Sample records for bond oxidation reaction

  1. Fiber reinforcement of reaction bonded oxide ceramics

    SciTech Connect

    Janssen, R.; Wendorff, J.; Claussen, N. [Advanced Ceramics Group, Hamburg (Germany)

    1995-12-01

    Pure oxide ceramic matrix composites (CMC) offer an encouraging route for materials capable of maintaining excellent stability in oxidizing atmospheres at high temperatures. The present paper deals with fiber-reinforced oxide matrix ceramics fabricated by reaction bonding. In order to produce a weak interface between fibers and matrix, two different approaches are discussed: (1) fiber/matrix debonding by adjusting the porosity of not fully densified matrices and (2) through formation of a weak fiber coating as a third component of the composite system.

  2. Oxidation kinetics, microstructure evolution and texture development in the reaction-bonded aluminum oxide (RBAO) process

    NASA Astrophysics Data System (ADS)

    Suvaci, Ender

    The reaction-bonded aluminum oxide (RBAO) process involves the solid state (T < 660°C) and liquid state (1000° < T < 660°C) oxidation of compacts of attrition milled Al and alpha alumina. When heated in air, the oxidation per unit area decreases for the higher surface attrition milled Al powders (i.e., 14.4 and 20.2 m2/g) but the total oxidation of the milled powder is ˜70% versus ˜9% for the as-received powder (surface area = 1.2 m2/g) because of the higher surface area. The solid state oxidation of Al powder sequentially follows parabolic, linear and non-linear rate laws. The solid state oxidation of RBAO compacts, liquid Al formation, and alpha alumina phase transformation during the RBAO process and their effect on final microstructure were investigated. Compact oxidation is controlled by heat transfer and the rate-controlling heat transfer mechanism is convection. Low heat transfer from the surface results in too rapid oxidation and a core-shell oxidation of the compact. The alpha-Al2O3 particles in the RBAO precursor behave like seed particles for the gamma to alpha alumina transformation in the RBAO process. Highly textured, dense alumina ceramics were fabricated by a new processing route which utilizes a mixture of Al metal powder, alpha alumina powder, alpha alumina platelet (template) particles and a liquid phase former. Texture development in liquid-phase sintered RBAO ceramics was studied during templated grain growth (TGG); a technique for developing crystallographic texture in ceramic bodies via the grain growth of aligned anisometric particles in a dense and fine grain size matrix. The process of TGG occurs in 3 stages: densification, initial growth of individual template particles, and template impingement and thickening. Texture development is directly related to the initial number of template particles and the inter-template spacing. The growth of alpha alumina template particles is anisotropic. Template growth in radial direction is controlled by diffusion through the liquid phase during a solution-precipitation growth process. Template growth in the thickness direction occurs by 2-D nucleation and growth.

  3. Oxidation behavior in reaction-bonded aluminum-silicon alloy/alumina powder compacts

    SciTech Connect

    Yokota, S.H.

    1992-12-01

    Goal of this research is to determine the feasibility of producing low-shrinkage mullite/alumina composites by applying the reaction-bonded alumina (RBAO) process to an aluminum-silicon alloy/alumina system. Mirostructural and compositional changes during heat treatment were studied by removing samples from the furnace at different steps in the heating schedule and then using optical and scanning electron microscopy, EDS and XRD to characterize the powder compacts. Results suggest that the oxidation behavior of the alloy compact is different from the model proposed for the pure Al/alumina system.

  4. Effects of aluminum and zirconia contents on the reaction bonded aluminum oxide process

    NASA Astrophysics Data System (ADS)

    Sheedy, Paul Martin

    The effects of aluminum and ZrO2 contents on the reaction and sintering of reaction bonded aluminum oxide (RBAO) were investigated. It was apparent that ZrO2-containing RBAO powders with higher initial aluminum contents (>45 vol%) were increasingly more difficult to react and sinter. During oxidation in air, samples often underwent a self-propagating high-temperature synthesis (SHS) reaction which led to catastrophic failure. This reaction and cracking behavior was more pronounced with increasing aluminum and ZrO2 contents of the powders. Subsequently, it was shown that the SHS reaction was actually two combustion phenomena: a thermal explosion reaction on the surface of the sample between aluminum and oxygen, which (in ZrO2-containing samples) triggered a self propagating aluminothermic reduction of ZrO2, forming Al2O3 and Al 3Zr. Therefore, methods for controlling the rate of the initial oxidation reaction were effective since both SHS reactions were prevented. Despite the use of controlled firing, initial samples with increasing aluminum contents proved difficult to densify. It was found that in all RBAO samples (regardless of ZrO2 content), the reactively formed Al 2O3 underwent the gamma to alpha-Al2O 3 transformation, which resulted in the development of a vermicular microstructure. In ZrO2-containing RBAO samples, this transformation was inhibited and occurred concurrently with the start of densification. In addition, the start of bulk shrinkage in these samples was delayed and the densification rates were decreased in comparison to samples without ZrO 2. This ultimately resulted in a decrease in the limiting density to which ZrO2-containing RBAO samples could be sintered. Surprisingly, in samples without ZrO2, increasing the aluminum content did not appear to have any effects upon the densification behavior of RBAO. In examining RBAO samples with similar aluminum contents but increasing ZrO2 contents, it became apparent that the grain growth inhibiting action of the ZrO2 prevented the complete removal of the vermicular microstructure. Thus, in ZrO2 containing RBAO samples with higher aluminum contents, where there was more reactively formed Al2O 3, the vermicular structure was even more difficult to eliminate.

  5. Reactions of fourth-period metal ions (Ca + - Zn + ) with O2: Metal-oxide ion bond energies

    NASA Astrophysics Data System (ADS)

    Fisher, Ellen R.; Elkind, J. L.; Clemmer, D. E.; Georgiadis, R.; Loh, S. K.; Aristov, N.; Sunderlin, L. S.; Armentrout, P. B.

    1990-08-01

    Reactions of Ca+, Zn+ and all first-row atomic transition metal ions with O2 are studied using guided ion beam techniques. While reactions of the ground states of Sc+, Ti+, and V+ are exothermic, the remaining metal ions react with O2 in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M+-O bond energies for these eight elements. Source conditions are varied such that the contributions of excited states of the metal ions can be explicitly considered for Mn+, Co+, Ni+, and Cu+. Results (in eV) at 0 K are D0(Ca+-O)= 3.57±0.05, D0(Cr+-O)=3.72±0.12, D0(Mn+-O)=2.95±0.13, D0(Fe+-O)=3.53±0.06 (reported previously), D0(Co+-O)=3.32±0.06, D0(Ni+-O) =2.74±0.07, D0(Cu+-O)=1.62±0.15, and D0(Zn+-O)=1.65±0.12. These values along with literature data for neutral metal oxide bond energies and ionization energies are critically evaluated. Periodic trends in the ionic metal oxide bond energies are compared with those of the neutral metal oxides and those of other related molecules.

  6. Catalytic anisotropy of MoO/sub 3/ in oxidation reactions in the light of bond-strength model of active sites

    SciTech Connect

    Ziolkowski, J.

    1983-04-01

    Catalytic anisotropy of molybdic oxide in oxidation of propylene has been observed. High selectivity to acrolein in the indicated reaction was ascribed to the (100) plane while the (010) plane was found to yield CO/sub 2/. The critical discussion of Volta's experimental data, performed in this paper, has shown that they may be interpreted in three alternative ways, differing in the ascription of the reaction products to the crystallographic planes. Different crystallographic planes exposed by the grains of MoO/sub 3/ have been analyzed in terms of the bond-strength model of active sites developed under the following main assumptions: (i) the reaction path depends on the number and configuration of the active oxygen atoms in the vicinity of the adsorption site, and (ii) the individual catalytic activity of a given surface oxygen atom is proportional to the reciprocal sum of the strength of the bonds to it from the adjacent cations. The analysis provided the arguments to indicate the most probable reaction pattern. According to it the main products expected to be formed in oxidation of propylene on different planes of MoO/sub 3/ are (100), CO, CO/sub 2/; (001), acrolein (acrylic acid, C/sub 2/-O, CO, CO/sub 2/--mainly at longer contact time); (101) and (101), acrolein; (010), inactive (possible minor yield of hexadiene and benzene).

  7. Reaction bonding of ceramics by gas-metal reactions

    SciTech Connect

    Derby, B. [Univ. of Oxford (United Kingdom)

    1995-09-01

    Reaction bonding may offer the potential for low final shrinkage ceramic processing using composite reactive metal and ceramic filler green bodies. However the process is shown to consist of two distinct steps of initial reaction leading to volume expansion followed by a second sintering step, often at a higher temperature, which leads to shrinkage. By careful choice of green compact composition and relative density it is possible to achieve zero final shrinkage. Control of the process to achieve zero-shrinkage is difficult because the initial powder milling leads to some metal pre-oxidation.

  8. Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

    SciTech Connect

    Klobukowski, Erik

    2011-12-29

    This work involves two projects. The first project entails the study of bulk gold as a catalyst in oxidation reactions of isocyanides and amines. The main goal of this project was to study the activation and reactions of molecules at metal surfaces in order to assess how organometallic principles for homogeneous processes apply to heterogeneous catalysis. Since previous work had used oxygen as an oxidant in bulk gold catalyzed reactions, the generality of gold catalysis with other oxidants was examined. Amine N-oxides were chosen for study, due to their properties and use in the oxidation of carbonyl ligands in organometallic complexes. When amine N-oxides were used as an oxidant in the reaction of isocyanides with amines, the system was able to produce ureas from a variety of isocyanides, amines, and amine N-oxides. In addition, the rate was found to generally increase as the amine N-oxide concentration increased, and decrease with increased concentrations of the amine. Mechanistic studies revealed that the reaction likely involves transfer of an oxygen atom from the amine N-oxide to the adsorbed isocyanide to generate an isocyanate intermediate. Subsequent nucleophilic attack by the amine yields the urea. This is in contrast to the bulk gold-catalyzed reaction mechanism of isocyanides with amines and oxygen. Formation of urea in this case was proposed to proceed through a diaminocarbene intermediate. Moreover, formation of the proposed isocyanate intermediate is consistent with the reactions of metal carbonyl ligands, which are isoelectronic to isocyanides. Nucleophilic attack at coordinated CO by amine N-oxides produces CO{sub 2} and is analogous to the production of an isocyanate in this gold system. When the bulk gold-catalyzed oxidative dehydrogenation of amines was examined with amine N-oxides, the same products were afforded as when O{sub 2} was used as the oxidant. When the two types of oxidants were directly compared using the same reaction system and conditions, it was found that the oxidative dehydrogenation of dibenzylamine to Nbenzylidenebenzylamine, with N-methylmorpholine N-oxide (NMMO), was nearly quantitative (96%) within 24 h. However, the reaction with oxygen was much slower, with only a 52% yield of imine product over the same time period. Moreover, the rate of reaction was found to be influenced by the nature of the amine N-oxide. For example, the use of the weakly basic pyridine N-oxide (PyNO) led to an imine yield of only 6% after 24 h. A comparison of amine N-oxide and O2 was also examined in the oxidation of PhCH{sub 2}OH to PhCHO catalyzed by bulk gold. In this reaction, a 52% yield of the aldehyde was achieved when NMMO was used, while only a 7% product yield was afforded when O{sub 2} was the oxidant after 48 h. The bulk gold-catalyzed oxidative dehydrogenation of cyclic amines generates amidines, which upon treatment with Aerosil and water were found to undergo hydrolysis to produce lactams. Moreover, 5-, 6-, and 7-membered lactams could be prepared through a one-pot reaction of cyclic amines by treatment with oxygen, water, bulk gold, and Aerosil. This method is much more atom economical than industrial processes, does not require corrosive acids, and does not generate undesired byproducts. Additionally, the gold and Aerosil catalysts can be readily separated from the reaction mixture. The second project involved studying iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, as a homogeneous catalyst for the generation of carbenes from diazo reagents and their reaction with heteroatom compounds. Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols. Fe(TPP)Cl was also found to be an effective catalyst for tandem N-H and O-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents. This approach provides a one-pot process for synthesizing piperazinones and morpholinones and related analogues such as quinoxalinones and benzoxazin-2-ones.

  9. Thermodynamic and kinetic study of cleavage of the N-O bond of N-oxides by a vanadium(III) complex: enhanced oxygen atom transfer reaction rates for adducts of nitrous oxide and mesityl nitrile oxide.

    PubMed

    Palluccio, Taryn D; Rybak-Akimova, Elena V; Majumdar, Subhojit; Cai, Xiaochen; Chui, Megan; Temprado, Manuel; Silvia, Jared S; Cozzolino, Anthony F; Tofan, Daniel; Velian, Alexandra; Cummins, Christopher C; Captain, Burjor; Hoff, Carl D

    2013-07-31

    Thermodynamic, kinetic, and computational studies are reported for oxygen atom transfer (OAT) to the complex V(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2, 1) from compounds containing N-O bonds with a range of BDEs spanning nearly 100 kcal mol(-1): PhNO (108) > SIPr/MesCNO (75) > PyO (63) > IPr/N2O (62) > MesCNO (53) > N2O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene; Py = pyridine; IPr = 1,3-bis(diisopropyl)phenylimidazol-2-ylidene; dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene). Stopped flow kinetic studies of the OAT reactions show a range of kinetic behavior influenced by both the mode and strength of coordination of the O donor and its ease of atom transfer. Four categories of kinetic behavior are observed depending upon the magnitudes of the rate constants involved: (I) dinuclear OAT following an overall third order rate law (N2O); (II) formation of stable oxidant-bound complexes followed by OAT in a separate step (PyO and PhNO); (III) transient formation and decay of metastable oxidant-bound intermediates on the same time scale as OAT (SIPr/MesCNO and IPr/N2O); (IV) steady-state kinetics in which no detectable intermediates are observed (dbabhNO and MesCNO). Thermochemical studies of OAT to 1 show that the V-O bond in O?V(N[t-Bu]Ar)3 is strong (BDE = 154 ± 3 kcal mol(-1)) compared with all the N-O bonds cleaved. In contrast, measurement of the N-O bond in dbabhNO show it to be especially weak (BDE = 10 ± 3 kcal mol(-1)) and that dissociation of dbabhNO to anthracene, N2, and a (3)O atom is thermodynamically favorable at room temperature. Comparison of the OAT of adducts of N2O and MesCNO to the bulky complex 1 show a faster rate than in the case of free N2O or MesCNO despite increased steric hindrance of the adducts. PMID:23805977

  10. Transition-metal-free oxidative carboazidation of acrylamides via cascade C-N and C-C bond-forming reactions.

    PubMed

    Qiu, Jun; Zhang, Ronghua

    2014-07-01

    A novel transition-metal-free oxidative carboazidation of acrylamides using inexpensive NaN3 and K2S2O8 was achieved, which not only provided an efficient method to prepare various N3-substituted oxindoles, but also represented a novel strategy for C-N and C-C bond formation via a free-radical cascade process. This transformation exhibits excellent functional group tolerance, affording the desired oxindoles in good to excellent yields. PMID:24854242

  11. Effect of processing parameters on reaction bonding of silicon nitride

    NASA Technical Reports Server (NTRS)

    Richman, M. H.; Gregory, O. J.; Magida, M. B.

    1980-01-01

    Reaction bonded silicon nitride was developed. The relationship between the various processing parameters and the resulting microstructures was to design and synthesize reaction bonded materials with improved room temperature mechanical properties.

  12. Reaction-bonded Si3N4 and SiC matrix composites

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.; Behrendt, Donald R.

    1992-01-01

    A development status evaluation is presented for the reaction-bonded SiC- and Si3N4-matrix types of fiber-reinforced ceramic-matrix composite (FRCMC). A variety of reaction-bonding methods are being pursued for FRCMC fabrication: CVI, CVD, directed metal oxidation, and self-propagating high-temperature synthesis. Due to their high specific modulus and strength, toughness, and fabricability, reaction-bonded FRCMC are important candidate materials for such heat-engine components as combustor liners, nozzles, and turbine and stator blading. The improvement of long-term oxidative stability in these composites is a major goal of current research.

  13. Photoinitiated reactions in weakly bonded complexes

    SciTech Connect

    Wittig, C.

    1993-05-01

    This paper discusses photoinitiated reactions in weakly bonded binary complexes in which the constituents are only mildly perturbed by the intermolecular bond. Such complexes, with their large zero point excursions, set the stage for events that occur following electronic excitation of one of the constituents. This can take several forms, but in all cases, entrance channel specificity is imposed by the character of the complex as well as the nature of the photoinitiation process. This has enabled us to examine aspects of bimolecular processes: steric effects, chemical branching ratios, and inelastic scattering. Furthermore, monitoring reactions directly in the time domain can reveal mechanisms that cannot be inferred from measurements of nascent product excitations. Consequently, we examined several systems that had been studied previously by our group with product state resolution. With CO{sub 2}/HI, in which reaction occurs via a HOCO intermediate, the rates agree with RRKM predictions. With N{sub 2}O/HI, the gas phase single collision reaction yielding OH + N{sub 2} has been shown to proceed mainly via an HNNO intermediate that undergoes a 1,3-hydrogen shift to the OH + N{sub 2} channel. With complexes, ab initio calculations and high resolution spectroscopic studies of analogous systems suggest that the hydrogen, while highly delocalized, prefers the oxygen to the nitrogen. We observe that OH is produced with a fast risetime (< 250 fs) which can be attributed to either direct oxygen-side attack or rapid HNNO decomposition and/or a termolecular contribution involving the nearby iodine.

  14. Boron oxides: Ab initio studies with natural bond orbital analysis

    Microsoft Academic Search

    A. V. Nemukhin; F. Weinhold

    1993-01-01

    We employ abinitio theory and natural bond orbital (NBO) analysis to describe the structure, energetics, vibrational properties, and bonding in small boron oxides, BmOn, supplementing recent studies on isovalent aluminum oxide clusters, Al2On, in order to extend the overview of bonding tendencies in group IIIA metal oxides. The comparison of analogous boron and aluminum species reveals many surprising differences, such

  15. Aqueous phase C-H bond oxidation reaction of arylalkanes catalyzed by a water-soluble cationic Ru(III) complex [(pymox-Me2)2RuCl2]+BF4-.

    PubMed

    Yi, Chae S; Kwon, Ki-Hyeok; Lee, Do W

    2009-04-01

    The cationic complex [(pymox-Me(2))RuCl(2)](+)BF(4)(-) was found to be a highly effective catalyst for the C-H bond oxidation reaction of arylalkanes in water. For example, the treatment of ethylbenzene (1.0 mmol) with t-BuOOH (3.0 mmol) and 1.0 mol % of the Ru catalyst in water (3 mL) cleanly produced PhCOCH(3) at room temperature. Both a large kinetic isotope effect (k(H)/k(D) = 14) and a relatively large Hammett value (rho = -1.1) suggest a solvent-caged oxygen rebounding mechanism via a Ru(IV)-oxo intermediate species. PMID:19245262

  16. One-electron oxidation of DNA: reaction at thymine.

    PubMed

    Joseph, Joshy; Schuster, Gary B

    2010-11-14

    The feature article is a review of the reaction of thymine in the one-electron oxidation of duplex DNA. Oxidation of DNA causes chemical reactions that result in remote damage (mutation) to a nucleobase. Normally this reaction occurs at guanine, but in oligonucleotides that lack guanines, or when the DNA contains a thymine-thymine mispair, reaction occurs primarily at thymine notwithstanding its high oxidation potential. Selective substitution of uracil for thymine in TT sequences indicates the operation of a tandem reaction mechanism at adjacent thymines. Analysis of the reaction products suggests that proton-coupled electron transfer generates the 5-thymidyl methyl radical, which is trapped by molecular oxygen to give eventually 5-formyl-2'-deoxyuridine and 5-(hydroxymethyl)-2'-deoxyuridine. In a second process, water adds to the 5,6-double bond of the oxidized thymine giving eventually the cis- and trans-diastereomers of 5,6-dihydroxy-5,6-dihydrothymidine. PMID:20830420

  17. Synthesis of Spirocyclic Pyrazolones by Oxidative C-N Bond Formation.

    PubMed

    Agejas, Javier; Ortega, Laura

    2015-06-19

    The two-step synthesis of spirocyclic pyrazolone derivatives from simple and commercially available reagents is described. The unusual reaction of 1,3-dicarbonyls with hydrazines and an iodine-mediated oxidative carbon-nitrogen bond formation, joined in a two-step, one-pot reaction, allows the straightforward synthesis of these spirocycles. PMID:26018762

  18. CO2-promoted oxidative cross-coupling reaction for C-S bond formation via masked strategy in an odourless way.

    PubMed

    Qiao, Zongjun; Ge, Nanyang; Jiang, Xuefeng

    2015-06-11

    Cu-catalyzed direct oxidative cross-coupling between boronic acids and masked sulfides delivering thioethers was described, in which the SO3(-), as a mask, has shown a distinctive effect on the oxidative cross-coupling condition. Disulfide could be suppressed efficiently via masked strategy under CO2 atmosphere. A broad scope of aromatics and scalable processes indicates its practicality, which could be further applied to drug late-stage modification and unsymmetrical dibenzothiophenes (DBTs) synthesis. PMID:26022891

  19. Reaction bonding of open cell SiCAl 2O 3 composites

    Microsoft Academic Search

    Xinwen Zhu; Dongliang Jiang; Shouhong Tan

    2001-01-01

    Based on the reaction-bonding aluminum oxide (RBAO) technology, open cell SiC-Al2O3 composites with high strength were fabricated from aqueous slurry by a replication process with polyurethane sponges as the substrates. TGA reveals that about 18 wt% of the initial Al powder in the start compositions oxidized after 1 h stirring. Mixing procedure has a strong effect on the slurry rheological

  20. Isotope Effects in C-H Bond Activation Reactions by

    E-print Network

    Jones, William D.

    Isotope Effects in C-H Bond Activation Reactions by Transition Metals WILLIAM D. JONES Department to occur via transient -alkane complexes. This Account summarizes how isotope effects can be used to probe, the subject of isotope effects in some of these reactions will be examined in detail, as these effects

  1. Chemistry of sulfur oxides on transition metal surfaces: a bond order conservation-Morse potential modeling perspective

    Microsoft Academic Search

    Harrell Sellers; Evgeny Shustorovich

    1996-01-01

    We have employed the bond order conservation-Morse potential (BOC-MP) method to analyze the chemistry of sulfur oxides on the copper and nickel group metals. Specifically, we have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation barriers) of the decomposition and oxidation of sulfur dioxide at low coverages on fcc (111) surfaces of Cu, Ag, Au, Ni,

  2. SULFUR DIOXIDE OXIDATION REACTIONS IN AQUEOUS SOLUTIONS

    EPA Science Inventory

    This is the final report on a three year project to study the kinetics and mechanisms of some 105 reactions involving the aqueous oxidation of sulfur dioxide and nitrogen oxides in mixed catalyst-oxidant systems at low pH (0-3). The 105 systems involve six redox reaction types: S...

  3. Dynamic fracture toughnesses of reaction-bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Kobayashi, A. S.; Emery, A. F.; Liaw, B. M.

    1983-01-01

    The room-temperature dynamic fracture response of reaction-bonded silicon nitride is investigated using a hybrid experimental-numerical procedure. In this procedure, experimentally determined crack velocities are utilized to drive a dynamic finite-element code or dynamic finite-difference code in its generation mode in order to extract numerically the dynamic stress intensity factor of the fracturing specimen. Results show that the dynamic fracture toughness vs crack velocity relations of the two reaction-bonded silicon nitrides do not follow the general trend in those relations of brittle polymers and steel. A definite slow crack velocity during the initial phase of dynamic crack propagation is observed in reaction-bonded silicon nitride, which results in a nonunique dynamic fracture toughness vs crack velocity relation. In addition, it is found that a propagating crack will continue to propagate under a static stress intensity factor substantially lower than K(IC).

  4. Nickel-catalysed P-C bond formation via P-H/C-CN cross coupling reactions.

    PubMed

    Zhang, Ji-Shu; Chen, Tieqiao; Yang, Jia; Han, Li-Biao

    2015-05-01

    Nickel-catalysed P-H/C-CN cross coupling reactions take place efficiently under mild reaction conditions affording the corresponding sp(2)C-P bonds. This transformation provides a convenient method for the preparation of arylphosphines and arylphosphine oxides from the readily available P-H compounds and arylnitriles. PMID:25845516

  5. Surface oxygen bond energy of Period IV transition metal oxides in the oxidation of carbon monoxide

    Microsoft Academic Search

    V. I. Marshneva; G. K. Boreskov

    1974-01-01

    The bond energies of oxygen have been determined by thermodesorption from Period IV transition metal oxides, both after treatment with oxygen and under steady state conditions of the catalytic oxidation of CO. With the exception of V2O5, there are several (2–3) forms of adsorbed oxygen with different bond energies on the surface of the oxide treated with oxygen.

  6. Reversible conversion of valence-tautomeric copper metal-organic frameworks dependent single-crystal-to-single-crystal oxidation/reduction: a redox-switchable catalyst for C-H bonds activation reaction.

    PubMed

    Huang, Chao; Wu, Jie; Song, Chuanjun; Ding, Ran; Qiao, Yan; Hou, Hongwei; Chang, Junbiao; Fan, Yaoting

    2015-06-11

    Upon single-crystal-to-single-crystal (SCSC) oxidation/reduction, reversible structural transformations take place between the anionic porous zeolite-like Cu(I) framework and a topologically equivalent neutral Cu(I)Cu(II) mixed-valent framework. The unique conversion behavior of the Cu(I) framework endowed it as a redox-switchable catalyst for the direct arylation of heterocycle C-H bonds. PMID:25994106

  7. Hydrogen-bond-assisted activation of allylic alcohols for palladium-catalyzed coupling reactions.

    PubMed

    Gumrukcu, Yasemin; de Bruin, Bas; Reek, Joost N H

    2014-03-01

    We report direct activation of allylic alcohols using a hydrogen-bond-assisted palladium catalyst and use this for alkylation and amination reactions. The novel catalyst comprises a palladium complex based on a functionalized monodentate phosphoramidite ligand in combination with urea additives and affords linear alkylated and aminated allylic products selectively. Detailed kinetic analysis show that oxidative addition of the allyl alcohol is the rate-determining step, which is facilitated by hydrogen bonds between the alcohol, the ligand functional group, and the additional urea additive. PMID:24436302

  8. Activation of CH Bonds:Stoichiometric Reactions William D. Jones

    E-print Network

    Jones, William D.

    Activation of C­H Bonds:Stoichiometric Reactions William D. Jones Department of Chemistry, University of Rochester, NY 14627 USA E-mail: jones@chem.rochester.edu The activation of hydrocarbon C . . . . . . . . . . . . . . . . . . . . . . . . 34 #12;10 William D. Jones 7 Arene Activation

  9. Oxygen-transfer reactions of methylrhenium oxides

    SciTech Connect

    Abu-Omar, M.M.; Espenson, J.H. [Iowa State Univ., Ames, IA (United States)] [Iowa State Univ., Ames, IA (United States); Appelman, E.H. [Argonne National Lab., IL (United States)] [Argonne National Lab., IL (United States)

    1996-12-18

    Methylrhenium dioxide, CH{sub 3}ReO{sub 2} (or MDO), is produced from methylrhenium trioxide, CH{sub 3}ReO{sub 3} (or MTO), and hypophosphorous acid in acidic aqueous medium. Its mechanism is discussed in light of MTO`s coordination ability and the inverse kinetic isotope effect (kie): H{sub 2}P(O)OH, k = 0.028 L mol{sup -1} s{sup -1}; D{sub 2}P(O)OH, k = 0.039 L mol{sup -1} s{sup -1}. The Re(V) complex, MDO, reduces perchlorate and other inorganic oxoanions (XO{sub n}{sup -}, where X = Cl, Br, or I and N = 4 or 3). The rate is controlled by the first oxygen abstraction from perchlorate to give chlorate, with a second-order rate constant at pH 0 and 25 {degrees}C of 7.3 L mol{sup -1} s{sup -1}. Organic oxygen-donors such as sulfoxides and pyridine N-oxides oxidize MDO to MTO as do metal oxo complexes: VO{sup 2+}{sub (aq)}, VO{sub 2}{sup +}{sub (aq)}, HOMoO{sub 2}{sup +}{sub (aq)}, and MnO{sub 4}{sup -}. The reaction between V{sup 2+}{sub (aq)} with MTO and the reduction of VO{sup 2+} with MDO made it possible to determine the free energy for MDO/MTO. Oxygen-atom transfer from oxygen-donors to MDO involves nucleophilic attack of X-O on the electrophilic Re(V) center of MDO; the reaction proceeds via an [MDO{center_dot}XO] adduct, which is supported by the saturation kinetics observed for some. The parameters that control and facilitate the kinetics of such oxygen-transfer processes are suggested and include the force constant for the asymmetric stretching of the element-oxygen bond.

