Science.gov

Sample records for activated iridium oxide

  1. Highly active iridium/iridium-tin/tin oxide heterogeneous nanoparticles as alternative electrocatalysts for the ethanol oxidation reaction.

    PubMed

    Du, Wenxin; Wang, Qi; Saxner, David; Deskins, N Aaron; Su, Dong; Krzanowski, James E; Frenkel, Anatoly I; Teng, Xiaowei

    2011-09-28

    Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high-energy density, and availability from biomass. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. In this paper, we have studied Iridium (Ir)-based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir(71)Sn(29) catalysts with an average diameter of 2.7 ± 0.6 nm through a "surfactant-free" wet chemistry approach. The complementary characterization techniques, including aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, are used to identify the "real" heterogeneous structure of Ir(71)Sn(29)/C particles as Ir/Ir-Sn/SnO(2), which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO(2) present on the surface. The Ir(71)Sn(29)/C heterogeneous catalyst exhibited high electrochemical activity toward the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed SnO(2) on surface. Our cross-disciplinary work, from novel "surfactant-free" synthesis of Ir-Sn catalysts, theoretical simulations, and catalytic measurements to the characterizations of "real" heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts but also have a transformative impact on the commercialization of DEFC technology by replacing Pt with low

  2. Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships.

    PubMed

    Bernicke, Michael; Ortel, Erik; Reier, Tobias; Bergmann, Arno; Ferreira de Araujo, Jorge; Strasser, Peter; Kraehnert, Ralph

    2015-06-08

    Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm(-2) .

  3. Synthesis of nanoporous activated iridium oxide films by anodized aluminum oxide templated atomic layer deposition.

    SciTech Connect

    Comstock, D. J.; Christensen, S. T.; Elam, J. W.; Pellin, M. J.; Hersam, M. C.

    2010-08-01

    Iridium oxide (IrOx) has been widely studied due to its applications in electrochromic devices, pH sensing, and neural stimulation. Previous work has demonstrated that both Ir and IrOx films with porous morphologies prepared by sputtering exhibit significantly enhanced charge storage capacities. However, sputtering provides only limited control over film porosity. In this work, we demonstrate an alternative scheme for synthesizing nanoporous Ir and activated IrOx films (AIROFs). This scheme utilizes atomic layer deposition to deposit a thin conformal Ir film within a nanoporous anodized aluminum oxide template. The Ir film is then activated by potential cycling in 0.1 M H{sub 2}SO{sub 4} to form a nanoporous AIROF. The morphologies and electrochemical properties of the films are characterized by scanning electron microscopy and cyclic voltammetry, respectively. The resulting nanoporous AIROFs exhibit a nanoporous morphology and enhanced cathodal charge storage capacities as large as 311 mC/cm{sup 2}.

  4. Excimer laser deinsulation of Parylene-C on iridium for use in an activated iridium oxide film-coated Utah electrode array.

    PubMed

    Yoo, Je-Min; Negi, Sandeep; Tathireddy, Prashant; Solzbacher, Florian; Song, Jong-In; Rieth, Loren W

    2013-04-30

    Implantable microelectrodes provide a measure to electrically stimulate neurons in the brain and spinal cord and record their electrophysiological activity. A material with a high charge capacity such as activated or sputter-deposited iridium oxide film (AIROF or SIROF) is used as an interface. The Utah electrode array (UEA) uses SIROF for its interface material with neural tissue and oxygen plasma etching (OPE) with an aluminium foil mask to expose the active area, where the interface between the electrode and neural tissue is formed. However, deinsulation of Parylene-C using OPE has limitations, including the lack of uniformity in the exposed area and reproducibility. While the deinsulation of Parylene-C using an excimer laser is proven to be an alternative for overcoming the limitations, the iridium oxide (IrOx) suffers from fracture when high laser fluence (>1000 mJ/cm2) is used. Iridium (Ir), which has a much higher fracture resistance than IrOx, can be deposited before excimer laser deinsulation and then the exposed Ir film area can be activated by electrochemical treatment to acquire the AIROF. Characterisation of the laser-ablated Ir film and AIROF by surface analysis (X-ray photoelectron spectroscopy, scanning electron microscope, and atomic force microscope) and electrochemical analysis (electrochemical impedance spectroscopy, and cyclic voltammetry) shows that the damage on the Ir film induced by laser irradiation is significantly less than that on SIROF, and the AIROF has a high charge storage capacity. The results show the potential of the laser deinsulation technique for use in high performance AIROF-coated UEA fabrication.

  5. Sputtered iridium oxide for stimulation electrode coatings.

    PubMed

    Mokwa, Wilfried; Wessling, Boerge; Schnakenberg, Uwe

    2007-01-01

    This work deals with the reactive RF-powered sputter deposition of iridium oxide for use as the active stimulation layer in functional medical implants. The oxygen gettered by the growing films is determined by an approach based on generic curves. Films deposited at different stages of oxygen integration show strong differences in electrochemical behaviour, caused by different morphologies. The dependence of electrochemical activity on morphology is further illustrated by RF sputtering onto heated substrates, as well as DC sputtering onto cold substrates.

  6. Cytotoxic activity and protein binding through an unusual oxidative mechanism by an iridium(I)-NHC complex.

    PubMed

    Gothe, Y; Marzo, T; Messori, L; Metzler-Nolte, N

    2015-02-21

    A new NHC iridium(I) complex (1) showing significant antiproliferative properties in vitro is described here. Its crystal structure, solution behaviour and interactions with the model proteins cytochrome c (cyt c) and lysozyme were investigated. High resolution ESI-MS measurements suggest that this iridium(i) complex acts as a prodrug and binds cyt c tightly through an unusual "oxidative" mechanism. Eventually, an iridium(III)-NHC fragment is found associated to the protein.

  7. Iridium material for hydrothermal oxidation environments

    DOEpatents

    Hong, Glenn T.; Zilberstein, Vladimir A.

    1996-01-01

    A process for hydrothermal oxidation of combustible materials in which, during at least a part of the oxidation, corrosive material is present and makes contact with at least a portion of the apparatus over a contact area on the apparatus. At least a portion of the contact surface area comprises iridium, iridium oxide, an iridium alloy, or a base metal overlaid with an iridium coating. Iridium has been found to be highly resistant to environments encountered in the process of hydrothermal oxidation. Such environments typically contain greater than 50 mole percent water, together with oxygen, carbon dioxide, and a wide range of acids, bases and salts. Pressures are typically about 27.5 to about 1000 bar while temperatures range as high as 800.degree. C.

  8. Electrodeposited iridium oxide for neural stimulation and recording electrodes.

    PubMed

    Meyer, R D; Cogan, S F; Nguyen, T H; Rauh, R D

    2001-03-01

    Iridium oxide films formed by electrodeposition onto noniridium metal substrates are compared with activated iridium oxide films (AIROFs) as a low impedance, high charge capacity coating for neural stimulation and recording electrodes. The electrodeposited iridium oxide films (EIROFs) were deposited on Au, Pt, PtIr, and 316 LVM stainless steel substrates from a solution of IrCl4, oxalic acid, and K2CO3. A deposition protocol involving 50 potential sweeps at 50 mV/s between limits of 0.0 V and 0.55 V (versus Ag AgCl) followed by potential pulsing between the same limits produced adherent films with a charge storage capacity of >25 mC/cm2. Characterization by cyclic voltammetry and impedance spectroscopy revealed no differences in the electrochemical behavior of EIROF on non-Ir substrates and AIROF. The mechanical stability of the oxides was evaluated by ultrasonication in distilled water followed by dehydration and rehydration. Stability under charge injection was evaluated using 200 micros, 5.9 A/cm2 (1.2 mC/cm2) cathodal pulses. Loss of iridium oxide charge capacity was comparable for AIROFs and the EIROFs, ranging from 1% to 8% of the capacity immediately after activation or deposition. The EIROFs were deposited and evaluated on silicon microprobe electrodes and on metallized polyimide electrodes being developed for neural recording and stimulation applications.

  9. Homogeneous and heterogenized iridium water oxidation catalysts

    NASA Astrophysics Data System (ADS)

    Macchioni, Alceo

    2014-10-01

    The development of an efficient catalyst for the oxidative splitting of water into molecular oxygen, protons and electrons is of key importance for producing solar fuels through artificial photosynthesis. We are facing the problem by means of a rational approach aimed at understanding how catalytic performance may be optimized by the knowledge of the reaction mechanism of water oxidation and the fate of the catalytic site under the inevitably harsh oxidative conditions. For the purposes of our study we selected iridium water oxidation catalysts, exhibiting remarkable performance (TOF > 5 s-1 and TON > 20000). In particular, we recently focused our attention on [Cp*Ir(N,O)X] (N,O = 2-pyridincarboxylate; X = Cl or NO3) and [IrCl(Hedta)]Na water oxidation catalysts. The former exhibited a remarkable TOF whereas the latter showed a very high TON. Furthermore, [IrCl(Hedta)]Na was heterogenized onto TiO2 taking advantage of the presence of a dandling -COOH functionality. The heterogenized catalyst maintained approximately the same catalytic activity of the homogeneous analogous with the advantage that could be reused many times. Mechanistic studies were performed in order to shed some light on the rate-determining step and the transformation of catalysts when exposed to "oxidative stress". It was found that the last oxidative step, preceding oxygen liberation, is the rate-determining step when a small excess of sacrificial oxidant is used. In addition, several intermediates of the oxidative transformation of the catalyst were intercepted and characterized by NMR, X-Ray diffractometry and ESI-MS.

  10. Iridium-Tin oxide solid-solution nanocatalysts with enhanced activity and stability for oxygen evolution

    NASA Astrophysics Data System (ADS)

    Li, Guangfu; Yu, Hongmei; Yang, Donglei; Chi, Jun; Wang, Xunying; Sun, Shucheng; Shao, Zhigang; Yi, Baolian

    2016-09-01

    Addressing major challenges from the material cost, efficiency and stability, it is highly desirable to develop high-performance catalysts for oxygen evolution reaction (OER). Herein we explore a facile surfactant-assisted approach for fabricating Irsbnd Sn (Ir/Sn = 0.6/0.4, by mol.) nano-oxide catalysts with good morphology control. Direct proofs from XRD and X-ray photoelectron spectra indicate hydrophilic triblock polymer (TBP, like Pluronic® F108) surfactant can boost the formation of stable solid-solution structure. With the TBP hydrophilic and block-length increase, the fabricated Irsbnd Sn oxides undergoing the rod-to-sphere transition obtain the relatively lower crystallization, decreased crystallite size, Ir-enriched surface and incremental available active sites, all of which can bolster the OER activity and stability. Meanwhile, it is observed that the coupled Ir oxidative etching takes a crucial role in determining the material structure and performance. Compared with commercial Ir black, half-cell tests confirm F108-assistant catalysts with over 40 wt% Ir loading reduction show 2-fold activity enhancement as well as significant stability improvement. The lowest cell voltage using 0.88 mg cm-2 Ir loading is only 1.621 V at 1000 mA cm-2 and 80 °C with a concomitant energy efficiency of 75.8% which is beyond the DOE 2017 efficiency target of 74%.

  11. Sputtered iridium oxide films (SIROFs) for low-impedance neural stimulation and recording electrodes.

    PubMed

    Cogan, S F; Plante, T D; Ehrlich, J

    2004-01-01

    Iridium oxide films formed by electrochemical activation of iridium metal (AIROF) or by electrochemical deposition (EIROF) are being evaluated as low-impedance charge-injection coatings for neural stimulation and recording. Iridium oxide may also be deposited by reactive sputtering from iridium metal in an oxidizing plasma. The characterization of sputtered iridium oxide films (SIROFs) as coatings for nerve electrodes is reported. SIROFs were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and potential transient measurements during charge-injection. The surface morphology of the SIROF transitions from smooth to highly nodular with increasing film thickness from 80 nm to 4600 nm. Charge-injection capacities exceed 0.75 mC/cm(2) with 0.75 ms current pulses in thicker films. The SIROF was deposited on both planar and non-planar substrates and photolithographically patterned by lift-off.

  12. Iridium-based double perovskites for efficient water oxidation in acid media

    NASA Astrophysics Data System (ADS)

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-08-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.

  13. Iridium-based double perovskites for efficient water oxidation in acid media

    PubMed Central

    Diaz-Morales, Oscar; Raaijman, Stefan; Kortlever, Ruud; Kooyman, Patricia J.; Wezendonk, Tim; Gascon, Jorge; Fu, W. T.; Koper, Marc T. M.

    2016-01-01

    The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2. PMID:27498694

  14. Mercury Underpotential Deposition to Determine Iridium and Iridium Oxide Electrochemical Surface Areas

    SciTech Connect

    Alia, Shaun M.; Hurst, Katherine E.; Kocha, Shyam S.; Pivovar, Bryan S.

    2016-06-02

    Determining the surface areas of electrocatalysts is critical for separating the key properties of area-specific activity and electrochemical surface area from mass activity. Hydrogen underpotential deposition and carbon monoxide oxidation are typically used to evaluate iridium (Ir) surface areas, but are ineffective on oxides and can be sensitive to surface oxides formed on Ir metals. Mercury underpotential deposition is presented in this study as an alternative, able to produce reasonable surface areas on Ir and Ir oxide nanoparticles, and able to produce similar surface areas prior to and following characterization in oxygen evolution. Reliable electrochemical surface areas allow for comparative studies of different catalyst types and the characterization of advanced oxygen evolution catalysts. Lastly, they also enable the study of catalyst degradation in durability testing, both areas of increasing importance within electrolysis and electrocatalysis.

  15. Mercury Underpotential Deposition to Determine Iridium and Iridium Oxide Electrochemical Surface Areas

    DOE PAGES

    Alia, Shaun M.; Hurst, Katherine E.; Kocha, Shyam S.; ...

    2016-06-02

    Determining the surface areas of electrocatalysts is critical for separating the key properties of area-specific activity and electrochemical surface area from mass activity. Hydrogen underpotential deposition and carbon monoxide oxidation are typically used to evaluate iridium (Ir) surface areas, but are ineffective on oxides and can be sensitive to surface oxides formed on Ir metals. Mercury underpotential deposition is presented in this study as an alternative, able to produce reasonable surface areas on Ir and Ir oxide nanoparticles, and able to produce similar surface areas prior to and following characterization in oxygen evolution. Reliable electrochemical surface areas allow for comparativemore » studies of different catalyst types and the characterization of advanced oxygen evolution catalysts. Lastly, they also enable the study of catalyst degradation in durability testing, both areas of increasing importance within electrolysis and electrocatalysis.« less

  16. Sputtered iridium oxide films (SIROFs) for neural stimulation electrodes

    PubMed Central

    Cogan, Stuart F.; Ehrlich, Julia; Plante, Timothy D.; Smirnov, Anton; Shire, Douglas B.; Gingerich, Marcus; Rizzo, Joseph F.

    2009-01-01

    Sputtered iridium oxide films (SIROFs) deposited by DC reactive sputtering from an iridium metal target have been characterized in vitro for their potential as neural recording and stimulation electrodes. SIROFs were deposited over gold metallization on flexible multielectrode arrays fabricated on thin (15 µm) polyimide substrates. SIROF thickness and electrode areas of 200–1300 nm and 1960–125600 µm2, respectively, were investigated. The charge-injection capacities of the SIROFs were evaluated in an inorganic interstitial fluid model in response to charge-balanced, cathodal-first current pulses. Charge injection capacities were measured as a function of cathodal pulse width (0.2 – 1 ms) and potential bias in the interpulse period (0.0 to 0.7 V vs. Ag|AgCl). Depending on the pulse parameters and electrode area, charge-injection capacities ranged from 1–9 mC/cm2, comparable with activated iridium oxide films (AIROFs) pulsed under similar conditions. Other parameters relevant to the use of SIROF on nerve electrodes, including the thickness dependence of impedance (0.05–105 Hz) and the current necessary to maintain a bias in the interpulse region were also determined. PMID:17271216

  17. On the Extreme Oxidation States of Iridium.

    PubMed

    Pyykkö, Pekka; Xu, Wen-Hua

    2015-06-22

    It has recently been suggested that the oxidation states of Ir run from the putative -III in the synthesized solid Na3 [Ir(CO)3 ] to the well-documented +IX in the species IrO4 (+) . Furthermore, [Ir(CO)3 ](3-) was identified as an 18-electron species. A closer DFT study now finds support for this picture: The orbitals spanned by the 6s,6p,5d orbitals of the iridium are all occupied. Although some have considerable ligand character, the deviations from 18 e leave the orbital symmetries unchanged. The isoelectronic systems from Os(-IV) to Au(-I) behave similarly, suggesting further possible species. To paraphrase Richard P. Feynmann "there is plenty of room at the bottom".

  18. Iridium ultrasmall nanoparticles, worm-like chain nanowires, and porous nanodendrites: One-pot solvothermal synthesis and catalytic CO oxidation activity

    NASA Astrophysics Data System (ADS)

    Zhang, Tao; Li, Shuai-Chen; Zhu, Wei; Ke, Jun; Yu, Jing-Wen; Zhang, Zhi-Ping; Dai, Lin-Xiu; Gu, Jun; Zhang, Ya-Wen

    2016-06-01

    We report a facile one-pot solvothermal synthesis of monodisperse iridium (Ir) ultrasmall (1.5-2.5 nm in diameter) nanoparticles (NPs), worm-like chain nanowires (NWs), and porous nanodendrites (NDs), for which CO oxidation reaction has been employed as a probe reaction to investigate the effects of nanoparticle size and surface-capping organics on the catalytic activities. Time-dependent experiments revealed that an oriented attachment mechanism induced by the strong adsorption of halide anions (Br- and I-) on specific facet of Ir nanoclusters or by decreasing the reduction rate of Ir precursors with changing their concentrations during the synthesis was responsible for the formation of Ir NWs and NDs. Annealing tests indicated that an O2-H2 atmosphere treatment turned out to be an effective measure to clean up the surface-capping organics of Ir NPs supported on commercial SiO2. Catalytic CO oxidation reaction illustrated that a significant improvement in the catalytic activity of CO oxidation reaction was achieved together with the changing of activation energies after such atmosphere treatment for the supported catalysts of the ultrasmall Ir NPs. It is noteworthy that this enhancement in catalytic activity could be ascribed to the changes in the surface status (including populations of Ir species in metallic and oxidized states, removal of surface capping organics, the variety of active sites, and total effective active site number) for the supported nanocatalysts during the atmosphere treatment.

  19. Heterogeneous Catalysis for Water Oxidation by an Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous Organosilica.

    PubMed

    Liu, Xiao; Maegawa, Yoshifumi; Goto, Yasutomo; Hara, Kenji; Inagaki, Shinji

    2016-07-04

    Heterogenization of metal-complex catalysts for water oxidation without loss of their catalytic activity is important for the development of devices simulating photosynthesis. In this study, efficient heterogeneous iridium complexes for water oxidation were prepared using bipyridine-bridged periodic mesoporous organosilica (BPy-PMO) as a solid chelating ligand. The BPy-PMO-based iridium catalysts (Ir-BPy-PMO) were prepared by postsynthetic metalation of BPy-PMO and characterized through physicochemical analyses. The Ir-BPy-PMOs showed high catalytic activity for water oxidation. The turnover frequency (TOF) values for Ir-BPy-PMOs were one order of magnitude higher than those of conventional heterogeneous iridium catalysts. The reusability and stability of Ir-BPy-PMO were also examined, and detailed characterization was conducted using powder X-ray diffraction, nitrogen adsorption, (13) C DD MAS NMR spectroscopy, TEM, and XAFS methods.

  20. Transformation of a Cp*-iridium(III) precatalyst for water oxidation when exposed to oxidative stress.

    PubMed

    Zuccaccia, Cristiano; Bellachioma, Gianfranco; Bortolini, Olga; Bucci, Alberto; Savini, Arianna; Macchioni, Alceo

    2014-03-17

    The reaction of [Cp*Ir(bzpy)NO3 ] (1; bzpy=2-benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water-oxidation catalyst, with several oxidants (H2 O2 , NaIO4 , cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates of the oxidative transformation. NMR spectroscopy and ESI-MS techniques provided evidence for the formation of many species that all had the intact Ir-bzpy moiety and a gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms of Cp* and iridium, which gives an oxygen-Ir coordinated epoxide, whereas the remaining three carbon atoms of Cp* are involved in a η(3) interaction with iridium (2 a). Formal addition of H2 O to 2 a or H2 O2 to 1 leads to 2 b, in which a double MeCOH functionalization of Cp* is present with one MeCOH engaged in an interaction with iridium. The structure of 2 b was unambiguously determined in the solid state and in solution by X-ray single-crystal diffractometry and advanced NMR spectroscopic techniques, respectively. Further oxidation led to the opening of Cp* and transformation of the diol into a diketone with one carbonyl coordinated at the metal (2 c). A η(3) interaction between the three non-oxygenated carbons of "ex-Cp*" and iridium is also present in both 2 b and 2 c. Isolated 2 b and mixtures of 2 a-c species were tested in water-oxidation catalysis by using CAN as sacrificial oxidant. They showed substantially the same activity than 1 (turnover frequency values ranged from 9 to 14 min(-1) ).

  1. Phase control of iridium and iridium oxide thin films in atomic layer deposition

    SciTech Connect

    Kim, Sung-Wook; Kwon, Se-Hun; Kwak, Dong-Kee; Kang, Sang-Won

    2008-01-15

    The atomic layer deposition of iridium (Ir) and iridium oxide (IrO{sub 2}) films was investigated using an alternating supply of (ethylcyclopentadienyl)(1,5-cyclooctadiene) iridium and oxygen gas at temperatures between 230 and 290 deg. C. The phase transition between Ir and IrO{sub 2} occurred at the critical oxygen partial pressure during the oxygen injection pulse. The oxygen partial pressure was controlled by the O{sub 2}/(Ar+O{sub 2}) ratio or deposition pressures. The resistivity of the deposited Ir and IrO{sub 2} films was about 9 and 120 {mu}{omega} cm, respectively. In addition, the critical oxygen partial pressure for the phase transition between Ir and IrO{sub 2} was increased with increasing the deposition temperature. Thus, the phase of the deposited film, either Ir or IrO{sub 2}, was controlled by the oxygen partial pressure and the deposition temperature. However, the formation of a thin Ir layer was detected between the IrO{sub 2} and SiO{sub 2} substrate. To remove this interfacial layer, the oxygen partial pressure is increased to a severe condition. And the impurity contents were below the detection limit of Auger electron spectroscopy in both Ir and IrO{sub 2} films.

  2. Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas I.; Narayan, Sri R.; Billings, Keith J.

    2011-01-01

    NASA requires a durable and efficient catalyst for the electrolysis of water in a polymer-electrolyte-membrane (PEM) cell. Ruthenium oxide in a slightly reduced form is known to be a very efficient catalyst for the anodic oxidation of water to oxygen, but it degrades rapidly, reducing efficiency. To combat this tendency of ruthenium oxide to change oxidation states, it is combined with iridium, which has a tendency to stabilize ruthenium oxide at oxygen evolution potentials. The novel oxygen evolution catalyst was fabricated under flowing argon in order to allow the iridium to preferentially react with oxygen from the ruthenium oxide, and not oxygen from the environment. Nanoparticulate iridium black and anhydrous ruthenium oxide are weighed out and mixed to 5 18 atomic percent. They are then heat treated at 300 C under flowing argon (in order to create an inert environment) for a minimum of 14 hours. This temperature was chosen because it is approximately the creep temperature of ruthenium oxide, and is below the sintering temperature of both materials. In general, the temperature should always be below the sintering temperature of both materials. The iridium- doped ruthenium oxide catalyst is then fabricated into a PEM-based membrane- electrode assembly (MEA), and then mounted into test cells. The result is an electrolyzer system that can sustain electrolysis at twice the current density, and at the same efficiency as commercial catalysts in the range of 100-200 mA/sq cm. At 200 mA/sq cm, this new system operates at an efficiency of 85 percent, which is 2 percent greater than commercially available catalysts. Testing has shown that this material is as stable as commercially available oxygen evolution catalysts. This means that this new catalyst can be used to regenerate fuel cell systems in space, and as a hydrogen generator on Earth.

  3. Optimization and electrochemical characterization of RF-sputtered iridium oxide microelectrodes for electrical stimulation

    NASA Astrophysics Data System (ADS)

    Kang, Xiaoyang; Liu, Jingquan; Tian, Hongchang; Yang, Bin; NuLi, Yanna; Yang, Chunsheng

    2014-02-01

    A reactively sputtered iridium oxide (IrOx) thin film has been developed as electrochemical modification material for microelectrodes to obtain high stability and charge storage capacity (CSC) in functional electrical stimulation. The effect of the oxygen flow and oxygen to argon ratio during sputtering process on the microstructure and electrochemical properties of the IrOx film is characterized. After optimization, the activated IrOx microelectrode shows the highest CSC of 36.15 mC cm-2 at oxygen flow of 25 sccm and oxygen to argon ratio of (2.5:1). Because the deposition process of the reactively sputtered iridium oxide is an exothermic reaction, it is difficult to form film patterning by the lift-off process. The lift-off process was focused on the partially carbonized photoresist (PR) and normal PR. The higher of the carbonization degree of PR reaches, the longer the immersion duration. However, the patterning process of the iridium oxide film becomes feasible when the sputtering pressure is increasing. The experimental results show that the iridium oxide films forms the pattern with the lowest duration of ultrasonic agitation when the deposition pressure is 4.2 Pa and pressure ratio between O2 and Ar pressure is 3:4.

  4. Multi-component nanoporous platinum-ruthenium-copper-osmium-iridium alloy with enhanced electrocatalytic activity towards methanol oxidation and oxygen reduction

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoting; Si, Conghui; Gao, Yulai; Frenzel, Jan; Sun, Junzhe; Eggeler, Gunther; Zhang, Zhonghua

    2015-01-01

    Multi-component nanoporous platinum-ruthenium-copper-osmium-iridium (np-PtRuCuOsIr) electrocatalyst has been facilely fabricated by chemical dealloying of mechanically alloyed AlCuPtRuOsIr precursor. The np-PtRuCuOsIr catalyst exhibits a typical three-dimensional bi-continuous interpenetrating ligament/channel structure with a length scale of ∼2.5 nm. The np-PtRuCuOsIr catalyst reaches a higher level in the mass activity (857.5 mA mgPt-1) and specific activity (3.0 mA cm-2) towards methanol oxidation compared to the commercial PtC catalyst (229.5 mA mgPt-1 and 0.5 mA cm-2 respectively). Moreover, the CO stripping peak of np-PtRuCuOsIr is 0.54 V (vs. SCE), 130 mV negative shift in comparison with the commercial PtC (0.67 V vs. SCE). The half-wave potential of np-PtRuCuOsIr is 0.900 V vs. RHE, 36 mV positive compared with that of the commercial PtC (0.864 V vs. RHE). The np-PtRuCuOsIr catalyst also shows 1.8 and 3.8 times enhancement in the mass and specific activity towards oxygen reduction than the commercial PtC. Moreover, the np-PtRuCuOsIr alloy exhibits superior oxygen reduction activities even after 15 K cycles, indicating its excellent long-term stability. The present np-PtRuCuOsIr can act as a promising candidate for the electrocatalyst in direct methanol fuel cells (DMFCs).

  5. Luminescent Iridium(III) Complex Labeled DNA for Graphene Oxide-Based Biosensors.

    PubMed

    Zhao, Qingcheng; Zhou, Yuyang; Li, Yingying; Gu, Wei; Zhang, Qi; Liu, Jian

    2016-02-02

    There has been growing interest in utilizing highly photostable iridium(III) complexes as new luminescent probes for biotechnology and life science. Herein, iridium(III) complex with carboxyl group was synthesized and activated with N-hydroxysuccinimide, followed by tagging to the amino terminate of single-stranded DNA (ssDNA). The Ir-ssDNA probe was further combined with graphene oxide (GO) nanosheets to develop a GO-based biosensor for target ssDNA detection. The quenching efficiency of GO, and the photostability of iridium(III) complex and GO-Ir-ssDNA biosensor, were also investigated. On the basis of the high luminescence quenching efficiency of GO toward iridium(III) complex, the GO-Ir-ssDNA biosensor exhibited minimal background signals, while strong emission was observed when Ir-ssDNA desorbed from GO nanosheets and formed a double helix with the specific target, leading to a high signal-to-background ratio. Moreover, it was found that luminescent intensities of iridium(III) complex and GO-Ir-ssDNA biosensor were around 15 and 3 times higher than those of the traditional carboxyl fluorescein (FAM) dye and the GO-FAM-ssDNA biosensor after UV irradiation, respectively. Our study suggested the sensitive and selective Ir-ssDNA probe was suitable for the development of highly photostable GO-based detection platforms, showing promise for application beyond the OLED (organic light emitting diode) area.

  6. Determination of surface coverage of catalysts: Temperature programmed experiments on platinum and iridium sponge catalysts after low temperature ammonia oxidation

    SciTech Connect

    Broek, A.C.M. van den; Grondelle, J. van; Santen, R.A. van

    1999-07-25

    The activity of iridium and platinum sponge catalysts was studied in the low temperature gas phase oxidation of ammonia with oxygen. Under the reaction conditions used, iridium was found to be more active and more selective to nitrogen than platinum. Furthermore it was established from activity measurements that both catalysts lose activity as a function of time on stream due to inhibition of the surface by reaction intermediates. The used catalysts were studied by XPS and temperature programmed techniques. It was found that the surface of the catalysts had a high coverage of NH and OH and some additional NH{sub 2}. It seems most likely that the reaction mechanism proceeds through a stepwise dehydrogenation of the ammonia molecule. It appears that the last dehydrogenation step (NH by OH to N and water) is the rate determining step. The high selectivity of iridium to nitrogen can be explained by the higher activity of iridium in dissociating NO.

  7. Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods.

    PubMed

    Kalisman, Philip; Nakibli, Yifat; Amirav, Lilac

    2016-02-11

    We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide (CdSe@CdS) nanorod photocatalysts. Seeded rods are grown using a colloidal hot-injection method and then moved to an aqueous medium by ligand exchange. CdSe@CdS nanorods, an iridium precursor and other salts are mixed and illuminated. The deposition process is initiated by absorption of photons by the semiconductor particle, which results with formation of charge carriers that are used to promote redox reactions. To insure photochemical oxidative growth we used an electron scavenger. The photogenerated holes oxidize the iridium precursor, apparently in a mediated oxidative pathway. This results in the growth of high quality crystalline iridium oxide particles, ranging from 0.5 nm to about 3 nm, along the surface of the rod. Iridium oxide grown on CdSe@CdS heterostructures was studied by a variety of characterization methods, in order to evaluate its characteristics and quality. We explored means for control over particle size, crystallinity, deposition location on the CdS rod, and composition. Illumination time and excitation wavelength were found to be key parameters for such control. The influence of different growth conditions and the characterization of these heterostructures are described alongside a detailed description of their synthesis. Of significance is the fact that the addition of iridium oxide afforded the rods astounding photochemical stability under prolonged illumination in pure water (alleviating the requirement for hole scavengers).

  8. Properties of mixed molybdenum oxide iridium oxide thin films synthesized by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Patil, P. S.; Kawar, R. K.; Sadale, S. B.; Inamdar, A. I.; Deshmukh, H. P.

    2006-09-01

    Molybdenum-doped iridium oxide thin films have been deposited onto corning glass- and fluorine-doped tin oxide coated corning glass substrates at 350 °C by using a pneumatic spray pyrolysis technique. An aqueous solution of 0.01 M ammonium molybdate was mixed with 0.01 M iridium trichloride solution in different volume proportions and the resultant solution was used as a precursor solution for spraying. The as-deposited samples were annealed at 600 °C in air medium for 1 h. The structural, electrical and optical properties of as-deposited and annealed Mo-doped iridium oxide were studied and values of room temperature electrical resistivity, and thermoelectric power were estimated. The as-deposited samples with 2% Mo doping exhibit more pronounced electrochromism than other samples, including pristine Ir oxide.

  9. Evaluation of oxide-coated iridium-rhenium chambers

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1994-01-01

    Iridium-coated rhenium (Ir-Re) provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase Ir-Re rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated Ir-Re, 22-N rocket chambers were tested with gaseous hydrogen/gaseous oxygen (GHz/G02) propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia (HfO2) or zirconia (ZrO2). Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of ZrO2 infiltrated with sol gel HfO2. The other chamber had a coating composed of an Ir-oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. Testing the Ir-oxide composite-coated chamber included over 29 min at mixture ratio 16. The thicker walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner walled coatings did not experience the macrocracking and chipping of the chambers that was seen with the thick, monolithic coatings. However, burn-throughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stoichiometric. The burn-throughs were probably the result of oxygen diffusion through the oxide coating that allowed the underlying Ir and Re layers to be oxidized. The results of this test program indicated that the thin-walled oxide

  10. Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

    NASA Technical Reports Server (NTRS)

    Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

    2010-01-01

    Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600?C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form? process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

  11. Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

    NASA Technical Reports Server (NTRS)

    Shchetkovskiy, Anatoliy; McKechnie, Timothy; Sadoway, Donald R.; Paramore, James; Melendez, Orlando; Curreri, Peter A.

    2010-01-01

    Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600 C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

  12. High-Temperature Oxidation Behavior of Iridium-Rhenium Alloys

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1995-01-01

    The life-limiting mechanism for radiation-cooled rockets made from iridium-coated rhenium (Ir/Re) is the diffusion of Re into the Ir layer and the subsequent oxidation of the resulting Ir-Re alloy from the inner surface. In a previous study, a life model for Ir/Re rockets was developed. It incorporated Ir-Re diffusion and oxidation data to predict chamber lifetimes as a function of temperature and oxygen partial pressure. Oxidation testing at 1540 deg C suggested that a 20-wt percent Re concentration at the inner wall surface should be established as the failure criterion. The present study was performed to better define Ir-oxidation behavior as a function of Re concentration and to supplement the data base for the life model. Samples ranging from pure Ir to Ir-40 wt percent Re (Ir-40Re) were tested at 1500 deg C, in two different oxygen environments. There were indications that the oxidation rate of the Ir-Re alloy increased significantly when it went from a single-phase solid solution to a two-phase mixture, as was suggested in previous work. However, because of testing anomalies in this study, there were not enough dependable oxidation data to definitively raise the Ir/Re rocket failure criterion from 20-wt percent Re to a Re concentration corresponding to entry into the two-phase region.

  13. Electrochemically reduced graphene and iridium oxide nanoparticles for inhibition-based angiotensin-converting enzyme inhibitor detection.

    PubMed

    Kurbanoglu, Sevinc; Rivas, Lourdes; Ozkan, Sibel A; Merkoçi, Arben

    2017-02-15

    In this work, a novel biosensor based on electrochemically reduced graphene oxide and iridium oxide nanoparticles for the detection of angiotensin-converting enzyme inhibitor drug, captopril, is presented. For the preparation of the biosensor, tyrosinase is immobilized onto screen printed electrode by using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-Hydroxysuccinimide coupling reagents, in electrochemically reduced graphene oxide and iridium oxide nanoparticles matrix. Biosensor response is characterized towards catechol, in terms of graphene oxide concentration, number of cycles to reduce graphene oxide, volume of iridium oxide nanoparticles and tyrosinase solution. The designed biosensor is used to inhibit tyrosinase activity by Captopril, which is generally used to treat congestive heart failure. It is an angiotensin-converting enzyme inhibitor that operates via chelating copper at the active site of tyrosinase and thioquinone formation. The captopril detections using both inhibition ways are very sensitive with low limits of detection: 0.019µM and 0.008µM for chelating copper at the active site of tyrosinase and thioquinone formation, respectively. The proposed methods have been successfully applied in captopril determination in spiked human serum and pharmaceutical dosage forms with acceptable recovery values.

  14. Design, analysis, and fabrication of oxide-coated iridium/rhenium combustion chambers

    NASA Technical Reports Server (NTRS)

    Jang, Q.; Tuffias, R. H.; Laferla, R.; Ghoniem, N. M.

    1993-01-01

    Iridium-coated rhenium (Ir/Re) combustion chambers provide high temperature, oxidation-resistant operation for radiation-cooled liquid-fueled rocket engines. A 22-N (5-lb(sub f)) chamber has been operated for 15 hours at 2200 C (4000 F) using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellant, with negligible internal erosion. The oxidation resistance of these chambers could be further increased by the addition of refractory oxide coatings, providing longer life and/or operation in more oxidizing and higher temperature environments. The oxide coatings would serve as a thermal and diffusion barrier for the iridium coating, lowering the temperature of the iridium layer while also preventing the ingress of oxygen and egress of iridium oxides. This would serve to slow the failure mechanisms of Ir/Re chambers, namely the diffusion of rhenium to the inner surface and the oxidation of iridium. Such protection could extend chamber lifetimes by tens or perhaps hundreds of hours, and allow chamber operation on stoichiometric or higher mixture ratio oxygen/hydrogen (O2/H2) propellant. Extensive thermomechanical, thermochemical, and mass transport modeling was performed as a key material/structure design tool. Based on the results of these analyses, several 22-N oxide-coated Ir/Re chambers were fabricated and delivered to NASA Lewis Research Center for hot-fire testing.

  15. Design, analysis, and fabrication of oxide-coated iridium/rhenium combustion chambers

    NASA Astrophysics Data System (ADS)

    Jang, Q.; Tuffias, R. H.; Laferla, R.; Ghoniem, N. M.

    1993-11-01

    Iridium-coated rhenium (Ir/Re) combustion chambers provide high temperature, oxidation-resistant operation for radiation-cooled liquid-fueled rocket engines. A 22-N (5-lb(sub f)) chamber has been operated for 15 hours at 2200 C (4000 F) using nitrogen tetroxide/monomethyl hydrazine (NTO/MMH) propellant, with negligible internal erosion. The oxidation resistance of these chambers could be further increased by the addition of refractory oxide coatings, providing longer life and/or operation in more oxidizing and higher temperature environments. The oxide coatings would serve as a thermal and diffusion barrier for the iridium coating, lowering the temperature of the iridium layer while also preventing the ingress of oxygen and egress of iridium oxides. This would serve to slow the failure mechanisms of Ir/Re chambers, namely the diffusion of rhenium to the inner surface and the oxidation of iridium. Such protection could extend chamber lifetimes by tens or perhaps hundreds of hours, and allow chamber operation on stoichiometric or higher mixture ratio oxygen/hydrogen (O2/H2) propellant. Extensive thermomechanical, thermochemical, and mass transport modeling was performed as a key material/structure design tool. Based on the results of these analyses, several 22-N oxide-coated Ir/Re chambers were fabricated and delivered to NASA Lewis Research Center for hot-fire testing.

  16. In vitro study of iridium electrodes for neural stimulation.

    PubMed

    Aryan, Naser Pour; Brendler, Christian; Rieger, Viola; Schleehauf, Sebastian; Heusel, Gerhard; Rothermel, Albrecht

    2012-01-01

    Iridium is one of the main electrode materials for applications like neural stimulation. Iridium has a higher charge injection capacity when activated and transformed into AIROF (activated iridium oxide film) using specific electrical signals. Activation is not possible in stimulating devices, if they do not include the necessary circuitry for activation. We introduce a method for iridium electrode activation requiring minimum additional on-chip hardware. In the main part, the lifetime behavior of iridium electrodes is investigated. These results may be interesting for applications not including on-chip activation hardware, and also because activation has drawbacks such as worse mechanical properties and reproducibility of AIROF.

  17. Oxygen atom transfer to a half-sandwich iridium complex: clean oxidation yielding a molecular product.

    PubMed

    Turlington, Christopher R; White, Peter S; Brookhart, Maurice; Templeton, Joseph L

    2014-03-12

    The oxidation of [Ir(Cp*)(phpy)(NCAr(F))][B(Ar(F))4] (1; Cp* = η(5)-pentamethylcyclopentadienyl, phpy = 2-phenylene-κC(1')-pyridine-κN, NCAr(F) = 3,5-bis(trifluoromethyl)benzonitrile, B(Ar(F))4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) with the oxygen atom transfer (OAT) reagent 2-tert-butylsulfonyliodosobenzene (sPhIO) yielded a single, molecular product at -40 °C. New Ir(Cp*) complexes with bidentate ligands derived by oxidation of phpy were synthesized to model possible products resulting from oxygen atom insertion into the iridium-carbon and/or iridium-nitrogen bonds of phpy. These new ligands were either cleaved from iridium by water or formed unreactive, phenoxide-bridged iridium dimers. The reactivity of these molecules suggested possible decomposition pathways of Ir(Cp*)-based water oxidation catalysts with bidentate ligands that are susceptible to oxidation. Monitoring the [Ir(Cp*)(phpy)(NCAr(F))](+) oxidation reaction by low-temperature NMR techniques revealed that the reaction involved two separate OAT events. An intermediate was detected, synthesized independently with trapping ligands, and characterized. The first oxidation step involves direct attack of the sPhIO oxidant on the carbon of the coordinated nitrile ligand. Oxygen atom transfer to carbon, followed by insertion into the iridium-carbon bond of phpy, formed a coordinated organic amide. A second oxygen atom transfer generated an unidentified iridium species (the "oxidized complex"). In the presence of triphenylphosphine, the "oxidized complex" proved capable of transferring one oxygen atom to phosphine, generating phosphine oxide and forming an Ir-PPh3 adduct in 92% yield. The final Ir-PPh3 product was fully characterized.

  18. Testing and evaluation of oxide-coated iridium/rhenium chambers

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1993-01-01

    Iridium-coated rhenium provides long life operation of radiation-cooled rockets at temperatures up to 2200 C. Ceramic oxide coatings could be used to increase iridium/rhenium rocket lifetimes and allow operation in highly oxidizing environments. Ceramic oxide coatings promise to serve as both thermal and diffusion barriers for the iridium layer. Seven ceramic oxide-coated iridium/rhenium, 22 N rocket chambers were tested on gaseous hydrogen/gaseous oxygen propellants. Five chambers had thick (over 10 mils), monolithic coatings of either hafnia or zirconia. Two chambers had coatings with thicknesses less than 5 mils. One of these chambers had a thin-walled coating of zirconia infiltrated with sol gel hafnia. The other chamber had a coating composed of an iridium/oxide composite. The purpose of this test program was to assess the ability of the oxide coatings to withstand the thermal shock of combustion initiation, adhere under repeated thermal cycling, and operate in aggressively oxidizing environments. All of the coatings survived the thermal shock of combustion and demonstrated operation at mixture ratios up to 11. The iridium/oxide composite coated chamber included testing for over 29 minutes at mixture ratio 16. The thicker-walled coatings provided the larger temperature drops across the oxide layer (up to 570 C), but were susceptible to macrocracking and eventual chipping at a stress concentrator. The cracks apparently resealed during firing, under compression of the oxide layer. The thinner-walled coatings did not experience the macrocracking and chipping of the chambers seen with the thick, monolithic coatings. However, burnthroughs in the throat region did occur in both of the thin-walled chambers at mixture ratios well above stochiometric. The burn-throughs were probably the result of oxygen-diffusion through the oxide coating that allowed the underlying iridium and rhenium layers to be oxidized. The results of this test program indicated that the thin

  19. Non-covalent interactions in water electrolysis: influence on the activity of Pt(111) and iridium oxide catalysts in acidic media.

    PubMed

    Ganassin, Alberto; Colic, Viktor; Tymoczko, Jakub; Bandarenka, Aliaksandr S; Schuhmann, Wolfgang

    2015-04-07

    Electrolyte components, which are typically not considered to be directly involved in catalytic processes at solid-liquid electrified interfaces, often demonstrate a significant or even drastic influence on the activity, stability and selectivity of electrocatalysts. While there has been certain progress in the understanding of these electrolyte effects, lack of experimental data for various important systems frequently complicates the rational design of new active materials. Modern proton-exchange membrane (PEM) electrolyzers utilize Pt- and Ir-based electrocatalysts, which are among the very few materials that are both active and stable under the extreme conditions of water splitting. We use model Pt(111) and Ir-oxide films grown on Ir(111) electrodes and explore the effect of alkali metal cations and sulfate-anions on the hydrogen evolution and the oxygen evolution reactions in acidic media. We demonstrate that sulfate anions decrease the activity of Ir-oxide towards the oxygen evolution reaction while Rb(+) drastically promotes hydrogen evolution reaction at the Pt(111) electrodes as compared to the reference HClO4 electrolytes. Issues related to the activity benchmarking for these catalysts are discussed.

  20. Comparative assessment of iridium oxide and platinum alloy wires using an in vitro glial scar assay.

    PubMed

    Ereifej, Evon S; Khan, Saida; Newaz, Golam; Zhang, Jinsheng; Auner, Gregory W; VandeVord, Pamela J

    2013-12-01

    The long-term effect of chronically implanted electrodes is the formation of a glial scar. Therefore, it is imperative to assess the biocompatibility of materials before employing them in neural electrode fabrication. Platinum alloy and iridium oxide have been identified as good candidates as neural electrode biomaterials due to their mechanical and electrical properties, however, effect of glial scar formation for these two materials is lacking. In this study, we applied a glial scarring assay to observe the cellular reactivity to platinum alloy and iridium oxide wires in order to assess the biocompatibility based on previously defined characteristics. Through real-time PCR, immunostaining and imaging techniques, we will advance the understanding of the biocompatibility of these materials. Results of this study demonstrate iridium oxide wires exhibited a more significant reactive response as compared to platinum alloy wires. Cells cultured with platinum alloy wires had less GFAP gene expression, lower average GFAP intensity, and smaller glial scar thickness. Collectively, these results indicated that platinum alloy wires were more biocompatible than the iridium oxide wires.

  1. A pH Sensor Based on a Stainless Steel Electrode Electrodeposited with Iridium Oxide

    ERIC Educational Resources Information Center

    Martinez, C. C. M.; Madrid, R. E.; Felice, C. J.

    2009-01-01

    A simple procedure to make an iridium oxide (IrO[subscript 2]) electrodeposited pH sensor, that can be used in a chemical, biomedical, or materials laboratory, is presented here. Some exercises, based on this sensor, that can be used to teach important concepts in the field of biomedical, biochemical, tissue, or materials engineering, are also…

  2. Electrochemical water oxidation with carbon-grafted iridium complexes.

    PubMed

    deKrafft, Kathryn E; Wang, Cheng; Xie, Zhigang; Su, Xin; Hinds, Bruce J; Lin, Wenbin

    2012-02-01

    Hydrogen production from water splitting provides a potential solution to storing harvested solar energy in chemical fuels, but this process requires active and robust catalysts that can oxidize water to provide a source of electrons for proton reduction. Here we report the direct, covalent grafting of molecular Ir complexes onto carbon electrodes, with up to a monolayer coverage. Carbon-grafted Ir complexes electrochemically oxidize water with a turnover frequency of up to 3.3 s(-1) and a turnover number of 644 during the first hour. Electrochemical water oxidation with grafted catalysts gave enhanced rates and stability compared to chemically driven water oxidation with the corresponding molecular catalysts. This strategy provides a way to systematically evaluate catalysts under tunable conditions, potentially providing new insights into electrochemical water oxidation processes and water oxidation catalyst design.

  3. Theoretical study of structure, stability, and the hydrolysis reactions of small iridium oxide nanoclusters.

    PubMed

    Zhou, Xin; Yang, Jingxiu; Li, Can

    2012-10-11

    The geometric structures and relative stabilities of small iridium oxide nanoclusters, Ir(m)O(n) (m = 1-5 and n = 1-2m), have been systematically investigated using density functional theory (DFT) calculations at the B3LYP level. Our results show that the lowest-energy structures of these clusters can be obtained by the sequential oxidation of small "core" iridium clusters. The iridium-monoxide-like clusters have relatively higher stability because of their relatively high binding energy and second difference in energies. On the basis of the optimized lowest-energy structures of neutral and cationic (IrO(2))(n) (n = 1-5), DFT has been used to study the hydrolysis reaction of these clusters with water molecules. The calculated results show that the addition of water molecules to the cationic species is much easier than the neutral ones. The overall hydrolysis reaction energies are more exothermic for the cationic clusters than for the neutral clusters. Our calculations indicate that H(2)O can be more easily split on the cationic iridium oxide clusters than on the neutral clusters.

  4. Activation of C-H bonds in nitrones leads to iridium hydrides with antitumor activity.

    PubMed

    Song, Xiaoda; Qian, Yong; Ben, Rong; Lu, Xiang; Zhu, Hai-Liang; Chao, Hui; Zhao, Jing

    2013-08-22

    We report the design and synthesis of a series of new cyclometalated iridium hydrides derived from the C-H bond activation of aromatic nitrones and the biological evaluation of these iridium hydrides as antitumor agents. The nitrone ligands are based on the structure of a popular antioxidant, α-phenyl-N-tert-butylnitrone (PBN). Compared to cisplatin, the iridium hydrides exhibit excellent antitumor activity on HepG2 cells. The metal-coordinated compound with the most potent anticancer activity, 2f, was selected for further analysis because of its ability to induce apoptosis and interact with DNA. During in vitro studies and in vivo efficacy analysis with tumor xenograft models in Institute of Cancer Research (ICR) mice, complex 2f exhibited antitumor activity that was markedly superior to that of cisplatin. Our results suggest, for the first time, that metal hydrides could be a new type of metal-based antitumor agent.

  5. Iridium/Iridium Silicide as an Oxidation Resistant Capping Layer for Soft X-ray Mirrors

    SciTech Connect

    Prisbrey, S; Vernon, S

    2004-04-05

    Rust on a sword, tarnish on the silverware, and a loss in reflectivity for soft x-ray mirrors are all caused by oxidation that changes the desired characteristics of a material. Methods to prevent the oxidation have varied over the centuries with the default method of a protective coating being the most common. The protective coating for x-ray mirrors is usually a self-limiting oxidized layer on the surface of the material that stops further oxidation of the material by limiting the diffusion of oxygen to the material underneath.

  6. Activation of surface oxygen sites on an iridium-based model catalyst for the oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Grimaud, Alexis; Demortiere, Arnaud; Saubanere, Matthieu; Dachraoui, Walid; Duchamp, Martial; Doublet, Marie-Liesse; Tarascon, Jean-Marie

    2017-01-01

    The oxygen evolution reaction (OER) is of prime importance in multiple energy storage devices; however, deeper mechanistic understanding is required to design enhanced electrocatalysts for the reaction. Current understanding of the OER mechanism based on oxygen adsorption on a metallic surface site fails to fully explain the activity of iridium and ruthenium oxide surfaces, and the drastic surface reconstruction observed for the most active OER catalysts. Here we demonstrate, using La2LiIrO6 as a model catalyst, that the exceptionally high activity found for Ir-based catalysts arises from the formation of active surface oxygen atoms that act as electrophilic centres for water to react. Moreover, with the help of transmission electron microscopy, we observe drastic surface reconstruction and iridium migration from the bulk to the surface. Therefore, we establish a correlation between surface activity and surface stability for OER catalysts that is rooted in the formation of surface reactive oxygen.

  7. Highly effective water oxidation catalysis with iridium complexes through the use of NaIO4.

    PubMed

    Codolà, Zoel; Cardoso, João M S; Royo, Beatriz; Costas, Miquel; Lloret-Fillol, Julio

    2013-05-27

    Exceptional water oxidation (WO) turnover frequencies (TOF=17,000 h(-1)), and turnover numbers (TONs) close to 400,000, the largest ever reported for a metal-catalyzed WO reaction, have been found by using [Cp*Ir(III)(NHC)Cl2] (in which NHC=3-methyl-1-(1-phenylethyl)-imidazoline-2-ylidene) as the pre-catalyst and NaIO4 as oxidant in water at 40 °C. The apparent TOF for [Cp*Ir(III)(NHC)X2] (1X, in which X stands for I (1I), Cl (1Cl), or triflate anion (1OTf)) and [(Cp*-NHCMe)Ir(III)I2] (2) complexes, is kept constant during almost all of the O2 evolution reaction when using NaIO4 as oxidant. The TOF was found to be dependent on the ligand and on the anion (TOF ranging from ≈600 to ≈1100 h(-1) at 25 °C). Degradation of the complexes by oxidation of the organic ligands upon reaction with NaIO4 has been investigated. (1)H NMR, ESI-MS, and dynamic light-scattering measurements (DLS) of the reaction medium indicated that the complex undergoes rapid degradation, even at low equivalents of oxidant, but this process takes place without formation of nanoparticles. Remarkably, three-month-old solution samples of oxidized pre-catalysts remain equally as active as freshly prepared solutions. A UV/Vis feature band at λmax =405 nm is observed in catalytic reaction solutions only when O2 evolves, which may be attributed to a resting state iridium speciation, most probably Ir-oxo species with an oxidation state higher than IV.

  8. Strongly improved electrochemical cycling durability by adding iridium to electrochromic nickel oxide films.

    PubMed

    Wen, Rui-Tao; Niklasson, Gunnar A; Granqvist, Claes G

    2015-05-13

    Anodically colored nickel oxide (NiO) thin films are of much interest as counter electrodes in tungsten oxide based electrochromic devices such as "smart windows" for energy-efficient buildings. However, NiO films are prone to suffering severe charge density degradation upon prolonged electrochemical cycling, which can lead to insufficient device lifetime. Therefore, a means to improve the durability of NiO-based films is an important challenge at present. Here we report that the incorporation of a modest amount of iridium into NiO films [Ir/(Ir + Ni) = 7.6 atom %] leads to remarkable durability, exceeding 10000 cycles in a lithium-conducting electrolyte, along with significantly improved optical modulation during extended cycling. Structure characterization showed that the face-centered-cubic-type NiO structure remained after iridium addition. Moreover, the crystallinity of these films was enhanced upon electrochemical cycling.

  9. Iridium in natural waters

    SciTech Connect

    Anbar, A.D.; Wasserburg, G.J.; Papanastassiou, D.A.

    1996-09-13

    Iridium, commonly used as a tracer of extraterrestrial material, was measured in rivers, oceans, and an estuarine environment. The concentration of iridium in the oceans ranges from 3.0 ({+-}1.3) x 10{sup 8} to 5.7 ({+-}0.8) x 10{sup 8} atoms per kilogram. Rivers contain from 17.4 ({+-}0.9) x 10{sup 8} to 92.9 ({+-}2.2) x 10{sup 8} atoms per kilogram and supply more dissolved iridium to the oceans than do extraterrestrial sources. In the Baltic Sea, {approximately}75% of riverine iridium is removed from solution. Iron-manganese oxyhydroxides scavenge iridium under oxidizing conditions, but anoxic environments are not a major sink for iridium. The ocean residence time of iridium is between 2 x 10{sup 3} and 2 x 10{sup 4} years. 32 refs., 3 figs., 1 tab.

  10. The next step in chemical propulsion: Oxide-iridium/rhenium combustion chambers

    SciTech Connect

    Fortini, Arthur J.; Tuffias, Robert H.

    1999-01-22

    Chemical propulsion systems are currently limited by materials issues. Until recently, the state-of-the-art material for liquid propellant combustion chambers was silicide-coated niobium. However, combustion chamber performance demands have exceeded the capabilities of this material system, requiring development of better materials. The iridium/rhenium combustion chamber, comprising a rhenium structural shell with an iridium inner liner for oxidation protection, represents the current state of the art in high-performance, high temperature, long-life propulsion systems using nitrogen tetroxide/monomethyl hydrazine propellant. However, oxygen/hydrogen (O{sub 2}/H{sub 2}) and new 'green' monopropellants under development to replace hydrazine will be significantly more oxidizing at operating temperature. For these more highly aggressive combustion environments, Ultramet has shown that substantial additional life can be obtained by lining the interior of the combustion chamber with a refractory metal oxide, which functions as a thermal and gas diffusion barrier and provides dramatically increased oxidation resistance. Ultramet has fabricated numerous 22-N (5-lb{sub f}) thrust chambers with this oxide-iridium/rhenium architecture that have been hot-fire tested at NASA Lewis Research Center in O{sub 2}/H{sub 2} propellant at mixture ratios of 6 and 16, with steady-state exterior wall temperatures ranging from 2433 to 2899 K, comprising the most severe temperature and oxidizing conditions ever utilized. Of the seven chambers tested to date, three failed due to facility problems, and two never failed. The best-performing chamber was hot-fired for 13,595 seconds (227 minutes; 3.8 hours) and showed no visible signs of degradation. Additional chambers are being fabricated for future testing.

  11. The next step in chemical propulsion: Oxide-iridium/rhenium combustion chambers

    NASA Astrophysics Data System (ADS)

    Fortini, Arthur J.; Tuffias, Robert H.

    1999-01-01

    Chemical propulsion systems are currently limited by materials issues. Until recently, the state-of-the-art material for liquid propellant combustion chambers was silicide-coated niobium. However, combustion chamber performance demands have exceeded the capabilities of this material system, requiring development of better materials. The iridium/rhenium combustion chamber, comprising a rhenium structural shell with an iridium inner liner for oxidation protection, represents the current state of the art in high-performance, high temperature, long-life propulsion systems using nitrogen tetroxide/monomethyl hydrazine propellant. However, oxygen/hydrogen (O2/H2) and new ``green'' monopropellants under development to replace hydrazine will be significantly more oxidizing at operating temperature. For these more highly aggressive combustion environments, Ultramet has shown that substantial additional life can be obtained by lining the interior of the combustion chamber with a refractory metal oxide, which functions as a thermal and gas diffusion barrier and provides dramatically increased oxidation resistance. Ultramet has fabricated numerous 22-N (5-lbf) thrust chambers with this oxide-iridium/rhenium architecture that have been hot-fire tested at NASA Lewis Research Center in O2/H2 propellant at mixture ratios of 6 and 16, with steady-state exterior wall temperatures ranging from 2433 to 2899 K, comprising the most severe temperature and oxidizing conditions ever utilized. Of the seven chambers tested to date, three failed due to facility problems, and two never failed. The best-performing chamber was hot-fired for 13,595 seconds (227 minutes; 3.8 hours) and showed no visible signs of degradation. Additional chambers are being fabricated for future testing.

  12. An iridium oxide microelectrode for monitoring acute local pH changes of endothelial cells.

    PubMed

    Ng, Shu Rui; O'Hare, Danny

    2015-06-21

    pH sensors were fabricated by anodically electrodepositing iridium oxide films (AEIROFs) onto microelectrodes on chips and coated with poly(ethyleneimine) (PEI) for mechanical stability. These demonstrate super-Nernstian response to pH from pH 4.0 to 7.7 in chloride-free phosphate buffer. The surface of the chip was coated with fibronectin for the attachment of porcine aortic endothelial cells (PAECs). The working capability of the pH sensor for monitoring acute local pH changes was investigated by stimulating the PAECs with thrombin. Our results show that thrombin induced acute extracellular acidification of PAECs and dissolution of fibronectin, causing the local pH to decrease. The use of PD98059, a mitogen-activated protein kinase (MAPK) inhibitor, reduced extracellular acidification and an increase in local pH was observed. This study shows that our pH sensors can facilitate the investigation of acute cellular responses to stimulation by monitoring the real-time, local pH changes of cells attached to the sensors.

  13. An Iridium(III) Complex Inhibits JMJD2 Activities and Acts as a Potential Epigenetic Modulator.

    PubMed

    Liu, Li-Juan; Lu, Lihua; Zhong, Hai-Jing; He, Bingyong; Kwong, Daniel W J; Ma, Dik-Lung; Leung, Chung-Hang

    2015-08-27

    A novel iridium(III) complex was synthesized and evaluated for its ability to target JMJD2 enzymatic activity. The iridium(III) complex 1 can inhibit JMJD2 activity and was selective for JMJD2 activity over JARID, JMJD3, and HDAC activities. Moreover, 1 suppressed the trimethylation of the p21 promoter on H3K9me3 and interrupted the JMJD2D-H3K9me3 interactions in human cells, suggesting that it could act as an epigenetic modulator. To our knowledge, 1 represents the first metal-based JMJD2 inhibitor reported in the literature.

  14. Possible Superconductivity Induced by Strong Spin-Orbit Coupling in Carrier Doped Iridium Oxides Insulators

    NASA Astrophysics Data System (ADS)

    Nishiguchi, Kazutaka; Shirakawa, Tomonori; Watanabe, Hiroshi; Arita, Ryotaro; Yunoki, Seiji

    2014-03-01

    5 d transition metal oxide Sr2IrO4 and its relevant Iridium oxides have attracted much interest because of exotic properties arising from highly entangled spin and orbital degrees of freedom due to strong spin-orbit coupling (SOC). Sr2IrO4 crystalizes in the layered perovskite structure, similar to cuprates. Five 5 d electrons in Ir occupy its t2 g orbitals which are split by strong SOC, locally inducing an effective total angular momentum Jeff = 1 / 2 , analogous to a S = 1 / 2 state in cuprates. Because of the similarities to cuprates, the possibility of superconductivity (SC) in Iridium oxides has been expected theoretically once mobile carriers are introduced into the Jeff = 1 / 2 antiferromagnetic insulator. To study theoretically possible SC in carrier doped Sr2IrO4, we investigate a three-orbital Hubbard model with SOC. By solving the Eliashberg equation in the random phase approximation, we find that Jeff = 1 / 2 antiferromagnetic fluctuations favor dx2 -y2-wave SC with a mixture of singlet and triplet Cooper pairings. We will also discuss the particle-hole asymmetry of the SC induced by electron and hole doping.

  15. Identification of an iridium(III) complex with anti-bacterial and anti-cancer activity.

    PubMed

    Lu, Lihua; Liu, Li-juan; Chao, Wei-chieh; Zhong, Hai-Jing; Wang, Modi; Chen, Xiu-Ping; Lu, Jin-Jian; Li, Ruei-nian; Ma, Dik-Lung; Leung, Chung-Hang

    2015-09-29

    Group 9 transition metal complexes have been widely explored as therapeutic agents due to their unique geometry, their propensity to undergo ligand exchanges with biomolecules and their diverse steric and electronic properties. These metal complexes can offer distinct modes of action in living organisms compared to carbon-based molecules. In this study, we investigated the antimicrobial and anti-proliferative abilities of a series of cyclometallated iridium(III) complexes. The iridium(III) complex 1 inhibited the growth of S. aureus with MIC and MBC values of 3.60 and 7.19 μM, respectively, indicating its potent bactericidal activity. Moreover, complex 1 also exhibited cytotoxicity against a number of cancer cell lines, with particular potency against ovarian, cervical and melanoma cells. This cyclometallated iridium(III) complex is the first example of a substitutionally-inert, Group 9 organometallic compound utilized as a direct and selective inhibitor of S. aureus.

  16. Identification of an iridium(III) complex with anti-bacterial and anti-cancer activity

    PubMed Central

    Lu, Lihua; Liu, Li-Juan; Chao, Wei-chieh; Zhong, Hai-Jing; Wang, Modi; Chen, Xiu-Ping; Lu, Jin-Jian; Li, Ruei-nian; Ma, Dik-Lung; Leung, Chung-Hang

    2015-01-01

    Group 9 transition metal complexes have been widely explored as therapeutic agents due to their unique geometry, their propensity to undergo ligand exchanges with biomolecules and their diverse steric and electronic properties. These metal complexes can offer distinct modes of action in living organisms compared to carbon-based molecules. In this study, we investigated the antimicrobial and anti-proliferative abilities of a series of cyclometallated iridium(III) complexes. The iridium(III) complex 1 inhibited the growth of S. aureus with MIC and MBC values of 3.60 and 7.19 μM, respectively, indicating its potent bactericidal activity. Moreover, complex 1 also exhibited cytotoxicity against a number of cancer cell lines, with particular potency against ovarian, cervical and melanoma cells. This cyclometallated iridium(III) complex is the first example of a substitutionally-inert, Group 9 organometallic compound utilized as a direct and selective inhibitor of S. aureus. PMID:26416333

  17. Anodic Deposition of a Robust Iridium-Based Water-Oxidation Catalyst from Organometallic Precursors

    SciTech Connect

    Blakemore, James D; Schley, Nathan D; Olack, G.; Incarvito, Christopher D; Brudvig, Gary W; Crabtree, Robert H

    2011-01-01

    Artificial photosynthesis, modeled on natural light-driven oxidation of water in Photosystem II, holds promise as a sustainable source of reducing equivalents for producing fuels. Few robust water-oxidation catalysts capable of mediating this difficult four-electron, four-proton reaction have yet been described. We report a new method for generating an amorphous electrodeposited material, principally consisting of iridium and oxygen, which is a robust and long-lived catalyst for water oxidation, when driven electrochemically. The catalyst material is generated by a simple anodic deposition from Cp*Ir aqua or hydroxo complexes in aqueous solution. This work suggests that organometallic precursors may be useful in electrodeposition of inorganic heterogeneous catalysts.

  18. Penetrating microelectrode arrays with low-impedance sputtered iridium oxide electrode coatings.

    PubMed

    Cogan, Stuart F; Ehrlich, Julia; Plante, Timothy D; Van Wagenen, Rick

    2009-01-01

    Sputtered iridium oxide (SIROF) is a candidate low-impedance coating for neural stimulation and recording electrodes. SIROF on planar substrates has exhibited a high charge-injection capacity and impedance suitable for indwelling cortical microelectrode applications. In the present work, the properties of SIROF electrode coatings deposited onto multi-shank penetrating arrays intended for intracortical and intraneural applications were examined. The charge-injection properties under constant current pulsing were evaluated for a range of pulsewidths and current densities using voltage transients to determine maximum potential excursions in an inorganic model of interstitial fluid at 37 degrees C. The charge-injection capacity of the SIROFs was significantly improved by the use of positive potential biasing in the interpulse period, but even without bias, the SIROFs reversibly inject higher charge than other iridium oxides or platinum. Typical deliverable charge levels of 25 to 160 nC/phase were obtained with 2000 mum(2) electrodes depending on pulsewidth and interpulse bias. Similar sized platinum electrodes could inject 3 to 8 nC/phase.

  19. Partially oxidized iridium clusters within dendrimers: size-controlled synthesis and selective hydrogenation of 2-nitrobenzaldehyde

    NASA Astrophysics Data System (ADS)

    Higaki, Tatsuya; Kitazawa, Hirokazu; Yamazoe, Seiji; Tsukuda, Tatsuya

    2016-06-01

    Iridium clusters nominally composed of 15, 30 or 60 atoms were size-selectively synthesized within OH-terminated poly(amidoamine) dendrimers of generation 6. Spectroscopic characterization revealed that the Ir clusters were partially oxidized. All the Ir clusters efficiently converted 2-nitrobenzaldehyde to anthranil and 2-aminobenzaldehyde under atmospheric hydrogen at room temperature in toluene via selective hydrogenation of the NO2 group. The selectivity toward 2-aminobenzaldehyde over anthranil was improved with the reduction of the cluster size. The improved selectivity is ascribed to more efficient reduction than intramolecular heterocyclization of a hydroxylamine intermediate on smaller clusters that have a higher Ir(0)-phase population on the surface.Iridium clusters nominally composed of 15, 30 or 60 atoms were size-selectively synthesized within OH-terminated poly(amidoamine) dendrimers of generation 6. Spectroscopic characterization revealed that the Ir clusters were partially oxidized. All the Ir clusters efficiently converted 2-nitrobenzaldehyde to anthranil and 2-aminobenzaldehyde under atmospheric hydrogen at room temperature in toluene via selective hydrogenation of the NO2 group. The selectivity toward 2-aminobenzaldehyde over anthranil was improved with the reduction of the cluster size. The improved selectivity is ascribed to more efficient reduction than intramolecular heterocyclization of a hydroxylamine intermediate on smaller clusters that have a higher Ir(0)-phase population on the surface. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01460g

  20. Characterization of sputtered iridium oxide thin films on planar and laser micro-structured platinum thin film surfaces for neural stimulation applications

    NASA Astrophysics Data System (ADS)

    Thanawala, Sachin

    Electrical stimulation of neurons provides promising results for treatment of a number of diseases and for restoration of lost function. Clinical examples include retinal stimulation for treatment of blindness and cochlear implants for deafness and deep brain stimulation for treatment of Parkinsons disease. A wide variety of materials have been tested for fabrication of electrodes for neural stimulation applications, some of which are platinum and its alloys, titanium nitride, and iridium oxide. In this study iridium oxide thin films were sputtered onto laser micro-structured platinum thin films by pulsed-DC reactive sputtering of iridium metal in oxygen-containing atmosphere, to obtain high charge capacity coatings for neural stimulation applications. The micro-structuring of platinum films was achieved by a pulsed-laser-based technique (KrF excimer laser emitting at lambda=248nm). The surface morphology of the micro-structured films was studied using different surface characterization techniques. In-vitro biocompatibility of these laser micro-structured films coated with iridium oxide thin films was evaluated using cortical neurons isolated from rat embryo brain. Characterization of these laser micro-structured films coated with iridium oxide, by cyclic voltammetry and impedance spectroscopy has revealed a considerable decrease in impedance and increase in charge capacity. A comparison between amorphous and crystalline iridium oxide thin films as electrode materials indicated that amorphous iridium oxide has significantly higher charge capacity and lower impedance making it preferable material for neural stimulation application. Our biocompatibility studies show that neural cells can grow and differentiate successfully on our laser micro-structured films coated with iridium oxide. This indicates that reactively sputtered iridium oxide (SIROF) is biocompatible.

  1. Nd2K2IrO7 and Sm2K2IrO7: Iridium(VI) Oxides Prepared under Ambient Pressure

    SciTech Connect

    Mugavero, III, S.; Smith, M; Yoon, W; zur Loye, H

    2009-01-01

    The most-oxidized iridium oxides known to date are prepared in a hydroxide flux under normal pressure. They contain iridium centers exclusively in the +VI oxidation state and are characterized crystallographically. The picture shows the structure of the Ln2K2IrO7 (Ln=Nd, Sm) and its structural components: IrO6 octahedra (black), KO10 polyhedra (beige), LnO10 polyhedra (blue).

  2. Long Life Testing of Oxide-Coated Iridium/Rhenium Rockets

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.

    1995-01-01

    22-N class rockets, composed of a rhenium (Re) substrate, an iridium (Ir) coating, and an additional composite coating consisting of Ir and a ceramic oxide, were tested on gaseous oxygen/gaseous hydrogen (GO2/GH2) propellants. Two rockets were tested, one for nearly 39 hours at a nominal mixture ratio (MR) of 4.6 and chamber pressure (Pc) of 469 kPa, and the other for over 13 hours at a nominal MR of 5.8 and 621 kPa Pc. Four additional Ir/Re rockets, with a composite Ir-oxide coating fabricated using a modified process, were also tested, including one for 1.3 hours at a nominal MR of 16.7 and Pc of 503 kPa. The long lifetimes demonstrated on low MR GO2/GH2 suggest greatly extended chamber lifetimes (tens of hours) in the relatively low oxidizing combustion environments of Earth storable propellants. The oxide coatings could also serve as a protective coating in the near injector region, where a still-mixing flowfield may cause degradation of the Ir layer. Operation at MR close to 17 suggests that oxide-coated Ir/Re rockets could be used in severely oxidizing combustion environments, such as high MR GO2/GH2, oxygen/hydrocarbon, and liquid gun propellants.

