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Sample records for iridium catalyzed c-c

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

    PubMed

    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

  2. Iridium-catalyzed enantioselective polyene cyclization.

    PubMed

    Schafroth, Michael A; Sarlah, David; Krautwald, Simon; Carreira, Erick M

    2012-12-19

    A highly enantioselective polycyclization method has been developed using the combination of Lewis acid activation with iridium-catalyzed allylic substitution. This strategy relies on direct use of branched, racemic allylic alcohols and furnishes a diverse and unique set of carbo- and heteropolycyclic ring systems in good yields and ≥99% ee. PMID:23193947

  3. Iridium-catalyzed enantioselective polyene cyclization.

    PubMed

    Schafroth, Michael A; Sarlah, David; Krautwald, Simon; Carreira, Erick M

    2012-12-19

    A highly enantioselective polycyclization method has been developed using the combination of Lewis acid activation with iridium-catalyzed allylic substitution. This strategy relies on direct use of branched, racemic allylic alcohols and furnishes a diverse and unique set of carbo- and heteropolycyclic ring systems in good yields and ≥99% ee.

  4. Olefin hydroaryloxylation catalyzed by pincer-iridium complexes.

    PubMed

    Haibach, Michael C; Guan, Changjian; Wang, David Y; Li, Bo; Lease, Nicholas; Steffens, Andrew M; Krogh-Jespersen, Karsten; Goldman, Alan S

    2013-10-01

    Aryl alkyl ethers, which are widely used throughout the chemical industry, are typically produced via the Williamson ether synthesis. Olefin hydroaryloxylation potentially offers a much more atom-economical alternative. Known acidic catalysts for hydroaryloxylation, however, afford very poor selectivity. We report the organometallic-catalyzed intermolecular hydroaryloxylation of unactivated olefins by iridium "pincer" complexes. These catalysts do not operate via the hidden Brønsted acid pathway common to previously developed transition-metal-based catalysts. The reaction is proposed to proceed via olefin insertion into an iridium-alkoxide bond, followed by rate-determining C-H reductive elimination to yield the ether product. The reaction is highly chemo- and regioselective and offers a new approach to the atom-economical synthesis of industrially important ethers and, potentially, a wide range of other oxygenates. PMID:24028199

  5. Iridium-Catalyzed Selective Isomerization of Primary Allylic Alcohols.

    PubMed

    Li, Houhua; Mazet, Clément

    2016-06-21

    This Account presents the development of the iridium-catalyzed isomerization of primary allylic alcohols in our laboratory over the past 8 years. Our initial interest was driven by the long-standing challenge associated with the development of a general catalyst even for the nonasymmetric version of this seemingly simple chemical transformation. The added value of the aldehyde products and the possibility to rapidly generate molecular complexity from readily accessible allylic alcohols upon a redox-economical isomerization reaction were additional sources of motivation. Certainly influenced by the success story of the related isomerization of allylic amines, most catalysts developed for the selective isomerization of allylic alcohols were focused on rhodium as a transition metal of choice. Our approach has been based on the commonly accepted precept that hydrogenation and isomerization are often competing processes, with the latter being usually suppressed in favor of the former. The cationic iridium complexes [(Cy3P)(pyridine)Ir(cod)]X developed by Crabtree (X = PF6) and Pfaltz (X = BArF) are usually considered as the most versatile catalysts for the hydrogenation of allylic alcohols. Using molecular hydrogen to generate controlled amounts of the active form of these complexes but performing the reaction in the absence of molecular hydrogen enabled deviation from the typical hydrogenation manifold and favored exclusively the isomerization of allylic alcohols into aldehydes. Isotopic labeling and crossover experiments revealed the intermolecular nature of the process. Systematic variation of the ligand on the iridium center allowed us to identify the structural features beneficial for catalytic activity. Subsequently, three generations of chiral catalysts have been investigated and enabled us to reach excellent levels of enantioselectivity for a wide range of 3,3-disubstituted aryl/alkyl and alkyl/alkyl primary allylic alcohols leading to β-chiral aldehydes. The

  6. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    NASA Astrophysics Data System (ADS)

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-10-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2‧-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4‧-dimethyl-2,2‧-bipyridine (Me2bpy), or dipyrido-[3,2-f:2‧,3‧-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir-CNHC distances are 2.043(5)-2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (-20.6 to -20.3 ppm) are more upfield than those with C2^C^C2 (-19.5 and -19.2 ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ = 340-530 nm (ɛ ≤ 103 dm3 mol-1 cm-1)) originate from a dπ(IrIII) → π*(N^N) metal-to-ligand charge transfer transition, where the dπ(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553-604 nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10-3-10-1.

  7. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    PubMed Central

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-01-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), or dipyrido-[3,2-f:2′,3′-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir–CNHC distances are 2.043(5)–2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (−20.6 to −20.3 ppm) are more upfield than those with C2^C^C2 (−19.5 and −19.2 ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ = 340–530 nm (ε ≤ 103 dm3 mol−1 cm−1)) originate from a dπ(IrIII) → π*(N^N) metal-to-ligand charge transfer transition, where the dπ(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553–604 nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10−3–10−1. PMID:26487542

  8. Ni-Catalyzed C-C Couplings Using Alkyl Electrophiles.

    PubMed

    Iwasaki, Takanori; Kambe, Nobuaki

    2016-10-01

    Much effort has been devoted to developing new methods using Ni catalysts for the cross-coupling reaction of alkyl electrophiles with organometallic reagents, and significant achievements in this area have emerged during the past two decades. Nickel catalysts have enabled the coupling reaction of not only primary alkyl electrophiles, but also sterically hindered secondary and tertiary alkyl electrophiles possessing β-hydrogens with various organometallic reagents to construct carbon skeletons. In addition, Ni catalysts opened a new era of asymmetric cross-coupling reaction using alkyl halides. Recent progress in nickel-catalyzed cross-coupling reaction of alkyl electrophiles with sp(3)-, sp(2)-, and sp-hybridized organometallic reagents including asymmetric variants as well as mechanistic insights of nickel catalysis are reviewed in this chapter. PMID:27580894

  9. Ni-Catalyzed C-C Couplings Using Alkyl Electrophiles.

    PubMed

    Iwasaki, Takanori; Kambe, Nobuaki

    2016-10-01

    Much effort has been devoted to developing new methods using Ni catalysts for the cross-coupling reaction of alkyl electrophiles with organometallic reagents, and significant achievements in this area have emerged during the past two decades. Nickel catalysts have enabled the coupling reaction of not only primary alkyl electrophiles, but also sterically hindered secondary and tertiary alkyl electrophiles possessing β-hydrogens with various organometallic reagents to construct carbon skeletons. In addition, Ni catalysts opened a new era of asymmetric cross-coupling reaction using alkyl halides. Recent progress in nickel-catalyzed cross-coupling reaction of alkyl electrophiles with sp(3)-, sp(2)-, and sp-hybridized organometallic reagents including asymmetric variants as well as mechanistic insights of nickel catalysis are reviewed in this chapter.

  10. Iridium-catalyzed enantioselective hydrogenation of unsaturated heterocyclic acids.

    PubMed

    Song, Song; Zhu, Shou-Fei; Pu, Liu-Yang; Zhou, Qi-Lin

    2013-06-01

    Spiral binding: A highly enantioselective hydrogenation of unsaturated heterocyclic acids has been developed by using chiral iridium/spirophosphino oxazoline catalysts (see scheme; BArF(-) =tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, Boc=tert-butoxycarbonyl). This reaction provided an efficient method for the preparation of optically active heterocyclic acids with excellent enantioselectivities. PMID:23610004

  11. Rh(I)-Catalyzed Insertion of Allenes into C-C Bonds of Benzocyclobutenols.

    PubMed

    Zhao, Chunliang; Liu, Li-Chuan; Wang, Jing; Jiang, Chenran; Zhang, Qing-Wei; He, Wei

    2016-01-15

    Herein we report a Rh(I)-catalyzed two carbon insertion into C-C bonds of benzocyclobutenols by employing symmetrical and unsymmetrical allenes. This reaction provides rapid access to alkylidene tetralins bearing two adjacent stereogenic centers in good yields and diasteroselectivities.

  12. Formation of C-C bonds via ruthenium-catalyzed transfer hydrogenation().

    PubMed

    Moran, Joseph; Krische, Michael J

    2012-01-01

    Ruthenium-catalyzed transfer hydrogenation of diverse π-unsaturated reactants in the presence of aldehydes provides products of carbonyl addition. Dehydrogenation of primary alcohols in the presence of the same π-unsaturated reactants provides identical products of carbonyl addition. In this way, carbonyl addition is achieved from the alcohol or aldehyde oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. In this account, the discovery of ruthenium-catalyzed C-C bond-forming transfer hydrogenations and the recent development of diastereo- and enantioselective variants are discussed. PMID:23430602

  13. Iron-Catalyzed C-C Cross-Couplings Using Organometallics.

    PubMed

    Guérinot, Amandine; Cossy, Janine

    2016-08-01

    Over the last decades, iron-catalyzed cross-couplings have emerged as an important tool for the formation of C-C bonds. A wide variety of alkenyl, aryl, and alkyl (pseudo)halides have been coupled to organometallic reagents, the most currently used being Grignard reagents. Particular attention has been devoted to the development of iron catalysts for the functionalization of alkyl halides that are generally challenging substrates in classical cross-couplings. The high functional group tolerance of iron-catalyzed cross-couplings has encouraged organic chemists to use them in the synthesis of bioactive compounds. Even if some points remain obscure, numerous studies have been carried out to investigate the mechanism of iron-catalyzed cross-coupling and several hypotheses have been proposed. PMID:27573401

  14. Iridium-Catalyzed Asymmetric Ring-Opening of Oxabenzonorbornadienes with N-Substituted Piperazine Nucleophiles.

    PubMed

    Yang, Wen; Luo, Renshi; Yang, Dingqiao

    2015-01-01

    Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with N-substituted piperazines was described. The reaction afforded the corresponding ring-opening products in high yields and moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]₂ and 5.0 mol % (S)-p-Tol-BINAP. The effects of various chiral bidentate ligands, catalyst loading, solvent, and temperature on the yield and enantioselectivity were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding trans-ring opened products based on the X-ray structure of product 2i. PMID:26633315

  15. Iridium/N-heterocyclic carbene-catalyzed C–H borylation of arenes by diisopropylaminoborane

    PubMed Central

    Igarashi, Takuya

    2016-01-01

    Summary Catalytic C–H borylation of arenes has been widely used in organic synthesis because it allows the introduction of a versatile boron functionality directly onto simple, unfunctionalized arenes. We report herein the use of diisopropylaminoborane as a boron source in C–H borylation of arenes. An iridium(I) complex with 1,3-dicyclohexylimidazol-2-ylidene is found to efficiently catalyze the borylation of arenes and heteroarenes. The resulting aminoborylated products can be converted to the corresponding boronic acid derivatives simply by treatment with suitable diols or diamines. PMID:27340457

  16. Iridium-catalyzed intermolecular dehydrogenative silylation of polycyclic aromatic compounds without directing groups.

    PubMed

    Murai, Masahito; Takami, Keishi; Takai, Kazuhiko

    2015-03-16

    This study describes the iridium-catalyzed intermolecular dehydrogenative silylation of C(sp(2))-H bonds of polycyclic aromatic compounds without directing groups. The reaction produced various arylsilanes through both Si-H and C-H bond activation, with hydrogen as the sole byproduct. Reactivity was affected by the electronic nature of the aromatic compounds, and silylation of electron-deficient and polycyclic aromatic compounds proceeded efficiently. Site-selectivity was controlled predominantly by steric factors. Therefore, the current functionalization proceeded with opposite chemo- and site-selectivity compared to that observed for general electrophilic functionalization of aromatic compounds.

  17. Iridium Catalyzed Dehydrogenation of Substituted Amine Boranes: Kinetics, Thermodynamics and Implications for Hydrogen Storage.

    SciTech Connect

    Dietrich, Brandon L.; Goldberg, Karen I.; Heinekey, D. M.; Autrey, Thomas; Linehan, John C.

    2008-10-06

    Dehydrogenation of ammonia borane (AB) and methylamine-borane (MeAB) is catalyzed efficiently by the iridium pincer complex (η3-1,3-(OPtBu2)2C6H3)Ir(H)2 (1). With MeAB and with MeAB/AB mixtures, rapid release of one equivalent of H2 is observed to yield soluble oligomeric products at rates similar to those previously reported for the dehydrogenation of AB catalyzed by 1. The rapid dehydrogenation reaction has allowed the experimental determination of the reaction enthalpy (ΔH) for the dehydrogenation of AB, MeAB, and AB/MeAB mixtures by calorimetry. The reactions are significantly more exothermic than suggested by some computational studies. This work was supported by the U.S. Department of Energy (DOE) as part of the Center of Excellence for Chemical Hydrogen Storage. PNNL is operated by Battelle for DOE.

  18. Iridium-catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of syngas.

    PubMed

    Olsen, Esben P K; Madsen, Robert

    2012-12-01

    A new iridium-catalyzed reaction in which molecular hydrogen and carbon monoxide are cleaved from primary alcohols in the absence of any stoichiometric additives has been developed. The dehydrogenative decarbonylation was achieved with a catalyst generated in situ from [Ir(coe)(2)Cl](2) (coe = cyclooctene) and racemic 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (rac-BINAP) in a mesitylene solution saturated with water. A catalytic amount of lithium chloride was also added to improve the catalyst turnover. The reaction has been applied to a variety of primary alcohols and gives rise to products in good to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)-BINAP species. First, dehydrogenation of the primary alcohol to the corresponding aldehyde takes place, which is then followed by decarbonylation to the product with one less carbon atom. PMID:23108889

  19. Diastereo- and enantioselective iridium-catalyzed allylation of cyclic ketone enolates: synergetic effect of ligands and barium enolates.

    PubMed

    Chen, Wenyong; Chen, Ming; Hartwig, John F

    2014-11-12

    We report asymmetric allylic alkylation of barium enolates of cyclic ketones catalyzed by a metallacyclic iridium complex containing a phosphoramidite ligand derived from (R)-1-(2-naphthyl)ethylamine. The reaction products contain adjacent quaternary and tertiary stereocenters. This process demonstrates that unstabilized cyclic ketone enolates can undergo diastereo- and enantioselective Ir-catalyzed allylic substitution reactions with the proper choice of enolate countercation. The products of these reactions can be conveniently transformed to various useful polycarbocyclic structures.

  20. 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.

  1. 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

  2. Rh(III)-Catalyzed Synthesis of N-Unprotected Indoles from Imidamides and Diazo Ketoesters via C-H Activation and C-C/C-N Bond Cleavage.

    PubMed

    Qi, Zisong; Yu, Songjie; Li, Xingwei

    2016-02-19

    The synthesis of N-unprotected indoles has been realized via Rh(III)-catalyzed C-H activation/annulation of imidamides with α-diazo β-ketoesters. The reaction occurs with the release of an amide coproduct, which originates from both the imidamide and the diazo as a result of C═N cleavage of the imidamide and C-C(acyl) cleavage of the diazo. A rhodacyclic intermediate has been isolated and a plausible mechanism has been proposed. PMID:26824751

  3. Highly regio- and enantioselective synthesis of N-substituted 2-pyridones: iridium-catalyzed intermolecular asymmetric allylic amination.

    PubMed

    Zhang, Xiao; Yang, Ze-Peng; Huang, Lin; You, Shu-Li

    2015-02-01

    The first iridium-catalyzed intermolecular asymmetric allylic amination reaction with 2-hydroxypyridines has been developed, thus providing a highly efficient synthesis of enantioenriched N-substituted 2-pyridone derivatives from readily available starting materials. This protocol features a good tolerance of functional groups in both the allylic carbonates and 2-hydroxypyridines, thereby delivering multifunctionalized heterocyclic products with up to 98% yield and 99% ee. PMID:25504907

  4. Iridium-Catalyzed Allylic Amination Route to α-Aminoboronates: Illustration of the Decisive Role of Boron Substituents

    PubMed Central

    Touchet, Sabrina; Molander, Gary A.; Carboni, Bertrand; Bouillon, Alexandre

    2012-01-01

    The development of a new route to α-aminoboronates using an iridium-catalyzed allylic amination on boronated substrates is described. Unlike the boronate group, the trifluoroborato substituent was found to govern the regioselectivity exclusively in favor of branched products. The transformation of an allylic substitution product into an α-aminoboronic ester in an efficient way validated the implementation of this approach. PMID:22350584

  5. Transition metal-catalyzed C-C bond formation via C-S bond cleavage: an overview.

    PubMed

    Modha, Sachin G; Mehta, Vaibhav P; Van der Eycken, Erik V

    2013-06-21

    Transition metal-catalyzed C-C bond formations have been well studied over the last four decades. An improved mechanistic understanding of such reactions has helped chemists to develop further improvements, modifications and even new reactions. In the area of transition metal-catalyzed cross-coupling reactions the C-S bond cleaving reactions have attracted a lot of attention in the last decade as they provide a good alternative to the use of organo-halide reagents in traditional cross-coupling reactions. The availability of a wide range of organo-sulfur species provides the opportunity for developing different transformations for the synthesis of interesting organic compounds. This tutorial review focuses on recent examples of the transition metal-catalyzed C-C bond forming reactions using organo-sulfur species.

  6. CO2 hydrogenation catalyzed by iridium complexes with a proton-responsive ligand

    DOE PAGES

    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 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. 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.

  8. pH-Dependent catalytic activity and chemoselectivity in transfer hydrogenation catalyzed by iridium complex with 4,4'-dihydroxy-2,2'-bipyridine.

    PubMed

    Himeda, Yuichiro; Onozawa-Komatsuzaki, Nobuko; Miyazawa, Satoru; Sugihara, Hideki; Hirose, Takuji; Kasuga, Kazuyuki

    2008-01-01

    Transfer hydrogenation catalyzed by an iridium catalyst with 4,4'-dihydroxy-2,2'-bipyridine (DHBP) in an aqueous formate solution exhibits highly pH-dependent catalytic activity and chemoselectivity. The substantial change in the activity is due to the electronic effect based on the acid-base equilibrium of the phenolic hydroxyl group of DHBP. Under basic conditions, high turnover frequency values of the DHBP complex, which can be more than 1000 times the value of the unsubstituted analogue, are obtained (up to 81 000 h(-1) at 80 degrees C). In addition, the DHBP catalyst exhibits pH-dependent chemoselectivity for alpha,beta-unsaturated carbonyl compounds. Selective reduction of the C=C bond of enone with high activity are observed under basic conditions. The ketone moieties can be reduced with satisfactory activity under acidic conditions. In particular, pH-selective chemoselectivity of the C=O versus C=C bond reduction was observed in the transfer hydrogenation of cinnamaldehyde. PMID:18989857

  9. Enantioselective hydrogenation. III. Methyl pyruvate hydrogenation catalyzed by alkaloid-modified iridium

    SciTech Connect

    Simons, K.E.; Johnston, P.; Plum, H.; Wells, P.B.; Ibbotson, A.

    1994-12-01

    Enantioselective hydrogenation of methyl pyruvate, MeCOCOOMe to methyl lactate, MeCH(OH)COOMe, is catalyzed in solution at room temperature by supported iridium catalysts modified with cinchona alkaloids. Modification with cinchonidine or quinine yields R-lactate in excess, whereas modification with cinchonine or quinidine favors S-lactate formation. Ir/SiO{sub 2} catalysts (20%) calcined at 393 to 573 K and reduced at 523 to 593 K were highly active for racemic hydrogenation in the absence of a modifier (rates typically 1.8 mol h{sup -1} g{sub cat}{sup -1}) and were comparably active when modified with cinchonidine but gave an enantiomeric excess of about 30%. Use of higher calcination or reduction temperatures led to substantially inferior activity and selectivity. The high rates recorded for both racemic and enantioselective reactions are dependent on the catalysts being activated before use by a procedure involving exposure of the catalyst to air after the initial reduction. Use of a Cl-free precursor gave an Ir/SiO{sub 2} catalyst (20%) of superior activity but inferior enantioselectivity. Ir/CaCO{sub 3} (5%) was more active for racemic hydrogenation than for enantioselective hydrogenation, but provided the highest value of the enantiomeric excess 39%. Kinematics of reaction are reported. Exchange of H for D in 10,11-dihydrocinchonidine at room temperature over Ir/CaCO{sub 3} occurred in the quinoline moiety but not in the quinuclidine ring system, indicating that the alkaloid was adsorbed to the Ir surface via the interaction of its {pi}-electron system. For both silica-supported and calcium carbonate-supported Ir, the presence of chloride ion in the catalyst was advantageous for the achievement of enantioselectivity. 25 refs., 2 figs., 3 tabs.

  10. Mechanochemical Iridium(III)-Catalyzed C-H Bond Amidation of Benzamides with Sulfonyl Azides under Solvent-Free Conditions in a Ball Mill.

    PubMed

    Hermann, Gary N; Becker, Peter; Bolm, Carsten

    2016-03-01

    Mechanochemical conditions have been applied to an iridium(III)-catalyzed C-H bond amidation process for the first time. In the absence of solvent, the mechanochemical activation enables the formation of an iridium species that catalyzes the ortho-selective amidation of benzamides with sulfonyl azides as the nitrogen source. As the reaction proceeds in the absence of organic solvents without external heating and yields the desired products in excellent yields within short reaction times, this method constitutes a powerful, fast, and environmentally benign alternative to the common solvent-based standard approaches.

  11. Donor-Flexible Nitrogen Ligands for Efficient Iridium-Catalyzed Water Oxidation Catalysis.

    PubMed

    Navarro, Miquel; Li, Mo; Müller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2016-05-10

    A pyridylideneamide ligand with variable donor properties owing to a pronounced zwitterionic and a neutral diene-type resonance structure was used as a dynamic ligand at a Cp* iridium center to facilitate water oxidation catalysis, a reaction that requires the stabilization of a variety of different iridium oxidation states and that is key for developing an efficient solar fuel device. The ligand imparts high activity (nearly three-fold increase of turnover frequency compared to benchmark systems), and exceptionally high turnover numbers, which indicate a robust catalytic cycle and little catalyst degradation.

  12. Enantioselective Rh-Catalyzed Carboacylation of C═N Bonds via C-C Activation of Benzocyclobutenones.

    PubMed

    Deng, Lin; Xu, Tao; Li, Hongbo; Dong, Guangbin

    2016-01-13

    Herein we describe the first enantioselective Rh-catalyzed carboacylation of oximes (imines) via C-C activation. In this transformation, the benzocyclobutenone C1-C2 bond is selectively activated by a low valent rhodium catalyst and subsequently the resulting two Rh-C bonds add across a C═N bond, which provides a unique approach to access chiral lactams. A range of polycyclic nitrogen-containing scaffolds were obtained in good yields with excellent enantioselectivity. Further derivatization of the lactam products led to a rapid entry to various novel fused heterocycles.

  13. Cu-catalyzed esterification reaction via aerobic oxygenation and C-C bond cleavage: an approach to α-ketoesters.

    PubMed

    Zhang, Chun; Feng, Peng; Jiao, Ning

    2013-10-01

    The Cu-catalyzed novel aerobic oxidative esterification reaction of 1,3-diones for the synthesis of α-ketoesters has been developed. This method combines C-C σ-bond cleavage, dioxygen activation and oxidative C-H bond functionalization, as well as provides a practical, neutral, and mild synthetic approach to α-ketoesters which are important units in many biologically active compounds and useful precursors in a variety of functional group transformations. A plausible radical process is proposed on the basis of mechanistic studies.

  14. Enantioselective Rh-Catalyzed Carboacylation of C═N Bonds via C-C Activation of Benzocyclobutenones.

    PubMed

    Deng, Lin; Xu, Tao; Li, Hongbo; Dong, Guangbin

    2016-01-13

    Herein we describe the first enantioselective Rh-catalyzed carboacylation of oximes (imines) via C-C activation. In this transformation, the benzocyclobutenone C1-C2 bond is selectively activated by a low valent rhodium catalyst and subsequently the resulting two Rh-C bonds add across a C═N bond, which provides a unique approach to access chiral lactams. A range of polycyclic nitrogen-containing scaffolds were obtained in good yields with excellent enantioselectivity. Further derivatization of the lactam products led to a rapid entry to various novel fused heterocycles. PMID:26674855

  15. Enantioselective allylic substitution of cinnamyl esters catalyzed by iridium-chiral aryl phosphite complex: conspicuous change in the mechanistic spectrum by a countercation and solvent.

    PubMed

    Kinoshita, Naosumi; Marx, Karsten H; Tanaka, Kiyoshi; Tsubaki, Kazunori; Kawabata, Takeo; Yoshikai, Naohiko; Nakamura, Eiichi; Fuji, Kaoru

    2004-11-12

    Iridium-catalyzed asymmetric allylic alkylation of monoaryl substrates 4-6 with chiral phosphites 1-3 has been investigated. Although branched isomers were formed with high regioselectivities, the enantioselectivities of these products were remarkably influenced by solvents, countercations, and additives (ZnCl(2) and LiCl).

  16. Synthesis of 2H-Azirines by Iridium-Catalyzed Decarboxylative Ring Contraction of Isoxazol-5(4H)-ones.

    PubMed

    Okamoto, Kazuhiro; Shimbayashi, Takuya; Yoshida, Masato; Nanya, Atsushi; Ohe, Kouichi

    2016-06-13

    A phosphine-free iridium-catalyzed reaction of isoxazol-5(4H)-ones (isoxazolones) has been developed, and affords 2H-azirines through decarboxylation and ring contraction. This method provides an efficient and environmentally benign protocol which could replace the conventional approaches used to synthesize 2H-azirines. PMID:27125870

  17. Synthesis of 2H-Azirines by Iridium-Catalyzed Decarboxylative Ring Contraction of Isoxazol-5(4H)-ones.

    PubMed

    Okamoto, Kazuhiro; Shimbayashi, Takuya; Yoshida, Masato; Nanya, Atsushi; Ohe, Kouichi

    2016-06-13

    A phosphine-free iridium-catalyzed reaction of isoxazol-5(4H)-ones (isoxazolones) has been developed, and affords 2H-azirines through decarboxylation and ring contraction. This method provides an efficient and environmentally benign protocol which could replace the conventional approaches used to synthesize 2H-azirines.

  18. Effects of Molecular Oxygen, Solvent, and Light on Iridium-Photoredox/Nickel Dual-Catalyzed Cross-Coupling Reactions.

    PubMed

    Oderinde, Martins S; Varela-Alvarez, Adrian; Aquila, Brian; Robbins, Daniel W; Johannes, Jeffrey W

    2015-08-01

    In order to achieve reproducibility during iridium-photoredox and nickel dual-catalyzed sp(3)-sp(2) carbon-carbon bond-forming reactions, we investigated the role that molecular oxygen (O2), solvent and light-source (CF lamp or blue LED) play in a variety of Ir-photoredox mediated transformations. The presence of O2 was discovered to be important for catalyst activation when air-stable Ni(II) precatalysts were used in DMF under CF lamp irradiation; however, O2 was not required for catalysis when conducted with Ni(COD)2 in the same reaction system. O2 is believed to promote rapid reduction of the Ni(II) precatalyst by Ir(II) to Ni(0). In addition to O2, the effects that solvent and light-source have on the dual-catalyzed decarboxylative cross-coupling reactions will be discussed. These findings have enabled us to develop a more robust dual-catalyzed decarboxylative cross-coupling protocol.

  19. Silver-catalyzed C-C bond formation between methane and ethyl diazoacetate in supercritical CO₂.

    PubMed

    Caballero, Ana; Despagnet-Ayoub, Emmanuelle; Díaz-Requejo, M Mar; Díaz-Rodríguez, Alba; González-Núñez, María Elena; Mello, Rossella; Muñoz, Bianca K; Ojo, Wilfried-Solo; Asensio, Gregorio; Etienne, Michel; Pérez, Pedro J

    2011-05-13

    Even in the context of hydrocarbons' general resistance to selective functionalization, methane's volatility and strong bonds pose a particular challenge. We report here that silver complexes bearing perfluorinated indazolylborate ligands catalyze the reaction of methane (CH(4)) with ethyl diazoacetate (N(2)CHCO(2)Et) to yield ethyl propionate (CH(3)CH(2)CO(2)Et). The use of supercritical carbon dioxide (scCO(2)) as the solvent is key to the reaction's success. Although the catalyst is only sparingly soluble in CH(4)/CO(2) mixtures, optimized conditions presently result in a 19% yield of ethyl propionate (based on starting quantity of the diazoester) at 40°C over 14 hours.

  20. Branch-Selective Alkene Hydroarylation by Cooperative Destabilization: Iridium-Catalyzed ortho-Alkylation of Acetanilides.

    PubMed

    Crisenza, Giacomo E M; Sokolova, Olga O; Bower, John F

    2015-12-01

    An iridium(I) catalyst system, modified with the wide-bite-angle and electron-deficient bisphosphine d(F) ppb (1,4-bis(di(pentafluorophenyl)phosphino)butane) promotes highly branch-selective hydroarylation reactions between diverse acetanilides and aryl- or alkyl-substituted alkenes. This provides direct and ortho-selective access to synthetically challenging anilines, and addresses long-standing issues associated with related Friedel-Crafts alkylations. PMID:26490739

  1. Branch-Selective Alkene Hydroarylation by Cooperative Destabilization: Iridium-Catalyzed ortho-Alkylation of Acetanilides

    PubMed Central

    Crisenza, Giacomo E M; Sokolova, Olga O; Bower, John F

    2015-01-01

    An iridium(I) catalyst system, modified with the wide-bite-angle and electron-deficient bisphosphine dFppb (1,4-bis(di(pentafluorophenyl)phosphino)butane) promotes highly branch-selective hydroarylation reactions between diverse acetanilides and aryl- or alkyl-substituted alkenes. This provides direct and ortho-selective access to synthetically challenging anilines, and addresses long-standing issues associated with related Friedel–Crafts alkylations. PMID:26490739

  2. Asymmetric Iridium-Catalyzed C-C Coupling of Chiral Diols via Site-Selective Redox-Triggered Carbonyl Addition.

    PubMed

    Shin, Inji; Krische, Michael J

    2016-01-01

    Cyclometalated π-allyliridium C,O-benzoate complexes modified by axially chiral chelating phosphine ligands display a pronounced kinetic preference for primary alcohol dehydrogenation, enabling highly site-selective redox-triggered carbonyl additions of chiral primary-secondary 1,3-diols with exceptional levels of catalyst-directed diastereoselectivity. Unlike conventional methods for carbonyl allylation, the present redox-triggered alcohol C-H functionalizations bypass the use of protecting groups, premetalated reagents, and discrete alcohol-to-aldehyde redox reactions.

  3. Cyclometalated iridium complexes of bis(aryl) phosphine ligands: catalytic C-H/C-D exchanges and C-C coupling reactions.

    PubMed

    Campos, Jesús; Espada, María F; López-Serrano, Joaquín; Carmona, Ernesto

    2013-06-01

    This work details the synthesis and structural identification of a series of complexes of the (η(5)-C5Me5)Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine ligands, PR'(Ar)2, for R' = Me and Ar = 2,4,6-Me3C6H2, 1b; 2,6-Me2-4-OMe-C6H2, 1c; 2,6-Me2-4-F-C6H2, 1d; R' = Et, Ar = 2,6-Me2C6H3, 1e. Both chloride- and hydride-containing compounds, 2b-2e and 3b-3e, respectively, are described. Reactions of chlorides 2 with NaBArF (BArF = B(3,5-C6H3(CF3)2)4) in the presence of CO form cationic carbonyl complexes, 4(+), with ν(CO) values in the narrow interval 2030-2040 cm(-1), indicating similar π-basicity of the Ir(III) center of these complexes. In the absence of CO, NaBArF forces κ(4)-P,C,C',C″ coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C-C coupling reaction converts the κ(4) species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using CD3OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3 experience only D incorporation into the Ir-H and Ir-CH2 sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported. PMID:23675910

  4. Iridium/Copper Co-catalyzed Anti-Stereoselective Ring Opening of Oxabenzonorbornadienes with Grignard Reagents.

    PubMed

    Cheng, Guo; Yang, Wen; Li, Yue; Yang, Dingqiao

    2016-09-01

    Cooperative catalysis has been widely considered as one of the most powerful strategies to improve synthetic efficiency. A new iridium/copper cocatalyst was developed for the ring-opening reaction of oxabenzonorbornadienes with a wide variety of Grignard reagents, which afforded the corresponding anti-2-substituted 1,2-dihydronaphthalen-1-ols in high yields (up to 99% yield) under mild conditions. The effects of catalyst loading, Lewis acid, Grignard reagent loading, and reaction temperature on the yield were investigated. To the best of our knowledge, it represents the first example of ring-opening reactions of oxabicyclic alkenes with Grignard reagent nucleophiles in a trans-stereoselective manner. PMID:27455165

  5. Iridium(III)-Catalyzed Regioselective Intermolecular Unactivated Secondary Csp(3) -H Bond Amidation.

    PubMed

    Xiao, Xinsheng; Hou, Cheng; Zhang, Zhenhui; Ke, Zhuofeng; Lan, Jianyong; Jiang, Huanfeng; Zeng, Wei

    2016-09-19

    For the first time, a highly regioselective intermolecular sulfonylamidation unactivated secondary Csp(3) -H bond has been achieved using Ir(III) catalysts. The introduced N,N'-bichelating ligand plays a crucial role in enabling iridium-nitrene insertion into a secondary Csp(3) -H bond via an outer-sphere pathway. Mechanistic studies and density functional theory (DFT) calculations demonstrated that a two-electron concerted nitrene insertion was involved in this Csp(3) -H amidation process. This method tolerates a broad range of linear and branched-chain N-alkylamides, and provides efficient access to diverse γ-sulfonamido-substituted aliphatic amines. PMID:27561950

  6. Transition-metal catalyzed oxidative cross-coupling reactions to form C-C bonds involving organometallic reagents as nucleophiles.

    PubMed

    Shi, Wei; Liu, Chao; Lei, Aiwen

    2011-05-01

    Transition-metal-catalyzed coupling reactions have become a versatile tool for chemical bond formation. From the variation of the coupling partners, coupling reactions can be classified into three models: traditional coupling, reductive coupling and oxidative coupling. The oxidative coupling, which is different from the traditional coupling, occurs between two nucleophiles. This critical review focuses on transition-metal-catalyzed oxidative coupling reactions involving organometallic reagents as nucleophiles. Since the scope of the oxidative coupling is highly diversified, this paper only reviews the oxidative coupling reactions concerning C-C bond formation, including the coupling between organometal reagents and hydrocarbons as well as coupling between two organometal reagents. Since terminal alkynes are normally activated by metal salts and in situ form the alkynyl metal reagents in coupling reactions, they are directly considered as organometal reagents in this review. Intramolecular oxidative couplings and oxidative cyclizations are not included in this critical review. Moreover, there are many examples of oxidative coupling leading to the formation of functional materials, such as the oxidative polymerization of thiophenes. Since several reviews in these areas have been published they are not included in this review either (99 references).

  7. Iridium-catalyzed hydrogen production from monosaccharides, disaccharide, cellulose, and lignocellulose.

    PubMed

    Li, Yang; Sponholz, Peter; Nielsen, Martin; Junge, Henrik; Beller, Matthias

    2015-03-01

    Hydrogen constitutes an important feedstock for clean-energy technologies as well as for production of bulk and fine chemicals. Hence, the development of novel processes to convert easily available biomass into H2 is of general interest. Herein, we demonstrate a one-pot protocol hydrogen generation from monosaccharides, disaccharide, and extremely demanding cellulose and lignocellulose substrates by using a pincer-type iridium catalyst. Applying ppm amounts of this catalyst, hydrogen is produced at temperatures lower than 120 °C. More specifically, catalyst turnover numbers (TONs) for lignocellulose from bamboo reached up to about 3000. Interestingly, even (used) cigarette filters, which are composed of cellulose acetate, produce hydrogen under optimized conditions.

  8. Iridium-catalyzed reductive carbon-carbon bond cleavage reaction on a curved pyridylcorannulene skeleton.

    PubMed

    Tashiro, Shohei; Yamada, Mihoko; Shionoya, Mitsuhiko

    2015-04-27

    The cleavage of CC bonds in π-conjugated systems is an important method for controlling their shape and coplanarity. An efficient way for the cleavage of an aromatic CC bond in a typical buckybowl corannulene skeleton is reported. The reaction of 2-pyridylcorannulene with a catalytic amount of IrCl3 ⋅n H2 O in ethylene glycol at 250 °C resulted in a structural transformation from the curved corannulene skeleton to a strain-free flat benzo[ghi]fluoranthene skeleton through a site-selective CC cleavage reaction. This cleavage reaction was found to be driven by both the coordination of the 2-pyridyl substituent to iridium and the relief of strain in the curved corannulene skeleton. This finding should facilitate the design of carbon nanomaterials based on CC bond cleavage reactions.

  9. Assessment of density functional methods for reaction energetics: iridium-catalyzed water oxidation as case study.

    PubMed

    Kazaryan, Andranik; Baerends, Evert Jan

    2013-04-01

    We investigate basis set convergence for a series of density functional theory (DFT) functionals (both hybrid and nonhybrid) and compare to coupled-cluster with single and double excitations and perturbative triples [CCSD(T)] benchmark calculations. The case studied is the energetics of the water oxidation reaction by an iridium-oxo complex. Complexation energies for the reactants and products complexes as well as the transition state (TS) energy are considered. Contrary to the expectation of relatively weak basis set dependence for DFT, the basis set effects are large, for example, more than 10 kcal mol(-1) difference from converged basis for the activation energy with "small" basis sets (DZ/6-31G** for Ir/other atoms, or SVP) and still more than 6 kcal mol(-1) for def2-TZVPP/6-31G**. Inclusion of the dispersion correction in DFT-D3 schemes affects the energies of reactant complex (RC), TS, and product complex (PC) by almost the same amount; it significantly improves the complexation energy (the formation of RC), but has little effect on the activation energy with respect to RC. With converged basis, some pure GGAs (PBE-D3, BP86-D3) as well as the hybrid functional B3LYP-D3 are very accurate compared to benchmark CCSD(T) calculations.

  10. Total synthesis of protosappanin A and its derivatives via palladium catalyzed ortho C-H activation/C-C cyclization under microwave irradiation.

    PubMed

    Liu, Jiaqi; Zhou, Xuan; Wang, Chenglong; Fu, Wanyong; Chu, Wenyi; Sun, Zhizhong

    2016-04-14

    A total synthesis method for protosappanin A, which is a complex natural product with many biological activities, was developed with 6 linear steps. Dibenzo[b,d]oxepinones as the key intermediates of the synthetic route were prepared by a palladium-catalyzed ortho C-H activation/C-C cyclization under microwave irradiation. 25 derivatives of protosappanin A were obtained. PMID:26997503

  11. Iodobenzene-catalyzed oxabicyclo[3.2.1]octane and [4.2.1]nonane synthesis via cascade C-O/C-C formation.

    PubMed

    Ngatimin, Marsewi; Frey, Raphael; Levens, Alison; Nakano, Yuji; Kowalczyk, Marcin; Konstas, Kristina; Hutt, Oliver E; Lupton, David W

    2013-11-15

    Iodobenzene-catalyzed 1,2-olefin functionalization via C-C and C-O bond formation has been achieved with electron rich aromatic groups and vinylogous esters acting as independent nucleophiles. The reaction provides oxabicyclo[3.2.1]octanes and [4.2.1]nonanes from commercially available 3-alkoxy cycohexen-2-ones in three steps.

  12. Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

    SciTech Connect

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

    Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has

  13. Iridium-Catalyzed Enantioselective Allylic Substitution of Enol Silanes from Vinylogous Esters and Amides.

    PubMed

    Chen, Ming; Hartwig, John F

    2015-11-01

    The enol silanes of vinylogous esters and amides are classic dienes for Diels-Alder reactions. Here, we report their reactivity as nucleophiles in Ir-catalyzed, enantioselective allylic substitution reactions. A variety of allylic carbonates react with these nucleophiles to give allylated products in good yields with high enantioselectivities and excellent branched-to-linear ratios. These reactions occur with KF or alkoxide as the additive, but mechanistic studies suggest that these additives do not activate the enol silanes. Instead, they serve as bases to promote the cyclometalation to generate the active Ir catalyst. The carbonate anion, which was generated from the oxidative addition of the allylic carbonate, likely activates the enol silanes to trigger their activity as nucleophiles for reactions with the allyliridium electrophile. The synthetic utility of this method was illustrated by the synthesis of the anti-muscarinic drug, fesoterodine. PMID:26441002

  14. Iridium-catalyzed ortho-selective C-H silylation of aromatic compounds directed toward the synthesis of π-conjugated molecules with Lewis acid-base interaction.

    PubMed

    Wakaki, Takayuki; Kanai, Motomu; Kuninobu, Yoichiro

    2015-04-01

    We successfully developed an iridium-catalyzed ortho-selective C-H silylation of aromatic compounds. The reaction exhibited a wide substrate scope, and a variety of π-conjugated molecules were synthesized in good to excellent yields, even in gram scale. Several silyl groups could also be introduced into the products. The experimental results indicated that the regioselectivity could be controlled by a Lewis acid-base interaction between the Lewis acidic silicon atoms of fluorinated hydrosilanes and the Lewis basic nitrogen atoms of aromatic compounds.

  15. Efficient synthesis of pyrrolo[1,2-a]quinoxalines catalyzed by a Brønsted acid through cleavage of C-C bonds.

    PubMed

    Xie, Caixia; Feng, Lei; Li, Wanli; Ma, Xiaojun; Ma, Xinkun; Liu, Yihan; Ma, Chen

    2016-09-28

    An efficient and convenient one-pot domino reaction for the direct synthesis of pyrrolo[1,2-a]quinoxalines has been developed. This approach utilizes an imine formation reaction, SEAr reaction and cleavage of C-C bonds catalyzed by a Brønsted acid. β-Diketones and β-keto esters are both well tolerated to give the corresponding products in moderate to excellent yields. PMID:27541576

  16. Ruthenium-Catalyzed Transfer Hydrogenation for C-C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs.

    PubMed

    Perez, Felix; Oda, Susumu; Geary, Laina M; Krische, Michael J

    2016-06-01

    Merging the chemistry of transfer hydrogenation and carbonyl or imine addition, a broad new family of redox-neutral or reductive hydrohydroxyalkylations and hydroaminomethylations have been developed. In these processes, hydrogen redistribution between alcohols and π-unsaturated reactants is accompanied by C-C bond formation, enabling direct conversion of lower alcohols to higher alcohols. Similarly, hydrogen redistribution between amines to π-unsaturated reactants results in direct conversion of lower amines to higher amines. Alternatively, equivalent products of hydrohydroxyalkylation and hydroaminomethylation may be generated through the reaction of carbonyl compounds or imines with π-unsaturated reactants under the conditions of 2-propanol-mediated reductive coupling. Finally, using vicinally dioxygenated reactants, that is, diol, ketols, or diones, successive transfer hydrogenative coupling occurs to generate 2 C-C bonds, resulting in products of formal [4+2] cycloaddition. PMID:27573275

  17. CYP96T1 of Narcissus sp. aff. pseudonarcissus Catalyzes Formation of the Para-Para' C-C Phenol Couple in the Amaryllidaceae Alkaloids

    PubMed Central

    Kilgore, Matthew B.; Augustin, Megan M.; May, Gregory D.; Crow, John A.; Kutchan, Toni M.

    2016-01-01

    The Amaryllidaceae alkaloids are a family of amino acid derived alkaloids with many biological activities; examples include haemanthamine, haemanthidine, galanthamine, lycorine, and maritidine. Central to the biosynthesis of the majority of these alkaloids is a C-C phenol-coupling reaction that can have para-para', para-ortho', or ortho-para' regiospecificity. Through comparative transcriptomics of Narcissus sp. aff. pseudonarcissus, Galanthus sp., and Galanthus elwesii we have identified a para-para' C-C phenol coupling cytochrome P450, CYP96T1, capable of forming the products (10bR,4aS)-noroxomaritidine and (10bS,4aR)-noroxomaritidine from 4′-O-methylnorbelladine. CYP96T1 was also shown to catalyzed formation of the para-ortho' phenol coupled product, N-demethylnarwedine, as less than 1% of the total product. CYP96T1 co-expresses with the previously characterized norbelladine 4′-O-methyltransferase. The discovery of CYP96T1 is of special interest because it catalyzes the first major branch in Amaryllidaceae alkaloid biosynthesis. CYP96T1 is also the first phenol-coupling enzyme characterized from a monocot. PMID:26941773

  18. An Electron-Poor C64 Nanographene by Palladium-Catalyzed Cascade C-C Bond Formation: One-Pot Synthesis and Single-Crystal Structure Analysis.

    PubMed

    Seifert, Sabine; Shoyama, Kazutaka; Schmidt, David; Würthner, Frank

    2016-05-23

    Herein, we report the one-pot synthesis of an electron-poor nanographene containing dicarboximide groups at the corners. We efficiently combined palladium-catalyzed Suzuki-Miyaura cross-coupling and dehydrohalogenation to synthesize an extended two-dimensional π-scaffold of defined size in a single chemical operation starting from N-(2,6-diisopropylphenyl)-4,5-dibromo-1,8-naphthalimide and a tetrasubstituted pyrene boronic acid ester as readily accessible starting materials. The reaction of these precursors under the conditions commonly used for Suzuki-Miyaura cross-coupling afforded a C64 nanographene through the formation of ten C-C bonds in a one-pot process. Single-crystal X-ray analysis unequivocally confirmed the structure of this unique extended aromatic molecule with a planar geometry. The optical and electrochemical properties of this largest ever synthesized planar electron-poor nanographene skeleton were also analyzed.

  19. Osmium(0)-Catalyzed C-C Coupling of Ethylene and α-Olefins with Diols, Ketols, or Hydroxy Esters via Transfer Hydrogenation.

    PubMed

    Park, Boyoung Y; Luong, Tom; Sato, Hiroki; Krische, Michael J

    2016-09-16

    Osmium(0) complexes derived from Os3(CO)12 and XPhos (2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl) catalyze the C-C coupling of α-hydroxy esters 1a-1i, α-ketols 1j-1o, or 1,2-diols dihydro-1j-1o with ethylene 2a to form ethylated tertiary alcohols 3a-3o. As illustrated in couplings of 1-octene 2b with vicinally dioxygenated reactants 1a, 1b, 1i, 1j, 1k, 1m, higher α-olefins are converted to adducts 4a, 4b, 4i, 4j, 4k, 4m with complete levels of branched regioselectivity. Oxidation level independent C-C coupling is demonstrated by the reaction of 1-octene 2b with diol dihydro-1k, α-ketol 1k, and dione dehydro-1k. Functionalized olefins 2c-2f react with ethyl mandelate 1a to furnish adducts 5a-8a as single regioisomers. The collective data, including deuterium labeling studies, are consistent with a catalytic mechanism involving olefin-dione oxidative coupling to form an oxa-osmacyclopentane, which upon reductive cleavage via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-alkylation with regeneration of the ketone. Single-crystal X-ray diffraction data of the dinuclear complex Os2(CO)4(O2CR)2(XPhos)2 and the trinuclear complex Os3(CO)11(XPhos) are reported. These studies suggest increased π-backbonding at the stage of the metal-olefin π-complex plays a critical role in facilitating alkene-carbonyl oxidative coupling, as isostructural ruthenium(0) complexes, which are weaker π-donors, do not catalyze the transformations reported herein. PMID:27580269

  20. Selective iridium-catalyzed alkylation of (hetero)aromatic amines and diamines with alcohols under mild reaction conditions.

    PubMed

    Blank, Benoît; Michlik, Stefan; Kempe, Rhett

    2009-01-01

    A P,N-ligand-coordinated iridium complex has been employed as an efficient catalyst for the selective monoalkylation of (hetero)aromatic amines with alcohols. A significant improvement of this alkylation method has been achieved, such that it can be performed at a temperature of 70 degrees C and with catalyst loadings as low as 0.1 mol % Ir, while still affording excellent yields of secondary amines. Furthermore, the high selectivity of this catalyst for the monoalkylation of aromatic amino functions has been successfully exploited for the alkylation of diamines in both symmetric and nonsymmetric fashions, providing a novel and very efficient synthetic tool for the preparation of N,N'-dialkylated aromatic diamines.

  1. Asymmetric synthesis of allylic sulfonic acids: enantio- and regioselective iridium-catalyzed allylations of Na2SO3.

    PubMed

    Liu, Wei; Zhao, Xiao-ming; Zhang, Hong-bo; Zhang, Liang; Zhao, Ming-zhu

    2014-12-15

    An enantioselective allylation reaction of allylic carbonates with sodium sulfite (Na2 SO3 ) catalyzed by Ir complex was accomplished, providing allylic sulfonic acids in good to excellent yields with a high level of enantio- and regioselectivities. (R)-2-Phenyl-2-sulfoacetic acid, a key intermediate for the synthesis of Cefsulodin and Sulbenicillin, was synthesized as well.

  2. Asymmetric synthesis of allylic sulfonic acids: enantio- and regioselective iridium-catalyzed allylations of Na2SO3.

    PubMed

    Liu, Wei; Zhao, Xiao-ming; Zhang, Hong-bo; Zhang, Liang; Zhao, Ming-zhu

    2014-12-15

    An enantioselective allylation reaction of allylic carbonates with sodium sulfite (Na2 SO3 ) catalyzed by Ir complex was accomplished, providing allylic sulfonic acids in good to excellent yields with a high level of enantio- and regioselectivities. (R)-2-Phenyl-2-sulfoacetic acid, a key intermediate for the synthesis of Cefsulodin and Sulbenicillin, was synthesized as well. PMID:25367779

  3. Mechanistic studies of the transfer dehydrogenation of cyclooctane catalyzed by iridium bis(phosphinite) p-XPCP pincer complexes.