  10. Diffusion bonding of the oxide dispersion strengthened steel PM2000

    NASA Astrophysics Data System (ADS)

    Sittel, Wiebke; Basuki, Widodo W.; Aktaa, Jarir

    2013-11-01

    Ferritic oxide dispersion strengthened (ODS) steels are well suited as structural materials, e.g. for claddings in fission reactors and for plasma facing components in fusion power plants due to their high mechanical and oxidation stability at high temperatures and their high irradiation resistance. PM2000 is an iron based ODS ferritic steel with homogeneously distributed nanometric yttria particles. Melting joining techniques are not suitable for such ODS materials because of the precipitation and agglomeration of the oxide particles and hence the loss of their strengthening effect. Solid state diffusion bonding is thus chosen to join PM2000 and is investigated in this work with a focus on oxide particles. The diffusion bonding process is aided by the computational modeling, including the influence of the ODS particles. For modeling the microstructure stability and the creep behavior of PM2000 at various, diffusion bonding relevant temperatures (50-80% Tm) are investigated. Particle distribution (TEM), strength (tensile test) and toughness (Charpy impact test) obtained at temperatures relevant for bonding serve as input for the prediction of optimal diffusion bonding parameters. The optimally bonded specimens show comparable strength and toughness relative to the base material.

  11. Tailoring oxidation degrees of graphene oxide by simple chemical reactions

    SciTech Connect

    Wang Gongkai [Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning 110004 (China); Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Sun Xiang; Lian Jie [Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Liu Changsheng [Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning 110004 (China)

    2011-08-01

    High quality graphene oxide (GO) with controllable degrees of oxidation was synthesized by simple chemical reactions inspired by approaches to unzip single wall carbon nanotubes using strong oxidizing agents. As compared to the conventional Hummers method, these reactions are less exo-therm involved without emission of toxic gases. The structural characteristics of the synthesized GO with various oxidation degrees were evaluated by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, thermal gravimetric analysis, and UV-vis-IR spectroscopy. GO with tailored degrees of oxidation displays tunable optoelectronic properties and may have a significant impact on developing graphene- or GO-based platforms for various technological applications.

  12. 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.

  13. Oxidative addition of the C-I bond on aluminum nanoclusters.

    PubMed

    Sengupta, Turbasu; Das, Susanta; Pal, Sourav

    2015-07-28

    Energetics and the in-depth reaction mechanism of the oxidative addition step of the cross-coupling reaction are studied in the framework of density functional theory (DFT) on aluminum nanoclusters. Aluminum metal in its bulk state is totally inactive towards carbon-halogen bond dissociation but selected Al nanoclusters (size ranging from 3 to 20 atoms) have shown a significantly lower activation barrier towards the oxidative addition reaction. The calculated energy barriers are lower than the gold clusters and within a comparable range with the conventional and most versatile Pd catalyst. Further investigations reveal that the activation energies and other reaction parameters are highly sensitive to the geometrical shapes and electronic structures of the clusters rather than their size, imposing the fact that comprehensive studies on aluminum clusters can be beneficial for nanoscience and nanotechnology. To understand the possible reaction mechanism in detail, the reaction pathway is investigated with the ab initio Born Oppenheimer Molecular Dynamics (BOMD) simulation and the Natural Bond Orbital (NBO) analysis. In short, our theoretical study highlights the thermodynamic and kinetic details of C-I bond dissociation on aluminum clusters for future endeavors in cluster chemistry. PMID:26123032

  14. Reaction of potassium superoxide with nitrogen oxide

    Microsoft Academic Search

    T. P. Firsova; E. Ya. Filatov

    1974-01-01

    1.A study was made of the reaction of technical potassium superoxide with nitrogen oxide (both pure and diluted with argon).2.The process proceeds at considerable speeds at the start, with a subsequent rapid slowing up and then a complete cessation of the reaction.3.The reaction goes with the formation of potassium nitrite as the main reaction product and potassium nitrate as the

  15. Metal-Free Preparation of Cycloalkyl Aryl Sulfides via Di-tert-butyl Peroxide-Promoted Oxidative C(sp3)[BOND]H Bond Thiolation of Cycloalkanes

    PubMed Central

    Zhao, Jincan; Fang, Hong; Han, Jianlin; Pan, Yi; Li, Guigen

    2014-01-01

    A concise thiolation of C(sp3)–H bond of cycloalkanes with diaryl disulfides in the presence of oxidant of di-tert-butylperoxide (DTBP) has been developed. This reaction without using any of metal catalyst, tolerates varieties of disulfides and cycloalkanes substrates, giving good to excellent chemical yields, which provides a useful approach to cycloalkyl aryl sulfides from unactivated cycloalkanes. PMID:25505857

  16. Transient liquid phase bonding of ferritic oxide dispersion strengthened alloys

    NASA Astrophysics Data System (ADS)

    Krishnardula, Venu Gopal

    2006-04-01

    Oxide dispersion strengthened (ODS) alloys possess excellent properties including resistance to oxidation, corrosion, creep and thermal fatigue. In addition, ferritic ODS alloys exhibit resistance to void swelling and are of particular interest to the nuclear industry. The present study involves the joining of fuel cans to end caps that will be utilized in the nuclear industry. Mechanically alloyed (MA) ODS alloys possess coarse columnar grain structure strengthened with nanosize yttria dispersoids. In that past, fusion welding techniques resulted in microstructural disruption leading to poor joints. This work investigated joining of two ferritic MA ODS alloys, MA956 and PM2000, using; (a) Transient liquid phase (TLP) bonding and (b) Solid-state diffusion bonding. TLP bonds were prepared with MA956 and PM2000 in the unrecrystallized and recrystallized conditions using electron beam physical vapor deposited (EBPVD) boron thin films as interlayers. The use of thin interlayers reduced the amount of substrate dissolution and minimized the bondline microstructural disruption. Different bond orientations were also investigated. Successful bonds with better microstructural continuity were obtained when substrates were joined in the unrecrystallized condition followed by post bond recrystallization heat treatment with the substrate faying surface aligned along the working (extrusion or rolling) direction than when substrates were aligned perpendicular to the working direction. This was attributed to the number of yttria stringers cut by the bondline, which is less when the substrate faying surface is lying parallel to the working direction than when the substrate faying surface is lying perpendicular to the working direction. Solid-state diffusion bonding was conducted using MA956 and PM2000 in the unrecrystallized and recrystallized conditions. Bonding occurred only when an unrecrystallized substrate was involved. Bonding occurred at unusually low stresses. This may be attributed to the grain boundary diffusion, owing to submicron grain size of the unrecrystallized substrates. Post bond heat treatment was conducted in order to induce recrystallization in the bonds. Room temperature mechanical testing was conducted on the bonds and the bulk. Bond shear strengths and tensile strengths of up to 80% and 110% of bulk, respectively, were obtained. Defects in the bulk material such as porosity and unwanted fine grain formation were observed. Pore formation at the bondline during post bond heat treatment seems to decrease the bond strength. These defects were attributed to prior thermomechanical history of the materials.

  17. Comparison of the Catalytic Oxidation Reaction on Graphene Oxide and Reduced Graphene Oxide

    E-print Network

    Kim, Sehun

    Comparison of the Catalytic Oxidation Reaction on Graphene Oxide and Reduced Graphene Oxide Laboratory (PAL), Pohang 790-784, Republic of Korea ABSTRACT: The capacities of graphene oxide (GO) and reduced graphene oxide (rGO) films grown on silicon substrate to cause the aniline to azobenzene oxidation

  18. Fabrication of low-to-zero shrinkage reaction-bonded mullite composites

    Microsoft Academic Search

    Dietmar Holz; Sonja Pagel; Chris Bowen; Suxing Wu; Nils Claussen

    1996-01-01

    The technology of reaction bonding Al2O3 (RBAO) can be modified by the use of Si-containing additives to yield low-to-zero shrinkage mullite composites. In the present work, SiC particles were added to the Al\\/Al2O3 precursor mixture. During air heat-treatment, first Al oxidizes to Al2O3 at 300–900 °C, thereafter SiC converts to SiO2 (900–1200 °C). Both phases form mullite (3Al2O3· SiO2) at

  19. Graphite Oxidation Thermodynamics/Reactions

    SciTech Connect

    Propp, W.A.

    1998-09-01

    The vulnerability of graphite-matrix spent nuclear fuel to oxidation by the ambient atmosphere if the fuel canister is breached was evaluated. Thermochemical and kinetic data over the anticipated range of storage temperatures (200 to 400 C) were used to calculate the times required for a total carbon mass loss of 1 mgcm-2 from a fuel specimen. At 200 C, the time required to produce even this small loss is large, 900,000 yr. However, at 400 C the time required is only 1.9 yr. The rate of oxidation at 200 C is negligible, and the rate even at 400 C is so small as to be of no practical consequence. Therefore, oxidation of the spent nuclear fuel upon a loss of canister integrity is not anticipated to be a concern based upon the results of this study.

  20. Low temperature direct bonding mechanisms of tetraethyl orthosilicate based silicon oxide films deposited by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Sabbione, C.; Di Cioccio, L.; Vandroux, L.; Nieto, J.-P.; Rieutord, F.

    2012-09-01

    Bonding behaviour and surface adhesion mechanisms of tetraethyl orthosilicate silicon oxide films are investigated. Prior to the bonding, infrared absorption spectroscopy was used to assess chemical composition of the bonding layers. The incorporation of -OH groups during the deposition process and the moisture absorption is shown and a specific effect of the applied RF power is highlighted. A strong correlation is found between trapped species and the evolution of the bonded layers during subsequent thermal annealing. The first observed phenomenon is an overall hardness reduction of the film deposited at low RF power which results in an increase of local adhesion area, hence an enhancement of the bonding energy. In the meantime, in this configuration water production is promoted in the volume of the film through silanol condensation and silicon oxidation occurs at the interface between the bonding layer and the silicon bulk. As a by-product of this reaction, hydrogen is released and it migrates towards the bonding interface. As a consequence, defects appear at the bonding interface. Thanks to the use of a stop barrier at the bulk interface, silicon oxidation is prevented, defect free bonding is obtained and the described scenario is confirmed.

  1. O-H bond oxidation by a monomeric Mn(III)-OMe complex.

    PubMed

    Wijeratne, Gayan B; Day, Victor W; Jackson, Timothy A

    2015-02-21

    Manganese-containing, mid-valent oxidants (Mn(III)-OR) that mediate proton-coupled electron-transfer (PCET) reactions are central to a variety of crucial enzymatic processes. The Mn-dependent enzyme lipoxygenase is such an example, where a Mn(III)-OH unit activates fatty acid substrates for peroxidation by an initial PCET. This present work describes the quantitative generation of the Mn(III)-OMe complex, [Mn(III)(OMe)(dpaq)](+) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate) via dioxygen activation by [Mn(II)(dpaq)](+) in methanol at 25 °C. The X-ray diffraction structure of [Mn(III)(OMe)(dpaq)](+) exhibits a Mn-OMe group, with a Mn-O distance of 1.825(4) Å, that is trans to the amide functionality of the dpaq ligand. The [Mn(III)(OMe)(dpaq)](+) complex is quite stable in solution, with a half-life of 26 days in MeCN at 25 °C. [Mn(III)(OMe)(dpaq)](+) can activate phenolic O-H bonds with bond dissociation free energies (BDFEs) of less than 79 kcal mol(-1) and reacts with the weak O-H bond of TEMPOH (TEMPOH = 2,2'-6,6'-tetramethylpiperidine-1-ol) with a hydrogen/deuterium kinetic isotope effect (H/D KIE) of 1.8 in MeCN at 25 °C. This isotope effect, together with other experimental evidence, is suggestive of a concerted proton-electron transfer (CPET) mechanism for O-H bond oxidation by [Mn(III)(OMe)(dpaq)](+). A kinetic and thermodynamic comparison of the O-H bond oxidation reactivity of [Mn(III)(OMe)(dpaq)](+) to other M(III)-OR oxidants is presented as an aid to gain more insight into the PCET reactivity of mid-valent oxidants. In contrast to high-valent counterparts, the limited examples of M(III)-OR oxidants exhibit smaller H/D KIEs and show weaker dependence of their oxidation rates on the driving force of the PCET reaction with O-H bonds. PMID:25597362

  2. Ammonia, oxidation leaching of chalcopyrite —reaction kinetics

    Microsoft Academic Search

    L. W. Beckstead; J. D. Miller

    1977-01-01

    The reaction for the ammonia, oxidation leaching of chalcopyrite, CuFeS2 + 4NH3 + 17\\/4 O2 + 2 OH- ? Cu(NH3)+2\\u000a 42 + l\\/2Fe2O3 + 2 SO4 + H2O was studied using monosize particles in an intensely stirred reactor under moderate pressures to determine the important\\u000a chemical factors which govern the kinetic response of the system. The reaction kinetics were studied

  3. Primary retention following nuclear recoil in ?-decay: Proposed synthesis of a metastable rare gas oxide ((38)ArO4) from ((38)ClO4(-)) and the evolution of chemical bonding over the nuclear transmutation reaction path.

    PubMed

    Timm, Matthew J; Matta, Chérif F

    2014-12-01

    Argon tetroxide (ArO4) is the last member of the N=50 e(-) isoelectronic and isosteric series of ions: SiO4(4-), PO4(3-), SO4(2-), and ClO4(-). A high level computational study demonstrated that while ArO4 is kinetically stable it has a considerable positive enthalpy of formation (of ~298kcal/mol) (Lindh et al., 1999. J. Phys. Chem. A 103, pp. 8295-8302) confirming earlier predictions by Pyykkö (1990. Phys. Scr. 33, pp. 52-53). ArO4 can be expected to be difficult to synthesize by traditional chemistry due to its metastability and has not yet been synthesized at the time of writing. A computational investigation of the changes in the chemical bonding of chlorate (ClO4(-)) when the central chlorine atom undergoes a nuclear transmutation from the unstable artificial chlorine isotope (38)Cl to the stable rare argon isotope (38)Ar through ?-decay, hence potentially leading to the formation of ArO4, is reported. A mathematical model is presented that allows for the prediction of yields following the recoil of a nucleus upon ejecting a ?-electron. It is demonstrated that below a critical angle between the ejected ?-electron and that of the accompanying antineutrino their respective linear momentums can cancel to such an extent as imparting a recoil to the daughter atom insufficient for breaking the Ar-O bond. As a result, a primary retention yield of ~1% of ArO4 is predicted following the nuclear disintegration. The study is conducted at the quadratic configuration interaction with single and double excitations [QCISD/6-311+G(3df)] level of theory followed by an analysis of the electron density by the quantum theory of atoms in molecules (QTAIM). Crossed potential energy surfaces (PES) were used to construct a PES from the metastable ArO4 ground singlet state to the Ar-O bond dissociation product ArO3+O((3)P) from which the predicted barrier to dissociation is ca. 22kcal/mol and the exothermic reaction energy is ca. 28kcal/mol [(U)MP2/6-311+G(d)]. PMID:25222874

  4. Palladium- and Nickel-Catalyzed Carbon–Carbon Bond Insertion Reactions with Alkylidenesilacyclopropanes

    PubMed Central

    Buchner, Kay M.; Woerpel, K. A.

    2010-01-01

    Palladium and nickel catalysts promoted highly selective carbon–carbon bond insertion reactions with di-tert-butyl-alkylidenesilacyclopropanes. Pd(PPh3)4 was demonstrated to be the optimal catalyst, allowing for a variety of carbon–carbon ?-bond insertion reactions. Depending on the nature of the carbon–carbon ? bond, the insertion reaction proceeded with either direct insertion into the carbon(sp2)–silicon bond or with allylic transposition. Ring-substituted alkylidenesilacyclopropanes required a nickel catalyst to afford insertion products. Using Ni(cod)2 as the carbon–carbon bond insertion catalyst, new double alkyne insertion products and alkene isomerization products were observed. PMID:20419110

  5. Hydrogen Bonding in Phosphine Oxide\\/Phosphate-Phenol Complexes

    Microsoft Academic Search

    Ruud Cuypers; Ernst J. R. Sudhölter; Han Zuilhof

    2010-01-01

    To develop a new solvent-impregnated resin (SIR) system for the removal of phenols and thiophenols from water, complex formation by hydrogen bonding of phosphine oxides and phosphates is studied using isothermal titration calorimetry (ITC) and quantum chemical modeling. Six different computational methods are used: B3LYP, M06-2X, MP2, spin component-scaled (SCS) MP2 [all four with 6-311+G(d,p) basis set], a complete basis

  6. Effects of Cu and Pd addition on Au bonding wire/Al pad interfacial reactions and bond reliability

    NASA Astrophysics Data System (ADS)

    Gam, Sang-Ah; Kim, Hyoung-Joon; Cho, Jong-Soo; Park, Yong-Jin; Moon, Jeong-Tak; Paik, Kyung-Wook

    2006-11-01

    Finer pitch wire bonding technology has been needed since chips have more and finer pitch I/Os. However, finer Au wires are more prone to Au-Al bond reliability and wire sweeping problems when molded with epoxy molding compound. One of the solutions for solving these problems is to add special alloying elements to Au bonding wires. In this study, Cu and Pd were added to Au bonding wire as alloying elements. These alloyed Au bonding wires—Au-1 wt.% Cu wire and Au-1 wt.% Pd wire—were bonded on Al pads and then subsequently aged at 175°C and 200°C. Cu and Pd additions to Au bonding wire slowed down interfacial reactions and crack formation due to the formation of a Cu-rich layer and a Pd-rich layer at the interface. Wire pull testing (WPT) after thermal aging showed that Cu and Pd addition enhanced bond reliability, and Cu was more effective for improving bond reliability than Pd. In addition, comparison between the results of observation of interfacial reactions and WPT proved that crack formation was an important factor to evaluate bond reliability.

  7. Reaction of Sc + , Ti + , and V + with CO. MC + and MO + bond energies

    NASA Astrophysics Data System (ADS)

    Clemmer, D. E.; Elkind, J. L.; Aristov, N.; Armentrout, P. B.

    1991-09-01

    The reactions of Sc+, Ti+, and V+ with CO are studied as a function of translational energy in a guided-ion-beam tandem mass spectrometer. Formation of both metal-carbide and metal-oxide ions are observed and rationalized by a direct atom abstraction mechanism. At high energies, the ScC+ and ScO+ cross sections exhibit additional features that are unusual but can be explained by an impulsive pairwise mechanism and formation of excited-state product ions, respectively. Thresholds of the reaction cross sections are interpreted to give the 0 K bond energies (in eV) D0(ScC+)=3.34±0.06, D0(TiC+)=4.05±0.24, D0(VC+)=3.87±0.14, D0(ScO+)=7.11±0.08, D0(TiO+)=6.88±0.07, and D0(VO+)=5.81±0.17. Additional studies are used to help verify the bond energy for ScO+ and yield a recommended value of 7.14±0.11 eV. The nature of the bonding in MO+ and MC+ is discussed and compared for these three metal ions.

  8. If C–H Bonds Could Talk – Selective C–H Bond Oxidation

    PubMed Central

    Newhouse, Timothy; Baran, Phil S.

    2014-01-01

    C–H oxidation has a long history and an ongoing presence in research at the forefront of chemistry and interrelated fields. As such, numerous highly useful texts and reviews have been written on this subject. Logically, these are generally written from the perspective of the scope and limitations of the reagents employed. This minireview instead attempts to emphasize chemoselectivity imposed by the nature of the substrate. Consequently many landmark discoveries in the field of C–H oxidation are not discussed, but hopefully the perspective taken herein will allow for the more ready incorporation of C–H oxidation reactions into synthetic planning. PMID:21413105

  9. The Mechanism of N?O Bond Cleavage in Rhodium-Catalyzed C?H Bond Functionalization of Quinoline N-oxides with Alkynes: A Computational Study.

    PubMed

    Li, Yingzi; Liu, Song; Qi, Zisong; Qi, Xiaotian; Li, Xingwei; Lan, Yu

    2015-07-01

    Metal-catalyzed C?H activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N-oxide is used as an arene source in C?H activation studies, the N?O bond can act as a directing group as well as an O-atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline N?O bond and alkynes, which results in C?H activation and O-atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a Rh?C bond, a reductive elimination to form an oxazinoquinolinium-coordinated Rh(I) intermediate, an oxidative addition to break the N?O bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop-1-yn-1-ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1-phenyl-2-quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity-determining step. These calculated data are consistent with the experimental observations. PMID:26059235

  10. Metal-Free Intermolecular Oxidative C-N Bond Formation via Tandem C-H and N-H Bond Functionalization

    PubMed Central

    Kantak, Abhishek A.; Potavathri, Shathaverdhan; Barham, Rose A.; Romano, Kaitlyn M.

    2011-01-01

    The development of a novel intermolecular oxidative amination reaction, a synthetic transformation that involves the simultaneous functionalization of both an N-H and C-H bond, is described. The process, which is mediated by an I(III) oxidant and contains no metal catalysts, provides a rapid and green method for synthesizing protected anilines from simple arenes and phthalimide. Mechanistic investigations indicate that the reaction proceeds via nucleophilic attack of the phthalimide on an aromatic radical cation, as opposed to the electrophilic aromatic amination that has been reported for other I(III) amination reactions. The application of this new reaction to the synthesis of a variety of substituted aniline derivatives is demonstrated. PMID:22010982

  11. Oxidation reactions on neutral cobalt oxide clusters: experimental and theoretical studies

    E-print Network

    Rocca, Jorge J.

    Oxidation reactions on neutral cobalt oxide clusters: experimental and theoretical studies Yan Xie.1039/b915590b Reactions of neutral cobalt oxide clusters (ComOn, m = 3­9, n = 3­13) with CO, NO, C2H2 the oxidation reactions; the Co3O4 cluster has the highest reactivity for reactions with CO and NO. Cluster

  12. Surface Femtochemistry: Investigation and Optimization of Bond-Forming Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Nuernberger, Patrick; Wolpert, Daniel; Weiss, Horst; Gerber, Gustav

    We investigate femtosecond laser-induced surface reactions by varying the properties of the surface, the reactant gases, and the laser. In optimal control experiments, we selectively manipulate the bond-forming catalytic reactions.

  13. Designing catalysts for functionalization of unactivated C-H bonds based on the CH activation reaction.

    PubMed

    Hashiguchi, Brian G; Bischof, Steven M; Konnick, Michael M; Periana, Roy A

    2012-06-19

    In an effort to augment or displace petroleum as a source of liquid fuels and chemicals, researchers are seeking lower cost technologies that convert natural gas (largely methane) to products such as methanol. Current methane to methanol technologies based on highly optimized, indirect, high-temperature chemistry (>800 °C) are prohibitively expensive. A new generation of catalysts is needed to rapidly convert methane and O(2) (ideally as air) directly to methanol (or other liquid hydrocarbons) at lower temperatures (~250 °C) and with high selectivity. Our approach is based on the reaction between CH bonds of hydrocarbons (RH) and transition metal complexes, L(n)M-X, to generate activated L(n)M-R intermediates while avoiding the formation of free radicals or carbocations. We have focused on the incorporation of this reaction into catalytic cycles by integrating the activation of the CH bond with the functionalization of L(n)M-R to generate the desired product and regenerate the L(n)M-X complex. To avoid free-radical reactions possible with the direct use of O(2), our approach is based on the use of air-recyclable oxidants. In addition, the solvent serves several roles including protection of the product, generation of highly active catalysts, and in some cases, as the air-regenerable oxidant. We postulate that there could be three distinct classes of catalyst/oxidant/solvent systems. The established electrophilic class combines electron-poor catalysts in acidic solvents that conceptually react by net removal of electrons from the bonding orbitals of the CH bond. The solvent protects the CH(3)OH by conversion to more electron-poor [CH(3)OH(2)](+) or the ester and also increases the electrophilicity of the catalyst by ligand protonation. The nucleophilic class matches electron-rich catalysts with basic solvents and conceptually reacts by net donation of electrons to the antibonding orbitals of the CH bond. In this case, the solvent could protect the CH(3)OH by deprotonation to the more electron-rich [CH(3)O](-) and increases the nucleophilicity of the catalysts by ligand deprotonation. The third grouping involves ambiphilic catalysts that can conceptually react with both the HOMO and LUMO of the CH bond and would typically involve neutral reaction solvents. We call this continuum base- or acid-modulated (BAM) catalysis. In this Account, we describe our efforts to design catalysts following these general principles. We have had the most success with designing electrophilic systems, but unfortunately, the essential role of the acidic solvent also led to catalyst inhibition by CH(3)OH above ~1 M. The ambiphilic catalysts reduced this product inhibition but were too slow and inefficient. To date, we have designed new base-assisted CH activation and L(n)M-R fuctionalization reactions and are working to integrate these into a complete, working catalytic cycle. Although we have yet to design a system that could supplant commercial processes, continued exploration of the BAM catalysis continuum may lead to new systems that will succeed in addressing this valuable goal. PMID:22482496

  14. Rules of Stereoselectivity in Tandem Oxidative Polycyclization Reaction with Rhenium(VII) Oxides

    E-print Network

    Keinan, Ehud

    Rules of Stereoselectivity in Tandem Oxidative Polycyclization Reaction with Rhenium(VII) Oxides, Israel ReceiVed April 17, 1998 The tandem oxidative polycyclization reaction with rhenium- (VII) reagents

  15. Homogeneous oxidation reactions of propanediols at low temperatures.

    PubMed

    Díaz, Eva; Sad, María Eugenia; Iglesia, Enrique

    2010-09-24

    O2 reacts with propanediols via homogeneous pathways at 400-500?K. 1,2-Propanediol forms CH3CHO, HCHO, and CO2 via oxidative C--C cleavage and acetone via dehydration routes, while symmetrical 1,3-propanediol undergoes dehydration and oxidative dehydrogenation to form, almost exclusively, acrolein (ca. 90?% selectivity). The products formed and their kinetic dependence on reactant concentrations are consistent with radical-mediated pathways initiated by O2 insertion into C--H bonds in a ? position relative to oxygen atoms in diol reactants. Propagation involves ?-scission reactions that form hydroxyl and hydroxyalkyl radicals. Acrolein/O2/H2O mixtures from the homogeneous oxidation of 1,3-propanediol form acrylic acid (with 90?% yield) in tandem reactors containing molybdenum-vanadium oxide catalysts. These data reveal the unique reactivity of diols, compared with triols and alkanols, in homogeneous oxidations, while also providing useful insight into the molecular basis for reactivity in biomass-derived oxygenates. PMID:20830723

  16. Influence of bond coat thickness on the cyclic rumpling of thermally grown oxides

    E-print Network

    Hutchinson, John W.

    Influence of bond coat thickness on the cyclic rumpling of thermally grown oxides D.S. Balint a in the thermally grown oxide (TGO) formed on a bond coat subject to cyclic thermal histories depend on the bond; Simulation 1. Introduction Modern gas turbines use multilayer coatings for environ- mental and thermal

  17. Insertion reactions into Pd[bond]O and Pd[bond]N bonds: preparation of alkoxycarbonyl, carbonato, carbamato, thiocarbamate, and thioureide complexes of palladium(II).

