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Sample records for singly charged peptide

  1. Electron Transport in Short Peptide Single Molecules

    NASA Astrophysics Data System (ADS)

    Cui, Jing; Brisendine, Joseph; Ng, Fay; Nuckolls, Colin; Koder, Ronald; Venkarataman, Latha

    We present a study of the electron transport through a series of short peptides using scanning tunneling microscope-based break junction method. Our work is motivated by the need to gain a better understanding of how various levels of protein structure contribute to the remarkable capacity of proteins to transport charge in biophysical processes such as respiration and photosynthesis. We focus here on short mono, di and tri-peptides, and probe their conductance when bound to gold electrodes in a native buffer environment. We first show that these peptides can bind to gold through amine, carboxyl, thiol and methyl-sulfide termini. We then focus on two systems (glycine and alanine) and show that their conductance decays faster than alkanes terminated by the same linkers. Importantly, our results show that the peptide bond is less conductive than a sigma carbon-carbon bond. This work was supported in part by NSF-DMR 1507440.

  2. Impact of multivalent charge presentation on peptide-nanoparticle aggregation.

    PubMed

    Schöne, Daniel; Schade, Boris; Böttcher, Christoph; Koksch, Beate

    2015-01-01

    Strategies to achieve controlled nanoparticle aggregation have gained much interest, due to the versatility of such systems and their applications in materials science and medicine. In this article we demonstrate that coiled-coil peptide-induced aggregation based on electrostatic interactions is highly sensitive to the length of the peptide as well as the number of presented charges. The quaternary structure of the peptide was found to play an important role in aggregation kinetics. Furthermore, we show that the presence of peptide fibers leads to well-defined nanoparticle assembly on the surface of these macrostructures. PMID:26124881

  3. Positive Charge of “Sticky” Peptides and Proteins Impedes Release From Negatively Charged PLGA Matrices

    PubMed Central

    Balmert, Stephen C.; Zmolek, Andrew C.; Glowacki, Andrew J.; Knab, Timothy D.; Rothstein, Sam N.; Wokpetah, Joseph M.; Fedorchak, Morgan V.; Little, Steven R.

    2015-01-01

    The influence of electrostatic interactions and/or acylation on release of charged (“sticky”) agents from biodegradable polymer matrices was systematically characterized. We hypothesized that release of peptides with positive charge would be hindered from negatively charged poly(lactic-co-glycolic acid) (PLGA) microparticles. Thus, we investigated release of peptides with different degrees of positive charge from several PLGA microparticle formulations, with different molecular weights and/or end groups (acid- or ester-terminated). Indeed, release studies revealed distinct inverse correlations between the amount of positive charge on peptides and their release rates from each PLGA microparticle formulation. Furthermore, we examined the case of peptides with net charge that changes from negative to positive within the pH range observed in degrading microparticles. These charge changing peptides displayed counterintuitive release kinetics, initially releasing faster from slower degrading (less acidic) microparticles, and releasing slower from the faster degrading (more acidic) microparticles. Importantly, trends between agent charge and release rates for model peptides also translated to larger, therapeutically relevant proteins and oligonucleotides. The results of these studies may improve future design of controlled release systems for numerous therapeutic biomolecules exhibiting positive charge, ultimately reducing time-consuming and costly trial and error iterations of such formulations. PMID:26085928

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

    PubMed

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

    2010-11-01

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

  5. Basophile: Accurate Fragment Charge State Prediction Improves Peptide Identification Rates

    SciTech Connect

    Wang, Dong; Dasari, Surendra; Chambers, Matthew C.; Holman, Jerry D.; Chen, Kan; Liebler, Daniel; Orton, Daniel J.; Purvine, Samuel O.; Monroe, Matthew E.; Chung, Chang Y.; Rose, Kristie L.; Tabb, David L.

    2013-03-07

    In shotgun proteomics, database search algorithms rely on fragmentation models to predict fragment ions that should be observed for a given peptide sequence. The most widely used strategy (Naive model) is oversimplified, cleaving all peptide bonds with equal probability to produce fragments of all charges below that of the precursor ion. More accurate models, based on fragmentation simulation, are too computationally intensive for on-the-fly use in database search algorithms. We have created an ordinal-regression-based model called Basophile that takes fragment size and basic residue distribution into account when determining the charge retention during CID/higher-energy collision induced dissociation (HCD) of charged peptides. This model improves the accuracy of predictions by reducing the number of unnecessary fragments that are routinely predicted for highly-charged precursors. Basophile increased the identification rates by 26% (on average) over the Naive model, when analyzing triply-charged precursors from ion trap data. Basophile achieves simplicity and speed by solving the prediction problem with an ordinal regression equation, which can be incorporated into any database search software for shotgun proteomic identification.

  6. Statistical characterization of the charge state and residue dependence of low-energy CID peptide dissociation patterns.

    PubMed

    Huang, Yingying; Triscari, Joseph M; Tseng, George C; Pasa-Tolic, Ljiljana; Lipton, Mary S; Smith, Richard D; Wysocki, Vicki H

    2005-09-15

    Data mining was performed on 28 330 unique peptide tandem mass spectra for which sequences were assigned with high confidence. By dividing the spectra into different sets based on structural features and charge states of the corresponding peptides, chemical interactions involved in promoting specific cleavage patterns in gas-phase peptides were characterized. Pairwise fragmentation maps describing cleavages at all Xxx-Zzz residue combinations for b and y ions reveal that the difference in basicity between Arg and Lys results in different dissociation patterns for singly charged Arg- and Lys-ending tryptic peptides. While one dominant protonation form (proton localized) exists for Arg-ending peptides, a heterogeneous population of different protonated forms or more facile interconversion of protonated forms (proton partially mobile) exists for Lys-ending peptides. Cleavage C-terminal to acidic residues dominates spectra from singly charged peptides that have a localized proton and cleavage N-terminal to Pro dominates those that have a mobile or partially mobile proton. When Pro is absent from peptides that have a mobile or partially mobile proton, cleavage at each peptide bond becomes much more prominent. Whether the above patterns can be found in b ions, y ions, or both depends on the location of the proton holder(s) in multiply protonated peptides. Enhanced cleavages C-terminal to branched aliphatic residues (Ile, Val, Leu) are observed in both b and y ions from peptides that have a mobile proton, as well as in y ions from peptides that have a partially mobile proton; enhanced cleavages N-terminal to these residues are observed in b ions from peptides that have a partially mobile proton. Statistical tools have been designed to visualize the fragmentation maps and measure the similarity between them. The pairwise cleavage patterns observed expand our knowledge of peptide gas-phase fragmentation behaviors and may be useful in algorithm development that employs

  7. Basophile: Accurate Fragment Charge State Prediction Improves Peptide Identification Rates

    DOE PAGESBeta

    Wang, Dong; Dasari, Surendra; Chambers, Matthew C.; Holman, Jerry D.; Chen, Kan; Liebler, Daniel; Orton, Daniel J.; Purvine, Samuel O.; Monroe, Matthew E.; Chung, Chang Y.; et al

    2013-03-07

    In shotgun proteomics, database search algorithms rely on fragmentation models to predict fragment ions that should be observed for a given peptide sequence. The most widely used strategy (Naive model) is oversimplified, cleaving all peptide bonds with equal probability to produce fragments of all charges below that of the precursor ion. More accurate models, based on fragmentation simulation, are too computationally intensive for on-the-fly use in database search algorithms. We have created an ordinal-regression-based model called Basophile that takes fragment size and basic residue distribution into account when determining the charge retention during CID/higher-energy collision induced dissociation (HCD) of chargedmore » peptides. This model improves the accuracy of predictions by reducing the number of unnecessary fragments that are routinely predicted for highly-charged precursors. Basophile increased the identification rates by 26% (on average) over the Naive model, when analyzing triply-charged precursors from ion trap data. Basophile achieves simplicity and speed by solving the prediction problem with an ordinal regression equation, which can be incorporated into any database search software for shotgun proteomic identification.« less

  8. Mechanism of Reversible Peptide-Bilayer Attachment: Combined Simulation and Experimental Single-Molecule Study.

    PubMed

    Schwierz, Nadine; Krysiak, Stefanie; Hugel, Thorsten; Zacharias, Martin

    2016-01-26

    The binding of peptides and proteins to lipid membrane surfaces is of fundamental importance for many membrane-mediated cellular processes. Using closely matched molecular dynamics simulations and atomic force microscopy experiments, we study the force-induced desorption of single peptide chains from phospholipid bilayers to gain microscopic insight into the mechanism of reversible attachment. This approach allows quantification of desorption forces and decomposition of peptide-membrane interactions into energetic and entropic contributions. In both simulations and experiments, the desorption forces of peptides with charged and polar side chains are much smaller than those for hydrophobic peptides. The adsorption of charged/polar peptides to the membrane surface is disfavored by the energetic components, requires breaking of hydrogen bonds involving the peptides, and is favored only slightly by entropy. By contrast, the stronger adsorption of hydrophobic peptides is favored both by energy and by entropy and the desorption forces increase with increasing side-chain hydrophobicity. Interestingly, the calculated net adsorption free energies per residue correlate with experimental results of single residues, indicating that side-chain free energy contributions are largely additive. This observation can help in the design of peptides with tailored adsorption properties and in the estimation of membrane binding properties of peripheral membrane proteins. PMID:26717083

  9. Dynamic Peptide Library for the Discovery of Charge Transfer Hydrogels.

    PubMed

    Berdugo, Cristina; Nalluri, Siva Krishna Mohan; Javid, Nadeem; Escuder, Beatriu; Miravet, Juan F; Ulijn, Rein V

    2015-11-25

    Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various π-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV-vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly. The methodology provides an in situ discovery tool for nanostructures that enable dynamic interfacing of supramolecular electronics with aqueous (biological) systems. PMID:26540455

  10. Single-electron charging effects

    SciTech Connect

    Ruggiero, S.T.

    1991-12-15

    The status of our project on single-electron tunneling is, again, excellent. As outlined in our original proposal, a key goal for this project has been the development of a scanning tunneling instrument for the purpose of imaging individual particles and tunneling into these particles at high magnetic fields. Further progress is discussed in this report.

  11. Metabolism of Peptide Reporters in Cell Lysates and Single Cells

    PubMed Central

    Proctor, Angela; Wang, Qunzhao; Lawrence, David S.; Allbritton, Nancy L.

    2013-01-01

    The stability of an Abl kinase substrate peptide in a cytosolic lysate and in single cells was characterized. In the cytosolic lysate, the starting peptide was metabolized at an average initial rate of 1.7 ± 0.3 zmol pg−;1 s−;1 with a t1/2 of 1.3 min. Five different fragments formed over time; however, a dominant cleavage site was identified. Multiple rational design cycles were utilized to develop a lead peptide with a phenylalanine and alanine replaced by an (N-methyl)phenylalanine and isoleucine, respectively, to attain cytosolic peptidase resistance while maintaining Abl substrate efficacy. This lead peptide possessed a 15-fold greater lifetime in the cytosolic lysate while attaining a 7-fold improvement in kcat as an Abl kinase substrate compared to the starting peptide. However, when loaded into single cells, the starting peptide and lead peptide possessed nearly identical degradation rates and an altered pattern of fragmentation relative to that in cell lysates. Preferential accumulation of a fragment with cleavage at an Ala-Ala bond in single cells suggested that dissimilar peptidases act on the peptides in the lysate versus single cells. A design strategy for peptide stabilization, analogous to that demonstrated for the lysate, should be effective for stabilization in single cells. PMID:22314840

  12. A new model for multiply charged adduct formation between peptides and anions in electrospray mass spectrometry.

    PubMed

    Liu, Xiaohua; Cole, Richard B

    2011-12-01

    A new model has been developed to account for adduct formation on multiply charged peptides observed in negative ion electrospray mass spectrometry. To obtain a stable adduct, the model necessitates an approximate matching of apparent gas-phase basicity (GB(app)) of a given proton bearing site on the peptide with the gas-phase basicity (GB) of the anion attaching at that site. Evidence supporting the model is derived from the fact that for [Glu] Fibrinopeptide B, higher GB anions dominated in adducts observed at higher negative charge states, whereas lower GB anions appeared predominately in lower charge state adducts. Singly charged adducts were only observed for lower GB anions: HSO(4)(-), I(-), CF(3)COO(-). Ions that have medium GBs (NO(3) (-), Br(-), H(2)PO(4)(-)) only form adducts having -2 charge states, whereas Cl(-) (higher GB) can form adducts having -3 charge states. The model portends that (1) carboxylate groups are much more basic than available amino groups; (2) apparent GBs of the various carboxylate groups on peptides do not vary substantially from one another; and (3) apparent GBs of the individual carboxylate and amino sites do not behave independently. This model was developed for negative ion attachment but an analogous mechanism is also proposed for the positive ion mode wherein (1) binding of a neutral at an amino site polarizes this amino group, but hardly affects apparent GBs of other sites; (2) proton addition (charge state augmentation) at one site can decrease the instrinsic GBs of other potential protonation sites and lower their apparent GBs. PMID:21997579

  13. A New Model for Multiply Charged Adduct Formation Between Peptides and Anions in Electrospray Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Liu, Xiaohua; Cole, Richard B.

    2011-12-01

    A new model has been developed to account for adduct formation on multiply charged peptides observed in negative ion electrospray mass spectrometry. To obtain a stable adduct, the model necessitates an approximate matching of apparent gas-phase basicity (GBapp) of a given proton bearing site on the peptide with the gas-phase basicity (GB) of the anion attaching at that site. Evidence supporting the model is derived from the fact that for [Glu] Fibrinopeptide B, higher GB anions dominated in adducts observed at higher negative charge states, whereas lower GB anions appeared predominately in lower charge state adducts. Singly charged adducts were only observed for lower GB anions: HSO{4/-}, I-, CF3COO-. Ions that have medium GBs (NO{3/-}, Br-, H2PO{4/-}) only form adducts having -2 charge states, whereas Cl- (higher GB) can form adducts having -3 charge states. The model portends that (1) carboxylate groups are much more basic than available amino groups; (2) apparent GBs of the various carboxylate groups on peptides do not vary substantially from one another; and (3) apparent GBs of the individual carboxylate and amino sites do not behave independently. This model was developed for negative ion attachment but an analogous mechanism is also proposed for the positive ion mode wherein (1) binding of a neutral at an amino site polarizes this amino group, but hardly affects apparent GBs of other sites; (2) proton addition (charge state augmentation) at one site can decrease the instrinsic GBs of other potential protonation sites and lower their apparent GBs.

  14. Statistical Characterization of the Charge State and Residue Dependence of Low-Energy CID Peptide Dissociation Patterns

    SciTech Connect

    Huang, Yingying; Triscari, Joseph M.; Tseng, George C.; Pasa-Tolic, Ljiljana; Lipton, Mary S.; Smith, Richard D.; Wysocki, Vicki H.

    2005-09-01

    Data mining was performed on 28 330 unique peptide tandem mass spectra for which sequences were assigned with high confidence. By dividing the spectra into different sets based on structural features and charge states of the corresponding peptides, chemical interactions involved in promoting specific cleavage patterns in gas-phase peptides were characterized. Pairwise fragmentation maps describing cleavages at all Xxx-Zzz residue combinations for b and y ions reveal that the difference in basicity between Arg and Lys results in different dissociation patterns for singly charged Arg- and Lys-ending tryptic peptides. While one dominant protonation form (proton localized) exists for Arg-ending peptides, a heterogeneous population of different protonated forms or more facile interconversion of protonated forms (proton partially mobile) exists for Lys-ending peptides. Cleavage C-terminal to acidic residues dominates spectra from peptides that have a localized proton and cleavage N-terminal to Pro dominates those that have a mobile or partially mobile proton. When Pro is absent from peptides that have a mobile or partially mobile proton, cleavage at each peptide bond becomes much more prominent. Whether the above patterns can be found in b ions, y ions, or both depends on the location of the proton holder(s). Enhanced cleavages C-terminal to branched aliphatic residues (Ile, Val, Leu) are observed in both b and y ions from peptides that have a mobile proton, as well as in y ions from peptides that have a partially mobile proton; enhanced cleavages N-terminal to these residues are observed in b ions from peptides that have a partially mobile proton. Statistical tools have been designed to visualize the fragmentation maps and measure the similarity between them. The pairwise cleavage patterns observed expand our knowledge of peptide gas-phase fragmentation behaviors and should be useful in algorithm development that employs improved models to predict fragment ion

  15. Charge-Compensated Metallacarborane Building Blocks for Conjugation with Peptides.

    PubMed

    Frank, René; Ahrens, Verena M; Boehnke, Solveig; Beck-Sickinger, Annette G; Hey-Hawkins, Evamarie

    2016-02-15

    The cobalt bis(dicarbollide) complex [commo-3,3'-Co(1,2-C2 B9 H11 )2 ](-) has captured much attention in biochemical and medical contexts, in particular for the treatment of tumors by boron neutron capture therapy (BNCT). Derivatives of cobalt bis(dicarbollide) are commonly prepared through ring-opening reactions of cyclic oxonium ions, so the corresponding products are usually charged. Furthermore, attempts to incorporate cobalt bis(dicarbollide) into peptides are rare, despite obvious potential advantages. Here the synthesis of an imidazolium-based charge-compensated cobalt bis(dicarbollide) building block, which allows additional modifications with moieties of biochemical relevance, such as monosaccharides, is reported. Furthermore, conjugates of these building blocks with the Y1 -receptor-selective derivative of neuropeptide Y ([F(7) ,P(34) ]-NPY) retained excellent response to hY1 receptors found to be overexpressed in breast tumors and metastases. PMID:26662708

  16. From a pro-apoptotic peptide to a lytic peptide: One single residue mutation.

    PubMed

    Zhou, Xi-Rui; Zhang, Qiang; Tian, Xi-Bo; Cao, Yi-Meng; Liu, Zhu-Qing; Fan, Ruru; Ding, Xiu-Fang; Zhu, Zhentai; Chen, Long; Luo, Shi-Zhong

    2016-08-01

    Further discovery and design of new anticancer peptides are important for the development of anticancer therapeutics, and study on the detailed acting mechanism and structure-function relationship of peptides is critical for anticancer peptide design and application. In this study, a novel anticancer peptide ZXR-1 (FKIGGFIKKLWRSKLA) derived from a known anticancer peptide mauriporin was developed, and a mutant ZXR-2 (FKIGGFIKKLWRSLLA) with only one residue difference at the 14th position (Lys→Leu) was also engineered. Replacement of the lysine with leucine made ZXR-2 more potent than ZXR-1 in general. Even with only one residue mutation, the two peptides displayed distinct anticancer modes of action. ZXR-1 could translocate into cells, target on the mitochondria and induce cell apoptosis, while ZXR-2 directly targeted on the cell membranes and caused membrane lysis. The variance in their acting mechanisms might be due to the different amphipathicity and positive charge distribution. In addition, the two Ile-Leu pairs (3-10 and 7-14) in ZXR-2 might also play a role in improving its cytotoxicity. Further study on the structure-function relationship of the two peptides may be beneficial for the design of novel anticancer peptides and peptide based therapeutics. PMID:27207743

  17. Structural Heterogeneity of Doubly-Charged Peptide b-Ions

    NASA Astrophysics Data System (ADS)

    Li, Xiaojuan; Huang, Yiqun; O'Connor, Peter B.; Lin, Cheng

    2011-02-01

    Performing collisionally activated dissociation (CAD) and electron capture dissociation (ECD) in tandem has shown great promise in providing comprehensive sequence information that was otherwise unobtainable by using either fragmentation method alone or in duet. However, the general applicability of this MS3 approach in peptide sequencing may be undermined by the formation of non-direct sequence ions, as sometimes observed under CAD, particularly when multiple stages of CAD are involved. In this study, varied-sized doubly-charged b-ions from three tachykinin peptides were investigated by ECD. Sequence scrambling was observed in ECD of all b-ions from neurokinin A (HKTDSFVGLM-NH2), suggesting the presence of N- and C-termini linked macro-cyclic conformers. On the contrary, none of the b-ions from eledoisin (pEPSKDAFIGLM-NH2) produced non-direct sequence ions under ECD, as it does not contain a free N-terminal amino group. ECD of several b-ions from Substance P (RPKPQQFFGLM-NH2) showed series of cm-Lys fragment ions which suggested that the macro-cyclic structure may also be formed by connecting the C-terminal carbonyl group and the ɛ-amino group of the lysine side chain. Theoretical investigation of selected Substance P b-ions revealed several low energy conformers, including both linear oxazolones and macro-ring structures, in corroboration with the experimental observation. This study showed that a b-ion may exist as a mixture of several forms, with their propensities influenced by its N-terminus, length, and certain side-chain groups. Further, the presence of several macro-cyclic structures may result in erroneous sequence assignment when the combined CAD and ECD methods are used in peptide sequencing.

  18. Negative-charge driven fragmentations for evidencing zwitterionic forms from doubly charged coppered peptides.

    PubMed

    Boutin, Michel; Bich, Claudia; Afonso, Carlos; Fournier, Françoise; Tabet, Jean-Claude

    2007-01-01

    In aqueous solution, amino acids (AA) and peptides are known to exist as zwitterions over a large pH range. However, in the gas phase, i.e. in electrospray (ESI), the zwitterionic form becomes unfavorable owing to the absence of stabilizing effects from intermolecular solvation. Nevertheless, during mass spectrometry experiments, the presence of a metallic cation can reinforce the zwitterionic character of the molecule and thus influence its fragmentation under low energy collision-induced dissociation (CID) conditions. The [M + Cu(II)](2+) complexes of six pentapeptides (YGGFL, YGGFL(NH(2)), YGGFK, YGGFQ, KYGGF and QYGGF) were analyzed by collision to highlight the presence of zwitterions. The experiments were performed on a 3D-ion trap equipped with an orthogonal ESI source. For each peptides studied, negative-charge driven fragmentations on globally positively charged ions were observed. These fragmentation mechanisms, generally observed in the negative mode, suggest the competitive deprotonation of the C-terminal carboxylic acid or of the tyrosine side-chain residue for each peptide studied and thus a zwitterionic form to preserve the charge balance. Moreover, the specific loss of (CH(3)--C(6)H(4)--O)(*) characterizes YGGFK compared to YGGFQ and the specific loss of styrene characterizes KYGGF compared to QYGGF. These results allow the differentiation of the two couples of isobaric pentapeptides. An unusual loss of NH(4) (+), which occurred from the N-terminus, was also observed for YGGFL, YGGFL(NH(2)), YGGFK and YGGFQ. Finally, the reduction of Cu(II) to Cu(I), concomitant with the (CH(3)--C(6)H(4)--O)(*) release, was pointed out for YGGFK. PMID:17149792

  19. Field effect of screened charges: electrical detection of peptides and proteins by a thin-film resistor.

    PubMed

    Lud, Simon Q; Nikolaides, Michael G; Haase, Ilka; Fischer, Markus; Bausch, Andreas R

    2006-02-13

    For many biotechnological applications the label-free detection of biomolecular interactions is becoming of outstanding importance. In this Article we report the direct electrical detection of small peptides and proteins by their intrinsic charges using a biofunctionalized thin-film resistor. The label-free selective and quantitative detection of small peptides and proteins is achieved using hydrophobized silicon-on-insulator (SOI) substrates functionalized with lipid membranes that incorporate metal-chelating lipids. The response of the nanometer-thin conducting silicon film to electrolyte screening effects is taken into account to determine quantitatively the charges of peptides. It is even possible to detect peptides with a single charge and to distinguish single charge variations of the analytes even in physiological electrolyte solutions. As the device is based on standard semiconductor technologies, parallelization and miniaturization of the SOI-based biosensor is achievable by standard CMOS technologies and thus a promising basis for high-throughput screening or biotechnological applications. PMID:16404758

  20. Charge transport in single crystal organic semiconductors

    NASA Astrophysics Data System (ADS)

    Xie, Wei

    Organic electronics have engendered substantial interest in printable, flexible and large-area applications thanks to their low fabrication cost per unit area, chemical versatility and solution processability. Nevertheless, fundamental understanding of device physics and charge transport in organic semiconductors lag somewhat behind, partially due to ubiquitous defects and impurities in technologically useful organic thin films, formed either by vacuum deposition or solution process. In this context, single-crystalline organic semiconductors, or organic single crystals, have therefore provided the ideal system for transport studies. Organic single crystals are characterized by their high chemical purity and outstanding structural perfection, leading to significantly improved electrical properties compared with their thin-film counterparts. Importantly, the surfaces of the crystals are molecularly flat, an ideal condition for building field-effect transistors (FETs). Progress in organic single crystal FETs (SC-FETs) is tremendous during the past decade. Large mobilities ~ 1 - 10 cm2V-1s-1 have been achieved in several crystals, allowing a wide range of electrical, optical, mechanical, structural, and theoretical studies. Several challenges still remain, however, which are the motivation of this thesis. The first challenge is to delineate the crystal structure/electrical property relationship for development of high-performance organic semiconductors. This thesis demonstrates a full spectrum of studies spanning from chemical synthesis, single crystal structure determination, quantum-chemical calculation, SC-OFET fabrication, electrical measurement, photoelectron spectroscopy characterization and extensive device optimization in a series of new rubrene derivatives, motivated by the fact that rubrene is a benchmark semiconductor with record hole mobility ~ 20 cm2V-1s-1. With successful preservation of beneficial pi-stacking structures, these rubrene derivatives form

  1. Cavity cooling a single charged levitated nanosphere.

    PubMed

    Millen, J; Fonseca, P Z G; Mavrogordatos, T; Monteiro, T S; Barker, P F

    2015-03-27

    Optomechanical cavity cooling of levitated objects offers the possibility for laboratory investigation of the macroscopic quantum behavior of systems that are largely decoupled from their environment. However, experimental progress has been hindered by particle loss mechanisms, which have prevented levitation and cavity cooling in a vacuum. We overcome this problem with a new type of hybrid electro-optical trap formed from a Paul trap within a single-mode optical cavity. We demonstrate a factor of 100 cavity cooling of 400 nm diameter silica spheres trapped in vacuum. This paves the way for ground-state cooling in a smaller, higher finesse cavity, as we show that a novel feature of the hybrid trap is that the optomechanical cooling becomes actively driven by the Paul trap, even for singly charged nanospheres. PMID:25860743

  2. Pronase E-Based Generation of Fluorescent Peptide Fragments: Tracking Intracellular Peptide Fate in Single Cells.

    PubMed

    Mainz, Emilie R; Dobes, Nicholas C; Allbritton, Nancy L

    2015-08-01

    The ability to track intracellular peptide proteolysis at the single cell level is of growing interest, particularly as short peptide sequences continue to play important roles as biosensors, therapeutics, and endogenous participants in antigen processing and intracellular signaling. We describe a rapid and inexpensive methodology to generate fluorescent peptide fragments from a parent sequence with diverse chemical properties, including aliphatic, nonpolar, basic, acidic, and non-native amino acids. Four peptide sequences with existing biochemical applications were fragmented using incubation with Pronase E and/or formic acid, and in each case a complete set of fluorescent fragments was generated for use as proteolysis standards in chemical cytometry. Fragment formation and identity was monitored with capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) and matrix assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-MS) to confirm the presence of all sequences and yield fragmentation profiles across Pronase E concentrations which can readily be used by others. As a pilot study, Pronase E-generated standards from an Abl kinase sensor and an ovalbumin antigenic peptide were then employed to identify proteolysis products arising from the metabolism of these sequences in single cells. The Abl kinase sensor fragmented at 4.2 ± 4.8 zmol μM(-1) s(-1) and the majority of cells possessed similar fragment identities. In contrast, an ovalbumin epitope peptide was degraded at 8.9 ± 0.1 zmol μM(-1) s(-1), but with differential fragment formation between individual cells. Overall, Pronase E-generated peptide standards were a rapid and efficient method to identify proteolysis products from cells. PMID:26171808

  3. Self-assembly and adsorption properties of Fmoc-substituted short peptide bearing charged side chains

    NASA Astrophysics Data System (ADS)

    Nakayama, Toru; Sakuraba, Taro; Yamamoto, Yohei

    2015-12-01

    Charge-separated peptide β-sheet with a positive charge on one side and a negative charge on the other side adsorbed on a mica surface with well-ordered geometry along the crystallographic direction of the mica surface. In MeOH and MeOH/H2O mixed solvent, the peptides do not form β-sheet structure. During the evaporation process of the solvent on a mica substrate, the peptides self-assembled to form β-sheet and adsorb on the surface via electrostatic interaction between negative charge of the mica surface and positive charge of the lysine side chain on one side of the β-sheet.

  4. Selective Acylation Enhances Membrane Charge Sensitivity of the Antimicrobial Peptide Mastoparan-X

    PubMed Central

    Etzerodt, Thomas; Henriksen, Jonas R.; Rasmussen, Palle; Clausen, Mads H.; Andresen, Thomas L.

    2011-01-01

    The partitioning of the wasp venom peptide mastoparan-X (MPX) into neutral and negatively charged lipid membranes has been compared with two new synthetic analogs of MPX where the Nα-terminal of MPX was acylated with propanoic acid (PA) and octanoic acid (OA). The acylation caused a considerable change in the membrane partitioning properties of MPX and it was found that the shorter acylation with PA gave improved affinity and selectivity toward negatively charged membranes, whereas OA decreased the selectivity. Based on these findings, we hypothesize that minor differences in the embedding and positioning of the peptide in the membrane caused by either PA or OA acylation play a critical role in the fine-tuning of the effective charge of the peptide and thereby the fine-tuning of the peptide's selectivity between neutral and negatively charged lipid membranes. This finding is unique compared to previous reports where peptide acylation enhanced membrane affinity but also resulted in impaired selectivity. Our result may provide a method of enhancing selectivity of antimicrobial peptides toward bacterial membranes due to their high negative charge—a finding that should be investigated for other, more potent antimicrobial peptides in future studies. PMID:21244836

  5. Heat dissipation in relativistic single charged fluids

    NASA Astrophysics Data System (ADS)

    Garcia-Perciante, A. L.; Sandoval-Villalbazo, A.; Brun-Battistini, D.

    2015-11-01

    When the temperature of a fluid is increased its out of equilibrium behavior is significantly modified. In particular kinetic theory predicts that the heat flux is not solely driven by a temperature gradient but can also be coupled to other thermodynamic vector forces. We explore the nature of heat conduction in a single component charged fluid in special relativity, where the electromagnetic field is introduced as an external force. We obtain an electrothermal effect, similar to the mixture's cross-effect, which is not present in the non-relativistic simple fluid. The general lines of the corresponding calculation will be shown, emphasizing the importance of reference frame invariance and the origin of the extra heat sources, in particular the role of the modified inertia and the difference in fluid's and molecules' proper times. The constitutive equation for the heat flux obtained using Chapman-Enskog's expansion in Marle's approximation will be analyzed together with the corresponding transport coefficients.The impact of this effect in the overall dynamics of the system here considered will be briefly discussed. The authors acknowledge support from CONACyT through grant CB2011/167563.

  6. A Theoretical Justification for Single Molecule Peptide Sequencing

    PubMed Central

    Swaminathan, Jagannath; Boulgakov, Alexander A.; Marcotte, Edward M.

    2015-01-01

    The proteomes of cells, tissues, and organisms reflect active cellular processes and change continuously in response to intracellular and extracellular cues. Deep, quantitative profiling of the proteome, especially if combined with mRNA and metabolite measurements, should provide an unprecedented view of cell state, better revealing functions and interactions of cell components. Molecular diagnostics and biomarker discovery should benefit particularly from the accurate quantification of proteomes, since complex diseases like cancer change protein abundances and modifications. Currently, shotgun mass spectrometry is the primary technology for high-throughput protein identification and quantification; while powerful, it lacks high sensitivity and coverage. We draw parallels with next-generation DNA sequencing and propose a strategy, termed fluorosequencing, for sequencing peptides in a complex protein sample at the level of single molecules. In the proposed approach, millions of individual fluorescently labeled peptides are visualized in parallel, monitoring changing patterns of fluorescence intensity as N-terminal amino acids are sequentially removed, and using the resulting fluorescence signatures (fluorosequences) to uniquely identify individual peptides. We introduce a theoretical foundation for fluorosequencing and, by using Monte Carlo computer simulations, we explore its feasibility, anticipate the most likely experimental errors, quantify their potential impact, and discuss the broad potential utility offered by a high-throughput peptide sequencing technology. PMID:25714988

  7. Extended Coverage of Singly and Multiply Phosphorylated Peptides from a Single Titanium Dioxide Microcolumn.

    PubMed

    Wakabayashi, Masaki; Kyono, Yutaka; Sugiyama, Naoyuki; Ishihama, Yasushi

    2015-10-20

    We developed a novel approach to enlarge phosphoproteome coverage by selective elution depending on the number of phosphoryl group of peptides from a single titanium dioxide (TiO2) microcolumn using hydrophilic interaction chromatography (HILIC). In this approach, acidic methylphosphonate buffer including organic solvent is used for selective elution of singly phosphorylated peptides from an aliphatic hydroxy acid-modified metal oxide chromatography (HAMMOC) microcolumn and basic elution conditions with phosphate, ammonium hydroxide, and pyrrolidine are then employed for eluting multiply phosphorylated peptides retained by the HAMMOC microcolumn. Finally, we successfully identified 11 300 nonredundant phosphopeptides from triplicate analyses of 100 μg of HeLa cell lysates using this approach. This simple strategy made it possible to accomplish comprehensive and efficient phosphoproteome analysis from limited sample amounts loaded onto a single HAMMOC microcolumn without additional fractionation or enrichment approaches. PMID:26402220

  8. Multipole correction of atomic monopole models of molecular charge distribution. I. Peptides

    NASA Technical Reports Server (NTRS)

    Sokalski, W. A.; Keller, D. A.; Ornstein, R. L.; Rein, R.

    1993-01-01

    The defects in atomic monopole models of molecular charge distribution have been analyzed for several model-blocked peptides and compared with accurate quantum chemical values. The results indicate that the angular characteristics of the molecular electrostatic potential around functional groups capable of forming hydrogen bonds can be considerably distorted within various models relying upon isotropic atomic charges only. It is shown that these defects can be corrected by augmenting the atomic point charge models by cumulative atomic multipole moments (CAMMs). Alternatively, sets of off-center atomic point charges could be automatically derived from respective multipoles, providing approximately equivalent corrections. For the first time, correlated atomic multipoles have been calculated for N-acetyl, N'-methylamide-blocked derivatives of glycine, alanine, cysteine, threonine, leucine, lysine, and serine using the MP2 method. The role of the correlation effects in the peptide molecular charge distribution are discussed.

  9. Absorption and excretion of undegradable peptides: role of lipid solubility and net charge.

    PubMed

    Pappenheimer, J R; Karnovsky, M L; Maggio, J E

    1997-01-01

    Absorption and excretion of undegradable peptides were investigated with use of octapeptides synthesized from D-amino acids. D-Tyrosine was included in each peptide to permit labeling with 125I, D-glutamic acid or D-lysine were included to vary net electric charge and D-serine or D-leucine were included to vary lipid solubility. Peptides were administered parenterally or orally to normal rats drinking 5% glucose or maltose. Forty-five percent of a lipid-insoluble, negatively charged octapeptide added to the drinking fluid in milligram quantities was absorbed from the intestine and excreted intact in urine; 90% of this peptide was recovered in urine after parenteral injection. In contrast, lipophilic D-octapeptides were largely excreted in feces, even after subcutaneous injection; the amounts excreted in feces were correlated with oil/aqueous partition coefficients. Evidence is presented that lipophilic peptides entering liver cells combine with bile salts to form hydrophilic complexes that are secreted rapidly at high concentration in bile. At physiological concentrations of bile salts (5-40 mM) and nanomolar concentrations of peptide the binding is so complete that these undegradable peptides are rapidly cleared from liver to duodenal fluid in association with the bile salts. After reaching the ileum the bile salts are reabsorbed to blood, leaving the original lipophilic peptides to be excreted in the feces from which they can be extracted, purified and identified by high-pressure liquid chromatography. These mechanisms are discussed in relation to a) the paracellular absorption of peptides and other solutes by solvent drag and b) the delivery and fate of biologically active peptides. PMID:8996209

  10. Specificity and mechanism of action of alpha-helical membrane-active peptides interacting with model and biological membranes by single-molecule force spectroscopy

    PubMed Central

    Sun, Shiyu; Zhao, Guangxu; Huang, Yibing; Cai, Mingjun; Shan, Yuping; Wang, Hongda; Chen, Yuxin

    2016-01-01

    In this study, to systematically investigate the targeting specificity of membrane-active peptides on different types of cell membranes, we evaluated the effects of peptides on different large unilamellar vesicles mimicking prokaryotic, normal eukaryotic, and cancer cell membranes by single-molecule force spectroscopy and spectrum technology. We revealed that cationic membrane-active peptides can exclusively target negatively charged prokaryotic and cancer cell model membranes rather than normal eukaryotic cell model membranes. Using Acholeplasma laidlawii, 3T3-L1, and HeLa cells to represent prokaryotic cells, normal eukaryotic cells, and cancer cells in atomic force microscopy experiments, respectively, we further studied that the single-molecule targeting interaction between peptides and biological membranes. Antimicrobial and anticancer activities of peptides exhibited strong correlations with the interaction probability determined by single-molecule force spectroscopy, which illustrates strong correlations of peptide biological activities and peptide hydrophobicity and charge. Peptide specificity significantly depends on the lipid compositions of different cell membranes, which validates the de novo design of peptide therapeutics against bacteria and cancers. PMID:27363513

  11. Specificity and mechanism of action of alpha-helical membrane-active peptides interacting with model and biological membranes by single-molecule force spectroscopy.

    PubMed

    Sun, Shiyu; Zhao, Guangxu; Huang, Yibing; Cai, Mingjun; Shan, Yuping; Wang, Hongda; Chen, Yuxin

    2016-01-01

    In this study, to systematically investigate the targeting specificity of membrane-active peptides on different types of cell membranes, we evaluated the effects of peptides on different large unilamellar vesicles mimicking prokaryotic, normal eukaryotic, and cancer cell membranes by single-molecule force spectroscopy and spectrum technology. We revealed that cationic membrane-active peptides can exclusively target negatively charged prokaryotic and cancer cell model membranes rather than normal eukaryotic cell model membranes. Using Acholeplasma laidlawii, 3T3-L1, and HeLa cells to represent prokaryotic cells, normal eukaryotic cells, and cancer cells in atomic force microscopy experiments, respectively, we further studied that the single-molecule targeting interaction between peptides and biological membranes. Antimicrobial and anticancer activities of peptides exhibited strong correlations with the interaction probability determined by single-molecule force spectroscopy, which illustrates strong correlations of peptide biological activities and peptide hydrophobicity and charge. Peptide specificity significantly depends on the lipid compositions of different cell membranes, which validates the de novo design of peptide therapeutics against bacteria and cancers. PMID:27363513

  12. A Maple Program That Illustrates the Effect of pH on Peptide Charge

    NASA Astrophysics Data System (ADS)

    Sokolik, Charles W.

    1998-11-01

    One topic covered early in an introductory biochemistry course is acid-base chemistry and the Henderson-Hasselbalch equation (buffer equation). Using this equation a biochemistry student can determine the partial charges of amino acids in a peptide chain. This is an important concept to master for a student who is learning the structure-function relationship in proteins. The program described in this paper, written for Maple V, release 3 (Waterloo Maple Software, Waterloo, ON, Canada), uses the Henderson-Hasselbalch equation to calculate the partial charges of individual amino acids and the net charge of a peptide over the pH range 0 to 14. The amino acid sequence of a peptide is entered and an animated histogram is displayed illustrating the partial charge of the amino acids over the pH range. A graph showing the net charge of the peptide from pH 0 to 14 is also given. The program has been used with success in an introductory biochemistry course as an in-class demonstration as well as for individual homework assignments. The program is available through the Web page of the Journal of Chemical Education.

  13. Modulating Charge Transfer Through Cyclic D,L α-Peptide Self-Assembly

    PubMed Central

    Horne, W. Seth; Ashkenasy, Nurit; Ghadiri, M. Reza

    2007-01-01

    We describe a concise solid support-based synthetic method for the preparation of cyclic D,L α-peptides bearing 1,4,5,8-naphthalenetetracarboxylic diimide (NDI) side chains. Studies of the structural and photoluminescence properties of these molecules in solution show that the hydrogen bond directed self-assembly of the cyclic D,L α-peptide backbone promotes intermolecular NDI excimer formation. The efficiency of NDI charge transfer in the resulting supramolecular assemblies is shown to depend on the length of the linker between the NDI and the peptide backbone, the distal NDI substituent, and the number of NDIs incorporated in a given structure. The design rationale and synthetic strategies described here should provide a basic blueprint for a series of self-assembling cyclic D,L α-peptide nanotubes with interesting optical and electronic properties. PMID:15624124

  14. Molecular charge dominates the inhibition of actomyosin in skinned muscle fibers by SH1 peptides.

    PubMed Central

    Chase, P B; Beck, T W; Bursell, J; Kushmerick, M J

    1991-01-01

    It is not definitively known whether the highly conserved region of myosin heavy chain around SH1 (Cys 707) is part of the actin-binding site. We tested this possibility by assaying for competitive inhibition of maximum Ca-activated force production of skinned muscle fibers by synthetic peptides which had sequences derived from the SH1 region of myosin. Force was inhibited by a heptapeptide (IRICRKG) with an apparent K0.5 of about 4 mM. Unloaded shortening velocity of fibers, determined by the slack test, and maximum Ca-activated myofibrillar MgATPase activity were also inhibited by this peptide, but both required higher concentrations. We found that other cationic peptides also inhibited force in a manner that depended on the charge of the peptide; increasing the net positive charge of the peptide increased its efficacy. The inhibition was not significantly affected by altering solution ionic strength (100-200 mM). Disulfide bond formation was not involved in the inhibitory mechanism because a peptide with Thr substituted for Cys was inhibitory in the presence or absence of DTT. Our data demonstrate that the net charge was the predominant molecular characteristic correlated with the ability of peptides from this region of myosin heavy chain to inhibit force production. Thus, the hypothesis that the SH1 region of myosin is an essential part of the force-producing interaction with actin during the cross-bridge cycle (Eto, M., R. Suzuki, F. Morita, H. Kuwayama, N. Nishi, and S. Tokura., 1990, J. Biochem. 108:499-504; Keane et al., 1990, Nature (Lond.). 344:265-268) is not supported. PMID:1912278

  15. Promotion of alpha-cyano-4-hydroxycinnamic acid and peptide cocrystallization within levitated droplets with net charge.

    PubMed

    Bogan, Michael J; Bakhoum, Samuel F W; Agnes, George R

    2005-02-01

    Many reactions occur as a result of charge imbalance within or between reactive species in reaction vessels that have zero net charge. Here, chemical processes taking place within reaction vessels having net excess charge were studied. For mass spectroscopists, a familiar example of vessels that defy electroneutrality are the charged droplets produced by an electrospray ion source. Evidence is presented that control of the magnitude of the net charge contained in a reaction vessel, in this case a levitated droplet, can be used to promote nucleation and crystal growth of a mixture of an organic acid, alpha-cyano-4-hydroxycinnamic acid (CHCA), with one or more peptides. This phenomenon was first observed during our ongoing development of wall-less sample preparation (WaSP), electrodynamic charged droplet processing methodology capable of creating micrometer-sized sample spots for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) from subnanoliter volumes of sample material. Peptide ion signal-to-noise (S/N) ratios obtained by MALDI-TOF-MS from sample spots created from droplets that had high relative magnitude of net charge were consistently greater than those detected from sample spots created from droplets that had lower net charge. To study this unexpected phenomenon further, WaSP methodology was developed to process different mass-to-charge (m/z) droplets levitated in an electrodynamic balance (EDB), facilitating their deposition onto different positions of a target to create arrays of droplet residues ordered from highest to lowest m/z. This capability allowed simultaneous levitation with subsequent separation of a population of droplets created from a single starting solution, but the droplets had varied magnitudes of net charge. After the droplets were ejected from the EDB and collected on a glass slide or MALDI plate, the solids contained in the deposited droplets were characterized using microscopy and MALDI

  16. High-confidence de novo peptide sequencing using positive charge derivatization and tandem MS spectra merging.

    PubMed

    An, Mingrui; Zou, Xiao; Wang, Qingsong; Zhao, Xuyang; Wu, Jing; Xu, Li-Ming; Shen, Hong-Yan; Xiao, Xueyuan; He, Dacheng; Ji, Jianguo

    2013-05-01

    De novo peptide sequencing holds great promise in discovering new protein sequences and modifications but has often been hindered by low success rate of mass spectra interpretation, mainly due to the diversity of fragment ion types and insufficient information for each ion series. Here, we describe a novel methodology that combines highly efficient on-tip charge derivatization and tandem MS spectra merging, which greatly boosts the performance of interpretation. TMPP-Ac-OSu (succinimidyloxycarbonylmethyl tris(2,4,6-trimethoxyphenyl)phosphonium bromide) was used to derivatize peptides at N-termini on tips to reduce mass spectra complexity. Then, a novel approach of spectra merging was adopted to combine the benefits of collision-induced dissociation (CID) and electron transfer dissociation (ETD) fragmentation. We applied this methodology to rat C6 glioma cells and the Cyprinus carpio and searched the resulting peptide sequences against the protein database. Then, we achieved thousands of high-confidence peptide sequences, a level that conventional de novo sequencing methods could not reach. Next, we identified dozens of novel peptide sequences by homology searching of sequences that were fully backbone covered but unmatched during the database search. Furthermore, we randomly chose 34 sequences discovered in rat C6 cells and verified them. Finally, we conclude that this novel methodology that combines on-tip positive charge derivatization and tandem MS spectra merging will greatly facilitate the discovery of novel proteins and the proteome analysis of nonmodel organisms. PMID:23536960

  17. The influence of the localised charge of C- and N-termini on peptide self-assembly.

    PubMed

    Bortolini, C; Jones, N C; Hoffmann, S V; Besenbacher, F; Dong, M

    2016-01-14

    The charge of a peptide influences final assembled structures. It is important to consider not only global charge, but also local, such as that found on the terminal residues. This work investigates the change of peptide self-assembly through the selection of different amino acid sequences and by varying the local charge of the residues on the C- and N-termini. PMID:26472087

  18. Strong Electrostatic Interactions Lead to Entropically Favorable Binding of Peptides to Charged Surfaces.

    PubMed

    Sprenger, K G; Pfaendtner, Jim

    2016-06-01

    Thermodynamic analyses can provide key insights into the origins of protein self-assembly on surfaces, protein function, and protein stability. However, obtaining quantitative measurements of thermodynamic observables from unbiased classical simulations of peptide or protein adsorption is challenging because of sampling limitations brought on by strong biomolecule/surface binding forces as well as time scale limitations. We used the parallel tempering metadynamics in the well-tempered ensemble (PTMetaD-WTE) enhanced sampling method to study the adsorption behavior and thermodynamics of several explicitly solvated model peptide adsorption systems, providing new molecular-level insight into the biomolecule adsorption process. Specifically studied were peptides LKα14 and LKβ15 and trpcage miniprotein adsorbing onto a charged, hydrophilic self-assembled monolayer surface functionalized with a carboxylic acid/carboxylate headgroup and a neutral, hydrophobic methyl-terminated self-assembled monolayer surface. Binding free energies were calculated as a function of temperature for each system and decomposed into their respective energetic and entropic contributions. We investigated how specific interfacial features such as peptide/surface electrostatic interactions and surface-bound ion content affect the thermodynamic landscape of adsorption and lead to differences in surface-bound conformations of the peptides. Results show that upon adsorption to the charged surface, configurational entropy gains of the released solvent molecules dominate the configurational entropy losses of the bound peptide. This behavior leads to an apparent increase in overall system entropy upon binding and therefore to the surprising and seemingly nonphysical result of an apparent increased binding free energy at elevated temperatures. Opposite effects and conclusions are found for the neutral surface. Additional simulations demonstrate that by adjusting the ionic strength of the solution

  19. Peptide nanoparticle delivery of charge-neutral splice-switching morpholino oligonucleotides.

    PubMed

    Järver, Peter; Zaghloul, Eman M; Arzumanov, Andrey A; Saleh, Amer F; McClorey, Graham; Hammond, Suzan M; Hällbrink, Mattias; Langel, Ülo; Smith, C I Edvard; Wood, Matthew J A; Gait, Michael J; El Andaloussi, Samir

    2015-04-01

    Oligonucleotide analogs have provided novel therapeutics targeting various disorders. However, their poor cellular uptake remains a major obstacle for their clinical development. Negatively charged oligonucleotides, such as 2'-O-Methyl RNA and locked nucleic acids have in recent years been delivered successfully into cells through complex formation with cationic polymers, peptides, liposomes, or similar nanoparticle delivery systems. However, due to the lack of electrostatic interactions, this promising delivery method has been unsuccessful to date using charge-neutral oligonucleotide analogs. We show here that lipid-functionalized cell-penetrating peptides can be efficiently exploited for cellular transfection of the charge-neutral oligonucleotide analog phosphorodiamidate morpholino. The lipopeptides form complexes with splice-switching phosphorodiamidate morpholino oligonucleotide and can be delivered into clinically relevant cell lines that are otherwise difficult to transfect while retaining biological activity. To our knowledge, this is the first study to show delivery through complex formation of biologically active charge-neutral oligonucleotides by cationic peptides. PMID:25594433

  20. Single molecule detection using charge-coupled device array technology

    SciTech Connect

    Denton, M.B.

    1992-07-29

    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.

  1. Using metal complex-labeled peptides for charge transfer-based biosensing with semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Medintz, Igor L.; Pons, Thomas; Trammell, Scott A.; Blanco-Canosa, Juan B.; Dawson, Philip E.; Mattoussi, Hedi

    2009-02-01

    Luminescent colloidal semiconductor quantum dots (QDs) have unique optical and photonic properties and are highly sensitive to charge transfer in their surrounding environment. In this study we used synthetic peptides as physical bridges between CdSe-ZnS core-shell QDs and some of the most common redox-active metal complexes to understand the charge transfer interactions between the metal complexes and QDs. We found that QD emission underwent quenching that was highly dependent on the choice of metal complex used. We also found that quenching traces the valence or number of metal complexes brought into close proximity of the nanocrystal surface. Monitoring of the QD absorption bleaching in the presence of the metal complex provided insight into the charge transfer mechanism. The data suggest that two distinct charge transfer mechanisms can take place. One directly to the QD core states for neutral capping ligands and a second to surface states for negatively charged capping ligands. A basic understanding of the proximity driven charge-transfer and quenching interactions allowed us to construct proteolytic enzyme sensing assemblies with the QD-peptide-metal complex conjugates.

  2. Charge properties of peptides derived from casein affect their bioavailability and cytoprotection against H2O2-induced oxidative stress.

    PubMed

    Wang, Bo; Xie, Ningning; Li, Bo

    2016-04-01

    The effects of charge properties of casein peptides on absorption stability, antioxidant activity, and cytoprotection were evaluated. Alcalase hydrolysates of casein were separated into 4 fractions by cation-exchange chromatography according to charge properties. After simulated digestion and Caco-2 cell transmembrane transport, we determined the total antioxidant capacity (Trolox equivalent antioxidative capacity and oxygen radical antioxidant activity) and nitrogen content of peptide fractions to estimate available antioxidant efficacy and bioavailability (BA) of peptides. Results showed that negatively charged peptide fractions had greater BA and antioxidant activities after digestion and absorption. The peptide permeates were used to test the cytoprotective effect against H2O2-induced oxidative damage in HepG-2 cells. All peptide permeates increased cell viability, elevated catalase activity, and decreased superoxide dismutase activity. However, negatively charged peptide fractions preserved cell viability to a greater degree. Therefore, the negatively charged peptides from casein may be potential antioxidants and could be used as ingredients in functional foods and dietary supplements. PMID:26851854

  3. Charged two-exciton emission from a single semiconductor nanocrystal

    SciTech Connect

    Hu, Fengrui; Zhang, Qiang; Zhang, Chunfeng; Wang, Xiaoyong; Xiao, Min

    2015-03-30

    Here, we study the photoluminescence (PL) time trajectories of single CdSe/ZnS nanocrystals (NCs) as a function of the laser excitation power. At the low laser power, the PL intensity of a single NC switches between the “on” and “off” levels arising from the neutral and positively charged single excitons, respectively. With the increasing laser power, an intermediate “grey” level is formed due to the optical emission from a charged multiexciton state composed of two excitons and an extra electron. Both the inter-photon correlation and the PL decay measurements demonstrate that lifetime-indistinguishable photon pairs are emitted from this negatively charged two-exciton state.

  4. Photoinitated charge separation in a hybrid titanium dioxide metalloporphyrin peptide material

    NASA Astrophysics Data System (ADS)

    Fry, H. Christopher; Liu, Yuzi; Dimitrijevic, Nada M.; Rajh, Tijana

    2014-08-01

    In natural systems, electron flow is mediated by proteins that spatially organize donor and acceptor molecules with great precision. Achieving this guided, directional flow of information is a desirable feature in photovoltaic media. Here, we design self-assembled peptide materials that organize multiple electronic components capable of performing photoinduced charge separation. Two peptides, c16-AHL3K3-CO2H and c16-AHL3K9-CO2H, self-assemble into fibres and provide a scaffold capable of binding a metalloporphyrin via histidine axial ligation and mineralize titanium dioxide (TiO2) on the lysine-rich surface of the resulting fibrous structures. Electron paramagnetic resonance studies of this self-assembled material under continuous light excitation demonstrate charge separation induced by excitation of the metalloporphyrin and mediated by the peptide assembly structure. This approach to dye-sensitized semiconducting materials offers a means to spatially control the dye molecule with respect to the semiconducting material through careful, strategic peptide design.

  5. Photoinitiated [corrected] charge separation in a hybrid titanium dioxide metalloporphyrin peptide material.

    PubMed

    Fry, H Christopher; Liu, Yuzi; Dimitrijevic, Nada M; Rajh, Tijana

    2014-01-01

    In natural systems, electron flow is mediated by proteins that spatially organize donor and acceptor molecules with great precision. Achieving this guided, directional flow of information is a desirable feature in photovoltaic media. Here, we design self-assembled peptide materials that organize multiple electronic components capable of performing photoinduced charge separation. Two peptides, c16-AHL3K3-CO2H and c16-AHL3K9-CO2H, self-assemble into fibres and provide a scaffold capable of binding a metalloporphyrin via histidine axial ligation and mineralize titanium dioxide (TiO2) on the lysine-rich surface of the resulting fibrous structures. Electron paramagnetic resonance studies of this self-assembled material under continuous light excitation demonstrate charge separation induced by excitation of the metalloporphyrin and mediated by the peptide assembly structure. This approach to dye-sensitized semiconducting materials offers a means to spatially control the dye molecule with respect to the semiconducting material through careful, strategic peptide design. PMID:25132637

  6. Charge State Coalescence During Electrospray Ionization Improves Peptide Identification by Tandem Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Meyer, Jesse G.; A. Komives, Elizabeth

    2012-08-01

    We report the effects of supercharging reagents dimethyl sulphoxide (DMSO) and m-nitrobenzyl alcohol ( m-NBA) applied to untargeted peptide identification, with special emphasis on non-tryptic peptides. Peptides generated from a mixture of five standard proteins digested with trypsin, elastase, or pepsin were separated with nanoflow liquid chromatography using mobile phases modified with either 5 % DMSO or 0.1 % m-NBA. Eluting peptides were ionized by online electrospray and sequenced by both CID and ETD using data-dependent MS/MS. Statistically significant improvements in peptide identifications were observed with DMSO co-solvent. In order to understand this observation, we assessed the effects of supercharging reagents on the chromatographic separation and the electrospray quality. The increase in identifications was not due to supercharging, which was greater for the 0.1 % m-NBA co-solvent and not observed for the 5.0 % DMSO co-solvent. The improved MS/MS efficiency using the DMSO modified mobile phase appeared to result from charge state coalescence.

  7. Charge State Coalescence During Electrospray Ionization Improves Peptide Identification by Tandem Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Meyer, Jesse G.; Komives, Elizabeth A.

    2012-05-01

    We report the effects of supercharging reagents dimethyl sulphoxide (DMSO) and m-nitrobenzyl alcohol (m-NBA) applied to untargeted peptide identification, with special emphasis on non-tryptic peptides. Peptides generated from a mixture of five standard proteins digested with trypsin, elastase, or pepsin were separated with nanoflow liquid chromatography using mobile phases modified with either 5 % DMSO or 0.1 % m-NBA. Eluting peptides were ionized by online electrospray and sequenced by both CID and ETD using data-dependent MS/MS. Statistically significant improvements in peptide identifications were observed with DMSO co-solvent. In order to understand this observation, we assessed the effects of supercharging reagents on the chromatographic separation and the electrospray quality. The increase in identifications was not due to supercharging, which was greater for the 0.1 % m-NBA co-solvent and not observed for the 5.0 % DMSO co-solvent. The improved MS/MS efficiency using the DMSO modified mobile phase appeared to result from charge state coalescence.

  8. Probing the Nature of Charge Transfer at Nano-Bio Interfaces: Peptides on Metal Oxide Nanoparticles.

    PubMed

    Tarakeshwar, Pilarisetty; Palma, Julio L; Holland, Gregory P; Fromme, Petra; Yarger, Jeffery L; Mujica, Vladimiro

    2014-10-16

    Characterizing the nano-bio interface has been a long-standing endeavor in the quest for novel biosensors, biophotovoltaics, and biocompatible electronic devices. In this context, the present computational work on the interaction of two peptides, A6K (Ac-AAAAAAK-NH2) and A7 (Ac-AAAAAAA-NH2) with semiconducting TiO2 nanoparticles is an effort to understand the peptide-metal oxide nanointerface. These investigations were spurred by recent experimental observations that nanostructured semiconducting metal oxides templated with A6K peptides not only stabilize large proteins like photosystem-I (PS-I) but also exhibit enhanced charge-transfer characteristics. Our results indicate that α-helical structures of A6K are not only energetically more stabilized on TiO2 nanoparticles, but the resulting hybrids also exhibit enhanced electron transfer characteristics. This enhancement can be attributed to substantial changes in the electronic characteristics at the peptide-TiO2 interface. Apart from understanding the mechanism of electron transfer (ET) in peptide-stabilized PS-I on metal oxide nanoparticles, the current work also has implications in the development of novel solar cells and photocatalysts. PMID:26278609

  9. First Observation of Charge Reduction and Desorption Kinetics of Multiply Protonated Peptides Soft Landed onto Self-Assembled Monolayer Surfaces

    SciTech Connect

    Hadjar, Omar; Futrell, Jean H.; Laskin, Julia

    2007-12-13

    The kinetics of charge reduction and desorption of different species produced by soft-landing of mass-selected ions was studied using in situ secondary ion mass spectrometry (SIMS) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). The improved SIMS capability described in this work utilizes an in-line 8 keV Cs+ ion gun and allows us to interrogate the surface both during the ion deposition and after the deposition is terminated. As a model system doubly protonated ions of Gramicidin S were deposited onto a fluorinated self-assembled monolayer (FSAM) surface. Our results demonstrate for the first time that various peptide-related peaks in FT-ICR SIMS spectra follow very different kinetics. We obtained unique kinetics signatures for doubly protonated, singly protonated and neutral peptides retained on the surface and followed their evolution as a function of time. The experimental results are in excellent agreement with a kinetic model that takes into account charge reduction and thermal desorption of different species from the surface.

  10. Optical tracing of multiple charges in single-electron devices

    NASA Astrophysics Data System (ADS)

    Faez, Sanli; van der Molen, Sense Jan; Orrit, Michel

    2014-11-01

    Single molecules that exhibit narrow optical transitions at cryogenic temperatures can be used as local electric-field sensors. We derive the single-charge sensitivity of aromatic organic dye molecules, based on quantum mechanical considerations. Through numerical modeling, we demonstrate that by using currently available technologies it is possible to optically detect charging events in a granular network with a sensitivity better than 10-5e /√{Hz } and track positions of multiple electrons, simultaneously, with nanometer spatial resolution. Our results pave the way for minimally invasive optical inspection of electronic and spintronic nanodevices and building hybrid optoelectronic interfaces that function at both single-photon and single-electron levels.

  11. Measurement of Charged Current Charged Single Pion Production in SciBooNE

    SciTech Connect

    Hiraide, K.

    2008-10-01

    The SciBooNE experiment is designed to measure neutrino cross sections on carbon around one GeV region. Charged current single charged pion production is a dominant background process for {nu}{sub {mu}} to {nu}{sub x} oscillation experiments with a few-GeV neutrino beam, and thus a precision measurement of the cross section is essential. This article reports preliminary results on this process from SciBooNE.

  12. Ionization detector, electrode configuration and single polarity charge detection method

    DOEpatents

    He, Z.

    1998-07-07

    An ionization detector, an electrode configuration and a single polarity charge detection method each utilize a boundary electrode which symmetrically surrounds first and second central interlaced and symmetrical electrodes. All of the electrodes are held at a voltage potential of a first polarity type. The first central electrode is held at a higher potential than the second central or boundary electrodes. By forming the first and second central electrodes in a substantially interlaced and symmetrical pattern and forming the boundary electrode symmetrically about the first and second central electrodes, signals generated by charge carriers are substantially of equal strength with respect to both of the central electrodes. The only significant difference in measured signal strength occurs when the charge carriers move to within close proximity of the first central electrode and are received at the first central electrode. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge. 10 figs.

  13. Ionization detector, electrode configuration and single polarity charge detection method

    DOEpatents

    He, Zhong

    1998-01-01

    An ionization detector, an electrode configuration and a single polarity charge detection method each utilize a boundary electrode which symmetrically surrounds first and second central interlaced and symmetrical electrodes. All of the electrodes are held at a voltage potential of a first polarity type. The first central electrode is held at a higher potential than the second central or boundary electrodes. By forming the first and second central electrodes in a substantially interlaced and symmetrical pattern and forming the boundary electrode symmetrically about the first and second central electrodes, signals generated by charge carriers are substantially of equal strength with respect to both of the central electrodes. The only significant difference in measured signal strength occurs when the charge carriers move to within close proximity of the first central electrode and are received at the first central electrode. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge.

  14. Charge-induced strains in single-walled carbon nanotubes.

    PubMed

    Li, Chun-Yu; Chou, Tsu-Wei

    2006-09-28

    This paper investigates the electromechanical coupling in single-walled carbon nanotubes. In the model system, the extra electric charge of the nanotube is assumed to be uniformly distributed on carbon atoms. The electrostatic interactions between charged carbon atoms are calculated using the Coulomb law. The deformation of the charged nanotube is obtained by using the molecular structural mechanics method and considering the electrostatic interactions as an external loading acting on carbon atoms. The axial strain is found to be a symmetric function of applied charge, and our predictions are in very good agreement with those from ab initio calculations. The present results indicate that the nanotube aspect ratio has a strong effect on the axial strain when the ratio is less than 10 and the general trend is that the strain increases with the aspect ratio. The peak axial and radial strains occur at nanotube diameters of around 1.2-1.5 nm. PMID:21727586

  15. Multifunctional Charge-Transfer Single Crystals through Supramolecular Assembly.

    PubMed

    Xu, Beibei; Luo, Zhipu; Wilson, Andrew J; Chen, Ke; Gao, Wenxiu; Yuan, Guoliang; Chopra, Harsh Deep; Chen, Xing; Willets, Katherine A; Dauter, Zbigniew; Ren, Shenqiang

    2016-07-01

    Centimeter-sized segregated stacking TTF-C60 single crystals are crystallized by a mass-transport approach combined with solvent-vapor evaporation for the first time. The intermolecular charge-transfer interaction in the long-range ordered superstructure enables the crystals to demonstrate external stimuli-controlled multifunctionalities and angle/electrical-potential-dependent luminescence. PMID:27146726

  16. Profiling Signaling Peptides in Single Mammalian Cells Using Mass Spectrometry

    PubMed Central

    Rubakhin, Stanislav S.; Churchill, James D.; Greenough, William T.; Sweedler, Jonathan V.

    2008-01-01

    The peptide content of individual mammalian cells is profiled using matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. Both enzymatic and non-enzymatic procedures, including a glycerol cell stabilization method, are reported for the isolation of individual mammalian cells in a manner compatible with MALDI MS measurements. Guided microdeposition of MALDI matrix allows samples to be created with suitable analyte-to-matrix ratios. More than fifteen peptides are observed in individual rat intermediate pituitary cells. The combination of accurate mass data, expected cleavages by proteolytic enzymes, and post-source decay sequencing allows identification of fourteen of these peptides as pro-opiomelanocortin prohormone-derived molecules. These protocols permit the classification of individual mammalian cells by peptide profile, the elucidation of cell-specific prohormone processing, and the discovery of new signaling peptides on a cell-to-cell basis in a wide variety of mammalian cell types. PMID:17037931

  17. Surface charge modulated aptasensor in a single glass conical nanopore.

    PubMed

    Cai, Sheng-Lin; Cao, Shuo-Hui; Zheng, Yu-Bin; Zhao, Shuang; Yang, Jin-Lei; Li, Yao-Qun

    2015-09-15

    In this work, we have proposed a label-free nanopore-based biosensing strategy for protein detection by performing the DNA-protein interaction inside a single glass conical nanopore. A lysozyme binding aptamer (LBA) was used to functionalize the walls of glass nanopore via siloxane chemistry and negatively charged recognition sites were thus generated. The covalent modification procedures and their recognition towards lysozyme of the single conical nanopore were characterized via ionic current passing through the nanopore membrane, which was measured by recording the current-voltage (I-V) curves in 1mM KCl electrolyte at pH=7.4. With the occurring of recognition event, the negatively charged wall was partially neutralized by the positively charged lysozyme molecules, leading to a sensitive change of the surface charge-dependent current-voltage (I-V) characteristics. Our results not only demonstrate excellent selectivity and sensitivity towards the target protein, but also suggest a route to extend this nanopore-based sensing strategy to the biosensing platform designs of a wide range of proteins based on a charge modulation. PMID:25884732

  18. Acidity-Mediated, Electrostatic Tuning of Asymmetrically Charged Peptides Interactions with Protein Nanopores.

    PubMed

    Asandei, Alina; Chinappi, Mauro; Kang, Hee-Kyoung; Seo, Chang Ho; Mereuta, Loredana; Park, Yoonkyung; Luchian, Tudor

    2015-08-01

    Despite success in probing chemical reactions and dynamics of macromolecules on submillisecond time and nanometer length scales, a major impasse faced by nanopore technology is the need to cheaply and controllably modulate macromolecule capture and trafficking across the nanopore. We demonstrate herein that tunable charge separation engineered at the both ends of a macromolecule very efficiently modulates the dynamics of macromolecules capture and traffic through a nanometer-size pore. In the proof-of-principle approach, we employed a 36 amino acids long peptide containing at the N- and C-termini uniform patches of glutamic acids and arginines, flanking a central segment of asparagines, and we studied its capture by the α-hemolysin (α-HL) and the mean residence time inside the pore in the presence of a pH gradient across the protein. We propose a solution to effectively control the dynamics of peptide interaction with the nanopore, with both association and dissociation reaction rates of peptide-α-HL interactions spanning orders of magnitude depending upon solution acidity on the peptide addition side and the transmembrane electric potential, while preserving the amplitude of the blockade current signature. PMID:26144534

  19. Single-Molecule Motions of MHC Class II Rely on Bound Peptides

    PubMed Central

    Kozono, Haruo; Matsushita, Yufuku; Ogawa, Naoki; Kozono, Yuko; Miyabe, Toshihiro; Sekiguchi, Hiroshi; Ichiyanagi, Kouhei; Okimoto, Noriaki; Taiji, Makoto; Kanagawa, Osami; Sasaki, Yuji C.

    2015-01-01

    The major histocompatibility complex (MHC) class II protein can bind peptides of different lengths in the region outside the peptide-binding groove. Peptide-flanking residues (PFRs) contribute to the binding affinity of the peptide for MHC and change the immunogenicity of the peptide/MHC complex with regard to T cell receptor (TCR). The mechanisms underlying these phenomena are currently unknown. The molecular flexibility of the peptide/MHC complex may be an important determinant of the structures recognized by certain T cells. We used single-molecule x-ray analysis (diffracted x-ray tracking (DXT)) and fluorescence anisotropy to investigate these mechanisms. DXT enabled us to monitor the real-time Brownian motion of the peptide/MHC complex and revealed that peptides without PFRs undergo larger rotational motions than peptides with PFRs. Fluorescence anisotropy further revealed that peptides without PFRs exhibit slightly larger motions on the nanosecond timescale. These results demonstrate that peptides without PFRs undergo dynamic motions in the groove of MHC and consequently are able to assume diverse structures that can be recognized by T cells. PMID:25606683

  20. Optimization of Single-Sided Charge-Sharing Strip Detectors

    NASA Technical Reports Server (NTRS)

    Hamel, L.A.; Benoit, M.; Donmez, B.; Macri, J. R.; McConnell, M. L.; Ryan, J. M.; Narita, T.

    2006-01-01

    Simulation of the charge sharing properties of single-sided CZT strip detectors with small anode pads are presented. The effect of initial event size, carrier repulsion, diffusion, drift, trapping and detrapping are considered. These simulations indicate that such a detector with a 150 m pitch will provide good charge sharing between neighboring pads. This is supported by a comparison of simulations and measurements for a similar detector with a coarser pitch of 225 m that could not provide sufficient sharing. The performance of such a detector used as a gamma-ray imager is discussed.

  1. Device simulation of charge collection and single-event upset

    SciTech Connect

    Dodd, P.E.

    1996-04-01

    In this paper the author reviews the current status of device simulation of ionizing-radiation-induced charge collection and single-event upset (SEU), with an emphasis on significant results of recent years. The author presents an overview of device-modeling techniques applicable to the SEU problem and the unique challenges this task presents to the device modeler. He examines unloaded simulations of radiation-induced charge collection in simple p/n diodes, SEU in dynamic random access memories (DRAM`s), and SEU in static random access memories (SRAM`s). The author concludes with a few thoughts on future issues likely to confront the SEU device modeler.