    PubMed

    Göttker-Schnetmann, Inigo; Brookhart, Maurice

    2004-08-01

    Reaction of bis(phosphinite) PCP iridium pincer complexes (p-XPCP)IrHCl (5a-f) [X = MeO (5a), Me (5b), H (5c), F (5d), C(6)F(5) (5e), Ar(F)(= 3,5-bis(trifluoromethyl)phenyl) (5f)] with NaOtBu in neat cyclooctane (COA) generates 1:1 mixtures of the respective (p-XPCP)IrH(2) complexes 4a-f and the cyclooctene (COE) olefin complexes (p-XPCP)Ir(COE) (6a-f) at 23 degrees C. At higher temperatures, complexes 4 and 6 are equilibrated because of the degenerate transfer dehydrogenation of COA with free COE (6 + COA right harpoon over left harpoon 4 + 2COE), as was shown by temperature-dependent equilibrium constants and spin saturation transfer experiments at 80 degrees C. At this temperature, the COE complexes 6 exchange with free COE on the NMR time scale with the more electron-deficient complexes 6 exchanging COE faster. The exchange is dissociative and zero order in [COE]. Further analysis reveals that the stoichiometric hydrogenation of COE by complex 4f, and thus the separated back reaction 4f + 2COE --> 6f + COA proceeds at temperatures as low as -100 degrees C with the intermediacy of two isomeric complexes (p-Ar(F)PCP)Ir(H)(2)(COE) (8f, 8f'). COE deuteration with the perdeuterated complex 4f-d(38) at -100 degrees C results in hydrogen incorporation into the hydridic sites of complexes 8f,8f'-d(38) but not in the hydridic sites of complex 4f-d(38), thus rendering COE migratory insertion in complexes 8f,8f' reversible and COE coordination by complex 4f rate-determining for the overall COE deuteration.

  4. Synthesis of a-Alkylated Ketones via Tandem Acceptorless Dehydrogenation/a-Alkylation from Secondary and Primary Alcohols Catalyzed by Metal-Ligand Bifunctional Iridium Complex [Cp*Ir(2,2'-bpyO)(H2O)].

    PubMed

    Wang, Rongzhou; Ma, Juan; Li, Feng

    2015-11-01

    A new strategy for the synthesis of α-alkylated ketones via tandem acceptorless dehydrogenation/α-alkylation from secondary and primary alcohols was proposed and accomplished. In the presence of metal-ligand bifunctional iridium complex [Cp*Ir(2,2'-bpyO)(H2O)], various desirable products were obtained in high yields. Compared with previous methods for the direct dehydrogenative coupling of secondary alcohols with primary alcohols to α-alkylated ketones, this protocol has obvious advantages including complete selectivity for α-alkylated ketones and more environmentally benign conditions. Notably, the study also exhibited the potential to develop tandem reactions catalyzed using a metal-ligand bifunctional iridium complex. PMID:26428210

  5. Labile Cu(I) catalyst/spectator Cu(II) species in copper-catalyzed C-C coupling reaction: operando IR, in situ XANES/EXAFS evidence and kinetic investigations.

    PubMed

    He, Chuan; Zhang, Guanghui; Ke, Jie; Zhang, Heng; Miller, Jeffrey T; Kropf, Arthur J; Lei, Aiwen

    2013-01-01

    Insights toward the Cu-catalyzed C-C coupling reaction were investigated through operando IR and in situ X-ray absorption near-edge structure/extended X-ray absorption fine structure. It was found that the Cu(I) complex formed from the reaction of CuI with β-diketone nucleophile was liable under the cross-coupling conditions, which is usually considered as active catalytic species. This labile Cu(I) complex could rapidly disproportionate to the spectator Cu(II) and Cu(0) species under the reaction conditions, which was an off-cycle process. In this copper-catalyzed C-C coupling reaction, β-diketone might act both as the substrate and the ligand. PMID:23214954

  6. Cuprous Oxide Catalyzed Oxidative C-C Bond Cleavage for C-N Bond Formation: Synthesis of Cyclic Imides from Ketones and Amines.

    PubMed

    Wang, Min; Lu, Jianmin; Ma, Jiping; Zhang, Zhe; Wang, Feng

    2015-11-16

    Selective oxidative cleavage of a C-C bond offers a straightforward method to functionalize organic skeletons. Reported herein is the oxidative C-C bond cleavage of ketone for C-N bond formation over a cuprous oxide catalyst with molecular oxygen as the oxidant. A wide range of ketones and amines are converted into cyclic imides with moderate to excellent yields. In-depth studies show that both α-C-H and β-C-H bonds adjacent to the carbonyl groups are indispensable for the C-C bond cleavage. DFT calculations indicate the reaction is initiated with the oxidation of the α-C-H bond. Amines lower the activation energy of the C-C bond cleavage, and thus promote the reaction. New insight into the C-C bond cleavage mechanism is presented. PMID:26494312

  7. Alkyne-aldehyde reductive C-C coupling through ruthenium-catalyzed transfer hydrogenation: direct regio- and stereoselective carbonyl vinylation to form trisubstituted allylic alcohols in the absence of premetallated reagents.

    PubMed

    Leung, Joyce C; Patman, Ryan L; Sam, Brannon; Krische, Michael J

    2011-10-24

    Nonsymmetric 1,2-disubstituted alkynes engage in reductive coupling to a variety of aldehydes under the conditions of ruthenium-catalyzed transfer hydrogenation by employing formic acid as the terminal reductant and delivering the products of carbonyl vinylation with good to excellent levels of regioselectivity and with complete control of olefin stereochemistry. As revealed in an assessment of the ruthenium counterion, iodide plays an essential role in directing the regioselectivity of C-C bond formation. Isotopic labeling studies corroborate reversible catalytic propargyl C-H oxidative addition in advance of the C-C coupling, and demonstrate that the C-C coupling products do not experience reversible dehydrogenation by way of enone intermediates. This transfer hydrogenation protocol enables carbonyl vinylation in the absence of stoichiometric metallic reagents. PMID:21953608

  8. Bronsted-Evans-Polany relationships for C-C bond forming and C-C bond breaking reactions in thiamine-catalyzed decarboxylation of 2-keto acids using density functional theory.

    SciTech Connect

    Assary, R. S.; Broadbelt, L. J.; Curtiss, L. A.

    2012-01-01

    The concept of generalized enzyme reactions suggests that a wide variety of substrates can undergo enzymatic transformations, including those whose biotransformation has not yet been realized. The use of quantum chemistry to evaluate kinetic feasibility is an attractive approach to identify enzymes for the proposed transformation. However, the sheer number of novel transformations that can be generated makes this impractical as a screening approach. Therefore, it is essential to develop structure/activity relationships based on quantities that are more efficient to calculate. In this work, we propose a structure/activity relationship based on the free energy of binding or reaction of non-native substrates to evaluate the catalysis relative to that of native substrates. While Broensted-Evans-Polanyi (BEP) relationships such as that proposed here have found broad application in heterogeneous catalysis, their extension to enzymatic catalysis is limited. We report here on density functional theory (DFT) studies for C-C bond formation and C-C bond cleavage associated with the decarboxylation of six 2-keto acids by a thiamine-containing enzyme (EC 1.2.7.1) and demonstrate a linear relationship between the free energy of reaction and the activation barrier. We then applied this relationship to predict the activation barriers of 17 chemically similar novel reactions. These calculations reveal that there is a clear correlation between the free energy of formation of the transition state and the free energy of the reaction, suggesting that this method can be further extended to predict the kinetics of novel reactions through our computational framework for discovery of novel biochemical transformations.

  9. Ruthenium-catalyzed C-C coupling of fluorinated alcohols with allenes: dehydrogenation at the energetic limit of β-hydride elimination.

    PubMed

    Sam, Brannon; Luong, Tom; Krische, Michael J

    2015-04-27

    Ruthenium(II) complexes catalyze the CC coupling of 1,1-disubstituted allenes and fluorinated alcohols to form homoallylic alcohols bearing all-carbon quaternary centers with good to complete levels of diastereoselectivity. Whereas fluorinated alcohols are relatively abundant and tractable, the corresponding aldehydes are often not commercially available because of their instability.

  10. NAD(P)H-Independent Asymmetric C=C Bond Reduction Catalyzed by Ene Reductases by Using Artificial Co-substrates as the Hydrogen Donor

    PubMed Central

    Winkler, Christoph K; Clay, Dorina; Entner, Marcello; Plank, Markus; Faber, Kurt

    2014-01-01

    To develop a nicotinamide-independent single flavoenzyme system for the asymmetric bioreduction of C=C bonds, four types of hydrogen donor, encompassing more than 50 candidates, were investigated. Six highly potent, cheap, and commercially available co-substrates were identified that (under the optimized conditions) resulted in conversions and enantioselectivities comparable with, or even superior to, those obtained with traditional two-enzyme nicotinamide adenine dinucleotide phosphate (NAD(P)H)-recycling systems. PMID:24382795

  11. Metal-catalyzed C-C bond cleavage in alkanes: effects of methyl substitution on transition-state structures and stability.

    PubMed

    Flaherty, David W; Hibbitts, David D; Iglesia, Enrique

    2014-07-01

    Methyl substituents at C-C bonds influence hydrogenolysis rates and selectivities of acyclic and cyclic C2-C8 alkanes on Ir, Rh, Ru, and Pt catalysts. C-C cleavage transition states form via equilibrated dehydrogenation steps that replace several C-H bonds with C-metal bonds, desorb H atoms (H*) from saturated surfaces, and form λ H2(g) molecules. Activation enthalpies (ΔH(‡)) and entropies (ΔS(‡)) and λ values for (3)C-(x)C cleavage are larger than for (2)C-(2)C or (2)C-(1)C bonds, irrespective of the composition of metal clusters or the cyclic/acyclic structure of the reactants. (3)C-(x)C bonds cleave through α,β,γ- or α,β,γ,δ-bound transition states, as indicated by the agreement between measured activation entropies and those estimated for such structures using statistical mechanics. In contrast, less substituted C-C bonds involve α,β-bound species with each C atom bound to several surface atoms. These α,β configurations weaken C-C bonds through back-donation to antibonding orbitals, but such configurations cannot form with (3)C atoms, which have one C-H bond and thus can form only one C-M bond. (3)C-(x)C cleavage involves attachment of other C atoms, which requires endothermic C-H activation and H* desorption steps that lead to larger ΔH(‡) values but also larger ΔS(‡) values (by forming more H2(g)) than for (2)C-(2)C and (2)C-(1)C bonds, irrespective of alkane size (C2-C8) or cyclic/acyclic structure. These data and their mechanistic interpretation indicate that low temperatures and high H2 pressures favor cleavage of less substituted C-C bonds and form more highly branched products from cyclic and acyclic alkanes. Such interpretations and catalytic consequences of substitution seem also relevant to C-X cleavage (X = S, N, O) in desulfurization, denitrogenation, and deoxygenation reactions.

  12. Tailored synthesis of various nanomaterials by using a graphene-oxide-based gel as a nanoreactor and nanohybrid-catalyzed C-C bond formation.

    PubMed

    Biswas, Abhijit; Banerjee, Arindam

    2014-12-01

    New graphene oxide (GO)-based hydrogels that contain vitamin B2/B12 and vitamin C (ascorbic acid) have been synthesized in water (at neutral pH value). These gel-based soft materials have been used to synthesize various metal nanoparticles, including Au, Ag, and Pd nanoparticles, as well as nanoparticle-containing reduced graphene oxide (RGO)-based nanohybrid systems. This result indicates that GO-based gels can be used as versatile reactors for the synthesis of different nanomaterials and hybrid systems on the nanoscale. Moreover, the RGO-based nanohybrid hydrogel with Pd nanoparticles was used as an efficient catalyst for C-C bond-formation reactions with good yields and showed high recyclability in Suzuki-Miyaura coupling reactions. PMID:25224859

  13. Aliphatic C-C Bond Cleavage of α-Hydroxy Ketones by Non-Heme Iron(II) Complexes: Mechanistic Insight into the Reaction Catalyzed by 2,4'-Dihydroxyacetophenone Dioxygenase.

    PubMed

    Rahaman, Rubina; Paria, Sayantan; Paine, Tapan Kanti

    2015-11-16

    2,4'-Dihydroxyacetophenone dioxygenase (DAD) is a bacterial non-heme enzyme that carries out oxygenative aliphatic C-C bond cleavage of 2,4'-dihydroxyacetophenone (an α-hydroxy ketone) with the incorporation of both the oxygen atoms of dioxygen into the cleavage products. The crystal structure of the iron enzyme DAD has recently been determined, but very little is known about the mechanism of the C-C bond cleavage reaction. With the objective of gaining insights into the mechanism of the reaction catalyzed by DAD, six new biomimetic iron(II)-α-hydroxy ketone complexes, [(Tp(Ph2))Fe(II)(PHAP)] (1), [(Tp(Ph2))Fe(II)(HCH)] (2), [(Tp(Ph2))Fe(II)(HBME)] (3), [(Tp(Ph2))Fe(II)(CHPE)] (4), [(6-Me3-TPA)Fe(II)(PHAP)](+) (5), and [(6-Me3-TPA)Fe(II)(HCH)](+) (6) (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate, 6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine, PHAP-H = 2-phenyl-2-hydroxyacetophenone, HCH-H = 2-hydroxycyclohexanone, HBME-H = 2-hydroxy-1,2-bis(4-methoxyphenyl)ethanone, and CHPE-H = 1-(4-chlorophenyl)-2-hydroxy-2-phenylethanone), have been isolated and characterized. The single-crystal X-ray structure of 2 shows a five-coordinate iron(II) complex with one tridentate facial ligand and a monoanionic bidentate α-hydroxy ketone, resulting in a distorted-square-pyramidal coordination geometry at the iron center. The iron(II) complexes react with dioxygen to oxidatively cleave the aliphatic C-C bonds of the coordinated α-hydroxy ketones to afford 2 equiv of carboxylic acids. Mechanistic studies reveal that the C-C bond cleavage reaction proceeds through an intradiol pathway. Additionally, the coordinated α-hydroxy ketones in all of the complexes, except in complex 4, undergo two-electron oxidation to form the corresponding 1,2-diketones. However, the yields of 1,2-diketones are higher with the iron complexes of the tripodal N4 ligand (6-Me3-TPA) in comparison to the facial N3 ligand (Tp(Ph2)). These results strongly support the natural selection of a facial N3

  14. 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.

  15. 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.

  16. Refining Radchem Detectors: Iridium

    NASA Astrophysics Data System (ADS)

    Arnold, C. W.; Bredeweg, T. A.; Vieira, D. J.; Bond, E. M.; Jandel, M.; Rusev, G.; Moody, W. A.; Ullmann, J. L.; Couture, A. J.; Mosby, S.; O'Donnell, J. M.; Haight, R. C.

    2013-10-01

    Accurate determination of neutron fluence is an important diagnostic of nuclear device performance, whether the device is a commercial reactor, a critical assembly or an explosive device. One important method for neutron fluence determination, generally referred to as dosimetry, is based on exploiting various threshold reactions of elements such as iridium. It is possible to infer details about the integrated neutron energy spectrum to which the dosimetry sample or ``radiochemical detector'' was exposed by measuring specific activation products post-irradiation. The ability of radchem detectors like iridium to give accurate neutron fluence measurements is limited by the precision of the cross-sections in the production/destruction network (189Ir-193Ir). The Detector for Advanced Neutron Capture Experiments (DANCE) located at LANSCE is ideal for refining neutron capture cross sections of iridium isotopes. Recent results from a measurement of neutron capture on 193-Ir are promising. Plans to measure other iridium isotopes are underway.

  17. 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.

  18. 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.

  19. TiCl4 catalyzed tandem construction of C-C and C-O bonds: a simple and one-pot atom-economical stereoselective synthesis of spiro-oxindoles.

    PubMed

    Basavaiah, Deevi; Rao, Jamjanam Srivardhana; Reddy, Raju Jannapu; Rao, Anumolu Jaganmohan

    2005-05-28

    An atom-economical stereoselective synthesis of [{1-acetyl-5-methyl-6,8-dioxabicyclo(3.2.1)octane}-7-spiro-3'-(indolin-2'-one)] derivatives, containing both the oxindole and 6,8-dioxabicyclo(3.2.1)octane moieties via TiCl(4) catalyzed coupling of 2-acetyl-6-methyl-2,3-dihydro-4H-pyran with isatin derivatives is described.

  20. 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.

  1. 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.

  2. Copper-catalyzed domino synthesis of 2-imino-1H-imidazol-5(2H)-ones and quinoxalines involving C-C bond cleavage with a 1,3-dicarbonyl unit as a leaving group.

    PubMed

    Yang, Yan; Ni, Fan; Shu, Wen-Ming; Wu, An-Xin

    2014-09-01

    Although 2-imino-1H-imidazol-5(2H)-ones have important biological activities in metabolism, their synthesis has rarely been investigated. Quinoxalines as "privileged scaffolds" in medicinal chemistry have been extensively investigated, but the development of novel and efficient synthetic methods remains very attractive. Herein, we have developed two copper-catalyzed domino reactions for the synthesis of 2-imino-1H-imidazol-5(2H)-ones and quinoxalines involving CC bond-cleavage with a 1,3-dicarbonyl unit as a leaving group. The domino sequence for the synthesis of 2-imino-1H-imidazol-5(2H)-ones includes aza-Michael addition, intramolecular cyclization, CC bond-cleavage, 1,2-rearrangement, and aerobic dehydrogenation reaction, whereas the domino sequence for the synthesis of quinoxalines includes aza-Michael addition, intramolecular cyclization, elimination reaction, and CC bond-cleavage reaction. The two domino reactions have significant advantages including high efficiency, mild reaction conditions, and high tolerance of various functional groups. PMID:25079446

  3. Solar abundance of iridium

    PubMed Central

    Drake, Stephen; Aller, Lawrence H.

    1976-01-01

    By a method of spectrum synthesis, which yields log gfA, where g is the statistical weight of the lower level, f is the oscillator strength, and A is the abundance, an attempt is made to deduce the solar iridium abundance from one relatively unblended, but fairly weak IrI line, λ 3220.78 Å. If the Corliss-Bozman f-value for this line is adopted, we find log A(Ir) = 0.82 on the scale log A(H) = 12.00. The discordance with the value found from carbonaceous chondrites may arise from faulty f-values or from difficulties arising from line blending in this far ultraviolet domain of the solar spectrum. PMID:16578735

  4. Iridium complexes of new NCP pincer ligands: catalytic alkane dehydrogenation and alkene isomerization.

    PubMed

    Jia, Xiangqing; Zhang, Lei; Qin, Chuan; Leng, Xuebing; Huang, Zheng

    2014-09-28

    Iridium complexes of novel NCP pincer ligands containing pyridine and phosphinite arms have been synthesized. One Ir complex shows good catalytic activity for alkane dehydrogenation, and all complexes are highly active for olefin isomerization. A combination of the Ir complex and a (PNN)Fe pincer complex catalyzes the formation of linear alkylboronates selectively from internal olefins via sequential olefin isomerization-hydroboration.

  5. 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.

  6. Toward the Digital Electrochemical Recognition of Cobalt, Iridium, Nickel, and Iron Ion Collisions by Catalytic Amplification.

    PubMed

    Dick, Jeffrey E; Bard, Allen J

    2016-07-13

    We report the electrochemical detection of femtomolar amounts of cobalt, iridium, nickel, and iron ions in solution by electrocatalyst formation and amplification. The metal oxides of these ions can be formed electrochemically and can catalyze the oxidation of water. Alternatively, the reduction of metal ions to metals, such as the reduction of IrCl6(3-) to iridium, is capable of electrocatalytically reducing protons to molecular hydrogen, as shown previously with Pt. These events, which manifest themselves in amperometry, correspond to the formation of electrocatalytic nuclei on the electrode surface, capable of electrocatalytically oxidizing water or reducing protons. An analysis of the frequency of anodic blips compared to theory implies that the requirement for water oxidation is 10 ± 1 ions of cobalt, 13 ± 4 ions of iridium, and 11 ± 3 ions of nickel. A similar analysis for iridium reduction and the corresponding catalytic reduction of protons implies that 6 ± 2 ions of iridium are required for proton reduction. These numbers are confirmed in an analysis of the time of first nucleation event, i.e. the time at which the first blip on the amperometric i-t experiment occurs. We further show that the anodic blips in detecting nickel increase in intensity upon increasing amounts of iron ions in solution to a ratio of Ni/Fe of ∼5, surprisingly close to that for bulk electrocatalysts of Ni-Fe. PMID:27295309

  7. Alkali metal mediated C-C bond coupling reaction

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto

    2015-02-01

    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)2, have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)2, the structure of [Li(Bz)2]- was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C1-C1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results.

  8. Iridium complexes of new NCP pincer ligands: catalytic alkane dehydrogenation and alkene isomerization.

    PubMed

    Jia, Xiangqing; Zhang, Lei; Qin, Chuan; Leng, Xuebing; Huang, Zheng

    2014-09-28

    Iridium complexes of novel NCP pincer ligands containing pyridine and phosphinite arms have been synthesized. One Ir complex shows good catalytic activity for alkane dehydrogenation, and all complexes are highly active for olefin isomerization. A combination of the Ir complex and a (PNN)Fe pincer complex catalyzes the formation of linear alkylboronates selectively from internal olefins via sequential olefin isomerization-hydroboration. PMID:25101950

  9. 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.

  10. Electronic Structure of Iridium Clusters on Graphene

    NASA Astrophysics Data System (ADS)

    Barker, Bradford A.; Bradley, Aaron J.; Ugeda, Miguel M.; Coh, Sinisa; Zettl, Alex; Crommie, Michael F.; Cohen, Marvin L.; Louie, Steven G.

    2015-03-01

    Graphene was predicted to exhibit non-trivial Z2 topology, but its exceedingly weak spin-orbit coupling prevented this from being observed. Previous theoretical work has proposed enhancing the spin-orbit coupling strength by depositing individual adatoms adsorbed onto the surface of graphene. We show experimental evidence that the iridium adatoms cluster, with a cluster size of at least two atoms. We investigate through theoretical calculations the orientation of the iridium dimers on graphene, contrast the electronic structure of iridium dimers with iridium monomers, and compare the theoretical iridium dimer electronic structure calculations with the experimental results determined via scanning tunneling spectroscopy. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  11. Photolytic water oxidation catalyzed by a molecular carbene iridium complex.

    PubMed

    Petronilho, Ana; Rahman, Mahfujur; Woods, James A; Al-Sayyed, Haris; Müller-Bunz, Helge; Don MacElroy, J M; Bernhard, Stefan; Albrecht, Martin

    2012-11-14

    The complex IrCl(2)(Cp*)(trz) (trz = triazolylidene), 2, was prepared from readily available 1,3-dimethyl-4-phenyl-1,2,3-triazolium salt. Under basic conditions, the C-bound phenyl group readily cyclometalates, while under acidic conditions, cyclometalation is reversed. The sensitivity of the C(aryl)-Ir bond but not the C(trz)-Ir bond towards acidolysis provided a basis for using 2 as a catalyst in Ce(IV)-mediated water oxidation. The catalytic activity is characterized by a robust catalytic cycle, affording excellent turnover numbers (TON > 20,000). Under cerium-free conditions and in the presence of hematite as a photoelectrode, light-induced activity was observed. The photoelectrochemical reaction is strongly pH-dependent, which requires pH adjustments when running multiple cycle experiments to regenerate the catalytic activity. Analogous chelating complexes display better stability and higher catalytic activity than the monodentate complex 2.

  12. 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.

  13. Gold-Catalyzed Synthesis of Heterocycles

    NASA Astrophysics Data System (ADS)

    Arcadi, Antonio

    2014-04-01

    The following sections are included: * Introduction * Synthesis of Heterocycles via Gold-Catalyzed Heteroatom Addition to Unsaturated C-C Bonds * Synthesis of Heterocyclic Derivatives through Gold-Catalyzed Cyclization of Polyunsaturated Compounds * Synthesis of Heterocyclic Compounds via α-Oxo Gold Carbenoid * Synthesis of Heterocyclic Derivatives through Gold-Catalyzed Cycloaddition Reactions * Synthesis of Heterocyclic Derivatives through Gold-Catalyzed Activation of Carbonyl Groups and Alcohols * Synthesis of Heterocyclic Compounds through Gold-Mediated C-H Bond Functionalization * Gold-Catalyzed Domino Cyclization/Oxidative Coupling Reactions * Conclusions * References

  14. Salt passivation during anodic iridium dissolution in chloride melts

    SciTech Connect

    Saltykova, N.A.; Pechorskaya, L.S.; Baraboshkin, A.N.; Kotovskii, S.N.; Kosikhin, L.T.

    1986-11-01

    Anodic iridium dissolution in chloride melts at 500-700/sup 0/C was studied by potentiostatic, potentiodynamic, and galvanostatic techniques. It was found that an iridium anode is passivated by hexachloroiridates, first by the iridium (III) salt and at more positive potentials by the iridium (IV) salt. Values for anode resistance during passivation by salt films were calculated. It was shown that the morphology of the dissolving anode surface is determined by the value of polarization.

  15. 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.

  16. Laser spectroscopy of iridium monoboride

    NASA Astrophysics Data System (ADS)

    Ye, Jianjun; Pang, H. F.; Wong, A. M.-Y.; Leung, J. W.-H.; Cheung, A. S.-C.

    2008-04-01

    High resolution laser induced fluorescence spectrum of IrB in the spectral region between 545 and 610nm has been recorded and analyzed. Reacting laser-ablated iridium atoms with 1% B2H6 seeded in argon produced the IrB molecule. This is the first experimental observation of the IrB molecule. Four vibronic transition bands, (v,0) with v =0-3 of an electronic transition system, have been observed. Spectra of all four isotopic molecules, Ir191B10, Ir193B10, Ir191B11, and Ir193B11, were recorded. Isotopic relationships confirmed the carrier of the spectra and the vibrational quantum number assignment. Preliminary analysis of rotational lines showed that these vibronic bands are with Ω'=2 and Ω″=3. The electronic transition identified is assigned as the [16.5]Π23-XΔ33 system. Partially resolved hyperfine structure which conforms to the Hund's case aβ coupling scheme has been observed and analyzed. The bond length r0 of the lower XΔ33 state of IrB was determined to be 1.7675Å.

  17. 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.

  18. 100. Catalog HHistory 1, C.C.C., 34 Landscaping, Negative No. P ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    100. Catalog H-History 1, C.C.C., 34 Landscaping, Negative No. P 733c (Photographer and date unknown) SLOPE MAINTENANCE WORK BY CCC. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  19. 98. Catalog HHistory 1, C.C.C., 19 Tree Planting, Negative No. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    98. Catalog H-History 1, C.C.C., 19 Tree Planting, Negative No. P 474c (Photographer and date unknown) TRANSPLANTING TREE. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  20. 101. Catalog HHistory 1, C.C.C., 34 Landscaping, Negative No. 1340 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    101. Catalog H-History 1, C.C.C., 34 Landscaping, Negative No. 1340 (Photographer and date unknown) BANK BLENDING WORK BY CCC. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  1. 99. Catalog HHistory 1, C.C.C., 23 Guard Rail Construction, Negative ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    99. Catalog H-History 1, C.C.C., 23 Guard Rail Construction, Negative No. P455e (Photographer and date unknown) GUARD RAIL INSTALLATION. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  2. Closing the gap between MC3 and MC5 metallacumulenes: the chemistry of the first structurally characterized transition-metal complex with M=C=C=C=CR2 as the molecular unit.

    PubMed

    Ilg, Kerstin; Werner, Helmut

    2002-06-17

    The reactions of the dihydrido compound [IrH2Cl(PiPr3)2] (3) with HC identical to CC(O)CHPh2 and HC identical to CC(OAc)=CPh2 lead to the formation of alkynyl-(hydrido)iridium(III) and vinylideneiridium(I) complexes 4-7 which, however, are not suitable precursors for the target molecule trans-[IrCl(=C=C=C=CPh2)-(PiPr3)2] (8). Compound 8 has been prepared in 77% yield from 3 and the vinyl triflate HC identical to CC(OTf)=CPh2 in the presence of NEt3. Treatment of 8 with CF3CO2H affords the vinylvinylidene complex trans-[IrCl(=C=CHC(O2C-CF3)=CPh2)(PiPr3)2] (10) by addition of the electrophile to the C beta-C gamma bond of the MC4 chain. In contrast, the reaction of 8 with HCl yields the five-coordinate butadienyliridium(III) compound [IrCl2-(eta 1-(Z)-CH=CHC(Cl)=CPh2)(PiPr3)2] (11). Salt metathesis of 8 with KI, KOH, and NaN3 leads to the formation of the substitution products trans-[IrX-(=C=C=C=CPh2)(PiPr3)2] (12-14) of which the hydroxo derivative 13 reacts with phenol to give trans-[Ir(OPh)(=C=C=C=CPh2)(PiPr3)2] (15). From 13 and methanol, the octahedral dihydridoiridium(III) complex [IrH2(CH=C=C=CPh2)(CO)(PiPr3)2] (16) is formed by fragmentation of the alcohol. In the presence of CO, both the methyl compound trans-[Ir(CH3)(=C=C=C=CPh2)-(PiPr3)2] (17) (generated from 8 and CH3Li) and the azido complex 14 (X=N3) undergo migratory insertion reactions to yield the four-coordinate iridium(I) carbonyls trans-[Ir(C(C identical to CCH3)=CPh2)(CO)(PiPr3)2] (18) and trans-[Ir(C identical to CC(N3)=CPh2)(CO)(PiPr3)2] (19), respectively. Compound 19 rearranges slowly to the thermodynamically more stable isomer trans-[Ir(C(N3)=C=C=CPh2)(CO)(PiPr3)2] (20). The molecular structures of 8 and 18 have been determined crystallographically. PMID:12391660

  3. Stereodivergent α-allylation of linear aldehydes with dual iridium and amine catalysis.

    PubMed

    Krautwald, Simon; Schafroth, Michael A; Sarlah, David; Carreira, Erick M

    2014-02-26

    We describe the fully stereodivergent, dual catalytic α-allylation of linear aldehydes. The reaction proceeds via direct iridium-catalyzed substitution of racemic allylic alcohols with enamines generated in situ. The use of an Ir(P,olefin) complex and a diarylsilyl prolinol ether as catalysts in the presence of dimethylhydrogen phosphate as the promoter proved to be crucial for achieving high enantio- and diastereoselectivity (>99% ee, up to >20:1 dr). The utility of the method is demonstrated in a concise enantioselective synthesis of the antidepressant (-)-paroxetine. PMID:24506196

  4. Stereodivergent α-allylation of linear aldehydes with dual iridium and amine catalysis.

    PubMed

    Krautwald, Simon; Schafroth, Michael A; Sarlah, David; Carreira, Erick M

    2014-02-26

    We describe the fully stereodivergent, dual catalytic α-allylation of linear aldehydes. The reaction proceeds via direct iridium-catalyzed substitution of racemic allylic alcohols with enamines generated in situ. The use of an Ir(P,olefin) complex and a diarylsilyl prolinol ether as catalysts in the presence of dimethylhydrogen phosphate as the promoter proved to be crucial for achieving high enantio- and diastereoselectivity (>99% ee, up to >20:1 dr). The utility of the method is demonstrated in a concise enantioselective synthesis of the antidepressant (-)-paroxetine.

  5. 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.

  6. Half-sandwich iridium complexes for homogeneous water-oxidation catalysis.

    PubMed

    Blakemore, James D; Schley, Nathan D; Balcells, David; Hull, Jonathan F; Olack, Gerard W; Incarvito, Christopher D; Eisenstein, Odile; Brudvig, Gary W; Crabtree, Robert H

    2010-11-17

    Iridium half-sandwich complexes of the types Cp*Ir(N-C)X, [Cp*Ir(N-N)X]X, and [CpIr(N-N)X]X are catalyst precursors for the homogeneous oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H(2)O)(3)]SO(4) and [(Cp*Ir)(2)(μ-OH)(3)]OH can show even higher turnover frequencies (up to 20 min(-1) at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic oxidation at pH > 7; conversely, at low pH, there are no oxidation waves up to 1.5 V vs NHE for the complexes. H(2)(18)O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distinguish the active homogeneous catalyst from heterogeneous nanoparticulate iridium dioxide.

  7. Note: electrochemical etching of sharp iridium tips.

    PubMed

    Lalanne, Jean-Benoît; Paul, William; Oliver, David; Grütter, Peter H

    2011-11-01

    We describe an etching procedure for the production of sharp iridium tips with apex radii of 15-70 nm, as determined by scanning electron microscopy, field ion microscopy, and field emission measurements. A coarse electrochemical etch followed by zone electropolishing is performed in a relatively harmless calcium chloride solution with high success rate.

  8. 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.

  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. 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.

  11. 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.

  12. Mapping the Globe with C & C Technologies

    NASA Astrophysics Data System (ADS)

    Kleiner, A. A.

    2001-12-01

    C & C Technologies is an international survey and mapping company with an entrepreneurial spirit that is evident throughout. C & C was recently awarded the MTS (Marine Technology Society) ROV Committee Corporate Excellence Award in recognition of their pioneering spirit displayed by the introduction of the HUGIN 3000 Autonomous Underwater Vehicle (AUV) to the offshore industry. This presentation will outline the wide variety of global mapping projects that C & C has performed for government, private sector, and academia. These include high-resolution mapping of Cater Lake, the Panama Canal, Antarctica, Lake Tahoe, and the HUGIN 3000ś discovery of the German submarine U-166 in 5000 feet of water in the Gulf of Mexico. Adacemic disciplines required to support these technical challenges will be characterized and job opportunities in this emerging field will be addressed.

  13. Rhodium-Catalyzed Ketone Methylation Using Methanol Under Mild Conditions: Formation of α-Branched Products**

    PubMed Central

    Chan, Louis K M; Poole, Darren L; Shen, Di; Healy, Mark P; Donohoe, Timothy J

    2014-01-01

    The rhodium-catalyzed methylation of ketones has been accomplished using methanol as the methylating agent and the hydrogen-borrowing method. The sequence is notable for the relatively low temperatures that are required and for the ability of the reaction system to form α-branched products with ease. Doubly alkylated ketones can be prepared from methyl ketones and two different alcohols by using a sequential one-pot iridium- and rhodium-catalyzed process. PMID:24288297

  14. 103. Catalog HHistory 1, C.C.C., 58 Landscaping, Negative No. 870 ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    103. Catalog H-History 1, C.C.C., 58 Landscaping, Negative No. 870 10 ca. 1936 PROPAGATION AND PLANTING. ROOTED PLANTS TRANSPLANTED FROM HOT BEDS TO CANS TO SHADED BEDS IN PREPARATION FOR PLANTING ON ROAD SLOPES. NURSERY AT NORTH ENTRANCE. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  15. 102. Catalog HHistory 1, C.C.C., 34 Landscaping, Negative No. 6040a ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    102. Catalog H-History 1, C.C.C., 34 Landscaping, Negative No. 6040a (Photographer and date unknown) BEAUTIFICATION PROGRAM STARTED AS SOON AS GRADING ALONG THE DRIVE WAS COMPLETED. CCC CAMP 3 SHOWN PLANTING LAUREL. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  16. 104. Catalog HHistory 1, C.C.C., 73 Picnic Furniture Construction, Negative ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    104. Catalog H-History 1, C.C.C., 73 Picnic Furniture Construction, Negative No. 8821 ca. 1936 WOOD UTILIZATION. COMPLETED RUSTIC BENCH MADE BY CCC ENROLLEES AT CAMP NP-3 FOR USE AT PARKING OVERLOOKS AND PICNIC GROUNDS. NOTE SAW IN BACKGROUND USED FOR HALVING CHESTNUT. - Skyline Drive, From Front Royal, VA to Rockfish Gap, VA , Luray, Page County, VA

  17. Charged bis-cyclometalated iridium(III) complexes with carbene-based ancillary ligands.

    PubMed

    Monti, Filippo; Kessler, Florian; Delgado, Manuel; Frey, Julien; Bazzanini, Federico; Accorsi, Gianluca; Armaroli, Nicola; Bolink, Henk J; Ortí, Enrique; Scopelliti, Rosario; Nazeeruddin, Md Khaja; Baranoff, Etienne

    2013-09-16

    Charged cyclometalated (C(^)N) iridium(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C(^)N ligands, in contrast to the classical design of charged complexes where N(^)N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C(^)N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C(^)C:) and four different pyridine-carbene (N(^)C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C(^)C: complexes show much larger photoluminescence quantum yields (ΦPL) of ca. 30%, compared to the N(^)C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly(methyl methacrylate) matrix, ΦPL 30-60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N(^)C:-type complexes possess a low-lying triplet metal-centered ((3)MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C(^)C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N(^)C: and :C(^)C: complexes.

  18. 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.

  19. Nickel-Catalyzed Reductive Couplings.

    PubMed

    Wang, Xuan; Dai, Yijing; Gong, Hegui

    2016-08-01

    The Ni-catalyzed reductive coupling of alkyl/aryl with other electrophiles has evolved to be an important protocol for the construction of C-C bonds. This chapter first emphasizes the recent progress on the Ni-catalyzed alkylation, arylation/vinylation, and acylation of alkyl electrophiles. A brief overview of CO2 fixation is also addressed. The chemoselectivity between the electrophiles and the reactivity of the alkyl substrates will be detailed on the basis of different Ni-catalyzed conditions and mechanistic perspective. The asymmetric formation of C(sp(3))-C(sp(2)) bonds arising from activated alkyl halides is next depicted followed by allylic carbonylation. Finally, the coupling of aryl halides with other C(sp(2))-electrophiles is detailed at the end of this chapter. PMID:27573395

  20. 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).

  1. 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).

  2. Handling System for Iridium-192 Seeds

    NASA Technical Reports Server (NTRS)

    Carpenter, W.; Wodicka, D.

    1973-01-01

    A complete system is proposed for safe handling of iridium-192 seeds used to internally irradiate malignant growths. A vibratory hopper feeds the seeds onto a transport system for deposit in a magazine or storage area. A circular magazine consisting of segmented plastic tubing with holes in the walls to accommodate the seeds seems feasible. The magazine is indexed to stop and release a seed for calibration and deposition.

  3. Transition metal-catalyzed functionalization of pyrazines.

    PubMed

    Nikishkin, Nicolai I; Huskens, Jurriaan; Verboom, Willem

    2013-06-14

    Transition metal-catalyzed reactions are generally used for carbon-carbon bond formation on pyrazines and include, but are not limited to, classical palladium-catalyzed reactions like Sonogashira, Heck, Suzuki, and Stille reactions. Also a few examples of carbon-heteroatom bond formation in pyrazines are known. This perspective reviews recent progress in the field of transition metal-catalyzed cross-coupling reactions on pyrazine systems. It deals with the most important C-C- and C-X-bond formation methodologies.

  4. Secondary interactions or ligand scrambling? Subtle steric effects govern the iridium(I) coordination chemistry of phosphoramidite ligands.

    PubMed

    Osswald, Tina; Rüegger, Heinz; Mezzetti, Antonio

    2010-01-25

    The like and unlike isomers of phosphoramidite (P*) ligands are found to react differently with iridium(I), which is a key to explaining the apparently inconsistent results obtained by us and other research groups in a variety of catalytic reactions. Thus, the unlike diastereoisomer (aR,S,S)-[IrCl(cod)(1 a)] (2 a; cod=1,5-cyclooctadiene, 1 a=(aR,S,S)-(1,1'-binaphthalene)-2,2'-diyl bis(1-phenylethyl)phosphoramidite) forms, upon chloride abstraction, the monosubstituted complex (aR,S,S)-[Ir(cod)(1,2-eta-1 a,kappaP)](+) (3 a), which contains a chelating P* ligand that features an eta(2) interaction between a dangling phenyl group and iridium. Under analogous conditions, the like analogue (aR,R,R)-1 a' gives the disubstituted species (aR,R,R)-[Ir(cod)(1 a',kappaP)(2)](+) (4 a') with monodentate P* ligands. The structure of 3 a was assessed by a combination of X-ray and NMR spectroscopic studies, which indicate that it is the configuration of the binaphthol moiety (and not that of the dangling benzyl N groups) that determines the configuration of the complex. The effect of the relative configuration of the P* ligand on its iridium(I) coordination chemistry is discussed in the context of our preliminary catalytic results and of apparently random results obtained by other groups in the iridium(I)-catalyzed asymmetric allylic alkylation of allylic acetates and in rhodium(I)-catalyzed asymmetric cycloaddition reactions. Further studies with the unlike ligand (aS,R,R)-(1,1'-binaphthalene)-2,2'-diyl bis{[1-(1-naphthalene-1-yl)ethyl]phosphoramidite} (1 b) showed a yet different coordination mode, that is, the eta(4)-arene-metal interaction in (aS,R,R)-[Ir(cod)(1,2,3,4-eta-1 b,kappaP)](+) (3 b).

  5. Iridium isotope ratio measurements by negative thermal ionization mass spectrometry and atomic weight of iridium

    NASA Astrophysics Data System (ADS)

    Walczyk, Thomas; Heumann, Klaus G.

    1993-02-01

    A technique of negative thermal ionization mass spectrometry (NTI-MS) for the precise iridium isotope ratio determination is presented. IrO-2 and IrO-3 ions are formed in a double-filament (Pt) ion source using (NH4)2IrCl6 as a sample compound. The IrO-2 ion current always exceeds the IrO-3 current by a factor of about 50-300 depending on the filament temperature and the oxygen gas introduced into the ion source. IrO-3 ion currents of more than 10-11 A can be obtained at the detector side from 100 ng iridium samples. The relative standard deviation of the 191Ir/193 ratio determination is 0.06%, which is much better than the data quoted in past literature. From such data the atomic weight of iridium could be calculated to be 192.21661 ± 0.00029. This value is a great improvement when compared with the iridium atomic weight of 192.22 ± 0.03 recommended by IUPAC. Additionally, an NTI-MS technique has been developed which allows the simultaneous measurement of iridium and osmium isotope ratio from osmiridium samples without any chemical separation. The iridium isotope ratios of three osmiridium samples agree well with the ratios determined from the hexachloroiridate compound. The direct 187Os/186OS determination from osmiridium samples opens the possibility of studying the evolution of osmium in the Earth's mantle due to the radioactive decay of 187Re into 187Os.

  6. Construction of Enantiopure Taxoid and Natural Product-like Scaffolds Using a C-C Bond Cleavage/Arylation Reaction.

    PubMed

    Weber, Manuel; Owens, Kyle; Masarwa, Ahmad; Sarpong, Richmond

    2015-11-01

    An approach to construct enantiopure complex natural product-like frameworks, including the first reported synthesis of a C17 oxygenated taxoid scaffold, is presented. A palladium-catalyzed C-C activation/cross-coupling is utilized to access these structures in a short sequence from (+)-carvone; the scope of this reaction is explored.

  7. Recent advances in copper-catalyzed asymmetric coupling reactions.

    PubMed

    Zhou, Fengtao; Cai, Qian

    2015-01-01

    Copper-catalyzed (or -mediated) asymmetric coupling reactions have received significant attention over the past few years. Especially the coupling reactions of aryl or alkyl halides with nucleophiles became a very powerful tool for the formation of C-C, C-N, C-O and other carbon-heteroatom bonds as well as for the construction of heteroatom-containing ring systems. This review summarizes the recent progress in copper-catalyzed asymmetric coupling reactions for the formation of C-C and carbon-heteroatom bonds. PMID:26734106

  8. Iridium Abundances across the Ordovician-Silurian Stratotype

    NASA Astrophysics Data System (ADS)

    Wilde, Pat; Berry, William B. N.; Quinby-Hunt, Mary S.; Orth, Charles J.; Quintana, Leonard R.; Gilmore, James S.

    1986-07-01

    Chemostratigraphic analyses in the Ordovician-Silurian boundary stratotype section, bracketing a major extinction event in the graptolitic shale section at Dob's Linn, Scotland, show persistently high iridium concentrations of 0.050 to 0.250 parts per billion. There is no iridium concentration spike in the boundary interval or elsewhere in the 13 graptolite zones examined encompassing about 20 million years. Iridium correlated with chromium, both elements showing a gradual decrease with time into the middle part of the Lower Silurian. The chromium-iridium ratio averages about 106. Paleogeographic and geologic reconstructions coupled with the occurrence of ophiolites and other deep crustal rocks in the source area suggest that the high iridium and chromium concentrations observed in the shales result from terrestrial erosion of exposed upper mantle ultramafic rocks rather than from a cataclysmic extraterrestrial event.

  9. 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.

  10. Validation of EXAFS Analysis of Iridium Compounds

    NASA Astrophysics Data System (ADS)

    Feiters, M. C.; Longo, A.; Banerjee, D.; van der Ham, C. J. M.; Hetterscheid, D. G. H.

    2016-05-01

    Results of iridium L3 edge EXAFS measurements of compounds relevant for water oxidation catalysis are compared to those of other structural techniques. The structural results from EXAFS for the Ir compounds investigated here compare well to those of other structural techniques. Multiple scattering contributions are important in the coordinated Cp* and NHC ligands as well as in the IrCl6 unit and the IrO2 rutile structure. NHC is relatively weak compared to Ir, Cl, and even Cp* and O, and often out of phase with the other contributions.

  11. 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.

  12. C-C Coupling of Benzyl Fluorides Catalyzed by an Electrophilic Phosphonium Cation.

    PubMed

    Zhu, Jiangtao; Pérez, Manuel; Stephan, Douglas W

    2016-07-11

    The activation and cleavage of benzyl fluorides by the electrophilic organofluorophosphonium catalyst, [(C6 F5 )3 PF][B(C6 F5 )4 ], is reported and used for the preparation of 1,1-diarylalkanes (37 examples) and substituted aryl homoallylic alkenes (14 examples). This procedure involves mild conditions, avoids harmful waste, and is compatible with a range of substituted arenes and allylic silanes. PMID:27239806

  13. Autyomatic Differentiation of C/C++

    2005-11-14

    Automatic differentiation (AD) tools mechanize the process of developing code for the computation of derivatives. AD avoids the inaccuracies inherent in numerical approximations. Furthermore, sophisticated AD algoirthms can often produce c ode that is more reliable and more efficient than code written by an expert programmer. ADIC is the first and only AD tool for C and C++ based on compiler technology. This compiler foundation makes possible analyses and optimizations not available in toos basedmore » on operator overloading. The earliest implementations of ADIC included support for ANSI C applications, ADIC 2.0 lverages EDG, a commercial C/C++ parser, to provide robust C++ differentiation support. Modern AD tools, including ADIC are implemented in a modular way, aiming to isolate language-dependent program analyses and semantic transformations. The component design leads to much higher implementation quality because the different components can be implemented by experts in each of the different domains involved. For example, a compiler expert can focus on parsing, canonicalizing, and unparising C and C++, while an expert in graph theory and algorithms can produce new differentiation modules without having to worry about the complexity of parsing and generating C++ code. Thsi separation of concerns was achieved through the use of language-independent program analysis interfaces (in collaboration with researcgers at Rice University) and a language-independent XML representation of the computational portions of programs (XAIF). In addition to improved robustness and faster development times, this design naturally enables the reuse of program analysis algorithms and differentiation modules in compiler-based AD tools for other languages. In fact, the analysis and differention components are used in both ADIC and the Open AD Fortran front-end (based on Rice's Open64 compiler.« less

  14. Iridium anomaly approximately synchronous with terminal eocene extinctions

    SciTech Connect

    Alvarez, W.; Asaro, F.; Michel, H.V.; Alvarez, L.W.

    1982-05-21

    An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.

  15. Iridium anomaly approximately synchronous with terminal eocene extinctions.

    PubMed

    Alvarez, W; Asaro, F; Michel, H V; Alvarez, L W

    1982-05-21

    An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.

  16. 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.

  17. Membrane-disrupting iridium(iii) oligocationic organometallopeptides.

    PubMed

    Salvadó, Iria; Gamba, Ilaria; Montenegro, Javier; Martínez-Costas, José; Brea, Jose Manuel; Loza, María Isabel; Vázquez López, Miguel; Vázquez, M Eugenio

    2016-09-21

    A series of oligoarginine peptide derivatives containing cyclometallated iridium(iii) units display remarkable cytotoxicity, comparable to that of cisplatin. In vitro studies with unilamellar vesicles support a membrane-disrupting mechanism of action.

  18. Scattering effects on the dosimetry of iridium-192

    SciTech Connect

    Serago, C.F. Department of Radiation Oncology, University of Miami, Miami, Florida ); Houdek, P.V. ); Pisciotta, V. ); Schwade, J.G. ); Abitbol, A.A.; Lewin, A.A. Department of Radiation Oncology, University of Miami, Miami, Florida ); Poole, D.O. ); Marcial-Vega, V. )

    1991-11-01

    Dosimetry calculations for iridium-192 sources generally assume that a sufficient medium surrounds both the iridium source(s) and the point of calculation so that full scattering conditions exist. In several clinical applications the iridium sources may be anatomically located so that the full scattering requirement is not satisfied. To assess the magnitude of this problem, relative measurements were made with a small ionization chamber in phantoms near air and lung-equivalent interfaces. Dose reduction caused by decreasing the volume of scattering material near these interfaces was then evaluated for a few clinical applications. The results show that reductions on the order of 8% may be expected at the interface with minimal dose reduction within the volume of the implant itself. In addition, the results indicate the verification of source strength of iridium sources in phantom require phantom dimensions determined by the source-chamber separation distance.