  3. Sol-Gel Deposition of Iridium Oxide for Biomedical Micro-Devices

    PubMed Central

    Nguyen, Cuong M.; Rao, Smitha; Yang, Xuesong; Dubey, Souvik; Mays, Jeffrey; Cao, Hung; Chiao, Jung-Chih

    2015-01-01

    Flexible iridium oxide (IrOx)-based micro-electrodes were fabricated on flexible polyimide substrates using a sol-gel deposition process for utilization as integrated pseudo-reference electrodes for bio-electrochemical sensing applications. The fabrication method yields reliable miniature on-probe IrOx electrodes with long lifetime, high stability and repeatability. Such sensors can be used for long-term measurements. Various dimensions of sol-gel iridium oxide electrodes including 1 mm × 1 mm, 500 μm × 500 μm, and 100 μm × 100 μm were fabricated. Sensor longevity and pH dependence were investigated by immersing the electrodes in hydrochloric acid, fetal bovine serum (FBS), and sodium hydroxide solutions for 30 days. Less pH dependent responses, compared to IrOx electrodes fabricated by electrochemical deposition processes, were measured at 58.8 ± 0.4 mV/pH, 53.8 ± 1.3 mV/pH and 48 ± 0.6 mV/pH, respectively. The on-probe IrOx pseudo-reference electrodes were utilized for dopamine sensing. The baseline responses of the sensors were higher than the one using an external Ag/AgCl reference electrode. Using IrOx reference electrodes integrated on the same probe with working electrodes eliminated the use of cytotoxic Ag/AgCl reference electrode without loss in sensitivity. This enables employing such sensors in long-term recording of concentrations of neurotransmitters in central nervous systems of animals and humans. PMID:25686309

  4. Sol-gel deposition of iridium oxide for biomedical micro-devices.

    PubMed

    Nguyen, Cuong M; Rao, Smitha; Yang, Xuesong; Dubey, Souvik; Mays, Jeffrey; Cao, Hung; Chiao, Jung-Chih

    2015-02-12

    Flexible iridium oxide (IrOx)-based micro-electrodes were fabricated on flexible polyimide substrates using a sol-gel deposition process for utilization as integrated pseudo-reference electrodes for bio-electrochemical sensing applications. The fabrication method yields reliable miniature on-probe IrOx electrodes with long lifetime, high stability and repeatability. Such sensors can be used for long-term measurements. Various dimensions of sol-gel iridium oxide electrodes including 1 mm × 1 mm, 500 µm × 500 µm, and 100 µm × 100 µm were fabricated. Sensor longevity and pH dependence were investigated by immersing the electrodes in hydrochloric acid, fetal bovine serum (FBS), and sodium hydroxide solutions for 30 days. Less pH dependent responses, compared to IrOx electrodes fabricated by electrochemical deposition processes, were measured at 58.8 ± 0.4 mV/pH, 53.8 ± 1.3 mV/pH and 48 ± 0.6 mV/pH, respectively. The on-probe IrOx pseudo-reference electrodes were utilized for dopamine sensing. The baseline responses of the sensors were higher than the one using an external Ag/AgCl reference electrode. Using IrOx reference electrodes integrated on the same probe with working electrodes eliminated the use of cytotoxic Ag/AgCl reference electrode without loss in sensitivity. This enables employing such sensors in long-term recording of concentrations of neurotransmitters in central nervous systems of animals and humans.

  5. Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and Durable Catalysts for Homogeneous Water Oxidation.

    PubMed

    Li, Mo; Takada, Kazutake; Goldsmith, Jonas I; Bernhard, Stefan

    2016-01-19

    A family of tetradentate bis(pyridine-2-sulfonamide) (bpsa) compounds was synthesized as a ligand platform for designing resilient and electronically tunable catalysts capable of performing water oxidation catalysis and other processes in highly oxidizing environments. These wrap-around ligands were coordinated to Ir(III) octahedrally, forming an anionic complex with chloride ions bound to the two remaining coordination sites. NMR spectroscopy documented that the more rigid ligand frameworks-[Ir(bpsa-Cy)Cl2](-) and [Ir(bpsa-Ph)Cl2](-)-produced C1-symmetric complexes, while the complex with the more flexible ethylene linker in [Ir(bpsa-en)Cl2](-) displays C2 symmetry. Their electronic structure was explored with DFT calculations and cyclic voltammetry in nonaqueous environments, which unveiled highly reversible Ir(III)/Ir(IV) redox processes and more complex, irreversible reduction chemistry. Addition of water to the electrolyte revealed the ability of these complexes to catalyze the water oxidation reaction efficiently. Electrochemical quartz crystal microbalance studies confirmed that a molecular species is responsible for the observed electrocatalytic behavior and ruled out the formation of active IrOx. The electrochemical studies were complemented by work on chemically driven water oxidation, where the catalytic activity of the iridium complexes was studied upon exposure to ceric ammonium nitrate, a strong, one-electron oxidant. Variation of the catalyst concentrations helped to illuminate the kinetics of these water oxidation processes and highlighted the robustness of these systems. Stable performance for over 10 days with thousands of catalyst turnovers was observed with the C1-symmetric catalysts. Dynamic light scattering experiments ascertained that a molecular species is responsible for the catalytic activity and excluded the formation of IrOx particles.

  6. Structural, kinetic, and thermodynamic study of the reversible thermal C-H activation/reductive elimination of alkanes at iridium

    SciTech Connect

    Buchanan, J.M.; Stryker, J.M.; Bergman, R.G.

    1986-04-02

    The hydrido alkyl iridium complex Cp*(PMe/sub 3/)Ir(Cy)(H) (1, Cp* = eta/sup 5/-C/sub 5/; Cy = cyclohexyl) has been isolated by air-free chromatography at -80/sup 0/C, and its molecular structure has been determined by X-ray diffraction. Thermolysis of 1 in benzene cleanly produces cyclohexane and Cp*(PMe/sub 3/)Ir(Ph)(H) (2). The rate of reaction is first-order in 1, zero-order in benzene, and inhibited by cyclohexane; its activation parameters are ..delta..H/sup + +/ = 35.6 +/- 0.5 kcal/mol and ..delta..S/sup + +/ = +10 +/- 2 eu. An inverse isotope effect, kappa/sub h/kappa/sub d/ = 0.7 +/- 0.1, is calculated from rates of cyclohexane and cyclohexane-d/sub 12/ reductive elimination at 130/sup 0/C, and deuterium scrambling between the hydride and ..cap alpha..-cyclohexyl positions is observed to occur competitively with reductive elimination. A mechanism is proposed in which cyclohexane loss from 1 is reversible and produces (Cp*(PMe/sub 3/)Ir), which oxidatively adds to a C-H bond in a benzene solvent molecule to form 2. Evidence is also presented for the possible intermediacy of a cyclohexane/(Cp*(PMe/sub 3/)Ir) sigma-complex, which is formed before free (Cp*(PMe/sub 3/)Ir) is released. Equilibrium constants for the equilibration of several pairs of alkanes and their corresponding iridium(III) hydrido alkyl complexes have been determined and imply the following trend in solution phase iridium-carbon bond dissociation enthalpies: phenyl >> n-pentyl > 2,3-dimethylbutyl > cyclopentyl approx. cyclohexyl > neopentyl.

  7. Neutron activation determination of iridium, gold, platinum, and silver in geologic samples

    USGS Publications Warehouse

    Millard, H.T.

    1987-01-01

    Low-level methods for the determination of iridium and other noble metals have become increasingly important in recent years due to interest in locating abundance anomalies associated with the Cretaceous and Tertiary (K-T) boundary. Typical iridium anomalies are in the range of 1 to 100 ??g/kg (ppb). Thus methods with detection limits near 0.1 ??g/kg should be adequate to detect K-T boundary anomalies. Radiochemical neutron activation analysis methods continue to be required although instrumental neutron activation analysis techniques employing elaborate gamma-counters are under development. In the procedure developed in this study samples irradiated in the epithermal neutron facility of the U. S. Geological Survey TRIGA Reactor (Denver, Colorado) are treated with a mini-fire assay technique. The iridium, gold, and silver are collected in a 1-gram metallic lead button. Primary contaminants at this stage are arsenic and antimony. These can be removed by heating the button with a mixture of sodium perioxide and sodium hydroxide. The resulting 0.2-gram lead bead is counted in a Compton suppression spectrometer. Carrier yields are determined by reirradiation of the lead beads. This procedure has been applied to the U.S.G.S. Standard Rock PCC-1 and samples from K-T boundary sites in the Western Interior of North America. ?? 1987 Akade??miai Kiado??.

  8. High activity, high yield tin modified platinum-iridium catalysts, and reforming process utilizing such catalysts

    SciTech Connect

    Baird, W.C. Jr.; Swan, G.A. III; Boyle, J.P.

    1993-06-22

    A process is described for improving the octane quality of a naphtha which comprises reforming said naphtha at reforming conditions wherein said reforming conditions are defined as follows: over a catalyst which includes from about 0.1 percent to about 1.0 percent platinum, from about 0.1 percent to about 1.0 percent iridium, and from about 0.02 percent to about 0.4 percent tin, wherein each of said metals is composited with and uniformly dispersed throughout an inorganic oxide support.

  9. Intramolecular C-H oxidative addition to iridium(I) triggered by trimethyl phosphite in N,N'-diphosphanesilanediamine complexes.

    PubMed

    Passarelli, Vincenzo; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-11-14

    The reaction of [Ir(SiNP)(cod)][PF6] ([1][PF6]) and of IrCl(SiNP)(cod) (5) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2) with trimethyl phosphite affords the iridium(iii) derivatives of the formula [IrHClx(SiNP-H){P(OMe)3}2-x]((1-x)+) (x = 0, 3(+); x = 1, 6) containing the κ(3)C,P,P'-coordinated SiNP-H ligand (SiNP-H = Si(CH2)(CH3){N(4-C6H4CH3)PPh2}2). The thermally unstable pentacoordinated cation [Ir(SiNP){P(OMe)3}(cod)](+) (2(+)) has been detected as an intermediate of the reaction and has been fully characterised in solution. Also, the mechanism of the C-H oxidative addition has been elucidated by DFT calculations showing that the square planar iridium(i) complexes of the formula [IrClx(SiNP){P(OMe)3}2-x]((1-x)+) (x = 0, 4(+); x = 1, 7) should be firstly obtained from 2(+) and finally should undergo the C-H oxidative addition to iridium(i) via a concerted intramolecular mechanism. The influence of the counterion of 2(+) on the outcome of the C-H oxidative addition reaction has also been investigated.

  10. Nanocomposites of iridium oxide and conducting polymers as electroactive phases in biological media.

    PubMed

    Moral-Vico, J; Sánchez-Redondo, S; Lichtenstein, M P; Suñol, C; Casañ-Pastor, N

    2014-05-01

    Much effort is currently devoted to implementing new materials in electrodes that will be used in the central nervous system, either for functional electrostimulation or for tests on nerve regeneration. Their main aim is to improve the charge capacity of the electrodes, while preventing damaging secondary reactions, such as peroxide formation, occurring while applying the electric field. Thus, hybrids may represent a new generation of materials. Two novel hybrid materials are synthesized using three known biocompatible materials tested in the neural system: polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and iridium oxide (IrO2). In particular, PPy-IrO2 and PEDOT-IrO2 hybrid nanocomposite materials are prepared by chemical polymerization in hydrothermal conditions, using IrO2 as oxidizing agent. The reaction yields a significant ordered new hybrid where the conducting polymer is formed around the IrO2 nanoparticles, encapsulating them. Scanning electron microscopy and backscattering techniques show the extent of the encapsulation. Both X-ray photoelectron and Fourier transform infrared spectroscopies identify the components of the phases, as well as the absence of impurities. Electrochemical properties of the final phases in powder and pellet form are evaluated by cyclic voltammetry. Biocompatibility is tested with MTT toxicity tests using primary cultures of cortical neurons grown in vitro for 6 and 9days.

  11. Virus-templated iridium oxide-gold hybrid nanowires for electrochromic application.

    PubMed

    Nam, Yoon Sung; Park, Heechul; Magyar, Andrew P; Yun, Dong Soo; Pollom, Thomas S; Belcher, Angela M

    2012-06-07

    A highly porous electrode comprised of biologically templated iridium oxide-gold (IrO(2)-Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO(2)-binding peptides on the viral surface and used as a template for the self-assembly of IrO(2) nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO(2) nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO(2) mineralization, forming a gold nanostring structure along the long axis of the virus. The resulting IrO(2)-Au hybrid nanowires exhibit a switching time of 35 ms for coloration and 25 ms for bleaching with a transmission change of about 30.5% at 425 nm. These values represent almost an order of magnitude faster switching responses than those of an IrO(2) nanowire film having the similar optical contrast. This work shows that genetically engineered viruses can serve as versatile templates to co-assemble multiple functional molecules, enabling control of the electrochemical properties of nanomaterials.

  12. Iridium versus Iridium: Nanocluster and Monometallic Catalysts Carrying the Same Ligand Behave Differently.

    PubMed

    Cano, Israel; Martínez-Prieto, Luis M; Chaudret, Bruno; van Leeuwen, Piet W N M

    2017-01-26

    A specific secondary phosphine oxide (SPO) ligand (tert-butyl(phenyl)phosphine oxide) was employed to generate two iridium catalysts, an Ir-SPO complex and IrNPs (iridium nanoparticles) ligated with SPO ligands, which were compared mutually and with several supported iridium catalysts with the aim to establish the differences in their catalytic properties. The Ir-SPO-based catalysts showed totally different activities and selectivities in the hydrogenation of various substituted aldehydes, in which H2 is likely cleaved by a metal-ligand cooperation, that is, the SPO ligand and a neighboring metal centre operate in tandem to activate the hydrogen molecule. In addition, the supported IrNPs behave very differently from both Ir-SPO catalysts. This study exemplifies perfectly the advantages and disadvantages related to the use of the main types of catalysts, and thus the dissimilarities between them.

  13. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue.

  14. Virus-templated iridium oxide-gold hybrid nanowires for electrochromic application

    NASA Astrophysics Data System (ADS)

    Nam, Yoon Sung; Park, Heechul; Magyar, Andrew P.; Yun, Dong Soo; Pollom, Thomas S.; Belcher, Angela M.

    2012-05-01

    A highly porous electrode comprised of biologically templated iridium oxide-gold (IrO2-Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO2-binding peptides on the viral surface and used as a template for the self-assembly of IrO2 nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO2 nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO2 mineralization, forming a gold nanostring structure along the long axis of the virus. The resulting IrO2-Au hybrid nanowires exhibit a switching time of 35 ms for coloration and 25 ms for bleaching with a transmission change of about 30.5% at 425 nm. These values represent almost an order of magnitude faster switching responses than those of an IrO2 nanowire film having the similar optical contrast. This work shows that genetically engineered viruses can serve as versatile templates to co-assemble multiple functional molecules, enabling control of the electrochemical properties of nanomaterials.A highly porous electrode comprised of biologically templated iridium oxide-gold (IrO2-Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO2-binding peptides on the viral surface and used as a template for the self-assembly of IrO2 nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO2 nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO2 mineralization, forming a gold nanostring

  15. Iridium oxide microelectrode arrays for in vitro stimulation of individual rat neurons from dissociated cultures.

    PubMed

    Eick, Stefan; Wallys, Jens; Hofmann, Boris; van Ooyen, André; Schnakenberg, Uwe; Ingebrandt, Sven; Offenhäusser, Andreas

    2009-01-01

    We present the first in vitro extracellular stimulation of individual neurons from dissociated cultures with iridium oxide (IrO(x)) electrodes. Microelectrode arrays with sputtered IrO(x) films (SIROF) were developed for electrophysiological investigations with electrogenic cells. The microelectrodes were characterized with scanning electron and atomic force microscopy, revealing rough and porous electrodes with enlarged surface areas. As shown by cyclic voltammetry and electrochemical impedance spectroscopy, the large surface area in combination with the good electrochemical properties of SIROF resulted in high charge storage capacity and low electrode impedance. Thus, we could transfer the good properties of IrO(x) as material for in vivo stimulation electrodes to multi-electrode arrays with electrode diameters as small as 10 mum for in vitro applications. Single rat cortical neurons from dissociated cultures were successfully stimulated to fire action potentials using single or trains of biphasic rectangular voltage-controlled stimulation pulses. The stimulated cell's membrane potential was simultaneously monitored using whole-cell current-clamp recordings. This experimental configuration allowed direct evaluation of the influence of pulse phase sequence, amplitude, and number on the stimulation success ratio and action potential latency. Negative phase first pulses were more effective for extracellular stimulation and caused reduced latency in comparison to positive phase first pulses. Increasing the pulse amplitude also improved stimulation reliability. However, in order to prevent cell or electrode damage, the pulse amplitude is limited to voltages below the threshold for irreversible electrochemical reactions at the electrode. As an alternative to increasing the amplitude, a higher number of stimulation pulses was also shown to increase stimulation success.

  16. Iridium Oxide Microelectrode Arrays for In Vitro Stimulation of Individual Rat Neurons from Dissociated Cultures

    PubMed Central

    Eick, Stefan; Wallys, Jens; Hofmann, Boris; van Ooyen, André; Schnakenberg, Uwe; Ingebrandt, Sven; Offenhäusser, Andreas

    2009-01-01

    We present the first in vitro extracellular stimulation of individual neurons from dissociated cultures with iridium oxide (IrOx) electrodes. Microelectrode arrays with sputtered IrOx films (SIROF) were developed for electrophysiological investigations with electrogenic cells. The microelectrodes were characterized with scanning electron and atomic force microscopy, revealing rough and porous electrodes with enlarged surface areas. As shown by cyclic voltammetry and electrochemical impedance spectroscopy, the large surface area in combination with the good electrochemical properties of SIROF resulted in high charge storage capacity and low electrode impedance. Thus, we could transfer the good properties of IrOx as material for in vivo stimulation electrodes to multi-electrode arrays with electrode diameters as small as 10 μm for in vitro applications. Single rat cortical neurons from dissociated cultures were successfully stimulated to fire action potentials using single or trains of biphasic rectangular voltage-controlled stimulation pulses. The stimulated cell's membrane potential was simultaneously monitored using whole-cell current-clamp recordings. This experimental configuration allowed direct evaluation of the influence of pulse phase sequence, amplitude, and number on the stimulation success ratio and action potential latency. Negative phase first pulses were more effective for extracellular stimulation and caused reduced latency in comparison to positive phase first pulses. Increasing the pulse amplitude also improved stimulation reliability. However, in order to prevent cell or electrode damage, the pulse amplitude is limited to voltages below the threshold for irreversible electrochemical reactions at the electrode. As an alternative to increasing the amplitude, a higher number of stimulation pulses was also shown to increase stimulation success. PMID:19949459

  17. Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions

    SciTech Connect

    Xu, Songchen; Manna, Kuntal; Ellern, Arkady; Sadow, Aaron D

    2014-12-08

    In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(η4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(η4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(η4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(η4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(μ-Cl)(η2-C8H14)2]2 (M = Rh, Ir) provide {κ4-PhB(OxMe2)2ImMes'CH2}Rh(μ-H)(μ-Cl)Rh(η2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(η3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {κ4-PhB(OxMe2)2ImMes'CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis

  18. An Iridium(IV) Species, [Cp*Ir(NHC)Cl]+, Related to a Water-Oxidation Catalyst

    SciTech Connect

    Brewster, Timothy P.; Blakemore, James D.; Schley, Nathan D.; Incarvito, Christopher D.; Hazari, Nilay; Brudvig, Gary W.; Crabtree, Robert H.

    2011-02-08

    The Ir precatalyst (3) contains both a Cp* and a κ2C2,C2'-1,3-diphenylimidazol-2-ylidene ligand, a C-C chelate, where one C donor is the NHC and the other is a cyclometalated N-phenyl wingtip group. The structure of 3 was confirmed by X-ray crystallography. Like our other recently described Cp*Ir catalysts, this compound is a precursor to a catalyst that can oxidize water to dioxygen. Electrochemical characterization of the new compound shows that it has a stable iridium(IV) oxidation state, [Cp*IrIV(NHC)Cl]+, in contrast with the unstable Ir(IV) state seen in our previous cyclometalated [Cp*IrIV(2-pyridyl-2'-phenyl)Cl] catalyst. The new iridium(IV) species has been characterized by EPR spectroscopy and has a rhombic symmetry, a consequence of the ligand environment. These results both support previous studies which suggest that Cp*Ir catalysts can be advanced through the relevant catalytic cycle(s) in one-electron steps and help clarify the electrochemical behavior of this class of water-oxidation catalysts.

  19. Iridium-mediated C-S bond activation and transformation: organoiridium(III) thioether, thiolato, sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral, electrochemical and theoretical aspects.

    PubMed

    Das, Ujjwal; Ghorui, Tapas; Adhikari, Basab; Roy, Sima; Pramanik, Shuvam; Pramanik, Kausikisankar

    2015-05-14

    An attractive methodology, single-electron transfer (SET) reductive cleavage of the C-S bond mediated by a metal in the presence of the external stimuli PPh3, has been applied to the kinetically inert IrCl3 in order to synthesize the thiolato complex [Ir(III)(L(S))Cl(PPh3)2] 3 from precursor thioether complexes [Ir(III)(L(SR))Cl2(PPh3)] (R = alkyl) 2. The aforesaid cleavage process in association with (arene)C-H activation furnishes a new class of organosulfur compounds of iridium(III). The thiolato chelate 3 displays a reversible oxidative wave at 0.75 V vs. Ag/AgCl signifying its remarkable nucleophilic character. The high electron density on the thiolato-S vis-à-vis superior nucleophilicity can be envisaged through the formation of a number of S-centered derivatives. This observation has been corroborated with the nature of HOMO in 3, which assumes 49% of S(3p). Notably, the facile oxidative nature of 3 makes it an apposite precursor for metal-stabilized thiyl radical species. Indeed, iridium(III)-stabilized 3˙(+) can be generated by chemical/electrochemical means. The axial EPR spectra with g ∼ 2.0 along with theoretical analysis of SOMO (S(3p) 24% + Ph(π) 43% + d(yz) 15%) and spin density (ρ(S) = +0.543, ρ(Ph) = +0.315, ρ(Ir) = +0.151) of one-electron oxidized 3˙(+) validate the iridium-stabilized thiyl radical description. This observation suggests that the CNS coordination mode in thiophenolato complex 3 is redox-active. Complex 3 is very prone to S-centered oxidation under normal aerobic conditions to yield metallosulfoxide [Ir(III)(L(SO2))Cl(PPh3)2] 4. The enhanced nucleophilicity of thiolato-S can also be manifested via the smooth S-C bond making process with alkyl halides (R'X, R' = Me and allyl; X = Br, I) and subsequent formation of thioether complexes of type [Ir(III)(L(SR'))ClX(PPh3)] 5. The organosulfur compounds of iridium(III) exhibit rich spectral properties including luminescence and the origin of these transitions is scrutinized with

  20. Contrasting Anticancer Activity of Half-Sandwich Iridium(III) Complexes Bearing Functionally Diverse 2-Phenylpyridine Ligands

    PubMed Central

    2015-01-01

    We report the synthesis, characterization, and antiproliferative activity of 15 iridium(III) half-sandwich complexes of the type [(η5-Cp*)Ir(2-(R′-phenyl)-R-pyridine)Cl] bearing either an electron-donating (−OH, −CH2OH, −CH3) or electron-withdrawing (−F, −CHO, −NO2) group at various positions on the 2-phenylpyridine (2-PhPy) chelating ligand giving rise to six sets of structural isomers. The X-ray crystal structures of [(η5-Cp*)Ir(2-(2′-fluorophenyl)pyridine)Cl] (1) and [(η5-Cp*)Ir(2-(4′-fluorophenyl)pyridine)Cl] (2) exhibit the expected “piano-stool” configuration. DFT calculations showed that substituents caused only localized effects on the electrostatic potential surface of the chelating 2-PhPy ligand of the complexes. Hydrolysis of all complexes is rapid, but readily reversed by addition of NaCl. The complexes show preferential binding to 9-ethylguanine over 9-methyladenine and are active catalysts for the oxidation of NADH to NAD+. Antiproliferative activity experiments in A2780 ovarian, MCF-7 breast, A549 lung, and HCT116 colon cancer cell lines showed IC50 values ranging from 1 to 89 μM, with the most potent complex, [(η5-Cp*)Ir(2-(2′-methylphenyl)pyridine)Cl] (13) (A2780 IC50 = 1.18 μM), being 10× more active than the parent, [(η5-Cp*)Ir(2-phenylpyridine)Cl], and 2× more active than [(η5-CpxPh)Ir(2-phenylpyridine)Cl]. Intriguingly, contrasting biological activities are observed between structural isomers despite exhibiting similar chemical reactivity. For pairs of structural isomers both the nature and position of the functional group can affect the hydrophobicity of the complex. An increase in hydrophobicity resulted in enhanced cellular-iridium accumulation in A2780 ovarian cells, which generally gave rise to an increase in potency. The structural isomers [(η5-Cp*)Ir(2-(4′-fluorophenyl)pyridine)Cl] (2) and [(η5-Cp*)Ir(2-phenyl-5-fluoropyridine)Cl] (4) preferentially localized in the cytosol > membrane and particulate

  1. Electrochemical deposition of iridium and iridium-nickel-alloys

    NASA Astrophysics Data System (ADS)

    Näther, J.; Köster, F.; Freudenberger, R.; Schöberl, C.; Lampke, T.

    2017-03-01

    To develop durable and reliable electronic contacts, precious metals are still very important for finish plating of contact surfaces. The lesser-known iridium might be an interesting alternative to substitute gold alloys, platinum or rhodium for applications with highest demands to wear and corrosion resistance such as sliding and plug contacts. As matters stand there is no commercial electrolyte for iridium plating. Initial investigation screened the parameter range for different iridium compounds when an iridium layer occurred on the substrates. This approach showed that the oxidation state of iridium is crucial to reach contenting deposits. Best results came from Ir(IV) electrolyte with high bromine concentration coming from the starting compound, while electrolytes made from Ir(III) compounds gave very poor deposits. In subsequent experiments different organic compounds were added to the electrolytes to improve plating efficiency and stability of the solutions. So found electrolytes gave crack-free deposits up to two microns with a micro-hardness of 600 HV. To reduce the iridium content in the layer, iridium-nickel-alloys were investigated, finding that a nickel-content of 10 wt% raised the layer hardness to more than 900 HV.

  2. Computationally Probing the Performance of Hybrid, Heterogeneous, and Homogeneous Iridium-Based Catalysts for Water Oxidation

    SciTech Connect

    García-Melchor, Max; Vilella, Laia; López, Núria; Vojvodic, Aleksandra

    2016-04-29

    An attractive strategy to improve the performance of water oxidation catalysts would be to anchor a homogeneous molecular catalyst on a heterogeneous solid surface to create a hybrid catalyst. The idea of this combined system is to take advantage of the individual properties of each of the two catalyst components. We use Density Functional Theory to determine the stability and activity of a model hybrid water oxidation catalyst consisting of a dimeric Ir complex attached on the IrO2(110) surface through two oxygen atoms. We find that homogeneous catalysts can be bound to its matrix oxide without losing significant activity. Hence, designing hybrid systems that benefit from both the high tunability of activity of homogeneous catalysts and the stability of heterogeneous systems seems feasible.

  3. Water oxidation with molecularly defined iridium complexes: insights into homogeneous versus heterogeneous catalysis.

    PubMed

    Junge, Henrik; Marquet, Nicolas; Kammer, Anja; Denurra, Stefania; Bauer, Matthias; Wohlrab, Sebastian; Gärtner, Felix; Pohl, Marga-Martina; Spannenberg, Anke; Gladiali, Serafino; Beller, Matthias

    2012-10-01

    Molecularly defined Ir complexes and different samples of supported IrO(2) nanoparticles have been tested and compared in the catalytic water oxidation with cerium ammonium nitrate (CAN) as the oxidant. By comparing the activity of nano-scaled supported IrO(2) particles to the one of organometallic complexes it is shown that the overall activity of the homogeneous Ir precursors is defined by both the formation of the homogeneous active species and its conversion to Ir(IV)-oxo nanoparticles. In the first phase of the reaction the activity is dominated by the homogeneous active species. With increasing reaction time, the influence of nano-sized Ir-oxo particles becomes more evident. Notably, the different conversion rates of the homogeneous precursor into the active species as well as the conversion into Ir-oxo nanoparticles and the different particle sizes have a significant influence on the overall activity. In addition to the homogeneous systems, IrO(2)@MCM-41 has also been synthesized, which contains stabilized nanoparticles of between 1 and 3 nm in size. This latter system shows a similar activity to IrCl(3)⋅xH(2)O and complexes 4 and 5. Mechanistic insights were obtained by in situ X-ray absorption spectroscopy and scanning transmission electron microscopy.

  4. Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site

    NASA Astrophysics Data System (ADS)

    Kuriyama, Hiromichi; Matsuno, Jobu; Niitaka, Seiji; Uchida, Masaya; Hashizume, Daisuke; Nakao, Aiko; Sugimoto, Kunihisa; Ohsumi, Hiroyuki; Takata, Masaki; Takagi, Hidenori

    2010-05-01

    Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been fabricated by the pulsed laser deposition of LixIr2O4 precursor and the subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a spinel (AB2O4) without A cations in the tetrahedral site, which is isostructural to λ-MnO2. Ir ions form a pyrochlore sublattice, which is known to give rise to a strong geometrical frustration. This Ir spinel was found to be a narrow gap insulator, in remarkable contrast to the metallic ground state of rutile-type IrO2. We argue that an interplay of a strong spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground state as in a layered perovskite Sr2IrO4.

  5. Magnetic symmetries in neutron and resonant x-ray Bragg diffraction patterns of four iridium oxides.

    PubMed

    Lovesey, S W; Khalyavin, D D; Manuel, P; Chapon, L C; Cao, G; Qi, T F

    2012-12-12

    The magnetic properties of Sr(2)IrO(4), Na(2)IrO(3), Sr(3)Ir(2)O(7) and CaIrO(3) are discussed, principally in the light of experimental data in recent literature for Bragg intensities measured in x-ray diffraction with enhancement at iridium L-absorption edges. The electronic structure factors we report, which incorporate parity-even and acentric entities, serve the immediate purpose of making full use of crystal and magnetic symmetry to refine our knowledge of the magnetic properties of the four iridates from resonant x-ray diffraction data. They also offer a platform on which to interpret future investigations, using dichroic signals, resonant x-ray diffraction and neutron diffraction, for example, as well as ab initio calculations of electronic structure. Unit-cell structure factors, suitable for x-ray Bragg diffraction enhanced by an electric dipole-electric dipole (E1-E1) event, reveal exactly which iridium multipoles are visible, e.g., a magnetic dipole parallel to the crystal c-axis (z-axis) and an electric quadrupole with yz-like symmetry in the specific case of CaIrO(3). Magnetic space-groups are assigned to Sr(2)IrO(4), Sr(3)Ir(2)O(7) and CaIrO(3), namely, P(I)cca, P(A)ban and Cm'cm', respectively, in the Belov-Neronova-Smirnova notation. The assignment for Sr(2)IrO(4) is possible because of our new high-resolution neutron diffraction data, gathered on a powder sample. In addition, the new data are used to show that the ordered magnetic moment of an Ir(4+) ion in Sr(2)IrO(4) does not exceed 0.29(4) μ(B). Na(2)IrO(3) has two candidate magnetic space-groups that are not resolved with currently available resonant x-ray data.

  6. Dual-Enzyme Characteristics of Polyvinylpyrrolidone-Capped Iridium Nanoparticles and Their Cellular Protective Effect against H2O2-Induced Oxidative Damage.

    PubMed

    Su, Hua; Liu, Dan-Dan; Zhao, Meng; Hu, Wei-Liang; Xue, Shan-Shan; Cao, Qian; Le, Xue-Yi; Ji, Liang-Nian; Mao, Zong-Wan

    2015-04-22

    Polyvinylpyrrolidone-stabilized iridium nanoparticles (PVP-IrNPs), synthesized by the facile alcoholic reduction method using abundantly available PVP as protecting agents, were first reported as enzyme mimics showing intrinsic catalase- and peroxidase-like activities. The preparation procedure was much easier and more importantly, kinetic studies found that the catalytic activity of PVP-IrNPs was comparable to previously reported platinum nanoparticles. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) characterization indicated that PVP-IrNPs had the average size of approximately 1.5 nm and mainly consisted of Ir(0) chemical state. The mechanism of PVP-IrNPs' dual-enzyme activities was investigated using XPS, Electron spin resonance (ESR) and cytochrome C-based electron transfer methods. The catalase-like activity was related to the formation of oxidized species Ir(0)@IrO2 upon reaction with H2O2. The peroxidase-like activity originated from their ability acting as electron transfer mediators during the catalysis cycle, without the production of hydroxyl radicals. Interestingly, the protective effect of PVP-IrNPs against H2O2-induced cellular oxidative damage was investigated in an A549 lung cancer cell model and PVP-IrNPs displayed excellent biocompatibility and antioxidant activity. Upon pretreatment of cells with PVP-IrNPs, the intracellular reactive oxygen species (ROS) level in response to H2O2 was decreased and the cell viability increased. This work will facilitate studies on the mechanism and biomedical application of nanomaterials-based enzyme mimic.

  7. Synthesis, characterization and catalytic activity of saturated and unsaturated N-heterocyclic carbene iridium(i) complexes.

    PubMed

    Chang, Yung-Hung; Fu, Ching-Feng; Liu, Yi-Hong; Peng, Shei-Ming; Chen, Jwu-Ting; Liu, Shiuh-Tzung

    2009-02-07

    Both saturated and unsaturated N-benzyl substituted heterocyclic carbene (NHC) iridum(i) complexes were synthesized. The unsaturated carbene complex [(un-NHC-Bn)Ir(CO)(2)Cl] in the cis form was prepared via the carbene transfer from the corresponding silver complex to [Ir(COD)(2)Cl](2) followed by ligand substitution with CO, whereas the saturated complex was obtained via the transfer from (sat-NHC-Bn)W(CO)(5). The treatment of phosphines with (NHC)Ir(CO)(2)Cl complexes yielded the products with the phosphine ligand trans to the carbene moiety via substitution. X-Ray structural determination shows that distances of Ir-C((carbene)) in both (un-NHC-Bn)Ir(CO)(PR(3))Cl and (un-NHC-Bn)Ir(CO)(PR(3))Cl are essentially the same. Analyses of spectroscopic and crystal structural data of iridium complexes [(NHC)Ir(CO)(PR(3))Cl] and Vaska's complex show similar corresponding data in both types of complexes, suggesting that the studied NHC ligands and phosphines have similar bonding with Ir(i) metal center. All iridium complexes studied in this work illustrated their catalytically activity on N-alkylation of amine with alcohol via hydrogen transfer reduction. It appears no dramatic difference on the catalytic activity among these iridium carbene complexes; but the saturated carbene complex (sat-NHC-Bn)Ir(CO)(PR(3))Cl appears to be slightly more active. For example, the reaction of benzyl alcohol with aniline in the presence of catalyst (1 mol%) under basic conditions at 100 degrees C provided the secondary amine (N-benzylaniline) in 96% yield.

  8. An iridium-mediated C-H activation/CO2-carboxylation reaction of 1,1-bisdiphenylphosphinomethane.

    PubMed

    Langer, Jens; Fabra, María José; García-Orduña, Pilar; Lahoz, Fernando J; Görls, Helmar; Oro, Luis A; Westerhausen, Matthias

    2010-09-07

    The reaction of 1,1-bisdiphenylphosphinomethane (dppm, 4 eq.) with [IrCl(coe)(2)](2) results in a solvent dependent equilibrium from which the complexes [IrCl(dppm)(dppm-H)(H)] (1) and [Ir(dppm)(2)]Cl (2) were isolated. When 2 is dissolved in methanol, [IrCl(dppm)(2)(H)][OCH(3)] (4) is formed as dominant species in solution. The C-H activation reaction which leads to 1 and 4 can be suppressed by adding an additional dppm ligand per iridium center resulting in the formation of [Ir(dppm)(3)]Cl (5). If the reaction of dppm with [IrX(coe)(2)](2) (X = Cl, I) is performed under an atmosphere of CO(2) the complexes [IrX(dppm)(H){(Ph(2)P)(2)C-COOH}] (6: X = Cl; 7: X = I) are formed by a CH activation/CO(2) carboxylation sequence. The reaction of 6 with NH(4)PF yields [IrCl(dppm)(2)(H)]PF(6).(10). Additionally the lithium compounds [Li(dme)(2)(dppm-H)] (3) and [Li(dme){(Ph(2)P)(2)CHCOO}](2) (8) were prepared for comparison. The molecular structures of the compounds 1, 3, 5, 7, 8 and of the related iridium complex [IrCl(dppm)(2)(H)]I (11) are reported.

  9. Iridium(I)-catalyzed regioselective C-H activation and hydrogen-isotope exchange of non-aromatic unsaturated functionality.

    PubMed

    Kerr, William J; Mudd, Richard J; Paterson, Laura C; Brown, Jack A

    2014-11-03

    Isotopic labelling is a key technology of increasing importance for the investigation of new CH activation and functionalization techniques, as well as in the construction of labelled molecules for use within both organic synthesis and drug discovery. Herein, we report for the first time selective iridium-catalyzed CH activation and hydrogen-isotope exchange at the β-position of unsaturated organic compounds. The use of our highly active [Ir(cod)(IMes)(PPh3 )][PF6 ] (cod=1,5-cyclooctadiene) catalyst, under mild reaction conditions, allows the regioselective β-activation and labelling of a range of α,β-unsaturated compounds with differing steric and electronic properties. This new process delivers high levels of isotope incorporation over short reaction times by using low levels of catalyst loading.

  10. Cleavage of ether, ester, and tosylate C(sp3)-O bonds by an iridium complex, initiated by oxidative addition of C-H bonds. Experimental and computational studies.

    PubMed

    Kundu, Sabuj; Choi, Jongwook; Wang, David Y; Choliy, Yuriy; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

    2013-04-03

    A pincer-ligated iridium complex, (PCP)Ir (PCP = κ(3)-C6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp(3))-O bonds of methyl esters (CH3-O2CR'), methyl tosylate (CH3-OTs), and certain electron-poor methyl aryl ethers (CH3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H)[κ(2)-CH2OC(O)Me] which then affords (PCP-CH2)Ir(H)(κ(2)-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ(2)-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

  11. Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction

    DOE PAGES

    Alia, Shaun M.; Rasimick, Brian; Ngo, Chilan; ...

    2016-07-15

    Unsupported iridium (Ir) nanoparticles, that serve as standard oxygen evolution reaction (OER) catalysts in acidic electrolyzers, were investigated for electrochemical performance and durability in rotating disk electrode (RDE) half-cells. Fixed potential holds and potential cycling were applied to probe the durability of Ir nanoparticles, and performance losses were found to be driven by particle growth (coarsening) at moderate potential (1.4 to 1.6 V) and Ir dissolution at higher potential (>/=1.8 V). Several different commercially available samples were evaluated and standardized conditions for performance comparison are reported. In conclusion, the electrocatalyst RDE results have also been compared to results obtained formore » performance and durability in electrolysis cells.« less

  12. Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction

    SciTech Connect

    Alia, Shaun M.; Rasimick, Brian; Ngo, Chilan; Neyerlin, K. C.; Kocha, Shyam S.; Pylypenko, Svitlana; Xu, Hui; Pivovar, Bryan S.

    2016-07-15

    Unsupported iridium (Ir) nanoparticles, that serve as standard oxygen evolution reaction (OER) catalysts in acidic electrolyzers, were investigated for electrochemical performance and durability in rotating disk electrode (RDE) half-cells. Fixed potential holds and potential cycling were applied to probe the durability of Ir nanoparticles, and performance losses were found to be driven by particle growth (coarsening) at moderate potential (1.4 to 1.6 V) and Ir dissolution at higher potential (>/=1.8 V). Several different commercially available samples were evaluated and standardized conditions for performance comparison are reported. In conclusion, the electrocatalyst RDE results have also been compared to results obtained for performance and durability in electrolysis cells.

  13. Enantioselective, iridium-catalyzed monoallylation of ammonia.

    PubMed

    Pouy, Mark J; Stanley, Levi M; Hartwig, John F

    2009-08-19

    Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.

  14. Enantioselective, Iridium-Catalyzed Monoallylation of Ammonia

    PubMed Central

    Pouy, Mark J.; Stanley, Levi M.; Hartwig, John F.

    2009-01-01

    Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations. PMID:19722644

  15. Iridium-Catalyzed Allylic Substitution

    NASA Astrophysics Data System (ADS)

    Hartwig, John F.; Pouy, Mark J.

    Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is generated by a base-induced cyclometalation at the methyl group of this substituent to generate an iridium metalacycle bound by the COD ligand of the [Ir(COD)Cl]2 precursor and one additional labile dative ligand. Such complexes catalyze the reactions of linear allylic esters with alkylamines, arylamines, phenols, alcohols, imides, carbamates, ammonia, enolates and enolate equivalents, as well as typical stabilized carbon nucleophiles generated from malonates and cyanoesters. Iridium catalysts for enantioselective allylic substitution have also been generated from phosphorus ligands with substituents bound by heteroatoms, and an account of the studies of such systems, along with a description of the development of iridium catalysts is included.

  16. Iridium-catalysed regioselective borylation of carboranes via direct B-H activation

    NASA Astrophysics Data System (ADS)

    Cheng, Ruofei; Qiu, Zaozao; Xie, Zuowei

    2017-03-01

    Carboranes are carbon-boron molecular clusters, which can be viewed as three-dimensional analogues to benzene. They are finding many applications in medicine, materials and organometallic chemistry. On the other hand, their exceptional thermal and chemical stabilities, as well as 3D structures, make them very difficult to be functionalized, in particular the regioselective functionalization of BH vertex among ten similar B-H bonds. Here we report a very efficient iridium-catalysed borylation of cage B(3,6)-H bonds of o-carboranes with excellent yields and regioselectivity using bis(pinacolato)diboron (B2pin2) as a reagent. Selective cage B(4)-H borylation has also been achieved by introducing a bulky TBDMS (tert-butyldimethylsilyl) group to one cage carbon vertex. The resultant 3,6-(Bpin)2-o-carboranes are useful synthons for the synthesis of a wide variety of B(3,6)-difunctionalized o-carboranes bearing cage B-X (X=O, N, C, I and Br) bonds.

  17. Iridium-catalysed regioselective borylation of carboranes via direct B–H activation

    PubMed Central

    Cheng, Ruofei; Qiu, Zaozao; Xie, Zuowei

    2017-01-01

    Carboranes are carbon–boron molecular clusters, which can be viewed as three-dimensional analogues to benzene. They are finding many applications in medicine, materials and organometallic chemistry. On the other hand, their exceptional thermal and chemical stabilities, as well as 3D structures, make them very difficult to be functionalized, in particular the regioselective functionalization of BH vertex among ten similar B–H bonds. Here we report a very efficient iridium-catalysed borylation of cage B(3,6)–H bonds of o-carboranes with excellent yields and regioselectivity using bis(pinacolato)diboron (B2pin2) as a reagent. Selective cage B(4)–H borylation has also been achieved by introducing a bulky TBDMS (tert-butyldimethylsilyl) group to one cage carbon vertex. The resultant 3,6-(Bpin)2-o-carboranes are useful synthons for the synthesis of a wide variety of B(3,6)-difunctionalized o-carboranes bearing cage B–X (X=O, N, C, I and Br) bonds. PMID:28300061

  18. Processing of Iridium and Iridium Alloys

    SciTech Connect

    Ohriner, Evan Keith

    2008-01-01

    Iridium and its alloys have been considered to be difficult to fabricate due to their high melting temperatures, limited ductility, sensitivity to impurity content, and chemical properties. The variety of processing methods used for iridium and its alloys are reviewed, including purification, melting, forming, joining, and powder metallurgy techniques. Also included are coating and forming by the methods of electroplating, chemical and physical vapor deposition, and melt particle deposition.

  19. Kinetics of the chemical oxidation of (5,10,15,20-tetraphenyl-21H,23H-porphinato)(chloro)(aqua)iridium(III)

    NASA Astrophysics Data System (ADS)

    Tyulyaeva, E. Yu.; Bichan, N. G.; Mozhzhukhina, E. G.; Lomova, T. N.

    2016-01-01

    The oxidation of (Cl)(H2O)IrTPP with atmospheric oxygen in the presence of concentrated H2SO4 accompanied by coordination of molecular O2 and substitution of axial ligands was studied spectrophotometrically. In 16.785-18.09 MH2SO4 at 298-318 K, (Cl)(H2O)IrTPP experienced two single-electron oxidations in sequence: with an increase in the oxidation state of the iridium cation and with formation of the π-radical cation form (HSO4)IrIVTPP•+ oxidized at the aromatic ligand ( k 298 = 7.2 × 10-6 mol-1 L s-1). Referring to the literature data on the oxidation of (Cl)(H2O)IrTPP in AcOH and CF3COOH, it was shown that the medium acidity and the nature of the axial ligands affect the electron removal site in the chemical oxidation of (Cl)(H2O)IrTPP with atmospheric oxygen in proton-donor solvents.

  20. Iridium at Kilauea

    NASA Astrophysics Data System (ADS)

    Bell, Peter M.

    Trace-element anomalies observed in rocks located stratigraphically at the Cretaceous-Tertiary boundary are considered significant evidence that the boundary is a record of a large meteorite impact (Science, 208, 1095-1108, 1980). In particular, trace metals, including iridium and other members of the platinum metals group, are thought to be enriched in rocks alien to the earth's surface. These elements are indeed enriched in meteorites relative to earth crustal rocks, but new evidence from analyses of the January 1983 eruption of Kilauea suggest that the analogy may be invalid. W.H. Zoller, J.R. Parrington, and J.M. Phelan Kotra reported neutron activation analyses of airborne particulate matter collected at the Mauna Loa Observatory and found “strikingly” large concentrations of iridium in addition to element concentrations expected from volcanic emissions (Science, 222, 1118, 1983). The only other platinum-group trace metal analyzed was gold, which was also found to be anomalously high. They concede that they need more data of other platinum group elements and more data on other volcanos, but the implication is that the Cretacious-Tertiary boundary may well be volcanic, not due to a large meteorite impact.

  1. Antibacterial activity of microstructured sacrificial anode thin films by combination of silver with platinum group elements (platinum, palladium, iridium).

    PubMed

    Köller, Manfred; Bellova, Petri; Javid, Siyamak Memar; Motemani, Yahya; Khare, Chinmay; Sengstock, Christina; Tschulik, Kristina; Schildhauer, Thomas A; Ludwig, Alfred

    2017-05-01

    Five different Ag dots arrays (16 to 400dots/mm(2)) were fabricated on a continuous platinum, palladium, or iridium thin film and for comparison also on titanium film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Staphylococcus aureus (S. aureus) were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards S. aureus was induced by Ag dot arrays on each of the platinum group thin film (sacrificial anode system for Ag) in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag). Among platinum group elements the Ir-Ag system exerted the highest antibacterial activity which was accompanied by most advanced dissolution of the Ag dots and Ag ion release compared to Ag dots on Pt or Pd.

  2. Synthesis and in vitro antitumor activity of novel iridium(III) complexes with enantiopure C2-symmetrical vicinal diamine ligands.

    PubMed

    Yang, Qing; Chang, Jun; Song, Jiao; Qian, Meng-Ting; Yu, Jian-Ming; Sun, Xun

    2013-08-15

    Four novel iridium(III) complexes with enantiopure C2-symmetrical vicinal diamine ligands were designed, synthesized, and characterized by FT-IR, NMR, and MS. The cytotoxicities of all of the complexes against the human solid tumor cell lines A2780, A549, KB, and MDA-MB-231 were evaluated. Both R,R-configured complexes (R,R)-5a and (R,R)-5b exhibited more potent or similar activity compared with oxaliplatin, whereas their corresponding (S,S)-isomers (S,S)-5a and (S,S)-5b were found to be mostly inactive. As indicated by the activation of caspase-3, the cleavage of PARP, and the upregulation of p53, the preliminary mechanism studies revealed that the mode of cell death initiated by (R,R)-5a in A2780 cells was predominantly p53-mediated apoptosis. In addition, the structure of (R,R)-5a was unambiguously confirmed through single crystal X-ray structure determination.

  3. Cp* Iridium Precatalysts for Selective C-H Oxidation via Direct Insertion. A Joint Experimental/Computational Study

    SciTech Connect

    Zhou, Meng; Balcells, David; Parent, Alexander R.; Crabtree, Robert H; Eisenstein, Odile

    2012-01-01

    A series of Cp*Ir complexes are active precatalysts in C–H oxidation of cis-decalin, cyclooctane, 1-acetylpyrrolidine, tetrahydrofurans, and γ-lactones. Moderate to high yields were achieved, and surprisingly, high selectivity for mono-oxidation of cyclooctane to cyclooctanone was observed. Kinetic isotope effect experiments in the C–H oxidation of ethylbenezene to acetophenone yield kH/kD = 15.4 ± 0.8 at 23 °C and 17.8 ± 1.2 at 0 °C, which are consistent with C–H oxidation being the rate-limiting step with a significant tunneling contribution. The nature of the active species was investigated by TEM, UV–vis, microfiltration, and control experiments. DFT calculations showed that the C–H oxidation of cis-decalin by Cp*Ir(ppy)(Cl) (ppy = o-phenylpyridine) follows a direct oxygen insertion mechanism on the singlet potential energy surface, rather than the radical rebound route that would be seen for the triplet, in good agreement with the retention of stereochemistry observed in this reaction.

  4. Novel C,N-Cyclometalated Benzimidazole Ruthenium(II) and Iridium(III) Complexes as Antitumor and Antiangiogenic Agents: A Structure-Activity Relationship Study.

    PubMed

    Yellol, Jyoti; Pérez, Sergio A; Buceta, Alicia; Yellol, Gorakh; Donaire, Antonio; Szumlas, Piotr; Bednarski, Patrick J; Makhloufi, Gamall; Janiak, Christoph; Espinosa, Arturo; Ruiz, José

    2015-09-24

    A series of novel C,N-cyclometalated benzimidazole ruthenium(II) and iridium(III) complexes of the types [(η(6)-p-cymene)RuCl(κ(2)-N,C-L)] and [(η(5)-C5Me5)IrCl(κ(2)-N,C-L)] (HL = methyl 1-butyl-2-arylbenzimidazolecarboxylate) with varying substituents (H, Me, F, CF3, MeO, NO2, and Ph) in the R4 position of the phenyl ring of 2-phenylbenzimidazole chelating ligand of the ruthenium (3a-g) and iridium complexes (4a-g) have been prepared. The cytotoxic activity of the new ruthenium(II) and iridium(III) compounds has been evaluated in a panel of cell lines (A2780, A2780cisR, A427, 5637, LCLC, SISO, and HT29) in order to investigate structure-activity relationships. Phenyl substitution at the R4 position shows increased potency in both Ru and Ir complexes (3g and 4g, respectively) as compared to their parent compounds (3a and 4a) in all cell lines. In general, ruthenium complexes are more active than the corresponding iridium complexes. The new ruthenium and iridium compounds increased caspase-3 activity in A2780 cells, as shown for 3a,d and 4a,d. Compound 4g is able to increase the production of ROS in A2780 cells. Furthermore, all the new compounds are able to overcome the cisplatin resistance in A2780cisR cells. In addition, some of the metal complexes effectively inhibit angiogenesis in the human umbilical vein endothelial cell line EA.hy926 at 0.5 μM, the ruthenium derivatives 3g (Ph) and 3d (CF3) being the best performers. QC calculations performed on some ruthenium model complexes showed only moderate or slight electron depletion at the phenyl ring of the C,N-cyclometalated ligand and the chlorine atom on increasing the electron withdrawing effect of the R substituent.

  5. Synthesis of benzimidazoles via iridium-catalyzed acceptorless dehydrogenative coupling.

    PubMed

    Sun, Xiang; Lv, Xiao-Hui; Ye, Lin-Miao; Hu, Yu; Chen, Yan-Yan; Zhang, Xue-Jing; Yan, Ming

    2015-07-21

    Iridium-catalyzed acceptorless dehydrogenative coupling of tertiary amines and arylamines has been developed. A number of benzimidazoles were prepared in good yields. An iridium-mediated C-H activation mechanism is suggested. This finding represents a novel strategy for the synthesis of benzimidazoles.

  6. Iridium Interfacial Stack (IRIS)

    NASA Technical Reports Server (NTRS)

    Spry, David James (Inventor)

    2015-01-01

    An iridium interfacial stack ("IrIS") and a method for producing the same are provided. The IrIS may include ordered layers of TaSi.sub.2, platinum, iridium, and platinum, and may be placed on top of a titanium layer and a silicon carbide layer. The IrIS may prevent, reduce, or mitigate against diffusion of elements such as oxygen, platinum, and gold through at least some of its layers.

  7. Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives

    PubMed Central

    Vagnini, Michael T.; Smeigh, Amanda L.; Blakemore, James D.; Eaton, Samuel W.; Schley, Nathan D.; D’Souza, Francis; Crabtree, Robert H.; Brudvig, Gary W.; Co, Dick T.; Wasielewski, Michael R.

    2012-01-01

    Photodriving the activity of water-oxidation catalysts is a critical step toward generating fuel from sunlight. The design of a system with optimal energetics and kinetics requires a mechanistic understanding of the single-electron transfer events in catalyst activation. To this end, we report here the synthesis and photophysical characterization of two covalently bound chromophore-catalyst electron transfer dyads, in which the dyes are derivatives of the strong photooxidant perylene-3,4:9,10-bis(dicarboximide) (PDI) and the molecular catalyst is the Cp∗Ir(ppy)Cl metal complex, where ppy = 2-phenylpyridine. Photoexcitation of the PDI in each dyad results in reduction of the chromophore to PDI•- in less than 10 ps, a process that outcompetes any generation of 3∗PDI by spin-orbit-induced intersystem crossing. Biexponential charge recombination largely to the PDI-Ir(III) ground state is suggestive of multiple populations of the PDI•--Ir(IV) ion-pair, whose relative abundance varies with solvent polarity. Electrochemical studies of the dyads show strong irreversible oxidation current similar to that seen for model catalysts, indicating that the catalytic integrity of the metal complex is maintained upon attachment to the high molecular weight photosensitizer. PMID:22586073

  8. Cyclometalated iridium(III) bipyridyl-phenylenediamine complexes with multicolor phosphorescence: synthesis, electrochemistry, photophysics, and intracellular nitric oxide sensing.

    PubMed

    Law, Wendell Ho-Tin; Leung, Kam-Keung; Lee, Lawrence Cho-Cheung; Poon, Che-Shan; Liu, Hua-Wei; Lo, Kenneth Kam-Wing

    2014-06-01

    We present a new class of phosphorescent cyclometalated iridium(III) bipyridyl-phenylenediamine complexes [Ir(N^C)2 (bpy-DA)](PF6 ) (bpy-DA=4-(N-(2-amino-5-methoxyphenyl)aminomethyl)-4'-methyl-2,2'-bipyridine; HN^C=2-(2,4-difluorophenyl)pyridine (Hdfppy) (1 a), 2-phenylpyridine (Hppy) (2 a), 2-phenylquinoline (Hpq) (3 a), 2-phenylcinchoninic acid methyl ester (Hpqe) (4 a)) and their triazole counterparts [Ir(N^C)2 (bpy-T)](PF6 ) (bpy-T=4-((6-methoxybenzotriazol-1-yl)methyl)-4'-methyl-2,2'-bipyridine; HN^C=Hdfppy (1 b), Hppy (2 b), Hpq (3 b), Hpqe (4 b)). Upon photoexcitation, the diamine complexes exhibited fairly weak green to red phosphorescence under ambient conditions whereas the triazole derivatives emitted strongly. The photophysical properties of complexes 2 a and 2 b have been studied in more detail. Upon protonation, the diamine complex 2 a displayed increased emission intensity, but the emission properties of its triazole counterpart complex 2 b were independent on the pH value of the solution. Also, complex 2 a was found to be readily converted into complex 2 b upon reaction with NO under aerated conditions, resulting in substantial emission enhancement of the solution. The reaction was highly specific toward NO over other reactive oxygen and nitrogen species (RONS) as revealed by spectroscopic analyses. The lipophilicity and cellular uptake efficiency of the diamine complexes have been examined and correlated to their molecular structures. Also, cell-based assays showed that these complexes were noncytotoxic toward human cervix epithelioid carcinoma (HeLa) cells (at 10 μM, 4 h, percentage survival ≈80-95%). Additionally, the diamine complexes have been used to visualize intracellular NO generated both exogenously in HeLa cells and endogenously in RAW 264.7 murine macrophages by laser-scanning confocal microscopy.

  9. Iridium-192 Production for Cancer Treatment

    SciTech Connect

    Rostelato, M.E.C.M.; Silva, C.P.G.; Rela, P.R.; Zeituni, C.A.; Lepki, V.; Feher, A.

    2004-10-05

    The purpose of this work is to settle a laboratory for Iridium -192 sources production, that is, to determine a wire activation method and to build a hot cell for the wires manipulation, quality control and packaging. The paper relates, mainly, the wire activation method and its quality control. The wire activation is carried out in our nuclear reactor, IEA- R1m.

  10. Catalytic Activity of Platinum Monolayer on Iridium and Rhenium Alloy Nanoparticles for the Oxygen Reduction Reaction

    SciTech Connect

    Karan, Hiroko I.; Sasaki, Kotaro; Kuttiyiel, Kurian; Farberow, Carrie A.; Mavrikakis, Manos; Adzic, Radoslav R.

    2012-05-04

    A new type of electrocatalyst with a core–shell structure that consists of a platinum monolayer shell placed on an iridium–rhenium nanoparticle core or platinum and palladium bilayer shell deposited on that core has been prepared and tested for electrocatalytic activity for the oxygen reduction reaction. Carbon-supported iridium–rhenium alloy nanoparticles with several different molar ratios of Ir to Re were prepared by reducing metal chlorides dispersed on Vulcan carbon with hydrogen gas at 400 °C for 1 h. These catalysts showed specific electrocatalytic activity for oxygen reduction reaction comparable to that of platinum. The activities of PtML/PdML/Ir2Re1, PtML/Pd2layers/Ir2Re1, and PtML/Pd2layers/Ir7Re3 catalysts were, in fact, better than that of conventional platinum electrocatalysts, and their mass activities exceeded the 2015 DOE target. Our density functional theory calculations revealed that the molar ratio of Ir to Re affects the binding strength of adsorbed OH and, thereby, the O2 reduction activity of the catalysts. The maximum specific activity was found for an intermediate OH binding energy with the corresponding catalyst on the top of the volcano plot. The monolayer concept facilitates the use of much less platinum than in other approaches. Finally, the results with the PtML/PdML/Ir2Re electrocatalyst indicate that it is a promising alternative to conventional Pt electrocatalysts in low-temperature fuel cells.

  11. Oxidative photoredox-catalytic activation of aliphatic nucleophiles for C(sp(3))-C(sp(2)) cross-coupling reactions.

    PubMed

    Jahn, Emanuela; Jahn, Ullrich

    2014-12-01

    In the light you will find the road (Led Zeppelin): Visible-light photoredox catalysis leads the way in overcoming the reactivity limitations of alkyl nucleophiles in cross-coupling reactions. Iridium-triggered oxidative photoredox activation of alkyltrifluoroborate or carboxylic acids affords alkyl radicals, which undergo nickel-catalyzed cross-coupling reactions.

  12. Iridium wire grid polarizer fabricated using atomic layer deposition.

    PubMed

    Weber, Thomas; Käsebier, Thomas; Szeghalmi, Adriana; Knez, Mato; Kley, Ernst-Bernhard; Tünnermann, Andreas

    2011-10-25

    In this work, an effective multistep process toward fabrication of an iridium wire grid polarizer for UV applications involving a frequency doubling process based on ultrafast electron beam lithography and atomic layer deposition is presented. The choice of iridium as grating material is based on its good optical properties and a superior oxidation resistance. Furthermore, atomic layer deposition of iridium allows a precise adjustment of the structural parameters of the grating much better than other deposition techniques like sputtering for example. At the target wavelength of 250 nm, a transmission of about 45% and an extinction ratio of 87 are achieved.

  13. Acid-catalyzed oxidative addition of a C-H bond to a square planar d⁸ iridium complex.

    PubMed

    Hackenberg, Jason D; Kundu, Sabuj; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

    2014-06-25

    While the addition of C-H bonds to three-coordinate Ir(I) fragments is a central theme in the field of C-H bond activation, addition to square planar four-coordinate complexes is far less precedented. The dearth of such reactions may be attributed, at least in part, to kinetic factors elucidated in seminal work by Hoffmann. C-H additions to square planar carbonyl complexes in particular are unprecedented, in contrast to the extensive chemistry of oxidative addition of other substrates (e.g., H2, HX) to Vaska's Complex and related species. We report that Bronsted acids will catalyze the addition of the alkynyl C-H bond of phenylacetylene to the pincer complex (PCP)Ir(CO). The reaction occurs to give exclusively the trans-C-H addition product. Our proposed mechanism, based on kinetics and DFT calculations, involves initial protonation of (PCP)Ir(CO) to generate a highly active five-coordinate cationic intermediate, which forms a phenylacetylene adduct that is then deprotonated to give product.

  14. Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

    PubMed Central

    Mejuto, Carmen; Royo, Beatriz

    2015-01-01

    Summary The coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD)] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene) complex with three [IrCl(CO)2] fragments, allowed the estimation of the Tolman electronic parameter (TEP) for the ligand, which was compared with the TEP value for a related 1,3,5-triphenylbenzene-tris-NHC ligand. The electronic properties of the tris-MIC ligand were studied by cyclic voltammetry measurements. In all cases, the tris-MIC ligand showed a stronger electron-donating character than the corresponding NHC-based ligands. The catalytic activity of the tri-rhodium complex was tested in the addition reaction of arylboronic acids to α,β-unsaturated ketones. PMID:26734104

  15. Solid-phase extraction of iridium from soil and water samples by using activated carbon cloth prior to its spectrophotometric determination.

    PubMed

    Ozkantar, Nebiye; Yilmaz, Erkan; Soylak, Mustafa; Tuzen, Mustafa

    2015-08-01

    A solid-phase extraction method for separation and preconcentration of Ir(IV) ion by using activated carbon cloth (ACC) has been presented. Ir(IV) as their 1-(2-pyridylazo) 2-naphtol (PAN) chelate was adsorbed on ACC at pH 2.0 and was eluted from ACC with acidic dimethylformamide (DMF). The Ir(IV) concentration was determined at 536 nm as Ir(IV)-PAN complex by using UV-vis spectrophotometer. The analytical parameters including pH, sample and eluent flow rates, amount of PAN, eluent type, concentration, and sample volume were optimized. The effects of foreign ions on the recoveries of iridium were also investigated. The preconcentration factor was calculated as 60. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were found as 0.039 and 0.129 μg L(-1), respectively. The method was applied to soil and water samples for iridium determination.

  16. Water reduction systems associated with homoleptic cyclometalated iridium complexes of various 2-phenylpyridines.

    PubMed

    Yuan, Yong-Jun; Yu, Zhen-Tao; Cai, Jian-Guang; Zheng, Chao; Huang, Wei; Zou, Zhi-Gang

    2013-08-01

    The photoreduction of water to hydrogen represents a promising method for generating sustainable clean fuel. The molecular processes of this photoreduction require an effective light absorber, such as the ruthenium polybipyridine complex, to collect and convert the solar energy into a usable chemical form. In the search for a highly active and stable photosensitizer (PS), iridium complexes are attractive because of their desirable photophysical characteristics. Herein, a series of homoleptic tris-cyclometalated iridium complexes, based on different 2-phenylpyridine ligands, were utilized as PSs in photocatalytic systems for hydrogen production with [Rh(dtb-bpy)3 ](PF6 )3 (dtb-bpy=4,4'-di-tert-butyl-2,2'-dipyridyl) serving as the water reduction catalyst (WRC) and triethanolamine (TEOA) as the electron donor. The photophysical and electrochemical properties of these complexes were systematically investigated. The excited state of neutral iridium complexes (PS*) could not be quenched by using TEOA as an electron donor, but they could be quenched by using [Rh(dtb-bpy)3 ](PF6 )3 as an electron acceptor, indicating that the PS* quenching pathway in catalytic reactions was most likely an oxidative quenching process. A set of long-lived and highly active systems for hydrogen evolution were obtained in Ir(III) -Rh(III) -TEOA systems. These systems maintained their activity for more than 72 h with visible-light irradiation, and the total turnover number was up to 3040. Comparative studies indicated that the photocatalytic performance of these homoleptic tris-cyclometalated iridium compounds was superior to that of the cationic iridium complex [Ir(ppy)2 (bpy)](PF6 ) (ppy=2-phenylpyridine, bpy=2,2'-dipyridyl) (4), which was used as a reference. The significant increase in the photocatalytic efficiencies was in part attributed to the higher photostability of the neutral Ir(III) complexes. This assumption was supported by their different coordination modes, photophysical, and

  17. Iridium: failures & successes

    NASA Astrophysics Data System (ADS)

    Christensen, CarissaBryce; Beard, Suzette

    2001-03-01

    This paper will provide an overview of the Iridium business venture in terms of the challenges faced, the successes achieved, and the causes of the ultimate failure of the venture — bankruptcy and system de-orbit. The paper will address technical, business, and policy issues. The intent of the paper is to provide a balanced and accurate overview of the Iridium experience, to aid future decision-making by policy makers, the business community, and technical experts. Key topics will include the history of the program, the objectives and decision-making of Motorola, the market research and analysis conducted, partnering strategies and their impact, consumer equipment availability, and technical issues — target performance, performance achieved, technical accomplishments, and expected and unexpected technical challenges. The paper will use as sources trade media and business articles on the Iridium program, technical papers and conference presentations, Wall Street analyst's reports, and, where possible, interviews with participants and close observers.

  18. Osmium-191/iridium-191m radionuclide

    DOEpatents

    Knapp, Jr., Furn F.; Butler, Thomas A.; Brihaye, Claude

    1987-01-01

    A generator system to provide iridium-191m for clinical imaging applications comprises an activated carbon adsorbent loaded with a compound containing the parent nuclide, osmium-191. The generator, which has a shelf-life in excess of two weeks and does not require a scavenger column, can be eluted with physiologically compatible saline.

  19. Osmium-191/iridium-191m radionuclide

    DOEpatents

    Knapp, F.F. Jr.; Butler, T.A.; Brihaye, C.

    1985-08-26

    A generator system to provide iridium-191m for clinical imaging applications comprises an activated carbon adsorbent loaded with a compound containing the parent nuclide, osmium-191. The generator, which has a shelf-life in excess of two weeks and does not require a scavenger column, can be eluted with physiologically compatible saline. 4 figs. 3 tabs.

  20. Hydridomethyl iridium complex

    SciTech Connect

    Bergman, R.G; Buchanan, J.M.; Stryker, J.M.; Wax, M.J.

    1989-07-18

    This patent describes a hydridomethyl complex of the formula: CpIr(P(R{sub 1}){sub 3})HMe. Cp represents a cyclopentadienyl or alkyl cyclopentadienyl radical; Ir represents an iridium atom; P represents a phosphorus atom; R{sub 1} represents an alkyl group; and Me represents a methyl group.

  1. Luminogenic iridium azide complexes

    PubMed Central

    Ohata, Jun; Vohidov, Farrukh; Aliyan, Amirhossein; Huang, Kewei; Martí, Angel A.

    2015-01-01

    The synthesis and characterization of luminogenic, bioorthogonal iridium probes is described. These probes exhibit long fluorescent lifetimes amenable to time-resolved applications. A simple, modular synthesis via 5-azidophenanthroline allows structural variation and allows optimization of cell labeling. PMID:26325066

  2. Iridium-coated rhenium thrusters by CVD

    NASA Technical Reports Server (NTRS)

    Harding, John T.; Kazaroff, John M.; Appel, Marshall A.

    1988-01-01

    Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the meltimg temperature of iridium, 2400 C (4350 F).

  3. Iridium-coated rhenium thrusters by CVD

    NASA Technical Reports Server (NTRS)

    Harding, J. T.; Kazaroff, J. M.; Appel, M. A.

    1989-01-01

    Operation of spacecraft thrusters at increased temperature reduces propellant requirements. Inasmuch as propellant comprises the bulk of a satellite's mass, even a small percentage reduction makes possible a significant enhancement of the mission in terms of increased payload. Because of its excellent high temperature strength, rhenium is often the structural material of choice. It can be fabricated into free-standing shapes by chemical vapor deposition (CVD) onto an expendable mandrel. What rhenium lacks is oxidation resistance, but this can be provided by a coating of iridium, also by CVD. This paper describes the process used by Ultramet to fabricate 22-N (5-lbf) and, more recently, 445-N (100-lbf) Ir/Re thrusters; characterizes the CVD-deposited materials; and summarizes the materials effects of firing these thrusters. Optimal propellant mixture ratios can be employed because the materials withstand an oxidizing environment up to the melting temperature of iridium, 2400 C (4350 F).

  4. New honeycomb iridium(V) oxides: NaIrO3 and Sr3CaIr2O9.

    PubMed

    Wallace, David C; McQueen, Tyrel M

    2015-12-21

    We report the structures and physical properties of two new iridates, NaIrO3 and Sr3CaIr2O9, both of which contain continuous two-dimensional honeycomb connectivity. NaIrO3 is produced by room temperature oxidative deintercalation of sodium from Na2IrO3, and contains edge-sharing IrO6 octahedra that form a planar honeycomb lattice. Sr3CaIr2O9, produced via conventional solid-state synthesis, hosts a buckled honeycomb lattice with novel corner-sharing connectivity between IrO6 octahedra. Both of these new compounds are comprised of Ir(5+) (5d(4)) and exhibit negligible magnetic susceptibility. They are thus platforms to investigate the origin of the nonmagnetic behavior exhibited by Ir(5+) oxides, and provide the first examples of a J = 0 state on a honeycomb lattice.

  5. Iridium Aluminide Coats For Protection Against Ox idation

    NASA Technical Reports Server (NTRS)

    Kaplan, Richard B.; Tuffias, Robert H.; La Ferla, Raffaele; Jang, Qin

    1996-01-01

    Iridium aluminide coats investigated for use in protecting some metallic substrates against oxidation at high temperatures. Investigation prompted by need for cost-effective anti-oxidation coats for walls of combustion chambers in rocket engines. Also useful in special terrestrial applications like laboratory combustion chambers and some chemical-processing chambers.