  2. Localization of the O-glycosylated sites in peptides by fixed-charge derivatization with a phosphonium group.

    PubMed

    Czeszak, Xavier; Morelle, Willy; Ricart, Guy; Tétaert, Daniel; Lemoine, Jérôme

    2004-08-01

    The present study demonstrates that matrix-assisted laser desorption ionization/postsource decay (MALDI/PSD) analysis of the molecular cation of glycopeptides derivatized at their amino terminus with a phosphonium group cleaves peptide backbone without removing the glycan. The predictable a-type fragment ions retain the glycan moiety, enabling unambiguous localization of O-glycans on the peptide chain. In contrast, collision-activated dissociation tandem mass spectrometry analysis carried out on the doubly charged protonated phosphonium cation results in the predominant loss of the sugar moiety from the peptide. This result supports the previously proposed charge-induced fragmentation mechanism of the sugar-peptide bond. MALDI/PSD analysis of glycopeptides converted to their acetyl phosphonium derivatives is an effective alternative to electron capture dissociation, as illustrated by the positioning of up to three GalNac residues along the full tandem repeat peptide sequence derived from the MUC 5AC mucin. PMID:15283567

  3. The fruitfly Drosophila melanogaster contains a novel charged adipokinetic-hormone-family peptide.

    PubMed Central

    Schaffer, M H; Noyes, B E; Slaughter, C A; Thorne, G C; Gaskell, S J

    1990-01-01

    A member of the RPCH/AKH (red-pigment-concentrating hormone/adipokinetic hormone) family of arthropod neuropeptides was identified in the fruitfly Drosophila melanogaster, and its structure was determined by automated Edman degradation and m.s. using fast-atom-bombardment ionization and a tandem hybrid instrument capable of high sensitivity. The sequence of this peptide, which we call 'DAKH', is pGlu-Leu-Thr-Phe-Ser-Pro-Asp-Trp-NH2 (where pGlu is pyroglutamic acid and Trp-NH2 is tryptophan carboxyamide). H.p.l.c. analyses of extracts of the three body segments revealed that more than 80% of the peptide is contained in the thorax. Although DAKH is typical of family members in its general structure and distribution in the animal, it is unique in containing a residue which is charged under physiological conditions. The evolutionary significance of this change is considered. PMID:2117437

  4. Charge, Color, and Conformation: Spectroscopy on Isomer-Selected Peptide Ions

    PubMed Central

    2016-01-01

    Monitoring the chromism induced by intramolecular hydrogen and charge transfers within proteins as well as the isomerization of both protein and cofactor is essential not only to understand photoactive signaling pathways but also to design targeted opto-switchable proteins. We used a dual-ion mobility drift tube coupled to a tunable picosecond laser to explore the optical and structural properties of a peptide chain bound to a chromophore—a prototype system allowing for a proton transfer coupled to conformational change. With the support of molecular dynamics and DFT calculations, we show how proton transfer between the peptide and its cofactor can dramatically modify the optical properties of the system and demonstrate that these changes can be triggered by collisional activation in the gas phase. PMID:26756462

  5. Increasing peptide identifications and decreasing search times for ETD spectra by pre-processing and calculation of parent precursor charge

    PubMed Central

    2012-01-01

    Background Electron Transfer Dissociation [ETD] can dissociate multiply charged precursor polypeptides, providing extensive peptide backbone cleavage. ETD spectra contain charge reduced precursor peaks, usually of high intensity, and whose pattern is dependent on its parent precursor charge. These charge reduced precursor peaks and associated neutral loss peaks should be removed before these spectra are searched for peptide identifications. ETD spectra can also contain ion-types other than c and z˙. Modifying search strategies to accommodate these ion-types may aid in increased peptide identifications. Additionally, if the precursor mass is measured using a lower resolution instrument such as a linear ion trap, the charge of the precursor is often not known, reducing sensitivity and increasing search times. We implemented algorithms to remove these precursor peaks, accommodate new ion-types in noise filtering routine in OMSSA and to estimate any unknown precursor charge, using Linear Discriminant Analysis [LDA]. Results Spectral pre-processing to remove precursor peaks and their associated neutral losses prior to protein sequence library searches resulted in a 9.8% increase in peptide identifications at a 1% False Discovery Rate [FDR] compared to previous OMSSA filter. Modifications to the OMSSA noise filter to accommodate various ion-types resulted in a further 4.2% increase in peptide identifications at 1% FDR. Moreover, ETD spectra when searched with charge states obtained from the precursor charge determination algorithm is shown to be up to 3.5 times faster than the general range search method, with a minor 3.8% increase in sensitivity. Conclusion Overall, there is an 18.8% increase in peptide identifications at 1% FDR by incorporating the new precursor filter, noise filter and by using the charge determination algorithm, when compared to previous versions of OMSSA. PMID:22321509

  6. Single-charge detection by an atomic precision tunnel junction

    SciTech Connect

    House, M. G. Peretz, E.; Keizer, J. G.; Hile, S. J.; Simmons, M. Y.

    2014-03-17

    We demonstrate sensitive detection of single charges using a planar tunnel junction 8.5 nm wide and 17.2 nm long defined by an atomically precise phosphorus doping profile in silicon. The conductance of the junction responds to a nearby gate potential and also to changes in the charge state of a quantum dot patterned 52 nm away. The response of this detector is monotonic across the entire working voltage range of the device, which will make it particularly useful for studying systems of multiple quantum dots. The charge sensitivity is maximized when the junction is most conductive, suggesting that more sensitive detection can be achieved by shortening the length of the junction to increase its conductance.

  7. Single-charge detection by an atomic precision tunnel junction

    NASA Astrophysics Data System (ADS)

    House, M. G.; Peretz, E.; Keizer, J. G.; Hile, S. J.; Simmons, M. Y.

    2014-03-01

    We demonstrate sensitive detection of single charges using a planar tunnel junction 8.5 nm wide and 17.2 nm long defined by an atomically precise phosphorus doping profile in silicon. The conductance of the junction responds to a nearby gate potential and also to changes in the charge state of a quantum dot patterned 52 nm away. The response of this detector is monotonic across the entire working voltage range of the device, which will make it particularly useful for studying systems of multiple quantum dots. The charge sensitivity is maximized when the junction is most conductive, suggesting that more sensitive detection can be achieved by shortening the length of the junction to increase its conductance.

  8. Correlating single-molecule and ensemble-average measurements of peptide adsorption onto different inorganic materials.

    PubMed

    Kim, Seong-Oh; Jackman, Joshua A; Mochizuki, Masahito; Yoon, Bo Kyeong; Hayashi, Tomohiro; Cho, Nam-Joon

    2016-06-01

    The coating of solid-binding peptides (SBPs) on inorganic material surfaces holds significant potential for improved surface functionalization at nano-bio interfaces. In most related studies, the goal has been to engineer peptides with selective and high binding affinity for a target material. The role of the material substrate itself in modulating the adsorption behavior of a peptide molecule remains less explored and there are few studies that compare the interaction of one peptide with different inorganic substrates. Herein, using a combination of two experimental techniques, we investigated the adsorption of a 16 amino acid-long random coil peptide to various inorganic substrates - gold, silicon oxide, titanium oxide and aluminum oxide. Quartz crystal microbalance-dissipation (QCM-D) experiments were performed in order to measure the peptide binding affinity for inorganic solid supports at the ensemble average level, and atomic force microscopy (AFM) experiments were conducted in order to determine the adhesion force of a single peptide molecule. A positive trend was observed between the total mass uptake of attached peptide and the single-molecule adhesion force on each substrate. Peptide affinity for gold was appreciably greater than for the oxide substrates. Collectively, the results obtained in this study offer insight into the ways in which inorganic materials can differentially influence and modulate the adhesion of SBPs. PMID:27174015

  9. Charge Transport in Azobenzene-Based Single-Molecule Junctions

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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.

  10. Charge Blinking Statistics of Semiconductor Nanocrystals Revealed by Carbon Nanotube Single Charge Sensors.

    PubMed

    Zbydniewska, Ewa; Duzynska, Anna; Popoff, Michka; Hourlier, Djamila; Lenfant, Stéphane; Judek, Jaroslaw; Zdrojek, Mariusz; Mélin, Thierry

    2015-10-14

    We demonstrate the relation between the optical blinking of colloidal semiconductor nanocrystals (NCs) and their electrical charge blinking for which we provide the first experimental observation of power-law statistics. To show this, we harness the performance of CdSe/ZnS NCs coupled with carbon nanotube field-effect transistors (CNTFETs), which act as single charge-sensitive electrometers with submillisecond time resolution, at room temperature. A random telegraph signal (RTS) associated with the NC single-trap charging is observed and exhibits power-law temporal statistics (τ(-α), with α in the range of ∼1-3), and a Lorentzian current noise power spectrum with a well-defined 1/f(2) corner. The spectroscopic analysis of the NC-CNTFET devices is consistent with the charging of NC defect states with a charging energy of Ec ≥ 200 meV. These results pave the way for a deeper understanding of the physics and technology of nanocrystal-based optoelectronic devices. PMID:26418364

  11. Charged-particle spectroscopy in organic semiconducting single crystals

    NASA Astrophysics Data System (ADS)

    Ciavatti, A.; Sellin, P. J.; Basiricò, L.; Fraleoni-Morgera, A.; Fraboni, B.

    2016-04-01

    The use of organic materials as radiation detectors has grown, due to the easy processability in liquid phase at room temperature and the possibility to cover large areas by means of low cost deposition techniques. Direct charged-particle detectors based on solution-grown Organic Semiconducting Single Crystals (OSSCs) are shown to be capable to detect charged particles in pulse mode, with very good peak discrimination. The direct charged-particle detection in OSSCs has been assessed both in the planar and in the vertical axes, and a digital pulse processing algorithm has been used to perform pulse height spectroscopy and to study the charge collection efficiency as a function of the applied bias voltage. Taking advantage of the charge spectroscopy and the good peak discrimination of pulse height spectra, an Hecht-like behavior of OSSCs radiation detectors is demonstrated. It has been possible to estimate the mobility-lifetime value in organic materials, a fundamental parameter for the characterization of radiation detectors, whose results are equal to μτcoplanar = (5 .5 ± 0.6 ) × 10-6 cm2/V and μτsandwich = (1 .9 ± 0.2 ) × 10-6 cm2/V, values comparable to those of polycrystalline inorganic detectors. Moreover, alpha particles Time-of-Flight experiments have been carried out to estimate the drift mobility value. The results reported here indicate how charged-particle detectors based on OSSCs possess a great potential as low-cost, large area, solid-state direct detectors operating at room temperature. More interestingly, the good detection efficiency and peak discrimination observed for charged-particle detection in organic materials (hydrogen-rich molecules) are encouraging for their further exploitation in the detection of thermal and high-energy neutrons.

  12. Measuring Critical Charges For Single-Event Upsets

    NASA Technical Reports Server (NTRS)

    Buehler, Martin G.; Blaes, Brent R.

    1988-01-01

    Concept for determining susceptibility of integrated circuits to single-event upsets (SEU's) based on direct measurement of critical charge causing upset. Test circuit is modified version of standard complementary metal-oxide/semiconductor static cell. Contains six transistors, connected to form latch that retains state of cell set by input pulses. Makes possible to evaluate vulnerability to SEU during design and development of digital equipment.

  13. Single-step Fabrication of Patterned Gold Film Array by an Engineered Multi-functional Peptide

    PubMed Central

    Hnilova, Marketa; Khatayevich, Dmitriy; Carlson, Alisa; Oren, Ersin Emre; Gresswell, Carolyn; Zheng, Sam; Ohuchi, Fumio; Sarikaya, Mehmet; Tamerler, Candan

    2013-01-01

    This study constitutes a demonstration of the biological route to controlled nano-fabrication via modular multi-functional inorganic-binding peptides. Specifically, we use gold- and silica-binding peptide sequences, fused into a single molecule via a structural peptide spacer, to assemble pre-synthesized gold nanoparticles on silica surface, as well as to synthesize nanometallic particles in situ on the peptide-patterned regions. The resulting film-like gold nanoparticle arrays with controlled spatial organization are characterized by various microscopy and spectroscopy techniques. The described bio-enabled, single-step synthetic process offers many advantages over conventional approaches for surface modifications, self-assembly and device fabrication due to the peptides’ modularity, inherent biocompatibility, material specificity and catalytic activity in aqueous environments. Our results showcase the potential of artificially-derived peptides to play a key role in simplifying the assembly and synthesis of multi-material nano-systems in environmentally benign processes. PMID:21962430

  14. ``Hot spots'' growth on single nanowire controlled by electric charge

    NASA Astrophysics Data System (ADS)

    Xi, Shaobo; Liu, Xuehua; He, Ting; Tian, Lei; Wang, Wenhui; Sun, Rui; He, Weina; Zhang, Xuetong; Zhang, Jinping; Ni, Weihai; Zhou, Xiaochun

    2016-06-01

    ``Hot spots'' - a kind of highly active site, which are usually composed of some unique units, such as defects, interfaces, catalyst particles or special structures - can determine the performance of nanomaterials. In this paper, we study a model system, i.e. ``hot spots'' on a single Ag nanowire in the galvanic replacement reaction (GRR), by dark-field microscopy. The research reveals that electric charge can be released by the formation reaction of AgCl, and consequently the electrochemical potential on Ag nanowire drops. The electric charge could induce the reduction of Ag+ to form the ``hot spots'' on the nanowire during the GRR. The appearance probability of ``hot spots'' is almost even along the Ag nanowire, while it is slightly lower near the two ends. The spatial distance between adjacent ``hot spots'' is also controlled by the charge, and obeys a model based on Boltzmann distribution. In addition, the distance distribution here has an advantage in electron transfer and energy saving. Therefore, it's necessary to consider the functions of electric charge during the synthesis or application of nanomaterials.``Hot spots'' - a kind of highly active site, which are usually composed of some unique units, such as defects, interfaces, catalyst particles or special structures - can determine the performance of nanomaterials. In this paper, we study a model system, i.e. ``hot spots'' on a single Ag nanowire in the galvanic replacement reaction (GRR), by dark-field microscopy. The research reveals that electric charge can be released by the formation reaction of AgCl, and consequently the electrochemical potential on Ag nanowire drops. The electric charge could induce the reduction of Ag+ to form the ``hot spots'' on the nanowire during the GRR. The appearance probability of ``hot spots'' is almost even along the Ag nanowire, while it is slightly lower near the two ends. The spatial distance between adjacent ``hot spots'' is also controlled by the charge, and obeys a

  15. Effects of pH and charge state on peptide assembly: the YVIFL model system.

    PubMed

    Do, Thanh D; LaPointe, Nichole E; Economou, Nicholas J; Buratto, Steven K; Feinstein, Stuart C; Shea, Joan-Emma; Bowers, Michael T

    2013-09-19

    Peptide oligomerization is necessary but not sufficient for amyloid fibril formation. Here, we use a combination of experiments and simulations to understand how pH influences the aggregation properties of a small hydrophobic peptide, YVIFL, which is a mutant form of [Leu-5]-Enkephalin. Transmission electron microscopy and atomic force microscopy measurements reveal that this peptide forms small aggregates under acidic conditions (pH = 2), but that extensive fibrillization only occurs under basic conditions (pH = 9 and 11). Ion-mobility mass spectrometry identifies key oligomers in the oligomerization process, which are further characterized at an atomistic level by molecular dynamics simulations. These simulations suggest that terminal charges play a critical role in determining aggregation propensity and aggregate morphology. They also reveal the presence of steric zipper oligomers under basic conditions, a possible precursor to fibril formation. Our experiments suggest that multiple aggregation pathways can lead to YVIFL fibrils, and that cooperative and multibody interactions are key mechanistic elements in the early stages of aggregation. PMID:23937333

  16. Influence of the Charge State on the Structures and Interactions of Vancomycin Antibiotics with Cell-Wall Analogue Peptides: Experimental and Theoretical Studies

    SciTech Connect

    Yang, Zhibo; Vorpagel, Erich R.; Laskin, Julia

    2009-02-16

    In this study we examined the effect of the charge state on the energetics and dynamics of dissociation of the non-covalent complex between the vancomycin and the cell wall peptide analogue Nα,Nε-diacetyl-L-Lys-D-Ala-D-Ala (V-Ac2KDADA). The binding energies between the vancomycin and the peptide were obtained from the RRKM modeling of the time- and energy resolved surface-induced dissociation (SID) experiments. Our results demonstrate that the stability of the complex toward fragmentation increases in the order: [V+Ac2KDADA+H]+2 < [V+Ac2KDADA+H]+ < [V+Ac2KDADA-H]-. Dissociation of the singly protonated and singly deprotonated complex is characterized by very large entropy effects indicating substantial increase in the conformational flexibility of the resulting products. The experimental threshold energies of 1.75 eV and 1.34 eV obtained for the [V+Ac2KDADA-H]- and [V+Ac2KDADA+H]+ , respectively, are in excellent agreement with the results of density functional theory (DFT) calculations. The increased stability of the deprotonated complex observed experimentally is attributed to the presence of three charged sites in the deprotonated complex as compared to only one charged site in the singly protonated complex. The low binding energy of 0.93 eV obtained for the doubly protonated complex suggests that this ion is destabilized by Coulomb repulsion between the singly protonated vancomycin and the singly protonated peptide comprising the complex.

  17. Modifying the electronic properties of single-walled carbon nanotubes using designed surfactant peptides

    NASA Astrophysics Data System (ADS)

    Samarajeewa, Dinushi R.; Dieckmann, Gregg R.; Nielsen, Steven O.; Musselman, Inga H.

    2012-07-01

    The electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino acid sequence of X(Valine)5(Lysine)2, where X indicates an aromatic amino acid containing either an electron-donating or electron-withdrawing functional group (i.e. p-amino-phenylalanine or p-cyano-phenylalanine). Circular dichroism spectra showed that the surfactant peptides primarily have random coil structures in an aqueous medium, both alone and in the presence of SWCNTs, simplifying analysis of the peptide/SWCNT interaction. The ability of the surfactant peptides to disperse individual SWCNTs in solution was verified using atomic force microscopy and ultraviolet-visible-near-infrared spectroscopy. The electronic properties of the surfactant peptide/SWCNT composites were examined using the observed nanotube Raman tangential band shifts and the observed additional features near the Fermi level in the scanning tunneling spectroscopy dI/dV spectra. The results revealed that SWCNTs functionalized with surfactant peptides containing electron-donor or electron-acceptor functional groups showed n-doped or p-doped altered electronic properties, respectively. This work unveils a facile and versatile approach to modify the intrinsic electronic properties of SWCNTs using a simple peptide structure, which is easily adaptable to obtain peptide/SWCNT composites for the design of tunable nanoscale electronic devices.The electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino

  18. "Hot spots" growth on single nanowire controlled by electric charge.

    PubMed

    Xi, Shaobo; Liu, Xuehua; He, Ting; Tian, Lei; Wang, Wenhui; Sun, Rui; He, Weina; Zhang, Xuetong; Zhang, Jinping; Ni, Weihai; Zhou, Xiaochun

    2016-06-01

    "Hot spots" - a kind of highly active site, which are usually composed of some unique units, such as defects, interfaces, catalyst particles or special structures - can determine the performance of nanomaterials. In this paper, we study a model system, i.e. "hot spots" on a single Ag nanowire in the galvanic replacement reaction (GRR), by dark-field microscopy. The research reveals that electric charge can be released by the formation reaction of AgCl, and consequently the electrochemical potential on Ag nanowire drops. The electric charge could induce the reduction of Ag(+) to form the "hot spots" on the nanowire during the GRR. The appearance probability of "hot spots" is almost even along the Ag nanowire, while it is slightly lower near the two ends. The spatial distance between adjacent "hot spots" is also controlled by the charge, and obeys a model based on Boltzmann distribution. In addition, the distance distribution here has an advantage in electron transfer and energy saving. Therefore, it's necessary to consider the functions of electric charge during the synthesis or application of nanomaterials. PMID:27240743

  19. Short Peptides Enhance Single Cell Adhesion and Viability onMicroarrays

    SciTech Connect

    Veiseh, Mandana; Veiseh, Omid; Martin, Michael C.; Asphahani,Fareid; Zhang, Miqin

    2007-01-19

    Single cell patterning holds important implications forbiology, biochemistry, biotechnology, medicine, and bioinformatics. Thechallenge for single cell patterning is to produce small islands hostingonly single cells and retaining their viability for a prolonged period oftime. This study demonstrated a surface engineering approach that uses acovalently bound short peptide as a mediator to pattern cells withimproved single cell adhesion and prolonged cellular viabilityon goldpatterned SiO2 substrates. The underlying hypothesis is that celladhesion is regulated bythe type, availability, and stability ofeffective cell adhesion peptides, and thus covalently bound shortpeptides would promote cell spreading and, thus, single cell adhesion andviability. The effectiveness of this approach and the underlyingmechanism for the increased probability of single cell adhesion andprolonged cell viability by short peptides were studied by comparingcellular behavior of human umbilical cord vein endothelial cells on threemodelsurfaces whose gold electrodes were immobilized with fibronectin,physically adsorbed Arg-Glu-Asp-Val-Tyr, and covalently boundLys-Arg-Glu-Asp-Val-Tyr, respectively. The surface chemistry and bindingproperties were characterized by reflectance Fourier transform infraredspectroscopy. Both short peptides were superior to fibronectin inproducing adhesion of only single cells, whereas the covalently boundpeptide also reduced apoptosis and necrosisof adhered cells. Controllingcell spreading by peptide binding domains to regulate apoptosis andviability represents a fundamental mechanism in cell-materialsinteraction and provides an effective strategy in engineering arrays ofsingle cells.

  20. Diet-induced neuropeptide expression: feasibility of quantifying extended and highly charged endogenous peptide sequences by selected reaction monitoring.

    PubMed

    Schmidlin, Thierry; Boender, Arjen J; Frese, Christian K; Heck, Albert J R; Adan, Roger A H; Altelaar, A F Maarten

    2015-10-01

    Understanding regulation and action of endogenous peptides, especially neuropeptides, which serve as inter- and intracellular signal transmitters, is key in understanding a variety of functional processes, such as energy balance, memory, circadian rhythm, drug addiction, etc. Therefore, accurate and reproducible quantification of these bioactive endogenous compounds is highly relevant. The biosynthesis of endogenous peptides, involving multiple possible trimming and modification events, hinders the de novo prediction of the active peptide sequences, making MS-based measurements very valuable in determining the actual active compounds. Here, we report an extended selected reaction monitoring (SRM)-based strategy to reproducibly and quantitatively monitor the abundances of a set of 15 endogenously occurring peptides from Rattus norvegicus hypothalamus. We demonstrate that SRM can be extended toward reproducible detection and quantification of peptides, bearing characteristics very different from tryptic peptides. We show that long peptide sequences, producing precursors with up to five and MS2 fragment ions with up to three charges, can be targeted by SRM on a triple quadrupole instrument. Using this approach to quantify endogenous peptide levels in hypothalami of animals subjected to different diets revealed several significant changes, most notably the significant upregulation of VGF-derived signaling peptide AQEE-30 upon high caloric feeding. PMID:26376940

  1. A compact source for bunches of singly charged atomic ions

    NASA Astrophysics Data System (ADS)

    Murböck, T.; Schmidt, S.; Andelkovic, Z.; Birkl, G.; Nörtershäuser, W.; Vogel, M.

    2016-04-01

    We have built, operated, and characterized a compact ion source for low-energy bunches of singly charged atomic ions in a vacuum beam line. It is based on atomic evaporation from an electrically heated oven and ionization by electron impact from a heated filament inside a grid-based ionization volume. An adjacent electrode arrangement is used for ion extraction and focusing by applying positive high-voltage pulses to the grid. The method is particularly suited for experimental environments which require low electromagnetic noise. It has proven simple yet reliable and has been used to produce μs-bunches of up to 106 Mg+ ions at a repetition rate of 1 Hz. We present the concept, setup and characterizing measurements. The instrument has been operated in the framework of the SpecTrap experiment at the HITRAP facility at GSI/FAIR to provide Mg+ ions for sympathetic cooling of highly charged ions by laser-cooled 24Mg+.

  2. Charging and discharging of single conjugated-polymer nanoparticles

    NASA Astrophysics Data System (ADS)

    Palacios, Rodrigo E.; Fan, Fu-Ren F.; Grey, John K.; Suk, Jungdon; Bard, Allen J.; Barbara, Paul F.

    2007-09-01

    Despite intense, long-term interest in organic semiconductors from both an applied and fundamental perspective, key aspects of the electronic properties of these materials remain poorly defined. A particularly challenging problem is the molecular nature of positive charge carriers, that is, holes or oxidized species in organics. Here, the unique ability of single-molecule spectroelectrochemistry (SMS-EC) to unravel complex electrochemical process in heterogeneous media is used to study the oxidation of nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole). A reversible hole-injection charging process has been observed that occurs primarily by initial injection of shallow (untrapped) holes, but soon after the injection, a small fraction of the holes becomes deeply trapped. Good agreement between experimental data and simulations strongly supports the presence of deep traps in the studied nanoparticles and highlights the ability of SMS-EC to study energetics and dynamics of deep traps in organic materials at the nanoscale.

  3. A spliced antigenic peptide comprising a single spliced amino acid is produced in the proteasome by reverse splicing of a longer peptide fragment followed by trimming.

    PubMed

    Michaux, Alexandre; Larrieu, Pierre; Stroobant, Vincent; Fonteneau, Jean-François; Jotereau, Francine; Van den Eynde, Benoît J; Moreau-Aubry, Agnès; Vigneron, Nathalie

    2014-02-15

    Peptide splicing is a novel mechanism of production of peptides relying on the proteasome and involving the linkage of fragments originally distant in the parental protein. Peptides produced by splicing can be presented on class I molecules of the MHC and recognized by CTLs. In this study, we describe a new antigenic peptide, which is presented by HLA-A3 and comprises two noncontiguous fragments of the melanoma differentiation Ag gp100(PMEL17) spliced together in the reverse order to that in which they appear in the parental protein. Contrary to the previously described spliced peptides, which are produced by the association of fragments of 3-6 aa, the peptide described in this work results from the ultimate association of an 8-aa fragment with a single arginine residue. As described before, peptide splicing takes place in the proteasome by transpeptidation involving an acyl-enzyme intermediate linking one of the peptide fragment to a catalytic subunit of the proteasome. Interestingly, we observe that the peptide causing the nucleophilic attack on the acyl-enzyme intermediate must be at least 3 aa long to give rise to a spliced peptide. The spliced peptide produced from this reaction therefore bears an extended C terminus that needs to be further trimmed to produce the final antigenic peptide. We show that the proteasome is able to perform the final trimming step required to produce the antigenic peptide described in this work. PMID:24453253

  4. Slowing down single-molecule trafficking through a protein nanopore reveals intermediates for peptide translocation

    NASA Astrophysics Data System (ADS)

    Mereuta, Loredana; Roy, Mahua; Asandei, Alina; Lee, Jong Kook; Park, Yoonkyung; Andricioaei, Ioan; Luchian, Tudor

    2014-01-01

    The microscopic details of how peptides translocate one at a time through nanopores are crucial determinants for transport through membrane pores and important in developing nano-technologies. To date, the translocation process has been too fast relative to the resolution of the single molecule techniques that sought to detect its milestones. Using pH-tuned single-molecule electrophysiology and molecular dynamics simulations, we demonstrate how peptide passage through the α-hemolysin protein can be sufficiently slowed down to observe intermediate single-peptide sub-states associated to distinct structural milestones along the pore, and how to control residence time, direction and the sequence of spatio-temporal state-to-state dynamics of a single peptide. Molecular dynamics simulations of peptide translocation reveal the time- dependent ordering of intermediate structures of the translocating peptide inside the pore at atomic resolution. Calculations of the expected current ratios of the different pore-blocking microstates and their time sequencing are in accord with the recorded current traces.

  5. Membrane binding of peptide models for early stages of amyloid formation: Lipid packing counts more than charge.

    PubMed

    Hoernke, Maria; Tassler, Stephanie; Koksch, Beate; Brezesinski, Gerald

    2016-06-01

    Amyloid formation is related to neurodegenerative diseases like Alzheimer's disease or Parkinson's disease. In the molecular onset of the diseases, soluble peptides adopt conformations that are rich in β-sheet and ultimately form aggregates. How this process is triggered or influenced by membrane binding, or how the membrane integrity is disturbed by the peptide binding and conformational transition is still under debate. In the present study, we systematically examine the effects of β-sheet prone model peptides on zwitterionic and negatively charged lipids in both mono- and bilayers and in various lipid phase states by infrared reflection absorption spectroscopy, grazing incidence X-ray diffraction, and small and wide angle X-ray scattering. No difference in the interaction of the peptides with zwitterionic or negatively charged lipids was observed. Furthermore, the interaction of β-sheet prone model peptides leaves the lipid structure largely unaffected. However, the lipid phase state decides upon the mode of interaction. Peptides insert into liquid-expanded layers and interact only with the head groups of liquid-condensed lipid layers. Using a zoo of complementary techniques and critically examining preparation procedures we are able to obtain an unambiguous picture of peptide binding to membranes. PMID:27134131

  6. Single Electron Charging and Quantum Effects in Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Foxman, Ethan Bradley

    1993-01-01

    We present an experimental study of a small region (~0.3 times 0.3 mum^2) of two-dimensional electron gas in a GaAs/rm Al_{x}Ga_{1-x}As heterostructure. The small electron gas is coupled to electrical leads through tunnel barriers formed by negatively biased Schottky gates on the surface of the heterostructure. Electron transport is studied as a function of gate voltage, magnetic field, temperature, bias voltage and tunneling barrier height. We observe a rich interplay between single electron charging and quantum effects. The conductance of such systems was known to consist of a series of nearly periodic conductance peaks.^{1,2} We further investigate this behavior and show that our observations are consistent with a model that synthesizes classical single electron charging and a discrete tunneling density of states.^{3,4}. We investigate the nature and origin of this tunneling density of states. The spectrum of states is determined through current-voltage measurements and low-bias conductance measurements. The tunneling density of states is mapped as a function of gate voltage and magnetic field. In the latter case, we show that our observations can be understood through a self-consistent model of single electron charging in the quantum Hall regime.^5. Lastly, we report conductance measurements in the regime where the conductance across the tunnel barriers separating the small electron gas from its leads becomes of order e^2/h. We observe that in this regime single electron charging effects are quenched. This effect is shown to arise from an increased capacitance across one of the barriers and from the increased lifetime broadening of states in the small electron gas. ^6 (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.) ftn^1J. H. F. Scott -Thomas, S. B. Field, M. A. Kastner, H. I. Smith, and D. A. Antoniadis, Phys. Rev. Lett. 62, 583 (1989). ^2U. Meirav, M. A. Kastner, and S. J. Wind

  7. Note: Charge transfer in a hydrated peptide group is determined mainly by its intrinsic hydrogen-bond energetics

    SciTech Connect

    Mirkin, Noemi G.; Krimm, Samuel

    2014-01-28

    Charge transfer in a hydrogen-bonded N-methylacetamide(H{sub 2}O){sub 3} system is obtained from ωB97X-D/6-31++G** and CHelpG atomic charge calculations of individual peptide-water interactions as well as that of the entire complex. In the latter, the electron transfer to water is 0.19 e, influenced primarily by the hydrogen bonds to the C=O group. The values of such charge transfer are paralleled by the corresponding intrinsic hydrogen-bond energies. These results support the desirability of incorporating charge transfer in molecular mechanics energy functions.

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

    PubMed Central

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

    2014-01-01

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

  9. The negatively charged regions of lactoferrin binding protein B, an adaptation against anti-microbial peptides.

    PubMed

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

    2014-01-01

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

  10. Tunable Raman photons in singly charged p -doped quantum dots

    NASA Astrophysics Data System (ADS)

    Carreño, F.; Antón, M. A.

    2016-03-01

    The obtention of spontaneous Raman photons is analyzed in singly charged p -doped quantum dots in the absence of an external magnetic field. The use of a far detuned single driving laser allows one to obtain a Raman photon line which exhibits a subnatural linewidth, and whose center can be tuned by changing the detuning and/or the Rabi frequency of the driving field. The Raman photons are produced along the undriven transition and they arise from a weak interaction of the trion states with the nuclear spins. The operating point for the gate voltage of the heterostructure can also be used to modify the linewidth and the peak value of the fluorescent signal.

  11. Topological charge analysis of ultrafast single skyrmion creation

    NASA Astrophysics Data System (ADS)

    Yin, Gen; Li, Yufan; Kong, Lingyao; Lake, Roger K.; Chien, C. L.; Zang, Jiadong

    2016-05-01

    Magnetic skyrmions are topologically nontrivial spin textures of potential interest for future information storage applications, and for such purposes, the control and understanding of single skyrmion creation is required. A scheme is analyzed to create single Néel-type and Bloch-type skyrmions in helimagnetic thin films utilizing the dynamical excitations induced by the Oersted field and the spin transfer torque given by a vertically injected spin-polarized current. A topological charge analysis using a lattice version of the topological charge provides insight into the locally triggered transition from a trivial to a nontrivial topological spin texture of the Néel or Bloch type skyrmion. The topological protection of the magnetic skyrmion is determined by the symmetric Heisenberg exchange energy. The critical switching current density is ˜107A/cm 2 , which decreases with the easy-plane type uniaxial anisotropy and thermal fluctuations. The in-plane spin polarization of the injected current performs better than out-of-plane polarization, and it provides ultrafast switching times (within 100 ps) and reliable switching outcomes.

  12. Single phase dynamic CMOS PLA using charge sharing technique

    NASA Technical Reports Server (NTRS)

    Dhong, Y. B.; Tsang, C. P.

    1991-01-01

    A single phase dynamic CMOS NOR-NOR programmable logic array (PLA) using triggered decoders and charge sharing techniques for high speed and low power is presented. By using the triggered decoder technique, the ground switches are eliminated, thereby, making this new design much faster and lower power dissipation than conventional PLA's. By using the charge-sharing technique in a dynamic CMOS NOR structure, a cascading AND gate can be implemented. The proposed PLA's are presented with a delay-time of 15.95 and 18.05 nsec, respectively, which compare with a conventional single phase PLA with 35.5 nsec delay-time. For a typical example of PLA like the Signetics 82S100 with 16 inputs, 48 input minterms (m) and 8 output minterms (n), the 2-SOP PLA using the triggered 2-bit decoder is 2.23 times faster and has 2.1 times less power dissipation than the conventional PLA. These results are simulated using maximum drain current of 600 micro-A, gate length of 2.0 micron, V sub DD of 5 V, the capacitance of an input miniterm of 1600 fF, and the capacitance of an output minterm of 1500 fF.

  13. Cryogenic CMOS circuits for single charge digital readout.

    SciTech Connect

    Gurrieri, Thomas M.; Longoria, Erin Michelle; Eng, Kevin; Carroll, Malcolm S.; Hamlet, Jason R.; Young, Ralph Watson

    2010-03-01

    The readout of a solid state qubit often relies on single charge sensitive electrometry. However the combination of fast and accurate measurements is non trivial due to large RC time constants due to the electrometers resistance and shunt capacitance from wires between the cold stage and room temperature. Currently fast sensitive measurements are accomplished through rf reflectrometry. I will present an alternative single charge readout technique based on cryogenic CMOS circuits in hopes to improve speed, signal-to-noise, power consumption and simplicity in implementation. The readout circuit is based on a current comparator where changes in current from an electrometer will trigger a digital output. These circuits were fabricated using Sandia's 0.35 {micro}m CMOS foundry process. Initial measurements of comparators with an addition a current amplifier have displayed current sensitivities of < 1nA at 4.2K, switching speeds up to {approx}120ns, while consuming {approx}10 {micro}W. I will also discuss an investigation of noise characterization of our CMOS process in hopes to obtain a better understanding of the ultimate limit in signal to noise performance.

  14. Cryogenic CMOS circuits for single charge digital readout

    NASA Astrophysics Data System (ADS)

    Eng, Kevin; Gurrieri, T. M.; Hamlet, J.; Carroll, M. S.

    2010-03-01

    The readout of a solid state qubit often relies on single charge sensitive electrometry. However the combination of fast and accurate measurements is non trivial due to large RC time constants due to the electrometers resistance and shunt capacitance from wires between the cold stage and room temperature. Currently fast sensitive measurements are accomplished through rf reflectrometry. I will present an alternative single charge readout technique based on cryogenic CMOS circuits in hopes to improve speed, signal-to-noise, power consumption and simplicity in implementation. The readout circuit is based on a current comparator where changes in current from an electrometer will trigger a digital output. These circuits were fabricated using Sandia's 0.35μm CMOS foundry process. Initial measurements of comparators with an addition a current amplifier have displayed current sensitivities of < 1nA at 4.2K, switching speeds up to ˜120ns, while consuming ˜10μW. I will also discuss an investigation of noise characterization of our CMOS process in hopes to obtain a better understanding of the ultimate limit in signal to noise performance.

  15. Light-Induced Charge Transport within a Single Asymmetric Nanowire

    SciTech Connect

    Liu, Chong; Hwang, Yun Yeong; Jeong, Hoon Eui; Yang, Peidong

    2011-01-21

    Artificial photosynthetic systems using semiconductor materials have been explored for more than three decades in order to store solar energy in chemical fuels such as hydrogen. By mimicking biological photosynthesis with two light-absorbing centers that relay excited electrons in a nanoscopic space, a dual-band gap photoelectrochemical (PEC) system is expected to have higher theoretical energy conversion efficiency than a single band gap system. This work demonstrates the vectorial charge transport of photo-generated electrons and holes within a single asymmetric Si/TiO2 nanowire using Kelvin probe force microscopy (KPFM). Under UV illumination, higher surface potential was observed on the n-TiO₂ side, relative to the potential of the p-Si side, as a result of majority carriers’ recombination at the Si/TiO₂ interface. These results demonstrate a new approach to investigate charge separation and transport in a PEC system. This asymmetric nanowire heterostructure, with a dual band gap configuration and simultaneously exposed anode and cathode surfaces represents an ideal platform for the development of technologies for the generation of solar fuels, although better photoanode materials remain to be discovered.

  16. A Study of Ion-Neutral Collision Cross Section Values for Low Charge States of Peptides, Proteins, and Peptide/Protein Complexes

    PubMed Central

    Fernandez-Lima, Francisco A.; Blase, Ryan C.; Russell, David H.

    2009-01-01

    Here, we report ion-helium collision cross sections (CCS) for a number of peptide, small protein, and peptide/protein ionic complexes. The CCS values reported here are compared to previously reported results.[1, 2] We also compare values for low charge state species, i.e., [M + H]+ and [M + 2H]2+, formed by MALDI with values for high charge state species formed by ESI, and the measured CCSs are compared with predicted CCS for solid-state and solution phase structures and calculated structures obtained by using a protein-protein structure algorithm generator, based on a combined Biomolecular complex Generation with Global Evaluation and Ranking[3] and Multi Dimensional Scaling[4]. PMID:21503273

  17. Single charge detection in capacitively coupled integrated single electron transistors based on single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Zhou, Xin; Ishibashi, Koji

    2012-09-01

    Single charge detection is demonstrated in the capacitively coupled integrated single electron transistors (SETs) in single-walled carbon nanotubes (SWCNTs) quantum dots. Two SETs are fabricated based on two different SWCNTs aligned in parallel, by taking advantage of the aligned growth of SWCNTs and subsequent transfer-printed techniques. In order to make both two SETs be capacitively coupled, a metal finger is fabricated on the top of them. The charge sensing is proved by the response of a detector current in one SWCNT-SET when the number of electrons in the other SWCNT-SET is changed by sweeping the corresponding gate voltages. In this integrated device, shifts of Coulomb oscillation peaks due to the single electron event are also observed.

  18. Antimicrobial Peptide Lactoferricin B-Induced Rapid Leakage of Internal Contents from Single Giant Unilamellar Vesicles.

    PubMed

    Moniruzzaman, Md; Alam, Jahangir Md; Dohra, Hideo; Yamazaki, Masahito

    2015-09-29

    Enzymatic digestion of bovine lactoferrin generates lactoferricin B (Lfcin B), a 25-mer peptide with strong antimicrobial activity of unknown mechanism. To elucidate the mechanistic basis of Lfcin B bactericidal activity, we investigated the interaction of Lfcin B with Escherichia coli and liposomes of lipid membranes. Lfcin B induced the influx of a membrane-impermeant fluorescent probe, SYTOX green, from the outside of E. coli into its cytoplasm. Lfcin B induced gradual leakage of calcein from large unilamellar vesicles (LUVs) of dioleoylphosphatidylglycerol (DOPG)/dioleoylphosphatidylcholine (DOPC) membranes. To clarify the cause of Lfcin B-induced leakage of calcein from the LUVs, we used the single giant unilamellar vesicle (GUV) method to investigate the interaction of Lfcin B with calcein-containing DOPG/DOPC-GUVs. We observed that a rapid leakage of calcein from a GUV started stochastically; statistical analysis provided a rate constant for Lfcin B-induced pore formation, kp. On the other hand, phase-contrast microscopic images revealed that Lfcin B induced a rapid leakage of sucrose from the single GUVs with concomitant appearance of a spherical GUV of smaller diameter. Because of the very fast leakage, and at the present time resolution of the experiments (33 ms), we could not follow the evolution of pore nor the process of the structural changes of the GUV. Here we used the term "local rupture" to express the rapid leakage of sucrose and determined the rate constant of local rupture, kL. On the basis of the comparison between kp and kL, we concluded that the leakage of calcein from single GUVs occurred as a result of a local rupture in the GUVs and that smaller pores inducing leakage of calcein were not formed before the local rupture. The results of the effect of the surface charge density of lipid membranes and that of salt concentration in buffer on kp clearly show that kp increases with an increase in the extent of electrostatic interactions due to

  19. Charge density wave transition in single-layer titanium diselenide

    DOE PAGESBeta

    Chen, P.; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y.; Chou, M. Y.; Mo, S. -K.; Hussain, Z.; Fedorov, A. -V.; Chiang, T. -C.

    2015-11-16

    A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering.more » The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.« less

  20. Charge density wave transition in single-layer titanium diselenide

    PubMed Central

    Chen, P; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y; Chou, M Y; Mo, S. -K.; Hussain, Z; Fedorov, A. -V.; Chiang, T. -C.

    2015-01-01

    A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene—a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The observed Bardeen-Cooper-Schrieffer (BCS) behaviour of the gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk. PMID:26568512

  1. Charge density wave transition in single-layer titanium diselenide

    SciTech Connect

    Chen, P.; Chan, Y. -H.; Fang, X. -Y.; Zhang, Y.; Chou, M. Y.; Mo, S. -K.; Hussain, Z.; Fedorov, A. -V.; Chiang, T. -C.

    2015-11-16

    A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene--a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The behavior of the Bardeen-Cooper-Schrieffer (BCS) gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.

  2. Electronic Structure, Dielectric Response, and Surface Charge Distribution of RGD (1FUV) Peptide

    NASA Astrophysics Data System (ADS)

    Adhikari, Puja; Wen, Amy M.; French, Roger H.; Parsegian, V. Adrian; Steinmetz, Nicole F.; Podgornik, Rudolf; Ching, Wai-Yim

    2014-07-01

    Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor.

  3. Electronic Structure, Dielectric Response, and Surface Charge Distribution of RGD (1FUV) Peptide

    PubMed Central

    Adhikari, Puja; Wen, Amy M.; French, Roger H.; Parsegian, V. Adrian; Steinmetz, Nicole F.; Podgornik, Rudolf; Ching, Wai-Yim

    2014-01-01

    Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor. PMID:25001596

  4. Charge transport in single CuO nanowires

    NASA Astrophysics Data System (ADS)

    Wu, Junnan; Yin, Bo; Wu, Fei; Myung, Yoon; Banerjee, Parag

    2014-11-01

    Charge transport in single crystal, p-type cupric oxide (CuO) nanowire (NW) was studied through temperature based (120 K-400 K) current-voltage measurements. CuO NW with a diameter of 85 nm was attached to Au electrodes 2.25 μm apart, using dielectrophoresis. At low electrical field (<0.89 × 103 V/cm), an ohmic conduction is observed with an activation energy of 272 meV. The injected electrons fill traps with an average energy, ET = 26.6 meV and trap density, NT = 3.4 × 1015 cm-3. After the traps are saturated, space charge limited current mechanism becomes dominant. For 120 K ≤ T ≤ 210 K phonon scattering limits mobility. For T ≥ 220 K, a thermally activated mobility is observed and is attributed to small polaron hopping with an activation energy of 44 meV. This mechanism yields a hole mobility of 0.0015 cm2/V s and an effective hole concentration of 4 × 1018 cm-3 at 250 K.

  5. Singly charged energetic helium emitted in solar flares

    NASA Technical Reports Server (NTRS)

    Hovestadt, D.; Hoefner, H.; Klecker, B.; Scholer, M.; Gloeckler, G.; Ipavich, F. M.; Fan, C. Y.; Fisk, L. A.; Ogallagher, J. J.

    1981-01-01

    First direct charge state measurements of 0.41-1.05 MeV per nucleon helium accelerated at the sun reveal surprisingly large abundances of singly ionized helium, with typical He(+)/He(++) ratios between 0.04 and 0.21. This unexpected overabundance of He(+) was observed in each of the three large solar-flare particle events which occurred between 1978 August and 1979 October. The data were obtained with the Max-Planck-Institut/University of Maryland Experiment on board the ISEE-3 spacecraft. The observations suggest either strong coronal temperature inhomogeneities including cool regions of approximately 100,000 K or injection of 'cold' chromospheric/photospheric material into the flare acceleration region.

  6. Conformation-specific spectroscopy of capped glutamine-containing peptides: role of a single glutamine residue on peptide backbone preferences.

    PubMed

    Walsh, Patrick S; Dean, Jacob C; McBurney, Carl; Kang, Hyuk; Gellman, Samuel H; Zwier, Timothy S

    2016-04-20

    The conformational preferences of a series of short, aromatic-capped, glutamine-containing peptides have been studied under jet-cooled conditions in the gas phase. This work seeks a bottom-up understanding of the role played by glutamine residues in directing peptide structures that lead to neurodegenerative diseases. Resonant ion-dip infrared (RIDIR) spectroscopy is used to record single-conformation infrared spectra in the NH stretch, amide I and amide II regions. Comparison of the experimental spectra with the predictions of calculations carried out at the DFT M05-2X/6-31+G(d) level of theory lead to firm assignments for the H-bonding architectures of a total of eight conformers of four molecules, including three in Z-Gln-OH, one in Z-Gln-NHMe, three in Ac-Gln-NHBn, and one in Ac-Ala-Gln-NHBn. The Gln side chain engages actively in forming H-bonds with nearest-neighbor amide groups, forming C8 H-bonds to the C-terminal side, C9 H-bonds to the N-terminal side, and an amide-stacked geometry, all with an extended (C5) peptide backbone about the Gln residue. The Gln side chain also stabilizes an inverse γ-turn in the peptide backbone by forming a pair of H-bonds that bridge the γ-turn and stabilize it. Finally, the entire conformer population of Ac-Ala-Gln-NHBn is funneled into a single structure that incorporates the peptide backbone in a type I β-turn, stabilized by the Gln side chain forming a C7 H-bond to the central amide group in the β-turn not otherwise involved in a hydrogen bond. This β-turn backbone structure is nearly identical to that observed in a series of X-(AQ)-Y β-turns in the protein data bank, demonstrating that the gas-phase structure is robust to perturbations imposed by the crystalline protein environment. PMID:27054830

  7. Using blocking peptides to control and analyze the mechanical properties of single fibrin fibers

    NASA Astrophysics Data System (ADS)

    Maddi, Pranav; O'Brien, E. Tim, III; Gorkun, Oleg; Falvo, Michael R.

    2011-10-01

    Fibrin is the main structural protein involved in blood clotting, and exhibits high strength and elasticity. Fibrin study traditionally focuses on fully formed clots, whereas we employ new AFM nanoManipulation techniques to study single fibrin fiber mechanics. We used 4 and 10 residue peptides to interfere with the knob-hole and αC interactions involved in fibrin polymerization to evaluate the contribution of each interaction to the fiber's mechanical properties. We varied the concentration of each peptide present during polymerization to find the concentration that inhibited polymerization by half. The presence of either peptide during fibrin polymerization did not affect single fiber breaking strain (δLL0). The breaking force of all treated fibers reduced from 10-50nN to 2-10nN, suggesting treated fibers are thinner or are the same diameter with some inhibition of interactions. Fibers polymerized with the knob-hole targeting peptide visibly lost elasticity after 100% strain, while fibers polymerized with the αC targeting peptide lost elasticity after reaching 150% strain, suggesting that the knob-hole interactions control single fiber elasticity.

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

    PubMed Central

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

    2013-01-01

    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 μM. 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 μM peptide concentration. However, R9C induces leakage of negatively charged but not neutral liposomes in a process that involves lipid mixing between liposomes. Our findings suggest that direct traversing of CPPs through the uncharged outer leaflet of the plasma membrane bilayer is unlikely and that permeabilization necessarily involves both anionic lipids and CPP-dependent fusion between opposing membranes. PMID:23663836

  9. Detection of post-translational modifications in single peptides using electron tunnelling currents

    NASA Astrophysics Data System (ADS)

    Ohshiro, Takahito; Tsutsui, Makusu; Yokota, Kazumichi; Furuhashi, Masayuki; Taniguchi, Masateru; Kawai, Tomoji

    2014-10-01

    Post-translational modifications alter the properties of proteins through the cleavage of peptide bonds or the addition of a modifying group to one or more amino acids. These modifications allow proteins to perform their primary biological functions, but single-protein studies of post-translational modifications have been hindered by a lack of suitable analysis methods. Here, we show that single amino acids can be identified using electron tunnelling currents measured as the individual molecules pass through a nanoscale gap between electrodes. We identify 12 different amino acids and the post-translational modification phosphotyrosine, which is involved in the process that switches enzymes on and off. Furthermore, we show that the conductance measurements can be used to partially sequence peptides of an epidermal growth factor receptor substrate, and can discriminate a peptide from its phosphorylated variant.

  10. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Rudenko, A. N.; Brener, S.; Katsnelson, M. I.

    2016-06-01

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n , two-phonon scattering in BP is less important and can be considered negligible at n ≳1013 cm-2 . At smaller n , however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μx x/μy y˜1.4 at n =1013 cm-2 and T =300 K ), the electron mobility is found to be significantly more anisotropic (μx x/μy y˜6.2 ). Absolute values of μx x do not exceed 250 (700 ) cm2 V-1 s-1 for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature.

  11. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus.

    PubMed

    Rudenko, A N; Brener, S; Katsnelson, M I

    2016-06-17

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n, two-phonon scattering in BP is less important and can be considered negligible at n≳10^{13}  cm^{-2}. At smaller n, however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μ_{xx}/μ_{yy}∼1.4 at n=10^{13} cm^{-2} and T=300  K), the electron mobility is found to be significantly more anisotropic (μ_{xx}/μ_{yy}∼6.2). Absolute values of μ_{xx} do not exceed 250 (700)  cm^{2} V^{-1} s^{-1} for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature. PMID:27367397

  12. Molecular dynamics simulation of non-covalent single-walled carbon nanotube functionalization with surfactant peptides.

    PubMed

    Barzegar, Abolfazl; Mansouri, Alireza; Azamat, Jafar

    2016-03-01

    Non-covalent functionalized single-walled carbon nanotubes (SWCNTs) with improved solubility and biocompatibility can successfully transfer drugs, DNA, RNA, and proteins into the target cells. Theoretical studies such as molecular docking and molecular dynamics simulations in fully atomistic scale were used to investigate the hydrophobic and aromatic π-π-stacking interaction of designing four novel surfactant peptides for non-covalent functionalization of SWCNTs. The results indicated that the designed peptides have binding affinity towards SWCNT with constant interactions during MD simulation times, and it can even be improved by increasing the number of tryptophan residues. The aromatic content of the peptides plays a significant role in their adsorption in SWCNT wall. The data suggest that π-π stacking interaction between the aromatic rings of tryptophan and π electrons of SWCNTs is more important than hydrophobic effects for dispersing carbon nanotubes; nevertheless SWCNTs are strongly hydrophobic in front of smooth surfaces. The usage of aromatic content of peptides for forming SWCNT/peptide complex was proved successfully, providing new insight into peptide design strategies for future nano-biomedical applications. PMID:26811869

  13. Development of a Single-Chain Peptide Agonist of the Relaxin-3 Receptor Using Hydrocarbon Stapling.

    PubMed

    Hojo, Keiko; Hossain, Mohammed Akhter; Tailhades, Julien; Shabanpoor, Fazel; Wong, Lilian L L; Ong-Pålsson, Emma E K; Kastman, Hanna E; Ma, Sherie; Gundlach, Andrew L; Rosengren, K Johan; Wade, John D; Bathgate, Ross A D

    2016-08-25

    Structure-activity studies of the insulin superfamily member, relaxin-3, have shown that its G protein-coupled receptor (RXFP3) binding site is contained within its central B-chain α-helix and this helical structure is essential for receptor activation. We sought to develop a single B-chain mimetic that retained agonist activity. This was achieved by use of solid phase peptide synthesis together with on-resin ruthenium-catalyzed ring closure metathesis of a pair of judiciously placed i,i+4 α-methyl, α-alkenyl amino acids. The resulting hydrocarbon stapled peptide was shown by solution NMR spectroscopy to mimic the native helical conformation of relaxin-3 and to possess potent RXFP3 receptor binding and activation. Alternative stapling procedures were unsuccessful, highlighting the critical need to carefully consider both the peptide sequence and stapling methodology for optimal outcomes. Our result is the first successful minimization of an insulin-like peptide to a single-chain α-helical peptide agonist which will facilitate study of the function of relaxin-3. PMID:27464307

  14. On the maximum charge state and proton transfer reactivity of peptide and protein ions formed by electrospray ionization.

    PubMed

    Schnier, P D; Gross, D S; Williams, E R

    1995-11-01

    A relatively simple model for calculation of the energetics of gas-phase proton transfer reactions and the maximum charge state of multiply protonated ions formed by electrospray ionization is presented. This model is based on estimates of the intrinsic proton transfer reactivity of sites of protonation and point charge Coulomb interactions. From this model, apparent gas-phase basicities (GB(app)) of multiply protonated ions are calculated. Comparison of this value to the gas-phase basicity of the solvent from which an ion is formed enables a maximum charge state to be calculated. For 13 commonly electrosprayed proteins, our calculated maximum charge states are within an average of 6% of the experimental values reported in the literature. This indicates that the maximum charge state for proteins is determined by their gas-phase reactivity. Similar results are observed for peptides with many basic residues. For peptides with few basic residues, we find that the maximum charge state is better correlated to the charge state in solution. For low charge state ions, we find that the most basic sites Arg, Lys, and His are preferentially protonated. A significant fraction of the less basic residues Pro, Trp, and Gln are protonated in high charge state ions. The calculated GB(app) of individual protonation sites varies dramatically in the high charge state ions. From these values, we calculate a reduced cross section for proton transfer reactivity that is significantly lower than the Langevin collision frequency when the GB(app) of the ion is approximately equal to the GB of the neutral base. PMID:24214055

  15. Peptide-induced Asymmetric Distribution of Charged Lipids in a Vesicle Bilayer Revealed by Small-Angle Neutron Scattering

    NASA Astrophysics Data System (ADS)

    Heller, William; Qian, Shuo

    2012-02-01

    Cellular membranes are complex mixtures of lipids, proteins and other small molecules that provide functional, dynamic barriers between the cell and its environment, as well as between environments within the cell. The lipid composition of the membrane is highly specific and controlled in terms of both content and lipid localization. Here, small-angle neutron scattering and selective deuterium labeling were used to probe the impact of the membrane-active peptides melittin and alamethicin on the structure of lipid bilayers composed of a mixture of the lipids dimyristoyl phosphatidylglycerol (DMPG) and chain-perdeuterated dimyristoyl phosphatidylcholine (DMPC). We found that both peptides enriched the outer leaflet of the bilayer with the negatively charged DMPG, creating an asymmetric distribution of lipids. The level of enrichment is peptide concentration-dependent and is stronger for melittin than alamethicin. The enrichment between the inner and outer bilayer leaflets occurs at very low peptide concentrations, and increases with peptide concentration, including when the peptide adopts a membrane-spanning, pore-forming state.

  16. Role of Charge and Solvation in the Structure and Dynamics of Alanine-Rich Peptide AKA2 in AOT Reverse Micelles.

    PubMed

    Martinez, Anna Victoria; Małolepsza, Edyta; Domínguez, Laura; Lu, Qing; Straub, John E

    2015-07-23

    The propensity of peptides to form α-helices has been intensely studied using theory, computation, and experiment. Important model peptides for the study of the coil-to-helix transition have been alanine-lysine (AKA) peptides in which the lysine residues are placed on opposite sides of the helix avoiding charge repulsion while enhancing solubility. In this study, the effects of capped versus zwitterionic peptide termini on the secondary structure of alanine-rich peptides in reverse micelles are explored. The reverse micelles are found to undergo substantial shape fluctuations, a property observed in previous studies of AOT reverse micelles in the absence of solvated peptide. The peptides are observed to interact with water, as well as the AOT surfactant, including interactions between the nonpolar residues and the aliphatic surfactant tails. Computation of IR spectra for the amide I band of the peptide allows for direct comparison with experimental spectra. The results demonstrate that capped AKA2 peptides form more stable α helices than zwitterionic AKA2 peptides in reverse micelles. The rotational anisotropy decay of water is found to be distinctly different in the presence or absence of peptide within the reverse micelle, suggesting that the introduction of peptide significantly alters the number of free waters within the reverse micelle nanopool. However, neither the nature of the peptide termini (capped or charged) nor the degree of peptide helicity is found to significantly alter the balance of interactions between the peptides and the environment. Observed changes in the degree of helicity in AKA2 peptides in bulk solution and in reverse micelle environments result from changes in peptide confinement and hydration as well as direct nonpolar and polar interactions with the water-surfactant interface. PMID:25337983

  17. Role of Charge and Solvation in the Structure and Dynamics of Alanine-Rich Peptide AKA2 in AOT Reverse Micelles

    PubMed Central

    2015-01-01

    The propensity of peptides to form α-helices has been intensely studied using theory, computation, and experiment. Important model peptides for the study of the coil-to-helix transition have been alanine–lysine (AKA) peptides in which the lysine residues are placed on opposite sides of the helix avoiding charge repulsion while enhancing solubility. In this study, the effects of capped versus zwitterionic peptide termini on the secondary structure of alanine-rich peptides in reverse micelles are explored. The reverse micelles are found to undergo substantial shape fluctuations, a property observed in previous studies of AOT reverse micelles in the absence of solvated peptide. The peptides are observed to interact with water, as well as the AOT surfactant, including interactions between the nonpolar residues and the aliphatic surfactant tails. Computation of IR spectra for the amide I band of the peptide allows for direct comparison with experimental spectra. The results demonstrate that capped AKA2 peptides form more stable α helices than zwitterionic AKA2 peptides in reverse micelles. The rotational anisotropy decay of water is found to be distinctly different in the presence or absence of peptide within the reverse micelle, suggesting that the introduction of peptide significantly alters the number of free waters within the reverse micelle nanopool. However, neither the nature of the peptide termini (capped or charged) nor the degree of peptide helicity is found to significantly alter the balance of interactions between the peptides and the environment. Observed changes in the degree of helicity in AKA2 peptides in bulk solution and in reverse micelle environments result from changes in peptide confinement and hydration as well as direct nonpolar and polar interactions with the water–surfactant interface. PMID:25337983

  18. Adsorption of peptide nucleic acid and DNA decamers at electrically charged surfaces.

    PubMed Central

    Fojta, M; Vetterl, V; Tomschik, M; Jelen, F; Nielsen, P; Wang, J; Palecek, E

    1997-01-01

    Adsorption behavior of peptide nucleic acid (PNA) and DNA decamers (GTAGATCACT and the complementary sequence) on a mercury surface was studied by means of AC impedance measurements at a hanging mercury drop electrode. The nucleic acid was first attached to the electrode by adsorption from a 5-microliter drop of PNA (or DNA) solution, and the electrode with the adsorbed nucleic acid layer was then washed and immersed in the blank background electrolyte where the differential capacity C of the electrode double layer was measured as a function of the applied potential E. It was found that the adsorption behavior of the PNA with an electrically neutral backbone differs greatly from that of the DNA (with a negatively charged backbone), whereas the DNA-PNA hybrid shows intermediate behavior. At higher surface coverage PNA molecules associate at the surface, and the minimum value of C is shifted to negative potentials because of intermolecular interactions of PNA at the surface. Prolonged exposure of PNA to highly negative potentials does not result in PNA desorption, whereas almost all of the DNA is removed from the surface at these potentials. Adsorption of PNA decreases with increasing NaCl concentration in the range from 0 to 50 mM NaCl, in contrast to DNA, the adsorption of which increases under the same conditions. PMID:9129832

  19. Quantum dot labeling using positive charged peptides in human hematopoetic and mesenchymal stem cells.

    PubMed

    Ranjbarvaziri, Sarah; Kiani, Sahar; Akhlaghi, Aliasghar; Vosough, Ahmad; Baharvand, Hossein; Aghdami, Nasser

    2011-08-01

    Quantum dots (QDs), as new and promising fluorescent probes, hold great potential in long term non-invasive bio-imaging, however there are many uncovered issues regarding their competency. In the present study, different QDs (525, 585 and 800 nm) were used to label CD133, CD34, CD14 and mesenchymal stem cells (MSCs) using positively charged peptides. Results demonstrated highly efficient internalization with the possible involvement of macropinocytosis. As indicated by LDH release and the TUNEL assay, no measurable effects on cell viability were detected at a concentration of 10 nM. QDs did not have any deleterious effects on normal cell functionality where both labeled CD133(+) cells and MSCs remarkably differentiated along multiple lineages with the use of the colony forming assay and adipo/osteo induction, respectively. Our results regarding QD maintenance revealed that these nano-particles are not properly stable and various excretion times have been observed depending on particle size and cell type. In vitro co-culture system and transplantation of labeled cells to an animal model showed that QDs leaked out from labeled cells and the released nano-particles were able to re-enter adjacent cells over time. These data suggest that before any utilization of QDs in bio-imaging and related applications, an efficient intra-cellular delivery technique should be considered to preserve QDs for a prolonged time as well as eliminating their leakage. PMID:21549422

  20. Self-Assembling Peptide Coatings Designed for Highly Luminescent Suspension of Single-Walled Carbon Nanotubes

    PubMed Central

    Tsyboulski, Dmitri A.; Bakota, Erica L.; Witus, Leah S.; Rocha, John-David R.; Hartgerink, Jeffrey D.; Weisman, R. Bruce

    2009-01-01

    A series of self-assembling multidomain peptides have been designed, synthesized, and tested for their ability to individually suspend single-walled carbon nanotubes (SWCNTs) in water while preserving strong near-IR nanotube luminescence. Photometric and spectral measurements on individual SWCNTs revealed that emission in the common biocompatible coating agents Pluronic F127, ss-DNA, and BSA is approximately an order of magnitude weaker than in the bio-incompatible ionic surfactant SDBS. By contrast, one of the engineered peptides gave SWCNT emission ~40% as intense as in SDBS. A strong inverse correlation was also found between the spectral line widths of coated SWCNTs and the efficiency of their emission. Peptides with rationally designed self-assembly properties appear to be promising coatings that may enable SWCNT optical sensing applications in biological environments. PMID:19053447

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

    PubMed

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

    2011-10-01

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

  2. Electrical detection of the biological interaction of a charged peptide via gallium arsenide junction-field-effect transistors

    NASA Astrophysics Data System (ADS)

    Lee, Kangho; Nair, Pradeep R.; Alam, Muhammad A.; Janes, David B.; Wampler, Heeyeon P.; Zemlyanov, Dmitry Y.; Ivanisevic, Albena

    2008-06-01

    GaAs junction-field-effect transistors (JFETs) are utilized to achieve label-free detection of biological interaction between a probe transactivating transcriptional activator (TAT) peptide and the target trans-activation-responsive (TAR) RNA. The TAT peptide is a short sequence derived from the human immunodeficiency virus-type 1 TAT protein. The GaAs JFETs are modified with a mixed adlayer of 1-octadecanethiol (ODT) and TAT peptide, with the ODT passivating the GaAs surface from polar ions in physiological solutions and the TAT peptide providing selective binding sites for TAR RNA. The devices modified with the mixed adlayer exhibit a negative pinch-off voltage (VP) shift, which is attributed to the fixed positive charges from the arginine-rich regions in the TAT peptide. Immersing the modified devices into a TAR RNA solution results in a large positive VP shift (>1 V) and a steeper subthreshold slope (˜80 mV/decade), whereas "dummy" RNA induced a small positive VP shift (˜0.3 V) without a significant change in subthreshold slopes (˜330 mV/decade). The observed modulation of device characteristics is analyzed with analytical modeling and two-dimensional numerical device simulations to investigate the electronic interactions between the GaAs JFETs and biological molecules.

  3. Electrical detection of the biological interaction of a charged peptide via gallium arsenide junction-field-effect transistors

    PubMed Central

    Lee, Kangho; Nair, Pradeep R.; Alam, Muhammad A.; Janes, David B.; Wampler, Heeyeon P.; Zemlyanov, Dmitry Y.; Ivanisevic, Albena

    2008-01-01

    GaAs junction-field-effect transistors (JFETs) are utilized to achieve label-free detection of biological interaction between a probe transactivating transcriptional activator (TAT) peptide and the target trans-activation-responsive (TAR) RNA. The TAT peptide is a short sequence derived from the human immunodeficiency virus-type 1 TAT protein. The GaAs JFETs are modified with a mixed adlayer of 1-octadecanethiol (ODT) and TAT peptide, with the ODT passivating the GaAs surface from polar ions in physiological solutions and the TAT peptide providing selective binding sites for TAR RNA. The devices modified with the mixed adlayer exhibit a negative pinch-off voltage (VP) shift, which is attributed to the fixed positive charges from the arginine-rich regions in the TAT peptide. Immersing the modified devices into a TAR RNA solution results in a large positive VP shift (>1 V) and a steeper subthreshold slope (∼80 mV∕decade), whereas “dummy” RNA induced a small positive VP shift (∼0.3 V) without a significant change in subthreshold slopes (∼330 mV∕decade). The observed modulation of device characteristics is analyzed with analytical modeling and two-dimensional numerical device simulations to investigate the electronic interactions between the GaAs JFETs and biological molecules. PMID:19484151

  4. Sequential enrichment of singly- and multiply-phosphorylated peptides with zwitterionic hydrophilic interaction chromatography material.

    PubMed

    Sheng, Qianying; Yang, Kaiya; Xue, Xingya; Li, Xiuling; Guo, Zhimou; Shen, Aijin; Ke, Yanxiong; Lan, Minbo; Liang, Xinmiao

    2015-09-25

    An interesting and novel method for the selective and sequential enrichment of singly- and multiply-phosphorylated peptides with a zwitterionic material "Click TE-Cys" is presented. Retention mechanisms between phosphopeptides and Click TE-Cys are systematically investigated by checking the influence of acetonitrile content, pH value, and buffer concentration on the retention of phosphopeptides. Both hydrophilic interaction and electrostatic interaction are involved in retention between phosphopeptides and Click TE-Cys. Based on these results, an optimized method is established for selective enrichment of phosphopeptides using Click TE-Cys. This method not only exhibits high selectivity for phosphopeptides, but also fractionates singly- and multiply-phosphorylated peptides into two fractions. This method was evaluated using relatively complex samples, including peptide mixtures of α-casein and bovine serum albumin (BSA) at a molar ratio of 1:10 and skim milk. This efficient and optimized protocol has great potential for enriching multiply-phosphorylated peptides and could be a valuable tool for specific enrichment of phosphopeptides in phosphoproteome analysis. PMID:26298604

  5. Strong thermo-induced single and two-photon green luminescence in self-organized peptide microtubes.

    PubMed

    Semin, S; van Etteger, A; Cattaneo, L; Amdursky, N; Kulyuk, L; Lavrov, S; Sigov, A; Mishina, E; Rosenman, G; Rasing, Th

    2015-03-01

    Diphenylalanine peptide nano- and microtubes formed by self-assembly demonstrate strongly enhanced and tunable single-photon and two-photon luminescence in the visible range, which appears after heat- or laser treatment of these self-organized peptide microtubes. This process significantly extends the functionality of these microstructures and can trigger a new interest in the optical properties of structures based on short peptides. PMID:25074710

  6. Structural transformation of peptide amphiphile self-assembly induced by headgroup charge and size regulation

    NASA Astrophysics Data System (ADS)

    Gao, Changrui; Bedzyk, Michael; Olvera, Monica; Kewalramani, Sumit; Palmer, Liam

    The ability to control the nano and the meso-scale architecture of molecular assemblies is one of the major challenges in nanoscience. Significantly, structural transformations of amphiphilic aggregates induced by variations in environmental conditions have attracted attention due to their biotechnological relevance. Here, we study the assembly in aqueous solution for a modular series of peptide amphiphiles with 3, 2 or 1 lysine groups conjugated to a C16 carbon tail (C16K3, C16K2 and C16K1) . This system design allow us to probe how the equilibrium structure of the self-assembly can be tuned by controlling the coupling between steric (via choice of headgroup: K3, K2, or K1) and electrostatic (via solution pH) interactions. Solution small- and wide-angle X-ray scattering (SAXS/WAXS) and transmission electron microscopy (TEM) studies reveal that depending on pH and number of lysines in the lipid headgroup, amphiphiles can assemble into a range of structures: spherical micelles, bilayer ribbons and vesicles. We also perform detailed phase space mapping of pH-and headgroup size dependency of the structures of assembly over 0.1-100 nm length scales via SAXS/WAXS. The experimental results in conjunction with molecular dynamics (MD) simulations deduce quantitative relations between pH-dependent molecular charges, steric constraints and self-assembly morphologies, which is significant for developing experimental routes to obtain assembly structures with specific nano- and meso-scale features through controlled external stimuli.

  7. Contactless measurements of charge migration within single molecules

    SciTech Connect

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

    2010-06-07

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

  8. Antitumor potential of a synthetic interferon-alpha/PLGF-2 positive charge peptide hybrid molecule in pancreatic cancer cells

    PubMed Central

    Yin, Hongmei; Chen, Naifei; Guo, Rui; Wang, Hong; Li, Wei; Wang, Guanjun; Cui, Jiuwei; Jin, Haofan; Hu, Ji-Fan

    2015-01-01

    Pancreatic cancer is the most aggressive malignant disease, ranking as the fourth leading cause of cancer-related death among men and women in the United States. Interferon alpha (IFNα) has been used to treat pancreatic cancer, but its clinical application has been significantly hindered due to the low antitumor activity. We used a “cDNA in-frame fragment library” screening approach to identify short peptides that potentiate the antitumor activity of interferons. A short positively charged peptide derived from the C-terminus of placental growth factor-2 (PLGF-2) was selected to enhance the activity of IFNα. For this, we constructed a synthetic interferon hybrid molecule (SIFα) by fusing the positively charged PLGF-2 peptide to the C-terminus of the human IFNα. Using human pancreatic cell lines (ASPC and CFPAC1) as a model system, we found that SIFα exhibited a significantly higher activity than did the wild-type IFNα in inhibiting the tumor cell growth. The enhanced activity of the synthetic SIFα was associated with the activation of interferon pathway target genes and the increased binding of cell membrane receptor. This study demonstrates the potential of a synthetic SIFα as a novel antitumor agent. PMID:26584517

  9. Deterministic Electrical Charge-State Initialization of Single Nitrogen-Vacancy Center in Diamond

    NASA Astrophysics Data System (ADS)

    Doi, Y.; Makino, T.; Kato, H.; Takeuchi, D.; Ogura, M.; Okushi, H.; Morishita, H.; Tashima, T.; Miwa, S.; Yamasaki, S.; Neumann, P.; Wrachtrup, J.; Suzuki, Y.; Mizuochi, N.

    2014-01-01

    Apart from applications in classical information-processing devices, the electrical control of atomic defects in solids at room temperature will have a tremendous impact on quantum devices that are based on such defects. In this study, we demonstrate the electrical manipulation of individual prominent representatives of such atomic solid-state defects, namely, the negative charge state of single nitrogen-vacancy defect centers (NV-) in diamond. We experimentally demonstrate, deterministic, purely electrical charge-state initialization of individual NV centers. The NV centers are placed in the intrinsic region of a p-i-n diode structure that facilitates the delivery of charge carriers to the defect for charge-state switching. The charge-state dynamics of a single NV center were investigated by time-resolved measurements and a nondestructive single-shot readout of the charge state. Fast charge-state switching rates (from negative to neutrally charged defects), which are greater than 0.72 ± 0.10 μs-1, were realized. Furthermore, in no-operation mode, the realized charge states were stable for presumably much more than 0.45 s. We believe that the results obtained are useful not only for ultrafast electrical control of qubits, long T2 quantum memory, and quantum sensors associated with single NV centers but also for classical memory devices based on single atomic storage bits working under ambient conditions.

  10. Quantitative analysis of single amino acid variant peptides associated with pancreatic cancer in serum by an isobaric labeling quantitative method.