  19. Low energy cyclotron production and cyclometalation chemistry of iridium-192.

    PubMed

    Langille, G; Yang, H; Zeisler, S K; Hoehr, C; Storr, T; Andreoiu, C; Schaffer, P

    2016-09-01

    This work demonstrates the labelling of a novel class of iridium lumophore with radioiridium, as proof-of-feasibility for producing and using the medically useful isotope iridium-192. Natural osmium was electroplated onto silver target backings in basic media and irradiated for up to two hours with ≤20μA of 12.8MeV protons. A range of iridium isotopes were generated, characterized and quantified using γ-spectroscopy methods. The target material was removed from the backings via oxidative dissolution with hydrogen peroxide, and the iridium radioisotopes isolated using an anion exchange resin. Both no-carrier-added as well as carrier-added formulations were then used in subsequent cyclometalation reactions. PMID:27344003

  20. Iridium anomaly approximately synchronous with terminal eocene extinctions.

    PubMed

    Alvarez, W; Asaro, F; Michel, H V; Alvarez, L W

    1982-05-21

    An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago. PMID:17819180

  1. 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

  2. Improvements in manufacture of iridium alloy materials

    NASA Astrophysics Data System (ADS)

    Ohriner, E. K.

    1992-10-01

    Iridium alloys are used as fuel-cladding material in radioisotope thermoelectric generators (RTG's). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyager 1 and 2, Galileo, and Ulysses spacecraft. This hardware was fabricated from small, 500-g drop-cast ingots. Porosity in these ingots and the resulting defects in the rolled sheets caused rejection of about 30 percent of the product. An improved manufacturing process was developed with the goal of substantially reducing the level of defects in the rolled sheets. The ingot size is increased to 10 kg and is produced by vacuum arc remelting. In addition, the ingot is hot extruded prior to rolling. Since implementation of the process in 1989, the average rate of rejection of the product has been reduced to below 10 percent.

  3. Improvements in manufacture of iridium alloy materials

    SciTech Connect

    Ohriner, E.K.

    1992-08-01

    Iridium alloys are used as fuel-cladding material in radioisotope thermoelectric generators (RTGs). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyager 1 and 2, Galileo, and Ulysses spacecraft. This hardware was fabricated from small, 500-g drop-cast ingots. Porosity in these ingots and the resulting defects in the rolled sheets caused rejection of about 30% of the product. An improved manufacturing process was developed with the goal of substantially reducing the level of defects in the rolled sheets. The ingot size is increased to 10 kg and is produced by vacuum arc remelting. In addition, the ingot is hot extruded prior to rolling. Since implementation of the process in 1989, the average rate of rejection of the product has been reduced to below 10%.

  4. Improvements in manufacture of iridium alloy materials

    SciTech Connect

    Ohriner, E.K.

    1992-01-01

    Iridium alloys are used as fuel-cladding material in radioisotope thermoelectric generators (RTGs). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyager 1 and 2, Galileo, and Ulysses spacecraft. This hardware was fabricated from small, 500-g drop-cast ingots. Porosity in these ingots and the resulting defects in the rolled sheets caused rejection of about 30% of the product. An improved manufacturing process was developed with the goal of substantially reducing the level of defects in the rolled sheets. The ingot size is increased to 10 kg and is produced by vacuum arc remelting. In addition, the ingot is hot extruded prior to rolling. Since implementation of the process in 1989, the average rate of rejection of the product has been reduced to below 10%.

  5. 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.}

  6. Decarboxylative coupling reactions: a modern strategy for C-C-bond formation.

    PubMed

    Rodríguez, Nuria; Goossen, Lukas J

    2011-10-01

    This critical review examines transition metal-catalyzed decarboxylative couplings that have emerged within recent years as a powerful strategy to form carbon-carbon or carbon-heteroatom bonds starting from carboxylic acids. In these reactions, C-C bonds to carboxylate groups are cleaved, and in their place, new carbon-carbon bonds are formed. Decarboxylative cross-couplings constitute advantageous alternatives to traditional cross-coupling or addition reactions involving preformed organometallic reagents. Decarboxylative reaction variants are also known for Heck reactions, direct arylation processes, and carbon-heteroatom bond forming reactions.

  7. Metalloenzyme-Like Zeolites as Lewis Acid Catalysts for C-C Bond Formation.

    PubMed

    Van de Vyver, Stijn; Román-Leshkov, Yuriy

    2015-10-19

    The use of metalloenzyme-like zeolites as Lewis acid catalysts for C-C bond formation reactions has received increasing attention over the past few years. In particular, the observation of direct aldol condensation reactions enabled by hydrophobic zeolites with isolated framework metal sites has encouraged the development of catalytic approaches for producing chemicals from biomass-derived compounds. The discovery of new Diels-Alder cycloaddition/dehydration routes and experimental and computational studies of Lewis acid catalyzed carbonyl-ene reactions have given a further boost to this rapidly evolving field. PMID:26465652

  8. Continuous flow Sonogashira C-C coupling using a heterogeneous palladium-copper dual reactor.

    PubMed

    Tan, Li-Min; Sem, Zhi-Yu; Chong, Wei-Yuan; Liu, Xiaoqian; Hendra; Kwan, Wei Lek; Lee, Chi-Lik Ken

    2013-01-01

    We report the development of a heterogeneous catalyst system on continuous flow chemistry. A palladium (Pd) coated tubular reactor was placed in line with copper (Cu) tubing using a continuous flow platform, and a Sonogashira C-C coupling reaction was used to evaluate the performance. The reactions were favorably carried out in the Cu reactor, catalyzed by the traces of leached Pd from the Pd reactor. The leached Pd and Cu were trapped with a metal scavaging resin at the back-end of the continuous flow system, affording a genuine approach toward green chemistry. PMID:23248977

  9. 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.

  10. Application of a C-C Bond-Forming Conjugate Addition Reaction in Asymmetric Dearomatization of β-Naphthols.

    PubMed

    Yang, Dongxu; Wang, Linqing; Kai, Ming; Li, Dan; Yao, Xiaojun; Wang, Rui

    2015-08-10

    A C-C bond-forming conjugate reaction was successfully applied to the enantioselective dearomatization of β-naphthols. A C(sp2)-C(sp3) bond is formed by using propargylic ketones as reactive partners. Good to excellent Z/E ratios and ee values were obtained by employing an in situ generated magnesium catalyst. Further transformations of the Z-configured C-C double bond in the products were achieved under mild reaction conditions. Moreover, the stereocontrolling element of this magnesium-catalyzed dearomatization reaction was explored by computational chemistry. PMID:26173841

  11. Iridium NEXT: A Global access for your sensor needs

    NASA Astrophysics Data System (ADS)

    Gupta, O. P.; Fish, C. S.

    2010-12-01

    The operational Iridium constellation is comprised of 66 satellites, used to primarily provide worldwide voice and data coverage to satellite phones, pagers and integrated transceivers. The satellites are in low Earth orbit at 781 km and inclination of 86.4 deg, resulting in unprecedented 24/7 coverage and real-time visibility of the entire globe. Recently, through funding from the National Science Foundation (NSF), Iridium has been utilized by the Johns Hopkins University Applied Physics Laboratory (APL), with help from The Boeing Company, as an infrastructure for a comprehensive network for space environment measurements. Known as the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), the Iridium-based system provides real-time magnetic field measurements using the satellites as part of a new observation network to forecast weather in space. In February 2007, Iridium announced Iridium NEXT, a novel design for a second-generation satellite constellation. Anticipated to begin launching in 2015, Iridium NEXT will maintain the existing Iridium constellation architecture of 66 cross-linked satellite LEO covering 100 percent of the globe. In the spirit of AMPERE, for commercial, government, and scientific organizations Iridium NEXT also plans to offer new earth and space observation opportunities through hosted hosted payloads on the 66 Iridium NEXT satellite network. To provide seamless support and access to this latest innovation in payload transportation, Iridium NEXT has teamed with Space Dynamics Laboratory - Utah State University which has delivered thousands of successful sensors and subsystems for over 400 space borne and aircraf based payloads. One such innovation called SensorPOD will offer unique benefits such as unprecedented spatial and temporal coverage, real-time relay of data to and from up to 5 Kg payloads in space, and access to space at a fraction of the cost of a dedicated missions such as 3U or larger Cubesats. In this

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

    DOEpatents

    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.

  13. 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...

  14. Characterization of Platinum and Iridium Oxyhydrate Surface Layers from Platinum and Iridium Foils.

    PubMed

    Johnson, Benjamin; Ranjan, Chinmoy; Greiner, Mark; Arrigo, Rosa; Schuster, Manfred Erwin; Höpfner, Britta; Gorgoi, Mihaela; Lauermann, Iver; Willinger, Marc; Knop-Gericke, Axel; Schlögl, Robert

    2016-07-01

    Platinum and iridium polycrystalline foils were oxidized electrochemically through anodization to create thin platinum and iridium hydrous oxide layers, which were analyzed through laboratory photoelectron spectroscopy during heating and time series (temperature-programmed spectroscopy). The films contain oxygen in the form of bound oxides, water, and hydroxides and were investigated by depth profiling with high-energy photoelectron spectroscopy. The Pt films are unstable and begin to degrade immediately after removal from the electrolyte to form core-shell structures with a metallic inner core and a hydrous oxide outer shell almost devoid of Pt. However, evidence was found for metastable intermediate states of degradation; therefore, it may be possible to manufacture PtOx phases with increased stability. Heating the film to even 100 °C causes accelerated degradation, which shows that stoichiometric oxides such as PtO2 or PtO are not the active species in the electrolyte. The Ir films exhibit increased stability and higher surface Ir content, and gentle heating at low temperatures leads to a decrease in defect density. Although both layers are based on noble metals, their surface structures are markedly different. The complexity of such hydrous oxide systems is discussed in detail with the goal of identifying the film composition more precisely. PMID:27226255

  15. Understanding Rotation about a C=C Double Bond

    ERIC Educational Resources Information Center

    Barrows, Susan E.; Eberlein, Thomas H.

    2005-01-01

    The study focuses on the process and energetic cost of twisting around a C=C double bond and provides instructors with a simple vehicle for rectifying the common misrepresentation of C=C double bonds as rigid and inflexible. Discussions of cis and trans isomers of cycloalkenes are a good entry point for introducing students to the idea of a…

  16. Iridium oxide-polymer nanocomposite electrode materials for water oxidation.

    PubMed

    Lattach, Youssef; Rivera, Juan Francisco; Bamine, Tahya; Deronzier, Alain; Moutet, Jean-Claude

    2014-08-13

    Nanocomposite anode materials for water oxidation have been readily synthesized by electrodeposition of iridium oxide nanoparticles into poly(pyrrole-alkylammonium) films, previously deposited onto carbon electrodes by oxidative electropolymerization of a pyrrole-alkylammonium monomer. The nanocomposite films were characterized by electrochemistry, transmission electron microscopy, and atomic force microscopy. They showed an efficient electrocatalytic activity toward the oxygen evolution reaction. Data from Tafel plots have demonstrated that the catalytic activity of the iridium oxide nanoparticles is maintained following their inclusion in the polymer matrix. Bulk electrolysis of water at carbon foam modified electrodes have shown that the iridium oxide-polymer composite presents a higher catalytic activity and a better operational stability than regular oxide films.

  17. 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.

  18. Synthesis of new heteroscorpionate iridium(I) and iridium(III) complexes.

    PubMed

    Roa, A E; Campos, J; Paneque, M; Salazar, V; Otero, A; Lara-Sánchez, A; Rodríguez, A M; López-Solera, I; Gómez, M V

    2015-04-21

    The reactivity of different heteroscorpionate ligands based on bis(pyrazol-1-yl)methane, with different iridium-(i) and -(iii) precursors is reported. The reaction of the heteroscorpionate lithium salts "Li(bdmpza)", [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], "Li(bdmpzdta)" [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] and "Li(S)-mbpam" [(S)-mbpam = (S)-(-)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] with 1 equivalent of [IrCl3(THF)3] in THF for 18 h affords high yields of neutral and anionic heteroscorpionate chloride iridium complexes [IrCl2(bdmpza)(THF)] (), [Li(THF)4][IrCl3(bdmpzdta)] () and [IrCl2{(S)-mbpam})(THF)] (). Solution of complex in acetonitrile at room temperature leads to complex [IrCl2{(S)-mbpam})(NCCH3)] (). Complexes and were isolated as enantiopure compounds. The reaction of the lithium salt "Li(bdmpza)" with [IrCl(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)]2 in THF for 18 h gave the Ir(i) complex [Ir(bdmpza)(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)] (). The reaction of complex with CO (2 atm) at room temperature leads to a new complex of Ir(iii), [Ir(bdmpza)(k(2)-CH2C(Me)[double bond, length as m-dash]C(Me)CH2)(CO)] (). Treatment of heteroscorpionate ligand precursors "Li(bdmpza)" and "Li(bdmpzdta)" with [IrCp*Cl2]2 in THF yielded the iridium(iii) complexes [Ir2Cp*2Cl2(bdmpzx)] (x = a , x = dta ). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers were obtained. Complex undergoes a decarboxylation process initiated by the HCl generated in the previous step leading to the known ionic complex [IrClCp*(bdmpm)][IrCl3Cp*] [bdmpm = bis(3,5-dimethylpyrazol-1-yl)methane] (). The

  19. Synthesis of new heteroscorpionate iridium(I) and iridium(III) complexes.

    PubMed

    Roa, A E; Campos, J; Paneque, M; Salazar, V; Otero, A; Lara-Sánchez, A; Rodríguez, A M; López-Solera, I; Gómez, M V

    2015-04-21

    The reactivity of different heteroscorpionate ligands based on bis(pyrazol-1-yl)methane, with different iridium-(i) and -(iii) precursors is reported. The reaction of the heteroscorpionate lithium salts "Li(bdmpza)", [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], "Li(bdmpzdta)" [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] and "Li(S)-mbpam" [(S)-mbpam = (S)-(-)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] with 1 equivalent of [IrCl3(THF)3] in THF for 18 h affords high yields of neutral and anionic heteroscorpionate chloride iridium complexes [IrCl2(bdmpza)(THF)] (), [Li(THF)4][IrCl3(bdmpzdta)] () and [IrCl2{(S)-mbpam})(THF)] (). Solution of complex in acetonitrile at room temperature leads to complex [IrCl2{(S)-mbpam})(NCCH3)] (). Complexes and were isolated as enantiopure compounds. The reaction of the lithium salt "Li(bdmpza)" with [IrCl(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)]2 in THF for 18 h gave the Ir(i) complex [Ir(bdmpza)(η(4)-CH2[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]CH2)] (). The reaction of complex with CO (2 atm) at room temperature leads to a new complex of Ir(iii), [Ir(bdmpza)(k(2)-CH2C(Me)[double bond, length as m-dash]C(Me)CH2)(CO)] (). Treatment of heteroscorpionate ligand precursors "Li(bdmpza)" and "Li(bdmpzdta)" with [IrCp*Cl2]2 in THF yielded the iridium(iii) complexes [Ir2Cp*2Cl2(bdmpzx)] (x = a , x = dta ). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers were obtained. Complex undergoes a decarboxylation process initiated by the HCl generated in the previous step leading to the known ionic complex [IrClCp*(bdmpm)][IrCl3Cp*] [bdmpm = bis(3,5-dimethylpyrazol-1-yl)methane] (). The

  20. 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.

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

    DOE PAGES

    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 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

  2. (4-Chloro-acetanilido-κ(2)N,O)bis-[2-(pyridin-2-yl)phenyl-κ(2)C(1),N]iridium(III).

    PubMed

    Sun, Lijun; Zhang, Songlin; Song, Qijun

    2013-02-01

    In the neutral mononuclear iridium(III) title compound, [Ir(C(8)H(7)ClNO)(C(11)H(8)N)(2)], the Ir(III) atom adopts an octa-hedral geometry, and is coordinated by two 2-phenyl-pyridyl ligands and one anionic 4-chloro-acetanilide ligand. The 2-phenyl-pyridyl ligands are arranged in a cis-C,C' and cis-N,N' fashion. Each 2-phenyl-pyridyl ligand forms a five-membered ring with the Ir(III) atom. The 2-phenyl-pyridyl planes are perpendicular to each other [dihedral angle = 89.9 (1)°]. The Ir-C and Ir-N bond lengths are comparable to those reported for related iridium(III) 2-phenyl-pyridyl complexes. The remaining two coordination sites are occupied by the amidate N and O atoms, which form a four-membered ring with the iridium atom (Ir-N-C-O). The amidate plane is nearly perpendicular to both 2-phenyl-pyridyl ligands [dihedral angles = 87.8 (2) and 88.3 (2)°]. PMID:23424440

  3. Oxo-rhenium catalyzed reductive coupling and deoxygenation of alcohols.

    PubMed

    Kasner, Gabrielle R; Boucher-Jacobs, Camille; Michael McClain, J; Nicholas, Kenneth M

    2016-06-01

    Representative benzylic, allylic and α-keto alcohols are deoxygenated to alkanes and/or reductively coupled to alkane dimers by reaction with PPh3 catalyzed by (PPh3)2ReIO2 (1). The newly discovered catalytic reductive coupling reaction is a rare C-C bond-forming transformation of alcohols. PMID:27174412

  4. 7. Historic American Buildings Survey, C. C. Adams, Photographer August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Historic American Buildings Survey, C. C. Adams, Photographer August 1931, SEED PACKING ROOM, Gift of New York State Department of Education. - Shaker North Family Washhouse (first), Shaker Road, New Lebanon, Columbia County, NY

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Magnetostratigraphy, Late devonian iridium anomaly, and impact hypotheses

    SciTech Connect

    Hurley, N.F.; Van der Voo, R. )

    1990-04-01

    Paleomagnetism, sedimentology, and fine-scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the Late Devonian of Western Australia. Thermal demagnetization experiments were carried out on 93 specimens of marginal-slope limestone form the northern Canning Basin. Samples are from a condensed sequence of deep-water (> 100 m) Frutexites microstromatolites. Frutexites is a shrublike cyanobacterial organism that probably precipitated hematite, or a metastable precursor, from sea water. When plotted within the microstratigraphic framework for the study area, the observed characteristic directions from the sampled interval (14.5 cm thick) are in five discrete, layer-parallel, normal- and reversed-polarity zones. The measured northeast-southwest declinations and shallow inclinations probably record Late Devonian magnetostratigraphy on a centimetre scale. The Frutexites bed studied there occurs close to the Frasnian/Famennian (Late Devonian) boundary, a time of mass extinction of a wide variety of marine organisms throughout the world. Anomalously high iridium concentrations observed in the Frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact. This study concludes that iridium, which is present over the span of five layer-parallel magnetic reversals, was concentrated over a long period of time by biologic processes. Thus, the Canning Basin iridium anomaly may be unrelated to meteorite impact.

  12. 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

  13. Hydrogen-Borrowing and Interrupted-Hydrogen-Borrowing Reactions of Ketones and Methanol Catalyzed by Iridium**

    PubMed Central

    Shen, Di; Poole, Darren L; Shotton, Camilla C; Kornahrens, Anne F; Healy, Mark P; Donohoe, Timothy J

    2015-01-01

    Reported herein is the use of catalytic [{Ir(cod)Cl}2] to facilitate hydrogen-borrowing reactions of ketone enolates with methanol at 65 °C. An oxygen atmosphere accelerates the process, and when combined with the use of a bulky monodentate phosphine ligand, interrupts the catalytic cycle by preventing enone reduction. Subsequent addition of pro-nucleophiles to the reaction mixture allowed a one-pot methylenation/conjugate addition protocol to be developed, which greatly expands the range of products that can be made by this methodology. PMID:25491653

  14. Iridium-Catalyzed Allylation of Chiral β-Stereogenic Alcohols: Bypassing Discrete Formation of Epimerizable Aldehydes

    PubMed Central

    Schmitt, Daniel C.; Dechert-Schmitt, Anne-Marie R.; Krische, Michael J.

    2012-01-01

    The cyclometallated π-allyliridium 3,4-dinitro-C,O-benzoate complex modified by (R)- or (S)-Cl,MeO-BIPHEP promotes the transfer hydrogenative coupling of allyl acetate to β-stereogenic alcohols with good to excellent levels of catalyst-directed diastereoselectivity to furnish homoallylic alcohols. Remote electronic effects of the C,O-benzoate of the catalyst play a critical role in suppressing epimerization of the transient α-stereogenic aldehyde. PMID:23231774

  15. Dehydrogenation of n-alkanes catalyzed by iridium ``pincer`` complexes: Regioselective formation of {alpha}-olefins

    SciTech Connect

    Liu, F.; Singh, B.; Goldman, A.S.; Pak, E.B.; Jensen, C.M.

    1999-04-28

    The development of methods for the functionalization of alkanes is of cardinal importance in catalytic chemistry. A specific functionalization of particularly great potential value is the conversion of n-alkanes to the corresponding 1-alkenes ({alpha}-olefins) since these serve as precursors for a wide range of commodity-scale chemicals (>2 {times} 10{sup 9} kg/yr). Such a conversion is also an intriguing challenge as viewed from a fundamental perspective. n-Alkanes are the simplest organic molecules with the potential to undergo regioselective transformations; {alpha}-olefins are the thermodynamically least stable of the corresponding double-bond isomers and any mechanism for their formation must presumably involve activation of the strongest bond (primary C-{single_bond}H) in the molecule.

  16. Iridium-Catalyzed Dynamic Kinetic Isomerization: Expedient Synthesis of Carbohydrates from Achmatowicz Rearrangement Products.

    PubMed

    Wang, Hao-Yuan; Yang, Ka; Bennett, Scott R; Guo, Sheng-rong; Tang, Weiping

    2015-07-20

    A highly stereoselective dynamic kinetic isomerization of Achmatowicz rearrangement products was discovered. This new internal redox isomerization provided ready access to key intermediates for the enantio- and diastereoselective synthesis of a series of naturally occurring sugars. The nature of the de novo synthesis also enables the preparation of both enantiomers.

  17. Microwave-assisted C-C bond forming cross-coupling reactions: an overview.

    PubMed

    Mehta, Vaibhav P; Van der Eycken, Erik V

    2011-10-01

    Among the fundamental transformations in the field of synthetic organic chemistry, transition-metal-catalyzed reactions provide some of the most attractive methodologies for the formation of C-C and C-heteroatom bonds. As a result, the application of these reactions has increased tremendously during the past decades and cross-coupling reactions became a standard tool for synthetic organic chemists. Furthermore, a tremendous upsurge in the development of new catalysts and ligands, as well as an increased understanding of the mechanisms, has contributed substantially to recent advances in the field. Traditionally, organic reactions are carried out by conductive heating with an external heat source (for example, an oil bath). However, the application of microwave irradiation is a steadily gaining field as an alternative heating mode since its dawn at the end of the last century. This tutorial review focuses on some of the recent developments in the field of cross-coupling reactions assisted by microwave irradiation.

  18. Structure, electrochemical properties and capacitance performance of polypyrrole electrodeposited onto 1-D crystals of iridium complex

    NASA Astrophysics Data System (ADS)

    Wysocka-Żołopa, Monika; Winkler, Krzysztof

    2015-12-01

    Composites of polypyrrole and one-dimensional iridium complex crystals [(C2H5)4N]0.55[IrCl2(CO)2] were prepared by in situ two-step electrodeposition. Initially, iridium complex crystals were formed during [IrCl2(CO)2]- complex oxidation. Next, pyrrole was electropolymerized on the surface of the iridium needles. The morphology of the composite was investigated by scanning and transmission electron microscopy. At positive potentials, the iridium complex crystals and the polypyrrole were oxidized. In aprotic solvents, oxidation of the iridium complex crystals resulted in their dissolution. In water containing tetra(n-butyl)ammonium chlorides, the 1-D iridium complex crystals were reversibly oxidized. The product of the iridium complex oxidation remained on the electrode surface in crystalline form. The iridium complex needles significantly influenced the redox properties of the polymer. The polypyrrole involved electrode processes become more reversible in presence of crystals of iridium complex. The current of polypyrrole oxidation was higher compared to that of pure polypyrrole and the capacitance properties of the polymer were significantly enhanced. A specific capacitance as high as 590 F g-1 was obtained for a composite of polypyrrole and 1-D crystals of the iridium complex in water containing tetra(n-butyl)ammonium chloride. This value is approximately twice as high as the capacitance of the pure polymer deposited onto the electrode surface.

  19. Testing of DLR C/C-SiC and C/C for HIFiRE 8 Scramjet Combustor

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Capriotti, Diego P.; Reimer, Thomas; Kutemeyer, Marius; Smart, Michael K.

    2014-01-01

    Ceramic Matrix Composites (CMCs) have been proposed for use as lightweight hot structures in scramjet combustors. Previous studies have calculated significant weight savings by utilizing CMCs (active and passive) versus actively cooled metallic scramjet structures. Both a carbon/carbon (C/C) and a carbon/carbon-silicon carbide (C/C-SiC) material fabricated by DLR (Stuttgart, Germany) are being considered for use in a passively cooled combustor design for Hypersonic International Flight Research Experimentation (HIFiRE) 8, a joint Australia / Air Force Research Laboratory hypersonic flight program, expected to fly at Mach 7 for approximately 30 sec, at a dynamic pressure of 55 kilopascals. Flat panels of the DLR C/C and C/C-SiC materials were installed downstream of a hydrogen-fueled, dual-mode scramjet combustor and tested for several minutes at conditions simulating flight at Mach 5 and Mach 6. Gaseous hydrogen fuel was used to fuel the scramjet combustor. The test panels were instrumented with embedded Type K and Type S thermocouples. Zirconia felt insulation was used during some of the tests to reduce heat loss from the back surface and thus increase the heated surface temperature of the C/C-SiC panel approximately 177 C (350 F). The final C/C-SiC panel was tested for three cycles totaling over 135 sec at Mach 6 enthalpy. Slightly more erosion was observed on the C/C panel than the C/C-SiC panels, but both material systems demonstrated acceptable recession performance for the HIFiRE 8 flight.

  20. Modeling of the Reaction Mechanism of Enzymatic Radical C-C Coupling by Benzylsuccinate Synthase.

    PubMed

    Szaleniec, Maciej; Heider, Johann

    2016-01-01

    Molecular modeling techniques and density functional theory calculations were performed to study the mechanism of enzymatic radical C-C coupling catalyzed by benzylsuccinate synthase (BSS). BSS has been identified as a glycyl radical enzyme that catalyzes the enantiospecific fumarate addition to toluene initiating its anaerobic metabolism in the denitrifying bacterium Thauera aromatica, and this reaction represents the general mechanism of toluene degradation in all known anaerobic degraders. In this work docking calculations, classical molecular dynamics (MD) simulations, and DFT+D2 cluster modeling was employed to address the following questions: (i) What mechanistic details of the BSS reaction yield the most probable molecular model? (ii) What is the molecular basis of enantiospecificity of BSS? (iii) Is the proposed mechanism consistent with experimental observations, such as an inversion of the stereochemistry of the benzylic protons, syn addition of toluene to fumarate, exclusive production of (R)-benzylsuccinate as a product and a kinetic isotope effect (KIE) ranging between 2 and 4? The quantum mechanics (QM) modeling confirms that the previously proposed hypothetical mechanism is the most probable among several variants considered, although C-H activation and not C-C coupling turns out to be the rate limiting step. The enantiospecificity of the enzyme seems to be enforced by a thermodynamic preference for binding of fumarate in the pro(R) orientation and reverse preference of benzyl radical attack on fumarate in pro(S) pathway which results with prohibitively high energy barrier of the radical quenching. Finally, the proposed mechanism agrees with most of the experimental observations, although the calculated intrinsic KIE from the model (6.5) is still higher than the experimentally observed values (4.0) which suggests that both C-H activation and radical quenching may jointly be involved in the kinetic control of the reaction. PMID:27070573

  1. Internal friction and gas desorption of {C}/{C} composites

    NASA Astrophysics Data System (ADS)

    Serizawa, H.; Sato, S.; Kohyama, A.

    1994-09-01

    {C}/{C} composites are the most promising candidates as high heat flux component materials, where temperature dependence of mechanical properties and gas desorption behavior at elevated temperature are important properties. At the beginning, the newly developed internal friction measurement apparatus, which enables the accurate measurement of dynamic elastic properties up to 1373 K along with the measurement of gas desorption behavior, was used. The materials studied were unidirectional (UD) {C}/{C} composites reinforced with mesophase pitch-based carbon fibers, which were heat treated at temperatures ranging from 1473 to 2773 K which produced a variety of graphitized microstructures. Two-dimensional (2D) {C}/{C} composites reinfored with flat woven fabrics of PAN type carbon fibers were also studied. These materials were heat treated at 1873 K. From the temperature spectrum of internal friction of 2D {C}/{C} composites, these internal friction peaks were detected and were related to gas desorption. Also the temperature dependence of Young's modulus of UD {C}/{C} composites, negative and positive dependence of Young's modulus were observed reflecting microstructure changes resulting from the heat treatments.

  2. 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.

  3. 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.

  4. Insights into the oxidative dehydrogenation of amines with nanoparticulate iridium oxide.

    PubMed

    Hammond, Ceri; Schümperli, Martin T; Hermans, Ive

    2013-09-23

    The aerobic oxidation of amines offers a promising route towards many versatile chemical compounds. Within this contribution, we extend our previous investigations of iridium oxide-catalyzed alcohol oxidation to amine substrates. In addition to demonstrating the versatility of this catalyst, particular attention is focused on the mechanisms of the reaction. Herein, we demonstrate that although amines are oxidized slower than the corresponding alcohols, the catalyst has a preference for amine substrates, and oxidizes various amines at turnover frequencies greater than other systems found in the open literature. Furthermore, the competition between double amine dehydrogenation, to yield the corresponding nitrile, and amine-imine coupling, to yield the corresponding coupled imine, has been found to arise from a competitive reaction pathway, and stems from an effect of substrate-to-metal ratio. Finally, the mechanism responsible for the formation of N-benzylidene-1-phenylmethanamine was examined, and attributed to the coupling of free benzyl amine substrate and benzaldehyde, formed in situ through hydrolysis of the primary reaction product, benzyl imine. PMID:23939827

  5. The Decomposition of Hydrazine in the Gas Phase and over an Iridium Catalyst

    SciTech Connect

    Schmidt, Michael W.; Gordon, Mark S.

    2013-09-30

    Hydrazine is an important rocket fuel, used as both a monopropellant and a bipropellant. This paper presents theoretical results to complement the extensive experimental studies of the gas phase and Ir catalyzed decompositions involved in the monopropellant applications of hydrazine. Gas phase electronic structure theory calculations that include electron correlation predict that numerous molecular and free radical reactions occur within the same energy range as the basic free radical pathways: NN bond breaking around 65 kcal/mol and NH bond breaking around 81 kcal/mol. The data suggest that a revision to existing kinetics modeling is desirable, based on the energetics and the new elementary steps reported herein. A supported Ir-6 octahedron model for the Shell 405 Iridium catalyst used in thrusters was developed. Self-Consistent Field and electron correlation calculations (with core potentials and associated basis sets) find a rich chemistry for hydrazine on this catalyst model. The model catalyst provides dramatically lower NN and NH bond cleavage energies and an even smaller barrier to breaking the NH bond by NH2 abstractions. Thus, the low temperature decomposition over the catalyst is interpreted in terms of consecutive NH2 abstractions to produce ammonia and nitrogen. The higher temperature channel, which has hydrogen and nitrogen products, may be due to a mixture of two mechanisms. These two mechanisms are successive NH cleavages with surface H + H recombinations, and the same type of assisted H-2 eliminations found to occur in the gas phase part of this study.

  6. Oxygen switch in visible-light photoredox catalysis: radical additions and cyclizations and unexpected C-C-bond cleavage reactions.

    PubMed

    Zhu, Shaoqun; Das, Arindam; Bui, Lan; Zhou, Hanjun; Curran, Dennis P; Rueping, Magnus

    2013-02-01

    Visible light photoredox catalyzed inter- and intramolecular C-H functionalization reactions of tertiary amines have been developed. Oxygen was found to act as chemical switch to trigger two different reaction pathways and to obtain two different types of products from the same starting material. In the absence of oxygen, the intermolecular addition of N,N-dimethyl-anilines to electron-deficient alkenes provided γ-amino nitriles in good to high yields. In the presence of oxygen, a radical addition/cyclization reaction occurred which resulted in the formation of tetrahydroquinoline derivatives in good yields under mild reaction conditions. The intramolecular version of the radical addition led to the unexpected formation of indole-3-carboxaldehyde derivatives. Mechanistic investigations of this reaction cascade uncovered a new photoredox catalyzed C-C bond cleavage reaction.

  7. Circularly polarised phosphorescent photoluminescence and electroluminescence of iridium complexes

    PubMed Central

    Li, Tian-Yi; Jing, Yi-Ming; Liu, Xuan; Zhao, Yue; Shi, Lin; Tang, Zhiyong; Zheng, You-Xuan; Zuo, Jing-Lin

    2015-01-01

    Nearly all the neutral iridium complexes widely used as dopants in PhOLEDs are racemic mixtures; however, this study observed that these complexes can be separated into stable optically active Λ and ∆ isomers and that their chirality is an intrinsic property. The circularly polarised phosphorescent photoluminescence (CPPPL) signals of Λ/Δ isomers are perfect mirror images with opposite polarisation and equal intensity exhibiting a “handedness” for the polarisation. For the first time, we applied the Λ/Δ iridium isomers as emitters in OLEDs, and the circularly polarised phosphorescent electroluminescence (CPPEL) spectra reveal completely positive or negative broad peaks consistent with the CPPPL spectra. The results demonstrate that the Λ/Δ isomers have potential application for 3D OLEDs because they can exhibit high efficiency and luminance, and 3D display technology based on circularly polarised light is the most comfortable for the eyes. PMID:26446521

  8. Processing and properties of iridium alloys for space power applications

    SciTech Connect

    Ohriner, E.K.

    1994-12-31

    Iridium alloys are used as fuel cladding in radioisotope thermoelectric generators due to their high-melting point, high- temperature strength, and oxidation and corrosion resistance. Although iridium has a face-centered cubic crystal structure, it undergoes a distinct ductile-to-brittle transition characteristic of many body-centered cubic metals. Improved ductility in the alloys is achieved through material purification and controlled alloy additions at the parts per million (ppm) level. A vacuum arc remelt operation produces a nearly defect-free casting, which is further processed to sheet products. A change in processing from drop castings of small arc-melted buttons to large arc-remelted ingots has substantially improved product yields. The effects of processing changes on alloy microstructure, sheet textures, oxidation effects, high-strain-rate ductility, and fabricability are discussed.

  9. Iridium alloy clad vent set manufacturing qualification studies

    SciTech Connect

    Ulrich, G.B. )

    1991-01-10

    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 Applied Technologies, Inc. (EG 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.

  10. Photoswitchable azobenzene-appended iridium(iii) complexes.

    PubMed

    Pérez-Miqueo, J; Altube, A; García-Lecina, E; Tron, A; McClenaghan, N D; Freixa, Z

    2016-09-21

    Iridium(iii) cyclometalated complexes have been used as models to study the effect that extended conjugation and substitution pattern has on the photochromic behavior of azobenzene-appended 2-phenylpyridyl (ppy) ligands. For this purpose four azobenzene-containing ppy ligands were synthesized. With these ligands, nine iridium(iii) complexes containing up to three appended azobenzenes were synthesized. Analysis of their photochromic behaviour by means of UV-vis and (1)H-NMR spectroscopy permitted us to conclude that the light-induced trans-to-cis isomerization of the azobenzene was strongly inhibited upon coordination to the Ir(iii) cation when the electronic conjugation was extended along the whole ligand. The use of an aliphatic spacer unit (either -CH2- or -OCH2-) between the azobenzene and the ppy fragment of the ligand sufficed to disrupt the electronic communication, and obtain photochromic organometallic complexes. PMID:27460186

  11. 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.

  12. Mononuclear iridium dinitrogen complexes bonded to zeolite HY

    DOE PAGES

    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 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

  13. Gold/Lewis Acid Catalyzed Cycloisomerization/Diastereoselective [3 + 2] Cycloaddition Cascade: Synthesis of Diverse Nitrogen-Containing Spiro Heterocycles.

    PubMed

    Wang, Bin; Liang, Man; Tang, Jian; Deng, Yuting; Zhao, Jinhong; Sun, Hao; Tung, Chen-Ho; Jia, Jiong; Xu, Zhenghu

    2016-09-16

    A novel early and late transition-metal relay catalysis has been developed by combining a gold-catalyzed cycloisomerization and a Yb(OTf)3-catalyzed diastereoselective [3 + 2] cycloaddition with aziridines in a selective C-C bond cleavage mode. Various biologically significant complex nitrogen-containing spiro heterocycles were rapidly constructed from readily available starting materials under mild conditions. PMID:27574831

  14. Water-Promoted Generation of a Diazairida Homobarrelene by C-C Coupling Between an Iridacyclic Alkylidene and Acetonitrile.

    PubMed

    Espada, María F; López-Serrano, Joaquín; Poveda, Manuel L; Carmona, Ernesto

    2015-07-20

    The stable cationic iridacyclopentenylidene [Tp(Me2)Ir(=CHC(Me)=C(Me)CH2(NCMe)]PF6 (A; Tp(Me2)=hydrotris(3,5-dimethylpyrazolyl)borate) has been obtained by α-hydride abstraction from the iridacyclopent-2-ene [Tp(Me2)Ir(CH2C(Me)=C(Me)CH2)(NCMe)]. Complex A exhibits Brønsted-Lowry acidity at the Ir-CH2 and proximal (relative to Ir-CH2 ) methyl sites. The coordination of an extra molecule of acetonitrile to the iridium center initiates the reversible isomerization of the chelating carbon chain of A to the monodentate butadienyl ligand of complex [Tp(Me2)Ir(CH=C(Me)C(Me)=CH2)(NCMe)2]PF6, which is capable to engage in a water-promoted C-C coupling with the MeCN co-ligands. The product is an aesthetically appealing bicyclic structure that resembles the hydrocarbon barrelene.

  15. 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

  16. 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

  17. Rh(III)-catalyzed selective coupling of N-methoxy-1H-indole-1-carboxamides and aryl boronic acids.

    PubMed

    Zheng, Jing; Zhang, Yan; Cui, Sunliang

    2014-07-01

    A Rh(III)-catalyzed selective coupling of N-methoxy-1H-indole-1-carboxamide and aryl boronic acids is reported. The coupling is mild and efficient toward diverse product formation, with selective C-C and C-C/C-N bond formation. Kinetic isotope effects studies were conducted to reveal a mechanism of C-H activation and electrophilic addition. PMID:24959967

  18. Direct, Sequential, and Stereoselective Alkynylation of C,C-Dibromophosphaalkenes.

    PubMed

    Shameem, Muhammad A; Esfandiarfard, Keyhan; Öberg, Elisabet; Ott, Sascha; Orthaber, Andreas

    2016-07-18

    The first direct alkynylation of C,C-dibromophosphaalkenes by a reaction with sulfonylacetylenes is reported. Alkynylation proceeds selectively in the trans position relative to the P substituent to afford bromoethynylphosphaalkenes. Owing to the absence of transition metals in the procedure, the previously observed conversion of dibromophosphaalkenes into phosphaalkynes through the phosphorus analog of the Fritsch-Buttenberg-Wiechell rearrangement is thus suppressed. The bromoethynylphosphaalkenes can subsequently be converted to C,C-diacetylenic, cross-conjugated phosphaalkenes by following a Sonogashira coupling protocol in good overall yields. By using the newly described method, full control over the stereochemistry at the P=C double bond is achieved. The substrate scope of this reaction is demonstrated for different dibromophosphaalkenes as well as different sulfonylacetylenes. PMID:27310813

  19. [Study on spectral emissivity of C/C composites].

    PubMed

    Zhu, Bo; Cao, Wei-Wei; Jing, Min; Dong, Xing-Guang; Wang, Cheng-Guo

    2009-11-01

    Different types of C/C composites were prepared by conventional molding, and the changes in normal spectral emissivity of samples were tested. The testing results show that spectral emissivity of C/C composite reinforced by short cut carbon fibers is generally higher than the sample reinforced by carbon cloth in the entire 2500-13000nm wavelength region. The structure of short cut carbon fibers is relatively loose and the number of material particles is less than other samples in unit volume, which increases the penetration depth of electromagnetic waves. This is the reason for higher normal spectral emissivity and better heat radiation property. Meanwhile, the test results of normal spectral emissivity for fiber perform and C/C composite samples show that the spectral emissivity of resin carbon is better than fiber carbon because of the difference in microstructure for the two kinds of carbon materials. Laser Raman spectroscopy was employed to analyze the microstructures of different carbon materials, and the results show that because sp3 and sp2 hybrid states of carbon atoms in resin carbon produced more vibration modes, the resin carbon also has higher normal spectral emissivity and better characteristics of heat radiation.

  20. 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.

  1. 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.

  2. Muon Catalyzed Fusion

    NASA Technical Reports Server (NTRS)

    Armour, Edward A.G.

    2007-01-01

    Muon catalyzed fusion is a process in which a negatively charged muon combines with two nuclei of isotopes of hydrogen, e.g, a proton and a deuteron or a deuteron and a triton, to form a muonic molecular ion in which the binding is so tight that nuclear fusion occurs. The muon is normally released after fusion has taken place and so can catalyze further fusions. As the muon has a mean lifetime of 2.2 microseconds, this is the maximum period over which a muon can participate in this process. This article gives an outline of the history of muon catalyzed fusion from 1947, when it was first realised that such a process might occur, to the present day. It includes a description of the contribution that Drachrnan has made to the theory of muon catalyzed fusion and the influence this has had on the author's research.

  3. 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.

  4. 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

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

    PubMed

    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

  6. 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.

  7. 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.

  8. 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.

  9. Levitation of iridium and liquid mercury by ultrasound.

    PubMed

    Xie, W J; Cao, C D; Lü, Y J; Wei, B

    2002-09-01

    Single-axis acoustic levitation of the heaviest solid (iridium, rho=22.6 g cm(-3)) and liquid (mercury, rho=13.6 g cm(-3) on the Earth is achieved by greatly enhancing both the levitation force and stability through optimizing the geometric parameters of the levitator. The acoustically levitated Pb-Sn eutectic alloy melt (rho=8.5 g cm(-3)) is highly undercooled by up to 38 K, which results in a microstructural transition of "lamellae-broken lamellae-dendrites." The drastic enhancement of levitation capability indicates a broader application range of single-axis acoustic levitation. PMID:12225198

  10. 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.

  11. Intercalation of graphene on iridium with sodium atoms

    NASA Astrophysics Data System (ADS)

    Rut'kov, E. V.; Gall', N. R.

    2015-06-01

    It has been shown that sodium atoms deposited on the surface of graphene atop iridium at T ≤ 850 K diffuse under the graphene layer into an intercalated state and accumulate there in significant concentrations ˜(2-3) × 1014 atoms cm-2. The release of the atoms from under the graphene "carpet" takes place upon destruction of the layer at T ≥ 1800 K. The physical nature of the differences in the processes of release of atoms of different alkali metals from under graphene has been discussed.

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

    SciTech Connect

    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.

  13. 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.

  14. C-C Bond Formation via Copper-Catalyzed Conjugate Addition Reactions to Enones in Water at Room Temperature

    PubMed Central

    Lipshutz, Bruce H.; Huang, Shenlin; Leong, Wendy Wen Yi; Isley, Nicholas A.

    2013-01-01

    Conjugate addition reactions to enones can now be done in water at room temperature with in situ-generated organocopper reagents. Mixing an enone, zinc powder, TMEDA, and an alkyl halide in a micellar environemnt containing catalytic amounts of Cu(I), Ag(I), and Au(III), leads to 1,4-adducts in good isolated yields: no organometallic precursor is involved. PMID:23190029

  15. A calculation of the diffusion energies for adatoms on surfaces of F.C.C. metals

    NASA Technical Reports Server (NTRS)

    Halicioglu, T.; Pound, G. M.

    1979-01-01

    The activation energies for diffusion were determined for gold, platinum and iridium adatoms on plane and plane PT surfaces and were found to be in good agreement with the measurements reported by Bassett and Webber. The Lennard-Jones pair potentials were used to model the interatomic forces, and relaxation of the substrate atoms in near proximity to the adatom was considered in detail. The present calculations clarify the mechanism of the observed two-dimensional diffusion of platinum and iridium atoms on a plane PT surface. The results are compared with those obtained using Morse potential functions and different relaxation techniques.

  16. C-C bond fission pathways of chloroalkenyl alkoxy radicals

    NASA Astrophysics Data System (ADS)

    Zhang, Dan; Zhang, Renyi; Allen, David T.

    2003-01-01

    Density-functional theory and ab initio molecular orbital calculations have been employed to determine the structures and energetics of the chloroalkenyl alkoxy radicals arising from Cl-initiated reactions of isoprene as well as the transition states and products of their decomposition reactions. Geometry optimizations of the various species were performed at the Becke three parameter Lee-Yang-Parr (B3LYP)/6-31G(d,p) level, and single-point energies were computed using second-order Møller-Plesset and coupled-cluster theory with single and double excitations including perturbative corrections for the triple excitations. The activation and reaction energies of C-C bond scission of the alkoxy radicals are in the ranges of 12-25 and -3-22 kcal mol-1, respectively. Using the obtained activation barriers and transition state structures, we have calculated the high-pressure limit decomposition rates of the chloroalkenyl alkoxy radicals using transition state theory, ranging from 1×10-5 to 2×104 s-1. The results indicate that C-C bond decomposition of the chloroalkenyl alkoxy radicals is rather slow and likely plays a minor role in the Cl-isoprene reactions. Implications of the present results on the formation yields of methyl vinyl ketone, methacrolein, and 1-chloro-3-methyl-3-buten-2-one are discussed.

  17. 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.

  18. 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.

  19. 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.

  20. Single step radiolytic synthesis of iridium nanoparticles onto graphene oxide

    NASA Astrophysics Data System (ADS)

    Rojas, J. V.; Molina Higgins, M. C.; Toro Gonzalez, M.; Castano, C. E.

    2015-12-01

    In this work a new approach to synthesize iridium nanoparticles on reduced graphene oxide is presented. The nanoparticles were directly deposited and grown on the surface of the carbon-based support using a single step reduction method through gamma irradiation. In this process, an aqueous isopropanol solution containing the iridium precursor, graphene oxide, and sodium dodecyl sulfate was initially prepared and sonicated thoroughly to obtain a homogeneous dispersion. The samples were irradiated with gamma rays with energies of 1.17 and 1.33 MeV emitted from the spontaneous decay of the 60Co irradiator. The interaction of gamma rays with water in the presence of isopropanol generates highly reducing species homogeneously distributed in the solution that can reduce the Ir precursor down to a zero valence state. An absorbed dose of 60 kGy was used, which according to the yield of reducing species is sufficient to reduce the total amount of precursor present in the solution. This novel approach leads to the formation of 2.3 ± 0.5 nm Ir nanoparticles distributed along the surface of the support. The oxygenated functionalities of graphene oxide served as nucleation sites for the formation of Ir nuclei and their subsequent growth. XPS results revealed that the interaction of Ir with the support occurs through Irsbnd O bonds.

  1. 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.

  2. 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

  3. Formylated chloro-bridged iridium(III) dimers as OLED materials: opening up new possibilities.

    PubMed

    Wong, Michael Y; Xie, Guohua; Tourbillon, Clarisse; Sandroni, Martina; Cordes, David B; Slawin, Alexandra M Z; Samuel, Ifor D W; Zysman-Colman, Eli

    2015-05-14

    In this study, a series of four formyl-substituted chloro-bridged iridium(iii) dimers were prepared. Their absorption, photophysical and electrochemical properties were studied in dichloromethane solution. It was found that as the formyl content increased on the cyclometalating ligands, emission unexpectedly became brighter. Organic light-emitting diodes (OLEDs) were fabricated using each of these iridium dimers as the emitter. The OLED fabricated using the brightest of the series, 2b, as the dopant afforded a decent external quantum efficiency (EQE) of 2.6%. This suggests that chloro-bridged iridium dimers are potential candidates as solid-state emitters.

  4. SiC/C nanocomposites with inverse opal structure.

    PubMed

    Emelchenko, G A; Zhokhov, A A; Masalov, V M; Maximuk, M Yu; Fursova, T N; Bazhenov, A V; Zverkova, I I; Khasanov, S S; Steinman, E A; Tereshenko, A N

    2010-11-26

    The synthesis, morphology, structural and optical characteristics of SiC/C nanocomposites with an inverse opal lattice have been investigated. The samples were prepared by thermochemical treatment of opal matrices filled with carbon compounds which was followed by silicon dioxide dissolution. The samples were studied by electron microscopy, x-ray diffraction, photoluminescence, IR and Raman scattering spectroscopy. The electron microscopy data revealed a highly porous periodic structure which was a three-dimensional replica of the voids of the initial opal lattice. The hexagonal silicon carbide was found to be non-uniformly distributed throughout the volume, its greater part located in the surface layer up to 50 µm deep. The data of x-ray diffraction, IR and Raman scattering spectroscopy enabled us to assume that the composite had hexagonal diamond fragments. The photoluminescence and optical reflection spectra of the composites have been measured. PMID:21030770

  5. Defect structures in deformed F.C.C. metals

    SciTech Connect

    Dai, Y.; Victoria, M.

