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Sample records for photoactive tungsten disulfide

  1. Monolayer Tungsten Disulfide Laser

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Wong, Zi Jing; Lu, Xiufang; Ni, Xingjie; Zhu, Hanyu; Chen, Xianhui; Wang, Yuan; Zhang, Xiang

    Two-dimensional van der Waals materials have opened a new paradigm for fundamental physics exploration and device applications because of their emerging physical properties. Unlike gapless graphene, monolayer transition-metal dichalcogenides are two-dimensional semiconductors that undergo an indirect-to-direct band gap transition, creating new optical functionalities for next-generation ultra-compact photonics and optoelectronics. Here, we report the realization of a two-dimensional excitonic laser by embedding monolayer tungsten disulfide in a microdisk resonator.

  2. Ferromagnetism in exfoliated tungsten disulfide nanosheets

    PubMed Central

    2013-01-01

    Two-dimensional-layered transition metal dichalcogenides nanosheets have attracted tremendous attention for their promising applications in spintronics because the atomic-thick nanosheets can not only enhance the intrinsic properties of their bulk counterparts, but also give birth to new promising properties. In this paper, ultrathin tungsten disulfide (WS2) nanosheets were gotten by liquid exfoliation route from its bulk form using dimethylformamide (DMF). Compared to the antiferromagnetism bulk WS2, ultrathin WS2 nanosheets show intrinsic room-temperature ferromagnetism (FM) with the maximized saturation magnetization of 0.004 emu/g at 10 K, where the appearance of FM in the nanosheets is partly due to the presence of zigzag edges in the magnetic ground state at the grain boundaries. PMID:24134699

  3. Observation of two distinct negative trions in tungsten disulfide monolayers

    DOE PAGESBeta

    Boulesbaa, Abdelaziz; Huang, Bing; Wang, Kai; Lin, Ming-Wei; Mahjouri-Samani, Masoud; Rouleau, Christopher M.; Xiao, Kai; Yoon, Mina; Sumpter, Bobby G.; Puretzky, Alexander A.; et al

    2015-09-25

    We report on the observation of two distinct photogenerated negative trion states TA and TB in two-dimensional tungsten disulfide (2D-WS2) monolayers. These trions are postulated to emerge from their parent excitons XA and XB, which originate from spin-orbit-split (SOS) levels in the conduction band (CB) and valence band (VB). Time-resolved spectroscopy measurements suggests that Pauli blocking controls a competition process between TA and TB photoformation, following dissociation of XA and XB through hole trapping at internal or substrate defect sites. While TA arises directly from its parent XA, TB emerges through a different transition accessible only after XB dissociates throughmore » a hole trapping channel. This discovery of additional optically-active band-edge transitions in atomically-thin metal dichalcogenides may revolutionize optoelectronic applications and fundamental research opportunities for many-body interaction physics. Ultrafast pump-probe spectroscopy of two-dimensional tungsten disulfide monolayers (2D-WS2) grown on sapphire substrates revealed two transient absorption spectral peaks that are attributed to distinct negative trions at ~2.02 eV (T1) and ~1.98 eV (T2). The dynamics measurements indicate that trion formation by the probe is enabled by photodoped electrons that remain after trapping of holes from excitons or free electron-hole pairs at defect sites in the crystal or on the substrate. Dynamics of the excitons XA and XB’s characteristic absorption bands, at ~2.03 and ~2.40 eV, respectively, were separately monitored and compared with the photoinduced absorption features. Selective excitation of the lowest exciton level XA using λpump < 2.4 eV forms only trion T1, which implies that the electron that remains from the dissociation of exciton XA is involved in the creation of this trion with a binding energy ~ 10 meV with respect to XA. The absorption peak that corresponds to trion T2 appears when λpump > 2.4 eV, which is just

  4. Observation of two distinct negative trions in tungsten disulfide monolayers

    SciTech Connect

    Boulesbaa, Abdelaziz; Huang, Bing; Wang, Kai; Lin, Ming-Wei; Mahjouri-Samani, Masoud; Rouleau, Christopher M.; Xiao, Kai; Yoon, Mina; Sumpter, Bobby G.; Puretzky, Alexander A.; Geohegan, David B.

    2015-09-25

    We report on the observation of two distinct photogenerated negative trion states TA and TB in two-dimensional tungsten disulfide (2D-WS2) monolayers. These trions are postulated to emerge from their parent excitons XA and XB, which originate from spin-orbit-split (SOS) levels in the conduction band (CB) and valence band (VB). Time-resolved spectroscopy measurements suggests that Pauli blocking controls a competition process between TA and TB photoformation, following dissociation of XA and XB through hole trapping at internal or substrate defect sites. While TA arises directly from its parent XA, TB emerges through a different transition accessible only after XB dissociates through a hole trapping channel. This discovery of additional optically-active band-edge transitions in atomically-thin metal dichalcogenides may revolutionize optoelectronic applications and fundamental research opportunities for many-body interaction physics. Ultrafast pump-probe spectroscopy of two-dimensional tungsten disulfide monolayers (2D-WS2) grown on sapphire substrates revealed two transient absorption spectral peaks that are attributed to distinct negative trions at ~2.02 eV (T1) and ~1.98 eV (T2). The dynamics measurements indicate that trion formation by the probe is enabled by photodoped electrons that remain after trapping of holes from excitons or free electron-hole pairs at defect sites in the crystal or on the substrate. Dynamics of the excitons XA and XB’s characteristic absorption bands, at ~2.03 and ~2.40 eV, respectively, were separately monitored and compared with the photoinduced absorption features. Selective excitation of the lowest exciton level XA using λpump < 2.4 eV forms only trion T1, which implies that the electron that remains

  5. Nanoparticles synthesis of tungsten disulfide via AOT-based microemulsions

    SciTech Connect

    Ghoreishi, S.M.; Meshkat, S.S.; Ghiaci, M.; Dadkhah, A.A.

    2012-06-15

    Graphical abstract: A controlled synthesis of WS2 nanoparticles (most probably inorganic fullerene (IF)) via microemulsion was applied for the first time to prepare WS2 (7–12 nm) by acidification of the water cores of the AOT reverse microemulsion. Highlights: ► An innovative reverse microemulsion technique was developed for WS{sub 2} synthesis. ► WS{sub 2} nanoparticles were obtained with narrow size distribution in range of 7–12 nm. ► Operating cost of microemulsion was lower in contrast to quartz reactor method. ► WS{sub 2} morphology could be controlled to obtain highly active and selective catalysts. ► Lower size of WS{sub 2} in this study overcomes the shortcoming of quartz reactor method. -- Abstract: The tungsten disulfide (WS{sub 2}) nanoparticles (most probably inorganic fullerene (IF)) with a narrow size distribution were synthesized by a reverse micelle technique for the first time. The particle size was controlled by varying water-to-surfactant molar ratio (W{sub 0}), aging time and reagent concentration. The synthesized WS{sub 2} nanoparticles were characterized by zetasizer, UV–visible spectrophotometers and transmission electron microscopy (TEM). The WS{sub 2} nanoparticles with particle diameter size of 7–12 nm were obtained via 24 h aging time. The particle size was controlled by changing the aging time and molar ratio of water/surfactant. Doubling W{sub 0} increased the amount and particle size of WS{sub 2} by 22 and 26%, respectively. The effect of aging time in the range of 6–24 h was investigated and the complete disappearance of yellowish color at 24 h resulted in an optically clear solution, which was the indication of WS{sub 2} formation with 100% conversion of reactant ((NH{sub 4}){sub 2}WS{sub 4}) in the batch reactor.

  6. Tungsten disulfide nanotubes reinforced biodegradable polymers for bone tissue engineering.

    PubMed

    Lalwani, Gaurav; Henslee, Allan M; Farshid, Behzad; Parmar, Priyanka; Lin, Liangjun; Qin, Yi-Xian; Kasper, F Kurtis; Mikos, Antonios G; Sitharaman, Balaji

    2013-09-01

    In this study, we have investigated the efficacy of inorganic nanotubes as reinforcing agents to improve the mechanical properties of poly(propylene fumarate) (PPF) composites as a function of nanomaterial loading concentration (0.01-0.2 wt.%). Tungsten disulfide nanotubes (WSNTs) were used as reinforcing agents in the experimental group. Single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs) were used as positive controls, and crosslinked PPF composites were used as the baseline control. Mechanical testing (compression and three-point bending) shows a significant enhancement (up to 28-190%) in the mechanical properties (compressive modulus, compressive yield strength, flexural modulus and flexural yield strength) of WSNT-reinforced PPF nanocomposites compared to the baseline control. In comparison to the positive controls, significant improvements in the mechanical properties of WSNT nanocomposites were also observed at various concentrations. In general, the inorganic nanotubes (WSNTs) showed mechanical reinforcement better than (up to 127%) or equivalent to that of carbon nanotubes (SWCNTs and MWCNTs). Sol fraction analysis showed significant increases in the crosslinking density of PPF in the presence of WSNTs (0.01-0.2 wt.%). Transmission electron microscopy (TEM) analysis on thin sections of crosslinked nanocomposites showed the presence of WSNTs as individual nanotubes in the PPF matrix, whereas SWCNTs and MWCNTs existed as micron-sized aggregates. The trend in the surface area of nanostructures obtained by Brunauer-Emmett-Teller (BET) surface area analysis was SWCNTs>MWCNTs>WSNTs. The BET surface area analysis, TEM analysis and sol fraction analysis results taken together suggest that chemical composition (inorganic vs. carbon nanomaterials), the presence of functional groups (such as sulfide and oxysulfide) and individual dispersion of the nanomaterials in the polymer matrix (absence of aggregation of the reinforcing agent) are the key parameters

  7. Observation of two distinct negative trions in tungsten disulfide monolayers

    NASA Astrophysics Data System (ADS)

    Boulesbaa, Abdelaziz; Huang, Bing; Wang, Kai; Lin, Ming-Wei; Mahjouri-Samani, Masoud; Rouleau, Christopher; Xiao, Kai; Yoon, Mina; Sumpter, Bobby; Puretzky, Alexander; Geohegan, David

    2015-09-01

    Ultrafast pump-probe spectroscopy of two-dimensional tungsten disulfide monolayers (2 D W S2) grown on sapphire substrates revealed two transient absorption spectral peaks that are attributed to distinct negative trions at ˜2.02 eV (T1) and ˜1.98 eV (T2) . The dynamics measurements indicate that trion formation by the probe is enabled by photodoped 2D WS2 crystals with electrons remaining after trapping of holes from excitons or free electron-hole pairs at defect sites in the crystal or on the substrate. Dynamics of the characteristic absorption bands of excitons XA and XB at ˜2.03 and ˜2.40 eV , respectively, were separately monitored and compared to the photoinduced absorption features. Selective excitation of the lowest exciton level XA using λpump<2.4 eV forms only trion T1, implying that the electron remaining from dissociation of exciton XA is involved in the creation of this trion with a binding energy ˜10 meV with respect to XA. The absorption peak corresponding to trion T2 appears when λpump<2.4 eV , which is just sufficient to excite exciton XB. The dynamics of trion T2 formation are found to correlate with the disappearance of the bleach of the XB exciton, indicating the involvement of holes participating in the bleach dynamics of exciton XB. Static electrical-doping photoabsorption measurements confirm the presence of an induced absorption peak similar to that of T2. Since the proposed trion formation process here involves exciton dissociation through hole trapping by defects in the 2D crystal or substrate, this discovery highlights the strong role of defects in defining optical and electrical properties of 2D metal chalcogenides, which is relevant to a broad spectrum of basic science and technological applications.

  8. Tungsten Disulfide Nanotubes Reinforced Biodegradable Polymers for Bone Tissue Engineering

    PubMed Central

    Lalwani, Gaurav; Henslee, Allan M.; Farshid, Behzad; Parmar, Priyanka; Lin, Liangjun; Qin, Yi-Xian; Kasper, F. Kurtis; Mikos, Antonios G.; Sitharaman, Balaji

    2013-01-01

    In this study, we have investigated the efficacy of inorganic nanotubes as reinforcing agents to improve the mechanical properties of poly(propylene fumarate) (PPF) composites as a function of nanomaterial loading concentration (0.01-0.2 wt%). Tungsten disulfide nanotubes (WSNTs) were used as reinforcing agents in the experimental groups. Single- and multi- walled carbon nanotubes (SWCNTs and MWCNTs) were used as positive controls, and crosslinked PPF composites were used as baseline control. Mechanical testing (compression and three-point bending) shows a significant enhancement (up to 28-190%) in the mechanical properties (compressive modulus, compressive yield strength, flexural modulus, and flexural yield strength) of WSNT reinforced PPF nanocomposites compared to the baseline control. In comparison to positive controls, at various concentrations, significant improvements in the mechanical properties of WSNT nanocomposites were also observed. In general, the inorganic nanotubes (WSNTs) showed a better (up to 127%) or equivalent mechanical reinforcement compared to carbon nanotubes (SWCNTs and MWCNTs). Sol fraction analysis showed significant increases in the crosslinking density of PPF in the presence of WSNTs (0.01-0.2 wt%). Transmission electron microscopy (TEM) analysis on thin sections of crosslinked nanocomposites showed the presence of WSNTs as individual nanotubes in the PPF matrix, whereas SWCNTs and MWCNTs existed as micron sized aggregates. The trend in the surface area of nanostructures obtained by BET surface area analysis was SWCNTs > MWCNTs > WSNTs. The BET surface area analysis, TEM analysis, and sol fraction analysis results taken together suggest that chemical composition (inorganic vs. carbon nanomaterials), presence of functional groups (such as sulfide and oxysulfide), and individual dispersion of the nanomaterials in the polymer matrix (absence of aggregation of the reinforcing agent) are the key parameters affecting the mechanical

  9. Tribological properties of nanolamellar tungsten disulfide doped with zinc oxide nanoparticles.

    PubMed

    An, V; Irtegov, Y; Anisimov, E; Druzyanova, V; Burtsev, N; Khaskelberg, M

    2015-01-01

    Tribological properties of nanolamellar tungsten disulfide doped with zinc oxide nanoparticles were studied. Nanolamellar tungsten disulfide and ZnO nanoparticles produced by electrospark erosion of metal granules in an H2O2 solution were analyzed using the XRD, SEM and TEM techniques. According to the tribological measurements, ZnO nanoparticles did not significantly change the friction coefficient of nanolamellar WS2 at 25 °C in air, whereas they positively impact on wear resistance of nanolamellar WS2 at 400 °C. PMID:26558176

  10. The electronic and optical properties of Tungsten Disulfide under high pressure

    NASA Astrophysics Data System (ADS)

    Shang, Jimin; Chen, Peng; Zhang, Lamei; Zhai, Fengxiao; Cheng, Xuerui

    2016-05-01

    Using first principles calculations, we have investigated the pressure effects on the electronic and optical properties of Tungsten Disulfide. The results show that the lattice out plane is more sensitive to the pressure than that in plane. In addition, the conduction band maximum drops down and the valence band minimum shifts up with respect to the Fermi level, respectively. Semiconductor to metal transition occurs at a critical pressure (∼36 GPa). Moreover, the dielectric function also has an obviously red shift, and the optical absorption can be improved accordingly. Our study supplies a route to optimize the performance of WS2 devices.

  11. High performance field-effect transistor based on multilayer tungsten disulfide.

    PubMed

    Liu, Xue; Hu, Jin; Yue, Chunlei; Della Fera, Nicholas; Ling, Yun; Mao, Zhiqiang; Wei, Jiang

    2014-10-28

    Semiconducting two-dimensional transition metal chalcogenide crystals have been regarded as the promising candidate for the future generation of transistor in modern electronics. However, how to fabricate those crystals into practical devices with acceptable performance still remains as a challenge. Employing tungsten disulfide multilayer thin crystals, we demonstrate that using gold as the only contact metal and choosing appropriate thickness of the crystal, high performance transistor with on/off ratio of 10(8) and mobility up to 234 cm(2) V(-1) s(-1) at room temperature can be realized in a simple device structure. Furthermore, low temperature study revealed that the high performance of our device is caused by the minimized Schottky barrier at the contact and the existence of a shallow impurity level around 80 meV right below the conduction band edge. From the analysis on temperature dependence of field-effect mobility, we conclude that strongly suppressed phonon scattering and relatively low charge impurity density are the key factors leading to the high mobility of our tungsten disulfide devices. PMID:25266248

  12. Excitonic Effects in Tungsten Disulfide Monolayers on Two-Layer Graphene.

    PubMed

    Giusca, Cristina E; Rungger, Ivan; Panchal, Vishal; Melios, Christos; Lin, Zhong; Lin, Yu-Chuan; Kahn, Ethan; Elías, Ana Laura; Robinson, Joshua A; Terrones, Mauricio; Kazakova, Olga

    2016-08-23

    Light emission in atomically thin heterostructures is known to depend on the type of materials and the number and stacking sequence of the constituent layers. Here we show that the thickness of a two-dimensional substrate can be crucial in modulating the light emission. We study the layer-dependent charge transfer in vertical heterostructures built from monolayer tungsten disulfide (WS2) on one- and two-layer epitaxial graphene, unravelling the effect that the interlayer electronic coupling has on the excitonic properties of such heterostructures. We bring evidence that the excitonic properties of WS2 can be effectively tuned by the number of supporting graphene layers. Integrating WS2 monolayers with two-layer graphene leads to a significant enhancement of the photoluminescence response, up to 1 order of magnitude higher compared to WS2 supported on one-layer graphene. Our findings highlight the importance of substrate engineering when constructing atomically thin-layered heterostructures. PMID:27434813

  13. Dual-wavelength passively Q-switched Nd:GYSGG laser by tungsten disulfide saturable absorber.

    PubMed

    Gao, Y J; Zhang, B Y; Song, Q; Wang, G J; Wang, W J; Hong, M H; Dou, R Q; Sun, D L; Zhang, Q L

    2016-06-20

    A dual-wavelength passively Q-switched Nd:GYSGG laser using vacuum evaporating tungsten disulfide (WS2) as a saturable absorber was demonstrated for the first time to the best of our knowledge. The WS2 saturable absorber was prepared simply by evaporating nanometer WS2 powders onto a quartz substrate in a vacuum. By inserting the WS2 saturable absorber into the laser cavity, stable Q-switched laser operation was achieved with a maximum average output power of 367 mW, a pulse repetition rate of 70.7 kHz, the shortest pulse width of 591 ns, and pulse energy of about 1.05 μJ. By vacuum evaporation method, a high-quality WS2 saturable absorber can be produced, and it seems to be a suitable method for fabrication of 2D transition metal dichalcogenides. PMID:27409120

  14. Electrical, optical and morphological properties of chemically deposited nanostructured tungsten disulfide thin films

    NASA Astrophysics Data System (ADS)

    Chate, P. A.; Sathe, D. J.; Hankare, P. P.

    2013-02-01

    Nanocrystalline tungsten disulfide thin films have been deposited on non-conducting glass substrates using triethanolamine bath. The film samples were characterized by X-ray diffraction, scanning electron microscopy, optical spectroscopy and thermoelectric techniques. The crystalline phase of the deposited sample was of hexagonal wurtzite-type. The optical band gap energy of the sample was found to be 1.46 eV. The electrical conductivity of the film sample was found to be in the order of 10-3 (Ω cm)-1. Thermoelectric measurement showed n-type of conductivity. The configuration of fabricated cell is n-WS2 | NaI (2 M) + I2 (1 M) | C(graphite). The efficiency of the cell was found to be 1.29%.

  15. Highly efficient supercapacitor electrode with two-dimensional tungsten disulfide and reduced graphene oxide hybrid nanosheets

    NASA Astrophysics Data System (ADS)

    Tu, Chao-Chi; Lin, Lu-Yin; Xiao, Bing-Chang; Chen, Yu-Shiang

    2016-07-01

    Two-dimensional (2D) nanostructures with their high surface area and large in-plane conductivity have been regarded as promising materials for supercapacitors (SCs). Tungsten disulfide (WS2) is highly suitable for charge accumulation with its abundant active sites in the interspacing between the 2D structures and the intraspacing of each atomic layer, as well as on the tungsten centers with the charges generated by the Faradaic reactions. This study proposes the preparation of well-constructed WS2/reduced graphene oxide (RGO) nanosheets using a simple molten salt process as the electroactive material for SCs, which presents a high specific capacitance (CF) of 2508.07 F g-1 at the scan rate of 1 mV s-1, because of the synergic effect of WS2 with its large charge-accumulating sites on the 2D planes and RGO with its highly enhanced conductivity and improved connections in the WS2 networks. The excellent cycling stability of 98.6% retention after 5000 cycles charge/discharge process and the Coulombic efficiency close to 100% for the entire measurement are also achieved for the WS2/RGO-based SC electrode. The results suggest the potential for the combination of the 2D metal sulfide and carbon materials as the charge storage material to solve the energy problems and attain a sustainable society.

  16. Rhenium-188 Labeled Tungsten Disulfide Nanoflakes for Self-Sensitized, Near-Infrared Enhanced Radioisotope Therapy.

    PubMed

    Chao, Yu; Wang, Guanglin; Liang, Chao; Yi, Xuan; Zhong, Xiaoyan; Liu, Jingjing; Gao, Min; Yang, Kai; Cheng, Liang; Liu, Zhuang

    2016-08-01

    Radioisotope therapy (RIT), in which radioactive agents are administered or implanted into the body to irradiate tumors from the inside, is a clinically adopted cancer treatment method but still needs improvement to enhance its performances. Herein, it is found that polyethylene glycol (PEG) modified tungsten disulfide (WS2 ) nanoflakes can be easily labeled by (188) Re, a widely used radioisotope for RIT, upon simple mixing. Like other high-Z elements acting as radiosensitizers, tungsten in the obtained (188) Re-WS2 -PEG would be able to absorb ionization radiation generated from (188) Re, enabling ''self-sensitization'' to enhance the efficacy of RIT as demonstrated in carefully designed in vitro experiments of this study. In the meanwhile, the strong NIR absorbance of WS2 -PEG could be utilized for NIR light-induced photothermal therapy (PTT), which if applied on tumors would be able to greatly relieve their hypoxia state and help to overcome hypoxia-associated radioresistance of tumors. Therefore, with (188) Re-WS2 -PEG as a multifunctional agent, which shows efficient passive tumor homing after intravenous injection, in vivo self-sensitized, NIR-enhanced RIT cancer treatment is realized, achieving excellent tumor killing efficacy in a mouse tumor model. This work presents a new concept of applying nanotechnology in RIT, by delivering radioisotopes into tumors, self-sensitizing the irradiation-induced cell damage, and modulating the tumor hypoxia state to further enhance the therapeutic outcomes. PMID:27345460

  17. Solid-phase reaction synthesis of mesostructured tungsten disulfide material with a high specific surface area

    SciTech Connect

    An, Gaojun; Lu, Changbo; Xiong, Chunhua

    2011-09-15

    Highlights: {yields} WS{sub 2} material was synthesized through solid-phase reaction. {yields} (NH{sub 4}){sub 2}WS{sub 4} as precursor and n-octadecylamine as template. {yields} WS{sub 2} material has high specific surface area (145.9 m{sup 2}/g). {yields} The whole preparation process is simple, convenient, green and clean. -- Abstract: A mesostructured tungsten disulfide (WS{sub 2}) material was prepared through a solid-phase reaction utilizing ammonium tetrathiotungstate as the precursor and n-octadecylamine as the template. The as-synthesized WS{sub 2} material was characterized by X-ray powder Diffraction (XRD), Low-temperature N{sub 2} Adsorption (BET method), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The characterization results indicate that the WS{sub 2} material has the typical mesopore structure (3.7 nm) with a high specific surface area (145.9 m{sup 2}/g), and large pore volume (0.18 cm{sup 3}/g). This approach is novel, green and convenient. The plausible mechanism for the formation of the mesostructured WS{sub 2} material is discussed herein.

  18. High-damage-resistant tungsten disulfide saturable absorber mirror for passively Q-switched fiber laser.

    PubMed

    Chen, Hao; Chen, YuShan; Yin, Jinde; Zhang, Xuejun; Guo, Tuan; Yan, Peiguang

    2016-07-25

    In this paper, we demonstrate a high-damage-resistant tungsten disulfide saturable absorber mirror (WS2-SAM) fabricated by magnetron sputtering technique. The WS2-SAM has an all-fiber-integrated configuration and high-damage-resistant merit because the WS2 layer is protected by gold film so as to avoid being oxidized and destroyed at high pump power. Employing the WS2-SAM in an Erbium-doped fiber laser (EDFL) with linear cavity, the stable Q-switching operation is achieved at central wavelength of 1560 nm, with the repetition rates ranging from 29.5 kHz to 367.8 kHz and the pulse duration ranging from 1.269 μs to 154.9 ns. For the condition of the maximum pump power of 600 mW, the WS2-SAM still works stably with an output power of 25.2 mW, pulse energy of 68.5 nJ, and signal-noise-ratio of 42 dB. The proposed WS2-SAM configuration provides a promising solution for advanced pulsed fiber lasers with the characteristics of high damage resistance, high output energy, and wide tunable frequency. PMID:27464082

  19. Biocompatibility of tungsten disulfide inorganic nanotubes and fullerene-like nanoparticles with salivary gland cells.

    PubMed

    Goldman, Elisheva B; Zak, Alla; Tenne, Reshef; Kartvelishvily, Elena; Levin-Zaidman, Smadar; Neumann, Yoav; Stiubea-Cohen, Raluca; Palmon, Aaron; Hovav, Avi-Hai; Aframian, Doron J

    2015-03-01

    Impaired salivary gland (SG) function leading to oral diseases is relatively common with no adequate solution. Previously, tissue engineering of SG had been proposed to overcome this morbidity, however, not yet clinically available. Multiwall inorganic (tungsten disulfide [WS2]) nanotubes (INT-WS2) and fullerene-like nanoparticles (IF-WS2) have many potential medical applications. A yet unexplored venue application is their interaction with SG, and therefore, our aim was to test the biocompatibility of INT/IF-WS2 with the A5 and rat submandibular cells (RSC) SG cells. The cells were cultured and subjected after 1 day to different concentrations of INT-WS2 and were compared to control groups. Growth curves, trypan blue viability test, and carboxyfluorescein succinimidyl ester (CFSE) proliferation assay were obtained. Furthermore, cells morphology and interaction with the nanoparticles were observed by light microscopy, scanning electron microscopy and transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy. The results showed no significant differences in growth curves, proliferation kinetics, and viability between the groups compared. Moreover, no alterations were observed in the cell morphology. Interestingly, TEM images indicated that the nanoparticles are uptaken by the cells and accumulate in cytoplasmic vesicles. These results suggest promising future medical applications for these nanoparticles. PMID:25366879

  20. Self-lubricating aluminum metal-matrix composites dispersed with tungsten disulfide and silicon carbide

    SciTech Connect

    Prasad, S.V.; Mecklenburg, K.R.

    1994-07-01

    This paper describes the synthesis and tribological behavior of self-lubricating aluminum alloy metal-matrix composites (MMCs). The formulations of MMCs comprised of tungsten disulfide (WS{sub 2}) and silicon carbide (SiC) particles dispersed in a commercial aluminum alloy (Al-0.40Si-0.75Mg) matrix. Composites were fabricated by a conventional powder metallurgy route involving blending, compacting and sintering. Friction and wear tests (up to a duration of one million cycles) were performed in a ball-on-disk configuration against a steel counterface. Wear scars on MMC disks and steel balls were analyzed in SEM/EDXS. In a dry nitrogen environment, the steady state friction coefficient of an Al-0.10SiC-0.03WS{sub 2}MMC was 0.05, whereas in laboratory air with relative humidity at approximately 65 percent it was 0.10. In both environments, transfer of aluminum to the steel counterface was absent. 20 refs., 12 figs., 2 tabs.

  1. Biocompatibility of Tungsten Disulfide Inorganic Nanotubes and Fullerene-Like Nanoparticles with Salivary Gland Cells

    PubMed Central

    Goldman, Elisheva B.; Zak, Alla; Tenne, Reshef; Kartvelishvily, Elena; Levin-Zaidman, Smadar; Neumann, Yoav; Stiubea-Cohen, Raluca; Palmon, Aaron; Hovav, Avi-Hai

    2015-01-01

    Impaired salivary gland (SG) function leading to oral diseases is relatively common with no adequate solution. Previously, tissue engineering of SG had been proposed to overcome this morbidity, however, not yet clinically available. Multiwall inorganic (tungsten disulfide [WS2]) nanotubes (INT-WS2) and fullerene-like nanoparticles (IF-WS2) have many potential medical applications. A yet unexplored venue application is their interaction with SG, and therefore, our aim was to test the biocompatibility of INT/IF-WS2 with the A5 and rat submandibular cells (RSC) SG cells. The cells were cultured and subjected after 1 day to different concentrations of INT-WS2 and were compared to control groups. Growth curves, trypan blue viability test, and carboxyfluorescein succinimidyl ester (CFSE) proliferation assay were obtained. Furthermore, cells morphology and interaction with the nanoparticles were observed by light microscopy, scanning electron microscopy and transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy. The results showed no significant differences in growth curves, proliferation kinetics, and viability between the groups compared. Moreover, no alterations were observed in the cell morphology. Interestingly, TEM images indicated that the nanoparticles are uptaken by the cells and accumulate in cytoplasmic vesicles. These results suggest promising future medical applications for these nanoparticles. PMID:25366879

  2. Mechanistic study of the hydrodesulfurization of methanethiol over tungsten disulfide; a survey of rare earth sulfides for hydrodesulfurization activity

    SciTech Connect

    Dowd, D.Q.

    1985-06-01

    Hydrodesulfurization is a process whereby sulfur bound in organic compounds is removed as hydrogen sulfide, and is important to the control of sulfur dioxide emissions in the combustion of petroleum and coal fuels. It involves the cleavage of carbon sulfur bonds, and is catalyzed by layered disulfides such as molybdenum and tungsten disulfide. The simplest example is the reaction CH/sub 3/SH + H/sub 2/ ..-->.. CH/sub 4/ + H/sub 2/S. The mechanism of even this protypical reaction is unclear. In an effort to clarify it, the kinetics of methanethiol hydrodesulfurization over tungsten disulfide at low pressures was established, with partial pressures of methanethiol and hydrogen varied over a hundred fold. The kinetic order in each reactant was positive when its partial pressure was low negative when its partial pressure was high. The negative order in hydrogen had not been previously seen. The product gases, methane and hydrogen sulfide, each exhibited negative kinetic orders at high partial pressures, zero kinetic orders at low partial pressures. A dual site Langmuir-Hinshelwood type mechanism, which defines one active site as two adjacent edge sulfur vacancies and the second as a neighboring sulfur atom, describes these results quite well. Seventeen rare earth sulfides were surveyed for catalytic activity toward methanethiol hydrodesulfurization. These sulfides included both stoichiometric and nonstoichiometric compositions and four different morphologies. In general, nonconductors were inactive and conductors were active. This correlation extended to the nonstoichiometric ..gamma..-phase sesquisulfides which exhibit both insulating and conducting properties. 96 refs.

  3. Mechanistic study of the hydrodesulfurization of methanethiol over tungsten disulfide. II. A survey of rare earth sulfides for hydrodesulfurization activity

    SciTech Connect

    Dowd, D.Q.

    1985-01-01

    I. Hydrodesulfurization is a process whereby sulfur bound in organic compounds is removed as hydrogen sulfide, and is important to the control of sulfur dioxide emissions in the combustion of petroleum and coal fuels. It involves the cleavage of carbon sulfur bonds, and is catalyzed by layered disulfides such as molybdenum and tungsten disulfide. The simplest example is the reaction CH/sub 3/SH + H/sub 2/ ..-->.. CH/sub 4/ + H/sub 2/S. The mechanism of even this prototypical reaction is unclear. In an effort to clarify it, the kinetics of methanethiol hydro desulfurization over tungsten disulfide at low pressures was established, with partial pressures of methanethiol and hydrogen varied over a hundred fold. The kinetic order in each reactant was positive when its partial pressure was low, negative when its partial pressure was high. The negative order in hydrogen had not been previously seen. The product gases, methane and hydrogen sulfide, each exhibited negative kinetic orders at high partial pressures, zero kinetic orders at low partial pressures. A dual site Langmuir-Hinshelwood type mechanism, which defines one active site as two adjacent edge sulfur vacancies and the second as a neighboring sulfur atom, describes these results quite well. II. Seventeen rare earth sulfides were surveyed for catalytic activity toward methanethiol hydrodesulfurization. These sulfides included both stoichiometric and nonstoichiometric compositions and four different morphologies. In general, nonconductors were inactive and conductors were active. This correlation extended to the nonstoichiometric ..gamma..-phase sesquisulfides which exhibit both insulating and conducting properties.

  4. Pressure-Modulated Conductivity, Carrier Density, and Mobility of Multilayered Tungsten Disulfide.

    PubMed

    Nayak, Avinash P; Yuan, Zhen; Cao, Boxiao; Liu, Jin; Wu, Junjie; Moran, Samuel T; Li, Tianshu; Akinwande, Deji; Jin, Changqing; Lin, Jung-Fu

    2015-09-22

    Tungsten disulfide (WS2) is a layered transition metal dichalcogenide (TMD) that differs from other two-dimensional (2D) compounds such as graphene due to its unique semiconducting, tunable-band-gap nature. Multilayered WS2 exhibits an indirect band gap Eg of ∼1.3 eV, along with a higher load-bearing ability that is promising for strain-tuning device applications, but the electronic properties of multilayered WS2 at higher strain conditions (i.e., static strain >12%) remain an open question. Here we have studied the structural, electronic, electrical, and vibrational properties of multilayered WS2 at hydrostatic pressures up to ∼35 GPa experimentally in a diamond anvil cell and theoretically using first-principles ab initio calculations. Our results show that WS2 undergoes an isostructural semiconductor-to-metallic (S-M) transition at approximately 22 GPa at 280 K, which arises from the overlap of the highest valence and lowest conduction bands. The S-M transition is caused by increased sulfur-sulfur interactions as the interlayer spacing decreases with applied hydrostatic pressure. The metalization in WS2 can be alternatively interpreted as a 2D to 3D (three-dimensional) phase transition that is associated with a substantial modulation of the charge carrier characteristics including a 6-order decrease in resistivity, a 2-order decrease in mobility, and a 4-order increase in carrier concentration. These distinct pressure-tunable characteristics of the dimensionalized WS2 differentiate it from other TMD compounds such as MoS2 and promise future developments in strain-modulated advanced devices. PMID:26258661

  5. Q-switched waveguide laser based on two-dimensional semiconducting materials: tungsten disulfide and black phosphorous.

    PubMed

    Tan, Yang; Guo, Zhinan; Ma, Linan; Zhang, Han; Akhmadaliev, Shavkat; Zhou, Shengqiang; Chen, Feng

    2016-02-01

    Owing to their unique properties, graphene-like two dimensional semiconducting materials, including Tungsten Disulfide (WS2) and Black Phosphorous (BP), have attracted increasing interest from basic research to practical applications. Herein, we demonstrated the ultrafast nonlinear saturable absorption response of WS2 and BP films in the waveguide structure. Through fabricating WS2 and BP films by evaporating the solutions on glass wafers. Saturable absorber films were attached onto the end-facet of the waveguide, which therefore constitutes a resonant cavity for the waveguide laser. Under a pump laser at 810 nm, we could obtain a stable Q-switched operation in the waveguide structure. This work indicated the significant potential of WS2 and BP for the ultrafast waveguide laser. PMID:26906854

  6. Free-standing hierarchically sandwich-type tungsten disulfide nanotubes/graphene anode for lithium-ion batteries.

    PubMed

    Chen, Renjie; Zhao, Teng; Wu, Weiping; Wu, Feng; Li, Li; Qian, Ji; Xu, Rui; Wu, Huiming; Albishri, Hassan M; Al-Bogami, A S; El-Hady, Deia Abd; Lu, Jun; Amine, Khalil

    2014-10-01

    Transition metal dichalcogenides (TMD), analogue of graphene, could form various dimensionalities. Similar to carbon, one-dimensional (1D) nanotube of TMD materials has wide application in hydrogen storage, Li-ion batteries, and supercapacitors due to their unique structure and properties. Here we demonstrate the feasibility of tungsten disulfide nanotubes (WS2-NTs)/graphene (GS) sandwich-type architecture as anode for lithium-ion batteries for the first time. The graphene-based hierarchical architecture plays vital roles in achieving fast electron/ion transfer, thus leading to good electrochemical performance. When evaluated as anode, WS2-NTs/GS hybrid could maintain a capacity of 318.6 mA/g over 500 cycles at a current density of 1A/g. Besides, the hybrid anode does not require any additional polymetric binder, conductive additives, or a separate metal current-collector. The relatively high density of this hybrid is beneficial for high capacity per unit volume. Those characteristics make it a potential anode material for light and high-performance lithium-ion batteries. PMID:25163033

  7. Layer-modulated synthesis of uniform tungsten disulfide nanosheet using gas-phase precursors

    NASA Astrophysics Data System (ADS)

    Park, Jusang; Lee, Wonseon; Choi, Taejin; Hwang, Sung-Hwan; Myoung, Jae Min; Jung, Jae-Hoon; Kim, Soo-Hyun; Kim, Hyungjun

    2015-01-01

    The synthesis of layered transition-metal-disulfide (MS2, M = Mo, W) nanosheets with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this report, we describe a synthesis process of WS2 nanosheets with layer controllability and high uniformity using chemical vapor deposition (CVD) and WCl6 and H2S as gas-phase precursors. Through this process, we can systematically modulate the thickness of WS2 nanosheets by controlling the duration of the reaction between WCl6 and H2S. The CVD-grown WS2 nanosheets exhibit good stoichiometry as well as dependencies of a clear Raman shift and bandgap on the number of layers. These properties are confirmed by X-ray photoemission spectroscopy, Raman spectroscopy, and photoluminescence measurements. The number of layers of WS2 nanosheets is confirmed by atomic force microscopy. Finally, we demonstrate the fabrication and performance of a photodetector based on a hybrid structure consisting of graphene and a WS2 nanosheet.The synthesis of layered transition-metal-disulfide (MS2, M = Mo, W) nanosheets with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this report, we describe a synthesis process of WS2 nanosheets with layer controllability and high uniformity using chemical vapor deposition (CVD) and WCl6 and H2S as gas-phase precursors. Through this process, we can systematically modulate the thickness of WS2 nanosheets by controlling the duration of the reaction between WCl6 and H2S. The CVD-grown WS2 nanosheets exhibit good stoichiometry as well as dependencies of a clear Raman shift and bandgap on the number of layers. These properties are confirmed by X-ray photoemission spectroscopy, Raman spectroscopy, and photoluminescence measurements. The number of layers of WS2 nanosheets is confirmed by atomic force microscopy. Finally, we demonstrate the fabrication

  8. Layer-modulated synthesis of uniform tungsten disulfide nanosheet using gas-phase precursors.

    PubMed

    Park, Jusang; Lee, Wonseon; Choi, Taejin; Hwang, Sung-Hwan; Myoung, Jae Min; Jung, Jae-Hoon; Kim, Soo-Hyun; Kim, Hyungjun

    2015-01-28

    The synthesis of layered transition-metal-disulfide (MS2, M = Mo, W) nanosheets with layer controllability and large-area uniformity is an essential requirement for their application in electronic and optical devices. In this report, we describe a synthesis process of WS2 nanosheets with layer controllability and high uniformity using chemical vapor deposition (CVD) and WCl6 and H2S as gas-phase precursors. Through this process, we can systematically modulate the thickness of WS2 nanosheets by controlling the duration of the reaction between WCl6 and H2S. The CVD-grown WS2 nanosheets exhibit good stoichiometry as well as dependencies of a clear Raman shift and bandgap on the number of layers. These properties are confirmed by X-ray photoemission spectroscopy, Raman spectroscopy, and photoluminescence measurements. The number of layers of WS2 nanosheets is confirmed by atomic force microscopy. Finally, we demonstrate the fabrication and performance of a photodetector based on a hybrid structure consisting of graphene and a WS2 nanosheet. PMID:25361429

  9. Tungsten

    SciTech Connect

    1996-08-01

    The name tungsten, derived from the Swedish words {open_quotes}tung{close_quotes} and {open_quotes}sten{close_quotes}, meaning heavy stone, was first applied to a tungsten-containing mineral in 1755. The mineral, itself, was subsequently identified by C.W. Scheele in 1781, and named scheelite. Metallic tungsten was first isolated from the mineral wolframite in 1783, and given the German name {open_quotes}wolfram,{close_quotes} which remains an alternative name for the element. Ultimately, the English word, tungsten, became the official name, while W remains the element`s chemical symbol. This article discusses the geology, exploitation, applications, and market overview of tungsten.

  10. Carbon disulfide

    Integrated Risk Information System (IRIS)

    Carbon disulfide ; CASRN 75 - 15 - 0 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic E

  11. Tungsten thermal neutron dosimeter

    NASA Technical Reports Server (NTRS)

    Ball, L. L.; Richardson, P. J.; Sheibley, D. W.

    1969-01-01

    Tungsten-185 activity, which is produced by neutron activation of tungsten-184, determines thermal neutron flux. Radiochemical separation methods and counting techniques for irradiated tungsten provide accurate determination of the radiation exposure.

  12. 46 CFR 153.1040 - Carbon disulfide.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Carbon disulfide. 153.1040 Section 153.1040 Shipping... § 153.1040 Carbon disulfide. (a) No person may load, carry, or discharge carbon disulfide unless the... charge of a carbon disulfide transfer operation shall ensure that carbon disulfide is discharged only...

  13. 46 CFR 153.1040 - Carbon disulfide.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Carbon disulfide. 153.1040 Section 153.1040 Shipping... § 153.1040 Carbon disulfide. (a) No person may load, carry, or discharge carbon disulfide unless the... charge of a carbon disulfide transfer operation shall ensure that carbon disulfide is discharged only...

  14. 46 CFR 153.1040 - Carbon disulfide.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Carbon disulfide. 153.1040 Section 153.1040 Shipping... § 153.1040 Carbon disulfide. (a) No person may load, carry, or discharge carbon disulfide unless the... charge of a carbon disulfide transfer operation shall ensure that carbon disulfide is discharged only...

  15. 46 CFR 153.1040 - Carbon disulfide.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Carbon disulfide. 153.1040 Section 153.1040 Shipping... § 153.1040 Carbon disulfide. (a) No person may load, carry, or discharge carbon disulfide unless the... charge of a carbon disulfide transfer operation shall ensure that carbon disulfide is discharged only...

  16. 46 CFR 153.1040 - Carbon disulfide.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Carbon disulfide. 153.1040 Section 153.1040 Shipping... § 153.1040 Carbon disulfide. (a) No person may load, carry, or discharge carbon disulfide unless the... charge of a carbon disulfide transfer operation shall ensure that carbon disulfide is discharged only...

  17. Quantification of Thiols and Disulfides

    PubMed Central

    Winther, Jakob R.; Thorpe, Colin

    2013-01-01

    Background Disulfide bond formation is a key posttranslational modification, with implications for structure, function and stability of numerous proteins. While disulfide bond formation is a necessary and essential process for many proteins, it is deleterious and disruptive for others. Cells go to great lengths to regulate thiol-disulfide bond homeostasis, typically with several, apparently redundant, systems working in parallel. Dissecting the extent of oxidation and reduction of disulfides is an ongoing challenge due, in part, to the facility of thiol/disulfide exchange reactions. Scope of the review In the present account, we briefly survey the toolbox available to the experimentalist for the chemical determination of thiols and disulfides. We have chosen to focus on the key chemical aspects of current methodology, together with identifying potential difficulties inherent in their experimental implementation. Major conclusions While many reagents have been described for the measurement and manipulation of the redox status of thiols and disulfides, a number of these methods remain underutilized. The ability to effectively quantify changes in redox conditions in living cells presents a continuing challenge. General Significance Many unresolved questions in the metabolic interconversion of thiols and disulfides remain. For example, while pool sizes of redox pairs and their intracellular distribution are being uncovered, very little is known about the flux in thiol-disulfide exchange pathways. New tools are needed to address this important aspect of cellular metabolism. PMID:23567800

  18. Optical control of charged exciton states in tungsten disulfide

    NASA Astrophysics Data System (ADS)

    Currie, M.; Hanbicki, A. T.; Kioseoglou, G.; Jonker, B. T.

    2015-05-01

    A method is presented for optically preparing WS2 monolayers to luminescence from only the charged exciton (trion) state-completely suppressing the neutral exciton. When isolating the trion state, we observed changes in the Raman A1g intensity and an enhanced feature on the low energy side of the E12g peak. Photoluminescence and optical reflectivity measurements confirm the existence of the prepared trion state. This technique also prepares intermediate regimes with controlled luminescence amplitudes of the neutral and charged exciton. This effect is reversible by exposing the sample to air, indicating the change is mitigated by surface interactions with the ambient environment. This method provides a tool to modify optical emission energy and to isolate physical processes in this and other two-dimensional materials.

  19. Optical control of charged exciton states in tungsten disulfide

    SciTech Connect

    Currie, M.; Hanbicki, A. T.; Jonker, B. T.; Kioseoglou, G.

    2015-05-18

    A method is presented for optically preparing WS{sub 2} monolayers to luminescence from only the charged exciton (trion) state–completely suppressing the neutral exciton. When isolating the trion state, we observed changes in the Raman A{sub 1g} intensity and an enhanced feature on the low energy side of the E{sup 1}{sub 2g} peak. Photoluminescence and optical reflectivity measurements confirm the existence of the prepared trion state. This technique also prepares intermediate regimes with controlled luminescence amplitudes of the neutral and charged exciton. This effect is reversible by exposing the sample to air, indicating the change is mitigated by surface interactions with the ambient environment. This method provides a tool to modify optical emission energy and to isolate physical processes in this and other two-dimensional materials.

  20. Photoactive devices including porphyrinoids with coordinating additives

    DOEpatents

    Forrest, Stephen R; Zimmerman, Jeramy; Yu, Eric K; Thompson, Mark E; Trinh, Cong; Whited, Matthew; Diev, Vlacheslav

    2015-05-12

    Coordinating additives are included in porphyrinoid-based materials to promote intermolecular organization and improve one or more photoelectric characteristics of the materials. The coordinating additives are selected from fullerene compounds and organic compounds having free electron pairs. Combinations of different coordinating additives can be used to tailor the characteristic properties of such porphyrinoid-based materials, including porphyrin oligomers. Bidentate ligands are one type of coordinating additive that can form coordination bonds with a central metal ion of two different porphyrinoid compounds to promote porphyrinoid alignment and/or pi-stacking. The coordinating additives can shift the absorption spectrum of a photoactive material toward higher wavelengths, increase the external quantum efficiency of the material, or both.

  1. Thermodynamic properties of zirconium disulfide

    SciTech Connect

    Volovik, L.S.; Kovalevskaya, E.I.; Litvinenko, V.F.

    1986-02-01

    This paper uses a method of comparative calculation -- double comparison -for the quantitative evaluation of the themodynamic characteristics of zirconium disulfide. The method enables one to apply known characteristics of compounds of the given or an adjacent group to analogous compounds of elements. The enthalpy of zirconium disulfide was determined by a formula and the calculation was carried out on the basis of data on the enthalpy of hafnium, niobium, and tantalum disulfides measured by the mixing method in the temperature range 500-1800 K.

  2. Reactive superhydrophobic surface and its photoinduced disulfide-ene and thiol-ene (bio)functionalization.

    PubMed

    Li, Junsheng; Li, Linxian; Du, Xin; Feng, Wenqian; Welle, Alexander; Trapp, Oliver; Grunze, Michael; Hirtz, Michael; Levkin, Pavel A

    2015-01-14

    Reactive superhydrophobic surfaces are highly promising for biotechnological, analytical, sensor, or diagnostic applications but are difficult to realize due to their chemical inertness. In this communication, we report on a photoactive, inscribable, nonwettable, and transparent surface (PAINTS), prepared by polycondensation of trichlorovinylsilane to form thin transparent reactive porous nanofilament on a solid substrate. The PAINTS shows superhydrophobicity and can be conveniently functionalized with the photoclick thiol-ene reaction. In addition, we show for the first time that the PAINTS bearing vinyl groups can be easily modified with disulfides under UV irradiation. The effect of superhydrophobicity of PAINTS on the formation of high-resolution surface patterns has been investigated. The developed reactive superhydrophobic coating can find applications for surface biofunctionalization using abundant thiol or disulfide bearing biomolecules, such as peptides, proteins, or antibodies. PMID:25486338

  3. Method of monitoring photoactive organic molecules in-situ during gas-phase deposition of the photoactive organic molecules

    SciTech Connect

    Forrest, Stephen R.; Vartanian, Garen; Rolin, Cedric

    2015-06-23

    A method for in-situ monitoring of gas-phase photoactive organic molecules in real time while depositing a film of the photoactive organic molecules on a substrate in a processing chamber for depositing the film includes irradiating the gas-phase photoactive organic molecules in the processing chamber with a radiation from a radiation source in-situ while depositing the film of the one or more organic materials and measuring the intensity of the resulting photoluminescence emission from the organic material. One or more processing parameters associated with the deposition process can be determined from the photoluminescence intensity data in real time providing useful feedback on the deposition process.

  4. Photovoltaic device comprising compositionally graded intrinsic photoactive layer

    DOEpatents

    Hoffbauer, Mark A; Williamson, Todd L

    2013-04-30

    Photovoltaic devices and methods of making photovoltaic devices comprising at least one compositionally graded photoactive layer, said method comprising providing a substrate; growing onto the substrate a uniform intrinsic photoactive layer having one surface disposed upon the substrate and an opposing second surface, said intrinsic photoactive layer consisting essentially of In.sub.1-xA.sub.xN,; wherein: i. 0.ltoreq.x.ltoreq.1; ii. A is gallium, aluminum, or combinations thereof; and iii. x is at least 0 on one surface of the intrinsic photoactive layer and is compositionally graded throughout the layer to reach a value of 1 or less on the opposing second surface of the layer; wherein said intrinsic photoactive layer is isothermally grown by means of energetic neutral atom beam lithography and epitaxy at a temperature of 600.degree. C. or less using neutral nitrogen atoms having a kinetic energy of from about 1.0 eV to about 5.0 eV, and wherein the intrinsic photoactive layer is grown at a rate of from about 5 nm/min to about 100 nm/min.

  5. Rational design of bleachable nonchemically amplified DUV photoactive compounds

    NASA Astrophysics Data System (ADS)

    Rathsack, Benjamen M.; Tattersall, Peter I.; Tabery, Cyrus E.; Lou, Kathleen; Stachowiak, Timothy B.; Medeiros, David R.; Albelo, Jeff A.; Pirogovsky, Peter Y.; McKean, Dennis R.; Willson, C. Grant

    2001-08-01

    Photoactive compounds have been designed, synthesized and characterized for deep ultraviolet non-chemically amplified resist applications. These resist materials may have potential use in next generation 257nm mask fabrication. Mask fabrication requires stringent linewidth specifications over long post-coat and post-exposure bake delays. Lithography simulation and imaging experiments have been done to determine the lithographic performance of resists formulated with these new photoactive compounds. Previously studied chromophores, 7 substituted 3-diazo 4- hydroxycoumarin and N-substituted 3-diazo-2, 4-piperidione, both have the transparency, bleaching and exposure rate kinetics in the DUV that are analogous to those exhibited by the diazonaphthoquinone chromophore at 365nm. The sulfonate linkages attached to these photoactive compounds provide dissolution rate inhibition of novolak that is very similar to the diazonaphthoquinone-sulfonates. The trifunctional diazopiperidione that incorporates three sulfonate linkages provides more efficient inhibition per chromophore than the corresponding bisfunctional photoactive compound. The diazocoumarin based novolak resist demonstrates image reversal (negative tone) with the use of a post-exposure bake. The post-exposure bake causes the exposed photoactive compound to decarboxylate, which dramatically reduces its solubility in aqueous base. The trifunctional diazopiperidione provides the best overall imaging results due to almost complete bleaching and high contrast.

  6. 40 CFR 721.1745 - Ethoxybenzothiazole disulfide.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Ethoxybenzothiazole disulfide. 721... Substances § 721.1745 Ethoxybenzothiazole disulfide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as ethoxybenzothiazole disulfide...

  7. 40 CFR 721.1745 - Ethoxybenzothiazole disulfide.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Ethoxybenzothiazole disulfide. 721... Substances § 721.1745 Ethoxybenzothiazole disulfide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as ethoxybenzothiazole disulfide...

  8. 40 CFR 721.1745 - Ethoxybenzothiazole disulfide.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Ethoxybenzothiazole disulfide. 721... Substances § 721.1745 Ethoxybenzothiazole disulfide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as ethoxybenzothiazole disulfide...

  9. 40 CFR 721.1745 - Ethoxybenzothiazole disulfide.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Ethoxybenzothiazole disulfide. 721... Substances § 721.1745 Ethoxybenzothiazole disulfide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as ethoxybenzothiazole disulfide...

  10. Tungsten filament fire

    NASA Astrophysics Data System (ADS)

    Ruiz, Michael J.; Perkins, James

    2016-05-01

    We safely remove the outer glass bulb from an incandescent lamp and burn up the tungsten filament after the glass is removed. This demonstration dramatically illustrates the necessity of a vacuum or inert gas for the environment surrounding the tungsten filament inside the bulb. Our approach has added historical importance since the incandescent light bulb is being replaced by compact fluorescent and LED lamps.

  11. Deuterium trapping in tungsten

    NASA Astrophysics Data System (ADS)

    Poon, Michael

    Tungsten is one of the primary material candidates being investigated for use in the first-wall of a magnetic confinement fusion reactor. An ion accelerator was used to simulate the type of ion interaction that may occur at a plasma-facing material. Thermal desorption spectroscopy (TDS) was the primary tool used to analyze the effects of the irradiation. Secondary ion mass spectroscopy (SIMS) was used to determine the distribution of trapped D in the tungsten specimen. The tritium migration analysis program (TMAP) was used to simulate thermal desorption profiles from the D depth distributions. Fitting of the simulated thermal desorption profiles with the measured TDS results provided values of the D trap energies. Deuterium trapping in single crystal tungsten was studied as a function of the incident ion fluence, ion flux, irradiation temperature, irradiation history, and surface impurity levels during irradiation. The results show that deuterium was trapped at vacancies and voids. Two deuterium atoms could be trapped at a tungsten vacancy, with trapping energies of 1.4 eV and 1.2 eV for the first and second D atoms, respectively. In a tungsten void, D is trapped as atoms adsorbed on the inner walls of the void with a trap energy of 2.1 eV, or as D2 molecules inside the void with a trap energy of 1.2 eV. Deuterium trapping in polycrystalline tungsten was also studied as a function of the incident fluence, irradiation temperature, and irradiation history. Deuterium trapping in polycrystalline tungsten also occurs primarily at vacancies and voids with the same trap energies as in single crystal tungsten; however, the presence of grain boundaries promotes the formation of large surface blisters with high fluence irradiations at 500 K. In general, D trapping is greater in polycrystalline tungsten than in single crystal tungsten. To simulate mixed materials comprising of carbon (C) and tungsten, tungsten specimens were pre-irradiated with carbon ions prior to D

  12. Mixed results with mixed disulfides.

    PubMed

    Brigelius-Flohé, Regina

    2016-04-01

    A period of research with Helmut Sies in the 1980s is recalled. Our experiments aimed at an in-depth understanding of metabolic changes due to oxidative challenges under near-physiological conditions, i.e. perfused organs. A major focus were alterations of the glutathione and the NADPH/NADP(+) system by different kinds of oxidants, in particular formation of glutathione mixed disulfides with proteins. To analyze mixed disulfides, a test was adapted which is widely used until today. The observations in perfused rat livers let us believe that glutathione-6-phosphate dehydrogenase (G6PDH), i.a. might be activated by glutathionylation. Although we did not succeed to verify this hypothesis for the special case of G6PDH, the regulation of enzyme/protein activities by glutathionylation today is an accepted posttranslational mechanism in redox biology in general. Our early experimental approaches are discussed in the context of present knowledge. PMID:27095221

  13. Novel combination of photoactive species: photoresists formed from selectively esterified novolacs and polyfunctional photoactive compounds

    NASA Astrophysics Data System (ADS)

    Jeffries, Alfred T., III; Brzozowy, David J.; Naiini, Ahmad A.; Gallagher-Wetmore, Paula M.

    1997-07-01

    The addition of selected PACs to resists comprised of selectively esterified DNQ novolacs improves their performance in terms of side wall angle and resolution compared to resists whose photoactive component is composed of entirely selectively esterified DNQ novolacs. The performance gain is particularly evident for the resists with two selectively esterified fractions. A conventional 60/40 m-cresol/p-cresol novolac was synthesized and fractionated into five nearly equal weight fractions using supercritical fluids (SCF) fractionation technique. Resists were made from either a single esterified fraction [fraction Two, esterification level (EL), 42%] or dual esterified fractions (fractions Two and Four, EL 21% each), a selection of PACs and the remaining unesterified fractions. They were compared to a control containing only the corresponding esterified fraction(s). The PACs A and B were effective at increasing the resist profile angle for 0.50 (mu) features in the singly esterified novalacs in comparison to the control material and exhibited flat tops. The resolution and profiles of dual esterified fraction resists improved significantly when low levels of PACs were added to dual esterified fraction control resist. The comparison was made from 0.40 (mu) features. The resist made using PAC C is the best candidate for photospeed although its profile angle is less in comparison to PACs A and B.

  14. KISMET tungsten dispersal experiment

    SciTech Connect

    Wohletz, K.; Kunkle, T.; Hawkins, W.

    1996-12-01

    Results of the KISMET tungsten dispersal experiment indicate a relatively small degree of wall-rock contamination caused by this underground explosive experiment. Designed as an add-on to the KISMET test, which was performed in the U-1a.02 drift of the LYNER facility at Nevada Test Site on 1 March 1995, this experiment involved recovery and analysis of wall-rock samples affected by the high- explosive test. The chemical, high-explosive blast drove tungsten powder, placed around the test package as a plutonium analog, into the surrounding wall- rock alluvium. Sample analyses by an analytical digital electron microscope (ADEM) show tungsten dispersed in the rock as tiny (<10 {mu}m) particles, agglomerates, and coatings on alluvial clasts. Tungsten concentrations, measured by energy dispersive spectral analysis on the ADEM, indicate penetration depths less than 0.1 m and maximum concentrations of 1.5 wt % in the alluvium.

  15. Multi-modal sensing using photoactive thin films

    NASA Astrophysics Data System (ADS)

    Ryu, Donghyeon; Loh, Kenneth J.

    2014-08-01

    The need for a reliable prognosis of the health of structural systems has promoted the development of sensing technologies capable of simultaneously detecting multiple types of damage. However, conventional sensors are designed to only measure a specific structural response (e.g., strain, displacement, or acceleration). This limitation forces one to use a wide variety of sensors densely instrumented on a given structure, which results in high overhead costs and requires extensive signal processing of raw sensor data. In this study, a photoactive thin film that has been engineered for multi-modal sensing to selectively detect strain and pH is proposed. In addition, the thin film is self-sensing in that it does not require external power to operate. Instead, light illumination causes the photoactive film to generate an electrical current, whose magnitude is directly related to applied strains (for deformations, impact or cracks) or pH (as a precursor of corrosion). First, the thin films were fabricated by spin-coating photoactive and conjugated polymers like poly(3-hexylthiophene) (P3HT). The thin film was also encoded with pH sensitivity by integrating polyaniline (PANI) as one component within the multilayered film architecture. Second, the optical response of the P3HT and PANI thin films subjected to applied strains or pH was characterized using absorption spectroscopy. Lastly, it was also verified that the thin films could selectively sense strain or pH depending on the wavelengths of light used for sensor interrogation.

  16. Minerals yearbook, 1988. Tungsten

    SciTech Connect

    Smith, G.R.

    1988-01-01

    Only one U.S. tungsten mine was open during 1988 while prices for concentrates rose only modestly from the previous year. Consequently, the United States continued to be highly import-dependent for tungsten concentrate and intermediate materials. A significant portion of these materials came from China. The report discusses the following topics: Domestic data coverage; Legislation and government programs; Domestic production; Consumption and uses; Prices; Foreign trade; World capacity; World review--Australia, Austria, India, Republic of Korea, Mongolia, Rwanda, Spain; Technology.

  17. Detection of photoactive siderophore biosynthetic genes in the marine environment.

    PubMed

    Gärdes, Astrid; Triana, Christopher; Amin, Shady A; Green, David H; Romano, Ariel; Trimble, Lyndsay; Carrano, Carl J

    2013-06-01

    Iron is an essential element for oceanic microbial life but its low bioavailability limits microorganisms in large areas of the oceans. To acquire this metal many marine bacteria produce organic chelates that bind and transport iron (siderophores). While it has been hypothesized that the global production of siderophores by heterotrophic bacteria and some cyanobacteria constitutes the bulk of organic ligands binding iron in the ocean because stability constants of siderophores and these organic ligands are similar, and because ligand concentrations rise sharply in response to iron fertilization events, direct evidence for this proposal is lacking. This lack is due to the difficulty in characterizing these ligands due both to their extremely low concentrations and their highly heterogeneous nature. The situation for characterizing photoactive siderophores in situ is more problematic because of their expected short lifetimes in the photic zone. An alternative approach is to make use of high sensitivity molecular technology (qPCR) to search for siderophore biosynthesis genes related to the production of photoactive siderophores. In this way one can access their "biochemical potential" and utilize this information as a proxy for the presence of these siderophores in the marine environment. Here we show, using qPCR primers designed to detect biosynthetic genes for the siderophores vibrioferrin, petrobactin and aerobactin that such genes are widespread and based on their abundance, the "biochemical potential" for photoactive siderophore production is significant. Concurrently we also briefly examine the microbial biodiversity responsible for such production as a function of depth and location across a North Atlantic transect. PMID:23700243

  18. Diffusion of tungsten on stepped tungsten surfaces

    NASA Astrophysics Data System (ADS)

    Choi, D. S.; Kim, S. K.; Gomer, R.

    1990-08-01

    Self-diffusion of thermally generated tungsten atoms near (123) and (257), on the zone (011)-(112) and on (023), on the zone (011)-(001) of a tungsten field emitter has been investigated by the field-emission fluctuation method, using a rectangular probe in order to investigate diffusion anisotropy. In agreement with earlier findings of Gong and Gomer [J. Chem. Phys. 88 (1988) 1359, 1370] diffusion of single W atoms along and across (011) terraces separated by (011) steps, i.e. step edges running along [111] is essentially isotropic with Ed = 16 kcal, D0 ≈ 10 -4 cm 2 s -1, while atoms can cross (001) oriented steps only with much activation energy: Ed ≈ 35 kcal, D0 = 10 -2 cm -2 s -1. Slow diffusion parallel to steps attributed previously by Gong Chem. Phys. 88 (1988) 1359, 1370] to kink motion was also seen along the zone (011)-(112) but seems more complicated than previously assumed, with several regimes, which may correspond to motions of different kink configurations. Distinct dips in the slow regime diffusion coefficients occurred at 910 K, somewhat higher than the previously seen onset of dips, 875 K, and may indicate roughening, as previously hypothesized. Slow diffusion perpendicular to steps was also seen in this zone and is not fully understood. It may arise from some step components always perpendicular to the short slit dimensions, or may correspond to more complicated surface configurations than the step and terrace pattern on an ideal emitter surface.

  19. Photocycle populations with femtosecond excitation of crystalline photoactive yellow protein

    NASA Astrophysics Data System (ADS)

    Hutchison, Christopher D. M.; Kaucikas, Marius; Tenboer, Jason; Kupitz, Christopher; Moffat, Keith; Schmidt, Marius; van Thor, Jasper J.

    2016-06-01

    We investigate photocycle excitation of crystalline photoactive yellow protein using femtosecond laser pulses. This work establishes the feasibility and suitable optical excitation conditions to perform femtosecond time resolved X-ray crystallographic measurements using an X-ray free electron laser. Flash photolysis experiments demonstrated photocycle yields of the long-lived 'pB' signalling state of PYP of up to 10% with pulse durations of 130, 500 and 850 fs at 450 nm wavelength. The power density dependence of the transient pB concentration depends strongly on the pulse duration primarily because photobleaching is prominent at the GW/mm2 level.

