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1

Astronomers Discover First Negatively-charged Molecule in Space  

NASA Astrophysics Data System (ADS)

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

2006-12-01

2

Negative ions of polyatomic molecules.  

PubMed Central

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

Christophorou, L G

1980-01-01

3

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

4

Small and reproducible isotope effects during methylation with trimethylsulfonium hydroxide (TMSH): a convenient derivatization method for isotope analysis of negatively charged molecules.  

PubMed

Negatively charged analytes must be derivatized prior to gas chromatography-isotope ratio mass spectrometry (GC-IRMS), with stringent control of isotope fractionation. Current methods require offline sample preparation. This study tests for the first time trimethylsulfonium hydroxide (TMSH) as online methylation agent prior to isotope analysis, addressing the herbicides bentazone and MCPA. Fully automated derivatization was achieved in a temperature-programmable GC injector, where reactants were injected into a packed liner, solvents were removed by split flow, and subsequent flash heating triggered the derivatization, thereby transferring derivatives onto the chromatographic column. Stoichiometric addition of TMSH resulted in complete conversion giving accurate and reproducible nitrogen isotope values of bentazone. In contrast, reproducible carbon isotope analysis required TMSH in > or = 250-fold excess. Contrary to expectations, delta(13)C values became more negative at smaller TMSH excess. This indicates that elevated methyl group concentrations in the pore space of the injection liner facilitated close-to-equilibrium rather than kinetic isotope fractionation resulting in reproducible derivatization conditions. delta(13)C results under these conditions compared favorably with liquid chromatography-IRMS: low standard deviations (0.3 per thousand for GC-IRMS, 0.1 per thousand for LC-IRMS) and a comparable offset of 1 per thousand compared to elemental analyzer-IRMS demonstrate that both methods represent expedient ways for online isotope analysis of anionic target compounds. PMID:20143836

Reinnicke, Sandra; Bernstein, Anat; Elsner, Martin

2010-03-01

5

Positively charged polyethylenimines enhance nasal absorption of the negatively charged drug, low molecular weight heparin  

Microsoft Academic Search

This study tests the hypothesis that positively charged polyethylenimines (PEIs) enhance nasal absorption of low molecular weight heparin (LMWH) by reducing the negative surface charge of the drug molecule. Physical interactions between PEIs and LMWH were studied by Fourier transform infrared (FTIR) spectroscopy, particle size analysis, conductivity measurements, zeta potential analysis, and azure A assay. The efficacy of PEIs in

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

2006-01-01

6

Characteristic features of charge transfer in the interaction between sensitizer molecules and AgCl(I) molecules  

NASA Astrophysics Data System (ADS)

We have used flash luminescence stimulation and photoinduced emission methods to study deep impurity states of AgCl(I) microcrystals with adsorbed organic cationic and anionic dye molecules. We have observed that when these molecules interact with the crystal, charge transfer occurs simultaneously from different orbitals and the transfer occurs differently from each orbital: some orbitals of the molecule pick up a negative charge, others at the same time give up a negative charge. We hypothesize that the type of transfer is determined by the overall charge.

Latyshev, A. N.; Chung, Nguyen Thi Kim; Suvorova, T. I.; Ovchinnikov, O. V.; Smirnov, M. S.; Egorushina, E. A.

2011-07-01

7

Arabinogalactan proteins are incorporated in negatively charged coffee brew melanoidins.  

PubMed

The charge properties of melanoidins in high molecular weight (HMw) coffee brew fractions, isolated by diafiltration and membrane dialysis, were studied. Ion exchange chromatography experiments with the HMw fractions showed that coffee brew melanoidins were negatively charged whereas these molecules did not expose any positive charge at the pH of coffee brew. Fractions with different ionic charges were isolated and subsequently characterized by means of the specific extinction coefficient (K(mix 405nm)), sugar composition, phenolic group content, nitrogen content, and the arabinogalactan protein (AGP) specific Yariv gel-diffusion assay. The isolated fractions were different in composition and AGP was found to be present in one of the HMw fractions. The AGP accounted for 6% of the coffee brew dry matter and had a moderate negative charge, probably caused by the presence of uronic acids. As the fraction that precipitated with Yariv was brown (K(mix 405nm) = 1.2), compared to a white color in the green bean, it was concluded that these AGPs had undergone Maillard reaction resulting in an AGP-melanoidin complex. The presence of mannose (presumably from galactomannan) indicates the incorporation of galactomannans in the AGP-melanoidin complex. As the uronic acid content in the more negatively charged melanoidin-rich, AGP-poor HMw fractions decreased, it was hypothesized that acidic groups are formed or incorporated during melanoidin formation. PMID:17263472

Bekedam, E Koen; De Laat, Marieke P F C; Schols, Henk A; Van Boekel, Martinus A J S; Smit, Gerrit

2007-02-01

8

Negatively charged hydrogen-bonded chains formed by tetrazole  

NASA Astrophysics Data System (ADS)

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

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

1999-09-01

9

Laboratory Infrared Spectroscopy of Gaseous Negatively Charged Polyaromatic Hydrocarbons  

NASA Astrophysics Data System (ADS)

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

Gao, Juehan; Berden, Giel; Oomens, Jos

2014-06-01

10

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

NSDL National Science Digital Library

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

Henderson, Tom

2006-03-15

11

Contactless measurements of charge migration within single molecules  

Microsoft Academic Search

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

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

2010-01-01

12

Pseudoparticle approach for charge-transferring molecule-surface collisions  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

13

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

14

Electrostatic plasma lens for focusing negatively charged particle beams  

SciTech Connect

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. [Institute of Physics NAS of Ukraine, Kiev 03028, Ave. Nauki 46 (Ukraine); Litovko, I. V. [Institute for Nuclear Research NAS of Ukraine, Kiev 03650, pr. Nauki 47 (Ukraine); Gushenets, V. I.; Oks, E. M. [High-Current Electronics Institute SB of RAS, Tomsk (Russian Federation)

2012-02-15

15

Increased negatively charged nitrogen-vacancy centers in fluorinated diamond  

NASA Astrophysics Data System (ADS)

We investigated the effect of fluorine-terminated diamond surface on the charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is achieved with CF4 plasma, and the surface chemistry is confirmed with x-ray photoemission spectroscopy. Photoluminescence of these ensemble NVs reveals that fluorine-treated surfaces lead to a higher and more stable negatively charged nitrogen vacancy (NV-) population than oxygen-terminated surfaces. NV- population is estimated by the ratio of negative to neutral charged NV zero-phonon lines. Surface chemistry control of NV- density is an important step towards improving the optical and spin properties of NVs for quantum information processing and magnetic sensing.

Cui, Shanying; Hu, Evelyn L.

2013-07-01

16

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

17

Electrostatic Power Generation from Negatively Charged, Simulated Lunar Regolith  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

18

Field Regulation of Single Molecule Conductivity by a Charged Atom  

NASA Astrophysics Data System (ADS)

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

Wolkow, Robert

2006-03-01

19

Positive, Neutral, and Negative Mass-Charges in General Relativity  

Microsoft Academic Search

As shown, any four-dimensional proper vector has two observable projections onto time line, attributed to our world and the mirror world (for a mass-bearing particle, the projections posses are attributed to positive and negative mass-charges). As predicted, there should be a class of neutrally mass-charged particles that inhabit neither our world nor the mirror world. Inside the space-time area (membrane)

Dmitri Rabounski; Florentin Smarandache

2009-01-01

20

Charging of dust particles in a negative ion plasma  

NASA Astrophysics Data System (ADS)

Positively charges nanoparticles have been detected during sounding rocket flights in the nighttime polar mesosphere. Simultaneous measurements of the plasma densities indicated the presence of few electrons and significant numbers of heavy negative ions. Model calculations show that dust particles immersed in such a plasma can acquire a positive charge if the relative density of the heavy negative ions is sufficiently large. We have performed laboratory experiments in a Q machine plasma to study the effect of the presence of heavy negative ions on the charging of micron-sized hollow glass microspheres. The plasma consists of singly-charged potassium ions and electrons. SF6 is added to the plasma, which readily attaches electrons to form essentially a positive ion (mass 39 amu)/negative ion (mass 146 amu) plasma. When the relative concentration of the remaining free electrons is reduced to less than 1 part per thousand, conditions are formed which favor the formation of positive dust. Results of Langmuir probe measurements are presented which indicate that the glass microspheres dispersed into this plasma acquire a positive charge.

Merlino, Robert

21

Negatively-charged helices in the gas phase.  

PubMed

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

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

2014-07-15

22

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

23

Space Charge Neutralization in the ITER Negative Ion Beams  

SciTech Connect

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

Surrey, Elizabeth [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom)

2007-08-10

24

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

NASA Astrophysics Data System (ADS)

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 force microscopy (KPFM) we also measured the local contact potential difference (LCPD). We observed that the LCPD is shifted depending on the sign of the charge and allows the discrimination of positively charged, neutral, and negatively charged atoms. To image pentacene molecules we modified AFM tips by means of vertical manipulation techniques, i.e. deliberately picking up known atoms and molecules, such as Au, Ag, Cl, CO, and pentacene. Using a CO terminated tip we resolved all individual atoms and bonds within a pentacene molecule. Three dimensional force maps showing the site specific distance dependence above the molecule were extracted. We compared our experimental results with density functional theory (DFT) calculations to gain insight on the physical origin of AFM contrast formation. We found that atomic resolution is only obtained due to repulsive force contributions originating from the Pauli exclusion principle. [4pt] [1] L. Gross, F. Mohn, P. Liljeroth, J. Repp, F. J. Giessibl, G. Meyer, Science 324, 1428 (2009). [0pt] [2] L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 325, 1110 (2009).

Gross, Leo

2010-03-01

25

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

26

The role of amphiphilicity and negative charge in glycoprotein 41 interactions in the hydrophobic pocket  

PubMed Central

The hydrophobic pocket within the coiled coil domain of HIV-1 gp41 is considered to be a hotspot suitable for small molecule intervention of fusion, although so far it has yielded only ?M inhibitors. Previous peptide studies have identified specific hydrophobic interactions and a Lys-Asp salt bridge as contributing to binding affinity in the pocket. Negative charge appears to be critical for activity of small molecules. We have examined the role of charge and amphiphilic character in the interaction, by studying a series of short pocket binding peptides differing in charge, helical content and in the presence or absence of the Lys-Asp salt bridge, and a series of fatty acid salts with varying charge and hydrocarbon length. Quantitative binding analysis revealed that long range electrostatic forces and a greasy non-specific hydrophobic interaction were sufficient for ?M potency. The results suggest that an extended interaction site may be necessary for higher potency. We examined a region of the coiled coil immediately C-terminal to the pocket, and found that specific salt bridge and hydrogen bond networks may reside in this region. Negatively charged groups extended towards or beyond the C-terminus of the pocket could therefore result in improved low molecular weight fusion inhibitors.

Gochin, Miriam; Cai, Lifeng

2009-01-01

27

Colloidal stability of negatively charged cellulose nanocrystalline in aqueous systems.  

PubMed

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

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

2012-09-01

28

Potential of Negatively Charged Pectin Nanoparticles Encapsulating Paclitaxel: Preparation & Characterization  

Microsoft Academic Search

Sugars with their three dimensional structures are important for many biological functions. We report preparation of negatively charged pectin nanoparticles and its efficacy as a drug delivery vehicle for anticancer drug Paclitaxel assessed. Pectin nanoparticles were prepared by ionic gelation having a mean diameter of ~300350nm, and were stable over a wide range of temperature and pH. FT-IR spectra revealed

Anita K. Verma; A. Chanchal; A. Kumar

2011-01-01

29

Single molecule detection using charge-coupled device array technology  

SciTech Connect

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

Denton, M.B.

1992-07-29

30

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

SciTech Connect

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

Wu Bin; Xia Lei; Li Hongkai; Zeng Xianjin; Tian Shanxi [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2012-01-15

31

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

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 asymmetry in the rovibrationally excited HD molecule  

NASA Astrophysics Data System (ADS)

The recently developed method for performing all-particle non-Born-Oppenheimer variational calculations on diatomic molecular systems excited to the first excited rotational state and simultaneously vibrationally excited is employed to study the charge asymmetry and the level lifetimes of the HD molecule. The method uses all-particle explicitly correlated Gaussian functions. The nonlinear parameters of the Gaussians are optimized with the aid of the analytical energy gradient determined with respect to these parameters.

Kirnosov, Nikita; Sharkey, Keeper; Adamowicz, Ludwik

2014-03-01

34

Negatively-charged particle pickup in the Enceladus plume  

NASA Astrophysics Data System (ADS)

One of the key discoveries of the Cassini spacecraft's traverses of the Enceladus plume was that of negatively-charged nanograins and ions, as detected by CAPS- ELS. The trajectories of these charged particles are expected to be affected by the motional electric field in the vicinity of the moon, especially those of the low mass ions. During some Enceladus encounters, the particles have been observed arriving at the spacecraft in the local ram direction, i.e. close to being at rest with respect to Enceladus, presumably shortly after their formation and before the acceleration associated with the pickup process. During other encounters however, the ions have been observed to arrive at the spacecraft well away from the ram direction, in the gyroplane at ~90 degrees to the local magnetic field direction, indicating their pickup by the local plasma flow. We present an overview of observations of these negative pickup nanograins in the Enceladus plume, and our interpretation of these observations, and attempts to trace the origins of the grains using a hybrid simulation of the plume.

Jones, G. H.; Arridge, C. S.; Coates, A. J.; Wellbrock, A.; Kriegel, H.; Meier, P.

2013-09-01

35

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

36

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

PubMed

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

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

2014-03-01

37

The positive space charge lens for focusing and manipulating high-current beams of negatively charged particles (review)  

Microsoft Academic Search

We describe a new approach for creation of effective axially symmetric plasma tools for focusing and manipulating high-current negatively charged particles beams, electrons and negative ions. This approach is based on the fundamental plasma optical concept of magnetic and electrostatic insulation of electrons, and non-magnetized positive ions providing controlled uncompensated positive space charge cloud formation. The recent advances in creation

A. Goncharov; A. Dobrovolskiy; S. Dunets; A. Evsyukov; V. Gushenets; V. Goretskiy; I. Litovko; E. Oks; I. Soloshenko

2010-01-01

38

Thermal-Energy Negative Ion-Molecule Reactions.  

National Technical Information Service (NTIS)

Some results of quantitative studies of negative ion reactions with neutrals by the recently developed flowing afterglow technique have been discussed. The versatility of the method allows a wide variety of reactants to be investigated. The laboratory stu...

E. E. Ferguson

1970-01-01

39

Spectroscopy of Negatively Charged Donors - and Excitons - in Quantum Wells.  

NASA Astrophysics Data System (ADS)

Negatively charged donors rm(D^ -) and excitons in quantum well systems have been systematically studied by far infrared (FIR) magnetospectroscopy and magneto-photoluminescence. A series of FIR magneto -transmission and magneto-photoconductivity studies of quasi -2D donor impurity states were carried out in several rm GaAs/Al_{0.3}Ga_{0.7 }As multiple-quantum-well (MQW) samples with different doping densities in the barrier and constant sheet doping in the well. The D^- singlet transition was observed for Si donors in a variety of GaAs/AlGaAs MQW samples. In addition to the D ^- singlet transition, the low frequency D^- triplet transition (T _-) which has been predicted by theory and the experimental observation of which has been the subject of some controversy, was clearly identified. Several other weak transitions were also observed including the D ^0 2p^--2s transition, another D^- transition, the D ^0 1s-3p^- transition and indications of the high frequency D^ - triplet transition (T_+). The occupancy of several D^0 and D^- states was calculated as a function of temperature with a simple statistical model, and compared with measured intensities of each transition at various temperatures agreement was qualitatively good. Saturation of the D^0 1s-2p^+ transition, the D^--singlet transition and cyclotron resonance in MQW samples was observed with the UCSB Free Electron Laser (FEL) under steady state conditions. From analysis of the D^0 1s-2p^+ data, effective lifetimes were found to vary systematically with laser frequency, decreasing from 62 ns at 84 cm^{-1 } (2p^+ state below the N = 0 L.L) to 3 ns at 124 cm^{ -1} (2p^+ state above the lowest L.L.). This behavior is very similar to that of the D^0 1s-2p^+ transition of uncompensated bulk GaAs. From a combination of low temperature photoluminescence (PL) and FIR magnetospectroscopy on several MQW samples with different donor doping (well only, barrier only, both well and barrier) a recombination line due to negatively charged excitons (X^-) was identified.

Ryu, Seong-Ryong

40

Molecules as wires: molecule-assisted movement of charge and energy.  

PubMed

In this chapter, we explore experimental and theoretical aspects of molecular wire-like charge transport from the mechanistic point of view. We discuss competition between coherent superexchange and sequential mechanisms of transport through donor-bridge-acceptor systems, where the donor and acceptor are either molecules or metal/semiconductor contacts. The focus is on the two major determinants of mechanism: electronic coupling and energy level matching. Some methods of calculating conductance are outlined, and the relationship between conductance in a metal/molecule/metal junction and electron transfer, where donor and acceptor have relatively discrete electronic energy levels is explored. Finally, we give several examples of chemical systems that have displayed wire-like behavior and discuss their characterization. PMID:22179336

Weiss, Emily A; Wasielewski, Michael R; Ratner, Mark A

2005-01-01

41

Positive-Space-Charge Lens for Focusing and Manipulating High-Current Beams of Negatively Charged Particles  

Microsoft Academic Search

We describe a new approach for the creation of effective axially symmetric plasma tools for focusing and manip- ulating high-current negatively charged particle beams, negative ions, and electrons. This approach is based on the fundamental plasma-optical concept of magnetic and electrostatic insulation of electrons and nonmagnetized positive ions providing controlled uncompensated positive-space-charge cloud formation. The recent advances in the creation

Andrey M. Dobrovolsky; Sergey P. Dunets; Anton N. Evsyukov; Alexey A. Goncharov; Vasiliy I. Gushenets; Irina V. Litovko; Efim M. Oks

2011-01-01

42

Effect of positively and negatively charged liposomes on skin permeation of drugs.  

PubMed

To clarify the effect of the surface charge of liposomes on percutaneous absorption, the permeation of liposomal drugs through rat skin was investigated in vitro and in vivo. Liposomes were prepared using egg yolk lecithin (EPC, phase transition temperature, -15 to -17 degrees C), cholesterol and dicetylphosphate (DP) or stearylamine (SA) (10:1:1, mol/mol). Also examined was the penetration behavior of positively and negatively charged liposomes, using a fluorescent probe (Nile Red). The in vitro penetration rate of melatonin (MT) entrapped in negatively charged liposomes was higher than that of positively charged ones (p<0.05). When the percutaneous absorption of ethosuximide (ES) encapsulated was estimated in vivo, the absorption of ES from negatively charged liposomes was slightly higher than that from positively charged liposomes. Additionally, the absorption of ES from both types of liposomes was superior to that from the lipid mixtures consisting of the same composition as the vesicles. The percutaneous absorption of betahistine (BH) from a gel formulation containing negatively charged liposomes of BH was much more than that from the formulation with positively charged ones, with 2-fold higher AUC (p<0.05). Histological studies revealed that the negatively charged liposomes diffused to the dermis and the lower portion of hair follicles through the stratum corneum and the follicles much faster than the positive vesicles at the initial time stage after application. Thus, the rapid penetration of negatively charged liposomes would contribute to the increased permeation of drugs through the skin. PMID:11378523

Ogiso, T; Yamaguchi, T; Iwaki, M; Tanino, T; Miyake, Y

2001-01-01

43

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

44

Electromagnetic plane waves with negative phase velocity in charged black strings  

SciTech Connect

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

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

2013-02-15

45

Interfacial charge transfer dynamics in small molecule-modified TiO2 nanoparticles  

Microsoft Academic Search

Direct molecule-semiconductor interfacial charge transfer interactions have received considerable research attention for their applications in various fields. In this study, the dynamics of molecule-TiO2 interfacial charge transfer complexes is monitored with femtosecond fluorescence upconversion and transient absorption. Small molecules (catechol, dopamine, benzhydroxamic acid, acetyl acetonate and salicylate)-modified TiO2 nanoparticles are prepared and the complexation is followed with optical absorption measurements.

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

2010-01-01

46

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

47

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

48

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

49

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

PubMed

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

Miyamoto, K; Wada, S; Hatayama, A

2010-02-01

50

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

PubMed Central

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

Stace, T M; Damiano, E R

2001-01-01

51

Origin of Negative Differential Resistance in a Strongly Coupled Single Molecule-Metal Junction Device  

NASA Astrophysics Data System (ADS)

A new mechanism is proposed to explain the origin of negative differential resistance (NDR) in a strongly coupled single molecule-metal junction. A first-principles quantum transport calculation in a Fe-terpyridine linker molecule sandwiched between a pair of gold electrodes is presented. Upon increasing the applied bias, it is found that a new phase in the broken symmetry wave function of the molecule emerges from the mixing of occupied and unoccupied molecular orbitals. As a consequence, a nonlinear change in the coupling between the molecule and the lead is evolved resulting in NDR. This model can be used to explain NDR in other classes of metal-molecule junction devices.

Pati, Ranjit; McClain, Mike; Bandyopadhyay, Anirban

2008-06-01

52

Picosecond Optical Spectroscopy of a Single Negatively Charged Self- Assembled InAs Quantum Dot.  

National Technical Information Service (NTIS)

We demonstrate an experimental technique for the transient read-out of the optical transitions in a single negatively charged self-assembled InAs quantum dot (QD) using resonant picosecond optical pulses and control of the QD charge state. Observable phen...

A. Amo, E. D. Kim, K. Truex, X. Xu Y. Wu

2010-01-01

53

Calculating Henry?s Constants of Charged Molecules Using SPARC  

EPA Science Inventory

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

54

Theoretical characterization of charge transport in one-dimensional collinear arrays of organic conjugated molecules.  

PubMed

A great deal of interest has recently focused on host-guest systems consisting of one-dimensional collinear arrays of conjugated molecules encapsulated in the channels of organic or inorganic matrices. Such architectures allow for controlled charge and energy migration processes between the interacting guest molecules and are thus attractive in the field of organic electronics. In this context, we characterize here at a quantum-chemical level the molecular parameters governing charge transport in the hopping regime in 1D arrays built with different types of molecules. We investigate the influence of several parameters (such as the symmetry of the molecule, the presence of terminal substituents, and the molecular size) and define on that basis the molecular features required to maximize the charge carrier mobility within the channels. In particular, we demonstrate that a strong localization of the molecular orbitals in push-pull compounds is generally detrimental to the charge transport properties. PMID:20217887

Viani, Lucas; Olivier, Yoann; Athanasopoulos, Stavros; da Silva Filho, Demetrio A; Hulliger, Jürg; Brédas, Jean-Luc; Gierschner, Johannes; Cornil, Jérôme

2010-04-01

55

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

56

Challenging chemical concepts through charge density of molecules and crystals  

NASA Astrophysics Data System (ADS)

Narrating my scientific career, I show in this paper how, starting as a computational and theoretical chemist, I got naturally involved with x-ray crystallographers because of the common interest in charge density and in the study of chemical bonds based on such an observable. The tools I devised and the conceptual developments I made to facilitate a profitable encounter between x-ray charge density and computational chemistry researchers are illustrated, with a special focus on the proposal and applications of the Source Function concept.

Gatti, Carlo

2013-04-01

57

Nonlinear charge transport in the helicoidal DNA molecule  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

58

Nonlinear charge transport in the helicoidal DNA molecule.  

PubMed

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

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

2012-12-01

59

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

60

Interaction of multiply charged ions with isolated polycyclic aromatic hydrocarbon molecules  

NASA Astrophysics Data System (ADS)

The interaction of multiply charged ions (He2+, O3+, and Xe20+, v <= 0.6 a.u.) with gas phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules (pyrene and coronene) was studied. Positively charged ionic products were analyzed with a linear time-of-flight mass spectrometer.

?awicki, A.; Capron, M.; Maisonny, R.; Maclot, S.; Lattouf, E.; Méry, A.; Rangama, J.; Holm, A. I. S.; Zettergren, H.; Seitz, F.; Johansson, H. A. B.; Rosén, S.; Schmidt, H. T.; Cederquist, H.; Manil, B.; Adoui, L.; Rousseau, P.; Huber, B. A.

2012-11-01

61

Dissociation of Methylamine Molecule Ions Formed in Charge Exchange Collisions with Positive Ions.  

National Technical Information Service (NTIS)

Mass spectra of methylamine were obtained after charge exchange with slow positive ions, and the intensities of the peaks were plotted as a function of the energy absorbed by the molecule during the charge exchange. The curves are integrated to give the e...

H. Sjogren

1965-01-01

62

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

63

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

64

Covalent Effects in Molecule-Surface Charge Exchange: O2 ON Ag(111).  

National Technical Information Service (NTIS)

The formation of negatively charged ions (oxygen) in the scattering of oxygen from silver surfaces is difficult to explain in the Brako-Newns scheme. To understand these processes, we have performed extended Hueckel tight binding calculations on model sil...

M. C. Zonnevylle R. Hoffmann P. J. Van Den Hoek R. A. Van Santen

1989-01-01

65

Water-developable negative-tone single-molecule resists: high-sensitivity nonchemically amplified resists  

NASA Astrophysics Data System (ADS)

A water developable, non-chemically amplified, negative tone single molecule resist (tris(4-hydroxy-3,5-dimethylphenyl)sulfonium tosylate, otherwise referred to as TAS-tBoc-Ts) was synthesized, characterized, and imaged using high resolution electron beam lithography. The solubility switching in the negative tone imaging mode in this material, which occurs for no or low temperature post-exposure bakes, occurs through photolytic conversion of some fraction of the ionic PAG molecules into non-ionic photoproducts which act as strong dissolution inhibitors to the remaining unreacted molecules in the film. It was also shown that this resist system can dmonstrate positive tone chemically amplified imaging behavior under different processing conditions, i.e. when using higher temperature post-exposure bakes above 100 °C . Pure water was found to be the preferential developer as compared to conventional aqueous alkaline TMAH developers in this particular system for negative tone imaging. Under 100 keV e-beam imaging and water development, a sensitivity of 66 ?C/cm2 and contrast of 7.9 was obtained. TAS-tBoc-Ts obtained 40 nm 1:2 line-space resolutions with a low LER of 5.3 nm using electron beam imaging with no apparent swelling or residue problems. This new material and its negative tone imaging process provide a possible path forward for designing non-chemically amplified resists that may obtain higher resolutions than current chemically amplified resists at competitive sensitivities.