  6. Selectively lighting up two-photon photodynamic activity in mitochondria with AIE-active iridium(iii) complexes.

    PubMed

    Liu, Jiangping; Jin, Chengzhi; Yuan, Bo; Liu, Xingguo; Chen, Yu; Ji, Liangnian; Chao, Hui

    2017-02-07

    Herein a series of mitochondria-targeted AIE (aggregation-induced emission)-active Ir(iii) complexes were designed to selectively exert one-/two-photon photodynamic activities in mitochondria to address the issues which current PDT are confronted with (i.e., shallow penetration depth of routinely used irradiation; systematic toxicity associated with effective drug concentration; concentration-quenched photodynamic activity at the target, etc.).

  7. Method for refining contaminated iridium

    DOEpatents

    Heshmatpour, B.; Heestand, R.L.

    1982-08-31

    Contaminated iridium is refined by alloying it with an alloying agent selected from the group consisting of manganese and an alloy of manganese and copper, and then dissolving the alloying agent from the formed alloy to provide a purified iridium powder.

  8. Method for refining contaminated iridium

    DOEpatents

    Heshmatpour, Bahman; Heestand, Richard L.

    1983-01-01

    Contaminated iridium is refined by alloying it with an alloying agent selected from the group consisting of manganese and an alloy of manganese and copper, and then dissolving the alloying agent from the formed alloy to provide a purified iridium powder.

  9. Iridium Satellite Signal Exploitation

    NASA Astrophysics Data System (ADS)

    McDonough, Peter

    2010-03-01

    The Iridium Satellite constellation is unique to satellite communication networks in that it allows for transmission of data between satellites instead of relying on transmission by the bent pipe methodology. As such, this network is far more secure than other satellite communication networks, and forces interception to occur within the locale of the transmission from modem to satellite or within the locale of the downlink from the satellite other modem. The purpose of this project was to demonstrate the security weaknesses within the Iridium protocol, showing that it was possible to track one of these satellites with a high gain antenna, resulting in the ability to anticipate transmission, to acquire the location of that transmission, and to uncover the content of that transmission. This project was completed as part of the summer student program at the Southwest Research Institute. The presentation will demonstrate the thought process used in chronological order, essentially demonstrating how I achieved the result from my point of view as the summer progressed.

  10. Iridium/Rhenium Parts For Rocket Engines

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.; Harding, John T.; Wooten, John R.

    1991-01-01

    Oxidation/corrosion of metals at high temperatures primary life-limiting mechanism of parts in rocket engines. Combination of metals greatly increases operating temperature and longevity of these parts. Consists of two transition-element metals - iridium and rhenium - that melt at extremely high temperatures. Maximum operating temperature increased to 2,200 degrees C from 1,400 degrees C. Increases operating lifetimes of small rocket engines by more than factor of 10. Possible to make hotter-operating, longer-lasting components for turbines and other heat engines.

  11. Oxidation preventative capping layer for deep-ultra-violet and soft x-ray multilayers

    DOEpatents

    Prisbrey, Shon T.

    2004-07-06

    The invention uses iridium and iridium compounds as a protective capping layer on multilayers having reflectivity in the deep ultra-violet to soft x-ray regime. The iridium compounds can be formed in one of two ways: by direct deposition of the iridium compound from a prepared target or by depositing a thin layer (e.g., 5-50 angstroms) of iridium directly onto an element. The deposition energy of the incoming iridium is sufficient to activate the formation of the desired iridium compound. The compounds of most interest are iridium silicide (IrSi.sub.x) and iridium molybdenide (IrMo.sub.x).

  12. Synthesis, structure, and reactivity of rhodium and iridium complexes of the chelating bis-sulfoxide tBuSOC2H4SOtBu. Selective O-H activation of 2-hydroxy-isopropyl-pyridine.

    PubMed

    Schaub, Thomas; Diskin-Posner, Yael; Radius, Udo; Milstein, David

    2008-07-21

    The chloro-bridged rhodium and iridium complexes [M2(BTSE)2Cl2] (M = Rh 1, Ir 2) bearing the chelating bis-sulfoxide tBuSOC2H4SOtBu (BTSE) were prepared by the reaction of [M2(COE)4Cl2] (M = Rh, Ir; COE = cyclooctene) with an excess of a racemic mixture of the ligand. The cationic compounds [M(BTSE)2][PF6] (M = Rh 3, Ir 4), bearing one S- and one O-bonded sulfoxide, were also obtained in good yields. The chloro-bridges in 2 can be cleaved with 2-methyl-6-pyridinemethanol and 2-aminomethyl pyridine, resulting in the iridium(I) complexes [Ir(BTSE)(Py)(Cl)] (Py = 2-methyl-6-pyridinemethanol 5, 2-aminomethyl-pyridine 6). In case of the bulky 2-hydroxy- isopropyl-pyridine, selective OH oxidative addition took place, forming the Ir(III)-hydride [Ir(BTSE)(2-isopropoxy-pyridine)(H)(Cl)] 7, with no competition from the six properly oriented C-H bonds. The cationic rhodium(I) and iridium(I) compounds [M(BTSE)(2-aminomethyl-pyridine)][X] (M = Rh 8, Ir 10), [Rh(BTSE)(2-hydroxy- isopropyl-pyridine)][X] 9(stabilized by intramolecular hydrogen bonding), [Ir(BTSE)(pyridine)2][PF6] 12, [Ir(BTSE)(alpha-picoline)2][PF6] 13, and [Rh(BTSE)(1,10-phenanthroline)][PF6] 14 were prepared either by chloride abstraction from the dimeric precursors or by replacement of the labile oxygen bonded sulfoxide in 3 or 4. Complex 14 exhibits a dimeric structure in the solid state by pi-pi stacking of the phenanthroline ligands.

  13. Hydridomethyl iridium complex

    DOEpatents

    Bergman, Robert G.; Buchanan, J. Michael; Stryker, Jeffrey M.; Wax, Michael J.

    1989-01-01

    A process for functionalizing methane comprising: (a) reacting methane with a hydridoalkyl metal complex of the formula: CpIr[P(R.sub.1).sub.3 ]H(R.sub.2) wherein Cp represents a cyclopentadienyl or alkylcyclopentadienyl radical having from 1 to 5 carbon atoms; Ir represents an iridium atom; P represents a phosphorus atom; R.sub.1 represents an alkyl group; R.sub.2 represents an alkyl group having at least two carbon atoms; and H represents a hydrogen atom, in the presence of a liquid alkane R.sub.3 H having at least three carbon atoms to form a hydridomethyl complex of the formula: CpIr[P(R.sub.1).sub.3 ]HMe where Me represents a methyl radical. (b) reacting said hydridomethyl complex with an organic halogenating agent such as a tetrahalomethane or a haloform of the formulas: CX'X"X'"X"" or CHX'X"X'"; wherein X', X", X"', and X"" represent halogens selected from bromine, iodine and chlorine, to halomethyl complex of step (a) having the formula: CpIr[P(R.sub.1).sub.3 ]MeX: (c) reacting said halomethyl complex with a mercuric halide of the formula HgX.sub.2 to form a methyl mercuric halide of the formula HgMeX; and (d) reacting said methyl mercuric halide with a molecular halogen of the formula X.sub.2 to form methyl halide.

  14. Iridium-imine and -amine complexes relevant to the (S)-metolachlor process: structures, exchange kinetics, and C-H activation by Iri causing racemization.

    PubMed

    Dorta, Romano; Broggini, Diego; Kissner, Reinhard; Togni, Antonio

    2004-09-20

    Iridium complexes of DMA-imine [2,6-dimethylphenyl-1'-methyl-2'-methoxyethylimine, 1 a) and (R)-DMA-amine [(1'R)-2,6-dimethylphenyl-1'-methyl-2'-methoxyethylamine, 2 a] that are relevant to the catalytic imine hydrogenation step of the Syngenta (S)-Metolachlor process were synthesized: metathetical exchange of [Ir2Cl2(cod)2] (cod=1,5-cyclooctadiene) with [Ag(1 a)2]BF4 and [Ag((R)-2 a)2]BF4 afforded [Ir(cod)(kappa2- -1 a)]BF4 (11) and [Ir(cod)(kappa2-(R)-2 a)]BF4 ((R)-19)), respectively. These complexes were then used in stopped-flow experiments to study the displacement of amine 2 a from complex 19 by imine 1 a to form the imine complex 11, thus modeling the product/substrate exchange step in the catalytic cycle. The data suggest a two-step associative mechanism characterized by k1=(2.6+/-0.3) x 10(2) M(-1) s(-1) and k2=(4.3+/-0.6) x 10(-2) s(-1) with the respective activation energies EA1=(7.5+/-0.6) kJ mol(-1) and EA2=(37+/-3) kJ mol(-1). Furthermore, complex 11 reacted with H2O to afford the hydrolysis product [Ir(cod)(eta(6-)-2,6-dimethylaniline)]BF4 (12), and with I2 to liberate quantitatively the DMA-iminium salt 14. On the other hand, the chiral amine complex (R)-19 formed the optically inactive eta6-bound compound [Ir(cod)(eta6-rac-2 a)]BF4 (rac-18) upon dissolution in THF at room temperature, presumably via intramolecular C-H activation. This racemization was found to be a two-step event with k'1=9.0 x 10(-4) s(-1) and k2=2.89 x 10(-5) s(-1), featuring an optically active intermediate prior to sp3 C-H activation. Compounds 11, 12, rac-18, and (R)-19 were structurally characterized by single-crystal X-ray analyses.

  15. Iridium emissions from Hawaiian volcanoes

    NASA Technical Reports Server (NTRS)

    Finnegan, D. L.; Zoller, W. H.; Miller, T. M.

    1988-01-01

    Particle and gas samples were collected at Mauna Loa volcano during and after its eruption in March and April, 1984 and at Kilauea volcano in 1983, 1984, and 1985 during various phases of its ongoing activity. In the last two Kilauea sampling missions, samples were collected during eruptive activity. The samples were collected using a filterpack system consisting of a Teflon particle filter followed by a series of 4 base-treated Whatman filters. The samples were analyzed by INAA for over 40 elements. As previously reported in the literature, Ir was first detected on particle filters at the Mauna Loa Observatory and later from non-erupting high temperature vents at Kilauea. Since that time Ir was found in samples collected at Kilauea and Mauna Loa during fountaining activity as well as after eruptive activity. Enrichment factors for Ir in the volcanic fumes range from 10,000 to 100,000 relative to BHVO. Charcoal impregnated filters following a particle filter were collected to see if a significant amount of the Ir was in the gas phase during sample collection. Iridium was found on charcoal filters collected close to the vent, no Ir was found on the charcoal filters. This indicates that all of the Ir is in particulate form very soon after its release. Ratios of Ir to F and Cl were calculated for the samples from Mauna Loa and Kilauea collected during fountaining activity. The implications for the KT Ir anomaly are still unclear though as Ir was not found at volcanoes other than those at Hawaii. Further investigations are needed at other volcanoes to ascertain if basaltic volcanoes other than hot spots have Ir enrichments in their fumes.

  16. Iridium in sea-water.

    PubMed

    Fresco, J; Weiss, H V; Phillips, R B; Askeland, R A

    1985-08-01

    Iridium in sea-water has been measured (after isolation from the saline matrix by reduction with magnesium) by neutron bombardment, radiochemical purification and high-resolution gamma-ray spectroscopy. The concentration obtained in a Pacific coastal water was 1.02 +/- 0.26 x 10(-14) g per g of sea-water. At such extremely low concentrations, seawater is an extremely unlikely source for anomalously high iridium concentrations measured in the Cretaceous-Tertiary boundary layer of deep-sea sediments.

  17. Biological activity of neutral and cationic iridium(III) complexes with κP and κP,κS coordinated Ph₂PCH₂S(O)xPh (x = 0-2) ligands.

    PubMed

    Ludwig, Gerd; Mijatović, Sanja; Ranđelović, Ivan; Bulatović, Mirna; Miljković, Djordje; Maksimović-Ivanić, Danijela; Korb, Marcus; Lang, Heinrich; Steinborn, Dirk; Kaluđerović, Goran N

    2013-11-01

    Neutral iridium(III) complexes of the type [Ir(η(5)-C₅Me₅)Cl₂{Ph₂PCH₂S(O)xPh-κP}] (1-3) with diphenylphosphino-functionalized methyl phenyl sulfides, sulfoxides, and sulfones Ph₂PCH₂S(O)xPh (x = 0, L1; 1, L2; 2, L3) and the cationic complex [Ir(η(5)-C₅Me₅)Cl{Ph₂PCH₂SPh-κP,κS}][PF6] (4) were synthesized and fully characterized analytically and spectroscopically. Furthermore, the structure of 2 was determined by X-ray diffraction analysis. The biological potential of the neutral and cationic iridium(III) complexes was tested in vitro against the cell lines 8505C, A253, MCF-7, SW480 and 518A2. Complex [Ir(η(5)-C₅Me₅)Cl₂{Ph₂PCH₂S(O)Ph-κP}] (2), with ligand L2 κP coordinated containing a pendent sulfinyl group, is the most active one (IC₅₀ values of about 3 μM), thus, with activities comparable to cisplatin. Complex 2 proved to have an even a higher antiproliferative activity than cisplatin against 8505C and SW480 cell lines, used as a model system of highly anaplastic cancers with low sensitivity to conventional chemotherapeutics such as cisplatin. Additional experiments demonstrated that apoptosis and autophagic cell death contribute to the drug's tumoricidal action.

  18. Regioselective introduction of heteroatoms at the C-8 position of quinoline N-oxides: remote C-H activation using N-oxide as a stepping stone.

    PubMed

    Hwang, Heejun; Kim, Jinwoo; Jeong, Jisu; Chang, Sukbok

    2014-07-30

    Reported herein is the metal-catalyzed regioselective C-H functionalization of quinoline N-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of N-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C-H activation using N-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated.

  19. Positional effects of hydroxy groups on catalytic activity of proton-responsive half-sandwich Cp*Iridium(III) complexes

    SciTech Connect

    Suna, Yuki; Fujita, Etsuko; Ertem, Mehmed Z.; Wang, Wan-Hui; Kambayashi, Hide; Manaka, Yuichi; Muckerman, James T.; Himeda, Yuichiro

    2014-11-12

    Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3'-, 4,4'-, 5,5'- or 6,6'-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV-vis titration data provided average pK a values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited the low pKa value of < 0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turn leads to an elevated pKa value of ~13.6 for the second deprotonation step. The crystal structures of the 4– and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 7.2 and 2.6) were investigated to compare the positional effects of the hydroxy groups. The 4– and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electrondonating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO₂ hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H₂ heterolysis and CO

  20. Positional effects of hydroxy groups on catalytic activity of proton-responsive half-sandwich Cp*Iridium(III) complexes

    DOE PAGES

    Suna, Yuki; Fujita, Etsuko; Ertem, Mehmed Z.; ...

    2014-11-12

    Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3'-, 4,4'-, 5,5'- or 6,6'-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV-vis titration data provided average pK a values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited the low pKa value of < 0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turn leadsmore » to an elevated pKa value of ~13.6 for the second deprotonation step. The crystal structures of the 4– and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 7.2 and 2.6) were investigated to compare the positional effects of the hydroxy groups. The 4– and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electrondonating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO₂ hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H₂ heterolysis and CO₂ insertion steps

  1. Double N,B-Type Bidentate Boryl Ligands Enabling a Highly Active Iridium Catalyst for C-H Borylation.

    PubMed

    Wang, Guanghui; Xu, Liang; Li, Pengfei

    2015-07-01

    Boryl ligands hold promise in catalysis due to their very high electron-donating property. In this communication double N,B-type boryl anions were designed as bidentate ligands to promote an sp(2) C-H borylation reaction. A symmetric pyridine-containing tetraaminodiborane(4) compound (1) was readily prepared as the ligand precursor that could be used, in combination with [Ir(OMe)(COD)]2, to in situ generate a highly active catalyst for a broad range of (hetero)arene substrates including highly electron-rich and/or sterically hindered ones. This work provides the first example of a bidentate boryl ligand in supporting homogeneous organometallic catalysis.

  2. Homolytic N–H Activation of Ammonia: Hydrogen Transfer of Parent Iridium Ammine, Amide, Imide, and Nitride Species

    PubMed Central

    2015-01-01

    The redox series [Irn(NHx)(PNP)] (n = II–IV, x = 3–0; PNP = N(CHCHPtBu2)2) was examined with respect to electron, proton, and hydrogen atom transfer steps. The experimental and computational results suggest that the IrIII imido species [Ir(NH)(PNP)] is not stable but undergoes disproportionation to the respective IrII amido and IrIV nitrido species. N–H bond strengths are estimated upon reaction with hydrogen atom transfer reagents to rationalize this observation and are used to discuss the reactivity of these compounds toward E–H bond activation. PMID:26192601

  3. Synthesis and luminescence properties of iridium(III) azide- and triazole-bisterpyridine complexes.

    PubMed

    Goldstein, Daniel C; Peterson, Joshua R; Cheng, Yuen Yap; Clady, Raphael G C; Schmidt, Timothy W; Thordarson, Pall

    2013-07-26

    We describe here the synthesis of azide-functionalised iridium(III) bisterpyridines using the "chemistry on the complex" strategy. The resulting azide-complexes are then used in the copper(I)-catalysed azide-alkyne Huisgen 1,3-dipolar cycloaddition "click chemistry" reaction to from the corresponding triazole-functionalised iridium(III) bisterpyridines. The photophysical characteristics, including lifetimes, of these compounds were also investigated. Interestingly, oxygen appears to have very little effect on the lifetime of these complexes in aqueous solutions. Unexpectedly, sodium ascorbate acid appears to quench the luminescence of triazole-functionalised iridium(III) bisterpyridines, but this effect can be reversed by the addition of copper(II) sulfate, which is known to oxidize ascorbate under aerobic conditions. The results demonstrate that iridium(III) bisterpyridines can be functionalized for use in "click chemistry" facilitating the use of these photophysically interesting complexes in the modification of polymers or surfaces, to highlight just two possible applications.

  4. Iridium-catalyst-based autonomous bubble-propelled graphene micromotors with ultralow catalyst loading.

    PubMed

    Wang, Hong; Sofer, Zdeněk; Eng, Alex Yong Sheng; Pumera, Martin

    2014-11-10

    A novel concept of an iridium-based bubble-propelled Janus-particle-type graphene micromotor with very high surface area and with very low catalyst loading is described. The low loading of Ir catalyst (0.54 at %) allows for fast motion of graphene microparticles with high surface area of 316.2 m(2)  g(-1). The micromotor was prepared with a simple and scalable method by thermal exfoliation of iridium-doped graphite oxide precursor composite in hydrogen atmosphere. Oxygen bubbles generated from the decomposition of hydrogen peroxide at the iridium catalytic sites provide robust propulsion thrust for the graphene micromotor. The high surface area and low iridium catalyst loading of the bubble-propelled graphene motors offer great possibilities for dramatically enhanced cargo delivery.

  5. IRIDIUM LINER FOR NASA 5 LBF CLASS MATERIAL TEST CHAMBER IRIDIUM LINER FOR ATLANTIC RESEARCH CORPORA

    NASA Technical Reports Server (NTRS)

    1995-01-01

    IRIDIUM LINER FOR NASA 5 LBF CLASS MATERIAL TEST CHAMBER IRIDIUM LINER FOR ATLANTIC RESEARCH CORPORATION 5 LBF CLASS ROCKET CHAMBER 25 LBF CLASS 75 HFC 25 TAC CERAMIC COMPOSITE ROCKET CHAMBER FROM REFRACTURY COMPOSITES INC. PURCHASE ORDER C-551941-

  6. Origins of Regioselectivity in Iridium Catalyzed Allylic Substitution.

    PubMed

    Madrahimov, Sherzod T; Li, Qian; Sharma, Ankit; Hartwig, John F

    2015-12-02

    Detailed studies on the origin of the regioselectivity for formation of branched products over linear products have been conducted with complexes containing the achiral triphenylphosphite ligand. The combination of iridium and P(OPh)3 was the first catalytic system shown to give high regioselectivity for the branched product with iridium and among the most selective for forming branched products among any combination of metal and ligand. We have shown the active catalyst to be generated from [Ir(COD)Cl]2 and P(OPh)3 by cyclometalation of the phenyl group on the ligand and have shown such species to be the resting state of the catalyst. A series of allyliridium complexes ligated by the resulting P,C ligand have been generated and shown to be competent intermediates in the catalytic system. We have assessed the potential impact of charge, metal-iridium bond length, and stability of terminal vs internal alkenes generated by attack at the branched and terminal positions of the allyl ligand, respectively. These factors do not distinguish the regioselectivity for attack on allyliridium complexes from that for attack on allylpalladium complexes. Instead, detailed computational studies suggest that a series of weak, attractive, noncovalent interactions, including interactions of H-bond acceptors with a vinyl C-H bond of the alkene ligand, favor formation of the branched product with the iridium catalyst. This conclusion underscores the importance of considering attractive interactions, as well as repulsive steric interactions, when seeking to rationalize selectivities.

  7. A molecular catalyst for water oxidation that binds to metal oxide surfaces

    PubMed Central

    Sheehan, Stafford W.; Thomsen, Julianne M.; Hintermair, Ulrich; Crabtree, Robert H.; Brudvig, Gary W.; Schmuttenmaer, Charles A.

    2015-01-01

    Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. Here we describe how a molecular iridium catalyst for water oxidation directly and robustly binds to oxide surfaces without the need for any external stimulus or additional linking groups. On conductive electrode surfaces, this heterogenized molecular catalyst oxidizes water with low overpotential, high turnover frequency and minimal degradation. Spectroscopic and electrochemical studies show that it does not decompose into iridium oxide, thus preserving its molecular identity, and that it is capable of sustaining high activity towards water oxidation with stability comparable to state-of-the-art bulk metal oxide catalysts. PMID:25757425

  8. Blistering during the atomic layer deposition of iridium

    SciTech Connect

    Genevée, Pascal E-mail: a.szeghalmi@uni-jena.de; Ahiavi, Ernest; Janunts, Norik; Pertsch, Thomas; Kley, Ernst-Bernhard; Szeghalmi, Adriana E-mail: a.szeghalmi@uni-jena.de; Oliva, Maria

    2016-01-15

    The authors report on the formation of blisters during the atomic layer deposition of iridium using iridium acetylacetonate and oxygen precursors. Films deposited on fused silica substrates led to sparsely distributed large blisters while in the case of silicon with native oxide additional small blisters with a high density was observed. It is found that the formation of blisters is favored by a higher deposition temperature and a larger layer thickness. Postdeposition annealing did not have a significant effect on the formation of blisters. Finally, changing purge duration during the film growth allowed us to avoid blistering and evidenced that impurities released from the film in gas phase were responsible for the formation of blisters.

  9. SO2 adsorption on silica supported iridium

    NASA Astrophysics Data System (ADS)

    Bounechada, Djamela; Anderson, David P.; Skoglundh, Magnus; Carlsson, Per-Anders

    2017-02-01

    The interaction of SO2 with Ir/SiO2 was studied by simultaneous in situ diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry, exposing the sample to different SO2 concentrations ranging from 10 to 50 ppm in the temperature interval 200-400 °C. Evidences of adsorption of sulfur species in both absence and presence of oxygen are found. For a pre-reduced sample in the absence of oxygen, SO2 disproportionates such that the iridium surface is rapidly saturated with adsorbed S while minor amounts of formed SO3 may adsorb on SiO2. Adding oxygen to the feed leads to the oxidation of sulfide species that either (i) desorb as SO2 and/or SO3, (ii) remain at metal sites in the form of adsorbed SO2, or (iii) spillover to the oxide support and form sulfates (SO42-). Notably, significant formation of sulfates on silica is possible only in the presence of both SO2 and O2, suggesting that SO2 oxidation to SO3 is a necessary first step in the mechanism of formation of sulfates on silica. During the formation of sulfates, a concomitant removal/rearrangement of surface silanol groups is observed. Finally, the interaction of SO2 with Ir/SiO2 depends primarily on the temperature and type of gas components but only to a minor extent on the inlet SO2 concentration.

  10. PURIFICATION OF IRIDIUM BY ELECTRON BEAM MELTING

    SciTech Connect

    Ohriner, Evan Keith

    2008-01-01

    The purification of iridium metal by electron beam melting has been characterized for 48 impurity elements. Chemical analysis was performed by glow discharge mass spectrographic (GDMS) analysis for all elements except carbon, which was analyzed by combustion. The average levels of individual elemental impurities in the starting powder varied from 37 g/g to 0.02 g/g. The impurity elements Li, Na, Mg, P, S, Cl, K, Ca, Mn, Co, Ni, Cu, Zn, As, Pd, Ag, Cd, Sn, Sb, Te, Ba, Ce, Tl, Pb, and Bi were not detectable following the purification. No significant change in concentration of the elements Ti, V, Zr, Nb, Mo, and Re was found. The elements B, C, Al, Si, Cr, Fe, Ru, Rh, and Pt were partially removed by vaporization during electron beam melting. Langmuir's equation for ideal vaporization into a vacuum was used to calculate for each impurity element the expected ratio of impurity content after melting to that before melting. Equilibrium vapor pressures were calculated using Henry's law, with activity coefficients obtained from published data for the elements Fe, Ti, and Pt. Activity coefficients were estimated from enthalpy data for Al, Si, V, Cr, Mn, Co, Ni, Zr, Nb, Mo, and Hf and an ideal solution model was used for the remaining elements. The melt temperature was determined from measured iridium weight loss. Excellent agreement was found between measured and calculated impurity ratios for all impurity elements. The results are consistent with some localized heating of the melt pool due to rastering of the electron beam, with an average vaporization temperature of 3100 K as compared to a temperature of 2965 K calculated for uniform heating of the melt pool. The results are also consistent with ideal mixing in the melt pool.

  11. Reactions of Anilines and Benzamides with a Fourteen-Electron Iridium(I) Bis(Phosphinite) Complex: N-H Oxidative Addition versus Lewis Base Coordination

    PubMed Central

    Sykes, Alison Cartwright; White, Peter

    2008-01-01

    Anilines react with (POCOP)Ir(C6H5)(H), 12, (POCOP = 2,6-(OPtBu2)2C6H3) to yield equilibrium mixtures of 12, the Ir(I) σ-complexes (POCOP)Ir(NH2Ar), 13, and the Ir(III) oxidative addition adducts (POCOP)Ir(H)(NHAr), 14. Quantitative studies of these equilibria for a series of anilines were carried out. Anilines possessing electron-withdrawing groups favor the Ir(III) oxidative addition adduct over the Ir(I) sigma complex. Low temperature studies using p-chloroaniline show that the Ir(I) σ-complex is the kinetic product of reaction and is likely the precursor to the Ir(III) oxidative addition adduct. Reductive elimination of complexes 14 in the presence of ethylene led to the corresponding anilines and the ethylene complex (POCOP)Ir(C2H4). Kinetic analysis of these reactions for 14e,f,g bearing electron-withdrawing aryl groups (Ar- = p-CF3C6H4-, C6F5-, 3,5-bis(CF3)C6H3-) shows the rate is independent of ethylene concentration. The ΔG‡ values for these reductive eliminations fall in the range of 21–22 kcal/mol. X-Ray analysis establishes 14f (Ar- = C6F5-) as a square pyramidal complex with the hydride occupying the apical site. Reaction of 12 with benzamides 21a,b yields quantitatively the Ir(III) oxidative addition adducts, (POCOP)Ir(H)(NHC(O)Ar), 22. X-Ray analysis of 22b (Ar- = C6F5-) shows significant interaction of the carbonyl oxygen with Ir in the site trans to hydride. The barrier to reductive elimination of 22a, 29 kcal/mol, is substantially higher than for complexes 14e,f,g. PMID:19079781

  12. TCP Performance Enhancement Over Iridium

    NASA Technical Reports Server (NTRS)

    Torgerson, Leigh; Hutcherson, Joseph; McKelvey, James

    2007-01-01

    In support of iNET maturation, NASA-JPL has collaborated with NASA-Dryden to develop, test and demonstrate an over-the-horizon vehicle-to-ground networking capability, using Iridium as the vehicle-to-ground communications link for relaying critical vehicle telemetry. To ensure reliability concerns are met, the Space Communications Protocol Standards (SCPS) transport protocol was investigated for its performance characteristics in this environment. In particular, the SCPS-TP software performance was compared to that of the standard Transmission Control Protocol (TCP) over the Internet Protocol (IP). This paper will report on the results of this work.

  13. Technique for surface oxidation of activated carbon

    SciTech Connect

    Sircar, S.; Golden, T.C.

    1987-10-27

    A method of activating a carbon adsorbent is described, which comprises oxidizing the surface of the carbon adsorbent with a mild oxidizing acid in the presence of a metal oxidation catalyst at an elevated temperature and boiling the mixture of the carbon adsorbent, mild oxidizing acid and metal oxidation catalyst to dryness. Then rinse the surface oxidizing carbon adsorbent with water; and dry the rinsed surface oxidized carbon adsorbent. In a process for the removal of water or carbon dioxide from a gas stream containing water or carbon dioxide of the type wherein the gas stream containing water or carbon dioxide is contacted with a solid phase adsorbent under pressure-swing adsorption or thermal-swing adsorption processing conditions, the improvement is described comprising utilizing an adsorbent produced by the activation of a carbon adsorbent. The activation comprises oxidizing the surface of the carbon adsorbent with a mold oxidizing acid in the presence of a metal oxidation catalyst at an elevated temperature and boiling the mixture of the carbon adsorbent, mild oxidizing acid and metal oxidation catalyst to dryness. Then rinse the surface oxidized carbon adsorbent with water; and dry the rinsed surface oxidized carbon adsorbent.

  14. On the dissolution of iridium by aluminum.

    SciTech Connect

    Hewson, John C.

    2009-08-01

    The potential for liquid aluminum to dissolve an iridium solid is examined. Substantial uncertainties exist in material properties, and the available data for the iridium solubility and iridium diffusivity are discussed. The dissolution rate is expressed in terms of the regression velocity of the solid iridium when exposed to the solvent (aluminum). The temperature has the strongest influence in the dissolution rate. This dependence comes primarily from the solubility of iridium in aluminum and secondarily from the temperature dependence of the diffusion coefficient. This dissolution mass flux is geometry dependent and results are provided for simplified geometries at constant temperatures. For situations where there is negligible convective flow, simple time-dependent diffusion solutions are provided. Correlations for mass transfer are also given for natural convection and forced convection. These estimates suggest that dissolution of iridium can be significant for temperatures well below the melting temperature of iridium, but the uncertainties in actual rates are large because of uncertainties in the physical parameters and in the details of the relevant geometries.

  15. Determining the Altitude of Iridium Flares

    NASA Technical Reports Server (NTRS)

    Foster, James; Owe, Manfred

    1999-01-01

    Iridium flares have nothing to do with the element iridium. Iridium is also the name of a telecommunications company that has been launching satellites into low orbits around the Earth. These satellites are being used for a new type of wireless phone and paging service. Flares have been observed coming from these satellites. These flares have the potential, especially when the full fleet of satellites is in orbit, to disrupt astronomical observations. The paper reviews using simple trigonometry how to calculate the altitude of one of these satellites.

  16. Isomerization of Internal Alkynes to Iridium(III) Allene Complexes via C-H Bond Activation: Expanded Substrate Scope, and Progress towards a Catalytic Methodology.

    PubMed

    Phadke, Neha; Findlater, Michael

    2015-11-10

    The synthesis of a series of allene complexes (POCOP)Ir(η²-RC=(.)=CR') 1b-4b (POCOP = 2,6-bis(di-tert-butylphosphonito)benzene) via isomerization of internal alkynes is reported. We have demonstrated that the application of this methodology is viable for the isomerization of a wide variety of alkyne substrates. Deuterium labeling experiments support our proposed mechanism. The structures of the allene complexes 1b-4b were determined using spectroscopic data analysis. Additionally, the solid-state molecular structure of complex 2b was determined using single crystal X-ray diffraction studies and it confirmed the assignment of an iridium-bound allene isomerization product. The rates of isomerization were measured using NMR techniques over a range of temperatures to allow determination of thermodynamic parameters. Finally, we report a preliminary step towards developing a catalytic methodology; the allene may be liberated from the metal center by exposure of the complex to an atmosphere of carbon monoxide.

  17. Selective DNA purine base photooxidation by bis-terdentate iridium(III) polypyridyl and cyclometalated complexes.

    PubMed

    Jacques, Alexandre; Kirsch-De Mesmaeker, Andrée; Elias, Benjamin

    2014-02-03

    Two bis-terdentate iridium(III) complexes with polypyridyl and cyclometalated ligands have been prepared and characterized. Their spectroscopic and electrochemical properties have been studied, and a photophysical scheme addressing their properties is proposed. Different types of excited states have been considered to account for the deactivation processes in each complex. Interestingly, in the presence of mono- or polynucleotides, a photoinduced electron-transfer process from a DNA purine base (i.e., guanine or adenine) to the excited complex is shown through luminescence quenching experiments. For the first time, this work reports evidence for selective DNA purine bases oxidation by excited iridium(III) bis-terdentate complexes.

  18. Electrodeposition of platinum-iridium alloy nanowires for hermetic packaging of microelectronics.

    PubMed

    Petrossians, Artin; Whalen, John J; Weiland, James D; Mansfeld, Florian

    2012-01-01

    An electrodeposition technique was applied for fabrication of dense platinum-iridium alloy nanowires as interconnect structures in hermetic microelectronic packaging to be used in implantable devices. Vertically aligned arrays of platinum-iridium alloy nanowires with controllable length and a diameter of about 200 nm were fabricated using a cyclic potential technique from a novel electrodeposition bath in nanoporous aluminum oxide templates. Ti/Au thin films were sputter deposited on one side of the alumina membranes to form a base material for electrodeposition. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to characterize the morphology and the chemical composition of the nanowires, respectively. SEM micrographs revealed that the electrodeposited nanowires have dense and compact structures. EDS analysis showed a 60:40% platinum-iridium nanowire composition. Deposition rates were estimated by determining nanowire length as a function of deposition time. High Resolution Transmission Electron Microscopy (HRTEM) images revealed that the nanowires have a nanocrystalline structure with grain sizes ranging from 3 nm to 5 nm. Helium leak tests performed using a helium leak detector showed leak rates as low as 1 × 10(-11) mbar L s(-1) indicating that dense nanowires were electrodeposited inside the nanoporous membranes. Comparison of electrical measurements on platinum and platinum-iridium nanowires revealed that platinum-iridium nanowires have improved electrical conductivity.

  19. Monte Carlo study of an unconventional superconducting phase in iridium oxide J(eff)=1/2 Mott insulators induced by carrier doping.

    PubMed

    Watanabe, Hiroshi; Shirakawa, Tomonori; Yunoki, Seiji

    2013-01-11

    Based on a microscopic theoretical study, we show that novel superconductivity is induced by carrier doping in layered perovskite Ir oxides where a strong spin-orbit coupling causes an effective total angular momentum J(eff)=1/2 Mott insulator. Using a variational Monte Carlo method, we find an unconventional superconducting state in the ground state phase diagram of a t(2g) three-orbital Hubbard model on the square lattice. This superconducting state is characterized by a d(x(2)-y(2))-wave "pseudospin singlet" formed by the J(eff)=1/2 Kramers doublet, which thus contains interorbital as well as both singlet and triplet components of t(2g) electrons. The superconducting state is found stable only by electron doping, but not by hole doping, for the case of carrier doped Sr2IrO4. We also study an effective single-orbital Hubbard model to discuss the similarities to high-T(c) cuprate superconductors and the multiorbital effects.

  20. Iridium-Catalyzed Asymmetric Hydrogenation of Unsaturated Carboxylic Acids.

    PubMed

    Zhu, Shou-Fei; Zhou, Qi-Lin

    2017-04-04

    Chiral carboxylic acid moieties are widely found in pharmaceuticals, agrochemicals, flavors, fragrances, and health supplements. Although they can be synthesized straightforwardly by transition-metal-catalyzed enantioselective hydrogenation of unsaturated carboxylic acids, because the existing chiral catalysts have various disadvantages, the development of new chiral catalysts with high activity and enantioselectivity is an important, long-standing challenge. Ruthenium complexes with chiral diphosphine ligands and rhodium complexes with chiral monodentate or bidentate phosphorus ligands have been the predominant catalysts for asymmetric hydrogenation of unsaturated acids. However, the efficiency of these catalysts is highly substrate-dependent, and most of the reported catalysts require a high loading, high hydrogen pressure, or long reaction time for satisfactory results. Our recent studies have revealed that chiral iridium complexes with chiral spiro-phosphine-oxazoline ligands and chiral spiro-phosphine-benzylamine ligands exhibit excellent activity and enantioselectivity in the hydrogenation of α,β-unsaturated carboxylic acids, including α,β-disubstituted acrylic acids, trisubstituted acrylic acids, α-substituted acrylic acids, and heterocyclic α,β-unsaturated acids. On the basis of an understanding of the role of the carboxy group in iridium-catalyzed asymmetric hydrogenation reactions, we developed a carboxy-group-directed strategy for asymmetric hydrogenation of olefins. Using this strategy, we hydrogenated several challenging olefin substrates, such as β,γ-unsaturated carboxylic acids, 1,1-diarylethenes, 1,1-dialkylethenes, and 1-alkyl styrenes in high yield and with excellent enantioselectivity. All these iridium-catalyzed asymmetric hydrogenation reactions feature high turnover numbers (up to 10000) and turnover frequencies (up to 6000 h(-1)), excellent enantioselectivities (greater than 95% ee with few exceptions), low hydrogen pressure (<12 atm

  1. Broadband iridium wire grid polarizer for UV applications.

    PubMed

    Weber, Thomas; Käsebier, Thomas; Kley, Ernst-Bernhard; Tünnermann, Andreas

    2011-02-15

    In this Letter, we present an iridium wire grid polarizer with a large spectral working range from IR down to the UV spectral region. The required grating period of 100 nm for an application below a wavelength of 300 nm was realized using a spatial frequency doubling technique based on ultrafast electron beam writing. The optical performance of the polarizer at a wavelength of 300 nm is a transmittance of almost 60% and an extinction ratio of about 30 (15 dB). Furthermore, the oxidation resistance is discussed.

  2. Antibacterial activity of graphite, graphite oxide, graphene oxide, and reduced graphene oxide: membrane and oxidative stress.

    PubMed

    Liu, Shaobin; Zeng, Tingying Helen; Hofmann, Mario; Burcombe, Ehdi; Wei, Jun; Jiang, Rongrong; Kong, Jing; Chen, Yuan

    2011-09-27

    Health and environmental impacts of graphene-based materials need to be thoroughly evaluated before their potential applications. Graphene has strong cytotoxicity toward bacteria. To better understand its antimicrobial mechanism, we compared the antibacterial activity of four types of graphene-based materials (graphite (Gt), graphite oxide (GtO), graphene oxide (GO), and reduced graphene oxide (rGO)) toward a bacterial model-Escherichia coli. Under similar concentration and incubation conditions, GO dispersion shows the highest antibacterial activity, sequentially followed by rGO, Gt, and GtO. Scanning electron microscope (SEM) and dynamic light scattering analyses show that GO aggregates have the smallest average size among the four types of materials. SEM images display that the direct contacts with graphene nanosheets disrupt cell membrane. No superoxide anion (O(2)(•-)) induced reactive oxygen species (ROS) production is detected. However, the four types of materials can oxidize glutathione, which serves as redox state mediator in bacteria. Conductive rGO and Gt have higher oxidation capacities than insulating GO and GtO. Results suggest that antimicrobial actions are contributed by both membrane and oxidation stress. We propose that a three-step antimicrobial mechanism, previously used for carbon nanotubes, is applicable to graphene-based materials. It includes initial cell deposition on graphene-based materials, membrane stress caused by direct contact with sharp nanosheets, and the ensuing superoxide anion-independent oxidation. We envision that physicochemical properties of graphene-based materials, such as density of functional groups, size, and conductivity, can be precisely tailored to either reducing their health and environmental risks or increasing their application potentials.

  3. Antitumor Activities of Metal Oxide Nanoparticles

    PubMed Central

    Vinardell, Maria Pilar; Mitjans, Montserrat

    2015-01-01

    Nanoparticles have received much attention recently due to their use in cancer therapy. Studies have shown that different metal oxide nanoparticles induce cytotoxicity in cancer cells, but not in normal cells. In some cases, such anticancer activity has been demonstrated to hold for the nanoparticle alone or in combination with different therapies, such as photocatalytic therapy or some anticancer drugs. Zinc oxide nanoparticles have been shown to have this activity alone or when loaded with an anticancer drug, such as doxorubicin. Other nanoparticles that show cytotoxic effects on cancer cells include cobalt oxide, iron oxide and copper oxide. The antitumor mechanism could work through the generation of reactive oxygen species or apoptosis and necrosis, among other possibilities. Here, we review the most significant antitumor results obtained with different metal oxide nanoparticles.

  4. Methanol dehydrogenation by iridium N-heterocyclic carbene complexes.

    PubMed

    Campos, Jesús; Sharninghausen, Liam S; Manas, Michael G; Crabtree, Robert H

    2015-06-01

    A series of homogeneous iridium bis(N-heterocyclic carbene) catalysts are active for three transformations involving dehydrogenative methanol activation: acceptorless dehydrogenation, transfer hydrogenation, and amine monoalkylation. The acceptorless dehydrogenation reaction requires base, yielding formate and carbonate, as well as 2-3 equivalents of H2. Of the few homogeneous systems known for this reaction, our catalysts tolerate air and employ simple ligands. Transfer hydrogenation of ketones and imines from methanol is also possible. Finally, N-monomethylation of anilines occurs through a "borrowing hydrogen" reaction. Notably, this reaction is highly selective for the monomethylated product.

  5. IRIDIUM (R): A Lockheed transition to commercial space

    NASA Technical Reports Server (NTRS)

    Tadano, Thomas N.

    1995-01-01

    At Lockheed Missiles & Space Company, the IRIDIUM commercial space program is dramatically revolutionizing spacecraft development and manufacturing processes to reduce cost while maintaining quality and reliability. This report includes the following sections: an overview of the IRIDIUM system, the Lockheed IRIDIUM project and challenges; cycle-time reduction through production reorganization; and design for manufacturing and quality.

  6. Iridium nanoparticles supported on hierarchical porous N-doped carbon: an efficient water-tolerant catalyst for bio-alcohol condensation in water

    PubMed Central

    Liu, Di; Chen, Xiufang; Xu, Guoqiang; Guan, Jing; Cao, Quan; Dong, Bo; Qi, Yunfei; Li, Chunhu; Mu, Xindong

    2016-01-01

    Nitrogen-doped hierarchical porous carbons were synthesized successfully by a controllable one-pot method using glucose and dicyandiamide as carbon source and nitrogen source via hydrothermal carbonization process. The nitrogen-doped materials, possessing high nitrogen content (up to 7 wt%), large surface area (>320 m2 g−1) and excellent hierarchical nanostructure, were employed as catalyst supports for immobilization of iridium nanoparticles for bio-alcohol condensation in water. The introduction of nitrogen atoms into the carbon framework significantly improved iridium nanoparticles dispersion and stabilization. The novel iridium catalysts exhibited superior catalytic activity in the aqueous phase condensation of butanol, offering high butanol conversion of 45% with impressive 2-ethylhexanol selectivity of 97%. The heterogeneous catalysts had great advantages of easy recovery and high catalytic stability. The outstanding catalytic performance could be attributed to excellent dispersion of iridium nanoparticles, stronger iridium-support interactions and interaction of nitrogen species with alcohol substrates. PMID:26912370

  7. Iridium nanoparticles supported on hierarchical porous N-doped carbon: an efficient water-tolerant catalyst for bio-alcohol condensation in water

    NASA Astrophysics Data System (ADS)

    Liu, Di; Chen, Xiufang; Xu, Guoqiang; Guan, Jing; Cao, Quan; Dong, Bo; Qi, Yunfei; Li, Chunhu; Mu, Xindong

    2016-02-01

    Nitrogen-doped hierarchical porous carbons were synthesized successfully by a controllable one-pot method using glucose and dicyandiamide as carbon source and nitrogen source via hydrothermal carbonization process. The nitrogen-doped materials, possessing high nitrogen content (up to 7 wt%), large surface area (>320 m2 g‑1) and excellent hierarchical nanostructure, were employed as catalyst supports for immobilization of iridium nanoparticles for bio-alcohol condensation in water. The introduction of nitrogen atoms into the carbon framework significantly improved iridium nanoparticles dispersion and stabilization. The novel iridium catalysts exhibited superior catalytic activity in the aqueous phase condensation of butanol, offering high butanol conversion of 45% with impressive 2-ethylhexanol selectivity of 97%. The heterogeneous catalysts had great advantages of easy recovery and high catalytic stability. The outstanding catalytic performance could be attributed to excellent dispersion of iridium nanoparticles, stronger iridium-support interactions and interaction of nitrogen species with alcohol substrates.

  8. Iridium nanoparticles supported on hierarchical porous N-doped carbon: an efficient water-tolerant catalyst for bio-alcohol condensation in water.

    PubMed

    Liu, Di; Chen, Xiufang; Xu, Guoqiang; Guan, Jing; Cao, Quan; Dong, Bo; Qi, Yunfei; Li, Chunhu; Mu, Xindong

    2016-02-25

    Nitrogen-doped hierarchical porous carbons were synthesized successfully by a controllable one-pot method using glucose and dicyandiamide as carbon source and nitrogen source via hydrothermal carbonization process. The nitrogen-doped materials, possessing high nitrogen content (up to 7 wt%), large surface area (>320 m(2) g(-1)) and excellent hierarchical nanostructure, were employed as catalyst supports for immobilization of iridium nanoparticles for bio-alcohol condensation in water. The introduction of nitrogen atoms into the carbon framework significantly improved iridium nanoparticles dispersion and stabilization. The novel iridium catalysts exhibited superior catalytic activity in the aqueous phase condensation of butanol, offering high butanol conversion of 45% with impressive 2-ethylhexanol selectivity of 97%. The heterogeneous catalysts had great advantages of easy recovery and high catalytic stability. The outstanding catalytic performance could be attributed to excellent dispersion of iridium nanoparticles, stronger iridium-support interactions and interaction of nitrogen species with alcohol substrates.

  9. Active Oxidation of SiC

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers,Dwight L.; Harder, Bryan J.

    2011-01-01

    The high temperature oxidation of silicon carbide occurs in either a passive or active mode, depending on temperature and oxygen potential. Passive oxidation forms a protective oxide film which limits attack of the SiC:SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g.) Active oxidation forms a volatile oxide and leads to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g). The transition points and rates of active oxidation are a major issue. Previous studies are reviewed and the leading theories of passive/active transitions summarized. Comparisons are made to the active/passive transitions in pure Si, which are relatively well-understood. Critical questions remain about the difference between the active-to-passive transition and passive-to-active transition. For Si, Wagner [2] points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. This suggests a significant oxygen potential difference between these two transitions and our experiments confirm this. For Si, the initial stages of active oxidation are characterized by the formation of SiO(g) and further oxidation to SiO2(s) as micron-sized rods, with a distinctive morphology. SiC shows significant differences. The active-to-passive and the passive-to-active transitions are close. The SiO2 rods only appear as the passive film breaks down. These differences are explained in terms of the reactions at the SiC/SiO2 interface. In order to understand the breakdown of the passive film, pre-oxidation experiments are conducted. These involve forming dense protective scales of 0.5, 1, and 2 microns and then subjecting the samples with these scales to a known active oxidation environment. Microstructural studies show that SiC/SiO2 interfacial reactions lead to a breakdown of the scale with a distinct morphology.

  10. Laser Spectroscopy of Iridium Monochloride

    NASA Astrophysics Data System (ADS)

    Linton, Colan; Adam, Allan G.; Foran, Samantha; Ma, Tongmei; Steimle, Timothy

    2016-06-01

    Iridium monochloride (IrCl) molecules have been produced in the gas phase using laser ablation sources at the University of New Brunswick (UNB) and Arizona State University (ASU). Low resolution laser induced fluorescence (LIF) spectra, obtained at UNB using a pulsed dye laser, showed three bands at 557, 545 and 534 nm which appeared to form an upper state vibrational progression. Dispersed fluorescence (DF) spectra, obtained by exciting each band at its band head frequency, showed a ground state vibrational progression extending from v=0 to 6. High resolution spectra (FWHM=0.006 wn), taken using a cw ring dye laser, showed resolved rotational lines, broadened by unresolved Ir (I=3/2) hyperfine structure, in both the 193Ir35Cl and 191Ir35Cl isotopologues. Vibrational assignments of 0-0, 1-0 and 2-0 for the three bands were determined from the isotope structure and the rotational analysis showed the transition to be ^3Φ_4 - ^3Φ_4, similar to that previously observed in IrF. Higher resolution spectra (FWHM=0.001 wn) of the 1-0 band, obtained at ASU, showed resolved hyperfine structure from which the magnetic and quadrupole hyperfine parameters in the ground and excited states were determined. The interpretation of the hyperfine parameters in terms of the electron configurations will be presented along with a comparison of the properties of IrCl and IrF.

  11. Characterization of Iridium Coated Rhenium Used in High-Temperature, Radiation-Cooled Rocket Thrusters

    NASA Technical Reports Server (NTRS)

    Stulen, R. H.; Boehme, D. R.; Clift, W. M.; McCarty, K. F.

    1990-01-01

    Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high-temperatures and oxidizing environments. While combustion efficiency is optimized at high temperatures, many refractory metals are unsuitable for thruster applications due to rapid material loss from the formation of volatile oxides. This process occurs during thruster operation by reaction of the combustion products with the material surface. Aerojet Technical Systems has developed a thruster cone chamber constructed of Re coated with Ir on the inside surface where exposure to the rocket exhaust occurs. Re maintains its structural integrity at high temperature and the Ir coating is applied as an oxidation barrier. Ir also forms volatile oxide species (IrO2 and IrO3) but at a considerably slower rate than Re. In order to understand the performance limits of Ir-coated Re thrusters, we are investigating the interdiffusion and oxidation kinetics of Ir/Re. The formation of iridium and rhenium oxides has been monitored in situ by Raman spectroscopy during high temperature exposure to oxygen. For pure Ir, the growth of oxide films as thin as approximately 200 A could be easily detected and the formation of IrO2 was observed at temperatures as low as 600 C. Ir/Re diffusion test specimens were prepared by magnetron sputtering of Ir on Re substrates. Concentration profiles were determined by sputter Auger depth profiles of the heat treated specimens. Significant interdiffusion was observed at temperatures as low as 1000 C. Measurements of the activation energy suggest that below 1350 C, the dominant diffusion path is along defects, most likely grain boundaries, rather than bulk diffusion through the grains. The phases that form during interdiffusion have been examined by x ray diffraction. Analysis of heated test specimens indicates that the Ir-Re reaction produces a solid solution phase of Ir dissolved in the HCP structure of Re.

  12. Annealing Increases Stability Of Iridium Thermocouples

    NASA Technical Reports Server (NTRS)

    Germain, Edward F.; Daryabeigi, Kamran; Alderfer, David W.; Wright, Robert E.; Ahmed, Shaffiq

    1989-01-01

    Metallurgical studies carried out on samples of iridium versus iridium/40-percent rhodium thermocouples in condition received from manufacturer. Metallurgical studies included x-ray, macroscopic, resistance, and metallographic studies. Revealed large amount of internal stress caused by cold-working during manufacturing, and large number of segregations and inhomogeneities. Samples annealed in furnace at temperatures from 1,000 to 2,000 degree C for intervals up to 1 h to study effects of heat treatment. Wire annealed by this procedure found to be ductile.

  13. Inactivation of plasminogen activator inhibitor by oxidants

    SciTech Connect

    Lawrence, D.A.; Loskutoff, D.J.

    1986-10-21

    The rapidly acting plasminogen activator inhibitor (PAI) purified from cultured bovine endothelial cells (BAEs) was inactivated during iodination with chloramine T and other oxidizing iodination systems. Inactivation was observed in the absence of iodine, suggesting that the loss of activity resulted from the oxidizing conditions employed. In an attempt to further study the nature of this inactivation, the PAI was treated with chloramine T under conditions that specifically oxidize methionine and cystein residues. Both PAI inhibitory activity and the ability of the PAI to form complexes with tissue-type PA were decreased in a dose-dependent manner by such treatment. PAI activity was measured with the lysis of /sup 125/I-labelled fibrin. The reductase is a DTT-dependent enzyme that specifically converts methionine sulfoxide to methionine. Little activity was restored by either the reductase or DTT alone. These results indicate that the oxidation of at least one critical methionine residue is responsible for the loss of PAI activity upon iodination. In this respect, the BAE PAI resembles ..cap alpha../sub 1/-protease inhibitor, a well-characterized elastase inhibitor that also is inactivated by oxidants. Both inhibitors are members of the serine protease inhibitor superfamily (Serpins), and both have a methionine residue in their reactive center.

  14. The pro-oxidant activity of aluminum.

    PubMed

    Exley, Christopher

    2004-02-01

    Aluminum, a non-redox-active metal is, nevertheless, a pro-oxidant both in in vitro preparations and in vivo. It facilitates both superoxide- and iron-driven biological oxidation by mechanisms that remain to be resolved. More than 10 years ago Fridovich and colleagues suggested that the facilitation of superoxide-driven biological oxidation by aluminum was due to an interaction between the metal and the superoxide radical anion (Free Radic. Biol. Med. 13: 79-81; 1992). This thesis has been examined herein and it is concluded that much, if not all, of the pro-oxidant activity of aluminum might be explained by the formation of an aluminum superoxide semireduced radical ion.

  15. Iridium-Coated Rhenium Combustion Chamber

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.; Tuffias, Robert H.; Rosenberg, Sanders D.

    1994-01-01

    Iridium-coated rhenium combustion chamber withstands operating temperatures up to 2,200 degrees C. Chamber designed to replace older silicide-coated combustion chamber in small rocket engine. Modified versions of newer chamber could be designed for use on Earth in gas turbines, ramjets, and scramjets.

  16. The Active Oxidation of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers, Dwight L.

    2009-01-01

    The high temperature oxidation of silicon carbide occurs in two very different modes. Passive oxidation forms a protective oxide film which limits further attack of the SiC: SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g) Active oxidation forms a volatile oxide and may lead to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g) Generally passive oxidation occurs at higher oxidant pressures and active oxidation occurs at lower oxidant pressures and elevated temperatures. Active oxidation is a concern for reentry, where the flight trajectory involves the latter conditions. Thus the transition points and rates of active oxidation are a major concern. Passive/active transitions have been studied by a number of investigators. An examination of the literature indicates many questions remain regarding the effect of impurity, the hysteresis of the transition (i.e. the difference between active-to-passive and passive-toactive), and the effect of total pressure. In this study we systematically investigate each of these effects. Experiments were done in both an alumina furnace tube and a quartz furnace tube. It is known that alumina tubes release impurities such as sodium and increase the kinetics in the passive region [1]. We have observed that the active-to-passive transition occurs at a lower oxygen pressure when the experiment is conducted in alumina tubes and the resultant passive silica scale contains sodium. Thus the tests in this study are conducted in quartz tubes. The hysteresis of the transition has been discussed in the detail in the original theoretical treatise of this problem for pure silicon by Wagner [2], yet there is little mention of it in subsequent literature. Essentially Wagner points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. A series of experiments were conducted for active-to-passive and passive-to-active

  17. Process for preparing active oxide powders

    DOEpatents

    Berard, Michael F.; Hunter, Jr., Orville; Shiers, Loren E.; Dole, Stephen L.; Scheidecker, Ralph W.

    1979-02-20

    An improved process for preparing active oxide powders in which cation hydroxide gels, prepared in the conventional manner are chemically dried by alternately washing the gels with a liquid organic compound having polar characteristics and a liquid organic compound having nonpolar characteristics until the mechanical water is removed from the gel. The water-free cation hydroxide is then contacted with a final liquid organic wash to remove the previous organic wash and speed drying. The dried hydroxide treated in the conventional manner will form a highly sinterable active oxide powder.

  18. [Atherosclerosis, oxidative stress and physical activity. Review].

    PubMed

    Calderón, Juan Camilo; Fernández, Ana Zita; María de Jesús, Alina Isabel

    2008-09-01

    Atherosclerosis and related diseases have emerged as the leading cause of morbidity and mortality in the western world and, therefore, as a problem of public health. Free radicals and reactive oxygen species have been suggested to be part of the pathophysiology of these diseases. It is well known that physical activity plays an important role as a public health measure by reducing the risk of developing atherosclerosis-related cardiovascular events in the general population. It is also known that physical activity increases in some tissues, the reactive oxygen species production. In this review the atherosclerosis-oxidative stress-physical activity relationship is focused on the apparent paradox by which physical activity reduces atherosclerosis and cardiovascular risk in parallel with the activation of an apparently damaging mechanism which is an increased oxidative stress. A hypothesis including the experimental and clinical evidence is presented to explain the aforementioned paradox.

  19. Diastereo- and Enantioselective Iridium Catalyzed Carbonyl (α-Cyclopropyl)allylation via Transfer Hydrogenation.

    PubMed

    Tsutsumi, Ryosuke; Hong, Suckchang; Krische, Michael J

    2015-09-07

    The first examples of diastereo- and enantioselective carbonyl α-(cyclopropyl)allylation are reported. Under the conditions of iridium catalyzed transfer hydrogenation using the chiral precatalyst (R)-Ir-I modified by SEGPHOS, carbonyl α-(cyclopropyl)allylation may be achieved with equal facility from alcohol or aldehyde oxidation levels. This methodology provides a conduit to hitherto inaccessible inaccessible enantiomerically enriched cyclopropane-containing architectures.

  20. Chlorido-containing ruthenium(II) and iridium(III) complexes as antimicrobial agents.

    PubMed

    Pandrala, Mallesh; Li, Fangfei; Feterl, Marshall; Mulyana, Yanyan; Warner, Jeffrey M; Wallace, Lynne; Keene, F Richard; Collins, J Grant

    2013-04-07

    A series of polypyridyl-ruthenium(II) and -iridium(III) complexes that contain labile chlorido ligands, [{M(tpy)Cl}(2){μ-bb(n)}](2/4+) {Cl-Mbb(n); where M = Ru or Ir; tpy = 2,2':6',2''-terpyridine; and bb(n) = bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane (n = 7, 12 or 16)} have been synthesised and their potential as antimicrobial agents examined. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of the series of metal complexes against four strains of bacteria - Gram positive Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), and Gram negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) - have been determined. All the ruthenium complexes were highly active and bactericidal. In particular, the Cl-Rubb(12) complex showed excellent activity against all bacterial cell lines with MIC values of 1 μg mL(-1) against the Gram positive bacteria and 2 and 8 μg mL(-1) against E. coli and P. aeruginosa, respectively. The corresponding iridium(III) complexes also showed significant antimicrobial activity in terms of MIC values; however and surprisingly, the iridium complexes were bacteriostatic rather than bactericidal. The inert iridium(III) complex, [{Ir(phen)(2)}(2){μ-bb(12)}](6+) {where phen = 1,10-phenanthroline) exhibited no antimicrobial activity, suggesting that it could not cross the bacterial membrane. The mononuclear model complex, [Ir(tpy)(Me(2)bpy)Cl]Cl(2) (where Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine), was found to aquate very rapidly, with the pK(a) of the iridium-bound water in the corresponding aqua complex determined to be 6.0. This suggests the dinuclear complexes [Ir(tpy)Cl}(2){μ-bb(n)}](4+) aquate and deprotonate rapidly and enter the bacterial cells as 4+ charged hydroxo species.

  1. Application of the Iridium Satellite System to Aeronautical Communications

    NASA Technical Reports Server (NTRS)

    Kerczewski, Robert J.; Meza, Mike; Gupta, Om

    2008-01-01

    The next generation air transportation system will require greater air-ground communications capacity to accommodate more air traffic with increased safety and efficiency. Communications will remain primarily terrestrially based, but satellite communications will have an increased role. Inmarsat s aeronautical services have been approved and are in use for aeronautical safety communications provided by geostationary satellites. More recently the approval process for the Iridium low earth orbit constellation is nearing completion. The current Iridium system will be able to provide basic air traffic services communications suitable for oceanic, remote and polar regions. The planned second generation of the Iridium system, called Iridium NEXT, will provide enhanced capabilities and enable a greater role in the future of aeronautical communications. This paper will review the potential role of satellite communications in the future of air transportation, the Iridium approval process and relevant system testing, and the potential role of Iridium NEXT.

  2. Analysis and Consequences of the Iridium 33-Cosmos 2251 Collision

    NASA Technical Reports Server (NTRS)

    Anz-Meador, P. D.; Liou, Jer-Chi

    2010-01-01

    The collision of Iridium 33 and Cosmos 2251, on 10 February 2009, was the first known unintentional hypervelocity collision in space of intact satellites. Iridium 33 was an active commercial telecommunications satellite, while Cosmos 2251 was a derelict communication satellite of the Strela-2M class. The collision occurred at a relative velocity of 11.6 km/s at an altitude of approximately 790 km over the Great Siberian Plain and near the northern apex of Cosmos 2251 s orbit. This paper describes the physical and orbital characteristics of the relevant spacecraft classes and reports upon our analysis of the resulting debris clouds size, mass, area-to-mass ratio, and relative velocity/directionality distributions. We compare these distributions to those predicted by the NASA breakup model and notable recent fragmentation events; in particular, we compare the area-to-mass ratio distribution for each spacecraft to that exhibited by the FY-1C debris cloud for the purpose of assessing the relative contribution of modern aerospace materials to debris clouds resulting from energetic collisions. In addition, we examine the long-term consequences of this event for the low Earth orbit (LEO) environment. Finally, we discuss "lessons learned", which may be incorporated into NASA s environmental models.

  3. Iridium anomaly in the Cretaceous section of the Eastern Kamchatka

    NASA Astrophysics Data System (ADS)

    Savelyev, Dmitry; Savelyeva, Olga

    2010-05-01

    The origin of iridium anomalies is widely discussed with regard to massive fauna and flora extinction at several geologic boundaries. Two hypotheses are most popular, cosmogenic and volcanogenic. Anomalies of iridium are known at many stratigraphic levels, both at the geologic series borders and within geologic series. Our studies revealed increased content of iridium in a section of Cretaceous oceanic deposits on the Kamchatsky Mys Peninsula (Eastern Kamchatka, Russia). The investigated section (56°03.353´N, 163°00.376´E) includes interbedded jaspers and siliceous limestones overlaying pillow-basalts. These deposits belong to the Smagin Formation of the Albian-Cenomanian age. In the middle and upper parts of the section two beds of black carbonaceous rocks with sapropelic organic matter were observed. Their formation marked likely episodes of oxygen depletion of oceanic intermediate water (oceanic anoxic events). Our geochemical studies revealed an enrichment of the carbonaceous beds in a number of major and trace elements (Al2O3, TiO2, FeO, MgO, K2O, P2O5, Cu, Zn, Ni, Cr, V, Mo, Ba, Y, Zr, Nb, REE, U, Au, Pt etc.) in comparison with associating jaspers and limestones. There are likely different sources which contributed to the enrichment. It is possible however to correlate the excess of Al, Ti, Zr, Nb with volcanogenic admixture, which is absent in limestones and jaspers. A possible source of the volcanogenic material was local volcanism as suggested by the close association of the investigated section with volcanic rocks (basaltic lavas and hyaloclastites). The basalts of the Smagin Formation were previously proposed to originate during Cretaceous activity of the Hawaiian mantle plume (Portnyagin et al., Geology, 2008). Neutron activation analysis indicated increased up to 9 ppb concentration of Ir at the bottom of the lower carbonaceous bed (inorganic part of the sample was analyzed comprising 46% of the bulk rock). In other samples Ir content was below

  4. Iridium and Radio Astronomy in Europe

    NASA Astrophysics Data System (ADS)

    Cohen, R. J.

    2004-06-01

    An account is given of the coordination of the Iridium mobile satellite system with the radio astronomy service in Europe, from the initial exploratory discussions at Jodrell Bank in 1991 to the signing of the so-called ``Interim Agreement'' in Paris in 1999. The technical issue of unwanted emissions from the Iridium downlink into the frequency band 1610.6-1613.8 MHz was not resolved, so the coordination agreement amounts to time sharing, albeit on more favourable terms for radio astronomy than agreements negotiated elsewhere. The European agreement fully recognizes the heavy use of the frequency band in European radio astronomy, and carries the promise that ``from 1 January 2006, European radioastronomers shall be able to collect measurement data consistent with the recommendation ITU-R RA.769-1.'' Some personal observations on the events are offered.

  5. The Chemical Vapor Deposition of Iridium.

    DTIC Science & Technology

    1981-07-01

    accepted types are made of porous tungsten impregnated with barium calcium aluminates (Levi, 1955; Brodie and Jenkins, 1956). The emission capability of the...not only does the chemical composition of the pore ends and the bulk material undergo alteration, but the crystal structure of the tungsten (Maloney... hexafluoride to iridium metal or IrF 6 species. In our work, IrF 6 was prepared and stored in fluorine-passivated apparatus, and between runs maintained at

  6. Benzo annulated cycloheptatriene PCP pincer iridium complexes.

    PubMed

    Leis, Wolfgang; Wernitz, Sophie; Reichart, Benedikt; Ruckerbauer, David; Wielandt, Johannes Wolfram; Mayer, Hermann A

    2014-08-28

    The benzo annulated cycloheptatriene PCP pincer ligand was prepared in five steps. Treatment of with Ir(CO)3Cl gave the meridional cyclometalated chlorohydrido carbonyl iridium complexes which differ in their arrangement of the H, Cl, and CO ligands around iridium. Storing in THF led to isomerization processes. Hydrogen shifts from the sp(3)-CH carbon bound to iridium into the ligand backbone produced the three isomers . Reductive elimination of HCl from these complexes resulted in the square planar Ir(i) carbonyl complexes . Abstraction of the hydrogen from the sp(3)-CH-Ir fragment could be achieved either by treatment of with Ph3CBF4 or by the elimination of H2 which is initiated by CF3SO3H. The mass spectrometric characterisation of using fast atom bombardment reveals a complex fragmentation pattern. These different "fragment" ions were further investigated by electro-spray ionisation (tandem) mass spectrometry in high and low resolution. The identified compounds were attributed to structures by DFT calculations.

  7. Green Phosphorescence and Electroluminescence of Sulfur Pentafluoride-Functionalized Cationic Iridium(III) Complexes.

    PubMed

    Shavaleev, Nail M; Xie, Guohua; Varghese, Shinto; Cordes, David B; Slawin, Alexandra M Z; Momblona, Cristina; Ortí, Enrique; Bolink, Henk J; Samuel, Ifor D W; Zysman-Colman, Eli

    2015-06-15

    We report on four cationic iridium(III) complexes [Ir(C^N)2(dtBubpy)](PF6) that have sulfur pentafluoride-modified 1-phenylpyrazole and 2-phenylpyridine cyclometalating (C^N) ligands (dtBubpy = 4,4'-di-tert-butyl-2,2'-bipyridyl). Three of the complexes were characterized by single-crystal X-ray structure analysis. In cyclic voltammetry, the complexes undergo reversible oxidation of iridium(III) and irreversible reduction of the SF5 group. They emit bright green phosphorescence in acetonitrile solution and in thin films at room temperature, with emission maxima in the range of 482-519 nm and photoluminescence quantum yields of up to 79%. The electron-withdrawing sulfur pentafluoride group on the cyclometalating ligands increases the oxidation potential and the redox gap and blue-shifts the phosphorescence of the iridium complexes more so than the commonly employed fluoro and trifluoromethyl groups. The irreversible reduction of the SF5 group may be a problem in organic electronics; for example, the complexes do not exhibit electroluminescence in light-emitting electrochemical cells (LEECs). Nevertheless, the complexes exhibit green to yellow-green electroluminescence in doped multilayer organic light-emitting diodes (OLEDs) with emission maxima ranging from 501 nm to 520 nm and with an external quantum efficiency (EQE) of up to 1.7% in solution-processed devices.

  8. Iridium Cyclooctene Complex That Forms a Hyperpolarization Transfer Catalyst before Converting to a Binuclear C–H Bond Activation Product Responsible for Hydrogen Isotope Exchange

    PubMed Central

    2016-01-01

    [IrCl(COE)2]2 (1) reacts with pyridine (py) and H2 to form crystallographically characterized IrCl(H)2(COE)(py)2 (2). 2 undergoes py loss to form 16-electron IrCl(H)2(COE)(py) (3), with equivalent hydride ligands. When this reaction is studied with parahydrogen, 1 efficiently achieves hyperpolarization of free py (and nicotinamide, nicotine, 5-aminopyrimidine, and 3,5-lutudine) via signal amplification by reversible exchange (SABRE) and hence reflects a simple and readily available precatayst for this process. 2 reacts further over 48 h at 298 K to form crystallographically characterized (Cl)(H)(py)(μ-Cl)(μ-H)(κ-μ-NC5H4)Ir(H)(py)2 (4). This dimer is active in the hydrogen isotope exchange process that is used in radiopharmaceutical preparations. Furthermore, while [Ir(H)2(COE)(py)3]PF6 (6) forms upon the addition of AgPF6 to 2, its stability precludes its efficient involvement in SABRE. PMID:27934314

  9. Electrochemical detection of arsenic(III) using iridium-implanted boron-doped diamond electrodes.

    PubMed

    Ivandini, Tribidasari A; Sato, Rika; Makide, Yoshihiro; Fujishima, Akira; Einaga, Yasuaki

    2006-09-15

    Iridium-modified, boron-doped diamond electrodes fabricated by an ion implantation method have been developed for electrochemical detection of arsenite (As(III)). Ir+ ions were implanted with an energy of 800 keV and a dose of 10(15) ion cm(-2). An annealing treatment at 850 degrees C for 45 min in H2 plasma (80 Torr) was required to rearrange metastable diamond produced by an implantation process. Characterization was investigated by SEM, AFM, Raman, and X-ray photoelectron spectroscopy. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. The electrodes exhibited high catalytic activity toward As(III) oxidation with the detection limit (S/N = 3), sensitivity, and linearity of 20 nM (1.5 ppb), 93 nA microM(-1) cm(-2), and 0.999, respectively. The precision for 10 replicate determinations of 50 microM As(III) was 4.56% relative standard deviation. The advantageous properties of the electrodes were its inherent stability with a very low background current. The electrode was applicable for analysis of spiked arsenic in tap water containing a significant amount of various ion elements. The results indicate that the metal-implanted method could be promising for controlling the electrochemical properties of diamond electrodes.

  10. Variation of iridium in a differentiated tholeiitic dolerite

    USGS Publications Warehouse

    Greenland, L.P.

