS)

The role of negatively charged ions in plasma on growth (without catalyst) and field emission properties of spherical carbon nanotube (CNT) tip has been theoretically investigated. A theoretical model of charge neutrality, including the kinetics of electrons, negatively and positively charged ions, neutral atoms, and the energy balance of various species has been developed. Numerical calculations of the spherical CNT tip radius for different relative density of negatively charged ions ?r(=nSF6-/nC+, where nSF6- and nC+ are the equilibrium densities of sulphur hexafluoride and carbon ions, respectively) have been carried out for the typical glow discharge plasma parameters. It is found that the spherical CNT tip radius decreases with ?r and hence the field emission of electrons from the spherical CNT tip increases. Some of our theoretical results are in accordance with the existing experimental observations.

Tewari, Aarti; Walia, Ritu; Sharma, Suresh C.

2012-01-01

114

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

SciTech Connect

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

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

2011-10-28

115

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

E-print Network

of chemical properties in a single molecule results in the partitioning of surfactants to water surfacesPotential Dependent Alignment and Hydrogen Bonding of Water Molecules at Charged Air/Water and CCl4/Water Interfaces D. E. Gragson and G. L. Richmond* Contribution from the Department of Chemistry, Uni

Richmond, Geraldine L.

116

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

117

An association study of asthma and related phenotypes with polymorphisms in negative regulator molecules of the TLR signaling pathway  

Microsoft Academic Search

Although associations between endotoxin exposure or respiratory infection and asthma have been recognized, the genetic effects in these conditions are unclear. Toll-like receptors (TLRs) play an essential role in innate host defense and in the control of adaptive immune responses. IL-1R-associated kinase-M (IRAK-M) and single immunoglobulin IL-1R-related molecule (SIGIRR) negatively regulate TLR-signaling pathways. To investigate whether polymorphisms in these genes

Kazuko Nakashima; Tomomitsu Hirota; Kazuhiko Obara; Makiko Shimizu; Aya Jodo; Makoto Kameda; Satoru Doi; Kimie Fujita; Taro Shirakawa; Tadao Enomoto; Fumio Kishi; Shigemi Yoshihara; Kenji Matsumoto; Hirohisa Saito; Yoichi Suzuki; Yusuke Nakamura; Mayumi Tamari

2006-01-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

119

Negatively charged Si vacancy in 4H SiC: A comparison between theory and experiment  

SciTech Connect

We use electron paramagnetic resonance and electron nuclear double resonance to identify the negatively charged Si vacancy in neutron-irradiated 4H SiC. The identification is based on resolved ligand hyperfine interactions with carbon and silicon nearest and next nearest neighbors and on the determination of the spin state, which is S=3/2. The magnetic resonance parameters of V{sub Si}{sup {minus}} are almost identical for the polytypes 3C, 4H, and 6H. The experimental findings are supported by theoretical ligand hyperfine interaction data based on a total-energy calculation using the standard local-density approximation of the density-functional theory. {copyright} {ital 1997} {ital The American Physical Society}

Wimbauer, T. [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall, D-85748 Garching (Germany)] [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall, D-85748 Garching (Germany); Meyer, B.K.; Hofstaetter, A.; Scharmann, A. [I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich Buff Ring 16, D-35392 Giessen (Germany)] [I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich Buff Ring 16, D-35392 Giessen (Germany); Overhof, H. [Fachbereich Physik, Universitaet-GH Paderborn, Warburgerstrasse 100 A, D-33098 Paderborn (Germany)] [Fachbereich Physik, Universitaet-GH Paderborn, Warburgerstrasse 100 A, D-33098 Paderborn (Germany)

1997-09-01

120

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

NASA Astrophysics Data System (ADS)

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

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

1998-06-01

121

Evolution of solitons and their reflection and transmission in a plasma having negatively charged dust grains  

NASA Astrophysics Data System (ADS)

Theoretical calculations are carried out for studying soliton's reflection and transmission in an inhomogeneous plasma comprising ions, two temperature electrons and negatively charged dust grains. Using reductive perturbation technique, relevant modified KdV equations are derived for the incident, reflected and transmitted solitons. Then a coupled equation is obtained based on these mKdV equations, which is solved for the reflected soliton under the use of solutions of mKdV equations corresponding to the incident and transmitted solitons. Based on the ratio of amplitudes of reflected and incident solitons, reflection coefficient is examined under the effect of dust grain density; the same is done for the transmission coefficient which is the ratio of amplitudes of transmitted and incident solitons. The transmission of the solitons becomes weaker under the effect of stronger magnetic field and higher dust density. However, this leads to the stronger reflection of the soliton.

Tomar, Renu; Bhatnagar, Anjali; Malik, Hitendra K.; Dahiya, Raj P.

2014-07-01

122

Efficient blue organic light-emitting devices with charge carrier confining nanostructure formed by wide band gap molecule doping  

NASA Astrophysics Data System (ADS)

We report on efficient blue organic light-emitting devices with an emission layer featuring a quasi-molecular quantum dot nanostructure as a charge carrier confining barrier, which was formed by doping a wide band gap molecule, 2-(2-hydroxyphenylbenzoxazole) lithium, into a newly synthesized blue host molecule, 9,10-bis-[4-(2,2-diphenylvinyl)-phenyl]-anthracene. The charge carrier confinement was greatly improved by doping with 10% wide band gap molecules, that led to a theoretical molecular quantum dot distance of 33 Å. The device showed enhanced efficiency ({\\sim }5\

Kim, Youngkyoo; Oh, Eonseok; Choi, Dongkwon; Lim, Hyuntaek; Ha, Chang-Sik

2004-01-01

123

Stark tuning of the charge states of a two-donor molecule in silicon.  

PubMed

A singly ionized two-donor molecule in silicon is an interesting test-bed system for implementing a quantum bit using charge degrees of freedom at the atomic limit of device fabrication. The operating principles of such a device are based on wavefunction symmetries defined by charge localizations and energy gaps in the spectrum. The Stark-shifted electronic structure of a two-donor phosphorus molecule is investigated using a multi-million-atom tight-binding framework. The effects of surface (S) and barrier (B) gates are analyzed for various voltage regimes. It is found that gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may alter in functionality. Effects such as interface ionization, saturation of the lowest energy gap, and sensitivity to donor and gate placements are also investigated. Excited molecular states of P(2) + are found to impose limits on the allowed donor separations and operating gate voltages for coherent operation. This work therefore outlines and analyzes the various issues that are of importance in the design and control of such donor molecular systems. PMID:21454928

Rahman, Rajib; Park, Seung H; Klimeck, Gerhard; Hollenberg, Lloyd C L

2011-06-01

124

Gas-phase positive and negative ion/molecule reactions in diborane and silane/diborane mixtures  

NASA Astrophysics Data System (ADS)

The gas phase ion chemistry of diborane and of silane/diborane mixtures was studied by ion trap mass spectrometry (ITMS), in both positive and negative ionization mode. Positive ion/molecule reactions in diborane mainly proceed through H2 or BH3 loss and lead to formation of B hydride clusters containing up to six B atoms, while in negative ionization clustering reactions proceed to a higher degree with formation of B8Hn- ions. In the silane/diborane system, the main ion/molecule reactions leading to ions containing both silicon and boron atoms were identified and rate constants of the main processes were determined for positive ions. In positive ionization, Si/B ions are mainly formed in reactions of few diborane ions with silane, while reactions of silane ions with B2H6 yield B2H5+ as the main product. Negative ionization of the same mixture produces a much larger amount of Si/B ionic species, due to several reactions of silane anions with diborane, resulting in BH3 or H2 neutral losses. These results indicate that negative ions may play an important role in formation of Si/B ion clusters in plasma chemical vapour deposition processes for production of semiconductor and photovoltaic materials.

Operti, Lorenza; Rabezzana, Roberto; Turco, Francesca; Vaglio, Gian Angelo

2007-06-01

125

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

126

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

PubMed

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

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

2015-01-01

127

Negative ion production in small angle scattering of highly charged ions from the (0001) surface of highly oriented pyrolytic graphite  

NASA Astrophysics Data System (ADS)

Highly charged N, O, F, and S ions, chosen for their electron affinities, were extracted from the Lawrence Livermore National Laboratory's EBIT II. After collimation, these ions struck a target of highly oriented pyrolytic graphite (HOPG) at an incident angle of 1.0 degree. Those ions scattered by 2.35 degrees (1.35 degree with respect to the surface) were charge state analyzed and the predominant charge state fractions were determined. As might be expected, there is a tendency for the fraction of negative ions to increase with increasing electron affinity; however, the negative ion yield is also strongly dependent on the ion velocity. For example, for sulfur the negative ion yields measured range from 0.13 to 0.23 of the scattered ions while for fluorine the range was 0.35 to 0.40. A pronounced velocity dependence found for the S- ions is described well by a Saha-Langmuir-type equation.

Reaves, M.; Kessel, Q. C.; Pollack, E.; Smith, W. W.; Briere, M. A.; Schneider, D. H.

1997-02-01

128

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

SciTech Connect

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

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

2014-10-15

129

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

Probing the Structure of Water Molecules at an Oil/Water Interface in the Presence of a Charged spectra of water molecules at an oil/water interface in the presence of a charged, soluble surfactant been able to compare the structure of interfacial water molecules with the structure of bulk water

Richmond, Geraldine L.

130

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

131

Cross sections for inelastic collisions of fast charged particles with atoms and molecules  

NASA Astrophysics Data System (ADS)

A large volume of data of these cross sections are required for solving problems of radiological physics and dosimetry, as well as for detailed analysis of the earliest stage of radiation actions on matter (including the biological cell and substances constituting it). One practical approach to the cross section determination is to test experimental data with general criteria. More recent studies concern the determination of the analytic expression most suitable for fitting the data on the oscillator-strength distribution or the energy distribution of secondary electrons from ionizing collisions of charged particles. There are three areas to which major efforts should be directed. First, methods of absolute cross-section measurements both for electron and ionic collisions must be thoroughly reviewed so that sources of systematic errors may be identified and corrected. Second, efforts should be devoted to the understanding of the data systematics, viz., the trends of cross sections for a series of molecules. Finally, electron and ionic collisions with molecules in condensed phases will be an important topic of study for years to come.

Inokuti, M.

132

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

133

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

PubMed

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

Wasielewski, Michael R

2006-07-01

134

MoleCoolQt - a molecule viewer for charge-density research.  

PubMed

MoleCoolQt is a molecule viewer for charge-density research. Features include the visualization of local atomic coordinate systems in multipole refinements based on the Hansen and Coppens formalism as implemented, for example, in the XD suite. Residual peaks and holes from XDfft are translated so that they appear close to the nearest atom of the asymmetric unit. Critical points from a topological analysis of the charge density can also be visualized. As in the program MolIso, color-mapped isosurfaces can be generated with a simple interface. Apart from its visualization features the program interactively helps in assigning local atomic coordinate systems and local symmetry, which can be automatically detected and altered. Dummy atoms - as sometimes required for local atomic coordinate systems - are calculated on demand; XD system files are updated after changes. When using the invariom database, potential scattering factor assignment problems can be resolved by the use of an interactive dialog. The following file formats are supported: XD, MoPro, SHELX, GAUSSIAN (com, FChk, cube), CIF and PDB. MoleCoolQt is written in C++ using the Qt4 library, has a user-friendly graphical user interface, and is available for several flavors of Linux, Windows and MacOS. PMID:22477783

Hübschle, Christian B; Dittrich, Birger

2011-02-01

135

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

PubMed Central

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 pKa values), and ?O is the Irving-Rossotti slope. The parameter ?OO is metal specific and has slightly different values for 5 and 6 membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, ?-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. PMID:21833149

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

2011-01-01

136

Mapping charge to function relationships of the DNA mimic protein Ocr   

E-print Network

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

Kanwar, Nisha

2014-06-28

137

Use of an artificial immune system derived method for the charge state assignment of small-molecule mass spectra.  

PubMed

Knowing the charge state of an ion in a mass spectrum is crucial to being able to assign a formula to it. For many small-molecule peaks in complex mass spectra, the intensities of the isotopic peaks are too low to allow the charge state to be calculated from isotopic spacings, which is the basis of the conventional method of determining the charge state of an ion. A novel artificial intelligence derived method for identifying the charge state of ions, in the absence of any isotopic information or a series of charge states, has been developed using an artificial immune system approach. This technique has been tested against synthetic and real data sets and has proven successful in identifying the majority of multiply charged ions, thereby significantly improving the peak assignment rate and confidence. PMID:22881189

Kilgour, David P A; Mackay, C Logan; Langridge-Smith, Patrick R R; O'Connor, Peter B

2012-09-01

138

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

NASA Technical Reports Server (NTRS)

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

Armstrong, T. W.

1972-01-01

139

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

PubMed

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 < 0.05) more cytotoxicity compared with IM-loaded LbL-MC. Biodistribution studies showed that PEGylation of LbL-MC decreased the liver and spleen uptake of IM-encapsulated LbL-MC. In conclusion, LbL-MC can be developed as a potential carrier for small 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

140

Negatively charged lipid membranes promote a disorder-order transition in the Yersinia YscU protein.  

PubMed

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

Weise, Christoph F; Login, Frédéric H; Ho, Oanh; Gröbner, Gerhard; Wolf-Watz, Hans; Wolf-Watz, Magnus

2014-10-21

141

Adsorption of polyelectrolyte versus surface charge: in situ single-molecule atomic force microscopy experiments on similarly, oppositely, and heterogeneously charged surfaces.  

PubMed

We have studied the effect of the pH and surface charge of mica on the adsorption of the positively charged weak polyelectrolyte (PE) poly(2-vinylpyridine) (P2VP) using atomic force microscopy (AFM) single-molecule experiments. These AFM experiments were performed in situ directly under aqueous media. If the mica's surface and the PE are oppositely charged (pH > 3), the PE forms a flat adsorbed layer of two-dimensionally (2D) equilibrated self-avoiding random walk coils. The adsorbed layer's structure remains almost unchanged if the pH is decreased to pH 3 (the mica's surface is weakly charged). At pH 2 (the mica surface is decorated by spots of different electrical charges), the polyelectrolyte chains take the form of a 2D compressed coil. In this pH range, at an increased P2VP concentration in solution, the PE segments preferentially adsorb onto the top of previously adsorbed segments, rather than onto an unoccupied surface. We explain this behavior as being caused by the heterogeneous character of the charged surface and the competitive adsorption of hydronium ions. The further increase of polymer concentration results in a complete coverage of the mica substrate and the charge overcompensation by P2VP chains adsorbed on the similarly charged substrate, due to van der Waals forces. PMID:17555343

Roiter, Yuri; Minko, Sergiy

2007-07-26

142

Influence of negatively charged interfaces on the ground and excited state properties of methylene blue.  

PubMed

Properties of the ground and excited states of methylene blue (MB) were studied in negatively charged vesicles, normal and reverse micelles and sodium chloride solutions. All these systems induce dimer formation as attested by the appearance of the dimer band in the absorption spectra (lamdaD approximately 600 nm). In reverse micelles the dimerization constant (KD) corrected for the aqueous pseudophase volume fraction is two-three orders of magnitude smaller than KD of MB in water, and it does not change when W0 is increased from 0.5 to 10. Differences in the fluorescence intensity as a function of dimer-monomer ratio as well as in the resonance light scattering spectra indicate that distinct types of dimers are induced in sodium dodecyl sulfate (SDS) micelles and aerosol-OT (sodium dioctyl sulfoxinate, AOT) reversed micelles. The properties of the photoinduced transient species of MB in these systems were studied by time-resolved near infrared (NIR) emission (efficiency of singlet oxygen generation), by laser flash photolysis (transient spectra, yield and decay rate of triplets) and by thermal lensing (amount of heat deposited in the medium). The competition between electron transfer (dye*-dye) and energy transfer (dye*-O2) reactions was accessed as a function of the dimer-monomer ratio. The lower yield of electron transfer observed for dimers in AOT reverse micelles and intact vesicles compared with SDS micelles and frozen vesicles at similar dimer-monomer ratios is related with the different types of aggregates induced by each interface. PMID:12812286

Severino, Divinomar; Junqueira, Helena C; Gugliotti, Marcos; Gabrielli, Dino S; Baptista, Mauricio S

2003-05-01

143

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

E-print Network

Monitoring FET flow control and wall adsorption of charged fluorescent dye molecules in nanochannels integrated into a multiple internal reflection infrared waveguide Youn-Jin Oh,a Thomas C. Gamble fabricated multiple internal reflection infrared waveguides embedded with a parallel array of nanofluidic

New Mexico, University of

144

Time Reversal Induces Negative Mass and Charge Conjugation: On the Physical Interpretation of the Irreducible Unitary Representations of Negative Mass and Energy of the Full Poincare Group  

E-print Network

This article proves that according to the principles of quantum mechanics the existence of elementary particles of negative mass is physically plausible. Heisenberg's uncertainty principle plays an important role in this demonstration. By reversing time, charge and mass are conjugated and the symmetry group is that of the Poincare with space-time reflections (full Poincare group). Particles that tunnel from the future time-like cone to the past time-like cone move backward in time with negative mass (and energy). These particles are interpreted as antiparticles of positive mass (and energy) that move forward in time. There is not a physical law that precludes two observers from seeing different mass signs of a particle, since the mass is not a Poincare invariant, but its square, p^2 = -m^2.

Jose N. Pecina-Cruz

2005-05-21

145

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

146

Role of negatively charged ions in plasma on the growth and field emission properties of spherical carbon nanotube tip  

SciTech Connect

The role of negatively charged ions in plasma on growth (without catalyst) and field emission properties of spherical carbon nanotube (CNT) tip has been theoretically investigated. A theoretical model of charge neutrality, including the kinetics of electrons, negatively and positively charged ions, neutral atoms, and the energy balance of various species has been developed. Numerical calculations of the spherical CNT tip radius for different relative density of negatively charged ions {epsilon}{sub r}(=n{sub SF{sub 6{sup -}}}/n{sub C{sup +}}, where n{sub SF{sub 6{sup -}}} and n{sub C}{sup +} are the equilibrium densities of sulphur hexafluoride and carbon ions, respectively) have been carried out for the typical glow discharge plasma parameters. It is found that the spherical CNT tip radius decreases with {epsilon}{sub r} and hence the field emission of electrons from the spherical CNT tip increases. Some of our theoretical results are in accordance with the existing experimental observations.

Tewari, Aarti; Walia, Ritu; Sharma, Suresh C. [Department of Physics, Maharaja Agrasen Institute of Technology, Sector-22, Rohini, Delhi-110086 (India)

2012-01-15

147

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

PubMed Central

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

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

2010-01-01

148

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

SciTech Connect

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

Pandey, A., E-mail: amrendra@prl.res.in; Bapat, B. [Physical Research Laboratory, Ahmedabad 380009 (India)] [Physical Research Laboratory, Ahmedabad 380009 (India); Shamasundar, K. R. [Indian Institute of Science Education and Research, Mohali, Sector 81, SAS Nagar 140306 (India)] [Indian Institute of Science Education and Research, Mohali, Sector 81, SAS Nagar 140306 (India)

2014-01-21

149

Revisiting the contribution of negative charges on the chaperonin cage wall to the acceleration of protein folding  

PubMed Central

Chaperonin GroEL mediates the folding of protein encapsulated in a GroES-sealed cavity (cage). Recently, a critical role of negative charge clusters on the cage wall in folding acceleration was proposed based on experiments using GroEL single-ring (SR) mutants SR1 and SRKKK2 [Tang YC, et al. (2006) Cell 125:903–914; Chakraborty K, et al. (2010) Cell 142:112–122]. Here, we revisited these experiments and discovered several inconsistencies. (i) SR1 was assumed to bind to GroES stably and to mediate single-round folding in the cage. However, we show that SR1 repeats multiple turnovers of GroES release/binding coupled with ATP hydrolysis. (ii) Although the slow folding observed for a double-mutant of maltose binding protein (DMMBP) by SRKKK2 was attributed to mutations that neutralize negative charges on the cage wall, we found that the majority of DMMBP escape from SRKKK2 and undergo spontaneous folding in the bulk medium. (iii) An osmolyte, trimethylamine N-oxide, was reported to accelerate SRKKK2-mediated folding of DMMBP by mimicking the effect of cage-wall negative charges of WT GroEL and ordering the water structure to promote protein compaction. However, we demonstrate that in-cage folding by SRKKK2 is unaffected by trimethylamine N-oxide. (iv) Although it was reported that SRKKK2 lost the ability to assist the folding of ribulose-1,5-bisphosphate carboxylase/oxygenase, we found that SRKKK2 retains this ability. Our results argue against the role of the negative charges on the cage wall of GroEL in protein folding. Thus, in chaperonin studies, folding kinetics need to be determined from the fraction of the real in-cage folding. PMID:22961256

Motojima, Fumihiro; Motojima-Miyazaki, Yuko; Yoshida, Masasuke

2012-01-01

150

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

PubMed Central

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

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

2014-01-01

151

Nearly perfect spin filter, spin valve and negative differential resistance effects in a Fe4-based single-molecule junction.  

PubMed

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

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

2014-01-01

152

Negative ion production in small angle scattering of highly charged ions from the (0001) surface of highly oriented pyrolytic graphite  

SciTech Connect

Highly charged N, O, F, and S ions, chosen for their electron affinities, were extracted from the Lawrence Livermore National Laboratory{close_quote}s EBIT II. After collimation, these ions struck a target of highly oriented pyrolytic graphite (HOPG) at an incident angle of 1.0 degree. Those ions scattered by 2.35 degrees (1.35 degree with respect to the surface) were charge state analyzed and the predominant charge state fractions were determined. As might be expected, there is a tendency for the fraction of negative ions to increase with increasing electron affinity; however, the negative ion yield is also strongly dependent on the ion velocity. For example, for sulfur the negative ion yields measured range from 0.13 to 0.23 of the scattered ions while for fluorine the range was 0.35 to 0.40. A pronounced velocity dependence found for the S{sup {minus}} ions is described well by a Saha-Langmuir-type equation. {copyright} {ital 1997 American Institute of Physics.}

Reaves, M.; Kessel, Q.C.; Pollack, E.; Smith, W.W. [Department of Physics and The Institute of Materials Science, The University of Connecticut, Storrs, Connecticut 06269 (United States); Briere, M.A.; Schneider, D.H. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

1997-02-01

153

Negatively charged residues in the endodomain are critical for specific assembly of spike protein into murine coronavirus  

PubMed Central

Coronavirus spike (S) protein assembles into virions via its carboxy-terminus, which is composed of a transmembrane domain and an endodomain. Here, the carboxy-terminal charge-rich motif in the endodomain was verified to be critical for the specificity of S assembly into mouse hepatitis virus (MHV). Recombinant MHVs exhibited a range of abilities to accommodate the homologous S endodomains from the betacoronaviruses bovine coronavirus and human SARS-associated coronavirus, the alphacoronavirus porcine transmissible gastroenteritis virus (TGEV), and the gammacoronavirus avian infectious bronchitis virus respectively. Interestingly, in TGEV endodomain chimeras the reverting mutations resulted in stronger S incorporation into virions, and a net gain of negatively charged residues in the charge-rich motif accounted for the improvement. Additionally, MHV S assembly could also be rescued by the acidic carboxy-terminal domain of the nucleocapsid protein. These results indicate an important role for negatively charged endodomain residues in the incorporation of MHV S protein into assembled virions. PMID:23628137

Yao, Qianqian; Masters, Paul S.; Ye, Rong

2013-01-01

154

Double electron removal and fragmentation model of the H2 molecule by highly charged ions  

NASA Astrophysics Data System (ADS)

A five-body classical trajectory Monte Carlo model has been developed to study double electron removal from H2 by collisions with highly charged ions at impact energies ranging from 1 eV/u to 1 GeV/u. The longitudinal and transverse final-state correlation between ejected electrons is calculated for double ionization of H2 by impact of Se28+ at 3.6 MeV/u and U92+ at 1 GeV/u; the electron-electron interaction is dynamically included during the collision when one of the electron's total energy becomes positive. Relativistic corrections are incorporated to reflect the Lorentz contraction of the projectile's electric field. The cross section dependence on the alignment of the H2 molecular axis was investigated. Here, transfer ionization of H2 by O8+ at 500 keV/u is found to have a maximum for the molecular axis aligned perpendicular to the projectile velocity, while no orientation dependence is found for double ionization at 500 keV/u. In contrast, a minimum in the cross section at 90° is found for 1-GeV/u U92++H2 collisions. A systematic study of the energy partitioning between the two product H+ ions has been made for Xe54++H2 from 1 eV/u to 1 MeV/u. Large deviations from Franck-Condon behavior are found for impact energies E<~10 keV/u. At low energies the proton energies are very energetic with the main contribution arising from collisional transfer from the projectile, while the proton energy spectrum at high impact energy is due to the Coulomb explosion of the isolated molecule.