Lawson, Richard A.; Lee, Cheng-Tsung; Yueh, Wang; Tolbert, Laren; Henderson, Clifford L.

2008-04-01

66

Intrinsic spin-relaxation induced negative tunnel magnetoresistance in a single-molecule magnet  

NASA Astrophysics Data System (ADS)

We investigate theoretically the effects of intrinsic spin-relaxation on the spin-dependent transport through a single-molecule magnet (SMM), which is weakly coupled to ferromagnetic leads. The tunnel magnetoresistance (TMR) is obtained by means of the rate-equation approach including not only the sequential but also the cotunneling processes. It is shown that the TMR is strongly suppressed by the fast spin-relaxation in the sequential region and can vary from a large positive to slight negative value in the cotunneling region. Moreover, with an external magnetic field along the easy-axis of SMM, a large negative TMR is found when the relaxation strength increases. Finally, in the high bias voltage limit the TMR for the negative bias is slightly larger than its characteristic value of the sequential region; however, it can become negative for the positive bias caused by the fast spin-relaxation.

Xie, Haiqing; Wang, Qiang; Xue, Hai-Bin; Jiao, HuJun; Liang, J.-Q.

2013-06-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

68

Pumped charge and spin current in a quantum dot molecule.  

PubMed

The effects of an ac electric field on the quantum transport behaviors in a parallel-coupled double quantum dot system are investigated theoretically. A dc charge current can be pumped at zero bias due to photon-assisted tunneling effects. The sign, magnitude and position of the pumped current peaks can be well controlled and manipulated by simply varying the gate voltage, the amplitude and frequency of the ac field. Furthermore, the possibility of electrically pumping a pure spin current in the presence of spin-orbit interaction is discussed. PMID:21399251

Pan, Hui; Yang, Shengyuan A; Niu, Qian

2010-07-14

69

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

70

Negative photoion spectroscopy of freon molecules in the vicinity of the Cl 2p edge  

SciTech Connect

Polar photodissociation of CF{sub n}Cl{sub 4-n} (n=0-2) has been studied using synchrotron radiation within the energy range 195-217 eV. The first observations of negative photoion fragments from these molecules after core excitation are reported. In addition to observing a number of previously known resonances two additional resonant states, just above the Cl 2p ionization limit, are observed and play an important role in the polar photodissociation process. The difficulties in identifying these above threshold spin-split features using negative photoion spectroscopy are discussed.

Scully, S.W.J.; Mackie, R.A.; Browning, R.; Dunn, K.F.; Latimer, C.J. [Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN (United Kingdom)

2004-10-01

71

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

72

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

PubMed Central

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

2014-01-01

73

Motion of neutral and negatively charged excitons in high magnetic fields  

NASA Astrophysics Data System (ADS)

The in-plane motion of excitons (X) and negatively charged excitons (X -) in a doped CdTe/CdMgTe quantum well has been measured at 4.2 K in magnetic fields up to 12 T, using spatially resolved photoluminescence (PL) spectroscopy. The populations of X and X - have been found to be in local dynamical equilibrium. The measured PL patterns in real space could therefore be described by considering free and mobile excitons in equilibrium with localised charged excitons.

Pulizzi, F.; Thijssen, W. H. A.; Christianen, P. C. M.; Maan, J. C.; Yakovlev, D. R.; Ossau, W.; Wojtowicz, T.; Karczewski, G.; Kossut, J.

2001-04-01

74

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

PubMed

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

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

2014-06-01

75

Terminal supraparticle assemblies from similarly charged protein molecules and nanoparticles.  

PubMed

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

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

2014-01-01

76

Fine structure of negatively and positively charged excitons in semiconductor quantum dots: electron-hole asymmetry.  

PubMed

We present new understanding of excitonic fine structure in close-to-symmetric InAs/GaAs and InGaAs/GaAs quantum dots. We demonstrate excellent agreement between spectroscopy and many-body pseudopotential theory in the energy splittings, selection rules and polarizations of the optical emissions from doubly charged excitons. We discover a marked difference between the fine structure of the doubly negatively and doubly positively charged excitons. The features in the doubly charged emission spectra are shown to arise mainly from the lack of inversion symmetry in the underlying crystal lattice. PMID:17358715

Ediger, M; Bester, G; Gerardot, B D; Badolato, A; Petroff, P M; Karrai, K; Zunger, A; Warburton, R J

2007-01-19

77

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

2011-12-19

78

Phonon Effects on Charge Transport Through a Two State Molecule  

NASA Astrophysics Data System (ADS)

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

Ulloa, Sergio E.; Yudiarsah, Efta

2008-03-01

79

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

80

Negatively Charged, Dye Labeled-Dideoxynucleotides for “Direct-Load” DNA Sequencing  

Microsoft Academic Search

A four-color set of negatively charged, single dye as well as energy transfer dye labeled-ddNTPs were synthesized and evaluated in combination with a novel polymerase in a “direct-load” DNA sequencing, obviating the laborious and time consuming post-reaction work-up.

Satyam Nampalli; Patrick J. Finn; Lei Sun; Haiguang Xiao; John R. Nelson; Gregory Grossmann; Parke K. Flick; Carl W. Fuller; Shiv Kumar

2003-01-01

81

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

PubMed

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

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

2013-04-01

82

The negative charge of Glu127 in protein kinase A and its biorecognition  

Microsoft Academic Search

A set of mutants of protein kinase A (PKA) in which Glu-127 was replaced by Gln, Asp, Asn, and Arg was prepared. Their Km and Vmax values show that the negative charge of Glu-127 (not merely its hydrogen bonding capacity) is indispensable for the kinase activity, since Glu-127\\/Gln is inactive, in spite of the fact that it can form hydrogen

Michael Batkin; Shmuel Shaltiel

1999-01-01

83

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

84

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

Microsoft Academic Search

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

Ilaria Bononi; Veronica Balatti; Soccorso Gaeta; Mauro Tognon

2008-01-01

85

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

86

Large tunable image-charge effects in single-molecule junctions  

NASA Astrophysics Data System (ADS)

Metal/organic interfaces critically determine the characteristics of molecular electronic devices, because they influence the arrangement of the orbital levels that participate in charge transport. Studies on self-assembled monolayers show molecule-dependent energy-level shifts as well as transport-gap renormalization, two effects that suggest that electric-field polarization in the metal substrate induced by the formation of image charges plays a key role in the alignment of the molecular energy levels with respect to the metal's Fermi energy. Here, we provide direct experimental evidence for an electrode-induced gap renormalization in single-molecule junctions. We study charge transport through single porphyrin-type molecules using electrically gateable break junctions. In this set-up, the position of the occupied and unoccupied molecular energy levels can be followed in situ under simultaneous mechanical control. When increasing the electrode separation by just a few ångströms, we observe a substantial increase in the transport gap and level shifts as high as several hundreds of meV. Analysis of this large and tunable gap renormalization based on atomic charges obtained from density functional theory confirms and clarifies the dominant role of image-charge effects in single-molecule junctions.

Perrin, Mickael L.; Verzijl, Christopher J. O.; Martin, Christian A.; Shaikh, Ahson J.; Eelkema, Rienk; van Esch, Jan H.; van Ruitenbeek, Jan M.; Thijssen, Joseph M.; van der Zant, Herre S. J.; Duli?, Diana

2013-04-01

87

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

88

Charge transfer, electronic quantum processes, and dissociation dynamics in molecule-surface collisions  

Microsoft Academic Search

In this paper some fundamental processes in molecule-surface dynamics are addressed; charge transfer from a metal surface to an incident or adsorbed particle, non-adiabatic electronic processes, and bond breaking dynamics. These processes are illustrated and discussed by referring to two recent experiments and the associated theories.The first example is Cl2 molecules impinging on a clean potassium surface [L. Hellberg, J.

Bengt Kasemo

1996-01-01

89

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

PubMed

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

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

2012-06-01

90

Spatiotemporal dynamics of charged species in the afterglow of plasmas containing negative ions.  

PubMed

The spatiotemporal evolution of charged species densities and wall fluxes during the afterglow of an electronegative discharge has been investigated. The decay of a plasma with negative ions consists of two stages. During the first stage of the afterglow, electrons dominate plasma diffusion and negative ions are trapped inside the vessel by the static electric field; the flux of negative ions to the walls is nearly zero. During this stage, the electron escape frequency increases considerably in the presence of negative ions, and can eventually approach free electron diffusion. During the second stage of the afterglow, electrons have disappeared, and positive and negative ions diffuse to the walls with the ion-ion ambipolar diffusion coefficient. Theories for plasma decay have been developed for equal and strongly different ion (T(i)) and electron (T(e)) temperatures. In the case T(i)=T(e), the species spatial profiles are similar and an analytic solution exists. When detachment is important in the afterglow (weakly electronegative gases, e.g., oxygen) the plasma decay crucially depends on the product of negative ion detachment frequency (gamma(d)) and diffusion time (tau(d)). If gamma(d)tau(d)>2, negative ions convert to electrons during their diffusion towards the walls. The presence of detached electrons results in "self-trapping" of the negative ions, due to emerging electric fields, and the negative ion flux to the walls is extremely small. In the case T(i)negative ion density fronts. During the afterglow, although negative ions diffuse freely in the plasma core, the negative ion fronts propagate towards the chamber walls with a nearly constant velocity. The evolution of ion fronts in the afterglow of electronegative plasmas is important, since it determines the time needed for negative ions to reach the wall, and thus influence surface reactions in plasma processing. PMID:11580449

Kaganovich, I D; Ramamurthi, B N; Economou, D J

2001-09-01

91

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

PubMed

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

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

2013-06-28

92

Detection of charges and molecules with self-assembled nano-oscillators.  

PubMed

Detection of a single or small amount of charges and molecules in biologically relevant aqueous solutions is a long-standing goal in analytical science and detection technology. Here we report on self-assembled nano-oscillators for charge and molecular binding detections in aqueous solutions. Each nano-oscillator consists of a nanoparticle linked to a solid surface via a molecular tether. By applying an oscillating electric field normal to the surface, the nanoparticles oscillate, which is detected individually with ?0.1 nm accuracy by a plasmonic imaging technique. From the oscillation amplitude and phase, the charge of the nanoparticles is determined with a detection limit of ?0.18 electron charges along with the charge polarity. We further demonstrate the detection of molecular binding with the self-assembled nano-oscillators. PMID:24942903

Shan, Xiaonan; Fang, Yimin; Wang, Shaopeng; Guan, Yan; Chen, Hong-Yuan; Tao, Nongjian

2014-07-01

93

Multistep photochemical charge separation in rod-like molecules based on aromatic insides and diimides  

Microsoft Academic Search

A series of intramolecular triads with linear, rod-like structures has been developed that undergo very efficient two-step electron transfer following direct excitation of a chromophore possessing a charge transfer (CT) excited state. The CT state of 4-aminonaphthalene-1,8-imide (ANI), produced by direct excitation of the chromophore, has about 70% of a negative charge transferred from the amine to the imide. Attachment

Scott R. Greenfield; Walter A. Svec; David Gosztola; Michael R. Wasielewski

1996-01-01

94

Influence of electrostatic interactions on the release of charged molecules from lipid cubic phases.  

PubMed

The release of positive, negative, and neutral hydrophilic drugs from pH responsive bicontinuous cubic phases was investigated under varying conditions of electrostatic interactions. A weak acid, linoleic acid (LA), or a weak base, pyridinylmethyl linoleate (PML), were added to the neutral monolinolein (ML) in order to form lyotropic liquid-crystalline (LLC) phases, which are negatively charged at neutral pH and positively charged at acidic pH. Release studies at low ionic strength (I = 20 mM) and at different pH values (3 and 7) revealed that electrostatic attraction between a positive drug, proflavine (PF), and the negatively charged LLC at pH = 7 or between a negative drug, antraquinone 2-sulfonic acid sodium salt (AQ2S), and the positively charged LLC at pH = 3 did delay the release behavior, while electrostatic repulsion affects the transport properties only to some extent. Release profiles of a neutral drug, caffeine, were not affected by the surface charge type and density in the cubic LLCs. Moreover, the influence of ionic strength was also considered up to 150 mM, corresponding to a Debye length smaller than the LLC water channels radius, which showed that efficient screening of electrostatic attractions occurring within the LLC water domains results in an increased release rate. Four transport models were applied to fit the release data, providing an exhaustive, quantitative insight on the role of electrostatic interactions in transport properties from pH responsive bicontinuous cubic phases. PMID:24673189

Negrini, Renata; Sánchez-Ferrer, Antoni; Mezzenga, Raffaele

2014-04-22

95

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

NSDL National Science Digital Library

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

Belcher, John

2010-04-11

96

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

97

Charge Manipulation in Molecules Encapsulated Inside Single-Wall Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

98

Charge Storage Effect on In2O3 Nanowires with Ruthenium Complex Molecules  

NASA Astrophysics Data System (ADS)

Charge storage effect on In2O3 nanowire field-effect transistors (FETs) is controlled by a chemical gate, ruthenium(II) terpyridine (Ru\\text{II-tpy) complex molecules. In2O3 nanowire FETs functionalized with a self-assembled monolayer of the molecules exhibit large hysteretic characteristics with regard to source--drain current vs gate voltage characteristics. The devices are operated with reversible switching behavior at gate voltage cycles of writing, reading, erasing, and reading, and their retention time is in excess of 1000 s. These results reveal that the reversible chemical reaction (i.e., oxidation and reduction of the molecules) of Ru\\text{II-tpy complexes produces a charging/discharging process of In2O3 nanowire FETs.

Choi, Insung; Lee, Junghyun; Jo, Gunho; Seo, Kyoungja; Choi, Nak-Jin; Lee, Takhee; Lee, Hyoyoung

2009-01-01

99

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

SciTech Connect

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

Denton, M.B.

1992-07-29

100

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

101

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

PubMed

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

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

2012-06-26

102

The ability of latrotoxin-like brain protein to induce fusion of negatively charged liposomes  

Microsoft Academic Search

A latrotoxin-like protein isolated from the bovine brain promoted fusion of negatively charged liposomes consisting of phosphatidylcholine, phosphatidylethanolamine, and cardiolipin in a molar ratio of 2:3:5. The fusogenic effect significantly increased at mild acidic pH 6.0 and under denaturation (4 M urea, 0.1% SDS). Using ANS as the fluorescent probe, it was found that hydrophobicity of the latrotoxin-like protein increases

I. O. Trikash; Ya. T. Terletskaya; L. I. Kolchinskaya; M. K. Malysheva; K. S. Serdyuk

1993-01-01

103

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

PubMed

The space charge effect of low energy, unbunched ion beams can be compensated by the trapping of ions or electrons into the beam potential. This has been studied for the 45 keV negative hydrogen ion beam in the CERN Linac4 Low Energy Beam Transport using the package IBSimu [T. Kalvas et al., Rev. Sci. Instrum. 81, 02B703 (2010)], which allows the space charge calculation of the particle trajectories. The results of the beam simulations will be compared to emittance measurements of an H(-) beam at the CERN Linac4 3 MeV test stand, where the injection of hydrogen gas directly into the beam transport region has been used to modify the space charge compensation degree. PMID:24593428

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

2014-02-01

104

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

NASA Astrophysics Data System (ADS)

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

Mizuno, T.; Itoh, A.

2014-04-01

105

Dynamics of Xanthine Oxidase and Fe 3+-ADP-Dependent Lipid Peroxidation in Negatively Charged Phospholipid Vesicles  

Microsoft Academic Search

Superoxide (O?2)-dependent lipid peroxidation on addition of xanthine oxidase (XO) and Fe3+-ADP was induced in egg phosphatidylcholine (PC) liposomes containing dicetylphosphate (DCP), which are negatively charged like biological membranes, but not in uncharged egg PC liposomes. Positively charged Fe3+ ADP interacted more with negatively charged egg PC-DCP liposomes than with uncharged egg PC liposomes. The activities of Fe3+-chelates for initiating

K. Fukuzawa; K. Soumi; M. Iemura; S. Goto; A. Tokumura

1995-01-01

106

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

107

Ultrafast Charge Rearrangement and Nuclear Dynamics upon Inner-Shell Multiple Ionization of Small Polyatomic Molecules  

NASA Astrophysics Data System (ADS)

Ionization and fragmentation of methylselenol (CH3SeH) molecules by intense (>1017W/cm2) 5 fs x-ray pulses (??=2keV) are studied by coincident ion momentum spectroscopy. We contrast the measured charge state distribution with data on atomic Kr, determine kinetic energies of resulting ionic fragments, and compare them to the outcome of a Coulomb explosion model. We find signatures of ultrafast charge redistribution from the inner-shell ionized Se atom to its molecular partners, and observe significant displacement of the atomic constituents in the course of multiple ionization.

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

2013-02-01

108

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

PubMed

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

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

2013-02-01

109

Gating the Charge State of Single Molecules by Local Electric Fields  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

111

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

112

Improved levitation and trapping of particles by negative dielectrophoresis by the addition of amphoteric molecules  

NASA Astrophysics Data System (ADS)

Addition of amphoteres could be used to improve the levitation and trapping of particles by negative dielectrophoresis. Addition of amphoteric molecules to electromanipulation media increases not only the permittivity of the medium and its viscosity but also its density. To investigate the effect of addition of amphoteres on levitation and trapping by negative dielectrophoresis, the electrokinetic behaviour of latex beads and viable yeast cells (Saccharomyces cerevisiae) was investigated in concentrated solutions of the amphoteric molecules N-[2-hydroxyethyl] piperazine-N'-[2-ethanesulfonic acid] (HEPES) and egr -aminocaproic acid (EACA) using different frequencies and voltages of the applied electrical signal and microelectrodes of different sizes. When using interdigitated electrodes without castellations, latex beads levitated an average of 43% higher when 0.67 M EACA solutions were used and a 54% higher after adding 0.67 M HEPES compared with the levitation heights when no amphoteres were added. Under the same conditions, yeast levitated 78% and 86% higher, respectively. At low voltages and low HEPES/EACA concentrations, the latex particles accumulated in bands between or above the electrodes. However, at the highest voltages and HEPES/EACA concentrations used, the particles formed a network of pearl chains above the electrode arrays. When using electrodes of the interdigitated castellated type of characteristic size 30 µm, latex particles levitated 32% and 40% higher when 0.67 M EACA and HEPES solutions were used in comparison with when no amphoteres were added. At these concentrations, the flow rate needed to dislodge the latex particles from the traps formed by the electric field pattern between the castellations of the interdigitated castellated electrodes was increased by 46% compared with the flow rate needed to achieve this when no amphoteres were added.

Flores-Rodriguez, Neftali; Markx, Gerard H.

2004-02-01

113

Highly selective uptake and release of charged molecules by pH-responsive polydopamine microcapsules.  

PubMed

A systematic study of the permeation of small molecules through Pdop microcapsules is reported. The zwitterionic Pdop microcapsules are prepared by oxidative polymerization of dopamine on polystyrene microspheres followed by core removal with THF. Rhodamine 6G, methyl orange and alizarin red are chosen as differently charged probing dyes. The loading amount is affected by pH and dye concentration. Highly selective and unidirectional uptake and release of charged molecules through Pdop microcapsules can be achieved by controlling pH value: at low pH, the Pdop particles incorporate cationic dye (rhodamine 6G); at high pH, they incorporate anionic dyes (methyl orange and alizarin red). In each case, the uptake is highly selective. PMID:21721126

Liu, Qinze; Yu, Bo; Ye, Weichun; Zhou, Feng

2011-09-01

114

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

PubMed Central

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

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

2012-01-01

115

Urinary proteins and red blood cell membrane negative charges in diabetes mellitus.  

PubMed

The nature and origin of proteinuria in diabetes mellitus have been investigated by measuring the urinary excretion of seven specific proteins of low (beta 2-microglobin, retinol-binding protein) or high molecular weight (albumin, transferrin, hemopexin and IgG). Using the Alcian Blue binding test, we also measured negative charges on red blood cell (RBC) membrane which according to recent studies might mirror the glomerular polyanion charge. A group of 190 diabetics was examined, including 90 patients with type I diabetes, 23 type II diabetics treated with diet and/or hypoglycaemic agents and 77 longstanding type II diabetics requiring insulin therapy. With the exception of beta 2-microglobulin all proteins measured were excreted in the urine of diabetics in significantly higher amounts than in controls. The assay of transferrin proved the most sensitive (58% positive) followed by albumin (49%), IgG (34%), hemopexin (28%) and retinol-binding protein (26%). Practically the same ranking was obtained when only type I diabetics were considered. RBC membrane negative charges were diminished in diabetics and negatively correlated with the urinary excretion of albumin (r = -0.61, n = 190). RBC charges were also negatively correlated with other urinary proteins of high molecular mass (r between - 0.5 and - 0.2) but presented no relation with urinary beta 2-microglobulin or retinol-binding protein. The loss of RBC charges in diabetics most likely reflects the concomitant depletion of the glomerular polyanion responsible for the increased glomerular leakage of high molecular mass plasma proteins. The preferential increase in transferrin excretion together with the progressive rise in the urinary excretion of IgG lead us to postulate that the loss of glomerular polyanion in diabetes is accompanied, from the early stage, by a progressive decrease in the size-selectivity of the glomerular filter. The urinary excretion of retinol-binding protein was weakly correlated with albuminuria (r = 0.26, n = 186). Eight % of diabetics showed an elevation of urinary retinol-binding protein without evidence of microalbuminuria, which clearly demonstrates that a proximal tubular impairment can occur independently of the glomerular alterations in the course of diabetic nephropathy. PMID:2253403

Bernard, A; Amor, A O; Goemare-Vanneste, J; Antoine, J L; Lauwerys, R; Colin, I; Vandeleene, B; Lambert, A

1990-10-15

116

Mutation of a negatively charged amino acid in thioredoxin modifies its reactivity with chloroplastic enzymes.  

PubMed

A new over-expression system has been set up for Escherichia coli thioredoxin, yielding 55 mg purified protein/10 g fresh cells. This system has been used to produce thioredoxin modified by site-directed mutagenesis. Taking advantage of the structural and enzymatic similarity between E. coli and spinach m-type thioredoxin, Asp61 of E. coli thioredoxin has been changed into Asn in order to investigate the impact of the suppression of a charged residue on the interaction of thioredoxin with target enzymes. The modification did not significantly alter the structure of the protein. Neither the rate of reduction of insulin and 5,5'-dithio-bis(2-nitrobenzoic acid) by the reduced thioredoxin, nor the reduction by NADPH-dependent thioredoxin reductase, have been modified. The major effect of the mutation was observed for chloroplast enzyme activation with thioredoxin reduced by dithiothreitol and with thioredoxin reduced by ferredoxin-dependent thioredoxin reductase in a light-activation reconstituted chloroplast system. The substitution of the negatively charged Asp61 by the neutral Asn led to an increase in the efficiency of spinach fructose-1,6-bisphosphatase activation by the dithiothreitol-reduced thioredoxin, and to an increase in both spinach fructose-1,6-bisphosphatase and corn NADP-dependent malate dehydrogenase activities in the light-activation system. This suggests that the suppression of the negative charge improves the reactivity of thioredoxin with chloroplast enzymes such as fructose-1,6-bisphosphatase and ferredoxin-dependent thioredoxin reductase. PMID:1848815

de Lamotte-Guery, F; Miginiac-Maslow, M; Decottignies, P; Stein, M; Minard, P; Jacquot, J P

1991-03-14

117

Overexpression of Hedgehog signaling molecules and its involvement in triple-negative breast cancer  

PubMed Central

The purpose of this study was to investigate the activation of Hedgehog (Hh) signaling molecules and its involvement in triple-negative breast cancer (TNBC). A total of 123 cases of paraffin blocks, including 83 cases of primary breast carcinoma, 30 cases of mammary hyperplasia and 10 cases of normal breast tissue, were immunohistochemically analyzed for Sonic Hedgehog (SHH), Patched-1 (PTCH1), Smoothened (SMO) and glioma-associated oncogene homoglog 1 (GLI1) expression. The expression of SMO and GLI1 in TNBC was significantly increased in comparison to non-triple-negative breast cancer (nTNBC). GLI1 expression manifested an inverse association with the estrogen receptor. The levels of GLI1 expression were increased in lymph node-positive cases. The expression of SHH and SMO was increased in high histological grades. Furthermore, the expression of SMO and GLI1 was correlated with superior tumor stage. The expression of SHH, SMO and GLI1 was significantly increased in breast cancer and mammary hyperplasia. PTCH1 expression was significantly decreased in breast cancer compared to mammary hyperplasia and normal breast tissue. For the first time, clinical evidence has been provided in support of significant roles of Hh signaling in TNBC. Hh signaling is involved in breast ductal changes and malignant transformation. Measures to inhibit Hh activity may improve the prognosis of TNBC patients.

Tao, Yajun; Mao, Jun; Zhang, Qingqing; Li, Lianhong

2011-01-01

118

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

PubMed

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

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

2014-01-01

119

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

2010-08-01

120

Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer  

PubMed Central

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

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

2011-01-01

121

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

PubMed

The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of ?-? stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the ?-? stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility. PMID:24658783

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

2014-05-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

123

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

124

Negative charge of the glutamic acid 417 residue is crucial for isomerohydrolase activity of RPE65.  