    PubMed

    Ruiz, José; Martínez, M Teresa; Florenciano, Félix; Rodríguez, Venancio; López, Gregorio; Pérez, José; Chaloner, Penny A; Hitchcock, Peter B

    2003-06-01

    Mononuclear palladium hydroxo complexes of the type [Pd(N[bond]N)(C(6)F(5))(OH)] [(N[bond]N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me(2)bipy), 1,10-phenanthroline (phen), or N,N,N',N'-tetramethylethylenediamine (tmeda)] have been prepared by reaction of [Pd(N[bond]N)(C(6)F(5))(acetone)]ClO(4) with KOH in methanol. These hydroxo complexes react, in methanol, with CO (1 atm, room temperature) to yield the corresponding methoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)Me)]. Similar alkoxycarbonyl complexes [Pd(N[bond]N)(C(6)F(5))(CO(2)R)] (N[bond]N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me, Et, or (i)Pr) are obtained when [Pd(N[bond]N)(C(6)F(5))Cl] is treated with KOH in the corresponding alcohol ROH and CO is bubbled through the solution. The reactions of [Pd(N[bond]N)(C(6)F(5))(OH)] (N[bond]N = bipy or Me(2)bipy) with CO(2), in tetrahydrofuran, lead to the formation of the binuclear carbonate complexes [(N[bond]N)(C(6)F(5))Pd(mu-eta(2)-CO(3))Pd(C(6)F(5))(N[bond]N)]. Complexes [Pd(N[bond]N)(C(6)F(5))(OH)] react in alcohol with PhNCS to yield the corresponding N-phenyl-O-alkylthiocarbamate complexes [Pd(N[bond]N)(C(6)F(5))[SC(OR)NPh

  18. An unusual carbon?carbon bond cleavage reaction during phosphinothricin biosynthesis

    SciTech Connect

    Cicchillo, Robert M.; Zhang, Houjin; Blodgett, Joshua A.V.; Whitteck, John T.; Li, Gongyong; Nair, Satish K.; van derDonk, Wilfred A.; Metcalf, William W.; (UIUC)

    2010-01-12

    Natural products containing phosphorus-carbon bonds have found widespread use in medicine and agriculture. One such compound, phosphinothricin tripeptide, contains the unusual amino acid phosphinothricin attached to two alanine residues. Synthetic phosphinothricin (glufosinate) is a component of two top-selling herbicides (Basta and Liberty), and is widely used with resistant transgenic crops including corn, cotton and canola. Recent genetic and biochemical studies showed that during phosphinothricin tripeptide biosynthesis 2-hydroxyethylphosphonate (HEP) is converted to hydroxymethylphosphonate (HMP). Here we report the in vitro reconstitution of this unprecedented C(sp{sup 3})-C(sp{sup 3}) bond cleavage reaction and X-ray crystal structures of the enzyme. The protein is a mononuclear non-haem iron(II)-dependent dioxygenase that converts HEP to HMP and formate. In contrast to most other members of this family, the oxidative consumption of HEP does not require additional cofactors or the input of exogenous electrons. The current study expands the scope of reactions catalysed by the 2-His-1-carboxylate mononuclear non-haem iron family of enzymes.

  19. An Unusual Carbon-Carbon Bond Cleavage Reaction During Phosphinothricin Biosynthesis

    PubMed Central

    Cicchillo, Robert M.; Zhang, Houjin; Blodgett, Joshua A.V.; Whitteck, John T.; Li, Gongyong; Nair, Satish K.; van der Donk, Wilfred A.; Metcalf, William W.

    2010-01-01

    Natural products containing phosphorus-carbon bonds have found widespread use in medicine and agriculture1. One such compound, phosphinothricin tripeptide (PTT), contains the unusual amino acid phosphinothricin (PT) attached to two alanine residues (Fig. 1). Synthetic PT (glufosinate) is a component of two top-selling herbicides (Basta® and Liberty®), and is widely used with resistant transgenic crops including corn, cotton and canola. Recent genetic and biochemical studies showed that during PTT biosynthesis 2-hydroxyethylphosphonate (HEP) is converted to hydroxymethylphosphonate (HMP) (Fig. 1)2. Reported here are the in vitro reconstitution of this unprecedented C(sp3)-C(sp3) bond cleavage reaction and X-ray crystal structures of the enzyme. The protein is a mononuclear non-heme iron(II)-dependent dioxygenase that converts HEP to HMP and formate. In contrast to most other members of this family, the oxidative consumption of HEP does not require additional cofactors or the input of exogenous electrons. The current study expands the scope of reactions catalyzed by the 2-His-1-carboxylate mononuclear non-heme iron family of enzymes. PMID:19516340

  20. Polyorganosilazane preceramic binder development for reaction bonded silicon nitride composites

    SciTech Connect

    Mohr, D.L.; Starr, T.L. [Georgia Tech Research Inst., Atlanta, GA (United States)

    1992-11-01

    This study has examined the use of two commercially available polyorganosilazanes for application as preceramic binders in a composite composed of silicon carbide fibers in a reaction bonded silicon nitride (RBSN) matrix. Ceramic monolithic and composite samples were produced. Density of monolithic and whisker reinforced RBSN samples containing the polysilazane binder was increased. Mercury intrusion porosimetry revealed a significant decrease in the pore sizes of samples containing a polyorganosilazane binder. Electron micrographs of samples containing the preceramic binder looked similar to control samples containing no precursor. Overall, incorporation of the polysilazane into monolithic and whisker reinforced samples resulted in significantly increased density and decreased porosity. Nitriding of the RBSN was slightly retarded by addition of the polysilazane binder. Samples with the preceramic binders contained increased contents of {alpha} versus {beta}-silicon nitride which may be due to interaction of hydrogen evolved from polysilazane pyrolysis with the nitriding process. Initial efforts to produce continuous fiber reinforced composites via this method have not realized the same improvements in density and porosity which have been observed for monolithic and whisker reinforced samples. Further, the addition of perceramic binder resulted in a more brittle fracture morphology as compared to similar composites made without the binder.

  1. Polyorganosilazane preceramic binder development for reaction bonded silicon nitride composites

    SciTech Connect

    Mohr, D.L.; Starr, T.L. (Georgia Tech Research Inst., Atlanta, GA (United States))

    1992-11-01

    This study has examined the use of two commercially available polyorganosilazanes for application as preceramic binders in a composite composed of silicon carbide fibers in a reaction bonded silicon nitride (RBSN) matrix. Ceramic monolithic and composite samples were produced. Density of monolithic and whisker reinforced RBSN samples containing the polysilazane binder was increased. Mercury intrusion porosimetry revealed a significant decrease in the pore sizes of samples containing a polyorganosilazane binder. Electron micrographs of samples containing the preceramic binder looked similar to control samples containing no precursor. Overall, incorporation of the polysilazane into monolithic and whisker reinforced samples resulted in significantly increased density and decreased porosity. Nitriding of the RBSN was slightly retarded by addition of the polysilazane binder. Samples with the preceramic binders contained increased contents of [alpha] versus [beta]-silicon nitride which may be due to interaction of hydrogen evolved from polysilazane pyrolysis with the nitriding process. Initial efforts to produce continuous fiber reinforced composites via this method have not realized the same improvements in density and porosity which have been observed for monolithic and whisker reinforced samples. Further, the addition of perceramic binder resulted in a more brittle fracture morphology as compared to similar composites made without the binder.

  2. Hydrogen bonding in phosphine oxide/phosphate-phenol complexes.

    PubMed

    Cuypers, Ruud; Sudhölter, Ernst J R; Zuilhof, Han

    2010-07-12

    To develop a new solvent-impregnated resin (SIR) system for the removal of phenols and thiophenols from water, complex formation by hydrogen bonding of phosphine oxides and phosphates is studied using isothermal titration calorimetry (ITC) and quantum chemical modeling. Six different computational methods are used: B3LYP, M06-2X, MP2, spin component-scaled (SCS) MP2 [all four with 6-311+G(d,p) basis set], a complete basis set extrapolation at the MP2 level (MP2/CBS), and the composite CBS-Q model. This reveals a range of binding enthalpies (DeltaH) for phenol-phosphine oxide and phenol-phosphate complexes and their thio analogues. Both structural (bond lengths/angles) and electronic elements (charges, bond orders) are studied. Furthermore, solvent effects are investigated theoretically by the PCM solvent model and experimentally via ITC. From our calculations, a trialkylphosphine oxide is found to be the most promising extractant for phenol in SIRs, yielding DeltaH=-14.5 and -9.8 kcal mol(-1) with phenol and thiophenol, respectively (MP2/CBS), without dimer formation that would hamper the phenol complexation. In ITC measurements, the DeltaH of this complex was most negative in the noncoordinating solvent cyclohexane, and slightly less so in pi-pi interacting solvents such as benzene. The strongest binding is found for the dimethyl phosphate-phenol complex [-15.1 kcal mol(-1) (MP2/CBS)], due to the formation of two H-bonds (P=OH-O- and P-O-HO-H); however, dimer formation of these phosphates competes with complexation of phenol, and would thus hamper their use in industrial extractions. CBS-Q calculations display erroneous trends for sulfur compounds, and are found to be unsuitable. Computationally relatively cheap SCS-MP2 and M06-2X calculations did accurately agree with the much more elaborate MP2/CBS method, with an average deviation of less than 1 kcal mol(-1). PMID:20602407

  3. A Macroscopic Reaction: Direct Covalent Bond Formation between Materials Using a Suzuki-Miyaura Cross-Coupling Reaction

    PubMed Central

    Sekine, Tomoko; Kakuta, Takahiro; Nakamura, Takashi; Kobayashi, Yuichiro; Takashima, Yoshinori; Harada, Akira

    2014-01-01

    Cross-coupling reactions are important to form C–C covalent bonds using metal catalysts. Although many different cross-coupling reactions have been developed and applied to synthesize complex molecules or polymers (macromolecules), if cross-coupling reactions are realized in the macroscopic real world, the scope of materials should be dramatically broadened. Here, Suzuki-Miyaura coupling reactions are realized between macroscopic objects. When acrylamide gel modified with an iodophenyl group (I-gel) reacts with a gel possessing a phenylboronic group (PB-gel) using a palladium catalyst, the gels bond to form a single object. This concept can also be adapted for bonding between soft and hard materials. I-gel or PB-gel selectively bonds to the glass substrates whose surfaces are modified with an electrophile or nucleophile, respectively. PMID:25231557

  4. A Macroscopic Reaction: Direct Covalent Bond Formation between Materials Using a Suzuki-Miyaura Cross-Coupling Reaction

    NASA Astrophysics Data System (ADS)

    Sekine, Tomoko; Kakuta, Takahiro; Nakamura, Takashi; Kobayashi, Yuichiro; Takashima, Yoshinori; Harada, Akira

    2014-09-01

    Cross-coupling reactions are important to form C-C covalent bonds using metal catalysts. Although many different cross-coupling reactions have been developed and applied to synthesize complex molecules or polymers (macromolecules), if cross-coupling reactions are realized in the macroscopic real world, the scope of materials should be dramatically broadened. Here, Suzuki-Miyaura coupling reactions are realized between macroscopic objects. When acrylamide gel modified with an iodophenyl group (I-gel) reacts with a gel possessing a phenylboronic group (PB-gel) using a palladium catalyst, the gels bond to form a single object. This concept can also be adapted for bonding between soft and hard materials. I-gel or PB-gel selectively bonds to the glass substrates whose surfaces are modified with an electrophile or nucleophile, respectively.

  5. Formation of porous surface layers in reaction bonded silicon nitride during processing

    NASA Technical Reports Server (NTRS)

    Shaw, N. J.; Glasgow, T. K.

    1979-01-01

    Microstructural examination of reaction bonded silicon nitride (RBSN) has shown that there is often a region adjacent to the as-nitrided surfaces that is even more porous than the interior of this already quite porous material. Because this layer of large porosity is considered detrimental to both the strength and oxidation resistance of RBSN, a study was undertaken to determine if its formation could be prevented during processing. All test bars studied were made from a single batch of Si powder which was milled for 4 hours in heptane in a vibratory mill using high density alumina cylinders as the grinding media. After air drying the powder, bars were compacted in a single acting die and hydropressed.

  6. Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C•(?O).

    PubMed

    Sebbar, Nadia; Bozzelli, Joseph W; Bockhorn, Henning

    2011-10-27

    Alkyl substituted aromatics are present in fuels and in the environment because they are major intermediates in the oxidation or combustion of gasoline, jet, and other engine fuels. The major reaction pathways for oxidation of this class of molecules is through loss of a benzyl hydrogen atom on the alkyl group via abstraction reactions. One of the major intermediates in the combustion and atmospheric oxidation of the benzyl radicals is benzaldehyde, which rapidly loses the weakly bound aldehydic hydrogen to form a resonance stabilized benzoyl radical (C6H5C(•)?O). A detailed study of the thermochemistry of intermediates and the oxidation reaction paths of the benzoyl radical with dioxygen is presented in this study. Structures and enthalpies of formation for important stable species, intermediate radicals, and transition state structures resulting from the benzoyl radical +O2 association reaction are reported along with reaction paths and barriers. Enthalpies, ?fH298(0), are calculated using ab initio (G3MP2B3) and density functional (DFT at B3LYP/6-311G(d,p)) calculations, group additivity (GA), and literature data. Bond energies on the benzoyl and benzoyl-peroxy systems are also reported and compared to hydrocarbon systems. The reaction of benzoyl with O2 has a number of low energy reaction channels that are not currently considered in either atmospheric chemistry or combustion models. The reaction paths include exothermic, chain branching reactions to a number of unsaturated oxygenated hydrocarbon intermediates along with formation of CO2. The initial reaction of the C6H5C(•)?O radical with O2 forms a chemically activated benzoyl peroxy radical with 37 kcal mol(-1) internal energy; this is significantly more energy than the 21 kcal mol(-1) involved in the benzyl or allyl + O2 systems. This deeper well results in a number of chemical activation reaction paths, leading to highly exothermic reactions to phenoxy radical + CO2 products. PMID:21942384

  7. Identification of bacterial carotenoid cleavage dioxygenase homologs that cleave the interphenyl ?,? double bond of stilbene derivatives via a monooxygenase reaction

    PubMed Central

    Marasco, Erin K.; Schmidt-Dannert, Claudia

    2013-01-01

    Carotenoid cleavage oxygenases (CCOs, also referred to as carotenoid cleavage dioxygenases (CCDs) in the literature) are a new class of non-heme iron-type enzymes that oxidatively cleave double bonds in the conjugated carbon chain of carotenoids. The oxidative cleavage mechanism of these enzymes is not clear and both monooxygenase and dioxygenase mechanisms have been proposed for different carotenoid cleavage enzymes. CCOs have been described from plants, animals, fungi and cyanobacteria but little is known about their distribution and activities in bacteria other than cyanobacteria. We surveyed bacterial genome sequences for CCO homologs and report the characterization of CCO homologs identified in Novosphingobium aromaticivorans DSM 12444 (NOV1 and NOV2) and in Bradyrhizobium sp. (BRA-J and BRA-S). In vitro and in vivo assays with carotenoid and stilbene compounds were used to investigate cleavage activities of the recombinant enzymes. The NOV enzymes cleaved the interphenyl ?-? double bond of stilbenes with an oxygen functional group at the 4’ carbon (e.g. resveratrol, piceatannol, and rhaponticin) to the corresponding aldehyde products. Carotenoids and apocarotenoids were not substrates for these enzymes. The two homologous enzymes from Bradyrhizobium sp. did not possess carotenoid or stilbene cleavage oxygenase activities, but showed activity with farnesol. To investigate whether oxidative cleavage of stilbenes proceeds via a monooxygenase or dioxygenase reaction, oxygen labeling studies were conducted with NOV2. Our labeling studies show that double-bond cleavage of stilbenes occurs via a monooxygenase reaction mechanism. PMID:18478524

  8. Mode specificity in bond selective reactions F + HOD ? HF + OD and DF + OH

    NASA Astrophysics Data System (ADS)

    Song, Hongwei; Guo, Hua

    2015-05-01

    The influence of vibrational excitations in the partially deuterated water (HOD) reactant on its bond selective reactions with F is investigated using a full-dimensional quantum wave packet method on an accurate global potential energy surface. Despite the decidedly early barrier of the F + H2O reaction, reactant vibrational excitation in each local stretching mode of HOD is found to significantly enhance the reaction which breaks the excited bond. In the mean time, excitation of the HOD bending mode also enhances the reaction, but with much lower efficacy and weaker bond selectivity. Except for low collision energies, all vibrational modes are more effective in promoting the bond selective reactions than the translational energy. These results are compared with the predictions of the recently proposed sudden vector projection model.

  9. Heterogeneous reaction of ozone with aluminum oxide

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1976-01-01

    Rates and collision efficiencies for ozone decomposition on aluminum oxide surfaces were determined. Samples were characterized by BET surface area, X-ray diffraction, particle size, and chemical analysis. Collision efficiencies were found to be between 2 times 10 to the -10 power and 2 times 10 to the -9 power. This is many orders of magnitude below the value of 0.000001 to 0.00001 needed for appreciable long-term ozone loss in the stratosphere. An activation energy of 7.2 kcal/mole was found for the heterogeneous reaction between -40 C and 40 C. Effects of pore diffusion, outgassing and treatment of the aluminum oxide with several chemical species were also investigated.

  10. Bimolecular Coupling Reactions through Oxidatively Generated Aromatic Cations: Scope and Stereocontrol.

    PubMed

    Cui, Yubo; Villafane, Louis A; Clausen, Dane J; Floreancig, Paul E

    2013-09-01

    Chromenes, isochromenes, and benzoxathioles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to form stable aromatic cations that react with a range of nucleophiles. These oxidative fragment coupling reactions provide rapid access to structurally diverse heterocycles. Conducting the reactions in the presence of a chiral Brønsted acid results in the formation of an asymmetric ion pair that can provide enantiomerically enriched products in a rare example of a stereoselective process resulting from the generation of a chiral electrophile through oxidative carbon-hydrogen bond cleavage. PMID:23913987

  11. Bimolecular Coupling Reactions through Oxidatively Generated Aromatic Cations: Scope and Stereocontrol

    PubMed Central

    Cui, Yubo; Villafane, Louis A.; Clausen, Dane J.

    2013-01-01

    Chromenes, isochromenes, and benzoxathioles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to form stable aromatic cations that react with a range of nucleophiles. These oxidative fragment coupling reactions provide rapid access to structurally diverse heterocycles. Conducting the reactions in the presence of a chiral Brønsted acid results in the formation of an asymmetric ion pair that can provide enantiomerically enriched products in a rare example of a stereoselective process resulting from the generation of a chiral electrophile through oxidative carbon–hydrogen bond cleavage. PMID:23913987

  12. Strength of hot isostatically pressed and sintered reaction bonded silicon nitrides containing Y2O3

    NASA Technical Reports Server (NTRS)

    Sanders, William A.; Mieskowski, Diane M.

    1989-01-01

    The hot isostatic pressing of reaction bonded Si3N4 containing Y2O3 produced specimens with greater room temperature strengths than those by high pressure nitrogen sintering of the same material. Average room temperature bend strengths for hot isostatically pressed reaction bonded silicon nitride and high pressure nitrogen sintered reaction bonded silicon nitride were 767 and 670 MPa, respectively. Values of 472 and 495 MPa were observed at 1370 C. For specimens of similar but lower Y2O3 content produced from Si3N4 powder using the same high pressure nitrogen sintering conditions, the room temperature strength was 664 MPa and the 1370 C strength was 402 MPa. The greater strengths of the reaction bonded silicon nitride materials in comparison to the sintered silicon nitride powder material are attributed to the combined effect of processing method and higher Y2O3 content.

  13. Mechanistic studies on metal-catalyzed carbon-nitrogen bond forming reactions

    E-print Network

    Strieter, Eric R

    2005-01-01

    Mechanistic studies on copper and palladium-catalyzed C-N bond forming reactions are described. To understand the mechanistic details of these processes, several principles of physical organic chemistry have been employed. ...

  14. Analytic bond-order potential for atomistic simulations of zinc oxide

    E-print Network

    Nordlund, Kai

    Analytic bond-order potential for atomistic simulations of zinc oxide Paul Erhart1 , Niklas Juslin2 for zinc oxide and its elemental constituents is derived based on an analytical bond-order formalism. The model potential provides a good description of the bulk properties of various solid structures of zinc

  15. Effects of Thermal Cycling on Thermal Expansion and Mechanical Properties of Sic Fiber-reinforced Reaction-bonded Si3n4 Composites

    NASA Technical Reports Server (NTRS)

    Bhatt, R. T.; Palczer, A. R.

    1994-01-01

    Thermal expansion curves for SiC fiber-reinforced reaction-bonded Si3N4 matrix composites (SiC/RBSN) and unreinforced RBSN were measured from 25 to 1400 C in nitrogen and in oxygen. The effects of fiber/matrix bonding and cycling on the thermal expansion curves and room-temperature tensile properties of unidirectional composites were determined. The measured thermal expansion curves were compared with those predicted from composite theory. Predicted thermal expansion curves parallel to the fiber direction for both bonding cases were similar to that of the weakly bonded composites, but those normal to the fiber direction for both bonding cases resulted in no net dimensional changes at room temperature, and no loss in tensile properties from the as-fabricated condition. In contrast, thermal cycling in oxygen for both composites caused volume expansion primarily due to internal oxidation of RBSN. Cyclic oxidation affected the mechanical properties of the weakly bonded SiC/RBSN composites the most, resulting in loss of strain capability beyond matrix fracture and catastrophic, brittle fracture. Increased bonding between the SiC fiber and RBSN matrix due to oxidation of the carbon-rich fiber surface coating and an altered residual stress pattern in the composite due to internal oxidation of the matrix are the main reasons for the poor mechanical performance of these composites.

  16. Proton transfer reactions and hydrogen-bond networks in protein environments

    PubMed Central

    Ishikita, Hiroshi; Saito, Keisuke

    2014-01-01

    In protein environments, proton transfer reactions occur along polar or charged residues and isolated water molecules. These species consist of H-bond networks that serve as proton transfer pathways; therefore, thorough understanding of H-bond energetics is essential when investigating proton transfer reactions in protein environments. When the pKa values (or proton affinity) of the H-bond donor and acceptor moieties are equal, significantly short, symmetric H-bonds can be formed between the two, and proton transfer reactions can occur in an efficient manner. However, such short, symmetric H-bonds are not necessarily stable when they are situated near the protein bulk surface, because the condition of matching pKa values is opposite to that required for the formation of strong salt bridges, which play a key role in protein–protein interactions. To satisfy the pKa matching condition and allow for proton transfer reactions, proteins often adjust the pKa via electron transfer reactions or H-bond pattern changes. In particular, when a symmetric H-bond is formed near the protein bulk surface as a result of one of these phenomena, its instability often results in breakage, leading to large changes in protein conformation. PMID:24284891

  17. Disulphide bond formation by glutathione via the glutathione-trimethylamine- N-oxide complex

    NASA Astrophysics Data System (ADS)

    Brzezinski, Bogumil; Labowski, M.; Zundel, Georg

    1995-07-01

    Glutathione and its diethyl ester complexes (1 : 1) with trimethylamine N-oxide (TMAO) were studied by FTIR and 1H NMR spectrocopy. Immediately after mixing, complexes with strong SH⋯ON ? S -⋯H +ON hydrogen bonds are formed. They show large proton polarizability due to the fluctuation of the proton within these bonds. These complexes are, however, not stable since disulphide bonds are formed. Thus, TMAO regulates the disulphide bond formation in glutathione systems.

  18. Copper-Catalyzed Oxidative Heck Reactions between Alkyltrifluoroborates and Vinylarenes

    PubMed Central

    Liwosz, Timothy W.; Chemler, Sherry R.

    2013-01-01

    We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented. PMID:23734764

  19. High temperature partial oxidation reactions over silver catalysts

    Microsoft Academic Search

    Anton Nagy; Gerhard Mestl

    1999-01-01

    The exceptional catalytic activity of silver for a number of partial oxidation reactions has been known for nearly a century. Despite the widespread use of silver in heterogeneous catalysis, there still remain unresolved questions about the mechanistic details of reaction. The ethylene epoxidation and formaldehyde synthesis reactions are the two industrially-relevant reactions which have received, by far, the most attention.

  20. Nitric oxide in star-forming regions: further evidence for interstellar N-O bonds.

    PubMed

    Ziurys, L M; McGonagle, D; Minh, Y; Irvine, W M

    1991-06-01

    Nitric oxide has been newly detected towards several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2 --> 1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both lambda-doubling components of NO were observed towards all sources. Column densities derived for nitric oxide in these clouds are N approximately 10(15)-10(16) cm-2, corresponding to fractional abundances of f approximately 0.5-1.0 x 10(-8), relative to H2. Towards Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude. The abundance of NO, unlike other simple interstellar nitrogen compounds, does appear to be reproduced by chemical models, at least to a good approximation. Regardless of the nature of formation of NO, it appears to be a common constituent of warm, dense molecular clouds. N-O bonds may therefore be more prevalent than previously thought. PMID:11538086

  1. From Polymer to Monomer: Cleavage and Rearrangement of Si-O-Si Bonds after Oxidation Yielded an Ordered Cyclic Crystallized Structure.

    PubMed

    Zuo, Yujing; Gou, Zhiming; Cao, Jinfeng; Yang, Zhou; Lu, Haifeng; Feng, Shengyu

    2015-07-27

    Polymerization reactions are very common in the chemical industry, however, the reaction in which monomers are obtained from polymers is rarely invesitgated. This work reveals for the first time that oxone can break the Si-O-Si bond and induce further rearrangement to yield an ordered cyclic structure. The oxidation of P1, which is obtained by reaction of 2,2'-1,2-ethanediylbis(oxy)bis(ethanethiol) (DBOET) with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (MM(Vi)), with oxone yielded cyclic crystallized sulfone-siloxane dimer (P1-ox) after unexpected cleavage and rearrangement of the Si-O-Si bond. PMID:26186500

  2. Carbon-Carbon Bond Cleavage Reaction: Synthesis of Multisubstituted Pyrazolo[1,5-a]pyrimidines.

    PubMed

    Saikia, Pallabi; Gogoi, Sanjib; Boruah, Romesh C

    2015-07-01

    A new carbon-carbon bond cleavage reaction was developed for the efficient synthesis of multisubstituted pyrazolo[1,5-a]pyrimidines. This base induced reaction of 1,3,5-trisubstituted pentane-1,5-diones and substituted pyrazoles afforded good yields of the pyrazolo[1,5-a]pyrimidines. PMID:26083788

  3. Direct Annulation of Hydrazides to 1,3,4-Oxadiazoles via Oxidative C(CO)-C(Methyl) Bond Cleavage of Methyl Ketones.

    PubMed

    Gao, Qinghe; Liu, Shan; Wu, Xia; Zhang, Jingjing; Wu, Anxin

    2015-06-19

    A new strategy for the synthesis of 1,3,4-oxadiazoles was established through direct annulation of hydrazides with methyl ketones. It was found that the use of K2CO3 as a base achieves an unexpected and highly efficient C-C bond cleavage. This reaction is proposed to go through oxidative cleavage of Csp(3)-H bonds, followed by cyclization and deacylation. PMID:26035338

  4. The nature of NO-bonding in N-oxide group.

    PubMed

    ?ukomska, Marlena; Rybarczyk-Pirek, Agnieszka J; Jab?o?ski, Miros?aw; Palusiak, Marcin

    2015-07-01

    The nature of the NO-bond in the N-oxide group was investigated by means of combined theoretical calculations (including QTAIM and NBO approaches) and statistical analyses of the contents of crystal structure databases. The N-O bond in the N-oxide group should be classified as the NO donating bond with an important contribution of ON back-donation (of the ?-electron type, when available). The visualization of the Laplacian of electron density in the region of an oxygen valence sphere suggests the presence of two lone pairs for the imine-N-oxide group (characterized by effective ON back-donation). A detailed bonding analysis performed by means of natural resonance theory indicates that the N?O bond is of an order of magnitude clearly greater than 1. In addition, the stability of the N?O bond in various N-oxides was estimated. The analyses of the hydrogen- and halogen-bonded complexes of the N-oxides reveal strong Lewis basicity of the N-oxide group. The formation of H- and X-bonding leads to N?O bond elongation due to its structural, topological and spectroscopic characteristics. Moreover, in pyridine-N-oxide, the electron-withdrawing -NO2 group additionally stabilizes the N?O bond, whereas the opposite effect can be observed for the electron-donating-NH2 substituent. This is due to a substituent effect on the ?-type ON back-donation. As a result, the oxygen atom in pyridine-N-oxide may change its availability during intermolecular interaction formation, as revealed in the interaction energy, which changes by about half of the estimated total interaction energy. PMID:26051488

  5. 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 ?-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. PMID:25756834

  6. THE OXIDATION NUMBER -HALF REACTION METHOD FOR BALANCING REDOX EQUATIONS

    E-print Network

    Le Roy, Robert J.