Wood, C. J.; Olson, R. E.

1999-02-01

155

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

PubMed

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

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

2014-11-19

156

Valence-bond/coherent-states approach to the charge equilibration model I. Valence-bond models for diatomic molecules.  

PubMed

A valence-bond (VB)/coherent-states (CS) approach to the charge equilibration (CE) model for diatomic molecules is presented in this work (VB part) and its sequel (CS part). By emphasizing theoretical aspects, this approach obtains the classical-electrostatics CE model from a quantum VB model in conjunction with the CS theory. For the VB part, a VB generalized CE (VB/GCE) model, which contains the CE model as a subcase, is derived from a two-electron, three-state VB model via the sequential application of seven approximations. Unlike its CE subcase, the VB/GCE model provides a satisfactory charge-transfer description at dissociation as illustrated with HF((g)) and other molecules. Through the previous derivation, CE charges and CE Coulomb interactions are elucidated in terms of VB Mulliken charges and VB atomic interactions, respectively. Modifications in the above derivation can generate a family of related VB/GCE models that includes the aforesaid VB/GCE model. Despite their classical appearance, all of the VB/GCE and CE models involve VB wave functions corresponding to ground and first-excited states. Moreover, all of the VB/GCE and CE energy and charge optimizations are proven to be equivalent to the variational eigenvector equation procedures of the underlying VB models. The quantum-mechanics/classical-electrostatics connection implicit in this work is further elaborated by means of VB CS sets in the sequel. The VB/CS treatment of polyatomic molecules and additional tests of the present approach will be reported in later papers in this series. PMID:19391590

Morales, Jorge A

2009-05-21

157

Why charged molecules move across a temperature gradient: the role of electric fields.  

PubMed

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. PMID:24877967

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

2014-05-16

158

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

SciTech Connect

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

Babichenko, V. S., E-mail: vsbabichenko@hotmail.com; Kagan, Yu. [National Research Centre Kurchatov Institute (Russian Federation)

2012-11-15

159

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

160

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

PubMed

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

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

2014-08-29

161

Extracting chemical potentials of quarks from ratios of negatively/positively charged particles in high-energy collisions  

NASA Astrophysics Data System (ADS)

The transverse momentum spectrums of ? -, ? +, K -, K +, , and p produced in p-Pb collisions at TeV measured by the CMS Collaboration and in Pb-Pb collisions at TeV measured by the ALICE Collaboration are described by the Tsallis distribution. Then, the ratios of negatively/positively charged particles are obtained. The chemical potentials of u-quark, d-quark, s-quark, baryon number, isospin, and strangeness are obtained by using different configurations of the ratios. Comparing with the masses of final-state particles, all the six types of chemical potentials are small.

Liu, Fu-Hu; Tian, Tian; Zhao, Hong; Li, Bao-Chun

2014-03-01

162

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

PubMed

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

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

2015-02-18

163

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

164

Ion Accelerator With Negatively Biased Decelerator Grid  

NASA Technical Reports Server (NTRS)

Three-grid ion accelerator in which accelerator grid is biased at negative potential and decelerator grid downstream of accelerator grid biased at smaller negative potential. This grid and bias arrangement reduces frequency of impacts, upon accelerator grid, of charge-exchange ions produced downstream in collisions between accelerated ions and atoms and molecules of background gas. Sputter erosion of accelerator grid reduced.

Brophy, John R.

1994-01-01

165

Lactosylated PLGA nanoparticles containing ?-polylysine for the sustained release and liver-targeted delivery of the negatively charged proteins.  

PubMed

The acidic internal pH environment, initial burst release and lack of targeting property are main limitations of poly(lactide-co-glycolide) (PLGA) nanoparticles for carrying proteins. In this study, ?-polylysine (?-PL) was used as an anti-acidic agent and a protein protectant to prepare PLGA nanoparticles for the protein delivery. To obtain the liver-targeting capability, lactosylated PLGA (Lac-PLGA) was synthesized by conjugation of lactose acid to PLGA at both ends, and then used to prepare nanoparticles containing ?-PL by the nanoprecipitation method. Bovine serumal bumin (BSA), a negatively charged protein, was efficiently loaded into Lac-PLGA/?-PL nanoparticles and exhibited significant decreased burst release in vitro, sustained release in the blood and increased liver distribution in mice after intravenous injections. The enhanced stability of BSA was due to its electrical interaction with ?-PL and the neutralized internal environment of nanoparticles. In conclusion, Lac-PLGA/?-PL nanoparticle system can be used as a promising carrier for the negatively charged proteins. PMID:25510599

Zhou, Ping; An, Tong; Zhao, Chuan; Li, Yuan; Li, Rongshan; Yang, Rui; Wang, Yinsong; Gao, Xiujun

2015-01-30

166

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

167

Kinetic-energy release and fragment distribution of exploding, highly charged C60 molecules  

NASA Astrophysics Data System (ADS)

The kinetic-energy distributions of fragment ions formed in slow Xe25+-C60 collisions have been determined with high-resolution time-of-flight mass spectrometry. The energy releases as well as the fragment size distributions are analyzed as functions of the number of electrons stabilized at the projectile, i.e., as a function of the average charge state of the intermediately formed C60 molecular ion. The evaluated energy releases are much higher than those reported for multiply charged ion collisions performed at high energies. The obtained results are consistent with the Coulomb explosion model, a fact which can be understood in terms of the high charge states involved.

Tomita, S.; Lebius, H.; Brenac, A.; Chandezon, F.; Huber, B. A.

2002-05-01

168

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

E-print Network

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

Madsen, Jonathan R

2013-08-13

169

Influence of molecular size, polarity and charge on the retention of organic molecules by nanofiltration  

Microsoft Academic Search

Because of the growing interest in nanofiltration for industrial use, a better insight in the retention mechanisms in nanofiltration is needed, which will make it possible to understand membrane performances for specific applications. In this paper, the retention of a series of organic molecules by four nanofiltration membranes was studied. The membranes that were used are NF70 (Dow\\/FilmTec), NTR 7450

B. Van der Bruggen; J. Schaep; D. Wilms; C. Vandecasteele

1999-01-01

170

Tunable Charge Transport in Single-Molecule Junctions via Electrolytic Gating  

E-print Network

-molecule junctions using an electro- lytic gate to controllably tune the energy level alignment of the system effect transistors and nanotube or graphene devices10,11 made using ionic liquids, electrolyte solutions to generate large interfacial capacitances on the nanoscale, thereby enhancing gate efficiencies.12

Venkataraman, Latha

171

Simple Bond-Charge Model for Potential-Energy Curves of Homonuclear Diatomic Molecules  

Microsoft Academic Search

For a homonuclear diatomic molecule near its equilibrium internuclear distance Re, in some bound electronic state, a potential-energy function W(R) of the form W = W0 + W1 ? R + W2 ? R2 has previously been shown to be a good approximation to the true potential. From this equation and the molecular virial theorem, there follow expressions for the

Robert G. Parr; Raymond F. Borkman

1968-01-01

172

Interaction of surfactants with bilayer of negatively charged lipid: effect on gel-to-liquid-crystalline phase transition of dilauroylphosphatidic acid vesicle membrane.  

PubMed

The interaction of surfactants with the vesicle membrane of the negatively charged lipid, dilauroylphosphatidic acid, was investigated through their effect on the gel-to-liquid-crystalline phase transition of the lipid bilayer. Three types of surfactants (anionic, cationic and non-ionic) with different hydrocarbon chain length were examined. (i) Anionic sodium alkylsulfates affected the phase transition temperature, Tm, only weakly. (ii) Non-ionic alkanoyl-N-methylglucamides decreased Tm monotonously with increasing concentration. The depression of Tm induced by these surfactants was analyzed by applying the van't Hoff model for the freezing-point depression, and the partition coefficients of the surfactants between bulk water and lipid membrane were estimated. (iii) Cationic alkyltrimethylammonium bromides affected Tm in a complex manner depending on the hydrocarbon chain length of the surfactants. Octyl-/tetradecyl-trimethylammonium bromide depressed/elevated Tm monotonously with increasing concentration, whereas the change in Tm induced by decyl- and dodecyltrimethylammonium bromides was not monotonous but biphasic. This complex behavior of the phase transition temperature was well explained, based on the statistical mechanical theory presented by Suezaki et al. (Biochim. Biophys. Acta, 818 (1985) 31-37), which takes into account the interaction between surfactant molecules incorporated in the lipid membrane. PMID:3242947

Inoue, T; Iwanaga, T; Fukushima, K; Shimozawa, R; Suezaki, Y

1988-10-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

174

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

PubMed Central

The pore region of the majority of K+ channels contains the highly conserved GYGD sequence, known as the K+ channel signature sequence, where the GYG is critical for K+ selectivity (Heginbotham, L., T. Abramson, and R. MacKinnon. 1992. Science. 258:1152–1155). Exchanging the aspartate residue with asparagine in this sequence abolishes ionic conductance of the Shaker K+ channel (D447N) (Hurst, R.S., L. Toro, and E. Stefani. 1996. FEBS Lett. 388:59–65). In contrast, we found that the corresponding mutation (D292N) in the pore forming ? subunit (hSlo) of the voltage- and Ca2+-activated K+ channel (BKCa, MaxiK) did not prevent conduction but reduced single channel conductance. We have investigated the role of outer pore negative charges in ion conduction (this paper) and channel gating (Haug, T., R. Olcese, T. Ligia, and E. Stefani. 2004. J. Gen Physiol. 124:185–197). In symmetrical 120 mM [K+], the D292N mutation reduced the outward single channel conductance by ?40% and nearly abolished inward K+ flow (outward rectification). This rectification was partially relieved by increasing the external K+ concentration to 700 mM. Small inward currents were resolved by introducing an additional mutation (R207Q) that greatly increases the open probability of the channel. A four-state multi-ion pore model that incorporates the effects of surface charge was used to simulate the essential properties of channel conduction. The conduction properties of the mutant channel (D292N) could be predicted by a simple ?8.5-fold reduction of the surface charge density without altering any other parameter. These results indicate that the aspartate residue in the BKCa pore plays a key role in conduction and suggest that the pore structure is not affected by the mutation. We speculate that the negative charge strongly accumulates K+ in the outer vestibule close to the selectivity filter, thus increasing the rate of ion entry into the pore. PMID:15277578

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

2004-01-01

175

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

PubMed

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

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

2007-07-14

176

Blockade ofthe negative co-stimulatory molecules PD-1 and CTLA-4 improves survival in primary and secondary fungal sepsis  

PubMed Central

Introduction Fungal sepsis is an increasingly common problem in intensive care unit patients.Mortality from fungal sepsis remains high despite antimicrobial therapy that is highly active against most fungal pathogens, a finding consistent with defective host immunity that is present in many patients with disseminated fungemia.One recently recognized immunologic defect that occurs in patients with sepsis is T cell "exhaustion" due to increased expression of programmed cell death -1 (PD-1).This study tested the ability of anti-PD-1 and anti-programmed cell death ligand -1 (anti-PD-L1) antagonistic antibodies to improve survival and reverse sepsis-induced immunosuppression in two mouse models of fungal sepsis. Methods Fungal sepsis was induced in mice using two different models of infection, that is, primary fungal sepsis and secondary fungal sepsis occurring after sub-lethal cecal ligation and puncture (CLP).Anti-PD-1 and anti-PD-L1 were administered 24 to 48 h after fungal infection and effects on survival, interferon gamma production, and MHC II expression were examined. Results Anti-PD-1 and anti-PD-L1 antibodies were highly effective at improving survival in primary and secondary fungal sepsis.Both antibodies reversed sepsis-induced suppression of interferon gamma and increased expression of MHC II on antigen presenting cells.Blockade of cytotoxic T-lymphocyte antigen-4 (CTLA-4), a second negative co-stimulatory molecule that is up-regulated in sepsis and acts like PD-1 to suppress T cell function, also improved survival in fungal sepsis. Conclusions Immuno-adjuvant therapy with anti-PD-1, anti-PD-L1 and anti-CTLA-4 antibodies reverse sepsis-induced immunosuppression and improve survival in fungal sepsis.The present results are consistent with previous studies showing that blockade of PD-1 and CTLA-4 improves survival in bacterial sepsis.Thus, immuno-adjuvant therapy represents a novel approach to sepsis and may have broad applicability in the disorder.Given the relative safety of anti-PD-1 antibody in cancer clinical trials to date, therapy with anti-PD-1 in patients with life-threatening sepsis who have demonstrable immunosuppression should be strongly considered. PMID:23663657

2013-01-01

177

Adsorption of water molecules on selected charged sodium-chloride clusters.  

PubMed

The adsorption of water molecules (H(2)O) on sodium chloride cluster cations and anions was studied at 298 K over a mass range of 100-1200 amu using a custom-built laser desorption ionization reactor and mass spectrometer. Under the conditions used, the cations Na(3)Cl(2)(+) and Na(4)Cl(3)(+) bind up to three water molecules, whereas the larger cations, Na(5)Cl(4)(+) to Na(19)Cl(18)(+), formed hydrates with one or two only. The overall trend is a decrease in hydration with increasing cluster size, with an abrupt drop occurring at the closed-shell Na(14)Cl(13)(+). As compared to the cluster cations, the cluster anions showed almost no adsorption. Among smaller clusters, a weak adsorption of one water molecule was observed for the cluster anions Na(6)Cl(7)(-) and Na(7)Cl(8)(-). In the higher mass region, a substantial adsorption of one water molecule was observed for Na(14)Cl(15)(-). Density functional theory (DFT) computations were carried out for the adsorption of one molecule of H(2)O on the cations Na(n)Cl(n-1)(+), for n = 2-8, and the anions Na(n)Cl(n+1)(-), for n = 1-7. For each ion, the structure of the hydrate, the hydration energy, and the standard-state enthalpy, entropy, and Gibbs energy of hydration at 298 K were computed. In addition, it was useful to compute the distortion energy, defined as the electronic energy lost due to weakening of the Na-Cl bonds upon adsorption of H(2)O. The results show that strong adsorption of a H(2)O molecule occurs for the linear cations only at an end Na ion and for the nonlinear cations only at a corner Na ion bonded to two Cl ions. An unexpected result of the theoretical investigation for the anions is that certain low-energy isomers of Na(6)Cl(7)(-) and Na(7)Cl(8)(-) bind H(2)O strongly enough to produce the observed weak adsorption. The possible implications of these results for the initial hydration of extended NaCl surfaces are discussed. PMID:22098193

Bradshaw, James A; Gordon, Sidney L; Leavitt, Andrew J; Whetten, Robert L

2012-01-12

178

Exchange-induced negative- U charge order in N-doped WO3 : A spin-Peierls-like system  

NASA Astrophysics Data System (ADS)

An unconventional spin-Peierls-type distortion was found in a nonmagnetic atom N doped pseudo-one-dimensional WO3 system. The periodicity of the initial ferromagnetic WO3: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 WO3 structure is the origin of this spin-Peierls-like transition that leads to the stabilization of an unusual negative- U charge-ordered system.

Huda, Muhammad N.; Yan, Yanfa; Wei, Su-Huai; Al-Jassim, Mowafak M.

2009-09-01

179

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

NASA Astrophysics Data System (ADS)

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

Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

2012-11-01

180

Excellent passivation of highly doped p-type Si surfaces by the negative-charge-dielectric Al2O3  

NASA Astrophysics Data System (ADS)

From lifetime measurements, including a direct experimental comparison with thermal SiO2, a-Si :H, and as-deposited a-SiNx:H, it is demonstrated that Al2O3 provides an excellent level of surface passivation on highly B-doped c-Si with doping concentrations around 1019cm-3. The Al2O3 films, synthesized by plasma-assisted atomic layer deposition and with a high fixed negative charge density, limit the emitter saturation current density of B-diffused p +-emitters to ˜10 and ˜30fA/cm2 on >100 and 54?/sq sheet resistance p+-emitters, respectively. These results demonstrate that highly doped p-type Si surfaces can be passivated as effectively as highly doped n-type surfaces.

Hoex, B.; Schmidt, J.; Bock, R.; Altermatt, P. P.; van de Sanden, M. C. M.; Kessels, W. M. M.

2007-09-01

181

The NK-lysin derived peptide NK-2 preferentially kills cancer cells with increased surface levels of negatively charged phosphatidylserine.  

PubMed

The NK-lysin derived peptide NK-2 is a potent antibacterial, but non-toxic to a human keratinocyte cell line and of low hemolytic activity. Its target selectivity is based upon a strong binding preference to membranes containing anionic phospholipids, which are normally not found on the surface of human cells. Here, we analyzed the interaction of NK-2 with normal human lymphocytes and seven different human cancer cell lines and demonstrate that some of these cells expose negatively charged surface phosphatidylserine (PS), which presumably facilitates killing of the cells by NK-2. This is underlined by the specific intercalation of the peptide into PS-containing liposomes analyzed by fluorescence-resonance energy transfer spectroscopy. PMID:16269280

Schröder-Borm, Hannah; Bakalova, Rumiana; Andrä, Jörg

2005-11-01

182

Isomer-selected photoelectron spectroscopy of isolated DNA oligonucleotides: phosphate and nucleobase deprotonation at high negative charge states.  

PubMed

Fractionation according to ion mobility and mass-to-charge ratio has been used to select individual isomers of deprotonated DNA oligonucleotide multianions for subsequent isomer-resolved photoelectron spectroscopy (PES) in the gas phase. Isomer-resolved PE spectra have been recorded for tetranucleotides, pentanucleotides, and hexanucleotides. These were studied primarily in their highest accessible negative charge states (3-, 4-, and 5-, respectively), as provided by electrospraying from room temperature solutions. In particular, the PE spectra obtained for pentanucleotide tetraanions show evidence for two coexisting classes of gas-phase isomeric structures. We suggest that these two classes comprise: (i) species with excess electrons localized exclusively at deprotonated phosphate backbone sites and (ii) species with at least one deprotonated base (in addition to several deprotonated phosphates). By permuting the sequence of bases in various [A(5-x)T(x)](4-) and [GT(4)](4-) pentanucleotides, we have established that the second type of isomer is most likely to occur if the deprotonated base is located at the first or last position in the sequence. We have used a combination of molecular mechanics and semiempirical calculations together with a simple electrostatic model to explore the photodetachment mechanism underlying our photoelectron spectra. Comparison of predicted to measured photoelectron spectra suggests that a significant fraction of the detected electrons originates from the DNA bases (both deprotonated and neutral). PMID:22524691

Vonderach, Matthias; Ehrler, Oli T; Matheis, Katerina; Weis, Patrick; Kappes, Manfred M

2012-05-01

183

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

SciTech Connect

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

Preezant, Yevgeni; Tessler, Nir [Department of Electrical Engineering, Microelecronic and Nanoelectronic Centers, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

2011-01-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

185

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

PubMed

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

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

2014-12-14

186

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

NASA Astrophysics Data System (ADS)

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

Kecke, Lars; Ankerhold, Joachim

2012-06-01

187

Dissociative adsorption of hydrogen molecule on aluminum clusters: effect of charge and doping.  

PubMed

The dissociative chemisorption of molecular hydrogen on charged and neutral aluminum clusters Al12X (X = Mg, Al, Si) was investigated using DFT and a modified G3(MP2)-RAD procedure. Reaction barriers and enthalpies were determined for both neutral and singly charged clusters. The lowest barrier for dissociative adsorption of H2 on a neutral cluster was found for the Al12Mg cluster, whereas the highest barrier was found to be on the closed-shell Al12Si. The interaction of H2 with Al13(+) is found to proceed via an association complex that is 0.07 eV lower in energy than the isolated species and from which the barrier to H2 dissociative adsorption is only 0.16 eV. The most exothermic reaction of H2 with Al12X occurs for the Al13(+)/H2 system. In comparison, reactions with the closed-shell Al13(-) and Al12Si clusters are found to be endothermic. The barriers for H2 desorption from the dihydrogenated clusters are generally quite substantial. PMID:19226122

Henry, David J; Yarovsky, Irene

2009-03-19

188

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

189

Rotational motion of charged molecules in aqueous solutions. A change in the diffusion mechanism  

NASA Astrophysics Data System (ADS)

The rotational motion of the anions polyphenyl 2 (PP2) and pyrene tetrasulfonate (PTS) was studied as a function of the solvent viscosity by time-resolved fluorescence depolarization spectroscopy using the single photon counting technique. The viscosity was varied by changing the temperature and the composition of the water-glycerol mixtures, respectively. At low viscosity the reorientational behavior of PP2 and PTS is well described by the Stokes-Einstein-Debye (SED) equation under stick boundary conditions. With increasing viscosity (??25 cP) however the rotational motion did no longer follow the SED predictions. Instead, we observed a much faster relaxation time, approaching an asymptotic value at very high viscosities. It seems that in the high viscosity regime microscopic collisional effects rather than the macroscopic hydrodynamic drag of the solvent determines the reorientational dynamics of the solute molecules.

Mikosch, W.; Dorfmüller, Th.; Eimer, W.

1994-12-01

190

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

191

Effects of charge density on the recognition properties of molecularly imprinted polyampholyte hydrogels  

E-print Network

Effects of charge density on the recognition properties of molecularly imprinted polyampholyte to a templated molecule. In this study, the effect of including both positive and negative charges simultaneously sulfonic acid (AMPS) as an anionic monomer, various ratios of positive to negative charges were tested

Rubloff, Gary W.

192

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

193

Non-Adiabatic Photoprocesses of Fundamental Importance toChemistry: From Electronic Relaxation of DNA Bases to IntramolecularCharge Transfer in Electron Donor-Acceptor Molecules  

Microsoft Academic Search

Substituent effects on ultrafast electronic relaxation (internal conversion) of nucleobases and intramolecular charge transfer\\u000a in electron donor-acceptor (EDA) molecules, containing benzonitrile and diphenylacetylene moieties, have been investigated\\u000a using laser spectroscopy and simple ab initio methods. The results demonstrate the central role biradical states play in the\\u000a nonadiabatic energy- and charge-transfer dynamics. Specifically, subpicosecond internal conversion characteristic of the naturally\\u000a occurring

Marek Z. Zgierski; Takashige Fujiwara; Edward C. Lim

194

Electropolymerization of negatively charged Ni(II) complex for the selective determination of dopamine in the presence of ascorbic acid.  