    1997-08-01

    A high density of small defect clusters, similar to those observed in irradiated or quenched metals, has been observed in the deformed f.c.c. metals Cu, Au and Ni. The preliminary results show that the defect clusters are predominantly stacking fault tetrahedral (SFT). The SFT number density, rather than the size distribution, is deformation dependent. The defect cluster density is greater in the vicinities of dislocation tangles and grain boundaries. Their size distribution is wider than that produced by irradiation with an important number of larger clusters being formed. It is argued that these deformation-produced clusters may play a role in determining the flow stress and work hardening at low deformations.

  6. Formation of annealing twins in f.c.c. crystals

    SciTech Connect

    Mahajan, S.; Pande, C.S.; Imam, M.A.; Rath, B.B.

    1997-06-01

    A microscopic model for the formation of annealing twins in f.c.c. crystals is proposed. It is argued that Shockley partial loops nucleate on consecutive {l_brace}111{r_brace} planes by growth accidents occurring on migrating {l_brace}111{r_brace} steps associated with a moving grain boundary. The higher the velocity of the boundary, the higher the twin density. The absence of twins in high stacking fault energy materials and the influence of temperature on twin density has been developed by examining the influence of deformation damage on the incidence of twinning in copper and the effect of boron in reducing twin density in annealed nickel.

  7. Catalyzed sodium chlorate candles

    NASA Technical Reports Server (NTRS)

    Malich, C. W.; Wydeven, T.

    1972-01-01

    The catalytic effect of cobalt powder on chlorate decomposition has been confirmed. Catalysis is enhanced by oxidation of the metal during burning. Catalysts other than cobalt compounds should also be effective; the complete elimination of fuel has shown that the oxidation of cobalt during decomposition is not a vital factor in the improved performance of catalyzed candles.

  8. Sub-Chronic Oral Exposure to Iridium (III) Chloride Hydrate in Female Wistar Rats: Distribution and Excretion of the Metal

    PubMed Central

    Iavicoli, Ivo; Fontana, Luca; Bergamaschi, Antonio; Conti, Marcelo Enrique; Pino, Anna; Mattei, Daniela; Bocca, Beatrice; Alimonti, Alessandro

    2012-01-01

    Iridium tissue distribution and excretion in female Wistar rats following oral exposure to iridium (III) chloride hydrate in drinking water (from 1 to 1000 ng/ml) in a sub-chronic oral study were determined. Samples of urine, feces, blood and organs (kidneys, liver, lung, spleen and brain) were collected at the end of exposure. The most prominent fractions of iridium were retained in kidney and spleen; smaller amounts were found in lungs, liver and brain. Iridium brain levels were lower than those observed in other tissues but this finding can support the hypothesis of iridium capability to cross the blood brain barrier. The iridium kidney levels rose significantly with the administered dose. At the highest dose, important amounts of the metal were found in serum, urine and feces. Iridium was predominantly excreted via feces with a significant linear correlation with the ingested dose, which is likely due to low intestinal absorption of the metal. However, at the higher doses iridium was also eliminated through urine. These findings may be useful to help in the understanding of the adverse health effects, particularly on the immune system, of iridium dispersed in the environment as well as in identifying appropriate biological indices of iridium exposure. PMID:22942873

  9. 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

  10. 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. PMID:25293511

  11. CYP719B1 is salutaridine synthase, the C-C phenol-coupling enzyme of morphine biosynthesis in opium poppy.

    PubMed

    Gesell, Andreas; Rolf, Megan; Ziegler, Jörg; Díaz Chávez, María Luisa; Huang, Fong-Chin; Kutchan, Toni M

    2009-09-01

    Morphine is a powerful analgesic natural product produced by the opium poppy Papaver somniferum. Although formal syntheses of this alkaloid have been reported, the morphine molecule contains five stereocenters and a C-C phenol linkage that to date render a total synthesis of morphine commercially unfeasible. The C-C phenol-coupling reaction along the biosynthetic pathway to morphine in opium poppy is catalyzed by the cytochrome P450-dependent oxygenase salutaridine synthase. We report herein on the identification of salutaridine synthase as a member of the CYP719 family of cytochromes P450 during a screen of recombinant cytochromes P450 of opium poppy functionally expressed in Spodoptera frugiperda Sf9 cells. Recombinant CYP719B1 is a highly stereo- and regioselective enzyme; of forty-one compounds tested as potential substrates, only (R)-reticuline and (R)-norreticuline resulted in formation of a product (salutaridine and norsalutaridine, respectively). To date, CYP719s have been characterized catalyzing only the formation of a methylenedioxy bridge in berberine biosynthesis (canadine synthase, CYP719A1) and in benzo[c]phenanthridine biosynthesis (stylopine synthase, CYP719A14). Previously identified phenol-coupling enzymes of plant alkaloid biosynthesis belong only to the CYP80 family of cytochromes. CYP719B1 therefore is the prototype for a new family of plant cytochromes P450 that catalyze formation of a phenol-couple.

  12. Iridium-alloy processing experience in FY 1990

    SciTech Connect

    Ohriner, E.K.

    1991-11-01

    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 melted, extruded, and then rolled to produce the sheet products. The work performed during FY 1990 included the consumable-electrode arc melting of four ingots and the extruding and rolling to sheet of four billets. Significant improvements made in the extruding and arc-melting processes during FY 1989 have been demonstrated to dramatically increase the rate of blank acceptance in nondestructive evaluations. Efforts to improve the rolling practice and to better characterize intermetallic particle distributions in the sheet are also described.

  13. 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.

  14. 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.

  15. Iridium abundance maxima in the Upper Cenomanian extinction interval

    NASA Astrophysics Data System (ADS)

    Orth, C. J.; Attrep, M., Jr.; Mao, X. Y.; Kauffman, E. G.; Diner, R.

    1988-04-01

    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.

  16. 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.

  17. 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.

  18. 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

  19. Palladium-Catalyzed Annulation of Arynes by ortho-Halobenzamides: Synthesis of Phenanthridinones

    PubMed Central

    Lu, Chun; Dubrovskiy, Anton V.

    2012-01-01

    The palladium-catalyzed annulation of arynes by substituted o-halobenzamides produces N-substituted phenanthridinones in good yields. This methodology provides this important heterocyclic ring system in a single step by simultaneous C-C and C-N bond formation, under relatively mild reaction conditions, and tolerates a variety of functional groups. PMID:23013049

  20. Synthesis of a chloro protected iridium nitrido complex.

    PubMed

    Sieh, Daniel; Schöffel, Julia; Burger, Peter

    2011-10-01

    Intramolecular activation processes of vulnerable ligand C-H bonds frequently limit the thermal stability and accessibility of late transition metal complexes with terminal metal nitrido units. In this study chloro substitution of the 2,6-ketimine N-aryl substituents (2,6-C(6)H(3)R(2), R = Cl) of the pyridine, diimine ligand is probed to increase the stability of square-planar iridium nitrido compounds. The thermal stability of iridium azido precursor and nitrido compounds was studied by a combination of thermoanalytical methods (DTG/MS and DSC) and were compared to the results for the related complexes with 2,6-dialkyl substituted N-aryl groups (R = Me, iPr). The investigations were complemented by DFT calculations, which allowed us to unravel details of the thermal decomposition pathways and provided mechanistic insights of further conversion steps and fluctional processes. The DTG/MS and DSC measurements revealed two different types of thermolysis pathways for the azido compounds. For the complexes with R = Cl and iPr substituents, two well-separated exothermic processes were observed. The first moderately exothermic loss of N(2) is followed by a second, strongly exothermic transformation. This contrasts the experimental results for the compound with 2,6-dimethyl substituents (R = Me), where both steps proceed concurrently in the same temperature range. The separation of the two thermal steps in the 2,6-dichloro substituted derivative allowed us to develop a protocol for the isolation of the highly insoluble nitrido complex, which was characterized by UV/vis, IR-spectroscopy and elemental analysis. Its constitution was further confirmed by reaction with silanes, which gave the corresponding silyl amido complexes.

  1. JMS Proxy and C/C++ Client SDK

    NASA Technical Reports Server (NTRS)

    Wolgast, Paul; Pechkam, Paul

    2007-01-01

    JMS Proxy and C/C++ Client SDK (JMS signifies "Java messaging service" and "SDK" signifies "software development kit") is a software package for developing interfaces that enable legacy programs (here denoted "clients") written in the C and C++ languages to communicate with each other via a JMS broker. This package consists of two main components: the JMS proxy server component and the client C library SDK component. The JMS proxy server component implements a native Java process that receives and responds to requests from clients. This component can run on any computer that supports Java and a JMS client. The client C library SDK component is used to develop a JMS client program running in each affected C or C++ environment, without need for running a Java virtual machine in the affected computer. A C client program developed by use of this SDK has most of the quality-of-service characteristics of standard Java-based client programs, including the following: Durable subscriptions; Asynchronous message receipt; Such standard JMS message qualities as "TimeToLive," "Message Properties," and "DeliveryMode" (as the quoted terms are defined in previously published JMS documentation); and Automatic reconnection of a JMS proxy to a restarted JMS broker.

  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. In vitro electrical properties for iridium oxide versus titanium nitride stimulating electrodes.

    PubMed

    Weiland, James D; Anderson, David J; Humayun, Mark S

    2002-12-01

    Stimulating electrode materials must be capable of supplying high-density electrical charge to effectively activate neural tissue. Platinum is the most commonly used material for neural stimulation. Two other materials have been considered: iridium oxide and titanium nitride. This study directly compared the electrical characteristics of iridium oxide and titanium nitride by fabricating silicon substrate probes that differed only in the material used to form the electrode. Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode. Direct measurement of the electrode potential in response to a biphasic current pulse confirmed that iridium oxide uses less voltage to transfer the same amount of charge, therefore using less power. The charge injection limit for titanium nitride was 0.87 mC/cm2, contradicting other reports estimating that titanium nitride was capable of injecting 22 mC/cm2. Iridium oxide charge storage was 4 mC/cm2, which is comparable to other published values for iridium oxide. Electrode efficiency will lead to an overall more efficient and effective device.

  4. Tritium catalyzed deuterium tokamaks

    SciTech Connect

    Greenspan, E.; Miley, G.H.; Jung, J.; Gilligan, J.

    1984-04-01

    A preliminary assessment of the promise of the Tritium Catalyzed Deuterium (TCD) tokamak power reactors relative to that of deuterium-tritium (D-T) and catalyzed deuterium (Cat-D) tokamaks is undertaken. The TCD mode of operation is arrived at by converting the /sup 3/He from the D(D,n)/sup 3/He reaction into tritium, by neutron capture in the blanket; the tritium thus produced is fed into the plasma. There are three main parts to the assessment: blanket study, reactor design and economic analysis and an assessment of the prospects for improvements in the performance of TCD reactors (and in the promise of the TCD mode of operation, in general).

  5. Pd loaded amphiphilic COF as catalyst for multi-fold Heck reactions, C-C couplings and CO oxidation

    PubMed Central

    Mullangi, Dinesh; Nandi, Shyamapada; Shalini, Sorout; Sreedhala, Sheshadri; Vinod, Chathakudath P.; Vaidhyanathan, Ramanathan

    2015-01-01

    COFs represent a class of polymers with designable crystalline structures capable of interacting with active metal nanoparticles to form excellent heterogeneous catalysts. Many valuable ligands/monomers employed in making coordination/organic polymers are prepared via Heck and C-C couplings. Here, we report an amphiphilic triazine COF and the facile single-step loading of Pd0 nanoparticles into it. An 18–20% nano-Pd loading gives highly active composite working in open air at low concentrations (Conc. Pd(0) <0.05 mol%, average TON 1500) catalyzing simultaneous multiple site Heck couplings and C-C couplings using ‘non-boronic acid’ substrates, and exhibits good recyclability with no sign of catalyst leaching. As an oxidation catalyst, it shows 100% conversion of CO to CO2 at 150 °C with no loss of activity with time and between cycles. Both vapor sorptions and contact angle measurements confirm the amphiphilic character of the COF. DFT-TB studies showed the presence of Pd-triazine and Pd-Schiff bond interactions as being favorable. PMID:26057044

  6. Biosynthetic pathway toward carbohydrate-like moieties of alnumycins contains unusual steps for C-C bond formation and cleavage

    PubMed Central

    Oja, Terhi; Klika, Karel D.; Appassamy, Laura; Sinkkonen, Jari; Mäntsälä, Pekka; Niemi, Jarmo; Metsä-Ketelä, Mikko

    2012-01-01

    Carbohydrate moieties are important components of natural products, which are often imperative for the solubility and biological activity of the compounds. The aromatic polyketide alnumycin A contains an extraordinary sugar-like 4′-hydroxy-5′-hydroxymethyl-2′,7′-dioxane moiety attached via a carbon-carbon bond to the aglycone. Here we have extensively investigated the biosynthesis of the dioxane unit through 13C labeling studies, gene inactivation experiments and enzymatic synthesis. We show that AlnA and AlnB, members of the pseudouridine glycosidase and haloacid dehalogenase enzyme families, respectively, catalyze C-ribosylation conceivably through Michael-type addition of d-ribose-5-phosphate and dephosphorylation. The ribose moiety may be attached both in furanose (alnumycin C) and pyranose (alnumycin D) forms. The C1′-C2′ bond of alnumycin C is subsequently cleaved and the ribose unit is rearranged into an unprecedented dioxolane (cis-bicyclo[3.3.0]-2′,4′,6′-trioxaoctan-3′β-ol) structure present in alnumycin B. The reaction is catalyzed by Aln6, which belongs to a previously uncharacterized enzyme family. The conversion was accompanied with consumption of O2 and formation of H2O2, which allowed us to propose that the reaction may proceed via hydroxylation of C1′ followed by retro-aldol cleavage and acetal formation. Interestingly, no cofactors could be detected and the reaction was also conducted in the presence of metal chelating agents. The last step is the conversion of alnumycin B into the final end-product alnumycin A catalyzed by Aln4, an NADPH-dependent aldo-keto reductase. This characterization of the dioxane biosynthetic pathway sets the basis for the utilization of C-C bound ribose, dioxolane and dioxane moieties in the generation of improved biologically active compounds. PMID:22474343

  7. Emissive osmium(II) complexes supported by N-heterocyclic carbene-based C^C^C-pincer ligands and aromatic diimines.

    PubMed

    Chung, Lai-Hon; Chan, Siu-Chung; Lee, Wing-Chun; Wong, Chun-Yuen

    2012-08-20

    Osmium(II) complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-methylimidazolin-2-ylidene)phenyl anion (C(1)^C^C(1)) or 1,3-bis(3-methylbenzimidazolin-2-ylidene)phenyl anion (C(2)^C^C(2)) and aromatic diimine (2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), or 4,4'-diphenyl-2,2'-bipyridine (Ph(2)bpy)) in the form of [Os(C^C^C)(N^N)(CO)](+) have been prepared. Crystal structures for these complexes show that the Os-C(NHC) bonds are essentially single (Os-C(NHC) distances = 2.079(5)-2.103(7) Å). Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ(max) = 493-536 nm, ε(max) = (5-10) × 10(3) dm(3) mol(-1) cm(-1), solvent = CH(3)CN) originate from a d(π)(Os(II)) → π*(N^N) metal-to-ligand charge transfer transition, where the d(π)(Os(II)) and π*(N^N) levels contain significant contribution from the C^C^C ligands. All these complexes are emissive in the red-spectral region (674-731 nm) with quantum yields of 10(-4)-10(-2) and emission lifetimes of around 1-6 μs. Transient absorption spectroscopy and spectroelectrochemical measurements have also been used to probe the nature of the emissive excited-states. Overall, this joint experimental and theoretical investigation reveals that the C^C^C ligands can be used to modulate the photophysical properties of a [Os(N^N)] core via the formation of the hybrid [Os + C^C^C] frontier orbitals. PMID:22873818

  8. Catalyzed Ceramic Burner Material

    SciTech Connect

    Barnes, Amy S., Dr.

    2012-06-29

    Catalyzed combustion offers the advantages of increased fuel efficiency, decreased emissions (both NOx and CO), and an expanded operating range. These performance improvements are related to the ability of the catalyst to stabilize a flame at or within the burner media and to combust fuel at much lower temperatures. This technology has a diverse set of applications in industrial and commercial heating, including boilers for the paper, food and chemical industries. However, wide spread adoption of catalyzed combustion has been limited by the high cost of precious metals needed for the catalyst materials. The primary objective of this project was the development of an innovative catalyzed burner media for commercial and small industrial boiler applications that drastically reduce the unit cost of the catalyzed media without sacrificing the benefits associated with catalyzed combustion. The scope of this program was to identify both the optimum substrate material as well as the best performing catalyst construction to meet or exceed industry standards for durability, cost, energy efficiency, and emissions. It was anticipated that commercial implementation of this technology would result in significant energy savings and reduced emissions. Based on demonstrated achievements, there is a potential to reduce NOx emissions by 40,000 TPY and natural gas consumption by 8.9 TBtu in industries that heavily utilize natural gas for process heating. These industries include food manufacturing, polymer processing, and pulp and paper manufacturing. Initial evaluation of commercial solutions and upcoming EPA regulations suggests that small to midsized boilers in industrial and commercial markets could possibly see the greatest benefit from this technology. While out of scope for the current program, an extension of this technology could also be applied to catalytic oxidation for volatile organic compounds (VOCs). Considerable progress has been made over the course of the grant

  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. Evaluation of oxide-coated iridium-rhenium chambers

    NASA Astrophysics Data System (ADS)

    Reed, Brian D.

    1994-03-01

    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

  11. Metal-ligand cooperation in catalytic intramolecular hydroamination: a computational study of iridium-pyrazolato cooperative activation of aminoalkenes.

    PubMed

    Tobisch, Sven

    2012-06-01

    The present study comprehensively explores diverse mechanistic pathways for intramolecular hydroamination of prototype 2,2-dimethyl-4-penten-1-amine by Cp*Ir chloropyrazole (1; Cp*=pentamethylcyclopentadienyl) in the presence of KOtBu base with the aid of density functional theory (DFT) calculations. The most accessible mechanistic pathway for catalytic turnover commences from Cp*Ir pyrazolato (Pz) substrate adduct 2⋅S, representing the catalytically competent compound and proceeds via initial electrophilic activation of the olefin C=C bond by the metal centre. It entails 1) facile and reversible anti nucleophilic amine attack on the iridium-olefin linkage; 2) Ir-C bond protonolysis via stepwise transfer of the ammonium N-H proton at the zwitterionic [Cp*IrPz-alkyl] intermediate onto the metal that is linked to turnover-limiting, reductive, cycloamine elimination commencing from a high-energy, metastable [Cp*IrPz-hydrido-alkyl] species; and 3) subsequent facile cycloamine liberation to regenerate the active catalyst species. The amine-iridium bound 2 a⋅S likely corresponds to the catalyst resting state and the catalytic reaction is expected to proceed with a significant primary kinetic isotope. This study unveils the vital role of a supportive hydrogen-bonded network involving suitably aligned β-basic pyrazolato and cycloamido moieties together with an external amine molecule in facilitating metal protonation and reductive elimination. Cooperative hydrogen bonding thus appears pivotal for effective catalysis. The mechanistic scenario is consonant with catalyst performance data and furthermore accounts for the variation in performance for [Cp*IrPz] compounds featuring a β- or γ-basic pyrazolato unit. As far as the route that involves amine N-H bond activation is concerned, a thus far undocumented pathway for concerted amidoalkene → cycloamine conversion through olefin protonation by the pyrazole N-H concurrent with N-C ring closure is disclosed as a

  12. Measurements of ψ (3686 )→K-Λ Ξ¯ ++c .c . and ψ (3686 )→γ K-Λ Ξ¯ ++c .c .

    NASA Astrophysics Data System (ADS)

    Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; An, F. F.; An, Q.; Bai, J. Z.; Baldini Ferroli, R.; Ban, Y.; Bennett, D. W.; Bennett, J. V.; Bertani, M.; Bettoni, D.; Bian, J. M.; Bianchi, F.; Boger, E.; Bondarenko, O.; Boyko, I.; Briere, R. A.; Cai, H.; Cai, X.; Cakir, O.; Calcaterra, A.; Cao, G. F.; Cetin, S. A.; Chang, J. F.; Chelkov, G.; Chen, G.; Chen, H. S.; Chen, H. Y.; Chen, J. C.; Chen, M. L.; Chen, S. J.; Chen, X.; Chen, X. R.; Chen, Y. B.; Cheng, H. P.; Chu, X. K.; Cibinetto, G.; Cronin-Hennessy, D.; Dai, H. L.; Dai, J. P.; Dbeyssi, A.; Dedovich, D.; Deng, Z. Y.; Denig, A.; Denysenko, I.; Destefanis, M.; de Mori, F.; Ding, Y.; Dong, C.; Dong, J.; Dong, L. Y.; Dong, M. Y.; Du, S. X.; Duan, P. F.; Fan, J. Z.; Fang, J.; Fang, S. S.; Fang, X.; Fang, Y.; Fava, L.; Feldbauer, F.; Felici, G.; Feng, C. Q.; Fioravanti, E.; Fritsch, M.; Fu, C. D.; Gao, Q.; Gao, X. Y.; Gao, Y.; Gao, Z.; Garzia, I.; Geng, C.; Goetzen, K.; Gong, W. X.; Gradl, W.; Greco, M.; Gu, M. H.; Gu, Y. T.; Guan, Y. H.; Guo, A. Q.; Guo, L. B.; Guo, Y.; Guo, Y. P.; Haddadi, Z.; Hafner, A.; Han, S.; Han, Y. L.; Hao, X. Q.; Harris, F. A.; He, K. L.; He, Z. Y.; Held, T.; Heng, Y. K.; Hou, Z. L.; Hu, C.; Hu, H. M.; Hu, J. F.; Hu, T.; Hu, Y.; Huang, G. M.; Huang, G. S.; Huang, H. P.; Huang, J. S.; Huang, X. T.; Huang, Y.; Hussain, T.; Ji, Q.; Ji, Q. P.; Ji, X. B.; Ji, X. L.; Jiang, L. L.; Jiang, L. W.; Jiang, X. S.; Jiao, J. B.; Jiao, Z.; Jin, D. P.; Jin, S.; Johansson, T.; Julin, A.; Kalantar-Nayestanaki, N.; Kang, X. L.; Kang, X. S.; Kavatsyuk, M.; Ke, B. C.; Kliemt, R.; Kloss, B.; Kolcu, O. B.; Kopf, B.; Kornicer, M.; Kühn, W.; Kupsc, A.; Lai, W.; Lange, J. S.; Lara, M.; Larin, P.; Leng, C.; Li, C. H.; Li, Cheng; Li, D. M.; Li, F.; Li, G.; Li, H. B.; Li, J. C.; Li, Jin; Li, K.; Li, K.; Li, Lei; Li, P. R.; Li, T.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. M.; Li, X. N.; Li, X. Q.; Li, Z. B.; Liang, H.; Liang, Y. F.; Liang, Y. T.; Liao, G. R.; Lin, D. X.; Liu, B. J.; Liu, C. X.; Liu, F. H.; Liu, Fang; Liu, Feng; Liu, H. B.; Liu, H. H.; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. P.; Liu, J. Y.; Liu, K.; Liu, K. Y.; Liu, L. D.; Liu, P. L.; Liu, Q.; Liu, S. B.; Liu, X.; Liu, X. X.; Liu, Y. B.; Liu, Z. A.; Liu, Zhiqiang; Liu, Zhiqing; Loehner, H.; Lou, X. C.; Lu, H. J.; Lu, J. G.; Lu, R. Q.; Lu, Y.; Lu, Y. P.; Luo, C. L.; Luo, M. X.; Luo, T.; Luo, X. L.; Lv, M.; Lyu, X. R.; Ma, F. C.; Ma, H. L.; Ma, L. L.; Ma, Q. M.; Ma, S.; Ma, T.; Ma, X. N.; Ma, X. Y.; Maas, F. E.; Maggiora, M.; Malik, Q. A.; Mao, Y. J.; Mao, Z. P.; Marcello, S.; Messchendorp, J. G.; Min, J.; Min, T. J.; Mitchell, R. E.; Mo, X. H.; Mo, Y. J.; Morales Morales, C.; Moriya, K.; Muchnoi, N. Yu.; Muramatsu, H.; Nefedov, Y.; Nerling, F.; Nikolaev, I. B.; Ning, Z.; Nisar, S.; Niu, S. L.; Niu, X. Y.; Olsen, S. L.; Ouyang, Q.; Pacetti, S.; Patteri, P.; Pelizaeus, M.; Peng, H. P.; Peters, K.; Pettersson, J.; Ping, J. L.; Ping, R. G.; Poling, R.; Pu, Y. N.; Qi, M.; Qian, S.; Qiao, C. F.; Qin, L. Q.; Qin, N.; Qin, X. S.; Qin, Y.; Qin, Z. H.; Qiu, J. F.; Rashid, K. H.; Redmer, C. F.; Ren, H. L.; Ripka, M.; Rong, G.; Ruan, X. D.; Santoro, V.; Sarantsev, A.; Savrié, M.; Schoenning, K.; Schumann, S.; Shan, W.; Shao, M.; Shen, C. P.; Shen, P. X.; Shen, X. Y.; Sheng, H. Y.; Song, W. M.; Song, X. Y.; Sosio, S.; Spataro, S.; Sun, G. X.; Sun, J. F.; Sun, S. S.; Sun, Y. J.; Sun, Y. Z.; Sun, Z. J.; Sun, Z. T.; Tang, C. J.; Tang, X.; Tapan, I.; Thorndike, E. H.; Tiemens, M.; Toth, D.; Ullrich, M.; Uman, I.; Varner, G. S.; Wang, B.; Wang, B. L.; Wang, D.; Wang, D. Y.; Wang, K.; Wang, L. L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, Q. J.; Wang, S. G.; Wang, W.; Wang, X. F.; Wang, Y. D.; Wang, Y. F.; Wang, Y. Q.; Wang, Z.; Wang, Z. G.; Wang, Z. H.; Wang, Z. Y.; Weber, T.; Wei, D. H.; Wei, J. B.; Weidenkaff, P.; Wen, S. P.; Wiedner, U.; Wolke, M.; Wu, L. H.; Wu, Z.; Xia, L. G.; Xia, Y.; Xiao, D.; Xiao, Z. J.; Xie, Y. G.; Xiu, Q. L.; Xu, G. F.; Xu, L.; Xu, Q. J.; Xu, Q. N.; Xu, X. P.; Yan, L.; Yan, W. B.; Yan, W. C.; Yan, Y. H.; Yang, H. X.; Yang, L.; Yang, Y.; Yang, Y. X.; Ye, H.; Ye, M.; Ye, M. H.; Yin, J. H.; Yu, B. X.; Yu, C. X.; Yu, H. W.; Yu, J. S.; Yuan, C. Z.; Yuan, W. L.; Yuan, Y.; Yuncu, A.; Zafar, A. A.; Zallo, A.; Zeng, Y.; Zhang, B. X.; Zhang, B. Y.; Zhang, C.; Zhang, C. C.; Zhang, D. H.; Zhang, H. H.; Zhang, H. Y.; Zhang, J. J.; Zhang, J. L.; Zhang, J. Q.; Zhang, J. W.; Zhang, J. Y.; Zhang, J. Z.; Zhang, K.; Zhang, L.; Zhang, S. H.; Zhang, X. Y.; Zhang, Y.; Zhang, Y. H.; Zhang, Y. T.; Zhang, Z. H.; Zhang, Z. P.; Zhang, Z. Y.; Zhao, G.; Zhao, H. S.; Zhao, J. W.; Zhao, J. Y.; Zhao, J. Z.; Zhao, Lei; Zhao, Ling; Zhao, M. G.; Zhao, Q.; Zhao, Q. W.; Zhao, S. J.; Zhao, T. C.; Zhao, Y. B.; Zhao, Z. G.; Zhemchugov, A.; Zheng, B.; Zheng, J. P.; Zheng, W. J.; Zheng, Y. H.; Zhong, B.; Zhou, L.; Zhou, Li; Zhou, X.; Zhou, X. K.; Zhou, X. R.; Zhou, X. Y.; Zhu, K.; Zhu, K. J.; Zhu, S.; Zhu, X. L.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Z. A.; Zhuang, J.; Zotti, L.; Zou, B. S.; Zou, J. H.; Besiii Collaboration

    2015-05-01

    Using a sample of 1.06 ×1 08ψ (3686 ) events produced in e+e- collisions at √{s }=3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays ψ (3686 )→K-Λ Ξ¯ ++c .c . and ψ (3686 )→γ K-Λ Ξ¯ ++c .c . . We observe two hyperons, Ξ (1690 )- and Ξ (1820 )- , in the K-Λ invariant mass distribution in the decay ψ (3686 )→K-Λ Ξ¯ ++c .c . with significances of 4.9 σ and 6.2 σ , respectively. The branching fractions of ψ (3686 )→K-Λ Ξ¯ ++c .c . , ψ (3686 )→K-Σ0Ξ¯ ++c .c . , ψ (3686 )→γ χc J→γ K-Λ Ξ¯ ++c .c . (J =0 , 1, 2), and ψ (3686 )→Ξ (1690 /1820 )-Ξ¯ ++c .c . with subsequent decay Ξ (1690 /1820 )-→K-Λ are measured for the first time.

  13. Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

    PubMed

    Park, Young Jun; Park, Jung-Woo; Jun, Chul-Ho

    2008-02-01

    components using a hydrogen-bonded self-assembled system as a catalyst support. This catalyst-recovery system provides a homogeneous phase at high temperature during the reaction and a heterogeneous phase at room temperature after the reaction. The product could be separated conveniently from the self-assembly support system by decanting the upper layer. The immobilized catalysts of both 2-aminopyridine and rhodium metal species sustained high catalytic activity for up to the eight catalytic reactions. In conclusion, the successful incorporation of an organocatalytic cycle into a transition metal catalyzed reaction led us to find MOCC for C-H and C-C bond activation. In addition, the hydrogen-bonded self-assembled support has been developed for an efficient and effective recovery system of homogeneous catalysts and could be successful in immobilizing both metal and organic catalysts.

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

    PubMed

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

    2016-02-01

    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. PMID:26753824

  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. 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.

  17. 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.

  18. 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.

  19. Palladium-Catalyzed Regioselective Difluoroalkylation and Carbonylation of Alkynes.

    PubMed

    Wang, Qiang; He, Yu-Tao; Zhao, Jia-Hui; Qiu, Yi-Feng; Zheng, Lan; Hu, Jing-Yuan; Yang, Yu-Chen; Liu, Xue-Yuan; Liang, Yong-Min

    2016-06-01

    A novel, four-component synthetic strategy to synthesize a series of β-difluoroalkyl unsaturated esters/amides with high regioslectivity is described. This Pd-catalyzed difluoroalkylation and carbonylation reaction can be carried out with simple starting materials. Through this protocol, two new C-C bonds (including one C-CF2 bond) and one C-O(N) bond are constructed simultaneously in a single step. The synthetic utility of this reaction system has been certified by the applicability to a wide scope of alkynes and nucleophiles. Preliminary mechanistic studies suggest that the difluoroalkyl radical pathway is involved in this reaction. PMID:27191858

  20. 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.

  1. 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.

  2. 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.

  3. High-Turnover Aromatic C-H Borylation Catalyzed by POCOP-Type Pincer Complexes of Iridium.

    PubMed

    Press, Loren P; Kosanovich, Alex J; McCulloch, Billy J; Ozerov, Oleg V

    2016-08-01

    The catalytic C-H borylation of arenes with HBpin (pin = pinacolate) using POCOP-type pincer complexes of Ir has been demonstrated, with turnover numbers exceeding 10 000 in some cases. The selectivity of C-H activation was based on steric preferences and largely mirrored that found in other Ir borylation catalysts. Catalysis in the (POCOP)Ir system depends on the presence of stoichiometric quantities of sacrificial olefin, which is hydrogenated to consume the H2 equivalents generated in the borylation of C-H bonds with HBpin. Smaller olefins such as ethylene or 1-hexene were more advantageous to catalysis than sterically encumbered tert-butylethylene (TBE). Olefin hydroboration is a competing side reaction. The synthesis and isolation of multiple complexes potentially relevant to catalysis permitted examination of several key elementary reactions. These experiments indicate that the C-H activation step in catalysis ostensibly involves oxidative addition of an aromatic C-H bond to the three-coordinate (POCOP)Ir species. The olefin is mechanistically critical to gain access to this 14-electron, monovalent Ir intermediate. C-H activation at Ir(I) here is in contrast to the olefin-free catalysis with state-of-the-art Ir complexes supported by neutral bidentate ligands, where the C-H activating step is understood to involve trivalent Ir-boryl intermediates. PMID:27327895

  4. N-tosylhydrazones: versatile reagents for metal-catalyzed and metal-free cross-coupling reactions.

    PubMed

    Shao, Zhihui; Zhang, Hongbin

    2012-01-21

    Transition metal-catalyzed cross-coupling reactions have been established as one of the most powerful tools for the construction of C-C and C-X bonds. In this context, the development of novel metal-catalyzed cross-coupling processes that do not require stoichiometric organometallic reagents is particularly attractive. Recently, N-tosylhydrazones have emerged as a new type of versatile coupling partners for transition metal-catalyzed cross-coupling reactions as well as metal-free cross-coupling reactions, and have attracted increasing attention. This tutorial review summarizes recent important developments in this area with N-tosylhydrazones as versatile coupling partners.

  5. 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

  6. Near-Infrared Phosphorescent Iridium(III) Benzonorrole Complexes Possessing Pyridine-based Axial Ligands.

    PubMed

    Maurya, Yogesh Kumar; Ishikawa, Takahiro; Kawabe, Yasunori; Ishida, Masatoshi; Toganoh, Motoki; Mori, Shigeki; Yasutake, Yuhsuke; Fukatsu, Susumu; Furuta, Hiroyuki

    2016-06-20

    Novel near-infrared phosphorescent iridium(III) complexes based on benzo-annulated N-linked corrole analogue (termed as benzonorrole) were synthesized. The structures of the complexes revealed octahedral coordination geometries involving an organometallic iridium-carbon bond with two external axial ligands. Interestingly, the iridium(III) complex exhibits near-infrared phosphorescence at room temperature at wavelengths beyond 900 nm. The significant redshift of the emission, as compared to the corrole congener, is originated from the ligand-centered triplet character. The fine-tuning of the photophysical properties of the complexes was achieved by introducing electron-donating and electron-withdrawing substituents on the axial pyridine ligands. PMID:27249778

  7. Preparation of iridium targets by electrodeposition for neutron capture cross section measurements

    DOE PAGES

    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.

  8. 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.

    2015-11-18

    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.

  9. Grain-boundary cavitation and weld-underbead cracking in DOP-26 iridium alloy

    SciTech Connect

    Mosley, W.C. Jr.

    1983-01-01

    Plutonium-238 oxide fuel pellets for the General Purpose Heat Source Radioisotopic thermoelectric generators to be used on the NASA Galileo Mission to Jupiter and the International Solar Polar Mission are produced and encapsulated in DOP-26 iridium alloy at the Savannah River Plant. DOP-26 iridium alloy was developed at the Oak Ridge National Laboratory and contains nominally 0.3 weight-percent tungsten, 60-ppM thorium and 50-ppM aluminum. Underbead cracks occasionally occur in the girth weld on the iridium alloy cladding in the area where the gas tungsten arc is quenched. A variety of electron beam techniques have been used to determine the cause of cracking. Results are discussed. (WHK)

  10. 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

    2016-07-01

    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. PMID:27168492

  11. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

    A method of bonding substrates by hydroxide-catalyzed hydration/dehydration involves applying a bonding material to at least one surface to be bonded, and placing the at least one surface sufficiently close to another surface such that a bonding interface is formed between them. A bonding material of the invention comprises a source of hydroxide ions, and may optionally include a silicate component, a particulate filling material, and a property-modifying component. Bonding methods of the invention reliably and reproducibly provide bonds which are strong and precise, and which may be tailored according to a wide range of possible applications. Possible applications for bonding materials of the invention include: forming composite materials, coating substrates, forming laminate structures, assembly of precision optical components, and preparing objects of defined geometry and composition. Bonding materials and methods of preparing the same are also disclosed.

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

    PubMed

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

    2014-02-01

    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.

  13. 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.

  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. PMID:27333555

  16. Tandem reactions initiated by copper-catalyzed cross-coupling: a new strategy towards heterocycle synthesis.

    PubMed

    Liu, Yunyun; Wan, Jie-Ping

    2011-10-21

    Copper-catalyzed cross-coupling reactions which lead to the formation of C-N, C-O, C-S and C-C bonds have been recognized as one of the most useful strategies in synthetic organic chemistry. During past decades, important breakthroughs in the study of Cu-catalyzed coupling processes demonstrated that Cu-catalyzed reactions are broadly applicable to a variety of research fields related to organic synthesis. Representatively, employing these coupling transformations as key steps, a large number of tandem reactions have been developed for the construction of various heterocyclic compounds. These tactics share the advantages of high atom economics of tandem reactions as well as the broad tolerance of Cu-catalyst systems. Therefore, Cu-catalyzed C-X (X = N, O, S, C) coupling transformation-initiated tandem reactions were quickly recognized as a strategy with great potential for synthesizing heterocyclic compounds and gained worldwide attention. In this review, recent research progress in heterocycle syntheses using tandem reactions initiated by copper-catalyzed coupling transformations, including C-N, C-O, C-S as well as C-C coupling processes are summarized. PMID:21879127

  17. Iridium {mu}-imido/amido A-frame complexes

    SciTech Connect

    Ye, Changqing; Sharp, P.R.

    1995-01-04

    The reaction of Ir{sub 2}Cl{sub 2}(CO){sub 2}({mu}-dppm){sub 2}(dppm=bis(diphenylphosphino)methane) with 2 equiv of LiNHR yields Ir{sub 2}({mu}-NR)(CO){sub 2}({mu}-dppm){sub 2}, (1) (R=p-tolyl,Ph,p-BrC{sub 6}H{sub 4}), or its tautomer Ir{sub 2}({mu}-NHR)(CO){sub 2}({mu}-dppm)-({mu}-dppm-H), (2) (dppm-H = bis(diphenylphosphino)methanide; R= Et, Bu{sup 5}). NMR data suggest that (1) (R=p-tolyl, Ph, p-BrC{sub 6}H{sub 4}) are in equilibrium with small amounts of (2) in polar solvents. An X-ray structural determination of (1) (R = p-tolyl) shows that the imido nitrogen atom links two iridium atoms at the apex of an A-frame complex. A very short N-C distance in the imido group suggests extensive N-lone pair donation to the tolyl ring. Crystals of (1) (R = p-tolyl) from benzene are tetragonal (P4{sub 3}) with a = 21.337(1) {Angstrom},c = 14.478-(2) {Angstrom}, and Z = 4. With the exception of R=p-NO{sub 2}C{sub 6}H{sub 4}, p-BrC{sub 6}H{sub 4}, and Et, the complexes react with 1 equiv of CO at ambient temperature to form Ir{sub 2}(CO){sub 3}({mu}-dppm){sub 2} as the major metal containing product. For R = Et, the reaction generates the unstable isocyanate complex Ir{sub 2}(CO){sub 4}({mu}-dppm){sub 2} and amine except for the p-NO{sub 2}C{sub 6}H{sub 4} complex, which gives a complex mixture of products.

  18. Nickel-Catalyzed Allylic Alkylation with Diarylmethane Pronucleophiles: Reaction Development and Mechanistic Insights.

    PubMed

    Sha, Sheng-Chun; Jiang, Hui; Mao, Jianyou; Bellomo, Ana; Jeong, Soo A; Walsh, Patrick J

    2016-01-18

    Palladium-catalyzed allylic substitution reactions are among the most efficient methods to construct C-C bonds between sp(3)-hybridized carbon atoms. In contrast, much less work has been done with nickel catalysts, perhaps because of the different mechanisms of the allylic substitution reactions. Palladium catalysts generally undergo substitution by a "soft"-nucleophile pathway, wherein the nucleophile attacks the allyl group externally. Nickel catalysts are usually paired with "hard" nucleophiles, which attack the metal before C-C bond formation. Introduced herein is a rare nickel-based catalyst which promotes substitution with diarylmethane pronucleophiles by the soft-nucleophile pathway. Preliminary studies on the asymmetric allylic alkylation are promising.

  19. Practical synthesis of pyrazoles via a copper-catalyzed relay oxidation strategy.

    PubMed

    Tang, Xiaodong; Huang, Liangbin; Yang, Jidan; Xu, Yanli; Wu, Wanqing; Jiang, Huanfeng

    2014-12-01

    Various 1,3- and 1,3,4-substituted pyrazoles are smoothly formed via copper-catalyzed cascade reactions of oxime acetates, amines and aldehydes. This relay oxidative process involves copper-promoted N-O bond cleavage and C-C/C-N/N-N bond formations to furnish pyrazolines, and sequential Cu-O2 system-involved oxidative dehydrogenation of pyrazolines to afford pyrazoles. This transformation provides a novel and versatile approach for the synthesis of pyrazoles, with an inexpensive copper catalyst and green oxidants. It is atom- and step-economical, and possesses a good functional group tolerance, as well as operational simplicity. PMID:25319768

  20. TBAI-catalyzed oxidative C-H functionalization: a new route to benzo[b]phosphole oxides.

    PubMed

    Zhang, Yun; Hu, Gaobo; Ma, Dumei; Xu, Pengxiang; Gao, Yuxing; Zhao, Yufen

    2016-02-14

    The first metal-free, efficient TBAI-catalyzed radical addition/cyclization of diaryl(arylethynyl)phosphine oxides with toluene derivatives has been developed, affording a general, one-step approach to structurally sophisticated benzo[b]phosphole oxides via sequential C-H functionalization along with the formation of two new C-C bonds.

  1. Cu(II)-catalyzed esterification reaction via aerobic oxidative cleavage of C(CO)-C(alkyl) bonds.

    PubMed

    Ma, Ran; He, Liang-Nian; Liu, An-Hua; Song, Qing-Wen

    2016-02-01

    A novel Cu(II)-catalyzed aerobic oxidative esterification of simple ketones for the synthesis of esters has been developed with wide functional group tolerance. This process is assumed to go through a tandem sequence consisting of α-oxygenation/esterification/nucleophilic addition/C-C bond cleavage and carbon dioxide is released as the only byproduct.

  2. An efficient copper-catalyzed cross-coupling reaction of alkyl-triflates with alkyl-Grignard reagents

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A highly efficient method for the formation of C-C covalent bonds by cross-coupling reaction between alkyl-triflates and alkyl-Grignard reagents catalyzed by copper catalyst, Li2CuCl4, is described. The reaction works with most primary triflates in diethyl ether at low temperature within 0.5-3 h an...

  3. Testing of DLR C/C-SiC for HIFiRE 8 Scramjet Combustor

    NASA Technical Reports Server (NTRS)

    Glass, David E.; Capriotti, Diego P.; Reimer, Thomas; Kutemeyer, Marius; Smart, Michael

    2013-01-01

    Ceramic Matrix Composites (CMCs) have been proposed for hot structures in scramjet combustors. Previous studies have calculated significant weight savings by utilizing CMCs (active and passive) versus actively cooled metallic scramjet structures. Both a C/C and a C/C-SiC material system fabricated by DLR (Stuttgart, Germany) are being considered for use in a passively cooled combustor design for HIFiRE 8, a joint Australia / AFRL hypersonic flight program, expected to fly at Mach 7 for approximately 30 sec, at a dynamic pressure of 55 kPa. Flat panels of the DLR C/C and the C/C-SiC were tested in the NASA Langley Direct Connect Rig (DCR) at Mach 5 and Mach 6 enthalpy for several minutes. Gaseous hydrogen fuel was used to fuel the scramjet combustor. The test panels were instrumented with embedded Type K and Type S thermocouples. Zirconia felt insulation was used in some of the tests to increase the surface temperature of the C/C-SiC panel for approximately 350degF. The final C/C-SiC panel was tested for 3 cycles totaling over 135 sec at Mach 6 enthalpy. Slightly more erosion was observed on the C/C panel than the C/C-SiC panels, but both material systems demonstrated acceptable recession performance for the HIFiRE 8 flight.

  4. 77 FR 10004 - C$ cMoney, Inc.; Order of Suspension of Trading

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-21

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  5. Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

    PubMed

    Gothe, Yvonne; Marzo, Tiziano; Messori, Luigi; Metzler-Nolte, Nils

    2016-08-22

    A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs.

  6. Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

    PubMed

    Gothe, Yvonne; Marzo, Tiziano; Messori, Luigi; Metzler-Nolte, Nils

    2016-08-22

    A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs. PMID:27443984

  7. Anion effects to deliver enhanced iridium catalysts for hydrogen isotope exchange processes.

    PubMed

    Kennedy, Alan R; Kerr, William J; Moir, Rory; Reid, Marc

    2014-10-28

    Synthesis of a series of iridium(I) complexes of the type [(COD)Ir(IMes)(PPh3)]X (X = BF4, OTf, and BArF) has been established. Application of these species in mild hydrogen isotope exchange processes revealed more efficient catalysis and, further, a wider solvent scope when employing larger, more weakly coordinating counterions. PMID:25208265

  8. 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.

  9. 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. PMID:25060043

  10. 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.

  11. 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.

  12. 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…

  13. Potential contributions to space geodesy from the IridiumNEXT constellation

    NASA Astrophysics Data System (ADS)

    Gunter, B. C.; Encarnação, J.; Ditmar, P.; Klees, R.

    2012-12-01

    The IridiumNEXT constellation will soon replace the existing Iridium satellite telecommunication network, with initial launches set to start in 2015. In addition to the primary task of providing global telecommunication services, each IridiumNEXT satellite will also carry a hosted payload that will provide both private and public institutions the opportunity to place an instrument suite on one or all of constellation's satellites. This creates the possibility to gather continuous, global observations of Earth over the entire 15 year projected mission lifetime. Access to such a platform creates the potential to investigate many of Earth's highly dynamic processes at a spatiotemporal resolution that is simply not possible from single-satellite missions. Space geodesy is one the numerous fields that would benefit from such a mission. Precise orbits of the IridiumNEXT satellites derived through an on-board GNSS receiver (plus accelerometers and star cameras) have the potential to observe the large-scale, high-frequency variations in Earth's gravity field at time scales as short as one day. Additional positioning data from ground-based laser ranging stations would help improve the orbit determination, in addition to providing the necessary link to improve estimates of geocenter motion and reference frames. In this presentation, we will analyze the expected geodetic science returns from such a mission and will discuss the instrumental requirements needed to achieve these objectives.

  14. Luminescent Iridium Complexes Used in Light-Emitting Electrochemical Cells (LEECs).

    PubMed

    Henwood, Adam F; Zysman-Colman, Eli

    2016-08-01

    Cationic iridium(III) complexes represent the single largest class of emitters used in light emitting electrochemical cells (LEECs). In this chapter, we highlight the state-of-the-art emitters in terms of efficiency and stability in LEEC devices, highlighting blue, green, yellow/orange, red and white devices, and provide an outlook to the future of LEECs. PMID:27573388

  15. A neutron activation analysis of iridium concentration in Yamato carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Yabushita, S.; Wada, K.; Moriyama, H.; Takeuchi, K.

    1988-09-01

    Iridium concentration in extra-terrestrial bodies is an important quantity in relation to Ir-rich geological layers. Ir concentration of a Yamato carbonaceous chondrite (Y-793321) has been measured by a neutron activation method. The measurement yields a value (0.57±0.06) μg per gramme for the chondrite.

  16. Arctic Ocean Communications: Performance Of High-Data Transmission Over The Iridium System

    NASA Astrophysics Data System (ADS)

    Wilkinson, J.; Valcic, L.; Doble, M. J.; Maksym, T. L.; Robst, J.

    2014-12-01

    The Iridium satellite communications service was launched over 15 years ago, and it is presently the "go to" service for transmitting data and voice from the polar regions. However there is very little information available regarding the metrics associated with the throughput of data via this system. During a recent campaign we released over 30 "dial-up" iridium enabled drifting buoys in a relatively small region of the Arctic Ocean. Over the past 6 months relatively large amounts of data have now been routinely downloaded (every hour) from these systems. Each platform, as well as the base station in the UK, independently monitored the throughput of data and here we present an analysis of the metrics (download speed, drop outs, power consumption etc.) associated with the transmission of data through the Iridium system. As the role of autonomous platforms in the polar region increases there is a greater need to better understand the issues associated with data transfer. Iridium is a vital component of any autonomous system and therefore the information presented here will be of value to the technological, scientific and engineering communities.

  17. Report of Iridium/{sup 238}PuO{sub 2} Compatibility Test

    SciTech Connect

    Taylor, D.H.

    2001-08-09

    This study indicates that the chemical purity of the fuel used presently to fabricate fueled clad vent sets will not present any special problems to the performance of the fueled clad vent sets as intended. However, cation impurities in the fuel can have a deleterious effect on the iridium cladding and vents and should be minimized as much as practical.