    PubMed

    Nie, Song; Yin, Haidi; Tan, Zhijing; Anderson, Michelle A; Ruffin, Mack T; Simeone, Diane M; Lubman, David M

    2014-12-01

    Single amino acid variations are highly associated with many human diseases. The direct detection of peptides containing single amino acid variants (SAAVs) derived from nonsynonymous single nucleotide polymorphisms (SNPs) in serum can provide unique opportunities for SAAV associated biomarker discovery. In the present study, an isobaric labeling quantitative strategy was applied to identify and quantify variant peptides in serum samples of pancreatic cancer patients and other benign controls. The largest number of SAAV peptides to date in serum including 96 unique variant peptides were quantified in this quantitative analysis, of which five variant peptides showed a statistically significant difference between pancreatic cancer and other controls (p-value < 0.05). Significant differences in the variant peptide SDNCEDTPEAGYFAVAVVK from serotransferrin were detected between pancreatic cancer and controls, which was further validated by selected reaction monitoring (SRM) analysis. The novel biomarker panel obtained by combining α-1-antichymotrypsin (AACT), Thrombospondin-1 (THBS1) and this variant peptide showed an excellent diagnostic performance in discriminating pancreatic cancer from healthy controls (AUC = 0.98) and chronic pancreatitis (AUC = 0.90). These results suggest that large-scale analysis of SAAV peptides in serum may provide a new direction for biomarker discovery research. PMID:25393578

  11. Linker peptide and affinity tag for detection and purification of single-chain Fv fragments.

    PubMed

    Küttner, Gabriele; Giessmann, Elke; Wessner, Helga; Scholz, Christa; Reinhardt, Dina; Winkler, Karsten; Marx, Uwe; Höhne, Wolfgang

    2004-05-01

    The peptide tag GATPQDLNTML, corresponding to amino acids 46-56 of the human immunodeficiency virus type 1 (HIV-1) capsid protein p24, is the linear epitope of the murine monoclonal antibody CB4-1. This antibody shows high affinity (KD = 1.8 x 10(-8) M) to the free epitope peptide in solution. The original p24 peptide tag and mutant derivatives were fused to the C terminus of a single-chain antibody (scFv) and characterized with respect to sensitivity in Western blot analyses and behavior in purification procedures using affinity chromatography. The p24 tag also proved to be a suitable alternative to the (Gly4Ser)3 linker commonly used to connect single-chain antibody variable regions derived from a heavy (VH) and light chain (VL). Binding of CB4-1 antibody to the p24 tag was not hampered when the tag was located internally in the protein sequence, and the specific antigen affinity of the scFv was only slightly reduced. All scFv variants were solubly expressed in Escherichia coli and could be purified from the periplasm. Our results highlight the p24 tag as a useful tool for purifying and detecting recombinantly expressed scFvs. PMID:15152607

  12. A Surface-Charge Study on Cellular-Uptake Behavior of F3-Peptide-Conjugated Iron Oxide Nanoparticles

    PubMed Central

    Zhang, Yu; Yang, Mo; Park, Ji-Ho; Singelyn, Jennifer; Ma, Huiqing; Sailor, Michael J.; Ruoslahti, Erkki; Ozkan, Mihrimah

    2011-01-01

    Surface-charge measurements of mammalian cells in terms of Zeta potential are demonstrated as a useful biological characteristic in identifying cellular interactions with specific nanomaterials. A theoretical model of the changes in Zeta potential of cells after incubation with nanoparticles is established to predict the possible patterns of Zeta-potential change to reveal the binding and internalization effects. The experimental results show a distinct pattern of Zeta potential change that allows the discrimination of human normal breast epithelial cells (MCF-10A) from human cancer breast epithelial cells (MCF-7) when the cells are incubated with dextran coated iron oxide nanoparticles that contain tumor-homing F3 peptides, where the tumor-homing F3 peptide specifically bound to nucleolin receptors that are overexpressed in cancer breast cells. PMID:19554564

  13. Control of single-electron charging of metallic nanoparticles onto amorphous silicon surface.

    PubMed

    Weis, Martin; Gmucová, Katarína; Nádazdy, Vojtech; Capek, Ignác; Satka, Alexander; Kopáni, Martin; Cirák, Július; Majková, Eva

    2008-11-01

    Sequential single-electron charging of iron oxide nanoparticles encapsulated in oleic acid/oleyl amine envelope and deposited by the Langmuir-Blodgett technique onto Pt electrode covered with undoped hydrogenated amorphous silicon film is reported. Single-electron charging (so-called quantized double-layer charging) of nanoparticles is detected by cyclic voltammetry as current peaks and the charging effect can be switched on/off by the electric field in the surface region induced by the excess of negative/positive charged defect states in the amorphous silicon layer. The particular charge states in amorphous silicon are created by the simultaneous application of a suitable bias voltage and illumination before the measurement. The influence of charged states on the electric field in the surface region is evaluated by the finite element method. The single-electron charging is analyzed by the standard quantized double layer model as well as two weak-link junctions model. Both approaches are in accordance with experiment and confirm single-electron charging by tunnelling process at room temperature. This experiment illustrates the possibility of the creation of a voltage-controlled capacitor for nanotechnology. PMID:19198289

  14. A novel single-domain peptide, anti-LPS factor from prawn: synthesis of peptide, antimicrobial properties and complete molecular characterization.

    PubMed

    Arockiaraj, Jesu; Kumaresan, Venkatesh; Bhatt, Prasanth; Palanisamy, Rajesh; Gnanam, Annie J; Pasupuleti, Mukesh; Kasi, Marimuthu; Chaurasia, Mukesh Kumar

    2014-03-01

    In this study, we reported a complete molecular characterization including bioinformatics features, gene expression, peptide synthesis and its antimicrobial activities of an anti-lipopolysaccharide (LPS) factor (ALF) cDNA identified from the established cDNA library of freshwater prawn Macrobrachium rosenbergii (named as MrALF). The mature protein has an estimated molecular weight of 11.240 kDa with an isoelectric point of 9.46. The bioinformatics analysis showed that the MrALF contains an antimicrobial peptide (AMP) region between T54 and P77 with two conserved cysteine residues (Cys55 and Cys76) which have an anti-parallel β-sheet confirmation. The β-sheet is predicted as cationic with hydrophobic nature containing a net charge of +5. The depicted AMP region is determined to be amphipathic with a predicted hydrophobic face 'FPVFI'. A highest MrALF gene expression was observed in hemocytes and is up-regulated with virus [white spot syndrome baculovirus (WSBV)], bacteria (Aeromonas hydrophila) and Escherichia coli LPS at various time points. The LPS binding region of MrALF peptide was synthesized to study the antimicrobial property, bactericidal efficiency and hemolytic capacity. The peptide showed antimicrobial activity against both the Gram-negative and Gram-positive bacteria. The bactericidal assay showed that the peptide recognized the LPS of bacterial cell walls and binding on its substrate and thereby efficiently distinguishing the pathogens. The hemolytic activity of MrALF peptide is functioning in a concentration dependant manner. In summary, the comprehensive analysis of MrALF showed it to be an effective antimicrobial peptide and thus it plays a crucial role in the defense mechanism of M. rosenbergii. PMID:24269604

  15. Development of Novel Drug and Gene Delivery Carriers Composed of Single-Walled Carbon Nanotubes and Designed Peptides With PEGylation.

    PubMed

    Ohta, Takahisa; Hashida, Yasuhiko; Yamashita, Fumiyoshi; Hashida, Mitsuru

    2016-09-01

    Single-walled carbon nanotubes (SWCNTs) attract great interest in biomedical applications including drug and gene delivery. In this study, we developed a novel delivery system using SWCNTs associated with designed polycationic and amphiphilic peptides. Wrapping of SWCNTs with H-(-Lys-Trp-Lys-Gly-)7-OH [(KWKG)7] resulted in stable dispersion in water, but the composite aggregated in the buffered solution. This dispersion instability was also evident in a cell culture medium with fetal bovine serum. To improve the aqueous dispersibility, the SWCNTs-(KWKG)7 composite was further modified with polyethylene glycol (PEG) at the lysine residues via amide bond formation and the highest modification extent of 13.3% of the amino groups which corresponded to 2 PEG chains in each peptide molecule was achieved with fluorescein isothiocyanate-labeled carboxyl-PEG12. The uptake of the SWCNTs composite by A549 human lung adenocarcinoma epithelial cells was evaluated by visual observation and fluorescence activated cell sorting analysis for SWCNTs wrapped with a mixture of (KWKG)7 with PEGylation and H-(-Cys-Trp-Lys-Gly-)-OH-(KWKG)6 [CWKG(KWKG)6] labeled with fluorescent boron-dipyrromethene tetramethylrhodamine and 7-fold higher uptake comparing with SWCNTs-peptide composite without PEGylation was obtained suggesting the importance of dispersibility in addition to a cationic charge. The superior potential of SWCNTs composites assisted by polycationic and amphiphilic peptides with PEGylation was thus demonstrated. PMID:27179670

  16. Bridging Adhesion of Mussel-Inspired Peptides: Role of Charge, Chain Length, and Surface Type

    PubMed Central

    2015-01-01

    The 3,4-dihydroxyphenylalanine (Dopa)-containing proteins of marine mussels provide attractive design paradigms for engineering synthetic polymers that can serve as high performance wet adhesives and coatings. Although the role of Dopa in promoting adhesion between mussels and various substrates has been carefully studied, the context by which Dopa mediates a bridging or nonbridging macromolecular adhesion to surfaces is not understood. The distinction is an important one both for a mechanistic appreciation of bioadhesion and for an intelligent translation of bioadhesive concepts to engineered systems. On the basis of mussel foot protein-5 (Mfp-5; length 75 res), we designed three short, simplified peptides (15–17 res) and one relatively long peptide (30 res) into which Dopa was enzymatically incorporated. Peptide adhesion was tested using a surface forces apparatus. Our results show that the short peptides are capable of weak bridging adhesion between two mica surfaces, but this adhesion contrasts with that of full length Mfp-5, in that (1) while still dependent on Dopa, electrostatic contributions are much more prominent, and (2) whereas Dopa surface density remains similar in both, peptide adhesion is an order of magnitude weaker (adhesion energy Ead ∼ −0.5 mJ/m2) than full length Mfp-5 adhesion. Between two mica surfaces, the magnitude of bridging adhesion was approximately doubled (Ead ∼ −1 mJ/m2) upon doubling the peptide length. Notably, the short peptides mediate much stronger adhesion (Ead ∼ −3.0 mJ/m2) between mica and gold surfaces, indicating that a long chain length is less important when different interactions are involved on each of the two surfaces. PMID:25540823

  17. On the Static Spacetime of a Single Point Charge

    NASA Astrophysics Data System (ADS)

    Tahvildar-Zadeh, A. Shadi

    Among all electromagnetic theories which (a) are derivable from a Lagrangian, (b) satisfy the dominant energy condition, and (c) in the weak field limit coincide with classical linear electromagnetics, we identify a certain subclass with the property that the corresponding spherically symmetric, asymptotically flat, electrostatic spacetime metric has the mildest possible singularity at its center, namely, a conical singularity on the time axis. The electric field moreover has a point defect on the time axis, its total energy is finite, and is equal to the ADM mass of the spacetime. By an appropriate scaling of the Lagrangian, one can arrange the total mass and total charge of these spacetimes to have any chosen values. For small enough mass-to-charge ratio, these spacetimes have no horizons and no trapped null geodesics. We also prove the uniqueness of these solutions in the spherically symmetric class, and we conclude by performing a qualitative study of the geodesics and test-charge trajectories of these spacetimes.

  18. Proton transfer reactions for improved peptide characterisation.

    PubMed

    Rožman, Marko; Schneider, Andrea; Gaskell, Simon J

    2011-06-01

    The combination of deprotonation (via ion/molecule and ion/ion reactions) and low-energy collision-induced dissociation (CID) has been explored for the enhanced characterisation of tryptic peptides via access to different precursor charge states. This approach allows instant access to fragmentation properties of singly and doubly protonated precursors (arising from the availability of mobile protons) in a single experiment. Considering both charge states extended our base of structurally informative data (in comparison with considering just a single charge state) due to generation of additional sequence ions and by obtaining supplementary structural information derived from selective cleavages. Roughly 37% of combined data sets (CID spectra of doubly and singly charged precursor) showed a greater database identification confidence than each set alone. Moreover, comparison between a number of sequence ions of the singly charged precursor and the doubly charged precursor provided a mean of distinguishing the two classes of tryptic peptides (arginine or lysine containing). PMID:21630380

  19. Charge division using carbon filaments for obtaining coordinate information from detection of single electrons

    SciTech Connect

    Bird, F.; Shapiro, S.; Ashford, V.; McShurley, D.; Reif, R.; Lirth, D.W.G.S.; Williams, S.

    1985-09-01

    Seven micron diameter Carbon filaments forming the anode of a multiwire proportional chamber have been used to detect single electrons. Charge division techniques applied to the 5 cm long wire resulted in a position resolution of sigma/L < 2% for a collected signal charge of 30 fC.

  20. A singly charged ion source for radioactive 11C ion acceleration

    NASA Astrophysics Data System (ADS)

    Katagiri, K.; Noda, A.; Nagatsu, K.; Nakao, M.; Hojo, S.; Muramatsu, M.; Suzuki, K.; Wakui, T.; Noda, K.

    2016-02-01

    A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive 11C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source was found to have favorable performance as a singly charged ion source.

  1. A singly charged ion source for radioactive ¹¹C ion acceleration.

    PubMed

    Katagiri, K; Noda, A; Nagatsu, K; Nakao, M; Hojo, S; Muramatsu, M; Suzuki, K; Wakui, T; Noda, K

    2016-02-01

    A new singly charged ion source using electron impact ionization has been developed to realize an isotope separation on-line system for simultaneous positron emission tomography imaging and heavy-ion cancer therapy using radioactive (11)C ion beams. Low-energy electron beams are used in the electron impact ion source to produce singly charged ions. Ionization efficiency was calculated in order to decide the geometric parameters of the ion source and to determine the required electron emission current for obtaining high ionization efficiency. Based on these considerations, the singly charged ion source was designed and fabricated. In testing, the fabricated ion source was found to have favorable performance as a singly charged ion source. PMID:26932062

  2. Intermolecular charge flux as the origin of infrared intensity enhancement upon halogen-bond formation of the peptide group

    NASA Astrophysics Data System (ADS)

    Torii, Hajime

    2010-07-01

    The changes in the vibrational properties of the peptide group upon formation of O⋯X and N⋯X halogen bonds are studied theoretically. Calculations are carried out for complexes of N-methylacetamide (NMA), a well known model molecule of the peptide group, with halogen-containing molecules. For comparison, calculations are also carried out for some NMA-water hydrogen-bonding complexes. It is shown that the infrared (IR) intensity of the amide I mode of the peptide group is enhanced significantly (up to about 520 km mol-1 or 2.6 times) upon CO⋯X halogen-bond formation, in spite of rather modest magnitudes of the intermolecular electric field and of the changes in the CO bond length and in the amide I vibrational frequency as compared with the cases of the CO⋯H(D) hydrogen bonding. From the analysis of the changes in the dipole derivative and in the electronic structure, it is shown that this IR intensity enhancement arises from the intermolecular charge flux. For the N⋯X halogen bonding complexes, some characteristic changes in the vibrational properties are seen, among which the IR intensity enhancement of the ND out-of-plane wagging mode is most notable. The reason why such large IR intensity enhancements are seen for these particular vibrational modes is examined.

  3. Temperature dependence of charge transport in conjugated single molecule junctions

    NASA Astrophysics Data System (ADS)

    Huisman, Eek; Kamenetska, Masha; Venkataraman, Latha

    2011-03-01

    Over the last decade, the break junction technique using a scanning tunneling microscope geometry has proven to be an important tool to understand electron transport through single molecule junctions. Here, we use this technique to probe transport through junctions at temperatures ranging from 5K to 300K. We study three amine-terminated (-NH2) conjugated molecules: a benzene, a biphenyl and a terphenyl derivative. We find that amine groups bind selectively to undercoordinate gold atoms gold all the way down to 5K, yielding single molecule junctions with well-defined conductances. Furthermore, we find that the conductance of a single molecule junction increases with temperature and we present a mechanism for this temperature dependent transport result. Funded by a Rubicon Grant from The Netherlands Organisation for Scientific Research (NWO) and the NSEC program of NSF under grant # CHE-0641523.

  4. Introducing charge transfer functionality into prebiotically relevant β-sheet peptide fibrils.

    PubMed

    Ivnitski, Denis; Amit, Moran; Rubinov, Boris; Cohen-Luria, Rivka; Ashkenasy, Nurit; Ashkenasy, Gonen

    2014-06-28

    Incorporation of naphthalene diimide moieties as side chains of short amphiphilic peptide results in the formation of fibrils that exhibit substantial intermolecular π-stacking interactions. These interactions can be manipulated without affecting the structure. The new system is suggested as a first step towards functional self-synthesizing materials. PMID:24828820

  5. Single-electron charging effects. Technical progress report

    SciTech Connect

    Ruggiero, S.T.

    1991-12-15

    The status of our project on single-electron tunneling is, again, excellent. As outlined in our original proposal, a key goal for this project has been the development of a scanning tunneling instrument for the purpose of imaging individual particles and tunneling into these particles at high magnetic fields. Further progress is discussed in this report.

  6. Antimicrobial/cytolytic peptides from the venom of the North African scorpion, Androctonus amoreuxi: biochemical and functional characterization of natural peptides and a single site-substituted analog.

    PubMed

    Almaaytah, Ammar; Zhou, Mei; Wang, Lei; Chen, Tianbao; Walker, Brian; Shaw, Chris

    2012-06-01

    The venoms of scorpions are complex cocktails of polypeptide toxins that fall into two structural categories: those that contain cysteinyl residues with associated disulfide bridges and those that do not. As the majority of lethal toxins acting upon ion channels fall into the first category, most research has been focused there. Here we report the identification and structural characterization of two novel 18-mer antimicrobial peptides from the venom of the North African scorpion, Androctonus amoreuxi. Named AamAP1 and AamAP2, both peptides are C-terminally amidated and differ in primary structure at just two sites: Leu-->Pro at position 2 and Phe-->Ile at position 17. Synthetic replicates of both peptides exhibited a broad-spectrum of antimicrobial activity against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli) and a yeast (Candida albicans), at concentrations ranging between 20 μM and 150 μM. In this concentration range, both peptides produced significant degrees of hemolysis. A synthetic replicate of AamAP1 containing a single substitution (His-->Lys) at position 8, generated a peptide (AamAP-S1) with enhanced antimicrobial potency (3-5 μM) against the three test organisms and within this concentration range, hemolytic effects were negligible. In addition, this His-->Lys variant exhibited potent growth inhibitory activity (ID(50) 25-40 μm) against several human cancer cell lines and endothelial cells that was absent in both natural peptides. Natural bioactive peptide libraries, such as those that occur in scorpion venoms, thus constitute a unique source of novel lead compounds with drug development potential whose biological properties can be readily manipulated by simple synthetic chemical means. PMID:22484288

  7. Ion/ion reactions of MALDI-derived peptide ions: increased sequence coverage via covalent and electrostatic modification upon charge inversion.

    PubMed

    Stutzman, John R; McLuckey, Scott A

    2012-12-18

    Atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI)-derived tryptic peptide ions have been subjected to ion/ion reactions with doubly deprotonated 4-formyl-1,3-benzenedisulfonic acid (FBDSA) in the gas-phase. The ion/ion reaction produces a negatively charged electrostatic complex composed of the peptide cation and reagent dianion, whereupon dehydration of the complex via collision-induced dissociation (CID) produces a Schiff base product anion. Collisional activation of modified lysine-terminated tryptic peptide anions is consistent with a covalent modification of unprotonated primary amines (i.e., N-terminus and ε-NH(2) of lysine). Modified arginine-terminated tryptic peptides have shown evidence of a covalent modification at the N-terminus and a noncovalent interaction with the arginine residue. The modified anions yield at least as much sequence information upon CID as the unmodified cations for the small tryptic peptides examined here and more sequence information for the large tryptic peptides. This study represents the first demonstration of gas-phase ion/ion reactions involving MALDI-derived ions. In this case, covalent and electrostatic modification charge inversion is shown to enhance MALDI tandem mass spectrometry of tryptic peptides. PMID:23078018

  8. A Study of Charged Current Single Charged Pion Productions on Carbon in a Few-GeV Neutrino Beam

    SciTech Connect

    Hiraide, Katsuki

    2009-01-01

    Understanding single charged pion production via neutrino-nucleus charged current interaction in the neutrino energy region of a few GeV is essential for future neutrino oscillation experiments since this process is a dominant background for vμ → vx oscillation measurements. There are two contributions to this process: single pion production via baryonic resonance (vμN → μ-+) and coherent pion production interacting with the entire nucleus (vμA → μ-+), where N is nucleon in the nucleus and A is the nucleus. The purpose of the study presented in this thesis is a precise measurement of charged current single charged pion productions, resonant and coherent pion productions, with a good final state separation in the neutrino energy region of a few GeV. In this thesis, we focus on the study of charged current coherent pion production from muon neutrinos scattering on carbon, vμ 12C → μ-12+, in the SciBooNE experiment. This is motivated by the fact that without measuring this component first, the precise determination of resonant pion production cross section can not be achieved since the contribution of coherent pion production in the region of small muon scattering angle is not small. Furthermore, the coherent process is particularly interesting because it is deeply rooted in fundamental physics via Adler's partially conserved axial-vector current theorem. We took data from June 2007 until August 2008, in both the neutrino and antineutrino beam. In total, 2.52 x 1020 protons on target were collected. We have performed a search for charged current coherent pion production by using SciBooNE's full neutrino data set, corresponding to 0.99 x 1020 protons on target. No evidence for coherent pion production is observed. We set 90% confidence level upper limits on the cross section ratio of charged

  9. Large Silver Halide Single Crystals as Charged Particle Track Detectors

    NASA Technical Reports Server (NTRS)

    Kusmiss, J. H.

    1972-01-01

    The trajectory of the particle is made visible under a microscope by the accumulation of metallic silver at regions of the lattice damaged by the particle. This decoration of the particle track is accomplished by exposure of the crystal to light. The decoration of normally present lattice imperfections such as dislocations can be suppressed by the addition to the crystal of less than ten parts per million of a suitable polyvalent metal impurity. An account of some preliminary attempts to grow thin single crystals of AgCl is given also, and suggestions for a more refined technique are offered.

  10. Room-temperature single charge sensitivity in carbon nanotube field-effect transistors

    NASA Astrophysics Data System (ADS)

    Peng, H. B.; Hughes, M. E.; Golovchenko, J. A.

    2006-12-01

    Electrical current fluctuation studies are reported for coaxial p-type and n-type single-wall carbon nanotube field-effect transistors (FETs). Abrupt discrete switching of the source-drain current is observed at room temperature. The authors attribute these random telegraph signals to charge fluctuating electron traps near the FET conduction channels. Evolution of the current-switching behavior associated with the occupancy of individual electron traps is demonstrated and analyzed statistically. The result strongly indicates room temperature single charge sensitivity in carbon nanotube FETs, which may offer potential applications for single molecule sensors based on suitably prepared FET devices.

  11. Dynamical Interactions of 5-Fluorouracil Drug with Dendritic Peptide Vectors: The Impact of Dendrimer Generation, Charge, Counterions, and Structured Water.

    PubMed

    De Luca, Sergio; Seal, Prasenjit; Ouyang, Defang; Parekh, Harendra S; Kannam, Sridhar Kumar; Smith, Sean C

    2016-06-30

    Molecular dynamics simulations are utilized to investigate the interactions between the skin cancer drug 5-fluorouracil (5FU) and peptide-based dendritic carrier systems. We find that these drug-carrier interactions do not conform to the traditional picture of long-time retention of the drug within a hydrophobic core of the dendrimer carrier. Rather, 5FU, which is moderately soluble in its own right, experiences weak, transient chattering interactions all over the dendrimer, mediated through multiple short-lived hydrogen bonding and close contact events. We find that charge on the periphery of the dendrimer actually has a negative effect on the frequency of drug-carrier interactions due to a counterion screening effect that has not previously been observed. However, charge is nevertheless an important feature since neutral dendrimers are shown to have a significant mutual attraction that can lead to clustering or agglomeration. This clustering is prevented due to charge repulsion for the titrated dendrimers, such that they remain independent in solution. PMID:27267604

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

    SciTech Connect

    Denton, M.B.

    1992-07-29

    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.

  13. Ratio of double to single ionization of He by photon and charged particle impact

    SciTech Connect

    Manson, S.T.

    1994-12-31

    The well-known relationship between ionization of atoms by fast charged particles and by photons, the Bethe-Born theory, is applied to the ratio of double ionization to single ionization of He, a process that has been under intense recent scrutiny. It is found that for sufficiently fast charged particles, this ratio for the single differential cross sections, differential in the energy transferred to the atom, {Delta}E, is equal to the photoionization ratio at a photon energy hv = {Delta}E, and this result is unmodified even for ionization by relativistic charged particles. In addition, a relation for the ratio of total charged particle impact ionization cross sections to the photoionization ratio is derived. The results are compared with recent experimental data and various discrepancies are uncovered. Possible sources of these discrepancies are discussed.

  14. Ultrafast charge separation at a polymer-single-walled carbon nanotube molecular junction.

    PubMed

    Stranks, Samuel D; Weisspfennig, Christian; Parkinson, Patrick; Johnston, Michael B; Herz, Laura M; Nicholas, Robin J

    2011-01-12

    We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are individually embedded in the P3HT matrix. PMID:21105722

  15. Detection of single-nucleotide variations by monitoring the blinking of fluorescence induced by charge transfer in DNA.

    PubMed

    Kawai, Kiyohiko; Majima, Tetsuro; Maruyama, Atsushi

    2013-08-19

    Charge transfer dynamics in DNA: Photo-induced charge separation and charge-recombination dynamics in DNA was assessed by monitoring the blinking of fluorescence. Single nucleotide variations, mismatch and one base deletion, were differentiated based on the length of the off-time of the blinking, which corresponds to the lifetime of the charge-separated state. PMID:23846860

  16. Gold plasmonic effects on charge transport through single molecule junctions

    NASA Astrophysics Data System (ADS)

    Adak, Olgun; Venkataraman, Latha

    2014-03-01

    We study the impact of surface plasmon polaritons, the coupling of electromagnetic waves to collective electron oscillations on metal surfaces, on the conductance of single-molecule junctions. We use a scanning-tunneling microscope based break junction setup that is built into an optical microscope to form molecular junctions. Coherent 685nm light is used to illuminate the molecular junctions formed with 4,4'-bipyridine with diffraction limited focusing performance. We employ a lock-in type technique to measure currents induced by light. Furthermore, the thermal expansion due to laser heating is mimicked by mechanically modulating inter-electrode separation. For each junction studied, we measure current, and use AC techniques to determine molecular junction resonance levels and coupling strengths. We use a cross correlations analysis technique to analyze and compare the effect of light to that of the mechanical modulation. Our results show that junction transmission characteristics are not altered under illumination, within the resolution of our instrument. We argue that photo-currents measured with lock-in techniques in these kinds of structures are due to thermal effects. This work was funded by the Center for Re-Defining Photovoltaic Efficiency through Molecule Scale Control, an EFRC funded by the US Department of Energy, Office of Basic Energy Sciences under Contract No. DESC0001085.

  17. Single amino acid variation underlies species-specific sensitivity to amphibian skin-derived opioid-like peptides

    PubMed Central

    Vardy, Eyal; Sassano, Maria F.; Rennekamp, Andrew J.; Kroeze, Wesley K.; Mosier, Philip D.; Westkaemper, Richard B.; Stevens, Craig W.; Katritch, Vsevolod; Stevens, Raymond C.; Peterson, Randel T.; Roth, Bryan L.

    2015-01-01

    It has been suggested that the evolution of vertebrate opioid receptors (ORs) follow a vector of increased functionality. Here we test this idea comparing human and frog ORs. Interestingly, some of the most potent opioid peptides known have been isolated from amphibian skin secretions. Here we show that such peptides (dermorphin and deltorphin) are highly potent in the human receptors and inactive in frog ORs. The molecular basis for the insensitivity of the frog ORs to these peptides was studied using chimeras and molecular modeling. Interestingly, the insensitivity of the delta opioid receptor (DOR) to deltorphin was due to variation of a single amino acid– Trp7.35—which is a leucine in mammalian DORs. Notably, Trp7.35 is completely conserved in all known DOR sequences from lamprey, fish and amphibians. The deltorphin-insensitive phenotype was verified in fish. Our results provide a molecular explanation for the species selectivity of skin-derived opioid peptides. PMID:26091169

  18. Consecutive Charging of a Molecule-on-Insulator Ensemble Using Single Electron Tunnelling Methods.

    PubMed

    Rahe, Philipp; Steele, Ryan P; Williams, Clayton C

    2016-02-10

    We present the local charge state modification at room temperature of small insulator-supported molecular ensembles formed by 1,1'-ferrocenedicarboxylic acid on calcite. Single electron tunnelling between the conducting tip of a noncontact atomic force microscope (NC-AFM) and the molecular islands is observed. By joining NC-AFM with Kelvin probe force microscopy, successive charge build-up in the sample is observed from consecutive experiments. Charge transfer within the islands and structural relaxation of the adsorbate/surface system is suggested by the experimental data. PMID:26713686

  19. High-sensitivity single NV magnetometry by spin-to-charge state mapping

    NASA Astrophysics Data System (ADS)

    Jaskula, Jean-Christophe; Shields, Brendan; Bauch, Erik; Lukin, Mikhail; Walsworth, Ronald; Trifonov, Alexei

    2015-05-01

    Nitrogen-Vacancy (NV) centers in diamond are atom-like quantum system in a solid state matrix whom its structure allows optical readout of the electronic spin. However, the optimal duration of optical readout is limited by a singlet state lifetime making single shot spin readout out of reach. On the other side, the NV center charge state readout can be extremely efficient (up to 99% fidelity) by using excitation at 594 nm. We will present a new method of spin readout utilizing a spin-depending photoionization process to map the electronic spin state of the NV onto the its charge state. Moreover, pre-selection on the charged state allows to minimize data acquisition time. This scheme improves single NV AC magnetometry by a factor of 5 and will benefit other single NV center experiments as well.

  20. Pion single charge exchange in three body nuclei at intermediate energies

    SciTech Connect

    Dowell, M.L.

    1994-01-01

    The purpose of this thesis is to present new experimental information about modifications to the pion-nucleon single charge exchange interaction, {pi}{sup +}n {yields}{pi}{sup 0} p or {pi}{sup {minus}} p {yields} {pi}{sup 0}n, due to the presence of other nucleons. The results of two experimental studies of pion single charge exchange in the three nucleon system near the {triangle}-resonance are presented. Both of these experiments were performed at the Clinton P. Anderson Meson Physics Facility (LAMPF), a division of the Los Alamos National Laboratory. Each explored different aspects of pion single charge exchange in three body nuclei--{sup 3}He and {sup 3}H. Since the nuclear wavefunctions of the three nucleon systems are believed to be well understood, it should be possible to perform theoretical calculations of pion interactions with this system and compare their predictions with the experimental results.

  1. Single Molecule Spectroscopy of Amino Acids and Peptides by Recognition Tunneling

    PubMed Central

    Zhao, Yanan; Ashcroft, Brian; Zhang, Peiming; Liu, Hao; Sen, Suman; Song, Weisi; Im, JongOne; Gyarfas, Brett; Manna, Saikat; Biswas, Sovan; Borges, Chad; Lindsay, Stuart

    2014-01-01

    The human proteome has millions of protein variants due to alternative RNA splicing and post-translational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single molecule protein sequencing is a critical step in the search for protein biomarkers. Here we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules and measuring the electron tunneling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic ‘fingerprints’ associated with each binding motif. With this recognition tunneling technique, we are able to identify D, L enantiomers, a methylated amino acid, isobaric isomers, and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore. PMID:24705512

  2. Single-molecule spectroscopy of amino acids and peptides by recognition tunnelling.

    PubMed

    Zhao, Yanan; Ashcroft, Brian; Zhang, Peiming; Liu, Hao; Sen, Suman; Song, Weisi; Im, JongOne; Gyarfas, Brett; Manna, Saikat; Biswas, Sovan; Borges, Chad; Lindsay, Stuart

    2014-06-01

    The human proteome has millions of protein variants due to alternative RNA splicing and post-translational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single-molecule protein sequencing is a critical step in the search for protein biomarkers. Here, we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules, then measuring the electron tunnelling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic 'fingerprints' associated with each binding motif. With this recognition tunnelling technique, we are able to identify D and L enantiomers, a methylated amino acid, isobaric isomers and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore. PMID:24705512

  3. Single-molecule spectroscopy of amino acids and peptides by recognition tunnelling

    NASA Astrophysics Data System (ADS)

    Zhao, Yanan; Ashcroft, Brian; Zhang, Peiming; Liu, Hao; Sen, Suman; Song, Weisi; Im, Jongone; Gyarfas, Brett; Manna, Saikat; Biswas, Sovan; Borges, Chad; Lindsay, Stuart

    2014-06-01

    The human proteome has millions of protein variants due to alternative RNA splicing and post-translational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single-molecule protein sequencing is a critical step in the search for protein biomarkers. Here, we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules, then measuring the electron tunnelling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic `fingerprints' associated with each binding motif. With this recognition tunnelling technique, we are able to identify D and L enantiomers, a methylated amino acid, isobaric isomers and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore.

  4. A unique charged tyrosine-containing member of the adipokinetic hormone/red-pigment-concentrating hormone peptide family isolated and sequenced from two beetle species.

    PubMed

    Gäde, G

    1991-05-01

    An identical neuropeptide was isolated from the corpora cardiaca of two beetle species, Melolontha melolontha and Geotrupes stercorosus. Its primary structure was determined by pulsed-liquid-phase sequencing employing Edman chemistry after enzymically deblocking the N-terminal pyroglutamate residue. The C-terminus was also blocked, as indicated by the lack of digestion when the peptide was incubated with carboxypeptidase A. The sequence of this peptide, which is designated Mem-CC, is pGlu-Leu-Asn-Tyr-Ser-Pro-Asp-Trp-NH2. It is a new member of the adipokinetic hormone/red-pigment-concentrating hormone (AKH/RPCH) family of peptides with two unusual structural features: it is charged and contains a tyrosine residue at position 4, where all other family members have a phenylalanine residue. Structure-activity studies in the migratory locust (Locusta migratoria) and the American cockroach (Periplaneta americana) revealed that the peptide was poorly active, owing to its structural uniqueness. PMID:2039445

  5. Charge-dependent transport switching of single molecular ions in a weak polyelectrolyte multilayer.

    PubMed

    Tauzin, Lawrence J; Shuang, Bo; Kisley, Lydia; Mansur, Andrea P; Chen, Jixin; de Leon, Al; Advincula, Rigoberto C; Landes, Christy F

    2014-07-22

    The tunable nature of weak polyelectrolyte multilayers makes them ideal candidates for drug loading and delivery, water filtration, and separations, yet the lateral transport of charged molecules in these systems remains largely unexplored at the single molecule level. We report the direct measurement of the charge-dependent, pH-tunable, multimodal interaction of single charged molecules with a weak polyelectrolyte multilayer thin film, a 10 bilayer film of poly(acrylic acid) and poly(allylamine hydrochloride) PAA/PAH. Using fluorescence microscopy and single-molecule tracking, two modes of interaction were detected: (1) adsorption, characterized by the molecule remaining immobilized in a subresolution region and (2) diffusion trajectories characteristic of hopping (D ∼ 10(-9) cm(2)/s). Radius of gyration evolution analysis and comparison with simulated trajectories confirmed the coexistence of the two transport modes in the same single molecule trajectories. A mechanistic explanation for the probe and condition mediated dynamics is proposed based on a combination of electrostatics and a reversible, pH-induced alteration of the nanoscopic structure of the film. Our results are in good agreement with ensemble studies conducted on similar films, confirm a previously-unobserved hopping mechanism for charged molecules in polyelectrolyte multilayers, and demonstrate that single molecule spectroscopy can offer mechanistic insight into the role of electrostatics and nanoscale tunability of transport in weak polyelectrolyte multilayers. PMID:24960617

  6. Charge-Dependent Transport Switching of Single Molecular Ions in a Weak Polyelectrolyte Multilayer

    PubMed Central

    2015-01-01

    The tunable nature of weak polyelectrolyte multilayers makes them ideal candidates for drug loading and delivery, water filtration, and separations, yet the lateral transport of charged molecules in these systems remains largely unexplored at the single molecule level. We report the direct measurement of the charge-dependent, pH-tunable, multimodal interaction of single charged molecules with a weak polyelectrolyte multilayer thin film, a 10 bilayer film of poly(acrylic acid) and poly(allylamine hydrochloride) PAA/PAH. Using fluorescence microscopy and single-molecule tracking, two modes of interaction were detected: (1) adsorption, characterized by the molecule remaining immobilized in a subresolution region and (2) diffusion trajectories characteristic of hopping (D ∼ 10–9 cm2/s). Radius of gyration evolution analysis and comparison with simulated trajectories confirmed the coexistence of the two transport modes in the same single molecule trajectories. A mechanistic explanation for the probe and condition mediated dynamics is proposed based on a combination of electrostatics and a reversible, pH-induced alteration of the nanoscopic structure of the film. Our results are in good agreement with ensemble studies conducted on similar films, confirm a previously-unobserved hopping mechanism for charged molecules in polyelectrolyte multilayers, and demonstrate that single molecule spectroscopy can offer mechanistic insight into the role of electrostatics and nanoscale tunability of transport in weak polyelectrolyte multilayers. PMID:24960617

  7. Potential-energy surfaces for charge exchange between singly charged ions and a LiF surface

    SciTech Connect

    Wirtz, Ludger; Burgdoerfer, Joachim; Dallos, Michal; Mueller, Thomas; Lischka, Hans

    2003-09-01

    We analyze the adiabatic potential-energy surfaces relevant for neutralization of singly charged ions in slow vertical incidence onto a lithium fluoride surface. The surface is represented by a cluster of varying size augmented by point charges of alternating sign in order to include the proper Madelung potential of the ionic crystal. Our calculation proceeds on the multiconfiguration self-consistent-field and multireference configuration-interaction levels. Size-consistency corrections based on the Davidson correction and multireference averaged quadratic coupled cluster methods are included as well. We emphasize the importance of a proper treatment of electron correlation signifying the polarization of the surrounding cluster environment in ab initio calculations of charge transfer at surfaces. From the topology of the surfaces, in particular the existence or absence of avoided crossings (or, more generally, conical intersections), qualitative predictions for the neutralization process can be made. The comparative analysis of potential curves for H{sup +}, C{sup +}, S{sup +}, and Ne{sup +} projectiles provides an explanation for the recently observed threshold behavior for potential sputtering.

  8. Charge transport and photoresponses in a single-stranded DNA/single-walled carbon nanotube composite film

    NASA Astrophysics Data System (ADS)

    Hong, Wonseon; Lee, Eunmo; Kue Park, Jun; Eui Lee, Cheol

    2013-06-01

    Electrical conductivity and photoresponse measurements have been carried out on a single-stranded DNA (ssDNA)/single-walled carbon nanotube (SWNT) composite film in comparison to those of a SWNT film. While the temperature-dependent electrical conductivity of the pristine SWNT film was described well by the combined mechanism of a three-dimensional variable-range hopping and hopping conduction, that of the ssDNA/SWNT composite film followed a fluctuation-induced tunneling model. Besides, competition of photoexcited charge carrier generation and oxygen adsorption/photodesorption in the photoresponses of the films was observed and discussed in view of the role of the DNA wrapping. Thus, the biopolymer coating of the SWNTs is shown to play a significant role in modifying the charge dynamics of the composite system.

  9. Nanojunctions in conducting polypyrrole single nanowire made by focused electron beam: Charge transport characteristics

    SciTech Connect

    Koo, Min Ho; Hong, Young Ki; Park, Dong Hyuk; Jo, Seong Gi; Joo, Jinsoo

    2011-07-15

    A focused electron (E)-beam with various doses was irradiated on the intended positions of conducting polypyrrole (PPy) single nanowire (NW) to fabricate nanojunctions. The current-voltage characteristics and their temperature dependence of the PPy single NW with nanojunctions were measured and analyzed. By increasing the E-beam dose and the number of nanojunctions, the current level of the single NW was dramatically decreased, and the conductance gap became more severe as the temperature decreased. The charge transport behavior varied from three-dimensional variable range hopping to fluctuation induced tunneling models, depending on the dose of focused E-beam. From micro-Raman spectra, the focused E-beam irradiation induced the de-doped states and conformational modification of polymer chains in the nanojunctions. The results suggest that the nanojunctions made by focused E-beam acted as a quasi-potential barrier for charge conduction in the conducting PPy single NW.

  10. Ion Beam Induced Charge Collection (IBICC) microscopy of ICs: Relation to Single Event Upsets (SEU)

    SciTech Connect

    Horn, K.M.; Doyle, B.L.; Sexton, F.W. ); Laird, J.S.; Saint, A.; Cholewa, M.; Legge, G.J.F. . Micro Analytical Research Center )

    1992-01-01

    Single Event Upset (SEU) Imaging is a new diagnostic technique recently developed using Sandia's nuclear microprobe. This technique directly images, with micron resolution, those regions within an integrated circuit which are susceptible to ion-induced malfunctions. Such malfunctions are an increasing threat to space-based systems which make use of current generation IC designs. A complimentary technique to SEU-Imaging involves measurement of the charge collection volumes within integrated circuits; charge collection is the underlying physical process responsible for single event phenomena. This technique, which we term. Ion Beam Induced Charge Collection (IBICC) has been used here and elsewhere to generate micron resolution maps of the charge collection response of integrated circuits. In this paper, we demonstrate the utility of combining the SEU-Imaging and IBICC techniques in order to gain a better understanding of single event upset phenomena. High resolution IBICC images are used to extract more detailed information from charge collection spectra than that obtained from conventional broad-area ion exposures, such as from radioactive sources. Lastly, we will comment on the applications for IBICC as a replacement of Electron Beam Induced Conduction/Current (EBIC) measurements. As reductions in circuit feature size continue in the sub-micron regime, IBICC could certainly prove to be a technologically valuable replacement for EBlC and an important business opportunity for all nuclear microprobe facilities. 12 ref.

  11. Ion Beam Induced Charge Collection (IBICC) microscopy of ICs: Relation to Single Event Upsets (SEU)

    SciTech Connect

    Horn, K.M.; Doyle, B.L.; Sexton, F.W.; Laird, J.S.; Saint, A.; Cholewa, M.; Legge, G.J.F.

    1992-07-01

    Single Event Upset (SEU) Imaging is a new diagnostic technique recently developed using Sandia`s nuclear microprobe. This technique directly images, with micron resolution, those regions within an integrated circuit which are susceptible to ion-induced malfunctions. Such malfunctions are an increasing threat to space-based systems which make use of current generation IC designs. A complimentary technique to SEU-Imaging involves measurement of the charge collection volumes within integrated circuits; charge collection is the underlying physical process responsible for single event phenomena. This technique, which we term. Ion Beam Induced Charge Collection (IBICC) has been used here and elsewhere to generate micron resolution maps of the charge collection response of integrated circuits. In this paper, we demonstrate the utility of combining the SEU-Imaging and IBICC techniques in order to gain a better understanding of single event upset phenomena. High resolution IBICC images are used to extract more detailed information from charge collection spectra than that obtained from conventional broad-area ion exposures, such as from radioactive sources. Lastly, we will comment on the applications for IBICC as a replacement of Electron Beam Induced Conduction/Current (EBIC) measurements. As reductions in circuit feature size continue in the sub-micron regime, IBICC could certainly prove to be a technologically valuable replacement for EBlC and an important business opportunity for all nuclear microprobe facilities. 12 ref.

  12. Impact of a single base pair substitution on the charge transfer rate along short DNA hairpins

    PubMed Central

    Renaud, Nicolas; Berlin, Yuri A.; Ratner, Mark A.

    2013-01-01

    Numerical studies of hole migration along short DNA hairpins were performed with a particular emphasis on the variations of the rate and quantum yield of the charge separation process with the location of a single guanine:cytosine (G:C) base pair. Our calculations show that the hole arrival rate increases as the position of the guanine:cytosine base pair shifts from the beginning to the end of the sequence. Although these results are in agreement with recent experimental findings, the mechanism governing the charge migration along these sequences is revisited here. Instead of the phenomenological two-step hopping mechanism via the guanine base, the charge propagation occurs through a delocalization of the hole density along the base pair stack. Furthermore, the variations of the charge transfer with the position of the guanine base are explained by the impact of the base pair substitutions on the delocalized conduction channels. PMID:23980166

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

    PubMed

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

    2015-03-01

    To develop advanced materials for electronic devices, it is of utmost importance to design organic building blocks with tunable functionality and to study their properties at the molecular level. For organic electronic and photovoltaic applications, the ability to vary the nature of charge carriers and so create either electron donors or acceptors is critical. Here we demonstrate that charge carriers in single-molecule junctions can be tuned within a family of molecules that contain electron-deficient thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed to increase electron affinity and maintain delocalized frontier orbitals while significantly decreasing the transport gap. Through thermopower measurements we show that the dominant charge carriers change from holes to electrons as the number of TDO units is increased. This results in a unique system in which the charge carrier depends on the backbone length, and provides a new means to tune p- and n-type transport in organic materials. PMID:25698329

  14. Characterizing SRAM Single Event Upset in Terms of Single and Double Node Charge Collection

    NASA Technical Reports Server (NTRS)

    Black, J. D.; Ball, D. R., II; Robinson, W. H.; Fleetwood, D. M.; Schrimpf, R. D.; Reed, R. A.; Black, D. A.; Warren, K. M.; Tipton, A. D.; Dodd, P. E.; Haddad, N. F.; Xapsos, M. A.; Kim, H.; Friendlich, M.

    2008-01-01

    A well-collapse source-injection mode for SRAM SEU is demonstrated through TCAD modeling. The recovery of the SRAM s state is shown to be based upon the resistive path from the p+-sources in the SRAM to the well. Multiple cell upset patterns for direct charge collection and the well-collapse source-injection mechanisms are then predicted and compared to recent SRAM test data.

  15. Development of a Charged Particle Microbeam for Targeted and Single Particle Subcellular Irradiation

    SciTech Connect

    Yanch, Jacquelyn C.

    2004-03-12

    The development of a charged particle microbeam for single particle, subcellular irradiations at the Massachusetts Institute of Technology Laboratory for Accelerator Beam Applications (MIT LABA) was initiated under this NEER aeard. The Microbeam apparatus makes use of a pre-existing electrostatic accelerator with a horizontal beam tube.

  16. A tetrastable naphthalenediimide: anion induced charge transfer, single and double electron transfer for combinational logic gates.

    PubMed

    Ajayakumar, M R; Hundal, Geeta; Mukhopadhyay, Pritam

    2013-09-11

    Herein we demonstrate the formation of the first tetrastable naphthalenediimide (NDI, 1a) molecule having multiple distinctly readable outputs. Differential response of 1a to fluoride anions induces intramolecular charge transfer (ICT), single/double electron transfer (SET/DET) leading to a set of combinational logic gates for the first time with a NDI moiety. PMID:23752683

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

    PubMed

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

    2014-05-01

    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 π-π 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 π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility. PMID:24658783

  18. Isolation of Camelid Single-Domain Antibodies Against Native Proteins Using Recombinant Multivalent Peptide Ligands.

    PubMed

    Alturki, Norah A; Henry, Kevin A; MacKenzie, C Roger; Arbabi-Ghahroudi, Mehdi

    2015-01-01

    Generation of antibodies against desired epitopes on folded proteins may be hampered by various characteristics of the target protein, including antigenic and immunogenic dominance of irrelevant epitopes and/or steric occlusion of the desired epitope. In such cases, peptides encompassing linear epitopes of the native protein represent attractive alternative reagents for immunization and screening. Peptide antigens are typically prepared by fusing or conjugating the peptide of interest to a carrier protein. The utility of such antigens depends on many factors including the peptide's amino acid sequence, display valency, display format (synthetic conjugate vs. recombinant fusion) and characteristics of the carrier. Here we provide detailed protocols for: (1) preparation of DNA constructs encoding peptides fused to verotoxin (VT) multimerization domain; (2) expression, purification, and characterization of the multivalent peptide-VT ligands; (3) concurrent panning of a non-immune phage-displayed camelid VHH library against the peptide-VT ligands and native protein; and (4) identification of VHHs enriched via panning using next-generation sequencing techniques. These methods are simple, rapid and can be easily adapted to yield custom peptide-VT ligands that appear to maintain the antigenic structures of the peptide. However, we caution that peptide sequences should be chosen with great care, taking into account structural, immunological, and biophysical information on the protein of interest. PMID:26424272

  19. Single housing during early adolescence causes time-, area- and peptide-specific alterations in endogenous opioids of rat brain

    PubMed Central

    Granholm, L; Roman, E; Nylander, I

    2015-01-01

    BACKGROUND AND PURPOSE A number of experimental procedures require single housing to assess individual behaviour and physiological responses to pharmacological treatments. The endogenous opioids are closely linked to social interaction, especially early in life, and disturbance in the social environment may affect opioid peptides and thereby confound experimental outcome. The aim of the present study was to examine time-dependent effects of single housing on opioid peptides in rats. EXPERIMENTAL APPROACH Early adolescent Sprague Dawley rats (post-natal day 22) were subjected to either prolonged (7 days) or short (30 min) single housing. Several brain regions were dissected and immunoreactive levels of Met-enkephalin-Arg6Phe7 (MEAP), dynorphin B and nociception/orphanin FQ, as well as serum corticosterone were measured using RIA. KEY RESULTS Prolonged single housing reduced immunoreactive MEAP in hypothalamus, cortical regions, amygdala, substantia nigra and periaqueductal grey. Short single housing resulted in an acute stress response as indicated by high levels of corticosterone, accompanied by elevated immunoreactive nociceptin/orphanin FQ in medial prefrontal cortex, nucleus accumbens and amygdala. Neither short nor prolonged single housing affected dynorphin B. CONCLUSIONS AND IMPLICATIONS Disruption in social environmental conditions of rats, through single housing during early adolescence, resulted in time-, area- and peptide-specific alterations in endogenous opioids in the brain. These results provide further evidence for an association between early life social environment and opioids. Furthermore, the results have implications for experimental design; in any pharmacological study involving opioid peptides, it is important to distinguish between effects induced by housing and treatment. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http

  20. Single-Molecule Protein Folding: A Study of the Surface-Mediated Conformational Dynamics of a Model Amphipathic Peptide

    NASA Astrophysics Data System (ADS)

    Cunningham, Joy; English, Douglas

    2004-03-01

    Most surface-active polypeptides, composed of 10-50 amino acids, are devoid of well-defined tertiary structure. The conformation of these proteins is greatly dependent upon their environment and may assume totally different characteristics in an aqueous environment, in a detergent micelle, or in an organic solvent. Most antimicrobial peptides are helix-forming and are activated upon interaction with a membrane-mimicking environment. We are seeking to physically characterize the mechanism of membrane-peptide interaction through studying a simple model peptide, MT-1. MT-1 was designed as a nonhomologous analogue of melittin, the principle component in bee venom. We are using single molecule spectroscopy to examine the induction of secondary structure upon interaction of MT-1 with various membrane-mimicking interfaces. Specifically, we monitor coil-to-helix transition through single molecule fluorescence resonance energy transfer (sm-FRET) to determine conformational distributions of folded and unfolded peptides at an interface. Studies with MT-1 will focus upon the biologically relevant issues of orientation, aggregation, and folding at surfaces using both ensemble and single molecule experiments.

  1. An instrument for charge measurement due to a single collision between two spherical particles

    NASA Astrophysics Data System (ADS)

    Xie, L.; Bao, N.; Jiang, Y.; Han, K.; Zhou, J.

    2016-01-01

    It universally exists in moving particular systems that particles can be electrified, in which the particles are chemically identical, just as toner particles, coal dust, and pharmaceutical powders. However, owing to the limit of experimental instruments, so far, there are yet no experiments to illustrate whether a particle can be electrified due to a single collision between two spherical particles, and there are also no experiments to measure the charge carried by a single particle due to a single collision between two particles. So we have developed an instrument for charge measurement due to a single collision between two spheres. The instrument consists of two-sphere collision device, collision charge measurement apparatus, and particles' trajectory tracking system. By using this instrument, we can investigate the collision contact electrification due to a single collision between two spheres and simultaneously record the moving trajectories of spheres after the collision to calculate the rebound angles to identify the contribution of the triboelectrification due to the rubbing between the contact surfaces and the collision contact electrification due to the normal pressure between the contact surfaces.

  2. An instrument for charge measurement due to a single collision between two spherical particles.

    PubMed

    Xie, L; Bao, N; Jiang, Y; Han, K; Zhou, J

    2016-01-01

    It universally exists in moving particular systems that particles can be electrified, in which the particles are chemically identical, just as toner particles, coal dust, and pharmaceutical powders. However, owing to the limit of experimental instruments, so far, there are yet no experiments to illustrate whether a particle can be electrified due to a single collision between two spherical particles, and there are also no experiments to measure the charge carried by a single particle due to a single collision between two particles. So we have developed an instrument for charge measurement due to a single collision between two spheres. The instrument consists of two-sphere collision device, collision charge measurement apparatus, and particles' trajectory tracking system. By using this instrument, we can investigate the collision contact electrification due to a single collision between two spheres and simultaneously record the moving trajectories of spheres after the collision to calculate the rebound angles to identify the contribution of the triboelectrification due to the rubbing between the contact surfaces and the collision contact electrification due to the normal pressure between the contact surfaces. PMID:26827339

  3. Formation of peptides from amino acids by single or multiple additions of ATP to suspensions of nucleoproteinoid microparticles

    NASA Technical Reports Server (NTRS)

    Nakashima, T.; Fox, S. W.

    1981-01-01

    The synthesis of peptides from individual amino acids or pairs of amino acids and ATP in the presence of catalysis by nucleoproteinoid microparticles is investigated. Experiments were performed with suspensions formed from the condensation of lysine-rich and acidic proteinoids with polyadenylic acid, to which were added glycine, phenylalanine, proline, lysine or glycine-phenylalanine mixtures, and ATP either at once or serially. Peptide yields are found to be greatest for equal amounts of acidic and basic proteinoids. The addition of imidazole is found to alter the preference of glycine-phenylalanine mixtures to form mixed heteropeptides rather than homopeptides. A rapid ATP decay in the peptide synthesis reaction is observed, and a greater yield is obtained for repeated small additions than for a single addition of ATP. The experimental system has properties similar to modern cells, and represents an organizational unit ready for the evolution of associated biochemical pathways.

  4. Gating of single molecule junction conductance by charge transfer complex formation

    NASA Astrophysics Data System (ADS)

    Vezzoli, Andrea; Grace, Iain; Brooke, Carly; Wang, Kun; Lambert, Colin J.; Xu, Bingqian; Nichols, Richard J.; Higgins, Simon J.

    2015-11-01

    The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference.The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference. Electronic supplementary information (ESI) available: Synthesis of 1c; experimental details of conductance measurements, formation of charge transfer complexes of 1c and 2 in solution; further details of theoretical methods. See DOI: 10.1039/c5nr04420k

  5. Observability of Charged Higgs Contribution in t-channel Single Top at LHC

    NASA Astrophysics Data System (ADS)

    Hashemi, Majid; Zebarjad, Seyyed Mohammad; Bakhshalizadeh, Hossein

    2016-05-01

    In this paper, the charged Higgs contribution in t-channel single top production is studied. The production process is a t-channel single top event with charged Higgs exchange. Therefore the signal is similar with Standard Model single top production in terms of the final state. In the first step, the signal cross section is calculated and compared to the other main production processes which are used for a heavy charged Higgs search at LHC, i.e., pp→ tbar {b}H- and pp→ H+ → tbar {b}. In the next step, an event generation and analysis is applied on signal and background events, in order to estimate the signal significance. The signal cross section is typically smaller than the associated production (tbar {b}H-) and resonance production (tbar {b}) by a factor of 10-3 and ranges from 10 f b to 1 f b for charged Higgs mass from 200 to 500 GeV at tan β = 50. Due to the small cross section of signal events and large SM background, the signal significance is small even after a dedicated kinematic analysis and selection of events, however, tan β values above 120 can be excluded at an integrated luminosity of 3000 f b -1.

  6. Impact of charge carrier injection on single-chain photophysics of conjugated polymers

    NASA Astrophysics Data System (ADS)

    Hofmann, Felix J.; Vogelsang, Jan; Lupton, John M.

    2016-06-01

    Charges in conjugated polymer materials have a strong impact on the photophysics and their interaction with the primary excited state species has to be taken into account in understanding device properties. Here, we employ single-molecule spectroscopy to unravel the influence of charges on several photoluminescence (PL) observables. The charges are injected either stochastically by a photochemical process or deterministically in a hole-injection sandwich device configuration. We find that upon charge injection, besides a blue-shift of the PL emission and a shortening of the PL lifetime due to quenching and blocking of the lowest-energy chromophores, the non-classical photon arrival time distribution of the multichromophoric chain is modified towards a more classical distribution. Surprisingly, the fidelity of photon antibunching deteriorates upon charging, whereas one would actually expect the opposite: the number of chromophores to be reduced. A qualitative model is presented to explain the observed PL changes. The results are of interest to developing a microscopic understanding of the intrinsic charge-exciton quenching interaction in devices.

  7. Photovoltaic effect and charge storage in single ZnO nanowires

    SciTech Connect

    Liao Zhimin; Xu Jun; Zhang Jingmin; Yu Dapeng

    2008-07-14

    Asymmetric Schottky barriers between ZnO nanowire and metal electrode have been fabricated at the two ends of the nanowire. An obvious photocurrent generated from the device at zero voltage bias can be switched on/off with quick response by controlling the light irradiation. Moreover, the device can still afford a current at zero bias after switching off light illumination, which is ascribed to the charge storage effect in single ZnO nanowires. The underlying mechanisms related to the photovoltaic effect and charge storage were discussed.

  8. Floating gate memory with charge storage dots array formed by Dps protein modified with site-specific binding peptides

    NASA Astrophysics Data System (ADS)

    Kamitake, Hiroki; Uenuma, Mutsunori; Okamoto, Naofumi; Horita, Masahiro; Ishikawa, Yasuaki; Yamashita, Ichro; Uraoka, Yukiharu

    2015-05-01

    We report a nanodot (ND) floating gate memory (NFGM) with a high-density ND array formed by a biological nano process. We utilized two kinds of cage-shaped proteins displaying SiO2 binding peptide (minTBP-1) on their outer surfaces: ferritin and Dps, which accommodate cobalt oxide NDs in their cavities. The diameters of the cobalt NDs were regulated by the cavity sizes of the proteins. Because minTBP-1 is strongly adsorbed on the SiO2 surface, high-density cobalt oxide ND arrays were obtained by a simple spin coating process. The densities of cobalt oxide ND arrays based on ferritin and Dps were 6.8 × 1011 dots cm-2 and 1.2 × 1012 dots cm-2, respectively. After selective protein elimination and embedding in a metal-oxide-semiconductor (MOS) capacitor, the charge capacities of both ND arrays were evaluated by measuring their C-V characteristics. The MOS capacitor embedded with the Dps ND array showed a wider memory window than the device embedded with the ferritin ND array. Finally, we fabricated an NFGM with a high-density ND array based on Dps, and confirmed its competent writing/erasing characteristics and long retention time.

  9. Energy and charge state dependences of transfer ionization to single capture ratio for fast multiply charged ions on helium

    NASA Astrophysics Data System (ADS)

    Unal, Ridvan

    The charge state and energy dependences of Transfer Ionization (TI) and Single Capture (SC) processes in collisions of multiply charged ions with He from intermediate to high velocities are investigated using coincident recoil ion momentum spectroscopy. The collision chamber is commissioned on the 15-degree port of a switching magnet, which allows the delivery of a beam with very little impurity. The target was provided from a supersonic He jet with a two-stage collimation. The two-stage, geometrically cooled, supersonic He jet has significantly reduced background contribution to the spectrum compared to a single stage He jet. In the case of a differentially pumped gas cell complex calculations based on assumptions for the correction due to the collisions with the contaminant beam led to corrections, which were up to 50%. The new setup allows one to make a direct separation of contaminant processes in the experimental data using the longitudinal momentum spectra. Furthermore, this correction is much smaller (about 8.8%) yielding better overall precision. The collision systems reported here are 1 MeV/u O(4--8)+ , 0.5--2.5 MeV/u F(4--9)+, 2.0 MeV/u Ti 15,17,18+, 1.6--1.75 MeV/u Cu18,20+ and 0.25--0.5 MeV/u I(15--25)+ ions interacting with helium. We have determined the sTIsSC ratio for high velocity highly charged ions on He at velocities in the range of 6 to 10 au and observed that the ratio is monotonically decreasing with velocity. Furthermore, we see a ratio that follows a q2 dependence up to approximately q = 9. Above q = 9 the experimental values exceed the q2 dependence prediction due to antiscreening. C. D. Lin and H. C. Tseng have performed coupled channel calculations for the energy dependence of TI and SC for F9+ + He and find values slightly higher than our measured values, but with approximately the same energy dependence. The new data, Si, Ti and Cu, go up only to q = 20 and show a smooth monotonically increasing TI/SC ratio. The TI/SC ratio for I (15

  10. Baculovirus display of single chain antibody (scFv) using a novel signal peptide

    PubMed Central

    2010-01-01

    Background Cells permissive to virus can become refractory to viral replication upon intracellular expression of single chain fragment variable (scFv) antibodies directed towards viral structural or regulatory proteins, or virus-coded enzymes. For example, an intrabody derived from MH-SVM33, a monoclonal antibody against a conserved C-terminal epitope of the HIV-1 matrix protein (MAp17), was found to exert an inhibitory effect on HIV-1 replication. Results Two versions of MH-SVM33-derived scFv were constructed in recombinant baculoviruses (BVs) and expressed in BV-infected Sf9 cells, N-myristoylation-competent scFvG2/p17 and N-myristoylation-incompetent scFvE2/p17 protein, both carrying a C-terminal HA tag. ScFvG2/p17 expression resulted in an insoluble, membrane-associated protein, whereas scFvE2/p17 was recovered in both soluble and membrane-incorporated forms. When coexpressed with the HIV-1 Pr55Gag precursor, scFvG2/p17 and scFvE2/p17 did not show any detectable negative effect on virus-like particle (VLP) assembly and egress, and both failed to be encapsidated in VLP. However, soluble scFvE2/p17 isolated from Sf9 cell lysates was capable of binding to its specific antigen, in the form of a synthetic p17 peptide or as Gag polyprotein-embedded epitope. Significant amounts of scFvE2/p17 were released in the extracellular medium of BV-infected cells in high-molecular weight, pelletable form. This particulate form corresponded to BV particles displaying scFvE2/p17 molecules, inserted into the BV envelope via the scFv N-terminal region. The BV-displayed scFvE2/p17 molecules were found to be immunologically functional, as they reacted with the C-terminal epitope of MAp17. Fusion of the N-terminal 18 amino acid residues from the scFvE2/p17 sequence (N18E2) to another scFv recognizing CD147 (scFv-M6-1B9) conferred the property of BV-display to the resulting chimeric scFv-N18E2/M6. Conclusion Expression of scFvE2/p17 in insect cells using a BV vector resulted in

  11. Charge noise, spin-orbit coupling, and dephasing of single-spin qubits

    SciTech Connect

    Bermeister, Adam; Keith, Daniel; Culcer, Dimitrie

    2014-11-10

    Quantum dot quantum computing architectures rely on systems in which inversion symmetry is broken, and spin-orbit coupling is present, causing even single-spin qubits to be susceptible to charge noise. We derive an effective Hamiltonian for the combined action of noise and spin-orbit coupling on a single-spin qubit, identify the mechanisms behind dephasing, and estimate the free induction decay dephasing times T{sub 2}{sup *} for common materials such as Si and GaAs. Dephasing is driven by noise matrix elements that cause relative fluctuations between orbital levels, which are dominated by screened whole charge defects and unscreened dipole defects in the substrate. Dephasing times T{sub 2}{sup *} differ markedly between materials and can be enhanced by increasing gate fields, choosing materials with weak spin-orbit, making dots narrower, or using accumulation dots.

  12. A sensitive charge scanning probe based on silicon single electron transistor

    NASA Astrophysics Data System (ADS)

    Lina, Su; Xinxing, Li; Hua, Qin; Xiaofeng, Gu

    2016-04-01

    Single electron transistors (SETs) are known to be extremely sensitive electrometers owing to their high charge sensitivity. In this work, we report the design, fabrication, and characterization of a silicon-on-insulator-based SET scanning probe. The fabricated SET is located about 10 μm away from the probe tip. The SET with a quantum dot of about 70 nm in diameter exhibits an obvious Coulomb blockade effect measured at 4.1 K. The Coulomb blockade energy is about 18 meV, and the charge sensitivity is in the order of 10‑5‑10‑3 e/Hz1/2. This SET scanning probe can be used to map charge distribution and sense dynamic charge fluctuation in nanodevices or circuits under test, realizing high sensitivity and high spatial resolution charge detection. Project supported by the Instrument Developing Project of the Chinese Academy of Sciences (No. YZ201152), the National Natural Science Foundation of China (No. 11403084), the Fundamental Research Funds for Central Universities (Nos. JUSRP51510, JUDCF12032), and the Graduate Student Innovation Program for Universities of Jiangsu Province (No. CXLX12_0724).

  13. Charge Carrier Lifetimes Exceeding 15 μs in Methylammonium Lead Iodide Single Crystals.

    PubMed

    Bi, Yu; Hutter, Eline M; Fang, Yanjun; Dong, Qingfeng; Huang, Jinsong; Savenije, Tom J

    2016-03-01

    The charge carrier lifetime in organic-inorganic perovskites is one of the most important parameters for modeling and design of solar cells and other types of devices. In this work, we use CH3NH3PbI3 single crystal as a model system to study optical absorption, charge carrier generation, and recombination lifetimes. We show that commonly applied photoluminescence lifetime measurements may dramatically underestimate the intrinsic carrier lifetime in CH3NH3PbI3, which could be due to severe charge recombination at the crystal surface and/or fast electron-hole recombination close to the surface. By using the time-resolved microwave conductivity technique, we investigated the lifetime of free mobile charges inside the crystals. Most importantly, we find that for homogeneous excitation throughout the crystal, the charge carrier lifetime exceeds 15 μs. This means that the diffusion length in CH3NH3PbI3 can be as large as 50 μm if it is no longer limited by the dimensions of the crystallites. PMID:26901658

  14. Charging and discharging of single colloidal particles at oil/water interfaces

    NASA Astrophysics Data System (ADS)

    Gao, Peng; Xing, Xiaochen; Li, Ye; Ngai, To; Jin, Fan

    2014-05-01

    The physical behavior of solid colloids trapped at a fluid-fluid interface remains in itself an open fundamental issue. Here, we show that the gradients of surface tension can induce particles to jet towards the oil/water interface with velocities as high as ~ 60 mm/s when particle suspensions come in contact with the interface. We hypothesize that rubbing between the particles and oil lead to the spontaneous accumulation of negative charges on the hemisphere of those interfacial particles that contact the oil phase by means of triboelectrification. The charging process is highly dependent on the sliding distances, and gives rise to long-ranged repulsions that protect interfacial particles from coagulating at the interface by the presence of electrolyte. These triboelectric charges, however, are compensated within several hours, which affect the stability of interfacial particles. Importantly, by charging different kinds of colloidal particles using various spreading solvents and dispersion methods, we have demonstrated that charging and discharging of single colloidal particles at oil/water interfaces impacts a broad range of dynamical behavior.

  15. Charging and discharging of single colloidal particles at oil/water interfaces

    PubMed Central

    Gao, Peng; Xing, XiaoChen; Li, Ye; Ngai, To; Jin, Fan

    2014-01-01

    The physical behavior of solid colloids trapped at a fluid-fluid interface remains in itself an open fundamental issue. Here, we show that the gradients of surface tension can induce particles to jet towards the oil/water interface with velocities as high as ≈ 60 mm/s when particle suspensions come in contact with the interface. We hypothesize that rubbing between the particles and oil lead to the spontaneous accumulation of negative charges on the hemisphere of those interfacial particles that contact the oil phase by means of triboelectrification. The charging process is highly dependent on the sliding distances, and gives rise to long-ranged repulsions that protect interfacial particles from coagulating at the interface by the presence of electrolyte. These triboelectric charges, however, are compensated within several hours, which affect the stability of interfacial particles. Importantly, by charging different kinds of colloidal particles using various spreading solvents and dispersion methods, we have demonstrated that charging and discharging of single colloidal particles at oil/water interfaces impacts a broad range of dynamical behavior. PMID:24786477

  16. Spectroscopy of Charge Carriers and Traps in Field-Doped Single Crystal Organic Semiconductors

    SciTech Connect

    Zhu, Xiaoyang

    2014-12-10

    The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering. Organic semiconductors are emerging as viable materials for low-cost electronics and optoelectronics, such as organic photovoltaics (OPV), organic field effect transistors (OFETs), and organic light emitting diodes (OLEDs). Despite extensive studies spanning many decades, a clear understanding of the nature of charge carriers in organic semiconductors is still lacking. It is generally appreciated that polaron formation and charge carrier trapping are two hallmarks associated with electrical transport in organic semiconductors; the former results from the low dielectric constants and weak intermolecular electronic overlap while the latter can be attributed to the prevalence of structural disorder. These properties have lead to the common observation of low charge carrier mobilities, e.g., in the range of 10-5 - 10-3 cm2/Vs, particularly at low carrier concentrations. However, there is also growing evidence that charge carrier mobility approaching those of inorganic semiconductors and metals can exist in some crystalline organic semiconductors, such as pentacene, tetracene and rubrene. A particularly striking example is single crystal rubrene (Figure 1), in which hole mobilities well above 10 cm2/Vs have been observed in OFETs operating at room temperature. Temperature dependent transport and spectroscopic measurements both revealed evidence of free carriers in rubrene. Outstanding questions are: what are the structural features and physical properties that make rubrene so unique? How do we establish fundamental design principles for the development of other organic semiconductors of high mobility? These questions are critically important but not comprehensive, as the nature of

  17. Single-charge transport in ambipolar silicon nanoscale field-effect transistors

    SciTech Connect

    Mueller, Filipp; Konstantaras, Georgios; Wiel, Wilfred G. van der; Zwanenburg, Floris A.

    2015-04-27

    We report single-charge transport in ambipolar nanoscale MOSFETs, electrostatically defined in near-intrinsic silicon. We use the ambipolarity to demonstrate the confinement of either a few electrons or a few holes in exactly the same crystalline environment underneath a gate electrode. We find similar electron and hole quantum dot properties while the mobilities differ quantitatively like in microscale devices. The understanding and control of individual electrons and holes are essential for spin-based quantum information processing.