PubMed

RPE65 is the isomerohydrolase essential for regeneration of 11-cis retinal, the chromophore of visual pigments. Here we compared the impacts of two mutations in RPE65, E417Q identified in patients with Leber congenital amaurosis (LCA), and E417D on isomerohydrolase activity. Although both mutations decreased the stability of RPE65 and altered its sub-cellular localization, E417Q abolished isomerohydrolase activity whereas the E417D mutant retained partial enzymatic activity suggesting that the negative charge of E417 is important for RPE65 catalytic activity. Loss of charge at this position may represent a mechanism by which the E417Q mutation causes blindness in LCA patients. PMID:20043869

Nikolaeva, Olga; Takahashi, Yusuke; Moiseyev, Gennadiy; Ma, Jian-Xing

2010-01-22

125

High intensity source of polarized negative hydrogen ions with resonant charge-exchange plasma ionizer  

NASA Astrophysics Data System (ADS)

The Moscow INR atomic-beam type source of polarized negative hydrogen ions is described. The production of H- ions is based on resonant charge exchange between polarized thermal hydrogen atoms and D- ions in a deuterium plasma. Improvements in the D- plasma source are outlined. The polarized source produces a pulsed H- beam with the peak current up to 1 mA and pulse duration of 180 ?s at repetition rate 10 Hz. The normalized emittance for 90% of the beam particles is 1.8 ? mm mrad. The polarization of low energy H- ions was measured to be 0.87+/-0.02.

Belov, A. S.; Esin, S. K.; Netchaeva, L. P.; Plokhinski, Yu. V.; Vasil'Ev, G. A.; Klenov, V. S.; Turbabin, A. V.; Yakushev, V. P.; Dudnikov, V. G.

1996-07-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

127

Negatively charged hydrogen species in n-type GaAs  

NASA Astrophysics Data System (ADS)

Se donors in doped n-type GaAs are passivated by exposure to a hydrogen plasma. The thermal reactivation of the passivated donors is investigated for the temperature range 154°C-191°C. By using the electric field of a reverse-biased Schottky-diode structure, the drift of the thermally dissociated hydrogen as a negatively charged species is demonstrated. The thermal dissociation of the SeH complex obeys first-order kinetics, with a dissociation energy ESeH=1.52+/-0.05 eV.

Leitch, A. W. R.; Prescha, Th.; Weber, J.

1991-07-01

128

Modification of enzyme surface negative charges via covalent immobilization for tailoring the activity and enantioselectivity  

Microsoft Academic Search

With the hydrolytic resolution of (R,S)-mandelates in biphasic media via an esterase (SNSM-87) from Klebsiella oxytoca as the model system, increasing of the ionization constants of catalytic imidazolium moiety (i.e. pK2R from 5.96 to 4.11 and pK2S from 5.16 to 3.66) was confirmed if the enzyme was immobilized on a hexamethylenamino-activated support (Sepabeads@ EC-HA) for decreasing the negative surface charges

Pei-Yun Wang; Shau-Wei Tsai

2009-01-01

129

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

PubMed

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

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

2012-08-14

130

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

131

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

PubMed Central

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

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

2012-01-01

132

Electron spin resonance, electron spin echo modulation, and electron nuclear double resonance studies on the photolysis of positively and negatively charged alkylphenothiazines in anionic aerosol dioctyl and cationic cetyltrimethylammonium bromide\\/hexanol reverse micelles  

Microsoft Academic Search

Photoionization of solubilized molecules in organized molecular assemblies has been used as model systems for light energy storage. In this article, positively charged (phenothiazinylalkyl)trimethylammonium bromides (PC[sub n]\\/TAB, n = 4, 6, 9, 12) and negatively charged sodium alkylphenothiazinesulfonates (PC[sub n]\\/S, n = 3, 6, 9, 12) incorporated into anionic aerosol dioctyl (AOT) and cationic cetylrimethylammonium bromide (CTAB)\\/hexanol reverse micelles have

Young Soo Kang; Larry Kevan

1993-01-01

133

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

134

Intermolecular interactions, charge-density distribution and the electrostatic properties of pyrazinamide anti-TB drug molecule: an experimental and theoretical charge-density study.  

PubMed

An experimental charge-density analysis of pyrazinamide (a first line antitubercular drug) was performed using high-resolution X-ray diffraction data [(sin??/?)max = 1.1?Å(-1)] measured at 100?(2)?K. The structure was solved by direct methods using SHELXS97 and refined by SHELXL97. The total electron density of the pyrazinamide molecule was modeled using the Hansen-Coppens multipole formalism implemented in the XD software. The topological properties of electron density determined from the experiment were compared with the theoretical results obtained from CRYSTAL09 at the B3LYP/6-31G** level of theory. The crystal structure was stabilized by N-H...N and N-H...O hydrogen bonds, in which the N3-H3B...N1 and N3-H3A...O1 interactions form two types of dimers in the crystal. Hirshfeld surface analysis was carried out to analyze the intermolecular interactions. The fingerprint plot reveals that the N...H and O...H hydrogen-bonding interactions contribute 26.1 and 18.4%, respectively, of the total Hirshfeld surface. The lattice energy of the molecule was calculated using density functional theory (B3LYP) methods with the 6-31G** basis set. The molecular electrostatic potential of the pyrazinamide molecule exhibits extended electronegative regions around O1, N1 and N2. The existence of a negative electrostatic potential (ESP) region just above the upper and lower surfaces of the pyrazine ring confirm the ?-electron cloud. PMID:24892603

Rajalakshmi, Gnanasekaran; Hathwar, Venkatesha R; Kumaradhas, Poomani

2014-06-01

135

Two weeks of permanence in negatively-charged air conditions causes alteration of natural killer cell function.  

PubMed

The effects of negatively-charged air conditions were analyzed as one of the approaches to improve health and quality of life. We previously reported that the use of a charcoal coating and application of an electric voltage yielded predominantly negatively-charged particles in an experimental room, and that 2.5 hours of living in these conditions caused a slight activation of the immune system (slight elevation of serum interleukin (IL)-2), regulated blood flow, and stabilized the autonomic nervous system when compared with control conditions (no dominance of negatively-charged particles). In this study, we expanded the previous study and placed 15 subjects in negatively-charged air conditions for two weeks during the night and analyzed various biological parameters. Although individual biological reactions differed from subject to subject, natural killer (NK) cell activity increased significantly following living in negatively-charged air conditions. Taken together, the results of the previous investigation and those of this study show that repeated elevation of IL-2 (although it immediately returned to the baseline level) causes chronic and recurrent stimulation to NK cells and results in the steady activation of NK cells. Negatively-charged air particles may be a good tool to improve health and quality of life. PMID:19505387

Takahashi, K; Otsuki, T; Mase, A; Kawado, T; Kotani, M; Nishimura, Y; Maeda, M; Murakami, S; Kumagai, N; Hayashi, H; Chen, Y; Shirahama, T; Miura, Y; Morimoto, K

2009-01-01

136

Exhibition of tunnel coupling of negatively charged dangling bonds on Si Surface Using Scanning Tunneling Microscope  

NASA Astrophysics Data System (ADS)

We have performed Scanning tunneling microscopy study of hydrogen terminated Si (100). We will show that single Si atoms in a solid state environment can be served as quantum dots. These negatively charged quantum dots can be tunnel coupled to the nearby Si quantum dots. We will demonstrate that this tunnel coupling can be controlled by adjusting the separation between the two Si atomic quantum dots. Moreover electron occupation in the tunnel coupled Si quantum dots can be controlled. We have used this tunnel coupling effect of Si atomic quantum dots to fabricate Quantum Cellular Automata Cells. Quantum Cellular Automata are used to transmit binary information through electrostatic interaction between adjacent cells without the transfer of charge from one cell to the next. Devices based on Quantum Cellular Automata will consume much less power compared to the conventional transistor based devices. Moreover, since there is no transfer of charge so power dissipation during its operation is minimal compared to conventional semiconductor devices. This Si based Quantum Cellular Automat Cell works at room temperature.

Baseer Haider, M.; Livadaru, L.; Pitters, J.; Wolkow, R.

2011-03-01

137

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

Microsoft Academic Search

The authors have discussed the validity of Saha's equation for the charging of negatively charged spherical particles in a complex plasma in thermal equilibrium, even when the tunneling of the electrons, through the potential energy barrier surrounding the particle is considered. It is seen that the validity requires the probability of tunneling of an electron through the potential energy barrier

M. S. Sodha; S. K. Mishra

2011-01-01

138

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

SciTech Connect

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

Surrey, Elizabeth; Porton, Michael [EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon 0X14 3DB (United Kingdom)

2011-09-26

139

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

PubMed

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

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

2013-06-19

140

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

141

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

NASA Astrophysics Data System (ADS)

We generalize the vacuum static black string solutions of Einstein's equations with negative cosmological constant recently discussed in literature, by including an electromagnetic field. These higher-dimensional configurations have no dependence on the 'compact' extra dimension, while their boundary topology is the product of time and Sd-3 × S1 or Hd-3 × S1. Rotating generalizations of the even dimensional black string configurations are considered as well. Different from the static, neutral case, no regular limit is found for a vanishing event horizon radius. We explore numerically the general properties of such classical solutions and, using a counterterm prescription, we compute their conserved charges and discuss their thermodynamics. We find that the thermodynamics of the black strings follows the pattern of the corresponding black hole solutions in AdS backgrounds.

Brihaye, Yves; Radu, Eugen; Stelea, Cristian

2007-09-01

142

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

143

First experimental evidence of dopamine interactions with negatively charged model biomembranes.  

PubMed

Dopamine is essential for receptor-related signal transduction in mammalian central and peripheral nervous systems. Weak interactions between the neurotransmitter and neuronal membranes have been suggested to modulate synaptic transmission; however, binding forces between dopamine and neuronal membranes have not yet been quantitatively described. Herein, for the first time, we have explained the nature of dopamine interactions with model lipid membranes assembled from neutral 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), negatively charged 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), and the mixture of these two lipids using isothermal titration calorimetry and differential scanning calorimetry. Dopamine binding to anionic membranes is a thermodynamically favored process with negative enthalpy and positive entropy, quantitatively described by the mole ratio partition coefficient, K. K increases with membrane charge to reach its maximal value, 705.4 ± 60.4 M(-1), for membrane composed from pure DMPG. The contribution of hydrophobic effects to the binding process is expressed by the intrinsic partition coefficient, K(0). The value of K(0) = 74.7 ± 6.4 M(-1) for dopamine/DMPG interactions clearly indicates that hydrophobic effects are 10 times weaker than electrostatic forces in this system. The presence of dopamine decreases the main transition temperature of DMPG, but no similar effect has been observed for DMPC. Basing on these results, we propose a simple electrostatic model of dopamine interactions with anionic membranes with the hydrophobic contribution expressed by K(0). We suggest that dopamine interacts superficially with phospholipid membranes without penetrating into the bilayer hydrocarbon core. The model is physiologically important, since neuronal membranes contain a large (even 20%) fraction of anionic lipids. PMID:23662798

Jodko-Piorecka, Katarzyna; Litwinienko, Grzegorz

2013-07-17

144

Recovery curves of the surface electric field after lightning discharges occurring between the positive charge pocket and negative charge centre in a thundercloud  

Microsoft Academic Search

Surface observations of the electric field recovery curves of the lightning discharges occurring between the positive charge pocket and negative main charge centre in an overhead thundercloud are reported. Such recovery curves are observed to have an additional step of very slow field-change observed at an after-discharge value of electric field equal to 5–6 kV m?1. The behavior of recovery

S. D. Pawar; A. K. Kamra

2002-01-01

145

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

146

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

147

From Self-Assembly to Charge Transport with Single Molecules - An Electrochemical Approach  

NASA Astrophysics Data System (ADS)

Structure formation and self-assembly of physisorbed and chemisorbed organic monolayers will be described on electrified solid-liquid interfaces employing in-situ scanning tunneling microscopy (STM) and surface-enhanced infrared spectroscopy (SEIRAS) in combination with electrochemical techniques. We present first a case study on self-assembly by directional hydrogen bonding and its interplay with the electrode potential choosing aromatic carboxylic acids, with an emphasis on 1,3,5-benzene-tricarboxylic acid (TMA). Structure and electrical characteristics of chemisorbed organic monolayers involving the formation of covalent bonds with the substrate surface will be discussed for a series of 4-methyl-4'-(n-mercaptoalkyl)biphenyls on Au(111) electrodes. In an attempt to explore single molecule properties, such as charge transport and redox-mediated tunneling, we subsequently introduce an STM-based technique to construct symmetric and asymmetric metal/(single) molecule/metal junctions. Employing ?,?-alkanedithiols and redox-active derivatives of viologens we demonstrate novel transport and single molecule electrochemical studies, which bear unique novel perspectives for fundamental as well as applied investigations.

Han, Bo; Li, Zhihai; Li, Chen; Pobelov, Ilya; Su, Guijin; Aguilar-Sanchez, Rocio; Wandlowski, Thomas

148

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

PubMed

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

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

2011-04-15

149

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

150

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

PubMed Central

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

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

2013-01-01

151

Moving towards strong-field femtosecond control of bond cleavage and charge localization in triatomic molecules  

NASA Astrophysics Data System (ADS)

A 3-D momentum imaging technique is employed to study intense ultrafast laser-induced dissociation of triatomic molecular ions from an ion beam. Utilizing our measured kinetic energy release and angular distribution spectra along with the calculated electronic structure of these molecules, we elucidate possible dissociation pathways and anticipate and explore various laser parameters that could be used to drive transitions to specific final products. For example, we have studied N2O^+, in which we find that for typical intense IR laser pulses (˜30 fs, transform-limited, 800 nm, ˜10^15 W/cm^2 pulses), the preferred bond cleavage (i.e., breaking the N-N bond vs. the N-O bond) and charge localization patterns are those that are the most energetically favorable. We investigate laser parameters that could be used to steer this and other systems to less likely outcomes.

Jochim, Bethany; Ablikim, U.; Zohrabi, M.; Gaire, B.; Carnes, K. D.; Esry, B. D.; Ben-Itzhak, I.

2012-06-01

152

Control of homogeneous charge compression ignition combustion in a two-cylinder gasoline direct injection engine with negative valve overlap  

Microsoft Academic Search

Homogeneous charge compression ignition (HCCI) has challenges in ignition timing control, combustion rate control, and operating\\u000a range extension. In this paper, HCCI combustion was studied in a two-cylinder gasoline direct injection (GDI) engine with\\u000a negative valve overlap (NVO). A two-stage gasoline direct injection strategy combined with negative valve overlap was used\\u000a to control mixture formation and combustion. The gasoline engine

Zhi Wang; Jianxin Wang; Shijin Shuai; Qingjun Ma; Guohong Tian

2007-01-01

153

MoleCoolQt - a molecule viewer for charge-density research  

PubMed Central

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

Hubschle, Christian B.; Dittrich, Birger

2011-01-01

154

Rational design of charge transport molecules for blue organic light emitting devices  

NASA Astrophysics Data System (ADS)

The efficiency and stability of blue OLEDs continue to be the primary roadblock to developing organic solid-state white lighting as well as power efficient displays. It is generally accepted that such high quantum efficiency can be achieved with the use of organometallic phosphor doped OLEDs. The transport layers can be designed to increase the carrier density as a way to reduce the drive voltage. We have developed a comprehensive library of charge transporting molecules using combination of theoretical modeling and experimental evidence. Our work focuses on using chemical structure design and computational methods to develop host, transport, emitter, and blocking materials for high efficiency blue OLEDs, along with device architectures to take advantage of these new materials. Through chemical modification of materials we are able to influence both the charge balance and emission efficiency of OLEDs, and understand the influence of the location of photon emission in OLEDs as a function of minor chemical modifications of host and electron transport materials. Design rules, structure-property relationships and results from state of the art OLEDs will be presented.

Padmaperuma, Asanga; Cosimbescu, Lelia; Koech, Phillip; Polikarpov, Evgueni; Swensen, James; Gaspar, Daniel

2012-02-01

155

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

156

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

2011-01-01

157

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

PubMed Central

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

Kecke, L; Ankerhold, J

2011-01-01

158

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

PubMed

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

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

2010-12-01

159

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

2013-05-13

160

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

161

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

NASA Technical Reports Server (NTRS)

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

Armstrong, T. W.

1972-01-01

162

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

NASA Astrophysics Data System (ADS)

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

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

1993-06-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

164

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

SciTech Connect

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

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

2009-06-08

165

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

166

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

167

Molecular Interactions of Alzheimer Amyloid-? Oligomer with Neutral and Negatively Charged Lipid Bilayers  

PubMed Central

Interaction of p3 (A?17-42) peptides with cell membrane 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-oleyl-phosphatidylcholine) and mixed anionic POPC/POPG (palmitoyl-oleyl-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 fibrililation are enhanced on anionic lipid bilayers. Although electrostatic interactions are main attractive forces to drive the p3 to adsorb on the bilayer surface, the adsorption of the p3 pentamer on the lipid bilayer with a preferential 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, Ca2+ ions are found to form ionic bridges to associate negatively charged residues of p3 with anionic headgroups of the lipid bilayer, resulting in A?–Ca2+–PO4? complexes. Intensive Ca2+ bound to lipid bilayer and Ca2+ ionic bridges may lead to the alternation of Ca2+ hemostasis responsible for neuronal dysfunction and death. This work provides insights into the mutual structure, dynamics, and interactions of both A? peptides and lipid bilayer at the atomic level, which expand our understanding of the complex behavior of amyloid-induced membrane disruption.

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

2013-01-01

168

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

PubMed

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

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

2014-02-15

169

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

SciTech Connect

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

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

2012-01-15

170

Control of ion flux and selectivity by negatively charged residues in the outer mouth of rat sodium channels.  

PubMed Central

1. The sodium channel has a ring of negatively charged amino acids on its external face. This common structural feature of cation-selective channels has been proposed to optimize conduction by electrostatic attraction of permeant cations into the channel mouth. We tested this idea by mutagenesis of mu1 rat skeletal sodium channels expressed in Xenopus oocytes. 2. Replacement of the external glutamate residue in domain II by cysteine reduces sodium current by decreasing single-channel conductance. While this effect can be reversed by the negatively charged sulfhydryl modifying reagent methanethiosulphonate ethylsulphonate (MTSES), the flux saturation behaviour cannot be rationalized simply by changes in the surface charge. 3. The analogous mutations in domains I, III and IV affect not only conductance but also selectivity. These changes in selectivity are only partially reversed by exposure to MTSES. 4. Our findings necessitate revision of prevailing concepts regarding the role of superficial negatively charged residues in the process of ion permeation. These residues do not act solely by electrostatic attraction of permeant ions, but instead may help to form ion-specific binding sites within the pore. Images Figure 1

Chiamvimonvat, N; Perez-Garcia, M T; Tomaselli, G F; Marban, E

1996-01-01

171

The effects of electric fields on charged molecules and particles in individual microenvironments  

NASA Astrophysics Data System (ADS)

Measurements of small air ion concentrations, electrostatic potential and AC electric field strengths were taken in an office setting to investigate the link between electric fields and charged molecule and particle concentrations in individual microenvironments. The results obtained indicate that the electromagnetic environments individuals can be exposed to whilst indoors can often bear little resemblance to those experienced outdoors in nature, and that many individuals may spend large periods of their time in "Faraday cage"-like conditions exposed to inappropriate levels and types of electric fields that can reduce localised concentrations of biologically essential and microbiocidal small air ions. Such conditions may escalate their risk of infection from airborne contaminants, including microbes, whilst increasing localised surface contamination. The degree of "electro-pollution" that individuals are exposed to was shown to be influenced by the type of microenvironment they occupy, with it being possible for very different types of microenvironment to exist within the same room. It is suggested that adopting suitable electromagnetic hygiene/productivity guidelines that seek to replicate the beneficial effects created by natural environments may greatly mitigate such problems.

Jamieson, K. S.; ApSimon, H. M.; Jamieson, S. S.; Bell, J. N. B.; Yost, M. G.

172

Charge symmetric dissociation of doubly ionized N2 and CO molecules  

NASA Astrophysics Data System (ADS)

We report a comparative study of the features in dissociative double ionization by high energy electron impact of N2 and CO molecules. The ratio of cross-section of charge symmetric dissociative ionization to non-dissociative ionization (CSD-to-ND ratio) and the kinetic energy release (KER) spectra of dissociation are experimentally measured and carefully corrected for various ion transmission losses and detector inefficiencies. Given that the double ionization cross sections of these iso-electronic diatomics are very similar, the large difference in the CSD-to-ND ratios must be attributable to the differences in the evolution dynamics of the dications. To understand these differences, potential energy curves (PECs) of dications have been computed using multi-reference configuration interaction method. The Franck-Condon factors and tunneling life times of vibrational levels of dications have also been computed. While the KER spectrum of N_2^{++} can be readily explained by considering dissociation via repulsive states and tunneling of meta-stable states, indirect dissociation processes such as predissociation and autoionization have to be taken into account to understand the major features of the KER spectrum of CO++. Direct and indirect processes identified on the basis of the PECs and experimental KER spectra also provide insights into the differences in the CSD-to-ND ratios.

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

2014-01-01

173

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

174

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

175

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

176

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

177

High-Current Proton BEAMS at Novosibirsk (Electron Compensation, Charge-Exchange Injection, Negative Ion Sources).  

National Technical Information Service (NTIS)

The results of experiments on the storage of intense proton beams in accelerators using the method of charge exchange injection are presented. Due to compensation of the proton space charge by electrons we obtained a proton beam in the storage ring with a...

I. I. Belchenko G. I. Budker G. E. Dereviankin G. I. Dimov V. G. Dudnikov

1977-01-01

178

Effects of removing the negatively charged N-terminal region of the salivary acidic proline-rich proteins by human leucocyte elastase.  

PubMed

Human leucocyte elastase from inflammatory gingival crevicular exudates (gingival crevicular fluid) contacts saliva and saliva-coated tooth surfaces coronal to the gingival margin. Major components of saliva are the salivary acidic proline-rich proteins (PRPs). These acidic PRPs, via the numerous negatively charged amino acid residues located predominantly within their amino-terminal region, bind to the hydroxyapatite mineral of the tooth surface and become part of the salivary pellicle. Thus the potential for human leucocyte elastase-mediated removal of the negatively charged amino-terminal region of acidic PRP variants (PRP-1, PRP-2, PRP-3, PRP-4, PIF-s and PIF-f) was examined. It was determined that each of the acidic PRP variants was susceptible to fragmentation by human leucocyte elastase, in which the 16 amino-terminal segment was removed, leaving the respective residual fragment named as the transitional product (tr). The transitional products were termed PRP-1tr, PRP-2tr (PIF-str), PRP-3tr and PRP-4tr (PIF-ftr). Each of the residual transitional products of acidic PRP had an amino-terminal beginning with serine residue no. 17, determined by amino acid sequencing. When samples of human leucocyte elastase-treated acidic PRPs were placed on native polyacrylamide gels and electrophoresed, the respective transitional products moved more slowly than the parental acidic PRP molecules, reflecting the loss of a portion of the negatively charged section. In comparison to the acidic PRPs, the acidic PRP transitional products had markedly reduced binding to hydroxyapatite. The transitional products were resistant to further enzymatic digestion as a function of increased incubation time and appeared to exert an antihuman leucocyte elastase effect. However, when increased concentrations of human leucocyte elastase were incubated with the acidic PRP, a more extensive digestion occurred, leaving a residual peptide with an amino-terminal beginning with alanine residue no. 44. Interestingly, intact acidic PRPs if prebound to hydroxyapatite particles, resisted digestion by human leucocyte elastase. In summary, human leucocyte elastase was capable of digesting fluid-phase (unbound) acidic PRP in a manner that eliminated part of their negatively charged region, which subsequently reduced their binding to hydroxyapatite. High concentrations of human leucocyte elastase, arriving from inflammatory gingival crevicular exudates, may interrupt the normal binding of fluid-phase acidic PRPs to hydroxyapatite. PMID:10414872

Boackle, R J; Dutton, S L; Robinson, W L; Vesely, J; Lever, J K; Su, H R; Chang, N S

1999-07-01

179

Modulation of tryptophan environment in membrane-bound melittin by negatively charged phospholipids: implications in membrane organization and function.  

PubMed

Melittin is a cationic hemolytic peptide isolated from the European honey bee, Apis mellifera. Since the association of the peptide in the membrane is linked with its physiological effects, a detailed understanding of the interaction of melittin with membranes is crucial. We have investigated the interaction of melittin with membranes of varying surface charge in the context of recent studies which show that the presence of negatively charged lipids in the membrane inhibits membrane lysis by melittin. The sole tryptophan residue in melittin has previously been shown to be critical for its hemolytic activity. The organization and dynamics of the tryptophan residue thus become important to understand the peptide activity in membranes of different charge types. Wavelength-selective fluorescence was utilized to monitor the tryptophan environment of membrane-bound melittin. Melittin exhibits a red edge excitation shift (REES) of 5 nm when bound to zwitterionic membranes while in negatively charged membranes, the magnitude of REES is reduced to 2-3 nm. Further, wavelength dependence of fluorescence polarization and near-UV circular dichroism spectra reveal characteristic differences in the tryptophan environment for melittin bound to zwitterionic and anionic membranes. These studies are supported by time-resolved fluorescence measurements of membrane-bound melittin. Tryptophan penetration depths for melittin bound to zwitterionic and anionic membranes were analyzed by the parallax method [Chattopadhyay, A., and London, E. (1987) Biochemistry 26, 39-45] utilizing differential fluorescence quenching obtained with phospholipids spin-labeled at two different depths. Our results provide further insight into molecular details of membrane lysis by melittin and the modulation of lytic activity by negatively charged lipids. PMID:9398147

Ghosh, A K; Rukmini, R; Chattopadhyay, A

1997-11-25

180

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

PubMed Central

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

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

2012-01-01

181

Negative differential resistance and pulsed current induced multi-level resistivity switching in charge ordered and disordered manganites  

Microsoft Academic Search

We have investigated direct and pulsed current induced electroresistance in two manganites with different electronic and magnetic ground states: charge-orbital ordered 50 % Ca doped NdMnO3 and 50 % Mn doped LaNiO3. It has been shown that negative differential resistance observed at high current density in these compounds is related to Joule heating. However, bi-level and multi-level resistivity switching induced

A. Rebello; R. Mahendiran

2008-01-01

182

Diagnosis of negative hydrogen ions and rovibrational distribution of H2 molecule in non-thermal plasmas  

NASA Astrophysics Data System (ADS)

Rovibrational excited hydrogen molecule plays an important role for the production of H- ions. The correlation between H- ion density and rovibrational distribution of H2 molecules has been investigated in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry and molecular beam mass spectrometry. The relative vibrational distribution of molecular hydrogen in the electronic ground state has been determined by the best fitting to the Fulcher-? band emission lines. It is shown that the ratio of the Q(0-0)(1) to Q(1-1)(1) line is very suitable and simple for the diagnosis of vibrational temperature in the range of 1500 to 7500 K. At certain discharge conditions (ac 40 kHz, 14 kV), the vibrational temperature decreases from 3600 to 2400 K as the pressure increases from 100 to 200 Pa and the negative ions density near the ground electrode also decreases as the pressure increases. Both the hydrogen ions density and the vibrational temperature increase with the increasing of discharge voltage. It is found that the evolution of negative atomic hydrogen ions density greatly depends on the vibrational temperature.