  20. High purity tungsten targets

    NASA Technical Reports Server (NTRS)

    1975-01-01

    High purity tungsten, which is used for targets in X-ray tubes was considered for space processing. The demand for X-ray tubes was calculated using the growth rates for dental and medical X-ray machines. It is concluded that the cost benefits are uncertain.

  1. Gas tungsten arc welder

    DOEpatents

    Christiansen, D.W.; Brown, W.F.

    A welder for automated closure of fuel pins by a gas tungsten arc process in which a rotating length of cladding is positioned adjacent a welding electrode in a sealed enclosure. An independently movable axial grinder is provided in the enclosure for refurbishing the used electrode between welds.

  2. Tungsten diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Van Orman, J. A.

    2014-03-01

    Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 min to several weeks, at temperatures from 1050 to 1450 °C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for W diffusion in forsterite: D=1.0×10-8exp(-365±28 kJ mol/RT) m s Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity. The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

  3. Selective oxidation of alcohols using photoactive VO@g-C3N4.

    EPA Science Inventory

    A photoactive VO@g-C3N4 catalyst has been developed for the selective oxidation of alcohols to the corresponding aldehydes and ketones. The visible light mediated activity of the catalyst could be attributed to photoactive graphitic carbon nitrides surface.

  4. Chemical downstream etching of tungsten

    SciTech Connect

    Blain, M.G.; Jarecki, R.L.; Simonson, R.J.

    1998-07-01

    The downstream etching of tungsten and tungsten oxide has been investigated. Etching of chemical vapor deposited tungsten and e-beam deposited tungsten oxide samples was performed using atomic fluorine generated by a microwave discharge of argon and NF{sub 3}. Etching was found to be highly activated with activation energies approximated to be 6.0{plus_minus}0.5thinspkcal/mol and 5.4{plus_minus}0.4thinspkcal/mol for W and WO{sub 3}, respectively. In the case of F etching of tungsten, the addition of undischarged nitric oxide (NO) directly into the reaction chamber results in the competing effects of catalytic etch rate enhancement and the formation of a nearly stoichiometric WO{sub 3} passivating tungsten oxide film, which ultimately stops the etching process. For F etching of tungsten oxide, the introduction of downstream NO reduces the etch rate. {copyright} {ital 1998 American Vacuum Society.}

  5. Transfer of molybdenum disulfide to various metals

    NASA Technical Reports Server (NTRS)

    Barton, G. C.; Pepper, S. V.

    1977-01-01

    Sliding friction experiments were conducted with molybdenum disulfide single crystals in contact with sputter cleaned surfaces of copper, nickel, gold, and 304 stainless steel. Transfer of the molybdenum disulfide to the metals was monitored with Auger electron spectroscopy. Results of the investigation indicate molybdenum disulfide transfers to all clean metal surfaces after a single pass over the metal surface with film thickness observed to increase with repeated passes over the same surfaces. Large particle transfer occurs when the orientation of the crystallites is other than basal. This is frequently accompanied by abrasion of the metal. Adhesion of molybdenum disulfide films occurred readily to copper and nickel, less readily to 304 stainless steel, and even less effectively to the gold, which indicates a chemical effect.

  6. Protein folding guides disulfide bond formation

    PubMed Central

    Qin, Meng; Wang, Wei; Thirumalai, D.

    2015-01-01

    The Anfinsen principle that the protein sequence uniquely determines its structure is based on experiments on oxidative refolding of a protein with disulfide bonds. The problem of how protein folding drives disulfide bond formation is poorly understood. Here, we have solved this long-standing problem by creating a general method for implementing the chemistry of disulfide bond formation and rupture in coarse-grained molecular simulations. As a case study, we investigate the oxidative folding of bovine pancreatic trypsin inhibitor (BPTI). After confirming the experimental findings that the multiple routes to the folded state contain a network of states dominated by native disulfides, we show that the entropically unfavorable native single disulfide [14–38] between Cys14 and Cys38 forms only after polypeptide chain collapse and complete structuring of the central core of the protein containing an antiparallel β-sheet. Subsequent assembly, resulting in native two-disulfide bonds and the folded state, involves substantial unfolding of the protein and transient population of nonnative structures. The rate of [14–38] formation increases as the β-sheet stability increases. The flux to the native state, through a network of kinetically connected native-like intermediates, changes dramatically by altering the redox conditions. Disulfide bond formation between Cys residues not present in the native state are relevant only on the time scale of collapse of BPTI. The finding that formation of specific collapsed native-like structures guides efficient folding is applicable to a broad class of single-domain proteins, including enzyme-catalyzed disulfide proteins. PMID:26297249

  7. Free-standing carbon nanotube-titania photoactive sheets.

    PubMed

    Koo, Youngmi; Malik, Rachit; Alvarez, Noe; Shanov, Vesselin N; Schulz, Mark; Sankar, Jag; Yun, Yeoheung

    2015-06-15

    We report on the development of a new photoactive material via titania (TiO2) nanoparticle deposition on free-standing aligned carbon nanotube (CNT) sheets. Controlling homogeneous dispersion of negatively charged TiO2 nanoparticles, achieved by adjusting pH higher than the point of zero charge (PZC), influenced electrochemical deposition of TiO2 on CNT sheets substrate. Varying deposition time with constant voltage, 5 V allowed different thickness of TiO2 to be deposited layer on the CNT sheets. The thickness and morphology of CNT-TiO2 sheets was verified by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Electrochemical experiments show that diffusion coefficient of Fe(CN)6(3-) was 5.56×10(-6) cm(2) s(-1) at pristine CNT sheets and 2.19×10(-6) cm(2) s(-1) at the CNT-TiO2 sheets. Photocatalytic activity for CNT-TiO2 sheets exhibits high photocurrent density (when deposition time=30 min, 4.3 μA cm(-2) in N2, 13.4 μA cm(-2) in CO2). This paper proved a possibility to use CNT-TiO2 sheets based on highly-aligned CNT sheets substrate as new photoactive material. PMID:25725399

  8. Photoactive High Explosives: Substituents Effects on Tetrazine Photochemistry and Photophysics.

    PubMed

    McGrane, S D; Bolme, C A; Greenfield, M T; Chavez, D E; Hanson, S K; Scharff, R J

    2016-02-18

    High explosives that are photoactive, i.e., can be initiated with light, offer significant advantages in reduced potential for accidental electrical initiation. We examined a series of structurally related tetrazine based photoactive high explosive materials to detail their photochemical and photophysical properties. Using photobleaching infrared absorption, we determined quantum yields of photochemistry for nanosecond pulsed excitation at 355 and 532 nm. Changes in mass spectrometry during laser irradiation in vacuum measured the evolution of gaseous products. Fluorescence spectra, quantum yields, and lifetimes were measured to observe radiative channels of energy decay that compete with photochemistry. For the 6 materials studied, quantum yields of photochemistry ranged from <10(-5) to 0.03 and quantum yield of fluorescence ranged from <10(-3) to 0.33. In all cases, the photoexcitation nonradiatively relaxed primarily to heat, appropriate for supporting photothermal initiation processes. The photochemistry observed was dominated by ring scission of the tetrazine, but there was evidence of more extensive multistep reactions as well. PMID:26797486

  9. Infection Mitigation Efficacy of Photoactive Titania on Orthopedic Implant Materials

    PubMed Central

    Azad, Abdul-Majeed; Hershey, Ryan; Aboelzahab, Asem; Goel, Vijay

    2011-01-01

    In order to impede infection and achieve accelerated wound healing in the postorthopaedic surgery patients, a simple and benign procedure for creating nanotubular or nanofibrillar structure of photoactive TiO2 on the surface of Ti plates and wires is described. The nanoscale TiO2 films on titanium were grown by hydrothermal processing in one case and by anodization in the presence of dilute mineral acids under mild and benign conditions in the other. Confocal microscopy results demonstrated at least 50% reduction in the population of E. coli colonies (concentration 2.15 × 107 cells/mL) on TiO2-coated implants upon an IR exposure of up to 30 s; it required ∼20 min of exposure to UV beam for the same effect. These findings suggest the probability of eliminating wound infection during and after orthopedic surgical procedures by brief illumination of photoactive titania films on the implants with an IR beam. PMID:21994891

  10. High-Throughput Preparation of New Photoactive Nanocomposites.

    PubMed

    Conterosito, Eleonora; Benesperi, Iacopo; Toson, Valentina; Saccone, Davide; Barbero, Nadia; Palin, Luca; Barolo, Claudia; Gianotti, Valentina; Milanesio, Marco

    2016-06-01

    New low-cost photoactive hybrid materials based on organic luminescent molecules inserted into hydrotalcite (layered double hydroxides; LDH) were produced, which exploit the high-throughput liquid-assisted grinding (LAG) method. These materials are conceived for applications in dye-sensitized solar cells (DSSCs) as a co-absorbers and in silicon photovoltaic (PV) panels to improve their efficiency as they are able to emit where PV modules show the maximum efficiency. A molecule that shows a large Stokes' shift was designed, synthesized, and intercalated into LDH. Two dyes already used in DSSCs were also intercalated to produce two new nanocomposites. LDH intercalation allows the stability of organic dyes to be improved and their direct use in polymer melt blending. The prepared nanocomposites absorb sunlight from UV to visible and emit from blue to near-IR and thus can be exploited for light-energy management. Finally one nanocomposite was dispersed by melt blending into a poly(methyl methacrylate)-block-poly(n-butyl acrylate) copolymer to obtain a photoactive film. PMID:27137753

  11. Intermediate State Dependence of Intramolecular Vibrations in Photoactive Yellow Protein

    NASA Astrophysics Data System (ADS)

    Deng, Yanting; Xu, Mengyang; Niessen, Katherine; Schmidt, Marius; Markelz, Andrea

    Photoactive proteins provide a testbed for the role of long-range collective motions in protein function. Long-range intramolecular vibrations of the protein scaffold may provide efficient energy relaxation, enhancement of chromophore vibrations that promote structural transitions and assistance in electron energy transfer. Photoactive yellow protein (PYP) is a cytoplasmic photocycling protein associated with the negative phototactic response to blue light in halohodospira halophile. We measure the intramolecular vibrations of PYP using crystal anisotropy terahertz microscopy (CATM) as a function of photoexcitation. Room temperature CATM measurements are performed in the dark and with continuous illumination at 488 nm, which is found to result in an approximately 20% steady photoexcited state (pB). We find a decrease in anisotropic absorption in frequency range 20-60 cm-1 with photoexcitation. This result may be due to an increase in sample disorder associated with the structural change in pB state. We compare the measured and calculated spectra using molecular dynamics and normal mode/quasiharmonic analysis to identify the nature of the motions giving rise to the resonant absorption bands.

  12. Tungsten oxide nanowire synthesis from amorphous-like tungsten films.

    PubMed

    Seelaboyina, Raghunandan

    2016-03-18

    A synthesis technique which can lead to direct integration of tungsten oxide nanowires onto silicon chips is essential for preparing various devices. The conversion of amorphous tungsten films deposited on silicon chips by pulsed layer deposition to nanowires by annealing is an apt method in that direction. This perspective discusses the ingenious features of the technique reported by Dellasega et al on the various aspects of tungsten oxide nanowire synthesis. PMID:26871521

  13. Tungsten oxide nanowire synthesis from amorphous-like tungsten films

    NASA Astrophysics Data System (ADS)

    Seelaboyina, Raghunandan

    2016-03-01

    A synthesis technique which can lead to direct integration of tungsten oxide nanowires onto silicon chips is essential for preparing various devices. The conversion of amorphous tungsten films deposited on silicon chips by pulsed layer deposition to nanowires by annealing is an apt method in that direction. This perspective discusses the ingenious features of the technique reported by Dellasega et al on the various aspects of tungsten oxide nanowire synthesis.

  14. Disulfide bond assignments by mass spectrometry of native natural peptides: cysteine pairing in disulfide bonded conotoxins.

    PubMed

    Gupta, Kallol; Kumar, Mukesh; Balaram, Padmanabhan

    2010-10-01

    The critical, and often most difficult, step in structure elucidation of diverse classes of natural peptides is the determination of correct disulfide pairing between multiple cysteine residues. Here, we present a direct mass spectrometric analytical methodology for the determination of disulfide pairing. Protonated peptides, having multiple disulfide bonds, fragmented under collision induced dissociation (CID) conditions and preferentially cleave along the peptide backbone, with occasional disulfide fragmentation either by C(β)-S bond cleavage through H(α) abstraction to yield dehydroalanine and cysteinepersulfide, or by S-S bond cleavage through H(β) abstraction to yield the thioaldehyde and cysteine. Further fragmentation of the initial set of product ions (MS(n)) yields third and fourth generation fragment ions, permitting a distinction between the various possible disulfide bonded structures. This approach is illustrated by establishing cysteine pairing patterns in five conotoxins containing two disulfide bonds. The methodology is extended to the Conus araneosus peptides Ar1446 and Ar1430, two 14 residue sequences containing 3 disulfide bonds. A distinction between 15 possible disulfide pairing schemes becomes possible using direct mass spectral fragmentation of the native peptides together with fragmentation of enzymatically nicked peptides. PMID:20843009

  15. Helium bubble bursting in tungsten

    SciTech Connect

    Sefta, Faiza; Juslin, Niklas; Wirth, Brian D.

    2013-12-28

    Molecular dynamics simulations have been used to systematically study the pressure evolution and bursting behavior of sub-surface helium bubbles and the resulting tungsten surface morphology. This study specifically investigates how bubble shape and size, temperature, tungsten surface orientation, and ligament thickness above the bubble influence bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom “islands,” craters, and pinholes. The present study provides insight into the mechanisms and conditions leading to various tungsten topology changes, which we believe are the initial stages of surface evolution leading to the formation of nanoscale fuzz.

  16. Titania-lanthanum phosphate photoactive and hydrophobic new generation catalyst

    NASA Astrophysics Data System (ADS)

    Jyothi, Chembolli K.; Jaimy, Kanakkanmavudi B.; Ghosh, Swapankumar; Sankar, Sasidharan; Smitha, V. S.; Warrier, K. G. K.

    2011-07-01

    Titania-lanthanum phosphate nanocomposites with multifunctional properties have been synthesized by aqueous sol-gel method. The precursor sols with varying TiO 2:LaPO 4 ratios were applied as thin coating on glass substrates in order to be transparent, hydrophobic, photocatalytically active coatings. The phase compositions of the composite powders were identified by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The anatase phase of TiO 2 in TiO 2-LaPO 4 composite precursors was found to be stable even on annealing at 800 °C. The glass substrates, coated with TL1 (TiO 2-LaPO 4 composition with 1 mol% LaPO 4) and TL50 (composite precursor containing TiO 2 and LaPO 4 with molar ratio 1:1) sols and annealed at 400 °C, produced contact angles of 74° and 92°, respectively, though it is only 62° for pure TiO 2 coating. The glass substrates, coated with TL50 sol, produced surfaces with relatively high roughness and uneven morphology. The TL1 material, annealed at 800 °C, has shown the highest UV photoactivity with an apparent rate constant, kapp=24×10 -3 min -1, which is over five times higher than that observed with standard Hombikat UV 100 ( kapp=4×10 -3 min -1). The photoactivity combined with a moderate contact angle (85.3°) shows that this material has a promise as an efficient self-cleaning precursor.

  17. Photoactive dye enhanced tissue ablation for endoscopic laser prostatectomy

    NASA Astrophysics Data System (ADS)

    Ahn, Minwoo; Nguyen, Trung Hau; Nguyen, Van Phuc; Oh, Junghwan; Kang, Hyun Wook

    2015-02-01

    Laser light has been widely used as a surgical tool to treat benign prostate hyperplasia with high laser power. The purpose of this study was to validate the feasibility of photoactive dye injection to enhance light absorption and eventually to facilitate tissue ablation with low laser power. The experiment was implemented on chicken breast due to minimal optical absorption Amaranth (AR), black dye (BD), hemoglobin powder (HP), and endoscopic marker (EM), were selected and tested in vitro with a customized 532-nm laser system with radiant exposure ranging from 0.9 to 3.9 J/cm2. Light absorbance and ablation threshold were measured with UV-VIS spectrometer and Probit analysis, respectively, and compared to feature the function of the injected dyes. Ablation performance with dye-injection was evaluated in light of radiant exposure, dye concentration, and number of injection. Higher light absorption by injected dyes led to lower ablation threshold as well as more efficient tissue removal in the order of AR, BD, HP, and EM. Regardless of the injected dyes, ablation efficiency principally increased with input parameter. Among the dyes, AR created the highest ablation rate of 44.2+/-0.2 μm/pulse due to higher absorbance and lower ablation threshold. Preliminary tests on canine prostate with a hydraulic injection system demonstrated that 80 W with dye injection yielded comparable ablation efficiency to 120 W with no injection, indicating 33 % reduced laser power with almost equivalent performance. In-depth comprehension on photoactive dye-enhanced tissue ablation can help accomplish efficient and safe laser treatment for BPH with low power application.

  18. How thioredoxin dissociates its mixed disulfide.

    PubMed

    Roos, Goedele; Foloppe, Nicolas; Van Laer, Koen; Wyns, Lode; Nilsson, Lennart; Geerlings, Paul; Messens, Joris

    2009-08-01

    The dissociation mechanism of the thioredoxin (Trx) mixed disulfide complexes is unknown and has been debated for more than twenty years. Specifically, opposing arguments for the activation of the nucleophilic cysteine as a thiolate during the dissociation of the complex have been put forward. As a key model, the complex between Trx and its endogenous substrate, arsenate reductase (ArsC), was used. In this structure, a Cys29(Trx)-Cys89(ArsC) intermediate disulfide is formed by the nucleophilic attack of Cys29(Trx) on the exposed Cys82(ArsC)-Cys89(ArsC) in oxidized ArsC. With theoretical reactivity analysis, molecular dynamics simulations, and biochemical complex formation experiments with Cys-mutants, Trx mixed disulfide dissociation was studied. We observed that the conformational changes around the intermediate disulfide bring Cys32(Trx) in contact with Cys29(Trx). Cys32(Trx) is activated for its nucleophilic attack by hydrogen bonds, and Cys32(Trx) is found to be more reactive than Cys82(ArsC). Additionally, Cys32(Trx) directs its nucleophilic attack on the more susceptible Cys29(Trx) and not on Cys89(ArsC). This multidisciplinary approach provides fresh insights into a universal thiol/disulfide exchange reaction mechanism that results in reduced substrate and oxidized Trx. PMID:19675666

  19. Mineral resource of the month: tungsten

    USGS Publications Warehouse

    Shedd, Kim B.

    2012-01-01

    The article offers information on tungsten. It says that tungsten is a metal found in chemical compounds such as in the scheelite and ore minerals wolframite. It states that tungsten has the highest melting point and it forms a compound as hard as diamond when combined with carbon. It states that tungsten can be used as a substitute for lead in fishing weights, ammunition, and hunting shot. Moreover, China started to export tungsten materials and products instead of tungsten raw materials.

  20. Interaction of tungsten with tungsten carbide in a copper melt

    NASA Astrophysics Data System (ADS)

    Bodrova, L. E.; Goida, E. Yu.; Pastukhov, E. A.; Marshuk, L. A.; Popova, E. A.

    2013-07-01

    The chemical interaction between tungsten and tungsten carbide in a copper melt with the formation of W2C at 1300°C is studied. It is shown that the mechanical activation of a composition consisting of copper melt + W and WC powders by low-temperature vibrations initiates not only the chemical interaction of its solid components but also their refinement.

  1. Voltammetric studies of poly(carbon disulfide)

    SciTech Connect

    Geng, L.; Xu, J.; Prasad, S.; Skotheim, T.A.; Lee, H.S.; McBreen, J.

    1992-12-31

    Poly(carbon disulfide) was studied by cyclic voltammetry using glassy carbon and platinum macro- and microdisk electrodes. The electron transfer kinetics is significantly faster at glassy carbon electrodes than at Pt electrodes. It is chemically reversible with moderate electron transfer rates. Voltammetric results of poly(carbon disulfide) are in good agreement with battery testing data. The k{sup 0} value measured at a Pt microdisk electrode is 7{times}10{sup 3} cm/sec. Electrochemical data suggest that PCS can be a potential cathode material for low current density lithium batteries.

  2. Disulfide-Functionalized Diblock Copolymer Worm Gels.

    PubMed

    Warren, Nicholas J; Rosselgong, Julien; Madsen, Jeppe; Armes, Steven P

    2015-08-10

    Two strategies for introducing disulfide groups at the outer surface of RAFT-synthesized poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA, or Gx-Hy for brevity) diblock copolymer worms are investigated. The first approach involved statistical copolymerization of GMA with a small amount of disulfide dimethacrylate (DSDMA, or D) comonomer to afford a G54-D0.50 macromolecular chain transfer agent (macro-CTA); this synthesis was conducted in relatively dilute solution in order to ensure mainly intramolecular cyclization and hence the formation of linear chains. Alternatively, a new disulfide-based bifunctional RAFT agent (DSDB) was used to prepare a G45-S-S-G45 (or (G45-S)2) macro-CTA. A binary mixture of a non-functionalized G55 macro-CTA was utilized with each of these two disulfide-based macro-CTAs in turn for the RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). By targeting a PHPMA DP of 130 and systematically varying the molar ratio of the two macro-CTAs, a series of disulfide-functionalized diblock copolymer worm gels were obtained. For both formulations, oscillatory rheology studies confirmed that higher disulfide contents led to stronger gels, presumably as a result of inter-worm covalent bond formation via disulfide/thiol exchange. Using the DSDB-based macro-CTA led to the strongest worm gels, and this formulation also proved to be more effective in suppressing the thermosensitive behavior that is observed for the nondisulfide-functionalized control worm gel. However, macroscopic precipitation occurred when the proportion of DSDB-based macro-CTA was increased to 50 mol %, whereas the DSDMA-based macro-CTA could be utilized at up to 80 mol %. Finally, the worm gel modulus could be reduced to that of a nondisulfide-containing worm gel by reductive cleavage of the inter-worm disulfide bonds using excess tris(2-carboxyethyl)phosphine (TCEP) to yield thiol groups. These new biomimetic worm gels are

  3. Preparation of tungsten oxide

    SciTech Connect

    Bulian, Christopher J.; Dye, Robert C.; Son, Steven F.; Jorgensen, Betty S.; Perry, W. Lee

    2009-09-22

    Tungsten trioxide hydrate (WO.sub.3.H.sub.2O) was prepared from a precursor solution of ammonium paratungstate in concentrated aqueous hydrochloric acid. The precursor solution was rapidly added to water, resulting in the crash precipitation of a yellow white powder identified as WO.sub.3.H.sub.2O nanosized platelets by x-ray diffraction and scanning electron microscopy. Annealing of the powder at 200.degree. C. provided cubic phase WO.sub.3 nanopowder, and at 400.degree. C. provided WO.sub.3 nanopowder as a mixture of monoclinic and orthorhombic phases.

  4. TUNGSTEN BASE ALLOYS

    DOEpatents

    Schell, D.H.; Sheinberg, H.

    1959-12-15

    A high-density quaternary tungsten-base alloy having high mechanical strength and good machinability composed of about 2 wt.% Ni, 3 wt.% Cu, 5 wt.% Pb, and 90wt.% W is described. This alloy can be formed by the powder metallurgy technique of hot pressing in a graphite die without causing a reaction between charge and the die and without formation of a carbide case on the final compact, thereby enabling re-use of the graphite die. The alloy is formable at hot- pressing temperatures of from about 1200 to about 1350 deg C. In addition, there is little component shrinkage, thereby eliminating the necessity of subsequent extensive surface machining.

  5. Photoactive extracts from Thevetia peruviana with antifungal properties against Cladosporium cucumerinum.

    PubMed

    Gata-Gonçalves, Lígia; Nogueira, J M F; Matos, Olívia; Bruno de Sousa, Raúl

    2003-04-01

    Seeds of Thevetia peruviana were screened for their antifungal photoactivity. Extracts obtained either with n-hexane or dichloromethane were fractionated by column chromatography and further analysed by thin-layer chromatography. All seed extracts and fractions were tested for inhibition of the fungus Cladosporium cucumerinum for the evaluation of photoactive inhibitory effects. Antifungal light-dependent activity was observed for some of the fractions and both crude extracts. The most photoactive fraction was analysed by capillary gas chromatography with mass spectrometry in order to identify its constituents. Two major groups of compounds were identified, terpenes and fatty acids and derivatives. Pulegone, linoleic acid and palmitic acid were the major compounds. Terpenes seem to be the major substances with antifungal photoactivity. PMID:12745247

  6. DISULFIND: a disulfide bonding state and cysteine connectivity prediction server

    PubMed Central

    Ceroni, Alessio; Passerini, Andrea; Vullo, Alessandro; Frasconi, Paolo

    2006-01-01

    DISULFIND is a server for predicting the disulfide bonding state of cysteines and their disulfide connectivity starting from sequence alone. Optionally, disulfide connectivity can be predicted from sequence and a bonding state assignment given as input. The output is a simple visualization of the assigned bonding state (with confidence degrees) and the most likely connectivity patterns. The server is available at . PMID:16844986

  7. 21 CFR 524.2101 - Selenium disulfide suspension.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Selenium disulfide suspension. 524.2101 Section... § 524.2101 Selenium disulfide suspension. (a) Specifications. The product contains 0.9-percent weight in weight (w/w) selenium disulfide (1-percent weight in volume (w/v)). (b) Sponsors. See Nos. 000061,...

  8. 21 CFR 524.2101 - Selenium disulfide suspension.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Selenium disulfide suspension. 524.2101 Section... § 524.2101 Selenium disulfide suspension. (a) Specifications. The product contains 0.9-percent weight in weight (w/w) selenium disulfide (1-percent weight in volume (w/v)). (b) Sponsors. See Nos. 000061,...

  9. 21 CFR 524.2101 - Selenium disulfide suspension.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Selenium disulfide suspension. 524.2101 Section... § 524.2101 Selenium disulfide suspension. (a) Specifications. The product contains 0.9-percent weight in weight (w/w) selenium disulfide (1-percent weight in volume (w/v)). (b) Sponsors. See Nos. 000061,...

  10. 21 CFR 524.2101 - Selenium disulfide suspension.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Selenium disulfide suspension. 524.2101 Section... § 524.2101 Selenium disulfide suspension. (a) Specifications. The product contains 0.9-percent weight in weight (w/w) selenium disulfide (1-percent weight in volume (w/v)). (b) Sponsors. See Nos. 000061,...

  11. 21 CFR 524.2101 - Selenium disulfide suspension.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Selenium disulfide suspension. 524.2101 Section... § 524.2101 Selenium disulfide suspension. (a) Specifications. The product contains 0.9-percent weight in weight (w/w) selenium disulfide (1-percent weight in volume (w/v)). (b) Sponsors. See Nos. 000061,...

  12. 40 CFR 180.467 - Carbon disulfide; tolerances for residues.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 25 2012-07-01 2012-07-01 false Carbon disulfide; tolerances for... § 180.467 Carbon disulfide; tolerances for residues. Tolerances are established for the nematicide, insecticide, and fungicide carbon disulfide, from the application of sodium tetrathiocarbonate, in or on...

  13. 40 CFR 180.467 - Carbon disulfide; tolerances for residues.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 24 2014-07-01 2014-07-01 false Carbon disulfide; tolerances for... § 180.467 Carbon disulfide; tolerances for residues. Tolerances are established for the nematicide, insecticide, and fungicide carbon disulfide, from the application of sodium tetrathiocarbonate, in or on...

  14. 46 CFR 153.520 - Special requirements for carbon disulfide.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Special requirements for carbon disulfide. 153.520... Equipment Special Requirements § 153.520 Special requirements for carbon disulfide. A containment system carrying carbon disulfide must meet the following: (a) Each cargo pump must be of the intank type...

  15. 46 CFR 153.520 - Special requirements for carbon disulfide.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Special requirements for carbon disulfide. 153.520... Equipment Special Requirements § 153.520 Special requirements for carbon disulfide. A containment system carrying carbon disulfide must meet the following: (a) Each cargo pump must be of the intank type...

  16. 46 CFR 153.520 - Special requirements for carbon disulfide.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Special requirements for carbon disulfide. 153.520... Equipment Special Requirements § 153.520 Special requirements for carbon disulfide. A containment system carrying carbon disulfide must meet the following: (a) Each cargo pump must be of the intank type...

  17. 40 CFR 180.467 - Carbon disulfide; tolerances for residues.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Carbon disulfide; tolerances for... § 180.467 Carbon disulfide; tolerances for residues. Tolerances are established for the nematicide, insecticide, and fungicide carbon disulfide, from the application of sodium tetrathiocarbonate, in or on...

  18. 40 CFR 180.467 - Carbon disulfide; tolerances for residues.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 24 2011-07-01 2011-07-01 false Carbon disulfide; tolerances for... § 180.467 Carbon disulfide; tolerances for residues. Tolerances are established for the nematicide, insecticide, and fungicide carbon disulfide, from the application of sodium tetrathiocarbonate, in or on...

  19. 40 CFR 180.467 - Carbon disulfide; tolerances for residues.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 25 2013-07-01 2013-07-01 false Carbon disulfide; tolerances for... § 180.467 Carbon disulfide; tolerances for residues. Tolerances are established for the nematicide, insecticide, and fungicide carbon disulfide, from the application of sodium tetrathiocarbonate, in or on...

  20. 46 CFR 153.520 - Special requirements for carbon disulfide.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Special requirements for carbon disulfide. 153.520... Equipment Special Requirements § 153.520 Special requirements for carbon disulfide. A containment system carrying carbon disulfide must meet the following: (a) Each cargo pump must be of the intank type...

  1. 46 CFR 153.520 - Special requirements for carbon disulfide.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Special requirements for carbon disulfide. 153.520... Equipment Special Requirements § 153.520 Special requirements for carbon disulfide. A containment system carrying carbon disulfide must meet the following: (a) Each cargo pump must be of the intank type...

  2. Photoactive yellow protein from the halophilic bacterium Salinibacter ruber.

    PubMed

    Memmi, Samy; Kyndt, John; Meyer, Terry; Devreese, Bart; Cusanovich, Michael; Van Beeumen, Jozef

    2008-02-19

    A gene for photoactive yellow protein (PYP) was identified from the genome sequence of the extremely halophilic aerobic bacterium Salinibacter ruber (Sr). The sequence is distantly related to the prototypic PYP from Halorhodospira halophila (Hh) (37% identity) and contains most of the amino acid residues identified as necessary for function. However, the Sr pyp gene is not flanked by its two biosynthetic genes as in other species. To determine as to whether the Sr pyp gene encodes a functional protein, we cloned and expressed it in Escherichia coli, along with the genes for chromophore biosynthesis from Rhodobacter capsulatus. The Sr PYP has a 31-residue N-terminal extension as compared to other PYPs that appears to be important for dimerization; however, truncation of these extra residues did not change the spectral and photokinetic properties. Sr PYP has an absorption maximum at 431 nm, which is at shorter wavelengths than the prototypical Hh PYP (at 446 nm). It is also photoactive, being reversibly bleached by either blue or white light. The kinetics of dark recovery is slower than any of the PYPs reported to date (4.27 x 10(-4) s(-1) at pH 7.5). Sr PYP appears to have a normal photocycle with the I1 and I2 intermediates. The presence of the I2' intermediate is also inferred on the basis of the effects of temperature and alchohol on recovery. Sr PYP has an intermediate spectral form in equilibrium with the 431 nm form, similar to R. capsulatus PYP and the Y42F mutant of Hh PYP. Increasing ionic strength stabilizes the 431 nm form at the expense of the intermediate spectral form, and the kinetics of recovery is accelerated 6.4-fold between 0 and 3.5 M salt. This is observed with ions from both the chaotropic and the kosmotropic series. Ionic strength also stabilizes PYP against thermal denaturation, as the melting temperature is increased from 74 degrees C in buffer alone to 92 degrees C in 2 M KCl. Sr accumulates KCl in the cytoplasm, like Halobacterium, to

  3. Enhancing protein stability with extended disulfide bonds.

    PubMed

    Liu, Tao; Wang, Yan; Luo, Xiaozhou; Li, Jack; Reed, Sean A; Xiao, Han; Young, Travis S; Schultz, Peter G

    2016-05-24

    Disulfide bonds play an important role in protein folding and stability. However, the cross-linking of sites within proteins by cysteine disulfides has significant distance and dihedral angle constraints. Here we report the genetic encoding of noncanonical amino acids containing long side-chain thiols that are readily incorporated into both bacterial and mammalian proteins in good yields and with excellent fidelity. These amino acids can pair with cysteines to afford extended disulfide bonds and allow cross-linking of more distant sites and distinct domains of proteins. To demonstrate this notion, we preformed growth-based selection experiments at nonpermissive temperatures using a library of random β-lactamase mutants containing these noncanonical amino acids. A mutant enzyme that is cross-linked by one such extended disulfide bond and is stabilized by ∼9 °C was identified. This result indicates that an expanded set of building blocks beyond the canonical 20 amino acids can lead to proteins with improved properties by unique mechanisms, distinct from those possible through conventional mutagenesis schemes. PMID:27162342

  4. Preliminary Hazards Assessment: Iron disulfide purification system

    SciTech Connect

    1991-07-30

    A process for the purification (washing) of iron disulfide (FeS{sub 2}) powder is conducted in the Northeast corner (Area 353) of the main plant building (Building 100). This location is about 130 feet from the fenced boundary of the Partnership School/Child Development Center. In the first steps of the process, raw iron disulfide powder is ground and separated by particle size. The ground and sized powder is then purified in a three-step acid washing process using both hydrochloric acid (HCI) and hydrofluoric (HF) acid. The iron disulfide process is an intermittent batch process conducted four to eight times a year. This study is a Preliminary Hazards Assessment (PHA) to assess the hazards associated with the iron disulfide process. This is a preliminary study and will be used to determine if additional safety analysis is necessary. The scope of the PHA includes assessment of the process steps of grinding, size classification, and purification. The purpose is to identify major hazards and determine if the current and newly added safeguards are adequate for operation. The PHA also lists recommendations for additional safety features that should be added to reduce the risks of operation.

  5. High strength uranium-tungsten alloys

    DOEpatents

    Dunn, Paul S.; Sheinberg, Haskell; Hogan, Billy M.; Lewis, Homer D.; Dickinson, James M.

    1991-01-01

    Alloys of uranium and tungsten and a method for making the alloys. The amount of tungsten present in the alloys is from about 4 wt % to about 35 wt %. Tungsten particles are dispersed throughout the uranium and a small amount of tungsten is dissolved in the uranium.

  6. High strength uranium-tungsten alloy process

    DOEpatents

    Dunn, Paul S.; Sheinberg, Haskell; Hogan, Billy M.; Lewis, Homer D.; Dickinson, James M.

    1990-01-01

    Alloys of uranium and tungsten and a method for making the alloys. The amount of tungsten present in the alloys is from about 4 wt % to about 35 wt %. Tungsten particles are dispersed throughout the uranium and a small amount of tungsten is dissolved in the uranium.

  7. METHOD OF MAKING TUNGSTEN FILAMENTS

    DOEpatents

    Frazer, J.W.

    1962-12-18

    A method of making tungsten filaments is described in which the tungsten is completely free of isotope impurities in the range of masses 234 to 245 for use in mass spectrometers. The filament comprises a tantalum core generally less than 1 mil in diameter having a coating of potassium-free tantalum-diffused tungsten molecularly bonded thereto. In the preferred process of manufacture a short, thin tantalum filament is first mounted between terminal posts mounted in insulated relation through a backing plate. The tungsten is most conveniently vapor plated onto the tantalum by a tungsten carbonyl vapor decomposition method having a critical step because of the tendency of the tantalum to volatilize at the temperature of operntion of the filament. The preferred recipe comprises volatilizing tantalum by resistance henting until the current drops by about 40%, cutting the voltage back to build up the tungsten, and then gradually building the temperature back up to balance the rate of tungsten deposition with the rate of tantalum volatilization. (AEC)

  8. Photo-active collagen systems with controlled triple helix architecture

    PubMed Central

    Tronci, Giuseppe; Russell, Stephen J.; Wood, David J.

    2016-01-01

    The design of photo-active collagen systems is presented as a basis for establishing biomimetic materials with varied network architecture and programmable macroscopic properties. Following in-house isolation of type I collagen, reaction with vinyl-bearing compounds of varied backbone rigidity, i.e. 4-vinylbenzyl chloride (4VBC) and glycidyl methacrylate (GMA), was carried out. TNBS colorimetric assay, 1H-NMR and ATR-FTIR confirmed covalent and tunable functionalization of collagen lysines. Depending on the type and extent of functionalization, controlled stability and thermal denaturation of triple helices were observed via circular dichroism (CD), whereby the hydrogen-bonding capability of introduced moieties was shown to play a major role. Full gel formation was observed following photo-activation of functionalized collagen solutions. The presence of a covalent network only slightly affected collagen triple helix conformation (as observed by WAXS and ATR-FTIR), confirming the structural organization of functionalized collagen precursors. Photo-activated hydrogels demonstrated an increased denaturation temperature (DSC) with respect to native collagen, suggesting that the formation of the covalent network successfully stabilized collagen triple helices. Moreover, biocompatibility and mechanical competence of obtained hydrogels were successfully demonstrated under physiologically-relevant conditions. These results demonstrate that this novel synthetic approach enabled the formation of biocompatible collagen systems with defined network architecture and programmable macroscopic properties, which can only partially be obtained with current synthetic methods.

  9. Photo-active float for field water disinfection.

    PubMed

    Shwetharani, R; Balakrishna, R Geetha

    2016-03-01

    The present study investigates the antibacterial activity of a photoactive float fabricated with visible light active N-F-TiO2 for the disinfection of field water widely contaminated with Gram positive and Gram negative bacteria like, Salmonella typhimurium (Gram negative), Escherichia coli (Gram negative), Staphylococcus aureus (Gram positive), Bacillus species (Gram positive), and Pseudomonas species (Gram negative). The antibacterial activity can be attributed to the unique properties of the photocatalyst, which releases reactive oxygen species in aqueous solution, under the illumination of sunlight. N-F-TiO2 nanoparticles efficiently photocatalyse the destruction of all the bacteria present in the contaminated water, giving clean water. The inactivation of bacteria is confirmed by a standard plate count method, MDA, RNA and DNA analysis. The purity of water was further validated by SPC indicating nil counts of bacteria after two days of storing and testing. The photocatalysts were characterized by XRD, BET measurement, SEM, EDX, UV-Vis and PL analysis. PMID:26924232

  10. Photoactive supercapacitors for solar energy harvesting and storage

    NASA Astrophysics Data System (ADS)

    Takshi, Arash; Yaghoubi, Houman; Tevi, Tete; Bakhshi, Sara

    2015-02-01

    In most applications an energy storage device is required when solar cells are applied for energy harvesting. In this work, we have demonstrated that composite films of a conducting polymer and a dye can be used as photoactive electrodes in an electrochemical cell for concurrent solar energy conversion and charge storage. A device was made of poly ethylenedioxythiophene:polystyrene sulfonate and (PEDOT:PSS) and a porphyrin dye which showed a capacitance of ∼1.04 mF. The device was charged up to 430 mV (open circuit voltage) under a solar simulated illumination and was able to store the charge for more than 10 min in the dark. Further study on the concentration of the dye revealed the importance of the ratio between the dye and the conducting polymer to optimize the photovoltage and capacitance of the device. Also, the effect of the dye material was studied by using a Ruthenium (Ru) based dye. The device with the Ru dye showed a photovolatge of 198 mV and charge stability of more than 2 h.

  11. Porous Silicon's Photoactivity in Water: Insights into Environmental Fate.

    PubMed

    Moor, Kyle J; Cates, Ezra L; Kim, Jae-Hong

    2016-01-19

    Interest in porous silicon (pSi) (and, more broadly, silicon nanoparticles (NPs)) has increased along with their concomitant use in various commercial and consumer products, yet little is known about their behavior in the natural environment. In this study, we have investigated the photosensitization, optical, and surface properties of pSi as a function of time in aqueous systems. Samples were prepared via an anodic electrochemical etching procedure, resulting in pSi particles with diameters of ca. 500 nm, composed of a porous network of Si nanocrystallites of 2-4 nm. Initially, pSi particles generated significant amounts of (1)O2, yet they rapidly lost much of this ability due to the formation of an oxide layer on the surface, as determined by X-ray photoelectron spectroscopy, which likely prevented further photosensitization events. Addition of natural organic matter (NOM) did not significantly impact pSi's photosensitization abilities. The pSi lacked any intrinsic bactericidal properties on Escherichia coli and did not produce enough (1)O2 to considerably affect populations of a model virus, PR772, highlighting its relatively benign nature toward microbial communities. Results from this study suggest that the photoactivity of pSi is unlikely to persist in aqueous systems and that it may instead behave more similarly to silica particles from an environmental perspective. PMID:26741883

  12. RECOVERY OF URANIUM FROM TUNGSTEN

    DOEpatents

    Newnam, K.

    1959-02-01

    A method is presented for the rccovery of uranium which has adhered to tungsten parts in electromagnetic isotope separation apparatus. Such a tungsten article is dissolved electrolytically in 20% NaOH by using the tungsten article as the anode. The resulting solution, containing soluble sodium lungstate and an insoluble slime, is then filtered. The slime residue is ignited successively with sodium nitrate and sodium pyrosulfate and leashed, and the resulting filtrates are combined with the original filtrate. Uranium is then recovered from the combined flltrates by diuranate precipitation.

  13. Thiol-Disulfide Exchange Reactions in the Mammalian Extracellular Environment.

    PubMed

    Yi, Michael C; Khosla, Chaitan

    2016-06-01

    Disulfide bonds represent versatile posttranslational modifications whose roles encompass the structure, catalysis, and regulation of protein function. Due to the oxidizing nature of the extracellular environment, disulfide bonds found in secreted proteins were once believed to be inert. This notion has been challenged by the discovery of redox-sensitive disulfides that, once cleaved, can lead to changes in protein activity. These functional disulfides are twisted into unique configurations, leading to high strain and potential energy. In some cases, cleavage of these disulfides can lead to a gain of function in protein activity. Thus, these motifs can be referred to as switches. We describe the couples that control redox in the extracellular environment, examine several examples of proteins with switchable disulfides, and discuss the potential applications of disulfides in molecular biology. PMID:27023663

  14. Tungsten Toxicity in Plants

    PubMed Central

    Adamakis, Ioannis-Dimosthenis S.; Panteris, Emmanuel; Eleftheriou, Eleftherios P.

    2012-01-01

    Tungsten (W) is a rare heavy metal, widely used in a range of industrial, military and household applications due to its unique physical properties. These activities inevitably have accounted for local W accumulation at high concentrations, raising concerns about its effects for living organisms. In plants, W has primarily been used as an inhibitor of the molybdoenzymes, since it antagonizes molybdenum (Mo) for the Mo-cofactor (MoCo) of these enzymes. However, recent advances indicate that, beyond Mo-enzyme inhibition, W has toxic attributes similar with those of other heavy metals. These include hindering of seedling growth, reduction of root and shoot biomass, ultrastructural malformations of cell components, aberration of cell cycle, disruption of the cytoskeleton and deregulation of gene expression related with programmed cell death (PCD). In this article, the recent available information on W toxicity in plants and plant cells is reviewed, and the knowledge gaps and the most pertinent research directions are outlined. PMID:27137642

  15. Excited States and Photochemistry of Chromophores in the Photoactive Proteins Explored by the Combined Quantum Mechanical and Molecular Mechanical Calculations.

    PubMed

    Liu, Lihong; Cui, Ganglong; Fang, Wei-Hai

    2015-01-01

    A photoactive protein usually contains a unique chromophore that is responsible for the initial photoresponse and functions of the photoactive protein are determined by the interaction between the chromophore and its protein surroundings. The combined quantum mechanical and molecular mechanical (QM/MM) approach is demonstrated to be a very useful tool for exploring structures and functions of a photoactive protein with the chromophore and its protein surroundings treated by the QM and MM methods, respectively. In this review, we summarize the basic formulas of the QM/MM approach and emphasize its applications to excited states and photoreactions of chromophores in rhodopsin protein, photoactive yellow protein, and green fluorescent protein. PMID:26415847

  16. Electrochemical Reduction of Tungsten Compounds to Produce Tungsten Powder

    NASA Astrophysics Data System (ADS)

    Erdoğan, Metehan; Karakaya, Ishak

    2010-08-01

    The production of tungsten by direct current reduction has been investigated. Experimental studies involved the electrochemical reduction of the solid tungsten compounds tungsten trioxide (WO3) and calcium tungstate (CaWO4) in the form of an assembled cathode of porous pellets attached to a current collector. Molten calcium chloride and a molten solution of calcium chloride and sodium chloride at eutectic composition, 48 pct mol NaCl, were used as the electrolytes. Reduced samples were characterized by means of X-ray diffraction analyses and scanning electron microscopy. The results of X-ray analyses, supported with thermodynamic computations, showed that WO3 cannot be used without loss in processes that involve the use of CaCl2 at high temperatures because it reacts with CaCl2 by releasing volatile tungsten oxychloride. In the electrochemical reduction of CaWO4, X-ray diffraction results indicated the presence of tungsten with significant concentrations of calcium compounds. Metallic tungsten was obtained after treating the reduced samples with dilute hydrochloric acid solutions.

  17. Increased monolayer domain size and patterned growth of tungsten disulfide through controlling surface energy of substrates

    NASA Astrophysics Data System (ADS)

    Godin, Kyle; Kang, Kyungnam; Fu, Shichen; Yang, Eui-Hyeok

    2016-08-01

    We report a surface energy-controlled low-pressure chemical vapor deposition growth of WS2 monolayers on SiO2 using pre-growth oxygen plasma treatment of substrates, facilitating increased monolayer surface coverage and patterned growth without lithography. Oxygen plasma treatment of the substrate caused an increase in the average domain size of WS2 monolayers by 78%  ±  2% while having a slight reduction in nucleation density, which translates to increased monolayer surface coverage. This substrate effect on growth was exploited to grow patterned WS2 monolayers by patterned plasma treatment on patterned substrates and by patterned source material with resolutions less than 10 µm. Contact angle-based surface energy measurements revealed a dramatic increase in polar surface energy. A growth model was proposed with lowered activation energies for growth and increased surface diffusion length consistent with the range of results observed. WS2 samples grown with and without oxygen plasma were similar high quality monolayers verified through transmission electron microscopy, selected area electron diffraction, atomic force microscopy, Raman, and photoluminescence measurements. This technique enables the production of large-grain size, patterned WS2 without a post-growth lithography process, thereby providing clean surfaces for device applications.

  18. Trion fine structure and coupled spin-valley dynamics in monolayer tungsten disulfide.

    PubMed

    Plechinger, Gerd; Nagler, Philipp; Arora, Ashish; Schmidt, Robert; Chernikov, Alexey; Del Águila, Andrés Granados; Christianen, Peter C M; Bratschitsch, Rudolf; Schüller, Christian; Korn, Tobias

    2016-01-01

    Monolayer transition-metal dichalcogenides have recently emerged as possible candidates for valleytronic applications, as the spin and valley pseudospin are directly coupled and stabilized by a large spin splitting. The optical properties of these two-dimensional crystals are dominated by tightly bound electron-hole pairs (excitons) and more complex quasiparticles such as charged excitons (trions). Here we investigate monolayer WS2 samples via photoluminescence and time-resolved Kerr rotation. In photoluminescence and in energy-dependent Kerr rotation measurements, we are able to resolve two different trion states, which we interpret as intravalley and intervalley trions. Using time-resolved Kerr rotation, we observe a rapid initial valley polarization decay for the A exciton and the trion states. Subsequently, we observe a crossover towards exciton-exciton interaction-related dynamics, consistent with the formation and decay of optically dark A excitons. By contrast, resonant excitation of the B exciton transition leads to a very slow decay of the Kerr signal. PMID:27586517

  19. Tungsten disulfide (WS2) based all-fiber-optic humidity sensor.

    PubMed

    Luo, Yunhan; Chen, Chaoying; Xia, Kai; Peng, Shuihua; Guan, Heyuan; Tang, Jieyuan; Lu, Huiui; Yu, Jianhui; Zhang, Jun; Xiao, Yi; Chen, Zhe

    2016-04-18

    We demonstrate a novel all-fiber-optic humidity sensor comprised of a WS2 film overlay on a side polished fiber (SPF). This sensor can achieve optical power variation of up to 6 dB in a relative humidity (RH) range of 35%-85%. In particular, this novel humidity fiber sensor has a linear correlation coefficient of 99.39%, sensitivity of 0.1213 dB/%RH, and a humidity resolution of 0.475%RH. Furthermore, this sensor shows good repeatability and reversibility, and fast response to breath stimulus. This WS2 based all-fiber optic humidity sensor is easy to fabricate, is compatible with pre-established fiber optic systems, and holds great potential in photonics applications such as in all-fiber optic humidity sensing networks. PMID:27137326

  20. Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer

    PubMed Central

    Song, Jeong-Gyu; Ryu, Gyeong Hee; Lee, Su Jeong; Sim, Sangwan; Lee, Chang Wan; Choi, Taejin; Jung, Hanearl; Kim, Youngjun; Lee, Zonghoon; Myoung, Jae-Min; Dussarrat, Christian; Lansalot-Matras, Clement; Park, Jusang; Choi, Hyunyong; Kim, Hyungjun

    2015-01-01

    The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo1−xWxS2 alloy using sulfurization of super-cycle atomic layer deposition Mo1−xWxOy. Various spectroscopic and microscopic results indicate that the synthesized Mo1−xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo1−xWxS2 multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet–visible spectrophotometer results reveal that a VCC Mo1−xWxS2 multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo1−xWxS2 multilayer. Further, we demonstrate that a VCC Mo1−xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption. PMID:26204328

  1. Valley polarization and coherence in atomically thin tungsten disulfide via optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Bairen; Zeng, Hualing; Dai, Junfeng; Gong, Zhirui; Cui, Xiaodong

    Atomically thin group-VI transition metal dichalcogenides (TMDC) has been emerging as a family of intrinsic 2-dimensional crystals with a sizeable bandgap, opening a potential avenue for ultimate electronics and optoelectronics. Besides, the characteristic structural inversion symmetry breaking in monolayers leads to non-zero but contrasting Berry curvatures and orbital magnetic moments at K/K' valleys. These features provide an opportunity to manipulate electrons' additional internal degrees of freedom, namely the valley degree of freedom, making monolayer TMDC a promising candidate for the conceptual valleytronics. Here, our experimental approach on valley dependent circular dichroism in monolayer and bilayer WS2 via optical spectroscopy are elaborated. Consequently, the polarization of photoluminescence inherits that of excitations, circularly and linearly polarized, confirming the valley dependent selectivity rule. However, the valley polarization and valley coherence in bilayer WS2 owing to the coupling of spin, valley and layer degrees of freedom, are anomalously robust compared with monolayer WS2. We propose potential mechanisms of the anomalous behavior in WS2 bilayers.

  2. Synthesis and Optical Control of Circular Polarization in monolayer Tungsten Disulfide

    NASA Astrophysics Data System (ADS)

    McCreary, Kathleen; Hanbicki, Aubrey; Jonker, Berend; Currie, Marc; Kioseoglou, George

    The unique electronic band structure in single layer WS2 provides the ability to selectively populate a desired valley by exciting with circularly polarized light. The valley population is reflected through the circular polarization of photoluminescence (PL). We investigate the circularly polarized PL in WS2 monolayers synthesized using chemical vapor deposition (CVD). The resulting polarization is strongly dependent on the sample preparation. As-grown CVD WS2 (still on the growth substrate) exhibits low polarized emission, regardless of laser excitation or laser power. Removing WS2 from the growth substrate and repositioning on the same substrate significantly impacts the optical properties. In transferred films, the excitonic state is optically controlled via high-powered laser exposure such that subsequent PL is solely from either the charged exciton state or the neutral exciton state. Neutral excitonic emission exhibits zero polarization whereas the trion polarization can exceed 25% at room temperature. The removal process may modify the strain, sample-to-substrate distance, and chemical doping in the WS2 monolayer, and work is underway to determine how these factors influence the valley populations. These results demonstrate a new method to control the excitonic state and PL polarization in monolayer WS2. . Supported by core programs at NRL and the NRL Nanoscience Institute, and by the Air Force Office of Scientific Research #AOARD 14IOA018-134141.

  3. Controlled preferential oxidation of grain boundaries in monolayer tungsten disulfide for direct optical imaging.

    PubMed

    Rong, Youmin; He, Kuang; Pacios, Mercè; Robertson, Alex W; Bhaskaran, Harish; Warner, Jamie H

    2015-04-28

    Synthetic 2D crystal films grown by chemical vapor deposition are typically polycrystalline, and determining grain size within domains and continuous films is crucial for determining their structure. Here we show that grain boundaries in the 2D transition metal dichalcogenide WS2, grown by CVD, can be preferentially oxidized by controlled heating in air. Under our developed conditions, preferential degradation at the grain boundaries causes an increase in their physical size due to oxidation. This increase in size enables their clear and rapid identification using a standard optical microscope. We demonstrate that similar treatments in an Ar environment do no show this effect, confirming that oxidation is the main role in the structural change. Statistical analysis of grain boundary (GB) angles shows dominant mirror formation. Electrical biasing across the GB is shown to lead to changes at the GB and their observation under an optical microscope. Our approach enables high-throughput screening of as-synthesized WS2 domains and continuous films to determine their crystallinity and should enable improvements in future CVD growth of these materials. PMID:25870912

  4. Heated die facilitates tungsten forming

    NASA Technical Reports Server (NTRS)

    Chattin, J. H.; Haystrick, J. E.; Laughlin, J. C.; Leidy, R. A.

    1966-01-01

    Tungsten forming in a press brake employs a bottom die assembly with a heating manifold between two water-cooled die sections. The manifold has hydrogen-oxygen burners spaced along its length for even heat during forming.

  5. Why Tungsten Instead of Wolfram?

    NASA Astrophysics Data System (ADS)

    Jensen, William B.

    2008-04-01

    In response to a reader query, the column traces the reason that American and British chemical literature use the name tungsten for element 74, while northern European literature uses the name wolfram.

  6. Energetics of short hydrogen bonds in photoactive yellow protein.

    PubMed

    Saito, Keisuke; Ishikita, Hiroshi

    2012-01-01

    Recent neutron diffraction studies of photoactive yellow protein (PYP) proposed that the H bond between protonated Glu46 and the chromophore [ionized p-coumaric acid (pCA)] was a low-barrier H bond (LBHB). Using the atomic coordinates of the high-resolution crystal structure, we analyzed the energetics of the short H bond by two independent methods: electrostatic pK(a) calculations and a quantum mechanical/molecular mechanical (QM/MM) approach. (i) In the QM/MM optimized geometry, we reproduced the two short H-bond distances of the crystal structure: Tyr42-pCA (2.50 Å) and Glu46-pCA (2.57 Å). However, the H atoms obviously belonged to the Tyr or Glu moieties, and were not near the midpoint of the donor and acceptor atoms. (ii) The potential-energy curves of the two H bonds resembled those of standard asymmetric double-well potentials, which differ from those of LBHB. (iii) The calculated pK(a) values for Glu46 and pCA were 8.6 and 5.4, respectively. The pK(a) difference was unlikely to satisfy the prerequisite for LBHB. (iv) The LBHB in PYP was originally proposed to stabilize the ionized pCA because deprotonated Arg52 cannot stabilize it. However, the calculated pK(a) of Arg52 and QM/MM optimized geometry suggested that Arg52 was protonated on the protein surface. The short H bond between Glu46 and ionized pCA in the PYP ground state could be simply explained by electrostatic stabilization without invoking LBHB. PMID:22173632

  7. Organic photovoltaic cells based on photoactive bacteriorhodopsin proteins

    NASA Astrophysics Data System (ADS)

    Al-Aribe, Khaled M.; Knopf, George K.; Bassi, Amarjeet S.

    2013-03-01

    Recent advances in materials engineering have enabled photovoltaic (PV) cells to be fabricated from solid state semiconductors, photosensitive organic dyes, and photoactive proteins. One type of organic PV cell is based on the natural light-harvesting protein bacteriorhodopsin (bR) found in the plasma membrane of a salt marsh archaebacteria. When exposed to sunlight, each bR molecule acts as a simple proton pump which transports hydrogen ions from the cytoplasmic to the extracellular side through a transmembrane ion channel. Two types of bR-PV cells comprised of photosensitive dry and aqueous (wet) bR thin films are described in this paper. The self-assembled monolayer of oriented purple membrane (PM) patches from the bR protein is created on a bio-functionalized gold (Au) surface using a biotin molecular recognition technique. The dry bR monolayer is covered with an optically transparent Indium Tin Oxide (ITO) electrode to complete the dry bR-PV device. In contrast, the aqueous bR-PV cell is created by immobilizing the bR monolayer on an Au-coated porous substrate and then inserting the assembly between two micro-reservoirs filled with KCl solutions. Platinum wire probes are then inserted in the opposing liquid reserviors near the porous bR monolayer. The dry bR-PV cell generated a photo-electric response of 9.73 mV/cm2, while the aqueous bR-PV produced 41.7 mV/cm2 and 33.3 μA/cm2. Although the generated voltages appear small, it may be sufficient to power various microelectromechanical systems (MEMS) and microfluidic devices.

  8. Alkali metal intercalates of molybdenum disulfide.

    NASA Technical Reports Server (NTRS)

    Somoano, R. B.; Hadek, V.; Rembaum, A.

    1973-01-01

    Study of some of the physicochemical properties of compounds obtained by subjecting natural molybdenite and single crystals of molybdenum disulfide grown by chemical vapor transport to intercalation with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Reported data and results include: (1) the intercalation of the entire alkali metal group, (2) stoichiometries and X-ray data on all of the compounds, and (3) superconductivity data for all the intercalation compounds.

  9. The alkaline earth intercalates of molybdenum disulfide

    NASA Technical Reports Server (NTRS)

    Somoano, R. B.; Hadek, V.; Rembaum, A.; Samson, S.; Woollam, J. A.

    1975-01-01

    Molybdenum disulfide has been intercalated with calcium and strontium by means of the liquid ammonia technique. Chemical, X-ray, and superconductivity data are presented. The X-ray data reveal a lowering of crystal symmetry and increase of complexity of the structure upon intercalation with the alkaline earth metals. The Ca and Sr intercalates start to superconduct at 4 and 5.6 K, respectively, and show considerable anisotropy regarding the critical magnetic field.

  10. Sterically hindered disulfide bridges in cystine diketopiperazine, cysteinyl-cysteine disulfide and derivatives.

    PubMed

    Ottnad, M; Hartter, P; Jung, G

    1975-06-01

    L-Cystine diketopiperazine (1), L-cysteinyl-cysteine disulfide -HCl (2), L-cysteinyl-cysteine disulfide methyl ester -HCl (3), and t-butyloxycarbonyl-L-cysteinyl-cysteine disulfide methyl ester (4) are investigated by CD, ultraviolet, 13C NMR, infrared and laser Raman spectroscopy. The temperature dependence of the 13C NMR signals of 1 reveals an exceptionally high energy barrier of deltaGNo. = 15.8 +/- 0.2 kcal/mol for the reversible change in helicity of the inherently dissymmetric disulfide bridge of 1. The P-helical diastereomer predominates in dimethyl-sulfoxide at 25 degrees C, with 80-85% of the molecules having this configuration. The Cotton effects of 1 are larger and show smaller temperature coefficients than the conformationally more mobile cystine compounds 2 and 3. After dissolving crystals of 1 in 95% ethanol there is a time-dependent decrease of the ellipticity of the negative Cotton effect at 225 nm, indicating a conformational change in going from crystal to solution. Besides 1, 2 and 3 are at present the only known examples of cystine derivatives with C-S-S-C torsional angles around 90 degrees, which do not exhibit optical activity in the long wavelength disulfide absorption, as is predicted for 1 from the Linderberg-Michl model. At 305 nm a new weak Cotton effect was discovered for 1. The solvent dependence of the CD spectra is discussed and the infrared and Raman spectra are assigned. PMID:1181260

  11. Effects of tungsten on environmental systems.

    PubMed

    Strigul, Nikolay; Koutsospyros, Agamemnon; Arienti, Per; Christodoulatos, Christos; Dermatas, Dimitris; Braida, Washington

    2005-10-01

    Tungsten is a metal with many industrial and military applications, including manufacturing of commercial and military ammunition. Despite its widespread use, the potential environmental effects of tungsten are essentially unknown. This study addresses environmental effects of particulate and soluble forms of tungsten, and to a minor extent certain tungsten alloy components, present in some munitions formulations. Dissolution of tungsten powder significantly acidifies soils. Tungsten powder mixed with soils at rates higher than 1% on a mass basis, trigger changes in soil microbial communities resulting in the death of a substantial portion of the bacterial component and an increase of the fungal biomass. It also induces the death of red worms and plants. These effects appear to be related with the soil acidification occurring during tungsten dissolution. Dissolved tungsten species significantly decrease microbial yields by as much as 38% for a tungsten media concentration of 89 mg l(-1). Soluble tungsten concentrations as low as 10(-5) mg l(-1), cause a decrease in biomass production by 8% which is possibly related to production of stress proteins. Plants and worms take up tungsten ions from soil in significant amounts while an enrichment of tungsten in the plant rhizosphere is observed. These results provide an indication that tungsten compounds may be introduced into the food chain and suggest the possibility of development of phytoremediation-based technologies for the cleanup of tungsten contaminated sites. PMID:16168748

  12. Solvothermal synthesis of nickel-tungsten sulfides for 2-propanol dehydration.

    PubMed

    Gómez-Gutiérrez, Claudia M; Luque, P A; Guerra-Rivas, G; López-Sánchez, J A; Armenta, M A; Quintana, J M; Olivas, A

    2015-01-01

    The bimetallic nickel-tungsten catalysts were prepared via solvothermal method. The X-ray Diffractometer (XRD) analysis revealed that the corresponding peaks at 14°, 34°, and 58° were for tungsten disulfide (WS2 ) hexagonal phase. The catalysts displayed different crystalline phase with nickel addition, and as an effect the WS2 surface area decreased from 74.7 to 2.0 m(2) g(--1) . In this sense, high-resolution transmission electron microscopy (HRTEM) showed the layers set in direction (002) with an onion-like morphology, and in the center of the particles there is a large amount of nickel contained with 6-8 layers covering it. The catalytic dehydration of 2-propanol was selective to propene in 100% at 250 °C for the sample with 0.7 of atomic ratio of Ni/Ni + W. PMID:25676058

  13. Process Of Bonding Copper And Tungsten

    DOEpatents

    Slattery, Kevin T.; Driemeyer, Daniel E.; Davis, John W.

    2000-07-18

    Process for bonding a copper substrate to a tungsten substrate by providing a thin metallic adhesion promoting film bonded to a tungsten substrate and a functionally graded material (FGM) interlayer bonding the thin metallic adhesion promoting film to the copper substrate. The FGM interlayer is formed by sintering a stack of individual copper and tungsten powder blend layers having progressively higher copper content/tungsten content, by volume, ratio values in successive powder blend layers in a lineal direction extending from the tungsten substrate towards the copper substrate. The resulting copper to tungsten joint well accommodates the difference in the coefficient of thermal expansion of the materials.

  14. Polarographic determination of tungsten in rocks

    USGS Publications Warehouse

    Reichen, L.E.

    1954-01-01

    This work was undertaken to develop a simpler and faster method than the classical gravimetric procedure for the determination of tungsten in rocks and ores. A new polarographic wave of tungsten is obtained in a supporting electrolyte of dilute hydrochloric acid containing tartrate ion. This permits the determination of tungsten both rapidly and accurately. No precipitation of the tungsten is necessary, and only the iron need be separated from the tungsten. The accuracy is within the limits of a polarographic procedure; comparison of polarographic and gravimetric results is given. The method reduces appreciably the amount of time ordinarily consumed in determination of tungsten.

  15. Tungsten in iron meteorites

    NASA Technical Reports Server (NTRS)

    Scott, E. R. D.