PubMed

Electrodes for the dopamine (DA) determination in biological samples have been developed with improved selectivity and sensitivity in an excess of ascorbic acid (AA). Negatively charged Ni(II) complex was synthesized and electropolymerized on the glassy carbon electrode to impart the surface with anionic characteristics that could act both as a catalyst and as a discriminating layer against AA based on the electrostatic interaction. Thus prepared electrodes enabled selective determination of DA even in a large excess of AA by differential pulse voltammetry at physiological pH. Linear response was found down to 1.0 x 10(-7) M with 5.0 x 10(-9) M of LOD (Limit of Detection). In a flow injection analysis performed in an amperometric mode, the detection limit was lowered by two orders of magnitude down to 1.0 x 10(-9) M with a linear range of 1.0 x 10(-9) to 1.0 x 10(-6) M. The relative standard deviation was found to be 3.36% from 25 independent measurements for 1.0 x 10(-5) M of DA. Stable oxidation current of DA was observed even after 30 days storage in air. The recoveries of DA in the 100-fold diluted human urine samples were 97.7% for 4 measurements. The rate constant for the DA oxidation was 1.3 x 10(-3) cm s(-1) from hydrodynamic experiments using a rotating disk electrode. PMID:18155968

Xu, Guang-Ri; Xu, Ming-Lu; Zhang, Jia-Min; Kim, Sunghyun; Bae, Zun-Ung

2008-02-01

195

Orally Administered Nano-curcumin to Attenuate Morphine Tolerance: Comparison between Negatively Charged PLGA and Partially and Fully PEGylated Nanoparticles  

PubMed Central

We have formulated hydrophobic curcurmin [1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] into stable nanoparticle suspensions (nano-curcumin) to overcome its relatively low bioavailability, high rate of metabolism and rapid elimination and clearance from the body. Employing the curcumin nanoformulations as the platform, we discovered that curcumin has the potential to alleviate morphine tolerance. The two types of stable polymeric nanoparticles - poly(lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) - and the hybrid of the two were generated using flash nanoprecipitation integrated with spray drying. The optimized formulations have high drug loading (>45%), small particles size with narrow distribution, and controlled surface properties. Mice behavioral studies (tail-flick and hot-plate tests) were conducted to verify the effects of nano-curcumin on attenuating morphine tolerance. Significant analgesia was observed in mice during both tail-flick and hot-plate tests using orally administrated nano-curcumin following subcutaneous injections of morphine. However, unformulated curcumin at the same dose showed no effect. Compared with PEGylated nano-curcumin, negatively charged PLGA nanoparticles showed better functionality. PMID:24195658

Shen, Hao; Hu, Xiaoyu; Szymusiak, Magdalena; Wang, Zaijie Jim; Liu, Ying

2014-01-01

196

Orally administered nanocurcumin to attenuate morphine tolerance: comparison between negatively charged PLGA and partially and fully PEGylated nanoparticles.  

PubMed

We have formulated hydrophobic curcurmin [1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] into stable nanoparticle suspensions (nanocurcumin) to overcome its relatively low bioavailability, high rate of metabolism, and rapid elimination and clearance from the body. Employing the curcumin nanoformulations as the platform, we discovered that curcumin has the potential to alleviate morphine tolerance. The two types of stable polymeric nanoparticles, poly(lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA), and the hybrid of the two were generated using flash nanoprecipitation integrated with spray drying. The optimized formulations have high drug loading (>45%), small particles size with narrow distribution, and controlled surface properties. Mice behavioral studies (tail-flick and hot-plate tests) were conducted to verify the effects of nanocurcumin on attenuating morphine tolerance. Significant analgesia was observed in mice during both tail-flick and hot-plate tests using orally administered nanocurcumin following subcutaneous injections of morphine. However, unformulated curcumin at the same dose showed no effect. Compared with PEGylated nanocurcumin, negatively charged PLGA nanoparticles showed better functionality. PMID:24195658

Shen, Hao; Hu, Xiaoyu; Szymusiak, Magdalena; Wang, Zaijie Jim; Liu, Ying

2013-12-01

197

The Effects of Hofmeister Cations at Negatively Charged Hydrophilic Sarah C. Flores, Jaibir Kherb, Nicole Konelick, Xin Chen, and Paul S. Cremer*  

E-print Network

to their ability to "salt in" or "salt out" proteins from aqueous solutions.3 For cations, the usual ordering of cations with highly negatively charged solid/aqueous interfaces. Vibrational sum frequency spectroscopy, some key differences between these surfaces. On TiO2, Li+ , which is the best hydrated monovalent

198

New Antibiotic Molecules: Bypassing the Membrane Barrier of Gram Negative Bacteria Increases the Activity of Peptide Deformylase Inhibitors  

Microsoft Academic Search

Background: Multi-drug resistant (MDR) bacteria have become a major concern in hospitals worldwide and urgently require the development of new antibacterial molecules. Peptide deformylase is an intracellular target now well-recognized for the design of new antibiotics. The bacterial susceptibility to such a cytoplasmic target primarily depends on the capacity of the compound to reach and accumulate in the cytosol. Methodology\\/Principal

Laurent Mamelli; Sylvain Petit; Jacqueline Chevalier; Carmela Giglione; Aurélie Lieutaud; Thierry Meinnel; Isabelle Artaud; Jean-Marie Pagès

2009-01-01

199

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

200

Absence of a guiding effect and charge transfer in the interaction of keV-energy negative ions with Al{sub 2}O{sub 3} nanocapillaries  

SciTech Connect

In this work, the efficient electron loss process was observed for the transmission of 10- to 18-keV Cu{sup -} and Cl{sup -} ions through Al{sub 2}O{sub 3} nanocapillaries. The fractions of the scattered particles were simultaneously measured using a position-sensitive microchannel plate detector. The neutrals were guided through the capillary via multiple grazing scattering. In particular, the scattered Cl{sup -} ions were observed in the transmission, whereas no Cu{sup -} ion was formed. In contrast to highly charged ions, these results support strongly the fact that the scattering events dominate the transport of negative ions through the nanocapillaries and that there is no direct evidence for the formation of negative charge patches inside the capillaries which are able to repulse and guide negative ions efficiently.

Chen Lin; Guo Yanling; Jia Juanjuan; Zhang Hongqiang; Cui Ying; Shao Jianxiong; Yin Yongzhi; Qiu Xiyu; Lv Xueyang; Sun Guangzhi; Wang Jun; Chen Yifeng; Xi Fayuan; Chen Ximeng [School of Nuclear Science and Technology, Lanzhou University, 730000 (China)

2011-09-15

201

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

PubMed Central

Purpose The widespread use of nanoparticles (NPs) in industrial and biomedical applications has prompted growing concern regarding their potential toxicity and impact on human health. This study therefore investigated the subchronic, systemic oral toxicity and no-observed-adverse-effect level (NOAEL) of 20 nm, negatively charged zinc oxide (ZnOSM20(?)) NPs in Sprague Dawley rats for 90 days. Methods The high-dose NP level was set at 500 mg/kg of bodyweight, and the mid- and low-dose levels were set at 250 and 125 mg/kg, respectively. The rats were observed during a 14-day recovery period after the last NP administration for the persistence or reduction of any adverse effects. Toxicokinetic and distribution studies were also conducted to determine the systemic distribution of the NPs. Results No rats died during the test period. However, ZnOSM20(?) NPs (500 mg/kg) induced changes in the levels of anemia-related factors, prompted acinar cell apoptosis and ductular hyperplasia, stimulated periductular lymphoid cell infiltration and excessive salivation, and increased the numbers of regenerative acinar cells in the pancreas. In addition, stomach lesions were seen at 125, 250, and 500 mg/kg, and retinal atrophy was observed at 250 and 500 mg/kg. The Zn concentration was dose-dependently increased in the liver, kidney, intestines, and plasma, but not in other organs investigated. Conclusion A ZnOSM20(?) NP NOAEL could not be established from the current results, but the lowest-observed-adverse-effect level was 125 mg/kg. Furthermore, the NPs were associated with a number of undesirable systemic actions. Thus, their use in humans must be approached with caution. PMID:25565828

Park, Hark-Soo; Shin, Sung-Sup; Meang, Eun Ho; Hong, Jeong-sup; Park, Jong-Il; Kim, Su-Hyon; Koh, Sang-Bum; Lee, Seung-Young; Jang, Dong-Hyouk; Lee, Jong-Yun; Sun, Yle-Shik; Kang, Jin Seok; Kim, Yu-Ri; Kim, Meyoung-Kon; Jeong, Jayoung; Lee, Jong-Kwon; Son, Woo-Chan; Park, Jae-Hak

2014-01-01

202

The electronic structure of metal-molecule hybrids in charged interfaces: surface-enhanced Raman selection rules derived from plasmon-like resonances.  

PubMed

DFT calculations predict that plasmon-like excitations in small metal clusters are able to selectively modify the relative intensities of specific SERS bands of adsorbed molecules. These electronic resonances provide new kinds of SERS selection rules which can explain the huge enhancement of mode 9a of pyridine in the spectra recorded at negative electrode potentials. PMID:25407303

Román-Pérez, J; López-Tocón, I; Castro, J L; Arenas, J F; Soto, J; Otero, J C

2015-01-28

203

Double ionization of the propyne molecule to ground and electronically excited states of the doubly charged ion  

NASA Astrophysics Data System (ADS)

Double ionization of the propyne molecule has been studied experimentally and theoretically. By appropriate selection of the projectile ion used in double-charge-transfer spectroscopy, double-ionization energies to singlet and triplet states of the propyne dication were measured. In the spectra giving the singlet-state information, nine distinct peaks were observed, the positions of which correspond to double-ionization energies between 30.0 ± 0.2 and 41.6 ± 0.3 eV; these correlate well with data computed using a modified multiple-scattering X ? method, and with previously published calculated data if appropriate groups of calculated state energies are considered in some cases. Eight peaks were observed in the spectra which gave triplet-state information; the positions of the peaks correspond to double-ionization energies between 29.4 ± 0.2 and 39.0 ± 0.4 eV, in good agreement with the six two-hole configuration energies in that range calculated using the modified multiple-scattering X ? method which predicts the 3E, 3A 2 and 3A 1 states arising from the 2e -11e -1 configuration to be degenerate.

Andrews, S. R.; Harris, F. M.; Parry, D. E.

1995-05-01

204

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

SciTech Connect

A study of the double ionization of He by high-energy N{sup 7+} ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N{sub 2}, O{sub 2}, and CO molecular ions produced in collisions with 97-MeV Ar{sup 14+} ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO{sup 2+} and CO{sup 3+} from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO{sup 1+} and CO{sup 2+} molecular ions, and the branching ratios for the most prominent charge division channels of CO{sup 2+} through CO{sup 7+} were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

Watson, R.L.

1993-01-01

205

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

SciTech Connect

A study of the double ionization of He by high-energy N[sup 7+] ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N[sub 2], O[sub 2], and CO molecular ions produced in collisions with 97-MeV Ar[sup 14+] ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO[sup 2+] and CO[sup 3+] from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO[sup 1+] and CO[sup 2+] molecular ions, and the branching ratios for the most prominent charge division channels of CO[sup 2+] through CO[sup 7+] were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

Watson, R.L.

1993-01-01

206

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

207

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

208

Charge steering of laser plasma accelerated fast ions in a liquid spray — creation of MeV negative ion and neutral atom beams  

SciTech Connect

The scenario of “electron capture and loss” has been recently proposed for the formation of negative ion and neutral atom beams with up to MeV kinetic energy [S. Ter-Avetisyan, et al., Appl. Phys. Lett. 99, 051501 (2011)]. Validation of these processes and of their generic nature is here provided in experiments where the ion source and the interaction medium have been spatially separated. Fast positive ions accelerated from a laser plasma source are sent through a cold spray where their charge is changed. Such formed neutral atom or negative ion has nearly the same momentum as the original positive ion. Experiments are released for protons, carbon, and oxygen ions and corresponding beams of negative ions and neutral atoms have been obtained. The electron capture and loss phenomenon is confirmed to be the origin of the negative ion and neutral atom beams. The equilibrium ratios of different charge components and cross sections have been measured. Our method is general and allows the creation of beams of neutral atoms and negative ions for different species which inherit the characteristics of the positive ion source.

Schnürer, M.; Abicht, F.; Priebe, G.; Braenzel, J. [Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin (Germany)] [Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin (Germany); Prasad, R. [Institute for Laser and Plasma Physics, Heinrich Heine University, Duesseldorf 40225 (Germany)] [Institute for Laser and Plasma Physics, Heinrich Heine University, Duesseldorf 40225 (Germany); Borghesi, M. [School of Mathematics and Physics, The Queen's University of Belfast, Belfast BT7 1NN (United Kingdom) [School of Mathematics and Physics, The Queen's University of Belfast, Belfast BT7 1NN (United Kingdom); ELI–Beamlines, Institute of Physics, Czech Academy of Science, 18221 Prague (Czech Republic); Andreev, A. [Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin (Germany) [Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin (Germany); Vavilov State Optical Institute, 119034 St. Petersburg (Russian Federation); Nickles, P. V. [WCU Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)] [WCU Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of); Jequier, S.; Tikhonchuk, V. [Centre Lasers Intenses et Applications, University of Bordeaux, CEA, CNRS, 33405 Talence (France)] [Centre Lasers Intenses et Applications, University of Bordeaux, CEA, CNRS, 33405 Talence (France); Ter-Avetisyan, S. [ELI–Beamlines, Institute of Physics, Czech Academy of Science, 18221 Prague (Czech Republic)] [ELI–Beamlines, Institute of Physics, Czech Academy of Science, 18221 Prague (Czech Republic)

2013-11-15

209

Inhibition of anion and glucose permeabilities by anesthetics in erythrocytes. The mechanisms of action of positively and negatively charged drugs.  

PubMed

(1) The mode of action of anesthetics as inhibitors of Cl- and glucose transports in human red cells was studied. The term anesthetic is taken in its broad meaning as defined by Seeman (Seeman, P. (1972) Pharmacol. Rev. 24, 583-655) and covers anionic and cationic liposoluble compounds which reversibly block the rising phase of the action potential, without effect on the resting membrane potential. (2) Phenothiazine derivatives were chosen as prototypes of anesthetics because they represent a set of compounds having the same basic chemical structure, the phenothiazine ring, but with either a positive or a negative charge. (3) The Cl- self-exchange is inhibited by both cationic and anionic derivatives. However, to obtain the same level of inhibition, it is necessary to use a concentration 10-100 times higher with cationic than with anionic drugs. (4) At a concentration which inhibits Cl- permeability, cationic derivatives induce a very strong morphological change (cup-shaped cells: stomatocytes or spherostomatocytes) and protect erythrocytes against osmotic hemolysis, signifying that the membrane is fully expanded. Conversely, with anionic derivatives, inhibition occurs at a concentration which does not induce any apparent shape change or protect against osmotic hemolysis: there is no significant membrane expansion. (5) Glucose permeability, measured by glucose exit, is inhibited by cationic and anionic phenothiazine, but always at a concentration which fully expands the membrane as indicated by morphological changes and anti-hemolytic effects. It is interesting to point out that whilst glucose exit shows inhibition by cationic derivatives, glucose exchange flux is scarcely altered. (6) It is concluded that cationic and anionic anesthetics are general inhibitors of transmembrane solute movements involving a facilitated-diffusion process. However, the mechanism of inhibition is not identical for all: inhibition of glucose permeability by anionic and cationic anesthetics, as well as inhibition of Cl- permeability by cationic anesthetics may be of a non-specific nature and result from their interaction with the bilayer (this indirect effect is discussed); on the other hand, inhibition of Cl- permeability by anionic anesthetics may result from a specific perturbation of the transport mechanism according to recent evidence in some cases (Cousin, J.L. and Motais, R. (1979) J. Membrane Biol. 46, 125-153; Zaki, L., Ruffing, W. Gärtner, E.M., Fasold, H., Motais, R. and Passow, H. (1977) 11th FEBS Meeting, Copenhagen, A4 17-671. PMID:6105880

Motais, R; Baroin, A; Motais, A; Baldy, S

1980-07-01

210

Imaging and inhibition of multi-drug resistance in cancer cells via specific association with negatively charged CdTe quantum dots  

Microsoft Academic Search

Photoluminescent semiconductor quantum dots (QDs) have received significant attention in biological and biomedical fields because of their attractive properties. In this contribution, we have explored and evaluated the utilization of water-soluble nanocrystal CdTe quantum dots (QDs) capped with negatively charged 3-mercapitalpropionic acid (MPA)-QDs to enhance the drug uptake into the target cancer cells and the efficiency of the biomarker and

Yanyan Zhou; Lixin Shi; Qingning Li; Hui Jiang; Gang Lv; Juan Zhao; Chunhui Wu; Matthias Selke; Xuemei Wang

2010-01-01

211

Electrochemical surface science: The study of monolayers of ad-atoms and solvent molecules at charged metal interfaces  

NASA Astrophysics Data System (ADS)

In parallel with the spectacular advances that have been made in recent years in the field of metal/vacuum surface science, there have been corresponding interesting developments of a complementary kind in electrochemical surface science. This article describes recent advances in the latter field, and their experimental and theoretical bases. However, the molecular situation at electrode interfaces is very complex compared with that at a metal/vacuum interface, owing to adsorption and orientation of solvent molecules, and the presence of solvated ions. Hence these topics must be considered as well as the surface science of the metal electrode itself. In comparison with metal/vacuum surface science, electrochemical studies on metal interfaces can utilize the electrode potential as an additional independent variable and thus control surface charge density, coverage by Faradaically deposited ad-atoms, co-adsorption of cations or anions and solvent dipole orientation. Modulations of electrode potential in time allow the kinetic relaxation characteristics of monolayers to be followed, and the potential-modulated reflectivity and spectral absorption of species in the interphase to be studied. Electrochemically controllable sub-monolayer coverages of, e.g., metal ad-atoms have interesting catalytic effects on other continuous electrochemical reactions, such as oxygen reduction or formic acid oxidation. Experiments based on electrochemical potential pulse and sweep, and current pulse methods enable chemisorption of ad-atom monolayers to be studied in fine detail. Multiple state chemisorption in monolayers is commonly observed, even on single crystal surfaces, and fine resolution of the states can be achieved by electrochemical techniques. The kinetics of monolayer deposition and desorption can also be followed, as well as the dynamics of reconstruction processes e.g. in 0 monolayers as a function of time and potential. The electrochemical methods allow direct determination of the differential isotherm for adsorption as well as the usual integral one. The former gives details of multiple state adsorption, and provides information on interaction effects in the monolayer and kinetics of its formation. Ionicity of ad-species can also be evaluated. Recent advances in combining electrochemical systems in situ with high-vacuum LEED, Auger and ESCA apparatus are described. Since electrochemical surface science has necessarily to be able to study processes at the interfaces of metals in contact with liquid solutions, an important area of the field has been the treatment and evaluation of solvent dipole adsorption and orientation as a function of electrode potential or surface charge density.

Conway, B. E.

212

Positronium ions and molecules  

NASA Technical Reports Server (NTRS)

Recent theoretical studies on positronium ions and molecules are discussed. A positronium ion is a three particle system consisting of two electrons in singlet spin state, and a positron. Recent studies include calculations of its binding energy, positron annihilation rate, and investigations of its doubly excited resonant states. A positronium molecule is a four body system consisting of two positrons and two electrons in an overall singlet spin state. The recent calculations of its binding energy against the dissociation into two positronium atoms, and studies of auto-detaching states in positronium molecules are discussed. These auto-dissociating states, which are believed to be part of the Rydberg series as a result of a positron attaching to a negatively charged positronium ion, Ps-, would appear as resonances in Ps-Ps scattering.

Ho, Y. K.

1990-01-01

213

Accurate mass measurements and ultrahigh-resolution: evaluation of different mass spectrometers for daily routine analysis of small molecules in negative electrospray ionization mode.  

PubMed

Six mass spectrometers based on different mass analyzer technologies, such as time-of-flight (TOF), hybrid quadrupole-TOF (Q-TOF), orbitrap, Fourier transform ion cyclotron resonance (FT-ICR), and triple quadrupole (QqQ), installed at independent laboratories have been tested during a single day of work for the analysis of small molecules in negative electrospray ionization (ESI) mode. The uncertainty in the mass measurements obtained from each mass spectrometer has been determined by taking the precision and accuracy of replicate measurements into account. The present study is focused on calibration processes (before, after, and during the mass measurement), the resolving power of the mass spectrometers, and the data processing for obtaining elemental formulae. The mass range between m/z 100 and 600 has been evaluated with a mix of four standards. This mass range includes small molecules usually detected in food and environmental samples. Negative ESI has been tested as there is almost no data on accurate mass (AM) measurements in this mode. Moreover, it has been used because it is the ESI mode for analysis of many compounds, such as pharmaceutical, herbicides, and fluorinated compounds. Natural organic matter has been used to demonstrate the significance of ultrahigh-resolution in complex mixtures. Sub-millidalton accuracy and precision have been obtained with Q-TOF, FT-ICR, and orbitrap achieving equivalent results. Poorer accuracy and precision have been obtained with the QqQ used: 11 mDa root-mean-square error and 6-11 mDa standard deviation. Some advice and requirements for daily AM routine analysis are also discussed here. PMID:21553215

Cortés-Francisco, Nuria; Flores, Cintia; Moyano, Encarnación; Caixach, Josep

2011-07-01

214

Combination of osteopontin and activated leukocyte cell adhesion molecule as potent prognostic discriminators in HER2- and ER-negative breast cancer  

PubMed Central

Background: To analyse the discriminative impact of osteopontin (OPN) and activated leukocyte cell adhesion molecule (ALCAM), combined with human epidermal growth factor 2 (HER2) and oestrogen receptor (ER) in breast cancer. Methods: Osteopontin, ALCAM, HER2 and ER mRNA expression in breast cancer tissues of 481 patients were analysed (mRNA microarray analysis, kinetic RT–PCR). Hierarchical clustering was performed in training cohort A (N=100, adjuvant treatment) and validation cohorts B (N=200, no adjuvant treatment, low-risk) and C (N=181, adjuvant treatment, high-risk). Results: Negative/low ER and HER2, high OPN and low ALCAM mRNA expression helped to identify patients at particularly high risk, showing shorter DFS, P<0.001, and OAS, P=0.001. Although both validation cohorts showed diverse risk and treatment profiles, this marker constellation was concordantly associated with shorter DFS and OAS (P<0.001 and P=0.075 for cohort B and P=0.043 and P<0.001 for cohort C, respectively). In multivariate analysis, this algorithm was the main independent prognostic factor. Cohort B: DFS, P=0.0065, OAS, not significant; cohort C: DFS, P=0.026, OAS, P<0.001. Conclusion: Activated leukocyte cell adhesion molecule and OPN mRNA expression has a strong discriminative impact on survival within cancer patients with low or negative expression of ER and HER2, so called ‘high-risk' breast cancers, and might help in identifying patients who could benefit from new treatment approaches like targeted therapies in the adjuvant setting. PMID:20736952

Ihnen, M; Wirtz, R M; Kalogeras, K T; Milde-Langosch, K; Schmidt, M; Witzel, I; Eleftheraki, A G; Papadimitriou, C; Jänicke, F; Briassoulis, E; Pectasides, D; Rody, A; Fountzilas, G; Müller, V

2010-01-01

215

Negative ion production in small angle scattering of highly charged ions from the (0001) surface of highly oriented pyrolytic graphite  

Microsoft Academic Search

Highly charged N, O, F, and S ions, chosen for their electron affinities, were extracted from the Lawrence Livermore National Laboratory’s EBIT II. After collimation, these ions struck a target of highly oriented pyrolytic graphite (HOPG) at an incident angle of 1.0 degree. Those ions scattered by 2.35 degrees (1.35 degree with respect to the surface) were charge state analyzed

M. Reaves; Q. C. Kessel; E. Pollack; W. W. Smith; M. A. Briere; D. H. Schneider

1997-01-01

216

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

2014-12-28

217

Electrophoretic deposition of TiO2 and composite TiO2-MnO2 films using benzoic acid and phenolic molecules as charging additives.  