Wang, W. G.; Xu, Y.; Yang, X. F.; Zhu, A. M.; Liu, Z. W.; Liu, X.

2008-01-01

183

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

184

Bright and dark triplet states of the negatively charged magnetoexcitons revealed in photoluminescence and time-resolved measurements  

SciTech Connect

Continuous and time-resolved magnetophotoluminescence measurements of three GaAs/Al{sub x}Ga{sub 1-x}As heterostructures have been made in high magnetic fields. The spectra revealed the presence of a singlet and two triplet states (the so-called ''bright'' and ''dark'' states) of the negatively charged magnetoexciton, in addition to the neutral exciton. For an asymmetrically doped single quantum well sample, the singlet and the dark triplet states converge (and possibly cross) at a field of about 40 T. The two single heterojunction samples on the other hand show no such convergence, and the singlet remains the fundamental state at least in fields to 60 T. The lifetimes of the charged magnetoexcitons increased linearly with field, whereas the neutral exciton was essentially field independent. The results clarify earlier experimental studies, and provide a confirmation of a recent theory of the behavior of charged magnetoexcitons in magnetic fields by Wojs [Phys Rev. B 62, 4630 (2000)].

Munteanu, F. M.; Rickel, D. G.; Perry, C. H.; Kim, Yongmin; Simmons, J. A.; Reno, J. L.

2000-12-15

185

Efficacy of self-assembled hydrogels composed of positively or negatively charged peptides as scaffolds for cell culture.  

PubMed

KASEA16(+) and KASEA16(-) peptides, the net charges of which are positive and negative, respectively, under a neutral condition could undergo self-assembly into nanofibers and form transparent hydrogels without peptide aggregation upon rapid pH neutralization. The numbers of NIH3T3 cells attached to the KASEA16(+) hydrogel and KASEA16(-) hydrogel were similar, and cells proliferated with time on both hydrogels. Cells on the KASEA16(+) hydrogel had spindle-like morphology, while cells on the KASEA16(-) hydrogel formed clusters without extending cytoplasmic processes. Comparison of differently charged peptides under a neutral condition suggested that the charges of the scaffolds should be taken into consideration for the best design and selection of scaffolds for cell culture. Since the KASEA16(+) peptide could form a stable hydrogel under a neutral condition and the hydrogel served as a scaffold for cell proliferation, the KASEA16(+) hydrogel will be a useful scaffold for cell culture. PMID:21123284

Nagayasu, Aya; Yokoi, Hidenori; Minaguchi, Jun A; Hosaka, Yoshinao Z; Ueda, Hiromi; Takehana, Kazushige

2012-02-01

186

Local description of the through phenyl transfer of a negative charge within resonance theory: topological effects in xylylene radical anions  

NASA Astrophysics Data System (ADS)

The topological effects specifying a di-substituted phenyl ring bearing a negative charge are investigated by considering the radical anions of para- and meta-xylylene isomers as model systems. The super exchange (SE) and double exchange (DE) component mechanisms describing the through phenyl transfer of a negative charge are considered and examined within `resonance' or `mesomeric' theory. The radical anion electronic events characterizing the DE and SE resonance structures are investigated by means of poly-electron population analysis. Correlated ab initio MO wavefunctions are used as the starting material in our calculations, and the various second quantized density operators are built on the basis of natural AOs. Conditional electronic events specifying SE or DE mechanisms are defined, and the corresponding probabilities are compared for meta and para topologies. The main trends are rationalized by comparing the effects provoked in phenyl ring when the negative charge is transferred from one substituent or the other. In para topology the effects are additive for the most important resonance structures, while in meta (characterized from `quantum interferences') the same effects are antagonist in all structures and for both SE and DE mechanisms.

Karafiloglou, Padeleimon; Launay, Jean-Pierre

1999-11-01

187

Charge transfer in systems of conjugated bonds in cyanobiphenyl molecules: Quantum-chemical calculations of the structure and vibrational spectra  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations of the IR absorption spectra and geometric and electronic structure of cyanobiphenyl molecules [Figure not available: see fulltext.] (I) were performed for various angles between benzene ring planes by the B3LYP/6-31+G** method. It was shown that the stablest conformation of I (X=OCH3, OC3H7) should be the twist conformation with ?= 37°, which was in agreement with the gas-phase experimental data. Rotation of benzene rings with respect to each other changed the relative orientation of the interacting ? orbitals of the bridge ring carbon atoms and caused charge redistribution over molecule atoms, in particular, over terminal X and CN group atoms. The calculated period of charge oscillations on the alkyl and nitro groups coincided with the period of reversible charge transfer (˜5-10 fs) between the conjugated subsystems (benzene ring + substituent) observed as the ? angle changed. The rate of charge transfer between the electron donor and electron acceptor groups was calculated to be (3-6)×105 m/s. Charge oscillations on benzene ring carbon atoms and donor and acceptor groups did not cause similar dipole moment oscillations and vibrations in the IR spectrum. The dipole moment of the molecule decreases as the angle between benzene ring planes increases, and the passage to the “perpendicular” conformation should increase the C?N stretching vibration frequency by ˜5 cm-1 and decrease the intensity of the IR band by ˜2 times. The elongation of the aliphatic chain in the X group did not cause noticeable changes in the geometric and electronic structure of the molecule.

Isaev, A. N.; Shorygin, P. P.

2009-03-01

188

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

PubMed

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

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

2013-07-20

189

Charge-transfer complex formation in gelation: the role of solvent molecules with different electron-donating capacities.  

PubMed

A naphthalenediimide (NDI)-based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge-transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron-donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies. PMID:24677404

Basak, Shibaji; Bhattacharya, Sumantra; Datta, Ayan; Banerjee, Arindam

2014-05-01

190

Reversal of the gating polarity of gap junctions by negative charge substitutions in the N-terminus of connexin 32.  

PubMed Central

Intercellular channels formed by connexins (gap junctions) are sensitive to the application of transjunctional voltage (V(j)), to which they gate by the separate actions of their serially arranged hemichannels (Harris, A. L., D. C. Spray, and M. V. L. Bennett. 1981. J. Gen. Physiol. 77:95-117). Single channel studies of both intercellular and conductive hemichannels have demonstrated the existence of two separate gating mechanisms, termed "V(j)-gating" and "loop gating" (Trexler, E. B., M. V. L. Bennett, T. A. Bargiello, and V. K. Verselis. 1996. Proc. Natl. Acad. Sci. U.S.A. 93:5836-5841). In Cx32 hemichannels, V(j)-gating occurs at negative V(j) (Oh, S., J. B. Rubin, M. V. L. Bennett, V. K. Verselis, and T. A. Bargiello. 1999. J. Gen. Physiol. 114:339-364; Oh, S., C. K. Abrams, V. K. Verselis, and T. A. Bargiello. 2000. J. Gen. Physiol. 116:13-31). A negative charge substitution at the second amino acid position in the N-terminus reverses the polarity of V(j)-gating of Cx32 hemichannels (Verselis, V. K., C. S. Ginter, and T. A. Bargiello. 1994. Nature. 368:348-351;. J. Gen. Physiol. 116:13-31). We report that placement of a negative charge at the 5th, 8th, 9th, or 10th position can reverse the polarity of Cx32 hemichannel V(j)-gating. We conclude that the 1st through 10th amino acid residues lie within the transjunctional electric field and within the channel pore, as in this position they could sense changes in V(j) and be largely insensitive to changes in absolute membrane potential (V(m)). Conductive hemichannels formed by Cx32*Cx43E1 containing a negatively charged residue at either the 8th or 10th position display bi-polar V(j)-gating; that is, the open probability of hemichannels formed by these connexins is reduced at both positive and negative potentials and is maximal at intermediate voltages. In contrast, Cx32*Cx43E1 hemichannels with negative charges at either the 2nd or 5th positions are uni-polar, closing only at positive V(j). The simplest interpretation of these data is that the Cx32 hemichannel can adopt at least two different open conformations. The 1st-5th residues are located within the electric field in all open channel conformations, while the 8th and 10th residues lie within the electric field in one conformation and outside the electric field in the other conformation.

Purnick, P E; Oh, S; Abrams, C K; Verselis, V K; Bargiello, T A

2000-01-01

191

Self-consistent charged-particle motion in negative-ion plasmas  

NASA Astrophysics Data System (ADS)

The self-consistent one-dimensional kinetic theory of relaxation of a low pressure quasineutral negative-ion plasma destroyed in a limited region by a powerful laser light pulse is developed. Using the self-similar method, well known in hydrodynamics, we examine the counterflow of the negative plasma species and show the important role of the self-consistent electric field. The negative-ion temperature determined from the ballistic model is valid when the ratio of negative-ion to positive-ion densities is lower than 0.1. The overshoot of electron density that was observed experimentally is described by this method. We show that the overshoot can disappear when the positive-ion mass or temperature goes up. The self-similar solutions are also supported by numerous experimental results. (c) 1995 The American Physical Society

Ivanov, A. A.; Elizarov, L. I.; Bacal, M.; Sionov, A. B.

1995-12-01

192

A comparison of approximate techniques for the determination of potential energy surfaces of ion-molecule charge transfer systems  

Microsoft Academic Search

The (HO2)+ molecular ion is used to experiment two approximate procedures which aim at reducing the computation effort that is needed for the determination of potential energy surfaces of ion–molecule charge transfer systems. The two procedures involve configuration interaction (CI) calculations of moderate sizes and are based on diagonal corrections of the electronic Hamiltonian matrix in a basis of projected-valence

B. Ramiro Diaz; P. Wahnon; V. Sidis

1992-01-01

193

Correlation of Charge-Transfer Energies of Tetracyanoethylene-Donor Complexes with Ionization Energies of Donor Molecules  

Microsoft Academic Search

Empirical correlations between the charge-transfer energies (hvCT) of donor-tetracyanoethylene (TCNE) complexes and the ionization energies (ID) of the donor molecules using linear equations of the formhave been used for more than three decades to interpret CT spectra and to estimate molecular ionization energies. Although many different values of parameters a and b have been derived for small population samples of

J. E. Frey

1987-01-01

194

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

PubMed

Methods to move solvated molecules are rare. Apart from electric fields, only thermal gradients are effective enough to move molecules inside a fluid. This effect is termed thermophoresis, and the underlying mechanisms are still poorly understood. Nevertheless, it is successfully used to quantify biomolecule binding in complex liquids. Here we show experiments that reveal that thermophoresis in water is dominated by two electric fields, both established by the salt ions of the solution. A local field around the molecule drives molecules along an energy gradient, whereas a global field moves the molecules by a combined thermoelectrophoresis mechanism known as the Seebeck effect. Both mechanisms combined predict the thermophoresis of DNA and RNA polymers for a wide range of experimental parameters. For example, we correctly predict a complex, nonlinear size transition, a salt-species-dependent offset, a maximum of thermophoresis over temperature, and the dependence of thermophoresis on the molecule concentration. PMID:24877967

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

2014-05-16

195

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

196

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

Microsoft Academic Search

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

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

2005-01-01

197

Role of negatively charged phospholipids in highly purified (Na+ + K+)-ATPase from rabbit kidney outer medulla studies on (Na+ + K+)-activated ATPase, XXXIX.  

PubMed

1. The requirement for specific polar head groups of phospholipids for activity of purified (Na+ + K+)ATPase from rabbit kidney outer medulla has been investigated. 2. Comparison of content and composition of phospholipids in microsomes and the purified enzyme indicates that purification leads to an increase in the phospholipid/protein ratio and in phosphatidylserine content. 3. The purified preparation contains 267 molecules phospholipid per molecule (Na+ + K+)-ATPase, viz. 95 phosphatidylcholine, 74 phosphatidylethanolamine, 48 spingomyelin, 35 phosphatidylserine and 15 phosphatidylinositol. 4. Complete conversion of phosphatidylserine into phosphatidylethanolamine by the enzyme phosphatidylserine decarboxylase has no effect on the (Na+ + K+)-ATPase activity of the purified preparation. 5. Complete hydrolysis of phosphatidylinositol by a phospholipase C from Staphylococcus aureus, which is specific for this phospholipid, has no effect on the (Na+ + K+)-ATPase activity. 6. Hydrolysis of 95% of the phosphatidylcholine and 60--70% of the spingomyelin and phosphatidylethanolamine by another phospholipase C (Clostridium welchii) lowers the (Na+ + K+)-ATPase activity by about 20%. 7. Combination of the phospholipid-converting enzymes has the same effect as can be calculated from the effects of the enzymes separately. Only complete conversion of both phosphatidylserine and phosphatidylinositol results in a loss of 44% of the (NA+ + K+)-ATPase activity and 36% of the potassium 4-nitrophenylphosphatase activity. 8. These experiments indicate that there is no absolute requirement for one of the polar head groups, although in the absence of negative charges the activity is lower than in their presence. PMID:147706

de Pont, J J; van Prooijen-van Eeden, A; Bonting, S L

1978-04-20

198

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

199

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

PubMed Central

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

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

2014-01-01

200

Negatively charged quantum well polaritons in a GaAs/AlAs microcavity: An analog of atoms in a cavity  

PubMed

The negatively charged exciton (X-) is observed to strongly couple with the microcavity- (MC-)confined photons in a GaAs quantum well containing a two-dimensional electron gas with 0charged polaritons. The coupling strength is found to depend on sqrt[n(e)], in analogy to two-level atoms in a cavity. The analysis of the reflection and photoluminescence spectra shows that X- is strongly admixed with the neutral exciton via their coupling with the MC photons. The linewidth dependence on n(e) indicates that electron-polariton scattering is effective. PMID:11017579

Rapaport; Harel; Cohen; Ron; Linder; Pfeiffer

2000-02-14

201

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

202

Interactions of native and modified cytochrome C with a negatively charged reverse micellar liquid interface  

Microsoft Academic Search

Native and chemically modified cytochrome C were dissolved in sodium bis(2-ethylhexyl) sulphosuccinate (AOT)-oil-buffer microemulsions. The native cytochrome C contains 19 lysine residues, these groups were modified by 1) acetic anhydride or 2) succinic anhydride. At pH 8.4 the native, acetylated and succinylated proteins carry +8, -3 and -12 elementary charges, respectively. The phase behaviour of the microemulsion systems was found

K. M. Larsson; M. P. Pileni

1993-01-01

203

Binding of GAPR-1 to negatively charged phospholipid membranes: unusual binding characteristics to phosphatidylinositol  

Microsoft Academic Search

plant pathogenesis-related proteins group 1 (PR-1). GAPR-1 strongly associates with lipid rafts at the cytosolic leaflet of the\\u000aGolgi membrane. The myristoyl moiety at the N-terminus of GAPR-1 contributes to membrane binding but is not sufficient\\u000afor stable membrane anchorage. GAPR-1 is positively charged at physiological pH, which allows for additional membrane\\u000ainteractions with proteins or lipids. To determine the

Josse Van Galen; Bas W. M. Van Balkom; Ramon L. Serrano; Dora Kaloyanova; Ruud Eerland; E. Stuven; J. Bernd Helms

2010-01-01

204

Capillary electrophoresis/electrospray ion trap mass spectrometry for the analysis of negatively charged derivatized and underivatized glycans.  

PubMed

The increasing interest in the development of glycoproteins for therapeutic purposes has created a greater demand for methods to characterize the sugar moieties bound to them. Traditionally, released carbohydrates are derivatized using such methods as permethylation or fluorescent tagging prior to analysis by high performance liquid chromatography (HPLC), capillary electrophoresis (CE), or direct infusion mass spectrometry. However, little research has been performed using CE with on-line mass spectrometry (MS) detection. The CE separation of neutral oligosaccharides requires the covalent attachment of a charged species for electrophoretic migration. Among charged labels which have shown promise in assisting CE and HPLC separation is the fluorophore 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS). This report describes the qualitative profiling of charged ANTS-derivatized and underivatized complex glycans by CE with on-line electrospray ion trap mass spectrometry. Several neutral standard glycans including a maltooligosaccharide ladder were derivatized with ANTS and subjected to CE/UV and CE/MS using low pH buffers consisting of citric and 6-aminocaproic acid salts. The ANTS-derivatized species were detected as negative ions, and multiple stage MS analysis provided valuable structural information. Fragment ions were easily identified, showing promise for the identification of unknowns. N-Linked glycans released from bovine fetuin were used to demonstrate the applicability of ANTS derivatization followed by CE/MS for the analysis of negatively charged glycans. Analyses were performed on both underivatized and ANTS-derivatized species, and sialylated glycans were separated and detected in both forms. The ability of the ion trap mass spectrometer to perform multiple stage analysis was exploited, with MS5 information obtained on selected glycans. This technique presents a complementary method to existing methodologies for the profiling of glycan mixtures. PMID:11803540

Gennaro, Lynn A; Delaney, Jeannine; Vouros, Paul; Harvey, David J; Domon, Bruno

2002-01-01

205

Negative charges in the DIII-DIV linker of human skeletal muscle Na+ channels regulate deactivation gating  

PubMed Central

Charge reversing, neutralizing and substituting mutations at D1309 and EE1314,15 in the DIII–DIV linker of the human skeletal muscle sodium channel hNav1.4 were constructed and expressed in Xenopus oocytes. The effects of these mutations on conductance, inactivation and deactivation were determined using on-cell macropatches. D1309R caused a depolarizing shift of the conductance–voltage (g(V)) curve and increased the apparent valency of activation. D1309R and EE1314,15RR increased time to peak activation. D1309R caused a depolarizing shift of the steady-state fast inactivation curve, whereas EE1314,15RR produced a hyperpolarizing shift and decreased the apparent valency. Charge reversal at either D1309 or EE1314,15 slowed open-state fast inactivation and accelerated closed-state fast inactivation. D1309R accelerated recovery from fast inactivation, whereas EE1314,15RR and EE1314,15QQ slowed recovery. Deactivation from the inactivated state was determined by the delay in the onset to recovery from fast inactivation. Recovery delay was abbreviated for D1309R but was prolonged for EE1314,15RR and EE1314,15QQ. Open-state deactivation was determined from the time constant of the decay (?D) of tail currents. ?D was slowed by D1309R, D1309E, EE1314,15RR and EE1314,15QQ. Our findings suggest an important role in deactivation gating in hNav1.4 for the negative cluster of charge at EE1314,15. These and previous findings suggest that clusters of negatively and positively charged residues in the hNav1.4 DIII–DIV linker differentially regulate the kinetics of fast inactivation.

Groome, James R; Fujimoto, Esther; Ruben, Peter C

2003-01-01

206

Negative charges in the DIII-DIV linker of human skeletal muscle Na+ channels regulate deactivation gating.  

PubMed

Charge reversing, neutralizing and substituting mutations at D1309 and EE1314,15 in the DIII-DIV linker of the human skeletal muscle sodium channel hNav1.4 were constructed and expressed in Xenopus oocytes. The effects of these mutations on conductance, inactivation and deactivation were determined using on-cell macropatches. D1309R caused a depolarizing shift of the conductance-voltage (g(V)) curve and increased the apparent valency of activation. D1309R and EE1314,15RR increased time to peak activation. D1309R caused a depolarizing shift of the steady-state fast inactivation curve, whereas EE1314,15RR produced a hyperpolarizing shift and decreased the apparent valency. Charge reversal at either D1309 or EE1314,15 slowed open-state fast inactivation and accelerated closed-state fast inactivation. D1309R accelerated recovery from fast inactivation, whereas EE1314,15RR and EE1314,15QQ slowed recovery. Deactivation from the inactivated state was determined by the delay in the onset to recovery from fast inactivation. Recovery delay was abbreviated for D1309R but was prolonged for EE1314,15RR and EE1314,15QQ. Open-state deactivation was determined from the time constant of the decay (tau D) of tail currents. tau D was slowed by D1309R, D1309E, EE1314,15RR and EE1314,15QQ. Our findings suggest an important role in deactivation gating in hNav1.4 for the negative cluster of charge at EE1314,15. These and previous findings suggest that clusters of negatively and positively charged residues in the hNav1.4 DIII-DIV linker differentially regulate the kinetics of fast inactivation. PMID:12588896

Groome, James R; Fujimoto, Esther; Ruben, Peter C

2003-04-01

207

Strong intramolecular electron-phonon coupling in the negatively charged aromatic superconductor picene.  

PubMed

Superconductivity was recently discovered in solid potassium-intercalated picene (K(3)22ph), in which the picene molecule becomes trianionic (22ph(3-)). In this Letter, we conduct a theory-based study of the superconductivity of 22ph(3-) within the framework of BCS theory. We estimate the density of states N(?(F)) on the Fermi level to be 2.2 states per (eV molecule spin) by using the theoretical intramolecular electron-phonon coupling l(x) and the experimental superconducting transition temperature T(c) of 18 K. The theoretical value is consistent with the 1.2 states per (eV molecule spin) determined experimentally for K(3)22ph with T(c)=18 K, indicating the validity of our theoretical treatment and the electron-phonon mechanism for superconductivity. The predicted l(x), 0.206 eV, for 22ph(3-) is larger than any value reported for organic superconductors, so picene may have the largest l(x) among the superconductors reported so far. PMID:21902418

Kato, Takashi; Kambe, Takashi; Kubozono, Yoshihiro

2011-08-12

208

X-ray absorption of the negative charge-transfer material SrFe1-xCoxO3  

Microsoft Academic Search

We studied the relation between the electronic structure and the phsyiscal properties of SrFe1-xCoxO3. The main technique used in the study was Fe 2p, Co 2p, and O 1s x-ray absorption spectroscopy. The experimental spectra were analyzed in terms of the configuration-interaction cluster model calculation. The analysis of the spectra shows that both SrFeO3 and SrCoO3 are in the negative-charge

M. Abbate; G. Zampieri; J. Okamoto; A. Fujimori; S. Kawasaki; M. Takano

2002-01-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

210

Nanostructures formed by self-assembly of negatively charged polymer and cationic surfactants.  

PubMed

The formation of nanoparticles by interaction of an anionic polyelectrolyte, sodium polyacrylate (NaPA), was studied with a series of oppositely charged surfactants with different chain lengths, alkyltrimethylammonium bromide (CnTAB). The binding and formation of nanoparticles was characterized by dynamic light scattering, zeta-potential, and self-diffusion NMR. The inner nanostructure of the particles was observed by direct-imaging cryogenic-temperature transmission electron microscopy (cryo-TEM), indicating aggregates of hexagonal liquid crystal with nanometric size. PMID:19143559

Nizri, G; Makarsky, A; Magdassi, S; Talmon, Y

2009-02-17

211

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

212

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

213

X-ray absorption of the negative charge-transfer material SrFe1-xCoxO3  

NASA Astrophysics Data System (ADS)

We studied the relation between the electronic structure and the phsyiscal properties of SrFe1-xCoxO3. The main technique used in the study was Fe 2p, Co 2p, and O 1s x-ray absorption spectroscopy. The experimental spectra were analyzed in terms of the configuration-interaction cluster model calculation. The analysis of the spectra shows that both SrFeO3 and SrCoO3 are in the negative-charge transfer regime (this means that their ground states are mostly covalent and contain considerable O 2p hole character). SrFeO3 is in a high-spin state and SrCoO3 in an intermediate-spin state stabilized by strong hybridization. The local electronic structure and the corresponding spin state are mostly preserved in SrFe1-xCoxO3. The relatively large O 2p hole weight in the ground state explains the absence of Jahn-Teller distortions, as well as the relatively large value of the magnetic moment observed at the O sites in these materials. SrFe1-x CoxO3 illustrates both ferromagnetism and magneto-resistance in a negative charge-transfer material.

Abbate, M.; Zampieri, G.; Okamoto, J.; Fujimori, A.; Kawasaki, S.; Takano, M.

2002-04-01

214

The phagocytosis and transforming activity of crystalline metal sulfide particles are related to their negative surface charge.  

PubMed

Crystalline nickel sulfide (alpha NiS) and cobalt sulfide (CoS2) particles can cause greater cell transformation and cellular toxicity than the respective amorphous metal sulfide particles. Cultured mammalian cells phagocytose the crystalline metal sulfide particles more readily than the amorphous ones. In the case of the nickel sulfides, the crystalline metal sulfide particles had negatively charged surfaces (Zeta potential: -27.012 mV) in contrast to the amorphous particles, which were positively charge (Zeta potential: +9.174 mV). X-ray photoelectron spectroscopy analysis of amorphous and crystalline NiS particles revealed that the outermost surface (1-4 nm) of the two particles had striking differences in Ni/S ratios and in their sulfur oxidation states. Rendering particles' surfaces more negative by reduction with lithium aluminum hydride enhanced their phagocytosis, and in the case of amorphous NiS chemical reduction resulted in an incidence of morphological transformation of Syrian hamster embryo cells comparable to that observed with untreated crystalline alpha NiS. PMID:7067046

Abbracchio, M P; Heck, J D; Costa, M

1982-01-01

215

Probing the role of negatively charged amino acid residues in ion permeation of skeletal muscle ryanodine receptor.  

