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Sample records for photoactive tungsten disulfide

  1. 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

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

    DOE PAGES

    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

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. Microwave dielectric properties of inorganic fullerene-like tungsten disulfide nanoparticles

    NASA Astrophysics Data System (ADS)

    Chang, Hong; Dimitrakis, Georgios; Xu, Fang; Yi, Chenbo; Kingman, Samuel; Zhu, Yanqiu

    2013-01-01

    The dielectric response of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanoparticles prepared by a sulfidization reaction of WO3 nanoparticles has been investigated, against commercial platelet 2H-WS2 particles, using a cavity perturbation technique at microwave frequencies at temperatures ranging from 20 to 750 °C. The IF-WS2 nanoparticles showed both temperature and frequency dependent dielectric properties. The different dielectric behaviour between the IF-WS2 and 2H-WS2 can be attributed to the different conductivity and structure peculiar to the materials. The microstructure and thermal stability of the IF-WS2 and 2H-WS2 were thoroughly examined, to correlate with the resulting dielectric responses.

  8. 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

  9. 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

  10. 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.

  11. 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

  12. 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

  13. Molybdenum disulfide catalyzed tungsten oxide for on-chip acetone sensing

    NASA Astrophysics Data System (ADS)

    Li, Hong; Ahn, Sung Hoon; Park, Sangwook; Cai, Lili; Zhao, Jiheng; He, Jiajun; Zhou, Minjie; Park, Joonsuk; Zheng, Xiaolin

    2016-09-01

    Acetone sensing is critical for acetone leak detection and holds a great promise for the noninvasive diagnosis of diabetes. It is thus highly desirable to develop a wearable acetone sensor that has low cost, miniature size, sub-ppm detection limit, great selectivity, as well as low operating temperature. In this work, we demonstrate a cost-effective on-chip acetone sensor with excellent sensing performances at 200 °C using molybdenum disulfide (MoS2) catalyzed tungsten oxide (WO3). The WO3 based acetone sensors are first optimized via combined mesoscopic nanostructuring and silicon doping. Under the same testing conditions, our optimized mesoporous silicon doped WO3 [Si:WO3(meso)] sensor shows 2.5 times better sensitivity with ˜1000 times smaller active device area than the state-of-art WO3 based acetone sensor. Next, MoS2 is introduced to catalyze the acetone sensing reactions for Si:WO3(meso), which reduces the operating temperature by 100 °C while retaining its high sensing performances. Our miniaturized acetone sensor may serve as a wearable acetone detector for noninvasive diabetes monitoring or acetone leakage detection. Moreover, our work demonstrates that MoS2 can be a promising nonprecious catalyst for catalytic sensing applications.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. Passively Q-switched mid-infrared fluoride fiber laser around 3 µm using a tungsten disulfide (WS2) saturable absorber

    NASA Astrophysics Data System (ADS)

    Wei, Chen; Luo, Hongyu; Zhang, Han; Li, Chun; Xie, Jitao; Li, Jianfeng; Liu, Yong

    2016-10-01

    In this letter, we demonstrate a passively Q-switched Ho3+/Pr3+ co-doped fluoride fiber laser centered at 2865.7 nm using a tungsten disulfide (WS2) saturable absorber (SA) for the first time, to the best of our knowledge. A multilayer WS2 film was fabricated using the sulfidation grown method and then transferred onto an Au mirror to act as the cavity feedback and SA device in a linear cavity. Under a launched pump power of 318.5 mW, stable Q-switched pulses with an average output power of 48.4 mW were achieved with a pulse duration of 1.73 µs and repetition rate of 131.6 kHz, resulting in a pulse energy of 0.37 µJ. Our experimental results confirm that WS2 can be an effective nonlinear modulator that is suitable for pulse generation at the 3 µm waveband.

  19. Tungsten disulfide nanosheet and exonuclease III co-assisted amplification strategy for highly sensitive fluorescence polarization detection of DNA glycosylase activity.

    PubMed

    Zhao, Jingjin; Ma, Yefei; Kong, Rongmei; Zhang, Liangliang; Yang, Wen; Zhao, Shulin

    2015-08-01

    Herein, we introduced a tungsten disulfide (WS2) nanosheet and exonuclease III (Exo III) co-assisted signal amplification strategy for highly sensitive fluorescent polarization (FP) assay of DNA glycosylase activity. Two DNA glycosylases, uracil-DNA glycosylase (UDG) and human 8-oxoG DNA glycosylase 1 (hOGG1), were tested. A hairpin-structured probe (HP) which contained damaged bases in the stem was used as the substrate. The removal of damaged bases from substrate by DNA glycosylase would lower the melting temperature of HP. The HP was then opened and hybridized with a FAM dye-labeled single strand DNA (DP), generating a duplex with a recessed 3'-terminal of DP. This design facilitated the Exo III-assisted amplification by repeating the hybridization and digestion of DP, liberating numerous FAM fluorophores which could not be adsorbed on WS2 nanosheet. Thus, the final system exhibited a small FP signal. However, in the absence of DNA glycosylases, no hybridization between DP and HP was occurred, hampering the hydrolysis of DP by Exo III. The intact DP was then adsorbed on the surface of WS2 nanosheet that greatly amplified the mass of the labeled-FAM fluorophore, resulting in a large FP value. With the co-assisted amplification strategy, the sensitivity was substantially improved. In addition, this method was applied to detect UDG activity in cell extracts. The study of the inhibition of UDG was also performed. Furthermore, this method is simple in design, easy in implementation, and selective, which holds potential applications in the DNA glycosylase related mechanism research and molecular diagnostics.

  20. 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

  1. The intercalation and exfoliation of tungsten disulfide

    NASA Astrophysics Data System (ADS)

    Miremadi, B. K.; Morrison, S. R.

    1988-05-01

    The exfoliation of WS2, the separation of this layer compound into single molecular layers suspended in solution, was found more difficult than the exfoliation of MoS2 reported earlier. The difficulty was found to be the resistance of the WS2 to intercalation. By ultrasonic treatments while exposed to hexane plus n-butylithium, the lithium was found to intercalate, and exfoliation by immersion in water became possible. Restacking the WS2 by drying in a basic solution led to much larger crystallites than the as-received material, while flocculating by decreasing the pH led to small crystallites with a high density of edge planes. Nickel and aluminum inclusions lead to poor restacking, with no regular c spacing between WS2 basal planes. The more vigorous exfoliation procedure applied to MoS2 also leads to loss of regular c spacing (the x-ray diffraction pattern is essentially that of single molecular layers).

  2. Protein disulfide engineering.

    PubMed

    Dombkowski, Alan A; Sultana, Kazi Zakia; Craig, Douglas B

    2014-01-21

    Improving the stability of proteins is an important goal in many biomedical and industrial applications. A logical approach is to emulate stabilizing molecular interactions found in nature. Disulfide bonds are covalent interactions that provide substantial stability to many proteins and conform to well-defined geometric conformations, thus making them appealing candidates in protein engineering efforts. Disulfide engineering is the directed design of novel disulfide bonds into target proteins. This important biotechnological tool has achieved considerable success in a wide range of applications, yet the rules that govern the stabilizing effects of disulfide bonds are not fully characterized. Contrary to expectations, many designed disulfide bonds have resulted in decreased stability of the modified protein. We review progress in disulfide engineering, with an emphasis on the issue of stability and computational methods that facilitate engineering efforts.

  3. Quantum entanglement in photoactive prebiotic systems.

    PubMed

    Tamulis, Arvydas; Grigalavicius, Mantas

    2014-06-01

    This paper contains the review of quantum entanglement investigations in living systems, and in the quantum mechanically modelled photoactive prebiotic kernel systems. We define our modelled self-assembled supramolecular photoactive centres, composed of one or more sensitizer molecules, precursors of fatty acids and a number of water molecules, as a photoactive prebiotic kernel systems. We propose that life first emerged in the form of such minimal photoactive prebiotic kernel systems and later in the process of evolution these photoactive prebiotic kernel systems would have produced fatty acids and covered themselves with fatty acid envelopes to become the minimal cells of the Fatty Acid World. Specifically, we model self-assembling of photoactive prebiotic systems with observed quantum entanglement phenomena. We address the idea that quantum entanglement was important in the first stages of origins of life and evolution of the biospheres because simultaneously excite two prebiotic kernels in the system by appearance of two additional quantum entangled excited states, leading to faster growth and self-replication of minimal living cells. The quantum mechanically modelled possibility of synthesizing artificial self-reproducing quantum entangled prebiotic kernel systems and minimal cells also impacts the possibility of the most probable path of emergence of protocells on the Earth or elsewhere. We also examine the quantum entangled logic gates discovered in the modelled systems composed of two prebiotic kernels. Such logic gates may have application in the destruction of cancer cells or becoming building blocks of new forms of artificial cells including magnetically active ones.

  4. Quantum entanglement in photoactive prebiotic systems.

    PubMed

    Tamulis, Arvydas; Grigalavicius, Mantas

    2014-06-01

    This paper contains the review of quantum entanglement investigations in living systems, and in the quantum mechanically modelled photoactive prebiotic kernel systems. We define our modelled self-assembled supramolecular photoactive centres, composed of one or more sensitizer molecules, precursors of fatty acids and a number of water molecules, as a photoactive prebiotic kernel systems. We propose that life first emerged in the form of such minimal photoactive prebiotic kernel systems and later in the process of evolution these photoactive prebiotic kernel systems would have produced fatty acids and covered themselves with fatty acid envelopes to become the minimal cells of the Fatty Acid World. Specifically, we model self-assembling of photoactive prebiotic systems with observed quantum entanglement phenomena. We address the idea that quantum entanglement was important in the first stages of origins of life and evolution of the biospheres because simultaneously excite two prebiotic kernels in the system by appearance of two additional quantum entangled excited states, leading to faster growth and self-replication of minimal living cells. The quantum mechanically modelled possibility of synthesizing artificial self-reproducing quantum entangled prebiotic kernel systems and minimal cells also impacts the possibility of the most probable path of emergence of protocells on the Earth or elsewhere. We also examine the quantum entangled logic gates discovered in the modelled systems composed of two prebiotic kernels. Such logic gates may have application in the destruction of cancer cells or becoming building blocks of new forms of artificial cells including magnetically active ones. PMID:24799958

  5. Disulfide bonds of acetylcholinesterase

    SciTech Connect

    MacPhee-Quigley, K.; Vedvick, T.; Taylor, P.; Taylor, S.

    1986-05-01

    The positions of the inter- and intrasubunit disulfide bridges were established for the 11S form of acetylcholinesterase (AChE) isolated from Torpedo californica. A major form of AChE localized within the basal lamina of the synapse is a dimensionally asymmetric molecule which contains either two (13S) or three (17S) sets of catalytic subunits linked to collagenous and non-collagenous structural subunits. Limited proteolysis yields a tetramer of catalytic subunits which sediments at 11S. Each catalytic subunit contains 8 cysteine residues. Initially, these Cys residues were identified following trypsin digestion of the reduced protein alkylated with (/sup 14/C)-iodoacetate. Peptides were resolved by gel filtration followed by reverse phase HPLC. To determine the disulfide bonding profile, native non-reduced 11S AChE was treated with a fluorescent, sulfhydryl-specific reagent, monobromobimane, prior to proteolytic digestion. One fluorescent Cys peptide was identified indicating that a single sulfhydryl residue was present in its reduced form. Three pairs of disulfide bonded peptides were identified, sequenced, and localized in the polypeptide chain. The Cys residue that is located in the C-terminal tryptic peptide was disulfide bonded to an identical peptide and thus forms the intersubunit crosslink. Finally, the cysteine positions have been compared with the sequence of the homologous protein, thyroglobulin. Both likely share a common pattern of folding.

  6. Extraordinary Second Harmonic Generation in Tungsten Disulfide Monolayers

    PubMed Central

    Janisch, Corey; Wang, Yuanxi; Ma, Ding; Mehta, Nikhil; Elías, Ana Laura; Perea-López, Néstor; Terrones, Mauricio; Crespi, Vincent; Liu, Zhiwen

    2014-01-01

    We investigate Second Harmonic Generation (SHG) in monolayer WS2 both deposited on a SiO2/Si substrate or suspended using transmission electron microscopy grids. We find unusually large second order nonlinear susceptibility, with an estimated value of deff ~ 4.5 nm/V nearly three orders of magnitude larger than other common nonlinear crystals. In order to quantitatively characterize the nonlinear susceptibility of two-dimensional (2D) materials, we have developed a formalism to model SHG based on the Green's function with a 2D nonlinear sheet source. In addition, polarized SHG is demonstrated as a useful method to probe the structural symmetry and crystal orientation of 2D materials. To understand the large second order nonlinear susceptibility of monolayer WS2, density functional theory based calculation is performed. Our analysis suggests the origin of the large nonlinear susceptibility in resonance enhancement and a large joint density of states, and yields an estimate of the nonlinear susceptibility value deff = 0.77 nm/V for monolayer WS2, which shows good order-of-magnitude agreement with the experimental result. PMID:24984953

  7. 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.

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  12. 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...

  13. 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.

  14. 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.

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

    DOEpatents

    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.

  16. 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.

  17. Tungsten Filament Fire

    ERIC Educational Resources Information Center

    Ruiz, Michael J.; Perkins, James

    2016-01-01

    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…

  18. 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.

  19. Oxidative addition of disulfides to the complex W(CO){sub 3}(phen)(EtCN). Synthesis, structure, and reactivity of W(CO){sub 2}(phen)(SR){sub 2}(R = Ph, Me, CH{sub 2}Ph, {sup t}Bu; phen = 1,10-phenanthroline) coordinatively unsaturated complexes of tungsten(II) that reversibly bind CO and other ligands

    SciTech Connect

    Lang, R.F.; Ju, T.D.; Kiss, G. |

    1994-08-31

    The complex W(CO){sub 3}(phen)(EtCN) undergoes oxidative addition with disulfides forming the formally 16-electron complexes W(CO){sub 2}(phen)(SR){sub 2}(R=Ph, {sup t}Bu, Me, benzyl). The reactions proceed through intermediates identified spectroscopically as the coordinated disulfide complexes. The rate of oxidative addition of coordinated disulfides is in the order {sup t}BuSSBu{sup t}<

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  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. 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.

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

    SciTech Connect

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

    2011-07-15

    Titania-lanthanum phosphate nanocomposites with multifunctional properties have been synthesized by aqueous sol-gel method. The precursor sols with varying TiO{sub 2}:LaPO{sub 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{sub 2} in TiO{sub 2}-LaPO{sub 4} composite precursors was found to be stable even on annealing at 800 deg. C. The glass substrates, coated with TL1 (TiO{sub 2}-LaPO{sub 4} composition with 1 mol% LaPO{sub 4}) and TL50 (composite precursor containing TiO{sub 2} and LaPO{sub 4} with molar ratio 1:1) sols and annealed at 400 deg. C, produced contact angles of 74 deg. and 92 deg., respectively, though it is only 62 deg. for pure TiO{sub 2} coating. The glass substrates, coated with TL50 sol, produced surfaces with relatively high roughness and uneven morphology. The TL1 material, annealed at 800 deg. C, has shown the highest UV photoactivity with an apparent rate constant, k{sub app}=24x10{sup -3} min{sup -1}, which is over five times higher than that observed with standard Hombikat UV 100 (k{sub app}=4x10{sup -3} min{sup -1}). The photoactivity combined with a moderate contact angle (85.3 deg.) shows that this material has a promise as an efficient self-cleaning precursor. - Graphical abstract: Multifunctional TiO{sub 2}-LaPO{sub 4} composite stabilizes anatase phase with enhanced photocatalytic activity, and moderately higher hydrophobicity is a promising material for self-cleaning application. Highlights: > Titania-lanthanum phosphate nanocomposites were synthesized by aqueous sol-gel method. > Transparent, hydrophobic, photoactive coatings were developed on glass substrates. > The glass substrates, coated with TL1 annealed at 400 deg. C, produced a contact angle of 74 deg

  7. Tungsten trioxide as a visible light photocatalyst for volatile organic carbon removal.

    PubMed

    Wicaksana, Yossy; Liu, Sanly; Scott, Jason; Amal, Rose

    2014-10-31

    Tungsten trioxide (WO3) has been demonstrated to possess visible light photoactivity and presents a means of overcoming the UV-light dependence of photocatalysts, such as titanium dioxide. In this study, WO3 nanostructures have been synthesised by a hydrothermal method using sodium tungstate (Na2WO4·2H2O), sulphate precursors and pH as structure-directing agents and parameters, respectively. By altering the concentration of the sulphate precursors and pH, it was shown that different morphologies and phases of WO3 can be achieved. The effect of the morphology of the final WO3 product on the visible light photoactivity of ethylene degradation in the gas phase was investigated. In addition, platinum (Pt) was photodeposited on the WO3 structures with various morphologies to enhance the photocatalytic properties. It was found that the photocatalytic properties of the WO3 samples greatly depend on their morphology, chemical composition and surface modification. WO3 with a cuboid morphology exhibited the highest visible light photoactivity compared to other morphologies, while adding Pt to the surface improved the performance of certain WO3 structures.

  8. 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.

  9. 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.

  10. 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.

  11. Synthesis of cyclic disulfide-rich peptides.

    PubMed

    Akcan, Muharrem; Craik, David J

    2013-01-01

    In this chapter we describe two SPPS approaches for producing cyclic disulfide-rich peptides in our laboratory, including cyclotides from plants, cyclic conotoxins from cone snail venoms, chlorotoxin from scorpion venom, and the sunflower trypsin inhibitor peptide, SFTI-1.

  12. 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.

  13. Disulfide chromophore and its optical activity.

    PubMed

    Maloň, Petr; Bednárová, Lucie; Straka, Michal; Krejčí, Lucie; Kumprecht, Lukáš; Kraus, Tomáš; Kubáňová, Markéta; Baumruk, Vladimír

    2010-01-01

    The compounds I-IV derived from α-D-cyclodextrin moiety by bridging and/or interconnecting with various patterns of disulfide bonds were chosen as models for the spectroscopic study of conformation of the disulfide bridge. The energy gap between the disulfide and cyclodextrin's electronic transitions allows us to investigate absorption and electronic circular dichroism spectra without disturbing spectral overlaps with amides or aromatic amino acids in peptides or proteins. Raman optical activity (ROA) spectra were measured and the bands due to S-S and C-S stretching motion identified. Comparison with the quantum mechanical calculations of simple models indicates that sense of disulfide twist follows sign of the measured S-S ROA band.

  14. 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.

  15. 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.

  16. Preparation of tungsten oxide

    DOEpatents

    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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. Thiol-disulfide exchange in signaling: disulfide bonds as a switch.

    PubMed

    Messens, Joris; Collet, Jean-François

    2013-05-01

    The major function of disulfide bonds is not only the stabilization of protein structures. Over the last 30 years, a change in perspective took place driven by groundbreaking experiments, which promoted disulfide bonds to central players in essential thiol-disulfide exchange reactions involved in signal transduction, thiol protection, and redox homeostasis regulation. This new view stimulated redox research and led to the discovery of novel redox pathways, redox enzymes, and new low-molecular-weight thiols. These redox-sensitive molecules operate along diverse pathways via a dynamic thiol-disulfide mechanism in which disulfide bonds are reversibly formed and reduced, thereby switching the molecules between different conformational and functional states. It is now clear that disulfide bonds play a pivotal role in cellular reduction and oxidation processes. However, in spite of the fundamental cell biological and medical importance of the thiol-disulfide exchange switches, we are only beginning to understand their principles of specificity, their mechanism of action, and their role in signal transduction. Our further progress in understanding the thiol-disulfide switches will strongly depend on the chemical tools and on the technological advances that will be made in the development of new methodologies.

  4. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 2 2011-10-01 2011-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  5. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 2 2014-10-01 2014-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  6. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 2 2013-10-01 2013-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  7. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 2 2012-10-01 2012-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  8. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 2 2010-10-01 2010-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  9. 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.

  10. 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.

  11. 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)

  12. Cellular Disulfide Bond Formation in Bioactive Peptides and Proteins

    PubMed Central

    Patil, Nitin A.; Tailhades, Julien; Hughes, Richard Anthony; Separovic, Frances; Wade, John D.; Hossain, Mohammed Akhter

    2015-01-01

    Bioactive peptides play important roles in metabolic regulation and modulation and many are used as therapeutics. These peptides often possess disulfide bonds, which are important for their structure, function and stability. A systematic network of enzymes—a disulfide bond generating enzyme, a disulfide bond donor enzyme and a redox cofactor—that function inside the cell dictates the formation and maintenance of disulfide bonds. The main pathways that catalyze disulfide bond formation in peptides and proteins in prokaryotes and eukaryotes are remarkably similar and share several mechanistic features. This review summarizes the formation of disulfide bonds in peptides and proteins by cellular and recombinant machinery. PMID:25594871

  13. 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.

  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. Tungsten resources of Brazil

    USGS Publications Warehouse

    White, Max Gregg

    1974-01-01

    Brazilian tungsten production, 85 percent of which is exported, comes almost entirely from scheelite-bearing tactites in northeast Brazil, and has reached an annual rate of about 2,000 metric tons (2,200 short tons) of scheelite concentrate with 70 percent WO3. Scheelite ore reserves, located principally in the State of Rio Grande do Norte, are estimated to be as high as 8,300,000 tons (9,100,000 short tons) containing 0.7 percent WO3. Minor deposits (or those about which only minimal information is available) of wolframite, with which some cassiterite is associated, are located in Sao Paulo, Santa Catarina, and Rio Grande do Sul. Both the scheelite and the wolframite deposits are considered . to be late Precambrian A (620 to 900 m.y.) or early Cambrian in age.

  16. 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.

  17. The two photocycles of photoactive yellow protein from Rhodobacter sphaeroides.

    PubMed

    Haker, Andrea; Hendriks, Johnny; van Stokkum, Ivo H M; Heberle, Joachim; Hellingwerf, Klaas J; Crielaard, Wim; Gensch, Thomas

    2003-03-01

    The absorption spectrum of the photoactive yellow protein from Rhodobacter sphaeroides (R-PYP) shows two maxima, absorbing at 360 nm (R-PYP(360)) and 446 nm (R-PYP(446)), respectively. Both forms are photoactive and part of a temperature- and pH-dependent equilibrium (Haker, A., Hendriks, J., Gensch, T., Hellingwerf, K. J., and Crielaard, W. (2000) FEBS Lett. 486, 52-56). At 20 degrees C, for PYP characteristic, the 446-nm absorbance band displays a photocycle, in which the depletion of the 446-nm ground state absorption occurs in at least three phases, with time constants of <30 ns, 0.5 micros, and 17 micros. Intermediates with both blue- and red-shifted absorption maxima are transiently formed, before a blue-shifted intermediate (pB(360), lambda(max) = 360 nm) is established. The photocycle is completed with a monophasic recovery of the ground state with a time constant of 2.5 ms. At 7 degrees C these photocycle transitions are slowed down 2- to 3-fold. Upon excitation of R-PYP(360) with a UV-flash (330 +/- 50 nm) a species with a difference absorption maximum at approximately 435 nm is observed that returns to R-PYP(360) on a minute time scale. Recovery can be accelerated by a blue light flash (450 nm). R-PYP(360) and R-PYP(446) differ in their overall protein conformation, as well as in the isomerization and protonation state of the chromophore, as determined with the fluorescent polarity probe Nile Red and Fourier Transform Infrared spectroscopy, respectively.

  18. 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.

  19. Disulfide by Design 2.0: a web-based tool for disulfide engineering in proteins

    PubMed Central

    2013-01-01

    Background Disulfide engineering is an important biotechnological tool that has advanced a wide range of research. The introduction of novel disulfide bonds into proteins has been used extensively to improve protein stability, modify functional characteristics, and to assist in the study of protein dynamics. Successful use of this technology is greatly enhanced by software that can predict pairs of residues that will likely form a disulfide bond if mutated to cysteines. Results We had previously developed and distributed software for this purpose: Disulfide by Design (DbD). The original DbD program has been widely used; however, it has a number of limitations including a Windows platform dependency. Here, we introduce Disulfide by Design 2.0 (DbD2), a web-based, platform-independent application that significantly extends functionality, visualization, and analysis capabilities beyond the original program. Among the enhancements to the software is the ability to analyze the B-factor of protein regions involved in predicted disulfide bonds. Importantly, this feature facilitates the identification of potential disulfides that are not only likely to form but are also expected to provide improved thermal stability to the protein. Conclusions DbD2 provides platform-independent access and significantly extends the original functionality of DbD. A web server hosting DbD2 is provided at http://cptweb.cpt.wayne.edu/DbD2/. PMID:24289175

  20. 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.

  1. 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.

  2. 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.

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  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. 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,...

  14. 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,...

  15. 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,...

  16. 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,...

  17. 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

  18. Influence of photoactive additive on growth of polymer microelements on the top of optical fiber

    NASA Astrophysics Data System (ADS)

    Fokina, M. I.; Burunkova, J. E.; Denisuk, I. Y.

    2007-06-01

    Kinetics of polymer microelements growing on the top of optical fiber with use of different photoactive additives (Rodamine B, Coumarin) was studied. Consequently, the technological principles of production of polymer self-adjoint microelements were founded

  19. 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.

  20. Mitochondrial protein import: An unexpected disulfide bond.

    PubMed

    Mokranjac, Dejana

    2016-08-15

    Most mitochondrial proteins are imported through the TIM23 translocation channel, the structure and molecular nature of which are still unclear. In this issue, Ramesh et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201602074) show that the TIM23 subunit Tim17 contains a disulfide bond that is crucial for protein translocation and channel gating. PMID:27502488

  1. Native Disulfide Bond Formation in Proteins

    PubMed Central

    Woycechowsky, Kenneth J.; Raines, Ronald T.