PubMed

Electrophoretic deposition (EPD) method has been developed for the fabrication of TiO(2) and MnO(2) films. Benzoic acid and phenolic molecules, such as 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, salicylic acid and salicylic acid sodium salt were investigated as charging additives for the EPD of TiO(2) and MnO(2) particles. The deposition yield has been studied as a function of the additive concentration and deposition time for cathodic deposits obtained from the suspensions, containing benzoic acid, 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and anodic deposits prepared from the suspensions, containing gallic acid and salicylic acid sodium salt. The results obtained for the phenolic molecules with different number of OH groups were analyzed and compared with corresponding experimental data for benzoic acid without OH groups. The adjacent OH groups, as well as adjacent OH and COOH groups bonded to the aromatic ring of the phenolic molecules were beneficial for adsorption of the molecules on oxide particles. The adsorption mechanisms involved the interaction of COOH groups and OH groups of the organic molecules with metal ions on the particle surfaces and complexation. Gallic acid was shown to be an effective charging additive, which provided stabilization of TiO(2) and MnO(2) particles in the suspensions and enabled their deposition. It was shown that composite TiO(2)-MnO(2) films can be obtained using gallic acid as a common dispersing agent for TiO(2) and MnO(2). The Ti/Mn ratio in the composite films was varied in the range of 0-1.3. The thickness of the films was varied in the range of 0-10 ?m. The mechanisms of particle charging and deposition were discussed. PMID:20850128

Wu, K; Wang, Y; Zhitomirsky, I

2010-12-15

218

Geoengineering with Charged Droplets  

NASA Astrophysics Data System (ADS)

Water molecules in a droplet are held together by intermolecular forces generated by hydrogen bonding which has a bonding energy of only about 0.2 eV. One can create a more rugged droplet by using an ion as a condensation nucleus. In that case, water molecules are held together by the interaction between the ion and the dipole moments of the water molecules surrounding the ion, in addition to any hydrogen bonding. In this research, properties of such charged droplets were investigated using first principle quantum mechanical calculations. A molecule which exhibits positive electron affinity is a good candidate to serve as the ionic condensation nucleus, because addition of an electron to such a molecule creates an energetically more stable state than the neutral molecule. A good example is the oxygen molecule (O2) where energy of O2 negative (O2-) ion is lower than that of the neutral O2 by about 0.5 eV. Examples of other molecules which have positive electron affinity include ozone (O3), nitrogen dioxide (NO2) and sulfur oxides (SOx, x=1-3). Atomic models used in the calculations consisted of a negative ion of one of the molecules mentioned above surrounded by water molecules. Calculations were performed using the DFT method with B3LYP hybrid functional and Pople type basis sets with polarization and diffuse functions. Energy of interaction between O2- ion and the water molecule was found to be ~0.7 eV. This energy is an order of magnitude greater than the thermal energy of even the highest temperatures encountered in the atmosphere. Once created, charged rugged droplets can survive in hot and dry climates where they can be utilized to create humidity and precipitation. The ion which serves as the nucleus of the droplet can attract not only water molecules but also other dipolar gases in the atmosphere. Such dipolar gases include industrial pollutants, for example nitrogen dioxide (NO2) or sulfur dioxide (SO2). Energy of interaction between O2- ion and pollutant molecules was calculated to be ~0.5 eV for NO2 and ~0.9 eV for SO2. These values are comparable to that of water, hence charged droplets have the potential to serve as scavengers of pollutants in the atmosphere. The charged droplet can also interact with quadrupolar gases depending on the charge distribution of the gas. A quadrupole of interest is carbon dioxide (CO2) where oxygens are slightly negative and carbon is slightly positive in a neutral molecule. When CO2 is in the vicinity of a negative ion, the carbon atom gets attracted to the ion, whereas oxygens are repelled from it. This interaction distorts the linear geometry of CO2, turning it into a small dipole. Energy of interaction between O2- ion and CO2 was calculated to be ~0.3 eV which is smaller than those of the above mentioned dipoles, but still significantly greater than the typical thermal energy at 25 C (~0.03 eV). One can expect the diffusion of atmospheric CO2 into the droplets to be enhanced due to the charge. Hence such droplets can help capture the CO2 in the atmosphere and sequester it simply as rain. Charged droplets can be created using electrical,optical, thermal or other means. A method which utilizes solar energy will be described in the presentation.

Gokturk, H.

2011-12-01

219

Quantum theory of atoms in molecules/charge-charge flux-dipole flux models for fundamental vibrational intensity changes on H-bond formation of water and hydrogen fluoride  

SciTech Connect

The Quantum Theory of Atoms In Molecules/Charge-Charge Flux-Dipole Flux (QTAIM/CCFDF) model has been used to investigate the electronic structure variations associated with intensity changes on dimerization for the vibrations of the water and hydrogen fluoride dimers as well as in the water-hydrogen fluoride complex. QCISD/cc-pVTZ wave functions applied in the QTAIM/CCFDF model accurately provide the fundamental band intensities of water and its dimer predicting symmetric and antisymmetric stretching intensity increases for the donor unit of 159 and 47 km mol{sup ?1} on H-bond formation compared with the experimental values of 141 and 53 km mol{sup ?1}. The symmetric stretching of the proton donor water in the dimer has intensity contributions parallel and perpendicular to its C{sub 2v} axis. The largest calculated increase of 107 km mol{sup ?1} is perpendicular to this axis and owes to equilibrium atomic charge displacements on vibration. Charge flux decreases occurring parallel and perpendicular to this axis result in 42 and 40 km mol{sup ?1} total intensity increases for the symmetric and antisymmetric stretches, respectively. These decreases in charge flux result in intensity enhancements because of the interaction contributions to the intensities between charge flux and the other quantities. Even though dipole flux contributions are much smaller than the charge and charge flux ones in both monomer and dimer water they are important for calculating the total intensity values for their stretching vibrations since the charge-charge flux interaction term cancels the charge and charge flux contributions. The QTAIM/CCFDF hydrogen-bonded stretching intensity strengthening of 321 km mol{sup ?1} on HF dimerization and 592 km mol{sup ?1} on HF:H{sub 2}O complexation can essentially be explained by charge, charge flux and their interaction cross term. Atomic contributions to the intensities are also calculated. The bridge hydrogen atomic contributions alone explain 145, 237, and 574 km mol{sup ?1} of the H-bond stretching intensity enhancements for the water and HF dimers and their heterodimer compared with total increments of 149, 321, and 592 km mol{sup ?1}, respectively.

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

2014-02-28

220

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

221

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

NASA Astrophysics Data System (ADS)

To assess the importance of charge-transfer on the interface properties, we studied the interaction of the tetracyanoethylene (TCNE) molecule with various copper surfaces. TCNE, a highly electrophilic molecule, appears as an ideal candidate to study the influence of high charge-transfer on the electronic and structural properties of molecule-surface interfaces. Indeed, various TCNE-transition metal complexes exhibit magnetism at room temperature, which is in agreement with a very significant change of the residual charge on the TCNE molecule. The adsorption of TCNE molecules on Cu(100) and Cu(111) surfaces was studied by scanning tunneling microscopy (STM) and by density functional theory (DFT) calculations with a local density approximation (LDA). DFT-LDA calculations were performed to determine the geometric and electronic structure of the studied interfaces. Mulliken analysis was used to evaluate the partial net charge on the adsorbed species. The density of states (DOS) diagrams provided informations on the nature of the frontier orbitals involved in the charge-transfer at molecule-metal interfaces. To validate the theoretical observations, a comparative study was conducted between our simulated STM images and experimental STM images provided by our collaborators. The theoretical STM images were obtained with the SPAGS-STM software using the Landauer-Buttiker formalism with a semi-empirical Hamiltonian based on the extended Huckel theory (EHT) and parameterized using DFT calculations. During the development of the SPAGS-STM software, we have created a discretization module allowing rapid generation of STM images. This module is based on an adaptive Delaunay meshing scheme to minimize the amount of tunneling current to be computed. The general idea consists into refining the mesh, and therefore the calculations, near large contrast zones rather than over the entire image. The adapted mesh provides an STM image resolution equivalent to that obtained with a conventional Cartesian grid but with a significantly smaller number of calculated pixels. This module is independent of the solver used to compute the tunneling current and can be transposed to different imaging techniques. Our work on the adsorption of TCNE molecules on Cu(100) surfaces revealed that the molecules assemble into a 1D chain, thereby buckling excessively a few Cu atoms from the surface. The large deformations observed at the molecule-metal interface show that the Cu atoms close to the TCNE nitrile groups assist the molecular assembly and show a distinct behavior compared with other Cu atoms. A strong charge-transfer is observed at the interface leading to an almost complete occupation of the state ascribed to the lowest unoccupied molecular orbital (LUMO) of TCNE in gas phase. In addition, a back-donation of charge from the molecule to the metal via the states associated with the highest occupied molecular orbitals (HOMO) of TCNE in gas phase may be seen. The magnitude of the charge-transfer between a TCNE molecule and Cu atoms is of the same order on the Cu(111) surface but causes much less buckling than that on the Cu(100) surface. However, experimental STM images of single TCNE molecules adsorbed on Cu(111) surfaces reveal a surprising electronic multistability. In addition, scanning tunneling spectroscopy (STS) reveals that one of these states has a magnetic nature and shows a Kondo resonance. STM simulations identified the source of two non-magnetic states. DFT-LDA calculations were able to ascribe the magnetic state to the partial occupation of a state corresponding to the LUMO+2 of TCNE. Moreover, the calculations showed that additional molecular deformations to those of TCNE in adsorbed phase, such the elongation of the C=C central bond and the bend of nitrile groups toward the surface, favor this charge-transfer to the LUMO+2. This suggested the presence of a Kondo state through the vibrational excitation of the stretching mode of the C=C central bond. The main results of this thesis led to the conclusion that strong charge-transfer between ad

Bedwani, Stephane

222

Positively and Negatively Charged Ionic Modifications to Cellulose Assessed as Cotton-Based Protease-Lowering and Haemostatic Wound Agents  

Technology Transfer Automated Retrieval System (TEKTRAN)

Recent developments in cellulose wound dressings targeted to different stages of wound healing have been based on structural and charge modifications that function to modulate events in the complex inflammatory and hemostatic phases of wound healing. Hemostasis and inflammation comprise two overlapp...

223

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

PubMed Central

The canonical AX-CPT task measures two forms of cognitive control: sustained goal-oriented control (“proactive” control) and transient changes in cognitive control following unexpected events (“reactive” control). We modified this task by adding negative and neutral International Affective Picture System (IAPS) pictures to assess the effects of negative emotion on these two forms of cognitive control. Proactive and reactive control styles were assessed based on measures of behavior and electrophysiology, including the N2 event-related potential component and source space activation (Low Resolution Tomography [LORETA]). We found slower reaction-times and greater DLPFC activation for negative relative to neutral stimuli. Additionally, we found that a proactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during actively maintained previously cued information and that a reactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during just-in-time environmentally triggered information. This pattern of results was evident in relatively neutral contexts, but in the face of negative emotion, these associations were not found, suggesting potential response style-by-emotion interaction effects on prefrontal neural activation PMID:24021156

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

2013-01-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

225

Positively and negatively charged ionic modifications to cellulose assessed as cotton-based protease-lowering and hemostatic wound agents  

Microsoft Academic Search

Recent developments in cellulose wound dressings targeted to different stages of wound healing have been based on structural\\u000a and charge modifications that function to modulate events in the complex inflammatory and hemostatic phases of wound healing.\\u000a Hemostasis and inflammation comprise two overlapping but distinct phases of wound healing wherein different dressing material\\u000a properties are required to bring pathological events under

J. V. Edwards; Phyllis Howley; Nicolette Prevost; Brian Condon; Judy Arnold; Robert Diegelmann

2009-01-01

226

Surface expression patterns of negative regulatory molecules identify determinants of virus-specific CD8+ T-cell exhaustion in HIV infection  

PubMed Central

A highly complex network of coinhibitory and costimulatory receptors regulates the outcome of virus-specific CD8+ T-cell responses. Here, we report on the expression patterns of multiple inhibitory receptors on HIV-specific, cytomegalovirus-specific, and bulk CD8+ T-cell memory populations. In contrast to cytomegalovirus-specific CD8+ T cells, the majority of HIV-specific CD8+ T cells exhibited an immature phenotype and expressed Programmed Death-1, CD160 and 2B4 but not lymphocyte activation gene-3. Notably, before antiretroviral therapy, simultaneous expression of these negative regulators correlated strongly with both HIV load and impaired cytokine production. Suppression of HIV replication by antiretroviral therapy was associated with reduced surface expression of inhibitory molecules on HIV-specific CD8+ T cells. Furthermore, in vitro manipulation of Programmed Death-1 and 2B4 inhibitory pathways increased the proliferative capacity of HIV-specific CD8+ T cells. Thus, multiple coinhibitory receptors can affect the development of HIV-specific CD8+ T-cell responses and, by extension, represent potential targets for new immune-based interventions in HIV-infected persons. PMID:21398582

Yamamoto, Takuya; Price, David A.; Casazza, Joseph P.; Ferrari, Guido; Nason, Martha; Chattopadhyay, Pratip K.; Roederer, Mario; Gostick, Emma; Katsikis, Peter D.; Douek, Daniel C.; Haubrich, Richard; Petrovas, Constantinos

2011-01-01

227

Charge/discharge characteristics of the coal-tar pitch carbon as negative electrode in Li-ion batteries  

NASA Astrophysics Data System (ADS)

The charge/discharge characteristics were studied for the coal-tar pitch-based carbon (CTPC), which was pyrolyzed under the condition to form anisotropic mesophase pitch and then heat treated at temperatures ranging from 500 to 1300°C in N 2 atmosphere. As the heat treatment temperature increased, the reversible capacity for the CTPC increased progressively up to 1000°C, while the irreversible capacity decreased continuously. Carbons synthesized through the extraction of anisotropic mesophases showed higher reversible and lower irreversible capacities than the directly pyrolyzed ones.

Kim, Jung-Sik

228

Neutral and negatively charged Al12X (X=Si, Ge, Sn, Pb) clusters studied from first principles S. F. Li1,2 and X. G. Gong1  

E-print Network

Neutral and negatively charged Al12X (X=Si, Ge, Sn, Pb) clusters studied from first principles S. F neutral and anionic Al12X X=Si, Ge, Sn, Pb clusters. We find that both neutral and charged Al12Si cluster prefer icosahedral structure, in agreement with previous calculations. However, each of Al12X X=Ge, Sn

Gong, Xingao

229

A negative charge in transmembrane segment 1 of domain II of the cockroach sodium channel is critical for channel gating and action of pyrethroid insecticides  

SciTech Connect

Voltage-gated sodium channels are the primary target of pyrethroids, an important class of synthetic insecticides. Pyrethroids bind to a distinct receptor site on sodium channels and prolong the open state by inhibiting channel deactivation and inactivation. Recent studies have begun to reveal sodium channel residues important for pyrethroid binding. However, how pyrethroid binding leads to inhibition of sodium channel deactivation and inactivation remains elusive. In this study, we show that a negatively charged aspartic acid residue at position 802 (D802) located in the extracellular end of transmembrane segment 1 of domain II (IIS1) is critical for both the action of pyrethroids and the voltage dependence of channel activation. Charge-reversing or -neutralizing substitutions (K, G, or A) of D802 shifted the voltage dependence of activation in the depolarizing direction and reduced channel sensitivity to deltamethrin, a pyrethroid insecticide. The charge-reversing mutation D802K also accelerated open-state deactivation, which may have counteracted the inhibition of sodium channel deactivation by deltamethrin. In contrast, the D802G substitution slowed open-state deactivation, suggesting an additional mechanism for neutralizing the action of deltamethrin. Importantly, Schild analysis showed that D802 is not involved in pyrethroid binding. Thus, we have identified a sodium channel residue that is critical for regulating the action of pyrethroids on the sodium channel without affecting the receptor site of pyrethroids.

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

2010-08-15

230

Mutation of conserved negatively charged residues in the S2 and S3 transmembrane segments of a mammalian K+ channel selectively modulates channel gating.  

PubMed Central

Voltage-gated channel proteins sense a change in the transmembrane electric field and respond with a conformational change that allows ions to diffuse across the pore-forming structure. Site-specific mutagenesis combined with electrophysiological analysis of expressed mutants in amphibian oocytes has previously established the S4 transmembrane segment as an element of the voltage sensor. Here, we show that mutations of conserved negatively charged residues in S2 and S3 of a brain K+ channel, thought of as countercharges for the positively charged residues in S4, selectively modulate channel gating without modifying the permeation properties. Mutations of Glu235 in S2 that neutralize or reverse charge increase the probability of channel opening and the apparent gating valence. In contrast, replacements of Glu272 by Arg or Thr268 by Asp in S3 decrease the open probability and the apparent gating valence. Residue Glu225 in S2 tolerated replacement only by acidic residues, whereas Asp258 in S3 was intolerant to any attempted change. These results imply that S2 and S3 are unlikely to be involved in channel lining, yet, together with S4, may be additional components of the voltage-sensing structure. PMID:7568145

Planells-Cases, R; Ferrer-Montiel, A V; Patten, C D; Montal, M

1995-01-01

231

R.E.D. Server: a web service for deriving RESP and ESP charges and building force field libraries for new molecules and molecular fragments  

PubMed Central

R.E.D. Server is a unique, open web service, designed to derive non-polarizable RESP and ESP charges and to build force field libraries for new molecules/molecular fragments. It provides to computational biologists the means to derive rigorously molecular electrostatic potential-based charges embedded in force field libraries that are ready to be used in force field development, charge validation and molecular dynamics simulations. R.E.D. Server interfaces quantum mechanics programs, the RESP program and the latest version of the R.E.D. tools. A two step approach has been developed. The first one consists of preparing P2N file(s) to rigorously define key elements such as atom names, topology and chemical equivalencing needed when building a force field library. Then, P2N files are used to derive RESP or ESP charges embedded in force field libraries in the Tripos mol2 format. In complex cases an entire set of force field libraries or force field topology database is generated. Other features developed in R.E.D. Server include help services, a demonstration, tutorials, frequently asked questions, Jmol-based tools useful to construct PDB input files and parse R.E.D. Server outputs as well as a graphical queuing system allowing any user to check the status of R.E.D. Server jobs. PMID:21609950

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

2011-01-01

232

R.E.D. Server: a web service for deriving RESP and ESP charges and building force field libraries for new molecules and molecular fragments.  

PubMed

R.E.D. Server is a unique, open web service, designed to derive non-polarizable RESP and ESP charges and to build force field libraries for new molecules/molecular fragments. It provides to computational biologists the means to derive rigorously molecular electrostatic potential-based charges embedded in force field libraries that are ready to be used in force field development, charge validation and molecular dynamics simulations. R.E.D. Server interfaces quantum mechanics programs, the RESP program and the latest version of the R.E.D. tools. A two step approach has been developed. The first one consists of preparing P2N file(s) to rigorously define key elements such as atom names, topology and chemical equivalencing needed when building a force field library. Then, P2N files are used to derive RESP or ESP charges embedded in force field libraries in the Tripos mol2 format. In complex cases an entire set of force field libraries or force field topology database is generated. Other features developed in R.E.D. Server include help services, a demonstration, tutorials, frequently asked questions, Jmol-based tools useful to construct PDB input files and parse R.E.D. Server outputs as well as a graphical queuing system allowing any user to check the status of R.E.D. Server jobs. PMID:21609950

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

2011-07-01

233

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

234

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

235

Basic vapor exposure for tuning the charge state distribution of proteins in negative electrospray ionization: elucidation of mechanisms by fluorescence spectroscopy.  

PubMed

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. PMID:22565506

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

2012-07-01

236

Revised Big Bang Nucleosynthesis with Long-lived, Negatively Charged Massive Particles: Updated Recombination Rates, Primordial 9Be Nucleosynthesis, and Impact of New 6Li Limits  

NASA Astrophysics Data System (ADS)

We extensively reanalyze the effects of a long-lived, negatively charged massive particle, X -, on big bang nucleosynthesis (BBN). The BBN model with an X - particle was originally motivated by the discrepancy between the 6, 7Li abundances predicted in the standard BBN model and those inferred from observations of metal-poor stars. In this model, 7Be is destroyed via the recombination with an X - particle followed by radiative proton capture. We calculate precise rates for the radiative recombinations of 7Be, 7Li, 9Be, and 4He with X -. In nonresonant rates, we take into account respective partial waves of scattering states and respective bound states. The finite sizes of nuclear charge distributions cause deviations in wave functions from those of point-charge nuclei. For a heavy X - mass, mX >~ 100 GeV, the d-wave ? 2P transition is most important for 7Li and 7, 9Be, unlike recombination with electrons. Our new nonresonant rate of the 7Be recombination for mX = 1000 GeV is more than six times larger than the existing rate. Moreover, we suggest a new important reaction for 9Be production: the recombination of 7Li and X - followed by deuteron capture. We derive binding energies of X nuclei along with reaction rates and Q values. We then calculate BBN and find that the amount of 7Be destruction depends significantly on the charge distribution of 7Be. Finally, updated constraints on the initial abundance and the lifetime of the X - are derived in the context of revised upper limits to the primordial 6Li abundance. Parameter regions for the solution to the 7Li problem and the primordial 9Be abundances are revised.

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

2014-09-01

237

Identification of novel small molecule inhibitors of 4-diphosphocytidyl-2-C-methyl-D-erythritol (CDP-ME) kinase of Gram-negative bacteria.  

PubMed

The biosyntheses of isoprenoids is essential for the survival in all living organisms, and requires one of the two biochemical pathways: (a) Mevalonate (MVA) Pathway or (b) Methylerythritol Phosphate (MEP) Pathway. The latter pathway, which is used by all Gram-negative bacteria, some Gram-positive bacteria and a few apicomplexan protozoa, provides an attractive target for the development of new antimicrobials because of its absence in humans. In this report, we describe two different approaches that we used to identify novel small molecule inhibitors of Escherichia coli and Yersinia pestis 4-diphosphocytidyl-2-C-methyl D-erythritol (CDP-ME) kinases, key enzymes of the MEP pathway encoded by the E. coli ispE and Y. pestisipk genes, respectively. In the first approach, we explored existing inhibitors of the GHMP kinases while in the second approach; we performed computational high-throughput screening of compound libraries by targeting the CDP-ME binding site of the two bacterial enzymes. From the first approach, we identified two compounds with 6-(benzylthio)-2-(2-hydroxyphenyl)-4-oxo-3,4-dihydro-2H-1,3-thiazine-5-carbonitrile and (Z)-3-methyl-4-((5-phenylfuran-2-yl)methylene)isoxazol-5(4H)-one scaffolds which inhibited E. coli CDP-ME kinase in vitro. We then performed substructure search and docking experiments based on these two scaffolds and identified twenty three analogs for structure-activity relationship (SAR) studies. Three new compounds from the isoxazol-5(4H)-one series have shown inhibitory activities against E. coli and Y. pestis CDP-ME kinases with the IC(50) values ranging from 7 to 13 ?M. The second approach by computational high-throughput screening (HTS) of two million drug-like compounds yielded two compounds with benzenesulfonamide and acetamide moieties which, at a concentration of 20 ?M, inhibited 80% and 65%, respectively, of control CDP-ME kinase activity. PMID:21903402

Tang, M; Odejinmi, S I; Allette, Y M; Vankayalapati, H; Lai, K

2011-10-01

238

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

239

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

E-print Network

York 10027 (Received: May 26, 1987) This paper presents a systematic study of gas-phase p-(N,N-dimethy1, and the spectroscopyof the stoichiometriccomplex with water, methanol, ammonia, and acetonitrile in the beam is reported~lecular~~'~charge separations have been studied. The solutesolvent interactions can be passive, as observed in the cage effect

Eisenthal, Kenneth B.

240

Nanoscale Charge Localization Induced by Random Orientations of Organic Molecules in Hybrid Perovskite CH3NH3PbI3.  

PubMed

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

Ma, Jie; Wang, Lin-Wang

2015-01-14

241

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

242

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

PubMed Central

The multicatalytic ubiquitin-proteasome system (UPS) carries out proteolysis in a highly orchestrated way and regulates a large number of cellular processes. Deregulation of the UPS in many disorders has been documented. In some cases, e.g. carcinogenesis, elevated proteasome activity has been implicated in disease development, while the etiology of other diseases, e.g. neurodegeneration, includes decreased UPS activity. Therefore, agents that alter proteasome activity could suppress as well as enhance a multitude of diseases. Metal oxide nanoparticles, often developed as diagnostic tools, have not previously been tested as modulators of proteasome activity. Here, several types of metal oxide nanoparticles were found to adsorb to the proteasome and show variable preferential binding for particular proteasome subunits with several peptide binding “hotspots” possible. These interactions depend on the size, charge, and concentration of the nanoparticles and affect proteasome activity in a time-dependent manner. Should metal oxide nanoparticles increase proteasome activity in cells, as they do in vitro, unintended effects related to changes in proteasome function can be expected. PMID:23930940

Falaschetti, Christine A.; Paunesku, Tatjana; Kurepa, Jasmina; Nanavati, Dhaval; Chou, Stanley S.; De, Mrinmoy; Song, MinHa; Jang, Jung-tak; Wu, Aiguo; Dravid, Vinayak P.; Cheon, Jinwoo; Smalle, Jan; Woloschak, Gayle E.