  18. Peptide-coated semiconductor quantum dots and their applications in biological imaging of single molecules in live cells and organisms

    NASA Astrophysics Data System (ADS)

    Pinaud, Fabien Florent

    2007-12-01

    A new surface chemistry has been developed for the solubilization and biofunctionalization of inorganic semiconductor nanocrystals fluorescent probes, also known as quantum dots. This chemistry is based on the surface coating of quantum dots with custom-designed polycysteine peptides and yields water-soluble, small, monodispersed and colloidally stable probes that remain bright and photostable in complex biological milieus. This peptide coating strategy was successfully tested on several types of core and core-shell quantum dots emitting from the visible (e.g. CdSe/ZnS) to the NIR spectrum range (e.g. CdTe/CdSe/ZnS). By taking advantage of the versatile physico-chemical properties of peptides, a peptide "toolkit" was designed and employed to impart several biological functions to individual quantum dots and control their biochemical activity at the nanometer scale. These biofunctionalized peptide-coated quantum dots were exploited in very diverse biological applications. Near-infrared emitting quantum dot probes were engineered with optimized blood circulation and biodistribution properties for in vivo animal imaging. Visible emitting quantum dots were used for single molecule tracking of raft-associated GPI-anchored proteins in live cells. This last application revealed the presence of discrete and non-caveolar lipid microdomains capable of impeding free lateral diffusions in the plasma membrane of Hela cells. Imaging and tracking of peptide-coated quantum dots provided the first direct evidence that microdomains having the composition and behavior expected for lipid rafts can induce molecular compartmentalization in the membrane of living cells.

  19. Pulsed nuclear pumping and spin diffusion in a single charged quantum dot.

    PubMed

    Ladd, Thaddeus D; Press, David; De Greve, Kristiaan; McMahon, Peter L; Friess, Benedikt; Schneider, Christian; Kamp, Martin; Höfling, Sven; Forchel, Alfred; Yamamoto, Yoshihisa

    2010-09-01

    We report the observation of a feedback process between the nuclear spins in a single charged quantum dot under coherently pulsed optical excitation and its trion transition. The optical pulse sequence intersperses resonant narrow-band pumping for spin initialization with off-resonant ultrafast pulses for coherent electron-spin rotation. A hysteretic sawtooth pattern in the free-induction decay of the single electron spin is observed; a mathematical model indicates a competition between optical nuclear pumping and nuclear spin-diffusion. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations. PMID:20867546

  20. Modeling and analysis of single-event transients in charge pumps

    NASA Astrophysics Data System (ADS)

    Zhenyu, Zhao; Junfeng, Li; Minxuan, Zhang; Shaoqing, Li

    2009-05-01

    It has been shown that charge pumps (CPs) dominate single-event transient (SET) responses of phase-locked loops (PLLs). Using a pulse to represent a single event hit on CPs, the SET analysis model is established and the characteristics of SET generation and propagation in PLLs are revealed. An analysis of single event transients in PLLs demonstrates that the settling time of the voltage-controlled oscillators (VCOs) control voltage after a single event strike is strongly dependent on the peak control voltage deviation, the SET pulse width, and the settling time constant. And the peak control voltage disturbance decreases with the SET strength or the filter resistance. Furthermore, the analysis in the proposed PLL model is confirmed by simulation results using MATLAB and HSPICE, respectively.

  1. Charge transfer at junctions of a single layer of graphene and a metallic single walled carbon nanotube.

    PubMed

    Paulus, Geraldine L C; Wang, Qing Hua; Ulissi, Zachary W; McNicholas, Thomas P; Vijayaraghavan, Aravind; Shih, Chih-Jen; Jin, Zhong; Strano, Michael S

    2013-06-10

    Junctions between a single walled carbon nanotube (SWNT) and a monolayer of graphene are fabricated and studied for the first time. A single layer graphene (SLG) sheet grown by chemical vapor deposition (CVD) is transferred onto a SiO₂/Si wafer with aligned CVD-grown SWNTs. Raman spectroscopy is used to identify metallic-SWNT/SLG junctions, and a method for spectroscopic deconvolution of the overlapping G peaks of the SWNT and the SLG is reported, making use of the polarization dependence of the SWNT. A comparison of the Raman peak positions and intensities of the individual SWNT and graphene to those of the SWNT-graphene junction indicates an electron transfer of 1.12 × 10¹³ cm⁻² from the SWNT to the graphene. This direction of charge transfer is in agreement with the work functions of the SWNT and graphene. The compression of the SWNT by the graphene increases the broadening of the radial breathing mode (RBM) peak from 3.6 ± 0.3 to 4.6 ± 0.5 cm⁻¹ and of the G peak from 13 ± 1 to 18 ± 1 cm⁻¹, in reasonable agreement with molecular dynamics simulations. However, the RBM and G peak position shifts are primarily due to charge transfer with minimal contributions from strain. With this method, the ability to dope graphene with nanometer resolution is demonstrated. PMID:23281165

  2. Single residue deletions along the length of the influenza HA fusion peptide lead to inhibition of membrane fusion function

    SciTech Connect

    Langley, William A.; Thoennes, Sudha; Bradley, Konrad C.; Galloway, Summer E.; Talekar, Ganesh R.; Cummings, Sandra F.; Vareckova, Eva; Russell, Rupert J.; Steinhauer, David A.

    2009-11-25

    A panel of eight single amino acid deletion mutants was generated within the first 24 residues of the fusion peptide domain of the of the hemagglutinin (HA) of A/Aichi/2/68 influenza A virus (H3N2 subtype). The mutant HAs were analyzed for folding, cell surface transport, cleavage activation, capacity to undergo acid-induced conformational changes, and membrane fusion activity. We found that the mutant DELTAF24, at the C-terminal end of the fusion peptide, was expressed in a non-native conformation, whereas all other deletion mutants were transported to the cell surface and could be cleaved into HA1 and HA2 to activate membrane fusion potential. Furthermore, upon acidification these cleaved HAs were able to undergo the characteristic structural rearrangements that are required for fusion. Despite this, all mutants were inhibited for fusion activity based on two separate assays. The results indicate that the mutant fusion peptide domains associate with target membranes in a non-functional fashion, and suggest that structural features along the length of the fusion peptide are likely to be relevant for optimal membrane fusion activity.

  3. Photogenerated charges and surface potential variations investigated on single Si nanorods by electrostatic force microscopy combined with laser irradiation

    PubMed Central

    2014-01-01

    Photogenerated charging properties of single Si nanorods (Si NRs) are investigated by electrostatic force microscopy (EFM) combined with laser irradiation. Under laser irradiation, Si NRs are positively charged. The amount of the charges trapped in single NRs as well as the contact potential difference between the tip and NRs' surface is achieved from an analytical fitting of the phase shift - voltage curve. Both of them significantly vary with the laser intensity and the NR's size and construction. The photogenerated charging and decharging rates are obtained at a timescale of seconds or slower, indicating that the Si NRs are promising candidates in photovoltaic applications. PMID:24940176

  4. Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

    SciTech Connect

    Pan, Shanlin

    2014-11-16

    Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an

  5. Charge states of medium energy He ions scattered from single and poly-crystal surfaces

    NASA Astrophysics Data System (ADS)

    Okazawa, T.; Shibuya, K.; Nishimura, T.; Kido, Y.

    2007-03-01

    High-resolution medium energy ion scattering (MEIS) spectroscopy has unveiled fine structures of surfaces and interfaces. However, problematic issues arise due to its excellent energy resolution. In particular, when one uses He+ beams, the He+ fraction η+ (1) for the scattering component from top-layer atoms is frequently non-equilibrated owing to short exit path length. This leads to significant uncertainties of the absolute amount of atoms located on top of a surface. To overcome this difficulty, it is essential to acquire reliable data of equilibrium and non-equilibrium charge fractions and also to model the charge exchange process based on a simple picture. In this paper, we analyze the MEIS spectra from single and poly crystals of Si, Ni and Cu together with c-axis oriented graphite and derive electron capture (σ10) and loss (σ01) cross sections dependent on emerging ion velocity. Here, we assume that a He ion when arrives at a Maffin-tin sphere after a large angle collision takes the He+ state and then undergoes many charge exchanging collisions with valence electrons until leaving an electronic surface. The velocity dependent σ10 and σ01 values derived well reproduce equilibrium and non-equilibrium charge fractions of He+ except for graphite and poly-crystal Si at relatively large emerging angles. Such a deviation comes from the markedly anisotropic distributions of the valence electrons of Si and graphite with strong covalent bonds.

  6. Gate-tuned spin to charge conversion in semiconducting single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Shigematsu, Ei; Nagano, Hiroshi; Dushenko, Sergey; Ando, Yuichiro; Tsuda, Tetsuya; Kuwabata, Susumu; Takenobu, Taishi; Tanaka, Takeshi; Kataura, Hiromichi; Shinjo, Teruya; Shiraishi, Masashi

    Interconversion of spin and charge current is a hot topic in the molecular spintronics. It was achieved for the first time in a conducting conjugated polymer 1, and shortly followed by spin-charge conversion in graphene. However, control over carrier type has not been shown yet. In this study we focused on single-walled carbon nanotubes (SWNT). Spin injection into semiconductor from metal ferromagnet is challenging due to the presence of Schottky barrier and conductance mismatch problem. To bypass it, we used ionic liquid electric gate and ferrimagnetic insulator. We prepared SWNT layer on top of ferrimagnetic yttrium iron garnet substrate. Using spin pumping we successfully observed spin-charge conversion in metallic SWNT. As for a semiconducting SWNT, we applied a top gate using ionic liquid. The drain-source current vs. gate voltage dependence showed tuning of the Fermi level and changing of carrier type. Under gate voltage application we measured electromotive force induced by spin pumping. Detected voltage changed its sign together with carrier type. This is first evidence of spin-charge conversion in carbon nanotubes 2. 1 K. Ando et al., Nature Mater. 12, 622 (2013). 2 E. Shigematsu et al., submitted.

  7. Single Centrosome Manipulation Reveals Its Electric Charge and Associated Dynamic Structure

    PubMed Central

    Hormeño, S.; Ibarra, B.; Chichón, F.J.; Habermann, K.; Lange, B.M.H.; Valpuesta, J.M.; Carrascosa, J.L.; Arias-Gonzalez, J.R.

    2009-01-01

    Abstract The centrosome is the major microtubule-organizing center in animal cells and consists of a pair of centrioles surrounded by a pericentriolar material. We demonstrate laser manipulation of individual early Drosophila embryo centrosomes in between two microelectrodes to reveal that it is a net negatively charged organelle with a very low isoelectric region (3.1 ± 0.1). From this single-organelle electrophoresis, we infer an effective charge smaller than or on the order of 103 electrons, which corresponds to a surface-charge density significantly smaller than that of microtubules. We show, however, that the charge of the centrosome has a remarkable influence over its own structure. Specifically, we investigate the hydrodynamic behavior of the centrosome by measuring its size by both Stokes law and thermal-fluctuation spectral analysis of force. We find, on the one hand, that the hydrodynamic size of the centrosome is 60% larger than its electron microscopy diameter, and on the other hand, that this physiological expansion is produced by the electric field that drains to the centrosome, a self-effect that modulates its structural behavior via environmental pH. This methodology further proves useful for studying the action of different environmental conditions, such as the presence of Ca2+, over the thermally induced dynamic structure of the centrosome. PMID:19686649

  8. Transport and Charge Manipulation in a Single Electron Silicon Double Quantum Dot

    NASA Astrophysics Data System (ADS)

    Wang, K.; Payette, C.; Dovzhenko, Y.; Petta, J. R.

    2013-03-01

    Silicon is one of the most promising candidates for ultra-coherent qubits due to its relatively early position in periodical table and the absence of nuclear spin in its naturally abundant isotope. Here we demonstrate a reliable recipe that enables us to reproducibly fabricate an accumulation mode few electron double quantum dot (DQD). We demonstrate tunable interdot tunnel coupling at single electron occupancy in the device. The charge state of the qubit is monitored by measuring the amplitude of the radio frequency signal that is reflected from a resonant circuit coupled to a charge sensor. By applying microwave radiation to the depletion gates, we probe the energy level structure of the DQD using photon assisted tunneling (PAT). We apply bursts of microwave radiation and monitor the dependence of the PAT peak height on the burst period to extract the charge relaxation time, T1. By experimentally tuning the charge qubit Hamiltonian, we measure the tunnel coupling and detuning dependence of T1. Supported by the United States Department of Defense. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the U.S. Government.

  9. Thermally Induced Charge Reversal of Layer-by-Layer Assembled Single-Component Polymer Films.

    PubMed

    Richardson, Joseph J; Tardy, Blaise L; Ejima, Hirotaka; Guo, Junling; Cui, Jiwei; Liang, Kang; Choi, Gwan H; Yoo, Pil J; De Geest, Bruno G; Caruso, Frank

    2016-03-23

    Temperature can be harnessed to engineer unique properties for materials useful in various contexts and has been shown to affect the layer-by-layer (LbL) assembly of polymer thin films and cause physical changes in preassembled polymer thin films. Herein we demonstrate that exposure to relatively low temperatures (≤ 100 °C) can induce physicochemical changes in cationic polymer thin films. The surface charge of polymer films containing primary and secondary amines reverses after heating (from positive to negative), and different characterization techniques are used to show that the change in surface charge is related to oxidation of the polymer that specifically occurs in the thin film state. This charge reversal allows for single-polymer LbL assembly to be performed with poly(allylamine) hydrochloride (PAH) through alternating heat/deposition steps. Furthermore, the negative charge induced by heating reduces the fouling and cell-association of PAH-coated planar and particulate substrates, respectively. This study highlights a unique property of thin films which is relevant to LbL assembly and biofouling and is of interest for the future development of thin polymer films for biomedical systems. PMID:26953514

  10. Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

    NASA Astrophysics Data System (ADS)

    Xin-Jun, Zhao; Zhi-Fu, Gao

    2016-07-01

    Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA (ssDNA) tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ssDNA are taken into account. The main results are as follows: i) when the temperature is lower than the critical switching temperature, the ssDNA will collapse due to the existence of electrostatic interaction between ssDNA and charged nanoparticle surface; ii) for the short ssDNA chains with the number of bases less than 10, the switching of ssDNA cannot happen, and the critical temperature does not exist; iii) when the temperature increases, the electrostatic attractive interaction between ssDNA and charged nanoparticle surface becomes weak dramatically, and ssDNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ssDNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ssDNA will not happen if the grafting densities are too high. Project supported by the Joint Funds of Xinjiang Natural Science Foundation, China (Grant No. 2015211C298).

  11. Superconducting single electron transistor for charge sensing in Si/SiGe-based quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, Zhen

    Si-based quantum devices, including Si/SiGe quantum dots (QD), are promising candidates for spin-based quantum bits (quits), which are a potential platform for quantum information processing. Meanwhile, qubit readout remains a challenging task related to semiconductor-based quantum computation. This thesis describes two readout devices for Si/SiGe QDs and the techniques for developing them from a traditional single electron transistor (SET). By embedding an SET in a tank circuit and operating it in the radio-frequency (RF) regime, a superconducting RF-SET has quick response as well as ultra high charge sensitivity and can be an excellent charge sensor for the QDs. We demonstrate such RF-SETs for QDs in a Si/SiGe heterostructure. Characterization of the SET in magnetic fields is studied for future exploration of advanced techniques such as spin detection and spin state manipulation. By replacing the tank circuit with a high-quality-factor microwave cavity, the embedded SET will be operated in the supercurrent regime as a single Cooper pair transistor (CPT) to further increase the charge sensitivity and reduce any dissipation. The operating principle and implementation of the cavity-embedded CPT (cCPT) will be introduced.

  12. Model for the light-induced magnetization in singly charged quantum dots

    NASA Astrophysics Data System (ADS)

    Henriques, A. B.; Cordeiro, R. C.; Koenraad, P. M.; Otten, F. W. M.; Bayer, M.

    2015-02-01

    Magnetization is induced in an ensemble of quantum dots, each charged with a single electron, when it is illuminated with a short circularly polarized light pulse that is resonant with the fundamental energy gap of the quantum dots. In this investigation, a quantum-mechanical model for the light-induced magnetization is presented. The phase of the magnetization precession as a function of the strength of the magnetic field in a Voigt geometry is in excellent agreement with experimental data measured on (In,Ga)As singly charged quantum dot ensembles. It is demonstrated that the precession of the hole in the trion plays a vital role because it determines the amplitude and phase of the magnetization precession. The model could also be easily extended to describe positively charged quantum dots. We also suggest that our theory, combined with measurements of the phase as a function of magnetic field, can be used as a technique to measure the resonant trion lifetime as a function of QD emission energy.

  13. Photoinduced charge transfer from vacuum-deposited molecules to single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Osada, Kazuki; Tanaka, Masatoshi; Ohno, Shinya; Suzuki, Takanori

    2016-06-01

    Variations of photoluminescence (PL) and Raman spectra of single-layer MoS2, MoSe2, WS2, and WSe2 due to the vacuum deposition of C60 or copper phthalocyanine (CuPc) molecules have been investigated. PL spectra are decomposed into two competitive components, an exciton and a charged exciton (trion), depending on carrier density. The variation of PL spectra is interpreted in terms of charge transfer across the interfaces between transition metal dichalcogenides (TMDs) and dopant molecules. We find that deposited C60 molecules inject photoexcited electrons into MoS2, MoSe2, and WS2 or holes into WSe2. CuPc molecules also inject electrons into MoS2, MoSe2, and WS2, while holes are depleted from WSe2 to CuPc. We then propose a band alignment between TMDs and dopant molecules. Peak shifts of Raman spectra and doped carrier density estimated using a three-level model also support the band alignment. We thus demonstrate photoinduced charge transfer from dopant molecules to single-layer TMDs.

  14. Observation and applications of single-electron charge signals in the XENON100 experiment

    NASA Astrophysics Data System (ADS)

    Aprile, E.; Alfonsi, M.; Arisaka, K.; Arneodo, F.; Balan, C.; Baudis, L.; Bauermeister, B.; Behrens, A.; Beltrame, P.; Bokeloh, K.; Brown, A.; Brown, E.; Bruenner, S.; Bruno, G.; Budnik, R.; Cardoso, J. M. R.; Chen, W.-T.; Choi, B.; Colijn, A. P.; Contreras, H.; Cussonneau, J. P.; Decowski, M. P.; Duchovni, E.; Fattori, S.; Ferella, A. D.; Fulgione, W.; Gao, F.; Garbini, M.; Ghag, C.; Giboni, K.-L.; Goetzke, L. W.; Grignon, C.; Gross, E.; Hampel, W.; Itay, R.; Kaether, F.; Kessler, G.; Kish, A.; Lamblin, J.; Landsman, H.; Lang, R. F.; Le Calloch, M.; Levy, C.; Lim, K. E.; Lin, Q.; Lindemann, S.; Lindner, M.; Lopes, J. A. M.; Lung, K.; Marrodán Undagoitia, T.; Massoli, F. V.; Melgarejo Fernandez, A. J.; Meng, Y.; Messina, M.; Molinario, A.; Naganoma, J.; Ni, K.; Oberlack, U.; Orrigo, S. E. A.; Pantic, E.; Persiani, R.; Piastra, F.; Plante, G.; Priel, N.; Rizzo, A.; Rosendahl, S.; dos Santos, J. M. F.; Sartorelli, G.; Schreiner, J.; Schumann, M.; Scotto Lavina, L.; Selvi, M.; Shagin, P.; Simgen, H.; Teymourian, A.; Thers, D.; Vitells, O.; Wang, H.; Weber, M.; Weinheimer, C.

    2014-03-01

    The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measure xenon nuclear recoils resulting from the scattering of dark matter weakly interacting massive particles (WIMPs). In this paper, we report the observation of single-electron charge signals which are not related to WIMP interactions. These signals, which show the excellent sensitivity of the detector to small charge signals, are explained as being due to the photoionization of impurities in the liquid xenon and of the metal components inside the TPC. They are used as a unique calibration source to characterize the detector. We explain how we can infer crucial parameters for the XENON100 experiment: the secondary-scintillation gain, the extraction yield from the liquid to the gas phase and the electron drift velocity.

  15. Charge trapping in aligned single-walled carbon nanotube arrays induced by ionizing radiation exposure

    SciTech Connect

    Esqueda, Ivan S.; Cress, Cory D.; Che, Yuchi; Cao, Yu; Zhou, Chongwu

    2014-02-07

    The effects of near-interfacial trapping induced by ionizing radiation exposure of aligned single-walled carbon nanotube (SWCNT) arrays are investigated via measurements of gate hysteresis in the transfer characteristics of aligned SWCNT field-effect transistors. Gate hysteresis is attributed to charge injection (i.e., trapping) from the SWCNTs into radiation-induced traps in regions near the SWCNT/dielectric interface. Self-consistent calculations of surface-potential, carrier density, and trapped charge are used to describe hysteresis as a function of ionizing radiation exposure. Hysteresis width (h) and its dependence on gate sweep range are investigated analytically. The effects of non-uniform trap energy distributions on the relationship between hysteresis, gate sweep range, and total ionizing dose are demonstrated with simulations and verified experimentally.

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

    PubMed Central

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

    2012-01-01

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

  17. Electrical detection of ferromagnetic resonance in single layers of permalloy: Evidence of magnonic charge pumping

    NASA Astrophysics Data System (ADS)

    Azevedo, A.; Cunha, R. O.; Estrada, F.; Alves Santos, O.; Mendes, J. B. S.; Vilela-Leão, L. H.; Rodríguez-Suárez, R. L.; Rezende, S. M.

    2015-07-01

    The generation of a DC voltage in single layers of permalloy (Ni81Fe19 ) when the magnetization is undergoing ferromagnetic resonance is investigated in a series of samples with thickness varying from 4.0 to 150 nm. By sweeping the external field at a fixed microwave frequency, we measure a DC voltage at the ends of the layer as a function of the in-plane angle for each sample. The asymmetric voltage signal generated at the resonance field is a superposition of symmetric Lorentzian and antisymmetric Lorentzian derivative line shapes. The in-plane dependence of both symmetric and antisymmetric signals cannot be explained as due to spin rectification (SRE) only. The results are well explained by a model that takes into account in addition to the SRE the contribution of the recent discovered effect of magnonic charge pumping that converts magnetization dynamics into charge current by means of the spin orbit coupling.

  18. Full control of quadruple quantum dot circuit charge states in the single electron regime

    SciTech Connect

    Delbecq, M. R. Nakajima, T.; Otsuka, T.; Amaha, S.; Watson, J. D.; Manfra, M. J.; Tarucha, S.

    2014-05-05

    We report the realization of an array of four tunnel coupled quantum dots in the single electron regime, which is the first required step toward a scalable solid state spin qubit architecture. We achieve an efficient tunability of the system but also find out that the conditions to realize spin blockade readout are not as straightforwardly obtained as for double and triple quantum dot circuits. We use a simple capacitive model of the series quadruple quantum dots circuit to investigate its complex charge state diagrams and are able to find the most suitable configurations for future Pauli spin blockade measurements. We then experimentally realize the corresponding charge states with a good agreement to our model.

  19. Full control of quadruple quantum dot circuit charge states in the single electron regime

    NASA Astrophysics Data System (ADS)

    Delbecq, M. R.; Nakajima, T.; Otsuka, T.; Amaha, S.; Watson, J. D.; Manfra, M. J.; Tarucha, S.

    2014-05-01

    We report the realization of an array of four tunnel coupled quantum dots in the single electron regime, which is the first required step toward a scalable solid state spin qubit architecture. We achieve an efficient tunability of the system but also find out that the conditions to realize spin blockade readout are not as straightforwardly obtained as for double and triple quantum dot circuits. We use a simple capacitive model of the series quadruple quantum dots circuit to investigate its complex charge state diagrams and are able to find the most suitable configurations for future Pauli spin blockade measurements. We then experimentally realize the corresponding charge states with a good agreement to our model.

  20. Biofunctionalization of Surfaces with Peptides, Proteins, or Subcellular Organelles: Single-Molecule Studies and Nanomedical Approach

    NASA Astrophysics Data System (ADS)

    Katranidis, A.; Choli-Papadopoulou, T.

    Immobilization of biologically active proteins and enzymes on surfaces is very important for the production of biofunctionalized surfaces for applications in medicine such as biosensors and in the diagnostics field. There are various approaches to immobilize and control the release of peptides/proteins from different surfaces. The identification of successful techniques to functionalize a particular material is a challenge. On the other hand, biomaterials are at the moment of great benefit for medicinal purposes and a lot of knowledge from different fields is required in order to design biomimetic scaffolds or biomimetic materials. The used methodologies are different for different materials and are mainly based on the special chemistry of the surfaces. Peptides with distinct properties are desired instead of entire proteins. However, in some cases, proteins cannot be replaced by peptide segments and therefore biochemical knowledge, such as in protein and/or genetic engineering is required.

  1. Effects of Lipid Composition on the Entry of Cell-Penetrating Peptide Oligoarginine into Single Vesicles.

    PubMed

    Sharmin, Sabrina; Islam, Md Zahidul; Karal, Mohammad Abu Sayem; Alam Shibly, Sayed Ul; Dohra, Hideo; Yamazaki, Masahito

    2016-08-01

    The cell-penetrating peptide R9, an oligoarginine comprising nine arginines, has been used to transport biological cargos into cells. However, the mechanisms underlying its translocation across membranes remain unclear. In this report, we investigated the entry of carboxyfluorescein (CF)-labeled R9 (CF-R9) into single giant unilamellar vesicles (GUVs) of various lipid compositions and the CF-R9-induced leakage of a fluorescent probe, Alexa Fluor 647 hydrazide (AF647), using a method developed recently by us. First, we investigated the interaction of CF-R9 with dioleoylphosphatidylglycerol (DOPG)/dioleoylphosphatidylcholine (DOPC) GUVs containing AF647 and small DOPG/DOPC vesicles. The fluorescence intensity of the GUV membrane due to CF-R9 (i.e., the rim intensity) increased with time to a steady-state value, and then the fluorescence intensity of the membranes of the small vesicles in the GUV lumen increased without leakage of AF647. This result indicates that CF-R9 entered the GUV lumen from the outside by translocating across the lipid membrane without forming pores through which AF647 could leak. The fraction of entry of CF-R9 at 6 min in the absence of pore formation, Pentry (6 min), increased with an increase in CF-R9 concentration, but the CF-R9 concentration in the lumen was low. We obtained similar results for dilauroyl-PG (DLPG)/ditridecanoyl-PC (DTPC) (2/8) GUVs. The values of Pentry (6 min) of CF-R9 for DLPG/DTPC (2/8) GUVs were larger than those obtained with DOPG/DOPC (2/8) GUVs at the same CF-R9 concentrations. In contrast, a high concentration of CF-R9 induced pores in DLPG/DTPC (4/6) GUVs through which CF-R9 entered the GUV lumen, so the CF-R9 concentration in the lumen was higher. However, CF-R9 could not enter DOPG/DOPC/cholesterol (2/6/4) GUVs. Analysis of the rim intensity showed that CF-R9 was located only in the outer monolayer of the DOPG/DOPC/cholesterol (2/6/4) GUVs. On the basis of analyses of these results, we discuss the elementary

  2. Imidate-Based Cross-Linkers for Structural Proteomics: Increased Charge of Protein and Peptide Ions and CID and ECD Fragmentation Studies

    NASA Astrophysics Data System (ADS)

    Koolen, Hector H. F.; Gomes, Alexandre F.; Schwab, Nicolas V.; Eberlin, Marcos N.; Gozzo, Fabio C.

    2014-07-01

    Chemical cross-linking is an attractive low-resolution technique for structural studies of protein complexes. Distance constraints obtained from cross-linked peptides identified by mass spectrometry (MS) are used to construct and validate protein models. Amidinating cross-linkers such as diethyl suberthioimidate (DEST) have been used successfully in chemical cross-linking experiments. In this work, the application of a commercial diimidate cross-linking reagent, dimethyl suberimidate (DMS), was evaluated with model peptides and proteins. The peptides were designed with acetylated N-termini followed by random sequences containing two Lys residues separated by an Arg residue. After cross-linking reactions, intra- and intermolecular cross-linked species were submitted to CID and ECD dissociations to study their fragmentation features in the gas phase. Fragmentation of intramolecular peptides by collision induced dissociation (CID) demonstrates a unique two-step fragmentation pathway involving formation of a ketimine as intermediate. Electron capture and electron transfer dissociation (ECD and ETD) experiments demonstrated that the cyclic moiety is not dissociated. Intermolecular species demonstrated previously described fragmentation behavior in both CID and ECD experiments. The charge state distributions (CSD) obtained after reaction with DMS were compared with those obtained with disuccinimidyl suberate (DSS). CSDs for peptides and proteins were increased after their reaction with DMS, owing to the higher basicity of DMS modified species. These features were also observed in LC-MS experiments with bovine carbonic anhydrase II (BCA) after cross-linking with DMS and tryptic proteolysis. Cross-linked peptides derived from this protein were identified at high confidence and those species were in agreement with the crystal structure of BCA.

  3. Normal mode analysis of single bunch, charge density dependent behavior in electron/positron beams

    NASA Astrophysics Data System (ADS)

    Ehrlichman, Michael

    Accelerator science in coming years will be increasingly dependent upon high single-bunch charges and/or small emittances. Under these conditions, single-particle dynamics are not a sufficient description of beam behavior and interactions between the beam particles must be taken into account. One such interaction is when collisions between the particles that compose a bunch perturb the motion of the colliding particles significantly and frequently enough to impact the beam dynamics. Multiple, small-angle, collisions blow up the emittance of the bunch and are referred to as intrabeam scattering (IBS). Here are documented the theoretical and experimental studies of IBS in storage rings undertaken as part of the CesrTA program. Under the conditions where IBS becomes dominant, other multi-particle effects can also appear. The additional effects we investigate include potential well distortion, coherent current-dependent tune shift, and direct space charge. CesrTA design and analysis is conducted in a normal mode coordinates environment which allows for natural handling of coupling. To that end, we develop a 6D normal modes decomposition of the linear beam optics. Multi-particle effects are also important for Energy Recovery Linear Accelerators (ERLs). Because the beam circulates for only a short period of time in an ERL, the beam lifetime imposed by Touschek scattering is not significant. However, the particles scattered out of the bunch can generate a radiation hazard where they collide with the beam pipe. We re-derive Piwinski's original Touschek scattering equation to check its validity when applied to ERL beams, then repurpose the formula to generate a profile of where scattered particles are generated and where they are lost. The results presented here advance our understanding of charge-dependent behavior in the sorts of high charge-density accelerators that will be implemented in coming years.

  4. Charge regulation phenomenon predicted from the modeling of polypeptide electrophoretic mobilities as a relevant mechanism of amyloid-beta peptide oligomerization.

    PubMed

    Deiber, Julio A; Peirotti, Marta B; Piaggio, Maria V

    2016-03-01

    Electrophoretic mobilities of amyloid-beta (1-40) and (1-42) peptides and their aggregates are modeled to study the amyloidogenic pathway associated with Alzheimer´s Disease. The near molecule pH generated by the intraparticle charge regulation phenomenon during the oligomerization of amyloid-beta (1-40) and (1-42) peptides is evaluated and discussed as a relevant mechanism supporting the "amyloid cascade hypothesis" proposed in the literature. A theoretical framework associated with the oligomerization of amyloid-beta peptides including simple scaling laws and the consideration of electrokinetic and hydrodynamic global properties of oligomers is presented. The central finding is the explanation of the near molecule pH change toward the pI when the oligomerization number increases. These results allow one to rationalize consecutive physical stages that validate the amyloid cascade hypothesis. Concluding remarks involving mainly the effects of pair and intraparticle charge regulation phenomena on the amyloidogenic pathway with some suggestions for future research are provided. PMID:26718015

  5. Soluble expression, purification and functional characterization of a coil peptide composed of a positively charged and hydrophobic motif.

    PubMed

    Riahi, Nesrine; Cappadocia, Laurent; Henry, Olivier; Omichinski, James; De Crescenzo, Gregory

    2016-02-01

    A de novo heterodimeric coiled-coil system formed by the association of two synthetic peptides, the Ecoil and Kcoil, has been previously designed and proven to be an excellent and versatile tool for various biotechnology applications. However, based on the challenges encountered during its chemical synthesis, the Kcoil peptide has been designated as a "difficult peptide". In this study, we explore the expression of the Kcoil peptide by a bacterial system as well as its subsequent purification. The maximum expression level was observed when the peptide was fused to thioredoxin and the optimized purification process consisted of three chromatographic steps: immobilized-metal affinity chromatography followed by cation-exchange chromatography and, finally, a reverse-phase high-performance liquid chromatography. This entire process led to a final volumetric production yield of 1.5 mg of pure Kcoil peptide per liter of bacterial culture, which represents a significant step towards the cost-effective production and application of coiled-coil motifs. Our results thus demonstrate for the first time that bacterial production is a viable alternative to the chemical synthesis of de novo designed coil peptides. PMID:26459292

  6. Design and simulation of ion optics for ion sources for production of singly charged ions

    NASA Astrophysics Data System (ADS)

    Zelenak, A.; Bogomolov, S. L.

    2004-05-01

    During the last 2 years different types of the singly charged ion sources were developed for FLNR (JINR) new projects such as Dubna radioactive ion beams, (Phase I and Phase II), the production of the tritium ion beam and the MASHA mass separator. The ion optics simulations for 2.45 GHz electron cyclotron resonance source, rf source, and the plasma ion source were performed. In this article the design and simulation results of the optics of new ion sources are presented. The results of simulation are compared with measurements obtained during the experiments.

  7. Evaluation of anisotropic charge carrier mobility of perylene single crystals by time-of-flight method

    NASA Astrophysics Data System (ADS)

    Kougo, Junichi; Ishikawa, Ken

    2016-03-01

    The charge carrier mobilities along the vertical and lateral directions of perylene platelet single crystals were measured by the time-of-flight (TOF) method. In the lateral directional measurement, the entire region between electrodes was irradiated to obtain measurable signals. The transient photocurrent was different from the conventional TOF measurements; hence, we developed an analytic method for lateral directional measurement. The electron mobilities along the thickness and lateral directions were 0.33 and 2.0 cm2·V-1·s-1 and the hole mobilities were 0.12 and 0.6 cm2·V-1·s-1, respectively.

  8. Charging a Capacitor from an External Fluctuating Potential using a Single Conical Nanopore

    PubMed Central

    Gomez, Vicente; Ramirez, Patricio; Cervera, Javier; Nasir, Saima; Ali, Mubarak; Ensinger, Wolfgang; Mafe, Salvador

    2015-01-01

    We explore the electrical rectification of large amplitude fluctuating signals by an asymmetric nanostructure operating in aqueous solution. We show experimentally and theoretically that a load capacitor can be charged to voltages close to 1 V within a few minutes by converting zero time-average potentials of amplitudes in the range 0.5–3 V into average net currents using a single conical nanopore. This process suggests that significant energy conversion and storage from an electrically fluctuating environment is feasible with a nanoscale pore immersed in a liquid electrolyte solution, a system characteristic of bioelectronics interfaces, electrochemical cells, and nanoporous membranes. PMID:25830563

  9. Charging a capacitor from an external fluctuating potential using a single conical nanopore.

    PubMed

    Gomez, Vicente; Ramirez, Patricio; Cervera, Javier; Nasir, Saima; Ali, Mubarak; Ensinger, Wolfgang; Mafe, Salvador

    2015-01-01

    We explore the electrical rectification of large amplitude fluctuating signals by an asymmetric nanostructure operating in aqueous solution. We show experimentally and theoretically that a load capacitor can be charged to voltages close to 1 V within a few minutes by converting zero time-average potentials of amplitudes in the range 0.5-3 V into average net currents using a single conical nanopore. This process suggests that significant energy conversion and storage from an electrically fluctuating environment is feasible with a nanoscale pore immersed in a liquid electrolyte solution, a system characteristic of bioelectronics interfaces, electrochemical cells, and nanoporous membranes. PMID:25830563

  10. Multiple charge-density-wave transitions in single-crystalline Lu2Ir3Si5

    NASA Astrophysics Data System (ADS)

    Sangeetha, N. S.; Thamizhavel, A.; Tomy, C. V.; Basu, Saurabh; Awasthi, A. M.; Rajak, Piu; Bhattacharyya, Somnath; Ramakrishnan, S.; Pal, D.

    2015-05-01

    The physical properties of the single-crystalline samples of Lu2Ir3Si5 have been investigated by magnetic susceptibility, resistivity, and heat capacity studies. We observed multiple charge-density-wave (CDW) transitions in all the measurements. A strong thermal hysteresis at these transitions suggests a possible first order CDW ordering. In addition, the first order nature is ascertained by a very narrow and a huge cusp (62 J/mol K) in the zero field specific heat data which also suggests strong electron-phonon interchain coupling.

  11. On the charge transfer between single-walled carbon nanotubes and graphene

    SciTech Connect

    Rao, Rahul Pierce, Neal; Dasgupta, Archi

    2014-08-18

    It is important to understand the electronic interaction between single-walled carbon nanotubes (SWNTs) and graphene in order to use them efficiently in multifunctional hybrid devices. Here, we deposited SWNT bundles on graphene-covered copper and SiO{sub 2} substrates by chemical vapor deposition and investigated the charge transfer between them by Raman spectroscopy. Our results revealed that, on both copper and SiO{sub 2} substrates, graphene donates electrons to the SWNTs, resulting in p-type doped graphene and n-type doped SWNTs.

  12. First-Principles Studies of Charge Separation in Single-Molecule Heterojunctions

    NASA Astrophysics Data System (ADS)

    Darancet, Pierre; Doak, Peter; Neaton, Jeffrey

    2010-03-01

    Single-molecule heterojunctions, consisting of donor and acceptor moieties linked by covalent bonds and coupled to metal electrodes, provide an interesting model system for understanding processes fundamental to organic solar cells, such as light absorption and charge separation. However, how the covalent contact with metallic leads influence these processes -- and metal-molecule interface electronic structure -- remains largely unknown. Using density functional theory and many-body perturbation theory, we discuss the influence of the metal contacts and binding groups on junction electronic level alignment for small asymmetric molecules containing covalently-linked moieties based on thiophene, durene and tetrafluoro-, dinitrile-, and metoxy-benzene. Implications for photocurrent and rectification are discussed.

  13. Inducing Transient Charge State of a Single Water Cluster on Cu(111) Surface.

    PubMed

    Guo, Yang; Ding, Zijing; Sun, Lihuan; Li, Jianmei; Meng, Sheng; Lu, Xinghua

    2016-04-26

    The hydrated electron on solid surface is a crucial species to interfacial chemistry. We present a joint low-temperature scanning tunneling microscopy and density functional theory investigation to explore the existence of a transient hydrated electron state induced by injecting tunneling electrons into a single water nonamer cluster on Cu(111) surface. The directional diffusion of water cluster under the Coulomb repulsive potential has been observed as evidence for the emergence of the transient hydrated electron. A critical structure transformation in water cluster for the emergence of hydrated electron has been identified. A charging mechanism has been proposed based on density functional theory calculation and scanning tunneling microscope results. PMID:27007702

  14. Observation of spin-charge conversion in chemical-vapor-deposition-grown single-layer graphene

    SciTech Connect

    Ohshima, Ryo; Sakai, Atsushi; Ando, Yuichiro; Shiraishi, Masashi; Shinjo, Teruya; Kawahara, Kenji; Ago, Hiroki

    2014-10-20

    Conversion of pure spin current to charge current in single-layer graphene (SLG) is investigated by using spin pumping. Large-area SLG grown by chemical vapor deposition is used for the conversion. Efficient spin accumulation in SLG by spin pumping enables observing an electromotive force produced by the inverse spin Hall effect (ISHE) of SLG. The spin Hall angle of SLG is estimated to be 6.1 × 10{sup −7}. The observed ISHE in SLG is ascribed to its non-negligible spin-orbit interaction in SLG.

  15. Electronic transport in single-helical protein molecules: Effects of multiple charge conduction pathways and helical symmetry

    NASA Astrophysics Data System (ADS)

    Kundu, Sourav; Karmakar, S. N.

    2016-07-01

    We propose a tight-binding model to investigate electronic transport properties of single helical protein molecules incorporating both the helical symmetry and the possibility of multiple charge transfer pathways. Our study reveals that due to existence of both the multiple charge transfer pathways and helical symmetry, the transport properties are quite rigid under influence of environmental fluctuations which indicates that these biomolecules can serve as better alternatives in nanoelectronic devices than its other biological counterparts e.g., single-stranded DNA.

  16. Laser spectroscopy of individual quantum dots charged with a single hole

    NASA Astrophysics Data System (ADS)

    Gerardot, B. D.; Barbour, R. J.; Brunner, D.; Dalgarno, P. A.; Badolato, A.; Stoltz, N.; Petroff, P. M.; Houel, J.; Warburton, R. J.

    2011-12-01

    We characterize the positively charged exciton (X1+) in single InGaAs quantum dots using resonant laser spectroscopy. Three samples with different dopant species (Be or C as acceptors, Si as a donor) are compared. The p-doped samples exhibit larger inhomogeneous broadening (×3) and smaller absorption contrast (×10) than the n-doped sample. For X1+ in the Be-doped sample, a dot dependent non-linear Fano effect is observed, demonstrating coupling to degenerate continuum states. However, for the C-doped sample, the X1+ lineshape and saturation broadening follows isolated atomic transition behaviour. This C-doped device structure is useful for single hole spin initialization, manipulation, and measurement.

  17. Determining charge carrier mobility in Schottky contacted single-carrier organic devices by impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Tang, Ying; Peng, Yingquan; Sun, Lei; Wei, Yi; Xu, Sunan

    2015-10-01

    Impedance spectroscopy (IS) is one of the most important methods for analyzing transport properties of semiconducting thin films. At present carrier mobility can be determined by IS methods only for Ohmic contacted single-carrier devices, which hinders the use of the IS method for determining the carrier mobility of thin films with high-lying lowest unoccupied molecular orbits or low-lying highest occupied molecular orbits. Based on the theory of space charge limited current conduction and thermionic emission at metal-organic interface, we developed a numerical IS model for single-carrier organic devices with Schottky injection contact. With the help of this model, a concise empirical formula is obtained from which the carrier mobility can be determined from the characteristic frequency of the negative differential susceptance and the Schottky energy barrier height at the injection contact.

  18. Ultrafast spectroscopic signature of charge transfer between single-walled carbon nanotubes and C60.

    PubMed

    Dowgiallo, Anne-Marie; Mistry, Kevin S; Johnson, Justin C; Blackburn, Jeffrey L

    2014-08-26

    The time scales for interfacial charge separation and recombination play crucial roles in determining efficiencies of excitonic photovoltaics. Near-infrared photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g., C60). However, little is known about crucial photochemical events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (τpet) and yield (ϕpet) in photoexcited SWCNT–C60 bilayer films. The rise time of the trion-induced absorbance enables the determination of the photoinduced electron transfer (PET) time of τpet ≤ 120 fs, while an experimentally determined trion absorbance cross section reveals the yield of charge transfer (ϕpet ≈ 38 ± 3%). The extremely fast electron transfer times observed here are on par with some of the best donor:acceptor pairs in excitonic photovoltaics and underscore the potential for efficient energy harvesting in SWCNT-based devices. PMID:25019648

  19. Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctions.

    PubMed

    Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Egler-Lucas, Carolina; Semenov, Sergey N; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

    2016-02-01

    Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios. PMID:26571004

  20. Surface charge density determination of single conical nanopores based on normalized ion current rectification.

    PubMed

    Liu, Juan; Kvetny, Maksim; Feng, Jingyu; Wang, Dengchao; Wu, Baohua; Brown, Warren; Wang, Gangli

    2012-01-17

    Current rectification is well known in ion transport through nanoscale pores and channel devices. The measured current is affected by both the geometry and fixed interfacial charges of the nanodevices. In this article, an interesting trend is observed in steady-state current-potential measurements using single conical nanopores. A threshold low-conductivity state is observed upon the dilution of electrolyte concentration. Correspondingly, the normalized current at positive bias potentials drastically increases and contributes to different degrees of rectification. This novel trend at opposite bias polarities is employed to differentiate the ion flux affected by the fixed charges at the substrate-solution interface (surface effect), with respect to the constant asymmetric geometry (volume effect). The surface charge density (SCD) of individual nanopores, an important physical parameter that is challenging to measure experimentally and is known to vary from one nanopore to another, is directly quantified by solving Poisson and Nernst-Planck equations in the simulation of the experimental results. The flux distribution inside the nanopore and the SCD of individual nanopores are reported. The respective diffusion and migration translocations are found to vary at different positions inside the nanopore. This knowledge is believed to be important for resistive pulse sensing applications because the detection signal is determined by the perturbation of the ion current by the analytes. PMID:22182684

  1. Chiral Charge Density Wave and Superconductivity in CuxTiSe2 Single Crystals

    NASA Astrophysics Data System (ADS)

    Karapetrov, Goran; Husanikova, P.; Cambel, V.; Szabó, P.; Samuely, P.; Fedor, J.; Iavarone, M.

    2015-03-01

    We investigate atomic scale scanning tunneling microscopy and spectroscopy in CuxTiSe2 single crystals at low temperatures. We map the CDW and superconducting phase diagram as a function of copper doping. STM measurements reveal coexistence of chiral charge density wave and superconductivity. In case of optimally doped and overdoped cases we find that the amplitude of charge density wave modulation is strongly suppressed with respect to strongly underdoped case (x < 0 . 06) with the chiral domain size remaining approximately the same. Superconductivity exhibits BCS character at variety of dopings with 2 Δ / kTc ~ 3 . 6 ÷ 3 . 7 indicating an intermediate coupling strength. Application of the external magnetic field introduces the Abrikosov vortex lattice that is weakly pinned. The size of the vortex core extracted from vortex images corresponds to the one extracted from the magnetization measurements. Our results suggest that, if charge density wave quantum critical point exist, it should be well above the optimal copper concentration of x=0.08. This work is supported by the Army Research Office Grant #W911NF-14-1-0567.

  2. Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Egler-Lucas, Carolina; Semenov, Sergey N.; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

    2016-02-01

    Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.

  3. Theoretical description of charge migration with a single Slater-determinant and beyond.

    PubMed

    Kuleff, Alexander I; Dreuw, Andreas

    2009-01-21

    Triggered by the interest to study charge migration in large molecular systems, a simple methodology has recently been proposed based on straightforward density functional theory calculations. This approach describes the time evolution of the initially created hole density in terms of the time evolution of the ionized highest occupied molecular orbital (HOMO). Here we demonstrate that this time-dependent analog of Koopmans' theorem is not valid, and instead of the time evolution of the HOMO, the time evolution of the orbitals that remain occupied in the cation determines the evolution of the initially created hole in the framework of time-dependent single-determinant theories. Numerical examples underline that for a proper description of charge migration processes, an explicit treatment of the electron correlation is indispensable. Moreover, they also demonstrate that the attempts to describe charge migration based on Kohn-Sham density functional theory using conventional exchange-correlation functionals are doomed to fail due to the well-known self-interaction error. PMID:19173505

  4. Reversal of the surface charge asymmetry in purple membrane due to single amino acid substitutions.

    PubMed Central

    Hsu, K C; Rayfield, G W; Needleman, R

    1996-01-01

    Twenty-seven mutant bacteriorhodopsin's were screened to determine the PKa for reversal of the permanent electric dipole moment. The photoelectric response of an aqueous purple-membrane suspension was used to determine the direction of the purple-membrane dipole moment as a function of pH. The pK(a) for the dipole reversal of wild-type bacteriorhodopsin is 4.5. Six of the 27 mutant bacteriorhodopsin's were found to have a pK(a) for dipole reversal larger than that of wild-type bacteriorhodopsin. Two of these mutants, L93T and L93W, involve a neutral amino acid substitution in the interior of the protein. The direction of the purple-membrane permanent electric dipole moment is determined by the purple-membrane surface charge asymmetry. We conclude that these two substitutions, which do not involve charge replacement, alter the pK(a) for the reversal of the purple-membrane surface charge asymmetry. We suggest that these changes to the pK(a) are due to altered protein folding at the surface of the purple-membrane induced by single-site substitutions in the protein interior. PMID:9172760

  5. Modifying the surface charge of single track-etched conical nanopores in polyimide.

    PubMed

    Ali, M; Schiedt, B; Healy, K; Neumann, R; Ensinger, W

    2008-02-27

    Chemical modification of nanopore surfaces is of great interest as it means that the surface composition is no longer fixed by the choice of substrate material, even to the point where large biomolecules can be attached to the pore walls. Controlling nanopore transport characteristics is one important application of surface modification which is very relevant given the significant interest in sensors based on the transport of ions and molecules through nanopores. Reported here is a method to change the surface charge polarity of single track-etched conical nanopores in polyimide, which also has the potential to attach more complex molecules to the carboxyl groups on the nanopore walls. These carboxyl groups were converted into terminal amino groups, first by activation with N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) followed by the covalent coupling of ethylenediamine. This results in a changed surface charge polarity. Regeneration of a carboxyl-terminated surface was also possible, by reaction of the amino groups with succinic anhydride. The success of these reactions was confirmed by measurements of the pore's pH sensitive current-voltage (I-V) characteristics before and after the chemical modification, which depend on surface charge. The permselectivity of the pores also changed accordingly with the modification. PMID:21730744

  6. Modifying the surface charge of single track-etched conical nanopores in polyimide

    NASA Astrophysics Data System (ADS)

    Ali, M.; Schiedt, B.; Healy, K.; Neumann, R.; Ensinger, W.

    2008-02-01

    Chemical modification of nanopore surfaces is of great interest as it means that the surface composition is no longer fixed by the choice of substrate material, even to the point where large biomolecules can be attached to the pore walls. Controlling nanopore transport characteristics is one important application of surface modification which is very relevant given the significant interest in sensors based on the transport of ions and molecules through nanopores. Reported here is a method to change the surface charge polarity of single track-etched conical nanopores in polyimide, which also has the potential to attach more complex molecules to the carboxyl groups on the nanopore walls. These carboxyl groups were converted into terminal amino groups, first by activation with N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) followed by the covalent coupling of ethylenediamine. This results in a changed surface charge polarity. Regeneration of a carboxyl-terminated surface was also possible, by reaction of the amino groups with succinic anhydride. The success of these reactions was confirmed by measurements of the pore's pH sensitive current-voltage (I-V) characteristics before and after the chemical modification, which depend on surface charge. The permselectivity of the pores also changed accordingly with the modification.

  7. Increase of Positive Net Charge and Conformational Rigidity Enhances the Efficacy of d-Enantiomeric Peptides Designed to Eliminate Cytotoxic Aβ Species.

    PubMed

    Ziehm, Tamar; Brener, Oleksandr; van Groen, Thomas; Kadish, Inga; Frenzel, Daniel; Tusche, Markus; Kutzsche, Janine; Reiß, Kerstin; Gremer, Lothar; Nagel-Steger, Luitgard; Willbold, Dieter

    2016-08-17

    Alzheimer's disease (AD) is a neurodegenerative disorder and the most common type of dementia. Until now, there is no curative therapy available. Previously, we selected the amyloid-beta (Aβ) targeting peptide D3 consisting of 12 d-enantiomeric amino acid residues by mirror image phage display as a potential drug candidate for the treatment of AD. In the current approach, we investigated the optimization potential of linear D3 with free C-terminus (D3COOH) by chemical modifications. First, the impact of the net charge was investigated and second, cyclization was introduced which is a well-known tool for the optimization of peptides for enhanced target affinity. Following this strategy, three D3 derivatives in addition to D3COOH were designed: C-terminally amidated linear D3 (D3CONH2), cyclic D3 (cD3), and cyclic D3 with an additional arginine residue (cD3r) to maintain the net charge of linear D3CONH2. These four compounds were compared to each other according to their binding affinities to Aβ(1-42), their efficacy to eliminate cytotoxic oligomers, and consequently their potency to neutralize Aβ(1-42) oligomer induced neurotoxicity. D3CONH2 and cD3r versions with equally increased net charge showed superior properties over D3COOH and cD3, respectively. The cyclic versions showed superior properties compared to their linear version with equal net charge, suggesting cD3r to be the most efficient compound among these four. Indeed, treatment of the transgenic AD mouse model Tg-SwDI with cD3r significantly enhanced spatial memory and cognition of these animals as revealed by water maze performance. Therefore, charge increase and cyclization imply suitable modification steps for an optimization approach of the Aβ targeting compound D3. PMID:27240424

  8. Low energy singly and multiply charged ion irradiation of astrophysical ices

    NASA Astrophysics Data System (ADS)

    Dawes, A.; Holtom, P. D.; Mukerji, R. J.; Davis, M. P.; Sivaraman, B.; McCullough, R. W.; Williams, I.; Mason, N. J.

    Ion induced processes play an important role in the chemical modification of astrophysical ices, both on the surfaces of satellites in the outer solar system and in the depths of dark molecular clouds where few photons penetrate. To date many laboratory studies have been developed to study energetic singly charged ion interactions with astrophysical ice analogues (e.g. Mennella, et al 2004; Strazzulla, Baratta & Palumbo 2001; Gerakines, Moore, & Hudson 2000) and have been found to produce new chemical species and cause significant effects on ice morphology (Palumbo 2005). However, the effects of low energy and multiply charged ions have not yet been investigated. Such ions are prevalent in many astrophysical environments: as primary and secondary particles generated by cosmic ray bombardment and as constituents of planetary magnetospheres (e.g. Jupiter and Saturn). These ions comprise a rich variety of reactive species in a variety of charge states with typical kinetic energies of few keV. The effect of slow, multiply charged ions (MCIs) with the surfaces of astrophysical ices and their possible effect on chemical processing is unclear. However, studies of MCI impacts with insulator surfaces suggest that they may play an important role due to surplus potential energy imparted at the surface of the target (Winter & Aumayr 2001). We have developed a research program to study ion interactions with astrophysical ices using an Electron Cyclotron Resonance (ECR) ion source at Queens University Belfast. Such a source can produce different species of ions with variable energy and different charge states. Ices are prepared in situ by depositing gas onto a cold infrared transmitting window. Samples are analysed using FTIR spectroscopy during irradiation. We have conducted a series of experiments to investigate the effects of ion charge state (potential vs. kinetic energy effects), ion energy (nuclear vs. electronic stopping processes) and sample temperature. In this poster

  9. Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering.

    PubMed

    Shi, Dong; Qin, Xiang; Li, Yuan; He, Yao; Zhong, Cheng; Pan, Jun; Dong, Huanli; Xu, Wei; Li, Tao; Hu, Wenping; Brédas, Jean-Luc; Bakr, Osman M

    2016-04-01

    We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD's paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD's intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells. PMID:27152342

  10. Tuning Charge and Correlation Effects for a Single Molecule on a Graphene Device

    NASA Astrophysics Data System (ADS)

    Tsai, Hsin-Zon; Wickenburg, Sebastian; Lu, Jiong; Lischner, Johannes; Omrani, Arash A.; Riss, Alexander; Karrasch, Christoph; Jung, Han Sae; Khajeh, Ramin; Wong, Dillon; Watanabe, Kenji; Taniguchi, Takashi; Zettl, Alex; Louie, Steven G.; Crommie, Michael F.

    Controlling electronic devices down to the single molecule level is a grand challenge of nanotechnology. Single-molecules have been integrated into devices capable of tuning electronic response, but a drawback for these systems is that their microscopic structure remains unknown due to inability to image molecules in the junction region. Here we present a combined STM and nc-AFM study demonstrating gate-tunable control of the charge state of individual F4TCNQ molecules at the surface of a graphene field effect transistor. This is different from previous studies in that the Fermi level of the substrate was continuously tuned across the molecular orbital energy level. Using STS we have determined the resulting energy level evolution of the LUMO, its associated vibronic modes, and the graphene Dirac point (ED). We show that the energy difference between ED and the LUMO increases as EF is moved away from ED due to electron-electron interactions that renormalize the molecular quasiparticle energy. This is attributed to gate-tunable image-charge screening in graphene and corroborated by ab initio calculations.

  11. Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering

    PubMed Central

    Shi, Dong; Qin, Xiang; Li, Yuan; He, Yao; Zhong, Cheng; Pan, Jun; Dong, Huanli; Xu, Wei; Li, Tao; Hu, Wenping; Brédas, Jean-Luc; Bakr, Osman M.

    2016-01-01

    We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD’s paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD’s intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells. PMID:27152342

  12. Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures

    NASA Astrophysics Data System (ADS)

    Payette, C.; Wang, K.; Koppinen, P. J.; Dovzhenko, Y.; Sturm, J. C.; Petta, J. R.

    2012-01-01

    We perform quantum Hall measurements on three types of commercially available modulation-doped Si/SiGe heterostructures to determine their suitability for depletion gate defined quantum dot devices. By adjusting the growth parameters, we are able to achieve electron gases with charge densities 1-3 × 1011/cm2 and mobilities in excess of 100 000 cm2/Vs. Double quantum dot devices fabricated on these heterostructures show clear evidence of single charge transitions as measured in dc transport and charge sensing and exhibit electron temperatures of 100 mK in the single quantum dot regime.

  13. Optimization for Single-Spike X-Ray FELs at LCLS with a Low Charge Beam

    SciTech Connect

    Wang, L.; Ding, Y.; Huang, Z.; /SLAC

    2011-12-14

    The Linac Coherent Light Source is an x-ray free-electron laser at the SLAC National Accelerator Laboratory, which is operating at x-ray wavelengths of 20-1.2 Angstrom with peak brightness nearly ten orders of magnitude beyond conventional synchrotron radiation sources. At the low charge operation mode (20 pC), the x-ray pulse length can be <10 fs. In this paper we report our numerical optimization and simulations to produce even shorter x-ray pulses by optimizing the machine and undulator setup at 20 pC charge. In the soft x-ray regime, with combination of slotted-foil or undulator taper, a single spike x-ray pulse is achievable with peak FEL power of a few 10s GW. Linac Coherent Light Source (LCLS), the world's first hard x-ray Free electron laser (FEL), has started operation since 2009. With nominal operation charge of 250 pC, the generated x-ray pulse length is from 70 fs to a few hundred fs. This marks the beginning of a new era of ultrashort x-ray sciences. In addition, a low charge (20pC) operation mode has also been established. Since the collective effects are reduced at the low charge mode, we can increase the compression factor and still achieve a few kA peak current. The expected electron beam and x-ray pulses are less than 10 fs. There are growing interests in even shorter x-ray pulses, such as fs to sub-fs regime. One of the simple solutions is going to even lower charge. As discussed, single-spike x-ray pulses can be generated using 1 pC charge. However, this charge level is out of the present LCLS diagnostic range. 20 pC is a reasonable operation charge at LCLS, based on the present diagnostic system. At 20 pC in the soft x-ray wavelength regime, we have experimentally demonstrated that FEL can work at undercompression or over-compression mode, such as 1 degree off the full-compression; at full-compression, however, there is almost no lasing. In hard x-ray wavelength regime, we observed that there are reasonable photons generated even at full

  14. Observation of Charge Separation and Space-Charge Region in Single-Crystal P3HT/C60 Heterojunction Nanowires.

    PubMed

    Park, Kyung Sun; Lee, Ki Seok; Baek, Jangmi; Lee, Lynn; Son, Byung Hee; Koo Lee, Yong-Eun; Ahn, Yeong Hwan; Park, Won Il; Kang, Youngjong; Sung, Myung M

    2016-08-22

    We directly observed charge separation and a space-charge region in an organic single-crystal p-n heterojunction nanowire, by means of scanning photocurrent microscopy. The axial p-n heterojunction nanowire had a well-defined planar junction, consisted of P3HT (p-type) and C60 (n-type) single crystals and was fabricated by means of the recently developed inkjet-assisted nanotransfer printing technique. The depletion region formed at the p-n junction was directly observed by exploring the spatial distribution of photogenerated carriers along the heterojunction nanowire under various applied bias voltages. Our study provides a facile approach toward the precise characterization of charge transport in organic heterojunction systems as well as the design of efficient nanoscale organic optoelectronic devices. PMID:27461905

  15. The Fate of a Normal Human Cell Traversed by a Single Charged Particle

    NASA Astrophysics Data System (ADS)

    Fournier, C.; Zahnreich, S.; Kraft, D.; Friedrich, T.; Voss, K.-O.; Durante, M.; Ritter, S.

    2012-09-01

    The long-term ``fate'' of normal human cells after single hits of charged particles is one of the oldest unsolved issues in radiation protection and cellular radiobiology. Using a high-precision heavy-ion microbeam we could target normal human fibroblasts with exactly one or five carbon ions and measured the early cytogenetic damage and the late behaviour using single-cell cloning. Around 70% of the first cycle cells presented visible aberrations in mFISH after a single ion traversal, and about 5% of the cells were still able to form colonies. In one third of selected high-proliferative colonies we observed clonal (radiation-induced) aberrations. Terminal differentiation and markers of senescence (PCNA, p16) in the descendants of cells traversed by one carbon ion occurred earlier than in controls, but no evidence of radiation-induced chromosomal instability was found. We conclude that cells surviving single-ion traversal, often carrying clonal chromosome aberrations, undergo accelerated senescence but maintain chromosomal stability.

  16. The Fate of a Normal Human Cell Traversed by a Single Charged Particle

    PubMed Central

    Fournier, C.; Zahnreich, S.; Kraft, D.; Friedrich, T.; Voss, K.-O.; Durante, M.; Ritter, S.

    2012-01-01

    The long-term “fate” of normal human cells after single hits of charged particles is one of the oldest unsolved issues in radiation protection and cellular radiobiology. Using a high-precision heavy-ion microbeam we could target normal human fibroblasts with exactly one or five carbon ions and measured the early cytogenetic damage and the late behaviour using single-cell cloning. Around 70% of the first cycle cells presented visible aberrations in mFISH after a single ion traversal, and about 5% of the cells were still able to form colonies. In one third of selected high-proliferative colonies we observed clonal (radiation-induced) aberrations. Terminal differentiation and markers of senescence (PCNA, p16) in the descendants of cells traversed by one carbon ion occurred earlier than in controls, but no evidence of radiation-induced chromosomal instability was found. We conclude that cells surviving single-ion traversal, often carrying clonal chromosome aberrations, undergo accelerated senescence but maintain chromosomal stability. PMID:22966418

  17. Single amino acid mutation in alpha-helical peptide affect second harmonic generation hyperpolarizability

    NASA Astrophysics Data System (ADS)

    Wei, Jing; Wang, Jin-Yun; Zhang, Min-Yi; Chai, Guo-Liang; Lin, Chen-Sheng; Cheng, Wen-Dan

    2013-01-01

    We investigate the effect of side chain on the first-order hyperpolarizability in α-helical polyalanine peptide with the 10th alanine mutation (Acetyl(ala)9X(ala)7NH2). Structures of various substituted peptides are optimized by ONIOM (DFT: AM1) scheme, and then linear and nonlinear optical properties are calculated by SOS//CIS/6-31G∗ method. The polarizability and first-order hyperpolarizability increase obviously only when 'X' represents phenylalanine, tyrosine and tryptophan. We also discuss the origin of nonlinear optical response and determine what caused the increase of first-order hyperpolarizability. Our results strongly suggest that side chains containing benzene, phenol and indole have important contributions to first-order hyperpolarizability.

  18. Electron Capture Dissociation of Trivalent Metal Ion-Peptide Complexes

    NASA Astrophysics Data System (ADS)

    Flick, Tawnya G.; Donald, William A.; Williams, Evan R.

    2013-02-01

    With electrospray ionization from aqueous solutions, trivalent metal ions readily adduct to small peptides resulting in formation of predominantly (peptide + MT - H)2+, where MT = La, Tm, Lu, Sm, Ho, Yb, Pm, Tb, or Eu, for peptides with molecular weights below ~1000 Da, and predominantly (peptide + MT)3+ for larger peptides. ECD of (peptide + MT - H)2+ results in extensive fragmentation from which nearly complete sequence information can be obtained, even for peptides for which only singly protonated ions are formed in the absence of the metal ions. ECD of these doubly charged complexes containing MT results in significantly higher electron capture efficiency and sequence coverage than peptide-divalent metal ion complexes that have the same net charge. Formation of salt-bridge structures in which the metal ion coordinates to a carboxylate group are favored even for (peptide + MT)3+. ECD of these latter complexes for large peptides results in electron capture by the protonation site located remotely from the metal ion and predominantly c/ z fragments for all metals, except Eu3+, which undergoes a one electron reduction and only loss of small neutral molecules and b/ y fragments are formed. These results indicate that solvation of the metal ion in these complexes is extensive, which results in the electrochemical properties of these metal ions being similar in both the peptide environment and in bulk water.

  19. Single-stranded DNA detection by solvent-induced assemblies of a metallo-peptide-based complex

    NASA Astrophysics Data System (ADS)

    Das, Priyadip; Reches, Meital

    2016-05-01

    DNA detection is highly important for the sensitive sensing of different pathogenic bacteria and viruses. The major challenge is to create a sensor that can selectively detect very small concentrations of DNA without the need for amplification or complicated equipment. Different technologies such as optical, electrochemical and microgravimetric approaches can detect DNA fragments. Here we show, for the first time, the use of self-assembled nanostructures generated by a metallo-peptide as an optical sensing platform for DNA detection. The system can selectively detect single stranded DNA fragments by fluorescence measurements as it can discriminate even one base mismatch and can perform in the presence of other interfering proteins. This system may be useful in lab-on-a-chip applications.DNA detection is highly important for the sensitive sensing of different pathogenic bacteria and viruses. The major challenge is to create a sensor that can selectively detect very small concentrations of DNA without the need for amplification or complicated equipment. Different technologies such as optical, electrochemical and microgravimetric approaches can detect DNA fragments. Here we show, for the first time, the use of self-assembled nanostructures generated by a metallo-peptide as an optical sensing platform for DNA detection. The system can selectively detect single stranded DNA fragments by fluorescence measurements as it can discriminate even one base mismatch and can perform in the presence of other interfering proteins. This system may be useful in lab-on-a-chip applications. Electronic supplementary information (ESI) available: Peptide and receptor synthesis, characterization of the final and intermediate products, experimental details and additional figures including SEM, TEM, DLS, XRD, UV analysis and AFM topographic analysis. See DOI: 10.1039/c5nr07714a

  20. Design of Asymmetric Peptide Bilayer Membranes.

    PubMed

    Li, Sha; Mehta, Anil K; Sidorov, Anton N; Orlando, Thomas M; Jiang, Zhigang; Anthony, Neil R; Lynn, David G

    2016-03-16

    Energetic insights emerging from the structural characterization of peptide cross-β assemblies have enabled the design and construction of robust asymmetric bilayer peptide membranes. Two peptides differing only in their N-terminal residue, phosphotyrosine vs lysine, coassemble as stacks of antiparallel β-sheets with precisely patterned charged lattices stabilizing the bilayer leaflet interface. Either homogeneous or mixed leaflet composition is possible, and both create nanotubes with dense negative external and positive internal solvent exposed surfaces. Cross-seeding peptide solutions with a preassembled peptide nanotube seed leads to domains of different leaflet architecture within single nanotubes. Architectural control over these cross-β assemblies, both across the bilayer membrane and along the nanotube length, provides access to highly ordered asymmetric membranes for the further construction of functional mesoscale assemblies. PMID:26942690

  1. Synchrotron radiation-based Fourier-transform infrared spectromicroscopy for characterization of the protein/peptide distribution in single microspheres

    PubMed Central

    Wang, Manli; Lu, Xiaolong; Yin, Xianzhen; Tong, Yajun; Peng, Weiwei; Wu, Li; Li, Haiyan; Yang, Yan; Gu, Jingkai; Xiao, Tiqiao; Chen, Min; Zhang, Jiwen

    2015-01-01

    The present study establishes a visualization method for the measurement of the distribution and localization of protein/peptide constituents within a single poly-lactide-co-glycolide (PLGA) microsphere using synchrotron radiation–based Fourier-transform infrared spectromicroscopy (SR-FTIR). The representative infrared wavenumbers specific for protein/peptide (Exenatide) and excipient (PLGA) were identified and chemical maps at the single microsphere level were generated by measuring and plotting the intensity of these specific bands. For quantitative analysis of the distribution within microspheres, Matlab software was used to transform the map file into a 3D matrix and the matrix values specific for the drug and excipient were extracted. Comparison of the normalized SR-FTIR maps of PLGA and Exenatide indicated that PLGA was uniformly distributed, while Exenatide was relatively non-uniformly distributed in the microspheres. In conclusion, SR-FTIR is a rapid, nondestructive and sensitive detection technology to provide the distribution of chemical constituents and functional groups in microparticles and microspheres. PMID:26579456

  2. Effect of Copper and Zinc on the Single Molecule Self-Affinity of Alzheimer’s Amyloid-β Peptides

    PubMed Central

    Hane, Francis T.; Hayes, Reid; Lee, Brenda Y.; Leonenko, Zoya

    2016-01-01

    The presence of trace concentrations of metallic ions, such as copper and zinc, has previously been shown to drastically increase the aggregation rate and neurotoxicity of amyloid-β (Aβ), the peptide implicated in Alzheimer’s disease (AD). The mechanism of why copper and zinc accelerate Aβ aggregation is poorly understood. In this work, we use single molecule force spectroscopy (SMFS) to probe the kinetic and thermodynamic parameters (dissociation constant, Kd, kinetic dissociation rate, koff, and free energy, ΔG) of the dissociation of an Aβ dimer, the amyloid species which initiates the amyloid cascade. Our results show that nanomolar concentrations of copper do not change the single molecule affinity of Aβ to another Aβ peptide in a statistically significant way, while nanomolar concentrations of zinc decrease the affinity of Aβ-Aβ by an order of magnitude. This suggests that the binding of zinc ion to Aβ may interfere with the binding of Aβ-Aβ, leading to a lower self-affinity. PMID:26808970

  3. Synchrotron radiation-based Fourier-transform infrared spectromicroscopy for characterization of the protein/peptide distribution in single microspheres.

    PubMed

    Wang, Manli; Lu, Xiaolong; Yin, Xianzhen; Tong, Yajun; Peng, Weiwei; Wu, Li; Li, Haiyan; Yang, Yan; Gu, Jingkai; Xiao, Tiqiao; Chen, Min; Zhang, Jiwen

    2015-05-01

    The present study establishes a visualization method for the measurement of the distribution and localization of protein/peptide constituents within a single poly-lactide-co-glycolide (PLGA) microsphere using synchrotron radiation-based Fourier-transform infrared spectromicroscopy (SR-FTIR). The representative infrared wavenumbers specific for protein/peptide (Exenatide) and excipient (PLGA) were identified and chemical maps at the single microsphere level were generated by measuring and plotting the intensity of these specific bands. For quantitative analysis of the distribution within microspheres, Matlab software was used to transform the map file into a 3D matrix and the matrix values specific for the drug and excipient were extracted. Comparison of the normalized SR-FTIR maps of PLGA and Exenatide indicated that PLGA was uniformly distributed, while Exenatide was relatively non-uniformly distributed in the microspheres. In conclusion, SR-FTIR is a rapid, nondestructive and sensitive detection technology to provide the distribution of chemical constituents and functional groups in microparticles and microspheres. PMID:26579456

  4. Direct Measurement of Pore Dynamics and Leakage Induced by a Model Antimicrobial Peptide in Single Vesicles and Cells.