    1978-01-01

    Tungsten concentrations have been determined by instrumental neutron activation in 104 iron meteorites, and range from 0.07 to 5 microg/g. In individual groups, concentrations vary by factors of between 1.5 and 8, but there are negative W-Ni correlations in 8 groups: IAB, IC, IIAB, IID, IIE, IIIAB, IIICD, and IIIF. The lowest W concentrations are found in groups IAB and IIICD, which also have the smallest slopes on a W-Ni plot. Eighteen anomalous irons have W concentrations between 5 microg/g (Butler) and 0.11 microg/g (Rafrueti). The distribution of W in irons shows similarities to that of other refractory sideophilic elements (except Mo), but is closest to the distribution of Ru and Pt. Assuming that chemical trends in group IIIAB were produced by fractional crystallization, a value of 1.6 can be deduced for the distribution coefficient of W between solid and liquid metal, as compared with 0.89 for Mo. Experimental evidence in support of these values is tenuous.

  16. Tungsten diffusion in silicon

    SciTech Connect

    De Luca, A.; Texier, M.; Burle, N.; Oison, V.; Pichaud, B.; Portavoce, A.; Grosjean, C.

    2014-01-07

    Two doses (10{sup 13} and 10{sup 15} cm{sup −2}) of tungsten (W) atoms were implanted in different Si(001) wafers in order to study W diffusion in Si. The samples were annealed or oxidized at temperatures between 776 and 960 °C. The diffusion profiles were measured by secondary ion mass spectrometry, and defect formation was studied by transmission electron microscopy and atom probe tomography. W is shown to reduce Si recrystallization after implantation and to exhibit, in the temperature range investigated, a solubility limit close to 0.15%–0.2%, which is higher than the solubility limit of usual metallic impurities in Si. W diffusion exhibits unusual linear diffusion profiles with a maximum concentration always located at the Si surface, slower kinetics than other metals in Si, and promotes vacancy accumulation close to the Si surface, with the formation of hollow cavities in the case of the higher W dose. In addition, Si self-interstitial injection during oxidation is shown to promote W-Si clustering. Taking into account these observations, a diffusion model based on the simultaneous diffusion of interstitial W atoms and W-Si atomic pairs is proposed since usual models used to model diffusion of metallic impurities and dopants in Si cannot reproduce experimental observations.

  17. Tungsten wire and tubing joined by nickel brazing

    NASA Technical Reports Server (NTRS)

    1965-01-01

    Thin tungsten wire and tungsten tubing are brazed together using a contacting coil of nickel wire heated to its melting point in an inert-gas atmosphere. This method is also effective for brazing tungsten to tungsten-rhenium parts.

  18. Human Defensin 5 Disulfide Array Mutants: Disulfide Bond Deletion Attenuates Antibacterial Activity Against Staphylococcus aureus

    PubMed Central

    Wanniarachchi, Yoshitha A.; Kaczmarek, Piotr; Wan, Andrea; Nolan, Elizabeth M.

    2011-01-01

    Human α-defensin 5 (HD5, HD5ox to specify the oxidized and disulfide linked form) is a 32-residue cysteine-rich host-defense peptide, expressed and released by small intestinal Paneth cells, that exhibits antibacterial activity against a number of Gram-negative and –positive bacterial strains. To ascertain the contributions of its disulfide array to structure, antimicrobial activity, and proteolytic stability, a series of HD5 double mutant peptides where pairs of cysteine residues corresponding to native disulfide linkages (Cys3—Cys31, Cys5—Cys20, Cys10—Cys30) were mutated to Ser or Ala residues were overexpressed in E. coli, purified and characterized. A hexa mutant peptide, HD5[Serhexa], where all six native Cys residues are replaced by Ser residues was also evaluated. Removal of a single native S—S linkage influences oxidative folding and regioisomerization, antibacterial activity, Gram-negative bacterial membrane permeabilization, and proteolytic stability. Whereas the majority of the HD5 mutant peptides show low-micromolar activity against Gram-negative E. coli ATCC 25922 in colony counting assays, the wild-type disulfide array is essential for low-micromolar activity against Gram-positive S. aureus ATCC 25923. Removal of a single disulfide bond attenuates the activity observed for HD5ox against this Gram-positive bacterial strain. This observation supports the notion that the HD5ox mechanism of antibacterial action differs for Gram-negative and Gram-positive species (Wei, G.; de Leeuw, E., Pazgier, M., Yuan, W., Zou, G., Wang, J., Ericksen, B., Lu, W.-Y.; Lehrer, R. I.; Lu, W. (2009) J. Biol. Chem. 284, 29180-29192), and that the native disulfide array is a requirement for its activity against S. aureus. PMID:21861459

  19. Increasing photoactivity of titanium dioxide immobilized on glass plate with optimization of heat attachment method parameters.

    PubMed

    Behnajady, Mohammad A; Modirshahla, Nasser; Mirzamohammady, Maryam; Vahid, Behrouz; Behnajady, Bahram

    2008-12-30

    In the present work the optimization of heat attachment method for increasing photoactivity of immobilized TiO2 on glass plate was investigated. Results show that sonication time, TiO2 suspension dosage, immobilization temperature, solvent type and immobilization replications are very effective on the photoactivity of immobilized TiO2 on glass plate on the removal of C.I. Acid Red 88 (AR88) and optimizing these parameters increases the photoactivity of immobilized catalyst. In other step, the effect of operational parameters such as light intensity and initial concentration of AR88 on the removal of AR88 was investigated with four times immobilized TiO2 on glass plate. Results show that removal rate decreases with increasing initial concentration of AR88 but increases with increasing UV-light intensity. PMID:18440135

  20. Photoactive films of photosystem I on transparent reduced graphene oxide electrodes.

    PubMed

    Darby, Emily; LeBlanc, Gabriel; Gizzie, Evan A; Winter, Kevin M; Jennings, G Kane; Cliffel, David E

    2014-07-29

    Photosystem I (PSI) is a photoactive electron-transport protein found in plants that participates in the process of photosynthesis. Because of PSI's abundance in nature and its efficiency with charge transfer and separation, there is a great interest in applying the protein in photoactive electrodes. Here, we developed a completely organic, transparent, conductive electrode using reduced graphene oxide (RGO) on which a multilayer of PSI could be deposited. The resulting photoactive electrode demonstrated current densities comparable to that of a gold electrode modified with a multilayer film of PSI and significantly higher than that of a graphene electrode modified with a monolayer film of PSI. The relatively large photocurrents produced by integrating PSI with RGO and using an opaque, organic mediator can be applied to the facile production of more economic solar energy conversion devices. PMID:25029217

  1. Origin of photoactivity of oxygen-deficient TiO{sub 2} under visible light

    SciTech Connect

    Lo, H.-H.; Gopal, Neeruganti O.; Ke, S.-C.

    2009-08-24

    As it is now well established that oxygen vacancies are spontaneously introduced during nitrogen doping of anatase TiO{sub 2}, there is a lively debate on whether nitrogen dopant or oxygen vacancy contributes to the visible light photoactivity of the doped catalyst. We showed that the coordinately unsaturated Ti site is integral to the visible light photoactivity in anatase oxygen-deficient TiO{sub 2} catalyst. Accordingly, oxygen vacancies may contribute to the visible light photoactivities in N-doped TiO{sub 2} and other nonmetallic ion-doped TiO{sub 2} as well. A redox active visible light photocatalyst has been developed based on oxygen-deficient structure in anatase TiO{sub 2}.

  2. The synthesis and imaging study of a series of novel photoactive polymers with diazoketo groups in their side chains

    NASA Astrophysics Data System (ADS)

    Liu, Lu; Zou, Yingquan; Yang, Yuchun; Huang, Yong; Liu, Qisheng; Niu, Huinan

    2009-12-01

    A kind of photoactive polymer with diazoketo groups in its side chains has been reported in SPIE and other related papers, and this photoactive polymer can be used in deep UV non-CARs (non-chemically amplified resists) system. Based on the work above, a series of novel photoactive monomers with substituents like phenyl, p-methylphenyl, p-methoxyphenyl, p-dimethylaminophenyl on the end of the molecule are designed and synthesized. By changing their substituents, the maximum-absorption wavelength of the photoactive monomers has been moved to 356nm, and it still has comparatively large absorption at 365nm (I-line). A series of photoactive polymers were obtained by polymerizing the monomer with methyl methacrylate and 2-hydroxyethyl methacrylate together. Upon irradiaton in the waveleng of 365nm, the diazoketo groups which are in the side chains of the photoactive polymers undergo the wolff rearrangment and afford ketens that react with water to provide base-soluble photoproducts. Applying this kind of photoactive polymers to non-CARs, a positive image can be obtained. This kind of photoactive polymers have great value in I-line non-CARs, TFT-LCD and IC discrete devices processing. And its anti-dry etching ability is enhanced by the introduction of the benzene ring.

  3. Temperature-controlled neutron reflectometry sample cell suitable for study of photoactive thin films

    SciTech Connect

    Yager, Kevin G.; Tanchak, Oleh M.; Barrett, Christopher J.; Watson, Mike J.; Fritzsche, Helmut

    2006-04-15

    We describe a novel cell design intended for the study of photoactive materials using neutron reflectometry. The cell can maintain sample temperature and control of ambient atmospheric environment. Critically, the cell is built with an optical port, enabling light irradiation or light probing of the sample, simultaneous with neutron reflectivity measurements. The ability to measure neutron reflectivity with simultaneous temperature ramping and/or light illumination presents unique opportunities for measuring photoactive materials. To validate the cell design, we present preliminary results measuring the photoexpansion of thin films of azobenzene polymer.

  4. Following the wetting of one-dimensional photoactive surfaces.

    PubMed

    Macias-Montero, Manuel; Borras, Ana; Alvarez, Rafael; Gonzalez-Elipe, Agustin R

    2012-10-23

    This article aims toward a full description of the wetting conversion from superhydrophobicity to superhydrophilicity under illumination with UV light of high-density ZnO nanorods surfaces by (i) following the evolution of the clusters and superstructures formed by the nanocarpet effect as a function of the water contact angle (WCA); (ii) characterization of the superhydrophobic and superhydrophilic states with an environmental scanning electron microscope (ESEM); and (iii) using the nanocarpet effect as a footprint of both local and apparent water contact angles. Thus, the main objective of the article is to provide a general vision of the wettability of 1D photoactive surfaces. In parallel, the nanocarpet (NC) formation by clustering of vertically aligned ZnO nanorods (NR) when water is dripped on their surface and then dried is studied for the first time by taking advantage of the possibility of tuning the surface water contact angle of the ZnO NR structure under UV preillumination. As a result, we demonstrate the feasibility of controlling the size and other morphological characteristics of the NCs. Moreover, a strong anisotropic wetting behavior, characterized by a Δθ = θ(parallel) - θ(perpendicular) = 30°, is shown on an asymmetrically aligned NC surface resulting from arrays of tilted NRs. The study of the condensation/evaporation of water on/from an as-prepared (superhydrophobic) or a preilluminated (superhydrophilic) NR surface examined by an environmental scanning electron microscope has evidenced the formation of supported water droplets with polygonal shapes in the first case and the complete filling of the inter-NR space in the latter. The long-term stability of the NC clusters has been utilized as a footprint to track the penetration depth of water within the inter-NR space in the three borderline regions of water droplets. This analysis has shown that for moderately hydrophobic surfaces (i.e., water contact angles lower than 130°) water

  5. A composite light-harvesting layer from photoactive polymer and halide perovskite for planar heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Wang, Heming; Rahaq, Yaqub; Kumar, Vikas

    2016-07-01

    A new route for fabrication of photoactive materials in organic-inorganic hybrid solar cells is presented in this report. Photoactive materials by blending a semiconductive conjugated polymer with an organolead halide perovskite were fabricated for the first time. The composite active layer was then used to make planar heterojunction solar cells with the PCBM film as the electron-acceptor. Photovoltaic performance of solar cells was investigated by J-V curves and external quantum efficiency spectra. We demonstrated that the incorporation of the conjugated photoactive polymer into organolead halide perovskites did not only contribute to the generation of charges, but also enhance stability of solar cells by providing a barrier protection to halide perovskites. It is expected that versatile of conjugated semi-conductive polymers and halide perovskites in photoactive properties enables to create various combinations, forming composites with advantages offered by both types of photoactive materials.

  6. A composite light-harvesting layer from photoactive polymer and halide perovskite for planar heterojunction solar cells.

    PubMed

    Wang, Heming; Rahaq, Yaqub; Kumar, Vikas

    2016-01-01

    A new route for fabrication of photoactive materials in organic-inorganic hybrid solar cells is presented in this report. Photoactive materials by blending a semiconductive conjugated polymer with an organolead halide perovskite were fabricated for the first time. The composite active layer was then used to make planar heterojunction solar cells with the PCBM film as the electron-acceptor. Photovoltaic performance of solar cells was investigated by J-V curves and external quantum efficiency spectra. We demonstrated that the incorporation of the conjugated photoactive polymer into organolead halide perovskites did not only contribute to the generation of charges, but also enhance stability of solar cells by providing a barrier protection to halide perovskites. It is expected that versatile of conjugated semi-conductive polymers and halide perovskites in photoactive properties enables to create various combinations, forming composites with advantages offered by both types of photoactive materials. PMID:27411487

  7. A composite light-harvesting layer from photoactive polymer and halide perovskite for planar heterojunction solar cells

    PubMed Central

    Wang, Heming; Rahaq, Yaqub; Kumar, Vikas

    2016-01-01

    A new route for fabrication of photoactive materials in organic-inorganic hybrid solar cells is presented in this report. Photoactive materials by blending a semiconductive conjugated polymer with an organolead halide perovskite were fabricated for the first time. The composite active layer was then used to make planar heterojunction solar cells with the PCBM film as the electron-acceptor. Photovoltaic performance of solar cells was investigated by J-V curves and external quantum efficiency spectra. We demonstrated that the incorporation of the conjugated photoactive polymer into organolead halide perovskites did not only contribute to the generation of charges, but also enhance stability of solar cells by providing a barrier protection to halide perovskites. It is expected that versatile of conjugated semi-conductive polymers and halide perovskites in photoactive properties enables to create various combinations, forming composites with advantages offered by both types of photoactive materials. PMID:27411487

  8. Fabrication techniques developed for small- diameter, thin-wall tungsten and tungsten alloy tubing

    NASA Technical Reports Server (NTRS)

    Brillhart, D. C.; Burt, W. R.; Karasek, F. J.; Mayfield, R. M.

    1968-01-01

    Report describes methods for the fabrication of tungsten and tungsten alloys into small-diameter, thin-wall tubing of nuclear quality. The tungsten, or tungsten alloy tube blanks are produced by double extrusion. Plug-drawing has emerged as an excellent secondary fabrication technique for the reduction of the overall tube dimensions.

  9. Tungsten contamination in ion implantation

    NASA Astrophysics Data System (ADS)

    Polignano, M. L.; Barbarossa, F.; Galbiati, A.; Magni, D.; Mica, I.

    2016-06-01

    In this paper the tungsten contamination in ion implantation processes is studied by DLTS analysis both in typical operating conditions and after contamination of the implanter by implantation of wafers with an exposed tungsten layer. Of course the contaminant concentration is orders of magnitude higher after contamination of the implanter, but in addition our data show that different mechanisms are active in a not contaminated and in a contaminated implanter. A moderate tungsten contamination is observed also in a not contaminated implanter, however in that case contamination is completely not energetic and can be effectively screened by a very thin oxide. On the contrary, the contamination due to an implantation in a previously contaminated implanter is reduced but not suppressed even by a relatively thick screen oxide. The comparison with SRIM calculations confirms that the observed deep penetration of the contaminant cannot be explained by a plain sputtering mechanism.

  10. Accurate pointing of tungsten welding electrodes

    NASA Technical Reports Server (NTRS)

    Ziegelmeier, P.

    1971-01-01

    Thoriated-tungsten is pointed accurately and quickly by using sodium nitrite. Point produced is smooth and no effort is necessary to hold the tungsten rod concentric. The chemically produced point can be used several times longer than ground points. This method reduces time and cost of preparing tungsten electrodes.

  11. Characteristics of strength and plasticity of tungsten and tungsten-base alloys I. Mechanical properties

    SciTech Connect

    Bukhanovskii, V.V.; Golovin, S.A.; Kharchenko, V.K.; Kravchenko, V.S.; Nikol'skii, V.N.; Ol'shanskii, A.B.

    1986-01-01

    The authors establish the temperature relationship of the strength and plastic properties of tungsten and tungsten-base alloys taking into consideration the statistical parameters of the spread caused by structural and technical factors and a quantitative determination of the influence in tension of dispersion hardening of tungsten with refractory particles of hafnium and yttrium oxides. The observed dip in plasticity in the dispersion-hardened tungsten alloys does not contradict the mechanism of high temperature embrittlement of commercially pure tungsten.

  12. Method of synthesizing tungsten nanoparticles

    DOEpatents

    Thoma, Steven G; Anderson, Travis M

    2013-02-12

    A method to synthesize tungsten nanoparticles has been developed that enables synthesis of nanometer-scale, monodisperse particles that can be stabilized only by tetrahydrofuran. The method can be used at room temperature, is scalable, and the product concentrated by standard means. Since no additives or stabilizing surfactants are required, this method is particularly well suited for producing tungsten nanoparticles for dispersion in polymers. If complete dispersion is achieved due to the size of the nanoparticles, then the optical properties of the polymer can be largely maintained.

  13. Nonlinear Saturable Absorption of Liquid-Exfoliated Molybdenum/Tungsten Ditelluride Nanosheets.

    PubMed

    Mao, Dong; Du, Bobo; Yang, Dexing; Zhang, Shengli; Wang, Yadong; Zhang, Wending; She, Xiaoyang; Cheng, Huachao; Zeng, Haibo; Zhao, Jianlin

    2016-03-01

    Molybdenum disulfide (MoS2 ) and tungsten disulfide (WS2 ), two representative transition metal dichalcogenide materials, have captured tremendous interest for their unique electronic, optical, and chemical properties. Compared with MoS2 and WS2 , molybdenum ditelluride (MoTe2 ) and tungsten ditelluride (WTe2 ) possess similar lattice structures while having smaller bandgaps (less than 1 eV), which is particularly interesting for applications in the near-infrared wavelength regime. Here, few-layer MoTe2 /WTe2 nanosheets are fabricated by a liquid exfoliation method using sodium deoxycholate bile salt as surfactant, and the nonlinear optical properties of the nanosheets are investigated. The results demonstrate that MoTe2 /WTe2 nanosheets exhibit nonlinear saturable absorption property at 1.55 μm. Soliton mode-locking operations are realized separately in erbium-doped fiber lasers utilizing two types of MoTe2 /WTe2 -based saturable absorbers, one of which is prepared by depositing the nanosheets on side polished fibers, while the other is fabricated by mixing the nanosheets with polyvinyl alcohol and then evaporating them on substrates. Numerous applications may benefit from the nonlinear saturable absorption features of MoTe2 /WTe2 nanosheets, such as visible/near-infrared pulsed laser, materials processing, optical sensors, and modulators. PMID:26800122

  14. Disulfide bonds and glycosylation in fungal peroxidases.

    PubMed

    Limongi, P; Kjalke, M; Vind, J; Tams, J W; Johansson, T; Welinder, K G

    1995-01-15

    Four conserved disulfide bonds and N-linked and O-linked glycans of extracellular fungal peroxidases have been identified from studies of a lignin and a manganese peroxidase from Trametes versicolor, and from Coprinus cinereus peroxidase (CIP) and recombinant C. cinereus peroxidase (rCIP) expressed in Aspergillus oryzae. The eight cysteine residues are linked 1-3, 2-7, 4-5 and 6-8, and are located differently from the four conserved disulfide bridges present in the homologous plant peroxidases. CIP and rCIP were identical in their glycosylation pattern, although the extent of glycan chain heterogeneity depended on the fermentation batch. CIP and rCIP have one N-linked glycan composed only of GlcNAc and Man at residue Asn142, and two O-linked glycans near the C-terminus. The major glycoform consists of single Man residues at Thr331 and at Ser338. T. versicolor lignin isoperoxidase TvLP10 contains a single N-linked glycan composed of (GlcNAc)2Man5 bound to Asn103, whereas (GlcNAc)2Man3 was found in T. versicolor manganese isoperoxidase TvMP2 at the same position. In addition, mass spectrometry of the C-terminal peptide of TvMP2 indicated the presence of five Man residues in O-linked glycans. No phosphate was found in these fungal peroxidases. PMID:7851395

  15. Converting a Sulfenic Acid Reductase into a Disulfide Bond Isomerase

    PubMed Central

    Chatelle, Claire; Kraemer, Stéphanie; Ren, Guoping; Chmura, Hannah; Marechal, Nils; Boyd, Dana; Roggemans, Caroline; Ke, Na; Riggs, Paul; Bardwell, James

    2015-01-01

    Abstract Aims: Posttranslational formation of disulfide bonds is essential for the folding of many secreted proteins. Formation of disulfide bonds in a protein with more than two cysteines is inherently fraught with error and can result in incorrect disulfide bond pairing and, consequently, misfolded protein. Protein disulfide bond isomerases, such as DsbC of Escherichia coli, can recognize mis-oxidized proteins and shuffle the disulfide bonds of the substrate protein into their native folded state. Results: We have developed a simple blue/white screen that can detect disulfide bond isomerization in vivo, using a mutant alkaline phosphatase (PhoA*) in E. coli. We utilized this screen to isolate mutants of the sulfenic acid reductase (DsbG) that allowed this protein to act as a disulfide bond isomerase. Characterization of the isolated mutants in vivo and in vitro allowed us to identify key amino acid residues responsible for oxidoreductase properties of thioredoxin-like proteins such as DsbC or DsbG. Innovation and Conclusions: Using these key residues, we also identified and characterized interesting environmental homologs of DsbG with novel properties, thus demonstrating the capacity of this screen to discover and elucidate mechanistic details of in vivo disulfide bond isomerization. Antioxid. Redox Signal. 23, 945–957. PMID:26191605

  16. 46 CFR 151.50-41 - Carbon disulfide (carbon bisulfide).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Carbon disulfide (carbon bisulfide). 151.50-41 Section... CARGOES BARGES CARRYING BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-41 Carbon disulfide (carbon bisulfide). (a) All openings shall be in the top of the tank. (b) Loading lines...

  17. 46 CFR 151.50-41 - Carbon disulfide (carbon bisulfide).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Carbon disulfide (carbon bisulfide). 151.50-41 Section... CARGOES BARGES CARRYING BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-41 Carbon disulfide (carbon bisulfide). (a) All openings shall be in the top of the tank. (b) Loading lines...

  18. 46 CFR 151.50-41 - Carbon disulfide (carbon bisulfide).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Carbon disulfide (carbon bisulfide). 151.50-41 Section... CARGOES BARGES CARRYING BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-41 Carbon disulfide (carbon bisulfide). (a) All openings shall be in the top of the tank. (b) Loading lines...

  19. 46 CFR 151.50-41 - Carbon disulfide (carbon bisulfide).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Carbon disulfide (carbon bisulfide). 151.50-41 Section... CARGOES BARGES CARRYING BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-41 Carbon disulfide (carbon bisulfide). (a) All openings shall be in the top of the tank. (b) Loading lines...

  20. 46 CFR 151.50-41 - Carbon disulfide (carbon bisulfide).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Carbon disulfide (carbon bisulfide). 151.50-41 Section... CARGOES BARGES CARRYING BULK LIQUID HAZARDOUS MATERIAL CARGOES Special Requirements § 151.50-41 Carbon disulfide (carbon bisulfide). (a) All openings shall be in the top of the tank. (b) Loading lines...

  1. Tungsten carbide: Crystals by the ton

    NASA Astrophysics Data System (ADS)

    Smith, E. N.

    1988-06-01

    A comparison is made of the conventional process of making tungsten carbide by carburizing tungsten powder and the Macro Process wherein the tungsten carbide is formed directly from the ore concentrate by an exothermic reaction of ingredients causing a simultaneous reduction and carburization. Tons of tungsten monocarbide crystals are formed in a very rapid reaction. The process is unique in that it is self regulating and produces a tungsten carbide compound with the correct stoichiometry. The high purity with respect to oxygen and nitrogen is achieved because the reactions occur beneath the molten metal. The morphology and hardness of these crystals has been studied by various investigators and reported in the listed references.

  2. Vacuum Gas Tungsten Arc Welding

    NASA Technical Reports Server (NTRS)

    Weeks, J. L.; Todd, D. T.; Wooten, J. R.

    1997-01-01

    A two-year program investigated vacuum gas tungsten arc welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. After a vacuum chamber and GTAW power supply were modified, several difficult-to-weld materials were studied and key parameters developed. Finally, Incoloy 903 weld overlays were produced without microfissures.

  3. Fabrication of tungsten wire needles

    SciTech Connect

    Roder, A.

    1983-02-01

    Fine point needles for field emissoin are conventionally produced by electrolytically or chemically etching tungsten wire. Points formed in this manner have a typical tip radius of about 0.5 microns and a cone angle of some 30 degrees. The construction of needle matrix detector chambers has created a need for tungsten needles whose specifications are: 20 mil tungsten wire, 1.5 inch total length, 3 mm-long taper (resulting in a cone angle of about 5 degrees), and 25 micron-radius point (similar to that found on sewing needles). In the process described here for producing such needles, tungsten wire, immersed in a NaOH solution and in the presence of an electrode, is connected first to an ac voltage and then to a dc supply, to form a taper and a point on the end of the wire immersed in the solution. The process parameters described here are for needles that will meet the above specifications. Possible variations will be discussed under each approprite heading.

  4. Mineral of the month: tungsten

    USGS Publications Warehouse

    Shedd, Kim B.

    2006-01-01

    Tungsten has the highest melting point of all metals, one of the highest densities and, when combined with carbon, is almost as hard as diamond. These and other properties make it useful in a wide variety of important commercial, industrial and military applications.

  5. Scintillating fiber ribbon --- tungsten calorimeter

    SciTech Connect

    Bross, A.; Crisler, M.; Kross, B.; Wrbanek, J.

    1989-07-14

    We describe an ultra-high density scintillating fiber and tungsten calorimeter used as an active beam-dump for electrons. Data showing the calorimeter response to electrons with momenta between 50 and 350 GeV/c are presented. 9 figs.

  6. Process development for cladding APT tungsten targets

    SciTech Connect

    Horner, M H; Barber, R; Dalder, E

    2000-11-27

    This report describes development of processes for cladding APT Target tungsten components with a thin layer (0.127-mm) of Alloy 718, Alloy 600 or 316L stainless steel alloy. The application requires that the cladding be thermally bonded to the tungsten in order to transfer heat generated in the tungsten volume to a surrounding coolant. High temperature diffusion bonding using the hot isostatic processing (HIP) technique was selected as the method for creating a metallurgical bond between pure tungsten tubes and rods and the cladding materials. Bonding studies using a uniaxially loaded vacuum hot press were conducted in preliminary experiments to determine acceptable time-temperature conditions for diffusion bonding. The results were successfully applied in cladding tungsten rods and tubes with these alloys. Temperatures 800-810 C were suitable for cladding tungsten with Alloy 600 and 316L stainless steel alloy, whereas tungsten was clad with Alloy 718 at 1020 C.

  7. Process Of Bonding Copper And Tungsten

    DOEpatents

    Slattery, Kevin T.; Driemeyer, Daniel E.

    1999-11-23

    Process for bonding a copper substrate to a tungsten substrate by providing a thin metallic adhesion promoting film bonded to a tungsten substrate and a functionally graded material (FGM) interlayer bonding the thin metallic adhesion promoting film to the copper substrate. The FGM interlayer is formed by thermal plasma spraying mixtures of copper powder and tungsten powder in a varied blending ratio such that the blending ratio of the copper powder and the tungsten powder that is fed to a plasma torch is intermittently adjusted to provide progressively higher copper content/tungsten content, by volume, ratio values in the interlayer in a lineal direction extending from the tungsten substrate towards the copper substrate. The resulting copper to tungsten joint well accommodates the difference in the coefficient of thermal expansion of the materials.

  8. Early events in the disulfide-coupled folding of BPTI.

    PubMed Central

    Bulaj, G.; Goldenberg, D. P.

    1999-01-01

    Recent studies of the refolding of reduced bovine pancreatic trypsin inhibitor (BPTI) have shown that a previously unidentified intermediate with a single disulfide is formed much more rapidly than any other one-disulfide species. This intermediate contains a disulfide that is present in the native protein (between Cys14 and 38), but it is thermodynamically less stable than the other two intermediates with single native disulfides. To characterize the role of the [14-38] intermediate and the factors that favor its formation, detailed kinetic and mutational analyses of the early disulfide-formation steps were carried out. The results of these studies indicate that the formation of [14-38] from the fully reduced protein is favored by both local electrostatic effects, which enhance the reactivities of the Cys14 and 38 thiols, and conformational tendencies that are diminished by the addition of urea and are enhanced at lower temperatures. At 25 degrees C and pH 7.3, approximately 35% of the reduced molecules were found to initially form the 14-38 disulfide, but the majority of these molecules then undergo intramolecular rearrangements to generate non-native disulfides, and subsequently the more stable intermediates with native disulfides. Amino acid replacements, other than those involving Cys residues, were generally found to have only small effects on either the rate of forming [14-38] or its thermodynamic stability, even though many of the same substitutions greatly destabilized the native protein and other disulfide-bonded intermediates. In addition, those replacements that did decrease the steady-state concentration of [14-38] did not adversely affect further folding and disulfide formation. These results suggest that the weak and transient interactions that are often detected in unfolded proteins and early folding intermediates may, in some cases, not persist or promote subsequent folding steps. PMID:10493584

  9. High heat flux properties of pure tungsten and plasma sprayed tungsten coatings

    NASA Astrophysics Data System (ADS)

    Liu, X.; Tamura, S.; Tokunaga, K.; Yoshida, N.; Noda, N.; Yang, L.; Xu, Z.

    2004-08-01

    High heat flux properties of pure tungsten and plasma sprayed tungsten coatings on carbon substrates have been studied by annealing and cyclic heat loading. The recrystallization temperature and an activation energy QR=126 kJ/mol for grain growth of tungsten coating by vacuum plasma spray (VPS) were estimated, and the microstructural changes of multi-layer tungsten and rhenium interface pre-deposited by physical vapor deposition (PVD) with anneal temperature were investigated. Cyclic load tests indicated that pure tungsten and VPS-tungsten coating could withstand 1000 cycles at 33-35 MW/m 2 heat flux and 3 s pulse duration, and inert gas plasma spray (IPS)-tungsten coating showed local cracks by 300 cycles but did not induce failure by further cycles. However, the failure of pure tungsten and VPS-tungsten coating by fatigue cracking was observed under higher heat load (55-60 MW/m 2) for 420 and 230 cycles, respectively.

  10. Twin disulfides for orthogonal disulfide pairing and the directed folding of multicyclic peptides

    NASA Astrophysics Data System (ADS)

    Wu, Chuanliu; Leroux, Jean-Christophe; Gauthier, Marc A.

    2012-12-01

    Multicyclic peptides are emerging as an exciting platform for drug and targeted ligand discovery owing to their expected greater target affinity/selectivity/stability versus linear or monocyclic peptides. However, although the precise pairing of cysteine residues in proteins is routinely achieved in nature, the rational pairing of cysteine residues within polypeptides is a long-standing challenge for the preparation of multicyclic species containing several disulfide bridges. Here, we present an efficient and straightforward approach for directing the intermolecular and intramolecular pairing of cysteine residues within peptides using a minimal CXC motif. Orthogonal disulfide pairing can be exploited in complex redox media to rationally produce dimeric peptides and bi/tricyclic peptides from fully reduced peptides containing 1-6 cysteine residues. This strategy, which does not rely on extensive manipulation of the primary sequence, post-translational modification or protecting groups, should greatly benefit the development of multicyclic peptide therapeutics and targeting ligands.

  11. Superconductivity in highly disordered dense carbon disulfide

    PubMed Central

    Dias, Ranga P.; Yoo, Choong-Shik; Struzhkin, Viktor V.; Kim, Minseob; Muramatsu, Takaki; Matsuoka, Takahiro; Ohishi, Yasuo; Sinogeikin, Stanislav

    2013-01-01

    High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ∼6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity. PMID:23818624

  12. Pressure-induced metallization of molybdenum disulfide.

    PubMed

    Chi, Zhen-Hua; Zhao, Xiao-Miao; Zhang, Haidong; Goncharov, Alexander F; Lobanov, Sergey S; Kagayama, Tomoko; Sakata, Masafumi; Chen, Xiao-Jia

    2014-07-18

    X-ray diffraction, Raman spectroscopy, and electrical conductivity measurements of molybdenum disulfide MoS(2) are performed at pressures up to 81 GPa in diamond anvil cells. Above 20 GPa, we find discontinuous changes in Raman spectra and x-ray diffraction patterns which provide evidence for isostructural phase transition from 2H(c) to 2H(a) modification through layer sliding previously predicted theoretically. This first-order transition, which is completed around 40 GPa, is characterized by a collapse in the c-lattice parameter and volume and also by changes in interlayer bonding. After the phase transition completion, MoS(2) becomes metallic. The reversibility of the phase transition is identified from all these techniques. PMID:25083660

  13. Circulation of oligonucleotides by disulfide bridge formation.

    PubMed Central

    Gao, H; Yang, M; Patel, R; Cook, A F

    1995-01-01

    An effective, convenient method for the circularization of oligonucleotides has been developed. This procedure involved preparation of an oligonucleotide with backbone-linked 5'- and 3'-terminal hexamethylenethiol groups, followed by oxidation of the thiol groups with air of oxygen to produce the corresponding circular sequence bridged via a bis(hexamethylene)-disulfide moiety. The method has been applied to the circularization of oligodeoxynucleotide sequences of varying lengths (5, 10, 15, 20, 30 and 40 bases), and the circularization process was highly efficient as shown by HPLC or gel electrophoresis of the crude reaction mixtures. Competing reactions such as dimerization were not significant except for the longer sequences (30 and 40 bases). The circularization of an eight base RNA sequence was also accomplished, as well as hexa-ethylene glycol bridged poly-T sequences capable of triplex formation. PMID:7596832

  14. Ultrafast response of monolayer molybdenum disulfide photodetectors

    PubMed Central

    Wang, Haining; Zhang, Changjian; Chan, Weimin; Tiwari, Sandip; Rana, Farhan

    2015-01-01

    The strong light emission and absorption exhibited by single atomic layer transitional metal dichalcogenides in the visible to near-infrared wavelength range make them attractive for optoelectronic applications. In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz. The fast photodetector response is a result of the short electron–hole and exciton lifetimes in this material. Recombination of photoexcited carriers in most two-dimensional metal dichalcogenides is dominated by nonradiative processes, most notable among which is Auger scattering. The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links. PMID:26572726

  15. Advances in rechargeable lithium molybdenum disulfide batteries

    NASA Technical Reports Server (NTRS)

    Brandt, K.; Stiles, J. A. R.

    1985-01-01

    The lithium molybdenum disulfide system as demonstrated in a C size cell, offers performance characteristics for applications where light weight and low volume are important. A gravimetric energy density of 90 watt hours per kilogram can be achieved in a C size cell package. The combination of charge retention capabilities, high energy density and a state of charge indicator in a rechargeable cell provides power package for a wide range of devices. The system overcomes the memory effect in Nicads where the full capacity of the battery cannot be utilized unless it was utilized on previous cycles. The development of cells with an advanced electrolyte formulation led to an improved rate capability especially at low temperatures and to a significantly improved life cycle.

  16. Diffusion of tungsten clusters on tungsten (110) surface

    SciTech Connect

    Chen, Dong; Hu, Wangyu; Yang, Jianyu; Deng, Huiqiu; Sun, Lixian; Gao, Fei

    2009-04-01

    Using molecular dynamics simulation and modified analytic embedded-atom method, we have investigated the self-diffusion of clusters on a tungsten (110) surface. As compared to the linear-chain configuration, the close-packed islands for tungsten clusters containing more than nine adatoms have been predicted to be more stable with the relatively lower binding energies. The migration energies show an interesting and oscillating behavior with increasing cluster size. The tetramer, hexamer and octamer have obviously higher migration energies than the others. The different atomic configurations and diffusion mechanisms have been determined during the diffusion processes. It is clear that the dimer-shearing mechanism occurs inside the hexamer, while it occurs at the periphery of heptamer. The successive hopping mechanism of individual atom is of critical importance in the migration of the clusters containing five or fewer adatoms. In addition, the diffusion of a cluster with nine adatoms is achieved through the changes of the cluster shape.

  17. Tungsten oxide nanowires grown on amorphous-like tungsten films.

    PubMed

    Dellasega, D; Pietralunga, S M; Pezzoli, A; Russo, V; Nasi, L; Conti, C; Vahid, M J; Tagliaferri, A; Passoni, M

    2015-09-11

    Tungsten oxide nanowires have been synthesized by vacuum annealing in the range 500-710 °C from amorphous-like tungsten films, deposited on a Si(100) substrate by pulsed laser deposition (PLD) in the presence of a He background pressure. The oxygen required for the nanowires formation is already adsorbed in the W matrix before annealing, its amount depending on deposition parameters. Nanowire crystalline phase and stoichiometry depend on annealing temperature, ranging from W18O49-Magneli phase to monoclinic WO3. Sufficiently long annealing induces the formation of micrometer-long nanowires, up to 3.6 μm with an aspect ratio up to 90. Oxide nanowire growth appears to be triggered by the crystallization of the underlying amorphous W film, promoting their synthesis at low temperatures. PMID:26292084

  18. Enzyme structure captures four cysteines aligned for disulfide relay

    PubMed Central

    Gat, Yair; Vardi-Kilshtain, Alexandra; Grossman, Iris; Major, Dan Thomas; Fass, Deborah

    2014-01-01

    Thioredoxin superfamily proteins introduce disulfide bonds into substrates, catalyze the removal of disulfides, and operate in electron relays. These functions rely on one or more dithiol/disulfide exchange reactions. The flavoenzyme quiescin sulfhydryl oxidase (QSOX), a catalyst of disulfide bond formation with an interdomain electron transfer step in its catalytic cycle, provides a unique opportunity for exploring the structural environment of enzymatic dithiol/disulfide exchange. Wild-type Rattus norvegicus QSOX1 (RnQSOX1) was crystallized in a conformation that juxtaposes the two redox-active di-cysteine motifs in the enzyme, presenting the entire electron-transfer pathway and proton-transfer participants in their native configurations. As such a state cannot generally be enriched and stabilized for analysis, RnQSOX1 gives unprecedented insight into the functional group environments of the four cysteines involved in dithiol/disulfide exchange and provides the framework for analysis of the energetics of electron transfer in the presence of the bound flavin adenine dinucleotide cofactor. Hybrid quantum mechanics/molecular mechanics (QM/MM) free energy simulations based on the X-ray crystal structure suggest that formation of the interdomain disulfide intermediate is highly favorable and secures the flexible enzyme in a state from which further electron transfer via the flavin can occur. PMID:24888638

  19. Disulfide Bond Oxidoreductase DsbA2 of Legionella pneumophila Exhibits Protein Disulfide Isomerase Activity

    PubMed Central

    Kpadeh, Zegbeh Z.; Jameson-Lee, Max; Yeh, Anthony J.; Chertihin, Olga; Shumilin, Igor A.; Dey, Rafik; Day, Shandra R.

    2013-01-01

    The extracytoplasmic assembly of the Dot/Icm type IVb secretion system (T4SS) of Legionella pneumophila is dependent on correct disulfide bond (DSB) formation catalyzed by a novel and essential disulfide bond oxidoreductase DsbA2 and not by DsbA1, a second nonessential DSB oxidoreductase. DsbA2, which is widely distributed in the microbial world, is phylogenetically distinct from the canonical DsbA oxidase and the DsbC protein disulfide isomerase (PDI)/reductase of Escherichia coli. Here we show that the extended N-terminal amino acid sequence of DsbA2 (relative to DsbA proteins) contains a highly conserved 27-amino-acid dimerization domain enabling the protein to form a homodimer. Complementation tests with E. coli mutants established that L. pneumophila dsbA1, but not the dsbA2 strain, restored motility to a dsbA mutant. In a protein-folding PDI detector assay, the dsbA2 strain, but not the dsbA1 strain, complemented a dsbC mutant of E. coli. Deletion of the dimerization domain sequences from DsbA2 produced the monomer (DsbA2N), which no longer exhibited PDI activity but complemented the E. coli dsbA mutant. PDI activity was demonstrated in vitro for DsbA2 but not DsbA1 in a nitrocefin-based mutant TEM β-lactamase folding assay. In an insulin reduction assay, DsbA2N activity was intermediate between those of DsbA2 and DsbA1. In L. pneumophila, DsbA2 was maintained as a mixture of thiol and disulfide forms, while in E. coli, DsbA2 was present as the reduced thiol. Our studies suggest that DsbA2 is a naturally occurring bifunctional disulfide bond oxidoreductase that may be uniquely suited to the majority of intracellular bacterial pathogens expressing T4SSs as well as in many slow-growing soil and aquatic bacteria. PMID:23435972

  20. Protein disulfide isomerase a multifunctional protein with multiple physiological roles

    NASA Astrophysics Data System (ADS)

    Ali Khan, Hyder; Mutus, Bulent

    2014-08-01

    Protein disulfide isomerase (PDI), is a member of the thioredoxin superfamily of redox proteins. PDI has three catalytic activities including, thiol-disulfide oxireductase, disulfide isomerase and redox-dependent chaperone. Originally, PDI was identified in the lumen of the endoplasmic reticulum and subsequently detected at additional locations, such as cell surfaces and the cytosol. This review will provide an overview of the recent advances in relating the structural features of PDI to its multiple catalytic roles as well as its physiological and pathophysiological functions related to redox regulation and protein folding.

  1. Radical cations of sulfides and disulfides: An ESR study

    SciTech Connect

    Bonazzola, L.; Michaut, J.P.; Roncin, J.

    1985-09-15

    Exposure of dilute solutions of dimethylsulfide, methanethiol, tetrahydrothiophene, terbutyl and diterbutyl-sulfides, dimethyl-disulfide, and diterbutyldisulfide, in freon at 77 K to /sup 60/Co ..gamma.. rays gave the corresponding cations. From the reported ESR spectra, g tensors were obtained. It was found that both sulfide and disulfide cations exhibit the same g tensor: (g/sub max/ = 2.034 +- 0.002, g/sub int/ = 2.017 +- 0.001, g/sub min/ = 2.001 +- 0.005). From this result it has been shown that the disulfide cation is planar. This finding was supported by fully optimized geometry ab initio calculations.

  2. Plasma Influence on Tungsten Powder

    NASA Astrophysics Data System (ADS)

    Zakharov, A.; Begrambekova, S.; Grunin, A.

    Modifications of tungsten powder comprised of micro particles with dimensions: 1 ± 0.2 μm and 5 ± 1.5 μm ("small" and «large" particles) under the influence of heating, electric field and hydrogen- and argon ion irradiation are investigated in this work. The processes in irradiated powder are described and discussed. Among them there are powder outgassing, particle emission from the powder surface in the electric field, pasting of small particles all over the large ones, integration of the adhered small particles and formation of the uniform layer around the groups of large particles, cone growth on uniform layers, formation of volumetric chains of sticking together tungsten particles and their transformations. Driving forces and processes providing different types of powder modifications and the role of each of them in the specific phenomena are discussed.

  3. 21 CFR 520.1802a - Piperazine-carbon disulfide complex suspension.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Piperazine-carbon disulfide complex suspension... § 520.1802a Piperazine-carbon disulfide complex suspension. (a) Specifications. Each fluid ounce of suspension contains 7.5 grams of piperazine-carbon disulfide complex. The piperazine-carbon disulfide...

  4. 21 CFR 520.1802a - Piperazine-carbon disulfide complex suspension.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Piperazine-carbon disulfide complex suspension... § 520.1802a Piperazine-carbon disulfide complex suspension. (a) Specifications. Each fluid ounce of suspension contains 7.5 grams of piperazine-carbon disulfide complex. The piperazine-carbon disulfide...

  5. 21 CFR 520.1802a - Piperazine-carbon disulfide complex suspension.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Piperazine-carbon disulfide complex suspension... § 520.1802a Piperazine-carbon disulfide complex suspension. (a) Specifications. Each fluid ounce of suspension contains 7.5 grams of piperazine-carbon disulfide complex. The piperazine-carbon disulfide...

  6. 21 CFR 520.1802a - Piperazine-carbon disulfide complex suspension.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Piperazine-carbon disulfide complex suspension... § 520.1802a Piperazine-carbon disulfide complex suspension. (a) Specifications. Each fluid ounce of suspension contains 7.5 grams of piperazine-carbon disulfide complex. The piperazine-carbon disulfide...

  7. 21 CFR 520.1802a - Piperazine-carbon disulfide complex suspension.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Piperazine-carbon disulfide complex suspension... § 520.1802a Piperazine-carbon disulfide complex suspension. (a) Specifications. Each fluid ounce of suspension contains 7.5 grams of piperazine-carbon disulfide complex. The piperazine-carbon disulfide...

  8. Rapid sequencing and disulfide mapping of peptides containing disulfide bonds by using 1,5-diaminonaphthalene as a reductive matrix.

    PubMed

    Fukuyama, Yuko; Iwamoto, Shinichi; Tanaka, Koichi

    2006-02-01

    MS/MS is indispensable for the amino acid sequencing of peptides. However, its use is limited for peptides containing disulfide bonds. We have applied the reducing properties of 1,5-diaminonaphthalene (1,5-DAN) as a MALDI matrix to amino acid sequencing and disulfide bond mapping of human urotensin II possessing one disulfide bond, and human guanylin possessing two disulfide bonds. 1,5-DAN was used in the same manner as the usual MALDI matrices without any pre-treatment of the peptide, and MS/MS was performed using a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometer (MALDI QIT TOFMS). The results demonstrated that MS/MS of the molecular ions reduced by 1,5-DAN provided a series of significant b-/y-product ions. All 11 amino acid residues of urotensin II were identified using 1,5-DAN, while only 5 out of 11 residues were identified using 2,5-dihydroxybenzoic acid (DHB); similarly 11 out of 15 amino acid residues of guanylin were identified using 1,5-DAN, while only three were identified using DHB. In addition, comparison of the theoretical and measured values of the mass differences between corresponding MS/MS product ions using 1,5-DAN and DHB narrowed down the possible disulfide bond arrangement candidates. Consequently, 1,5-DAN as a reductive matrix facilitates rapid amino acid sequencing and disulfide mapping for peptides containing disulfide bonds. PMID:16382486

  9. Photoactive Self-Shaping Hydrogels as Noncontact 3D Macro/Microscopic Photoprinting Platforms.

    PubMed

    Liao, Yue; An, Ning; Wang, Ning; Zhang, Yinyu; Song, Junfei; Zhou, Jinxiong; Liu, Wenguang

    2015-12-01

    A photocleavable terpolymer hydrogel cross-linked with o-nitrobenzyl derivative cross-linker is shown to be capable of self-shaping without losing its physical integrity and robustness due to spontaneous asymmetric swelling of network caused by UV-light-induced gradient cleavage of chemical cross-linkages. The continuum model and finite element method are used to elucidate the curling mechanism underlying. Remarkably, based on the self-changing principle, the photosensitive hydrogels can be developed as photoprinting soft and wet platforms onto which specific 3D characters and images are faithfully duplicated in macro/microscale without contact by UV light irradiation under the cover of customized photomasks. Importantly, a quick response (QR) code is accurately printed on the photoactive hydrogel for the first time. Scanning QR code with a smartphone can quickly connect to a web page. This photoactive hydrogel is promising to be a new printing or recording material. PMID:26439808

  10. Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein.

    PubMed

    Pande, Kanupriya; Hutchison, Christopher D M; Groenhof, Gerrit; Aquila, Andy; Robinson, Josef S; Tenboer, Jason; Basu, Shibom; Boutet, Sébastien; DePonte, Daniel P; Liang, Mengning; White, Thomas A; Zatsepin, Nadia A; Yefanov, Oleksandr; Morozov, Dmitry; Oberthuer, Dominik; Gati, Cornelius; Subramanian, Ganesh; James, Daniel; Zhao, Yun; Koralek, Jake; Brayshaw, Jennifer; Kupitz, Christopher; Conrad, Chelsie; Roy-Chowdhury, Shatabdi; Coe, Jesse D; Metz, Markus; Xavier, Paulraj Lourdu; Grant, Thomas D; Koglin, Jason E; Ketawala, Gihan; Fromme, Raimund; Šrajer, Vukica; Henning, Robert; Spence, John C H; Ourmazd, Abbas; Schwander, Peter; Weierstall, Uwe; Frank, Matthias; Fromme, Petra; Barty, Anton; Chapman, Henry N; Moffat, Keith; van Thor, Jasper J; Schmidt, Marius

    2016-05-01

    A variety of organisms have evolved mechanisms to detect and respond to light, in which the response is mediated by protein structural changes after photon absorption. The initial step is often the photoisomerization of a conjugated chromophore. Isomerization occurs on ultrafast time scales and is substantially influenced by the chromophore environment. Here we identify structural changes associated with the earliest steps in the trans-to-cis isomerization of the chromophore in photoactive yellow protein. Femtosecond hard x-ray pulses emitted by the Linac Coherent Light Source were used to conduct time-resolved serial femtosecond crystallography on photoactive yellow protein microcrystals over a time range from 100 femtoseconds to 3 picoseconds to determine the structural dynamics of the photoisomerization reaction. PMID:27151871

  11. Synthesis of nitrogen doped faceted titanium dioxide in pure brookite phase with enhanced visible light photoactivity.

    PubMed

    Pan, Jian; Jiang, San Ping

    2016-05-01

    Brookite titanium dioxide (TiO2) is rarely studied, as compared with anatase and rutile phases TiO2, due to its comparatively lower photoactivity. It has been recently reported that brookite TiO2 with active facets exhibits excellent performance, however, synthesis of such faceted brookite TiO2 is difficult because of its low thermodynamic phase stability and low structural symmetric. Furthermore, like faceted anatase and rutile TiO2, faceted brookite TiO2 is not responsive to visible light due to its wide bandgap. In this study, a novel dopant, hydrazine, was introduced in the development of nitrogen doping. By applying this dopant, nitrogen doped brookite nanorods with active {120}, {111} and {011¯} facets were successfully synthesized. The resultant materials exhibited remarkably enhanced visible-light photoactivity in photodegradation. PMID:26866886

  12. Low-Temperature Curable Photo-Active Anisotropic Conductive Films (PA-ACFs)

    NASA Astrophysics Data System (ADS)

    Kim, Il; Paik, Kyung-Wook

    2014-09-01

    Photo-active anisotropic conductive films (PA-ACFs) with curing temperatures below 120°C were introduced using photo-active curing agents. The PA-ACFs showed no curing before UV activation, and the crosslinking systems of the PA-ACFs were not activated under fluorescent light exposure. However, after UV activation, the PA-ACFs were completely cured at 120°C within 10 s. Flex-on-board (FOB) assembly using PA-ACFs had adhesion strength and joint resistances similar to those of the FOB assemblies using conventional epoxy-based ACFs. This study demonstrates that PA-ACFs provide reliable interconnection and minimal thermal deformation among all the commercially available ACFs, especially for low T g substrate applications.

  13. Tungsten and tungsten-alloy powder metallurgy. (Latest citations from the NTIS data base). Published Search

    SciTech Connect

    Not Available

    1992-10-01

    The bibliography contains citations concerning the processing and fabrication of tungsten, tungsten alloys, and tungsten composites. Compacting, pressing, sintering, extruding, and rolling are among the methods described. Infiltration of porous tungsten shapes is included, as well as mechanical properties, thermal properties, and microstructure of end products. Applications include rocket nozzles, nuclear reactor materials, and porous ionizers. (Contains a minimum of 116 citations and includes a subject term index and title list.)

  14. Tin-tungsten mineralizing processes in tungsten vein deposits: Panasqueira, Portugal

    NASA Astrophysics Data System (ADS)

    Lecumberri-Sanchez, P.; Pinto, F.; Vieira, R.; Wälle, M.; Heinrich, C. A.

    2015-12-01

    Tungsten has a high heat resistance, density and hardness, which makes it widely applied in industry (e.g. steel, tungsten carbides). Tungsten deposits are typically magmatic-hydrothermal systems. Despite the economic significance of tungsten, there are no modern quantitative analytical studies of the fluids responsible for the formation of its highest-grade deposit type (tungsten vein deposits). Panasqueira (Portugal) is a tungsten vein deposit, one of the leading tungsten producers in Europe and one of the best geologically characterized tungsten vein deposits. In this study, compositions of the mineralizing fluids at Panasqueira have been determined through combination of detailed petrography, microthermometric measurements and LA-ICPMS analyses, and geochemical modeling has been used to determine the processes that lead to tungsten mineralization. We characterized the fluids related to the various mineralizing stages in the system: the oxide stage (tin and tungsten mineralization), the sulfide stage (chalcopyrite and sphalerite mineralization) and the carbonate stage. Thus, our results provide information on the properties of fluids related with specific paragenetic stages. Furthermore we used those fluid compositions in combination with host rock mineralogy and chemistry to evaluate which are the controlling factors in the mineralizing process. This study provides the first quantitative analytical data on fluid composition for tungsten vein deposits and evaluates the controlling mineralization processes helping to determine the mechanisms of formation of the Panasqueira tin-tungsten deposit and providing additional geochemical constraints on the local distribution of mineralization.

  15. Improved molybdenum disulfide-silver motor brushes have extended life

    NASA Technical Reports Server (NTRS)

    Horton, J. C.; King, H. M.

    1964-01-01

    Motor brushes of proper quantities of molybdenum disulfide and copper or silver are manufactured by sintering techniques. Graphite molds are used. These brushes operate satisfactorily for long periods in normal atmosphere or in a high-vacuum environment.

  16. Thiosaccharine disulfide: Synthesis, crystal structure, spectroscopic characterization and theoretical study

    NASA Astrophysics Data System (ADS)

    Ferullo, Ricardo M.; Granados, Alejandro; Lanterna, Anabel; Güida, Jorge A.; Piro, Oscar E.; Castellano, Eduardo E.; Dennehy, Mariana

    2013-01-01

    The title compound, (thiosaccharine disulfide), bis[1,1'dioxide-2,3-dihidro-1,2-benzoisothiazol]disulfide, (tsac)2 has been synthesized and fully characterized by UV-Visible, IR, Raman, 1H and 13C NMR spectroscopy elemental analysis and structural X-ray crystallography. A DFT theoretical study has been performed and good agreement between experimental and theoretical values of structural parameters and vibration frequencies have been achieved.

  17. Disulfide Mispairing During Proinsulin Folding in the Endoplasmic Reticulum.

    PubMed

    Haataja, Leena; Manickam, Nandini; Soliman, Ann; Tsai, Billy; Liu, Ming; Arvan, Peter

    2016-04-01

    Proinsulin folding within the endoplasmic reticulum (ER) remains incompletely understood, but it is clear that in mutant INS gene-induced diabetes of youth (MIDY), progression of the (three) native disulfide bonds of proinsulin becomes derailed, causing insulin deficiency, β-cell ER stress, and onset of diabetes. Herein, we have undertaken a molecular dissection of proinsulin disulfide bond formation, using bioengineered proinsulins that can form only two (or even only one) of the native proinsulin disulfide bonds. In the absence of preexisting proinsulin disulfide pairing, Cys(B19)-Cys(A20) (a major determinant of ER stress response activation and proinsulin stability) preferentially initiates B-A chain disulfide bond formation, whereas Cys(B7)-Cys(A7) can initiate only under oxidizing conditions beyond that existing within the ER of β-cells. Interestingly, formation of these two "interchain" disulfide bonds demonstrates cooperativity, and together, they are sufficient to confer intracellular transport competence to proinsulin. The three most common proinsulin disulfide mispairings in the ER appear to involve Cys(A11)-Cys(A20), Cys(A7)-Cys(A20), and Cys(B19)-Cys(A11), each disrupting the critical Cys(B19)-Cys(A20) pairing. MIDY mutations inhibit Cys(B19)-Cys(A20) formation, but treatment to force oxidation of this disulfide bond improves folding and results in a small but detectable increase of proinsulin export. These data suggest possible therapeutic avenues to ameliorate ER stress and diabetes. PMID:26822090

  18. Disulfide-Bond-Forming Pathways in Gram-Positive Bacteria

    PubMed Central

    2015-01-01

    Disulfide bonds are important for the stability and function of many secreted proteins. In Gram-negative bacteria, these linkages are catalyzed by thiol-disulfide oxidoreductases (Dsb) in the periplasm. Protein oxidation has been well studied in these organisms, but it has not fully been explored in Gram-positive bacteria, which lack traditional periplasmic compartments. Recent bioinformatics analyses have suggested that the high-GC-content bacteria (i.e., actinobacteria) rely on disulfide-bond-forming pathways. In support of this, Dsb-like proteins have been identified in Mycobacterium tuberculosis, but their functions are not known. Actinomyces oris and Corynebacterium diphtheriae have recently emerged as models to study disulfide bond formation in actinobacteria. In both organisms, disulfide bonds are catalyzed by the membrane-bound oxidoreductase MdbA. Remarkably, unlike known Dsb proteins, MdbA is important for pathogenesis and growth, which makes it a potential target for new antibacterial drugs. This review will discuss disulfide-bond-forming pathways in bacteria, with a special focus on Gram-positive bacteria. PMID:26644434

  19. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  20. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  1. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  2. Scalable Production of Molybdenum Disulfide Based Biosensors.

    PubMed

    Naylor, Carl H; Kybert, Nicholas J; Schneier, Camilla; Xi, Jin; Romero, Gabriela; Saven, Jeffery G; Liu, Renyu; Johnson, A T Charlie

    2016-06-28

    We demonstrate arrays of opioid biosensors based on chemical vapor deposition grown molybdenum disulfide (MoS2) field effect transistors (FETs) coupled to a computationally redesigned, water-soluble variant of the μ-opioid receptor (MOR). By transferring dense films of monolayer MoS2 crystals onto prefabricated electrode arrays, we obtain high-quality FETs with clean surfaces that allow for reproducible protein attachment. The fabrication yield of MoS2 FETs and biosensors exceeds 95%, with an average mobility of 2.0 cm(2) V(-1) s(-1) (36 cm(2) V(-1) s(-1)) at room temperature under ambient (in vacuo). An atomic length nickel-mediated linker chemistry enables target binding events that occur very close to the MoS2 surface to maximize sensitivity. The biosensor response calibration curve for a synthetic opioid peptide known to bind to the wild-type MOR indicates binding affinity that matches values determined using traditional techniques and a limit of detection ∼3 nM (1.5 ng/mL). The combination of scalable array fabrication and rapid, precise binding readout enabled by the MoS2 transistor offers the prospect of a solid-state drug testing platform for rapid readout of the interactions between novel drugs and their intended protein targets. PMID:27227361

  3. Monoclonal antibody disulfide reduction during manufacturing

    PubMed Central

    Hutterer, Katariina M.; Hong, Robert W.; Lull, Jonathon; Zhao, Xiaoyang; Wang, Tian; Pei, Rex; Le, M. Eleanor; Borisov, Oleg; Piper, Rob; Liu, Yaoqing Diana; Petty, Krista; Apostol, Izydor; Flynn, Gregory C.

    2013-01-01

    Manufacturing-induced disulfide reduction has recently been reported for monoclonal human immunoglobulin gamma (IgG) antibodies, a widely used modality in the biopharmaceutical industry. This effect has been tied to components of the intracellular thioredoxin reduction system that are released upon cell breakage. Here, we describe the effect of process parameters and intrinsic molecule properties on the extent of reduction. Material taken from cell cultures at the end of production displayed large variations in the extent of antibody reduction between different products, including no reduction, when subjected to the same reduction-promoting harvest conditions. Additionally, in a reconstituted model in which process variables could be isolated from product properties, we found that antibody reduction was dependent on the cell line (clone) and cell culture process. A bench-scale model using a thioredoxin/thioredoxin reductase regeneration system revealed that reduction susceptibility depended on not only antibody class but also light chain type; the model further demonstrates that the trend in reducibility was identical to DTT reduction sensitivity following the order IgG1λ > IgG1κ > IgG2λ > IgG2κ. Thus, both product attributes and process parameters contribute to the extent of antibody reduction during production. PMID:23751615

  4. Intrinsic structural defects in monolayer molybdenum disulfide

    SciTech Connect

    Zhou, Wu; Idrobo Tapia, Juan C

    2013-01-01

    Monolayer molybdenum disulfide (MoS2) is a two-dimensional direct band gap semiconductor with distinctive mechanical, electronic, optical and chemical properties that can be utilized for novel nanoelectronics and optoelectronics devices. The performance of these electronic devices strongly depends on the quality and defect morphology of the MoS2 layers. Yet, little is known about the atomic structure of defects present in monolayer MoS2 and their influences on the material properties. Here we provide a systematic study of various intrinsic structural defects, including point defects, grain boundaries, and edges, in chemical vapor phase grown monolayer MoS2 via direct atomic resolution imaging, and explore their energy landscape and electronic properties using first-principles calculations. We discover that one-dimensional metallic wires can be created via two different types of 60 grain boundaries consisting of distinct 4-fold ring chains. A new type of edge reconstruction, representing a transition state during growth, was also identified, providing insights into the material growth mechanism. The atomic scale study of structural defects presented here brings new opportunities to tailor the properties of MoS2 via controlled synthesis and defect engineering.

  5. Overexpression of protein disulfide isomerase in Aspergillus.

    PubMed

    El-Adawi, H; Khanh, N Q; Gassen, H

    2000-10-01

    One of the major problems with the production of biotechnologically valuable proteins has been the purification of the product. For Escherichia coli and Saccharomyces cerevisiae, there are several techniques for the purification of intracellular proteins, but these are time consuming and often result in poor yields. Purification can be considerably facilitated, if the product is secreted from the host cell. In the work presented, we have constructed an expression vector (pSGNH2) for the secretion of protein disulfide isomerase (PDI; EC 5.3.4.1) from Aspergillus niger, in which the retention signal His-Asp-Glu-Leu (H-D-E-L) was modified to Ala-Leu-Glu-Gln (A-L-E-Q) via the polymerase chain reaction (PCR) method. The PDI gene was placed under the control of the A. oryzae alpha-amylase promoter. This expression vector was transformed into A. niger NRRL3, resulting in PDI secretion into the medium. The catalytic activity of overexpressed PDI from A. niger was indistinguishable from that of PDI isolated from bovine liver. With further strain improvement and optimization of culture conditions, it could be possible to raise the PDI production to the bioprocessing scale. PMID:10977899

  6. Transfer-Free Growth of Atomically Thin Transition Metal Disulfides Using a Solution Precursor by a Laser Irradiation Process and Their Application in Low-Power Photodetectors.