    2010-01-01

    Summary Native disulfide bond formation is critical for the proper folding of many proteins. Recent studies using newly identified protein oxidants, folding catalysts, and mutant cells provide insight into the mechanism of oxidative protein folding in vivo. This insight promises new strategies for more efficient protein production. PMID:11006541

  2. Recovery of molybdenum from molybdenum disulfide

    SciTech Connect

    Vanderpool, C.D.; MacInnis, M.B.

    1986-07-08

    A process is described for recovering molybdenum from molybdenum disulfide. The process consists of: (a) forming a slurry of the molybdenum disulfide in a solution of an alkali metal hydroxide, the amount of alkali metal hydroxide being sufficient to react with at least a portion of the molybdenum disulfide to form an alkali metal molybdate and an alkali sulfate; (b) heating the slurry in an oxidizing atmosphere at an elevated temperature and pressure and for a sufficient time to convert at least a portion of the molybdenum disulfide to the alkali metal molybdate and provide a pregnant liquor of the alkali metal molybdate and a residue; (c) separating the pregnant liquor from the residue; (d) adding a sufficient amount of a hexamine to the pregnant liquor to form an hexamine-molybdenum compound containing the major portion of the molybdenum which is in the pregnant liquor; (e) adjusting the pH of the resulting hexamine-treated pregnant liquor to from about 1.5 to about 3.8 to precipitate the major portion of the hexamine-molybdenum compound; and (f) separating the hexamine-molybdenum compound from the resulting mother liquor.

  3. 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.

  4. Layer-dependent modulation of tungsten disulfide photoluminescence by lateral electric fields.

    PubMed

    He, Zhengyu; Sheng, Yuewen; Rong, Youmin; Lee, Gun-Do; Li, Ju; Warner, Jamie H

    2015-03-24

    Large single-crystal domains of WS2 are grown by chemical vapor deposition, and their photoluminescent properties under a lateral electric field are studied. We demonstrate that monolayer and bilayer WS2 have opposite responses to lateral electric fields, with WS2 photoluminescence (PL) substantially reduced in monolayer and increased in bilayers with increasing lateral electric field strength. Temperature-dependent PL measurements are also undertaken and show behavior distinctly different than that of the lateral electric field effects, ruling out heating as the cause of the PL changes. The PL variation in both monolayer and bilayer WS2 is attributed to the transfer of photoexcited electrons from one conduction band extremum to another, modifying the resultant recombination pathways. This effect is observed in 2D transition metal dichalcogenides due to their large exciton binding energy and small energy difference between the two conduction band extrema.

  5. 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.

  6. Effect of nickel on the physicochemical and catalytic properties of tungsten disulfide

    SciTech Connect

    Kondrat'ev, S.I.; Antoshin, G.V.; Fedorovskaya, E.A.; Nikishenko, S.B.; Slinkin, A.A.

    1985-12-01

    The authors used x-ray photoelectron spectroscopy (ESCA) and magnetic susceptibility methods to investigate Ni-WS/sub 2/ catalysts prepared by impregnation and mutual precipitation. These systems were found to have two types of Ni/sup 2 +/ ions, presumably in D /SUB 3h/ and t /SUB d/ environments, as well as Ni/sup 3 +/ or isolated Ni/sup 2 +/ ions, the latter being highly mobile. The Ni-WS/sub 2/ systems were found to contain different active centers than the original WS/sub 2/ and the promotion effect is connected with a reduction in the activation energy for the hydrodesulfurization of thiophene. The promotion effect of nickel does not depend on the method of introducing the promoter into the catalyst. The mechanisms for promotion by cobalt and nickel in MoS/sub 2/ and WS/sub 2/, respectively, were found to be similar.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. Trion fine structure and coupled spin–valley dynamics in monolayer tungsten disulfide

    PubMed Central

    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

  12. 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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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. PMID:27398214

  2. 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

  3. 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

  4. Synchrotron ultrafast techniques for photoactive transition metal complexes.

    PubMed

    Borfecchia, Elisa; Garino, Claudio; Salassa, Luca; Lamberti, Carlo

    2013-07-28

    In the last decade, the use of time-resolved X-ray techniques has revealed the structure of light-generated transient species for a wide range of samples, from small organic molecules to proteins. Time resolutions of the order of 100 ps are typically reached, allowing one to monitor thermally equilibrated excited states and capture their structure as a function of time. This review aims at providing a general overview of the application of time-resolved X-ray solution scattering (TR-XSS) and time-resolved X-ray absorption spectroscopy (TR-XAS), the two techniques prevalently employed in the investigation of light-triggered structural changes of transition metal complexes. In particular, we herein describe the fundamental physical principles for static XSS and XAS and illustrate the theory of time-resolved XSS and XAS together with data acquisition and analysis strategies. Selected pioneering examples of photoactive transition metal complexes studied by TR-XSS and TR-XAS are discussed in depth.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. Tungsten silicide formation from sequentially sputtered tungsten and silicon films

    NASA Astrophysics Data System (ADS)

    Molarius, J. M.; Franssila, S.; Drozdy, G.; Saarilahti, J.

    1991-11-01

    As-deposited tungsten silicide films have typically high resistivity and require annealing to lower the resistivity to practical values. Rapid thermal annealing (RTA) has emerged as the main method because impurity diffusion in silicides is extremely fast. In this study we have explored the possibility of reducing the required thermal budget for tungsten silicide annealing by sputtering multilayer W /Si films. In addition to direct technological relevance, multilayer structures offer new insights into silicide formation. We propose a hypothesis "oxygen supply to interface ratio" for explaining why multilayer W /Si structures are beneficial for silicide formation. We have prevented the possible oxygen barrier formation at the W /Si interface by diminishing the oxygen supply by several means: substrate heating during deposition, multiple thin layers, a silicon capping layer and argon purging during RTA. Tetragonal WSi 2 is formed at 700°C and no silicon-rich phases are observed. Low-resistivity WSi 2 is produced by RTA at 1000°C, 120 s. Sheet resistance values around 3 ω/□ amends the use of tungsten silicide in practical polycide structures. The ultimate resistivity of our WSi 2, 30 μω · cm, is among the lowest reported for tungsten silicide, and it is achieved in a very straightforward fashion, using typical production equipment.

  10. 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.

  11. Functional Differences in Yeast Protein Disulfide Isomerases

    PubMed Central

    Nørgaard, Per; Westphal, Vibeke; Tachibana, Christine; Alsøe, Lene; Holst, Bjørn; Winther, Jakob R.

    2001-01-01

    PDI1 is the essential gene encoding protein disulfide isomerase in yeast. The Saccharomyces cerevisiae genome, however, contains four other nonessential genes with homology to PDI1: MPD1, MPD2, EUG1, and EPS1. We have investigated the effects of simultaneous deletions of these genes. In several cases, we found that the ability of the PDI1 homologues to restore viability to a pdi1-deleted strain when overexpressed was dependent on the presence of low endogenous levels of one or more of the other homologues. This shows that the homologues are not functionally interchangeable. In fact, Mpd1p was the only homologue capable of carrying out all the essential functions of Pdi1p. Furthermore, the presence of endogenous homologues with a CXXC motif in the thioredoxin-like domain is required for suppression of a pdi1 deletion by EUG1 (which contains two CXXS active site motifs). This underlines the essentiality of protein disulfide isomerase-catalyzed oxidation. Most mutant combinations show defects in carboxypeptidase Y folding as well as in glycan modification. There are, however, no significant effects on ER-associated protein degradation in the various protein disulfide isomerase-deleted strains. PMID:11157982

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. Oxidant Sensing by Reversible Disulfide Bond Formation*

    PubMed Central

    Cremers, Claudia M.; Jakob, Ursula

    2013-01-01

    Maintenance of the cellular redox balance is crucial for cell survival. An increase in reactive oxygen, nitrogen, or chlorine species can lead to oxidative stress conditions, potentially damaging DNA, lipids, and proteins. Proteins are very sensitive to oxidative modifications, particularly methionine and cysteine residues. The reversibility of some of these oxidative protein modifications makes them ideally suited to take on regulatory roles in protein function. This is especially true for disulfide bond formation, which has the potential to mediate extensive yet fully reversible structural and functional changes, rapidly adjusting the protein's activity to the prevailing oxidant levels. PMID:23861395

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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...

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  12. Pyrazine-derived disulfide-reducing agent for chemical biology.

    PubMed

    Lukesh, John C; Wallin, Kelly K; Raines, Ronald T

    2014-08-28

    For fifty years, dithiothreitol (DTT) has been the preferred reagent for the reduction of disulfide bonds in proteins and other biomolecules. Herein we report on the synthesis and characterization of 2,3-bis(mercaptomethyl)pyrazine (BMMP), a readily accessible disulfide-reducing agent with reactivity under biological conditions that is markedly superior to DTT and other known reagents.

  13. 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.

  14. "CLASPing" tungsten's effects on microtubules with "PINs".

    PubMed

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

    2015-01-01

    Tungsten, supplied as sodium tungstate, inhibits root elongation in Arabidopsis thaliana, which has been attributed to a diminishing of PIN2 and PIN3 auxin efflux carriers. In this work, we sought to analyze the effect of tungsten on cortical microtubules and CLASP (Cytoplasmic Linker Associated Protein), which are also involved in the anisotropic cell expansion of root cells. Seedlings grown in a tungsten-free substrate for 4 d and then transplanted into a tungsten-containing substrate exhibited randomly oriented microtubules in a time-dependent manner. While tungsten had no effect on roots treated for 3 h, microtubule alignment was obviously affected in the transition and elongation zones after a 6, 12, 24, 48 h tungsten treatment, at prolonged tungsten administrations and in seedlings grown directly in the presence of tungsten. This change in microtubule orientation may be associated with the reduction of CLASP protein expression induced by tungsten, as evidenced in experiments with plants expressing the CLASP-GFP protein. A possible mechanism, by which the coordinated functions of CLASP, PIN2 and microtubules are affected, as revealed by inhibited root growth, is discussed. PMID:26313814

  15. Intramolecular versus intermolecular disulfide bonds in prion proteins.

    PubMed

    Welker, Ervin; Raymond, Lynne D; Scheraga, Harold A; Caughey, Byron

    2002-09-01

    Prion protein (PrP) is the major component of the partially protease-resistant aggregate that accumulates in mammals with transmissible spongiform encephalopathies. The two cysteines of the scrapie form, PrP(Sc), were found to be in their oxidized (i.e. disulfide) form (Turk, E., Teplow, D. B., Hood, L. E., and Prusiner, S. B. (1988) Eur. J. Biochem. 176, 21-30); however, uncertainty remains as to whether the disulfide bonds are intra- or intermolecular. It is demonstrated here that the monomers of PrP(Sc) are not linked by intermolecular disulfide bonds. Furthermore, evidence is provided that PrP(Sc) can induce the conversion of the oxidized, disulfide-intact form of the monomeric cellular prion protein to its protease-resistant form without the temporary breakage and subsequent re-formation of the disulfide bonds in cell-free reactions.

  16. Sunlight highly photoactive Bi2WO6-TiO2 heterostructures for rhodamine B degradation.

    PubMed

    Colón, G; Murcia López, S; Hidalgo, M C; Navío, J A

    2010-07-14

    Highly efficient Bi(2)WO(6)-TiO(2) heterostructures are synthesized by means of a hydrothermal method; they have high photoactivity for the degradation of rhodamine B under sunlike irradiation. An interesting synergetic effect between TiO(2) and Bi(2)WO(6) leads to an improved charge carrier separation mechanism, causing the excellent photocatalytic performance.

  17. 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

  18. 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....

  19. 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....

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

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 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, 2010 CFR

    2010-07-01

    ... 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. 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....

  3. Chemical methods for producing disulfide bonds in peptides and proteins to study folding regulation.

    PubMed

    Okumura, Masaki; Shimamoto, Shigeru; Hidaka, Yuji

    2014-04-01

    Disulfide bonds play a critical role in the folding of secretory and membrane proteins. Oxidative folding reactions of disulfide bond-containing proteins typically require several hours or days, and numerous misbridged disulfide isomers are often observed as intermediates. The rate-determining step in refolding is thought to be the disulfide-exchange reaction from nonnative to native disulfide bonds in folding intermediates, which often precipitate during the refolding process because of their hydrophobic properties. To overcome this, chemical additives or a disulfide catalyst, protein disulfide isomerase (PDI), are generally used in refolding experiments to regulate disulfide-coupled peptide and protein folding. This unit describes such methods in the context of the thermodynamic and kinetic control of peptide and protein folding, including (1) regulation of disulfide-coupled peptides and protein folding assisted by chemical additives, (2) reductive unfolding of disulfide-containing peptides and proteins, and (3) regulation of disulfide-coupled peptide and protein folding using PDI.

  4. Superconductivity in highly disordered dense carbon disulfide.

    PubMed

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

    2013-07-16

    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.

  5. 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

  6. 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.

  7. Carbon disulfide removal by zero valent iron.

    PubMed

    McGeough, Karen L; Kalin, Robert M; Myles, Philip

    2007-07-01

    The use of zero valent iron (Fe0) for the remediation of water contaminated with carbon disulfide (CS2), a common groundwater contaminant, has been evaluated in this study. Mineralogical analysis of Fe0 filings and polished Fe0 cross-sections indicates that iron sulfide is formed due to the removal of carbon disulfide from solution by Fe0. The kinetics of CS2 removal by Fe0 was examined through both batch and column testing, and it is demonstrated that CS2 is removed rapidly from solution. A linear relationship was observed, through batch testing, between the pseudo-first-order rate constant (k(obs)) and the surface area concentration of Fe0 (rho(a)). Data obtained from kinetic batch tests performed at four temperature levels conformed to the Arrhenius equation, and the calculated apparent activation energy (E(a)) was 37 +/- 2.3 kJ mol(-1), indicating that the kinetics of CS2 removal by Fe0 is controlled by a chemical surface reaction. The temperature correction factors for CS2 from a reference of 25 degrees C were x 1.4 for 18 degrees C, x 1.7 for 15 degrees C, x 2.0 for 12 degrees C, and x 2.3 for 9 degrees C. Surface area normalization of k(obs) obtained through batch and column testing gives specific reaction rate constants (k(SA)) within 1 order of magnitude, indicating that k(SA) values are useful as a general descriptor of CS2-Fe0 reaction kinetics and that these values provide a clear starting point for design calculations prior to commencing site-specific treatability studies for permeable reactive barrier design.

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Catalysis of protein disulfide bond isomerization in a homogeneous substrate.

    PubMed

    Kersteen, Elizabeth A; Barrows, Seth R; Raines, Ronald T

    2005-09-13

    Protein disulfide isomerase (PDI) catalyzes the rearrangement of nonnative disulfide bonds in the endoplasmic reticulum of eukaryotic cells, a process that often limits the rate at which polypeptide chains fold into a native protein conformation. The mechanism of the reaction catalyzed by PDI is unclear. In assays involving protein substrates, the reaction appears to involve the complete reduction of some or all of its nonnative disulfide bonds followed by oxidation of the resulting dithiols. The substrates in these assays are, however, heterogeneous, which complicates mechanistic analyses. Here, we report the first analysis of disulfide bond isomerization in a homogeneous substrate. Our substrate is based on tachyplesin I, a 17-mer peptide that folds into a beta hairpin stabilized by two disulfide bonds. We describe the chemical synthesis of a variant of tachyplesin I in which its two disulfide bonds are in a nonnative state and side chains near its N and C terminus contain a fluorescence donor (tryptophan) and acceptor (N(epsilon)-dansyllysine). Fluorescence resonance energy transfer from 280 to 465 nm increases by 28-fold upon isomerization of the disulfide bonds into their native state (which has a lower E(o') = -0.313 V than does PDI). We use this continuous assay to analyze catalysis by wild-type human PDI and a variant in which the C-terminal cysteine residue within each Cys-Gly-His-Cys active site is replaced with alanine. We find that wild-type PDI catalyzes the isomerization of the substrate with kcat/K(M) = 1.7 x 10(5) M(-1) s(-1), which is the largest value yet reported for catalysis of disulfide bond isomerization. The variant, which is a poor catalyst of disulfide bond reduction and dithiol oxidation, retains virtually all of the activity of wild-type PDI in catalysis of disulfide bond isomerization. Thus, the C-terminal cysteine residues play an insignificant role in the isomerization of the disulfide bonds in nonnative tachyplesin I. We conclude

  16. Photodecolorization of Rhodamine B on tungsten-doped TiO2/activated carbon under visible-light irradiation.

    PubMed

    Li, Youji; Zhou, Xiaoming; Chen, Wei; Li, Leiyong; Zen, Mengxiong; Qin, Shidong; Sun, Shuguo

    2012-08-15

    Tungsten-doped TiO(2)/activated carbon catalysts have been prepared by a supercritical-pretreatment-assisted sol-gel process. The structural features of the photocatalysts have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV/Vis diffuse-reflectance spectroscopy (DRS), electron dispersive X-ray (EDX), photoluminescence spectroscopy, and Brunauer-Emmett-Teller (BET) analysis. The results revealed that a W-TiO(2) layer was coated on the AC surface, and had higher surface area and smaller crystallite size than TiO(2)/AC obtained by a similar route. The W dopant was responsible for narrowing the band gap of TiO(2) and shifting its optical response from the ultraviolet (UV) to the visible-light region. The photocatalytic performances of the supported catalysts have been evaluated for the degradation of Rhodamine B (RhB) solution under visible-light irradiation. Compared with bulk W-TiO(2), the photoactivity was obviously enhanced when it was coated onto AC. In addition, it was found that the reactivity showed a significant relationship with the amount of W dopant, and the photoactivity order of the catalysts from weak to strong showed good agreement with their PL intensities. The effects of TiO(2) content, tungsten ion content, catalyst amount, pH, and initial RhB concentration have been examined as operational parameters. The photocatalytic reactions followed pseudo-first-order kinetics and are discussed in terms of the Langmuir-Hinshelwood model.

  17. 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.

  18. 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...

  19. 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...

  20. 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...

  1. 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...

  2. 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...

  3. Synthesis of radioiodine labeled dibenzyl disulfide for evaluation of tumor cell uptake.

    PubMed

    Ryu, Eun Kyoung; Choe, Yearn Seong; Byun, Sang Sung; Lee, Kyung-Han; Chi, Dae Yoon; Choi, Yong; Kim, Byung-Tae

    2004-03-01

    Benzyl 4-halobenzyl and ally benzyl disulfide were synthesized as diallyl disulfide analogues and their tumor growth inhibitory effects on the cancer cells (SNU C5 and MCF-7) were comparable to that of diallyl disulfide, indicating that the disulfide functional group was responsible for the tumor growth inhibitory effects. Cu(I)-assisted radioiodination of benzyl 4-bromobenzyl disulfide gave benzyl 4-[123I/125I]iodobenzyl disulfide in 30-40% radiochemical yield. The radiolabeled disulfide was taken up by the cancer cells in a time-dependent manner, and the uptake was inhibited by the pretreatment of S-methyl methanethiosulfonate (MMTS), phorone and diallyl disulfide. This study suggested that the radiolabeled dibenzyl disulfide was taken up by the cancer cells via thiol-disulfide exchange and retained inside the cells. PMID:14980597

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. Single crystal tungsten kinetic energy penetrators

    SciTech Connect

    Cline, C.F.; Gogolewski, R.P.

    1992-05-01

    We have explored the terminal ballistic performance of single crystal tungsten as a kinetic energy penetrator. Scientific speculation as to the anticipated penetration performance and nature of the interaction between such a kinetic energy penetrator and semi-infinite and spaced metallic targets has led us to perform laboratory scale experiments and metallographic examinations of post-impact penetrator materials. The single tungsten crystals were ground into kinetic energy penetrators with the [l angle]111[r angle] and [l angle]100[r angle] crystal direction being coincident with the axis of symmetry of the penetrators. The crystals were electro-polished to their final diameter. We, compared the terminal performance at current ordnance speeds of [l angle]111[r angle] single crystal tungsten to 90W-10 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against a spaced steel (triple) target at sixty-five degrees obliquity. We also compared the terminal performance of [l angle]100[r angle] and [l angle]111[r angle] single crystal tungsten with 90W-10 and 98W02 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against monolithic 4340 alloy steel (HRC = 36) at normal impact. We radiographed the penetrators during the interactions with the targets, we recovered portions of the penetrators after the ballistic experiments, and we conducted metallographic examinations of penetrator remnants. From the radiographic records and the metallographic examinations, we drew conclusions pertaining to insights into the terminal interactions of the penetrators with the targets and suggestions as to improved compositions of the cemented tungsten penetrators.

  12. Chemically active organically doped sol-gel materials: enzymatic sensors, chemical sensors, and photoactive materials

    NASA Astrophysics Data System (ADS)

    Avnir, David; Braun, S.; Lev, Ovadia; Ottolenghi, M.

    1992-12-01

    Organically-doped porous sol-gel matrices of optical grade have evolved in recent years into a wide class of materials with diverse applications. We review recent progress made in our laboratories in three domains of applications: the trapping of enzymes with the consequent design of (e.g. glucose) sensors; the development of chemical sensors; and the design of photoactive material for (solar) light energy conversion.

  13. 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

  14. 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.

  15. 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.

  16. Raman Signatures of Polytypism in Molybdenum Disulfide.

    PubMed

    Lee, Jae-Ung; Kim, Kangwon; Han, Songhee; Ryu, Gyeong Hee; Lee, Zonghoon; Cheong, Hyeonsik

    2016-02-23

    Since the stacking order sensitively affects various physical properties of layered materials, accurate determination of the stacking order is important for studying the basic properties of these materials as well as for device applications. Because 2H-molybdenum disulfide (MoS2) is most common in nature, most studies so far have focused on 2H-MoS2. However, we found that the 2H, 3R, and mixed stacking sequences exist in few-layer MoS2 exfoliated from natural molybdenite crystals. The crystal structures are confirmed by HR-TEM measurements. The Raman signatures of different polytypes are investigated by using three different excitation energies that are nonresonant and resonant with A and C excitons, respectively. The low-frequency breathing and shear modes show distinct differences for each polytype, whereas the high-frequency intralayer modes show little difference. For resonant excitations at 1.96 and 2.81 eV, distinct features are observed that enable determination of the stacking order.

  17. Raman Signatures of Polytypism in Molybdenum Disulfide.

    PubMed

    Lee, Jae-Ung; Kim, Kangwon; Han, Songhee; Ryu, Gyeong Hee; Lee, Zonghoon; Cheong, Hyeonsik

    2016-02-23

    Since the stacking order sensitively affects various physical properties of layered materials, accurate determination of the stacking order is important for studying the basic properties of these materials as well as for device applications. Because 2H-molybdenum disulfide (MoS2) is most common in nature, most studies so far have focused on 2H-MoS2. However, we found that the 2H, 3R, and mixed stacking sequences exist in few-layer MoS2 exfoliated from natural molybdenite crystals. The crystal structures are confirmed by HR-TEM measurements. The Raman signatures of different polytypes are investigated by using three different excitation energies that are nonresonant and resonant with A and C excitons, respectively. The low-frequency breathing and shear modes show distinct differences for each polytype, whereas the high-frequency intralayer modes show little difference. For resonant excitations at 1.96 and 2.81 eV, distinct features are observed that enable determination of the stacking order. PMID:26756836

  18. 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

  19. 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.

  20. Carbon disulfide traveling-wave Kerr cells.

    PubMed

    Chenoweth, A J; Gaddy, O L; Holshouser, D F

    1966-10-01

    Carbon disulfide has identical microwave and optical dielectric constants, as well as extremely low optical and microwave loss. These properties make it possible to construct long travelingwave light modulators at microwave frequencies using the Kerr electrooptic effect induced in CS(2) by an electric field propagating on a TEM transmission line.Several experiments with traveling-wave Kerr cells consisting of resonant strip transmission lines immersed in CS(2) are described. A decrease in the microwave power required for modulation by a factor of two, by cooling the modulators to a temperature of -55 degrees C, is demonstrated. Simultaneous modulation of light at two microwave frequencies by excitation of two of the longitudinal modes of the strip line resonator is also described. Relatively high efficiency modulation with long devices of this type is also reported. In these experiments, the microwave power required for large depths of modulation is reduced by almost two orders of magnitude compared to previously reported CS(2) light modulators, and is within less than a factor of two of the calculated power for cells up to 44 cm in length. For longer cells, increasingly larger than predicted powers are required.

  1. Utilization of Photoactive Kaolinite/TiO2 Composite in Cement-Based Building Materials

    NASA Astrophysics Data System (ADS)

    Matějka, V.; Kovář, P.; Bábková, P.; Přikryl, J.; Mamulová-Kutláková, K.; Čapková, P.

    Titanium dioxide (TiO2) is the most studied photocatalyst with application potential in many branches of industry. Building industry represent the sector, where the photoactive TiO2 have been already successfully utilized. Concretes, plasters, paints are building materials where the photoactive TiO2 is widely tested. However the amount of TiO2 in these materials is limited with respect to their final properties. If the TiO2 replaces the certain amount of cement in concretes, the resulting compressive strength decreases when this photocatalyst is added in non-adequate content. The surface of kaolinite particles can serve as a matrix for nanosized TiO2 growing what results in photoactive composite - kaolin/TiO2 formation. After the calcination of this composite the process of kaolinite dehydroxylation is responsible for metakaolinite formation and composite metakaolinite/TiO2 with latently hydraulic properties originates. If the metakoline/TiO2 is used for partial cement replacement the compressive strength of resulting samples is notably increased and its surface shows photodegradation ability against rhodamine B.

  2. 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.