    PubMed

    Burton, Matthew G; Huang, Qi M; Hossain, Mohammed A; Wade, John D; Palombo, Enzo A; Gee, Michelle L; Clayton, Andrew H A

    2016-06-28

    Antimicrobial peptides are promising therapeutic alternatives to counter growing antimicrobial resistance. Their precise mechanism of action remains elusive, however, particularly with respect to live bacterial cells. We investigated the interaction of a fluorescent melittin analogue with single giant unilamellar vesicles, giant multilamellar vesicles, and bilamellar Gram-negative Escherichia coli (E. coli) bacteria. Time-lapse fluorescence lifetime imaging microscopy was employed to determine the population distribution of the fluorescent melittin analogue between pore state and membrane surface state, and simultaneously measure the leakage of entrapped fluorescent species from the vesicle (or bacterium) interior. In giant unilamellar vesicles, leakage from vesicle interior was correlated with an increase in level of pore states, consistent with a stable pore formation mechanism. In giant multilamellar vesicles, vesicle leakage occurred more gradually and did not appear to correlate with increased pore states. Instead pore levels remained at a low steady-state level, which is more in line with coupled equilibria. Finally, in single bacterial cells, significant increases in pore levels were observed over time, which were correlated with only partial loss of cytosolic contents. These observations suggested that pore formation, as opposed to complete dissolution of membrane, was responsible for the leakage of contents in these systems, and that the bacterial membrane has an adaptive capacity that resists peptide attack. We interpret the three distinct pore dynamics regimes in the context of the increasing physical and biological complexity of the membranes. PMID:27281288

  5. Single-molecule investigation of the interactions between reconstituted planar lipid membranes and an analogue of the HP(2-20) antimicrobial peptide

    SciTech Connect

    Mereuta, Loredana; Luchian, Tudor Park, Yoonkyung; Hahm, Kyung-Soo

    2008-09-05

    In this study, we employed electrophysiology experiments carried out at the single-molecule level to study the mechanism of action of the HPA3 peptide, an analogue of the linear antimicrobial peptide, HP(2-20), isolated from the N-terminal region of the Helicobacter pylori ribosomal protein. Amplitude analysis of currents fluctuations induced by HPA3 peptide at various potentials in zwitterionic lipid membranes reveal the existence of reproducible conductive states in the stochastic behavior of such events, which directly supports the existence of transmembrane pores induced the peptide. From our data recorded both at the single-pore and macroscopic levels, we propose that the HPA3 pore formation is electrophoretically facilitated by trans-negative transmembrane potentials, and HPA3 peptides translocate into the trans monolayers after forming the pores. We present evidence according to which the decrease in the membrane dipole potential of a reconstituted lipid membranes leads to an augmentation of the membrane activity of HPA3 peptides, and propose that a lower electric dipole field of the interfacial region of the membrane caused by phloretin facilitates the surface-bound HPA3 peptides to break free from one leaflet of the membrane, insert into the membrane and contribute to pore formation spanning the entire thickness of the membrane.

  6. PH dependent adhesive peptides

    DOEpatents

    Tomich, John; Iwamoto, Takeo; Shen, Xinchun; Sun, Xiuzhi Susan

    2010-06-29

    A novel peptide adhesive motif is described that requires no receptor or cross-links to achieve maximal adhesive strength. Several peptides with different degrees of adhesive strength have been designed and synthesized using solid phase chemistries. All peptides contain a common hydrophobic core sequence flanked by positively or negatively charged amino acids sequences.

  7. DNA recovery from a single bacterial cell using charge-reversible magnetic nanoparticles.

    PubMed

    Maeda, Yoshiaki; Toyoda, Takahiro; Mogi, Takeyuki; Taguchi, Tomoyuki; Tanaami, Takeo; Yoshino, Tomoko; Matsunaga, Tadashi; Tanaka, Tsuyoshi

    2016-03-01

    Highly efficient DNA recovery from a single bacterial cell was performed by means of imidazole-modified magnetic nanoparticles (Imi-MNPs). The modification by imidazole was confirmed by Fourier transform infrared spectroscopy. The Imi-MNPs were highly efficient at DNA extraction owing to the charge-reversible properties of Imi-MNPs, whereby DNA is attached to the particles at low pH and eluted at high pH because of electrostatic interactions. The DNA recovery ratio was determined by real-time PCR, and it revealed that complete recovery was guaranteed at ≥10(3) genome copies of Bacillus subtilis. Extraction of DNA from single bacterial cells was followed by PCR amplification of 16S rDNA and capillary electrophoresis. We achieved detection of single bacterial cells with a detection rate of 80%. We believe that our DNA recovery strategy may serve as a powerful tool for efficient DNA extraction and should be useful for quality control of cosmetics, foods, and pharmaceutical products. PMID:26704992

  8. Search for pair produced stable singly charged heavy particles in Z 0 decays

    NASA Astrophysics Data System (ADS)

    Akrawy, M. Z.; Alexander, G.; Allison, J.; Allport, P. P.; Anderson, K. J.; Armitage, J. C.; Arnison, G. T. J.; Ashton, P.; Azuelos, G.; Baines, J. T. M.; Ball, A. H.; Banks, J.; Barker, G. J.; Barlow, R. J.; Batley, J. R.; Beck, A.; Becker, J.; Behnke, T.; Bell, K. W.; Bella, G.; Bethke, S.; Biebel, O.; Binder, U.; Bloodworth, I. J.; Bock, P.; Breuker, H.; Brown, R. M.; Brun, R.; Buijs, A.; Burckhart, H. J.; Capiluppi, P.; Carnegie, R. K.; Carter, A. A.; Carter, J. R.; Chang, C. Y.; Charlton, D. G.; Chrin, J. T. M.; Clarke, P. E. L.; Cohen, I.; Collins, W. J.; Conboy, J. E.; Couch, M.; Coupland, M.; Cuffiani, M.; Dado, S.; Dallavalle, G. M.; Debu, P.; Deninno, M. M.; Dieckmann, A.; Dittmar, M.; Dixit, M. S.; Duchovni, E.; Duerdoth, I. P.; Dumas, D. J. P.; El Mamouni, H.; Elcombe, P. A.; Estabrooks, P. G.; Etzion, E.; Fabbri, F.; Farthouat, P.; Fischer, H. M.; Fong, D. G.; French, M. T.; Fukunaga, C.; Gaidot, A.; Ganel, O.; Gary, J. W.; Gascon, J.; Geddes, N. I.; Gee, C. N. P.; Geich-Gimbel, C.; Gensler, S. W.; Gentit, F. X.; Giacomelli, G.; Gibson, V.; Gibson, W. R.; Gillies, J. D.; Goldberg, J.; Goodrick, M. J.; Gorn, W.; Granite, D.; Gross, E.; Grunhaus, J.; Hagedorn, H.; Hagemann, J.; Hansroul, M.; Hargrove, C. K.; Harrus, I.; Hart, J.; Hattersley, P. M.; Hauschild, M.; Hawkes, C. M.; Heflin, E.; Hemingway, R. J.; Heuer, R. D.; Hill, J. C.; Hillier, S. J.; Ho, C.; Hobbs, J. D.; Hobson, P. R.; Hochman, D.; Holl, B.; Homer, R. J.; Hou, S. R.; Howarth, C. P.; Hughes-Jones, R. E.; Humbert, R.; Igo-Kemenes, P.; Ihssen, H.; Imrie, D. C.; Janissen, L.; Jawahery, A.; Jeffreys, P. W.; Jeremie, H.; Jimack, M.; Jobes, M.; Jones, R. W. L.; Jovanovic, P.; Karlen, D.; Kawagoe, K.; Kawamoto, T.; Kellogg, R. G.; Kennedy, B. W.; Kleinwort, C.; Klem, D. E.; Knop, G.; Kobayashi, T.; Kokott, T. P.; Köpke, L.; Kowalewski, R.; Kreutzmann, H.; Kroll, J.; Kuwano, M.; Kyberd, P.; Lafferty, G. D.; Lamarche, F.; Larson, W. J.; Layter, J. G.; Le Du, P.; Leblanc, P.; Lee, A. M.; Lehto, M. H.; Lellouch, D.; Lennert, P.; Lessard, L.; Levinson, L.; Lloyd, S. L.; Loebinger, F. K.; Lorah, J. M.; Lorazo, B.; Losty, M. J.; Ludwig, J.; Ma, J.; Macbeth, A. A.; Mannelli, M.; Marcellini, S.; Maringer, G.; Martin, A. J.; Martin, J. P.; Mashimo, T.; Mättig, P.; Maur, U.; McMahon, T. J.; McNutt, J. R.; Meijers, F.; Menszner, D.; Merritt, F. S.; Mes, H.; Michelini, A.; Middleton, R. P.; Mikenberg, G.; Mildenberger, J.; Miller, D. J.; Milstene, C.; Minowa, M.; Mohr, W.; Montanari, A.; Mori, T.; Moss, M. W.; Murphy, P. G.; Murray, W. J.; Nellen, B.; Nguyen, H. H.; Nozaki, M.; O'Dowd, A. J. P.; O'Neale, S. W.; O'Neill, B. P.; Oakham, F. G.; Odorici, F.; Ogg, M.; Oh, H.; Oreglia, M. J.; Orito, S.; Pansart, J. P.; Patrick, G. N.; Pawley, S. J.; Pfister, P.; Pilcher, J. E.; Pinfold, J. L.; Plane, D. E.; Poli, B.; Pouladdej, A.; Prebys, E.; Pritchard, T. W.; Quast, G.; Raab, J.; Redmond, M. W.; Rees, D. L.; Regimbald, M.; Riles, K.; Roach, C. M.; Robins, S. A.; Rollnik, A.; Roney, J. M.; Rossberg, S.; Rossi, A. M.; Routenburg, P.; Runge, K.; Runolfsson, O.; Sanghera, S.; Sansum, R. A.; Sasaki, M.; Saunders, B. J.; Schaile, A. D.; Schaile, O.; Schappert, W.; Scharff-Hansen, P.; Schreiber, S.; Schwarz, J.; Shapira, A.; Shen, B. C.; Sherwood, P.; Simon, A.; Singh, P.; Siroli, G. P.; Skuja, A.; Smith, A. M.; Smith, T. J.; Snow, G. A.; Springer, R. W.; Sproston, M.; Stephens, K.; Stier, H. E.; Stroehmer, R.; Strom, D.; Takeda, H.; Takeshita, T.; Thackray, N. J.; Tsukamoto, T.; Turner, M. F.; Tysarczyk-Niemeyer, G.; Van den plas, D.; VanDalen, G. J.; Vasseur, G.; Virtue, C. J.; von der Schmitt, H.; von Krogh, J.; Wagner, A.; Wahl, C.; Walker, J. P.; Ward, C. P.; Ward, D. R.; Watkins, P. M.; Watson, A. T.; Watson, N. K.; Weber, M.; Weisz, S.; Wells, P. S.; Wermes, N.; Weymann, M.; Wilson, G. W.; Wilson, J. A.; Wingerter, I.; Winterer, V.-H.; Wood, N. C.; Wotton, S.; Wuensch, B.; Wyatt, T. R.; Yaari, R.; Yang, Y.; Yekutieli, G.; Yoshida, T.; Zeuner, W.; Zorn, G. T.; OPAL Collaboration

    1990-12-01

    A direct search for the exclusive pair production of stable singly charged heavy (SCH) particles in Z 0 decays at the LEP e +e - collider is presented. In a scan around the Z 0 resonance of 0.4 pb - integrated luminosity, no evidence is seen for the production of slow-moving charged particles as measured by their time-of-flight. We set an upper limit of 1 × 10 -3 on the Z 0 branching ratio into a pair of SCH fermions in the mass range 29-40 GeV/ c2, corresponding to a 3 MeV upper limit on such a contribution to the total width of the Z 0. We exclude a fourth generation SCH lepton in the mass range 18.5-42.8 GeV/ c2. We also exclude a stable supersymmetric partner of the right-handed lepton, l˜R, in the mass range 21.5-38.8 GeV/ c2. All limits are at 95% confidence level.

  9. Single bunch transverse instability in a circular accelerator with chromaticity and space charge

    NASA Astrophysics Data System (ADS)

    Balbekov, V.

    2015-10-01

    The transverse instability of a bunch in a circular accelerator is elaborated in this paper. A new tree-modes model is proposed and developed to describe the most unstable modes of the bunch. This simple and flexible model includes chromaticity and space charge, and can be used with any bunch and wake forms. The dispersion equation for the bunch eigentunes is obtained in form of a third-order algebraic equation. The known head-tail and TMCI modes appear as the limiting cases which are distinctly bounded at zero chromaticity only. It is shown that the instability parameters depend only slightly on the bunch model but they are rather sensitive to the wake shape. In particular, space charge effects are investigated in the paper and it is shown that their influence depends on sign of wake field enhancing the bunch stability if the wake is negative. The resistive wall wake is considered in detail including a comparison of single and collective effects. A comparison of the results with earlier publications is carried out.

  10. Single bunch transverse instability in a circular accelerator with chromaticity and space charge

    SciTech Connect

    Balbekov, V.

    2015-10-21

    The transverse instability of a bunch in a circular accelerator is elaborated in this paper. A new tree-modes model is proposed and developed to describe the most unstable modes of the bunch. This simple and flexible model includes chromaticity and space charge, and can be used with any bunch and wake forms. The dispersion equation for the bunch eigentunes is obtained in form of a third-order algebraic equation. The known head-tail and TMCI modes appear as the limiting cases which are distinctly bounded at zero chromaticity only. It is shown that the instability parameters depend only slightly on the bunch model but they are rather sensitive to the wake shape. In particular, space charge effects are investigated in the paper and it is shown that their influence depends on sign of wake field enhancing the bunch stability if the wake is negative. In addition, the resistive wall wake is considered in detail including a comparison of single and collective effects. A comparison of the results with earlier publications is carried out.

  11. Single bunch transverse instability in a circular accelerator with chromaticity and space charge

    DOE PAGESBeta

    Balbekov, V.

    2015-10-21

    The transverse instability of a bunch in a circular accelerator is elaborated in this paper. A new tree-modes model is proposed and developed to describe the most unstable modes of the bunch. This simple and flexible model includes chromaticity and space charge, and can be used with any bunch and wake forms. The dispersion equation for the bunch eigentunes is obtained in form of a third-order algebraic equation. The known head-tail and TMCI modes appear as the limiting cases which are distinctly bounded at zero chromaticity only. It is shown that the instability parameters depend only slightly on the bunchmore » model but they are rather sensitive to the wake shape. In particular, space charge effects are investigated in the paper and it is shown that their influence depends on sign of wake field enhancing the bunch stability if the wake is negative. In addition, the resistive wall wake is considered in detail including a comparison of single and collective effects. A comparison of the results with earlier publications is carried out.« less

  12. Single charge exchange in collision of fast protons with hydrogen molecules

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim; Sattarpour, Seyedeh Hedyeh

    2015-11-01

    Single charge transfer process in collision of energetic protons with molecular hydrogens is theoretically studied using a first-order two-effective-center Born approximation. The correct boundary conditions are incorporated in the formalism and the Hartree-Fock molecular wave function for molecular targets and the residual ions are used to calculate the transition amplitude. The interference patterns in the capture differential cross-sections (DCSs) for a given fixed orientation of the molecule, due to the scattering from the two-atomic centers in the molecular targets, are examined. The dependence of the DCSs upon the angle between the molecular axis and the direction of the incident velocity is theoretically investigated. Both average differential and integral cross-sections are calculated. The obtained results are compared with the available experimental data.

  13. Photoinduced charge transfer and acetone sensitivity of single-walled carbon nanotube-titanium dioxide hybrids.

    PubMed

    Ding, Mengning; Sorescu, Dan C; Star, Alexander

    2013-06-19

    The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT-TiO2 core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT-TiO2 hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO2 and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range. PMID:23734594

  14. Pion nucleus single charge exchange reactions above the. delta. (1232) resonance

    SciTech Connect

    Rokni, S.H.

    1987-06-01

    Forward-angle differential cross sections for the (..pi../sup +/, ..pi../sup 0/) reaction leading to the Isobaric Analog State in the residual nuclei at 300, 425, 500 and 550 MeV have been measured. Targets ranged in mass from /sup 7/Li to /sup 208/Pb. A description of the experimental setup and the analysis is presented. The 0/sup 0/ cross sections are found to rise markedly between 300 and 425 MeV, contrary to the extrapolation from the lower energy data and to the behavior of the free pion-nucleon single charge exchange process. The angular distributions are sharply forward peaked. Systematics of the data indicate increased volume penetration with increasing pion beam energy. The cross sections are compared with the results of Glauber model calculations indicating the significance of higher order processes even at these energies. 67 refs., 40 figs., 22 tabs.

  15. Charge transfer processes and ultraviolet induced absorption in Yb:YAG single crystal laser materials

    NASA Astrophysics Data System (ADS)

    Rydberg, S.; Engholm, M.

    2013-06-01

    Charge transfer (CT) transitions and UV induced color centers in Yb:YAG single crystals have been investigated. A simultaneous pair formation of a stable Yb2+ ion and a hole related (O-) color center (hole polaron) are observed through a CT-process. Slightly different types of hole related color centers are formed in Yb:YAG crystals containing small levels of iron impurities. Furthermore, excitation spectroscopy on the UV irradiated Yb:YAG samples could confirm an energy transfer process between Yb3+ and Yb2+ ions. The findings are important for an increased knowledge of the physical loss mechanisms observed in Yb-doped laser materials, such as the nonlinear decay process in Yb:YAG crystals as well as the photodarkening phenomenon in Yb-doped fiber lasers.

  16. Isotope-Resolved and Charge-Sensitive Force Imaging Using Scanned Single Molecules

    NASA Astrophysics Data System (ADS)

    Sun, Yan; Rastawicki, Dominik; Liu, Yang; Mar, Warren; Manoharan, Hari; Miglio, Anna; Melinte, Sorin; Charlier, Jean-Christophe; Rignanese, Gian-Marco; He, Lianhua; Liu, Fang; Zhou, Aihui

    Originally conceived as surface imaging instruments, the scanning tunnelling microscope (STM) and the atomic force microscope (AFM) were recently used to probe molecular chemical bonds with exquisite sensitivity. Remarkably, molecule-functionalized scanning tips can also provide direct access to the inelastic electron tunneling spectrum (IETS) of the terminal molecule. Here we report atomic manipulation experiments addressing carbon monoxide (CO) isotopes at low temperatures. The unique and quantifiable dependence of the CO vibrational modes offers insight into tip-controlled force and charge sensing of surface adsorbates, subsurface defects, and quantum nanostructures. The specific behavior of the monitored vibrational modes originates from the interplay of interaction forces between the top electrode--a scanned tip functionalized with a single molecule--and the atomic scale force field surrounding the target atomically-assembled nanostructure. We also present density functional theory (DFT) computations that have been performed in order to scrutinize and visualize the vibrational spectroscopic fingerprints and local force fields.

  17. Characterization of Single-Sided Charge-Sharing CZT Strip Detectors for Gamma-Ray Astronomy

    NASA Technical Reports Server (NTRS)

    Donmez, Burcin; Macri, John R.; Ryan, James M.; Legere, Jason S.; McConnell, Mark L.; Widholm, Mark; Narita, Tomohiko; Hamel, Louis-Andre

    2006-01-01

    We report progress in the study of thick single-sided charge-sharing cadmium zinc telluride (CZT) strip detector modules designed to perform spectroscopy and 3-D imaging of gamma-rays. We report laboratory measurements including spectroscopy, efficiency and 3-D imaging capability of prototype detectors (15 15 7.5 cu mm) with 11x11 unit cells. We also report on Monte Carlo simulations (GEANT4 v7.1) to investigate the effect of multihits on detector performance in both spectroscopy and imaging. We compare simulation results with data obtained from laboratory measurements and discuss the implications for future strip detector designs. Keywords: CZT, strip detectors, gamma-ray

  18. Charge transport in single Au / alkanedithiol / Au junctions: coordination geometries and conformational degrees of freedom.

    PubMed

    Li, Chen; Pobelov, Ilya; Wandlowski, Thomas; Bagrets, Alexei; Arnold, Andreas; Evers, Ferdinand

    2008-01-01

    Recent STM molecular break-junction experiments have revealed multiple series of peaks in the conductance histograms of alkanedithiols. To resolve a current controversy, we present here an in-depth study of charge transport properties of Au|alkanedithiol|Au junctions. Conductance histograms extracted from our STM measurements unambiguously confirm features showing more than one set of junction configurations. On the basis of quantum chemistry calculations, we propose that certain combinations of different sulfur-gold couplings and trans/gauche conformations act as the driving agents. The present study may have implications for experimental methodology: whenever conductances of different junction conformations are not statistically independent, the conductance histogram technique can exhibit a single series only, even though a much larger abundance of microscopic realizations exists. PMID:18076172

  19. Synthesis and Mechanism Insight of a Peptide-Grafted Hyperbranched Polymer Nanosheet with Weak Positive Charges but Excellent Intrinsically Antibacterial Efficacy.

    PubMed

    Gao, Jingyi; Wang, Mingzhi; Wang, Fangyingkai; Du, Jianzhong

    2016-06-13

    Antimicrobial resistance is an increasingly problematic issue in the world and there is a present and urgent need to develop new antimicrobial therapies without drug resistance. Antibacterial polymers are less susceptible to drug resistance but they are prone to inducing serious side effects due to high positive charge. Herein we report a peptide-grafted hyperbranched polymer which can self-assemble into unusual nanosheets with highly effective intrinsically antibacterial activity but weak positive charges (+ 6.1 mV). The hyperbranched polymer was synthesized by sequential Michael addition-based thiol-ene and free radical mediated thiol-ene reactions, and followed by ring-opening polymerization of N-carboxyanhydrides (NCAs). The nanosheet structure was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies. Furthermore, a novel "wrapping and penetrating" antibacterial mechanism of the nanosheets was revealed by TEM and it is the key to significantly decrease the positive charges but have a very low minimum inhibitory concentration (MIC) of 16 μg mL(-1) against typical Gram-positive and Gram-negative bacteria. Overall, our synthetic strategy demonstrates a new insight for synthesizing antibacterial nanomaterials with weak positive charges. Moreover, the unique antibacterial mechanism of our nanosheets may be extended for designing next-generation antibacterial agents without drug resistance. PMID:27181113

  20. Covalent and non-covalent binding in the ion/ion charge inversion of peptide cations with benzene-disulfonic acid anions.

    PubMed

    Stutzman, John R; Luongo, Carl A; McLuckey, Scott A

    2012-06-01

    Protonated angiotensin II and protonated leucine enkephalin-based peptides, which included YGGFL, YGGFLF, YGGFLH, YGGFLK and YGGFLR, were subjected to ion/ion reactions with the doubly deprotonated reagents 4-formyl-1,3-benzenedisulfonic acid (FBDSA) and 1,3-benzenedisulfonic acid (BDSA). The major product of the ion/ion reaction is a negatively charged complex of the peptide and reagent. Following dehydration of [M + FBDSA-H](-) via collisional-induced dissociation (CID), angiotensin II (DRVYIHPF) showed evidence for two product populations, one in which a covalent modification has taken place and one in which an electrostatic modification has occurred (i.e. no covalent bond formation). A series of studies with model systems confirmed that strong non-covalent binding of the FBDSA reagent can occur with subsequent ion trap CID resulting in dehydration unrelated to the adduct. Ion trap CID of the dehydration product can result in cleavage of amide bonds in competition with loss of the FBDSA adduct. This scenario is most likely for electrostatically bound complexes in which the peptide contains both an arginine residue and one or more carboxyl groups. Otherwise, loss of the reagent species from the complex, either as an anion or as a neutral species, is the dominant process for electrostatically bound complexes. The results reported here shed new light on the nature of non-covalent interactions in gas phase complexes of peptide ions that can be used in the rationale design of reagent ions for specific ion/ion reaction applications. PMID:22707160

  1. High-Fidelity Rapid Initialization and Read-Out of an Electron Spin via the Single Donor D- Charge State

    NASA Astrophysics Data System (ADS)

    Watson, T. F.; Weber, B.; House, M. G.; Büch, H.; Simmons, M. Y.

    2015-10-01

    We demonstrate high-fidelity electron spin read-out of a precision placed single donor in silicon via spin selective tunneling to either the D+ or D- charge state of the donor. By performing read-out at the stable two electron D0↔D- charge transition we can increase the tunnel rates to a nearby single electron transistor charge sensor by nearly 2 orders of magnitude, allowing faster qubit read-out (1 ms) with minimum loss in read-out fidelity (98.4%) compared to read-out at the D+↔D0 transition (99.6%). Furthermore, we show that read-out via the D- charge state can be used to rapidly initialize the electron spin qubit in its ground state with a fidelity of FI=99.8 %.

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

    PubMed

    Shankla, Manish; Aksimentiev, Aleksei

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Shankla, Manish; Aksimentiev, Aleksei

    2014-10-01

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

  4. Ratio of double to single ionization of helium: The relationship between ionization by photons and by bare charged particles

    SciTech Connect

    Manson, S.T. ); McGuire, J.H. )

    1995-01-01

    It is well known that cross sections for ionization of atoms by fast charged particles and by photons are related by the Bethe-Born theory. We employ this relationship to derive a corresponding relation for the ratio [ital R] of double to single ionization including the first two terms of the Bethe expansion. For sufficiently fast charged particles, where the second term can be ignored, the ratios as a function of [Delta][ital E]---the energies transferred to the atom by the projectile---for ionization by charged particles [ital R][sub [ital z

  5. Theoretical study of the charge transport through C60-based single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Bilan, S.; Zotti, L. A.; Pauly, F.; Cuevas, J. C.

    2012-05-01

    We present a theoretical study of the conductance and thermopower of single-molecule junctions based on C60 and C60-terminated molecules. We first analyze the transport properties of gold-C60-gold junctions and show that these junctions can be highly conductive (with conductances above 0.1G0, where G0=2e2/h is the quantum of conductance). Moreover, we find that the thermopower in these junctions is negative due to the fact that the lowest unoccupied molecular orbital dominates the charge transport, and its magnitude can reach several tens of microvolts per kelvin, depending on the contact geometry. On the other hand, we study the suitability of C60 as an anchoring group in single-molecule junctions. For this purpose, we analyze the transport through several dumbbell derivatives using C60 as anchors, and we compare the results with those obtained with thiol and amine groups. Our results show that the conductance of C60-terminated molecules is rather sensitive to the binding geometry. Moreover, the conductance of the molecules is typically reduced by the presence of the C60 anchors, which in turn makes the junctions more sensitive to the functionalization of the molecular core with appropriate side groups.

  6. Charging the Quantum Capacitance of Graphene with a Single Biological Ion Channel

    PubMed Central

    2015-01-01

    The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents. PMID:24754625

  7. Peptide docking of HIV-1 p24 with single chain fragment variable (scFv) by CDOCKER algorithm

    NASA Astrophysics Data System (ADS)

    Karim, Hana Atiqah Abdul; Tayapiwatana, Chatchai; Nimmanpipug, Piyarat; Zain, Sharifuddin M.; Rahman, Noorsaadah Abdul; Lee, Vannajan Sanghiran

    2014-10-01

    In search for the important residues that might have involve in the binding interaction between the p24 caspid protein of HIV-1 fragment (MET68 - PRO90) with the single chain fragment variable (scFv) of FAB23.5, modern computational chemistry approach has been conducted and applied. The p24 fragment was initially taken out from the 1AFV protein molecule consisting of both light (VL) and heavy (VH) chains of FAB23.5 as well as the HIV-1 caspid protein. From there, the p24 (antigen) fragment was made to dock back into the protein pocket receptor (antibody) by using the CDOCKER algorithm to conduct the molecular docking process. The score calculated from the CDOCKER gave 15 possible docked poses with various docked ligand's positions, the interaction energy as well as the binding energy. The best docked pose that imitates the original antigen's position was determined and further processed to the In Situ minimization to obtain the residues interaction energy as well as to observe the hydrogen bonds interaction in the protein-peptide complex. Based on the results demonstrated, the specific residues in the complex that have shown immense lower interaction energies in the 5Å vicinity region from the peptide are from the heavy chain (VH:TYR105) and light chain (VL: ASN31, TYR32, and GLU97). Those residues play vital roles in the binding mechanism of Antibody-Antigen (Ab-Ag) complex of p24 with FAB23.5.

  8. A stable and functional single peptide phycoerythrin (15.45 kDa) from Lyngbya sp. A09DM.

    PubMed

    Sonani, Ravi Raghav; Rastogi, Rajesh Prasad; Joshi, Meghna; Madamwar, Datta

    2015-03-01

    A functional and stable truncated-phycoerythrin (T-PE) was found as a result of spontaneous in vitro truncation. Truncation was noticed to occur during storage of purified native-phycoerythrin (N-PE) isolated from Lyngbya sp. A09DM. SDS and native-PAGE analysis revealed the truncation of N-PE, containing α (19.0 kDa)--and β (21.5 kDa)--subunits to the only single peptide of ∼15.45 kDa (T-PE). The peptide mass fingerprinting (PMF) and MS/MS analysis indicated that T-PE is the part of α-subunit of N-PE. UV-visible absorption peak of N-PE was found to split into two peaks (540 and 565 nm) after truncation, suggesting the alterations in its folded state. The emission spectra of both N-PE and T-PE show the emission band centered at 581 nm (upon excitation at 559 nm) suggested the maintenance of fluorescence even after significant truncation. Urea-induced denaturation and Gibbs-free energy (ΔGD°) calculations suggested that the folding and structural stability of T-PE was almost similar to that of N-PE. Presented bunch of evidences revealed the truncation in N-PE without perturbing its folding, structural stability and functionality (fluorescence), and thereby suggested its applicability in fluorescence based biomedical techniques where smaller fluorescence molecules are more preferable. PMID:25485942

  9. Recognition of a single amino acid change on the surface of a major transplantation antigen is in the context of self peptide.

    PubMed

    Pullen, J K; Tallquist, M D; Melvold, R W; Pease, L R

    1994-04-01

    The transcripts encoding two strongly alloantigenic class I mutant molecules, Kdm4 and Kdm5, were characterized and found to encode products that differ from the parental Kd glycoprotein by single amino acid substitutions. The Kdm4 molecule has an amino acid change at position 114, an integral component of a beta-sheet associated with pockets D and E of the peptide binding site. The basis for strong alloantigenicity of the variant molecule can be attributed to differences in peptide binding that were visualized by HPLC analysis of eluted peptides. In contrast, the Kdm5 molecule differs from the parent at position 158, a component of the alpha-helix that is not associated with any of the pockets of the peptide binding site. No differences in peptide binding by Kdm5 in comparison with the parent Kd molecule were seen by HPLC, suggesting that the variant and parent molecules bind the same set of peptides. The ability of (dm4 x dm5) F1 hybrid mice to recognize and lyse BALB/c stimulator cells indicates that the alloantigenic properties determined by the 158 substitution result from the interactions of the alpha-helix regions (changed in dm5) with the pockets of the binding site (changed in dm4). We conclude that self peptides shared by the F1 hybrid and the BALB/c stimulator cells are recognized in the context of structural features of the helices of the Ag-presenting molecule as alloantigenic determinants. PMID:8144927

  10. Lipid surface charge does not influence conductance or calcium block of single sodium channels in planar bilayers.

    PubMed Central

    Worley, J F; French, R J; Pailthorpe, B A; Krueger, B K

    1992-01-01

    We have studied the effects of membrane surface charge on Na+ ion permeation and Ca2+ block in single, batrachotoxin-activated Na channels from rat brain, incorporated into planar lipid bilayers. In phospholipid membranes with no net charge (phosphatidylethanolamine, PE), at low divalent cation concentrations (approximately 100 microM Mg2+), the single channel current-voltage relation was linear and the single channel conductance saturated with increasing [Na+] and ionic strength, reaching a maximum (gamma max) of 31.8 pS, with an apparent dissociation constant (K0.5) of 40.5 mM. The data could be approximated by a rectangular hyperbola. In negatively charged bilayers (70% phosphatidylserine, PS; 30% PE) slightly larger conductances were observed at each concentration, but the hyperbolic form of the conductance-concentration relation was retained (gamma max = 32.9 pS and K0.5 = 31.5 mM) without any preferential increase in conductance at lower ionic strengths. Symmetrical application of Ca2+ caused a voltage-dependent block of the single channel current, with the block being greater at negative potentials. For any given voltage and [Na+] this block was identical in neutral and negatively charged membranes. These observations suggest that both the conduction pathway and the site(s) of Ca2+ block of the rat brain Na channel protein are electrostatically isolated from the negatively charged headgroups on the membrane lipids. PMID:1318097

  11. Infrared Multiphoton Dissociation of Peptide Cations in a Dual Pressure Linear Ion Trap Mass Spectrometer

    PubMed Central

    Gardner, Myles W.; Smith, Suncerae I.; Ledvina, Aaron R.; Madsen, James A.; Coon, Joshua J.; Schwartz, Jae C.; Stafford, George C.; Brodbelt, Jennifer S.

    2009-01-01

    A dual pressure linear ion trap mass spectrometer was modified to permit infrared multiphoton dissociation (IRMPD) in each of the two cells - the first a high pressure cell operated at nominally 5 × 10-3 Torr and the second a low pressure cell operated at nominally 3 × 10-4 Torr. When IRMPD was performed in the high pressure cell, most peptide ions did not undergo significant photodissociation; however, in the low pressure cell peptide cations were efficiently dissociated with less than 25 ms of IR irradiation regardless of charge state. IRMPD of peptide cations allowed the detection of low m/z product ions including the y1 fragments and immonium ions which are not typically observed by ion trap collision induced dissociation (CID). Photodissociation efficiencies of ~100% and MS/MS (tandem mass spectrometry) efficiencies of greater than 60% were observed for both multiply and singly protonated peptides. In general, higher sequence coverage of peptides was obtained using IRMPD over CID. Further, greater than 90% of the product ion current in the IRMPD mass spectra of doubly charged peptide ions was composed of singly charged product ions compared to the CID mass spectra in which the abundances of the multiply and singly charged product ions were equally divided. Highly charged primary product ions also underwent efficient photodissociation to yield singly charged secondary product ions, thus simplifying the IRMPD product ion mass spectra. PMID:19739654

  12. Open questions in electronic sputtering of solids by slow highly charged ions with respect to applications in single ion implantation

    SciTech Connect

    Schenkel, T.; Rangelow, I.W.; Keller, R.; Park, S.J.; Nilsson, J.; Persaud, A.; Radmilivitc, V.R.; Liddle, J.A.; Grabiec, P.; Bokor, J.; Schneider, D.H.

    2003-07-16

    In this article we discuss open questions in electronic sputtering of solids by slow, highly charged ions in the context of their application in a single ion implantation scheme. High yields of secondary electrons emitted when highly charged dopant ions impinge on silicon wafers allow for formation of non-Poissonian implant structures such as single atom arrays. Control of high spatial resolution and implant alignment require the use of nanometer scale apertures. We discuss electronic sputtering issues on mask lifetimes, and damage to silicon wafers.

  13. Experimental determination of single-event upset (SEU) as a function of collected charge in bipolar integrated circuits

    NASA Technical Reports Server (NTRS)

    Zoutendyk, J. A.; Malone, C. J.; Smith, L. S.

    1984-01-01

    Single-Event Upset (SEU) in bipolar integrated circuits (ICs) is caused by charge collection from ion tracks in various regions of a bipolar transistor. This paper presents experimental data which have been obtained wherein the range-energy characteristics of heavy ions (Br) have been utilized to determine the cross section for soft-error generation as a function of charge collected from single-particle tracks which penetrate a bipolar static RAM. The results of this work provide a basis for the experimental verification of circuit-simulation SEU modeling in bipolar ICs.

  14. Single-Shot Charge Readout Using a Cryogenic Heterojunction Bipolar Transistor Preamplifier Inline with a Silicon Single Electron Transistor at Millikelvin Temperatures

    NASA Astrophysics Data System (ADS)

    Curry, Matthew; England, Troy; Wendt, Joel; Pluym, Tammy; Lilly, Michael; Carr, Stephen; Carroll, Malcolm

    Single-shot readout is a requirement for many implementations of quantum information processing. The single-shot readout fidelity is dependent on the signal-to-noise-ratio (SNR) and bandwidth of the readout detection technique. Several different approaches are being pursued to enhance read-out including RF-reflectometry, RF-transmission, parametric amplification, and transistor-based cryogenic preamplification. The transistor-based cryogenic preamplifier is attractive in part because of the reduced experimental complexity compared with the RF techniques. Here we present single-shot charge readout using a cryogenic Heterojunction-Bipolar-Transistor (HBT) inline with a silicon SET charge-sensor at millikelvin temperatures. For the relevant range of HBT DC-biasing, the current gain is 100 to 2000 and the power dissipation is 50 nW to 5 μW, with the microfabricated SET and discrete HBT in an integrated package mounted to the mixing chamber stage of a dilution refrigerator. We experimentally demonstrate a SNR of up to 10 with a bandwidth of 1 MHz, corresponding to a single-shot time-domain charge-sensitivity of approximately 10-4 e / √Hz. This measured charge-sensitivity is comparable to the values reported using the RF techniques. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.

  15. Testing multistage gain and offset trimming in a single photon counting IC with a charge sharing elimination algorithm

    NASA Astrophysics Data System (ADS)

    Krzyżanowska, A.; Gryboś, P.; Szczygieł, R.; Maj, P.

    2015-12-01

    Designing a hybrid pixel detector readout electronics operating in a single photon counting mode is a very challenging process, where many main parameters are optimized in parallel (e.g. gain, noise, and threshold dispersion). Additional requirements for a smaller pixel size with extended functionality push designers to use new deep sub-micron technologies. Minimizing the channel size is possible, however, with a decreased pixel size, the charge sharing effect becomes a more important issue. To overcome this problem, we designed an integrated circuit prototype produced in CMOS 40 nm technology, which has an extended functionality of a single pixel. A C8P1 algorithm for the charge sharing effect compensation was implemented. In the algorithm's first stage the charge is rebuilt in a signal rebuilt hub fed by the CSA (charge sensitive amplifier) outputs from four neighbouring pixels. Then, the pixel with the biggest amount of charge is chosen, after a comparison with all the adjacent ones. In order to process the data in such a complicated way, a certain architecture of a single channel was proposed, which allows for: ṡ processing the signal with the possibility of total charge reconstruction (by connecting with the adjacent pixels), ṡ a comparison of certain pixel amplitude to its 8 neighbours, ṡ the extended testability of each block inside the channel to measure CSA gain dispersion, shaper gain dispersion, threshold dispersion (including the simultaneous generation of different pulse amplitudes from different pixels), ṡ trimming all the necessary blocks for proper operation. We present a solution for multistage gain and offset trimming implemented in the IC prototype. It allows for minimization of the total charge extraction errors, minimization of threshold dispersion in the pixel matrix and minimization of errors of comparison of certain pixel pulse amplitudes with all its neighbours. The detailed architecture of a single channel is presented together

  16. A single peptide-major histocompatibility complex ligand triggers digital cytokine secretion in CD4(+) T cells.

    PubMed

    Huang, Jun; Brameshuber, Mario; Zeng, Xun; Xie, Jianming; Li, Qi-jing; Chien, Yueh-hsiu; Valitutti, Salvatore; Davis, Mark M

    2013-11-14

    We have developed a single-molecule imaging technique that uses quantum-dot-labeled peptide-major histocompatibility complex (pMHC) ligands to study CD4(+) T cell functional sensitivity. We found that naive T cells, T cell blasts, and memory T cells could all be triggered by a single pMHC to secrete tumor necrosis factor-α (TNF-α) and interleukin-2 (IL-2) cytokines with a rate of ∼1,000, ∼10,000, and ∼10,000 molecules/min, respectively, and that additional pMHCs did not augment secretion, indicating a digital response pattern. We also found that a single pMHC localized to the immunological synapse induced the slow formation of a long-lasting T cell receptor (TCR) cluster, consistent with a serial engagement mechanism. These data show that scaling up CD4(+) T cell cytokine responses involves increasingly efficient T cell recruitment rather than greater cytokine production per cell. PMID:24120362

  17. Quantum computing over long time scales in a singly charged quantum dot

    NASA Astrophysics Data System (ADS)

    Sun, Bo

    In this thesis, we will study the continuous wave optical spectroscopy of self-assembled quantum dots (SAQDs), focusing on the use of these dots toward quantum computing and information processing applications. Probing the strong field interaction between an intense optical pump beam and a neutral quantum dot will reveal Autler-Townes splitting and Mollow absorption spectrum. The presence of these two phenomenon confirm the isolated nature of the exciton trapped in the quantum dot and the suppression of many-body physics due to exciton confinement. This curbs the decoherence caused by exciton-exciton interactions in higher dimensional heterostructures. After confirming the atom-like nature of the SAQD, we then charge the SAQD with a single electron and use the electron spin as our qubit. By applying a magnetic field perpendicular to the sample growth direction, we turn on the spin flip Raman transitions and create two lambda (Λ) systems that can be used to coherently manipulate the spin. A single laser resonant with one of the transitions can quickly initialize the spin state via optical pumping while two lasers, one on each leg of the lambda, can initialize the spin into an arbitrary superposition state through coherent population trapping. The developed dark state spectroscopy is then used to demonstrate interaction between the optically generated hole spin with the background nuclear spins. This hole assisted dynamic nuclear polarization creates a feedback mechanism which locks the nuclear field to the laser detunings and suppresses nuclear spin fluctuations. We use dark state spectroscopy to measure a two orders of magnitude increase of the electron spin coherence time, a result of the narrowing of the nuclear field distribution. Furthermore, we find that this nuclear spin narrowing can persist in the dark, without laser interaction, for well over 1s even in the presence of a fluctuating electron charge and electron spin polarization. We have opened the door

  18. Single photon emission at 1.55 μm from charged and neutral exciton confined in a single quantum dash

    SciTech Connect

    Dusanowski, Ł. Syperek, M.; Mrowiński, P.; Rudno-Rudziński, W.; Misiewicz, J.; Sęk, G.; Somers, A.; Kamp, M.; Höfling, S.; Reithmaier, J. P.

    2014-07-14

    We investigate charged and neutral exciton complexes confined in a single self-assembled InAs/InGaAlAs/InP quantum dash emitting at 1.55 μm. The emission characteristics have been probed by measuring high-spatial-resolution polarization-resolved photoluminescence and cross-correlations of photon emission statistics at T = 5 K. The photon auto-correlation histogram of the emission from both the neutral and charged exciton indicates a clear antibunching dip with as-measured g{sup (2)}(0) values of 0.18 and 0.31, respectively. It proves that these exciton complexes confined in single quantum dashes of InP-based material system can act as true single photon emitters being compatible with standard long-distance fiber communication technology.

  19. Partial Dissolution of Charge Order Phase Observed in β-(BEDT-TTF)2PF6 Single Crystal Field Effect Transistor.

    PubMed

    Sakai, Masatoshi; Moritoshi, Norifumi; Kuniyoshi, Shigekazu; Yamauchi, Hiroshi; Kudo, Kazuhiro; Masu, Hyuma

    2016-04-01

    The effect of an applied gate electric field on the charge-order phase in β-(BEDT-TTF)2PF6 single-crystal field-effect transistor structure was observed at around room temperature by technical improvement with respect to sample preparation and electrical measurements. A relatively slight but systematic increase of the electrical conductance induced by the applied gate electric field and its temperature dependence was observed at around the metal-insulator transition temperature (TMI). The temperature dependence of the modulated electrical conductance demonstrated that TMI was shifted toward the lower side by application of a gate electric field, which corresponds to partial dissolution of the charge-order phase. The thickness of the partially dissolved charge order region was estimated to be several score times larger than the charge accumulation region. PMID:27451615

  20. Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures

    NASA Astrophysics Data System (ADS)

    Wang, K.; Payette, C.; Dovzhenko, Y.; Koppinen, P.; Petta, J. R.

    2012-02-01

    We perform quantum Hall measurements on three types of commercially available modulation doped Si/SiGe heterostructures [1] to determine their suitability for depletion gate defined quantum dot devices. By adjusting the growth parameters, we are able to achieve two dimensional electron gases with low charge densities and high mobilities. We extract an electron temperature of 100 mK in the single quantum dot regime. Double quantum dots fabricated on these heterostructures show clear evidence of single charge transitions [2] as measured in dc transport and charge sensing. [4pt] [1] C. B. Simmons et al, Phys. Rev. Lett. 106, 156804 (2011).[0pt] [2] R. Hanson et al, Rev. Mod. Phys. 79, 1217 (2007).

  1. Effect of charging on CdSe/CdS dot-in-rods single-photon emission

    NASA Astrophysics Data System (ADS)

    Manceau, M.; Vezzoli, S.; Glorieux, Q.; Pisanello, F.; Giacobino, E.; Carbone, L.; De Vittorio, M.; Bramati, A.

    2014-07-01

    The photon statistics of CdSe/CdS dot-in-rods nanocrystals is studied with a method involving postselection of the photon detection events based on the photoluminescence count rate. We show that flickering between two states needs to be taken into account to interpret the single-photon emission properties. With postselection we are able to identify two emitting states: the exciton and the charged exciton (trion), characterized by different lifetimes and different second-order correlation functions. Measurements of the second-order autocorrelation function at zero delay with postselection shows a degradation of the single-photon emission for CdSe/CdS dot-in-rods in a charged state that we explain by deriving the neutral and charged biexciton quantum yields.

  2. Charged single alpha-helices in proteomes revealed by a consensus prediction approach.

    PubMed

    Gáspári, Zoltán; Süveges, Dániel; Perczel, András; Nyitray, László; Tóth, Gábor

    2012-04-01

    Charged single α-helices (CSAHs) constitute a recently recognized protein structural motif. Its presence and role is characterized in only a few proteins. To explore its general features, a comprehensive study is necessary. We have set up a consensus prediction method available as a web service (at http://csahserver.chem.elte.hu) and downloadable scripts capable of predicting CSAHs from protein sequences. Using our method, we have performed a comprehensive search on the UniProt database. We found that the motif is very rare but seems abundant in proteins involved in symbiosis and RNA binding/processing. Although there are related proteins with CSAH segments, the motif shows no deep conservation in protein families. We conclude that CSAH-containing proteins, although rare, are involved in many key biological processes. Their conservation pattern and prevalence in symbiosis-associated proteins suggest that they might be subjects of relatively rapid molecular evolution and thus can contribute to the emergence of novel functions. PMID:22310480

  3. Can singly charged oxygen vacancies induce ferromagnetism in biaxial strained ZnO?

    NASA Astrophysics Data System (ADS)

    Gai, Yanqin; Jiang, Jiaping; Wu, Yuxi; Tang, Gang

    2016-04-01

    The electronic and magnetic properties of the singly charged oxygen vacancy ({{V}{{O}}}+) in undoped ZnO under biaxial strains are investigated by density functional theory calculations. A net magnetic moment (MM) of 0.561 μB is obtained for {{V}{{O}}}+ in ZnO under no strains, but the magnetic interaction between them is antiferromagnetic. The formation energy of V O and {{V}{{O}}}+, the MM induced by {{V}{{O}}}+, as well as the coupling type and strength between {{V}{{O}}}+{{s}} vary with the application of biaxial strains. Compressive strains can enhance the concentrations of V O and {{V}{{O}}}+, enlarge the MM, and strengthen the antiferromagnetic interactions between them at lower V O concentrations. However, at higher V O concentrations, the coupling varies from sizable antiferromagnetic to negligible weak ferromagnetic, and then becomes paramagnetic with the increase of compression. Antiferromagnetic results are further confirmed by the local density approximation with Hubbard U (LDA + U) calculations.

  4. Mobility of singly-charged lanthanide cations in rare gases: Theoretical assessment of the state specificity

    SciTech Connect

    Buchachenko, Alexei A.; Viehland, Larry A.

    2014-03-21

    High quality, ab initio calculations are reported for the potential energy curves governing the interactions of four singly-charged lanthanide ions (Yb{sup +}, Eu{sup +}, Lu{sup +}, and Gd{sup +}) with the rare gases (RG = He–Xe). Scalar-relativistic coupled cluster calculations are used for the first three S-state ions, but for Gd{sup +}({sup 10}D°) it is necessary to take the interaction anisotropy into account with the help of the multi-reference technique. The potential energy curves are used to determine the ion mobility and other transport properties describing the motion of the ions through the dilute RG, both as functions of the temperature, T, in the low-field limit, and at fixed T as functions of the ratio of the electrostatic field strength to the gas number density, E/N. The calculated mobilities are in good agreement with the very limited experimental data that have become available recently. The calculations show a pronounced dependence of the transport properties on the electronic configuration of the ion, as well as a significant effect of the spin-orbit coupling on the transport properties of the Gd{sup +} ion, and predict that state-specific mobilities could be detectable in Gd{sup +}–RG experiments.

  5. A placental growth factor-positively charged peptide potentiates the antitumor activity of interferon-gamma in human brain glioblastoma U87 cells

    PubMed Central

    Liu, Yu; Chen, Naifei; Yin, Hongmei; Zhang, Leilei; Li, Wei; Wang, Guanjun; Cui, Jiuwei; Yang, Bo; Hu, Ji-Fan

    2016-01-01

    Interferons have been marketed to treat hematological malignancies, but their efficacy in the treatment of solid tumors has been significantly hindered by low antitumor efficacy and numerous side effects. We used a “cDNA in-frame fragment” library screening method to identify short cDNA peptides that potentiate the anti-tumor activity of interferons. In this study, we synthesized a hybrid molecule by fusing a short positively charged peptide derived from placental growth factor-2 to the C-terminus of human IFNγ. Using the human brain glioblastoma U87 cell line as a model system, we found that the hybrid interferon exhibited significantly higher activity than did the wild-type IFNγ in inhibiting tumor cell growth. As compared with the unmodified IFNγ, the hybrid interferon was better at inhibiting cell invasion in a matri-gel assay and at decreasing tumor colony formation. The enhanced antitumor activity of the synthetic interferon was correlated with the activation of interferon pathway genes and the blockade of tumor cell division at the S-G2/M phase. This study demonstrates the potential of a synthetic IFNγ for use as a novel antitumor agent.

  6. Peptide fibrils with altered stability, activity, and cell selectivity

    PubMed Central

    Chen, Long; Liang, Jun F.

    2014-01-01

    Peptides have some unique and superior features compared to proteins. However, the use of peptides as therapeutics is hampered by their low stability and cell selectivity. In this study, a new lytic peptide (CL-1, FLGALFRALSRLL) was constructed. Under the physiological condition, peptide CL-1 self-assembled into dynamically stable aggregates with fibrils-like structures. Aggregated CL-1 demonstrated dramatically altered activity and stability in comparison with single molecule CL-1 and other lytic peptides: when incubated with co-cultured bacteria and tissue cells, CL-1 aggregates killed bacteria selectively but spared co-cultured human cells; CL-1 aggregates kept intact in human serum for more than five hours. Peptide-cell interaction studies performed on lipid monolayers and live human tissue cells revealed that in comparison with monomeric CL-1, aggregated CL-1 had decreased cell affinity and membrane insertion capability on tissue cells. A dynamic process involving aggregate dissociation and rearrangement seemed to be an essential step for membrane bound CL-1 aggregates to realize its cytotoxicity to tissue cells. Our study suggests that peptide aggregation could be as important as the charge and secondary structure of a peptide in affecting peptide-cell interactions. Controlling peptide self-assembly represents a new way to increase the stability and cell selectivity of bioactive peptides for wide biomedical applications. PMID:23713839

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  8. Immunoreactive prohormone atrial natriuretic peptides 1-30 and 31-67 - Existence of a single circulating amino-terminal peptide

    NASA Technical Reports Server (NTRS)

    Chen, Yu-Ming; Whitson, Peggy A.; Cintron, Nitza M.

    1990-01-01

    Sep-Pak C18 extraction of human plasma and radioimmunoassay using antibodies which recognize atrial natriuretic peptide (99-128) and the prohormone sequences 1-30 and 31-67 resulted in mean values from 20 normal subjects of 26.2 (+/- 9.2), 362 (+/- 173) and 368 (+/- 160) pg/ml, respectively. A high correlation coefficient between values obtained using antibodies recognizing prohormone sequences 1-30 and 31-67 was observed (R = 0.84). Extracted plasma immunoreactivity of 1-30 and 31-67 both eluted at 46 percent acetonitrile. In contrast, chromatographic elution of synthetic peptides 1-30 and 31-67 was observed at 48 and 39 percent acetonitrile, respectively. Data suggest that the radioimmunoassay of plasma using antibodies recognizing prohormone sequences 1-30 and 31-67 may represent the measurement of a unique larger amino-terminal peptide fragment containing antigenic sites recognized by both antisera.

  9. Effects of Voluntary Locomotion and Calcitonin Gene-Related Peptide on the Dynamics of Single Dural Vessels in Awake Mice

    PubMed Central

    Gao, Yu-Rong

    2016-01-01

    The dura mater is a vascularized membrane surrounding the brain and is heavily innervated by sensory nerves. Our knowledge of the dural vasculature has been limited to pathological conditions, such as headaches, but little is known about the dural blood flow regulation during behavior. To better understand the dynamics of dural vessels during behavior, we used two-photon laser scanning microscopy (2PLSM) to measure the diameter changes of single dural and pial vessels in the awake mouse during voluntary locomotion. Surprisingly, we found that voluntary locomotion drove the constriction of dural vessels, and the dynamics of these constrictions could be captured with a linear convolution model. Dural vessel constrictions did not mirror the large increases in intracranial pressure (ICP) during locomotion, indicating that dural vessel constriction was not caused passively by compression. To study how behaviorally driven dynamics of dural vessels might be altered in pathological states, we injected the vasodilator calcitonin gene-related peptide (CGRP), which induces headache in humans. CGRP dilated dural, but not pial, vessels and significantly reduced spontaneous locomotion but did not block locomotion-induced constrictions in dural vessels. Sumatriptan, a drug commonly used to treat headaches, blocked the vascular and behavioral the effects of CGRP. These findings suggest that, in the awake animal, the diameters of dural vessels are regulated dynamically during behavior and during drug-induced pathological states. SIGNIFICANT STATEMENT The vasculature of the dura has been implicated in the pathophysiology of headaches, but how individual dural vessels respond during behavior, both under normal conditions and after treatment with the headache-inducing peptide calcitonin gene-related peptide (CGRP), is poorly understood. To address these issues, we imaged individual dural vessels in awake mice and found that dural vessels constricted during voluntary locomotion, and

  10. Side-chain control of porosity closure in single- and multiple-peptide-based porous materials by cooperative folding

    NASA Astrophysics Data System (ADS)

    Martí-Gastaldo, C.; Antypov, D.; Warren, J. E.; Briggs, M. E.; Chater, P. A.; Wiper, P. V.; Miller, G. J.; Khimyak, Y. Z.; Darling, G. R.; Berry, N. G.; Rosseinsky, M. J.

    2014-04-01

    Porous materials are attractive for separation and catalysis—these applications rely on selective interactions between host materials and guests. In metal-organic frameworks (MOFs), these interactions can be controlled through a flexible structural response to the presence of guests. Here we report a MOF that consists of glycyl-serine dipeptides coordinated to metal centres, and has a structure that evolves from a solvated porous state to a desolvated non-porous state as a result of ordered cooperative, displacive and conformational changes of the peptide. This behaviour is driven by hydrogen bonding that involves the side-chain hydroxyl groups of the serine. A similar cooperative closure (reminiscent of the folding of proteins) is also displayed with multipeptide solid solutions. For these, the combination of different sequences of amino acids controls the framework's response to the presence of guests in a nonlinear way. This functional control can be compared to the effect of single-point mutations in proteins, in which exchange of single amino acids can radically alter structure and function.

  11. Peptide hormone release monitored from single vesicles in "membrane lawns" of differentiated male pituitary cells: SNAREs and fusion pore widening.

    PubMed

    Stenovec, Matjaž; Gonçalves, Paula P; Zorec, Robert

    2013-03-01

    In this study we used live-cell immunocytochemistry and confocal microscopy to study the release from a single vesicle in a simplified system called membrane lawns. The lawns were prepared by exposing differentiated pituitary prolactin (PRL)-secreting cells to a hypoosmotic shear stress. The density of the immunolabeled ternary soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) complexes that bind complexin was approximately 10 times lower than the PRL-positive, lawn-resident vesicles; this indicates that some but not all vesicles are associated with ternary SNARE complexes. However, lawn-resident PRL vesicles colocalized relatively well with particular SNARE proteins: synaptobrevin 2 (35%), syntaxin 1 (22%), and 25-kDa synaptosome associated protein (6%). To study vesicle discharge, we prepared lawn-resident vesicles, derived from atrial natriuretic peptide tagged with emerald fluorescent protein (ANP.emd)-transfected cells, which label vesicles. These maintained the structural passage to the exterior because approximately 40% of ANP.emd-loaded vesicles were labeled by extracellular PRL antibodies. Cargo release from the lawn-resident vesicles, monitored by the decline in the ANP.emd fluorescence intensity, was similar to that in intact cells. It is likely that SNARE proteins are required for calcium-dependent release from these vesicles. This is because the expression of the dominant-negative SNARE peptide, which interferes with SNARE complex formation, reduced the number of PRL-positive spots per cell (PRL antibodies placed extracellularly) significantly, from 58 ± 9 to 4 ± 2. In dominant-negative SNARE-treated cells, the PRL-positive area was reduced from 0.259 ± 0.013 to 0.123 ± 0.014 μm(2), which is consistent with a hindered vesicle luminal access for extracellular PRL antibodies. These results indicate that vesicle discharge is regulated by SNARE-mediated fusion pore widening. PMID:23372020

  12. Multi-Hierarchical Self-Assembly of Collagen Mimetic Peptides into AAB Type Heterotrimers, Nanofibers and Hydrogels Driven by Charged Pair Interactions

    NASA Astrophysics Data System (ADS)

    O'Leary, Lesley Russell

    2011-12-01

    Replicating the multi-hierarchical self-assembly of collagen (peptide chain to triple helix to nanofiber and, finally, to a hydrogel) has long attracted scientists, both from the fundamental science perspective of supramolecular chemistry and for the potential biomedical applications perceived in tissue engineering. In terms of triple helical formation, collagen is the most abundant protein in the human body with at least 28 types, yet research involving collagen mimetic systems has only recently began to consider the innate ability of collagen to control helix composition and register. Collagen triple helices can be homotrimeric or heterotrimeric and while some types of natural collagen form only one specific composition of helix, others can form multiple. It is critical to fully understand and, if possible, reproduce the control that native collagen has on helix composition and register. In terms of nanofiber formation, many approaches to drive the self-assembly of synthetic systems through the same steps as natural collagen have been partially successful, but none have simultaneously demonstrated all levels of structural assembly. In this work, advancements in the ability to control helix composition and replicate the multi-hierarchical assembly of collagen are described. Both positive and negative design for the assembly of AAB type collagen heterotrimers were utilized by promoting heterotrimer formation though the use of charged amino acids to form intra-helix electrostatic interactions, while simultaneously discouraging homotrimers, resulting in the identification of multiple peptide systems with full control over the composition of the resulting triple helix. Similar salt-bridged hydrogen bonds between charged residues were incorporated into nanofiber forming peptides, one of which successfully assembled into sticky-ended triple helices, nanofibers with characteristic triple helical packing visible in the solution state, and strong hydrogels that are

  13. Use of a Spreadsheet to Calculate the Net Charge of Peptides and Proteins as a Function of pH: An Alternative to Using "Canned" Programs to Estimate the Isoelectric Point of These Important Biomolecules

    ERIC Educational Resources Information Center

    Sims, Paul A.

    2010-01-01

    An approach is presented that utilizes a spreadsheet to allow students to explore different means of calculating and visualizing how the charge on peptides and proteins varies as a function of pH. In particular, the concept of isoelectric point is developed to allow students to compare the results of their spreadsheet calculations with those of…

  14. Active charge state control of single NV centres in diamond by in-plane Al-Schottky junctions

    PubMed Central

    Schreyvogel, C.; Polyakov, V.; Wunderlich, R.; Meijer, J.; Nebel, C. E.

    2015-01-01

    In this paper, we demonstrate an active control of the charge state of a single nitrogen-vacancy (NV) centre by using in-plane Schottky-diode geometries with aluminium on hydrogen-terminated diamond surface. A switching between NV+, NV0 and NV− can be performed with the Al-gates which apply electric fields in the hole depletion region of the Schottky junction that induces a band bending modulation, thereby shifting the Fermi-level over NV charge transition levels. We simulated the in-plane band structure of the Schottky junction with the Software ATLAS by solving the drift-diffusion model and the Poisson-equation self-consistently. We simulated the IV-characteristics, calculated the width of the hole depletion region, the position of the Fermi-level intersection with the NV charge transition levels for different reverse bias voltages applied on the Al-gate. We can show that the field-induced band bending modulation in the depletion region causes a shifting of the Fermi-level over NV charge transition levels in such a way that the charge state of a single NV centre and thus its electrical and optical properties is tuned. In addition, the NV centre should be approx. 1–2 μm away from the Al-edge in order to be switched with moderate bias voltages. PMID:26177799

  15. Investigation of the structure of anti-human seminal plasma protein single-chain antibody and its association with linker peptide length

    PubMed Central

    JIANG, XIN; ZHAI, JUN; SONG, DONGKUI; QU, QINGSHAN; LI, MING; XING, LI; MIAO, SHUZHAI

    2015-01-01

    To enhance the activity of seminoprotein single-chain variable fragment (γ-Sm-ScFv) antibodies, modulation of the length of the linker peptide, which connects the variable region of the heavy chain (VH) and the light chain (VL) of single-chain antibodies, was performed in the present study. Homologous modeling of single VH and VL were performed, respectively. Subsequently, modeling of the whole ScFv sequence, which was previously modified with added linkers of different lengths was also performed, and the (Gly4Ser)n peptide chain structure was used as the linker. The similarities between VH and VL prior to and following the addition of the linker were compared by applying the algorithm of protein similarity, based on spherical coordinates layering. In addition, changes in the fore and aft distance, and diffusion radius were calculated using a MATLAB tool, based on which changes in structural stability were analyzed. Finally, the single-chain antibody was assessed in a nude mouse model. When n=3 or n=6, the similarity between the original distance and VH and VL were the highest, and the fore and aft distance and diffusion radius were relatively close. In addition, the nude mouse model indicated that, when n=3 or n=6, the inhibitory rate of the single-chain antibody against tumor cells was significantly higher, compared with the other linker peptides of different lengths. The effect of structural changes of the linker peptides in the single-chain antibodies on the whole antibody molecule was examined at different levels using a combination of mathematical modeling, bioinformatics methods and biological experiments. The findings of the present study may provide a foundation for further investigation into the preparation of single-chain antibodies. PMID:26099852

  16. Single polarity charge sensing in high pressure xenon using a coplanar anode configuration

    NASA Astrophysics Data System (ADS)

    Sullivan, Clair Julia

    A new design of a high pressure xenon ionization chamber has been fabricated in an attempt to eliminate the problems associated with acoustical vibrations of the Frisch grid. The function of the traditional Frisch grid has been accomplished by employing a coplanar anode system capable of single polarity charge sensing by means of the Shockley-Ramo theorem. Two different detectors have been built in order to determine if the operation of a high pressure xenon detector in coplanar anode mode is possible. The first is the helical detector comprised of two anode wires wound about a central ceramic core. Through calculation, it is shown that for a cathode bias of -5 kV a potential of 363 V is necessary to collect all of the electrons on the collecting anode, however this is contradicted by the observed pulse waveforms. The results of several experiments are presented that demonstrate the helical detector should work, however in the interest in determining if a coplanar high pressure xenon detector is viable, emphasis was placed on the second detector design. The second design is a parallel plate detector, more analogous to the coplanar semiconductor devices. This detector has demonstrated that it is possible to operate a high pressure xenon detector in coplanar anode mode. However, it is shown that the performance of this detector is limited by high surface leakage current and detector capacitance. Additionally, since the leakage current increases with potential between the two anodes, it is not possible to obtain very high resolution gamma-ray spectroscopy since the required potential between the two anodes for coplanar operation is so high that the detector is already dominated by surface leakage current as this value.

  17. Charge dynamics of MgO single crystals subjected to KeV electron irradiation

    NASA Astrophysics Data System (ADS)

    Boughariou, A.; Blaise, G.; Braga, D.; Kallel, A.

    2004-04-01

    A scanning electron microscope has been equipped to study the fundamental aspects of charge trapping in insulating materials, by measuring the secondary electron emission (SEE) yield σ with a high precision (a few percent), as a function of energy, electron current density, and dose. The intrinsic secondary electron emission yield σ0 of uncharged MgO single crystals annealed at 1000 °C, 2 h, has been studied at four energies 1.1, 5, 15, and 30 keV on three different crystal orientations (100), (110), and (111). At low energies (1.1 and 5 keV) σ0 depends on the crystalline orientation wheras at high energies (30 keV) no differentiation occurs. It is shown that the value of the second crossover energy E2, for which the intrinsic SEE yield σ0=1, is extremely delicate to measure with precision. It is about 15 keV±500 eV for the (100) orientation, 13.5 keV±500 eV for the (110), and 18.5 keV±500 eV for the (111) one. At low current density J⩽105 pA/cm2, the variation of σ with the injected dose makes possible the observation of a self-regulated regime characterized by a steady value of the SEE yield σst=1. At low energies 1.1 and 5 keV, there is no current density effects in MgO, but at high energies ≈30 keV, apparent current density effects come from a bad collect of secondary electrons, due to very high negative surface potential. At 30 keV energy, an intense erratic electron exoemission was observed on the MgO (110) orientation annealed at 1500 °C. This phenomenon is the result of a disruptive process similar to flashover, which takes place at the surface of the material.

  18. Anisotropy, phonon modes, and free charge carrier parameters in monoclinic β -gallium oxide single crystals

    NASA Astrophysics Data System (ADS)

    Schubert, M.; Korlacki, R.; Knight, S.; Hofmann, T.; Schöche, S.; Darakchieva, V.; Janzén, E.; Monemar, B.; Gogova, D.; Thieu, Q.-T.; Togashi, R.; Murakami, H.; Kumagai, Y.; Goto, K.; Kuramata, A.; Yamakoshi, S.; Higashiwaki, M.

    2016-03-01

    We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and far-infrared active modes. We apply our model approach to monoclinic β -Ga2O3 single-crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and (2 ¯01 ), are investigated by generalized spectroscopic ellipsometry within infrared and far-infrared spectral regions. We determine the frequency dependence of 4 independent β -Ga2O3 Cartesian dielectric function tensor elements by matching large sets of experimental data using a point-by-point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infrared and far-infrared active transverse optic phonon modes with Au and Bu symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in β -Ga2O3 . We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin-doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in β -Ga2O3 and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and far-infrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for β -Ga2O3 .

  19. Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix.

    PubMed

    Mollahosseini, Mehdi; Karunaratne, Erandika; Gibson, George N; Gascón, Jose A; Papadimitrakopoulos, Fotios

    2016-05-11

    One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliphatic spacer. Small amounts of FC60 (up to 3 molar %) were shown to coassembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow E(S)ii line widths) for the resulting ground-state complex signals a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices. PMID:27127896

  20. Charge integration successive approximation analog-to-digital converter for focal plane applications using a single amplifier

    NASA Technical Reports Server (NTRS)

    Zhou, Zhimin (Inventor); Pain, Bedabrata (Inventor)

    1999-01-01

    An analog-to-digital converter for on-chip focal-plane image sensor applications. The analog-to-digital converter utilizes a single charge integrating amplifier in a charge balancing architecture to implement successive approximation analog-to-digital conversion. This design requires minimal chip area and has high speed and low power dissipation for operation in the 2-10 bit range. The invention is particularly well suited to CMOS on-chip applications requiring many analog-to-digital converters, such as column-parallel focal-plane architectures.

  1. Back-action-induced excitation of electrons in a silicon quantum dot with a single-electron transistor charge sensor

    SciTech Connect

    Horibe, Kosuke; Oda, Shunri; Kodera, Tetsuo

    2015-02-02

    Back-action in the readout of quantum bits is an area that requires a great deal of attention in electron spin based-quantum bit architecture. We report here back-action measurements in a silicon device with quantum dots and a single-electron transistor (SET) charge sensor. We observe the back-action-induced excitation of electrons from the ground state to an excited state in a quantum dot. Our measurements and theoretical fitting to the data reveal conditions under which both suitable SET charge sensor sensitivity for qubit readout and low back-action-induced transition rates (less than 1 kHz) can be achieved.

  2. Single CdSe/ZnS nanocrystals in an ion trap: charge and mass determination and photophysics evolution with changing mass, charge, and temperature.

    PubMed

    Bell, David M; Howder, Collin R; Johnson, Ryan C; Anderson, Scott L

    2014-03-25

    We report measurements of fluorescence intermittency (blinking) and spectral behavior for single semiconductor nanocrystal quantum dots (QDs) isolated in the gas phase and discuss the effects on fluorescence of the QD charge state and heating to the point of sublimation. Core-shell CdSe/ZnS QDs were trapped in a quadrupole ion trap and detected by laser-induced fluorescence. The mass (M) and charge (Q) were determined nondestructively, and both were followed continuously over the course of hours or days. Emission spectra of the trapped QDs are significantly red-shifted relative to the solution-phase emission from the same particles. The temperature of the trapped QDs is determined by the balance between laser heating and collisional cooling and thermal emission, and it is possible to heat the particles to remove ligands or to the point of sublimation. QDs are observed to be emissive during sublimation, for up to 85% mass loss, with emission intensity roughly proportional to the surface area. Eventually, the fluorescence quantum yield drops suddenly, and the QDs begin to blink. The method used is versatile and will allow studies of quantum dot optical properties as a function of size, ligand removal, heating, surface oxidation, and other manipulations, where these properties are continuously correlated with the mass and charge. PMID:24410129

  3. STM studies of an atomic-scale gate electrode formed by a single charged vacancy in GaAs

    NASA Astrophysics Data System (ADS)

    Lee, Donghun; Daughton, David; Gupta, Jay

    2009-03-01

    Electric-field control of spin-spin interactions at the atomic level is desirable for the realization of spintronics and spin-based quantum computation. Here we demonstrate the realization of an atomic-scale gate electrode formed by a single charged vacancy on the GaAs(110) surface[1]. We can position these vacancies with atomic precision using the tip of a home-built, low temperature STM. Tunneling spectroscopy of single Mn acceptors is used to quantify the electrostatic field as a function of distance from the vacancy. Single Mn acceptors are formed by substituting Mn adatoms for Ga atoms in the first layer of the p-GaAs(110) surface[2]. Depending on the distance, the in-gap resonance of single Mn acceptors can shift as much as 200meV. Our data indicate that the electrostatic field decays according to a screened Coulomb potential. The charge state of the vacancy can be switched to neutral, as evidenced by the Mn resonance returning to its unperturbed position. Reversible control of the local electric field as well as charged states of defects in semiconductors can open new insights such as realizing an atomic-scale gate control and studying spin-spin interactions in semiconductors. http://www.physics.ohio-state.edu/sim jgupta [1] D. Lee and J.A. Gupta (in preparation) [2] D. Kitchen et al., Nature 442, 436-439 (2006)

  4. Frequency and Distribution of Single-Nucleotide Polymorphisms within mprF in Methicillin-Resistant Staphylococcus aureus Clinical Isolates and Their Role in Cross-Resistance to Daptomycin and Host Defense Antimicrobial Peptides.