    1971-01-01

    Iridium has been determined in a drill core from the Great Lake (Tasmania) dolerite sheet. Iridium decreases systematically from the mafic dolerites (0.25 ppb) to the granophyres (0.006 ppb). The trend with differentiation closely parallels that of chromium. ?? 1971.

  11. Bactericidal activity of partially oxidized nanodiamonds.

    PubMed

    Wehling, Julia; Dringen, Ralf; Zare, Richard N; Maas, Michael; Rezwan, Kurosch

    2014-06-24

    Nanodiamonds are a class of carbon-based nanoparticles that are rapidly gaining attention, particularly for biomedical applications, i.e., as drug carriers, for bioimaging, or as implant coatings. Nanodiamonds have generally been considered biocompatible with a broad variety of eukaryotic cells. We show that, depending on their surface composition, nanodiamonds kill Gram-positive and -negative bacteria rapidly and efficiently. We investigated six different types of nanodiamonds exhibiting diverse oxygen-containing surface groups that were created using standard pretreatment methods for forming nanodiamond dispersions. Our experiments suggest that the antibacterial activity of nanodiamond is linked to the presence of partially oxidized and negatively charged surfaces, specifically those containing acid anhydride groups. Furthermore, proteins were found to control the bactericidal properties of nanodiamonds by covering these surface groups, which explains the previously reported biocompatibility of nanodiamonds. Our findings describe the discovery of an exciting property of partially oxidized nanodiamonds as a potent antibacterial agent.

  12. Iridium enrichment in airborne particles from kilauea volcano: january 1983.

    PubMed

    Zoller, W H; Parrington, J R; Kotra, J M

    1983-12-09

    Airborne particulate matter from the January 1983 eruption of Kilauea volcano was inadvertently collected on air filters at Mauna Loa Observatory at a sampling station used to observe particles in global circulation. Analyses of affected samples revealed unusually large concentrations of selenium, arsenic, indium, gold, and sulfur, as expected for volcanic emissions. Strikingly large concentrations of iridium were also observed, the ratio of iridium to aluminum being 17,000 times its value in Hawaiian basalt. Since iridium enrichments have not previously been observed in volcanic emissions, the results for Kilauea suggest that it is part of an unusual volcanic system which may be fed by magma from the mantle. The iridium enrichment appears to be linked with the high fluorine content of the volcanic gases, which suggests that the iridium is released as a volatile IrF(6).

  13. Particulate oxidative burden associated with firework activity.

    PubMed

    Godri, Krystal J; Green, David C; Fuller, Gary W; Dall'Osto, Manuel; Beddows, David C; Kelly, Frank J; Harrison, Roy M; Mudway, Ian S

    2010-11-01

    Firework events are capable of inducing particulate matter (PM) episodes that lead to exceedances of regulatory limit values. As short-term peaks in ambient PM concentration have been associated with negative impacts on respiratory and cardiovascular health, we performed a detailed study of the consequences of firework events in London on ambient air quality and PM composition. These changes were further related to the oxidative activity of daily PM samples by assessing their capacity to drive the oxidation of physiologically important lung antioxidants including ascorbate, glutathione and urate (oxidative potential, OP). Twenty-four hour ambient PM samples were collected at the Marylebone Road sampling site in Central London over a three week period, including two major festivals celebrated with pyrotechnic events: Guy Fawkes Night and Diwali. Pyrotechnic combustion events were characterized by increased gas phase pollutants levels (NO(x) and SO(2)), elevated PM mass concentrations, and trace metal concentrations (specifically Sr, Mg, K, Ba, and Pb). Relationships between NO(x), benzene, and PM(10) were used to apportion firework and traffic source fractions. A positive significant relationship was found between PM oxidative burden and individual trace metals associated with each of these apportioned source fractions. The level of exposure to each source fraction was significantly associated with the total OP. The firework contribution to PM total OP, on a unit mass basis, was greater than that associated with traffic sources: a 1 μg elevation in firework and traffic PM fraction concentration was associated with a 6.5 ± 1.5 OP(T) μg(-1) and 5.2 ± 1.4 OP(T) μg(-1) increase, respectively. In the case of glutathione depletion, firework particulate OP (3.5 ± 0.8 OP(GSH) μg(-1)) considerably exceeded that due to traffic particles (2.2 ± 0.8 OP(GSH) μg(-1)). Therefore, in light of the elevated PM concentrations caused by firework activity and the increased

  14. Synthesis of 2-pyridyl-benzimidazole iridium(III), ruthenium(II), and platinum(II) complexes. study of the activity as inhibitors of amyloid-β aggregation and neurotoxicity evaluation.

    PubMed

    Yellol, Gorakh S; Yellol, Jyoti G; Kenche, Vijaya B; Liu, Xiang Ming; Barnham, Kevin J; Donaire, Antonio; Janiak, Christoph; Ruiz, José

    2015-01-20

    The design of small molecules that can target the aggregation of Aβ as potential therapeutic agents for Alzheimer's disease is an area of study that has attracted a lot of attention recently. The novel ligand methyl 1-butyl-2-pyridyl-benzimidazole carboxylate was prepared for the synthesis of a series of new iridium(III), ruthenium(II), and platinum(II) 2-pyridyl-benzimidazole complexes. The crystal structure of the half-sandwich iridium(III) complex was established by X-ray diffraction. An arrangement of two cationic complexes in the unit cell is observed, and it seems to be organized by weak π···π interactions that are taking place between two symmetry-related benzimidazole ring systems. All new compounds inhibited aggregation of Aβ1-42 in vitro as shown by both thioflavin T fluorescence assay and transmission electron microscopy. Among them the Ir compound rescued the toxicity of Aβ1-42 in primary cortical neurons effectively.

  15. Iridium Interfacial Stack - IrIS

    NASA Technical Reports Server (NTRS)

    Spry, David

    2012-01-01

    Iridium Interfacial Stack (IrIS) is the sputter deposition of high-purity tantalum silicide (TaSi2-400 nm)/platinum (Pt-200 nm)/iridium (Ir-200 nm)/platinum (Pt-200 nm) in an ultra-high vacuum system followed by a 600 C anneal in nitrogen for 30 minutes. IrIS simultaneously acts as both a bond metal and a diffusion barrier. This bondable metallization that also acts as a diffusion barrier can prevent oxygen from air and gold from the wire-bond from infiltrating silicon carbide (SiC) monolithically integrated circuits (ICs) operating above 500 C in air for over 1,000 hours. This TaSi2/Pt/Ir/Pt metallization is easily bonded for electrical connection to off-chip circuitry and does not require extra anneals or masking steps. There are two ways that IrIS can be used in SiC ICs for applications above 500 C: it can be put directly on a SiC ohmic contact metal, such as Ti, or be used as a bond metal residing on top of an interconnect metal. For simplicity, only the use as a bond metal is discussed. The layer thickness ratio of TaSi2 to the first Pt layer deposited thereon should be 2:1. This will allow Si from the TaSi2 to react with the Pt to form Pt2Si during the 600 C anneal carried out after all layers have been deposited. The Ir layer does not readily form a silicide at 600 C, and thereby prevents the Si from migrating into the top-most Pt layer during future anneals and high-temperature IC operation. The second (i.e., top-most) deposited Pt layer needs to be about 200 nm to enable easy wire bonding. The thickness of 200 nm for Ir was chosen for initial experiments; further optimization of the Ir layer thickness may be possible via further experimentation. Ir itself is not easily wire-bonded because of its hardness and much higher melting point than Pt. Below the iridium layer, the TaSi2 and Pt react and form desired Pt2Si during the post-deposition anneal while above the iridium layer remains pure Pt as desired to facilitate easy and strong wire-bonding to the Si

  16. Iridium Film For Charge-Coupled Device

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.

    1990-01-01

    Usability extended to different environments. Application of thin film of iridium to back surface of back-surface-illuminated charge-coupled device expected to increase and stabilize quantum efficiency at wavelengths less than 4,500 Angstrom. Enhances quantum efficiency according to principle discussed in "Metal Film Increases CCD Output" (NPO-16815). Does not react with hydrogen, so device need not be kept in oxygen: Advantage where high absorption of ultraviolet light by oxygen undesirable; for example, when device used to make astronomical observations from high altitudes.

  17. Catalytic Transfer of Magnetism using a Neutral Iridium Phenoxide Complex

    PubMed Central

    Ruddlesden, Amy J.; Mewis, Ryan E.; Green, Gary G. R.; Whitwood, Adrian C.; Duckett, Simon B.

    2016-01-01

    A novel neutral iridium carbene complex Ir(κC,O-L1)(COD) (1) [where COD = cyclooctadiene and L1 = 3-(2-methylene-4-nitrophenolate)-1-(2,4,6-trimethylphenyl) imidazolylidene] with a pendant alkoxide ligand has been prepared and characterized. It contains a strong Ir-O bond and X-ray analysis reveals a distorted square planar structure. NMR spectroscopy reveals dynamic solution state behavior commensurate with rapid seven-membered ring flipping. In CD2Cl2 solution, under hydrogen at low temperature, this complex dominates although it exists in equilibrium with a reactive iridium dihydride cyclooctadiene complex. 1 reacts with pyridine and H2 to form neutral Ir(H)2(κC,O-L1)(py)2 which also exists in two conformers that differ according to the orientation of the seven-membered metallocycle and whilst its Ir-O bond remains intact, the complex undergoes both pyridine and H2 exchange. As a consequence, when placed under parahydrogen, efficient polarization transfer catalysis (PTC) is observed via the Signal Amplification By Reversible Exchange (SABRE) approach. Due to the neutral character of this catalyst, good hyperpolarization activity is shown in a wide range of solvents for a number of substrates. These observations reflect a dramatic improvement in solvent tolerance of SABRE over that reported for the best PTC precursor IrCl(IMes)(COD). For THF, the associated 1H NMR signal enhancement for the ortho proton signal of pyridine shows an increase of 600-fold at 298 K. The level of signal enhancement can be increased further through warming or varying the magnetic field experienced by the sample at the point of catalytic magnetization transfer.

  18. REPEATED REDUCTIVE AND OXIDATIVE TREATMENTS ON GRANULAR ACTIVATED CARBON

    EPA Science Inventory

    Fenton oxidation and Fenton oxidation preceded by reduction solutions were applied to granular activated carbon (GAC) to chemically regenerate the adsorbent. No adsorbate was present on the GAC so physicochemical effects from chemically aggressive regeneration of the carbon coul...

  19. An Analysis of the FY-1C, Iridium 33, and Cosmos 2251 Fragments

    NASA Technical Reports Server (NTRS)

    Liou, J.-C.

    2014-01-01

    The beginning of the year 2013 marks the sixth anniversary of the destruction of the Fengyun-1C (FY-1C) weather satellite as the result of an anti-satellite test conducted by China in January 2007 and the fourth anniversary of the accidental collision between Cosmos 2251 and the operational Iridium 33 in February 2009. These two events represent the worst satellite breakups in history. A total of 5579 fragments have been cataloged by the U.S. Space Surveillance Network (SSN), and almost 5000 of them were still in orbit in January 2013. In addition to these cataloged objects, hundreds of thousands (or more) of fragments down to the millimeter size regime were also generated during the breakups. These fragments are too small to be tracked by the SSN, but are large enough to be a safety concern for human space activities and robotic missions in low Earth orbit (LEO, the region below 2000 km altitude). Like their cataloged siblings, many of them remain in orbit today. These two breakup events dramatically changed the landscape of the orbital debris environment in LEO. The spatial density of the cataloged population in January 2013 is shown as the top blue curve. The combined FY-1C, Iridium 33, and Cosmos 2251 fragments (black curve) account for about 50 percent of the cataloged population below an altitude of 1000 km. They are also responsible for the concentrations at 770 km and 850 km, altitudes at which the collisions occurred. The effects of the FY-1C, Iridium 33, and Cosmos 2251 fragments will continue to be felt for decades to come. For example, approximately half of the generated FY-1C fragments will remain in orbit 20 years from now. In general, the Iridium 33 and Cosmos 2251 fragments will decay faster than the FY-1C fragments because of their lower altitudes. Of the Iridium 33 and Cosmos 2251 fragments, the former have much shorter orbital lifetimes than the latter, because lightweight composite materials were heavily used in the construction of the Iridium

  20. Diminiode thermionic conversion with 111-iridium electrodes

    NASA Technical Reports Server (NTRS)

    Koeger, E. W.; Bair, V. L.; Morris, J. F.

    1976-01-01

    Preliminary data indicating thermionic-conversion potentialities for a 111-iridium emitter and collector spaced 0.2 mm apart are presented. These results comprise output densities of current and of power as functions of voltage for three sets of emitter, collector, and reservoir temperatures: 1553, 944, 561 K; 1605, 898, 533 K; and 1656, 1028, 586 K. For the 1605 K evaluation, estimates produced work-function values of 2.22 eV for the emitter and 1.63 eV for the collector with a 2.0-eV barrier index (collector work function plus interelectrode voltage drop) corresponding to the maximum output of 5.5 W/sq cm at 0.24 volt. The current, voltage curve for the 1656 K 111-iridium diminiode yields a 6.2 W/sq cm maximum at 0.25 volt and is comparable with the 1700 K envelope for a diode with an etched-rhenium emitter and a 0.025-mm electrode gap made by TECO and evaluated by NASA.

  1. Ab initio phase diagram of iridium

    NASA Astrophysics Data System (ADS)

    Burakovsky, L.; Burakovsky, N.; Cawkwell, M. J.; Preston, D. L.; Errandonea, D.; Simak, S. I.

    2016-09-01

    The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z method, the solid phases along the melting curve are determined by comparing the solid-liquid equilibrium boundaries of candidate crystal structures. The inverse Z method involves quenching the liquid into the most stable solid phase at various temperatures and pressures to locate a solid-solid boundary. Although excellent agreement with the available experimental data (to ≲65 GPa) is found for the equation of state (EOS) of Ir, it is the third-order Birch-Murnaghan EOS with B0'=5 rather than the more widely accepted B0'=4 that describes our ab initio data to higher pressure (P ) . Our results suggest the existence of a random-stacking hexagonal close-packed structure of iridium at high P . We offer an explanation for the 14-layer hexagonal structure observed in experiments by Cerenius and Dubrovinsky.

  2. Iridium-catalyzed H/D exchange: ligand complexes with improved efficiency and scope.

    PubMed

    Parmentier, Michael; Hartung, Thomas; Pfaltz, Andreas; Muri, Dieter

    2014-09-01

    Hydrogen isotope exchange (HIE) is one of the most attractive tools for the introduction of deuterium or tritium to an organic compound. Herein, iridium complexes with N,P-ligands, highly active catalysts for asymmetric double bond reductions, have been tested for their HIE capabilities. Electron-rich ligands, containing dicyclohexylphosphines or phosphinites, have been identified as excellent ligands for efficient deuterium incorporation. Substrates with strong directing groups, that is, pyridines, ketones, and amides, as well as weak ligating units, such as, nitro, sulfones, and sulfonamides, could be labeled efficiently. With the addition of tris(pentafluorophenyl) borane to the reaction mixture, also highly deactivating nitrile substituents were well tolerated in the reaction. Based on the excellent results obtained with the chiral ThrePhox ligand, a structurally simpler, achiral ligand was developed. The iridium complex containing this ligand, proved to be a powerful catalyst for HIE reactions.

  3. Superconductivity in Ca10(Ir4As8)(Fe2As2)5 with Square-Planar Coordination of Iridium

    PubMed Central

    Kudo, Kazutaka; Mitsuoka, Daisuke; Takasuga, Masaya; Sugiyama, Yuki; Sugawara, Kento; Katayama, Naoyuki; Sawa, Hiroshi; Kubo, Hiroaki S.; Takamori, Kenta; Ichioka, Masanori; Fujii, Tatsuo; Mizokawa, Takashi; Nohara, Minoru

    2013-01-01

    We report the unprecedented square-planar coordination of iridium in the iron iridium arsenide Ca10(Ir4As8)(Fe2As2)5. This material experiences superconductivity at 16 K. X-ray photoemission spectroscopy and first-principles band calculation suggest Ir(II) oxidation state, which yields electrically conductive Ir4As8 layers. Such metallic spacer layers are thought to enhance the interlayer coupling of Fe2As2, in which superconductivity emerges, thus offering a way to control the superconducting transition temperature. PMID:24173038

  4. Monoalkylation of acetonitrile by primary alcohols catalyzed by iridium complexes.

    PubMed

    Anxionnat, Bruno; Pardo, Domingo Gomez; Ricci, Gino; Cossy, Janine

    2011-08-05

    The monoalkylation of acetonitrile by primary alcohols was achieved in a one-pot sequence in the presence of iridium catalysts. A diversity of nitriles has been obtained from aryl- and alkyl-methanols in excellent yield.

  5. Acute radiodermatitis from occupational exposure to iridium 192

    SciTech Connect

    Becker, J.; Rosen, T. )

    1989-12-01

    Industrial radiography using the man-made radioisotope iridium 192 is commonplace in the southern states. Despite established procedures and safeguards, accidental exposure may result in typical acute radiodermatitis. We have presented a clinical example of this phenomenon.9 references.

  6. Enhanced gastric nitric oxide synthase activity in duodenal ulcer patients.

    PubMed Central

    Rachmilewitz, D; Karmeli, F; Eliakim, R; Stalnikowicz, R; Ackerman, Z; Amir, G; Stamler, J S

    1994-01-01

    Nitric oxide, the product of nitric oxide synthase in inflammatory cells, may have a role in tissue injury through its oxidative metabolism. Nitric oxide may have a role in the pathogenesis of duodenal ulcer and may be one of the mechanisms responsible for the association between gastric infection with Helicobacter pylori and peptic disease. In this study, calcium independent nitric oxide synthase activity was detected in human gastric mucosa suggesting expression of the inducible isoform. In 17 duodenal ulcer patients gastric antral and fundic nitric oxide synthase activity was found to be two and 1.5-fold respectively higher than its activity in the antrum and fundus of 14 normal subjects (p < 0.05). H pylori was detected in the antrum of 15 of 17 duodenal ulcer patients and only in 7 of 14 of the control subjects. Antral nitric oxide synthase activity in H pylori positive duodenal ulcer patients was twofold higher than in H pylori positive normal subjects (p < 0.05). In duodenal ulcer patients antral and fundic nitric oxide synthase activity resumed normal values after induction of ulcer healing with ranitidine. Eradication of H pylori did not further affect gastric nitric oxide synthase activity. These findings suggest that in duodenal ulcer patients stimulated gastric mucosal nitric oxide synthase activity, though independent of the H pylori state, may contribute to the pathogenesis of the disease. PMID:7525417

  7. GPS/GNSS Interference from Iridium Data Transmitters

    NASA Astrophysics Data System (ADS)

    Berglund, H. T.; Blume, F.; Estey, L.; White, S.

    2011-12-01

    The Iridium satellite communication system broadcasts in the 1610 to 1626.5 MHz band. The L1 frequencies broadcast by GPS, Galileo and GLONASS satellites are 1575.42 MHz, 1575.42 MHz and 1602 MHz + n × 0.5625 MHz, respectively (each GLONASS satellite uses a unique frequency). The proximity of the Iridium frequency band with the L1 frequencies of the GPS, Galileo and GLONASS systems leaves GNSS receivers susceptible to interference from Iridium data transmissions. Interference from Iridium transmissions can cause cycle slips and loss of lock on the carrier and code phases, thereby degrading the quality of GNSS observations and position estimates. In 2008, UNAVCO staff members observed that the percent of slips vs. the number of observations increased as the distance between a GPS choke ring antenna (TRM29659.00) and an Iridium antenna decreased. From those observations they suggested that Iridium antennas and GPS antennas should be separated by >30 m to minimize cycle slips caused by the interference from Iridium data transmissions. A second test conducted in 2009 using a newer Trimble GNSS choke ring antenna (TRM59800.00) showed similar results to the previous test despite the wider frequency range of the newer antenna. More recent testing conducted to investigate the response of new receiver models to iridium transmissions has shown that many GNSS enabled models, when combined with GNSS enabled antennas, have increased sensitivity to interference when compared to older GPS-only models. The broader frequency spectrum of the Low Noise Amplifiers (LNA) installed in many newer GNSS antennas can increase the impact of near-band RF interference on tracking performance. Our testing has shown that the quality of data collected at sites collocated with iridium communications is highly degraded for antenna separations exceeding 100m. Using older GPS antenna models (e.g. TRM29659.00) with newer GNSS enabled receivers can reduce this effect. To mitigate the effects that

  8. Methane activation and oxidation in sulfuric acid.

    PubMed

    Goeppert, Alain; Dinér, Peter; Ahlberg, Per; Sommer, Jean

    2002-07-15

    The H/D exchange observed when methane is contacted with D(2)SO(4) at 270-330 degrees C shows that the alkane behaves as a sigma base and undergoes rapid and reversible protonation at this temperature. DFT studies of the hydrogen exchange between a monomer and a dimer of sulfuric acid and methane show that the transition states involved in the exchange are bifunctional, that is one hydrogen atom is transferred from a hydroxy group in sulfuric acid to methane, while one hydrogen atom is abstracted from methane by a non-hydroxy oxygen atom in sulfuric acid. All the transition states include a CH(5) moiety, which shows similarities to the methanium ion CH(5) (+). The calculated potential activation energy of the hydrogen exchange for the monomer is 174 kJ mol(-1), which is close to the experimental value (176 kJ mol(-1)). Solvation of the monomer and the transition state of the monomer with an extra sulfuric acid molecule, decrease the potential activation energy by 6 kJ mol(-1). The acid-base process is in competition, however, with an oxidative process involving methane and sulfuric acid which leads to CO(2), SO(2), and water, and thus to a decrease of acidity and loss of reactivity of the medium.

  9. Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions.

    PubMed

    Shen, Xiaodong; Huo, Haohua; Wang, Chuanyong; Zhang, Bo; Harms, Klaus; Meggers, Eric

    2015-06-26

    Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,β-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,β-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.

  10. Synthesis, characterisation and application of iridium(III) photosensitisers for catalytic water reduction.

    PubMed

    Gärtner, Felix; Cozzula, Daniela; Losse, Sebastian; Boddien, Albert; Anilkumar, Gopinatan; Junge, Henrik; Schulz, Thomas; Marquet, Nicolas; Spannenberg, Anke; Gladiali, Serafino; Beller, Matthias

    2011-06-14

    The synthesis of novel, monocationic iridium(III) photosensitisers (Ir-PSs) with the general formula [Ir(III)(C^N)(2)(N^N)](+) (C^N: cyclometallating phenylpyridine ligand, N^N: neutral bidentate ligand) is described. The structures obtained were examined by cyclic voltammetry, UV/Vis and photoluminescence spectroscopy and X-ray analysis. All iridium complexes were tested for their ability as photosensitisers to promote homogeneously catalysed hydrogen generation from water. In the presence of [HNEt(3)][HFe(3)(CO)(11)] as a water-reduction catalyst (WRC) and triethylamine as a sacrificial reductant (SR), seven of the new iridium complexes showed activity. [Ir(6-iPr-bpy)(ppy)(2)]PF(6) (bpy: 2,2'-bipyridine, ppy: 2-phenylpyridine) turned out to be the most efficient photosensitiser. This complex was also tested in combination with other WRCs based on rhodium, platinum, cobalt and manganese. In all cases, significant hydrogen evolution took place. Maximum turnover numbers of 4550 for this Ir-PS and 2770 for the Fe WRC generated in situ from [HNEt(3)][HFe(3)(CO)(11)] and tris[3,5-bis(trifluoromethyl)phenyl]phosphine was obtained. These are the highest overall efficiencies for any Ir/Fe water-reduction system reported to date. The incident photon to hydrogen yield reaches 16.4% with the best system.

  11. Supported Molecular Iridium Catalysts: Resolving Effects of Metal Nuclearity and Supports as Ligands

    SciTech Connect

    Lu, Jing; Serna, Pedro; Aydin, Cerem; Browning, Nigel D.; Gates, Bruce C.

    2012-02-07

    The performance of a supported catalyst is influenced by the size and structure of the metal species, the ligands bonded to the metal, and the support. Resolution of these effects has been lacking because of the lack of investigations of catalysts with uniform and systematically varied catalytic sites. We now demonstrate that the performance for ethene hydrogenation of isostructural iridium species on supports with contrasting properties as ligands (electron-donating MgO and electron-withdrawing HY zeolite) can be elucidated on the basis of molecular concepts. Spectra of the working catalysts show that the catalytic reaction rate is determined by the dissociation of H{sub 2} when the iridium, either as mono- or tetra-nuclear species, is supported on MgO and is not when the support is the zeolite. The neighboring iridium sites in clusters are crucial for activation of both H{sub 2} and C{sub 2}H{sub 4} when the support is MgO but not when it is the zeolite, because the electron-withdrawing properties of the zeolite support enable even single site-isolated Ir atoms to bond to both C{sub 2}H{sub 4} and H{sub 2} and facilitate the catalysis.

  12. Synthesis and characterization of nitrides of iridium and palladiums

    SciTech Connect

    Crowhurst, Jonathan C.; Goncharov, Alexander F.; Sadigh, B.; Zaug, J.M.; Aberg, D.; Meng, Yue; Prakapenka, Vitali B.

    2008-08-14

    We describe the synthesis of nitrides of iridium and palladium using the laser-heated diamond anvil cell. We have used the in situ techniques of x-ray powder diffraction and Raman scattering to characterize these compounds and have compared our experimental findings where possible to the results of first-principles theoretical calculations. We suggest that palladium nitride is isostructural with pyrite, while iridium nitride has a monoclinic symmetry and is isostructural with baddeleyite.

  13. Iridium{reg_sign} worldwide personal communication system

    SciTech Connect

    Helm, J.

    1997-01-01

    The IRIDIUM system is a personal worldwide communication system designed to support portable, low power subscriber units through the use of a constellation of satellites in low earth polar orbit. The satellites are networked together to form a system which provides continuous line-of-sight communications between the IRIDIUM system and any point within 30 km of the earth{close_quote}s surface. The system architecture and operation are described. {copyright} {ital 1997 American Institute of Physics.}

  14. Laser Induced Fluorescence Spectrum of Iridium Monophosphide

    NASA Astrophysics Data System (ADS)

    Pang, H. F.; Liu, Anwen; Cheung, A. S.-C.

    2009-06-01

    Laser induced fluorescence spectrum of IrP in the spectral region between 380-600 nm has been studied. Reacting laser ablated iridium atoms with 1% PH_3 seeded in argon produced the IrP molecule. A few vibronic transitions have been recorded. Preliminary analysis of the rotational structure indicated that these vibronic bands are with Ω^' = 0 and Ω^'' = 0 and is likely to be ^{1}Σ - X ^{1}Σ transition. Vibrational separation of the excited state is estimated to be about 442 cm^{-1}. The ground state bond length is determined to be 1.766 Å. This work represents the first experimental investigation of the spectra of IrP.

  15. Solventless synthesis of iridium(0) nanoparticles

    NASA Astrophysics Data System (ADS)

    Redón, R.; Ramírez-Crescencio, F.; Fernández-Osorio, A. L.

    2011-11-01

    In this article, we present the results of a solvent-free synthesis of iridium(0) nanoparticles, both water washed and unwashed. IrCl3 and NaBH4, as starting materials, are mixed using an agate mortar and milled for 15 min until a black powder is obtained, which is heated in a nitrogen-controlled atmosphere oven at 200 °C for 2 h. If the product of the reaction is not washed before heating, NaBH4 and IrO2 impurities are observed. On the other hand, if the reaction product is washed before the heating, the obtained powder is free of impurities. We study the effect of the variation in reducing agent concentration and the annealing temperature used after the reaction. In all cases, the calculated particle size is less than 10 nm.

  16. Steric and Electronic Influence of Aryl Isocyanides on the Properties of Iridium(III) Cyclometalates.

    PubMed

    Maity, Ayan; Le, Linh Q; Zhu, Zhuan; Bao, Jiming; Teets, Thomas S

    2016-03-07

    Cyclometalated iridium complexes with efficient phosphorescence and good electrochemical stability are important candidates for optoelectronic devices. Isocyanide ligands are strong-field ligands: when attached to transition metals, they impart larger HOMO-LUMO energy gaps, engender higher oxidative stability at the metal center, and support rugged organometallic complexes. Aryl isocyanides offer more versatile steric and electronic control by selective substitution at the aryl ring periphery. Despite a few reports of alkyl isocyanide of cyclometalated iridium(III), detailed studies on analogous aryl isocyanide complexes are scant. We report the synthesis, photophysical properties, and electrochemical properties of 11 new luminescent cationic biscyclometalated bis(aryl isocyanide)iridium(III) complexes. Three different aryl isocyanides--2,6-dimethylphenyl isocyanide (CNAr(dmp)), 2,6-diisopropylphenyl isocyanide (CNAr(dipp)), and 2-naphthyl isocyanide (CNAr(nap))--were combined with four cyclometalating ligands with differential π-π* energies--2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (F2ppy), 2-benzothienylpyridine (btp), and 2-phenylbenzothiazole (bt). Five of them were crystallographically characterized. All new complexes show wide redox windows, with reduction potentials falling in a narrow range of -2.02 to -2.37 V and oxidation potentials spanning a wider range of 0.97-1.48 V. Efficient structured emission spans from the blue region for [(F2ppy)2Ir(CNAr)2]PF6 to the orange region for [(btp)2Ir(CNAr)2]PF6, demonstrating that isocyanide ligands can support redox-stable luminescent complexes with a range of emission colors. Emission quantum yields were generally high, reaching a maximum of 0.37 for two complexes, whereas btp-ligated complexes had quantum yields below 1%. The structure of the CNAr ligand has a minimal effect on the photophysical properties, which are shown to arise from ligand-centered excited states with very little contribution from

  17. Enhanced oxidation resistance of active nanostructures via dynamic size effect

    NASA Astrophysics Data System (ADS)

    Liu, Yun; Yang, Fan; Zhang, Yi; Xiao, Jianping; Yu, Liang; Liu, Qingfei; Ning, Yanxiao; Zhou, Zhiwen; Chen, Hao; Huang, Wugen; Liu, Ping; Bao, Xinhe

    2017-02-01

    A major challenge limiting the practical applications of nanomaterials is that the activities of nanostructures (NSs) increase with reduced size, often sacrificing their stability in the chemical environment. Under oxidative conditions, NSs with smaller sizes and higher defect densities are commonly expected to oxidize more easily, since high-concentration defects can facilitate oxidation by enhancing the reactivity with O2 and providing a fast channel for oxygen incorporation. Here, using FeO NSs as an example, we show to the contrary, that reducing the size of active NSs can drastically increase their oxidation resistance. A maximum oxidation resistance is found for FeO NSs with dimensions below 3.2 nm. Rather than being determined by the structure or electronic properties of active sites, the enhanced oxidation resistance originates from the size-dependent structural dynamics of FeO NSs in O2. We find this dynamic size effect to govern the chemical properties of active NSs.

  18. Light activated nitric oxide releasing materials

    NASA Astrophysics Data System (ADS)

    Muizzi Casanas, Dayana Andreina

    The ability to control the location and dosage of biologically active molecules inside the human body can be critical to maximizing effective treatment of cardiovascular diseases like angina. The current standard of treatment relies on the metabolism of organonitrate drugs into nitric oxide (NO), which are not specific, and also show problems with densitization with long-term use. There is a need then to create a treatment method that gives targeted release of NO. Metal-nitrosyl (M-NO) complexes can be used for delivery of NO since the release of NO can be controlled with light. However, the NO-releasing drug must be activated with red light to ensure maximum penetration of light through tissue. However, the release of NO from M-NO complexes with red-light activation is a significant challenge since the energy required to break the metal-NO bond is usually larger than the energy provided by red light. The goal of this project was to create red- sensitive, NO-releasing materials based on Ru-salen-nitrosyl compounds. Our approach was to first modify Ru salen complexes to sensitize the photochemistry for release of NO after red light irradiation. Next, we pursued polymerization of the Ru-salen complexes. We report the synthesis and quantitative photochemical characterization of a series of ruthenium salen nitrosyl complexes. These complexes were modified by incorporating electron donating groups in the salen ligand structure at key locations to increase electron density on the Ru. Complexes with either an --OH or --OCH3 substituent showed an improvement in the quantum yield of release of NO upon blue light irradiation compared to the unmodified salen. These --OH and --OCH3 complexes were also sensitized for NO release after red light activation, however the red-sensitive complexes were unstable and showed ligand substitution on the order of minutes. The substituted complexes remained sensitive for NO release, but only after blue light irradiation. The Ru

  19. Mobility of iridium in terrestrial environments: Implications for the interpretation of impact-related mass-extinctions

    NASA Astrophysics Data System (ADS)

    Martín-Peinado, F. J.; Rodríguez-Tovar, F. J.

    2010-08-01

    Traditionally, iridium has been considered an element of low mobility, but its behavior is still debated. Ir concentration in a soil affected by a catastrophic mining spill in 1998 that covered the soil with a layer of tailings offers the opportunity to analyse an exceptional Ir-bearing horizon 10 years after deposition. This has enabled comparisons with the values of past Ir-bearing horizons associated to impact-related mass-extinction events. Iridium concentration in the tailings (0.349 ppm) was 5-fold higher than the anomaly in the K-Pg at The Moody Creek Mine section (the highest values obtained from terrestrial sections). The oxidative weathering of the tailings caused the release of Ir and infiltration into the soil. Iridium distribution in depth indicates redistribution throughout the profile in relation to the change in the physico-chemical properties of the soil. With regard to the background concentration in the soil (0.056 ppm), anomalous values of Ir (0.129 ppm) can be detected to 11 cm below the layer of tailings. The correlation analysis between the Ir concentration and the main properties and constituents of the soils indicated a significant correlation with sulfur, iron, clay content, and pH. Selective extractions were made to study the forms in which Ir can be mobilized in the soil. The residual/insoluble fraction was >90% of the total Ir concentration in soil. Soluble-in-water concentration of Ir (1.5% of total) was detected in the uppermost 2-3 cm of the soil, which were directly affected by the leaching of acidic waters coming from the oxidation of the pyrite tailings. Iridium retention in the affected part of the soil reached 9% of the total Ir concentration; this retention could be related to the amorphous iron forms dissolved by the oxalic-oxalate extraction. However, according to our research, original Ir abundance could be secondarily modified, and then a direct analysis of the iridium values recorded in sediments could induce

  20. Plasma electrolytic oxide coatings on valve metals and their activity in CO oxidation

    NASA Astrophysics Data System (ADS)

    Lukiyanchuk, I. V.; Rudnev, V. S.; Tyrina, L. M.; Chernykh, I. V.

    2014-10-01

    Two approaches have been examined for obtaining titanium- or aluminum-supported catalysts with transition and noble metals using the plasma electrolytic oxidation (PEO) technique. Elemental compositions, distribution of active elements and catalytic activity in CO oxidation have been compared for composites formed by one-stage PEO technique and those obtained as a result of modification of PEO coatings by impregnation.

  1. Active Oxygen Generator by Silent Discharge and Oxidation Power in Formation of Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Tanaka, Masaaki; Kawagoe, Yasuyuki; Tsukazaki, Hisashi; Yamanishi, Kenichiro

    We have studied the low pressure silent discharge type active oxygen generator in terms of the application to the formation of oxide thin films. In this paper the oxidation power of active oxygen in the oxide thin film formation is compared with that of oxygen and ozone by forming silicon oxide thin films. It was confirmed that the oxidation power is in turn of active oxygen > ozone > oxygen from the experimental result of the number of x in SiOx thin film. Furthermore we applied active oxygen to the formation of the thin film high temperature super conductor and active oxygen was found to be effective to the formation of the thin film with high performance.

  2. DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)

    EPA Science Inventory

    There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

  3. Iridium complexes demonstrating broadband emission through controlled geometric distortion and applications thereof

    SciTech Connect

    Li, Jian; Turner, Eric

    2016-04-12

    Iridium compounds and their uses are disclosed herein. For example, carbazole containing iridium compounds are disclosed. The compounds are useful in many devices, including, but not limited to, electroluminescent devices.

  4. Antimicrobial activity of amine oxides: mode of action and structure-activity correlation.

    PubMed

    Subík, J; Takácsová, G; Psenák, M; Devínsky, F

    1977-08-01

    The effect of N-alkyl derivatives of saturated heterocyclic amine oxides on the growth and metabolism of microorganisms has been studied. 4-Dodecylmorpholine-N-oxide inhibited the differentiation and growth of Bacillus cereus, of different species of filamentous fungi, and of the yeast Saccharomyces cerevisiae. For vegetative cells, the effect of 4-dodecylmorpholine-N-oxide was lethal. Cells of S. cerevisiae, after interaction with 4-dodecylmorpholine-N-oxide, released intracellular K(+) and were unable to oxidize or ferment glucose. The functions of isolated yeast mitochondria were also impaired. 4-Dodecylmorpholine-N-oxide at growth-inhibiting concentrations induced rapid lysis of osmotically stabilized yeast protoplasts, with the rate of lysis a function of temperature and of amine oxide concentration. A study of the relationships between structure, antimicrobial activity, and cytolytic activity was made with a group of structurally different amine oxides involving a series of homologous 4-alkylmorpholine-N-oxides, 1-alkylpiperidine-N-oxides, 1-dodecylpyrrolidine-N-oxide, 1-dodecylperhydroasepine-N-oxide, and N,N-dimethyldodecylamine oxide. Disorganization of the membrane structure after interaction of cells with the tested amine oxides was primarily responsible for the antimicrobial activity of the amine oxides. This activity was found to be dependent on the chain length of the hydrophobic alkyl group and was only moderately influenced by other substituents of the polarized N-oxide group.

  5. Hypoxia-Induced Oxidative Stress Modulation with Physical Activity

    PubMed Central

    Debevec, Tadej; Millet, Grégoire P.; Pialoux, Vincent

    2017-01-01

    Increased oxidative stress, defined as an imbalance between prooxidants and antioxidants, resulting in molecular damage and disruption of redox signaling, is associated with numerous pathophysiological processes and known to exacerbate chronic diseases. Prolonged systemic hypoxia, induced either by exposure to terrestrial altitude or a reduction in ambient O2 availability is known to elicit oxidative stress and thereby alter redox balance in healthy humans. The redox balance modulation is also highly dependent on the level of physical activity. For example, both high-intensity exercise and inactivity, representing the two ends of the physical activity spectrum, are known to promote oxidative stress. Numerous to-date studies indicate that hypoxia and exercise can exert additive influence upon redox balance alterations. However, recent evidence suggests that moderate physical activity can attenuate altitude/hypoxia-induced oxidative stress during long-term hypoxic exposure. The purpose of this review is to summarize recent findings on hypoxia-related oxidative stress modulation by different activity levels during prolonged hypoxic exposures and examine the potential mechanisms underlying the observed redox balance changes. The paper also explores the applicability of moderate activity as a strategy for attenuating hypoxia-related oxidative stress. Moreover, the potential of such moderate intensity activities used to counteract inactivity-related oxidative stress, often encountered in pathological, elderly and obese populations is also discussed. Finally, future research directions for investigating interactive effects of altitude/hypoxia and exercise on oxidative stress are proposed. PMID:28243207

  6. Investigation of oxidation process of mechanically activated ultrafine iron powders

    NASA Astrophysics Data System (ADS)

    Lysenko, E. N.; Nikolaev, E. V.; Vlasov, V. A.; Zhuravkov, S. P.

    2016-02-01

    The oxidation of mechanically activated ultrafine iron powders was studied using X- ray powder diffraction and thermogravimetric analyzes. The powders with average particles size of 100 nm were made by the electric explosion of wire, and were subjected to mechanical activation in planetary ball mill for 15 and 40 minutes. It was shown that a certain amount of FeO phase is formed during mechanical activation of ultrafine iron powders. According to thermogravimetric analysis, the oxidation process of non-milled ultrafine iron powders is a complex process and occurs in three stages. The preliminary mechanical activation of powders considerably changes the nature of the iron powders oxidation, leads to increasing in the temperature of oxidation onset and shifts the reaction to higher temperatures. For the milled powders, the oxidation is more simple process and occurs in a single step.

  7. IR-doped ruthenium oxide catalyst for oxygen evolution

    NASA Technical Reports Server (NTRS)

    Valdez, Thomas I. (Inventor); Narayanan, Sekharipuram R. (Inventor)

    2012-01-01

    A method for preparing a metal-doped ruthenium oxide material by heating a mixture of a doping metal and a source of ruthenium under an inert atmosphere. In some embodiments, the doping metal is in the form of iridium black or lead powder, and the source of ruthenium is a powdered ruthenium oxide. An iridium-doped or lead-doped ruthenium oxide material can perform as an oxygen evolution catalyst and can be fabricated into electrodes for electrolysis cells.

  8. Enhanced colonic nitric oxide generation and nitric oxide synthase activity in ulcerative colitis and Crohn's disease.

    PubMed Central

    Rachmilewitz, D; Stamler, J S; Bachwich, D; Karmeli, F; Ackerman, Z; Podolsky, D K

    1995-01-01

    Recent studies have suggested that nitric oxide (NO.), the product of nitric oxide synthase in inflammatory cells, may play a part in tissue injury and inflammation through its oxidative metabolism. In this study the colonic generation of oxides of nitrogen (NOx) and nitric oxide synthase activity was determined in ulcerative colitis and Crohn's disease. Colonic biopsy specimens were obtained from inflammatory bowel disease patients and from normal controls. Mucosal explants were cultured in vitro for 24 hours and NOx generation was determined. Nitric oxide synthase activity was monitored by the conversion of [3H]-L-arginine to citrulline. Median NOx generation by inflamed colonic mucosa of patients with active ulcerative colitis and Crohn's colitis was 4.2- and 8.1-fold respectively higher than that by normal human colonic mucosa. In ulcerative colitis and Crohn's colitis nitric oxide synthase activity was 10.0- and 3.8-fold respectively higher than in normal subjects. Colonic NOx generation is significantly decreased by methylprednisolone and ketotifen. The decrease in NOx generation by cultured colonic mucosa induced by methylprednisolone suggests that NO synthase activity is induced during the culture and the steroid effect may contribute to its therapeutic effect. Enhanced colonic NOx generation by stimulated nitric oxide synthase activity in ulcerative colitis and Crohn's disease may contribute to tissue injury. PMID:7541008

  9. Oxidative activation of dihydropyridine amides to reactive acyl donors.

    PubMed

    Funder, Erik Daa; Trads, Julie B; Gothelf, Kurt V

    2015-01-07

    Amides of 1,4-dihydropyridine (DHP) are activated by oxidation for acyl transfer to amines, alcohols and thiols. In the reduced form the DHP amide is stable towards reaction with amines at room temperature. However, upon oxidation with DDQ the acyl donor is activated via a proposed pyridinium intermediate. The activated intermediate reacts with various nucleophiles to give amides, esters, and thio-esters in moderate to high yields.

  10. Active Oxidation of a UHTC-Based CMC

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Splinter, Scott C.

    2012-01-01

    The active oxidation of ceramic matrix composites (CMC) is a severe problem that must be avoided for multi-use hypersonic vehicles. Much work has been performed studying the active oxidation of silicon-based CMCs such as C/SiC and SiC-coated carbon/carbon (C/C). Ultra high temperature ceramics (UTHC) have been proposed as a possible material solution for high-temperature applications on hypersonic vehicles. However, little work has been performed studying the active oxidation of UHTCs. The intent of this paper is to present test data indicating an active oxidation process for a UHTC-based CMC similar to the active oxidation observed with Si-based CMCs. A UHTC-based CMC was tested in the HyMETS arc-jet facility (or plasma wind tunnel, PWT) at NASA Langley Research Center, Hampton, VA. The coupon was tested at a nominal surface temperature of 3000 F (1650 C), with a stagnation pressure of 0.026 atm. A sudden and large increase in surface temperature was noticed with negligible increase in the heat flux, indicative of the onset of active oxidation. It is shown that the surface conditions, both temperature and pressure, fall within the region for a passive to active transition (PAT) of the oxidation.

  11. Highly fluorescent and biocompatible iridium nanoclusters for cellular imaging.

    PubMed

    Vankayala, Raviraj; Gollavelli, Ganesh; Mandal, Badal Kumar

    2013-08-01

    Highly fluorescent iridium nanoclusters were synthesized and investigated its application as a potential intracellular marker. The iridium nanoclusters were prepared with an average size of ~2 nm. Further, these nanoclusters were refluxed with aromatic ligands, such as 2,2'-binaphthol (BINOL) in order to obtain fluorescence properties. The photophysical properties of these bluish-green emitting iridium nanoclusters were well characterized by using UV-Visible, fluorescence and lifetime decay measurements. The emission spectrum for these nanoclusters exhibit three characteristic peaks at 449, 480 and 515 nm. The fluorescence quantum yield of BINOL-Ir NCs were estimated to be 0.36 and the molar extinction co-efficients were in the order of 10(6) M(-1)cm(-1). In vitro cytotoxicity studies in HeLa cells reveal that iridium nanoclusters exhibited good biocompatibility with an IC50 value of ~100 μg/ml and also showed excellent co-localization and distribution throughout the cytoplasm region without entering into the nucleus. This research has opened a new window in developing the iridium nanoparticle based intracellular fluorescent markers and has wide scope to act as biomedical nanocarrier to carry many biological molecules and anticancer drugs.

  12. Mechanism of Olefin Asymmetric Hydrogenation Catalyzed by Iridium Phosphino-Oxazoline: A Pair Natural Orbital Coupled Cluster Study.

    PubMed

    Sparta, Manuel; Riplinger, Christoph; Neese, Frank

    2014-03-11

    Since the development of chiral phosphino-oxazoline iridium catalysts, which hydrogenate unfunctionalized alkenes enantioselectively, the asymmetric hydrogenation of prochiral olefins has become important in the production of chiral compounds. For the last 10 years, details of the mechanism, including formal oxidation state assignment of the metal center and the nature of intermediates and transition states have been debated. Various contributions have been given from a theoretical point of view, but due to the size of the structures, these have been forced to rely on density functional theory (DFT) methods. In our investigation of the catalytic cycle, we employ both DFT and a correlated ab initio method, namely, the newly implemented domain-based local pair natural orbital coupled-cluster theory with single and double excitations and the inclusion of perturbative triples correction (DLPNO-CCSD(T)). Our results show that the most likely active paths involve the formation of an intermediate Ir(V) species. Furthermore, we have been able to predict the absolute configuration of the major products, and where comparison to experiment is possible, the results of our calculations agree with the enantiomeric excess obtained from hydrogenating five prochiral substrates. This work also shows that it is now possible to study catalytic reactions with untruncated models (having up to 88 atoms) at the CCSD(T) level of theory.

  13. Testing of electroformed deposited iridium/powder metallurgy rhenium rockets

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.; Dickerson, Robert

    1996-01-01

    High-temperature, oxidation-resistant chamber materials offer the thermal margin for high performance and extended lifetimes for radiation-cooled rockets. Rhenium (Re) coated with iridium (Ir) allow hours of operation at 2200 C on Earth-storable propellants. One process for manufacturing Ir/Re rocket chambers is the fabrication of Re substrates by powder metallurgy (PM) and the application of Ir coatings by using electroformed deposition (ED). ED Ir coatings, however, have been found to be porous and poorly adherent. The integrity of ED Ir coatings could be improved by densification after the electroforming process. This report summarizes the testing of two 22-N, ED Ir/PM Re rocket chambers that were subjected to post-deposition treatments in an effort to densify the Ir coating. One chamber was vacuum annealed, while the other chamber was subjected to hot isostatic pressure (HIP). The chambers were tested on gaseous oxygen/gaseous hydrogen propellants, at mixture ratios that simulated the oxidizing environments of Earth-storable propellants. ne annealed ED Ir/PM Re chamber was tested for a total of 24 firings and 4.58 hr at a mixture ratio of 4.2. After only 9 firings, the annealed ED Ir coating began to blister and spall upstream of the throat. The blistering and spalling were similar to what had been experienced with unannealed, as-deposited ED Ir coatings. The HIP ED Ir/PM Re chamber was tested for a total of 91 firings and 11.45 hr at mixture ratios of 3.2 and 4.2. The HIP ED Ir coating remained adherent to the Re substrate throughout testing; there were no visible signs of coating degradation. Metallography revealed, however, thinning of the HIP Ir coating and occasional pores in the Re layer upstream of the throat. Pinholes in the Ir coating may have provided a path for oxidation of the Re substrate at these locations. The HIP ED Ir coating proved to be more effective than vacuum annealed and as-deposited ED Ir. Further densification is still required to

  14. Oxidative modification and poor protective activity of HDL on LDL oxidation in thalassemia.

    PubMed

    Unchern, Supeenun; Laohareungpanya, Narumon; Sanvarinda, Yupin; Pattanapanyasat, Kovit; Tanratana, Pansakorn; Chantharaksri, Udom; Sibmooh, Nathawut

    2010-07-01

    Oxidative modification of low-density lipoprotein (LDL) has been reported in thalassemia, which is a consequence of oxidative stress. However, the levels of oxidized high-density lipoprotein (HDL) in thalassemia have not been evaluated and it is unclear whether HDL oxidation may be linked to LDL oxidation. In this study, the levels of total cholesterol, iron, protein, conjugated diene (CD), lipid hydroperoxide (LOOH), and thiobarbituric acid reactive substances (TBARs) were determined in HDL from healthy volunteers and patients with beta-thalassemia intermedia with hemoglobin E (beta-thal/Hb E). The protective activity of thalassemic HDL on LDL oxidation was also investigated. The iron content of HDL(2) and HDL(3) from beta-thal/HbE patients was higher while the cholesterol content was lower than those in healthy volunteers. Thalassemic HDL(2) and HDL(3) had increased levels of lipid peroxidation markers i.e., conjugated diene, LOOH, and TBARs. Thalassemic HDL had lower peroxidase activity than control HDL and was unable to protect LDL from oxidation induced by CuSO(4). Our findings highlight the oxidative modification and poor protective activity of thalassemic HDL on LDL oxidation which may contribute to cardiovascular complications in thalassemia.

  15. Oxidative Regulation of Large Conductance Calcium-Activated Potassium Channels

    PubMed Central

    Tang, Xiang D.; Daggett, Heather; Hanner, Markus; Garcia, Maria L.; McManus, Owen B.; Brot, Nathan; Weissbach, Herbert; Heinemann, Stefan H.; Hoshi, Toshinori

    2001-01-01

    Reactive oxygen/nitrogen species are readily generated in vivo, playing roles in many physiological and pathological conditions, such as Alzheimer's disease and Parkinson's disease, by oxidatively modifying various proteins. Previous studies indicate that large conductance Ca2+-activated K+ channels (BKCa or Slo) are subject to redox regulation. However, conflicting results exist whether oxidation increases or decreases the channel activity. We used chloramine-T, which preferentially oxidizes methionine, to examine the functional consequences of methionine oxidation in the cloned human Slo (hSlo) channel expressed in mammalian cells. In the virtual absence of Ca2+, the oxidant shifted the steady-state macroscopic conductance to a more negative direction and slowed deactivation. The results obtained suggest that oxidation enhances specific voltage-dependent opening transitions and slows the rate-limiting closing transition. Enhancement of the hSlo activity was partially reversed by the enzyme peptide methionine sulfoxide reductase, suggesting that the upregulation is mediated by methionine oxidation. In contrast, hydrogen peroxide and cysteine-specific reagents, DTNB, MTSEA, and PCMB, decreased the channel activity. Chloramine-T was much less effective when concurrently applied with the K+ channel blocker TEA, which is consistent with the possibility that the target methionine lies within the channel pore. Regulation of the Slo channel by methionine oxidation may represent an important link between cellular electrical excitability and metabolism. PMID:11222629

  16. Oxygen Activation and Photoelectrochemical Oxidation on Oxide Surfaces

    DTIC Science & Technology

    2013-12-04

    ruthenium complexes, Chemical Communications, (09 2011): 0. doi: 10.1039/c1cc15071e 13.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 30.00...Christopher R. K. Glasson, Javier J. Concepcion, Thomas J. Meyer. Self-Assembled Bilayer Films of Ruthenium (II)/Polypyridyl Complexes through Layer- by-Layer...Christopher R. K. Glasson, Patrick L. Holland, Thomas J. Meyer. Electrogenerated polypyridyl ruthenium hydride and ligand activation for water

  17. Electrogenerated chemiluminescence from heteroleptic iridium(III) complexes with multicolor emission.

    PubMed

    Zhou, Yuyang; Gao, Hongfang; Wang, Xiaomei; Qi, Honglan

    2015-02-16

    Electrogenerated chemiluminescence (ECL) with different emission colors is important in the development of multichannel analytical techniques. In this report, five new heteroleptic iridium(III) complexes were synthesized, and their photophysical, electrochemical, and ECL properties were studied. Here, 2-(2,4-difluorophenyl)pyridine (dfppy, complex 1), 2-phenylbenzo[d]thiazole (bt, complex 2), and 2-phenylpyridine (ppy, complex 3) were used as the main ligands to tune the emission color, while avobenzone (avo) was used as the ancillary ligand. For comparison, complexes 4 and 5 with 2-phenylpyridine and 2-phenylbenzo[d]thiazole as the main ligand, respectively, and acetyl acetone (acac) as the ancillary ligand were also synthesized. All five iridium(III) complexes had strong intraligand absorption bands (π–π*) in the UV region (below 350 nm) and a featureless MLCT (d−π*) transition in the visible 400–500 nm range. Multicolored emissions were observed for these five iridium(III) complexes, including green, orange, and red for complexes 4, 5, 2, 1, 3, respectively. Density functional theory calculations indicate that the electronic density of the highest occupied molecular orbital is entirely located on the C^N ligands and the iridium atom, while the formation of the lowest unoccupied molecular orbital (LUMO) is complicated. The LUMO is mainly assigned to the ancillary ligand for complexes 1 and 3 but to the C^N ligand for complexes 2, 4, and 5. Cyclic voltammetry studies showed that all these complexes have a reversible oxidation wave, but no reduction waves were found in the electrochemical windows of CH2Cl2. The E1/2(ox) values of these complexes ranged from 0.642 to 0.978 V for complexes 3, 4, 2, 5, 1, (in increasing order) and are all lower than that of Ru(bpy)3(2+). Most importantly, when using tripropylamine as a coreactant, complexes 1–5 exhibited intense ECL signals with an emission wavelength centered at 616, 580, 663, 536, and 569 nm, respectively

  18. Experimental determination of the solubility of iridium in silicate melts: Preliminary results

    NASA Technical Reports Server (NTRS)

    Borisov, Alexander; Dingwell, Donald B.; Oneill, Hugh ST.C.; Palme, Herbert

    1992-01-01

    Little is known of the geochemical behavior of iridium. Normally this element is taken to be chalcophile and/or siderophile so that during planetary differentiation processes, e.g., core formation, iridium is extracted from silicate phases into metallic phases. Experimental determination of the metal/silicate partition coefficient of iridium is difficult simply because it is so large. Also there are no data on the solubility behavior of iridium in silicate melts. With information on the solubility of iridium in silicate melts it is possible, in combination with experimental data for Fe-Ir alloys, to calculate the partition coefficient between a metallic phase and a silicate melt.

  19. Oxidative esterification via photocatalytic C-H activation

    EPA Science Inventory

    Direct oxidative esterification of alcohol via photocatalytic C-H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.

  20. A Chiral Nitrogen Ligand for Enantioselective, Iridium-Catalyzed Silylation of Aromatic C-H Bonds.

    PubMed

    Su, Bo; Zhou, Tai-Gang; Li, Xian-Wei; Shao, Xiao-Ru; Xu, Pei-Lin; Wu, Wen-Lian; Hartwig, John F; Shi, Zhang-Jie

    2017-01-19

    Iridium catalysts containing dative nitrogen ligands are highly active for the borylation and silylation of C-H bonds, but chiral analogs of these catalysts for enantioselective silylation reactions have not been developed. We report a new chiral pyridinyloxazoline ligand for enantioselective, intramolecular silylation of symmetrical diarylmethoxy diethylsilanes. Regioselective and enantioselective silylation of unsymmetrical substrates was also achieved in the presence of this newly developed system. Preliminary mechanistic studies imply that C-H bond cleavage is irreversible, but not the rate-determining step.

  1. The Collision of Iridium 33 and Cosmos 2251: The Shape of Things to Come

    NASA Technical Reports Server (NTRS)

    Nicholas, Johnson

    2009-01-01

    The collision of Iridium 33 and Cosmos 2251 was the most severe accidental fragmentation on record. More than 1800 debris approx. 10 cm and larger were produced. If solar activity returns to normal, half of the tracked debris will reenter within five years. Less than 60 cataloged debris had reentered by 1 October 2009. Some debris from both satellites will remain in orbit through the end of the century. The collision rate of one every five years will increase without future removal of large derelict spacecraft and launch vehicle orbital stages.

  2. Field desorption of Na and Cs from graphene on iridium

    NASA Astrophysics Data System (ADS)

    Bernatskii, D. P.; Pavlov, V. G.

    2015-08-01

    Field electron and desorption microscopy has been used to study specific features of the field desorption of sodium and cesium ions adsorbed on the surface of iridium with graphene. It was found that adsorbed sodium atoms most strongly reduce the work function on graphene islands situated over densely packed faces of iridium. A strong electric field qualitatively similarly affects the sodium and cesium desorption processes from a field emitter to give two desorption phases and has no noticeable effect on the disintegration of the graphene layer.

  3. Energetic basis of catalytic activity of layered nanophase calcium manganese oxides for water oxidation

    PubMed Central

    Birkner, Nancy; Nayeri, Sara; Pashaei, Babak; Najafpour, Mohammad Mahdi; Casey, William H.; Navrotsky, Alexandra

    2013-01-01

    Previous measurements show that calcium manganese oxide nanoparticles are better water oxidation catalysts than binary manganese oxides (Mn3O4, Mn2O3, and MnO2). The probable reasons for such enhancement involve a combination of factors: The calcium manganese oxide materials have a layered structure with considerable thermodynamic stability and a high surface area, their low surface energy suggests relatively loose binding of H2O on the internal and external surfaces, and they possess mixed-valent manganese with internal oxidation enthalpy independent of the Mn3+/Mn4+ ratio and much smaller in magnitude than the Mn2O3-MnO2 couple. These factors enhance catalytic ability by providing easy access for solutes and water to active sites and facile electron transfer between manganese in different oxidation states. PMID:23667149

  4. Mitochondrial oxidant stress in locus coeruleus is regulated by activity and nitric oxide synthase

    PubMed Central

    Sanchez–Padilla, J.; Guzman, J.N.; Ilijic, E.; Kondapalli, J.; Galtieri, D.J.; Yang, B.; Schieber, S.; Oertel, W.; Wokosin, D.; Schumacker, P. T.; Surmeier, D. J.

    2014-01-01

    Summary Loss of noradrenergic locus coeruleus (LC) neurons is a prominent feature of aging–related neurodegenerative diseases, like Parkinson’s disease (PD). The basis of this vulnerability is not understood. To explore possible physiological determinants, LC neurons were studied using electrophysiological and optical approaches in ex vivo mouse brain slices. These studies revealed that autonomous activity in LC neurons was accompanied by oscillations in dendritic Ca2+ concentration attributable to opening of L–type Ca2+ channels. This oscillation elevated mitochondrial oxidant stress and was attenuated by inhibition of nitric oxide synthase. The relationship between activity and stress was malleable, as arousal and carbon dioxide, each increased the spike rate, but differentially affected mitochondrial oxidant stress. Oxidant stress also was increased in an animal model of PD. Thus, our results point to activity–dependent Ca2+ entry and a resulting mitochondrial oxidant stress as factors contributing to the vulnerability of LC neurons. PMID:24816140

  5. Corrosion-resistant iridium-platinum anode material for high polarization application in corrosive acids

    SciTech Connect

    Farmer, J.; Summers, L.; Lewis, P.

    1993-09-08

    The present invention relates to highly corrosion resistant components for use in an electrochemical cell. Specifically, these components are resistant to corrosion under very extreme conditions such as exposure to aqua regia in the presence of a constant current density of 100mA/m{sup 2}. The components are comprised of an iridium-platinum alloy that comprises less than 30% iridium. In a preferred embodiment of the present invention, the iridium-platinum alloy comprises 15-20% iridium. In another preferred embodiment of the present invention, the iridium-platinum alloy is deposited on the surface of an electrochemical cell component by magnetron sputtering. The present invention also relates to a method for conducting an electrochemical reaction in the presence of highly corrosive acids under a high degree of polarization wherein the electrochemical cell comprises a component, preferably the anode, containing an iridium-platinum alloy that comprises less than 30% iridium.

  6. Nanostructured manganese oxides as highly active water oxidation catalysts: a boost from manganese precursor chemistry.

    PubMed

    Menezes, Prashanth W; Indra, Arindam; Littlewood, Patrick; Schwarze, Michael; Göbel, Caren; Schomäcker, Reinhard; Driess, Matthias

    2014-08-01

    We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1oxidizing agent. Photocatalytic water oxidation in the presence of [Ru(bpy)3 ](2+) (bpy=2,2'-bipyridine) as a sensitizer and peroxodisulfate as an electron acceptor was carried out for all three manganese oxides including the newly formed amorphous MnOx . Both Mn2 O3 and the amorphous MnOx exhibit tremendous enhancement in oxygen evolution during photocatalysis and are much higher in comparison to so far known bioinspired manganese oxides and calcium-manganese oxides. Also, for the first time, a new approach for the representation of activities of water oxidation catalysts has been proposed by determining the amount of accessible manganese centers.

  7. Oxidation kinetics of ferrous sulfate over active carbon

    SciTech Connect

    Roennholm, M.R.; Waernaa, J.; Salmi, T.; Turunen, I.; Luoma, M.

    1999-07-01

    Catalyzed oxidation kinetics of dissolved Fe{sup 2+} ions to Fe{sup 3+} over active carbon in concentrated H{sub 2}SO{sub 4}-FeSO{sub 4} solutions was studied with isothermal and isobaric experiments carried out in a laboratory-scale pressurized autoclave. The experiments were performed at temperatures between 60 and 130 C, and the pressure of oxygen (O{sub 2}) was varied between 4 and 10 bar. The kinetic results revealed that the oxidation rate was enhanced by increasing the temperature and pressure and that the catalytic and noncatalytic oxidations proceed as parallel processes. A rate equation was obtained for the catalytic oxidation process, based on the assumption that the oxidation of Fe{sup 2+} with adsorbed oxygen is rate determining. The total oxidation rate was simulated by including a previously determined rate equation for the noncatalytic oxidation into the global model, from which the kinetic parameters of the catalytic oxidation rate were determined. A comparison of the model fit with the experimental data revealed that the proposed rate equation is applicable for the prediction of the Fe{sup 2+} oxidation kinetics in acidic ferrous sulfate solutions.

  8. Oxidized mitochondrial DNA activates the NLRP3 inflammasome during apoptosis.

    PubMed

    Shimada, Kenichi; Crother, Timothy R; Karlin, Justin; Dagvadorj, Jargalsaikhan; Chiba, Norika; Chen, Shuang; Ramanujan, V Krishnan; Wolf, Andrea J; Vergnes, Laurent; Ojcius, David M; Rentsendorj, Altan; Vargas, Mario; Guerrero, Candace; Wang, Yinsheng; Fitzgerald, Katherine A; Underhill, David M; Town, Terrence; Arditi, Moshe

    2012-03-23

    We report that in the presence of signal 1 (NF-κB), the NLRP3 inflammasome was activated by mitochondrial apoptotic signaling that licensed production of interleukin-1β (IL-1β). NLRP3 secondary signal activators such as ATP induced mitochondrial dysfunction and apoptosis, resulting in release of oxidized mitochondrial DNA (mtDNA) into the cytosol, where it bound to and activated the NLRP3 inflammasome. The antiapoptotic protein Bcl-2 inversely regulated mitochondrial dysfunction and NLRP3 inflammasome activation. Mitochondrial DNA directly induced NLRP3 inflammasome activation, because macrophages lacking mtDNA had severely attenuated IL-1β production, yet still underwent apoptosis. Both binding of oxidized mtDNA to the NLRP3 inflammasome and IL-1β secretion could be competitively inhibited by the oxidized nucleoside 8-OH-dG. Thus, our data reveal that oxidized mtDNA released during programmed cell death causes activation of the NLRP3 inflammasome. These results provide a missing link between apoptosis and inflammasome activation, via binding of cytosolic oxidized mtDNA to the NLRP3 inflammasome.

  9. Oxidized Mitochondrial DNA Activates the NLRP3 Inflammasome During Apoptosis

    PubMed Central

    Shimada, Kenichi; Crother, Timothy R.; Karlin, Justin; Dagvadorj, Jargalsaikhan; Chiba, Norika; Chen, Shuang; Ramanujan, V. Krishnan; Wolf, Andrea J.; Vergnes, Laurent; Ojcius, David M.; Rentsendorj, Altan; Vargas, Mario; Guerrero, Candace; Wang, Yinsheng; Fitzgerald, Katherine A.; Underhill, David M.; Town, Terrence; Arditi, Moshe

    2012-01-01

    SUMMARY We report that in the presence of signal 1 (NF-κB), the NLRP3 inflammasome was activated by mitochondrial apoptotic signaling that licensed production of interleukin-1β (IL-1β). NLRP3 secondary signal activators such as ATP induced mitochondrial dysfunction and apoptosis, resulting in release of oxidized mitochondrial DNA (mtDNA) into the cytosol, where it bound to and activated the NLRP3 inflammasome. The anti-apoptotic protein Bcl-2 inversely regulated mitochondrial dysfunction and NLRP3 inflammasome activation. Mitochondrial DNA directly induced NLRP3 inflammasome activation, because macrophages lacking mtDNA had severely attenuated IL-1β production, yet still underwent apoptosis. Both binding of oxidized mtDNA to the NLRP3 inflammasome and IL-1β secretion could be competitively inhibited by the oxidized nucleoside, 8-OH-dG. Thus, our data reveal that oxidized mtDNA released during programmed cell death causes activation of the NLRP3 inflammasome. These results provide a missing link between apoptosis and inflammasome activation, via binding of cytosolic oxidized mtDNA to the NLRP3 inflammasome. PMID:22342844

  10. Characterization of nitrated phenolic compounds for their anti-oxidant, pro-oxidant, and nitration activities.

    PubMed

    Iwasaki, Yusuke; Nomoto, Maki; Oda, Momoko; Mochizuki, Keisuke; Nakano, Yuki; Ishii, Yuji; Ito, Rie; Saito, Koichi; Umemura, Takashi; Nishikawa, Akiyoshi; Nakazawa, Hiroyuki

    2011-09-01

    Coffee is one of the most widely consumed beverages worldwide. Evidence of the health benefits and the important contribution of coffee brew to the intake of anti-oxidants in the diet has increased coffee consumption. Chlorogenic acid (ChA) and caffeic acid (CaA) are the major phenolic compounds in coffee. However, phenolic compounds, which are generally effective anti-oxidants, can become pro-oxidants in the presence of Cu(2+) to induce DNA damage under certain conditions. On the other hand, sodium nitrite (NaNO(2)) is widely used as a food additive to preserve and tinge color on cured meat and fish. It is possible that phenolic compounds react with NaNO(2) under acidic conditions, such as gastric juice. In this study, we identified compounds produced by the reaction between ChA or CaA in coffee and NaNO(2) in artificial gastric juice. The identified phenolic compounds and nitrated phenolic compounds were assessed for their anti-oxidant, pro-oxidant, and nitration activities by performing an in vitro assay. The nitrated phenolic compounds seemed to show increased anti-oxidant activity and decreased pro-oxidant activity. However, one nitrated CaA compound that has a furoxan ring showed the ability to release NO(2)(-) in the neutral condition.

  11. Enhanced oxidation resistance of active nanostructures via dynamic size effect

    PubMed Central

    Liu, Yun; Yang, Fan; Zhang, Yi; Xiao, Jianping; Yu, Liang; Liu, Qingfei; Ning, Yanxiao; Zhou, Zhiwen; Chen, Hao; Huang, Wugen; Liu, Ping; Bao, Xinhe

    2017-01-01

    A major challenge limiting the practical applications of nanomaterials is that the activities of nanostructures (NSs) increase with reduced size, often sacrificing their stability in the chemical environment. Under oxidative conditions, NSs with smaller sizes and higher defect densities are commonly expected to oxidize more easily, since high-concentration defects can facilitate oxidation by enhancing the reactivity with O2 and providing a fast channel for oxygen incorporation. Here, using FeO NSs as an example, we show to the contrary, that reducing the size of active NSs can drastically increase their oxidation resistance. A maximum oxidation resistance is found for FeO NSs with dimensions below 3.2 nm. Rather than being determined by the structure or electronic properties of active sites, the enhanced oxidation resistance originates from the size-dependent structural dynamics of FeO NSs in O2. We find this dynamic size effect to govern the chemical properties of active NSs. PMID:28223687

  12. Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium: biological relevance and synthetic strategies.

    PubMed

    Barry, Nicolas P E; Sadler, Peter J

    2012-04-21

    This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B-H activation, transmetalation reactions and/or direct formation of metal-metal bonds are discussed (103 references).

  13. Achieving Zero Stress in Iridium, Chromium, and Nickle Thin Films

    NASA Technical Reports Server (NTRS)

    Broadway, David M.; Weimer, Jeffrey; Gurgew, Danielle; Lis, Tomasz; Ramsey, Brian D.; O'Dell, Stephen L.; Ames, A.; Bruni, R.

    2015-01-01

    We examine a method for achieving zero intrinsic stress in thin films of iridium, chromium, and nickel deposited by magnetron sputter deposition. The examination of the stress in these materials is motivated by efforts to advance the optical performance of light-weight x-ray space telescopes into the regime of sub-arc second resolution that rely on control of the film stress to values within 10-100 MPa. A characteristic feature of the intrinsic stress behavior in chromium and nickel is their sensitivity to the magnitude and sign of the intrinsic stress with argon gas pressure, including the existence of a critical pressure that results in zero film stress. This critical pressure scales linearly with the film's density. While the effect of stress reversal with argon pressure has been previously reported by Hoffman and others for nickel and chromium, we have discovered a similar behavior for iridium. Additionally, we have identified zero stress in iridium shortly after island coalescence. This feature of film growth is used for achieving a total internal stress of -2.89 MPa for a 15.8 nm thick iridium film. The surface roughness of this low-stress film was examined using scanning probe microscopy (SPM) and x-ray reflectivity (XRR) at CuKa and these results presented and discussed.