  18. The substituent effect of 2-R-o-carborane on the photophysical properties of iridium(III) cyclometalates.

    PubMed

    Park, Jihyun; Lee, Young Hoon; Ryu, Ji Yeon; Lee, Junseong; Lee, Min Hyung

    2016-04-01

    A family of heteroleptic iridium(iii) cyclometalates, [4-(2-RCB)ppy]2Ir(acac) (3c-3g; CB = o-carboran-1-yl; ppy = 2-phenylpyridinato-C(2),N; acac = acetylacetonate; R = (i)Pr (3c), (i)Bu (3d), Ph (3e), CF3C6H4 (3f), C6F5 (3g)) with various 2-R substituted o-carboranes at the 4-position in the phenyl ring of the ppy ligand, were prepared. The X-ray crystal structure of all complexes, including 3a (R = H) and 3b (R = Me), showed that while the carboranyl C-C bond distance increases with the increasing steric effect of the 2-R substituent (3a-3d), the bond distance is more likely to be influenced by the electronic effect of the substituent for the 2-aryl substituted complexes (3e-3g). The absorption and emission bands of all complexes were red-shifted with respect to those of the parent (ppy)2Ir(acac) (4). While 3a-3d exhibited intense green phosphorescence with good quantum efficiency in toluene (ΦPL = 0.17-0.47), the complexes were poorly emissive in THF (ΦPL < 0.004). In a PMMA film, however, 3a-3d became substantially emissive (ΦPL = 0.11-0.14, 8 wt% Ir), albeit less emissive than 4 (ΦPL = 0.15). In contrast, the 2-aryl substituted 3e-3g were almost non-emissive in both the solution and solid states. All complexes underwent facile carborane-centered, electrochemical reduction (Eonset = -2.01 to -1.22 V). The potential values of these reductions increased with increases in the electron accepting ability of the 2-R group (H < alkyl < aryl) and were largely shifted anodically with respect to those of 4 and 5-carborane substituted complexes. This reduction behavior of 3a-3g implies that the LUMO contribution of 2-R-o-carborane units increases through the substitution at the 4-position of the ppy ligand and is influenced by the nature of the 2-R group, which may be responsible for facile carboranyl C-C bond variation leading to efficient quenching of the emissive excited states. PMID:26923990

  19. 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

  20. High temperature reactive ion etching of iridium thin films with aluminum mask in CF4/O2/Ar plasma

    NASA Astrophysics Data System (ADS)

    Yeh, Chia-Pin; Lisker, Marco; Kalkofen, Bodo; Burte, Edmund P.

    2016-08-01

    Reactive ion etching (RIE) technology for iridium with CF4/O2/Ar gas mixtures and aluminum mask at high temperatures up to 350 °C was developed. The influence of various process parameters such as gas mixing ratio and substrate temperature on the etch rate was studied in order to find optimal process conditions. The surface of the samples after etching was found to be clean under SEM inspection. It was also shown that the etch rate of iridium could be enhanced at higher process temperature and, at the same time, very high etching selectivity between aluminum etching mask and iridium could be achieved.

  1. Iridium and Spherules in Late Eocene Impact Deposits

    NASA Technical Reports Server (NTRS)

    Kyte, F. T.; Liu, S.

    2002-01-01

    We have been independently examining the Ir (FTK) and spherule (SL) contents of recently discovered late Eocene impact deposits from the south Atlantic and western Indian oceans. These include ODP Sites 1090 [14,15], 709 [lo], and 699 [Liu in prep.]. Iridium abundances at these sites are within the typical range reported for late Eocene deposits, with peak concentrations between 100 and 1000 pg/g. In Table 1 we present estimated net Ir fluences (in ng Ir/cm ) for these and nine other sites. Although there are fewer sites than the K/T boundary, the average of 9 ng Ir/cm2 is probably a good estimate of the late Eocene global flux. This is enough Ir for a 6 km comet (assuming 250 ng/g Ir, p=1.5), is sufficient to produce the Popigai or Chesapeake Bay structures, and is 16% of the flux estimated for the K/T boundary (55 ng/cm2 [ 161). Figure 1 shows the relative abundances of Ir, glassy microtektites and cpx-bearing spherules in sediments from Sites 699 and 1090, which are separated by only 3100 km. Although these two sites have similar Ir anomalies, the abundances of spherules are quite different. Site 1090 has well-defined peaks for both types of spherules, with a peak of 562 cpx spheruledg, while Site 699 contains only a few glassy microtektites and no cpx spherules. While the different abundances of spherules may reflect a heterogeneous distribution of spherules on the Earth s surface, an equally likely cause of this difference may be differential preservation of spherules in the sediment. recovered are only a trace residue of the initial impact deposit. Earlier work found 0.22 ng/g Ir in glassy microtektites from Site 689 [17], an insufficient concentration to support 0.16 ng/g in the bulk sediment at this site. We measured 15 ng/g Ir in a group of 95 cpx spherules from Site 1090 with sizes from 63 to -200 pm, a set typical of the size distribution at this site. Although this is a significant concentration it also cannot support the Ir peak. We presently lack

  2. 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

  3. Identification of an iridium-containing compound with a formal oxidation state of IX.

    PubMed

    Wang, Guanjun; Zhou, Mingfei; Goettel, James T; Schrobilgen, Gary J; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian

    2014-10-23

    One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2-4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d(1), with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4](+)), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4](+) species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4](+) and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d(0) electron configuration, is the most stable of all possible [IrO4](+) isomers. PMID:25341786

  4. Identification of an iridium-containing compound with a formal oxidation state of IX

    NASA Astrophysics Data System (ADS)

    Wang, Guanjun; Zhou, Mingfei; Goettel, James T.; Schrobilgen, Gary J.; Su, Jing; Li, Jun; Schlöder, Tobias; Riedel, Sebastian

    2014-10-01

    One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2, 3, 4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d1, with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4]+), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4]+ species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4]+ and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d0 electron configuration, is the most stable of all possible [IrO4]+ isomers.

  5. Diastereoselective B(C6F5)3-Catalyzed Reductive Carbocyclization of Unsaturated Carbohydrates.

    PubMed

    Bender, Trandon A; Dabrowski, Jennifer A; Zhong, Hongyu; Gagné, Michel R

    2016-08-19

    A B(C6F5)3-catalyzed method for the selective conversion of unsaturated carbohydrates to cyclopentanes and cyclopropanes is disclosed. Catalyst activation of tertiary silanes generates the ion pair [(C6F5)3B-H][ROSi2] whose components synergistically activate C-O bonds for diastereoselective C-C bond formation. Sila-THF cations are invoked as key intermediates facilitating carbocyclizations. Complex chiral synthons are thereby obtained in a single pot.

  6. Palladium-catalyzed cross-dehydrogenative functionalization of C(sp(2))-H Bonds.

    PubMed

    Wu, Yinuo; Wang, Jun; Mao, Fei; Kwong, Fuk Yee

    2014-01-01

    The catalytic cross-dehydrogenative coupling (CDC) reaction has received intense attention in recent years. The attractive feature of this coupling process is the formation of a C-C bond from two C-H moieties under oxidative conditions. In this Focus Review, recent advances in the palladium-catalyzed CDC reactions of C(sp(2) )-H bond are summarized, with a focus on the period from 2011 to early 2013. PMID:24123795

  7. Palladium-catalyzed Heck-type cross-couplings of unactivated alkyl iodides.

    PubMed

    McMahon, Caitlin M; Alexanian, Erik J

    2014-06-01

    A palladium-catalyzed, intermolecular Heck-type coupling of alkyl iodides and alkenes is described. This process is successful with a variety of primary and secondary unactivated alkyl iodides as reaction partners, including those with hydrogen atoms in the β position. The mild catalytic conditions enable intermolecular C-C bond formations with a diverse set of alkyl iodides and alkenes, including substrates containing base- or nucleophile-sensitive functionality.

  8. Electron attachment properties of c-C4F8O in different environments

    NASA Astrophysics Data System (ADS)

    Chachereau, A.; Fedor, J.; Janečková, R.; Kočišek, J.; Rabie, M.; Franck, C. M.

    2016-09-01

    The electron attachment properties of octafluorotetrahydrofuran (c-C4F8O) are investigated using two complementary experimental setups. The attachment and ionization cross sections of c-C4F8O are measured using an electron beam experiment. The effective ionization rate coefficient, electron drift velocity and electron diffusion coefficient in c-C4F8O diluted to concentrations lower than 0.6% in the buffer gases N2, CO2 and Ar, are measured using a pulsed Townsend experiment. A kinetic model is proposed, which combines the results of the two experiments.

  9. Highly Active Iridium/Iridium Tin/Tin Oxide Heterogeneous Nanoparticles as Alternative Electrocatalysts for the Ethanol Oxidation Reaction

    SciTech Connect

    Du W.; Su D.; Wang Q.; Saxner D.; Deskins N.A.; Krzanowski J.E.; Frenkel A.I.; Teng X.

    2011-08-03

    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{sub 71}Sn{sub 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{sub 71}Sn{sub 29}/C particles as Ir/Ir-Sn/SnO{sub 2}, which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO{sub 2} present on the surface. The Ir{sub 71}Sn{sub 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{sub 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

  10. Access to Isoquinolines and Isoquinolin-3-ols via Rh(III)-Catalyzed Coupling/Cyclization Cascade Reaction of Arylimidates and Diazo Compounds.

    PubMed

    Li, Xing Guang; Sun, Min; Jin, Qiao; Liu, Kai; Liu, Pei Nian

    2016-05-01

    A Rh(III)-catalyzed coupling/cyclization cascade reaction is described, which involves arylimidates and diazo compounds and proceeds via intermolecular C-C bond formation and subsequent intramolecular C-N bond formation. Mechanistic investigation revealed that the reaction is a two-step process: the initial Rh(III)-catalyzed coupling/cyclization proceeds very fast and the following dehydration is rather slow. The reaction provides a direct approach to isoquinolines and isoquinolin-3-ols without any oxidants. PMID:27042947

  11. 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.

  12. C/C composite brake disk nondestructive evaluation by IR thermography

    NASA Astrophysics Data System (ADS)

    Chu, Tsuchin P.; Poudel, Anish; Filip, Peter

    2012-06-01

    This paper discusses the non-destructive evaluation of thick Carbon/Carbon (C/C) composite aircraft brake disks by using transient infrared thermography (IRT) approach. Thermal diffusivity measurement technique was applied to identify the subsurface anomalies in thick C/C brake disks. In addition, finite element analysis (FEA) modeling tool was used to determine the transient thermal response of the C/C disks that were subjected to flash heating. For this, series of finite element models were built and thermal responses with various thermal diffusivities subjected to different heating conditions were investigated. Experiments were conducted to verify the models by using custom built in-house IRT system and commercial turnkey system. The analysis and experimental results showed good correlation between thermal diffusivity value and anomalies within the disk. It was demonstrated that the step-heating transient thermal approach could be effectively applied to obtain the whole field thermal diffusivity value of C/C composites.

  13. 21. Historic American Buildings Survey Copyright C.C. Pierce Original: ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    21. Historic American Buildings Survey Copyright - C.C. Pierce Original: About 1902 Re-photo: April 1940 QUANDRANGLE (view from north) - Mission Nuestra Senora de la Soledad, Soledad, Monterey County, CA

  14. 5. Historic American Buildings Survey C.C. Woodburn, Photographer. January 12, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey C.C. Woodburn, Photographer. January 12, 1934 DETAIL OF ENTRANCE (WEST ELEVATION) - Ferdinand Daniel Pulver House, County Road F-70 Vicinity, Vandalia, Jasper County, IA

  15. FIRST DETECTION OF c-C{sub 3}H{sub 2} IN A CIRCUMSTELLAR DISK

    SciTech Connect

    Qi Chunhua; Wilner, David J.; Rosenfeld, Katherine A.; Oeberg, Karin I.

    2013-03-01

    We report the first detection of c-C{sub 3}H{sub 2} in a circumstellar disk. The c-C{sub 3}H{sub 2} J = 6-5 line (217.882 GHz) is detected and imaged through Atacama Large Millimeter Array (ALMA) Science Verification observations toward the disk around the Herbig Ae star HD 163296 at 0.''8 resolution. The emission is consistent with that arising from a Keplerian rotating disk. Two additional c-C{sub 3}H{sub 2} transitions are also tentatively detected, bolstering the identification of this species, but with insufficient signal-to-noise ratio to constrain the spatial distribution. Using a previously developed model for the physical structure of this disk, we fit a radial power-law distribution model to the c-C{sub 3}H{sub 2} 6-5 emission and find that c-C{sub 3}H{sub 2} is present in a ring structure from an inner radius of about 30 AU to an outer radius of about 165 AU. The column density is estimated to be 10{sup 12}-10{sup 13} cm{sup -2}. The clear detection and intriguing ring structure suggest that c-C{sub 3}H{sub 2} has the potential to become a useful probe of radiation penetration in disks.

  16. Computational studies on the regioselectivity of metal-catalyzed synthesis of 1,2,3 triazoles via click reaction: a review.

    PubMed

    Hosseinnejad, Tayebeh; Fattahi, Bahareh; Heravi, Majid M

    2015-10-01

    Recently, the experimental and computational chemists have been attracted widely to the click synthesis of 1,2,3 triazoles and their derivatives, mainly due to the fact that they are interesting from structural and mechanistic points of view. Moreover, catalyzed click have been well established as a successful strategy showing high regioselectivity and high yield for the synthesis of 1,2,3-triazoles. In this review, we try to highlight the recently reported computational assessments on the origins and predection of regioselectivity in the catalyzed click synthesis of triazoles from the mechanistic and thermodynamical points of view. In this light, density functional theory (DFT) calculations on the free energy profiles of azide-alkyne cycloaddition reactions have been underscored. The stereoelectronic features for the role of copper, ruthenium, and iridium as catalyst on regioselectivity of click reactions have also be discussed. Graphical Abstract Computational origins for the regioselective behavior of 1,2,3 triazoles click synthesis. PMID:26385849

  17. Advances in nickel-catalyzed cycloaddition reactions to construct carbocycles and heterocycles.

    PubMed

    Thakur, Ashish; Louie, Janis

    2015-08-18

    Transition-metal catalysis has revolutionized the field of organic synthesis by facilitating the construction of complex organic molecules in a highly efficient manner. Although these catalysts are typically based on precious metals, researchers have made great strides in discovering new base metal catalysts over the past decade. This Account describes our efforts in this area and details the development of versatile Ni complexes that catalyze a variety of cycloaddition reactions to afford interesting carbocycles and heterocycles. First, we describe our early work in investigating the efficacy of N-heterocyclic carbene (NHC) ligands in Ni-catalyzed cycloaddition reactions with carbon dioxide and isocyanate. The use of sterically hindered, electron donating NHC ligands in these reactions significantly improved the substrate scope as well as reaction conditions in the syntheses of a variety of pyrones and pyridones. The high reactivity and versatility of these unique Ni(NHC) catalytic systems allowed us to develop unprecedented Ni-catalyzed cycloadditions that were unexplored due to the inefficacy of early Ni catalysts to promote hetero-oxidative coupling steps. We describe the development and mechanistic analysis of Ni/NHC catalysts that couple diynes and nitriles to form pyridines. Kinetic studies and stoichiometric reactions confirmed a hetero-oxidative coupling pathway associated with this Ni-catalyzed cycloaddition. We then describe a series of new substrates for Ni-catalyzed cycloaddition reactions such as vinylcyclopropanes, aldehydes, ketones, tropones, 3-azetidinones, and 3-oxetanones. In reactions with vinycyclopropanes and tropones, DFT calculations reveal noteworthy mechanistic steps such as a C-C σ-bond activation and an 8π-insertion of vinylcyclopropane and tropone, respectively. Similarly, the cycloaddition of 3-azetidinones and 3-oxetanones also requires Ni-catalyzed C-C σ-bond activation to form N- and O-containing heterocycles. PMID:26200651

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

    PubMed Central

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

    2013-01-01

    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. PMID:23458659

  19. Formation of C-C and C-O bonds and oxygen removal in reactions of alkanediols, alkanols, and alkanals on copper catalysts.

    PubMed

    Sad, María E; Neurock, Matthew; Iglesia, Enrique

    2011-12-21

    This study reports evidence for catalytic deoxygenation of alkanols, alkanals, and alkanediols on dispersed Cu clusters with minimal use of external H(2) and with the concurrent formation of new C-C and C-O bonds. These catalysts selectively remove O-atoms from these oxygenates as CO or CO(2) through decarbonylation or decarboxylation routes, respectively, that use C-atoms present within reactants or as H(2)O using H(2) added or formed in situ from CO/H(2)O mixtures via water-gas shift. Cu catalysts fully convert 1,3-propanediol to equilibrated propanol-propanal intermediates that subsequently form larger oxygenates via aldol-type condensation and esterification routes without detectable involvement of the oxide supports. Propanal-propanol-H(2) equilibration is mediated by their chemisorption and interconversion at surfaces via C-H and O-H activation and propoxide intermediates. The kinetic effects of H(2), propanal, and propanol pressures on turnover rates, taken together with measured selectivities and the established chemical events for base-catalyzed condensation and esterification reactions, indicate that both reactions involve kinetically relevant bimolecular steps in which propoxide species, acting as the base, abstract the α-hydrogen in adsorbed propanal (condensation) or attack the electrophilic C-atom at its carbonyl group (esterification). These weakly held basic alkoxides render Cu surfaces able to mediate C-C and C-O formation reactions typically catalyzed by basic sites inherent in the catalyst, instead of provided by coadsorbed organic moieties. Turnover rates for condensation and esterification reactions decrease with increasing Cu dispersion, because low-coordination corner and edge atoms prevalent on small clusters stabilize adsorbed intermediates and increase the activation barriers for the bimolecular kinetically relevant steps required for both reactions. PMID:22023723

  20. General and Mild Cobalt-Catalyzed C-Alkylation of Unactivated Amides and Esters with Alcohols.

    PubMed

    Deibl, Nicklas; Kempe, Rhett

    2016-08-31

    The borrowing hydrogen or hydrogen autotransfer methodology is an elegant and sustainable or green concept to construct carbon-carbon bonds. In this concept, alcohols, which can be obtained from barely used and indigestible biomass, such as lignocellulose, are employed as alkylating reagents. An especially challenging alkylation is that of unactivated esters and amides. Only noble metal catalysts based on iridium and ruthenium have been used to accomplish these reactions. Herein, we report on the first base metal-catalyzed α-alkylation of unactivated amides and esters by alcohols. Cobalt complexes stabilized with pincer ligands, recently developed in our laboratory, catalyze these reactions very efficiently. The precatalysts can be synthesized easily from commercially available starting materials on a multigram scale and are self-activating under the basic reaction conditions. This Co catalyst class is also able to mediate alkylation reactions of both esters and amides. In addition, we apply the methodology to synthesize ketones and to convert alcohols into aldehydes elongated by two carbon atoms. PMID:27490682

  1. Anodically Electrodeposited Iridium Oxide Films (AEIROF) from Alkaline Solutions for Electrochromic Display Devices

    NASA Astrophysics Data System (ADS)

    Yamanaka, Kazusuke

    1989-04-01

    Anodically electrodeposited iridium oxide films from alkaline solutions were investigated for application to electrochromic devices. Micro-crystalline (diameter: 15Å) films obtained by the electrolysis of aqueous alkaline solutions containing iridium chloride, oxalic acid and potassium carbonate showed good electrochromic reaction reversibility. The coloration efficiency of the films was about one third that of typical evaporated tungsten oxide films, and the response rate measured by the amount of injected charge was about double. The cycle lives of the cells, composed of electrodeposited films, 1M H3PO4-NaOH (pH{=}3˜ 5), and an activated carbon cloth, were more than 8× 106 with a 0.6 V, 1 Hz continuous square wave.

  2. The treatment of malignant diseases in Romania using stainless steel encapsulated iridium-192 sources

    NASA Astrophysics Data System (ADS)

    Stanef, I.; Matache, G.; Ciocǎltei, V.; Gheorghiev, G.

    1994-01-01

    Iridium-192 sources supplied by the Institute for Nuclear Physics and Engineering have been used in Romanian radiotherapy clinics since 1980. The source assembly is sealed in a protective stainless steel sheath which satisfies the requirements of international standards. Since this sheath acts as a filter to change the characteristic spectrum it has been necessary to determine experimentally an accurate value of the specific gamma-ray constant. Some clinical aspects of the complex treatment of carcinomas with iridium-192 are reviewed. Results of the calculation of the dose distribution around single and multiple sources are given for different applications in the treatment of carcinomas of the vaginal and uterine cervix, oral cavity, rectum and vagina.

  3. Iridium-bearing sublimates at a hot-spot volcano (Piton de la Fournaise, Indian Ocean)

    SciTech Connect

    Toutain, J.P. ); Meyer, G.

    1989-12-01

    Sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites (Piton de la Fournaise, Poas, Momotombo, Etna, Ardoukoba and Erta-Ale). They have been analyzed for Ir and other volatile elements (Se, As, Cu, Au, Ag, Pb, Tl) by means of instrumental neutron activation analysis (INAA) and proton induced X-Ray emission (PIXE). Among the investigated volcanoes, only Piton de la Fournaise is found to release detectable amounts of iridium. Ir in Piton de la Fournaise sublimates is associated with F-minerals. This confirms its gaseous transport as a volatile fluoride compound. Iridium seems to be preferentialy released by hot-spot type volcanoes, and its detection in Piton de la Fournaise sublimates provides a positive argument in favor of a volcanic hypothesis to explain the KTB events.

  4. First Applications of DoD Iridium RUDICS in the NSF Polar Programs

    NASA Astrophysics Data System (ADS)

    Valentic, T.; Stehle, R.

    2008-12-01

    We will present the first deployment and application of the new Iridium RUDICS service to remote instrumentation projects within the National Science Foundation's polar programs. The rise of automated observing networks has increased the demand for real-time connectivity to remote instruments, not only for immediate access to data, but to also interrogate health and status. Communicating with field sites in the polar regions is complicated by the remoteness from existing infrastructure, low temperatures and limited connection options. Sites located above 78° latitude are not able to see geostationary satellites, leaving the Iridium constellation as the only one that provide a direct connection. Some others, such as Orbcomm, only provide a store-and-forward service. Iridium is often used as a dial up modem to establish a PPP connection to the Internet with data files transferred via FTP. On low-bandwidth, high-latency networks like Iridium (2400bps with ping times of seconds), this approach is time consuming and inefficient. The dial up time alone takes upwards of a minute, and standard TCP/IP and FTP protocols are hampered by the long latencies. Minimizing transmission time is important for reducing battery usage and connection costs. The new Iridium RUDICS service can be used for more efficient transfers. RUDICS is an acronym for "Router-based Unstructured Digital Inter-working Connectivity Solution" and provides a direct connection between an instrument in the field and a server on the Internet. After dialing into the Iridium gateway, a socket connection is opened to a registered port on a user's server. Bytes sent to or from the modem appear at the server's socket. The connection time is reduced to about 10 seconds because the modem training and PPP negotiation stages are eliminated. The remote device does not need to have a full TCP/IP stack, allowing smaller instruments such as data loggers to directly handle the data transmission. Alternative protocols can

  5. An inconvenient influence of iridium(III) isomer on OLED efficiency.

    PubMed

    Baranoff, Etienne; Bolink, Henk J; De Angelis, Filippo; Fantacci, Simona; Di Censo, Davide; Djellab, Karim; Grätzel, Michael; Nazeeruddin, Md Khaja

    2010-10-14

    The recently reported heteroleptic cyclometallated iridium(III) complex [Ir(2-phenylpyridine)(2)(2-carboxy-4-dimethylaminopyridine)] N984 and its isomer N984b have been studied more in detail. While photo- and electrochemical properties are very similar, DFT/TDDFT calculations show that the two isomers have different HOMO orbital characteristics. As a consequence, solution processed OLEDs made using a mixture of N984 and isomer N984b similar to vacuum processed devices show that the isomer has a dramatic detrimental effect on the performances of the device. In addition, commonly used thermogravimetric analysis is not suitable for showing the isomerization process. The isomer could impact performances of vacuum processed OLEDs using heteroleptic cyclometallated iridium(III) complexes as dopant.

  6. Research of remote control for Chinese Antarctica Telescope based on iridium satellite communication

    NASA Astrophysics Data System (ADS)

    Xu, Lingzhe; Yang, Shihai

    2010-07-01

    Astronomers are ever dreaming of sites with best seeing on the Earth surface for celestial observation, and the Antarctica is one of a few such sites only left owing to the global air pollution. However, Antarctica region is largely unaccessible for human being due to lacking of fundamental living conditions, travel facilities and effective ways of communication. Worst of all, the popular internet source as a general way of communication scarcely exists there. Facing such a dilemma and as a solution remote control and data transmission for telescopes through iridium satellite communication has been put forward for the Chinese network Antarctic Schmidt Telescopes 3 (AST3), which is currently under all round research and development. This paper presents iridium satellite-based remote control application adapted to telescope control. The pioneer work in China involves hardware and software configuration utilizing techniques for reliable and secure communication, which is outlined in the paper too.

  7. Surface studies of iridium-alloy grain boundaries associated with weld cracking

    SciTech Connect

    Mosley, W.C.

    1982-01-01

    Plutonium-238 oxide fuel pellets for the General Purpose Heat Source (GPHS) Radioisotopic Thermoelectric Generators to be used on the NASA Galileo Mission to Jupiter and the International Solar Polar Mission are produced and encapsulated in iridium alloy at the Savannah River Plant (SRP). Underbead cracks occasionally occur in the girth weld on the iridium-alloy-clad vent sets in the region where the gas tungsten arc is quenched. Grain-boundary structures and compositions were characterized by scanning electron microscopy/x-ray energy spectroscopy, electron microprobe analysis and scanning Auger microprobe analysis to determine the cause of weld quench area cracking. Results suggest that weld quench area cracking may be caused by gas porosity or liquation in the grain boundaries.

  8. The activity of platinum, iridium and rhodium drug complexes against Leishmania donovani.

    PubMed

    Croft, S L; Neal, R A; Craciunescu, D G; Certad-Fombona, G

    1992-03-01

    The activities of twenty seven Platinum, Rhodium and Iridium drug complexes were determined against Leishmania donovani amastigotes in mouse peritoneal macrophages in vitro. Eight compounds showed antileishmanial activity of which only three, Rh(III)-mepacrine, Ir(III) pyrrolidine dithiocarbamate and Ir(III) diethyl dithiocarbamate had ED50 values of less than 1 microM. The two Iridium complexes produced, respectively, a 50% and 39% suppression of L. donovani amastigotes in the liver of BALB/c mice following the subcutaneous administration of 200 mg/kg for 5 consecutive days. Ultrastructural studies suggest that the amastigote kinetoplast-mitochondrion complex is the primary site of action of the Ir and Rh complexes. PMID:1598504

  9. 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. PMID:25919917

  10. Rhodium(i), rhodium(iii) and iridium(iii) carbaporphyrins.

    PubMed

    Adiraju, Venkata A K; Ferrence, Gregory M; Lash, Timothy D

    2016-09-21

    Treatment of a benzocarbaporphyrin with [Rh(CO)2Cl]2 in refluxing dichloromethane gave a rhodium(i) dicarbonyl complex, and further reaction in refluxing pyridine afforded an organometallic rhodium(iii) derivative. The carbaporphyrin also reacted with [Ir(COD)Cl]2 and pyridine in refluxing p-xylene to generate a related iridium(iii) compound. These novel metalated porphyrinoids retained strongly diatropic characteristics and were fully characterized by XRD. PMID:27529466

  11. Solvent free selective dehydrogenation of indolic and carbazolic molecules with an iridium pincer catalyst.

    PubMed

    Brayton, Daniel F; Jensen, Craig M

    2014-06-01

    A previously known iridium POCOP pincer catalyst was found to selectively dehydrogenate the heterocyclic portion of several indolic and carbazolic molecules. These molecules were found to have an "activity window" (172-178 °C) upon which only the heterocyclic ring underwent dehydrogenation. All reactions were run solvent free, yields for selected substrates were excellent, and the products were isolated by either distillation or alumina plug filtration. PMID:24763968

  12. Electrochemical and chemical routes to hydride loss from an iridium dihydride.

    PubMed

    Walden, A G; Kumar, A; Lease, N; Goldman, A S; Miller, A J M

    2016-06-14

    With a view towards replacing sacrificial hydrogen acceptors in alkane dehydrogenation catalysis, electrochemical methods for oxidative activation of a pincer-ligated iridium hydride intermediate were explored. A 1H(+)/2e(-) oxidation process was observed in THF solvent, with net hydride loss leading to a reactive cationic intermediate that can be trapped by chloride. Analogous reactivity was observed with the concerted hydride transfer reagent Ph3C(+), connecting chemical and electrochemical hydride loss pathways. PMID:26979786

  13. Selective Aromatic C–H Hydroxylation Enabled by η6-Coordination to Iridium(III)

    PubMed Central

    D'Amato, Erica M.; Neumann, Constanze N.; Ritter, Tobias

    2016-01-01

    We report an aromatic C–H hydroxylation protocol in which the arene is activated through η6-coordination to an iridium(III) complex. η6-Coordination of the arene increases its electrophilicity and allows for high positional selectivity of hydroxylation at the site of least electron density. Through investigation of intermediate η5-cyclohexadienyl adducts and arene exchange reactions, we evaluate incorporation of arene π-activation into a catalytic cycle for C–H functionalization. PMID:26877574

  14. 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) ). PMID:24523138

  15. An iridium abundance anomaly at the palynological cretaceous-tertiary boundary in northern new Mexico.

    PubMed

    Orth, C J; Gilmore, J S; Knight, J D; Pillmore, C L; Tschudy, R H; Fassett, J E

    1981-12-18

    An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.

  16. 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) ).

  17. Silanediol-Catalyzed Chromenone Functionalization.

    PubMed

    Hardman-Baldwin, Andrea M; Visco, Michael D; Wieting, Joshua M; Stern, Charlotte; Kondo, Shin-Ichi; Mattson, Anita E

    2016-08-01

    Promising levels of enantiocontrol are observed in the silanediol-catalyzed addition of silyl ketene acetals to benzopyrylium triflates. This rare example of enantioselective, intermolecular chromenone functionalization with carbonyl-containing nucleophiles has potential applications in the synthesis of bioactive chromanones and tetrahydroxanthones. PMID:27453257

  18. Iodine-Catalyzed Polysaccharide Esterification

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A review is provided of the recent reports to use iodine-catalyzed esterification reaction to produce esters from polysaccharides. The process entails reaction of the polysaccharide with an acid anhydride in the presence of a catalytic level of iodine, and in the absence of additional solvents. T...

  19. Pd-catalyzed steroid reactions.

    PubMed

    Czajkowska-Szczykowska, Dorota; Morzycki, Jacek W; Wojtkielewicz, Agnieszka

    2015-05-01

    We review the most important achievements of the last decade in the field of steroid synthesis in the presence of palladium catalysts. Various palladium-catalyzed cross-coupling reactions, including Heck, Suzuki, Stille, Sonogashira, Negishi and others, are exemplified with steroid transformations.

  20. 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??.

  1. The kinetics and mechanism of the organo-iridium catalysed racemisation of amines.

    PubMed

    Stirling, Matthew J; Mwansa, Joseph M; Sweeney, Gemma; Blacker, A John; Page, Michael I

    2016-08-01

    The dimeric iodo-iridium complex [IrCp*I2]2 (Cp* = pentamethylcyclopentadiene) is an efficient catalyst for the racemisation of secondary and tertiary amines at ambient and higher temperatures with a low catalyst loading. The racemisation occurs with pseudo-first-order kinetics and the corresponding four rate constants were obtained by monitoring the time dependence of the concentrations of the (R) and (S) enantiomers starting with either pure (R) or (S) and show a first-order dependence on catalyst concentration. Low temperature (1)H NMR data is consistent with the formation of a 1 : 1 complex with the amine coordinated to the iridium and with both iodide anions still bound to the metal-ion, but at the higher temperatures used for kinetic studies binding is weak and so no saturation zero-order kinetics are observed. A cross-over experiment with isotopically labelled amines demonstrates the intermediate formation of an imine which can dissociate from the iridium complex. Replacing the iodides in the catalyst by other ligands or having an amide substituent in Cp* results in a much less effective catalysts for the racemisation of amines. The rate constants for a deuterated amine yield a significant primary kinetic isotope effect kH/kD = 3.24 indicating that hydride transfer is involved in the rate-limiting step.

  2. Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes.

    PubMed

    Lee, Ho Won; Jeong, Hyunjin; Kim, Young Kwan; Ha, Yunkyoung

    2015-10-01

    Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds. Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4'-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N'-dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and could be extended to additional research on flexible applications. PMID:26726407

  3. Formic acid dehydrogenation with bioinspired iridium complexes: a kinetic isotope effect study and mechanistic insight.

    PubMed

    Wang, Wan-Hui; Xu, Shaoan; Manaka, Yuichi; Suna, Yuki; Kambayashi, Hide; Muckerman, James T; Fujita, Etsuko; Himeda, Yuichiro

    2014-07-01

    Highly efficient hydrogen generation from dehydrogenation of formic acid is achieved by using bioinspired iridium complexes that have hydroxyl groups at the ortho positions of the bipyridine or bipyrimidine ligand (i.e., OH in the second coordination sphere of the metal center). In particular, [Ir(Cp*)(TH4BPM)(H2 O)]SO4 (TH4BPM: 2,2',6,6'-tetrahydroxyl-4,4'-bipyrimidine; Cp*: pentamethylcyclopentadienyl) has a high turnover frequency of 39 500 h(-1) at 80 °C in a 1 M aqueous solution of HCO2 H/HCO2 Na and produces hydrogen and carbon dioxide without carbon monoxide contamination. The deuterium kinetic isotope effect study clearly indicates a different rate-determining step for complexes with hydroxyl groups at different positions of the ligands. The rate-limiting step is β-hydrogen elimination from the iridium-formate intermediate for complexes with hydroxyl groups at ortho positions, owing to a proton relay (i.e., pendent-base effect), which lowers the energy barrier of hydrogen generation. In contrast, the reaction of iridium hydride with a proton to liberate hydrogen is demonstrated to be the rate-determining step for complexes that do not have hydroxyl groups at the ortho positions.

  4. Consumable arc-melting, extruding, and rolling process for iridium sheet

    SciTech Connect

    Heestand, R.L.; Copeland, G.L.; Martin, M.M.

    1986-06-01

    An iridium alloy has been used as cladding for the /sup 238/PuO/sub 2/ fuel in radioisotope thermoelectric generators (RTGs) for recent interplanetary spacecraft such as Voyagers 1 and 2 and will be used for the Galileo and Ulysses spacecraft. The iridium alloy sheet for the fuel cladding used on these missions was fabricated by hot and cold rolling of arc-melted and drop-cast 0.5-kg ingots. Upon completion of production for these spacecraft, an opportunity was taken to conduct process improvement studies that would increase processing batch sizes, develop a more uniform product, decrease rejections due to internal delaminations and surface defects, and reduce costs. The studies to scale up and improve the fabrication process are described. In the new process, iridium is electron beam melted, alloyed by arc melting, and then consumable arc melted to form a cylindrical ingot of approximately 7 kg for extrusion. The ingot is extruded to sheet bar and hot and cold rooled into sheet. Sheet evaluated from the first two ingots showed 100% acceptance with no defects on inspection. An improved uniformity of microstructure was obtained, and chemistry was controlled within specification limits.

  5. Ultrasonic detection of laminar-type defects in iridium alloy blanks

    SciTech Connect

    Cook, K.V.; Cunningham, R.A. Jr.; Simpson, W.A. Jr.; McClung, R.W.

    1986-07-01

    Encapsulated isotopic heat sources for use in generating electrical power for space applications require flight-quality hardware material. Iridium is the chosen material for such applications, and Oak Ridge National Laboratory has been the prime supplier of iridium alloy forming blanks 52 mm in diameter by 0.66 mm thick (1.0 by 0.026 in.). Prior to the work reported here, these blanks were ultrasonically examined by using 0.9-mm-diam (0.035-in.) simulated flaw standards. However, as a result of this effort, the sensitivity of our ultrasonic pulse-echo test system has been increased. The improved ultrasonic test system permits blank inspection at the 0.5-mm-diam (0.020-in.) simulated flaw detection level. This test system was successfully demonstrated on the initial blanks provided via an improved processing route (consumable arc-melting, extruding, and rolling). The equipment modification and/or selection and the specific focused search unit immersion technique developed to provide this capability are described. The improved flaw detection capability also provides data maps of a common type of defect in iridium (delaminations).

  6. Effects of Anti-Oxidant Migration on Friction and Wear of C/C Aircraft Brakes

    NASA Astrophysics Data System (ADS)

    Don, Jarlen; Wang, Zhe

    2009-04-01

    The surfaces of carbon-carbon (C/C) aircraft brakes are usually coated with anti-oxidant to protect them from oxidation. These surfaces do not include the friction surfaces since it is known that when anti-oxidant get onto the friction surface, the friction coefficient decreases. The anti-oxidant migration (AOM), however, happens during processing, heat treatment and application. In this study, phosphorus based anti-oxidants inhibited 3-D C/C aircraft brake system was investigated. The effects of their migration on friction and wear in the 3-D C/C brakes were revealed by sub-scale dynamometer tests and microscopic analysis. Dynamometer results showed that when AOM occurred, both landing and taxi coefficients decreased in humid environment and the wear was slightly lowered. Microscopic study showed that under high humidity conditions there was no formation of the friction film.

  7. Investigation of TiC C Eutectic and WC C Peritectic High-Temperature Fixed Points

    NASA Astrophysics Data System (ADS)

    Sasajima, Naohiko; Yamada, Yoshiro

    2008-06-01

    TiC C eutectic (2,761°C) and WC C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC C and three WC C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC C peritectic within 1 day was 17 mK with a melting range of ˜70 mK. The repeatability of the freezing temperature of the WC C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC C cells were easily constructed, like metal carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC C peritectic has more potential than the TiC C eutectic as a high-temperature reference point. The investigation of the purification of the TiC C cell during filling and the plateau observation are also reported.

  8. INTERSTELLAR DETECTION OF c-C{sub 3}D{sub 2}

    SciTech Connect

    Spezzano, S.; Bruenken, S.; Schilke, P.; Schlemmer, S.; Caselli, P.; Menten, K. M.; McCarthy, M. C.; Bizzocchi, L.; Trevino-Morales, S. P.; Aikawa, Y.

    2013-06-01

    We report the first interstellar detection of c-C{sub 3}D{sub 2}. Doubly deuterated cyclopropenylidene, a carbene, has been detected toward the starless cores TMC-1C and L1544 using the IRAM 30 m telescope. The J{sub K{sub a,K{sub c}}} = 3{sub 0,3}-2{sub 1,2}, 3{sub 1,3}-2{sub 0,2}, and 2{sub 2,1}-1{sub 1,0} transitions of this species have been observed at 3 mm in both sources. The expected 1:2 intensity ratio has been found in the 3{sub 0,3}-2{sub 1,2} and 3{sub 1,3}-2{sub 0,2} lines, belonging to the para and ortho species, respectively. We also observed lines of the main species, c-C{sub 3}H{sub 2}, singly deuterated c-C{sub 3}HD, and the species with one {sup 13}C off of the principal axis of the molecule, c-H{sup 13}CC{sub 2}H. The lines of c-C{sub 3}D{sub 2} have been observed with high signal-to-noise ratio, better than 7.5{sigma} in TMC-1C and 9{sigma} in L1544. The abundance of doubly deuterated cyclopropenylidene with respect to the normal species is found to be 0.4%-0.8% in TMC-1C and 1.2%-2.1% in L1544. The deuteration of this small hydrocarbon ring is analyzed with a comprehensive gas-grain model, the first including doubly deuterated species. The observed abundances of c-C{sub 3}D{sub 2} can be explained solely by gas-phase processes, supporting the idea that c-C{sub 3}H{sub 2} is a good indicator of gas-phase deuteration.

  9. Grain Growth Behavior, Tensile Impact Ductility, and Weldability of Cerium-Doped Iridium Alloys

    SciTech Connect

    McKamey, C.G.

    2002-05-28

    An iridium alloy doped with small amounts of cerium and thorium is being developed as a potential replacement for the iridium-based DOP-26 alloy (doped with thorium only) that is currently used by the National Aeronautics and Space Administration (NASA) for cladding and post-impact containment of the radioactive fuel in radioisotope thermoelectric generator (RTG) heat sources which provide electric power for interplanetary spacecraft. This report summarizes results of studies conducted to date under the Iridium Alloy Characterization and Development subtask of the Radioisotope Power System Materials Production and Technology Program to characterize the properties of the iridium-based alloy (designated as DOP-40) containing both cerium and thorium. Included within this report are data on grain growth of sheet material in vacuum and low-pressure oxygen environments, grain growth in vacuum of the clad vent set cup material, weldability, and the effect of grain size and test temperature on tensile properties. Where applicable, data for the DOP-26 alloy are included for comparison. Both grain size and grain-boundary cohesion affect the ductility of iridium alloys. In this study it was found that cerium and thorium, when added together, refine grain size more effectively than when thorium is added by itself (especially at high temperatures). In addition, the effect of cerium additions on grain-boundary cohesion is similar to that of thorium. Mechanical testing at both low ({approx} 10{sup -3}s{sup -1}) and high ({approx} 10{sup -3}s{sup -1}) strain rates showed that the Ce/Th-doped alloys have tensile ductilities that are as good or better than the DOP-26 alloy. The general conclusion from these studies is that cerium can be used to replace some of the radioactive thorium currently used in DOP-26 while maintaining or improving its metallurgical properties. The current DOP-26 alloy meets all requirements for cladding the radioactive fuel in the RTG heat source, but the

  10. Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f. c. c. -f. c. c. nucleation-II. The non-classical regime

    SciTech Connect

    Le Goues, F.K.; Aaronson, H.I.; Lee, Y.W.

    1984-10-01

    In a previous paper, the shape of the critical nucleus and its influence upon nucleation kinetics were studied at near zero supersaturation, i.e. in the classical nucleation regime, using a discrete lattice plane model of the coherent interphase boundary energy. In order to extend these studies to higher supersaturations, a discrete lattice point model, based on a formalism developed by Cook, de Fontaine and Hilliard, is employed in the present paper and applied to homogeneous nucleation of coherent f.c.c. precipitates in an f.c.c. matrix. Concentration profiles and free energies of formation of critical nuclei are calculated from this model as a function of temperature and supersaturation and compared with results obtained from the Cahn-Hilliard continuum non-classical model and the previously used discrete lattice plane classical model. As predicted in effect by Cahn and Hilliard, the three models converge at very low supersaturations, and the continuum and the discrete lattice point (but not the classical discrete lattice plane) models also do so near the spinodal. Thus the most important differences between the continuum and the discrete lattice point models develop at intermediate supersaturations. The main advantages of the discrete lattice point model are that it allows the influence of crystalline anisotropy to be taken into account, permits treatment of arbitrarily steep variations in composition and provides a more convenient milieu for the incorporation of volume strain energy, as is done in the next paper in this series.

  11. Visualization of Zn²⁺ ions in live zebrafish using a luminescent iridium(III) chemosensor.

    PubMed

    Ma, Dik-Lung; He, Hong-Zhang; Zhong, Hai-Jing; Lin, Sheng; Chan, Daniel Shiu-Hin; Wang, Liang; Lee, Simon Ming-Yuen; Leung, Chung-Hang; Wong, Chun-Yuen

    2014-08-27

    A novel luminescent cyclometalated iridium(III) complex-based chemosensor (1) bearing a zinc-specific receptor, tris(2-pyridylmethyl)amine, and the 3-phenyl-1H-pyrazole ligand has been designed and synthesized. Upon the addition of Zn(2+) ions to a solution of iridium(III) complex 1, a pronounced luminescence color change from blue to green can be observed, which may be attributed to the suppression of photoinduced electron transfer upon complexation of complex 1 with Zn(2+) ions. The interaction of iridium(III) complex 1 with Zn(2+) ions was investigated by UV-vis absorption titration, emission titration, and (1)H NMR titration. Furthermore, the iridium(III) complex 1 exhibited good selectivity for Zn(2+) over 13 other common metal ions, including K(+), Ag(+), Na(+), Ni(2+), Fe(3+), Hg(2+), Cd(2+), Mg(2+), Ca(2+), Cu(2+), Mn(2+), Co(2+), and Pb(2+) ions. The practical application of the iridium(III) complex 1 in visualizing intracellular Zn(2+) distribution in live zebrafish was also demonstrated.

  12. Iridium contents in the Late Cretaceous-Early Tertiary clays in relation to the K/T boundary, North Jordan

    NASA Astrophysics Data System (ADS)

    Abboud, Iyad Ahmed

    2016-06-01

    The mineralogy, lithology, and geochemistry of five discrete laminations across the K/T boundary of clayey shale at the Yarmouk River area, Jordan, were examined. There were no marked changes in the mineralogy of the clayey shale within the K/T boundary. This outcrop consists of more than 100 m of Maastrichtian oil shale overlying about 20 m limestone. Marly limestone included many clay laminations from organic and volcanic origins, which are considered an evidence of the K/T boundary through detected iridium anomalies. Any of these particular lamellae range from 2 mm to 5 mm in thickness. Smectite was the predominant clay mineral in smectitic shale laminations. It was located at eight meters above the K/T boundary and includes some anomalous concentrations of iridium and traces of other elements. The analysis of geochemical platinum group at the K/T boundary clays showed anomalous enrichments of iridium, compared with other carbonate rocks as a result of weathering processes of oil shale, or through concentration from weathering of basalt flows, but not pointing to an impact process. The clays in late Maastrichtian have Ir-Sc prevailed anomalies and synchronize with increasing of terrigenous and volcanogenic traced elements. Kaolin, smectite, and volkonskoite were the dominant clay minerals at the K/T boundary with high concentrations of iridium. The concentration levels of iridium in some laminations of the Yarmouk sediments ranged between 1.6 and 7.8 ppb.

  13. Catalyzed oxidation for nanowire growth

    NASA Astrophysics Data System (ADS)

    Tai, Kaiping; Sun, Ke; Huang, Bo; Dillon, Shen J.

    2014-04-01

    A simple, low-cost and scalable route to substrate-supported nanowire growth is reported based on catalyzed oxidation. The process shares common features with popular catalyzed nanowire growth techniques such as vapor-liquid-solid (VLS), vapor-solid-solid (VSS), or vapor-quasi-solid (VQS) that use catalyst nanoparticles to direct the deposition of reactants from the vapor phase. Catalyzed oxidation for nanowire growth (CONG) utilizes catalyzed anion (e.g. O2) reduction from the vapor phase and metal (e.g. Fe) oxidation from the substrate to produce oxide nanowires (e.g. Fe3O4). The approach represents a new class of nanowire growth methodology that may be applied to a broad range of systems. CONG does not require expensive chemical vapor deposition or physical vapor deposition equipment and can be implemented at intermediate temperatures (400-600 °C) in a standard laboratory furnace. This work also demonstrates a passive approach to catalyst deposition that allows the process to be implemented simply with no lithography or physical vapor deposition steps. This effort validates the general approach by synthesizing MnO, Fe3O4, WO3, MgO, TiO2, ZnO, ReO3, and NiO nanowires via CONG. The process produces single crystalline nanowires that can be grown to high aspect ratio and as high-density nanowire forests. Applications of the as-grown Fe3O4 and ReO3 nanowires for lithium ion battery systems are demonstrated to display high areal energy density and power.

  14. Catalyzed oxidation for nanowire growth.

    PubMed

    Tai, Kaiping; Sun, Ke; Huang, Bo; Dillon, Shen J

    2014-04-11

    A simple, low-cost and scalable route to substrate-supported nanowire growth is reported based on catalyzed oxidation. The process shares common features with popular catalyzed nanowire growth techniques such as vapor-liquid-solid (VLS), vapor-solid-solid (VSS), or vapor-quasi-solid (VQS) that use catalyst nanoparticles to direct the deposition of reactants from the vapor phase. Catalyzed oxidation for nanowire growth (CONG) utilizes catalyzed anion (e.g. O2) reduction from the vapor phase and metal (e.g. Fe) oxidation from the substrate to produce oxide nanowires (e.g. Fe3O4). The approach represents a new class of nanowire growth methodology that may be applied to a broad range of systems. CONG does not require expensive chemical vapor deposition or physical vapor deposition equipment and can be implemented at intermediate temperatures (400-600 °C) in a standard laboratory furnace. This work also demonstrates a passive approach to catalyst deposition that allows the process to be implemented simply with no lithography or physical vapor deposition steps. This effort validates the general approach by synthesizing MnO, Fe3O4, WO3, MgO, TiO2, ZnO, ReO3, and NiO nanowires via CONG. The process produces single crystalline nanowires that can be grown to high aspect ratio and as high-density nanowire forests. Applications of the as-grown Fe3O4 and ReO3 nanowires for lithium ion battery systems are demonstrated to display high areal energy density and power.

  15. Laser-induced fluorescence of cyclohexadienyl (c-C6H7) radical in the gas phase.

    PubMed

    Imamura, Takashi; Zhang, Weijun; Horiuchi, Hiroaki; Hiratsuka, Hiroshi; Kudo, Takako; Obi, Kinichi

    2004-10-01

    A laser-induced fluorescence spectrum was observed in the 500-560 nm region when a mixture of 1,4-cyclohexadiene and oxalyl chloride was photolyzed at 193 nm. The observed excitation spectrum was assigned to the A (2)A(2)<--X (2)B(1) transition of the cyclohexadienyl radical c-C6H7, produced by abstraction of a hydrogen atom from 1,4-cyclohexadiene by Cl atoms. The origin of the A<--X transition of c-C(6)H(7) was at 18 207 cm(-1). From measurements of the dispersed fluorescence spectra and ab initio calculations, the frequencies of several vibrational modes in both the ground and excited states of c-C(6)H(7) were determined: nu(5)(C-H in-plane bend)=1571, nu(8)(C-H in-plane bend)=1174, nu(10)(C-C-C in-plane bend)=981, nu(12)(C-C-C in-plane bend)=559, nu(16)(C-C-C out-of-plane bend)=375, and nu(33)(C-C-C in-plane bend)=600 cm(-1) for the ground state and nu(8)=1118, nu(10)=967, nu(12)=502, nu(16)=172, and nu(33)=536 cm(-1) for the excited states.