    PubMed

    Bayer, Arnold S; Mishra, Nagendra N; Chen, Liang; Kreiswirth, Barry N; Rubio, Aileen; Yang, Soo-Jin

    2015-08-01

    MprF is responsible for the lysinylation of phosphatidylglycerol (PG) to synthesize the positively charged phospholipid (PL) species, lysyl-PG (L-PG). It has been proposed that the single-nucleotide polymorphisms (SNPs) within the mprF open reading frame (ORF) are associated with a gain-in-function phenotype in terms of daptomycin resistance in Staphylococcus aureus. (Note that although the official term is daptomycin nonsusceptibility, we use the term daptomycin resistance in this paper for ease of presentation.) Using 22 daptomycin-susceptible (DAP(s))/daptomycin-resistant (DAP(r)) clinical methicillin-resistant S. aureus (MRSA) strain pairs, we assessed (i) the frequencies and distribution of putative mprF gain-in-function SNPs, (ii) the relationships of the SNPs to both daptomycin resistance and cross-resistance to the prototypical endovascular host defense peptide (HDP) thrombin-induced platelet microbicidal protein (tPMP), and (iii) the impact of mprF SNPs on positive surface charge phenotype and modifications of membrane PL profiles. Most of the mprF SNPs identified in our DAP(r) strains were clustered within the two MprF loci, (i) the central bifunctional domain and (ii) the C-terminal synthase domain. Moreover, we were able to correlate the presence and location of mprF SNPs in DAP(r) strains with HDP cross-resistance, positive surface charge, and L-PG profiles. Although DAP(r) strains with mprF SNPs in the bifunctional domain showed higher resistance to tPMPs than DAP(r) strains with SNPs in the synthase domain, this relationship was not observed in positive surface charge assays. These results demonstrated that both charge-mediated and -unrelated mechanisms are involved in DAP resistance and HDP cross-resistance in S. aureus. PMID:26055370

  5. Frequency and Distribution of Single-Nucleotide Polymorphisms within mprF in Methicillin-Resistant Staphylococcus aureus Clinical Isolates and Their Role in Cross-Resistance to Daptomycin and Host Defense Antimicrobial Peptides

    PubMed Central

    Bayer, Arnold S.; Mishra, Nagendra N.; Chen, Liang; Kreiswirth, Barry N.; Rubio, Aileen

    2015-01-01

    MprF is responsible for the lysinylation of phosphatidylglycerol (PG) to synthesize the positively charged phospholipid (PL) species, lysyl-PG (L-PG). It has been proposed that the single-nucleotide polymorphisms (SNPs) within the mprF open reading frame (ORF) are associated with a gain-in-function phenotype in terms of daptomycin resistance in Staphylococcus aureus. (Note that although the official term is daptomycin nonsusceptibility, we use the term daptomycin resistance in this paper for ease of presentation.) Using 22 daptomycin-susceptible (DAPs)/daptomycin-resistant (DAPr) clinical methicillin-resistant S. aureus (MRSA) strain pairs, we assessed (i) the frequencies and distribution of putative mprF gain-in-function SNPs, (ii) the relationships of the SNPs to both daptomycin resistance and cross-resistance to the prototypical endovascular host defense peptide (HDP) thrombin-induced platelet microbicidal protein (tPMP), and (iii) the impact of mprF SNPs on positive surface charge phenotype and modifications of membrane PL profiles. Most of the mprF SNPs identified in our DAPr strains were clustered within the two MprF loci, (i) the central bifunctional domain and (ii) the C-terminal synthase domain. Moreover, we were able to correlate the presence and location of mprF SNPs in DAPr strains with HDP cross-resistance, positive surface charge, and L-PG profiles. Although DAPr strains with mprF SNPs in the bifunctional domain showed higher resistance to tPMPs than DAPr strains with SNPs in the synthase domain, this relationship was not observed in positive surface charge assays. These results demonstrated that both charge-mediated and -unrelated mechanisms are involved in DAP resistance and HDP cross-resistance in S. aureus. PMID:26055370

  6. Pulling peptides across nanochannels: resolving peptide binding and translocation through the hetero-oligomeric channel from Nocardia farcinica.

    PubMed

    Singh, Pratik Raj; Bárcena-Uribarri, Iván; Modi, Niraj; Kleinekathöfer, Ulrich; Benz, Roland; Winterhalter, Mathias; Mahendran, Kozhinjampara R

    2012-12-21

    We investigated translocation of cationic peptides through nanochannels derived from the Gram-positive bacterium Nocardia farcinica at the single-molecule level. The two subunits NfpA and NfpB form a hetero-oligomeric cation selective channel. On the basis of amino acid comparison we performed homology modeling and obtained a channel structurally related to MspA of Mycobacterium smegmatis. The quantitative single-molecule measurements provide an insight into transport processes of solutes through nanochannels. High-resolution ion conductance measurements in the presence of peptides of different charge and length revealed the kinetics of peptide binding. The observed asymmetry in peptide binding kinetics indicated a unidirectional channel insertion in the lipid bilayer. In the case of cationic peptides, the external voltage acts as a driving force that promotes the interaction of the peptide with the channel surface. At low voltage, the peptide just binds to the channel, whereas at higher voltage, the force is strong enough to pull the peptide across the channel. This allows distinguishing quantitatively between peptide binding and translocation through the channel. PMID:23121560

  7. Single-dose safety, tolerability, and pharmacokinetics of the antibiotic GSK1322322, a novel peptide deformylase inhibitor.

    PubMed

    Naderer, Odin J; Dumont, Etienne; Zhu, John; Kurtinecz, Milena; Jones, Lori S

    2013-05-01

    GSK1322322 is a potent inhibitor of peptide deformylase, an essential bacterial enzyme required for protein maturation. GSK1322322 is active against community-acquired skin and respiratory tract pathogens, including methicillin-resistant Staphylococcus aureus, multidrug-resistant Streptococcus pneumoniae, and atypical pathogens. This phase I, randomized, double-blind, placebo-controlled, 2-part, single-dose, dose escalation study (first time in humans) evaluated the safety, tolerability, and pharmacokinetics of GSK1322322 (powder-in-bottle formulation) in healthy volunteers. In part A, dose escalation included GSK1322322 doses of 100, 200, 400, 800, and 1,500 mg under fasting conditions and 800 mg administered with a high-fat meal. In part B, higher doses of GSK1322322 (2,000, 3,000, and 4,000 mg) were evaluated under fasting conditions. Of the 39 volunteers enrolled in the study, 29 and 10 volunteers were treated with GSK1322322 and placebo, respectively. Upon single-dose administration, GSK1322322 was absorbed rapidly, with median times to maximum plasma concentration (T(max)) ranging from 0.5 to 1.0 h. The maximum observed plasma concentration (C(max)) and exposure (area under the concentration-time curve [AUC]) of GSK1322322 were greater than dose proportional between 100 and 1,500 mg and less than dose proportional between 1,500 and 4,000 mg. Administration of the drug with a high-fat meal reduced the rate of absorption (reduced C(max) and delayed T(max)) without affecting the extent of absorption (no effect on AUC). GSK1322322 was generally well tolerated, with all adverse events being mild to moderate in intensity during both parts of the study. The most frequently reported adverse event was headache. Data from this study support further evaluation of GSK1322322. PMID:23403431

  8. Heat-shock protein peptide complex–96 vaccination for recurrent glioblastoma: a phase II, single-arm trial

    PubMed Central

    Bloch, Orin; Crane, Courtney A.; Fuks, Yelena; Kaur, Rajwant; Aghi, Manish K.; Berger, Mitchel S.; Butowski, Nicholas A.; Chang, Susan M.; Clarke, Jennifer L.; McDermott, Michael W.; Prados, Michael D.; Sloan, Andrew E.; Bruce, Jeffrey N.; Parsa, Andrew T.

    2014-01-01

    Background Outcomes for patients with recurrent glioblastoma multiforme (GBM) are poor and may be improved by immunotherapy. We investigated the safety and efficacy of an autologous heat-shock protein peptide complex–96 (HSPPC-96) vaccine for patients with recurrent GBM. Methods In this open-label, single-arm, phase II study, adult patients with surgically resectable recurrent GBM were given vaccine after gross total resection. The primary endpoint was overall survival at 6 months. Secondary endpoints included overall survival, progression-free survival, safety, and immune profiling. Outcome analyses were performed in the intention-to-treat and efficacy populations. Results Between October 3, 2007 and October 24, 2011, 41 patients underwent gross total resection of recurrent GBM and received a median of 6 doses of HSPPC-96 vaccine. Following treatment, 90.2% of patients were alive at 6 months (95% confidence interval [CI]: 75.9–96.8) and 29.3% were alive at 12 months (95% CI: 16.6–45.7). Median overall survival was 42.6 weeks (95% CI: 34.7–50.5). Twenty-seven (66%) patients were lymphopenic prior to therapy, and patients with lymphocyte counts below the cohort median demonstrated decreased overall survival (hazard ratio: 4.0; 95% CI: 1.4–11.8; P = .012). There were no treatment-related deaths. There were 37 serious (grades 3–5) adverse events reported, with 17 attributable to surgical resection and a single grade 3 constitutional event related to the vaccine. Conclusion The HSPPC-96 vaccine is safe and warrants further study of efficacy for the treatment of recurrent GBM. Significant pretreatment lymphopenia may impact the outcomes of immunotherapy and deserves additional investigation. PMID:24335700

  9. Alternative Mechanisms for the Interaction of the Cell-Penetrating Peptides Penetratin and the TAT Peptide with Lipid Bilayers

    PubMed Central

    Yesylevskyy, Semen; Marrink, Siewert-Jan; Mark, Alan E.

    2009-01-01

    Abstract Cell-penetrating peptides (CPPs) have recently attracted much interest due to their apparent ability to penetrate cell membranes in an energy-independent manner. Here molecular-dynamics simulation techniques were used to study the interaction of two CPPs: penetratin and the TAT peptide with 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospolipid bilayers shed light on alternative mechanisms by which these peptides might cross biological membranes. In contrast to previous simulation studies of charged peptides interacting with lipid bilayers, no spontaneous formation of transmembrane pores was observed. Instead, the simulations suggest that the peptides may enter the cell by micropinocytosis, whereby the peptides induce curvature in the membrane, ultimately leading to the formation of small vesicles within the cell that encapsulate the peptides. Specifically, multiple peptides were observed to induce large deformations in the lipid bilayer that persisted throughout the timescale of the simulations (hundreds of nanoseconds). Pore formation could be induced in simulations in which an external potential was used to pull a single penetratin or TAT peptide into the membrane. With the use of umbrella-sampling techniques, the free energy of inserting a single penetratin peptide into a DPPC bilayer was estimated to be ∼75 kJmol−1, which suggests that the spontaneous penetration of single peptides would require a timescale of at least seconds to minutes. This work also illustrates the extent to which the results of such simulations can depend on the initial conditions, the extent of equilibration, the size of the system, and the conditions under which the simulations are performed. The implications of this with respect to the current systems and to simulations of membrane-peptide interactions in general are discussed. PMID:19580742

  10. Chemically assembled double-dot single-electron transistor analyzed by the orthodox model considering offset charge

    NASA Astrophysics Data System (ADS)

    Kano, Shinya; Maeda, Kosuke; Tanaka, Daisuke; Sakamoto, Masanori; Teranishi, Toshiharu; Majima, Yutaka

    2015-10-01

    We present the analysis of chemically assembled double-dot single-electron transistors using orthodox model considering offset charges. First, we fabricate chemically assembled single-electron transistors (SETs) consisting of two Au nanoparticles between electroless Au-plated nanogap electrodes. Then, extraordinary stable Coulomb diamonds in the double-dot SETs are analyzed using the orthodox model, by considering offset charges on the respective quantum dots. We determine the equivalent circuit parameters from Coulomb diamonds and drain current vs. drain voltage curves of the SETs. The accuracies of the capacitances and offset charges on the quantum dots are within ±10%, and ±0.04e (where e is the elementary charge), respectively. The parameters can be explained by the geometrical structures of the SETs observed using scanning electron microscopy images. Using this approach, we are able to understand the spatial characteristics of the double quantum dots, such as the relative distance from the gate electrode and the conditions for adsorption between the nanogap electrodes.

  11. Chemically assembled double-dot single-electron transistor analyzed by the orthodox model considering offset charge

    SciTech Connect

    Kano, Shinya; Maeda, Kosuke; Majima, Yutaka; Tanaka, Daisuke; Sakamoto, Masanori; Teranishi, Toshiharu

    2015-10-07

    We present the analysis of chemically assembled double-dot single-electron transistors using orthodox model considering offset charges. First, we fabricate chemically assembled single-electron transistors (SETs) consisting of two Au nanoparticles between electroless Au-plated nanogap electrodes. Then, extraordinary stable Coulomb diamonds in the double-dot SETs are analyzed using the orthodox model, by considering offset charges on the respective quantum dots. We determine the equivalent circuit parameters from Coulomb diamonds and drain current vs. drain voltage curves of the SETs. The accuracies of the capacitances and offset charges on the quantum dots are within ±10%, and ±0.04e (where e is the elementary charge), respectively. The parameters can be explained by the geometrical structures of the SETs observed using scanning electron microscopy images. Using this approach, we are able to understand the spatial characteristics of the double quantum dots, such as the relative distance from the gate electrode and the conditions for adsorption between the nanogap electrodes.

  12. Piezoelectricity of porous polytetrafluoroethylene single- and multiple-film electrets containing high charge densities of both polarities

    NASA Astrophysics Data System (ADS)

    Künstler, W.; Xia, Z.; Weinhold, T.; Pucher, A.; Gerhard-Multhaupt, R.

    Single-film bipolar electrets of porous polytetrafluoroethylene are generated by means of a two-step corona-charging process at elevated temperatures. Quasi-static direct piezoelectric coefficients of up to 0.15 nC/N have been observed on these films. In addition, multiple-layer stacks of porous and non-porous polytetrafluoroethylene films with monopolar charge were also investigated. While the piezoelectric responses of the stacks were not as high as those of the single films, the multiple-film arrangements may have other advantages such as better electrical shielding or tunable mechanical properties and adjustable acoustical impedance. Our new results are discussed in the context of the emerging field of porous polymer electrets with many potential device applications.

  13. FAST TRACK COMMUNICATION Single-charge rotating black holes in four-dimensional gauged supergravity

    NASA Astrophysics Data System (ADS)

    Chow, David D. K.

    2011-02-01

    We consider four-dimensional U(1)4 gauged supergravity, and obtain asymptotically AdS4, non-extremal, charged, rotating black holes with one non-zero U(1) charge. The thermodynamic quantities are computed. We obtain a generalization that includes a NUT parameter. The general solution has a discrete symmetry involving inversion of the rotation parameter, and has a string frame metric that admits a rank-2 Killing-Stäckel tensor.

  14. Binding of the Cationic Peptide (KL)4K to Lipid Monolayers at the Air-Water Interface: Effect of Lipid Headgroup Charge, Acyl Chain Length, and Acyl Chain Saturation.

    PubMed

    Hädicke, André; Blume, Alfred

    2016-04-28

    The binding of the cationic peptide (KL)4K to monolayers of different anionic lipids was determined by adsorption experiments. The chemical structure of the anionic phospholipids was changed in different ways. First, the hydrophobic region of phosphatidylglycerols was altered by elongation of the acyl chain length. Second, an unsaturated chain was introduced. Third, lipids with negatively charged headgroups of different chemical structure were compared. (KL)4K itself shows no surface activity and does not bind to monolayers of zwitterionic lipids. Analysis of (KL)4K binding to anionic lipid monolayers reveals a competition between two binding processes: (i) incorporation of the peptide into the acyl chain region (surface pressure increase) and (ii) electrostatic interaction screening the negative charges with reduction of charge repulsion (surface pressure decrease due to monolayer condensation). The lipid acyl chain length and the chemical structure of the headgroup have minor effects on the binding properties. However, a strong dependence on the phase state of the monolayer was observed. In the liquid-expanded (LE) phase, the fluid monolayer provides enough space, so that peptide insertion due to hydrophobic interactions dominates. For monolayers in the liquid-condensed (LC) phase, peptide binding followed by monolayer condensation is the main effect. PMID:27049846

  15. Mass Spectrometry of Single GABAergic Somatic Motorneurons Identifies a Novel Inhibitory Peptide, As-NLP-22, in the Nematode Ascaris suum

    NASA Astrophysics Data System (ADS)

    Konop, Christopher J.; Knickelbine, Jennifer J.; Sygulla, Molly S.; Wruck, Colin D.; Vestling, Martha M.; Stretton, Antony O. W.

    2015-12-01

    Neuromodulators have become an increasingly important component of functional circuits, dramatically changing the properties of both neurons and synapses to affect behavior. To explore the role of neuropeptides in Ascaris suum behavior, we devised an improved method for cleanly dissecting single motorneuronal cell bodies from the many other cell processes and hypodermal tissue in the ventral nerve cord. We determined their peptide content using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). The reduced complexity of the peptide mixture greatly aided the detection of peptides; peptide levels were sufficient to permit sequencing by tandem MS from single cells. Inhibitory motorneurons, known to be GABAergic, contain a novel neuropeptide, As-NLP-22 (SLASGRWGLRPamide). From this sequence and information from the A. suum expressed sequence tag (EST) database, we cloned the transcript ( As-nlp-22) and synthesized a riboprobe for in situ hybridization, which labeled the inhibitory motorneurons; this validates the integrity of the dissection method, showing that the peptides detected originate from the cells themselves and not from adhering processes from other cells (e.g., synaptic terminals). Synthetic As-NLP-22 has potent inhibitory activity on acetylcholine-induced muscle contraction as well as on basal muscle tone. Both of these effects are dose-dependent: the inhibitory effect on ACh contraction has an IC50 of 8.3 × 10-9 M. When injected into whole worms, As-NLP-22 produces a dose-dependent inhibition of locomotory movements and, at higher levels, complete paralysis. These experiments demonstrate the utility of MALDI TOF/TOF MS in identifying novel neuromodulators at the single-cell level.

  16. Mass Spectrometry of Single GABAergic Somatic Motorneurons Identifies a Novel Inhibitory Peptide, As-NLP-22, in the Nematode Ascaris suum.

    PubMed

    Konop, Christopher J; Knickelbine, Jennifer J; Sygulla, Molly S; Wruck, Colin D; Vestling, Martha M; Stretton, Antony O W

    2015-12-01

    Neuromodulators have become an increasingly important component of functional circuits, dramatically changing the properties of both neurons and synapses to affect behavior. To explore the role of neuropeptides in Ascaris suum behavior, we devised an improved method for cleanly dissecting single motorneuronal cell bodies from the many other cell processes and hypodermal tissue in the ventral nerve cord. We determined their peptide content using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). The reduced complexity of the peptide mixture greatly aided the detection of peptides; peptide levels were sufficient to permit sequencing by tandem MS from single cells. Inhibitory motorneurons, known to be GABAergic, contain a novel neuropeptide, As-NLP-22 (SLASGRWGLRPamide). From this sequence and information from the A. suum expressed sequence tag (EST) database, we cloned the transcript (As-nlp-22) and synthesized a riboprobe for in situ hybridization, which labeled the inhibitory motorneurons; this validates the integrity of the dissection method, showing that the peptides detected originate from the cells themselves and not from adhering processes from other cells (e.g., synaptic terminals). Synthetic As-NLP-22 has potent inhibitory activity on acetylcholine-induced muscle contraction as well as on basal muscle tone. Both of these effects are dose-dependent: the inhibitory effect on ACh contraction has an IC50 of 8.3 × 10(-9) M. When injected into whole worms, As-NLP-22 produces a dose-dependent inhibition of locomotory movements and, at higher levels, complete paralysis. These experiments demonstrate the utility of MALDI TOF/TOF MS in identifying novel neuromodulators at the single-cell level. Graphical Abstract ᅟ. PMID:26174364

  17. Effect of body biasing on single-event induced charge collection in deep N-well technology

    NASA Astrophysics Data System (ADS)

    Ding, Yi; Hu, Jian-Guo; Qin, Jun-Rui; Tan, Hong-Zhou

    2015-07-01

    As the device size decreases, the soft error induced by space ions is becoming a great concern for the reliability of integrated circuits (ICs). At present, the body biasing technique is widely used in highly scaled technologies. In the paper, using the three-dimensional technology computer-aided design (TCAD) simulation, we analyze the effect of the body biasing on the single-event charge collection in deep N-well technology. Our simulation results show that the body biasing mainly affects the behavior of the source, and the effect of body biasing on the charge collection for the nMOSFET and pMOSFET is quite different. For the nMOSFET, the RBB will increase the charge collection, while the FBB will reduce the charge collection. For the pMOSFET, the effect of RBB on the SET pulse width is small, while the FBB has an adverse effect. Moreover, the differenceof the effect of body biasing on the charge collection is compared in deep N-well and twin well.

  18. The combined use of a singly charged ion beam and undulator radiation for photoelectron spectrometry studies on atomic ions

    NASA Astrophysics Data System (ADS)

    Bizau, J. M.; Cubaynes, D.; Richter, M.; Wuilleumier, F.; Obert, J.; Putaux, J. C.

    1992-01-01

    We present the first photoelectron spectrometry experiment on a singly charged ion beam. Taking advantage of the high photon flux emitted in the undulator SU6 of Super-ACO, we have measured photoelectron spectra produced in the resonant photoionization of Ca+ ions at 33.2-eV photon energy. The success of this experiment depended strongly on the photon flux available. We demonstrate the capability of photoelectron spectrometry to precisely calibrate the photon spectrum emitted in the undulator.

  19. Explicitly correlated wave functions for atoms and singly charged ions from Li through Sr: Variational and Diffusion Monte Carlo results

    NASA Astrophysics Data System (ADS)

    Buendía, E.; Gálvez, F. J.; Maldonado, P.; Sarsa, A.

    2014-11-01

    Total energies calculated from explicitly correlated wave functions for the ground state of the atoms Li to Sr and their singly charged anions and cations are obtained. Accurate all electron, non-relativistic Variational and Diffusion Monte Carlo energies are reported. The quality of the results, when comparing with exact estimations and experimental electron affinities and ionization potential is similar for all of the atoms studied. The parameterization of the explicitly correlated wave functions for all of the atomic systems studied is provided.

  20. Measurement of differential cross sections for single neutral pion produced by charged-current interactions in MINERvA

    NASA Astrophysics Data System (ADS)

    Le, Trung; Minerva Collaboration

    2014-09-01

    MINERvA is a neutrino scattering experiment which uses the intense neutrino beam from the NuMI beam line at FNAL. The detector employs high spatial resolution, is fully active, and designed to study interactions of neutrinos using different nuclei. We present the differential cross sections for single neutral pion produced by charged-current interactions of anti-neutrinos in plastic scintillator. We also compare the differential cross sections to predictions by the GENIE event generator.

  1. Biocatalytic self-assembly of supramolecular charge-transfer nanostructures based on n-type semiconductor-appended peptides.

    PubMed

    Nalluri, Siva Krishna Mohan; Berdugo, Cristina; Javid, Nadeem; Frederix, Pim W J M; Ulijn, Rein V

    2014-06-01

    The reversible in situ formation of a self-assembly building block (naphthalenediimide (NDI)-dipeptide conjugate) by enzymatic condensation of NDI-functionalized tyrosine (NDI-Y) and phenylalanine-amide (F-NH2) to form NDI-YF-NH2 is described. This coupled biocatalytic condensation/assembly approach is thermodynamically driven and gives rise to nanostructures with optimized supramolecular interactions as evidenced by substantial aggregation induced emission upon assembly. Furthermore, in the presence of di-hydroxy/alkoxy naphthalene donors, efficient charge-transfer complexes are produced. The dynamic formation of NDI-YF-NH2 and electronic and H-bonding interactions are analyzed and characterized by different methods. Microscopy (TEM and AFM) and rheology are used to characterize the formed nanostructures. Dynamic nanostructures, whose formation and function are driven by free-energy minimization, are inherently self-healing and provide opportunities for the development of aqueous adaptive nanotechnology. PMID:24788665

  2. Influence of temperature and crown ether complex formation on the charge partitioning between z and c fragments formed after electron capture by small peptide dications

    NASA Astrophysics Data System (ADS)

    Ehlerding, Anneli; Jensen, Camilla S.; Wyer, Jean A.; Holm, Anne I. S.; Jørgensen, Palle; Kadhane, Umesh; Larsen, Mikkel K.; Panja, Subhasis; Poully, Jean Christophe; Worm, Esben S.; Zettergren, Henning; Hvelplund, Preben; Brøndsted Nielsen, Steen

    2009-04-01

    Electron capture by peptide dications results in N-C[alpha] bond cleavage to give c+ and z or c and z+ fragments. In this work we have investigated how crown ether (18-crown-6 = CE) complex formation and a change in the internal energy affect the charge division between the z and c fragments. Both complex formation and a high temperature have the effect of breaking internal ionic hydrogen bonds. The crown ether complex also lowers the probability of internal proton transfer between the two fragments, and reduces the recombination energy of the charged group it targets. The systems under study were doubly protonated di- and tripeptides, [AK+2H]2+, [AR+2H]2+, [KK+2H]2+ and [GHK+2H]2+ (A = alanine, K = lysine, R = arginine, G = glycine and H = histidine). For crown ether complexes the formation of z+ ions was always preferred over c+ ions. In the case of [GHK+2H]2+, the bare ion dissociated into z2+ + c1 and z1 + c2+ from cleavage of the first and second N-C[alpha] bond, respectively, whereas z1+ fragment ions had higher yield than c2+ for [GHK+2H]2+(CE). The internal energy of the ions was changed by storing them in a 22-pole ion trap in which they were equilibrated to a temperature between -60 and 90 °C in collisions with helium gas. The average internal energy increased by about 0.4 eV from the lowest to the highest temperature for the dipeptides and 0.6 eV for the tripeptide. More fragmentation occurred at the higher temperature, as observed by an increase in the formation of b+ and y+ ions after breakage of the peptide bond of vibrationally hot even-electron cations and from secondary reactions of z+ radical cations within the time window of the experiment. However, the z+ to c+ partitioning was not found to depend significantly on temperature in the measured range. In addition the decay of [GHK+H]+/[GHK+2H]+ and [AK+H]+ formed after electron capture by [GHK+2H]2+ and [AK+2H]2+ was found to occur on a microsecond to millisecond timescale. The data are well

  3. Multidomain Peptides: Sequence-Nanostructure Relationships and Biological Applications

    NASA Astrophysics Data System (ADS)

    Bakota, Erica Laraine

    2011-12-01

    Peptides are materials that, as a result of their polymeric nature, possess enormous versatility and customizability. Multidomain peptides are a class of peptides that self-assemble to form stable, cytocompatible hydrogels. They have an ABA block motif, in which the A block is composed of charged amino acids, such as lysine, and the B block consists of alternating hydrophilic and hydrophobic amino acids, such as glutamine and leucine. The B block forms a facial amphiphile that drives self-assembly. The charged A blocks simultaneously limit self-assembly and improve solubility. Self-assembly is triggered by charge screening of these charged amino acids, enabling the formation of beta-sheet fibers. The development of an extended nanofiber network can result in the formation of a hydrogel. Systematic modifications to both the A and B blocks were investigated, and it was found that sequence modifications have a large impact on peptide nanostructure and hydrogel rheology. The first modification examined is the substitution of amino acids within the hydrophilic positions of the B block. The second set of modifications investigated was the incorporation of aromatic amino acids in the B block. Finally, the charged block was varied to generate different net charges on the peptides, a change which impacted the ability to use these peptides in cell culture. Two applications of multidomain peptide nanofibers are explored, the first of which is the delivery of novel therapies in vivo. One multidomain peptide is able to form hydrogels that undergo shear-thinning and rapid recovery. This gel can be loaded with cytokines and growth factors that have been secreted by embryonic stem cells, and these molecules can be subsequently released in a therapeutic setting. Another application for multidomain peptide is their use as biocompatible surfactants. Single-walled carbon nanotubes have been widely investigated for their unique optical and electrical properties, but their solubility in

  4. Three independent techniques localize expression of transcript afp-11 and its bioactive peptide products to the paired AVK neurons in Ascaris suum: in situ hybridization, immunocytochemistry, and single cell mass spectrometry.

    PubMed

    Jarecki, Jessica L; Viola, India R; Andersen, Kari M; Miller, Andrew H; Ramaker, Megan A; Vestling, Martha M; Stretton, Antony O

    2013-03-20

    We utilized three independent techniques, immunocytochemistry (ICC), single cell mass spectrometry (MS), and in situ hybridization (ISH), to localize neuropeptides and their transcripts in the nervous system of the nematode Ascaris suum . AF11 (SDIGISEPNFLRFa) is an endogenous peptide with potent paralytic effects on A. suum locomotory behavior. A highly specific antibody to AF11 showed robust immunostaining for AF11 in the paired AVK neurons in the ventral ganglion. We traced the processes from the AVK neurons into the ventral nerve cord and identified them as ventral cord interneurons. MS and MS/MS of single dissected AVKs detected AF11, two previously characterized peptides (AF25 and AF26), seven novel sequence-related peptides, including several sharing a PNFLRFamide C-terminus, and peptide NY, a peptide with an unrelated sequence. Also present in a subset of AVKs was AF2, a peptide encoded by the afp-4 transcript. By sequencing the afp-11 transcript, we discovered that it encodes AF11, all the AF11-related peptides detected by MS in AVK, and peptide NY. ISH detected the afp-11 transcript in AVK neurons, consistent with other techniques. ISH did not detect afp-11 in the ALA neuron, although both ICC and MS found AF11 in ca. 30% of ALAs. All 10 AF11-related peptides reduced acetylcholine-induced muscle contraction, but they differed in their rate of reversal of inhibition after removal of the peptide. PMID:23509978

  5. The Positively Charged COOH-terminal Glycosaminoglycan-binding CXCL9(74-103) Peptide Inhibits CXCL8-induced Neutrophil Extravasation and Monosodium Urate Crystal-induced Gout in Mice.

    PubMed

    Vanheule, Vincent; Janssens, Rik; Boff, Daiane; Kitic, Nikola; Berghmans, Nele; Ronsse, Isabelle; Kungl, Andreas J; Amaral, Flavio Almeida; Teixeira, Mauro Martins; Van Damme, Jo; Proost, Paul; Mortier, Anneleen

    2015-08-28

    The ELR(-)CXC chemokine CXCL9 is characterized by a long, highly positively charged COOH-terminal region, absent in most other chemokines. Several natural leukocyte- and fibroblast-derived COOH-terminally truncated CXCL9 forms missing up to 30 amino acids were identified. To investigate the role of the COOH-terminal region of CXCL9, several COOH-terminal peptides were chemically synthesized. These peptides display high affinity for glycosaminoglycans (GAGs) and compete with functional intact chemokines for GAG binding, the longest peptide (CXCL9(74-103)) being the most potent. The COOH-terminal peptide CXCL9(74-103) does not signal through or act as an antagonist for CXCR3, the G protein-coupled CXCL9 receptor, and does not influence neutrophil chemotactic activity of CXCL8 in vitro. Based on the GAG binding data, an anti-inflammatory role for CXCL9(74-103) was further evidenced in vivo. Simultaneous intravenous injection of CXCL9(74-103) with CXCL8 injection in the joint diminished CXCL8-induced neutrophil extravasation. Analogously, monosodium urate crystal-induced neutrophil migration to the tibiofemural articulation, a murine model of gout, is highly reduced by intravenous injection of CXCL9(74-103). These data show that chemokine-derived peptides with high affinity for GAGs may be used as anti-inflammatory peptides; by competing with active chemokines for binding and immobilization on GAGs, these peptides may lower chemokine presentation on the endothelium and disrupt the generation of a chemokine gradient, thereby preventing a chemokine from properly performing its chemotactic function. The CXCL9 peptide may serve as a lead molecule for further development of inhibitors of inflammation based on interference with chemokine-GAG interactions. PMID:26183778

  6. Structural and Functional Characterization of a Single-chain Peptide-MHC Molecule that Modulates both Naive and Activated CD8plus T Cells

    SciTech Connect

    D Samanta; G Mukherjee; U Ramagopal; R Chaparro; S Nathenson; T DiLorenzo; S Almo

    2011-12-31

    Peptide-MHC (pMHC) multimers, in addition to being tools for tracking and quantifying antigen-specific T cells, can mediate downstream signaling after T-cell receptor engagement. In the absence of costimulation, this can lead to anergy or apoptosis of cognate T cells, a property that could be exploited in the setting of autoimmune disease. Most studies with class I pMHC multimers used noncovalently linked peptides, which can allow unwanted CD8{sup +} T-cell activation as a result of peptide transfer to cellular MHC molecules. To circumvent this problem, and given the role of self-reactive CD8{sup +} T cells in the development of type 1 diabetes, we designed a single-chain pMHC complex (scK{sup d}.IGRP) by using the class I MHC molecule H-2K{sup d} and a covalently linked peptide derived from islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP{sub 206-214}), a well established autoantigen in NOD mice. X-ray diffraction studies revealed that the peptide is presented in the groove of the MHC molecule in canonical fashion, and it was also demonstrated that scK{sup d}.IGRP tetramers bound specifically to cognate CD8{sup +} T cells. Tetramer binding induced death of naive T cells and in vitro- and in vivo-differentiated cytotoxic T lymphocytes, and tetramer-treated cytotoxic T lymphocytes showed a diminished IFN-{gamma} response to antigen stimulation. Tetramer accessibility to disease-relevant T cells in vivo was also demonstrated. Our study suggests the potential of single-chain pMHC tetramers as possible therapeutic agents in autoimmune disease. Their ability to affect the fate of naive and activated CD8{sup +} T cells makes them a potential intervention strategy in early and late stages of disease.

  7. Absolute single and multiple charge exchange cross sections for highly charged C, O, and Ne ions on H{sub 2}O, CO, and CO{sub 2}

    SciTech Connect

    Mawhorter, R. J.; Chutjian, A.; Djuric, N.; Hossain, S.; MacAskill, J. A.; Smith, S. J.; Simcic, J.; Cravens, T. E.; Lisse, C. M.; Williams, I. D.

    2007-03-15

    Reported herein are measured absolute single, double, and triple charge exchange (CE) cross sections for the highly charged ions (HCIs) C{sup q+} (q=5,6), O{sup q+} (q=6,7,8), and Ne{sup q+} (q=7,8) colliding with the molecular species H{sub 2}O, CO, and CO{sub 2}. Present data can be applied to interpreting observations of x-ray emissions from comets as they interact with the solar wind. As such, the ion impact energies of 7.0q keV (1.62-3.06 keV/amu) are representative of the fast solar wind, and data at 1.5q keV for O{sup 6+} (0.56 keV/amu) on CO and CO{sub 2} and 3.5q keV for O{sup 5+} (1.09 keV/amu) on CO provide checks of the energy dependence of the cross sections at intermediate and typical slow solar wind velocities. The HCIs are generated within a 14 GHz electron cyclotron resonance ion source. Absolute CE measurements are made using a retarding potential energy analyzer, with measurement of the target gas cell pressure and incident and final ion currents. Trends in the cross sections are discussed in light of the classical overbarrier model (OBM), extended OBM, and with recent results of the classical trajectory Monte Carlo theory.

  8. Transport behavior of a single Ca(2+), K(+), and Na(+) in a water-filled transmembrane cyclic peptide nanotube.

    PubMed

    Yan, Xiliang; Fan, Jianfen; Yu, Yi; Xu, Jian; Zhang, Mingming

    2015-05-26

    Molecular dynamics simulations have been performed to investigate the transport properties of a single Ca(2+), K(+), and Na(+) in a water-filled transmembrane cyclic peptide nanotube (CPNT). Two transmembrane CPNTs, i.e., 8×(WL)n=4,5/POPE (with uniform lengths but various radii), were applied to clarify the dependence of ionic transport properties on the channel radius. A huge energy barrier keeps Ca(2+) out of the octa-CPNT, while Na(+) and K(+) can be trapped in two CPNTs. The dominant electrostatic interaction of a cation with water molecules leads to a high distribution of channel water around the cation and D-defects in the first and last gaps, and significantly reduces the axial diffusion of channel water. Water-bridged interactions were mostly found between the artificially introduced Ca(2+) and the framework of the octa-CPNT, and direct coordinations with the tube wall mostly occur for K(+) in the octa-CPNT. A cation may drift rapidly or behave lazily in a CPNT. K(+) behaves most actively and can visit the whole deca-CPNT quickly. The first solvation shells of Ca(2+) and Na(+) are basically saturated in two CPNTs, while the hydration of K(+) is incomplete in the octa-CPNT. The solvation structure of Ca(2+) in the octa-CPNT is most stable, while that of K(+) in the deca-CPNT is most labile. Increasing the channel radius induces numerous interchange attempts between the first-shell water molecules of a cation and the ones in the outer region, especially for the K(+) system. PMID:25894098

  9. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, Paul

    1996-01-01

    An ionization detector electrode and signal subtraction apparatus and method provides at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector.

  10. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, P.

    1996-06-25

    An ionization detector electrode and signal subtraction apparatus and method provide at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector. 9 figs.

  11. Lepton production at the LHC from singly- and doubly-charged bilepton

    SciTech Connect

    Sa Borges, J.; Coutinho, Y. A.; Barreto, E. R.

    2013-03-25

    Some extensions of the standard model predict the existence of particles having two units of leptonic charge, known as bileptons. One of such models is based on the SU(3){sub c} Multiplication-Sign SU(3){sub L} Multiplication-Sign U(1){sub X} symmetry group (3-3-1). Our search uses the minimal version of this model, having exotic charges for the quarks and gauge bosons. It predicts the existence of bileptons as vector particles having one unit of electric charge (V{sup {+-}}) or two units of electric charge (Y{sup {+-}{+-}}). Our aim is to establish the signatures for the production of four fermions in pp collisions at the LHC for 7 TeV center of mass energy. We present the total cross section and we show the leptons invariant mass and transverse momentum distributions. We conclude that LHC collider can show a clear signature for a process induced by bileptons as a signal of new physics.

  12. Power loss of a single electron charge distribution confined in a quantum plasma

    SciTech Connect

    Mehramiz, A.; Mahmoodi, J.; Sobhanian, S.

    2011-05-15

    The dielectric tensor for a quantum plasma is derived by using a linearized quantum hydrodynamic theory. The wave functions for a nanostructure bound system have been investigated. Finally, the power loss for an oscillating charge distribution of a mixed state will be calculated, using the dielectric function formalism.

  13. Charge state control in single InAs/GaAs quantum dots by external electric and magnetic fields

    SciTech Connect

    Tang, Jing; Cao, Shuo; Gao, Yunan; Sun, Yue; Jin, Kuijuan; Xu, Xiulai; Geng, Weidong; Williams, David A.

    2014-07-28

    We report a photoluminescence (PL) spectroscopy study of charge state control in single self-assembled InAs/GaAs quantum dots by applying electric and/or magnetic fields at 4.2 K. Neutral and charged exciton complexes were observed under applied bias voltages from −0.5 V to 0.5 V by controlling the carrier tunneling. The highly negatively charged exciton emission becomes stronger with increasing pumping power, arising from the fact that electrons have a smaller effective mass than holes and are more easily captured by the quantum dots. The integrated PL intensity of negatively charged excitons is affected significantly by a magnetic field applied along the sample growth axis. This observation is explained by a reduction in the electron drift velocity caused by an applied magnetic field, which increases the probability of non-resonantly excited electrons being trapped by localized potentials at the wetting layer interface, and results in fewer electrons distributed in the quantum dots. The hole drift velocity is also affected by the magnetic field, but it is much weaker.

  14. Operation of a Single-Photon-Counting X-Ray Charge-Coupled Device Camera Spectrometer in a Petawatt Environment

    SciTech Connect

    Stoeckl, C.; Theobald, W.; Sangster, T.C.; Key, M.H.; Patel, P.; Zhang, B.B.; Clarke, R.; Karsch, S.; Norreys, P.

    2004-10-12

    The use of a single-photon-counting x-ray CCD (charge-coupled device) camera as an x-ray spectrometer is a well-established technique in ultrashort-pulse laser experiments. In single-photon-counting mode, the pixel value of each readout pixel is proportional to the energy deposited from the incident x-ray photon. For photons below 100 keV, a significant fraction of the events deposits all the energy in a single pixel. A histogram of the pixel readout values gives a good approximation of the x-ray spectrum. This technique requires almost no alignment, but it is very sensitive to signal-to-background issues, especially in a high-energy petawatt environment.

  15. Fragmentation efficiencies of peptide ions following low energy collisional activation

    NASA Astrophysics Data System (ADS)

    Summerfield, Scott G.; Gaskell, Simon J.

    1997-11-01

    Low energy fragmentations of protonated peptides in the gas phase are generally attributed to charge-directed processes. The extent and location of peptide backbone fragmentation is accordingly influenced by the extent to which charge is sequestered on amino acid side-chains. We describe systematic studies of the efficiencies of decomposition of peptide ions to assess in particular the influence of the presence of basic amino acid residues and of the protonation state. In a set of analogues containing two arginine, two histidine or two lysine residues, the extent of fragmentation of [M + 2H]2+ ions decreases with increased basicity, reflecting decreased backbone protonation. The collisionally activated dissociation of multiply protonated melittin ions shows an increase in fragmentation efficiency with higher charge state (using activation conditions which are similar for each charge state). For a single charge state, acetylation of primary amine groups increases fragmentation efficiency, consistent with the reduction in basicity of lysine side-chains. Conversion of arginine residues to the less basic dimethylpyrimidylornithine, however, decreases fragmentation efficiency, suggesting more effective sequestering of ionizing protons; the effect may be attributable to a disfavouring of proton-bridged structures but this hypothesis requires further study. Preliminary data for the decompositions of [M- 2H]2- ions derived from peptides containing two acidic residues suggest that the sequestration of charge away from the backbone is again detrimental to efficient fragmentation. Apparently diagnostic cleavages adjacent to aspartic acid residues are observed.

  16. Impact of Multiple Negative Charges on Blood Clearance and Biodistribution Characteristics of 99mTc-Labeled Dimeric Cyclic RGD Peptides

    PubMed Central

    2015-01-01

    This study sought to evaluate the impact of multiple negative charges on blood clearance kinetics and biodistribution properties of 99mTc-labeled RGD peptide dimers. Bioconjugates HYNIC-P6G-RGD2 and HYNIC-P6D-RGD2 were prepared by reacting P6G-RGD2 and P6D-RGD2, respectively, with excess HYNIC-OSu in the presence of diisopropylethylamine. Their IC50 values were determined to be 31 ± 5 and 41 ± 6 nM, respectively, against 125I-echistatin bound to U87MG glioma cells in a whole-cell displacement assay. Complexes [99mTc(HYNIC-P6G-RGD2)(tricine)(TPPTS)] (99mTc-P6G-RGD2) and [99mTc(HYNIC-P6D-RGD2)(tricine)(TPPTS)] (99mTc-P6D-RGD2) were prepared in high radiochemical purity (RCP > 95%) and specific activity (37–110 GBq/μmol). They were evaluated in athymic nude mice bearing U87MG glioma xenografts for their biodistribution. The most significant difference between 99mTc-P6D-RGD2 and 99mTc-P6G-RGD2 was their blood radioactivity levels and tumor uptake. The initial blood radioactivity level for 99mTc-P6D-RGD2 (4.71 ± 1.00%ID/g) was ∼5× higher than that of 99mTc-P6G-RGD2 (0.88 ± 0.05%ID/g), but this difference disappeared at 60 min p.i. 99mTc-P6D-RGD2 had much lower tumor uptake (2.20–3.11%ID/g) than 99mTc-P6G-RGD2 (7.82–9.27%ID/g) over a 2 h period. Since HYNIC-P6D-RGD2 and HYNIC-P6G-RGD2 shared a similar integrin αvβ3 binding affinity (41 ± 6 nM versus 31 ± 5 nM), the difference in their blood activity and tumor uptake is most likely related to the nine negative charges and high protein binding of 99mTc-P6D-RGD2. Despite its low uptake in U87MG tumors, the tumor uptake of 99mTc-P6D-RGD2 was integrin αvβ3-specific. SPECT/CT studies were performed using 99mTc-P6G-RGD2 in athymic nude mice bearing U87MG glioma and MDA-MB-231 breast cancer xenografts. The SPECT/CT data demonstrated the tumor-targeting capability of 99mTc-P6G-RGD2, and its tumor uptake depends on the integrin αvβ3 expression levels on tumor cells and neovasculature. It was concluded that

  17. Widespread CD4+ T-cell reactivity to novel hTERT epitopes following vaccination of cancer patients with a single hTERT peptide GV1001.

    PubMed

    Inderberg-Suso, Else-Marit; Trachsel, Sissel; Lislerud, Kari; Rasmussen, Anne-Marie; Gaudernack, Gustav

    2012-08-01

    Understanding the basis of a successful clinical response after treatment with therapeutic cancer vaccines is essential for the development of more efficacious therapy. After vaccination with the single telomerase (hTERT) 16-mer peptide, GV1001, some patients experienced clinical responses and long-term survival. This study reports in-depth immunological analysis of the T-cell response against telomerase (hTERT) in clinically responding patients compared with clinical non-responders following vaccination with the single hTERT 16-mer peptide, GV1001. Extensive characterization of CD4+ T-cell clones specific for GV1001 generated from a lung cancer patient in complete remission after vaccination demonstrated a very broad immune response to this single peptide vaccine with differences in fine specificity, HLA restriction, affinity and function. Some CD4+ T-cell clones were cytotoxic against peptide-loaded target cells and also recognized processed recombinant hTERT protein. Furthermore, T-cell responses against several unrelated hTERT epitopes, some of which are novel, were detected, indicating extensive epitope spreading which was confirmed in other clinical responders. In contrast, patients responding immunologically, but not clinically, after vaccination did not display this intramolecular epitope spreading. Multifunctional CD4+ T-cell clones specific for novel hTERT epitopes were generated and shown to recognize a melanoma cell line. Pentamer analysis of T cells in peripheral blood also demonstrated the presence of an important CD8+ T-cell response recognizing an HLA-B7 epitope embedded in GV1001 not previously described. These results indicate that the highly diverse hTERT-specific T-cell response, integrating both T helper and CTL responses, is essential for tumor regression and the generation of long-term T-cell memory. PMID:22934259

  18. Widespread CD4+ T-cell reactivity to novel hTERT epitopes following vaccination of cancer patients with a single hTERT peptide GV1001

    PubMed Central

    Inderberg-Suso, Else-Marit; Trachsel, Sissel; Lislerud, Kari; Rasmussen, Anne-Marie; Gaudernack, Gustav

    2012-01-01

    Understanding the basis of a successful clinical response after treatment with therapeutic cancer vaccines is essential for the development of more efficacious therapy. After vaccination with the single telomerase (hTERT) 16-mer peptide, GV1001, some patients experienced clinical responses and long-term survival. This study reports in-depth immunological analysis of the T-cell response against telomerase (hTERT) in clinically responding patients compared with clinical non-responders following vaccination with the single hTERT 16-mer peptide, GV1001. Extensive characterization of CD4+ T-cell clones specific for GV1001 generated from a lung cancer patient in complete remission after vaccination demonstrated a very broad immune response to this single peptide vaccine with differences in fine specificity, HLA restriction, affinity and function. Some CD4+ T-cell clones were cytotoxic against peptide-loaded target cells and also recognized processed recombinant hTERT protein. Furthermore, T-cell responses against several unrelated hTERT epitopes, some of which are novel, were detected, indicating extensive epitope spreading which was confirmed in other clinical responders. In contrast, patients responding immunologically, but not clinically, after vaccination did not display this intramolecular epitope spreading. Multifunctional CD4+ T-cell clones specific for novel hTERT epitopes were generated and shown to recognize a melanoma cell line. Pentamer analysis of T cells in peripheral blood also demonstrated the presence of an important CD8+ T-cell response recognizing an HLA-B7 epitope embedded in GV1001 not previously described. These results indicate that the highly diverse hTERT-specific T-cell response, integrating both T helper and CTL responses, is essential for tumor regression and the generation of long-term T-cell memory. PMID:22934259

  19. Isolation and structure of a novel charged member of the red-pigment-concentrating hormone-adipokinetic hormone family of peptides isolated from the corpora cardiaca of the blowfly Phormia terraenovae (Diptera).

    PubMed

    Gäde, G; Wilps, H; Kellner, R

    1990-07-15

    A hypertrehalosaemic neuropeptide from the corpora cardiaca of the blowfly Phormia terraenovae has been isolated by reversed-phase h.p.l.c., and its primary structure was determined by pulsed-liquid phase sequencing employing Edman chemistry after enzymically deblocking the N-terminal pyroglutamate residue. The C-terminus was also blocked, as indicated by the lack of digestion when the peptide was incubated with carboxypeptidase A. The octapeptide has the sequence pGlu-Leu-Thr-Phe-Ser-Pro-Asp-Trp-NH2 and is clearly defined as a novel member of the RPCH/AKH (red-pigment-concentrating hormone/adipokinetic hormone) family of peptides. It is the first charged member of this family to be found. The synthetic peptide causes an increase in the haemolymph carbohydrate concentration in a dose-dependent fashion in blowflies and therefore is named 'Phormia terraenovae hypertrehalosaemic hormone' (Pht-HrTH). In addition, receptors in the fat-body of the American cockroach (Periplaneta americana) recognize the peptide, resulting in carbohydrate elevation in the blood. However, fat-body receptors of the migratory locust (Locusta migratoria) do not recognize this charged molecule, and thus no lipid mobilization is observed in this species. PMID:2386478

  20. Visualization of single-wall carbon nanotube (SWNT) networks in conductive polystyrene nanocomposites by charge contrast imaging.

    PubMed

    Loos, Joachim; Alexeev, Alexander; Grossiord, Nadia; Koning, Cor E; Regev, Oren

    2005-09-01

    The morphology of conductive nanocomposites consisting of low concentration of single-wall carbon nanotubes (SWNT) and polystyrene (PS) has been studied using atomic force microscopy (AFM), transmission electron microscopy (TEM) and, in particular, scanning electron microscopy (SEM). Application of charge contrast imaging in SEM allows visualization of the overall SWNT dispersion within the polymer matrix as well as the identification of individual or bundled SWNTs at high resolution. The contrast mechanism involved will be discussed. In conductive nanocomposites the SWNTs are homogeneously dispersed within the polymer matrix and form a network. Beside fairly straight SWNTs, strongly bended SWNTs have been observed. However, for samples with SWNT concentrations below the percolation threshold, the common overall charging behavior of an insulating material is observed preventing the detailed morphological investigation of the sample. PMID:15885910

  1. Single Charge Current in a Normal Mesoscopic Region Attached to Superconductor Leads via a Coupled Poisson Nonequilibrium Green Function Formalism

    PubMed Central

    Marin, F. P.

    2014-01-01

    We study the I-V characteristic of mesoscopic systems or quantum dot (QD) attached to a pair of superconducting leads. Interaction effects in the QD are considered through the charging energy of the QD; that is, the treatment of current transport under a voltage bias is performed within a coupled Poisson nonequilibrium Green function (PNEGF) formalism. We derive the expression for the current in full generality but consider only the regime where transport occurs only via a single particle current. We show for this case and for various charging energies values U 0 and associated capacitances of the QD the effect on the I-V characteristic. Also the influence of the coupling constants on the I-V characteristic is investigated. Our approach puts forward a novel interpretation of experiments in the strong Coulomb regime. PMID:24977220

  2. Positive and negative singly charged ion production of a laser induced plasma using a capillary graphite target.

    PubMed

    Saquilayan, G Q; Wada, M

    2016-02-01

    A new type of laser ion source is being developed aiming at the production of positive and negative singly charged ions using a capillary graphite target structure. The initial results of the laser plasma produced inside of the 10 mm diameter conduit indicated the formation of the secondary charged particle production inside the target. A high speed camera clearly recorded the plasma plume expansion inside the target. The time-of-flight spectrum of the laser produced plasma in vacuum showed that the signal of the positive ions formed two peaks as the laser power density exceeded 10 GW/cm(2). The addition of neutral gas to the system produced a signal corresponding to negative ions after the positive signal. PMID:26931968

  3. Fractionally Charged Zero-Energy Single-Particle Excitations in a Driven Fermi Sea.

    PubMed

    Moskalets, Michael

    2016-07-22

    A voltage pulse of a Lorentzian shape carrying half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasiparticle with an effectively fractional charge e/2. A prominent feature of such an excitation is a narrow peak in the energy distribution function lying exactly at the Fermi energy μ. Another spectacular feature is that the distribution function has symmetric tails around μ, which results in a zero-energy excitation. This sounds improbable since at zero temperature all available states below μ are fully occupied. The resolution lies in the fact that such a voltage pulse also excites electron-hole pairs, which free some space below μ and thus allow a zero-energy quasiparticle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in an experiment. PMID:27494490

  4. Complexes between high charge density cationic polyelectrolytes and anionic single- and double-tail surfactants.

    PubMed

    Mantzaridis, C; Mountrichas, G; Pispas, S

    2009-05-21

    Polyelectrolyte/surfactant complexes formed between well-defined linear flexible polyelectrolytes, namely, quaternized poly[3,5-bis(dimethylaminomethylene)hydroxystyrene] (Q-N-PHOS), bearing two cationic sites on each repeating unit, and two different anionic surfactants, namely, sodium dodecyl sulfate (SDS) with one hydrocarbon tail and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) with two hydrocarbon chains, are studied by means of fluorescence spectroscopy, electrophoretic, dynamic and static light scattering, and atomic force microscopy. Depending on the surfactant state in initial solutions (i.e., below or above nominal critical micelle concentration, cmc) and final (-/+) charge ratio, self-assembly in nanoparticles of variable size, stability, and effective charge is possible. Spherical, rather polydispserse complexes are formed in all cases. Critical aggregation concentrations (cac) depend on the surfactant type, while hydrophobicity of the main polyelectrolyte chain plays a role in colloidal stability of the complex nanoparticles. PMID:19388679

  5. Fractionally Charged Zero-Energy Single-Particle Excitations in a Driven Fermi Sea

    NASA Astrophysics Data System (ADS)

    Moskalets, Michael

    2016-07-01

    A voltage pulse of a Lorentzian shape carrying half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasiparticle with an effectively fractional charge e /2 . A prominent feature of such an excitation is a narrow peak in the energy distribution function lying exactly at the Fermi energy μ . Another spectacular feature is that the distribution function has symmetric tails around μ , which results in a zero-energy excitation. This sounds improbable since at zero temperature all available states below μ are fully occupied. The resolution lies in the fact that such a voltage pulse also excites electron-hole pairs, which free some space below μ and thus allow a zero-energy quasiparticle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in an experiment.

  6. Single ion induced surface nanostructures: a comparison between slow highly charged and swift heavy ions.

    PubMed

    Aumayr, Friedrich; Facsko, Stefan; El-Said, Ayman S; Trautmann, Christina; Schleberger, Marika

    2011-10-01

    This topical review focuses on recent advances in the understanding of the formation of surface nanostructures, an intriguing phenomenon in ion-surface interaction due to the impact of individual ions. In many solid targets, swift heavy ions produce narrow cylindrical tracks accompanied by the formation of a surface nanostructure. More recently, a similar nanometric surface effect has been revealed for the impact of individual, very slow but highly charged ions. While swift ions transfer their large kinetic energy to the target via ionization and electronic excitation processes (electronic stopping), slow highly charged ions produce surface structures due to potential energy deposited at the top surface layers. Despite the differences in primary excitation, the similarity between the nanostructures is striking and strongly points to a common mechanism related to the energy transfer from the electronic to the lattice system of the target. A comparison of surface structures induced by swift heavy ions and slow highly charged ions provides a valuable insight to better understand the formation mechanisms. PMID:21900733

  7. Design of Accumulators and Liquid/Gas Charging of Single Phase Mechanically Pumped Fluid Loop Heat Rejection Systems

    NASA Technical Reports Server (NTRS)

    Bhandari, Pradeep; Dudik, Brenda; Birur, Gajanana; Karlmann, Paul; Bame, David; Mastropietro, A. J.

    2012-01-01

    For single phase mechanically pumped fluid loops used for thermal control of spacecraft, a gas charged accumulator is typically used to modulate pressures within the loop. This is needed to accommodate changes in the working fluid volume due to changes in the operating temperatures as the spacecraft encounters varying thermal environments during its mission. Overall, the three key requirements on the accumulator to maintain an appropriate pressure range throughout the mission are: accommodation of the volume change of the fluid due to temperature changes, avoidance of pump cavitation and prevention of boiling in the liquid. The sizing and design of such an accumulator requires very careful and accurate accounting of temperature distribution within each element of the working fluid for the entire range of conditions expected, accurate knowledge of volume of each fluid element, assessment of corresponding pressures needed to avoid boiling in the liquid, as well as the pressures needed to avoid cavitation in the pump. The appropriate liquid and accumulator strokes required to accommodate the liquid volume change, as well as the appropriate gas volumes, require proper sizing to ensure that the correct pressure range is maintained during the mission. Additionally, a very careful assessment of the process for charging both the gas side and the liquid side of the accumulator is required to properly position the bellows and pressurize the system to a level commensurate with requirements. To achieve the accurate sizing of the accumulator and the charging of the system, sophisticated EXCEL based spreadsheets were developed to rapidly come up with an accumulator design and the corresponding charging parameters. These spreadsheets have proven to be computationally fast and accurate tools for this purpose. This paper will describe the entire process of designing and charging the system, using a case study of the Mars Science Laboratory (MSL) fluid loops, which is en route to

  8. Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

    NASA Astrophysics Data System (ADS)

    Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

    2013-09-01

    Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy n- and VxOyCln- ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln- and VxOyCl(L)(n-1)- clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1-2)- and VxOy (1-2)- anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a

  9. Moving Away from the Reference Genome: Evaluating a Peptide Sequencing Tagging Approach for Single Amino Acid Polymorphism Identifications in the Genus Populus

    SciTech Connect

    Abraham, Paul E; Adams, Rachel M; Tuskan, Gerald A; Hettich, Robert {Bob} L

    2013-01-01

    The genetic diversity across natural populations of the model organism, Populus, is extensive, containing a single nucleotide polymorphism roughly every 200 base pairs. When deviations from the reference genome occur in coding regions, they can impact protein sequences. Rather than relying on a static reference database to profile protein expression, we employed a peptide sequence tagging (PST) approach capable of decoding the plasticity of the Populus proteome. Using shotgun proteomics data from two genotypes of P. trichocarpa, a tag-based approach enabled the detection of 6,653 unexpected sequence variants. Through manual validation, our study investigated how the most abundant chemical modification (methionine oxidation) could masquerade as a sequence variant (AlaSer) when few site-determining ions existed. In fact, precise localization of an oxidation site for peptides with more than one potential placement was indeterminate for 70% of the MS/MS spectra. We demonstrate that additional fragment ions made available by high energy collisional dissociation enhances the robustness of the peptide sequence tagging approach (81% of oxidation events could be exclusively localized to a methionine). We are confident that augmenting fragmentation processes for a PST approach will further improve the identification of single amino acid polymorphism in Populus and potentially other species as well.

  10. Investigation of electrically-active deep levels in single-crystalline diamond by particle-induced charge transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Kada, W.; Kambayashi, Y.; Ando, Y.; Onoda, S.; Umezawa, H.; Mokuno, Y.; Shikata, S.; Makino, T.; Koka, M.; Hanaizumi, O.; Kamiya, T.; Ohshima, T.

    2016-04-01

    To investigate electrically-active deep levels in high-resistivity single-crystalline diamond, particle-induced charge transient spectroscopy (QTS) techniques were performed using 5.5 MeV alpha particles and 9 MeV carbon focused microprobes. For unintentionally-doped (UID) chemical vapor deposition (CVD) diamond, deep levels with activation energies of 0.35 eV and 0.43 eV were detected which correspond to the activation energy of boron acceptors in diamond. The results suggested that alpha particle and heavy ion induced QTS techniques are the promising candidate for in-situ investigation of deep levels in high-resistivity semiconductors.

  11. Charge Dependence and Electric Quadrupole Effects on Single-Nucleon Removal in Relativistic and Intermediate Energy Nuclear Collisions

    NASA Technical Reports Server (NTRS)

    Norbury, John W.

    1992-01-01

    Single nucleon removal in relativistic and intermediate energy nucleus-nucleus collisions is studied using a generalization of Weizsacker-Williams theory that treats each electromagnetic multipole separately. Calculations are presented for electric dipole and quadrupole excitations and incorporate a realistic minimum impact parameter, Coulomb recoil corrections, and the uncertainties in the input photonuclear data. Discrepancies are discussed. The maximum quadrupole effect to be observed in future experiments is estimated and also an analysis of the charge dependence of the electromagnetic cross sections down to energies as low as 100 MeV/nucleon is made.

  12. Charge dependence and electric quadrupole effects on single-nucleon removal in relativistic and intermediate energy nuclear collisions

    NASA Technical Reports Server (NTRS)

    Norbury, J. W.; Townsend, L. W. (Principal Investigator)

    1990-01-01

    Single-nucleon removal in relativistic and intermediate energy nucleus-nucleus collisions is studied using a generalization of Weizsacker-Williams theory that treats each electromagnetic multipole separately. Calculations are presented for electric dipole and quadrupole excitations and incorporate a realistic minimum impact parameter, Coulomb recoil corrections, and the uncertainties in the input photonuclear data. Discrepancies are discussed. The maximum quadrupole effect to be observed in future experiments is estimated and also an analysis of the charge dependence of the electromagnetic cross sections down to energies as low as 100 MeV/nucleon is made.

  13. Investigating photoinduced charge transfer in double- and single-emission PbS@CdS core@shell quantum dots

    NASA Astrophysics Data System (ADS)

    Zhao, Haiguang; Liang, Hongyan; Gonfa, Belete Atomsa; Chaker, Mohamed; Ozaki, Tsuneyuki; Tijssen, Peter; Vidal, François; Ma, Dongling

    2013-12-01

    We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ~0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices.We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core

  14. Differentiation between Shallow and Deep Charge Trap States on Single Poly(3-hexylthiophene) Chains through Fluorescence Photon Statistics.

    PubMed

    Grußmayer, Kristin S; Steiner, Florian; Lupton, John M; Herten, Dirk-Peter; Vogelsang, Jan

    2015-12-01

    Blinking of the photoluminescence (PL) emitted from individual conjugated polymer chains is one of the central observations made by single-molecule spectroscopy (SMS). Important information, for example regarding excitation energy transfer, can be extracted by evaluating dynamic quenching. However, the nature of trap states, which are responsible for PL quenching, often remains obscured. We present a detailed investigation of the photon statistics of single poly(3-hexylthiophene) (P3HT) chains obtained by SMS. The photon statistics provide a measure of the number and brightness of independently emitting areas on a single chain. These observables can be followed during blinking. A decrease in PL intensity is shown to be correlated with either 1) a decrease in the average brightness of the emitting sites; or 2) a decrease in the number of emitting regions. We attribute these phenomena to the formation of 1) shallow charge traps, which can weakly affect all emitting areas of a single chain at once; and 2) deep traps, which have a strong effect on small regions within the single chains. PMID:26490757

  15. Minimizing the energy spread within a single bunch by shaping its charge distribution

    SciTech Connect

    Loew, G.A.; Wang, J.W.

    1985-03-01

    It has been known for some time that partial compensation of the longitudinal wake field effects can be obtained for any bunch by placing it ahead of the accelerating crest (in space), thereby letting the positive rising sinusoidal field offset the negative beam loading field. The work presented in this paper shows that it is possible to obtain complete compensation, i.e., to reduce the energy spread essentially to zero by properly shaping the longitudinal charge distribution of the bunch and by placing it at the correct position on the wave. 3 refs., 5 figs., 3 tabs.

  16. Predominant Occupation of the Class I MHC Molecule H-2Kwm7 with a Single Self-peptide Suggests a Mechanism for its Diabetes-protective Effect

    SciTech Connect

    Brims, D.; Qian, J; Jarchum, I; Mikesh, L; Palmieri, E; Ramagopal, U; Malashkevich, V; Chaparro, R; Lund, T; et. al.

    2010-01-01

    Type 1 diabetes (T1D) is an autoimmune disease characterized by T cell-mediated destruction of insulin-producing pancreatic {beta} cells. In both humans and the non-obese diabetic (NOD) mouse model of T1D, class II MHC alleles are the primary determinant of disease susceptibility. However, class I MHC genes also influence risk. These findings are consistent with the requirement for both CD{sup 4+} and CD{sup 8+} T cells in the pathogenesis of T1D. Although a large body of work has permitted the identification of multiple mechanisms to explain the diabetes-protective effect of particular class II MHC alleles, studies examining the protective influence of class I alleles are lacking. Here, we explored this question by performing biochemical and structural analyses of the murine class I MHC molecule H-2K{sup wm7}, which exerts a diabetes-protective effect in NOD mice. We have found that H-2K{sup wm7} molecules are predominantly occupied by the single self-peptide VNDIFERI, derived from the ubiquitous protein histone H2B. This unexpected finding suggests that the inability of H-2K{sup wm7} to support T1D development could be due, at least in part, to the failure of peptides from critical {beta}-cell antigens to adequately compete for binding and be presented to T cells. Predominant presentation of a single peptide would also be expected to influence T-cell selection, potentially leading to a reduced ability to select a diabetogenic CD{sup 8+} T-cell repertoire. The report that one of the predominant peptides bound by T1D-protective HLA-A*31 is histone derived suggests the potential translation of our findings to human diabetes-protective class I MHC molecules.

  17. Single peptide and anti-idiotype based immunizations can broaden the antibody response against the variable V3 domain of HIV-1 in mice.

    PubMed

    Boudet, F; Keller, H; Kieny, M P; Thèze, J

    1995-05-01

    The third variable (V3) domain of the human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 is a major target of neutralizing antibodies in infected persons and in experimental immunized animals. Given the high degree of sequence variability of V3, the humoral response toward this region is very type-specific. In the present study, we evaluated the potential of a single peptide and an anti-idiotypic antibody to broaden the anti-V3 antibody specificity in BALB/c mice. We show that a synthetic peptide derived from the V3 determinant of HIV-1 MN isolate (V3MN), when used as an immunogen, was able to induce an antibody response to multiple (up to six) HIV-1 strains. The extent of this cross-reactivity, which tended to enlarge as the injections increased, appeared to be inversely correlated with the binding affinity to V3MN peptide. These data thus present evidence that, despite its great sequence heterogeneity, the V3 loop encompasses conserved amino-acid positions and/or stretches which may be less immunogenic than their variable counterparts. We additionally demonstrate that a rabbit anti-idiotype (Ab2), recognizing a binding site related idiotype on a V3-specific mouse monoclonal antibody (Ab1), could mount a broadened humoral response (Ab3) in mice. Unlike nominal antibody Ab1 which strictly reacted with the European HIV-1 LAI isolate, elicited Ab3 recognized the two divergent HIV-1 strains SF2 and 1286, originating respectively from North America and Central Africa, in addition to LAI. The reasons accounting for this Ab2-induced enlargement of the V3 antibody response are discussed. Our findings suggest that single peptide and anti-idiotype based immunizations may provide viable approaches to overcome, at least in part, HIV epitope variability. PMID:7783749

  18. Single photon emission up to liquid nitrogen temperature from charged excitons confined in GaAs-based epitaxial nanostructures

    NASA Astrophysics Data System (ADS)

    Dusanowski, Ł.; Syperek, M.; Maryński, A.; Li, L. H.; Misiewicz, J.; Höfling, S.; Kamp, M.; Fiore, A.; Sek, G.

    2015-06-01

    We demonstrate a non-classical photon emitter at near infrared wavelength based on a single (In,Ga)As/GaAs epitaxially grown columnar quantum dot. Charged exciton complexes have been identified in magneto-photoluminescence. Photon auto-correlation histograms from the recombination of a trion confined in a columnar dot exhibit sub-Poissonian statistics with an antibunching dip yielding g(2)(0) values of 0.28 and 0.46 at temperature of 10 and 80 K, respectively. Our experimental findings allow considering the GaAs-based columnar quantum dot structure as an efficient single photon source operating at above liquid nitrogen temperatures, which in some characteristics can outperform the existing solutions of any material system.

  19. Single photon emission up to liquid nitrogen temperature from charged excitons confined in GaAs-based epitaxial nanostructures

    SciTech Connect

    Dusanowski, Ł. Syperek, M.; Maryński, A.; Misiewicz, J.; Sęk, G.; Li, L. H.; Höfling, S.; Kamp, M.; Fiore, A.

    2015-06-08

    We demonstrate a non-classical photon emitter at near infrared wavelength based on a single (In,Ga)As/GaAs epitaxially grown columnar quantum dot. Charged exciton complexes have been identified in magneto-photoluminescence. Photon auto-correlation histograms from the recombination of a trion confined in a columnar dot exhibit sub-Poissonian statistics with an antibunching dip yielding g{sup (2)}(0) values of 0.28 and 0.46 at temperature of 10 and 80 K, respectively. Our experimental findings allow considering the GaAs-based columnar quantum dot structure as an efficient single photon source operating at above liquid nitrogen temperatures, which in some characteristics can outperform the existing solutions of any material system.

  20. Effective Control of the Charge and Magnetic States of Transition-Metal Atoms on Single-Layer Boron Nitride

    SciTech Connect

    Huang, B.; Xiang, H. J.; Yu, J. J.; Wei, S. H.

    2012-05-18

    Developing approaches to effectively control the charge and magnetic states is critical to the use of magnetic nanostructures in quantum information devices but is still challenging. Here we suggest that the magnetic and charge states of transition-metal (TM) doped single-layer boron-nitride (SLBN) systems can be easily controlled by the (internal) defect engineering and (external) electric fields (E{sub ext}). The relative positions and symmetries of the in-gap levels induced by defect engineering and the TM d-orbital energy levels effectively determine the charge states and magnetic properties of the TM/SLBN system. Remarkably, the application of an E{sub ext} can easily control the size of the crystal field splitting of the TM d orbitals and thus, leading to the spin crossover in TM/SLBN, which could be used as E{sub ext}-driven nonvolatile memory devices. Our conclusion obtained from TM/SLBN is valid generally in other TM adsorbed layered semiconductors.

  1. Dynamics of charge migration in poly(para-phenylene vinylene) films and nanocomposites with single walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Mulazzi, E.; Galli, D. E.; Lefrant, S.; Wéry, J.; Massuyeau, F.; Faulques, E.

    2016-02-01

    We present in this paper a comprehensive study of the migration dynamics of the charges underlying transient photoluminescence (PL) processes in poly(para-phenylene vinylene) (PPV) samples from room temperature to 13 K. In order to interpret experimental data, we have modelled the long-time PL decays (from 100 to 1000 ps) using a time function proportional to {{t}-(1+α )} in which the parameter α is evaluated in a Monte Carlo simulation on polymeric chains. The one dimensional chains (2000 sites long) are formed by random sequences of long and short conjugated segments whose bimodal distributions have been elaborated in previous works in order to reproduce the PL band shapes and peak positions. Intra-chain and inter-chain dynamics are taken into account in the migration of the photogenerated charges from short to long conjugated segments. The statistical analysis is performed by averaging over a total of 106 trials for each initial conditions. The values of α have been determined for pristine PPV films and PPV composite films with single-walled carbon nanotubes. This theoretical analysis is in good agreement with experimental data and provides a coherent description for the migration of the photogenerated charges in such inhomogeneous polymeric systems.

  2. Charge transfer of single laser crystallized intrinsic and phosphorus-doped Si-nanocrystals visualized by Kelvin probe force microscopy

    SciTech Connect

    Xu, Jie; Xu, Jun Lu, Peng; Shan, Dan; Li, Wei; Chen, Kunji

    2014-10-07

    Isolated intrinsic and phosphorus doped (P-doped) Si-nanocrystals (Si-NCs) on n- and p-Si substrates are fabricated by excimer laser crystallization techniques. The formation of Si-NCs is confirmed by atomic force microscopy (AFM) and conductive AFM measurements. Kelvin probe force microscopy (KPFM) is then carried out to visualize the trapped charges in a single Si-NC dot which derives from the charge transfer between Si-NCs and Si substrates due to their different Fermi levels. The laser crystallized P-doped Si-NCs have a similar Fermi level around the mid-gap to the intrinsic counterparts, which might be caused by the inactivated impurity atoms or the surface states-related Fermi level pinning. A clear rise of the Fermi level in P-doped Si-NCs is observed after a short time thermal annealing treatment, indicating the activation of dopants in Si-NCs. Moreover, the surface charge quantity can be estimated using a simple parallel plate capacitor model for a quantitative understanding of the KPFM results at the nanoscale.

  3. Dynamics of charge migration in poly(para-phenylene vinylene) films and nanocomposites with single walled carbon nanotubes.