    PubMed

    Huang, Chi-Chih; Medina, Henry; Chen, Yu-Ze; Su, Teng-Yu; Li, Jian-Guang; Chen, Chia-Wei; Yen, Yu-Ting; Wang, Zhiming M; Chueh, Yu-Lun

    2016-04-13

    Although chemical vapor deposition is the most common method to synthesize transition metal dichalcogenides (TMDs), several obstacles, such as the high annealing temperature restricting the substrates used in the process and the required transfer causing the formation of wrinkles and defects, must be resolved. Here, we present a novel method to grow patternable two-dimensional (2D) transition metal disulfides (MS2) directly underneath a protective coating layer by spin-coating a liquid chalcogen precursor onto the transition metal oxide layer, followed by a laser irradiation annealing process. Two metal sulfides, molybdenum disulfide (MoS2) and tungsten disulfide (WS2), are investigated in this work. Material characterization reveals the diffusion of sulfur into the oxide layer prior to the formation of the MS2. By controlling the sulfur diffusion, we are able to synthesize continuous MS2 layers beneath the top oxide layer, creating a protective coating layer for the newly formed TMD. Air-stable and low-power photosensing devices fabricated on the synthesized 2D WS2 without the need for a further transfer process demonstrate the potential applicability of TMDs generated via a laser irradiation process. PMID:26906714

  7. Seed growth of tungsten diselenide nanotubes from tungsten oxides.

    PubMed

    Kim, Hyun; Yun, Seok Joon; Park, Jin Cheol; Park, Min Ho; Park, Ji-Hoon; Kim, Ki Kang; Lee, Young Hee

    2015-05-13

    We report growth of tungsten diselenide (WSe2) nanotubes by chemical vapor deposition with a two-zone furnace. WO3 nanowires were first grown by annealing tungsten thin films under argon ambient. WSe2 nanotubes were then grown at the tips of WO3 nanowires through selenization via two steps: (i) formation of tubular WSe2 structures on the outside of WO3 nanowires, resulting in core (WO3)-shell (WSe2) and (ii) growth of WSe2 nanotubes at the tips of WO3 nanowires. The observed seed growth is markedly different from existing substitutional growth of WSe2 nanotubes, where oxygen atoms are replaced by selenium atoms in WO3 nanowires to form WSe2 nanotubes. Another advantage of our growth is that WSe2 film was grown by simply supplying hydrogen gas, where the native oxides were reduced to thin film instead of forming oxide nanowires. Our findings will contribute to engineer other transition metal dichacogenide growth such as MoS2, WS2, and MoSe2. PMID:25581340

  8. Novel properties of Tungsten ditelluride

    NASA Astrophysics Data System (ADS)

    Liu, Huimei; National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Cent Collaboration

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 Tesla. By using density functional theory calculations, we qualitatively reproduced the observed spin texture. Since the spin texture would forbid back scatterings that are directly involved in the resistivity, we suggest that the SOC and the related spin and orbital angular momentum textures may play an important role in the anomalously large magnetoresistance of WTe2. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we also boost the electronic properties by applying a high pressure, and introduce superconductivity successfully.

  9. Strengthening mechanisms of tungsten powder reinforced uranium

    SciTech Connect

    Lewis, M.A.K.; Hill, M.A.; Rollett, A.D.; Dunn, P.S.; Mortensen, A.; Massachusetts Inst. of Tech., Cambridge, MA )

    1989-01-01

    Tungsten powder reinforced uranium exhibits a three-fold increase in yield strength due to precipitation hardening. The tungsten-rich interphase precipitates form at moving phase boundaries during slow cooling. Further increases in yield strength, attained with increasing tungsten content, are due to composite strengthening; this is verified by increasing elastic modulus with increasing tungsten content. Age hardening behavior is observed, with strengthening occurring at aging temperatures low in the alpha phase. Aging higher in alpha gives initial strengthening followed by rapid overaging. Beta phase aging results in a very soft structure with precipitates visible optically. Wrought material exhibits significant strain hardening as well as composite strengthening due to elongation of the tungsten particles. 7 refs., 15 figs., 4 tabs.

  10. Mirrorlike pulsed laser deposited tungsten thin film

    SciTech Connect

    Mostako, A. T. T.; Khare, Alika; Rao, C. V. S.

    2011-01-15

    Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10{sup -5} Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness {approx}782 nm.

  11. Mirrorlike pulsed laser deposited tungsten thin film.

    PubMed

    Mostako, A T T; Rao, C V S; Khare, Alika

    2011-01-01

    Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ∼782 nm. PMID:21280810

  12. Strengthening mechanisms of tungsten powder reinforced uranium

    SciTech Connect

    Krawizcki, M.A.

    1990-04-01

    Tungsten powder reinforced uranium composites exhibit a three-fold increase in yield strength due to precipitation hardening. The tungsten-rich interphase precipitates form at the moving beta to alpha phase boundary during slow cooling. Further increases in yield strength, attained with increasing tungsten content, are due to composite strengthening. The composite strengthening is verified by increasing elastic modulus with increasing tungsten content. Age hardening behavior is observed, with strengthening occurring at aging temperatures low, in the alpha phase. Temperatures higher in alpha give initial strengthening followed by rapid overaging. Beta phase aging temperatures result in a very soft structure with interphase precipitates observable optically. Wrought material exhibits significant strain hardening as well as composite strengthening due to elongation of the tungsten particles. 36 refs., 36 figs., 10 tabs.

  13. Rhenium Disulfide Depletion-Load Inverter

    NASA Astrophysics Data System (ADS)

    McClellan, Connor; Corbet, Chris; Rai, Amritesh; Movva, Hema C. P.; Tutuc, Emanuel; Banerjee, Sanjay K.

    2015-03-01

    Many semiconducting Transition Metal Dichalcogenide (TMD) materials have been effectively used to create Field-Effect Transistor (FET) devices but have yet to be used in logic designs. We constructed a depletion-load voltage inverter using ultrathin layers of Rhenium Disulfide (ReS2) as the semiconducting channel. This ReS2 inverter was fabricated on a single micromechanically-exfoliated flake of ReS2. Electron beam lithography and physical vapor deposition were used to construct Cr/Au electrical contacts, an Alumina top-gate dielectric, and metal top-gate electrodes. By using both low (Aluminum) and high (Palladium) work-function metals as two separate top-gates on a single ReS2 flake, we create a dual-gated depletion mode (D-mode) and enhancement mode (E-mode) FETs in series. Both FETs displayed current saturation in the output characteristics as a result of the FET ``pinch-off'' mechanism and On/Off current ratios of 105. Field-effect mobilities of 23 and 17 cm2V-1s-1 and subthreshold swings of 97 and 551 mV/decade were calculated for the E-mode and D-mode FETs, respectively. With a supply voltage of 1V, at low/negative input voltages the inverter output was at a high logic state of 900 mV. Conversely with high/positive input voltages, the inverter output was at a low logic state of 500 mV. The inversion of the input signal demonstrates the potential for using ReS2 in future integrated circuit designs and the versatility of depletion-load logic devices for TMD research. NRI SWAN Center and ARL STTR Program.

  14. Polycrystalline silicon on tungsten substrates

    NASA Technical Reports Server (NTRS)

    Bevolo, A. J.; Schmidt, F. A.; Shanks, H. R.; Campisi, G. J.

    1979-01-01

    Thin films of electron-beam-vaporized silicon were deposited on fine-grained tungsten substrates under a pressure of about 1 x 10 to the -10th torr. Mass spectra from a quadrupole residual-gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. During separate silicon depositions, the atomically clean substrates were maintained at various temperatures between 400 and 780 C, and deposition rates were between 20 and 630 A min. Surface contamination and interdiffusion were monitored by in situ Auger electron spectrometry before and after cleaning, deposition, and annealing. Auger depth profiling, X-ray analysis, and SEM in the topographic and channeling modes were utilized to characterize the samples with respect to silicon-metal interface, interdiffusion, silicide formation, and grain size of silicon. The onset of silicide formation was found to occur at approximately 625 C. Above this temperature tungsten silicides were formed at a rate faster than the silicon deposition. Fine-grain silicon films were obtained at lower temperatures.

  15. Development of tungsten fibre-reinforced tungsten composites towards their use in DEMO—potassium doped tungsten wire

    NASA Astrophysics Data System (ADS)

    Riesch, J.; Han, Y.; Almanstötter, J.; Coenen, J. W.; Höschen, T.; Jasper, B.; Zhao, P.; Linsmeier, Ch; Neu, R.

    2016-02-01

    For the next step fusion reactor the use of tungsten is inevitable to suppress erosion and allow operation at elevated temperature and high heat loads. Tungsten fibre-reinforced composites overcome the intrinsic brittleness of tungsten and its susceptibility to operation embrittlement and thus allow its use as a structural as well as an armour material. That this concept works in principle has been shown in recent years. In this contribution we present a development approach towards its use in a future fusion reactor. A multilayer approach is needed addressing all composite constituents and manufacturing steps. A huge potential lies in the optimization of the tungsten wire used as fibre. We discuss this aspect and present studies on potassium doped tungsten wire in detail. This wire, utilized in the illumination industry, could be a replacement for the so far used pure tungsten wire due to its superior high temperature properties. In tensile tests the wire showed high strength and ductility up to an annealing temperature of 2200 K. The results show that the use of doped tungsten wire could increase the allowed fabrication temperature and the overall working temperature of the composite itself.

  16. Development of quantitative atomic modeling for tungsten transport study using LHD plasma with tungsten pellet injection

    NASA Astrophysics Data System (ADS)

    Murakami, I.; Sakaue, H. A.; Suzuki, C.; Kato, D.; Goto, M.; Tamura, N.; Sudo, S.; Morita, S.

    2015-09-01

    Quantitative tungsten study with reliable atomic modeling is important for successful achievement of ITER and fusion reactors. We have developed tungsten atomic modeling for understanding the tungsten behavior in fusion plasmas. The modeling is applied to the analysis of tungsten spectra observed from plasmas of the large helical device (LHD) with tungsten pellet injection. We found that extreme ultraviolet (EUV) emission of W24+ to W33+ ions at 1.5-3.5 nm are sensitive to electron temperature and useful to examine the tungsten behavior in edge plasmas. We can reproduce measured EUV spectra at 1.5-3.5 nm by calculated spectra with the tungsten atomic model and obtain charge state distributions of tungsten ions in LHD plasmas at different temperatures around 1 keV. Our model is applied to calculate the unresolved transition array (UTA) seen at 4.5-7 nm tungsten spectra. We analyze the effect of configuration interaction on population kinetics related to the UTA structure in detail and find the importance of two-electron-one-photon transitions between 4p54dn+1- 4p64dn-14f. Radiation power rate of tungsten due to line emissions is also estimated with the model and is consistent with other models within factor 2.

  17. Thiol/disulfide homeostasis in patients with ankylosing spondylitis

    PubMed Central

    Dogru, Atalay; Balkarli, Ayse; Cetin, Gozde Yildirim; Neselioglu, Salim; Erel, Ozcan; Tunc, Sevket Ercan; Sahin, Mehmet

    2016-01-01

    Ankylosing spondylitis (AS) is a chronic inflammatory disease. In many inflammatory diseases, increased production of pro-inflammatory cytokines is associated with an increase in oxidative stress mediators. Thiol/disulfide homeostasis is a marker for oxidative stress. The aim of this study was to examine the dynamic thiol/disulfide homeostasis in AS. Sixty-nine patients with AS and 60 age- and sex-matched controls were included in the study. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and visual analogue scale (VAS) were used to determine the disease activity. Native thiol, total thiol, and disulfide levels were measured with a novel automated method recently described by Erel and Neselioglu. The aforementioned method is also optionally manual spectrophotometric assay. The total thiol levels were significantly lower in the AS group compared with the control group (p = 0.03). When the patients were divided into active (n = 35) and inactive (n = 34) subgroups using BASDAI scores, the native plasma thiol and total thiol levels were significantly lower in the active AS patients compared to the inactive AS patients (p = 0.02, p = 0.03 respectively). There was a negative correlation between the plasma native thiol levels and VAS, BASDAI scores. Thiol/disulfide homeostasis may be used for elucidating the effects of oxidative stress in AS. Understanding the role of thiol/disulfide homeostasis in AS might provide new therapeutic intervention strategies for patients.

  18. Disulfide Bridges: Bringing Together Frustrated Structure in a Bioactive Peptide.

    PubMed

    Zhang, Yi; Schulten, Klaus; Gruebele, Martin; Bansal, Paramjit S; Wilson, David; Daly, Norelle L

    2016-04-26

    Disulfide bridges are commonly found covalent bonds that are usually believed to maintain structural stability of proteins. Here, we investigate the influence of disulfide bridges on protein dynamics through molecular dynamics simulations on the cysteine-rich trypsin inhibitor MCoTI-II with three disulfide bridges. Correlation analysis of the reduced cyclic peptide shows that two of the three disulfide distances (Cys(11)-Cys(23) and Cys(17)-Cys(29)) are anticorrelated within ∼1 μs of bridge formation or dissolution: when the peptide is in nativelike structures and one of the distances shortens to allow bond formation, the other tends to lengthen. Simulations over longer timescales, when the denatured state is less structured, do not show the anticorrelation. We propose that the native state contains structural elements that frustrate one another's folding, and that the two bridges are critical for snapping the frustrated native structure into place. In contrast, the Cys(4)-Cys(21) bridge is predicted to form together with either of the other two bridges. Indeed, experimental chromatography and nuclear magnetic resonance data show that an engineered peptide with the Cys(4)-Cys(21) bridge deleted can still fold into its near-native structure even in its noncyclic form, confirming the lesser role of the Cys(4)-Cys(21) bridge. The results highlight the importance of disulfide bridges in a small bioactive peptide to bring together frustrated structure in addition to maintaining protein structural stability. PMID:27119635

  19. Thiol/disulfide redox states in signaling and sensing

    PubMed Central

    Go, Young-Mi; Jones, Dean P.

    2015-01-01

    Rapid advances in redox systems biology are creating new opportunities to understand complexities of human disease and contributions of environmental exposures. New understanding of thiol-disulfide systems have occurred during the past decade as a consequence of the discoveries that thiol and disulfide systems are maintained in kinetically controlled steady-states displaced from thermodynamic equilibrium, that a widely distributed family of NADPH oxidases produces oxidants that function in cell signaling, and that a family of peroxiredoxins utilize thioredoxin as a reductant to complement the well-studied glutathione antioxidant system for peroxide elimination and redox regulation. This review focuses on thiol/disulfide redox state in biologic systems and the knowledge base available to support development of integrated redox systems biology models to better understand the function and dysfunction of thiol-disulfide redox systems. In particular, central principles have emerged concerning redox compartmentalization and utility of thiol/disulfide redox measures as indicators of physiologic function. Advances in redox proteomics show that, in addition to functioning in protein active sites and cell signaling, cysteine residues also serve as redox sensors to integrate biologic functions. These advances provide a framework for translation of redox systems biology concepts to practical use in understanding and treating human disease. Biological responses to cadmium, a widespread environmental agent, are used to illustrate the utility of these advances to the understanding of complex pleiotropic toxicities. PMID:23356510

  20. Does Electron Capture Dissociation Cleave Protein Disulfide Bonds?

    PubMed Central

    Ganisl, Barbara; Breuker, Kathrin

    2012-01-01

    Peptide and protein characterization by mass spectrometry (MS) relies on their dissociation in the gas phase into specific fragments whose mass values can be aligned as ‘mass ladders’ to provide sequence information and to localize possible posttranslational modifications. The most common dissociation method involves slow heating of even-electron (M+n H)n+ ions from electrospray ionization by energetic collisions with inert gas, and cleavage of amide backbone bonds. More recently, dissociation methods based on electron capture or transfer were found to provide far more extensive sequence coverage through unselective cleavage of backbone N–Cα bonds. As another important feature of electron capture dissociation (ECD) and electron transfer dissociation (ETD), their unique unimolecular radical ion chemistry generally preserves labile posttranslational modifications such as glycosylation and phosphorylation. Moreover, it was postulated that disulfide bond cleavage is preferred over backbone cleavage, and that capture of a single electron can break both a backbone and a disulfide bond, or even two disulfide bonds between two peptide chains. However, the proposal of preferential disulfide bond cleavage in ECD or ETD has recently been debated. The experimental data presented here reveal that the mechanism of protein disulfide bond cleavage is much more intricate than previously anticipated. PMID:24363980

  1. Environmental fate of tungsten from military use.

    PubMed

    Clausen, Jay L; Korte, Nic

    2009-04-01

    This manuscript describes the distribution, fate and transport of tungsten used in training rounds at three small arms ranges at Camp Edwards on the Massachusetts Military Reservation (MMR), USA. Practice with tungsten/nylon rounds began in 2000 subsequent to a 1997 US Environmental Protection Agency ban on training with lead. Training with the tungsten rounds was halted in 2005 because of concerns regarding tungsten's environmental mobility and potential toxicity. This study, therefore, examines how tungsten partitions in the environment when fired on a small arms training range. Soil sampling revealed surface soil concentrations, highest at the berm face, up to 2080 mg/kg. Concentrations decreased rapidly with depth--at least by an order of magnitude by 25 cm. Nonetheless, tungsten concentrations remained above background to at least 150 cm. Pore-water samples from lysimeters installed in berm areas revealed a range of concentrations (<1-400 mg/L) elevated with respect to background although there was no discernable trend with depth. Groundwater monitoring well samples collected approximately 30 m below ground surface showed tungsten (0.001-0.56 mg/L) attributable to range use. PMID:19217645

  2. Photoactive chitosan: A step towards a green strategy for pollutant degradation

    PubMed Central

    Walalawela, Niluksha; Greer, Alexander

    2014-01-01

    This article is a highlight of the paper by Ferrari et al. in this issue of Photochemistry and Photobiology. It describes the innovative use of rose bengal-conjugated chitosan as a reusable green catalyst that photo-degrades phenolic compounds in aqueous media, and thereby has decontamination potential of polluted waters. Whether a next-generation photoactive polymer that produces singlet oxygen is a solution to pollutant degradation can be argued. It is as yet unclear what polymeric sensitizer would be practical on a large scale. Nonetheless pursuing this goal is worthwhile. PMID:25270888

  3. One-Photon and Two-Photon Pump-Probe Spectroscopy of Photoactive Yellow Protein

    NASA Astrophysics Data System (ADS)

    Lyngnes, O.; Gibbs, H. M.; Li, C. F.; Devanathan, S. B.; Meyer, T. E.; Tollin, G.; Cusanovich, M. A.

    We present the results of nonlinear optical pump-probe experiments on photoactive yellow protein (PYP). We are able to completely bleach the 446 nm absorption peak of PYP by one-photon excitation using a cw argon laser. We calculate the corresponding index change and find it to be similar to that of bacteriorhodopsin. We also determine an upper limit to the two photon absorption cross-section of PYP by looking for bleaching of the 446 nm absorption peak under irradiation by femtosecond pulses at 820-910 nm. No TPA signal is observed.

  4. Photoactive energetic materials: linear and nonlinear photochemistry of chromophore linked energetic materials

    NASA Astrophysics Data System (ADS)

    Greenfield, Margo; McGrane, Shawn; Bolme, Cindy; Chavez, David; Veauthier, Jacqueline; Hanson, Susan; Myers, Thomas; Scharff, Jason

    2015-06-01

    In general, conventional molecular explosives are white to off-white in color and only absorb ultraviolet light. A novel approach to synthetically link optically active energetic chromophores to existing molecular energetic materials has resulted in increased photoactivity in the visible (532 nm) region of the electromagnetic spectrum. Tetrazine, an energetic optically active chromophore, which absorbs around 532 nm, has been derivatized with various energetic materials including pentaeythritol tetranitrate (PETN), nitroglycerine (NG) and dinitroazetidine (DNAZ). We report the corresponding photochemistry and photochemical quantum yields of these new materials under various wavelength and intensity regimes.

  5. Time-resolved serial crystallography captures high-resolution intermediates of photoactive yellow protein

    DOE PAGESBeta

    Tenboer, Jason; Basu, Shibom; Zatsepin, Nadia; Pande, Kanupriya; Milathianaki, Despina; Frank, Matthias; Hunter, Mark; Boutet, Sebastien; Williams, Garth J.; Koglin, Jason E.; et al

    2014-12-05

    We report that serial femtosecond crystallography using ultrashort pulses from X-ray Free Electron Lasers (XFELs) offers the possibility to study light-triggered dynamics of biomolecules. Using microcrystals of the blue light photoreceptor, photoactive yellow protein, as a model system, we present high resolution, time-resolved difference electron density maps of excellent quality with strong features, which allow the determination of structures of reaction intermediates to 1.6 Å resolution. These results open the way to the study of reversible and non-reversible biological reactions on time scales as short as femtoseconds under conditions which maximize the extent of reaction initiation throughout the crystal.

  6. Synthesis of Photoactive Materials by Sonication: Application in Photocatalysis and Solar Cells.

    PubMed

    Colmenares, Juan C; Kuna, Ewelina; Lisowski, Paweł

    2016-10-01

    In recent years, a good number of methods have become available for the preparation of an important group of photoactive materials for applications in photocatalysis and solar cells. Nevertheless, the benefits derived from preparing those materials through unconventional approaches are very attractive from the green chemistry point of view. This critical review work is focused on sonication as one of these promising new synthetic procedures that allow control over size, morphology, nanostructure and tuning of catalytic properties. Ultrasound-based procedures offer a facile, versatile synthetic tool for the preparation of light-activated materials often inaccessible through conventional methods. PMID:27573501

  7. Improving the efficiency of organic solar cells by varying the material concentration in the photoactive layer

    NASA Astrophysics Data System (ADS)

    Latimer, Kevin Anthony

    Polymer-fullerene bulk heterojunction solar cells have been a rapidly improving technology over the past decade. To further improve the relatively low energy conversion efficiencies of these solar cells, several modifications need to be made to the overall device structure. Emerging technologies include cells that are fabricated with interfacial layers to facilitate charge transport, and tandem structures are being introduced to harness the absorption spectrum of polymers with varying bandgap energies. When new structures are implemented, each layer of the cell must be optimized in order for the entire device to function efficiently. The most volatile layer of these devices is the photoactive layer solution of poly-3(hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC 61BM). Even slight variations in pre-application and post-treatment will lead to large variations in the electrical, physical, and optical properties of the solar cell module. To improve the effectiveness of the photoactive layer, the material concentration of P3HT and PC61BM in the liquid phase, prior to application, was altered. The weight ratio of P3HT to PC61BM was kept at a constant 1 to 0.8, while the amounts of each dissolved in 2 mL of chlorobenzene were varied. Solar cells were fabricated, and J-V characterizations were performed to determine the electrical traits of the devices. Atomic force microscopy (AFM) measurements were done on the photoactive layer films to determine the physical characteristics of the films such as overall surface topology and RMS roughness. Also, variable angle spectroscopic ellipsometry (VASE) was used to determine film thickness and extinction coefficient of the active layers. To further understand the optical properties of the polymer-fullerene blend, the absorption spectrum of the films were calculated through UV-VIS spectrophotometry. It was found that an increased concentration of the polymer-fullerene blend prior to application

  8. Plasma-polymerized carbon disulfide thin-film rechargeable batteries

    SciTech Connect

    Sadhir, R.K.; Schoch, K.F. Jr.

    1996-06-01

    This paper discusses the results on deposition conditions, rates of polymerization, and properties of carbon disulfide films prepared by two techniques, viz., plasma polymerization and argon-plasma-assisted polymerization of carbon disulfide. A higher rate of polymerization and sulfur content was obtained for carbon disulfide films prepared by the plasma-polymerization technique. A Li/LiClO{sub 4} propylene carbonate/PPCS cell was assembled using lithium foil, 2 M LiClO{sub 4}/PC electrolyte with polyolefin separator, and PPCS deposited on Pt foil. The electrode area was 1.3 cm{sup 2}. The cell cycled reversibly between 1 and 3 V and retained its capacity (5 mA h/g) well over 12 cycles. 14 refs., 11 figs., 5 tabs.

  9. Disulfide Bond Formation in Prokaryotes: History, Diversity and Design

    PubMed Central

    Hatahet, Feras; Boyd, Dana; Beckwith, Jon

    2014-01-01

    The formation of structural disulfide bonds is essential for the function and stability of a great number of proteins, particularly those that are secreted. There exists a variety of dedicated cellular catalysts and pathways from Archaea to humans that ensure the formation of native disulfide bonds. In this review we describe the initial discoveries of these pathways and report progress in recent years in our understanding of the diversity of these pathways in prokaryotes, including those newly discovered in some Archaea. We will also discuss the various successful efforts to achieve laboratory-based evolution and design of synthetic disulfide bond formation machineries in the bacterium E. coli. These latter studies have also led to new more general insights into the redox environment of the cytoplasm and bacterial cell envelope. PMID:24576574

  10. Properties of tungsten-rhenium and tungsten-rhenium with hafnium carbide

    NASA Astrophysics Data System (ADS)

    Leonhardt, Todd

    2009-07-01

    Historically, tungsten-25wt.% rhenium alloy has been manufactured into wire for the thermocouple market, but recent demands for high-temperature structural components have forced the development of novel processing techniques for tungsten-rhenium and tungsten-rhenium with hafnium carbide. With a melting temperature of 3,050°C, and a recrystallization temperature near 1,900°C, tungsten-rhenium alloys are being used in aerospace, temperature measuring, and friction stir welding applications. The mechanical properties and microstructures of tungsten-25wt.% rhenium and tungsten-25wt.% rhenium with hafnium carbide are reported at ambient temperature, 1,371°C, and 1,926°C, after processing by three methods: hot isostatic pressing, swaging, and extrusion.

  11. Role of solubility and tungsten powder size on densification of tungsten-based composites

    SciTech Connect

    Griffo, A.; Liu, Y.; German, R.M.

    1994-10-19

    The densification behavior of new tungsten-based alloys was evaluated as a function of the solubility of tungsten in the liquid and the particle size of the tungsten powder. The matrix phase was a combination of nickel or iron, and an aluminide-based intermetallics, Ni3A1, Ni2Al3, and Fe3Al. The aluminides were used to lower the matrix solubility for tungsten to inhibit grain coarsening. In addition, the low solubility systems used two different tungsten powders to examine the role of powder size on densification. Dilatometric experiments were performed to determined the liquid formation temperatures and to study the densification dynamics. A low solubility matrix required higher sintering temperatures and smaller tungsten particles to achieve near full density.

  12. Fabrication and properties of tungsten heavy metal alloys containing 30% to 90% tungsten

    SciTech Connect

    Gurwell, W.E.; Nelson, R.G.; Dudder, G.B.; Davis, N.C.

    1984-09-01

    In 1983, Pacific Northwest Laboratory conducted a survey of tungsten heavy metal alloys having lower-than-normal (<90%) tungsten content. The purpose of the work was to develop tougher, more impact-resistant high-density alloys for applications benefitting from improved mechanical properties. Tungsten heavy metal alloys of 30 to 90% tungsten content were fabricated and their mechanical properties measured. Although ultimate strength was essentially independent of tungsten content, lower tungsten-content alloys had lower yield stress, hardness, and density, and decidedly higher elongations and impact energies. Cold work was effective in raising strength and hardness but detrimental to elongation and impact energies. Precipitation hardening and strain aging raised hardness effectively but had less influence on other mechanical properties. 34 figures, 7 tables.

  13. Identification of disulfides from the biodegradation of dibenzothiophene.

    PubMed

    Bressler, D C; Fedorak, P M

    2001-11-01

    Several investigations have identified benzothiophene-2,3-dione in the organic solvent extracts of acidified cultures degrading dibenzothiophene via the Kodama pathway. In solution at neutral pH, the 2,3-dione exists as 2-mercaptophenylglyoxylate, which cyclizes upon acidification and is extracted as the 2,3-dione. The fate of these compounds in microbial cultures has never been determined. This study investigated the abiotic reactions of 2-mercaptophenylglyoxylate incubated aerobically in mineral salts medium at neutral pH. Oxidation led to the formation of 2-oxo-2-(2-thiophenyl)ethanoic acid disulfide, formed from two molecules of 2-mercaptophenylglyoxylate. Two sequential abiotic, net losses of both a carbon and an oxygen atom produced two additional disulfides, 2-oxo-2-(2-thiophenyl)ethanoic acid 2-benzoic acid disulfide and 2,2'-dithiosalicylic acid. The methods developed to extract and detect these three disulfides were then used for the analysis of a culture of Pseudomonas sp. strain BT1d grown on dibenzothiophene as its sole carbon and energy source. All three of the disulfides were detected, indicating that 2-mercaptophenylglyoxylate is an important, short-lived intermediate in the breakdown of dibenzothiophene via the Kodama pathway. The disulfides eluded previous investigations because of (i) their high polarity, being dicarboxylic acids; (ii) the need to lower the pH of the aqueous medium to <1 to extract them into an organic solvent such as dichloromethane; (iii) their poor solubility in organic solvents, (iv) their removal from organic extracts of cultures during filtration through the commonly used drying agent anhydrous sodium sulfate; and (v) their high molecular masses (362, 334, and 306 Da) compared to that of dibenzothiophene (184 Da). PMID:11679330

  14. Dielectronic recombination of tungsten ions

    NASA Astrophysics Data System (ADS)

    Li, Bowen; O’Sullivan, Gerry; Dong, Chenzhong; Chen, Ximeng

    2016-08-01

    Ab initio calculations of dielectronic recombination rate coefficients of Ne-, Pd- and Ag-like tungsten have been performed. Energy levels, radiative transition probabilities and autoionization rates were calculated using the Flexible Atomic Code. The contributions from different channels to the total rate coefficients are discussed. The present calculated rate coefficients are compared with other calculations where available. Excellent agreement has been found for Ne-like W while a large discrepancy was found for Pd-like W, which implies that more ab initio calculations and experimental measurements are badly needed. Further calculations demonstrated that the influence of configuration interaction is small while nonresonant radiative stabilizing (NRS) contribution to doubly excited non-autoionizing states are vital. The data obtained are expected to be useful for modeling plasmas for fusion applications, especially for the ITER community, which makes experimental verification even more essential.

  15. Tungsten Ditelluride: a layered semimetal.

    PubMed

    Lee, Chia-Hui; Silva, Eduardo Cruz; Calderin, Lazaro; Nguyen, Minh An T; Hollander, Matthew J; Bersch, Brian; Mallouk, Thomas E; Robinson, Joshua A

    2015-01-01

    Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe2 in electronic device architectures such as field effect transistors may need to be reevaluated. PMID:26066766

  16. Tungsten Ditelluride: a layered semimetal

    NASA Astrophysics Data System (ADS)

    Lee, Chia-Hui; Silva, Eduardo Cruz; Calderin, Lazaro; Nguyen, Minh An T.; Hollander, Matthew J.; Bersch, Brian; Mallouk, Thomas E.; Robinson, Joshua A.

    2015-06-01

    Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe2 in electronic device architectures such as field effect transistors may need to be reevaluated.

  17. High strength and density tungsten-uranium alloys

    DOEpatents

    Sheinberg, Haskell

    1993-01-01

    Alloys of tungsten and uranium and a method for making the alloys. The amount of tungsten present in the alloys is from about 55 vol % to about 85 vol %. A porous preform is made by sintering consolidated tungsten powder. The preform is impregnated with molten uranium such that (1) uranium fills the pores of the preform to form uranium in a tungsten matrix or (2) uranium dissolves portions of the preform to form a continuous uranium phase containing tungsten particles.

  18. Thermal properties of plasma-sprayed tungsten deposits

    NASA Astrophysics Data System (ADS)

    Kang, Hyun-Ki

    2004-10-01

    Tungsten powder was plasma-sprayed onto a graphite substrate in order to examine the microstructures, porosities, and thermal conductivities of tungsten deposits. Tungsten was partially oxidized to tungsten oxide (WO 3) after plasma spraying. Most pores were found in the vicinity of lamellar layers in association with oxidation. It was revealed that both tungsten oxide and the lamellar structure with pores have a significant influence on the electrical and thermal conductivity.

  19. High strength and density tungsten-uranium alloys

    SciTech Connect

    Sheinberg, H.

    1991-01-01

    Alloys of tungsten and uranium and a method for making the alloys. Amount of tungsten present in the alloys is from about 55 to 85. A porous preform is made by sintering consolidated tungsten powder. The preform is impregnated with molten uranium such that (1) uranium fills the pores of the of the preform to form uranium in a tungsten matrix or (2) uranium dissolves portions of the preform to form a continuous uranium phase containing tungsten particles.

  20. High strength and density tungsten-uranium alloys

    SciTech Connect

    Sheinberg, H.

    1993-11-16

    Alloys of tungsten and uranium and a method for making the alloys. The amount of tungsten present in the alloys is from about 55 vol % to about 85 vol %. A porous preform is made by sintering consolidated tungsten powder. The preform is impregnated with molten uranium such that (1) uranium fills the pores of the preform to form uranium in a tungsten matrix or (2) uranium dissolves portions of the preform to form a continuous uranium phase containing tungsten particles.

  1. High strength and density tungsten-uranium alloys

    SciTech Connect

    Sheinberg, H.

    1991-12-31

    Alloys of tungsten and uranium and a method for making the alloys. Amount of tungsten present in the alloys is from about 55 to 85. A porous preform is made by sintering consolidated tungsten powder. The preform is impregnated with molten uranium such that (1) uranium fills the pores of the of the preform to form uranium in a tungsten matrix or (2) uranium dissolves portions of the preform to form a continuous uranium phase containing tungsten particles.

  2. Electrochemical study of thiols and disulfides using modified electrodes

    SciTech Connect

    Linders, C.R.; Patriarche, G.J.; Kauffman, J.M.

    1986-01-01

    The electrochemical oxidative behavior of cysteine and several disulfides, such as cysteine, lipoic acid and disulfiram, have been investigated using a carbon paste (EPC) and a modified carbon paste (EPCM) electrode. The study has permitted the differentiation of the oxidative behavior of the thiol and of the disulfides. Modification of the carbon paste, by incorporating cobalt(II) phthalocyanine, offers interesting properties due to the electrocatalytic capability of the electrode. Using these types of electrodes the different molecules have been quantitatively determined at concentrations as low as 2.10/sup -7/ M. 14 references, 2 figures, 1 table.

  3. Structures and related properties of helical, disulfide-stabilized peptides

    SciTech Connect

    Pagel, M.D. |

    1993-11-01

    The three dimensional structure of several peptides were determined by NMR spectroscopy and distance geometry calculations. Each peptide formed a predictable, rigid structure, consisting of an {alpha}-helix, a {open_quotes}scaffold{close_quotes} region which packed along one face of the helix, and two disulfide bridges which covalently connect the helix and scaffold regions. The peptide Apa-M5 was designed to constrain the M5 peptide from MLCK in a helical geometry using the apamin disulfide scaffold. This scaffold constrains the N- terminal end of the helix with two disulfide bridges and a reverse turn. Like the M5 peptide, Apa-M5 was found to bind calmodulin in a Ca{sup 2+}-dependent 1:1 stoichiometry. However, the dissociation constant of the (Apa-M5)-calmodulin complex, 107 nM, was 100-fold higher than the dissociation constant of the M5-calmodulin complex. This difference was due to a putative steric overlap between the Apa-M5 scaffold and calmodulin. The peptide Apa-Cro was designed to replace the large structural protein matrix of {lambda} Cro with the apamin disulfide scaffold. However, Apa-Cro did not bind the consensus DNA operator half-site of {lambda} Cro, probably due to a steric overlap between the Apa-Cro disulfide framework and the DNA. The amino acid sequence of the scaffold-disulfide bridge arrangement of the peptide Max was derived from the core sequence of scyllatoxin, which contains an {alpha}-helix constrained at the C-terminal end by two disulfide bridges and a two-stranded {beta}sheet scaffold. Max was shown to fold with >84% yield to form a predictable, stable structure that is similar to scyllatoxin. The folding and stability properties of Max make this scaffold and disulfide bridge arrangement an ideal candidate for the development of hybrid sequence peptides. The dynamics of a fraying C-terminal end of the helix of the peptide Apa-AlaN was determined by analysis of {sup 15}N NMR relaxation properties.

  4. Effect of deposition conditions on properties of plasma polymerized carbon disulfide

    SciTech Connect

    Sadhir, R.K.; Schoch, K.F. Jr.

    1995-12-31

    This paper discusses the results on deposition conditions, rates of polymerization and properties of carbon disulfide films prepared by two techniques viz. plasma polymerization and argon-plasma-assisted polymerization of carbon disulfide. A higher rate of polymerization and sulfur content was obtained for carbon disulfide films prepared by plasma polymerization technique. The ultimate objective of this research work was to prepare thin film solid state batteries using the optimized carbon disulfide polymer films deposited by plasma techniques, as active material.

  5. Localized cell stimulation by nitric oxide using a photoactive porous coordination polymer platform

    NASA Astrophysics Data System (ADS)

    Diring, Stéphane; Wang, Dan Ohtan; Kim, Chiwon; Kondo, Mio; Chen, Yong; Kitagawa, Susumu; Kamei, Ken-Ichiro; Furukawa, Shuhei

    2013-10-01

    Functional cellular substrates for localized cell stimulation by small molecules provide an opportunity to control and monitor cell signalling networks chemically in time and space. However, despite improvements in the controlled delivery of bioactive compounds, the precise localization of gaseous biomolecules at the single-cell level remains challenging. Here we target nitric oxide, a crucial signalling molecule with site-specific and concentration-dependent activities, and we report a synthetic strategy for developing spatiotemporally controllable nitric oxide-releasing platforms based on photoactive porous coordination polymers. By organizing molecules with poor reactivity into polymer structures, we observe increased photoreactivity and adjustable release using light irradiation. We embed photoactive polymer crystals in a biocompatible matrix and achieve precisely controlled nitric oxide delivery at the cellular level via localized two-photon laser activation. The biological relevance of the exogenous nitric oxide produced by this strategy is evidenced by an intracellular change in calcium concentration, mediated by nitric oxide-responsive plasma membrane channel proteins.

  6. Multifunctional Single-Phase Photocatalysts: Extended Near Infrared Photoactivity and Reliable Magnetic Recyclability.

    PubMed

    Li, Xiaoning; Zhu, Zhu; Li, Feng; Huang, Yan; Hu, Xiang; Huang, Haoliang; Peng, Ranran; Zhai, XiaoFang; Fu, Zhengping; Lu, Yalin

    2015-01-01

    A practical photocatalyst should be able to integrate together various functions including the extended solar conversion, a feasible and economic recyclability, and above the room temperature operation potential, et al., in order to fulfill the spreading application needs in nowadays. In this report, a multifunctional single-phase photocatalyst which possesses a high photoactivity extended into the near infrared region, an easy magnetic recyclability and the high temperature stability was developed by doping Co into a new layer-structured Bi7Fe3Ti3O21 material. Light absorption and photocatalytic activity of the resulted Bi7Fe(3-x)CoxTi3O21 photocatalyst were extended to the long wavelength as far as 800 nm. Its strong ferromagnetism above the room temperature enables the nanopowders fully recyclable in viscous solutions simply with a magnet bar in an experimental demonstration. Furthermore, such photoactivity and magnetic recyclability were heavily tested under high-temperature and high-viscosity conditions, which was intended to simulate the actual industrial environments. This work brings the bright light to a full availability of a new multifunctional photocatalyst, via integrating the much enhanced ferromagnetic, ferroelectric, optoelectronic properties, most importantly, into a single-phase structure. PMID:26503907

  7. Understanding the adsorptive and photoactivity properties of Ag-graphene oxide nanocomposites.

    PubMed

    Martínez-Orozco, R D; Rosu, H C; Lee, Soo-Wohn; Rodríguez-González, V

    2013-12-15

    Nanocomposites of graphene oxide (GO) and silver nanoparticles (AgNPs) were synthetized using a practical photochemical silver functionalization. Their photocatalytic activities were evaluated with two dyes, Rhodamine B and Indigo Carmine, under visible-light irradiation. The prepared nanocomposites were characterized by HRTEM, FESEM, XRD, Raman, FTIR and UV-vis absorption spectroscopy. These nanocomposites present new defect domains of sp(3) type in combination with several graphitic functional groups that act as nucleation sites for anchoring AgNPs, while the sp(2)-sp(3) edge defects domains of GO generate the photoactivity. Furthermore, their photocatalytic performances are governed by their large adsorption capacity, and strong interaction with dye chromophores. A comprehensive photocatalytic way underlying the importance of adsorption is suggested to explain the low visible-light responsive photoactivity of the AgNPs-GO nanocomposites and the possible binding-site saturation. Then, the usage of H2SO4 allows the production of ionic species and helps to confirm the strong adsorption of both dyes. The ability to synthesize AgNPs-GO nanocomposites with extensive adsorptive capacity is certainly of interest for the efficient removal of hazardous materials. PMID:24035508

  8. The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers.

    PubMed

    Aristidou, Nicholas; Sanchez-Molina, Irene; Chotchuangchutchaval, Thana; Brown, Michael; Martinez, Luis; Rath, Thomas; Haque, Saif A

    2015-07-01

    In this paper we report on the influence of light and oxygen on the stability of CH3 NH3 PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2 O3 /CH3 NH3 PbI3 photoactive layers rapidly decompose yielding methylamine, PbI2 , and I2 as products. We show that this degradation is initiated by the reaction of superoxide (O2 (-) ) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O2 (-) species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O2 (-) generation is significantly reduced when the mp-Al2 O3 film is replaced with an mp-TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3 NH3 PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability. PMID:26014846

  9. Temperature enhancement of photoactivity of N-triphenylmethylsalicylidene imine in solid state

    NASA Astrophysics Data System (ADS)

    Lewanowicz, Aleksandra

    2003-10-01

    Spectral behavior of chromic N-triphenylmethylsalicylidene imine in solid state has been investigated as function of temperature in 300-77 K temperature range. The analysis of the absorption, fluorescence and fluorescence excitation spectra together with the results of microscopic observation has been taken into account in monitoring of changing features. Direct evidence of the keto tautomer (open form) and intermediate formation has been presented, and dynamics of the intramolecular processes have been shortly discussed. The experimental activation energies equal to 5.9 kcal/mol and 9.5 kcal/mol have been extracted from the kinetics of thermally driven changes of luminescence. Those values have been attributed to 540-nm and 510-nm as well as 490-nm emitting species. Besides radiative transition, two main nonradiative deactivation channels, nonradiative transition and photochemical reaction, have been considered in explanation of the thermally enhanced photoactivity of the crystal under study. Contrary to a model anil compound, the photoactivity of studied molecular system with bulky substituent could be realized as dual-type behavior, thermochromic as well as photochromic simultaneously. The changes of the crystal color have been discussed in the frame of the proposed scheme. The scheme represents junction of thermochromic and photochromic behaviors following the proton transfer photochemical reaction acting as the first step of molecular rearrangement.

  10. Characteristics of titanium dioxide microdispersions with different photo-activity suitable for sunscreen formulations.

    PubMed

    Kubáč, L; Akrman, J; Kejlová, K; Bendová, H; Klánová, K; Hladíková, Z; Pikal, P; Kovaříková, L; Kašparová, L; Jírová, D

    2015-03-15

    The aim of the study was the comparison of photo-activity of three types of titanium dioxide (TiO2) micro-dispersions intended for use as UV filters for cosmetic sunscreen products. The dispersions were also investigated with regard to their influence on the stability of photo-protective systems in cosmetic emulsions, their skin penetration/absorption and their photo-toxicity for humans and skin bacterial flora. All the tested micro-dispersions of rutile TiO2 type (agglomerates with diameter 120-150 nm), with primary particle size lower than 100 nm, demonstrated no phototoxic effect and insignificant antimicrobial behaviour. On the other hand, TiO2 with insufficient deactivation of photo-activity had significant negative impact on the stability of other organic UV filters and therefore on the stability of declared UV protective factors (SPF, UVA-PF). The study demonstrated that the level of deactivation of TiO2 is one of the highly important factors for evaluation of UV filters used as sunscreens. PMID:25655716

  11. Thermal Annealing Effect on Poly(3-hexylthiophene): Fullerene:Copper-Phthalocyanine Ternary Photoactive Layer

    PubMed Central

    Derouiche, H.; Mohamed, A. B.

    2013-01-01

    We have fabricated poly(3-hexylthiophene) (P3HT)/copper phthalocyanine (CuPc)/fullerene (C60) ternary blend films. This photoactive layer is sandwiched between an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT/PSS) photoanode and a bathocuproine (BCP)/aluminium photocathode. The thin films have been characterized by atomic force microscope (AFM) and ultraviolet/visible spectroscopy in order to study the influence of P3HT doping on the morphological and optical properties of the photoactive layer. We have also compared the I-V characteristics of three different organic solar cells: ITO/PEDOT:PSS/CuPc0.5:C600.5/BCP/Al and ITO/PEDOT:PSS/P3HT0.3:CuPc0.3:C600.4/BCP/Al with and without annealing. Both structures show good photovoltaic behaviour. Indeed, the incorporation of P3HT into CuPc:C60 thin film improves all the photovoltaic characteristics. We have also seen that thermal annealing significantly improves the optical absorption ability and stabilizes the organic solar cells making it more robust to chemical degradation. PMID:23766722

  12. Photoactive transparent nano-crystalline glass-ceramic for remazole red dye degradation

    SciTech Connect

    Gad-Allah, Tarek A.; Margha, Fatma H.

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► Preparation and characterization of novel transparent nanocrystalline glass-ceramic. ► Precipitation of photoactive phases by using controlled heat-treatment. ► Conservation of transparency along with photoactivity. ► Using the prepared nanocrystalline glass-ceramic in water purification. -- Abstract: Transparent glass ceramic material was prepared from alkali-borosilicate glass containing titania by proper heat treatment scheme. The prepared samples were characterized using differential thermal analysis, X-ray diffraction, transmission electron microscope, selected area electron diffraction and UV–visible spectroscopy. The applied heat treatment program allowed the crystallization of nano-crystalline anatase, rutile, barium titanate, titanium borate and silicate phases while maintaining the transparency. The precipitated nano-crystalline anatase and rutile phases were responsible for the observed high photocatalytic activity of the prepared samples. Samples of 24.29 and 32.39 TiO{sub 2} wt% showed better efficiency for the decolorization of remazole red dye compared with commercial-TiO{sub 2} used in preparation of glass-ceramic. The reuse of prepared glass-ceramic photocatalyst with nearly same efficiency for different times was also proved.

  13. Localized cell stimulation by nitric oxide using a photoactive porous coordination polymer platform

    PubMed Central

    Diring, Stéphane; Wang, Dan Ohtan; Kim, Chiwon; Kondo, Mio; Chen, Yong; Kitagawa, Susumu; Kamei, Ken-ichiro; Furukawa, Shuhei

    2013-01-01

    Functional cellular substrates for localized cell stimulation by small molecules provide an opportunity to control and monitor cell signalling networks chemically in time and space. However, despite improvements in the controlled delivery of bioactive compounds, the precise localization of gaseous biomolecules at the single-cell level remains challenging. Here we target nitric oxide, a crucial signalling molecule with site-specific and concentration-dependent activities, and we report a synthetic strategy for developing spatiotemporally controllable nitric oxide-releasing platforms based on photoactive porous coordination polymers. By organizing molecules with poor reactivity into polymer structures, we observe increased photoreactivity and adjustable release using light irradiation. We embed photoactive polymer crystals in a biocompatible matrix and achieve precisely controlled nitric oxide delivery at the cellular level via localized two-photon laser activation. The biological relevance of the exogenous nitric oxide produced by this strategy is evidenced by an intracellular change in calcium concentration, mediated by nitric oxide-responsive plasma membrane channel proteins. PMID:24158008

  14. Multifunctional Single-Phase Photocatalysts: Extended Near Infrared Photoactivity and Reliable Magnetic Recyclability

    PubMed Central

    Li, Xiaoning; Zhu, Zhu; Li, Feng; Huang, Yan; Hu, Xiang; Huang, Haoliang; Peng, Ranran; Zhai, XiaoFang; Fu, Zhengping; Lu, Yalin

    2015-01-01

    A practical photocatalyst should be able to integrate together various functions including the extended solar conversion, a feasible and economic recyclability, and above the room temperature operation potential, et al., in order to fulfill the spreading application needs in nowadays. In this report, a multifunctional single-phase photocatalyst which possesses a high photoactivity extended into the near infrared region, an easy magnetic recyclability and the high temperature stability was developed by doping Co into a new layer-structured Bi7Fe3Ti3O21 material. Light absorption and photocatalytic activity of the resulted Bi7Fe3-xCoxTi3O21 photocatalyst were extended to the long wavelength as far as 800 nm. Its strong ferromagnetism above the room temperature enables the nanopowders fully recyclable in viscous solutions simply with a magnet bar in an experimental demonstration. Furthermore, such photoactivity and magnetic recyclability were heavily tested under high-temperature and high-viscosity conditions, which was intended to simulate the actual industrial environments. This work brings the bright light to a full availability of a new multifunctional photocatalyst, via integrating the much enhanced ferromagnetic, ferroelectric, optoelectronic properties, most importantly, into a single-phase structure. PMID:26503907

  15. Photoaffinity labeling of the multidrug-resistance-related P-glycoprotein with photoactive analogs of verapamil

    SciTech Connect

    Safa, A.R. )

    1988-10-01

    Verapamil, a phenylalkylamine calcium channel blocker, has been shown to reverse multidrug resistance in tumor cells, possibly by increasing drug retention through interaction with an outward drug transporter of the resistant cells. In this study two photoactive radioactive analogs of verapamil, N-(p-azido(3,5-{sup 3}H)benzoyl)aminomethyl verapamil and N-(p-azido(3-{sup 125}I)salicyl)aminomethyl verapamil, were synthesized and used to identify the possible biochemical target(s) for verapamil in multidrug-resistance DC-3F/VCRd-5L Chinese hamster lung cells selected for resistance to vincristine. The results show that a specifically labeled 150- to 180-kDa membrane protein in resistant cells was immunoprecipitated with a monoclonal antibody specific for P-glycoprotein. Phenylalkylamine binding specificity was established by competitive blocking of specific photolabeling with the nonradioactive photoactive analogs as well as with verapamil. Photoaffinity labeling was also inhibited by 50 {mu}M concentrations of the calcium channel blockers nimodipine, nifedipine, nicardipine, azidopine, bepridil, and diltiazem and partially by prenylamine. Moreover, P-glycoprotein labeling was inhibited in a dose-dependent manner by vinblastine with half-maximal inhibition at 0.2 {mu}M compared to that by verapamil at 8 {mu}M. These data provide direct evidence that P-glycoprotein has broad drug recognition capacity and that it serves as a molecular target for calcium channel blocker action in reversing multidrug resistance.

  16. The effect of fluoride on the crystallinity and photoactivity of titanium dioxide

    NASA Astrophysics Data System (ADS)

    Brauer, Jonathan Isaac

    -synthesized samples were amorphous, but could be converted to the anatase phase by two different methods. Thermal annealing was shown to convert the amorphous particles to the anatase polymorph. The presence of surface fluoride was found to significantly lower the temperature to observe the amorphous to anatase transition. In the second method, stirring the powders in acidic solutions of NaF at room temperature for 12-168 hours produced the anatase phase with an average crystallite size of 4 nm. It was found that the phase transition only occurs when the pH is below the point of zero charge of the particles. The photoactivity of the nitrogen and nitrogen / fluoride-doped particles was tested for their ability to degrade methylene blue (MB) with visible light (> 400 nm). In general the particles with a surface fluoride were more photoactive that those without. In addition, particles with nitrogen were more photoactive than pure TiO2. By analyzing the decomposition products with electrospray ionization mass spectrometry and UV-Vis spectroscopy, it was possible to elucidate a different decomposition pathway for the nitrogen-doped samples. When TEA was the dopant precursor, MB primarily decomposed by a ring-cleavage pathway using superoxide. In contrast, when NH4Cl was the dopant precursor, MB decomposed through demethylation pathway induced by hydroxyl radicals. The as-synthesized particles were found to be more photoactive those thermally annealed. The loss of photoactivity could be ascribed to two main factors: (1) loss of nitrogen and fluoride and (2) loss of surface area by sintering.

  17. Two-dimensional tungsten oxide nanowire networks

    NASA Astrophysics Data System (ADS)

    Zhao, Y. M.; Li, Y. H.; Ahmad, I.; McCartney, D. G.; Zhu, Y. Q.; Hu, W. B.

    2006-09-01

    The authors report the synthesis and characterization of two-dimensional (2D) single crystalline nanonetworks consisting of tungsten oxide nanowires with diameters of ca. 20nm. The 2D networks are believed to result from the nanowire growth along the four crystallographic equivalent directions of ⟨110⟩ in the tetragonal WO2.9 structure. These 2D tungsten oxide networks may be potential precursors for creating 2D networks comprising WS2 nanotubes.

  18. International strategic mineral issues summary report: tungsten

    USGS Publications Warehouse

    Werner, Antony B.T.; Sinclair, W. David; Amey, Earle B.

    1998-01-01

    In 1995, China and the former Soviet Union accounted for over three-fourths of the world's mine production of tungsten. China alone produced about two-thirds of world output. Given its vast resources, China will likely maintain its prominent role in world tungsten supply. By the year 2020, changes in supply patterns are likely to result from declining output from individual deposits in Australia, Austria, and Portugal and the opening of new mines in Canada, China, and the United Kingdom.

  19. Laser microsintering of tungsten in vacuum

    NASA Astrophysics Data System (ADS)

    Ebert, Robby; Ullmann, Frank; Hartwig, Lars; Suess, Tino; Kloetzer, Sascha; Streek, Andre; Schille, Joerg; Regenfuss, Peter; Exner, Horst

    2010-02-01

    Laser microsintering of tungsten powder is investigated as a function of laser output power, pulse interval and vacuum level. The intensities are calculated for the evaporation thresholds of tungsten powder particles of various sizes. In addition, the powder layer generation and the resulting layer thicknesses are calculated. The powder abrasion occurring during the process was taken into consideration. Polished sections and REM images were prepared in order to analyse the experimental outcomes. The dependence of sinter density on the parameters is discussed.

  20. Strain aging in tungsten heavy alloys

    SciTech Connect

    Dowding, R.J.; Tauer, K.J. . Materials Technology Lab.)

    1991-01-01

    This paper reports on tungsten heavy alloys which are two-phase mixtures of body center cubic (BCC) tungsten surrounded by a face center cubic (FCC) matrix. The matrix is most often composed of nickel and iron in a ratio of 70:30 but, occasionally, the matrix may also contain cobalt or copper. Nickel, however, is always the primary matrix component. The tungsten heavy alloy is fabricated through powder metallurgy techniques. Elemental powders are blended, pressed to shape, and sintered. Depending upon the tungsten content, the sintering temperatures are usually in the range of 1450{degrees}C to 1525{degrees}C. These temperatures are high enough that, as a result, the matrix is at the liquid phase and the process is known as liquid phase sintering. At the liquid phase temperature, the matrix becomes saturated with tungsten, but this does not change the FCC character of the matrix. The sintering is usually done in a hydrogen atmosphere furnace in order to reduce the oxides on the tungsten powder surfaces and create clean, active surfaces which will enhance the adherence between the tungsten and the matrix. The hydrogen atmosphere also creates the presence of excess dissolved hydrogen in the alloy. It has been shown that the hydrogen degrades the toughness and ductility of the heavy alloy. A post-sintering vacuum heat treatment is generally required to insure that there is no residual hydrogen present. The as-sintered tensile strength of a 90% tungsten, 7% nickel, 3% iron alloy (90W) is in the range of 800 to 940 MPa and can be increased significantly by cold working, usually rolling or swaging. Swaging to reductions in area of 20% can result in tensile strengths of 1250 MPa or more. As the strength increases, the elongation, which may have been 30% or more, decreases to less than 5%.

  1. 21 CFR 520.1802b - Piperazine-carbon disulfide complex boluses.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Piperazine-carbon disulfide complex boluses. 520....1802b Piperazine-carbon disulfide complex boluses. (a) Specifications. Each bolus contains 20 grams of piperazine-carbon disulfide complex. (b) Sponsor. See 000009 in § 510.600(c) of this chapter. (c)...

  2. 21 CFR 520.1802c - Piperazine-carbon disulfide complex with phenothiazine suspension.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Piperazine-carbon disulfide complex with... ANIMAL DRUGS § 520.1802c Piperazine-carbon disulfide complex with phenothiazine suspension. (a) Specifications. Each fluid ounce contains 5 grams of piperazine-carbon disulfide complex and 0.83 gram...

  3. 21 CFR 520.1802b - Piperazine-carbon disulfide complex boluses.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Piperazine-carbon disulfide complex boluses. 520....1802b Piperazine-carbon disulfide complex boluses. (a) Specifications. Each bolus contains 20 grams of piperazine-carbon disulfide complex. (b) Sponsor. See 000009 in § 510.600(c) of this chapter. (c)...

  4. 21 CFR 520.1802c - Piperazine-carbon disulfide complex with phenothiazine suspension.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Piperazine-carbon disulfide complex with... ANIMAL DRUGS § 520.1802c Piperazine-carbon disulfide complex with phenothiazine suspension. (a) Specifications. Each fluid ounce contains 5 grams of piperazine-carbon disulfide complex and 0.83 gram...

  5. 21 CFR 520.1802b - Piperazine-carbon disulfide complex boluses.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Piperazine-carbon disulfide complex boluses. 520....1802b Piperazine-carbon disulfide complex boluses. (a) Specifications. Each bolus contains 20 grams of piperazine-carbon disulfide complex. (b) Sponsor. See 000009 in § 510.600(c) of this chapter. (c)...

  6. 21 CFR 520.1802c - Piperazine-carbon disulfide complex with phenothiazine suspension.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Piperazine-carbon disulfide complex with... ANIMAL DRUGS § 520.1802c Piperazine-carbon disulfide complex with phenothiazine suspension. (a) Specifications. Each fluid ounce contains 5 grams of piperazine-carbon disulfide complex and 0.83 gram...

  7. 21 CFR 520.1802b - Piperazine-carbon disulfide complex boluses.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Piperazine-carbon disulfide complex boluses. 520....1802b Piperazine-carbon disulfide complex boluses. (a) Specifications. Each bolus contains 20 grams of piperazine-carbon disulfide complex. (b) Sponsor. See 000009 in § 510.600(c) of this chapter. (c)...

  8. 21 CFR 520.1802c - Piperazine-carbon disulfide complex with phenothiazine suspension.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Piperazine-carbon disulfide complex with... ANIMAL DRUGS § 520.1802c Piperazine-carbon disulfide complex with phenothiazine suspension. (a) Specifications. Each fluid ounce contains 5 grams of piperazine-carbon disulfide complex and 0.83 gram...

  9. 21 CFR 520.1802c - Piperazine-carbon disulfide complex with phenothiazine suspension.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Piperazine-carbon disulfide complex with... ANIMAL DRUGS § 520.1802c Piperazine-carbon disulfide complex with phenothiazine suspension. (a) Specifications. Each fluid ounce contains 5 grams of piperazine-carbon disulfide complex and 0.83 gram...

  10. 21 CFR 520.1802b - Piperazine-carbon disulfide complex boluses.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Piperazine-carbon disulfide complex boluses. 520....1802b Piperazine-carbon disulfide complex boluses. (a) Specifications. Each bolus contains 20 grams of piperazine-carbon disulfide complex. (b) Sponsor. See 000009 in § 510.600(c) of this chapter. (c)...

  11. Conserved residues flanking the thiol/disulfide centers of protein disulfide isomerase are not essential for catalysis of thiol/disulfide exchange.

    PubMed

    Lu, X; Gilbert, H F; Harper, J W

    1992-05-01

    Protein disulfide isomerase (PDI) catalyzes the oxidative folding of proteins containing disulfide bonds by increasing the rate of disulfide bond rearrangements which normally occur during the folding process. The amino acid sequences of the N- and C-terminal redox active sites (PWCGHCK) in PDI are completely conserved from yeast to man and display considerable identity with the redox-active center of thioredoxin (EWCGPCK). Available data indicate that the two thiol/disulfide centers of PDI can function independently in the isomerase reaction and that the cysteine residues in each active site are essential for catalysis. To evaluate the role of residues flanking the active-site cysteines of PDI in function, a variety of mutations were introduced into the N-terminal active site of PDI within the context of both a functional C-terminal active site and an inactive C-terminal active site in which serine residues replaced C379 and C382. Replacement of non-cysteine residues (W34 to Ser, G36 to Ala, and K39 to Arg) resulted in only a modest reduction in catalytic activity in both the oxidative refolding of RNase A and the reduction of insulin (10-27%), independent of the status of the C-terminal active site. A somewhat larger effect was observed with the H37P mutation where approximately 80% of the activity attributable to the N-terminal domain (approximately 40%) was lost. However, the H37P mutant N-terminal site expressed within the context of an inactive C-terminal domain exhibits 30% activity, approximately 70% of the activity of the N-terminal site alone.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1567868

  12. HEALTH AND ENVIRONMENTAL EFFECTS PROFILE FOR CARBON DISULFIDE

    EPA Science Inventory

    The Health and Environmental Effects Profile for Carbon Disulfide was prepared to support listings of hazardous constituents of a wide range of waste streams under Section 3001 of the Resource Conservation and Recovery Act (RCRA) and to provide health-related limits for emergency...

  13. Application of the solid lubricant molybdenum disulfide by sputtering

    NASA Technical Reports Server (NTRS)

    Przybyszewski, J.; Spalvins, T.

    1968-01-01

    Molybdenum disulfide lubricant film is deposited on two substrates, niobium and nickel-chromium alloys, by means of physical direct-current sputtering. The sputtering system uses a three-electrode /triode/ geometry - a thermionic cathode, an anode, and the target, all enclosed in a vacuum chamber.

  14. Response of soil organisms to dimethyl disulfide fumigation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    After the commonly used soil fumigant methyl bromide (MeBr) was phased out in the United States, alternatives to MeBr such as dimethyl disulfide (DMDS) which is known to have broad pest control spectrum, is increasingly used. However, effectiveness of DMDS has been mainly investigated to study targe...

  15. A kinetic study on pantetheinase inhibition by disulfides.

    PubMed

    Pitari, G; Maurizi, G; Ascenzi, P; Ricci, G; Duprè, S

    1994-11-15

    The mammalian enzyme pantetheinase, which hydrolyzes pantetheine to pantothenic acid and cysteamine, is inhibited by many thiol reagents and activated by thiols. Two thiol groups of different reactivity and accessibility are involved in the catalytic process [Ricci, G., Nardini, M., Chiaraluce, R., Duprè, S. & Cavallini, D. (1986) Biochim. Biophys. Acta 870, 82-91]. The inhibition kinetics by some natural and synthetic disulfides [pantethine, cystamine, 5,5'-dithiobis(2-nitrobenzoic acid), 4,4'-dithiodipyridine and oxidized mercaptoethanol] has been studied by two experimental approaches, either by monitoring activity after incubation of the enzyme with the inhibitor or by determining the progress curves in the presence of substrate and inhibitor. Data reported here indicate that pantetheinase reacts irreversibly with various disulfides in a time-dependent manner with the formation of a mixed disulfide apparently preceeded by a conformational change, giving a modified E* form with new kinetic parameters. This modified form may be further competitively inhibited by disulfides interacting with the enzyme at the active site. PMID:7957261

  16. Tungsten targets the tumor microenvironment to enhance breast cancer metastasis.

    PubMed

    Bolt, Alicia M; Sabourin, Valérie; Molina, Manuel Flores; Police, Alice M; Negro Silva, Luis Fernando; Plourde, Dany; Lemaire, Maryse; Ursini-Siegel, Josie; Mann, Koren K

    2015-01-01

    The number of individuals exposed to high levels of tungsten is increasing, yet there is limited knowledge of the potential human health risks. Recently, a cohort of breast cancer patients was left with tungsten in their breasts following testing of a tungsten-based shield during intraoperative radiotherapy. While monitoring tungsten levels in the blood and urine of these patients, we utilized the 66Cl4 cell model, in vitro and in mice to study the effects of tungsten exposure on mammary tumor growth and metastasis. We still detect tungsten in the urine of patients' years after surgery (mean urinary tungsten concentration at least 20 months post-surgery = 1.76 ng/ml), even in those who have opted for mastectomy, indicating that tungsten does not remain in the breast. In addition, standard chelation therapy was ineffective at mobilizing tungsten. In the mouse model, tungsten slightly delayed primary tumor growth, but significantly enhanced lung metastasis. In vitro, tungsten did not enhance 66Cl4 proliferation or invasion, suggesting that tungsten was not directly acting on 66Cl4 primary tumor cells to enhance invasion. In contrast, tungsten changed the tumor microenvironment, enhancing parameters known to be important for cell invasion and metastasis including activated fibroblasts, matrix metalloproteinases, and myeloid-derived suppressor cells. We show, for the first time, that tungsten enhances metastasis in an animal model of breast cancer by targeting the microenvironment. Importantly, all these tumor microenvironmental changes are associated with a poor prognosis in humans. PMID:25324207

  17. Tungsten Targets the Tumor Microenvironment to Enhance Breast Cancer Metastasis

    PubMed Central

    Bolt, Alicia M.; Sabourin, Valérie; Molina, Manuel Flores; Police, Alice M.; Negro Silva, Luis Fernando; Plourde, Dany; Lemaire, Maryse; Ursini-Siegel, Josie; Mann, Koren K.