  16. 76 FR 44800 - Election of Reduced Research Credit Under Section 280C(c)(3)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-27

    ... research credit. The final regulations simplify how taxpayers make the election and affect taxpayers that... return because each member would be required to file a separate Form 6765 to make the election under... 280C(c)(3) is made is generally sufficient to clearly indicate the intent of the common parent to...

  17. Light Induced C-C Coupling of 2-Chlorobenzazoles with Carbamates, Alcohols, and Ethers.

    PubMed

    Lipp, Alexander; Lahm, Günther; Opatz, Till

    2016-06-01

    A light induced, transition-metal-free C-C coupling reaction of 2-chlorobenzazoles with aliphatic carbamates, alcohols, and ethers is presented. Inexpensive reagents, namely sodium acetate, benzophenone, water, and acetonitrile, are employed in a simple reaction protocol using a cheap and widely available 25 W energy saving UV-A lamp at ambient temperature. PMID:27128627

  18. Synthesis and Applications of Rhodacyclopentanones Derived From C-C Bond Activation

    PubMed Central

    Shaw, Megan H.; Bower, John F.

    2016-01-01

    Rhodacyclopentanones, an “sp3-rich” class of metallacycle, underpin an emerging range of catalytic methodologies for the direct generation of complex scaffolds. This review highlights strategies for accessing rhodacyclopentanones (and related species) by C-C bond activation of cyclobutanones or cyclopropanes. The scope and mechanism of methodologies that exploit these activation modes is outlined. PMID:27385089

  19. Biosynthesis of l-Sorbose and l-Psicose Based on C-C Bond Formation Catalyzed by Aldolases in an Engineered Corynebacterium glutamicum Strain.

    PubMed

    Yang, Jiangang; Li, Jitao; Men, Yan; Zhu, Yueming; Zhang, Ying; Sun, Yuanxia; Ma, Yanhe

    2015-07-01

    The property of loose stereochemical control at aldol products from aldolases helped to synthesize multiple polyhydroxylated compounds with nonnatural stereoconfiguration. In this study, we discovered for the first time that some fructose 1,6-diphosphate aldolases (FruA) and tagatose 1,6-diphosphate (TagA) aldolases lost their strict stereoselectivity when using l-glyceraldehyde and synthesized not only l-sorbose but also a high proportion of l-psicose. Among the aldolases tested, TagA from Bacillus licheniformis (BGatY) showed the highest enzyme activity with l-glyceraldehyde. Subsequently, a "one-pot" reaction based on BGatY and fructose-1-phosphatase (YqaB) generated 378 mg/liter l-psicose and 199 mg/liter l-sorbose from dihydroxyacetone-phosphate (DHAP) and l-glyceraldehyde. Because of the high cost and instability of DHAP, a microbial fermentation strategy was used further to produce l-sorbose/l-psicose from glucose and l-glyceraldehyde, in which DHAP was obtained from glucose through the glycolytic pathway, and some recombination pathways based on FruA or TagA and YqaB were constructed in Escherichia coli and Corynebacterium glutamicum strains. After evaluation of different host cells and combinations of FruA or TagA with YqaB and optimization of gene expression, recombinant C. glutamicum strain WT(pXFTY) was selected and produced 2.53 g/liter total ketoses, with a yield of 0.50 g/g l-glyceraldehyde. Moreover, deletion of gene cgl0331, encoding the Zn-dependent alcohol dehydrogenase in C. glutamicum, was confirmed for the first time to significantly decrease conversion of l-glyceraldehyde to glycerol and to increase yield of target products. Finally, fed-batch culture of strain SY14(pXFTY) produced 3.5 g/liter l-sorbose and 2.3 g/liter l-psicose, with a yield of 0.61 g/g l-glyceraldehyde. This microbial fermentation strategy also could be applied to efficiently synthesize other l-sugars.

  20. 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.

  1. 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

  2. Development of U.S. Government General Technical Requirements for UAS Flight Safety Systems Utilizing the Iridium Satellite Constellation

    NASA Technical Reports Server (NTRS)

    Murray, Jennifer; Birr, Richard

    2010-01-01

    This slide presentation reviews the development of technical requirements for Unmanned Aircraft Systems (UAS) utilization of the Iridium Satellite Constellation to provide flight safety. The Federal Aviation Authority (FAA) required an over-the-horizon communication standard to guarantee flight safety before permitting widespread UAS flights in the National Air Space (NAS). This is important to ensure reliable control of UASs during loss-link and over-the-horizon scenarios. The core requirement was to utilize a satellite system to send GPS tracking data and other telemetry from a flight vehicle down to the ground. Iridium was chosen as the system because it is one of the only true satellite systems that has world wide coverage, and the service has a highly reliable link margin. The Iridium system, the flight modems, and the test flight are described.

  3. Synthesis of a highly reactive (benzyne)ruthenium complex: C-C, C-H, N-H, and O-H activation reactions

    SciTech Connect

    Hartwig, J.F.; Andersen, R.A.; Bergman, R.G. )

    1989-03-29

    The authors report here the synthesis and chemistry of an exceptionally reactive ruthenium benzyne complex, (PMe{sub 3}){sub 4}Ru({eta}{sup 2}-C{sub 6}H{sub 4}) (1). The ruthenium-carbon bond in this molecule reacts with a wide range of organic substrates that are typically inert toward late transition-metal-carbon bonds, including those in benzyne complexes. For example, complex 1 reacts cleanly with arylamine N-H bonds, water O-H bonds, and benzyl and aryl C-H bonds. It reacts with acetophenone to yield an O-bound enolate complex, inserts benzaldehyde cleanly, and cleaves the C-C bond of acetone.

  4. Ammonia and hydrazine. Transition-metal-catalyzed hydroamination and metal-free catalyzed functionalization

    SciTech Connect

    Bertrand, Guy

    2012-06-29

    high temperatures and long reaction times. To address this issue, we have developed several new families of carbon- and boron-based ligands, which are even better donors. The corresponding metal complexes (particularly gold, rhodium, iridium, and ruthenium) of all these species will be tested in the Markovnikov and anti-Markovnikov hydroamination of alkynes, allenes, and also alkenes with ammonia and hydrazine. We will also develop metal-free catalytic processes for the functionalization of ammonia and hydrazine. By possessing both a lone pair of electrons and an accessible vacant orbital, singlet carbenes resemble and can mimic the chemical behavior of transition metals. Our preliminary results demonstrate that specially designed carbenes can split the N–H bond of ammonia by an initial nucleophilic activation that prevents the formation of Lewis acid-base adducts, which is the major hurdle for the transition metal catalyzed functionalization of NH3. The use of purely organic compounds as catalysts will eliminate the major drawbacks of transition-metal-catalysis technology, which are the excessive cost of metal complexes (metal + ligands) and in many cases the toxicity of the metal.

  5. Techniques for Achieving Zero Stress in Thin Films of Iridium, Chromium, and Nickel

    NASA Technical Reports Server (NTRS)

    Broadway, David M.; O'Dell, Stephen L.; Ramsey, Brian D.; Weimer, Jeffrey

    2015-01-01

    We examine techniques for achieving zero intrinsic stress in thin films of iridium, chromium, and nickel deposited by magnetron sputter deposition. The intrinsic stress is further correlated to the microstructural features and physical properties such as surface roughness and optical density at a scale appropriate to soft X-ray wavelengths. 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-arcsecond resolution through various deposition techniques 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 and deposition rate, including the existence of a critical argon process pressure that results in zero film stress which scales linearly with the atomic mass of the sputtered species. While the effect of stress reversal with argon pressure has been previously reported by Hoffman and others for nickel and chromium, we report this effect for iridium. In addition to stress reversal, we identify zero stress in the optical functioning iridium layer shortly after island coalescence for low process pressures at a film thickness of approximately 35nm. The measurement of the low values of stress during deposition was achieved with the aid of a sensitive in-situ instrument capable of a minimum detectable level of stress, assuming a 35nm thick film, in the range of 0.40-6.0 MPa for <111> oriented crystalline silicon substrate thicknesses of 70-280 microns, respectively.

  6. Efficient light harvesting and energy transfer in a red phosphorescent iridium dendrimer.

    PubMed

    Cho, Yang-Jin; Hong, Seong Ahn; Son, Ho-Jin; Han, Won-Sik; Cho, Dae Won; Kang, Sang Ook

    2014-12-15

    A series of red phosphorescent iridium dendrimers of the type [Ir(btp)2(pic-PCn)] (Ir-Gn; n = 0, 1, 2, and 3) with two 2-(benzo[b]thiophen-2-yl)pyridines (btp) and 3-hydroxypicolinate (pic) as the cyclometalating and ancillary ligands were prepared in good yields. Dendritic generation was grown at the 3 position of the pic ligand with 4-(9H-carbazolyl)phenyl dendrons connected to 3,5-bis(methyleneoxy)benzyloxy branches (PCn; n = 0, 2, 4, and 8). The harvesting photons on the PCn dendrons followed by efficient energy transfer to the iridium center resulted in high red emissions at ∼600 nm by metal-to-ligand charge transfer. The intensity of the phosphorescence gradually increased with increasing dendrimer generation. Steady-state and time-resolved spectroscopy were used to investigate the energy-transfer mechanism. On the basis of the fluorescence quenching rate constants of the PCn dendrons, the energy-transfer efficiencies for Ir-G1, Ir-G2, and Ir-G3 were 99, 98, and 96%, respectively. The energy-transfer efficiency for higher-generation dendrimers decreased slightly because of the longer distance between the PC dendrons and the core iridium(III) complex, indicating that energy transfer in Ir-Gn is a Förster-type energy transfer. Finally, the light-harvesting efficiencies for Ir-G1, Ir-G2, and Ir-G3 were determined to be 162, 223, and 334%, respectively.

  7. Cyclometalated iridium(III) complexes for phosphorescence sensing of biological metal ions.

    PubMed

    You, Youngmin; Cho, Somin; Nam, Wonwoo

    2014-02-17

    Phosphorescence signaling provides a valuable alternative to conventional bioimaging based on fluorescence. The benefits of using phosphorescent molecules include improved sensitivity and capabilities for effective elimination of background signals by time-gated acquisition. Cyclometalated Ir(III) complexes are promising candidates for facilitating phosphorescent bioimaging because they provide synthetic versatility and excellent phosphorescence properties. In this Forum Article, we present our recent studies on the development of phosphorescence sensors for the detection of metal ions based on cyclometalated iridium(III) complexes. The constructs contained cyclometalating (C^N) ligands with the electron densities and band-gap energies of the C^N ligand structures systematically varied. Receptors that chelated zinc, cupric, and chromium ions were tethered to the ligands to create phosphorescence sensors. The alterations in the C^N ligand structures had a profound influence on the phosphorescence responses to metal ions. Mechanistic studies suggested that the phosphorescence responses could be explained on the basis of the modulation of photoinduced electron transfer (PeT) from the receptor to the photoexcited iridium species. The PeT behaviors strictly adhered to the Rehm-Weller principle, and the occurrence of PeT was located in the Marcus-normal region. It is thus anticipated that improved responses will be obtainable by increasing the excited-state reduction potential of the iridium(III) complexes. Femtosecond transient absorption experiments provided evidence for the presence of an additional photophysical mechanism that involved metal-ion-induced alteration of the intraligand charge-transfer (ILCT) transition state. Utility of the mechanism by PeT and ILCT has been demonstrated for the phosphorescence sensing of biologically important transition-metal ions. In particular, the phosphorescence zinc sensor could report the presence of intracellular zinc pools by

  8. Nickel-catalyzed cross-coupling reactions of o-carboranyl with aryl iodides: facile synthesis of 1-aryl-o-carboranes and 1,2-diaryl-o-carboranes.

    PubMed

    Tang, Cen; Xie, Zuowei

    2015-06-22

    A nickel-catalyzed arylation at the carbon center of o-carborane cages has been developed, thus leading to the preparation of a series of 1-aryl-o-carboranes and 1,2-diaryl-o-carboranes in high yields upon isolation. This method represents the first example of transition metal catalyzed C,C'-diarylation by cross-coupling reactions of o-carboranyl with aryl iodides.

  9. Intercalated samarium as an agent enabling the intercalation of oxygen under a monolayer graphene film on iridium

    NASA Astrophysics Data System (ADS)

    Afanas'eva, E. Yu.; Rut'kov, E. V.; Gall', N. R.

    2016-06-01

    Using thermal desorption time-of-flight mass spectrometry and thermionic methods, it is shown that oxygen does not intercalate under a graphene monolayer grown correctly on iridium, at least at temperatures of T = 300-400 K and exposures below 12000 L. However, if the graphene film on iridium is preliminary intercalated with samarium atoms (up to coverage of θSm = 0.2-0.45), the penetration of oxygen atoms under the graphene film is observed. The oxygen atoms in the intercalated state are chemically bonded to samarium atoms and remain under graphene up to high temperatures (~2150 K).

  10. Rhodium(III)-catalyzed C-H activation/[4+3] annulation of N-phenoxyacetamides and α,β-unsaturated aldehydes: an efficient route to 1,2-oxazepines at room temperature.

    PubMed

    Duan, Pingping; Lan, Xia; Chen, Ying; Qian, Shao-Song; Li, Jie Jack; Lu, Liang; Lu, Yanbo; Chen, Bo; Hong, Mei; Zhao, Jing

    2014-10-18

    An efficient Rh(III)-catalyzed coupling reaction of N-phenoxyacetamides with α,β-unsaturated aldehydes to give 1,2-oxazepines via C-H activation/[4+3] annulation has been developed. This transformation does not require oxidants and features C-C/C-N bond formation to yield seven-membered oxazepine rings at room temperature. Further derivation of 1,2-oxazepines leads to important chroman derivatives.

  11. Palynological and iridium anomalies at Cretaceous-Tertiary boundary, south-central Saskatchewan

    USGS Publications Warehouse

    Nichols, D.J.; Jarzen, D.M.; Orth, C.J.; Oliver, P.Q.

    1986-01-01

    The Cretaceous-Tertiary boundary in south-central Saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of Cretaceous pollen taxa. Evidence of disruption of the terrestrial flora includes the fern-spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species. The reorganized earliest Tertiary flora is made up largely of surviving species that assumed new roles of dominance. Persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal Cretaceous event, it returned quickly to the pre-event condition.

  12. Catalytic dehydrogenation of cycloalkanes to arenes by a dihydrido iridium P-C-P pincer complex

    SciTech Connect

    Gupta, M.; Hagen, C.; Cramer, R.E.; Jensen, C.M.; Kaska, W.C.

    1997-01-29

    We recently found that the iridium P-C-P pincer complex IrH{sub 2}[C{sub 6}H{sub 3}-2,6-(CH{sub 2}-PBu{sup T}{sub 2}){sub 2}] (1) is a highly active, homogeneous catalyst for the transfer dehydrogenation of cyclooctane with unusual long-term stability at temperatures as high as 200 {degree}C. This reactivity has now been extended to the catalytic transfer dehydrogenation of cycloalkanes to arenes. We report this novel catalytic activity as well as the results of an X-ray structure determination of 1. 15 refs., 1 fig., 1 tab.

  13. Salvage irradiation of oropharynx and mobile tongue about /sup 192/iridium brachytherapy in Centre Alexis Vautrin

    SciTech Connect

    Langlois, D.; Hoffstetter, S.; Malissard, L.; Pernot, M.; Taghian, A.

    1988-05-01

    Between 1972 and 1984, 123 patients were treated using /sup 192/Iridium afterloading techniques for recurrence or new cancer of the tongue or oropharynx arising in previously irradiated tissues. The actuarial local control was 67% at 2 years and 59% at 5 years. Local control of the tumor was achieved in the majority of these patients, the actuarial survival was only 48% at 2 years and 24% at 5 years. Twenty-eight patients developed mucosal necrosis. We analyzed prognostic factors for survival, local control, and complication. We proposed a selection for this salvage therapy.

  14. Theoretical studies on the photophysical properties of some Iridium (III) complexes used for OLED

    NASA Astrophysics Data System (ADS)

    Urinda, Sharmistha; Das, Goutam; Pramanik, Anup; Sarkar, Pranab

    2016-09-01

    The structural and photophysical properties of four heteroleptic Iridium (III) complexes, based on 1-phenylpyrazole ligand, have been investigated theoretically. The effect of chemical substitution on the absorption and the emission spectra of the complexes has been studied and compared with the experimental data. We observe a significant structural change in the lowest triplet excited state as compared to the ground singlet state. We compute the emission wavelength of the complexes by considering the spin-orbit coupling. Using these understandings, we predict two new complexes having deeper blue emission which are supposed to be better efficient OLED materials.

  15. 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

  16. Flexible, high-density microphotodiode array with integrated sputtered iridium oxide electrodes for retinal stimulation

    NASA Astrophysics Data System (ADS)

    Yang, Frank; Chang, Mao-Yen; Yang, Chung-Hua; Teng, Chih-Ciao; Fan, Long-Sheng

    2016-01-01

    To assess the charge-injection capacity of the sputtered iridium oxide film (SIROF) electrode on the retinal CMOS image sensor (CIS) chip, a polyimide-based flex device was designed and fabricated to package the retinal CIS chip. The polyimide-flex-based packaging process keeps the surface of photosensors clean, and the measured connection resistance meets the packaging requirement of the low-power retinal CIS chip. The in vitro experimental results show that the small SIROF electrodes can provide a biphasic charge injection per phase of 3.9 nC/ph to achieve the stimulation threshold at a polarization potential of -0.44 V.

  17. Iridium Complexes and Clusters in Dealuminated Zeolite HY: Distribution between Crystalline and Impurity Amorphous Regions

    SciTech Connect

    Martinez-Macias, Claudia; Xu, Pinghong; Hwang, Son-Jong; Lu, Jing; Chen, Cong-Yan; Browning, Nigel D.; Gates, Bruce C.

    2014-07-08

    Dealuminated zeolite HY was used to support Ir(CO)2 complexes formed from Ir(CO)2(C5H7O2). Infrared and X-ray absorption spectra and atomic-resolution electron microscopy images identify these complexes, and the images and 27Al NMR spectra identify impurity amorphous regions in the zeolite where the iridium is more susceptible to aggregation than in the crystalline regions. The results indicate a significant stability limitation of metal in amorphous impurity regions of zeolites.

  18. Relationship between mass extinction and iridium across the Cretaceous-Paleogene boundary in New Jersey

    USGS Publications Warehouse

    Miller, K.G.; Sherrell, Robert M.; Browning, J.V.; Field, M.P.; Gallagher, W.; Olsson, R.K.; Sugarman, P.J.; Tuorto, S.; Wahyudi, H.

    2010-01-01

    We directly link iridium (Ir) anomalies in New Jersey to the mass extinction of marine plankton marking the Cretaceous-Paleogene (K-Pg) boundary. We confirm previous reports of an Ir anomaly 20 cm below the extinction of Cretaceous macrofauna (the "Pinna" bed) with new results from a muddy sand section from Tighe Park, Freehold, New Jersey (United States), but we also show that Ir anomalies correlate with marine mass extinctions at three other clay-rich New Jersey sections. Thus, we attribute the anomaly at Freehold to the downward movement of Ir and reaffirm the link between impact and mass extinction. ?? 2010 Geological Society of America.

  19. Sizeable Kane-Mele-like spin orbit coupling in graphene decorated with iridium clusters

    NASA Astrophysics Data System (ADS)

    Qin, Yuyuan; Wang, Siqi; Wang, Rui; Bu, Haijun; Wang, Xuefeng; Wang, Xinran; Song, Fengqi; Wang, Baigeng; Wang, Guanghou

    2016-05-01

    The spin-orbit coupling strength of graphene can be enhanced by depositing iridium nanoclusters. Weak localization is intensely suppressed near zero fields after the cluster deposition, rather than changing to weak anti-localization. Fitting the magnetoresistance gives the spin relaxation time, which increases by two orders with the application of a back gate. The spin relaxation time is found to be proportional to the electronic elastic scattering time, demonstrating the Elliot-Yafet spin relaxation mechanism. A sizeable Kane-Mele-like coupling strength of over 5.5 meV is determined by extrapolating the temperature dependence to zero.

  20. Platinum-catalyzed reduction of amides with hydrosilanes bearing dual Si-H groups: a theoretical study of the reaction mechanism.

    PubMed

    Nakatani, Naoki; Hasegawa, Jun-ya; Sunada, Yusuke; Nagashima, Hideo

    2015-11-28

    A platinum-catalyzed amide reduction through hydrosilylation with 1,2-bis(dimethylsilyl)benzene (BDSB) was investigated on a theoretical basis. While the platinum-catalyzed hydrosilylation of alkenes is well known, that of carbonyl groups rarely occurs. The only exception involves the use of bifunctional hydrosilanes having dual, closely located Si-H groups, which accelerate the hydrosilylation of carbonyl groups, leading to successful reduction of amides to amines under mild conditions. In the present study, we determined through density functional theory calculations that the platinum-catalyzed hydrosilylation of the C=O bond proceeds via a Pt(IV)-disilyl-dihydride intermediate with an associated activation energy of 29.6 kcal mol(-1). Although it was believed that the hydrosilylation of carbonyl groups does not occur via the classical Chalk-Harrod cycle, the computational results support a mechanism involving the insertion of the amide C=O bond into a Pt-H bond. This insertion readily occurs because a Pt-H bond in the Pt(IV)-disilyl-dihydride intermediate is highly activated due to the strong σ-donating interaction of the silyl groups. The modified Chalk-Harrod mechanism that occurs preferentially in rhodium-catalyzed hydrosilylation as well as the ionic outer sphere mechanism associated with iridium-catalyzed amide reduction were both safely ruled out as mechanisms for this platinum-catalyzed amide reduction, because of the unexpectedly large activation barrier (>40 kcal mol(-1)) for the Si-O bond formation. PMID:26497866

  1. Thermodynamics of Enzyme-Catalyzed Reactions Database

    National Institute of Standards and Technology Data Gateway

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  2. Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.

    PubMed

    Alcaide, Benito; Almendros, Pedro

    2014-03-18

    Although gold is chemically inert as a bulk metal, the landmark discovery that gold nanoparticles can be effective catalysts has opened up new and exciting research opportunities in the field. In recent years, there has been growth in the number of reactions catalyzed by gold complexes [gold(I) and gold(III)], usually as homogeneous catalysts, because they are soft Lewis acids. In addition, alkynes and allenes have interesting reactivities and selectivities, notably their ability to produce complex structures in very few steps. In this Account, we describe our work in gold catalysis with a focus on the formation of C-C and C-O bonds using allenes and alkynes as starting materials. Of these, oxa- and carbo-cyclizations are perhaps the best known and most frequently studied. We have divided those contributions into sections arranged according to the nature of the starting material (allene versus alkyne). Gold-catalyzed carbocyclizations in allenyl C2-linked indoles, allenyl-β-lactams, and allenyl sugars follow different mechanistic pathways. The cyclization of indole-tethered allenols results in the efficient synthesis of carbazole derivatives, for example. However, the compound produced from gold-catalyzed 9-endo carbocyclization of (aryloxy)allenyl-tethered 2-azetidinones is in noticeable contrast to the 5-exo hydroalkylation product that results from allenyl sugars. We have illustrated the unusual preference for the 4-exo-dig cyclization in allene chemistry, as well as the rare β-hydride elimination reaction, in gold catalysis from readily available α-allenols. We have also observed in γ-allenols that a (methoxymethyl)oxy protecting group not only masks a hydroxyl functionality but also exerts directing effects as a controlling unit in a gold-catalyzed regioselectivity reversal. Our recent work has also led to a combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled

  3. Recent advances in osmium-catalyzed hydrogenation and dehydrogenation reactions.

    PubMed

    Chelucci, Giorgio; Baldino, Salvatore; Baratta, Walter

    2015-02-17

    CONSPECTUS: A current issue in metal-catalyzed reactions is the search for highly efficient transition-metal complexes affording high productivity and selectivity in a variety of processes. Moreover, there is also a great interest in multitasking catalysts that are able to efficiently promote different organic transformations by careful switching of the reaction parameters, such as temperature, solvent, and cocatalyst. In this context, osmium complexes have shown the ability to catalyze efficiently different types of reactions involving hydrogen, proving at the same time high thermal stability and simple synthesis. In the catalytic reduction of C═X (X = O, N) bonds by both hydrogenation (HY) and transfer hydrogenation (TH) reactions, the most interest has been focused on homogeneous systems based on rhodium, iridium, and in particular ruthenium catalysts, which have proved to catalyze chemo- and stereoselective hydrogenations with remarkable efficiency. By contrast, osmium catalysts have received much less attention because they are considered less active on account of their slower ligand exchange kinetics. Thus, this area remained almost neglected until recent studies refuted these prejudices. The aim of this Account is to highlight the impressive developments achieved over the past few years by our and other groups on the design of new classes of osmium complexes and their applications in homogeneous catalytic reactions involving the hydrogenation of carbon-oxygen and carbon-nitrogen bonds by both HY and TH reactions as well as in alcohol deydrogenation (DHY) reactions. The work described in this Account demonstrates that osmium complexes are emerging as powerful catalysts for asymmetric and non-asymmetric syntheses, showing a remarkably high catalytic activity in HY and TH reactions of ketones, aldehydes, imines, and esters as well in DHY reactions of alcohols. Thus, for instance, the introduction of ligands with an NH function, possibly in combination with a

  4. Baeyer-Villiger C-C bond cleavage reaction in gilvocarcin and jadomycin biosynthesis

    PubMed Central

    Tibrewal, Nidhi; Pahari, Pallab; Wang, Guojun; Kharel, Madan K.; Morris, Caleb; Downey, Theresa; Hou, Yanpeng; Bugni, Tim S.; Rohr, Jürgen

    2012-01-01

    GilOII has been unambiguously identified as the key enzyme performing the crucial C-C bond cleavage reaction responsible for the unique rearrangement of a benz[a]anthracene skeleton to the benzo[d]naphthopyranone backbone typical for the gilvocarcin type natural anticancer antibiotics. Further investigations of this enzyme led to the isolation of a hydroxy-oxepinone intermediate which allowed important conclusions regarding the cleavage mechanism. PMID:23102024

  5. Characterization of Brazed Joints of C-C Composite to Cu-clad-Molybdenum

    NASA Technical Reports Server (NTRS)

    Singh, M.; Asthana, R.

    2008-01-01

    Carbon-carbon composites with either pitch+CVI matrix or resin-derived matrix were joined to copper-clad molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived C-C composite due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the pitch+CVI C-C composites was observed. The relatively low brazing temperatures (<950 C) precluded melting of the clad layer and restricted the redistribution of alloying elements but led to metallurgically sound composite joints. The Knoop microhardness (HK) distribution across the joint interfaces revealed sharp gradients at the Cu-clad-Mo/braze interface and higher hardness in Ticusil (approx.85-250 HK) than in Cusil-ABA (approx.50-150 HK). These C-C/Cu-clad-Mo joints with relatively low thermal resistance may be promising for thermal management applications.

  6. Active Brazing of C/C Composite to Copper by AgCuTi Filler Metal

    NASA Astrophysics Data System (ADS)

    Zhang, Kexiang; Xia, Lihong; Zhang, Fuqin; He, Lianlong

    2016-05-01

    Brazing between the carbon-fiber-reinforced carbon composite (C/C composite) and copper has gained increasing interest because of its important application in thermal management systems in nuclear fusion reactors and in the aerospace industry. In order to examine the "interfacial shape effect" on the mechanical properties of the joint, straight and conical interfacial configurations were designed and machined on the surface of C/C composites before joining to copper using an Ag-68.8Cu-4.5Ti (wt pct) alloy. The microstructure and interfacial microchemistry of C/C composite/AgCuTi/Cu brazed joints were comprehensively investigated by using high-resolution transmission electron microscopy. The results indicate that the joint region of both straight and conical joints can be described as a bilayer. Reaction products of Cu3Ti3O and γ-TiO were formed near the copper side in a conical interface joint, while no reaction products were found in the straight case. The effect of Ag on the interfacial reaction was discussed, and the formation mechanism of the joints during brazing was proposed. On the basis of the detailed microstructure presented, the mechanical performance of the brazed joints was discussed in terms of reaction and morphology across the joint.

  7. Detection of interstellar ethylene oxide (c-C2H4O).

    PubMed

    Dickens, J E; Irvine, W M; Ohishi, M; Ikeda, M; Ishikawa, S; Nummelin, A; Hjalmarson, A

    1997-11-10

    We report the identification of 10 transitions that support the detection of the small cyclic molecule ethylene oxide (c-C2H4O) in Sgr B2N. Although one of these transitions is severely blended, so that an accurate intensity and line width could not be determined, and two other lines are only marginally detected, we have done Gaussian fits to the remaining seven lines and have performed a rotation diagram analysis. Our results indicate a rotation temperature T(rot) = 18 K and a molecular column density N(c-C2H4O) = 3.3 x 10(14) cm-2, corresponding to a fractional abundance relative to molecular hydrogen of order 6 x 10(-11). This is a factor of more than 200 higher than the abundance for this molecule suggested by the "new standard" chemistry model of Lee, Bettens, & Herbst. This result suggests that grain chemistry might play an effective role in the production of c-C2H4O. No transitions of this molecule were detected in either Sgr B2M or Sgr B2NW.

  8. C-Alkylation of Ketones and Related Compounds by Alcohols: Transition-Metal-Catalyzed Dehydrogenation.

    PubMed

    Huang, Fei; Liu, Zhuqing; Yu, Zhengkun

    2016-01-18

    Transition-metal-catalyzed C-alkylation of ketones and secondary alcohols, with alcohols, avoids use of organometallic or environmentally unfriendly alkylating agents by means of borrowing hydrogen (BH) or hydrogen autotransfer (HA) activation of the alcohol substrates. Water is formed as the only by-product, thus making the BH process atom-economical and environmentally benign. Diverse homogeneous and heterogeneous transition-metal catalysts, ketones, and alcohols can be used for this transformation, thus rendering the BH process promising for replacing those procedures that use traditional alkylating agents. This Minireview summarizes the advances during the last five years in transition-metal-catalyzed BH α-alkylation of ketones, and β-alkylation of secondary alcohols with alcohols. A discussion on the application of the BH strategy for C-C bond formation is included. PMID:26639633

  9. Graphene-Catalyzed Direct Friedel-Crafts Alkylation Reactions: Mechanism, Selectivity, and Synthetic Utility.

    PubMed

    Hu, Feng; Patel, Mehulkumar; Luo, Feixiang; Flach, Carol; Mendelsohn, Richard; Garfunkel, Eric; He, Huixin; Szostak, Michal

    2015-11-18

    Transition-metal-catalyzed alkylation reactions of arenes have become a central transformation in organic synthesis. Herein, we report the first general strategy for alkylation of arenes with styrenes and alcohols catalyzed by carbon-based materials, exploiting the unique property of graphenes to produce valuable diarylalkane products in high yields and excellent regioselectivity. The protocol is characterized by a wide substrate scope and excellent functional group tolerance. Notably, this process constitutes the first general application of graphenes to promote direct C-C bond formation utilizing polar functional groups anchored on the GO surface, thus opening the door for an array of functional group alkylations using benign and readily available graphene materials. Mechanistic studies suggest that the reaction proceeds via a tandem catalysis mechanism in which both of the coupling partners are activated by interaction with the GO surface. PMID:26496423

  10. Silver-Catalyzed Cross-Coupling of Isocyanides and Active Methylene Compounds by a Radical Process.

    PubMed

    Liu, Jianquan; Liu, Zhenhua; Liao, Peiqiu; Zhang, Lin; Tu, Tao; Bi, Xihe

    2015-09-01

    Isocyanides are versatile building blocks, and have been extensively exploited in C-H functionalization reactions. However, transition-metal-catalyzed direct C-H functionalization reactions with isocyanides suffer from over-insertion of isocyanides. Reported herein is a radical coupling/isomerization strategy for the cross-coupling of isocyanides with active methylene compounds through silver-catalysis. The method solves the over-insertion issue and affords a variety of otherwise difficult to synthesize β-aminoenones and tricarbonylmethanes under base- and ligand-free conditions. This report presents a new fundamental C-C bond-forming reaction of two basic chemicals.

  11. Switching the Cleavage Sites in Palladium on Carbon-Catalyzed Carbon-Carbon Bond Disconnection.

    PubMed

    Hattori, Tomohiro; Takakura, Ryoya; Ichikawa, Tomohiro; Sawama, Yoshinari; Monguchi, Yasunari; Sajiki, Hironao

    2016-04-01

    We have demonstrated a palladium on carbon-catalyzed approach to regioselectively alter the cleavage sites of the C-C bonds of cinnamaldehyde derivatives by a slight change in the reaction conditions in isopropanol under an O2 atmosphere. Styrene derivatives could be selectively formed by the addition of Na2CO3 in association with the dissociation of carbon monoxide, while benzaldehyde derivatives were generated by the addition of CuCl and morpholine instead of Na2CO3. PMID:26944077

  12. Palladium-Catalyzed Alkoxycarbonylation of Unactivated Secondary Alkyl Bromides at Low Pressure.

    PubMed

    Sargent, Brendon T; Alexanian, Erik J

    2016-06-22

    Catalytic carbonylations of organohalides are important C-C bond formations in chemical synthesis. Carbonylations of unactivated alkyl halides remain a challenge and currently require the use of alkyl iodides under harsh conditions and high pressures of CO. Herein we report a palladium-catalyzed alkoxycarbonylation of secondary alkyl bromides that proceeds at low pressure (2 atm CO) under mild conditions. Preliminary mechanistic studies are consistent with a hybrid organometallic-radical process. These reactions efficiently deliver esters from unactivated alkyl bromides across a diverse range of substrates and represent the first catalytic carbonylations of alkyl bromides with carbon monoxide.

  13. Copper-catalyzed intermolecular trifluoromethylarylation of alkenes: mutual activation of arylboronic acid and CF3+ reagent.

    PubMed

    Wang, Fei; Wang, Dinghai; Mu, Xin; Chen, Pinhong; Liu, Guosheng

    2014-07-23

    A novel copper-catalyzed intermolecular trifluoromethylarylation of alkenes is developed using less active ether-type Togni's reagent under mild reaction conditions. Various alkenes and diverse arylboronic acids are compatible with these conditions. Preliminary mechanistic studies reveal that a mutual activation process between arylboronic acid and CF3(+) reagent is essential. In addition, the reaction might involve a rate-determining transmetalation, and the final aryl C-C bond is derived from reductive elimination of the aryl(alkyl)Cu(III) intermediate. PMID:24983408

  14. Peptide-Catalyzed Stereoselective Conjugate Addition Reactions of Aldehydes to Maleimide.

    PubMed

    Grünenfelder, Claudio E; Kisunzu, Jessica K; Wennemers, Helma

    2016-07-18

    The tripeptide H-dPro-Pro-Asn-NH2 is presented as a catalyst for asymmetric conjugate addition reactions of aldehydes to maleimide. The peptidic catalyst promotes the reaction between various aldehydes and unprotected maleimide with high stereoselectivities and yields. The obtained products were readily derivatized to the corresponding pyrrolidines, lactams, lactones, and peptide-like compounds. (1) H NMR spectroscopic, crystallographic, and computational investigations provided insight into the conformational properties of H-dPro-Pro-Asn-NH2 and revealed the importance of hydrogen bonding between the peptide and maleimide for catalyzing the stereoselective C-C bond formation.

  15. Palladium-Catalyzed Deaminative Phenanthridinone Synthesis from Aniline via C-H Bond Activation.

    PubMed

    Yedage, Subhash L; Bhanage, Bhalchandra M

    2016-05-20

    This work reports palladium-catalyzed phenanthridinone synthesis using the coupling of aniline and amide by formation of C-C and C-N bonds in a one-pot fashion via dual C-H bond activation. It involves simultaneous cleavage of four bonds and the formation of two new bonds. The present protocol is ligand-free, takes place under mild reaction conditions, and is environmentally benign as nitrogen gas and water are the only side products. This transformation demonstrates a broad range of aniline and amide substrates with different functional groups and has been scaled up to gram level. PMID:27088815

  16. Palladium-Catalyzed Deaminative Phenanthridinone Synthesis from Aniline via C-H Bond Activation.

    PubMed

    Yedage, Subhash L; Bhanage, Bhalchandra M

    2016-05-20

    This work reports palladium-catalyzed phenanthridinone synthesis using the coupling of aniline and amide by formation of C-C and C-N bonds in a one-pot fashion via dual C-H bond activation. It involves simultaneous cleavage of four bonds and the formation of two new bonds. The present protocol is ligand-free, takes place under mild reaction conditions, and is environmentally benign as nitrogen gas and water are the only side products. This transformation demonstrates a broad range of aniline and amide substrates with different functional groups and has been scaled up to gram level.

  17. Access to the Cinnoline Scaffold via Rhodium-Catalyzed Intermolecular Cyclization under Mild Conditions.

    PubMed

    Song, Chao; Yang, Chen; Zhang, Feifei; Wang, Jinhu; Zhu, Jin

    2016-09-16

    Herein, we report Rh(III)-catalyzed, N-amino (hydrazine)-directed C-H functionalization with α-diazo-β-ketoesters for access to the cinnoline scaffold. A diverse set of nondiscriminating conditions obtained for a highly efficient test transformation prompted use of a substrate-replacement technique for an in-depth search of experimental parameter space and pinpointing of the optimized conditions. A successive C-H activation/C-C coupling/intramolecular dehydration mechanistic sequence is proposed. The ability to perform gram-scale synthesis proves the synthetic utility of this simple, yet efficient, method. PMID:27584580

  18. Transition-Metal-Catalyzed Direct Addition of Aryl C-H Bonds to Unsaturated Electrophiles.

    PubMed

    Shi, Xian-Ying; Han, Wen-Jing; Li, Chao-Jun

    2016-06-01

    The direct addition of Csp(2) -H bonds onto polar C=C, C=O, and C=N bonds is both synthetically and mechanistically important, because using aromatic C-H substrates in place of organometallic reagents provides a more direct and atom-economical alternative to many important compounds without the pre-generation of organometallic compounds from stoichiometric halides and the unavoidable generation of stoichiometric metal halide waste. In this account, we summarize our contributions to the transition-metal-catalyzed addition of aromatic C-H bonds to polar C=C, C=O, and C=N bonds via directing-group-assisted regiospecific reactions. These synthetic methods provide efficient access to benzylic alcohols, alkylbenzenes, 3-substituted phthalides, N-substituted phthalimides, N-aryl benzamides, and indene derivatives from commercially available reagents. It is worth noting that valuable heterocycles such as 3-substituted phthalides and N-substituted phthalimides can be obtained in one step by this approach. PMID:27059538

  19. Blue light emission from cyclometallated iridium (III) cyano complexes: Syntheses, crystal structures, and photophysical properties

    SciTech Connect

    Sanner, Robert D.; Cherepy, Nerine J.; Young, Jr., Victor G.

    2015-11-02

    In this study, we describe the synthesis and crystal structures of four iridium compounds containing the 2-(4,6-difluorophenyl)pyridyl ligand. Cleavage of dichloro-bridged iridium(III) dimers with phosphorus ligands leads to (46dfppy)2Ir(L)(Cl) where L = PPh3 or P(OPh)3. Treatment of the chloro compounds with cyanide forms the cyano complexes (46dfppy)2Ir(L)(CN). All complexes exhibit a trans effect in their molecular structures due to the phosphorus ligands, with the phosphite having a greater effect than the phosphine. With L = PPh3, blue photoluminescence with CIE coordinates (x = 0.16, y = 0.24), quantum yield of 0.66 ± 0.15 and 4.5 ± 0.5 μs decay time is measured. For L = P(OPh)3, blue photoluminescence with CIE coordinates (x = 0.16, y = 0.21), quantum yield of 0.65 ± 0.15 and 2.9 ± 0.3 μs decay time is measured.

  20. Blue light emission from cyclometallated iridium (III) cyano complexes: Syntheses, crystal structures, and photophysical properties

    DOE PAGES

    Sanner, Robert D.; Cherepy, Nerine J.; Young, Jr., Victor G.

    2015-11-02

    In this study, we describe the synthesis and crystal structures of four iridium compounds containing the 2-(4,6-difluorophenyl)pyridyl ligand. Cleavage of dichloro-bridged iridium(III) dimers with phosphorus ligands leads to (46dfppy)2Ir(L)(Cl) where L = PPh3 or P(OPh)3. Treatment of the chloro compounds with cyanide forms the cyano complexes (46dfppy)2Ir(L)(CN). All complexes exhibit a trans effect in their molecular structures due to the phosphorus ligands, with the phosphite having a greater effect than the phosphine. With L = PPh3, blue photoluminescence with CIE coordinates (x = 0.16, y = 0.24), quantum yield of 0.66 ± 0.15 and 4.5 ± 0.5 μs decay timemore » is measured. For L = P(OPh)3, blue photoluminescence with CIE coordinates (x = 0.16, y = 0.21), quantum yield of 0.65 ± 0.15 and 2.9 ± 0.3 μs decay time is measured.« less

  1. The kinetics and mechanism of the organo-iridium-catalysed enantioselective reduction of imines.

    PubMed

    Stirling, Matthew J; Sweeney, Gemma; MacRory, Kerry; Blacker, A John; Page, Michael I

    2016-04-14

    The iridium complex of pentamethylcyclopentadiene and (S,S)-1,2-diphenyl-N'-tosylethane-1,2-diamine is an effective catalyst for the asymmetric transfer hydrogenation of imine substrates under acidic conditions. Using the Ir catalyst and a 5 : 2 ratio of formic acid : triethylamine as the hydride source for the asymmetric transfer hydrogenation of 1-methyl-3,4-dihydroisoquinoline and its 6,7-dimethoxy substituted derivative, in either acetonitrile or dichloromethane, shows unusual enantiomeric excess (ee) profiles for the product amines. The reactions initially give predominantly the (R) enantiomer of the chiral amine products with >90% ee but which then decreases significantly during the reaction. The decrease in ee is not due to racemisation of the product amine, but because the rate of formation of the (R)-enantiomer follows first-order kinetics whereas that for the (S)-enantiomer is zero-order. This difference in reaction order explains the change in selectivity as the reaction proceeds - the rate formation of the (R)-enantiomer decreases exponentially with time while that for the (S)-enantiomer remains constant. A reaction scheme is proposed which requires rate-limiting hydride transfer from the iridium hydride to the iminium ion for the first-order rate of formation of the (R)-enantiomer amine and rate-limiting dissociation of the product for the zero-order rate of formation of the (S)-enantiomer.

  2. Treatment of carcinoma of the penis by iridium 192 wire implant

    SciTech Connect

    Daly, N.J.; Douchez, J.; Combes, P.F.

    1982-07-01

    Since 1971, a group of 22 adult patients with squamous cell carcinoma of the penis have been treated by iridium 192 wire implants. There were 6 T1 tumors, 14 T2 tumors and 2 T3; only one patient (T3) presented with local failure after implant. Local necrosis occurred in 2 patients without local tumoral recurrence, but was sufficient enough to warrant amputation. Thus 19/22 (86%) patients were locally cured with penile conservation. In these patients the most frequent posttherapeutic complication is chronic urethral stenosis (9/19 patients, 47%) requiring repeated instrumental dilations. Four patients presented with initial inguinal mestastatic nodes; only one was cured by radiosurgical treatment. Among patients without metastatic nodes at the time of diagnosis, none had delayed metastatic nodes. Three patients died of nodal evolution, 5 patients died of intercurrent disease without evidence of disease and 14 are now alive and NED. It appears that iridium 192 wire implant is the most effective conservative treatment of invasive squamous cell carcinoma of the penis; however, these results confirm that no particular treatment is required for inguinal nodal areas for patients who initially present with no disease.

  3. [Brachytherapy in France: current situation and economic outlook due to the unavailability of iridium wires].

    PubMed

    Le Vu, B; Boucher, S

    2014-10-01

    In 2013, about 6000 patients were treated with brachytherapy, the number diminishing by 2.6% per year since 2008. Prostate, breast and gynecological cancers are the most common types of cancers. Since 2008, the number of brachytherapy facilities has decreased by 18%. In medicoeconomic terms, brachytherapy faces many problems: the coding system is outdated; brachytherapy treatments cost as much as internal radiation; fees do not cover costs; since iridium wire has disappeared from the market, the technique will be transferred to more expensive high-speed or pulse dose rates. The French financing grid based on the national study of costs lags behind changes in such treatments and in the best of cases, hospitals resorting to alternatives such as in-hospital brachytherapy are funded at 46% of their additional costs. Brachytherapy is a reference technique. With intense pressure on hospital pricing, financing brachytherapy facilities will become even more problematic as a consequence of the disappearance of iridium 192 wires. The case of brachytherapy illustrates the limits of the French financing system and raises serious doubts as to its responsiveness. PMID:25195115

  4. Iridium- and Osmium-decorated Reduced Graphenes as Promising Catalysts for Hydrogen Evolution.

    PubMed

    Lim, Chee Shan; Sofer, Zdeněk; Toh, Rou Jun; Eng, Alex Yong Sheng; Luxa, Jan; Pumera, Martin

    2015-06-22

    Renewable energy sources are highly sought after as a result of numerous worldwide problems concerning the environment and the shortage of energy. Currently, the focus in the field is on the development of catalysts that are able to provide water splitting catalysis and energy storage for the hydrogen evolution reaction (HER). While platinum is an excellent material for HER catalysis, it is costly and rare. In this work, we investigated the electrocatalytic abilities of various graphene-metal hybrids to replace platinum for the HER. The graphene materials were doped with 4f metals, namely, iridium, osmium, platinum and rhenium, as well as 3d metals, namely, cobalt, iron and manganese. We discovered that a few hybrids, in particular iridium- and osmium-doped graphenes, have the potential to become competent electrocatalysts owing to their low costs and-more importantly-to their promising electrochemical performances towards the HER. One of the more noteworthy observations of this work is the superiority of these two hybrids over MoS2 , a well-known electrocatalyst for the HER. PMID:25908556

  5. Iridium-191 angiocardiography for the detection and quantitation of left-to-right shunting

    SciTech Connect

    Treves, S.; Cheng, C.; Samuel, A.; Lambrecht, R.; Babchyck, B.; Zimmerman, R.; Norwood, W.

    1980-12-01

    An osmium-191 ..-->.. iridium-191 generator that can deliver multiple doses of Ir-191m for first-pass radionuclide angiography has been developed. Iridium-191m has a physical half-life of 4.96 sec and decays with emission of 65-keV and 129-keV photons in 58 and 30% abundance, respectively. Using a gamma camera, Ir-191m radionuclide angiography was carried out, in dogs and ten patients, for the detection and quantitation of left-to-right shunting. In a one-year-old patient, 25 mCi of Ir-191m results in a whole-body radiation absorbed dose of 35 mrad. Multiple Ir-191m angiograms can be performed, seconds to minutes apart, without interference from background. The 15.4-day half-life of Os-191 permits transportation of the generator to centers far from the production facility. With the low radiation dose, high information density, and the ability to repeat studies with Ir-191m, clinical use of radionuclide angiography should be expanded.

  6. Electron-beam processing of kilogram quantities of iridium for radioisotope thermoelectric generator applications

    SciTech Connect

    Huxford, T.J.; Ohriner, E.K.

    1992-01-01

    Iridium alloys are used as fuel-cladding materials in radioisotope thermoelectric generators (RTGs). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyagers I and 2, Galilee, and Ulysses spacecraft. An integral part of the production of iridium-sheet metal involves electron-beam (EB) processing. These processes include the degassing of powder-pressed compacts followed by multiple meltings in order to purify 500-g buttons of Ir-0.3% W alloy. Starting in 1972 and continuing into 1992, our laboratory EB processing was Performed (ca. 1970) in a 60-kW (20 kV at 3 A), two-gun system. In 1991, a new 150-kW EB gun facility was installed to complement the older unit. This paper describes how the newly installed system was qualified for production of RTG developmental work is discussed that will potentially improve the existing process by utilizing the capabilities of the new EB system.

  7. Electron-beam processing of kilogram quantities of iridium for radioisotope thermoelectric generator applications

    SciTech Connect

    Huxford, T.J.; Ohriner, E.K.

    1992-12-31

    Iridium alloys are used as fuel-cladding materials in radioisotope thermoelectric generators (RTGs). Hardware produced at the Oak Ridge National Laboratory (ORNL) has been used in Voyagers I and 2, Galilee, and Ulysses spacecraft. An integral part of the production of iridium-sheet metal involves electron-beam (EB) processing. These processes include the degassing of powder-pressed compacts followed by multiple meltings in order to purify 500-g buttons of Ir-0.3% W alloy. Starting in 1972 and continuing into 1992, our laboratory EB processing was Performed (ca. 1970) in a 60-kW (20 kV at 3 A), two-gun system. In 1991, a new 150-kW EB gun facility was installed to complement the older unit. This paper describes how the newly installed system was qualified for production of RTG developmental work is discussed that will potentially improve the existing process by utilizing the capabilities of the new EB system.

  8. Earth Radiation Imbalance from a Constellation of 66 Iridium Satellites: Technological Aspects

    NASA Technical Reports Server (NTRS)

    Wiscombe, W.; Chiu, C. J-Y.