    PubMed

    Mulazzi, E; Galli, D E; Lefrant, S; Wéry, J; Massuyeau, F; Faulques, E

    2016-02-01

    We present in this paper a comprehensive study of the migration dynamics of the charges underlying transient photoluminescence (PL) processes in poly(para-phenylene vinylene) (PPV) samples from room temperature to 13 K. In order to interpret experimental data, we have modelled the long-time PL decays (from 100 to 1000 ps) using a time function proportional to [Formula: see text] in which the parameter α is evaluated in a Monte Carlo simulation on polymeric chains. The one dimensional chains (2000 sites long) are formed by random sequences of long and short conjugated segments whose bimodal distributions have been elaborated in previous works in order to reproduce the PL band shapes and peak positions. Intra-chain and inter-chain dynamics are taken into account in the migration of the photogenerated charges from short to long conjugated segments. The statistical analysis is performed by averaging over a total of 10(6) trials for each initial conditions. The values of α have been determined for pristine PPV films and PPV composite films with single-walled carbon nanotubes. This theoretical analysis is in good agreement with experimental data and provides a coherent description for the migration of the photogenerated charges in such inhomogeneous polymeric systems. PMID:26744381

  4. Photogeneration of charge carrier correlated with amplified spontaneous emission in single crystals of a thiophene/phenylene co-oligomer.

    PubMed

    Saeki, Akinori; Seki, Shu; Shimizu, Yasuhiro; Yamao, Takeshi; Hotta, Shu

    2010-04-01

    Thiophene/phenylene co-oligomers have substantial promise for the use of not only organic electronics but also organic optical devices. However, considerably less is known about the correlation between their optical and optoelectronic properties. We have investigated the charge carrier generation in 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) single crystals by flash-photolysis time-resolved microwave conductivity (TRMC) and transient absorption spectroscopy (TAS). It was found that the dependence of photocarrier generation efficiency on excitation photon density differed from that of emission efficiency once amplified spontaneous emission (ASE) and resultant spectrally narrowed emission occur upon exposure to 355 nm. In contrast, the dependences of emission and photocarrier generation efficiencies were identical when ASE was not involved at a different excitation wavelength (193 nm). An approximated analytical solution of rate equation considering ASE or singlet-singlet annihilation was applied to the experiments, exhibiting good agreement. On the basis of TRMC, TAS, and extinction coefficient of radical cation assessed by pulse radiolysis, the minimum charge carrier mobility was estimated, without electrodes, to be 0.12 cm(2) V(-1) s(-1). The dynamics of charge carrier and triplet excited state is discussed, accompanying with examination by time-dependent density functional theory. The present work would open the way to a deeper understanding of the fate of excited state in optically robust organic semiconducting crystals. PMID:20387943

  5. Experimental study of the stochastic heating of a single Brownian particle by charge fluctuations

    NASA Astrophysics Data System (ADS)

    Schmidt, Christian; Piel, Alexander

    2016-08-01

    The Brownian motion of a micro-particle, which is suspended in the sheath of a radio-frequency discharge, is studied by high-speed video microscopy. In this environment, stochastic heating by charge fluctuations is expected, which should lead to an anisotropic kinetic temperature of the particle with a preferential heating in the direction of the mean electric field in the sheath. The stochastic heating should become more effective at low gas pressures where cooling by the neutral gas becomes ineffective. Our refined experiments confirm the anisotropic heating and the temperature rise for diminishing pressure. Particle-in-cell simulations have guided us in modifying the gap width of the discharge and to specify the dependence of the plasma density on gas pressure as n i ∝ p 1 / 2 . Since the stochastic heating rate also depends on the life-time of charge fluctuations, a temperature scaling T kin ∝ p 3 / 2 results, which is in agreement with the experimental data. The experimental procedure to eliminate other spurious heating mechanisms is described in detail.

  6. Azimuthal Single-Spin Asymmetries of Charged Pions in Jets in p↑ p Collisions at STAR

    NASA Astrophysics Data System (ADS)

    Adkins, Kevin; STAR Collaboration

    2015-04-01

    The transversity distribution h1(x), which describes the transverse spin structure of quarks inside of transversely polarized protons, is only accessible through channels that couple h1(x) to another chiral odd distribution, such as the Collins fragmentation function (ΔD(z,kT)). Significant Collins asymmetries of charged pions have been observed in semi-inclusive deep inelastic scattering (SIDIS) data. These SIDIS asymmetries combined with e+e- process asymmetries from Belle have allowed for the extraction of h1(x) and ΔD(z ,kT). Uncertainties on h1(x) remain large due to the limited statistics and kinematic reach of the available data. In transversely polarized hadronic collisions, Collins asymmetries may be isolated and extracted by measuring the spin dependent azimuthal distributions of charged pions in jets. This presentation will show the first significant midrapditiy (| η | < 1) Collins asymmetries measured in √{ s} = 200 and 500 GeV p↑ p collisions. These results access higher momentum scales than the existing SIDIS data and will allow for a comprehensive study of evolution and factorization of the Collins channel.

  7. Hydrogen retrapping after thermal charging of hydrogen in iron single crystal

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Lam; Lee, Jai-Young

    1989-09-01

    A theory to estimate and describe the behavior of supersaturated hydrogen in interstitial sites of a normal lattice and in trap sites is suggested, and the experimental proof is provided by thermal analysis. In this theory, variation with temperature changes of the equilibrium state between hydrogen in trapping sites and in normal lattice sites, which occurs during rapid cooling after hydrogen charging at high temperature, is considered. Two evolution rate peaks of hy-drogen corresponding to a reversible trap, a dislocation, and to an irreversible trap, a microvoid, are observed, respectively, at 388 and 538 K in a thermal analysis plot. The hydrogen amount released from the reversible trap is increased with decreasing microvoid concentration, even though the reversible trap density is maintained at the same level. According to the theoretical analysis, supersaturated hydrogen dissolved in a normal lattice site by a rapid cooling of hydrogen-charged iron from high temperature is predominantly retrapped into the vacant irreversible trap-ping sites. The remaining hydrogen exists in the normal lattice interstitial sites and will maintain local equilibrium with hydrogen in the reversible trap sites. The apparent hydrogen diffusivities at 293 K with each type of trap are estimated to be 1 × 10-6 cm2/s for reversible traps and 4 × 10-8 cm2/s for microvoid traps, based on changes in the hydrogen amount released from each type of trap with the room-temperature anneal time in vacuum.

  8. Accumulative charge separation for solar fuels production: coupling light-induced single electron transfer to multielectron catalysis.

    PubMed

    Hammarström, Leif

    2015-03-17

    The conversion and storage of solar energy into a fuel holds promise to provide a significant part of the future renewable energy demand of our societies. Solar energy technologies today generate heat or electricity, while the large majority of our energy is used in the form of fuels. Direct conversion of solar energy to a fuel would satisfy our needs for storable energy on a large scale. Solar fuels can be generated by absorbing light and converting its energy to chemical energy by electron transfer leading to separation of electrons and holes. The electrons are used in the catalytic reduction of a cheap substrate with low energy content into a high-energy fuel. The holes are filled by oxidation of water, which is the only electron source available for large scale solar fuel production. Absorption of a single photon typically leads to separation of a single electron-hole pair. In contrast, fuel production and water oxidation are multielectron, multiproton reactions. Therefore, a system for direct solar fuel production must be able to accumulate the electrons and holes provided by the sequential absorption of several photons in order to complete the catalytic reactions. In this Account, the process is termed accumulative charge separation. This is considerably more complicated than charge separation on a single electron level and needs particular attention. Semiconductor materials and molecular dyes have for a long time been optimized for use in photovoltaic devices. Efforts are made to develop new systems for light harvesting and charge separation that are better optimized for solar fuel production than those used in the early devices presented so far. Significant progress has recently been made in the discovery and design of better homogeneous and heterogeneous catalysts for solar fuels and water oxidation. While the heterogeneous ones perform better today, molecular catalysts based on transition metal complexes offer much greater tunability of electronic and

  9. Synthetic surfactant containing SP-B and SP-C mimics is superior to single-peptide formulations in rabbits with chemical acute lung injury

    PubMed Central

    Hernández-Juviel, José M.; Gordon, Larry M.; Waring, Alan J.

    2014-01-01

    Background. Chemical spills are on the rise and inhalation of toxic chemicals may induce chemical acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Although the pathophysiology of ALI/ARDS is well understood, the absence of specific antidotes has limited the effectiveness of therapeutic interventions. Objectives. Surfactant inactivation and formation of free radicals are important pathways in (chemical) ALI. We tested the potential of lipid mixtures with advanced surfactant protein B and C (SP-B and C) mimics to improve oxygenation and lung compliance in rabbits with lavage- and chemical-induced ALI/ARDS. Methods. Ventilated young adult rabbits underwent repeated saline lung lavages or underwent intratracheal instillation of hydrochloric acid to induce ALI/ARDS. After establishment of respiratory failure rabbits were treated with a single intratracheal dose of 100 mg/kg of synthetic surfactant composed of 3% Super Mini-B (S-MB), a SP-B mimic, and/or SP-C33 UCLA, a SP-C mimic, in a lipid mixture (DPPC:POPC:POPG 5:3:2 by weight), the clinical surfactant Infasurf®, a bovine lung lavage extract with SP-B and C, or synthetic lipids alone. End-points consisted of arterial oxygenation, dynamic lung compliance, and protein and lipid content in bronchoalveolar lavage fluid. Potential mechanism of surfactant action for S-MB and SP-C33 UCLA were investigated with captive bubble surfactometry (CBS) assays. Results. All three surfactant peptide/lipid mixtures and Infasurf equally lowered the minimum surface tension on CBS, and also improved oxygenation and lung compliance. In both animal models, the two-peptide synthetic surfactant with S-MB and SP-C33 UCLA led to better arterial oxygenation and lung compliance than single peptide synthetic surfactants and Infasurf. Synthetic surfactants and Infasurf improved lung function further in lavage- than in chemical-induced respiratory failure, with the difference probably due to greater capillary-alveolar protein

  10. Synthetic surfactant containing SP-B and SP-C mimics is superior to single-peptide formulations in rabbits with chemical acute lung injury.

    PubMed

    Walther, Frans J; Hernández-Juviel, José M; Gordon, Larry M; Waring, Alan J

    2014-01-01

    Background. Chemical spills are on the rise and inhalation of toxic chemicals may induce chemical acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Although the pathophysiology of ALI/ARDS is well understood, the absence of specific antidotes has limited the effectiveness of therapeutic interventions. Objectives. Surfactant inactivation and formation of free radicals are important pathways in (chemical) ALI. We tested the potential of lipid mixtures with advanced surfactant protein B and C (SP-B and C) mimics to improve oxygenation and lung compliance in rabbits with lavage- and chemical-induced ALI/ARDS. Methods. Ventilated young adult rabbits underwent repeated saline lung lavages or underwent intratracheal instillation of hydrochloric acid to induce ALI/ARDS. After establishment of respiratory failure rabbits were treated with a single intratracheal dose of 100 mg/kg of synthetic surfactant composed of 3% Super Mini-B (S-MB), a SP-B mimic, and/or SP-C33 UCLA, a SP-C mimic, in a lipid mixture (DPPC:POPC:POPG 5:3:2 by weight), the clinical surfactant Infasurf(®), a bovine lung lavage extract with SP-B and C, or synthetic lipids alone. End-points consisted of arterial oxygenation, dynamic lung compliance, and protein and lipid content in bronchoalveolar lavage fluid. Potential mechanism of surfactant action for S-MB and SP-C33 UCLA were investigated with captive bubble surfactometry (CBS) assays. Results. All three surfactant peptide/lipid mixtures and Infasurf equally lowered the minimum surface tension on CBS, and also improved oxygenation and lung compliance. In both animal models, the two-peptide synthetic surfactant with S-MB and SP-C33 UCLA led to better arterial oxygenation and lung compliance than single peptide synthetic surfactants and Infasurf. Synthetic surfactants and Infasurf improved lung function further in lavage- than in chemical-induced respiratory failure, with the difference probably due to greater capillary-alveolar protein

  11. Estimation of the spatial distribution of traps using space-charge-limited current measurements in an organic single crystal

    NASA Astrophysics Data System (ADS)

    Dacuña, Javier; Xie, Wei; Salleo, Alberto

    2012-09-01

    We used a mobility edge transport model and solved the drift-diffusion equation to characterize the space-charge-limited current of a rubrene single-crystal hole-only diode. The current-voltage characteristics suggest that current is injection-limited at high voltage when holes are injected from the bottom contact (reverse bias). In contrast, the low-voltage regime shows that the current is higher when holes are injected from the bottom contact as compared to hole injection from the top contact (forward bias), which does not exhibit injection-limited current in the measured voltage range. This behavior is attributed to an asymmetric distribution of trap states in the semiconductor, specifically, a distribution of traps located near the top contact. Accounting for a localized trap distribution near the contact allows us to reproduce the temperature-dependent current-voltage characteristics in forward and reverse bias simultaneously, i.e., with a single set of model parameters. We estimated that the local trap distribution contains 1.19×1011 cm-2 states and decays as exp(-x/32.3nm) away from the semiconductor-contact interface. The local trap distribution near one contact mainly affects injection from the same contact, hence breaking the symmetry in the charge transport. The model also provides information of the band mobility, energy barrier at the contacts, and bulk trap distribution with their corresponding confidence intervals.

  12. High-Resolution Size-Discrimination of Single Nonionic Synthetic Polymers with a Highly Charged Biological Nanopore.

    PubMed

    Baaken, Gerhard; Halimeh, Ibrahim; Bacri, Laurent; Pelta, Juan; Oukhaled, Abdelghani; Behrends, Jan C

    2015-06-23

    Electrophysiological studies of the interaction of polymers with pores formed by bacterial toxins (1) provide a window on single molecule interaction with proteins in real time, (2) report on the behavior of macromolecules in confinement, and (3) enable label-free single molecule sensing. Using pores formed by the staphylococcal toxin α-hemolysin (aHL), a particularly pertinent observation was that, under high salt conditions (3-4 M KCl), the current through the pore is blocked for periods of hundreds of microseconds to milliseconds by poly(ethylene glycol) (PEG) oligomers (degree of polymerization approximately 10-60). Notably, this block showed monomeric sensitivity on the degree of polymerization of individual oligomers, allowing the construction of size or mass spectra from the residual current values. Here, we show that the current through the pore formed by aerolysin (AeL) from Aeromonas hydrophila is also blocked by PEG but with drastic differences in the voltage-dependence of the interaction. In contrast to aHL, AeL strongly binds PEG at high transmembrane voltages. This fact, which is likely related to AeL's highly charged pore wall, allows discrimination of polymer sizes with particularly high resolution. Multiple applications are now conceivable with this pore to screen various nonionic or charged polymers. PMID:26028280

  13. Current suppression in a double-island single-electron transistor for detection of degenerate charge configurations of a floating double-dot

    NASA Astrophysics Data System (ADS)

    Brenner, R.; Greentree, Andrew D.; Hamilton, A. R.

    2003-12-01

    We have investigated a double-island single-electron transistor (DISET) coupled to a floating metal double-dot (DD). Low-temperature transport measurements were used to map out the charge configurations of both the DISET and the DD. A suppression of the current through the DISET was observed whenever the charge configurations of the DISET and the DD were energetically codegenerate. This effect was used to distinguish between degenerate and nondegenerate charge configurations of the DD. We also show that this detection scheme reduces the susceptibility of the DISET to interference from random charge noise.

  14. Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation

    NASA Astrophysics Data System (ADS)

    Boulicault, Jean E.; Alves, Sandra; Cole, Richard B.

    2016-05-01

    MALDI-MS has been developed for the negative ion mode analysis of polyoxometalates (POMs). Matrix optimization was performed using a variety of matrix compounds. A first group of matrixes offers MALDI mass spectra containing abundant intact singly charged anionic adduct ions, as well as abundant in-source fragmentations at elevated laser powers. A relative ranking of the ability to induce POM fragmentation is found to be: DAN > CHCA > CNA > DIT> HABA > DCTB > IAA. Matrixes of a second group provide poorer quality MALDI mass spectra without observable fragments. Sample preparation, including the testing of salt additives, was performed to optimize signals for a model POM, POMc12, the core structure of which bears four negative charges. The matrix 9-cyanoanthracene (CNA) provided the best signals corresponding to singly charged intact POMc12 anions. Decompositions of these intact anionic species were examined in detail, and it was concluded that hydrogen radical-induced mechanisms were not prevalent, but rather that the observed prompt fragments originate from transferred energy derived from initial electronic excitation of the CNA matrix. Moreover, in obtained MALDI mass spectra, clear evidence of electron transfer to analyte POM species was found: a manifestation of the POMs ability to readily capture electrons. The affinity of polyanionic POMc12 toward a variety of cations was evaluated and the following affinity ranking was established: Fe3+ > Al3+ > Li+ > Ga3+ > Co2+ > Cr3+ > Cu2+ > [Mn2+, Mg2+] > [Na+, K+]. Thus, from the available cationic species, specific adducts are preferentially formed, and evidence is given that these higher affinity POM complexes are formed in the gas phase during the early stages of plume expansion.

  15. Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation

    NASA Astrophysics Data System (ADS)

    Boulicault, Jean E.; Alves, Sandra; Cole, Richard B.

    2016-08-01

    MALDI-MS has been developed for the negative ion mode analysis of polyoxometalates (POMs). Matrix optimization was performed using a variety of matrix compounds. A first group of matrixes offers MALDI mass spectra containing abundant intact singly charged anionic adduct ions, as well as abundant in-source fragmentations at elevated laser powers. A relative ranking of the ability to induce POM fragmentation is found to be: DAN > CHCA > CNA > DIT> HABA > DCTB > IAA. Matrixes of a second group provide poorer quality MALDI mass spectra without observable fragments. Sample preparation, including the testing of salt additives, was performed to optimize signals for a model POM, POMc12, the core structure of which bears four negative charges. The matrix 9-cyanoanthracene (CNA) provided the best signals corresponding to singly charged intact POMc12 anions. Decompositions of these intact anionic species were examined in detail, and it was concluded that hydrogen radical-induced mechanisms were not prevalent, but rather that the observed prompt fragments originate from transferred energy derived from initial electronic excitation of the CNA matrix. Moreover, in obtained MALDI mass spectra, clear evidence of electron transfer to analyte POM species was found: a manifestation of the POMs ability to readily capture electrons. The affinity of polyanionic POMc12 toward a variety of cations was evaluated and the following affinity ranking was established: Fe3+ > Al3+ > Li+ > Ga3+ > Co2+ > Cr3+ > Cu2+ > [Mn2+, Mg2+] > [Na+, K+]. Thus, from the available cationic species, specific adducts are preferentially formed, and evidence is given that these higher affinity POM complexes are formed in the gas phase during the early stages of plume expansion.

  16. Negative Ion MALDI Mass Spectrometry of Polyoxometalates (POMs): Mechanism of Singly Charged Anion Formation and Chemical Properties Evaluation.

    PubMed

    Boulicault, Jean E; Alves, Sandra; Cole, Richard B

    2016-08-01

    MALDI-MS has been developed for the negative ion mode analysis of polyoxometalates (POMs). Matrix optimization was performed using a variety of matrix compounds. A first group of matrixes offers MALDI mass spectra containing abundant intact singly charged anionic adduct ions, as well as abundant in-source fragmentations at elevated laser powers. A relative ranking of the ability to induce POM fragmentation is found to be: DAN > CHCA > CNA > DIT> HABA > DCTB > IAA. Matrixes of a second group provide poorer quality MALDI mass spectra without observable fragments. Sample preparation, including the testing of salt additives, was performed to optimize signals for a model POM, POMc12, the core structure of which bears four negative charges. The matrix 9-cyanoanthracene (CNA) provided the best signals corresponding to singly charged intact POMc12 anions. Decompositions of these intact anionic species were examined in detail, and it was concluded that hydrogen radical-induced mechanisms were not prevalent, but rather that the observed prompt fragments originate from transferred energy derived from initial electronic excitation of the CNA matrix. Moreover, in obtained MALDI mass spectra, clear evidence of electron transfer to analyte POM species was found: a manifestation of the POMs ability to readily capture electrons. The affinity of polyanionic POMc12 toward a variety of cations was evaluated and the following affinity ranking was established: Fe(3+) > Al(3+) > Li(+) > Ga(3+) > Co(2+) > Cr(3+) > Cu(2+) > [Mn(2+), Mg(2+)] > [Na(+), K(+)]. Thus, from the available cationic species, specific adducts are preferentially formed, and evidence is given that these higher affinity POM complexes are formed in the gas phase during the early stages of plume expansion. Graphical Abstract ᅟ. PMID:27142457

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Single Sublattice Endotaxial Phase Separation Driven by Charge Frustration in a Complex Oxide

    PubMed Central

    2013-01-01

    Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO3 perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO3 network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO3 network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation. PMID:23750709

  19. Charge-Insensitive Single-Atom Spin-Orbit Qubit in Silicon.

    PubMed

    Salfi, Joe; Mol, Jan A; Culcer, Dimitrie; Rogge, Sven

    2016-06-17

    High fidelity entanglement of an on-chip array of spin qubits poses many challenges. Spin-orbit coupling (SOC) can ease some of these challenges by enabling long-ranged entanglement via electric dipole-dipole interactions, microwave photons, or phonons. However, SOC exposes conventional spin qubits to decoherence from electrical noise. Here, we propose an acceptor-based spin-orbit qubit in silicon offering long-range entanglement at a sweet spot where the qubit is protected from electrical noise. The qubit relies on quadrupolar SOC with the interface and gate potentials. As required for surface codes, 10^{5} electrically mediated single-qubit and 10^{4} dipole-dipole mediated two-qubit gates are possible in the predicted spin lifetime. Moreover, circuit quantum electrodynamics with single spins is feasible, including dispersive readout, cavity-mediated entanglement, and spin-photon entanglement. An industrially relevant silicon-based platform is employed. PMID:27367400

  20. Charge-Insensitive Single-Atom Spin-Orbit Qubit in Silicon

    NASA Astrophysics Data System (ADS)

    Salfi, Joe; Mol, Jan A.; Culcer, Dimitrie; Rogge, Sven

    2016-06-01

    High fidelity entanglement of an on-chip array of spin qubits poses many challenges. Spin-orbit coupling (SOC) can ease some of these challenges by enabling long-ranged entanglement via electric dipole-dipole interactions, microwave photons, or phonons. However, SOC exposes conventional spin qubits to decoherence from electrical noise. Here, we propose an acceptor-based spin-orbit qubit in silicon offering long-range entanglement at a sweet spot where the qubit is protected from electrical noise. The qubit relies on quadrupolar SOC with the interface and gate potentials. As required for surface codes, 105 electrically mediated single-qubit and 104 dipole-dipole mediated two-qubit gates are possible in the predicted spin lifetime. Moreover, circuit quantum electrodynamics with single spins is feasible, including dispersive readout, cavity-mediated entanglement, and spin-photon entanglement. An industrially relevant silicon-based platform is employed.

  1. Controlling charge balance and exciton recombination by bipolar host in single-layer organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Qiao, Xianfeng; Tao, Youtian; Wang, Qiang; Ma, Dongge; Yang, Chuluo; Wang, Lixiang; Qin, Jingui; Wang, Fosong

    2010-08-01

    Highly efficient single-layer organic light-emitting diodes with reduced efficiency roll-off are demonstrated by using a bipolar host material of 2,5-bis(2-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (o-CzOXD) doped with iridium complexes as the emissive layer. For example, the green single-layer device, employing fac-tris(2-phenylpyridine)iridium Ir(ppy)3 as dopant, shows a peak current efficiency of 45.57 cd A-1, corresponding to external quantum efficiency (EQE) of 12.42%, and still exhibits efficiencies of 45.26 cd A-1 and 40.42 cd A-1 at luminance of 1000 and 10 000 cd m-2, respectively. In addition, the yellow and red single-layer devices, with bis(2-(9,9- diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N ,C3)iridium(acetylacetonate) (fbi)2Ir(acac) and bis(1-phenylisoquinolinolato-C2,N)iridium(acetylacetonate) (piq)2Ir(acac) as emitter, also show high EQE of 7.04% and 7.28%, respectively. The transport properties of o-CzOXD film are well investigated by current-voltage measurement, from which both hole and electron mobility are determined. It is found that the o-CzOXD shows appealing bipolar transport character, which is favor for the balanced charge distribution in the whole doped zone. More importantly, the multifunctional role of hole trapping and electron transporting of the iridium complex in o-CzOXD further balances the charge carriers and broadens the recombination zone. As a result, the recombination of electrons and holes is significantly improved and the triplet-triplet annihilation and triplet-polaron quenching processes are effectively suppressed, eventually leading to the high efficiency as well as the reduced efficiency roll-off.

  2. [Plant signaling peptides. Cysteine-rich peptides].

    PubMed

    Ostrowski, Maciej; Kowalczyk, Stanisław

    2015-01-01

    Recent bioinformatic and genetic analyses of several model plant genomes have revealed the existence of a highly abundant group of signaling peptides that are defined as cysteine-rich peptides (CRPs). CRPs are usually in size between 50 and 90 amino acid residues, they are positively charged, and they contain 4-16 cysteine residues that are important for the correct conformational folding. Despite the structural differences among CRP classes, members from each class have striking similarities in their molecular properties and function. The present review presents the recent progress in research on signaling peptides from several families including: EPF/EPFL, SP11/SCR, PrsS, RALF, LURE, and some other peptides belonging to CRP group. There is convincing evidence indicating multiple roles for these CRPs as signaling molecules during the plant life cycle, ranging from stomata development and patterning, self-incompatibility, pollen tube growth and guidance, reproductive processes, and nodule formation. PMID:26281357

  3. Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

    SciTech Connect

    Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

    2013-09-01

    Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of multiply charged vanadium oxide cluster anions including VxOyn- and VxOyCln- ions (x = 1 − 14, y= 2 − 36, n = 1 − 3), protonated clusters, and ligand-bound VxOyn- species. These cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L= Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln- and VxOyCl(L)(n-1)- clusters predominantly containing 14 vanadium atoms. Accurate mass measurement using high-resolution mass spectrometry (m/∆m = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1-2)- and VxOy(1-2)- anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions generated from solution. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster ions originating directly from solution produced comparatively complex CID spectra. These results indicate that low-energy CID results in formation of stable cage-like structures of VxOyCl and VxOy anions. Furthermore, solution-phase synthesis of one precursor cluster combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of multiply charged gas-phase metal oxide clusters for subsequent investigations of structure and reactivity.

  4. Electron Capture Dissociation of Sodium-Adducted Peptides on a Modified Quadrupole/Time-of-Flight Mass Spectrometer

    NASA Astrophysics Data System (ADS)

    Voinov, Valery G.; Hoffman, Peter D.; Bennett, Samuel E.; Beckman, Joseph S.; Barofsky, Douglas F.

    2015-12-01

    Electron capture dissociation (ECD), which generally preserves the position of labile post-translational modifications, can be a powerful method for de novo sequencing of proteins and peptides. In this report, ECD product-ion mass spectra of singly and doubly sodiated, nonphosphorylated, and phosphorylated peptides are presented and compared with the ECD mass spectra of their protonated counterparts. ECD of doubly charged, singly sodiated peptides yielded essentially the same sequence information as was produced by the corresponding doubly protonated peptides. The presence of several sodium binding sites on the polypeptide backbone, however, resulted in more complicated spectra. This situation is aggravated by the zwitterionic equilibrium of the free acid peptide precursors. The product-ion spectra of doubly and triply charged peptides possessing two sodium ions were further complicated by the existence of isomers created by the differential distribution of sodium binding sites. Triply charged, phosphorylated precursors containing one sodium, wherein the sodium is attached exclusively to the PO4 group, were found to be as useful for sequence analysis as the fully protonated species. Although sodium adducts are generally minimized during sample preparation, it appears that they can nonetheless provide useful sequence information. Additionally, they enable straightforward identification of a peptide's charge state, even on low-resolution instruments. The experiments were carried out using a radio frequency-free electromagnetostatic cell retrofitted into the collision-induced dissociation (CID) section of a hybrid quadrupole/time-of-flight tandem mass spectrometer.

  5. Electron Capture Dissociation of Sodium-Adducted Peptides on a Modified Quadrupole/Time-of-Flight Mass Spectrometer.

    PubMed

    Voinov, Valery G; Hoffman, Peter D; Bennett, Samuel E; Beckman, Joseph S; Barofsky, Douglas F

    2015-12-01

    Electron capture dissociation (ECD), which generally preserves the position of labile post-translational modifications, can be a powerful method for de novo sequencing of proteins and peptides. In this report, ECD product-ion mass spectra of singly and doubly sodiated, nonphosphorylated, and phosphorylated peptides are presented and compared with the ECD mass spectra of their protonated counterparts. ECD of doubly charged, singly sodiated peptides yielded essentially the same sequence information as was produced by the corresponding doubly protonated peptides. The presence of several sodium binding sites on the polypeptide backbone, however, resulted in more complicated spectra. This situation is aggravated by the zwitterionic equilibrium of the free acid peptide precursors. The product-ion spectra of doubly and triply charged peptides possessing two sodium ions were further complicated by the existence of isomers created by the differential distribution of sodium binding sites. Triply charged, phosphorylated precursors containing one sodium, wherein the sodium is attached exclusively to the PO4 group, were found to be as useful for sequence analysis as the fully protonated species. Although sodium adducts are generally minimized during sample preparation, it appears that they can nonetheless provide useful sequence information. Additionally, they enable straightforward identification of a peptide's charge state, even on low-resolution instruments. The experiments were carried out using a radio frequency-free electromagnetostatic cell retrofitted into the collision-induced dissociation (CID) section of a hybrid quadrupole/time-of-flight tandem mass spectrometer. Graphical Abstract ᅟ. PMID:26266643

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

    PubMed

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

    2014-12-01

    DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100 pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100 nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits. PMID:25344689

  7. Possibility of measuring Adler angles in charged current single pion neutrino-nucleus interactions

    NASA Astrophysics Data System (ADS)

    Sánchez, F.

    2016-05-01

    Uncertainties in modeling neutrino-nucleus interactions are a major contribution to systematic errors in long-baseline neutrino oscillation experiments. Accurate modeling of neutrino interactions requires additional experimental observables such as the Adler angles which carry information about the polarization of the Δ resonance and the interference with nonresonant single pion production. The Adler angles were measured with limited statistics in bubble chamber neutrino experiments as well as in electron-proton scattering experiments. We discuss the viability of measuring these angles in neutrino interactions with nuclei.

  8. Energy Charge, Redox State, and Metabolite Turnover in Single Human Hepatocytes Revealed by Capillary Microsampling Mass Spectrometry.

    PubMed

    Zhang, Linwen; Vertes, Akos

    2015-10-20

    Metabolic analysis of single cells to uncover cellular heterogeneity and metabolic noise is limited by the available tools. In this study, we demonstrate the utility of capillary microsampling electrospray ionization mass spectrometry with ion mobility separation for nontargeted analysis of single cells. On the basis of accurate mass measurements and collision cross-section determination, a large number of chemical species, 22 metabolites and 54 lipids, were identified. To assess the cellular response to metabolic modulators, the adenylate energy charge (AEC) levels for control and rotenone treated cells were evaluated. A significant reduction in the AEC values was observed for rotenone treated cells. For the cells under oxidative stress, the mean value for the [reduced glutathione (GSH)]/[oxidized glutathione (GSSG)] ratio was significantly decreased, whereas the distribution of the [uridine diphosphate N-acetylhexosamine (UDP-HexNAc)]/[uridine diphosphate hexose (UDP-hexose)] ratio exhibited dramatic tailing to higher values. Lipid turnover rates were studied by pulse-chase experiments at the single cell level. PMID:26398405

  9. Operation of a single-photon-counting x-ray charge-coupled device camera spectrometer in a petawatt environment

    SciTech Connect

    Stoeckl, C.; Theobald, W.; Sangster, T.C.; Key, M.H.; Patel, P.; Zhang, B.B.; Clarke, R.; Karsch, S.; Norreys, P.

    2004-10-01

    The use of a single-photon-counting x-ray charge-coupled device (CCD) camera as an x-ray spectrometer is a well-established technique in ultrashort-pulse laser experiments. In single-photon-counting mode, the pixel value of each readout pixel is proportional to the energy deposited from the incident x-ray photon. For photons below 100 keV, a significant fraction of the events deposits all the energy in a single pixel. A histogram of the pixel readout values gives a good approximation of the x-ray spectrum. This technique requires almost no alignment, but it is very sensitive to signal-to-background issues, especially in a high-energy petawatt environment. Shielding the direct line of sight to the target was not sufficient to obtain a high-quality spectrum, for the experiments reported here the CCD camera had to be shielded from all sides with up to 10 cm of lead.

  10. Exciton Recombination, Energy-, and Charge Transfer in Single- and Multilayer Quantum-Dot Films on Silver Plasmonic Resonators.

    PubMed

    Shin, Taeho; Cho, Kyung-Sang; Yun, Dong-Jin; Kim, Jinwoo; Li, Xiang-Shu; Moon, Eui-Seong; Baik, Chan-Wook; Il Kim, Sun; Kim, Miyoung; Choi, Jun Hee; Park, Gyeong-Su; Shin, Jai-Kwang; Hwang, Sungwoo; Jung, Tae-Sung

    2016-01-01

    We examine exciton recombination, energy-, and charge transfer in multilayer CdS/ZnS quantum dots (QDs) on silver plasmonic resonators using photoluminescence (PL) and excitation spectroscopy along with kinetic modeling and simulations. The exciton dynamics including all the processes are strongly affected by the separation distance between QDs and silver resonators, excitation wavelength, and QD film thickness. For a direct contact or very small distance, interfacial charge transfer and tunneling dominate over intrinsic radiative recombination and exciton energy transfer to surface plasmons (SPs), resulting in PL suppression. With increasing distance, however, tunneling diminishes dramatically, while long-range exciton-SP coupling takes place much faster (>6.5 ns) than intrinsic recombination (~200 ns) causing considerable PL enhancement. The exciton-SP coupling strength shows a strong dependence on excitation wavelengths, suggesting the state-specific dynamics of excitons and the down-conversion of surface plasmons involved. The overlayers as well as the bottom monolayer of QD multilayers exhibit significant PL enhancement mainly through long-range exciton-SP coupling. The overall emission behaviors from single- and multilayer QD films on silver resonators are described quantitatively by a photophysical kinetic model and simulations. The present experimental and simulation results provide important and useful design rules for QD-based light harvesting applications using the exciton-surface plasmon coupling. PMID:27184469

  11. Exciton Recombination, Energy-, and Charge Transfer in Single- and Multilayer Quantum-Dot Films on Silver Plasmonic Resonators

    NASA Astrophysics Data System (ADS)

    Shin, Taeho; Cho, Kyung-Sang; Yun, Dong-Jin; Kim, Jinwoo; Li, Xiang-Shu; Moon, Eui-Seong; Baik, Chan-Wook; Il Kim, Sun; Kim, Miyoung; Choi, Jun Hee; Park, Gyeong-Su; Shin, Jai-Kwang; Hwang, Sungwoo; Jung, Tae-Sung

    2016-05-01

    We examine exciton recombination, energy-, and charge transfer in multilayer CdS/ZnS quantum dots (QDs) on silver plasmonic resonators using photoluminescence (PL) and excitation spectroscopy along with kinetic modeling and simulations. The exciton dynamics including all the processes are strongly affected by the separation distance between QDs and silver resonators, excitation wavelength, and QD film thickness. For a direct contact or very small distance, interfacial charge transfer and tunneling dominate over intrinsic radiative recombination and exciton energy transfer to surface plasmons (SPs), resulting in PL suppression. With increasing distance, however, tunneling diminishes dramatically, while long-range exciton-SP coupling takes place much faster (>6.5 ns) than intrinsic recombination (~200 ns) causing considerable PL enhancement. The exciton-SP coupling strength shows a strong dependence on excitation wavelengths, suggesting the state-specific dynamics of excitons and the down-conversion of surface plasmons involved. The overlayers as well as the bottom monolayer of QD multilayers exhibit significant PL enhancement mainly through long-range exciton-SP coupling. The overall emission behaviors from single- and multilayer QD films on silver resonators are described quantitatively by a photophysical kinetic model and simulations. The present experimental and simulation results provide important and useful design rules for QD-based light harvesting applications using the exciton-surface plasmon coupling.

  12. Ultrashort pulsed laser tools for testing of semiconductor elements hardness to single event effects, caused by cosmic heavy charged particles

    NASA Astrophysics Data System (ADS)

    Gordienko, Alexandra V.; Mavritskii, Oleg B.; Egorov, Andrey N.; Pechenkin, Alexander A.; Savchenkov, Dmitriy V.

    2015-03-01

    The installations for laser testing of microelectronic elements (first of all - integrated circuits) of devices for space applications for hardness to local radiation effects from heavy charged particles are presented. The possibility of a focused pulsed laser radiation application to the study of local radiation effects, caused by single heavy charged particles, is explained. The fundamentals of an approach to the construction of test sets, based on the picosecond and femtosecond lasers and systems for focusing their radiation, are considered. The main technical requirements for the basic modules of sets for laser testing (laser wavelength and pulse duration and repetition rate, spatial beam parameters and minimal spot size, speed of object movement and so on) are substantiated. All worked out sets have a full-featured software for the operational management of all modules of the laser test facility, including the positioning of the object, to provide feedback from the measurement results of the reaction of the object on the laser excitation. The parameters of developed laser hardware and software systems and their foreign counterparts are compared. Further improvement directions for laser testing tools are briefly outlined. The discussion is also presented of described hardware technical and operational characteristics, allowing to use it for a variety of scientific research studies, requiring selective (with submicron spatial resolution) object excitation by ultrashort laser pulses and recording responses to this effect with the exact timing of the moment of excitation, as well as to perform a variety of high precision technological operations.

  13. Nanoscale Charge Percolation Analysis in Polymer-Sorted (7,5) Single-Walled Carbon Nanotube Networks.

    PubMed

    Bottacchi, Francesca; Bottacchi, Stefano; Späth, Florian; Namal, Imge; Hertel, Tobias; Anthopoulos, Thomas D

    2016-08-01

    The current percolation in polymer-sorted semiconducting (7,5) single-walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field-effect measurements, atomic force microscopy (AFM), and conductive AFM (C-AFM) techniques. From AFM measurements, the nanotube length in the as-processed (7,5) SWNTs network is found to range from ≈100 to ≈1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈58%. Analysis of the field-effect charge transport measurements in the SWNT network using a 2D homogeneous random-network stick-percolation model yields an exponent coefficient for the transistors OFF currents of 16.3. This value is indicative of an almost ideal random network containing only a small concentration of metallic SWNTs. Complementary C-AFM measurements on the other hand enable visualization of current percolation pathways in the xy plane and reveal the isotropic nature of the as-spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field-effect charge transport measurements for quantification of key network parameters including current percolation, metallic nanotubes content, surface coverage, and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nanocomposites. PMID:27375031

  14. Fluorescence time-lapse imaging of single cells targeted with a focused scanning charged-particle microbeam

    NASA Astrophysics Data System (ADS)

    Bourret, Stéphane; Vianna, François; Devès, Guillaume; Atallah, Vincent; Moretto, Philippe; Seznec, Hervé; Barberet, Philippe

    2014-04-01

    Charged particle microbeams provide unique features to study targeted and non-targeted radiation response and have recently emerged as a powerful tool to investigate radiation-induced DNA damage and repair. We have developed a charged particle microbeam delivering protons and alpha particles in the MeV energy range equipped with online time-lapse imaging capabilities. The beam is focused to a sub-micrometer beam spot under vacuum by means of a triplet of magnetic quadrupoles and extracted in air through a 200 nm Si3N4 window. The end-station is equipped with an automated fluorescence microscope used for single cell targeting and online time-lapse imaging. Cells are kept in their medium during the irradiation procedure and the sample temperature is regulated to 37 °C. An overall targeting accuracy of 2.0 ± 0.7 μm has been measured by tracking the re-localization of the XRCC1 protein. First measurements of this re-localization shows the ability of our system to follow online the radiation-induced re-localization of proteins in the first minutes after irradiation.

  15. Spin and charge modulations in a single-hole-doped Hubbard ladder: Verification with optical lattice experiments

    NASA Astrophysics Data System (ADS)

    Zhu, Zheng; Weng, Zheng-Yu; Ho, Tin-Lun

    2016-03-01

    We show that pronounced modulations in spin and charge densities can be induced by the insertion of a single hole in an otherwise half-filled two-leg Hubbard ladder. Accompanied with these modulations is a loosely bound structure of the doped charge with a spin-1/2, in contrast to the tightly bound case where such modulations are absent. These behaviors are caused by the interference of the Berry phases associated with a string of flipped spins (or "phase strings") left behind as a hole travels through a spin bath with a short-range antiferromagnetic order. The key role of the phase strings is also reflected in how the system responds to increasing spin polarization and the on-site repulsion, addition of a second hole, and increasing asymmetry between intra- and interchain hopping. Remarkably, all these properties persist down to ladders as short as ˜10 sites, as the smoking gun of the phase-string effect. They can therefore be studied in cold-atom experiments using the recently developed fermion microscope.

  16. Exciton Recombination, Energy-, and Charge Transfer in Single- and Multilayer Quantum-Dot Films on Silver Plasmonic Resonators

    PubMed Central

    Shin, Taeho; Cho, Kyung-Sang; Yun, Dong-Jin; Kim, Jinwoo; Li, Xiang-Shu; Moon, Eui-Seong; Baik, Chan-Wook; Il Kim, Sun; Kim, Miyoung; Choi, Jun Hee; Park, Gyeong-Su; Shin, Jai-Kwang; Hwang, Sungwoo; Jung, Tae-Sung

    2016-01-01

    We examine exciton recombination, energy-, and charge transfer in multilayer CdS/ZnS quantum dots (QDs) on silver plasmonic resonators using photoluminescence (PL) and excitation spectroscopy along with kinetic modeling and simulations. The exciton dynamics including all the processes are strongly affected by the separation distance between QDs and silver resonators, excitation wavelength, and QD film thickness. For a direct contact or very small distance, interfacial charge transfer and tunneling dominate over intrinsic radiative recombination and exciton energy transfer to surface plasmons (SPs), resulting in PL suppression. With increasing distance, however, tunneling diminishes dramatically, while long-range exciton-SP coupling takes place much faster (>6.5 ns) than intrinsic recombination (~200 ns) causing considerable PL enhancement. The exciton-SP coupling strength shows a strong dependence on excitation wavelengths, suggesting the state-specific dynamics of excitons and the down-conversion of surface plasmons involved. The overlayers as well as the bottom monolayer of QD multilayers exhibit significant PL enhancement mainly through long-range exciton-SP coupling. The overall emission behaviors from single- and multilayer QD films on silver resonators are described quantitatively by a photophysical kinetic model and simulations. The present experimental and simulation results provide important and useful design rules for QD-based light harvesting applications using the exciton-surface plasmon coupling. PMID:27184469

  17. Probing single- to multi-cell level charge transport in Geobacter sulfurreducens DL-1

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaocheng; Hu, Jinsong; Petersen, Emily R.; Fitzgerald, Lisa A.; Jackan, Charles S.; Lieber, Alexander M.; Ringeisen, Bradley R.; Lieber, Charles M.; Biffinger, Justin C.

    2013-11-01

    Microbial fuel cells, in which living microorganisms convert chemical energy into electricity, represent a potentially sustainable energy technology for the future. Here we report the single-bacterium level current measurements of Geobacter sulfurreducens DL-1 to elucidate the fundamental limits and factors determining maximum power output from a microbial fuel cell. Quantized stepwise current outputs of 92(±33) and 196(±20) fA are generated from microelectrode arrays confined in isolated wells. Simultaneous cell imaging/tracking and current recording reveals that the current steps are directly correlated with the contact of one or two cells with the electrodes. This work establishes the amount of current generated by an individual Geobacter cell in the absence of a biofilm and highlights the potential upper limit of microbial fuel cell performance for Geobacter in thin biofilms.

  18. Charge density wave order in 1D mirror twin boundaries of single-layer MoSe2

    NASA Astrophysics Data System (ADS)

    Barja, Sara; Wickenburg, Sebastian; Liu, Zhen-Fei; Zhang, Yi; Ryu, Hyejin; Ugeda, Miguel M.; Hussain, Zahid; Shen, Zhi-Xun; Mo, Sung-Kwan; Wong, Ed; Salmeron, Miquel B.; Wang, Feng; Crommie, Michael F.; Ogletree, D. Frank; Neaton, Jeffrey B.; Weber-Bargioni, Alexander

    2016-08-01

    We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe2 and MoS2. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent density of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.

  19. ORBXYZ: a 3D single-particle orbit code for following charged-particle trajectories in equilibrium magnetic fields

    SciTech Connect

    Anderson, D.V.; Cohen, R.H.; Ferguson, J.R.; Johnston, B.M.; Sharp, C.B.; Willmann, P.A.

    1981-06-30

    The single particle orbit code, TIBRO, has been modified extensively to improve the interpolation methods used and to allow use of vector potential fields in the simulation of charged particle orbits on a 3D domain. A 3D cubic B-spline algorithm is used to generate spline coefficients used in the interpolation. Smooth and accurate field representations are obtained. When vector potential fields are used, the 3D cubic spline interpolation formula analytically generates the magnetic field used to push the particles. This field has del.BETA = 0 to computer roundoff. When magnetic induction is used the interpolation allows del.BETA does not equal 0, which can lead to significant nonphysical results. Presently the code assumes quadrupole symmetry, but this is not an essential feature of the code and could be easily removed for other applications. Many details pertaining to this code are given on microfiche accompanying this report.

  20. Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.; Arnold, James (Technical Monitor)

    1999-01-01

    The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

  1. Experimental and theoretical studies of the He(2+)-He system - Differential cross sections for direct, single-, and double-charge-transfer scattering at keV energies

    NASA Technical Reports Server (NTRS)

    Gao, R. S.; Dutta, C. M.; Lane, N. F.; Smith, K. A.; Stebbings, R. F.; Kimura, M.

    1992-01-01

    Measurements and calculations of differential cross sections for direct scattering, single-charge transfer, and double-charge transfer in collisions of 1.5-, 2.0-, 6.0-, and 10.0-keV (He-3)2+ with an He-4 target are reported. The measurements cover laboratory scattering angles below 1.5 deg with an angular resolution of about 0.03 deg. A quantum-mechanical molecular-state representation is employed in the calculations; in the case of single-charge transfer a two-state close-coupling calculation is carried out taking into account electron-translation effects. The theoretical calculations agree well with the experimental results for direct scattering and double-charge transfer. The present calculation identifies the origins of oscillatory structures observed in the differential cross sections.

  2. Four-body corrected first Born approximation for single charge exchange at high impact energies

    NASA Astrophysics Data System (ADS)

    Mančev, Ivan

    1995-06-01

    Single electron capture is investigated by means of the four-body boundary corrected first Born approximation (CB1-4B). The "post" form of the transition amplitude for a general heteronuclear case (Zp; e1) + (ZT; e2) → (Zp; e1, e2) + ZT is derived in the form of readily obtainable two-dimensional real integrals. We investigate the sensitivity of the total cross sections to the choice of ground state wave function for helium-like atoms. Also, the influence of non-captured electron on the final results is studied. As an illustration, the CB1-4B method is used to compute the total cross sections for reactions: H(1s) + H(1s) → H-(1s2) + H+, He+(1s) + H(1s) → He(1s2) + H+ and He+(1s) + He+(1s) → He(1s2) + α. The theoretical cross sections are found to be in good agreement with the available experimental data.

  3. Manipulating single-wall carbon nanotubes by chemical doping and charge transfer with perylene dyes.

    PubMed

    Ehli, Christian; Oelsner, Christian; Guldi, Dirk M; Mateo-Alonso, Aurelio; Prato, Maurizio; Schmidt, Cordula; Backes, Claudia; Hauke, Frank; Hirsch, Andreas

    2009-06-01

    Single-wall carbon nanotubes (SWNTs) are emerging as materials with much potential in several disciplines, in particular in electronics and photovoltaics. The combination of SWNTs with electron donors or acceptors generates active materials, which can produce electrical energy when irradiated. However, SWNTs are very elusive species when characterization of their metastable states is required. This problem mainly arises because of the polydispersive nature of SWNT samples and the inevitable presence of SWNTs in bundles of different sizes. Here, we report the complete and thorough characterization of an SWNT radical ion-pair state induced by complexation with a perylene dye, which combines excellent electron-accepting and -conducting features with a five-fused ring π-system. At the same time, the perylene dye enables the dispersion of SWNTs by means of π-π interactions, which gives individual SWNTs in solution. This work clears a path towards electronic and optoelectronic devices in which regulated electrical transport properties are important. PMID:21378855

  4. The Charging Process in a High-speed, Single-cylinder, Four-stroke Engine

    NASA Technical Reports Server (NTRS)

    Reynolds, Blake; Schecter, Harry; Taylor, E S

    1939-01-01

    Experimental measurements and theoretical calculations were made on an aircraft-type, single cylinder engine, in order to determine the physical nature of the inlet process, especially at high piston speeds. The engine was run at speeds from 1,500 to 2,600 r.p.m. (mean piston speeds of 1,370 to 2,380 feet per minute). Measurements were made of the cylinder pressure during the inlet stroke and of the power output and volumetric efficiency. Measurements were also made, with the engine not running, to determine the resistance and mass of air in the inlet valve port at various crank angles. Results of analysis indicate that mass has an appreciable effect, but friction plays the major part in restricting flow. The observed fact that the volumetric efficiency is considerably less than 100 percent is attributed to thermal effects. An estimate was made of the magnitude of these effects in the present case, and their general nature is discussed.

  5. Self-assembly of fibronectin mimetic peptide-amphiphile nanofibers

    NASA Astrophysics Data System (ADS)

    Rexeisen, Emilie Lynn

    umbilical vein endothelial cells and alpha5beta1 integrins immobilized on an AFM tip preferred binding to a fibronectin mimetic peptide that contained both hydrophilic and hydrophobic residues in the linker and a medium length spacer. Most cells require a three-dimensional scaffold in order to thrive. To incorporate the fibronectin mimetic peptide into a three-dimensional structure, a single hydrocarbon tail was attached to form a peptideamphiphile. Single-tailed peptide-amphiphiles have been shown to form nanofibers in solution and gel after screening of the electrostatic charges in the headgroup. These gels show promise as scaffolds for tissue engineering. A fibronectin mimetic peptide-amphiphile containing a linker with alternating hydrophobic and hydrophilic residues was designed to form nanofibers in solution. The critical micelle concentration of the peptide-amphiphile was determined to be 38 muM, and all subsequent experiments were performed above this concentration. Circular dichroism (CD) spectroscopy indicated that the peptide headgroup of the peptide-amphiphile forms an alpha+beta secondary structure; whereas, the free peptide forms a random secondary structure. Cryogenic-transmission electron microscopy (cryo-TEM) and small angle neutron scattering showed that the peptide-amphiphile self-assembled into nanofibers. The cryo-TEM images showed single nanofibers with a diameter of 10 nm and lengths on the order of microns. Images of higher peptideamphiphile concentrations showed evidence of bundling between individual nanofibers, which could give rise to gelation behavior at higher concentrations. The peptide-amphiphile formed a gel at concentrations above 6 mM. A 10 mM sample was analyzed with oscillating plate rheometry and was found to have an elastic modulus within the range of living tissue, showing potential as a possible scaffold for tissue engineering.

  6. Effective cytoplasmic release of siRNA from liposomal carriers by controlling the electrostatic interaction of siRNA with a charge-invertible peptide, in response to cytoplasmic pH.

    PubMed

    Itakura, Shoko; Hama, Susumu; Matsui, Ryo; Kogure, Kentaro

    2016-05-19

    Condensing siRNA with cationic polymers is a major strategy used in the development of siRNA carriers that can avoid degradation by nucleases and achieve effective delivery of siRNA into the cytoplasm. However, ineffective release of siRNA from such condensed forms into the cytoplasm is a limiting step for induction of RNAi effects, and can be attributed to tight condensation of siRNA with the cationic polymers, due to potent electrostatic interactions. Here, we report that siRNA condensed with a slightly acidic pH-sensitive peptide (SAPSP), whose total charge is inverted from positive to negative in response to cytoplasmic pH, is effectively released via electrostatic repulsion of siRNA with negatively charged SAPSP at cytoplasmic pH (7.4). The condensed complex of siRNA and positively-charged SAPSP at acidic pH (siRNA/SAPSP) was found to result in almost complete release of siRNA upon charge inversion of SAPSP at pH 7.4, with the resultant negatively-charged SAPSP having no undesirable interactions with endogenous mRNA. Moreover, liposomes encapsulating siRNA/SAPSP demonstrated knockdown efficiencies comparable to those of commercially available siRNA carriers. Taken together, SAPSP may be very useful as a siRNA condenser, as it facilitates effective cytoplasmic release of siRNA, and subsequent induction of specific RNAi effects. PMID:27145993

  7. The production of Multiple Small Peptaibol Families by Single 14-Module Peptide Synthetases in Trichoderma/Hypocrea

    SciTech Connect

    Degenkolb, Thomas; Aghchehb, Razieh Karimi; Dieckmann, Ralf; Neuhof, Torsten; Baker, Scott E.; Druzhinina, Irina S.; Kubicek, Christian P.; Brückner, Hans; von Dohren, Hans

    2012-03-01

    The most common peptaibibiotic structures are 11-residue peptaibols found widely distributed in the genus Trichoderma/Hypocrea. Frequently associated are 14-residue peptaibols sharing partial sequence identity. Genome sequencing projects of 3 Trichoderma strains of the major clades reveal the presence of up to 3 types of nonribosomal peptide synthetases with 7, 14, or 18-20 amino acid adding modules. We here provide evidence that the 14-module NRPS type found in T. virens, T. reesei (teleomorph Hypocrea jecorina) and T. atroviride produces both 11- and 14- residue peptaibols based on the disruption of the respective NRPS gene of T. reesei, and bioinformatic analysis of their amino acid activating domains and modules. The structures of these peptides may be predicted from the gene structures and have been confirmed by analysis of families of 11- and 14-residue peptaibols from the strain 618, termed hypojecorins A (23 sequences determined, 4 new) and B (3 new sequences), and the recently established trichovirins A from T. virens. The distribution of 11- and 14-residue products is strain-specific and depends on growth conditions as well. Possible mechanisms of module skipping are discussed.

  8. Enhancement of glucose uptake in muscular cell by soybean charged peptides isolated by electrodialysis with ultrafiltration membranes (EDUF): activation of the AMPK pathway.

    PubMed

    Roblet, Cyril; Doyen, Alain; Amiot, Jean; Pilon, Geneviève; Marette, André; Bazinet, Laurent

    2014-03-15

    Soy peptides consumption has been associated with beneficial effects in type 2 diabetes patients. However, the peptide fractions responsible for these effects, and their mechanisms of action, have not been identified yet. In this study, we have isolated soybean peptides by electrodialysis with an ultrafiltration membrane (EDUF) at 50 V/100 kDa, and tested them for their capacity to improve glucose uptake in L6 muscle cells. We observed that these fractions were able to significantly enhance glucose uptake in the presence of insulin. The reported bioactivity would be due to the low molecular weight peptides (300-500 Da) recovered. Moreover, we observed that an enhancement of glucose uptake was correlated to the activation of the AMPK enzyme, well known for its capacity to increase glucose uptake in muscle cells. To our knowledge, this is the first time that bioactive peptides with glucose uptake activity have been isolated from a complex soy matrix, and that the implication of AMPK in it is demonstrated. PMID:24206695

  9. Single electron charging at temperatures above 4 K in ultrasmall lateral quantum dots patterned on shallow GaAs/AlGaAs heterostructures

    NASA Astrophysics Data System (ADS)

    Borsosfoldi, Z.; Rahman, M.; Larkin, I. A.; Long, A. R.; Davies, J. H.; Weaver, J. M. R.; Holland, M. C.; Williamson, J. G.

    1995-06-01

    We demonstrate single electron charging in fully controllable nanoscale quantum devices at temperatures above 4 K. Hitherto, single electron devices operating at ``high'' temperatures have been two-terminal, having no control electrode, whereas fully tunable structures such as quantum dots have only shown charging effects at temperatures of 4 K or less. We have fabricated ultrasmall quantum dots on modulation doped heterostructures where the two-dimensional electron gas is less than 30 nm from the surface. Dots with lithographic diameter 150 nm show Coulomb oscillations up to temperatures of 7 K. Higher temperature operation allows potential applications to be considered without the need, for example, of a dilution fridge.

  10. Bi-specific splice-switching PMO oligonucleotides conjugated via a single peptide active in a mouse model of Duchenne muscular dystrophy.

    PubMed

    Shabanpoor, Fazel; McClorey, Graham; Saleh, Amer F; Järver, Peter; Wood, Matthew J A; Gait, Michael J

    2015-01-01

    The potential for therapeutic application of splice-switching oligonucleotides (SSOs) to modulate pre-mRNA splicing is increasingly evident in a number of diseases. However, the primary drawback of this approach is poor cell and in vivo oligonucleotide uptake efficacy. Biological activities can be significantly enhanced through the use of synthetically conjugated cationic cell penetrating peptides (CPPs). Studies to date have focused on the delivery of a single SSO conjugated to a CPP, but here we describe the conjugation of two phosphorodiamidate morpholino oligonucleotide (PMO) SSOs to a single CPP for simultaneous delivery and pre-mRNA targeting of two separate genes, exon 23 of the Dmd gene and exon 5 of the Acvr2b gene, in a mouse model of Duchenne muscular dystrophy. Conjugations of PMOs to a single CPP were carried out through an amide bond in one case and through a triazole linkage ('click chemistry') in the other. The most active bi-specific CPP-PMOs demonstrated comparable exon skipping levels for both pre-mRNA targets when compared to individual CPP-PMO conjugates both in cell culture and in vivo in the mdx mouse model. Thus, two SSOs with different target sequences conjugated to a single CPP are biologically effective and potentially suitable for future therapeutic exploitation. PMID:25468897

  11. Bi-specific splice-switching PMO oligonucleotides conjugated via a single peptide active in a mouse model of Duchenne muscular dystrophy

    PubMed Central

    Shabanpoor, Fazel; McClorey, Graham; Saleh, Amer F.; Järver, Peter; Wood, Matthew J.A.; Gait, Michael J.

    2015-01-01

    The potential for therapeutic application of splice-switching oligonucleotides (SSOs) to modulate pre-mRNA splicing is increasingly evident in a number of diseases. However, the primary drawback of this approach is poor cell and in vivo oligonucleotide uptake efficacy. Biological activities can be significantly enhanced through the use of synthetically conjugated cationic cell penetrating peptides (CPPs). Studies to date have focused on the delivery of a single SSO conjugated to a CPP, but here we describe the conjugation of two phosphorodiamidate morpholino oligonucleotide (PMO) SSOs to a single CPP for simultaneous delivery and pre-mRNA targeting of two separate genes, exon 23 of the Dmd gene and exon 5 of the Acvr2b gene, in a mouse model of Duchenne muscular dystrophy. Conjugations of PMOs to a single CPP were carried out through an amide bond in one case and through a triazole linkage (‘click chemistry’) in the other. The most active bi-specific CPP–PMOs demonstrated comparable exon skipping levels for both pre-mRNA targets when compared to individual CPP–PMO conjugates both in cell culture and in vivo in the mdx mouse model. Thus, two SSOs with different target sequences conjugated to a single CPP are biologically effective and potentially suitable for future therapeutic exploitation. PMID:25468897

  12. A small single-"finger" peptide from the erythroid transcription factor GATA-1 binds specifically to DNA as a zinc or iron complex.

    PubMed

    Omichinski, J G; Trainor, C; Evans, T; Gronenborn, A M; Clore, G M; Felsenfeld, G

    1993-03-01

    Sequence-specific DNA binding has been demonstrated for a synthetic peptide comprising only one of the two "finger"-like domains of the erythroid transcription factor GATA-1 (also termed Eryf-1, NF-E1, or GF-1). Quantitative analysis of gel-retardation assays yields a specific association constant of 1.2 x 10(8) M, compared with values of about 10(9) M for the full-length natural GATA-1 protein. By the use of peptides of various lengths, it was possible to delineate the smallest region necessary for specific binding. A single C-terminal finger of the double-finger motif is necessary but not sufficient for sequence-specific interaction. Basic amino acids located C-terminal to the finger (some more than 20 amino acids away) are also essential for tight binding. In addition to demonstrating that zinc is important for the formation of an active binding complex, we show that other ions, notably Fe2+, can fulfill this role. Our results make it clear that the GATA-1 metal binding motif is quite distinct from that found in the steroid hormone family and that GATA-1 is a member of a separate class of DNA binding proteins. PMID:8446581

  13. Anti-metastatic effects of DNA vaccine encoding single-chain trimer composed of MHC I and vascular endothelial growth factor receptor 2 peptide.

    PubMed

    Chen, Ruiling; Wang, Shengchao; Yao, Yunliang; Zhou, Yun; Zhang, Chong; Fang, Jie; Zhang, Dayong; Zhang, Lihuang; Pan, Jianping

    2015-05-01

    Vascular endothelial growth factor receptor 2 (VEGFR2)-mediated signaling is the key rate-limiting step in angiogenesis. VEGFR2 serves as the most important target of anti-angiogenic therapy for cancers. Single-chain trimer (SCT) comprising antigen peptide, β2-microglobulin (β2m), and major histocompatibility complex (MHC) class I heavy chain was a particularly powerful strategy involved in the increase of the potency of DNA vaccine against tumors and infections. In the present study, we constructed an SCT-encoding VEGFR2 antigen peptide [aa400-408, also known as kinase insert domain-containing receptor (KDR2)], β2m, and mouse MHC class I heavy chain H-2Db [pcDNA3.1(+)-KDR2-β2m-H-2Db, or SCT-KDR2]. The constructed SCT-KDR2 DNA was efficiently expressed in the human A293 embryonic kidney cell line. Intradermal immunization of C57BL/6 mice with SCT-KDR2 DNA was able to successfully break self-immunological tolerance and induce robust cytotoxic T‑lymphocyte (CTL) response to VEGFR2, leading to marked suppression of tumor cell‑induced angiogenesis and metastasis in murine models of B16 melanoma and 3LL Lewis lung carcinoma. Taken together, the results showed that VEGFR2-targeted SCT vaccination is an effective modality that can be utilized in anti-angiogenic active immunotherapy for various types of cancer. PMID:25739076

  14. Synthetic antimicrobial peptide design.

    PubMed

    Powell, W A; Catranis, C M; Maynard, C A

    1995-01-01

    To guide the design of potential plant pathogen-resistance genes, synthetic variants of naturally occurring antimicrobial gene products were evaluated. Five 20-amino acid (ESF1, ESF4, ESF5, ESF6, ESF13), one 18-amino acid (ESF12), and one 17-amino acid (ESF17) amphipathic peptide sequences were designed, synthesized, and tested with in vitro bioassays. Positive charges on the hydrophilic side of the peptide were shown to be essential for antifungal activity, yet the number of positive charges could be varied with little or no change in activity. The size could be reduced to 18 amino acids, but at 17 amino acids a significant reduction in activity was observed. ESF1, 5, 6, and 12 peptides were inhibitory to the germination of conidia from Cryphonectria parasitica, Fusarium oxysporum f. sp. lycopersici, and Septoria musiva but did not inhibit the germination of pollen from Castanea mollissima and Salix lucida. ESF12 also had no effect on the germination of Malus sylvestris and Lycopersicon esculentum pollen, but inhibited the growth of the bacteria Agrobacterium tumefaciens, Erwinia amylovora, and Pseudomonas syringae. The minimal inhibitory concentrations of the active ESF peptides were similar to those of the naturally occurring control peptides, magainin II and cecropin B. The significant differential in sensitivity between the microbes and plant cells indicated that the active ESF peptides are potentially useful models for designing plant pathogen-resistance genes. PMID:7579625

  15. Hydrogen Attachment/Abstraction Dissociation (HAD) of Gas-Phase Peptide Ions for Tandem Mass Spectrometry.

    PubMed

    Takahashi, Hidenori; Sekiya, Sadanori; Nishikaze, Takashi; Kodera, Kei; Iwamoto, Shinichi; Wada, Motoi; Tanaka, Koichi

    2016-04-01

    Dissociation of gas-phase peptide ions through interaction with low-energy hydrogen (H) radical (∼0.15 eV) was observed with a quadrupole ion trap mass spectrometry. The H radical generated by thermal dissociation of H2 molecules passing through a heated tungsten capillary (∼2000 °C) was injected into the ion trap containing target peptide ions. The fragmentation spectrum showed abundant c-/z- and a-/x-type ions, attributable to H attachment/abstraction to/from peptide ion. Because the low-energy neutral H radical initiated the fragmentation, the charge state of the precursor ion was maintained during the dissociation. As a result, precursor ions of any charge state, including singly charged positive and negative ions, could be analyzed for amino acid sequence. The sequence coverage exceeding 90% was obtained for both singly protonated and singly deprotonated substance P peptide. This mass spectrometry also preserved labile post-translational modification bonds. The modification sites of triply phosphorylated peptide (kinase domain of insulin receptor) were identified with the sequence coverage exceeding 80%. PMID:27002918

  16. SINGLE-WALLED CARBON NANOTUBE–MEDIATED SMALL INTERFERING RNA DELIVERY AND SILENCING GASTRIN-RELEASING PEPTIDE RECEPTOR IN HUMAN NEUROBLASTOMA CELLS

    PubMed Central

    Qiao, Jingbo; Hong, Tu; Guo, Honglian; Xu, Ya-Qiong; Chung, Dai H.

    2015-01-01

    Small interfering RNA (siRNA) has the potential to influence expression with a high degree of target gene specificity. However, the clinical application of siRNA therapeutics has proven to be less promising as evidenced by poor intracellular uptake, instability in vivo, and non-specific immune stimulations. Recently, we have demonstrated that single-walled carbon nanotube (SWNT)-mediated siRNA delivery can enhance the efficiency of siRNA-mediated gastrin-releasing peptide receptor (GRP-R) gene silencing by stabilizing siRNA while selectively targeting tumor tissues. Based on our recent findings, we introduce a novel technique to silence specific gene(s) in human neuroblastoma through SWNT-mediated siRNA delivery in vitro and in vivo. PMID:23749575

  17. B-type natriuretic peptide and C-reactive protein in the prediction of atrial fibrillation risk: the CHARGE-AF Consortium of community-based cohort studies

    PubMed Central

    Sinner, Moritz F.; Stepas, Katherine A.; Moser, Carlee B.; Krijthe, Bouwe P.; Aspelund, Thor; Sotoodehnia, Nona; Fontes, João D.; Janssens, A. Cecile J.W.; Kronmal, Richard A.; Magnani, Jared W.; Witteman, Jacqueline C.; Chamberlain, Alanna M.; Lubitz, Steven A.; Schnabel, Renate B.; Vasan, Ramachandran S.; Wang, Thomas J.; Agarwal, Sunil K.; McManus, David D.; Franco, Oscar H.; Yin, Xiaoyan; Larson, Martin G.; Burke, Gregory L.; Launer, Lenore J.; Hofman, Albert; Levy, Daniel; Gottdiener, John S.; Kääb, Stefan; Couper, David; Harris, Tamara B.; Astor, Brad C.; Ballantyne, Christie M.; Hoogeveen, Ron C.; Arai, Andrew E.; Soliman, Elsayed Z.; Ellinor, Patrick T.; Stricker, Bruno H.C.; Gudnason, Vilmundur; Heckbert, Susan R.; Pencina, Michael J.; Benjamin, Emelia J.; Alonso, Alvaro

    2014-01-01

    Aims B-type natriuretic peptide (BNP) and C-reactive protein (CRP) predict atrial fibrillation (AF) risk. However, their risk stratification abilities in the broad community remain uncertain. We sought to improve risk stratification for AF using biomarker information. Methods and results We ascertained AF incidence in 18 556 Whites and African Americans from the Atherosclerosis Risk in Communities Study (ARIC, n=10 675), Cardiovascular Health Study (CHS, n = 5043), and Framingham Heart Study (FHS, n = 2838), followed for 5 years (prediction horizon). We added BNP (ARIC/CHS: N-terminal pro-B-type natriuretic peptide; FHS: BNP), CRP, or both to a previously reported AF risk score, and assessed model calibration and predictive ability [C-statistic, integrated discrimination improvement (IDI), and net reclassification improvement (NRI)]. We replicated models in two independent European cohorts: Age, Gene/Environment Susceptibility Reykjavik Study (AGES), n = 4467; Rotterdam Study (RS), n = 3203. B-type natriuretic peptide and CRP were significantly associated with AF incidence (n = 1186): hazard ratio per 1-SD ln-transformed biomarker 1.66 [95% confidence interval (CI), 1.56–1.76], P < 0.0001 and 1.18 (95% CI, 1.11–1.25), P < 0.0001, respectively. Model calibration was sufficient (BNP, χ2 = 17.0; CRP, χ2 = 10.5; BNP and CRP, χ2 = 13.1). B-type natriuretic peptide improved the C-statistic from 0.765 to 0.790, yielded an IDI of 0.027 (95% CI, 0.022–0.032), a relative IDI of 41.5%, and a continuous NRI of 0.389 (95% CI, 0.322–0.455). The predictive ability of CRP was limited (C-statistic increment 0.003). B-type natriuretic peptide consistently improved prediction in AGES and RS. Conclusion B-type natriuretic peptide, not CRP, substantially improved AF risk prediction beyond clinical factors in an independently replicated, heterogeneous population. B-type natriuretic peptide may serve as a benchmark to evaluate novel putative AF risk biomarkers. PMID:25037055

  18. Measurement and Calculation of Absolute Single- and Multiple-Charge-Exchange Cross Sections for Feq+ Ions Impacting CO and CO2

    SciTech Connect

    Simcic, J.; Mawhorter, R. J.; Cadez, I.; Greenwood, J. B.; Chutjian, A.; Smith, S. J.

    2010-01-01

    Absolute cross sections are reported for single, double, and triple charge exchange of Feq+ (q=5- 13) ions with CO and CO2. The highly-charged Fe ions are generated in an electron cyclotron resonance ion source. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental results are compared with new calculations of these cross sections in the n-electron classical trajectory Monte-Carlo approximation, in which the ensuing radiative and non-radiative cascades are approximated with scaled hydrogenic transition probabilities and scaled Auger rates. The present data are needed in astrophysical applications of solar- and stellar-wind charge-exchange with comets, planetary atmospheres, and circumstellar clouds.

  19. Investigation of free charge carrier dynamics in single-crystalline CVD diamond by two-photon absorption

    SciTech Connect

    Ivakin, E V; Kisialiou, I G; Ralchenko, V G; Bolshakov, A P; Ashkinazi, E E; Sharonov, G V

    2014-11-30

    By using the methods of transient gratings (TGs) and induced absorption, we have studied the kinetics of plasma of free charge carriers (FCCs) created by the action of a picosecond laser pulse in two high-purity diamond single crystals synthesised from the gas phase. The gratings with different spatial periods have been excited at the wavelengths of 266 or 213 nm (above and below the fundamental absorption edge in diamond) and probed with continuous-wave radiation in the visible region. At the moderate FCC concentrations (∼7 × 10{sup 17} cm{sup -3}), the coefficient of ambipolar diffusion and the carrier recombination time of two crystals are 20.3 and 18.9 cm{sup 2} s{sup -1} and 30 and 190 ns, respectively. The increase in the carrier concentration up to 5 × 10{sup 19} cm{sup -3} reduces the TG lifetime. We have determined the conditions under which the relaxation of the grating of carriers leads to the formation of a thermal grating, with the amplitude sufficient for its experimental observation. (interaction of laser radiation with matter. laser plasma)

  20. Beam-single and beam-two-foil experimental facility to study physics of highly charged ions

    SciTech Connect

    Ahmad, Nissar; Wani, A.A.; Ram, R.; Abhilash, S.R.; Kumar, Rakesh; Patnaik, J.K.; De, Sankar; Karn, R.K.; Nandi, T.