  14. The Marine Geochemistry of Rhenium, Iridium and Platinum

    DTIC Science & Technology

    1991-09-01

    fields ( Koeberl 1989). Iridium enrichment factors, defined reiaiive to Hawaiian basalt (and relative to Sc) range from 104 to 105. The transport of Ir in...and M. B. McElroy. (1984). "Changes in atmospheric C02: influence of marine biota at high latitudes." J. Geoohys. Res. 89: 4629-4637. Koeberl , C

  15. Discovery of tantalum, rhenium, osmium, and iridium isotopes

    SciTech Connect

    Robinson, R.; Thoennessen, M.

    2012-09-15

    Currently, thirty-eight tantalum, thirty-eight rhenium, thirty-nine osmium, and thirty-eight iridium isotopes have been observed and the discovery of these isotopes is described here. For each isotope a brief synopsis of the first refereed publication, including the production and identification method, is presented.

  16. Remote Sensing Missions for Earth Observation on Iridium NEXT

    NASA Astrophysics Data System (ADS)

    Gupta, O. P.

    2009-12-01

    A unique opportunity exists to host up to 66 earth observation sensors on Iridium’s proposed NEXT LEO constellation in a manner that can revolutionize earth observation and weather predictions. A constellation approach to sensing, using the real-time communications backbone of Iridium, will enable unprecedented geospatial and temporal sampling for now-casting of weather on a global basis as well as global climate monitoring. The NEXT constellation, which, like Iridium’s current LEO constellation, is expected to consist of 66 interconnected satellites in 6 near polar orbiting planes, provides a unique platform for hosting a variety of earth observation missions. Several remote sensing missions were recommended by Group on Earth Observations (GEO), NASA, NOAA, and ESA for consideration by Iridium during 2008. These include GPS radio occultation sensors, earth radiation budget measurements, altimetry, ocean and land imaging, and troposphere and stratospheric winds measurements including polar winds measurements. These missions are also considered high priority climate missions by the Decadal Survey. Study teams consisting of Iridium, NASA/JPL and multiple industrial partners of Iridium have conducted detailed studies of these missions for compatibility with NEXT. These studies have established technical feasibility, unique benefits from a constellation approach, and cost effectiveness for these solutions on NEXT.

  17. The Iridium (tm) system: Personal communications anytime, anyplace

    NASA Astrophysics Data System (ADS)

    Hatlelid, John E.; Casey, Larry

    The Iridium system is designed to provide handheld personal communications between diverse locations around the world at any time and without prior knowledge of the location of the personal units. This paper provides an overview of the system, the services it provides, its operation, and an overview of the commercial practices and relatively high volume satellite production techniques which will make the system cost effective. A constellation of 66 satellites will provide an orbiting, spherical-shell, infrastructure for this global calling capability. The satellites act as tall cellular towers and allow convenient operation for portable handheld telephones. The system will provide a full range of services including voice, paging, data, geolocation, and fax capabilities. Motorola is a world leader in the production of high volume, high quality, reliable telecommunications hardware. One of Iridium's goals is to apply these production techniques to high reliability space hardware. Concurrent engineering, high performance work teams, advanced manufacturing technologies, and improved assembly and test methods are some of the techniques that will keep the Iridium system cost effective. Mobile, global, flexible personal communications are coming that will allow anyone to call or receive a call from/to anyplace at anytime. The Iridium system will provide communications where none exist today. This connectivity will allow increased information transfer, open new markets for various business endeavors, and in general increase productivity and development.

  18. Mononuclear iridium dinitrogen complexes bonded to zeolite HY

    SciTech Connect

    Yang, Dong; Chen, Mingyang; Martinez-Macias, Claudia; Dixon, David A.; Gates, Bruce C.

    2014-11-07

    In this study, the adsorption of N2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N2 in H2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N2. Four supported species formed in various flowing gases: Ir(N2), Ir(N2)(N2), Ir(C2H5)(N2), and Ir(H)(N2). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N2, Ir(N2) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N2) formed transiently in flowing CO, and in the presence of H2, rather stable iridium hydride complexes formed. Here, four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.

  19. Iridium alloy Clad Vent Set manufacturing qualification studies

    NASA Astrophysics Data System (ADS)

    Ulrich, George B.

    Metallurgical qualification studies to demonstrate the manufacturing readiness of the iridium alloy Clad Vent Set (CVS) for the General Purpose Heat Source program at the Oak Ridge Y-12 Plant are described. Microstructural data for various materials/test conditions are presented.

  20. The Iridium (tm) system: Personal communications anytime, anyplace

    NASA Technical Reports Server (NTRS)

    Hatlelid, John E.; Casey, Larry

    1993-01-01

    The Iridium system is designed to provide handheld personal communications between diverse locations around the world at any time and without prior knowledge of the location of the personal units. This paper provides an overview of the system, the services it provides, its operation, and an overview of the commercial practices and relatively high volume satellite production techniques which will make the system cost effective. A constellation of 66 satellites will provide an orbiting, spherical-shell, infrastructure for this global calling capability. The satellites act as tall cellular towers and allow convenient operation for portable handheld telephones. The system will provide a full range of services including voice, paging, data, geolocation, and fax capabilities. Motorola is a world leader in the production of high volume, high quality, reliable telecommunications hardware. One of Iridium's goals is to apply these production techniques to high reliability space hardware. Concurrent engineering, high performance work teams, advanced manufacturing technologies, and improved assembly and test methods are some of the techniques that will keep the Iridium system cost effective. Mobile, global, flexible personal communications are coming that will allow anyone to call or receive a call from/to anyplace at anytime. The Iridium system will provide communications where none exist today. This connectivity will allow increased information transfer, open new markets for various business endeavors, and in general increase productivity and development.

  1. Tubular solid oxide fuel cell demonstration activities

    SciTech Connect

    Veyo, S.E.

    1995-08-01

    The development of a viable fuel cell driven electrical power generation system involves not only the development of cell and stack technology, but also the development of the overall system concept, the strategy for control, and the ancillary subsystems. The design requirements used to guide system development must reflect a customer focus in order to evolve a commercial product. In order to obtain useful customer feedback, Westinghouse has practiced the deployment with customers of fully integrated, automatically controlled, packaged solid oxide fuel cell power generation systems. These field units have served to demonstrate to customers first hand the beneficial attributes of the SOFC, to expose deficiencies through experience in order to guide continued development, and to garner real world feedback and data concerning not only cell and stack parameters, but also transportation, installation, permitting and licensing, start-up and shutdown, system alarming, fault detection, fault response, and operator interaction.

  2. Human blood platelets lack nitric oxide synthase activity.

    PubMed

    Böhmer, Anke; Gambaryan, Stepan; Tsikas, Dimitrios

    2015-01-01

    Reports on expression and functionality of nitric oxide synthase (NOS) activity in human blood platelets and erythrocytes are contradictory. We used a specific gas chromatography-mass spectrometry (GC-MS) method to detect NOS activity in human platelets. The method measures simultaneously [(15)N]nitrite and [(15)N]nitrate formed from oxidized (15)N-labeled nitric oxide ((15)NO) upon its NOS-catalyzed formation from the substrate l-[guanidino-(15)N2]-arginine. Using this GC-MS assay, we did not detect functional NOS in non-stimulated platelets and in intact platelets activated by various agonists (adenosine diphosphate, collagen, thrombin, or von Willebrand factor) or lysed platelets. l-[guanidino-nitro]-Arginine-inhibitable NOS activity was measured after addition of recombinant human endothelial NOS to lysed platelets. Previous and recent studies from our group challenge expression and functionality of NOS in human platelets and erythrocytes.

  3. Utilization of Low Bandwidth Iridium Modems for Polar Seismology

    NASA Astrophysics Data System (ADS)

    Parker, T.

    2012-12-01

    Transmission of realtime seismic data is a desirable goal when a rapid response is needed. However, for many science applications sample waveform data, system state of health, and the ability to command and control the seismic station are operationally adequate. Determining the optimal telemetry requirements for a remote polar seismic experiment requires balancing science objective against the expensive, over-subscribed support available in the polar environments? For example there is a significant difference in the resources needed for a permanent "monitoring" effort versus a short-term experiment. We will describe IRIS/PASSCAL's successful approach to utilizing Iridium telemetry for short-term seismic experiments and suggest viable use of an Iridium RUDICs system for higher data-rate, permanent seismic stations such as a monitoring scenario. Most seismic stations are configured to record at a rate that exceeds twice the data rate of a single Iridium Internet modem. The power requirement to run continuous Iridium telemetry better than doubles that of a standalone seismic station. Doubling station power roughly doubles station logistics by requiring an increased number of support flights for installation and service. The tradeoffs between desirable and adequate telemetry requirements and the ramifications these requirements have on support services must be considered for a successful seismic station. We describe two Iridium telemetry systems, developed by the IRIS/PASSCAL Polar Program, for use with seismic stations in Antarctica and the Arctic. The first system uses an inexpensive Iridium 9602 modem based device and short burst data (SBD) transmission to monitor station performance, provide some command and control, and return a small amount of representative seismic data. Power requirements for this SBD system are approximately 10Ah per year for a daily message. The second system uses an Iridium 9522b modem based device the DOD RUDICs system for a 2400 Baud

  4. Paraoxonase Activity and Oxidative Status in Patients with Tinnitus

    PubMed Central

    Akyüz, Servet; Somuk, Battal Tahsin; Soyalic, Harun; Yılmaz, Beyhan; Taskin, Abdullah; Bilinc, Hasan; Aksoy, Nurten

    2016-01-01

    Background and Objectives The aim of this study was to investigate serum paraoxanase-1 (PON) activity, total oxidant status (TOS), total antioxidant status (TAS), and the oxidative stress index (OSI) in tinnitus; and to compare the results with data from healthy subjects. Subjects and Methods A total of 114 subjects-54 patients with tinnitus and 60 healthy controls were enrolled in this study. Serum PON activity, TOS, TAS, and OSI levels were measured. Results In the tinnitus group, TAS, and PON were significantly lower than in the control group (p<0.001). However, the TOS, and OSI levels were significantly higher in the tinnitus group than in the control group (p<0.001). Conclusions According to the data obtained from the present study, patients with tinnitus were exposed to potent oxidative stress. Oxidative stress may be the key contributing factor to the pathogenesis of tinnitus. PMID:27144229

  5. The cellular uptake and localization of non-emissive iridium(III) complexes as cellular reaction-based luminescence probes.

    PubMed

    Li, Chunyan; Liu, Yi; Wu, Yongquan; Sun, Yun; Li, Fuyou

    2013-01-01

    Improvement of cellular uptake and subcellular resolution remains a major obstacle in the successful and broad application of cellular optical probes. In this context, we design and synthesize seven non-emissive cyclometalated iridium(III) solvent complexes [Ir(CˆN)(2)(solv)(2)](+)L(-) (LIr2-LIr8, in which CˆN = 2-phenylpyridine (ppy) or its derivative; solv = DMSO, H(2)O or CH(3)CN; L(-) = PF(6)(-) or OTf(-)) applicable in live cell imaging to facilitate selective visualization of cellular structures. Based on the above variations (including different counter ions, solvent ligands, and CˆN ligands), structure-activity relationship analyses reveal a number of clear correlations: (1) variations in counter anions and solvent ligands of iridium(III) complexes do not affect cellular imaging behavior, and (2) length of the side carbon chain in CˆN ligands has significant effects on cellular uptake and localization/accumulation of iridium complexes in living cells. Moreover, investigation of the uptake mechanism via low-temperature and metabolism inhibitor assays reveal that [Ir(4-Meppy)(2)(CH(3)CN)(2)](+)OTf(-) (LIr5) with 2-phenylpyridine derivative with side-chain of methyl group at the 4-position as CˆN ligand permeates the outer and nuclear membranes of living cells through an energy-dependent, non-endocytic entry pathway, and translocation of the complex from the cell periphery towards the perinuclear region possibly occurs through a microtubule-dependent transport pathway. Nuclear pore complexes (NPCs) appear to selectively control the transport of iridium(III) complexes between the cytoplasm and nucleus. A generalization of trends in behavior and structure-activity relationships is presented, which should provide further insights into the design and optimization of future probes.

  6. Antiferroptotic activity of non-oxidative dopamine.

    PubMed

    Wang, Ding; Peng, Yingpeng; Xie, Yangchun; Zhou, Borong; Sun, Xiaofang; Kang, Rui; Tang, Daolin

    2016-11-25

    Dopamine is a neurotransmitter that has many functions in the nervous and immune systems. Ferroptosis is a non-apoptotic form of regulated cell death that is involved in cancer and neurodegenerative diseases. However, the role of dopamine in ferroptosis remains unidentified. Here, we show that the non-oxidative form of dopamine is a strong inhibitor of ferroptotic cell death. Dopamine dose-dependently blocked ferroptosis in cancer (PANC1 and HEY) and non-cancer (MEF and HEK293) cells following treatment with erastin, a small molecule ferroptosis inducer. Notably, dopamine reduced erastin-induced ferrous iron accumulation, glutathione depletion, and malondialdehyde production. Mechanically, dopamine increased the protein stability of glutathione peroxidase 4, a phospholipid hydroperoxidase that protects cells against membrane lipid peroxidation. Moreover, dopamine suppressed dopamine receptor D4 protein degradation and promoted dopamine receptor D5 gene expression. Thus, our findings uncover a novel function of dopamine in cell death and provide new insight into the regulation of iron metabolism and lipid peroxidation by neurotransmitters.

  7. IRIDIUM OXIDE PH MICROELECTRODE. (R825549C027)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  8. Catalysts for oxidation of mercury in flue gas

    DOEpatents

    Granite, Evan J.; Pennline, Henry W.

    2010-08-17

    Two new classes of catalysts for the removal of heavy metal contaminants, especially mercury (Hg) from effluent gases. Both of these classes of catalysts are excellent absorbers of HCl and Cl.sub.2 present in effluent gases. This adsorption of oxidizing agents aids in the oxidation of heavy metal contaminants. The catalysts remove mercury by oxidizing the Hg into mercury (II) moieties. For one class of catalysts, the active component is selected from the group consisting of iridium (Ir) and iridum-platinum (Ir/Pt) alloys. The Ir and Ir/Pt alloy catalysts are especially corrosion resistant. For the other class of catalyst, the active component is partially combusted coal or "Thief" carbon impregnated with Cl.sub.2. Untreated Thief carbon catalyst can be self-activating in the presence of effluent gas streams. The Thief carbon catalyst is disposable by means of capture from the effluent gas stream in a particulate collection device (PCD).

  9. Iridium-Catalyzed, Hydrosilyl-Directed Borylation of Unactivated Alkyl C−H Bonds

    PubMed Central

    Larsen, Matthew A.; Cho, Seung Hwan; Hartwig, John

    2016-01-01

    We report the iridium-catalyzed borylation of primary and secondary alkyl C−H bonds directed by a Si−H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C−H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C−H bonds, the borylation occurs selectively at a secondary C−H bond γ to the hydrosilyl group, and these reactions of secondary C−H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon−boron or carbon−silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation. PMID:26745739

  10. Formation of C–C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation

    PubMed Central

    Bower, John F.; Krische, Michael J.

    2011-01-01

    The formation of C–C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C–C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile–nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C–H bonds. PMID:21822399

  11. Iridium-Catalyzed, Hydrosilyl-Directed Borylation of Unactivated Alkyl C-H Bonds.

    PubMed

    Larsen, Matthew A; Cho, Seung Hwan; Hartwig, John

    2016-01-27

    We report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond γ to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.

  12. Ultrasound assisted, thermally activated persulfate oxidation of coal tar DNAPLs.

    PubMed

    Peng, Libin; Wang, Li; Hu, Xingting; Wu, Peihui; Wang, Xueqing; Huang, Chumei; Wang, Xiangyang; Deng, Dayi

    2016-11-15

    The feasibility of ultrasound assisted, thermally activated persulfate for effective oxidation of twenty 2-6 ringed coal tar PAHs in a biphasic tar/water system and a triphasic tar/soil/water system were investigated and established. The results indicate that ultrasonic assistance, persulfate and elevated reaction temperature are all required to achieve effective oxidation of coal tar PAHs, while the heating needed can be provided by ultrasonic induced heating as well. Further kinetic analysis reveals that the oxidation of individual PAH in the biphasic tar/water system follows the first-order kinetics, and individual PAH oxidation rate is primary determined by the mass transfer coefficients, tar/water interfacial areas, the aqueous solubility of individual PAH and its concentration in coal tar. Based on the kinetic analysis and experimental results, the contributions of ultrasound, persulfate and elevated reaction temperature to PAHs oxidation were characterized, and the effects of ultrasonic intensity and oxidant dosage on PAHs oxidation efficiency were investigated. In addition, the results indicate that individual PAH degradability is closely related to its reactivity as well, and the high reactivity of 4-6 ringed PAHs substantially improves their degradability.

  13. Oxidative esterification via photocatalytic C-H activation

    EPA Pesticide Factsheets

    Direct oxidative esterification of alcohol via photocatalytic C??H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.This dataset is associated with the following publication:Varma , R., S. Verma, R.B.N. Baig, C. Han, and M. Nadagouda. Oxidative esterification via photocatalytic C-H activation. GREEN CHEMISTRY. Royal Society of Chemistry, Cambridge, UK, 18: 251-254, (2015).

  14. Neural activity triggers neuronal oxidative metabolism followed by astrocytic glycolysis.

    PubMed

    Kasischke, Karl A; Vishwasrao, Harshad D; Fisher, Patricia J; Zipfel, Warren R; Webb, Watt W

    2004-07-02

    We have found that two-photon fluorescence imaging of nicotinamide adenine dinucleotide (NADH) provides the sensitivity and spatial three-dimensional resolution to resolve metabolic signatures in processes of astrocytes and neurons deep in highly scattering brain tissue slices. This functional imaging reveals spatiotemporal partitioning of glycolytic and oxidative metabolism between astrocytes and neurons during focal neural activity that establishes a unifying hypothesis for neurometabolic coupling in which early oxidative metabolism in neurons is eventually sustained by late activation of the astrocyte-neuron lactate shuttle. Our model integrates existing views of brain energy metabolism and is in accord with known macroscopic physiological changes in vivo.

  15. Analytical and preparative enantioseparation and main chiroptical properties of Iridium(III) bis(4,6-difluorophenylpyridinato)picolinato.

    PubMed

    Citti, Cinzia; Battisti, Umberto M; Ciccarella, Giuseppe; Maiorano, Vincenzo; Gigli, Giuseppe; Abbate, Sergio; Mazzeo, Giuseppe; Castiglioni, Ettore; Longhi, Giovanna; Cannazza, Giuseppe

    2016-10-07

    Almost all Iridium(III) complexes employed both as dopants in PhOLEDs and as pharmaceuticals and fluorescence bioprobes are racemic mixtures. In this study the single enantiomers of the most stable diastereomeric form fac-trans-N-N, bis[2-(4,6-difluorophenyl)pyridinato-C(2),N](picolinato)iridium(III) (FIrpic) were separated and analysed. The data obtained showed that the complex can be separated into stable optically active Λ and Δ isomers employing cellulose based chiral stationary phase both in normal and polar phase mode. Their chirality was confirmed and their absolute configuration assigned employing several methods (DFT and TDDFT calculations, CD and VCD). The CPL spectroscopy of the isolated enantiomers of FIrpic was also recorded due to its possible value in the OLEDs field. The chromatographic method was applied for a semipreparative purpose demonstrating that polar organic solvent chromatography (POSC) could be used to avoid the low-solubility issues associated with these Iridium(III) complexes. Finally, the chemical and stereochemical stability of the single isomers was evaluated under thermal stress by liquid chromatography coupled to high-resolution mass spectrometry (LC-QTOF) on both chiral and achiral columns. No racemization and/or isomerization was observed; however, the dissociation of the ancillary ligand was demonstrated employing LC-QTOF.

  16. Partially Oxidized Sub-10 nm MnO Nanocrystals with High Activity for Water Oxidation Catalysis

    PubMed Central

    Jin, Kyoungsuk; Chu, Arim; Park, Jimin; Jeong, Donghyuk; Jerng, Sung Eun; Sim, Uk; Jeong, Hui-Yun; Lee, Chan Woo; Park, Yong-Sun; Yang, Ki Dong; Kumar Pradhan, Gajendra; Kim, Donghun; Sung, Nark-Eon; Hee Kim, Sun; Nam, Ki Tae

    2015-01-01

    The oxygen evolution reaction (OER) is considered a major bottleneck in the overall water electrolysis process. In this work, highly active manganese oxide nano-catalysts were synthesized via hot injection. Facile surface treatment generated Mn(III) species on monodisperse 10 nm MnO nanocrystals (NCs). Size dependency of MnO NCs on OER activity was also investigated. Surprisingly, the partially oxidized MnO NCs only required 530 mV @ 5 mA cm−2 under near neutral conditions. PMID:25998696

  17. Nitric oxide-donor SNAP induces Xenopus eggs activation.

    PubMed

    Jeseta, Michal; Marin, Matthieu; Tichovska, Hana; Melicharova, Petra; Cailliau-Maggio, Katia; Martoriati, Alain; Lescuyer-Rousseau, Arlette; Beaujois, Rémy; Petr, Jaroslav; Sedmikova, Marketa; Bodart, Jean-François

    2012-01-01

    Nitric oxide (NO) is identified as a signaling molecule involved in many cellular or physiological functions including meiotic maturation and parthenogenetic activation of mammalian oocytes. We observed that nitric oxide donor SNAP was potent to induce parthenogenetic activation in Xenopus eggs. NO-scavenger CPTIO impaired the effects of SNAP, providing evidence for the effects of the latter to be specific upon NO release. In Xenopus eggs, SNAP treatment induced pigment rearrangement, pronucleus formation and exocytosis of cortical granules. At a biochemical level, SNAP exposure lead to MAPK and Rsk inactivation within 30 minutes whereas MPF remained active, in contrast to calcium ionophore control where MPF activity dropped rapidly. MAPK inactivation could be correlated to pronuclear envelope reformation observed. In SNAP-treated eggs, a strong increase in intracellular calcium level was observed. NO effects were impaired in calcium-free or calcium limited medium, suggesting that that parthenogenetic activation of Xenopus oocytes with a NO donor was mainly calcium-dependent.

  18. Simulation of dose distribution for iridium-192 brachytherapy source type-H01 using MCNPX

    SciTech Connect

    Purwaningsih, Anik

    2014-09-30

    Dosimetric data for a brachytherapy source should be known before it used for clinical treatment. Iridium-192 source type H01 was manufactured by PRR-BATAN aimed to brachytherapy is not yet known its dosimetric data. Radial dose function and anisotropic dose distribution are some primary keys in brachytherapy source. Dose distribution for Iridium-192 source type H01 was obtained from the dose calculation formalism recommended in the AAPM TG-43U1 report using MCNPX 2.6.0 Monte Carlo simulation code. To know the effect of cavity on Iridium-192 type H01 caused by manufacturing process, also calculated on Iridium-192 type H01 if without cavity. The result of calculation of radial dose function and anisotropic dose distribution for Iridium-192 source type H01 were compared with another model of Iridium-192 source.

  19. Simulation of dose distribution for iridium-192 brachytherapy source type-H01 using MCNPX

    NASA Astrophysics Data System (ADS)

    Purwaningsih, Anik

    2014-09-01

    Dosimetric data for a brachytherapy source should be known before it used for clinical treatment. Iridium-192 source type H01 was manufactured by PRR-BATAN aimed to brachytherapy is not yet known its dosimetric data. Radial dose function and anisotropic dose distribution are some primary keys in brachytherapy source. Dose distribution for Iridium-192 source type H01 was obtained from the dose calculation formalism recommended in the AAPM TG-43U1 report using MCNPX 2.6.0 Monte Carlo simulation code. To know the effect of cavity on Iridium-192 type H01 caused by manufacturing process, also calculated on Iridium-192 type H01 if without cavity. The result of calculation of radial dose function and anisotropic dose distribution for Iridium-192 source type H01 were compared with another model of Iridium-192 source.

  20. Ester-Modified Cyclometalated Iridium(III) Complexes as Mitochondria-Targeting Anticancer Agents

    PubMed Central

    Wang, Fang-Xin; Chen, Mu-He; Hu, Xiao-Ying; Ye, Rui-Rong; Tan, Cai-Ping; Ji, Liang-Nian; Mao, Zong-Wan

    2016-01-01

    Organometallic iridium complexes are potent anticancer candidates which act through different mechanisms from cisplatin-based chemotherapy regimens. Here, ten phosphorescent cyclometalated iridium(III) complexes containing 2,2′-bipyridine-4,4′-dicarboxylic acid and its diester derivatives as ligands are designed and synthesized. The modification by ester group, which can be hydrolysed by esterase, facilitates the adjustment of drug-like properties. The quantum yields and emission lifetimes are influenced by variation of the ester substituents on the Ir(III) complexes. The cytotoxicity of these Ir(III) complexes is correlated with the length of their ester groups. Among them, 4a and 4b are found to be highly active against a panel of cancer cells screened, including cisplatin-resistant cancer cells. Mechanism studies in vitro indicate that they undergo hydrolysis of ester bonds, accumulate in mitochondria, and induce a series of cell-death related events mediated by mitochondria. Furthermore, 4a and 4b can induce pro-death autophagy and apoptosis simultaneously. Our study indicates that ester modification is a simple and feasible strategy to enhance the anticancer potency of Ir(III) complexes. PMID:27958338

  1. Hysteresis in the Active Oxidation of SiC

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Harder, Bryan J.; Myers, Dwight L.

    2011-01-01

    Si and SiC show both passive oxidation behavior where a protective film of SiO2 forms and active oxidation behavior where a volatile suboxide SiO(g) forms. The active-to-passive and passive-to-active oxidation transitions are explored for both Si and SiC. Si shows a dramatic difference between the P(O2) for the two transitions of 10-4 bar. The active-to-passive transition is controlled by the condition for SiO2/Si equilibrium and the passive-to-active transition is controlled by the decomposition of SiO2. In the case of SiC, the P(O2) for these transitions are much closer. The active-to-passive transition appears to be controlled by the condition for SiO2/SiC equilibrium. The passive-to-active transition appears to be controlled by the interfacial reaction of SiC and SiO2 and subsequent generation of gases at the interface which leads to scale breakdown.

  2. Oxide Protective Coats for Ir/Re Rocket Combustion Chambers

    NASA Technical Reports Server (NTRS)

    Fortini, Arthur; Tuffias, Robert H.

    2003-01-01

    An improved material system has been developed for rocket engine combustion chambers for burning oxygen/ hydrogen mixtures or novel monopropellants, which are highly oxidizing at operating temperatures. The baseline for developing the improved material system is a prior iridium/rhenium system for chambers burning nitrogen tetroxide/monomethyl hydrazine mixtures, which are less oxidizing. The baseline combustion chamber comprises an outer layer of rhenium that provides structural support, plus an inner layer of iridium that acts as a barrier to oxidation of the rhenium. In the improved material system, the layer of iridium is thin and is coated with a thermal fatigue-resistant refractory oxide (specifically, hafnium oxide) that serves partly as a thermal barrier to decrease the temperature and thus the rate of oxidation of the rhenium. The oxide layer also acts as a barrier against the transport of oxidizing species to the surface of the iridium. Tests in which various oxygen/hydrogen mixtures were burned in iridium/rhenium combustion chambers lined with hafnium oxide showed that the operational lifetimes of combustion chambers of the improved material system are an order of magnitude greater than those of the baseline combustion chambers.

  3. Activation by nitric oxide of an oxidative-stress response that defends Escherichia coli against activated macrophages.

    PubMed

    Nunoshiba, T; deRojas-Walker, T; Wishnok, J S; Tannenbaum, S R; Demple, B

    1993-11-01

    Nitric oxide is a free radical (NO) formed biologically through the oxidation of L-arginine by nitric oxide synthases. NO is produced transiently in mammalian cells for intercellular signaling and in copious quantities to cause cytostasis and cytotoxicity. In the latter situation, NO is a deliberate cytotoxic product of activated macrophages, along with other reactive oxygen species such as hydrogen peroxide (H2O2) and superoxide (O2-). Escherichia coli has a complex set of responses to H2O2 and O2- that involves approximately 80 inducible proteins; we wondered whether these bacteria might induce analogous defenses against nitric oxide. We show here that a multigene system controlled by the redox-sensitive transcriptional regulator SoxR is activated by NO in vivo. This induction confers bacterial resistance to activated murine macrophages with kinetics that parallel the production of NO by these cells. Elimination of specific SoxR-regulated genes diminishes the resistance of these bacteria to the cytotoxic macrophages. The required functions include manganese-containing superoxide dismutase, endonuclease IV (a DNA-repair enzyme for oxidative damage), and micF, an antisense regulator of the outer membrane porin OmpF. These results demonstrate that SoxR is a sensor for cellular exposure to NO, and that the soxRS response system may contribute to bacterial virulence.

  4. Network flexibility of the IRIDIUM (R) Global Mobile Satellite System

    NASA Technical Reports Server (NTRS)

    Hutcheson, Jonathan; Laurin, Mala

    1995-01-01

    The IRIDIUM system is a global personal communications system supported by a constellation of 66 low earth orbit (LEO) satellites and a collection of earth-based 'gateway' switching installations. Like traditional wireless cellular systems, coverage is achieved by a grid of cells in which bandwidth is reused for spectral efficiency. Unlike any cellular system ever built, the moving cells can be shared by multiple switching facilities. Noteworthy features of the IRIDIUM system include inter-satellite links, a GSM-based telephony architecture, and a geographically controlled system access process. These features, working in concert, permit flexible and reliable administration of the worldwide service area by gateway operators. This paper will explore this unique concept.

  5. Iridium alloy clad vent set manufacturing qualification studies

    NASA Astrophysics Data System (ADS)

    Ulrich, George B.

    1991-01-01

    Qualification studies have been successfully conducted to demonstrate iridium alloy Clad Vent Set (CVS) manufacturing readiness for the General Purpose Heat Source (GPHS) program at the Oak Ridge Y-12 Plant. These studies were joint comparison evaluations of both the Y-12 Plant and EG&G Mound G-MAT) products. Note: EG&G-MAT formerly manufactured the iridium alloy CVS. The comparison evaluations involved work in a number of areas; however, only the CVS cup metallurgical evalution will be presented here. The initial metallurgical comparisons in conjunction with follow-up metallurgical work showed the Y-12 Plant CVS product to be comparable to the fully qualified (for Galileo and Ulysses missions) EG&G-MAT product. This allowed the Y-12 Plant to commence pilot production of CVS components for potential use in the CRAF and CASSINI missions.

  6. Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation

    PubMed Central

    2015-01-01

    To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnOx, a promising OER catalyst. We conclusively demonstrate that adding Au to MnOx significantly enhances OER activity relative to MnOx in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnOx catalysts reported to date. We also provide evidence that it is a local rather than bulk interaction between Au and MnOx that leads to the observed enhancement in the OER activity. Engineering improvements in nonprecious metal-based catalysts by the addition of Au or other noble metals could still represent a scalable catalyst as even trace amounts of Au are shown to lead a significant enhancement in the OER activity of MnOx. PMID:24661269

  7. Highly active oxide photocathode for photoelectrochemical water reduction.

    PubMed

    Paracchino, Adriana; Laporte, Vincent; Sivula, Kevin; Grätzel, Michael; Thimsen, Elijah

    2011-06-01

    A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H(2) production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm(-2) at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

  8. Highly active oxide photocathode for photoelectrochemical water reduction

    NASA Astrophysics Data System (ADS)

    Paracchino, Adriana; Laporte, Vincent; Sivula, Kevin; Grätzel, Michael; Thimsen, Elijah

    2011-06-01

    A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H2 production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm-2 at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

  9. Modulation of nitric oxide synthase activity in macrophages

    PubMed Central

    Jorens, P. G.; Matthys, K. E.

    1995-01-01

    L-Arginine is converted to the highly reactive and unstable nitric oxide (NO) and L-citrulline by an enzyme named nitric oxide synthase (NOS). NO decomposes into other nitrogen oxides such as nitrite (NO2-) and nitrate (NO2-), and in the presence of superoxide anion to the potent oxidizing agent peroxynitrite (ONOO−). Activated rodent macrophages are capable of expressing an inducible form of this enzyme (iNOS) in response to appropriate stimuli, i.e., lipopolysaccharide (LPS) and interferon-γ (IFNγ). Other cytokines can modulate the induction of NO biosynthesis in macrophages. NO is a major effector molecule of the anti-microbial and cytotoxic activity of rodent macrophages against certain micro-organisms and tumour cells, respectively. The NO synthesizing pathway has been demonstrated in human monocytes and other cells, but its role in host defence seems to be accessory. A delicate functional balance between microbial stimuli, host-derived cytokines and hormones in the microenvironment regulates iNOS expression. This review will focus mainly on the known and proposed mechanisms of the regulation of iNOS induction, and on agents that can modulate NO release once the active enzyme has been expressed in the macrophage. PMID:18475620

  10. Effects of tillage on the Fe oxides activation in soil

    NASA Astrophysics Data System (ADS)

    Chi, Guangyu; Chen, Xin; Shi, Yi; Wang, Jun; Zheng, Taihui

    2009-07-01

    Since mid-1950s, the wetland ecosystems in Sanjiang Plain of Northeast China have been experiencing greater changes in land use, which had negative effects on the soil environments. This study assessed the effects of soil tillage on the activation of soil Fe in the region. The test ecosystems included natural wetland, paddy field and upland field converted from wetland. Soil samples at the depths of 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, 40-60 cm, 60-90 cm and 90-120 cm were collected from each of the ecosystems for the analysis of vertical distribution of soil pH, organic carbon, chelate Fe oxides and Fe(II). The results showed that the conversion of wetland into paddy field and upland field induced a decrease of organic carbon content in 0-10 cm soil layer by 61.8% (P <0.05) and 70.0% (P < 0.05), respectively. The correlations among iron forms and soil organic carbon showed that chelate Fe oxides and Fe(II) was correlated positively with soil organic carbon and chelate ratio had a more positive relationship with organic carbon than chelate Fe oxides and Fe(II). The results of chelate Fe oxides, Fe(II) and chelate ratio of Fe suggested that reclamation could prevent the Fe activation and organic matter is credited for having an important influence on the process of Fe activation.

  11. Mononuclear iridium dinitrogen complexes bonded to zeolite HY

    DOE PAGES

    Yang, Dong; Chen, Mingyang; Martinez-Macias, Claudia; ...

    2014-11-07

    In this study, the adsorption of N2 on structurally well-defined dealuminated HY zeolite-supported iridium diethylene complexes was investigated. Iridium dinitrogen complexes formed when the sample was exposed to N2 in H2 at 298 K, as shown by infrared spectra recorded with isotopically labeled N2. Four supported species formed in various flowing gases: Ir(N2), Ir(N2)(N2), Ir(C2H5)(N2), and Ir(H)(N2). Their interconversions are summarized in a reaction network, showing, for example, that, in the presence of N2, Ir(N2) was the predominant dinitrogen species at temperatures of 273-373 K. Ir(CO)(N2) formed transiently in flowing CO, and in the presence of H2, rather stable iridiummore » hydride complexes formed. Here, four structural models of each iridium complex bonded at the acidic sites of the zeolite were employed in a computational investigation, showing that the calculated vibrational frequencies agree well with experiment when full calculations are done at the level of density functional theory, independent of the size of the model of the zeolite.« less

  12. Mono- and bis-tolylterpyridine iridium(III) complexes

    SciTech Connect

    Hinkle, Lindsay M.; Young, Jr., Victor G.; Mann, Kent R.

    2012-01-20

    The first structure report of trichlorido[4'-(p-tolyl)-2,2':6',2{double_prime}-terpyridine]iridium(III) dimethyl sulfoxide solvate, [IrCl{sub 3}(C{sub 22}H{sub 17}N{sub 3})] {center_dot} C{sub 2}H{sub 6}OS, (I), is presented, along with a higher-symmetry setting of previously reported bis[4'-(p-tolyl)-2,2':6',2{double_prime}-terpyridine]iridium(III) tris(hexafluoridophosphate) acetonitrile disolvate, [Ir(C{sub 22}H{sub 17}N{sub 3})2](PF{sub 6}){sub 3} {center_dot} 2C{sub 2}H{sub 3}N, (II) [Yoshikawa, Yamabe, Kanehisa, Kai, Takashima & Tsukahara (2007). Eur. J. Inorg. Chem. pp. 1911-1919]. For (I), the data were collected with synchrotron radiation and the dimethyl sulfoxide solvent molecule is disordered over three positions, one of which is an inversion center. The previously reported structure of (II) is presented in the more appropriate C2/c space group. The iridium complex and one PF{sub 6}{sup -} anion lie on twofold axes in this structure, making half of the molecule unique.

  13. Exploring Electro-active Functionality of Transparent Oxide Materials

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo

    2013-09-01

    Ceramics, one of the earliest materials used by humans, have been used since the Stone Age and are also one of the core materials supporting modern society. In this article, I will review the features of transparent oxides, the main components of ceramics, and the progress of research on their electro-active functionalities from the viewpoint of material design. Specifically, the emergence of the functionality of the cement component 12CaO.7Al2O3, the application of transparent oxide semiconductors to thin-film transistors for flat panel displays, and the design of wide-gap p-type semiconductors are introduced along with the progress in their research. In addition, oxide semiconductors are comprehensively discussed on the basis of the band lineup.

  14. Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

    PubMed Central

    Hermann, Anton; Sitdikova, Guzel F.; Weiger, Thomas M.

    2015-01-01

    All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences. PMID:26287261

  15. Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels.

    PubMed

    Hermann, Anton; Sitdikova, Guzel F; Weiger, Thomas M

    2015-08-17

    All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences.

  16. Oxidative activation of benzidine and its derivatives by peroxidases.

    PubMed Central

    Josephy, P D

    1985-01-01

    Benzidine (4,4'-diaminobiphenyl) is a known human carcinogen; exposure to this substance resulted in an epidemic of bladder cancer among workers in the dye industry in Europe and North America. The chemical or enzymatic oxidation of benzidine proceeds via a racial cation detectable by electron spin resonance. Peroxidase-catalyzed oxidation of benzidine generates reactive electrophiles which readily form adducts with phenol and thiol compounds. The structures of these novel metabolites are described. Peroxidases, including prostaglandin synthase, catalyze benzidine binding to protein and nucleic acid; the nature of the resulting adducts is unknown. The relevance of these processes to benzidine carcinogenesis in vivo is the subject of research and debate. A central question remains: is benzidine activated in extra-hepatic target tissues such as bladder epithelium, or transported to these tissues following hepatic oxidative metabolism? PMID:3007087

  17. Evaluation of Molybdenum as a Surrogate for Iridium in the GPHS Weld Development

    SciTech Connect

    Stine, Andrew Martin; Pierce, Stanley W.; Moniz, Paul F.

    2015-10-17

    The welding equipment used for welding iridium containers (clads) at Los Alamos National Laboratory is twenty five years old and is undergoing an upgrade. With the upgrade, there is a requirement for requalification of the welding process, and the opportunity for process improvement. Testing of the new system and requalification will require several welds on iridium test parts and clads, and any efforts to improve the process will add to the need for iridium parts. The extreme high cost of iridium imposes a severe limitation on the extent of test welding that can be done. The 2 inch diameter, 0.027 inch thick, iridium blank disc that the clad cup is formed from, is useful for initial weld trials, but it costs $5000. The development clad sets needed for final tests and requalification cost $15,000 per set. A solution to iridium cost issue would be to do the majority of the weld development on a less expensive surrogate metal with similar weld characteristics. One such metal is molybdenum. Since its melting index (melting temperature x thermal conductivity) is closest to iridium, welds on molybdenum should be similar in size for a given weld power level. Molybdenum is inexpensive; a single 2 inch molybdenum disc costs only $9. In order to evaluate molybdenum as a surrogate for iridium, GTA welds were first developed to provide full penetration on 0.030 inch thick molybdenum discs at speeds of 20, 25, and 30 inches per minute (ipm). These weld parameters were then repeated on the standard 0.027 inch thick iridium blanks. The top surface and bottom surface (root) width and grain structure of the molybdenum and iridium welds were compared, and similarities were evident between the two metals. Due to material and thickness differences, the iridium welds were approximately 35% wider than the molybdenum welds. A reduction in iridium weld current of 35% produce welds slightly smaller than the molybdenum welds yet showed that current could be scaled according to molybdenum/iridium

  18. Sulfur oxidation in rice field soil: activity, enumeration, isolation and characterization of thiosulfate-oxidizing bacteria.

    PubMed

    Stubner, S; Wind, T; Conrad, R

    1998-12-01

    In rice paddy fields the bulk soil is anoxic, but oxygenated zones occur in the surrounding of the rice roots to where oxygen is transported via the aerenchyma system of the rice plants. In the anaerobic soil compartments sulfate is consumed by sulfate-reducing bacteria. In the rhizosphere the reduced sulfur compounds can be reoxidized by sulfur-oxidizing bacteria. Measurements of the potential activity of thiosulfate-oxidizing bacteria in soil slurries derived from planted rice soil microcosms showed turnover rates of 2-6 mumol d-1 g-dw-1. Thiosulfate was oxidized to sulfate with tetrathionate as intermediate. Most probable number (MPN) enumeration with three aerobic media and one anaerobic nitrate-amended medium showed that thiosulfate-oxidizing bacteria were abundant in paddy soil and in rhizosphere soil at numbers of 10(5) to 10(6) per gram dry weight soil. Nine isolates of S-oxidizing bacteria were obtained from enrichment cultures or from the highest dilutions of the MPN series and were affiliated to four different phylogenetic groups. These isolates were characterized by physiological properties and by comparative 16S rDNA sequence analysis. Three isolates (TA1-AE1, TA1-A1 and TA12-21) were shown to be facultatively chemolithoautotrophic strains of Ancylobacter aquaticus. Three further isolates (Tv6-2b, Z2A-6A and Z4A-2A) were also facultatively chemolithoautotrophic and were affiliated with the Xanthobacter sp. group, probably representing new strains of X. flavus or X. tagetidis. Strain SZ-2111 was phylogenetically related to Bosea thiooxidans. However, the genus Bosea is described as obligately heterotrophic, whereas strain 5Z-2111 was able to grow autotrophically. The isolates 5Z-C1 and TBW3 were obligate chemolithoautotrophs and were closely affiliated with Thiobacillus thioparus. Our results showed that S-oxidizing bacteria were abundant and active in rice paddy soil and consisted of physiologically and phylogenetically diverse populations.

  19. Semiconductor films on flexible iridium substrates

    DOEpatents

    Goyal, Amit

    2005-03-29

    A laminate semiconductor article includes a flexible substrate, an optional biaxially textured oxide buffer system on the flexible substrate, a biaxially textured Ir-based buffer layer on the substrate or the buffer system, and an epitaxial layer of a semiconductor. Ir can serve as a substrate with an epitaxial layer of a semiconductor thereon.

  20. Rockot Launch Vehicle Commercial Operations for Grace and Iridium Program

    NASA Astrophysics Data System (ADS)

    Viertel, Y.; Kinnersley, M.; Schumacher, I.

    2002-01-01

    The GRACE mission and the IRIDIUM mission on ROCKOT launch vehicle are presented. Two identical GRACE satellites to measure in tandem the gravitational field of the earth with previously unattainable accuracy - it's called the Gravity Research and Climate Experiment, or and is a joint project of the U.S. space agency, NASA and the German Centre for Aeronautics and Space Flight, DLR. In order to send the GRACE twins into a 500x500 km , 89deg. orbit, the Rockot launch vehicle was selected. A dual launch of two Iridium satellites was scheduled for June 2002 using the ROCKOT launch vehicle from Plesetsk Cosmodrome in Northern Russia. This launch will inject two replacement satellites into a low earth orbit (LEO) to support the maintenance of the Iridium constellation. In September 2001, Eurockot successfully carried out a "Pathfinder Campaign" to simulate the entire Iridium mission cycle at Plesetsk. The campaign comprised the transport of simulators and related equipment to the Russian port-of-entry and launch site and also included the integration and encapsulation of the simulators with the actual Rockot launch vehicle at Eurockot's dedicated launch facilities at Plesetsk Cosmodrome. The pathfinder campaign lasted four weeks and was carried out by a joint team that also included Khrunichev, Russian Space Forces and Eurockot personnel on the contractors' side. The pathfinder mission confirmed the capability of Eurockot Launch Services to perform the Iridium launch on cost and on schedule at Plesetsk following Eurockot's major investment in international standard preparation, integration and launch facilities including customer facilities and a new hotel. In 2003, Eurockot will also launch the Japanese SERVI'S-1 satellite for USEF. The ROCKOT launch vehicle is a 3 stage liquid fuel rocket whose first 2 stages have been adapted from the Russian SS-19. A third stage, called "Breeze", can be repeatedly ignited and is extraordinarily capable of manoeuvre. Rockot can place

  1. Antibacterial Activity of Polymer Coated Cerium Oxide Nanoparticles

    PubMed Central

    Shah, Vishal; Shah, Shreya; Shah, Hirsh; Rispoli, Fred J.; McDonnell, Kevin T.; Workeneh, Selam; Karakoti, Ajay; Kumar, Amit; Seal, Sudipta

    2012-01-01

    Cerium oxide nanoparticles have found numerous applications in the biomedical industry due to their strong antioxidant properties. In the current study, we report the influence of nine different physical and chemical parameters: pH, aeration and, concentrations of MgSO4, CaCl2, KCl, natural organic matter, fructose, nanoparticles and Escherichia coli, on the antibacterial activity of dextran coated cerium oxide nanoparticles. A least-squares quadratic regression model was developed to understand the collective influence of the tested parameters on the anti-bacterial activity and subsequently a computer-based, interactive visualization tool was developed. The visualization allows us to elucidate the effect of each of the parameters in combination with other parameters, on the antibacterial activity of nanoparticles. The results indicate that the toxicity of CeO2 NPs depend on the physical and chemical environment; and in a majority of the possible combinations of the nine parameters, non-lethal to the bacteria. In fact, the cerium oxide nanoparticles can decrease the anti-bacterial activity exerted by magnesium and potassium salts. PMID:23110109

  2. Structural identification and cardiovascular activities of oxidized phospholipids.

    PubMed

    Salomon, Robert G

    2012-09-14

    Free radical-induced oxidation of membrane phospholipids generates complex mixtures of oxidized phospholipids (oxPLs). The combinatorial operation of a few dozen reaction types on a few dozen phospholipid structures results in the production of a dauntingly vast diversity of oxPL molecular species. Structural identification of the individual oxPL in these mixtures is a redoubtable challenge that is absolutely essential to allow determination of the biological activities of individual species. With an emphasis on cardiovascular consequences, this Review focuses on biological activities of oxPLs whose molecular structures are known and highlights 2 diametrically opposite approaches that were used to determine those structures, that is, (1) the classic approach from bioactivity of a complex mixture to isolation and structural characterization of the active molecule followed by confirmation of the structure by unambiguous chemical synthesis and (2) hypothesis of products that are likely to be generated by lipid oxidation, followed by synthesis, and then detection in vivo guided by the availability of authentic standards, and last, characterization of biological activities. Especially important for the application of the second paradigm is the capability of LC-MS/MS and derivatizations to selectively detect and quantify specific oxPL in complex mixtures, without the need for their isolation or complete separation. This technology can provide strong evidence for identity by comparisons with pure, well-characterized samples available by chemical syntheses. Those pure samples are critical for determining the biological activities attributable to specific molecular species of oxPLs in the complex mixtures generated in vivo as a consequence of oxidative stress.

  3. Antioxidant and nitric oxide inhibition activities of Thai medicinal plants.

    PubMed

    Makchuchit, Sunita; Itharat, Arunporn; Tewtrakul, Supinya

    2010-12-01

    Nineteen Thai medicinal plants used in Thai traditional medicine preparation to treat colds, asthma and fever were studied for their antioxidant and NO inhibitory activities. Three extracts were obtained from each plant. First extract obtained by macerating the plant part in 95% ethanol (Et) residue was boiled in water, where water extract (EW) was obtained. The third extract (HW) was obtained by boiling each plant in water similar to that of Thai traditional medicine practice. These extracts were tested for their antioxidant activity using DPPH assay, and anti-inflammatory activity by determination of inhibitory activity on lipopolysaccharide (LPS) induced nitric oxide (NO) production in RAW 264.7 cell lines using Griess reagent. Results indicated that Et, EW and HW of Syzygium aromaticum showed the highest antioxidant activity (EC50 = 6.56, 4.73 and 5.30 microg/ml, respectively). Et of Atractylodes lancea exhibited the most potent inhibitory activity on lipopolysaccharide (LPS) induced nitric oxide (NO) production in RAW 264.7 cells, with IC50 value of 9.70 microg/ml, followed by Et of Angelica sinensis and Cuminum cyminum (IC50 = 12.52 and 13.56 microg/ml, respectively) but water extract (EW, HW) of all plants were apparently inactive. These results of anti-inflammatory activity of these plants correspond with the traditional use for fever; cold, allergic-related diseases and inflammatory-related diseases.

  4. Real-Time Characterization of Formation and Breakup of Iridium Clusters in Highly Dealuminated Zeolite Y

    SciTech Connect

    Uzun, Alper; Gates, Bruce C.

    2009-01-15

    The chemistry of formation of iridium clusters from mononuclear iridium diethylene complexes anchored in dealuminated Y zeolite, and their subsequent breakup -- all including changes in the metal-metal, metal-support, and metal-ligand interactions -- is demonstrated by time-resolved EXAFS, XANES, and IR spectroscopy.

  5. Oxidative stress, activity behaviour and body mass in captive parrots

    PubMed Central

    Larcombe, S. D.; Tregaskes, C. A.; Coffey, J.; Stevenson, A. E.; Alexander, L. G.; Arnold, K. E.

    2015-01-01

    Many parrot species are kept in captivity for conservation, but often show poor reproduction, health and survival. These traits are known to be influenced by oxidative stress, the imbalance between the production of reactive oxygen species (ROS) and ability of antioxidant defences to ameliorate ROS damage. In humans, oxidative stress is linked with obesity, lack of exercise and poor nutrition, all of which are common in captive animals. Here, we tested whether small parrots (budgerigars, Melopsittacus undulatus) maintained in typical pet cages and on ad libitum food varied in oxidative profile, behaviour and body mass. Importantly, as with many birds held in captivity, they did not have enough space to engage in extensive free flight. Four types of oxidative damage, single-stranded DNA breaks (low-pH comet assay), alkali-labile sites in DNA (high-pH comet assay), sensitivity of DNA to ROS (H2O2-treated comet assay) and malondialdehyde (a byproduct of lipid peroxidation), were uncorrelated with each other and with plasma concentrations of dietary antioxidants. Without strenuous exercise over 28 days in a relatively small cage, more naturally ‘active’ individuals had more single-stranded DNA breaks than sedentary birds. High body mass at the start or end of the experiment, coupled with substantial mass gain, were all associated with raised sensitivity of DNA to ROS. Thus, high body mass in these captive birds was associated with oxidative damage. These birds were not lacking dietary antioxidants, because final body mass was positively related to plasma levels of retinol, zeaxanthin and α-tocopherol. Individuals varied widely in activity levels, feeding behaviour, mass gain and oxidative profile despite standardized living conditions. DNA damage is often associated with poor immunocompetence, low fertility and faster ageing. Thus, we have candidate mechanisms for the limited lifespan and fecundity common to many birds kept for conservation purposes. PMID

  6. Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship

    SciTech Connect

    Guo, Yu; Senanayake, Sanjaya; Gu, Dong; Jin, Zhao; Du, Pei -Pei; Si, Rui; Xu, Wen -Qian; Huang, Yu -Ying; Tao, Jing; Song, Qi -Sheng; Jia, Chun -Jia; Schueth, Ferdi

    2015-01-12

    Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5–0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) described the high homogeneity in the supported Au nanoparticles. The ex-situ and in-situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in-situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reduction by hydrogen (H₂-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeOx catalysts with very similar structural characteristics in CO oxidation.

  7. Uniform 2 nm gold nanoparticles supported on iron oxides as active catalysts for CO oxidation reaction: Structure-activity relationship

    DOE PAGES

    Guo, Yu; Senanayake, Sanjaya; Gu, Dong; ...

    2015-01-12

    Uniform Au nanoparticles (~2 nm) with narrow size-distribution (standard deviation: 0.5–0.6 nm) supported on both hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O) have been prepared by either deposition-precipitation (DP) or colloidal-deposition (CD) methods. Different structural and textural characterizations were applied to the dried, calcined and used gold-iron oxide samples. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) described the high homogeneity in the supported Au nanoparticles. The ex-situ and in-situ X-ray absorption fine structure (XAFS) characterization monitored the electronic and short-range local structure of active gold species. The synchrotron-based in-situ X-ray diffraction (XRD), together with the corresponding temperature-programmed reductionmore » by hydrogen (H₂-TPR), indicated a structural evolution of the iron-oxide supports, correlating to their reducibility. An inverse order of catalytic activity between DP (Au/Fe_OH < Au/Fe_O) and CD (Au/Fe_OH > Au/Fe_O) was observed. Effective gold-support interaction results in a high activity for gold nanoparticles, locally generated by the sintering of dispersed Au atoms on the oxide support in the DP synthesis, while a hydroxylated surface favors the reactivity of externally introduced Au nanoparticles on Fe_OH support for the CD approach. This work reveals why differences in the synthetic protocol translate to differences in the catalytic performance of Au/FeOx catalysts with very similar structural characteristics in CO oxidation.« less

  8. Nitric oxide-induced calcium release: activation of type 1 ryanodine receptor by endogenous nitric oxide.

    PubMed

    Kakizawa, Sho; Yamazawa, Toshiko; Iino, Masamitsu

    2013-01-01

    Ryanodine receptors (RyRs), located in the sarcoplasmic/endoplasmic reticulum (SR/ER) membrane, are required for intracellular Ca2+ release that is involved in a wide range of cellular functions. In addition to Ca2+-induced Ca2+ release in cardiac cells and voltage-induced Ca2+ release in skeletal muscle cells, we recently identified another mode of intracellular Ca2+ mobilization mediated by RyR, i.e., nitric oxide-induced Ca2+ release (NICR), in cerebellar Purkinje cells. NICR is evoked by neuronal activity, is dependent on S-nitrosylation of type 1 RyR (RyR1) and is involved in the induction of long-term potentiation (LTP) of cerebellar synapses. In this addendum, we examined whether peroxynitrite, which is produced by the reaction of nitric oxide with superoxide, may also have an effect on the Ca2+ release via RyR1 and the cerebellar LTP. We found that scavengers of peroxynitrite have no significant effect either on the Ca2+ release via RyR1 or on the cerebellar LTP. We also found that an application of a high concentration of peroxynitrite does not reproduce neuronal activity-dependent Ca2+ release in Purkinje cells. These results support that NICR is induced by endogenous nitric oxide produced by neuronal activity through S-nitrosylation of RyR1.

  9. Sensitized near-infrared emission from ytterbium(III) via direct energy transfer from iridium(III) in a heterometallic neutral complex.

    PubMed

    Mehlstäubl, Marita; Kottas, Gregg S; Colella, Silvia; De Cola, Luisa

    2008-05-14

    A tetrametallic iridium-ytterbium complex has been synthesised that shows sensitized near-infrared emission (lambda(max) = 976 nm) upon excitation of the iridium unit in the visible region (400 nm) due to efficient energy transfer from the iridium units to the Yb(III) ion. The iridium phosphorescence is quenched nearly quantitatively while the ytterbium ion emits brightly in the NIR.

  10. Microsomal ethanol oxidation: activity in vitro and in vivo.

    PubMed

    Roach, M K

    1975-01-01

    Studies by several investigators have confirmed that the microsomal fraction of mammalian liver oxidizes ethanol to acetaldehyde in a reaction that requires NADPH and oxygen. Efforts to identify the enzymes involved have produced conflicting opinions of the reaction mechanism, however. Initially, the microsomal mixed function oxidase system was assumed to be capable of oxidizing ethanol in a mechanism that did not involve either alcohol dehydrogenase or catalase. Later evidence suggested that the oxidative enzyme was, in fact, catalase, a contaminant of microsomal preparations and that the mixed function oxidase system merely furnished hydrogen peroxide to the reaction. Much current research supports the latter interpretation. Other workers provide evidence that favors a system in which catalase does not participate. Attempts to define the reaction process have involved studies with catalase inhibitors, kinetic studies of the different reaction systems, and physical separation of catalase from the microsomal components. Questions of the mechanism of microsomal ethanol oxidation may prove to be purely academic, however. Efforts to prove that the system has significant in vivo activity generally have not been successful.

  11. Enantiopure Ferrocene-Based Planar-Chiral Iridacycles: Stereospecific Control of Iridium-Centred Chirality.

    PubMed

    Arthurs, Ross A; Ismail, Muhammad; Prior, Christopher C; Oganesyan, Vasily S; Horton, Peter N; Coles, Simon J; Richards, Christopher J

    2016-02-24

    Reaction of [IrCp*Cl2 ]2 with ferrocenylimines (Fc=NAr, Ar=Ph, p-MeOC6 H4 ) results in ferrocene C-H activation and the diastereoselective synthesis of half-sandwich iridacycles of relative configuration Sp *,RIr *. Extension to (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline gave highly diastereoselective control over the new elements of planar chirality and metal-based pseudo-tetrahedral chirality, to give both neutral and cationic half-sandwich iridacycles of absolute configuration Sc ,Sp ,RIr . Substitution reactions proceed with retention of configuration, with the planar chirality controlling the metal-centred chirality through an iron-iridium interaction in the coordinatively unsaturated cationic intermediate.

  12. Cyclometalated iridium(III) complexes as mitochondria-targeted anticancer agents.

    PubMed

    Xiong, Kai; Chen, Yu; Ouyang, Cheng; Guan, Rui-Lin; Ji, Liang-Nian; Chao, Hui

    2016-06-01

    Four cyclometalated iridium(III) complexes [Ir(dfppy)2(L)](+) (dfppy = 2-(2,4-difluorophenyl)pyridine, L = 6-(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, Ir1; 6-(isoquinolin-1-yl)-1,3,5-triazine-2,4-diamine, Ir2; 6-(quinolin-2-yl)-1,3,5-triazine-2,4-diamine, Ir3; 6-(isoquinolin-3-yl)-1,3,5-triazine-2,4-diamine, Ir4) have been synthesized and characterized. Distinct from cisplatin, Ir1-Ir4 could specifically target mitochondria and induced apoptosis against various cancer cell lines, especially for cisplatin resistant cells. ICP-MS results indicated that Ir1-Ir4 were taken up via different mechanism for cancer cells and normal cells, which resulted in their high selectivity. The structure-activity relationship and signaling pathways were also discussed.

  13. Iridium abundance maxima at the latest Ordovician mass extinction horizon, Yangtze Basin, China: Terrestrial or extraterrestrial

    SciTech Connect

    Kun Wang; Chatterton, B.D.E. ); Attrep, M. Jr; Orth, C.J. )

    1992-01-01

    Neutron activation analyses of the Chinese Ordovician/Silurian (O/S) boundary sections at two distant localities in the Yangtze Basin, spanning the horizon of a major latest Ordovician global extinction event, show the maxima of iridium abundances to be coincident with the extinction horizon at the base of the graptolite Glyptograptus persculputs zone. The 0.23 ppb Ir maximum in the Yichang type section is almost as large as the late Eocene impact Ir anomaly. However, the authors have observed that the Ir abundances in the Chinese sections are closely correlated with the sedimentation rates, and therefore have concluded that Ir maxima do not indicate a cataclysmic extraterrestrial impact at this extinction level.

  14. Influence of graphene oxide and reduced graphene oxide on the activity and conformation of lysozyme.

    PubMed

    Bai, Yitong; Ming, Zhu; Cao, Yuye; Feng, Shicheng; Yang, Hua; Chen, Lingyun; Yang, Sheng-Tao

    2017-03-08

    The dramatically different bio-effects of graphene and graphene oxide (GO) have been widely observed in diverse biological systems, which determine the applications and toxicity of graphene materials. To elucidate the mechanism at molecular level, it is urgent to investigate the enzyme-graphene interaction and its consequences. In this study, we comparatively studied the influence of GO and reduced GO (RGO) on the activity and conformation of lysozyme to provide better understandings of their different bio-effects. Both GO and RGO adsorbed large quantities of lysozyme after incubation. GO inhibited lysozyme activity seriously, while RGO nearly had no influence on the enzyme activity. The different inhibitions of enzyme activity could be explained by the lysozyme conformational changes, where GO induced more changes to the protein conformation according to UV-vis absorbance, far-UV circular dichroism spectra, intrinsic fluorescence quenching, and infrared spectra. Based on the spectroscopic changes of lysozyme, GO induced the loss of secondary structure and exposed the active site of lysozyme more to the aqueous environment. In addition, neither GO nor RGO induced the fibrillation of lysozyme after 12d incubation. The results collectively indicated that the oxidation degree significantly impacted the enzyme-graphene interaction. The implications to the designs of enzyme-graphene system for bio-related applications and the toxicological effects of graphene materials are discussed.

  15. Catalytic Activity and Impedance Behavior of Screen-Printed Nickel Oxide as Efficient Water Oxidation Catalysts.

    PubMed

    Singh, Archana; Fekete, Monika; Gengenbach, Thomas; Simonov, Alexandr N; Hocking, Rosalie K; Chang, Shery L Y; Rothmann, Mathias; Powar, Satvasheel; Fu, Dongchuan; Hu, Zheng; Wu, Qiang; Cheng, Yi-Bing; Bach, Udo; Spiccia, Leone

    2015-12-21

    We report that films screen printed from nickel oxide (NiO) nanoparticles and microballs are efficient electrocatalysts for water oxidation under near-neutral and alkaline conditions. Investigations of the composition and structure of the screen-printed films by X-ray diffraction, X-ray absorption spectroscopy, and scanning electron microscopy confirmed that the material was present as the cubic NiO phase. Comparison of the catalytic activity of the microball films to that of films fabricated by using NiO nanoparticles, under similar experimental conditions, revealed that the microball films outperform nanoparticle films of similar thickness owing to a more porous structure and higher surface area. A thinner, less-resistive NiO nanoparticle film, however, was found to have higher activity per Ni atom. Anodization in borate buffer significantly improved the activity of all three films. X-ray photoelectron spectroscopy showed that during anodization, a mixed nickel oxyhydroxide phase formed on the surface of all films, which could account for the improved activity. Impedance spectroscopy revealed that surface traps contribute significantly to the resistance of the NiO films. On anodization, the trap state resistance of all films was reduced, which led to significant improvements in activity. In 1.00 m NaOH, both the microball and nanoparticle films exhibit high long-term stability and produce a stable current density of approximately 30 mA cm(-2) at 600 mV overpotential.

  16. Oxidation of activated carbon: application to vinegar decolorization.

    PubMed

    López, Francisco; Medina, Francisco; Prodanov, Marin; Güell, Carme

    2003-01-15

    This article reports studies on the feasibility of increasing the decoloring capacity of a granular activated carbon (GAC) by using oxidation with air at 350 degrees C to modify its surface activity and porosity. The GAC, obtained from olive stones, had a maximum decolorization capacity of 92% for doses of 20 g/l, while the maximum decolorization capacity of the modified granular activated carbon (MGAC) was about 96% at a dose of 10 g/l. The increase in decoloring capacity is thought to be due to an increase in mesopore area (from 129 to 340 m2/g) in the MGAC. The maximum decoloring values and the doses needed to attain them are very close to values obtained in previous studies using coconut shell powder-activated carbon (94 and 98% for red and white vinegar for a dose of 10 g/l, respectively).

  17. Nitric oxide radical scavenging active components from Phyllanthus emblica L.

    PubMed

    Kumaran, A; Karunakaran, R Joel

    2006-03-01

    An activity-directed fractionation and purification process was used to identify the nitric oxide (NO) scavenging components of Phyllanthus emblica. Dried fruit rind of P. emblica was extracted with methanol and then separated into hexane, ethyl acetate, and water fractions. Among these only the ethyl acetate phase showed strong NO scavenging activity in vitro, when compared with water and hexane phases. The ethyl acetate fraction was then subjected to separation and purification using Sephadex LH-20 chromatography. Five compounds showing strong NO scavenging activity were identified by spectral methods (1H NMR, 13C NMR, and MS) and by comparison with literature values to be Gallic acid, Methyl gallate, Corilagin, Furosin, and Geraniin. In addition, HPLC identification and quantification of isolated compounds were also performed. Gallic acid was found to be a major compound in the ethyl acetate extract and Geraniin showed highest NO scavenging activity among the isolated compounds.

  18. Antimicrobial activity of the metals and metal oxide nanoparticles.

    PubMed

    Dizaj, Solmaz Maleki; Lotfipour, Farzaneh; Barzegar-Jalali, Mohammad; Zarrintan, Mohammad Hossein; Adibkia, Khosro

    2014-11-01

    The ever increasing resistance of pathogens towards antibiotics has caused serious health problems in the recent years. It has been shown that by combining modern technologies such as nanotechnology and material science with intrinsic antimicrobial activity of the metals, novel applications for these substances could be identified. According to the reports, metal and metal oxide nanoparticles represent a group of materials which were investigated in respect to their antimicrobial effects. In the present review, we focused on the recent research works concerning antimicrobial activity of metal and metal oxide nanoparticles together with their mechanism of action. Reviewed literature indicated that the particle size was the essential parameter which determined the antimicrobial effectiveness of the metal nanoparticles. Combination therapy with the metal nanoparticles might be one of the possible strategies to overcome the current bacterial resistance to the antibacterial agents. However, further studies should be performed to minimize the toxicity of metal and metal oxide nanoparticles to apply as proper alternatives for antibiotics and disinfectants especially in biomedical applications.

  19. Iridium-catalyzed enantioselective hydrogenation of imines in supercritical carbon dioxide

    SciTech Connect

    Kainz, S.; Brinkmann, A.; Leitner, W.; Pfaltz, A.

    1999-07-14

    Supercritical carbon dioxide (scCO{sub 2}) was shown to be a reaction medium with unique properties for highly efficient iridium-catalyzed enantioselective hydrogenation of prochiral imines. Cationic iridium(I) complexes with chiral phosphinodihydrooxazoles, modified with perfluoroalkyl groups in the ligand or in the anion, were synthesized and tested in the hydrogenation of N-(1-phenylethylidene)aniline. Both the side chains and the lipophilic anions increased the solubility, but the choice of the anion also had a dramatic effect on the enantioselectivity with tetrakis-3,5-bis(trifluoromethyl)phenylborate (BARF) leading to the highest asymmetric induction. (R)-N-phenyl-1-phenylethylamine was formed quantitatively within 1 h in scCO{sub 2}[d(CO{sub 2}) = 0.75 g mL{sup {minus}1}] at 40 C and a H{sub 2} pressure of 30 bar with enantiomeric excesses of up to 81% using 0.078 mol % catalyst. The use of scCO{sub 2} instead of conventional solvents such as CH{sub 2}Cl{sub 2} allowed the catalyst loading to be lowered significantly owing to a change in the rate profile of the reaction. the homogeneous nature of the catalytically active species under the reaction conditions was demonstrated and was found to depend strongly on the composition of the reaction mixture and especially on the presence of the substrate. Utilizing the selective extractive properties of scCO{sub 2}, the product could be readily separated from the catalyst, which could be recycled several times without significant loss of activity and enantioselectivity. High-pressure FT-IR and NMR investigations revealed that the reactivity of the products to form the corresponding carbamic acids plays an important role for the application of this new methodology.

  20. Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

    PubMed Central

    He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; Carley, Albert F.; Borisevich, Albina Y.; Mineo, Yuki; Haruta, Masatake; Hutchings, Graham J.; Kiely, Christopher J.

    2016-01-01

    The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst. PMID:27671143

  1. Iridium: Global OTH data communications for high altitude scientific ballooning

    NASA Astrophysics Data System (ADS)

    Denney, A.

    beneficial points provided by the Iridium platform include pure global accessibility (as well as polar), cost effectiveness because it is available as a COTS (Commercially Off The Shelf) technology, reliability in that the equipment must operate in extreme conditions (near space), integration and development time into current systems must be minimized. As a bonus Motorola and NAL Research Corporation are developing SBD (Short Burst Data) into the Iridium network. This may lead the way to a global IP (Internet Protocol) node based ballooning platform. The Iridium satellite data modems employ the Iridium Low-Earth Orbit (LEO) satellite network. The scope of this paper is to introduce an OTH communications alternative, albeit not necessarily a primary one, to existing ballooning platforms using COTS based emerging technologies. Design aspects, characteristics, actual flight testing statistics, principles of the Iridium modems and communication paths are described including payload and support instrumentation interfacing. Not limited to high altitude ballooning, the Iridium communications platform opens a new era in remote commanding and data retrieval.

  2. Water-Soluble Iridium-NHC-Phosphine Complexes as Catalysts for Chemical Hydrogen Batteries Based on Formate.

    PubMed

    Horváth, Henrietta; Papp, Gábor; Szabolcsi, Roland; Kathó, Ágnes; Joó, Ferenc

    2015-09-21

    Molecular hydrogen, obtained by water electrolysis or photocatalytic water splitting, can be used to store energy obtained from intermittent sources such as wind and solar power. The storage and safe transportation of H2 , however, is an open and central question in such a hydrogen economy. Easy-to-synthesize, water-soluble iridium-N-heterocyclic carbene-phosphine (Ir(I) -NHC-phosphine) catalysts show unprecedented high catalytic activity in dehydrogenation of aqueous sodium formate. Fast reversible generation and storage of hydrogen can be achieved with these catalysts by a simple decrease or increase in the hydrogen pressure, respectively.

  3. Design and photocatalytic activity of nanosized zinc oxides

    NASA Astrophysics Data System (ADS)

    Gancheva, M.; Markova-Velichkova, M.; Atanasova, G.; Kovacheva, D.; Uzunov, I.; Cukeva, R.

    2016-04-01

    Zinc oxide particles with various morphologies were successfully prepared via three synthesis methods: precipitation; tribophysical treatment and sonochemistry. The as-synthesized samples were characterized by X-ray diffraction (XRD); infrared spectroscopy (IR); scanning electron microscope (SEM); BET specific surface area; electron-paramagnetic resonance (EPR), UV-Vis absorption/diffuse reflectance and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of the samples were evaluated by degradation of Malachite Green (MG) in an aqueous solution under UV and visible irradiation. The obtained ZnO powders possess crystallites size below 20 nm. The ZnO with spherical particles were obtained by precipitation method. The sonochemistry approach leads to preparation of ZnO with nanorod particles. The calculated band gaps of various ZnO powders belong to the range from 3.12 to 3.30 eV. The obtained polycrystalline zinc oxides exhibit good photocatalytic activity which is strongly influenced by the preparation conditions. The nanorod ZnO exhibits high photocatalytic activity under UV irradiation which is attributed to the morphology and the geometric surface of the particles. The ZnO obtained by precipitation has better photocatalytic efficiency under visible irradiation due to high B.E.T. specific surface area and the low level of band gap. Tribophysical treatment of a particle size-homogeneous system leads to deterioration of the photocatalytic activity of the material.