2013-01-01

243

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

244

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

245

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

246

Charge Falling Through a Charged Ring Model  

NSDL National Science Digital Library

The Charge Falling Through a Charged Ring shows dynamics of a charged ball as it is released and falls through a ring of charge. The ball and the ring can be charged with a positive blue) or a (red) negative charge.

Krizaj, Dejan

2010-11-09

247

Mechanism of A-B intersite charge transfer and negative thermal expansion in A-site-ordered perovskite LaCu3Fe4O12  

NASA Astrophysics Data System (ADS)

Temperature induced intermetallic charge transfer and negative thermal expansion in compounds hold promise for many applications. Here, we report, by the first-principles calculations, the mechanism behind these effects and the associated electrical and magnetic properties of an A-site-ordered perovskite LaCu3Fe4O12. We find that the sensitive expansion of Cu-O bonds to temperature can trigger a transformation from Cu3+ to Cu2+, which imposes a covalent state transition of B-site Fe from +3 to +3.75. The resultant shrinkage of the Fe-O bonds is demonstrated to play a pivotal role in the volume contraction of the oxide at high temperatures.

Li, Hongping; Lv, Shuhui; Wang, Zhongchang; Xia, Yanjie; Bai, Yijia; Liu, Xiaojuan; Meng, Jian

2012-05-01

248

Complex frequency-dependent polarizability through the ? ? ?* excitation energy of azobenzene molecules by a combined charge-transfer and point-dipole interaction model.  

PubMed

The complex frequency-dependent polarizability and ? ? ?* excitation energy of azobenzene compounds are investigated by a combined charge-transfer and point-dipole interaction (CT/PDI) model. To parametrize the model, we adopted time-dependent density functional theory (TDDFT) calculations of the frequency-dependent polarizability extended with excited-state lifetimes to include also its imaginary part. The results of the CT/PDI model are compared with the TDDFT calculations and experimental data demonstrating that the CT/PDI model is fully capable to reproduce the static polarizability as well as the ? ? ?* excitation energy for these compounds. In particular, azobenzene molecules with different functional groups in the para-position have been included serving as a severe test of the model. The ? ? ?* excitation is to a large extent localized to the azo bond, and substituting with electron-donating or electron-attracting groups on the phenyl rings results in charge-transfer effects and a shift in the excitation energy giving rise to azobenzene compounds with a range of different colors. In the CT/PDI model, the ? ? ?* excitation in azobenzenes is manifested as drastically increasing atomic induced dipole moments in the azo group as well as in the adjacent carbon atoms, whereas the shifts in the excitation energies are due to charge-transfer effects. PMID:25356936

Haghdani, Shokouh; Davari, Nazanin; Sandnes, Runar; Åstrand, Per-Olof

2014-11-26

249

The Role of the Strictly Conserved Positively Charged Residue Differs among the Gram-positive, Gram-negative, and Chloroplast YidC Homologs.  

PubMed

Recently, the structure of YidC2 from Bacillus halodurans revealed that the conserved positively charged residue within transmembrane segment one (at position 72) is located in a hydrophilic groove that is embedded in the inner leaflet of the lipid bilayer. The arginine residue was essential for the Bacillus subtilis SpoIIIJ (YidC1) to insert MifM and to complement a SpoIIIJ mutant strain. Here, we investigated the importance of the conserved positively charged residue for the function of the Escherichia coli YidC, Streptococcus mutans YidC2, and the chloroplast Arabidopsis thaliana Alb3. Like the Gram-positive B. subtilis SpoIIIJ, the conserved arginine was required for functioning of the Gram-positive S. mutans YidC2 and was necessary to complement the E. coli YidC depletion strain and to promote insertion of a YidC-dependent membrane protein synthesized with one but not two hydrophobic segments. In contrast, the conserved positively charged residue was not required for the E. coli YidC or the A. thaliana Alb3 to functionally complement the E. coli YidC depletion strain or to promote insertion of YidC-dependent membrane proteins. Our results also show that the C-terminal half of the helical hairpin structure in cytoplasmic loop C1 is important for the activity of YidC because various deletions in the region either eliminate or impair YidC function. The results here underscore the importance of the cytoplasmic hairpin region for YidC and show that the arginine is critical for the tested Gram-positive YidC homolog but is not essential for the tested Gram-negative and chloroplast YidC homologs. PMID:25359772

Chen, Yuanyuan; Soman, Raunak; Shanmugam, Sri Karthika; Kuhn, Andreas; Dalbey, Ross E

2014-12-19

250

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

251

Binding of a ruthenium complex to a thioether ligand embedded in a negatively charged lipid bilayer: a two-step mechanism.  

PubMed

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2O)](2+) (terpy = 2,2';6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface. PMID:24782232

Bahreman, Azadeh; Rabe, Martin; Kros, Alexander; Bruylants, Gilles; Bonnet, Sylvestre

2014-06-10

252

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

253

Impact of multiple negative charges on blood clearance and biodistribution characteristics of 99mTc-labeled dimeric cyclic RGD peptides.  

PubMed

This study sought to evaluate the impact of multiple negative charges on blood clearance kinetics and biodistribution properties of (99m)Tc-labeled RGD peptide dimers. Bioconjugates HYNIC-P6G-RGD2 and HYNIC-P6D-RGD2 were prepared by reacting P6G-RGD2 and P6D-RGD2, respectively, with excess HYNIC-OSu in the presence of diisopropylethylamine. Their IC50 values were determined to be 31 ± 5 and 41 ± 6 nM, respectively, against (125)I-echistatin bound to U87MG glioma cells in a whole-cell displacement assay. Complexes [(99m)Tc(HYNIC-P6G-RGD2)(tricine)(TPPTS)] ((99m)Tc-P6G-RGD2) and [(99m)Tc(HYNIC-P6D-RGD2)(tricine)(TPPTS)] ((99m)Tc-P6D-RGD2) were prepared in high radiochemical purity (RCP > 95%) and specific activity (37-110 GBq/?mol). They were evaluated in athymic nude mice bearing U87MG glioma xenografts for their biodistribution. The most significant difference between (99m)Tc-P6D-RGD2 and (99m)Tc-P6G-RGD2 was their blood radioactivity levels and tumor uptake. The initial blood radioactivity level for (99m)Tc-P6D-RGD2 (4.71 ± 1.00%ID/g) was ?5× higher than that of (99m)Tc-P6G-RGD2 (0.88 ± 0.05%ID/g), but this difference disappeared at 60 min p.i. (99m)Tc-P6D-RGD2 had much lower tumor uptake (2.20-3.11%ID/g) than (99m)Tc-P6G-RGD2 (7.82-9.27%ID/g) over a 2 h period. Since HYNIC-P6D-RGD2 and HYNIC-P6G-RGD2 shared a similar integrin ?v?3 binding affinity (41 ± 6 nM versus 31 ± 5 nM), the difference in their blood activity and tumor uptake is most likely related to the nine negative charges and high protein binding of (99m)Tc-P6D-RGD2. Despite its low uptake in U87MG tumors, the tumor uptake of (99m)Tc-P6D-RGD2 was integrin ?v?3-specific. SPECT/CT studies were performed using (99m)Tc-P6G-RGD2 in athymic nude mice bearing U87MG glioma and MDA-MB-231 breast cancer xenografts. The SPECT/CT data demonstrated the tumor-targeting capability of (99m)Tc-P6G-RGD2, and its tumor uptake depends on the integrin ?v?3 expression levels on tumor cells and neovasculature. It was concluded that the multiple negative charges have a significant impact on the blood clearance kinetics and tumor uptake of (99m)Tc-labeled dimeric cyclic RGD peptides. PMID:25144854

Yang, Yong; Ji, Shundong; Liu, Shuang

2014-09-17

254

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

PubMed Central

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

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

2010-01-01

255

Role of Molecular Charge in Nucleocytoplasmic Transport  

PubMed Central

Transport of genetic materials and proteins between the nucleus and cytoplasm of eukaryotic cells is mediated by nuclear pore complexes (NPCs). A selective barrier formed by phenylalanine-glycine (FG) nucleoporins (Nups) with net positive charges in the NPC allows for passive diffusion of signal-independent small molecules and transport-receptor facilitated translocation of signal-dependent cargo molecules. Recently, negative surface charge was postulated to be another essential criterion for selective passage through the NPC. However, the charge-driven mechanism in determining the transport kinetics and spatial transport route for either passive diffusion or facilitated translocation remains obscure. Here we employed high-speed single-molecule fluorescence microscopy with an unprecedented spatiotemporal resolution of 9 nm and 400 µs to uncover these mechanistic fundamentals for nuclear transport of charged substrates through native NPCs. We found that electrostatic interaction between negative surface charges on transiting molecules and the positively charged FG Nups, although enhancing their probability of binding to the NPC, never plays a dominant role in determining their nuclear transport mode or spatial transport route. A 3D reconstruction of transport routes revealed that small signal-dependent endogenous cargo protein constructs with high positive surface charges that are destined to the nucleus, rather than repelled from the NPC as suggested in previous models, passively diffused through an axial central channel of the NPC in the absence of transport receptors. Finally, we postulated a comprehensive map of interactions between transiting molecules and FG Nups during nucleocytoplasmic transport by combining the effects of molecular size, signal and surface charge. PMID:24558427

Goryaynov, Alexander; Yang, Weidong

2014-01-01

256

Insights on the interaction of met-enkephalin with negatively charged membranes--an infrared and solid-state NMR spectroscopic study.  

PubMed

Enkephalins are pentapeptides found in the human nervous system, where they are involved in the relief of pain. The interaction of these neuropeptides with the nerve cell membranes would be a key-step in the receptor binding. We have used both Fourier-transform infrared and solid-state NMR spectroscopies to shed light on the interactions responsible for the association of enkephalins with negatively charged membranes. More specifically, we have investigated the interaction of methionine-enkephalin (Menk) with DMPG and DMPS vesicles. Our results suggest that Menk interacts electrostatically with both model membranes via its terminal NH3+ group. However, the peptide induced the formation of elongated DMPG vesicles in the magnetic field. On the other hand, the association of Menk with DMPS bilayers was concentration-dependent and disrupted the membrane at high peptide concentrations. The different effect of methionine-enkephalin with the two types of anionic membranes is most likely related to the different fluidity of these systems. PMID:14726000

Marcotte, Isabelle; Ouellet, Marise; Auger, Michèle

2004-02-01

257

Negative mobility dependence in polythiophenes P3OT and P3HT evidenced by the charge extraction by linearly increasing voltage method  

NASA Astrophysics Data System (ADS)

We investigated mobility in the regioregular poly(3-octylthiophene) (RR-P3OT) and regioregular poly(3-hexylthiophene) (RR-P3HT) by the Charge Extraction by Linearly Increasing Voltage method (CELIV). The samples were produced by the drop-casting and spin-coating methods on the Indium-Tin-Oxide substrate and provided with Al contacts. In both materials we had observed the “negative” mobility dependence at low electric fields, i.e., the mobility used to decrease with increasing electric field (in P3HT, this was only observed here in the drop-casted sample). Such behaviour was never observed by CELIV in P3OT before. Data were analysed within the Poole-Frenkel and Gaussian disorder models. The higher energetic disorder parameters were obtained in P3OT as compared to P3HT. This could be related to the longer side-chains of P3OT. We had demonstrated that in both materials with increasing temperature conductivity grows due to the thermally activated mobility. This paper has been presented at “ECHOS06”, Paris, 28 30 juin 2006.

Kažukauskas, V.; Pranaitis, M.; ?yras, V.; Sicot, L.; Kajzar, F.

2007-03-01

258

Disinfection of Escherichia coli Gram negative bacteria using surface modified TiO2: optimization of Ag metallization and depiction of charge transfer mechanism.  

PubMed

The antibacterial activity of silver deposited TiO2 (Ag-TiO2 ) against Gram negative Escherichia coli bacteria was investigated by varying the Ag metal content from 0.10 to 0.50% on the surface of TiO2 . Ag depositions by the photoreduction method were found to be stable. Surface silver metallization was confirmed by EDAX and XPS studies. Photoluminescence studies show that the charge carrier recombination is less for 0.1% Ag-TiO2 and this catalyst shows superior bactericidal activity under solar light irradiation compared to Sol gel TiO2 (SG-TiO2 ) due to the surface plasmon effect. The energy levels of deposited Ag are dependent on the Ag content and it varies from -4.64 eV to -1.30 eV with respect to the vacuum energy level based on atomic silver to bulk silver deposits. The ability of electron transfer from Ag deposit to O2 depends on the position of the energy levels. The 0.25% and 0.50% Ag depositions showed detrimental effect on bactericidal activity due to the mismatch of energy levels. The effect of the EROS (External generation of the Reactive Oxygen Species by 0.1% Ag-TiO2 ) and IROS (Interior generation of Reactive Oxygen Species within the bacteria) on the bactericidal inactivation is discussed in detail. PMID:24995499

Gomathi Devi, LakshmipathiNaik; Nagaraj, Basavalingaiah

2014-01-01

259

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

260

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

261

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

NASA Astrophysics Data System (ADS)

Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

Wodtke, Alec M.

2013-06-01

262

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

PubMed

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). PMID:25296829

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

2014-10-01

263

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

E-print Network

- - ENTHALPIES OF FORMATION OF NEGATIVE IONS MnO , MnO , AND 2 3 - MnO AS DETERMINED BY ION with the participation of these ions have been measured and the o - enthalpies of formation {D H (MnO , O K) = (-266 into the effusion chamber. In the first case, decomposition of MnO with 2 formation of Mn O was performed

Rudnyi, Evgenii B.

264

Optical and Electrical Detection of Single Molecule Translocation through Carbon Nanotubes  

PubMed Central

Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as fluorescence was recorded from charged dye molecules translocating through the SWCNT. Fluorescence bursts generally follow ion-current peaks with a delay time consistent with diffusion from the end of the SWCNT to the fluorescence collection point. The fluorescence amplitude distribution of the bursts is consistent with single molecule signals. Thus each peak in the ion current flowing through the SWCNT is associated with the translocation of a single molecule. Ion current peaks (as opposed to blockades) were produced by both positively (Rhodamine 6G) and negatively (Alexa 546) charged molecules, showing that the charge filtering responsible for the current bursts is caused by the molecules themselves. PMID:23248975

Song, Weisi; Pang, Pei; He, Jin; Lindsay, Stuart

2013-01-01

265

Periodic charge distributions in the myosin rod amino acid sequence match cross-bridge spacings in muscle  

Microsoft Academic Search

The amino acid sequence of the rod portion of nematode myosin, deduced from the sequence of the unc-54 heavy chain gene of Caenorhabditis elegans, is highly repetitive and has the characteristics of an alpha-helical coiled coil. The molecular surface contains alternate clusters of positive and negative charge. Interactions between charge clusters on adjacent molecules could account for the observed spacings

Andrew D. McLachlan; Jonathan Karn

1982-01-01

266

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

267

Charge Challenge  

NSDL National Science Digital Library

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

2012-06-26

268

Models for Cometary Comae Containing Negative Ions  

NASA Technical Reports Server (NTRS)

The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of IP/Halley. The anions O(-), OH(-), C(-), CH(-) and CN(-) have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu [I]. Organic molecular anions such as C4H(-) and C6H(-) are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been fully explored. We present details of our new models for the chemistry of cometary comae that include atomic and molecular anions. We calculate the impact of these anions on the charge balance and examine their importance for cometary coma chemistry.

Cordiner, M. A.; Charnley, S. B.

2012-01-01

269

A model for the abrogation of the SOS response by an SOS protein: a negatively charged helix in DinI mimics DNA in its interaction with RecA  

PubMed Central

DinI is a recently described negative regulator of the SOS response in Escherichia coli. Here we show that it physically interacts with RecA and prevents the binding of single-stranded DNA to RecA, which is required for the activation of the latter. DinI also displaces ssDNA from a stable RecA–DNA cofilament, thus eliminating the SOS signal. In addition, DinI inhibits RecA-mediated homologous DNA pairing, but has no effect on actively proceeding strand exchange. Biochemical data, together with the molecular structure, define the C-terminal ?-helix in DinI as the active site of the protein. In an unusual example of molecular mimicry, a negatively charged surface on this ?-helix, by imitating single-stranded DNA, interacts with the loop L2 homologous pairing region of RecA and interferes with the activation of RecA. PMID:11230150

Voloshin, Oleg N.; Ramirez, Benjamin E.; Bax, Ad; Camerini-Otero, R. Daniel

2001-01-01

270

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

271

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

272

Negative Numbers  

NSDL National Science Digital Library

This article is an account of how negative numbers became part of the "vocabulary" of mathematicians and of some of the earliest appearances of negative numbers in calculations of the ancient civilizations of China, India and Greece. Although negative numbers were used in calculations, negative answers to mathematical problems were considered meaningless or impossible. The troubled history of negative numbers presented in this article shows how the simple mathematical principles taken for granted today have taken thousands of years to develop.

Howard, Jill

2009-05-01

273

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

274

Fragmentation of multiply charged hydrocarbon molecules C{sub n}H{sup q+} (n{<=} 4, q{<=} 9) produced in high-velocity collisions: Branching ratios and kinetic energy release of the H{sup +} fragment  

SciTech Connect

Fragmentation branching ratios for channels involving H{sup +} emission and associated kinetic energy release of the H{sup +} fragment [KER(H{sup +})] have been measured for multicharged C{sub n}H{sup q+} molecules produced in high velocity (3.6 a.u.) collisions between C{sub n}H{sup +} projectiles and helium atoms. For CH{sup q+} (q{<=} 4) molecules, measured KER(H{sup +}) were found well below predictions of the simple point charge Coulomb model (PCCM) for all q values. Multireference configuration interaction (MRCI) calculations for ground as well as electronic excited states were performed which allowed a perfect interpretation of the CH{sup q+} experimental results for low charges (q = 2-3) as well as for the highest charge (q = 4). In this last case we could show, on the basis of ionization cross sections calculations and experimental measurements performed on the same systems at slightly higher velocity (4.5 a.u.), the prominent role played by inner-shell ionization followed by Auger relaxation and could extract the lifetime of this Auger relaxation giving rise to the best agreement between the experiment and the calculations. For dissociation of C{sub 2}H{sup q+} and C{sub 3}H{sup q+} with the highest charges (q{>=} 5), inner-shell ionization contributed in a prominent way to the ion production. In these two cases it was shown that measured KER(H{sup +}) were in good agreement with PCCM predictions when those were corrected for Auger relaxation with the same Auger lifetime value as in CH{sup 3+}.

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

2011-09-15

275

Detection of heavy-metal ions using liquid crystal droplet patterns modulated by interaction between negatively charged carboxylate and heavy-metal cations.  

PubMed

Herein, we demonstrated a simple, sensitive, and rapid label-free detection method for heavy-metal (HM) ions using liquid crystal (LC) droplet patterns on a solid surface. Stearic-acid-doped LC droplet patterns were spontaneously generated on an n-octyltrichlorosilane (OTS)-treated glass substrate by evaporating a solution of the nematic LC, 4-cyano-4'-pentylbiphenyl (5CB), dissolved in heptane. The optical appearance of the droplet patterns was a dark crossed texture when in contact with air, which represents the homeotropic orientation of the LC. This was caused by the steric interaction between the LC molecules and the alkyl chains of the OTS-treated surface. The dark crossed appearance of the acid-doped LC patterns was maintained after the addition of phosphate buffered saline (PBS) solution (pH 8.1 at 25°C). The deprotonated stearic-acid molecules self-assembled through the LC/aqueous interface, thereby supporting the homeotropic anchoring of 5CB. However, the optical image of the acid-doped LC droplet patterns incubated with PBS containing HM ions appeared bright, indicating a planar orientation of 5CB at the aqueous/LC droplet interface. This dark to bright transition of the LC patterns was caused by HM ions attached to the deprotonated carboxylate moiety, followed by the sequential interruption of the self-assembly of the stearic acid at the LC/aqueous interface. The results showed that the acid-doped LC pattern system not only enabled the highly sensitive detection of HM ions at a sub-nanomolar concentration but it also facilitated rapid detection (<10 min) with simple procedures. PMID:25059128

Han, Gyeo-Re; Jang, Chang-Hyun

2014-10-01

276

Negative ions at Titan and Enceladus: recent results.  

PubMed

The detection of heavy negative ions (up to 13 800 amu) in Titan's ionosphere is one of the tantalizing new results from the Cassini mission. These heavy ions indicate for the first time the existence of heavy hydrocarbon and nitrile molecules in this primitive Earth-like atmosphere. These ions were suggested to be precursors of aerosols in Titan's atmosphere and may precipitate to the surface as tholins. We present the evidence for and the analysis of these heavy negative ions at Titan. In addition we examine the variation of the maximum mass of the Titan negative ions with altitude and latitude for the relevant encounters so far, and we discuss the implications for the negative ion formation process. We present data from a recent set of encounters where the latitude was varied between encounters, with other parameters fixed. Models are beginning to explain the low mass negative ions, but the formation process for the higher mass ions is still not understood. It is possible that the structures may be chains, rings or even fullerenes. Negative ions, mainly water clusters in this case, were seen during Cassini's recent close flybys of Enceladus. We present mass spectra from the Enceladus plume, showing water clusters and additional species. As at Titan, the negative ions indicate chemical complexities which were unknown before the Cassini encounters, and are indicative of a complex balance between neutrals and positively and negatively charged ions. PMID:21302552

Coates, Andrew J; Wellbrock, Anne; Lewis, Gethyn R; Jones, Geraint H; Young, David T; Crary, Frank J; Waite, J Hunter; Johnson, Robert E; Hille, Thomas W; Sittler, Edward C

2010-01-01

277

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

278

Lattice-gas model of DNA charge inversion by a positively charged polyelectrolyte  

NASA Astrophysics Data System (ADS)

The model of DNA charge inversion by Nguyen and Shklovskii [T. T. Nguyen and B. I. Shklovskii, Phys. Rev. Lett. 89, 018101 (2002)] is extended. A single double-helix strand of DNA is represented by a lattice of negative charges at the positions of the protruding oxygens of the phosphates along the DNA backbone, and the adsorbed polyelectrolyte molecules are represented by charged dimers. A lattice-gas model is used in which dimers adsorbing either parallel or perpendicular to the lattice are treated as separate species, and the model allows for vacancies between adsorbed species. The mean field theory used is formulated as a saddle-point approximation of the exact functional integral representation of the grand canonical partition function, opening the way for the inclusion of the effects of charge fluctuation corrections.

Bishop, Marilyn F.; McMullen, Tom

2006-08-01

279

Charge transfer doping of silicon.  

PubMed

We demonstrate a novel doping mechanism of silicon, namely n-type transfer doping by adsorbed organic cobaltocene (CoCp2*) molecules. The amount of transferred charge as a function of coverage is monitored by following the ensuing band bending via surface sensitive core-level photoelectron spectroscopy. The concomitant loss of electrons in the CoCp2* adlayer is quantified by the relative intensities of chemically shifted Co2p components in core-level photoelectron spectroscopy which correspond to charged and neutral molecules. Using a previously developed model for transfer doping, the evolution in relative intensities of the two components as a function of coverage has been reproduced successfully. A single, molecule-specific parameter, the negative donor energy of -(0.50±0.15)??eV suffices to describe the self-limiting doping process with a maximum areal density of transferred electrons of 2×1013??cm-2 in agreement with the measured downward band bending. The advantage of this doping mechanism over conventional doping for nanostructures is addressed. PMID:24785050

Rietwyk, K J; Smets, Y; Bashouti, M; Christiansen, S H; Schenk, A; Tadich, A; Edmonds, M T; Ristein, J; Ley, L; Pakes, C I

2014-04-18

280

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

281

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

282

Interaction of the neuropeptide met-enkephalin with zwitterionic and negatively charged bicelles as viewed by 31P and 2H solid-state NMR.  