    2006-03-15

    A facility for lifetime measurement of metastable states in highly charged ions using the beam-foil technique with a single-foil and a two-foil target has been developed. In the two-foil technique, one foil moves with respect to the other and the option of varying the thickness of the fixed foil online has been implemented. A holder with multiple foils is used as a fixed target, and moved along x, y, and {theta}, the angle of rotation with respect to beam direction along the z axis. Using this facility, the He-like 1s2p {sup 3}P{sub 2}{sup o} and Li-like 1s2s2p {sup 4}P{sub 5l/2}{sup o} titanium lifetimes have been measured and compared with earlier values. In addition to this, the processes which occur when excited states collide with carbon foils of different thicknesses have also been investigated. Preliminary results suggest the scope of studying intrashell transitions during ion-solid collision using this setup. In this article, the setup is described in detail and representative results are briefly discussed.

  1. Ab initio investigation of sulfur monofluoride and its singly charged cation and anion in their ground electronic state

    NASA Astrophysics Data System (ADS)

    Song, Li; Shan-Jun, Chen; Yan, Chen; Peng, Chen

    2016-03-01

    The SF radical and its singly charged cation and anion, SF+ and SF-, have been investigated on the MRCI/aug-cc-pVXZ (X = Q, 5, 6) levels of theory with Davidson correction. Both the core-valence correlation and the relativistic effect are considered. The extrapolating to the complete basis set (CBS) limit is adopted to remove the basis set truncation error. Geometrical parameters, potential energy curves (PECs), vibrational energy levels, spectroscopic constants, ionization potentials, and electron affinities of the ground electronic state for all these species are obtained. The information with respect to molecular characteristics of the SFn (n = -1, 0, +1) systems derived in this work will help to extend our knowledge and to guide further experimental or theoretical researches. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304023 and 11447172), the Young and Middle-Aged Talent of Education Burea of Hubei Province, China (Grant No. Q20151307), and the Yangtze Youth Talents Fund of Yangtze University, China (Grant No. 2015cqr21).

  2. Charge transport and glassy dynamics of poly(ethylene oxide)-based single-ion conductors under geometrical confinement

    NASA Astrophysics Data System (ADS)

    Runt, James; Iacob, Ciprian

    2015-03-01

    Segmental and local dynamics as well as charge transport are investigated in a series of poly(ethylene oxide)-based single-ion conductors (ionomers) with varying counterions (Li +, Na +) confined in uni-directional nanoporous silica membranes. The dynamics are explored over a wide frequency and temperature range by broadband dielectric relaxation spectroscopy. Slowing of segmental dynamics and a decrease in dc conductivity (strongly coupled with segmental relaxation) of the confined ionomers are associated with surface effects - resulting from interfacial hydrogen bonding between the host nanoporous silica membrane and the guest ionomers. These effects are significantly reduced or eliminated upon pore surface modification through silanization. The primary transport properties for the confined ionomers decrease by about one decade compared to the bulk ionomer. A model assuming reduced mobility of an adsorbed layer at the pore wall/ionomer interface is shown to provide a quantitative explanation for the decrease in effective transport quantities in non-silanized porous silica membranes. Additionally, the effect of confinement on ion aggregation in ionomers by using X-ray scattering will also be discussed. Supported by the National Science Foundation, Polymers Program.

  3. Rapid Charge Transport in Dye-Sensitized Solar Cells Made from Vertically Aligned Single-Crystal Rutile TiO2 Nanowires

    SciTech Connect

    Feng, X.; Zhu, K.; Frank, A. J.; Grimes, C. A.; Mallouk, T. E.

    2012-03-12

    A rapid solvothermal approach was used to synthesize aligned 1D single-crystal rutile TiO2 nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. The NW arrays showed a more than 200 times faster charge transport (see picture) and a factor four lower defect state density than conventional rutile nanoparticle films.

  4. A pharmacokinetic/pharmacodynamic model for AMG 416, a novel calcimimetic peptide, following a single intravenous dose in healthy subjects.

    PubMed

    Shen, Jun; Xiao, Jim; Pickthorn, Karen; Huang, Saling; Bell, Gregory; Vick, Andrew; Chen, Ping

    2014-10-01

    AMG 416 is a novel peptide agonist of the calcium-sensing receptor. In support of the clinical development program, a pharmacokinetic (PK)/pharmacodynamic (PD) model was developed to describe the relationship between plasma AMG 416 levels and serum intact parathyroid hormone (iPTH) concentrations in healthy male subjects. AMG 416 plasma concentrations were characterized by a three-compartment linear PK model, while serum iPTH levels were described by an indirect response model with drug effect on the production of iPTH characterized with an inhibitory Emax model. The production of iPTH was modeled by a circadian rhythm function. The systemic clearance of plasma AMG 416 was estimated to be 6.94 L/h. Two sine functions best described iPTH circadian rhythm with an amplitude estimated to be 0.15 and 0.08, respectively. The maximum response Emax and the potency parameter EC50 were estimated to be 0.69 and 21.0 ng/mL, respectively. This work improved our understanding of the interaction between AMG 416 PK and iPTH concentrations in healthy adult male subjects. Data suggest additional PK/PD studies with AMG 416 are warranted in the hemodialysis population. PMID:24752908

  5. The membrane interaction of amphiphilic model peptides affects phosphatidylserine headgroup and acyl chain order and dynamics. Application of the phospholipid headgroup electrometer concept to phosphatidylserine

    SciTech Connect

    de Kroon, A.I.P.M.; Killian, J.A.; de Gier, J.; de Kruijff, B. )

    1991-01-29

    Deuterium nuclear magnetic resonance ({sup 2}H NMR) was used to study the interaction of amphiphilic model peptides with model membranes consisting of 1,2-dioleoyl-sn-glycero-3-phospho-L-serine deuterated either at the {beta}-position of the serine moiety ((2-{sup 2}H)DOPS) or at the 11-position of the acyl chains ((11,11-{sup 2}H{sub 2})DOPS). The peptides are derived from the sequences H-Ala-Met-Leu-Trp-Ala-OH and H-Arg-Met-Leu-Trp-Ala-OH and contain a positive charge of +1 or +2 at the amino terminus or one positive charge at each end of the molecule. Upon titration of dispersions of DOPS with the peptides, the divalent peptides show a similar extent of binding to the DOPS bilyers, which is larger than that of the single charged peptide. Under these conditions the values of the quadrupolar splitting of both (2-{sup 2}H)DOPS and (11,11-{sup 2}H{sub 2})DOPS are decreased, indicating that the peptides reduce the order of both the DOPS headgroup and the acyl chains. The extent of the decrease depends on the amount of peptide bound and on the position of the charged moieties in the peptide molecule. Titrations of DOPS with poly(L-lysine){sub 100}, which were included for reasons of comparison, reveal increased {Delta}v{sub q} values. When the peptide-lipid titrations are carried out without applying a freeze-thaw procedure to achieve full equilibration, two-component {sup 2}H NMR spectra occur. The apparently limited accessibility of the lipid to the peptides under these circumstances is discussed in relation to the ability of the peptides to exhibit transbilayer movement. {sup 2}H spin-lattice relaxation time T1 measurements demonstrate a decrease of the rates of motion of both headgroup and acyl chains of DOPS in the presence of the peptides.

  6. Effective cytoplasmic release of siRNA from liposomal carriers by controlling the electrostatic interaction of siRNA with a charge-invertible peptide, in response to cytoplasmic pH

    NASA Astrophysics Data System (ADS)

    Itakura, Shoko; Hama, Susumu; Matsui, Ryo; Kogure, Kentaro

    2016-05-01

    Condensing siRNA with cationic polymers is a major strategy used in the development of siRNA carriers that can avoid degradation by nucleases and achieve effective delivery of siRNA into the cytoplasm. However, ineffective release of siRNA from such condensed forms into the cytoplasm is a limiting step for induction of RNAi effects, and can be attributed to tight condensation of siRNA with the cationic polymers, due to potent electrostatic interactions. Here, we report that siRNA condensed with a slightly acidic pH-sensitive peptide (SAPSP), whose total charge is inverted from positive to negative in response to cytoplasmic pH, is effectively released via electrostatic repulsion of siRNA with negatively charged SAPSP at cytoplasmic pH (7.4). The condensed complex of siRNA and positively-charged SAPSP at acidic pH (siRNA/SAPSP) was found to result in almost complete release of siRNA upon charge inversion of SAPSP at pH 7.4, with the resultant negatively-charged SAPSP having no undesirable interactions with endogenous mRNA. Moreover, liposomes encapsulating siRNA/SAPSP demonstrated knockdown efficiencies comparable to those of commercially available siRNA carriers. Taken together, SAPSP may be very useful as a siRNA condenser, as it facilitates effective cytoplasmic release of siRNA, and subsequent induction of specific RNAi effects.Condensing siRNA with cationic polymers is a major strategy used in the development of siRNA carriers that can avoid degradation by nucleases and achieve effective delivery of siRNA into the cytoplasm. However, ineffective release of siRNA from such condensed forms into the cytoplasm is a limiting step for induction of RNAi effects, and can be attributed to tight condensation of siRNA with the cationic polymers, due to potent electrostatic interactions. Here, we report that siRNA condensed with a slightly acidic pH-sensitive peptide (SAPSP), whose total charge is inverted from positive to negative in response to cytoplasmic pH, is

  7. Encapsulation of bioactive whey peptides in soy lecithin-derived nanoliposomes: Influence of peptide molecular weight.

    PubMed

    Mohan, Aishwarya; McClements, David Julian; Udenigwe, Chibuike C

    2016-12-15

    Encapsulation of peptides can be used to enhance their stability, delivery and bioavailability. This study focused on the effect of the molecular weight range of whey peptides on their encapsulation within soy lecithin-derived nanoliposomes. Peptide molecular weight did not have a major impact on encapsulation efficiency or liposome size. However, it influenced peptide distribution amongst the surface, core, and bilayer regions of the liposomes, as determined by electrical charge (ζ-potential) and FTIR analysis. The liposome ζ-potential depended on peptide molecular weight, suggesting that the peptide charged groups were in different locations relative to the liposome surfaces. FTIR analysis indicated that the least hydrophobic peptide fractions interacted more strongly with choline on the liposome surfaces. The results suggested that the peptides were unequally distributed within the liposomes, even at the same encapsulation efficiency. These findings are important for designing delivery systems for commercial production of encapsulated peptides with improved functional attributes. PMID:27451165

  8. Single-cell, time-resolved study of the effects of the antimicrobial peptide alamethicin on Bacillus subtilis.

    PubMed

    Barns, Kenneth J; Weisshaar, James C

    2016-04-01

    Alamethicin is a well-studied antimicrobial peptide (AMP) that kills Gram-positive bacteria. It forms narrow, barrel-stave pores in planar lipid bilayers. We present a detailed, time-resolved microscopy study of the sequence of events during the attack of alamethicin on individual, live Bacillus subtilis cells expressing GFP in the cytoplasm. At the minimum inhibitory concentration (MIC), the first observed symptom is the halting of growth, as judged by the plateau in measured cell length vs time. The data strongly suggest that this growth-halting event occurs prior to membrane permeabilization. Gradual degradation of the proton-motive force, inferred from a decrease in pH-dependent GFP fluorescence intensity, evidently begins minutes later and continues over about 5 min. There follows an abrupt permeabilization of the cytoplasmic membrane to the DNA stain Sytox Orange and concomitant loss of small osmolytes, causing observable cell shrinkage, presumably due to decreased turgor pressure. This permeabilization of the cytoplasmic membrane occurs uniformly across the entire membrane, not locally, on a timescale of 5s or less. GFP gradually leaks out of the cell envelope, evidently impeded by the shrunken peptidoglycan layer. Disruption of the cell envelope by alamethicin occurs in stages, with larger and larger species permeating the envelope as time evolves over tens of minutes. Some of the observed symptoms are consistent with the formation of barrel-stave pores, but the data do not rule out "chaotic pore" or "carpet" mechanisms. We contrast the effects of alamethicin and the human cathelicidin LL-37 on B. subtilis. PMID:26777771

  9. Design of Peptide-Membrane Interactions to Modulate Single-File Water Transport through Modified Gramicidin Channels

    PubMed Central

    Portella, Guillem; Polupanow, Tanja; Zocher, Florian; Boytsov, Danila A.; Pohl, Peter; Diederichsen, Ulf; de Groot, Bert L.

    2012-01-01

    Water permeability through single-file channels is affected by intrinsic factors such as their size and polarity and by external determinants like their lipid environment in the membrane. Previous computational studies revealed that the obstruction of the channel by lipid headgroups can be long-lived, in the range of nanoseconds, and that pore-length-matching membrane mimetics could speed up water permeability. To test the hypothesis of lipid-channel interactions modulating channel permeability, we designed different gramicidin A derivatives with attached acyl chains. By combining extensive molecular-dynamics simulations and single-channel water permeation measurements, we show that by tuning lipid-channel interactions, these modifications reduce the presence of lipid headgroups in the pore, which leads to a clear and selective increase in their water permeability. PMID:23083713

  10. The peptide motif of the single dominantly expressed class I molecule of the chicken MHC can explain the response to a molecular defined vaccine of infectious bursal disease virus (IBDV).

    PubMed

    Butter, Colin; Staines, Karen; van Hateren, Andrew; Davison, T Fred; Kaufman, Jim

    2013-08-01

    In contrast to typical mammals, the chicken MHC (the BF-BL region of the B locus) has strong genetic associations with resistance and susceptibility to infectious pathogens as well as responses to vaccines. We have shown that the chicken MHC encodes a single dominantly expressed class I molecule whose peptide-binding motifs can determine resistance to viral pathogens, such as Rous sarcoma virus and Marek's disease virus. In this report, we examine the response to a molecular defined vaccine, fp-IBD1, which consists of a fowlpox virus vector carrying the VP2 gene of infectious bursal disease virus (IBDV) fused with β-galactosidase. We vaccinated parental lines and two backcross families with fp-IBD1, challenged with the virulent IBDV strain F52/70, and measured damage to the bursa. We found that the MHC haplotype B15 from line 15I confers no protection, whereas B2 from line 61 and B12 from line C determine protection, although another locus from line 61 was also important. Using our peptide motifs, we found that many more peptides from VP2 were predicted to bind to the dominantly expressed class I molecule BF2*1201 than BF2*1501. Moreover, most of the peptides predicted to bind BF2*1201 did in fact bind, while none bound BF2*1501. Using peptide vaccination, we identified one B12 peptide that conferred protection to challenge, as assessed by bursal damage and viremia. Thus, we show the strong genetic association of the chicken MHC to a T cell vaccine can be explained by peptide presentation by the single dominantly expressed class I molecule. PMID:23644721

  11. Impact of single-dose application of TGF-β, copper peptide, stanozolol and ascorbic acid in hydrogel on midline laparatomy wound healing in a diabetic mouse model.

    PubMed

    Konerding, Moritz A; Ziebart, Thomas; Wolloscheck, Tanja; Wellmann, Axel; Ackermann, Maximilian

    2012-08-01

    Despite numerous advances and improvements in surgical techniques the incidence of incisional hernias after laparotomy remains high. The aim of this study was to investigate possible effects of single application of ascorbic acid, stanozolol, a synthetic anabolic steroid, copper peptide and transforming growth factor-β (TGF-β) on laparotomy wound healing in an incisional wound model in diabetic mice. After diabetes induction with streptozotozin in Balb-c mice, midline laparatomies were carried out. Closure of the linea alba was followed by single-dose application of the agents dissolved in a hydrogel before skin closure. The functional outcome was assessed in terms of maximum tensile strength. In addition, vessel densities, collagen contents and proliferation, were measured. The breaking strength of the skin 14 days after surgery was significantly higher in ascorbic acid (ΑΑ)-treated incisional wounds, whereas the other agents did not show a significantly better functional outcome. No significant differences were seen in vessel densities. Collagen type III contents was higher in the ΑΑ-treated animals, whereas the percentage of Ki67-positive nuclei was lower compared to the other groups. These data underline the positive effect of topically applied ascorbic acid in wound healing. PMID:22614259

  12. Recruitment of Oligoclonal Viral-Specific T cells to Kill Human Tumor Cells Using Single-Chain Antibody-Peptide-HLA Fusion Molecules.

    PubMed

    Noy, Roy; Haus-Cohen, Maya; Oved, Kfir; Voloshin, Tali; Reiter, Yoram

    2015-06-01

    Tumor progression is often associated with the development of diverse immune escape mechanisms. One of the main tumor escape mechanism is HLA loss, in which human solid tumors exhibit alterations in HLA expression. Moreover, tumors that present immunogenic peptides via class I MHC molecules are not susceptible to CTL-mediated lysis, because of the relatively low potency of the tumor-specific CLTs. Here, we present a novel cancer immunotherapy approach that overcomes these problems by using the high affinity and specificity of antitumor antibodies to recruit potent antiviral memory CTLs to attack tumor cells. We constructed a recombinant molecule by genetic fusion of a cytomegalovirus (CMV)-derived peptide pp65 (NLVPMVATV) to scHLA-A2 molecules that were genetically fused to a single-chain Fv Ab fragment specific for the tumor cell surface antigen mesothelin. This fully covalent fusion molecule was expressed in E. coli as inclusion bodies and refolded in vitro. The fusion molecules could specifically bind mesothelin-expressing cells and mediate their lysis by NLVPMVATV-specific HLA-A2-restricted human CTLs. More importantly, these molecules exhibited very potent antitumor activity in vivo in a nude mouse model bearing preestablished human tumor xenografts that were adoptively transferred along with human memory CTLs. These results represent a novel and powerful approach to immunotherapy for solid tumors, as demonstrated by the ability of the CMV-scHLA-A2-SS1(scFv) fusion molecule to mediate specific and efficient recruitment of CMV-specific CTLs to kill tumor cells. PMID:25852061

  13. Kinetic Energy Release of the Singly and Doubly Charged Methylene Chloride Molecule: The Role of Fast Dissociation.

    PubMed

    Alcantara, K F; Rocha, A B; Gomes, A H A; Wolff, W; Sigaud, L; Santos, A C F

    2016-09-01

    The center of mass kinetic energy release distribution (KERD) spectra of selected ionic fragments, formed through dissociative single and double photoionization of CH2Cl2 at photon energies around the Cl 2p edge, were extracted from the shape and width of the experimentally obtained time-of-flight (TOF) distributions. The KERD spectra exhibit either smooth profiles or structures, depending on the moiety and photon energy. In general, the heavier the ionic fragments, the lower their average KERDs are. In contrast, the light H(+) fragments are observed with kinetic energies centered around 4.5-5.5 eV, depending on the photon energy. It was observed that the change in the photon energy involves a change in the KERDs, indicating different processes or transitions taking place in the breakup process. In the particular case of double ionization with the ejection of two charged fragments, the KERDs present have characteristics compatible with the Coulombic fragmentation model. Intending to interpret the experimental data, singlet and triplet states at Cl 2p edge of the CH2Cl2 molecule, corresponding to the Cl (2p → 10a1*) and Cl (2p → 4b1*) transitions, were calculated at multiconfigurational self-consistent field (MCSCF) level and multireference configuration interaction (MRCI). These states were selected to form the spin-orbit coupling matrix elements, which after diagonalization result in a spin-orbit manifold. Minimum energy pathways for dissociation of the molecule were additionally calculated aiming to give support to the presence of the ultrafast dissociation mechanism in the molecular breakup. PMID:27523328

  14. Antimicrobial peptides

    PubMed Central

    2014-01-01

    With increasing antibiotics resistance, there is an urgent need for novel infection therapeutics. Since antimicrobial peptides provide opportunities for this, identification and optimization of such peptides have attracted much interest during recent years. Here, a brief overview of antimicrobial peptides is provided, with focus placed on how selected hydrophobic modifications of antimicrobial peptides can be employed to combat also more demanding pathogens, including multi-resistant strains, without conferring unacceptable toxicity. PMID:24758244

  15. Composition and method for self-assembly and mineralization of peptide amphiphiles

    DOEpatents

    Stupp, Samuel I.; Beniash, Elia; Hartgerink, Jeffrey D.

    2009-06-30

    The present invention is directed to a composition useful for making homogeneously mineralized self assembled peptide-amphiphile nanofibers and nanofiber gels. The composition is generally a solution comprised of a positively or negatively charged peptide-amphiphile and a like signed ion from the mineral. Mixing this solution with a second solution containing a dissolved counter-ion of the mineral and/or a second oppositely charged peptide amphiphile, results in the rapid self assembly of the peptide-amphiphiles into a nanofiber gel and templated mineralization of the ions. Templated mineralization of the initially dissolved mineral cations and anions in the mixture occurs with preferential orientation of the mineral crystals along the fiber surfaces within the nanofiber gel. One advantage of the present invention is that it results in homogenous growth of the mineral throughout the nanofiber gel. Another advantage of the present invention is that the nanofiber gel formation and mineralization reactions occur in a single mixing step and under substantially neutral or physiological pH conditions. These homogeneous nanostructured composite materials are useful for medical applications especially the regeneration of damaged bone in mammals. This invention is directed to the synthesis of peptide-amphiphiles with more than one amphiphilic moment and to supramolecular compositions comprised of such multi-dimensional peptide-amphiphiles. Supramolecular compositions can be formed by self assembly of multi-dimensional peptide-amphiphiles by mixing them with a solution comprising a monovalent cation.

  16. Composition and method for self-assembly and mineralization of peptide-amphiphiles

    DOEpatents

    Stupp, Samuel I.; Beniash, Elia; Hartgerink, Jeffrey D.

    2012-02-28

    The present invention is directed to a composition useful for making homogeneously mineralized self assembled peptide-amphiphile nanofibers and nanofiber gels. The composition is generally a solution comprised of a positively or negatively charged peptide-amphiphile and a like signed ion from the mineral. Mixing this solution with a second solution containing a dissolved counter-ion of the mineral and/or a second oppositely charged peptide amphiphile, results in the rapid self assembly of the peptide-amphiphiles into a nanofiber gel and templated mineralization of the ions. Templated mineralization of the initially dissolved mineral cations and anions in the mixture occurs with preferential orientation of the mineral crystals along the fiber surfaces within the nanofiber gel. One advantage of the present invention is that it results in homogenous growth of the mineral throughout the nanofiber gel. Another advantage of the present invention is that the nanofiber gel formation and mineralization reactions occur in a single mixing step and under substantially neutral or physiological pH conditions. These homogeneous nanostructured composite materials are useful for medical applications especially the regeneration of damaged bone in mammals. This invention is directed to the synthesis of peptide-amphiphiles with more than one amphiphilic moment and to supramolecular compositions comprised of such multi-dimensional peptide-amphiphiles. Supramolecular compositions can be formed by self assembly of multi-dimensional peptide-amphiphiles by mixing them with a solution comprising a monovalent cation.

  17. Investigation of bn-44 Peptide Fragments Using High Resolution Mass Spectrometry and Isotope Labeling

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Yu, Jiayi; Wang, Huixin; Wei, Zhonglin; Guo, Xinhua; Xiao, Zhaohui; Zeng, Zhoufang; Kong, Wei

    2014-12-01

    An N-terminal deuterohemin-containing hexapeptide (DhHP-6) was designed as a short peptide cytochrome c (Cyt c) mimetic to study the effect of N-terminal charge on peptide fragmentation pathways. This peptide gave different dissociation patterns than normal tryptic peptides. Upon collision-induced dissociation (CID) with an ion trap mass spectrometer, the singly charged peptide ion containing no added proton generated abundant and characteristic bn-44 ions instead of bn-28 (an) ions. Studies by high resolution mass spectrometry (HRMS) and isotope labeling indicate that elimination of 44 Da fragments from b ions occurs via two different pathways: (1) loss of CH3CHO (44.0262) from a Thr side chain; (2) loss of CO2 (43.9898) from the oxazolone structure in the C-terminus. A series of analogues were designed and analyzed. The experimental results combined with Density Functional Theory (DFT) calculations on the proton affinity of the deuteroporphyrin demonstrate that the production of these novel bn-44 ions is related to the N-terminal charge via a charge-remote rather than radical-directed fragmentation pathway.

  18. Antiferromagnetic resonance in charge ordering state of Pr 0.5Ca 0.5MnO 3- δ single crystal

    NASA Astrophysics Data System (ADS)

    Kawamata, S.; Noguchi, S.; Okuda, K.; Nojiri, H.; Motokawa, M.

    2001-05-01

    An antiferromagnetic resonance (AFMR) is observed in the charge ordered antiferromagnetic phase of Pr 0.5Ca 0.5MnO 3- δ single crystal for the first time. Above the Néel temperature, TN=173 K, a paramagnetic resonance with g=2.0 is observed. There is no significant change of the resonance spectra at the charge ordering transition temperature, TCO=242 K. Below TN, a branch of AFMR is found. Since the resonance field of this mode increases linearly as the frequency is decreased, this branch is assigned as the spin-flop mode. Below 60 K, the critical fields, BC, evaluated as the extrapolation of this mode to zero frequency agree well with the insulator-metal transition fields, BCO, at which the melting of the charge-ordering phase occurs. Present results indicate that the temperature dependence of BCO is affected by the temperature dependence of BC.

  19. Application of Peptide LC Retention Time Information in a Discriminant Function for Peptide Identification by Tandem Mass Spectrometry

    SciTech Connect

    Strittmatter, Eric F.; Kangas, Lars J.; Petritis, Konstantinos; Mottaz, Heather M.; Anderson, Gordon A.; Shen, Yufeng; Jacobs, Jon M.; Camp, David G.; Smith, Richard D.

    2004-07-09

    We describe the application of a peptide retention time reversed phase liquid chromatography (RPLC) prediction model previously reported (Petritis et al. Anal. Chem. 99, 2002, 11049) for improved peptide identification. The model uses peptide sequence information to generate a theoretical (predicted) elution time that can be compared with the observed elution time. Using data from a set of known proteins, the retention time parameter was incorporated into a discriminant function for use with tandem mass spectrometry (MS/MS) data analyzed with the peptide/protein identification program SEQUEST. For singly charged ions, the number of identifications increased by 12% when the elution time metric is included compared to when mass spectral data is the sole source of information in the context of a Drosophila melanogaster database. A 3-4% improvement was obtained for doubly and triply charged ions for the same biological system. Application to the larger Rattus norvegicus (rat) and human proteome databases resulted in an 8-9% overall increase in the number of identifications, when both the discriminant function and elution time are used. The effect of adding “runner-up” hits (peptide matches that are not the highest scoring for a spectra) from SEQUEST is also explored, and we find that the number of confident identifications is further increased when these hits are also considered. Finally, application of the discriminant functions derived in this work with ~2.2 million spectra from 330 LC-MS/MS analyses of peptides from human plasma protein resulted in a 19% increase in confident peptide identifications (9551 vs 8049) using elution time information. Further improvements from the use of elution time information can be expected as both the experimental control of elution time reproducibility and the predictive capability are improved.

  20. Single photon emission of a charge-tunable GaAs/Al{sub 0.25}Ga{sub 0.75}As droplet quantum dot device

    SciTech Connect

    Langer, Fabian Plischke, David; Kamp, Martin; Höfling, Sven

    2014-08-25

    In this work, we report the fabrication of a charge-tunable GaAs/Al{sub 0.25}Ga{sub 0.75}As quantum dot (QD) device containing QDs deposited by modified droplet epitaxy producing almost strain and composition gradient free QDs. We obtained a QD density in the low 10{sup 9 }cm{sup −2} range that enables us to perform spectroscopy on single droplet QDs showing linewidths as narrow as 40 μeV. The integration of the QDs into a Schottky diode allows us to controllably charge a single QD with up to four electrons, while non-classical photoluminescence is proven by photon auto-correlation measurements showing photon-antibunching (g{sup (2)}(0) = 0.05).

  1. Factors Affecting Peptide Interactions with Surface-Bound Microgels.

    PubMed

    Nyström, Lina; Nordström, Randi; Bramhill, Jane; Saunders, Brian R; Álvarez-Asencio, Rubén; Rutland, Mark W; Malmsten, Martin

    2016-02-01

    Effects of electrostatics and peptide size on peptide interactions with surface-bound microgels were investigated with ellipsometry, confocal microscopy, and atomic force microscopy (AFM). Results show that binding of cationic poly-L-lysine (pLys) to anionic, covalently immobilized, poly(ethyl acrylate-co-methacrylic acid) microgels increased with increasing peptide net charge and microgel charge density. Furthermore, peptide release was facilitated by decreasing either microgel or peptide charge density. Analogously, increasing ionic strength facilitated peptide release for short peptides. As a result of peptide binding, the surface-bound microgels displayed pronounced deswelling and increased mechanical rigidity, the latter quantified by quantitative nanomechanical mapping. While short pLys was found to penetrate the entire microgel network and to result in almost complete charge neutralization, larger peptides were partially excluded from the microgel network, forming an outer peptide layer on the microgels. As a result of this difference, microgel flattening was more influenced by the lower Mw peptide than the higher. Peptide-induced deswelling was found to be lower for higher Mw pLys, the latter effect not observed for the corresponding microgels in the dispersed state. While the effects of electrostatics on peptide loading and release were similar to those observed for dispersed microgels, there were thus considerable effects of the underlying surface on peptide-induced microgel deswelling, which need to be considered in the design of surface-bound microgels as carriers of peptide loads, for example, in drug delivery or in functionalized biomaterials. PMID:26750986

  2. Biosynthesis of a biologically active single peptide chain containing the human common alpha and chorionic gonadotropin beta subunits in tandem.

    PubMed Central

    Sugahara, T; Pixley, M R; Minami, S; Perlas, E; Ben-Menahem, D; Hsueh, A J; Boime, I

    1995-01-01

    One of the distinguishing features of the gonadotropin and thyrotropin hormone family is their heterodimeric structure, consisting of a common alpha subunit and a hormone-specific beta subunit. Subunit assembly is vital to the function of these hormones: The conformation of the heterodimer is essential for controlling secretion, hormone-specific posttranslational modifications, and signal transduction. To address whether alpha and beta subunits can be synthesized as one chain and also maintain biological activity, a chimera composed of the human chorionic gonadotropin (hCG) beta subunit genetically fused to the alpha subunit was constructed. The resulting polypeptide hCG molecule not only was efficiently secreted but also displayed an increased biological activity in vitro and in vivo. These data show that the alpha and hCG beta subunits encoded as a single chain retain a biologically active conformation similar to that seen in the heterodimer. This approach can be used to investigate structure-function relationships of the glycoprotein hormone family that were previously not tractable because of the absolute dependence on assembly for the biological response. Moreover, other bioactive multisubunit ligands can be engineered where the combination efficiency and specificity of heterodimers and homodimers are otherwise difficult to control. Images Fig. 2 Fig. 3 PMID:7892221

  3. Inclusive cross sections for pairs of identified light charged hadrons and for single protons in e+e- at √{s }=10.58 GeV

    NASA Astrophysics Data System (ADS)

    Seidl, R.; Abdesselam, A.; Adachi, I.; Aihara, H.; Al Said, S.; Asner, D. M.; Aushev, T.; Ayad, R.; Babu, V.; Badhrees, I.; Bakich, A. M.; Barberio, E.; Bhardwaj, V.; Bhuyan, B.; Biswal, J.; Bozek, A.; Bračko, M.; Browder, T. E.; Červenkov, D.; Chekelian, V.; Chen, A.; Cheon, B. G.; Chilikin, K.; Cho, K.; Chobanova, V.; Choi, Y.; Cinabro, D.; Dalseno, J.; Dash, N.; Dingfelder, J.; Doležal, Z.; Drásal, Z.; Dutta, D.; Eidelman, S.; Farhat, H.; Fast, J. E.; Ferber, T.; Fulsom, B. G.; Gaur, V.; Gabyshev, N.; Garmash, A.; Gillard, R.; Giordano, F.; Goh, Y. M.; Goldenzweig, P.; Golob, B.; Haba, J.; Hara, T.; Hayasaka, K.; Hayashii, H.; He, X. H.; Hou, W.-S.; Hsu, C.-L.; Iijima, T.; Inami, K.; Ishikawa, A.; Itoh, R.; Iwasaki, Y.; Jacobs, W. W.; Jaegle, I.; Joffe, D.; Joo, K. K.; Kang, K. H.; Kato, E.; Katrenko, P.; Kawasaki, T.; Kim, D. Y.; Kim, H. J.; Kim, J. B.; Kim, J. H.; Kim, K. T.; Kim, M. J.; Kim, S. H.; Kim, Y. J.; Kodyš, P.; Korpar, S.; Križan, P.; Krokovny, P.; Kuzmin, A.; Kwon, Y.-J.; Lange, J. S.; Lee, D. H.; Li, L.; Li Gioi, L.; Libby, J.; Liu, Y.; Liventsev, D.; Lukin, P.; Masuda, M.; Matvienko, D.; Miyabayashi, K.; Miyake, H.; Miyata, H.; Mizuk, R.; Mohanty, S.; Moll, A.; Moon, H. K.; Mori, T.; Mussa, R.; Nakano, E.; Nakao, M.; Nanut, T.; Natkaniec, Z.; Nayak, M.; Niiyama, M.; Nisar, N. K.; Nishida, S.; Ogawa, S.; Okuno, S.; Oswald, C.; Pakhlov, P.; Pakhlova, G.; Pal, B.; Park, C. W.; Park, H.; Pedlar, T. K.; Pestotnik, R.; Petrič, M.; Piilonen, L. E.; Ribežl, E.; Ritter, M.; Rostomyan, A.; Ryu, S.; Sahoo, H.; Sakai, K.; Sakai, Y.; Sandilya, S.; Santelj, L.; Sanuki, T.; Savinov, V.; Schneider, O.; Schnell, G.; Schwanda, C.; Seino, Y.; Senyo, K.; Seon, O.; Sevior, M. E.; Shebalin, V.; Shibata, T.-A.; Shiu, J.-G.; Simon, F.; Sohn, Y.-S.; Sokolov, A.; Solovieva, E.; Starič, M.; Sumihama, M.; Sumisawa, K.; Sumiyoshi, T.; Tamponi, U.; Teramoto, Y.; Trusov, V.; Uchida, M.; Uglov, T.; Unno, Y.; Uno, S.; Usov, Y.; Van Hulse, C.; Vanhoefer, P.; Varner, G.; Vorobyev, V.; Vossen, A.; Wagner, M. N.; Wang, C. H.; Wang, M.-Z.; Wang, P.; Watanabe, M.; Watanabe, Y.; Williams, K. M.; Won, E.; Yamaoka, J.; Yashchenko, S.; Yelton, J.; Yusa, Y.; Zhang, Z. P.; Zhilich, V.; Zhulanov, V.; Belle Collaboration

    2015-11-01

    We report the first double differential cross sections of two charged pions and kaons (e+e-→h h X ) in electron-positron annihilation as a function of the fractional energies of the two hadrons for any charge and hadron combination. The dependence of these dihadron cross sections on the topology (same, opposite hemisphere or anywhere) is also studied with the help of the event shape variable thrust and its axis. The ratios of these dihadron cross sections for different charges and hadron combinations directly shed light on the contributing fragmentation functions. For example, we find that the ratio of same-sign pion pairs over opposite-sign pion pairs drops toward higher fractional energies where disfavored fragmentation is expected to be suppressed. These dihadron results are obtained from a 655 fb-1 data sample collected near the ϒ (4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. Extending the previously published single-pion and single-kaon cross sections, single-proton (e+e-→p X ) cross sections are extracted from a 159 fb-1 data subsample.

  4. Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ.

    PubMed

    García, Raúl; Herranz, M Ángeles; Leary, Edmund; González, M Teresa; Bollinger, Gabino Rubio; Bürkle, Marius; Zotti, Linda A; Asai, Yoshihiro; Pauly, Fabian; Cuevas, Juan Carlos; Agraït, Nicolás; Martín, Nazario

    2015-01-01

    We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a π-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10(-7) G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species. PMID:26199662

  5. Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ

    PubMed Central

    García, Raúl; Herranz, M Ángeles; González, M Teresa; Bollinger, Gabino Rubio; Bürkle, Marius; Zotti, Linda A; Asai, Yoshihiro; Pauly, Fabian; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-01-01

    Summary We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a π-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10−7 G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species. PMID:26199662

  6. Systematic screening of the cellular uptake of designed alpha-helix peptides.

    PubMed

    Usui, Kenji; Kikuchi, Takuya; Mie, Masayasu; Kobatake, Eiry; Mihara, Hisakazu

    2013-05-01

    The cellular penetration (CP) activity of functional molecules has attracted significant attention as one of the most promising new approaches for drug delivery. In particular, cell-penetrating peptides (CPPs) have been studied extensively in cellular engineering. Because there have been few large-scale systematic studies to identify peptide sequences with optimal CP activity or that are suitable for further applications in cell engineering, such as cell-specific penetration and cell-selective culture, we screened and compared the cellular uptake (CU) activity of 54 systematically designed α-helical peptides in HeLa cells. Furthermore, the CU activity of 24 designed peptides was examined in four cell lines using a cell fingerprinting technique and statistical approaches. The CU activities in various cells depended on amino acid residues of peptide sequences as well as charge, α-helical content and hydrophobicity of the peptides. Notably, the mutation of a single residue significantly altered the CU ability of a peptide, highlighting the variability of cell uptake mechanisms. Moreover, these results demonstrated the feasibility of cell-selective culture by conducting cell-selective permeation and death in cultures containing two cell types. These studies may lead to further peptide library design and screening for new classes of CPPs with useful functions. PMID:23498920

  7. Dragging human mesenchymal stem cells with the aid of supramolecular assemblies of single-walled carbon nanotubes, molecular magnets, and peptides in a magnetic field.

    PubMed

    de Paula, Ana Cláudia C; Sáfar, Gustavo A M; Góes, Alfredo M; Bemquerer, Marcelo P; Ribeiro, Marcos A; Stumpf, Humberto O

    2015-01-01

    Human adipose-derived stem cells (hASCs) are an attractive cell source for therapeutic applicability in diverse fields for the repair and regeneration of damaged or malfunctioning tissues and organs. There is a growing number of cell therapies using stem cells due to their characteristics of modulation of immune system and reduction of acute rejection. So a challenge in stem cells therapy is the delivery of cells to the organ of interest, a specific site. The aim of this paper was to investigate the effects of a supramolecular assembly composed of single-walled carbon nanotubes (SWCNT), molecular magnets (lawsone-Co-phenanthroline), and a synthetic peptide (FWYANHYWFHNAFWYANHYWFHNA) in the hASCs cultures. The hASCs were isolated, characterized, expanded, and cultured with the SWCNT supramolecular assembly (SWCNT-MA). The assembly developed did not impair the cell characteristics, viability, or proliferation. During growth, the cells were strongly attached to the assembly and they could be dragged by an applied magnetic field of less than 0.3 T. These assemblies were narrower than their related allotropic forms, that is, multiwalled carbon nanotubes, and they could therefore be used to guide cells through thin blood capillaries within the human body. This strategy seems to be useful as noninvasive and nontoxic stem cells delivery/guidance and tracking during cell therapy. PMID:25688350

  8. Dragging Human Mesenchymal Stem Cells with the Aid of Supramolecular Assemblies of Single-Walled Carbon Nanotubes, Molecular Magnets, and Peptides in a Magnetic Field

    PubMed Central

    de Paula, Ana Cláudia C.; Sáfar, Gustavo A. M.; Góes, Alfredo M.; Bemquerer, Marcelo P.; Ribeiro, Marcos A.; Stumpf, Humberto O.

    2015-01-01

    Human adipose-derived stem cells (hASCs) are an attractive cell source for therapeutic applicability in diverse fields for the repair and regeneration of damaged or malfunctioning tissues and organs. There is a growing number of cell therapies using stem cells due to their characteristics of modulation of immune system and reduction of acute rejection. So a challenge in stem cells therapy is the delivery of cells to the organ of interest, a specific site. The aim of this paper was to investigate the effects of a supramolecular assembly composed of single-walled carbon nanotubes (SWCNT), molecular magnets (lawsone-Co-phenanthroline), and a synthetic peptide (FWYANHYWFHNAFWYANHYWFHNA) in the hASCs cultures. The hASCs were isolated, characterized, expanded, and cultured with the SWCNT supramolecular assembly (SWCNT-MA). The assembly developed did not impair the cell characteristics, viability, or proliferation. During growth, the cells were strongly attached to the assembly and they could be dragged by an applied magnetic field of less than 0.3 T. These assemblies were narrower than their related allotropic forms, that is, multiwalled carbon nanotubes, and they could therefore be used to guide cells through thin blood capillaries within the human body. This strategy seems to be useful as noninvasive and nontoxic stem cells delivery/guidance and tracking during cell therapy. PMID:25688350

  9. Over 10,000 peptide identifications from the HeLa proteome by using single-shot capillary zone electrophoresis combined with tandem mass spectrometry.

    PubMed

    Sun, Liangliang; Hebert, Alexander S; Yan, Xiaojing; Zhao, Yimeng; Westphall, Michael S; Rush, Matthew J P; Zhu, Guijie; Champion, Matthew M; Coon, Joshua J; Dovichi, Norman J

    2014-12-01

    Capillary zone electrophoresis (CZE)-tandem mass spectrometry (MS/MS) has recently attracted attention as a tool for shotgun proteomics. However, its performance for this analysis has so far fallen far below that of reversed-phase liquid chromatography (RPLC)-MS/MS. The use of a CZE method with a wide separation window (up to 90 min) and high peak capacity (ca. 300) is reported. This method was coupled to an Orbitrap Fusion mass spectrometer through an electrokinetically pumped sheath-flow interface for the analysis of complex proteome digests. Single-shot CZE-MS/MS lead to the identification of over 10 000 peptides and 2100 proteins from a HeLa cell proteome digest in approximately 100 min. This performance is nearly an order of magnitude better than earlier CZE studies and is within a factor of two to four of the state-of-the-art nano ultrahigh-pressure LC system. PMID:25346227

  10. The Presence of a Single N-terminal Histidine Residue Enhances the Fusogenic Properties of a Membranotropic Peptide Derived from Herpes Simplex Virus Type 1 Glycoprotein H

    PubMed Central

    Galdiero, Stefania; Falanga, Annarita; Vitiello, Mariateresa; Raiola, Luca; Russo, Luigi; Pedone, Carlo; Isernia, Carla; Galdiero, Massimiliano

    2010-01-01

    Herpes simplex virus type 1 (HSV-1)-induced membrane fusion remains one of the most elusive mechanisms to be deciphered in viral entry. The structure resolution of glycoprotein gB has revealed the presence of fusogenic domains in this protein and pointed out the key role of gB in the entry mechanism of HSV-1. A second putative fusogenic glycoprotein is represented by the heterodimer comprising the membrane-anchored glycoprotein H (gH) and the small secreted glycoprotein L, which remains on the viral envelope in virtue of its non-covalent interaction with gH. Different domains scattered on the ectodomain of HSV-1 gH have been demonstrated to display membranotropic characteristics. The segment from amino acid 626 to 644 represents the most fusogenic region identified by studies with synthetic peptides and model membranes. Herein we have identified the minimal fusogenic sequence present on gH. An enlongation at the N terminus of a single histidine (His) has proved to profoundly increase the fusogenic activity of the original sequence. Nuclear magnetic resonance (NMR) studies have shown that the addition of the N-terminal His contributes to the formation and stabilization of an α-helical domain with high fusion propensity. PMID:20348105

  11. A single mutation in the hepta-peptide active site of Aspergillus niger PhyA phytase leads to myriad of biochemical changes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The active site motif of proteins belonging to ‘Histidine Acid Phosphatase’ (HAP) contains a hepta-peptide region, RHGXRXP. A close comparison among fungal and yeast HAPs has revealed the fourth residue of the hepta-peptide to be E instead of A, which is the case with A. niger phyA phytase. However,...

  12. Efficient Covalent Bond Formation in Gas-Phase Peptide-Peptide Ion Complexes with the Photoleucine Stapler.

    PubMed

    Shaffer, Christopher J; Andrikopoulos, Prokopis C; Řezáč, Jan; Rulíšek, Lubomír; Tureček, František

    2016-04-01

    Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* n L m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N2 from the L* diazirine rings underwent insertion into X-H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific (13)C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)(+) ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H](+) ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide-peptide ion interactions in the gas phase. Graphical Abstract ᅟ. PMID:26817657

  13. Efficient Covalent Bond Formation in Gas-Phase Peptide-Peptide Ion Complexes with the Photoleucine Stapler

    NASA Astrophysics Data System (ADS)

    Shaffer, Christopher J.; Andrikopoulos, Prokopis C.; Řezáč, Jan; Rulíšek, Lubomír; Tureček, František

    2016-04-01

    Noncovalent complexes of hydrophobic peptides GLLLG and GLLLK with photoleucine (L*) tagged peptides G(L* n L m )K (n = 1,3, m = 2,0) were generated as singly charged ions in the gas phase and probed by photodissociation at 355 nm. Carbene intermediates produced by photodissociative loss of N2 from the L* diazirine rings underwent insertion into X-H bonds of the target peptide moiety, forming covalent adducts with yields reaching 30%. Gas-phase sequencing of the covalent adducts revealed preferred bond formation at the C-terminal residue of the target peptide. Site-selective carbene insertion was achieved by placing the L* residue in different positions along the photopeptide chain, and the residues in the target peptide undergoing carbene insertion were identified by gas-phase ion sequencing that was aided by specific 13C labeling. Density functional theory calculations indicated that noncovalent binding to GL*L*L*K resulted in substantial changes of the (GLLLK + H)+ ground state conformation. The peptide moieties in [GL*L*LK + GLLLK + H]+ ion complexes were held together by hydrogen bonds, whereas dispersion interactions of the nonpolar groups were only secondary in ground-state 0 K structures. Born-Oppenheimer molecular dynamics for 100 ps trajectories of several different conformers at the 310 K laboratory temperature showed that noncovalent complexes developed multiple, residue-specific contacts between the diazirine carbons and GLLLK residues. The calculations pointed to the substantial fluidity of the nonpolar side chains in the complexes. Diazirine photochemistry in combination with Born-Oppenheimer molecular dynamics is a promising tool for investigations of peptide-peptide ion interactions in the gas phase.

  14. Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices.

    PubMed

    Allen, Christopher S; Liu, Guoquan; Chen, Yabin; Robertson, Alex W; He, Kuang; Porfyrakis, Kyriakos; Zhang, Jin; Briggs, G Andrew D; Warner, Jamie H

    2014-01-01

    In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G(+) peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm(-1) and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm(-1). PMID:24241690

  15. Reactive Center Loop (RCL) Peptides Derived from Serpins Display Independent Coagulation and Immune Modulating Activities.

    PubMed

    Ambadapadi, Sriram; Munuswamy-Ramanujam, Ganesh; Zheng, Donghang; Sullivan, Colin; Dai, Erbin; Morshed, Sufi; McFadden, Baron; Feldman, Emily; Pinard, Melissa; McKenna, Robert; Tibbetts, Scott; Lucas, Alexandra

    2016-02-01

    Serpins regulate coagulation and inflammation, binding serine proteases in suicide-inhibitory complexes. Target proteases cleave the serpin reactive center loop scissile P1-P1' bond, resulting in serpin-protease suicide-inhibitory complexes. This inhibition requires a near full-length serpin sequence. Myxomavirus Serp-1 inhibits thrombolytic and thrombotic proteases, whereas mammalian neuroserpin (NSP) inhibits only thrombolytic proteases. Both serpins markedly reduce arterial inflammation and plaque in rodent models after single dose infusion. In contrast, Serp-1 but not NSP improves survival in a lethal murine gammaherpesvirus68 (MHV68) infection in interferon γ-receptor-deficient mice (IFNγR(-/-)). Serp-1 has also been successfully tested in a Phase 2a clinical trial. We postulated that proteolytic cleavage of the reactive center loop produces active peptide derivatives with expanded function. Eight peptides encompassing predicted protease cleavage sites for Serp-1 and NSP were synthesized and tested for inhibitory function in vitro and in vivo. In engrafted aorta, selected peptides containing Arg or Arg-Asn, not Arg-Met, with a 0 or +1 charge, significantly reduced plaque. Conversely, S-6 a hydrophobic peptide of NSP, lacking Arg or Arg-Asn with -4 charge, induced early thrombosis and mortality. S-1 and S-6 also significantly reduced CD11b(+) monocyte counts in mouse splenocytes. S-1 peptide had increased efficacy in plasminogen activator inhibitor-1 serpin-deficient transplants. Plaque reduction correlated with mononuclear cell activation. In a separate study, Serp-1 peptide S-7 improved survival in the MHV68 vasculitis model, whereas an inverse S-7 peptide was inactive. Reactive center peptides derived from Serp-1 and NSP with suitable charge and hydrophobicity have the potential to extend immunomodulatory functions of serpins. PMID:26620556

  16. Search for a heavy charged Higgs boson decaying to tb in the single lepton final state at CMS

    NASA Astrophysics Data System (ADS)

    Garabedian, Alex; CMS Collaboration

    2015-04-01

    A possible extension to the Standard Model (SM) of particle physics would be to introduce a second Higgs Doublet. In such an extension, a total of five Higgs particles would exist: two of which are electrically charged. We present the search for charged Higgs bosons, being produced in association with a top quark and itself decaying into a top-bottom quark pair. Furthermore, we focus on the semi-leptonic channel where one top quark decays hadronically and the other leptonically. Results will be shown using the full 8TeV dataset collected at the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC).

  17. Concepts for Biologically Active Peptides

    PubMed Central

    Kastin, Abba J.; Pan, Weihong

    2012-01-01

    Here we review a unique aspect of CNS research on biologically active peptides that started against a background of prevalent dogmas but ended by exerting considerable influence on the field. During the course of refuting some doctrines, we introduced several concepts that were unconventional and paradigm-shifting at the time. We showed that (1) hypothalamic peptides can act ‘up’ on the brain as well as ‘down’ on the pituitary, (2) peripheral peptides can affect the brain, (3) peptides can cross the blood-brain barrier, (4) the actions of peptides can persist longer than their half-lives in blood, (5) perinatal administration of peptides can exert actions persisting into adulthood, (6) a single peptide can have more than one action, (7) dose-response relationships of peptides need not be linear, (8) the brain produces antiopiate as well as opiate peptides, (9) there is a selective high affinity endogenous peptide ligand for the mu-opiate receptor, (10) a peptide’s name does not restrict its effects, and (11) astrocytes assume an active role in response to metabolic disturbance and hyperleptinemia. The evolving questions in our laboratories reflect the diligent effort of the neuropeptide community to identify the roles of peptides in the CNS. The next decade is expected to see greater progress in the following areas: (a) interactions of peptides with other molecules in the CNS; (b) peptide involvement in cell-cell interactions; and (c) peptides in neuropsychiatric, autoimmune, and neurodegenerative diseases. The development of peptidomics and gene silencing approaches will expedite the formation of many new concepts in a new era. PMID:20726835

  18. Proline-15 creates an amphipathic wedge in maculatin 1.1 peptides that drives lipid membrane disruption.

    PubMed

    Sani, Marc-Antoine; Lee, Tzong-Hsien; Aguilar, Marie-Isabel; Separovic, Frances

    2015-10-01

    The membrane interaction of peptides derived from maculatin 1.1 and caerin 1.1, with the sequence motif of N and C termini of maculatin 1.1, was compared in order to understand the role of these common sequence motifs, which encompass critical proline residues, on peptide secondary structure and on membrane binding and disruption in zwitterionic and anionic membranes. The peptides incorporated a single substitution with lysine or deletion of the central region to mimic the length of the antimicrobial peptides, citropin 1.1 and aurein 1.2. The impact of these changes in the sequence, length and physicochemical properties, on lytic activity and structure was assessed by dye-release from lipid vesicles and the change in the bilayer order as a function of membrane-bound peptide mass. All peptides adopted similar degrees of helical structure in both membrane systems. In addition, all peptide analogues were less active than either maculatin 1.1 or caerin 1.1 in dye release assays. The membrane binding was analyzed by dual polarization interferometry and the results showed that membrane binding was significantly affected by changes in the hydrophobic environment of Pro-15. Moreover, changes in the relative distribution of charge and hydrophobicity flanking Pro-15 also caused significant changes to the membrane order. Overall, the proline residue plays an important role in inducing a peptide structure that enhances the activity of these antimicrobial peptides. PMID:26079051

  19. Investigation of pyroelectric phenomenon in TGS single crystals - A new method using a digital pyroelectric charge meter

    NASA Astrophysics Data System (ADS)

    Trybus, M.; Proszak, W.; Woś, B.

    2011-07-01

    A new method for the precise measurements of pyroelectric effect is presented. The paper contains the design and implementation of pyroelectric charge measurement system using compensation method with digital control. The system was assembled, calibrated and used in measurements of the pyroelectric effect. Results were compared with measurements made using traditional static methods for the same samples.

  20. The physics of a single-event upset in integrated circuits: A review and critique of analytical models for charge collection

    NASA Technical Reports Server (NTRS)

    Vonroos, O.; Zoutendyk, J.

    1983-01-01

    When an energetic particle (kinetic energy 0.5 MeV) originating from a radioactive decay or a cosmic ray transverse the active regions of semiconductor devices used in integrated circuit (IC) chips, it leaves along its track a high density electron hole plasma. The subsequent decay of this plasma by drift and diffusion leads to charge collection at the electrodes large enough in most cases to engender a false reading, hence the name single-event upset (SEU). The problem of SEU's is particularly severe within the harsh environment of Jupiter's radiation belts and constitutes therefore a matter of concern for the Galileo mission. The physics of an SEU event is analyzed in some detail. Owing to the predominance of nonlinear space charge effects and the fact that positive (holes) and negative (electrons) charges must be treated on an equal footing, analytical models for the ionized-charge collection and their corresponding currents as a function of time prove to be inadequate even in the simplest case of uniformly doped, abrupt p-n junctions in a one-dimensional geometry. The necessity for full-fledged computer simulation of the pertinent equations governing the electron-hole plasma therefore becomes imperative.

  1. Modeling the Interaction between Integrin-Binding Peptide (RGD) and Rutile Surface: The Effect of Na+ on Peptide Adsorption

    SciTech Connect

    Wu, Chunya; Skelton, Adam; Chen, Mingjun; Vlcek, Lukas; Cummings, Peter T

    2011-01-01

    The dynamics of a single tripeptide Arg-Gly-Asp (RGD) adsorbing onto negatively charged hydroxylated rutile (110) surface in aqueous solution was studied using molecular dynamics (MD) simulations. The results indicate that the adsorbed Na{sup +} ions play an important role in determining the binding geometry of RGD. With an initial 'horseshoe' configuration, the charged side groups (COO{sup -} and NH{sub 2}) of the peptide are able to interact with the surface through direct hydrogen bonds (H bonds) in the very early stage of adsorption. The Na{sup +} ions approach the positively charged Arg side chain, competing with the Arg side chain for adsorption to the negatively charged hydroxyl oxygen. In coordination with the structural adjustment of the peptide, the Arg residue is driven to detach from the rutile surface. In contrast, the Na+ ions in close proximity to the negatively charged Asp side chain contribute to the binding of the COO{sup -} group on the surface, helping the carboxyl oxygen not involved in COO{sup -}-surface H bonds to orientate toward the hydroxyl hydrogens. Once both carboxyl oxygens form enough H bonds with the hydroxyl hydrogens, the redundant ions move toward a more favorable adsorption site.

  2. Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices

    NASA Astrophysics Data System (ADS)

    Allen, Christopher S.; Liu, Guoquan; Chen, Yabin; Robertson, Alex W.; He, Kuang; Porfyrakis, Kyriakos; Zhang, Jin; Briggs, G. Andrew D.; Warner, Jamie H.

    2013-12-01

    In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G+ peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm-1 and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm-1.In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G+ peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm-1 and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm-1. Electronic supplementary information (ESI) available: AFM line scans of the substrate before and after functionalization; scheme for measuring amorphous carbon coverage from TEM images; diameter comparisons of ac-TEM image and simulation of C60 molecule; Raman spectra D peak comparison; optical response of transfer properties of pristine devices; comparison between swept and pulsed Vg measurements

  3. Magnetic Field Induced Charged Exciton Studies in a GaAs/Al(0.3)Ga(0.7)As Single Heterojunction

    SciTech Connect

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

    1999-05-25

    The magnetophotoluminescence (MPL) behavior of a GaAs/Al0.3Ga0.7As single heterojunction has been investigated to 60T. We observed negatively charged singlet and triplet exciton states that are formed at high magnetic fields beyond the {nu}=l quantum Hall state. The variation of the charged exciton binding energies are in good agreement with theoretical predictions. The MPL transition intensities for these states showed intensity variations (maxima and minima) at the {nu}=l/3 and 1/5 fractional quantum Hall (FQH) state as a consequence of a large reduction of electron-hole screening at these filling factors.

  4. Charge-carrier mobilities in Cd(0.8)Zn(0.2)Te single crystals used as nuclear radiation detectors

    NASA Technical Reports Server (NTRS)

    Burshtein, Z.; Jayatirtha, H. N.; Burger, A.; Butler, J. F.; Apotovsky, B.; Doty, F. P.

    1993-01-01

    Charge-carrier mobilities were measured for the first time in Cd(0.8)Zn(0.2)Te single crystals using time-of-flight measurements of charge carriers produced by short (10 ns) light pulses from a frequency-doubled Nd:YAG laser (532 nm). The electron mobility displayed a T exp -1.1 dependence on the absolute temperature T in the range 200-320 K, with a room-temperature mobility of 1350 sq cm/V s. The hole mobility displayed a T exp -2.0 dependence in the same temperature range, with a room-temperature mobility of 120 sq cm/V s. Cd(0.8)Zn(0.2)Te appears to be a very favorable material for a room-temperature electronic nuclear radiation detector.

  5. Delocalized and localized charged excitons in single CdSe/CdS dot-in-rods revealed by polarized photoluminescence blinking

    NASA Astrophysics Data System (ADS)

    Ihara, Toshiyuki; Sato, Ryota; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

    2014-07-01

    CdSe/CdS heterostructured nanocrystals with quasi-type-II band alignments provide an interesting platform for studying the photoluminescence (PL) blinking associated with their unique morphologies. By using simultaneous measurements of the PL intensity, lifetime, and polarization anisotropy, we reveal the role of the electron delocalization during the blinking of single CdSe/CdS dot-in-rods. We found that a significant change in the PL polarization anisotropy distinguishes between two kinds of charged excitons with different electron delocalizations. We report our observation of unique polarized PL blinking governed by the band alignments and the Coulomb interactions between the charges inside and outside the dot-in-rod.

  6. AMG 416 (velcalcetide) is a novel peptide for the treatment of secondary hyperparathyroidism in a single-dose study in hemodialysis patients.

    PubMed

    Martin, Kevin J; Pickthorn, Karen; Huang, Saling; Block, Geoffrey A; Vick, Andrew; Mount, Peter F; Power, David A; Bell, Gregory

    2014-01-01

    AMG 416 (velcalcetide), a novel peptide agonist of the calcium-sensing receptor, lowers plasma parathyroid hormone in preclinical uremic animal models and in normal healthy individuals. Here, we studied its efficacy in hemodialysis patients suffering from secondary hyperparathyroidism. Major inclusion criteria were hemodialysis for at least 3 months, serum parathyroid hormone over 300 pg/ml, a corrected serum calcium of 9.0 mg/dl or more, and stable doses of vitamin D analogs for at least 3 weeks prior to screening. Twenty-eight patients were enrolled in one of five cohorts (5, 10, 20, 40, 60 mg). Cohorts 1-3 (four patients each) were treated in a two-period crossover design, while cohorts 4 and 5 (eight patients each) were randomized 1:1 to AMG 416 or placebo. Patients were admitted to a clinical research unit following hemodialysis and studied for 3 days prior to discharge for hemodialysis. Single intravenous doses of AMG 416 from 5 to 60 mg were well tolerated, and plasma levels increased in a dose-related manner. AMG 416 treatment was associated with significant, dose-dependent reductions in serum parathyroid hormone and fibroblast growth factor 23. Compared with placebo, all dose groups of 10 mg or more were associated with attenuation in the rise in serum phosphate during the interdialytic period. Dose-dependent reductions in serum calcium were observed and were well tolerated. Thus, AMG 416 represents a novel therapeutic approach for the treatment of secondary hyperparathyroidism in hemodialysis patients. PMID:23903371

  7. A mechanism of charge transport in electroluminescent structures consisting of porous silicon and single-crystal silicon

    SciTech Connect

    Evtukh, A. A. Kaganovich, E. B.; Manoilov, E. G.; Semenenko, N. A.

    2006-02-15

    Electroluminescent structures that emit in the visible region of the spectrum and are based on porous silicon (por-Si) formed on the p-Si substrate electrolytically using an internal current source are fabricated. The photoluminescent and electroluminescent properties, as well as the current-and capacitance-voltage characteristics of the structures are studied. Electroluminescence is observed only if the forward bias voltage is applied to the structure; the electroluminescence mechanism is based on the injection and is related to the radiative recombination of electrons and holes in quantum-dimensional Si nanocrystals. The injection of holes is controlled by the condition of their accumulation in the space-charge region of p-Si and by a comparatively low concentration of electronic states at the por-Si/p-Si interface. The charge transport in por-Si is caused by the direct tunneling of charge carriers between the quantum-mechanical levels, which is ensured by an appreciable number of quantum-dimensional Si nanocrystals. The leakage currents are low as a result of a small variance in the sizes of Si nanocrystals and the absence of comparatively large nanocrystals.

  8. The Impact of Interlayer Electronic Coupling on Charge Transport in Organic Semiconductors: A Case Study on Titanylphthalocyanine Single Crystals.

    PubMed

    Zhang, Zongpeng; Jiang, Lang; Cheng, Changli; Zhen, Yonggang; Zhao, Guangyao; Geng, Hua; Yi, Yuanping; Li, Liqiang; Dong, Huanli; Shuai, Zhigang; Hu, Wenping

    2016-04-18

    Traditionally, it is believed that three-dimensional transport networks are preferable to those of lower dimensions. We demonstrate that inter-layer electronic couplings may result in a drastic decrease of charge mobilities by utilizing field-effect transistors (FET) based on two phases of titanyl phthalocyanine (TiOPc) crystals. The α-phase crystals with electronic couplings along two dimensions show a maximum mobility up to 26.8 cm(2)  V(-1)  s(-1) . In sharp contrast, the β-phase crystals with extra significant inter-layer electronic couplings show a maximum mobility of only 0.1 cm(2)  V(-1)  s(-1) . Theoretical calculations on the bulk crystals and model slabs reveal that the inter-layer electronic couplings for the β-phase devices will diminish remarkably the device charge transport abilities owing to the coupling direction perpendicular to the current direction. This work provides new insights into the impact of the dimensionality and directionality of the packing arrangements on charge transport in organic semiconductors. PMID:26990048

  9. Effects of peptide acetylation and dimethylation on electrospray ionization efficiency.

    PubMed

    Cho, Kyung-Cho; Kang, Jeong Won; Choi, Yuri; Kim, Tae Woo; Kim, Kwang Pyo

    2016-02-01

    Peptide acetylation and dimethylation have been widely used to derivatize primary amino groups (peptide N-termini and the ε-amino group of lysines) for chemical isotope labeling of quantitative proteomics or for affinity tag labeling for selection and enrichment of labeled peptides. However, peptide acetylation results in signal suppression during electrospray ionization (ESI) due to charge neutralization. In contrast, dimethylated peptides show increased ionization efficiency after derivatization, since dimethylation increases hydrophobicity and maintains a positive charge on the peptide under common LC conditions. In this study, we quantitatively compared the ESI efficiencies of acetylated and dimethylated model peptides and tryptic peptides of BSA. Dimethylated peptides showed higher ionization efficiency than acetylated peptides for both model peptides and tryptic BSA peptides. At the proteome level, peptide dimethylation led to better protein identification than peptide acetylation when tryptic peptides of mouse brain lysate were analyzed with LC-ESI-MS/MS. These results demonstrate that dimethylation of tryptic peptides enhanced ESI efficiency and provided up to two-fold improved protein identification sensitivity in comparison with acetylation. Copyright © 2016 John Wiley & Sons, Ltd. PMID:26889926

  10. Lack of Effects of a Single High-Fat Meal Enriched with Vegetable n-3 or a Combination of Vegetable and Marine n-3 Fatty Acids on Intestinal Peptide Release and Adipokines in Healthy Female Subjects

    PubMed Central

    Narverud, Ingunn; Myhrstad, Mari C. W.; Herzig, Karl-Heinz; Karhu, Toni; Dahl, Tuva B.; Halvorsen, Bente; Ulven, Stine M.; Holven, Kirsten B.

    2016-01-01

    Peptides released from the small intestine and colon regulate short-term food intake by suppressing appetite and inducing satiety. Intake of marine omega-3 (n-3) fatty acids (FAs) from fish and fish oils is associated with beneficial health effects, whereas the relation between intake of the vegetable n-3 fatty acid α-linolenic acid and diseases is less clear. The aim of the present study was to investigate the postprandial effects of a single high-fat meal enriched with vegetable n-3 or a combination of vegetable and marine n-3 FAs with their different unsaturated fatty acid composition on intestinal peptide release and the adipose tissue. Fourteen healthy lean females consumed three test meals with different fat quality in a fixed order. The test meal consisted of three cakes enriched with coconut fat, linseed oil, and a combination of linseed and cod liver oil. The test days were separated by 2 weeks. Fasting and postprandial blood samples at 3 and 6 h after intake were analyzed. A significant postprandial effect was observed for cholecystokinin, peptide YY, glucose-dependent insulinotropic polypeptide, amylin and insulin, which increased, while leptin decreased postprandially independent of the fat composition in the high-fat meal. In conclusion, in healthy, young, lean females, an intake of a high-fat meal enriched with n-3 FAs from different origin stimulates intestinal peptide release without any difference between the different fat compositions.

  11. Analysis of Neutron and Singly Charged Particle Multiplicities Induced by Collision of 4.5A GeV/c 16O with Emulsion Nuclei

    SciTech Connect

    El-Nagdy, M.S.; Abdel-Halim, S.M.; Nabil Yasin, M.

    2005-03-17

    The analysis of neutron n and singly charged particle Q=1 participated from 16O at 4.5A GeV/c interactions with emulsion nuclei are presented. The average multiplicities of shower particle for n and Q=1 stay more or less constant when compared with analogous data on P-A at similar momentum. The multiplicity distributions as well as the average values of the various secondary particles are studied, discussed and compared with the calculations according cascade evaporation model. The results lead to assume that the n and Q=1 from 16O tend to collide peripherally with target emulsion or in other words to make gentle reactions.

  12. Calculation of the acid-base equilibrium constants at the alumina/electrolyte interface from the ph dependence of the adsorption of singly charged ions (Na+, Cl-)

    NASA Astrophysics Data System (ADS)

    Gololobova, E. G.; Gorichev, I. G.; Lainer, Yu. A.; Skvortsova, I. V.

    2011-05-01

    A procedure was proposed for the calculation of the acid-base equilibrium constants at an alumina/electrolyte interface from experimental data on the adsorption of singly charged ions (Na+, Cl-) at various pH values. The calculated constants (p K {1/0}= 4.1, p K {2/0}= 11.9, p K {3/0}= 8.3, and p K {4/0}= 7.7) are shown to agree with the values obtained from an experimental pH dependence of the electrokinetic potential and the results of potentiometric titration of Al2O3 suspensions.

  13. Cell-Penetrating HIV1 TAT Peptides Can Generate Pores in Model Membranes

    PubMed Central

    Ciobanasu, Corina; Siebrasse, Jan Peter; Kubitscheck, Ulrich

    2010-01-01

    Abstract Cell-penetrating peptides like the cationic human immunodeficiency virus-1 trans-acting activator of transcription (TAT) peptide have the capability to traverse cell membranes and to deliver large molecular cargoes into the cellular interior. We used optical sectioning and state-of-the-art single-molecule microscopy to examine the passive membrane permeation of fluorescently labeled TAT peptides across the membranes of giant unilamellar vesicles (GUVs). In GUVs formed by phosphatidylcholine and cholesterol only, no translocation of TAT up to a concentration of 2 μM into the GUVs could be observed. At the same peptide concentration, but with 40 mol % of anionic phosphatidylserine in the membrane, rapid translocation of TAT peptides across the bilayers was detected. Efficient translocation of TAT peptides was observed across GUVs containing 20 mol % of phosphatidylethanolamine, which is known to induce a negative curvature into membranes. We discovered that TAT peptides are not only capable of penetrating membranes directly in a passive manner, but they were also able to form physical pores with sizes in the nanometer range, which could be passed by small dye tracer molecules. Lipid topology and anionic charge of the lipid bilayer are decisive parameters for pore formation. PMID:20655843

  14. Protein quantification by MALDI-selected reaction monitoring mass spectrometry using sulfonate derivatized peptides.

    PubMed

    Lesur, Antoine; Varesio, Emmanuel; Hopfgartner, Gérard

    2010-06-15

    The feasibility of protein absolute quantification with matrix-assisted laser desorption/ionization (MALDI) using the selected reaction monitoring (SRM) acquisition mode on a triple quadrupole linear ion trap mass spectrometer (QqQ(LIT)) equipped with a high-frequency laser is demonstrated. A therapeutic human monoclonal antibody (mAb) was used as a model protein, and four tryptic peptides generated by fast tryptic digestion were selected as quantification surrogates. MALDI produces mostly singly charged peptides which hardly fragment under low-energy collision-induced dissociation (CID), and therefore the benefits of using 4-sulfophenyl isothiocyanate (SPITC) as a fragmentation enhancer derivatization agent were evaluated. Despite a moderate impact on the sensitivity, the N-terminus sulfonated peptides generate nearly complete y-ion ladders when native peptides produce few fragments. This aspect provides an alternative SRM transition set for each peptide. As a consequence, SRM transitions selectivity can be tuned more easily for peptide quantitation in complex matrices when monitoring several SRM transitions. From a quantitative point of view, the signal response depending on mAb concentration was found to be linear over 2.5 orders of magnitude for the most sensitive peptide, allowing precise and accurate measurement by MALDI-SRM/MS. PMID:20481516

  15. Effects of crystallographic facet-specific peptide adsorption along single ZnO nanorods on the characteristic fluorescence intensification on nanorod ends (FINE) phenomenon.

    PubMed

    Singh, Manpreet; Zhuo, Xiaolu; Choi, Daniel S; Gonzalez, Lorelis E; Wang, Jianfang; Hahm, Jong-in

    2015-11-28

    The precise effect of crystallographically discriminating biomolecular adsorption on the fluorescence intensification profiles of individual zinc oxide nanorod (ZnO NR) platforms was elucidated in this study by employing peptide binding epitopes biased towards particular ZnO crystal surfaces and isolating the peptides on given crystalline facets of ZnO NRs. Subsequently, the fluorescence emission profiles of the preferentially bound peptide cases on the basal versus prismic planes of ZnO NRs were carefully evaluated both experimentally and via computer simulations. The phenomenon of fluorescence intensification on NR ends (FINE) was persistently observed on the individual ZnO NR platforms, regardless of the location of the bound peptides. In contrast to the consistent occurrence of FINE, the degree and magnitude of FINE were largely influenced by the discriminatory peptide adsorption to different ZnO NR facets. The temporal stability of the fluorescence signal