    THE OXIDATION NUMBER - HALF REACTION METHOD FOR BALANCING REDOX EQUATIONS The redox-balancing processes. 3. Balance the separate half reactions: a) with respect to the element being oxidized or reduced) 5. If necessary, add 'spectator' ions or molecules to balance the equation with respect to atoms

  7. Formation of chemical bonds with visible light: The sensitized oxidation of iodide and water

    NASA Astrophysics Data System (ADS)

    Gardner, James M.

    This thesis reports on visible light sensitized oxidation chemistry that drives the formation of I-I and O-O bonds in solution and at surfaces. Chapter 1 introduces the reader to a general overview of the fundamental iodine redox chemistry related to the making and breaking of I-I bonds. The relevance of I-I bonds to the functionality to dye-sensitized solar cells (DSSCs) is discussed. In Chapter 2, the importance of strong photo-oxidants for solar water splitting and the transient generation of free iodine atoms are examined. The synthesis of the photo-oxidants was completed by Jovan Giaimuccio. Chapter 3 further expands on the formation of iodine atoms from potent photo-oxidants and the cleaving of I-I bonds from the direct photochemistry of I3-. Maria Abrahamsson is gratefully acknowledged for assistance with low temperature measurements. Chapter 4 addresses the mechanistic details of iodide oxidation and concerted I-I bond formation as compared with sequential oxidation and bond forming steps. The synthesis of the photo-catalysts was completed by Andras Marton. A limitation for producing functional water oxidation photocatalysts is the generation of significant concentrations of oxidizing equivalents to drive the multi-electron water oxidation chemistry necessary to form O-O bonds. The design of visible light absorbing, high surface area semiconductors with minimized distances for hole diffusion to the solution interface could improve water oxidation efficiency and are discussed in Chapter 5. Su Kim is acknowledged for assistance in assembling high surface area semiconductor electrodes for water splitting. Within Appendix 1 we discuss the synthesis and characterization of the rutile, anatase, and brookite phase nanoparticles of TiO2, which are known to be photo-oxidants capable of oxidizing water to O2. David Reyes-Coronado is gratefully acknowledged for the synthesis of TiO2 nanoparticles during an extended research collaboration with our laboratories.

  8. Synergistic H4NI-AcOH Catalyzed Oxidation of the Csp(3)-H Bonds of Benzylpyridines with Molecular Oxygen.

    PubMed

    Ren, Lanhui; Wang, Lianyue; Lv, Ying; Li, Guosong; Gao, Shuang

    2015-05-01

    The oxidation of benzylpyridines forming benzoylpyridines was achieved based on a synergistic H4NI-AcOH catalyst and molecular oxygen in high yield under solvent-free conditions. This is the first nonmetallic catalytic system for this oxidation transformation using molecular oxygen as the oxidant. The catalytic system has a wide scope of substrates and excellent chemoselectivity, and this procedure can also be scaled up. The study of a preliminary reaction mechanism demonstrated that the oxidation of the Csp(3)-H bonds of benzylpyridines was promoted by the pyridinium salts formed by AcOH and benzylpyridines. The synergistic effect of H4NI-AcOH was also demonstrated by control experiments. PMID:25885281

  9. Csp(3)-csp(3) bond cleavage in the palladium-catalyzed aminohydroxylation of allylic hydrazones using atmospheric oxygen as the sole oxidant.

    PubMed

    Chen, Yu-Chen; Zhu, Ming-Kui; Loh, Teck-Peng

    2015-06-01

    A C-C bond cleavage was observed in the palladium-catalyzed aminohydroxylation of allylic hydrazones, using atmospheric oxygen as the sole oxidant. This reaction could also proceed in a one-pot manner, starting from keto-alkene compounds and phenylhydrazine. PMID:25973749

  10. In-process oxidation protection in fluxless brazing or diffusion bonding of aluminum alloys

    NASA Technical Reports Server (NTRS)

    Okelly, K. P.; Featherston, A. B.

    1974-01-01

    Aluminum is cleaned of its oxide coating and is sealed immediately with polymeric material which makes it suitable for fluxless brazing or diffusion bonding. Time involved between cleaning and brazing is no longer critical factor.

  11. Transient liquid phase bonding of ferritic oxide-dispersion-strengthened alloys

    Microsoft Academic Search

    Venu G. Krishnardula; Nofrijon I. Sofyan; William F. Gale; Jeffrey W. Fergus

    2006-01-01

    Joining of two ferritic oxide-dispersion-strengthened (ODS) alloys, MA956 and PM2000, using transient liquid phase (TLP) bonding\\u000a is discussed. Thin-film boron coatings of different thicknesses were used as interlayers and different bond orientations with\\u000a substrates cut along and normal to the direction of extrusion were studied, with postbond heat treatment and microscopic evaluation\\u000a of the bonds. Microstructural continuity was achieved in

  12. Bonding nature of metal\\/oxide incoherent interfaces by first-principles calculations

    Microsoft Academic Search

    Katsuyuki Matsunaga; Takeo Sasaki; Naoya Shibata; Teruyasu Mizoguchi; Takahisa Yamamoto; Yuichi Ikuhara

    2006-01-01

    A bonding mechanism of large-mismatched metal\\/oxide heterointerfaces, classified as incoherent interfaces, is investigated by first-principles calculations. As a model system, incoherent Ni\\/ZrO2(111) interfaces are selected, and the interfacial bonding characters and their relevance to the interface strength are analyzed. It is found that the chemical bonds of the interfacial atomic pairs are strongly dependent on the atomic configurations in the

  13. REACTIONS BETWEEN REFRACTORY OXIDES AND GRAPHITE

    Microsoft Academic Search

    K. L. Komarek; A. Coucoulas; N. Klinger

    1963-01-01

    Reactions of alumina, magnesia, spinel, and beryllia with graphite were ; studied in vacuum by measuring the amount of carbon monoxide formed. Two types ; of reactions were observed: a diffusion-controlled reaction with alumina, ; beryllia, and thoria, and a phase boundary-controlled reaction with magnesia, ; beryllia, spinel, and titania. The following activation energies were obtained: ; 316 kcal for

  14. The Oxidation Behavior of TBC with Cold Spray CoNiCrAlY Bond Coat

    Microsoft Academic Search

    W. R. Chen; E. Irissou; X. Wu; J.-G. Legoux; B. R. Marple

    2011-01-01

    Cold gas dynamic spray (CGDS) has been considered a potential technique to produce the metallic bond coat for TBC applications, because of its fast deposition rate and low deposition temperature. This article presents the influence of spray processes for bond coat, including air plasma spray, high velocity oxy-fuel, and in particular CGDS, on the oxidation performance of TBCs with a

  15. ATR-FTIR Spectroscopy Reveals Bond Formation During Bacterial Adhesion to Iron Oxide

    E-print Network

    Chorover, Jon

    ATR-FTIR Spectroscopy Reveals Bond Formation During Bacterial Adhesion to Iron Oxide Sanjai J contribute to bacterial adhesion at positively charged surfaces, direct bonding of cell surface The contribution of various bacterial surface functional groups to adhesion at hematite and ZnSe surfaces

  16. The effect of oxidation heat treatment of porcelain bond strength in selected base metal alloys.

    PubMed

    Wu, Y; Moser, J B; Jameson, L M; Malone, W F

    1991-10-01

    Base metal alloys have been widely used for fixed partial dentures in the past decade. The oxidation heat treatment (degassing) of these alloys is a controversial step to prepare the metal surface for bonding porcelain. This study evaluated the effect of oxidation heat treatment on the porcelain bond strength of base metal alloys and investigated composition changes that may have occurred during this process. PMID:1791553

  17. Reaction-diffusion analysis for one-step plasma etching and bonding of microfluidic devices

    NASA Astrophysics Data System (ADS)

    Rosso, Michel; van Steijn, Volkert; de Smet, Louis C. P. M.; Sudhölter, Ernst J. R.; Kleijn, Chris R.; Kreutzer, Michiel T.

    2011-04-01

    A self-similar reaction front develops in reactive ion etching when the ions penetrate channels of shallow height h. This relates to the patterning of microchannels using a single-step etching and bonding, as described by Rhee et al. [Lab Chip 5, 102 (2005)]. Experimentally, we report that the front location scales as xf˜ht1/2 and the width is time-invariant and scales as ?˜h. Mean-field reaction-diffusion theory and Knudsen diffusion give a semiquantitative understanding of these observations and allow optimization of etching times in relation to bonding requirements.

  18. Transition-Metal-Catalyzed Laboratory-Scale Carbon–Carbon Bond-Forming Reactions of Ethylene

    PubMed Central

    Saini, Vaneet; Stokes, Benjamin J.; Sigman, Matthew S.

    2014-01-01

    Ethylene, the simplest alkene, is the most abundantly synthesized organic molecule by volume. It is readily incorporated into transitionmetal–catalyzed carbon-carbon bond-forming reactions through migratory insertions into alkylmetal intermediates. Because of its D2h symmetry, only one insertion outcome is possible. This limits byproduct formation and greatly simplifies analysis. As described within this Minireview, many carbon–carbon bond-forming reactions incorporate a molecule (or more) of ethylene at ambient pressure and temperature. In many cases, a useful substituted alkene is incorporated into the product. PMID:24105881

  19. Selectivity of chemisorbed oxygen in CH bond activation and CO oxidation and kinetic consequences for CH4O2 catalysis on Pt and Rh clusters

    E-print Network

    Iglesia, Enrique

    oxidative insertion of a Pt atom into one of the C­H bonds in CH4, forming a three-centered HC3­Pt for CH4­O2 catalysis on Pt and Rh clusters Ya-Huei (Cathy) Chin a , Corneliu Buda b , Matthew Neurock b as the reaction probability ratios for OÃ reactions with CO and CH4, during CH4­O2 catalysis on Pt and Rh clusters

  20. Bonding

    MedlinePLUS

    ... is a procedure that uses a tooth-colored composite resin (plastic) to repair a tooth. Bonding can ... cleaned regularly by a dental hygienist. Risks The composite resin used in bonding isn't nearly as ...

  1. Evaluation of reaction mechanism of coal-metal oxide interactions in chemical-looping combustion

    SciTech Connect

    Siriwardane, Ranjani; Richards, George; Poston, James [US Department of Energy, National Energy Technology Laboratory, 3610 Collins Ferry Road, P.O. Box 880, Morgantown, WV 26507-0880 (United States); Tian, Hanjing; Miller, Duane; Simonyi, Thomas [US Department of Energy, National Energy Technology Laboratory, 3610 Collins Ferry Road, P.O. Box 880, Morgantown, WV 26507-0880 (United States); URS, 3610 Collins Ferry Road, Morgantown, WV 26505 (United States)

    2010-11-15

    The knowledge of reaction mechanism is very important in designing reactors for chemical-looping combustion (CLC) of coal. Recent CLC studies have considered the more technically difficult problem of reactions between abundant solid fuels (i.e. coal and waste streams) and solid metal oxides. A definitive reaction mechanism has not been reported for CLC reaction of solid fuels. It has often been assumed that the solid/solid reaction is slow and therefore requires that reactions be conducted at temperatures high enough to gasify the solid fuel, or decompose the metal oxide. In contrast, data presented in this paper demonstrates that solid/solid reactions can be completed at much lower temperatures, with rates that are technically useful as long as adequate fuel/metal oxide contact is achieved. Density functional theory (DFT) simulations as well as experimental techniques such as thermo-gravimetric analysis (TGA), flow reactor studies, in situ X-ray photo electron spectroscopy (XPS), in situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to evaluate how the proximal interaction between solid phases proceeds. The data indicate that carbon induces the Cu-O bond breaking process to initiate the combustion of carbon at temperatures significantly lower than the spontaneous decomposition temperature of CuO, and the type of reducing medium in the vicinity of the metal oxide influences the temperature at which the oxygen release from the metal oxide takes place. Surface melting of Cu and wetting of carbon may contribute to the solid-solid contacts necessary for the reaction. (author)

  2. Electrochromic reactions in manganese oxides I. Raman analysis

    SciTech Connect

    Bernard, M.C.; Hugot-Le Goff, A.; Thi, B.V. (Univ. Pierre et Marie Curie, Paris (France). UPR 15 du CNRS Physique des Liquides et Electrochimie); Cordoba de Torresi, S. (Univ. Estadual de Campinas (Brazil). Dept. de Fisica Aplicada)

    1993-11-01

    Like nickel oxide, manganese oxide is a widely studied material in the primary batteries field. The reactions taking place during voltametric cycling of manganese oxides can be determined using in situ Raman spectroscopy. The main difficulty for the oxide identification is to obtain relevant Raman reference spectra because of the many possible compounds and, for some of these compounds, of their instability in the laser beam. As a consequence, several modifications of different tetra-, tri- and divalent manganese oxides and oxyhydroxides were carefully studied. The electrochromic behavior of three types of manganese oxides, two prepared by thermal oxidations and the other by electrochemical deposition, were then compared. The presence of nonstoichiometry in the pristine material was necessary to obtain a reversible electrochromic effect. The reaction during electrochromic cycling is more complicated than a simple passage from MnO[sub 2] to MnOOH.

  3. Oxidative cross-coupling of pyridine N-oxides and ethers between C(sp(2))-H/C(sp(3))-H bonds under transition-metal-free conditions.

    PubMed

    Sun, Wei; Xie, Zuguang; Liu, Jie; Wang, Lei

    2015-04-21

    A novel and efficient method based on the cross-coupling reactions of pyridine N-oxides with ethers between C(sp(2))-H/C(sp(3))-H bonds in the presence of TBHP was developed. The strategy provides an alternative approach to the pyridine moiety under transition-metal-free conditions. PMID:25785666

  4. Cu-catalyzed oxidative Povarov reactions between N-alkyl N-methylanilines and saturated oxa- and thiacycles.

    PubMed

    Kawade, Rahul Kisan; Huple, Deepak B; Lin, Rong-Jing; Liu, Rai-Shung

    2015-04-18

    Cu-catalyzed oxidative Povarov reactions between N,N-dialkylanilines and saturated oxa- or thiacycles with tert-butyl hydroperoxide (TBHP) are described; notably, the reactions use neither [4?] nor [2?]-motifs as the initial reagents. The use of cheap alkane-based substances as building units is of mechanistic and practical interest as two inert sp(3) C-H bonds are activated. PMID:25777971

  5. Iodine Oxide Thermite Reactions: Physical and Biological Effects

    NASA Astrophysics Data System (ADS)

    Russell, Rod; Pantoya, Michelle; Bless, Stephan; Clark, William

    2009-06-01

    We investigated the potential for some thermite-like material reactions to kill bacteria spores. Iodine oxides and silver oxides react vigorously with metals like aluminum, tantalum, and neodymium. These reactions theoretically produce temperatures as high as 8000K, leading to vaporization of the reactants, producing very hot iodine and/or silver gases. We performed a series of computations and experiments to characterize these reactions under both quasi-static and ballistic impact conditions. Criteria for impact reaction were established. Measurements of temperature and pressure changes and chemical evolution will be reported. Basic combustion characterizations of these reactions, such as thermal equilibrium analysis and reaction propagation rates as well as ignition sensitivity, will be discussed. Additionally, testing protocols were developed to characterize the biocidal effects of these reactive materials on B. subtilis spores. The evidence from these tests indicates that these reactions produce heat, pressure, and highly biocidal gases.

  6. Neutron Scattering Studies of Poly(ethylene Terephthalate) and Molecular Relaxation Through the Bond Interchange Reaction.

    NASA Astrophysics Data System (ADS)

    Dubner, Walter Sterling

    1990-01-01

    In this work, the neutron scattering technique was extended to investigate bond interchange using intermediate angle neutron scattering (IANS). Methodology was developed to use IANS data to explore this reaction in poly(ethylene terephthalate), or PET. To effectively use the IANS region, background scattering was measured from block copolymers formed from perdeutero (D) and normal or hydrogenous (H) PET. Models have been developed from neutron transport theory, which allow backgrounds from other materials to be calculated. Currently, these models represent the best extrapolation technique for estimating backgrounds from a single known reference background. Using IANS data, the bond interchange reaction in melt processed samples of PET-H/PET-D was investigated. From this study, a statistical segment length, b, of 16.3 +/- 2.2 A was determined for PET. Furthermore, the copolymer formed through interchange showed a block number average degree of polymerization, n, of 2.2 +/- 0.2. This n was consistent with the value expected for complete randomization of the original PET -H and PET-D chains. However, it was also shown that care must be exercised in determining b when n is small. Subsequently, the bond interchange reaction was explored in drawn PET films. Solutions of the drawn films were used to reduce difficulties associated with analyzing anisotropic samples. This study showed that bond interchange occurred in drawn films at 70 and 90^circ C. An apparent activation energy of 16.2 +/- 8.0 kcal/mole was determined for the effective bond scission reaction. To explore the connection between bond interchange and mechanical properties of PET, creep experiments were performed between 47 and 70^circC, to investigate relaxation processes below the glass transition temperature of PET (ca 70^circC). The results of these creep studies reflected established relaxation behavior associated with gauche-trans isomerization. The creep studies were connected to the isomerization results by a bond interchange kinetic model. This model was used to fit established PET secondary isomerization data, and showed that the time constants for secondary gauche-trans isomerization are consistent with the bond interchange reaction. Therefore, it was concluded that chemical changes associated with bond interchange may influence the physical properties of PET. An understanding of the controlling molecular processes that influence the physical behavior of polymers can lead to industrial processes which are better able to impact desirable polymer properties.

  7. Oxidation reactions of cytosine DNA components by hydroxyl radical and one-electron oxidants in aerated aqueous solutions.

    PubMed

    Wagner, J Richard; Cadet, Jean

    2010-04-20

    Indirect evidence strongly suggests that oxidation reactions of cytosine and its minor derivative 5-methylcytosine play a major role in mutagenesis and cancer. Therefore, there is an emerging necessity to identify the final oxidation products of these reactions, to search for their formation in cellular DNA, and to assess their mutagenic features. In this Account, we report and discuss the main *OH and one-electron-mediated oxidation reactions, two of the most potent sources of DNA damage, of cytosine and 5-methylcytosine nucleosides that have been recently characterized. The addition of *OH to the 5,6-unsaturated double bond of cytosine and 5-methylcytosine generates final degradation products that resemble those observed for uracil and thymine. The main product from the oxidation of cytosine, cytosine glycol, has been shown to undergo dehydration at a much faster rate as a free nucleoside than when inserted into double-stranded DNA. On the other hand, the predominant *OH addition at C5 of cytosine or 5-methylcytosine leads to the formation of 5-hydroxy-5,6-dihydro radicals that give rise to novel products with an imidazolidine structure. The mechanism of the formation of imidazolidine products is accounted for by rearrangement reactions that in the presence of molecular oxygen likely involve an intermediate pyrimidine endoperoxide. The reactions of the radical cations of cytosine and 5-methylcytosine are governed by competitive hydration, mainly at C6 of the pyrimidine ring, and deprotonation from the exocyclic amino and methyl group, leading in most cases to products similar to those generated by *OH. 5-Hydroxypyrimidines, the dehydration products of cytosine and uracil glycols, have a low oxidation potential, and their one-electron oxidation results in a cascade of decomposition reactions involving the formation of isodialuric acid, dialuric acid, 5-hydroxyhydantoin, and its hydroxyketone isomer. In biology, GC --> AT transitions are the most common mutations in the genome of aerobic organisms, including the lacI gene in bacteria, lacI transgenes in rodents, and the HPRT gene in rodents and humans, so a more complete understanding of cytosine oxidation is an essential research goal. The data and insights presented here shed new light on oxidation reactions of cytosine and 5-methylcytosine and should facilitate their validation in cellular DNA. PMID:20078112

  8. Students' Understandings of Chemical Bonds and the Energetics of Chemical Reactions.

    ERIC Educational Resources Information Center

    Boo, Hong Kwen

    1998-01-01

    Investigates Grade 12 students' understandings of the nature of chemical bonds and the energetics elicited across five familiar chemical reactions following a course of instruction. Discusses the many ways in which students can misconstruct concepts and principles. Contains 63 references. (DDR)

  9. Mechanistic Studies of the Reactions of Silicon-Carbon Double Bonds. Addition of Alcohols to

    E-print Network

    Leigh, William J.

    Mechanistic Studies of the Reactions of Silicon-Carbon Double Bonds. Addition of Alcohols to 1 their results in terms of a mechanism (a more refined version of one initially proposed by Wiberg5) involving- plex proton transfer. Further refinement of this mechanism has been possible through the use

  10. Neutron Scattering Studies of Poly(ethylene Terephthalate) and Molecular Relaxation Through the Bond Interchange Reaction

    Microsoft Academic Search

    Walter Sterling Dubner

    1990-01-01

    In this work, the neutron scattering technique was extended to investigate bond interchange using intermediate angle neutron scattering (IANS). Methodology was developed to use IANS data to explore this reaction in poly(ethylene terephthalate), or PET. To effectively use the IANS region, background scattering was measured from block copolymers formed from perdeutero (D) and normal or hydrogenous (H) PET. Models have

  11. Single-molecule chemical reactions tracked at the atomic-bond level.

    PubMed

    Lu, Jiong; Loh, Kian Ping

    2013-12-16

    On the right track: Recent advances in noncontact atomic force microscopy (nc-AFM) have enabled the bond-resolved imaging of reaction pathways. In particular, unprecedented insights into complex enediyne cyclization cascades on silver surfaces were gained by single-molecule imaging. PMID:24155108

  12. Fabrication of ceramic composite coatings using electrophoretic deposition, reaction bonding and low temperature sintering

    Microsoft Academic Search

    Zhoucheng Wang; Jane Shemilt; Ping Xiao

    2002-01-01

    We have developed a novel combination of electrophoretic deposition (EPD), reaction bonding and low temperature sintering techniques for the fabrication of yttria stablised zirconia (YSZ)\\/alumina composite coatings on Fecralloys. A mixture of ethanol and acetylacetone solvent was found to be an effective medium for YSZ and aluminium particle suspension. With the particle size of YSZ and aluminium being significantly reduced

  13. Natural bond orbital analysis of the intrinsic reaction barriers in nucleophilic displacements

    Microsoft Academic Search

    Ikchoon Lee

    2003-01-01

    Applications of natural bond orbital (NBO) analysis to the intrinsic reaction barriers involved in identity nucleophilic substitutions of halides (X = F, Cl or Br) at various carbon centres such as methyl, acyl, vinyl, imidoyl, cyclopropenyl and cyclopentadienyl halides are surveyed. The most important transition state stabilization in the piattack (SN~) path is the proximate sigma --> sigma* charge-transfer interactions,

  14. Iodine Oxide Thermite Reactions: Physical and Biological Effects

    Microsoft Academic Search

    Rod Russell; Michelle Pantoya; Stephan Bless; William Clark

    2009-01-01

    We investigated the potential for some thermite-like material reactions to kill bacteria spores. Iodine oxides and silver oxides react vigorously with metals like aluminum, tantalum, and neodymium. These reactions theoretically produce temperatures as high as 8000K, leading to vaporization of the reactants, producing very hot iodine and\\/or silver gases. We performed a series of computations and experiments to characterize these

  15. Application of chemical structure and bonding of actinide oxide materials for forensic science

    Microsoft Academic Search

    Wilkerson; Marianne Perry

    2010-01-01

    We are interested in applying our understanding of actinide chemical structure and bonding to broaden the suite of analytical tools available for nuclear forensic analyses. Uranium- and plutonium-oxide systems form under a variety of conditions, and these chemical species exhibit some of the most complex behavior of metal oxide systems known. No less intriguing is the ability of AnO (An:

  16. Bond length estimates for oxide crystals with a molecular power law expression

    NASA Astrophysics Data System (ADS)

    Gibbs, G. V.; Ross, Nancy L.; Cox, David F.

    2015-07-01

    A molecular power law bond length regression expression, R(M-O) = 1.39( s/ r)-0.22, defined in terms of the quotient, s/ r, where s is the averaged Pauling bond strength for the bonded interaction comprising a given molecular coordination polyhedron and r is the periodic table row number for the M atom, serves to replicate the bulk of the 470 individual experimental M-O average bond lengths estimated with Shannon's (Acta Crystallogr A 32(5):751-767, 1976) crystal radii for oxides to within 0.10 Å. The success of the molecular expression is ascribed to a one-to-one deep-seated connection that obtains between the electron density accumulated between bonded pairs of atoms and the average Pauling bond strength. It also implies that the bonded interactions that constitute oxide crystals are governed in large part by local forces. Although the expression reproduces the bond lengths involving rare earth atoms typically to within ~0.05 Å, it does not reproduce the lanthanide ionic radius contraction. It also fails to reproduce the experimental bond lengths for selected transition cations like Cu1+, Ag1+ and VILSFe2+ and for cations like IVK+, VIBa2+ and IIU6+.

  17. Fragmentation reactions of aromatic cation radicals: a tool for the detection of electron transfer mechanisms in biomimetic and enzymatic oxidations.

    PubMed

    Baciocchi, E

    1995-07-01

    1. Mechanistic criteria, based on the side-chain fragmentation reactions of aromatic cation radicals, involving the cleavage of a beta bond (i.e. C-H, C-Si and C-S) have been developed for the detection of electron transfer mechanisms in oxidative processes of alkylbenzenes and aromatic sulphides. 2. For benzylic oxidations, the distinction between electron transfer (ET) and hydrogen atom transfer mechanism (HAT) has been based: (a) on studies of intramolecular selectivity, which, with appropriate substrates (5-Z-1,2,3,-trimethylbenzenes and 4-Z-1,2-dimethylbenzenes, where Z = OMe, alkyl), turns out to be much higher in ET than in HAT processes; and (b) on products studies concerning the reactions of bicumyl and benzyltrimethylsilanes since in these systems, the nature of products can be significantly different for ET and HAT mechanisms. 3. These criteria have been applied to the reactions of alkylbenzenes with an NO3 radical (shown to be an ET process) as well as to the microsomal and biomimetic (by iron porphyrins in the presence of PhIO) side-chain oxidation of the same compounds, where the mechanistic probes have suggested a HAT mechanism, with the exception of the biomimetic oxidation of 4-methoxybenzyltrimethylsilane in CH2Cl2-H2O-MeOH, which probably occurs by an ET mechanism. 4. For the enzymatic and biomimetic oxidation of aromatic sulphides an oxygen transfer is suggested, since, with cumyl phenyl sulphide and 4-methoxybenzyl phenyl sulphide, these reactions lead exclusively to the corresponding sulphoxides and sulphones, whereas the same substrates, in genuine ET reactions, form cation radicals which undergo C-H and C-S bond cleavage. 5. An oxygen transfer mechanism is also likely in the biomimetic and enzymatic oxidations of sulphoxides since in these reactions 4-methoxybenzyl phenyl sulphoxide is exclusively converted to sulphone, whereas in ET reactions it forms only C-S bond cleavage products. PMID:7483664

  18. Intramolecular oxidative C-N bond formation for the synthesis of carbazoles: comparison of reactivity between the copper-catalyzed and metal-free conditions.

    PubMed

    Cho, Seung Hwan; Yoon, Jungho; Chang, Sukbok

    2011-04-20

    New synthetic procedures for intramolecular oxidative C-N bond formation have been developed for the preparation of carbazoles starting from N-substituted amidobiphenyls under either Cu-catalyzed or metal-free conditions using hypervalent iodine(III) as an oxidant. Whereas iodobenzene diacetate or bis(trifluoroacetoxy)iodobenzene alone undergoes the reaction to provide carbazole products in moderate to low yields, combined use of copper(II) triflate and the iodine(III) species significantly improves the reaction efficiency, giving a more diverse range of products in good to excellent yields. On the basis of mechanistic studies including kinetic profile, isotope effects, and radical inhibition experiments, the copper species is proposed to catalytically activate the hypervalent iodine(III) oxidants. The synthetic utility of the present approach was nicely demonstrated in a direct synthesis of indolo[3,2-b]carbazole utilizing a double C-N bond formation. PMID:21446710

  19. Potential energy surfaces for CH bond cleavage reactions

    SciTech Connect

    Harding, L.B.