PubMed

Sequence comparison suggests that the ryanodine receptors (RyRs) have pore architecture similar to that of the bacterial K+ channel KcsA. The lumenal loop linking the two most C-terminal transmembrane spanning segments in the RyRs has a predicted pore helix and an amino acid motif (GGGIG) similar to the selectivity filter (TVGYG) of KcsA identified by x-ray analysis. The RyRs have many negatively charged amino acid residues in the two regions linking the GGGIG motif and predicted pore helix with the two most C-terminal transmembrane spanning segments. We tested the role of these residues by generating single-site mutants, focusing on amino acid residues conserved among the mammalian RyRs. Replacement of two acidic residues immediately after the GGGIG motif in skeletal muscle ryanodine receptor (RyR1-D4899 and -E4900) with asparagine and glutamine profoundly affected ion permeation and selectivity. By comparison, mutagenesis of aspartate and glutamate residues in the putative linker regions showed a K+ conductance and selectivity for Ca2+ compared to K+ (P(Ca)/P(K)) close to wild-type. The results show that the negatively charged carboxyl oxygens of D4899 and E4900 side chains are major determinants of RyR ion conductance and selectivity. PMID:15863483

Wang, Ying; Xu, Le; Pasek, Daniel A; Gillespie, Dirk; Meissner, Gerhard

2005-07-01

216

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

PubMed

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

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

2014-01-28

217

Mechanism of how salt-gradient-induced charges affect the translocation of DNA molecules through a nanopore.  

PubMed

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

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

2013-08-01

218

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

219

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

220

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

Microsoft Academic Search

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

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

2011-01-01

221

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

222

Stepwise Solvation of the Intramolecular-Charge-Transfer Molecule p-(Dimethylamino)benzonitrile,  

National Technical Information Service (NTIS)

This paper presents a systematic study of p-(N, N-dimethylamino)benzonitrile (DMABN) both in a supersonic jet expansion and in a thermalized vapor. From the jet studies, the excited- and ground-state vibrational spectra of the isolated molecule ar resolve...

L. W. Peng M. Dantus A. H. Zewail K. Kemnitz J. M. Hicks

1987-01-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

224

Complexation of ionomers and surfactant molecules of the same charge in a nonpolar solvent  

Microsoft Academic Search

Complexation between sulfonated polystyrene ionomers and bis(2-ethylhexyl) sulfosuccinate sodium salt (aerosol OT, AOT) surfactant molecules in m-xylene was studied by ultracentrifugation, vapor pressure osmometry, viscometry, and dynamic light scattering. When the dilute ionomer solution is mixed with the AOT solution, complexation takes place for both the slightly aggregated state of AOT and reversed micelles of AOT containing water. In the

Kirill N. Bakeev; Sergey A. Chugunov; A. B. Zezin; V. A. Kabanov; I. Teraoka; W. J. MacKnight

1994-01-01

225

Superoxide-anion formation in collisions of positively charged argon ions with oxygen molecules  

NASA Astrophysics Data System (ADS)

The formation of superoxide O2- anions by collisions of energetic Ar+ ions with oxygen molecules at impact energies of 50-350 keV is reported. Cross sections are about 2 orders of magnitude smaller compared to O2+ ion formation, which is attributed to the larger energy transfer required.

Angelin, E. J.; Hippler, Rainer

2013-05-01

226

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

227

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

2013-01-10

228

Numerical Simulation of Light Induced Charge Transfer Dynamics across Metal-Molecule Junctions  

NASA Astrophysics Data System (ADS)

This dissertation contains two major foci: 1. the technical focus on the finite-difference time-domain method (FDTD) as the major computational tool used throughout all projects and 2. the physical focus on light-induced charge dynamics across various metallic and molecular junctions. In the first two chapters we discuss two new methodological developments for the numerical simulation of plasmonic systems. We provide an analytic proof for the validity of calculating the scattering cross section (SCS) in the near field and then verify it with a numerical validation. We then present an extension of the Huygens subgridding (HSG) scheme onto Lorentz media, enabling dramatically increased resolution at critical regions in the computational domain. In the last two chapters we discuss simulations of the light induced charge dynamics in plasmonic systems, consisting of silver nanoconstructs and/or atomic linkers. These are direct applications of the methods in the first part. We first discuss our simulations on silver nanoconstructs only, whose charge dynamics is controlled by tuning the parameters for the incident light excitation. We then study a system consisting of a silver nano-junction bridged by a molecular linker, for which a combination of the FDTD-HSG technique and quantum dynamics are used to simulate both qualitative and quantitative behaviors of electron transport through a silver-molecular junction.

Hu, Zixuan

229

A molecule to detect and perturb the confinement of charge carriers in quantum dots.  

PubMed

This paper describes unprecedented bathochromic shifts (up to 970 meV) of the optical band gaps of CdS, CdSe, and PbS quantum dots (QDs) upon adsorption of an organic ligand, phenyldithiocarbamate (PTC), and the use of PTC to map the quantum confinement of specific charge carriers within the QDs as a function of their radius. For a given QD material and physical radius, R, the magnitude of the increase in apparent excitonic radius (?R) upon delocalization by PTC directly reflects the degree of quantum confinement of one or both charge carriers. The plots of ?R vs R for CdSe and CdS show that exciton delocalization by PTC occurs specifically through the excitonic hole. Furthermore, the plot for CdSe, which spans a range of R over multiple confinement regimes for the hole, identifies the radius (R?1.9 nm) at which the hole transitions between regimes of strong and intermediate confinement. This demonstration of ligand-induced delocalization of a specific charge carrier is a first step toward eliminating current-limiting resistive interfaces at organic-inorganic junctions within solid-state hybrid devices. Facilitating carrier-specific electronic coupling across heterogeneous interfaces is especially important for nanostructured devices, which comprise a high density of such interfaces. PMID:22032799

Frederick, Matthew T; Amin, Victor A; Cass, Laura C; Weiss, Emily A

2011-12-14

230

Electron-intramolecular-phonon coupling and possible superconductivity in negatively charged coronene and corannulene  

NASA Astrophysics Data System (ADS)

Electron-intramolecular-phonon coupling and its role in the occurrence of possible superconductivity in the monoanions of coronene (C24H12) and corannulene (C20H10) are studied. Electron-intramolecular-phonon coupling constants are calculated from the intramolecular vibronic coupling constants. The C-C stretching E2g mode of 1668 cm-1 plays an essential role in the electron-intramolecular-phonon coupling in the monoanion of coronene while the low frequency E2 modes, which have a radial character, and the C-C stretching mode of 1669 cm-1, which has a tangential character, afford large electron-intramolecular-phonon coupling constants in the monoanion of corannulene. The calculated total electron-intramolecular-phonon coupling constant for the monoanion of corannulene (0.269 eV) is much larger than that for coronene monoanion (0.076 eV). The intermediate characteristics between sigma and pi orbital interaction properties owing to the bowl-shaped structure of corannulene make orbital interactions between two neighboring carbon atoms strong, and thus electron-intramolecular-phonon coupling is stronger in the monoanion of corannulene than that in the monoanion of coronene. Possible superconducting transition temperature Tc value for the monoanion of corannulene is estimated to be an order of magnitude larger than that for the monoanion of coronene; for example, the calculated values of Tcs for the monoanions of coronene and corannulene are about 0.05-8.86 and 29.17-65.56 K, respectively, in the range of n(0)=4-5 and mu*=0.10-0.20, where n(0) is the density of states at the Fermi level (states per eV, per spin, and per molecule) and mu* is the Coulomb pseudopotential. The relationships between structures and Tcs in alkali-doped A3C60 complexes and graphite intercalation compounds (GICs) are also discussed from a viewpoint that corannulene can be viewed as a fragment of C60 and coronene as a fragment of one-sheet graphite.

Kato, Takashi; Yamabe, Tokio

2002-08-01

231

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

232

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

NASA Astrophysics Data System (ADS)

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

Rauch, Jens; Kolch, Walter; Mahmoudi, Morteza

2012-11-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

234

Negatively charged amino acid residues in the nicotinic receptor delta subunit that contribute to the binding of acetylcholine.  

PubMed Central

In nicotinic receptors, the binding sites for acetylcholine are likely to contain negatively charged amino acid side chains that interact with the positively charged quaternary ammonium group of acetylcholine and of other potent agonists. We previously found that a 61-residue segment of the delta subunit contains aspartate or glutamate residues within 1 nm of cysteines in the acetylcholine binding site on the alpha subunit. We have now mutated, one at a time, the 12 aspartates and glutamates in this segment of the mouse muscle delta subunit and have expressed the mutant receptors in Xenopus oocytes. Both the concentration of acetylcholine eliciting half-maximal current (Kapp) and the Ki for the inhibition by acetylcholine of alpha-bungarotoxin binding were increased 100-fold by the mutation of delta Asp180 to Asn and 10-fold by the mutation of delta Glu189 to Gln. These two residues, and their homologs in the gamma and epsilon subunits, are likely to contribute to the acetylcholine binding sites.

Czajkowski, C; Kaufmann, C; Karlin, A

1993-01-01

235

N-(2-Carboxybenzyl) grafted chitosan as adsorptive agent for simultaneous removal of positively and negatively charged toxic metal ions.  

PubMed

A chitosan material, cross-linked and grafted with N-(2-carboxybenzyl) groups, was evaluated as adsorbent to sufficiently remove both positively charged ions (Cu(II), Ni(II)) and negatively charged ones (Cr(VI), As(V)) from aqueous solutions. After complete characterization study with FTIR, SEM and BET analysis, the evaluation of adsorption was done with experiments at pH range 2-12 and then varying the initial concentrations of ions. Langmuir-Freundlich equation was used to fit the adsorption data and showed maximum adsorption capacities 308 mg/g at 25 °C for copper and 381 mg/g for nickel ions. The adsorption capacity of As(V) was 208 mg/g and 175 mg/g for Cr(VI). Also, a mechanistic (phenomenological) model of adsorption kinetics is employed to fit the kinetic data found using parameters with physical meaning, and clearly understand the process dynamics. The regeneration of adsorbents was presented in ten cycles of reuse (adsorption-desorption), showing the strong reuse potential of the adsorbent used. PMID:23270947

Kyzas, George Z; Kostoglou, Margaritis; Lazaridis, Nikolaos K; Bikiaris, Dimitrios N

2013-01-15

236

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

237

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

SciTech Connect

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

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

2012-07-15

238

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

PubMed

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

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

2013-10-16

239

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

240

Investigation of N-acyl homoserine lactone (AHL) molecule production in Gram-negative bacteria isolated from cooling tower water and biofilm samples.  

PubMed

In this study, 99 Gram-negative rod bacteria were isolated from cooling tower water, and biofilm samples were examined for cell-to-cell signaling systems, N-acyl homoserine lactone (AHL) signal molecule types, and biofilm formation capacity. Four of 39 (10 %) strains isolated from water samples and 14 of 60 (23 %) strains isolated from biofilm samples were found to be producing a variety of AHL signal molecules. It was determined that the AHL signal molecule production ability and the biofilm formation capacity of sessile bacteria is higher than planktonic bacteria, and there was a statistically significant difference between the AHL signal molecule production of these two groups (p < 0.05). In addition, it was found that bacteria belonging to the same species isolated from cooling tower water and biofilm samples produced different types of AHL signal molecules and that there were different types of AHL signal molecules in an AHL extract of bacteria. In the present study, it was observed that different isolates of the same strains did not produce the same AHLs or did not produce AHL molecules, and bacteria known as AHL producers did not produce AHL. These findings suggest that detection of signal molecules in bacteria isolated from cooling towers may contribute to prevention of biofilm formation, elimination of communication among bacteria in water systems, and blockage of quorum-sensing controlled virulence of these bacteria. PMID:23250628

Haslan, Ezgi; Kimiran-Erdem, Ayten

2013-09-01

241

Ion Accelerator With Negatively Biased Decelerator Grid  

NASA Technical Reports Server (NTRS)

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

Brophy, John R.

1994-01-01

242

Direct detection of the ultrafast response of charges and molecules in the photoinduced neutral-to-ionic transition of the organic tetrathiafulvalene-p-chloranil solid.  

PubMed

Ultrafast dynamics of charge and molecular degrees of freedom in a photoinduced neutral-ionic transition of an organic solid, tetrathiafulvalene-p-chloranil, were directly detected for the first time by transient reflectivity measurements using 15 fs laser pulses. The results reveal that ionic domains are photogenerated in the neutral lattice via collective charge-transfer processes within 20 fs, and subsequently molecular deformations and bendings occur, giving rise to large changes in the molecular ionicity and charge redistributions in molecules, respectively. We show that such couplings between charge and molecular degrees of freedom play important roles in photoinduced transitions of organic molecular compounds. PMID:21231630

Uemura, H; Okamoto, H

2010-12-17

243

Direct Detection of the Ultrafast Response of Charges and Molecules in the Photoinduced Neutral-to-Ionic Transition of the Organic Tetrathiafulvalene-p-Chloranil Solid  

NASA Astrophysics Data System (ADS)

Ultrafast dynamics of charge and molecular degrees of freedom in a photoinduced neutral-ionic transition of an organic solid, tetrathiafulvalene-p-chloranil, were directly detected for the first time by transient reflectivity measurements using 15 fs laser pulses. The results reveal that ionic domains are photogenerated in the neutral lattice via collective charge-transfer processes within 20 fs, and subsequently molecular deformations and bendings occur, giving rise to large changes in the molecular ionicity and charge redistributions in molecules, respectively. We show that such couplings between charge and molecular degrees of freedom play important roles in photoinduced transitions of organic molecular compounds.

Uemura, H.; Okamoto, H.

2010-12-01

244

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

SciTech Connect

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

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

2012-05-25

245

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

NASA Astrophysics Data System (ADS)

We report on sequential multiphoton ionization of N2, H2S and SF6 by intense, femtosecond duration pulses of x-rays from the LCLS free electron laser. Following either K- or L-shell excitation, we observe ionization and fragmentation of the molecule by Auger electron, photoelectron, and ion time-of-flight spectroscopy. Intense excitation of the K-shell leads to depletion and double core hole effects, observed in N2 [1, 2]. For L-shell excitation, additional relaxation channels suppress depletion, allowing ionization to continue until energetically forbidden. The investigation of multiphoton ionization has produced a better understanding of molecular plasmas created by intense ultrafast x-ray exposure.

Murphy, B. F.; Fang, L.; Osipov, T. Y.; Hoener, M.; Berrah, N.

2012-05-01

246

Regulation of gating by negative charges in the cytoplasmic pore in the Kir2.1 channel.  

PubMed

Inward rectifier K(+) channels commonly exhibit long openings (slow gating) punctuated by rapid open-close transitions (fast gating), suggesting that two separate gates may control channel open-closed transitions. Previous studies have suggested possible gate locations at the selectivity filter and at the 'bundle crossing', where the two transmembrane segments (M1 and M2) cross near the cytoplasmic end of the pore. Wild-type Kir2.1 channels exhibit only slow gating, but mutations in the cytoplasmic pore domain at E224 and E299 have been shown to induce fast flickery gating. Since these mutations also affect polyamine affinity, we conjectured that the fast gating mechanism might affect the kinetics of polyamine block/unblock if located more intracellularly than the polyamine blocking site in the pore. Neutralization of either E224 or E299 induced fast gating and slowed both block and unblock rates by the polyamine diamine 10. The slowing of polyamine block/unblock was partly relieved by raising pH from 7.2 to 9.0, which also slowed fast gating kinetics. These findings indicate that the fast flickery gate is located intracellularly with respect to the polyamine pore-plugging site near D172, thereby excluding the selectivity filter, and implicating the bundle crossing or more intracellular site as the gate. As additional proof, fast gating induced at the selectivity filter by disrupting P loop salt bridges in WT-E138D-E138D-WT tandem had no effect on polyamine block and unblock rates. The pH sensitivity of fast gating in E224 and E299 mutants was attributed to the protonation state of H226, since the double mutant E224Q/H226K induced fast gating which was pH insensitive. Moreover, introducing a negative charge in the 224-226 region was sufficient to prevent fast gating, since the double mutant E224Q/H226E rescued wild-type Kir2.1 slow gating. These observations implicate E224 and E299 as allosteric modulators of a fast gate, located at the bundle crossing or below in Kir2.1 channels. By suppressing fast gating, these negative charges facilitate polyamine block and unblock, which may be their physiologically important role. PMID:15459242

Xie, Lai-Hua; John, Scott A; Ribalet, Bernard; Weiss, James N

2004-11-15

247

Regulation of gating by negative charges in the cytoplasmic pore in the Kir2.1 channel  

PubMed Central

Inward rectifier K+ channels commonly exhibit long openings (slow gating) punctuated by rapid open–close transitions (fast gating), suggesting that two separate gates may control channel open–closed transitions. Previous studies have suggested possible gate locations at the selectivity filter and at the ‘bundle crossing’, where the two transmembrane segments (M1 and M2) cross near the cytoplasmic end of the pore. Wild-type Kir2.1 channels exhibit only slow gating, but mutations in the cytoplasmic pore domain at E224 and E299 have been shown to induce fast flickery gating. Since these mutations also affect polyamine affinity, we conjectured that the fast gating mechanism might affect the kinetics of polyamine block/unblock if located more intracellularly than the polyamine blocking site in the pore. Neutralization of either E224 or E299 induced fast gating and slowed both block and unblock rates by the polyamine diamine 10. The slowing of polyamine block/unblock was partly relieved by raising pH from 7.2 to 9.0, which also slowed fast gating kinetics. These findings indicate that the fast flickery gate is located intracellularly with respect to the polyamine pore-plugging site near D172, thereby excluding the selectivity filter, and implicating the bundle crossing or more intracellular site as the gate. As additional proof, fast gating induced at the selectivity filter by disrupting P loop salt bridges in WT-E138D–E138D-WT tandem had no effect on polyamine block and unblock rates. The pH sensitivity of fast gating in E224 and E299 mutants was attributed to the protonation state of H226, since the double mutant E224Q/H226K induced fast gating which was pH insensitive. Moreover, introducing a negative charge in the 224–226 region was sufficient to prevent fast gating, since the double mutant E224Q/H226E rescued wild-type Kir2.1 slow gating. These observations implicate E224 and E299 as allosteric modulators of a fast gate, located at the bundle crossing or below in Kir2.1 channels. By suppressing fast gating, these negative charges facilitate polyamine block and unblock, which may be their physiologically important role.

Xie, Lai-Hua; John, Scott A; Ribalet, Bernard; Weiss, James N

2004-01-01

248

Structural requirement for the rapid movement of charged molecules across membranes. Experiments with tetraphenylborate analogues.  

PubMed Central

Charge-pulse experiments were performed in the presence of structural analogues of tetraphenylborate (TPB) on membranes made of dioleoyl phosphatidylethanolamine and dioleoyl phosphatidylcholine. The analysis of the experimental results using a previously proposed model allowed the calculation of the partition coefficient, beta, and of the translocation rate constant, kappa i. The temperature dependence of the partition coefficients was used to calculate the thermodynamics of the adsorption of the lipophilic ions to the membranes. The analysis of the translocation rate constants obtained at different temperatures yielded detailed information on the free energy of the TPB-analogues within artificial lipid bilayer membranes, and on the activation energy of the translocation rate constants. The adsorption of the different TPB-analogues to the membranes was only slightly affected by their structure, whereas a dramatic influence of the structure on the free energy of the lipophilic ions within the membranes was observed. The free energy of the ions in the membranes decreased from triphenylcyanoborate (TPCB) to tetrakis(3-trifluoromethylphenyl)borate (TTFPB) by more than 31 kJ/mol (7.4 kcal/mol). This could be concluded from the observed increase in the translocation rate constant by almost six orders of magnitude. The change of the free energy in the membrane was used for the estimation of an effective radius of the TPB-analogues with respect to TPB.

Benz, R

1988-01-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

250

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

251

Interaction of bee venom melittin with zwitterionic and negatively charged phospholipid bilayers: a spin-label electron spin resonance study.  

PubMed

Electron spin resonance (ESR) spectroscopy was used to study the penetration and interaction of bee venom melittin with dimyristoylphosphatidylcholine (DMPC) and ditetradecylphosphatidylglycerol (DTPG) bilayer membranes. Melittin is a surface-active, amphipathic peptide and serves as a useful model for a variety of membrane interactions, including those of presequences and signal peptides, as well as the charged subdomain of the cardiac regulatory protein phospholamban. Derivatives of phosphatidylcholine and phosphatidylglycerol spin-labeled at various positions along the sn-2 acyl chain were used to establish the chain flexibility gradient for the two membranes in the presence and absence of melittin. Negatively charged DTPG bilayer membranes showed a higher capacity for binding melittin without bilayer disruption than did membranes formed by the zwitterionic DMPC, demonstrating the electrostatic neutralization of bound melittin by DTPG. The temperature dependence of the ESR spectra showed that the gel-to-liquid crystalline phase transition is eliminated by binding melittin to DTPG bilayers, whereas a very broad transition remains in the case of DMPC bilayers. None of the spin labels used showed a two-component spectrum characteristic of a specific restriction of their chain motion by melittin, but the outer hyperfine splittings and effective chain order parameters were increased for all labels upon binding melittin. This indicates a reduced flexibility of the lipid chains induced by a surface orientation of the bound melittin. Whereas the characteristic shape of the chain flexibility gradient was maintained upon melittin addition to DMPC bilayers, the chain flexibility profile in DTPG bilayers was much more strongly perturbed. It was found that the steepest change in segmental flexibility was shifted toward the bilayer interior when melittin was bound to DTPG membranes, indicating a greater depth of penetration than in DMPC membranes. pH titration of stearic acid labeled at the C-5 position, used as a probe of interfacial interactions, showed net downward shifts in interfacial pK of 0.8 and 1.2 pH units contributed from the positive charge of melittin, outweighing upward shifts from interfacial dehydration, when melittin was bound to DTPG and DMPC, respectively. The perturbation of the outer hyperfine splitting was used to determine the interactions of melittin with spin-labeled lipids of different polar headgroups in DTPG and DMPC. Anionic lipids (phosphatidylserine, phosphatidylglycerol, and stearic acid) and zwitterionic lipids (phosphatidylethanolamine and phosphatidylcholine) had the largest outer splittings in the presence of melittin. Neutral lipids (protonated stearic acid and diacylglycerol) displayed the largest increase in outer splitting on binding melittin, which was attributed to a change in the vertical location of these lipids in the bilayer. Both effects were more pronounced in DTPG than in DMPC. PMID:9017202

Kleinschmidt, J H; Mahaney, J E; Thomas, D D; Marsh, D

1997-02-01

252

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

SciTech Connect

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

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

1997-12-01

253

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

PubMed Central

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

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

2014-01-01

254

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

PubMed

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

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

2014-01-01

255

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

Microsoft Academic Search

Six mass spectrometers based on different mass analyzer technologies, such as time-of-flight (TOF), hybrid quadrupole-TOF\\u000a (Q-TOF), orbitrap, Fourier transform ion cyclotron resonance (FT-ICR), and triple quadrupole (QqQ), installed at independent\\u000a laboratories have been tested during a single day of work for the analysis of small molecules in negative electrospray ionization\\u000a (ESI) mode. The uncertainty in the mass measurements obtained from

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

256

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

257

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

PubMed

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

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

2014-05-01

258

Theoretical study of the BeLi, BeNa, MgLi, MgNa, and AlBe molecules and their negative ions  

NASA Technical Reports Server (NTRS)

The alkaline earth-alkali diatomics are found to have weak bonds, because the diffuse alkali valence s orbitals cannot form a bond of sufficient strength to pay the promotion energy of the alkaline-earth atoms. This leads to van der Waals bonding in the neutrals as well as the negative ions. In fact, the negative ions have larger binding energies than the neutrals as a result of the much larger polarizability of the negative ion. The binding energy of AlBe is significantly larger than the Be-alkali molecules, due to a covalent contribution to the bonding. The binding energy in AlBe(-) is considerably larger than AlBe; the binding energy of the X 3Sigma(-) state of AlBe(-) is computed to be 1.36 eV, as compared with 0.57 eV for the X 2Pi state of AlBe.

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

1992-01-01

259

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

260

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

2013-07-15

261

Circumambulatory movement of negative charge ("ring walk") during gas-phase dissociation of 2,3,4-trimethoxybenzoate anion.  