PubMed

The interaction of the neuropeptide methionine-enkephalin (Menk) with bicelles was investigated by solid-state NMR. Bicelles composed of dimyristoylphosphatidylcholine (DMPC) and dicaproylphosphatidylcholine (DCPC) were modified to investigate the effect of the lipid headgroup and electrostatic charges on the association with Menk. A total of 10 mol % of DMPC was replaced by zwitterionic phosphatidylethanolamine (DMPE), anionic phosphatidylglycerol (DMPG), or phosphatidylserine (DMPS). The preparation of DMPE-doped bicelles (Bic/PE) is reported for the first time. The (31)P and (2)H NMR results revealed changes in the lipid dynamics when Menk interacts with the bicellar systems. (2)H NMR experiments showed a disordering effect of Menk on the lipid chains in all the bicelles except Bic/PG, whereas the study of the choline headgroups indicated a decreased order of the lipids only in Bic/PE and Bic/PG. Our results suggest that the insertion depth of Menk into bicelles is modulated by their composition, more specifically by the balance between hydrophobic and electrostatic interactions. Menk would be buried at the lipid polar/apolar interface, the depth of penetration into the hydrophobic membrane core following the scaling Bic > Bic/PE > Bic/PS at the slightly acidic pH used in this study. The peptide would not insert into the bilayer core of Bic/PG and would rather remain at the surface. PMID:12829487

Marcotte, Isabelle; Dufourc, Erick J; Ouellet, Marise; Auger, Michèle

2003-07-01

283

Interaction of the Neuropeptide Met-Enkephalin with Zwitterionic and Negatively Charged Bicelles as Viewed by 31P and 2H Solid-State NMR  

PubMed Central

The interaction of the neuropeptide methionine-enkephalin (Menk) with bicelles was investigated by solid-state NMR. Bicelles composed of dimyristoylphosphatidylcholine (DMPC) and dicaproylphosphatidylcholine (DCPC) were modified to investigate the effect of the lipid headgroup and electrostatic charges on the association with Menk. A total of 10 mol % of DMPC was replaced by zwitterionic phosphatidylethanolamine (DMPE), anionic phosphatidylglycerol (DMPG), or phosphatidylserine (DMPS). The preparation of DMPE-doped bicelles (Bic/PE) is reported for the first time. The 31P and 2H NMR results revealed changes in the lipid dynamics when Menk interacts with the bicellar systems. 2H NMR experiments showed a disordering effect of Menk on the lipid chains in all the bicelles except Bic/PG, whereas the study of the choline headgroups indicated a decreased order of the lipids only in Bic/PE and Bic/PG. Our results suggest that the insertion depth of Menk into bicelles is modulated by their composition, more specifically by the balance between hydrophobic and electrostatic interactions. Menk would be buried at the lipid polar/apolar interface, the depth of penetration into the hydrophobic membrane core following the scaling Bic > Bic/PE > Bic/PS at the slightly acidic pH used in this study. The peptide would not insert into the bilayer core of Bic/PG and would rather remain at the surface. PMID:12829487

Marcotte, Isabelle; Dufourc, Erick J.; Ouellet, Marise; Auger, Michèle

2003-01-01

284

Molecule Shapes  

NSDL National Science Digital Library

Explore molecule shapes by building molecules in 3D! How does molecule shape change with different numbers of bonds and electron pairs? Find out by adding single, double or triple bonds and lone pairs to the central atom. Then, compare the model to real molecules!

Simulations, Phet I.; Moore, Emily; Olson, Jonathan; Lancaster, Kelly; Chamberlain, Julia; Perkins, Kathy

2011-10-10

285

Molecular charge transfer by adsorbing TCNQ/TTF molecules via?-? interaction: a simple and effective strategy to modulate the electronic and magnetic behaviors of zigzag SiC nanoribbons.  

PubMed

By means of first-principles computations, we first propose a simple and effective strategy through the molecular charge transfer via noncovalent ?-? interaction to modulate the electronic and magnetic properties of zigzag SiC nanoribbons (zSiCNRs). This charge transfer is induced by adsorbing the electron-withdrawing/donating tetracyanoquinodimethane (TCNQ) or tetrathiafulvalene (TTF) molecules on the surface of the pristine zSiCNR. It is revealed that all the TCNQ- and TTF-modified zSiCNR-systems can exhibit considerable adsorption energies in the range from -137.2 to -184.0 kJ mol(-1) and from -71.3 to -76.9 kJ mol(-1), respectively, indicating that these zSiCNR-complexes possess high structure stabilities. This kind of a molecular charge transfer via?-? interaction can break the magnetic degeneracy of zSiCNRs, and the sole ferromagnetic (FM) metallicity and even antiferromagnetic (AFM) half-metallicity can be achieved. These intriguing findings will be advantageous for promoting SiC-based nanomaterials in the application of spintronics and multifunctional nanodevices in the near future. PMID:25407886

Liu, Dan; Yu, Guangtao; Sun, Yuanhui; Huang, Xuri; Guan, Jia; Zhang, Hui; Li, Hui; Chen, Wei

2015-01-14

286

Negative-ion source applications.  

PubMed

In this paper heavy negative-ion sources which we developed and their applications for materials science are reviewed. Heavy negative ions can be effectively produced by the ejection of a sputtered atom through the optimally cesiated surface of target with a low work function. Then, enough continuous negative-ion currents for materials-science applications can be obtained. We developed several kinds of sputter-type heavy negative-ion sources such as neutral- and ionized-alkaline metal bombardment-type heavy negative-ion source and rf-plasma sputter type. In the case where a negative ion is irradiated on a material surface, surface charging seldom takes place because incoming negative charge of the negative ion is well balanced with outgoing negative charge of the released secondary electron. In the negative-ion implantation into an insulator or insulated conductive material, high precision implantation processing with charge-up free properties can be achieved. Negative-ion implantation technique, therefore, can be applied to the following novel material processing systems: the surface modification of micrometer-sized powders, the nanoparticle formation in an insulator for the quantum devices, and the nerve cell growth manipulation by precise control of the biocompatibility of polymer surface. When a negative ion with low kinetic energy approaches the solid surface, the kinetic energy causes the interatomic bonding (kinetic bonding), and formation of a metastable material is promoted. Carbon films with high constituent of sp(3) bonding, therefore, can be formed by carbon negative-ion beam deposition. PMID:18315249

Ishikawa, J

2008-02-01

287

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

PubMed

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

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

2014-03-17

288

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

289

Dynamics of low-energy electrons in liquid water with consideration of Coulomb interaction with positively charged water molecules induced by electron collision  

NASA Astrophysics Data System (ADS)

To explain the electron energy relaxation process in water, we performed dynamical calculations of electrons in water using a simulation code developed in this study to calculate mean diffusion distances and mean energies of incident and secondary electrons released by the impact of the incident electron, as well as spatial probability-distribution of the secondary electrons. In addition to the following molecular processes of water: ionization: electronic, vibrational, and rotational excitation by electron impact; dissociative electron attachment; and elastic electron scattering, which were basic parameters used by Monte Carlo simulation, we newly took into account Coulomb interactions between electrons and positively ionized water molecules to calculate classical electron trajectories. We found that the Coulomb interactions enhance the number of collisions for the vibrational and rotational excitation processes at the incident 500 eV electron energy. The secondary electrons diffuse to an average of 3 nm from their original position, resulting much different spatial probability-distribution of those electrons in comparison to those previously reported. We also found that approximately 20% of the secondary electrons were returned to the parent ions within 100 fs. By the electron re-capturing to either bonding or antibionding orbital, the molecules might be converted to some electronic excitation states. We suggest that the spatial probability-distribution of electrons, taken into account the re-capturing process, should be essential for detailed analysis of following chemical process arising in nanometer scales, such as biomolecular damage caused by radiation.

Kai, Takeshi; Yokoya, Akinari; Ukai, Masatoshi; Fujii, Kentaro; Higuchi, Mariko; Watanabe, Ritsuko

2014-09-01

290

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, Régis; Yachandra, Vittal K.; Yano, Junko; Neese, Frank; Anxolabéhère-Mallart, Elodie

2014-01-01

291

A model for the abrogation of the SOS response by an SOS protein: a negatively charged helix in DinI mimics DNA in its interaction with RecA.  

PubMed

DinI is a recently described negative regulator of the SOS response in Escherichia coli. Here we show that it physically interacts with RecA and prevents the binding of single-stranded DNA to RecA, which is required for the activation of the latter. DinI also displaces ssDNA from a stable RecA-DNA cofilament, thus eliminating the SOS signal. In addition, DinI inhibits RecA-mediated homologous DNA pairing, but has no effect on actively proceeding strand exchange. Biochemical data, together with the molecular structure, define the C-terminal alpha-helix in DinI as the active site of the protein. In an unusual example of molecular mimicry, a negatively charged surface on this alpha-helix, by imitating single-stranded DNA, interacts with the loop L2 homologous pairing region of RecA and interferes with the activation of RecA. PMID:11230150

Voloshin, O N; Ramirez, B E; Bax, A; Camerini-Otero, R D

2001-02-15

292

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

293

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

SciTech Connect

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

Wang, Qi; Li, Rong; Xu, Yuanlan [School of Optical and Electronic Information, Huazhong University of Science and Technology, No. 1037 Luoyu Road, Hongshan District, Wuhan City, Hubei Province 430074 (China); Zhang, Jianbing; Miao, Xiangshui; Zhang, Daoli, E-mail: zhang-daoli@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, No. 1037 Luoyu Road, Hongshan District, Wuhan City, Hubei Province 430074 (China); Wuhan National Laboratory for Optoelectronics, 1037 Luoyu Road, Hongshan District, Wuhan City, Hubei Province 430074 (China)

2014-06-21

294

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

295

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

NASA Astrophysics Data System (ADS)

We study charge transport through single benzene molecular junction (BMJ) directly sandwiched between two platinum electrodes by using a tight-binding model and the non-equilibrium Green?s function approach. Pronounced negative differential conductance is observed at finite bias voltage, resulting from charge redistribution in BMJ and a Coulomb blockade effect at the interface of molecule-electrode contacts. In the presence of a transverse electric field, hysteretic switching behavior and large spin-polarization of current are obtained, indicating the potential application of BMJ for acting as a nanoscale current modulator or spintronic molecular device.

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

2014-11-01

296

Three chamber negative ion source  

DOEpatents

A negative ion vessel is divided into an excitation chamber, a negative ionization chamber and an extraction chamber by two magnetic filters. Input means introduces neutral molecules into a first chamber where a first electron discharge means vibrationally excites the molecules which migrate to a second chamber. In the second chamber a second electron discharge means ionizes the molecules, producing negative ions which are extracted into or by a third chamber. A first magnetic filter prevents high energy electrons from entering the negative ionization chamber from the excitation chamber. A second magnetic filter prevents high energy electrons from entering the extraction chamber from the negative ionizing chamber. An extraction grid at the end of the negative ion vessel attracts negative ions into the third chamber and accelerates them. Another grid, located adjacent to the extraction grid, carries a small positive voltage in order to inhibit positive ions from migrating into the extraction chamber and contour the plasma potential. Additional electrons can be suppressed from the output flux using ExB forces provided by magnetic field means and the extractor grid electric potential.

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

1985-01-01

297

Rational Design of ?-Helical Antimicrobial Peptides to Target Gram-negative Pathogens, Acinetobacter baumannii and Pseudomonas aeruginosa: Utilization of Charge, ’Specificity Determinants,’ Total Hydrophobicity, Hydrophobe Type and Location as Design Parameters to Improve the Therapeutic Ratio  

PubMed Central

The rapidly growing problem of increased resistance to classical antibiotics makes the development of new classes of antimicrobial agents with lower rates of resistance urgent. Amphipathic cationic ?-helical antimicrobial peptides have been proposed as a potential new class of antimicrobial agents. The goal of this study was to take a broad-spectrum, 26-residue, antimicrobial peptide in the all-D conformation, peptide D1 (K13) with excellent biologic properties and address the question of whether a rational design approach could be used to enhance the biologic properties if the focus was on Gram-negative pathogens only. To test this hypothesis, we used 11 and 6 diverse strains of Acinetobacter baumannii and Pseudo-monas aeruginosa, respectively. We optimized the number and location of positively charged residues on the polar face, the number, location, and type of hydrophobe on the non-polar face and varied the number of ’specificity determinants’ in the center of the non-polar face from 1 to 2 to develop four new antimicrobial peptides. We demonstrated not only improvements in antimicrobial activity, but also dramatic reductions in hemolytic activity and unprecedented improvements in therapeutic indices. Compared to our original starting peptide D1 (V13), peptide D16 had a 746-fold improvement in hemolytic activity (i.e. decrease), maintained antimicrobial activity, and improved the therapeutic indices by 1305-fold and 895-fold against A. baumannii and P. aeruginosa, respectively. The resulting therapeutic indices for D16 were 3355 and 895 for A. baumannii and P. aeruginosa, respectively. D16 is an ideal candidate for commercialization as a clinical therapeutic to treat Gram-negative bacterial infections. PMID:21219588

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

2011-01-01

298

Rational design of ?-helical antimicrobial peptides to target Gram-negative pathogens, Acinetobacter baumannii and Pseudomonas aeruginosa: utilization of charge, 'specificity determinants,' total hydrophobicity, hydrophobe type and location as design parameters to improve the therapeutic ratio.  

PubMed

The rapidly growing problem of increased resistance to classical antibiotics makes the development of new classes of antimicrobial agents with lower rates of resistance urgent. Amphipathic cationic ?-helical antimicrobial peptides have been proposed as a potential new class of antimicrobial agents. The goal of this study was to take a broad-spectrum, 26-residue, antimicrobial peptide in the all-D conformation, peptide D1 (K13) with excellent biologic properties and address the question of whether a rational design approach could be used to enhance the biologic properties if the focus was on Gram-negative pathogens only. To test this hypothesis, we used 11 and 6 diverse strains of Acinetobacter baumannii and Pseudomonas aeruginosa, respectively. We optimized the number and location of positively charged residues on the polar face, the number, location, and type of hydrophobe on the non-polar face and varied the number of 'specificity determinants' in the center of the non-polar face from 1 to 2 to develop four new antimicrobial peptides. We demonstrated not only improvements in antimicrobial activity, but also dramatic reductions in hemolytic activity and unprecedented improvements in therapeutic indices. Compared to our original starting peptide D1 (V13), peptide D16 had a 746-fold improvement in hemolytic activity (i.e. decrease), maintained antimicrobial activity, and improved the therapeutic indices by 1305-fold and 895-fold against A. baumannii and P. aeruginosa, respectively. The resulting therapeutic indices for D16 were 3355 and 895 for A. baumannii and P. aeruginosa, respectively. D16 is an ideal candidate for commercialization as a clinical therapeutic to treat Gram-negative bacterial infections. PMID:21219588

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

2011-04-01

299

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

300

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

301

A comparative study on the effect of Curcumin and Chlorin-p6 on the diffusion of two organic cations across a negatively charged lipid bilayer probed by second harmonic spectroscopy  

NASA Astrophysics Data System (ADS)

The influence of Curcumin and Chlorin-p6 (Cp6) on the real time diffusion kinetics of two organic cations, LDS (LDS-698) and Malachite Green (MG) across a negatively charged phospholipid bilayer is investigated by Second Harmonic (SH) spectroscopy. The diffusion time constant of LDS at neutral pH in liposomes containing either Curcumin or Cp6 is significantly reduced, the effect being more pronounced with Curcumin. At acidic pH, the quantum of reduction in the diffusion time constant of MG by both the drugs was observed to be similar. The relative changes in the average diffusion time constants of the cations with increasing drug concentration at pH 5.0 and 7.4 shows a substantial pH effect for Curcumin induced membrane permeability, while a modest pH effect was observed for Cp6 induced membrane permeability. Based on available evidence this can be attributed to the increased interaction between the drug and the polar head groups of the lipid at pH 7.4 where the drug resides closer to the lipid-water interface.

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

2014-09-01

302

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

303

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

304

Negative probability  

E-print Network

This article was written for the Logic in Computer Science column in the February 2015 issue of the Bulletin of the European Association for Theoretical Computer Science. The intended audience is general computer science audience. The uncertainty principle asserts a limit to the precision with which position x and momentum p of a particle can be known simultaneously. You may know the probability distributions of x and p individually but the joint distribution makes no physical sense. Yet Wigner exhibited such a joint distribution f(x,p). There was, however, a little trouble with it: some of its values were negative. Nevertheless Wigner's discovery attracted attention and found applications. There are other joint distribution, all with negative values, which produce the correct marginal distributions of x and p. But only Wigner's distribution produces the correct marginal distributions for all linear combinations of position and momentum. We offer a simple proof of the uniqueness and discuss related issues.

Andreas Blass; Yuri Gurevich

2015-02-02

305

Doping of graphene by adsorption of polar molecules at oxidized zigzag edges  

E-print Network

We have theoretically investigated the electronic and magnetic properties of graphene whose zigzag edges are oxidized. The alteration of these properties by adsorption of $\\mathrm{H_{2}O}$ and $\\mathrm{NH_3}$ molecules have been considered. It was found that the adsorbed molecules form a cluster along the oxidized zigzag edges of graphene due to interaction with the electro-negative oxygen. Graphene tends to donate a charge to the adsorbates through the oxygen atoms and the efficiency of donation depends on the intermolecular distance and on the location of the adsorbed molecules relative to the plane of graphene. It was found that by appropriate selection of the adsorbates, a controllable and gradual growth of $p$-doping in graphene with a variety of adsorbed molecules can be achieved

Berashevich, Julia

2009-01-01

306

Negative refraction and superconductivity  

NASA Astrophysics Data System (ADS)

We discuss exotic properties of charged hydrodynamical systems, in the broken superconducting phase, probed by electromagnetic waves. Motivated by general arguments from hydrodynamics, we observe that negative refraction, namely the propagation in opposite directions of the phase velocities and of the energy flux, is expected for low enough frequencies. We corroborate this general idea by analyzing a holographic superconductor in the AdS/CFT correspondence, where the response functions can be explicitly computed. We study the dual gravitational theory both in the probe and in the backreacted case. We find that, while in the first case the refractive index is positive at every frequency, in the second case there is negative refraction at low enough frequencies. This is in agreement with hydrodynamic considerations.

Amariti, Antonio; Forcella, Davide; Mariotti, Alberto; Siani, Massimo

2011-10-01

307

Negative Refraction and Superconductivity  

E-print Network

We discuss exotic properties of charged hydrodynamical systems, in the broken superconducting phase, probed by electromagnetic waves. Motivated by general arguments from hydrodynamics, we observe that negative refraction, namely the propagation in opposite directions of the phase velocities and of the energy flux, is expected for low enough frequencies. We corroborate this general idea by analyzing a holographic superconductor in the AdS/CFT correspondence, where the response functions can be explicitly computed. We study the dual gravitational theory both in the probe and in the backreacted case. We find that, while in the first case the refractive index is positive at every frequency, in the second case there is negative refraction at low enough frequencies. This is in agreement with hydrodynamic considerations.

Antonio Amariti; Davide Forcella; Alberto Mariotti; Massimo Siani

2011-07-06

308

Charmonium molecules?  

SciTech Connect

In this talk we present some recent studies of multiquark components in the charmonium sector. We study the possible existence of compact four quark-states and meson-meson molecules in the charmonium spectroscopy.

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

2010-08-05

309

Walking Molecules   

E-print Network

Inspired by the motor protein kinesin, an ambitious and unprecedented mimic is proposed – a synthetic molecular motor that can walk. This thesis aims to explain the basic principles which define such walking molecules, ...

Symes, Mark D

2009-01-01

310

Accessibility of the CLC-0 pore to charged methanethiosulfonate reagents.  

PubMed

Using the substituted-cysteine-accessibility method, we previously showed that a cysteine residue introduced to the Y512 position of CLC-0 was more rapidly modified by a negatively charged methanethiosulfonate (MTS) reagent, 2-sulfonatoethyl MTS (MTSES), than by the positively charged 2-(trimethylammonium)ethyl MTS (MTSET). This result suggests that a positive intrinsic pore potential attracts the negatively charged MTS molecule. In this study, we further test this hypothesis of a positive pore potential in CLC-0 and find that the preference for the negatively charged MTS is diminished significantly in modifying the substituted cysteine at a deeper pore position, E166. To examine this conundrum, we study the rates of MTS inhibitions of the E166C current and those of the control mutant current from E166A. The results suggest that the inhibition of E166C by intracellularly applied MTS reagents is tainted by the modification of an endogenous cysteine, C229, located at the channel's dimer interface. After this endogenous cysteine is mutated, CLC-0 resumes its preference for selecting MTSES in modifying E166C, reconfirming the idea that the pore of CLC-0 is indeed built with a positive intrinsic potential. These experiments also reveal that MTS modification of C229 can inhibit the current of CLC-0 depending on the amino acid placed at position 166. PMID:20141750

Zhang, Xiao-Dong; Yu, Wei-Ping; Chen, Tsung-Yu

2010-02-01

311

The experimental charge density in crystals  

NASA Astrophysics Data System (ADS)

The experimental charge density distribution in single crystals has been determined through the analysis of X- ray and neutron diffraction data. The crystal structure of 2-pyridone (C5H5NO) has been redetermined from high resolution X-ray data collected at 123K. The molecule is in the lactam form. Bond lengths and bond angles have been determined with e.s.d.'s of 0.001A and 0.1A. The hydrogen-bonded cyclic dimers that occur in vapor and in solution are absent in the crystal where molecules are linked by H-H ... O interaction (H ..., 2.57A) and weak C-H ... ? or van der Waals interactions occurring on both sides of the pyridone ring. The electronic charge density distribution in the crystal and its Laplacian have been calculated for atoms at rest. The total electrostatic potential has been mapped for an isolated molecule and the molecular dipole moment has been determined (8.8(19) Debyes). Critical points in the electron density have been located for the bonds within the molecule and for the molecular interactions cited above. For the C-H ... ? interactions, only the spherical components of the valence density for the pryridone ring atoms contribute effectively at the critical points. Hence these interactions may be described better as van der Waals. New X-ray diffraction data for adenosine (C10H13N5O4) have been collected at high resolution (sin/theta //lambda /le 1.38A-1) at 123K. The multipole model refinement, based on F2 and including 10,083 reflections, give R(F2) = 0.046 and Rw(F2) = 0.077 with goodness of fit gof = 1.64. The electrostatic potential, the total charge density and the Laplacian of the total charge density have been mapped for pseudoatoms at rest in crystal. The topological properties have been analyzed at the (3, - 1) bond critical points. The deformation charge density determines the trajectory of the bonding path. The charge density in the L-shell of an atom shows significant local maxima on the covalent bonding direction and non-bonding direction. At the bond critical points, ?b is consistently greater in the adenine base than in the ribose sugar. The Laplacian at all H-bond critical points is positive, indication a lack of covalent bonding. A weak H-bond C2-H2 ... O2' is observed at the critical point. High resolution X-ray data (sin?/lambda/le 1.22A-1) have been collected at 123K for the structure of dimethyl oxalate. The crystal packing involves 10 short intermolecular interactions including at least one weak H bond. The critical points of the intramolecular and intermolecular have been located and analyzed. The negative Laplacian and charge density at the C2-O2 bonding critical point are surprisingly small. This is caused by the extensive negative deformation charge density near the methyl group on the bonding direction. The thermal vibrations of the molecule have been analyzed from the neutron diffraction data collected at 123K, 70K and 15K. The internal vibrations of the H atoms have been calculated and translated into the local coordinate. The value of U3 of H1 atom is much smaller than these of H2 and H3 at each temperature, indicating a non-rigid rotor for the methyl group. (Abstract shortened by UMI.)