    1996-12-31

    Ab initio, multi-reference, configuration interaction calculations are reported for CH{sub 4}{leftrightarrow}CH{sub 3}+H, CH{sub 3}F{leftrightarrow}CH{sub 2}F+H, CH{sub 2}F{sub 2}{leftrightarrow}CHF{sub 2}+H, and CHF{sub 3}{leftrightarrow}CF{sub 3}+H. Two equivalent, barrier-less paths are found for the CH{sub 3}+H recombination, two inequivalent, barrier-less paths are found for the CH{sub 2}F+H and CHF{sub 2}+H recombinations (depending on which side of the radical the H atom approaches), and only one barrier-less path is found for the CF{sub 3}+H recombination. Minimum energy path for H atom approaching CF{sub 3} from the concave side is predicted to have a barrier of 27 kcal/mole. Both minimum energy path energies and transitional frequencies as function of R{sub CH} for all 4 reactions are predicted to be similar.

  20. The Effect of Metal Oxide on Nanoparticles from Thermite Reactions

    ERIC Educational Resources Information Center

    Moore, Lewis Ryan

    2006-01-01

    The purpose of this research was to determine how metal oxide used in a thermite reaction can impact the production of nanoparticles. The results showed the presence of nanoparticles (less than 1 micron in diameter) of at least one type produced by each metal oxide. The typical particles were metallic spheres, which ranged from 300 nanometers in…

  1. Removal of VOCs by Oxidation Reaction in Wet Scrubber

    Microsoft Academic Search

    Juntima Chungsiriporn; Charun Bunyakan; Romporn Nikom

    Emission of volatile organic compound (VOCs) including toluene, MEK, and acetone causes serious odour problem. The VOCs emitted from painting, coating, automotive, and printing industries generate air pollution, flammability problem and health effect. Wet scrubber, add-on control device, combining of absorption and oxidation reaction was used to treat the VOCs in polluted air. Solution of strong oxidizing agent, sodium hypochlorite

  2. An On-Target Performic Acid Oxidation Method Suitable for Disulfide Bond Elucidation Using Capillary Electrophoresis - Mass Spectrometry

    E-print Network

    Williams, Brad J.

    2011-08-08

    methods before or after MS detection have been developed to aid in disulfide bond assignment, such as tandem MS followed by database searching or modification of the disulfide bond via chemical reduction or oxidation. Despite these technological...

  3. HETEROGENEOUS REACTIONS OF NITROGEN OXIDES IN SIMULATED ATMOSPHERES

    EPA Science Inventory

    A laboratory study has been conducted on heterogeneous reactions of nitrogen dioxide and nitric oxide to evaluate their potential role in reaction in polluted urban atmosphere. The results of this study suggest that nitrogen dioxide decomposes on a wide variety of solids likely t...

  4. CHEMICAL REACTIONS OF AQUATIC HUMIC MATERIALS WITH SELECTED OXIDANTS

    EPA Science Inventory

    A study was conducted to identify the specific organic reaction products of natural aquatic humic materials with selected oxidants (KMnO4, HOCl, Cl02, O3 and monochloramine). Reaction products were identified by GC/MS after solvent extraction and derivatization. The two most reac...

  5. Studying Chemical Reactions, One Bond at a Time, with Single Molecule AFM Techniques

    NASA Astrophysics Data System (ADS)

    Fernandez, Julio M.

    2008-03-01

    The mechanisms by which mechanical forces regulate the kinetics of a chemical reaction are unknown. In my lecture I will demonstrate how we use single molecule force-clamp spectroscopy and protein engineering to study the effect of force on the kinetics of thiol/disulfide exchange. Reduction of disulfide bond via the thiol/disulfide exchange chemical reaction is crucial in regulating protein function and is of common occurrence in mechanically stressed proteins. While reduction is thought to proceed through a substitution nucleophilic bimolecular (SN2) reaction, the role of a mechanical force in modulating this chemical reaction is unknown. We apply a constant stretching force to single engineered disulfide bonds and measure their rate of reduction by dithiothreitol (DTT). We find that while the reduction rate is linearly dependent on the concentration of DTT, it is exponentially dependent on the applied force, increasing 10-fold over a 300 pN range. This result predicts that the disulfide bond lengthens by 0.34 å at the transition state of the thiol/disulfide exchange reaction. In addition to DTT, we also study the reduction of the engineered disulfide bond by the E. coli enzyme thioredoxin (Trx). Thioredoxins are enzymes that catalyze disulfide bond reduction in all organisms. As before, we apply a mechanical force in the range of 25-450 pN to the engineered disulfide bond substrate and monitor the reduction of these bonds by individual enzymes. In sharp contrast with the data obtained with DTT, we now observe two alternative forms of the catalytic reaction, the first requiring a reorientation of the substrate disulfide bond, causing a shortening of the substrate polypeptide by 0.76±0.07 å, and the second elongating the substrate disulfide bond by 0.21±0.01 å. These results support the view that the Trx active site regulates the geometry of the participating sulfur atoms, with sub-ångström precision, in order to achieve efficient catalysis. Single molecule atomic force microscopy (AFM) techniques, as shown here, can probe dynamic rearrangements within an enzyme's active site which cannot be resolved with any other current structural biological technique. Furthermore, our work at the single bond level directly demonstrates that thiol/disulfide exchange in proteins is a force-dependent chemical reaction. Our findings suggest that mechanical force plays a role in disulfide reduction in vivo, a property which has never been explored by traditional biochemistry. 1.-Wiita, A.P., Ainavarapu, S.R.K., Huang, H.H. and Julio M. Fernandez (2006) Force-dependent chemical kinetics of disulfide bond reduction observed with single molecule techniques. Proc Natl Acad Sci U S A. 103(19):7222-7 2.-Wiita, A.P., Perez-Jimenez, R., Walther, K.A., Gräter, F. Berne, B.J., Holmgren, A., Sanchez-Ruiz, J.M., and Fernandez, J.M. (2007) Probing the chemistry of thioredoxin catalysis with force. Nature, 450:124-7.

  6. From reactants to products via simple hydrogen-bonding networks: Information transmission in chemical reactions

    PubMed Central

    Brancato, Giuseppe; Coutrot, Frédéric; Leigh, David A.; Murphy, Aden; Wong, Jenny K. Y.; Zerbetto, Francesco

    2002-01-01

    The transmission of information is ubiquitous in nature and often occurs through supramolecular hydrogen bonding processes. Here we report that there is a remarkable correlation during synthesis between the efficiency of the hydrogen-bond-directed assembly of peptide-based [2]rotaxanes and the symmetry distortion of the macrocycle in the structure of the final product. It transpires that the ability of the flexible macrocycle-precursor to wrap around an unsymmetrical hydrogen bonding template affects both the reaction yield and a quantifiable measure of the symmetry distortion of the macrocycle in the product. When the yields of peptide rotaxane-forming reactions are high, so is the symmetry distortion in the macrocycle; when the yields are low, indicating a poor fit between the components, the macrocycle symmetry is relatively unaffected by the thread. Thus during a synthetic sequence, as in complex biological assembly processes, hydrogen bonding can code and transmit “information”—in this case a distortion from symmetry—between chemical entities by means of a supramolecularly driven multicomponent assembly process. If this phenomenon is general, it could have far reaching consequences for the use of supramolecular-directed reactions in organic chemistry. PMID:11959948

  7. Interplay of Experiment and Theory in Elucidating Mechanisms of Oxidation Reactions by a Nonheme Ru(IV)O Complex.

    PubMed

    Dhuri, Sunder N; Cho, Kyung-Bin; Lee, Yong-Min; Shin, Sun Young; Kim, Jin Hwa; Mandal, Debasish; Shaik, Sason; Nam, Wonwoo

    2015-07-01

    A comprehensive experimental and theoretical study of the reactivity patterns and reaction mechanisms in alkane hydroxylation, olefin epoxidation, cyclohexene oxidation, and sulfoxidation reactions by a mononuclear nonheme ruthenium(IV)-oxo complex, [Ru(IV)(O)(terpy)(bpm)](2+) (1), has been conducted. In alkane hydroxylation (i.e., oxygen rebound vs oxygen non-rebound mechanisms), both the experimental and theoretical results show that the substrate radical formed via a rate-determining H atom abstraction of alkanes by 1 prefers dissociation over oxygen rebound and desaturation processes. In the oxidation of olefins by 1, the observations of a kinetic isotope effect (KIE) value of 1 and styrene oxide formation lead us to conclude that an epoxidation reaction via oxygen atom transfer (OAT) from the Ru(IV)O complex to the C?C double bond is the dominant pathway. Density functional theory (DFT) calculations show that the epoxidation reaction is a two-step, two-spin-state process. In contrast, the oxidation of cyclohexene by 1 affords products derived from allylic C-H bond oxidation, with a high KIE value of 38(3). The preference for H atom abstraction over C?C double bond epoxidation in the oxidation of cyclohexene by 1 is elucidated by DFT calculations, which show that the energy barrier for C-H activation is 4.5 kcal mol(-1) lower than the energy barrier for epoxidation. In the oxidation of sulfides, sulfoxidation by the electrophilic Ru-oxo group of 1 occurs via a direct OAT mechanism, and DFT calculations show that this is a two-spin-state reaction in which the transition state is the lowest in the S = 0 state. PMID:26075466

  8. Reactions of calcium orthosilicate and barium zirconate with oxides and sulfates of various elements

    NASA Technical Reports Server (NTRS)

    Zaplatynsky, I.

    1979-01-01

    Calcium orthosilicate and barium zirconate were evaluated as the insulation layer of thermal barrier coatings for air cooled gas turbine components. Their reactions with various oxides and sulfates were studied at 1100 C and 1300 C for times ranging up to 400 and 200 hours, respectively. These oxides and sulfates represent potential impurities or additives in gas turbine fuels and in turbine combustion air, as well as elements of potential bond coat alloys. The phase compositions of the reaction products were determined by X-ray diffraction analysis. BaZrO3 and 2CaO-SiO2 both reacted with P2O5, V2O5, Cr2O3, Al2O3, and SiO2. In addition, 2CaO-SiO2 reacted with Na2O, BaO, MgO, and CoO and BaZrO3 reacted with Fe2O3.

  9. Cluster reactivity experiments: Employing mass spectrometry to investigate the molecular level details of catalytic oxidation reactions

    PubMed Central

    Johnson, Grant E.; Tyo, Eric C.; Castleman, A. W.

    2008-01-01

    Mass spectrometry is the most widely used tool in the study of the properties and reactivity of clusters in the gas phase. In this article, we demonstrate its use in investigating the molecular-level details of oxidation reactions occurring on the surfaces of heterogeneous catalysts via cluster reactivity experiments. Guided ion beam mass spectrometry (GIB-MS) employing a quadrupole–octopole–quadrupole (Q–O–Q) configuration enables mass-selected cluster ions to be reacted with various chemicals, providing insight into the effect of size, stoichiometry, and ionic charge state on the reactivity of catalyst materials. For positively charged tungsten oxide clusters, it is shown that species having the same stoichiometry as the bulk, WO3+, W2O6+, and W3O9+, exhibit enhanced activity and selectivity for the transfer of a single oxygen atom to propylene (C3H6), suggesting the formation of propylene oxide (C3H6O), an important monomer used, for example, in the industrial production of plastics. Furthermore, the same stoichiometric clusters are demonstrated to be active for the oxidation of CO to CO2, a reaction of significance to environmental pollution abatement. The findings reported herein suggest that the enhanced oxidation reactivity of these stoichiometric clusters may be due to the presence of radical oxygen centers (W–O?) with elongated metal–oxygen bonds. The unique insights gained into bulk-phase oxidation catalysis through the application of mass spectrometry to cluster reactivity experiments are discussed. PMID:18687883

  10. Transient liquid phase bonding of ferritic oxide dispersion strengthened alloys

    Microsoft Academic Search

    Venu Gopal Krishnardula

    2006-01-01

    Oxide dispersion strengthened (ODS) alloys possess excellent properties including resistance to oxidation, corrosion, creep and thermal fatigue. In addition, ferritic ODS alloys exhibit resistance to void swelling and are of particular interest to the nuclear industry. The present study involves the joining of fuel cans to end caps that will be utilized in the nuclear industry. Mechanically alloyed (MA) ODS

  11. Pulsed Plasma-Assisted Diffusion Bonding of Oxide Dispersion-Strengthened FeCrAl Alloys

    NASA Astrophysics Data System (ADS)

    Tatlock, Gordon J.; Dyadko, Eugene G.; Dryepondt, Sebastien N.; Wright, Ian G.

    2007-07-01

    The successful joining of oxide dispersion-strengthened (ODS) alloy PM2000 rods by pulsed plasma-assisted diffusion bonding is reported. During secondary recrystallization after joining, the alloy grains grew across the original interface, which was then marked by a row of remnant alumina particles. These did not appear to act as pinning sites for the alloy grain boundaries, which moved easily past them, leaving a strong diffusion bond.

  12. A critical study of the role of the surface oxide layer in titanium bonding

    NASA Technical Reports Server (NTRS)

    Dias, S.; Wightman, J. P.

    1982-01-01

    The molecular understanding of the role which the surface oxide layer of the adherend plays in titanium bonding is studied. The effects of Ti6-4 adherends pretreatment, bonding conditions, and thermal aging of the lap shear specimens were studied. The use of the SEM/EDAX and ESCA techniques to study surface morphology and surface composition was emphasized. In addition, contact angles and both infrared and visible reflection spectroscopy were used in ancillary studies.

  13. Compositional Effects on Aluminide Oxidation Performance: Objectives for Improved Bond Coats

    Microsoft Academic Search

    B. A. Pint; J. A. Haynes; I. G. Wright; C. Leyens

    2001-01-01

    In order to achieve long thermal barrier coating lifetimes, underlying metallic bond coats need to form adherent, slow-growing AlâOâ layers. A set of guidelines for developing aluminide bond coat compositions is proposed in order to maximize oxidation performance, i.e. forming a slow-growing adherent alumina scale. These criteria are based on results from cast, model alloy compositions and coatings made in

  14. The Oxidation Behavior of TBC with Cold Spray CoNiCrAlY Bond Coat

    Microsoft Academic Search

    W. R. Chen; E. Irissou; X. Wu; J.-G. Legoux; B. R. Marple

    2011-01-01

    Cold gas dynamic spray (CGDS) has been considered a potential technique to produce the metallic bond coat for TBC applications,\\u000a because of its fast deposition rate and low deposition temperature. This article presents the influence of spray processes\\u000a for bond coat, including air plasma spray, high velocity oxy-fuel, and in particular CGDS, on the oxidation performance of\\u000a TBCs with a

  15. Structures of the aluminum oxides studied by ab initio methods with natural bond orbital analysis

    Microsoft Academic Search

    A. V. Nemukhin; F. Weinhold

    1992-01-01

    We present a comprehensive theoretical analysis for the low-lying isomeric structures, energetics, and vibrational properties of dinuclear aluminum oxides Al2On (n=1–4) to aid interpretation of experimental spectroscopic data for these species. We also carried out natural population and natural bond orbital (NBO) analysis of the correlated and uncorrelated abinitio wave functions in order to elucidate the general bonding principles governing

  16. Reactions of Propylene Oxide on Supported Silver Catalysts: Insights into Pathways Limiting Epoxidation Selectivity

    SciTech Connect

    Kulkarni, Apoorva; Bedolla-Pantoja, Marco; Singh, Suyash; Lobo, Raul F.; Mavrikakis, Manos; Barteau, Mark A.

    2012-02-04

    The reactions of propylene oxide (PO) on silver catalysts were studied to understand the network of parallel and sequential reactions that may limit the selectivity of propylene epoxidation by these catalysts. The products of the anaerobic reaction of PO on Ag/a-Al2O3 were propanal, acetone and allyl alcohol for PO conversions below 2–3%. As the conversion of PO was increased either by increasing the temperature or the contact time, acrolein was formed at the expense of propanal, indicating that acrolein is a secondary reaction product in PO decomposition. With addition of oxygen to the feedstream the conversion of PO increased moderately. In contrast to the experiments in absence of oxygen, CO2 was a signi?cant product while the selectivity to propanal decreased as soon as oxygen was introduced in the system. Allyl alcohol disappeared completely from the product stream in the presence of oxygen, reacting to form acrolein and CO2. The product distribution may be explained by a network of reactions involving two types of oxametallacycles formed by ring opening of PO: one with the oxygen bonded to C1 (OMC1, linear) and the other with oxygen bonded to C2 (OMC2, branched). OMC1 reacts to form PO, propanal, and allyl alcohol.

  17. A critical study of the role of the surface oxide layer in titanium bonding

    NASA Technical Reports Server (NTRS)

    Dias, S.; Wightman, J. P.

    1983-01-01

    Scanning electron microscope/X-ray photoelectron spectroscopy (SEM/XPS) analysis of fractured adhesively bonded Ti 6-4 samples is discussed. The text adhesives incuded NR 056X polyimide, polypheylquinoxaline (PPQ), and LARC-13 polyimide. Differentiation between cohesive and interfacial failure was based on the absence of presence of a Ti 2p XPS photopeak. In addition, the surface oxide layer on Ti-(6A1-4V) adherends is characterized and bond strength and durability are addressed. Bond durability in various environmental conditions is discussed.

  18. Experimental and Molecular Dynamics Simulations of Tribochemical Reactions with ZDDP: Zinc Phosphate–Iron Oxide Reaction

    Microsoft Academic Search

    Clotilde Minfray; Thierry Le Mogne; Jean-Michel Martin; Tasuku Onodera; Sayaka Nara; Shuko Takahashi; Hideyuki Tsuboi; Michihisa Koyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Carlos A. Del Carpio; Akira Miyamoto

    2008-01-01

    Zinc phosphate glass is considered to be the main constituent of tribofilms generated under boundary lubrication with zinc dialkyldithiophosphate (ZDDP), a well-known antiwear additive. The reaction occurring during friction between zinc phosphate glasses and steel native iron oxide layer is investigated by both an experimental approach and by Molecular Dynamics simulations (MD). The importance of this “tribochemical” reaction in the

  19. Studies of the kinetics and mechanisms of perfluoroether reactions on iron and oxidized iron surfaces

    NASA Technical Reports Server (NTRS)

    Napier, Mary E.; Stair, Peter C.

    1992-01-01

    Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of three model fluorinated ethers on clean polycrystalline iron surfaces and iron surfaces chemically modified with oxygen. Low temperature adsorption of the model fluorinated ethers on the clean, oxygen modified and oxidized iron surfaces was molecular. Thermally activated defluorination of the three model compounds was observed on the clean iron surface at remarkably low temperatures, 155 K and below, with formation of iron fluoride. Preferential C-F bond scission occurred at the terminal fluoromethoxy, CF3O, of perfluoro-1-methoxy-2-ethoxy ethane and perfluoro-1-methoxy-2-ethoxy propane and at CF3/CF2O of perfluoro-1,3-diethoxy propane. The reactivity of the clean iron toward perfluoroalkylether decomposition when compared to other metals is due to the strength of the iron fluoride bond and the strong electron donating ability of the metallic iron. Chemisorption of an oxygen overlayer lowered the reactivity of the iron surface to the adsorption and decomposition of the three model fluorinated ethers by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface at 138 K, through a Lewis acid assisted cleavage of the carbon oxygen bond, with preferential attack at the terminal fluoromethoxy, CF3O. The oxidized iron surface did not passivate, but became more reactive with time. Perfluoro-1-methoxy-2-ethoxy propane and perfluoro-1,3-diethoxy propane desorbed prior to the observation of decomposition on the oxidized iron surface.

  20. Thermal oxidative degradation reactions of perfluoroalkylethers

    NASA Technical Reports Server (NTRS)

    Paciorek, K. L.; Ito, T. I.; Kratzer, R. H.

    1981-01-01

    The mechanisms operative in thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes are investigated. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids is not established. It was determined that this behavior is not associated with hydrogen end groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres is dependent on the surface/volume ratio. Once a limiting ratio is reached, a steady rate appears to be attained. Based on elemental analysis and oxygen consumption data, CF2OCF2CF2O2, no. CF2CF2O, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys is much more drastic in the case of Fomblin Z fluids than that observed for the hexafluoropropene derived materials. The effectiveness of antioxidation anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys is very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appears to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes this takes place to a much lesser degree with M-50.

  1. Palladium(II) catalyzed intramolecular oxidation of conjugated kienes forming carbon-carbon bonds

    SciTech Connect

    Gatti, R.G.P.; Nilsson, Y.I.M.; Baeckvall, J.E. [Univ. of Uppsala (Sweden)

    1995-12-31

    As an extension of the earlier developed 1,4-oxidation of conjugated dienes, it would be interesting to investigate the possibility to form carbon-carbon bonds, especially in the creation of cyclic systems (eq.). Stabilized carbon nucleophiles were unsuccessful, but if instead a vinyl palladium is generated via chloropalladation this inserts into the diene to form a carbon-carbon bond. The overall 1,4-oxidation of the vinylic carbon and the chloride across the diene occurs in an anti fashion. A suggested mechanism involve a {pi}-allyl-palladium intermediate.

  2. Reaction bonded silicon carbide material characteristics as related to its use in high power laser systems

    NASA Astrophysics Data System (ADS)

    Pitschman, Matthew; Miller, Travis; Hedges, Alan R.; Rummel, Steve

    2014-09-01

    Reaction bonded silicon carbide (RB SiC) is a durable material that is well-suited for use as a high power laser mirror substrate. The reaction bonded material has a low mass density, a high Young's Modulus, good thermal conductivity, and a very low coefficient of thermal expansion. All of these properties are beneficial in mirror substrates used in multikilowatt lasers. In conjunction with the development of RB SiC, special polishing processes, fabrication processes, and coatings have also been developed. In this paper we will present a comparison of the material properties of RB SiC and other mirror materials currently used in high power lasers. A brief overview of the critical fabrication and coating processes will also be reviewed. Finally, we will present thermal heat load test data showing the surface deformation of various high power mirrors used under heat loads typically found in laser systems operating at average powers greater than 10 kilowatts.

  3. Covalent organic frameworks formed with two types of covalent bonds based on orthogonal reactions.

    PubMed

    Zeng, Yongfei; Zou, Ruyi; Luo, Zhong; Zhang, Huacheng; Yao, Xin; Ma, Xing; Zou, Ruqiang; Zhao, Yanli

    2015-01-28

    Covalent organic frameworks (COFs) are excellent candidates for various applications. So far, successful methods for the constructions of COFs have been limited to a few condensation reactions based on only one type of covalent bond formation. Thus, the exploration of a new judicious synthetic strategy is a crucial and emergent task for the development of this promising class of porous materials. Here, we report a new orthogonal reaction strategy to construct COFs by reversible formations of two types of covalent bonds. The obtained COFs consisting of multiple components show high surface area and high H2 adsorption capacity. The strategy is a general protocol applicable to construct not only binary COFs but also more complicated systems in which employing regular synthetic methods did not work. PMID:25581488

  4. Reaction Pathways and Energetics of Etheric C?O Bond Cleavage Catalyzed by Lanthanide Triflates

    SciTech Connect

    Assary, Rajeev S.; Atesin, Abdurrahman C.; Li, Zhi; Curtiss, Larry A.; Marks, Tobin J.

    2013-07-15

    Efficient and selective cleavage of etheric C?O bonds is crucial for converting biomass into platform chemicals and liquid transportation fuels. In this contribution, computational methods at the DFT B3LYP level of theory are employed to understand the efficacy of lanthanide triflate catalysts (Ln(OTf)3, Ln = La, Ce, Sm, Gd, Yb, and Lu) in cleaving etheric C?O bonds. In agreement with experiment, the calculations indicate that the reaction pathway for C?O cleavage occurs via a C?H ? O?H proton transfer in concert with weakening of the C?O bond of the coordinated ether substrate to ultimately yield a coordinated alkenol. The activation energy for this process falls as the lanthanide ionic radius decreases, reflecting enhanced metal ion electrophilicity. Details of the reaction mechanism for Yb(OTf)3-catalyzed ring opening are explored in depth, and for 1-methyl-d3-butyl phenyl ether, the computed primary kinetic isotope effect of 2.4 is in excellent agreement with experiment (2.7), confirming that etheric ring-opening pathway involves proton transfer from the methyl group alpha to the etheric oxygen atom, which is activated by the electrophilic lanthanide ion. Calculations of the catalytic pathway using eight different ether substrates indicate that the more rapid cleavage of acyclic versus cyclic ethers is largely due to entropic effects, with the former C?O bond scission processes increasing the degrees of freedom/particles as the transition state is approached.

  5. Thermal oxidative degradation reactions of perfluoroalklethers

    NASA Technical Reports Server (NTRS)

    Paciorek, K. L.; Harris, D. H.; Smythe, M. E.; Kratzer, R. H.

    1983-01-01

    The objective of this contract was to investigate the mechanisms operative in thermal and thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids has not been established. It was determined that this behavior was not associated with hydrogen end-groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres was found to be dependent on the surface/volume ratio. Once a limiting ratio was reached, a steady rate appeared to be attained. Based on elemental analysis and oxygen consumption data, -CF2OCF2CF2O-, not -CF2CF2O-, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys was found to be much more drastic in the case of Fomblin Z fluids than that observed for the hexalfuoropropane oxide derived materials. The effectiveness of antioxidation/anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys was very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appeared to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes; this took place to a much lesser degree with M-50.

  6. Intramolecular anodic olefin coupling reactions: using competition studies to probe the mechanism of oxidative cyclization reactions.

    PubMed

    Xu, Hai-Chao; Moeller, Kevin D

    2010-04-16

    A competition experiment was designed so that the relative rates of anodic cyclization reactions under various electrolysis conditions can be determined. Reactions with ketene dithioacetal and enol ether-based substrates that use lithium methoxide as a base were shown to proceed through radical cation intermediates that were trapped by a sulfonamide anion. Results for the oxidative coupling of a vinyl sulfide with a sulfonamide anion using the same conditions were consistent with the reaction proceeding through a nitrogen-radical. PMID:20302359

  7. Brazing of reaction-bonded silicon carbide and Inconel 600 with an iron-based alloy

    Microsoft Academic Search

    J. R. McDermid; R. A. L. Drew

    1990-01-01

    The objective of the present work was to join reaction-bonded silicon carbide to Inconel 600 (IN600, a nickel-based superalloy) for use in high temperature applications by brazing with an Fe-20wt% alloy. This joining method resulted in the molten filler metal reacting with the IN600 to form a Ni-Fe-Si solution, which in turn formed a liquid with the free silicon phase

  8. Classification of metal-oxide bonded interactions based on local potential- and kinetic-energy densities.

    PubMed

    Gibbs, G V; Cox, D F; Crawford, T D; Rosso, K M; Ross, N L; Downs, R T

    2006-02-28

    A classification of the hydrogen fluoride H-F-bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio /Vr(c)/ / Gr(c) where /Vr(c)/ is the magnitude of the local potential-energy density and Gr(c) is the local kinetic-energy density, each evaluated at a bond critical point r(c). A calculation of the ratio for the M-O bonded interactions comprising a relatively large number of oxide molecules and earth materials, together with the constraints imposed by the values of inverted Delta2rho r(c) and the local electronic energy density, Hr(c) = Gr(c) + Vr(c), in the H-F study, yielded practically the same classification for the oxides. This is true despite the different trends that hold between the bond critical point and local energy density properties with the bond lengths displayed by the H-F and M-O bonded interactions. On the basis of the ratio, Li-O, Na-O, and Mg-O bonded interactions classify as closed-shell ionic bonds, Be-O, Al-O, Si-O, B-O, and P-O interactions classify as bonds of intermediate character with the covalent character increasing from Be-O to P-O. N-O interactions classify as shared covalent bonds. C-O and S-O bonded interactions classify as both intermediate and covalent bonded interactions. The C-O double- and triple-bonded interactions classify as intermediate-bonded interactions, each with a substantial component of covalent character and the C-O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded interactions. The ratios for the Be-O, Al-O, and Si-O bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between the ratio and the character of the bonded interactions is consistent with trends expected from electronegativity considerations. The ratio increases as the net charges and the coordination numbers for the atoms for several Ni-sulfides decrease. On the contrary, the ratio for the Si-O bonded interactions for the orthosilicate, forsterite, Mg2SiO4, and the high-pressure silica polymorph, stishovite, decreases as the observed net atomic charges and the coordination numbers of Si and O increase in value. The ratio for the Ni-Ni bonded interactions for the Ni-sulfides and bulk Ni metal indicate that the interactions are intermediate in character with a substantial component of ionic character. PMID:16512733

  9. Bond length and radii variations in fluoride and oxide molecules and crystals

    NASA Astrophysics Data System (ADS)

    Nicoll, J. S.; Gibbs, G. V.; Boisen, M. B.; Downs, R. T.; Bartelmehs, K. L.

