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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

2013-09-20

3

Image charge effects in single-molecule junctions: Breaking of symmetries and negative-differential resistance in a benzene single-electron transistor  

NASA Astrophysics Data System (ADS)

Both experiments and theoretical studies have demonstrated that the interaction between the current-carrying electrons and the induced polarization charge in single-molecule junctions leads to a strong renormalization of molecular charging energies. However, the effect on electronic excitations and molecular symmetries remain unclear. Using a theoretical framework developed for semiconductor-nanostructure-based single-electron transistors (SETs), we demonstrate that the image charge interaction breaks the molecular symmetries in a benzene-based single-molecule transistor operating in the Coulomb blockade regime. This results in the appearance of a so-called blocking state, which gives rise to negative-differential resistance (NDR). We show that the appearance of NDR and its magnitude in the symmetry-broken benzene SET depends in a complicated way on the interplay between the many-body matrix elements, the lead tunnel coupling asymmetry, and the bias polarity. In particular, the current reducing property of the blocking state causing the NDR is shown to vanish under strongly asymmetric tunnel couplings, when the molecule is coupled stronger to the drain electrode. The calculated I-V characteristic may serve as an indicator for image charge broken molecular symmetries in experimental situations.

Kaasbjerg, K.; Flensberg, K.

2011-09-01

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

Electrostatic repulsion of positively charged vesicles and negatively charged objects  

PubMed

A positively charged, mixed bilayer vesicle in the presence of negatively charged surfaces (for example, colloidal particles) can spontaneously partition into an adhesion zone of definite area and another zone that repels additional negative objects. Although the membrane itself has nonnegative charge in the repulsive zone, negative counterions on the interior of the vesicle spontaneously aggregate there and present a net negative charge to the exterior. Beyond the fundamental result that oppositely charged objects can repel, this mechanism helps to explain recent experiments on surfactant vesicles. PMID:10411499

Aranda-Espinoza; Chen; Dan; Lubensky; Nelson; Ramos; Weitz

1999-07-16

6

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

7

Charging of dust grains in a plasma with negative ions  

SciTech Connect

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

Kim, Su-Hyun; Merlino, Robert L. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)

2006-05-15

8

Imaging Photoinduced Charge Transport in Single Molecules  

NASA Astrophysics Data System (ADS)

The ability to perform sub-Angstrom imaging of photoinduced charge transport in single molecules in ultrahigh vacuum with a low temperature scanning tunneling microscope (STM) indicates the defeat of diffraction limited resolution and the opportunity to understand in new directions nanostructures and their functions. The experiments are enabled by the enhanced field due to coupling of the light from cw and femtosecond lasers to the plasmons in the STM nano-junction and the enhanced field to the molecule that can be monitored by tunneling electrons. By imaging the tunneling electrons as a function of energy and time, it is then possible to record the spatial and temporal evolution of the topography, and the electronic, vibrational, and magnetic states of single molecules. The observation of photoinduced phenomena in nanostructures, including molecules, is relevant to a number of technologies, such as photocatalysis, solar energy harvesting, and optical communication.

Ho, Wilson

2010-03-01

9

Modeling combined transport of water and charged graded-size molecules across the glomerular capillary wall  

Microsoft Academic Search

Clearance studies using various probe molecules established that the passage of molecules\\/proteins across the glomerular capillary wall of mammalian kidneys is increasingly restricted as their size and net negative charge increase. An extended mathematical model, based on the Fiber Matrix theory, was developed to describe the dynamics of the size- and charge-selective functions of the glomerular capillary barrier using mainly

Ehab I. Mohamed; Amani M. Bayoumi

2010-01-01

10

Probing charge transport through individual molecules on silicon surfaces  

NASA Astrophysics Data System (ADS)

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

Hersam, Mark

2005-03-01

11

The formation of negatively charged particles in thermoemission plasmas  

SciTech Connect

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

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

2008-01-15

12

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

13

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

14

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

15

Mean field theory of charged dendrimer molecules  

NASA Astrophysics Data System (ADS)

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.

Lewis, Thomas; Pryamitsyn, Victor; Ganesan, Venkat

2011-11-01

16

Design optimization of negative charge pumps for IGBT driver ICs  

Microsoft Academic Search

An optimized design methodology for negative bias charge pumps is proposed. The circuit discussed gives an output voltage negative to the ground and can be used with n-substrate CMOS processes. Negative bias voltages are used in IGBT gate drivers. The analysis in this paper is done for a resistive load, but it can be applied also to capacitive loads in

Markku H. Åberg

1994-01-01

17

Multiple electron capture processes between highly charged ions and molecules  

Microsoft Academic Search

We have determined the absolute cross sections for one electron capture and total electron capture between slow, highly charged ions and multi-electron molecule targets (H2, N2, CO, CO2, CH4) under single collision conditions. It is found that the cross sections increase as the charge of the projectile ions increases and as the ionization potential of the target molecules decreases, as

Kazumoto Hosaka; Hiroyuki Tawara; Ichihiro Yamada; Hiroyuki A. Sakaue; Franciszek Krok; Frederik J. Currell; Nobuyuki Nakamura; Shunsuke Ohtani; Hirofumi Watanabe; Atsunori Danjo; Masahiro Kimura; Atsushi Matsumoto; Makoto Sakurai; Masuhiro Yoshino

1997-01-01

18

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

SciTech Connect

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

Davydov, S. Yu., E-mail: sergei_davydov@mail.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation)

2011-05-15

19

Interfacial charge transfer absorption: Application to metal molecule assemblies  

NASA Astrophysics Data System (ADS)

Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features, but has been only rarely observed experimentally. Interfacial charge transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here, we utilize a previously published model [C. Creutz, B.S. Brunschwig, N. Sutin, J. Phys. Chem. B 109 (2005) 10251] to predict IFCTA spectra of metal molecule assemblies and compare the literature observations to these predictions. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that IFCTA is not detectable. However, few experiments designed to detect IFCTA have been done. We suggest approaches to optimizing the conditions for observing the process.

Creutz, Carol; Brunschwig, Bruce S.; Sutin, Norman

2006-05-01

20

Electrostatic plasma lens for focusing negatively charged particle beams  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

21

Design optimization of negative charge pumps for IGBT driver ICs  

NASA Astrophysics Data System (ADS)

An optimized design methodology for negative bias charge pumps is proposed. The circuit discussed gives an output voltage negative to the ground and can be used with n-substrate CMOS processes. Negative bias voltages are used in IGBT gate drivers. The analysis in this paper is done for a resistive load, but it can be applied also to capacitive loads in steady state cases with constant average current. The design rules are derived from theoretical calculations and verified with simulations.

Åberg, Markku H.

1994-01-01

22

Perspectives to produce positively or negatively charged polyhydroxyalkanoic acids  

Microsoft Academic Search

An overview is provided on the possibilities of producing positively and negatively charged poly(?-hydroxyalkanoates), PHAs.\\u000a A large variety of bacterial polyesters with functionalized terminal side chains can be produced in microbial fermentation\\u000a processes by a direct polymerization of respective carbon sources, that is, carbon sources that carry functional groups in\\u000a their ?-position. However, charged PHAs are not accessible by a

Carmen Scholz

2010-01-01

23

Trojan wavepackets and electromagnetically induced binding between two negative charges  

NASA Astrophysics Data System (ADS)

We exhibit the existence of 3D localized wavepackets in the Coulomb field of two negative charges place in a circularly polarized electromagnetic field. We use the Born-Oppenheimer approximation to determine the energy of a steady state configuration as a function of the inter-charge distance. The energy exhibits a minimum for certain excitations of the electronic wavepacket which proves the existence of the binding. Supporting numerical simulations are also presented.

Kalinski, Maciej

1997-04-01

24

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

25

Capture of negative exotic particles by atoms, ions and molecules  

Microsoft Academic Search

This article describes the capture of heavy negative particles (??, ??, K?, ) by normal atoms, ions and molecules to form exotic systems. Capture by even the hydrogen atom presents great challenges for theoretical treatment. The wide variety of methods used are reviewed, including perturbative, two-state adiabatic and diabatic, time-independent quantum mechanical, time-dependent semiclassical and quantum mechanical and quasi-classical treatments.

James S Cohen

2004-01-01

26

Capture of negative exotic particles by atoms, ions and molecules  

Microsoft Academic Search

This article describes the capture of heavy negative particles (mgr-, pgr-, K-, \\\\barp ) by normal atoms, ions and molecules to form exotic systems. Capture by even the hydrogen atom presents great challenges for theoretical treatment. The wide variety of methods used are reviewed, including perturbative, two-state adiabatic and diabatic, time-independent quantum mechanical, time-dependent semiclassical and quantum mechanical and quasi-classical

James S. Cohen

2004-01-01

27

The sheath structure around a negatively charged rocket payload  

Microsoft Academic Search

The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. In this case the tethered mother\\/daughter functioned as a double probe, the

T. Neubert; M. J. Mandell; S. Sasaki; B. E. Gilchrist; P. M. Banks; P. R. Williamson; W. J. Raitt; N. B. Meyers; K. I. Oyama; I. Katz

1990-01-01

28

Attosecond snapshots: imaging charge transfer in molecules using EUV light  

NASA Astrophysics Data System (ADS)

Electron dynamics underlie the charge and energy transfer processes in molecules. These processes, although extremely fast, can be resolved by sub-femtosecond light pulses and the electron motion can, to some extent, be controlled. A novel scheme for electron localization using intense IR lasers has recently been developed using phase-locked multiple pulses, in which the charge centre can be isolated. This process can be identified by the asymmetry in the dissociation products. We propose the use of an extreme ultraviolet probe of the molecular ion prior to dissociation to image the density and phase of the electron orbital. We hope this will provide rich insight into the charge transfer process in small molecules, which may be extended to larger systems.

McCann, J. F.; McLaughlin, B. M.; Calvert, C. R.; King, R. B.; Bryan, W. A.; Newell, W. R.; Greenwood, J. B.; Williams, I. D.

2012-11-01

29

Gram-Negative Bacterial Sensors for Eukaryotic Signal Molecules  

PubMed Central

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

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

2009-01-01

30

A search for doubly charged negative cluster ions in sputtering  

Microsoft Academic Search

The emission of negative cluster ions sputtered under cesium impact from various elemental and multicomponent specimens (B, C, Al, Si, Cu, LiF, MgF2, CdS, and InP) was investigated by means of secondary-ion mass spectrometry. In all cases abundant yields of singly charged cluster ions were observed in the mass range covered by the instrument ( <= 280 amu). On the

H. Gnaser; H. Oechsner

1993-01-01

31

Charge exchange of a polar molecule at its cation  

SciTech Connect

The Landau-Herring method is used to derive an analytic expression for the one-electron exchange interaction of a polar molecule with its positively charged ion, induced by a {sigma}-electron. Analogously to the classical Van der Pole method, the exchange interaction potential is averaged over the rotational states of colliding particles. The resonant charge-transfer cross section is calculated, and the effect of the dipole moments of the core on the cross section is analyzed. It is shown that allowance for the dependence of the exchange potential on the orientation of the dipole moments relative to the molecular axis may change the dependence of the cross section on the velocity of colliding particles, which is typical of the resonant charge exchange, from the resonance to the quasi-resonance dependence.

Buslov, E. Yu., E-mail: buslov@phys.vsu.ru; Zon, B. A., E-mail: zon@niif.vsu.ru [Voronezh State University (Russian Federation)

2011-01-15

32

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

33

Charge state reduction of oligonucleotide negative ions from electrospray ionization  

SciTech Connect

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

Cheng, X.; Gale, D.C.; Udseth, H.R.; Smith, R.D. (Pacific Northwest Lab., Richland, WA (United States))

1995-02-01

34

Photodetachment of gaseous multiply charged anions, copper phthalocyanine tetrasulfonate tetraanion: Tuning molecular electronic energy levels by charging and negative electron binding  

SciTech Connect

The authors report photodetachment photoelectron spectroscopy (PES) of gaseous copper phthalocyanine (CuPc) tetrasulfonate quadruply charged anions, [CuPc(SO{sub 3}){sub 4}]{sup 4{minus}}, and its monoprotonated and -sodiumated triply charged anions, [CuPc(SO{sub 3}){sub 4}H]{sup 3{minus}} and [CuPc(SO{sub 3}){sub 4}Na]{sup 3{minus}}. The [CuPc(SO{sub 3}){sub 4}]{sup 4{minus}} tetraanion was found to possess a negative electron binding energy of {minus}0.9 eV, whereas the trianions have binding energies of 1.0 and 1.2 eV for the sodiumated and protonated species, respectively. The PES spectral features of the three multiply charged anions were observed to be similar to that of the parent CuPc neutral molecule, except that the anions have lower binding energies due to the presence of the negative charges ({minus}SO{sub 3}{sup {minus}}). The data thus suggested a stepwise tuning of the molecular electronic energy levels of the CuPc molecule through charging, wherein the molecular orbital energies of the parent molecule were systematically pushed up by the negative charges. The authors further carried out semiempirical calculations, which provided insight into the nature of the localized charges on the peripheral {minus}SO{sub 3}{sup {minus}} groups and the intramolecular electrostatic interactions in the multiply charged anions and confirmed the interpretation of the stepwise tuning of molecular energy levels by charging. Photon energy-dependent studies revealed the effects of the repulsive Coulomb barriers on the photodetachment PES spectra of the multiply charged anions. The barrier heights were estimated to be about 3.5 and 2.5 eV for the tetra- and trianions, respectively. The authors also observed excited states for the multiply charged anions and resonant tunneling through the repulsive Coulomb barriers via the excited states.

Wang, X.B.; Ferris, K.; Wang, L.S.

2000-01-13

35

The sheath structure around a negatively charged rocket payload  

NASA Astrophysics Data System (ADS)

The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. Our experimental results come from the CHARGE 2 sounding rocket experiment in which the payload was split into two separate sections (mother and daugther) connected with a conducting, insulated tether. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. In this case the tethered mother/daughter functioned as a double probe, the negative probe (mother) reaching large negative potentials, while the positive probe (daughter) stayed close to the ambient plasma potential. A floating probe array was mounted on the mother with probes located 25, 50, 75, and 100 cm from the rocket surface. The internal impedance of the array was smaller than the probe/plasma impedance, which influenced the potential measurements. However, the measurements contain signatures, which we interpret as resulting from the outward expansion of the ion sheath with increasing negative mother potential. This conclusion is substantiated by NASCAP/LEO computer simulations of space charge limited flow. At high potentials, the observed ion current flowing to the mother increased more strongly with bias potential than found from the simulations. It is suggested that the enhancement of the current is generated by secondary electrons emitted by the ions bombarding the payload skin. The effects of the motion of the mother (540-580 m/s) and of the ambient magnetic field have been assessed by the code. It was estimated that the ion current to the mother was increased by 20% relative to a stationary payload, while the incorporation of a magnetic field had no practical influence on the simulation results. © Copyright 1990 by the American Geophysical Union

1990-05-01

36

Method and Device for Separation of Charged Molecules by Solution Isoelectric Focusing.  

National Technical Information Service (NTIS)

The invention provides a novel solution isoelectric focusing device and method that can reproducibly fractionate charged molecules into well-defined pools. This approach can be applied to mixtures of charged molecules, such as eukaryotic proteome samples ...

D. W. Speicher X. Zuo

2004-01-01

37

Charge Transport in Azobenzene-Based Single-Molecule Junctions  

NASA Astrophysics Data System (ADS)

The azobenzene class of molecules has become an archetype of molecular photoswitch research, due to their simple structure and the significant difference of the electronic system between their cis and trans isomers. However, a detailed understanding of the charge transport for the two isomers, when embedded in a junction with electrodes is still lacking. In order to clarify this issue, we investigate charge transport properties through single Azobenzene-ThioMethyl (AzoTM) molecules in a mechanically controlled break junction (MCBJ) system at 4.2 K. Single-molecule conductance, I-V characteristics, and IETS spectra of molecular junctions are measured and compared with first-principles transport calculations. Our studies elucidate the origin of a slightly higher conductance of junctions with cis isomer and demonstrate that IETS spectra of cis and trans forms show distinct vibrational fingerprints that can be used for identifying the isomer.[1] 1. Y. Kim, A. Garcia-Lekue, D. Sysoiev, T. Frederiksen, U. Groth, E. Scheer, Phys. Rev. Lett. (accepted).

Garcia-Lekue, Aran; Kim, Youngsang; Sysoiev, Dmytro; Frederiksen, Thomas; Groth, Ulrich; Scheer, Elke

2013-03-01

38

Modeling the selective partitioning of cations into negatively charged nanopores in water  

NASA Astrophysics Data System (ADS)

Partitioning and transport of water and small solutes into and through nanopores are important to a variety of chemical and biological processes and applications. Here we study water structure in negatively charged model cylindrical [carbon nanotube (CNT)-like] nanopores, as well as the partitioning of positive ions of increasing size (Na+, K+, and Cs+) into the pore interior using extensive molecular dynamics simulations. Despite the simplicity of the simulation system-containing a short CNT-like nanopore in water carrying a uniformly distributed charge of qpore=-ne surrounded by n (=0,...,8) cations, making the overall system charge neutral-the results provide new and useful insights on both the pore hydration and ion partitioning. For n=0, that is, for a neutral nanopore, water molecules partition into the pore and form single-file hydrogen-bonded wire spanning the pore length. With increasing n, water molecules enter the pore from both ends with preferred orientations, resulting in a mutual repulsion between oriented water molecules at the pore center and creating a cavity-like low density region at the center. For low negative charge densities on the pore, the driving force for partitioning of positive ions into the pore is weak, and no partitioning is observed. Increasing the pore charge gradually leads to partitioning of positive ions into the pore. Interestingly, over a range of intermediate negative charge densities, nanopores display both thermodynamic as well as kinetic selectivity toward partitioning of the larger K+ and Cs+ ions into their interior over the smaller Na+ ions. Specifically, the driving force is in the order K+>Cs+>Na+, and K+ and Cs+ ions enter the pore much more rapidly than Na+ ions. At higher charge densities, the driving force for partitioning increases for all cations-it is highest for K+ ions-and becomes similar for Na+ and Cs+ ions. The variation of thermodynamic driving force and the average partitioning time with the pore charge density together suggest the presence of free energy barriers in the partitioning process. We discuss the role of ion hydration in the bulk and in the pore interior as well as of the pore hydration in determining the barrier heights for ion partitioning and the observed thermodynamic and kinetic selectivities.

Yang, Lu; Garde, Shekhar

2007-02-01

39

Photoinduced charge transfer from polymers to fullerene molecules revisited.  

NASA Astrophysics Data System (ADS)

We study the process of photoinduced charge transfer (PCT) between conjugated polymers and fullerene molecules as electron acceptors, using the technique of picosecond transient, and steady state photomodulation at various modulation frequencies and temperatures. The polymers studied were MEH-PPV and regio-regular P3HT [RR-P3HT], which are some of the common polymers that are used in organic photovoltaic, as well as polyfluorene [PFO] with optical gap in the blue spectral range; whereas the fullerene molecules where C60, C70 and their PCBM variations. In all cases we found PCT as evident by the formation of strong photoinduced absorption (PA) polaron bands in the mid ir spectral range. Surprisingly we also found PCT with photon energy below the polymer optical gap. This below-gap PCT process will be discussed and compared with the more usual PCT process with above gap excitation.

Drori, Tomer; Sheng, Chuanxiang; Ndobe, Alex; Yang, Cungeng; Tong, Minghong; Vardeny, Valy

2007-03-01

40

Intramolecular charge transfer in donor-acceptor molecules  

SciTech Connect

The photophysical properties of donor-acceptor molecules, push-pull polyenes and carotenoids, have been studied by absorption and fluorescence spectroscopy. The compounds bear various acceptor and donor groups, linked together by chains of different length and structure. The position of the absorption and fluorescence maxima and their variation in solvents of increasing polarity are in agreement with long-distance intramolecular charge-transfer processes, the linker acting as a molecular wire. The effects of the linker length and structure and of the nature of acceptor and donor are presented.

Slama-Schwok, A.; Blanchard-Desce, M.; Lehn, J.M. (College de France, Paris (France))

1990-05-17

41

Guiding slow polar molecules with a charged wire  

SciTech Connect

We demonstrate experimentally the guiding of cold and slow ND{sub 3} molecules along a thin charged wire over a distance of {approx}0.34 m through an entire molecular beam apparatus. Trajectory simulations confirm that both linear and quadratic high-field-seeking Stark states can be efficiently guided from the beam source up to the detector. A density enhancement up to a factor 7 is reached for beams with velocities ranging down to {approx}150 m/s generated by the rotating nozzle technique.

Strebel, M.; Spieler, S.; Stienkemeier, F.; Mudrich, M. [Physikalisches Institut, Universitaet Freiburg, D-79104 Freiburg (Germany)

2011-11-15

42

The sheath structure around a negatively charged rocket payload  

SciTech Connect

The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. In this case the tethered mother/daughter functioned as a double probe, the negative probe (mother) reaching large negative potentials, while the positive probe (daughter) stayed close to the ambient plasma potential. A floating probe array was mounted on the mother with probes located, 25, 50, 75, and 100 cm from the rocket surface. The internal impedance of the array was smaller than the probe/plasma impedance, which influenced the potential measurements. However, the measurements contain signatures, which the authors interpret as resulting from the outward expansion of the ion sheath with increasing negative mother potential. This conclusion is substantiated by NASCAP/LEO computer simulations of space charge limited flow. At high potentials, the observed ion current flowing to the mother increased more strongly with bias potential than found from the simulations. It is suggested that the enhancement of the current is generated by secondary electrons emitted by the ions bombarding the payload skin. The effects of the motion of the mother (540-580 m/s) and of the ambient magnetic field have been assessed by the code. It was estimated that the ion current to the mother was increased by 20% relative to a stationary payload, while the incorporation of a magnetic field had no practical influence on the simulation results.

Neubert, T.; Gilchrist, B.E.; Banks, P.M.; Williamson, P.R. (Stanford Univ., CA (United States)); Mandell, M.J.; Katz, I. (S-Cubed, La Jolla, CA (United States)); Sasaki, S.; Oyama, K.I. (Inst. for Space and Astronautical Sciences, Tokyo (Japan)); Raitt, W.J.; Meyers, N.B. (Utah State Univ., Logan (United States))

1990-05-01

43

Negative Ion Fragmentation of Cysteic Acid Containing Peptides: Cysteic Acid as a Fixed Negative Charge  

NASA Astrophysics Data System (ADS)

We present here a study of the collision induced dissociation (CID) of deprotonated cysteic acid containing peptides produced by MALDI. The effect of cysteic acid (Cox) position is interrogated by considering the positional isomers, CoxLVINVLSQG, LVINVLSQGCox, and LVINVCoxLSQG. Although considerable variation between the CID spectra is observed, the mechanistic picture that emerges involves charge retention at the deprotonated cysteic acid side chain. Fragmentation occurs in the proximity of the cysteic acid group by charge directed mechanisms as well as remote from this group to form ions, which may be rationalized by charge remote mechanisms. Additionally, the formation of the SO{3/-•} ion is observed in all cases. Fragmentation of CoxLVINVLSQCox provides both N- and C-terminal, y and b ions, respectively indicating that the negative charge may be retained at either of the cysteic acids; however, there is some evidence that charge retention at the C-terminal cysteic acid may be preferred. Fragmentation of tryptic type peptides containing a C-terminal arginine or lysine residue is considered through comparison of three peptides CoxLVINKLSQG, CoxLVINVLSQK, and CoxLVINVLSQR. Lastly, we rationalize the formation of b n-1 + H2O and a n-1 ions through a mechanism involving rearrangement of the C-terminal residue to form a mixed anhydride intermediate.

Williams, Brad J.; Barlow, Christopher K.; Kmiec, Kevin L.; Russell, William K.; Russell, David H.

2011-09-01

44

Charge transfer and weak chemisorption of oxygen molecules in nanoporous carbon consisting of a disordered network of nanographene sheets  

NASA Astrophysics Data System (ADS)

The adsorption/desorption processes of oxygen are investigated in nanoporous carbon (activated carbon fiber (ACF)) consisting of a disordered network of nanographene sheets. The heat-induced desorption at 200 °C shows the decomposition of oxygen-including functional groups weakly bonded to nanographene edges. The removal of these oxygen-including negatively charged functional groups brings about a change in the type of majority carriers, from holes to electrons, through charge transfer from the functional groups to the interior of nanographene sheets. The oxygen adsorption brings ACF back to the electronic state with holes being majority carriers. In this process, a large concentration of negatively charged O2? - molecules with ? ~ 0.1 are created through charge transfer from nanographene sheets to the adsorbed oxygen molecules. The changes in the thermoelectric power and the electrical resistance in the oxygen desorption process is steeper than that in the oxygen adsorption process. This suggests the irreversibility between the two processes.

Sumanasekera, G. U.; Chen, G.; Takai, K.; Joly, J.; Kobayashi, N.; Enoki, T.; Eklund, P. C.

2010-08-01

45

Charge transfer and weak chemisorption of oxygen molecules in nanoporous carbon consisting of a disordered network of nanographene sheets.  

PubMed

The adsorption/desorption processes of oxygen are investigated in nanoporous carbon (activated carbon fiber (ACF)) consisting of a disordered network of nanographene sheets. The heat-induced desorption at 200?°C shows the decomposition of oxygen-including functional groups weakly bonded to nanographene edges. The removal of these oxygen-including negatively charged functional groups brings about a change in the type of majority carriers, from holes to electrons, through charge transfer from the functional groups to the interior of nanographene sheets. The oxygen adsorption brings ACF back to the electronic state with holes being majority carriers. In this process, a large concentration of negatively charged O(2)(?-) molecules with ? ? 0.1 are created through charge transfer from nanographene sheets to the adsorbed oxygen molecules. The changes in the thermoelectric power and the electrical resistance in the oxygen desorption process is steeper than that in the oxygen adsorption process. This suggests the irreversibility between the two processes. PMID:21386498

Sumanasekera, G U; Chen, G; Takai, K; Joly, J; Kobayashi, N; Enoki, T; Eklund, P C

2010-08-04

46

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

NASA Astrophysics Data System (ADS)

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

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

1982-08-01

47

Perspectives to produce positively or negatively charged polyhydroxyalkanoic acids.  

PubMed

An overview is provided on the possibilities of producing positively and negatively charged poly(?-hydroxyalkanoates), PHAs. A large variety of bacterial polyesters with functionalized terminal side chains can be produced in microbial fermentation processes by a direct polymerization of respective carbon sources, that is, carbon sources that carry functional groups in their ?-position. However, charged PHAs are not accessible by a direct approach and must be synthesized via polymer-analogous reactions of functionalized bacterial polyesters. PHA polyanions are produced by converting the terminal functional groups into carboxylate groups, while PHA polycations are produced by introducing terminal amino groups. PHAs with terminal vinyl groups emerged as most suitable PHA precursors, as they can be produced in relatively high yields and the double bonds are sufficiently reactive. The oxidation of vinyl groups yields PHA polyanions. The conversion of terminal vinyl groups into epoxides with a subsequent ring-opening reaction with an amine yields PHA polycations. Other functionalized PHA that potentially lend themselves to polymer-analogous reactions are reviewed. PMID:20721548

Scholz, Carmen

2010-08-19

48

Single molecule detection using charge-coupled device array technology  

NASA Astrophysics Data System (ADS)

An ultra sensitive technique for the detection of fluorescent species in a flowing stream has been developed. The extension of this technique to the detection of fluorescently tagged nucleotides will be a significant benefit to one of the novel approaches for DNA sequencing being developed at Los Alamos National Laboratories. The detection scheme is based on a novel mode of operating a charge-coupled device (CCD) which greatly enhances the discrimination between fluorescence from the analyte and the background Raman scattering from the solvent. Register shifts between rows in the CCD are synchronized with the sample flow velocity so that fluorescence from a single species is collected in a single moving charge packet occupying an area approaching that of a single pixel while the background is spread evenly among a large number of pixels. This research has demonstrated that this technique is highly effective for the detection of fluorescently labelled latex microspheres. With additional development, the authors believe that this technique will achieve single molecule detection.

Denton, M. B.

1994-04-01

49

Inhibition of herpes simplex virus infection by negatively charged and neutral carbohydrate polymers.  

PubMed

Different natural and semisynthetic polysaccharides were evaluated for their inhibitory effect on in vitro replication of herpes simplex virus (HSV) types 1 and 2. Some neutral and negatively charged carbohydrates were able to inhibit viral infection by interfering mainly with the adsorption process showing a dose-dependent relationship. Their effect was shown within the concentration range of 200-0.8 micrograms/ml, and the inhibiting compounds were in order of action: dextran sulfate = scleroglucan = lambda carrageenan > glyloid sulfate 4324 > locust beam gum towards HSV-1 and dextran sulfate = glyloid sulfate 4324 = lambda carrageenan > scleroglucan > glycogen sulfate 4435 towards HSV-2. The data obtained indicate that the antiviral activity of polysaccharides was not only related to their electric charge. Other characteristics of the molecules such as the polymeric backbone, the carbohydrate moieties and the degree of polymerization could play a role in influencing their antiviral properties. PMID:7666126

Marchetti, M; Pisani, S; Pietropaolo, V; Seganti, L; Nicoletti, R; Orsi, N

1995-04-01

50

Charge transfer processes in collisions of slow highly charged ions with polar molecules CO and C3H8  

Microsoft Academic Search

Charge transfer processes resulting from low energy collisions of polar molecules CO and C3H8 with highly charged Be2+ and B2+ ions have been investigated experimentally and theoretically. The potential for the one-electron exchange interaction between a polar molecule and highly charged atomic ion were obtained in closed analytical form in the framework of a semiclassical approach. Obtained results were used

M. V. Khoma; Makoto Imai; O. M. Karbovanets; Y. Kikuchi; M. Saito; Y. Haruyama; M. I. Karbovanets; I. Yu Kretinin; A. Itoh; R. J. Buenker

2009-01-01

51

Penetration of negatively charged lipid interfaces by the doubly deprotonated dipicolinate.  