    2015-01-01

    The number of individuals exposed to high levels of tungsten is increasing, yet there is limited knowledge of the potential human health risks. Recently, a cohort of breast cancer patients was left with tungsten in their breasts following testing of a tungsten-based shield during intraoperative radiotherapy. While monitoring tungsten levels in the blood and urine of these patients, we utilized the 66Cl4 cell model, in vitro and in mice to study the effects of tungsten exposure on mammary tumor growth and metastasis. We still detect tungsten in the urine of patients’ years after surgery (mean urinary tungsten concentration at least 20 months post-surgery = 1.76 ng/ml), even in those who have opted for mastectomy, indicating that tungsten does not remain in the breast. In addition, standard chelation therapy was ineffective at mobilizing tungsten. In the mouse model, tungsten slightly delayed primary tumor growth, but significantly enhanced lung metastasis. In vitro, tungsten did not enhance 66Cl4 proliferation or invasion, suggesting that tungsten was not directly acting on 66Cl4 primary tumor cells to enhance invasion. In contrast, tungsten changed the tumor microenvironment, enhancing parameters known to be important for cell invasion and metastasis including activated fibroblasts, matrix metalloproteinases, and myeloid-derived suppressor cells. We show, for the first time, that tungsten enhances metastasis in an animal model of breast cancer by targeting the microenvironment. Importantly, all these tumor microenvironmental changes are associated with a poor prognosis in humans. PMID:25324207

  18. Disulfide-based multifunctional conjugates for targeted theranostic drug delivery.

    PubMed

    Lee, Min Hee; Sessler, Jonathan L; Kim, Jong Seung

    2015-11-17

    Theranostics, chemical entities designed to combine therapeutic effects and imaging capability within one molecular system, have received considerable attention in recent years. Much of this interest reflects the promise inherent in personalized medicine, including disease-targeted treatments for cancer patients. One important approach to realizing this latter promise involves the development of so-called theranostic conjugates, multicomponent constructs that selectively target cancer cells and deliver cytotoxic agents while producing a readily detectable signal that can be monitored both in vitro and in vivo. This requires the synthesis of relatively complex systems comprising imaging reporters, masked chemotherapeutic drugs, cleavable linkers, and cancer targeting ligands. Ideally, the cleavage process should take place within or near cancer cells and be activated by cellular components that are associated with cancer states or specifically expressed at a higher level in cancer cells. Among the cleavable linkers currently being explored for the construction of such localizing conjugates, disulfide bonds are particularly attractive. This is because disulfide bonds are stable in most blood pools but are efficiently cleaved by cellular thiols, including glutathione (GSH) and thioredoxin (Trx), which are generally found at elevated levels in tumors. When disulfide bonds are linked to fluorophores, changes in emission intensity or shifts in the emission maxima are typically seen upon cleavage as the result of perturbations to internal charge transfer (ICT) processes. In well-designed systems, this allows for facile imaging. In this Account, we summarize our recent studies involving disulfide-based fluorescent drug delivery conjugates, including preliminary tests of their biological utility in vitro and in vivo. To date, a variety of chemotherapeutic agents, such as doxorubicin, gemcitabine, and camptothecin, have been used to create disulfide-based conjugates, as have

  19. Coenzyme A disulfide reductase, the primary low molecular weight disulfide reductase from Staphylococcus aureus. Purification and characterization of the native enzyme.

    PubMed

    delCardayre, S B; Stock, K P; Newton, G L; Fahey, R C; Davies, J E

    1998-03-01

    The human pathogen Staphylococcus aureus does not utilize the glutathione thiol/disulfide redox system employed by eukaryotes and many bacteria. Instead, this organism produces CoA as its major low molecular weight thiol. We report the identification and purification of the disulfide reductase component of this thiol/disulfide redox system. Coenzyme A disulfide reductase (CoADR) catalyzes the specific reduction of CoA disulfide by NADPH. CoADR has a pH optimum of 7.5-8.0 and is a dimer of identical subunits of Mr 49,000 each. The visible absorbance spectrum is indicative of a flavoprotein with a lambdamax = 452 nm. The liberated flavin from thermally denatured enzyme was identified as flavin adenine dinucleotide. Steady-state kinetic analysis revealed that CoADR catalyzes the reduction of CoA disulfide by NADPH at pH 7.8 with a Km for NADPH of 2 muM and for CoA disulfide of 11 muM. In addition to CoA disulfide CoADR reduces 4,4'-diphosphopantethine but has no measurable ability to reduce oxidized glutathione, cystine, pantethine, or H2O2. CoADR demonstrates a sequential kinetic mechanism and employs a single active site cysteine residue that forms a stable mixed disulfide with CoA during catalysis. These data suggest that S. aureus employs a thiol/disulfide redox system based on CoA/CoA-disulfide and CoADR, an unorthodox new member of the pyridine nucleotide-disulfide reductase superfamily. PMID:9488707

  20. Tungsten and tungsten alloy powder metallurgy. (Latest citations from the Compendex database). Published Search

    SciTech Connect

    Not Available

    1993-06-01

    The bibliography contains citations concerning tungsten powder preparation and processing. Studies include sintering, densification, shrinkage, phase analysis, and heat treatment. The physical and mechanical properties of tungsten powder metal products are included. The effects of additives and particle size on the sintering and sintered articles are also described. (Contains 250 citations and includes a subject term index and title list.)

  1. Magnetic Fe@g-C3N4: A Photoactive Catalyst for the Hydrogenation of Alkenes and Alkynes

    EPA Science Inventory

    A photoactive catalyst, Fe@g-C3N4, has been developed for the hydrogenation of alkenes and alkynes using hydrazine hydrate as a source of hydrogen. The magnetically separable Fe@g-C3N4 eliminates the use of high pressure hydrogenation and the reaction can be accomplished using vi...

  2. Mitochondrial Ccs1 contains a structural disulfide bond crucial for the import of this unconventional substrate by the disulfide relay system

    PubMed Central

    Groß, Dominik P.; Burgard, Caroline A.; Reddehase, Silvia; Leitch, Jeffry M.; Culotta, Valeria C.; Hell, Kai

    2011-01-01

    The copper chaperone for superoxide dismutase 1 (Ccs1) provides an important cellular function against oxidative stress. Ccs1 is present in the cytosol and in the intermembrane space (IMS) of mitochondria. Its import into the IMS depends on the Mia40/Erv1 disulfide relay system, although Ccs1 is, in contrast to typical substrates, a multidomain protein and lacks twin CxnC motifs. We report on the molecular mechanism of the mitochondrial import of Saccharomyces cerevisiae Ccs1 as the first member of a novel class of unconventional substrates of the disulfide relay system. We show that the mitochondrial form of Ccs1 contains a stable disulfide bond between cysteine residues C27 and C64. In the absence of these cysteines, the levels of Ccs1 and Sod1 in mitochondria are strongly reduced. Furthermore, C64 of Ccs1 is required for formation of a Ccs1 disulfide intermediate with Mia40. We conclude that the Mia40/Erv1 disulfide relay system introduces a structural disulfide bond in Ccs1 between the cysteine residues C27 and C64, thereby promoting mitochondrial import of this unconventional substrate. Thus the disulfide relay system is able to form, in addition to double disulfide bonds in twin CxnC motifs, single structural disulfide bonds in complex protein domains. PMID:21865601

  3. Virus Capsids as Targeted Nanoscale Delivery Vessels of Photoactive Compounds for Site-Specific Photodynamic Therapy

    NASA Astrophysics Data System (ADS)

    Cohen, Brian A.

    The research presented in this work details the use of a viral capsid as an addressable delivery vessel of photoactive compounds for use in photodynamic therapy. Photodynamic therapy is a treatment that involves the interaction of light with a photosensitizing molecule to create singlet oxygen, a reactive oxygen species. Overproduction of singlet oxygen in cells can cause oxidative damage leading to cytotoxicity and eventually cell death. Challenges with the current generation of FDA-approved photosensitizers for photodynamic therapy primarily stem from their lack of tissue specificity. This work describes the packaging of photoactive cationic porphyrins inside the MS2 bacteriophage capsid, followed by external modification of the capsid with cancer cell-targeting G-quadruplex DNA aptamers to generate a tumor-specific photosensitizing agent. First, a cationic porphyrin is loaded into the capsids via nucleotide-driven packaging, a process that involves charge interaction between the porphyrin and the RNA inside the capsid. Results show that over 250 porphyrin molecules associate with the RNA within each MS2 capsid. Removal of RNA from the capsid severely inhibits the packaging of the cationic porphyrins. Porphyrin-virus constructs were then shown to photogenerate singlet oxygen, and cytotoxicity in non-targeted photodynamic treatment experiments. Next, each porphyrin-loaded capsid is externally modified with approximately 60 targeting DNA aptamers by employing a heterobifunctional crosslinking agent. The targeting aptamer is known to bind the protein nucleolin, a ubiquitous protein that is overexpressed on the cell surface by many cancer cell types. MCF-7 human breast carcinoma cells and MCF-10A human mammary epithelial cells were selected as an in vitro model for breast cancer and normal tissue, respectively. Fluorescently tagged virus-aptamer constructs are shown to selectively target MCF-7 cells versus MCF-10A cells. Finally, results are shown in which porphyrin

  4. Plasmon enhanced broadband optical absorption in ultrathin silicon nanobowl array for photoactive devices applications

    NASA Astrophysics Data System (ADS)

    Sun, Rui-Nan; Peng, Kui-Qing; Hu, Bo; Hu, Ya; Zhang, Fu-Qiang; Lee, Shuit-Tong

    2015-07-01

    Both photonic and plasmonic nanostructures are key optical components of photoactive devices for light harvesting, enabling solar cells with significant thickness reduction, and light detectors capable of detecting photons with sub-band gap energies. In this work, we study the plasmon enhanced broadband light absorption and electrical properties of silicon nanobowl (SiNB) arrays. The SiNB-metal photonic-plasmonic nanostructure-based devices exhibited superior light-harvesting ability across a wide range of wavelengths up to the infrared regime well below the band edge of Si due to effective optical coupling between the SiNB array and incident sunlight, as well as electric field intensity enhancement around metal nanoparticles due to localized surface plasmon resonance. The photonic-plasmonic nanostructure is expected to result in infrared-light detectors and high-efficiency solar cells by extending light-harvesting to infrared frequencies.

  5. Structural Determinats Underlying Photoprotection in the Photoactive Orange Carotenoid Protein of Cyanobacteria

    SciTech Connect

    Wilson, Adjele; Kinney, James N.; Zwart, Petrus H.; Punginelli, Claire; D'Haene, Sandrine; Perreau, Francois; Klein, Michael G.; Kirilovsky, Diana; Kerfeld, Cheryl

    2010-04-01

    The photoprotective processes of photosynthetic organisms involve the dissipation of excess absorbed light energy as heat. Photoprotection in cyanobacteria is mechanistically distinct from that in plants; it involves the Orange Carotenoid Protein (OCP), a water-soluble protein containing a single carotenoid. The OCP is a new member of the family of blue light photoactive proteins; blue-green light triggers the OCP-mediated photoprotective response. Here we report structural and functional characterization of the wildtype and two mutant forms of the OCP, from the model organism Synechocystis PCC6803. The structural analysis provides highresolution detail of the carotenoidprotein interactions that underlie the optical properties of the OCP, unique among carotenoid-proteins in binding a single pigment per polypeptide chain. Collectively, these data implicate several key amino acids in the function of the OCP and reveal that the photoconversion and photoprotective responses of the OCP to blue-green light can be decoupled.

  6. Photoactive yellow protein-based protein labeling system with turn-on fluorescence intensity.

    PubMed

    Hori, Yuichiro; Ueno, Hideki; Mizukami, Shin; Kikuchi, Kazuya

    2009-11-25

    Protein labeling provides significant information about protein function. In this research, we developed a novel protein labeling technique by utilizing photoactive yellow protein (PYP). PYP is a small protein (14 kDa) derived from purple bacteria and binds to 7-hydroxycoumarin-3-carboxylic acid as well as to a natural ligand, 4-hydroxycinnamic acid, through a thioester bond with Cys69. Based on the structure and fluorescence property of this coumarin derivative, we designed two fluorescent probes that bind to PYP. One has an azido moiety, which allows stepwise labeling by click chemistry, and the other is a fluorogenic probe. The live-cell imaging and specific labeling of PYP were achieved by using both probes. The flexibility of the probe design and the small size of the tag protein are great advantages of this system against the existing methods. This novel labeling technique can be used in a wide variety of applications for biological research. PMID:19877615

  7. Plasmon enhanced broadband optical absorption in ultrathin silicon nanobowl array for photoactive devices applications

    SciTech Connect

    Sun, Rui-Nan; Peng, Kui-Qing Hu, Bo; Hu, Ya; Zhang, Fu-Qiang; Lee, Shuit-Tong

    2015-07-06

    Both photonic and plasmonic nanostructures are key optical components of photoactive devices for light harvesting, enabling solar cells with significant thickness reduction, and light detectors capable of detecting photons with sub-band gap energies. In this work, we study the plasmon enhanced broadband light absorption and electrical properties of silicon nanobowl (SiNB) arrays. The SiNB-metal photonic-plasmonic nanostructure-based devices exhibited superior light-harvesting ability across a wide range of wavelengths up to the infrared regime well below the band edge of Si due to effective optical coupling between the SiNB array and incident sunlight, as well as electric field intensity enhancement around metal nanoparticles due to localized surface plasmon resonance. The photonic-plasmonic nanostructure is expected to result in infrared-light detectors and high-efficiency solar cells by extending light-harvesting to infrared frequencies.

  8. Influence of a chromophore analogue in the protein cage of a photoactive yellow protein.

    PubMed

    Hamada, Norio; Tan, Zhe; Kanematsu, Yasuo; Inazumi, Naoya; Nakamura, Ryosuke

    2015-09-26

    Time-resolved spectra of a photoactive yellow protein (PYP) containing cyano-p-coumaric acid (CHCA) were recorded. To understand the mechanism of photo-isomerization, an electron-withdrawing CN group was introduced into the PYP to alter the C[double bond, length as m-dash]C double bond character. Free CHCA chromophores in aqueous solution underwent photo-isomerization whereas PYP with a bound CHCA (PYP-CN) exhibited no photocycle at acidic or alkaline pH or in urea and other solutions. Furthermore, no photocycle was observed with PYP mutants after illumination. This phenomenon cannot be fully explained by the electron-withdrawing properties of the CN group. We conclude that the CHCA chromophore in PYP was locked in the protein cage and that the CN group interacted with the protein residues. PMID:26178816

  9. Simulations of Two-dimensional Infrared and Stimulated Resonance Raman Spectra of Photoactive Yellow Protein

    PubMed Central

    Preketes, Nicholas K; Biggs, Jason D; Ren, Hao; Andricioaei, Ioan; Mukamel, Shaul

    2012-01-01

    We present simulations of one and two-dimensional infrared (2DIR) and stimulated resonance Raman (SRR) spectra of the dark state (pG) and early red-shifted intermediate (pR) of photoactive yellow protein (PYP). Shifts in the amide I and Glu46 COOH stretching bands distinguish between pG and pR in the IR absorption and 2DIR spectra. The one-dimensional SRR spectra are similar to the spontaneous RR spectra. The two-dimensional SRR spectra show large changes in cross peaks involving the C=O stretch of the two species and are more sensitive to the chromophore structure than 2DIR spectra. PMID:24244064

  10. Small Molecule-Photoactive Yellow Protein Labeling Technology in Live Cell Imaging.

    PubMed

    Gao, Feng; Gao, Tang; Zhou, Kechao; Zeng, Wenbin

    2016-01-01

    Characterization of the chemical environment, movement, trafficking and interactions of proteins in live cells is essential to understanding their functions. Labeling protein with functional molecules is a widely used approach in protein research to elucidate the protein location and functions both in vitro and in live cells or in vivo. A peptide or a protein tag fused to the protein of interest and provides the opportunities for an attachment of small molecule probes or other fluorophore to image the dynamics of protein localization. Here we reviewed the recent development of no-wash small molecular probes for photoactive yellow protein (PYP-tag), by the means of utilizing a quenching mechanism based on the intramolecular interactions, or an environmental-sensitive fluorophore. Several fluorogenic probes have been developed, with fast labeling kinetics and cell permeability. This technology allows quick live-cell imaging of cell-surface and intracellular proteins without a wash-out procedure. PMID:27589715

  11. Structure of the photoactive yellow protein reconstituted with caffeic acid at 1.16 A resolution.

    PubMed

    van Aalten, Daan M F; Crielaard, Wim; Hellingwerf, Klaas J; Joshua-Tor, Leemor

    2002-04-01

    A structural study is described of the photoactive yellow protein (PYP) reconstituted with the chromophore derivative 3,4-dihydroxycinnamic acid. The crystal structure of PYP reconstituted with this chromophore at 1.16 A resolution is reported in space group P6(5). This is the first high-resolution structure of a photoreceptor containing a modified chromophore. The introduction of an extra hydroxyl group in the native chromophore (i.e. p-coumaric acid) appears to perturb the structure of the hybrid yellow protein only slightly. The chromophore is bound by the protein in two different conformations, separated by a rotation of 180 degrees of the catechol ring. In combination with available spectroscopic data, it is concluded that the caffeic acid chromophore binds to the protein in a strained conformation, which leads to a faster ejection from the chromophore-binding pocket upon pB formation. PMID:11914481

  12. Absorption and quasiguided mode analysis of organic solar cells with photonic crystal photoactive layers.

    PubMed

    Tumbleston, John R; Ko, Doo-Hyun; Samulski, Edward T; Lopez, Rene

    2009-04-27

    We analyze optical absorption enhancements and quasiguided mode properties of organic solar cells with highly ordered nanostructured photoactive layers comprised of the bulk heterojunction blend, poly-3-hexylthiophene/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) and a low index of refraction conducting material (LICM). This photonic crystal geometry is capable of enhancing spectral absorption by approximately 17% in part due to the excitation of quasiguided modes near the band edge of P3HT:PCBM. A nanostructure thickness between 200 nm and 300 nm is determined to be optimal, while the LICM must have an index of refraction approximately 0.3 lower than P3HT:PCBM to produce absorption enhancements. Quasiguided modes that differ in lifetime by an order of magnitude are also identified and yield absorption that is concentrated in the P3HT:PCBM flash layer. PMID:19399146

  13. Design and application of carbon nanomaterials for photoactive and charge transport layers in organic solar cells

    NASA Astrophysics Data System (ADS)

    Jin, Sunghwan; Jun, Gwang Hoon; Jeon, Seokwoo; Hong, Soon Hyung

    2016-04-01

    Commercialization of organic solar cell (OSC) has faltered due to their low power conversion efficiency (PCE) compared to inorganic solar cell. Low electrical conductivity, low charge mobility, and short-range light absorption of most organic materials limit the PCE of OSCs. Carbon nanomaterials, especially carbon nanotubes (CNTs) and graphenes, are of great interest for use in OSC applications due to their high electrical conductivity, mobility, and unique optical properties for enhancing the performance of OSCs. In this review, recent progress toward the integration of carbon nanomaterials into OSCs is described. The role of carbon nanomaterials and strategies for their integration into various layers of OSCs, including the photoactive layer and charge transport layer, are discussed. Based on these, we also discuss the prospects of carbon nanomaterials for specific OSC layers to maximize the PCE.

  14. Toward an Enhancement of the Photoactivity of Multiphotochromic Dimers Using Plasmon Resonance: A Theoretical Study.

    PubMed

    Fihey, Arnaud; Le Guennic, Boris; Jacquemin, Denis

    2015-08-01

    Building dimers of organic photochromic compounds paves the way to multifunctional switches, but such architectures often undergo partial photoreactivity only. Combining photochromism of molecules and plasmon resonance of gold nanoparticles (NPs) is known to affect the photochromism of monomers, yet the impact on multimers remains unknown. Here we propose a theoretical study of dimers of dithienylethenes by the mean of a hybrid calculation scheme (discrete-interaction model/quantum mechanics). We aim to assess how the optical properties of multiphotochromes are tuned by the influence of the plasmon resonances. We show that, for a typical chemisorption orientation on the NP, the absorption bands responsible for the photochromism are significantly enhanced for both the doubly open and mixed closed-open isomers of the dyad, hinting that plasmon resonance could be used to boost the generally poor photoactivity of dithienylethene dyads. PMID:26267018

  15. Nonnative Disulfide Bond Formation Activates the σ32-Dependent Heat Shock Response in Escherichia coli

    PubMed Central

    Müller, Alexandra; Hoffmann, Jörg H.; Meyer, Helmut E.; Narberhaus, Franz; Jakob, Ursula

    2013-01-01

    Formation of nonnative disulfide bonds in the cytoplasm, so-called disulfide stress, is an integral component of oxidative stress. Quantification of the extent of disulfide bond formation in the cytoplasm of Escherichia coli revealed that disulfide stress is associated with oxidative stress caused by hydrogen peroxide, paraquat, and cadmium. To separate the impact of disulfide bond formation from unrelated effects of these oxidative stressors in subsequent experiments, we worked with two complementary approaches. We triggered disulfide stress either chemically by diamide treatment of cells or genetically in a mutant strain lacking the major disulfide-reducing systems TrxB and Gor. Studying the proteomic response of E. coli exposed to disulfide stress, we found that intracellular disulfide bond formation is a particularly strong inducer of the heat shock response. Real-time quantitative PCR experiments showed that disulfide stress induces the heat shock response in E. coli σ32 dependently. However, unlike heat shock treatment, which induces these genes transiently, transcripts of σ32-dependent genes accumulated over time in disulfide stress-treated cells. Analyzing the stability of σ32, we found that this constant induction can be attributed to an increase of the half-life of σ32 upon disulfide stress. This is concomitant with aggregation of E. coli proteins treated with diamide. We conclude that oxidative stress triggers the heat shock response in E. coli σ32 dependently. The component of oxidative stress responsible for the induction of heat shock genes is disulfide stress. Nonnative disulfide bond formation in the cytoplasm causes protein unfolding. This stabilizes σ32 by preventing its DnaK- and FtsH-dependent degradation. PMID:23585533

  16. Potential Impacts from Using Photoactive Roads as AN Air Quality Mitigation Strategy

    NASA Astrophysics Data System (ADS)

    Toro, C.; Jobson, B. T.; Shen, S.; Chung, S. H.; Haselbach, L.

    2013-12-01

    Mobile sources are major contributors to photochemical air pollution in urban areas. It has been proposed that the use of TiO2 coated roadways ('photoactive roads') could be an effective approach to reduce mobile source emissions by oxidizing NOx and VOC emissions at the roadway surface. However, studies have shown that formation of HONO and aldehydes can occur from some TiO2 treated surfaces during the photocatalytic oxidation of NOx and VOC, respectively. By changing the NOx-to-VOC ratio and generating photolabile HOx radical precursors, photoactive roads may enhance ozone formation rates in urban areas. In this work we present results that quantify NOx and VOC loss rates onto TiO2 treated asphalt and concrete samples, as well as HONO and aldehydes yields that result from the photocatalytic process. The treatment used a commercially available product. These objectives are relevant considering that the quantification of pollutant loss rates and yields of byproducts have not been determined for asphalt and that in the US more than 90% of the roadway surface is made of this material. Surface reaction probabilities (γ) and byproduct yields were determined using a CSTR photochemical chamber under varying conditions of water vapor and UV-A light intensity. Our results indicate that asphalt surfaces have a significantly higher molar yield of HONO compared to concrete surfaces with similar TiO2 loading. Concrete surfaces have reaction probabilities with NO one order of magnitude higher than asphalt samples. Fresh asphalt samples showed negligible photocatalytic activity, presumably due to absorption of TiO2 into the bitumen substrate. Laboratory-prepared asphalt samples with a higher degree of exposed aggregates showed increased HONO molar yields when compared to real-road asphalt samples, whose HONO molar yield was ~1%. Preliminary results for aldehydes formation showed similar molar yields between aged asphalt and concrete, even though aged asphalt samples had twice

  17. Photoactive layer-by-layer films of cellulose phosphate and titanium dioxide containing phosphotungstic acid

    NASA Astrophysics Data System (ADS)

    Ullah, Sajjad; Acuña, José Javier Sáez; Pasa, André Avelino; Bilmes, Sara A.; Vela, Maria Elena; Benitez, Guillermo; Rodrigues-Filho, Ubirajara Pereira

    2013-07-01

    A versatile layer-by-layer (LbL) procedure for the preparation of highly dispersed, adherent and porous multilayer films of TiO2 nanoparticles (NPs) and phosphotungstic acid (HPW) on a variety of substrates at room temperature was developed based on the use of cellulose phosphate (CP) as an efficient and non-conventional polyelectrolyte. UV/vis absorption spectroscopy confirmed the linear and regular growth of the films with the number of immersion cycles and a strong adsorption ability of CP towards TiO2 NPs. FTIR spectroscopy showed that HPW binds to the surface of TiO2 through the oxygen atom at the corner of the Keggin structure. XPS results showed that the interaction between TiO2 and CP is through Ti-O-P linkage. A model is proposed for the TiO2-HPW interaction based on XPS and FTIR results. FEG/SEM study of the surface morphology revealed a porous film structure with a homogenous distribution of the TiO2 NPs induced by CP. HRTEM studies showed that the resulting composite films consist of crystalline anatase and rutile phases and poly-nano-crystalline HPW with a semi-crystalline TiO2-HPW interface. These CP/TiO2 and CP/TiO2/HPW LbL films showed good photoactivity against both saturated and unsaturated species, for instance, stearic acid (SA), crystal violet (CV) and methylene blue (MB) under UV irradiation. The CP/HPW films formed on bacterial cellulose (BC) showed good photochromic response which is enhanced in presence of TiO2 due to an interfacial electron transfer from TiO2 to HPW. This simple and environmentally safe method can be used to form coatings on a variety of surfaces with photoactive TiO2 and TiO2/HPW films.

  18. Process for recovering tungsten from organic solutions

    SciTech Connect

    Powers, J.A.; Patton, J.C.; Christini, J.N.

    1989-11-21

    This patent describes on improvement in a process wherein tungsten values are extracted from an aqueous alkali metal tungstate solution containing impurities by an organic solution containing an amine extractant wherein the organic solution consists essentially of from about 6% to about 10% by volume of the amine extractant, and the balance of the organic solution being an aromatic solvent consisting essentially of a mixture of alkyl benzenes wherein the alkyl benzenes have molecular weights of 120, 134, or 148, and the total number of carbon atoms in the alkyl chains attached to the benzene ring are either 3, 4, or 5, and thereafter the tungsten values are removed from the organic solution by contacting the organic solution with a stripping agent to form a tungsten containing strip solution. The improvement comprises carrying out the stripping step in an aqueous continuous mode, and having as the stripping agent, an aqueous solution formed from ammonium metatungstate. Wherein the aqueous solution has a tungsten concentration which allows the tungsten containing strip solution to have a specific gravity of no greater than about 1.5, and sufficient ammonia to maintain the pH of the stripping agent at from about 5 to about 8.

  19. Evaporites and strata-bound tungsten mineralization

    SciTech Connect

    Ririe, G.T. )

    1989-02-01

    Discoidal gypsum crystal cavities occur in quartzites that host varying amounts of strata-bound scheelite mineralization near Halls Creek in Western Australia. The host quartzites have been regionally metamorphosed to greenschist facies and are contained within a Middle Proterozoic sequence that includes pelites, mafic and felsic volcanics, and volcaniclastic rocks. Textural, fluid inclusion, and oxygen isotope data indicate that scheelite was present in the host quartzites prior to regional metamorphism. The presence of crystal cavities after gypsum in the quartzites implies an evaporitic origin for this sequence. The continental-sabkha playa basins of the Mojave Desert, California, are suggested to be possible modern analogs-e.g., Searles Lake, where the tungsten content is up to 70 ppm WO{sub 3} in brines and 118 ppm in muds, and exceeds the amount of tungsten in all known deposits in the United States. Metamorphism of a continental evaporitic sequence containing tungsten could produce an assemblage of rocks very similar to those reported from several stratabound tungsten deposits. Some of these, such as at Halls Creek, may be related to original accumulations of tungsten in nonmarine evaporitic environments.

  20. Surfacing With Tungsten-containing Ores

    NASA Astrophysics Data System (ADS)

    Kozyrev, N. A.; Galevsky, G. V.; Valuev, D. V.; Shurupov, V. M.; Kozyreva, O. E.

    2015-09-01

    Experimental research has been carried out into AN 26C flux surfacing with flux cored wires made of dust-like carbon and fluorine containing components and tungsten- containing ores. The investigations have revealed the fact that tungsten can be reduced immediately from tungsten-containing oxide materials. The chemical composition of added metal has been determined, as well as slag compositions after surfacing; hardness, wear resistance have been investigated and metallographic tests have been carried out. Thermodynamic calculations of reactions of WO3, as well as W2C and WC carbides reduction to W by carbon and carbon oxide have been made in standard conditions at temperature T = 1500 - 6000 K. The obtained thermodynamic characteristics of reactions have demonstrated that in the course of WO3 reduction tungsten is most likely to be obtained in terms of thermodynamics, subsequently W2C and WC carbides. After these reactions those of W2C and WC carbides obtaining are thermodynamically possible via reduced tungsten and carbon composition.

  1. Some Tungsten Oxidation-Reduction Chemistry: A Paint Pot Titration.

    ERIC Educational Resources Information Center

    Pickering, Miles; Monts, David L.

    1982-01-01

    Reports an oxidation-reduction experiment using tungsten, somewhat analogous to the classical student experiment involving oxidation-reduction of vanadium. Includes experimental procedures, results, and toxicity/cost of tungsten compounds. (Author/JN)

  2. Growth of tungsten oxide on carbon nanowalls templates

    SciTech Connect

    Wang, Hua; Su, Yan; Chen, Shuo; Quan, Xie

    2013-03-15

    Highlights: ► Tungsten oxide deposited on carbon nanowalls by hot filament chemical vapor deposition technique. ► This composite has two-dimensional uniform morphology with a crystalline structure of monoclinic tungsten trioxide. ► Surface photoelectric voltage measurements show that this product has photoresponse properties. - Abstract: In the present work we present a simple approach for coupling tungsten oxide with carbon nanowalls. The two-dimensional carbon nanowalls with open boundaries were grown using plasma enhanced hot filament chemical vapor deposition, and the subsequent tungsten oxide growth was performed in the same equipment by direct heating of a tungsten filament. The tungsten oxide coating is found to have uniform morphology with a crystalline structure of monoclinic tungsten trioxide. Surface photoelectric voltage measurements show that this product has photoresponse properties. The method of synthesis described here provides an operable route to the production of two-dimensional tungsten oxide nanocomposites.

  3. Element 74, the Wolfram Versus Tungsten Controversy

    SciTech Connect

    Holden,N.E.

    2008-08-11

    Two and a quarter centuries ago, a heavy mineral ore was found which was thought to contain a new chemical element called heavy stone (or tungsten in Swedish). A few years later, the metal was separated from its oxide and the new element (Z=74) was called wolfram. Over the years since that time, both the names wolfram and tungsten were attached to this element in various countries. Sixty years ago, IUPAC chose wolfram as the official name for the element. A few years later, under pressure from the press in the USA, the alternative name tungsten was also allowed by IUPAC. Now the original, official name 'wolfram' has been deleted by IUPAC as one of the two alternate names for the element. The history of this controversy is described here.

  4. Moderate temperature sodium cells. I - Transition metal disulfide cathodes

    NASA Technical Reports Server (NTRS)

    Abraham, K. M.; Pitts, L.; Schiff, R.

    1980-01-01

    TiS2, VS2, and Nb(1.1)S2 transition metal disulfides were evaluated as cathode materials for a moderate temperature rechargeable Na cell operating at 130 C. The 1st discharge of TiS2 results in a capacity of 0.85 eq/mole; approximately half of the Na in the 1st phase spanning the Na range from zero to 0.30 and almost all the Na in the 2nd phase spanning the 0.37 to 0.80 range are rechargeable. VS2 intercalates up to one mole of Na/mole of VS2 in the 1st discharge; the resulting Na(x)VS2 ternary consists of 3 phases in the 3 ranges of Na from zero to 1. Niobium disulfide undergoes a phase change in the 1st discharge; the average rechargeable capacity in extended cycling of this cathode is 0.50 eq/mole.

  5. Tibial dyschondroplasia in growing chickens experimentally intoxicated with tetramethylthiuram disulfide.

    PubMed

    Vargas, M I; Lamas, J M; Alvarenga, V

    1983-07-01

    Graded levels of tetramethylthiuram disulfide (0, 30, 60, 120, and 240 ppm) were incorporated into a broiler starter ration fed to chickens from one day old to 8 weeks of age. Clinical signs of leg abnormalities were observed as early as 5 days after the beginning of the trial. After the 3rd week, the joints were shown to present lesions, especially in the femorotibial articulation, comparable to the ones found in perosis. Tibiotarsus and other organs from the birds were examined for pathological changes at weekly intervals. Histologically, the tibiotarsus has shown an osteochondrodystrophy identical to that of tibial dyschondroplasia (TD), although it varied according to the level of tetramethylthiuram disulfide. The histopathology of the thyroid gland of the chickens involved in the present experiment will be reported in a separate manuscript. PMID:6622364

  6. Evolution of interlayer coupling in twisted molybdenum disulfide bilayers

    NASA Astrophysics Data System (ADS)

    Liu, Kaihui; Zhang, Liming; Cao, Ting; Jin, Chenhao; Qiu, Diana; Zhou, Qin; Zettl, Alex; Yang, Peidong; Louie, Steve G.; Wang, Feng

    2014-09-01

    Van der Waals coupling is emerging as a powerful method to engineer physical properties of atomically thin two-dimensional materials. In coupled graphene-graphene and graphene-boron nitride layers, interesting physical phenomena ranging from Fermi velocity renormalization to Hofstadter’s butterfly pattern have been demonstrated. Atomically thin transition metal dichalcogenides, another family of two-dimensional-layered semiconductors, can show distinct coupling phenomena. Here we demonstrate the evolution of interlayer coupling with twist angles in as-grown molybdenum disulfide bilayers. We find that the indirect bandgap size varies appreciably with the stacking configuration: it shows the largest redshift for AA- and AB-stacked bilayers, and a significantly smaller but constant redshift for all other twist angles. Our observations, together with ab initio calculations, reveal that this evolution of interlayer coupling originates from the repulsive steric effects that leads to different interlayer separations between the two molybdenum disulfide layers in different stacking configurations.

  7. Pressure-time profile of multiply shocked carbon disulfide

    NASA Astrophysics Data System (ADS)

    Sutherland, G. T.; Gupta, Y. M.; Bellamy, P. M.

    1986-02-01

    An experimental method was developed to measure the pressure-time profile of a liquid in a reverberation of multiple-shock experiment. Profiles, with peak pressures to 30 kbars, were measured for carbon disulfide using shorted quartz gauges (25.4 mm diameter by 3.15 mm thick); these gauges formed the back surfaces of cells which contained the carbon disulfide. Sapphire plates were used both as impactors and as the front surfaces of the cell. Up to six pressure steps were clearly observed in the quartz-gauge output. Measured pressure-time profiles were compared to profiles calculated with available equations of state. The experiments agreed well with profiles predicted with an equation of state proposed by Sheffield (1983). Calibration experiments were performed to characterize both the initial current response and the subsequent current ramping of the shorted quartz gauges used in this study.

  8. High hemoglobin mixed disulfide content in hemolysates from stressed shark.

    PubMed

    Dafré, A L; Reischl, E

    1990-01-01

    1. Hemolysate from heavily stressed smooth hammerhead shark, Sphyrna zygaena, shows three electrophoretic components, SZ I, SZ II and SZ III, whose relative concentrations are 36.4 +/- 6.8, 36.4 +/- 5.0 and 20.8 +/- 5.7%, respectively. After reduction with DTE only SZ I remained. 2. SZ I reacted with glutathione disulfide reconstitute SZ II and SZ III. 3. Non-reduced, DTE-reduced, and denatured hemoglobin were found to have 2.0 +/- 0.4, 3.7 +/- 0.6, and 9.4 +/- 0.7-SH groups, respectively. 4. Erythrocyte non-protein--SH (NPSH), including glutathione present as mixed disulfide with SZ II and SZ III, is 1.7 NPSH/Hb. PMID:2361357

  9. A degradable polydopamine coating based on disulfide-exchange reaction.

    PubMed

    Hong, Daewha; Lee, Hojae; Kim, Beom Jin; Park, Taegyun; Choi, Ji Yu; Park, Matthew; Lee, Juno; Cho, Hyeoncheol; Hong, Seok-Pyo; Yang, Sung Ho; Jung, Sun Ho; Ko, Sung-Bo; Choi, Insung S

    2015-12-21

    Although the programmed degradation of biocompatible films finds applications in various fields including biomedical and bionanotechnological areas, coating methods have generally been limited to be substrate-specific, not applicable to any kinds of substrates. In this paper, we report a dopamine derivative, which allows for both universal coating of various substrates and stimuli-responsive film degradation, inspired by mussel-adhesive proteins. Two dopamine moieties are linked together by the disulfide bond, the cleavage of which enables the programmed film degradation. Mechanistic analysis of the degradable films indicates that the initial cleavage of the disulfide linkage causes rapid uptake of water molecules, hydrating the films, which leads to rapid degradation. Our substrate-independent coating of degradable films provides an advanced tool for drug delivery systems, tissue engineering, and anti-fouling strategies. PMID:26572596

  10. Performance and Safety Characteristics of Lithium-molybdenum Disulfide Cells

    NASA Technical Reports Server (NTRS)

    Stiles, J. A.

    1984-01-01

    The lithium-molybdenum disulfide system offers attractive characteristics including high rate capability, successful operation up to 75 C, a very low self-discharge rate, a good cycle life and safety characteristics which compare favorably to those of other lithium cells. Moreover, the materials and manufacturing costs for the system is effectively controlled, so the cells should ultimately be competitive with currently marketed rechargeable cells.

  11. A degradable polydopamine coating based on disulfide-exchange reaction

    NASA Astrophysics Data System (ADS)

    Hong, Daewha; Lee, Hojae; Kim, Beom Jin; Park, Taegyun; Choi, Ji Yu; Park, Matthew; Lee, Juno; Cho, Hyeoncheol; Hong, Seok-Pyo; Yang, Sung Ho; Jung, Sun Ho; Ko, Sung-Bo; Choi, Insung S.

    2015-11-01

    Although the programmed degradation of biocompatible films finds applications in various fields including biomedical and bionanotechnological areas, coating methods have generally been limited to be substrate-specific, not applicable to any kinds of substrates. In this paper, we report a dopamine derivative, which allows for both universal coating of various substrates and stimuli-responsive film degradation, inspired by mussel-adhesive proteins. Two dopamine moieties are linked together by the disulfide bond, the cleavage of which enables the programmed film degradation. Mechanistic analysis of the degradable films indicates that the initial cleavage of the disulfide linkage causes rapid uptake of water molecules, hydrating the films, which leads to rapid degradation. Our substrate-independent coating of degradable films provides an advanced tool for drug delivery systems, tissue engineering, and anti-fouling strategies.Although the programmed degradation of biocompatible films finds applications in various fields including biomedical and bionanotechnological areas, coating methods have generally been limited to be substrate-specific, not applicable to any kinds of substrates. In this paper, we report a dopamine derivative, which allows for both universal coating of various substrates and stimuli-responsive film degradation, inspired by mussel-adhesive proteins. Two dopamine moieties are linked together by the disulfide bond, the cleavage of which enables the programmed film degradation. Mechanistic analysis of the degradable films indicates that the initial cleavage of the disulfide linkage causes rapid uptake of water molecules, hydrating the films, which leads to rapid degradation. Our substrate-independent coating of degradable films provides an advanced tool for drug delivery systems, tissue engineering, and anti-fouling strategies. Electronic supplementary information (ESI) available: Synthesis, characterization, and other additional details. See DOI: 10

  12. Raman scattering from rapid thermally annealed tungsten silicide

    NASA Technical Reports Server (NTRS)

    Kumar, Sandeep; Dasgupta, Samhita; Jackson, Howard E.; Boyd, Joseph T.

    1987-01-01

    Raman scattering as a technique for studying the formation of tungsten silicide is presented. The tungsten silicide films have been formed by rapid thermal annealing of thin tungsten films sputter deposited on silicon substrates. The Raman data are interpreted by using data from resistivity measurements, Auger and Rutherford backscattering measurements, and scanning electron microscopy.

  13. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  14. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  15. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  16. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  17. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  18. Ultra-broad band absorber made by tungsten and aluminium

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhao, Ding; Li, Qiang; Qiu, Min

    2016-01-01

    A broadband absorber comprising tungsten cubic arrays, a alumina layer and a tungsten film, is numerically and experimentally investigated, which exhibits near-unity absorption of visible and near-infrared light from 400 nm to 1150 nm. Benefiting from high melting points of tungsten and alumina, this device has great application potential in solar cells and thermal emission.

  19. Equipment simulation of selective tungsten deposition

    SciTech Connect

    Werner, C.; Ulacia, J.I.; Hopfmann, C.; Flynn, P. )

    1992-02-01

    This paper presents the numerical modeling of a cold wall reactor for selective tungsten chemical vapor deposition. In a two dimensional simulation the mass and heat transfer equations were solved considering the five chemical species H{sub 2}, WF{sub 6}, HF, WF{sub x}, and SiF{sub y}. Detailed models for multicomponent diffusion and for the autocatalytic tungsten nucleation process were implemented. Model results are in good agreement with experimental findings. The simulations are used to study the impact of reactor design on selectivity.

  20. Method of making tungsten powder compacts

    SciTech Connect

    Peralta, R.E.

    1991-06-25

    This patent describes a process for forming a compact. It comprises essentially of pure tungsten metal powder by the steps of contacting a tungsten metal powder with and aqueous acid mixture at a sufficient concentration and for a sufficient period of time of etch the surface of the powder, the acid comprises a mixture of hydrofluoric acid and hydrochloric acid, and isostaticly pressuring the powder at an ambient temperature at a pressure of from about 18,000 to about 20,000 psi. for a sufficient period of time to form a compact.

  1. Identification of disulfide bond isomerase substrates reveals bacterial virulence factors

    PubMed Central

    Ren, Guoping; Champion, Matthew M.; Huntley, Jason F.

    2014-01-01

    Summary Bacterial pathogens are exposed to toxic molecules inside the host and require efficient systems to form and maintain correct disulfide bonds for protein stability and function. The intracellular pathogen Francisella tularensis encodes a disulfide bond formation protein ortholog, DsbA, which previously was reported to be required for infection of macrophages and mice. However, the molecular mechanisms by which F. tularensis DsbA contributes to virulence are unknown. Here, we demonstrate that F. tularensis DsbA is a bifunctional protein that oxidizes and, more importantly, isomerizes complex disulfide connectivity in substrates. A single amino acid in the conserved cis-proline loop of the DsbA thioredoxin domain was shown to modulate both isomerase activity and F. tularensis virulence. Trapping experiments in F. tularensis identified over 50 F. tularensis DsbA substrates, including outer membrane proteins, virulence factors, and many hypothetical proteins. Six of these hypothetical proteins were randomly selected and deleted, revealing two novel proteins, FTL_1548 and FTL_1709, which are required for F. tularensis virulence. We propose that the extreme virulence of F. tularensis is partially due to the bifunctional nature of DsbA, that many of the newly-identified substrates are required for virulence, and that the development of future DsbA inhibitors could have broad anti-bacterial implications. PMID:25257164

  2. Polymerizable disulfide paclitaxel prodrug for controlled drug delivery.

    PubMed

    Ding, Yi; Chen, Wulian; Hu, Jianhua; Du, Ming; Yang, Dong

    2014-11-01

    A polymerizable disulfide paclitaxel (PTX) prodrug was synthesized by the consequential esterification reactions of 3,3'-dithiodipropionic acid (DTPA), a disulfide compound containing two active carboxyl groups, with 2-hydroxyethyl methacrylate (HEMA) and PTX. The structure of the prodrug was confirmed by (1)H NMR characterization. Then, the polymerizable prodrug was copolymerized with poly(ethylene glycol) methyl ether methacrylate (PEGMEA) to obtain a copolymer with hydrophilic PEG side chains and PTX covalently linked onto the backbone via disulfide bonds. The loading content of PTX was 23%. In aqueous solution, this copolymer prodrug could self-assemble into micelles, with hydrophobic PTX as the cores and hydrophilic PEG-segment as the shells. In vitro cell assay demonstrated that this copolymer prodrug showed more apparent cytotoxicity to cancer cells than to human normal cells. After incubation for 48 h, the cell viability of HEK-293 cells (human embryo kidney cells) at 0.1 μg/mL PTX still remained more than 90%, however, that of HeLa cells (human cervical cancer cells) decreased to 52%. PMID:25280719

  3. Dissecting the Machinery That Introduces Disulfide Bonds in Pseudomonas aeruginosa

    PubMed Central

    Arts, Isabelle S.; Ball, Geneviève; Leverrier, Pauline; Garvis, Steven; Nicolaes, Valérie; Vertommen, Didier; Ize, Bérengère; Tamu Dufe, Veronica; Messens, Joris; Voulhoux, Romé; Collet, Jean-François

    2013-01-01

    ABSTRACT Disulfide bond formation is required for the folding of many bacterial virulence factors. However, whereas the Escherichia coli disulfide bond-forming system is well characterized, not much is known on the pathways that oxidatively fold proteins in pathogenic bacteria. Here, we report the detailed unraveling of the pathway that introduces disulfide bonds in the periplasm of the human pathogen Pseudomonas aeruginosa. The genome of P. aeruginosa uniquely encodes two DsbA proteins (P. aeruginosa DsbA1 [PaDsbA1] and PaDsbA2) and two DsbB proteins (PaDsbB1 and PaDsbB2). We found that PaDsbA1, the primary donor of disulfide bonds to secreted proteins, is maintained oxidized in vivo by both PaDsbB1 and PaDsbB2. In vitro reconstitution of the pathway confirms that both PaDsbB1 and PaDsbB2 shuttle electrons from PaDsbA1 to membrane-bound quinones. Accordingly, deletion of both P. aeruginosa dsbB1 (PadsbB1) and PadsbB2 is required to prevent the folding of several P. aeruginosa virulence factors and to lead to a significant decrease in pathogenicity. Using a high-throughput proteomic approach, we also analyzed the impact of PadsbA1 deletion on the global periplasmic proteome of P. aeruginosa, which allowed us to identify more than 20 new potential substrates of this major oxidoreductase. Finally, we report the biochemical and structural characterization of PaDsbA2, a highly oxidizing oxidoreductase, which seems to be expressed under specific conditions. By fully dissecting the machinery that introduces disulfide bonds in P. aeruginosa, our work opens the way to the design of novel antibacterial molecules able to disarm this pathogen by preventing the proper assembly of its arsenal of virulence factors. PMID:24327342

  4. Visible emission spectroscopy of highly charged tungsten ions in LHD: II. Evaluation of tungsten ion temperature

    NASA Astrophysics Data System (ADS)

    Fujii, K.; Takahashi, Y.; Nakai, Y.; Kato, D.; Goto, M.; Morita, S.; Hasuo, M.; Experiment Group2, LHD

    2015-12-01

    We demonstrated a polarization-resolved high resolution spectroscopy of a visible emission line of highly charged tungsten ions (λ0 = 668.899 nm, Shinohara et al Phys. Scr. 90 125402) for the large helical device (LHD) plasma, where the tungsten ions were introduced by a pellet injection. Its spectral profile shows broadening and polarization dependence, which are attributed to the Doppler and Zeeman effects, respectively. The tungsten ion temperature was evaluated for the first time from the broadening of visible the emission line, with its emission location determined by the Abel inversion of the chord-integrated emission intensities observed with multiple chords. The tungsten ion temperature was found to be close to the helium-like argon ion temperature, which is used as an ion temperature monitor in LHD.

  5. Optically monitored spray coating system for the controlled deposition of the photoactive layer in organic solar cells

    NASA Astrophysics Data System (ADS)

    Vak, Doojin; van Embden, Joel; Wong, Wallace W. H.; Watkins, Scott

    2015-01-01

    A spray deposition process equipped with an in situ optical thickness monitoring system has been developed to fabricate the photoactive layer of solar cells. Film thickness is monitored by a photodiode-LED couple after each deposition cycle. Using optimized conditions, the thickness of the spray deposited photoactive films can be tuned to increase linearly with the number of deposition cycles over a wide range of deposition conditions. After instrument calibration, optimization of the active layer thickness can be accomplished by simply setting the desired absorbance of the film. The simple process outlined here may be used for the rapid optimization of thin film photovoltaic devices. As proof of this, we fabricate a poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester as well as a P3HT and indene-C60 bis-adduct organic solar cells, which achieve a champion power conversion efficiency of 4.2%.

  6. Spinarc gas tungsten arc torch holder

    NASA Technical Reports Server (NTRS)

    Brace, D. F.; Crockett, J. L.

    1970-01-01

    Semiautomatic welding torch enables operator to control arc length, torch angle, and spring tension when welding small diameter aluminum tubing. Tungsten is preset for the weld to make arc initiation easier and to eliminate searching for the joint through a dark welding lens.

  7. Evidence of hydrogen embrittlement of tungsten carbide.

    PubMed

    Kennedy, G C

    1978-02-01

    Tungsten carbide vessels containing materials at high temperature and high pressure are used in many laboratories. We note that any oils at medium to high temperature which can break down and liberate hydrogen cause rapid failure of the pressure vessel, whereas perfluorated kerosenes used as lubricants inside a pressure vessel give sharply increased life of the vessel. PMID:18699072

  8. Gas tungsten arc welder with electrode grinder

    DOEpatents

    Christiansen, David W.; Brown, William F.

    1984-01-01

    A welder for automated closure of fuel pins by a gas tungsten arc process in which a rotating length of cladding is positioned adjacent a welding electrode in a sealed enclosure. An independently movable axial grinder is provided in the enclosure for refurbishing the used electrode between welds.

  9. Joining of Tungsten Armor Using Functional Gradients

    SciTech Connect

    John Scott O'Dell

    2006-12-31

    The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

  10. Amalgam containing nickel or tungsten dispersions. I.

    PubMed

    Reisbick, M H; Bunshah, R F; Agarwal, N

    1977-12-01

    Wetting tests were conducted to determine compatability between select dispersion powders and Ag3Sn. Subsequently, a method was perfected for incorporating nickel or tungsten powder into the Ag3 Sn ingot. Initial studies reveal good distributions of the dispersed phase in the ingots and the comminuted alloys, after amalgamation, appear to retain their normal working characteristics. PMID:277462

  11. Electrospark doping of steel with tungsten

    NASA Astrophysics Data System (ADS)

    Denisova, Yulia; Shugurov, Vladimir; Petrikova, Elizaveta; Seksenalina, Malika; Ivanova, Olga; Ikonnikova, Irina; Kunitsyna, Tatyana; Vlasov, Victor; Klopotov, Anatoliy; Ivanov, Yuriy

    2016-01-01

    The paper is devoted to the numerical modeling of thermal processes and the analysis of the structure and properties of the surface layer of carbon steel subjected to electrospark doping with tungsten. The problem of finding the temperature field in the system film (tungsten) / substrate (iron) is reduced to the solution of the heat conductivity equation. A one-dimensional case of heating and cooling of a plate with the thickness d has been considered. Calculations of temperature fields formed in the system film / substrate synthesized using methods of electrospark doping have been carried out as a part of one-dimensional approximation. Calculations have been performed to select the mode of the subsequent treatment of the system film / substrate with a high-intensity pulsed electron beam. Authors revealed the conditions of irradiation allowing implementing processes of steel doping with tungsten. A thermodynamic analysis of phase transformations taking place during doping of iron with tungsten in equilibrium conditions has been performed. The studies have been carried out on the surface layer of the substrate modified using the method of electrospark doping. The results showed the formation in the surface layer of a structure with a highly developed relief and increased strength properties.

  12. Polyol mediated synthesis of tungsten trioxide and Ti doped tungsten trioxide

    SciTech Connect

    Porkodi, P.; Yegnaraman, V.; Jeyakumar, D. . E-mail: djkr@rediffmail.com

    2006-08-10

    Polyol mediated synthesis for the preparation of tungsten trioxide and titanium doped tungsten trioxide has been reported. The reaction was carried out using chlorides of tungsten and titanium in diethylene glycol medium and water as the reagent for hydrolysis at 190 deg. C. Formation of a blue coloured dimensionally stable suspension of the precursor materials was observed during the course of the reaction. The particle sizes of the precursor materials were observed to be around 100 nm. The precursor materials were annealed to give tungsten trioxide and titanium doped tungsten trioxide. The precursor materials were characterised using TGA/DTA, FT-IR, optical spectra, SEM, TEM and powder XRD methods. It was observed that the doping of titanium could be effected at least up to 10% of Ti in WO{sub 3}. The TGA/DTA studies indicated that WO{sub 3-x}.H{sub 2}O is the dominant material that formed during the polyol mediated synthesis. The XRD data of the annealed samples revealed that the crystalline phase could be manipulated by varying the extent of titanium doping in the tungsten trioxide matrix.

  13. Lignin-assisted exfoliation of molybdenum disulfide in aqueous media and its application in lithium ion batteries.

    PubMed

    Liu, Wanshuang; Zhao, Chenyang; Zhou, Rui; Zhou, Dan; Liu, Zhaolin; Lu, Xuehong

    2015-06-01

    In this article, alkali lignin (AL)-assisted direct exfoliation of MoS2 mineral into single-layer and few-layer nanosheets in water is reported for the first time. Under optimized conditions, the concentration of MoS2 nanosheets in the obtained dispersion can be as high as 1.75 ± 0.08 mg mL(-1), which is much higher than the typical reported concentrations (<1.0 mg mL(-1)) using synthetic polymers or compounds as surfactants. The stabilizing mechanism primarily lies in the electrostatic repulsion between negative charged AL, as suggested by zeta-potential measurements. When the exfoliated MoS2 nanosheets are applied as electrode materials for lithium ion batteries, they show much improved electrochemical performance compared with the pristine MoS2 mineral because of the enhanced ion and electron transfer kinetics. This facile, scalable and eco-friendly aqueous-based process in combination with renewable and ultra-low-cost lignin opens up possibilities for large-scale fabrication of MoS2-based nanocomposites and devices. Moreover, herein we demonstrate that AL is also an excellent surfactant for exfoliation of many other types of layered materials, including graphene, tungsten disulfide and boron nitride, in water, providing rich opportunities for a wider range of applications. PMID:25970569

  14. Quantum Mechanical/Molecular Mechanical Studies on Spectral Tuning Mechanisms of Visual Pigments and Other Photoactive Proteins†

    PubMed Central

    Altun, Ahmet; Yokoyama, Shozo; Morokuma, Keiji

    2008-01-01

    The protein environments surrounding the retinal tune electronic absorption maximum from 350 to 630 nm. Hybrid quantum mechanical/molecular mechanical (QM/MM) methods can be used in calculating excitation energies of retinal in its native protein environments and in studying the molecular basis of spectral tuning. We hereby review recent QM/MM results on the phototransduction of bovine rhodopsin, bacteriorhodopsin, sensory rhodopsin II, nonretinal photoactive yellow protein and their mutants. PMID:18331400

  15. Synthesis and enzymatic photo-activity of an O2 tolerant hydrogenase-CdSe@CdS quantum rod bioconjugate.

    PubMed

    Hamon, C; Ciaccafava, A; Infossi, P; Puppo, R; Even-Hernandez, P; Lojou, E; Marchi, V

    2014-05-21

    This communication reports on the preparation of stable and photo-active nano-heterostructures composed of O2 tolerant [NiFe] hydrogenase extracted from the Aquifex aeolicus bacterium grafted onto hydrophilic CdSe/CdS quantum rods in view of the development of H2/O2 biofuel cells. The resulting complex is efficient towards H2 oxidation, displays good stability and new photosensitive properties. PMID:24468861

  16. Synthesis of tungsten oxide tapered needles with nanotips

    NASA Astrophysics Data System (ADS)

    Wang, Shiliang; He, Yuehui; Zou, Jin; Cao, Peng; Jiang, Yao; Huang, Baiyun; Liu, C. T.; Liaw, P. K.

    2007-05-01

    Tungsten oxide tapered needles with nanotips were synthesized on a large scale by reacting tungsten nanopowders with hydrous nickel nitrate in hydrogen atmosphere. The resultant tungsten oxide needles have lengths more than 100 μm, root diameters of several hundred nanometers and tip diameters of several nanometers, showing a perfectly axisymmetric configuration. HRTEM and SAED analyses showed that the synthesized tungsten oxide tapered needles have a single-crystalline structure with growth direction of [0 1 0]. The effects of the experimental conditions (the ratio between tungsten and hydrous nickel nitrate, the size of tungsten powders, and the reaction atmosphere) on the morphology of the products were systematically investigated. It was found that tungsten oxide nanowires, submicro-/micro-whiskers and microtubules could be facilely obtained under different experimental conditions. The unique configuration and the single-crystal structure of the tapered needles may make them a potential candidate for field emitters and probing tips.

  17. Electrokinetic treatment of firing ranges containing tungsten-contaminated soils.

    PubMed

    Braida, Washington; Christodoulatos, Christos; Ogundipe, Adebayo; Dermatas, Dimitris; O'Connor, Gregory

    2007-11-19

    Tungsten-based alloys and composites are being used and new formulations are being considered for use in the manufacturing of different types of ammunition. The use of tungsten heavy alloys (WHA) in new munitions systems and tungsten composites in small caliber ammunition could potentially release substantial amounts of this element into the environment. Although tungsten is widely used in industrial and military applications, tungsten's potential environmental and health impacts have not been thoroughly addressed. This necessitates the research and development of remedial technologies to contain and/or remove tungsten from soils that may serve as a source for water contamination. The current work investigates the feasibility of using electrokinetics for the remediation of tungsten-contaminated soils in the presence of other heavy metals of concern such as Cu and Pb with aim to removing W from the soil while stabilizing in situ, Pb and Cu. PMID:17686582

  18. Formation of an unusually short hydrogen bond in photoactive yellow protein.

    PubMed

    Saito, Keisuke; Ishikita, Hiroshi

    2013-03-01

    The photoactive chromophore of photoactive yellow protein (PYP) is p-coumaric acid (pCA). In the ground state, the pCA chromophore exists as a phenolate anion, which is H-bonded by protonated Glu46 (O(Glu46)-O(pCA)=~2.6Å) and protonated Tyr42. On the other hand, the O(Glu46)-O(pCA) H-bond was unusually short (O(Glu46)-O(pCA)=2.47Å) in the intermediate pR(CW) state observed in time-resolved Laue diffraction studies. To understand how the existence of the unusually short H-bond is energetically possible, we analyzed the H-bond energetics adopting a quantum mechanical/molecular mechanical (QM/MM) approach based on the atomic coordinates of the PYP crystal structures. In QM/MM calculations, the O(Glu46)-O(pCA) bond is 2.60Å in the ground state, where Tyr42 donates an H-bond to pCA. In contrast, when the hydroxyl group of Tyr42 is flipped away from pCA, the H-bond was significantly shortened to 2.49Å in the ground state. The same H-bond pattern reproduced the unusually short H-bond in the pR(CW) structure (O(Glu46)-O(pCA)=2.49Å). Intriguingly, the potential-energy profile resembles that of a single-well H-bond, suggesting that the pK(a) values of the donor (Glu46) and acceptor (pCA) moieties are nearly equal. The present results indicate that the "equal pK(a)" requirement for formation of single-well or low-barrier H-bond (LBHB) is satisfied only when Tyr42 does not donate an H-bond to pCA, and argue against the possibility that the O(Glu46)-O(pCA) bond is an LBHB in the ground state, where Tyr42 donates an H-bond to pCA. PMID:23201477

  19. Photoactive bile salts with critical micellar concentration in the micromolar range.

    PubMed

    Gomez-Mendoza, Miguel; Marin, M Luisa; Miranda, Miguel A

    2016-05-14

    The aggregation behavior of bile salts is strongly dependent on the number of hydroxyl groups. Thus, cholic acid (CA), with three hydroxyls, starts forming aggregates at 15 mM, while deoxycholic, chenodeoxycholic or ursodeoxycholic acids, with two hydroxyls, start aggregating at 5-10 mM; for lithocholic acid, with only one hydroxyl group, aggregation is observed at lower concentration (2-3 mM). Here, the singular self-assembling properties of dansyl and naproxen derivatives of CA (3β-Dns-CA and 3β-NPX-CA, respectively) have been demonstrated on the basis of their photoactive properties. Thus, the emission spectra of 3β-Dns-CA registered at increasing concentrations (25-140 μM) showed a remarkable non-linear enhancement in the emission intensity accompanied by a hypsochromic shift of the maximum and up to a three-fold increase in the singlet lifetime. The inflection point at around 50-70 μM pointed to the formation of unprecedented assemblies at such low concentrations. In the case of 3β-NPX-CA, when the NPX relative triplet lifetime was plotted against concentration, a marked increase (up to two-fold) was observed at 40-70 μM, indicating the formation of new 3β-NPX-CA assemblies at ca. 50 μM. Additional evidence supporting the formation of new 3β-Dns-CA or 3β-NPX-CA assemblies at 40-70 μM was obtained from singlet excited state quenching experiments using iodide. Moreover, to address the potential formation of hybrid assemblies, 1 : 1 mixtures of 3β-Dns-CA and 3β-NPX-CA (2-60 μM, total concentration) were subjected to steady-state fluorescence experiments, and their behavior was compared to that of the pure photoactive derivatives. A lower increase in the emission was observed for 3β-NPX-CA in the mixture, while a huge increase was experienced by 3β-Dns-CA in the same concentration range (up to 60 μM total). A partial intermolecular energy transfer from NPX to Dns, consistent with their reported singlet energies, was revealed, pointing to the

  20. Origin of photoactivity in graphitic carbon nitride and strategies for enhancement of photocatalytic efficiency: insights from first-principles computations.

    PubMed

    Zhang, Haijun; Zuo, Xueqin; Tang, Huaibao; Li, Guang; Zhou, Zhen

    2015-03-01

    The origin of the photoactivity in graphitic carbon nitride (g-C3N4) and the strategies for improving its photocatalytic efficiency were systematically investigated using first-principles computations. We found that g-C3N4 composed of tri-s-triazine units (g-CN1) is preferable in photocatalysis, owing to its visible-light absorption and appropriate band edge potentials. Despite the benefit of nanocrystallization of g-CN1, excessively minimized and passivated g-CN1 nanosheets (g-CN1NSs) should be inhibited, due to the intensely broadened band gaps in these structures. C- or N-vacancies in g-CN1NSs lead to gap states and smaller band widths, which should also be restrained. Compared with C substitution in B doped g-CN1NSs, N-substitution is favourable for enhancing the photoactivity of g-CN1NSs, due to the red-shift light absorption and the absence of gap states within this structure. Both WTe2 coupled and CdSe cluster loaded g-CN1NSs have decreased band gaps and directly separated carriers, which are beneficial to promote the photoactivity of g-CN1NSs. Among these modified g-CN1NS photocatalysts, WTe2 coupled g-CN1NSs are more preferable, as a result of their smaller band gap, free gap states and more rapid migration of excitons. PMID:25648139

  1. Improving the Visible Light Photoactivity of Supported Fullerene Photocatalysts through the Use of [C₇₀] Fullerene.

    PubMed

    Moor, Kyle J; Valle, Dhyan C; Li, Chuanhao; Kim, Jae-Hong

    2015-05-19

    We herein present the first instance of employing [C₇₀] fullerene for photocatalytic ¹O₂ production in water, through covalent immobilization onto a mesoporous silica support via nucelophilic amine addition directly to fullerene's cage. This attachment approach prevents the aggregation of individual fullerene molecules in water, thus allowing fullerene to retain its photoactivity, yet is much less complex than other techniques commonly pursued to create such supported-fullerene materials, which typically rely on water-soluble fullerene derivatives and elaborate immobilization methods. The solid-supported C₇₀ material exhibits significantly improved aqueous visible-light photoactivity compared to previous C₆₀- and C₆₀-derivative-based supported fullerene materials. Further, this material rapidly inactivates MS2 bacteriophage under sunlight illumination, oxidizes various organic contaminants, and does not appear to be significantly fouled by natural organic matter (NOM), highlighting the potential of these materials in real-world applications. Collectively, the ease of preparation and significantly enhanced visible-light photoactivity of these materials advance fullerene-based technologies for water treatment. PMID:25950200

  2. Method for removal of asphaltene depositions with amine-activated disulfide oil

    SciTech Connect

    Sharp, S.P.