  3. Tungsten wire for incandescent lamps

    SciTech Connect

    Walter, J.L.; Briant, C.L. )

    1990-09-01

    Tungsten wire for incandescent lamp filaments must operate at high temperatures and for long times. To meet these requirements, the grain morphology of the wire must be controlled to reduce the propensity for grain boundary sliding. The morphology is a function of the distribution of very small pockets of potassium in the wire and the mechanical processing from ingot to wire. The behavior of the filament is directly related to the grain morphology. This paper describes the mechanism by which the potassium is incorporated into and distributed in the ingot. The elongation and spheroidization of the bubbles during hot rolling and swaging is also examined and related to the grain morphology of wire. Some indications of the relationship between grain morphology and filament behavior are also given.

  4. 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.

  5. 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.

  6. Ion mobility mass spectrometry as a potential tool to assign disulfide bonds arrangements in peptides with multiple disulfide bridges.

    PubMed

    Echterbille, Julien; Quinton, Loïc; Gilles, Nicolas; De Pauw, Edwin

    2013-05-01

    Disulfide bridges play a major role in defining the structural properties of peptides and proteins. However, the determination of the cysteine pairing is still challenging. Peptide sequences are usually achieved using tandem mass spectrometry (MS/MS) spectra of the totally reduced unfolded species, but the cysteine pairing information is lost. On the other hand, MS/MS experiments performed on native folded species show complex spectra composed of nonclassical ions. MS/MS alone does not allow either the cysteine pairing or the full sequence of an unknown peptide to be determined. The major goal of this work is to set up a strategy for the full structural characterization of peptides including disulfide bridges annotation in the sequence. This strategy was developed by combining ion mobility spectrometry (IMS) and collision-induced dissociation (CID). It is assumed that the opening of one S-S bridge in a peptide leads to a structural evolution which results in a modification of IMS drift time. In the presence of multiple S-S bridges, the shift in arrival time will depend on which disulfide(s) has (have) been reduced and on the shape adopted by the generated species. Due to specific fragmentations observed for each species, CID experiments performed after the mobility separation could provide not only information on peptide sequence but also on the localization of the disulfide bridges. To achieve this goal, synthetic peptides containing two disulfides were studied. The openings of the bridges were carried out following different experimental conditions such as reduction, reduction/alkylation, or oxidation. Due to disulfide scrambling highlighted with the reduction approaches, oxidation of S-S bonds into cysteic acids appeared to be the best strategy. Cysteine connectivity was then unambiguously determined for the two peptides, without any disulfide scrambling interference.

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. Thiol/disulfide homeostasis in patients with ankylosing spondylitis.

    PubMed

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

    2016-08-01

    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. PMID:27483176

  18. Disulfide bond formation in prokaryotes: history, diversity and design.

    PubMed

    Hatahet, Feras; Boyd, Dana; Beckwith, Jon

    2014-08-01

    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 Escherichia coli. These latter studies have also led to new more general insights into the redox environment of the cytoplasm and bacterial cell envelope. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

  19. A molybdenum disulfide/carbon nanotube heterogeneous complementary inverter

    NASA Astrophysics Data System (ADS)

    Huang, Jun; Somu, Sivasubramanian; Busnaina, Ahmed

    2012-08-01

    We report a simple, bottom-up/top-down approach for integrating drastically different nanoscale building blocks to form a heterogeneous complementary inverter circuit based on layered molybdenum disulfide and carbon nanotube (CNT) bundles. The fabricated CNT/MoS2 inverter is composed of n-type molybdenum disulfide (MOS2) and p-type CNT transistors, with a high voltage gain of 1.3. The CNT channels are fabricated using directed assembly while the layered molybdenum disulfide channels are fabricated by mechanical exfoliation. This bottom-up fabrication approach for integrating various nanoscale elements with unique characteristics provides an alternative cost-effective methodology to complementary metal-oxide-semiconductors, laying the foundation for the realization of high performance logic circuits.

  20. A molybdenum disulfide/carbon nanotube heterogeneous complementary inverter.

    PubMed

    Huang, Jun; Somu, Sivasubramanian; Busnaina, Ahmed

    2012-08-24

    We report a simple, bottom-up/top-down approach for integrating drastically different nanoscale building blocks to form a heterogeneous complementary inverter circuit based on layered molybdenum disulfide and carbon nanotube (CNT) bundles. The fabricated CNT/MoS(2) inverter is composed of n-type molybdenum disulfide (MOS(2)) and p-type CNT transistors, with a high voltage gain of 1.3. The CNT channels are fabricated using directed assembly while the layered molybdenum disulfide channels are fabricated by mechanical exfoliation. This bottom-up fabrication approach for integrating various nanoscale elements with unique characteristics provides an alternative cost-effective methodology to complementary metal-oxide-semiconductors, laying the foundation for the realization of high performance logic circuits.

  1. 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.

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

    SciTech Connect

    Tenboer, Jason; Basu, Shibom; Zatsepin, Nadia; Pande, Kanupriya; Milathianaki, Despina; Frank, Matthias; Hunter, Mark; Boutet, Sebastien; Williams, Garth J.; Koglin, Jason E.; Oberthuer, Dominik; Heymann, Michael; Kupitz, Christopher; Conrad, Chelsie; Coe, Jesse; Roy-Chowdhury, Shatabdi; Weierstall, Uwe; James, Daniel; Wang, Dingjie; Grant, Thomas; Barty, Anton; Yefanov, Oleksandr; Scales, Jennifer; Gati, Cornelius; Seuring, Carolin; Srajer, Vukica; Henning, Robert; Schwander, Peter; Fromme, Raimund; Ourmazd, Abbas; Moffat, Keith; Van Thor, Jasper J.; Spence, John C. H.; Fromme, Petra; Chapman, Henry N.; Schmidt, Marius

    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.

  3. 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

  4. Time-Resolved Serial Crystallography Captures High Resolution Intermediates of Photoactive Yellow Protein

    PubMed Central

    Tenboer, Jason; Basu, Shibom; Zatsepin, Nadia; Pande, Kanupria; Milathianaki, Despina; Frank, Matthias; Hunter, Mark; Boutet, Sébastien; Williams, Garth J.; Koglin, Jason E.; Oberthuer, Dominik; Heymann, Michael; Kupitz, Christopher; Conrad, Chelsie; Coe, Jesse; Roy-Chowdhury, Shatabdi; Weierstall, Uwe; James, Daniel; Wang, Dingjie; Grant, Thomas; Barty, Anton; Yefanov, Oleksandr; Scales, Jennifer; Gati, Cornelius; Seuring, Carolin; Srajer, Vukica; Henning, Robert; Schwander, Peter; Fromme, Raimund; Ourmazd, Abbas; Moffat, Keith; Van Thor, Jasper; Spence, John H. C.; Fromme, Petra; Chapman, Henry N.; Schmidt, Marius

    2015-01-01

    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. PMID:25477465

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

    PubMed

    Tenboer, Jason; Basu, Shibom; Zatsepin, Nadia; Pande, Kanupriya; Milathianaki, Despina; Frank, Matthias; Hunter, Mark; Boutet, Sébastien; Williams, Garth J; Koglin, Jason E; Oberthuer, Dominik; Heymann, Michael; Kupitz, Christopher; Conrad, Chelsie; Coe, Jesse; Roy-Chowdhury, Shatabdi; Weierstall, Uwe; James, Daniel; Wang, Dingjie; Grant, Thomas; Barty, Anton; Yefanov, Oleksandr; Scales, Jennifer; Gati, Cornelius; Seuring, Carolin; Srajer, Vukica; Henning, Robert; Schwander, Peter; Fromme, Raimund; Ourmazd, Abbas; Moffat, Keith; Van Thor, Jasper J; Spence, John C H; Fromme, Petra; Chapman, Henry N; Schmidt, Marius

    2014-12-01

    Serial femtosecond crystallography using ultrashort pulses from x-ray free electron lasers (XFELs) enables studies of the light-triggered dynamics of biomolecules. We used microcrystals of photoactive yellow protein (a bacterial blue light photoreceptor) as a model system and obtained high-resolution, time-resolved difference electron density maps of excellent quality with strong features; these allowed the determination of structures of reaction intermediates to a resolution of 1.6 angstroms. Our results open the way to the study of reversible and nonreversible biological reactions on time scales as short as femtoseconds under conditions that maximize the extent of reaction initiation throughout the crystal.

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

    PubMed

    Tenboer, Jason; Basu, Shibom; Zatsepin, Nadia; Pande, Kanupriya; Milathianaki, Despina; Frank, Matthias; Hunter, Mark; Boutet, Sébastien; Williams, Garth J; Koglin, Jason E; Oberthuer, Dominik; Heymann, Michael; Kupitz, Christopher; Conrad, Chelsie; Coe, Jesse; Roy-Chowdhury, Shatabdi; Weierstall, Uwe; James, Daniel; Wang, Dingjie; Grant, Thomas; Barty, Anton; Yefanov, Oleksandr; Scales, Jennifer; Gati, Cornelius; Seuring, Carolin; Srajer, Vukica; Henning, Robert; Schwander, Peter; Fromme, Raimund; Ourmazd, Abbas; Moffat, Keith; Van Thor, Jasper J; Spence, John C H; Fromme, Petra; Chapman, Henry N; Schmidt, Marius

    2014-12-01

    Serial femtosecond crystallography using ultrashort pulses from x-ray free electron lasers (XFELs) enables studies of the light-triggered dynamics of biomolecules. We used microcrystals of photoactive yellow protein (a bacterial blue light photoreceptor) as a model system and obtained high-resolution, time-resolved difference electron density maps of excellent quality with strong features; these allowed the determination of structures of reaction intermediates to a resolution of 1.6 angstroms. Our results open the way to the study of reversible and nonreversible biological reactions on time scales as short as femtoseconds under conditions that maximize the extent of reaction initiation throughout the crystal. PMID:25477465

  7. 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.

  8. 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.

  9. Surface morphologies of He-implanted tungsten

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.; Meyer, F. W.; Hijazi, H.; Unocic, K. A.; Garrison, L. M.; Parish, C. M.

    2016-09-01

    Surface morphologies of tungsten surfaces, both polycrystalline and single-crystal [1 1 0], were investigated using SEM and FIB/SEM techniques after implantations at elevated surfaces temperatures (1200-1300 K) using well-characterized, mono-energetic He ion beams with a wide range of ion energies (218 eV-250 keV). Nanofuzz was observed on polycrystalline tungsten (PCW) following implantation of 100-keV He ions at a flux threshold of 0.9 × 1016 cm-2 s-1, but not following 200-keV implantations with similar fluxes. No nanofuzz formation was observed on single-crystal [1 1 0] tungsten (SCW), despite fluxes exceeding those demonstrated previously to produce nanofuzz on polycrystalline tungsten. Pre-damaging the single-crystal tungsten with implanted C impurity interstitials did not significantly affect the surface morphologies resulting from the high-flux He ion implantations. The main factor leading to the different observed surface structures for the pristine and C-implanted single-crystal W samples appeared to be the peak He ion flux characterizing the different exposures. It was speculated that nanofuzz formation was not observed for any SCW target exposures because of increased incubation fluences required for such targets.

  10. Electroanalytical determination of tungsten and molybdenum in proteins.

    PubMed

    Hagedoorn, P L; van't Slot, P; van Leeuwen, H P; Hagen, W R

    2001-10-01

    Recent crystal structure determinations accelerated the progress in the biochemistry of tungsten-containing enzymes. In order to characterize these enzymes, a sensitive determination of this metal in protein-containing samples is necessary. An electroanalytical tungsten determination has successfully been adapted to determine the tungsten and molybdenum content in enzymes. The tungsten and molybdenum content can be measured simultaneously from 1 to 10 microg of purified protein with little or no sample handling. More crude protein samples require precipitation of interfering surface active material with 10% perchloric acid. This method affords the isolation of novel molybdenum- and tungsten-containing proteins via molybdenum and tungsten monitoring of column fractions, without using radioactive isotopes. A screening of soluble proteins from Pyrococcus furiosus for tungsten, using anion-exchange column chromatography to separate the proteins, has been performed. The three known tungsten-containing enzymes from P. furiosus were recovered with this screening.

  11. 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)

  12. 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.

  13. 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.

  14. Controlled Light-Mediated Preparation of Gold Nanoparticles by a Norrish Type I Reaction of Photoactive Polymers.

    PubMed

    Mäsing, Florian; Mardyukov, Artur; Doerenkamp, Carsten; Eckert, Hellmut; Malkus, Ursula; Nüsse, Harald; Klingauf, Jürgen; Studer, Armido

    2015-10-19

    Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light-mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.

  15. 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...

  16. 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)...

  17. 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...

  18. 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)...

  19. 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...

  20. 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...

  1. 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)...

  2. 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)...

  3. 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...

  4. 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)...

  5. 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....

  6. 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....

  7. 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....

  8. 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....

  9. 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....

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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.

  13. Thermal annealing effect on poly(3-hexylthiophene): fullerene:copper-phthalocyanine ternary photoactive layer.

    PubMed

    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.

  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. n-Type reduced graphene oxide field-effect transistors (FETs) from photoactive metal oxides.

    PubMed

    Yoo, Heejoun; Kim, Youngmin; Lee, Junghyun; Lee, Hyemi; Yoon, Yeoheung; Kim, Giyoun; Lee, Hyoyoung

    2012-04-16

    Graphene is of considerable interest as a next-generation semiconductor material to serve as a possible substitute for silicon. For real device applications with complete circuits, effective n-type graphene field effect transistors (FETs) capable of operating even under atmospheric conditions are necessary. In this study, we investigated n-type reduced graphene oxide (rGO) FETs of photoactive metal oxides, such as TiO(2) and ZnO. These metal oxide doped FETs showed slight n-type electric properties without irradiation. Under UV light these photoactive materials readily generated electrons and holes, and the generated electrons easily transferred to graphene channels. As a result, the graphene FET showed strong n-type electric behavior and its drain current was increased. These n-doping effects showed saturation curves and slowly returned back to their original state in darkness. Finally, the n-type rGO FET was also highly stable in air due to the use of highly resistant metal oxides and robust graphene as a channel. PMID:22422712

  16. 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.

  17. 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.

  18. Differential photoactivity of aqueous [C60] and [C70] fullerene aggregates.

    PubMed

    Moor, Kyle J; Snow, Samuel D; Kim, Jae-Hong

    2015-05-19

    Many past studies have focused on the aqueous photochemical properties of colloidal suspensions of C60 and various [C60] fullerene derivatives, yet few have investigated the photochemistry of other larger cage fullerene species (e.g., C70, C74, C84, etc.) in water. This is a critical knowledge gap because these larger fullerenes may exhibit different properties compared to C60, including increased visible light absorption, altered energy level structures, and variable cage geometries, which may greatly affect aggregate properties and resulting aqueous photoactivity. Herein, we take the first steps toward a detailed investigation of the aqueous photochemistry of larger cage fullerene species, by focusing on [C70] fullerene. We find that aqueous suspensions of C60 and C70, nC60 and nC70, respectively, exhibit many similar physicochemical properties, yet nC70 appears to be significantly more photoactive than nC60. Studies are conducted to elucidate the mechanism behind nC70's superior (1)O2 generation, including the measurement of (1)O2 production as a function of incident excitation wavelength, analysis of X-ray diffraction data to determine crystal packing arrangements, and the excited state dynamics of aggregate fullerene species via transient absorption spectroscopy.

  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. Eliminating disulfide exchange during glutamyl endopeptidase digestion of native protein.

    PubMed

    Dormady, S J; Lei, J; Regnier, F E

    1999-12-24

    Numerous advantages of using immobilized enzymes over free-solution protein digests have been cited in the literature. This investigation examines both the rate of hydrolysis and the extent of disulfide bond exchange in disulfide bridged dipeptide fragments formed during proteolysis of native protein. Glutamyl endopeptidase as both an immobilized enzyme and in free solution was used in these studies. It was found that extensive hydrolysis of insulin was achieved in 2 min with immobilized enzyme cartridges operated in the stopped-flow mode orders. This is orders of magnitude faster than was seen in free solution. Other advantages ranging from ease of use and reduction in sample size to the potential for automation were also noted with the immobilized enzyme cartridge. Normal free-solution proteolysis generally requires 12-24 h, based on the lower enzyme-to-substrate ratio in solution. A disturbing feature noted in these lengthy free-solution reactions was the tendency to form disulfide bridged peptide artifacts. This could lead to the erroneous conclusion that disulfide bonding in a sample was not that of the native protein. It is concluded that the advantage of immobilized enzymes over free-solution reactions will be most important in the pharmaceutical industry where proteolytic fragment "fingerprinting" of recombinant proteins is being used to confirm structure.

  1. Tissue factor activation: is disulfide bond switching a regulatory mechanism?

    PubMed Central

    Ghosh, Samit; Mandal, Samir K.

    2007-01-01

    A majority of tissue factor (TF) on cell surfaces exists in a cryptic form (ie, coagulation function inactive) but retains its functionality in cell signaling. Recent studies have suggested that cryptic TF contains unpaired cysteine thiols and that activation involves the formation of the disulfide bond Cys186-Cys 209 and that protein disulfide isomerase (PDI) regulates TF coagulant and signaling activities by targeting this disulfide bond. This study was carried out to investigate the validity of this novel concept. Although treatment of MDA 231 tumor cells, fibroblasts, and stimulated endothelial cells with the oxidizing agent HgCl2 markedly increased the cell-surface TF coagulant activity, the increase is associated with increased anionic phospholipids at the cell surface. Annexin V, which binds to anionic phospholipids, attenuated the increased TF coagulant activity. It is noteworthy that treatment of cells with reducing agents also increased the cell surface TF activity. No evidence was found for either detectable expression of PDI at the cell surface or association of TF with PDI. Furthermore, reduction of PDI with the gene silencing had no effect on either TF coagulant or cell signaling functions. Overall, the present data undermine the recently proposed hypothesis that PDI-mediated disulfide exchange plays a role in regulating TF procoagulant and cell signaling functions. PMID:17726162

  2. Disulfide bonds in ER protein folding and homeostasis

    PubMed Central

    Feige, Matthias J.; Hendershot, Linda M.

    2010-01-01

    Proteins that are expressed outside the cell must be synthesized, folded and assembled in a way that ensures they can function in their designate location. Accordingly these proteins are primarily synthesized in the endoplasmic reticulum (ER), which has developed a chemical environment more similar to that outside the cell. This organelle is equipped with a variety of molecular chaperones and folding enzymes that both assist the folding process, while at the same time exerting tight quality control measures that are largely absent outside the cell. A major post-translational modification of ER-synthesized proteins is disulfide bridge formation, which is catalyzed by the family of protein disulfide isomerases. As this covalent modification provides unique structural advantages to extracellular proteins, multiple pathways to their formation have evolved. However, the advantages that disulfide bonds impart to these proteins come at a high cost to the cell. Very recent reports have shed light on how the cell can deal with or even exploit the side reactions of disulfide bond formation to maintain homeostasis of the ER and its folding machinery. PMID:21144725

  3. 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

  4. Disulfide Bond Formation in Yeast NAD+-Specific Isocitrate Dehydrogenase†

    PubMed Central

    Garcia, Joshua A.; Minard, Karyl I.; Lin, An-Ping; McAlister-Henn, Lee

    2009-01-01

    The tricarboxylic acid cycle NAD+-specific isocitrate dehydrogenase (IDH) of Saccharomyces cerevisiae is an octameric enzyme composed of four heterodimers of regulatory IDH1 and catalytic IDH2 subunits. Recent structural analyses revealed the close proximity of Cys-150 residues from IDH2 in adjacent heterodimers, and features of the structure for the ligand-free enzyme suggested that formation of a disulfide bond between these residues might stabilize an inactive form of the enzyme. We constructed two mutant forms of IDH, one containing a C150S substitution in IDH2 and the other containing C56S/C242S substitutions in IDH2 leaving Cys-150 as the sole cysteine residue. Treatment of the affinity-purified enzymes with diamide resulted in the formation of disulfide bonds and in decreased activities for the wild-type and C56S/C242S enzymes. Both effects were reversible by the addition of dithiothreitol. Diamide had no effect on the C150S mutant enzyme, suggesting that Cys-150 is essential for the formation of a disulfide bond that inhibits IDH activity. Diamide-induced formation of the Cys-150 disulfide bond was also observed in vivo for yeast transformants expressing the wild-type or C56S/C242S enzymes but not for a transformant expressing the C150S enzyme. Finally, natural formation of the Cys-150 disulfide bond with a concomitant decrease in cellular IDH activity was observed during the stationary phase for the parental strain and for transformants expressing wild-type or C56S/C242S enzymes but not for a transformant expressing the C150S enzyme. A reduction in viability for the latter strain suggests that a decrease in IDH activity is important for metabolic changes in stationary phase cells. PMID:19645416

  5. Sulfhydryl oxidation, not disulfide isomerization, is the principal function of protein disulfide isomerase in yeast Saccharomyces cerevisiae.

    PubMed

    Solovyov, Anton; Xiao, Ruoyu; Gilbert, Hiram F

    2004-08-13

    Protein disulfide isomerase (PDI) is an essential protein folding assistant of the eukaryotic endoplasmic reticulum that catalyzes both the formation of disulfides during protein folding (oxidase activity) and the isomerization of disulfides that may form incorrectly (isomerase activity). Catalysis of thiol-disulfide exchange by PDI is required for cell viability in Saccharomyces cerevisiae, but there has been some uncertainty as to whether the essential role of PDI in the cell is oxidase or isomerase. We have studied the ability of PDI constructs with high oxidase activity and very low isomerase activity to complement the chromosomal deletion of PDI1 in S. cerevisiae. A single catalytic domain of yeast PDI (PDIa') has 50% of the oxidase activity but only 5% of the isomerase activity of wild-type PDI in vitro. Titrating the expression of PDI using the inducible/repressible GAL1-10 promoter shows that the amount of wild-type PDI protein needed to sustain a normal growth rate is 60% or more of the amount normally expressed from the PDI1 chromosomal location. A single catalytic domain (PDIa') is needed in molar amounts that are approximately twice as high as those required for wild-type PDI, which contains two catalytic domains. This comparison suggests that high (>60%) PDI oxidase activity is critical to yeast growth and viability, whereas less than 6% of its isomerase activity is needed.

  6. Redox potentials of tungsten and its alloying partners-fundamentals of tungsten determination by redox titration.

    PubMed

    Wünsch, G

    1980-08-01

    The fundamentals of tungsten determination by redox titration in hydrochloric acid medium are describe. Conditional redox potentials are given for W, Cr, V, Fe, Ti, Mo, Cu and Sn as a function of HCl concentration. The basic experimental conditions and the difference in conditional potentials required for consecutive titrations are discussed. Any mixture of tungsten with other metals can be analysed without separation if it does not contain both Cr and Ti or both Mo and V.

  7. Thermal cycling and high power density hydrogen ion beam irradiation of tungsten layers on tungsten substrate

    NASA Astrophysics Data System (ADS)

    Airapetov, A. A.; Begrambekov, L. B.; Gretskaya, I. Yu; Grunin, A. V.; Dyachenko, M. Yu; Puntakov, N. A.; Sadovskiy, Ya A.

    2016-09-01

    Tungsten layers with iron impurity were deposited on tungsten substrates modeling re-deposited layers in a fusion device. The samples were tested by thermocycling and hydrogen ion beam tests. Thermocycling revealed globule formation on the surface. The size of the globules depended on iron impurity content in the coating deposited. Pore formation was observed which in some cases lead to exfoliation of the coatings. Hydrogen ion irradiation lead to formation of blisters on the coating and finally its exfoliation.

  8. Effects of positively charged redox molecules on disulfide-coupled protein folding.

    PubMed

    Okumura, Masaki; Shimamoto, Shigeru; Nakanishi, Takeyoshi; Yoshida, Yu-ichiro; Konogami, Tadafumi; Maeda, Shogo; Hidaka, Yuji

    2012-11-01

    In vitro folding of disulfide-containing proteins is generally regulated by redox molecules, such as glutathione. However, the role of the cross-disulfide-linked species formed between the redox molecule and the protein as a folding intermediate in the folding mechanism is poorly understood. In the present study, we investigated the effect of the charge on a redox molecule on disulfide-coupled protein folding. Several types of aliphatic thiol compounds including glutathione were examined for the folding of disulfide-containing-proteins, such as lysozyme and prouroguanylin. The results indicate that the positive charge and its dispersion play a critical role in accelerating disulfide-coupled protein folding.

  9. On the involvement of intramolecular protein disulfide in the irreversible inactivation of 3-hydroxy-3-methylglutaryl-CoA reductase by diallyl disulfide.

    PubMed

    Omkumar, R V; Kadam, S M; Banerji, A; Ramasarma, T

    1993-06-24

    Treatment with diallyl disulfide, a constituent of garlic oil, irreversibly inactivated microsomal and a soluble 50 kDa form of HMG-CoA reductase. No radioactivity was found to be protein-bound on treating the soluble enzyme with [35S]diallyl disulfide, indicating the absence of the mixed disulfide of the type allyl-S-S-protein. SDS-PAGE and Western blot analyses of the diallyl-disulfide-treated protein showed no traces of the dimer of the type protein-S-S-protein, but clearly indicated BME-reversible increased mobility, as expected of an intramolecular protein disulfide. The sulfhydryl groups, as measured by alkylation with iodo[2-14C]acetic acid, were found to decrease in the diallyl-disulfide-treated enzyme protein. Tryptic peptide analysis also gave support for the possible presence of disulfide-containing peptides in such a protein. It appears that diallyl disulfide inactivated HMG-CoA reductase by forming an internal protein disulfide that became inaccessible for reduction by DTT, and thereby retaining the inactive state of the enzyme. PMID:8518292

  10. 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.

  11. 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.

  12. 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.

  13. Aminobisphenolate supported tungsten disulphido and dithiolene complexes.

    PubMed

    Salojärvi, E; Peuronen, A; Sillanpää, R; Damlin, P; Kivelä, H; Lehtonen, A

    2015-05-28

    Dioxotungsten(vi) complexes with tetradentate amino bisphenolates were converted into the corresponding Cs-symmetric amino bisphenolate disulphido complexes by a reaction with either Lawesson's reagent or P2S5. Further reaction with diethyl acetylenedicarboxylate leads to the formation of diamagnetic tungsten(iv) dithiolene compounds. The syntheses, crystal structures, spectroscopic and electrochemical characterization of such disulphido and dithiolene complexes are presented.