PubMed

The possibility that a negatively charged organic molecule penetrates the lipid interface in a reverse micellar system is examined using UV-vis absorption and NMR spectroscopy. The hypothesis that deprotonated forms of dipicolinic acid, H(2)dipic, such as Hdipic(-) and dipic(2-), can penetrate the lipid interface in a microemulsion is based on our previous finding that the insulin-enhancing anionic [VO(2)dipic](-) complex was found to reside in the hydrophobic layer of the reverse micelle (Crans et al. J. Am. Chem. Soc. 2006, 128, 4437-4445). Penetration of a polar and charged compound, namely Hdipic(-) or dipic(2-), into a hydrophobic environment is perhaps unexpected given the established rules regarding the fundamental properties of compound solubility. As such, this work has broad implications in organic chemistry and other disciplines of science. These studies required a comprehensive investigation of the different dipic species and their association in aqueous solutions at varying pH values. Combining the aqueous studies using absorption and NMR spectroscopy with those in microemulsions defines the differences observed in the heterogeneous environment. Despite the expected repulsion between the surfactant head groups and the dianionic probe molecule, these studies demonstrate that dipic resides deep in the hydrophobic portion of the reverse micellar interface. In summary, these results provide evidence that ionic molecules can reside in nonpolar locations in microheterogeneous environments. This suggests that additional factors such as solvation are important to molecule location. Documented ability to penetrate lipid surfaces of similar charge provides a rationale for why specific drugs with less than optimal hydrophobicity are successful even though they violate Lipinski's rules. PMID:19053583

Crans, Debbie C; Trujillo, Alejandro M; Bonetti, Sandra; Rithner, Christopher D; Baruah, Bharat; Levinger, Nancy E

2008-12-19

52

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

PubMed

Simulations were performed for up to 150 simplified spherical horse heart cytochrome c molecules in the presence of a charged surface, which serves as an approximate model for a lipid membrane. Screened electrostatic and short-ranged attractive as well as repulsive van der Waals forces for interparticle and particle-membrane interactions are utilized in the simulations. At a distance from the membrane, where particle-membrane interactions are negligible, the simulation is coupled to a noninteraction continuum analogous to a heat bath [Geyer et al., J. Chem. Phys. 120, 4573 (2004)]. From the particles' density profiles perpendicular to the planar surface binding isotherms are derived and compared to experimental results [Heimburg et al. (1999)]. Using a negatively charged structureless membrane surface a saturation effect was found for relatively large particle concentrations. Since biological membranes often contain membrane proteins, we also studied the influence of additional charges on our model membrane mimicking bacterial reaction centers. We find that the onset of the saturation occurs for much lower concentrations and is sensitive to the detailed implementation. Therefore we suggest that local distortion of membrane planarity (undulation), or lipid demixing, or the presence of charged integral membrane proteins create preferential binding sites on the membrane. Only then do we observe saturation at physiological concentrations. PMID:15260567

Gorba, C; Geyer, T; Helms, V

2004-07-01

53

Enhanced Memory for Negatively Emotionally Charged Pictures Without Selective Rumination  

Microsoft Academic Search

Emotionally charged materials have been found to elicit higher levels of recall in many studies. However, the use of slow presentations and\\/or uncontrolled retention intervals may have allowed subjects to rehearse emotional materials preferentially. The authors presented a series of 5 pictures (1 emotionally charged) at a rate of 4 pictures per second, precluding selective rehearsal. In Experiment 1, subjects

Christine R. Harris; Harold Pashler

2005-01-01

54

Effect of charge distribution along surfactant molecules on physico-chemical properties of surfactant systems  

Microsoft Academic Search

It is known that electrical charge of a surfactant distributes along the molecule including the hydrophobic tail. The charge distributions of some hydrogenated\\/fluorinated surfactant molecules have been estimated by semiempirical quantum chemical methods PM3. The relationships between the charge distribution and the physico-chemical properties of surfactant systems, in particular the mixed surfactant systems, i.e., cationic–anionic surfactant mixture, ionic surfactant–alkyl alcohol

Guo-Xi Zhao; Bu-Yao Zhu; Zeng-Pei Dou; Peng Yan; Jin-Xin Xiao

2008-01-01

55

Charge transfer processes in collisions of slow highly charged ions with polar molecules CO and C3H8  

NASA Astrophysics Data System (ADS)

Charge transfer processes resulting from low energy collisions of polar molecules CO and C3H8 with highly charged Be2+ and B2+ ions have been investigated experimentally and theoretically. The potential for the one-electron exchange interaction between a polar molecule and highly charged atomic ion were obtained in closed analytical form in the framework of a semiclassical approach. Obtained results were used for close-coupling calculations of total cross sections for single electron transfer in the studied reactions.

Khoma, M. V.; Imai, Makoto; Karbovanets, O. M.; Kikuchi, Y.; Saito, M.; Haruyama, Y.; Karbovanets, M. I.; Kretinin, I. Yu; Itoh, A.; Buenker, R. J.

2009-04-01

56

Charge measurements on individual particles exiting laboratory precipitators with positive and negative corona at various temperatures  

NASA Astrophysics Data System (ADS)

The values of charge on individual particles exiting three different laboratory precipitators have been measured in an experimental apparatus containing a Millikan cell. Measurements were obtained for dioctylphthalate (DOP) droplets and fly ash particles at temperatures from 23 to 343 °C. At comparable voltages and currents for positive and negative coronas, the data show that the ratio of the values of negative-to-positive charge for radii in the range 0.6-1.3 ?m increases from about 1 to 2 as the temperature increases from 37 to 343 °C. The predictions of a mathematical model of electrostatic precipitation which employs an ionic charging theory show good agreement with all the positive charging data, but show good agreement with the negative charging data only at temperatures below 37 °C. The differences in the measurements and the model predictions are consistent with the postulation of free electron charging at elevated temperatures in negative corona.

McDonald, Jack R.; Anderson, Marlin H.; Mosley, Ronald B.; Sparks, Leslie E.

1980-07-01

57

First Observation of Doubly Charged Negative Gold Cluster Ions  

Microsoft Academic Search

Singly charged gold cluster anions in the size range n=16-30 have been captured, stored and size selected in a Penning trap. After application of an electron beam doubly charged gold cluster anions have been observed for 20<=n<=30. To our knowledge this is the first observation of metal cluster dianions. The threshold appearance size is in good agreement with a simple

A. Herlert; S. Krückeberg; L. Schweikhard; M. Vogel; C. Walther

1999-01-01

58

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

NASA Astrophysics Data System (ADS)

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

Fang, Yigang; Liu, Fangwei; Liu, Jianbo

2013-01-01

59

Investigation of charge localization and charge delocalization in model molecules by multiphoton ionization photoelectron spectroscopy and DFT calculations.  

PubMed

In this work we focus on the question to which degree a surplus charge is localized or delocalized in extended molecular systems. Molecules consisting of a flexible tail and the benzene chromophore, such as n-propylbenzene, 2-phenylethyl alcohol and 2-phenylethylamine, are used as model molecules. Their S0-S1 resonance enhanced multiphoton ionization (MPI) spectra containing origin transitions of different conformers appear at similar wavelengths. This shows, that in the neutral the electronic excitation is localized at the benzene chromophore. Geometry differences between the neutral and the cation can be qualitatively derived from intensities of vibrational transitions or the onset behavior in MPI high-resolution photoelectron (MPI-PE) spectra. We identify two possible reasons for structural changes: Charge-dipole interaction and charge delocalization. Whereas both effects can be active for the folded gauche conformers, the charge-dipole interaction is expected to be small for the extended anti conformers and geometry changes are attributed to charge delocalization. Density functional calculations of structures and energies qualitatively confirm the experimental results for all molecules and their conformers. They predict charge delocalization into the end group of below 20% for n-propylbenzene and 2-phenylethyl alcohol. In the case of 2-phenylethylamine the charge is equally shared by the near-isoenergetic charge sites of the benzene chromophore and the amine group. PMID:11040519

Weinkauf, R; Lehrer, F; Schlag, E W; Metsala, A

2000-01-01

60

Probing the charge-transfer dynamics in DNA at the single-molecule level.  

PubMed

Photoinduced charge-transfer fluorescence quenching of a fluorescent dye produces the nonemissive charge-separated state, and subsequent charge recombination makes the reaction reversible. While the information available from the photoinduced charge-transfer process provides the basis for monitoring the microenvironment around the fluorescent dyes and such monitoring is particularly important in live-cell imaging and DNA diagnosis, the information obtainable from the charge recombination process is usually overlooked. When looking at fluorescence emitted from each single fluorescent dye, photoinduced charge-transfer, charge-migration, and charge recombination cause a "blinking" of the fluorescence, in which the charge-recombination rate or the lifetime of the charge-separated state (?) is supposed to be reflected in the duration of the off time during the single-molecule-level fluorescence measurement. Herein, based on our recently developed method for the direct observation of charge migration in DNA, we utilized DNA as a platform for spectroscopic investigations of charge-recombination dynamics for several fluorescent dyes: TAMRA, ATTO 655, and Alexa 532, which are used in single-molecule fluorescence measurements. Charge recombination dynamics were observed by transient absorption measurements, demonstrating that these fluorescent dyes can be used to monitor the charge-separation and charge-recombination events. Fluorescence correlation spectroscopy (FCS) of ATTO 655 modified DNA allowed the successful measurement of the charge-recombination dynamics in DNA at the single-molecule level. Utilizing the injected charge just like a pulse of sound, such as a "ping" in active sonar systems, information about the DNA sequence surrounding the fluorescent dye was read out by measuring the time it takes for the charge to return. PMID:21875061

Kawai, Kiyohiko; Matsutani, Eri; Maruyama, Atsushi; Majima, Tetsuro

2011-09-12

61

Charge Perturbation Detection System for DNA and Other Molecules.  

National Technical Information Service (NTIS)

Methods and apparatus for direct detection of chemical reactions are provided. In a preferred embodiment, electric charge perturbations of the local environment during enzyme-catalyzed reactions are sensed by an electrode system with an immobilized target...

M. Karhanek N. Pourmand R. W. Davis

2005-01-01

62

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

63

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

SciTech Connect

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

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

2005-05-15

64

A highly negatively charged ?-Keggin germanodecatungstate efficient for Knoevenagel condensation.  

PubMed

A tetra-n-butylammonium (TBA) salt of a ?-Keggin -6-charged germanodecatungstate, [?-H(2)GeW(10)O(36)](6-) (I), could act as an efficient homogeneous catalyst for Knoevenagel condensation of active methylene compounds with carbonyl compounds. PMID:22790486

Sugahara, Kosei; Kimura, Toshihiro; Kamata, Keigo; Yamaguchi, Kazuya; Mizuno, Noritaka

2012-07-13

65

Solid Propellant Charge Design with Negative Effective Pressure Exponent Using Forced Cone Burning.  

National Technical Information Service (NTIS)

A novel method of making a solid propellant rocket motor or gas generator charge with a negative effective burning rate pressure exponent (negative drb/dP) is presented. The negative exponent characteristic can be obtained independently of burning rate an...

R. D. Irvine P. C. Winch

1986-01-01

66

Clinical study on the treatment of chronic wound with negatively-charged aerosol  

PubMed Central

Background: Aerosols are defined as the mixture of liquid or solid particles/droplets that are stably suspending in air. When carrying a certain amount of negative charge, they will be defined as negatively-charged aerosol. This report investigates the effect of negatively-charged aerosol on the healing of chronic wound. Methods: 140 patients with chronic wound were assigned randomly into two groups. Normal, routine treatment was applied on chronic wounds of 73 patients depending on wounds situation (control group). While another 67 similar patients received negatively-charged aerosol therapy (2 hours per time, twice a day) and were used as experimental group. Wound healing assessment including the patients’ complication, detection of bacteria in wound secretions, and evaluation of wound healing. Results: The results of our study showed that after the application of negatively-charged aerosols, and condition and infection rate of wounds from experiment group were better and lower than that of control group. In comparison with control group, the relative size of wounds from experiment group was significantly smaller (P<0.05) at post-treatment day 0, 7, 14, 21 and 28. Also, the time required for wound healing in the experimental group was significantly shorter (P<0.05) than that in the control group. Conclusion: Negatively-charged aerosol therapy can accelerate wound healing speed and improve the healing of chronic wounds. Thus, we wound recommend the consideration of Negatively-charged aerosol therapies in addition to normal wound treatment in cases of chronic wound.

Xie, Xiaoxia; Chen, Lei; Zhang, Zhao-Qiang; Shi, Yan; Xie, Julin

2013-01-01

67

Calculating Henryâ??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 ...

68

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

69

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

70

Enhanced memory for negatively emotionally charged pictures without selective rumination.  

PubMed

Emotionally charged materials have been found to elicit higher levels of recall in many studies. However, the use of slow presentations and/or uncontrolled retention intervals may have allowed subjects to rehearse emotional materials preferentially. The authors presented a series of 5 pictures (1 emotionally charged) at a rate of 4 pictures per second, precluding selective rehearsal. In Experiment 1, subjects recalled the pictures immediately or after performing an arithmetic task for 20 s. In Experiment 2, the pictures were described as to-be-ignored distractors, and the memory test was unexpected. Stimulus emotionality greatly enhanced recall in all conditions. The speed of the presentations and the fact that enhancement did not spread to temporally adjacent items argues against some widely discussed mechanisms for emotional enhancement. PMID:15982084

Harris, Christine R; Pashler, Harold

2005-06-01

71

Aberration of a negative ion beam caused by space charge effect  

SciTech Connect

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

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

2010-02-15

72

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.

2013-01-01

73

Chemisorption of hydrogen molecules on carbon nanotubes: charging effect from first-principles calculations  

Microsoft Academic Search

We report a systematic investigation of the charging effect on hydrogen molecule chemisorption on (3, 3), (5, 5), (5, 0), and (8, 0) carbon nanotubes by first-principles calculations. The influence of injected charge on the chemisorption energy barriers is found to be sensitive to the nanotube diameter and chirality. The calculated results also indicate that electron injection is more effective

Bin Zhou; Wanlin Guo; Chun Tang

2008-01-01

74

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

Microsoft Academic Search

During collisions between slow highly charged ions and neutral atoms or molecules, a lot of electrons can be transferred into multiply excited levels of the highly charged ions, and finally the product ions are stabilized by ejection of electrons (autoionization decay) or photons (radiative decay). The ratios of the radiative decay to the autoionization decay after double-electron transfer processes in

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

1997-01-01

75

Charge transfer in metal-atom-containing molecules in the gas phase  

Microsoft Academic Search

The presence of charge transfer (CT) is ubiquitous in metal-atom-containing molecules in the gas phase. The states of interest range from ground states to the lower excited states, given the generally low ionisation potentials of metal atoms. This review is written from an experimentalist's perspective, to describe the specifics of CT states in stable molecules containing a metal atom or

Niloufar Shafizadeh; Benoit Soep; Jean Michel Mestdagh; W. H. Breckenridge

2009-01-01

76

Geant4 Model for the Stopping Power of Low Energy Negatively Charged Hadrons  

Microsoft Academic Search

An original model is presented for the simulation of the energy loss of negatively charged hadrons. It calculates the stopping power by regarding the target atoms as an ensemble of quantum harmonic oscillators; this approach allows to account for charge dependent effects in the stopping power, which are relevant at energies below a few MeV. The resulting antiproton stopping powers

Stphane Chauvie; Petteri Nieminen; Maria Grazia Pia

2007-01-01

77

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

NSDL National Science Digital Library

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

Henderson, Tom

2006-03-15

78

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

79

Ionization of water molecules by fast charged projectiles  

SciTech Connect

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

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

2011-07-15

80

Charge transfer and polarization at interfaces with conjugated molecules  

NASA Astrophysics Data System (ADS)

The function and efficiency of organic electronic devices is determined to a significant extent by the electronic properties of organic/organic heterojunctions and interfaces between electrodes and organic semiconductors. The energy level alignment between metal electrodes and active organic layers can be adjusted over wide ranges by employing interlayers of strong molecular acceptors and donors that undergo charge transfer reactions with the metal. It will be shown that such interlayers lead to lower charge injection barriers than pristine metals, even when the work function is the same. It is argued that the molecularly modified electrodes are electronically more rigid than their pristine metal counterparts, i.e., the electron spill-out at the organic-terminated surface is less pronounced compared to metal surfaces. The energy levels at organic/organic heterojunctions comprising donors and acceptors as used in organic photovoltaic cells are essentially independent of deposition sequence, as long as supporting electrodes to not induce energy level pinning. When a high work function electrode is used, the energy levels may become Fermi-level pinned and an electric field drops right at the heterojunction. This effect is exemplified for the donor diindenoperylene and the acceptor C60. The electric field distribution within an organic opto-electronic device may thus be adjusted locally by employing interfacial energy level pinning, even at weakly interacting organic/organic interfaces.

Koch, Norbert

2012-02-01

81

Rectification effect for spin- and charge-currents in a shuttled molecule transistor  

NASA Astrophysics Data System (ADS)

We have investigated the spin-dependent electronic transports through a shuttled molecule, a molecule self-excitedly oscillating due to suffering an external electric field. When the shuttled molecule is coupled asymmetrically to a ferromagnetic and a normal metal leads, a pronounced dual rectification effect is predicted for both spin- and charge-currents in the Coulomb blockade regime. As compared to the conventional rectifier based on a static quantum dot, the proposed rectifier based on a movable individual molecule has higher rectification efficiency.

Wang, Rui-Qiang; Hu, Liang-Bin

2010-09-01

82

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

NASA Astrophysics Data System (ADS)

This study examined the meteorological characteristics of precipitation systems that produced 38 "sprite-class" negative cloud-to-ground (CG) strokes (i.e., peak currents in excess of 100 kA and charge moment changes in excess of 800 C km) as well as those that produced three confirmed negative sprites on 23 different days during 2009-2011. Within 15 km of the negative sprite-parent/class stroke, the median characteristics for these systems were to produce negative CGs as 69.2% of all CGs, and for the 30 dBZ radar reflectivity contour to reach on average 14.2 km above mean sea level (MSL), during a 25 min period encompassing the occurrence of the stroke. The median contiguous area of 30 dBZ composite radar echo (i.e., maximum value in the vertical column) for these systems was 6.73 × 103 km2. All but three of the discharges occurred in intense multicellular convection, with 30 dBZ exceeding 10 km MSL in altitude, while the others occurred in the stratiform regions of mesoscale convective systems. All but six of the systems produced greater than 50% negative CG lightning, though flash rates tended to be low near the stroke (1-2 min-1 on average). The results suggest that negative sprite-parent/class lightning typically occurs in precipitation systems of similar size and intensity as those that produce positive sprites, but not necessarily the same systems, and the negative lightning normally strikes ground in the convection rather than the stratiform precipitation. However, upper-level positive charge in the convection may play an important role in sprite-class/parent lightning of either polarity.

Lang, Timothy J.; Cummer, Steven A.; Rutledge, Steven A.; Lyons, Walter A.

2013-07-01

83

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

NASA Astrophysics Data System (ADS)

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

Müser, M. H.

2012-04-01

84

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

PubMed

Although ice melts and water freezes under equilibrium conditions at 0 degrees C, water can be supercooled under homogeneous conditions in a clean environment down to -40 degrees C without freezing. The influence of the electric field on the freezing temperature of supercooled water (electrofreezing) is of topical importance in the living and inanimate worlds. We report that positively charged surfaces of pyroelectric LiTaO3 crystals and SrTiO3 thin films promote ice nucleation, whereas the same surfaces when negatively charged reduce the freezing temperature. Accordingly, droplets of water cooled down on a negatively charged LiTaO3 surface and remaining liquid at -11 degrees C freeze immediately when this surface is heated to -8 degrees C, as a result of the replacement of the negative surface charge by a positive one. Furthermore, powder x-ray diffraction studies demonstrated that the freezing on the positively charged surface starts at the solid/water interface, whereas on a negatively charged surface, ice nucleation starts at the air/water interface. PMID:20133568

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

2010-02-01

85

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

86

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

87

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

SciTech Connect

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

Nishiura, M.; Tsumori, K. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Matsumoto, Y. [Tokushima Bunri University, Yamashiro-cho, Tokushima, 770-8514 (Japan); Wada, M. [Doshisha University, Kyotanabe, 610-0321 (Japan); Inoue, T. [Japan Atomic Energy Agency, 801-1, Mukoyama, Naka 311-0193 (Japan)

2011-09-26

88

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

90

Charge Measurement of Atoms and Atomic Resolution of Molecules with Noncontact AFM  

Microsoft Academic Search

Individual gold and silver adatoms [1] and pentacene molecules [2] on ultrathin NaCl films on Cu(111) were investigated using a qPlus tuning fork atomic force microscope (AFM) operated at 5 Kelvin with oscillation amplitudes in the sub-ångstrom regime. Charging a gold adatom by one electron charge increased the force on the AFM tip by a few piconewtons. Employing Kelvin probe

Leo Gross

2010-01-01

91

One and two-electron processes in collisions between hydrogen molecules and slow highly charged ions  

Microsoft Academic Search

A coincidence time-of-flight technique coupled with projectile charge state analysis was used to study electron capture in collisions between slow highly charged ions and hydrogen molecules. We found single electron capture with no target excitation to be the dominant process for both C6+ projectiles at a velocity of 0.8 atomic units and Ar11+ projectiles at v=0.63a.u. Double electron capture and

E. Wells; K. D. Carnes; H. Tawara; R. Ali; Emil Y. Sidky; Clara Illescas; I. Ben-Itzhak

2005-01-01

92

Single- and double-electron charge transfer in collisions of ?-particles with hydrogen molecules  

NASA Astrophysics Data System (ADS)

Total, partial, and angular differential cross sections of single- and double-electron charge transfer in collisions between ?-particles and hydrogen molecules in the ground state in the interval of collision energies from 3 to 80 keV have been calculated. New data for charge transfer cross sections can be used for simulations and spectroscopy of ?-particles in thermonuclear diverter plasma of nuclear reactors.

Nikulin, V. K.; Gushchina, N. A.; Tsarev, Yu. N.

2013-07-01

93

Drift-Tube Studies of Exoergic Ion-Molecule Collisions and Photon-Induced Charge Transfer.  

NASA Astrophysics Data System (ADS)

Rate coefficients and product-ion yields were determined for ion-molecule collisions at near-thermal energies involving the molecule dimethyl-methylphosphonate (DMMP) and several atmospheric ions. A similar study was done with He^{++} ions and several atmospheric gases. A third experiment was an attempt to observe the laser-stimulated charge transfer in collisions of Ne^+ with He. All measurements were carried out using a selected-ion drift tube mass spectrometer. The results of the study with DMMP showed that most reactions appear to proceed by dissociative charge transfer, although some evidence for ion-molecule reaction was found in the case of O_sp{2} {+}. Also, the only loss mechanism for ground state NO^+ ions is three -body association, and hydronium ions transfer a proton to DMMP. Rate coefficients obtained in the study with He^{++} ions were found to be quite close to the predictions of ion-molecule capture theories. Singly and doubly charged product ions were observed in several cases, indicating that both single and double charge transfer, and possibly transfer ionization, occur. The experiment on laser-stimulated charge transfer produced measurements of upper limits to the cross section that are considerably lower than some theoretical predictions.

Tosh, Ronald E.

1992-01-01

94

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

SciTech Connect

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

Wegner, P.C.

1986-02-11

95

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

96

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

97

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

98

Production of small doubly charged negative carbon cluster ions by sputtering  

Microsoft Academic Search

Carbon cluster ions with a double negative charge, and lifetimes of at least 10 mus, have been produced by sputtering graphite, and observed in a double-focusing mass spectrometer. Ions as small as C2-7 have been detected. The intensities of the doubly charged clusters (C2-n where n=7-28) follow an alternating pattern, with even-n clusters being more intense than neighboring odd-n clusters.

Stephen N. Schauer; Peter Williams; R. N. Compton

1990-01-01

99

Measurement of negative-ion and -cluster sputtering with highly-charged heavy ions  

Microsoft Academic Search

A single-detector technique for the measurement of negative ion time-of-flight spectra is introduced in this work. Spectra are presented for 390 keV Xe44+ ions at normal incidence on different samples. Mass distributions for Cn and SinOm clusters indicate that highly charged ions lead to a statistical off-surface formation of heavy clusters, whereas low-energy singly-charged ions may directly produce heavy carbon

G. Schiwietz; M. Briere; D. Schneider; J. McDonald; C. Cunningham

1995-01-01

100

Peptide-based cationic molecules for the production of positive charged liposomes and micelles.  

PubMed

This paper describes the synthesis and the physico-chemical characterization of cationic peptides (CPs) for possible application as non-viral gene delivery systems. Particularly, the production of cationic liposomes and micelle solutions was considered. Liposomes were prepared by REV-phase and extrusion presenting an average diameter reflecting the pore size of the membrane used for the extrusion. After DNA complexation the mean diameter of complexes decreased by increasing the number of positive charges. The non-complexed liposome preparations showed a net positive zeta potential comprised between 17.8-30 mV. After adding Defibrotide (DFT) to liposomes (at a 1:4 +/- molar ratio) the zeta potential fell down to a net negative value indicating the formation of the ionic complex. Concerning micelles, before complexation it was not possible to measure their size by PCS. However, after DFT complexation the size of complexes highly increased. In addition, as previously seen for liposomes, before complexation, the five CPs solutions showed a positive zeta potential ranging from 10-17.8 mV, while after addition of DFT the zeta potential fell to negative values. Concerning toxicity studies, in general CP-liposomes displayed a lower toxicity towards K562 cells as compared to the corresponding CP-solution. Taking into account these results, the studied CPs could be efficiently used to obtain both cationic liposomes and micelles. Moreover they are able to complex DNA with different interaction strength, depending on the type of peptide-based cationic molecule used. PMID:18246485

Cortesi, R; Marastoni, M; Tomatis, R; Menegatti, E; Esposito, E; Nastruzzi, C

2008-03-01

101

Effects of contact and efficient charge transport in G4-DNA molecules  

NASA Astrophysics Data System (ADS)

We report a theoretical study highlighting the fundamental effects of contact between molecule and electrodes and of the off-diagonal disorder on the transport properties of guanine-quadruplex DNA (G4-DNA) molecules. On the basis of the effective tight-binding model which simulates charge transport through G4-DNA, the transmission coefficient and localization length are numerically calculated by using the transfer-matrix method. In contrast to the physical intuition that a strong coupling at the molecule-metal interface will lead to a large conductance, we find that the averaged transmission coefficient is decreased by increasing the coupling when the coupling strength surpasses a critical value and the optimal configuration of contact for efficient charge transport through G4-DNA is obtained. In addition, the localization length of G4-DNA, especially at band centers, is much larger than that of poly(G)-poly(cytosine) molecules, suggesting that G4-DNA is potentially better as a conducting molecular wire than double-stranded DNA molecules. Several effectively delocalized states can be found in realistic G4-DNA molecules at low temperatures. These results may provide perspectives for experimental work aimed at controlling charge transport through DNA-based nanodevices.

Guo, Ai-Min; Xiong, Shi-Jie

2009-07-01

102

Role of C-terminal negative charges and tyrosine residues in fibril formation of ?-synuclein  

PubMed Central

?-Synuclein (140 amino acids), one of the causative proteins of Parkinson's disease, forms amyloid fibrils in brain neuronal cells. In order to further explore the contributions of the C-terminal region of ?-synuclein in fibril formation and also to understand the overall mechanism of fibril formation, we reduced the number of negatively charged residues in the C-terminal region using mutagenesis. Mutants with negative charges deleted displayed accelerated fibril formation compared with wild-type ?-synuclein, demonstrating that negative charges located in the C-terminal region of ?-synuclein modulate fibril formation. Additionally, when tyrosine residues located at position 125, 133, and 136 in the C-terminal region were changed to alanine residue(s), we found that all mutants containing the Tyr136Ala mutation showed delays in fibril formation compared with wild type. Mutation of Tyr136 to various amino acids revealed that aromatic residues located at this position act favorably toward fibril formation. In mutants where charge neutralization and tyrosine substitution were combined, we found that these two factors influence fibril formation in complex fashion. These findings highlight the importance of negative charges and aromatic side chains in the C-terminal region of ?-synuclein in fibril formation.

Izawa, Yasutaka; Tateno, Hironobu; Kameda, Hiroshi; Hirakawa, Kazuya; Hato, Keiko; Yagi, Hisashi; Hongo, Kunihiro; Mizobata, Tomohiro; Kawata, Yasushi

2012-01-01

103

Chemical equilibrium between excitons, electrons, and negatively charged excitons in semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

The principle of chemical equilibrium is found to govern formation of negatively charged excitons (X-) by excitons (X) and free electrons (e-). An optical spectroscopy study of undoped CdTe/Cd0.88Mn0.12Te double quantum wells (QW's) revealed formation of a negatively charged exciton state in the thicker QW due to the interwell tunneling of photoexcited electrons. A peculiar, nonmonotonic behavior of the ratio of X to X- densities as a function of the excitation density evidenced that the chemical law of action of masses corresponding to the reaction X+e-<==>X- is fulfilled.

Siviniant, J.; Scalbert, D.; Kavokin, A. V.; Coquillat, D.; Lascaray, J.-P.

1999-01-01

104

Synthesis and characterizations of new negatively charged organic–inorganic hybrid materials  

Microsoft Academic Search

A series of organic–inorganic hybrid membranes were prepared on microporous alumina substrates through dip-coating with the sol–gel solution of negatively charged polymer precursors PEO-[Si(OEt)3]2SO3H (preparation of which discussed in [C.M. Wu, T.W. Xu, W.H. Yang, Synthesis and characterizations of new negatively charged organic–inorganic hybrid materials: effect of molecular weight of sol–gel precursor, J. Solid State Chem. 177 (4–5) (2004) 1660–1666]).

Cuiming Wu; Tongwen Xu; Ming Gong; Weihua Yang

2005-01-01

105

Vacuum-UV negative photoion spectroscopy of gas-phase polyatomic molecules  

Microsoft Academic Search

This review describes recent experiments to detect anions following vacuum-UV photoexcitation of gas-phase polyatomic molecules. Using synchrotron radiation in the range 10–35?eV at a resolution down to 0.02?eV, negative ions formed are detected by mass spectrometry. The molecules studied in detail include CF4, SF6 and CH4; the CF3X series where X?=?Cl, Br, I; the CH3Y series where Y?=?F, Cl, Br

Matthew J. Simpson; Richard P. Tuckett

2011-01-01

106

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

107

Contrast of the biological activity of negatively and positively charged microwave synthesized CdSe/ZnS quantum dots.  

PubMed

Quantum dots (QDs) are semiconductor nanocrystals that have found use in bioimaging, cell tracking, and drug delivery. This article compares the cytotoxicity and cellular interactions of positively and negatively charged CdSe/CdS/ZnS QDs prepared by a microwave method using a murine alveolar macrophage-like cell culture model. Keeping the core semiconductor the same, QD charge was varied by altering the surface capping molecule; negatively charged QDs were formed with mercaptopropionic acid (MPA-QDs) and positively charged QDs with thiocholine (THIO-QDs). The size and charge of these two QDs were investigated in three types of media (RPMI, RPMI + FBS, and X-VIVO serum-free media) relevant for the biological studies. MPA-QDs were found to have negative zeta potential in RPMI, RPMI + FBS, and serum-free media and had sizes ranging from 8 to 54 nm. THIO-QDs suspended in RPMI alone were <62 nm in size, while large aggregates (greater than 1000 nm) formed when these QDs were suspended in RPMI + FBS and serum-free media. THIO-QDs retained positive zeta potential in RPMI and were found to have a negative zeta potential in RPMI + FBS and nearly neutral zeta potential in serum-free media. In a cell culture model, both MPA-QDs and THIO-QDs caused comparable levels of apoptosis and necrosis. Both QDs induced significant tumor necrosis factor-alpha (TNF-?) secretion only at high concentrations (>250 nM). Both types of QDs were internalized via clathrin-dependent endocytosis. Using real-time, live cell imaging, we found that MPA-QDs interact with the cell surface within minutes and progress through the endocytic pathway to the lysosomes upon internalization. With the THIO-QDs, the internalization process was slower, but the pathways could not be mapped because of spectroscopic interference caused by QD aggregates. Finally, MPA-QDs were found to associate with cell surface scavenger receptors, while the THIO-QDs did not. This study indicates that the surface charge and aggregation characteristics of QDs change drastically in biological culture conditions and, in turn, influence nanoparticle and cellular interactions. PMID:22092015

Nagy, Amber; Zane, Andrew; Cole, Sara L; Severance, Michael; Dutta, Prabir K; Waldman, W James

2011-11-30

108

Copper-mediated growth of amyloid ? fibrils in the presence of oxidized and negatively charged liposomes  

Microsoft Academic Search

Amyloid ? protein (A?) from Alzheimer's disease formed fibrillar aggregates and their morphology depended on oxidized and negatively charged liposomes. The morphology of fibrillar aggregates was affected by Cu2+, together with their growth kinetics. This is because Cu2+ inhibited the nucleation step in the formation of amyloid A? fibrillar aggregates by forming A?\\/Cu complex inactive to the growth of fibrillar

Toshinori Shimanouchi; Ryo Onishi; Nachi Kitaura; Hiroshi Umakoshi; Ryoichi Kuboi

109

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

PubMed

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

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

2013-01-31

110

Negative Evidences for Charge/Spin Density Wave in ZrTe5  

NASA Astrophysics Data System (ADS)

Experimental searches were made for evidences for the charge- or spin-density wave state in the trigonal-prismatic pseudo-linear chain compound ZrTe5. Negative evidences for such phase transitions were provided by the absence of lattice modulation, ohmic resistivity at high electric fields, and by temperature and angular dependences of electrical resistivity and magnetic susceptibility.