PubMed

A dramatic "ortho effect" was observed during gas-phase dissociation of ortho-, meta-, and para-methoxybenzoate anions. Upon activation under mass spectrometric collisional activation conditions, anions generated from all three isomers undergo a CO2 loss. Of the m/z 107 ions generated in this way, only the 1-dehydro-2-methoxybenzene anion from the ortho isomer underwent an exclusive formaldehyde loss. A peak for a formaldehyde loss in the spectra of 2,4-, 2,5-, and 2,6-dimethoxybenzoates and the absence of an analogous peak from 3,4- and 3,5-dimethoxy derivatives confirmed that this is a diagnostically useful ortho-isomer-specific phenomenon. Moreover, the spectrum from 2,3-dimethoxybenzoic acid showed peaks for two consecutive formaldehyde losses. The 1-dehydro-2,3,4-trimethoxybenzene anion (m/z 167) generated from 2,3,4-trimethoxybenzoate in this way endures three consecutive eliminations of formaldehyde units. For this, the negative charge, initially located on position 1, circumambulates to position 2, then to position 3, and finally to position 4 to form the final phenyl anion. The proposed stepwise fragmentation pathway, which resembles the well-known E1cB-elimination mechanism, is supported by tandem mass spectrometric observations made with 2-[(13)C(2)H3]methoxy-3-[(13)C]methoxy-4-methoxybenzoic acid, and ab initio calculations. In addition, the spectra of ions such as 1-dehydro-3,4-dimethoxybenzene anion show peaks for consecutive methyl radical losses, a feature that establishes the 1,2-relationship between the two methoxy groups. PMID:24749904

Herath, Kithsiri B; Weisbecker, Carl S; Singh, Sheo B; Attygalle, Athula B

2014-05-16

262

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

Microsoft Academic Search

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

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

2007-01-01

263

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

SciTech Connect

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

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

1984-10-01

264

Basal electric and magnetic fields of celestial bodies come from positive-negative charge separation caused by gravitation of quasi-Casimir pressure in weak interaction  

NASA Astrophysics Data System (ADS)

According to f =d(mv)/dt=m(dv/dt)+ v(dm/dt), a same gravitational formula had been de-duced from the variance in physical mass of QFT and from the variance in mass of inductive energy-transfer of GR respectively: f QF T = f GR = -G (mM/r2 )((r/r)+(v/c)) when their interaction-constants are all taken the experimental values (H05-0029-08, E15-0039-08). f QF T is the quasi-Casimir pressure. f GR is equivalent to Einstein's equation, then more easy to solve it. The hypothesis of the equivalent principle is not used in f QF T , but required by f GR . The predictions of f QF T and f GR are identical except that f QF T has quantum effects but f GR has not and f GR has Lense-Thirring effect but f QF T has not. The quantum effects of gravitation had been verified by Nesvizhevsky et al with the ultracold neutrons falling in the earth's gravitational field in 2002. Yet Lense-Thirring effect had not been measured by GP-B. It shows that f QF T is essential but f GR is phenomenological. The macro-f QF T is the statistic average pressure collided by net virtual neutrinos ? 0 flux (after self-offset in opposite directions) and in direct proportion to the mass. But micro-f QF T is in direct proportion to the scattering section. The electric mass (in inverse proportion to de Broglie wavelength ?) far less than nucleonic mass and the electric scattering section (in direct proportion to ?2 ) far large than that of nucleon, then the net ? 0 flux pressure exerted to electron far large than that to nucleon and the electric displacement far large than that of nucleon, it causes the gravitational polarization of positive-negative charge center separation. Because the gravity far less than the electromagnetic binding force, in atoms the gravitational polarization only produces a little separation. But the net ? 0 flux can press a part freedom electrons in plasma of ionosphere into the earth's surface, the static electric force of redundant positive ions prevents electrons from further falling and till reach the equilibrium of stable spatial charge distribution, which is just the cause of the geomagnetic field and the geo-electric field (the observational value on the earth surface is about 120 V/m downward equivalent to 500000 Coulomb negative charges in the earth surface). All celestial bodies are gravitation sources and attract the molecules and ions in space to its circumference by the gravitation of own and other celestial bodies, e.g., all planets in the solar system have their own atmospheres. Therefore, the origin mechanism of geo-electric and geomagnetic fields caused by gravitation is very universal, at least it is appli-cable to all the planets in the solar system. For planets, the joint result of the gravitations of the planets and the sun makes the negative charges and dipolar charges distributed in the surfaces of the celestial bodies. The quicker the rotation is, the larger the angular momentum U is, then larger the accompanying current and magnetic moment P, it accord a experiential law found by subsistent observational data of all celestial bodies in solar system: P = -G 1/2 U cos ? / c (1), ? is the angle between the net ? 0 flux direction (mark by CMB) and the rotational axis of celestial body (Chen Shao-Guang, Chinese Science Bulletin, 26,233,1981). Uranian and Neptunian P predicted with Eq.(1) in 1981 are about -3.4•1028 Gs•cm3 and 1.9•1028 Gs•cm3 respectively (use new rotate speed measured by Voyager 2). The P measured by Voyager 2 in 1986 and 1989 are about -1.9 •1028 Gs•cm3 and 1.5•1028 Gs•cm3 respectively (the contribution of quadrupole P is converted into the contribution of dipole P alone). The neutron star pos-sesses much high density and rotational speed because of the conservation of the mass and the angular momentum during the course of the formation, then has strong gravity and largerU. From Eq.(1) there is a larger P and extremely strong surface magnetic field in neutron star. The origin mechanism of basal electric and magnetic fields of celestial bodies will affect directly all fields refer

Chen, Shao-Guang

265

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

266

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

267

Sulfobutylated poly(vinyl alcohol)-graft-poly(lactide-co-glycolide)s facilitate the preparation of small negatively charged biodegradable nanospheres.  

PubMed

The manufacturing conditions for small nanoparticles (NP) in the range of 100-500 nm are difficult to control. Novel biodegradable, brush-like branched polyesters with a negatively charged hydrophilic backbone, poly(2-sulfobutyl-vinyl alcohol)-g-poly(lactide-co-glycolide), facilitate their preparation by a modified solvent displacement procedure. Furthermore, the structure and the surface properties of the colloidal systems are investigated. NP were characterized by photon correlation spectroscopy (PCS), zeta-potential measurement (ZPM), particle charge detection (PCD), nuclear magnetic resonance spectroscopy (NMR) and transmission electron microscopy (TEM). Varying the manufacturing conditions NP with mean diameters of about 100 up to 500 nm and, depending on polymer composition, negatively charged surfaces were obtained. The NP visualized by TEM showed smooth surfaces. Furthermore, surface characterization and NMR studies suggested a core/corona structure of the particles. This study demonstrates that a simple solvent displacement technique can be used for the reproducible preparation of discrete NP with defined negatively charged surfaces and narrow size distributions. These NP may have potential for peroral or parenteral protein delivery systems. PMID:10825550

Jung, T; Breitenbach, A; Kissel, T

2000-07-01

268

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

NASA Astrophysics Data System (ADS)

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

Tarnowsky, Terence J.; Westfall, Gary D.

2013-07-01

269

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

SciTech Connect

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

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

2013-11-15

270

Surface patch binding induced intermolecular complexation and phase separation in aqueous solutions of similarly charged gelatin-chitosan molecules.  

PubMed

The formation of selective surface patch binding induced complex coacervates between polyions, chitosan (cationic polyelectrolyte), and alkali-processed gelatin (polyampholyte), both carrying similar net charge, was investigated for two volumetric mixing ratios: r = [chitosan]/[gelatin] = 1:5 and 1:10. Formation of soluble intermolecular complexes between gelatin and chitosan molecules was observed in a narrow range of pH, though these biopolymers had the same kind of net charge, which was evidenced from electrophoretic measurement. This clearly established the role played by selective surface patch binding driven interactions. The temperature sweep measurements conducted on these coacervate samples through rheology and differential scanning calorimetry (DSC) studies yielded two characteristic melting temperatures located at approximately 68 +/- 3 degrees C and 82 +/- 3 degrees C. In the flow mode, the shear viscosity (eta) of the coacervate samples was found to scale with (power-law model) applied shear rate (gamma*) as eta(gamma*) approximately (gamma*)(-k); this yielded k = 0.76 +/- 0.2 (1 s(-1) < gamma* < 100 s(-1)), indicating non-Newtonian behavior. The static structure factor (I(q)) deduced from small angle neutron scattering (SANS) data in the low q (q is the scattering wavevector) (0.018 A(-1) < q < 0.072 A(-1)) region was fitted to the Debye-Bueche regime, I(q) approximately 1/(1 + zeta(2)q(2))2 that yielded a size of zeta approximately 215 +/- 20 A (for r = 1:10) and zeta approximately 260 +/- 20 A (for r = 1:5) samples, implying change in the size of inhomogeneities present with mixing ratio. In the intermediate q region, called the Ornstein-Zernike regime, I(q) approximately 1/(1 + xi(2)q(2)) gave a correlation length of xi approximately 10.0 +/- 2.0 A independent of the mixing ratio. The results taken together imply the existence of a weakly interconnected and heterogeneous network structure inside the coacervate phase separated by domains of polymer-poor regions. PMID:17676887

Gupta, Amar Nath; Bohidar, H B; Aswal, V K

2007-08-30

271

Recoil ion mass spectrometry. Part 2. Formation of slow, multiply charged recoil ions in collisions of fast negative ions with Ar and Kr atoms  

Microsoft Academic Search

Mass spectrometric studies have been conducted on slow, multiply charged recoil ions produced in collisions of O-, Si-, C- and C-2 ions with neutral beams of Ar and Kr atoms at impact energies in the range 40-70 keV. A crossed-beams apparatus incorporating a quadrupole mass spectrometer has been coupled to the mass-selective negative ion injection system of a tandem heavy-ion

F. A. Rajgara; U. T. Raheja; C. P. Safvan; M. Krishnamurthy; E. Krishnakumar; D. Mathur

1993-01-01

272

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

273

Effect of protein stabilization on charge state distribution in positive- and negative-ion electrospray ionization mass spectra  

Microsoft Academic Search

Changes in protein conformation are thought to alter charge state distributions observed in electrospray ionization mass spectra\\u000a (ESI-MS) of proteins. In most cases, this has been demonstrated by unfolding proteins through acidification of the solution.\\u000a This methodology changes the properties of the solvent so that changes in the ESI-MS charge envelopes from conformational\\u000a changes are difficult to separate from the

Stephen J. Watt; Margaret M. Sheil; Jennifer L. Beck; Pavel Prosselkov; Gottfried Otting; Nicholas E. Dixon

2007-01-01

274

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

NASA Astrophysics Data System (ADS)

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 silicon-molecular electronic devices for DRAM and Flash memory applications utilizing redox-active molecules. This work exploits the ability of molecules to store charges with single-electron precision at room temperature. The hybrid devices are fabricated by forming self-assembled monolayers of redox-active molecules on Si and oxide (SiO2 and HfO2) surfaces via formation of covalent linkages. The molecules possess discrete quantum states from which electrons can tunnel to the Si substrate at discrete applied voltages (oxidation process, cell write), leaving behind a positively charged layer of molecules. The reduction (erase) process, which is the process of electrons tunneling back from Si to the molecules, neutralizes the positively charged molecular monolayer. Hybrid silicon-molecular capacitor test structures were electrically characterized with an electrolyte gate using cyclic voltammetry (CyV) and impedance spectroscopy (CV) techniques. The redox voltages, kinetics (write/erase speeds) and charge-retention characteristics were found to be strongly dependent on the Si doping type and densities, and ambient light. It was also determined that the redox energy states in the molecules communicate with the valence band of the Si substrate. This allows tuning of write and read states by modulating minority carriers in n- and p-Si substrates. Ultra-thin dielectric tunnel barriers (SiO2, HfO2) were placed between the molecules and the Si substrate to augment charge-retention for Flash memory applications. The redox response was studied as a function of tunnel oxide thickness, dielectric permittivity and energy barrier, and modified Butler-Volmer expressions were postulated to describe the redox kinetics. The speed vs. retention performance of the devices was improved via asymmetric layered tunnel barriers. The properties of molecules can be tailored by molecular design and synthetic chemistry. In this work, it was demonstrated that an alternate route to tune/enhance the properties of the hybrid device is to engineer the substrate (silicon) component. The molecules were attached to diode surfaces to tune redox voltages and improve charge-retention characteristics. N+ pockets embedded in P-Si well were utilized to obtain multiple states from a two-state molecule. The structure was also employed as a characterization tool in investigating the intrinsic properties of the molecules such as lateral conductivity within the monolayer. Redox molecules were also incorporated on an ultra thin gate-oxide of Si MOSFETs with the intent of studying the interaction of redox states with Si MOSFETs. The discrete molecular states were manifested in the drain current and threshold voltage characteristics of the device. This work demonstrates the multi-state modulation of Si-MOSFETs' drain current via redox-active molecular monolayers. Polymeric films of redox-active molecules were incorporated to improve the charge-density (ON/OFF ratio) and these structures may be employed for multi-state, low-voltage Flash memory applications. The most critical aspect of this research effort is to build a reliable and high density solid state memory technology. To this end, efforts were directed towards replacement of the electrolytic gate, which forms an extremely thin insulating double layer (˜10 nm) at the electrolyte-molecule interface, with a combination of an ultra-thin high-K dielectric layer and a metal gate. Several interesting observations were made in the research approaches towards integration and provided valuable insights into the electrolyte-redox systems. In summary, this work provides fundamental insigh

Gowda, Srivardhan Shivappa

275

Double-negative T cells from MRL-lpr/lpr mice mediate cytolytic activity when triggered through adhesion molecules and constitutively express perforin gene  

PubMed Central

The lpr gene induces in mice, accumulation of large numbers of CD4-CD8- (double negative [DN]) T lymphocytes which bear adhesion molecules not characteristic of normal resting T cells. These cells fail to acquire interleukin 2 (IL-2) receptors, produce IL-2, and proliferate when activated with mitogens or monoclonal antibodies (mAbs) against the T cell receptor (TCR). Because of these poor functions in vitro, the nature and significance of DN T cells in the autoimmune disease process is not clear. In the current study, we describe a surprising finding that mAbs against CD3-TCR-alpha/beta complex can strongly trigger the lytic activity of the DN T cells to induce redirected lysis of Fc receptor-positive targets. Similar redirected lysis was also inducible using mAbs against CD44 and gp90MEL-14, molecules involved in the binding of lymphocytes to endothelial cells. The spontaneous cytotoxic potential of the DN T cells was further corroborated by demonstrating that the lpr DN T cells constitutively transcribed perforin gene but failed to express granzyme A. The current study suggests that DN T cells are capable of mediating lysis of autologous cells bearing the specific ligands for adhesion molecules involved in the signaling of cytotoxicity. These findings provide a novel insight into the functional significance of DN T cells in lpr mice and their potential role in the pathogenesis of autoimmune disease.

1993-01-01

276

Interfacial charge injection barriers in organic light-emitting diodes: the effect of thin interlayers of organic donor-acceptor molecules TTF and TCNQ  

NASA Astrophysics Data System (ADS)

Energy level alignment at interfaces between tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) films on representative anode materials Au, ITO and PEDOT-PSS are investigated by ultraviolet photoelectron spectroscopy (UPS). Both materials have broadly uniform behavior independent of the chemical composition of the substrate. The position of the vacuum level of the deposited films is fixed with respect to the substrate Fermi energy, and the hole injection barrier is likewise constant. The magnitude of the vacuum level shift is a simple linear function of the substrate work function. A 4 nm thick interlayer in TTF/TCNQ/Au and TCNQ/TTF/Au compound interfaces does not alter the alignment of the outer material with the substrate. Charge transfer in conjunction with subsequent structural relaxation of the ionic donor or acceptor molecule is proposed to explain the results. Lastly, we discuss how donor-acceptor molecules might be used to mediate charge injection into organic light emitting diodes (OLEDs) and similar organic electronic devices.

Murdey, Richard J.; Salaneck, William R.

2004-11-01

277

Single molecule studies of force-induced s2 site exposure in the Mammalian notch negative regulatory domain.  

PubMed

Notch signaling in metazoans is responsible for key cellular processes related to embryonic development and tissue homeostasis. Proteolitic cleavage of the S2 site within an extracellular NRR domain of Notch is a key early event in Notch signaling. We use single molecule force-extension (FX) atomic force microscopy (AFM) to study force-induced exposure of the S2 site in the NRR domain from mouse Notch 1. Our FX AFM measurements yield a histogram of N-to-C termini lengths, which we relate to conformational transitions within the NRR domain. We detect four classes of such conformational transitions. From our steered molecular dynamics (SMD) results, we associate first three classes of such events with the S2 site exposure. AFM experiments yield their mean unfolding forces as 69 ± 42, 79 ± 45, and 90 ± 50 pN, respectively, at 400 nm/s AFM pulling speeds. These forces are matched by the SMD results recalibrated to the AFM force loading rates. Next, we provide a conditional probability analysis of the AFM data to support the hypothesis that a whole sequence of conformational transitions within those three clases is the most probable pathway for the force-induced S2 site exposure. Our results support the hypothesis that force-induced Notch activation requires ligand binding to exert mechanical force not in random but in several strokes and over a substantial period of time. PMID:24735465

Ploscariu, Nicoleta; Kuczera, Krzysztof; Malek, Katarzyna E; Wawrzyniuk, Magdalena; Dey, Ashim; Szoszkiewicz, Robert

2014-05-01

278

Theoretical studies on the anisotropy of the first hyperpolarizabilities of one- and two-dimensional charge-transfer molecules: role of solvent polarity  

Microsoft Academic Search

The effects of solvent polarity on the geometry and static first hyperpolarizability of one- and two-dimensional charge transfer molecules based on para-nitroaniline (PNA) and 1,3-diamino-4,6-dinitrobenzene (DADB) were studied using a polarizable continuum model (PCM) at the B3LYP\\/6-31+G(d,p) level of theory. The inclusion of solvent does not change the geometry significantly, but produces a change in the calculated results of the

Hai-Peng Li; Kui Han; Gang Tang; Ming-Xue Li; Xiao-Peng Shen; Zhi-Min Huang

2009-01-01

279

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

280

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

281

Geoengineering with Charged Droplets  

NASA Astrophysics Data System (ADS)

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

Gokturk, H.

2011-12-01

282

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

283

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

PubMed Central

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

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

2013-01-01

284

Numerical study of a butanol\\/heptane fuelled Homogeneous Charge Compression Ignition (HCCI) engine utilizing negative valve overlap  

Microsoft Academic Search

► The calibration and comparison to experimental data of a parallel computing multizone combustion model. ► Simulation of operational characteristics of an n-butanol\\/n-heptane fuelled HCCI engine. ► Advanced engine design with the negative valve overlap (NVO) technology.

Sona Visakhamoorthy; John Z. Wen; Siva Sivoththaman; Charles Robert Koch

2012-01-01

285

[Comparative investigation of molecules releasing from intra-hollow calcium-alginate capsules using fluorimetry].  

PubMed

In this paper, the authors employ three different types of dye molecules, Nile red, Rhodamine 6G, fluorescein and a fluorescent protein-R-phycoerythrin (R-PE). The Rhodamine 6G is positively charged molecules, fluorescein is negatively charged molecules, and Nile red is neutral molecules. The R-phycoerythrins have either a net positive or negative charge which is balanced at the isoelectric point (4.22). It is negatively charged molecules also under our experimental condition. The Nile red, rhodamine 6G, fluorescein and R-phycoerythrin are trapped into alginate calcium hollow capsule respectively. The diffusion processes of those molecules from calcium alginate capsule to solution are measured based on a fluorescence method. The results indicate that electrical characteristics of encapsulated molecules have effect on their diffusion behaviors. The positively charged rhodamine 6G is well accordance with a model of control release from porous polymer membranes. The neutral molecules not only can be released from porous polymer framework, they also can directly dissolve out through polymer membrane. The electrostatic repulsion between fluorescein and negatively charged calcium alginate membranes will accelerate the molecular motion, which is propitious to molecules directly dissolving out through polymer membrane. Based on Fick's law of diffusion, R-PEs can be releases from porous polymer framework It shows the longest equilibrium time. Comparing neutral molecules, negatively and positively charge molecules show the stronger interaction on electric polymer membrane, which results in that the diffusion coefficients of rhodamine 6G and fluorescein are less than that of neutral molecule Nile red. The consequences obtained here should readily explain analogous control releasing behaviors of other functional molecules. PMID:21714262

Li, Ye; Li, Yang; Xu, Shu-Na; Li, Kun; Lu, Yi-Qiang

2011-04-01

286

Phosphate group-driven fragmentation of multiply charged phosphopeptide anions. Improved recognition of peptides phosphorylated at serine, threonine, or tyrosine by negative ion electrospray tandem mass spectrometry.  

PubMed

The nanoelectrospray product ion spectra of multiply charged phosphopeptide anions reveal the occurrence of phosphate-specific high-mass fragment ions of the type [M - nH - 79](n-1)-. These so far unrecognized fragments, which are observed for phosphoserine-, phosphothreonine-, and phosphotyrosine-containing peptides, are the counterparts of the established inorganic phosphopeptide marker ion found at m/z 79 = [PO3]-. The high-mass marker ions are formed with high efficiency at moderate collision offset values and are particularly useful for sensitive recognition of pSer-, pThr-, and pTyr-peptides due to the low background level in MS/MS spectra at m/z values above those of the precursor ions. By virtue of this feature, the detection of the new phosphorylation-specific fragment ions appears to be more sensitive than the detection of the low-mass phosphate marker ion at m/z 79, where a higher interference by nonspecific background signals is generally observed. The number of phosphate groups within a phosphopeptide can also be estimated on the basis of the [M - nH - 79](n-1)- ions, since these exhibit an effective, sequential neutral loss of H3PO4 of the residing phosphate groups. A mechanistic explanation for the formation of the [M - nH - 79](n-1)- ions from multiply charged phosphopeptides is given. The high-mass marker ions are proposed to originate from phosphopeptide anions, which carry two negative charges located at the phosphate group. A new search tool denominated "variable m/z gain analysis", which utilizes these newly recognized high-mass fragments for spotting of phosphopeptides in a negative ion parent scan, is proposed. The findings strengthen the value of negative ion ESI-MS/MS for analysis of protein phosphorylation. PMID:16478119

Edelson-Averbukh, Marina; Pipkorn, Rüdiger; Lehmann, Wolf D

2006-02-15

287

Negative Charges in the Transmembrane Domains of the HERG K Channel Are Involved in the Activation- and Deactivation-gating Processes  

PubMed Central

The transmembrane domains of HERG (S1–S3) contain six negative charges: three are conserved in all voltage-gated K channels (D456 and D466 in S2, D501 in S3) and three are unique to the EAG family (D411 in S1, D460 in S2, and D509 in S3). We infer the functional role of these aspartates by studying how substituting them with cysteine, one at a time, affects the channel function. D456C is not functional, suggesting that this negative charge may play a critical role in channel protein folding during biogenesis, as has been shown for its counterpart in the Shaker channel. Data from the other five functional mutants suggest that D411 can stabilize the HERG channel in the closed state, while D460 and D509 have the opposite effect. D466 and D501 both may contribute to voltage-sensing during the activation process. On the other hand, all five aspartates work in a concerted fashion in contributing to the slow deactivation process of the HERG channel. Accessibility tests of the introduced thiol groups to extracellular MTS reagents indicate that water-filled crevices penetrate deep into the HERG protein core, reaching the cytoplasmic halves of S1 and S2. At these deep locations, accessibility of 411C and 466C to the extracellular aqueous phase is voltage dependent, suggesting that conformational changes occur in S1 and S2 or the surrounding crevices during gating. Increasing extracellular [H+] accelerates HERG deactivation. This effect is suppressed by substituting the aspartates with cysteine, suggesting that protonation of these aspartates may contribute to the signaling pathway whereby external [H+] influences conformational changes in the channel's cytoplasmic domains (where deactivation takes place). There is no evidence for a metal ion binding site coordinated by negative charges in the transmembrane domains of HERG, as the one described for the EAG channel.

Liu, Jie; Zhang, Mei; Jiang, Min; Tseng, Gea-Ny

2003-01-01

288

Matrix Assisted Ionization: New Aromatic and Nonaromatic Matrix Compounds Producing Multiply Charged Lipid, Peptide, and Protein Ions in the Positive and Negative Mode Observed Directly from Surfaces  

NASA Astrophysics Data System (ADS)

Matrix assisted inlet ionization (MAII) is a method in which a matrix:analyte mixture produces mass spectra nearly identical to electrospray ionization without the application of a voltage or the use of a laser as is required in laserspray ionization (LSI), a subset of MAII. In MAII, the sample is introduced by, for example, tapping particles of dried matrix:analyte into the inlet of the mass spectrometer and, therefore, permits the study of conditions pertinent to the formation of multiply charged ions without the need of absorption at a laser wavelength. Crucial for the production of highly charged ions are desolvation conditions to remove matrix molecules from charged matrix:analyte clusters. Important factors affecting desolvation include heat, vacuum, collisions with gases and surfaces, and even radio frequency fields. Other parameters affecting multiply charged ion production is sample preparation, including pH and solvent composition. Here, findings from over 100 compounds found to produce multiply charged analyte ions using MAII with the inlet tube set at 450 °C are presented. Of the compounds tested, many have -OH or -NH2 functionality, but several have neither (e.g., anthracene), nor aromaticity or conjugation. Binary matrices are shown to be applicable for LSI and solvent-free sample preparation can be applied to solubility restricted compounds, and matrix compounds too volatile to allow drying from common solvents. Our findings suggest that the physical properties of the matrix such as its morphology after evaporation of the solvent, its propensity to evaporate/sublime, and its acidity are more important than its structure and functional groups.

Li, Jing; Inutan, Ellen D.; Wang, Beixi; Lietz, Christopher B.; Green, Daniel R.; Manly, Cory D.; Richards, Alicia L.; Marshall, Darrell D.; Lingenfelter, Steven; Ren, Yue; Trimpin, Sarah

2012-10-01

289

The role of charge and multiple faces of the CD8 alpha/alpha homodimer in binding to major histocompatibility complex class I molecules: support for a bivalent model.  