  14. Detonation in tungsten-loaded HMX

    SciTech Connect

    Goldstein, S.; Mader, C.L.

    1985-01-01

    The detonation behavior of X-0233, a heavily tungsten-loaded HMX explosive, has been studied using failure diameter measurements, plate dents, and aquarium tests. A model with features resembling those of a weak detonation describe the experimental results. 7 refs., 10 figs.

  15. Gas-driven permeation of deuterium through tungsten and tungsten alloys

    DOE PAGES

    Buchenauer, Dean A.; Karnesky, Richard A.; Fang, Zhigang Zak; Ren, Chai; Oya, Yasuhisa; Otsuka, Teppei; Yamauchi, Yuji; Whaley, Josh A.

    2016-03-25

    Here, to address the transport and trapping of hydrogen isotopes, several permeation experiments are being pursued at both Sandia National Laboratories (deuterium gas-driven permeation) and Idaho National Laboratories (tritium gas- and plasma-driven tritium permeation). These experiments are in part a collaboration between the US and Japan to study the performance of tungsten at divertor relevant temperatures (PHENIX). Here we report on the development of a high temperature (≤1150 °C) gas-driven permeation cell and initial measurements of deuterium permeation in several types of tungsten: high purity tungsten foil, ITER-grade tungsten (grains oriented through the membrane), and dispersoid-strengthened ultra-fine grain (UFG) tungstenmore » being developed in the US. Experiments were performed at 500–1000 °C and 0.1–1.0 atm D2 pressure. Permeation through ITER-grade tungsten was similar to earlier W experiments by Frauenfelder (1968–69) and Zaharakov (1973). Data from the UFG alloy indicates marginally higher permeability (< 10×) at lower temperatures, but the permeability converges to that of the ITER tungsten at 1000 °C. The permeation cell uses only ceramic and graphite materials in the hot zone to reduce the possibility for oxidation of the sample membrane. Sealing pressure is applied externally, thereby allowing for elevation of the temperature for brittle membranes above the ductile-to-brittle transition temperature.« less

  16. Inactivation of food-borne spoilage and pathogenic micro-organisms on the surface of a photoactive polymer.

    PubMed

    Zerdin, Katherine; Scully, Andrew D

    2010-01-01

    The photodynamic action of a novel photoactive polymer comprising covalently bound anthraquinone (AQ) moieties was evaluated after developing a methodology to reliably immobilize viable micro-organisms onto polymer film surfaces. The survival of Escherichia coli, Bacillus cereus (vegetative cells and spores), Fusarium oxysporum and Saccharomyces cerevisiae microbes inoculated on the surface of inert polymeric substrates was assessed to determine the effect of inoculum composition, drying rate and exposure to ultraviolet (UV-A) radiation. Their survival was highly dependent on microbial genus, with E. coli consistently displaying markedly shorter survival times than the other microbes, and B. cereus spores being the most resistant. Inoculation of the microbes onto the surface of the photoactive polymer films, followed by exposure to UV-A radiation, dramatically accelerated the inactivation of all microbial types studied compared with their survival on the surface of inert polymer substrates. Simultaneous exposure to both oxygen and UV-A radiation is required to affect cell survival, which is consistent with this effect most likely originating from the photoinduced production of singlet oxygen by the photoactive polymer. These results provide further compelling evidence that singlet oxygen produced exogenously by this photoactive polymeric substrate can successfully inactivate a broad spectrum of microbes on the substrate's surface.

  17. 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...

  18. 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

  19. 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

  20. A novel database of disulfide patterns and its application to the discovery of distantly related homologs.

    PubMed

    van Vlijmen, Herman W T; Gupta, Abhas; Narasimhan, Lakshmi S; Singh, Juswinder

    2004-01-23

    Disulfide bonds are conserved strongly among proteins of related structure and function. Despite the explosive growth of protein sequence databases and the vast numbers of sequence search tools, no tool exists to draw relations between the disulfide patterns of homologous proteins. We present a comprehensive database of disulfide bonding patterns and a search method to find proteins with similar disulfide patterns. The disulfide database was constructed using disulfide annotations extracted from SwissProt, and was expanded significantly from 16,736 to 94,499 disulfide-containing domains by an inference method that combines SwissProt annotations with Pfam multiple alignments. To search the database, we define a disulfide description, called the disulfide signature, which encodes both spacings between cysteine residues and cysteine connectivity. A web tool was developed that allows users to search for related disulfide patterns and for subpatterns resulting from the removal of one or more disulfides from the pattern. We explore the possibility of using disulfide pattern conservation to identify protein homologs that are undetectable by PSI-BLAST. Examples include the homology between a sea anemone antihypertensive/antiviral protein and a sea anemone neurotoxin, and the homology between tick anticoagulant peptide and bovine trypsin inhibitor. In both examples, there is a clear structural similarity and a functional relationship. We used the database to find structural homologs for the Cripto CFC domain. The identification of a von Willebrand Factor C (VWFC)-like domain agrees with its functional role and explains mutation data. We believe that the rapid increase in structure determinations arising from structural genomics efforts and advances in mass spectrometry techniques will greatly increase the number of disulfide annotations. This information will become a valuable resource for structural and functional annotations of proteins. The availability of a searchable

  1. Fabrication of carbohydrate microarrays on a poly(2-hydroxyethyl methacrylate)-based photoactive substrate.

    PubMed

    Sundhoro, Madanodaya; Wang, Hui; Boiko, Scott T; Chen, Xuan; Jayawardena, H Surangi N; Park, JaeHyeung; Yan, Mingdi

    2016-01-21

    We report the fabrication of carbohydrate microarrays on a photoactive polymer, poly(HEMA-co-HEMA-PFPA), synthesized by RAFT copolymerization of 2-hydroxyethyl methacrylate (HEMA) and perfluorophenyl azide (PFPA)-derivatized HEMA (HEMA-PFPA). PFPA allows the covalent immobilization of carbohydrates whereas the HEMA polymer provides an antifouling surface, thus the microarrays can be used directly without pretreating the array with a blocking agent. The microarrays were prepared by spin-coating the polymer followed by printing the carbohydrates. Subsequent irradiation simultaneously immobilized the carbohydrates and crosslinked the polymer matrix. The obtained 3D carbohydrate microarrays showed enhanced fluorescence signals upon treating with a fluorescent lectin in comparison with a 2D microarray. The signals were acquired at a lower lectin concentration and a shorter incubation time. When treated with E. coli bacteria, the carbohydrate microarray showed results that were consistent with their binding patterns. PMID:26646384

  2. 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

  3. Modern synthetic tools toward the preparation of sophisticated phthalocyanine-based photoactive systems.

    PubMed

    Ragoussi, Maria-Eleni; Torres, Tomás

    2014-10-01

    Phthalocyanines are ideal components in a variety of electronic applications due to their extraordinary photophysical characteristics combined with their synthetic versatility and robustness. They have attracted substantial attention in recent decades and are now established building blocks of sophisticated molecular materials. Synthetically, a great deal of this progress is attributed to the use of modern synthetic tools, which gave rise to phthalocyanine-based systems that could not have been envisaged in the past. In particular, Pd-catalyzed cross-coupling reactions, together with other transition-metal-catalyzed procedures, "click" chemistry, and ruthenium metathesis have been employed extensively en route to an abundant range of elaborate phthalocyanine mono- and multicomponent photoactive architectures. Herein, we describe the synthesis of a selection of key examples that are representative in certain optoelectronic applications.

  4. Maximal light-energy transfer through a dielectric/metal-layered electrode on a photoactive device.

    PubMed

    Kim, Kyoung-Ho; Park, Q-Han

    2014-01-27

    We report the fabrication of an optimized low reflective dielectric/metal-layered electrode that provides significant electrical conductivity and light transparency in the near-infrared wavelength regime. By making the metal film thickness thick enough and choosing a proper dielectric layer with a certain thickness, we show that our suggested electrode significantly reduces the light reflection while preserving high electrical conductivity. We demonstrate our optimized electrodes present a highly conductive surface with a sheet resistance of 5.2 Ω/sq and a high light transmittance of near 85% in the near-infrared regime. We also apply our optimized electrode to thin-film organic photovoltaic devices and show the electrode helps in absorbing light energy inside an active layer. We believe that this simple but powerful layered electrode will pave the way for designing transparent electrodes on photoactive devices.

  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. 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.

  7. Thermionic emission and negative dI/dV in photoactive graphene heterostructures.

    PubMed

    Rodriguez-Nieva, Joaquin F; Dresselhaus, Mildred S; Levitov, Leonid S

    2015-03-11

    Transport in photoactive graphene heterostructures, originating from the dynamics of photogenerated hot carriers, is governed by the processes of thermionic emission, electron-lattice thermal imbalance, and cooling. These processes give rise to interesting photoresponse effects, in particular negative differential resistance (NDR) arising in the hot-carrier regime. The NDR effect stems from a strong dependence of electron-lattice cooling on the carrier density, which results in the carrier temperature dropping precipitously upon increasing bias. The ON-OFF switching between the NDR regime and the conventional cold emission regime, as well as the gate-controlled closed-circuit current that is present at zero bias voltage, can serve as signatures of hot-carrier dominated transport.

  8. Subpicosecond Excited-State Proton Transfer Preceding Isomerization During the Photorecovery of Photoactive Yellow Protein

    PubMed Central

    Carroll, Elizabeth C.; Song, Sang-Hun; Kumauchi, Masato; van Stokkum, Ivo H. M.; Jailaubekov, Askat; Hoff, Wouter D.; Larsen, Delmar S.

    2010-01-01

    The ultrafast excited-state dynamics underlying the receptor state photorecovery is resolved in the M100A mutant of the photoactive yellow protein (PYP) from Halorhodospira halophila. The M100A PYP mutant, with its distinctly slower photocycle than wt PYP, allows isolation of the pB signaling state for study of the photodynamics of the protonated chromophore cis-p-coumaric acid. Transient absorption signals indicate a subpicosecond excited-state proton-transfer reaction in the pB state that results in chromophore deprotonation prior to the cis–trans isomerization required in the photorecovery dynamics of the pG state. Two terminal photoproducts are observed, a blue-absorbing species presumed to be deprotonated trans-p-coumaric acid and an ultraviolet-absorbing protonated photoproduct. These two photoproducts are hypothesized to originate from an equilibrium of open and closed folded forms of the signaling state, I2 and I2’. PMID:20953237

  9. 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

  10. 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

  11. 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

  12. High-performance liquid chromatographic method of photoactive compounds based on diazonaphthoquinone for positive photoresists.

    PubMed

    Kim, Byoung-Hyoun; Kim, Yon Hee; Moon, Dong Cheul

    2013-02-01

    An analytical method for the compositional and quantitative analysis of photoactive compounds (PACs) in positive photoresist (Posi PR) has been developed by high-performance liquid chromatography (HPLC). Under optimum HPLC conditions, various types of PACs consisting of a mixture of isomers were satisfactorily separated with no interference. This method was applied to the quantitative analysis of PACs in Posi PR. All correlation coefficients were better than or equal to 0.998. The precision and accuracy showed no significant deviation and were measured with acceptable values. The intra-batch precision and accuracy (%) of quality control samples ranged from 0.80 to 1.46% and from 101.7 to 102.8%. Consequently, the method was demonstrated to be acceptable for the analysis of PACs in Posi PR. We believe that the HPLC method developed in this work can be used for the compositional and quantitative analysis of PACs in Posi PR.

  13. 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

  14. Scorpion venom peptides with no disulfide bridges: a review.

    PubMed

    Almaaytah, Ammar; Albalas, Qosay

    2014-01-01

    Scorpion venoms are rich sources of biologically active peptides that are classified into disulfide-bridged peptides (DBPs) and non-disulfide-bridged peptides (NDBPs). DBPs are the main scorpion venom components responsible for the neurotoxic effects observed during scorpion envenomation as they usually target membrane bound ion channels of excitable and non-excitable cells. Several hundred DBPs have been identified and functionally characterized in the past two decades. The NDBPs represent a novel group of molecules that have gained great interest only recently due to their high diversity both in their primary structures and bioactivities. This review provides an overview of scorpion NDBPs focusing on their therapeutic applications, modes of discovery, mechanisms of NDBPs genetic diversity and structural properties. It also provides a simple classification for NDBPs that could be adopted and applied to other NDBPs identified in future studies.

  15. 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.

  16. 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.

  17. Scorpion venom peptides with no disulfide bridges: a review.

    PubMed

    Almaaytah, Ammar; Albalas, Qosay

    2014-01-01

    Scorpion venoms are rich sources of biologically active peptides that are classified into disulfide-bridged peptides (DBPs) and non-disulfide-bridged peptides (NDBPs). DBPs are the main scorpion venom components responsible for the neurotoxic effects observed during scorpion envenomation as they usually target membrane bound ion channels of excitable and non-excitable cells. Several hundred DBPs have been identified and functionally characterized in the past two decades. The NDBPs represent a novel group of molecules that have gained great interest only recently due to their high diversity both in their primary structures and bioactivities. This review provides an overview of scorpion NDBPs focusing on their therapeutic applications, modes of discovery, mechanisms of NDBPs genetic diversity and structural properties. It also provides a simple classification for NDBPs that could be adopted and applied to other NDBPs identified in future studies. PMID:24184590

  18. Mechanism of Protein Kinetic Stabilization by Engineered Disulfide Crosslinks

    PubMed Central

    Sanchez-Romero, Inmaculada; Ariza, Antonio; Wilson, Keith S.; Skjøt, Michael; Vind, Jesper; De Maria, Leonardo; Skov, Lars K.; Sanchez-Ruiz, Jose M.

    2013-01-01

    The impact of disulfide bonds on protein stability goes beyond simple equilibrium thermodynamics effects associated with the conformational entropy of the unfolded state. Indeed, disulfide crosslinks may play a role in the prevention of dysfunctional association and strongly affect the rates of irreversible enzyme inactivation, highly relevant in biotechnological applications. While these kinetic-stability effects remain poorly understood, by analogy with proposed mechanisms for processes of protein aggregation and fibrillogenesis, we propose that they may be determined by the properties of sparsely-populated, partially-unfolded intermediates. Here we report the successful design, on the basis of high temperature molecular-dynamics simulations, of six thermodynamically and kinetically stabilized variants of phytase from Citrobacter braakii (a biotechnologically important enzyme) with one, two or three engineered disulfides. Activity measurements and 3D crystal structure determination demonstrate that the engineered crosslinks do not cause dramatic alterations in the native structure. The inactivation kinetics for all the variants displays a strongly non-Arrhenius temperature dependence, with the time-scale for the irreversible denaturation process reaching a minimum at a given temperature within the range of the denaturation transition. We show this striking feature to be a signature of a key role played by a partially unfolded, intermediate state/ensemble. Energetic and mutational analyses confirm that the intermediate is highly unfolded (akin to a proposed critical intermediate in the misfolding of the prion protein), a result that explains the observed kinetic stabilization. Our results provide a rationale for the kinetic-stability consequences of disulfide-crosslink engineering and an experimental methodology to arrive at energetic/structural descriptions of the sparsely populated and elusive intermediates that play key roles in irreversible protein

  19. 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.

  20. Extracellular disulfide bridges stabilize TRPC5 dimerization, trafficking, and activity.

    PubMed

    Hong, Chansik; Kwak, Misun; Myeong, Jongyun; Ha, Kotdaji; Wie, Jinhong; Jeon, Ju-Hong; So, Insuk

    2015-04-01

    Crucial cysteine residues can be involved in the modulation of protein activity via the modification of thiol (-SH) groups. Among these reactions, disulfide bonds (S-S) play a key role in the folding, stability, and activity of membrane proteins. However, the regulation of extracellular cysteines in classical transient receptor potential (TRPC) channels remains controversial. Here, we examine the functional importance of the extracellular disulfide bond in TRPC5 in modulating channel gating and trafficking. Specifically, we investigated TRPC5 activity in transiently transfected HEK293 cells with wild-type (WT) or cysteine (C553 and C558) mutants in the pore loop. Using reducing agents, we determined that a disulfide linkage mediates the tetrameric formation of the TRPC5 channel. By measuring the TRPC5 current, we observed that C553S or C558S mutants completely lose channel activity induced by lanthanides or receptor stimulation. Co-expression of TRPC5 (WT) with mutants demonstrated a dominant-negative function in mutants, which inhibited the activity of TRPC5 (WT). We generated TRPC5-TRPC5 dimers and observed reduced activity of WT-mutant (C553S or C558S) dimers compared to WT-WT dimers. When pretreated with reducing agents for 12 h, the TRPC5 current decreased due to a reduction in membrane TRPC5 distribution. In addition, we identified a reduced expression of C553S mutant in plasma membrane. We analyzed a dimeric interaction of wild-type and mutant TRPC5 using co-immunoprecipitation and FRET method, indicating a weak interaction between dimeric partners. These results indicated that the disulfide bond between conserved extracellular cysteines, especially C553, is essential for functional TRPC5 activity by channel multimerization and trafficking.

  1. 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

  2. Oxidation of kinetically trapped thiols by protein disulfide isomerase.

    PubMed

    Walker, K W; Gilbert, H F

    1995-10-17

    The formation of a stabilized structure during oxidative protein folding can severely retard disulfide formation if the structure must be disrupted to gain access to buried cysteines. These kinetic traps can slow protein folding and disulfide bond formation to the extent that unassisted folding is too slow to be kinetically competent in the cell. Protein disulfide isomerase (PDI) facilitates the oxidation of a kinetically trapped state of RTEM-1 beta-lactamase in which two cysteines that form the single disulfide bond in the native protein are buried and approximately 500-fold less reactive than exposed cysteines. Under second-order conditions, PDI-dependent oxidation of reduced, folded beta-lactamase is 500-fold faster than GSSG-dependent oxidation. The rate difference observed between PDI and GSSG can be accounted for by the 520-fold higher kinetic reactivity of PDI as an oxidant. Noncovalent interactions between PDI (35 microM) and beta-lactamase increase the reactivity or unfolding of beta-lactamase in the steady-state by less than 3-fold. At high concentrations of PDI or alkylating agents, the reaction of beta-lactamase cysteines approaches a constant rate, limited by the spontaneous unfolding of the protein (kunfold = 0.024 +/- 0.005 min-1). PDI does not substantially increase the rate of beta-lactamase unfolding; however, once beta-lactamase spontaneously unfolds, PDI at concentrations greater than 44 +/- 4 microM, oxidizes the unfolded substrate before it can refold (kfold = 1.5 +/- 0.2 min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

  3. 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

  4. 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.

  5. 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

  6. Disulfide linked pyrazole derivatives inhibit phagocytosis of opsonized blood cells.

    PubMed

    Purohit, Meena K; Scovell, Iain; Neschadim, Anton; Katsman, Yulia; Branch, Donald R; Kotra, Lakshmi P

    2013-04-15

    Immune thrombocytopenia (ITP) is caused by production of an autoantibody to autologous platelets. ITP can be treated either by reducing platelet destruction or by increasing platelet production. Fcγ receptor mediated phagocytosis of the opsonized blood cells is a well-accepted mechanism for the underlying pathogenesis of ITP and inhibition of this phagocytosis process with small molecules is a potential strategy for the development of drugs against ITP. A broad screen indicated that 4-methyl-1-phenyl-pyrazole derivative (1) could inhibit the phagocytosis of opsonized blood cells with weak potency. We reveal here the discovery of the polysulfide products, synthesis of various 1-phenyl-pyrazole derivatives, and the biological evaluation of pyrazole derivatives as inhibitors of phagocytosis for potential use as therapeutics for ITP. Substitution at C4 of the pyrazole moiety in the disulfide-bridged dimers influenced the potency in the increasing order of 10 ~/= 11~/= 16 < 19 < 20. A novel scaffold, 20 with an IC(50) of 100 nM inhibiting opsonized blood cell phagocytosis was identified as a potential candidate for further studies. Confirmation of the disulfide bridge additionally provides clues for the non-thiol or non-disulfide bridge carrying ligands targeting ITP and other similar disorders.

  7. Labile disulfide bonds are common at the leucocyte cell surface

    PubMed Central

    Metcalfe, Clive; Cresswell, Peter; Ciaccia, Laura; Thomas, Benjamin; Barclay, A. Neil

    2011-01-01

    Redox conditions change in events such as immune and platelet activation, and during viral infection, but the biochemical consequences are not well characterized. There is evidence that some disulfide bonds in membrane proteins are labile while others that are probably structurally important are not exposed at the protein surface. We have developed a proteomic/mass spectrometry method to screen for and identify non-structural, redox-labile disulfide bonds in leucocyte cell-surface proteins. These labile disulfide bonds are common, with several classes of proteins being identified and around 30 membrane proteins regularly identified under different reducing conditions including using enzymes such as thioredoxin. The proteins identified include integrins, receptors, transporters and cell–cell recognition proteins. In many cases, at least one cysteine residue was identified by mass spectrometry as being modified by the reduction process. In some cases, functional changes are predicted (e.g. in integrins and cytokine receptors) but the scale of molecular changes in membrane proteins observed suggests that widespread effects are likely on many different types of proteins including enzymes, adhesion proteins and transporters. The results imply that membrane protein activity is being modulated by a ‘redox regulator’ mechanism. PMID:22645650

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. Tungsten-uranium penetrator target interaction

    SciTech Connect

    Dunn, P S; Damkroger, B K

    1994-10-01

    Several studies performed in recent years have been directed at determining the penetration mechanism of long rod kinetic energy penetrators into Rolled Homogeneous Armor (RHA). Much of the work has centered on comparing U-0.75Ti and Tungsten Heavy Alloys (WHA), with the goal being to relate the superior ballistic performance of the uranium materials to a fundamental difference in penetration mechanisms. This has been found to be true, with the dominant mechanisms being adiabatic shear in U-0.75Ti and bulk deformation in WHA. Recent work has sought to achieve improvements in the ballistic performance of the tungsten materials via both mechanical property improvements and alloy modifications designed to bring about adiabatic shear. As an alternative, the authors propose the consideration of materials which utilize mechanisms other than bulk deformation and adiabatic shear to optimize ballistic performance. This paper will present the postmortem analysis of a uranium-20 vol% tungsten composite penetrator fired into RHA at 0{degrees} obliquity. The analysis shows that the penetration mechanism in this material is bulk heating and extensive co-melting of the target and penetrator at the penetration interface. The results of the analysis will then be compared to a similar analysis made of targets into which U-0.75Ti penetrators had been fired.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Tungsten-induced carcinogenesis in human bronchial epithelial cells

    PubMed Central

    Laulicht, Freda; Brocato, Jason; Cartularo, Laura; Vaughan, Joshua; Wu, Feng; Kluz, Thomas; Sun, Hong; Oksuz, Betul Akgol; Shen, Steven; Paena, Massimilano; Medici, Serenella; Zoroddu, Maria Antonietta; Costa, Max

    2015-01-01

    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 seq. 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 shows 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

  19. 40 CFR 421.310 - Applicability: Description of the secondary tungsten and cobalt subcategory.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... or tungsten carbide scrap raw materials. ... secondary tungsten and cobalt subcategory. 421.310 Section 421.310 Protection of Environment ENVIRONMENTAL... CATEGORY Secondary Tungsten and Cobalt Subcategory § 421.310 Applicability: Description of the...

  20. 40 CFR 421.310 - Applicability: Description of the secondary tungsten and cobalt subcategory.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... or tungsten carbide scrap raw materials. ... secondary tungsten and cobalt subcategory. 421.310 Section 421.310 Protection of Environment ENVIRONMENTAL... CATEGORY Secondary Tungsten and Cobalt Subcategory § 421.310 Applicability: Description of the...

  1. The enhanced photoactivity of nanosized Bi{sub 2}WO{sub 6} catalyst for the degradation of 4-chlorophenol

    SciTech Connect

    Fu Hongbo Yao Wenqing; Zhang Liwu; Zhu Yongfa

    2008-10-02

    Nanosized Bi{sub 2}WO{sub 6} catalyst exhibited the enhanced photoactivity for the degradation of 4-chlorophenol (4-CP) under visible irradiation compared to the sample prepared by high-temperature solid reaction. The photoactivity of the catalyst was sensitive to pH variation of the suspension. Nanosized Bi{sub 2}WO{sub 6} catalyst showed the highest activity at pH 7.2. The photodegradation of 4-CP by nanosized Bi{sub 2}WO{sub 6} catalyst followed a pseudo-first-order reaction. After three recycling runs for the photodegradation of 4-CP, the activity of the catalyst did not show any significant loss, suggesting that the catalyst was stable under visible irradiation.

  2. 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%.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. Two-photoactive-center model applied to photorefractive self-focusing in biased LiNbO{sub 3}

    SciTech Connect

    Devaux, Fabrice; Safioui, Jassem; Chauvet, Mathieu; Passier, Remy

    2010-01-15

    We propose a time-dependent, three-dimensional numerical model where iron impurities and polarons are both considered photoactive centers to explain beam self-trapping in biased lithium niobate crystal. It shows that the intensity-dependent behavior reported experimentally is due to the competition between the drift current and the nonlinear photovoltaic current. For low light intensity, beam self-focusing occurs, while beam-splitting is observed at a higher intensity level.

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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.

  14. The controlled photoactivity of nanoparticles derived from ionic interactions between a water soluble polymeric photosensitizer and polysaccharide quencher.