Okada, Shigeto; Sambongi, Takashi; Ido, Masayuki; Tazuke, Yûichi; Aoki, Ryozo; Fujita, Osamu

1982-02-01

111

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

NSDL National Science Digital Library

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

Henderson, Tom

2006-03-15

112

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

NASA Astrophysics Data System (ADS)

In this paper, the air purification effect of positively and negatively charged ions generated by discharge plasma at atmospheric pressure is reported. We have developed a novel ion generation device which consists of a cylindrical glass tube and attached inner and outer mesh electrodes. With the application of AC voltage between the electrodes, positively charged ions and negatively charged ions have been generated at atmospheric pressure. The ion densities of 3.0× 104--7.0× 104 counts/cm3 have been obtained with the AC voltage of 1.8-2.3 kV (effective value). We have examined the air purification properties of this device. By the operation of this device, the initial oxygen nitride (NO) density of 10 ppm in 1 m3 (in cigarette smoke) was decreased to 1 ppm after 30 min. The number of suspended germs in air has been significantly reduced by the use of this type of ion generation device.

Nishikawa, Kazuo; Nojima, Hideo

2001-08-01

113

Thermal equilibrium governing the formation of negatively charged excitons in resonant tunneling diodes  

NASA Astrophysics Data System (ADS)

The thermal equilibrium of the formation of negatively charged excitons is studied in this work, by measuring the current and quantum-well photoluminescence in biased resonant tunneling double barrier diodes. We observe that the intensity ratio of negatively charged and neutral excitons depends linearly on the current for fixed temperature and illumination conditions. We propose that the results can be interpreted in terms of a mass-action law governing the concentrations of neutral and charged excitons and free electrons. Measurements at different temperatures and bias yield an electron concentration and a dwell time in the well that are in good agreement with the values previously reported in the literature. We also analyze the dependence of the luminescence on excitation intensity.

Vercik, A.; Gobato, Y. Galvao; Brasil, M. J. S. P.

2002-08-01

114

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

NASA Astrophysics Data System (ADS)

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

Atlas, Susan; Valone, Steven

2008-03-01

115

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

2010-11-08

116

The controlled introduction of multiple negative charge at single amino acid sites in subtilisin Bacillus lentus.  

PubMed

The use of methanethiosulfonates as thiol-specific modifying reagents in the strategy of combined site-directed mutagenesis and chemical modification allows virtually unlimited opportunities for creating new protein surface environments. As a consequence of our interest in electrostatic manipulation as a means of tailoring enzyme activity and specificity, we have adopted this approach for the controlled incorporation of multiple negative charges at single sites in the representative serine protease, subtilisin Bacillus lentus (SBL). A series of mono-, di- and triacidic acid methanethiosulfonates were synthesized and used to modify cysteine mutants of SBL at positions 62 in the S2 site, 156 and 166 in the S1 site and 217 in the S1' site. Kinetic parameters for these chemically modified mutant (CMM) enzymes were determined at pH 8.6 under conditions which ensured complete ionization of the unnatural amino acid side-chains introduced. The presence of up to three negative charges in the S1, S1' and S2 subsites of SBL resulted in up to 11-fold lowered activity, possibly due to interference with oxyanion stabilization of the transition state of the hydrolytic reactions catalyzed. Each unit increase in negative charge resulted in a raising of K(M) and a reduction of k(cat). However, no upper limit was observed for increases in K(M), whereas decreases in k(cat) reached a limiting value. Comparison with sterically similar but uncharged CMMs revealed that electrostatic effects of negative charges at positions 62, 156 and 217 are detrimental, but are beneficial at position 166. These results indicate that the ground-state binding of SBL to the standard substrate, Suc-AAPF-pNA, to SBL is reduced, but without drastic attenuation of catalytic efficiency, and show that SBL tolerates high levels of charge at single sites. PMID:10632039

Davis, B G; Shang, X; DeSantis, G; Bott, R R; Jones, J B

1999-11-01

117

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

118

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.

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

2010-01-01

119

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation.  

PubMed

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity. PMID:16851544

Eckenrode, Heather M; Jen, Shih-Hui; Han, Jun; Yeh, An-Gong; Dai, Hai-Lung

2005-03-17

120

Charge transfer in metal-atom-containing molecules in the gas phase  

NASA Astrophysics Data System (ADS)

The presence of charge transfer (CT) is ubiquitous in metal-atom-containing molecules in the gas phase. The states of interest range from ground states to the lower excited states, given the generally low ionisation potentials of metal atoms. This review is written from an experimentalist's perspective, to describe the specifics of CT states in stable molecules containing a metal atom or of transient CT states in dynamical processes. The large body of experimental evidence allows the description of such states in an empirical or semi-empirical manner, including partial point charges and polarised electron clouds on the ions. These simple models are compared with more quantitative models, allowing the development of sophisticated descriptions. The simple perspective deriving from experimental evidence is justified, when it is possible via accurate quantum calculations and allows building a rather complete framework for the ionic bond or CT-induced dynamics.

Shafizadeh, Niloufar; Soep, Benoit; Mestdagh, Jean Michel; Breckenridge, W. H.

121

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

PubMed

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

2012-07-31

122

Fragmentation of H2O molecules following the interaction with slow, highly charged Ne ions  

Microsoft Academic Search

We measured the energy and angular distribution of fragment ions from collisions of 2-90 keV Neq+ ions (q = 1, 3, 5, 7 and 9) with H2O molecules. A strong dependence on the charge state of the incident ion was observed. The results are interpreted within the framework of a Coulomb explosion model. Deviations from this model in the energy

Z. D. Pesic; J.-Y. Chesnel; R. Hellhammer; B. Sulik; N. Stolterfoht

2004-01-01

123

The Importance of the Metal-Molecule Interface for Charge Transport: A Theoretical and Experimental Study  

NASA Astrophysics Data System (ADS)

This contribution discusses the influence of the metal binding group on the charge transport and optical properties of percolated networks of nanoparticles interlinked with bis-dithiocarbamate or dithiol derivatives. DFT calculations show that the bis-dithiocarbamate derivatives form valence states that are delocalized on the metal and the molecule. This is a characteristic, which is classically not known from the thiol-gold interface. Conclusive experimental and theoretical evidence for the excellent electronic behavior of dithiocarbamate groups is provided.

von Wrochem, Florian; Nothofer, Heinz-G.; Ford, William E.; Scholz, Frank; Yasuda, Akio; Wessels, Jurina M.

2005-09-01

124

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

125

Charge dependence of one and two electron processes in collisions between hydrogen molecules and fast projectiles  

SciTech Connect

The ratio of double- to single-ionization (DI/SI) as well as the ratio of ionization-excitation to single-ionization (IE/SI) in hydrogen molecules was studied by examining the effect of the projectile charge on these processes. The DI/SI and IE/SI ratios were measured using the coincidence time of flight technique at a fixed velocity (1 MeV/amu) over a range of projectile charge states (q = 1-9,14,20). Preliminary results indicate that for a highly charged F{sup 9+} projectile the DI/SI and IE/SI ratios are 6.8% and 24.7%, respectively, a large increase from the ratios of 0.13% and 1.95%, respectively, for H{sup +} projectiles. For low charge states, the DI/SI is negligible relative to the IE/SI ratio, while for more highly charged projectiles the DI/SI ratio becomes comparable to the IE/SI ratio. This indicates that double-ionization increases much more rapidly with projectile charge than ionization-excitation.

Wells, E.; Ben-Itzhak, I.; Carnes, K.D.; Krishnamurthi, V.

1996-05-01

126

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

PubMed

A microscopic formalism based on computing many-particle densities is applied to the analysis of the diffusion-controlled kinetics of pattern formation in oppositely charged molecules on surfaces or adsorbed at interfaces with competing long-range Coulomb and short-range Lennard-Jones interactions. Particular attention is paid to the proper molecular treatment of energetic interactions driving pattern formation in inhomogeneous systems. The reverse Monte Carlo method is used to visualize the spatial molecular distribution based on the calculated radial distribution functions (joint correlation functions). We show the formation of charge domains for certain combinations of temperature and dynamical interaction parameters. The charge segregation evolves into quasicrystalline clusters of charges, due to the competing long- and short-range interactions. The clusters initially co-exist with a gas phase of charges that eventually add to the clusters, generating "fingers" or line of charges of the same sign, very different than the nanopatterns expected by molecular dynamics in systems with competing interactions in two dimensions, such as strain or dipolar versus van der Waals interactions. PMID:20866821

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

2010-08-09

127

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

SciTech Connect

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

Pivovarov, Alexander L.; Guryanov, Georgiy M. [Corning Incorporated, SP-FR-01-01, Corning, New York 14831 (United States)

2012-07-15

128

Why positive hole carriers and negatively charged planes are conducive to high temperature superconductivity  

NASA Astrophysics Data System (ADS)

The vast majority of superconducting materials have positive Hall coefficient in the normal state, indicating that hole carriers dominate the normal state transport. This was noticed even before BCS theory, and has been amply confirmed by materials found since then: the sign of the Hall coefficient is the strongest normal state predictor of superconductivity. In the superconducting state instead, superfluid carriers are always electron-like, i.e. negative, as indicated by the fact that the magnetic field generated by rotating superconductors is always parallel, never antiparallel, to the body's angular momentum ("London moment"). BCS theory ignores these facts. In contrast, the theory of hole superconductivity, developed over the past 20 years (papers listed in http://physics.ucsd.edu/˜jorge/hole.html) makes charge asymmetry the centerpiece of the action. The Coulomb repulsion between holes is shown to be smaller than that between electrons, thus favoring pairing of holes, and this fundamental electron-hole asymmetry is largest in materials where the conducting structures have excess negative charge, as is the case in the cuprates, arsenides and MgB2. Charge asymmetry implies that superconductivity is driven by lowering of kinetic energy, associated with expansion of the carrier wavefunction and with expulsion of negative charge from the interior to the surface of the material, where it carries the Meissner current. This results in a macroscopic electric field (pointing outward) in the interior of superconductors, and a macroscopic spin current flowing near the surface in the absence of external fields, a kind of macroscopic zero point motion of the superfluid (spin Meissner effect). London's electrodynamic equations are modified in a natural way to describe this physics. It is pointed out that a dynamical explanation of the Meissner effect requires radial outflow of charge in the transition to superconductivity, as predicted by this theory and not predicted by BCS. The theory provides clear guidelines regarding where new higher Tc superconductors will and will not be found.

Hirsch, J. E.

2011-03-01

129

Radiative behavior of negatively charged excitons in CdTe-based quantum wells: A spectral and temporal analysis  

Microsoft Academic Search

Using reflectivity and picosecond time-resolved photoluminescence, we have studied the intrinsic optical properties of negatively charged excitons in modulation doped CdTe quantum wells. In emission, we observe simultaneously a low energy exponential tail in the charged exciton spectral line and a linear increase of its radiative lifetime with temperature. In absorption, we find a consistent decrease of the charged exciton

V. Ciulin; P. Kossacki; S. Haacke; J.-D. Ganière; B. Deveaud; A. Esser; M. Kutrowski; T. Wojtowicz

2000-01-01

130

Determining charge transport pathways through single porphyrin molecules using scanning tunneling microscopy break junctions.  

PubMed

Charge transport in a porphyrin with four identical pyridyl substituents, 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP), was investigated using the scanning tunneling microscopy break junction method. To determine the dominant pathway, we studied two structurally similar porphyrins, o-DPyP and p-DPyP. Our experiments reveal that charge transport through TPyP in a break junction configuration does not follow the traditional assumption, i.e., the shortest path between the neighboring side groups. Instead, the charge transport pathway was dominated by the farthest anchoring groups. Furthermore, these single molecule experiments can distinguish between the two structural isomers, which is important in molecular discrimination, porphyrin chemistry, and molecular electronics. PMID:22133080

Li, Zhihai; Borguet, Eric

2011-12-07

131

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

132

Interaction of poly( l -lysines) with negatively charged membranes: an FT-IR and DSC study  

Microsoft Academic Search

The influence of the binding of poly(l-lysine) (PLL) to negatively charged membranes containing phosphatidylglycerols (PG) was studied by DSC and FT-IR spectroscopy.\\u000a We found a general increase in the main transition temperature as well as increase in hydrophobic order of the membrane upon\\u000a PLL binding. Furthermore we observed stronger binding of hydration water to the lipid head groups after PLL

Christian Schwieger; Alfred Blume

2007-01-01

133

Influence of bismuth on the charging ability of negative plates in lead–acid batteries  

Microsoft Academic Search

To examine the influence of bismuth on the charging ability of negative plates in lead–acid batteries, plates are made from three types of oxides: (i) leady oxide of high quality which contains virtually no bismuth (termed ‘control oxide’); (ii) control oxide in which bismuth oxide is blended at bismuth levels from 0.01 to 0.12wt.%; (iii) leady oxide produced from Pasminco

L. T Lam; H Ceylan; N. P Haigh; J. E Manders

2002-01-01

134

Effect of free electrons on nanoparticle charging in a negative direct current corona charger  

Microsoft Academic Search

A two-dimensional numerical model is proposed in this letter to take into account the effects of free electrons on nanoparticle charging in a negative direct current wire-tube corona charger. Numerical results are in excellent agreement with the experimental data by using a capturing probability of electrons onto nanoparticles with a value of 0.013. These free electrons contribute greatly to the

A. Aliat; C.-J. Tsai; C.-T. Hung; J.-S. Wu

2008-01-01

135

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

136

A new inorganic–organic negatively charged membrane: membrane preparation and characterizations  

Microsoft Academic Search

A new series of negatively charged inorganic–organic hybrid membranes were prepared by the sol–gel and oxidation processes of 3-(mercaptopropyl) trimethoxysilane (MPTS). The membranes were conducted IEC, streaming potential, and pure water flux measurements as well as SEM observation, FTIR and TGA analysis. It is shown that IECs of the membranes increase with an increase of the coating times within a

Cuiming Wu; Tongwen Xu; Weihua Yang

2003-01-01

137

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

Microsoft Academic Search

An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X^- particle has a lifetime tau_X ≳ 10^3 s, it

Masayasu Kamimura; Yasushi Kino; Emiko Hiyama

2009-01-01

138

Charge regulation via a negative feedback: transition metal atoms in semiconductors and insulators  

NASA Astrophysics Data System (ADS)

Transition metal (TM) atoms in semiconductors and insulators produce energy levels in the band gap, whose occupation can be altered by shifting the Fermi level e.g. via doping. Changes in level occupation correspond to changes in the formal oxidation state. Such changes are associated with inward/outward lattice relaxations recorded as ``ionic radii'', different magnetic moments, and a core shift in x-ray photoemission. We show, via density-functional calculations within the plane-wave supercell method for TM atoms including Cr, Mn, Fe, and Co in the semiconductor hosts GaAs and Cu2O, as well as in the ionic insulator host MgO, that changes in gap-level occupation result in only very small changes of charge on the TM atom itself. We show that this is due to an inherent negative feedback that regulates the TM charge via a TM--ligand rehybridization. Further, the inward/outward lattice relaxations and XPS core shifts, often associated with a change of the TM charge, in fact follow from the TM-ligand rehybridization, as the TM charge is kept unchanged via the inherent negative feedback.

Raebiger, Hannes; Lany, Stephan; Zunger, Alex

2008-03-01

139

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

140

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

PubMed

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 600ng 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 CD138(neg)) cells. The high-sensitivity microarray approach led to the identification of a set of 20 genes differentially expressed in MM CD138(neg) 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

2013-02-14

141

Charge dependence of one and two electron processes in collisions between hydrogen molecules and fast projectiles  

SciTech Connect

The ratio of double to single ionization (DI/SI) as well as the ratio of ionization-excitation to single ionization (IE/SI) in hydrogen molecules was studied by examining the effect of the projectile charge on these processes. The DI/SI and IE/SI ratios were measured using the coincidence time of flight technique at a fixed velocity (corresponding to 1 MeV/amu) over a range of projectile charge states (q=1-9,14,20). The results for a highly charged Cu{sup 20+} projectile, for example, indicate that the DI/SI and IE/SI ratios are 11{percent} and 45{percent}, respectively, a large increase from the ratios of 0.13{percent} and 1.95{percent}, respectively, for H{sup +} projectiles. The DI/SI ratio increases much more rapidly with projectile charge than the IE/SI ratio. In addition, the results show that the rate of increase of both these ratios decreases for highly charged projectiles. {copyright} {ital 1997 American Institute of Physics.}

Wells, E.; Ben-Itzhak, I.; Carnes, K.D. [James R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States); Krishnamurthi, V. [James R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States)]|[Etec Systems Inc., 26460 Corporate Ave., Hayward, California 94545 (United States)

1997-02-01

142

Charge dynamics and phonon induced oscillatory relaxation rates of indirect excitons in quantum dot molecules  

NASA Astrophysics Data System (ADS)

Optoelectronic control of quantum dots is a thriving area of research with impact on fundamental physics and quantum information devices. Time-resolved photoluminescence experiments, carried out in charge tunable coupled quantum dots, have demonstrated non-monotonic behavior of neutral indirect exciton lifetimes over a wide range of applied electric fields [1]. We present a model for neutral indirect exciton lifetimes in electric field tunable quantum dot molecules. Our model includes field-dependent oscillatory phonon-induced relaxation rates [2], carrier tunneling rates, and carrier relaxation into nearby charged exciton states. To this end we have used a multi-excitonic Hamiltonian, and calculated the exciton population dynamics using a master equation with electric field dependent rates. We find that lifetime suppression is dominated by scattering with LA phonons at low fields, and that the maximum lifetime gives information on the effective dimensions of the molecule. In contrast, at high fields the lifetime suppression is dominated by the interplay of carrier population exchange with nearby charged excitons. This prompts for ways of controlling exciton lifetimes and possible decoherence in quantum dots. [1] K. C. Wijesundara et al., (unpublished), [2] J. I. Climente et al., Phys. Rev. B 74, 035313 (2006).

Rolon, J. E.; Wijesundara, K. C.; Stinaff, E. A.; Ulloa, S. E.

2011-03-01

143

'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

144

One- and two-electron processes in collisions between hydrogen molecules and slow highly charged ions  

NASA Astrophysics Data System (ADS)

A coincidence time-of-flight technique coupled with projectile charge state analysis was used to study electron capture in collisions between slow highly charged ions and hydrogen molecules. We found single electron capture with no target excitation to be the dominant process for both C6+ projectiles at a velocity of 0.8 atomic units and Ar11+ projectiles at v = 0.63 a.u. Double electron capture and transfer excitation, however, were found to be comparable and occur about 30% of the time relative to single capture. Most projectiles (96%) auto-ionize quickly following double capture into doubly excited states. The data are compared to classical and quantum mechanical model calculations.

Wells, E.; Carnes, K. D.; Tawara, H.; Ali, R.; Sidky, Emil Y.; Illescas, Clara; Ben-Itzhak, I.

2005-12-01

145

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

NASA Astrophysics Data System (ADS)

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

Rojas, Geoffrey; Ganesh, P.; Kelly, Simon; Sumpter, Bobby; Schlueter, John; Maksymovych, Petro

2013-03-01

146

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

PubMed

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

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

2013-06-11

147

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

PubMed

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

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

2012-06-07

148

Effects of negatively charged aerosol on blood and cerebrospinal fluid parameters in rats  

NASA Astrophysics Data System (ADS)

Adult male rats were exposed for 90 to 140 minutes to negatively charged tapwater aerosol. Blood and cerebrospinal fluid samples were collected to determine effects of the exposure on selected hematologic and serum chemistry parameters, and ionized calcium and pH in cerebrospinal fluid. Of the 27 variables assayed, 24 yielded sufficient data for statistical analysis. Two parameters, serum alkaline phosphatase and mean corpuscular hemoglobin concentration, were significantly different (p<0.05) from control values, probably representing chance occurrences. It appears that whatever biological effects may be exerted by electro-aerosols, they are not mediated by the parameters investigated in this study.

Wehner, A. P.; Ragan, H. A.; Jaffe, R. A.; Weigel, R. J.; Lundstrom, D. L.

1983-09-01

149

Interaction of melittin with negatively charged phospholipids: consequences for lipid organization.  

PubMed

A characterization of the structural alterations induced by melittin in model-membranes of dioleoylphosphatidic acid and egg phosphatidylglycerol is presented, based on the use of 31P-NMR, freeze-fracture electron microscopy and small angle X-ray scattering. In accordance with earlier findings on the cardiolipin-melittin system, melittin is found to have an inverted phase inducing effect on these negatively charged lipids, in contrast to the influence on zwitterionic phospholipids. In phosphatidic acid this is expressed in the formation of an HII phase; in phosphatidylglycerol a less ordered, non-lamellar structure with low water content is adopted. PMID:3666135

Batenburg, A M; van Esch, J H; Leunissen-Bijvelt, J; Verkleij, A J; de Kruijff, B

1987-10-19

150

[Increase of the negative charge of erythrocyte membrane proteins in hereditary neuromuscular diseases].  

PubMed

The parameters of erythrocyte ghost protein's fluorophores by nitrate's anions were studied in patients with various hereditary myodystrophy. In all the groups under examination the share of fluorophores accessible to a quencher was close to 1. In erythrocyte membranes of healthy donors the relevant constant quenchering was about 17.3 +/- 1.9 M-1 while those of patients were decreased by 3.1 (Duchenne's myodystrophy) and by about 2.0 (other forms of primary and secondary progressive muscular dystrophies). The most probable reason for the decreasing constant of quenchering is the increase of negative charges on the erythrocyte membrane proteins. PMID:2279101

Khrennikov, V Iu; Deev, A I; Sitnikov, V F; Tagiev, A F

1990-10-01

151

Negative capacitance in organic semiconductor devices: Bipolar injection and charge recombination mechanism  

NASA Astrophysics Data System (ADS)

The authors report negative capacitance at low frequencies in organic semiconductor based diodes and show that it appears only under bipolar injection conditions. They account quantitatively for this phenomenon by the recombination current due to electron-hole annihilation. Simple addition of the recombination current to the well established model of space charge limited current in the presence of traps yields excellent fits to the experimentally measured admittance data. The dependence of the extracted characteristic recombination time on the bias voltage is indicative of a recombination process which is mediated by localized traps.

Ehrenfreund, E.; Lungenschmied, C.; Dennler, G.; Neugebauer, H.; Sariciftci, N. S.

2007-07-01

152

Small-molecule negative modulators of adrenomedullin: design, synthesis, and 3D-QSAR study.  

PubMed

Adrenomedullin (AM) is a peptidic hormone that was isolated in 1993, the function of which is related to several diseases such as diabetes, hypertension, and cancer. Compound 1 is one of the first nonpeptidic small-molecule negative modulators of AM, identified in a high-throughput screen carried out at the National Cancer Institute. Herein we report the synthesis of a series of analogues of 1. The ability of the synthesized compounds to disrupt the binding between AM and its monoclonal antibody has been measured, together with surface plasmon resonance (SPR)-based binding assays as implemented with Biacore technology. These data were used to derive a three-dimensional quantitative structure-activity relationship (3D-QSAR) model, with a q(2) (LOO) value of 0.8240. This study has allowed us to identify relevant features for effective binding to AM: the presence of a hydrogen-bond donor group and an aromatic ring. Evaluation of the ability of selected compounds to modify cAMP production in Rat2 cells showed that the presence of a free carboxylic acid is essential for negative AM modulation. PMID:18759242

Roldós, Virginia; Martín-Santamaría, Sonsoles; Julián, Miguel; Martínez, Alfredo; Choulier, Laurence; Altschuh, Danièle; de Pascual-Teresa, Beatriz; Ramos, Ana

2008-09-01

153

Negative Oxide Charge in Thermally Oxidized Cr-Contaminated n-Type Silicon Wafers  

NASA Astrophysics Data System (ADS)

The evaluation of thermally oxidized Cr-contaminated Si surfaces, by an AC surface photovoltage (SPV) method, indicates that a certain amount of contaminating Cr atoms resides in the SiO2 thin film, resulting in the creation of a negative oxide charge in the form of a (CrOSi)- and/or CrO2- networks, which are postulated to be analogous to the (AlOSi)- network. For samples oxidized at temperatures between 550 and 700 °C for 10 min, the AC SPV gives evidence that the induced negative oxide charge causes a strongly inverted state of the Si surface. At oxidation temperatures higher than 700 °C and/or a longer oxidation time than 10 min, AC SPV is reduced, meaning that the strongly inverted state changes into a less depleted state, and finally, the AC SPV disappears. In this case, a collapse of the (CrOSi)- and/or CrO2- networks is expected with a possible change into Cr2O3.

Hirofumi Shimizu,; Sadayoshi Shimada,; Masanori Ikeda,

2010-03-01

154

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.

Yamasaki, Y; Teramoto, Y; Yoshikawa, K

2001-01-01

155

Thermodynamic Evidence for Negative Charge Stabilization by a Catalytic Metal Ion within an RNA Active Site  

PubMed Central

Protein and RNA enzymes that catalyze phosphoryl transfer reactions frequently contain active site metal ions that interact with the nucleophile and leaving group. Mechanistic models generally hinge upon the assumption that the metal ions stabilize negative charge buildup along the reaction coordinate. However, experimental data that test this assumption directly remain difficult to acquire. We have used an RNA substrate bearing a 3’-thiol group to investigate the energetics of a metal ion interaction directly relevant to transition state stabilization in the Tetrahymena group I ribozyme reaction. Our results show that this interaction lowers the pKa of the 3’-thiol by 2.6 units, stabilizing the bound 3’-thiolate by 3.6 kcal/mol. These data, combined with prior studies, provide strong evidence that this metal ion interaction facilitates the forward reaction by stabilization of negative charge build-up on the leaving group 3’-oxygen and facilitates the reverse reaction by deprotonation and activation of the nucleophilic 3’-hydroxyl group.

Sengupta, Raghuvir N.

2012-01-01

156

Saccharification of natural lignocellulose biomass and polysaccharides by highly negatively charged heteropolyacids in concentrated aqueous solution.  

PubMed

Highly negatively charged heteropolyacids (HPAs), in particular H(5) BW(12) O(40) , efficiently promoted saccharification of crystalline cellulose into water-soluble saccharides in concentrated aqueous solutions (e.g., 82?% total yield and 77?% glucose yield, based on cellulose with a 0.7?M H(5) BW(12) O(40) solution); the performance was much better than those of previously reported systems with commonly utilized mineral acids (e.g., H(2) SO(4) and HCl) and HPAs (e.g., H(3) PW(12) O(40) and H(4) SiW(12) O(40)). Besides crystalline cellulose, the present system was applicable to the selective transformation of cellobiose, starch, and xylan to the corresponding monosaccharides such as glucose and xylose. In addition, one-pot synthesis of levulinic acid and sorbitol directly from cellulose was realized by using concentrated HPA solutions. The present system, concentrated aqueous solutions of highly negatively charged HPAs, was further applicable to saccharification of natural (non-purified) lignocellulose biomass, such as "rice plant straw", "oil palm empty fruit bunch (palm EFB) fiber", and "Japanese cedar sawdust", giving a mixture of the corresponding water-soluble saccharides, such as glucose (main product), galactose, mannose, xylose, arabinose, and cellobiose, in high yields (?77?% total yields of saccharides based on holocellulose). Separation of the saccharides and H(5) BW(12) O(40) was easy, and the retrieved H(5) BW(12) O(40) could repeatedly be used without appreciable loss of the high performance. PMID:21404445

Ogasawara, Yoshiyuki; Itagaki, Shintaro; Yamaguchi, Kazuya; Mizuno, Noritaka

2011-03-14

157

Protein aggregation during overexpression limited by peptide extensions with large net negative charge.  

PubMed

Folding of the human coxsackie and adenovirus receptor immunoglobulin (Ig) variable-type domain (CAR D1) during overexpression in the Escherichia coli cytoplasm was shown previously to be partially rescued by fusion to a 22-residue C-terminal peptide. Here, peptide sequence features required for solubilization and folding of CAR D1 and similar Ig variable-type domains from two other human membrane proteins were investigated. Peptide extensions with net negative charge > -6 fully solubilized CAR D1, and approximately half of the peptide-solubilized protein was correctly folded. The Ig variable-type domains from human A33 antigen and myelin P-zero proteins were only partially solubilized by peptide extensions with net charge of -12, however, and only the solubilized P-zero domain appeared to fold correctly whereas the A33 domain formed soluble microaggregates of misfolded protein. Our results suggest a model where the large net charge of peptide extensions increases electrostatic repulsion between nascent polypeptides. The resulting decrease in aggregation rate can enable some polypeptides to fold spontaneously into their native protein conformations. Analysis of the solubility and folding status of sets of structurally homologous proteins, such as the Ig variable-type domains described here, during overexpression could provide insights into how amino acid and gene sequences influence the efficiency of spontaneous protein folding. PMID:15249042

Zhang, Yian-Biao; Howitt, Jason; McCorkle, Sean; Lawrence, Paul; Springer, Karen; Freimuth, Paul

2004-08-01

158

Formation of destabilised carbenium ions by charge inversion of negative ions  

NASA Astrophysics Data System (ADS)

The [alpha]-carbomethoxy carbenium ions CH3OC(=O)C+R1R2 where R1 = R2 = H (1+, R1 = H, R2 = CH3 (2+), R1 = R2 = CH3 (3+) and R1 = H, R2 = C6H5 (4+) have been prepared by collisional charge inversion and by neutralisation-reionisation of the appropriate enolate ions. In addition, the [alpha]-benzoyl carbenium ions C6H5C(=O)C+R1R2 where R1 = R2 = H (5+), R1 = H, R2 = CH3 (6+) and R1 = R2 = CH3 (7+) have been prepared by the same methods. In all cases the charge inversion and neutralisation-reionisation mass spectra are very similar. For the [alpha]-carbomethoxy carbenium ions the major fragmentation reaction involves elimination of CH3O&[radical sign] to form the appropriate ketene molecular ion. The spectra are quite different from those obtained by collision-induced dissociation of [alpha]-carbomethoxy carbenium ions prepared by electron ionisation. The ions formed by charge inversion fragments to a much lesser extent by rearrangement, presumably because they have a higher mean internal energy. For the [alpha]-benzoyl carbenium ions formation of the ketene molecular ion is negligible, a major reaction channel being elimination fo CR1R2 to form the benzoyl ion. A recovered positive ion signal at the same m/z value as the enolate precursor is observed only for 3+ and 4+, indicating that only the most stable of the destabilised carbenium ions will be observed as intact species when formed by charge inversion of negative ions.

Tkaczyk, Martin; Harrison, Alex G.