  4. Bias-enhanced nucleation of diamond on iridium: A comprehensive study of the first stages by sequential surface analysis

    NASA Astrophysics Data System (ADS)

    Chavanne, A.; Arnault, J.-C.; Barjon, J.; Arabski, J.

    2011-03-01

    The chemical evolution of the iridium surface along the successive steps of BEN was investigated using electron spectroscopy techniques (XPS, AES). To this end, a sequential study was carried out in an UHV analysis chamber connected to a MPCVD reactor. First, experimental results were obtained on iridium surfaces exposed to a methane plasma without bias. They show a sp 2 carbon layer formation on iridium, probably due to the segregation during cooling of carbon solubilized at high temperature in iridium. In this scenario, the iridium surface would be uncovered by carbon as BEN starts. Then, the consequences of BEN were observed: (i) formation of a thicker carbon layer at the iridium surface due to carbon segregation and sub-implantation (ii) chemical modification of iridium neighboring within the first nanometers; (iii) diamond nucleation.

  5. Luminescent iridium(III) complexes as novel protein staining agents.

    PubMed

    Jia, Junli; Fei, Hao; Zhou, Ming

    2012-05-01

    This article reports a new class of luminescent metal complexes, biscyclometalated iridium(III) complexes with an ancillary bathophenanthroline disulfonate ligand, for staining protein bands that are separated by electrophoresis. The performances of these novel staining agents have been studied in comparison with tris(bathophenanthroline disulfonate) ruthenium(II) tetrasodium salt (i.e. RuBPS) using a commercially available imaging system. The staining agents showed different limits of detection, linear dynamic ranges, and protein-to-protein variations. The overall performances of all three stains were found to be better than or equivalent to RuBPS under the experimental conditions.

  6. Determination of iridium in mafic rocks by atomic absorption

    USGS Publications Warehouse

    Grimaldi, F.S.; Schnepfe, M.M.

    1970-01-01

    Iridium is determined in mineralized mafic rocks by atomic absorption after fire-assay concentration into a gold bead. Interelement interferences in the atomic-absorption determination are removed and Ir sensitivity is increased by buffering the solutions with a mixture of copper and sodium sulphates. Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated in the atomic-absorption determination. The sensitivity and detection limits are 3.2 and 0.25 ppm of Ir, respectively. ?? 1970.

  7. Luminescent cyclometallated iridium(III) complexes having acetylide ligands

    DOEpatents

    Thompson, Mark E.; Bossi, Alberto; Djurovich, Peter Ivan

    2014-09-02

    The present invention relates to phosphorescent (triplet-emitting) organometallic materials. The phosphorescent materials of the present invention comprise Ir(III)cyclometallated alkynyl complexes for use as triplet light-emitting materials. The Ir(III)cyclometallated alkynyl complexes comprise at least one cyclometallating ligand and at least one alkynyl ligand bonded to the iridium. Also provided is an organic light emitting device comprising an anode, a cathode and an emissive layer between the anode and the cathode, wherein the emissive layer comprises a Ir(III)cyclometallated alkynyl complex as a triplet emitting material.

  8. Iridium-catalyzed reductive nitro-Mannich cyclization.

    PubMed

    Gregory, Alex W; Chambers, Alan; Hawkins, Alison; Jakubec, Pavol; Dixon, Darren J

    2015-01-02

    A new chemoselective reductive nitro-Mannich cyclization reaction sequence of nitroalkyl-tethered lactams has been developed. Relying on the rapid and chemoselective iridium(I)-catalyzed reduction of lactams to the corresponding enamine, subsequent nitro-Mannich cyclization of tethered nitroalkyl functionality provides direct access to important alkaloid natural-product-like structures in yields up to 81 % and in diastereoselectivities that are typically good to excellent. An in-depth understanding of the reaction mechanism has been gained through NMR studies and characterization of reaction intermediates. The new methodology has been applied to the total synthesis of (±)-epi-epiquinamide in four steps.

  9. The solubility of hydrogen in rhodium, ruthenium, iridium and nickel.

    NASA Technical Reports Server (NTRS)

    Mclellan, R. B.; Oates, W. A.

    1973-01-01

    The temperature variation of the solubility of hydrogen in rhodium, ruthenium, iridium, and nickel in equilibrium with H2 gas at 1 atm pressure has been measured by a technique involving saturating the solvent metal with hydrogen, quenching, and analyzing in resultant solid solutions. The solubilities determined are small (atom fraction of H is in the range from 0.0005 to 0.00001, and the results are consistent with the simple quasi-regular model for dilute interstitial solid solutions. The relative partial enthalpy and excess entropy of the dissolved hydrogen atoms have been calculated from the solubility data and compared with well-known correlations between these quantities.

  10. Measurements of the hard-x-ray reflectivity of iridium

    SciTech Connect

    Romaine, S.; Bruni, R.; Gorenstein, P.; Zhong, Z

    2007-01-10

    In connection with the design of a hard-x-ray telescope for the Constellation X-Ray Observatory we measured the reflectivity of an iridium-coated zerodur substrate as a function of angle at 55, 60, 70, and 80 keV at the National Synchrotron Light Source of Brookhaven National Laboratory. The optical constants were derived from the reflectivity data. The real component of the index of refraction is in excellent agreement with theoretical values at all four energies. However, the imaginary component, which is related to the mass attenuation coefficient, is 50% to 70% larger at 55, 60, and 70 keV than theoretical values.

  11. Reductive activation of Cr(Vi) by nitric oxide synthase.

    PubMed

    Porter, Ryan; Jáchymová, Marie; Martásek, Pavel; Kalyanaraman, B; Vásquez-Vivar, Jeannette

    2005-05-01

    Chromium(VI) is a recognized toxicant whose effects have been linked to its reduction to lower oxidation states. Although Cr(VI) is reduced by several systems, it is anticipated that its reduction by nitric oxide synthase (NOS) could have significant effects in endothelial and brain cells that express high constitutive levels of the enzyme. This possibility was examined by electron paramagnetic resonance that showed the formation of a stable Cr(V) species from NOS/Cr(VI). The formation of Cr(V) was calcium/calmodulin-independent indicating that Cr(VI) to Cr(V) reduction occurs at the flavin-containing domain of NOS. Accordingly, Cr(VI) reduction by the reductase domain of NOS and the chimera protein cytochrome-P450-reductase+tail-nNOS also generated Cr(V). Activation of tetrahydrobiopterin (BH(4))-free NOS with calcium/calmodulin diminished Cr(V) steady-state levels while increasing superoxide formation. Since SOD restored Cr(V) to control levels, this result was taken as evidence for a reaction between Cr(V) and superoxide. Supplementation of NOS with BH(4) cofactor not only failed to increase Cr(V) yields but generated superoxide and hydroxyl radical. Since the holoenzyme does not generate superoxide, this reaction indicated that Cr(V) mediates the oxidation of BH(4)-bound to the enzyme. In the presence of L-arginine, however, Cr(VI) neither enhances superoxide release nor inhibits NO formation from fully active NOS. This suggests that L-arginine protects BH(4) from Cr(V)-mediated oxidation. While Cr(V) was inactive toward NO, spin trapping experiments with 5-tert-butoxycarbonyl 5-methyl-1-pyrroline N-oxide and oxygen consumption measurements showed that Cr(V) reacts with superoxide by a one-electron-transfer mechanism to generate oxygen and Cr(IV). Thus, reduction of Cr(VI) to Cr(V) by NOS occurs in resting and fully active states. It is likely that the reaction between Cr(V) and superoxide influences the cytotoxic mechanisms of Cr(VI) in cells.

  12. Theoretical investigation of the activity of cobalt oxides for the electrochemical oxidation of water.

    PubMed

    Bajdich, Michal; García-Mota, Mónica; Vojvodic, Aleksandra; Nørskov, Jens K; Bell, Alexis T

    2013-09-11

    The presence of layered cobalt oxides has been identified experimentally in Co-based anodes under oxygen-evolving conditions. In this work, we report the results of theoretical investigations of the relative stability of layered and spinel bulk phases of Co oxides, as well as the stability of selected surfaces as a function of applied potential and pH. We then study the oxygen evolution reaction (OER) on these surfaces and obtain activity trends at experimentally relevant electro-chemical conditions. Our calculated volume Pourbaix diagram shows that β-CoOOH is the active phase where the OER occurs in alkaline media. We calculate relative surface stabilities and adsorbate coverages of the most stable low-index surfaces of β-CoOOH: (0001), (0112), and (1014). We find that at low applied potentials, the (1014) surface is the most stable, while the (0112) surface is the more stable at higher potentials. Next, we compare the theoretical overpotentials for all three surfaces and find that the (1014) surface is the most active one as characterized by an overpotential of η = 0.48 V. The high activity of the (1014) surface can be attributed to the observation that the resting state of Co in the active site is Co(3+) during the OER, whereas Co is in the Co(4+) state in the less active surfaces. Lastly, we demonstrate that the overpotential of the (1014) surface can be lowered further by surface substitution of Co by Ni. This finding could explain the experimentally observed enhancement in the OER activity of Ni(y)Co(1-y)O(x) thin films with increasing Ni content. All energetics in this work were obtained from density functional theory using the Hubbard-U correction.

  13. NITRIC OXIDE, MITOCHONDRIAL HYPERPOLARIZATION AND T-CELL ACTIVATION

    PubMed Central

    Nagy, Gyorgy; Koncz, Agnes; Fernandez, David; Perl, Andras

    2007-01-01

    T lymphocyte activation is associated with nitric oxide (NO) production that plays an essential role in multiple T cell functions. NO acts as a messenger, activating soluble guanyl cyclase and participating in the transduction signaling pathways involving cyclic GMP. NO modulates mitochondrial events that are involved in apoptosis and regulates mitochondrial membrane potential and mitochondrial biogenesis in many cell types, including lymphocytes. Mitochondrial hyperpolarization (MHP), an early and reversible event during both T lymphocyte activation and apoptosis, is regulated by NO. Here, we discuss recent evidence that NO-induced MHP represents a molecular switch in multiple T cell signaling pathways. Overproduction of NO in systemic lupus erythematosus (SLE) induces mitochondrial biogenesis and alters Ca2+ signaling. Thus, while NO plays a physiological role in lymphocyte cell signaling, its overproduction may disturb normal T cell function, contributing to the pathogenesis of autoimmunity. PMID:17462531

  14. Local structure of Iridium organometallic catalysts covalently bonded to carbon nanotubes.

    NASA Astrophysics Data System (ADS)

    Blasco, J.; Cuartero, V.; Subías, G.; Jiménez, M. V.; Pérez-Torrente, J. J.; Oro, L. A.; Blanco, M.; Álvarez, P.; Blanco, C.; Menéndez, R.

    2016-05-01

    Hybrid catalysts based on Iridium N-heterocyclic carbenes anchored to carbon nanotubes (CNT) have been studied by XAFS spectroscopy. Oxidation of CNT yields a large amount of functional groups, mainly hydroxyl groups at the walls and carboxylic groups at the tips, defects and edges. Different kinds of esterification reactions were performed to functionalize oxidized CNT with imidazolium salts. Then, the resulting products were reacted with an Ir organometallic compound to form hybrid catalysts efficient in hydrogen transfer processes. XANES spectroscopy agree with the presence of Ir(I) in these catalysts and the EXAFS spectra detected differences in the local structure of Ir atoms between the initial Ir organometallic compound and the Ir complexes anchored to the CNT. Our results confirm that the halide atom, present in the Ir precursor, was replaced by oxygen from -OH groups at the CNT wall in the first coordination shell of Ir. The lability of this group accounts for the good recyclability and the good efficiency shown by these hybrid catalysts.

  15. Osmium, ruthenium, iridium and uranium in silicates and chromite from the eastern Bushveld Complex, South Africa

    USGS Publications Warehouse

    Gijbels, R.h.; Millard, H.T.; Desborough, G.A.; Bartel, A.J.

    1974-01-01

    Osmium, ruthenium, iridium and uranium contents were determined in eight ortho pyroxene, seven plagioclase, and three chromite mineral separates from the eastern Bushveld Complex. Neutron activation analysis was used to measure the platinum metals, and uranium was determined by a fission track technique. The platinum metals were found to be present within each mine??ral in the proportions Os:Ru:Ir = 1:7:1, while the concentrations of these metals in the minerals are in the ratios orthopyroxene:plagioclase:chromite = 1:16:700. The concentration of uranium was found to range from 11 to 66 ppb (parts per billion) and not to vary significantly from mineral to mineral. The data for the platinum metals are consistent with a model in which the eastern Bushveld Complex was formed by the fractional crystallization of two separately injected magmas. A computer fit of this model to these data indicates that the initial concentrations of Os, Ru and Ir in the first magma were 0.24, 2.0 and 0.21 ppb and in the second magma were 0.16, 1.1 and 0.18 ppb, respectively. The fit also yields the distribution coefficients for the partitioning between the liquid and cumulus orthopyroxene, cumulus plagioclase and cumulus chromite. These coefficients (mineral/liquid) for osmium are 4.5, 66 and 2700; for ruthenium, they are 5, 65 and 2700; and for iridium, they are 4, 60 and 1600. To make this fit, it was necessary to hypothesize the existence of two types of chromite: one type with a large distribution coefficient, presumably formed as a cumulus phase at high temperature, and another, more prevalent type with a smaller distribution coefficient, which may have been formed by postcumulus growth at a lower temperature. This hypothesis is supported by data for coexisting chromite-silicate pairs, which indicate that the chromite grains expelled these platinum metals as they cooled. ?? 1974.

  16. Switching on electrocatalytic activity in solid oxide cells

    NASA Astrophysics Data System (ADS)

    Myung, Jae-Ha; Neagu, Dragos; Miller, David N.; Irvine, John T. S.

    2016-09-01

    Solid oxide cells (SOCs) can operate with high efficiency in two ways—as fuel cells, oxidizing a fuel to produce electricity, and as electrolysis cells, electrolysing water to produce hydrogen and oxygen gases. Ideally, SOCs should perform well, be durable and be inexpensive, but there are often competitive tensions, meaning that, for example, performance is achieved at the expense of durability. SOCs consist of porous electrodes—the fuel and air electrodes—separated by a dense electrolyte. In terms of the electrodes, the greatest challenge is to deliver high, long-lasting electrocatalytic activity while ensuring cost- and time-efficient manufacture. This has typically been achieved through lengthy and intricate ex situ procedures. These often require dedicated precursors and equipment; moreover, although the degradation of such electrodes associated with their reversible operation can be mitigated, they are susceptible to many other forms of degradation. An alternative is to grow appropriate electrode nanoarchitectures under operationally relevant conditions, for example, via redox exsolution. Here we describe the growth of a finely dispersed array of anchored metal nanoparticles on an oxide electrode through electrochemical poling of a SOC at 2 volts for a few seconds. These electrode structures perform well as both fuel cells and electrolysis cells (for example, at 900 °C they deliver 2 watts per square centimetre of power in humidified hydrogen gas, and a current of 2.75 amps per square centimetre at 1.3 volts in 50% water/nitrogen gas). The nanostructures and corresponding electrochemical activity do not degrade in 150 hours of testing. These results not only prove that in operando methods can yield emergent nanomaterials, which in turn deliver exceptional performance, but also offer proof of concept that electrolysis and fuel cells can be unified in a single, high-performance, versatile and easily manufactured device. This opens up the possibility of

  17. Switching on electrocatalytic activity in solid oxide cells.

    PubMed

    Myung, Jae-Ha; Neagu, Dragos; Miller, David N; Irvine, John T S

    2016-09-22

    Solid oxide cells (SOCs) can operate with high efficiency in two ways-as fuel cells, oxidizing a fuel to produce electricity, and as electrolysis cells, electrolysing water to produce hydrogen and oxygen gases. Ideally, SOCs should perform well, be durable and be inexpensive, but there are often competitive tensions, meaning that, for example, performance is achieved at the expense of durability. SOCs consist of porous electrodes-the fuel and air electrodes-separated by a dense electrolyte. In terms of the electrodes, the greatest challenge is to deliver high, long-lasting electrocatalytic activity while ensuring cost- and time-efficient manufacture. This has typically been achieved through lengthy and intricate ex situ procedures. These often require dedicated precursors and equipment; moreover, although the degradation of such electrodes associated with their reversible operation can be mitigated, they are susceptible to many other forms of degradation. An alternative is to grow appropriate electrode nanoarchitectures under operationally relevant conditions, for example, via redox exsolution. Here we describe the growth of a finely dispersed array of anchored metal nanoparticles on an oxide electrode through electrochemical poling of a SOC at 2 volts for a few seconds. These electrode structures perform well as both fuel cells and electrolysis cells (for example, at 900 °C they deliver 2 watts per square centimetre of power in humidified hydrogen gas, and a current of 2.75 amps per square centimetre at 1.3 volts in 50% water/nitrogen gas). The nanostructures and corresponding electrochemical activity do not degrade in 150 hours of testing. These results not only prove that in operando methods can yield emergent nanomaterials, which in turn deliver exceptional performance, but also offer proof of concept that electrolysis and fuel cells can be unified in a single, high-performance, versatile and easily manufactured device. This opens up the possibility of

  18. Wet oxidation of activated sludge: transformations and mechanisms.

    PubMed

    Urrea, José Luis; Collado, Sergio; Laca, Amanda; Díaz, Mario

    2014-12-15

    Wet oxidation (WO) is an interesting alternative for the solubilization and mineralization of activated sludge. The effects of different temperatures (160-200 °C) and pressures (4-8 MPa), on the evolution of chemical composition and rheological characteristics of a thickened activated sludge during WO are analyzed in this work. Soluble COD increases initially to a maximum and then diminishes, while the apparent viscosity of the mixture falls continuously throughout the experiment. Based on the experimental evolution of the compositions and rheological characteristics of the sludge, a mechanism consisting of two stages in series is proposed. Initially, the solid organic compounds are solubilized following a pseudo-second order kinetic model with respect to solid COD. After that, the solubilized COD was oxidized, showing a pseudofirst kinetic order, by two parallel pathways: the complete mineralization of the organic matter and the formation of highly refractory COD. Kinetic parameters of the model, including the activation energies are mentioned, with good global fitting to the experiments described.

  19. Redox Potentials, Laccase Oxidation, and Antilarval Activities of Substituted Phenols

    PubMed Central

    Prasain, Keshar; Nguyen, Thi D. T.; Gorman, Maureen J.; Barrigan, Lydia M.; Peng, Zeyu; Kanost, Michael R.; Syed, Lateef U.; Li, Jun; Zhu, Kun Yan; Hua, Duy H.

    2012-01-01

    Laccases are copper-containing oxidases that are involved in sclerotization of the cuticle of mosquitoes and other insects. Oxidation of exogenous compounds by insect laccases may have the potential to produce reactive species toxic to insects. We investigated two classes of substituted phenolic compounds, halogenated di- and trihydroxybenzenes and substituted di-tert-butylphenols, on redox potential, oxidation by laccase and effects on mosquito larval growth. An inverse correlation between the oxidation potentials and laccase activity of halogenated hydroxybenzenes was found. Substituted di-tert-butylphenols however were found to impact mosquito larval growth and survival. In particular, 2,4-di-tert-butyl-6-(3-methyl-2-butenyl)phenol (15) caused greater than 98% mortality of Anopheles gambiae larvae in a concentration of 180 nM, whereas 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-2-methylpropanal oxime (13) and 6,8-di-tert-butyl-2,2-dimethyl-3,4-dihydro-2H-chromene (33) caused 93% and 92% mortalities in concentrations of 3.4 and 3.7 μM, respectively. Larvae treated with di-tert-butylphenolic compounds died just before pupation. PMID:22300888

  20. Dynamic high-temperature characterization of an iridium alloy in tension

    SciTech Connect

    Song, Bo; Nelson, Kevin; Jin, Helena; Lipinski, Ronald J.; Bignell, John; Ulrich, G. B.; George, E. P.

    2015-09-01

    Iridium alloys have been utilized as structural materials for certain high-temperature applications, due to their superior strength and ductility at elevated temperatures. The mechanical properties, including failure response at high strain rates and elevated temperatures of the iridium alloys need to be characterized to better understand high-speed impacts at elevated temperatures. A DOP-26 iridium alloy has been dynamically characterized in compression at elevated temperatures with high-temperature Kolsky compression bar techniques. However, the dynamic high-temperature compression tests were not able to provide sufficient dynamic high-temperature failure information of the iridium alloy. In this study, we modified current room-temperature Kolsky tension bar techniques for obtaining dynamic tensile stress-strain curves of the DOP-26 iridium alloy at two different strain rates (~1000 and ~3000 s-1) and temperatures (~750°C and ~1030°C). The effects of strain rate and temperature on the tensile stress-strain response of the iridium alloy were determined. The DOP-26 iridium alloy exhibited high ductility in stress-strain response that strongly depended on both strain rate and temperature.

  1. Active metal oxides and polymer hybrids as biomaterials

    NASA Astrophysics Data System (ADS)

    Jarrell, John D.

    show that silver doping improved the photoactivity of oxide coatings, but hindered activity of a specific hybrid. Doped titanium oxide and polymer hybrid coatings have potential for improving soft tissue integration of medical implants and wound healing by modulating cell proliferation, attachment, inflammation and providing controlled delivery of bioactive and antimicrobial compounds and photon induced electro-chemical activity.

  2. A cyclometalated iridium(III) complex with enhanced phosphorescence emission in the solid state (EPESS): synthesis, characterization and its application in bioimaging.

    PubMed

    Wu, Huazhou; Yang, Tianshe; Zhao, Qiang; Zhou, Jing; Li, Chunyan; Li, Fuyou

    2011-03-07

    Iridium(III) complexes with intense phosphorescence in solution have been widely applied in organic light-emitting diodes, chemosensors and bioimaging. However, little attention has been paid to iridium(III) complexes showing weak phosphorescence in solution and enhanced phosphorescence emission in the solid state (EPESS). In the present study, two β-diketonate ligands with different degrees of conjugation, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HL1) and 1-phenyl-3-methyl-4-phenylacetyl-5-pyrazolone (HL2), have been synthesized to be used as ancillary ligands for two iridium(III) complexes, Ir(ppy)(2)(L1) and Ir(ppy)(2)(L2) (Hppy = 2-phenylpyridine). The two complexes have been characterized by single-crystal X-ray crystallography, (1)H NMR and elemental analysis. Interestingly, Ir(ppy)(2)(L1) is EPESS-active whereas Ir(ppy)(2)(L2) exhibits moderately intense emission both in solution and as a neat film, indicating that the degree of conjugation of the β-diketone ligands determines the EPESS-activity. The single-crystal X-ray analysis has indicated that there are π-π interactions between the adjacent ppy ligands in Ir(ppy)(2)(L1) but not in Ir(ppy)(2)(L2). Finally, EPESS-active Ir(ppy)(2)(L1) has been successfully embedded in polymer nanoparticles and used as a luminescent label in bioimaging.

  3. Oxalomalate affects the inducible nitric oxide synthase expression and activity.

    PubMed

    Irace, Carlo; Esposito, Giuseppe; Maffettone, Carmen; Rossi, Antonietta; Festa, Michela; Iuvone, Teresa; Santamaria, Rita; Sautebin, Lidia; Carnuccio, Rosa; Colonna, Alfredo

    2007-03-13

    Inducible nitric oxide synthase (iNOS) is an homodimeric enzyme which produces large amounts of nitric oxide (NO) in response to inflammatory stimuli. Several factors affect the synthesis and catalytic activity of iNOS. Particularly, dimerization of NOS monomers is promoted by heme, whereas an intracellular depletion of heme and/or L-arginine considerably decreases NOS resistance to proteolysis. In this study, we found that oxalomalate (OMA, oxalomalic acid, alpha-hydroxy-beta-oxalosuccinic acid), an inhibitor of both aconitase and NADP-dependent isocitrate dehydrogenase, inhibited nitrite production and iNOS protein expression in lipopolysaccharide (LPS)-activated J774 macrophages, without affecting iNOS mRNA content. Furthermore, injection of OMA precursors to LPS-stimulated rats also decreased nitrite production and iNOS expression in isolated peritoneal macrophages. Interestingly, alpha-ketoglutarate or succinyl-CoA administration reversed OMA effect on NO production, thus correlating NO biosynthesis with the anabolic capacity of Krebs cycle. When protein synthesis was blocked by cycloheximide in LPS-activated J774 cells treated with OMA, iNOS protein levels, evaluated by Western blot analysis and (35)S-metabolic labelling, were decreased, suggesting that OMA reduces iNOS biosynthesis and induces an increase in the degradation rate of iNOS protein. Moreover, we showed that OMA inhibits the activity of the iNOS from lung of LPS-treated rats by enzymatic assay. Our results, demonstrating that OMA acts regulating synthesis, catalytic activity and degradation of iNOS, suggest that this compound might have a potential role in reducing the NO overproduction occurring in some pathological conditions.

  4. Impaired enzymatic defensive activity, mitochondrial dysfunction and proteasome activation are involved in RTT cell oxidative damage.

    PubMed

    Cervellati, Carlo; Sticozzi, Claudia; Romani, Arianna; Belmonte, Giuseppe; De Rasmo, Domenico; Signorile, Anna; Cervellati, Franco; Milanese, Chiara; Mastroberardino, Pier Giorgio; Pecorelli, Alessandra; Savelli, Vinno; Forman, Henry J; Hayek, Joussef; Valacchi, Giuseppe

    2015-10-01

    A strong correlation between oxidative stress (OS) and Rett syndrome (RTT), a rare neurodevelopmental disorder affecting females in the 95% of the cases, has been well documented although the source of OS and the effect of a redox imbalance in this pathology has not been yet investigated. Using freshly isolated skin fibroblasts from RTT patients and healthy subjects, we have demonstrated in RTT cells high levels of H2O2 and HNE protein adducts. These findings correlated with the constitutive activation of NADPH-oxidase (NOX) and that was prevented by a NOX inhibitor and iron chelator pre-treatment, showing its direct involvement. In parallel, we demonstrated an increase in mitochondrial oxidant production, altered mitochondrial biogenesis and impaired proteasome activity in RTT samples. Further, we found that the key cellular defensive enzymes: glutathione peroxidase, superoxide dismutase and thioredoxin reductases activities were also significantly lower in RTT. Taken all together, our findings suggest that the systemic OS levels in RTT can be a consequence of both: increased endogenous oxidants as well as altered mitochondrial biogenesis with a decreased activity of defensive enzymes that leads to posttranslational oxidant protein modification and a proteasome activity impairment.

  5. Analysis of Abrasive Blasting of DOP-26 Iridium Alloy

    SciTech Connect

    Ohriner, Evan Keith; Zhang, Wei; Ulrich, George B

    2012-01-01

    The effects of abrasive blasting on the surface geometry and microstructure of DOP-26 iridium alloy (Ir-0.3% W-0.006% Th 0.005% Al) have been investigated. Abrasive blasting has been used to control emissivity of components operating at elevated temperature. The effects of abrasive blasting conditions on surface morphology were investigated both experimentally and by numerical modeling. The simplified model, based on finite element analysis of a single angular particle impacting on Ir alloy disk, calculates the surface deformation and residual strain distribution. The experimental results and modeling results both indicate that the surface geometry is not sensitive to the abrasive blast process conditions of nozzle pressure and standoff distance considered in this study. On the other hand, the modeling results suggest that the angularity of the abrasive particle has an important role in determining surface geometry, which in turn, affects the emissivity. Abrasive blasting causes localized surface strains and localized recrystallization, but it does not affect grain size following extended exposure at elevated temperature. The dependence of emissivity of the DOP-26 alloy on mean surface slope follows a similar trend to that reported for pure iridium.

  6. Testing of Wrought Iridium/Chemical Vapor Deposition Rhenium Rocket

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.; Schneider, Steven J.

    1996-01-01

    A 22-N class, iridium/rhenium (Ir/Re) rocket chamber, composed of a thick (418 miocrometer) wrought iridium (Ir) liner and a rhenium substrate deposited via chemical vapor deposition, was tested over an extended period on gaseous oxygen/gaseous hydrogen (GO2/GH2) propellants. The test conditions were designed to produce species concentrations similar to those expected in an Earth-storable propellant combustion environment. Temperatures attained in testing were significantly higher than those expected with Earth-storable propellants, both because of the inherently higher combustion temperature of GO2/GH2 propellants and because the exterior surface of the rocket was not treated with a high-emissivity coating that would be applied to flight class rockets. Thus the test conditions were thought to represent a more severe case than for typical operational applications. The chamber successfully completed testing (over 11 hr accumulated in 44 firings), and post-test inspections showed little degradation of the Ir liner. The results indicate that use of a thick, wrought Ir liner is a viable alternative to the Ir coatings currently used for Ir/Re rockets.

  7. Microindentation hardness evaluation of iridium alloy clad vent set cups

    NASA Astrophysics Data System (ADS)

    Ulrich, George B.; DeRoos, Larry F.; Stinnette, Samuel E.

    1993-01-01

    An iridium alloy, DOP-26, is used as cladding for 238PuO2 fuel in radioisotope heat sources for space power systems. Presently, DOP-26 iridium alloy clad vent sets (CVS) are being manufactured at the Oak Ridge Y-12 Plant for potential use in the National Aeronautics and Space Administration's Cassini mission to Saturn. Wrought/ground/stress relieved blanks are warm formed into CVS cups. These cups are then annealed to recrystallize the material for subsequent fabrication/assembly operations as well as for final use. One of the cup manufacturing certification requirements is to test for Vickers microindentation hardness. New microindentation hardness specification limits, 210 to 310 HV, have been established for a test load of 1000 grams-force (gf). The original specification limits, 250 to 350 HV, were for 200 gf testing. The primary reason for switching to a higher test load was to reduce variability in the test data. The DOP-26 alloy exhibits microindentation hardness load dependence, therefore, new limits were needed for 1000 gf testing. The new limits were established by testing material from 15 CVS cups using 200 gf and 1000 gf loads and then statistically analyzing the data. Additional work using a Knoop indenter and a 10 gf load indicated that the DOP-26 alloy grain boundaries have higher hardnesses than the grain interiors.

  8. Microindentation hardness evaluation of iridium alloy clad vent set cups

    SciTech Connect

    Ulrich, G.B.; DeRoos, L.F.; Stinnette, S.E. )

    1993-01-15

    An iridium alloy, DOP-26, is used as cladding for [sup 238]PuO[sub 2] fuel in radioisotope heat sources for space power systems. Presently, DOP-26 iridium alloy clad vent sets (CVS) are being manufactured at the Oak Ridge Y-12 Plant for potential use in the National Aeronautics and Space Administration's Cassini mission to Saturn. Wrought/ground/stress relieved blanks are warm formed into CVS cups. These cups are then annealed to recrystallize the material for subsequent fabrication/assembly operations as well as for final use. One of the cup manufacturing certification requirements is to test for Vickers microindentation hardness. New microindentation hardness specification limits, 210 to 310 HV, have been established for a test load of 1000 grams-force (gf). The original specification limits, 250 to 350 HV, were for 200 gf testing. The primary reason for switching to a higher test load was to reduce variability in the test data. The DOP-26 alloy exhibits microindentation hardness load dependence, therefore, new limits were needed for 1000 gf testing. The new limits were established by testing material from 15 CVS cups using 200 gf and 1000 gf loads and then statistically analyzing the data. Additional work using a Knoop indenter and a 10 gf load indicated that the DOP-26 alloy grain boundaries have higher hardnesses than the grain interiors.

  9. Microindentation hardness evaluation of iridium alloy clad vent set cups

    SciTech Connect

    Ulrich, G.B.; DeRoos, L.F.; Stinnette, S.E.

    1992-05-15

    An iridium alloy, DOP-26, is used as cladding for {sup 238}PuO{sup 2} fuel in radioisotope heat sources for space power systems. Presently, DOP-26 iridium alloy clad vent sets (CVS) are being manufactured at the Oak Ridge Y-12 Plant for potential use in the National Aeronautics and Space Administration`s Cassini mission to Saturn. Wrought/ground/stress relieved blanks are warm formed into CVS cups. These cups are then annealed to recrystallize the material for subsequent fabrication/assembly operations as well as for final use. One of the cup manufacturing certification requirements is to test for Vickers microindentation hardness. New microindentation hardness specification limits, 210 to 310 HV, have been established for a test load of 1000 grams-force (gf). The original specification limits, 250 to 350 HV, were for 200 gf testing. The primary reason for switching to a higher test load was to reduce variability in the test data. The DOP-26 alloy exhibits microindentation hardness load dependence, therefore, new limits were needed for 1000 gf testing. The new limits were established by testing material from 15 CVS cups using 200 gf and 1000 gf loads and then statistically analyzing the data. Additional work using a Knoop indenter and a 10 gf load indicated that the DOP-26 alloy grain boundaries have higher hardnesses than the grain interiors.

  10. Microindentation hardness evaluation of iridium alloy clad vent set cups

    SciTech Connect

    Ulrich, G.B.; DeRoos, L.F.; Stinnette, S.E.

    1992-05-15

    An iridium alloy, DOP-26, is used as cladding for {sup 238}PuO{sup 2} fuel in radioisotope heat sources for space power systems. Presently, DOP-26 iridium alloy clad vent sets (CVS) are being manufactured at the Oak Ridge Y-12 Plant for potential use in the National Aeronautics and Space Administration's Cassini mission to Saturn. Wrought/ground/stress relieved blanks are warm formed into CVS cups. These cups are then annealed to recrystallize the material for subsequent fabrication/assembly operations as well as for final use. One of the cup manufacturing certification requirements is to test for Vickers microindentation hardness. New microindentation hardness specification limits, 210 to 310 HV, have been established for a test load of 1000 grams-force (gf). The original specification limits, 250 to 350 HV, were for 200 gf testing. The primary reason for switching to a higher test load was to reduce variability in the test data. The DOP-26 alloy exhibits microindentation hardness load dependence, therefore, new limits were needed for 1000 gf testing. The new limits were established by testing material from 15 CVS cups using 200 gf and 1000 gf loads and then statistically analyzing the data. Additional work using a Knoop indenter and a 10 gf load indicated that the DOP-26 alloy grain boundaries have higher hardnesses than the grain interiors.

  11. Activation of peroxisome proliferator-activated receptor-{alpha} enhances fatty acid oxidation in human adipocytes

    SciTech Connect

    Lee, Joo-Young; Hashizaki, Hikari; Goto, Tsuyoshi; Sakamoto, Tomoya; Takahashi, Nobuyuki; Kawada, Teruo

    2011-04-22

    Highlights: {yields} PPAR{alpha} activation increased mRNA expression levels of adipocyte differentiation marker genes and GPDH activity in human adipocytes. {yields} PPAR{alpha} activation also increased insulin-dependent glucose uptake in human adipocytes. {yields} PPAR{alpha} activation did not affect lipid accumulation in human adipocytes. {yields} PPAR{alpha} activation increased fatty acid oxidation through induction of fatty acid oxidation-related genes in human adipocytes. -- Abstract: Peroxisome proliferator-activated receptor-{alpha} (PPAR{alpha}) is a key regulator for maintaining whole-body energy balance. However, the physiological functions of PPAR{alpha} in adipocytes have been unclarified. We examined the functions of PPAR{alpha} using human multipotent adipose tissue-derived stem cells as a human adipocyte model. Activation of PPAR{alpha} by GW7647, a potent PPAR{alpha} agonist, increased the mRNA expression levels of adipocyte differentiation marker genes such as PPAR{gamma}, adipocyte-specific fatty acid-binding protein, and lipoprotein lipase and increased both GPDH activity and insulin-dependent glucose uptake level. The findings indicate that PPAR{alpha} activation stimulates adipocyte differentiation. However, lipid accumulation was not changed, which is usually observed when PPAR{gamma} is activated. On the other hand, PPAR{alpha} activation by GW7647 treatment induced the mRNA expression of fatty acid oxidation-related genes such as CPT-1B and AOX in a PPAR{alpha}-dependent manner. Moreover, PPAR{alpha} activation increased the production of CO{sub 2} and acid soluble metabolites, which are products of fatty acid oxidation, and increased oxygen consumption rate in human adipocytes. The data indicate that activation of PPAR{alpha} stimulates both adipocyte differentiation and fatty acid oxidation in human adipocytes, suggesting that PPAR{alpha} agonists could improve insulin resistance without lipid accumulation in adipocytes. The expected

  12. Phosphorescent Neutral Iridium (III) Complexes for Organic Light-Emitting Diodes.

    PubMed

    Bin Mohd Yusoff, Abd Rashid; Huckaba, Aron J; Nazeeruddin, Mohammad Khaja

    2017-04-01

    The development of transition metal complexes for application in light-emitting devices is currently attracting significant research interest. Among phosphorescent emitters, those involving iridium (III) complexes have proven to be exceedingly useful due to their relatively short triplet lifetime and high phosphorescence quantum yields. The emission wavelength of iridium (III) complexes significantly depends on the ligands, and changing the electronic nature and the position of the ligand substituents can control the properties of the ligands. In this chapter, we discuss recent developments of phosphorescent transition metal complexes for organic light-emitting diode applications focusing solely on the development of iridium metal complexes.

  13. Oxidatively fragmented phosphatidylcholines activate human neutrophils through the receptor for platelet-activating factor.

    PubMed

    Smiley, P L; Stremler, K E; Prescott, S M; Zimmerman, G A; McIntyre, T M

    1991-06-15

    Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) activates neutrophils (polymorphonuclear leukocytes, PMN) through a receptor that specifically recognizes short sn-2 residues. We oxidized synthetic [2-arachidonoyl]phosphatidylcholine to fragment and shorten the sn-2 residue, and then examined the phospholipid products for the ability to stimulate PMN. 1-Palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine was fragmented by ozonolysis to 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine. This phospholipid activated human neutrophils at submicromolar concentrations, and is effects were inhibited by specific PAF receptor antagonists WEB2086, L659,989, and CV3988. 1-Palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine next was fragmented by an uncontrolled free radical-catalyzed reaction: it was treated with soybean lipoxygenase to form its sn-2 15-hydroperoxy derivative (which did not activate neutrophils) and then allowed to oxidize under air. The secondary oxidation resulted in the formation of numerous fragmented phospholipids (Stremler, K. E., Stafforini, D. M., Prescott, S. M., and McIntyre, T. M. (1991) J. Biol. Chem. 266, 11095-11103), some of which activated PMN. Hydrolysis of sn-2 residues with phospholipase A2 destroyed biologic activity, as did hydrolysis with PAF acetylhydrolase. PAF acetylhydrolase is specific for short or intermediate length sn-2 residues and does not hydrolyze the starting material (Stremler, K. E., Stafforini, D. M., Prescott, S. M., and McIntyre, T. M. (1991) J. Biol. Chem. 266, 11095-11103). Neutrophil activation was completely blocked by L659,989, a specific PAF receptor antagonist. We conclude that diacylphosphatidylcholines containing an sn-2 polyunsaturated fatty acyl residue can be oxidatively fragmented to species with sn-2 residues short enough to activate the PAF receptor of neutrophils. This suggests a new mechanism for the appearance of biologically active phospholipids, and shows

  14. Antiurease and anti-oxidant activity of Vaccinium macrocarpon fruit.

    PubMed

    Noreen, Shabana; Shaheen, Ghazala; Akram, Muhammad; Rashid, Abid; Shah, Syed Muhammad Ali

    2016-07-01

    The objective of present study was to evaluate the antiurease and anti-oxidant activity of Vaccinium macrocarpon fruit. The parent extract was ethanolic extract while its sub fractions were prepared in n-hexane, chloroform and n-butanol. The method based on scavenging activity and reduction capability of 1, 1-diphenyl-2-picrylhydrazyl radical (DPPH). N-butanol fraction was the most effective antioxidant with 87.0±1.15 activity but the activity was less than ascorbic acid i.e. 93.74±0.12. Highly significant urease inhibition was shown by crude ethanolic extract (71.00±0.2a) with IC50 (392.66±2.1) followed by aqueous fraction (68.00±0.5e) with IC50 (159.83±2.8). The results of crude ethanolic extract and aqueous extracts were highly significant (p<0.05) than standard Thiourea. Present study showed that Vaccinium macrocarpon exhibits potent antiurease and antioxidant activities.

  15. Sodium channel activation mechanisms. Insights from deuterium oxide substitution

    SciTech Connect

    Alicata, D.A.; Rayner, M.D.; Starkus, J.G. )

    1990-04-01

    Schauf and Bullock, using Myxicola giant axons, demonstrated that solvent substitution with deuterium oxide (D2O) significantly affects both sodium channel activation and inactivation kinetics without corresponding changes in gating current or tail current rates. They concluded that (a) no significant component of gating current derives from the final channel opening step, and (b) channels must deactivate (during tail currents) by a different pathway from that used in channel opening. By contrast, Oxford found in squid axons that when a depolarizing pulse is interrupted by a brief (approximately 100 microseconds) return to holding potential, subsequent reactivation (secondary activation) is very rapid and shows almost monoexponential kinetics. Increasing the interpulse interval resulted in secondary activation rate returning towards control, sigmoid (primary activation) kinetics. He concluded that channels open and close (deactivate) via the same pathway. We have repeated both sets of observations in crayfish axons, confirming the results obtained in both previous studies, despite the apparently contradictory conclusions reached by these authors. On the other hand, we find that secondary activation after a brief interpulse interval (50 microseconds) is insensitive to D2O, although reactivation after longer interpulse intervals (approximately 400 microseconds) returns towards a D2O sensitivity similar to that of primary activation. We conclude that D2O-sensitive primary activation and D2O-insensitive tail current deactivation involve separate pathways. However, D2O-insensitive secondary activation involves reversal of the D2O-insensitive deactivation step. These conclusions are consistent with parallel gate models, provided that one gating particle has a substantially reduced effective valence.

  16. A preliminary study of factors affecting the calibration stability of the iridium versus iridium-40 percent rhodium thermocouple

    NASA Technical Reports Server (NTRS)

    Ahmed, Shaffiq; Germain, Edward F.; Daryabeigi, Kamran; Alderfer, David W.; Wright, Robert E.

    1987-01-01

    An iridium versus iridium-40% rhodium thermocouple was studied. Problems associated with the use of this thermocouple for high temperature applications (up to 2000 C) were investigated. The metallurgical studies included X-ray, macroscopic, resistance, and metallographic studies. The thermocouples in the as-received condition from the manufacturer revealed large amounts of internal stress caused by cold working during manufacturing. The thermocouples also contained a large amount of inhomogeneities and segregations. No phase transformations were observed in the alloy up to 1100 C. It was found that annealing the thermocouple at 1800 C for two hours, and then at 1400 C for 2 to 3 hours yielded a fine grain structure, relieving some of the strains, and making the wire more ductile. It was also found that the above annealing procedure stabilized the thermal emf behavior of the thermocouple for application below 1800 C (an improvement from + or - 1% to + or - 0.02% within the range of the test parameters used).

  17. Treatment of activated carbon to enhance catalytic activity for reduction of nitric oxide with ammonia

    SciTech Connect

    Ku, B.J.; Rhee, H.K. . Dept. of Chemical Engineering); Lee, J.K.; Park, D. )

    1994-11-01

    Catalytic activity of activated carbon treated with various techniques was examined in a fixed bed reactor for the reduction of nitric oxide with ammonia at 150 C. Activated carbon derived from coconut shell impregnated with an aqueous solution of ammonium sulfate, further treated with sulfuric acid, dried at 120 C, and then heated in an inert gas stream at 400 C, showed the highest catalytic activity within the range of experimental conditions. The enhancement of catalytic activity of modified activated carbon could be attributed to the increase in the amount of oxygen function groups which increased the adsorption site for ammonia. Catalytic activity of activated carbons depended on the surface area and the oxygen content as well.

  18. Versatile bonding and coordination modes of ditriazolylidene ligands in rhodium(iii) and iridium(iii) complexes.

    PubMed

    Farrell, Kevin; Müller-Bunz, Helge; Albrecht, Martin

    2016-10-12

    Metalation of novel ditriazolium salts containing a trimethylene (-CH2CH2CH2-) or dimethylether linker (-CH2OCH2-) was probed with different rhodium(iii) and iridium(iii) precursors. When using [MCp*Cl2]2, a transmetalation protocol via a triazolylidene silver intermediate was effective, while base-assisted metalation with MCl3via sequential deprotonation of the triazolium salt with KOtBu and addition of the metal precursor afforded homoleptic complexes. The N-substituent on the triazole heterocycle directed the metalation process and led to Ctrz,Ctrz,CPh-tridentate chelating ditriazolylidene complexes for N-phenyl substituents. With ethyl substituents, only Ctrz,Ctrz-bidentate complexes were formed, while metalation with mesityl substituents was unsuccessful, presumably due to steric constraints. Through modification of the reaction conditions for the metalation step, an intermediate species was isolated that contains a Ctrz,CPh-bidentate chelate en route to the formation of the tridentate ligand system. Accordingly, Cphenyl-H bond activation occurs prior to formation of the second metal-triazolylidene bond. Stability studies with a Ctrz,Ctrz,CPh-tridentate chelating ditriazolylidene iridium complex towards DCl showed deuterium incorporation at both N-phenyl groups and indicate that Cphenyl-H bond activation is reversible while the Ctrz-Ir bond is robust. The flexible linker between the two triazolylidene donor sites provides access to both facial and meridional coordination modes.

  19. Cobalt-containing oxide layers on titanium, their composition, morphology, and catalytic activity in CO oxidation

    NASA Astrophysics Data System (ADS)

    Vasilyeva, M. S.; Rudnev, V. S.; Ustinov, A. Yu.; Korotenko, I. A.; Modin, E. B.; Voitenko, O. V.

    2010-12-01

    In this study possibility to form the layered compositions CoO x + SiO 2/TiO 2/Ti by plasma electrolytic oxidation (PEO) method was shown. Compositions have been obtained by both one-stage PEO method (Method I) with addition of Co(CH 3COO) 2 into silicate electrolyte and impregnation of preliminary obtained by the PEO method SiO 2/TiO 2/Ti systems in aqueous solutions containing cobalt salts with their following annealing (Method II). XRD, XPS and SEM/EDX were used to investigate the phase and element composition, microstructure of the coatings prepared by the two various methods. Catalytic activity of the cobalt-containing composites was investigated in the CO oxidation reaction. Under experimental conditions, the structures obtained by impregnation and annealing method were more active, than those obtained by one-stage PEO method. The surface structures of cobalt-containing coatings obtained by the PEO method and by impregnation and annealing differ in both quantitative and qualitative relation. The cobalt content on the surface of impregnating coatings is three times as much as that for those formed by one-stage PEO method. It is found that coatings obtained by the Method II have a more developed surface. The surface of CoO x + SiO 2/TiO 2/Ti compositions obtained by the PEO method contains, presumably Co(OH) 2 and Co 3O 4. The surface of the similar compositions obtained by the Method II, possibly contains CoO, either Co 2O 3, or CoOOH. The combination of these factors, perhaps, also provides a higher activity of the compositions formed by the Method II.

  20. Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

    SciTech Connect

    He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; Carley, Albert F.; Borisevich, Albina Y.; Mineo, Yuki; Haruta, Masatake; Hutchings, Graham J.; Kiely, Christopher J.

    2016-09-27

    The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviors after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. As a result, correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst.

  1. Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

    DOE PAGES

    He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; ...

    2016-09-27

    The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviors after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to revealmore » the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. As a result, correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst.« less

  2. Analysis and Implications of the Iridium 33-Cosmos 2251 Collision

    NASA Astrophysics Data System (ADS)

    Kelso, T. S.

    On 2009 February 10, Iridium 33--an operational US communications satellite in low-Earth orbit--was struck and destroyed by Cosmos 2251--a long-defunct Russian communications satellite. This is the first time since the dawn of the Space Age that two satellites have collided in orbit. To better understand the circumstances of this event and the ramifications for avoiding similar events in the future, this paper provides a detailed analysis of the predictions leading up to the collision, using various data sources, and looks in detail at the collision, the evolution of the debris clouds, and the long-term implications for satellite operations. The only publicly available system available to satellite operators for screening for close approaches, SOCRATES, did predict this close approach, but it certainly wasn't the closest approach predicted for the week of February 10. In fact, at the time of the collision, SOCRATES ranked this close approach 152 of the 11,428 within 5 km of any payload. A detailed breakdown is provided to help understand the limitations of screening for close approaches using the two-line orbital element sets. Information is also provided specifically for the Iridium constellation to provide an understanding of how these limitations affect decision making for satellite operators. Post-event analysis using high-accuracy orbital data sources will be presented to show how that information might have been used to prevent this collision, had it been available and used. Analysis of the collision event, along with the distribution of the debris relative to the original orbits, will be presented to help develop an understanding of the geometry of the collision and the near-term evolution of the resulting debris clouds. Additional analysis will be presented to show the long-term evolution of the debris clouds, including orbital lifetimes, and estimate the increased risk for operations conducted by Iridium and other satellite operators in the low-Earth orbit

  3. Reuse performance of granular-activated carbon and activated carbon fiber in catalyzed peroxymonosulfate oxidation.

    PubMed

    Yang, Shiying; Li, Lei; Xiao, Tuo; Zhang, Jun; Shao, Xueting

    2017-03-01

    Recently, activated carbon was investigated as an efficient heterogeneous metal-free catalyst to directly activate peroxymonosulfate (PMS) for degradation of organic compounds. In this paper, the reuse performance and the possible deactivation reasons of granular-activated carbon (GAC) and activated carbon fiber (ACF) in PMS activation were investigated. As results indicated, the reusability of GAC, especially in the presence of high PMS dosage, was relatively superior to ACF in catalyzed PMS oxidation of Acid Orange 7 (AO7), which is much more easily adsorbed by ACF than by GAC. Pre-oxidation experiments were studied and it was demonstrated that PMS oxidation on ACF would retard ACF's deactivation to a big extent. After pre-adsorption with AO7, the catalytic ability of both GAC and ACF evidently diminished. However, when methanol was employed to extract the AO7-spent ACF, the catalytic ability could recover quite a bit. GAC and ACF could also effectively catalyze PMS to degrade Reactive Black 5 (RB5), which is very difficult to be adsorbed even by ACF, but both GAC and ACF have poor reuse performance for RB5 degradation. The original organic compounds or intermediate products adsorbed by GAC or ACF would be possibly responsible for the deactivation.

  4. Iridium-catalyzed hydrogen transfer: synthesis of substituted benzofurans, benzothiophenes, and indoles from benzyl alcohols.

    PubMed

    Anxionnat, Bruno; Gomez Pardo, Domingo; Ricci, Gino; Rossen, Kai; Cossy, Janine

    2013-08-02

    An iridium-catalyzed hydrogen transfer has been developed in the presence of p-benzoquinone, allowing the synthesis of a diversity of substituted benzofurans, benzothiophenes, and indoles from substituted benzylic alcohols.

  5. CuO impregnated activated carbon for catalytic wet peroxide oxidation of phenol.

    PubMed

    Liou, Rey-May; Chen, Shih-Hsiung

    2009-12-15

    This paper presents an original approach to the removal of phenol in synthetic wastewater by catalytic wet peroxide oxidation with copper binding activated carbon (CuAC) catalysts. The characteristics and oxidation performance of CuAC in the wet hydrogen peroxide catalytic oxidation of phenol were studied in a batch reactor at 80 degrees C. Complete conversion of the oxidant, hydrogen peroxide, was observed with CuAC catalyst in 20 min oxidation, and a highly efficient phenol removal and chemical oxygen demand (COD) abatement were achieved in the first 30 min. The good oxidation performance of CuAC catalyst was contributed to the activity enhancement of copper oxide, which was binding in the carbon matrix. It can be concluded that the efficiency of oxidation dominated by the residual H2O2 in this study. An over 90% COD removal was achieved by using the multiple-step addition in this catalytic oxidation.

  6. Activity of Cu-activated carbon fiber catalyst in wet oxidation of ammonia solution.

    PubMed

    Hung, Chang-Mao

    2009-07-30

    Aqueous solutions of 200-1000 mg/L of ammonia were oxidized in a trickle-bed reactor using Cu-activated carbon fiber (ACF) catalysts, which were prepared by incipient wet impregnation with aqueous solutions of copper nitrate that was deposited on ACF substrates. The results reveal that the conversion of ammonia by wet oxidation in the presence of Cu-ACF catalysts was a function of the metal loading weight ratio of the catalyst. The total conversion efficiency of ammonia was 95% during wet oxidation over the catalyst at 463 K at an oxygen partial pressure of 3.0 MPa. Moreover, the effect of the initial concentration of ammonia and the reaction temperature on the removal of ammonia from the effluent streams was also studied at a liquid space velocity of less than 3.0 h(-1).

  7. Synthesis of Iridium(III) Carboxamides via the Bimetallic Reaction between Cp(PMe(3))IrPh(OH) and [Cp(PMe(3))Ir(Ph)NCR](+).

    PubMed

    Tellers, David M.; Ritter, Joachim C. M.; Bergman, Robert G.

    1999-10-18

    Reaction of Cp(PMe(3))IrPh(OH) (1) with nitriles is undetectably slow in benzene solution at room temperature. However, in the presence of Cp(PMe(3))IrPh(OTf) (2) (OTf = O(3)SCF(3)), the reaction is strongly catalyzed, leading to iridium(III) carboxamides Cp(PMe(3))IrPh[NHC(O)R] (6a-d) [R = C(6)H(4)CH(3) (6a), C(6)H(5) (6b), C(6)H(4)CF(3) (6c), CH(3) (6d)]. We propose that these transformations occur by initial displacement of the trifluoromethanesulfonate ("triflate") anion of 2 by a molecule of nitrile, leading to a nitrile-substituted iridium cation, [Cp(PMe(3))IrPh(NCR)](+) (10). Following this, the nucleophilic hydroxide group of 1 attacks the (activated) nitrile molecule bound in 10, leading (after proton transfer) to the iridium carboxamide complex. In the case of nitriles possessing hydrogens alpha to the cyano group, competitive loss of one of these protons is observed, leading to iridium C-bound cyanoenolates such as Cp(PMe(3))(Ph)Ir(CH(2)CN) (7). Protonolysis of carboxamides 6a-d with HCl yields Cp(PMe(3))IrPh(Cl) (9) and the free amides. A pronounced solvent effect is observed when the reaction between 1 and nitriles catalyzed by 2 is carried out in THF solution. The basic hydroxide ligand of 1 induces an overall dehydration/cyclization reaction of the coordinated aromatic nitrile. For example, the reaction of 1 with p-trifluorotolunitrile and a catalytic amount of 2 leads to the formation of 6c, water, [Ph(PMe(3))Ir[C(5)Me(4)CH(2)C(C(6)H(4)CF(3))N

  8. Activation of carbon dioxide on metal and metal oxide surfaces

    SciTech Connect

    Tan, C.D.; Chuang, S.S.C.

    1995-12-31

    The environmental concern about the impact of CO{sub 2} has grown recently due to its rapidly increasing concentration. Deforestation strongly affects the natural reduction of CO{sub 2} by water into carbohydrates by photosynthesis. Industrial utilization of CO{sub 2} by heterogeneous catalytic reactions can be one of the effective ways to cut the CO{sub 2} level. The first step in catalytic reaction of CO{sub 2} is the adsorption. The objective of this study is to investigate the adsorption of CO{sub 2} on the Rh/Al{sub 2}O{sub 3} surfaces. Rh is selected for this study because of its unique activity to catalyze a number of CO{sub 2} related reactions. In situ infrared results show that CO{sub 2} adsorbed on the alumina oxide support as bidentate carbonate and non-coordinated carbon which are the dominant species during the CO{sub 2} adsorption.

  9. Concepts for Cost-Effective Enhanced Cryosat Continuity: Opportunity in the Iridium PRIME Context

    NASA Astrophysics Data System (ADS)

    Le Roy, Y.; Caubet, E.; Silverstrin, P.; Legrand, C.

    2016-08-01

    The Iridium-PRIME offer, recently initiated by the Iridium company, consists in hosting payloads on customized low cost Iridium-NEXT platforms on which the main telecom mission antenna (L-band) is removed. This leaves significant resources in terms of mass, volume and power consumption to host up to three payloads on these customized platforms. The Iridium-PRIME satellites will be inserted in the Iridium-NEXT constellation to take benefit of the low cost operation service (command, control and data telemetry through the life time of the Iridium-PRIME mission). Given the synergy between schedules of the Iridium-PRIME program (launches starting around 2020) and of a possible CryoSat Follow-On (FO) mission (launch around 2022) and the adequacy of the available on-board resources for such a mission, ESA tasked Thales Alenia Space, as responsible for the SIRAL radar instrument of the currently in-orbit CryoSat mission, to study the feasibility of a concept for enhanced continuity of CryoSat on an Iridium- PRIME satellite as potential low-cost fast-track solution. The study aimed to define a cost-effective topographic payload including not only the SIRAL radar but also the necessary sub-systems to retrieve the SIRAL antenna baseline attitude (star trackers) with high accuracy and to perform a Precise Orbit Determination (POD). All these aspects are presented in this paper. In addition, possible evolutions/improvements of the Ku-band radar instrument were analysed and are presented: adding a Ka-band nadir measurement capability and a Ku-band or Ka-band wide swath mode measurement capability. The transmission issue for the SIRAL science data is also discussed in the paper.

  10. Novel Quadrifilar Helix Antenna Combining GNSS, Iridium, and a UHF Communications Monopole

    DTIC Science & Technology

    2012-04-01

    R. J. Davis; “ Ferrite Loaded UHF Sleeve Monopole Integrated with a GPS Patch Antenna for a Handset”. Submitted for publication in “ Microwave and...Novel Quadrifilar Helix Antenna Combining GNSS, Iridium, and a UHF Communications Monopole P. G. Elliot, E. N. Rosario, R. J. Davis The MITRE...Corporation, Bedford, MA 01730 Abstract- A GPS/GNSS/Iridium antenna co-located with a UHF communications monopole on a handset was developed to

  11. Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C-H Borylation.

    PubMed

    Sadler, Scott A; Hones, Andrew C; Roberts, Bryan; Blakemore, David; Marder, Todd B; Steel, Patrick G

    2015-05-15

    In the absence of a steric directing group, iridium-catalyzed C-H borylation of N-protected indazoles occurs rapidly and selectively at C-3 and the resulting boronate esters can be utilized in a range of downstream conversions. The functional group tolerance of the iridium-catalyzed C-H borylation reaction enables simple and efficient multidirectional syntheses of substituted indazoles to be realized.

  12. Inhibition of Beta-Amyloid Fibrillation by Luminescent Iridium(III) Complex Probes.

    PubMed

    Lu, Lihua; Zhong, Hai-Jing; Wang, Modi; Ho, See-Lok; Li, Hung-Wing; Leung, Chung-Hang; Ma, Dik-Lung

    2015-09-30

    We report herein the application of kinetically inert luminescent iridium(III) complexes as dual inhibitors and probes of beta-amyloid fibrillogenesis. These iridium(III) complexes inhibited Aβ1-40 peptide aggregation in vitro, and protected against Aβ-induced cytotoxicity in neuronal cells. Furthermore, the complexes differentiated between the aggregated and unaggregated forms of Aβ1-40 peptide on the basis of their emission response.

  13. Inhibition of Beta-Amyloid Fibrillation by Luminescent Iridium(III) Complex Probes

    PubMed Central

    Lu, Lihua; Zhong, Hai-Jing; Wang, Modi; Ho, See-Lok; Li, Hung-Wing; Leung, Chung-Hang; Ma, Dik-Lung

    2015-01-01

    We report herein the application of kinetically inert luminescent iridium(III) complexes as dual inhibitors and probes of beta-amyloid fibrillogenesis. These iridium(III) complexes inhibited Aβ1–40 peptide aggregation in vitro, and protected against Aβ-induced cytotoxicity in neuronal cells. Furthermore, the complexes differentiated between the aggregated and unaggregated forms of Aβ1–40 peptide on the basis of their emission response. PMID:26419607

  14. Inhibition of Beta-Amyloid Fibrillation by Luminescent Iridium(III) Complex Probes

    NASA Astrophysics Data System (ADS)

    Lu, Lihua; Zhong, Hai-Jing; Wang, Modi; Ho, See-Lok; Li, Hung-Wing; Leung, Chung-Hang; Ma, Dik-Lung

    2015-09-01

    We report herein the application of kinetically inert luminescent iridium(III) complexes as dual inhibitors and probes of beta-amyloid fibrillogenesis. These iridium(III) complexes inhibited Aβ1-40 peptide aggregation in vitro, and protected against Aβ-induced cytotoxicity in neuronal cells. Furthermore, the complexes differentiated between the aggregated and unaggregated forms of Aβ1-40 peptide on the basis of their emission response.

  15. Laminar iridium coating produced by pulse current electrodeposition from chloride molten salt

    NASA Astrophysics Data System (ADS)

    Zhu, Li'an; Bai, Shuxin; Zhang, Hong; Ye, Yicong

    2013-10-01

    Due to the unique physical and chemical properties, Iridium (Ir) is one of the most promising oxidation-resistant coatings for refractory materials above 1800 °C in aerospace field. However, the Ir coatings prepared by traditional methods are composed of columnar grains throughout the coating thickness. The columnar structure of the coating is considered to do harm to its oxidation resistance. The laminar Ir coating is expected to have a better high-temperature oxidation resistance than the columnar Ir coating does. The pulse current electrodeposition, with three independent parameters: average current density (Jm), duty cycle (R) and pulse frequency (f), is considered to be a promising method to fabricate layered Ir coating. In this study, laminar Ir coatings were prepared by pulse current electrodeposition in chloride molten salt. The morphology, roughness and texture of the coatings were determined by scanning electron microscope (SEM), profilometer and X-ray diffraction (XRD), respectively. The results showed that the laminar Ir coatings were composed of a nucleation layer with columnar structure and a growth layer with laminar structure. The top surfaces of the laminar Ir coatings consisted of cauliflower-like aggregates containing many fine grains, which were separated by deep grooves. The laminar Ir coating produced at the deposition condition of 20 mA/cm2 (Jm), 10% (R) and 6 Hz (f) was quite smooth (Ra 1.01 ± 0.09 μm) with extremely high degree of preferred orientation of <1 1 1>, and its laminar structure was well developed with clear boundaries and uniform thickness of sub-layers.

  16. Controlling enzymatic activity by immobilization on graphene oxide.

    PubMed

    Bolibok, Paulina; Wiśniewski, Marek; Roszek, Katarzyna; Terzyk, Artur P

    2017-04-01

    In this study, graphene oxide (GO) has been applied as a matrix for enzyme immobilization. The protein adsorption capacity of GO is much higher than of other large surface area carbonaceous materials. Its structure and physicochemical properties are reported beneficial also for enzymatic activity modifications. The experimental proof was done here that GO-based biocatalytic systems with immobilized catalase are modifiable in terms of catalyzed reaction kinetic constants. It was found that activity and stability of catalase, considered here as model enzyme, closely depend on enzyme/GO ratio. The changes in kinetic parameters can be related to secondary structure alterations. The correlation between enzyme/GO ratio and kinetic and structure parameters is reported for the first time and enables the conscious control of biocatalytic processes and their extended applications. The biological activity of obtained biocatalytic systems was confirmed in vitro by the use of functional test. The addition of immobilized catalase improved the cells' viability after they were exposed to hydrogen peroxide and tert-butyl-hydroperoxide used as source of reactive oxygen species.

  17. Iridium-alloy processing experience in FY 1989

    SciTech Connect

    Ohriner, E.K.

    1990-11-01

    Iridium-alloy blanks and foil are produced at the Oak Ridge National Laboratory for use as fuel cladding material in radioisotope thermoelectric generators for space power sources. Until 1984, the material was produced from small 500-g drop castings. A new process has been developed in which consumable electrodes of about 10 kg are arc melted, extruded, and then rolled to produce the sheet products. The work performed during FY 1989 included the arc melting of three electrodes and the extruding and rolling to sheet of three billets. Significant improvements have been made in the extruding and arc-melting processes. Preliminary results show that these improvements have had an important effect in increasing the rate of blank acceptance in nondestructive evaluations. 4 refs., 33 figs., 11 tabs.

  18. Iridium abundance maxima in the Upper Cenomanian extinction interval

    NASA Technical Reports Server (NTRS)

    Orth, C. J.; Attrep, M., Jr.; Mao, X. Y.; Kauffman, E. G.; Diner, R.

    1988-01-01

    Two iridium abundance peaks, both 0.11 ppb (whole-rock basis) over a local background of 0.017 ppb, have been found in Middle Cretaceous marine rocks near Pueblo, Colorado. They occur just below the 92-million-year-old Cenomanian-Turonian (C-T) stage boundary. No other peaks were found in 45 meters of strata (about 2.5 million years of deposition) above and below the boundary interval. The broad lower peak straddles the first in a series of extinctions of benthic and nektonic macrobiota which comprise the C-T extinction event. The sharp upper peak occurs stratigraphically about 1.2 meters above the lower peak. The excess Ir might be from meteoroid impacts.

  19. Comparative modelling of chemical ordering in palladium-iridium nanoalloys

    SciTech Connect

    Davis, Jack B. A.; Johnston, Roy L.; Rubinovich, Leonid; Polak, Micha

    2014-12-14

    Chemical ordering in “magic-number” palladium-iridium nanoalloys has been studied by means of density functional theory (DFT) computations, and compared to those obtained by the Free Energy Concentration Expansion Method (FCEM) using derived coordination dependent bond energy variations (CBEV), and by the Birmingham Cluster Genetic Algorithm using the Gupta potential. Several compositions have been studied for 38- and 79-atom particles as well as the site preference for a single Ir dopant atom in the 201-atom truncated octahedron (TO). The 79- and 38-atom nanoalloy homotops predicted for the TO by the FCEM/CBEV are shown to be, respectively, the global minima and competitive low energy minima. Significant reordering of minima predicted by the Gupta potential is seen after reoptimisation at the DFT level.

  20. Intercalation of graphene on iridium with samarium atoms

    NASA Astrophysics Data System (ADS)

    Afanas'eva, E. Yu.; Rut'kov, E. V.; Gall, N. R.

    2016-07-01

    Intercalation of graphene on Ir (111) with Sm atoms is studied by methods of thermal desorption spectroscopy and thermionic emission. It is shown that adsorption of samarium at T = 300 K on graphene to concentrations of N ≤ 6 × 1014 atoms cm-2 followed by heating of the substrate leads to practically complete escape of adsorbate underneath the graphene layer. At N > 6 × 1014 atoms cm-2 and increasing temperature, a fraction of adsorbate remains on graphene in the form of two-dimensional "gas" and samarium islands and are desorbed in the range of temperatures of 1000-1200 K. Samarium remaining under the graphene is desorbed from the surface in the temperature range 1200-2150 K. Model conceptions for the samarium-graphene-iridium system in a wide temperature range are developed.

  1. Large Deformation Change in Iridium Isotopes from Laser Spectroscopy

    SciTech Connect

    D. Verney; L. Cabaret; J. Crawford; H.T. Duong; J. Genevey; G. Hubert; F. Ibrahim; M. Krieg; F. Le Blanc; J.K.P. Lee; G. Le Scornet; D. Lunney; J. Obert; J. Oms; J. Pinard; J.C. Putaux; B. Roussiere; J. Sauvage; V. Sebastian

    1999-12-31

    Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2} {yields}5d{sup 7}6s6p {sup 6}F{sub 11/2} have been studied for the {sup 182-189}Ir, {sup 186}Ir{sup m} and {sup 191,193}Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between {sup 187}Ir and {sup 186}Ir and between {sup 186}Ir{sup m} and {sup 186}Ir{sup g} has been observed.

  2. Dynamic High-Temperature Characterization of an Iridium Alloy in Compression at High Strain Rates

    SciTech Connect

    Song, Bo; Nelson, Kevin; Lipinski, Ronald J.; Bignell, John L.; Ulrich, G. B.; George, E. P.

    2014-06-01

    Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-temperature high-strain-rate performance are needed for understanding high-speed impacts in severe elevated-temperature environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain-rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. Current high-temperature Kolsky compression bar techniques are not capable of obtaining satisfactory high-temperature high-strain-rate stress-strain response of thin iridium specimens investigated in this study. We analyzed the difficulties encountered in high-temperature Kolsky compression bar testing of thin iridium alloy specimens. Appropriate modifications were made to the current high-temperature Kolsky compression bar technique to obtain reliable compressive stress-strain response of an iridium alloy at high strain rates (300 – 10000 s-1) and temperatures (750°C and 1030°C). Uncertainties in such high-temperature high-strain-rate experiments on thin iridium specimens were also analyzed. The compressive stress-strain response of the iridium alloy showed significant sensitivity to strain rate and temperature.

  3. Iridium NEXT partnership for Earth observation: exploiting global satellite constellations for new remote sensing capabilities

    NASA Astrophysics Data System (ADS)

    Gupta, Om P.

    2008-08-01

    A unique opportunity exists to host up to 66 earth observation sensors on the Iridium NEXT LEO constellation in a manner that can revolutionize earth observation and weather predictions. A constellation approach to sensing, using the real-time communications backbone of Iridium, will enable unprecedented geospatial and temporal sampling for now-casting of weather on a global basis as well as global climate monitoring. The Iridium NEXT constellation, with 66 interconnected satellites in 6 near polar orbiting planes, provides a unique platform for hosting a variety of earth observation missions. The opportunity is proposed as a Public-Private Partnership (PPP) allowing for the sharing of infrastructure by government agencies. This has the potential to augment current and planned climate and weather observation programs in a very cost effective manner not achievable in any other way. Iridium, with the assistance of the Group on Earth Observations (GEO), NASA, NOAA, and ESA, has evaluated a number of sensing missions that would be a good fit to the Iridium NEXT constellation. These include GPS radio occultation sensors, earth radiation budget measurements, radio altimetry, tropospheric and stratospheric winds measurements including polar winds measurements, and atmospheric chemistry. Iridium NEXT launches start in 2013 and constellation operational life will extend beyond 2030. Detailed feasibility studies on specific missions are planned to begin later this year.

  4. Activation of Manganese Oxidants with Bisulfite for Enhanced Oxidation of Organic Contaminants: The Involvement of Mn(III).