    1983-04-12

    A method for treating and removing unwanted asphaltene deposits from oil and gas wells, surface equipment, flow lines, and pore spaces of oil-baring formations comprises treatment with an amine -activated aliphatic disulfide oil as an asphaltene solvent. In a preferred aspect, the aliphatic disulfide oil is a dialkyl disulfide oil and is activated by the addition of 10 weight percent of diethylamine. In a specific use, the activated disulfide oil is used to remove asphaltene deposits from an oilbearing formation and a producing well penetrating the formation.

  3. The influence of gold(i) on the mechanism of thiolate, disulfide exchange.

    PubMed

    Garusinghe, Gamage S P; Bessey, S Max; Bruce, Alice E; Bruce, Mitchell R M

    2016-07-28

    The mechanism of gold(i)-thiolate, disulfide exchange was investigated by using initial-rate kinetic studies, 2D ((1)H-(1)H) ROESY NMR spectroscopy, and electrochemical/chemical techniques. The rate law for exchange is overall second order, first order in gold(i)-thiolate and disulfide. 2D NMR experiments show evidence of association between gold(i)-thiolate and disulfide. Electrochemical/chemical investigations do not show evidence of free thiolate and are consistent with a mechanism involving formation of a [Au-S, S-S], four-centered metallacycle intermediate during gold(i)-thiolate, disulfide exchange. PMID:27353236

  4. Formation of disulfide bonds in insect prophenoloxidase enhances immunity through improving enzyme activity and stability.

    PubMed

    Lu, Anrui; Peng, Qin; Ling, Erjun

    2014-06-01

    Type 3 copper proteins, including insect prophenoloxidase (PPO), contain two copper atoms in the active site pocket and can oxidize phenols. Insect PPO plays an important role in immunity. Insects and other invertebrates show limited recovery from pathogen invasion and wounds if phenoloxidase (PO) activity is low. In most insect PPOs, two disulfide bonds are present near the C-terminus. However, in Pimpla hypochondriaca (a parasitoid wasp), each PPO contains one disulfide bond. We thus questioned whether the formation of two sulfide bonds in insect PPOs improved protein stability and/or increased insect innate immunity over time. Using Drosophila melanogaster PPO1 as a model, one or two disulfide bonds were deleted to evaluate the importance of disulfide bonds in insect immunity. rPPO1 and mutants lacking disulfide bonds could be expressed and showed PO activity. However, the PO activities of mutants lacking one or two disulfide bonds significantly decreased. Deletion of disulfide bonds also reduced PPO thermostability. Furthermore, antibacterial activities against Escherichia coli and Bacillus subtilis significantly decreased when disulfide bonds were deleted. Therefore, the formation of two disulfide bond(s) in insect PPO enhances antibacterial activity by increasing PO activity and stability. PMID:24480295

  5. Imaging disulfide dinitroxides at 250 MHz to monitor thiol redox status

    NASA Astrophysics Data System (ADS)

    Elajaili, Hanan; Biller, Joshua R.; Rosen, Gerald M.; Kao, Joseph P. Y.; Tseytlin, Mark; Buchanan, Laura A.; Rinard, George A.; Quine, Richard W.; McPeak, Joseph; Shi, Yilin; Eaton, Sandra S.; Eaton, Gareth R.

    2015-11-01

    Measurement of thiol-disulfide redox status is crucial for characterization of tumor physiology. The electron paramagnetic resonance (EPR) spectra of disulfide-linked dinitroxides are readily distinguished from those of the corresponding monoradicals that are formed by cleavage of the disulfide linkage by free thiols. EPR spectra can thus be used to monitor the rate of cleavage and the thiol redox status. EPR spectra of 1H,14N- and 2H,15N-disulfide dinitroxides and the corresponding monoradicals resulting from cleavage by glutathione have been characterized at 250 MHz, 1.04 GHz, and 9 GHz and imaged by rapid-scan EPR at 250 MHz.

  6. Thiol-disulfide exchange in peptides derived from human growth hormone.

    PubMed

    Chandrasekhar, Saradha; Epling, Daniel E; Sophocleous, Andreas M; Topp, Elizabeth M

    2014-04-01

    Disulfide bonds stabilize proteins by cross-linking distant regions into a compact three-dimensional structure. They can also participate in hydrolytic and oxidative pathways to form nonnative disulfide bonds and other reactive species. Such covalent modifications can contribute to protein aggregation. Here, we present experimental data for the mechanism of thiol-disulfide exchange in tryptic peptides derived from human growth hormone in aqueous solution. Reaction kinetics was monitored to investigate the effect of pH (6.0-10.0), temperature (4-50°C), oxidation suppressants [ethylenediaminetetraacetic acid (EDTA) and N2 sparging], and peptide secondary structure (amide cyclized vs. open form). The concentrations of free thiol containing peptides, scrambled disulfides, and native disulfide-linked peptides generated via thiol-disulfide exchange and oxidation reactions were determined using reverse-phase HPLC and liquid chromatography-mass spectrometry. Concentration versus time data were fitted to a mathematical model using nonlinear least squares regression analysis. At all pH values, the model was able to fit the data with R(2) ≥ 0.95. Excluding oxidation suppressants (EDTA and N2 sparging) resulted in an increase in the formation of scrambled disulfides via oxidative pathways but did not influence the intrinsic rate of thiol-disulfide exchange. In addition, peptide secondary structure was found to influence the rate of thiol-disulfide exchange. PMID:24549831

  7. Biologically oriented organic sulfur chemistry. 15. Organic disulfides and related substances. 41. Inhibition of the fungal pathogen Histoplasma capsulatum by some organic disulfides.

    PubMed

    Field, L; Grimaldi, J A; Hanley, W S; Holladay, M W; Ravichandran, R; Schaad, L J; Tate, C E

    1977-08-01

    In an extension of promising inhibitory results in vitro against Histoplasma capsulatum, correlated earlier using substituent constants developed by regression analysis with 77 disulfides, one symmetrical and 14 unsymmetrical disulfides were prepared (3--17). About half were active in vitro against H. capsulatum (and one against Candida albicans). Groups that seemed most to lead to promising inhibition among the unsymmetrical disulfides were o-HO2CC6H4, (CH2)4SO2Na, Me2NC(S), p-ClC6H4, and perhaps p-CH3C6H4; the first two also might be used to increase solubility. Earlier inhibitory promise of the morpholino group did not materialize. None of the group 3--17 was significantly active in vivo. The unsymmetrical disulfides were prepared by reaction of thiols with sulfenyl chlorides or with acyclic or cyclic thiosulfonates. Two six-membered heterocyclic disulfides (5 and 6) were prepared by a novel cyclization, in which carbon disulfide reacted with an (N-alkylamino)ethyl Bunte salt, followed by ring closure; an explanation is suggested for formation of a thiazoline when the N-alkyl group is absent. One of the disulfides disproportionated with astonishing ease (31; 0.3--1 h at 25 degrees C). PMID:330858

  8. A comprehensive study of isomerization and protonation reactions in the photocycle of the photoactive yellow protein.

    PubMed

    Wei, Lili; Wang, Hongjuan; Chen, Xuebo; Fang, Weihai; Wang, Haobin

    2014-12-14

    The light-activated photoactive yellow protein (PYP) chromophore uses a series of reactions to trigger photo-motility and biological responses, and generate a wide range of structural signals. To provide a comprehensive mechanism of the overall process at the atomic level, we apply a CASPT2//CASSCF/AMBER QM/MM protocol to investigate the relaxation pathways for a variety of possible isomerization and proton transfer reactions upon photoexcitation of the wild-type PYP. The nonadiabatic relay through an S1/S0 conical intersection [CI(S1/S0)] is found to play a decisive major role in bifurcating the excited state relaxation into a complete and short photocycle. Two major and one minor deactivation channels were found starting from the CI(S1/S0)-like intermediate IT, producing the cis isomers pR1, ICP, and ICT through "hula twist", "bicycle pedal" and one-bond flip isomerization reactions. The overall photocycle can be achieved by competitive parallel/sequential reactions, in which the ground state recovery is controlled by a series of slow volume-conserving bicycle pedal/hula twist and one-bond flip isomerization reactions, as well as fast protonation-deprotonation processes and the hydrophobic-hydrophilic state transformation. PMID:25195953

  9. pH Dependence of the Photoactive Yellow Protein Photocycle Investigated by Time-Resolved Crystallography

    SciTech Connect

    Tripathi, Shailesh; Šrajer, Vukica; Purwar, Namrta; Henning, Robert; Schmidt, Marius

    2012-05-24

    Visualizing the three-dimensional structures of a protein during its biological activity is key to understanding its mechanism. In general, protein structure and function are pH-dependent. Changing the pH provides new insights into the mechanisms that are involved in protein activity. Photoactive yellow protein (PYP) is a signaling protein that serves as an ideal model for time-dependent studies on light-activated proteins. Its photocycle is studied extensively under different pH conditions. However, the structures of the intermediates remain unknown until time-resolved crystallography is employed. With the newest beamline developments, a comprehensive time series of Laue data can now be collected from a single protein crystal. This allows us to vary the pH. Here we present the first structure, to our knowledge, of a short-lived protein-inhibitor complex formed in the pB state of the PYP photocycle at pH 4. A water molecule that is transiently stabilized in the chromophore active site prevents the relaxation of the chromophore back to the trans configuration. As a result, the dark-state recovery is slowed down dramatically. At pH 9, PYP stops cycling through the pB state altogether. The electrostatic environment in the chromophore-binding site is the likely reason for this altered kinetics at different pH values.

  10. Photoactive titania float for disinfection of water; evaluation of cell damage by bioanalytical techniques.

    PubMed

    Shwetharani, R; Jyothi, M S; Laveena, P D; Geetha Balakrishna, R

    2014-01-01

    A photoactive float was fabricated with the modified titania to cause a feasible disinfection of water, contaminated with E. coli. The commercially available titania was doped with neodymium by pulverization technique to enhance its activity in sunlight and a multiapproach technique was used to evaluate the extended efficiency of the doped sample. X-ray diffraction patterns depicted the retention of anatase phase on doping and the existence of neodymium was confirmed by the energy dispersive atomic X-ray analysis and the X-ray photoelectron spectroscopy. Transmission electron microscopy and Bruner-Emmett-Teller analysis depicted a marginal increase in the particle size and a decrease in the surface area, respectively. Doping induces semiconductor behavior with lower band energy that could respond to visible light and exhibit better disinfection activity. The "f" and "d" transitions of the lanthanide in doped sample caused new electronic behavior of trapping/detrapping effect together with bandgap narrowing. The amount of malondialdehyde, protein, DNA and RNA released on destruction of E. coli was observed to be 0.915 × 10(-3) μg mL(-1), 859.912 μg mL(-1), 20.173 μg mL(-1) and 1146.073 μg mL(-1), respectively. The above analytical methods along with standard plate count method substantiated the enhanced disinfection efficiency of the doped sample in sunlight. PMID:24689654

  11. Neutron and x-ray structural studies of short hydrogen bonds in photoactive yellow protein (PYP).

    SciTech Connect

    Fisher, S. Z.; Langan, P.; Anderson, S.; Henning, R.; Moffat, K.; Thiyagarajan, P.; Schultz, A. J.; LANL; Univ. of Chicago; Northwestern Univ.

    2007-11-01

    Photoactive yellow protein (PYP) from Halorhodospira halophila is a soluble 14 kDa blue-light photoreceptor. It absorbs light via its para-coumaric acid chromophore (pCA), which is covalently attached to Cys69 and is believed to be involved in the negative phototactic response of the organism to blue light. The complete structure (including H atoms) of PYP has been determined in D{sub 2}O-soaked crystals through the application of joint X-ray (1.1 {angstrom}) and neutron (2.5 {angstrom}) structure refinement in combination with cross-validated maximum-likelihood simulated annealing. The resulting XN structure reveals that the phenolate O atom of pCA accepts deuterons from Glu46 O{sup {epsilon}2} and Tyr42 O{sup {eta}} in two unusually short hydrogen bonds. This arrangement is stabilized by the donation of a deuteron from Thr50 O{sup {gamma}1} to Tyr42 O{sup {eta}}. However, the deuteron position between pCA and Tyr42 is only partially occupied. Thus, this atom may also interact with Thr50, possibly being disordered or fluctuating between the two bonds.

  12. Predicting the reaction coordinates of millisecond light-induced conformational changes in photoactive yellow protein

    PubMed Central

    Vreede, Jocelyne; Juraszek, Jarek; Bolhuis, Peter G.

    2010-01-01

    Understanding the dynamics of large-scale conformational changes in proteins still poses a challenge for molecular simulations. We employ transition path sampling of explicit solvent molecular dynamics trajectories to obtain atomistic insight in the reaction network of the millisecond timescale partial unfolding transition in the photocycle of the bacterial sensor photoactive yellow protein. Likelihood maximization analysis predicts the best model for the reaction coordinates of each substep as well as tentative transition states, without further simulation. We find that the unfolding of the α-helical region 43–51 is followed by sequential solvent exposure of both Glu46 and the chromophore. Which of these two residues is exposed first is correlated with the presence of a salt bridge that is part of the N-terminal domain. Additional molecular dynamics simulations indicate that the exposure of the chromophore does not result in a productive pathway. We discuss several possibilities for experimental validation of these predictions. Our results open the way for studying millisecond conformational changes in other medium-sized (signaling) proteins. PMID:20133754

  13. Vibrational energy flow in photoactive yellow protein revealed by infrared pump-visible probe spectroscopy.

    PubMed

    Nakamura, Ryosuke; Hamada, Norio

    2015-05-14

    Vibrational energy flow in the electronic ground state of photoactive yellow protein (PYP) is studied by ultrafast infrared (IR) pump-visible probe spectroscopy. Vibrational modes of the chromophore and the surrounding protein are excited with a femtosecond IR pump pulse, and the subsequent vibrational dynamics in the chromophore are selectively probed with a visible probe pulse through changes in the absorption spectrum of the chromophore. We thus obtain the vibrational energy flow with four characteristic time constants. The vibrational excitation with an IR pulse at 1340, 1420, 1500, or 1670 cm(-1) results in ultrafast intramolecular vibrational redistribution (IVR) with a time constant of 0.2 ps. The vibrational modes excited through the IVR process relax to the initial ground state with a time constant of 6-8 ps in parallel with vibrational cooling with a time constant of 14 ps. In addition, upon excitation with an IR pulse at 1670 cm(-1), we observe the energy flow from the protein backbone to the chromophore that occurs with a time constant of 4.2 ps. PMID:25896223

  14. Contrasting the Excited-State Dynamics of the Photoactive Yellow Protein Chromophore: Protein versus Solvent Environments

    PubMed Central

    Vengris, Mikas; van der Horst, Michael A.; Zgrablić, Goran; van Stokkum, Ivo H. M.; Haacke, Stefan; Chergui, Majed; Hellingwerf, Klaas J.; van Grondelle, Rienk; Larsen, Delmar S.

    2004-01-01

    Wavelength- and time-resolved fluorescence experiments have been performed on the photoactive yellow protein, the E46Q mutant, the hybrids of these proteins containing a nonisomerizing “locked” chromophore, and the native and locked chromophores in aqueous solution. The ultrafast dynamics of these six systems is compared and spectral signatures of isomerization and solvation are discussed. We find that the ultrafast red-shifting of fluorescence is associated mostly with solvation dynamics, whereas isomerization manifests itself as quenching of fluorescence. The observed multiexponential quenching of the protein samples differs from the single-exponential lifetimes of the chromophores in solution. The locked chromophore in the protein environment decays faster than in solution. This is due to additional channels of excited-state energy dissipation via the covalent and hydrogen bonds with the protein environment. The observed large dispersion of quenching timescales observed in the protein samples that contain the native pigment favors both an inhomogeneous model and an excited-state barrier for isomerization. PMID:15345563

  15. Efficient tool to calculate two-dimensional optical spectra for photoactive molecular complexes.

    PubMed

    Duan, Hong-Guang; Dijkstra, Arend G; Nalbach, Peter; Thorwart, Michael

    2015-10-01

    We combine the coherent modified Redfield theory (CMRT) with the equation of motion-phase matching approach (PMA) to calculate two-dimensional photon-echo spectra for photoactive molecular complexes with an intermediate strength of the coupling to their environment. Both techniques are highly efficient, yet they involve approximations at different levels. By explicitly comparing with the numerically exact quasiadiabatic path integral approach, we show for the Fenna-Matthews-Olson complex that the CMRT describes the decay rates in the population dynamics well, but final stationary populations and the oscillation frequencies differ slightly. In addition, we use the combined CMRT+PMA to calculate two-dimensional photon-echo spectra for a simple dimer model. We find excellent agreement with the exact path integral calculations at short waiting times where the dynamics is still coherent. For long waiting times, differences occur due to different final stationary states, specifically for strong system-bath coupling. For weak to intermediate system-bath couplings, which is most important for natural photosynthetic complexes, the combined CMRT+PMA gives reasonable results with acceptable computational efforts. PMID:26565273

  16. Study of minority carrier diffusion lengths in photoactive layers of multijunction solar cells

    SciTech Connect

    Mintairov, S. A. Andreev, V. M.; Emelyanov, V. M.; Kalyuzhnyy, N. A.; Timoshina, N. K.; Shvarts, M. Z.; Lantratov, V. M.

    2010-08-15

    A technique for determining a minority carrier's diffusion length in photoactive III-V layers of solar cells by approximating their spectral characteristics is presented. Single-junction GaAs, Ge and multi-junction GaAs/Ge, GaInP/GaAs, and GaInP/GaInAs/Ge solar cells fabricated by hydride metal-organic vapor-phase epitaxy (H-MOVPE) have been studied. The dependences of the minority carrier diffusion length on the doping level of p-Ge and n-GaAs are determined. It is shown that the parameters of solid-state diffusion of phosphorus atoms to the p-Ge substrate from the n-GaInP nucleation layer are independent of the thickness of the latter within 35-300 nm. It is found that the diffusion length of subcells of multijunction structures in Ga(In)As layers is smaller in comparison with that of single-junction structures.

  17. Effect of niobium on the structure and photoactivity of anatase (TiO2) nanoparticles.

    PubMed

    Hirano, Masanori; Matsushima, Kazumasa

    2006-03-01

    Anatase-type TiO2 nanoparticles doped with 0-30 mol% niobium were directly formed from precursor solutions of TiOSO4 and NbCl5 under mild hydrothermal conditions at 120-180 degrees C for 5 h using the hydrolysis of urea. When the niobium content increased from 0 to 30 mol%, the crystallite size of anatase increased from 8.5 to 19 nm. The band gap of anatase was slightly decreased by making solid solutions with niobium. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution after maintained in the dark or under UV-light irradiation. To form anatase-type solid solutions by doping 5-15 mol% niobium into TiO2 was effective for improvement of the photoactivity of TiO2. The photocatalytic activity (the photooxidation rate) and the adsorption amount of MB for the sample containing 15 mol% niobium became more than approximately nine times and six times as much as those of the hydrothermal anatase-type pure TiO2, respectively. PMID:16573134

  18. Design of a Photoactive Hybrid Bilayer Dielectric for Flexible Nonvolatile Organic Memory Transistors.

    PubMed

    Chen, Hongliang; Cheng, Nongyi; Ma, Wei; Li, Mingliang; Hu, Shuxin; Gu, Lin; Meng, Sheng; Guo, Xuefeng

    2016-01-26

    Organic field-effect transistors (OFETs) featuring a photoactive hybrid bilayer dielectric (PHBD) that comprises a self-assembled monolayer (SAM) of photochromic diarylethenes (DAEs) and an ultrathin solution-processed hafnium oxide layer are described here. We photoengineer the energy levels of DAE SAMs to facilitate the charging and discharging of the interface of the two dielectrics, thus yielding an OFET that functions as a nonvolatile memory device. The transistors use light signals for programming and electrical signals for erasing (≤3 V) to produce a large, reversible threshold-voltage shift with long retention times and good nondestructive signal processing ability. The memory effect can be exercised by more than 10(4) memory cycles. Furthermore, these memory cells have demonstrated the capacity to be arrayed into a photosensor matrix on flexible plastic substrates to detect the spatial distribution of a confined light and then store the analog sensor input as a two-dimensional image with high precision over a long period of time. PMID:26673624

  19. Visualizing reaction pathways in photoactive yellow protein from nanoseconds to seconds

    PubMed Central

    Ihee, Hyotcherl; Rajagopal, Sudarshan; Šrajer, Vukica; Pahl, Reinhard; Anderson, Spencer; Schmidt, Marius; Schotte, Friedrich; Anfinrud, Philip A.; Wulff, Michael; Moffat, Keith

    2005-01-01

    Determining 3D intermediate structures during the biological action of proteins in real time under ambient conditions is essential for understanding how proteins function. Here we use time-resolved Laue crystallography to extract short-lived intermediate structures and thereby unveil signal transduction in the blue light photoreceptor photoactive yellow protein (PYP) from Halorhodospira halophila. By analyzing a comprehensive set of Laue data during the PYP photocycle (forty-seven time points from one nanosecond to one second), we track all atoms in PYP during its photocycle and directly observe how absorption of a blue light photon by its p-coumaric acid chromophore triggers a reversible photocycle. We identify a complex chemical mechanism characterized by five distinct structural intermediates. Structural changes at the chromophore in the early, red-shifted intermediates are transduced to the exterior of the protein in the late, blue-shifted intermediates through an initial “volume-conserving” isomerization of the chromophore and the progressive disruption of hydrogen bonds between the chromophore and its surrounding binding pocket. These results yield a comprehensive view of the PYP photocycle when seen in the light of previous biophysical studies on the system. PMID:15870207

  20. pH Dependence of the Photoactive Yellow Protein Photocycle Investigated by Time-Resolved Crystallography

    PubMed Central

    Tripathi, Shailesh; Šrajer, Vukica; Purwar, Namrta; Henning, Robert; Schmidt, Marius

    2012-01-01

    Visualizing the three-dimensional structures of a protein during its biological activity is key to understanding its mechanism. In general, protein structure and function are pH-dependent. Changing the pH provides new insights into the mechanisms that are involved in protein activity. Photoactive yellow protein (PYP) is a signaling protein that serves as an ideal model for time-dependent studies on light-activated proteins. Its photocycle is studied extensively under different pH conditions. However, the structures of the intermediates remain unknown until time-resolved crystallography is employed. With the newest beamline developments, a comprehensive time series of Laue data can now be collected from a single protein crystal. This allows us to vary the pH. Here we present the first structure, to our knowledge, of a short-lived protein-inhibitor complex formed in the pB state of the PYP photocycle at pH 4. A water molecule that is transiently stabilized in the chromophore active site prevents the relaxation of the chromophore back to the trans configuration. As a result, the dark-state recovery is slowed down dramatically. At pH 9, PYP stops cycling through the pB state altogether. The electrostatic environment in the chromophore-binding site is the likely reason for this altered kinetics at different pH values. PMID:22339869

  1. Strong Ionic Hydrogen Bonding Causes a Spectral Isotope Effect in Photoactive Yellow Protein

    PubMed Central

    Kaledhonkar, Sandip; Hara, Miwa; Stalcup, T. Page; Xie, Aihua; Hoff, Wouter D.

    2013-01-01

    Standard hydrogen bonds are of great importance for protein structure and function. Ionic hydrogen bonds often are significantly stronger than standard hydrogen bonds and exhibit unique properties, but their role in proteins is not well understood. We report that hydrogen/deuterium exchange causes a redshift in the visible absorbance spectrum of photoactive yellow protein (PYP). We expand the range of interpretable isotope effects by assigning this spectral isotope effect (SIE) to a functionally important hydrogen bond at the active site of PYP. The inverted sign and extent of this SIE is explained by the ionic nature and strength of this hydrogen bond. These results show the relevance of ionic hydrogen bonding for protein active sites, and reveal that the inverted SIE is a novel, to our knowledge, tool to probe ionic hydrogen bonds. Our results support a classification of hydrogen bonds that distinguishes the properties of ionic hydrogen bonds from those of both standard and low barrier hydrogen bonds, and show how this classification helps resolve a recent debate regarding active site hydrogen bonding in PYP. PMID:24314088

  2. Enhanced visible-light photoactivity of La-doped ZnS thin films

    NASA Astrophysics Data System (ADS)

    Chen, Yuan; Huang, Gui-Fang; Huang, Wei-Qing; Zou, B. S.; Pan, Anlian

    2012-09-01

    ZnS and La-doped ZnS thin films were successfully synthesized using chemical-bath deposition on conductive glass substrates. The effects of La-doping on the surface morphology, composition, structure and optical properties of the films were investigated. The photocatalytic performances of undoped and doped ZnS films were evaluated by photodegrading methyl orange aqueous solution under both ultraviolet-light and visible-light irradiation. The results show that the stoichiometry ratio and the properties of ZnS can be tailored by the La-doping concentration. An appropriate amount of La-doping effectively extends the absorption edge to visible-light region, which leads to the significant enhancement of the photocatalytic activity of ZnS thin films under visible-light irradiation. The mechanism of enhanced visible-light photoactivity by La-doping is briefly discussed. The present study provides a simple method for designing the highly efficient semiconductor photocatalysts that can effectively utilize sunlight.

  3. Non-covalent functionalization of WS2 monolayer with small fullerenes: tuning electronic properties and photoactivity.

    PubMed

    Luo, Cai-Yun; Huang, Wei-Qing; Hu, Wangyu; Peng, P; Huang, Gui-Fang

    2016-09-14

    Atomically thin two-dimensional transition metal dichalcogenides (TMDCs) heterostructures have recently attracted growing interest due to their massive potential in solar energy applications due to their band gap in the visible spectral range and extremely strong light-matter interactions. Herein, heterostructures composed of WS2 and MoS2 monolayers, as representative TMDCs, with small fullerenes (B12 and C20) are investigated to explore their applications in solar energy conversion using first principles calculations based on density functional theory (DFT). The WS2 (MoS2) monolayer and fullerene form a van der Waals (vdW) heterostructure. Compared to pure monolayers, the heterostructures have a smaller band gap, which favours enhancing visible light absorption. The amount of charge transfer at the interface induced by vdW interactions depends on the type of fullerene. Most importantly, a type-II staggered band alignment is formed between WS2 (MoS2) and fullerene with the latter possessing the higher electron affinity which results in the robust separation of photoexcited charge carriers between them. These results indicate that the electronic properties and photoactivity of TMDCs monolayers can be tuned by non-covalent coupling with small fullerenes, thus meeting the needs of various applications. PMID:27483028

  4. Multiscale Approach to the Determination of the Photoactive Yellow Protein Signaling State Ensemble

    PubMed Central

    A. Rohrdanz, Mary; Zheng, Wenwei; Lambeth, Bradley; Vreede, Jocelyne; Clementi, Cecilia

    2014-01-01

    The nature of the optical cycle of photoactive yellow protein (PYP) makes its elucidation challenging for both experiment and theory. The long transition times render conventional simulation methods ineffective, and yet the short signaling-state lifetime makes experimental data difficult to obtain and interpret. Here, through an innovative combination of computational methods, a prediction and analysis of the biological signaling state of PYP is presented. Coarse-grained modeling and locally scaled diffusion map are first used to obtain a rough bird's-eye view of the free energy landscape of photo-activated PYP. Then all-atom reconstruction, followed by an enhanced sampling scheme; diffusion map-directed-molecular dynamics are used to focus in on the signaling-state region of configuration space and obtain an ensemble of signaling state structures. To the best of our knowledge, this is the first time an all-atom reconstruction from a coarse grained model has been performed in a relatively unexplored region of molecular configuration space. We compare our signaling state prediction with previous computational and more recent experimental results, and the comparison is favorable, which validates the method presented. This approach provides additional insight to understand the PYP photo cycle, and can be applied to other systems for which more direct methods are impractical. PMID:25356903

  5. Diaryl Disulfides as Novel Stabilizers of Tumor Suppressor Pdcd4

    PubMed Central

    Schmid, Tobias; Blees, Johanna S.; Bajer, Magdalena M.; Wild, Janine; Pescatori, Luca; Cuzzucoli Crucitti, Giuliana; Scipione, Luigi; Costi, Roberta; Henrich, Curtis J.; Brüne, Bernhard; Colburn, Nancy H.; Di Santo, Roberto

    2016-01-01

    The translation inhibitor and tumor suppressor Pdcd4 was reported to be lost in various tumors and put forward as prognostic marker in tumorigenesis. Decreased Pdcd4 protein stability due to PI3K-mTOR-p70S6K1 dependent phosphorylation of Pdcd4 followed by β-TrCP1-mediated ubiquitination, and proteasomal destruction of the protein was characterized as a major mechanism contributing to the loss of Pdcd4 expression in tumors. In an attempt to identify stabilizers of Pdcd4, we used a luciferase-based high-throughput compatible cellular assay to monitor phosphorylation-dependent proteasomal degradation of Pdcd4 in response to mitogen stimulation. Following a screen of approximately 2000 compounds, we identified 1,2-bis(4-chlorophenyl)disulfide as a novel Pdcd4 stabilizer. To determine an initial structure-activity relationship, we used 3 additional compounds, synthesized according to previous reports, and 2 commercially available compounds for further testing, in which either the linker between the aryls was modified (compounds 2–4) or the chlorine residues were replaced by groups with different electronic properties (compounds 5 and 6). We observed that those compounds with alterations in the sulfide linker completely lost the Pdcd4 stabilizing potential. In contrast, modifications in the chlorine residues showed only minor effects on the Pdcd4 stabilizing activity. A reporter with a mutated phospho-degron verified the specificity of the compounds for stabilizing the Pdcd4 reporter. Interestingly, the active diaryl disulfides inhibited proliferation and viability at concentrations where they stabilized Pdcd4, suggesting that Pdcd4 stabilization might contribute to the anti-proliferative properties. Finally, computational modelling indicated that the flexibility of the disulfide linker might be necessary to exert the biological functions of the compounds, as the inactive compound appeared to be energetically more restricted. PMID:26982744

  6. Presence of tungsten-containing fibers in tungsten refining and manufacturing processes.

    PubMed

    McKernan, John L; Toraason, Mark A; Fernback, Joseph E; Petersen, Martin R

    2009-04-01

    In tungsten refining and manufacturing processes, a series of tungsten oxides are typically formed as intermediates in the production of tungsten powder. The present study was conducted to characterize airborne tungsten-containing fiber dimensions, elemental composition and concentrations in the US tungsten refining and manufacturing industry. During the course of normal employee work activities, seven personal breathing zone and 62 area air samples were collected and analyzed using National Institute for Occupational Safety and Health (NIOSH) fiber sampling and counting methods to determine dimensions, composition and airborne concentrations of fibers. Mixed models were used to identify relationships between potential determinants and airborne fiber concentrations. Results from transmission electron microscopy analyses indicated that airborne fibers with length >0.5 microm, diameter >0.01 microm and aspect ratios > or =3:1 were present on 35 of the 69 air samples collected. Overall, the airborne fibers detected had a geometric mean length approximately 3 microm and diameter approximately 0.3 microm. Ninety-seven percent of the airborne fibers identified were in the thoracic fraction (i.e. aerodynamic diameter < or = 10 microm). Energy dispersive X-ray spectrometry results indicated that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Based on NIOSH fiber counting 'B' rules (length > 5 microm, diameter < 3 microm and aspect ratio > or = 5:1), airborne fiber concentrations ranged from below the limit of detection to 0.085 fibers cm(-3), with calcining being associated with the highest airborne concentrations. The mixed model procedure indicated that process temperature had a marginally significant relationship to airborne fiber concentration. This finding was expected since heated processes such as calcining created the highest airborne fiber concentrations. The

  7. Geosynchronous Performance of a Lithium-titanium Disulfide Battery

    NASA Technical Reports Server (NTRS)

    Otzinger, B.

    1985-01-01

    An ambient temperature rechargeable Lithium-Titanium disulfide (Li-TiS2) five cell battery has completed the first orbital year of accelerated synchronous orbit testing. A novel charge/discharge, state of charge (SOC) control scheme is utilized, together with taper current charge backup to overcome deleterious effects associated with high end of charge and low end of discharge voltages. It is indicated that 10 orbital years of simulated synchronous operation may be achieved. Preliminary findings associated with cell matching and battery performance are identified.

  8. Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes

    PubMed Central

    Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D.; Boubanga-Tombet, Stephane; Blancon, Jean-Christophe; Najmaei, Sina; Ajayan, Pulickel M.; Lou, Jun; Taylor, Antoinette J.; Prasankumar, Rohit P.

    2016-01-01

    We have performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. The ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems. PMID:26876194

  9. First total synthesis of mycothiol and mycothiol disulfide.

    PubMed

    Lee, Sungwon; Rosazza, John P N

    2004-02-01

    [reaction: see text] The first total synthesis of mycothiol and mycothiol disulfide was achieved by linking D-2,3,4,5,6-penta-O-acetyl-myo-inositol, O-(3,4,6-tri-O-acetyl)-2-azido-2-deoxy-alpha,beta-D-glucopyranosyl) trichloroacetimidate, and N,S-diacetyl-L-cysteine and deprotecting peracetylated mycothiol. The first full spectral characterization is reported for underivatized mycothiol. The structure of mycothiol was confirmed by spectral analysis of the known bimane derivative. PMID:14748594

  10. Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes

    DOE PAGESBeta

    Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D.; Boubanga-Tombet, Stephane; Blancon, Jean-Christophe; Najmaei, Sina; Ajayan, Pulickel M.; Lou, Jun; Taylor, Antoinette J.; Prasankumar, Rohit P.

    2016-02-15

    We performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. Furthermore, the ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems.

  11. A 65 Ah rechargeable lithium molybdenum disulfide battery

    NASA Technical Reports Server (NTRS)

    Brandt, K.

    1986-01-01

    A rechargeable lithium molybdenum disulfide battery which has a number of superior performance characteristics which includes a high energy density, a high power density, and a long charge retention time was developed. The first cell sizes developed included a C size cell and an AA size cell. Over the last two years, a project to demonstrate the feasibility of the scale up to this technology to a BC size cell with 65 Ah capacity was undertaken. The objective was to develop, build, and test a .6 kWh storage battery consisting of 6 BC cells in series.

  12. Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes.

    PubMed

    Seo, Minah; Yamaguchi, Hisato; Mohite, Aditya D; Boubanga-Tombet, Stephane; Blancon, Jean-Christophe; Najmaei, Sina; Ajayan, Pulickel M; Lou, Jun; Taylor, Antoinette J; Prasankumar, Rohit P

    2016-01-01

    We have performed ultrafast optical microscopy on single flakes of atomically thin CVD-grown molybdenum disulfide, using non-degenerate femtosecond pump-probe spectroscopy to excite and probe carriers above and below the indirect and direct band gaps. These measurements reveal the influence of layer thickness on carrier dynamics when probing near the band gap. Furthermore, fluence-dependent measurements indicate that carrier relaxation is primarily influenced by surface-related defect and trap states after above-bandgap photoexcitation. The ability to probe femtosecond carrier dynamics in individual flakes can thus give much insight into light-matter interactions in these two-dimensional nanosystems. PMID:26876194

  13. The effect of tensile stress on the conformational free energy landscape of disulfide bonds.

    PubMed

    Anjukandi, Padmesh; Dopieralski, Przemyslaw; Ribas-Arino, Jordi; Marx, Dominik

    2014-01-01

    Disulfide bridges are no longer considered to merely stabilize protein structure, but are increasingly recognized to play a functional role in many regulatory biomolecular processes. Recent studies have uncovered that the redox activity of native disulfides depends on their C-C-S-S dihedrals, χ2 and χ'2. Moreover, the interplay of chemical reactivity and mechanical stress of disulfide switches has been recently elucidated using force-clamp spectroscopy and computer simulation. The χ2 and χ'2 angles have been found to change from conformations that are open to nucleophilic attack to sterically hindered, so-called closed states upon exerting tensile stress. In view of the growing evidence of the importance of C-C-S-S dihedrals in tuning the reactivity of disulfides, here we present a systematic study of the conformational diversity of disulfides as a function of tensile stress. With the help of force-clamp metadynamics simulations, we show that tensile stress brings about a large stabilization of the closed conformers, thereby giving rise to drastic changes in the conformational free energy landscape of disulfides. Statistical analysis shows that native TDi, DO and interchain Ig protein disulfides prefer open conformations, whereas the intrachain disulfide bridges in Ig proteins favor closed conformations. Correlating mechanical stress with the distance between the two a-carbons of the disulfide moiety reveals that the strain of intrachain Ig protein disulfides corresponds to a mechanical activation of about 100 pN. Such mechanical activation leads to a severalfold increase of the rate of the elementary redox S(N)2 reaction step. All these findings constitute a step forward towards achieving a full understanding of functional disulfides. PMID:25286308

  14. The Effect of Tensile Stress on the Conformational Free Energy Landscape of Disulfide Bonds

    PubMed Central

    Anjukandi, Padmesh; Dopieralski, Przemyslaw; Ribas–Arino, Jordi; Marx, Dominik

    2014-01-01

    Disulfide bridges are no longer considered to merely stabilize protein structure, but are increasingly recognized to play a functional role in many regulatory biomolecular processes. Recent studies have uncovered that the redox activity of native disulfides depends on their C–C–S–S dihedrals, and . Moreover, the interplay of chemical reactivity and mechanical stress of disulfide switches has been recently elucidated using force–clamp spectroscopy and computer simulation. The and angles have been found to change from conformations that are open to nucleophilic attack to sterically hindered, so–called closed states upon exerting tensile stress. In view of the growing evidence of the importance of C–C–S–S dihedrals in tuning the reactivity of disulfides, here we present a systematic study of the conformational diversity of disulfides as a function of tensile stress. With the help of force-clamp metadynamics simulations, we show that tensile stress brings about a large stabilization of the closed conformers, thereby giving rise to drastic changes in the conformational free energy landscape of disulfides. Statistical analysis shows that native TDi, DO and interchain Ig protein disulfides prefer open conformations, whereas the intrachain disulfide bridges in Ig proteins favor closed conformations. Correlating mechanical stress with the distance between the two –carbons of the disulfide moiety reveals that the strain of intrachain Ig protein disulfides corresponds to a mechanical activation of about 100 pN. Such mechanical activation leads to a severalfold increase of the rate of the elementary redox reaction step. All these findings constitute a step forward towards achieving a full understanding of functional disulfides. PMID:25286308

  15. Tungsten-induced carcinogenesis in human bronchial epithelial cells.

    PubMed

    Laulicht, Freda; Brocato, Jason; Cartularo, Laura; Vaughan, Joshua; Wu, Feng; Kluz, Thomas; Sun, Hong; Oksuz, Betul Akgol; Shen, Steven; Peana, Massimiliano; Medici, Serenella; Zoroddu, Maria Antonietta; Costa, Max

    2015-10-01

    Metals such as arsenic, cadmium, beryllium, and nickel are known human carcinogens; however, other transition metals, such as tungsten (W), remain relatively uninvestigated with regard to their potential carcinogenic activity. Tungsten production for industrial and military applications has almost doubled over the past decade and continues to increase. Here, for the first time, we demonstrate tungsten's ability to induce carcinogenic related endpoints including cell transformation, increased migration, xenograft growth in nude mice, and the activation of multiple cancer-related pathways in transformed clones as determined by RNA sequencing. Human bronchial epithelial cell line (Beas-2B) exposed to tungsten developed carcinogenic properties. In a soft agar assay, tungsten-treated cells formed more colonies than controls and the tungsten-transformed clones formed tumors in nude mice. RNA-sequencing data revealed that the tungsten-transformed clones altered the expression of many cancer-associated genes when compared to control clones. Genes involved in lung cancer, leukemia, and general cancer genes were deregulated by tungsten. Taken together, our data show the carcinogenic potential of tungsten. Further tests are needed, including in vivo and human studies, in order to validate tungsten as a carcinogen to humans. PMID:26164860

  16. Restoration of structural stability and ligand binding after removal of the conserved disulfide bond in tear lipocalin

    PubMed Central

    Gasymov, Oktay K.; Abduragimov, Adil R.; Glasgow, Ben J.

    2014-01-01

    Disulfide bonds play diverse structural and functional roles in proteins. In tear lipocalin (TL), the conserved sole disulfide bond regulates stability and ligand binding. Probing protein structure often involves thiol selective labeling for which removal of the disulfide bonds may be necessary. Loss of the disulfide bond may destabilize the protein so strategies to retain the native state are needed. Several approaches were tested to regain the native conformational state in the disulfide-less protein. These included the addition of thrimethylamine N-oxide (TMAO) and the substitution of the Cys residues of disulfide bond with residues that can either form a potential salt bridge or others that can create a hydrophobic interaction. TMAO stabilized the protein relaxed by removal of the disulfide bond. In the disulfide-less mutants of TL, 1.0 M TMAO increased the free energy change (ΔG0) significantly from 2.1 to 3.8 kcal/mol. Moderate recovery was observed for the ligand binding tested with NBD-cholesterol. Because the disulfide bond of TL is solvent exposed, the substitution of the disulfide bond with a potential salt bridge or hydrophobic interaction did not stabilize the protein. This approach should work for buried disulfide bonds. However, for proteins with solvent exposed disulfide bonds, the use of TMAO may be an excellent strategy to restore the native conformational states in disulfide-less analogs of the proteins. PMID:25223802

  17. Restoration of structural stability and ligand binding after removal of the conserved disulfide bond in tear lipocalin.

    PubMed

    Gasymov, Oktay K; Abduragimov, Adil R; Glasgow, Ben J

    2014-10-01

    Disulfide bonds play diverse structural and functional roles in proteins. In tear lipocalin (TL), the conserved sole disulfide bond regulates stability and ligand binding. Probing protein structure often involves thiol selective labeling for which removal of the disulfide bonds may be necessary. Loss of the disulfide bond may destabilize the protein so strategies to retain the native state are needed. Several approaches were tested to regain the native conformational state in the disulfide-less protein. These included the addition of trimethylamine N-oxide (TMAO) and the substitution of the Cys residues of disulfide bond with residues that can either form a potential salt bridge or others that can create a hydrophobic interaction. TMAO stabilized the protein relaxed by removal of the disulfide bond. In the disulfide-less mutants of TL, 1.0M TMAO increased the free energy change (ΔG(0)) significantly from 2.1 to 3.8kcal/mol. Moderate recovery was observed for the ligand binding tested with NBD-cholesterol. Because the disulfide bond of TL is solvent exposed, the substitution of the disulfide bond with a potential salt bridge or hydrophobic interaction did not stabilize the protein. This approach should work for buried disulfide bonds. However, for proteins with solvent exposed disulfide bonds, the use of TMAO may be an excellent strategy to restore the native conformational states in disulfide-less analogs of the proteins. PMID:25223802

  18. Identification of protein disulfide isomerase 1 as a key isomerase for disulfide bond formation in apolipoprotein B100.

    PubMed

    Wang, Shiyu; Park, Shuin; Kodali, Vamsi K; Han, Jaeseok; Yip, Theresa; Chen, Zhouji; Davidson, Nicholas O; Kaufman, Randal J

    2015-02-15

    Apolipoprotein (apo) B is an obligatory component of very low density lipoprotein (VLDL), and its cotranslational and posttranslational modifications are important in VLDL synthesis, secretion, and hepatic lipid homeostasis. ApoB100 contains 25 cysteine residues and eight disulfide bonds. Although these disulfide bonds were suggested to be important in maintaining apoB100 function, neither the specific oxidoreductase involved nor the direct role of these disulfide bonds in apoB100-lipidation is known. Here we used RNA knockdown to evaluate both MTP-dependent and -independent roles of PDI1 in apoB100 synthesis and lipidation in McA-RH7777 cells. Pdi1 knockdown did not elicit any discernible detrimental effect under normal, unstressed conditions. However, it decreased apoB100 synthesis with attenuated MTP activity, delayed apoB100 oxidative folding, and reduced apoB100 lipidation, leading to defective VLDL secretion. The oxidative folding-impaired apoB100 was secreted mainly associated with LDL instead of VLDL particles from PDI1-deficient cells, a phenotype that was fully rescued by overexpression of wild-type but not a catalytically inactive PDI1 that fully restored MTP activity. Further, we demonstrate that PDI1 directly interacts with apoB100 via its redox-active CXXC motifs and assists in the oxidative folding of apoB100. Taken together, these findings reveal an unsuspected, yet key role for PDI1 in oxidative folding of apoB100 and VLDL assembly. PMID:25518935

  19. Legionella pneumophila utilizes a Single Player Disulfide-Bond Oxidoreductase System to Manage Disulfide Bond Formation and Isomerization

    PubMed Central

    Kpadeh, Zegbeh Z.; Day, Shandra R.; Mills, Brandy W.; Hoffman, Paul S.

    2015-01-01

    Legionella pneumophila uses a single homodimeric disulfide bond (DSB) oxidoreductase DsbA2 to catalyze extracytoplasmic protein folding and to correct DSB errors through protein-disulfide isomerase (PDI) activity. In Escherichia coli, these functions are separated to avoid futile cycling. In L. pneumophila, DsbA2 is maintained as a mixture of disulfides (S-S) and free thiols (SH), but when expressed in E. coli, only the SH form is observed. We provide evidence to suggest that structural differences in DsbB oxidases (LpDsbB1 and LpDsbB2) and DsbD reductases (LpDsbD1 and LpDsbD2) (compared to E. coli) permit bifunctional activities without creating a futile cycle. LpdsbB1 and LpdsbB2 partially complemented an EcdsbB mutant while neither LpdsbD1 nor LpdsbD2 complemented an EcdsbD mutant unless DsbA2 was also expressed. When the dsb genes of E. coli were replaced with those of L. pneumophila, motility was restored and DsbA2 was present as a mixture of redox forms. A dominant-negative approach to interfere with DsbA2 function in L. pneumophila determined that DSB oxidase activity was necessary for intracellular multiplication and assembly/function of the Dot/Icm Type IVb secretion system. Our studies show that a single-player system may escape the futile cycle trap by limiting transfer of reducing equivalents from LpDsbDs to DsbA2. PMID:25534767

  20. Microstructural evolution of tungsten oxide thin films

    NASA Astrophysics Data System (ADS)

    Hembram, K. P. S. S.; Thomas, Rajesh; Rao, G. Mohan

    2009-10-01

    Tungsten oxide thin films are of great interest due to their promising applications in various optoelectronic thin film devices. We have investigated the microstructural evolution of tungsten oxide thin films grown by DC magnetron sputtering on silicon substrate. The structural characterization and surface morphology were carried out using X-ray diffraction and Scanning Electron Microscopy (SEM). The as deposited films were amorphous, where as, the films annealed above 400 °C were crystalline. In order to explain the microstructural changes due to annealing, we have proposed a "instability wheel" model for the evolution of the microstructure. This model explains the transformation of mater into various geometries within them selves, followed by external perturbation.

  1. Femtosecond fiber laser additive manufacturing of tungsten

    NASA Astrophysics Data System (ADS)

    Bai, Shuang; Liu, Jian; Yang, Pei; Zhai, Meiyu; Huang, Huan; Yang, Lih-Mei

    2016-04-01

    Additive manufacturing (AM) is promising to produce complex shaped components, including metals and alloys, to meet requirements from different industries such as aerospace, defense and biomedicines. Current laser AM uses CW lasers and very few publications have been reported for using pulsed lasers (esp. ultrafast lasers). In this paper, additive manufacturing of Tungsten materials is investigated by using femtosecond (fs) fiber lasers. Various processing conditions are studied, which leads to desired characteristics in terms of morphology, porosity, hardness, microstructural and mechanical properties of the processed components. Fully dense Tungsten part with refined grain and increased hardness was obtained and compared with parts made with different pulse widths and CW laser. The results are evidenced that the fs laser based AM provides more dimensions to modify mechanical properties with controlled heating, rapid melting and cooling rates compared with a CW or long pulsed laser. This can greatly benefit to the make of complicated structures and materials that could not be achieved before.

  2. Ultrasonic ranking of toughness of tungsten carbide

    NASA Technical Reports Server (NTRS)

    Vary, A.; Hull, D. R.

    1983-01-01

    The feasibility of using ultrasonic attenuation measurements to rank tungsten carbide alloys according to their fracture toughness was demonstrated. Six samples of cobalt-cemented tungsten carbide (WC-Co) were examined. These varied in cobalt content from approximately 2 to 16 weight percent. The toughness generally increased with increasing cobalt content. Toughness was first determined by the Palmqvist and short rod fracture toughness tests. Subsequently, ultrasonic attenuation measurements were correlated with both these mechanical test methods. It is shown that there is a strong increase in ultrasonic attenuation corresponding to increased toughness of the WC-Co alloys. A correlation between attenuation and toughness exists for a wide range of ultrasonic frequencies. However, the best correlation for the WC-Co alloys occurs when the attenuation coefficient measured in the vicinity of 100 megahertz is compared with toughness as determined by the Palmqvist technique.

  3. UVIS tungsten lamp cross-check

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia

    2009-07-01

    This proposal will verify the operation of the spare UVIS channel calsystem tungsten lamp. Internal flatfields will be obtained in one filter from each of the twelve filter wheels, providing an initial baseline and comparison for those taken with the primary lamp {WF09, 11422}. Filters for this proposal were chosen based upon a balance of multiple factors: reasonable countrate with calsystem tungsten lamp {no long exposure times}, science priority of the filter, overall coverage of UVIS wavelength regime, and slot location in the wheel. Exposures will be taken in the default full-frame, four-amp, unbinned readout mode.This proposal corresponds to the spare lamp portion of SMOV activity id WFC3-09.

  4. WFC3 SS UVIS Spare Tungsten Lamp

    NASA Astrophysics Data System (ADS)

    MacKenty, John

    2012-10-01

    Part of side switch activities.This proposal will verify the operation of the spare UVIS channel calsystem tungsten lamp. Internal flatfields will be obtained in one filter from each of the twelve filter wheels, providing an initial baseline and comparison for those taken with the primary lamp {WF09}. Filters for this proposal were chosen based upon a balance of multiple factors: reasonable countrate with calsystem tungsten lamp {no long exposure times}, science priority of the filter, overall coverage of UVIS wavelength regime, and slot location in the wheel. Exposures will be taken in the default full-frame, four-amp, unbinned readout mode.This proposal corresponds to the spare lamp portion of SS SMOV activity ID: WF09b

  5. Tungsten fiber reinforced superalloys - A status review

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Signorelli, R. A.

    1981-01-01

    After a review of refractory metal fiber/alloy matrix composite development, a discussion is presented of the fabrication techniques used in production of tungsten fiber reinforced superalloys (TFRS), their most significant properties, and their potential applications in the hot section components of gas turbine engines. Emphasis is given the development of airfoil-fabrication technology, with a view to the production of TFRS turbine blades, and attention is given the first-generation TFRS material, a tungsten alloy fiber/FeCrAlY composite currently under evaluation. Detailed properties, design criteria and cost data are presented for this material. Among the properties covered are stress-rupture strength, high and low cycle fatigue, thermal fatigue, impact strength, oxidation and corrosion and thermal conductivity.

  6. Bend ductility of tungsten heavy alloys

    SciTech Connect

    Gurwell, W.E.; Garnich, M.R.; Dudder, G.B.; Lavender, C.A.

    1992-11-01

    A bend ductility test is used to indicate the formability of tungsten heavy alloys sheet. The primary test bends a notchless Charpy impact specimen to a bend angle of approximately 100C. This can be augmented by a bend-completion test. Finite element modeling as well as strain-gaged bend specimens elucidate the strain distribution in the specimen as a function of material thickness and bend angle. The bend ductilities of 70%W, 807.W and 90%W alloys are characterized. As expected, decreasing thickness or tungsten content enhances bend ductility. Oxidation is not detrimental; therefore, controlled atmosphere is not required for cooling. The potentially detrimental effects of mechanical working (e.g., rolling, roller-leveling, grit blasting, and peening) and machining (e.g., cutting and sanding) are illustrated.

  7. Lithium/disulfide cells capable of long cycle life

    SciTech Connect

    Kaun, T.D.; Holifield, T.F.; DeLuca, W.H.

    1988-01-01

    The lithium-alloy/disulfide cell has undergone improvements to provide a very stable, high performance upper-plateau (UP) FeS/sub 2/ electrode. Prismatic UP FeS/sub 2/ cell tests (12--24 Ah capacity) with a LiCl-LiBr-KBr eutectic electrolyte have demonstrated 1000 deep discharge cycles at 400/degree/C with less than a 20% drop in capacity and without reduced power capability. Previous lithium-alloy/disulfide cells, which were based on a two voltage-plateau FeS/sub 2/ electrode and LiCl-KCl eutectic electrolyte had a life expectancy of only 100 cycles. Both time- and cycle-related capacity loss mechanisms have been eliminated with the improved cell design. In addition, new cell design features of overcharge tolerance and overdischarge safeguarding enhance battery durability. The performance prospects of a Li-alloy/UP FeS/sub 2/ battery for an IDSEP van application are discussed. A specific energy of 150 Wh/kg for this battery after 1000 cycles of operation is projected. 8 refs., 5 figs., 1 tab.

  8. Methods of measuring Protein Disulfide Isomerase activity: a critical overview

    NASA Astrophysics Data System (ADS)

    Watanabe, Monica; Laurindo, Francisco; Fernandes, Denise

    2014-09-01

    Protein disulfide isomerase is an essential redox chaperone from the endoplasmic reticulum (ER) and is responsible for correct disulfide bond formation in nascent proteins. PDI is also found in other cellular locations in the cell, particularly the cell surface. Overall, PDI contributes to ER and global cell redox homeostasis and signaling. The knowledge about PDI structure and function progressed substantially based on in vitro studies using recombinant PDI and chimeric proteins. In these experimental scenarios, PDI reductase and chaperone activities are readily approachable. In contrast, assays to measure PDI isomerase activity, the hallmark of PDI family, are more complex. Assessment of PDI roles in cells and tissues mainly relies on gain- or loss-of-function studies. However, there is limited information regarding correlation of experimental readouts with the distinct types of PDI activities. In this mini-review, we evaluate the main methods described for measuring the different kinds of PDI activity: thiol reductase, thiol oxidase, thiol isomerase and chaperone. We emphasize the need to use appropriate controls and the role of critical interferents (e.g., detergent, presence of reducing agents). We also discuss the translation of results from in vitro studies with purified recombinant PDI to cellular and tissue samples, with critical comments on the interpretation of results.

  9. Diversity of the Epsilonproteobacteria Dsb (disulfide bond) systems

    PubMed Central

    Bocian-Ostrzycka, Katarzyna M.; Grzeszczuk, Magdalena J.; Dziewit, Lukasz; Jagusztyn-Krynicka, Elżbieta K.

    2015-01-01

    The bacterial proteins of the Dsb family—important components of the post-translational protein modification system—catalyze the formation of disulfide bridges, a process that is crucial for protein structure stabilization and activity. Dsb systems play an essential role in the assembly of many virulence factors. Recent rapid advances in global analysis of bacteria have thrown light on the enormous diversity among bacterial Dsb systems. While the Escherichia coli disulfide bond-forming system is quite well understood, the mechanisms of action of Dsb systems in other bacteria, including members of class Epsilonproteobacteria that contain pathogenic and non-pathogenic bacteria colonizing extremely diverse ecological niches, are poorly characterized. Here we present a review of current knowledge on Epsilonproteobacteria Dsb systems. We have focused on the Dsb systems of Campylobacter spp. and Helicobacter spp. because our knowledge about Dsb proteins of Wolinella and Arcobacter spp. is still scarce and comes mainly from bioinformatic studies. Helicobacter pylori is a common human pathogen that colonizes the gastric epithelium of humans with severe consequences. Campylobacter spp. is a leading cause of zoonotic enteric bacterial infections in most developed and developing nations. We focus on various aspects of the diversity of the Dsb systems and their influence on pathogenicity, particularly because Dsb proteins are considered as potential targets for a new class of anti-virulence drugs to treat human infections by Campylobacter or Helicobacter spp. PMID:26106374

  10. Protected peptide disulfides by oxidative detachment from a support.

    PubMed

    Rietman, B H; Smulders, R H; Eggen, I F; van Vliet, A; van de Werken, G; Tesser, G I

    1994-09-01

    A new and efficient procedure for the preparation of protected cyclized and protected symmetrical dimeric peptide disulfides is described. A thiol is immobilized onto a solid phase through coupling of the thiol function with a resin-linked trityl group. Following conventional peptide assembly using the Fmoc-strategy, detachment is performed by oxidation with iodine in a suitable organic solvent. When N,N-dimethylformamide is used as the solvent, and the peptide chain contains an acetamidomethylthio function, located N-terminally in a N alpha-(9-fluorenylmethyloxycarbonyl), or N alpha-tert-butyloxycarbonyl cysteinyl residue, or occurring in the chain, then the corresponding fully protected cyclic peptide disulfide will be obtained in high yield and purity. In other solvents (e.g. dioxane or chloroform-methanol 1:1, v/v), the iodine-mediated oxidation gave not only the cyclic product, but also substantial amounts of the parallel symmetrical dimeric peptide retaining Cys(Acm) at the two identical N-termini. PMID:7822095

  11. A laboratory and theoretical study of protonated carbon disulfide, HSCS+.

    PubMed

    McCarthy, M C; Thaddeus, P; Wilke, Jeremiah J; Schaefer, Henry F

    2009-06-21

    The rotational spectrum of protonated carbon disulfide, HSCS(+), has been detected in the centimeter-wave band in a molecular beam by Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined from ten transitions in the K(a)=0 ladder of the normal isotopic species, HS(13)CS(+), and DSCS(+). The present assignment agrees well with high-level coupled cluster calculations of the HSCS(+) structure, which, like earlier work, predict this isomer to be the ground state on the HCS(2) (+) potential energy surface; HCSS(+), an isomer with C(2v) symmetry, is predicted to lie more than 20 kcal/mol higher in energy. Other properties of HSCS(+) including its dipole moment, anharmonic vibrational frequencies, and infrared intensities have also been computed at the coupled cluster level of theory with large basis sets. Because carbon disulfide possesses a fairly large proton affinity, and because this nonpolar molecule may plausibly exist in astronomical sources, HSCS(+) is a good candidate for detection with radio telescopes in the submillimeter band where the stronger b-type transitions of this protonated cation are predicted to lie. PMID:19548724

  12. Health effects following chronic dosing with tungsten-iron and tungsten-polymer shot in adult game-farm mallards.

    PubMed

    Mitchell, R R; Fitzgerald, S D; Aulerich, R J; Balander, R J; Powell, D C; Tempelman, R J; Stickle, R L; Stevens, W; Bursian, S J

    2001-07-01

    Permanent approval of shot composed of tungsten-iron and tungsten-polymer for waterfowl hunting by the U.S. Fish and Wildlife Service was pending the results of the present study that examined the health and reproductive effects of the two shot types on mallards (Anas platyrhynchos) over a 150-day period. We collected data pertaining to the effects of tungsten-iron and tungsten-polymer shot on mortality, body weight, organ weight, tissue pathology, and shot erosion. Thirty-two bird groups (sexes equal) of adult mallards were dosed orally with eight #4 steel shot (control), eight #4 tungsten-iron shot, or eight #4 tungsten-polymer shot on days 0, 30, 60, 90, and 120 of a 150-day trial (26 January 1998 to 25 June 1998). An additional 12 mallards (sexes equal) were dosed orally with eight #4 lead shot (positive control) on day 0 of the study. All lead-dosed ducks died by day 25, whereas no ducks died in the other treatment groups. Significant liver hemosiderosis was present in all control and tungsten-iron-dosed males, in five of eight control and three of eight tungsten-iron-dosed females, and in one tungsten-polymer-dosed male examined. The rate of shot erosion was highest for tungsten-polymer shot (99%), followed by tungsten-iron (72%), and steel (55%) shot. Tungsten-iron or tungsten-polymer shot repeatedly administered to adult mallards did not have deleterious health effects during the 150-day trial based on mortality, body weights, organ weights, and histology of the liver and kidneys. PMID:11504218

  13. Biotechnology Based Process for Production of a Disulfide-Bridged Peptide.

    PubMed

    Goswami, Animesh; Goldberg, Steven L; Hanson, Ronald L; Johnston, Robert M; Lyngberg, Olav K; Chan, Yeung; Lo, Ehrlic; Chan, Steven H; de Mas, Nuria; Ramirez, Antonio; Doyle, Richard; Ding, Wei; Gao, Mian; Krystek, Stanley R; Wan, Changhong; Kim, Yeoun Jin; Calambur, Deepa; Witmer, Mark; Bryson, James W

    2016-05-18

    A disulfide-bridged peptide drug development candidate contained two oligopeptide chains with 11 and 12 natural amino acids joined by a disulfide bond at the N-terminal end. An efficient biotechnology based process for the production of the disulfide-bridged peptide was developed. Initially, the two individual oligopeptide chains were prepared separately by designing different fusion proteins and expressing them in recombinant E. coli. Enzymatic or chemical cleavage of the two fusion proteins provided the two individual oligopeptide chains which could be conjugated via disulfide bond by conventional chemical reaction to the disulfide-bridged peptide. A novel heterodimeric system to bring the two oligopeptide chains closer and induce disulfide bond formation was designed by taking advantage of the self-assembly of a leucine zipper system. The heterodimeric approach involved designing fusion proteins with the acidic and basic components of the leucine zipper, additional amino acids to optimize interaction between the individual chains, specific cleavage sites, specific tag to ensure separation, and two individual oligopeptide chains. Computer modeling was used to identify the nature and number of amino acid residue to be inserted between the leucine zipper and oligopeptides for optimum interaction. Cloning and expression in rec E. coli, fermentation, followed by cell disruption resulted in the formation of heterodimeric protein with the interchain disulfide bond. Separation of the desired heterodimeric protein, followed by specific cleavage at methionine by cyanogen bromide provided the disulfide-bridged peptide. PMID:27098672

  14. Regulation of interleukin-4 signaling by extracellular reduction of intramolecular disulfides

    SciTech Connect

    Curbo, Sophie; Gaudin, Raphael; Carlsten, Mattias; Malmberg, Karl-Johan; Troye-Blomberg, Marita; Ahlborg, Niklas; Karlsson, Anna; Johansson, Magnus; Lundberg, Mathias

    2009-12-25

    Interleukin-4 (IL-4) contains three structurally important intramolecular disulfides that are required for the bioactivity of the cytokine. We show that the cell surface of HeLa cells and endotoxin-activated monocytes can reduce IL-4 intramolecular disulfides in the extracellular space and inhibit binding of IL-4 to the IL-4R{alpha} receptor. IL-4 disulfides were in vitro reduced by thioredoxin 1 (Trx1) and protein disulfide isomerase (PDI). Reduction of IL-4 disulfides by the cell surface of HeLa cells was inhibited by auranofin, an inhibitor of thioredoxin reductase that is an electron donor to both Trx1 and PDI. Both Trx1 and PDI have been shown to be located at the cell surface and our data suggests that these enzymes are involved in catalyzing reduction of IL-4 disulfides. The pro-drug N-acetylcysteine (NAC) that promotes T-helper type 1 responses was also shown to mediate the reduction of IL-4 disulfides. Our data provides evidence for a novel redox dependent pathway for regulation of cytokine activity by extracellular reduction of intramolecular disulfides at the cell surface by members of the thioredoxin enzyme family.

  15. Selective inhibition of nicotinamide adenine dinucleotide kinases by dinucleoside disulfide mimics of nicotinamide adenine dinucleotide analogues.