Yang, Huan-Wang

1997-12-01

312

Negative ion formation processes: A general review  

SciTech Connect

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

Alton, G.D.

1990-01-01

313

Biological Molecules  

NSDL National Science Digital Library

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

Anderson, Paul

2013-03-12

314

Single-molecule transistors.  

PubMed

The use of a gate electrode allows us to gain deeper insight into the electronic structure of molecular junctions. It is widely used for spectroscopy of the molecular levels and its excited states, for changing the charge state of the molecule and investigating higher order processes such as co-tunneling and the Kondo effect. Gate electrodes have been implemented in several types of nanoscale devices such as electromigration junctions, mechanically controllable break junctions, and devices with carbon-based electrodes. Here we review the state-of-the-art in the field of single-molecule transitors. We discuss the experimental challenges and describe the advances made for the different approaches. PMID:25310767

Perrin, Mickael L; Burzurí, Enrique; van der Zant, Herre S J

2015-02-10

315

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

316

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

317

Preface: Charge transport in nanoscale junctions  

NASA Astrophysics Data System (ADS)

Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

318

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

319

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

PubMed

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

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

2015-01-01

320

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

PubMed Central

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

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

2015-01-01

321

Surface Charge Heterogeneity in Amphibole Cleavage Fragments and Asbestos Fibers  

Microsoft Academic Search

Aspect ratio and electrophoretic mobility data for amphibole particles reveal that short fibers and blocky cleavage fragments have a smaller net charge than highly elongated particles. Asbestos fibers and cleavage fragments of the same dimensions exhibit the same net negative surface charge but positively charged ends and negatively charged lateral surfaces.

Joseph E. Schiller; Sequoyah L. Payne; Sanaa E. Khalafalla

1980-01-01

322

Surface Charge Heterogeneity in Amphibole Cleavage Fragments and Asbestos Fibers  

NASA Astrophysics Data System (ADS)

Aspect ratio and electrophoretic mobility data for amphibole particles reveal that short fibers and blocky cleavage fragments have a smaller net charge than highly elongated particles. Asbestos fibers and cleavage fragments of the same dimensions exhibit the same net negative surface charge but positively charged ends and negatively charged lateral surfaces.

Schiller, Joseph E.; Payne, Sequoyah L.; Khalafalla, Sanaa E.

1980-09-01

323

Surface charge heterogeneity in amphibole cleavage fragments and asbestos fibers.  

PubMed

Aspect ratio and electrophoretic mobility data for amphibole particles reveal that short fibers and blocky cleavage fragments have a smaller net charge than highly elongated particles. Asbestos fibers and cleavage fragments of the same dimensions exhibit the same net negative surface charge but positively charged ends and negatively charged lateral surfaces. PMID:17745966

Schiller, J E; Payne, S L; Khalafalla, S E

1980-09-26

324

Computational and ESR studies of electron attachment to decafluorocyclopentane, octafluorocyclobutane, and hexafluorocyclopropane: electron affinities of the molecules and the structures of their stable negative ions as determined from 13C and 19F hyperfine coupling constants.  

PubMed

High-resolution ESR spectra of the ground-state negative ions of hexafluorocyclopropane (c-C3F6*-), octafluorocyclobutane (c-C4F8*-), and decafluorocyclopentane (c-C5F10*-) are reported and their isotropic 19F hyperfine coupling constants (hfcc) of 198.6 +/- 0.4 G, 147.6 +/- 0.4 G, and 117.9 +/- 0.4 G, respectively, are in inverse ratio to the total number of fluorine atoms per anion. Together with the small value of 5.2 +/- 0.4 G determined for the isotropic 13C hfcc of c-C4F8*-, these results indicate that in each case the singly occupied molecular orbital (SOMO) is delocalized over the equivalent fluorines and possesses a nodal plane through the carbon atoms of a time-averaged D(nh) structure. A series of quantum chemical computations were carried out to further characterize these anions and their neutral counterparts. Both the B3LYP density functional and second-order Møller-Plesset perturbation theory (MP2) indicate that c-C3F6*- adopts a D(3h) geometry and a (2)A2'' ground electronic state, that c-C4F8*- adopts a D(4h) geometry and a (2)A2u ground electronic state, and that c-C5F10*- adopts a C(s) structure and a (2)A' electronic state. Moreover, the 19F hyperfine coupling constants computed with the MP2 method and a high quality triple-zeta basis set are within 1% of the experimental values. Also, the values computed for the 13C hfcc of c-C4F8*- are consistent with the experimental value of 5.2 G. Therefore, in keeping with the ESR results, these negative ions derived from first-row elements can be characterized as pi* species. In addition, the hypervalency of these perfluorocycloalkane radical anions has been clarified. PMID:16045345

ElSohly, Adel M; Tschumper, Gregory S; Crocombe, Richard A; Wang, Jih Tzong; Williams, Ffrancon

2005-08-01

325

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

E-print Network

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

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

2015-01-01

326

Radiating Charge  

NSDL National Science Digital Library

The electric field lines from a point charge evolve in time as the charge moves. Watch radiation propagate outward at the speed of light as you wiggle the charge. Stop a moving charge to see bremsstrahlung (braking) radiation. Explore the radiation patterns as the charge moves with sinusoidal, circular, or linear motion. You can move the charge any way you like, as long as you donât exceed the speed of light.

Simulations, Phet I.; Dubson, Michael; Paul, Ariel

2013-02-01

327

The large quadrupole of water molecules  

PubMed Central

Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical?molecular mechanical (QM?MM) calculations at the MP2?aug-cc-pVQZ level on a B3LYP?aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM?MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM?MM multipoles is much closer than that from the site models to the potential from the QM?MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment. PMID:21476758

Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshiko

2011-01-01

328

The large quadrupole of water molecules  

NASA Astrophysics Data System (ADS)

Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical/molecular mechanical (QM/MM) calculations at the MP2/aug-cc-pVQZ level on a B3LYP/aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM/MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM/MM multipoles is much closer than that from the site models to the potential from the QM/MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment.

Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshiko

2011-04-01

329

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

PubMed Central

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

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

2014-01-01

330

Vascular permeability in a human tumour xenograft: molecular charge dependence  

PubMed Central

Molecular charge is one of the main determinants of transvascular transport. There are, however, no data available on the effect of molecular charge on microvascular permeability of macromolecules in solid tumours. To this end, we measured tumour microvascular permeability to different proteins having similar size but different charge. Measurements were performed in the human colon adenocarcinoma LS174T transplanted in transparent dorsal skinfold chambers in severe combined immunodeficient (SCID) mice. Bovine serum albumin (BSA) and IgG were fluorescently labelled and were either cationized by conjugation with hexamethylenediamine or anionized by succinylation. The molecules were injected i.v. and the fluorescence in tumour tissue was quantified by intravital fluorescence microscopy. The fluorescence intensity and pharmacokinetic data were used to calculate the microvascular permeability. We found that tumour vascular permeability of cationized BSA (pI-range: 8.6–9.1) and IgG (pI: 8.6–9.3) was more than two-fold higher (4.25 and 4.65 × 10?7cm s?1) than that of the anionized BSA (pI ? 2.0) and IgG (pI: 3.0–3.9; 1.11 and 1.93 × 10?7cm s?1, respectively). Our results indicate that positively charged molecules extravasate faster in solid tumours compared to the similar-sized compounds with neutral or negative charges. However, the plasma clearance of cationic molecules was ?2 × faster than that of anionic ones, indicating that the modification of proteins enhances drug delivery to normal organs as well. Therefore, caution should be exercised when such a strategy is used to improve drug and gene delivery to solid tumours. © 2000 Cancer Research Campaign PMID:10789717

Dellian, M; Yuan, F; Trubetskoy, V S; Torchilin, V P; Jain, R K

2000-01-01

331

Production of Intense Negative Ion Beams in Magnetically Insulated Diodes.  

NASA Astrophysics Data System (ADS)

This work presents a study of the production of intense negative ion beams in magnetically insulated diodes in order to develop an understanding of this process by measuring the ion beam parameters as a function of diode and cathode plasma conditions in different magnetically insulated diodes. We tried a coral diode, a racetrack diode and an annular diode. We used the UCI APEX pulse line that has a nominal output of 1MV, 140kA under matched conditions with a pulse length of 50nsec. Negative ion intensity and divergence were measured with Faraday-cups and CR-39 track detectors. Cathode plasma was produced by passive dielectric cathodes and later, by an independent plasma gun. This plasma gun was introduced in order to be able to control cathode plasma parameters and production time. Negative ion currents had an intensity of a few A/cm^2 with a divergence ranging between a few tenths milliradians for an active TiH _2 plasma gun and 300 milliradians for a passive polyethelene cathode. Negative ions were usually emitted from a few "hot spots" on the cathode surface. These "hot spots" are believed to cause transverse electrical fields in the diode gap responsible for the beam divergence. Mass spectrometry measurements showed that the ion beam consists of mainly H^- ions when using a polyethelene or a TiH_2 cathodes, and mainly of negative carbon ions when using a carbon cathode. About 10% of the negative ions produced were due to residual gas molecules adsorbed on the cathode surface. Very good beam repeatability with low beam divergence was achieved with the plasma gun. Negative ion production in the cathode plasma seems to be insensitive to the type of diode used. Beam properties on the other hand, are of course sensitive to diode geometry. The above results are discussed in connection with other measurements done on magnetically insulated diodes by other groups. A picture is suggested in which negative ions are produced by collision of neutrals and electrons at the low density interface between the cathode plasma and the electron negative charge layer.

Lindenbaum, Hayim

332

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

333

Measurements of Charged Precipitation in a New Mexico Thunderstorm: Lower Positive Charge Centers  

Microsoft Academic Search

We designed an instrument to measure the charge and vertical velocity of individual precipitation particles inside thunderclouds. A balloon carried the particle charge instrument, an electric field meter, and a standard meteorological radiosonde upward into thunderclouds over Langmuir Laboratory in central New Mexico. During one balloon flight the instruments encountered two regions of positive charge below the main negative charge

Thomas C. Marshall; William P. Winn

1982-01-01

334

A Initio Studies of the Dissociation of AN Energetic Solid (nitromethane) in the Presence of Neighboring Charge Defects.  

NASA Astrophysics Data System (ADS)

The aim of this work is to study the effect of charged defects on intermolecular reactions which may occur in hot spots of energetic materials by ab initio means, using UHF and MBPT. Nitromethane was selected as a prototype energetic material, using the geometry of the crystalline solid at 4.6 K. Charged defects were first simulated with point charges of +/-1 electron charge and then by the free ions, namely F^- and Li^+. Point charges were placed at the nitrogen site of the nearest neighbor in the lattice. The nearest hydrogen was then pulled off of nitromethane on a trajectory directly at the point charge. The energy to remove hydrogen was 4.72 eV for no charge, 3.85 eV for a negative charge and 4.64 eV for a positive charge. For a "miss" trajectory, with a closest approach of 2 A.U. (1.06 A), the negative charge gave a barrier of 4.42 eV and slightly bound local minimum, while the positive charge showed an increased barrier height of 5.16 eV in removing H^0 with a net lower energy out to infinity. Using an F^- ion instead of a negative point charge lowered the barrier height from 4.72 eV with no defect to 1.96 eV with the free ion. A bound H-F species was formed, producing the exothermic reaction NO_2CH_3 + F^- --> NO _2CH_sp{2} {-} + HF, which is energetically favored even without allowing the nitromethyl radical to relax. An isoelectric neon case shows no tendency for dissociation. This is strong evidence that it is the charged defect that has a large effect on the dissociation barrier of a nearby nitromethane molecule and not just electronic interactions between atoms. That one charged defect, F^ -, in a lattice site can produce another charged defect, NO_2CH_sp {2}{-}, may allow another reaction to follow in a chain. This work has shown conclusively that the presence of nearby charges or charged species has a strong effect on the barrier height energy to remove an atom from nitromethane. The discovery of an exothermic pathway for the dissociation of nitromethane into the more reactive nitromethyl radical using a free ion charged defect should have important implications in hot spot mechanisms in energetic materials.

Kaldon, Philip Edward

335

Methods and applications in single molecule electronics  

NASA Astrophysics Data System (ADS)

In recent years it has become possible to measure charge transport in a single molecule contacted to two metal electrodes. However, a thorough understanding of how a molecule behaves while contacted to two electrodes and how it interacts with its environment is still lacking. This thesis demonstrates various experimental methods for understanding and controlling charge transport in a single molecule junction and the application of these methods to various molecular systems to help elucidate the conduction mechanisms invoked. First, the conductance of DNA is examined in a controlled environment while varying the length, sequence, base-pair matching, bias, temperature, and electrochemical gate of the molecule. These studies show that the conductance of DNA is extremely sensitive to changes in length, sequence, and base-matching, but not as sensitive to temperature and electrochemical gate. Despite the variety of experimental methods applied, the subtleties of the conduction mechanism remain uncertain, and as such necessitate the development of additional tools for understanding the behavior of a single molecule junction. Next, the Conductance Screening Tool for Molecules (CSTM) is described. This is a new tool capable of creating 1000's of single molecules junctions in a matter of minutes. This tool has been used to study the conductance of alkanedithiols, molecules in an array, and single amino acid residues. This system allows for greater speed and flexibility in determining the conductance of a single molecule junction, and provides a capability for performing large-scale systematic studies of molecular systems to determine the conduction mechanism. Finally, an additional experimental method capable of extracting information about the interaction between a molecule and its environment is developed. Here, electron-phonon interactions in a single molecule contacted to two electrodes are studied. This method allows one to obtain a specific, chemical signature of a single molecule, to extract information about changes in the configuration of a single molecule junction during an experiment, and to correlate these changes with changes in the conductance of the molecule.

Hihath, Joshua

336

Insight into acid-base nucleation experiments by comparison of the chemical composition of positive, negative, and neutral clusters.  

PubMed

We investigated the nucleation of sulfuric acid together with two bases (ammonia and dimethylamine), at the CLOUD chamber at CERN. The chemical composition of positive, negative, and neutral clusters was studied using three Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometers: two were operated in positive and negative mode to detect the chamber ions, while the third was equipped with a nitrate ion chemical ionization source allowing detection of neutral clusters. Taking into account the possible fragmentation that can happen during the charging of the ions or within the first stage of the mass spectrometer, the cluster formation proceeded via essentially one-to-one acid-base addition for all of the clusters, independent of the type of the base. For the positive clusters, the charge is carried by one excess protonated base, while for the negative clusters it is carried by a deprotonated acid; the same is true for the neutral clusters after these have been ionized. During the experiments involving sulfuric acid and dimethylamine, it was possible to study the appearance time for all the clusters (positive, negative, and neutral). It appeared that, after the formation of the clusters containing three molecules of sulfuric acid, the clusters grow at a similar speed, independent of their charge. The growth rate is then probably limited by the arrival rate of sulfuric acid or cluster-cluster collision. PMID:25406110

Bianchi, Federico; Praplan, Arnaud P; Sarnela, Nina; Dommen, Josef; Kürten, Andreas; Ortega, Ismael K; Schobesberger, Siegfried; Junninen, Heikki; Simon, Mario; Tröstl, Jasmin; Jokinen, Tuija; Sipilä, Mikko; Adamov, Alexey; Amorim, Antonio; Almeida, Joao; Breitenlechner, Martin; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Kangasluoma, Juha; Keskinen, Helmi; Kim, Jaeseok; Kirkby, Jasper; Laaksonen, Ari; Lawler, Michael J; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Riccobono, Francesco; Rissanen, Matti P; Rondo, Linda; Tomé, António; Virtanen, Annele; Viisanen, Yrjö; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M; Ye, Penglin; Curtius, Joachim; Kulmala, Markku; Worsnop, Douglas R; Donahue, Neil M; Baltensperger, Urs

2014-12-01

337

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids  

PubMed Central

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. 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

338

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

339

Human intestinal absorption--neutral molecules and ionic species.  

PubMed

Analysis of percentage human intestinal absorption (%HIA) for 280 drugs shows that an excellent fit can be obtained using only three descriptors for neutral molecules with a SD of 13.9%. Use of descriptors for individual cations and anions does not lead to any better goodness-of-fit. It is noted that diffusion coefficients in water for ionized molecules are almost identical to those for the corresponding neutral molecules. Comparison of equation coefficients for HIA with those for other processes shows that HIA resembles diffusion in water but does not resemble permeation through biological bilayers. It is shown that compound substituent effects on HIA are near those for diffusion but are far away from substituent effects on permeation through a typical bilayer. Calculations indicate that rates of permeation through an unstirred mucosal layer are of the same order as experimental rates of permeation in HIA. It is concluded that for the 280 compound set, diffusion through the unstirred mucosal layer is the rate determining step. The effect on pK(a) in transfer of acids and bases from water to another solvent, and of diffusion past a negative charge in a phase/bilayer is also considered. PMID:24902952

Abraham, Michael H

2014-07-01

340

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

341

The molecular charge distribution, the hydration shell, and the unique properties of liquid water.  

PubMed

The most essential features of a water molecule that give rise to its unique properties are examined using computer simulations of different water models. The charge distribution of a water molecule characterized by molecular multipoles is quantitatively linked to the liquid properties of water via order parameters for the degree (S(2)) and symmetry (?S(2)) of the tetrahedral arrangement of the nearest neighbors, or "hydration shell." ?S(2) also appears to determine the long-range tetrahedral network and interfacial structure. From the correlations, some models are shown to be unable to reproduce certain properties due to the limitations of the model itself rather than the parameterization, which indicates that they are lacking essential molecular features. Moreover, since these properties depend not only on S(2) but also on ?S(2), the long-range structure in these models may be incorrect. Based on the molecular features found in the models that are best able to reproduce liquid properties, the most essential features of a water molecule in liquid water appear to be a charge distribution with a large dipole, a large quadrupole, and negative charge out of the molecular plane, as well as a symmetrically ordered tetrahedral hydration shell that results from this charge distribution. The implications for modeling water are also discussed. PMID:25554164

Tan, Ming-Liang; Cendagorta, Joseph R; Ichiye, Toshiko

2014-12-28

342

Influence of dendrimer surface charge on the bioactivity of 2-methoxyestradiol complexed with dendrimers  

PubMed Central

We report the complexation of a potential anticancer agent 2-methoxyestradiol (2-ME) with generation 5 (G5) poly(amidoamine) dendrimers having different surface functional groups for therapeutic applications. The complexation experiment shows that approximately 6–8 drug molecules can be complexed with one dendrimer molecule regardless the type of the dendrimer terminal groups. The bioactivity of 2-ME complexed with dendrimers was found to be significantly dependent on the surface charge of G5 dendrimers. In vitro cell biological assays show that amine, hydroxyl, and acetamide-terminated G5 dendrimers with positive, slightly positive, and close to neutral surface charges, respectively are able to deliver 2-ME to inhibit cancer cell growth. In contrast, 2-ME complexed with carboxyl-terminated G5 dendrimers with negative surface charges does not show its inherent bioactivity. Further molecular dynamics simulation studies show that the compact structure of carboxylated G5 dendrimers complexed with 2-ME does not allow the release of the drug molecules even at a pH of 5.0, which is the typical pH value in lysosome. Our findings indicate that the surface modification of dendrimers with different charges is crucial for the development of formulations of various anticancer drugs for therapeutic applications. PMID:20852741

Chen, Xisui; Shen, Mingwu; Xiao, Shili; Zhu, Meifang; Baker, James R.

2010-01-01

343

The Origins of Positive and Negative in Electricity  

ERIC Educational Resources Information Center

Benjamin Franklin first introduced the terms positive and negative into electrical theory in the year 1747. The positive and negative terms originally had nothing to do with inherent electrical charge, but rather indicated which object had an excess of electrical fluid indicating positive, and which had a deficiency, indicating negative.

Jensen, William B.

2005-01-01

344

Zero-Net-Charge Air Ionizer  

NASA Technical Reports Server (NTRS)

Instrument monitors air supplied by air ionizer and regulates ionizer to ensure net charge neutral. High-impedance electrometer and nulling control amplifier regulate output of air ionizer. Primarily intended to furnish ionized air having no net charge, instrument adaptable to generating air with positive or negative net charge is so desired. Useful where integrated circuit chips are manufactured, inspected, tested or assembled.

Woods, W. R., Jr.

1985-01-01

345

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 reeccelerated 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.degree. to 500.degree. 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, James E. (Idaho Falls, ID)

1987-01-01

346

Take Charge!  

NSDL National Science Digital Library

Students come to understand static electricity by learning about the nature of electric charge, and different methods for charging objects. In a hands-on activity, students induce an electrical charge on various objects, and experiment with electrical repulsion and attraction.

Integrated Teaching And Learning Program

347

Charge-Swapping Q Balls  

NASA Astrophysics Data System (ADS)

Q balls are nontopological solitonic solutions to a wide class of field theories that possess global symmetries. Here we show that in these same theories there also exists a tower of novel composite Q -ball solutions where, within one composite Q ball, positive and negative charges coexist and swap at a frequency lower than the natural frequency of an individual Q ball. These charge-swapping Q balls are constructed by assembling Q balls and anti-Q balls tightly such that their nonlinear cores overlap. We explain why charge-swapping Q balls can form and why they swap charges.

Copeland, Edmund J.; Saffin, Paul M.; Zhou, Shuang-Yong

2014-12-01

348

Charge-swapping q balls.  

PubMed

Q balls are nontopological solitonic solutions to a wide class of field theories that possess global symmetries. Here we show that in these same theories there also exists a tower of novel composite Q-ball solutions where, within one composite Q ball, positive and negative charges coexist and swap at a frequency lower than the natural frequency of an individual Q ball. These charge-swapping Q balls are constructed by assembling Q balls and anti-Q balls tightly such that their nonlinear cores overlap. We explain why charge-swapping Q balls can form and why they swap charges. PMID:25526114

Copeland, Edmund J; Saffin, Paul M; Zhou, Shuang-Yong

2014-12-01

349

Explicit vs Implicit Water Simulations of Charged Dendrimers Sebastian Huimann,  

E-print Network

into the solution, thereby charging the remaining molecule, which results in the electro- static swelling- capsulation agents. For polyelectrolyte chains and stars, it is well-known that charging them leads

Likos, Christos N.

350

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

351

Surface treatment of silica nanoparticles for stable and charge-controlled colloidal silica  

PubMed Central

An attempt was made to control the surface charge of colloidal silica nanoparticles with 20 nm and 100 nm diameters. Untreated silica nanoparticles were determined to be highly negatively charged and have stable hydrodynamic sizes in a wide pH range. To change the surface to a positively charged form, various coating agents, such as amine containing molecules, multivalent metal cation, or amino acids, were used to treat the colloidal silica nanoparticles. Molecules with chelating amine sites were determined to have high affinity with the silica surface to make agglomerations or gel-like networks. Amino acid coatings resulted in relatively stable silica colloids with a modified surface charge. Three amino acid moiety coatings (L-serine, L-histidine, and L-arginine) exhibited surface charge modifying efficacy of L-histidine > L-arginine > L-serine and hydrodynamic size preservation efficacy of L-serine > L-arginine > L-histidine. The time dependent change in L-arginine coated colloidal silica was investigated by measuring the pattern of the backscattered light in a Turbiscan™. The results indicated that both the 20 nm and 100 nm L-arginine coated silica samples were fairly stable in terms of colloidal homogeneity, showing only slight coalescence and sedimentation. PMID:25565824

Kim, Kyoung-Min; Kim, Hye Min; Lee, Won-Jae; Lee, Chang-Woo; Kim, Tae-il; Lee, Jong-Kwon; Jeong, Jayoung; Paek, Seung-Min; Oh, Jae-Min

2014-01-01

352

Effect of net surface charge on physical properties of the cellulose nanoparticles and their efficacy for oral protein delivery.  