PubMed Central

The CD8 dimer interacts with the alpha 3 domain of major histocompatibility complex class I molecules through two immunoglobulin variable-like domains. In this study a crystal structure-informed mutational analysis has been performed to identify amino acids in the CD8 alpha/alpha homodimer that are likely to be involved in binding to class I. Several key residues are situated on the top face of the dimer within loops analogous to the complementarity-determining regions (CDRs) of immunoglobulin. In addition, other important amino acids are located in the A and B beta-strands on the sides of the dimer. The potential involvement of amino acids on both the top and the side faces of the molecule is consistent with a bivalent model for the interaction between a single CD8 alpha/alpha homodimer and two class I molecules and may have important implications for signal transduction in class I-expressing cells. This study also demonstrates a role for the positive surface potential of CD8 in class I binding and complements previous work demonstrating the importance of a negatively charged loop on the alpha 3 domain of class I for CD8 alpha/alpha-class I interaction. We propose a model whereby residues located on the CDR-like loops of the CD8 homodimer interact with the alpha 3 domain of MHC class I while amino acids on the side of the molecule containing the A and B beta-strands contact the alpha 2 domain of class I. Images

Giblin, P A; Leahy, D J; Mennone, J; Kavathas, P B

1994-01-01

290

Influence of composition on phase occurrence during charge process of AB 5+ x Ni-MH negative electrode materials  

Microsoft Academic Search

Multi-substituted LaNi5-type alloys (AB5+x) are widely used as negative electrode materials in commercial Ni-MH batteries. Cobalt substitution on Ni sites allows to enhance battery cycle life by reducing alloy pulverization induced by hydrogen cycling. This improvement is attributed to the occurrence of a three-phase process (?, ? and ?) during electrochemical hydrogen loading. In order to better understand the effect

S. Vivet; M. Latroche; Y. Chabre; J.-M. Joubert; B. Knosp; A. Percheron-Guégan

2005-01-01

291

Electronic structure of the two-dimensional negative charge-transfer material Sr3 FeM O7 ( M=Fe , Co)  

NASA Astrophysics Data System (ADS)

We studied the relation between the electronic structure and the physical properties of Sr3FeMO7 ( M=Fe , Co). The main technique used in the study was Fe 2p , Co 2p , and O 1s x-ray-absorption spectroscopy. The experimental spectra were analyzed in terms of cluster model and band-structure calculations. The analysis of the spectra shows that both Sr3FeFeO7 and Sr3FeCoO7 are in the negative-charge-transfer regime (this means that their ground states are highly covalent and contain considerable O 2p hole character). The Fe ions are in a high-spin state and the Co ions in an intermediate-spin state stabilized by strong hybridization. The electronic structure helps to explain the trends in the electrical conductivity and the observed magnetic moments. Further, the relatively large O 2p hole weight in the ground state explains also the absence of Jahn-Teller distortions. Sr3FeCoO7 illustrates ferromagnetism and magnetoresistance in a two-dimensional negative-charge-transfer material.

Abbate, M.; Mogni, L.; Prado, F.; Caneiro, A.

2005-05-01

292

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

293

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

294

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

PubMed Central

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

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

2011-01-01

295

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

PubMed Central

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; Groome, James R.; Nomura, Yoshiko; Luo, Ningguang; Dong, Ke

2011-01-01

296

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

297

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

SciTech Connect

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

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

2010-08-15

298

Charge Falling Through a Charged Ring Model  

NSDL National Science Digital Library

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

Krizaj, Dejan

2010-11-09

299

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

PubMed

Manipulation for simplifying or increasing the observed charge state distributions of proteins can be highly desirable in mass spectrometry experiments. In the present work, we implemented a vapor introduction technique to an Agilent Jet Stream ESI (Agilent Technologies, Santa Clara, CA, USA) source. An apparatus was designed to allow for the enrichment of the nitrogen sheath gas with basic vapors. An optical setup, using laser-induced fluorescence and a pH-chromic dye, permits the pH profiling of the droplets as they evaporate in the electrospray plume. Mechanisms of pH droplet modification and its effect on the protein charging phenomenon are elucidated. An important finding is that the enrichment with basic vapors of the nitrogen sheath gas, which surrounds the nebulizer spray, leads to an increase in the spray current. This is attributed to an increase in the electrical conductivity of water-amine enriched solvent at the tip exit. Here, the increased current results in a generation of additional electrolytically produced OH(-) ions and a corresponding increase in the pH at the tip exit. Along the electrospray plume, the pH of the droplets increases due to both droplet evaporation and exposure to basic vapors from the seeded sheath gas. The pH evolution in the ESI plume obtained using pure and basic seeded sheath gas was correlated with the evolution of the charge state distribution observed in mass spectra of proteins, in the negative ion mode. Taking advantage of the Agilent Jet Stream source geometry, similar protein charge state distributions and ion intensities obtained with basic initial solutions, can be obtained using native solution conditions by seeding the heated sheath gas with basic vapors. PMID:22565506

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

2012-07-01

300

Kinetic energy release in thermal ion–molecule reactions: The Nb2+–(benzene) single charge–transfer reaction  

Microsoft Academic Search

We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge–transfer reaction of Nb2+ with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer mechanism,

James R. Gorda; Ben S. Freiser; Steven W. Buckner

1991-01-01

301

Kinetic energy release in thermal ion-molecule reactions: The Nb2 + -(benzene) single charge-transfer reaction  

Microsoft Academic Search

We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge--transfer reaction of Nb{sup 2+} with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer

James R. Gord; Ben S. Freiser; Steven W. Buckner

1991-01-01

302

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

SciTech Connect

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

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

2010-06-28

303

FAST TRACK COMMUNICATION: Effects of charge transfer interaction of graphene with electron donor and acceptor molecules examined using Raman spectroscopy and cognate techniques  

NASA Astrophysics Data System (ADS)

The effects of the interaction of few-layer graphene with electron donor and acceptor molecules have been investigated by employing Raman spectroscopy, and the results compared with those from electrochemical doping. The G-band softens progressively with increasing concentration of tetrathiafulvalene (TTF) which is an electron donor, while the band stiffens with increasing concentration of tetracyanoethylene (TCNE) which is an electron acceptor. Interaction with both TTF and TCNE broadens the G-band. Hole and electron doping by electrochemical means, however, stiffen and sharpen the G-band. The 2D-band position is also affected by interaction with TTF and TCNE. More importantly, the intensity of the 2D-band decreases markedly with the concentration of either. The ratio of intensities of the 2D-band and G-band decreases with an increase in TTF or TCNE concentration, and provides a means for carrier titration in the charge transfer system. Unlike the intensity of the 2D-band, that of the D-band increases on interaction with TTF or TCNE. All of these effects occur due to molecular charge transfer, also evidenced by the occurrence of charge transfer bands in the electronic absorption spectra. The electrical resistivity of graphene varies in opposite directions on interaction with TTF and TCNE, the resistivity depending on the concentration of either compound.

Voggu, Rakesh; Das, Barun; Sekhar Rout, Chandra; Rao, C. N. R.

2008-11-01

304

Redox-Active Star Molecules Incorporating the 4-Benzoylpyridinium Cation - Implications for the Charge Transfer Along Branches vs. Across the Perimeter in Dendrimer  

NASA Technical Reports Server (NTRS)

Dendrimers are self-repeating globular branched star molecules, whose fractal structure continues to fascinate, challenge, and inspire. Functional dendrimers may incorporate redox centers, and potential applications include antennae molecules for light harvesting, sensors, mediators, and artificial biomolecules. We report the synthesis and redox properties of four star systems incorporating the 4-benzoyl-N-alkylpyridinium cation; the redox potential varies along the branches but remains constant at fixed radii. Bulk electrolysis shows that at a semi-infinite time scale all redox centers are electrochemically accessible. However, voltammetric analysis (cyclic voltammetry and differential pulse voltammetry) shows that on1y two of the three redox-active centers in the perimeter are electrochemically accessible during potential sweeps as slow as 20 mV/s and as fast as 10 V/s. On the contrary, both redox centers along branches are accessible electrochemically within the same time frame. These results are explained in terms of slow through-space charge transfer and the globular 3-D folding of the molecules and are discussed in terms of their implications on the design of efficient redox functional dendrimers.

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

2004-01-01

305

In-111 chimeric negative-charged-Z2D3 PL-F(ab`){sub 2} imaging of proliferating smooth muscle cell in atherosclerotic lesions  

SciTech Connect

Metabolically active plaques have proliferating smooth muscle cells. In-111-labeled negative-charged modified Z2-D3 PL-F(ab`){sub 2} (NC-Z2D3) specific for an antigen in proliferating smooth muscle cells has been shown to accumulate in rabbit atherosclerotic plaques. The safety, biodistribution and accumulation of NC-Z2D3 were assessed in 11 patients with angiographically confirmed carotid atheromas eligible for endarterectomy. NC-Z2D3 (250 mcg) labeled with 5 mCi of In-11 was administered by slow i.v. inj.. Planar and SPECT images were obtained 4, 24, 48 and 72 hrs later. Endarterectomy was then performed and the specimens were analyzed. Focal uptake of In-111-NCZ2D3 at the site of the carotid plaques was seen at 4 hrs. Target to control ratio at 4 hrs was 2.20 {plus_minus} 0.3, 1.98 {plus_minus} 0.03 at 24 hrs, 1.60 {plus_minus} 0.2 at 48 hrs and 1.45 {plus_minus} 0.2 at 72 hrs. The pattern of uptake was frequently more extended than the stenotic regions as delineated by the angiograms. Avidin-Biotin-Peroxidase immunostaining of the specimens revealed staining of proliferating smooth muscle cells at the site of the plaque. Percent of the injected dose per gram localization in the specimens was 0.0475 {plus_minus} 0.007. Blood clearance followed a biexponential curve with a mean t{1/2} of 920 minutes. Nonspecific localization of the antibody was observed in the liver, bone-marrow and kidneys. Adverse reactions were not seen. This study demonstrates the feasibility of targeting active atherosclerotic lesions with negatively charge-modified antibody.

Carrio, I.; Pieri, P.L.; Narula, J. [and others

1996-05-01

306

Charge transfer in systems of conjugated bonds in cyanobiphenyl molecules: Quantum-chemical calculations of the structure and vibrational spectra  

Microsoft Academic Search

Quantum-chemical calculations of the IR absorption spectra and geometric and electronic structure of cyanobiphenyl molecules\\u000a \\u000a (I) were performed for various angles between benzene ring planes by the B3LYP\\/6-31+G** method. It was shown that the stablest\\u000a conformation of I (X=OCH3, OC3H7) should be the twist conformation with ?= 37°, which was in agreement with the gas-phase experimental data. Rotation of benzene

A. N. Isaev; P. P. Shorygin

2009-01-01

307

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

PubMed

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2 O)](2+) (terpy=2,2';6',2"-terpyridine, dcbpy=6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface. PMID:24782232

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

2014-06-10

308

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

309

Observation of field-induced charge carriers in high-mobility organic transistors of a thienothiophene-based small molecule: Electron spin resonance measurements  

NASA Astrophysics Data System (ADS)

Electron spin resonance (ESR) measurements are performed on field-induced charge carriers in high-mobility organic transistors of polycrystalline dioctylbenzothieno[2,3-b]benzothiophene (C8-BTBT) films. The angular dependences of the ESR spectra are well fitted by orthorhombic g values with the largest component of gY = 2.0110 nearly parallel to the normal direction of the substrate but tilted by 5°. The results indicate a highly organized end-on alignment of C8-BTBT molecules at the device interface. The ESR linewidth exhibits motional narrowing down to 4 K, providing microscopic evidence for high carrier mobilities within the crystalline domains of C8-BTBT.

Tanaka, Hisaaki; Kozuka, Masato; Watanabe, Shun-Ichiro; Ito, Hiroshi; Shimoi, Yukihiro; Takimiya, Kazuo; Kuroda, Shin-Ichi

2011-08-01

310

A study of donor-acceptor in the charge transfer molecular complexes of some thiacrown ethers with dihalogen molecules by DFT method.  

PubMed

The molecular complexes of 1,3,5-trithiane, (TT), tetrathia-8-crown-4, (TT8C4), and trithia-9-crown-3 , (TT9C3) with dihalogens in the ground state were investigated in the gas and dicholoromethane phases using B3LYP method and 6-31G** and 6-31+G** bases sets. In both TT and TT8C4 complexes, it is predicted that charge transfer takes place from the dihalogen to the thiacrown ether molecule; the magnitude trend of the total CT was ICl > IBr > I2, and Cl2 > Br2 > I2, respectively. There was not such a trend with TT9C3. The frequency analysis showed that all complexes in the excited state were unstable. The analysis of natural bond orbitals and comparison of the calculated thermodynamic quantities of the complexes between the gas phase and tetrachloromethane solution confirmed the results. PMID:23841337

Oftadeh, Mohsen; Moghadary, Mitra; Solimannejad, Mohammad; Semnani, Abolfazl

2013-01-01

311

Theoretical investigation of the stability of highly charged C60 molecules produced with intense near-infrared laser pulses.  

PubMed

We theoretically investigated the stability of highly charged C(60) (z+) cations produced from C(60) with an ultrashort intense laser pulse of lambda approximately 1800 nm. We first calculated the equilibrium structures and vibrational frequencies of C(60) (z+) as well as C(60). We then calculated key energies relevant to dissociation of C(60) (z+), such as the excess vibrational energy acquired upon sudden tunnel ionization from C(60). By comparing the magnitudes of the calculated energies, we found that C(60) (z+) cations up to z approximately 12 can be produced as a stable or quasistable (microsecond-order lifetime) intact parent cation, in agreement with the recent experimental report by V. R. Bhardwaj et al. [Phys. Rev. Lett. 93, 043001 (2004)] that almost only intact parent C(60) (z+) cations up to z=12 are detected by a mass spectrometer. The results of Rice-Ramsperger-Kassel-Marcus calculation suggest that the lifetime of C(60) (z+) drastically decreases by ten orders of magnitude as z increases from z=11 to z=13. Using the time-dependent adiabatic state approach, we also investigated the vibrational excitation of C(60) and C(60) (z+) by an intense near-infrared pulse. The results indicate that large-amplitude vibration with energy of >10 eV is induced in the delocalized h(g)(1)-like mode of C(60) (z+). PMID:17115751

Sahnoun, Riadh; Nakai, Katsunori; Sato, Yukio; Kono, Hirohiko; Fujimura, Yuichi; Tanaka, Motohiko

2006-11-14

312

A fixed-charge model for alcohol polarization in the condensed phase, and its role in small molecule hydration.  

PubMed

We present a simple optimization strategy for incorporating experimental dielectric response information on neat liquids in classical molecular models of alcohol. Using this strategy, we determine simple and transferable hydroxyl modulation rules that, when applied to an existing molecular parameter set, result in a newly dielectric corrected (DC) parameter set. We applied these rules to the general Amber force field (GAFF) to form an initial set of GAFF-DC parameters, and we found this to lead to significant improvement in the calculated dielectric constant and hydration free energy values for a wide variety of small molecule alcohol models. Tests of the GAFF-DC parameters in the SAMPL4 blind prediction event for hydration show these changes improve agreement with experiment. Surprisingly, these simple modifications also outperform detailed quantum mechanical electric field calculations using a self-consistent reaction field environment coupling term. This work provides a potential benchmark for future developments in methods for representing condensed-phase environments in electronic structure calculations. PMID:24702668

Fennell, Christopher J; Wymer, Karisa L; Mobley, David L

2014-06-19

313

Charge transfer excitations in water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C60  

NASA Astrophysics Data System (ADS)

We present a study of charge transfer (CT) excited states for a recently synthesized group of water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C60. The ZnPcS donors (ZnPcS2, ZnPcS3, and ZnPcS4) are promising materials for achieving solar cell device production with the photoactive area prepared from aqueous solution. Experimentally, decreasing the number of sulfonate substituent groups for ZnPc increased the photocurrent and lowered the open circuit voltage VOC. Measurements show that the VOC is largest for ZnPc-S4/C60 and lowest for ZnPc-S3/C60. The degree of sulfonation and the measured device VOC does not result in the expected pattern of values based on donor-acceptor HOMO/LUMO energy differences. Variations in film morphology may account for the unexpected pattern of VOC values. Our charge transfer excited state calculations show that the lowest CT excitation energy among the group of ZnPcS/C60 donor-acceptor pairs corresponds to the disulfonated ZnPc/C60 system. The largest CT excited state energies belong to the tetrasulfonated ZnPc/C60 complex. We also examine the effect of geometrical orientation on the CT energies for the ZnPcS donor-acceptor pairs.

Zope, Rajendra; Basurto, Luis; Olguin, Marco; Baruah, Tunna

2013-03-01

314

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

315

Vibrationally state selected ion molecule experimental and computational studies of both reactant charge states of [nitrogen dioxide + ethyne]+ and HOD+ with nitrogen dioxide  

NASA Astrophysics Data System (ADS)

Ion molecule studies have not only determined reactivity of systems that would have otherwise been unavailable, but also provide a perspective that improves the understanding of the mechanisms that drive reaction. Presented here are studies of three ion molecule systems one of which is accompanied by an extensive set of direct dynamics trajectory calculations. In the first system presented, NO2+ in six different vibrational states was reacted with C2H2 over the center-of-mass energy range from 0.03 to 3.3 eV. The effects of the symmetric bend overtone (0200) excitation are particularly strong (factor of 4) while the delta overtone (0220) effects are much weaker. A large set of quasi-classical trajectories were calculated at the PBE1PBE/6-311G** level of theory, in an attempt to understand the mechanistic origins of this observation. The trajectories reproduce experiment where comparable. Analysis of these trajectories resolves the mechanistic origins of this vibrational effect. Similar experimental measurements were made for the first excited electronic state of this system where the charge is localized on the acetylene. The C 2H2+ reactant was prepared in four distinct modes. Because both reactants have one unpaired electron, collisions can occur with either singlet or triplet coupling of these unpaired electrons, and the contributions the three channels (charge, O-, and O transfer) are separated based on distinct recoil dynamics. The effects of C2H 2+ vibration are modest, but mode specific. Integral cross sections and product recoil velocity distributions were also measured for reaction of HOD+ with NO2, in which the HOD+ reactant was prepared in its ground state, and with mode-selective excitation in the 001 (OH stretch), 100 (OD stretch) and bend (010) modes. In addition, we measured the 300 K thermal kinetics in a selected ion flow tube reactor and report product branching ratios different from previous measurements. Reaction is found to occur on both the singlet and triplet surfaces with near unit efficiency. Origins of discrepancies in the thermal versus beam experiments are discussed. Nine mechanisms contribute to four product channels (proton, deuteron, charge, and O- transfer) with the contributions from each resolved. Vibrational effects allow determination of energy partitioning in proton and deuteron transfer reactions near the product ion dissociation threshold.

Boyle, Jason M.

316

The lymphoid protein tyrosine phosphatase Lyp interacts with the adaptor molecule Grb2 and functions as a negative regulator of T-cell activation  

Microsoft Academic Search

ObjectiveFollowing activation of T cells, phosphorylation of tyrosine residues occurs through a complex signaling process involving protein tyrosine kinases, phosphatases, and a variety of adapter molecules including Grb2. We have attempted to identify new signaling molecules that are important for the activation response.

Ronald J Hill; Sergey Zozulya; Ying-Lin Lu; Kevin Ward; Mikhail Gishizky; Bahija Jallal

2002-01-01

317

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

Microsoft Academic Search

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

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

2010-01-01

318

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

319

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

Microsoft Academic Search

Fragmentation branching ratios for channels involving H+ emission and associated kinetic energy release of the H+ fragment [KER(H+)] have been measured for multicharged CnHq+ molecules produced in high velocity (3.6 a.u.) collisions between CnH+ projectiles and helium atoms. For CHq+ (q <= 4) molecules, measured KER(H+) were found well below predictions of the simple point charge Coulomb model (PCCM) for

K. Béroff; N. T. van-Oanh; M. Chabot; T. Tuna; T. Pino; G. Martinet; A. Le Padellec; Y. Carpentier; L. Lavergne

2011-01-01

320

Measurement of negatively charged pion spectra in inelastic p+p interactions at 20, 31, 40, 80 and 158 GeV/c  

NASA Astrophysics Data System (ADS)

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/ c ( 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN super proton synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus-nucleus and proton-nucleus collisions.

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

2014-03-01

321

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

PubMed

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

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

2012-11-26

322

Promiscuous activation of transient receptor potential vanilloid 1 (TRPV1) channels by negatively charged intracellular lipids: the key role of endogenous phosphoinositides in maintaining channel activity.  

PubMed

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

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

2013-12-01

323

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

324

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

2013-11-01

325

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

326

A theoretical study on optical and charge transport properties of anthra-[1,2-b:4,3-b?:5,6-b?:8,7-b?]tetrathiophene molecules  

NASA Astrophysics Data System (ADS)

The optical and charge transport properties of 1,2,4,5-tetrakis(5-methylthiophen-2yl)benzene (TMTB), electron donating and withdrawing groups substituted anthra-[1,2-b:4,3-b?:5,6-b?:8,7-b?]tetrathiophene (ATT) molecules have been studied. The ground and excited states geometry was optimized using the density functional theory (DFT) and time-dependent DFT methods. The absorption and emission spectra were calculated at TD-B3LYP/6-311G(d, p) level of theory. It has been observed that the effect of solvent and the substitution of functional groups on the calculated absorption and emission spectra of ATT molecules is negligible. The charge transfer integral, site energy and reorganization energy for hole and electron transport in ATT molecules have been calculated. Molecular dynamics simulations were performed to find the most favorable conformation. The calculated charge transport properties show that the rate of charge transfer strongly depends on ?-stacking angle and the studied molecules can be used as an organic semiconductor.

Saranya, G.; Navamani, K.; Senthilkumar, K.

2014-03-01

327

The negative charge of glutamic acid-820 in the gastric H+,K+-ATPase alpha-subunit is essential for K+ activation of the enzyme activity.  

PubMed Central

To investigate the role of Glu820, located in transmembrane domain M6 of the alpha-subunit of gastric H+,K+-ATPase, a number of mutants was prepared and expressed in Sf9 cells using a baculovirus encoding for both H+,K+-ATPase subunits. The wild-type enzyme and the E820D (Glu820-->Asp) mutant showed a similar biphasic activation by K+ on the ATPase activity (maximum at 1 mM). The mutant E820A had a markedly decreased K+ affinity (maximum at 40-100 mM). The other mutants, E820Q, E820N, E820L and E820K, showed no K+-activated ATPase activity at all, whereas all mutants formed a phosphorylated intermediate. After preincubation with K+ before phosphorylation mutant E820D showed a similar K+-sensitivity as the wild-type enzyme. The mutants E820N and E820Q had a 10-20 times lower sensitivity, whereas the other three mutants were hardly sensitive towards K+. Upon preincubation with 3-(cyanomethyl)-2-methyl-8-(phenylmethoxy) imidazo [1,2a]-pyridine (SCH28080), all mutants showed similar sensitivity for this drug as the wild-type enzyme, except mutant E820Q, which could only partly be inhibited, and mutant E820K, which was completely insensitive towards SCH28080. These experiments suggest that, with a relatively large residue at position 820, the binding of SCH28080 is obstructed. The various mutants showed a behaviour in K+-stimulated-dephosphorylation experiments similar to that for K+-activated-ATPase-activity measurements. These results indicate that K+ binding, and indirectly the transition to the E2 form, is only fully possible when a negatively charged residue is present at position 820 in the alpha-subunit.

Hermsen, H P; Swarts, H G; Koenderink, J B; De Pont, J J

1998-01-01

328

The negative charge of glutamic acid-820 in the gastric H+,K+-ATPase alpha-subunit is essential for K+ activation of the enzyme activity.  

PubMed

To investigate the role of Glu820, located in transmembrane domain M6 of the alpha-subunit of gastric H+,K+-ATPase, a number of mutants was prepared and expressed in Sf9 cells using a baculovirus encoding for both H+,K+-ATPase subunits. The wild-type enzyme and the E820D (Glu820-->Asp) mutant showed a similar biphasic activation by K+ on the ATPase activity (maximum at 1 mM). The mutant E820A had a markedly decreased K+ affinity (maximum at 40-100 mM). The other mutants, E820Q, E820N, E820L and E820K, showed no K+-activated ATPase activity at all, whereas all mutants formed a phosphorylated intermediate. After preincubation with K+ before phosphorylation mutant E820D showed a similar K+-sensitivity as the wild-type enzyme. The mutants E820N and E820Q had a 10-20 times lower sensitivity, whereas the other three mutants were hardly sensitive towards K+. Upon preincubation with 3-(cyanomethyl)-2-methyl-8-(phenylmethoxy) imidazo [1,2a]-pyridine (SCH28080), all mutants showed similar sensitivity for this drug as the wild-type enzyme, except mutant E820Q, which could only partly be inhibited, and mutant E820K, which was completely insensitive towards SCH28080. These experiments suggest that, with a relatively large residue at position 820, the binding of SCH28080 is obstructed. The various mutants showed a behaviour in K+-stimulated-dephosphorylation experiments similar to that for K+-activated-ATPase-activity measurements. These results indicate that K+ binding, and indirectly the transition to the E2 form, is only fully possible when a negatively charged residue is present at position 820 in the alpha-subunit. PMID:9531486

Hermsen, H P; Swarts, H G; Koenderink, J B; De Pont, J J

1998-04-15

329

Triggered Upward Negative Lightning Leaders  

NASA Astrophysics Data System (ADS)

Lightning flashes with upward negative-leaders were triggered at Langmuir Laboratory using small rockets during the 2008 and 2012 storm seasons. The flashes were observed by the Laboratory's Lightning Mapping Array (LMA), a high speed video camera, electric-field-change sensors, current viewing resistors, electric-field mills, and a broadband interferometer. Both the current and the electric-field indicated that an upward negative leader was initiated, which transferred positive charge from the cloud to ground. LMA observations show that in all cases the thunderstorms had a normal polarity charge structure, with upper positive charge over mid-level negative charge. The triggered upward leaders provided an indication that there was also a lower positive charge layer under the the mid-level negative charge. The flashes were observed to propagate into lower positive charge and, in one case, continue upward to near the boundary of the main negative charge region.

Trueblood, J.; Eack, K.; Winn, W. P.; Edens, H. E.; Aulich, G. D.; Eastvedt, E. M.; Petersen, D.; Stock, M.; Lapierre, J. L.; Sonnenfeld, R. G.