    2012-01-01

    Iridium Communications Inc. is launching a new generation of polar orbiting communication satellites in 2015-2017. Iridium will provide a hosted payload bay on each of the 66 satellites (plus 6 in-space spares). This offers the potential for a paradigm shift in the way we measure Earth radiation imbalance from space, as well as massive cost savings. Because the constellation provides 24/7 global coverage, there is no need to account for diurnal cycle via extrapolations from uncalibrated narrowband geostationary imagers. And the spares can be rolled over to view the Sun and deep space, then transfer their calibration to the other members of the constellation during the frequent cross-overs. In part using simulations of the constellation viewing realistic Earth scenes, this presentation will address the technological aspects of such a constellation: (1) the calibration strategy; (2) the highly-accurate and stable radiometers for measuring outgoing flux; and (3) the GRACE-inspired algorithms for representing the outgoing flux field in spherical harmonics and thus achieving rv500-km spatial resolution and two-hour temporal resolution.

  9. High-Performance Computer Modeling of the Cosmos-Iridium Collision

    SciTech Connect

    Olivier, S; Cook, K; Fasenfest, B; Jefferson, D; Jiang, M; Leek, J; Levatin, J; Nikolaev, S; Pertica, A; Phillion, D; Springer, K; De Vries, W

    2009-08-28

    This paper describes the application of a new, integrated modeling and simulation framework, encompassing the space situational awareness (SSA) enterprise, to the recent Cosmos-Iridium collision. This framework is based on a flexible, scalable architecture to enable efficient simulation of the current SSA enterprise, and to accommodate future advancements in SSA systems. In particular, the code is designed to take advantage of massively parallel, high-performance computer systems available, for example, at Lawrence Livermore National Laboratory. We will describe the application of this framework to the recent collision of the Cosmos and Iridium satellites, including (1) detailed hydrodynamic modeling of the satellite collision and resulting debris generation, (2) orbital propagation of the simulated debris and analysis of the increased risk to other satellites (3) calculation of the radar and optical signatures of the simulated debris and modeling of debris detection with space surveillance radar and optical systems (4) determination of simulated debris orbits from modeled space surveillance observations and analysis of the resulting orbital accuracy, (5) comparison of these modeling and simulation results with Space Surveillance Network observations. We will also discuss the use of this integrated modeling and simulation framework to analyze the risks and consequences of future satellite collisions and to assess strategies for mitigating or avoiding future incidents, including the addition of new sensor systems, used in conjunction with the Space Surveillance Network, for improving space situational awareness.

  10. Establishment of the platinum-iridium kilogram mass standards at NMIJ after the Extraordinary Calibrations

    NASA Astrophysics Data System (ADS)

    Mizushima, Shigeki; Fujii, Kenichi

    2016-04-01

    The Bureau International des Poids et Mesures has carried out calibrations of the platinum-iridium kilogram mass standards by referencing the international prototype of the kilogram for the first time since the third periodic verification of national prototypes of the kilogram was carried out in 1988-92. This calibration campaign was designated ‘Extraordinary Calibrations’ in the second phase, in which two platinum-iridium kilogram mass standards of the National Metrology Institute of Japan were calibrated with a standard uncertainty of 3.5 μg. By adding these new calibration data into our data sets from 1991, we established our mass unit with a standard uncertainty of 3.3 μg by least-squares analysis using an exponential model, which is useful for compensating for mass increase after cleaning the mass standards. Moreover, it was found that our established mass unit following the Extraordinary Calibrations shifted against our previously maintained mass unit by  -20.8 μg as of the beginning of 2015. The analysis with a linear model revealed that the amount of mass increase over time of some standards was significantly smaller than that suggested at the third periodic verification of national prototypes of the kilogram. The analysis with the exponential model gave an exponent of 0.217 with a standard uncertainty of 0.057. This suggests that the mass increase due to surface contamination cannot be explained by a diffusion-limited process.

  11. Determination of the amount of physical adsorption of water vapour on platinum-iridium surfaces

    NASA Astrophysics Data System (ADS)

    Mizushima, S.; Ueda, K.; Ooiwa, A.; Fujii, K.

    2015-08-01

    This paper presents the measurement of the physical adsorption of water vapour on platinum-iridium surfaces using a vacuum mass comparator. This value is of importance for redefining the kilogram, which will be realized under vacuum in the near future. Mirror-polished artefacts, consisting of a reference artefact and a test artefact, were manufactured for this experiment. The surface area difference between the reference and test artefacts was 226.2 cm2. This surface area difference was approximately 3.2 times the geometric surface area of the prototype of the kilogram made of platinum-iridium (71.7 cm2). The measurement results indicate that the amount of physical adsorption at a relative humidity of 50% is 0.0129 μg cm{{-}2} , with a standard uncertainty of 0.0016 μg cm{{-}2} . This value is 0.03 to 0.16 times that observed in other studies.

  12. Results of an Iridium-Based Data Communication System Providing Internet Access to Polar Expeditions

    NASA Astrophysics Data System (ADS)

    Mohammad, A.; Frost, V.; Braaten, D.

    2003-12-01

    The Polar Radar for Ice Sheet Measurements (PRISM) Project at the University of Kansas has developed and field-tested a versatile communications system for use by researchers in high-latitude Polar Regions. The PRISM project is developing advanced intelligent remote sensing technology that involves radar systems, an autonomous rover, and communications systems to measure detailed ice sheet characteristics, and to determine bed conditions (frozen or wet) below active ice sheets in both Greenland and Antarctica. We also have a very strong public outreach and educational program aimed at K-12 educators and students that requires data, voice and video feeds from Polar field locations in near real time. Hence, PRISM requires a robust communications system for use in the field between a base camp and the mobile remote sensing system, and from the field back to the University of Kansas and onto the Internet. The communication system that has been developed is truly mobile and is relatively inexpensive. We initially considered various satellite services during the design phase of this project. The two feasible options for high-latitude locations were Iridium, with its low-bit-rate service (2.4 Kb/s), and Inmarsat/Intelsat with broadband service. We selected the Iridium option for testing and development because it provided coverage in both Antarctica and Greenland. To achieve higher capacity communications, the multilink point-to-point protocol (MLPPP) implemented in Linux was tuned to operate efficiently over the Iridium satellite system. This mechanism combines multiple channels to obtain a seamless data connection with a capacity equal to the sum of the individual link rates. We used four Iridium modems to obtain an aggregate capacity of about 9.6 Kb/s. Standard Internet protocols (TCP/IP) were then used to provide end-to-end connectivity. The communications system field experiments were conducted at the NorthGRIP ice core drilling camp in Greenland (75° 06' N, 42° 20

  13. 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.

  14. Application of AirCell Cellular AMPS Network and Iridium Satellite System Dual Mode Service to Air Traffic Management

    NASA Technical Reports Server (NTRS)

    Shamma, Mohammed A.

    2004-01-01

    The AirCell/Iridium dual mode service is evaluated for potential applications to Air Traffic Management (ATM) communication needs. The AirCell system which is largely based on the Advanced Mobile Phone System (AMPS) technology, and the Iridium FDMA/TDMA system largely based on the Global System for Mobile Communications(GSM) technology, can both provide communication relief for existing or future aeronautical communication links. Both have a potential to serve as experimental platforms for future technologies via a cost effective approach. The two systems are well established in the entire CONUS and globally hence making it feasible to utilize in all regions, for all altitudes, and all classes of aircraft. Both systems have been certified for air usage. The paper summarizes the specifications of the AirCell/Iridium system, as well as the ATM current and future links, and application specifications. the paper highlights the scenarios, applications, and conditions under which the AirCell/Iridium technology can be suited for ATM Communication.

  15. A Hexakis Terpyridine-Fullerene Ligand in Six-Fold Ruthenium, Iridium, and Iron Complexes: Synthesis and Electrochemical Properties.

    PubMed

    Yan, Weibo; Réthoré, Céline; Menning, Sebastian; Brenner-Weiß, Gerald; Muller, Thierry; Pierrat, Philippe; Bräse, Stefan

    2016-08-01

    An unprecedented straightforward route to six-fold terpyridine ligands around C60 , the latter being regioselectively functionalized in pseudo-octahedral positions using a six-fold Bingel reaction, is reported. Ruthenium, iridium, and iron complexes have been synthesized, and unambiguously characterized by NMR, MS, and cyclic voltammetry. PMID:27189254

  16. Enhancement of activity of RuSex electrocatalyst by modification with nanostructured iridium towards more efficient reduction of oxygen

    NASA Astrophysics Data System (ADS)

    Dembinska, Beata; Kiliszek, Malgorzata; Elzanowska, Hanna; Pisarek, Marcin; Kulesza, Pawel J.

    2013-12-01

    Electrocatalytic activity of carbon (Vulcan XC-72) supported selenium-modified ruthenium, RuSex/C, nanoparticles for reduction of oxygen was enhanced through intentional decoration with iridium nanostructures (dimensions, 2-3 nm). The catalytic materials were characterized in oxygenated 0.5 mol dm-3 H2SO4 using cyclic and rotating ring disk voltammetric techniques as well as using transmission electron microscopy and scanning electron microscopy equipped with X-ray dispersive analyzer. Experiments utilizing gas diffusion electrode aimed at mimicking conditions existing in the low-temperature fuel cell. Upon application of our composite catalytic system, the reduction of oxygen proceeded at more positive potentials, and higher current densities were observed when compared to the behavior of the simple iridium-free system (RuSex/C) investigated under the analogous conditions. The enhancement effect was more pronounced than that one would expect from simple superposition of voltammetric responses for the oxygen reduction at RuSex/C and iridium nanostructures studied separately. Nanostructured iridium acted here as an example of a powerful catalyst for the reduction of H2O2 (rather than O2) and, when combined with such a moderate catalyst as ruthenium-selenium (for O2 reduction), it produced an integrated system of increased electrocatalytic activity in the oxygen reduction process. The proposed system retained its activity in the presence of methanol that could appear in a cathode compartment of alcohol fuel cell.

  17. Thinking Problems of the Present Collision Warning Work by Analyzing the Intersection Between Cosmos 2251 and Iridium 33

    NASA Astrophysics Data System (ADS)

    Wang, R. L.; Liu, W.; Yan, R. D.; Gong, J. C.

    2013-08-01

    After Cosmos 2251 and Iridium 33 collision breakup event, the institutions at home and abroad began the collision warning analysis for the event. This paper compared the results from the different research units and discussed the problems of the current collision warning work, then gave the suggestions of further study.

  18. Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones.

    PubMed

    Li, Yan-Yun; Yu, Shen-Luan; Shen, Wei-Yi; Gao, Jing-Xing

    2015-09-15

    Chiral alcohols are important building blocks in the pharmaceutical and fine chemical industries. The enantioselective reduction of prochiral ketones catalyzed by transition metal complexes, especially asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH), is one of the most efficient and practical methods for producing chiral alcohols. In both academic laboratories and industrial operations, catalysts based on noble metals such as ruthenium, rhodium, and iridium dominated the asymmetric reduction of ketones. However, the limited availability, high price, and toxicity of these critical metals demand their replacement with abundant, nonprecious, and biocommon metals. In this respect, the reactions catalyzed by first-row transition metals, which are more abundant and benign, have attracted more and more attention. As one of the most abundant metals on earth, iron is inexpensive, environmentally benign, and of low toxicity, and as such it is a fascinating alternative to the precious metals for catalysis and sustainable chemical manufacturing. However, iron catalysts have been undeveloped compared to other transition metals. Compared with the examples of iron-catalyzed asymmetric reduction, cobalt- and nickel-catalyzed ATH and AH of ketones are even seldom reported. In early 2004, we reported the first ATH of ketones with catalysts generated in situ from iron cluster complex and chiral PNNP ligand. Since then, we have devoted ourselves to the development of ATH and AH of ketones with iron, cobalt, and nickel catalysts containing novel chiral aminophosphine ligands. In our study, the iron catalyst containing chiral aminophosphine ligands, which are expected to control the stereochemistry at the metal atom, restrict the number of possible diastereoisomers, and effectively transfer chiral information, are successful catalysts for enantioselective reduction of ketones. Among these novel chiral aminophosphine ligands, 22-membered macrocycle P2N4

  19. 77 FR 12578 - Notice of Intent To Grant Exclusive Patent License; C&C Ventures, Doing Business as Randolph...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-01

    ... Department of the Navy Notice of Intent To Grant Exclusive Patent License; C&C Ventures, Doing Business as... hereby gives notice of its intent to grant to C&C Ventures, doing business as Randolph Products, a... response. Authority: 35 U.S.C. 207, 37 CFR Part 404. Dated: February 22, 2012. J.M. Beal,...

  20. Gold-catalyzed naphthalene functionalization.

    PubMed

    Pérez, Pedro J; Díaz-Requejo, M Mar; Rivilla, Iván

    2011-01-01

    The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'(4) (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO(2)Et (R = H, Me) from N(2)C(R)CO(2)Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C-H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed.

  1. Gold-catalyzed naphthalene functionalization

    PubMed Central

    Rivilla, Iván

    2011-01-01

    Summary The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO2Et (R = H, Me) from N2C(R)CO2Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C–H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed. PMID:21647320

  2. Gold-catalyzed naphthalene functionalization.

    PubMed

    Pérez, Pedro J; Díaz-Requejo, M Mar; Rivilla, Iván

    2011-01-01

    The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'(4) (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO(2)Et (R = H, Me) from N(2)C(R)CO(2)Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C-H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed. PMID:21647320

  3. GEOS-C C-band transponder prelaunch calibration and test data

    NASA Technical Reports Server (NTRS)

    Selser, A. R.

    1976-01-01

    The delay characteristics and spacecraft telemetry housekeeping data for the GEOS-C C-Band transponders are presented. The data are presented in graphical form to provide a convenient method for computing radar range measurement corrections as a function of signal strength at the transponder and spacecraft environment. The data are also presented in tabular form along with the mathematical models used to derive the curves. Also included are a list of the operating characteristics of each transponder and a description of the calibration test equipment set-up.

  4. An erbium-based bifuctional heterogeneous catalyst: a cooperative route towards C-C bond formation.

    PubMed

    Oliverio, Manuela; Costanzo, Paola; Macario, Anastasia; De Luca, Giuseppina; Nardi, Monica; Procopio, Antonio

    2014-07-15

    Heterogeneous bifuctional catalysts are multifunctional synthetic catalysts enabling efficient organic transformations by exploiting two opposite functionalities without mutual destruction. In this paper we report the first Er(III)-based metallorganic heterogeneous catalyst, synthesized by post-calcination MW-assisted grafting and modification of the natural aminoacid L-cysteine. The natural acid-base distance between sites was maintained to assure the cooperation. The applicability of this new bifunctional heterogeneous catalyst to C-C bond formation and the supposed mechanisms of action are discussed as well.

  5. Unlocking Hydrogenation for C-C Bond Formation: A Brief Overview of Enantioselective Methods

    PubMed Central

    Hassan, Abbas; Krische, Michael J.

    2011-01-01

    Hydrogenation of π-unsaturated reactants in the presence of carbonyl compounds or imines promotes reductive C-C coupling, providing a byproduct-free alternative to stoichiometric organometallic reagents in an ever-increasing range of C=X (X = O, NR) additions. Under transfer hydrogenation conditions, hydrogen exchange between alcohols and π-unsaturated reactants triggers generation of electrophile-nucleophile pairs, enabling carbonyl addition directly from the alcohol oxidation level, bypassing discrete alcohol oxidation and generation of stoichiometric byproducts. PMID:22125398

  6. C/C composites for rocket chamber applications. Part 2: Fabrication and evaluation tests of rocket chamber

    NASA Astrophysics Data System (ADS)

    Sato, Masahiro; Tadano, Makoto; Ueda, Shuichi; Kuroda, Yukio; Kusaka, Kazuo; Suemitsu, Takeshi; Hasegawa, Satoshi; Kude, Yukinori

    1995-05-01

    Carbon fiber-reinforced carbon matrix (C/C) composites coated with SiC are promising candidates for use in the main structural materials of the body of spaceplanes and combustion chambers of rocket engines, because of their superior properties of high specific strength, specific modulus, and fracture strength at high temperatures. However, C/C composite has poor resistance to oxidation, and protection from the oxidating environment is crucial. Conventional C/C composites for use in the high-temperature components of rocket engines are coated with SiC. However, due to the difference in the thermal expansion rates of the SiC coating layer and the base materials, cracks occur in the SiC coating layer during the coating process, and oxygen diffuses to the base material through the cracks during repeated temperature cycling in the rocket combustion environment. To protect the base materials from oxidation at high temperatures, we have employed SiC C/C-coated composites with a modified matrix and also developed SiC C/C functionally gradient materials (FGM's). In this test series, three kinds of combustion chambers were constructed for the Reaction Control System (RCS) subscale engine of H-II Orbiting Plane (HOPE): (1) Conventional C/C composites, (2) SiC C/C-coated composites with a modified matrix, and (3) SiC C/C FGM's. Firing tests were performed at sea level at a temperature around 2000 K using nitrogen tetroxide (NTO)/monomethyl hydrazine (MMH) propellant to evaluate the durability of these chambers. This test series showed that conventional C/C composite developed no microcracks and delamination in the coating layer at 1940 K. Modified matrix C/C composite also did not suffer microcracks and delamination at the boundary between the SiC and the base materials when the inner surface temperature was 1875 K. However, microcracks were observed at injector flange surface after these test cycles. In the test series of FGM's chamber, it was shown that coating with FGM

  7. Rh-Catalyzed Five-Membered Heterocycle Synthesis

    NASA Astrophysics Data System (ADS)

    Kathiravan, Subban; Nicholls, Ian A.

    The following sections are included: * Introduction * Rhodium-catalyzed nitrogen containing five-membered heterocycle synthesis * Rhodium-catalyzed oxygen containing five-membered heterocycle synthesis * Rhodium-catalyzed sulfur containing five-membered heterocycle synthesis * Rhodium-catalyzed phosphorous containing five-membered heterocycle synthesis * Rhodium-catalyzed silicon containing five-membered heterocycle synthesis * Rhodium-catalyzed synthesis of bis-heterocycles * Conclusions and outlook * References

  8. Cobalt-Catalyzed C(sp(2))-H Borylation: Mechanistic Insights Inspire Catalyst Design.

    PubMed

    Obligacion, Jennifer V; Semproni, Scott P; Pappas, Iraklis; Chirik, Paul J

    2016-08-24

    A comprehensive study into the mechanism of bis(phosphino)pyridine (PNP) cobalt-catalyzed C-H borylation of 2,6-lutidine using B2Pin2 (Pin = pinacolate) has been conducted. The experimentally observed rate law, deuterium kinetic isotope effects, and identification of the catalyst resting state support turnover limiting C-H activation from a fully characterized cobalt(I) boryl intermediate. Monitoring the catalytic reaction as a function of time revealed that borylation of the 4-position of the pincer in the cobalt catalyst was faster than arene borylation. Cyclic voltammetry established the electron withdrawing influence of 4-BPin, which slows the rate of C-H oxidative addition and hence overall catalytic turnover. This mechanistic insight inspired the next generation of 4-substituted PNP cobalt catalysts with electron donating and sterically blocking methyl and pyrrolidinyl substituents that exhibited increased activity for the C-H borylation of unactivated arenes. The rationally designed catalysts promote effective turnover with stoichiometric quantities of arene substrate and B2Pin2. Kinetic studies on the improved catalyst, 4-(H)2BPin, established a change in turnover limiting step from C-H oxidative addition to C-B reductive elimination. The iridium congener of the optimized cobalt catalyst, 6-(H)2BPin, was prepared and crystallographically characterized and proved inactive for C-H borylation, a result of the high kinetic barrier for reductive elimination from octahedral Ir(III) complexes. PMID:27476954

  9. Optimizing the throughput of an M/G/C/C topological network

    NASA Astrophysics Data System (ADS)

    Khalid, Ruzelan; Ishak, Nurhanis; Baten, Md Azizul; Nawawi, Mohd. Kamal Mohd.

    2015-12-01

    An M/G/C/C state dependent queuing network approach models the behavior of entities (e.g., pedestrians and vehicles) flowing through a space. For a space consisting of various complex topological networks, the challenge is how to control such flow so that its throughput can be optimized. This paper discusses the throughput optimization of an M/G/C/C system using a network flow programming model. For this, we first decompose each available network and analyze its performance separately. The performance reports the effect of arrival rates to the throughput, blocking probability, expected number of pedestrians and expected travel time of each of the network. The best arrival rate of each network is then searched and fed to the network flow programming model to find the optimal arrival rates of source networks. The effect of the optimal arrival rates to the performance of the whole network is then analyzed and compared to that of using arbitrary arrival rates. Results show that with the right control of arrival rates, pedestrians can smoothly and efficiently be flowed through a network.

  10. Molecular dynamics prediction of phonon-mediated thermal conductivity of f.c.c. Cu

    NASA Astrophysics Data System (ADS)

    Evteev, Alexander V.; Momenzadeh, Leila; Levchenko, Elena V.; Belova, Irina V.; Murch, Graeme E.

    2014-03-01

    The phonon-mediated thermal conductivity of f.c.c. Cu is investigated in detail in the temperature range 40-1300 K. The calculations are performed in the framework of equilibrium molecular dynamics making use of the Green-Kubo formalism and one of the most reliable embedded-atom method potentials for Cu. It is found that the temporal decay of the heat current autocorrelation function (HCACF) of the Cu model at low and intermediate temperatures demonstrate a more complex behaviour than the two-stage decay observed previously for the f.c.c. Ar model. After the first stage of decay, it demonstrates a peak in the temperature range 40-800 K. A decomposition model of the HCACF is introduced. In the framework of that model we demonstrate that a classical description of the phonon thermal transport in the Cu model can be used down to around one quarter of the Debye temperature (about 90 K). Also, we find that above 300 K the thermal conductivity of the Cu model varies with temperature more rapidly than ?, following an exponent close to -1.4 in agreement with previous calculations on the Ar model. Phonon thermal conductivity of Cu is found to be about one order of magnitude higher than Ar. The phonon contribution to the total thermal conductivity of Cu can be estimated to be about 0.5% at 1300 K and about 10% at 90 K.

  11. CEOS: A Small, Low Cost Spectrometer for Use on the Iridium NEXT Constellation

    NASA Astrophysics Data System (ADS)

    Murphy, S. D.; Slagowski, S.; Greenbaum, A.; Landis, D.; Mustard, J. F.; Chance, K.

    2012-12-01

    As part of the proposed GEOScan sensor payload to be placed onboard the Iridium NEXT constellation; a small, low cost spectrometer will be included. The Compact Earth Observing Spectrometer (CEOS) is an ultraviolet-visible and near infrared (UV/VIS/NIR) optical spectrometer ideally suited for detailed earth observations. CEOS is derived from a spectrometer originally designed for NASA's O/OREOS mission, a CubeSat launched in November 2010 that is still performing extended science operations. It is also slated to be the key science payload component of VIOLET, a CubeSat mission designed to characterize the spectral characteristics of the upper atmosphere. The CEOS has several unique design elements that allow for high performance over a broad range of environmental conditions. The CEOS design allows for a range of customizations to tune the instrument performance for a wide range of science applications. The baseline instrument provides 200-1000 nm spectral coverage with 1 nm FWHM optical resolution, which is ideal for wide variety of science objectives. However by simply exchanging gratings in the instrument, it can be customized for narrower spectral range with significantly higher resolution. The CEOS instrument will also add a significant feature to allow for more detailed earth science observations. The optical portion of the spectrometer will be augmented with a second optical path designed to measure spectra from 1000 - 2000 nm. This will make the finished instrument capable of detailed spectral measurements from 200 - 2000 nm, covering the ultraviolet through near-infrared. The instrument will be designed to allow the independent operation of both the UV/VIS and NIR portions of the instrument to provide flexibility in science data product volumes. We will describe the design of this spectrometer as well as discuss the details of its design heritage. In addition to Iridium NEXT, we will describe other platforms that this spectrometer may be suited for. We

  12. Migration of Single Iridium Atoms and Tri-iridium Clusters on MgO Surfaces. Aberration-Corrected STEM Imaging and ab-initio Calculations

    SciTech Connect

    Han, Chang W.; Iddir, Hakim; Uzun, Alper; Curtiss, Larry A.; Browning, Nigel D.; Gates, Bruce C.; Ortalan, Volkan

    2015-11-06

    To address the challenge of fast, direct atomic-scale visualization of the diffusion of atoms and clusters on surfaces, we used aberration-corrected scanning transmission electron microscopy (STEM) with high scan speeds (as little as ~0.1 s per frame) to visualize the diffusion of (1) a heavy atom (Ir) on the surface of a support consisting of light atoms, MgO(100), and (2) an Ir3 cluster on MgO(110). Sequential Z-contrast images elucidate the diffusion mechanisms, including the hopping of Ir1 and the rotational migration of Ir3 as two Ir atoms remain anchored to the surface. Density functional theory (DFT) calculations provided estimates of the diffusion energy barriers and binding energies of the iridium species to the surfaces. The results show how the combination of fast-scan STEM and DFT calculations allow real-time visualization and fundamental understanding of surface diffusion phenomena pertaining to supported catalysts and other materials.

  13. The role of chemokine C-C motif ligand 2 genotype and cerebrospinal fluid chemokine C-C motif ligand 2 in neurocognition among HIV-infected patients

    PubMed Central

    Thames, April D.; Briones, Marisa S.; Magpantay, Larry I.; Martinez-Maza, Otoniel; Singer, Elyse J.; Hinkin, Charles H.; Morgello, Susan; Gelman, Benjamin B.; Moore, David J.; Heizerling, Keith; Levine, Andrew J.

    2015-01-01

    Objectives We examined interrelationships between chemokine C-C motif ligand 2 (CCL2) genotype and expression of inflammatory markers in the cerebrospinal fluid (CSF), plasma viral load, CD4+ cell count and neurocognitive functioning among HIV-infected adults. We hypothesized that HIV-positive carriers of the ‘risk’ CCL2 −2578G allele, caused by a single nucleotide polymorphism (SNP) at rs1024611, would have a higher concentration of CCL2 in CSF, and that CSF CCL2 would be associated with both higher concentrations of other proinflammatory markers in CSF and worse neurocognitive functioning. Design A cross-sectional study of 145 HIV-infected individuals enrolled in the National NeuroAIDS Tissue Consortium cohort for whom genotyping, CSF and neurocognitive data were available. Methods Genomic DNA was extracted from peripheral blood mononuclear cells and/or frozen tissue specimens. CSF levels of CCL2, interleukin (IL)-2, IL-6, tumour necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), soluble tumor necrosis factor receptor 2, sIL-6Rα, sIL-2, sCD14 and B-cell activating factor were quantified. Neurocognitive functioning was measured using a comprehensive battery of neuropsychological tests. Results Carriers of the CCL2 −2578G allele had a significantly higher concentration of CCL2 in CSF. CSF CCL2 level was positively and significantly associated with other CSF neuroinflammatory markers and worse cognitive functioning. There was a significant association between genotype and plasma viral load, such that carriers of the CCL2 −2578G allele with high viral load expressed greater levels of CCL2 and had higher neurocognitive deficit scores than other genotype/viral load groups. Conclusion Individuals with the CCL2 −2578G allele had higher levels of CCL2 in CSF, which was associated with increased pro-inflammatory markers in CSF and worse neurocognitive functioning. The results highlight the potential role of intermediate phenotypes in studies of

  14. Transition-metal-catalyzed carbon-heteroatom three-component cross-coupling reactions: a new concept for carbothiolation of alkynes.

    PubMed

    Kuniyasu, Hitoshi; Kurosawa, Hideo

    2002-06-17

    The deep-seated understanding of flexible ligand behavior of thiolate on transition-metals has paved the way to achieve metal-catalyzed carbothiolations of terminal alkynes. The strategy of the reaction is quite simple: 1) generation of the complex with C-Pt-S fragments formed after the Pd-catalyzed C-S bond-forming cross-coupling reaction, 2) insertion of an alkyne into Pt-S bond to form the complex with a C-Pt-C fragment, and 3) C-C bond-forming reductive elimination.

  15. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    PubMed

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  16. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    PubMed

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  17. 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.

  18. Iridium Oxide Nanotube Electrodes for Highly Sensitive and Prolonged Intracellular Measurement of Action Potentials

    PubMed Central

    Lin, Ziliang Carter; Xie, Chong; Osakada, Yasuko; Cui, Yi; Cui, Bianxiao

    2014-01-01

    Intracellular recording of action potentials is important to understand electrically-excitable cells. Recently, vertical nanoelectrodes have been developed to achieve highly sensitive, minimally invasive, and large scale intracellular recording. It has been demonstrated that the vertical geometry is crucial for the enhanced signal detection. Here we develop nanoelectrodes made up of nanotubes of iridium oxide. When cardiomyocytes are cultured upon those nanotubes, the cell membrane not only wraps around the vertical tubes but also protrudes deep into the hollow center. We show that this geometry enhances cell-electrode coupling and results in measuring much larger intracellular action potentials. The nanotube electrodes afford much longer intracellular access and are minimally invasive, making it possible to achieve stable recording up to an hour in a single session and more than 8 days of consecutive daily recording. This study suggests that the electrode performance can be significantly improved by optimizing the electrode geometry. PMID:24487777

  19. Anion-Anion Bonding and Topology in Ternary Iridium Tin Selenides

    NASA Astrophysics Data System (ADS)

    Trump, Benjamin; Tutmaher, Jake; McQueen, Tyrel

    Iridium compounds have been under intense scrutiny due to strong relativistic effects (spin-orbit coupling) which have comparable energy scales to crystal field stabilization and electron correlations, which could lead to non-trivial behavior. Here we report the synthesis, characterization, and physical properties of two new, and one known, Ir-Sn-Se compounds. Resistivity, specific heat, and magnetization measurements show that all three have insulating and diamagnetic behavior, indicative of low spin 5d6 Ir3+. Furthermore, electronic structures calculations on Ir2Sn3Se3 show a single, spherical, non-spin-orbit split valence band that supports mobile p-type carriers, and imply that Ir2Sn3Se3 is topologically non-trivial under tensile strain, due to inversion of Ir- d and Se- p states. Work supported by NSF, Division of Materials Research (DMR), Solid State Chemistry (SSMC), CAREER Grant under Award DMR-1253562, and the ICDD Ludo Frevel Crystallography Scholarship.

  20. Catalytic dehydroaromatization of n-alkanes by pincer-ligated iridium complexes

    NASA Astrophysics Data System (ADS)

    Ahuja, Ritu; Punji, Benudhar; Findlater, Michael; Supplee, Carolyn; Schinski, William; Brookhart, Maurice; Goldman, Alan S.

    2011-02-01

    Aromatic hydrocarbons are among the most important building blocks in the chemical industry. Benzene, toluene and xylenes are obtained from the high temperature thermolysis of alkanes. Higher alkylaromatics are generally derived from arene-olefin coupling, which gives branched products—that is, secondary alkyl arenes—with olefins higher than ethylene. The dehydrogenation of acyclic alkanes to give alkylaromatics can be achieved using heterogeneous catalysts at high temperatures, but with low yields and low selectivity. We present here the first catalytic conversion of n-alkanes to alkylaromatics using homogeneous or molecular catalysts—specifically ‘pincer’-ligated iridium complexes—and olefinic hydrogen acceptors. For example, the reaction of n-octane affords up to 86% yield of aromatic product, primarily o-xylene and secondarily ethylbenzene. In the case of n-decane and n-dodecane, the resulting alkylarenes are exclusively unbranched (that is, n-alkyl-substituted), with selectivity for the corresponding o-(n-alkyl)toluene.

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

    DOE PAGES

    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 formore » performance and durability in electrolysis cells.« less

  2. Ascent of dinosaurs linked to an iridium anomaly at the Triassic-Jurassic boundary.

    PubMed

    Olsen, P E; Kent, D V; Sues, H-D; Koeberl, C; Huber, H; Montanari, A; Rainforth, E C; Fowell, S J; Szajna, M J; Hartline, B W

    2002-05-17

    Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.

  3. Conodont survival and low iridium abundances across the Permian-Triassic boundary in South China

    SciTech Connect

    Clark, D.L.; Wang, C.Y.; Orth, C.J.; Gilmore, J.S.

    1986-08-29

    The Permian-Triassic sedimentary sequence of China includes one of the most complete and fossiliferous Paleozoic-Mesozoic boundaries known. Closely spaced sampling across the boundary, which is an important extinction event for most organisms, has produced good conodont faunas that show little diversity change. A drop in conodont abundance is the only apparent response to the extinction event. A low concentration of iridium in the boundary clay (0.002 part per billion +/- 20 percent), as well as in samples immediately below and above, that range form 0.004 to 0.034 part per billion do not support the proposal of an extraterrestrial impact event at this boundary in China. 21 references, 2 tables.

  4. Noisy CO oxidation on Iridium(111) surfaces. Experiments explained by theory under realistic assumptions

    NASA Astrophysics Data System (ADS)

    Wehner, S.; Cisternas, J.; Descalzi, O.; Küppers, J.

    2014-01-01

    Noise is an everywhere phenomenon. Its influence could be described theoretically quite easily, but is hard to measure in an experiment. Catalytic reactions on surfaces can be described by nonlinear reaction-diffusion equations. For one of such surface reactions - CO oxidation on Iridium(111) surfaces - the probability distribution of CO2 rates around the mean value - showing the influence of noise - could be measured directly in a ultra high vacuum (UHV) experiment. This opens the way to address such a fundamental phenomenon like noise by all three modern methods of physics - experimental, computational and analytical. We show the measured effect of colored noise on a bistable surface reaction and explain all observations directly with the underlying theoretical description - the Langmuir-Hinshelwood reaction scheme - by solving the equations under realistic assumptions. It is a great pleasure to dedicate this work to Prof. Dr. Helmut R. Brand on the occasion of his 60th birthday.

  5. Hot rocket plume experiment - Survey and conceptual design. [of rhenium-iridium bipropellants

    NASA Technical Reports Server (NTRS)

    Millard, Jerry M.; Luan, Taylor W.; Dowdy, Mack W.

    1992-01-01

    Attention is given to a space-borne engine plume experiment study to fly an experiment which will both verify and quantify the reduced contamination from advanced rhenium-iridium earth-storable bipropellant rockets (hot rockets) and provide a correlation between high-fidelity, in-space measurements and theoretical plume and surface contamination models. The experiment conceptual design is based on survey results from plume and contamination technologists throughout the U.S. With respect to shuttle use, cursory investigations validate Hitchhiker availability and adaptability, adequate remote manipulator system (RMS) articulation and dynamic capability, acceptable RMS attachment capability, adequate power and telemetry capability, and adequate flight altitude and attitude/orbital capability.

  6. 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.

  7. Spin-orbit coupled jeff=1/2 iridium moments on the geometrically frustrated fcc lattice

    DOE PAGES

    Cook, A. M.; Matern, S.; Hickey, C.; Aczel, A. A.; Paramekanti, A.

    2015-07-01

    Motivated by experiments on La2ZnIrO6 and La2MgIrO6, we study the magnetism of spin-orbit coupled jeff = 1/2 iridium moments on the three-dimensional geometrically-frustrated face-centered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. Using Luttinger-Tisza and Monte Carlo simulations, we find a rich variety of orders, including collinear A-type antiferromagnetism, collinear stripe order with moments along the {111}-direction, and incommensurate non-coplanar spirals, and determine their magnetic ordering transition temperatures. We argue that thermodynamic data on these iridates underscore the presence of a dominant Kitaev exchange, and suggest a possible resolution to the puzzle of why La2ZnIrO6,more » but not La2MgIrO6, exhibits 'weak' ferromagnetism.« less

  8. 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).

  9. Method of making a long life high current density cathode from tungsten and iridium powders using a quaternary compound as the impregnant

    SciTech Connect

    Branovich, L.E.; Smith, B.; Freemen, G.L.; Eckart, D.W.

    1990-09-18

    This patent describes a method of making a long life high current density cathode. It is suitable for operation in microwave devices. It is made from tungsten and iridium powders using a quaternary compound including barium, oxygen, a metal selected from the group consisting of osmium, iridium, rhodium, and rhenium, and a metal selected from the group consisting of strontium, calcium, scandium, and titanium as the impregnant.

  10. Molecular dynamics study of C-C bond ordering in diacylglycerolipid monolayers

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander L.; Ripatti, Pauli O.; Balabaev, Nikolay K.

    2000-02-01

    Molecular dynamics investigation of diacyldlycerolipid (DG) monolayers was carried out. Each lipid molecule contained stearic fatty acid chain (C18:0) in position 3-D and one of the fatty acid chains C18:0, C18:1(omega 9), C18:2(omega 6), C18:3(omega 3), C20:4(omega 6) or C22:6(omega 3) in position 2-D [for the nomenclature see M. Sundaralingam, Ann. N.Y. Acad. Sci. U.S.A., 195, 324 - 355 (1972)]. A polar head group of the lipid molecules was treated as an effective sphere. 1.5 nanosecond simulations were performed at temperature 303 K for monolayers 18:0/18:1(omega) 9cis DG, 18:0/18:2(omega) 6cis DG, 18:0/18:3(omega) 3cis DG, 18:0/20:4(omega) 6cis DG, 18:0/22:6(omega) 3cis DG and at T equals 326 K for 18:0/18:0 DG monolayer. The monolayers consisted of 48 glycerolipids of the same type arranged in a rectangular simulation cell. The average areas per lipid molecule over the simulations were 65.6 Angstrom2 in 18:0/18:0 DG monolayer, 66.2 Angstrom2 in 18:0/18:1(omega) 9cis DG, 66.1 angstrom2 in 18:0/18:2(omega) 6cis DG, 67.4 angstrom2 in 18:0/18:3(omega) 3cis DG, 70.6 angstrom2 in 18:0/20:4(omega) 6cis DG and 71.4 Angstrom2 in 18:0/22:6(omega) 3cis DG monolayer. The C-C bond orientation distributions and C-C bond order parameter profiles about the monolayer normals were calculated. The C-C bond orientation distribution function widths turned out to be depended on both bond location in the chain and chemical structure of the segment.

  11. Molecular dynamics study of C-C bond ordering in diacylglycerolipid monolayers

    NASA Astrophysics Data System (ADS)

    Rabinovich, Alexander L.; Ripatti, Pauli O.; Balabaev, Nikolay K.

    2001-02-01

    Molecular dynamics investigation of diacyldlycerolipid (DG) monolayers was carried out. Each lipid molecule contained stearic fatty acid chain (C18:0) in position 3-D and one of the fatty acid chains C18:0, C18:1(omega 9), C18:2(omega 6), C18:3(omega 3), C20:4(omega 6) or C22:6(omega 3) in position 2-D [for the nomenclature see M. Sundaralingam, Ann. N.Y. Acad. Sci. U.S.A., 195, 324 - 355 (1972)]. A polar head group of the lipid molecules was treated as an effective sphere. 1.5 nanosecond simulations were performed at temperature 303 K for monolayers 18:0/18:1(omega) 9cis DG, 18:0/18:2(omega) 6cis DG, 18:0/18:3(omega) 3cis DG, 18:0/20:4(omega) 6cis DG, 18:0/22:6(omega) 3cis DG and at T equals 326 K for 18:0/18:0 DG monolayer. The monolayers consisted of 48 glycerolipids of the same type arranged in a rectangular simulation cell. The average areas per lipid molecule over the simulations were 65.6 Angstrom2 in 18:0/18:0 DG monolayer, 66.2 Angstrom2 in 18:0/18:1(omega) 9cis DG, 66.1 angstrom2 in 18:0/18:2(omega) 6cis DG, 67.4 angstrom2 in 18:0/18:3(omega) 3cis DG, 70.6 angstrom2 in 18:0/20:4(omega) 6cis DG and 71.4 Angstrom2 in 18:0/22:6(omega) 3cis DG monolayer. The C-C bond orientation distributions and C-C bond order parameter profiles about the monolayer normals were calculated. The C-C bond orientation distribution function widths turned out to be depended on both bond location in the chain and chemical structure of the segment.

  12. Bond Fission and Non-Radiative Decay in Iridium(III) Complexes.

    PubMed

    Zhou, Xiuwen; Burn, Paul L; Powell, Benjamin J

    2016-06-01

    We investigate the role of metal-ligand bond fission in the nonradiative decay of excited states in iridium(III) complexes with applications in blue organic light-emitting diodes (OLEDs). We report density functional theory (DFT) calculations of the potential energy surfaces upon lengthening an iridium-nitrogen (Ir-N) bond. In all cases we find that for bond lengths comparable to those of the ground state the lowest energy state is a triplet with significant metal-to-ligand change transfer character ((3)MLCT). But, as the Ir-N bond is lengthened there is a sudden transition to a regime where the lowest excited state is a triplet with significant metal centered character ((3)MC). Time-dependent DFT relativistic calculations including spin-orbit coupling perturbatively show that the radiative decay rate from the (3)MC state is orders of magnitude slower than that from the (3)MLCT state. The calculated barrier height between the (3)MLCT and (3)MC regimes is clearly correlated with previously measured nonradiative decay rates, suggesting that thermal population of the (3)MC state is the dominant nonradiative decay process at ambient temperature. In particular, fluorination both drives the emission of these complexes to a deeper blue color and lowers the (3)MLCT-(3)MC barrier. If the Ir-N bond is shortened in the (3)MC state another N atom is pushed away from the Ir, resulting in the breaking of this bond, suggesting that once the Ir-N bond breaks the damage to the complex is permanent-this will have important implications for the lifetimes of devices using this type of complex as the active material. The consequences of these results for the design of more efficient blue phosphors for OLED applications are discussed. PMID:27175618

  13. Cationic iridium(III) complexes with two carbene-based cyclometalating ligands: cis versus trans isomers.

    PubMed

    Monti, Filippo; La Placa, Maria Grazia I; Armaroli, Nicola; Scopelliti, Rosario; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Kessler, Florian

    2015-03-16

    A series of cationic iridium(III) complexes with two carbene-based cyclometalating ligands and five different N^N bipyridine and 1,10-phenanthroline ancillary ligands is presented. For the first time--in the frame of a rarely studied class of bis(heteroleptic) iridium complexes with two carbene-based cyclometalating ligands--a pair of cis and trans isomers has been isolated. All complexes (trans-1-5 and cis-3) were characterized by (1)H NMR, (13)C NMR, (31)P NMR, and HRMS (ESI-TOF); in addition, crystal structures of cis-3 and trans-4 are reported and discussed. Cyclic voltammetric studies show that the whole series exhibits highly reversible oxidation and reduction processes, suggesting promising potential for optoelectronic applications. Ground-state DFT and TD-DFT calculations nicely predict the blue shift experimentally observed in the room-temperature absorption and emission spectra of cis-3, compared to the trans complexes. In CH3CN, cis-3 displays a 4-fold increase in photoluminescence quantum yield (PLQY) with respect to trans-3, as a consequence of drastically slower nonradiative rate constant. By contrast, at 77 K, the emission properties of all the compounds, including the cis isomer, are much more similar, with a pronounced hypsochromic shift for the trans complexes. A similar behavior is found in solid state (1% w/w poly(methyl methacrylate) matrix), with all complexes displaying PLQY of ∼70-80%, comparable emission lifetimes (τ ≈ 1.3 μs), and a remarkable rigidochromic shift. To rationalize the more pronounced nonradiative deactivation (and smaller PLQY) observed for photoexcited trans complexes, comparative temperature-dependent emission studies in the range of 77-450 K for cis-3 and trans-3 were made in propylene glycol, showing that solvation effects are primarily responsible for the observed behavior.

  14. 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

  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. 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

  17. Facile P-C/C-H Bond-Cleavage Reactivity of Nickel Bis(diphosphine) Complexes.

    PubMed

    Zhang, Shaoguang; Li, Haixia; Appel, Aaron M; Hall, Michael B; Bullock, R Morris

    2016-07-01

    Unusual cleavage of P-C and C-H bonds of the P2 N2 ligand, in heteroleptic [Ni(P2 N2 )(diphosphine)](2+) complexes under mild conditions, results in the formation of an iminium formyl nickelate featuring a C,P,P-tridentate coordination mode. The structures of both the heteroleptic [Ni(P2 N2 )(diphosphine)](2+) complexes and the resulting iminium formyl nickelate have been characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were employed to investigate the mechanism of the P-C/C-H bond cleavage, which involves C-H bond cleavage, hydride rotation, Ni-C/P-H bond formation, and P-C bond cleavage. PMID:27189413

  18. Architectural Visualization of C/C++ Source Code for Program Comprehension

    SciTech Connect

    Panas, T; Epperly, T W; Quinlan, D; Saebjornsen, A; Vuduc, R

    2006-09-01

    Structural and behavioral visualization of large-scale legacy systems to aid program comprehension is still a major challenge. The challenge is even greater when applications are implemented in flexible and expressive languages such as C and C++. In this paper, we consider visualization of static and dynamic aspects of large-scale scientific C/C++ applications. For our investigation, we reuse and integrate specialized analysis and visualization tools. Furthermore, we present a novel layout algorithm that permits a compressive architectural view of a large-scale software system. Our layout is unique in that it allows traditional program visualizations, i.e., graph structures, to be seen in relation to the application's file structure.

  19. C-C chemokine receptor type 4 antagonist Compound 22 ameliorates experimental autoimmune encephalomyelitis.

    PubMed

    Moriguchi, Kota; Miyamoto, Katsuichi; Tanaka, Noriko; Ueno, Rino; Nakayama, Takashi; Yoshie, Osamu; Kusunoki, Susumu

    2016-02-15

    Chemokines and chemokine receptors play important roles in the immune response. We previously reported the pathogenic role of C-C chemokine receptor type 4 (CCR4) in experimental autoimmune encephalomyelitis (EAE). Here, we examined whether CCR4 antagonism modulates the disease course of EAE. Wild-type and CCR4-knockout mice were induced EAE and were administered Compound 22, an antagonist of CCR4. Compound 22 significantly ameliorated the severity of EAE in wild-type mice, but not in the CCR4-knockout mice. Compound 22 inhibited Th1 and Th17 polarization of antigen-induced T-cell responses. Therefore, CCR4 antagonists might be potential therapeutic agents for multiple sclerosis. PMID:26857495

  20. Two-State Reactivity Mechanism of Benzene C-C Activation by Trinuclear Titanium Hydride.

    PubMed

    Zhu, Bo; Guan, Wei; Yan, Li-Kai; Su, Zhong-Min

    2016-09-01

    The cleavage of inert C-C bonds is a central challenge in modern chemistry. Multinuclear transition metal complexes would be a desirable alternative because of the synergetic effect of multiple metal centers. In this work, carbon-carbon bond cleavage and rearrangement of benzene by a trinuclear titanium hydride were investigated using density functional theory. The reaction occurs via a novel "two-state reactivity" mechanism. The important elementary steps consist of hydride transfer, benzene coordination, dehydrogenation, oxidative addition, hydride-proton exchange, and reductive elimination. Most importantly, the ground-state potential energy surface switches from nearly degenerate triplet and antiferromagnetic singlet states to a closed-shell singlet state in the dearomatization of benzene, which effectively decreases the activation barrier. Furthermore, the roles of the transition metal centers and hydrides were clarified. PMID:27549571

  1. Matching plasmon resonances to the C=C and C-H bonds in estradiol

    NASA Astrophysics Data System (ADS)

    Mbomson, Ifeoma G.; McMeekin, Scott; De La Rue, Richard; Johnson, Nigel P.

    2015-03-01

    We tune nanoantennas to resonate within mid-infrared wavelengths to match the vibrational resonances of C=C and C-H of the hormone estradiol. Modelling and fabrication of the nanoantennas produce plasmon resonances between 2 μm to 7 μm. The hormone estradiol was dissolved in ethanol and evaporated, leaving thickness of a few hundreds of nanometres on top of gold asymmetric split H-like shaped on a fused silica substrate. The reflectance was measured and a red-shift is recorded from the resonators plasmonic peaks. Fourier transform infrared spectroscopy is use to observe enhanced spectra of the stretching modes for the analyte which belongs to alkenyl biochemical group.

  2. Modelling of c-C2H4O Formation on Grain-Surfaces

    NASA Astrophysics Data System (ADS)

    Occhiogrosso, Angela; Viti, S.; Ward, M. D.; Price, S. D.

    2013-01-01

    Ethylene oxide (c-C2H4O) is a ring-shaped organic compound that may lead to the synthesis of amino acids and the early metabolic pathways in the interstellar medium (ISM) (Cleaves 2003; Miller & Schlesinger 1993). This molecule has been detected towards several high-mass star forming regions (Ikeda et al. 2001) but to date, its observational abundances cannot be reproduced by chemical models. We include new experimental results in the UCL_CHEM chemical model with the aim of reproducing the abundances of ethylene oxide across high-mass sources. In particular, we focused on the solid state reaction investigated by Ward & Price (2011). By comparing our theoretical column densities with those from the observations we found that the reaction between atomic oxygen and ethylene on grains is a viable route of formation for ethylene oxide (Occhiogrosso et al., accepted by MNRAS).