    PubMed

    Petrelli, Riccardo; Sham, Yuk Yin; Chen, Liqiang; Felczak, Krzysztof; Bennett, Eric; Wilson, Daniel; Aldrich, Courtney; Yu, Jose S; Cappellacci, Loredana; Franchetti, Palmarisa; Grifantini, Mario; Mazzola, Francesca; Di Stefano, Michele; Magni, Giulio; Pankiewicz, Krzysztof W

    2009-08-01

    Diadenosine disulfide (5) was reported to inhibit NAD kinase from Listeria monocytogenes and the crystal structure of the enzyme-inhibitor complex has been solved. We have synthesized tiazofurin adenosine disulfide (4) and the disulfide 5, and found that these compounds were moderate inhibitors of human NAD kinase (IC(50)=110 microM and IC(50)=87 microM, respectively) and Mycobacterium tuberculosis NAD kinase (IC(50)=80 microM and IC(50)=45 microM, respectively). We also found that NAD mimics with a short disulfide (-S-S-) moiety were able to bind in the folded (compact) conformation but not in the common extended conformation, which requires the presence of a longer pyrophosphate (-O-P-O-P-O-) linkage. Since majority of NAD-dependent enzymes bind NAD in the extended conformation, selective inhibition of NAD kinases by disulfide analogues has been observed. Introduction of bromine at the C8 of the adenine ring restricted the adenosine moiety of diadenosine disulfides to the syn conformation making it even more compact. The 8-bromoadenosine adenosine disulfide (14) and its di(8-bromoadenosine) analogue (15) were found to be the most potent inhibitors of human (IC(50)=6 microM) and mycobacterium NAD kinase (IC(50)=14-19 microM reported so far. None of the disulfide analogues showed inhibition of lactate-, and inosine monophosphate-dehydrogenase (IMPDH), enzymes that bind NAD in the extended conformation. PMID:19596199

  16. 46 CFR 151.50-40 - Additional requirements for carbon disulfide (carbon bisulfide) and ethyl ether.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Additional requirements for carbon disulfide (carbon... Special Requirements § 151.50-40 Additional requirements for carbon disulfide (carbon bisulfide) and ethyl... waterways at the loading and unloading points. (f) The special requirements of § 151.50-41 for...

  17. 21 CFR 520.1802 - Piperazine-carbon disulfide complex oral dosage forms.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Piperazine-carbon disulfide complex oral dosage forms. 520.1802 Section 520.1802 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... § 520.1802 Piperazine-carbon disulfide complex oral dosage forms....

  18. 21 CFR 520.1802 - Piperazine-carbon disulfide complex oral dosage forms.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Piperazine-carbon disulfide complex oral dosage forms. 520.1802 Section 520.1802 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... § 520.1802 Piperazine-carbon disulfide complex oral dosage forms....

  19. 21 CFR 520.1802 - Piperazine-carbon disulfide complex oral dosage forms.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Piperazine-carbon disulfide complex oral dosage forms. 520.1802 Section 520.1802 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... § 520.1802 Piperazine-carbon disulfide complex oral dosage forms....

  20. 46 CFR 151.50-40 - Additional requirements for carbon disulfide (carbon bisulfide) and ethyl ether.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Additional requirements for carbon disulfide (carbon... Special Requirements § 151.50-40 Additional requirements for carbon disulfide (carbon bisulfide) and ethyl... waterways at the loading and unloading points. (f) The special requirements of § 151.50-41 for...

  1. 21 CFR 520.1802 - Piperazine-carbon disulfide complex oral dosage forms.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Piperazine-carbon disulfide complex oral dosage forms. 520.1802 Section 520.1802 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... § 520.1802 Piperazine-carbon disulfide complex oral dosage forms....

  2. 46 CFR 151.50-40 - Additional requirements for carbon disulfide (carbon bisulfide) and ethyl ether.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 5 2010-10-01 2010-10-01 false Additional requirements for carbon disulfide (carbon... Special Requirements § 151.50-40 Additional requirements for carbon disulfide (carbon bisulfide) and ethyl... waterways at the loading and unloading points. (f) The special requirements of § 151.50-41 for...

  3. 21 CFR 520.1802 - Piperazine-carbon disulfide complex oral dosage forms.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Piperazine-carbon disulfide complex oral dosage forms. 520.1802 Section 520.1802 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND... § 520.1802 Piperazine-carbon disulfide complex oral dosage forms....

  4. 46 CFR 151.50-40 - Additional requirements for carbon disulfide (carbon bisulfide) and ethyl ether.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Additional requirements for carbon disulfide (carbon... Special Requirements § 151.50-40 Additional requirements for carbon disulfide (carbon bisulfide) and ethyl... waterways at the loading and unloading points. (f) The special requirements of § 151.50-41 for...

  5. 46 CFR 151.50-40 - Additional requirements for carbon disulfide (carbon bisulfide) and ethyl ether.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Additional requirements for carbon disulfide (carbon... Special Requirements § 151.50-40 Additional requirements for carbon disulfide (carbon bisulfide) and ethyl... waterways at the loading and unloading points. (f) The special requirements of § 151.50-41 for...

  6. Controlled nanostructuration of polycrystalline tungsten thin films

    SciTech Connect

    Girault, B.; Eyidi, D.; Goudeau, P.; Guerin, P.; Bourhis, E. Le; Renault, P.-O.; Sauvage, T.

    2013-05-07

    Nanostructured tungsten thin films have been obtained by ion beam sputtering technique stopping periodically the growing. The total thickness was maintained constant while nanostructure control was obtained using different stopping periods in order to induce film stratification. The effect of tungsten sublayers' thicknesses on film composition, residual stresses, and crystalline texture evolution has been established. Our study reveals that tungsten crystallizes in both stable {alpha}- and metastable {beta}-phases and that volume proportions evolve with deposited sublayers' thicknesses. {alpha}-W phase shows original fiber texture development with two major preferential crystallographic orientations, namely, {alpha}-W<110> and unexpectedly {alpha}-W<111> texture components. The partial pressure of oxygen and presence of carbon have been identified as critical parameters for the growth of metastable {beta}-W phase. Moreover, the texture development of {alpha}-W phase with two texture components is shown to be the result of a competition between crystallographic planes energy minimization and crystallographic orientation channeling effect maximization. Controlled grain size can be achieved for the {alpha}-W phase structure over 3 nm stratification step. Below, the {beta}-W phase structure becomes predominant.

  7. The tungsten divertor experiment at ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Neu, R.; Asmussen, K.; Krieger, K.; Thoma, A.; Bosch, H.-S.; Deschka, S.; Dux, R.; Engelhardt, W.; García-Rosales, C.; Gruber, O.; Herrmann, A.; Kallenbach, A.; Kaufmann, M.; Mertens, V.; Ryter, F.; Rohde, V.; Roth, J.; Sokoll, M.; Stäbler, A.; Suttrop, W.; Weinlich, M.; Zohm, H.; Alexander, M.; Becker, G.; Behler, K.; Behringer, K.; Behrisch, R.; Bergmann, A.; Bessenrodt-Weberpals, M.; Brambilla, M.; Brinkschulte, H.; Büchl, K.; Carlson, A.; Chodura, R.; Coster, D.; Cupido, L.; de Blank, H. J.; de Peña Hempel, S.; Drube, R.; Fahrbach, H.-U.; Feist, J.-H.; Feneberg, W.; Fiedler, S.; Franzen, P.; Fuchs, J. C.; Fußmann, G.; Gafert, J.; Gehre, O.; Gernhardt, J.; Haas, G.; Herppich, G.; Herrmann, W.; Hirsch, S.; Hoek, M.; Hoenen, F.; Hofmeister, F.; Hohenöcker, H.; Jacobi, D.; Junker, W.; Kardaun, O.; Kass, T.; Kollotzek, H.; Köppendörfer, W.; Kurzan, B.; Lackner, K.; Lang, P. T.; Lang, R. S.; Laux, M.; Lengyel, L. L.; Leuterer, F.; Manso, M. E.; Maraschek, M.; Mast, K.-F.; McCarthy, P.; Meisel, D.; Merkel, R.; Müller, H. W.; Münich, M.; Murmann, H.; Napiontek, B.; Neu, G.; Neuhauser, J.; Niethammer, M.; Noterdaeme, J.-M.; Pasch, E.; Pautasso, G.; Peeters, A. G.; Pereverzev, G.; Pitcher, C. S.; Poschenrieder, W.; Raupp, G.; Reinmüller, K.; Riedl, R.; Röhr, H.; Salzmann, H.; Sandmann, W.; Schilling, H.-B.; Schlögl, D.; Schneider, H.; Schneider, R.; Schneider, W.; Schramm, G.; Schweinzer, J.; Scott, B. D.; Seidel, U.; Serra, F.; Speth, E.; Silva, A.; Steuer, K.-H.; Stober, J.; Streibl, B.; Treutterer, W.; Troppmann, M.; Tsois, N.; Ulrich, M.; Varela, P.; Verbeek, H.; Verplancke, Ph; Vollmer, O.; Wedler, H.; Wenzel, U.; Wesner, F.; Wolf, R.; Wunderlich, R.; Zasche, D.; Zehetbauer, T.; Zehrfeld, H.-P.

    1996-12-01

    Tungsten-coated tiles, manufactured by plasma spray on graphite, were mounted in the divertor of the ASDEX Upgrade tokamak and cover almost 90% of the surface facing the plasma in the strike zone. Over 600 plasma discharges have been performed to date, around 300 of which were auxiliary heated with heating powers up to 10 MW. The production of tungsten in the divertor was monitored by a W I line at 400.8 nm. In the plasma centre an array of spectral lines at 5 nm emitted by ionization states around W XXX was measured. From the intensity of these lines the W content was derived. Under normal discharge conditions W-concentrations around 0741-3335/38/12A/013/img12 or even lower were found. The influence on the main plasma parameters was found to be negligible. The maximum concentrations observed decrease with increasing heating power. In several low power discharges accumulation of tungsten occurred and the temperature profile was flattened. The concentrations of the intrinsic impurities carbon and oxygen were comparable to the discharges with the graphite divertor. Furthermore, the density and the 0741-3335/38/12A/013/img13 limits remained unchanged and no negative influence on the energy confinement or on the H-mode threshold was found. Discharges with neon radiative cooling showed the same behaviour as in the graphite divertor case.

  8. Hydrogen permeation through disordered nanostructured tungsten films

    NASA Astrophysics Data System (ADS)

    Nemanič, V.; Zajec, B.; Dellasega, D.; Passoni, M.

    2012-10-01

    We report results on long-term hydrogen outgassing and permeation studies of structurally highly disordered tungsten films, deposited on 40 mm diameter highly permeable Eurofer substrates, using the Pulsed Laser Deposition technique. Hydrogen interaction with tungsten is becoming a highly relevant topic since tungsten was recognized as the most promising candidate for the first wall of future fusion reactors. Prediction of hydrogen isotopes migration and their abundance after plasma exposure is uncertain due to a great role played by structural disorder that is formed on the W surface. Vacancy sites are theoretically predicted to trap multiple H atoms exothermically, but their density and their potential influence on permeability has not been experimentally investigated yet. In our work, permeability of W films having different thicknesses (1 and 10 μm) was initially extremely low, and was gradually increasing over a several-day campaign. The final values at 400 °C, lying between P = 1.46 × 10-15 mol H2/(m s Pa0.5) and P = 4.8 × 10-15 mol H2/(m s Pa0.5), were substantially lower than those known for well ordered films. Surprisingly, the 10 μm thick W film initially contained a very high amount of hydrogen, ˜0.1 H/W, which was gradually releasing during the twenty-day campaign.

  9. Continuum source tungsten coil atomic fluorescence spectrometry.

    PubMed

    Gu, Jiyan; Donati, George L; Young, Carl G; Jones, Bradley T

    2011-04-01

    A simple continuum source tungsten coil atomic fluorescence spectrometer is constructed and evaluated. The heart of the system is the atomizer: a low-cost tungsten filament extracted from a 150 W light bulb. The filament is resistively heated with a small, solid-state, constant-current power supply. The atomizer is housed in a glass chamber and purged with a 1 L/min flow of a conventional welding gas mixture: 10% H(2)/Ar. A 25 μL sample aliquot is pipetted onto the tungsten coil, the liquid is dried at low current, and then the atomic vapor is produced by applying a current in the range 3.5-5.5 A. The atomization current does not produce temperatures high enough to excite atomic emission. Radiation from a 300 W xenon lamp is focused through the atomic vapor, exciting atomic fluorescence. Fluorescence signals are collected using a hand-held charge-coupled device (CCD) spectrometer. Simultaneous determination of ten elements (Ag, Bi, Cr, Cu, Ga, In, Mg, Mn, and Tl) results in detection limits in the range 0.3 to 10 ng. The application of higher atomization currents (10 A) leads to straightforward detection of atomic emission signals with no modifications to the instrument. PMID:21396184

  10. Mechanical behavior of tungsten shaped charge liner materials

    SciTech Connect

    Lassila, D.H.

    1993-08-01

    Radiographs of jets produced by shaped charges with tungsten liners have documented both ductile and brittle breakup behavior. The relationships between the varying breakup behavior of tungsten shaped charge jets and metallurgical characteristics and/or mechanical behavior of the liner are not understood. In this paper the mechanical behavior of warm-forged and chemical-vapor-deposition (CVD) tungsten is discussed relative to the typical deformation history of an element of liner material which becomes part of the jet. The analyses suggest the following: (1) tungsten liner material is damaged, or possibly pulverized, during shock loading at the high-explosive detonation front; (2) pulverized material is consolidated in the convergence zone under conditions of high pressure, and (3) variations in observed breakup behavior of tungsten may be related to high temperature embrittlement. The low temperature ductile-brittle transition temperature of tungsten (DBTT) is not believed to be directly related to observed variations in break-up behavior of jets.

  11. Measurement of thermophysical property of plasma forming tungsten nanofiber layer

    NASA Astrophysics Data System (ADS)

    Kajita, Shin; Yagi, Takashi; Kobayashi, Kenichi; Tokitani, Masayuki; Ohno, Noriyasu

    2016-05-01

    Thermophysical property of a nanostructured tungsten layer formed on a tungsten film was investigated. A 1-µm-thick tungsten film deposited on a quartz glass substrate was irradiated with a high density helium plasma at the surface temperature of 1500 K. The plasma irradiation led to the formation of highly porous fiberform-nanostructured tungsten layer with a thickness of 3.5 µm. Impulse heating was applied at the interface of the film/substrate, and transient heat diffusion was observed using a pulsed light heating thermoreflectance apparatus. The thermoreflectance signals clearly differed between the nanostructure existing and mechanically removed regions; the difference can be attributed to thermal effusivity of the nanostructured tungsten layer. The estimated thermal conductivity of the nanostructured tungsten decreases to ∼2% of that of bulk when the density of the nanostructure is assumed to be ∼6% of the bulk value.

  12. The tungsten powder study of the dispenser cathode

    NASA Astrophysics Data System (ADS)

    Bao, Ji-xiu; Wan, Bao-fei

    2006-06-01

    The intercorrelation of tungsten powder properties, such as grain size, distribution and morphology, and porous matrix parameters with electron emission capability and longevity of Ba dispenser cathodes has been investigated for the different grain morphologies. It is shown that a fully cleaning step of the tungsten powder is so necessary that the tungsten powder will be reduction of oxide in hydrogen atmosphere above 700 °C. The porosity of the tungsten matrix distributes more even and the closed pore is fewer, the average granule size of the tungsten powder distributes more convergent. The porosity of the tungsten matrix and the evaporation of the activator are bigger and the pulse of the cathode is smaller when the granularity is bigger by the analysis of the electronic microscope and diode experiment.

  13. Selective Dynamic Assembly of Disulfide Macrocyclic Helical Foldamers with Remote Communication of Handedness.

    PubMed

    Tsiamantas, Christos; de Hatten, Xavier; Douat, Céline; Kauffmann, Brice; Maurizot, Victor; Ihara, Hirotaka; Takafuji, Makoto; Metzler-Nolte, Nils; Huc, Ivan

    2016-06-01

    Disulfide bridge formation was investigated in helical aromatic oligoamide foldamers. Depending on the position of thiol-bearing side chains, exclusive intramolecular or intermolecular disulfide bridging may occur. The two processes are capable of self-sorting, presumably by dynamic exchange. Quantitative assessment of helix handedness inversion rates showed that bridging stabilizes the folded structures. Intermolecular disulfide bridging serendipitously yielded a well-defined, C2 -symmetrical, two-helix bundle-like macrocyclic structure in which complete control over relative handedness, that is, helix-helix handedness communication, is mediated remotely by the disulfide bridged side chains in the absence of contacts between helices. MM calculations suggest that this phenomenon is specific to a given side chain length and requires disulfide functions. PMID:27101565

  14. Dynamic Chemistry of Disulfide Terminated Oligonucleotides in Duplexes and Double-Crossover Tiles.

    PubMed

    De Stefano, Mattia; Vesterager Gothelf, Kurt

    2016-06-16

    Designed nanostructures formed by self-assembly of multiple DNA strands suffer from low stability at elevated temperature and under other denaturing conditions. Here, we propose a method for covalent coupling of DNA strands in such structures by the formation of disulfide bonds; this allows disassembly of the structure under reducing conditions. The dynamic chemistry of disulfides and thiols was applied to crosslink DNA strands with terminal disulfide modifications. The formation of disulfide-linked DNA duplexes consisting of three strands is demonstrated, as well as a more-complex DNA double-crossover tile. All the strands in the fully disulfide-linked structures are covalently and geometrically interlocked, and it is demonstrated that the structures are stable under heating and in the presence of denaturants. Such a reversible system can be exploited in applications where higher DNA stability is needed only temporarily, such as delivery of cargoes to cells by DNA nanostructures. PMID:26994867

  15. Enlightening the photoactive site of channelrhodopsin-2 by DNP-enhanced solid-state NMR spectroscopy

    PubMed Central

    Becker-Baldus, Johanna; Bamann, Christian; Saxena, Krishna; Gustmann, Henrik; Brown, Lynda J.; Brown, Richard C. D.; Reiter, Christian; Bamberg, Ernst; Wachtveitl, Josef; Schwalbe, Harald; Glaubitz, Clemens

    2015-01-01

    Channelrhodopsin-2 from Chlamydomonas reinhardtii is a light-gated ion channel. Over recent years, this ion channel has attracted considerable interest because of its unparalleled role in optogenetic applications. However, despite considerable efforts, an understanding of how molecular events during the photocycle, including the retinal trans-cis isomerization and the deprotonation/reprotonation of the Schiff base, are coupled to the channel-opening mechanism remains elusive. To elucidate this question, changes of conformation and configuration of several photocycle and conducting/nonconducting states need to be determined at atomic resolution. Here, we show that such data can be obtained by solid-state NMR enhanced by dynamic nuclear polarization applied to 15N-labeled channelrhodopsin-2 carrying 14,15-13C2 retinal reconstituted into lipid bilayers. In its dark state, a pure all-trans retinal conformation with a stretched C14-C15 bond and a significant out-of-plane twist of the H-C14-C15-H dihedral angle could be observed. Using a combination of illumination, freezing, and thermal relaxation procedures, a number of intermediate states was generated and analyzed by DNP-enhanced solid-state NMR. Three distinct intermediates could be analyzed with high structural resolution: the early P1500 K-like state, the slowly decaying late intermediate P4480, and a third intermediate populated only under continuous illumination conditions. Our data provide novel insight into the photoactive site of channelrhodopsin-2 during the photocycle. They further show that DNP-enhanced solid-state NMR fills the gap for challenging membrane proteins between functional studies and X-ray–based structure analysis, which is required for resolving molecular mechanisms. PMID:26216996

  16. Photoactive metal carbonyl complexes as potential agents for targeted CO delivery.

    PubMed

    Gonzales, Margarita A; Mascharak, Pradip K

    2014-04-01

    The surprising discovery of carbon monoxide (CO) as a signaling molecule in mammalian physiology has recently raised interest in this toxic gas among researchers in biochemical and pharmaceutical community. CO is endogenously produced mainly from catabolism of heme by the enzyme heme oxygenase (HO) and participates in a myriad of anti-inflammatory, anti-proliferative, and vasoregulatory pathways. In animal models, low doses of CO have exhibited beneficial effects in suppression of organ graft rejection and safeguarding the heart during reperfusion after cardiopulmonary bypass surgery. The salutary effects of CO have naturally drawn attention of the pharmaceutical industry for its use as a cytoprotective agent. Safety-related concerns of the use of this noxious gas have prompted research in the area of syntheses of CO-releasing molecules (CORMs) and to date, several metal carbonyls (metal complexes of CO) have been employed as CORMs in promoting prolonged (and safe) delivery of low doses of CO to cellular targets. Because many carbonyl complexes release CO upon illumination, investigators have recently began to explore the possibility of "controlled CO delivery" through the use of light. During the past few years, a number of photoactive CORMs or "photoCORMs" have been synthesized that release CO upon illumination with UV or visible light. The utility of these photoCORMs in CO delivery has also been confirmed. Novel design principles for isolation of photoCORMs have started to appear in recent reports. Scrutiny of the literature reveals the emergence of a new exciting area of drug development in such efforts. The potential of photoCORMs as CO-donating pharmaceuticals along with a brief overview of the physiological roles of CO is presented in this review. PMID:24287103

  17. Hierarchical Organization of Organic Dyes and Protein Cages into Photoactive Crystals.

    PubMed

    Mikkilä, Joona; Anaya-Plaza, Eduardo; Liljeström, Ville; Caston, Jose R; Torres, Tomas; Escosura, Andrés de la; Kostiainen, Mauri A

    2016-01-26

    Phthalocyanines (Pc) are non-natural organic dyes with wide and deep impact in materials science, based on their intense absorption at the near-infrared (NIR), long-lived fluorescence and high singlet oxygen ((1)O2) quantum yields. However, Pcs tend to stack in buffer solutions, losing their ability to generate singlet oxygen, which limits their scope of application. Furthermore, Pcs are challenging to organize in crystalline structures. Protein cages, on the other hand, are very promising biological building blocks that can be used to organize different materials into crystalline nanostructures. Here, we combine both kinds of components into photoactive biohybrid crystals. Toward this end, a hierarchical organization process has been designed in which (a) a supramolecular complex is formed between octacationic zinc Pc (1) and a tetraanionic pyrene (2) derivatives, driven by electrostatic and π-π interactions, and (b) the resulting tetracationic complex acts as a molecular glue that binds to the outer surface anionic patches of the apoferritin (aFt) protein cage, inducing cocrystallization. The obtained ternary face-centered cubic (fcc) packed cocrystals, with diameters up to 100 μm, retain the optical properties of the pristine dye molecules, such as fluorescence at 695 nm and efficient light-induced (1)O2 production. Considering that (1)O2 is utilized in important technologies such as photodynamic therapy (PDT), water treatments, diagnostic arrays and as an oxidant in organic synthesis, our results demonstrate a powerful methodology to create functional biohybrid systems with unprecedented long-range order. This approach should greatly aid the development of nanotechnology and biomedicine. PMID:26691783

  18. On the Involvement of Single-Bond Rotation in the Primary Photochemistry of Photoactive Yellow Protein

    PubMed Central

    Stahl, Andreas D.; Hospes, Marijke; Singhal, Kushagra; van Stokkum, Ivo; van Grondelle, Rienk; Groot, Marie Louise; Hellingwerf, Klaas J.

    2011-01-01

    Prior experimental observations, as well as theoretical considerations, have led to the proposal that C4-C7 single-bond rotation may play an important role in the primary photochemistry of photoactive yellow protein (PYP). We therefore synthesized an analog of this protein's 4-hydroxy-cinnamic acid chromophore, (5-hydroxy indan-(1E)-ylidene)acetic acid, in which rotation across the C4-C7 single bond has been locked with an ethane bridge, and we reconstituted the apo form of the wild-type protein and its R52A derivative with this chromophore analog. In PYP reconstituted with the rotation-locked chromophore, 1), absorption spectra of ground and intermediate states are slightly blue-shifted; 2), the quantum yield of photochemistry is ∼60% reduced; 3), the excited-state dynamics of the chromophore are accelerated; and 4), dynamics of the thermal recovery reaction of the protein are accelerated. A significant finding was that the yield of the transient ground-state intermediate in the early phase of the photocycle was considerably higher in the rotation-locked samples than in the corresponding samples reconstituted with p-coumaric acid. In contrast to theoretical predictions, the initial photocycle dynamics of PYP were observed to be not affected by the charge of the amino acid residue at position 52, which was varied by 1), varying the pH of the sample between 5 and 10; and 2), site-directed mutagenesis to construct R52A. These results imply that C4-C7 single-bond rotation in PYP is not an alternative to C7=C8 double-bond rotation, in case the nearby positive charge of R52 is absent, but rather facilitates, presumably with a compensatory movement, the physiological Z/E isomerization of the blue-light-absorbing chromophore. PMID:21889456

  19. Towards artificial molecular motor-based electroactive/photoactive biomimetic muscles

    NASA Astrophysics Data System (ADS)

    Huang, Tony Jun

    2007-04-01

    Artificial molecular motors have recently attracted considerable interest from the nanoscience and nanoengineering community. These molecular-scale systems utilize a 'bottom-up' technology centered around the design and manipulation of molecular assemblies, and are potentially capable of delivering efficient actuations at dramatically reduced length scales when compared to traditional microscale actuators. When stimulated by light, electricity, or chemical reagents, a group of artificial molecular motors called bistable rotaxanes - which are composed of mutually recognizable and intercommunicating ring and dumbbell-shaped components - experience relative internal motions of their components just like the moving parts of macroscopic machines. Bistable rotaxanes' ability to precisely and cooperatively control mechanical motions at the molecular level reveals the potential of engineering systems that operate with the same elegance, efficiency, and complexity as biological motors function within the human body. We are in a process of developing a new class of bistable rotaxane-based electroactive/photoactive biomimetic muscles with unprecedented performance (strain: 40-60%, operating frequency: up to 1 MHz, energy density: ~50 J/cm 3, multi-stimuli: chemical, electricity, light). As a substantial step towards this longterm objective, we have proven, for the first time, that rotaxanes are mechanically switchable in condensed phases on solid substrates. We have further developed a rotaxane-powered microcantilever actuator utilizing an integrated approach that combines "bottom-up" assembly of molecular functionality with "top-down" micro/nano fabrication. By harnessing the nanoscale mechanical motion from artificial molecular machines and eliciting a nanomechanical response in a microscale device, this system mimics natural skeletal muscle and provides a key component for the development of nanoelectromechanical system (NEMS).

  20. Photoaffinity labeling of tubulin subunits with a photoactive analogue of vinblastine

    SciTech Connect

    Safa, A.R.; Hamel, E.; Felsted, R.L.

    1987-01-13

    A photoactive, radioactive analogue of vinblastine, N-(p-azido(3,5-/sup 3/H)benzoyl)-N'-(beta-amino-ethyl)vindesine (( /sup 3/H)NABV), was used to localize the Vinca alkaloid binding site(s) on calf brain tubulin after establishing that its in vitro interactions with tubulin were comparable to those of vinblastine. Microtubule assembly was inhibited by 50% with 2 microM NABV or vinblastine. At higher drug concentrations, NABV and vinblastine both induced tubulin aggregation, and both drugs inhibited tubulin-dependent GTP hydrolysis. Vinblastine and NABV inhibited each other's binding to tubulin, but the binding of neither drug was inhibited by colchicine. Two classes of binding sites for NABV and vinblastine were found on calf brain tubulin. High-affinity sites had apparent KD values of 4.2 and 0.54 microM for NABV and vinblastine, respectively, whereas the low-affinity binding sites showed apparent KD values of 26 and 14 microM for NABV and vinblastine, respectively. Mixtures of tubulin and (/sup 3/H)NABV were irradiated at 302 nm and analyzed for incorporation of radioactivity into protein. Photolabeling of both the alpha- and beta-subunits of tubulin with increasing concentrations of (/sup 3/H)NABV exhibited a biphasic pattern characteristic of specific and nonspecific reactions. Nonspecific labeling was determined in the presence of excess vinblastine. Saturable specific covalent incorporation into both subunits of tubulin was observed, with an alpha:beta ratio of 3:2 and maximum saturable incorporation of 0.086 and 0.056 mol of (/sup 3/H)NABV/mol of alpha-tubulin and beta-tubulin, respectively. Such photolabeling of the tubulin subunits will permit precise localization of Vinca alkaloid binding sites, including identification of the amino acid residues involved, an essential requirement for understanding the interactions of these drugs with tubulin.

  1. Structural changes in the photoactive site of proteorhodopsin during the primary photoreaction.

    PubMed

    Bergo, Vladislav; Amsden, Jason J; Spudich, Elena N; Spudich, John L; Rothschild, Kenneth J

    2004-07-20

    Proteorhodopsin (PR), found in marine gamma-proteobacteria, is a newly discovered light-driven proton pump similar to bacteriorhodopsin (BR). Because of the widespread distribution of proteobacteria in the worldwide oceanic waters, this pigment may contribute significantly to the global solar energy input in the biosphere. We examined structural changes that occur during the primary photoreaction (PR --> K) of wild-type pigment and two mutants using low-temperature FTIR difference spectroscopy. Several vibrations detected in the 3500-3700 cm(-1) region are assigned on the basis of H(2)O --> H(2)(18)O exchange to the perturbation of one or more internal water molecules. Substitution of the negatively charged Schiff base counterion, Asp97, with the neutral asparagine caused a downshift of the ethylenic (C=C) and Schiff base (C=N) stretching modes, in agreement with the 27 nm red shift of the visible lambda(max). However, this replacement did not alter the normal all-trans to 13-cis isomerization of the chromophore or the environment of the detected water molecule(s). In contrast, substitution of Asn230, which is in a position to interact with the Schiff base, with Ala induces a 5 nm red shift of the visible lambda(max) and alters the PR chromophore structure, its isomerization to K, and the environment of the detected internal water molecules. The combination of FTIR and site-directed mutagenesis establishes that both Asp97 and Asn230 are perturbed during the primary phototransition. The environment of Asn230 is further altered during the thermal decay of K. These results suggest that significant differences exist in the conformational changes which occur in the photoactive sites of proteorhodopsin and bacteriorhodopsin during the primary photoreaction. PMID:15248764

  2. Unveiling the mechanism of photoinduced isomerization of the photoactive yellow protein (PYP) chromophore

    SciTech Connect

    Gromov, Evgeniy V.

    2014-12-14

    A detailed theoretical analysis, based on extensive ab initio second-order approximate coupled cluster calculations, has been performed for the S{sub 1} potential energy surface (PES) of four photoactive yellow protein (PYP) chromophore derivatives that are hydrogen bonded with two water molecules and differ merely in the carbonyl substituent. The main focus is put on contrasting the isomerization properties of these four species in the S{sub 1} excited state, related to torsion around the chromophore's single and double carbon-carbon bonds. The analysis provides evidence of the different isomerization behavior of these four chromophore complexes, which relates to the difference in their carbonyl substituents. While a stable double-bond torsion pathway exists on the S{sub 1} PES of the chromophores bearing the –O–CH{sub 3} and –NH{sub 2} substituents, this is not the case for the –S–CH{sub 3} and –CH{sub 3} substituted species. The presence of the –S–CH{sub 3} group leads to a strong instability of the chromophore with respect to the single-bond twist, whereas in the case of the –CH{sub 3} substituent a crossing of the S{sub 1} and S{sub 2} PESs occurs, which perturbs the pathway. Based on this analysis, the key factors that support the double-bond torsion have been identified. These are (i) the hydrogen bonds at the phenolic oxygen of the chromophore, (ii) the weak electron-acceptor character of the carbonyl group, and (iii) the ethylene-like pattern of the torsion in the beginning of the process. Our results suggest that the interplay between these factors determines the chromophore's isomerization in the solvent environment and in the native PYP environment.

  3. Transfer Printed P3HT/PCBM Photoactive Layers: From Material Intermixing to Device Characteristics.

    PubMed

    Abdellah, Alaa; Falco, Aniello; Schwarzenberger, Ulrich; Scarpa, Giuseppe; Lugli, Paolo

    2016-02-01

    The fabrication of organic electronic devices involving complex stacks of solution-processable functional materials has proven challenging. Significant material intermixing often occurs as a result of cross-solubility and postdeposition treatments, rendering the realization of even the simplest bilayer architectures rather cumbersome. In this study we investigate the feasibility of a dry transfer printing process for producing abrupt bilayer organic photodiodes (OPDs) and the effect of thermal annealing on the integrity of the bilayer. The process involves the transfer of readily deposited thin films of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) using a polydimethylsiloxane (PDMS) stamp. Fabricated structures are characterized by means of cross-sectional scanning electron microscopy (SEM), UV/vis absorption spectroscopy, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Joint consideration of all results unveils abrupt interfaces with no thermal treatment applied and significant material intermixing for samples annealed above 100 °C. The role of the thermally assisted intermixing in determining the performance of complete devices is evaluated through the comparison of J-V characteristics and external quantum efficiencies (EQEs) of identical photodiodes subject to different annealing conditions. It is shown that the performance of such devices approaches the one of bulk heterojunction photodiodes upon thermal annealing at 140 °C for 5 min. Our results demonstrate that transfer printing is a reliable and simple process for the realization of functional multilayers, paving the way for organic electronic devices incorporating complex stacks. It further contributes to a fundamental understanding of material composition within photoactive layers by elucidating the process of thermally assisted intermixing. PMID:26754413

  4. How Robust are Semiconductor Nanorods? Investigating the Stability and Chemical Decomposition Pathways of Photoactive Nanocrystals

    SciTech Connect

    Reichert, Malinda D; Lin, Chia-Cheng; Vela, Javier

    2014-07-08

    Anisotropic II–VI semiconductor nanostructures are important photoactive materials for various energy conversion and optical applications. However, aside from the many available surface chemistry studies and from their ubiquitous photodegradation under continuous illumination, the general chemical reactivity and thermal stability (phase and shape transformations) of these materials are poorly understood. Using CdSe and CdS nanorods as model systems, we have investigated the behavior of II–VI semiconductor nanorods against various conditions of extreme chemical and physical stress (acids, bases, oxidants, reductants, and heat). CdSe nanorods react rapidly with acids, becoming oxidized to Se or SeO2. In contrast, CdSe nanorods remain mostly unreactive when treated with bases or strong oxidants, although bases do partially etch the tips of the nanorods (along their axis). Roasting (heating in air) of CdSe nanorods results in rock-salt CdO, but neither CdSe nor CdO is easily reduced by hydrogen (H2). Another reductant, n-BuLi, reduces CdSe nanorods to metallic Cd. Variable temperature X-ray diffraction experiments show that axial annealing and selective axial melting of the nanorods precede particle coalescence. Furthermore, thermal analysis shows that the axial melting of II–VI nanorods is a ligand-dependent process. In agreement with chemical reactivity and thermal stability observations, silica-coating experiments show that the sharpest (most curved) II–VI surfaces are most active against heterogeneous nucleation of a silica shell. These results provide valuable insights into the fate and possible ways to enhance the stability and improve the use of II–VI semiconductor nanostructures in the fields of optics, magnetism, and energy conversion.

  5. Toxicologic evaluation of tungsten: 28-day inhalation study of tungsten blue oxide in rats.

    PubMed

    Rajendran, Narayanan; Hu, Shu-Chieh; Sullivan, Dennis; Muzzio, Miguel; Detrisac, Carol J; Venezia, Carmen

    2012-12-01

    The toxicity and toxicokinetics of tungsten blue oxide (TBO) were examined. TBO is an intermediate in the production of tungsten powder, and has shown the potential to cause cellular damage in in vitro studies. However, in vivo evidence seems to indicate a lack of adverse effects. The present study was undertaken to address the dearth of longer-term inhalation toxicity studies of tungsten oxides by investigating the biological responses induced by TBO when administered via nose-only inhalation to rats at levels of 0.08, 0.325, and 0.65 mg TBO/L of air for 6 h/day for 28 consecutive days, followed by a 14-day recovery period. Inhaled TBO was absorbed systemically and blood levels of tungsten increased as inhaled concentration increased. Among the tissues analyzed for tungsten levels, lung, femur and kidney showed increased levels, with lung at least an order of magnitude greater than kidney or femur. By exposure day 14, tungsten concentration in tissues had reached steady-state. Increased lung weight was noted for both terminal and recovery animals and was attributed to deposition of TBO in the lungs, inducing a macrophage influx. Microscopic evaluation of tissues revealed a dose-related increase in alveolar pigmented macrophages, alveolar foreign material and individual alveolar foamy macrophages in lung. After a recovery period there was a slight reduction in the incidence and severity of histopathological findings. Based on the absence of other adverse effects, the increased lung weights and the microscopic findings were interpreted as nonadverse response to exposure and were not considered a specific reaction to TBO. PMID:23216159

  6. Cell-free synthesis system suitable for disulfide-containing proteins

    SciTech Connect

    Matsuda, Takayoshi; Watanabe, Satoru; Kigawa, Takanori

    2013-02-08

    Highlights: ► Cell-free synthesis system suitable for disulfide-containing proteins is proposed. ► Disulfide bond formation was facilitated by the use of glutathione buffer. ► DsbC catalyzed the efficient shuffling of incorrectly formed disulfide bonds. ► Milligram quantities of functional {sup 15}N-labeled BPTI and lysozyme C were obtained. ► Synthesized proteins were both catalytically functional and properly folded. -- Abstract: Many important therapeutic targets are secreted proteins with multiple disulfide bonds, such as antibodies, cytokines, hormones, and proteases. The preparation of these proteins for structural and functional analyses using cell-based expression systems still suffers from several issues, such as inefficiency, low yield, and difficulty in stable-isotope labeling. The cell-free (or in vitro) protein synthesis system has become a useful protein production method. The openness of the cell-free system allows direct control of the reaction environment to promote protein folding, making it well suited for the synthesis of disulfide-containing proteins. In this study, we developed the Escherichia coli (E. coli) cell lysate-based cell-free synthesis system for disulfide-containing proteins, which can produce sufficient amounts of functional proteins for NMR analyses. Disulfide bond formation was facilitated by the use of glutathione buffer. In addition, disulfide isomerase, DsbC, catalyzed the efficient shuffling of incorrectly formed disulfide bonds during the protein synthesis reaction. We successfully synthesized milligram quantities of functional {sup 15}N-labeled higher eukaryotic proteins, bovine pancreatic trypsin inhibitor (BPTI) and human lysozyme C (LYZ). The NMR spectra and functional analyses indicated that the synthesized proteins are both catalytically functional and properly folded. Thus, the cell-free system is useful for the synthesis of disulfide-containing proteins for structural and functional analyses.

  7. Intradomain Confinement of Disulfides in the Folding of Two Consecutive Modules of the LDL Receptor

    PubMed Central

    Martínez-Oliván, Juan; Fraga, Hugo; Arias-Moreno, Xabier; Ventura, Salvador; Sancho, Javier

    2015-01-01

    The LDL receptor internalizes circulating LDL and VLDL particles for degradation. Its extracellular binding domain contains ten (seven LA and three EGF) cysteine-rich modules, each bearing three disulfide bonds. Despite the enormous number of disulfide combinations possible, LDLR oxidative folding leads to a single native species with 30 unique intradomain disulfides. Previous folding studies of the LDLR have shown that non native disulfides are initially formed that lead to compact species. Accordingly, the folding of the LDLR has been described as a "coordinated nonvectorial” reaction, and it has been proposed that early compaction funnels the reaction toward the native structure. Here we analyze the oxidative folding of LA4 and LA5, the modules critical for ApoE binding, isolated and in the LA45 tandem. Compared to LA5, LA4 folding is slow and inefficient, resembling that of LA5 disease-linked mutants. Without Ca++, it leads to a mixture of many two-disulfide scrambled species and, with Ca++, to the native form plus two three-disulfide intermediates. The folding of the LA45 tandem seems to recapitulate that of the individual repeats. Importantly, although the folding of the LA45 tandem takes place through formation of scrambled isomers, no interdomain disulfides are detected, i.e. the two adjacent modules fold independently without the assistance of interdomain covalent interactions. Reduction of incredibly large disulfide combinatorial spaces, such as that in the LDLR, by intradomain confinement of disulfide bond formation might be also essential for the efficient folding of other homologous disulfide-rich receptors. PMID:26168158

  8. In-Depth Characterization of Protein Disulfide Bonds by Online Liquid Chromatography-Electrochemistry-Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Switzar, Linda; Nicolardi, Simone; Rutten, Julie W.; Oberstein, Saskia A. J. Lesnik; Aartsma-Rus, Annemieke; van der Burgt, Yuri E. M.

    2016-01-01

    Disulfide bonds are an important class of protein post-translational modifications, yet this structurally crucial modification type is commonly overlooked in mass spectrometry (MS)-based proteomics approaches. Recently, the benefits of online electrochemistry-assisted reduction of protein S-S bonds prior to MS analysis were exemplified by successful characterization of disulfide bonds in peptides and small proteins. In the current study, we have combined liquid chromatography (LC) with electrochemistry (EC) and mass analysis by Fourier transform ion cyclotron resonance (FTICR) MS in an online LC-EC-MS platform to characterize protein disulfide bonds in a bottom-up proteomics workflow. A key advantage of a LC-based strategy is the use of the retention time in identifying both intra- and interpeptide disulfide bonds. This is demonstrated by performing two sequential analyses of a certain protein digest, once without and once with electrochemical reduction. In this way, the "parent" disulfide-linked peptide detected in the first run has a retention time-based correlation with the EC-reduced peptides detected in the second run, thus simplifying disulfide bond mapping. Using this platform, both inter- and intra-disulfide-linked peptides were characterized in two different proteins, ß-lactoglobulin and ribonuclease B. In order to prevent disulfide reshuffling during the digestion process, proteins were digested at a relatively low pH, using (a combination of) the high specificity proteases trypsin and Glu-C. With this approach, disulfide bonds in ß-lactoglobulin and ribonuclease B were comprehensively identified and localized, showing that online LC-EC-MS is a useful tool for the characterization of protein disulfide bonds.

  9. Conformational analysis and design of cross-strand disulfides in antiparallel β-sheets.

    PubMed

    Indu, S; Kochat, V; Thakurela, S; Ramakrishnan, C; Varadarajan, Raghavan

    2011-01-01

    Cross-strand disulfides bridge two cysteines in a registered pair of antiparallel β-strands. A nonredundant data set comprising 5025 polypeptides containing 2311 disulfides was used to study cross-strand disulfides. Seventy-six cross-strand disulfides were found of which 75 and 1 occurred at non-hydrogen-bonded (NHB) and hydrogen-bonded (HB) registered pairs, respectively. Conformational analysis and modeling studies demonstrated that disulfide formation at HB pairs necessarily requires an extremely rare and positive χ¹ value for at least one of the cysteine residues. Disulfides at HB positions also have more unfavorable steric repulsion with the main chain. Thirteen pairs of disulfides were introduced in NHB and HB pairs in four model proteins: leucine binding protein (LBP), leucine, isoleucine, valine binding protein (LIVBP), maltose binding protein (MBP), and Top7. All mutants LIVBP T247C V331C showed disulfide formation either on purification, or on treatment with oxidants. Protein stability in both oxidized and reduced states of all mutants was measured. Relative to wild type, LBP and MBP mutants were destabilized with respect to chemical denaturation, although the sole exposed NHB LBP mutant showed an increase of 3.1°C in T(m). All Top7 mutants were characterized for stability through guanidinium thiocyanate chemical denaturation. Both exposed and two of the three buried NHB mutants were appreciably stabilized. All four HB Top7 mutants were destabilized (ΔΔG⁰ = -3.3 to -6.7 kcal/mol). The data demonstrate that introduction of cross-strand disulfides at exposed NHB pairs is a robust method of improving protein stability. All four exposed Top7 disulfide mutants showed mild redox activity. PMID:21058397

  10. The Disulfide Bonds within BST-2 Enhance Tensile Strength during Viral Tethering.

    PubMed

    Du Pont, Kelly E; McKenzie, Aidan M; Kokhan, Oleksandr; Sumner, Isaiah; Berndsen, Christopher E

    2016-02-16

    Human BST-2/tetherin is a host factor that inhibits the release of enveloped viruses, including HIV-1, HIV-2, and SIV, from the cell surface by tethering viruses to the host cell membrane. BST-2 has an α-helical ectodomain that forms disulfide-linked dimers between two monomers forming a coiled coil. The ectodomain contains three cysteine residues that can participate in disulfide bond formation and are critical for viral tethering. The role of the disulfides in viral tethering is unknown but proposed to be for maintaining the dimer. We explored the role of the disulfides in the structure of BST-2 using experimental, biophysical methods. To understand the role of the disulfides in viral tethering, we used a new approach in viral tethering, steered molecular dynamics. We find that the disulfides coordinate the unfolding of the BST-2 monomers, which adds tensile strength to the coiled coil. Structural differences between oxidized and reduced BST-2 are apparent during unfolding, showing the monomers slide past each other in the absence of the disulfides. We found no evidence to support dissociation of the dimer upon reduction of the disulfide bonds. Moreover, the structure of BST-2 in the absence of the disulfides is similar to that of the oxidized form of BST-2, supporting previous X-ray crystallography and cellular work that showed the disulfides are not required for expression of BST-2. These data provide new insights into viral tethering by using novel techniques in the analysis of BST-2 to give amino acid level insight into functions of BST-2. PMID:26789136

  11. Disulfide structures of highly bridged peptides: a new strategy for analysis.

    PubMed Central

    Gray, W. R.

    1993-01-01

    A new approach is described for analyzing disulfide linkage patterns in peptides containing tightly clustered cystines. Such peptides are very difficult to analyze with traditional strategies, which require that the peptide chain be split between close or adjacent Cys residues. The water-soluble tris-(2-carboxyethyl)-phosphine (TCEP) reduced disulfides at pH 3, and partially reduced peptides were purified by high performance liquid chromatography with minimal thiol-disulfide exchange. Alkylation of free thiols, followed by sequencer analysis, provided explicit assignment of disulfides that had been reduced. Thiol-disulfide exchange occurred during alkylation of some peptides, but correct deductions were still possible. Alkylation competed best with exchange when peptide solution was added with rapid mixing to 2.2 M iodoacetamide. Variants were developed in which up to three alkylating agents were used to label different pairs of thiols, allowing a full assignment in one sequencer analysis. Model peptides used included insulin (three bridges, intra- and interchain disulfides; -Cys.Cys- pair), endothelin and apamin (two disulfides; -Cys.x.Cys- pair), conotoxin GI and isomers (two disulfides; -Cys.Cys- pair), and bacterial enterotoxin (three bridges within 13 residues; two -Cys.Cys- pairs). With insulin, all intermediates in the reduction pathway were identified; with conotoxin GI, analysis was carried out successfully for all three disulfide isomers. In addition to these known structures, the method has been applied successfully to the analysis of several previously unsolved structures of similar complexity. Rates of reduction of disulfide bonds varied widely, but most peptides did not show a strongly preferred route for reduction. PMID:8251945

  12. Experimental setup for tungsten transport studies at the NSTX tokamak

    SciTech Connect

    Clementson, J.; Beiersdorfer, P.; Roquemore, A. L.; Skinner, C. H.; Mansfield, D. K.; Hartzfeld, K.; Lepson, J. K.

    2010-10-15

    Tungsten particles have been introduced into the National Spherical Torus Experiment (NSTX) in Princeton with the purpose to investigate the effects of tungsten injection on subsequent plasma discharges. An experimental setup for the study of tungsten particle transport is described where the particles are introduced into the tokamak using a modified particle dropper, otherwise used for lithium-powder injection. An initial test employing a grazing-incidence extreme ultraviolet spectrometer demonstrates that the tungsten-transport setup could serve to infer particle transport from the edge to the hot central plasmas of NSTX.

  13. Femtosecond laser-induced periodic surface structure formation on tungsten

    SciTech Connect

    Vorobyev, A. Y.; Guo Chunlei

    2008-09-15

    In this paper, we demonstrate the generation of periodic surface structures on a technologically important material, tungsten, at both 400 and 800 nm, despite that the table values of dielectric constants for tungsten at these two wavelengths suggest the absence of surface plasmons, a wave necessary for forming periodic structures on metals. Furthermore, we find that the structure periods formed on tungsten are significantly less than the laser wavelengths. We believe that the dielectric constants of tungsten change significantly due to intense laser pulse heating and surface structuring and roughening at nanometer scales, permitting surface plasmon excitation and periodic structure formation.

  14. A visible light-sensitive tungsten carbide/tungsten trioxde composite photocatalyst

    SciTech Connect

    Kim, Young-ho; Irie, Hiroshi; Hashimoto, Kazuhito

    2008-05-05

    A photocatalyst composed of tungsten carbide (WC) and tungsten oxide (WO{sub 3}) has been prepared by the mechanical mixing of each powder. Its photocatalytic activity was evaluated by the gaseous isopropyl alcohol decomposition process. The photocatalyst showed high visible light photocatalytic activity with a quantum efficiency of 3.2% for 400-530 nm light. The photocatalytic mechanism was explained by means of enhanced oxygen reduction reaction due to WC, which may serve as a multielectron reduction catalyst, as well as the photogeneration of holes in the valence band of WO{sub 3}.

  15. Characterization of IgG2 Disulfide Bonds with LC/MS/MS and Postcolumn Online Reduction.

    PubMed

    Liu, Hongji; Lei, Qing Paula; Washabaugh, Michael

    2016-05-17

    The complication of IgG2 disulfide connections demands advances in techniques for disulfide bond determination. We have developed a new LC/MS/MS method for improved disulfide analysis. With postcolumn introduction of dithiothreitol (DTT) and ammonium hydroxide, each disulfide-containing peptide eluted out of LC in an acidic mobile phase can be rapidly reduced prior to MS analysis. The reduction can be driven to near completion. The reagents are MS-friendly, and the reaction occurs at no cost of separation (little is added to the postcolumn dead volume of the LC system). Comparing LC/MS data with and without online reduction, a direct correlation can be established between a disulfide peptide and its composing peptides using retention time. With disulfide online removal, high-quality MS/MS fragmentation data can be acquired and allows for definitive determination of the disulfide peptide. This technique is especially valuable in determining the disulfide bond linkage of complicated molecules such as the hinge-containing disulfide peptides produced from IgG2 disulfide isoforms. Due to over/under enzymatic cleavages, multiple hinge-containing disulfide peptides are produced from each isoform. Twenty-two hinge-containing disulfide peptides in total have been confidently identified with this technique. Without the method, successful identification to many of these peptides would have become extremely difficult. PMID:27111505

  16. Evaluation of disulfide scrambling during the enzymatic digestion of bevacizumab at various pH values using mass spectrometry.

    PubMed

    Sung, Wang-Chou; Chang, Chiung-Wen; Huang, Sheng-Yu; Wei, Ting-Yu; Huang, Yi-Li; Lin, Yu-Hua; Chen, Han-Min; Chen, Sung-Fang

    2016-09-01

    Disulfide linkages play an important role in protein stability and activity. Thus, it is critical to characterize disulfide bonds to ensure the quality and function of protein pharmaceuticals. There are, however, problems associated with maintaining disulfide linkages in the conventional procedures that are used to digest a protein. In order to preserve enzyme activity during the digestion of a protein, it is commonly carried out at neutral to basic environment which increases the possibilities of disulfide bond scrambling. However, it is not easy to differentiate whether the scrambled disulfide linkages are initiated by the sample itself or whether they are induced during the protease digestion process. In this study, the optimum pH for minimizing disulfide bond rearrangements during the digestion process was determined. Three sets of proteases, trypsin plus Glu-C, Lys-C and thermolysin were used, followed by dimethyl labeling and mass spectrometry for a bevacizumab (Avastin) disulfide linkage analysis. No disulfide linkage scrambling was detected at pH6 when Lys-C or trypsin plus Glu-C were used as enzymes. When thermolysin was applied, some scrambled disulfide bonds were identified at pH5, 6 and 7. Nevertheless, there was less disulfide bond scrambling at a lower pH. All correct disulfide bonds on bevacizumab could be identified using this approach. The results demonstrated that by choosing the proper enzymes, using a lower pH environment for the digestion could reduce the degree of artifact disulfide scrambling. PMID:27238563

  17. Boron carbide coating deposition on tungsten and testing of tungsten layers and coating under intense plasma load

    NASA Astrophysics Data System (ADS)

    Airapetov, A. A.; Begrambekov, L. B.; Buzhinskiy, O. I.; Grunin, A. V.; Gordeev, A. A.; Zakharov, A. M.; Kalachev, A. M.; Sadovskiy, Ya. A.; Shigin, P. A.

    2015-12-01

    A device intended for boron carbide coating deposition and material testing under high heat loads is presented. A boron carbide coating 5 μm thick was deposited on the tungsten substrate. These samples were subjected to thermocycling loads in the temperature range of 400-1500°C. Tungsten layers deposited on tungsten substrates were tested in similar conditions. Results of the surface analysis are presented.

  18. Boron carbide coating deposition on tungsten and testing of tungsten layers and coating under intense plasma load

    SciTech Connect

    Airapetov, A. A.; Begrambekov, L. B.; Buzhinskiy, O. I.; Grunin, A. V.; Gordeev, A. A.; Zakharov, A. M.; Kalachev, A. M.; Sadovskiy, Ya. A.; Shigin, P. A.

    2015-12-15

    A device intended for boron carbide coating deposition and material testing under high heat loads is presented. A boron carbide coating 5 μm thick was deposited on the tungsten substrate. These samples were subjected to thermocycling loads in the temperature range of 400–1500°C. Tungsten layers deposited on tungsten substrates were tested in similar conditions. Results of the surface analysis are presented.

  19. A conserved disulfide motif in human tear lipocalins influences ligand binding.

    PubMed

    Glasgow, B J; Abduragimov, A R; Yusifov, T N; Gasymov, O K; Horwitz, J; Hubbell, W L; Faull, K F

    1998-02-24

    Structural and functional characteristics of the disulfide motif have been determined for tear lipocalins, members of a novel group of proteins that carry lipids. Amino acid sequences for two of the six isolated isoforms were assigned by a comparison of molecular mass measurements with masses calculated from the cDNA-predicted protein sequence and available N-terminal protein sequence data. A third isoform was tentatively sequence assigned using the same criteria. The most abundant isoform has a measured mass of 17 446.3 Da, consistent with residues 19-176 of the putative precursor (calculated mass 17 445.8 Da). Chemical derivatization of native and reduced/denatured protein confirmed the presence of a single intramolecular disulfide bond in the native protein. Reactivity of native, reduced, and denatured protein with 4-pyridine disulfide and dithiobis(2-nitrobenzoic acid) indicated that access to the free cysteine is markedly restricted by the intact disulfide bridge. Mass measurements of tryptic fragments identified C119 as the free cysteine and showed that the single intramolecular disulfide bond joined residues C79 and C171. Circular dichroism indicated that tear lipocalins have a predominant beta-pleated sheet structure (44%) that is essentially retained after reduction of the disulfide bond. Circular dichroism in the far-UV showed reduced molecular asymmetry and enhanced urea-induced unfolding with disulfide reduction indicative of relaxation of protein structure. Circular dichroism in the near-UV shows that the disulfide bond contributes to the asymmetry of aromatic sites. The effect of disulfide reduction on ligand binding was monitored using the intrinsic optical activity of bound retinol. The intact disulfide bond diminishes the affinity of tear lipocalins for retinol and restricts the displacement of native lipids by retinol. Disulfide reduction is accompanied by a dramatic alteration in ligand-induced conformational changes that involves aromatic

  20. Photoactivity of g-C3 N4 /S-Doped Porous Carbon Composite: Synergistic Effect of Composite Formation.

    PubMed

    Seredych, Mykola; Łoś, Szymon; Giannakoudakis, Dimitrios A; Rodríguez-Castellón, Enrique; Bandosz, Teresa J

    2016-04-21

    A composite of g-C3 N4 with visible-light photoactive S-doped carbon was synthesized. Synergistic effects in surface chemistry and electrical conductivity, and a decrease in the band gap (Eg , estimated from optical measurements) from 2.91 eV for g-C3 N4 to 2.79 eV for the composite were found. Both the carbon and the composite showed photosensitivity but only the composite revealed a visible-light-driven reduction activity. PMID:26990914

  1. Selective and efficient electrochemical biosensing of ultrathin molybdenum disulfide sheets

    NASA Astrophysics Data System (ADS)

    Narayanan, Tharangattu N.; Vusa, Chiranjeevi S. R.; Alwarappan, Subbiah

    2014-08-01

    Atomically thin molybdenum disulfide (MoS2) sheets were synthesized and isolated via solvent-assisted chemical exfoliation. The charge-dependent electrochemical activities of these MoS2 sheets were studied using positively charged hexamine ruthenium (III) chloride and negatively charged ferricyanide/ferrocyanide redox probes. Ultrathin MoS2 sheet-based electrodes were employed for the electrochemical detection of an important neurotransmitter, namely dopamine (DA), in the presence of ascorbic acid (AA). MoS2 electrodes were identified as being capable of distinguishing the coexistence of the DA and the AA with an excellent stability. Moreover, the enzymatic detection of the glucose was studied by immobilizing glucose oxidase on the MoS2. This study opens enzymatic and non-enzymatic electrochemical biosensing applications of atomic MoS2 sheets, which will supplement their established electronic applications.

  2. Insulator-metal transition of highly compressed carbon disulfide

    SciTech Connect

    Dias, Ranga P.; Yoo, Choong-Shik; Kim, Minseob; Tse, John S.

    2012-04-24

    We present integrated spectral, structural, resistance, and theoretical evidences for simple molecular CS{sub 2} transformations to an insulating black polymer with threefold carbon atoms at 9 GPa, then to a semiconducting polymer above 30 GPa, and finally to a metallic solid above 50 GPa. The metallic phase is a highly disordered three-dimensional network structure with fourfold carbon atoms at the carbon-sulfur distance of {approx}1.70 {angstrom}. Based on first-principles calculations, we present two plausible structures for the metallic phase: {alpha}-chalcopyrite and tridymite, both of which exhibit metallic ground states and disordered diffraction features similar to that measured. We also present the phase and chemical transformation diagram for carbon disulfide, showing a large stability field of the metallic phase to 100 GPa and 800 K.

  3. On the Formation of Cometary Carbon Disulfide (CS2)

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie; Moore, marla; Ferrante, Robert F.

    2009-01-01

    The formation of cometary CS molecules from carbon disulfide, CS2 , was proposed about 20 years before the latter's detection in comet 122P/de Vico by Jackson et al. (2002). However, the origin of CS2 has received little attention from either experimentalists or theorists. As part of our on-going laboratory program to investigate cometary molecules we have examined chemical reactions that lead to CS2 in the solid state. Icy mixtures of known cometary molecules were proton irradiated near 10 K to doses of several eV per molecule. Mid-IR spectroscopy was used as an in situ probe to record both CS2 formation in the ices and the destruction of precursors. We find that the most likely route to cometary CS2 is through OCS by way of the S + CO reaction.

  4. Wet chemical thinning of molybdenum disulfide down to its monolayer

    SciTech Connect

    Amara, Kiran Kumar; Chu, Leiqiang; Kumar, Rajeev; Toh, Minglin; Eda, Goki

    2014-09-01

    We report on the preparation of mono- and bi-layer molybdenum disulfide (MoS{sub 2}) from a bulk crystal by facile wet chemical etching. We show that concentrated nitric acid (HNO{sub 3}) effectively etches thin MoS{sub 2} crystals from their edges via formation of MoO{sub 3}. Interestingly, etching of thin crystals on a substrate leaves behind unreacted mono- and bilayer sheets. The flakes obtained by chemical etching exhibit electronic quality comparable to that of mechanically exfoliated counterparts. Our findings indicate that the self-limiting chemical etching is a promising top-down route to preparing atomically thin crystals from bulk layer compounds.

  5. Temperature effect on optical spectra of monolayer molybdenum disulfide

    NASA Astrophysics Data System (ADS)

    Soklaski, Ryan; Liang, Yufeng; Yang, Li

    2014-05-01

    Recently, measured optical absorption and photoluminescence spectra reveal substantial frequency shifts of both exciton and trion peaks as monolayer molybdenum disulfide, MoS2, is cooled from 363 K to 4 K. First-principles simulations using the GW-Bethe-Salpeter equation approach satisfactorily reproduce these frequency shifts by incorporating the thermal expansion effect. Studying these temperature effects in monolayer MoS2 is crucial for rectifying the results of available experiments with the previous predictions of zero-temperature-limit simulations. Moreover, our estimated thermal expansion coefficient of monolayer MoS2 is less than that of bulk counterpart by tracking the frequency shifts of the exciton peaks in optical spectra. This may serve as a convenient way to estimate thermal expansion coefficients of general two-dimensional chalcogenides.

  6. High Performance Molybdenum Disulfide Amorphous Silicon Heterojunction Photodetector

    PubMed Central

    Esmaeili-Rad, Mohammad R.; Salahuddin, Sayeef

    2013-01-01

    One important use of layered semiconductors such as molybdenum disulfide (MoS2) could be in making novel heterojunction devices leading to functionalities unachievable using conventional semiconductors. Here we demonstrate a metal-semiconductor-metal heterojunction photodetector, made of MoS2 and amorphous silicon (a-Si), with rise and fall times of about 0.3 ms. The transient response does not show persistent (residual) photoconductivity, unlike conventional a-Si devices where it may last 3–5 ms, thus making this heterojunction roughly 10X faster. A photoresponsivity of 210 mA/W is measured at green light, the wavelength used in commercial imaging systems, which is 2−4X larger than that of a-Si and best reported MoS2 devices. The device could find applications in large area electronics, such as biomedical imaging, where a fast response is critical. PMID:23907598

  7. Peptide Bond Formation in Water Mediated by Carbon Disulfide.

    PubMed

    Leman, Luke J; Huang, Zheng-Zheng; Ghadiri, M Reza

    2015-09-01

    Demonstrating plausible nonenzymatic polymerization mechanisms for prebiotic monomers represents a fundamental goal in prebiotic chemistry. While a great deal is now known about the potentially prebiotic synthesis of amino acids, our understanding of abiogenic polymerization processes to form polypeptides is less well developed. Here, we show that carbon disulfide (CS2), a component of volcanic emission and sulfide mineral weathering, and a widely used synthetic reagent and solvent, promotes peptide bond formation in modest yields (up to ∼20%) from α-amino acids under mild aqueous conditions. Exposure of a variety of α-amino acids to CS2 initially yields aminoacyl dithiocarbamates, which in turn generate reactive 2-thiono-5-oxazolidone intermediates, the thio analogues of N-carboxyanhydrides. Along with peptides, thiourea and thiohydantoin species are produced. Amino acid stereochemistry was preserved in the formation of peptides. Our findings reveal that CS2 could contribute to peptide bond formation, and possibly other condensation reactions, in abiogenic settings. PMID:26308392

  8. Temperature effect on optical spectra of monolayer molybdenum disulfide

    SciTech Connect

    Soklaski, Ryan; Liang, Yufeng; Yang, Li

    2014-05-12

    Recently, measured optical absorption and photoluminescence spectra reveal substantial frequency shifts of both exciton and trion peaks as monolayer molybdenum disulfide, MoS{sub 2}, is cooled from 363 K to 4 K. First-principles simulations using the GW-Bethe-Salpeter equation approach satisfactorily reproduce these frequency shifts by incorporating the thermal expansion effect. Studying these temperature effects in monolayer MoS{sub 2} is crucial for rectifying the results of available experiments with the previous predictions of zero-temperature-limit simulations. Moreover, our estimated thermal expansion coefficient of monolayer MoS{sub 2} is less than that of bulk counterpart by tracking the frequency shifts of the exciton peaks in optical spectra. This may serve as a convenient way to estimate thermal expansion coefficients of general two-dimensional chalcogenides.

  9. Microwave frequency effects on the photoactivity of TiO 2: Dielectric properties and the degradation of 4-chlorophenol, bisphenol A and methylene blue

    NASA Astrophysics Data System (ADS)

    Horikoshi, Satoshi; Sakai, Futoshi; Kajitani, Masatsugu; Abe, Masahiko; Serpone, Nick

    2009-03-01

    Microwave frequency (2.45 GHz and 5.8 GHz) effects on the photoactivity of P-25 TiO 2 were examined for the photodecomposition of 4-chlorophenol (4-CP), bisphenol A (BPA) and methylene blue (MB), and by the characterization of dielectric properties. Changes in microwave (MW) irradiation efficiency between water and the TiO 2 particulates were examined at two MW frequencies on the basis of penetration depth of the microwaves and the dielectric loss factor. TiO 2 particles in aqueous media were less photoactive under 5.8-GHz microwave radiation in degrading the organic substrates than under 2.45-GHz microwaves for otherwise identical temperature conditions. Factors that affect the photoactivity of TiO 2 at the two frequencies are briefly discussed.