    PubMed

    Sun, Bo; Guan, Xiaohong; Fang, Jingyun; Tratnyek, Paul G

    2015-10-20

    MnO4(-) was activated by HSO3(-), resulting in a process that oxidizes organic contaminants at extraordinarily high rates. The permanganate/bisulfite (PM/BS) process oxidized phenol, ciprofloxacin, and methyl blue at pHini 5.0 with rates (kobs ≈ 60-150 s(-1)) that were 5-6 orders of magnitude faster than those measured for permanganate alone, and ∼5 to 7 orders of magnitude faster than conventional advanced oxidation processes for water treatment. Oxidation of phenol was fastest at pH 4.0, but still effective at pH 7.0, and only slightly slower when performed in tap water. A smaller, but still considerable (∼3 orders of magnitude) increase in oxidation rates of methyl blue was observed with MnO2 activated by HSO3(-) (MO/BS). The above results, time-resolved spectroscopy of manganese species under various conditions, stoichiometric analysis of pH changes, and the effect of pyrophosphate on UV absorbance spectra suggest that the reactive intermediate(s) responsible for the extremely rapid oxidation of organic contaminants in the PM/BS process involve manganese(III) species with minimal stabilization by complexation. The PM/BS process may lead to a new category of advanced oxidation technologies based on contaminant oxidation by reactive manganese(III) species, rather than hydroxyl and sulfate radicals.

  5. Inhibition of the p53/hDM2 protein-protein interaction by cyclometallated iridium(III) compounds

    PubMed Central

    Liu, Li-Juan; He, Bingyong; Miles, Jennifer A.; Wang, Wanhe; Mao, Zhifeng; Che, Weng Ian; Lu, Jin-Jian; Chen, Xiu-Ping; Wilson, Andrew J.; Ma, Dik-Lung; Leung, Chung-Hang

    2016-01-01

    Inactivation of the p53 transcription factor by mutation or other mechanisms is a frequent event in tumorigenesis. One of the major endogenous negative regulators of p53 in humans is hDM2, a ubiquitin E3 ligase that binds to p53 causing proteasomal p53 degradation. In this work, a library of organometallic iridium(III) compounds were synthesized and evaluated for their ability to disrupt the p53/hDM2 protein-protein interaction. The novel cyclometallated iridium(III) compound 1 [Ir(eppy)2(dcphen)](PF6) (where eppy = 2-(4-ethylphenyl)pyridine and dcphen = 4, 7-dichloro-1, 10-phenanthroline) blocked the interaction of p53/hDM2 in human amelanotic melanoma cells. Finally, 1 exhibited anti-proliferative activity and induced apoptosis in cancer cell lines consistent with inhibition of the p53/hDM2 interaction. Compound 1 represents the first reported organometallic p53/hDM2 protein-protein interaction inhibitor. PMID:26883110

  6. New yellow-emitting phosphorescent cyclometalated iridium(III) complex

    NASA Astrophysics Data System (ADS)

    Ivanov, P.; Tomova, R.; Petrova, P.; Stanimirov, S.; Petkov, I.

    2012-12-01

    We have synthesized a new yellow iridium complex Iridium(III) bis[2-phenylbenzothiazolato-N,C2']-(1-phenylicosane-1,3-dionate) (bt)2Ir(bsm), based on the benzothiazole derivative. The synthesized molecule was identified by 1H NMR and elemental analysis. The UV-Visible absorption and photoluminescence (PL) spectra of (bt)Ir2(bsm) in CH2Cl2 solution were found at 273 nm and 559 nm, respectively. The complex was used as a dopant into a hole-transporting layer (HTL) in a multilayered organic light emitting device (OLED) structure: ITO/doped-HTL/EL/ETL/M. ITO was a transparent anode of In2O3:SnO2, M- a metallic Al cathode, HTL- 4,4'-bis(9H-carbazol-9-yl)biphenyl (CBP) incorporated in poly(N-vinylcarbazole) (PVK) matrix, EL- electroluminescent layer of bis(8-hydroxy-2-methylquinoline)-(4-phenylphenoxy)aluminum (BAlq) and ETL- electron-transporting layer of tris(8-hydroxyquinolinato)aluminum (Alq3). The electroluminescent (EL) spectra of OLEDs were basically the sum of the emissions of BAlq at 496 nm and the emission of (bt)2Ir(bsm) at 559 nm. With increasing (bt)2Ir(bsm) concentration, the relative electroluminescent intensity of greenish-blue emission (at 496 nm) decreased, while the yellow (at 559 nm) - increased and CIE coordinates of the device shifted from (0.21, 0.33) at 0 wt % to (0.40, 0.48) at 8 wt % of the dopant. It was found that OLED with 0.5 wt % (bt)2Ir(bsm) had the best performance and stable color chromaticity at various voltages.

  7. Iridium-Coated Rhenium Radiation-Cooled Rockets

    NASA Technical Reports Server (NTRS)

    Reed, Brian D.; Biaglow, James A.; Schneider, Steven J.

    1997-01-01

    Radiation-cooled rockets are used for a range of low-thrust propulsion functions, including apogee insertion, attitude control, and repositioning of satellites, reaction control of launch vehicles, and primary propulsion for planetary space- craft. The key to high performance and long lifetimes for radiation-cooled rockets is the chamber temperature capability. The material system that is currently used for radiation-cooled rockets, a niobium alloy (C103) with a fused silica coating, has a maximum operating temperature of 1370 C. Temperature limitations of C103 rockets force the use of fuel film cooling, which degrades rocket performance and, in some cases, imposes a plume contamination issue from unburned fuel. A material system composed of a rhenium (Re) substrate and an iridium (Ir) coating has demonstrated operation at high temperatures (2200 C) and for long lifetimes (hours). The added thermal margin afforded by iridium-coated rhenium (Ir/Re) allows reduction or elimination of fuel film cooling. This, in turn, leads to higher performance and cleaner spacecraft environments. There are ongoing government- and industry-sponsored efforts to develop flight Ir/ Re engines, with the primary focus on 440-N, apogee insertion engines. Complementing these Ir/Re engine development efforts is a program to address specific concerns and fundamental characterization of the Ir/Re material system, including (1) development of Ir/Re rocket fabrication methods, (2) establishment of critical Re mechanical properly data, (3) development of reliable joining methods, and (4) characterization of Ir/Re life-limiting mechanisms.

  8. The Electric Dipole Moment of Iridium Monosilicide, IrSi

    NASA Astrophysics Data System (ADS)

    Le, Anh; Steimle, Timothy C.; Cheng, Lan; Stanton, John F.

    2013-06-01

    The optical spectrum of iridium monosilicide (IrSi) was recently observed using REMPI spectroscopy in the range 17200 to 23850 cm^{-1}. The observation was supported by an ab initio calculation which predicted a X^{2}Δ_{5/2} state. Here, we report on the analysis of the optical Stark effect for the X^{2}Δ_{5/2} and [16.0]1.5 (v=6) states. The (6,0)[16.0]1.5 - X^{2}Δ_{5/2} and the (7,0)[16.0]3.5- X^{2}Δ_{5/2} bands of IrSi have been recorded using high-resolution laser-induced fluorescence spectroscopy. The observed optical Stark shifts for the ^{193}IrSi and ^{191}IrSi isotopologues were analyzed to produce the electric dipole moments of -0.4139(64)D and 0.7821(63)D for the X^{2}Δ_{5/2} and [16.0]1.5 (v=6) states, respectively. The negative sign of electric dipole moment of the X^{2}Δ_{5/2} state is supported by high-level quantum-chemical calculations employing all-electron scalar-relativistic CCSD(T) method augmented with spin-orbit corrections as well as corrections due to full triple excitations. In particular, electron-correlation effects have been shown to be essential in the prediction of the negative sign of the dipole moment. A comparison with other iridium containing molecules will be made. Maria A. Garcia, Carolin Vietz, Fernando Ruipérez, Michael D. Morse, and Ivan Infante, Kimika Fakultatea, Euskal Herriko. J. Chem. Phys., (submitted)

  9. Process for catalytically oxidizing cycloolefins, particularly cyclohexene

    DOEpatents

    Mizuno, Noritaka; Lyon, David K.; Finke, Richard G.

    1993-01-01

    This invention is a process for catalytically oxidizing cycloolefins, particularly cyclohexenes, to form a variety of oxygenates. The catalyst used in the process is a covalently bonded iridium-heteropolyanion species. The process uses the catalyst in conjunction with a gaseous oxygen containing gas to form 2-cyclohexen-1-ol and also 2-cyclohexen-1-one.

  10. Feasibility Analysis on the Utilization of the Iridium Satellite Communications Network for Resident Space Objects in Low Earth Orbit

    DTIC Science & Technology

    2013-03-21

    turquoise -colored plane (containing Iridium_68) and orange-colored plane (containing Iridium_40) compared to the spacing between the turquoise -colored...plane and the white-colored plane (containing Iridium_11). The turquoise -colored and orange-colored planes can be thought of as planes one and six...United States, the turquoise - colored plane is descending, or transiting north to south, and the orange-colored plane is ascending, or transiting

  11. Effects of Potassium Permanganate Oxidation on Subsurface Microbial Activity

    NASA Technical Reports Server (NTRS)

    Rowland, Martin A.; Brubaker, Gaylen R.; Westray, Mark; Morris, Damon; Kohler, Keisha; McCool, Alex (Technical Monitor)

    2001-01-01

    In situ chemical oxidation has the potential for degrading large quantities of organic contaminants and can be more effective and timely than traditional ex situ treatment methods. However, there is a need to better characterize the potential effects of this treatment on natural processes. This study focuses on potential inhibition to anaerobic dechlorination of trichloroethene (TCE) in soils from a large manufacturing facility as a result of in situ oxidation using potassium permanganate (KMn04)Previous microcosm studies established that natural attenuation occurs on-site and that it is enhanced by the addition of ethanol to the system. A potential remediation scheme for the site involves the use of potassium permanganate to reduce levels of TCE in heavily contaminated areas, then to inject ethanol into the system to "neutralize" excess oxidant and enhance microbial degradation. However, it is currently unknown whether the exposure of indigenous microbial populations to potassium permanganate may adversely affect biological reductive dechlorination by these microorganisms. Consequently, additional microcosm studies were conducted to evaluate this remediation scheme and assess the effect of potassium permanganate addition on biological reductive dechlorination of TCE. Samples of subsurface soil and groundwater were collected from a TCE-impacted area of the site. A portion of the soil was pretreated with nutrients and ethanol to stimulate microbial activity, while the remainder of the soil was left unamended. Soil/groundwater microcosms were prepared in sealed vials using the nutrient-amended and unamended soils, and the effects of potassium permanganate addition were evaluated using two permanganate concentrations (0.8 and 2.4 percent) and two contact times (1 and 3 weeks). TCE was then re-added to each microcosm and TCE and dichloroethene (DCE) concentrations were monitored to determine the degree to which microbial dechlorination occurred following chemical

  12. Measurement of nitrous oxide reductase activity in aquatic sediments

    SciTech Connect

    Miller, L.G.; Oremland, R.S.; Paulsen, S.

    1986-01-01

    Denitrification in aquatic sediments was measured by an N/sub 2/O reductase assay. Sediments consumed small added quantities of N/sub 2/O over short periods (a few hours). In experiments with sediment slurries, N/sub 2/O reductase activity was inhibited by 0/sub 2/, C/sub 2/H/sub 2/, heat treatment, and by high levels of nitrate (1 mM) or sulfide (10 mM). However, ambient levels of nitrate (<100 ..mu..M) did not influence activity, and moderate levels (about 150 ..mu..M) induced only a short lag before reductase activity began. Moderate levels of sulfide (<1 mM) had no effect on N/sub 2/O reductase activity. Nitrous oxide reductase displayed Michaelis-Menten kinetics in sediments from freshwater, estuarine, and alkaline-saline environments. An in situ assay was devised in which a solution of N/sub 2/O was injected into sealed glass cores containing intact sediment. Two estimates of net rates of denitrification in San Francisco Bay under approximated in situ conditions were 0.009 and 0.041 mmol of N/sub 2/O per m/sup 2/ per h. Addition of chlorate to inhibit denitrification in these intact-core experiments (to estimate gross rates of N/sub 2/O consumption) resulted in approximately a 14% upward revision of estimates of net rates. These results were comparable to an in situ estimate of 0.022 mmol of N/sub 2/O per m/sup 2/ per h made with the acetylene block assay.

  13. Measurement of nitrous oxide reductase activity in aquatic sediments

    USGS Publications Warehouse

    Miller, L.G.; Oremland, R.S.; Paulsen, S.

    1986-01-01

    Denitrification in aquatic sediments was measured by an N2O reductase assay. Sediments consumed small added quantities of N2O over short periods (a few hours). In experiments with sediment slurries, N2O reductase activity was inhibited by O2, C2H2, heat treatment, and by high levels of nitrate (1 mM) or sulfide (10 mM). However, ambient levels of nitrate (<100 μM) did not influence activity, and moderate levels (about 150 μM) induced only a short lag before reductase activity began. Moderate levels of sulfide (<1 mM) had no effect on N2O reductase activity. Nitrous oxide reductase displayed Michaelis-Menten kinetics in sediments from freshwater (Km = 2.17 μM), estuarine (Km = 14.5 μM), and alkaline-saline (Km = 501 μM) environments. An in situ assay was devised in which a solution of N2O was injected into sealed glass cores containing intact sediment. Two estimates of net rates of denitrification in San Francisco Bay under approximated in situ conditions were 0.009 and 0.041 mmol of N2O per m2 per h. Addition of chlorate to inhibit denitrification in these intact-core experiments (to estimate gross rates of N2O consumption) resulted in approximately a 14% upward revision of estimates of net rates. These results were comparable to an in situ estimate of 0.022 mmol of N2O per m2 per h made with the acetylene block assay.

  14. Phorbol ester induces elevated oxidative activity and alkalization in a subset of lysosomes

    SciTech Connect

    Chen, Chii-Shiarng )

    2002-01-01

    Background: Lysosomes are acidic organelles that play multiple roles in various cellular oxidative activities such as the oxidative burst during cytotoxic killing. It remains to be determined how lysosomal lumen oxidative activity and pH interact and are regulated. Here, I report the use of fluorescent probes to measure oxidative activity and pH of lysosomes in live macrophages upon treatment with the tumor promotor phorbol 12-myristate 13-acetate (PMA), and provide novel insight regarding the regulation of lysosomal oxidative activity and pH. Results: The substrate used to measure oxidative activity was bovine serum albumin covalently coupled to dihydro-2?, 4,5,6,7,7?-hexafluorofluorescein (OxyBURST Green H2HFF BSA). During pulse-chase procedures with live macrophages, this reduced dye was internalized through an endocytic pathway and accumulated in the lysosomes. Oxidation of this compound results in a dramatic increase of fluorescence intensity. By using low-light level fluorescence microscopy, I determined that phorbol ester treatment results in increased oxidative activity and pH elevation in different subsets of lysosomes. Furthermore, lysosomes with stronger oxidative activity tended to exclude the acidotropic lysosomal indicator, and thus exhibit higher alkalinity. Conclusions: Results indicate that there is a regulatory mechanism between lysosomal oxidative activity and pH. Activation of lysosomal Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase by phorbol ester may result in increase of intralysosomal O2?- and H2O2, concurrent with pH elevation due to consumption of H+ and generation of OH-. Furthermore, effect of phorbol ester on elevated oxidative activity and pH is heterogeneous among total lysosomal population. Higher oxidative activity and/or pH are only observed in subsets of lysosomes.

  15. Nitric oxide released from activated platelets inhibits platelet recruitment.

    PubMed Central

    Freedman, J E; Loscalzo, J; Barnard, M R; Alpert, C; Keaney, J F; Michelson, A D

    1997-01-01

    Vessel injury and thrombus formation are the cause of most ischemic coronary syndromes and, in this setting, activated platelets stimulate platelet recruitment to the growing thrombus. Recently, a constitutive nitric oxide synthase (NOS) has been identified in human platelets. To further define the capacity of platelets to produce nitric oxide (NO), as well as to study the role of this NO in platelet recruitment, we adapted a NO-selective microelectrode for use in a standard platelet aggregometer, thereby permitting simultaneous measurement of platelet aggregation and NO production. Treatment of platelets with the NO synthase inhibitor -NG-nitroarginine methyl ester (L-NAME), reduced NO production by 92+/-8% in response to 5 microM ADP compared to control but increased aggregation by only 15+/-2%. In contrast, L-NAME had a more pronounced effect on platelet recruitment as evidenced by a 35+/-5% increase in the extent of aggregation, a 33+/-3% decrease in cyclic GMP content, and a 31+/-5% increase in serotonin release from a second recruitable population of platelets added to stimulated platelets at the peak of NO production. To study platelet recruitment accurately, we developed an assay that monitors two platelet populations simultaneously. Nonbiotinylated platelets were incubated with L-NAME or vehicle and activated with ADP. At peak NO production, biotinylated platelets were added. As measured by three-color flow cytometry, there was a 56+/-11% increase in the number of P selectin- positive platelets in the nonbiotinylated population treated with L-NAME as compared to control. When biotinylated platelets were added to the L-NAME-treated nonbiotinylated population, the number of P selectin positive biotinylated plate-lets increased by 180+/-32% as compared to biotinylated platelets added to the control. In summary, stimulated platelets produce NO that modestly inhibits platelet activation but markedly inhibits additional platelet recruitment. These data suggest

  16. Activation energy of tantalum-tungsten oxide thermite reactions

    SciTech Connect

    Cervantes, Octavio G.; Munir, Zuhair A.; Kuntz, Joshua D.; Gash, Alexander E.

    2011-01-15

    The activation energy of a sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the high-pressure spark plasma sintering (HPSPS) technique at 300 and 400 C. The ignition temperatures were investigated under high heating rates (500-2000 C min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Samples consolidated at 300 C exhibit an abrupt change in temperature response prior to the main ignition temperature. This change in temperature response is attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465 to 670 C. The activation energies of the SG derived Ta-WO{sub 3} thermite composite consolidated at 300 and 400 C were determined to be 38{+-} 2 kJ mol{sup -1} and 57 {+-} 2 kJ mol{sup -1}, respectively. (author)

  17. Activation Energy of Tantalum-Tungsten Oxide Thermite Reaction

    SciTech Connect

    Cervantes, O; Kuntz, J; Gash, A; Munir, Z

    2010-02-25

    The activation energy of a high melting temperature sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the High Pressure Spark Plasma Sintering (HPSPS) technique to 300 and 400 C to produce pellets with dimensions of 5 mm diameter by 1.5 mm height. A custom built ignition setup was developed to measure ignition temperatures at high heating rates (500-2000 C {center_dot} min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Unlike the 400 C samples, results show that the samples consolidated to 300 C undergo an abrupt change in temperature response prior to ignition. This change in temperature response has been attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465-670 C. The activation energy of the SG derived Ta-WO{sup 3} thermite composite consolidated to 300 and 400 C were determined to be 37.787 {+-} 1.58 kJ {center_dot} mol{sup -1} and 57.381 {+-} 2.26 kJ {center_dot} mol{sup -1}, respectively.

  18. Porous platinum mesoflowers with enhanced activity for methanol oxidation reaction

    SciTech Connect

    Zhuang Lina; Wang Wenjin; Hong Feng; Yang Shengchun; You Hongjun; Fang Jixiang; Ding Bingjun

    2012-07-15

    Porous Pt and Pt-Ag alloy mesoflowers (MFs) with about 2 {mu}m in diameter and high porosity were synthesized using Ag mesoflowers as sacrificial template by galvanic reaction. The silver content in Pt-Ag alloys can be facilely controlled by nitric acid treatment. And the pure Pt MFs can be obtained by selective removal of silver element from Pt{sub 72}Ag{sub 28} MFs electrochemically. Both Pt{sub 45}Ag{sub 55}, Pt{sub 72}Ag{sub 28} and pure Pt show a high catalytic performance in methanol oxidation reaction (MOR). Especially, pure Pt MFs exhibited a 2 to 3 times current density enhancement in MOR compared with the commercial used Pt black, which can be attributed to their porous nanostructure with 3-dimentional nature and small crystal sizes. - Graphical Abstract: The CVs of MOR on Pt (red) and Pt black (green) catalysts in 0.1 M HClO{sub 4} and 0.5 M CH{sub 3}OH for specific mass current. The insert shows the SEM images of two porous Pt MFs. Platinum mesoflowers (MFs) with about 2 {mu}m in diameter and high porosity were synthesised with Ag mesoflowers as sacrificial template by galvanic replacement. The porous Pt MFs exhibited a more than 3 times enhancement in electrocatalytic performance for methanol oxidation reaction compared the commercial used Pt black. Highlights: Black-Right-Pointing-Pointer Porous Pt and Pt-Ag mesoflowers (MFs) were synthesized using Ag MFs sacrifical template. Black-Right-Pointing-Pointer Pt MFs presents an improved catalytic activity in MOR compared with Pt black. Black-Right-Pointing-Pointer We provided a facile approach for the development of high performance Pt electrocatalysts for fuel cells.

  19. Selective Electrocatalytic Activity of Ligand Stabilized Copper Oxide Nanoparticles

    SciTech Connect

    Kauffman, Douglas R; Ohodnicki, Paul R; Kail, Brian W; Matranga, Christopher

    2011-01-01

    Ligand stabilization can influence the surface chemistry of Cu oxide nanoparticles (NPs) and provide unique product distributions for electrocatalytic methanol (MeOH) oxidation and CO{sub 2} reduction reactions. Oleic acid (OA) stabilized Cu{sub 2}O and CuO NPs promote the MeOH oxidation reaction with 88% and 99.97% selective HCOH formation, respectively. Alternatively, CO{sub 2} is the only reaction product detected for bulk Cu oxides and Cu oxide NPs with no ligands or weakly interacting ligands. We also demonstrate that OA stabilized Cu oxide NPs can reduce CO{sub 2} into CO with a {approx}1.7-fold increase in CO/H{sub 2} production ratios compared to bulk Cu oxides. The OA stabilized Cu oxide NPs also show 7.6 and 9.1-fold increases in CO/H{sub 2} production ratios compared to weakly stabilized and non-stabilized Cu oxide NPs, respectively. Our data illustrates that the presence and type of surface ligand can substantially influence the catalytic product selectivity of Cu oxide NPs.

  20. Activated carbon and tungsten oxide supported on activated carbon catalysts for toluene catalytic combustion.

    PubMed

    Alvarez-Merino, M A; Ribeiro, M F; Silva, J M; Carrasco-Marín, F; Maldonado-Hódar, F J

    2004-09-01

    We have used activated carbon (AC) prepared from almond shells as a support for tungsten oxide to develop a series of WOx/AC catalysts for the catalytic combustion of toluene. We conducted the reaction between 300 and 350 degrees C, using a flow of 500 ppm of toluene in air and space velocity (GHSV) in the range 4000-7000 h(-1). Results show that AC used as a support is an appropriate material for removing toluene from dilute streams. By decreasing the GHSV and increasing the reaction temperature AC becomes a specific catalyst for the total toluene oxidation (SCO2 = 100%), but in less favorable conditions CO appears as reaction product and toluene-derivative compounds are retained inside the pores. WOx/AC catalysts are more selective to CO2 than AC due to the strong acidity of this oxide; this behavior improves with increased metal loading and reaction temperature and contact time. The catalytic performance depends on the nonstoichiometric tungsten oxide obtained during the pretreatment. In comparison with other supports the WOx/AC catalysts present, at low reaction temperatures, higher activity and selectivity than WO, supported on SiO2, TiO2, Al2O3, or Y zeolite. This is due to the hydrophobic character of the AC surface which prevents the adsorption of water produced from toluene combustion thus avoiding the deactivation of the active centers. However, the use of WOx/AC system is always restricted by its gasification temperature (around 400 degrees C), which limits the ability to increase the conversion values by increasing reaction temperatures.

  1. Cloud droplet activation through oxidation of organic aerosol influenced by temperature and particle phase state

    NASA Astrophysics Data System (ADS)

    Slade, Jonathan H.; Shiraiwa, Manabu; Arangio, Andrea; Su, Hang; Pöschl, Ulrich; Wang, Jian; Knopf, Daniel A.

    2017-02-01

    Chemical aging of organic aerosol (OA) through multiphase oxidation reactions can alter their cloud condensation nuclei (CCN) activity and hygroscopicity. However, the oxidation kinetics and OA reactivity depend strongly on the particle phase state, potentially influencing the hydrophobic-to-hydrophilic conversion rate of carbonaceous aerosol. Here, amorphous Suwannee River fulvic acid (SRFA) aerosol particles, a surrogate humic-like substance (HULIS) that contributes substantially to global OA mass, are oxidized by OH radicals at different temperatures and phase states. When oxidized at low temperature in a glassy solid state, the hygroscopicity of SRFA particles increased by almost a factor of two, whereas oxidation of liquid-like SRFA particles at higher temperatures did not affect CCN activity. Low-temperature oxidation appears to promote the formation of highly-oxygenated particle-bound fragmentation products with lower molar mass and greater CCN activity, underscoring the importance of chemical aging in the free troposphere and its influence on the CCN activity of OA.

  2. A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction.

    PubMed

    Seitz, Linsey C; Dickens, Colin F; Nishio, Kazunori; Hikita, Yasuyuki; Montoya, Joseph; Doyle, Andrew; Kirk, Charlotte; Vojvodic, Aleksandra; Hwang, Harold Y; Norskov, Jens K; Jaramillo, Thomas F

    2016-09-02

    Oxygen electrochemistry plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrOx/SrIrO3) catalyst formed during electrochemical testing by strontium leaching from surface layers of thin films of SrIrO3 This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 millivolts of overpotential for 30 hours of continuous testing in acidic electrolyte. Density functional theory calculations suggest the formation of highly active surface layers during strontium leaching with IrO3 or anatase IrO2 motifs. The IrOx/SrIrO3 catalyst outperforms known IrOx and ruthenium oxide (RuOx) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte.

  3. Enhanced dewaterability of waste activated sludge by Fe(II)-activated peroxymonosulfate oxidation.

    PubMed

    Liu, Jun; Yang, Qi; Wang, Dongbo; Li, Xiaoming; Zhong, Yu; Li, Xin; Deng, Yongchao; Wang, Liqun; Yi, Kaixin; Zeng, Guangming

    2016-04-01

    The effect of Fe(II)-activated peroxymonosulfate (Fe(II)-PMS) oxidation on the waste activated sludge (WAS) dewatering and its mechanisms were investigated in this study. The capillary suction time (CST), specific resistance to filterability (SRF) of sludge and water content (WC) of dewatered sludge cake were chosen as the main parameters to evaluate the sludge dewaterability. Experimental results showed that Fe(II)-PMS effectively disintegrated sludge and improved sludge dewaterability. High CST and SRF reduction (90% and 97%) was achieved at the optimal conditions of PMS (HSO5(-)) 0.9 mmol/gVSS, Fe(II) 0.81 mmol/gVSS, and pH 6.8. Extracellular polymeric substances (EPS) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy before and after Fe(II)-PMS oxidation were determined to explain the enhanced dewatering mechanism. The release of EPS-bound water induced by the destruction of EPS was the primary reason for the improvement of sludge dewaterability during Fe(II)-PMS oxidation.

  4. Nitrous oxide activation by a cobalt(ii) complex for aldehyde oxidation under mild conditions.

    PubMed

    Corona, Teresa; Company, Anna

    2016-10-07

    Nitrous oxide (N2O) is a waste gas produced in many industrial processes with an important environmental impact. Thus, its application as an oxidant is highly desirable because it produces innocuous N2 as a by-product. In this work we report a new cobalt(ii) complex that reacts with N2O under mild conditions and the catalytic application of this system to carry out the oxidation of aldehydes.

  5. Activation of Peroxymonosulfate by Benzoquinone: A Novel Nonradical Oxidation Process.

    PubMed

    Zhou, Yang; Jiang, Jin; Gao, Yuan; Ma, Jun; Pang, Su-Yan; Li, Juan; Lu, Xue-Ting; Yuan, Li-Peng

    2015-11-03

    The reactions between peroxymonosulfate (PMS) and quinones were investigated for the first time in this work, where benzoquinone (BQ) was selected as a model quinone. It was demonstrated that BQ could efficiently activate PMS for the degradation of sulfamethoxazole (SMX; a frequently detected antibiotic in the environments), and the degradation rate increased with solution pH from 7 to 10. Interestingly, quenching studies suggested that neither hydroxyl radical (•OH) nor sulfate radical (SO4•-) was produced therein. Instead, the generation of singlet oxygen (1O2) was proved by using two chemical probes (i.e., 2,2,6,6-tetramethyl-4-piperidinol and 9,10-diphenylanthracene) with the appearance of 1O2 indicative products detected by electron paramagnetic resonance spectrometry and liquid chromatography mass spectrometry, respectively. A catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PMS and BQ and the subsequent decomposition of this intermediate into 1O2. Accordingly, a kinetic model was developed, and it well described the experimental observation that the pH-dependent decomposition rate of PMS was first-order with respect to BQ. These findings have important implications for the development of novel nonradical oxidation processes based on PMS, because 1O2 as a moderately reactive electrophile may suffer less interference from background organic matters compared with nonselective •OH and SO4•-.

  6. Antibacterial Activity of Dental Composites Containing Zinc Oxide Nanoparticles

    PubMed Central

    Sevinç, Berdan Aydin; Hanley, Luke

    2010-01-01

    The resin-based dental composites commonly used in restorations result in more plaque accumulation than other materials. Bacterial biofilm growth contributes to secondary caries and failure of resin-based dental composites. Methods to inhibit biofilm growth on dental composites have been sought for several decades. It is demonstrated here that zinc oxide nanoparticles (ZnO-NPs) blended at 10% (w/w) fraction into dental composites display antimicrobial activity and reduce growth of bacterial biofilms by roughly 80% for a single-species model dental biofilm. Antibacterial effectiveness of ZnO-NPs was assessed against Streptococcus sobrinus ATCC 27352 grown both planktonically and as biofilms on composites. Direct contact inhibition was observed by scanning electron microscopy and confocal laser scanning microscopy while biofilm formation was quantified by viable counts. An 80% reduction in bacterial counts was observed with 10% ZnO-NP-containing composites compared with their unmodified counterpart, indicating a statistically significant suppression of biofilm growth. Although, 20% of the bacterial population survived and could form a biofilm layer again, 10% ZnO-NP-containing composites maintained at least some inhibitory activity even after the third generation of biofilm growth. Microscopy demonstrated continuous biofilm formation for unmodified composites after one day growth, but only sparsely distributed biofilms formed on 10% ZnO-NP-containing composites. The minimum inhibitory concentration of ZnO-NPs suspended in S. sobrinus planktonic culture was 50 μg/ml. 10% ZnO-NP-containing composites qualitatively showed less biofilm after one day anaerobic growth of a three-species initial colonizer biofilm after when compared to unmodified composites, but did not significantly reduce growth after three days. PMID:20225252

  7. Persulfate Oxidation Regeneration of Granular Activated Carbon: Reversible Impacts on Sorption Behavior

    EPA Science Inventory

    Chemical oxidation regeneration of granular activated carbon (GAC) is a developing technology that can be carried out utilizing thermally-activated persulfate. During chemical regeneration of GAC, aggressive oxidative conditions lead to high acidity (pH < 2) and the accumulation ...

  8. Perovskite-supported palladium for methane oxidation - structure-activity relationships.

    PubMed

    Eyssler, Arnim; Lu, Ye; Matam, Santhosh Kumar; Weidenkaff, Anke; Ferri, Davide

    2012-01-01

    Palladium is the precious metal of choice for methane oxidation and perovskite-type oxides offer the possibility to stabilize it as PdO, considered crucial for catalytic activity. Pd can adopt different oxidation and coordination states when associated with perovskite-type oxides. Here, we review our work on the effect of perovskite composition on the oxidation and coordination states of Pd and its influence on catalytic activity for methane oxidation in the case of typical Mn, Fe and Co perovskite-based oxidation catalysts. Especially X-ray absorption near edge structure (XANES) spectroscopy is shown to be crucial to fingerprint the different coordination states of Pd. Pd substitutes Fe and Co in the octahedral sites but without modifying catalytic activity with respect to the Pd-free perovskite. On LaMnO(3) palladium is predominantly exposed at the surface thus bestowing catalytic activity for methane oxidation. However, the occupancy of B-cation sites of the perovskite structure by Pd can be exploited to cyclically activate Pd and to protect it from particle growth. This is explicitly demonstrated for La(Fe, Pd)O(3), where catalytic activity for methane oxidation is enhanced under oscillating redox conditions at 500 °C, therefore paving the way to the practical application in three-way catalysts for stoichiometric natural gas engines.

  9. UV-activated persulfate oxidation and regeneration of NOM-Saturated granular activated carbon.

    PubMed

    An, Dong; Westerhoff, Paul; Zheng, Mengxin; Wu, Mengyuan; Yang, Yu; Chiu, Chao-An

    2015-04-15

    A new method of ultraviolet light (UV) activated persulfate (PS) oxidation was investigated to regenerate granular activated carbon (GAC) in drinking water applications. The improvements in iodine and methylene blue numbers measured in the GAC after ultraviolet- (UV) activated persulfate suggested that the GAC preloaded with natural organic matter (NOM) was chemically regenerated. An experimental matrix for UV-activated persulfate regeneration included a range of persulfate doses and different UV wavelengths. Over 87% of the initial iodine number for GAC was restored under the optimum conditions, perfulfate dosage 60 g/L and UV exposure 1.75 × 10(4) mJ/cm(2). The persulfate dosages had little effect on the recovery of the methylene blue number, which was approximately 65%. Persulfate activation at 185 nm was superior to activation at 254 nm. UV activation of persulfate in the presence of GAC produced acid, lowering the solution pH. Higher persulfate concentrations and UV exposure resulted in greater GAC regeneration. Typical organic and inorganic byproducts (e.g., benzene compounds and sulfate ions) were measured as a component of treated water quality safety. This study provides a proof-of-concept that can be used to optimize pilot-scale and full-scale UV-activated persulfate for regeneration of NOM-saturated GAC.

  10. Endothelial nitric oxide synthase activation and nitric oxide function: new light through old windows.

    PubMed

    Bird, Ian M

    2011-09-01

    The principle mechanisms operating at the level of endothelial nitric oxide synthase (eNOS) itself to control its activity are phosphorylation, the auto-regulatory properties of the protein itself, and Ca(2)(+)/calmodulin binding. It is now clear that activation of eNOS is greatest when phosphorylation of certain serine and threonine residues is accompanied by elevation of cytosolic [Ca2+](i). While eNOS also contains an autoinhibitory loop, Rafikov et al. (2011) present the evidence for a newly identified 'flexible arm' that operates in response to redox state. Boeldt et al. (2011) also review the evidence that changes in the nature of endothelial Ca(2)(+) signaling itself in different physiologic states can extend both the amplitude and duration of NO output, and a failure to change these responses in pregnancy is associated with preeclampsia. The change in Ca(2)(+) signaling is mediated through altering capacitative entry mechanisms inherent in the cell, and so many agonist responses using this mechanism are altered. The term 'adaptive cell signaling' is also introduced for the first time to describe this phenomenon. Finally NO is classically regarded as a regulator of vascular function, but NO has other actions. One proposed role is regulation of steroid biosynthesis but the physiologic relevance was unclear. Ducsay & Myers (2011) now present new evidence that NO may provide the adrenal with a mechanism to regulate cortisol output according to exposure to hypoxia. One thing all three of these reviews show is that even after several decades of study into NO biosynthesis and function, there are clearly still many things left to discover.

  11. Nitrous oxide emissions from the oxidation tank of a pilot activated sludge plant.

    PubMed

    Lotito, Adriana Maria; Wunderlin, Pascal; Joss, Adriano; Kipf, Marco; Siegrist, Hansruedi

    2012-07-01

    This study discusses the results of the continuous monitoring of nitrous oxide emissions from the oxidation tank of a pilot conventional wastewater treatment plant. Nitrous oxide emissions from biological processes for nitrogen removal in wastewater treatment plants have drawn great attention over the last years, due to the high greenhouse effect. However, even if several studies have been carried out to quantify nitrous oxide emission rates from different types of treatment, quite wide ranges have been reported. Only grab samples or continuous measurements over limited periods were considered in previous studies, which can account for the wide variability of the obtained results. Through continuous monitoring over several months, our work tries to fill this gap of knowledge and get a deeper insight into nitrous oxide daily and weekly emission dynamics. Moreover, the influence of some operating conditions (sludge age, dissolved oxygen concentration in the oxidation tank, nitrogen load) was studied to determine good practices for wastewater treatment plant operation aiming at the reduction of nitrous oxide emissions. The dissolved oxygen set-point is shown to play a major role in nitrous oxide emissions. Low sludge ages and high nitrogen loads are responsible for higher emissions as well. An interesting pattern has been observed, with quite negligible emissions during most of the day and a peak with a bell-like shape in the morning in the hours of maximum nitrogen load in the plant, correlated to the ammonia and nitrite peaks in the tank.

  12. Preparation and photocatalytic activity of TiO2-exfoliated graphite oxide composite using an ecofriendly graphite oxidation method

    NASA Astrophysics Data System (ADS)

    Baldissarelli, Vanessa Zanon; de Souza, Thiago; Andrade, Luisa; Oliveira, Luiz Fernando Cappa de; José, Humberto Jorge; Moreira, Regina de Fátima Peralta Muniz

    2015-12-01

    A simple and effective stepwise-method was developed to produce expanded exfoliated graphite oxide (EGO). Using a combination of ozone exposure and thermal treatment we demonstrate that a graphite surface can be modified to generate a graphene-like surface containing oxygen and sp3 carbon. This expanded exfoliated graphite oxide is useful for the production, through thermal treatment, of photocatalytic TiO2-EGO composites which are more active than those produce by the Hummers method. The photocatalytic activity of TiO2-EGO in methylene blue (MB) bleaching under UV light is enhanced in comparison with TiO2 P25.

  13. Effect of chromium oxide as active site over TiO2-PILC for selective catalytic oxidation of NO.

    PubMed

    Zhang, Jingxin; Zhang, Shule; Cai, Wei; Zhong, Qin

    2013-12-01

    This study introduced TiO2-pillared clays (TiO2-PILC) as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350 degrees C, the NO conversion was 61% under conditions of GHSV = 23600 hr(-1). The BET data showed that the support particles had a mesoporous structure. H2-TPR showed that Cr(10)TiP (10 wt.% Cr doping on TiO2-PILC) clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO + O2 adsorption, the intensity of evolution of superoxide ions (O2(-)) increased. The content of Cr3+ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr3+ increased to 50.28%. Additionally, O(alpha)/O(beta) increased markedly through the oxidation process. The NO conversion decreased when SO2 was added into the system, but when the SO2 was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO4(2-).

  14. Peptide-functionalized luminescent iridium complexes for lifetime imaging of CXCR4 expression.

    PubMed

    Kuil, Joeri; Steunenberg, Peter; Chin, Patrick T K; Oldenburg, Joppe; Jalink, Kees; Velders, Aldrik H; van Leeuwen, Fijs W B

    2011-08-16

    The chemokine receptor 4 (CXCR4) is over-expressed in 23 types of cancer in which it plays a role in, among others, the metastatic spread. For this reason it is a potential biomarker for the field of diagnostic oncology. The antagonistic Ac-TZ14011 peptide, which binds to CXCR4, has been conjugated to luminescent iridium dyes to allow for CXCR4 visualization. The iridium dyes are cyclometalated octahedral iridium(III) 2-phenylpyridine complexes that can be functionalized with one, two or three targeting Ac-TZ14011 peptides. Confocal microscopy and fluorescence lifetime imaging microscopy (FLIM) showed that the peptide-iridium complex conjugates can be used to visualize CXCR4 expression in tumor cells. The CXCR4 receptor affinity and specific cell binding of the mono-, di- and trimeric peptide derivatives were assessed by using flow cytometry. The three derivatives possessed nanomolar receptor affinity and could distinguish between cell lines with different CXCR4 expression levels. This yields the first example of a neutral iridium(III) complex functionalized with peptides for FLIM-based visualization of a cancer associated membrane receptor.

  15. Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice.

    PubMed

    Gabrielli, Paolo; Barbante, Carlo; Plane, John M C; Varga, Anita; Hong, Sungmin; Cozzi, Giulio; Gaspari, Vania; Planchon, Frédéric A M; Cairns, Warren; Ferrari, Christophe; Crutzen, Paul; Cescon, Paolo; Boutron, Claude F

    2004-12-23

    An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65 million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre-sized meteoric smoke particles, formed from the recondensation of ablated meteoroids in the atmosphere at altitudes >70 kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 +/- 5 kilotons per year of meteoric smoke during the Holocene.

  16. Oxidative stress activates FUS1 and RLM1 transcription in the yeast Saccharomyces cerevisiae in an oxidant-dependent Manner.

    PubMed

    Staleva, Liliana; Hall, Andrea; Orlow, Seth J

    2004-12-01

    Mating in haploid Saccharomyces cerevisiae occurs after activation of the pheromone response pathway. Biochemical components of this pathway are involved in other yeast signal transduction networks. To understand more about the coordination between signaling pathways, we used a "chemical genetic" approach, searching for compounds that would activate the pheromone-responsive gene FUS1 and RLM1, a reporter for the cell integrity pathway. We found that catecholamines (l-3,4-hydroxyphenylalanine [l-dopa], dopamine, adrenaline, and noradrenaline) elevate FUS1 and RLM1 transcription. N-Acetyl-cysteine, a powerful antioxidant in yeast, completely reversed this effect, suggesting that FUS1 and RLM1 activation in response to catecholamines is a result of oxidative stress. The oxidant hydrogen peroxide also was found to activate transcription of an RLM1 reporter. Further genetic analysis combined with immunoblotting revealed that Kss1, one of the mating mitogen-activated protein kinases (MAPKs), and Mpk1, an MAPK of the cell integrity pathway, participated in l-dopa-induced stimulation of FUS1 and RLM1 transcription. We also report that Mpk1 and Hog1, the high osmolarity MAPK, were phosphorylated upon induction by hydrogen peroxide. Together, our results demonstrate that cells respond to oxidative stress via different signal transduction machinery dependent upon the nature of the oxidant.

  17. Oxidation of alcohols and activated alkanes with Lewis acid-activated TEMPO.

    PubMed

    Nguyen, Thuy-Ai D; Wright, Ashley M; Page, Joshua S; Wu, Guang; Hayton, Trevor W

    2014-11-03

    The reactivity of MCl3(η(1)-TEMPO) (M = Fe, 1; Al, 2; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) with a variety of alcohols, including 3,4-dimethoxybenzyl alcohol, 1-phenyl-2-phenoxyethanol, and 1,2-diphenyl-2-methoxyethanol, was investigated using NMR spectroscopy and mass spectrometry. Complex 1 was effective in cleanly converting these substrates to the corresponding aldehyde or ketone. Complex 2 was also able to oxidize these substrates; however, in a few instances the products of overoxidation were also observed. Oxidation of activated alkanes, such as xanthene, by 1 or 2 suggests that the reactions proceed via an initial 1-electron concerted proton-electron transfer (CPET) event. Finally, reaction of TEMPO with FeBr3 in Et2O results in the formation of a mixture of FeBr3(η(1)-TEMPOH) (23) and [FeBr2(η(1)-TEMPOH)]2(μ-O) (24), via oxidation of the solvent, Et2O.

  18. Markers of oxidative stress and erythrocyte antioxidant enzyme activity in older men and women with differing physical activity.

    PubMed

    Rowiński, Rafał; Kozakiewicz, Mariusz; Kędziora-Kornatowska, Kornelia; Hübner-Woźniak, Elżbieta; Kędziora, Józef

    2013-11-01

    The aim of the present study was to examine the relationship between markers of oxidative stress and erythrocyte antioxidant enzyme activity and physical activity in older men and women. The present study included 481 participants (233 men and 248 women) in the age group 65-69 years (127 men and 125 women) and in the age group 90 years and over (106 men and 123 women). The classification of respondents by physical activity was based on answers to the question if, in the past 12 months, they engaged in any pastimes which require physical activity. The systemic oxidative stress status was assessed by measuring plasma iso-PGF2α and protein carbonyl concentration as well as erythrocyte antioxidant enzymes activity, i.e., superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR). The concentration of plasma iso-PGF2α and protein carbonyls (CP) was lower in groups of younger men and women compared to the respective older groups. In all examined groups, physical activity resulted in decrease of these oxidative stress markers and simultaneously caused adaptive increase in the erythrocyte SOD activity. Additionally, in active younger men CAT, GPx, and GR activities were higher than in sedentary ones. In conclusion, oxidative stress increase is age-related, but physical activity can reduce oxidative stress markers and induce adaptive increase in the erythrocyte antioxidant enzyme activity, especially SOD, even in old and very old men and women.

  19. Efficient asymmetric transfer hydrogenation of ketones in ethanol with chiral iridium complexes of spiroPAP ligands as catalysts.

    PubMed

    Liu, Wei-Peng; Yuan, Ming-Lei; Yang, Xiao-Hui; Li, Ke; Xie, Jian-Hua; Zhou, Qi-Lin

    2015-04-11

    Highly efficient iridium catalyzed asymmetric transfer hydrogenation of simple ketones with ethanol as a hydrogen donor has been developed. By using chiral spiro iridium catalysts (S)- a series of alkyl aryl ketones were hydrogenated to chiral alcohols with up to 98% ee.

  20. Effect of oxidation and extent of oxidation on biologically active PACs in asphalt products.

    PubMed

    Trumbore, David; Osborn, Linda; Blackburn, Gary; Niebo, Ron; Kriech, Anthony; Maxim, L Daniel

    2011-10-01

    Recent studies have reported divergent results in rodent cancer assays using fume condensates from a variety of asphalt products. This paper presents results of a study investigating the role of oxidation, or extent of oxidation, on these findings. Five straight run asphalts, made from widely used crude oils, were used as inputs to both production scale and laboratory oxidation units and processed to a range of softening points used in common roofing products. For each of the five asphalts studied, the oxidation reaction significantly decreased measures of polycyclic aromatic compounds (PACs) that have been linked, previously and in analyses included in this study, to tumor induction in rodent bioassays. Mutagenicity index determined by the modified Ames assay was reduced between 41% and 50% from the input asphalt to the final oxidized product. A fluorescence method tuned to a subset of PAC compounds that have been associated with carcinogenic behavior in mouse bioassays was reduced between 39% and 71%. The decrease was largest in the first quarter of the oxidation reaction. These findings indicate that oxidation, by itself, was not a likely factor in the tumor induction seen in the previous studies. Rather, other factors such as the conditions of fume generation and crude source (coupled with possible differences in distillation endpoints) were more likely to have determined the outcomes. Analyses of previously published data, presented in this paper, suggest that the modified Ames and fluorescence assays are valuable screening tools for use in future health-related asphalt research.

  1. Oxidized LDL induces in vitro lymphocyte activation in antiphospholipid syndrome.

    PubMed

    Laczik, Renata; Szodoray, Peter; Veres, Katalin; Lakos, Gabriella; Sipka, Sandor; Szegedi, Gyula; Soltész, Pal

    2010-06-01

    Oxidized low-density lipoprotein (oxLDL) is a key feature of the atheromatosus plaque and plays a critical role in foam cell formation and perpetuation of inflammatory processes. In antiphospholipid syndrome (APS), oxLDL molecules form complexes with beta2GPI and become target antigens for autoantibodies, which are detectable in the sera of these patients. oxLDL takes part in the pathogenesis of APS and in the concomitant accelerated atherosclerosis, yet the exact associated immune mechanisms are not clear in details. The aim of this study was to assess the activation and proliferation response of peripheral blood mononuclear cells (PBMCs) derived from patients with APS in the presence of oxLDL. Thirteen patients with APS and nine healthy individuals were enrolled in the study. Separated PBMCs of these patients were cultured in the presence of immunogenic epitope of oxLDL. Lymphocyte proliferation and cytokine secretion (TNF-alpha, IL-2, IFN-gamma, IL-4, and IL-10) were assessed by ELISA. We found significant PBMC proliferation in APS compared to healthy controls (PI/proliferation index/APS: 1.76 vs. PI control: 0.56; p = 0.032). A significant IL-2 and IFN-gamma secretion were detected upon oxLDL stimulus in patients with APS compared to controls (IL-2 cytokine secretion index (CSI) APS: 278.5, IL-2 CSI controls: 65.1; p = 0.025; IFN-gamma CSI APS: 163.2, IFN-gamma CSI controls: 77.4; p = 0.025). Based on our findings, we assume that oxLDL via Th1-type cytokine production and lymphocyte proliferation may contribute to the perpetuation of immune processes in APS.

  2. Resveratrol-loaded Nanoparticles Induce Antioxidant Activity against Oxidative Stress

    PubMed Central

    Kim, Jae-Hwan; Park, Eun-Young; Ha, Ho-Kyung; Jo, Chan-Mi; Lee, Won-Jae; Lee, Sung Sill; Kim, Jin Wook

    2016-01-01

    Resveratrol acts as a free radical scavenger and a potent antioxidant in the inhibition of numerous reactive oxygen species (ROS). The function of resveratrol and resveratrol-loaded nanoparticles in protecting human lung cancer cells (A549) against hydrogen peroxide was investigated in this study. The 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assay was performed to evaluate the antioxidant properties. Resveratrol had substantially high antioxidant capacity (trolox equivalent antioxidant capacity value) compared to trolox and vitamin E since the concentration of resveratrol was more than 50 μM. Nanoparticles prepared from β-lactoglobulin (β-lg) were successfully developed. The β-lg nanoparticle showed 60 to 146 nm diameter in size with negatively charged surface. Non-cytotoxicity was observed in Caco-2 cells treated with β-lg nanoparticles. Fluorescein isothiocynate-conjugated β-lg nanoparticles were identified into the cell membrane of Caco-2 cells, indicating that nanoparticles can be used as a delivery system. Hydrogen peroxide caused accumulation of ROS in a dose- and time-dependent manner. Resveratrol-loaded nanoparticles restored H2O2-induced ROS levels by induction of cellular uptake of resveratrol in A549 cells. Furthermore, resveratrol activated nuclear factor erythroid 2-related factor 2-Kelch ECH associating protein 1 (Nrf2-Keap1) signaling in A549 cells, thereby accumulation of Nrf2 abundance, as demonstrated by western blotting approach. Overall, these results may have implications for improvement of oxidative stress in treatment with nanoparticles as a biodegradable and non-toxic delivery carrier of bioactive compounds. PMID:26732454

  3. ALTERNATIVE ROUTES FOR CATALYST PREPARATION: USE OF ULTRASOUND AND MICROWAVE IRRADIATION FOR THE PREPARATION OF VANADIUM PHOSPHORUS OXIDE CATALYST AND THEIR ACTIVITY FOR HYDROCARBON OXIDATION

    EPA Science Inventory

    Vanadium phosphorus oxide (VPO) has been prepared using ultrasound and microwave irradiation methods and compared with the catalyst prepared by conventional method for both the phase composition and activity for hydrocarbon oxidation. It is found that ultrasound irradiation metho...

  4. CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand

    SciTech Connect

    Onishi, Naoya; Xu, Shaoan; Manaka, Yuichi; Suna, Yuki; Wang, Wan -Hui; Muckerman, James T.; Fujita, Etsuko; Himeda, Yuichiro

    2015-02-18

    In this study, the catalytic cycle for the production of formic acid by CO₂ hydrogenation and the reverse reaction has received renewed attention because they are viewed as offering a viable scheme for hydrogen storage and release. In this Forum Article, CO₂ hydrogenation catalyzed by iridium complexes bearing N^N-bidentate ligands is reported. We describe how a ligand containing hydroxyl groups as proton-responsive substituents enhances catalytic performance by an electronic effect of the oxyanions and a pendent-base effect through secondary coordination sphere interaction. In particular, [(Cp*IrCl)₂(TH2BPM)]Cl₂ (Cp* = pentamethyl cyclopentadienyl, TH2BPM = 4,4',6,6'-tetrahydroxy-2,2'-bipyrimidine) promotes enormously the catalytic hydrogenation of CO₂ by these synergistic effects under atmospheric pressure and at room temperature. Additionally, newly designed complexes with azole-type ligands are applied to CO₂ hydrogenation. The catalytic efficiencies of the azole-type complexes are much higher than that of the unsubstituted bipyridine complex [Cp*Ir(bpy)(OH₂)]SO₄. Furthermore, the introduction of one or more hydroxyl groups into ligands such as 2-pyrazolyl-6-hydroxypyridine, 2-pyrazolyl-4,6-dihydroxyl pyrimidine, and 4-pyrazolyl-2,6-dihydroxyl pyrimidine enhanced catalytic activity. It is clear that the incorporation of electron-donating hydroxyl groups into proton-responsive ligands is effective for promoting the hydrogenation of CO₂.

  5. Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy)

    NASA Technical Reports Server (NTRS)

    Alvarez, Walter; Asaro, Frank; Montanari, Alessandro

    1990-01-01

    The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where the average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.

  6. CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand

    DOE PAGES

    Onishi, Naoya; Xu, Shaoan; Manaka, Yuichi; ...

    2015-02-18

    In this study, the catalytic cycle for the production of formic acid by CO₂ hydrogenation and the reverse reaction has received renewed attention because they are viewed as offering a viable scheme for hydrogen storage and release. In this Forum Article, CO₂ hydrogenation catalyzed by iridium complexes bearing N^N-bidentate ligands is reported. We describe how a ligand containing hydroxyl groups as proton-responsive substituents enhances catalytic performance by an electronic effect of the oxyanions and a pendent-base effect through secondary coordination sphere interaction. In particular, [(Cp*IrCl)₂(TH2BPM)]Cl₂ (Cp* = pentamethyl cyclopentadienyl, TH2BPM = 4,4',6,6'-tetrahydroxy-2,2'-bipyrimidine) promotes enormously the catalytic hydrogenation of CO₂ bymore » these synergistic effects under atmospheric pressure and at room temperature. Additionally, newly designed complexes with azole-type ligands are applied to CO₂ hydrogenation. The catalytic efficiencies of the azole-type complexes are much higher than that of the unsubstituted bipyridine complex [Cp*Ir(bpy)(OH₂)]SO₄. Furthermore, the introduction of one or more hydroxyl groups into ligands such as 2-pyrazolyl-6-hydroxypyridine, 2-pyrazolyl-4,6-dihydroxyl pyrimidine, and 4-pyrazolyl-2,6-dihydroxyl pyrimidine enhanced catalytic activity. It is clear that the incorporation of electron-donating hydroxyl groups into proton-responsive ligands is effective for promoting the hydrogenation of CO₂.« less

  7. Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy).

    PubMed

    Alvarez, W; Asaro, F; Montanari, A

    1990-12-21

    The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.

  8. Increased oxidative stress in pemphigus vulgaris is related to disease activity and HLA-association.

    PubMed

    Shah, Amit Aakash; Dey-Rao, Rama; Seiffert-Sinha, Kristina; Sinha, Animesh A

    2016-06-01

    Pemphigus vulgaris (PV) is a rare blistering skin disorder characterized by the disadhesion of keratinocytes due to autoantibody attack against epidermal targets including desmoglein (Dsg) 3, Dsg 1 and possibly other adhesion and non-adhesion molecules. The mechanisms leading to immune-mediated pathology in PV are multifactorial and not fully understood. Recently, oxidative stress (antioxidant/oxidant disequilibrium) has been proposed as a contributory mechanism of autoimmune skin diseases, including PV. In this study, we directly assessed oxidative stress via measurement of total antioxidant capacity (TAC) using ELISA in 47 PV patients, 25 healthy controls and 18 bullous pemphigoid (BP) patients. We also performed microarray gene expression analysis on a separate set of 21 PV patients and 10 healthy controls to evaluate transcriptional dysregulation in oxidative stress-related pathways. Our data indicate that there is a significant reduction in TAC levels in PV patients compared with healthy controls, as well as BP patients. Furthermore, PV patients with active disease have significantly lower TAC levels than PV patients in remission. We also find that HLA allele status has a significant influence on oxidative stress. These findings are corroborated by microarray analysis showing differentially expressed genes involved in oxidative stress between the aforementioned groups. Collectively, our findings provide support for a role of oxidative stress in PV. Whether increased oxidative stress leads to disease manifestation and/or activity, or if disease activity leads to increased oxidative stress remains unknown. Future longitudinal studies may help to further elucidate the relationship between PV and oxidative stress.

  9. High Strain Rate Tensile Testing of DOP-26 Iridium

    SciTech Connect

    Schneibel, Joachim H; Carmichael Jr, Cecil Albert; George, Easo P

    2007-11-01

    The iridium alloy DOP-26 was developed through the Radioisotope Power Systems Program in the Office of Nuclear Energy of the Department of Energy. It is used for clad vent set cups containing radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for spacecraft. This report describes mechanical testing results for DOP-26. Specimens were given a vacuum recrystallization anneal of 1 hour at 1375 C and tested in tension in orientations parallel and perpendicular to the rolling direction of the sheet from which they were fabricated. The tests were performed at temperatures ranging from room temperature to 1090 C and strain rates ranging from 1 x 10{sup -3} to 50 s{sup -1}. Room temperature testing was performed in air, while testing at elevated temperatures was performed in a vacuum better than 1 x 10{sup -4} Torr. The yield stress (YS) and the ultimate tensile stress (UTS) decreased with increasing temperature and increased with increasing strain rate. Between 600 and 1090 C, the ductility showed a slight increase with increasing temperature. Within the scatter of the data, the ductility did not depend on the strain rate. The reduction in area (RA), on the other hand, decreased with increasing strain rate. The YS and UTS values did not differ significantly for the longitudinal and transverse specimens. The ductility and RA values of the transverse specimens were marginally lower than those of the longitudinal specimens.

  10. Phosphorescent sensor for phosphorylated peptides based on an iridium complex.

    PubMed

    Kang, Jung Hyun; Kim, Hee Jin; Kwon, Tae-Hyuk; Hong, Jong-In

    2014-07-03

    A bis[(4,6-difluorophenyl)pyridinato-N,C(2')]iridium(III) picolinate (FIrpic) derivative coupled with bis(Zn(2+)-dipicolylamine) (ZnDPA) was developed as a sensor (1) for phosphorylated peptides, which are related to many cellular mechanisms. As a control, a fluorescent sensor (2) based on anthracene coupled to ZnDPA was also prepared. When the total negative charge on the phosphorylated peptides was changed to -2, -4, and -6, the emission intensity of sensor 1 gradually increased by factors of up to 7, 11, and 16, respectively. In contrast, there was little change in the emission intensity of sensor 1 upon the addition of a neutral phosphorylated peptide, non-phosphorylated peptides, or various anions such as CO3(2-), NO3(-), SO4(2-), phosphate, azide, and pyrophosphate. Furthermore, sensor 1 could be used to visually discriminate between phosphorylated peptides and adenosine triphosphate in aqueous solution under a UV-vis lamp, unlike fluorescent sensor 2. This enhanced luminance of phosphorescent sensor 1 upon binding to a phosphorylated peptide is attributed to a reduction in the repulsion between the Zn(2+) ions due to the phenoxy anion, its strong metal-to-ligand charge transfer character, and a reduction in self-quenching.

  11. Iridium profiles and delivery across the Cretaceous/Paleogene boundary

    NASA Astrophysics Data System (ADS)

    Esmeray-Senlet, Selen; Miller, Kenneth G.; Sherrell, Robert M.; Senlet, Turgay; Vellekoop, Johan; Brinkhuis, Henk

    2017-01-01

    We examined iridium (Ir) anomalies at the Cretaceous/Paleogene (K/Pg) boundary in siliciclastic shallow marine cores of the New Jersey Coastal Plain, USA, that were deposited at an intermediate distance (∼2500 km) from the Chicxulub, Mexico crater. Although closely spaced and generally biostratigraphically complete, the cores show heterogeneity in terms of preservation of the ejecta layers, maximum concentration of Ir measured (∼0.1-2.4 ppb), and total thickness of the Ir-enriched interval (11-119 cm). We analyzed the shape of the Ir profiles with a Lagrangian particle-tracking model of sediment mixing. Fits between the mixing model and measured Ir profiles, as well as visible burrows in the cores, show that the shape of the Ir profiles was determined primarily by sediment mixing via bioturbation. In contrast, Tighe Park 1 and Bass River cores show post-depositional remobilization of Ir by geochemical processes. There is a strong inverse relationship between the maximum concentration of Ir measured and the thickness of the sediments over which Ir is spread. We show that the depth-integrated Ir inventory is similar in the majority of the cores, indicating that the total Ir delivery at time of the K/Pg event was spatially homogeneous over this region. Though delivered through a near-instantaneous source, stratospheric dispersal, and settling, our study shows that non-uniform Ir profiles develop due to changes in the regional delivery and post-depositional modification by bioturbation and geochemical processes.

  12. Earth's Radiation Imbalance from a Constellation of 66 Iridium Satellites

    NASA Astrophysics Data System (ADS)

    Chiu, J. C.; Wiscombe, W. J.

    2012-04-01

    The Earth Radiation Imbalance (ERI) at the top of the atmosphere is the primary driving force for climate change. If ERI is not zero, then Earth's temperature, both oceanic and atmospheric, will change gradually over time, tending toward a new steady state. The best estimates of current ERI from climate models range from 0.4 to 0.9 W/m2 (the imbalance being caused mainly by increasing CO2), but current satellite systems do not have the accuracy to measure ERI to even one significant digit. In this paper, we will describe a proposed constellation of 66 Earth radiation budget instruments, to be hosted on Iridium satellites. This system represents a quantum leap over current systems in several ways, in particular in providing ERI to at least one significant digit, thus enabling a crucial test of climate models. Because of its 24/7 coverage, the system will also provide ERI at three-hourly time scales without requiring extrapolations from narrowband geostationary instruments. This would allow studies of ERI's response to fast-evolving phenomena like dust storms and hurricanes. This offers a new, synoptic view of Earth radiation budget that will transform it from a monthly average into a dynamical variable alongside standard meteorological variables like temperature and pressure.

  13. Oxidative modification of caspase-9 facilitates its activation via disulfide-mediated interaction with Apaf-1.

    PubMed

    Zuo, Yong; Xiang, Binggang; Yang, Jie; Sun, Xuxu; Wang, Yumei; Cang, Hui; Yi, Jing

    2009-04-01

    Intracellular reactive oxygen species (ROS) are known to regulate apoptosis. Activation of caspase-9, the initial caspase in the mitochondrial apoptotic cascade, is closely associated with ROS, but it is unclear whether ROS regulate caspase-9 via direct oxidative modification. The present study aims to elucidate the molecular mechanisms by which ROS mediate caspase-9 activation. Our results show that the cellular oxidative state facilitates caspase-9 activation. Hydrogen peroxide treatment causes the activation of caspase-9 and apoptosis, and promotes an interaction between caspase-9 and apoptotic protease-activating factor 1 (Apaf-1) via disulfide formation. In addition, in an in vitro mitochondria-free system, the thiol-oxidant diamide promotes auto-cleavage of caspase-9 and the caspase-9/Apaf-1 interaction by facilitating the formation of disulfide-linked complexes. Finally, a point mutation at C403 of caspase-9 impairs both H(2)O(2)-promoted caspase-9 activation and interaction with Apaf-1 through the abolition of disulfide formation. The association between cytochrome c and the C403S mutant is significantly weaker than that between cytochrome c and wild-type caspase-9, indicating that oxidative modification of caspase-9 contributes to apoptosome formation under oxidative stress. Taken together, oxidative modification of caspase-9 by ROS can mediate its interaction with Apaf-1, and can thus promote its auto-cleavage and activation. This mechanism may facilitate apoptosome formation and caspase-9 activation under oxidative stress.

  14. Activated carbon enhanced ozonation of oxalate attributed to HO oxidation in bulk solution and surface oxidation: effect of activated carbon dosage and pH.

    PubMed

    Xing, Linlin; Xie, Yongbing; Minakata, Daisuke; Cao, Hongbin; Xiao, Jiadong; Zhang, Yi; Crittenden, John C

    2014-10-01

    Ozonation of oxalate in aqueous phase was performed with a commercial activated carbon (AC) in this work. The effect of AC dosage and solution pH on the contribution of hydroxyl radicals (HO) in bulk solution and oxidation on the AC surface to the removal of oxalate was studied. We found that the removal of oxalate was reduced by tert-butyl alcohol (tBA) with low dosages of AC, while it was hardly affected by tBA when the AC dosage was greater than 0.3g/L. tBA also inhibited ozone decomposition when the AC dosage was no more than 0.05g/L, but it did not work when the AC dosage was no less than 0.1g/L. These observations indicate that HO in bulk solution and oxidation on the AC surface both contribute to the removal of oxalate. HO oxidation in bulk solution is significant when the dosage of AC is low, whereas surface oxidation is dominant when the dosage of AC is high. The oxalate removal decreased with increasing pH of the solution with an AC dosage of 0.5g/L. The degradation of oxalate occurs mainly through surface oxidation in acid and neutral solution, but through HO oxidation in basic bulk solution. A mechanism involving both HO oxidation in bulk solution and surface oxidation was proposed for AC enhanced ozonation of oxalate.

  15. Antibacterial Activity of Zinc Oxide-Coated Nanoporous Alumina

    DTIC Science & Technology

    2012-05-17

    2012 Available online 17 May 2012 Keywords: Aluminum oxide Zinc oxide Atomic layer deposition Nanoporous material Antibacterial material a b s t r...standard and mixed online with each sample through a tee. Isotopes (e.g., 66Zn and 115In) were evaluated in a peak hop- ping mode; a dwell time of...20 pore sizes nm and (n) 100 nm pore sizes that were examined against Staphylococcus epidermidis. several potential dermatologic applications for

  16. One-electron activation of water oxidation catalysis.

    PubMed

    Tamaki, Yusuke; Vannucci, Aaron K; Dares, Christopher J; Binstead, Robert A; Meyer, Thomas J

    2014-05-14

    Rapid water oxidation catalysis is observed following electrochemical oxidation of [Ru(II)(tpy)(bpz)(OH)](+) to [Ru(V)(tpy)(bpz)(O)](3+) in basic solutions with added buffers. Under these conditions, water oxidation is dominated by base-assisted Atom Proton Transfer (APT) and direct reaction with OH(-). More importantly, we report here that the Ru(IV)═O(2+) form of the catalyst, produced by 1e(-) oxidation of [Ru(II)(tpy)(bpz)(OH2)](2+) to Ru(III) followed by disproportionation to [Ru(IV)(tpy)(bpz)(O)](2+) and [Ru(II)(tpy)(bpz)(OH2)](2+), is also a competent water oxidation catalyst. The rate of water oxidation by [Ru(IV)(tpy)(bpz)(O)](2+) is greatly accelerated with added PO4(3-) with a turnover frequency of 5.4 s(-1) reached at pH 11.6 with 1 M PO4(3-) at an overpotential of only 180 mV.

  17. Mono- and dinuclear cationic iridium(III) complexes bearing a 2,5-dipyridylpyrazine (2,5-dpp) ligand.

    PubMed

    Donato, Loïc; McCusker, Catherine E; Castellano, Felix N; Zysman-Colman, Eli

    2013-08-05

    The synthesis, X-ray structures, photophysical, and electrochemical characterization of mono- (1) and dinuclear (2) cationic iridium(III) complexes bearing a 2,5-dipyridylpyrazine (2,5-dpp) ancillary ligand are reported. Upon the complexation of a first equivalent of iridium, the photoluminescence shifts markedly into the deep red (λem = 710 nm, ΦPL = 0.9%) compared to other cationic iridium complexes such as [Ir(ppy)2(bpy)]PF6. With the coordination of a second equivalent of iridium, room temperature luminescence is completely quenched. Both 1 and 2 are luminescent at low temperatures but with distinct excited state decay kinetics; the emission of 2 is significantly red-shifted compared to 1. Emission both at 298 and 77 K results from a mixed charge-transfer state. Density functional theory (DFT) calculations and electrochemical behavior point to an electronic communication between the two iridium complexes.

  18. In situ oxidation of carbon-encapsulated cobalt nanocapsules creates highly active cobalt oxide catalysts for hydrocarbon combustion

    NASA Astrophysics Data System (ADS)

    Wang, Han; Chen, Chunlin; Zhang, Yexin; Peng, Lixia; Ma, Song; Yang, Teng; Guo, Huaihong; Zhang, Zhidong; Su, Dang Sheng; Zhang, Jian

    2015-06-01

    Combustion catalysts have been extensively explored to reduce the emission of hydrocarbons that are capable of triggering photochemical smog and greenhouse effect. Palladium as the most active material is widely applied in exhaust catalytic converter and combustion units, but its high capital cost stimulates the tremendous research on non-noble metal candidates. Here we fabricate highly defective cobalt oxide nanocrystals via a controllable oxidation of carbon-encapsulated cobalt nanoparticles. Strain gradients induced in the nanoconfined carbon shell result in the formation of a large number of active sites featuring a considerable catalytic activity for the combustion of a variety of hydrocarbons (methane, propane and substituted benzenes). For methane combustion, the catalyst displays a unique activity being comparable or even superior to the palladium ones.

  19. Theranostic iridium(III) complexes as one- and two-photon phosphorescent trackers to monitor autophagic lysosomes.

    PubMed

    He, Liang; Tan, Cai-Ping; Ye, Rui-Rong; Zhao, Yi-Zhi; Liu, Ya-Hong; Zhao, Qiang; Ji, Liang-Nian; Mao, Zong-Wan

    2014-11-03

    During autophagy, the intracellular components are captured in autophagosomes and delivered to lysosomes for degradation and recycling. Changes in lysosomal trafficking and contents are key events in the regulation of autophagy, which has been implicated in many physiological and pathological processes. In this work, two iridium(III) complexes (LysoIr1 and LysoIr2) are developed as theranostic agents to monitor autophagic lysosomes. These complexes display lysosome-activated phosphorescence and can specifically label lysosomes with high photostability. Simultaneously, they can induce autophagy potently without initiating an apoptosis response. We demonstrate that LysoIr2 can effectively implement two functions, namely autophagy induction and lysosomal tracking, in the visualization of autophagosomal-lysosomal fusion. More importantly, they display strong two-photon excited fluorescence (TPEF), which is favorable for live cell imaging and in vivo applications.

  20. Reversible α-Hydrogen and α-Alkyl Elimination in PC(sp(3))P Pincer Complexes of Iridium.

    PubMed

    Jonasson, Klara J; Polukeev, Alexey V; Marcos, Rocío; Ahlquist, Mårten S G; Wendt, Ola F

    2015-08-03

    Despite significant progress in recent years, the cleavage of unstrained C(sp(3))-C(sp(3)) bonds remains challenging. A C-C coupling and cleavage reaction in a PC(sp(3))P iridium pincer complex is mechanistically studied; the reaction proceeds via the formation of a carbene intermediate and can be described as a competition between α-hydrogen and α-alkyl elimination; the latter process was observed experimentally and is an unusual way of C(sp(3))-C(sp(3)) bond scission, which has previously not been studied in detail. Mechanistic details that are based upon kinetic studies, activation parameters, and DFT calculations are also discussed. A full characterization of a C-C agostic intermediate is presented.