2013-12-01

330

IR spectroscopic studies of charge transfer in organic semiconductors  

NASA Astrophysics Data System (ADS)

Charge transfer (CT) mechanisms are crucial for device performance in organic electronics, but they are still not understood on a fundamental level. Here we want to show that in situ IR spectroscopy is very well suited to investigate CT effects in organic semiconductors in a qualitative and quantitative way. We study the ambipolar transport material 4,4´-bis(N-carbazolyl)-1,1´-biphenyl (CBP) as matrix and cesium carbonate (Cs2CO3) as n-dopant. To achieve doped layers, both materials were evaporated simultaneously. The system is one of the rare ones for n-doping of organic layers. In the spectra of the doped layers, additional absorption bands appear in the mid IR range. These can be assigned to the negatively charged matrix molecules that indicate electron transfer. The charged molecules exhibit these different absorption bands, as the charge transfer leads to a change in bond length and bond strength of the molecules. Our results very well agree with density functional theory calculations of the vibrational spectra of both, charged and non-charged molecules. By fitting the spectra of the doped layers as a superposition of the vibrational oscillators of neutral and charged species, we were able to quantify the amount of charged matrix molecules and to determine the doping efficiency of the investigated systems. For CBP n-doped with Cs2CO3 a hindrance of the CT due to air exposure could be observed.

Beck, Sebastian; Gerbert, David; Krekeler, Christian; Glaser, Tobias; Pucci, Annemarie

2014-05-01

331

Dissociative electron attachment to molecules and unstable species relevant in plasma processing  

NASA Astrophysics Data System (ADS)

Collisions between low energy electrons (0 to 10 eV) and molecules can lead to formation of negatively charged fragment ions by dissociative electron attachment. Electron attachment to plasma species, such as unstable molecules, formed in 2.45 GHz microwave discharges of CS2/He [1], C3F6/He, SF6/He, CH4/He and CCl4/He has been investigated with ERIC (Electron Radical Interaction Chamber), which includes a trochoidal electron monochromator and time-of-flight mass spectrometer. Knowledge of the spectra of negative ions formed as a function of electron energy for unstable molecules may be useful for understanding chemical processes and negative ion formation in plasmas. It may also be possible to identify unstable molecules in gas sampled from plasmas with these characteristic negative ion spectra. [1] Dissociative electron attachment to the unstable carbon monosulfide molecule CS, K. Graupner, T. A. Field and L. Feketeova, New J. Phys, 8 (2006) 314.

Graupner, Karola; Field, Thomas

2007-10-01

332

Role of negatively charged residues in the fifth and sixth transmembrane domains of the catalytic subunit of gastric H+,K+-ATPase.  

PubMed

The role of six negatively charged residues located in or around the fifth and sixth transmembrane domain of the catalytic subunit of gastric H+,K+-ATPase, which are conserved in P-type ATPases, was investigated by site-directed mutagenesis of each of these residues. The acid residues were converted into their corresponding acid amides. Sf9 cells were used as the expression system using a baculovirus with coding sequences for the alpha- and beta-subunits of H+,K+-ATPase behind two different promoters. Both subunits of all mutants were expressed like the wild type enzyme in intracellular membranes of Sf9 cells as indicated by Western blotting experiments, an enzyme-linked immunosorbent assay, and confocal laser scan microscopy studies. The mutants D824N, E834Q, E837Q, and D839N showed no 3-(cyanomethyl)-2-methyl-8(phenylmethoxy)-imidazo[1, 2a]pyridine (SCH 28080)-sensitive ATP dependent phosphorylation capacity. Mutants E795Q and E820Q formed a phosphorylated intermediate, which, like the wild type enzyme, was hydroxylamine-sensitive, indicating that an acylphosphate was formed. Formation of the phosphorylated intermediate from the E795Q mutant was similarly inhibited by K+ (I50 = 0.4 mM) and SCH 28080 (I50 = 10 nM) as the wild type enzyme, when the membranes were preincubated with these ligands before phosphorylation. The dephosphorylation reaction was K+-sensitive, whereas ADP had hardly any effect. Formation of the phosphorylated intermediate of mutant E820Q was much less sensitive toward K+ (I50 = 4.5 mM) and SCH 28080 (I50 = 1.7 microM) than the wild type enzyme. The dephosphorylation reaction of this intermediate was not stimulated by either K+ or ADP. In contrast to the wild type enzyme and mutant E795Q, mutant E820Q did not show any K+-stimulated ATPase activity. These findings indicate that residue Glu820 might be involved in K+ binding and transition to the E2 form of gastric H+,K+-ATPase. PMID:8939913

Swarts, H G; Klaassen, C H; de Boer, M; Fransen, J A; De Pont, J J

1996-11-22

333

Investigations of correlation between nitro group charges and C-nitro bond strength, and amino group effects on C-nitro bonds in planar conjugated molecules  

NASA Astrophysics Data System (ADS)

The correlation between the nitro group charges ( QNitro) and the C-Nitro bond length ( RC-Nitro), and the positional effects of amino groups on C-nitro bond strength in planar conjugated molecules such as the amino-nitro derivatives of benzene, naphthalene, anthracene, phenanthrene, alkene, and minor heterocyclic nitrogen compounds are computationally investigated. All calculations are performed using density functional theory (DFT) and the general gradient approximation (GGA) method with the Beck-LYP hybrid functional and the DNP basis set in Acceryls' code Dmol 3. The results are: (1) QNitro can be used as a structural parameter to estimate the strength of the C-Nitro bond, and further the stability of the nitro compound for 15 fitted lines show there is a good linear QNitro- RC-Nitro relationship in any group of derivatives. In addition, QNitro is more sensitive to structural changes and more effective to assess the C-Nitro bond strength than RC-Nitro; (2) the nitrating reaction of aromatic hydrocarbon can be qualitatively predicted and compared by QNitro: the more QNitro, the easier the nitrating condition, and the higher occurrence ratio of the corresponding nitrating product and (3) the amino groups on even positions can significantly strengthen C-Nitro bonds, other than those on odd positions. Therefore, in synthesizing insensitive explosives, it should be recommendable to introduce amino groups on even positions, particularly on 2-position due to the combination of the hydrogen bond, the induction effect and the mesomeric effect, which can obviously increase the molecular stability.

Zhang, Chaoyang

2006-05-01

334

Gas-phase charge permutation using ion\\/ion reactions and applications on the identification and characterization of macro-molecules  

Microsoft Academic Search

The advent of electrospray ionization capable of producing multiply charged ions from macromolecules has opened a new avenue to study the high-mass species. Gas phase charge permutation methodologies have been explored to manipulate the ion charge states and identities which may shed the light on the investigation of the properties of macromolecular species. In this thesis, macromolecule analysis has been

Min He

2005-01-01

335

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

336

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

NASA Astrophysics Data System (ADS)

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

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

337

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

SciTech Connect

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

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

2010-01-01

338

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

PubMed Central

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

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

2013-01-01

339

Formation of Hexagonal Fullerene Layers from Neutral and Negatively Charged Fullerenes in {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 Containing Gold Cations with the C3v Symmetry.  

PubMed

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

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

2014-07-01

340

Size and Charge Selectivity of the Glomerular Filter in Patients with Insulin-Dependent Diabetes mellitus: Urinary Immunoglobulins and Glycosaminoglycans  

Microsoft Academic Search

Background: In diabetic nephropathy, a reduction in negative membrane charge in the glomerular filter, i.e., the number of sulphated groups of glycosaminoglycans, has been argued to lead to increases in excretion of negatively charged molecules, such as albumin and IgG4. However, albuminuria and an increased excretion rate of IgG may also be caused by an increase in radius or number

Ole Torffvit; Bengt Rippe

1999-01-01

341

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

342

Surface impact ionization of polar-molecule clusters through pickup of alkali atoms  

NASA Astrophysics Data System (ADS)

The observation that clusters of neutral H2O () or SO2 (ref. 5) molecules, on impact with essentially any solid surface, can decay efficiently into positively and negatively charged fragments has defied explanation, not least because the kinetic energy per molecule can be much smaller than the molecular ionization potentials. Here we present a microscopic model of the charging mechanism, based on a mass analysis of charged SO2 cluster fragments, which appears to be applicable to polar-molecule clusters more generally. Our mass spectra reveal that all positively charged fragments carry an alkali ion (sodium, potassium or caesium), whereas the negative fragments are simply (SO2)n-. The yields of both charged species are comparable, and can be enhanced significantly by pre-treating the sample surface with additional alkali atoms. The key to charge separation in the clusters therefore appears to be the pickup of a neutral (but readily ionized) adatom during impact, followed by delocalization of the adatom's valence electron within the cluster and the subsequent collision-induced fragmentation of the cluster into charged pieces. This process could be of practical use in, for example, charge-pair generation and surface analysis; it may also be relevant to atmospheric ionization processes.

Gebhardt, C. R.; Schröder, H.; Kompa, K.-L.

1999-08-01

343

Negative ions in comets  

NASA Technical Reports Server (NTRS)

Negative ion sources in comets are identified and cometary plasma effects caused by negative ions are examined. The primary negative ion sources are shown to be: (1) for the inner coma - photodissociation of HCN, electron attachment of OH, and collision with alkalis; (2) in the vicinity of the nucleus - interplanetary dust collisions with the nucleus; and (3) for both the contaminated solar wind region and sporadic discharges in the nonhomogeneous inner coma plasma - dissociative electron attachment and charge inversion during keV positive ion scattering by cometary dust. Negative ion abundance for Halley's Comet has been estimated to be 10 to the -6th - 10 to the -10th of electron densities.

Wekhof, A.

1981-01-01

344

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

Microsoft Academic Search

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

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

2001-01-01

345

Imagining dissociation dynamics: Experimental study of electron attachment to water molecule by COLTRIMS technique  

Microsoft Academic Search

When water collides with a low-energy electron within a certain range of energy, the electron can attach to the water molecule. This electron can then autodetach leading to vibrational excitation, rotational excitation, or the anion can dissociate leading to a negatively charged fragment. This phenomena, called dissociative electron attachment (DEA), occurs in various occasions in science and industry. In this

Hidehito Adaniya

2009-01-01

346

Basal lamina secreted by MDCK cells has size- and charge-selective properties  

PubMed Central

The role electrical charge plays in determining glomerular permeability to macromolecules remains unclear. If the glomerular basement membrane (GBM) has any significant role in permselectivity, physical principles would suggest a negatively charged GBM would reject similarly charged more than neutral species. However, recent in vivo studies with negative and neutral glomerular probes showed the opposite. Whether this observation is due to unique characteristics of the probes used or is a general physiological phenomenon remains to be seen. The goal of this study was to use the basement membrane deposited by Madin-Darby canine kidney epithelial cells as a simple model of a biologically derived, negatively charged filter to evaluate size- and charge-based sieving properties. Fluorescein isothiocyanate-labeled carboxymethylated Ficoll 400 (FITC-CM Ficoll 400) and amino-4-methyl-coumarin-labeled Ficoll 400 (AMC Ficoll 400) were used as negatively charged and neutral tracer molecules, respectively, during pressure-driven filtration. Streaming potential measurement indicated the presence of fixed, negative charge in the basal lamina. The sieving coefficient for neutral Ficoll 400 decreased by ?0.0013 for each 1-? increment in solute radius, compared with a decrease of 0.0023 per ? for the anionic Ficoll 400. In this system, molecular charge played a significant role in determining the sieving characteristics of the membrane, pointing to solute charge as a potential contributor to GBM permselectivity.

Ferrell, Nicholas; Groszek, Joseph; Li, Lingyan; Smith, Ross; Butler, Robert S.; Zorman, Christian A.; Roy, Shuvo

2011-01-01

347

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

Microsoft Academic Search

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 à 10⁻⁹ and 1.2 à 10⁻⁹ cm³ molecule⁻¹ s⁻¹ were measured for V{sup 2+} and Ta{sup 2+}, respectively. The total kinetic energy of the product ions

James R. Gord; Ben S. Freiser; Steven W. Buckner

1991-01-01

348

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

Microsoft Academic Search

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.

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

1991-01-01

349

Two-dimensional charge-transfer molecules for second-order non-linear optics: synthesis, characterization and second harmonic generation of N,N?-dialkyl-2,4-dinitro-1,5-diaminobenzene compounds  

Microsoft Academic Search

Two-dimensional charge-transfer molecules based on N,N'-dialkyl-2,4-dinitro-1,5-diaminobenzene have been synthesized. 1H and 13C-NMR spectroscopy, elemental analysis and mass spectroscopy were used to elucidate their chemical structures. The physical and non-linear optical properties of this new family of dyes containing alkyl chain; C3H7, C6H13, C8H17, C10H21, C11H23 and C18H37 are discussed, taking into account the possible role of alkyl chain length. These

H. S. Nalwa; T. Watanabe; K. Ogino; H. Sato; S. Miyata

1998-01-01

350

The lytic activity of the bee venom peptide melittin is strongly reduced by the presence of negatively charged phospholipids or chloroplast galactolipids in the membranes of phosphatidylcholine large unilamellar vesicles.  

PubMed

We have investigated the dependence of the lytic activity of the bee venom peptide melittin on the lipid composition of its target membrane. The lysis of large unilamellar liposomes, measured as loss of the fluorescent dye carboxyfluorescein, in the presence of melittin was strongly reduced when the negatively charged lipids phosphatidylglycerol (PG) or phosphatidylserine (PS), or the plant chloroplast lipids monogalactosyldiacylglycerol (MGDG) or digalactosyldiacylglycerol (DGDG) were incorporated into egg phosphatidylcholine (EPC) membranes. This reduction was evident at concentrations below 10 wt% of the additional lipids. It was not due to reduced binding of melittin to the vesicles. It was also not related to a reduced insertion depth of the peptide into the bilayer, as shown by quenching of the intrinsic tryptophan fluorescence of the peptide by the aqueous quencher sodium nitrate. Fourier transform infrared spectroscopy (FTIR) revealed specific interactions of the peptide with the headgroups of the inhibitory lipids. The phosphate peak in PG was shifted by two wavenumbers after the addition of melittin. There was no shift in EPC or PS. Instead, in PS the COO- peak was strongly distorted in the presence of melittin. These data indicate ionic interactions between the basic peptide and the negative charges on the membrane surface. The galactolipids are uncharged. Here the evidence points to hydrogen bonding between melittin and OH-groups of the sugar headgroups. Liposomes containing DGDG were the only case where we found evidence for changes in fatty acyl chain motion due to the presence of melittin, from the CH2-scissoring peaks. PMID:8914580

Hincha, D K; Crowe, J H

1996-10-23

351

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

352

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

SciTech Connect

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

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

2013-03-21

353

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

354

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

355

Positive Darwinian Selection Promotes Charge Profile Diversity in the Antigen-binding Cleft of Class I Major-Histocompatibility-Complex Molecules1  

Microsoft Academic Search

Certain major-histocompatibility-complex (MHC) loci are highly polymorphic, and the mechanism of maintenance of this polymorphism remains controversial. Recent studies of the pattern of nucleotide substitution at MHC loci have produced strong evidence that this polymorphism is maintained mainly by positive Darwinian selection that operates on the antigen recognition site ( ARS) of the MHC molecule. The ARS of the class

Austin L. Hughes; Tatsuya Ota; Masatoshi Nei

356

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

PubMed

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

Han, Gyeo-Re; Jang, Chang-Hyun

2014-10-01

357

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

PubMed

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

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

2001-09-10

358

Charge transfer doping of silicon.  

PubMed

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

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

2014-04-18

359

Charge Transfer Doping of Silicon  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

360

Negative Numbers  

NSDL National Science Digital Library

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

Howard, Jill

2009-05-01

361

The effect of vibrational and electronic energy on near-resonant charge-transfer processes involving the rare gases and simple molecules  

Microsoft Academic Search

Charge transfer between H2+ and Ar, O2+ and Xe has been investigated as a function of the vibrational quantum number of the molecular ion within the energy range 20-1000 eV. The reverse reactions have also been studied and the ratio of the cross sections for the two spin-orbit levels of the ground-state rare-gas ion, sigma (2P32\\/)\\/ sigma (2P12\\/) determined. The

C. J. Latimer; F. M. Campbell

1982-01-01

362

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

363

Influence of surface charge field on the electron impact fragmentation pattern of KCl molecules in the free surface vaporization of single crystals  

Microsoft Academic Search

A mass-spectrometric method was used to investigate the temperature dependence of the electron impact fragmentation pattern of KCl molecules [ion current ratio I(K+)\\/I(KCl+)] vaporizing from a free surface of a potassium chloride single crystal. In the temperature range 766–945 K a very good correlation is observed between the variation in fragmentation pattern with temperature and the pattern of the curve

M. F. Butman; A. A. Smirnov; L. S. Kudin; Z. A. Munir

2000-01-01

364

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

365

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

2012-10-15

366

Charge state distributions in molecular dissociation  

NASA Astrophysics Data System (ADS)

Experiments were conducted to measure the charge state distributions resulting from molecular breakup and to compare them to that obtained for atomic ions at the same velocity. Elements (N, Mg, Mn, and Zn) chosen for study are those of interest to Trace Element Accelerator Mass Spectrometry (TEAMS) because they do not readily form negative ions which are necessary for injection into the tandem accelerator. A final energy of 1.4 MeV to 1.7 MeV was used in this experiment. AlO was chosen as an additional molecule to be studied because it was known to be more tightly bound than the SiX molecules. The SiX+ or AlO+ molecules were selected after acceleration and passed into a 30° beam line for breakup and analysis of the charge states of the fragments. The SiX+ or AlO + molecule ions were passed through an N2 gas cell to simulate the conditions in the terminal of the accelerator during molecular breakup. The molecular fragment ions and the atomic ions at the same velocity reached equilibrium charge state distributions in the N2 gas with an approximate target thickness of 0.43 ?g/cm2. Atomic ions of the fragments were produced in the terminal by electron stripping, e.g. Si+, N+, Mg+, Mn+, Zn+, Al+, and O+. The terminal voltage was chosen so that the singly charged ions were accelerated out of the accelerator at the respective fragment ion velocity produced in the molecular breakup. Calculations of charge state distributions resulting from molecular ion beam breakup by Cooney exist for the di- atomic molecule N2. The measured charge state fractions for SiX molecular fragments were found essentially the same as that measured for the atomic ions at the same velocity. Both charge state distributions peak at the same charge state and have approximately the same magnitude. Equilibrium fraction ratios with Cooney's fitting parameters are in agreement with the Si data and the general trend of the other fragments is represented. The present work provides charge state fractions that may be used to generate TEAMS relative sensitivity factors for impurities in semiconductor materials.

Renfrow, Steven Neal

367

Charge-transfer processes in collisions of H+ ions with H2, D2, CO, and CO2 molecules in the energy range 0.2-4.0 keV  

NASA Astrophysics Data System (ADS)

Charge-transfer processes resulting from collisions of H+ ions with H2, D2, CO, and CO2 molecules have been experimentally investigated in the energy range of 0.2-4.0 keV by using the initial growth-rate method. Theoretical analysis based on a molecular-orbital expansion method for H2 and CO targets was also carried out. The observed cross sections are compared with previous experimental and theoretical data. The present results for H2 are found to be in excellent accord with the recommended data by Barnett [Oak Ridge National Laboratory Report No. ORNL-6086 (1990)], and hence, confirm the accuracy of the recommended data. But, at 0.2 keV, the present data for D2 are found to be smaller than those for H2. For the CO molecule, the present data qualitatively agree well with most previous measurements, but show the stronger energy dependence, while the present theory shows a pronounced structure at around 0.25 keV and ties well with other low-energy measurements below 0.1 keV. For the CO2 molecule, the present results are in excellent accord with other measurements above 1 keV, while they show some differences below this energy where our experimental result displays the stronger energy dependence. These data are useful for various applications.

Kusakabe, Toshio; Asahina, Kensuke; Gu, Jiang P.; Hirsch, Gerhard; Buenker, Robert J.; Kimura, Mineo; Tawara, Hiroyuki; Nakai, Yohta

2000-12-01

368

A model for molecules with twisted intramolecular charge transfer characteristics: solvent polarity effect on the nonradiative rates of dyes in a series of water—ethanol mixed solvents  

NASA Astrophysics Data System (ADS)

The model of Grabowski et al. has been modified and used to account for the absence of a fluorescence band from the twisted form of molecules with torsional mechanisms. We have measured the ground and excited state spectroscopic properties of rhodamine B dissolved in a series of water—ethanol mixed solvents, and used the data to test the model. We also applied our model to 8-anilino-1-naphthalenesulfonate (ANS) in the same solvent system, using previously published decay and quantum yield data. The results show that the variation of the nonradiative rates may be attributed to changes in solvent polarity for both systems.

Chang, Tzyh-Lee; Cheung, Herbert C.

1990-10-01

369

1,3-Bis(nitroimido)-1,2,3-triazolate anion, the N-nitroimide moiety, and the strategy of alternating positive and negative charges in the design of energetic materials.  

PubMed

This unique study reports on the 1,3-bis(nitroimido)-1,2,3-triazolate anion. This compound provides unique insight into both academic and practical considerations surrounding high-nitrogen systems. The bonding in this energetic anion can be represented multiple ways, one of which includes a chain of alternating positive/negative charges nine atoms long. The validity of this resonance structure is discussed in terms of experimental, computational, and valence bond results. The prepared materials based on this energetic anion were also characterized chemically (infrared, Raman, NMR, X-ray) and as high explosives in terms of their energetic performances (detonation velocity, pressure, etc.) and sensitivities (impact, friction, electrostatic), and the 1,3-bis(nitroimido)-1,2,3-triazolate anion is found to be very high performing with high thermal stabilities while being quite sensitive to mechanical stimuli. PMID:23190185

Klapötke, Thomas M; Petermayer, Christian; Piercey, Davin G; Stierstorfer, Jörg

2012-12-26

370

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

PubMed

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

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

2007-12-01

371

Negative Leadership.  

National Technical Information Service (NTIS)

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

D. M. Oberlander

2013-01-01

372

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

373

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

PubMed Central

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

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

2014-01-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

375

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

376

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

PubMed

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

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

2014-03-17

377

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

PubMed

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

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

2014-07-21

378

Accelerating water transport through a charged SWCNT: a molecular dynamics simulation.  

PubMed

The properties of a nanotube, such as the hydrophobicity and charge of the surface, can significantly affect water transport behavior. However, our knowledge of the effects of charge density, dipole orientation, frequency of flipping, and movement behavior on water flow through carbon nanotubes (CNTs) is far from adequate. This study is aimed at gaining insight into the transport of single-file water molecules in a charged carbon nanotube. It was shown that the water chains inside the charged nanotube exhibit bipolar properties. The water dipoles are parallel to the z-axis, and point toward (D-defect) and away from (L-defect) the center of the nanotube for a negatively charged nanotube and a positively charged one, respectively. Compared with a pristine single-wall carbon nanotube (SWCNT), the charged nanotubes, including both positively charged and negatively charged, favor the water-filling process due to electrostatic interactions. According to the dipole distribution in the nanotube, the water dipole only flips in the middle region because of the bipolar nature of water chains. Additionally, flipping of the entire water chain is inhibited, which allows for the enhanced water flux. A negatively charged single-walled carbon nanotube (N-SWCNT) accelerated water transport by tuning the single-file flow from a "hopping" to a "continuous" mode, thus decreasing the energy barrier. The hydrogen bonds between water molecules inside the nanotube are also strengthened in the negatively charged nanotube, favoring water transport. Any distortion of uniformity will lead to additional energy barriers to water flux. Our results provide a comprehensive view of molecular events underpinning the water transport inside a SWCNT, which may be of assistance in creating innovative designs for water nanochannels. PMID:23884179

Lu, Diannan

2013-09-14

379

Photocurrent Generation Enhanced by Charge Delocalization over Stacked Perylenediimide Chromophores Assembled within DNA.  

PubMed

We now report the photocurrent generation and charge transfer dynamics of stacked perylenediimide (PDI) molecules within a ?-stack array of DNA. The cofacially stacked PDI dimer and trimer were found to strongly enhance the photocurrent generation compared to an isolated PDI monomer. Femtosecond time-resolved transient absorption experiments revealed that the excitation of the stacked PDI dimer and trimer provided the broad transient absorption band, which was attributed to the charge delocalization of a negative charge over the PDI chromophores. The lifetime of the charge delocalization of the PDI dimer and trimer (nearly 1 ns) was much longer than that of the charge separated state of the PDI monomer. A comparison between the photocurrent measurements and time-resolved transient absorption measurements demonstrated that the cofacially stacked structure could possibly lead to the charge delocalization and increase the lifetime of the charge-separated state that is essential to enhancing the photocurrent generation. PMID:24786843

Takada, Tadao; Ashida, Akane; Nakamura, Mitsunobu; Fujitsuka, Mamoru; Majima, Tetsuro; Yamana, Kazushige

2014-05-14

380

Charge-transfer processes in collisions of ground-state C+ ions with H2, D2, CO, and CO2 molecules in the energy range from 0.15 to 4.5 keV  

NASA Astrophysics Data System (ADS)

Charge-transfer processes in collisions of C+ ions with H2, D2, CO, and CO2 molecules have been studied based on joint experimental and theoretical approaches in the collision energy from 0.15 to 4.5 keV. In the present experiment, the ground-state C+(2P) ion projectiles have been produced by carefully energy-controlled electron impact to minimize the influence of the metastable-state ions. The observed cross sections are compared with the present theoretical prediction, and while the theoretical results are somewhat smaller than the measurements, they are found to be in reasonable agreement for H2, D2, and CO above around 1 keV. The present experimental cross sections for CO and CO2 are smaller by a factor of 2 to 3 than those of earlier measurements. We provide some remarks on the effect of the metastable-state ions.

Kusakabe, Toshio; Hosomi, Kenji; Nakanishi, Hiroshi; Tawara, Hiroyuki; Sasao, Mamiko; Nakai, Yohta; Kimura, Mineo

1999-07-01

381

Negative ions at Titan and Enceladus: recent results.  

PubMed

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

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

2010-01-01

382

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

2013-11-27

383

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