  3. C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes: synthesis, structures, photophysics and electrochemistry.

    PubMed

    Weber, Lothar; Kahlert, Jan; Brockhinke, Regina; Böhling, Lena; Halama, Johannes; Brockhinke, Andreas; Stammler, Hans-Georg; Neumann, Beate; Nervi, Carlo; Harder, Rachel A; Fox, Mark A

    2013-08-14

    Six new C,C'-bis(benzodiazaborolyl)dicarba-closo-dodecaboranes, 1,A-R2-1,A-C2B10H10, where R represents the group 2-(1,3-Et2-1,3,2-N2BC6H4) or 2-(1,3-Ph2-1,3,2-N2BC6H4) and A is 2, 7 or 12, were synthesized from o-, m-, and p-dicarbadodecaboranes (carboranes) by lithiation and subsequent treatment with the respective 2-bromo-1,3,2-benzodiazaboroles. UV-visible and fluorescence spectra of all carboranes display low energy charge transfer emissions. While such emissions with Stokes shifts between 17,330 and 21,290 cm(-1) are typical for C,C'-bis(aryl)-ortho-carboranes, the observed low-energy emissions with Stokes shifts between 8320 and 15,170 cm(-1) for the meta- and para-isomers are unusual as high-energy emissions are typical for meta- and para-dicarbadodecaboranes. Fluorescence quantum yields (φF) for the novel 1,7- and 1,12-bis(benzodiazaborolyl)-carboranes depend on the substituents at the nitrogen atoms of the heterocycle. Thus, the para-carborane with N-ethyl substituents 1,12-(1',3'-Et2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 has a φF value of 41% in cyclohexane solution and only of 9% in the solid state, whereas the analogous 1,12-(1',3'-Ph2-1',3',2'-N2BC6H4)2-1,12-C2B10H10 shows quantum yields of 3% in cyclohexane solution and 72% in the solid state. X-ray crystallographic, computational and cyclic voltammetry studies for these carboranes are also presented.

  4. Overview of C/C-SiC Composite Development for the Orion Launch Abort System

    NASA Technical Reports Server (NTRS)

    Allen, Lee R.; Valentine, Peter G.; Schofield, Elizabeth S.; Beshears, Ronald D.; Coston, James E.

    2012-01-01

    Past and present efforts by the authors to further understanding of the ceramic matrix composite (CMC) material used in the valve components of the Orion Launch Abort System (LAS) Attitude Control Motor (ACM) will be presented. The LAS is designed to quickly lift the Orion Crew Exploration Vehicle (CEV) away from its launch vehicle in emergency abort scenarios. The ACM is a solid rocket motor which utilizes eight throttleable nozzles to maintain proper orientation of the CEV during abort operations. Launch abort systems have not been available for use by NASA on manned launches since the last Apollo ]Saturn launch in 1975. The CMC material, carbon-carbon/silicon-carbide (C/C-SiC), is manufactured by Fiber Materials, Inc. and consists of a rigid 4-directional carbon-fiber tow weave reinforced with a mixed carbon plus SiC matrix. Several valve and full system (8-valve) static motor tests have been conducted by the motor vendor. The culmination of these tests was the successful flight test of the Orion LAS Pad Abort One (PA ]1) vehicle on May 6, 2010. Due to the fast pace of the LAS development program, NASA Marshall Space Flight Center assisted the LAS community by performing a series of material and component evaluations using fired hardware from valve and full ]system development motor tests, and from the PA-1 flight ACM motor. Information will be presented on the structure of the C/C-SiC material, as well as the efficacy of various non ]destructive evaluation (NDE) techniques, including but not limited to: radiography, computed tomography, nanofocus computed tomography, and X-ray transmission microscopy. Examinations of the microstructure of the material via scanning electron microscopy and energy dispersive spectroscopy will also be discussed. The findings resulting from the subject effort are assisting the LAS Project in risk assessments and in possible modifications to the final ACM operational design.

  5. Syntheses, Spectroscopic, Electrochemical, and Third-Order Nonlinear Optical Studies of a Hybrid Tris{ruthenium(alkynyl)/(2-phenylpyridine)}iridium Complex.

    PubMed

    Zhao, Huajian; Simpson, Peter V; Barlow, Adam; Moxey, Graeme J; Morshedi, Mahbod; Roy, Nivya; Philip, Reji; Zhang, Chi; Cifuentes, Marie P; Humphrey, Mark G

    2015-08-10

    The synthesis of fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡CH)}3] (10), which bears pendant ethynyl groups, and its reaction with [RuCl(dppe)2]PF6 to afford the heterobimetallic complex fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡C-trans-[RuCl(dppe)2])}3] (11) is described. Complex 10 is available from the two-step formation of iodo-functionalized fac-tris[2-(4-iodophenyl)pyridine]iridium(III) (6), followed by ligand-centered palladium-catalyzed coupling and desilylation reactions. Structural studies of tetrakis[2-(4-iodophenyl)pyridine-N,C1′](μ-dichloro)diiridium 5, 6, fac-[Ir{N,C1′-(2,2′-NC5H4C6H3-5′-C≡C-1-C6H2-3,5-Et2-4-C≡CH)}3] (8), and 10 confirm ligand-centered derivatization of the tris(2-phenylpyridine)iridium unit. Electrochemical studies reveal two (5) or one (6–10) Ir-centered oxidations for which the potential is sensitive to functionalization at the phenylpyridine groups but relatively insensitive to more remote derivatization. Compound 11 undergoes sequential Ru-centered and Ir-centered oxidation, with the potential of the latter significantly more positive than that of Ir(N,C′-NC5H4-2-C6H4-2)3. Ligand-centered π–π* transitions characteristic of the Ir(N,C′-NC5H4-2-C6H4-2)3 unit red-shift and gain in intensity following the iodo and alkynyl incorporation. Spectroelectrochemical studies of 6, 7, 9, and 11 reveal the appearance in each case of new low-energy LMCT bands following formal IrIII/IV oxidation preceded, in the case of 11, by the appearance of a low-energy LMCT band associated with the formal RuII/III oxidation process. Emission maxima of 6–10 reveal a red-shift upon alkynyl group introduction and arylalkynyl π-system lengthening; this process is quenched upon incorporation of the ligated ruthenium moiety on proceeding to 11. Third-order nonlinear optical studies of 11 were undertaken at the benchmark wavelengths of 800 nm (fs pulses) and 532

  6. χc 0(3915 ) as the lightest c c ¯s s ¯ state

    NASA Astrophysics Data System (ADS)

    Lebed, Richard F.; Polosa, Antonio D.

    2016-05-01

    The state χc 0(3915 ) has recently been demoted by the Particle Data Group from its previous status as the conventional c c ¯ 23P0 state, largely due to the absence of expected D D ¯ decays. We propose that χc 0(3915 ) is actually the lightest c c ¯s s ¯ state, and calculate the spectrum of such states using the diquark model, identifying many of the observed charmoniumlike states that lack open-charm decay modes as c c ¯s s ¯. Among other results, we argue that Y (4140 ) is a JP C=1++ c c ¯s s ¯ state that has been not been seen in two-photon fusion largely as a consequence of the Landau-Yang theorem.

  7. Iridium-catalyzed allylic substitutions with cyclometalated phosphoramidite complexes bearing a dibenzocyclooctatetraene ligand: preparation of (π-allyl)Ir complexes and computational and NMR spectroscopic studies.

    PubMed

    Raskatov, Jevgenij A; Jäkel, Mascha; Straub, Bernd F; Rominger, Frank; Helmchen, Günter

    2012-11-01

    (π-Allyl)Ir complexes derived from dibenzocyclooctatetraene and phosphoramidites by cyclometalation are effective catalysts for allylic substitution reactions of linear monosubstituted allylic carbonates. These catalysts provide exceptionally high degrees of regioselectivity and allow the reactions to be run under aerobic conditions. A series of (π-allyl)Ir complexes were prepared and characterized by X-ray crystal structure analyses. An allylic amination with aniline displayed different resting states depending on the presence of a strong base. DFT calculations were carried out on the mechanistic aspects of these reactions. The results suggest that for the (π-allyl)Ir complexes, the formation and reactions with nucleophiles proceed with comparable rates. PMID:23018807

  8. Development of a luminescent G-quadruplex-selective iridium(III) complex for the label-free detection of adenosine

    PubMed Central

    Lu, Lihua; Zhong, Hai-Jing; He, Bingyong; Leung, Chung-Hang; Ma, Dik-Lung

    2016-01-01

    A panel of six luminescent iridium(III) complexes were synthesized and evaluated for their ability to act as G-quadruplex-selective probes. The novel iridium(III) complex 1 was found to be highly selective for G-quadruplex DNA, and was employed for the construction of a label-free G-quadruplex-based adenosine detection assay in aqueous solution. Two different detection strategies were investigated for adenosine detection, and the results showed that initial addition of adenosine to the adenosine aptamer gave superior results. The assay exhibited a linear response for adenosine in the concentration range of 5 to 120 μM (R2 = 0.992), and the limit of detection for adenosine was 5 μM. Moreover, this assay was highly selective for adenosine over other nucleosides, and exhibited potential use for biological sample analysis. PMID:26778273

  9. Development of a luminescent G-quadruplex-selective iridium(III) complex for the label-free detection of adenosine

    NASA Astrophysics Data System (ADS)

    Lu, Lihua; Zhong, Hai-Jing; He, Bingyong; Leung, Chung-Hang; Ma, Dik-Lung

    2016-01-01

    A panel of six luminescent iridium(III) complexes were synthesized and evaluated for their ability to act as G-quadruplex-selective probes. The novel iridium(III) complex 1 was found to be highly selective for G-quadruplex DNA, and was employed for the construction of a label-free G-quadruplex-based adenosine detection assay in aqueous solution. Two different detection strategies were investigated for adenosine detection, and the results showed that initial addition of adenosine to the adenosine aptamer gave superior results. The assay exhibited a linear response for adenosine in the concentration range of 5 to 120 μM (R2 = 0.992), and the limit of detection for adenosine was 5 μM. Moreover, this assay was highly selective for adenosine over other nucleosides, and exhibited potential use for biological sample analysis.

  10. 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).

  11. Solution-processable deep red-emitting supramolecular phosphorescent polymer with novel iridium complex for organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Liang, Aihui; Huang, Gui; Wang, Zhiping; Wu, Wenjin; Zhong, Yu; Zhao, Shan

    2016-07-01

    A novel bis(dibenzo-24-crown-8)-functionalized iridium complex with an emission peak at 665 nm was synthesized. Several deep red-emitting supramolecualr phosphorescent polymers (SPPs) as a class of solutionprocessable electroluminescent (EL) emitters were formed by utilizing the efficient non-bonding self-assembly between the resulting iridium complex and bis(dibenzylammonium)-tethered monomers. These SPPs show an intrinsic glass transition with a T g of ca. 90 °C. The photophysical and electroluminescent properties are strongly dependent on the hosts' structures of the supramolecular phosphorescent polymers. The polymer light-emitting diode based on SPP3 displayed a maximal external quantum efficiency (EQE) of 2.14% ph·el-1 and the Commission Internationale de L'Eclairage (CIE) coordinates of (0.70, 0.29).

  12. Solution-processable deep red-emitting supramolecular phosphorescent polymer with novel iridium complex for organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Liang, Aihui; Huang, Gui; Wang, Zhiping; Wu, Wenjin; Zhong, Yu; Zhao, Shan

    2016-09-01

    A novel bis(dibenzo-24-crown-8)-functionalized iridium complex with an emission peak at 665 nm was synthesized. Several deep red-emitting supramolecualr phosphorescent polymers (SPPs) as a class of solutionprocessable electroluminescent (EL) emitters were formed by utilizing the efficient non-bonding self-assembly between the resulting iridium complex and bis(dibenzylammonium)-tethered monomers. These SPPs show an intrinsic glass transition with a T g of ca. 90 °C. The photophysical and electroluminescent properties are strongly dependent on the hosts' structures of the supramolecular phosphorescent polymers. The polymer light-emitting diode based on SPP3 displayed a maximal external quantum efficiency (EQE) of 2.14% ph·el-1 and the Commission Internationale de L'Eclairage (CIE) coordinates of (0.70, 0.29).

  13. Luminescence switch-on assay of interferon-gamma using a G-quadruplex-selective iridium(III) complex.

    PubMed

    Lin, Sheng; He, Bingyong; Yang, Chao; Leung, Chung-Hang; Mergny, Jean-Louis; Ma, Dik-Lung

    2015-11-18

    In this study, we synthesized a series of 9 luminescent iridium(III) complexes and studied their ability to function as luminescent probes for G-quadruplex DNA. The iridium(III) complex 8 [Ir(pbtz)2(dtbpy)]PF6 (where pbtz = 2-phenylbenzo[d]thiazole; dtbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) showed high selectivity for G-quadruplex DNA over single-stranded and double-stranded DNA, and was subsequently utilized for the development of a label-free oligonucleotide-based assay for interferon-gamma (IFN-γ), an important biomarker for a range of immune and infectious diseases, in aqueous solution. We further demonstrated that this assay could monitor IFN-γ levels even in the presence of cellular debris. This assay represents the first G-quadruplex-based assay for IFN-γ detection described in the literature.

  14. Transformation of cellulose and its derived carbohydrates into formic and lactic acids catalyzed by vanadyl cations.

    PubMed

    Tang, Zhenchen; Deng, Weiping; Wang, Yanliang; Zhu, Enze; Wan, Xiaoyue; Zhang, Qinghong; Wang, Ye

    2014-06-01

    The transformation of cellulose or cellulose-derived carbohydrates into platform chemicals is the key to establish biomass-based sustainable chemical processes. The systems able to catalyze the conversion of cellulose into key chemicals in water without the consumption of hydrogen are limited. We report that simple vanadyl (VO(2+)) cations catalyze the conversions of cellulose and its monomer, glucose, into lactic acid and formic acid in water. We have discovered an interesting shift of the major product from formic acid to lactic acid on switching the reaction atmosphere from oxygen to nitrogen. Our studies suggest that VO(2+) catalyzes the isomerization of glucose to fructose, the retro-aldol fragmentation of fructose to two trioses, and the isomerization of trioses, which leads to the formation of lactic acid under anaerobic conditions. The oxidative cleavage of C-C bonds in the intermediates caused by the redox conversion of VO2(+)/VO(2+) under aerobic conditions results in formic acid and CO2. We demonstrate that the addition of an alcohol suppresses the formation of CO2 and enhances the formic acid yield significantly to 70-75 %.

  15. Lewis super-acid catalyzed cyclizations: a new route to fragrance compounds.

    PubMed

    Coulombel, Lydie; Grau, Fanny; Weïwer, Michel; Favier, Isabelle; Chaminade, Xavier; Heumann, Andreas; Bayón, J Carles; Aguirre, Pedro A; Duñach, Elisabet

    2008-06-01

    This review deals with the application of Lewis super acids such as Al(III), In(III), and Sn(IV) triflates and triflimidates as catalysts in the synthesis of fragrance materials. Novel catalytic reactions involving C-C and C-heteroatom bond-forming reactions, as well as cycloisomerization processes are presented. In particular, Sn(IV) and Al(III) triflates were employed as catalysts in the selective cyclization of unsaturated alcohols to cyclic ethers, as well as in the cyclization of unsaturated carboxylic acids to lactones. The addition of thiols and thioacids to non-activated olefins, both in intra- and intermolecular versions, was efficiently catalyzed by In(III) derivatives. Sn(IV) Triflimidates catalyzed the cycloisomerization of highly substituted 1,6-dienes to gem-dimethyl-substituted cyclohexanes bearing an isopropylidene substituent. The hydroformylation of these unsaturated substrates, catalyzed by a Rh(I) complex with a bulky phosphite ligand, selectively afforded the corresponding linear aldehydes. The olfactory evaluation of selected heterocycles, carbocycles, and aldehydes synthesized is also discussed.

  16. Transformation of cellulose and its derived carbohydrates into formic and lactic acids catalyzed by vanadyl cations.

    PubMed

    Tang, Zhenchen; Deng, Weiping; Wang, Yanliang; Zhu, Enze; Wan, Xiaoyue; Zhang, Qinghong; Wang, Ye

    2014-06-01

    The transformation of cellulose or cellulose-derived carbohydrates into platform chemicals is the key to establish biomass-based sustainable chemical processes. The systems able to catalyze the conversion of cellulose into key chemicals in water without the consumption of hydrogen are limited. We report that simple vanadyl (VO(2+)) cations catalyze the conversions of cellulose and its monomer, glucose, into lactic acid and formic acid in water. We have discovered an interesting shift of the major product from formic acid to lactic acid on switching the reaction atmosphere from oxygen to nitrogen. Our studies suggest that VO(2+) catalyzes the isomerization of glucose to fructose, the retro-aldol fragmentation of fructose to two trioses, and the isomerization of trioses, which leads to the formation of lactic acid under anaerobic conditions. The oxidative cleavage of C-C bonds in the intermediates caused by the redox conversion of VO2(+)/VO(2+) under aerobic conditions results in formic acid and CO2. We demonstrate that the addition of an alcohol suppresses the formation of CO2 and enhances the formic acid yield significantly to 70-75 %. PMID:24798653

  17. Metal Nanoparticles Catalyzed Selective Carbon-Carbon Bond Activation in the Liquid Phase.

    PubMed

    Ye, Rong; Yuan, Bing; Zhao, Jie; Ralston, Walter T; Wu, Chung-Yeh; Unel Barin, Ebru; Toste, F Dean; Somorjai, Gabor A

    2016-07-13

    Understanding the C-C bond activation mechanism is essential for developing the selective production of hydrocarbons in the petroleum industry and for selective polymer decomposition. In this work, ring-opening reactions of cyclopropane derivatives under hydrogen catalyzed by metal nanoparticles (NPs) in the liquid phase were studied. 40-atom rhodium (Rh) NPs, encapsulated by dendrimer molecules and supported in mesoporous silica, catalyzed the ring opening of cyclopropylbenzene at room temperature under hydrogen in benzene, and the turnover frequency (TOF) was higher than other metals or the Rh homogeneous catalyst counterparts. Comparison of reactants with various substitution groups showed that electron donation on the three-membered ring boosted the TOF of ring opening. The linear products formed with 100% selectivity for ring opening of all reactants catalyzed by the Rh NP. Surface Rh(0) acted as the active site in the NP. The capping agent played an important role in the ring-opening reaction kinetics. Larger particle size tended to show higher TOF and smaller reaction activation energy for Rh NPs encapsulated in either dendrimer or poly(vinylpyrrolidone). The generation/size of dendrimer and surface group also affected the reaction rate and activation energy. PMID:27322570

  18. Iridium-catalysed dehydrocoupling of aryl phosphine-borane adducts: synthesis and characterisation of high molecular weight poly(phosphinoboranes).

    PubMed

    Paul, Ursula S D; Braunschweig, Holger; Radius, Udo

    2016-06-30

    The thermal dehydrogenative coupling of aryl phosphine-borane adducts with iridium complexes bearing a bis(phosphinite) pincer ligand is reported. This catalysis produces high molecular weight poly(phosphinoboranes) [ArPH-BH2]n (Ar = Ph, (p)Tol, Mes). Furthermore, we investigated the reactivity of these pincer complexes towards primary phosphines and their respective borane adducts on a stoichiometric scale. PMID:27320239

  19. Rapid selective electrocatalytic reduction of carbon dioxide to formate by an iridium pincer catalyst immobilized on carbon nanotube electrodes.

    PubMed

    Kang, Peng; Zhang, Sheng; Meyer, Thomas J; Brookhart, Maurice

    2014-08-11

    An iridium pincer dihydride catalyst was immobilized on carbon nanotube-coated gas diffusion electrodes (GDEs) by using a non-covalent binding strategy. The as-prepared GDEs are efficient, selective, durable, gas permeable electrodes for electrocatalytic reduction of CO2 to formate. High turnover numbers (ca. 54,000) and turnover frequencies (ca. 15 s(-1)) were enabled by the novel electrode architecture in aqueous solutions saturated in CO2 with added HCO3(-).

  20. Spectroscopic characterization of alumina-supported bis(allyl)iridium complexes : site-isolation, reactivity, and decomposition studies.

    SciTech Connect

    Trovitch, R. J.; Guo, N.; Janicke, M. T.; Li, H.; Marshall, C. L.; Miller, J. T.; Sattelberger, A. P.; John, K. D.; Baker, R. T.; LANL; Univ. of Ottawa

    2010-01-01

    The covalent attachment of tris(allyl)iridium to partially dehydroxylated ?-alumina is found to proceed via surface hydroxyl group protonation of one allyl ligand to form an immobilized bis(allyl)iridium moiety, (?AlO)Ir(allyl)2, as characterized by CP-MAS 13C NMR, inductively coupled plasma-mass spectrometry, and Ir L3 edge X-ray absorption spectroscopy. Extended X-ray absorption fine-structure (EXAFS) measurements taken on unsupported Ir(allyl)3 and several associated tertiary phosphine addition complexes suggest that the ?3-allyl ligands generally account for an Ir-C coordination number of 2 rather than 3, with an average Ir-C distance of 2.16 A. Using this knowledge, combined EXAFS and X-ray absorption near-edge structure studies reveal that a small amount of Ir0 is also formed upon reaction of Ir(allyl)3 with the surface. It was found that the addition of either 2,6-dimethylphenyl isocyanide or carbon monoxide to the supported complex allows spectroscopic identification of the supported bis(allyl)iridium complexes, (?AlO)Ir(allyl)2(CNAr) [Ar = 2,6-(CH3)2C6H4] and (?AlO)Ir(allyl)2(CO)2, respectively. Although samples of the supported bis(allyl)iridium complex are active for the dehydrogenation of cyclohexane to benzene at temperatures between 180 and 220C, in situ temperature-programmed reaction XAFS and continuous-flow reactor studies suggest that Ir0 nanoparticles, rather than a well-defined Ir3+ complex, are responsible for the observed activity.

  1. Spectroscopic characterization of alumina-supported bis(allyl)iridium complexes: site-isolation, reactivity, and decomposition studies.

    PubMed

    Trovitch, Ryan J; Guo, Neng; Janicke, Michael T; Li, Hongbo; Marshall, Christopher L; Miller, Jeffrey T; Sattelberger, Alfred P; John, Kevin D; Baker, R Thomas

    2010-03-01

    The covalent attachment of tris(allyl)iridium to partially dehydroxylated gamma-alumina is found to proceed via surface hydroxyl group protonation of one allyl ligand to form an immobilized bis(allyl)iridium moiety, (=AlO)Ir(allyl)(2), as characterized by CP-MAS (13)C NMR, inductively coupled plasma-mass spectrometry, and Ir L(3) edge X-ray absorption spectroscopy. Extended X-ray absorption fine-structure (EXAFS) measurements taken on unsupported Ir(allyl)(3) and several associated tertiary phosphine addition complexes suggest that the eta(3)-allyl ligands generally account for an Ir-C coordination number of 2 rather than 3, with an average Ir-C distance of 2.16 A. Using this knowledge, combined EXAFS and X-ray absorption near-edge structure studies reveal that a small amount of Ir(0) is also formed upon reaction of Ir(allyl)(3) with the surface. It was found that the addition of either 2,6-dimethylphenyl isocyanide or carbon monoxide to the supported complex allows spectroscopic identification of the supported bis(allyl)iridium complexes, (=AlO)Ir(allyl)(2)(CNAr) [Ar = 2,6-(CH(3))(2)C(6)H(4)] and (=AlO)Ir(allyl)(2)(CO)(2), respectively. Although samples of the supported bis(allyl)iridium complex are active for the dehydrogenation of cyclohexane to benzene at temperatures between 180 and 220 degrees C, in situ temperature-programmed reaction XAFS and continuous-flow reactor studies suggest that Ir(0) nanoparticles, rather than a well-defined Ir(3+) complex, are responsible for the observed activity. PMID:20112918

  2. Solvent-Dependent Structure of Iridium Dihydride Complexes: Different Geometries at Low and High Dielectricity of the Medium.

    PubMed

    Polukeev, Alexey V; Marcos, Rocío; Ahlquist, Mårten S G; Wendt, Ola F

    2016-03-14

    The hydride iridium pincer complex [(PCyP)IrH2] (PCyP=cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane, 1) reveals remarkably solvent-dependent hydride chemical shifts, isotope chemical shifts, JHD and T1(min), with rHH increasing upon moving to more polar medium. The only known example of such behaviour (complex [(POCOP)IrH2], POCOP=2,6-(tBu2PO)2C6H3) was explained by the coordination of a polar solvent molecule to the iridium (J. Am. Chem. Soc. 2006, 128, 17114). Based on the existence of an agostic bond between α-C-H and iridium in 1 in all solvents, we argue that the coordination of solvent can be rejected. DFT calculations revealed that the structures of 1 and [(POCOP)IrH2] depend on the dielectric permittivity of the medium and these compounds adopt trigonal-bipyramidal geometries in non-polar media and square-pyramidal geometries in polar media. PMID:26880293

  3. Using iridium films to compensate for piezo-electric materials processing stresses in adjustable x-ray optics

    NASA Astrophysics Data System (ADS)

    Ames, A.; Bruni, R.; Cotroneo, V.; Johnson-Wilke, R.; Kester, T.; Reid, P.; Romaine, S.; Tolier-McKinstry, S.; Wilke, R. H. T.

    2015-09-01

    Adjustable X-ray optics represent a potential enabling technology for simultaneously achieving large effective area and high angular resolution for future X-ray Astronomy missions. The adjustable optics employ a bimorph mirror composed of a thin (1.5 μm) film of piezoelectric material deposited on the back of a 0.4 mm thick conical mirror segment. The application of localized electric fields in the piezoelectric material, normal to the mirror surface, result in localized deformations in mirror shape. Thus, mirror fabrication and mounting induced figure errors can be corrected, without the need for a massive reaction structure. With this approach, though, film stresses in the piezoelectric layer, resulting from deposition, crystallization, and differences in coefficient of thermal expansion, can distort the mirror. The large relative thickness of the piezoelectric material compared to the glass means that even 100MPa stresses can result in significant distortions. We have examined compensating for the piezoelectric processing related distortions by the deposition of controlled stress chromium/iridium films on the front surface of the mirror. We describe our experiments with tuning the product of the chromium/iridium film stress and film thickness to balance that resulting from the piezoelectric layer. We also evaluated the repeatability of this deposition process, and the robustness of the iridium coating.

  4. Method of making a cathode from tungsten and iridium powders using a strontium peroxide containing material as the impregnant

    SciTech Connect

    Branovich, L.E.; Freeman, G.L.; Smith, B.

    1988-11-25

    This invention relates in general to a method of making a long-life high-current-density cathode and in particular, to a method of making such a cathode from a mixture of tungsten and iridium powders using a strontium peroxide containing material as the impregnant. The general object of this invention is to provide an improved method of making a long life high current density cathode. A more specific object of the invention is to provide such a method in which lower temperatures can be used than were used in S.N. 204,327 for the impregnation of the tungsten-iridium billet. It has now been found that the aforementioned objects can be attained by a method that uses a strontium peroxide-containing material as the impregnant. More particularly, according to the invention, a suitable porous billet of tungsten, or tungsten-iridium, or tungsten-osmium or tungsten-rhodium is impregnated with a strontium peroxide containing material in a hydrogen atmosphere and slowly heated to above 215 C to decompose the strontium peroxide, SrO/sub 2/ to form strontium oxide, SrO, and oxygen, O/sub 2/.

  5. Structural characterization and comparison of iridium, platinum and gold/palladium ultra-thin film coatings for STM of biomolecules

    SciTech Connect

    Sebring, R.; Arendt, P.; Imai, B.; Bradbury, E.M.; Gatewood, J.; Panitz, J.; Yau, P.

    1997-10-30

    Scanning tunneling microscopy (STM) is capable of atomic resolution and is ideally suited for imaging surfaces with uniform work function. A biological sample on a conducting substrate in air does not meet this criteria and requires a conductive coating for stable and reproducible STM imaging. In this paper, the authors describe the STM and transmission electron microscopy (TEM) characterization of ultra-thin ion-beam sputtered films of iridium and cathode sputtered gold/palladium and platinum films on highly ordered pyrolytic graphite (HOPG) which were developed for use as biomolecule coatings. The goals were the development of metal coatings sufficiently thin and fine grained that 15--20 {angstrom} features of biological molecules could be resolved using STM, and the development of a substrate/coating system which would allow complementary TEM information to be obtained for films and biological molecules. The authors demonstrate in this paper that ion-beam sputtered iridium on highly ordered pyrolytic graphite (HOPG) has met both these goals. The ion-beam sputtered iridium produced a very fine grained (< 10 {angstrom}) continuous film at 5--6 {angstrom} thickness suitable for stable air STM imaging. In comparison, cathode sputtered platinum produced 16 {angstrom} grains with the thinnest continuous film at 15 {angstrom} thickness, and the sputtered gold/palladium produced 25 {angstrom} grains with the thinnest continuous film at 18 {angstrom} thickness.

  6. Metal Azolate/Carboxylate Frameworks as Catalysts in Oxidative and C-C Coupling Reactions.

    PubMed

    Tăbăcaru, Aurel; Xhaferaj, Nertil; Martins, Luísa M D R S; Alegria, Elisabete C B A; Chay, Rogério S; Giacobbe, Carlotta; Domasevitch, Konstantin V; Pombeiro, Armando J L; Galli, Simona; Pettinari, Claudio

    2016-06-20

    The five metal azolate/carboxylate (MAC) compounds [Cd(dmpzc)(DMF)(H2O)] (Cd-dmpzc), [Pd(H2dmpzc)2Cl2] (Pd-dmpzc), [Cu(Hdmpzc)2] (Cu-dmpzc), [Zn4O(dmpzc)3]·Solv (Zn-dmpzc·S), and [Co4O(dmpzc)3]·Solv (Co-dmpzc·S) were isolated by coupling 3,5-dimethyl-1H-pyrazol-4-carboxylic acid (H2dmpzc) to cadmium(II), palladium(II), copper(II), zinc(II), and cobalt(II) salts. While Cd-dmpzc and Pd-dmpzc had never been prepared in the past, for Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S we optimized alternative synthetic paths that, in the case of the copper(II) and cobalt(II) derivatives, are faster and grant higher yields than the previously reported ones. The crystal structure details were determined ab initio (Cd-dmpzc and Pd-dmpzc) or refined (Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S) by means of powder X-ray diffraction (PXRD). While Cd-dmpzc is a nonporous 3D MAC framework, Pd-dmpzc shows a 3D hybrid coordination/hydrogen-bonded network, in which Pd(H2dmpzc)2Cl2 monomers are present. The thermal behavior of the five MAC compounds was investigated by coupling thermal analysis to variable-temperature PXRD. Their catalytic activity was assessed in oxidative and C-C coupling reactions, with the copper(II) and cadmium(II) derivatives being the first nonporous MAC frameworks to be tested as catalysts. Cu-dmpzc is the most active catalyst in the partial oxidation of cyclohexane by tert-butyl hydroperoxide in acetonitrile (yields up to 12% after 9 h) and is remarkably active in the solvent-free microwave-assisted oxidation of 1-phenylethanol to acetophenone (yields up to 99% at 120 °C in only 0.5 h). On the other hand, activated Zn-dmpzc·S (Zn-dmpzc) is the most active catalyst in the Henry C-C coupling reaction of aromatic aldehydes with nitroethane, showing appreciable diastereoselectivity toward the syn-nitroalkanol isomer (syn:anti selectivity up to 79:21). PMID:27266480

  7. Formation of C-C bonds by mandelonitrile lyase in organic solvents.

    PubMed

    Wehtje, E; Adlercreutz, P; Mattiasson, B

    1990-06-01

    Mandelonitrile lyase (EC 4.1.2.10) catalyzes the formation of D-mandelonitrile from HCN and benzaldehyde. Mandelonitrile lyase was immobilized by adsorption to support materials, for example, Celite. The enzyme preparations were used in diisopropyl ether for production of D-mandelonitrile. In order to obtain optically pure D-mandelonitrile it was necessary to use reaction conditions which favor the enzymatic reaction and suppress the competing spontaneous reaction, which yields a racemic mixture of D, L-mandelonitrile. The effects of substrate concentrations, water content, and support materials on both the spontaneous and enzymatic reactions were studied. The enzymatic reaction was carried out under conditions where the importance of the spontaneous reaction was negligible and high enantiomeric purity of D-mandelonitrile was achieved (at least 98% enantiomeric excess). The operational stability of the enzyme preparations was studied in batch as well as in continuous systems. It was vital to control the water content in the system to maintain an active preparation. In a packed bed reactor the enzyme preparations were shown to be active and stable. The reactors were run for 50 h with only a small decrease in product yield. PMID:18592607

  8. Photoinduced C-C reactions on insulators toward photolithography of graphene nanoarchitectures.

    PubMed

    Palma, Carlos-Andres; Diller, Katharina; Berger, Reinhard; Welle, Alexander; Björk, Jonas; Cabellos, Jose Luis; Mowbray, Duncan J; Papageorgiou, Anthoula C; Ivleva, Natalia P; Matich, Sonja; Margapoti, Emanuela; Niessner, Reinhard; Menges, Bernhard; Reichert, Joachim; Feng, Xinliang; Räder, Hans Joachim; Klappenberger, Florian; Rubio, Angel; Müllen, Klaus; Barth, Johannes V

    2014-03-26

    On-surface chemistry for atomically precise sp(2) macromolecules requires top-down lithographic methods on insulating surfaces in order to pattern the long-range complex architectures needed by the semiconductor industry. Here, we fabricate sp(2)-carbon nanometer-thin films on insulators and under ultrahigh vacuum (UHV) conditions from photocoupled brominated precursors. We reveal that covalent coupling is initiated by C-Br bond cleavage through photon energies exceeding 4.4 eV, as monitored by laser desorption ionization (LDI) mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) gives insight into the mechanisms of C-Br scission and C-C coupling processes. Further, unreacted material can be sublimed and the coupled sp(2)-carbon precursors can be graphitized by e-beam treatment at 500 °C, demonstrating promising applications in photolithography of graphene nanoarchitectures. Our results present UV-induced reactions on insulators for the formation of all sp(2)-carbon architectures, thereby converging top-down lithography and bottom-up on-surface chemistry into technology.

  9. Spectroscopic Characterization of Lanthanum-Mediated Dehydrogenation and C-C Bond Coupling of Ethylene.

    PubMed

    Kumari, Sudesh; Cao, Wenjin; Zhang, Yuchen; Roudjane, Mourad; Yang, Dong-Sheng

    2016-07-01

    La(C2H2) and La(C4H6) are observed from the reaction of laser-vaporized La atoms with ethylene molecules by photoionization time-of-flight mass spectrometry and characterized by mass-analyzed threshold ionization spectroscopy. La(C2H2) is identified as a metallacyclopropene and La(C4H6) as a metallacyclopentene. The three-membered ring is formed by concerted H2 elimination and the five-membered cycle by dehydrogenation and C-C bond coupling. Both metallacycles prefer a doublet ground state with a La 6s-based unpaired electron. Ionization of the neutral doublet state of either complex produces a singlet ion state by removing the La-based electron. The ionization allows accurate measurements of the adiabatic ionization energy of the neutral doublet state and metal-ligand and ligand-based vibrational frequencies of the neutral and ionic states. Although the La atom is in a formal oxidation state of +2, the ionization energies of these metal-hydrocarbon cycles are lower than that of the neutral La atom. Deuteration has a small effect on the ionization energies of the two cyclic radicals but distinctive effects on their vibrational frequencies. PMID:27322131

  10. Central C-C Bonding Increases Optical and Chemical Stability of NIR Fluorophores

    PubMed Central

    Hyun, Hoon; Owens, Eric A.; Narayana, Lakshminarayana; Wada, Hideyuki; Gravier, Julien; Bao, Kai; Frangioni, John V.; Choi, Hak Soo; Henary, Maged

    2014-01-01

    Functional near-infrared (NIR) fluorophores have played a major role in the recent advances in bioimaging. However, the optical and physicochemical stabilities of NIR fluorophores in the biological and physiological environment are still a challenge. Especially, the ether linkage on the meso carbon of heptamethine core is fragile when exposed to serum proteins or other amine-rich biomolecules. To solve such a structural limitation, a rigid carbon-carbon bond was installed onto the framework of ether-linked NIR fluorophores through the Suzuki coupling. The robust fluorophores replaced as ZW800-1C and ZW800-3C displayed enhanced optical and chemical stability in various solvents and a 100% warm serum environment (> 99%, 24 h). The biodistribution and clearance of C-C coupled ZW800 compounds were almost identical to the previously developed oxygen-substituted ZW800 compounds. When conjugated with a small molecule ligand, ZW800-1C maintained the identical stable form in warm serum (>98%, 24 h), while ZW800-1A hydrolyzed quickly after 4 h incubation (34%, 24 h). PMID:25530846

  11. The Tautomeric Half-reaction of BphD, a C-C Bond Hydrolase Kinetic and Structural Evidence Supporting a Key Role for Histidine 265 of the Catalytic triad

    SciTech Connect

    Horsman, Geoff P.; Bhowmik, Shiva; Seah, Stephen Y.K.; Kumar, Pravindra; Bolin, Jeffrey T.; Eltis, Lindsay D.

    2010-01-07

    BphD of Burkholderia xenovorans LB400 catalyzes an unusual C-C bond hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) to afford benzoic acid and 2-hydroxy-2,4-pentadienoic acid (HPD). An enol-keto tautomerization has been proposed to precede hydrolysis via a gem-diol intermediate. The role of the canonical catalytic triad (Ser-112, His-265, Asp-237) in mediating these two half-reactions remains unclear. We previously reported that the BphD-catalyzed hydrolysis of HOPDA ({lambda}{sub max} is 434 nm for the free enolate) proceeds via an unidentified intermediate with a red-shifted absorption spectrum ({lambda}{sub max} is 492 nm) (Horsman, G. P., Ke, J., Dai, S., Seah, S. Y. K., Bolin, J. T., and Eltis, L. D. (2006) Biochemistry 45, 11071-11086). Here we demonstrate that the S112A variant generates and traps a similar intermediate ({lambda}{sub max} is 506 nm) with a similar rate, 1/{tau} {approx} 500 s{sup -1}. The crystal structure of the S112A:HOPDA complex at 1.8-{angstrom} resolution identified this intermediate as the keto tautomer, (E)-2,6-dioxo-6-phenyl-hex-3-enoate. This keto tautomer did not accumulate in either the H265A or the S112A/H265A double variants, indicating that His-265 catalyzes tautomerization. Consistent with this role, the wild type and S112A enzymes catalyzed tautomerization of the product HPD, whereas H265A variants did not. This study thus identifies a keto intermediate, and demonstrates that the catalytic triad histidine catalyzes the tautomerization half-reaction, expanding the role of this residue from its purely hydrolytic function in other serine hydrolases. Finally, the S112A:HOPDA crystal structure is more consistent with hydrolysis occurring via an acyl-enzyme intermediate than a gem-diol intermediate as solvent molecules have poor access to C6, and the closest ordered water is 7{angstrom} away.

  12. A Numerical Study on the Thermal Conductivity of 3D Woven C/C Composites at High Temperature

    NASA Astrophysics Data System (ADS)

    Shigang, Ai; Rujie, He; Yongmao, Pei

    2015-12-01

    Experimental data for Carbon/Carbon (C/C) constituent materials are combined with a three dimensional steady state heat transfer finite element analysis to demonstrate the average in-plane and out-of-plane thermal conductivities (TCs) of C/C composites. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibres and (b) a meso scale comparable with the carbon fibre yarns. Micro-scale model calculate the TCs at the fibre yarn scale in the three orthogonal directions ( x, y and z). The output results from the micro-scale model are then incorporated in the meso-scale model to obtain the global TCs of the 3D C/C composite. The simulation results are quite consistent with the theoretical and experimental counterparts reported in references. Based on the numerical approach, TCs of the 3D C/C composite are calculated from 300 to 2500 K. Particular attention is given in elucidating the variations of the TCs with temperature. The multi-scale models provide an efficient approach to predict the TCs of 3D textile materials, which is helpful for the thermodynamic property analysis and structure design of the C/C composites.

  13. a Computational Investigation of c-C3H2...HX(X = F, Cl, Br) H-Bonded Complexes

    NASA Astrophysics Data System (ADS)

    Varadwaj, Pradeep R.; Varadwaj, Arpita; Peslherbe, Gilles H.

    2011-06-01

    Cyclopropenylidene (c-C3H2) is of significant importance in interstellar chemistry and synthetic chemistry (e.g., transition metal and organic catalysis). Because of its peculiar structure, c-C3H2 can act as a hydrogen-bond donor or acceptor. In order to gain insight into this feature, the ground-state potential energy surfaces of singlet c-C3H2 complexed with hydrogen halides HX (X = F, Cl, Br) have been explored extensively by density-functional theory (B3LYP) and {ab initio} quantum chemistry (MP2) with a variety of basis sets, cc-pVxZ and aug-cc-pVxZ (x = D, T). The complexes characterized have the carbenic end of c-C3H2 H-bonded to HX, with some proton transfer occurring, the extent of which follows the order HF < HCl < HBr. Accompanying the complex formation are the dipole moment enhancement, the charge transfer, red shifts of the HX vibrational stretching frequencies together with the significant enhancement of band intensity and concomitant HX bond elongation. The nature of H-bonding in these complexes has been explored, based on energy decomposition schemes and the Bader's quantum theory of atoms-in-molecules, with the conclusion that c-C3H2 is a strong H-bond acceptor with respect to the hydrogen halides.

  14. Mechanism and Selectivity in Nickel-Catalyzed Cross-Electrophile Coupling of Aryl Halides with Alkyl Halides

    PubMed Central

    Biswas, Soumik; Weix, Daniel J.

    2013-01-01

    The direct cross-coupling of two different electrophiles, such as an aryl halide with an alkyl halide, offers many advantages over conventional cross-coupling methods that require a carbon nucleophile. Despite its promise as a versatile synthetic strategy, a limited understanding of the mechanism and origin of cross selectivity has hindered progress in reaction development and design. Herein, we shed light on the mechanism for the nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides and demonstrate that the selectivity arises from an unusual catalytic cycle that combines both polar and radical steps to form the new C-C bond. PMID:23952217

  15. An Umpolung Strategy for the Synthesis of β-Aminoketones via Copper-Catalyzed Electrophilic Amination of Cyclopropanols.

    PubMed

    Ye, Zhishi; Dai, Mingji

    2015-05-01

    A novel copper-catalyzed electrophilic amination of cyclopropanols with O-benzoyl-N,N-dialkylhydroxylamines to synthesize various β-aminoketones via a sequence that includes C-C bond cleavage and Csp(3)-N bond formation is reported. The reaction conditions are mild and tolerate a wide range of functional groups including benzoate, tosylate, expoxide, and α,β-unsaturated carbonyls, which are incompatible in the traditional amine nucleophilic conjugate addition and the Mannich reaction conditions. Preliminary mechanistic studies and a proposed catalytic cycle of this umpolung β-aminoketone synthesis process have been described as well. PMID:25885943

  16. An Umpolung Strategy for the Synthesis of β-Aminoketones via Copper-Catalyzed Electrophilic Amination of Cyclopropanols.

    PubMed

    Ye, Zhishi; Dai, Mingji

    2015-05-01

    A novel copper-catalyzed electrophilic amination of cyclopropanols with O-benzoyl-N,N-dialkylhydroxylamines to synthesize various β-aminoketones via a sequence that includes C-C bond cleavage and Csp(3)-N bond formation is reported. The reaction conditions are mild and tolerate a wide range of functional groups including benzoate, tosylate, expoxide, and α,β-unsaturated carbonyls, which are incompatible in the traditional amine nucleophilic conjugate addition and the Mannich reaction conditions. Preliminary mechanistic studies and a proposed catalytic cycle of this umpolung β-aminoketone synthesis process have been described as well.

  17. Lanthanide-Catalyzed Reversible Alkynyl Exchange by Carbon-Carbon Single-Bond Cleavage Assisted by a Secondary Amino Group.

    PubMed

    Shao, Yinlin; Zhang, Fangjun; Zhang, Jie; Zhou, Xigeng

    2016-09-12

    Lanthanide-catalyzed alkynyl exchange through C-C single-bond cleavage assisted by a secondary amino group is reported. A lanthanide amido complex is proposed as a key intermediate, which undergoes unprecedented reversible β-alkynyl elimination followed by alkynyl exchange and imine reinsertion. The in situ homo- and cross-dimerization of the liberated alkyne can serve as an additional driving force to shift the metathesis equilibrium to completion. This reaction is formally complementary to conventional alkyne metathesis and allows the selective transformation of internal propargylamines into those bearing different substituents on the alkyne terminus in moderate to excellent yields under operationally simple reaction conditions. PMID:27510403

  18. Cyclo-octafluorobutane (PFC-318, c-C4F8) in the global atmosphere

    NASA Astrophysics Data System (ADS)

    Muhle, J.; Vollmer, M. K.; Ivy, D. J.; Fraser, P.; Arnold, T.; Harth, C. M.; Salameh, P.; O'Doherty, S.; Young, D.; Steele, P.; Krummel, P. B.; Leist, M.; Rhee, T. S.; Schmidbauer, N.; Lunder, C.; Kim, J.; Kim, K.; Reimann, S.; Simmonds, P.; Prinn, R. G.; Weiss, R. F.

    2011-12-01

    The perfluorocarbon (PFC) cyclo-octafluorobutane (PFC-318, c-C4F8) is a very long-lived (up to 3,200 years) and potent greenhouse gas (100-year global warming potential up to 10,300) with a wide range of industrial uses. We present an update of our PFC-318 archived air and in situ measurements from remote and urban AGAGE (Advanced Global Atmospheric Gases Experiment) sites and affiliated stations in both hemispheres. Most importantly, we have significantly improved our Southern Hemisphere (SH) data density by measuring the Cape Grim Air Archive (1970s-2010). Combined with our previously presented measurements of archived Northern Hemisphere (NH) flasks (1973-2009), we provide thirty year spanning records for both hemispheres. We have also further extended our in situ records by continuing our measurements at all remote stations, with the longest hemispheric records starting in November 2007 at Jungfraujoch (NH) and in June 2010 at Cape Grim (SH). We compare our data with those of Oram (1999) and Oram et al. (2011), who focus on SH data alone, and with other previous data sets. From our measurements, we derive emission estimates using a chemical transport model and inverse method, and compare our results to previous measurement based emission estimates (top-down) and to the EDGAR emission database (bottom-up). As stated previously (Mühle et al., 2010), we find emissions of ~1 Gg/yr in recent years while EDGAR estimates only 0.02 Gg/yr for 2005, similar to what Oram et al. (2011) find. We conclude that PFC-318 is the third most important PFC in terms of abundance and CO2-equivalent emissions. We continue to observe mostly baseline concentrations at remote AGAGE stations and urban sites in the USA, Europe, and Australia, in contrast to frequent pollution episodes measured at sites in East Asia, indicating significant regional emissions in East Asia, as found by Saito et al. (2010). EDGAR, Emission Database for Global Atmospheric Research, release version 4.1. http

  19. C-C chemokine receptor-7 mediated endocytosis of antibody cargoes into intact cells.

    PubMed

    Charest-Morin, Xavier; Pépin, Rémy; Gagné-Henley, Angélique; Morissette, Guillaume; Lodge, Robert; Marceau, François

    2013-01-01

    The C-C chemokine receptor-7 (CCR7) is a G protein coupled receptor that has a role in leukocyte homing, but that is also expressed in aggressive tumor cells. Preclinical research supports that CCR7 is a valid target in oncology. In view of the increasing availability of therapeutic monoclonal antibodies that carry cytotoxic cargoes, we studied the feasibility of forcing intact cells to internalize known monoclonal antibodies by exploiting the cycle of endocytosis and recycling triggered by the CCR7 agonist CCL19. Firstly, an anti-CCR7 antibody (CD197; clone 150503) labeled surface recombinant CCR7 expressed in intact HEK 293a cells and the fluorescent antibody was internalized following CCL19 treatment. Secondly, a recombinant myc-tagged CCL19 construction was exploited along the anti-myc monoclonal antibody 4A6. The myc-tagged ligand was produced as a conditioned medium of transfected HEK 293a cells that contained the equivalent of 430 ng/ml of immunoreactive CCL19 (average value, ELISA determination). CCL19-myc, but not authentic CCL19, carried the fluorophore-labeled antibody 4A6 into other recipient cells that expressed recombinant CCR7 (microscopy, cytofluorometry). The immune complexes were apparent in endosomal structures, co-localized well with the small GTPase Rab5 and progressed toward Rab7-positive endosomes. A dominant negative form of Rab5 (GDP-locked) inhibited this endocytosis. Further, endosomes in CCL19-myc- or CCL19-stimulated cells were positive for β-arrestin2, but rarely for β-arrestin1. Following treatment with CCL19-myc and the 4A6 antibody, the melanoma cell line A375 that expresses endogenous CCR7 was specifically stained using a secondary peroxidase-conjugated antibody. Agonist-stimulated CCR7 can transport antibody-based cargoes, with possible therapeutic applications in oncology.

  20. Observation of Spontaneous C=C Bond Breaking in the Reaction between Atomic Boron and Ethylene in Solid Neon.

    PubMed

    Jian, Jiwen; Lin, Hailu; Luo, Mingbiao; Chen, Mohua; Zhou, Mingfei

    2016-07-11

    A ground-state boron atom inserts into the C=C bond of ethylene to spontaneously form the allene-like compound H2 CBCH2 on annealing in solid neon. This compound can further isomerize to the propyne-like HCBCH3 isomer under UV light excitation. The observation of this unique spontaneous C=C bond insertion reaction is consistent with theoretical predictions that the reaction is thermodynamically exothermic and kinetically facile. This work demonstrates that the stronger C=C bond, rather than the less inert C-H bond, can be broken to form organoboron species from the reaction of a boron atom with ethylene even at cryogenic temperatures. PMID:27240114