PubMed

Both net positively and negatively charged cellulose-based nanoparticles were prepared from oppositely charged carboxymethylcellulose (CMC) and quaternized cellulose (QC). Effect of surface charge on efficacy of cellulose nanoparticles for delivering both positively and negatively charged proteins was investigated. Lysozyme (LYS) and bovine serum albumin (BSA), which possess positive and negative charge at physiological pH respectively, were used as models. The results revealed that high encapsulation efficiency (67.7% and 85.1%) could be achieved when negatively charged protein was encapsulated in positively charged nanoparticles, or positively charged protein was encapsulated in negatively charged nanoparticles. Proteins encapsulated in optimal cellulose nanoparticles could be sustainably released and no obvious protein denaturation was detected. Both net positively and negatively charged nanoparticles exhibited low cytotoxicity due to cellulose's good biocompatibility. Not only net positively charged nanoparticles demonstrated high cellular uptake efficiency, but also net negatively charged nanoparticles showed somewhat efficient cellular uptake. PMID:25659666

Song, Yongbo; Chen, Lingyun

2015-05-01

353

A study of the role played by the Hartree-Fock orbital exchange in the formation of the energy of the first singlet charge-transfer excited state by the example of JK-62 and JK-201 sensitizing dye molecules  

NASA Astrophysics Data System (ADS)

Based on the time-dependent density functional theory with the use of the functionals B3LYP, B97-2, BHandHLYP, BMK, MPWB1K, PBE1W, PBE1PBE, ?-HCTHh, and TPSS in the 6-31G(d) basis set of atomic orbitals, we have performed a quantum-chemical investigation of electronic and spectral properties of JK-62 and JK-201 bis-dimethylfluorenyl dye sensitizers for Grätzel photoelectric converters. In terms of the Bader theory, we have done a complete analysis of the electron-density distribution function in the dye molecules under study, which proves the occurrence of intramolecular nonvalent interactions, which, in turn, stabilize a planar mutual arrangement of structural fragments of dye molecules. The role that the Hartree-Fock orbital exchange plays in the energy formation of the first and most intense electronic transition, which is responsible for the primary current generation in a solar cell, has been elucidated.

Baryshnikov, G. V.; Minaev, B. F.; Slepets, A. A.; Minaeva, V. A.

2014-03-01

354

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

355

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

356

Electron-impact-induced tryptophan molecule fragmentation  

NASA Astrophysics Data System (ADS)

The fragmentation of a gas-phase tryptophan molecule by a low-energy (<70 eV) electron impact was studied both experimentally and theoretically. Various positively charged fragments were observed and analyzed. A special attention was paid to the energy characteristics of the ionic fragment yield. The geometrical parameters of the initial molecule rearrangement were also analyzed. The fragmentation observed was due to either a simple bond cleavage or more complex reactions involving molecular rearrangements.

Tamuliene, Jelena; Romanova, Liudmila G.; Vukstich, Vasyl S.; Papp, Alexander V.; Snegursky, Alexander V.

2015-01-01

357

Generating high-efficiency neutral beams by using negative ions in an inductively coupled plasma source  

NASA Astrophysics Data System (ADS)

To minimize radiation damage caused by charge buildup or ultraviolet and x-ray photons during etching, we developed a high-performance neutral-beam etching system. The neutral-beam source consists of an inductively coupled plasma (ICP) source and parallel top and bottom carbon plates. The bottom carbon plate has numerous apertures for extracting neutral beams from the plasma. When a direct current (dc) bias is applied to the top and bottom plates, the generated positive or negative ions are accelerated toward the bottom plate. Most of them are then efficiently converted into neutral atoms, either by neutralization in charge-transfer collisions with gas molecules during ion transport and with the aperture sidewalls in the bottom plate, or by recombination with low-energy electrons near the end of the bottom plate. We found that negative ions are more efficiently converted into neutral atoms than positive ions. The neutralization efficiency of negative ions was almost 100%, and the maximum neutral flux density was equivalent to 4.0 mA/cm2. A neutral beam can thus be efficiently produced from the ICP source and apertures in our new neutral-beam source. copyright 2002 American Vacuum Society.

Samukawa, Seiji; Sakamoto, Keisuke; Ichiki, Katsunori

2002-09-01

358

CHARGE IMBALANCE  

SciTech Connect

The purpose of this article is to review the theory of charge imbalance, and to discuss its relevance to a number of experimental situations. We introduce the concepts of quasiparticle charge and charge imbalance, and discuss the generation and detection of charge imbalance by tunneling. We describe the relaxation of the injected charge imbalance by inelastic scattering processes, and show how the Boltzmann equation can be solved to obtain the steady state quasiparticle distribution and the charge relaxation rate. Details are given of experiments to measure charge imbalance and the charge relaxation rate when inelastic scattering is the predominant relaxation mechanism. Experiments on and theories of other charge relaxation mechanisms are discussed, namely relaxation via elastic scattering in the presence of energy gap anisotropy, or in the presence of a pair breaking mechanism such as magnetic impurities or an applied supercurrent or magnetic field. We describe three other situations in which charge imbalance occurs, namely the resistance of the NS interface, phase slip centers, and the flow of a supercurrent in the presence of a temperature gradient.

Clarke, John

1980-09-01

359

Controlling intramolecular hydrogen transfer in a porphycene molecule with single atoms or molecules located nearby.  

PubMed

Although the local environment of a molecule can play an important role in its chemistry, rarely has it been examined experimentally at the level of individual molecules. Here we report the precise control of intramolecular hydrogen-transfer (tautomerization) reactions in single molecules using scanning tunnelling microscopy. By placing, with atomic precision, a copper adatom close to a porphycene molecule, we found that the tautomerization rates could be tuned up and down in a controlled fashion, surprisingly also at rather large separations. Furthermore, we extended our study to molecular assemblies in which even the arrangement of the pyrrolic hydrogen atoms in the neighbouring molecule influences the tautomerization reaction in a given porphycene, with positive and negative cooperativity effects. Our results highlight the importance of controlling the environment of molecules with atomic precision and demonstrate the potential to regulate processes that occur in a single molecule. PMID:24345945

Kumagai, Takashi; Hanke, Felix; Gawinkowski, Sylwester; Sharp, John; Kotsis, Konstantinos; Waluk, Jacek; Persson, Mats; Grill, Leonhard

2014-01-01

360

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

361

Solvated calcium ions in charged silica nanopores  

NASA Astrophysics Data System (ADS)

Hydroxyl surface density in porous silica drops down to nearly zero when the pH of the confined aqueous solution is greater than 10.5. To study such extreme conditions, we developed a model of slit silica nanopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca2+ counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca2+ counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca2+ counterions arrange themselves according to the so-called "Stern layer," no diffuse layer is observed. The presence of Ca2+ counterions affects the pore filling for strong confinement where the surface effects are large. At full loading, no significant changes are observed in the layering of the first two adsorbed water layers compared to nanopores with fully hydroxylated surfaces. However, the water structure and water orientational ordering with respect to the surface is much more disturbed. Due to the super hydrophilicity of the Ca2+-silica nanopores, water dynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silica surfaces. These findings, which suggest the breakdown of the linear Poisson-Boltzmann theory, provide important information about the properties of nanoconfined electrolytes upon extreme conditions where the surface charge and ion concentration are large.

Bonnaud, Patrick A.; Coasne, Benoît; Pellenq, Roland J.-M.

2012-08-01

362

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

363

Apparatus for irradiation with charged particle beams  

SciTech Connect

An apparatus according to the present invention for irradiating a specimen with charged particle beams comprises a single charged particle generating source from which the charged particle beams formed of electrons and negative ions, respectively, can be simultaneously derived; a specimen holder on which the specimen is placed; and charged particle irradiation means which is interposed between the charged particle generating source and the specimen holder in order to focus the charged particle beams and to irradiate the surface of the specimen with the focused beams, and which includes at least one magnetic lens and at least one electrostatic lens that are individually disposed.

Tamura, H.; Ishitani, T.; Shimase, A.

1984-10-23

364

Enzyme molecule control of the substrate microflows and some problems of optical diagnostics  

NASA Astrophysics Data System (ADS)

We studied the enzyme acetylcholinesterase (AChE) that catalyses the hydrolysis of acetylcholine (ACh) -- cell neuromediator. After transfer of excitation ACh must be removed from the synaptic cleft in hundreds of microseconds. This is accomplished by removing of acetate (A) and choline (Ch) that are the products of 'cutting' of ACh by AChE. High activity of the enzyme is related with the large dipole moment of AChE that attracts positively charged molecules of ACh into active site (AS) and also with the fast removing of the reaction products from AS. One of the hypothesis accounting for the fast removing of A and Ch from the AS pocket presumes the existence of a 'back door' that allows them to leave the pocket without interference with the molecules of ACh that penetrate inside the AS. We made an attempt of verification of the 'back door' hypothesis by means of computational experiment for 2D and 3D spaces. We considered the problem of penetration of ACh and exit of the negatively charged A and positively charged Ch under the conditions of fluctuating potential relief of the AChE AS. For the laser spectroscopy we pose two problems: (a) determination of the dipole moment of AChE in the case this molecule is surrounded by ACh molecules by means of the electro-optical method and (b) detection of AS conformations related with functioning of the 'back door' (the ring-system of Trp84). We report on Raman spectroscopy study of the influence of crown-esters on amino groups.

Romanovsky, Yury M.; Netrebko, Alexei V.; Netrebko, Nina V.; Kroo, Stanislav V.; Chikishev, Andrey Y.; Sakodynskaya, Inna G.; Molodozhenya, Vladislav

1999-05-01

365

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

366

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

367

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

368

Distribution of water molecules at Ag(111)/electrolyte interface as studied with surface X-ray scattering  

NASA Astrophysics Data System (ADS)

The spatial distribution of water molecules at solid-electrolyte interfaces has received extensive theoretical study, due to the importance of this interface in electrochemistry and other sciences. Such studies suggest that adjacent to the interface water is arranged in several layers, that the molecular arrangements in the inner layer is similar to bulk water, and that the inner-layer molecules have an oxygen-up (oxygen-down) average orientation for negative (positive) electrode charge (or, equivalently, potential). However, little of this has been verified by experimental measurements. In this paper we report surface X-ray scattering measurements of the water distribution perpendicular to a Ag(111)-electrolyte interface in 0.1M NaF at two potentials: +0.52 and -0.23 V from the potential of zero charge (PZC) on the electrode. We find that, first, the water is ordered in layers extending about three molecular diameters from the electrode. Second, the extent of ordering and the distance between the electrode and first water layer depend on potential, the latter being consistent with an oxygen-up (oxygen-down) average molecular orientation for negative (positive) electrode potential. Third, the inner water layer contains 1.55 × 10 15 (at -0.23 V) and 2.6 × 10 15 (at +0.52 V) water molecules per cm -2, remarkably more than expected from the bulk water density (i.e., ˜ 1.15 × 10 15cm -2). Such a large compression shows that the molecular arrangements in the inner layer are significantly different from bulk, which has not been anticipated in current models of charged, aqueous interfaces. We give a qualitative explanation of this large density as resulting from the strong electric field at the charged Ag(111) electrode and present a tentative model of the molecular arrangements.

Toney, Michael F.; Howard, Jason N.; Richer, Jocelyn; Borges, Gary L.; Gordon, Joseph G.; Melroy, Owen R.; Wiesler, David G.; Yee, Dennis; Sorensen, Larry B.

1995-07-01

369

DFT study of adsorption of picric acid molecule on the surface of single-walled ZnO nanotube; as potential new chemical sensor  

NASA Astrophysics Data System (ADS)

Using density functional theory (DFT), we have investigated the adsorption of picric acid (PA) molecule on the surface of (8,0) single-walled ZnO nanotube (ZnONT). The results show that the PA molecule can be chemisorbed on the surface of ZnONT with adsorption energies of -82.01 and -75.26 kJ/mol in gas and aqueous phase, respectively. Frontier molecular orbital analysis show that HOMO/LUMO gap of ZnONT reduces from 1.66 and 1.75 eV in the pristine nanotube to 0.83 and 0.72 eV in PA-adsorbed form in gas and aqueous phase, respectively. It suggests that the process can affect the electronic properties of the studied nanotube which would lead to its conductance change upon the adsorption of PA molecule. The modifying effect on the electrical conductance of ZnONT underlies the working mechanism of gas sensors for detecting the PA molecules. Analyses of the adsorption behavior of the electrically charged ZnONT toward PA molecule in the gas phase show that the PA molecule can be strongly adsorbed on the negatively charged ZnONT surface with significant adsorption energy (-135.1 kJ/mol). However, from the HOMO/LUMO gap changes, it can be concluded that the positive ZnONT might sensitively detect the PA molecule in comparison to the negative tube. These results can provide helpful information for experimental investigation to develop novel nanotube-based sensors.

Farmanzadeh, Davood; Tabari, Leila

2015-01-01

370

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

371

Water Molecule Residence Times  

NSDL National Science Digital Library

How long will a molecule of Water stay in a particular reservoir? What is the average time a molecule of Water will stay in an ocean? What is the average time a molecule of water will stay in a river? A lake? As groundwater? A glacier? How long will a water vapor molecule stay suspended in the atmosphere? Why is the residence ...

Science, Sill -.

2010-11-16

372

The electric charges on single raindrops and snowflakes  

Microsoft Academic Search

An account is given of 16 months' observations on the charges of individual raindrops and snowflakes. The results show an excess of positively charged drops and of total positive charge, except for storm rain. The average charge per drop is greater in the case of negative than of positive raindrops, but the reverse holds for snowflakes. Observations were also made

J. Alan Chalmers; F. Pasquill

1938-01-01

373

Residual dust charges in discharge afterglow L. Couedel,  

E-print Network

Residual dust charges in discharge afterglow L. Cou¨edel, M. Mikikian, and L. Boufendi GREMI, AUSTRALIA An on-ground measurement of dust particle residual charges in the afterglow of a dusty plasma. It was found that positively-charged, negatively-charged and neutral dust particles coexisted for more than one

Paris-Sud XI, Université de

374

Residual dust charges in an afterglow plasma , M. Mikikian  

E-print Network

Residual dust charges in an afterglow plasma L. Couëdel , M. Mikikian , L. Boufendi and A. A, AUSTRALIA Abstract. An on-ground measurement of dust particle residual charges in the afterglow of a dusty the gravitational force. It was found that positively-charged, negatively-charged and neutral dust particles

Paris-Sud XI, Université de

375

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

376

Maxwell?s equal-area law for charged Anti-de Sitter black holes  

NASA Astrophysics Data System (ADS)

In this Letter we present the construction of the Maxwell equal-area law in the Hawking temperature graph for a charged black hole in Anti-de Sitter background. We are able to find exact solution for the corresponding isotherm and entropies for “gaseous” (large) black holes and “liquid” (near-extremal) black holes. Isothermal construction removes the unphysical, negative heat capacity, regions. Furthermore, extremal black holes turn out to be dual to un-shrinkable molecules of Van der Waals real fluid, which may explain their thermodynamical stability.

Spallucci, Euro; Smailagic, Anais

2013-06-01

377

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.

378

Correlations Between the Charge of Proteins and the Number of Ionizable Groups They Incorporate: Studies Using Protein Charge  

E-print Network

Correlations Between the Charge of Proteins and the Number of Ionizable Groups They Incorporate: Studies Using Protein Charge Ladders, Capillary Electrophoresis, and Debye-Hu¨ckel Theory Jeffrey D of net charge (either positive or negative), the values of µelectro and the values of charge measured

Deutch, John

379

Theoretical study of the cooperativity in substituted dimethyl ethers complexed with two water molecules. Red or blue shifts of the ?(CH) vibrations?  

NASA Astrophysics Data System (ADS)

The cooperative interactions in CH3OCH3, CH3OCH2F, CH3OCHF2, CH2FOCHF2 and CHF2OCHF2 complexed with two H2O molecules are investigated using the B3LYP method with the 6-311++G(d,p) level. The calculations include the optimized geometries, the cooperative energies along with a natural bond orbital (NBO analysis). Cyclic complexes characterized by OwHw…O and CH…Ow hydrogen bonds are formed. The pairwise or two body interaction energies are computed. The results show that the OwHw…O interaction energies increase with the proton affinity of the O atom of the ethers and that the CH…Ow interaction energies increase with increasing acidity of the CH bond. This is in agreement with the intermolecular distances. The cooperative energy represents 15-20% of the total energy. When nF = 2-4, blue shifts are predicted for the ?(CH) vibration for the 1-1 complexes but red shifts are predicted for the 1-2 complexes. The variation of the CH distances is explained by a competition between the variation of the intramolecular hyperconjugation energies and the intermolecular hyperconjugation energies. The charge transfer between the ether and water molecules is analyzed. When the negative charge on one H2O molecule decreases, the positive charge on the other H2O molecule increases, indicating a nice reciprocal effect.

Chandra, Asit K.; Zeegers-Huyskens, Thérèse

2013-01-01

380

Effect of Streaming Negative Ions on Dust Acoustic Wave Propagation in Complex Plasma  

SciTech Connect

The role of streaming negative ions on the dust acoustic wave (DAW) propagation has been investigated based on orbit motion limited (OML) theory of dust grain charging. The complex plasma being assumed as composed of Boltzmanian electrons, inertial positive ions, streaming negative ions and the variable charge dust grains. Dust charge is assumed to be fluctuating. It is found that the dust acoustic wave becomes unstable when ratio of the thermal velocity with the streaming velocity of negative ions crosses some threshold value.

Sarkar, Susmita [Department of Applied Mathematics, University of Calcutta, 92, Acharyya Prafulla Chandra Road, Calcutta-700009 (India); Roy, Banamali; Khan, M.; Gupta, M. R. [Centre for Plasma Studies, Jadavpur University, Kolkata-700032 (India)

2005-10-31

381

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

382

Thread bonds in molecules  

E-print Network

Unusual chemical bonds are proposed. Each bond is almost covalent but is characterized by the thread of a small radius $\\sim 0.6\\times 10^{-11}$cm, between two nuclei in a molecule. The main electron density is concentrated outside the thread as in a covalent bond. The thread is formed by the electron wave function which has a tendency to be singular on it. The singularity along the thread is cut off by electron "vibrations" due to the interaction with zero point electromagnetic oscillations. The electron energy has its typical value of (1-10)eV. Due to the small tread radius the uncertainty of the electron momentum inside the thread is large resulting in a large electron kinetic energy $\\sim 1 MeV$. This energy is compensated by formation of a potential well due to the reduction of the energy of electromagnetic zero point oscillations. This is similar to formation of a negative van der Waals potential. Thread bonds are stable and cannot be created or destructed in chemical or optical processes.

Ivlev, B

2015-01-01

383

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

384

A rocket-borne mass analyzer for charged aerosol particles in the mesosphere  

SciTech Connect

An electrostatic mass spectrometer for nanometer-sized charged aerosol particles in the mesosphere has been developed and tested. The analyzer is mounted on the forward end of a rocket and has a slit opening for admitting a continuous sample of air that is exhausted through ports at the sides. Within the instrument housing are two sets of four collection plates that are biased with positive and negative voltages for the collection of negative and positive aerosol particles, respectively. Each collection plate spans about an order of magnitude in mass which corresponds to a factor of 2 in radius. The number density of the charge is calculated from the current collected by the plates. The mean free path for molecular collisions in the mesosphere is comparable to the size of the instrument opening; thus, the analyzer performance is modeled by a Monte Carlo computer code that finds the aerosol particles trajectories within the instrument including both the electrostatic force and the forces from collisions of the aerosol particles with air molecules. Mass sensitivity curves obtained using the computer models are near to those obtained in the laboratory using an ion source. The first two flights of the instrument returned data showing the charge number densities of both positive and negative aerosol particles in four mass ranges.

Knappmiller, Scott; Robertson, Scott; Sternovsky, Zoltan [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80309-0392 (United States); Friedrich, Martin [Institute of Communication Networks and Satellite Communications, Graz University of Technology, A-8010 Graz (Austria)

2008-10-15

385

A rocket-borne mass analyzer for charged aerosol particles in the mesosphere  

NASA Astrophysics Data System (ADS)

An electrostatic mass spectrometer for nanometer-sized charged aerosol particles in the mesosphere has been developed and tested. The analyzer is mounted on the forward end of a rocket and has a slit opening for admitting a continuous sample of air that is exhausted through ports at the sides. Within the instrument housing are two sets of four collection plates that are biased with positive and negative voltages for the collection of negative and positive aerosol particles, respectively. Each collection plate spans about an order of magnitude in mass which corresponds to a factor of 2 in radius. The number density of the charge is calculated from the current collected by the plates. The mean free path for molecular collisions in the mesosphere is comparable to the size of the instrument opening; thus, the analyzer performance is modeled by a Monte Carlo computer code that finds the aerosol particles trajectories within the instrument including both the electrostatic force and the forces from collisions of the aerosol particles with air molecules. Mass sensitivity curves obtained using the computer models are near to those obtained in the laboratory using an ion source. The first two flights of the instrument returned data showing the charge number densities of both positive and negative aerosol particles in four mass ranges.

Knappmiller, Scott; Robertson, Scott; Sternovsky, Zoltan; Friedrich, Martin

2008-10-01

386

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

387

Atomic-orbital-based approximate self-interaction correction scheme for molecules and solids  

NASA Astrophysics Data System (ADS)

We present an atomic-orbital-based approximate scheme for self-interaction correction (SIC) to the local-density approximation (LDA) of density-functional theory. The method, based on the idea of Filippetti and Spaldin [Phys. Rev. B 67, 125109 (2003)], is implemented in a code using localized numerical atomic-orbital basis sets and is now suitable for both molecules and extended solids. After deriving the fundamental equations as a nonvariational approximation of the self-consistent SIC theory, we present results for a wide range of molecules and insulators. In particular, we investigate the effect of re-scaling the self-interaction correction and we establish a link with the existing atomiclike corrective scheme LDA+U . We find that when no re-scaling is applied, i.e., when we consider the entire atomic correction, the Kohn-Sham highest occupied molecular orbital (HOMO) eigenvalue is a rather good approximation to the experimental ionization potential for molecules. Similarly the HOMO eigenvalues of negatively charged molecules reproduce closely the molecular affinities. In contrast a re-scaling of about 50% is necessary to reproduce insulator band gaps in solids, which otherwise are largely overestimated. The method therefore represents a Kohn-Sham based single-particle theory and offers good prospects for applications where the actual position of the Kohn-Sham eigenvalues is important, such as quantum transport.

Pemmaraju, C. D.; Archer, T.; Sánchez-Portal, D.; Sanvito, S.

2007-01-01

388

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

389

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.

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

2013-01-01

390

Amplified terminal protection assay of small molecule/protein interactions via a highly characteristic solid-state Ag/AgCl process.  

PubMed

In this work, we describe a new sensitive strategy for electrochemical detection of protein via small molecule/protein interactions. This assay is based on a terminal protection mechanism that small molecule-linked single-stranded DNA (ssDNA) is protected against hydrolysis by exonuclease I when the target protein is captured by the corresponding small molecule recognition element. Positively charged gold nanoparticles (AuNPs) are attached to the termini-protected and negatively charged ssDNA through electrostatic interactions. Subsequent AuNP-catalyzed silver enhancement followed by a highly characteristic and sensitive solid-state Ag/AgCl process is introduced to the sensing platform to amplify the signal output. By combining the amplification ability resulting from the silver deposition on the surface-captured AuNPs with the inherent high sensitivity of the electrochemical solid-state Ag/AgCl process, our method expands its range to the detection of macromolecules that bind to specific small molecules and enables low picomolar detection of protein. As a model of biotin/streptavidin interaction, a detection limit of 10 pM for streptavidin is readily achieved with desirable sensitivity and specificity, which indicates that the terminal protection assay coupled with the electrochemical solid-state Ag/AgCl process can offer a promising platform for the determination of various of types of proteins or small molecule-protein interactions. PMID:23274192

Wang, Qiong; Jiang, Bingying; Xu, Jin; Xie, Jiaqing; Xiang, Yun; Yuan, Ruo; Chai, Yaqin

2013-05-15

391

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

392

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

393

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

394

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