1991-11-01

159

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

2010-10-22

160

Exploring the bond topological properties and the charge depletion-impact sensitivity relationship of high energetic TNT molecule via theoretical charge density analysis  

Microsoft Academic Search

To understand the energetic properties of 2,3,4-Trinitrotolune (TNT) molecule, a quantum chemical calculation and the electronic charge density analysis have been performed. The density functional theory (B3P86\\/6-311G??) calculation was carried out using Gaussian03 software. The energy-minimized wave function obtained from DFT was used for the charge density analysis. The inductive and steric effects of methyl and nitro substituents are not

Arputharaj David Stephen; Rajesh B. Pawar; Poomani Kumaradhas

2010-01-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

162

Hyperfine interaction in the ground state of the negatively charged nitrogen vacancy center in diamond  

NASA Astrophysics Data System (ADS)

The N14 , N15 , and C13 hyperfine interactions in the ground state of the negatively charged nitrogen vacancy (NV-) center have been investigated using electron-paramagnetic-resonance spectroscopy. The previously published parameters for the N14 hyperfine interaction do not produce a satisfactory fit to the experimental NV- electron-paramagnetic-resonance data. The small anisotropic component of the NV- hyperfine interaction can be explained from dipolar interaction between the nitrogen nucleus and the unpaired-electron probability density localized on the three carbon atoms neighboring the vacancy. Optical spin polarization of the NV- ground state was used to enhance the electron-paramagnetic-resonance sensitivity enabling detailed study of the hyperfine interaction with C13 neighbors. The data confirmed the identification of three equivalent carbon nearest neighbors but indicated the next largest C13 interaction is with six, rather than as previously assumed three, equivalent neighboring carbon atoms.

Felton, S.; Edmonds, A. M.; Newton, M. E.; Martineau, P. M.; Fisher, D.; Twitchen, D. J.; Baker, J. M.

2009-02-01

163

Theoretical investigation on the stability of negatively charged formic acid clusters.  

PubMed

Recent experimental results on negatively charged formic acid clusters generated by the impact of (252)Cf fission fragments on icy formic acid target are compared to quantum mechanical calculations. Structures for the clusters series, (HCOOH)nOH(-), where 2 < or = n < or = 4, are proposed based on ab initio electronic structure methods. The results show that cluster growth does not have a regular pattern of nucleation. A stability analysis was performed considering the commonly defined stability function. Temporal behavior of the clusters was evaluated by Born-Oppenheimer molecular dynamics to check the mechanism that provides cluster stability. The evaluated temporal profiles indicate the importance of hydrogen atom migration between the formic acid moieties in maintaining the stability of the structures and the water formation due to hydrogen abstraction by the hydroxyl approach. PMID:20540546

Baptista, Leonardo; Andrade, Diana P P; Rocha, Alexandre B; Rocco, Maria Luiza M; Boechat-Roberty, Heloisa Maria; da Silveira, Enio Frota

2010-07-01

164

Negatively Charged Nitrogen-Vacancy Centers in a 5 nm Thin (12)C Diamond Film.  

PubMed

We report successful introduction of negatively charged nitrogen-vacancy (NV(-)) centers in a 5 nm thin, isotopically enriched ([(12)C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NV(-) in such a thin layer even when the surface is terminated by hydrogen atoms. NV(-) centers are found to have spin coherence times of between T2 ? 10-100 ?s at room temperature. Changing the surface termination to oxygen or fluorine leads to a slight increase in the NV(-) density, but not to any significant change in T2. The minimum detectable magnetic field estimated by this T2 is 3 nT after 100 s of averaging, which would be sufficient for the detection of nuclear magnetic fields exerted by a single proton. We demonstrate the suitability for nanoscale NMR by measuring the fluctuating field from ?10(4) proton nuclei placed on top of the 5 nm diamond film. PMID:24020334

Ohashi, K; Rosskopf, T; Watanabe, H; Loretz, M; Tao, Y; Hauert, R; Tomizawa, S; Ishikawa, T; Ishi-Hayase, J; Shikata, S; Degen, C L; Itoh, K M

2013-09-20

165

Long-range attraction of negatively charged dust particles in weakly ionized dense dust clouds  

NASA Astrophysics Data System (ADS)

The new Plasma Kristall Experiment (PK-4) is scheduled to fly on the International Space Station in 2012 with one of the experiments designed to investigate the existence of two fluid phases and a critical point in complex plasmas. A crucial issue is the parameter regime where the critical point could be found and this requires, as a first step, knowledge of the parameter range where dust-dust attraction can exist. This problem is addressed in the present work, extending previous works on long-range screening and attraction of negatively charged dust particles in plasmas. The roles of nonlinearities, ion-neutral collisions, electron dynamics, and plasma source on the depth and long-range behavior of the attractive well are established and the impact of these results on the PK-4 experiments is discussed.

de Angelis, U.; Regnoli, G.; Ratynskaia, S.

2010-04-01

166

Photo-induced charge-transfer processes in fullerene-containing dyad and triad molecules  

NASA Astrophysics Data System (ADS)

We report on pulsed electron-spin-resonance (ESR) investigations of novel model systems for photo-induced electron-transfer processes. The schematic structures of the molecules are T5-C60 and A-T5-C60, i.e., the fullerene C60 is used as the acceptor, and quinquethiophene (T5) or anthracene (A) act as a donor. In frozen solutions of both the dyad and triad, we find rather long-lived radical signals (lifetime ~2 ?s) after laser-pulse excitation. The observed signals can be assigned by the g factor and the linewidth to the anion C60- and the cation T5+. We have examined the influence of the solvent polarity (toluene or benzonitrile) and of the excitation wavelength (355 nm or 532 nm) on the efficiency of the charge transfer.

Knorr, S.; Grupp, A.; Mehring, M.; Grube, G.; Effenberger, F.

1999-09-01

167

Recent Theoretical Progress for Treating Charged Particle Ionization of Atoms and Molecules  

NASA Astrophysics Data System (ADS)

The field of atomic and molecular ionization by charged particle impact has seen exciting advances over the last few years as a result of the development of the COLTRIMS method. Using COLTRIMS, one can get three-dimensional fully differential cross sections (FDCS) for essentially any projectile and any target. This work complements the results of more conventional spectrometers which means that we are getting a much clearer picture of the ionization process. As a result of the rapid experimental advances, the theoretical models are being more stringently tested. This talk will examine the theoretical advances that have been made in the last few years for light and heavy particle ionization of atoms and molecules.

Madison, Don

2007-06-01

168

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

169

Negatively charged phospholipids suppress IFN-{gamma} production in T cells  

SciTech Connect

The effect of phospholipids on IFN-{gamma} production in mouse T cells was investigated. Phosphatidylserine (PS), which has a negatively charged head group, completely inhibited IFN-{gamma} production in splenic naive T cells and antigen-dependent IFN-{gamma} production in Th1 clone 42-6A cells, whereas other phospholipids, which have neutrally charged head group, had no effect. The structural requirements for IFN-{gamma} inhibitory effects by PS were investigated, and dimyristoyl-PS (C14: 0) and dipalmitoyl-PS (C16: 0) had no effect on IFN-{gamma} production, and interestingly, distearoyl-PS (18: 0) increased IFN-{gamma} production. Dioleoyl-PS (C18: 1), dilinoleoyl-PS (C18: 2), and oleoyl-lyso-PS (C18: 1) completely inhibited IFN-{gamma} production. To clarify this mechanism, we focused on the stability of IFN-{gamma} mRNA, and the treatment of splenic naive T cells with PS brought about 40% reductions in IFN-{gamma} mRNA expression in the presence of actinomycin D. Collectively, IFN-{gamma} inhibitory effects by PS are highly dependent on the molecular structure of PS and involve the decreasing of the stability of IFN-{gamma} mRNA.

Yotsumoto, Satoshi [School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392 (Japan); Kakiuchi, Terutaka [Toho University School of Medicine, 5-21-16 Omori-nishi, Ota-ku, Tokyo 143-8540 (Japan); Aramaki, Yukihiko [School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392 (Japan)]. E-mail: aramaki@ps.toyaku.ac.jp

2005-12-30

170

Soliton propagation in a moving electron-positron pair plasma having negatively charged dust grains  

NASA Astrophysics Data System (ADS)

We consider an electron-positron pair plasma that has negatively charged dust grains. Being the same mass of the electrons and positrons, both of these species contribute to the wave excitation in the plasma. Since the frequency of oscillations is high, the dust grains are considered to be fixed and they only provide the restoring force for the wave excitation. For the sake of completeness, we include the finite temperatures of the electrons and positrons species and derive the expressions for the phase velocities. Two types of modes propagating in opposite directions occur in this pair plasma model. Based on Korteweg-de Vries (KdV) equation, it is realized that these modes evolve only into compressive solitons. However, usual KdV approach fails when both the species carry the same temperatures and also drift with the same velocity. Under this situation, modified KdV (mKdV) equation is derived that shows the occurrence of rarefactive solitons also, which carry the same amplitudes as the compressive solitons attain corresponding to mKdV equation. In addition to the expressions of peak amplitude and width of the solitons, we calculate soliton energy for examining their propagation characteristics in detail under the effect of positron to electron temperature ratio ?, their drift velocities (ve0 and vp0), dust concentration nd0, and dust charge valency Zd. The issue of nonvanishing coefficient of nonlinearity is also discussed in greater detail.

Malik, Rakhee; Malik, Hitendra K.; Kaushik, Subhash C.

2012-03-01

171

Negatively charged phospholipids suppress IFN-gamma production in T cells.  

PubMed

The effect of phospholipids on IFN-gamma production in mouse T cells was investigated. Phosphatidylserine (PS), which has a negatively charged head group, completely inhibited IFN-gamma production in splenic naïve T cells and antigen-dependent IFN-gamma production in Th1 clone 42-6A cells, whereas other phospholipids, which have neutrally charged head group, had no effect. The structural requirements for IFN-gamma inhibitory effects by PS were investigated, and dimyristoyl-PS (C14: 0) and dipalmitoyl-PS (C16: 0) had no effect on IFN-gamma production, and interestingly, distearoyl-PS (18: 0) increased IFN-gamma production. Dioleoyl-PS (C18: 1), dilinoleoyl-PS (C18: 2), and oleoyl-lyso-PS (C18: 1) completely inhibited IFN-gamma production. To clarify this mechanism, we focused on the stability of IFN-gamma mRNA, and the treatment of splenic naïve T cells with PS brought about 40% reductions in IFN-gamma mRNA expression in the presence of actinomycin D. Collectively, IFN-gamma inhibitory effects by PS are highly dependent on the molecular structure of PS and involve the decreasing of the stability of IFN-gamma mRNA. PMID:16289110

Yotsumoto, Satoshi; Kakiuchi, Terutaka; Aramaki, Yukihiko

2005-11-07

172

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

PubMed

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

Kast, Denis; Kecke, L; Ankerhold, J

2011-08-03

173

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

174

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

SciTech Connect

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). Current experimental data of the cross sections are far from being complete or even satisfactory for tentative applications. One practical approach to the cross-section determination is to test experimental data with general criteria. For example, the Bethe theory indicates a close connection between photoabsorption and energy absorption by glancing collisions. Development and use of these data constraints, first put forth by Platzman, can now be demonstrated in many examples. 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; initial reports on efforts toward this direction are encouraging. 46 refs.

Inokuti, Mitio

1985-01-01

175

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

PubMed Central

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

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

2010-01-01

176

Multielectron Effects in Charge Asymmetric Molecules Induced by Asymmetric Laser Fields  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

177

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

SciTech Connect

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

Wasielewski, Michael R. (NWU)

2008-10-03

178

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.

179

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

SciTech Connect

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

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

2008-03-07

180

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

NASA Astrophysics Data System (ADS)

Previous observations have shown that most of sprites are produced by positive cloud-to-ground (+CG) lightning discharges. Sprites produced by -CGs have a much lower occurrence rate and are rarely detected. Since January 2008, a low light camera has been installed at Duke University (35.970 N, 79.094 E) and continuously record sprite events. Among more than 300 sprites captured, 4 events are produced by -CGs, which are confirmed by both the National Lightning Detection Network (NLDN) and local measurements of lightning-radiated magnetic fields. With the broad band magnetic field measurement (1 Hz - 25 kHz) and a 2-D Finite Difference Time Domain (FDTD) model, we were able to extract the lightning source current moment waveform and further infer the lightning-driven electric fields at sprite locations. Comparing with typical sprites produced by +CGs, the negative sprites initiate immediately after sprite halos and are associated with large charge moment change up to ~ 1000 C km. Thus the negative downward streamers travel and terminate at higher ambient fields comparing to the positive downward streamers existing in typical positive sprites.

Li, J.; Cummer, S. A.

2011-12-01

181

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

PubMed

Negative differential resistance - a decrease in current with increasing bias voltage - is a counter-intuitive effect that is observed in various molecular junctions. Here, we present a novel mechanism that may be responsible for such an effect, based on strong Coulomb interaction between electrons in the molecule and electrons on the atoms closest to the molecule. The Coulomb interaction induces electron-hole binding across the molecule-electrode interface, resulting in a renormalized and enhanced molecule-electrode coupling. Using a self-consistent non-equilibrium Green's function approach, we show that the effective coupling is non-monotonic in bias voltage, leading to negative differential resistance. The model is in accord with recent experimental observations that showed a correlation between the negative differential resistance and the coupling strength. We provide detailed suggestions for experimental tests which may help to shed light on the origin of the negative differential resistance. Finally, we demonstrate that the interface Coulomb interaction affects not only the I-V curves but also the thermoelectric properties of molecular junctions. PMID:24160536

Dubi, Yonatan

2013-10-21

182

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

NASA Astrophysics Data System (ADS)

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

Dubi, Yonatan

2013-10-01

183

Electronegativity equalization method: parameterization and validation for organic molecules using the Merz-Kollman-Singh charge distribution scheme.  

PubMed

The electronegativity equalization method (EEM) was developed by Mortier et al. as a semiempirical method based on the density-functional theory. After parameterization, in which EEM parameters A(i), B(i), and adjusting factor kappa are obtained, this approach can be used for calculation of average electronegativity and charge distribution in a molecule. The aim of this work is to perform the EEM parameterization using the Merz-Kollman-Singh (MK) charge distribution scheme obtained from B3LYP/6-31G* and HF/6-31G* calculations. To achieve this goal, we selected a set of 380 organic molecules from the Cambridge Structural Database (CSD) and used the methodology, which was recently successfully applied to EEM parameterization to calculate the HF/STO-3G Mulliken charges on large sets of molecules. In the case of B3LYP/6-31G* MK charges, we have improved the EEM parameters for already parameterized elements, specifically C, H, N, O, and F. Moreover, EEM parameters for S, Br, Cl, and Zn, which have not as yet been parameterized for this level of theory and basis set, we also developed. In the case of HF/6-31G* MK charges, we have developed the EEM parameters for C, H, N, O, S, Br, Cl, F, and Zn that have not been parameterized for this level of theory and basis set so far. The obtained EEM parameters were verified by a previously developed validation procedure and used for the charge calculation on a different set of 116 organic molecules from the CSD. The calculated EEM charges are in a very good agreement with the quantum mechanically obtained ab initio charges. PMID:18988249

Jirousková, Zuzana; Vareková, Radka Svobodová; Vanek, Jakub; Koca, Jaroslav

2009-05-01

184

An angle-resolved translational energy spectrometer for investigating low-energy, highly charged ion-atom (molecule) collisions  

Microsoft Academic Search

An experimental apparatus for investigating low-collision energy gas-phase reactions of highly charged ions with atoms and molecules by angle-resolved translational energy spectroscopy is described. The basic function of the apparatus is to slow down highly charged ions extracted at 2–3 kV from the Cornell superconducting solenoid, cryogenic electron beam ion source (CEBIS) to energies below 100 qeV. The slowing down

J. Vancura; J. J. Perotti; J. Flidr; V. O. Kostroun

1993-01-01

185

Extraction mechanisms of charged organic dye molecules into silica-surfactant nanochannels in a porous alumina membrane.  

PubMed

Extraction mechanisms of charged organic dye molecules are examined for an assembly of silica-surfactant nanochannels with a channel diameter of 3.4 nm, which is formed inside the pores of an anodic alumina membrane by a surfactant-template method. Experimental results confirm that the extraction mechanism depends on the sign of a charge of the dye molecules. The extraction of the cationic rhodamine 6G is predominantly caused by an ion-pair extraction process, whereas an anion-exchange process is mainly responsible for the extraction of the anionic sulforhodamine B. These extraction mechanisms are discussed by considering the microstructures of the silica-surfactant nanochannels. PMID:17723343

Yamaguchi, Akira; Watanabe, Jun; Mahmoud, Mekawy M; Fujiwara, Rise; Morita, Kotaro; Yamashita, Tomohisa; Amino, Yosuke; Chen, Yong; Radhakrishnan, Logudurai; Teramae, Norio

2005-07-14

186

In vitro and in vivo evaluation of superparamagnetic iron oxide nanoparticles coated by bisphosphonates: the effects of electrical charge and molecule length.  

PubMed

Physicochemical coating properties are often considered to be determining factors for in vivo characteristics of superparamagnetic iron oxide nanoparticles, used as contrast agent in Magnetic Resonance Imaging (MRI). To investigate the electrical charge (modified by zero, one or two ammonium groups) and the molecule length (3, 5 or 7 methylene chains) effects of bisphosphonate-type coatings, we assessed the complement activation, in vivo plasma and tissue relaxation time alterations of intravenously injected small iron oxide nanoparticles (<25 nm) on male healthy Wistar rats. The presence of ammonium groups induces a weak activation of the complement whatever the size and the concentration of particles, whereas hydroxyethylenebisphosphonate (HEBP)-coated particles are poor complement activators only at the lowest concentration. In vivo, HEBP-coated nanoparticles have the greatest prolonged relaxation time effects, despite their higher negative electrical charge, contrary to two ammonium bearing coatings. No significant differences were observed between mono-ammonium molecular coatings. PMID:23459107

Karimi, A; Denizot, B; Passirani, C; Hindré, F; Roux, J; Legras, P; Le Jeune, J J

2013-02-28

187

The relationship between the distribution of anode striations and negative and positive charge accumulation in a plasma display panel  

NASA Astrophysics Data System (ADS)

Anode striations and wall charges, common phenomena in the plasma display panel (PDP) discharge process, are investigated by simulations in both alternating current coplanar and novel shadow mask PDPs. The formation process of striations is presented and the formation mechanism is investigated. The results reveal that in both structures there is an obvious correspondence between the striation distribution and both the negative and the positive charge accumulation on the dielectric layer above the anode. Each of the two contributions to the total wall charge reaches its peak at the positions where the striations emerge. The total wall charge distribution on the other hand, which is the sum of the wall charge collected from electrons and ions, does not show any striation effect at all.

Zhang, P. P.; Tu, Y.; Yang, L. L.

2011-12-01

188

Valence band tunneling model for charge transfer of redox-active molecules attached to n- and p-silicon substrates  

SciTech Connect

In this work, monolayers of the redox-active molecules, with cationic- accessible states, were incorporated on p- and n-type silicons of varying doping concentrations. The redox voltages and kinetics were found to be strongly dependent on the silicon doping concentrations, and ambient light in case of n-Si substrate, while there was no significant impact of substrate doping concentration or ambient light in case of p-Si substrate. These results suggest the redox energy states in the molecule align within the valence band of the silicon substrate. Based on this, a model for electronic coupling and charge transfer at the molecule-semiconductor interfaces is proposed.

Gowda, Srivardhan; Mathur, Guru; Misra, Veena [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2007-04-02

189

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

SciTech Connect

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

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

2008-08-28

190

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

NASA Astrophysics Data System (ADS)

It has been proposed that the apparent discrepancies between the inferred primordial abundances of Li6 and Li7 and the predictions of big bang nucleosynthesis (BBN) can be resolved by the existence of a negatively charged massive unstable supersymmetric particle (X-) during the BBN epoch. Here, we present new BBN calculations with an X- particle utilizing an improved nuclear reaction network including captures of nuclei by the particle, nuclear reactions and ? decays of normal nuclei and nuclei bound to the X- particles (X nuclei), and new reaction rates derived from recent rigorous quantum many-body dynamical calculations. We find that this is still a viable model to explain the observed Li6 and Li7 abundances. We also show that with the new rates the production of heavier nuclei is suppressed and there is no signature on abundances of nuclei heavier than Be in the X--particle catalyzed BBN model as has been previously proposed. We also consider the version of this model whereby the X- particle decays into the present cold dark matter. We analyze this paradigm in light of the recent constraints on the dark-matter mass deduced from the possible detected events in the CDMS-II experiment. We conclude that based upon the inferred range for the dark-matter mass, only X- decay via the weak interaction can achieve the desired Li7 destruction while also reproducing the observed Li6 abundance.

Kusakabe, Motohiko; Kajino, Toshitaka; Yoshida, Takashi; Mathews, Grant J.

2010-04-01

191

Multiply charged negative ions of hydrogen in linearly polarized laser fields  

NASA Astrophysics Data System (ADS)

Motivated by the prediction of the appearance of atomic multiply charged negative ions (AMCNI) of hydrogen, induced by a linearly polarized laser field, we present an analytical quantum mechanical treatment of the appearance and structure of AMCNI in a linearly polarized field, based on high-frequency Floquet theory (HFFT). For the simplest AMCNI of hydrogen, H2- and H3-, the values of ?0 at which the first bound state appears are ?0=1.62×102 and ?0=1.02×104, where ?0=I1/2/?2 is the amplitude of the oscillation of a free electron in the field with frequency ? and intensity I (unless stated otherwise, we use atomic units throughout this paper). Whereas in vacuum at least one of the electrons of an AMCNI autodetaches, an intense high-frequency field can change the character of the ion dramatically, such that bound states of AMCNI can appear. Due to the interaction with the field, the electrons of the AMCNI oscillate in phase along the polarization axis. This ``quiver'' motion enables the electrons to be spatially separated over distances of order ?0, reducing the repulsive e-e interaction as ?0 increases. In other words, for ?0 large enough, the field enables a configuration in which the electrons, while widely separated, are bound to one proton. For the prediction of bound states of HN- with N>3, however, a relativistic description or low-frequency theory is required.

van Duijn, Ernst; Muller, H. G.

1997-09-01

192

EPR proof of the negatively charged acceptor state Zn- in silicon  

NASA Astrophysics Data System (ADS)

The electronic properties of Zn in monocrystalline silicon were studied by means of electron paramagnetic resonance (EPR). In high-ohmic p- and n-type Si doped with Zn two new line sets were observed. One of them show the characteristic behavior of the 1/2<-->-1/2 and 3/2<-->-3/2 transitions of a ?8 state in tetrahedral symmetry and can be detected for all sample orientations. The line positions of this set can be well described with a spin Hamiltonian for S=3/2 including the linear and cubic Zeeman-interaction and the fitted parameters /|g|=1.1749+/-0.0005 and |f|=0.0402+/-0.00050). For magnetic field directions around B||<100>, a second line set consisting of seven additional lines were detected which can be described by the spin transitions within a coupled (?7-?8)-ground state manifold. Based on the analysis of the experimental data this spectrum has been identified as arising from the negative charge state of the isolated substitutional Zns- in silicon.

Gehlhoff, W.; Näser, A.; Bracht, H.

1999-12-01

193

Carrier control via charge transfer at the topological-insulator/organic-molecule interface  

NASA Astrophysics Data System (ADS)

A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications.

Tanigaki, Katsumi; Tanabe, Yoichi; Kuynh, Khuong; Urata, Takahiro; Nouchi, Ryo; Heguri, Satoshi; Shimotani, Hidekazu

2013-03-01

194

Negative-Charge Production by Slow Hydrogen Atoms in Ar, Kr, Xe, CO, CO2, and CH4.  

National Technical Information Service (NTIS)

Experimental cross sections for negative-charge production by neutral hydrogen atoms in the energy range from 80 eV - 2 keV in Ar, Kr, Xe, CO, CO2, and CH4 are reported. The results agree well with earlier measurements at higher energies. (Author)

R. C. Dehmel R. Meger H. H. Fleischmann M. Steinberg

1971-01-01

195

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.

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

2011-01-01

196

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

SciTech Connect

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

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

2012-12-15

197

Unfolding action of alcohols on a highly negatively charged state of cytochrome C.  

PubMed

It is well-known that hydrophobic effect play a major role in alcohol-protein interactions leading to structure unfolding. Studies with extremely alkaline cytochrome c (U(B) state, pH 13) in the presence of the first four alkyl alcohols suggests that the hydrophobic effect persistently overrides even though the protein carries a net charge of -17 under these conditions. Equilibrium unfolding of the U(B) state is accompanied by an unusual expansion of the chain involving an intermediate, I(alc), from which water is preferentially excluded, the extent of water exclusion being greater with the hydrocarbon content of the alcohol. The mobility and environmental averaging of side chains in the I(alc) state are generally constrained relative to those in the U(B) state. A few nuclear magnetic resonance-detected tertiary interactions are also found in the I(alc) state. The fact that the I(alc) state populates at low concentrations of methanol and ethanol and the fact that the extent of chain expansion in this state approaches that of the U(B) state indicate a definite influence of electrostatic repulsion severed by the low dielectric of the water/alcohol mixture. Interestingly, the U(B) ? I(alc) segment of the U(B) ? I(alc) ? U equilibrium, where U is the unfolded state, accounts for roughly 85% of the total number of water molecules preferentially excluded in unfolding. Stopped-flow refolding results report on a submillisecond hydrophobic collapse during which almost the entire buried surface area associated with the U(B) state is recovered, suggesting the overwhelming influence of hydrophobic interaction over electrostatic repulsions. PMID:22439732

Sashi, Pulikallu; Yasin, U Mahammad; Bhuyan, Abani K

2012-04-06

198

Molecular interactions of Alzheimer amyloid-? oligomers with neutral and negatively charged lipid bilayers.  

PubMed

Interaction of p3 (A?(17-42)) peptides with cell membranes is crucial for the understanding of amyloid toxicity associated with Alzheimer's disease (AD). Such p3-membrane interactions are considered to induce the disruption of membrane permeability and integrity, but the exact mechanisms of how p3 aggregates, particularly small p3 oligomers, induce receptor-independent membrane disruption are not yet completely understood. Here, we investigate the adsorption, orientation, and surface interaction of the p3 pentamer with lipid bilayers composed of both pure zwitterionic POPC (palmitoyl-oleoyl-phosphatidylcholine) and mixed anionic POPC-POPG (palmitoyl-oleoyl-phosphatidylglycerol) (3 : 1) lipids using explicit-solvent molecular dynamics (MD) simulations. MD simulation results show that the p3 pentamer has much stronger interactions with mixed POPC-POPG lipids than pure POPC lipids, consistent with experimental observation that A? adsorption and fibrillation are enhanced on anionic lipid bilayers. Although electrostatic interactions are main attractive forces to drive the p3 pentamer to adsorb on the bilayer surface, the adsorption of the p3 pentamer on the lipid bilayer with C-terminal ?-strands facing toward the bilayer surface is a net outcome of different competitions between p3 peptides-lipid bilayer and ions-p3-bilayer interactions. More importantly, Ca(2+) ions are found to form ionic bridges to associate negatively charged residues of p3 with anionic headgroups of the lipid bilayer, resulting in A?-Ca(2+)-PO4(-) complexes. Intensive Ca(2+) bound to the lipid bilayer and Ca(2+) ionic bridges may lead to Ca(2+) hemostasis responsible for neuronal dysfunction and death. This work provides insights into the mutual structure, dynamics, and interactions of both A? peptides and lipid bilayers at the atomic level, which expand our understanding of the complex behavior of amyloid-induced membrane disruption. PMID:23493873

Yu, Xiang; Wang, Qiuming; Pan, Qingfen; Zhou, Feimeng; Zheng, Jie

2013-03-14

199

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

SciTech Connect

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

Kusakabe, Motohiko [Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582 (Japan); Kajino, Toshitaka [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Department of Astronomical Science, Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 (Japan); Yoshida, Takashi [Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Mathews, Grant J. [Department of Physics, Center for Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2010-04-15

200

Pico and nano-second laser flash photolysis study on photoinduced charge separation in oligothiophene-C 60 dyad molecules  

Microsoft Academic Search

Photoinduced charge separation (CS) and charge recombination (CR) processes of octathiophene-C60 and dodecathiophene-C60 dyad molecules (8T-C60 and 12T-C60, respectively) have been investigated by time-resolved absorption spectroscopy in the visible and near-IR regions. In toluene, 18T*-C60 and 112T*-C60 showed energy transfer to 1C*-moiety predominantly, while 60 contribution of CS was small. In various polar solvents, on the other hand, CS states

Mamoru Fujitsuka; Keisuke Matsumoto; Osamu Ito; Takashi Yamashiro; Yoshio Aso; Tetsuo Otsubo

2001-01-01

201

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

PubMed

The rate coefficients for capture of charged particles by dipolar polarizable symmetric top molecules in the quantum collision regime are calculated within an axially nonadiabatic channel approach. It uses the adiabatic approximation with respect to rotational transitions of the target within first-order charge-dipole interaction and takes into account the gyroscopic effect that decouples the intrinsic angular momentum from the collision axis. The results are valid for a wide range of collision energies (from single-wave capture to the classical limit) and dipole moments (from the Vogt-Wannier and fly-wheel to the adiabatic channel limit). PMID:24007001

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

2013-08-28

202

Theoretical Study of the Binding of Positrons of Gaseous Molecules.  

National Technical Information Service (NTIS)

While a positron will not readily become attached to a neutral symmetrical atom or molecule, it will be bound by negatively charged molecules and molecular fragments. The positron affinities have been calculated for certain isoelectronic series using a Ha...

A. B. Kunz J. T. Waber

1982-01-01

203

Influence of gas molecules on the charge carrier mobility in thin films of semiconducting perylene tetracarboxylic imides  

NASA Astrophysics Data System (ADS)

Thin films (30 nm) of crystalline N,N'-dimethylperylene-3,4,9,10-biscarboximide (MePTCDI) or amorphous 1,6,7,12-tetrachloro-N,N'-dimethylperylene-3,4,9,10-biscarboximide (Cl4MePTCDI) were prepared by physical vapor deposition and characterized by conductivity and field effect measurements at pristine films and under increasing partial pressure of oxygen, ethanol, acetone, or n-butane. Changes in the conductivity of the films were observed. Field effect measurements served to differentiate between changes in the charge carrier mobility ? and changes of the charge carrier concentration n. ? was found to decrease significantly, whereas rather small changes were found in n. Gas molecules that diffused into the films changed ? at least ten times more efficiently than those molecules just adsorbed on the surface.

Graaf, Harald; Schlettwein, Derck

2006-12-01

204

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

NASA Astrophysics Data System (ADS)

A new design of a linear time of flight mass spectrometer (ToFMS) is implemented that gives nearly field-free interaction region without compromising on the mass resolution. The design addresses problems that would arise in a conventional Wiley-McLaren type of ToFMS: (i) field leakages into the charged particle-molecule interaction region from various components of the mass spectrometer, including that through the high transparency mesh used to obtain evenly distributed electric fields; (ii) complete collection and transportation of the ions produced in the interaction region to the detector, which is essential for high sensitivity and cross section measurements. This ToFMS works over a wide range of masses from H+ to a few hundred Daltons and would be the most suitable for low energy charged particle-molecule interaction studies. Performance of the ToFMS has been tested by measuring the partial ionization cross sections for electron impact on CF4.

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

2011-11-01

205

Three-Center Coulombic Over-Barrier Model for Multiple Electron Capture by Slow Highly Charged Ions from Diatomic Molecules  

Microsoft Academic Search

A three-center Coulombic over-barrier model is proposed for the process of multiple electron capture from homonuclear diatomic molecules in collisions with slow highly charged ions. The present model, based on the over-barrier model for atomic targets given by Niehaus, takes further into account the two-center nature of molecular targets by introducing a three-center Coulomb potential for respective electrons. Cross sections

A. Ichimura; T. Ohyama-Yamaguchi

1999-01-01

206

Stable negative ions and shape resonances in a series of organic molecules.  