    1994-05-01

    Molecular orbital calculations completed on fluoride molecules containing first and second row cations have generated bond lengths, R, that match those observed for coordinated polyhedra in crystals to within ˜0.04 Å, on average. The calculated bond lengths and those observed for fluoride crystals can be ranked with the expression R=Kp -0.22, where p=s/r, s is the Pauling strength of the bond, r is the row number of the cation and K=1.34. The exponent -0.22 (? -2/9) is the same as that observed for oxide, nitride and sulfide molecules and crystals. Bonded radii for the fluoride anion, obtained from theoretical electron density maps, increase linearly with bond length. Those calculated for the cations as well as for the fluoride anion match calculated promolecule radii to within ˜0.03 Å, on average, suggesting that the electron density distributions in the vicinity of the minima along the bond paths possess a significant atomic component despite bond type. Bonded radii for Si and O ions provided by experimental electron density maps measured for the oxides coesite, danburite and stishovite match those calculated for a series of monosilicic acid molecules. The resulting radii increase with bond length and coordination number with the radius of the oxide ion increasing at a faster rate than that of the Si cation. The oxide ion within danburite exhibits several distinct radii, ranging between 0.9 and 1.2 Å, rather than a single radius with each exhibiting a different radius along each of the nonequivalent bonds with B, Si and Ca. Promolecule radii calculated for the coordinated polyhedra in danburite match procrystal radii obtained in a structure analysis to within 0.002 Å. The close agreement between these two sets of radii and experimentally determined bonded radii lends credence to Slater's statement that the difference between the electron density distribution observed for a crystal and that calculated for a procrystal (IAM) model of the crystal “would be small and subtle, and very hard to determine by examination of the total charge density.”

  10. Computational studies of polysiloxanes : oxidation potentials and decomposition reactions.

    SciTech Connect

    Assary, R. S.; Curtiss, L. A.; Redfern, P. C.; Zhang, Z.; Amine, K. (Center for Nanoscale Materials); ( CSE); ( MSD); (Northwestern Univ.)

    2011-06-23

    Silicon-containing solvents have tremendous potential for application as electrolytes for electrical energy storage devices such as lithium-ion (air) batteries and supercapacitors. Quantum chemical methods were employed to investigate trends in oxidation potentials and decomposition reactions of a series of polysiloxanes. Various electron-donating and -withdrawing substituents can be used to tune the oxidation potential in shorter chain siloxanes but not in longer ones. Decomposition reactions of siloxanes in their oxidized states were investigated and compared against their carbon analogues. These studies suggest that the Si-O group provides added stability for siloxanes over their carbon analogues. Computational studies have also been performed for various disiloxanes and siloxanes with spacer groups to understand their thermochemical stability and oxidation potentials.

  11. Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

    E-print Network

    Zare, Richard N.

    the reaction by photolyzing Cl2 with linearly polarized 355 nm light. Excitation of the first C­H overtoneBond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2 Hans reaction is investigated by co-expanding a mixture of Cl2 and CH2D2 into a vacuum chamber and initiating

  12. Coupling of oxidative dehydrogenation and aromatization reactions of butane

    SciTech Connect

    Xu, Wen-Qing; Suib, S.L. (Univ. of Connecticut, Storrs, CT (United States))

    1994-01-01

    Coupling of oxidative dehydrogenation and aromatization of butane by using a dual function catalyst has led to a significant enhancement of the yields (from 25 to 40%) and selectivities to aromatics (from 39 to 64%). Butane is converted to aromatics by using either zinc-promoted [Ga]-ZSM-5 or zinc and gallium copromoted [Fe]-ZSM-5 zeolite as a catalyst. However, the formation of aromatics is severely limited by hydrocracking of butane to methane, ethane, and propane due to the hydrogen formed during aromatization reactions. On the other hand, the oxidative dehydrogenation of butane to butene over molybdate catalysts is found to be accompanied by a concurrent undesirable reaction, i.e., total oxidation. When two of these reactions (oxidative dehydrogenation and aromatization of butane) are coupled by using a dual function catalyst they have shown to complement each other. It is believed that the rate-limiting step for aromatization (butane to butene) is increased by adding an oxidative dehydrogenation catalyst (Ga-Zn-Mg-Mo-O). The formation of methane, ethane, and propane was suppressed due to the removal of hydrogen initially formed as water. Studies of ammonia TPD show that the acidities of [Fe]-ZSM-5 are greatly affected by the existence of metal oxides such as Ga[sub 2]O[sub 3], MgO, ZnO, and MoO[sub 3]. 40 refs., 9 figs., 1 tab.

  13. Indium(III) chloride-catalyzed oxidative cleavage of carbon–carbon multiple bonds by tert-butyl hydroperoxide in water—a safer alternative to ozonolysis

    Microsoft Academic Search

    Brindaban C. Ranu; Sukalyan Bhadra; Laksmikanta Adak

    2008-01-01

    An efficient and general method for the oxidative cleavage of alkenes and alkynes using tert-butyl hydroperoxide and indium(III) chloride as catalyst in water to give the corresponding carboxylic acids or ketones has been achieved. The reaction conditions are compatible with sensitive moieties such as peptide bonds, tert-butyl carboxylic esters and N-Boc-protected tryptophan. The catalyst could be recycled.

  14. C-H vs C-C Bond Activation of Acetonitrile and Benzonitrile via Oxidative Addition: Rhodium vs Nickel and Cp* vs Tp

    E-print Network

    Jones, William D.

    C-H vs C-C Bond Activation of Acetonitrile and Benzonitrile via Oxidative Addition: Rhodium vs@chem.rochester.edu Abstract: The photochemical reaction of (C5Me5)Rh(PMe3)H2 (1) in neat acetonitrile leads to formation of the C-H activation product, (C5Me5)Rh(PMe3)(CH2CN)H (2). Thermolysis of this product in acetonitrile

  15. Carbon-nitrogen bond-forming reactions in supercritical and expanded-liquid carbon dioxide media : green synthetic chemistry with multiscale reaction and phase behavior modeling

    E-print Network

    Ciccolini, Rocco P

    2008-01-01

    The goal of this work was to develop a detailed understanding of carbon-nitrogen (C-N) bond-forming reactions of amines carried out in supercritical and expanded-liquid carbon dioxide (CO2) media. Key motivations behind ...

  16. Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product

    NASA Technical Reports Server (NTRS)

    David, Dennis D.; Dee, Louis A.; Beeson, Harold D.

    1997-01-01

    Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.

  17. Isothermal oxidation behavior of cryomilled NiCrAlY bond coat: Homogeneity and growth rate of TGO

    Microsoft Academic Search

    Kaka Ma; Julie M. Schoenung

    2011-01-01

    Isothermal oxidation behavior of thermal barrier coatings (TBCs) with cryomilled NiCrAlY bond coats, in comparison with equivalent TBCs with conventional bond coats was investigated. The growth rate and homogeneity of the thermally grown oxide (TGO) were quantified and characterized through rigorous statistical evaluation. The initial TGO growth follows parabolic growth kinetics in both systems, but the cryomilled coatings exhibit improved

  18. On the Nature of Carbon-Hydrogen Bond Activation at Rhodium and Related Reactions

    E-print Network

    Jones, William D.

    the past 20 years, substantial progress has been made in the understanding of the activation of C(IV) as a stoichiometric oxidant, for the conversion of alkanes into alcohols and alkyl chlorides (eq 1). While the initial for future investigations in this field. In the 1970s, Crabtree et al. reported a reaction in which an olefin

  19. Predicting gold-mediated catalytic oxidative-coupling reactions from single crystal studies.

    PubMed

    Xu, Bingjun; Madix, Robert J; Friend, Cynthia M

    2014-03-18

    Though metallic gold is chemically inert under ambient conditions, its surface is extremely reactive and selective for many key oxidative chemical transformations when activated by atomic oxygen. A molecular-level understanding of the mechanism of these processes could allow researchers to design "green" catalytic processes mediated by gold-based materials. This Account focuses on the mechanistic framework for oxidative-coupling reactions established by fundamental studies on oxygen-activated Au(111) and the application of these principles to steady-state catalytic conditions. We also discuss the importance of the paradigms discovered both for predicting new oxidative-coupling reactions and for understanding existing literature. The mechanistic framework for the oxidative coupling of alcohols on gold surfaces predicts that new oxidative-coupling reactions should occur between amines and aldehydes and amines and alcohols as well as through alcohol carbonylation. Adsorbed atomic oxygen on the gold surface facilitates the activation of the substrates, and nucleophilic attack and ?-H elimination are the two fundamental reactions that propagate the versatile chemistry that ensues. In the self-coupling of primary alcohols, adsorbed atomic oxygen first activates the O-H bond in the hydroxyl group at ?150 K, which forms the corresponding adsorbed alkoxy groups. The rate-limiting step of the self-coupling reaction is the ?-H elimination reaction of alkoxy groups to form the corresponding aldehydes and occurs with an activation barrier of approximately 12 kcal/mol. The remaining alkoxy groups nucleophilically attack the electron-deficient aldehyde carbonyl carbon to yield the adsorbed "hemiacetal". This intermediate undergoes facile ?-H elimination to produce the final coupling products, esters with twice the number of carbon atoms as the starting alcohols. This mechanistic insight suggests that cross-coupling occurs between alcohols and aldehydes, based on the logic that the nucleophilic reaction should be independent of the origin of the aldehydes, whether formed in situ or introduced externally. As a further example, adsorbed amides, formed from deprotonation of amines by atomic oxygen, can also attack aldehydes nucleophilically to yield the corresponding amides. Our mechanistic framework can also explain more elaborate gold-mediated chemistry, such as a unique carbonylation reaction via two subsequent nucleophilic attacks. These model studies on well-defined Au(111) at low pressure predict steady-state catalytic behavior on nanoporous gold under practical conditions. The fundamental principles of this research can also explain many other oxygen-assisted gold-mediated reactions observed under ambient conditions. PMID:24387694

  20. The nitric acid oxidation of 2-octanol. A model reaction for multiple heterogeneous liquid–liquid reactions

    Microsoft Academic Search

    B. A. A. van Woezik; K. R. Westerterp

    2000-01-01

    The oxidation of 2-octanol with nitric acid has been selected as a model reaction for a heterogeneous liquid–liquid reaction with an undesired side reaction. 2-Octanol is first oxidized to 2-octanone, which can be further oxidized to carboxylic acids. An extensive experimental program has been followed using heat flow calorimetry supported by chemical analysis. A series of oxidation experiments has been

  1. High-Temperature Thermoelectric Characterization of IIIV Semiconductor Thin Films by Oxide Bonding

    E-print Network

    -temperature material characterization of semiconductor thin films for thermoelectric power generation, photovoltaicHigh-Temperature Thermoelectric Characterization of III­V Semiconductor Thin Films by Oxide Bonding-temperature thermoelectric charac- terization of thin-film III­V semiconductor materials that suffer from the side- effect

  2. Copper-catalyzed intramolecular N-S bond formation by oxidative dehydrogenative cyclization.

    PubMed

    Wang, Zhen; Kuninobu, Yoichiro; Kanai, Motomu

    2013-07-19

    Copper-catalyzed synthesis of benzo[d]isothiazol-3(2H)-ones and N-acyl-benzothiazetidine by intramolecular dehydrogenative cyclization is described. In this reaction, a new nitrogen-sulfur (N-S) bond is formed by N-H/S-H coupling. The present reaction has high functional group tolerance and gives products in gram scale. This method promotes double cyclization, allowing for synthesis of a drug intermediate. PMID:23786601

  3. Thermochemical properties and bond dissociation enthalpies of 3- to 5-member ring cyclic ether hydroperoxides, alcohols, and peroxy radicals: cyclic ether radical + (3)O(2) reaction thermochemistry.

    PubMed

    Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

    2014-05-01

    The formation of cyclic ethers is a major product in the oxidation of hydrocarbons, and the oxidation of biomass derived alcohols. Cyclic ethers are formed in the initial reactions of alkyl radicals with dioxygen in combustion and precombustion processes that occur at moderate temperatures. They represent a significant part of the oxygenated pollutants found in the exhaust gases of engines. Cyclic ethers can also be formed from atmospheric reactions of olefins. Additionally, cyclic ethers have been linked to the formation of the secondary organic aerosol (SOA) in the atmosphere. In combustion and thermal oxidation processes these cyclic ethers will form radicals that react with (3)O2 to form peroxy radicals. Density functional theory and higher level ab initio calculations are used to calculate thermochemical properties and bond dissociation enthalpies of 3 to 5 member ring cyclic ethers (oxirane, yC2O, oxetane, yC3O, and oxolane, yC4O), corresponding hydroperoxides, alcohols, hydroperoxy alkyl, and alkyl radicals which are formed in these oxidation reaction systems. Trends in carbon-hydrogen bond dissociation energies for the ring and hydroperoxide group relative to ring size and to distance from the ether group are determined. Bond dissociation energies are calculated for use in understanding effects of the ether oxygen in the cyclic ethers, their stability, and kinetic properties. Geometries, vibration frequencies, and enthalpies of formation, ?H°f,298, are calculated at the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), the composite CBS-QB3, and G3MP2B3 methods. Entropy and heat capacities, S°(T) and Cp°(T) (5 K ? T ? 5000), are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations. The strong effects of ring strain on the bond dissociation energies in these peroxy systems are also of fundamental interest. Oxetane and oxolane exhibit a significant stabilization, 10 kcal mol(-1), lower ?fH°298 when an oxygen group is on the ether carbon relative to the isomer with the oxygen group on a secondary carbon. Relative to alkane systems the ether oxygen decreases bond dissociation energies (BDEs) on carbon sites adjacent to the ether by ?5 kcal mol(-1), and increases BDEs on nonether carbons ?1 kcal mol(-1). The cyclic structures have significant effects on the C-H, CO-OH, COO-H, and CO-H bond dissociation enthalpies. These values can be used to help calibrate calculations of larger more complex bicyclic and tricyclic hydrocarbon and ether species. PMID:24660891

  4. Bonding Model for Transition Metal and Rare Earth Monoxides and Laser Spectroscopy of Nickel-Oxide

    NASA Astrophysics Data System (ADS)

    Srdanov, Vojislav I.

    We discovered that, for the transition metal and the rare earth monoxide series, the sum of the ionization potential of the metal, the energy of the lowest ( ...np) configuration of the metal ion and the thermochemical dissociation energy of the molecule adds up to a constant number. The correlation is particularly striking for the rare earth monoxides where the standard deviation is less than 1%. Based on this correlation we developed a new bonding scheme common for both the transition metal and rare earth monoxides. We propose that the bonding is invariant within the series and consists of an ionic and a covalent contribution. In our model a covalent contribution to the bonding of the inner-core d and f orbitals is negligible. This is in contrast to the current paradigm regarding the significant role of the d orbitals in the bonding in the first and second row transition metal oxides. Our model also appears to be in conflict with the M^{2+} O^{2-} ligand-field bonding model currently accepted for the rare earth monoxides. Based on the empirical correlation and the proposed bonding mechanism, however, we give a number of predictions regarding yet unmeasured fundamental quantities of some of the oxides such as permanent dipole moments, dissociation energies and equilibrium bond distances. We also present the results of the first high resolution laser spectroscopic study of the NiO molecule. Several bands in the green spectral region were found to originate from the ground state of NiO; their analysis allowed us to determine the following fundamental parameters: Ground state symmetry: ^3Sigma^-; Vibrational frequency: omega_{ rm e} = 8.39.1 cm^{ -1}; Equilibrium distance: r_ {rm e} = 1.627 A. With this work the determination of the ground state parameters for the first row transition metal oxides is now complete.

  5. Intramolecular Hydrogen Bonding: A Potential Strategy for More Bioavailable Inhibitors of Neuronal Nitric Oxide Synthase

    PubMed Central

    Labby, Kristin Jansen; Xue, Fengtian; Kraus, James M.; Ji, Haitao; Mataka, Jan; Li, Huiying; Martásek, Pavel; Roman, Linda J.; Poulos, Thomas L.; Silverman, Richard B.

    2012-01-01

    Selective neuronal nitric oxide synthase (nNOS) inhibitors have therapeutic applications in the treatment of numerous neurodegenerative diseases. Here we report the synthesis and evaluation of a series of inhibitors designed to have increased cell membrane permeability via intramolecular hydrogen bonding. Their potencies were examined in both purified enzyme and cell-based assays; a comparison of these results demonstrates that two of the new inhibitors display significantly increased membrane permeability over previous analogs. NMR spectroscopy provides evidence of intramolecular hydrogen bonding under physiological conditions in two of the inhibitors. Crystal structures of the inhibitors in the nNOS active site confirm the predicted non-intramolecular hydrogen bonded binding mode. Intramolecular hydrogen bonding may be an effective approach for increasing cell membrane permeability without affecting target protein binding. PMID:22370337

  6. Ab initio valence-bond cluster model for ionic solids: Alkaline-earth oxides

    NASA Astrophysics Data System (ADS)

    Lorda, A.; Illas, F.; Rubio, J.; Torrance, J. B.

    1993-03-01

    A linear M-O-M (M=metal, O=oxygen) cluster embedded in a Madelung field, and also including the quantum effects of the neighboring ions, is used to represent the alkaline-earth oxides. For this model an ab initio wave function is constructed as a linear combination of Slater determinants written in an atomic orbital basis set, i.e., a valence-bond wave function. Each valence-bond determinant (or group of determinants) corresponds to a resonating valence-bond structure. We have obtained ab initio valence-bond cluster-model wave functions for the electronic ground state and the excited states involved in the optical-gap transitions. Numerical results are reasonably close to the experimental values. Moreover, the model contains the ionic model as a limiting case and can be readily extended and improved.

  7. Nickel-Catalyzed C?O/C?H Cross-Coupling Reactions for C?C Bond Formation.

    PubMed

    Chen, Tieqiao; Han, Li-Biao

    2015-07-20

    Halides not required: Nickel-catalyzed C?O/C?H cross-couplings for the construction of C?C bonds have recently been disclosed. By carefully optimizing the nickel catalyst, new C?C bond-forming reactions were developed, and even quaternary stereogenic centers are now accessible in high yields from readily available phenoxide derivatives and hydrocarbons. PMID:26073575

  8. Efficient and directed peptide bond formation in the gas phase via ion/ion reactions

    PubMed Central

    McGee, William M.; McLuckey, Scott A.

    2014-01-01

    Amide linkages are among the most important chemical bonds in living systems, constituting the connections between amino acids in peptides and proteins. We demonstrate the controlled formation of amide bonds between amino acids or peptides in the gas phase using ion/ion reactions in a mass spectrometer. Individual amino acids or peptides can be prepared as reagents by (i) incorporating gas phase–labile protecting groups to silence otherwise reactive functional groups, such as the N terminus; (ii) converting the carboxyl groups to the active ester of N-hydroxysuccinimide; and (iii) incorporating a charge site. Protonation renders basic sites (nucleophiles) unreactive toward the N-hydroxysuccinimide ester reagents, resulting in sites with the greatest gas phase basicities being, in large part, unreactive. The N-terminal amines of most naturally occurring amino acids have lower gas phase basicities than the side chains of the basic amino acids (i.e., those of histidine, lysine, or arginine). Therefore, reagents may be directed to the N terminus of an existing “anchor” peptide to form an amide bond by protonating the anchor peptide’s basic residues, while leaving the N-terminal amine unprotonated and therefore reactive. Reaction efficiencies of greater than 30% have been observed. We propose this method as a step toward the controlled synthesis of peptides in the gas phase. PMID:24474750

  9. Chemical etching of manganese oxides for electrocatalytic oxygen reduction reaction.

    PubMed

    Lei, Kaixiang; Han, Xiaopeng; Hu, Yuxiang; Liu, Xue; Cong, Liang; Cheng, Fangyi; Chen, Jun

    2015-07-25

    Mixed-valent MnOx (1 < x < 2) was selectively synthesized by chemically etching MnO and Mn2O3 with ceric ammonium nitrate. The obtained MnOx exhibited greatly enhanced electrocatalytic activity toward the oxygen reduction reaction (ORR) as compared to the corresponding pristine oxides. PMID:26097914

  10. Water O-H bond activation by gas-phase plutonium atoms: reaction mechanisms and ab initio molecular dynamics study.

    PubMed

    Li, Peng; Niu, Wenxia; Gao, Tao; Wang, Hongyan

    2014-10-01

    A thorough description of the reaction mechanisms, taking into account different possible spin states, offers insights into the gas-phase reaction of plutonium atoms with water. Two possible reactions (isomerization and dehydrogenation) are presented. These reactions are found to be exothermic, with the best thermochemical conditions observed for the dehydrogenation reaction at around 23.5 kcal?mol(-1). The nature of the chemical-bonding evolution along the reaction pathways are investigated by employing various methods including electron localization function, atoms in molecules, and Mayer bond order. Total, partial, and overlap population density of state diagrams and analyses are also presented. Reaction rates at elevated temperatures (T=298-2?000 K) are calculated by using variational transition-state theory with one-dimensional tunneling effects. In dynamics simulations, only the dehydrogenation reaction is observed, and found to be in good agreement with experimental values. PMID:25044793

  11. Biotransformations Utilizing ?-Oxidation Cycle Reactions in the Synthesis of Natural Compounds and Medicines

    PubMed Central

    Œwizdor, Alina; Panek, Anna; Milecka-Tronina, Natalia; Ko?ek, Teresa

    2012-01-01

    ?-Oxidation cycle reactions, which are key stages in the metabolism of fatty acids in eucaryotic cells and in processes with a significant role in the degradation of acids used by microbes as a carbon source, have also found application in biotransformations. One of the major advantages of biotransformations based on the ?-oxidation cycle is the possibility to transform a substrate in a series of reactions catalyzed by a number of enzymes. It allows the use of sterols as a substrate base in the production of natural steroid compounds and their analogues. This route also leads to biologically active compounds of therapeutic significance. Transformations of natural substrates via ?-oxidation are the core part of the synthetic routes of natural flavors used as food additives. Stereoselectivity of the enzymes catalyzing the stages of dehydrogenation and addition of a water molecule to the double bond also finds application in the synthesis of chiral biologically active compounds, including medicines. Recent advances in genetic, metabolic engineering, methods for the enhancement of bioprocess productivity and the selectivity of target reactions are also described. PMID:23443116

  12. Plasma induced oxidative cleavage of disulfide bonds in polypeptides during nanoelectrospray ionization.

    PubMed

    Xia, Yu; Cooks, R Graham

    2010-04-01

    Cleavage of the disulfide bond within a polypeptide was observed when the nanoelectrospray (nanoESI) plume of a peptide solution interacted with a low-temperature helium plasma in air. Online mass spectrometric analysis revealed that chain separation accompanied by a mass increase of 1 or 16 Da for each chain was common to peptides having an interchain disulfide bond, while for peptides having intrachain disulfide bonds, the reaction products typically showed mass increases of 17 Da. Experimental results suggested that hydroxyl radicals initiated from the plasma were likely to be responsible via dissociative addition to the disulfide bond (RSSR'), giving rise to RSH and R'SO*. When the hydroxyl radical addition product ions ([M + nH + OH](n*+), n is the charge state) generated from peptides having intrachain peptides were subjected to collision-induced dissociation (CID) in an ion trap, a-, b-, and y-type sequence ions within the cyclic structure defined by the disulfide bond were observed in addition to the exocyclic cleavages typically seen from CID of [M + nH](n+) peptide ions. Rich structural information could thus be obtained. These findings were demonstrated in 14 peptides containing disulfide bonds and further by bovine insulin, which has three disulfide bonds. Collisional activation of the [M + 5H + OH](5*+) insulin ions provided 76% of the possible backbone cleavages as compared to 26% acquired from CID of the [M + 5H](5+) ions. PMID:20196567

  13. Cyclic Oxidation Behavior of HVOF Bond Coatings Deposited on La- and Y-doped Superalloys

    SciTech Connect

    Pint, Bruce A [ORNL; Bestor, Michael A [ORNL; Haynes, James A [ORNL

    2011-01-01

    One suggested strategy for improving the performance of thermal barrier coating (TBC) systems used to protect hot section components in gas turbines is the addition of low levels of dopants to the Ni-base superalloy substrate. To quantify the benefit of these dopants, the oxidation behavior of three commercial superalloys with different Y and La contents was evaluated with and without a NiCoCrAlYHfSi bond coating deposited by high velocity oxygen fuel (HVOF) spraying. Cyclic oxidation experiments were conducted in dry O{sub 2} at 1050, 1100 and 1150 C. At the highest temperature, the bare superalloy without La showed more attack due to its lower Al content but no difference in oxidation rate or scale adhesion was noted at lower temperatures. With a bond coating, the alumina scale was non-uniform in thickness and spalled at each temperature. Among the three coated superalloys, no clear difference in oxide growth rate or scale adhesion was observed. Evaluations with a YSZ top coat and a bond coating without Hf are needed to better determine the effect of superalloy dopants on high temperature oxidation performance.

  14. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay: The effect of mononucleotide structure on phosphodiester bond formation

    NASA Astrophysics Data System (ADS)

    Ferris, James P.; Kamaluddin

    1989-11-01

    Adenine deoxynucleotides bind more strongly to Na+-montmorillonite than do the corresponding ribonucleotides. Thymidine nucleotides binds less strongly to Na+-montmorillonite than do the corresponding adenine deoxynucleotides. Oligomers of 2'-dpA up to the tetramer were detected in the reaction 2'-d-5'-AMP with EDAC (a water-soluble carbodiimide) in the presence of Na+-montmorillonite. Reaction of 3'-d-5'-AMP with EDAC on Na+-montmorillonite yields 3'-d-2',5'-pApA while the reaction of 2'-d-3'-AMP yields almost exclusively 3',5'-cdAMP. The reaction of 5'-TMP under the same reaction conditions give 3',5'-cpTpT and 3',5'-pTpT while 3'-TMP gives mainly 3',5'-cpT. The yield of dinucleotide products (dpNpN) containing the phosphodiester bond is 1% or less when Na+-montmorillonite is omitted from the reaction mixture.

  15. Reactions of nitric oxide and nitrogen dioxide with coenzyme Q: involvement of the isoprenic chain.

    PubMed

    Astolfi, Paola; Charles, Laurence; Gigmes, Didier; Greci, Lucedio; Rizzoli, Corrado; Sorana, Federico; Stipa, Pierluigi

    2013-02-28

    The formation of a di-tert-alkyl nitroxide has been observed by Electron Spin Resonance during the exposure of coenzyme CoQ(10), in both the oxidized and reduced forms, to nitrogen dioxide (?NO(2)) or to nitric oxide (?NO) in the presence of oxygen. The same kind of nitroxide has been observed also with CoQ(1), CoQ(3) or with 1-phenyl-3-methyl-2-butene, chosen as model compounds. In all cases, the formation of the nitroxide may be justified only by admitting the involvement of the isoprenic chain of the coenzymes and in particular the addition of ?NO(2) to the double bond. A mechanism which accounts for the formation of the nitroxide as well as the other compounds observed in the reactions is proposed and confirmed by a spectroscopic investigation (FT-IR, (1)H NMR, X-ray analysis) and by ESI-MS. PMID:23334659

  16. Identification and cleavage of breakable single bonds by selective oxidation, reduction, and hydrolysis. Annual report, October 1, 1980-September 30, 1981

    SciTech Connect

    Hirschon, A.S.; Zevely, J.; Mayo, F.R.