  1. Novel insights into enhanced dewaterability of waste activated sludge by Fe(II)-activated persulfate oxidation.

    PubMed

    Zhen, Guangyin; Lu, Xueqin; Li, Yuyou; Zhao, Youcai; Wang, Baoying; Song, Yu; Chai, Xiaoli; Niu, Dongjie; Cao, Xianyan

    2012-09-01

    The potential of Fe(II)-activated persulfate (S(2)O(8)(2-)) oxidation on enhancing the dewaterability of sludge flocs from 3-full scale wastewater treatment plants (WWTPs) were investigated. Normalized capillary suction time (CST) was applied to evaluate sludge dewaterability. Both extracellular polymeric substances (EPS) and metabolic activity of microorganisms were determined to explore the responsible mechanism. Fe(II)-S(2)O(8)(2-) oxidation effectively improved sludge dewaterability. The most important mechanisms were proposed to be the degradation of EPS incorporated in sludge flocs and rupture of microbial cells. Three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy confirmed that the powerful SO(4)(-) from Fe(II)-S(2)O(8)(2-) system destroyed the particular functional groups of fluorescing substances (i.e., aromatic protein-, tryptophan protein-, humic- and fulvic-like substances) in EPS and caused cleavage of linkages in the polymeric backbone and simultaneous destruction of microbial cells, resulting in the release of EPS-bound water, intracellular materials and water of hydration inside cells, and subsequent enhancement of dewaterability.

  2. Activation energy of thermal desorption of silicon oxide layers on silicon substrates

    NASA Astrophysics Data System (ADS)

    Enta, Yoshiharu; Osanai, Shodai; Ogasawara, Takahito

    2017-02-01

    Thermal desorption rates of silicon oxide layers, from 20 to 120 nm in thickness, on silicon substrates in vacuum have been accurately obtained from intervals between ring structures formed inside voids on the oxide layers. From the temperature dependence of the desorption rate, the activation energy and frequency factor of the desorption reaction have been derived as a function of the oxide thickness. The obtained values are compared with the previous studies, and as a result, the activation energy is found to be almost constant ( 4 eV) in a wide range of the oxide thickness. The frequency factor decreases as the inverse square of the oxide thickness. The decomposition kinetics of the oxide layer is also discussed from the obtained results.

  3. Reforming catalyst of separate platinum-containing and iridium-containing particles

    SciTech Connect

    Schoennagel, H.J.

    1981-04-21

    Catalyst compositions are provided comprising a refractory support, about 0.1 to about 2 percent by weight of platinum, about 0.1 to about 2 percent by weight of iridium and about 0.1 to about 5 weight percent of halogen where the platinum and iridium are contained on separate particles of said support. The relative weight ratio of the particles containing platinum and those containing iridium is between about 10:1 to about 1:10. The compositions are useful as hydrocarbon conversion catalysts and are especially applicable for use in catalyzing the reforming of naphtha petroleum fractions. There is also disclosed a reforming process conducted in the presence of hydrogen, under reforming conditions, in the presence of the above catalyst.

  4. Preparation of iridium targets by electrodeposition for neutron capture cross section measurements

    DOE PAGES

    Bond, Evelyn M.; Moody, W. Allen; Arnold, Charles; ...

    2016-03-01

    Here, the preparation of 191Ir and 193Ir electrodeposits for neutron capture cross-section measurements at the detector for advanced neutron capture experiments located at the at Los Alamos Neutron Science Center is described. The electrodeposition of iridium in the desired thickness of 0.4–1 mg/cm2 is challenging. Better yields and thicknesses were obtained using electrodeposition from isopropyl alcohol solutions than from ammonium sulfate solutions. 191Ir and 193Ir targets were initially prepared using the standard single-sided electrodeposition cell. Iridium electrodepositions using a double-sided electrodeposition cell were developed and were optimized, resulting in thick, uniform iridium deposits. LA UR 15-22475.

  5. Preparation of iridium targets by electrodeposition for neutron capture cross section measurements

    SciTech Connect

    Bond, Evelyn M.; Moody, W. Allen; Arnold, Charles; Bredeweg, Todd A.; Jandel, Marian; Rusev, Gencho Y.

    2016-03-01

    Here, the preparation of 191Ir and 193Ir electrodeposits for neutron capture cross-section measurements at the detector for advanced neutron capture experiments located at the at Los Alamos Neutron Science Center is described. The electrodeposition of iridium in the desired thickness of 0.4–1 mg/cm2 is challenging. Better yields and thicknesses were obtained using electrodeposition from isopropyl alcohol solutions than from ammonium sulfate solutions. 191Ir and 193Ir targets were initially prepared using the standard single-sided electrodeposition cell. Iridium electrodepositions using a double-sided electrodeposition cell were developed and were optimized, resulting in thick, uniform iridium deposits. LA UR 15-22475.

  6. Ammonia stimulates growth and nitrite-oxidizing activity of Nitrobacter winogradskyi

    PubMed Central

    Ma, Shouguang; Zhang, Demin; Zhang, Wenjun; Wang, Yinong

    2014-01-01

    The aim of this study was to obtain a nitrite-oxidizing bacterium with high nitrite oxidation activity for controlling nitrite levels. A nitrite-oxidizing bacterium, ZS-1, was isolated from the water of a coastal Pseudosciaena crocea-rearing pond. The strain was identified as Nitrobacter winogradskyi based on the phylogenetic analyses of the 16S ribosomal ribonucleic acid gene and nxrA sequence of ZS-1. Under aerobic condition, the nitrite-oxidizing activity of ZS-1 did not change considerably in the range of pH 7–9, but was strongly inhibited by lower (pH = 6) and higher (pH = 10) pH values. The optimum temperature range is 25–32 °C. Lower temperature made the adaptive phase of ZS-1 longer but did not affect its maximum nitrite oxidization rate. The nitrite-oxidizing activity of ZS-1 started to be inhibited by ammonia and nitrate when the concentrations of ammonia and nitrate reached 25 mg L−1 and 100 mg L−1, respectively. The inhibition was stronger with higher concentration of ammonia or nitrate. The nitrite-oxidizing activity of ZS-1, however, was not inhibited by high concentration of nitrite (500 mg L−1). The nitrite-oxidizing activity of ZS-1 was increased by low ammonia concentration (1 mg L−1 to 10 mg L−1). PMID:26019486

  7. Moderate endurance exercise in patients with sickle cell anaemia: effects on oxidative stress and endothelial activation.

    PubMed

    Faes, Camille; Balayssac-Siransy, Edwige; Connes, Philippe; Hivert, Ludovic; Danho, Clotaire; Bogui, Pascal; Martin, Cyril; Pialoux, Vincent

    2014-01-01

    Very few studies have investigated the effects of exercise on the biological parameters involved in vaso-occlusive events in sickle cell anaemia (SCA). The aim of this study was to test how a mild-moderate endurance exercise modulates oxidative stress, nitric oxide bioavailability and endothelial activation in SCA patients and healthy individuals. Eleven patients with SCA and 15 healthy subjects completed a 20-min duration submaximal cycling exercise at ≈45 Watts. Plasma markers of oxidative stress, antioxidant activity, endothelial activation and nitric oxide bioavailability were investigated before and after the exercise. Nitric oxide levels, anti-oxidant capacity, soluble (s)E-selectin and sP-selectin did not change in response to this exercise. Except for the malondialdehyde levels, which increased in the two groups, the other markers of oxidative stress remained unchanged in both groups in response to exercise. Soluble vascular cell adhesion molecule 1 levels were increased at the end of exercise in both groups. sL-selectin decreased and soluble intercellular adhesion molecule 1 increased with exercise in SCA patients only. The present data suggest that patients with SCA may undertake mild-moderate physical activities without any acute clinical complications, but care should be taken because oxidative stress and endothelial activation significantly increased in some patients.

  8. Inhibition, Inactivation, and Recovery of Ammonia-Oxidizing Activity in Cometabolism of Trichloroethylene by Nitrosomonas europaea

    PubMed Central

    Hyman, M. R.; Russell, S. A.; Ely, R. L.; Williamson, K. J.; Arp, D. J.

    1995-01-01

    The kinetics of the cometabolism of trichloroethylene (TCE) by the ammonia-oxidizing soil bacterium Nitrosomonas europaea in short-term (<10-min) incubations were investigated. Three individual effects of TCE cometabolism on this bacterium were characterized. First, we observed that TCE is a potent competitive inhibitor of ammonia oxidation by N. europaea. The K(infi) value for TCE (30 (mu)M) is similar to the K(infm) for ammonia (40 (mu)M). Second, we examined the toxicity associated with TCE cometabolism by N. europaea. Stationary-phase cells of N. europaea oxidized approximately 60 nmol of TCE per mg of protein before ammonia-oxidizing activity was completely inactivated by reactive intermediates generated during TCE oxidation. At the TCE concentrations used in these experiments, ammonia did not provide significant protection against inactivation. Third, we have determined the ability of cells to recover ammonia-oxidizing activity after exposure to TCE. Cells recovering from TCE inactivation were compared with cells recovering from the specific inactivation of ammonia-oxidizing activity by light. The recovery kinetics were indistinguishable when 40% or less of the activity was inactivated. However, at increased levels of inactivation, TCE-inactivated cells did not recover as rapidly as light-inactivated cells. The kinetics of recovery appear to be dependent on both the extent of inactivation of ammonia-oxidizing activity and the degree of specificity of the inactivating treatment. PMID:16534997

  9. Removal of arsenic(V) from aqueous solutions using iron-oxide-coated modified activated carbon.

    PubMed

    Zhang, Q L; Gao, Nai-Yun; Lin, Y C; Xu, Bin; Le, Lin-sheng

    2007-08-01

    Removal of arsenic(V) from aqueous solutions was evaluated with the following three different sorption materials: coal-based activated carbon 12 x 40 (activated carbon), iron(II) oxide (FeO)/activated carbon-H, and iron oxide. The apparent characteristics and physical chemistry performances of these adsorbents were investigated by X-ray diffraction, nitrogen adsorption, and scanning electronic microscope. Also, batch experiments for arsenic removal were performed, and the effects of pH value on arsenic(V) removal were studied. The results suggest that the main phases of the iron oxide surface are magnetite, maghemite, hematite, and goethite; fine and uniform iron oxide particles can cover activated carbon surfaces and affect the surface area or pore structures of activated carbon; adsorption kinetics obey a pseudo-first-order rate equation; and adsorption capacities of adsorbents are affected by the values of pH. The optimum value of pH for iron oxide lies in a narrow range between 4.0 and 5.5, and arsenic(V) removal by FeO/activated carbon-H is ideal and stable in the pH range 3 to 7, while activated carbon has the lowest adsorption capacity in the entire pH range. Also, the adsorption characteristics of FeO/activated carbon-H composites and virgin activated carbon match well the Langmuir adsorption model, while those of iron oxide fit well the Freundlich adsorption model.

  10. Iridium-catalyzed C-H borylation of heteroarenes: scope, regioselectivity, application to late-stage functionalization, and mechanism.

    PubMed

    Larsen, Matthew A; Hartwig, John F

    2014-03-19

    A study on the iridium-catalyzed C-H borylation of heteroarenes is reported. Several heteroarenes containing multiple heteroatoms were found to be amenable to C-H borylation catalyzed by the combination of an iridium(I) precursor and tetramethylphenanthroline. The investigations of the scope of the reaction led to the development of powerful rules for predicting the regioselectivity of borylation, foremost of which is that borylation occurs distal to nitrogen atoms. One-pot functionalizations are reported of the heteroaryl boronate esters formed in situ, demonstrating the usefulness of the reported methodology for the synthesis of complex heteroaryl structures. Application of this methodology to the synthesis and late-stage functionalization of biologically active compounds is also demonstrated. Mechanistic studies show that basic heteroarenes can bind to the catalyst and alter the resting state from the olefin-bound complex observed during arene borylation to a species containing a bound heteroarene, leading to catalyst deactivation. Studies on the origins of the observed regioselectivity show that borylation occurs distal to N-H bonds due to rapid N-H borylation, creating an unfavorable steric environment for borylation adjacent to these bonds. Computational studies and mechanistic studies show that the lack of observable borylation of C-H bonds adjacent to basic nitrogen is not the result of coordination to a bulky Lewis acid prior to C-H activation, but the combination of a higher-energy pathway for the borylation of these bonds relative to other C-H bonds and the instability of the products formed from borylation adjacent to basic nitrogen.

  11. A magnetism-based approach to examining spin-orbit coupling effects in solid systems of isolated iridium octahedra

    NASA Astrophysics Data System (ADS)

    Phelan, Brendan F.

    This thesis explores the relative strengths of Spin-Orbit Coupling (SOC) in several perovskite-like systems that feature uninterrupted arrays of isolated IrO6 octahedra. Iridate compounds are particularly interesting to the community due to their relevance to emergent material properties such as insulating antiferromagnets, superconductors, and topological insulators. Recently literature has pointed to a complex interaction between SOC and crystal field splitting (CFS) in d5 metals. I utilize a straightforward, magnetic approach to determine the relative strengths of SOC vs CFS by chemically modifying structure and oxidation state. This contrasts with other work where advanced spectroscopic measurements are utilized to probe energy levels within a single compound. The focus of this study lies in two main methodologies: 1) Tracking the evolution of the Ir magnetic moment on progressing from 5 d5 Ir4+ to 5d 4 Ir5+ oxidation states that are clearly best described by a transition from a J=1/2 to a J=0 Ir magnetic state. In these cases, the evolution of the magnetic susceptibility shows the dominance of spin-orbit coupling in determining the magnetic properties of a material with highly isolated IrO6 octahedra. 2) Distorting J=0 Ir5+ systems where there is no emergence of an enhanced magnetic moment in the series on increasing the structural distortions, as would have been the case for significant crystal field splitting that reinforces the notion that spin-orbit coupling is the dominant force in determining the magnetism of iridium-oxygen octahedra in perovskite-like structures. The organization of this thesis is as follows: Chapter 1 presents a brief introduction to solid-state chemistry, iridates, and magnetism. Chapter 2 is an overview of experimental methodology and instrumentation. Chapter 3, presents a study of tuning the oxidation state of a new structure type: SrxLa11-xIr4O24. Chapter 4 presents a structural tuning of the Ir5+ system: Ba 2-xSrxYIrO6. Finally

  12. Oxidation-promoted activation of a ferrocene C-H bond by a rhodium complex.

    PubMed

    Labande, Agnès; Debono, Nathalie; Sournia-Saquet, Alix; Daran, Jean-Claude; Poli, Rinaldo

    2013-05-14

    The oxidation of a rhodium(I) complex containing a ferrocene-based heterodifunctional phosphine N-heterocyclic carbene (NHC) ligand produces a stable, planar chiral rhodium(III) complex with an unexpected C-H activation on ferrocene. The oxidation of rhodium(I) to rhodium(III) may be accomplished by initial oxidation of ferrocene to ferrocenium and subsequent electron transfer from rhodium to ferrocenium. Preliminary catalytic tests showed that the rhodium(III) complex is active for the Grignard-type arylation of 4-nitrobenzaldehyde via C-H activation of 2-phenylpyridine.

  13. LPS-Induced Macrophage Activation and Plasma Membrane Fluidity Changes are Inhibited Under Oxidative Stress.

    PubMed

    de la Haba, Carlos; Morros, Antoni; Martínez, Paz; Palacio, José R

    2016-12-01

    Macrophage activation is essential for a correct and efficient response of innate immunity. During oxidative stress membrane receptors and/or membrane lipid dynamics can be altered, leading to dysfunctional cell responses. Our aim is to analyze membrane fluidity modifications and cell function under oxidative stress in LPS-activated macrophages. Membrane fluidity of individual living THP-1 macrophages was evaluated by the technique two-photon microscopy. LPS-activated macrophage function was determined by TNFα secretion. It was shown that LPS activation causes fluidification of macrophage plasma membrane and production of TNFα. However, oxidative stress induces rigidification of macrophage plasma membrane and inhibition of cell activation, which is evidenced by a decrease of TNFα secretion. Thus, under oxidative conditions macrophage proinflammatory response might develop in an inefficient manner.

  14. Thermocouples of molybdenum and iridium alloys for more stable vacuum-high temperature performance

    NASA Technical Reports Server (NTRS)

    Morris, J. F. (Inventor)

    1978-01-01

    Thermocouples providing stability and performance reliability in systems involving high temperatures and vacuums by employing a bimetallic thermocouple sensor are described. Each metal of the sensor is selected from a group of metals comprising molybdenum and iridium and alloys containing only those two metals. The molybdenum, iridium thermocouple sensor alloys provide bare metal thermocouple sensors having advantageous vapor pressure compatibility and performance characteristics. The compatibility and physical characteristics of the thermocouple sensor alloys result in improved emf, temperature properties and thermocouple hot junction performance.

  15. New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical Properties.

    PubMed

    Niu, Zhi-Gang; Xie, Hui; He, Li-Rong; Li, Kai-Xiu; Xia, Qing; Wu, Dong-Min; Li, Gao-Nan

    2016-01-01

    A new iridium(III) complex based on the triazole-pyridine ligand with tetrathiafulvalene unit, [Ir(ppy)2(L)]PF6 (1), has been synthesized and structurally characterized. The absorption spectra, luminescent spectra and electrochemical behaviors of L and 1 have been investigated. Complex 1 is found to be emissive at room temperature with maxima at 481 and 510 nm. The broad and structured emission bands are suggested a mixing of 3LC (3π-π*) and 3CT (3MLCT) excited states. The influence of iridium ion coordination on the redox properties of the TTF has also been investigated by cyclic voltammetry.

  16. High-strain-rate, high-temperature biaxial testing of DOP-26 iridium

    SciTech Connect

    George, T.G.

    1988-05-01

    High-strain-rate biaxial punch tests were performed on DOP-26 (Ir-0.3 wt.% tungsten) iridium-alloy disc given annealing and aging heat treatments. Test temperatures ranged between 600 and 1440/degree/C, and punch velocity was held constant at 45 m/s. Three types of samples were evaluated: Z-batch old-process discs, B-batch old-process discs, and B-batch new-process discs. The results indicate that batch-to-batch variations in ductility are significant and that new-process iridium is slightly more ductile than old-process material. 12 refs., 43 figs., 26 tabs.

  17. Activated Metal Oxide Surfaces as Highly Reactive Environments

    DTIC Science & Technology

    1990-08-03

    underway. " Synthesis of Ultra-High Surface Area Fe203 by Precipitation Methods Yong-Xi Li A series of precipitations of Fe(OH) 3 (from FeCl 3) at...Progress was also made on developing new aerogel procedures for synthesis of ultra-high surface area magnesium oxide. Finally,’ome metal oxide molecules...were studied in chemical reactions and by theoretical methods .-) Three students earned Ph.D. degrees and one an M.S. degree. A visiting professor and

  18. Role of Nanostructured Dual-Oxide Supports in Enhanced Catalytic Activity: Theory of CO Oxidation Over Au/IrO2/TiO2

    NASA Astrophysics Data System (ADS)

    Liu, Zhi-Pan; Jenkins, Stephen J.; King, David A.

    2004-10-01

    The synergetic effect in multicomponent catalysts is a topic of profound industrial importance and intense academic interest. On a newly identified multicomponent catalyst, Au/IrO2/TiO2, first-principles density-functional theory is analyzed to clarify the outstanding catalytic activity of the system for oxidative reactions at high temperatures. By comparing CO oxidation on interfaces and single-component surfaces, it is revealed that a high dispersion of a more active oxide (IrO2), on a more inert oxide (TiO2) is the key. It preserves the sintering resistance of Au supported on less active oxides, while at the same time promoting oxidative reactions that occur at the Au/active-oxide interface.

  19. Dietary moderately oxidized oil activates the Nrf2 signaling pathway in the liver of pigs

    PubMed Central

    2012-01-01

    Background Previous studies have shown that administration of oxidized oils increases gene expression and activities of various enzymes involved in xenobiotic metabolism and stress response in the liver of rats and guinea pigs. As these genes are controlled by nuclear factor erythroid-derived 2-like 2 (Nrf2), we investigated the hypothesis that feeding of oxidized fats causes an activation of that transcription factor in the liver which in turn activates the expression of antioxidant, cytoprotective and detoxifying genes. Methods Twenty four crossbred pigs were allocated to two groups of 12 pigs each and fed nutritionally adequate diets with either fresh rapeseed oil (fresh fat group) or oxidized rapeseed oil prepared by heating at a temperature of 175°C for 72 h (oxidized fat group). Results After 29 days of feeding, pigs of the oxidized fat group had a markedly increased nuclear concentration of the transcription factor Nrf2 and a higher activity of cellular superoxide dismutase and T4-UDP glucuronosyltransferase in liver than the fresh fat group (P < 0.05). In addition, transcript levels of antioxidant and phase II genes in liver, like superoxide dismutase 1, heme oxygenase 1, glutathione peroxidase 1, thioredoxin reductase 1, microsomal glutathione-S-transferase 1, UDP glucuronosyltransferase 1A1 and NAD(P)H:quinone oxidoreductase 1 in the liver were higher in the oxidized fat group than in the fresh fat group (P < 0.05). Moreover, pigs of the oxidized fat group had an increased hepatic nuclear concentration of the transcription factor NF-κB which is also an important transcription factor mediating cellular stress response. Conclusion The present study shows for the first time that administration of an oxidized fat activates the Nrf2 in the liver of pigs which likely reflects an adaptive mechanism to prevent cellular oxidative damage. Activation of the NF-κB pathway might also contribute to this effect of oxidized fat. PMID:22364167

  20. Salidroside Suppresses HUVECs Cell Injury Induced by Oxidative Stress through Activating the Nrf2 Signaling Pathway.

    PubMed

    Zhu, Yao; Zhang, Ya-Jie; Liu, Wei-Wei; Shi, Ai-Wu; Gu, Ning

    2016-08-09

    Oxidative stress plays an important role in the pathogenesis of cardiovascular diseases. Salidroside (SAL), one of the main effective constituents of Rhodiola rosea, has been reported to suppress oxidative stress-induced cardiomyocyte injury and necrosis by promoting transcription of nuclear factor E2-related factor 2 (Nrf2)-regulated genes such as heme oxygenase-1 (HO-1) and NAD(P)H dehydrogenase (quinone1) (NQO1). However, it has not been indicated whether SAL might ameliorate endothelial injury induced by oxidative stress. Here, our study demonstrated that SAL might suppress HUVEC cell injury induced by oxidative stress through activating the Nrf2 signaling pathway. The results of our study indicated that SAL decreased the levels of intercellular reactive oxygen species (ROS) and malondialdehyde (MDA), and improved the activities of superoxide dismutase (SOD) and catalase (CAT), resulting in protective effects against oxidative stress-induced cell damage in HUVECs. It suppressed oxidative stress damage by inducing Nrf2 nuclear translocation and activating the expression of Nrf2-regulated antioxidant enzyme genes such as HO-1 and NQO1 in HUVECs. Knockdown of Nrf2 with siRNA abolished the cytoprotective effects against oxidative stress, decreased the expression of Nrf2, HO-1, and NQO1, and inhibited the nucleus translocation of Nrf2 in HUVECs. This study is the first to demonstrate that SAL suppresses HUVECs cell injury induced by oxidative stress through activating the Nrf2 signaling pathway.

  1. Intrinsic relation between catalytic activity of CO oxidation on Ru nanoparticles and Ru oxides uncovered with ambient pressure XPS.

    PubMed

    Qadir, Kamran; Joo, Sang Hoon; Mun, Bongjin S; Butcher, Derek R; Renzas, J Russell; Aksoy, Funda; Liu, Zhi; Somorjai, Gabor A; Park, Jeong Young

    2012-11-14

    Recent progress in colloidal synthesis of nanoparticles with well-controlled size, shape, and composition, together with development of in situ surface science characterization tools, such as ambient pressure X-ray photoelectron spectroscopy (APXPS), has generated new opportunities to unravel the surface structure of working catalysts. We report an APXPS study of Ru nanoparticles to investigate catalytically active species on Ru nanoparticles under oxidizing, reducing, and CO oxidation reaction conditions. The 2.8 and 6 nm Ru nanoparticle model catalysts were synthesized in the presence of poly(vinyl pyrrolidone) polymer capping agent and deposited onto a flat Si support as two-dimensional arrays using the Langmuir-Blodgett deposition technique. Mild oxidative and reductive characteristics indicate the formation of surface oxide on the Ru nanoparticles, the thickness of which is found to be dependent on nanoparticle size. The larger 6 nm Ru nanoparticles were oxidized to a smaller extent than the smaller Ru 2.8 nm nanoparticles within the temperature range of 50-200 °C under reaction conditions, which appears to be correlated with the higher catalytic activity of the bigger nanoparticles. We found that the smaller Ru nanoparticles form bulk RuO(2) on their surfaces, causing the lower catalytic activity. As the size of the nanoparticle increases, the core-shell type RuO(2) becomes stable. Such in situ observations of Ru nanoparticles are useful in identifying the active state of the catalysts during use and, hence, may allow for rational catalyst designs for practical applications.

  2. Aldosterone Increases Oxidant Stress to Impair Guanylyl Cyclase Activity by Cysteinyl Thiol Oxidation in Vascular Smooth Muscle Cells*S⃞

    PubMed Central

    Maron, Bradley A.; Zhang, Ying-Yi; Handy, Diane E.; Beuve, Annie; Tang, Shiow-Shih; Loscalzo, Joseph; Leopold, Jane A.

    2009-01-01

    Hyperaldosteronism is associated with impaired endothelium-dependent vascular reactivity owing to increased reactive oxygen species and decreased bioavailable nitric oxide (NO·); however, the effects of aldosterone on vasodilatory signaling pathways in vascular smooth muscle cells (VSMC) remain unknown. Soluble guanylyl cyclase (GC) is a heterodimer that is activated by NO· to convert cytosolic GTP to cGMP, a second messenger required for normal VSMC relaxation. Here, we show that aldosterone (10-9-10-7 mol/liter) diminishes GC activity by activating NADPH oxidase in bovine aortic VSMC to increase reactive oxygen species levels and induce oxidative posttranslational modification(s) of Cys-122, a β1-subunit cysteinyl residue demonstrated previously to modulate NO· sensing by GC. In VSMC treated with aldosterone, Western immunoblotting detected evidence of GC β1-subunit disulfide bonding, whereas mass spectrometry analysis of a homologous peptide containing the Cys-122-bearing sequence exposed to conditions of increased oxidant stress confirmed cysteinyl sulfinic acid (m/z 435), sulfonic acid (m/z 443), and disulfide (m/z 836) bond formation. The functional effect of these modifications was examined by transfecting COS-7 cells with wild-type GC or mutant GC containing an alanine substitution at Cys-122 (C122A). Exposure to aldosterone or hydrogen peroxide (H2O2) significantly decreased cGMP levels in cells expressing wild-type GC. In contrast, aldosterone or H2O2 did not influence cGMP levels in cells expressing the mutant C122A GC, confirming that oxidative modification of Cys-122 specifically impairs GC activity. These findings demonstrate that pathophysiologically relevant concentrations of aldosterone increase oxidant stress to convert GC to an NO·-insensitive state, resulting in disruption of normal vasodilatory signaling pathways in VSMC. PMID:19141618

  3. Luminescent Rhenium(I) and Iridium(III) Polypyridine Complexes as Biological Probes, Imaging Reagents, and Photocytotoxic Agents.

    PubMed

    Lo, Kenneth Kam-Wing

    2015-12-15

    in the cytotoxic activity, cellular uptake, and bioimaging applications of these complexes. Additionally, we and other research groups have demonstrated that many transition metal complexes have facile cellular uptake and organelle-localization properties and that their cytotoxic activity can be readily controlled. For example, complexes that can target the nucleus, nucleolus, mitochondria, lysosomes, endoplasmic reticulum, and Golgi apparatus have been identified. We anticipate that this selective localization property can be utilized in the development of intracellular sensors and bioimaging reagents. Thus, we have functionalized luminescent rhenium(I) and iridium(III) polypyridine complexes with various pendants, including molecule-binding moieties, sugar molecules, bioorthogonal functional groups, and polymeric chains such as poly(ethylene glycol) and polyethylenimine, and examined their potentials as biological reagents. This Account describes our design of luminescent rhenium(I) and iridium(III) polypyridine complexes and explains how they can serve as a new generation of biological reagents for diagnostic and therapeutic applications.

  4. Catalytic wet oxidation of ammonia solution: activity of the nanoscale platinum-palladium-rhodium composite oxide catalyst.

    PubMed

    Hung, Chang-Mao

    2009-04-15

    Aqueous solutions of 400-1000 mg/L of ammonia were oxidized in a trickle-bed reactor (TBR) in this study of nanoscale platinum-palladium-rhodium composite oxide catalysts, which were prepared by the co-precipitation of H(2)PtCl(6), Pd(NO(3))(3) and Rh(NO(3))(3). Hardly any of the dissolved ammonia was removed by wet oxidation in the absence of any catalyst, whereas about 99% of the ammonia was reduced during wet oxidation over nanoscale platinum-palladium-rhodium composite oxide catalysts at 503 K in an oxygen partial pressure of 2.0 MPa. A synergistic effect exists in the nanoscale platinum-palladium-rhodium composite structure, which is the material with the highest ammonia reduction activity. The nanometer-sized particles were characterized by TEM, XRD and FTIR. The effect of the initial concentration and reaction temperature on the removal of ammonia from the effluent streams was also studied at a liquid hourly space velocity of under 9 h(-1) in the wet catalytic processes.

  5. Shape-dependent bactericidal activity of copper oxide nanoparticle mediated by DNA and membrane damage

    SciTech Connect

    Laha, Dipranjan; Pramanik, Arindam; Laskar, Aparna; Jana, Madhurya; Pramanik, Panchanan; Karmakar, Parimal

    2014-11-15

    Highlights: • Spherical and sheet shaped copper oxide nanoparticles were synthesized. • Physical characterizations of these nanoparticles were done by TEM, DLS, XRD, FTIR. • They showed shape dependent antibacterial activity on different bacterial strain. • They induced both membrane damage and ROS mediated DNA damage in bacteria. - Abstract: In this work, we synthesized spherical and sheet shaped copper oxide nanoparticles and their physical characterizations were done by the X-ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. The antibacterial activity of these nanoparticles was determined on both gram positive and gram negative bacterial. Spherical shaped copper oxide nanoparticles showed more antibacterial property on gram positive bacteria where as sheet shaped copper oxide nanoparticles are more active on gram negative bacteria. We also demonstrated that copper oxide nanoparticles produced reactive oxygen species in both gram negative and gram positive bacteria. Furthermore, they induced membrane damage as determined by atomic force microscopy and scanning electron microscopy. Thus production of and membrane damage are major mechanisms of the bactericidal activity of these copper oxide nanoparticles. Finally it was concluded that antibacterial activity of nanoparticles depend on physicochemical properties of copper oxide nanoparticles and bacterial strain.

  6. High reactivity of nanosized niobium oxide cluster cations in methane activation: A comparison with vanadium oxides

    SciTech Connect

    Ding, Xun-Lei E-mail: chemzyx@iccas.ac.cn; Wang, Dan; Wu, Xiao-Nan; Li, Zi-Yu; Zhao, Yan-Xia E-mail: chemzyx@iccas.ac.cn; He, Sheng-Gui

    2015-09-28

    The reactions between methane and niobium oxide cluster cations were studied and compared to those employing vanadium oxides. Hydrogen atom abstraction (HAA) reactions were identified over stoichiometric (Nb{sub 2}O{sub 5}){sub N}{sup +} clusters for N as large as 14 with a time-of-flight mass spectrometer. The reactivity of (Nb{sub 2}O{sub 5}){sub N}{sup +} clusters decreases as the N increases, and it is higher than that of (V {sub 2}O{sub 5}){sub N}{sup +} for N ≥ 4. Theoretical studies were conducted on (Nb{sub 2}O{sub 5}){sub N}{sup +} (N = 2–6) by density functional calculations. HAA reactions on these clusters are all favorable thermodynamically and kinetically. The difference of the reactivity with respect to the cluster size and metal type (Nb vs V) was attributed to thermodynamics, kinetics, the electron capture ability, and the distribution of the unpaired spin density. Nanosized Nb oxide clusters show higher HAA reactivity than V oxides, indicating that niobia may serve as promising catalysts for practical methane conversion.

  7. Possible world-wide middle miocene iridium anomaly and its relationship to periodicity of impacts and extinctions

    NASA Technical Reports Server (NTRS)

    Asaro, F.; Alvarez, W.; Michel, H. V.; Alvarez, L. W.; Anders, Mark H.; Montanari, A.; Kennett, James P.

    1988-01-01

    In a study of one million years of Middle Miocene sediment deposition in ODP Hole 689B in the Weddell Sea near Antarctica, a single iridium (Ir) anomaly of 44 (+ or - 10) x 10 to the 12th gram Ir per gram rock (ppt) was observed in core 6H, section 3, 50 to 60 cm, after background contributions associated with manganese precipitates and clay are subtracted. The ODP Hole 689B is 10,000 km away from another site, DSDP Hole 588B in the Tasman Sea north of New Zealand, where a single Ir anomaly of 144 + or - 7 ppt over a background of 11 ppt was found in an earlier study of 3 million years of deposition. From chemical measurements the latter deposition was thought to be impact-related. Ir measurements were made, following neutron activation, with the Iridium Coincidence Spectrometer. The age vs depth calibration curves given in the DSDP and ODP preliminary reports indicate the ages of the Iranomalies are identical, 11.7 million years, but the absolute and relative uncertainties in the curves are not known. Based on the newest age data the age estimate is 10 million years. As the Ir was deposited at the two sites at about the same time and they are one quarter of the way around the world from each other it seems likely that the deposition was world-wide. The impact of a large asteroid or comet could produce the wide distribution, and this data is supportive of the impact relationship deduced for Deep Sea Drilling Project (DSDP) 588B from the chemical evidence. If the surface densities of Ir at the two sites are representative of the world-wide average, the diameter of a Cl type asteroid containing the necessary Ir would be 3 + or - 1 km, which is large enough to cause world-wide darkness and hence extinctions although the latter point is disputed.

  8. Surface activity of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers

    SciTech Connect

    Alexandridis, P.; Athanassiou, V.; Fukuda, Shinya; Hatton, T.A. )

    1994-08-01

    The surface tension of aqueous solutions of seven poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) Pluronic copolymers, covering a wide range of molecular weights (3400-14600) and PPO/PEO ratios (0.19-1.79), was determined over the 10[sup [minus]5]-10% w/v concentration range, at two temperatures (25 and 35[degree]C). Two breaks (changes in slope) were observed in the surface tension vs log concentration curve for most of the copolymers. The low-concentration break, occurring at bulk copolymer concentrations of approximately 10[sup [minus]3]%, is believed to originate from rearrangement of the copolymer molecules on the surface at complete coverage of the air/water interface. The breaks at the high-concentration part of the surface tension curve occurred at concentrations that correspond to the critical micellization concentration values as determined by a dye solubilization technique. The surface area per copolymer molecule, A, increased as a function of the number of EO segments, N[sub EO], obeying a scaling law (A [approx] N[sub EO][sup 1/2]) similar to that of lower molecular weight C[sub i]E[sub j] nonionic surfactants. 56 refs., 6 figs., 2 tabs.

  9. Understanding the role of gold nanoparticles in enhancing the catalytic activity of manganese oxides in water oxidation reactions.

    PubMed

    Kuo, Chung-Hao; Li, Weikun; Pahalagedara, Lakshitha; El-Sawy, Abdelhamid M; Kriz, David; Genz, Nina; Guild, Curtis; Ressler, Thorsten; Suib, Steven L; He, Jie

    2015-02-16

    The Earth-abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn(3+) species, a small amount of AuNPs (<5%) in α-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α-MnO2.

  10. Activity of Cu{sup 2+} ions on the tetrahedral and octahedral sites of spinel oxide catalysts for CO oxidation

    SciTech Connect

    Ghose, J.; Murthy, K.S.R.C.

    1996-09-01

    In studies of CO oxidation on substituted copper chromite spinel oxide catalyst decreases as the Cu{sup 2+} content of the catalyst decreases, either by substitution with a divalent ion, i.e., Cu{sub 1-x} Mg{sub x} [Cr{sub 2}]O{sub 4}, or by reduction of Cu{sup 2+} to Cu{sup 1+}. Crystallographic studies have shown that Cu[Cr{sub 2}]O{sub 4} changes from normal to partially inverse when Cr{sup 3+} is replaced by Al{sup 3+}. Thus, in aluminum-substituted copper chromite catalysts, copper is present on both tetrahedral and octahedral sites of the spinel lattice, i.e., Cu{sub 1-x}Al{sub x} [Cu{sub x}Cr{sub 2-(x+y)}Al{sub y}]O{sub 4}. ESCA studies have shown that upon Al substitution some of the tetrahedral Cu{sup 2+} ions are reduced to Cu{sup 1+} and this causes a reduction in the catalytic activity of the catalysts. The present work was taken up to compare the activity of Cu{sup 2+} on tetrahedral sites with that on octahedral sites of the spinel oxide catalysts. For this, CO oxidation studies were carried out on the inverse spinel CuFe{sub 2}O{sub 4} and on the normal spinel CuRh{sub 2}O{sub 4} catalysts. 7 refs., 1 fig.

  11. Oxidation of calmodulin alters activation and regulation of CaMKII.

    PubMed

    Robison, A J; Winder, Danny G; Colbran, Roger J; Bartlett, Ryan K

    2007-04-27

    Increases in reactive oxygen species and mis-regulation of calcium homeostasis are associated with various physiological conditions and disease states including aging, ischemia, exposure to drugs of abuse, and neurodegenerative diseases. In aged animals, this is accompanied by a reduction in oxidative repair mechanisms resulting in increased methionine oxidation of the calcium signaling protein calmodulin in the brain. Here, we show that oxidation of calmodulin results in an inability to: (1) activate CaMKII; (2) support Thr(286) autophosphorylation of CaMKII; (3) prevent Thr(305/6) autophosphorylation of CaMKII; (4) support binding of CaMKII to the NR2B subunit of the NMDA receptor; and (5) compete with alpha-actinin for binding to CaMKII. Moreover, oxidized calmodulin does not efficiently bind calcium/calmodulin-dependent protein kinase II (CaMKII) in rat brain lysates or in vitro. These observations contrast from past experiments performed with oxidized calmodulin and the plasma membrane calcium ATPase, where oxidized calmodulin binds to, and partially activates the PMCA. When taken together, these data suggest that oxidative stress may perturb neuronal and cardiac function via a decreased ability of oxidized calmodulin to bind, activate, and regulate the interactions of CaMKII.

  12. Oxidative Profile and δ-Aminolevulinate Dehydratase Activity in Healthy Pregnant Women with Iron Supplementation

    PubMed Central

    De Lucca, Leidiane; Rodrigues, Fabiane; Jantsch, Letícia B.; Neme, Walter S.; Gallarreta, Francisco M. P.; Gonçalves, Thissiane L.

    2016-01-01

    An oxidative burst occurs during pregnancy due to the large consumption of oxygen in the tissues and an increase in metabolic demands in response to maternal physiological changes and fetal growth. This study aimed to determine the oxidative profile and activity of δ-aminolevulinate dehydratase (δ-ALA-D) in pregnant women who received iron supplementation. Oxidative stress parameters were evaluated in 25 pregnant women with iron supplementation, 25 pregnant women without supplementation and 25 non-pregnant women. The following oxidative stress parameters were evaluated: thiobarbituric acid reactive substances (TBARS), protein thiol groups (P-SH), non-protein thiol levels (NP-SH), vitamin C levels, catalase and δ-ALA-D activity. Markers of oxidative stress and cell damage, such as TBARS in plasma were significantly higher in pregnant women without supplementation. Levels of P-SH, NP-SH and δ-ALA-D activity were significantly lower in pregnant women without supplementation compared to non-pregnant and pregnant women with supplementation, while vitamin C levels were significantly lower in pregnant women without supplementation when compared to non-pregnant women. The increase in the generation of oxidative species and decrease of antioxidants suggest the loss of physiological oxidative balance during normal pregnancy, which was not observed in pregnant women with iron supplementation, suggesting a protective effect of iron against oxidative damage. PMID:27153075

  13. Role of peroxisome proliferator-activated receptor-α in fasting-mediated oxidative stress

    PubMed Central

    Abdelmegeed, Mohamed A.; Moon, Kwan-Hoon; Hardwick, James P.; Gonzalez, Frank J.; Song, Byoung-Joon

    2009-01-01

    The peroxisome proliferator-activated receptor-α (PPARα) regulates lipid homeostasis, particularly in the liver. This study was aimed at elucidating the relationship between hepatosteatosis and oxidative stress during fasting. Fasted Ppara-null mice exhibited marked hepatosteatosis, which was associated with elevated levels of lipid peroxidation, nitric oxide synthase activity, and hydrogen peroxide accumulation. Total glutathione (GSH), mitochondrial GSH, and the activities of major anti-oxidant enzymes were also lower in the fasted Ppara-null mice. Consequently, the number and extent of nitrated proteins were markedly increased in the fasted Ppara-null mice, although high levels of protein nitration were still detected in the fed Ppara-null mice while many oxidatively-modified proteins were only found in the fasted Ppara-null mice. However, the role of inflammation in increased oxidative stress in the fasted Ppara-null mice was minimal based on the similar levels of tumor necrosis factor-α change in all groups. These results with increased oxidative stress observed in the fasted Ppara-null mice compared with other groups demonstrate a role for PPARα in fasting-mediated oxidative stress and that inhibition of PPARα functions may increase the susceptibility to oxidative damage in the presence of another toxic agent. PMID:19539749

  14. Molecular Basis for Enzymatic Sulfite Oxidation -- HOW THREE CONSERVED ACTIVE SITE RESIDUES SHAPE ENZYME ACTIVITY

    SciTech Connect

    Bailey, Susan; Rapson, Trevor; Johnson-Winters, Kayunta; Astashkin, Andrei; Enemark, John; Kappler, Ulrike

    2008-11-10

    Sulfite dehydrogenases (SDHs) catalyze the oxidation and detoxification of sulfite to sulfate, a reaction critical to all forms of life. Sulfite-oxidizing enzymes contain three conserved active site amino acids (Arg-55, His-57, and Tyr-236) that are crucial for catalytic competency. Here we have studied the kinetic and structural effects of two novel and one previously reported substitution (R55M, H57A, Y236F) in these residues on SDH catalysis. Both Arg-55 and His-57 were found to have key roles in substrate binding. An R55M substitution increased Km(sulfite)(app) by 2-3 orders of magnitude, whereas His-57 was required for maintaining a high substrate affinity at low pH when the imidazole ring is fully protonated. This effect may be mediated by interactions of His-57 with Arg-55 that stabilize the position of the Arg-55 side chain or, alternatively, may reflect changes in the protonation state of sulfite. Unlike what is seen for SDHWT and SDHY236F, the catalytic turnover rates of SDHR55M and SDHH57A are relatively insensitive to pH (~;;60 and 200 s-1, respectively). On the structural level, striking kinetic effects appeared to correlate with disorder (in SDHH57A and SDHY236F) or absence of Arg-55 (SDHR55M), suggesting that Arg-55 and the hydrogen bonding interactions it engages in are crucial for substrate binding and catalysis. The structure of SDHR55M has sulfate bound at the active site, a fact that coincides with a significant increase in the inhibitory effect of sulfate in SDHR55M. Thus, Arg-55 also appears to be involved in enabling discrimination between the substrate and product in SDH.

  15. Production of Oxygen from Lunar Regolith using Molten Oxide Electrolysis

    NASA Technical Reports Server (NTRS)

    Sibille, Laurent; Sadoway, Donald R.; Sirk, Aislinn; Tripathy, Prabhat; Melendez, Orlando; Standish, Evan; Dominquez, Jesus A.; Stefanescu, Doru M.; Curreri, Peter A.; Poizeau, Sophie

    2009-01-01

    This slide presentation reviews the possible use of molten oxide electrolysis to extract oxygen from the Lunar Regolith. The presentation asserts that molten regolith electrolysis has advanced to be a useful method for production of oxygen and metals in situ on the Moon. The work has demonstrated an 8 hour batch of electrolysis at 5 amps using Iridium inert anodes.

  16. Catalytic catechol oxidation by copper complexes: development of a structure-activity relationship.

    PubMed

    Ording-Wenker, Erica C M; Siegler, Maxime A; Lutz, Martin; Bouwman, Elisabeth

    2015-07-21

    A large library of Cu(II) complexes with mononucleating and dinucleating ligands was synthesized to investigate their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC). X-ray structure determination for a number of these complexes revealed relatively large Cu···Cu distances and the formation of polymeric species. Comparison of the 3,5-DTBC oxidation rates showed that ligands that stabilize the biomimetic dinuclear Cu(II) μ-thiolate complex also result in copper compounds that are much more active in the oxidation of 3,5-DTBC. This oxidation activity is however inhibited by the presence of chloride ions. The highest kcat that was observed was 6900 h(-1), which is one of the highest turnover frequencies reported so far for catechol oxidation in CH3CN.

  17. Nitric Oxide Regulates Neuronal Activity via Calcium-Activated Potassium Channels

    PubMed Central

    Zhong, Lei Ray; Estes, Stephen; Artinian, Liana; Rehder, Vincent

    2013-01-01

    Nitric oxide (NO) is an unconventional membrane-permeable messenger molecule that has been shown to play various roles in the nervous system. How NO modulates ion channels to affect neuronal functions is not well understood. In gastropods, NO has been implicated in regulating the feeding motor program. The buccal motoneuron, B19, of the freshwater pond snail Helisoma trivolvis is active during the hyper-retraction phase of the feeding motor program and is located in the vicinity of NO-producing neurons in the buccal ganglion. Here, we asked whether B19 neurons might serve as direct targets of NO signaling. Previous work established NO as a key regulator of growth cone motility and neuronal excitability in another buccal neuron involved in feeding, the B5 neuron. This raised the question whether NO might modulate the electrical activity and neuronal excitability of B19 neurons as well, and if so whether NO acted on the same or a different set of ion channels in both neurons. To study specific responses of NO on B19 neurons and to eliminate indirect effects contributed by other cells, the majority of experiments were performed on single cultured B19 neurons. Addition of NO donors caused a prolonged depolarization of the membrane potential and an increase in neuronal excitability. The effects of NO could mainly be attributed to the inhibition of two types of calcium-activated potassium channels, apamin-sensitive and iberiotoxin-sensitive potassium channels. NO was found to also cause a depolarization in B19 neurons in situ, but only after NO synthase activity in buccal ganglia had been blocked. The results suggest that NO acts as a critical modulator of neuronal excitability in B19 neurons, and that calcium-activated potassium channels may serve as a common target of NO in neurons. PMID:24236040

  18. First stages of silicon oxidation with the activation relaxation technique

    NASA Astrophysics Data System (ADS)

    Ganster, Patrick; Béland, Laurent Karim; Mousseau, Normand

    2012-08-01

    Using the art nouveau method, we study the initial stages of silicon oxide formation. After validating the method's parameters with the characterization of point defects diffusion mechanisms in pure Stillinger-Weber silicon, which allows us to recover some known results and to detail vacancy and self-interstitial diffusion paths, the method is applied onto a system composed of an oxygen layer deposited on a silicon substrate. We observe the oxygen atoms as they move rapidly into the substrate. From these art nouveau simulations, we extract the energy barriers of elementary mechanisms involving oxygen atoms and leading to the formation of an amorphouslike silicon oxide. We show that the kinetics of formation can be understood in terms of the energy barriers between various coordination environments.

  19. Photo-Activated Synthesis of Functional Oxide Thin Films

    DTIC Science & Technology

    2010-03-01

    o (d200 = 2.53 Å), corresponding to lattice constant ~ 5.07 Å. In cubic fluorite structure, lattice parameter (d) can be calculated from ionic...noted that aliovalently introduced oxygen vacancies have an effect on anion ionic radius, therefore lattice constant in doped fluorite structure cannot...denotes the dopant content.[26] This relation indicates that oxygen deficiency decreases the lattice constant of fluorite -structured oxides. It is

  20. Cysteamine modulates oxidative stress and blocks myofibroblast activity in CKD.

    PubMed

    Okamura, Daryl M; Bahrami, Nadia M; Ren, Shuyu; Pasichnyk, Katie; Williams, Juliana M; Gangoiti, Jon A; Lopez-Guisa, Jesus M; Yamaguchi, Ikuyo; Barshop, Bruce A; Duffield, Jeremy S; Eddy, Allison A

    2014-01-01

    Therapy to slow the relentless expansion of interstitial extracellular matrix that leads to renal functional decline in patients with CKD is currently lacking. Because chronic kidney injury increases tissue oxidative stress, we evaluated the antifibrotic efficacy of cysteamine bitartrate, an antioxidant therapy for patients with nephropathic cystinosis, in a mouse model of unilateral ureteral obstruction. Fresh cysteamine (600 mg/kg) was added to drinking water daily beginning on the day of surgery, and outcomes were assessed on days 7, 14, and 21 after surgery. Plasma cysteamine levels showed diurnal variation, with peak levels similar to those observed in patients with cystinosis. In cysteamine-treated mice, fibrosis severity decreased significantly at 14 and 21 days after unilateral ureteral obstruction, and renal oxidized protein levels decreased at each time point, suggesting reduced oxidative stress. Consistent with these results, treatment of cultured macrophages with cysteamine reduced cellular generation of reactive oxygen species. Furthermore, treatment with cysteamine reduced α-smooth muscle actin-positive interstitial myofibroblast proliferation and mRNA levels of extracellular matrix proteins in mice and attenuated myofibroblast differentiation and proliferation in vitro, but did not augment TGF-β signaling. In a study of renal ischemia reperfusion, cysteamine therapy initiated 10 days after injury and continued for 14 days decreased renal fibrosis by 40%. Taken together, these data suggest previously unrecognized antifibrotic actions of cysteamine via TGF-β-independent mechanisms that include oxidative stress reduction and attenuation of the myofibroblast response to kidney injury and support further investigation into the potential benefit of cysteamine therapy in the treatment of CKD.

  1. RhoA GTPase oxidation stimulates cell proliferation via nuclear factor-κB activation.

    PubMed

    Kim, Jae-Gyu; Kwon, Hyung-Joo; Wu, Guang; Park, Yohan; Lee, Jae-Yong; Kim, Jaebong; Kim, Sung-Chan; Choe, Myoen; Kang, Seung Goo; Seo, Goo-Young; Kim, Pyeung-Hyeun; Park, Jae-Bong

    2017-02-01

    Reactive oxygen species (ROS) produced by many kinds of stimuli are essential for cellular signaling including cell proliferation. The dysregulation of ROS, therefore, is related to a variety of diseases including cancer. However, it was not clearly elucidated how ROS regulate cell proliferation and tumorigenesis. In this study, we investigated a mechanism by which the oxidation of RhoA GTPase regulates nuclear factor-κB (NF-κB) and cell proliferation. Hydrogen peroxide activated NF-κB and RhoA GTPase, but did not activate RhoA C16/20A mutant, an oxidation-resistant form. Remarkably, the oxidation of RhoA reduced its affinity towards RhoGDI, leading to the dissociation of RhoA-RhoGDI complex. Si-Vav2, a guanine nucleotide exchange factor (GEF), inhibited RhoA activation upon hydrogen peroxide. The oxidized RhoA (oxRhoA)-GTP was readily bound to IκB kinase γ (IKKγ), whereas oxidized RhoGDI did not bind to IKKγ. The oxRhoA-GTP bound to IKKγ activated IKKβ, leading to IκB phosphorylation and degradation, consequently NF-κB activation. Hydrogen peroxide induced cell proliferation, but RhoA C16/20A mutant suppressed cell proliferation and tumorigenesis. Conclusively, RhoA oxidation at Cys16/20 is critically involved in cell proliferation and tumorigenesis through NF-κB activation in response to ROS.

  2. Single Silver Adatoms on Nanostructured Manganese Oxide Surfaces: Boosting Oxygen Activation for Benzene Abatement.

    PubMed

    Chen, Yaxin; Huang, Zhiwei; Zhou, Meijuan; Ma, Zhen; Chen, Jianmin; Tang, Xingfu

    2017-02-21

    The involvement of a great amount of active oxygen species is a crucial requirement for catalytic oxidation of benzene, because complete mineralization of one benzene molecule needs 15 oxygen atoms. Here, we disperse single silver adatoms on nanostructured hollandite manganese oxide (HMO) surfaces by using a thermal diffusion method. The single-atom silver catalyst (Ag1/HMO) shows high catalytic activity in benzene oxidation, and 100% conversion is achieved at 220 °C at a high space velocity of 23 000 h(-1). The Mars-van Krevelen mechanism is valid in our case as the reaction orders for both benzene and O2 approach one, according to reaction kinetics data. Data from H2 temperature-programmed reduction and O core-level X-ray photoelectron spectra (XPS) reveal that Ag1/HMO possesses a great amount of active surface lattice oxygen available for benzene oxidation. Valence-band XPS and density functional theoretical calculations demonstrate that the single Ag adatoms have the upshifted 4d orbitals, thus facilitating the activation of gaseous oxygen. Therefore, the excellent activation abilities of Ag1/HMO toward both surface lattice oxygen and gaseous oxygen account for its high catalytic activity in benzene oxidation. This work may assist with the rational design of efficient metal-oxide catalysts for the abatement of volatile organic compounds such as benzene.

  3. Templated electrodeposition and photocatalytic activity of cuprous oxide nanorod arrays.

    PubMed

    Haynes, Keith M; Perry, Collin M; Rivas, Marlene; Golden, Teresa D; Bazan, Antony; Quintana, Maria; Nesterov, Vladimir N; Berhe, Seare A; Rodríguez, Juan; Estrada, Walter; Youngblood, W Justin

    2015-01-14

    Cuprous oxide (Cu2O) nanorod arrays have been prepared via a novel templated electrodeposition process and were characterized for their photocatalytic behavior in nonaqueous photoelectrochemical cells. Zinc oxide (ZnO) nanorod films serve as sacrificial templates for the in situ formation of polymer nanopore membranes on transparent conductive oxide substrates. Nitrocellulose and poly(lactic acid) are effective membrane-forming polymers that exhibit different modes of template formation, with nitrocellulose forming conformal coatings on the ZnO surface while poly(lactic acid) acts as an amorphous pore-filling material. Robust template formation is sensitive to the seeding method used to prepare the precursor ZnO nanorod films. Photoelectrochemical cells prepared from electrodeposited Cu2O films using methyl viologen as a redox shuttle in acetonitrile electrolyte exhibit significant charge recombination that can be partially suppressed by a combination of surface passivation methods. Surface-passivated nanostructured Cu2O films show enhanced photocurrent relative to planar electrodeposited Cu2O films of similar thickness. We have obtained the highest photocurrent ever reported for electrodeposited Cu2O in a nonaqueous photoelectrochemical cell.

  4. In Vitro Oxidation of Collagen Promotes the Formation of Advanced Oxidation Protein Products and the Activation of Human Neutrophils.

    PubMed

    Bochi, Guilherme Vargas; Torbitz, Vanessa Dorneles; de Campos, Luízi Prestes; Sangoi, Manuela Borges; Fernandes, Natieli Flores; Gomes, Patrícia; Moretto, Maria Beatriz; Barbisan, Fernanda; da Cruz, Ivana Beatrice Mânica; Moresco, Rafael Noal

    2016-04-01

    The accumulation of advanced oxidation protein products (AOPPs) has been linked to several pathological conditions. Here, we investigated collagen as a potential source for AOPP formation and determined the effects of hypochlorous acid (HOCl)-treated collagen (collagen-AOPPs) on human neutrophil activity. We also assessed whether alpha-tocopherol could counteract these effects. Exposure to HOCl increased the levels of collagen-AOPPs. Collagen-AOPPs also stimulated the production of AOPPs, nitric oxide (NO), superoxide radicals (O2(-)), and HOCl by neutrophils. Collagen-AOPPs induced apoptosis and decreased the number of viable cells. Alpha-tocopherol prevented the formation of collagen-AOPPs, strongly inhibited the collagen-AOPP-induced production of O2(-) and HOCl, and increased the viability of neutrophils. Our results suggest that collagen is an important protein that interacts with HOCl to form AOPPs, and consequently, collagen-AOPP formation is related to human neutrophil activation and cell death.

  5. Method of treating intermetallic alloy hydrogenation/oxidation catalysts for improved impurity poisoning resistance, regeneration and increased activity

    DOEpatents

    Wright, Randy B.

    1992-01-01

    Alternate, successive high temperature oxidation and reduction treatments, in either order, of intermetallic alloy hydrogenation and intermetallic alloy oxidation catalysts unexpectedly improves the impurity poisoning resistance, regeneration capacity and/or activity of the catalysts. The particular alloy, and the final high temperature treatment given alloy (oxidation or reduction) will be chosen to correspond to the function of the catalyst (oxidation or hydrogenation).

  6. Triiodothyronine activates lactate oxidation without impairing fatty acid oxidation and improves weaning from extracorporeal membrane oxygenation

    SciTech Connect

    Kajimoto, Masaki; Ledee, Dolena R.; Xu, Chun; Kajimoto, Hidemi; Isern, Nancy G.; Portman, Michael A.

    2014-01-01

    Background: Extracorporeal membrane oxygenation (ECMO) provides a rescue for children with severe cardiac failure. We previously showed that triiodothyronine (T3) improves cardiac function by modulating pyruvate oxidation during weaning. This study was focused on fatty acid (FA) metabolism modulated by T3 for weaning from ECMO after cardiac injury. Methods: Nineteen immature piglets (9.1-15.3 kg) were separated into 3 groups with ECMO (6.5 hours) and wean: normal circulation (Group-C);transient coronary occlusion (10 minutes) followed by ECMO (Group-IR); and IR with T3 supplementation (Group-IR-T3). 13-Carbon labeled lactate, medium-chain and long-chain FAs were infused as oxidative substrates. Substrate fractional contribution to the citric acid cycle (FC) was analyzed by 13-Carbon nuclear magnetic resonance. Results: ECMO depressed circulating T3 levels to 40% baseline at 4 hours and were restored in Group-IR-T3. Group-IR decreased cardiac power, which was not fully restorable and 2 pigs were lost because of weaning failure. Group-IR also depressed FC-lactate, while the excellent contractile function and energy efficiency in Group-IR-T3 occurred along with a marked FC-lactate increase and [ATP]/[ADP] without either decreasing FC-FAs or elevating myocardial oxygen consumption over Group-C or -IR. Conclusions: T3 releases inhibition of lactate oxidation following ischemia-reperfusion injury without impairing FA oxidation. These findings indicate that T3 depression during ECMO is maladaptive, and that restoring levels improves metabolic flux and enhances contractile function during weaning.

  7. Inhibition of fatty acid oxidation activates transforming growth factor-beta in cerebrospinal fluid and decreases spontaneous motor activity.

    PubMed

    Fujikawa, Teppei; Fujita, Ryo; Iwaki, Yoko; Matsumura, Shigenobu; Fushiki, Tohru; Inoue, Kazuo

    2010-10-05

    We have previously reported that transforming growth factor (TGF)-beta in the cerebrospinal fluid (CSF) is involved in the mechanism underlying the regulation of spontaneous motor activity (SMA) by the central nervous system after exercise. However, it remained unclear what physiological condition triggers the activation of TGF-beta. We hypothesized that the shortage of energy derived from fatty acid (FA) oxidation observed in the early phase of exercise activated TGF-beta in the CSF. To test this hypothesis, we investigated whether mercaptoacetate (MA), an inhibitor of FA oxidation, could induce an activation of TGF-beta in the CSF and a decrease in SMA. Intraperitoneal (i.p.) administration of MA activated TGF-beta in CSF in rats and depressed SMA; 2-deoxyglucose, an inhibitor of carbohydrate oxidation, on the other hand, depressed SMA but failed to activate CSF TGF-beta. Intracisternal administration of anti-TGF-beta antibody abolished the depressive effect of MA on SMA. We also found that the depression of SMA and the activation of TGF-beta in the CSF by i.p. MA administration were eliminated by vagotomy. Our data suggest that TGF-beta in the CSF is activated by the inhibition of FA oxidation via the vagus nerve and that this subsequently induces depression of SMA.

  8. Screening SIRT1 Activators from Medicinal Plants as Bioactive Compounds against Oxidative Damage in Mitochondrial Function

    PubMed Central

    Wang, Yi; Liang, Xinying; Chen, Yaqi; Zhao, Xiaoping

    2016-01-01

    Sirtuin type 1 (SIRT1) belongs to the family of NAD+ dependent histone deacetylases and plays a critical role in cellular metabolism and response to oxidative stress. Traditional Chinese medicines (TCMs), as an important part of natural products, have been reported to exert protective effect against oxidative stress in mitochondria. In this study, we screened SIRT1 activators from TCMs and investigated their activities against mitochondrial damage. 19 activators were found in total by in vitro SIRT1 activity assay. Among those active compounds, four compounds, ginsenoside Rb2, ginsenoside F1, ginsenoside Rc, and schisandrin A, were further studied to validate the SIRT1-activation effects by liquid chromatography-mass spectrometry and confirm their activities against oxidative damage in H9c2 cardiomyocytes exposed to tert-butyl hydroperoxide (t-BHP). The results showed that those compounds enhanced the deacetylated activity of SIRT1, increased ATP content, and inhibited intracellular ROS formation as well as regulating the activity of Mn-SOD. These SIRT1 activators also showed moderate protective effects on mitochondrial function in t-BHP cells by recovering oxygen consumption and increasing mitochondrial DNA content. Our results suggested that those compounds from TCMs attenuated oxidative stress-induced mitochondrial damage in cardiomyocytes through activation of SIRT1. PMID:26981165

  9. Dynamic High-Temperature Tensile Characterization of an Iridium Alloy with Kolsky Tension Bar Techniques

    SciTech Connect

    Song, Bo; Nelson, Kevin; Lipinski, Ronald; Bignell, John; Ulrich, G. B.; George, Easo P.

    2015-05-29

    In this study, conventional Kolsky tension bar techniques were modified to characterize an iridium alloy in tension at elevated strain rates and temperatures. The specimen was heated to elevated temperatures with an induction coil heater before dynamic loading; whereas, a cooling system was applied to keep the bars at room temperature during heating. A preload system was developed to generate a small pretension load in the bar system during heating in order to compensate for the effect of thermal expansion generated in the high-temperature tensile specimen. A laser system was applied to directly measure the displacements at both ends of the tensile specimen in order to calculate the strain in the specimen. A pair of high-sensitivity semiconductor strain gages was used to measure the weak transmitted force due to the low flow stress in the thin specimen at elevated temperatures. The dynamic high-temperature tensile stress–strain curves of a DOP-26 iridium alloy were experimentally obtained at two different strain rates (~1000 and 3000 s-1) and temperatures (~750 and 1030°C). The effects of strain rate and temperature on the tensile stress–strain response of the iridium alloy were determined. Finally, the iridium alloy exhibited high ductility in stress–strain response that strongly depended on strain-rate and temperature.

  10. Dynamic High-Temperature Tensile Characterization of an Iridium Alloy with Kolsky Tension Bar Techniques

    DOE PAGES

    Song, Bo; Nelson, Kevin; Lipinski, Ronald; ...

    2015-05-29

    In this study, conventional Kolsky tension bar techniques were modified to characterize an iridium alloy in tension at elevated strain rates and temperatures. The specimen was heated to elevated temperatures with an induction coil heater before dynamic loading; whereas, a cooling system was applied to keep the bars at room temperature during heating. A preload system was developed to generate a small pretension load in the bar system during heating in order to compensate for the effect of thermal expansion generated in the high-temperature tensile specimen. A laser system was applied to directly measure the displacements at both ends ofmore » the tensile specimen in order to calculate the strain in the specimen. A pair of high-sensitivity semiconductor strain gages was used to measure the weak transmitted force due to the low flow stress in the thin specimen at elevated temperatures. The dynamic high-temperature tensile stress–strain curves of a DOP-26 iridium alloy were experimentally obtained at two different strain rates (~1000 and 3000 s-1) and temperatures (~750 and 1030°C). The effects of strain rate and temperature on the tensile stress–strain response of the iridium alloy were determined. Finally, the iridium alloy exhibited high ductility in stress–strain response that strongly depended on strain-rate and temperature.« less

  11. Acylsilanes in Iridium-Catalyzed Directed Amidation Reactions and Formation of Heterocycles via Siloxycarbenes.

    PubMed

    Becker, Peter; Pirwerdjan, Ramona; Bolm, Carsten

    2015-12-14

    Exposing ortho-amido aroylsilanes to visible light or heat leads to cyclization reactions that provide N-heterocyclic compounds via siloxycarbenes as key intermediates. The previously unreported starting materials have been prepared by directed amidations of aromatic acylsilanes in the presence of an iridium catalyst followed by N-alkylation.

  12. Single orientation graphene synthesized on iridium thin films grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Dangwal Pandey, A.; Krausert, K.; Franz, D.; Grânäs, E.; Shayduk, R.; Müller, P.; Keller, T. F.; Noei, H.; Vonk, V.; Stierle, A.

    2016-08-01

    Heteroepitaxial iridium thin films were deposited on (0001) sapphire substrates by means of molecular beam epitaxy, and subsequently, one monolayer of graphene was synthesized by chemical vapor deposition. The influence of the growth parameters on the quality of the Ir films, as well as of graphene, was investigated systematically by means of low energy electron diffraction, x-ray reflectivity, x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Our study reveals (111) oriented iridium films with high crystalline quality and extremely low surface roughness, on which the formation of large-area epitaxial graphene is achieved. The presence of defects, like dislocations, twins, and 30° rotated domains in the iridium films is also discussed. The coverage of graphene was found to be influenced by the presence of 30° rotated domains in the Ir films. Low iridium deposition rates suppress these rotated domains and an almost complete coverage of graphene was obtained. This synthesis route yields inexpensive, air-stable, and large-area graphene with a well-defined orientation, making it accessible to a wider community of researchers for numerous experiments or applications, including those which use destructive analysis techniques or irreversible processes. Moreover, this approach can be used to tune the structural quality of graphene, allowing a systematic study of the influence of defects in various processes like intercalation below graphene.

  13. Total Synthesis of Cryptocaryol A by Enantioselective Iridium-Catalyzed Alcohol C-H Allylation.

    PubMed

    Perez, Felix; Waldeck, Andrew R; Krische, Michael J

    2016-04-11

    The polyketide natural product cryptocaryol A is prepared in 8 steps via iridium catalyzed enantioselective diol double C-H allylation, which directly generates an acetate-based triketide stereodiad. In 4 previously reported total syntheses, 17-28 steps were required.

  14. Catalytic cleavage of ether C-O bonds by pincer iridium complexes.

    PubMed

    Haibach, Michael C; Lease, Nicholas; Goldman, Alan S

    2014-09-15

    The development of efficient catalytic methods to cleave the relatively unreactive C-O bonds of ethers remains an important challenge in catalysis. Building on our group's recent work, we report the dehydroaryloxylation of aryl alkyl ethers using pincer iridium catalysts. This method represents a rare fully atom-economical method for ether C-O bond cleavage.

  15. Iridium-catalyzed regio- and enantioselective allylic substitution of silyl dienolates derived from dioxinones.

    PubMed

    Chen, Ming; Hartwig, John F

    2014-11-03

    Reported herein is the iridium-catalyzed regio- and enantioselective allylic substitution reactions of unstabilized silyl dienolates derived from dioxinones. Asymmetric allylic substitution of a variety of allylic trichloroethyl carbonates with these silyl dienolates gave γ-allylated products selectively in 60-84% yield and 90-98% ee.

  16. Synthesis and luminescence properties of iridium complexes chelated with coumarin ligands.

    PubMed

    Park, Hye Rim; Kim, Bo Young; Kim, Young Kwan; Ha, Yunkyoung

    2013-05-01

    According to a recent report, the organic light-emitting diodes (OLEDs) using the iridium complexes of coumarin derivatives as emissive dopants are highly efficient and stable. Unlike the other Ir(III) phopsphorescent dopants, these coumarin-based Ir(III) complexes can effectively trap and transport electrons in the emissive layer. We have prepared a series of phosphorescent cyclometalated Ir(III) complexes containing 3-(2-pyridinyl)coumarin (pc) as an ancillary ligand. The new heteroleptic iridium complexes, Ir(C--N)2(pc) (CAN = 2-(2,4-difluorophenyl)pyridine (F2-ppy), 2-phenylpyridine (ppy) and 2-phenylquinoline (pq)) were characterized by 1H NMR and mass spectrometer. As main ligands, F2-ppy, ppy and pq were employed, which should have the drastically different ligand molecular orbital energy levels. The iridium complexes showed various emission ranges from 560 to 610 nm, depending upon the relative energy levels of their main and ancillary ligands. The photoabsorption, photoluminescence and electroluminescence of the complexes were studied. We also investigated the electrochemical properties of the iridium complexes to compare the HOMO and LUMO energy levels of these phosphorescent materials.

  17. Iridium-catalyzed selective α-alkylation of unactivated amides with primary alcohols.

    PubMed

    Guo, Le; Liu, Yinghua; Yao, Wubing; Leng, Xuebing; Huang, Zheng

    2013-03-01

    The first α-alkylation of unactivated amides with primary alcohols is described. An effective and robust iridium pincer complex has been developed for selective α-alkylation of tertiary and secondary acetamides involving a "borrowing hydrogen" methodology. The method is compatible with alcohols bearing various functional groups. This presents a convenient and environmentally benign protocol for α-alkylation of amides.

  18. A monolith immobilised iridium Cp* catalyst for hydrogen transfer reactions under flow conditions.

    PubMed

    Rojo, Maria Victoria; Guetzoyan, Lucie; Baxendale, Ian R

    2015-02-14

    An immobilised iridium hydrogen transfer catalyst has been developed for use in flow based processing by incorporation of a ligand into a porous polymeric monolithic flow reactor. The monolithic construct has been used for several redox reductions demonstrating excellent recyclability, good turnover numbers and high chemical stability giving negligible metal leaching over extended periods of use.

  19. The growth of graphite phase on an iridium field electron emitter

    NASA Astrophysics Data System (ADS)

    Bernatskii, D. P.; Pavlov, V. G.

    2016-06-01

    The growth of graphite on the surface of an iridium tip in pyrolysis of benzene to give a ribbed crystal has been found by the methods of field electron and desorption microscopy. The formation of a graphite crystal results in the electric field factor increasing. The adsorption of alkali metals on the surface of graphite is accompanied by the intercalation effect.

  20. Grazing incidence X-ray reflectivity of gold and iridium coated flat mirrors

    NASA Astrophysics Data System (ADS)

    Aschenbach, Bernd; Braeuninger, Heinrich; Burkert, Wolfgang

    In the context of developing high reflectivity coatings for X-ray telescopes highly polished Zerodur and BK-7 glass flats have been coated with either gold or iridium. Grazing incidence reflectivity measurements at various X-ray energies are reported and compared with standard theory prediction.