    PubMed

    Park, Wooram; Park, Sin-jung; Na, Kun

    2011-11-01

    In order to design a water soluble polymeric photosensitizer (WPS) with controllable photoactivity, a nano-photosensitizer (NPS) was prepared from a polyelectrolyte complex between polyethylene glycol-polyethylenimine-chlorine e6 conjugate (PEG-PEI-Ce6) and Black Hole Quencher-3 chondroitin sulfate conjugate (BHQ-3-CS). NPSs have a unimodal size distribution below 100 nm. Photoquenching of the NPS was dependent on the weight ratio of BHQ-3-CS/WPS. This phenomenon was maintained in a salt condition up to 300 mm, indicating that the photoactivity of the NPS disappears in the normal blood stream of the body. The quenched photoactivity was restored by the enzyme degradation of BHQ-3-CS after esterase treatment. In a HCT-116 (human colon cancer) cell test, the rapid cellular internalization of the NPS without any other ligands was observed by confocal imaging. Upon light irradiation after internalization, phototoxicity was detected via MTT colorimetric assay. Also, when the NPS was subcutaneously injected in both tumoral and normal regions of HCT-116 tumor-bearing mice, the fluorescence signal in the tumors rapidly increased compared to the normal region due to the enzymatic-triggered dissociation of the NPS in vivo. These results suggest that the NPS can provide both tumor diagnosis and therapy simultaneously, and has great potential for biological studies and clinical treatments of various tumors. PMID:21803417

  15. Ultrafast Optical Microscopy of Single Monolayer Molybdenum Disulfide Flakes

    DOE PAGES

    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.

  16. Disulfide bond cleavage: a redox reaction without electron transfer.

    PubMed

    Hofbauer, Florian; Frank, Irmgard

    2010-05-01

    By using Car-Parrinello molecular dynamics (CPMD) simulations we have simulated a mechanically induced redox reaction. Previous single-molecule atomic force microscopy (AFM) experiments demonstrated that the reduction of disulfide bonds in proteins with the weak reducing agent dithiothreitol depends on a mechanical destabilization of the breaking bond. With reactive molecular dynamics simulations the single steps of the reaction mechanism can be elucidated and the motion of the electrons can be monitored. The simulations show that the redox reaction consists of the heterolytic cleavage of the S--S bond followed by a sequence of proton transfers. PMID:20349464

  17. 9-Fluorenylmethyl (Fm) Disulfides: Biomimetic Precursors for Persulfides.

    PubMed

    Park, Chung-Min; Johnson, Brett A; Duan, Jicheng; Park, Jeong-Jin; Day, Jacob J; Gang, David; Qian, Wei-Jun; Xian, Ming

    2016-03-01

    The development of a functional disulfide, FmSSPy-A (Fm = 9-fluorenylmethyl; Py = pyridinyl), is reported. It can effectively convert small molecule and protein thiols (-SH) to form -S-SFm adducts under mild conditions. This method allows for a H2S-free and biomimetic protocol to generate highly reactive persulfides (in their anionic forms). The high nucleophilicity of persulfides toward a number of thiol-blocking reagents is also demonstrated. The method holds promise for further understanding the chemical biology of persulfides and S-sulfhydration. PMID:26870874

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Conversion of light-energy into molecular strain in the photocycle of the photoactive yellow protein.

    PubMed

    Gamiz-Hernandez, Ana P; Kaila, Ville R I

    2016-01-28

    The Photoactive Yellow Protein (PYP) is a light-driven photoreceptor, responsible for the phototaxis of halophilic bacteria. Recently, a new short-lived intermediate (pR0) was characterized in the PYP photocycle using combined time-resolved X-ray crystallography and density functional theory calculations. The pR0 species was identified as a highly contorted cis-intermediate, which is stabilized by hydrogen bonds with protein residues. Here we show by hybrid quantum mechanics/classical mechanics (QM/MM) molecular dynamics simulations, and first-principles calculations of optical properties, that the optical shifts in the early steps of the PYP photocycle originate from the conversion of light energy into molecular strain, stored in the pR0 state, and its relaxation in subsequent reaction steps. Our calculations quantitatively reproduce experimental data, which enables us to identify molecular origins of the optical shifts. Our combined approach suggests that the short-lived pR0 intermediate stores ∼1/3 of the photon energy as molecular strain, thus providing the thermodynamic driving force for later conformational changes in the protein.

  4. 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.

  5. Photoactive TiO2 coatings obtained by Plasma Electrolytic Oxidation in refrigerated electrolytes

    NASA Astrophysics Data System (ADS)

    Franz, Silvia; Perego, Daniele; Marchese, Ottavia; Lucotti, Andrea; Bestetti, Massimiliano

    2016-11-01

    The effect of synthesis conditions on the properties of nanoporous TiO2 coatings obtained by PEO in refrigerated electrolytes have been investigated. Linear sweep voltammetry was carried out on the TiO2 coatings, in dark and under UV-C irradiation, in order to assess the photoelectrochemical behavior of samples. The largest photocurrents (0.18 mA/cm2) were measured on TiO2 coatings obtained by PEO in refrigerated aqueous solutions. UV-vis spectra revealed that lowering the processing temperature from 20 to -3.5 °C induced a blue-shift of the absorption band of the TiO2 coatings from 3.05 to 3.42 eV. The main advantage of PEO in refrigerated aqueous solutions over current approaches, based on anodic oxidation and thermal treatments, is that the synthesis of photoactive TiO2 coatings can be carried out in a relatively easy, quick and reproducible way, without annealing pre- and post-treatments. Furthermore, by controlling the solution temperature in PEO process, the photocurrent of the resulting TiO2 coating reaches quite high values.

  6. 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

  7. 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

  8. Photoactive composite films prepared from mixtures of polystyrene microgel dispersions and poly(3-hexylthiophene) solutions.

    PubMed

    Chen, Mu; Cui, Zhengxing; Edmondson, Steve; Hodson, Nigel; Zhou, Mi; Yan, Junfeng; O'Brien, Paul; Saunders, Brian R

    2015-11-14

    Whilst polystyrene microgels belong to the oldest family of microgel particles, their behaviours when deposited onto substrates or prepared as composites have received little attention. Because polystyrene microgels are solvent-swellable, and inherently colloidally stable, they are well suited to form composites with conjugated polymers. Here, we investigate the morphology and light absorption properties of spin coated composite films prepared from mixed dispersions of polystyrene microgels and poly(3-hexylthiophene) (P3HT) for the first time. We compare the morphologies of the composite films to spin coated microgel films. The films were studied using optical microscopy, SEM, AFM, wide-angle X-ray diffraction and UV-visible spectroscopy. The films contained flattened microgel particles with an aspect ratio of ∼10. Microgel islands containing hexagonally close packed particles were evident for both the pure microgel and microgel/P3HT composite films. The latter were electrically conducting. The composite film morphology was dependent on the microgel and P3HT concentration used for film preparation and a morphology phase diagram was constructed. The P3HT phase acted as an electrically conducting cement and increased the robustness of the films to solvent washing. The composite films were photoactive due to the P3HT component. The absorbance for the films was tuneable and increased linearly with both microgel and P3HT concentration. The results of the study should apply to other organic swellable microgel/conjugated polymer combinations and may lead to new colloidal composites for future optoelectronic applications.

  9. 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

  10. 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

  11. Photophysical, photochemical and photobiological properties of pyrrolocoumarins; a new class of photoactive compounds.

    PubMed

    Gibbs, N K; Quanten, E; Baydoun, S; Knox, C N; Roelandts, R; de Schryver, F; Truscott, T G; Young, A R

    1988-07-01

    With the aim of finding new photoactive compounds that may reduce the side effects of 8-methoxypsoralen photochemotherapy we report on some photophysical, photochemical and photobiological properties of recently synthesized pyrrolocoumarins, in particular 4-methyl-N-ethyl-pyrrolo[3,2-g]coumarin (PCNEt) which has an absorption maximum in the UV-A (320-400 nm). Laser (347 nm) flash photolysis studies showed triplet transients that were quenched by O2 and by ground state PCNEt. Singlet minus triplet spectra were broad (350-550 nm) and, at 700 nm, indicated solvated electron and radical production. PCNEt complexes with DNA in the dark and photobinds to thymine but does not form DNA cross-links. PCNEt was phototoxic in yeast with an action spectrum similar to its absorption spectrum. PCNEt showed photohaemolytic activity but was not phototoxic on guinea pig skin. These data suggest that PCNEt may photosensitize via several mechanisms: direct DNA photobinding, photodynamic action, or photoproduction of radicals.

  12. High-throughput biophysics of functional tuning in photoactive yellow protein

    NASA Astrophysics Data System (ADS)

    Hoff, Wouter; Philip, Andrew; Papadantonakis, George

    2007-03-01

    The relationship between the structure of a protein and its function is a central unresolved problem in biology. We use photoactive yellow protein (PYP) to develop quantitative high-throughput methods to study this problem. PYP is a small bacterial photoreceptor with rhodopsin-like photochemistry based on its p-coumaric acid (pCA) chromophore. The absorbance maximum and pKa of the pCA in the active site of native PYP are shifted from 400 nm and 9.0 in water to 446 nm and 2.8 in the protein. Thus, PYP offers a unique model system to probe protein-ligand interactions. Here we show that high-throughput microscale methods can be used for quantitative biophysical studies of the absorbance spectrum PYP, its fluorescence quantum yield, apparent pKa of the pCA, protein stability against chemical denaturation, and kinetics of the last PYP photocycle step. A wide range of properties was observed among the mutants, and structural features that tune functional properties were identified. These results open the way for high-throughput quantitative biophysical studies of PYP.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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…

  4. 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…

  5. 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.

  6. 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.

  7. Engineered disulfides improve mechanical properties of recombinant spider silk

    PubMed Central

    Grip, S; Johansson, J; Hedhammar, M

    2009-01-01

    Nature's high-performance polymer, spider silk, is composed of specific proteins, spidroins, which form solid fibers. So far, fibers made from recombinant spidroins have failed in replicating the extraordinary mechanical properties of the native material. A recombinant miniature spidroin consisting of four poly-Ala/Gly-rich tandem repeats and a nonrepetitive C-terminal domain (4RepCT) can be isolated in physiological buffers and undergoes self assembly into macrofibers. Herein, we have made a first attempt to improve the mechanical properties of 4RepCT fibers by selective introduction of AA → CC mutations and by letting the fibers form under physiologically relevant redox conditions. Introduction of AA → CC mutations in the first poly-Ala block in the miniature spidroin increases the stiffness and tensile strength without changes in ability to form fibers, or in fiber morphology. These improved mechanical properties correlate with degree of disulfide formation. AA → CC mutations in the forth poly-Ala block, however, lead to premature aggregation of the protein, possibly due to disulfide bonding with a conserved Cys in the C-terminal domain. Replacement of this Cys with a Ser, lowers thermal stability but does not interfere with dimerization, fiber morphology or tensile strength. These results show that mutagenesis of 4RepCT can reveal spidroin structure-activity relationships and generate recombinant fibers with improved mechanical properties. PMID:19388023

  8. Discovery and applications of disulfide-rich cyclic peptides.

    PubMed

    Cemazar, Masa; Kwon, Soohyun; Mahatmanto, Tunjung; Ravipati, Anjaneya S; Craik, David J

    2012-01-01

    Cyclic peptides typically have much higher stability and improved biopharmaceutical properties over their linear counterparts. Our work focuses on the discovery of naturally occurring disulfide-rich cyclic peptides and their applications in drug design. These peptides provide a design basis for re-engineering natural acyclic peptides to improve their biopharmaceutical properties by chemically linking their termini. Here we describe examples of the discovery of the cyclotide family of peptides, their chemical re-engineering to introduce desired pharmaceutical activities, studies of their biopharmaceutical properties and applications of cyclization technologies to naturally occurring toxins, including conotoxins and scorpion toxins. In the case of the conotoxin Vc1.1, we produced an orally active peptide with potential for the treatment of neuropathic pain by cyclising the native peptide. In the case of the scorpion toxin chlorotoxin, a cyclised derivative had improved biopharmaceutical properties as a tumour imaging agent over the naturally occurring linear chlorotoxin. Ongoing chemical and structural studies of these classes of disulfide-rich peptides promise to increase their value for use in dissecting biological processes in plants and mammals while also providing leads to new classes of biopharmaceuticals.

  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. 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.

  11. Lithium/disulfide cells capable of long cycle life

    NASA Astrophysics Data System (ADS)

    Kaun, T. D.; Holifield, T. F.; Deluca, W. H.

    The lithium-alloy/disulfide cell has undergone improvements to provide a very stable, high performance Upper-Plateau (UP) FeS2 electrode. Prismatic UP FeS2 cell tests (12 to 24 Ah capacity) with a LiCl-LiBr-KBr eutectic electrolyte have demonstrated 1000 deep discharge cycles at 400 C with less than a 20 percent drop in capacity and without reduced power capability. Previous lithium-alloy/disulfide cells, which were based on a two voltage-plateau FeS2 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 FeS2 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.

  12. Folding and activity of hybrid sequence, disulfide-stabilized peptides

    SciTech Connect

    Pease, J.H.B.; Storrs, R.W.; Wemmer, D.E. )

    1990-08-01

    Peptides have been synthesized that have hybrid sequences, partially derived from the bee venom peptide apamin and partially from the S peptide of ribonuclease A. The hybrid peptides were demonstrated by NMR spectroscopy to fold, forming the same disulfides and basic three-dimensional structure as native apamin, containing a {beta}-turn and an {alpha}-helix. These hybrids were active in complementing S protein, reactivating nuclease activity. In addition, the hybrid peptide was effective in inducing antibodies that cross-react with the RNase, without conjugation to a carrier protein. The stability of the folded structure of this peptide suggests that it should be possible to elicit antibodies that will react not only with a specific sequence, but also with a specific secondary structure. Hybrid sequence peptides also provide opportunities to study separately nucleation and propagation steps in formation of secondary structure. The authors show that in S peptide the {alpha}-helix does not end abruptly but rather terminates gradually over four or five residues. In general, these hybrid sequence peptides, which fold predictably because of disulfide bond formation, can provide opportunities for examining structure - function relationships for many biologically active sequences.

  13. 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

  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. 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...

  16. 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...

  17. 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....

  18. 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...

  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. 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....

  1. 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....

  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. 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...

  4. 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....

  5. 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.

  6. Corrosion and wear resistance of tungsten carbide-cobalt and tungsten carbide-cobalt-chromium thermal spray coatings

    SciTech Connect

    Quets, J.; Alford, J.R.

    1999-07-01

    Tungsten carbide thermal spray coatings provide wear surfaces to new and overhauled components for various industries. Their wear resistance is obtained by incorporating small tungsten carbide particles into a metal matrix. This presentation will show what parameters influence their corrosion resistance in the ASTM B-117 Salt Spray Corrosion Test,

  7. Au nanostructure-decorated TiO2 nanowires exhibiting photoactivity across entire UV-visible region for photoelectrochemical water splitting.

    PubMed

    Pu, Ying-Chih; Wang, Gongming; Chang, Kao-Der; Ling, Yichuan; Lin, Yin-Kai; Fitzmorris, Bob C; Liu, Chia-Ming; Lu, Xihong; Tong, Yexiang; Zhang, Jin Z; Hsu, Yung-Jung; Li, Yat

    2013-08-14

    Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV-visible region from 300 to 800 nm by manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV-visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV-visible light for solar fuel production.

  8. Tungsten tetraboride, an inexpensive superhard material

    PubMed Central

    Mohammadi, Reza; Lech, Andrew T.; Xie, Miao; Weaver, Beth E.; Yeung, Michael T.; Tolbert, Sarah H.; Kaner, Richard B.

    2011-01-01

    Tungsten tetraboride (WB4) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB4 was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesized material is phase pure. The zero-pressure bulk modulus, as measured by high-pressure X-ray diffraction for WB4, is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 ± 2.9 GPa under an applied load of 0.49 N. Various ratios of rhenium were added to WB4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to approximately 50 GPa at 0.49 N. Powders of tungsten tetraboride with and without 1 at.% Re addition are thermally stable up to approximately 400 °C in air as measured by thermal gravimetric analysis. PMID:21690363

  9. Concentration dependent hydrogen diffusion in tungsten

    NASA Astrophysics Data System (ADS)

    Ahlgren, T.; Bukonte, L.

    2016-10-01

    The diffusion of hydrogen in tungsten is studied as a function of temperature, hydrogen concentration and pressure using Molecular Dynamics technique. A new analysis method to determine diffusion coefficients that accounts for the random oscillation of atoms around the equilibrium position is presented. The results indicate that the hydrogen migration barrier of 0.25 eV should be used instead of the presently recommended value of 0.39 eV. This conclusion is supported by both experiments and density functional theory calculations. Moreover, the migration volume at the saddle point for H in W is found to be positive: ΔVm ≈ 0.488 Å3, leading to a decrease in the diffusivity at high pressures. At high H concentrations, a dramatic reduction in the diffusion coefficient is observed, due to site blocking and the repulsive H-H interaction. The results of this study indicates that high flux hydrogen irradiation leads to much higher H concentrations in tungsten than expected.

  10. Fuzzy tungsten in a magnetron sputtering device

    NASA Astrophysics Data System (ADS)

    Petty, T. J.; Khan, A.; Heil, T.; Bradley, J. W.

    2016-11-01

    Helium ion induced tungsten nanostructure (tungsten fuzz) has been studied in a magnetron sputtering device. Three parameters were varied, the fluence from 3.4 × 1023-3.0 × 1024 m-2, the He ion energy from 25 to 70 eV, and the surface temperature from 900 to 1200 K. For each sample, SEM images were captured, and measurements of the fuzz layer thickness, surface roughness, reflectivity, and average structure widths are provided. A cross-over point from pre-fuzz to fully formed fuzz is found at 2.4 ± 0.4 × 1024 m-2, and a temperature of 1080 ± 60 K. No significant change was observed in the energy sweep. The fuzz is compared to low fluence fuzz created in the PISCES-A linear plasma device. Magnetron fuzz is less uniform than fuzz created by PISCES-A and with generally larger structure widths. The thicknesses of the magnetron samples follow the original Φ1/2 relation as opposed to the incubation fluence fit.

  11. Dynamic compaction of tungsten carbide powder.

    SciTech Connect

    Gluth, Jeffrey Weston; Hall, Clint Allen; Vogler, Tracy John; Grady, Dennis Edward

    2005-04-01

    The shock compaction behavior of a tungsten carbide powder was investigated using a new experimental design for gas-gun experiments. This design allows the Hugoniot properties to be measured with reasonably good accuracy despite the inherent difficulties involved with distended powders. The experiments also provide the first reshock state for the compacted powder. Experiments were conducted at impact velocities of 245, 500, and 711 m/s. A steady shock wave was observed for some of the sample thicknesses, but the remainder were attenuated due to release from the back of the impactor or the edge of the sample. The shock velocity for the powder was found to be quite low, and the propagating shock waves were seen to be very dispersive. The Hugoniot density for the 711 m/s experiment was close to ambient crystal density for tungsten carbide, indicating nearly complete compaction. When compared with quasi-static compaction results for the same material, the dynamic compaction data is seen to be significantly stiffer for the regime over which they overlap. Based on these initial results, recommendations are made for improving the experimental technique and for future work to improve our understanding of powder compaction.

  12. 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.

  13. High temperature annealing of ion irradiated tungsten

    SciTech Connect

    Ferroni, Francesco; Yi, Xiaoou; 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 and 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.

  14. High temperature annealing of ion irradiated tungsten

    DOE PAGES

    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

  15. Tungsten - Yttrium Based Nuclear Structural Materials

    NASA Astrophysics Data System (ADS)

    Ramana, Chintalapalle; Chessa, Jack; Martinenz, Gustavo

    2013-04-01

    The challenging problem currently facing the nuclear science community in this 21st century is design and development of novel structural materials, which will have an impact on the next-generation nuclear reactors. The materials available at present include reduced activation ferritic/martensitic steels, dispersion strengthened reduced activation ferritic steels, and vanadium- or tungsten-based alloys. These materials exhibit one or more specific problems, which are either intrinsic or caused by reactors. This work is focussed towards tungsten-yttrium (W-Y) based alloys and oxide ceramics, which can be utilized in nuclear applications. The goal is to derive a fundamental scientific understanding of W-Y-based materials. In collaboration with University of Califonia -- Davis, the project is designated to demonstrate the W-Y based alloys, ceramics and composites with enhanced physical, mechanical, thermo-chemical properties and higher radiation resistance. Efforts are focussed on understanding the microstructure, manipulating materials behavior under charged-particle and neutron irradiation, and create a knowledge database of defects, elemental diffusion/segregation, and defect trapping along grain boundaries and interfaces. Preliminary results will be discussed.

  16. Chemical methods and approaches to the regioselective formation of multiple disulfide bonds.

    PubMed

    Shimamoto, Shigeru; Katayama, Hidekazu; Okumura, Masaki; Hidaka, Yuji

    2014-04-01

    Disulfide-bond formation plays an important role in the stabilization of the native conformation of peptides and proteins. In the case of multidisulfide-containing peptides and proteins, numerous folding intermediates are produced, including molecules that contain non-native and native disulfide bonds during in vitro folding. These intermediates can frequently be trapped covalently during folding and subsequently analyzed. The structural characterization of these kinetically trapped disulfide intermediates provides a clue to understanding the oxidative folding pathway. To investigate the folding of disulfide-containing peptides and proteins, in this unit, chemical methods are described for regulating regioselective disulfide formation (1) by using a combination of several types of thiol protecting groups, (2) by incorporating unique SeCys residues into a protein or peptide molecule, and (3) by combining with post-translational modification.

  17. 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.

  18. 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

  19. In-Depth Characterization of Protein Disulfide Bonds by Online Liquid Chromatography-Electrochemistry-Mass Spectrometry.

    PubMed

    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.

  20. Human CD4 Metastability Is a Function of the Allosteric Disulfide Bond in Domain 2.

    PubMed

    Owen, Gavin R; Channell, Jennifer A; Forsyth, V Trevor; Haertlein, Michael; Mitchell, Edward P; Capovilla, Alexio; Papathanasopoulos, Maria; Cerutti, Nichole M

    2016-04-19

    CD4 is expressed on the surface of specific leukocytes where it plays a key role in the activation of immunostimulatory T-cells and acts as a primary receptor for HIV-1 entry. CD4 has four ecto-domains (D1-D4) of which D1, D2, and D4 contain disulfide bonds. Although disulfide bonds commonly serve structural or catalytic functions, a rare class of disulfide bonds possessing unusually high dihedral strain energy and a relative ease of reduction can impact protein function by shuffling their redox state. D2 of CD4 possesses one such "allosteric" disulfide. While it is becoming accepted that redox exchange of the D2 allosteric disulfide plays an essential role in regulating CD4 activity, the biophysical consequences of its reduction remain incompletely understood. By analyzing the hydrodynamic volume, secondary structure, and thermal stability of the reduced and nonreduced forms of the single D1 and D2 domains, as well as the various redox isomers of two domain CD4, we have shown that ablation of the allosteric disulfide bond in domain 2 results in both a favorable structural collapse and an increase in the stability of CD4. Conversely, ablating the structural disulfide of D1 results in destabilizing structural rearrangements in CD4. These findings expand our understanding of the mechanisms by which oxidoreduction of the D2 allosteric disulfide regulates CD4 function; they reveal the intrinsic disulfide-dependent metastability of D2 and illustrate that redox shuffling of the allosteric disulfide results in previously undescribed conformational changes in CD4 that are likely important for its interaction with its protein partners. PMID:27009680

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. Photoactive composite films prepared from mixtures of polystyrene microgel dispersions and poly(3-hexylthiophene) solutions.

    PubMed

    Chen, Mu; Cui, Zhengxing; Edmondson, Steve; Hodson, Nigel; Zhou, Mi; Yan, Junfeng; O'Brien, Paul; Saunders, Brian R

    2015-11-14

    Whilst polystyrene microgels belong to the oldest family of microgel particles, their behaviours when deposited onto substrates or prepared as composites have received little attention. Because polystyrene microgels are solvent-swellable, and inherently colloidally stable, they are well suited to form composites with conjugated polymers. Here, we investigate the morphology and light absorption properties of spin coated composite films prepared from mixed dispersions of polystyrene microgels and poly(3-hexylthiophene) (P3HT) for the first time. We compare the morphologies of the composite films to spin coated microgel films. The films were studied using optical microscopy, SEM, AFM, wide-angle X-ray diffraction and UV-visible spectroscopy. The films contained flattened microgel particles with an aspect ratio of ∼10. Microgel islands containing hexagonally close packed particles were evident for both the pure microgel and microgel/P3HT composite films. The latter were electrically conducting. The composite film morphology was dependent on the microgel and P3HT concentration used for film preparation and a morphology phase diagram was constructed. The P3HT phase acted as an electrically conducting cement and increased the robustness of the films to solvent washing. The composite films were photoactive due to the P3HT component. The absorbance for the films was tuneable and increased linearly with both microgel and P3HT concentration. The results of the study should apply to other organic swellable microgel/conjugated polymer combinations and may lead to new colloidal composites for future optoelectronic applications. PMID:26347070

  6. 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.

  7. 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.