PubMed

We report on the theoretical determination of low-lying shape resonances in a selected set of seven molecules. The finite element discrete model method is used and the absolute differences between calculated and experimental values, where known, are [less, approximate]0.15 eV for the resonances lowest in energy. Difficulties expected with the higher calculated values are discussed. This article reports results for ortho-benzyne, benzene, naphthalene, anthracene, styrene, formamide, and acetamide. Comparisons are made with a few other calculations, again where available. PMID:24050345

Gallup, G A

2013-09-14

207

Stable negative ions and shape resonances in a series of organic molecules  

NASA Astrophysics Data System (ADS)

We report on the theoretical determination of low-lying shape resonances in a selected set of seven molecules. The finite element discrete model method is used and the absolute differences between calculated and experimental values, where known, are <~0.15 eV for the resonances lowest in energy. Difficulties expected with the higher calculated values are discussed. This article reports results for ortho-benzyne, benzene, naphthalene, anthracene, styrene, formamide, and acetamide. Comparisons are made with a few other calculations, again where available.

Gallup, G. A.

2013-09-01

208

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

SciTech Connect

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

Takeuchi, S.; Sasao, M.; Sugawara, H.; Tanaka, N.; Kisaki, M.; Okamoto, A.; Shinto, K.; Kitajima, S.; Nishiura, M.; Wada, M. [Tohoku University, Sendai 980-8579 (Japan); National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Doshisha University, Kyotanabe, Kyoto 610-0321 (Japan)

2008-02-15

209

Resonant two-color high-resolution spectroscopy of a negatively charged exciton in a self-assembled quantum dot  

Microsoft Academic Search

We report high-resolution resonant two-color laser spectroscopy on single self-assembled InGaAs quantum dots. The negatively charged exciton in a quantum dot can decay radiatively into both electron-spin ground states, the states with an electron in the quantum dot with its spin parallel or antiparallel to an applied magnetic field. The two decay paths can be used for optical spin alignment

M. Kroner; K. M. Weiss; B. Biedermann; S. Seidl; A. W. Holleitner; A. Badolato; P. M. Petroff; P. Öhberg; R. J. Warburton; K. Karrai

2008-01-01

210

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

Microsoft Academic Search

The analysis presented below suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms with no distinction between phenolic, carboxylic or inorganic hydroxide functional groups: logKML=?O logKHL+?O; where KML is the metal–ligand formation constant, KHL is the corresponding proton–ligand formation constant, and ?O and ?O are termed the Irving–Rossotti slope and intercept, respectively. Linear free energy relationships

Richard F. Carbonaro; Dominic M. Di Toro

2007-01-01

211

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

Microsoft Academic Search

The analysis presented below suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms with no distinction between phenolic, carboxylic or inorganic hydroxide functional groups: log KML = alphaO log KHL + betaO; where KML is the metal ligand formation constant, KHL is the corresponding proton ligand formation constant, and alphaO and betaO are termed the Irving

Richard F. Carbonaro; Dominic M. di Toro

2007-01-01

212

The charge-exchange scattering of negative pions by protons at 96.6 MeV  

Microsoft Academic Search

The angular distribution of gamma rays from the charge-exchange scattering of 96.6 MeV negative pions by protons has been measured at 14 angles between 20° and 151.2°. The gamma-ray detector utilized a lead converter and counter telescope. The correction for loss of electrons in the converter was determined experimentally and the calculated efficiency of the detector checked by direct measurement

S. G. F. Frank; J. R. Holt; T. Massam; G. Myatt

1967-01-01

213

The charge-exchange scattering of negative pions by protons at 96.6 MeV  

Microsoft Academic Search

The angular distribution of ? rays from the charge-exchange scattering of 96.6 MeV negative pions by protons has been measured at 14 angles between 20° and 151.2°. The ?-ray detector utilized a lead converter and counter telescope. The correction for loss of electrons in the converter was determined experimentally and the calculated efficiency of the detector checked by direct measurement

S. G. F. Frank; J. R. Holt; T. Massam; G. Myatt

1967-01-01

214

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

Microsoft Academic Search

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

Sandeep Patel; Charles L. Brooks III

2006-01-01

215

Optically induced electron transfer from conjugated organic molecules to charged metal clusters  

Microsoft Academic Search

The formation of small gold clusters at the initial stage of the metal growth on a thin film of the conjugated organic semiconductor diindenoperylene (DIP) leads to charging during ultraviolet photoemission spectroscopy (UPS) investigations. Additional irradiation of the sample with visible light was successfully applied to re-establish charge neutrality on the sample surface. By varying the light energy, we demonstrate

N. Koch; A. C. Dürr; J. Ghijsen; R. L. Johnson; J.-J. Pireaux; J. Schwartz; F. Schreiber; H. Dosch; A. Kahn

2003-01-01

216

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

PubMed

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

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

2012-02-01

217

Memory for media: Investigation of false memories for negatively and positively charged public events  

Microsoft Academic Search

Despite a large body of false memory research, little has addressed the potential influence of an event's emotional content on susceptibility to false recollections. The Paradoxical Negative Emotion (PNE) hypothesis predicts that negative emotion generally facilitates memory but also heightens susceptibility to false memories. Participants were asked whether they could recall 20 “widely publicised” public events (half fictitious) ranging in

Stephen Porter; Kristian Taylor; Leanne ten Brinke

2008-01-01

218

The influence of positive or negative charges in the passive and iontophoretic skin penetration of porphyrins used in photodynamic therapy.  

PubMed

Meso-tetra-(N-methylpiridinium-4-yl)-porphyrin (TMPyP) and meso-tetra-(4-sulfonatophenyl)-porphyrin (TPPS(4)) are photosensitizing drugs (PS) used in photodynamic therapy (PDT). Based on the fact that these compounds present similar chemical structures but opposite charges at pH levels near physiological conditions, this work aims to evaluate the in vitro and in vivo influence of these electrical charges on the iontophoretic delivery of TMPyP and TPPS(4), attempting to achieve maximum accumulation of PS in skin tissue. The iontophoretic transport of these drugs from a hydrophilic gel was investigated in vitro using porcine ear skin and vertical, flow-through diffusion cells. In vivo experiments using rats were also carried out, and the penetration of the PSs was analyzed by fluorescence microscopy to visualize the manner of how these compounds were distributed in the skin after a short period of iontophoresis application. In vitro, both passive and iontophoretic delivery of the positively charged TMPyP were much greater (20-fold and 67-fold, respectively) than those of the negatively charged TPPS(4). TPPS(4) iontophoresis in vivo increased the fluorescence of the skin only in the very superficial layers. On the other hand, iontophoresis of the positively charged drug expressively increased the rat epidermis and dermis fluorescence, indicating high amounts of this drug throughout the skin layers. Moreover, TMPyP was homogeneously distributed around and into the nuclei of the skin cells, suggesting its potential use in topical PDT. PMID:21118720

Gelfuso, Guilherme M; Gratieri, Taís; Souza, Joel G; Thomazine, José A; Lopez, Renata F V

2010-11-29

219

N-(1-Naphthyl) Ethylenediamine Dinitrate: A New Matrix for Negative Ion MALDI-TOF MS Analysis of Small Molecules  

NASA Astrophysics Data System (ADS)

An organic salt, N-(1-naphthyl) ethylenediamine dinitrate (NEDN), with rationally designed properties of a strong UV absorbing chromophore, hydrogen binding and nitrate anion donors, has been employed as a matrix to analyze small molecules ( m/z < 1000) such as oligosaccharides, peptides, metabolites and explosives using negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Compared with conventional matrixes such as ?-cyano-4-hydroxycinnamic acid (CCA) and 2,5-dihydroxybenzoic acid (DHB), NEDN provides a significant improvement in detection sensitivity and yields very few matrix-associated fragment and cluster ions interfering with MS analysis. For low-molecular-weight saccharides, the lowest detection limit achieved ranges from 500 amol to 5 pmol, depending on the molecular weight and the structure of the analytes. Additionally, the mass spectra in the lower mass range ( m/z < 200) consist of only nitrate and nitric acid cluster ions, making the matrix particularly useful for structural identification of oligosaccharides by post-source decay (PSD) MALDI-MS. Such a characteristic is illustrated by using maltoheptaose as a model system. This work demonstrates that NEDN is a novel negative ion-mode matrix for MALDI-MS analysis of small molecules with nitrate anion attachment.

Chen, Rui; Chen, Suming; Xiong, Caiqiao; Ding, Xunlei; Wu, Chih-Che; Chang, Huan-Cheng; Xiong, Shaoxiang; Nie, Zongxiu

2012-09-01

220

The effect of the number of parallel DNA molecules on electric charge transport through 'standing DNA'  

NASA Astrophysics Data System (ADS)

We present morphological and electrical characterization of double-stranded DNA (dsDNA) molecules covalently bound to two metal electrodes: an underlying gold surface and a gold nanoparticle (GNP). Conductive atomic force microscope (cAFM) with a metallized tip is used to perform current-voltage (I-V) measurements through dsDNA molecules, connected to GNPs of different diameters 5, 10 and 20 nm. The number of DNA molecules coating the GNP is expected to vary with the surface area of the GNP. This number and the portion of the GNP surface area enabling hybridization of the DNA determine the number of DNA molecules connecting the GNP to the gold surface. The larger the diameter of the GNP the higher the expected number of dsDNA molecules connecting it to the gold surface and thus the expected current. Our results show similar currents for all three GNP sizes, indicating that current flows through the same number of molecules regardless of the diameter of the measured GNP. The measured currents, 220 nA at 2 V, are in accordance with our previous reports (Cohen et al 2005 Proc. Natl Acad. Sci. USA 102 11589-93 Cohen et al 2006 Faraday Discuss. 131 367-76) in which we demonstrated the validity of the experimental system. In particular, for the 5 nm GNP, we conclude that the current possibly flows through two to three molecules, likely only one, and that a single short dsDNA molecule can support at least ~70 nA, and probably 220 nA.

Ullien, Daniela; Cohen, Hezy; Porath, Danny

2007-10-01

221

Molecular wires in single-molecule junctions: charge transport and vibrational excitations.  

PubMed

We investigate the effect of vibrations on the electronic transport through single-molecule junctions, using the mechanically controlled break junction technique. The molecules under investigation are oligoyne chains with appropriate end groups, which represent both an ideally linear electrical wire and an ideal molecular vibrating string. Vibronic features can be detected as satellites to the electronic transitions, which are assigned to longitudinal modes of the string by comparison with density functional theory data. PMID:20521299

Ballmann, Stefan; Hieringer, Wolfgang; Secker, Daniel; Zheng, Qinglin; Gladysz, John A; Görling, Andreas; Weber, Heiko B

2010-07-12

222

Comparison of two cationic polymeric flocculant architectures on the destabilization of negatively charged latex suspensions  

Microsoft Academic Search

Flocculation studies between cationic polymers and oppositely charged colloidal particles are reported in which both flocculation kinetics and floc structures are systematically investigated. The flocculation rate constant, stability ratio and kinetics laws are experimentally determined using particle counting for two polymer architectures; a cationic linear polymer and a two-branched polymer. Comparisons are also made using NaCl at different ionic concentrations

Daniel Palomino; David Hunkeler; Serge Stoll

2011-01-01

223

Mounting to Measure Asymmetry of Charged Particle Emission in the Capture of Negative Muons by Nuclei.  

National Technical Information Service (NTIS)

A high aperture mounting including proportional counters to measure ionization losses of charged particles and a spectrometer based on CsI(Tl) crystal for measuring their energy are described. The measurement of asymmetry for separated by masses single-ch...

M. P. Balandin V. M. Grebenyuk V. G. Zinov A. D. Konin T. Kozlovski

1977-01-01

224

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

NASA Astrophysics Data System (ADS)

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

Tarafder, Kartick; Wang, Lin-Wang

2013-03-01

225

Implications of surface charge and curvature for the binding orientation of Thermomyces lanuginosus lipase on negatively charged or zwitterionic phospholipid vesicles as studied by ESR spectroscopy.  

PubMed

The triglyceride lipase (EC 3.1.1.3) Thermomyces lanuginosus lipase (TLL) binds with high affinity to unilamellar phospholipid vesicles that serve as a diluent interface for both lipase and substrate, but it displays interfacial activation on only small and negatively charged such vesicles [Cajal, Y., et al. (2000) Biochemistry 39, 413-423]. The productive-mode binding orientation of TLL at the lipid-water interface of small unilamellar vesicles (SUV) consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) was previously determined using electron spin resonance (ESR) spectroscopy in combination with site-directed spin-labeling [Hedin, E. M. K., et al. (2002) Biochemistry 41, 14185-14196]. In our investigation, we have studied the interfacial orientation of TLL when bound to large unilamellar vesicles (LUV) consisting of POPG, and bound to SUV consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC). Eleven single-cysteine TLL mutants were spin-labeled as previously described, and studied upon membrane binding using the water soluble spin-relaxation agent chromium(III) oxalate (Crox). Furthermore, dansyl-labeled vesicles revealed the intermolecular fluorescence quenching efficiency between each spin-label positioned on TLL, and the lipid membrane. ESR exposure and fluorescence quenching data show that TLL associates closer to the negatively charged PG surface than the zwitterionic PC surface, and binds to both POPG LUV and POPC SUV predominantly through the concave backside of TLL opposite the active site, as revealed by the contact residues K74C-SL, R209C-SL, and T192C-SL. This orientation is significantly different compared to that on the POPG SUV, and might explain the differences in activation of the lipase. Evidently, both the charge and accessibility (curvature) of the vesicle surface determine the TLL orientation at the phospholipid interface. PMID:16342956

Hedin, Eva M K; Høyrup, Pernille; Patkar, Shamkant A; Vind, Jesper; Svendsen, Allan; Hult, Karl

2005-12-20

226

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

PubMed

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

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

2009-04-01

227

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

NASA Astrophysics Data System (ADS)

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

Strange, M.; Thygesen, K. S.

2012-11-01

228

Single and double charge transfer of He2+ ions with molecules at near-thermal energies  

NASA Astrophysics Data System (ADS)

Rate coefficients have been measured for charge-transfer reactions of He2+ ions with H2, N2, O2, CO, CO2, and H2O. The experiments were carried out using a selected-ion drift-tube mass spectrometer. Total rate coefficients are found to be very large and are generally close to the limiting Langevin capture rate coefficients or the corresponding ADO coefficients. The product-ion spectra indicate that both single and double charge transfer and possibly transfer ionization occur in these reactions.

Tosh, R. E.; Johnsen, R.

1993-02-01

229

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

Microsoft Academic Search

Although ice melts and water freezes under equilibrium conditions at 0°C, water can be supercooled under homogeneous conditions in a clean environment down to -40°C without freezing. The influence of the electric field on the freezing temperature of supercooled water (electrofreezing) is of topical importance in the living and inanimate worlds. We report that positively charged surfaces of pyroelectric LiTaO3

David Ehre; Etay Lavert; Meir Lahav; Igor Lubomirsky

2010-01-01

230

Precise Measurement of Effective Mass of Positive and Negative Charge Carriers in Liquid Helium II  

Microsoft Academic Search

The resonance of charge carriers trapped under the surface of He II is observed at 200 MHz. The effective masses are found to be m+*=(45+\\/-2)m4 and m-*=(76+\\/-2)m4, where m4 is a bare 4He mass. The ionic radii are deduced to be R+=6.0+\\/-0.1 Å and R-=11.4+\\/-0.1 Å.

J. Poitrenaud; F. I. B. Williams

1972-01-01

231

Spin coherence generation in negatively charged self-assembled (In,Ga)As quantum dots by pumping excited trion states  

NASA Astrophysics Data System (ADS)

Spin coherence generation in an ensemble of negatively charged (In,Ga)As/GaAs quantum dots was investigated by picosecond time-resolved pump-probe spectroscopy measuring ellipticity. Robust coherence of the ground-state electron spins is generated by pumping excited charged exciton (trion) states. The phase of the coherent state, as evidenced by the spin ensemble precession about an external magnetic field, varies relative to spin coherence generation resonant with the ground state. The phase variation depends on the pump photon energy. It is determined by (a) pumping dominantly either singlet or triplet excited states, leading to a phase inversion, and (b) the subsequent carrier relaxation into the ground states. From the dependence of the precession phase and the measured g factors, information about the quantum dot shell splitting and the exchange energy splitting between triplet and singlet states can be extracted in the ensemble.

Henriques, A. B.; Schwan, A.; Varwig, S.; Maia, A. D. B.; Quivy, A. A.; Yakovlev, D. R.; Bayer, M.

2012-09-01

232

The local diurnal variation of cloud electrification and the global diurnal variation of negative charge on the Earth  

NASA Astrophysics Data System (ADS)

Both the amplitude and the phase of the ionospheric potential and Carnegie curve of atmospheric electricity are considered to distinguish causes for the negatively charged earth in fair weather. Satellite-observed longitudinal distributions of electrical activity are convolved with local diurnal variations of cloud-to-ground lightning and point discharge current to produce universal diurnal variations which are compared with the Carnegie curve. The amplitude ratio (maximum-minimum)/mean) for the predicted universal diurnal variation of point discharge shows good agreement with the Carnegie curve, whereas the predicted amplitude ratio for lightning is 2-3 times greater. These comparisons suggest that conduction current other than lightning is the dominant charging agent for the Earth's surface.

Williams, E. R.; Heckman, S. J.

1993-03-01

233

Investigation of multi-state charge-storage properties of redox-active organic molecules in silicon-molecular hybrid devices for DRAM and Flash applications  

Microsoft Academic Search

Molecular electronics has recently spawned a considerable amount of interest with several molecules possessing charge-conduction and charge-storage properties proposed for use in electronic devices. Hybrid silicon-molecular technology has the promise of augmenting the current silicon technology and provide for a transitional path to future molecule-only technology. The focus of this dissertation work has been on developing a class of hybrid

Srivardhan Shivappa Gowda

2007-01-01

234

Electron correlation and nuclear charge dependence of parity-violating properties in open-shell diatomic molecules  

NASA Astrophysics Data System (ADS)

The scaling of nuclear-spin-dependent parity-violating effects with increasing nuclear charge Z is discussed in two series of isoelectronic open-shell diatomic molecules. The parameter Wa characterizing the strength of parity violation in diatomic molecules is calculated in the framework of the zeroth-order regular approximation and found to be in good agreement with the R(Z)Zk scaling law derived for atoms, in which R(Z) represents a relativistic enhancement factor. The influence of electron correlation is studied on the molecular level, with spin-polarization effects being conveniently accounted for by a previously established approximate relation between the hyperfine coupling tensor and Wa. For high-accuracy predictions of parity-violating effects in radium fluoride, the necessity for systematically improvable correlation calculations is emphasized.

Isaev, T. A.; Berger, R.

2012-12-01

235

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

NASA Astrophysics Data System (ADS)

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

Chen, Qiong; Yang, Wanli; Feng, Mang

2012-10-01

236

Low Temperature Studies of the Excited-State Structure of Negatively Charged Nitrogen-Vacancy Color Centers in Diamond  

NASA Astrophysics Data System (ADS)

We report a study of the E3 excited-state structure of single negatively charged nitrogen-vacancy (NV) defects in diamond, combining resonant excitation at cryogenic temperatures and optically detected magnetic resonance. A theoretical model is developed and shows excellent agreement with experimental observations. In addition, we show that the two orbital branches associated with the E3 excited state are averaged when operating at room temperature. This study leads to an improved physical understanding of the NV defect electronic structure, which is invaluable for the development of diamond-based quantum information processing.

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

2009-05-01

237

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.

Prince, Alison; Pfaffinger, Paul J.

2013-01-01

238

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

239

Liquid-like ordering of negatively charged poly(amidoamine) (PAMAM) dendrimers in solution.  

PubMed

A structural investigation in water solution of the sodium carboxylate-terminated (generation G3.5) Tomalia-type poly(amidoamine) dendrimers has been performed by means of the small angle X-ray scattering (SAXS) technique. A long-range intermolecular interaction, revealed by the presence of sharp peaks in SAXS spectra, gives evidence of a considerable structural order in the system, even at low concentration of the dispersed phase. The experimental interdendrimer structure factor S(q) was analyzed in the framework of the Ornstein-Zernike integral equation by using the hypernetted chain approximation (HNCA) as closure relation. The effective interdendrimer interaction, modeled as a screened Coulombic plus hard-sphere repulsion potential, allows the estimation of the dendrimers' effective surface charge Z(eff). The present analysis strongly supports the findings that the effective intra- and interdendrimer charge interactions, as well as the dendrimer solution environment conditions, are crucial parameters for the modulation of the degree of structural organization in solution, suitable for a number of potential applications. PMID:19437728

Lombardo, Domenico

2009-03-01

240

Dissociation and fragmentation of N 2 molecules by slow highly charged ions  

Microsoft Academic Search

Single and multiple electron capture processes are investigated in slow collisions between highly charged Xeq+ (q=15–21) ions and molecular nitrogen. The formation of N2q+ ions by electron capture, dissociation of molecular ion N2+ and Coulomb Explosion of N2q+ (1

X. L. Zhu; X. Ma; B. Wei; H. P. Liu; Z. L. Wang; S. Sha; W. T. Feng; S. P. Cao; D. B. Qian; B. Li; L. F. Chen

2005-01-01

241

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

Microsoft Academic Search

Doubly charged metal ion-ligand L clusters, M2+ (L)n, where M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, can be produced in the gas phase by electrospray of solutions of chloride, bromide or nitrate salts of M2+ in methanol-water. L may be added to the solution or to the gas phase. The ions produced by electrospray at

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

1990-01-01

242

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

2011-12-16

243

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

SciTech Connect

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

Rao, K. C.; Prabhudesai, V. S.; Kumar, S. V. K. [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005 (India)

2011-11-15

244

Charge state of lysozyme molecules in the gas phase produced by IR-laser ablation of droplet beam.  

PubMed

Molecules exhibit their intrinsic properties in their isolated forms. Investigations of isolated large biomolecules require an understanding of the detailed mechanisms for their emergence in the gas phase because these properties may depend on the isolation process. In this study, we apply droplet-beam laser-ablation mass spectrometry to isolate protein molecules in the gas phase by IR-laser ablation of aqueous protein solutions, and we discuss the isolation mechanism. Multiply charged hydrated lysozyme clusters were produced by irradiation of the IR laser onto a droplet beam of aqueous lysozyme solutions with various pH values prepared by addition of sodium hydroxide to the solution. The ions produced in the gas phase show significantly low abundance and have a lower number of charges on them than those in the aqueous solutions, which we explained using a nanodroplet model. This study gives quantitative support for the nanodroplet model, which will serve as a fundamental basis for further studies of biomolecules in the gas phase. PMID:23234475

Kohno, Jun-ya; Nabeta, Kyohei; Sasaki, Nobuteru

2012-12-28

245

Synthesis and characterizations of new negatively charged organic–inorganic hybrid materials: effect of molecular weight of sol–gel precursor  

Microsoft Academic Search

A series of negatively charged hybrid (organic–inorganic) materials were prepared through sol–gel process. The alkoxysilane-containing sol–gel precursors PEO-[Si(OEt)3]2SO3H were obtained by endcapping polyethylene oxide (PEO) of different molecular weights with 2,4-diisocyanate toluene (TDI), followed by a coupling reaction with phenylaminomethyl triethoxysilane (ND-42) and sulfonation afterwards. The negatively charged precursors were then hydrolyzed and condensed to generate hybrid sol–gel materials, which

Cuiming Wu; Tongwen Xu; Weihua Yang

2004-01-01

246

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

Microsoft Academic Search

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

S. Mazumdar; R. T. Clay

2008-01-01

247

Negatively charged excitons in semimagnetic CdSe/ZnSe/ZnMnSe quantum dots  

SciTech Connect

Low-temperature (T = 1.6 K) photoluminescence (PL) of individual CdSe/ZnSe/ZnMnSe quantum dots (QDs) with different magnitudes of the sp-d exchange interaction between the magnetic impurity ions and charge carriers has been studied in a magnetic field up to 12 T applied in the Faraday and Voigt geometry. The magnitude of the interaction was controlled by changing the fraction ({eta}{sub e,h}) of the squared wave function of charge carriers in the semimagnetic barrier by means of variation of the nonmagnetic (ZnSe) layer thickness. It is established that the sp-d exchange interaction leads to a change in the sign of the effective hole g factor even for {eta}{sub e,h} {approx} 5%, while further increase in the interaction magnitude is accompanied by a rapid growth in the magnitude of spin splitting for both electrons and holes. The quantum yield of PL exhibits a significant decrease due to nonradiative Auger recombination with the excitation of Mn ions only for {eta}{sub e,h} {approx} 12%, while the rate of the holes spin relaxation starts growing only for still higher {eta}{sub e,h} values. In a strong magnetic field perpendicular to the sample plane, the alignment of Mn spins leads to suppression of the Auger recombination only in the excited spin state. For a small rate of the hole spin relaxation, this leads to a rather unusual result: the emission from an excited trion state predominates in strong magnetic fields.

Brichkin, A. S., E-mail: brich@issp.ac.ru; Chernenko, A. V.; Chekhovich, E. A.; Dorozhkin, P. S.; Kulakovskii, V. D. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation); Ivanov, S. V.; Toropov, A. A. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2007-08-15

248

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

PubMed

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

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

2009-12-01

249

Continuum electrostatic investigations of charge transfer processes in biological molecules using a microstate description.  

PubMed

Charge transfer through biological macromolecules is essential for many biological processes such as for instance photosynthesis and respiration. In these processes, protons or electrons are transferred between titratable residues or redox-active cofactors, respectively. Often their transfer is tightly coupled. Computational methods based on continuum electrostatics are widely used in theoretical biochemistry to analyze the function of even very complex biochemical systems. These methods allow one to consider the pH and the redox potential of the solution as well as explicitly considering membrane potentials in the calculations. Combining continuum electrostatic calculations with a statistical thermodynamic analysis, it is possible to calculate equilibrium parameters such as protonation or oxidation probabilities. Moreover, it is also possible to simulate reaction kinetics by using parameters calculated from continuum electrostatics. One needs to consider that the transfer rate between two sites depends on the current charge configuration of neighboring sites. We formulate the kinetics of charge transfer systems in a microstate formalism. A unique transfer rate constant can be assigned to the interconversion of microstates. Mutual interactions between sites participating in the transfer reactions are naturally taken into account. This formalism is applied to the kinetics of electron transfer in the tetraheme-subunit and the special pair of the reaction center of Blastochloris viridis. It is shown that continuum electrostatic calculations can be used in combination with an existing rate law to obtain electron transfer rate constants. The relaxation electron transfer kinetics after photo-oxidation of the special pair of photosynthetic reaction center is simulated by a microstate formalism and it is shown to be in good agreement with experimental data. A flux analysis is used to follow the individual electron transfer steps. This method of simulating the complex kinetics of biomolecules based on structural data is a first step on the way from structural biology to systems biology. PMID:21322484

Bombarda, Elisa; Ullmann, G Matthias

2011-01-01

250

Charge-transfer photodissociation of adsorbed molecules via electron image states  

SciTech Connect

The 248 and 193 nm photodissociations of submonolayer quantities of CH{sub 3}Br and CH{sub 3}I adsorbed on thin layers of n-hexane indicate that the dissociation is caused by dissociative electron attachment from subvacuum level photoelectrons created in the copper substrate. The characteristics of this photodissociation-translation energy distributions and coverage dependences show that the dissociation is mediated by an image potential state which temporarily traps the photoelectrons near the n-hexane-vacuum interface, and then the charge transfers from this image state to the affinity level of a coadsorbed halomethane which then dissociates.

Jensen, E. T. [Physics Department, University of Northern British Columbia, 3333 University Way, Prince George, British Columbia V2N 4Z9 (Canada)

2008-01-28

251

Ab initio study of charge transport through single oxygen molecules in atomic aluminum contacts  

NASA Astrophysics Data System (ADS)

We present ab initio calculations of transport properties of atomic-sized aluminum contacts in the presence of oxygen. The experimental situation is modeled by considering a single oxygen atom (O) or one of the O2 and O3 molecules bridging the gap between electrodes forming ideal, atomically sharp pyramids. The transport characteristics are computed for these geometries with increasing distances between the leads, simulating the opening of a break junction. To facilitate comparison with experiments further, the vibrational modes of the oxygen connected to the electrodes are studied. It is found that in the contact regime, the change of transport properties due to the presence of oxygen is strong and should be detectable in experiments. All three types of oxygen exhibit a comparable behavior in their vibrational frequencies and conductances, which are well below the conductance of pure aluminum atomic contacts. The conductance decreases for an increasing number of oxygen atoms. In the tunneling regime, the conductance decays exponentially with distance and the decay length depends on whether or not oxygen is present in the junction. This fact may provide a way to identify the presence of a gas molecule in metallic atomic contacts.

Wohlthat, S.; Pauly, F.; Viljas, J. K.; Cuevas, J. C.; Schön, Gerd

2007-08-01

252

Investigation on the aggregation behaviors of DDAB/NaDEHP catanionic vesicles in the absence and presence of a negatively charged polyelectrolyte.  

PubMed

The aggregation behaviors of the cationic and anionic (catanionic) surfactant vesicles formed by didodecyldimethylammonium bromide (DDAB)/sodium bis(2-ethylhexyl) phosphate (NaDEHP) in the absence and presence of a negatively charged polyelectrolyte are investigated. The amount of the charge on the vesicle can be tuned by controlling the DDAB/NaDEHP surfactant molar ratio. The charged vesicular dispersions made of DDAB/NaDEHP are mixed with a negatively charged polyelectrolyte, poly(4-styrenesulfonic acid-co-maleic acid) sodium (PSSAMA), to form complexes. Depending on the polyelectrolyte/vesicle charge ratio, complex flocculation or precipitation occurs. Characterization of the catanionic vesicles and the complexes are performed by transmission electron microscope (TEM), Cryo-TEM, dynamic light scattering (DLS), conductivity, turbidity, zeta potential, isothermal titration calorimetry (ITC) and small-angle X-ray scattering (SAXS) measurements. PMID:21336341

Li, Feifei; Luan, Yuxia; Liu, Xiaoli; Xu, Guiying; Li, Xiuhong; Li, Xiaolong; Wang, Jie

2011-02-18

253

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

PubMed

Oxidative toxicity of semiconductor and metal nanomaterials to cells has been well established. However, it may result from many different mechanisms, some requiring direct cell contact and others resulting from the diffusion of reactive species in solution. Published results are contradictory due to differences in particle preparation, bacterial strain, and experimental conditions. It has been recently found that C(60) nanoparticles can cause direct oxidative damage to bacterial proteins and membranes, including causing a loss of cell membrane potential (depolarization). However, this did not correlate with toxicity. In this study we perform a similar analysis using fluorescent CdTe quantum dots, adapting our tools to make use of the particles' fluorescence. We find that two Gram positive strains show direct electron transfer to CdTe, resulting in changes in CdTe fluorescence lifetimes. These two strains also show changes in membrane potential upon nanoparticle binding. Two Gram negative strains do not show these effects-nevertheless, they are over 10-fold more sensitive to CdTe than the Gram positives. We find subtoxic levels of Cd(2+) release from the particles upon irradiation of the particles, but significant production of hydroxyl radicals, suggesting that the latter is a major source of toxicity. These results help establish mechanisms of toxicity and also provide caveats for use of certain reporter dyes with fluorescent nanoparticles which will be of use to anyone performing these assays. The findings also suggest future avenues of inquiry into electron transfer processes between nanomaterials and bacteria. PMID:20085260

Dumas, Eve; Gao, Cherry; Suffern, Diana; Bradforth, Stephen E; Dimitrijevic, Nada M; Nadeau, Jay L

2010-02-15

254

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

SciTech Connect

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

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

2010-01-01

255

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

256

Charging of atoms, clusters, and molecules on metal-supported oxides: A general and long-ranged phenomenon  

NASA Astrophysics Data System (ADS)

The density-functional theory is used to investigate the adsorption of Au atoms, Au clusters, and NO2 molecules on transition-metal-supported oxides. As compared to unsupported oxides, the adsorbates on supported oxide films are charged and experience a higher adsorption energy. The origin of the effect is explored by considering two different oxides (MgO and Al2O3 ) and a range of supporting metals. Moreover, the limits of the enhancement are probed by explicit calculations for thick MgO films and low coverage. The long-range character of the phenomenon is attributed to electrostatic polarization. The absolute strength depends on several contributions and their relative importance changes with system composition.