    1981-11-12

    The objective of this project is to determine the structure of bituminous coal by determining the proportions of the various kinds of connecting bonds and how they can best be broken. Results obtained during the past quarter are presented for the following tasks: (1) extractions and fractionations of coal products which covers pyridine extraction, fractionation of TIPS fractions, EDA extraction of Illinois No. 6 coal and swelling ratios of coal samples; (2) experiments on breakable single bonds which cover reactions of ethylenediamine and model ethers, reaction of pyridine-extracted coal with Me/sub 3/SiI, Baeyer-Villiger oxidations, reaction to diphenylmethane with 15% HNO/sub 3/, cleavage of TIPS with ZnI/sub 2/, and cleavage of black acids; and (3) oxygen oxidation No. 18. Some of the highlights of these studies are: (1) some model ethers are not cleaved by EDA under extraction conditions; (2) oxidation of diaryl ketones with m-chloroperbenzoic acid and saponification of the resulting esters in promising for identifying ketones, (3) treatment of a black acid with pyridine hydroiodide reduced the acid's molecular weight and increased its solubility in pyridine, but treatment with ZnI/sub 2/ was ineffective; (4) in comparison with 0.1 M K/sub 2/S/sub 2/O/sub 8/, 0.01 M persulfate is relatively ineffective in accelerating oxidation of BnNH/sub 2/-extracted coal in water suspension. 2 figures, 3 tables.

  17. Bond energies, reaction volumes, and kinetics for ?- and ?-complexes of MoCO5L.

    PubMed

    Gittermann, Shannon M; Letterman, Roger G; Jiao, Tianjie; Leu, Ging-Long; DeYonker, Nathan J; Webster, Charles Edwin; Burkey, Theodore J

    2011-08-18

    The photosubstitution reactions of molybdenum hexacarbonyl with ? and ? donor ligands were investigated using photoacoustic calorimetry and computational methods in a series of linear alkane solvents (pentane, hexane, heptane, octane, decane, and dodecane). The results show that reaction volumes make a significant contribution to the photoacoustic signal and must be considered during thermodynamic calculations based on photoacoustic measurements. The enthalpies of CO substitution by an alkane solvent and subsequent substitution by each Lewis base were determined. Corresponding Mo-L bond energies (kcal mol(-1)) were calculated: L = linear alkanes (13), triethylsilane (26), 1-hexyne (27), 1-hexene (27), and benzene (17). The relative energies are in agreement with computational results. The experimental reaction volume for CO substitution by alkane was positive (15 mL mol(-1)) and negative or close to zero for alkane substitution by a Lewis base (for example, -11 mL mol(-1) for triethylsilane and 3.6 mL mol(-1) for benzene). The errors in the experimental and computational reaction volumes are large and often comparable to the reaction volumes. An improved calibration of the methods as well as a better understanding of the underlying physics involved is needed. For the Lewis bases reported in this study, the second-order rate constants for the displacement of a coordinated alkane are less than diffusion control (5 × 10(6)-4 × 10(7) M(-1) s(-1)) and decrease monotonically with the alkane chain length. The rate constants correlate better with steric effects than with bond energies. An interchange mechanism is consistent with the results. PMID:21780751

  18. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay - The effect of mononucleotide structure on phosphodiester bond formation

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; KAMALUDDIN

    1989-01-01

    The formation of oligomers from deoxynucleotides, catalyzed by Na(+)-montmorillonite, was investigated with special attention given to the effect of the monomer structure on the phosphodiester bond formation. It was found that adenine deoxynucleotides bind more strongly to montmorillonite than do the corresponding ribonucleotides and thymidine nucleotides. Tetramers of 2-prime-dpA were detected in the reaction of 2-prime-d-5-prime-AMP with a water-soluble carbodiimide EDAC in the presence of Na(+)-montmorillonite, illustrating the possible role of minerals in the formation of biopolymers on the primitive earth.

  19. Relationships between toughness and microstructure of reaction bonded Si3N4

    NASA Technical Reports Server (NTRS)

    Lightfoot, Annamarie; Sigalovsky, Julia; Haggerty, John S.

    1992-01-01

    Fracture toughnesses of nominally identical batches of reaction bonded silicon nitride (RBSN) differed significantly (about 2.0 and about 2.7 MPa sq rt m). Detailed fractographic and microstructural characterizations investigated underlying factors. Subtile differences between high and low toughness RBSN and between constituent Si powders have been revealed through SEM/FEG, TEM, BET, Hg-porosimetry, and XRD. The results illustrate the need for behavioral models to guide microstructural design and to interpret properties of brittle materials with intermediate levels of porosity.

  20. Selective molecular recognition, C-H bond activation, and catalysis in nanoscale reaction vessels

    SciTech Connect

    Fiedler, Dorothea; Leung, Dennis H.; Raymond, Kenneth N.; Bergman, Robert G.

    2004-11-27

    Supramolecular chemistry represents a way to mimic enzyme reactivity by using specially designed container molecules. We have shown that a chiral self-assembled M{sub 4}L{sub 6} supramolecular tetrahedron can encapsulate a variety of cationic guests, with varying degrees of stereoselectivity. Reactive iridium guests can be encapsulated and the C-H bond activation of aldehydes occurs, with the host cavity controlling the ability of substrates to interact with the metal center based upon size and shape. In addition, the host container can act as a catalyst by itself. By restricting reaction space and preorganizing the substrates into reactive conformations, it accelerates the sigmatropic rearrangement of enammonium cations.

  1. The oxidative burst reaction in mammalian cells depends on gravity

    PubMed Central

    2013-01-01

    Gravity has been a constant force throughout the Earth’s evolutionary history. Thus, one of the fundamental biological questions is if and how complex cellular and molecular functions of life on Earth require gravity. In this study, we investigated the influence of gravity on the oxidative burst reaction in macrophages, one of the key elements in innate immune response and cellular signaling. An important step is the production of superoxide by the NADPH oxidase, which is rapidly converted to H2O2 by spontaneous and enzymatic dismutation. The phagozytosis-mediated oxidative burst under altered gravity conditions was studied in NR8383 rat alveolar macrophages by means of a luminol assay. Ground-based experiments in “functional weightlessness” were performed using a 2 D clinostat combined with a photomultiplier (PMT clinostat). The same technical set-up was used during the 13th DLR and 51st ESA parabolic flight campaign. Furthermore, hypergravity conditions were provided by using the Multi-Sample Incubation Centrifuge (MuSIC) and the Short Arm Human Centrifuge (SAHC). The results demonstrate that release of reactive oxygen species (ROS) during the oxidative burst reaction depends greatly on gravity conditions. ROS release is 1.) reduced in microgravity, 2.) enhanced in hypergravity and 3.) responds rapidly and reversible to altered gravity within seconds. We substantiated the effect of altered gravity on oxidative burst reaction in two independent experimental systems, parabolic flights and 2D clinostat / centrifuge experiments. Furthermore, the results obtained in simulated microgravity (2D clinorotation experiments) were proven by experiments in real microgravity as in both cases a pronounced reduction in ROS was observed. Our experiments indicate that gravity-sensitive steps are located both in the initial activation pathways and in the final oxidative burst reaction itself, which could be explained by the role of cytoskeletal dynamics in the assembly and function of the NADPH oxidase complex. PMID:24359439

  2. Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution

    NASA Astrophysics Data System (ADS)

    Rustad, James R.; Casey, William H.

    2012-03-01

    Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation, CO2 capture and storage and water-oxidation catalysis; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface. Oxygen atoms in POM exchange isotopes at different rates, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface.

  3. Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution.

    PubMed

    Rustad, James R; Casey, William H

    2012-03-01

    Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation, CO2 capture and storage and water-oxidation catalysis; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface. Oxygen atoms in POM exchange isotopes at different rates, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface. PMID:22231599

  4. Reactions of metal ions at surfaces of hydrous iron oxide

    USGS Publications Warehouse

    Hem, J.D.

    1977-01-01

    Cu, Ag and Cr concentrations in natural water may be lowered by mild chemical reduction involving ferric hydroxide-ferrous ion redox processes. V and Mo solubilities may be controlled by precipitation of ferrous vanadate or molybdate. Concentrations as low as 10-8.00 or 10-9.00 M are readily attainable for all these metals in oxygen-depleted systems that are relatively rich in Fe. Deposition of manganese oxides such as Mn3O4 can be catalyzed in oxygenated water by coupling to ferrous-ferric redox reactions. Once formed, these oxides may disproportionate, giving Mn4+ oxides. This reaction produces strongly oxidizing conditions at manganese oxide surfaces. The solubility of As is significantly influenced by ferric iron only at low pH. Spinel structures such as chromite or ferrites of Cu, Ni, and Zn, are very stable and if locally developed on ferric hydroxide surfaces could bring about solubilities much below 10-9.00 M for divalent metals near neutral pH. Solubilities calculated from thermodynamic data are shown graphically and compared with observed concentrations in some natural systems. ?? 1977.

  5. Condensed-phase, halogen-bonded CF3I and C2F5I adducts for perfluoroalkylation reactions.

    PubMed

    Sladojevich, Filippo; McNeill, Eric; Börgel, Jonas; Zheng, Shao-Liang; Ritter, Tobias

    2015-03-16

    A family of practical, liquid trifluoromethylation and pentafluoroethylation reagents is described. We show how halogen bonding can be used to obtain easily handled liquid reagents from gaseous CF3I and CF3CF2I. The synthetic utility of the new reagents is exemplified by a novel direct arene trifluoromethylation reaction as well as adaptations of other perfluoroalkylation reactions. PMID:25651531

  6. Classification of metal-oxide bonded interactions based on local potential-and kinetic-energy densities

    E-print Network

    Crawford, T. Daniel

    Classification of metal-oxide bonded interactions based on local potential- and kinetic number of oxide molecules and earth materials, together with the constraints imposed by the values of 2 the same classification for the oxides. This is true despite the different trends that hold between

  7. Selective oxidation of carbolide C–H bonds by an engineered macrolide P450 mono-oxygenase

    PubMed Central

    Li, Shengying; Chaulagain, Mani Raj; Knauff, Allison R.; Podust, Larissa M.; Montgomery, John; Sherman, David H.

    2009-01-01

    Regio- and stereoselective oxidation of an unactivated C–H bond remains a central challenge in organic chemistry. Considerable effort has been devoted to identifying transition metal complexes, biological catalysts, or simplified mimics, but limited success has been achieved. Cytochrome P450 mono-oxygenases are involved in diverse types of regio- and stereoselective oxidations, and represent a promising biocatalyst to address this challenge. The application of this class of enzymes is particularly significant if their substrate spectra can be broadened, selectivity controlled, and reactions catalyzed in the absence of expensive heterologous redox partners. In this study, we engineered a macrolide biosynthetic P450 mono-oxygenase PikC (PikCD50N-RhFRED) with remarkable substrate flexibility, significantly increased activity compared to wild-type enzyme, and self-sufficiency. By harnessing its unique desosamine-anchoring functionality via a heretofore under-explored “substrate engineering” strategy, we demonstrated the ability of PikC to hydroxylate a series of carbocyclic rings linked to the desosamine glycoside via an acetal linkage (referred to as “carbolides”) in a regioselective manner. Complementary analysis of a number of high-resolution enzyme-substrate cocrystal structures provided significant insights into the function of the aminosugar-derived anchoring group for control of reaction site selectivity. Moreover, unexpected biological activity of a select number of these carbolide systems revealed their potential as a previously unrecorded class of antibiotics. PMID:19833867

  8. Hydrogen production from methane through catalytic partial oxidation reactions

    NASA Astrophysics Data System (ADS)

    Freni, S.; Calogero, G.; Cavallaro, S.

    This paper reviews recent developments in syn-gas production processes used for partial methane oxidation with and/or without steam. In particular, we examined different process charts (fixed bed, fluidised bed, membrane, etc.), kinds of catalysts (powders, foams, monoliths, etc.) and catalytically active phases (Ni, Pt, Rh, etc.). The explanation of the various suggested technical solutions accounted for the reaction mechanism that may selectively lead to calibrated mixtures of CO and H 2 or to the unwanted formation of products of total oxidation (CO 2 and H 2O) and pyrolysis (coke). Moreover, the new classes of catalysts allow the use of small reactors to treat large amounts of methane (monoliths) or separate hydrogen in situ from the other reaction products (membrane). This leads to higher conversions and selectivity than could have been expected thermodynamically. Although catalysts based on Rh are extremely expensive, they can be used to minimise H 2O formation by maximising H 2 yield.

  9. Reactions of formaldehyde and methanol on clean, carburized and oxidized Mo(100) surfaces

    NASA Astrophysics Data System (ADS)

    Ko, E. I.; Madix, R. J.

    1981-12-01

    The reactions of formaldehyde and methanol have been studied on clean, carburized, and oxidized Mo(100) surfaces using temperature programmed reaction spectroscopy (TPRS). The thermal cracking of ethylene at 550 K and the adsorption of molecular oxygen at 1050 K were used to carburize and oxidize, respectively, the clean surface to saturation. Both the carbide and oxide surfaces showed (1×1) LEED features. Methanol decomposed to give hydrogen atoms and methoxy intermediates upon adsorption on the clean Mo(100) surface at 200 K. The methoxy intermediate was stable up to 340 K. Adsorbed carbon and oxygen suppressed the dissociation of the hydroxyl hydrogen from the alcohol and yielded a significantly different activity and selectivity compared to the very reactive clean surface. The binding energies for both formaldehyde and methanol on the three surfaces were similar, demonstrating the weak sensitivity of donor-acceptor bonds to surface modifiers. The results in this study were very similar to those previously observed for W(100) though different adlayer structures were present. This similarity suggested that the modification in surface reactivity was primarily a compositional effect.

  10. Mechanistic variety in zirconium-catalyzed bond-forming reaction of arsines.

    PubMed

    Roering, Andrew J; Davidson, Jillian J; MacMillan, Samantha N; Tanski, Joseph M; Waterman, Rory

    2008-09-01

    Triamidoamine-supported zirconium complexes have been demonstrated to catalyze a range of bond-forming events utilizing arsines. Three different mechanisms have been observed in these reactions. In the first mechanism, triamidoamine-supported zirconium complexes of the general type (N3N)ZrX (N3N =N(CH2CH2NSiMe3)33-; X = monoanionic ligand) catalyzed the dehydrogenative dimerization of diphenylarsine. Mechanistic analysis revealed that As-As bond formation proceeds via sigma-bond metathesis steps similar to the previously reported dehydrocoupling of phosphines by the same catalysts. In the second mechanism, sterically encumbered primary arsines appear to be dehydrocoupled via alpha elimination of an arsinidene fragment. Dehydrocoupling of dmpAsH2 (dmp = 2,6-dimesitylphenyl) to form (dmp)As = As(dmp) by (N3N)Zr-complexes appeared to proceed via elimination of dmpAs: from the arsenido intermediate, (N3N)ZrAsH(dmp). Further support for -arsinidene elimination came from the thermal decomposition of (N3N)ZrAsHMes (9) to (MesAs)4 (10), which obeyed first-order kinetics. In the third mechanism, the observation of stoichiometric insertion reactivity of the Zr-As bond with polar substrates, PhCH2NC, PhCN, (1-napthyl)NCS, and CS2, led to the development of intermolecular hydroarsination catalysis of terminal alkynes. Here, (N3N)ZrAsPh2 (2) catalyzed the addition of diphenylarsine to phenylacetylene and 1-hexyne to give the respective vinylarsine products. Arsenido complexes 2 and 9 and tetraarsine 10 have been structurally characterized. PMID:18698453

  11. An in vitro study to evaluate the effects of addition of zinc oxide to an orthodontic bonding agent

    PubMed Central

    Jatania, Archana; Shivalinga, B. M.

    2014-01-01

    Objective: The objective of this study is to test the antimicrobial effect of zinc oxide when incorporated into an orthodontic bonding material and to check the effect of addition of zinc oxide on the shear bond strength of the bonding material. Materials and Methods: Zinc oxide was added to a resin modified light cure glass ionomer cement (GIC) (Fuji Ortho LC GC America, Alsip, Ill) to make modified bonding agent containing 13% and 23.1% ZnO and the antimicrobial assay was done using agar disc diffusion method. Discs of the modified bonding agent were prepared and a culture of Streptococcus mutans mixed with soft agar was poured over it and incubated at 38°C for 48 h and zones of inhibition were measured. The test was repeated after a month to check the antimicrobial effect. In addition shear bond strength of the brackets bonded with the modified bonding agent was tested. Results: The agar disc showed zones of inhibition around the modified bonding agent and the antimicrobial activity was more when the concentration of ZnO was increased. The antimicrobial effect was present even after a month. The shear bond strength decreased as the concentration of ZnO increased. Conclusion: The incorporation of ZnO into a resin modified light cure GIC (Fuji Ortho LC GC America, Alsip, Ill) added antimicrobial property to the original compound. PMID:24966757

  12. Pulsed Plasma-Assisted Diffusion Bonding of Oxide Dispersion-Strengthened FeCrAl Alloys

    Microsoft Academic Search

    Gordon J. Tatlock; Eugene G. Dyadko; Sebastien N. Dryepondt; Ian G. Wright

    2007-01-01

    The successful joining of oxide dispersion-strengthened (ODS) alloy PM2000 rods by pulsed plasma-assisted diffusion bonding is reported. During secondary recrystallization after joining, the alloy grains grew across the original interface, which was then marked by a row of remnant alumina particles. These did not appear to act as pinning sites for the alloy grain boundaries, which moved easily past them,

  13. Pulsed Plasma-Assisted Diffusion Bonding of Oxide Dispersion-Strengthened–FeCrAl Alloys

    Microsoft Academic Search

    Gordon J. Tatlock; Eugene G. Dyadko; Sebastien N. Dryepondt; Ian G. Wright

    2007-01-01

    The successful joining of oxide dispersion-strengthened (ODS) alloy PM2000 rods by pulsed plasma-assisted diffusion bonding\\u000a is reported. During secondary recrystallization after joining, the alloy grains grew across the original interface, which\\u000a was then marked by a row of remnant alumina particles. These did not appear to act as pinning sites for the alloy grain boundaries,\\u000a which moved easily past them,

  14. Transition-metal-catalyzed C-N bond forming reactions using organic azides as the nitrogen source: a journey for the mild and versatile C-h amination.

    PubMed

    Shin, Kwangmin; Kim, Hyunwoo; Chang, Sukbok

    2015-04-21

    Owing to the prevalence of nitrogen-containing compounds in functional materials, natural products and important pharmaceutical agents, chemists have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. While metal-catalyzed C-N cross-coupling reactions have been established as one of the most general protocols for C-N bond formation, these methods require starting materials equipped with functional groups such as (hetero)aryl halides or their equivalents, thus generating stoichiometric amounts of halide salts as byproducts. To address this aspect, a transition-metal-catalyzed direct C-H amination approach has emerged as a step- and atom-economical alternative to the conventional C-N cross-coupling reactions. However, despite the significant recent advances in metal-mediated direct C-H amination reactions, most available procedures need harsh conditions requiring stoichiometric external oxidants. In this context, we were curious to see whether a transition-metal-catalyzed mild C-H amination protocol could be achieved using organic azides as the amino source. We envisaged that a dual role of organic azides as an environmentally benign amino source and also as an internal oxidant via N-N2 bond cleavage would be key to develop efficient C-H amination reactions employing azides. An additional advantage of this approach was anticipated: that a sole byproduct is molecular nitrogen (N2) under the perspective catalytic conditions. This Account mainly describes our research efforts on the development of rhodium- and iridium-catalyzed direct C-H amination reactions with organic azides. Under our initially optimized Rh(III)-catalyzed amination conditions, not only sulfonyl azides but also aryl- and alkyl azides could be utilized as facile amino sources in reaction with various types of C(sp(2))-H bonds bearing such directing groups as pyridine, amide, or ketoxime. More recently, a new catalyst system using Ir(III) species was developed for the direct C-H amidation of arenes and alkenes with acyl azides under exceptionally mild conditions. As a natural extension, amidation of primary C(sp(3))-H bonds could also be realized on the basis of the superior activity of the Cp*Ir(III) catalyst. Mechanistic investigations revealed that a catalytic cycle is operated mainly in three stages: (i) chelation-assisted metallacycle formation via C-H bond cleavage; (ii) C-N bond formation through the in situ generation of a metal-nitrenoid intermediate followed by the insertion of an imido moiety to the metal carbon bond; (iii) product release via protodemetalation with the concomitant catalyst regeneration. In addition, this Account also summarizes the recent advances in the ruthenium- and cobalt-catalyzed amination reactions using organic azides, developed by our own and other groups. Comparative studies on the relative performance of those catalytic systems are briefly described. PMID:25821998

  15. Manganese chlorins immobilized on silica as oxidation reaction catalysts.

    PubMed

    Castro, Kelly A D F; Pires, Sónia M G; Ribeiro, Marcos A; Simões, Mário M Q; Neves, M Graça P M S; Schreiner, Wido H; Wypych, Fernando; Cavaleiro, José A S; Nakagaki, Shirley

    2015-07-15

    Synthetic strategies that comply with the principles of green chemistry represent a challenge: they will enable chemists to conduct reactions that maximize the yield of products with commercial interest while minimizing by-products formation. The search for catalysts that promote the selective oxidation of organic compounds under mild and environmentally friendly conditions constitutes one of the most important quests of organic chemistry. In this context, metalloporphyrins and analogues are excellent catalysts for oxidative transformations under mild conditions. In fact, their reduced derivatives chlorins are also able to catalyze organic compounds oxidation effectively, although they have been still little explored. In this study, we synthesized two chlorins through porphyrin cycloaddition reactions with 1.3-dipoles and prepared the corresponding manganese chlorins (MnCHL) using adequate manganese(II) salts. These MnCHL were posteriorly immobilized on silica by following the sol-gel process and the resulting solids were characterized by powder X-ray diffraction (PXRD), UVVIS spectroscopy, FTIR, XPS, and EDS. The catalytic activity of the immobilized MnCHL was investigated in the oxidation of cyclooctene, cyclohexene and cyclohexane and the results were compared with the ones obtained under homogeneous conditions. PMID:25841060

  16. Characterization of catalytic lanthanum oxide for double bond isomerization of n-butenes 

    E-print Network

    Fox, Janan Sherlene

    1978-01-01

    of the rare earth oxides should have favorable cata- lytic propert1es for oxidat1on reactions. 8oreskov and co-workers have also investigated homomolecular and isotopic exchange of oxygen on cerium diox1de (25) and lanthanum oxide (26). The observed... activation energies for cerium dioxide were approximately the same for both the homomolecular and the isotopic exchange, viz. , 28 and 29 kcal/mol, respectively; the reaction order with respect to oxygen was 0. 84. The rate-limiting step of the reac...

  17. Reaction rate oscillations during catalytic CO oxidation: A brief overview

    NASA Technical Reports Server (NTRS)

    Tsotsis, T. T.; Sane, R. C.

    1987-01-01

    It is not the intent here to present a comprehensive review of the dynamic behavior of the catalytic oxidation of CO. This reaction is one of the most widely studied in the field of catalysis. A review paper by Engel and Ertl has examined the basic kinetic and mechanistic aspects, and a comprehensive paper by Razon and Schmitz was recently devoted to its dynamic behavior. Those interested in further study of the subject should consult these reviews and a number of general review papers on catalytic reaction dynamics. The goal is to present a brief overview of certain interesting aspects of the dynamic behavior of this reaction and to discuss a few questions and issues, which are still the subject of study and debate.

  18. Optimization of reaction conditions in selective oxidation of styrene over fine crystallite spinel-type CaFe{sub 2}O{sub 4} complex oxide catalyst

    SciTech Connect

    Pardeshi, Satish K., E-mail: skpar@chem.unipune.ernet.in [Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007 (India); Pawar, Ravindra Y. [Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007 (India)] [Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007 (India)

    2010-05-15

    The CaFe{sub 2}O{sub 4} spinel-type catalyst was synthesized by citrate gel method and well characterized by thermogravimetric analysis, atomic absorption spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy. The crystallization temperature of the spinel particle prepared by citrate gel method was 600 {sup o}C which was lower than that of ferrite prepared by other methods. CaFe{sub 2}O{sub 4} catalysts prepared by citrate gel method show better activity for styrene oxidation in the presence of dilute H{sub 2}O{sub 2} (30%) as an oxidizing agent. In this reaction the oxidative cleavage of carbon-carbon double bond of styrene takes place selectively with 38 {+-} 2 mol% conversion. The major product of the reaction is benzaldehyde up to 91 {+-} 2 mol% and minor product phenyl acetaldehyde up to 9 {+-} 2 mol%, respectively. The products obtained in the styrene oxidation reaction were analyzed by gas chromatography and mass spectroscopy. The influence of the catalyst, reaction time, temperature, amount of catalyst, styrene/H{sub 2}O{sub 2} molar ratio and solvents on the conversion and product distribution were studied.

  19. RH and H2 production in reactions between ROH and small molybdenum oxide cluster anions.

    PubMed

    Waller, Sarah E; Jarrold, Caroline C

    2014-09-18

    To test recent computational studies on the mechanism of metal oxide cluster anion reactions with water [Ramabhadran, R. O.; et al. J. Phys. Chem. Lett. 2010, 1, 3066; Ramabhadran, R. O.; et al. J. Am. Chem. Soc. 2013, 135, 17039], the reactivity of molybdenum oxo–cluster anions, Mo(x)O(y)(–) (x = 1 – 4; y ? 3x) toward both methanol (MeOH) and ethanol (EtOH) has been studied using mass spectrometric analysis of products formed in a high-pressure, fast-flow reactor. The size-dependent product distributions are compared to previous Mo(x)O(y)(–) + H2O/D2O reactivity studies, with particular emphasis on the Mo2O(y)(–) and Mo3O(y)(–) series. In general, sequential oxidation, Mo(x)O(y)(–) + ROH ? Mo(x)O(y+1)(–) + RH, and addition reactions, Mo(x)O(y)(–) + ROH ? Mo(x)O(y+1)RH(–), largely corresponded with previously studied Mo(x)O(y)(–) + H2O/D2O reactions [Rothgeb, D. W., Mann, J. E., and Jarrold, C. C. J. Chem. Phys. 2010, 133, 054305], though with much lower rate constants than those determined for Mo(x)O(y)(–) + H2O/D2O reactions. This finding is consistent with the computational studies that suggested that ?H mobility on the cluster–water complex was an important feature in the overall reactivity. There were several notable differences between cluster–ROH and cluster–water reactions associated with lower R–OH bond dissociation energies relative to the HO–H dissociation energy. PMID:24661103

  20. Calorimetric study of the oxygen bond energy in a binary V?Ti catalyst and individual vanadium and titanium oxides

    Microsoft Academic Search

    V. M. Bondareva; T. V. Andrushkevich; Yu. D. Pankratiev

    1997-01-01

    Bond energy of oxygen in a binary V?Ti catalyst and individual V and Ti oxides has been studied by the calorimetric method.\\u000a The samples studied were shown to be significantly different in bond energy, homogeneity of surface oxygen and mobility of\\u000a the bulk one. Vanadium and titanium oxides appeared to interact in the binary system to form an active surface

  1. A NCS mediated oxidative C-H bond functionalization: direct esterification between a C(sp(3))-H bond and carboxylic acids.