  8. Facile synthesis of highly photoactive α-Fe₂O₃-based films for water oxidation.

    PubMed

    Wang, Gongming; Ling, Yichuan; Wheeler, Damon A; George, Kyle E N; Horsley, Kimberly; Heske, Clemens; Zhang, Jin Z; Li, Yat

    2011-08-10

    This work reports a facile method for preparing highly photoactive α-Fe(2)O(3) films as well as their implementation as photoanodes for water oxidation. Transparent α-Fe(2)O(3) films were prepared by a new deposition-annealing (DA) process using nontoxic iron(III) chloride as the Fe precursor, followed by annealing at 550 °C in air. Ti-doped α-Fe(2)O(3) films were prepared by the same method, with titanium butoxide added as the Ti precursor. Impedance measurements show that the Ti-dopant serves as an electron donor and increases the donor density by 2 orders of magnitude. The photoelectrochemical performance of undoped and Ti-doped α-Fe(2)O(3) photoanodes was characterized and optimized through controlled variation of the Fe and Ti precursor concentration, annealing conditions, and the number of DA cycles. Compared to the undoped sample, the photocurrent onset potential of Ti-doped α-Fe(2)O(3) is shifted about 0.1-0.2 V to lower potential, thus improving the photocurrent and incident photon to current conversion efficiency (IPCE) at lower bias voltages. Significantly, the optimized Ti-doped α-Fe(2)O(3) film achieved the highest photocurrent density (1.83 mA/cm(2)) and IPCE values at 1.02 V vs RHE for α-Fe(2)O(3) photoanode. The enhanced photocurrent is attributed to the improved donor density and reduced electron-hole recombination at the time scale beyond a few picoseconds, as a result of Ti doping. PMID:21766825

  9. 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).

  10. 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

  11. High photoactivity in ultrathin as-grown hematite films prepared by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Klug, Jeffrey; Becker, Nicholas; Riha, Shannon; Martinson, Alex; Elam, Jeffrey; Pellin, Michael; Proslier, Thomas

    2013-03-01

    Nanostructured hematite (α-Fe2O3) has been widely studied for use in a variety of thin film applications including solar energy conversion, water oxidation, catalysis, and gas sensing. Among established deposition methods, atomic layer deposition (ALD) is a leading technique for large-scale, controlled synthesis of a wide range of nanostructured materials. In this work, ALD of Fe2O3 is demonstrated using FeCl3 and H2O precursors at growth temperatures between 200 -350° C. Self-limiting growth of Fe2O3 is observed with a growth rate of ~ 0 . 06 nm/cycle. As-deposited, films are nanocrystalline with low Cl impurities and a mixture of α- and γ-Fe2O3. Post-deposition annealing in O2 leads to phase-pure hematite with increased out-of-plane grain size. Photoelectrochemical measurements under simulated solar illumination reveal high photoactivity toward water oxidation in both as-deposited and post-annealed films. Planar films deposited at low temperature (235°C) exhibit remarkably high photocurrent densities ~ 0 . 71 mA/cm2 at 1.53 V vs. the reversible hydrogen electrode (RHE) without further processing. Films annealed in air at 500°C show current densities of up to 0.84 mA/cm2 (1.53V vs. RHE). This work was supported by the U.S. Department of Energy, Office of Science under contract No. DE-AC02-06CH11357 and by the American Recovery and Reinvestment Act (ARRA) through the US Department of Energy, Office of High Energy Physics.

  12. 40 CFR 440.60 - Applicability; description of the tungsten ore subcategory.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... tungsten ore subcategory. 440.60 Section 440.60 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Tungsten Ore Subcategory § 440.60 Applicability; description of the tungsten ore subcategory. The provisions of this subpart F are applicable to discharges from (a) mines that produce tungsten ore and...

  13. 40 CFR 440.60 - Applicability; description of the tungsten ore subcategory.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... tungsten ore subcategory. 440.60 Section 440.60 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Tungsten Ore Subcategory § 440.60 Applicability; description of the tungsten ore subcategory. The provisions of this subpart F are applicable to discharges from (a) mines that produce tungsten ore and...

  14. 40 CFR 440.60 - Applicability; description of the tungsten ore subcategory.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... tungsten ore subcategory. 440.60 Section 440.60 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Tungsten Ore Subcategory § 440.60 Applicability; description of the tungsten ore subcategory. The provisions of this subpart F are applicable to discharges from (a) mines that produce tungsten ore and...

  15. Tungsten and tungsten-copper for coal-fired MHD power generation

    SciTech Connect

    Farrar, L.C. ); Shields, J.A. Jr. )

    1992-08-01

    This paper reports that magnetohydrodynamics (MHD) can improve the thermal efficiency and reduce levels of SO{sub x} and NO emissions of existing coal-fired power generation plants. Although the thermal and electrochemical environments for a coal-fired MHD channel challenge the materials used, platinum, tungsten, and tungsten-copper have been found to be suitable choices. Evaluations indicate these materials perform adequately as electrodes and other gas-side surfaces in the coal-fired MHD channel. Analysis of test elements has resulted in the identification of wear mechanisms. Testing of a prototypical coal-fired MHD channel incorporating these materials is under way and will be completed in 1993.

  16. Measurement of uptake and release of tritium by tungsten

    SciTech Connect

    Nakayama, M.; Torikai, Y.; Saito, M.; Penzhorn, R.D.; Isobe, K.; Yamanishi, T.; Kurishita, H.

    2015-03-15

    Tungsten is currently contemplated as plasma facing material for the divertor of future fusion machines. In this paper the uptake of tritium by tungsten and its release behavior have been investigated. Tungsten samples have been annealed at various temperatures and loaded at also different temperatures with deuterium containing 7.2 % tritium at a pressure of 1.2 kPa. A specific system was designed to assess the release of tritiated water and molecular tritium by the samples. Due to the rather low solubility of hydrogen isotopes in tungsten it is particularly important to be aware of the presence of hydrogen traps or thin oxide films. As shown in this work, traps or oxide films may affect the retention capability of tungsten and lead to significantly modified release properties. It became clear that there were capture sites that had different thermal stability and different capture intensity in tungsten after polishing, or oxide films that were grown on the surface of tungsten and had barrier effects.

  17. A facile one-step electrochemical strategy of doping iron, nitrogen, and fluorine into titania nanotube arrays with enhanced visible light photoactivity.

    PubMed

    Hua, Zulin; Dai, Zhangyan; Bai, Xue; Ye, Zhengfang; Gu, Haixin; Huang, Xin

    2015-08-15

    Highly ordered iron, nitrogen, and fluorine tri-doped TiO2 (Fe, (N, F)-TiO2) nanotube arrays were successfully synthesized by a facile one-step electrochemical method in an NH4F electrolyte containing Fe ions. The morphology, structure, composition, and photoelectrochemical property of the as-prepared nanotube arrays were characterized by various methods. The photoactivities of the samples were evaluated by the degradation of phenol in an aqueous solution under visible light. Tri-doped TiO2 showed higher photoactivities than undoped TiO2 under visible light. The optimum Fe(3+) doping amount at 0.005M exhibited the highest photoactivity and exceeded that of undoped TiO2 by a factor of 20 times under visible light. The formation of N 2p level near the valence band (VB) contributed to visible light absorption. Doping fluorine and appropriate Fe(3+) ions reduced the photogenerated electrons-holes recombination rate and enhanced visible light photoactivity. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results indicated the presence of synergistic effects in Fe, N, and F tri-doped TiO2, which enhanced visible light photoactivity. The Fe, (N, F)-TiO2 photocatalyst exhibited high stability.

  18. Tungsten Stable Isotope Compositions of Ferromanganese Crusts

    NASA Astrophysics Data System (ADS)

    Abraham, K.; Barling, J.; Hein, J. R.; Schauble, E. A.; Halliday, A. N.

    2014-12-01

    We report the first accurate and precise data for mass-dependent fractionation of tungsten (W) stable isotopes, using a double spike technique and MC-ICPMS. Results are expressed relative to the NIST 3136 W isotope standard as per mil deviations in 186W/184W (δ186W). Although heavy element mass-dependent fractionations are expected to be small, Tl and U both display significant low temperature isotopic fractionations. Theoretical calculations indicate that W nuclear volume isotopic effects should be smaller than mass-dependent fractionations at low temperatures. Hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from seawater and have been used as paleoceanographic recorders of temporal changes in seawater chemistry. Crusts are strongly enriched in W and other metals, and are a promising medium for exploring W isotopic variability. Tungsten has a relatively long residence time in seawater of ~61,000 years, mainly as the tungstate ion (WO42-). Water depth profiles show conservative behaviour. During adsorption on Fe-Mn crusts, W species form inner-sphere complexes in the hexavalent (W6+) state. The major host phase is thought to be Mn oxides and the lighter W isotope is expected to be absorbed preferentially. Surface scrapings of 13 globally distributed hydrogenetic Fe-Mn crusts display δ186W from -0.08 to -0.22‰ (±0.03‰, 2sd). A trend toward lighter W isotope composition exists with increasing water depth (~1500 to ~5200m) and W concentration. One hydrothermal Mn-oxide sample is anomalously light and Mn nodules are both heavy and light relative to Fe-Mn crusts. Tungsten speciation depends on concentration, pH, and time in solution and is not well understood because of the extremely slow kinetics of the reactions. In addition, speciation of aqueous and/or adsorbed species might be sensitive to pressure, showing similar thermodynamic stability but different effective volumes. Thus, W stable isotopes might be used as a water-depth barometer in

  19. 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.

  20. 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.

  1. Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation

    PubMed Central

    Zhu, Gaohua; Liu, Jun; Zheng, Qiye; Zhang, Ruigang; Li, Dongyao; Banerjee, Debasish; Cahill, David G.

    2016-01-01

    Thermal conductivity of two-dimensional (2D) materials is of interest for energy storage, nanoelectronics and optoelectronics. Here, we report that the thermal conductivity of molybdenum disulfide can be modified by electrochemical intercalation. We observe distinct behaviour for thin films with vertically aligned basal planes and natural bulk crystals with basal planes aligned parallel to the surface. The thermal conductivity is measured as a function of the degree of lithiation, using time-domain thermoreflectance. The change of thermal conductivity correlates with the lithiation-induced structural and compositional disorder. We further show that the ratio of the in-plane to through-plane thermal conductivity of bulk crystal is enhanced by the disorder. These results suggest that stacking disorder and mixture of phases is an effective mechanism to modify the anisotropic thermal conductivity of 2D materials. PMID:27767030

  2. 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

  3. 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.

  4. 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

  5. Neutron irradiation effects on the microstructural development of tungsten and tungsten alloys

    NASA Astrophysics Data System (ADS)

    Hasegawa, Akira; Fukuda, Makoto; Yabuuchi, Kiyohiro; Nogami, Shuhei

    2016-04-01

    Data on the microstructural development of tungsten (W) and tungsten rhenium (Re) alloys were obtained after neutron irradiation at 400-800 °C in the Japan Materials Testing Reactor (JMTR), the experimental fast test reactor Joyo, and the High Flux Isotope Reactor (HFIR) for irradiation damage levels in the range of 0.09-1.54 displacement per atom (dpa). Microstructural observations showed that a small amount of Re (3-5%) in W-Re alloys is effective in suppressing void formation. In W-Re alloys with Re concentrations greater than 10%, acicular precipitates are the primary structural defects. In the HFIR-irradiated specimen, in which a large amount of Re was expected to be produced by the nuclear transmutation of W to Re because of the reactor's high thermal neutron flux, voids were not observed even in pure W. The synergistic effects of displacement damage and solid transmutation elements on microstructural development are discussed, and the microstructural development of tungsten materials utilized in fusion reactors is predicted.

  6. Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

    NASA Astrophysics Data System (ADS)

    Ingham, B.; Hendy, S. C.; Chong, S. V.; Tallon, J. L.

    2005-08-01

    Tungsten trioxide adopts a variety of structures which can be intercalated with charged species to alter the electronic properties, thus forming “tungsten bronzes.” Similar effects are observed upon removing oxygen from WO3 . We present a computational study of cubic and hexagonal alkali bronzes and examine the effects on cell size and band structure as the size of the intercalated ion is increased. With the exception of hydrogen (which is predicted to be unstable as an intercalate), the behavior of the bronzes are relatively consistent. NaWO3 is the most stable of the cubic systems, although in the hexagonal system the larger ions are more stable. The band structures are identical, with the intercalated atom donating its single electron to the tungsten 5d valence band. A study of fractional doping in the NaxWO3 system (0⩽x⩽1) showed a linear variation in cell parameter and a systematic shift in the Fermi level into the conduction band. In the oxygen-deficient WO3-x system the Fermi level undergoes a sudden jump into the conduction band at around x=0.2 . Lastly, three compounds of a layered WO4•α,ω -diaminoalkane hybrid series were studied and found to be insulating, with features in the band structure similar to those of the parent WO3 compound that relate well to experimental UV-visible spectroscopy results.

  7. Tensile behavior of tungsten and tungsten-alloy wires from 1300 to 1600 K

    NASA Technical Reports Server (NTRS)

    Hee, Man Yun

    1988-01-01

    The tensile behavior of a 200-micrometer-diameter tungsten lamp (218CS-W), tungsten + 1.0 atomic percent (a/o) thoria (ST300-W), and tungsten + 0.4 a/o hafnium carbide (WHfC) wires was determined over the temperature range 1300 t0 1600 K at strain rates of 3.3 X 10 to the -2 to 3.3 X 10 to the -5/sec. Although most tests were conducted on as-drawn materials, one series of tests was undertaken on ST300-W wires in four different conditions: as-drawn and vacuum-annealed at 1535 K for 1 hr, with and without electroplating. Whereas heat treatment had no effect on tensile properties, electropolishing significantly increased both the proportional limit and ductility, but not the ultimate tensile strength. Comparison of the behavior of the three alloys indicates that the HfC-dispersed material possesses superior tensile properties. Theoretical calculations indicate that the strength/ductility advantage of WHfC is due to the resistance to recrystallization imparted by the dispersoid.

  8. Electrode potentials of tungsten in fused alkali chlorides

    NASA Astrophysics Data System (ADS)

    Ivanov, A. B.; Volkovich, V. A.; Poskryakov, D. A.; Vasin, B. D.; Griffiths, T. R.

    2016-09-01

    Anodic dissolution of tungsten was studied at 823-1173 K in the melts based on NaCl-CsCl, NaCl-KCl-CsCl and LiCl-KCl-CsCl eutectic mixtures. The process results in the formation of W(IV) ions. Prolonged contact with silica results in oxidation W(IV) ions and decreasing tungsten concentration in the electrolyte due to formation of volatile higher oxidation state chloro- and oxychloro-species. Tungsten electrode potentials were measured in NaCl-CsCl and NaCl-KCl-CsCl based melts using potentiometry.

  9. Thermal expansion method for lining tantalum alloy tubing with tungsten

    NASA Technical Reports Server (NTRS)

    Watson, G. K.; Whittenberger, J. D.; Mattson, W. F.

    1973-01-01

    A differential-thermal expansion method was developed to line T-111 (tantalum - 8 percent tungsten - 2 percent hafnium) tubing with a tungsten diffusion barrier as part of a fuel element fabrication study for a space power nuclear reactor concept. This method uses a steel mandrel, which has a larger thermal expansion than T-111, to force the tungsten against the inside of the T-111 tube. Variables investigated include lining temperature, initial assembly gas size, and tube length. Linear integrity increased with increasing lining temperature and decreasing gap size. The method should have more general applicability where cylinders must be lined with a thin layer of a second material.

  10. Chemically assisted ion beam etching of polycrystalline and (100)tungsten

    NASA Technical Reports Server (NTRS)

    Garner, Charles

    1987-01-01

    A chemically assisted ion-beam etching technique is described which employs an ion beam from an electron-bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 microns thick with good anisotropy and pattern definition over areas of 30 sq mm, and with a high degree of selectivity. (100) tungsten foils etched with this process exhibit preferred-orientation etching, while polycrystalline tungsten films exhibit high etch rates. This technique can be used to pattern the dispenser cathode surfaces serving as electron emitters in traveling-wave tubes to a controlled porosity.

  11. Reproductive effects and duckling survivability 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; Tempelmen, R J; Stevens, W; Bursia, S J

    2001-07-01

    Tungsten-iron and tungsten-polymer shot were given conditional approval for waterfowl hunting by the U.S. Fish and Wildlife Service based partly on the results of a 30-day acute toxicity trial utilizing mallards (Anas platyrhynchos). Final approval of the two tungsten-containing shot was contingent on the results of a 150-day study that assessed the health and reproductive effects of tungsten-iron and tungsten-polymer shot in adult mallards. Reproductive data are presented in this paper. Sixteen male and 16 female 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). Reproductive performance was assessed during the last 90 days (day 61 to day 150) of the trial. There were no significant differences in egg production and fertility and hatchability of eggs from tungsten-iron- and tungsten-polymer-dosed ducks compared to control ducks. There was no evidence of differences in percent survivability and body weight of ducklings from tungsten-iron and tungsten-polymer mallards compared to ducklings from control ducks. Tungsten-iron or tungsten-polymer shot repeatedly administered to adult mallards during the 150 day trial did not adversely affect reproduction or their offspring.

  12. A Study of Tungsten-Technetium Alloys

    NASA Technical Reports Server (NTRS)

    Maltz, J. W.

    1965-01-01

    Technetium is a sister element to rhenium and has many properties that are similar to rhenium. It is predicted that technetium will have about the same effects on tungsten as rhenium in regard to increase in workability, lowered ductile to brittle transition temperature, and improved ductility. The objectives of the current work are to recover technetium from fission product wastes at Hanford Atomic Products Operation and reduce to purified metal; prepare W-Tc alloys containing up to 50 atomic% Tc; fabricate the alloy ingots to sheet stock, assessing the effect of technetium on workability; and perform metallurgical and mechanical properties evaluation of the fabricated alloys. Previous reports have described the separation and purification of 800 g of technetium metal powder, melting of technetium and W-Tc alloys, and some initial observation of the alloy material.

  13. Tungsten-doped thin film materials

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Gao, Chen; Takeuchi, Ichiro; Schultz, Peter G.

    2003-12-09

    A dielectric thin film material for high frequency use, including use as a capacitor, and having a low dielectric loss factor is provided, the film comprising a composition of tungsten-doped barium strontium titanate of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3, where X is between about 0.5 and about 1.0. Also provided is a method for making a dielectric thin film of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3 and doped with W, where X is between about 0.5 and about 1.0, a substrate is provided, TiO.sub.2, the W dopant, Ba, and optionally Sr are deposited on the substrate, and the substrate containing TiO.sub.2, the W dopant, Ba, and optionally Sr is heated to form a low loss dielectric thin film.

  14. Thermomechanical processing of tungsten-copper composites

    SciTech Connect

    Ohriner, E.K.; Bryskin, B.

    1996-05-01

    A tungsten-40 wt% Cu composite was consolidated by liquid-phase sintering and further processed to full density by a number of deformation methods. Fully dense materials were obtained by hot extrusion or cold rolling of the W-Cu composite. Subsequent processing by cold rolling, cold swaging, or hot swaging did not produce large changes in the aspect ratio of the W particles. The materials develop high hardness with small grain sizes of 5 {mu}m or less. The work-hardening, recrystallization, and grain growth of the material are characterized, and the hardness and tensile properties are related to processing parameters. Wire with tensile strengths up to 1120 MPa were produced. Further improvements in properties are anticipated with optimized processing parameters.

  15. 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

  16. Preventing disulfide bond formation weakens non-covalent forces among lysozyme aggregates.

    PubMed

    Ravi, Vijay Kumar; Goel, Mohit; Kotamarthi, Hema Chandra; Ainavarapu, Sri Rama Koti; Swaminathan, Rajaram

    2014-01-01

    Nonnative disulfide bonds have been observed among protein aggregates in several diseases like amyotrophic lateral sclerosis, cataract and so on. The molecular mechanism by which formation of such bonds promotes protein aggregation is poorly understood. Here in this work we employ previously well characterized aggregation of hen eggwhite lysozyme (HEWL) at alkaline pH to dissect the molecular role of nonnative disulfide bonds on growth of HEWL aggregates. We employed time-resolved fluorescence anisotropy, atomic force microscopy and single-molecule force spectroscopy to quantify the size, morphology and non-covalent interaction forces among the aggregates, respectively. These measurements were performed under conditions when disulfide bond formation was allowed (control) and alternatively when it was prevented by alkylation of free thiols using iodoacetamide. Blocking disulfide bond formation affected growth but not growth kinetics of aggregates which were ∼50% reduced in volume, flatter in vertical dimension and non-fibrillar in comparison to control. Interestingly, single-molecule force spectroscopy data revealed that preventing disulfide bond formation weakened the non-covalent interaction forces among monomers in the aggregate by at least ten fold, thereby stalling their growth and yielding smaller aggregates in comparison to control. We conclude that while constrained protein chain dynamics in correctly disulfide bonded amyloidogenic proteins may protect them from venturing into partial folded conformations that can trigger entry into aggregation pathways, aberrant disulfide bonds in non-amyloidogenic proteins (like HEWL) on the other hand, may strengthen non-covalent intermolecular forces among monomers and promote their aggregation.

  17. Human β-defensin 4 with non-native disulfide bridges exhibit antimicrobial activity.

    PubMed

    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.

  18. 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

  19. 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

  20. Additional disulfide bonds in insulin: Prediction, recombinant expression, receptor binding affinity, and stability

    PubMed Central

    Vinther, Tine N; Pettersson, Ingrid; Huus, Kasper; Schlein, Morten; Steensgaard, Dorte B; Sørensen, Anders; Jensen, Knud J; Kjeldsen, Thomas; Hubalek, František

    2015-01-01

    The structure of insulin, a glucose homeostasis-controlling hormone, is highly conserved in all vertebrates and stabilized by three disulfide bonds. Recently, we designed a novel insulin analogue containing a fourth disulfide bond located between positions A10-B4. The N-terminus of insulin's B-chain is flexible and can adapt multiple conformations. We examined how well disulfide bond predictions algorithms could identify disulfide bonds in this region of insulin. In order to identify stable insulin analogues with additional disulfide bonds, which could be expressed, the Cβ cut-off distance had to be increased in many instances and single X-ray structures as well as structures from MD simulations had to be used. The analogues that were identified by the algorithm without extensive adjustments of the prediction parameters were more thermally stable as assessed by DSC and CD and expressed in higher yields in comparison to analogues with additional disulfide bonds that were more difficult to predict. In contrast, addition of the fourth disulfide bond rendered all analogues resistant to fibrillation under stress conditions and all stable analogues bound to the insulin receptor with picomolar affinities. Thus activity and fibrillation propensity did not correlate with the results from the prediction algorithm. PMID:25627966

  1. Characterization of disulfide bonds by planned digestion and tandem mass spectrometry.

    PubMed

    Na, Seungjin; Paek, Eunok; Choi, Jong-Soon; Kim, Duwoon; Lee, Seung Jae; Kwon, Joseph

    2015-04-01

    The identification of disulfide bonds provides critical information regarding the structure and function of a protein and is a key aspect in understanding signaling cascades in biological systems. Recent proteomic approaches using digestion enzymes have facilitated the characterization of disulfide-bonds and/or oxidized products from cysteine residues, although these methods have limitations in the application of MS/MS. For example, protein digestion to obtain the native form of disulfide bonds results in short lengths of amino acids, which can cause ambiguous MS/MS analysis due to false positive identifications. In this study we propose a new approach, termed planned digestion, to obtain sufficient amino acid lengths after cleavage for proteomic approaches. Application of the DBond software to planned digestion of specific proteins accurately identified disulfide-linked peptides. RNase A was used as a model protein in this study because the disulfide bonds of this protein have been well characterized. Application of this approach to peptides digested with Asp-N/C (chemical digestion) and trypsin under acid hydrolysis conditions identified the four native disulfide bonds of RNase A. Missed cleavages introduced by trypsin treatment for only 3 hours generated sufficient lengths of amino acids for identification of the disulfide bonds. Analysis using MS/MS successfully showed additional fragmentation patterns that are cleavage products of S-S and C-S bonds of disulfide-linkage peptides. These fragmentation patterns generate thioaldehydes, persulfide, and dehydroalanine. This approach of planned digestion with missed cleavages using the DBond algorithm could be applied to other proteins to determine their disulfide linkage and the oxidation patterns of cysteine residues.

  2. 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

  3. Enhanced toughness and stable crack propagation in a novel tungsten fibre-reinforced tungsten composite produced by chemical vapour infiltration

    NASA Astrophysics Data System (ADS)

    Riesch, J.; Höschen, T.; Linsmeier, Ch; Wurster, S.; You, J.-H.

    2014-04-01

    Tungsten is a promising candidate for the plasma-facing components of a future fusion reactor, but its use is strongly restricted by its inherent brittleness. An innovative concept to overcome this problem is tungsten fibre-reinforced tungsten composite. In this paper we present the first mechanical test of such a composite material using a sample containing multiple fibres. The in situ fracture experiment was performed in a scanning electron microscope for close observation of the propagating crack. Stable crack propagation accompanied with rising load bearing capacity is observed. The fracture toughness is estimated using the test results and the surface observation.

  4. Processes of carbon disulfide degradation under the action of a pulsed corona discharge

    NASA Astrophysics Data System (ADS)

    Kuznetsov, D. L.; Filatov, I. E.; Uvarin, V. V.

    2016-08-01

    Experiments on decomposition of carbon disulfide CS2 in air under the action of a pulsed nanosecond corona discharge have been carried out. The energetic efficiency of the degradation amounted to 290-340 g (kW h)-1, which is significantly higher than with the use of a corona discharge at a constant voltage. The main degradation products are sulfur dioxide SO2, carbonyl sulfide COS, sulfuric acid, and carbon dioxide. Processes occurring in pulsed corona discharge plasma and leading to carbon disulfide degradation are considered. Different methods of air purification from carbon disulfide are compared.

  5. 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

  6. 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.

  7. 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.

  8. Polarographic determination of tungsten and molybdenum in sedimentary rocks

    SciTech Connect

    Vakhobova, R.U.; Lykova, F.P.; Milyavskii, Yu. S.; Rachinskaya, G.F.

    1985-12-01

    In order to determine microamounts of tungsten and molybdenum, one the most sensitive versions of polarography is used in this paper, called catalytic currents. In the development of a procedure for the determination of tungsten and molybdenum in geochemical items, the reduction of hydroxylamine (HA) is used, catalyzed by tungsten and molybdenum compounds in the presence of pyrocatechol, as on a background of dicarboxylic acids and hydroxy acids the HA reduction half-wave potentials, catalyzed by these elements, coincide. The investigations were conducted on a PPT-1 polarograph in the classical regime in a thermostatically controlled cell with a mercury dripping electrode and a saturated calomel comparison electrode. The authors develop a procedure for the simultaneous determination of n.10/sup -5/-n.10/sup -4/% of tungsten and molybdenum in sedimentary rocks.