Frondelius, Pentti; Hellman, Anders; Honkala, Karoliina; Häkkinen, Hannu; Grönbeck, Henrik

2008-08-01

257

Cell type-specific activation of AKT and ERK signaling pathways by small negatively-charged magnetic nanoparticles.  

PubMed

The interaction of nanoparticles (NPs) with living organisms has become a focus of public and scientific debate due to their potential wide applications in biomedicine, but also because of unwanted side effects. Here, we show that superparamagnetic iron oxide NPs (SPIONs) with different surface coatings can differentially affect signal transduction pathways. Using isogenic pairs of breast and colon derived cell lines we found that the stimulation of ERK and AKT signaling pathways by SPIONs is selectively dependent on the cell type and SPION type. In general, cells with Ras mutations respond better than their non-mutant counterparts. Small negatively charged SPIONs (snSPIONs) activated ERK to a similar extent as epidermal growth factor (EGF), and used the same upstream signaling components including activation of the EGF receptor. Importantly, snSPIONs stimulated the proliferation of Ras transformed breast epithelial cells as efficiently as EGF suggesting that NPs can mimic physiological growth factors. PMID:23162692

Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

2012-11-16

258

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

PubMed Central

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

Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

2012-01-01

259

Negatively charged residues and hydrogen bonds tune the ligand histidine pKa values of Rieske iron-sulfur proteins.  

PubMed

Rieske proteins carry a redox-active iron-sulfur cluster, which is bound by two histidine and two cysteine side chains. The reduction potential of Rieske proteins depends on pH. This pH dependence can be described by two pK(a) values, which have been assigned to the two iron-coordinating histidines. Rieske proteins are commonly grouped into two major classes: Rieske proteins from quinol-oxidizing cytochrome bc complexes, in which the ligand histidines titrate in the physiological pH range, and bacterial ferredoxin Rieske proteins, in which the ligand histidines are protonated at physiological pH. In the study presented here, we have calculated pK(a) values of the cluster ligand histidines using a combined density functional theory/continuum electrostatics approach. Experimental pK(a) values for a bc-type and a ferredoxin Rieske protein could be reproduced. We could identify functionally important differences between the two proteins: hydrogen bonds toward the cluster, which are present in bc-type Rieske proteins, and negatively charged residues, which are present in ferredoxin Rieske proteins. We removed these differences by mutating the proteins in our calculations. The Rieske centers in the mutated proteins have very similar pK(a) values. We thus conclude that the studied structural differences are the main reason for the different pH-titration behavior of the proteins. Interestingly, the shift caused by neutralizing the negative charges in ferredoxin Rieske proteins is larger than the shift caused by removing the hydrogen bonds toward the cluster in bc-type Rieske proteins. PMID:15449929

Klingen, Astrid R; Ullmann, G Matthias

2004-10-01

260

Raman spectroscopy of intermolecular charge transfer complex between a conjugated polymer and an organic acceptor molecule  

NASA Astrophysics Data System (ADS)

Intermolecular donor-acceptor charge transfer complex (CTC) formed in the electronic groundstate between poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and 2,4,7-trinitrofluorenone (TNF) has been investigated by Raman and optical absorption spectroscopies. Blending of MEH-PPV and TNF results in appearance of the CTC absorption band in the optical gap of the both components and in changes in the characteristic MEH-PPV Raman bands including shifts, change in bandwidth, and intensity. The experimental data are similar in films and solutions indicating the CTC formation in both. We associate the low-frequency shift of the strongest MEH-PPV Raman band at ~1580 cm-1 reaching 5 cm-1 with partial electron transfer from MEH-PPV to TNF amounting ~0.2e-. We suggest that polymer conjugated segments can form the CTC of variable composition MEH-PPV:TNF=1:X, where X<=0.5 is per MEH-PPV monomer unit. Our Raman data indicate that MEH-PPV conjugated segments involved in the CTC become more planar; however, their conjugation length seemingly does not change.

Bruevich, V. V.; Makhmutov, T. Sh.; Elizarov, S. G.; Nechvolodova, E. M.; Paraschuk, D. Yu.

2007-09-01

261

An angle-resolved translational energy spectrometer for investigating low-energy, highly charged ion--atom (molecule) collisions  

SciTech Connect

An experimental apparatus for investigating low-collision energy gas-phase reactions of highly charged ions with atoms and molecules by angle-resolved translational energy spectroscopy is described. The basic function of the apparatus is to slow down highly charged ions extracted at 2--3 kV from the Cornell superconducting solenoid, cryogenic electron beam ion source (CEBIS) to energies below 100 qeV. The slowing down and monochromatization of the beam is done by an ion optical system that consists of two 180[degree] hemispherical electrostatic analyzers with a tuneable deceleration lens located between them. The low-energy beam available for experiments has an angular spread of 0.5[degree] and an energy spread of 0.4 qeV. The ion optical system is mounted on a 508 mm by 576 mm electrically isolated platform inside a large vacuum chamber, and the modular nature of the apparatus allows for quick and easy rearrangement of the ion optical elements for different experiments. A brief overview of in-plane scattering kinematics is given.

Vancura, J.; Perotti, J.J.; Flidr, J.; Kostroun, V.O. (Nuclear Science and Engineering Program, Ward Laboratory, Cornell University, Ithaca, New York 14853 (United States))

1993-11-01

262

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

263

Negative Oxygen Ion Formation in a Pulsed Inductively RF Excited Argon-Oxygen Discharge and the Influence of Highly Excited Oxygen Molecules  

NASA Astrophysics Data System (ADS)

The temporal behavior of negative oxygen ions oxygen / argon mixtures was investigated in the afterglow of a pulsed inductively excited modified GEC reactor. The objective of this investigation is an improved understanding of the production reactions of the negative ions and the loss processes of negative ions during the plasma decay phase. Collisions of O-minus ions with O atoms and metastable oxygen molecules lead to considerable electron production in the afterglow. This late supply of electrons entails a delayed formation of a so-called ion-ion plasma. Discharges with admixtures of argon (up to 8:2 argon : oxygen) are also strongly electronegative. An increase of the absolute O-minus density is observed with increasing argon fraction. At low pressures and high contents of argon it is necessary to consider an additional production reaction channel for the negative ions in order to explain the measured increase of the negative ion density. Appearance potential mass spectroscopy measurements show an increase of highly excited oxygen molecules with increasing argon fraction. It is, therefore, likely that additional negative ions are generated by dissociative attachment of highly excited metastable oxygen molecules [1]. [1] D. Hayashi and K. Kadota, J. Appl. Phys. 83 (1998) 697 This project is funded by the Bundesminister für Bildung und Forschung BMBF (FKZ 13N8052).

Katsch, H.-M.; Manthey, C.; Döbele, H.-F.

2003-10-01

264

Ultrafiltration and reverse osmosis of small non-charged molecules: a comparison study of rejection in a stirred and an unstirred batch cell  

Microsoft Academic Search

This study deals with the estimation of rejection coefficient for small non-charged molecules in an aqueous solution, with reverse osmosis and ultrafiltration membranes in a stirred and an unstirred cell. In a stirred cell with high stirring velocity, the concentration near the membrane is close to the bulk concentration. Rejection is, therefore, known with good precision. On the other hand,

S. Nicolas; B. Balannec; F. Beline; B. Bariou

2000-01-01

265

Energies of solute molecules from an atom charge-dipole interaction model with a surrounding dielectric: Application to Gibbs energies of proton transfer between carboxylic acids in water  

Microsoft Academic Search

An expression is derived for the electrostatic energy of an array of charged, polarizable atoms representing a solute molecule in a cavity in a dielectric continuum, using a generalization of the theory of the reaction field. Explicit formulas are obtained for the case of a spherical cavity. The formulas are used to calculate Gibbs energies and entropies of proton transfer

Clifford E. Felder; Jon Applequist

1981-01-01

266

Effect of negatively charged excitons on the phase coherent photorefractive effect in ZnSe quantum wells  

NASA Astrophysics Data System (ADS)

We investigate the effect of negatively charged excitons (trions) on the efficiency and dephasing rate of the phase coherent photorefractive (PCP) effect in ZnSe/Zn0.9Mg0.1Se single quantum wells using 90 fs light pulses. Intensity, temperature and spectrally dependent measurements are performed in a transient four-wave mixing configuration. In the presence of trions the PCP effect is composed of both a fast dephasing component that is caused by the formation of a trion grating and a slower decaying component caused by an exciton grating. With decreasing temperature the trion dephasing rate significantly increases while the exciton dephasing rate remains almost constant. The trion dephasing rate also increases with decreasing barrier width between the ZnSe quantum well (QW) and the GaAs substrate which is attributed to an enhanced electron density of captured substrate electrons in the QW. Model calculations based on the optical Bloch equations are in agreement with the experimentally observed PCP traces.

Kabir, A.; Wagner, H. P.

2009-03-01

267

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

268

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

269

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

NASA Astrophysics Data System (ADS)

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.

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

2007-07-01

270

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

PubMed Central

A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2×1 surface at a temperature of 80 K. Current–voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope at cryogenic temperatures, repeated measurements can be routinely taken over the same molecule. Taking advantage of this improved stability, we show that current–voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip–molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip–molecule distance. By using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single-molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices.

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

2005-01-01

271

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

272

Absence of a guiding effect and charge transfer in the interaction of keV-energy negative ions with Al2O3 nanocapillaries  

NASA Astrophysics Data System (ADS)

In this work, the efficient electron loss process was observed for the transmission of 10- to 18-keV Cu- and Cl- ions through Al2O3 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- ions were observed in the transmission, whereas no Cu- 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

2011-09-01

273

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

PubMed Central

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

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

2011-01-01

274

Propafenone blocks human cardiac Kir2.x channels by decreasing the negative electrostatic charge in the cytoplasmic pore.  

PubMed

Human cardiac inward rectifier current (IK1) is generated by Kir2.x channels. Inhibition of IK1 could offer a useful antiarrhythmic strategy against fibrillatory arrhythmias. Therefore, elucidation of Kir2.x channels pharmacology, which still remains elusive, is mandatory. We characterized the electrophysiological and molecular basis of the inhibition produced by the antiarrhythmic propafenone of the current generated by Kir2.x channels (IKir2.x) and the IK1 recorded in human atrial myocytes. Wild type and mutated human Kir2.x channels were transiently transfected in CHO and HEK-293 cells. Macroscopic and single-channel currents were recorded using the patch-clamp technique. At concentrations >1?M propafenone inhibited IKir2.x the order of potency being Kir2.3?IK1>Kir2.2>Kir2.1 channels. Blockade was irrespective of the extracellular K(+) concentration whereas markedly increased when the intracellular K(+) concentration was decreased. Propafenone decreased inward rectification since at potentials positive to the K(+) equilibrium potential propafenone-induced block decreased in a voltage-dependent manner. Importantly, propafenone favored the occurrence of subconductance levels in Kir2.x channels and decreased phosphatidylinositol 4,5-bisphosphate (PIP2)-channel affinity. Blind docking and site-directed mutagenesis experiments demonstrated that propafenone bound Kir2.x channels at the cytoplasmic domain, close to, but not in the pore itself, the binding site involving two conserved Arg residues (residues 228 and 260 in Kir2.1). Our results suggested that propafenone incorporated into the cytoplasmic domain of the channel in such a way that it decreased the net negative charge sensed by K(+) ions and polyamines which, in turn, promotes the appearance of subconductance levels and the decrease of PIP2 affinity of the channels. PMID:23648307

Amorós, Irene; Dolz-Gaitón, Pablo; Gómez, Ricardo; Matamoros, Marcos; Barana, Adriana; de la Fuente, Marta González; Núñez, Mercedes; Pérez-Hernández, Marta; Moraleda, Ignacio; Gálvez, Enrique; Iriepa, Isabel; Tamargo, Juan; Caballero, Ricardo; Delpón, Eva

2013-05-03

275

Charge overlap effects for first-order molecule-molecule interactions, through high partial wave order, using the N2-N2 interaction as a model  

NASA Astrophysics Data System (ADS)

Results are presented for the individual partial wave components of the first-order non-expanded Coulomb energy for the N2-N2 interaction as a function of intermolecular separation R, for 3·5 ?- R ?- 9·5a0 and for partial wave indices la and lb corresponding to (la + lb) ?- 8. These results permit the evaluation of the first-order Coulomb energy, its R-1 multipole expansion, and the charge overlap corrections to the multipole expansion, as a function of R, relative molecular configuration, and (la + lb). Calculations of this type are used in a discussion of the relative importance of first-order charge overlap effects, and of the convergence of the partial wave calculations, as a function of R, configuration, and (la + lb). The difficulties in obtaining reliable results for charge overlap, and related effects, are also discussed briefly.

Koide, A.; Proctor, T. R.; Allnatt, A. R.; Meath, William J.

276

Strong anisotropy in the proton emission following fragmentation of H2O molecules by impact with slow, highly charged Xenon ions  

Microsoft Academic Search

We measured the energy and angular distribution of ionic fragments produced by the interaction of 1-220 keV Xe22+ ions with water molecules. The measured distributions strongly depend on the projectile charge state and energy, as seen from the comparison of the results with previously published data for 5 keV He2+, and 2 and 90 keV Ne(3-9)+ ions. A significant forward-backward

Z. D. Pesic; R. Hellhammer; B. Sulik; N. Stolterfoht

2009-01-01

277

Isotope effect in charge-transfer collisions of slow H+ and D+ ions with H2 , HD, and D2 molecules  

NASA Astrophysics Data System (ADS)

Marked characteristics in charge-transfer cross sections between collisions of H+ and D+ ions with H2 , HD, and D2 molecules, the so-called isotope effect, are observed in the energy range from 0.18to1.0keV/u . The observed cross-section ratios ?(D++D2)/?(H++H2) of charge transfer in D++D2 and in H++H2 collisions are found to be 0.665 at 0.18keV/u and gradually increases, finally approaching unity at higher energies. Similar behavior and magnitude within the error bars of the cross-section ratios ?(H++HD)/?(H++H2) and ?(D++HD)/?(H++H2) have been observed, although the present calculation predicts a sizable difference for heteronuclear molecules. The cross section differences due to the target isotope effect are pronounced even in the high-eV to low-keV region. On the other hand, charge-transfer cross-section ratios for the same target but different projectile isotopes, e.g., ?(H++HD)/?(D++HD) and ?(D++D2)/?(H++D2) , are constant near unity, which indicates a minor role of collision-induced vibrations as compared to the target vibrational spacing. It is understood that the isotope effect in the charge transfer of ion-molecule collisions originates from the combination of a small offset in binding and vibrational energies and the different spaces occupied by the wave functions of the target H2 , HD, and D2 molecules.

Kusakabe, Toshio; Pichl, Lukáš; Buenker, Robert J.; Kimura, Mineo; Tawara, Hiroyuki

2004-11-01

278

The role of boron impurity in the activation of free charge carriers in layers of porous silicon during the adsorption of acceptor molecules  

Microsoft Academic Search

Infrared-absorption spectroscopy and electron spin resonance are used to study the role of boron impurity in the activation\\u000a of free charge carriers in layers of porous silicon that have been exposed to nitrogen dioxide acceptor molecules. It is found\\u000a that the higher the level of doping is for the substrates used in the production of porous silicon, the higher the

L. A. Osminkina; E. A. Konstantinova; K. S. Sharov; P. K. Kashkarov; V. Yu. Timoshenko

2005-01-01

279

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

280

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.; Buleau, S.; Giguère, M.; Motojima, T.; Anderson, R.; Matsumoto, J.; Kieffer, J.-C.; Légaré, F.; Shiromaru, H.; Sanderson, J.

2013-09-01

281

Using self-consistent energy surfaces to calculate the population distributions of neutral clusters and negatively charged clusters consisting of sulfuric acid and water  

NASA Astrophysics Data System (ADS)

We synthesize self-consistent Gibbs free energy surfaces for clusters of sulfuric acid, water, and bisulfate ions from a variety of sources including: a thermodynamic model of electrolyte solutions, the capillarity approximation, experimental measurements, and quantum chemical calculations. From these free energy surfaces, the equilibrium population distributions are calculated for neutral clusters of sulfuric acid and water and negatively charged clusters, consisting of sulfuric acid and water surrounding a bisulfate ion.

Smith, Jamison A.; Froyd, Karl D.; Toon, Owen B.

2013-05-01

282

The Activation of the Contact Phase of Coagulation by Physiologic Surfaces in Plasma: The Effect of Large Negatively Charged Liposomal Vesicles  

Microsoft Academic Search

The endogenous. negatively charged surface that induces activation of the contact coagulation factors was investi- gated in plasmas taken from women in late pregnancy and control subjects of child-bearing age. The plasmas from the two groups of subjects were incubated at 4#{176}C for 24 hours either in plastic or in glass tubes and the factor VII coagulant activity (VlIc) was

K. A. Mitropoulos; J. C. Martin; B. E. A. Reeves; M. P. Esnouf

283

Effect of pH and conductivity on hindered diffusion of perchlorate ions during transport through negatively charged nanofiltration and ultrafiltration membranes  

Microsoft Academic Search

Hindered (effective) diffusion of perchlorate anion (ClO4?) through negatively-charged porous nanofiltration and ultrafiltration membranes was determined by means of diffusion cell experiments. Three electrolytes, KCl, K2SO4, and CaCl2, were employed to determine their effects on the effective diffusion of perchlorate through membrane pores under varying pH levels (4, 6, 8, and 10). In addition, the effect of electrolyte concentration on

Yeomin Yoon; Gary Amy; Jaekyung Yoon

2005-01-01

284

Loading/release behavior of (chitosan/DNA)n layer-by-layer films toward negatively charged anthraquinone and its application in electrochemical detection of natural DNA damage.  

PubMed

In the present work, positively charged chitosan (CS) and negatively charged DNA were alternately adsorbed on the surface of pyrolytic graphite (PG) electrodes, forming (CS/DNA)(n) layer-by-layer films. Cyclic voltammetry (CV) results showed that negatively charged electroactive probe, 9,10-anthraquinone-2,6-disulfonate (AQDS), could be loaded into the (CS/DNA)(n) films from its solution (1 mM at pH 7.0, containing 0.1 M NaCl), designated as (CS/DNA)(n)-AQDS, and then released from the films in blank buffers. The loading/release behavior of (CS/DNA)(n) films toward AQDS was found to be obviously different between double-stranded (dsDNA) and single-stranded DNA (ssDNA). The release rate of AQDS from (CS/dsDNA)(n) films was much slower than that from the ssDNA counterparts mainly because AQDS could be intercalated into the double helix structure of dsDNA despite the repulsion between likely charged AQDS and DNA. The loading/release behavior of (CS/DNA)(n) films toward AQDS in recognition of dsDNA and ssDNA was then successfully applied to electrochemically detect the damage of natural DNA caused by Fenton reaction. To further understand the essence of the interactions involved in the AQDS loading/release process for (CS/DNA)(n) films, comparison experiments were performed, in which either positively charged intercalator brilliant cresyl blue (BCB) was used to replace AQDS as the redox probe, or poly(diallyldimethylammonium) (PDDA) with relatively high positive charge density was used to replace CS as the constituent of layer-by-layer films with DNA. The loading/release behavior of DNA films toward electroactive intercalator may open new possibilities for dsDNA/ssDNA recognition and of DNA damage detection by electrochemistry. PMID:17768042

Liu, Yi; Hu, Naifei

2007-07-28

285

Co-signaling molecules of the B7CD28 family in positive and negative regulation of T lymphocyte responses  

Microsoft Academic Search

Co-signaling molecules in the B7-CD28 family have been intensively studied over the past decade and have brought much excitement to the field of immune regulation. The discovery of new functions for the classical pathways CD80\\/CD86\\/CD28\\/CTLA-4 and the identification of novel pathways of the family, including B7-H1\\/B7-DC\\/PD-1, B7-H2\\/ICOS, B7-H3, B7-H4 and BTLA, are greatly broadening our understanding of the control of

Shengdian Wang; Lieping Chen

2004-01-01

286

A family of extracytoplasmic proteins that allow transport of large molecules across the outer membranes of gram-negative bacteria.  

PubMed Central

Seventeen fully sequenced and two partially sequenced extracytoplasmic proteins of purple, gram-negative bacteria constitute a homologous family termed the putative membrane fusion protein (MFP) family. Each such protein apparently functions in conjunction with a cytoplasmic membrane transporter of the ATP-binding cassette family, major facilitator superfamily, or heavy metal resistance/nodulation/cell division family to facilitate transport of proteins, peptides, drugs, or carbohydrates across the two membranes of the gram-negative bacterial cell envelope. Evidence suggests that at least some of these transport systems also function in conjunction with a distinct outer membrane protein. We report here that the phylogenies of these proteins correlate with the types of transport systems with which they function as well as with the natures of the substrates transported. Characterization of the MFPs with respect to secondary structure, average hydropathy, and average similarity provides circumstantial evidence as to how they may allow localized fusion of the two gram-negative bacterial cell membranes. The membrane fusion protein of simian virus 5 is shown to exhibit significant sequence similarity to representative bacterial MFPs.

Dinh, T; Paulsen, I T; Saier, M H

1994-01-01

287

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

288

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

PubMed

A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2x1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope at cryogenic temperatures, repeated measurements can be routinely taken over the same molecule. Taking advantage of this improved stability, we show that current-voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip-molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip-molecule distance. By using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single-molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices. PMID:15956214

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

2005-06-13

289

Meso-scale simulation of the line-edge structure based on resist polymer molecules by negative-tone process  

NASA Astrophysics Data System (ADS)

We studied the line edge structure forming in the negative tone process using meso scale simulations. Our simulation is based on the dissipative particle dynamics (DPD) method. The simulation model of the lithographic process is developed in which the dynamics of a polymer chain in continuous model can be observed. In the negative tone process, the cross linking reaction is the key step to obtain the high resolution patterns. First we develop the model for the cross linking reaction. From our results in the dissolution test of the film, as the density of cross links increases, the soluble film to the developing liquid changed to the swelling (or insoluble) one. Once the threshold between soluble and insoluble conditions with changing the number of cross links, we can perform two kinds of simulations; 1) layered model simulation, and 2) line pattern simulation. In the layered model, more roughened edge can be found in the case of a thick interface than in the case of a thin interface. Our simulations can be applicable to study the LER problem and the dynamics of polymer chain including the chemical reaction will be one of the important origins of LER.

Morita, Hiroshi

2011-03-01

290

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

PubMed Central

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

Ahyayauch, Hasna; Raab, Michal; Busto, Jon V.; Andraka, Nagore; Arrondo, Jose-Luis R.; Masserini, Massimo; Tvaroska, Igor; Goni, Felix M.

2012-01-01

291

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

Microsoft Academic Search

A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2×1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of

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

2005-01-01

292

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...

293

Salt effects on hydrophobic interaction and charge screening in the folding of a negatively charged peptide to a coiled coil (leucine zipper).  

PubMed

The stability of a coiled coil or leucine zipper is controlled by hydrophobic interactions and electrostatic forces between the constituent helices. We have designed a 30-residue peptide with the repeating seven-residue pattern of a coiled coil, (abcdefg)n, and with Glu in positions e and g of each heptad. The glutamate side chains prevented folding at pH values above 6 because of electrostatic repulsion across the helix dimer interface as well as within the individual helices. Protonation of the carboxylates changed the conformation from a random coil monomer to a coiled coil dimer. Folding at alkaline pH where the peptide had a net charge of -7e was promoted by the addition of salts. The nature of the charge screening cation was less important than that of the anion. The high salt concentrations (>1 M) necessary to induce folding indicated that the salt-induced folding resulted from alterations in the protein-water interaction. Folding was promoted by the kosmotropic anions sulfate and fluoride and to a lesser extent by the weak kosmotrope formate, whereas chloride and the strong chaotrope perchlorate were ineffective. Kosmotropes are excluded from the protein surface, which is preferentially hydrated, and this promotes folding by strengthening hydrophobic interactions at the coiled coil interface. Although charge neutralization also contributed to folding, it was effective only when the screening cation was partnered by a good kosmotropic anion. Folding conformed to a two-state transition from random coil monomer to coiled coil dimer and was enthalpy driven and characterized by a change in the heat capacity of unfolding of 3.9 +/- 1.2 kJ mol-1 K-1. The rate of folding was analyzed by fluorescence stopped-flow measurements. Folding occurred in a biphasic reaction in which the rapid formation of an initial dimer (kf = 2 x 10(7) M-1 s-1) was followed by an equally rapid concentration-independent rearrangement to the folded dimer (k > 100 s-1). PMID:9585569

Jelesarov, I; Dürr, E; Thomas, R M; Bosshard, H R

1998-05-19

294

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

PubMed Central

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

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

2013-01-01

295

Vacancy transfer to the K shell in very heavy quasi-molecules studied with highly charged, decelerated heavy ions  

Microsoft Academic Search

The total K-excitation cross section has been measured over a wide range of projectile charge states q for the very heavy collision systems 54Xeq+ to Xe(Z1+Z2=108) at 2.2 and 3.6 MeV u-1 and for 62Smq+ to Xe(Z1+Z2=116) at 3.6 and 4.7 MeV u-1. High projectile charge states corresponding to up to N-like ions were used and single collision conditions in

P. H. Mokler; D. H. H. Hoffmann; W. A. Schonfeldt; D. Maor; Z. Stachura; A. Warczak

1984-01-01

296

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

2011-05-23

297

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

298

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

299

CROSS SECTIONS FOR COLLISION PROCESSES OF Li ATOMS INTERACTING WITH ELECTRONS, PROTONS, MULTIPLY CHARGED IONS, AND HYDROGEN MOLECULES  

Microsoft Academic Search

The available experimental and theoretical cross section data for collision processes of Li atoms in the ground state and excited (up ton= 3) states with electrons, protons, and multiply charged ions have been collected and critically assessed. The electron-impact processes include excitation from the ground state, transitions between excited states withn= 2, 3, and ionization from all states considered. The

D. Wutte; R. K. JANEV; F. Aumayr; M. Schneider; J. Schweinzer; J. J. Smith; H. P. WINTER

1997-01-01

300

The binding of tyrosine hydroxylase to negatively charged lipid bilayers involves the N-terminal region of the enzyme  

Microsoft Academic Search

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamines. We have studied the association of recombinant human TH with model membranes by using either liposomes or silica gel beads coated with single phospholipid bilayers (TRANSIL®). The use of TRANSIL beads has allowed the determination of apparent dissociation constants (Kd) for the binding of the enzyme to negatively

Matth??as Thórólfsson; Anne P. Døskeland; Arturo Muga; Aurora Mart??nez

2002-01-01

301

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

PubMed

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

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

2013-09-08

302

The charged milieu: a major player in fertilization reactions.  

PubMed

In previous studies, we have found that negatively charged, but not uncharged, amino acids and sugars block sea urchin fertilization. These studies were developed from modeling work in non-living systems using derivatized agarose beads that suggested that charge-charge bonding may control at least some adhesive interactions. In the present study, the effects of positively charged, negatively charged and uncharged molecules were examined in the sea urchin sperm-egg system in over 300 individual trials. The results indicate that depending on the specific molecules utilized, both sperm and egg are exquisitely sensitive to charged but not uncharged molecules and to pH changes in sea water caused by some of the charged molecules. It is shown that egg activation, as well as sperm motility and sperm-egg interactions, can be affected by charged molecules. One compound, fructose-1-phosphate blocked fertilization in S. purpuratus sea urchins but not in Lytechinus pictus sea urchins. These findings indicate that charge alone cannot explain all the results. In this case, the presence of a ketone instead of an aldehyde group indicates that species-specific components may control fertilization reactions. The present study is a comprehensive survey of the effects of charge, pH and molecular structure on the fertilization activation continuum in a model system of sea urchins. PMID:15032323

Maldonado, Marcela; Weerasinghe, Gayani; Ambroise, Fabienne; Yamoah, Edward; Londono, Monica; Pelayo, Juan Carlos; Grigorian, Melina; Oppenheimer, Steven B

2004-02-01

303

Quasi-ohmic single molecule charge transport through highly conjugated meso-to-meso ethyne-bridged porphyrin wires.  

PubMed

Understanding and controlling electron transport through functional molecules are of primary importance to the development of molecular scale devices. In this work, the single molecule resistances of meso-to-meso ethyne-bridged (porphinato)zinc(II) structures (PZn(n) compounds), connected to gold electrodes via (4'-thiophenyl)ethynyl termini, are determined using scanning tunneling microscopy-based break junction methods. These experiments show that each ?,?-di[(4'-thiophenyl)ethynyl]-terminated PZn(n) compound (dithiol-PZn(n)) manifests a dual molecular conductance. In both the high and low conductance regimes, the measured resistance across these metal-dithiol-PZn(n)-metal junctions increases in a near linear fashion with molecule length. These results signal that meso-to-meso ethyne-bridged porphyrin wires afford the lowest ? value (? = 0.034 Å(-1)) yet determined for thiol-terminated single molecules that manifest a quasi-ohmic resistance dependence across metal-dithiol-PZn(n)-metal junctions. PMID:22500812

Li, Zhihai; Park, Tae-Hong; Rawson, Jeff; Therien, Michael J; Borguet, Eric

2012-05-04

304

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

305

Charge effect on the photoinactivation of Gram-negative and Gram-positive bacteria by cationic meso-substituted porphyrins  

PubMed Central

Background In recent times photodynamic antimicrobial therapy has been used to efficiently destroy Gram (+) and Gram (-) bacteria using cationic porphyrins as photosensitizers. There is an increasing interest in this approach, namely in the search of photosensitizers with adequate structural features for an efficient photoinactivation process. In this study we propose to compare the efficiency of seven cationic porphyrins differing in meso-substituent groups, charge number and charge distribution, on the photodynamic inactivation of a Gram (+) bacterium (Enterococcus faecalis) and of a Gram (-) bacterium (Escherichia coli). The present study complements our previous work on the search for photosensitizers that might be considered good candidates for the photoinactivation of a large spectrum of environmental microorganisms. Results Bacterial suspension (107 CFU mL-1) treated with different photosensitizers concentrations (0.5, 1.0 and 5.0 ?M) were exposed to white light (40 W m-2) for a total light dose of 64.8 J cm-2. The most effective photosensitizers against both bacterial strains were the Tri-Py+-Me-PF and Tri-Py+-Me-CO2Me at 5.0 ?M with a light fluence of 64.8 J cm-2, leading to > 7.0 log (> 99,999%) of photoinactivation. The tetracationic porphyrin also proved to be a good photosensitizer against both bacterial strains. Both di-cationic and the monocationic porphyrins were the least effective ones. Conclusion The number of positive charges, the charge distribution in the porphyrins' structure and the meso-substituent groups seem to have different effects on the photoinactivation of both bacteria. As the Tri-Py+-Me-PF porphyrin provides the highest log reduction using lower light doses, this photosensitizer can efficiently photoinactivate a large spectrum of environmental bacteria. The complete inactivation of both bacterial strains with low light fluence (40 W m-2) means that the photodynamic approach can be applied to wastewater treatment under natural light conditions which makes this technology cheap and feasible in terms of the light source.