  10. Cyclic disulfide C8 iminoporfiromycin: nucleophilic activation of a porfiromycin.

    PubMed

    Lee, Sang Hyup; Kohn, Harold

    2004-04-01

    The clinical success of mitomycin C (1) and its associated toxicities and resistance have led to efforts to prepare semisynthetic analogues (i.e., KW-2149 (3), BMS-181174 (4)) that have improved pharmacological profiles. In this study, we report the preparation and evaluation of the novel 7-N-(1'-amino-4',5'-dithian-2'-yl)porfiromycin C(8) cyclized imine (6) and its reference compound, 7-N-(1'-aminocyclohex-2'-yl)porfiromycin C(8) cyclized imine (13). Porfiromycin 6 contains a disulfide unit that, upon cleavage, may provide thiol(s) that affect drug reactivity. We demonstrated that phosphines dramatically accelerated 6 activation and solvolysis in methanolic solutions ("pH 7.4") compared with 13. Porfiromycins 6 and 13 efficiently cross-linked EcoRI-linearized pBR322 DNA upon addition of Et3P. We found enhanced levels of interstrand cross-link (ISC) adducts for 6 and 13 compared with porfiromycin (7) and that 6 was more efficient than 13. The large Et3P-mediated rate enhancements for the solvolysis of 6 compared with 13 and a N(7)-substituted analogue of 1, and the increased levels of ISC adducts for 6 compared with 13 and 7 are attributed to a nucleophile-assisted disulfide cleavage process that permits porfiromycin activation and nucleophile (MeOH, DNA) adduction. The in vitro antiproliferative activities of 6 and 13 using the A549 tumor cell line (lung adenocarcinoma) were determined under aerobic and hypoxic conditions and then compared with 7. Both 6 and 13 were more cytotoxic than 7, with 13 being more potent than 6. The C(8) iminoporfiromycins 6 and 13 displayed anticancer profiles similar to 3. PMID:15053618

  11. Disulfide bonds regulate binding of exogenous ligand to human cytoglobin.

    PubMed

    Tsujino, Hirofumi; Yamashita, Taku; Nose, Azusa; Kukino, Kaori; Sawai, Hitomi; Shiro, Yoshitsugu; Uno, Tadayuki

    2014-06-01

    Cytoglobin (Cgb) was discovered a decade ago and is a fourth member of the group of hexacoordinated globin-folded proteins. Although some crystal structures have been reported and several functions have been proposed for Cgb, its physiological role remains uncertain. In this study, we measured cyanide binding to the ferric state of the wild-type (WT) Cgb, and found that the binding consisted of multiple steps. These results indicated that Cgb may be comprised of several forms, and the presence of monomers, dimers, and tetramers was subsequently confirmed by SDS-PAGE. Remarkably, each species contained two distinguishable forms, and, in the monomer, analyses of alternative cysteine states suggested the presence of an intramolecular disulfide bond (monomer SS form) and a structure with unpaired thiol groups (monomer SH form). These confirmed that forms were separated by gel-exclusion chromatography, and that the cyanide binding of the separated fractions was again measured; they showed different affinities for cyanide, with the monomer fraction showing the highest affinity. In addition, the ferrous state in each fraction showed distinct carbon monoxide (CO)-binding properties, and the affinities for cyanide and CO suggested a linear correlation. Furthermore, we also prepared several variants involving the two cysteine residues. The C38S and C83S variants showed a binding affinity for cyanide similar to the value for the monomer SH form, and hence the fraction with the highest affinity for exogenous ligands was designated as a monomer SS form. We concluded that polymerization could be a mechanism that triggers the exertion of various physiological functions of this protein and that an appropriate disulfide bond between the two cysteine residues was critical for regulating the binding affinity of Cgb, which can act as a ROS scavenger, for exogenous ligands. PMID:24632414

  12. Solid-state chemistry route for supported tungsten and tungsten carbide nanoparticles

    SciTech Connect

    Hugot, N.; Desforges, A.; Fontana, S.; Mareche, J.F.; Herold, C.; Albiniak, A.

    2012-10-15

    Nanoparticles of tungsten and tungsten carbide have been prepared using solid-state chemistry methods. After the vapor phase impregnation of a tungsten hexachloride precursor on a carbon support, a temperature-programmed reduction/carburization was performed. Several parameters were investigated and the evolution of obtained samples was followed by XRD and TEM. The optimization of the reaction parameters led to the preparation of W, W{sub 2}C and WC particles well dispersed on the support. WC phase however could not be obtained alone with less than 10 nm mean size. This could be explained by the carburization mechanism and the carbon diffusion on the support. - Graphical abstract: Bright field picture of carbon-supported WC nanoparticles dispersed on the surface of the sample 1223 K in 10% CH{sub 4}/90% H{sub 2}. Highlights: Black-Right-Pointing-Pointer We aimed at the preparation of supported nanoparticulate tungsten derivatives. Black-Right-Pointing-Pointer Several parameters were investigated. Black-Right-Pointing-Pointer The evolution of obtained samples was followed by XRD and TEM. Black-Right-Pointing-Pointer The optimal preparation led to W, W{sub 2}C and WC particles dispersed on the support.

  13. Disulfide Trapping for Modeling and Structure Determination of Receptor:Chemokine Complexes

    PubMed Central

    Kufareva, Irina; Gustavsson, Martin; Holden, Lauren G.; Qin, Ling; Zheng, Yi; Handel, Tracy M.

    2016-01-01

    Despite the recent breakthrough advances in GPCR crystallography, structure determination of protein-protein complexes involving chemokine receptors and their endogenous chemokine ligands remains challenging. Here we describe disulfide trapping, a methodology for generating irreversible covalent binary protein complexes from unbound protein partners by introducing two cysteine residues, one per interaction partner, at selected positions within their interaction interface. Disulfide trapping can serve at least two distinct purposes: (i) stabilization of the complex to assist structural studies, and/or (ii) determination of pairwise residue proximities to guide molecular modeling. Methods for characterization of disulfide-trapped complexes are described and evaluated in terms of throughput, sensitivity, and specificity towards the most energetically favorable cross-links. Due to abundance of native disulfide bonds at receptor:chemokine interfaces, disulfide trapping of their complexes can be associated with intramolecular disulfide shuffling and result in misfolding of the component proteins; because of this, evidence from several experiments is typically needed to firmly establish a positive disulfide crosslink. An optimal pipeline that maximizes throughput and minimizes time and costs by early triage of unsuccessful candidate constructs is proposed. PMID:26921956

  14. Direct measurement of the tryptophan-mediated photocleavage kinetics of a protein disulfide bond.

    PubMed

    Abaskharon, Rachel M; Gai, Feng

    2016-04-14

    Disulfide cleavage is one of the major causes underlying ultraviolet (UV) light-induced protein damage. While previous studies have provided strong evidence to support the notion that this process is mediated by photo-induced electron transfer from the excited state of an aromatic residue (e.g., tryptophan) to the disulfide bond, many mechanistic details are still lacking. For example, we do not know how quickly this process occurs in a protein environment. Herein, we design an experiment, which uses the unfolding kinetics of a protein as an observable, to directly assess the kinetics and mechanism of photo-induced disulfide cleavage. Our results show that this disulfide bond cleavage event takes place in ∼2 μs via a mechanism involving electron transfer from the triplet state of a tryptophan (Trp) residue to the disulfide bond. Furthermore, we find that one of the photoproducts of this reaction, a Trp-SR adduct, is formed locally, thus preventing the protein from re-cross-linking. Taken together, these findings suggest that a Trp-disulfide pair could be used as a photo-trigger to initiate protein folding dynamics and control the biological activities of disulfide-containing peptides. PMID:26997094

  15. Evaluation of protein disulfide conversion in vitro using a continuous flow dialysis system.

    PubMed

    Jiang, Xinzhao Grace; Wang, Tian; Kaltenbrunner, Oliver; Chen, Kenneth; Flynn, Gregory C; Huang, Gang

    2013-01-15

    Recombinant therapeutic proteins are heterogeneous due to chemical and physical modifications. Understanding the impact of these modifications on drug safety and efficacy is critical for optimal process development and for setting reasonable specification limits. In this study, we describe the development of an in vitro continuous flow dialysis system to evaluate potential in vivo behavior of thiol adducted species and incorrectly disulfide bonded species of therapeutic proteins. The system is capable of maintaining the low-level cysteine concentrations found in human blood. Liabilities of cysteamine adducted species, incorrectly disulfide bonded species, and the correctly disulfide bonded form of an Fc-fusion protein were studied using this system. Results showed that 90% of the cysteamine adduct converted into the correctly disulfide bonded form and incorrectly disulfide bonded species in approximately 4 h under physiological conditions. Approximately 50% of incorrectly disulfide bonded species converted into the correctly bonded form in 2 days. These results provide valuable information on potential in vivo stability of the cysteamine adduct, incorrectly disulfide bonded species, and the correctly bonded form of the Fc-fusion protein. These are important considerations when evaluating the criticality of product quality attributes. PMID:23022378

  16. Human β-Defensin 4 with Non-Native Disulfide Bridges Exhibit Antimicrobial Activity

    PubMed Central

    Sharma, Himanshu; Nagaraj, Ramakrishnan

    2015-01-01

    Human defensins play multiple roles in innate immunity including direct antimicrobial killing and immunomodulatory activity. They have three disulfide bridges which contribute to the stability of three anti-parallel β-strands. The exact role of disulfide bridges and canonical β-structure in the antimicrobial action is not yet fully understood. In this study, we have explored the antimicrobial activity of human β-defensin 4 (HBD4) analogs that differ in the number and connectivity of disulfide bridges. The cysteine framework was similar to the disulfide bridges present in μ-conotoxins, an unrelated class of peptide toxins. All the analogs possessed enhanced antimicrobial potency as compared to native HBD4. Among the analogs, the single disulfide bridged peptide showed maximum potency. However, there were no marked differences in the secondary structure of the analogs. Subtle variations were observed in the localization and membrane interaction of the analogs with bacteria and Candida albicans, suggesting a role for disulfide bridges in modulating their antimicrobial action. All analogs accumulated in the cytosol where they can bind to anionic molecules such as nucleic acids which would affect several cellular processes leading to cell death. Our study strongly suggests that native disulfide bridges or the canonical β-strands in defensins have not evolved for maximal activity but they play important roles in determining their antimicrobial potency. PMID:25785690

  17. Using CO to NOX Ratios to Understand the Impact of Photoactive Roadways on Urban Atmospheric Chemistry and their Efficiency in Mitigating Air Pollution

    NASA Astrophysics Data System (ADS)

    Toro, C.; Jobson, B. T.; Haselbach, L.; Shen, S.

    2015-12-01

    Photoactive roadways and the incorporation of diverse photocatalytic surfaces into the built environment have been proposed as a strategy to improve air quality in urban areas. Laboratory studies show that surfaces treated with TiO2 are efficient in removing nitrogen oxides (NOX). Nonetheless, measurements under ambient conditions capable of isolating the impact of the photoactive surface are scarce. Previous work by our group demonstrated that CO remains stable during the timescale where NOX removal is detected, and thus can be used as a tracer. The work presented herein focuses on outdoor tests comparing CO to NOX ratios (CO/NOX) before and after interacting with photoactive pavement materials. The samples were placed in a Teflon chamber receiving a controlled flow of ambient air supplemented with a constant addition of CO and NO calibration gases. Experiments started before sunrise and continued until sunset to understand the variation due to changing UV levels. CO and NOx were monitored at the input and output of the chamber; O3 was monitored at the input. Preliminary results with asphalt roadway samples indicate that while the input CO/NOX remains constant during the day, the output CO/NOX shows a maximum during early morning and subsequently decreases to a steady value throughout the afternoon. Our previous laboratory work indicates that NO2 removal by photoactive asphalt is smaller than that of NO. We hypothesize that the decrease in the CO/NOx ratio after early morning hours is caused by 1) the enhancement in O3 concentrations as the atmospheric photochemistry increases resulting in more NO2 entering the chamber and 2) NO2 released during photocatalytic NO removal process. Therefore, as the NO2/NO increases, the efficiency of photoactive process decreases indicating that the potential benefit from photoactive roads would likely be driven by a balance between UV levels and local photochemistry.

  18. Presence of Tungsten-Containing Fibers in Tungsten Refining and Manufacturing Processes

    PubMed Central

    Mckernan, John L.; Toraason, Mark A.; Fernback, Joseph E.; Petersen, Martin R.

    2009-01-01

    In tungsten refining and manufacturing processes, a series of tungsten oxides are typically formed as intermediates in the production of tungsten powder. The present study was conducted to characterize airborne tungsten-containing fiber dimensions, elemental composition and concentrations in the US tungsten refining and manufacturing industry. During the course of normal employee work activities, seven personal breathing zone and 62 area air samples were collected and analyzed using National Institute for Occupational Safety and Health (NIOSH) fiber sampling and counting methods to determine dimensions, composition and airborne concentrations of fibers. Mixed models were used to identify relationships between potential determinants and airborne fiber concentrations. Results from transmission electron microscopy analyses indicated that airborne fibers with length >0.5 μm, diameter >0.01 μm and aspect ratios ≥3:1 were present on 35 of the 69 air samples collected. Overall, the airborne fibers detected had a geometric mean length ≈3 μm and diameter ≈0.3 μm. Ninety-seven percent of the airborne fibers identified were in the thoracic fraction (i.e. aerodynamic diameter ≤ 10 μm). Energy dispersive X-ray spectrometry results indicated that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Based on NIOSH fiber counting ‘B’ rules (length > 5 μm, diameter < 3 μm and aspect ratio ≥ 5:1), airborne fiber concentrations ranged from below the limit of detection to 0.085 fibers cm−3, with calcining being associated with the highest airborne concentrations. The mixed model procedure indicated that process temperature had a marginally significant relationship to airborne fiber concentration. This finding was expected since heated processes such as calcining created the highest airborne fiber concentrations. The finding of airborne tungsten-containing fibers in

  19. Structural stability of human alpha-thrombin studied by disulfide reduction and scrambling.

    PubMed

    Rajesh Singh, R; Chang, Jui Yoa

    2003-09-23

    Human alpha-thrombin is a very important plasma serine protease, which is involved in physiologically vital processes like hemostasis, thrombosis, and activation of platelets. Knowledge regarding the structural stability of alpha-thrombin is essential for understanding its biological regulation. Here, we investigated the structural and conformational stability of alpha-thrombin using the techniques of disulfide reduction and disulfide scrambling. alpha-Thrombin is composed of a light A-chain (36 residues) and a heavy B-chain (259 residues) linked covalently by an inter-chain disulfide bond (Cys(1)-Cys(122)). The B-chain is stabilized by three intra-chain disulfide bonds (Cys(42)-Cys(58), Cys(168)-Cys(182), and Cys(191)-Cys(220)) (Chymotrypsinogen nomenclature). Upon reduction with dithiothreitol (DTT), alpha-thrombin unfolded in a 'sequential' manner with sequential reduction of Cys(168)-Cys(182) within the B-chain followed by the inter-chain disulfide, generating two distinct partially reduced intermediates, I-1 and I-2, respectively. Conformational stability of alpha-thrombin was investigated by the technique of disulfide scrambling. alpha-Thrombin denatures by scrambling its native disulfide bonds in the presence of denaturant [urea, guanidine hydrochloride (GdmCl) or guanidine thiocyanate (GdmSCN)] and a thiol initiator. During the process, cleavage of the inter-chain disulfide bond and release of the A-chain from B-chain was the foremost event. The three disulfides in the B-chain subsequently scrambled to form three major isomers (designated as X-Ba, X-Bb, and X-Bc). Complete denaturation of alpha-thrombin was observed at low concentrations of denaturants (0.5 M GdmSCN, 1.5 M GdmCl, or 3 M urea) indicating low conformational stability of the protease. PMID:14499592

  20. Disulfide oil hazard assessment using categorical analysis and a mode of action determination.

    PubMed

    Morgott, David; Lewis, Christopher; Bootman, James; Banton, Marcy

    2014-01-01

    Diethyl and diphenyl disulfides, naphtha sweetening (Chemical Abstracts Service [CAS] # 68955-96-4), are primarily composed of low-molecular-weight dialkyl disulfides extracted from C4 to C5 light hydrocarbon streams during the refining of crude oil. The substance, commonly known as disulfide oil (DSO), can be composed of up to 17 different disulfides and trisulfides with monoalkyl chain lengths no greater than C4. The disulfides in DSO constitute a homologous series of chemical constituents that are perfectly suited for a hazard evaluation using a read-across/worst-case approach. The DSO constituents exhibit a common mode of action that is operable at all trophic levels. The observed oxidative stress response is mediated by reactive oxygen species and free radical intermediates generated after disulfide bond cleavage and subsequent redox cycling of the resulting mercaptan. Evidence indicates that the lowest series member, dimethyl disulfide (DMDS), can operate as a worst-case surrogate for other members of the series, since it displays the highest toxicity. Increasing the alkyl chain length or degree of substitution has been shown to serially reduce disulfide toxicity through resonance stabilization of the radical intermediate or steric inhibition of the initial enzymatic step. The following case study examines the mode of action for dialkyl disulfide toxicity and documents the use of read-across information from DMDS to assess the hazards of DSO. The results indicate that DSO possesses high aquatic toxicity, moderate environmental persistence, low to moderate acute toxicity, high repeated dose toxicity, and a low potential for genotoxicity, carcinogenicity, and reproductive/developmental effects. PMID:24189075

  1. Tungsten fiber reinforced superalloys: A status review

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Signorelli, R. A.

    1981-01-01

    Improved performance of heat engines is largely dependent upon maximum cycle temperatures. Tungsten fiber reinforced superalloys (TFRS) are the first of a family of high temperature composites that offer the potential for significantly raising hot component operating temperatures and thus leading to improved heat engine performance. This status review of TFRS research emphasizes the promising property data developed to date, the status of TFRS composite airfoil fabrication technology, and the areas requiring more attention to assure their applicability to hot section components of aircraft gas turbine engines.

  2. Xenon-Ion Drilling of Tungsten Films

    NASA Technical Reports Server (NTRS)

    Garner, C. E.

    1986-01-01

    High-velocity xenon ions used to drill holes of controlled size and distribution through tungsten layer that sheaths surface of controlled-porosity dispenser cathode of traveling wave-tube electron emitter. Controlled-porosity dispenser cathode employs barium/calcium/ aluminum oxide mixture that migrates through pores in cathode surface, thus coating it and reducing its work function. Rapid, precise drilling technique applied to films of other metals and used in other applications where micron-scale holes required. Method requires only few hours, as opposed to tens of hours by prior methods.

  3. Low temperature photoresponse of monolayer tungsten disulphide

    SciTech Connect

    Cao, Bingchen; Shen, Xiaonan; Shang, Jingzhi; Cong, Chunxiao; Yang, Weihuang; Eginligil, Mustafa E-mail: meginligil@ntu.edu.sg; Yu, Ting E-mail: meginligil@ntu.edu.sg

    2014-11-01

    High photoresponse can be achieved in monolayers of transition metal dichalcogenides. However, the response times are inconveniently limited by defects. Here, we report low temperature photoresponse of monolayer tungsten disulphide prepared by exfoliation and chemical vapour deposition (CVD) method. The exfoliated device exhibits n-type behaviour; while the CVD device exhibits intrinsic behaviour. In off state, the CVD device has four times larger ratio of photoresponse for laser on/off and photoresponse decay–rise times are 0.1 s (limited by our setup), while the exfoliated device has few seconds. These findings are discussed in terms of charge trapping and localization.

  4. Synthesis of nanocrystalline tungsten carbide (WC) powder

    NASA Astrophysics Data System (ADS)

    Singla, Gourav; Singh, K.; Pandey, O. P.

    2013-06-01

    Nanocrystalline tungsten carbide (WC) has been obtained from bulk WO3 by in situ reduction and carbonization reactions at low temperature (˜ 600 °C) by taking Mg as reductant and acetone C3H6O as carbon source. It was aimed to elucidate carburization behavior of WO3 powder and to establish optimal conditions for the synthesis of nanocrystalline WC. The role of reaction time on the synthesis of WC has been investigated and discussed. The synthesized powders were characterized by X-ray powder diffraction, differential thermal analyzer (DTA), thermo gravimetric analysis (TGA).

  5. A diffusion model for tungsten powder carburization

    NASA Astrophysics Data System (ADS)

    McCarty, Lewis V.; Donelson, Richard; Hehemann, Robert f.

    1991-01-01

    A mathematical model describes the carburization kinetics of tungsten powders mixed with carbon and heated in hydrogen. It is based on diffusion of carbon through a shell of WC growing into particles which are modeled as spheres. The activation energy is 58 kcal/mole in the temperature range 1056 to 1833 °C. Hydrogen gas is important to transport carbon as methane or acetylene, but increased hydrogen pressure increases the rate of carburization so little that an adsorbed species such as CH probably controls the carbon concentration at the particle surface.

  6. Tungsten imido catalysts for selective ethylene dimerisation.

    PubMed

    Wright, Christopher M R; Turner, Zoë R; Buffet, Jean-Charles; O'Hare, Dermot

    2016-02-14

    A tungsten imido complex W(NDipp)Me3Cl (Dipp = 2,6-(i)Pr-C6H3) is active for the selective dimerisation of ethylene to yield 1-butene under mild conditions. Immobilisation and activation of W(NDipp)Cl4(THF) on layered double hydroxides, silica or polymethylaluminoxane yields active solid state catalysts for the selective dimerisation of ethylene. The polymethylaluminoxane-based catalyst displays a turnover frequency (4.0 molC2H4 molW(-1) h(-1)) almost 7 times that of the homogeneous catalyst. PMID:26779579

  7. Impact of temperature during He+ implantation on deuterium retention in tungsten, tungsten with carbon deposit and tungsten carbide

    NASA Astrophysics Data System (ADS)

    Oya, Yasuhisa; Sato, Misaki; Li, Xiaochun; Yuyama, Kenta; Fujita, Hiroe; Sakurada, Shodai; Uemura, Yuki; Hatano, Yuji; Yoshida, Naoaki; Ashikawa, Naoko; Sagara, Akio; Chikada, Takumi

    2016-02-01

    Temperature dependence on deuterium (D) retention for He+ implanted tungsten (W) was studied by thermal desorption spectroscopy (TDS) to evaluate the tritium retention behavior in W. The activation energies were evaluated using Hydrogen Isotope Diffusion and Trapping (HIDT) simulation code and found to be 0.55 eV, 0.65 eV, 0.80 eV and 1.00 eV. The heating scenarios clearly control the D retention behavior and, dense and large He bubbles could work as a D diffusion barrier toward the bulk, leading to D retention enhancement at lower temperature of less than 430 K, even if the damage was introduced by He+ implantation. By comparing the D retention for W, W with carbon deposit and tungsten carbide (WC), the dense carbon layer on the surface enhances the dynamic re-emission of D as hydrocarbons, and induces the reduction of D retention. However, by He+ implantation, the D retention was increased for all the samples.

  8. Charge transfer of iron(III) monomeric and oligomeric aqua hydroxo complexes: semiempirical investigation into photoactivity.

    PubMed

    Lopes, Ludovic; de Laat, Joseph; Legube, Bernard

    2002-05-01

    Aqueous hydrolyses of iron(III) solutions were studied using electronic spectroscopy. Complete spectra from 200 to 800 nm were obtained for the four ferric aqua hydroxo complexes: Fe(H(2)O)(6)(3+), Fe(OH)(H(2)O)(5)(2+), Fe(OH)(2)(H(2)O)(4)(+), and the dimer Fe(2)(mu-Omicron Eta)(2)(H(2)O)(8)(4+). Semiempirical Zindo/s calculations were employed to assign which types of electronic transfers are involved so that the photoactivity as regards the photoreduction dissociation Fe(III)(aq) Fe(II)(aq) + OH* can be discussed. Fe(3+) exhibits two LMCT from non-bonding p orbitals (nLp) located at 190 and 240 nm. Fe(OH)(2+) shows two major nLp(OH) --> d transitions at 205 and 295 nm. As regards its geometry, computed investigations using an Fe-OH distance of 2.05 A better fit than using a shorter distance ( approximately 1.8 A); the same conclusion remains constant for all hydroxo complexes. The dihydroxo form's spectrum was confronted to its common cis and trans expectable isomers plus an unusual pentacoordinate one. Even if the trans isomer is supposed to be the lowest Gibbs free energy species in solution, there is some evidence of the presence of the cis form; hence, both species must be close in energy. Other isolated nLp(OH) --> d transfer wavelengths are 235, 245, and 335 nm. As for the dimer, this study provides some clue in favor of the bis(mu-hydroxo)) description. Both water and hydroxo ligands are involved along the electronic transitions toward only d(1) metal-centered orbitals at 220 and 260 nm for H(2)O, 335 and 470 nm for OH(-), and 205 nm for both. Charge transfers for the hydrogen oxide bridge form Fe(2)(mu-Eta(3)Omicron(2))(H(2)O)(8)(5+) were also computed. Finally predictions about the two bis(mu-hydroxo) bridge trimer Fe(3)(OH)(4)(H(2)O)(10)(5+) enable one to foresee a huge and broad charge transfer in the UV region (approximately 240 nm) followed by a multi nLp(OH) --> d(1) transfer extending up to approximately 650 nm. PMID:11978119

  9. Role of a helix B lysine residue in the photoactive site in channelrhodopsins.

    PubMed

    Li, Hai; Govorunova, Elena G; Sineshchekov, Oleg A; Spudich, John L

    2014-04-15

    In most studied microbial rhodopsins two conserved carboxylic acid residues (the homologs of Asp-85 and Asp-212 in bacteriorhodopsin) and an arginine residue (the homolog of Arg-82) form a complex counterion to the protonated retinylidene Schiff base, and neutralization of the negatively charged carboxylates causes red shifts of the absorption maximum. In contrast, the corresponding neutralizing mutations in some relatively low-efficiency channelrhodopsins (ChRs) result in blue shifts. These ChRs do not contain a lysine residue in the second helix, conserved in higher efficiency ChRs (Lys-132 in the crystallized ChR chimera). By action spectroscopy of photoinduced channel currents in HEK293 cells and absorption spectroscopy of detergent-purified pigments, we found that in tested ChRs the Lys-132 homolog controls the direction of spectral shifts in the mutants of the photoactive site carboxylic acid residues. Analysis of double mutants shows that red spectral shifts occur when this Lys is present, whether naturally or by mutagenesis, and blue shifts occur when it is replaced with a neutral residue. A neutralizing mutation of the Lys-132 homolog alone caused a red spectral shift in high-efficiency ChRs, whereas its introduction into low-efficiency ChR1 from Chlamydomonas augustae (CaChR1) caused a blue shift. Taking into account that the effective charge of the carboxylic acid residues is a key factor in microbial rhodopsin spectral tuning, these findings suggest that the Lys-132 homolog modulates their pKa values. On the other hand, mutation of the Arg-82 homolog that fulfills this role in bacteriorhodopsin caused minimal spectral changes in the tested ChRs. Titration revealed that the pKa of the Asp-85 homolog in CaChR1 lies in the alkaline region unlike in most studied microbial rhodopsins, but is substantially decreased by introduction of a Lys-132 homolog or neutralizing mutation of the Asp-212 homolog. In the three ChRs tested the Lys-132 homolog also alters

  10. Transient low-barrier hydrogen bond in the photoactive state of green fluorescent protein.

    PubMed

    Nadal-Ferret, Marc; Gelabert, Ricard; Moreno, Miquel; Lluch, José M

    2015-12-14

    In this paper, we have analyzed the feasibility of spontaneous proton transfer in GFP at the Franck-Condon region directly after photoexcitation. Computation of a sizeable portion of the potential energy surface at the Franck-Condon region of A the structure shows the process of proton transfer to be unfavorable by 3 kcal mol(-1) in S1 if no further structural relaxation is permitted. The ground vibrational state is found to lie above the potential energy barrier of the proton transfer in both S0 and S1. Expectation values of the geometry reveal that the proton shared between the chromophore and W22, and the proton shared between Ser205 and Glu222 are very close to the center of the respective hydrogen bonds, giving support to the claim that the first transient intermediate detected after photoexcitation (I0*) has characteristics similar to those of a low-barrier hydrogen bond [Di Donato et al., Phys. Chem. Chem. Phys., 2012, 13, 16295]. A quantum dynamical calculation of the evolution in the excited state shows an even larger probability of finding those two protons close to the center compared to in the ground state, but no formation of the proton-transferred product is observed. A QM/MM photoactive state geometry optimization, initiated using a configuration obtained by taking the A minimum and moving the protons to the product side, yields a minimum energy structure with the protons transferred and in which the His148 residue is substantially closer to the now anionic chromophore. These results indicate that: (1) proton transfer is not possible if structural relaxation of the surroundings of the chromophore is prevented; (2) protons H1 and H3 especially are found very close to the point halfway between the donor and acceptor after photoexcitation when the zero-point energy is considered; (3) a geometrical parameter exists (the His148-Cro distance) under which the structure with the protons transferred is not a minimum, and that, if included, should lead to the

  11. Electrodeposited ZnO with squaraine sentisizers as photoactive anode of DSCs

    NASA Astrophysics Data System (ADS)

    Venditti, Iole; Barbero, Nadia; Vittoria Russo, Maria; Di Carlo, Aldo; Decker, Franco; Fratoddi, Ilaria; Barolo, Claudia; Dini, Danilo

    2014-03-01

    The adsorption behavior of two symmetrical indolenine-based squaraines, indicated with VG1-C2 and VG1-C10, sensitizing electrodeposited mesoporous zinc oxide (ZnO), was studied and compared with that of di-tetrabutylammonium cis-bis(isothiocyanato) bis(2,2‧-bipyridyl-4,4‧-dicarboxylato) ruthenium (II) (N719). The choice of squaraines as metal-free dye-sensitizers was motivated by their far-red NIR sensitivity with respect to the traditional Ru complex-based dyes, the ease of their preparation and their higher molar extinction coefficient. The electrochemically grown ZnO here described were porous due to the high volume yield of electrodeposition (about 104 cm3 of ZnO per unit charge of electrolysis). In the present analysis the process of sensitization of TiO2 with the same set of dyes and the performance of the corresponding DSCs were also considered for sake of comparison. VG1-C2 sensitizer proved to be particularly effective electron injector in ZnO electrodes giving larger photocurrents in VG1-C2-sensitized ZnO with respect to TiO2. The latter system presented higher kinetic stability of the photoinjected charges as evidenced by the larger photovoltages of TiO2-based DSCs with respect to ZnO-based devices with the same sensitizer. The long alkyl substituents in squaraine VG1-C10 inhibit electron injection in ZnO and a specific effect of electrical passivation of the ZnO surface introduced by the bulky apolar groups was claimed. Overall efficiencies in the order of 1% were measured with the ZnO-based DSCs under AM 1.5 solar simulator when the photoactive area and the thickness of ZnO films were 0.5 cm2 and 2 μm, respectively. These results on ZnO-based DSCs with the oxide prepared at temperatures below 260 °C are particularly interesting considering the relatively large area and small thickness of the related electrodes, which makes them in principle useful for application in weakly absorbing devices utilizing flexible substrates.

  12. Measurement of the Properties of Tungsten at High Temperatures

    NASA Technical Reports Server (NTRS)

    Margrave, J. L.

    1985-01-01

    The thermophysical properties of tungsten and other materials were measured using containerless techniques. Levitation of liquid silver, gallium and tungsten were studied. The studies of liquid aluminum are almost complete and are expected to derive new, reliable properties for liquid aluminum.

  13. Gas Tungsten Arc Welding. Welding Module 6. Instructor's Guide.

    ERIC Educational Resources Information Center

    Missouri Univ., Columbia. Instructional Materials Lab.

    This guide is intended to assist vocational educators in teaching a three-unit module in gas tungsten arc welding. The module has been designed to be totally integrated with Missouri's Vocational Instruction Management System. The basic principles involved in gas tungsten arc welding, supplies, and applications are covered. The materials included…

  14. Processing of tungsten scrap into powders by electroerosion disintegration

    SciTech Connect

    Fominskii, L.P.; Leuchuk, M.V.; Myuller, A.S.; Tarabrina, V.P.

    1985-04-01

    Utilization of tungsten and tungsten alloy swarf and other waste and also of rejected and worn parts is a matter of great importance in view of the shortage of this metal. The authors examine the electroerosion (EE) disintegration of tungsten in water as a means of utilizing swarf and other loose waste. Unlike chemical methods, EE disintegration ensures ecological purity since there are no effluent waters or toxic discharges. Swarf and trimmings of rods of diameters up to 20 mm obtained after the lathe-turning of tungsten bars sintered from PVN and PVV tungsten powders were disintegrated in water at room temperature between tungsten electrodes. The phase composition of the powder was studied using FeK /SUB alpha/ radiation, by x-ray diffraction methods in a DRON-2 diffractometer with a graphite monochromator on the secondary beam. When tungsten is heated to boiling during EE disintegration, the impurities present in it can evaporate and burn out. Thus, tungsten powder produced by EE disintegration can be purer than the starting metal.

  15. Calibration and Temperature Profile of a Tungsten Filament Lamp

    ERIC Educational Resources Information Center

    de Izarra, Charles; Gitton, Jean-Michel

    2010-01-01

    The goal of this work proposed for undergraduate students and teachers is the calibration of a tungsten filament lamp from electric measurements that are both simple and precise, allowing to determine the temperature of tungsten filament as a function of the current intensity. This calibration procedure was first applied to a conventional filament…

  16. Thermal Spray Coating of Tungsten for Tokamak Device

    NASA Astrophysics Data System (ADS)

    Jiang, Xianliang; F, Gitzhofer; M, I. Boulos

    2006-03-01

    Thermal spray, such as direct current (d.c.) plasma spray or radio frequency induced plasma spray, was used to deposit tungsten coatings on the copper electrodes of a tokamak device. The tungsten coating on the outer surface of one copper electrode was formed directly through d.c. plasma spraying of fine tungsten powder. The tungsten coating/lining on the inner surface of another copper electrode could be formed indirectly through induced plasma spraying of coarse tungsten powder. Scanning electron microscopy (SEM) was used to examine the cross section and the interface of the tungsten coating. Energy Dispersive Analysis of X-ray (EDAX) was used to analyze the metallic elements attached to a separated interface. The influence of the particle size of the tungsten powder on the density, cracking behavior and adhesion of the coating is discussed. It is found that the coarse tungsten powder with the particle size of 45 ~ 75 μm can be melted and the coating can be formed only by using induced plasma. The coating deposited from the coarse powder has much higher cohesive strength, adhesive strength and crack resistance than the coating made from the fine powder with a particle size of 5 μm.

  17. Microstructure and tensile properties of tungsten at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Shen, Tielong; Dai, Yong; Lee, Yongjoong

    2016-01-01

    In order to support the development of the 5 MW spallation target for the European Spallation Source, the effect of fabrication process on microstructure, ductile-to-brittle transition temperature (DBTT), tensile and fracture behaviour of powder-metallurgy pure tungsten materials has been investigated. A hot-rolled (HR) tungsten piece of 12 mm thickness and a hot-forged (HF) piece of about 80 mm thickness were used to simulate the thin and thick blocks in the target. The two tungsten pieces were characterized with metallography analysis, hardness measurement and tensile testing. The HR piece exhibits an anisotropic grain structure with an average size of about 330 × 140 × 40 μm in rolling, long transverse and short transverse (thickness) directions. The HF piece possesses a bimodal grain structure with about 310 × 170 × 70 μm grain size in deformed part and about 25 μm sized grains remained from sintering process. Hardness (HV0.2) of the HR piece is slightly greater than that of the HF one. The ductility of the HR tungsten specimens is greater than that of the HF tungsten. For the HF tungsten piece, specimens with small grains in gauge section manifest lower ductility but higher strength. The DBTT evaluated from the tensile results is 250-300 °C for the HR tungsten and about 350 °C for the HF tungsten.

  18. Lignin-assisted exfoliation of molybdenum disulfide in aqueous media and its application in lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Liu, Wanshuang; Zhao, Chenyang; Zhou, Rui; Zhou, Dan; Liu, Zhaolin; Lu, Xuehong

    2015-05-01

    In this article, alkali lignin (AL)-assisted direct exfoliation of MoS2 mineral into single-layer and few-layer nanosheets in water is reported for the first time. Under optimized conditions, the concentration of MoS2 nanosheets in the obtained dispersion can be as high as 1.75 +/- 0.08 mg mL-1, which is much higher than the typical reported concentrations (<1.0 mg mL-1) using synthetic polymers or compounds as surfactants. The stabilizing mechanism primarily lies in the electrostatic repulsion between negative charged AL, as suggested by zeta-potential measurements. When the exfoliated MoS2 nanosheets are applied as electrode materials for lithium ion batteries, they show much improved electrochemical performance compared with the pristine MoS2 mineral because of the enhanced ion and electron transfer kinetics. This facile, scalable and eco-friendly aqueous-based process in combination with renewable and ultra-low-cost lignin opens up possibilities for large-scale fabrication of MoS2-based nanocomposites and devices. Moreover, herein we demonstrate that AL is also an excellent surfactant for exfoliation of many other types of layered materials, including graphene, tungsten disulfide and boron nitride, in water, providing rich opportunities for a wider range of applications.In this article, alkali lignin (AL)-assisted direct exfoliation of MoS2 mineral into single-layer and few-layer nanosheets in water is reported for the first time. Under optimized conditions, the concentration of MoS2 nanosheets in the obtained dispersion can be as high as 1.75 +/- 0.08 mg mL-1, which is much higher than the typical reported concentrations (<1.0 mg mL-1) using synthetic polymers or compounds as surfactants. The stabilizing mechanism primarily lies in the electrostatic repulsion between negative charged AL, as suggested by zeta-potential measurements. When the exfoliated MoS2 nanosheets are applied as electrode materials for lithium ion batteries, they show much improved

  19. MS2DB+: a software for determination of disulfide bonds using multi-ion analysis.

    PubMed

    Murad, William; Singh, Rahul

    2013-06-01

    MS2DB+ is an open-source platform-independent web application for determining, in polynomial time, the disulfide linkages in proteins using tandem mass spectrometry (MS/MS) data. It utilizes an efficient approximation algorithm which allows the consideration of multiple ion-types (a, a(o), a*, b, b(o), b*, c, x, y, y(o), y*, and z) in the analysis. Once putative disulfide bonds are identified, a graph optimization approach is used to obtain the most likely global disulfide connectivity pattern. PMID:23096131

  20. Characterization of the kringle fold and identification of a ubiquitous new class of disulfide rotamers.

    PubMed

    Ozhogina, Olga A; Bominaar, Emile L

    2009-11-01

    The disulfide-bridged chains in the kringle (K) and fibronectin type II (FN2) domains are characterized using a taxonomy that considers the regularities in both beta-secondary structure and cystine cluster. The structural core of the kringle fold comprises an assembly of two beta-hairpins (a "beta-meander") accommodating two overlapping disulfides; one cystine is incorporated in adjacent beta-strands, whereas the other is located just beyond the ends of non-adjacent beta-strands. The dispositions of the (N, C) termini of the two overlapping disulfides in the kringle fold are given as (m, j+1) and (i-1, k+1), in which m, i, j, and k (mdisulfide kringle-cross". The metrics of this motif are quantified, revealing structural differences between the two families of the kringle fold. The conformations of disulfides in the kringle fold are poorly accommodated by existing classification schemes. To elucidate the nature of these rotamers we have performed density functional theory (DFT) calculations for diethyl disulfide. A new classification for the disulfide conformations in proteins is proposed, consisting of six rotamer types: spiral, trans-spiral, corner, trans, hook, and staple. Its relation with previous classification schemes is specified. A survey of high-resolution X-ray structures reveals that the disulfide conformations are clustered around the averaged conformations for the six classes. Average conformation dihedral and distance values are in excellent agreement with the DFT values. The two overlapping disulfides in kringle domains adopt the trans-spiral conformation that appears to be ubiquitous (~17%) in proteins. One of the disulfides stretches across the beta

  1. Kinetics and intracellular location of intramolecular disulfide bond formation mediated by the cytoplasmic redox system encoded by vaccinia virus

    SciTech Connect

    Bisht, Himani; Brown, Erica; Moss, Bernard

    2010-03-15

    Poxviruses encode a redox system for intramolecular disulfide bond formation in cytoplasmic domains of viral proteins. Our objectives were to determine the kinetics and intracellular location of disulfide bond formation. The vaccinia virus L1 myristoylated membrane protein, used as an example, has three intramolecular disulfide bonds. Reduced and disulfide-bonded forms of L1 were distinguished by electrophoretic mobility and reactivity with monoclonal and polyclonal antibodies. Because disulfide bonds formed during 5 min pulse labeling with radioactive amino acids, a protocol was devised in which dithiothreitol was present at this step. Disulfide bond formation was detected by 2 min after removal of reducing agent and was nearly complete in 10 min. When the penultimate glycine residue was mutated to prevent myristoylation, L1 was mistargeted to the endoplasmic reticulum and disulfide bond formation failed to occur. These data suggested that viral membrane association was required for oxidation of L1, providing specificity for the process.

  2. High-throughput instant quantification of protein expression and purity based on photoactive yellow protein turn off/on label.

    PubMed

    Kim, Youngmin; Ganesan, Prabhakar; Ihee, Hyotcherl

    2013-08-01

    Quantifying the concentration and purity of a target protein is essential for high-throughput protein expression test and rapid screening of highly soluble proteins. However, conventional methods such as PAGE and dot blot assay generally involve multiple time-consuming tasks requiring hours or do not allow instant quantification. Here, we demonstrate a new method based on the Photoactive yellow protein turn Off/On Label (POOL) system that can instantly quantify the concentration and purity of a target protein. The main idea of POOL is to use Photoactive Yellow Protein (PYP), or its miniaturized version, as a fusion partner of the target protein. The characteristic blue light absorption and the consequent yellow color of PYP is absent when initially expressed without its chromophore, but can be turned on by binding its chromophore, p-coumaric acid. The appearance of yellow color upon adding a precursor of chromophore to the co-expressed PYP can be used to check the expression amount of the target protein via visual inspection within a few seconds as well as to quantify its concentration and purity with the aid of a spectrometer within a few minutes. The concentrations measured by the POOL method, which usually takes a few minutes, show excellent agreement with those by the BCA Kit, which usually takes ∼1 h. We demonstrate the applicability of POOL in E. coli, insect, and mammalian cells, and for high-throughput protein expression screening. PMID:23740751

  3. Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography

    NASA Astrophysics Data System (ADS)

    Jung, Yang Ouk; Lee, Jae Hyuk; Kim, Joonghan; Schmidt, Marius; Moffat, Keith; Šrajer, Vukica; Ihee, Hyotcherl

    2013-03-01

    Trans-to-cis isomerization, the key reaction in photoactive proteins, usually cannot occur through the standard one-bond-flip mechanism. Owing to spatial constraints imposed by a protein environment, isomerization probably proceeds through a volume-conserving mechanism in which highly choreographed atomic motions are expected, the details of which have not yet been observed directly. Here we employ time-resolved X-ray crystallography to visualize structurally the isomerization of the p-coumaric acid chromophore in photoactive yellow protein with a time resolution of 100 ps and a spatial resolution of 1.6 Å. The structure of the earliest intermediate (IT) resembles a highly strained transition state in which the torsion angle is located halfway between the trans- and cis-isomers. The reaction trajectory of IT bifurcates into two structurally distinct cis intermediates via hula-twist and bicycle-pedal pathways. The bifurcating reaction pathways can be controlled by weakening the hydrogen bond between the chromophore and an adjacent residue through E46Q mutation, which switches off the bicycle-pedal pathway.

  4. Synthesis and characterization of high-photoactivity electrodeposited Cu{sub 2}O solar absorber by photoelectrochemistry and ultrafast spectroscopy.

    SciTech Connect

    Paracchino, A.; Brauer, J. C.; Moser , J-E.; Thimsen, E.; Graetzel, M.

    2012-03-08

    We present a systematic study on the effects of electrodeposition parameters on the photoelectrochemical properties of Cu{sub 2}O. The influence of deposition variables (temperature, pH, and deposition current density) on conductivity has been widely explored in the past for this semiconductor, but the optimization of the electrodeposition process for the photoelectrochemical response in aqueous solutions under AM 1.5 illumination has received far less attention. In this work, we analyze the photoactivity of Cu{sub 2}O films deposited at different conditions and correlate the photoresponse to morphology, film orientation, and electrical properties. The photoelectrochemical response was measured by linear sweep voltammetry under chopped simulated AM 1.5 illumination. The highest photocurrent obtained was -2.4 mA cm{sup -2} at 0.25 V vs RHE for a film thickness of 1.3 {micro}m. This is the highest reported value reached so far for this material in an aqueous electrolyte under AM 1.5 illumination. The optical and electrical properties of the most photoactive electrode were investigated by UV-vis spectroscopy and electrochemical impedance, while the minority carrier lifetime and diffusion length were measured by optical-pump THz-probe spectroscopy.

  5. Photoactive Metal-Organic Framework and Its Film for Light-Driven Hydrogen Production and Carbon Dioxide Reduction.

    PubMed

    Wu, Pengyan; Guo, Xiangyang; Cheng, Linjuan; He, Cheng; Wang, Jian; Duan, Chunying

    2016-08-15

    The design of a new photocatalytic system and integrating the essential components in a structurally controlled manner to create artificially photosynthetic systems is high desirable. By incorporating a photoactive triphenylamine moiety to assemble a Gd-based metal-organic framework as a heterogeneous photosensitizer, new artificial systems were constructed for the proton and carbon dioxide reduction under irradiation. The assembled MOFs exhibited a one-dimensional metal-oxygen pillar that was connected together by the depronated TCA(3-) ligands to form a three-dimensional noninterpenetrating porous framework. The combining of proton reduction and/or the carbon dioxide reduction catalysts, i.e., the Fe-Fe hydrogenase active site models and the Ni(Cyclam) complexes, initiated a photoinduced single electron transfer from its excited state to the substrate. The system exhibited an initial TOF of 320 h(-1) of hydrogen per catalyst and an overall quantum yield of about 0.21% and is able to reduce carbon dioxide under irradiation. The deposit of the photoactive Gd-TCA into the film of an α-Al2O3 plate provided a platform for the practical applications through prolonging the lifetime of the artifical system and allowed the easily operated devices being recyclable as a promising photocatalytic system. PMID:27479135

  6. Photoactive and self-sensing P3HT-based thin films for strain and corrosion monitoring

    NASA Astrophysics Data System (ADS)

    Ryu, Donghyeon; Loh, Kenneth J.

    2014-03-01

    Structural systems deteriorate due to excessive deformation and corrosive environments. If damage is left undetected, they can propagate to cause sudden collapse. However, one of the main difficulties of monitoring damage progression is that, for example, excessive/plastic deformation and corrosion are drastically different physical processes. Strain is a mechanical phenomenon, whereas corrosion is a complex electrochemical process. The current strategy for structural health monitoring (SHM) is to use either different types of sensors or to employ system identification for quantifying overall changes to the structure. In this study, an alternative SHM paradigm is proposed in that a single, multifunctional material would be able to selectively sense different but simultaneously occurring structural damage. In particular, a photoactive and self-sensing thin film was developed for monitoring strain and corrosion. Another unique aspect was that the films were self-sensing and did not depend on external electrical energy for operations. First, the thin films were fabricated using photoactive poly(3-hexylthiophene) (P3HT) and other functional polymers using spin-coating and layerby- layer assembly. Second, the fabricated thin films were interrogated using an ultraviolet-visible (UV-Vis) spectrophotometer for quantifying their optical response to applied external stimuli, such as strain and exposure to pH buffer solutions. Lastly, the multifunctional thin films were tested and validated for strain and pH sensing. Interrogation of these separate responses was achieved by illuminating the thin films different wavelengths of light and then measuring the corresponding electrical current generated.

  7. Light-switched inhibitors of protein tyrosine phosphatase PTP1B based on phosphonocarbonyl phenylalanine as photoactive phosphotyrosine mimetic.

    PubMed

    Wagner, Stefan; Schütz, Anja; Rademann, Jörg

    2015-06-15

    Phosphopeptide mimetics containing the 4-phosphonocarbonyl phenylalanine (pcF) as a photo-active phosphotyrosine isoster are developed as potent, light-switchable inhibitors of the protein tyrosine phosphatase PTP1B. The photo-active inhibitors 6-10 are derived from phosphopeptide substrates and are prepared from the suitably protected pcF building block 12 by Fmoc-based solid phase peptide synthesis. All pcF-containing peptides are moderate inhibitors of PTP1B with KI values between 10 and 50μM. Irradiation of the inhibitors at 365nm in the presence of the protein PTP1B amplify the inhibitory activity of pcF-peptides up to 120-fold, switching the KI values of the best inhibitors to the sub-micromolar range. Photo-activation of the inhibitors results in the formation of triplet intermediates of the benzoylphosphonate moiety, which deactivate PTP1B following an oxidative radical mechanism. Deactivation of PTP1B proceeds without covalent crosslinking of the protein target with the photo-switched inhibitors and can be reverted by subsequent addition of reducing agent dithiothreitol (DTT). PMID:25907367

  8. Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography

    SciTech Connect

    Jung, Yang Ouk; Lee, Jae Hyuk; Kim, Joonghan; Schmidt, Marius; Moffat, Keith; Šrajer, Vukica; Ihee, Hyotcherl

    2013-02-03

    Trans-to-cis isomerization, the key reaction in photoactive proteins, usually cannot occur through the standard one-bond-flip mechanism. Owing to spatial constraints imposed by a protein environment, isomerization probably proceeds through a volume-conserving mechanism in which highly choreographed atomic motions are expected, the details of which have not yet been observed directly. Here we employ time-resolved X-ray crystallography to visualize structurally the isomerization of the p-coumaric acid chromophore in photoactive yellow protein with a time resolution of 100 ps and a spatial resolution of 1.6 Å. The structure of the earliest intermediate (IT) resembles a highly strained transition state in which the torsion angle is located halfway between the trans- and cis-isomers. The reaction trajectory of IT bifurcates into two structurally distinct cis intermediates via hula-twist and bicycle-pedal pathways. The bifurcating reaction pathways can be controlled by weakening the hydrogen bond between the chromophore and an adjacent residue through E46Q mutation, which switches off the bicycle-pedal pathway.

  9. A facile solvothermal method to produce ZnS quantum dots-decorated graphene nanosheets with superior photoactivity

    NASA Astrophysics Data System (ADS)

    Yu, Linhui; Ruan, Hong; Zheng, Yi; Li, Danzhen

    2013-09-01

    Zinc sulfide-graphene (ZnS-GR) nanocomposites with a high degree of dispersion and high coverage of ZnS quantum dots (QDs) have been synthesized by a facile solvothermal method without any dispersant, during which the formation of ZnS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. ZnS-GR nanocomposites exhibit much higher photoactivity than nanoparticle crystal ZnS (NPC-ZnS) prepared in the absence of graphene (GR), as evaluated by degradation of methylene blue (MB) in the liquid phase under ultraviolet (UV) light. Among them, the ZnS-GR nanocomposite with a 5% mass fraction of GR prepared at 120 ° C has the highest photocatalytic activity. The conversion and mineralization over MB are 96.7% and 57.1% respectively, which is much higher than that of NPC-ZnS. The high photoactivity of ZnS-GR nanocomposites can be ascribed to the integrated effect of an extremely high specific surface area and the excellent electron conductivity of GR and its significant influence on the morphology and structure of the samples. Moreover, it is found that the oxidation of MB is driven mainly by the participation of ṡOH radicals. Accordingly, a potential photocatalytic mechanism of ZnS-GR nanocomposites in the photocatalytic process has been proposed in this work. It is expected that our work could provide valuable information on the design of metal sulfide decorated GR with excellent properties.

  10. A facile solvothermal method to produce ZnS quantum dots-decorated graphene nanosheets with superior photoactivity.

    PubMed

    Yu, Linhui; Ruan, Hong; Zheng, Yi; Li, Danzhen

    2013-09-20

    Zinc sulfide-graphene (ZnS-GR) nanocomposites with a high degree of dispersion and high coverage of ZnS quantum dots (QDs) have been synthesized by a facile solvothermal method without any dispersant, during which the formation of ZnS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. ZnS-GR nanocomposites exhibit much higher photoactivity than nanoparticle crystal ZnS (NPC-ZnS) prepared in the absence of graphene (GR), as evaluated by degradation of methylene blue (MB) in the liquid phase under ultraviolet (UV) light. Among them, the ZnS-GR nanocomposite with a 5% mass fraction of GR prepared at 120 ° C has the highest photocatalytic activity. The conversion and mineralization over MB are 96.7% and 57.1% respectively, which is much higher than that of NPC-ZnS. The high photoactivity of ZnS-GR nanocomposites can be ascribed to the integrated effect of an extremely high specific surface area and the excellent electron conductivity of GR and its significant influence on the morphology and structure of the samples. Moreover, it is found that the oxidation of MB is driven mainly by the participation of .OH radicals. Accordingly, a potential photocatalytic mechanism of ZnS-GR nanocomposites in the photocatalytic process has been proposed in this work. It is expected that our work could provide valuable information on the design of metal sulfide decorated GR with excellent properties. PMID:23965531

  11. Toward improving the graphene-semiconductor composite photoactivity via the addition of metal ions as generic interfacial mediator.

    PubMed

    Zhang, Nan; Yang, Min-Quan; Tang, Zi-Rong; Xu, Yi-Jun

    2014-01-28

    We report a simple and general approach to improve the transfer efficiency of photogenerated charge carriers across the interface between graphene (GR) and semiconductor CdS by introducing a small amount of metal ions (Ca(2+), Cr(3+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+)) as "mediator" into their interfacial layer matrix, while the intimate interfacial contact between GR and CdS is maintained. This simple strategy can not only significantly improve the visible-light-driven photoactivity of GR-CdS semiconductor composites for targeting selective photoredox reaction, including aerobic oxidation of alcohol and anaerobic reduction of nitro compound, but also drive a balance between the positive effect of GR on retarding the recombination of electron-hole pairs photogenerated from semiconductor and the negative "shielding effect" of GR resulting from the high weight addition of GR. Our current work highlights that the significant issue on improving the photoactivity of GR-semiconductor composites via strengthening interfacial contact is not just a simple issue of tighter connection between GR and the semiconductor, but it is also the optimization of the atomic charge carrier transfer pathway across the interface between GR and the semiconductor. PMID:24304042

  12. Photoactive Langmuir-Blodgett, Freely Suspended and Free Standing Films of Carboxylate Ligand-Coated ZnO Nanocrystals.

    PubMed

    Paczesny, Jan; Wolska-Pietkiewicz, Małgorzata; Binkiewicz, Ilona; Wadowska, Monika; Wróbel, Zbigniew; Matuła, Kinga; Nogala, Wojciech; Lewiński, Janusz; Hołyst, Robert

    2016-06-01

    A new possibility for the formation of macroscopic and photoactive structures from zinc oxide nanocrystals is described. Photoactive freely suspended and free-standing films of macroscopic area (up to few square millimeters) and submicrometer thickness (up to several hundreds of nanometers) composed of carboxylate ligand-coated zinc oxide nanocrystallites (RCO2-ZnO NCs) of diameter less than 5 nm are prepared according to a modified Langmuir-Schaefer method. First, the suspension of RCO2-ZnO NCs is applied onto the air/water interface. Upon compression, the films become turbid and elastic. The integrity of such structures is ensured by interdigitation of ligands stabilizing ZnO NCs. Great elasticity allows transfer of the films onto a metal frame as a freely suspended film. Such membranes are afterward extracted from the supporting frame to form free-standing films of macroscopic area. Because the integrity of the films is maintained by ligands, no abolishment of quantum confinement occurs, and films retain spectroscopic properties of initial RCO2-ZnO NCs. The mechanism of formation of thin films of RCO2-ZnO NCs at the air/water interface is discussed in detail. PMID:27158733

  13. Combined use of ion mobility and collision-induced dissociation to investigate the opening of disulfide bridges by electron-transfer dissociation in peptides bearing two disulfide bonds.

    PubMed

    Massonnet, Philippe; Upert, Gregory; Smargiasso, Nicolas; Gilles, Nicolas; Quinton, Loïc; De Pauw, Edwin

    2015-01-01

    Disulfide bonds are post-translational modifications (PTMs) often found in peptides and proteins. They increase their stability toward enzymatic degradations and provide the structure and (consequently) the activity of such folded proteins. The characterization of disulfide patterns, i.e., the cysteine connectivity, is crucial to achieve a global picture of the active conformation of the protein of interest. Electron-transfer dissociation (ETD) constitutes a valuable tool to cleave the disulfide bonds in the gas phase, avoiding chemical reduction/alkylation in solution. To characterize the cysteine pairing, the present work proposes (i) to reduce by ETD one of the two disulfide bridges of model peptides, resulting in the opening of the cyclic structures, (ii) to separate the generated species by ion mobility, and (iii) to characterize the species using collision-induced dissociation (CID). Results of this strategy applied to several peptides show different behaviors depending on the connectivity. The loss of SH· radical species, observed for all the peptides, confirms the cleavage of the disulfides during the ETD process. PMID:25915795

  14. Tungsten recycling in the United States in 2000

    USGS Publications Warehouse

    Shedd, Kim B.

    2011-01-01

    This report, which is one of a series of reports on metals recycling, defines and quantifies the flow of tungsten-bearing materials in the United States from imports and stock releases through consumption and disposition in 2000, with particular emphasis on the recycling of industrial scrap (new scrap) and used products (old scrap). Because of tungsten's many diverse uses, numerous types of scrap were available for recycling by a wide variety of processes. In 2000, an estimated 46 percent of U.S. tungsten supply was derived from scrap. The ratio of tungsten consumed from new scrap to that consumed from old scrap was estimated to be 20:80. Of all the tungsten in old scrap available for recycling, an estimated 66 percent was either consumed in the United States or exported to be recycled.

  15. In situ TEM characterization of shear-stress-induced interlayer sliding in the cross section view of molybdenum disulfide.

    PubMed

    Oviedo, Juan Pablo; KC, Santosh; Lu, Ning; Wang, Jinguo; Cho, Kyeongjae; Wallace, Robert M; Kim, Moon J

    2015-02-24

    The experimental study of interlayer sliding at the nanoscale in layered solids has been limited thus far by the incapability of mechanical and imaging probes to simultaneously access sliding interfaces and overcome through mechanical stimulus the van der Waals and Coulombic interactions holding the layers in place. For this purpose, straightforward methods were developed to achieve interlayer sliding in molybdenum disulfide (MoS2) while under observation within a transmission electron microscope. A method to manipulate, tear, and slide free-standing atomic layers of MoS2 is demonstrated by electrostatically coupling it to an oxidized tungsten probe attached to a micromanipulator at a bias above ±7 V. A first-principles model of a MoS2 bilayer polarized by a normal electric field of 5 V/nm, emanating from the tip, demonstrates the appearance of a periodic negative sliding potential energy barrier when the layers slide into the out-of-registry stacking configuration, hinting at electrostatic gating as a means of modifying the interlayer tribology to facilitate shear exfoliation. A method to shear focused ion beam prepared MoS2 cross section samples using a nanoindenter force sensor is also demonstrated, allowing both the observation and force measurement of its interlayer dynamics during shear-induced sliding. From this experiment, the zero normal load shear strength of MoS2 can be directly obtained: 25.3 ± 0.6 MPa. These capabilities enable the site-specific mechanical testing of dry lubricant-based nanoelectromechanical devices and can lead to a better understanding of the atomic mechanisms from which the interlayer tribology of layered materials originates. PMID:25494557

  16. Photoactive Nitric Oxide Delivery Systems based on Metal Nitrosyl-Biomaterial Composites

    NASA Astrophysics Data System (ADS)

    Heilman, Brandon James

    Gaseous NO has been recognized as a potent antibiotic even against highly drug-resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) in both animal and human studies. However, difficulties in the delivery of the toxic (and reactive) gas demands innovative techniques to deliver NO in a controlled manner to malignant sites throughout the body. Metal nitrosyls reported by our group have demonstrated rapid NO release under the complete control of visible and NIR light. Careful incorporation of these photoactive nitrosyls into polymer matrices has afforded a set of nitrosyl-polymer composites in order to localize the NO-donors at a targeted site, ensure reliable NO release kinetics in vivo, and prevent potentially cytotoxic interactions of the metal nitrosyl or its reaction-products with the treatment site. The work presented in this thesis was pursued to derive clinically relevant NO-delivery systems and demonstrate their utility for the treatment of infection. In chapter 2, an NO-releasing polyurethane film (PUX-NO) is described with dispersed xerogel particles containing up to 3 mol% of [Mn(PaPy 3)(NO)](ClO4) entrapped in a silica matrix and swelled with excess moisture. The polyurethane based xerogel-nitrosyl (PUX-NO) films demonstrated rapid NO photorelease upon illumination with low-power visible light which was sufficient to eradicate clinically relevant loads (105 CFU mL-1 ) of several gram-positive and gram-negative pathogenic bacteria, including a strain of methicillin-resistant of S. aureus. The results of this study suggest that PUX-NO films are suitable for use as a NO-releasing occlusive film for the treatment of skin and soft-tissue infections or chronic, non-healing wounds. Since the NO-release rate from the films can be modulated by simple adjustment of the intensity of the light source, the films could be used to first clear the microbial burden from the wound site using high fluxes of NO, and then, provide a moderate

  17. Tungsten and tungsten alloy powder metallurgy. (Latest citations from the EI Compendex*plus database). Published Search

    SciTech Connect

    Not Available

    1994-12-01

    The bibliography contains citations concerning tungsten powder preparation and processing. Studies include sintering, densification, shrinkage, phase analysis, and heat treatment. The physical and mechanical properties of tungsten powder metal products are included. The effects of additives and particle size on the sintering and sintered articles are also described. (Contains 250 citations and includes a subject term index and title list.)

  18. Tungsten and tungsten alloy powder metallurgy. (Latest citations from the EI Compendex*plus database). Published Search

    SciTech Connect

    Not Available

    1994-04-01

    The bibliography contains citations concerning tungsten powder preparation and processing. Studies include sintering, densification, shrinkage, phase analysis, and heat treatment. The physical and mechanical properties of tungsten powder metal products are included. The effects of additives and particle size on the sintering and sintered articles are also described. (Contains 250 citations and includes a subject term index and title list.)

  19. Vaccum Gas Tungsten Arc Welding, phase 1

    NASA Technical Reports Server (NTRS)

    Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

    1995-01-01

    This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

  20. High temperature annealing of ion irradiated tungsten

    DOE PAGESBeta

    Ferroni, Francesco; Yi, Xiaoou; Arakawa, Kazuto; Fitzgerald, Steven P.; Edmondson, Philip D.; Roberts, Steve G.

    2015-03-21

    In this study, transmission electron microscopy of high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications (500–1200°C). Bulk isochronal and isothermal annealing of ion irradiated pure tungsten (2 MeV W+ ions, 500°C, 1014 W+/cm2) with temperatures of 800, 950, 1100 and 1400°C, from 0.5 to 8 h, was followed by ex situ characterization of defect size, number density, Burgers vector and nature. Loops with diameters larger than 2–3 nm were considered for detailed analysis, among which all loops had View the MathML source andmore » were predominantly of interstitial nature. In situ annealing experiments from 300 up to 1200°C were also carried out, including dynamic temperature ramp-ups. These confirmed an acceleration of loop loss above 900°C. At different temperatures within this range, dislocations exhibited behaviour such as initial isolated loop hopping followed by large-scale rearrangements into loop chains, coalescence and finally line–loop interactions and widespread absorption by free-surfaces at increasing temperatures. An activation energy for the annealing of dislocation length was obtained, finding Ea=1.34±0.2 eV for the 700–1100°C range.« less