  9. Tungsten-nickel-cobalt alloy and method of producing same

    DOEpatents

    Dickinson, James M.; Riley, Robert E.

    1977-03-15

    An improved tungsten alloy having a tungsten content of approximately 95 weight percent, a nickel content of about 3 weight percent, and the balance being cobalt of about 2 weight percent is described. A method for producing said tungsten-nickel-cobalt alloy is further described and comprises (a) coating the tungsten particles with a nickel-cobalt alloy, (b) pressing the coated particles into a compact shape, (c) heating said compact in hydrogen to a temperature in the range of 1400.degree. C and holding at this elevated temperature for a period of about 2 hours, (d) increasing this elevated temperature to about 1500.degree. C and holding for 1 hour at this temperature, (e) cooling to about 1200.degree. C and replacing the hydrogen atmosphere with an inert argon atmosphere while maintaining this elevated temperature for a period of about 1/2 hour, and (f) cooling the resulting alloy to room temperature in this argon atmosphere.

  10. Surface binding energies of beryllium/tungsten alloys

    NASA Astrophysics Data System (ADS)

    Gyoeroek, Michael; Kaiser, Alexander; Sukuba, Ivan; Urban, Jan; Hermansson, Kersti; Probst, Michael

    2016-04-01

    Binding energies of beryllium and tungsten atoms on surfaces of the alloys Be2W and Be12W were obtained from density functional theory calculations. Values of 4.08-5.63 eV for beryllium and 6.81-10.04 eV for tungsten were obtained. An analytical force field agrees for beryllium, but its tungsten surface atoms are too strongly bound. The surface binding energies of Be and W on Be12W surfaces is slightly smaller than on the pure Be and W surfaces, respectively. For higher tungsten content, i.e. for Be2W, the situation is more complicated. For some surfaces of this alloy the surface binding energies are enhanced while for others they are diminished, compared to the pure metal surfaces. The dependency of the cohesive energy on the mole fraction follows a linear relationship.

  11. Growth of tungsten oxide nanorods with carbon caps.

    PubMed

    Kichambare, Padmakar; Hii, King-Fu; Vallance, R Ryan; Sadanadan, B; Rao, Apparao M; Javed, Kazi; Menguc, M Pinar

    2006-02-01

    Hybrid nanostructures consisting of tungsten oxide nanorods with mushroom-shaped carbon caps were grown on electrochemically etched tungsten tips by thermal chemical vapor deposition with methane and argon. These nanorods grow along the radial direction and are very straight and smooth. Electron microscopy revealed a dominant diameter and length of approximately 50 nm and approximately 0.6 microm, respectively. High-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) revealed the presence of crystalline monoclinic W18O49 in the nanorods, and the cap was entirely amorphous carbon. A plausible growth mechanism involves the reduction of tungsten oxide WO3, present on the tungsten surface, by methane at 900 degrees C. PMID:16573057

  12. Characterization of the impurities in tungsten/silicon-germanium contacts

    SciTech Connect

    Gregg, H.A. Sr.

    1986-03-26

    Secondary ion mass spectrometry and Auger electron spectrometry depth profiling were used to determine impurity distributions in sputter deposited tungsten films over N-type and P-type 80/20 silicon-germanium elements of thermoelectric devices. These analyses showed that silicon, oxygen, sodium, boron, and phosphorous were present as impurities in the tungsten film. All these impurities except oxygen and sodium came from the substrate. Oxygen was gettered by the tungsten films, while sodium was possibly the result of sample handling. Further, the results from this study indicate that an oxide build-up, primarily at the tungsten/silicon-germanium interface of the N-type materials, is the major contributor to contact resistance in thermoelectric devices.

  13. OBJECT KINETIC MONTE CARLO SIMULATIONS OF CASCADE ANNEALING IN TUNGSTEN

    SciTech Connect

    Nandipati, Giridhar; Setyawan, Wahyu; Heinisch, Howard L.; Roche, Kenneth J.; Kurtz, Richard J.; Wirth, Brian D.

    2014-03-31

    The objective of this work is to study the annealing of primary cascade damage created by primary knock-on atoms (PKAs) of various energies, at various temperatures in bulk tungsten using the object kinetic Monte Carlo (OKMC) method.

  14. Tungsten Mobility During Alteration Processes: An Experimental Approach

    NASA Astrophysics Data System (ADS)

    Yin, N. H.; Fabre, S.; Quitté, G.

    2016-08-01

    Most chondrites show evidence of relatively low temperature alteration. Mass-dependent fractionation of non-traditional stable isotopes such as tungsten (W) are well suited to trace metal-silicate differentiation and alteration processes.

  15. Some observations on uranium carbide alloy/tungsten compatibility.

    NASA Technical Reports Server (NTRS)

    Phillips, W. M.

    1972-01-01

    Results of chemical compatibility tests between both pure tungsten and thoriated tungsten run at 1800 C for up to 3300 hours with uranium carbide alloys. Alloying with zirconium carbide appeared to widen the homogeneity range of uranium carbide, making additional carbon available for reaction with the tungsten. Reaction layers were formed both by vapor phase reaction and by physical contact, producing either or both UWC2 and W2C, depending upon the phases present in the starting fuel alloy. Formation of UWC2 results in slow growth of the reaction layer with time, while W2C reaction layers grow rapidly, allowing equilibrium to be reached in less than 2500 hours at 1800 C. Neither the presence of a thermal gradient nor the presence of thoria in the tungsten clad affect the reactions observed.

  16. A Compact Gas/Tungsten-Arc Welding Torch

    NASA Technical Reports Server (NTRS)

    Morgen, Gene E.

    1991-01-01

    Compact gas/tungsten-arc welding torch delivers 100-A current, yet used in confined spaces inaccessible to even smallest commercially available torch. Despite its extremely small size, torch contains all usual components and delivers high current.

  17. Refractory metals welded or brazed with tungsten inert gas equipment

    NASA Technical Reports Server (NTRS)

    Wisner, J. P.

    1965-01-01

    Appropriate brazing metals and temperatures facilitate the welding or brazing of base metals with tungsten inert gas equipment. The highest quality bond is obtained when TIG welding is performed in an inert atmosphere.

  18. Tungsten isotope ratio determinations by negative thermal ionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Völkening, Joachim; Köppe, Manfred; Heumann, Klaus G.

    1991-07-01

    A precise determination of the isotopic abundances of tungsten with natural isotopic composition is presented. WO-3 ions are generated by negative thermal ionization (NTI) in a double-filament ion source. La2O3 is used as a chemical substance to reduce the electron work function of the rhenium filament material. An ionization efficiency of 1% is obtained for sample loadings of 100 ng. The isotopic abundances are measured with relative standard deviations of 0.2% for the least abundant 180W isotope and 0.02-0.004% for the other tungsten isotopes. These improved isotopic data are used to recalculate the atomic weight of tungsten as 183.8417 ± 0.0001. The new NTI technique is an ideal tool for the application of isotope dilution mass spectrometry to analyse tungsten traces and for the measurement of isotopic shifts of this element in meteorites produced by the decay of 182Hf.

  19. 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

  20. Ductile tungsten-nickel-alloy and method for manufacturing same

    DOEpatents

    Ludwig, Robert L.

    1978-01-01

    The tensile elongation of a tungsten-nickel-iron alloy containing essentially 95 weight percent reprocessed tungsten, 3.5 weight percent nickel, and 1.5 weight percent iron is increased from a value of less than about 1 percent up to about 23 percent by the addition of less than 0.5 weight percent of a reactive metal consisting of niobium and zirconium.

  1. Processing effects on the mechanical properties of tungsten heavy alloys

    NASA Technical Reports Server (NTRS)

    Kishi, Toshihito; German, R. M.

    1990-01-01

    Tungsten heavy alloys exhibit significant mechanical property sensitivities to the fabrication variables. These sensitivities are illustrated in this examination of vacuum sintering and the effects of composition, sintering temperature, and sintering time on the mechanical properties of tungsten heavy alloys. Measurements were conducted to assess the density, strength, hardness, and elongation dependencies. A detrimental aspect of vacuum sintering is matrix phase evaporation, although vacuum sintering does eliminate the need for postsintering heat treatments.

  2. 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).

  3. 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.

  4. 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.

  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. A novel method to synthesize highly photoactive Cu2O microcrystalline films for use in photoelectrochemical cells.

    PubMed

    Li, Changli; Li, Yanbo; Delaunay, Jean-Jacques

    2014-01-01

    Large-scale and high-quality Cu2O microcrystalline films with high photoactivity are synthesized using a novel and low-cost method. The enhanced photoactivity is achieved through the formation of Cu2O microcrystalline films having well-defined crystal facets and porous structure. Cu2O microcrystalline films are fabricated by decomposing previously synthesized Cu(OH)2 nanowires on a Cu foil under a vacuum. Subsequent crystal growth during the annealing process is driven by outward diffusion of Cu ions and oxidation. Crystal growth induces coalescence of the nanowires and results in the formation of Cu2O microcrystals enclosed by four {111} facets. Photoelectrochemical evaluation of the annealed samples performed under chopped simulated AM 1.5G illumination reveals that the sample annealed at 500 °C for 2 h exhibited the highest photocurrent of 4.07 mA/cm(2) at 0 V/RHE. This large photocurrent is ascribed to a high carrier density (~1.36 × 10(18) cm(-3)) and a low carrier transfer resistance in electrolyte, as evidenced by electrochemical impedance spectroscopy. The obtained low-cost Cu2O microcrystalline film (2 h) may serve as an excellent solar absorber and carrier provider for use in photovoltaics and artificial photosynthesis. PMID:24299015

  7. 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.

  8. Irradiation effects in tungsten-copper laminate composite

    DOE PAGES

    Garrison, L. M.; Katoh, Yutai; Snead, Lance L.; Byun, Thak Sang; Reiser, Jens; Rieth, Michael

    2016-09-19

    Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410–780 °C and fast neutron fluences of 0.02–9.0 × 1025 n/m2, E > 0.1 MeV, 0.0039–1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa thismore » was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. In conclusion, tor elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.« less

  9. Alternative processing methods for tungsten-base composite materials

    SciTech Connect

    Ohriner, E.K.; Sikka, V.K.

    1995-12-31

    Tungsten composite materials contain large amounts of tungsten distributed in a continuous matrix phase. Current commercial materials include the tungsten-nickel-iron with cobalt replacing some or all of the iron, and also tungsten-copper materials. Typically, these are fabricated by liquid-phase sintering of blended powders. Liquid-phase sintering offers the advantages of low processing costs, established technology, and generally attractive mechanical properties. However, liquid-phase sintering is restricted to a very limited number of matrix alloying elements and a limited range of tungsten and alloying compositions. In the past few years, there has been interest in a wider range of matrix materials that offer the potential for superior composite properties. These must be processed by solid-state processes and at sufficiently low temperatures to avoid undesired reactions between the tungsten and the matrix phase. These processes, in order of decreasing process temperature requirements, include hot-isostatic pressing (HIPing), hot extrusion, and dynamic compaction. The HIPing and hot extrusion processes have also been used to improve mechanical properties of conventional liquid-phase-sintered materials. Results of laboratory-scale investigations of solid-state consolidation of a variety of matrix materials, including titanium, hafnium, nickel aluminide, and steels are reviewed. The potential advantages and disadvantages of each of the possible alternative consolidation processes are identified. Postconsolidation processing to control microstructure and macrostructure is discussed, including novel methods of controlling microstructure alignment.

  10. Alternative processing methods for tungsten-base composite materials

    SciTech Connect

    Ohriner, E.K.; Sikka, V.K.

    1996-06-01

    Tungsten composite materials contain large amounts of tungsten distributed in a continuous matrix phase. Current commercial materials include the tungsten-nickel-iron with cobalt replacing some or all of the iron, and also tungsten-copper materials. Typically, these are fabricated by liquid-phase sintering of blended powders. Liquid-phase sintering offers the advantages of low processing costs, established technology, and generally attractive mechanical properties. However, liquid-phase sintering is restricted to a very limited number of matrix alloying elements and a limited range of tungsten and alloying compositions. In the past few years, there has been interest in a wider range of matrix materials that offer the potential for superior composite properties. These must be processed by solid-state processes and at sufficiently low temperatures to avoid undesired reactions between the tungsten and the matrix phase. These processes, in order of decreasing process temperature requirements, include hot isostatic pressing (HEPing), hot extrusion, and dynamic compaction. The HIPing and hot extrusion processes have also been used to improve mechanical properties of conventional liquid-phase-sintered materials. The results of laboratory-scale investigations of solid-state consolidation of a variety of matrix materials, including titanium, hafnium, nickel aluminide, and steels are reviewed. The potential advantages and disadvantages of each of the possible alternative consolidation processes are identified. Post consolidation processing to control microstructure and macrostructure is discussed, including novel methods of controlling microstructure alignment.

  11. 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

  12. T-1018 UCLA Spacordion Tungsten Powder Calorimeter

    SciTech Connect

    Trentalange, Stephen; Tsai, Oleg; Igo, George; Huang, Huan; Pan, Yu Xi; Dunkelberger, Jay; Xu, Wen Qin; Soha, Aria; Heppelmann, Steven; Gagliardi, Carl; /Texas A-M

    2011-11-16

    The present experiments at the BNL-RHIC facility are evolving towards physics goals which require the detection of medium energy electromagnetic particles (photons, electrons, neutral pions, eta mesons, etc.), especially at forward angles. New detectors will place increasing demands on energy resolution, hadron rejection and two-photon resolution and will require large area, high performance electromagnetic calorimeters in a variety of geometries. In the immediate future, either RHIC or JLAB will propose a facility upgrade (Electron-Ion Collider, or EIC) with physics goals such as electron-heavy ion collisions (or p-A collisions) with a wide range of calorimeter requirements. An R and D program based at Brookhaven National Laboratory has awarded the group funding of approximately $110,000 to develop new types of calorimeters for EIC experiments. The UCLA group is developing a method to manufacture very flexible and cost-effective, yet high quality calorimeters based on scintillating fibers and tungsten powder. The design and features of the calorimeter can be briefly stated as follows: an arbitrarily large number of small diameter fibers (< 0.5 mm) are assembled as a matrix and held rigidly in place by a set of precision screens inside an empty container. The container is then back-filled with tungsten powder, compacted on a vibrating table and infused with epoxy under vacuum. The container is then removed. The resulting sub-modules are extremely uniform and achieve roughly the density of pure Lead. The sub-modules are stacked together to achieve a final detector of the desired shape. There is no dead space between sub-modules and the fibers can be in an accordion geometry bent to prevent 'channeling' of the particles due to accidental alignment of their track with the module axis. This technology has the advantage of being modular and inexpensive to the point where the construction work may be divided among groups the size of typical university physics departments

  13. Heterologous expression of five disulfide-bonded insecticidal spider peptides.

    PubMed

    Estrada, Georgina; Silva, Anita O; Villegas, Elba; Ortiz, Ernesto; Beirão, Paulo S L; Corzo, Gerardo

    2016-09-01

    The genes of the five disulfide-bonded peptide toxins 1 and 2 (named Oxytoxins or Oxotoxins) from the spider Oxyopes lineatus were cloned into the expression vector pQE30 containing a 6His-tag and a Factor Xa proteolytic cleavage region. These two recombinant vectors were transfected into Escherichia coli BL21 cells and expressed under induction with isopropyl thiogalactoside (IPTG). The product of each gene was named HisrOxyTx1 or HisrOxyTx2, and the protein expression was ca 14 and 6 mg/L of culture medium, respectively. Either recombinant toxin HisrOxyTx1 or HisrOxyTx2 were found exclusively in inclusion bodies, which were solubilized using a chaotropic agent, and then, purified using affinity chromatography and reverse-phase HPLC (RP-HPLC). The HisrOxyTx1 and HisrOxyTx2 products, obtained from the affinity chromatographic step, showed several peptide fractions having the same molecular mass of 9913.1 and 8030.1 Da, respectively, indicating that both HisrOxyTx1 and HisrOxyTx2 were oxidized forming several distinct disulfide bridge arrangements. The isoforms of both HisrOxyTx1 and HisrOxyTx2 after DTT reduction eluted from the column as a single protein component of 9923 and 8040 Da, respectively. In vitro folding of either HisrOxyTx1 or HisrOxyTx2 yielded single oxidized components, which were cleaved independently by the proteolytic enzyme Factor Xa to give the recombinant peptides rOxyTx1 and rOxyTx2. The experimental molecular masses of rOxyTx1 and rOxyTx2 were 8059.0 and 6176.4 Da, respectively, which agree with their expected theoretical masses. The recombinant peptides rOxyTx1 and rOxyTx2 showed lower but comparable toxicity to the native toxins when injected into lepidopteran larvae; furthermore, rOxyTx1 was able to inhibit calcium ion currents on dorsal unpaired median (DUM) neurons from Periplaneta americana. PMID:27263806

  14. Heterologous expression of five disulfide-bonded insecticidal spider peptides.

    PubMed

    Estrada, Georgina; Silva, Anita O; Villegas, Elba; Ortiz, Ernesto; Beirão, Paulo S L; Corzo, Gerardo

    2016-09-01

    The genes of the five disulfide-bonded peptide toxins 1 and 2 (named Oxytoxins or Oxotoxins) from the spider Oxyopes lineatus were cloned into the expression vector pQE30 containing a 6His-tag and a Factor Xa proteolytic cleavage region. These two recombinant vectors were transfected into Escherichia coli BL21 cells and expressed under induction with isopropyl thiogalactoside (IPTG). The product of each gene was named HisrOxyTx1 or HisrOxyTx2, and the protein expression was ca 14 and 6 mg/L of culture medium, respectively. Either recombinant toxin HisrOxyTx1 or HisrOxyTx2 were found exclusively in inclusion bodies, which were solubilized using a chaotropic agent, and then, purified using affinity chromatography and reverse-phase HPLC (RP-HPLC). The HisrOxyTx1 and HisrOxyTx2 products, obtained from the affinity chromatographic step, showed several peptide fractions having the same molecular mass of 9913.1 and 8030.1 Da, respectively, indicating that both HisrOxyTx1 and HisrOxyTx2 were oxidized forming several distinct disulfide bridge arrangements. The isoforms of both HisrOxyTx1 and HisrOxyTx2 after DTT reduction eluted from the column as a single protein component of 9923 and 8040 Da, respectively. In vitro folding of either HisrOxyTx1 or HisrOxyTx2 yielded single oxidized components, which were cleaved independently by the proteolytic enzyme Factor Xa to give the recombinant peptides rOxyTx1 and rOxyTx2. The experimental molecular masses of rOxyTx1 and rOxyTx2 were 8059.0 and 6176.4 Da, respectively, which agree with their expected theoretical masses. The recombinant peptides rOxyTx1 and rOxyTx2 showed lower but comparable toxicity to the native toxins when injected into lepidopteran larvae; furthermore, rOxyTx1 was able to inhibit calcium ion currents on dorsal unpaired median (DUM) neurons from Periplaneta americana.

  15. Disulfide structure of the pheromone binding protein from the silkworm moth, Bombyx mori.

    PubMed

    Leal, W S; Nikonova, L; Peng, G

    1999-12-24

    Disulfide bond formation is the only known posttranslational modification of insect pheromone binding proteins (PBPs). In the PBPs from moths (Lepidoptera), six cysteine residues are highly conserved at positions 19, 50, 54, 97, 108 and 117, but to date nothing is known about their respective linkage or redox status. We used a multiple approach of enzymatic digestion, chemical cleavage, partial reduction with Tris-(2-carboxyethyl)phosphine, followed by digestion with endoproteinase Lys-C to determine the disulfide connectivity in the PBP from Bombyx mori (BmPBP). Identification of the reaction products by on-line liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS) and protein sequencing supported the assignment of disulfide bridges at Cys-19-Cys-54, Cys-50-Cys-108 and Cys-97-Cys-117. The disulfide linkages were identical in the protein obtained by periplasmic expression in Escherichia coli and in the native BmPBP.

  16. Accelerated exchange of a buried water molecule in selectively disulfide-reduced bovine pancreatic trypsin inhibitor.

    PubMed

    Denisov, Vladimir P; Peters, Jörg; Hörlein, Hans Dietrich; Halle, Bertil

    2004-09-28

    Using magnetic relaxation dispersion (MRD), we have previously shown that the four internal water molecules in bovine pancreatic trypsin inhibitor (BPTI) exchange with bulk water on time scales between 10(-8) and 10(-4) s at room temperature. Because this exchange is controlled by the protein structure, internal water molecules can be used to probe rare conformational fluctuations. Here, we report (2)H and (17)O MRD data at three temperatures for wild-type BPTI and two BPTI variants where the 14-38 disulfide bond has been cleaved by a double Cys --> Ser mutation or by disulfide reduction and carboxamidomethylation. The MRD data show that the internal water molecules are conserved on disulfide cleavage. However, the exchange rate of the water molecule buried near the disulfide bond is enhanced by 2-4 orders of magnitude. The relation of water exchange to other dynamic processes in BPTI is discussed.

  17. Generation of a Multicomponent Library of Disulfide Donor-Acceptor Architectures Using Dynamic Combinatorial Chemistry.

    PubMed

    Drożdż, Wojciech; Kołodziejski, Michał; Markiewicz, Grzegorz; Jenczak, Anna; Stefankiewicz, Artur R

    2015-07-17

    We describe here the generation of new donor-acceptor disulfide architectures obtained in aqueous solution at physiological pH. The application of a dynamic combinatorial chemistry approach allowed us to generate a large number of new disulfide macrocyclic architectures together with a new type of [2]catenanes consisting of four distinct components. Up to fifteen types of structurally-distinct dynamic architectures have been generated through one-pot disulfide exchange reactions between four thiol-functionalized aqueous components. The distribution of disulfide products formed was found to be strongly dependent on the structural features of the thiol components employed. This work not only constitutes a success in the synthesis of topologically- and morphologically-complex targets, but it may also open new horizons for the use of this methodology in the construction of molecular machines.

  18. Generation of a Multicomponent Library of Disulfide Donor-Acceptor Architectures Using Dynamic Combinatorial Chemistry

    PubMed Central

    Drożdż, Wojciech; Kołodziejski, Michał; Markiewicz, Grzegorz; Jenczak, Anna; Stefankiewicz, Artur R.

    2015-01-01

    We describe here the generation of new donor-acceptor disulfide architectures obtained in aqueous solution at physiological pH. The application of a dynamic combinatorial chemistry approach allowed us to generate a large number of new disulfide macrocyclic architectures together with a new type of [2]catenanes consisting of four distinct components. Up to fifteen types of structurally-distinct dynamic architectures have been generated through one-pot disulfide exchange reactions between four thiol-functionalized aqueous components. The distribution of disulfide products formed was found to be strongly dependent on the structural features of the thiol components employed. This work not only constitutes a success in the synthesis of topologically- and morphologically-complex targets, but it may also open new horizons for the use of this methodology in the construction of molecular machines. PMID:26193265

  19. Substrate-Initiated Synthesis of Cell-Penetrating Poly(disulfide)s

    PubMed Central

    Molinard, Guillaume; Roux, Aurélien; Sakai, Naomi; Matile, Stefan

    2015-01-01

    Lessons from surface-initiated polymerization are applied to grow cell-penetrating poly(disulfide)s directly on substrates of free choice. Reductive depolymerization after cellular uptake should then release the native substrates and minimize toxicity. In the presence of thiolated substrates, propagators containing a strained disulfide from asparagusic or, preferably, lipoic acid and a guanidinium cation polymerize into poly(disulfide)s in less than 5 min at room temperature at pH 7. Substrate-initiated polymerization of cationic poly(disulfide)s and their depolymerization with dithiothreitol causes the appearance and disappearance of transport activity in fluorogenic vesicles. The same process is further characterized by gel-permeation chromatography and fluorescence resonance energy transfer. PMID:23363440

  20. Tungsten-molybdenum fractionation in estuarine environments

    NASA Astrophysics Data System (ADS)

    Mohajerin, T. Jade; Helz, George R.; Johannesson, Karen H.