2009-01-01

306

The temporal dynamics of ambivalence: changes in positive and negative affect in relation to consumption of an "emotionally charged" food.  

PubMed

Ambivalence is thought to impact consumption of food, alcohol and drugs, possibly via influences on craving, with cravers often being simultaneously drawn toward and repelled from ingestion. So far, little is known about the temporal dynamics of ambivalence, especially as it varies in relationship to consumption. Participants (n=482, 56.8% female) completed the Positive and Negative Affect Schedule prior to, immediately and 30 min after the opportunity to eat a bar of chocolate. Affective ambivalence was calculated based on the relative strengths of and discrepancy between ratings of positive and negative affect. Ambivalence peaked prior to a decision about consumption and subsequently decreased, whether or not the decision was in favor of or against consuming. Decreasing ambivalence was driven by a drop in positive affect over time; positivity decreased more rapidly in those who consumed chocolate. Findings represent a first step in characterizing the dynamics of ambivalence in interactions with a target stimulus. PMID:21741021

Hormes, Julia M; Rozin, Paul

2011-02-26

307

Effect of polar protic and polar aprotic solvents on negative-ion electrospray ionization and chromatographic separation of small acidic molecules.  

PubMed

A comprehensive study investigated the effect of polar protic (methanol and water) and polar aprotic (acetonitrile and acetone) solvents on the chromatographic separation and negative-ion electrospray (ESI) response of 49 diverse small, acidic molecules. Flow injection experiments on a triple quadrupole were used to measure the response in neat solvents after optimization of source conditions and implementation of a rigorous quality control program (the later ensured that changes in analyte response were due to the analyte/solvent measured and not changes in instrument performance over time). In all solvents, compounds with electron-withdrawing groups and extended conjugation ionized best due to resonance and inductive effects. Ionization was greatest in methanol or water for all compounds that elicited a response, thus revealing that enhanced sensitivity and lower limits of detection are achieved with polar protic solvents. Response in acetone was equal to or slightly lower than response in acetonitrile in flow injection experiments; however, the water/acetonitrile and water/acetone mobile phases produced the better chromatographic separation. Water/methanol produced slightly less satisfactory separation but the greatest overall response. This increase in response was attributed to the protic nature of methanol and the elution of compounds in a higher organic mobile phase composition (retention times were ?30% later in methanol). This work is intended to facilitate rational liquid chromatography/mass spectrometry method development for small molecule applications, including metabolomics. PMID:23066894

Huffman, Brian A; Poltash, Michael L; Hughey, Christine A

2012-11-02

308

Cationic hydrous thorium dioxide colloids - a useful tool for staining negatively charged surface matrices of bacteria for use in energy-filtered transmission electron microscopy  

PubMed Central

Background Synthesis of cationic hydrous thorium dioxide colloids (ca. 1.0 to 1.7 nm) has been originally described by Müller [22] and Groot [11] and these have been used by Groot to stain acidic glucosaminoglycans for ultrastructure research of different tissues by conventional transmission electron microscopy. Results Synthesis of colloidal thorium dioxide has been modified and its use as a suitable stain of acidic mucopolysaccharides and other anionic biopolymers from bacteria, either as whole mount preparations or as preembedment labels, is described. The differences in stain behavior relative to commonly used rutheniumred-lysine and Alcian Blue™ electron dense acidic stains has been investigated and its use is exemplified for Pseudomonas aeruginosa adjacent cell wall biopolymers. For the first time thorificated biopolymers, i.e. bacterial outer cell wall layers, have been analysed at the ultrastructural level with electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), leading to excellent contrast and signal strength for these extracellular biopolymers. Conclusion Application of cationic hydrous ThO2 colloids for tracing acidic groups of the bacterial surface and/or EPS has been shown to be rather effective by transmission electron microscopy. Because of its high electron density and its good diffusibility it stains and outlines electro-negative charges within these biopolymers. In combination with ESI, based on integrated energy-filtered electron microscopy (EFTEM) Th-densities and thus negative charge densities can be discriminated from other elemental densities, especially in environmental samples, such as biofilms.

Lunsdorf, Heinrich; Kristen, Ingeborg; Barth, Elke

2006-01-01

309

Kinetic energy release in thermal ion-molecule reactions: Single charge-transfer reactions of V sup 2+ and Ta sup 2+ with benzene  

SciTech Connect

Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) has been used to study the single charge-transfer reactions of V{sup 2+} and Ta{sup 2+} with benzene under thermal conditions. Thermal charge-transfer rate constants of 2.0 {times} 10{sup {minus}9} and 1.2 {times} 10{sup {minus}9} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} were measured for V{sup 2+} and Ta{sup 2+}, respectively. The total kinetic energy of the product ions was determined to be 1.91 {plus minus} 0.50 eV for the V{sup 2+} case and 2.82 {plus minus} 0.50 eV for the Ta{sup 2+} case. These results and a previous study of the Nb{sup 2+}-benzene single charge-transfer system suggest a simple long-distance electron-transfer mechanism proceeding by ionization of the 1a{sub 2u} orbital of benzene with significant internal excitation of the nascent C{sub 6}H{sub 6}{sup +} product.

Gord, J.R.; Freiser, B.S (Purdue Univ., West Lafayette, IN (United States)); Buckner, S.W. (Univ. of Arizona, Tucson (United States))

1991-10-17

310

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

311

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

PubMed

Using Si as the substrate, we have fabricated multiple internal reflection infrared waveguides embedded with a parallel array of nanofluidic channels. The channel width is maintained substantially below the mid-infrared wavelength to minimize infrared scattering from the channel structure and to ensure total internal reflection at the channel bottom. A Pyrex slide is anodically bonded to the top of the waveguide to seal the nanochannels, while simultaneously enabling optical access in the visible range from the top. The Si channel bottom and sidewalls are thermally oxidized to provide an electrically insulating barrier, and the Si substrate surrounding the insulating SiO(2) layer is selectively doped to function as a gate. For fluidic field effect transistor (FET) control, a DC potential is applied to the gate to manipulate the surface charge on SiO(2) channel bottom and sidewalls and therefore their zeta-potential. Depending on the polarity and magnitude, the gate potential can accelerate, decelerate, or reverse the flow. Here, we demonstrate that this nanofluidic infrared waveguide can be used to monitor the FET flow control of charged, fluorescent dye molecules during electroosmosis by multiple internal reflection Fourier transform infrared spectroscopy. Laser scanning confocal fluorescence microscopy is simultaneously used to provide a comparison and verification of the IR analysis. Using the infrared technique, we probe the vibrational modes of dye molecules, as well as those of the solvent. The observed infrared absorbance accounts for the amount of dye molecules advancing or retracting in the nanochannels, as well as adsorbing to and desorbing from the channel bottom and sidewalls. PMID:18231663

Oh, Youn-Jin; Gamble, Thomas C; Leonhardt, Darin; Chung, Chan-Hwa; Brueck, Steven R J; Ivory, Cornelius F; Lopez, Gabriel P; Petsev, Dimiter N; Han, Sang M

2007-11-22

312

Structural characterization of negatively charged glycosaminoglycans using high-energy (50-150 keV) collisional activation  

NASA Astrophysics Data System (ADS)

Anionic glycosaminoglycan mono- and disaccharides (IVA, IH and IS) were subjected to very high-energy collisions (50-150 keV ion kinetic energy prior to collision) with Neon gas in an accelerator mass spectrometer, to explore the possibility of using this method to structurally characterize anionic sugars. Experiments were also conducted for the Na+.IH2- and Na+.IS3- sodiated complexes. This high-energy ion collision technique is applied here to sugars for the first time. Low-energy collision-induced dissociation (CID) measurements obtained using resonance excitation in a quadrupole ion-trap are presented for comparison. The high-energy measurements produce a rich variety of fragment ions, illustrating the general utility of the technique for providing detailed information for structurally characterizing sugar ions. We discuss the observed fragmentation patterns with reference to the known fragmentation behavior of small gas-phase monoanions, multiply charged anions and cation-dianion complexes.

Taylor, Christopher J.; Burke, Ruth M.; Wu, Bohan; Panja, Subhasis; Nielsen, Steen Brøndsted; Dessent, Caroline E. H.

2009-08-01

313

Binding of cationic pentapeptides with modified side chain lengths to negatively charged lipid membranes: Complex interplay of electrostatic and hydrophobic interactions.  

PubMed

Basic amino acids play a key role in the binding of membrane associated proteins to negatively charged membranes. However, side chains of basic amino acids like lysine do not only provide a positive charge, but also a flexible hydrocarbon spacer that enables hydrophobic interactions. We studied the influence of hydrophobic contributions to the binding by varying the side chain length of pentapeptides with ammonium groups starting with lysine to lysine analogs with shorter side chains, namely omithine (Orn), alpha, gamma-diaminobutyric acid (Dab) and alpha, beta-diaminopropionic acid (Dap). The binding to negatively charged phosphatidylglycerol (PG) membranes was investigated by calorimetry, FT-infrared spectroscopy (FT-IR) and monolayer techniques. The binding was influenced by counteracting and sometimes compensating contributions. The influence of the bound peptides on the lipid phase behavior depends on the length of the peptide side chains. Isothermal titration calorimetry (ITC) experiments showed exothermic and endothermic effects compensating to a different extent as a function of side chain length. The increase in lipid phase transition temperature was more significant for peptides with shorter side chains. FTIR-spectroscopy revealed changes in hydration of the lipid bilayer interface after peptide binding. Using monolayer techniques, the contributions of electrostatic and hydrophobic effects could clearly be observed. Peptides with short side chains induced a pronounced decrease in surface pressure of PG monolayers whereas peptides with additional hydrophobic interactions decreased the surface pressure much less or even lead to an increase, indicating insertion of the hydrophobic part of the side chain into the lipid monolayer. PMID:22433675

Hoernke, Maria; Schwieger, Christian; Kerth, Andreas; Blume, Alfred

2012-07-01

314

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

2012-05-08

315

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

316

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

PubMed

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

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

2009-08-27

317

Second-Harmonic Generation in Langmuir-Blodgett Monolayer of a Two-Dimensional Charge-Transfer Molecule: N,N'-Dioctadecyl-4,6-Dinitro-1,3-Diaminobenzene  

NASA Astrophysics Data System (ADS)

A new amphiphilic dye, N,N'-dioctadecyl-4,6-dinitro-1,3-diaminobenzene (DIODD), which is capable of forming Langmuir-Blodgett (LB) films, has been synthesized and represents a model for a two-dimensional charge transfer (2-D CT) molecule. The stable Langmuir-Blodgett monolayers of a 1:1 mixture of dye and arachidic acid were deposited onto a glass substrate. The Langmuir-Blodgett monolayers exhibited a well-defined fringing pattern resulting from second-harmonic generation. These experimental results have been analyzed in connection with theoretical calculations for the model compounds. Our theoretical calculations demonstrate the superiority of two-dimensional charge transfer molecules over one-dimensional charge transfer molecules in the case in which the LB molecules incline from the normal to the substrate. The molecular orientation of the DIODD molecule is close to the optimum orientation applicable for maximizing ?111(2). Second-order nonlinear optical susceptibilities ?111(2) and ?133(2) determined by analyzing the data were 2.2× 10-8 and 7.7× 10-9 esu, respectively at a tilt angle of 60°. This work presents the first example of a two-dimensional charge transfer molecule displaying second-harmonic generation from a Langmuir-Blodgett monolayer.

Nalwa, Hari S.; Nakajima, Kenji; Watanabe, Toshiyuki; Nakamura, Kazushi; Yamada, Akira; Miyata, Seizo

1991-05-01

318

Conserved negative charges in the transmembrane segments of subunit K of the NADH:ubiquinone oxidoreductase determine its dependence on YidC for membrane insertion.  

PubMed

All members of the Oxa1/Alb3/YidC family have been implicated in the biogenesis of respiratory and energy transducing proteins. In Escherichia coli, YidC functions together with and independently of the Sec system. Although the range of proteins shown to be dependent on YidC continues to increase, the exact role of YidC in insertion remains enigmatic. Here we show that YidC is essential for the insertion of subunit K of the NADH:ubiquinone oxidoreductase and that the dependence is due to the presence of two conserved glutamate residues in the transmembrane segments of subunit K. The results suggest a model in which YidC serves as a membrane chaperone for the insertion of the less hydrophobic, negatively charged transmembrane segments of NuoK. PMID:19959836

Price, Claire E; Driessen, Arnold J M

2009-12-03

319

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

SciTech Connect

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

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

2007-12-15

320

Three-way Interaction between 14-3-3 Proteins, the N-terminal Region of Tyrosine Hydroxylase, and Negatively Charged Membranes*  

PubMed Central

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of catecholamines, is activated by phosphorylation-dependent binding to 14-3-3 proteins. The N-terminal domain of TH is also involved in interaction with lipid membranes. We investigated the binding of the N-terminal domain to its different partners, both in the unphosphorylated (TH-(1–43)) and Ser19-phosphorylated (THp-(1–43)) states by surface plasmon resonance. THp-(1–43) showed high affinity for 14-3-3 proteins (Kd ? 0.5 ?m for 14-3-3? and -? and 7 ?m for 14-3-3?). The domains also bind to negatively charged membranes with intermediate affinity (concentration at half-maximal binding S0.5 = 25–58 ?m (TH-(1–43)) and S0.5 = 135–475 ?m (THp-(1–43)), depending on phospholipid composition) and concomitant formation of helical structure. 14-3-3? showed a preferential binding to membranes, compared with 14-3-3?, both in chromaffin granules and with liposomes at neutral pH. The affinity of 14-3-3? for negatively charged membranes (S0.5 = 1–9 ?m) is much higher than the affinity of TH for the same membranes, compatible with the formation of a ternary complex between Ser19-phosphorylated TH, 14-3-3?, and membranes. Our results shed light on interaction mechanisms that might be relevant for the modulation of the distribution of TH in the cytoplasm and membrane fractions and regulation of l-DOPA and dopamine synthesis.

Halskau, ?yvind; Ying, Ming; Baumann, Anne; Kleppe, Rune; Rodriguez-Larrea, David; Almas, Bj?rg; Haavik, Jan; Martinez, Aurora

2009-01-01

321

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

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

322

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

SciTech Connect

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

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

2008-05-21

323

Water-molecule fragmentation induced by charge exchange in slow collisions with He+ and He2+ ions in the keV-energy region  

NASA Astrophysics Data System (ADS)

Charge exchange and fragmentation in the collision systems He2++H2O and He++H2O are theoretically investigated at projectile energies of a few keV. The calculations are based on the electron nuclear dynamics (END) method which solves the time-dependent Schrödinger equation. Total and differential cross sections for charge exchange are evaluated by averaging over 10 orientations of the H2O molecule. Summed total electron capture cross sections are found to be in good agreement with available experimental data. Projectile scattering was studied in the full angular range with respect to the incident beam direction. The theory provides a description of the fragmentation mechanisms such as Coulomb explosion and binary collision processes. For impact parameters below 3.5a.u. , we find that single and double electron capture occurs, resulting always in full fragmentation of H2O independent of the target orientation for He2+3 ions. Hydrogen and oxygen fragments and its respective ions, are studied as a function of emission angle and energy. In the binary collisions regime the theoretical results are found to be in excellent agreement with previous experimental data. In the Coulomb explosion regime the theoretical data are found to peak at specific angles including 90°, which is consistent with the experiment.

Cabrera-Trujillo, R.; Deumens, E.; Öhrn, Y.; Quinet, O.; Sabin, J. R.; Stolterfoht, N.

2007-05-01

324

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.

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

325

Pair Tunneling through Single Molecules  

NASA Astrophysics Data System (ADS)

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

Raikh, Mikhail

2007-03-01

326

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.

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

2010-01-01

327

Optimization of molecular cavities in the PCM of neutral molecules using charge dependent atomic radii: applications to the semi-empirical AM1 and MNDO\\/PM3 methods  

Microsoft Academic Search

An improvement in the results from the polarizable continuum model (PCM), when coupled to the AM1 and MNDO\\/PM3 semi-empirical methods, has been obtained by an optimization of the molecular cavities using charge-dependent atomic radii. A set of neutral molecules, containing different functional groups, was used to parametrize functions relating Mulliken atomic net charges to atomic radii. Another set of neutral

Paulo F. B. Gonçalves; Paolo R. Livotto

1999-01-01

328

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

PubMed

The adhesion and cohesion of water molecules on graphene-coated and bare copper and mica substrates under charge injection have been extensively studied by first-principles calculations. Water adsorption on graphene-coated copper surface is weakened by injecting negative charges into the substrate, while enhanced by positive charges. Both negatively and positively charge injecting on graphene-coated mica strengthen the adsorption between water and the surface. While the adhesive and cohesive energies of water adsorption on charged bare copper and mica exhibit similar trends and much stronger response to charge injection. The charge sensitivity of water adsorbing on positively charged surfaces is significantly weakened by the graphene coating layer, mainly due to lower interfacial charge exchange. Our results suggest a viable way to modify water adsorption on a graphene-coated surface and unveil the role of graphene as a passivation layer for the wetting of a charged substrate. PMID:24056998

Guo, Yufeng; Guo, Wanlin

2013-09-13

329

Pair tunnelling through a molecule: linear thermopower  

NASA Astrophysics Data System (ADS)

We present the calculations of the linear thermopower in single electron molecular transistors. The molecule with its vibrational internal degrees of freedom used as central object in a single electron transistor can in some cases be characterised by negative effective charging energy. This allows to model the system by Anderson Hamiltonian with negative U. Here we extend the previous calculations of the conductance of such system and study the linear thermopower of a dot characterised by negative value of the on-dot interaction U. We focus on the weak tunnelling limit, for which a rate equation approach is valid.

Gierczak, M.; Wysoki?ski, K. I.

2008-03-01

330

Structure and electronic properties of Hn@C20 molecule  

NASA Astrophysics Data System (ADS)

Density functional theory has been employed to optimize the structure of endohedral doped C20 fullerene. We have also investigated electronic properties. We have found that C20 cage can accommodate up to 8 hydrogen atoms. Some hydrogen atoms get chemisorbed on the inner surface of C20 cage and form C-H bond. Structural deformation is found to increase with increase in H-atoms. From the analysis of electronic properties, we observe that due to endohedral doping of hydrogen atoms inside C20, H-atoms acquire net negative charge by accepting electrons and fullerene molecules acquire positive charge by donating electrons to H-atoms. For endohedral complexes where H3 triangular molecule formation takes place, the nature of net charge transfer changes, i.e. fractional electronic charge is transferred from H-atoms to fullerene. C20 doped with odd number of H-atoms should be more reactive compared to the even number case. Most of the present results are similar to those of endohedral C60.Research highlightsC20 cage may accommodate up to 8 hydrogen atoms. For more than 8 hydrogen atoms, cage wall eventually breaks and binding energy changes drastically. H-atoms acquire net negative charge by accepting electrons and fullerene molecule acquires positive charge. For complexes where H3 triangular molecule formation takes place, the nature of charge transfer gets reversed. C20 doped with odd number of H-atoms should be more reactive compared to the even number case.

Kumar, Ranjan; Rani, Anita

2011-03-01

331

Effects of introducing negative charges into the molecular surface of thermolysin by site-directed mutagenesis on its activity and stability.  

PubMed

Thermolysin is remarkably activated and stabilized by neutral salts, and surface charges are suggested important in its activity and stability. The effects of introducing negative charge into the molecular surface on its activity and stability are described. Seven serine residues were selected, and each of them was changed for aspartate by site-directed mutagenesis in a thermolysin mutant. In the hydrolysis of N-[3-(2-furyl)acryloyl]-glycyl-l-leucine amide, the k(cat)/K(m) values of all mutants were almost similar to that of the wild-type enzyme (WT). However, those of six out of seven mutants were enhanced 17-19 times with 4 M NaCl, being slightly higher than WT. The remaining casein-hydrolyzing activities of the S53D and S65D mutants (Ser53 and Ser65 are replaced with Asp, respectively) after 30-min incubation with 10 mM CaCl(2) at 85 degrees C were 78 and 63%, being higher than those of WT (51%) and the other mutants (35-53%). S53D was stabilized with increase in the enthalpy change of activation for thermal inactivation while S65D was with decrease in the entropy change of activation. The stability of WT was enhanced by CaCl(2) and reached the level of S53D and S65D at 100 mM, suggesting that S53D and S65D might be stabilized by reinforcement of the Ca(2+)-binding structures. PMID:18187054

Takita, Teisuke; Aono, Takahiro; Sakurama, Haruko; Itoh, Takafumi; Wada, Takumi; Minoda, Masashi; Yasukawa, Kiyoshi; Inouye, Kuniyo

2007-12-15

332

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

NASA Astrophysics Data System (ADS)

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

Guo, Yufeng; Guo, Wanlin

2013-10-01

333

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

334

Intramolecular excited-state electron transfer in a covalently linked porphyrin-viologen molecule: direct observation of the charge-separated intermediate by resonance Raman spectroscopy  

SciTech Connect

The authors wish to report the observation of intramolecular excited-state electron transfer in porphyrin-viologen 1 by resonance Raman (RR) spectroscopy. The literature contains numerous examples of photochemical studies of porphyrins covalently linked to various electron acceptor units. Other workers have investigated long-range excited-state electron transfer in rigid model systems. In many instances, electron-transfer quenching of the porphyrin excited state has been inferred from fluorescence quenching experiments or lifetime measurements. Both fluorescence quenching and shortened lifetimes may result from processes other than electron transfer, however. Direct evidence for excited-state electron transfer requires techniques such as absorption spectroscopy or ESR spectroscopy. For example, in a series of porphyrin-viologen molecules related to 1 it was found that fluorescence quenching does occur, but the data were inconclusive with respect to whether the quenching results in electron transfer to the viologen center. They now describe a study in which they correlate the typical fluorescence and lifetime because the reduced viologen, Bz/sub 2/V/sup .+/ is easily detected by RR spectroscopy. Importantly, the porphyrin-viologen system appears to yield relatively long-lived charge-separated species following photoexcitation.

McMahon, R.J.; Force, R.K.; Patterson, H.H.; Wrighton, M.S.

1988-04-13

335

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

SciTech Connect

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

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

2000-01-27

336

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

337

Nanoscale space charge generation in local oxidation nanolithography  

NASA Astrophysics Data System (ADS)

We have measured the surface potential and the space charge generated during the first stages of atomic force microscopy field-induced oxidation. Space charge densities are about 1017 cm-3 for oxidation times below 10 ms. In a dry atmosphere, the surface potential is negative. However, in humid air the surface potential could be either positive or negative. This effect is attributed to a screening effect of the water molecules. These results explain and support the use of local oxidation patterns as templates for building molecular architectures. They also establish the space charge build up as an intrinsic feature in local oxidation experiments.

Chiesa, Marco; Garcia, Ricardo

2010-06-01

338

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

339

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, R.N.

1990-01-03

340

Charge injection/ejection and trapping in low-density polyethylene at low and medium fields  

NASA Astrophysics Data System (ADS)

Very long time dc measurements have been carried out to analyze charge injection/ejection and trapping in low-density polyethylene. The basic idea was to compare the total charge involved in the charging step and the total charge stored in the material. The equality of the two charges demonstrates that the charge carriers do not pass through the sample. The injected electrons are trapped very close to the cathode to form a negative layer. It is suggested that near the anode the field ionizes the impurity atoms and/or the neutral molecules associated with structural defects to produce positive ions.

Neagu, Eugen R.; Marat-Mendes, Jose N.

2003-07-01

341

Alteration of negatively charged residues in the 89 to 99 domain of apoA-I affects lipid homeostasis and maturation of HDL.  

PubMed

In this study, we investigated the role of positively and negatively charged amino acids within the 89-99 region of apolipoprotein A-I (apoA-I), which are highly conserved in mammals, on plasma lipid homeostasis and the biogenesis of HDL. We previously showed that deletion of the 89-99 region of apoA-I increased plasma cholesterol and phospholipids, but it did not affect plasma triglycerides. Functional studies using adenovirus-mediated gene transfer of two apoA-I mutants in apoA-I-deficient mice showed that apoA-I[D89A/E91A/E92A] increased plasma cholesterol and caused severe hypertriglyceridemia. HDL levels were reduced, and approximately 40% of the apoA-I was distributed in VLDL/IDL. The HDL consisted of mostly spherical and a few discoidal particles and contained pre?1 and ?4-HDL subpopulations. The lipid, lipoprotein, and HDL profiles generated by the apoA-I[K94A/K96A] mutant were similar to those of wild-type (WT) apoA-I. Coexpression of apoA-I[D89A/E91A/E92A] and human lipoprotein lipase abolished hypertriglyceridemia, restored in part the ?1,2,3,4 HDL subpopulations, and redistributed apoA-I in the HDL2/HDL3 regions, but it did not prevent the formation of discoidal HDL particles. Physicochemical studies showed that the apoA-I[D89A/E91A/E92A] mutant had reduced ?-helical content and effective enthalpy of thermal denaturation, increased exposure of hydrophobic surfaces, and increased affinity for triglyceride-rich emulsions. We conclude that residues D89, E91, and E92 of apoA-I are important for plasma cholesterol and triglyceride homeostasis as well as for the maturation of HDL. PMID:21504968

Kateifides, Andreas K; Gorshkova, Irina N; Duka, Adelina; Chroni, Angeliki; Kardassis, Dimitris; Zannis, Vassilis I

2011-04-19

342

Charge Challenge  

NSDL National Science Digital Library

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

Kansas, University O.

2006-01-01

343

Exploring the pH dependent SERS spectra of 2-mercaptoimidazole molecule adsorbed on silver nanocolloids in the light of Albrecht's "A" term and Herzberg-Teller charge transfer contribution.  

PubMed

The pH dependent surface-enhanced Raman scattering (SERS) spectra of biologically and industrially significant, 2-mercaptoimidazole (2-MI) molecule at 1.0×10(-10)M concentration have been investigated. The pH dependent SERS spectra are compared with the corresponding normal Raman spectra (NRS) of the molecule. The vibrational analyses of the pH dependent NRS spectra of the molecule reveal that in the acidic pH medium, the cationic form of the molecule is preponderant, while in the neutral pH, the existence of the cationic, normal, ylidic, and anionic forms of the molecule are all prevalent. However, in the alkaline pH medium, the anionic form of the molecule is estimated to be dominant. The SERS spectral analyses suggest the predominant adsorption of the cationic and the normal forms of the molecule on the nanocolloidal silver surface at acidic pH of the medium. However, at neutral pH, the cationic and/or normal, ylidic forms of the molecule take active part in the adsorption process, while considerable interactions of the normal, ylidic and/or anionic forms of the molecule with the nanocolloidal silver surface are presaged at alkaline pH of the medium. The genesis of selective enhancements of the Raman bands in the SERS spectra of the molecule recorded at various pH values of the medium has been unveiled from the view of the Albretcht's "A" and Herzberg-Teller (HT) charge transfer (CT) contribution. PMID:23540827

Chandra, Subhendu; Chowdhury, Joydeep; Ghosh, Manash; Talapatra, G B

2013-03-13

344

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

PubMed

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

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

2008-12-24

345

Antibacterial activity of highly negative charged polyoxotungstates, K 27[KAs 4W 40O 140] and K 18[KSb 9W 21O 86], and Keggin-structural polyoxotungstates against Helicobacter pylori  

Microsoft Academic Search

The antibacterial activity of polyoxometalates (PMs) against Helicobacter pylori was investigated based on determinations of minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC), time-killing of the bacteria, bacterial morphology and PM-uptake into the bacteria cell. The result of MIC values revealed that, of 13 PMs used in this study, highly negative-charged polyoxotungstates, such as K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural

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

2005-01-01

346

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

Microsoft Academic Search

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

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

2001-01-01

347

Solitons in finite- and infinite-length negative-defect trans-polyacetylene and the corresponding Brooker (polymethinecyanine) cations. II. Charge density wave  

NASA Astrophysics Data System (ADS)

The charge density wave structures of Brooker cations C 2 n-1 H 2 n+3 N +2 and their isoelectronic polyenes C 2 n+1 H -2 n+3 are studied using ab initio SCF, AM1, and an empirical technique. The net charge on the soliton in the Brooker ions is +1 with no net charge residing on the atoms at the chain ends. Hence two ? electrons are confined to the chain end regions: the properties and energy levels of the central region closely resemble those of the polyene cations rather than the isoelectronic polyene anions. In both the polyene and Brooker ions, the charge density wave is predicted to be slightly broader than that found previously (part I of this paper) for the corresponding geometric soliton; at least 20 CH units are required between the soliton centre and the chain ends in order that the infinite-chain limit of the soliton is established. When the chain length exceeds 17 CH units, it was shown in part I that AM1 calculations predict a lowering of the symmetry of the equilibrium geometry from C 2v to C s, with the geometric soliton localized at one end of the chain. Here, the charge distribution is shown to follow the geometric soliton, retaining its qualitative nature. Ions with asymmetric structures would be very useful as molecular switches as a small applied electric field could cause the ion to isomerize, with the soliton carrying its charge to the distant end of the ion.

Craw, J. S.; Reimers, J. R.; Bacskay, G. B.; Wong, A. T.; Hush, N. S.

1992-11-01

348

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

NASA Astrophysics Data System (ADS)

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

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

2006-04-01

349

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

Microsoft Academic Search

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

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

1998-01-01

350

Imaging compaction of single supercoiled DNA molecules by atomic force microscopy.  

PubMed

Supercoiled pGEMEX DNA, 3993 bp in length, was immobilized on different substrates (freshly cleaved mica, standard amino mica and modified amino mica with increased hydrophobicity and surface charge density compared with standard amino mica) and was visualized by atomic force microscopy (AFM) in air. Plectonemically supercoiled DNA (scDNA) molecules, as well as extremely compacted single molecules, were visualized on amino-modified mica, characterized by increased hydrophobicity and surface charge density. We show four-fold increase in DNA folding on the mica surface with high positive charge density. This result is consistent with a strongly enhanced molecular flexibility facilitated by shielding of the DNA phosphate charges. The formation of minitoroids with about a 50 nm diameter and molecules in spherical conformation was the final stage of single molecule compaction. A possible model of conformational transitions for scDNA in vitro in the absence of protein is proposed based on AFM image analysis. Compaction of the single scDNA molecules, up to minitoroids and spheroids, appears to be caused by screening of the negatively charged DNA phosphate groups. The high surface charge density from positively charged amino groups on mica, on which DNA molecules were immobilized, is an obvious candidate for the screening effect. PMID:19202207

Limanskaya, Olga Y; Limanskii, Alex P

2008-12-01

351

Trapped-molecule charge-transfer complexes with huge dipoles: M-C(2)F(6)-X (M = Na to Cs, X = Cl to I).  