    2016-03-01

    Dissolved tungsten (W) and molybdenum (Mo) concentrations were measured in surface waters and sediment pore waters of Terrebonne Bay, a shallow estuary in the Mississippi River delta, to investigate the biogeochemical processes that fractionate these Group 6 elements relative to one another during transit from weathering to sedimentary environments. Although many of the chemical properties of W and Mo are similar, the two elements behave autonomously, and the fractionation mechanisms are only partly understood. In sulfidic pore waters, dissolved Mo is depleted relative to river water-seawater mixtures, whereas dissolved W is >10-fold enriched. Reductive dissolution of poorly crystalline phases like ferrihydrite, which is a preferential host of W relative to Mo in grain coatings on river-borne particles, can explain the dissolved W enrichment. Dissolved W becomes increasingly enriched as H2S(aq) rises above about 60 μM due to transformation of WO42- to thiotungstates as well as to additional reductive dissolution of phases that host W. In contrast, as rising sulfide transforms MoO42- to thiomolybdates in pore waters, dissolved Mo is suppressed, probably owing to equilibration with an Fe-Mo-S phase. This putative phase appears to control the aqueous ion product, Q = [Fe2+][MoS42-]0.6 [H2S0]0.4/[H+]0.8, at a value of 10-7.78. Concentrations of dissolved W and Mo in pore waters bear no relation to concentrations in surface waters of the same salinity. In surface waters, dissolved Mo is nearly conserved in the estuarine mixing zone. Dissolved W appears also to be conserved except for several cases where W may have been enhanced by exchange with underlying, W-rich pore waters. With increasing salinity, the molar Mo/W ratio rises from about 10 to about 1000 in surface waters whereas it is mostly <10 in underlying pore waters and in highly sulfidic pore waters is mostly near 1. Differences in two chemical properties may account for this fractionation of Mo with respect to

  1. Conferring specificity in redox pathways by enzymatic thiol/disulfide exchange reactions.

    PubMed

    Netto, Luis Eduardo S; de Oliveira, Marcos Antonio; Tairum, Carlos A; da Silva Neto, José Freire

    2016-01-01

    Thiol-disulfide exchange reactions are highly reversible, displaying nucleophilic substitutions mechanism (S(N)2 type). For aliphatic, low molecular thiols, these reactions are slow, but can attain million times faster rates in enzymatic processes. Thioredoxin (Trx) proteins were the first enzymes described to accelerate thiol-disulfide exchange reactions and their high reactivity is related to the high nucleophilicity of the attacking thiol. Substrate specificity in Trx is achieved by several factors, including polar, hydrophobic, and topological interactions through a groove in the active site. Glutaredoxin (Grx) enzymes also contain the Trx fold, but they do not share amino acid sequence similarity with Trx. A conserved glutathione binding site is a typical feature of Grx that can reduce substrates by two mechanisms (mono and dithiol). The high reactivity of Grx enzymes is related to the very acid pK(a) values of reactive Cys that plays roles as good leaving groups. Therefore, although distinct oxidoreductases catalyze similar thiol–disulfide exchange reactions, their enzymatic mechanisms vary. PDI and DsbA are two other oxidoreductases, but they are involved in disulfide bond formation, instead of disulfide reduction, which is related to the oxidative environment where they are found. PDI enzymes and DsbC are endowed with disulfide isomerase activity, which is related with their tetra-domain architecture. As illustrative description of specificity in thiol-disulfide exchange, redox aspects of transcription activation in bacteria, yeast, and mammals are presented in an evolutionary perspective. Therefore, thiol-disulfide exchange reactions play important roles in conferring specificity to pathways, a required feature for signaling.

  2. Structure-based approach to the prediction of disulfide bonds in proteins.

    PubMed

    Salam, Noeris K; Adzhigirey, Matvey; Sherman, Woody; Pearlman, David A

    2014-10-01

    Protein engineering remains an area of growing importance in pharmaceutical and biotechnology research. Stabilization of a folded protein conformation is a frequent goal in projects that deal with affinity optimization, enzyme design, protein construct design, and reducing the size of functional proteins. Indeed, it can be desirable to assess and improve protein stability in order to avoid liabilities such as aggregation, degradation, and immunogenic response that may arise during development. One way to stabilize a protein is through the introduction of disulfide bonds. Here, we describe a method to predict pairs of protein residues that can be mutated to form a disulfide bond. We combine a physics-based approach that incorporates implicit solvent molecular mechanics with a knowledge-based approach. We first assign relative weights to the terms that comprise our scoring function using a genetic algorithm applied to a set of 75 wild-type structures that each contains a disulfide bond. The method is then tested on a separate set of 13 engineered proteins comprising 15 artificial stabilizing disulfides introduced via site-directed mutagenesis. We find that the native disulfide in the wild-type proteins is scored well, on average (within the top 6% of the reasonable pairs of residues that could form a disulfide bond) while 6 out of the 15 artificial stabilizing disulfides scored within the top 13% of ranked predictions. Overall, this suggests that the physics-based approach presented here can be useful for triaging possible pairs of mutations for disulfide bond formation to improve protein stability.

  3. Method for direct production of carbon disulfide and hydrogen from hydrocarbons and hydrogen sulfide feedstock

    SciTech Connect

    Miao, Frank Q.; Erekson, Erek James

    1998-12-01

    A method for converting hydrocarbons and hydrogen sulfide to carbon disulfide and hydrogen is provided comprising contacting the hydrocarbons and hydrogen sulfide to a bi-functional catalyst residing in a controlled atmosphere for a time and at a temperature sufficient to produce carbon disulfide and hydrogen. Also provided is a catalyst for converting carbon sulfides and hydrogen sulfides to gasoline range hydrocarbons comprising a mixture containing a zeolite catalyst and a hydrogenating catalyst.

  4. Impaired color discrimination among viscose rayon workers exposed to carbon disulfide

    SciTech Connect

    Raitta, C.; Teir, H.; Tolonen, M.; Nurminen, M.; Helpioe, E.M.; Malmstroem, S.

    1981-03-01

    A possible effect of chronic carbon disulfide exposure on the optic nerve was studied by giving the Farnsworth Munsell 100-Hue Test for color discrimination to 62 exposed and 40 nonexposed men. Carbon disulfide exposure did not relate to specific pattern defects in color discrimination, but impaired color discrimination occurred significantly more often in the exposed group than among the referents. The abnormal findings suggest an impairment in the receptiveness of the ganglion cells or demyelination of the optic nerve fibers.

  5. Creep behavior of tungsten/niobium and tungsten/niobium-1 percent zirconium composites

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Titran, R. H.

    1988-01-01

    A study was conducted to determine the feasibility of using tungsten fiber reinforced niobium or niobium-1 percent zirconium matrix composites to meet the anticipated increased temperature and creep resistance requirements imposed by advanced space power systems. The results obtained on the short time tensile properties indicated that W/Nb composites showed significant improvements in high temperature strength and offer significant mass reductions for high temperature space power systems. The prime material requirement for space power systems applications is long time creep resistance. A study was conducted to determine the effect of high temperature exposure on the properties of these composites, with emphasis upon their creep behavior at elevated temperatures.

  6. Mechanistic, kinetic, and processing aspects of tungsten chemical mechanical polishing

    NASA Astrophysics Data System (ADS)

    Stein, David

    This dissertation presents an investigation into tungsten chemical mechanical polishing (CMP). CMP is the industrially predominant unit operation that removes excess tungsten after non-selective chemical vapor deposition (CVD) during sub-micron integrated circuit (IC) manufacture. This work explores the CMP process from process engineering and fundamental mechanistic perspectives. The process engineering study optimized an existing CMP process to address issues of polish pad and wafer carrier life. Polish rates, post-CMP metrology of patterned wafers, electrical test data, and synergy with a thermal endpoint technique were used to determine the optimal process. The oxidation rate of tungsten during CMP is significantly lower than the removal rate under identical conditions. Tungsten polished without inhibition during cathodic potentiostatic control. Hertzian indenter model calculations preclude colloids of the size used in tungsten CMP slurries from indenting the tungsten surface. AFM surface topography maps and TEM images of post-CMP tungsten do not show evidence of plow marks or intergranular fracture. Polish rate is dependent on potassium iodate concentration; process temperature is not. The colloid species significantly affects the polish rate and process temperature. Process temperature is not a predictor of polish rate. A process energy balance indicates that the process temperature is predominantly due to shaft work, and that any heat of reaction evolved during the CMP process is negligible. Friction and adhesion between alumina and tungsten were studied using modified AFM techniques. Friction was constant with potassium iodate concentration, but varied with applied pressure. This corroborates the results from the energy balance. Adhesion between the alumina and the tungsten was proportional to the potassium iodate concentration. A heuristic mechanism, which captures the relationship between polish rate, pressure, velocity, and slurry chemistry, is presented

  7. An intact interchain disulfide bond is required for the neurotoxicity of tetanus toxin.

    PubMed Central

    Schiavo, G; Papini, E; Genna, G; Montecucco, C

    1990-01-01

    Tetanus toxin is composed of a heavy chain (100 kDa) and a light chain (50 kDa) held together by a single interchain disulfide bridge. An additional intrachain disulfide is present in the carboxy-terminal part of the heavy chain. Reduction of the two disulfide bonds in tetanus toxin with both chemical and proteinaceous reducing agents was studied. Dithiothreitol and 2-mercaptoethanol cleaved both the inter- and intrachain disulfide bridges of the toxin, while glutathione and cysteine were ineffective. Specific reduction of the single interchain disulfide link was achieved with the thioredoxin-thioredoxin reductase system, thus indicating that this bond is exposed at the protein surface. Also, dead or permeabilized cells were able to reduce the toxin. Such reduced toxin bound to neuronal membranes as well as the native toxin but was not neurotoxic. These findings open the possibility that reduction by cytoplasmic agents released by dead cells contributes to detoxification of tetanus toxin. Moreover, together with the notion that the light chain is the active form of the toxin in the cytoplasm, these results suggest that the interchain disulfide bond of tetanus toxin plays a role in nerve cell penetration. Images PMID:2254033

  8. Stabilization of cyclohexanone monooxygenase by a computationally designed disulfide bond spanning only one residue.

    PubMed

    van Beek, Hugo L; Wijma, Hein J; Fromont, Lucie; Janssen, Dick B; Fraaije, Marco W

    2014-01-01

    Enzyme stability is an important parameter in biocatalytic applications, and there is a strong need for efficient methods to generate robust enzymes. We investigated whether stabilizing disulfide bonds can be computationally designed based on a model structure. In our approach, unlike in previous disulfide engineering studies, short bonds spanning only a few residues were included. We used cyclohexanone monooxygenase (CHMO), a Baeyer-Villiger monooxygenase (BVMO) from Acinetobacter sp. NCIMB9871 as the target enzyme. This enzyme has been the prototype BVMO for many biocatalytic studies even though it is notoriously labile. After creating a small library of mutant enzymes with introduced cysteine pairs and subsequent screening for improved thermostability, three stabilizing disulfide bonds were identified. The introduced disulfide bonds are all within 12 Å of each other, suggesting this particular region is critical for unfolding. This study shows that stabilizing disulfide bonds do not have to span many residues, as the most stabilizing disulfide bond, L323C-A325C, spans only one residue while it stabilizes the enzyme, as shown by a 6 °C increase in its apparent melting temperature.

  9. Bovicin HJ50-Like Lantibiotics, a Novel Subgroup of Lantibiotics Featured by an Indispensable Disulfide Bridge

    PubMed Central

    Wang, Jian; Ma, Hongchu; Ge, Xiaoxuan; Zhang, Jie; Teng, Kunling; Sun, Zhizeng; Zhong, Jin

    2014-01-01

    Lantibiotics are ribosomally-synthesized and posttranslationally modified peptides with potent antimicrobial activities. Discovery of novel lantibiotics has been greatly accelerated with the soaring release of genomic information of microorganisms. As a unique class II lantibiotic, bovicin HJ50 is produced by Streptococcus bovis HJ50 and contains one rare disulfide bridge. By using its precursor BovA as a drive sequence, 16 BovA-like peptides were revealed in a wide variety of species. From them, three representative novel lan loci from Clostridium perfringens D str. JGS1721, Bacillus cereus As 1.348 and B. thuringiensis As 1.013 were identified by PCR screening. The corresponding mature lantibiotics designated perecin, cerecin and thuricin were obtained and structurally elucidated to be bovicin HJ50-like lantibiotics especially by containing a conserved disulfide bridge. The disulfide bridge was substantiated to be essential for the function of bovicin HJ50-like lantibiotics as its disruption eliminated their antimicrobial activities. Further analysis indicated that the disulfide bridge played a crucial role in maintaining the hydrophobicity of bovicin HJ50, which might facilitate it to exert antimicrobial function. This study unveiled a novel subgroup of disulfide-containing lantibiotics from bacteria of different niches and further demonstrated the indispensable role of disulfide bridge in these novel bovicin HJ50-like lantibiotics. PMID:24821187

  10. Disulfide-Linked Dinitroxides for Monitoring Cellular Thiol Redox Status through Electron Paramagnetic Resonance Spectroscopy.

    PubMed

    Legenzov, Eric A; Sims, Stephen J; Dirda, Nathaniel D A; Rosen, Gerald M; Kao, Joseph P Y

    2015-12-01

    Intracellular thiol-disulfide redox balance is crucial to cell health, and may be a key determinant of a cancer's response to chemotherapy and radiation therapy. The ability to assess intracellular thiol-disulfide balance may thus be useful not only in predicting responsiveness of cancers to therapy, but in assessing predisposition to disease. Assays of thiols in biology have relied on colorimetry or fluorimetry, both of which require UV-visible photons, which do not penetrate the body. Low-frequency electron paramagnetic resonance imaging (EPRI) is an emerging magnetic imaging technique that uses radio waves, which penetrate the body well. Therefore, in combination with tailored imaging agents, EPRI affords the opportunity to image physiology within the body. In this study, we have prepared water-soluble and membrane-permeant disulfide-linked dinitroxides, at natural isotopic abundance, and with D,(15)N-substitution. Thiols such as glutathione cleave the disulfides, with simple bimolecular kinetics, to yield the monomeric nitroxide species, with distinctive changes in the EPR spectrum. Using the D,(15)N-substituted disulfide-dinitroxide and EPR spectroscopy, we have obtained quantitative estimates of accessible intracellular thiol in cultured human lymphocytes. Our estimates are in good agreement with published measurements. This suggests that in vivo EPRI of thiol-disulfide balance is feasible. Finally, we discuss the constraints on the design of probe molecules that would be useful for in vivo EPRI of thiol redox status. PMID:26523485

  11. Stabilization of cyclohexanone monooxygenase by a computationally designed disulfide bond spanning only one residue.

    PubMed

    van Beek, Hugo L; Wijma, Hein J; Fromont, Lucie; Janssen, Dick B; Fraaije, Marco W

    2014-01-01

    Enzyme stability is an important parameter in biocatalytic applications, and there is a strong need for efficient methods to generate robust enzymes. We investigated whether stabilizing disulfide bonds can be computationally designed based on a model structure. In our approach, unlike in previous disulfide engineering studies, short bonds spanning only a few residues were included. We used cyclohexanone monooxygenase (CHMO), a Baeyer-Villiger monooxygenase (BVMO) from Acinetobacter sp. NCIMB9871 as the target enzyme. This enzyme has been the prototype BVMO for many biocatalytic studies even though it is notoriously labile. After creating a small library of mutant enzymes with introduced cysteine pairs and subsequent screening for improved thermostability, three stabilizing disulfide bonds were identified. The introduced disulfide bonds are all within 12 Å of each other, suggesting this particular region is critical for unfolding. This study shows that stabilizing disulfide bonds do not have to span many residues, as the most stabilizing disulfide bond, L323C-A325C, spans only one residue while it stabilizes the enzyme, as shown by a 6 °C increase in its apparent melting temperature. PMID:24649397

  12. The presence of disulfide bonds reveals an evolutionarily conserved mechanism involved in mitochondrial protein translocase assembly

    PubMed Central

    Wrobel, Lidia; Sokol, Anna M.; Chojnacka, Magdalena; Chacinska, Agnieszka

    2016-01-01

    Disulfide bond formation is crucial for the biogenesis and structure of many proteins that are localized in the intermembrane space of mitochondria. The importance of disulfide bond formation within mitochondrial proteins was extended beyond soluble intermembrane space proteins. Tim22, a membrane protein and core component of the mitochondrial translocase TIM22, forms an intramolecular disulfide bond in yeast. Tim22 belongs to the Tim17/Tim22/Tim23 family of protein translocases. Here, we present evidence of the high evolutionary conservation of disulfide bond formation in Tim17 and Tim22 among fungi and metazoa. Topological models are proposed that include the location of disulfide bonds relative to the predicted transmembrane regions. Yeast and human Tim22 variants that are not oxidized do not properly integrate into the membrane complex. Moreover, the lack of Tim17 oxidation disrupts the TIM23 translocase complex. This underlines the importance of disulfide bond formation for mature translocase assembly through membrane stabilization of weak transmembrane domains. PMID:27265872

  13. Oxidation of Disulfides to Thiolsulfinates with Hydrogen Peroxide and a Cyclic Seleninate Ester Catalyst.

    PubMed

    McNeil, Nicole M R; McDonnell, Ciara; Hambrook, Miranda; Back, Thomas G

    2015-06-11

    Cyclic seleninate esters function as mimetics of the antioxidant selenoenzyme glutathione peroxidase. They catalyze the reduction of harmful peroxides with thiols, which are converted to disulfides in the process. The possibility that the seleninate esters could also catalyze the further oxidation of disulfides to thiolsulfinates and other overoxidation products under these conditions was investigated. This has ramifications in potential medicinal applications of seleninate esters because of the possibility of catalyzing the unwanted oxidation of disulfide-containing spectator peptides and proteins. A variety of aryl and alkyl disulfides underwent facile oxidation with hydrogen peroxide in the presence of catalytic benzo-1,2-oxaselenolane Se-oxide affording the corresponding thiolsulfinates as the principal products. Unsymmetrical disulfides typically afforded mixtures of regioisomers. Lipoic acid and N,N'-dibenzoylcystine dimethyl ester were oxidized readily under similar conditions. Although isolated yields of the product thiolsulfinates were generally modest, these experiments demonstrate that the method nevertheless has preparative value because of its mild conditions. The results also confirm the possibility that cyclic seleninate esters could catalyze the further undesired oxidation of disulfides in vivo.

  14. The disulfide proteome and other reactive cysteine proteomes: analysis and functional significance.

    PubMed

    Lindahl, Marika; Mata-Cabana, Alejandro; Kieselbach, Thomas

    2011-06-15

    Ten years ago, proteomics techniques designed for large-scale investigations of redox-sensitive proteins started to emerge. The proteomes, defined as sets of proteins containing reactive cysteines that undergo oxidative post-translational modifications, have had a particular impact on research concerning the redox regulation of cellular processes. These proteomes, which are hereafter termed "disulfide proteomes," have been studied in nearly all kingdoms of life, including animals, plants, fungi, and bacteria. Disulfide proteomics has been applied to the identification of proteins modified by reactive oxygen and nitrogen species under stress conditions. Other studies involving disulfide proteomics have addressed the functions of thioredoxins and glutaredoxins. Hence, there is a steadily growing number of proteins containing reactive cysteines, which are probable targets for redox regulation. The disulfide proteomes have provided evidence that entire pathways, such as glycolysis, the tricarboxylic acid cycle, and the Calvin-Benson cycle, are controlled by mechanisms involving changes in the cysteine redox state of each enzyme implicated. Synthesis and degradation of proteins are processes highly represented in disulfide proteomes and additional biochemical data have established some mechanisms for their redox regulation. Thus, combined with biochemistry and genetics, disulfide proteomics has a significant potential to contribute to new discoveries on redox regulation and signaling.

  15. Optical absorption and transmission in a molybdenum disulfide monolayer

    NASA Astrophysics Data System (ADS)

    Rukelj, Zoran; Štrkalj, Antonio; Despoja, Vito

    2016-09-01

    Our recently proposed theoretical formulation [presented in D. Novko et al., Phys. Rev. B 93, 125413 (2016), 10.1103/PhysRevB.93.125413] is used to study optical absorption and transmission in molybdenum disulfide (MoS2) monolayer as a function of incident photon energy and angle. The investigation is not focused on exploration of well-documented spin-orbit split excitons around optical absorption onset, but rather on the most intensive features in absorption spectrum in the visible and near-ultraviolet photon energy range (1.7 -4 eV ). It is shown that three most intensive peaks, at 2.7, 3.1, and 3.7 eV, result from transitions between Mo(d ) and S(p ) valence and conduction bands and that the character of their charge/current density fluctuations is intrinsically in plane, located in the molybdenum plane. This also implies that MoS2 monolayer is completely transparent when illuminated by grazing incidence p -polarized light. The validity of the presented results is supported by our effective two-band tight-binding model and finally by good agreement with some recent experimental results.

  16. Cardiovascular effects in viscose rayon workers exposed to carbon disulfide.

    PubMed

    Kotseva, K; Braeckman, L; De Bacquer, D; Bulat, P; Vanhoorne, M

    2001-01-01

    The objectives of this study were to investigate the cardiovascular effects in workers currently exposed to carbon disulfide (CS2) below the threshold limit value (TLV) of 31 mg/m3 and to determine the prevalence of coronary heart disease (CHD) after long-term exposure. 172 men (91 workers exposed to CS2 in a viscose rayon factory and 81 referent workers) were examined using a medical and job history questionnaire, Rose's questionnaire, and electrocardiography at rest, and by measuring blood pressure and serum lipids and lipoproteins. Personal exposures were monitored simultaneously with active sampling and findings were analyzed according to the NIOSH 1600 method. As a result of technical and organizational improvements, personal CS2 exposures were well below the TLV (5.4-13.02 mg/m3). No significant effect of CS2 on blood pressure or lipids (total cholesterol, HDL and LDL cholesterol, triglycerides, and apolipoproteins AI and B) was found, even after allowance for confounding factors. The prevalence of CHD (ECG abnormalities and chest pain) was higher in the viscose rayon workers than in the workers with no exposure but reached statistical significance for men with exposure histories often years and more only (cumulative CS9 index > or = 150 mg/m3, the most highly exposed group). The findings suggest that the coronary risk is increased in workers previously exposed to high CS2 concentrations but not in those exposed to CS2 levels below the current TLV. PMID:11210016

  17. Biotechnology for removal of carbon disulfide emissions. Final report

    SciTech Connect

    McIntosh, M.J.

    1995-07-01

    Biological removal in a ``biofilter`` plant of carbon disulfide and hydrogen sulfide from the air effluent of a viscose plant at Teepak, Inc., is analyzed from process and economic standpoints by use of the Aspen Plus simulation program. The metabolic product from the biofilter, 3% sulfuric acid, must be transformed at the source into either a marketable or recyclable commodity (such as 95% sulfuric acid, high-quality sulfur, or high-quality gypsum) or a material with reasonable landfill costs (such as sulfur or gypsum). The simulations indicate that the total capital requirement for production of concentrated sulfuric acid is $48.9 million; for high-quality gypsum, $40.4 million; and for high-quality sulfur, $29.4 million. Production of concentrated sulfur for landfill is not economically practical. The process to neutralize the 3% acid effluent with limestone and landfill the resulting low-quality gypsum requires the lowest total investment of the processes simulated, $8.7 million, including the biofilter plant.

  18. Induction of tibial dyschondroplasia in turkeys by tetramethylthiuram disulfide (thiram).

    PubMed

    Simsa, S; Hasdai, A; Dan, H; Ornan, E M

    2007-08-01

    Tibial dyschondroplasia (TD) is a prevalent skeletal abnormality associated with rapid growth rate in many avian species; it causes enormous economic losses and is an animal welfare problem. Tibial dyschondroplasia is characterized by the presence of a nonvascularized, nonmineralized lesion that extends from the epiphyseal growth plate into the metaphysis of the proximal tibiotarsal bones. The mechanisms underlying TD development are not known, although they have been extensively studied in broilers using different induction models. However, an effective model for TD induction in turkeys has never been described. The objective of this study was to establish such a model by using tetramethylthiuram disulfide (thiram), an agent that is frequently used in broilers to induce TD. We found that dramatically longer exposures to much higher concentrations of thiram were required to induce TD in turkeys vs. broilers. In contrast to broilers, in which 50 mg/kg of thiram induces a high incidence of severe TD within 10 d, in turkeys, an exposure to 400 mg/kg of thiram for 11 wk was necessary for the development of severe TD lesions. These results show different mechanisms for TD induction in these 2 closely related species, suggesting differences in TD etiology between them.

  19. Toward barrier free contact to molybdenum disulfide using graphene electrodes.

    PubMed

    Liu, Yuan; Wu, Hao; Cheng, Hung-Chieh; Yang, Sen; Zhu, Enbo; He, Qiyuan; Ding, Mengning; Li, Dehui; Guo, Jian; Weiss, Nathan O; Huang, Yu; Duan, Xiangfeng

    2015-05-13

    Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) have attracted tremendous interest as a new class of electronic materials. However, there are considerable challenges in making reliable contacts to these atomically thin materials. Here we present a new strategy by using graphene as the back electrodes to achieve ohmic contact to MoS2. With a finite density of states, the Fermi level of graphene can be readily tuned by a gate potential to enable a nearly perfect band alignment with MoS2. We demonstrate for the first time a transparent contact to MoS2 with zero contact barrier and linear output behavior at cryogenic temperatures (down to 1.9 K) for both monolayer and multilayer MoS2. Benefiting from the barrier-free transparent contacts, we show that a metal-insulator transition can be observed in a two-terminal MoS2 device, a phenomenon that could be easily masked by Schottky barriers found in conventional metal-contacted MoS2 devices. With further passivation by boron nitride (BN) encapsulation, we demonstrate a record-high extrinsic (two-terminal) field effect mobility up to 1300 cm(2)/(V s) in MoS2 at low temperature.

  20. Distribution of protein disulfide isomerase during maturation of pig oocytes.

    PubMed

    Ohashi, Yumi; Hoshino, Yumi; Tanemura, Kentaro; Sato, Eimei

    2013-01-01

    Oocyte maturation in mammals is characterized by a dramatic reorganization of the endoplasmic reticulum (ER). In mice, the ER forms accumulations in the germinal vesicle (GV) stage and distinctive cortical clusters in metaphase II (MII) of the oocyte. Multiple evidence suggests that this ER distribution is important in preparing the oocyte for Ca(2+) oscillations, which trigger oocyte activation at fertilization. In this study, we investigated the time course and illustrated the possible functional role of ER distribution during maturation of porcine oocytes by immunostaining with protein disulfide isomerase (PDI). PDI forms clusters in the cytoplasm of oocytes. After immunostaining, PDI clusters were identified throughout the cytoplasm from the GV to metaphase I (MI) stage; however, at the MII stage, the PDI formed large clusters (1-2 µm) in the animal pole around the first polar body. PDI distribution was prevented by bacitracin, a PDI inhibitor. Our experiments indicated that, during porcine oocyte maturation, PDI undergoes a dramatic reorganization. This characteristic distribution is different from that in the mouse oocyte. Moreover, our study suggested that formation of PDI clusters in the animal pole is a specific characteristic of matured porcine oocytes. PMID:23302077