PubMed

Novel intermolecular complexes, with a small molecule sterically trapped between a pair of ions, are designed and characterized. The molecule is found to undergo minor shape distortions and to remain almost neutral, and the complexes to have very large dipole moments (up to approximately 40 D). The systems' stability, ion-molecule interaction and stored energy are investigated, and the vertical excitation, ionization and electron-attachment are described. Variations of geometry and of the above properties with the alkali-metal and halogen components are analysed as well. PMID:19030594

Naumkin, Fedor Y

2008-10-17

352

A pAD1Encoded Small RNA Molecule, mD, Negatively Regulates Enterococcus faecalis Pheromone Response by Enhancing Transcription Termination  

Microsoft Academic Search

pAD1 is a 60-kb hemolysin-bacteriocin plasmid in Enterococcus faecalis that encodes a conjugative mating response to a peptide sex pheromone, cAD1, secreted by plasmid-free bacteria. The pheromone response is regulated by two proteins: TraE1, which positively regulates all or most conjugative structural genes, and TraA, which negatively regulates traE1. TraA binds to pAD1 DNA at the iad (encoding the inhibitor

HARUYOSHI TOMITA; DON B. CLEWELL

2000-01-01

353

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

Microsoft Academic Search

The effect of chemical modification of metal oxide surface with dye molecules in organic-inorganic hybrid solid solar cells was studied by using double layered cells consisting of poly(3-hexylthiophene) (P3HT) and a flat layer of dense TiO2. The external quantum efficiency of the chemically modified cell was nearly double that expected from the photosensitizing effect of the dye molecules. The additional

Naomi Kudo; Satoshi Honda; Yuta Shimazaki; Hideo Ohkita; Shinzaburo Ito; Hiroaki Benten

2007-01-01

354

Human Skin Cells Synthesize HLA-DR Molecules of the Same Charge and Molecular Weight as those Synthesized by Autologous Lymphocytes  

Microsoft Academic Search

Between 5 and 14% of human skin cells, separated by trypsinization, express HLA-DR antigen as detected by indirect immunofluorescence with monoclonal anti-DR antibody. To determine the source and structure of these DR molecules, skin cell suspensions were biosynthetically labeled with 35S-methionine and the radiolabeled DR molecules were analyzed by the method of two-dimensional polyacrylamide gel electrophoresis. The results indicated the

Vera B. Morhenn; Dominique J. Charron; Edgar G. Engleman

1982-01-01

355

Negative Charges in the Flexible N-Terminal Domain of Rho GDP-Dissociation Inhibitors (RhoGDIs) Regulate the Targeting of the RhoGDI-Rac1 Complex to Membranes.  

PubMed

In its resting state, Rho GDP-dissociation inhibitor (RhoGDI) ? forms a soluble cytoplasmic heterodimer with the GDP-bound form of Rac. Upon stimulation, the dissociation of RhoGDI? from the RhoGDI?-Rac complex is a mandatory step for Rac activation; however, this mechanism is poorly understood. In this study, we examined how the cytoplasm/membrane cycles of the RhoGDI-Rac complex are regulated, as well as where RhoGDI dissociates from the RhoGDI-Rac complex, during Fc?R-mediated phagocytosis. The negatively charged and flexible N terminus (25 residues) of RhoGDI?, particularly its second negative amino acid cluster possessing five negatively charged amino acids, was a pivotal regulator in the cytoplasm/membrane cycles of the RhoGDI-Rac complex. We also found that RhoGDI? translocated to the phagosomes as a RhoGDI?-Rac1 complex, and this translocation was mediated by an interaction between the polybasic motif in the C terminus of Rac1 and anionic phospholipids produced on phagosomes, such as phosphatidic acid, that is, by a phagosome-targeting mechanism of Rac1. Thus, we demonstrated that the targeting/accumulation of the RhoGDI?-Rac1 complex to phagosomes is regulated by a balance between three factors: 1) the negatively charged and flexible N-terminal of RhoGDI?, 2) the binding affinity of RhoGDI? for Rac1, and 3) anionic phospholipids produced on phagosomes. Moreover, we demonstrated that the mechanism of targeting/accumulation of the RhoGDI?-Rac1 complex is also applicable for the RhoGDI?-Rac1 complex. PMID:23918979

Ueyama, Takehiko; Son, Jeonghyun; Kobayashi, Takeshi; Hamada, Takeshi; Nakamura, Takashi; Sakaguchi, Hirofumi; Shirafuji, Toshihiko; Saito, Naoaki

2013-08-05

356

A consistent parametrisation for the production rates of negatively charged hadrons and neutral strange particles in nucleon-nucleon, nucleon-nucleus and nucleus-nucleus collisions  

Microsoft Academic Search

A parametrisation of negative hadron and neutral strange particle production was developed which consistently describes presently available data from nucleon-nucleon, nucleon-nucleus and nucleus-nucleus collisions at a beam energy of 200 GeV per nucleon. Average multiplicities of negative hadrons are found to be proportional to the number of wounded nucleons, averageKs0 multiplicities proportional to the number of wounded quarks, and average

K. Kadija; I. Derado; N. Schmitz; P. Seyboth

1995-01-01

357

Charge exchange in CO-oxidation with supported gold clusters  

NASA Astrophysics Data System (ADS)

The oxidation of CO molecules bound to supported gold clusters evolves through a series of configurational changes along the potential energy surface of the total system. The possibilities of theoretical approaches and models for description of catalytic processes are analyzed, and, in particular, the vulnerability of the DFT method is shown for such processes. The analysis of experimental data shows that the formation of the CO2 molecule occurs via a straightforward chemical process, which competes with a charge exchange process involving formation of negatively charged gold clusters. The structure of the gold cluster for one pathway involves the planar form whereas the other pathway goes via the two-layer cluster structure. From this information, we can infer the selectivity and efficiency of the catalyst as functions of the cluster size and determine that the typical distance for the tunnelling electron transition to form negatively charged clusters is 1-2?nm that means that this electron is taken from the support.

Berry, R. S.; Smirnov, B. M.

2012-03-01

358

Polymer flocculation mechanism in animal slurry established by charge neutralization.  

PubMed

Flocculation and filtration of animal manure is practically and environmentally beneficial. However, the flocculation mechanism in manure need to be clarified to use the technique efficiently rather than relying on trial-and-error. Manures were flocculated with polyacrylamides. Floc size, dewaterability, dry matter and turbidity were measured. At optimal polymer volume, the charge neutralization was determined, i.e. amount of negative manure particle charge neutralized by positive polymer charge. The optimal cationic polymer properties were linear and very high molecular weight, which caused efficient particle catching. And it had medium charge density, which caused efficient particle attachment. The required charge neutralization was 5-23% (15% for the optimal polymer). Polymer bridging proved the dominant flocculation mechanism; patch flocculation may be slightly significant for some polymers, while coagulation proved insignificant. Manure's high ionic strength, high dry matter content and highly charged small molecules caused bridging to be more dominant in manure than in other typically flocculated media. PMID:22196952

Hjorth, Maibritt; Jørgensen, Bodil Ulbjerg

2011-12-08

359

Evidence for the lower limit of the reaction window of endoergicities applicable to triple-electron-capture reactions of fast-moving doubly charged ions with atoms and molecules  

NASA Astrophysics Data System (ADS)

It has been proposed that the endoergicities of triple-electron-capture (TEC) reactions involving doubly charged ions must fall within a reaction window from 12 to 33 eV in order that the reactions have a finite probability. The upper limit has been confirmed previously in experiments involving Cl2+ and O2+ ions interacting with krypton. The lower limit was studied by reacting O2+ with CS2 molecules. It was shown that TEC reactions did not occur significantly below an endoergicity of about 10 eV, thus confirming the approximate lower limit for the window.

Jeffreys, N.; Griffiths, I. W.; Parry, D. E.; Harris, F. M.

1997-06-01

360

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

SciTech Connect

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

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

2007-04-30

361

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

362

Consistent parametrisation for the production rates of negatively charged hadrons and neutral strange particles in nucleon-nucleon, nucleon-nucleus and nucleus-nucleus collisions.  

National Technical Information Service (NTIS)

A parametrisation of negative hadron and neutral strange particle production was developed which consistently describes presently available data from nucleon-nuceon, nucleon-nucleus, and nucleus-nucleus collisions at a beam energy of 200 GeV per nucleon. ...

K. Kadija I. Derado N. Schmitz P. Seyboth

1994-01-01

363

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

PubMed

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(-) and a Na(+) 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(+) and F(-) 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 ?C(p) stays positive and even increases slightly upon charging the Na(+) ion, it decreases upon charging the F(-) 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. PMID:23534665

Sedlmeier, Felix; Netz, Roland R

2013-03-21

364

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

NASA Astrophysics Data System (ADS)

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- and a Na+ 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+ and F- 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 ?Cp stays positive and even increases slightly upon charging the Na+ ion, it decreases upon charging the F- 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.

2013-03-01

365

Crucial roles of charged saccharide moieties in survival of gram negative bacteria against protamine revealed by combination of grazing incidence x-ray structural characterizations and Monte Carlo simulations  

NASA Astrophysics Data System (ADS)

Grazing incidence x-ray scattering techniques and Monte Carlo (MC) simulations are combined to reveal the influence of molecular structure (genetic mutation) and divalent cations on the survival of gram negative bacteria against cationic peptides such as protamine. The former yields detailed structures of bacterial lipopolysaccharide (LPS) membranes with minimized radiation damages, while the minimal computer model based on the linearized Poisson-Boltzmann theory allows for the simulation of conformational changes of macromolecules (LPSs and peptides) that occur in the time scale of ms. The complementary combination of the structural characterizations and MC simulation demonstrates that the condensations of divalent ions ( Ca2+ or Mg2+ ) in the negatively charged core saccharides are crucial for bacterial survival.

Oliveira, Rafael G.; Schneck, Emanuel; Quinn, Bonnie E.; Konovalov, Oleg V.; Brandenburg, Klaus; Gutsmann, Thomas; Gill, Tom; Hanna, Charles B.; Pink, David A.; Tanaka, Motomu

2010-04-01

366

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

367

Ionic liquids containing the triply negatively charged tricyanomelaminate anion and a B(C6F5)3 adduct anion.  

PubMed

Room-temperature ionic liquids containing the triply charged tricyanomelaminate (tcmel) ion [C(3)N(6)(CN)(3)](3-) were synthesized. The 1-methyl-3-methylimidazolium (MMIm), 1-ethyl-3-methylimidazolium (EMIm), and 1-butyl-3-methylimidazolium (BMIm) salts of the tricyanomelaminate ion have glass transition temperatures (-6, -20, and -30 °C) similar to those found for the analogous monomeric dicyanoamide salts. They are thermally stable up to over 200 °C and dissolve in polar organic solvents. Addition of B(C(6)F(5))(3) to M(3) [tcmel] (M=Na, MMIm, EMIm, BMIm) yields salts containing the very voluminous adduct ion [C(3)N(6) {CN·B(C(6)F(5))(3)}(3)](3-) (tcmel_3B). The solid-state structure of [MMIm](3-) [tcmel] shows only long cation···anion contacts but in large number, while the solid-state structure of [Na(THF)(3)](3-) [tcmel_3B]·1.76 THF displays strong interactions of the sodium cation with the amido nitrogen atoms of the anion. Hence this adduct anion cannot be regarded as a weakly coordinating anion. A similar situation is found for the MMIm salt, [MMIm](3) [tcmel_3B]·2.66?CH(2)Cl(2), in which weak hydrogen bonds with the acidic proton of the MMIm ion are observed. On the basis of computations the energetics, structural trends, and charge transfer of adduct anion formation were studied. PMID:22052735

Voss, Karsten; Becker, Martin; Villinger, Alexander; Emel'yanenko, Vladimir N; Hellmann, Robert; Kirchner, Barbara; Uhlig, Frank; Verevkin, Sergey P; Schulz, Axel

2011-11-03

368

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

PubMed

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

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

2013-10-14

369

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

370

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

371

The effects of photochemical and mechanical damage on the excited state dynamics of charge-transfer molecular crystals composed of tetracyanobenzene and aromatic donor molecules.  

PubMed

Charge-transfer molecular crystals are structurally well-defined systems whose electron transfer dynamics can be studied using time-resolved spectroscopy. In this paper, five 1:1 complexes, consisting of 1,2,4,5-tetracyanobenzene as the electron acceptor and durene, 9-methylanthracene, naphthalene, phenanthrene, and pyrene as electron donors, are studied using time-resolved fluorescence and transient absorption in the diffuse reflectance geometry. Two different sample morphologies were studied: single crystals and powders prepared by pulverizing the crystals and diluting them with barium sulfate microparticles. Fluorescence lifetime and transient absorption measurements performed on the crystals and the powders yielded different results. The crystals typically exhibited long-lived monoexponential fluorescence decays, while the powders had shorter multiexponential decays. Exposure of both types of samples to high laser fluence was also shown to induce faster excited state decay dynamics as observed using fluorescence and diffuse reflectance. In addition to the more rapid decays, these molecular crystals exhibited relatively high photobleaching quantum yields on the order of 10(-4). Previous work that interpreted picosecond decays in the transient absorption as evidence for rapid recombination and charge dissociation should be re-evaluated based on the susceptibility of this class of compounds to mechanical and photochemical damage. PMID:21319859

Dillon, Robert J; Bardeen, Christopher J

2011-02-14

372

Momentum spectroscopy of fragment ions of a multiply charged N2O molecule under impact of 10-keV electrons  

NASA Astrophysics Data System (ADS)

The dissociative ionization of a N2O molecule is studied at an electron energy of 10 keV using the multiple-ion-coincidence imaging technique. The complete as well as the incomplete Coulomb explosion pathways for N2O2+ and N2O3+ ions are examined and identified. The precursor-specific relative partial ionization cross sections for resulting fragment ions are obtained. It is found that about 81.8% of single ionization, 17.8% of double ionization, and about 0.4% of triple ionization of the parent molecule contribute to the total fragment ion yield. Furthermore, the relative ionic fractions for ion-pair and ion-triple formation are also determined. The kinetic energy release distributions for different coincidence channels are obtained and compared with the available data at lower energies of electron and photon impacts and with that of high-energy ion impact. From the angular correlation studies of fragment ions, it is inferred that states with bent geometries are involved for most of the fragmentation channels of N2O2+ and N2O3+ ions. The concerted and/or sequential nature of the six dissociation pathways is also assigned. No other experimental or theoretical data exist in the literature to compare with the results obtained at the considered impact energy.

Bhatt, Pragya; Singh, Raj; Yadav, Namita; Shanker, R.

2012-11-01

373

Hydration of methane intercalated in Na-smectites with distinct layer charge: insights from molecular simulations.  

PubMed

Molecular dynamic simulations have been carried out to investigate the behavior of methane hydration in Na-smectite interlayers with different layer-charge distributions and water contents under certain pressure-temperature (P-T) conditions, which is analogous to the methane hydrate-bearing marine sediments. It was found that sufficient interlayer water is necessary for coordinating with methane and forming hydrate-like structures. Methane molecules are solvated by nearly 12-13 water molecules and coordinated with six oxygen atoms from the clay surface in the interlayer of nontronite as well as in montmorillonite. The mobility of the interlayer water of smectite, which is determined by the layer-charge amount and distribution of smectite, also influences the stability of hydrate methane complexes. The tetrahedral negative charge site is closer to the surface than the octahedral charge site and is more effective in confining water than methane water molecules. PMID:21193200

Zhou, Qing; Lu, Xiancai; Liu, Xiandong; Zhang, Lihu; He, Hongping; Zhu, Jianxi; Yuan, Peng

2010-11-25

374

Effect of Charged and Nonionic Membrane Additives on Physicochemical Properties and Stability of Niosomes  

Microsoft Academic Search

The aim of this study was to investigate an influence of different types of membrane additives including negative charge (dicetylphosphate,\\u000a DCP), positive charge (stearylamine, STR) and non-ionic molecule (cholesteryl poly-24-oxyethylene ether, SC24) on the physicochemical\\u000a properties of drug-free and drug-loaded niosomes. Salicylic acid having different proportions of ionized and unionized species\\u000a at different pH was selected as a model drug.

Varaporn Buraphacheep Junyaprasert; Veerawat Teeranachaideekul; Tasaneeya Supaperm

2008-01-01

375

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

PubMed

Charge transfer states around the donor-acceptor interface in an organic solar cell determine the device performance in terms of the open circuit voltage. In the present work, we propose a computational scheme based on constrained density functional tight binding theory (c-DFTB) to assess the energy of the lowest charge transfer (CT) state in such systems. A comparison of the c-DFTB scheme with Hartree-Fock based configuration interaction of singles (CIS) and with time-dependent density functional theory (TD-DFT) using the hybrid functional B3LYP reveals that CIS and c-DFTB reproduce the correct Coulomb asymptotics between cationic donor and anionic acceptor configurations, whereas TD-DFT gives a qualitatively wrong excitation energy. Together with an embedding scheme accounting for the polarizable medium, this c-DFTB scheme is applied to several donor-acceptor combinations used in molecular solar cells. The external quantum efficiency of photovoltaic cells based on zinc phthalocyanine-C60 blends reveals a CT band remaining much narrower than the density of states of acceptor HOMO and donor LUMO, an observation which can be interpreted in a natural way in terms of Marcus transfer theory. A detailed comparison with c-DFTB calculations reveals an energy difference of 0.32 eV between calculated and observed absorption from the electronic ground state into the CT state. In a blend of a functionalized thiophene and C60, the photoluminescence spectra differ significantly from neat films, allowing again an assignment to CT states. The proposed computational scheme reproduces the observed trends of the observed open circuit voltages in photovoltaic devices relying on several donor-acceptor blends, finding an offset of 1.16 eV on average. This value is similar as in polymer-fullerene photovoltaic systems where it amounts to about 0.9 eV, indicating that the photophysics of CT states in molecular donor-acceptor blends and in polymer-fullerene blends are governed by the same mechanisms. PMID:24135026

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

2013-10-18

376

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

377

Charge separation in CO oxidation involving supported gold clusters  

NASA Astrophysics Data System (ADS)

The character of the catalytic oxidation of CO by supported gold cluster catalysts is analyzed with emphasis on the unique characteristics of this process. The scheme of this process used here has the reagent CO molecule captured in the interface between the cluster and support, with oxygen molecules or atoms located on the support surface to react with the CO. (Other models have also been presented.) The experimental data indicate that, together with configurational transitions that lead to the CO molecule joining an oxygen atom to form the CO2 molecule, the charge separation due to capture of the CO molecule by the supported gold cluster is important. The process of release of the CO2 molecule results in charge exchange; the time for this process is relatively long because of the large distance separating positive and negative charges, a distance exceeding the cluster radius. This provides a high efficiency of the oxidation of CO with this catalyst despite the relatively high activation energy for the configurational transition.

Berry, R. S.; Smirnov, B. M.

2011-12-01

378

Charge separation in CO oxidation involving supported gold clusters  

SciTech Connect

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

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

2011-12-15

379

Ionisation and fragmentation of tetraphenyl iron (III) porphyrin chloride induced by slow multiply charged ion impact  

NASA Astrophysics Data System (ADS)

Ionisation and ion-induced fragmentation of tetraphenyl iron (III) porphyrin chloride (FeTPPCl) molecules have been studied after slow collisions (v˜ 0.2 a.u.) with multiply charged ions (O3+, Ar8+). Intact molecules and large fragments are observed in charge states up to q=4. For q=1, the intact molecule is the most abundant species, in particular, when projectiles in higher charge states are used. When the internal energy of the singly charged ion is increased by the energy transfer during the collision, the singly charged system de-excites by the emission of a neutral Cl-atom, a free electron or possibly a negative Cl anion. The processes are observed as direct as well as delayed processes on a ?s-time scale. For q=2 to 4 the loss of the Cl-atom and some phenyl groups becomes more likely due to the lower stability and the larger energy transfer. The charge state distribution of atomic fragments is found to be very different, in particular, when Cq+ and Clq+ ions are compared. In the first case mainly singly charged ions are detected, whereas in the second case ions in charge states up to q=6 are observed with high intensities. These phenomena are discussed in terms of the intramolecular charge mobility.

Bernigaud, V.; Manil, B.; Maunoury, L.; Rangama, J.; Huber, B. A.

2009-01-01

380

Scavenger receptor in fish is a lipopolysaccharide recognition molecule involved in negative regulation of NF-?B activation by competing with TNF receptor-associated factor 2 recruitment into the TNF-? signaling pathway.  

PubMed

Scavenger receptors (SRs) play crucial roles in innate immunity by acting as pattern recognition receptors. Although SRs are widely documented in mammals, data on their occurrence and functions in ancient vertebrates are limited. In this study, we report, to our knowledge, the first cloning and functional characterization of an SR molecule from teleost fish (Tetraodon nigroviridis). This SR (TnSR) was identified as a homolog to mammalian scavenger receptor class A member 5 with the conserved structure of a class A SR. TnSR contained multidomains in a type II transmembrane receptor, including an SR cysteine-rich domain, two coiled-coil collagenous domains, a transmmebrane domain, and a short N-terminal intracellular region with an unexpected TNFR-associated factor 2-binding consensus motif similar to that in human MSR molecules. Phylogenetic analysis suggested that TnSR may be an ancient member of class A SRs resulting from the close relationship between scavenger receptor class A member 5 and macrophage SR in vertebrates associated with the subtle differences in TnSR structure. Subcellular localization analysis showed that TnSR was a cell membrane receptor with homotrimer forms involved in the recognition and internalization of LPS from surface membranes into lysosomes. Functionally, TnSR expression was dramatically induced by LPS stimulation. TnSR served as a negative regulator in LPS-induced NF-?B activation by the competitive recruitment of TNFR-associated factor 2 from the TNF-? signaling pathway. To our knowledge, this is the first report showing that SR plays an inhibitory role in LPS-elicited inflammation by cross-talking with the TNF-? inflammatory pathway. These findings contribute to a better understanding of the biological and evolutionary history of the SR family. PMID:22988031

Meng, Zhen; Zhang, Xiao-yu; Guo, Jian; Xiang, Li-xin; Shao, Jian-zhong

2012-09-17

381

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

PubMed Central

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

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

2007-01-01

382

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

ERIC Educational Resources Information Center

|To help in interpreting the polarity of a molecule, charge separation can be visualized by mapping the electrostatic potential at the van der Waals surface using a color gradient or by indicating positive and negative regions of the electrostatic potential using different colored isosurfaces. Although these visualizations capture the molecular…

Schonborn, Konrad; Host, Gunnar; Palmerius, Karljohan

2010-01-01

383

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

384

Permeability of cartilage to neutral and charged polysaccharides  

SciTech Connect

The authors investigated macromolecular transport through a negatively charged membrane made from articular cartilage. Sections (150-1000 ..mu..) of cartilage obtained at autopsy from a horse fetlock were clamped between two 15 ml chambers containing .15 M sodium chloride in pH 7.4, .004 M phosphate. Tracers were introduced into chamber A and transport was determined by radiolabel transferred to chamber B over time. Structural integrity was preserved as shown by histological staining. In three experiments, size selectivity was measured using polydisperse uncharged /sup 3/H-dextran. The authors determined the elution patterns from a calibrated Sephadex S300 column of samples from each chamber. The relative transport of molecules over the size range of 1.0 to 10.0 nm was determined by comparing the two elution patterns. They found a sharp cutoff at an effective molecular radius of 2.5 nm. In an additional three experiments, charge selectivity was investigated by comparing the simultaneous transport of /sup 3/H-inulin and /sup 14/C-carboxy inulin. Both tracers have an effective molecular radius of 1.1 nm. The negatively charged carboxy inulin was transferred 15% faster than the uncharged inulin. They conclude: a) there is a maximum effective radius for uncharged dextrans that can be transferred across this membrane which is smaller than that reported for proteins and b) negatively charged cartilagenous membranes do not retard the transport of negatively charged inulin.

Haselton, F.R.; Fishman, A.P.; Sampson, P.M.

1986-05-01

385

Single-molecule optoelectronics.  

PubMed

With discrete states, several-atom Ag(n) nanoclusters exhibit molecule-like behavior with strong visible fluorescence and robust optical properties. This new class of single-molecule fluorophores has been created and electrically contacted in thin films to produce the first electroluminescent single molecules. A direct reporter of nanoscale charge injection and transport through discrete energy levels, bright Ag(n) electroluminescence has been harnessed to create single-molecule light-emitting diodes (LEDs) and optoelectronic logic gates and even to demonstrate full addition operations. These experiments utilizing the small size and quantum behavior of individual Ag nanoclusters usher in the new field of single-molecule optoelectronics. PMID:16028887

Lee, Tae-Hee; Gonzalez, Jose I; Zheng, Jie; Dickson, Robert M

2005-07-01

386

Polysialic acid–neural cell adhesion molecule in brain plasticity: From synapses to integration of new neurons  

Microsoft Academic Search

Isoforms of the neuronal cell adhesion molecule (NCAM) carrying the linear homopolymer of alpha 2,8-linked sialic acid (polysialic acid, PSA) have emerged as particularly attractive candidates for promoting plasticity in the nervous system. The large negatively charged PSA chain of NCAM is postulated to be a spacer that reduces adhesion forces between cells allowing dynamic changes in membrane contacts. Accumulating

Eduardo Gascon; Laszlo Vutskits; Jozsef Zoltan Kiss

2007-01-01

387

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

388

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

389

Fragmentation of biomolecules using slow highly charged ions  

SciTech Connect

We present first results of biomolecular fragmentation studies with slow highly charged ions (HCI). A layer of the tripeptide RVA was deposited on gold targets and irradiated with slow (few 100 keV) ions, e.g. Xe{sup 50+} and Xe{sup 15+}, extracted from the LLNL EBIT (electron beam ion trap). The secondary ions released upon ion impact were mass analyzed via Time-Of-Flight Secondary-Ion-Mass-Spectrometry (TOF-SIMS). The results show a strong dependence of the positive and negative ion yields on the charge state of the incident ion. We also found that incident ions with high charge states cause the ejection of fragments with a wide mass range as well as the intact molecule (345 amu). The underlying mechanisms are not yet understood but electron depletion of the target due to the high incident charge is likely to cause a variety of fragmentation processes. 6 refs., 2 figs.

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

1996-11-01

390

Asymptotic neutrality of diatomic molecules  

Microsoft Academic Search

We use the no-binding theorem of Thomas-Fermi theory to prove that a large diatomic molecule is “almost” neutral. That is to say, that if the total nuclear charge isZ then the numberN of electrons required for the diatomic molecule to be stable satisfies\\u000a

Jan Philip Solovej

1990-01-01

391

Molecule nanoweaver  

DOEpatents

A method, apparatus, and system for constructing uniform macroscopic films with tailored geometric assemblies of molecules on the nanometer scale. The method, apparatus, and system include providing starting molecules of selected character, applying one or more force fields to the molecules to cause them to order and condense with NMR spectra and images being used to monitor progress in creating the desired geometrical assembly and functionality of molecules that comprise the films.

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

2009-03-10

392

Dasatinib, an orally active small molecule inhibitor of both the src and abl kinases, selectively inhibits growth of basal-type/"triple-negative" breast cancer cell lines growing in vitro.  

PubMed

Dasatinib is an orally active small molecule kinase inhibitor of both the src and abl proteins. To evaluate the potential role of dasatinib in breast cancer we used 39 human breast cancer cell lines that have been molecular profiled using Agilent Microarrays. They represent both luminal and basal breast cancer subtypes based on the relative gene expression of cytokeratin (CK) 8/CK18 and CK5/CK17, respectively, and those that have undergone an epithelial-to-mesenchymal transition (post-EMT) based on their expression of vimentin and the loss of CKs. When treated with 1 mICROM dasatinib in vitro 8 of them were highly sensitive (>60% growth inhibition), 10 of them were moderately sensitive (40-59% growth inhibition), and 21 were resistant to dasatinib. A highly significant relationship between breast cancer subtype and sensitivity to dasatinib was observed (chi2 = 9.66 and P = 0.008). Specifically, basal-type and post-EMT breast cancer cell lines were most sensitive to growth inhibition by dasatinib. In an attempt to identify potential predictive markers of dasatinib response other than breast cancer subtype we analyzed the baseline gene expression profiles for differentially expressed genes. We identified a set of three biologically relevant genes whose elevated expression is associated with dasatinib inhibition including moesin, caveolin-1, and yes-associated protein-1 with a sensitivity and specificity of 88 and 86%, respectively. Importantly, these data provide scientific rationale for the clinical development of dasatinib in the treatment of women with "triple-negative" breast cancer, a subtype that is categorized as being aggressive and lacking effective treatments (i.e. hormonal manipulation or trastuzumab). PMID:17268817

Finn, Richard S; Dering, Judy; Ginther, Charles; Wilson, Cindy A; Glaspy, Padraic; Tchekmedyian, Nishan; Slamon, Dennis J

2007-02-01

393

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

PubMed

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

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

2005-05-01

394

Single-molecule DNA detection with an engineered MspA protein nanopore  

PubMed Central

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

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

2008-01-01

395

Process for increasing ionic charge in mass spectrometry  

SciTech Connect

Processes and apparatus are described for the analysis of molecules or fragments thereof, which are capable of carrying multiple charges, by reacting the multiply charged molecules or fragments thereof with other ions using mass spectrometry.

McLuckey, Scott A [West Lafayette, IN; He, Min [West Lafayette, IN

2009-06-23

396

Negative ion densities in the deep ionosphere of Titan  

NASA Astrophysics Data System (ADS)

The largest Kronian moon Titan has a unique nitrogen-rich atmosphere hosting complex organic chemistry that produces large pre-biotic molecules (tholins), and this could be similar to the upper atmosphere of early Earth. As tholin production has been shown to originate in Titan's extensive ionosphere, positive and heavy negative ions play crucial roles. The Cassini spacecraft Radio and Plasma Wave Science (RPWS) Langmuir Probe (LP) provides in-situ measurements of Titan's ionosphere, and we present here data from 46 deep flybys in the time period October 2004 to July 2012 of charge densities of positive and negative ions as well as electrons. These densities have been mapped with respect to altitude and solar zenith angle (SZA) in an altitude range of 880-1400 km. The inferred electron number densities are consistent with earlier presented observational results. Negative ion charge densities exhibit a trend that exponentially increases towards lower altitudes within the covered altitude range. This is especially evident on the night side of Titan (SZA > 110°). The negative ion charge densities at the lowest traversed altitudes (near 960 km) are inferred to be in the range 300-2000 cm-3. The results show that very few free electrons exist in the deepest regions (880-1050 km) of Titan's ionosphere. Instead this part of Titan's ionosphere is dominated by both negatively and positively charged heavy (>100 amu) organic ions. We therefore believe a dust/aerosol-ion plasma exist here, similar to what is found in noctilucent clouds in Earth's mesosphere.

Shebanits, Oleg; Wahlund, Jan-Erik; Mandt, Kathleen; Karin, Ågren; Edberg, Niklas; Waite, Hunter

2013-04-01

397

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

398

Adhesion molecules  

PubMed Central

Adhesion molecules are known to -be important components of an active T-cell mediated immune response. Signals generated at a site of inflammation cause circulating T cells to respond by rolling, arrest and then transmigration through the endothelium, all of which are mediated by adhesion molecules. Consequently, strategies have been developed to treat immune disorders with specific antibodies that block the interaction of adhesion molecules. However, the therapeutic effects of such remedies are not always achieved. Our recent investigations have revealed that intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) work together with chemokines to induce immunosuppression mediated by Mesenchymal stem cells (MSCs), thus demonstrating the dual role of adhesion molecules in immune responses. Since MSCs represent an important component of the stromal cells in an inflammatory microenvironment, our findings provide novel information for understanding the regulation of immune responses and for designing new strategies to treat immune disorders.

Ren, Guangwen; Roberts, Arthur I

2011-01-01

399

Negative Influence  

NSDL National Science Digital Library

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

Robertson, William C.

2006-01-01

400

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