    PubMed

    Zheng, Yang; Mao, Jincheng; Rong, Guangwei; Xu, Xinfang

    2015-05-12

    A transition metal free oxidative C-H bond functionalization/esterification of ?-alkoxy alkanes with acids is described in this report. This method is effectively mediated by NCS instead of traditional oxidants, like TBHP or its derivatives, and directly generates the esterification products in moderate to high yield under mild conditions. This tranformation constitutes a practical and general approach toward various ?-acyloxy ethers with broad substrate generality; alkyl-, aryl-, alkenyl- and alkynyl-carboxylic acids are all well tolerated. PMID:25921733

  2. 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

  3. Iron-oxidation-state-dependent O-O bond cleavage of meta-chloroperbenzoic acid to form an iron(IV)-oxo complex

    PubMed Central

    Ray, Kallol; Lee, Sang Mok; Que, Lawrence

    2008-01-01

    The mechanism of formation of [FeIV(O)(N4Py)]2+ (2, N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) from the reaction of [FeII(N4Py)(CH3CN)]2+ (1) with m-chloroperbenzoic acid (mCPBA) in CH2Cl2 at ?30 °C has been studied on the basis of the visible spectral changes observed and the reaction stoichiometry. It is shown that the conversion of 1 to 2 in 90% yield requires 1.5 equiv peracid and takes place in two successive one-electron steps via an [FeIII(N4Py)OH]2+(3) intermediate. The first oxidation step uses 0.5 equiv peracid and produces 0.5 equiv 3-chlorobenzoic acid, while the second step uses 1 equiv peracid and affords byproducts derived from chlorophenyl radical. We conclude that the FeII(N4Py) center promotes O-O bond heterolysis, while the FeIII(N4Py) center favors O-O bond homolysis, so the nature of O-O bond cleavage is dependent on the iron oxidation state. PMID:18443654

  4. How valence bond theory can help you understand your (bio)chemical reaction.

    PubMed

    Shurki, Avital; Derat, Etienne; Barrozo, Alexandre; Kamerlin, Shina Caroline Lynn

    2015-03-01

    Almost a century has passed since valence bond (VB) theory was originally introduced to explain covalent bonding in the H2 molecule within a quantum mechanical framework. The past century has seen constant improvements in this theory, with no less than two distinct Nobel prizes based on work that is essentially developments in VB theory. Additionally, ongoing advances in both methodology and computational power have greatly expanded the scope of problems that VB theory can address. In this Tutorial Review, we aim to give the reader a solid understanding of the foundations of modern VB theory, using a didactic example of a model SN2 reaction to illustrate its immediate applications. This will be complemented by examples of challenging problems that at present can only be efficiently addressed by VB-based approaches. Finally, the ongoing importance of VB theory is demonstrated. It is concluded that VB will continue to be a major driving force for chemistry in the century to come. PMID:25352378

  5. Specific Bonds between an Iron Oxide Surface and Outer Membrane Cytochromes MtrC and OmcA from Shewanella oneidensis MR-1

    SciTech Connect

    Lower, Brian H.; Shi, Liang; Yongsunthon, Ruchirej; Droubay, Timothy C.; Mccready, David E.; Lower, Steven

    2007-07-31

    Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly to Fe(III) in a mineral during anaerobic respiration.  A prerequisite for this type of reaction would be the formation of a stable bond between a cytochrome and an iron oxide surface.  Atomic force microscopy (AFM) was used to detect whether a specific bond forms between a hematite (Fe2O3) thin film, created with oxygen plasma assisted molecular beam epitaxy (MBE), and recombinant MtrC or OmcA molecules coupled to gold substrates.  Force spectra displayed a unique force signature indicative of a specific bond between each cytochrome and the hematite surface.  The strength of the OmcA-hematite bond was approximately twice as strong as the MtrC-hematite bond, but direct binding to hematite was twice as favorable for MtrC.  Reversible folding/unfolding reactions were observed for mechanically denatured MtrC molecules bound to hematite.  The force measurements for the hematite-cytochrome pairs were compared to spectra collected between an iron oxide and S. oneidensis under anaerobic conditions.  There is a strong correlation between the whole cell and pure protein force spectra suggesting that the unique binding attributes of each cytochrome complement one another and allow both MtrC and OmcA to play a prominent role in the transfer of electrons to Fe(III) in minerals.  Finally, by comparing the magnitude of binding force for the whole cell vs. pure protein data, we were able to estimate that a single bacterium of S. oneidensis (2 x 0.5 ?m) expresses ~104 cytochromes on its outer surface. 

  6. Energetics of tert-butoxyl addition reaction to norbornadiene: a method for estimating the pi-bond strength of a carbon-carbon double bond.

    PubMed

    Nunes, Paulo M; Estácio, Sílvia G; Lopes, Gustavo T; Agapito, Filipe; Santos, Rui C; Costa Cabral, Benedito J; Borges dos Santos, Rui M; Martinho Simões, José A

    2009-06-11

    The energetics of tert-butoxyl radical addition reaction to norbornadiene was investigated by time-resolved photoacoustic calorimetry (TR-PAC). The result, together with the C-O bond dissociation enthalpy (BDE) in the addition product, allowed us to calculate the pi-bond dissociation enthalpy in norbornadiene. Quantum chemistry (QC) methods were also used to obtain several enthalpies of reaction of the addition of oxygen-centered radicals to alkenes. The pi-bond dissociation enthalpies in these molecules were calculated by a procedure similar to that used in the case of norbornadiene and were compared with the pi-BDE values obtained by the method proposed by Benson. These two different approaches yield similar values for the pi-BDEs in alkenes, indicating that the addition method proposed in the present study is a valid way to derive that quantity. The influence of strain in the pi-BDEs of cyclic alkenes was investigated and allowed us to justify the difference between the pi-BDE in norbornene and norbornadiene. Finally, the thermochemistry of the addition and abstraction reactions involving these two molecules and tert-butoxyl radical was analyzed. PMID:19449831

  7. Initial reaction of hafnium oxide deposited by remote plasma atomic layer deposition method

    SciTech Connect

    Won, Youngdo; Park, Sangwook; Koo, Jaehyoung; Kim, Seokhoon; Kim, Jinwoo; Jeon, Hyeongtag [Department of Chemistry, Hanyang University, Seoul 133-791 (Korea, Republic of); Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2005-12-26

    A remote plasma atomic layer deposition (RPALD) method has been applied to grow a hafnium oxide thin film on the Si substrate. The deposition process was monitored by in situ XPS and the as-deposited structure and chemical bonding were examined by TEM and XPS. The in situ XPS measurement showed the presence of a hafnium silicate phase at the initial stage of the RPALD process up to the 20th cycle and indicated that no hafnium silicide was formed. The initial hafnium silicate was amorphous and grew to a thickness of approximately 2 nm. Based on these results and model reactions for silicate formation, we proposed an initial growth mechanism that includes adatom migration at nascent step edges. Density functional theory calculations on model compounds indicate that the hafnium silicate is thermodynamically favored over the hafnium silicide by as much as 250 kJ/mol.

  8. Reaction injection molding and direct covalent bonding of OSTE+ polymer microfluidic devices

    NASA Astrophysics Data System (ADS)

    Sandström, N.; Shafagh, R. Z.; Vastesson, A.; Carlborg, C. F.; van der Wijngaart, W.; Haraldsson, T.

    2015-07-01

    In this article, we present OSTE+RIM, a novel reaction injection molding (RIM) process that combines the merits of off-stoichiometric thiol–ene epoxy (OSTE+) thermosetting polymers with the fabrication of high quality microstructured parts. The process relies on the dual polymerization reactions of OSTE+ polymers, where the first curing step is used in OSTE+RIM for molding intermediately polymerized parts with well-defined shapes and reactive surface chemistries. In the facile back-end processing, the replicated parts are directly and covalently bonded and become fully polymerized using the second curing step, generating complete microfluidic devices. To achieve unprecedented rapid processing, high replication fidelity and low residual stress, OSTE+RIM uniquely incorporates temperature stabilization and shrinkage compensation of the OSTE+ polymerization during molding. Two different OSTE+ formulations were characterized and used for the OSTE+RIM fabrication of optically transparent, warp-free and natively hydrophilic microscopy glass slide format microfluidic demonstrator devices, featuring a storage modulus of 2.3?GPa and tolerating pressures of at least 4?bars.

  9. Diffuse Reflectance Fourier Transform Infrared Spectroscopic Study of Chemical Bonding and Hydrothermal Stability of an Aminosilane on Metal Oxide Surfaces

    Microsoft Academic Search

    Somsak Naviroj; Jack L Koenig; Hatsuo Ishida

    1985-01-01

    Fourier transform infrared spectroscopy was used to study the metal oxide\\/silane interface. Structures of ?-aminopropyldimethylethoxysilane (?-APDMES) coupling agent on the surface of metal oxide powders are proposed. The structures depend on the surface characteristics of the substrate. The amine group of the silane molecule forms a hydrogen bond with the silica surface. The enhanced intensity of the amine band around

  10. Efficient photocatalytic selective nitro-reduction and C-H bond oxidation over ultrathin sheet mediated CdS flowers.

    PubMed

    Pahari, Sandip Kumar; Pal, Provas; Srivastava, Divesh N; Ghosh, Subhash Ch; Panda, Asit Baran

    2015-06-11

    We report here a visible light driven selective nitro-reduction and oxidation of saturated sp(3) C-H bonds using ultrathin (0.8 nm) sheet mediated uniform CdS flowers as catalyst under a household 40 W CFL lamp and molecular oxygen as oxidant. The CdS flowers were synthesized using a simple surfactant assisted hydrothermal method. PMID:26024214

  11. FT-ICR Study of Reaction Induced Fragmentation of Silicon Clusters with Nitric Oxide

    E-print Network

    Maruyama, Shigeo

    FT-ICR Study of Reaction Induced Fragmentation of Silicon Clusters with Nitric Oxide Shigeo of small silicon cluster ions (Si n + : 20 n 29) with nitric oxide was studied by using the FT with argon, and were exposed to the reactant gas, nitric oxide, in the ICR cell. Results of reaction for all

  12. Overall Rate Constant Measurements of the Reaction of Chloroalkylperoxy Radicals with Nitric Oxide

    E-print Network

    Elrod, Matthew J.

    Overall Rate Constant Measurements of the Reaction of Chloroalkylperoxy Radicals with Nitric Oxide of the NO reaction with chloroalkylperoxy radicals derived from the Cl-initiated oxidation of several atmospherically the OH-initiated oxidation of alkenes) with NO yielded identical rate constants for all of the alkenes

  13. Molecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition: Gas-Phase Radical Reactions

    E-print Network

    Schlegel, H. Bernhard

    Molecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition: Gas-Phase Radical Reactions-phase reactions involved in the radical mechanism for zinc oxide chemical vapor deposition have been examined in the radical and closed shell mechanisms for zinc oxide chemical vapor deposition shows that the barrier

  14. Two-dimensional gold nanostructures with high activity for selective oxidation of carbon–hydrogen bonds

    PubMed Central

    Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou

    2015-01-01

    Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold–gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon–hydrogen bonds with molecular oxygen. PMID:25902034

  15. Two-dimensional gold nanostructures with high activity for selective oxidation of carbon-hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou

    2015-04-01

    Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold-gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon-hydrogen bonds with molecular oxygen.

  16. Influence of Sulfur, Platinum, and Hafnium on the Oxidation Behavior of CVD NiAl Bond Coatings

    Microsoft Academic Search

    J. A. Haynes; B. A. Pint; K. L. More; Y. Zhang; I. G. Wright

    2002-01-01

    The influences of S, Pt, and Hf on the oxidation behavior of chemical vapor deposition (CVD) NiAl bond coatings on high-S and low-S superalloys were investigated. Cyclic and isothermal-oxidation testing at 1150°C revealed that alumina-scale adherence to NiAl coatings was very sensitive to substrate S impurities. Scale spallation, as well as the growth of voids at the oxide–metal interface, increased

  17. Using multi-layered roll bonding and reaction annealing to process gamma-titanium aluminide sheet material

    NASA Astrophysics Data System (ADS)

    Chaudhari, Gajanan Prabhakar

    The process of roll bonding and reaction annealing was used to process gamma-titanium aluminide sheets with a nearly fully lamellar microstructure. Cold roll bonding was employed to bond elemental Al and Ti foils. The bonded sheets were annealed at 600 °C to convert all of the Al into TiAl3. The effect of rolling strain on the reaction kinetics was studied. Accumulative roll bonding was also employed to study the effect of increased rolling strain on the microstructures resulting after annealing. After the first annealing stage, a cold rolling step resulted in a denser microstructure. A second annealing treatment at 1300 °C for 6 h resulted in a microstructure consisting of two phases, gamma and alpha2, along with Kirkendall porosity. Further densification of the sheets was carried out using hot rolling. A final heat treatment at 1400 °C for 0.3 h resulted in nearly fully lamellar microstructure. The porosity evolution was evaluated at different stages of processing. The mechanical properties of the processed sheet were determined and compared with the data available in the literature. The process of bi-metal multi-layer roll bonding was modeled using the equilibrium force balance method (slab method). The effect of anisotropy and strain hardening was included in the model. The effect of different variables such as total reduction, coefficient of friction, roll radius and initial foil thickness ratio, on the thickness fraction of metals in the bonded composite was investigated. The model enables the estimation of the final composition of the roll bonded composite. The results of the model were compared with the experimental results, and good agreement was observed.

  18. Extended reaction scope of thiamine diphosphate dependent cyclohexane-1,2-dione hydrolase: from C-C bond cleavage to C-C bond ligation.

    PubMed

    Loschonsky, Sabrina; Wacker, Tobias; Waltzer, Simon; Giovannini, Pier Paolo; McLeish, Michael J; Andrade, Susana L A; Müller, Michael

    2014-12-22

    ThDP-dependent cyclohexane-1,2-dione hydrolase (CDH) catalyzes the C?C bond cleavage of cyclohexane-1,2-dione to 6-oxohexanoate, and the asymmetric benzoin condensation between benzaldehyde and pyruvate. One of the two reactivities of CDH was selectively knocked down by mutation experiments. CDH-H28A is much less able to catalyze the C?C bond formation, while the ability for C?C bond cleavage is still intact. The double variant CDH-H28A/N484A shows the opposite behavior and catalyzes the addition of pyruvate to cyclohexane-1,2-dione, resulting in the formation of a tertiary alcohol. Several acyloins of tertiary alcohols are formed with 54-94?% enantiomeric excess. In addition to pyruvate, methyl pyruvate and butane-2,3-dione are alternative donor substrates for C?C bond formation. Thus, the very rare aldehyde-ketone cross-benzoin reaction has been solved by design of an enzyme variant. PMID:25382418

  19. Selectivity of Chemisorbed Oxygen in C–H Bond Activation and CO Oxidation and Kinetic Consequences for CH?–O? Catalysis on Pt and Rh Clusters

    SciTech Connect

    Chin, Ya-Huei; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique

    2011-10-06

    Rate measurements, density functional theory (DFT) within the framework of transition state theory, and ensemble-averaging methods are used to probe oxygen selectivities, defined as the reaction probability ratios for O* reactions with CO and CH?, during CH?–O? catalysis on Pt and Rh clusters. CO? and H?O are the predominant products, but small amounts of CO form as chemisorbed oxygen atoms (O*) are depleted from cluster surfaces. Oxygen selectivities, measured using ¹²CO–¹³CH?–O? reactants, increase with O?/ CO ratio and O* coverage and are much larger than unity at all conditions on Pt clusters. These results suggest that O* reacts much faster with CO than with CH?, causing any CO that forms and desorbs from metal cluster surfaces to react along the reactor bed with other O* to produce CO? at any residence time required for detectable extents of CH? conversion. O* selectivities were also calculated by averaging DFTderived activation barriers for CO and CH? oxidation reactions over all distinct surface sites on cubo-octahedral Pt clusters (1.8 nm diameter, 201 Pt atoms) at low O* coverages, which are prevalent at low O? pressures during catalysis. CO oxidation involves non-activated molecular CO adsorption as the kinetically relevant step on exposed Pt atoms vicinal of chemisorbed O* atoms (on *–O* site pairs). CH? oxidation occurs via kinetically relevant C–H bond activation on *–* site pairs involving oxidative insertion of a Pt atom into one of the C–H bonds in CH?, forming a three-centered HC?–Pt–H transition state. C–H bond activation barriers reflect the strength of Pt–CH? and Pt–H interactions at the transition state, which correlates, in turn, with the Pt coordination and with CH? * binding energies. Ensemble-averaged O* selectivities increase linearly with O?/CO ratios, which define the O* coverages, via a proportionality constant. The proportionality constant is given by the ratio of rate constants for O? dissociation and C–H bond activation elementary steps; the values for this constant are much larger than unity and are higher on larger Pt clusters (1.8–33 nm) at all temperatures (573–1273 K) relevant for CH?–O? reactions. The barriers for the kinetically relevant C–H bond dissociation step increase, while those for CO oxidation remain unchanged as the Pt coordination number and cluster size increase, and lead, in turn, to higher O* selectivities on larger Pt clusters. Oxygen selectivities were much larger on Rh than Pt, because the limiting reactants for CO oxidation were completely consumed in ¹²CO–¹³CH?–O? mixtures, consistent with lower CO/O? ratios measured by varying the residence time and O?/CH? ratio independently in CH?–O? reactions. These mechanistic assessments and theoretical treatments for O* selectivity provide rigorous evidence of low intrinsic limits of the maximum CO yields, thus confirming that direct catalytic partial oxidation of CH? to CO (and H?) does not occur at the molecular scale on Pt and Rh clusters. CO (and H?) are predominantly formed upon complete O? depletion from the sequential reforming steps.

  20. Multiple-Site Concerted Proton-Electron Transfer Reactions of Hydrogen-Bonded Phenols are Non-adiabatic and Well Described by Semi-Classical Marcus Theory

    PubMed Central

    Schrauben, Joel N.; Cattaneo, Mauricio; Day, Thomas C.; Tenderholt, Adam L.; Mayer, James M.

    2012-01-01

    Photo-oxidations of hydrogen-bonded phenols using excited state polyarenes are described, to derive fundamental understanding of multiple-site concerted proton-electron transfer reactions (MS-CPET). Experiments have examined phenol-bases having ?CPh2NH2, ?Py, and ?CH2Py groups ortho to the phenol hydroxyl group and tert-butyl groups in the 4,6-positions for stability (HOAr-NH2, HOAr-Py, and HOAr-CH2Py, respectively; Py = pyridyl; Ph = phenyl). The photo-oxidations proceed by intramolecular proton transfer from the phenol to the pendent base concerted with electron transfer to the excited polyarene. For comparison, 2,4,6-tBu3C6H2OH, a phenol without a pendent base and tert-butyl groups in the 2,4,6-positions, has also been examined. Many of these bimolecular reactions are fast, with rate constants near the diffusion limit. Combining the photochemical kCPET values with those from prior thermal stopped-flow kinetic studies gives datasets for the oxidations of HOAr-NH2 and of HOAr-CH2Py that span over 107 in kCPET and nearly 0.9 eV in driving force (?Go?). Plots of log(kCPET) vs. ?Go? define a single Marcus parabola in each case, each including both excited state anthracenes and ground state aminium radical cations. These two datasets are thus well described by semi-classical Marcus theory, providing a strong validation of the use of this theory for MS-CPET. The parabolas give ?CPET ? 1.15–1.2 eV and Hab ? 20–30 cm?1. These experiments represent the most direct measurements of Hab for MS-CPET reactions to date. Although rate constants are available only up to the diffusion limit, the parabolas clearly peak well below the adiabatic limit of ca. 6 × 1012 s?1. Thus, this is a very clear demonstration that the reactions are non-adiabatic. The non-adiabatic character slows the reactions by a factor of ~45. Results for the oxidation of HOAr-Py, in which the phenol and base are conjugated, and for oxidation of 2,4,6-tBu3C6H2OH, which lacks a base, show that both have substantially lower ? and larger pre-exponential terms. The implications of these results for MS-CPET reactions are discussed. PMID:22974135

  1. Diffusion and reaction of nitric oxide in suspension cell cultures.

    PubMed Central

    Chen, B; Keshive, M; Deen, W M

    1998-01-01

    A reaction-diffusion model was developed to predict the fate of nitric oxide (NO) released by cells of the immune system. The model was used to analyze data obtained previously using macrophages attached to microcarrier beads suspended in a stirred vessel. Activated macrophages synthesize NO, which is oxidized in the culture medium by molecular oxygen and superoxide (O2-, also released by the cells), yielding mainly nitrite (NO2-) and nitrate (NO3-) as the respective end products. In the analysis the reactor was divided into a "stagnant film" with position-dependent concentrations adjacent to a representative carrier bead and a well-mixed bulk solution. It was found that the concentration of NO was relatively uniform in the film. In contrast, essentially all of the O2- was calculated to be consumed within approximately 2 microm of the cell surfaces, due to its reaction with NO to yield peroxynitrite. The decomposition of peroxynitrite caused its concentration to fall to nearly zero over a distance of approximately 30 microm from the cells. Although the film regions (which had an effective thickness of 63 microm) comprised just 2% of the reactor volume and were predicted to account for only 6% of the NO2- formation under control conditions, they were calculated to be responsible for 99% of the NO3- formation. Superoxide dismutase in the medium (at 3.2 microM) was predicted to lower the ratio of NO3- to NO2- formation rates from near unity to <0.5, in reasonable agreement with the data. The NO3-/NO2- ratio was predicted to vary exponentially with the ratio of O2- to NO release rates from the cells. Recently reported reactions involving CO2 and bicarbonate were found to have important effects on the concentrations of peroxynitrite and nitrous anhydride, two of the compounds that have been implicated in NO cytotoxicity and mutagenesis. PMID:9675176

  2. Thermochemical properties and bond dissociation energies of C3-C5 cycloalkyl hydroperoxides and peroxy radicals: cycloalkyl radical + (3)O2 reaction thermochemistry.

    PubMed

    Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

    2012-07-19

    Cyclic aliphatic hydrocarbons are major components in modern fuels; they can be present in the reactants, and they can be formed during the gas-phase oxidation processes. In combustion and thermal oxidation processes, these cyclics will form radicals that react with (3)O(2) to form peroxy radicals. In this study, density functional theory and higher level ab initio calculations are used to calculate thermochemical properties and bond dissociation energies of 3-5-membered cycloalkanes, corresponding hydroperoxides, hydroperoxycycloalkyl radicals, and cycloalkyl radicals that occur in these reaction systems. Geometries, vibration frequencies, and thermochemical properties, ?H(f 298)°, are calculated with the B3LYP/6-31 g(d,p), B3LYP/6-31 g(2d,2p), composite CBS-QB3, and G3MP2B3 methods. Standard enthalpies of formation at 298 K are evaluated using isodesmic reaction schemes with several work reactions for each species. Group additivity contributions are developed, and application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities, S°(T) and C(p)°(T) (5 K ? T ? 5000), are determined using geometric parameters and frequencies from the B3LYP/6-31 g(d,p) calculations. PMID:22779400

  3. Mass transfer model for two-layer TBP oxidation reactions

    SciTech Connect

    Laurinat, J.E.

    1994-09-28

    To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments. Three cases were investigated: (1) transfer of water into the TBP layer with sparging of both the aqueous and TBP layers, (2) transfer of water into the TBP layer with sparging of just the TBP layer, and (3) transfer of butanol into the aqueous layer with sparging of both layers. The TBP layer was comprised of 99% pure TBP (spiked with butanol for the butanol transfer experiments), and the aqueous layer was comprised of either water or an aluminum nitrate solution. The liquid layers were air sparged to simulate the mixing due to the evolution of gases generated by oxidation reactions. A plastic tube and a glass frit sparger were used to provide different size bubbles. Rates of mass transfer were measured using infrared spectrophotometers provided by SRTC/Analytical Development.

  4. Bond length and local energy density property connections for non-transition-metal oxide-bonded interactions.

    PubMed

    Gibbs, G V; Spackman, M A; Jayatilaka, D; Rosso, K M; Cox, D F

    2006-11-01

    For a variety of molecules and earth materials, the theoretical local kinetic energy density, G(r(c)), increases and the local potential energy density, V(r(c)), decreases as the M-O bond lengths (M = first- and second-row metal atoms bonded to O) decrease and the electron density, rho(r(c)), accumulates at the bond critical points, r(c). Despite the claim that the local kinetic energy density per electronic charge, G(r(c))/rho(r(c)), classifies bonded interactions as shared interactions when less than unity and closed-shell when greater, the ratio was found to increase from 0.5 to 2.5 au as the local electronic energy density, H(r(c)) = G(r(c)) + V(r(c)), decreases and becomes progressively more negative. The ratio appears to be a measure of the character of a given M-O bonded interaction, the greater the ratio, the larger the value of rho(r(c)), the smaller the coordination number of the M atom and the more shared the bonded interaction. H(r(c))/rho(r(c)) versus G(r(c))/rho(r(c)) scatter diagrams categorize the M-O bonded interactions into domains with the local electronic energy density per electron charge, H(r(c))/rho(r(c)), tending to decrease as the electronegativity differences for the bonded pairs of atoms decrease. The values of G(r(c)) and V(r(c)), estimated with a gradient-corrected electron gas theory expression and the local virial theorem, are in good agreement with theoretical values, particularly for the bonded interactions involving second-row M atoms. The agreement is poorer for shared C-O and N-O bonded interactions. PMID:17078623

  5. Desorption of single-stranded nucleic acids from graphene oxide by disruption of hydrogen bonding.

    PubMed

    Park, Joon Soo; Na, Hee-Kyung; Min, Dal-Hee; Kim, Dong-Eun

    2013-03-21

    Graphene oxide (GO) is known to interact with single-stranded nucleic acids through pi-stacking interactions and hydrogen bonds between the nucleobases and the hexagonal cells of GO. It also quenches the fluorescence when the fluorophore comes near to the GO mesh. When single-stranded (ss) regions of either DNA or RNA are present, those regions were adsorbed onto the surface of GO with a quenching of fluorescence located proximally to the GO surface. We demonstrated that bound single-stranded nucleic acids can be readily dissociated from GO by disrupting hydrogen bonding with urea, which was confirmed with fluorescence measurement and gel electrophoresis. Hydrogen bonding mainly contributes to the interaction between GO and single-stranded nucleic acids such as ssDNA and RNA. The GO-coated mesoporous silica nanoparticles (GO-MSNs) were synthesized for better separation of RNAs from cells. Cellular RNAs were readily adsorbed and eluted with ease by using GO-MSN and urea, respectively, demonstrating that GO-MSN and urea elution is a facile RNA extraction method. PMID:23361154

  6. Preparation of superacids by metal oxides for reactions of butanes and pentanes

    Microsoft Academic Search

    Kazushi Arata

    1996-01-01

    Recent works on preparation of solid superacid catalysts which are active for reactions of butanes and pentanes are reviewed. Sulfated metal oxides are obtained by adsorbing sulfate ion onto amorphous oxides of Fe, Ti, Zr, Hf, Sn, and Si followed by calcination in air; a superacid of Al2O3 is prepared from the crystallized oxide. Superacids by metal oxides are synthesized

  7. Contribution of individual disulfide bonds to the oxidative folding of ribonuclease A.

    PubMed

    Ruoppolo, M; Vinci, F; Klink, T A; Raines, R T; Marino, G

    2000-10-01

    The eight cysteine residues of ribonuclease A form four disulfide bonds in the native protein. We have analyzed the folding of three double RNase A mutants (C65A/C72A, C58A/C110A, and C26A/C84A, lacking the C65-C72, C58-C110, and C26-C84 disulfide bonds, respectively) and two single mutants (C110A and C26A), in which a single cysteine is replaced with an alanine and the paired cysteine is present in the reduced form. The folding of these mutants was carried out in the presence of oxidized and reduced glutathione, which constitute the main redox agents present within the ER. The use of mass spectrometry in the analysis of the folding processes allowed us (i) to follow the formation of intermediates and thus the pathway of folding of the RNase A mutants, (ii) to quantitate the intermediates that formed, and (iii) to compare the rates of formation of intermediates. By comparison of the folding kinetics of the mutants with that of wild-type RNase A, the contribution of each disulfide bond to the folding process has been evaluated. In particular, we have found that the folding of the C65A/C72A mutant occurs on the same time scale as that of the wild-type protein, thus suggesting that the removal of the C65-C72 disulfide bond has no effect on the kinetics of RNase A folding. Conversely, the C58A/C110A and C26A/C84A mutants fold much more slowly than the wild-type protein. The removal of the C58-C110 and C26-C84 disulfide bonds has a dramatic effect on the kinetics of RNase A folding. Results described in this paper provide specific information about conformational folding events in the regions involving the mutated cysteine residues, thus contributing to a better understanding of the complex mechanism of oxidative folding. PMID:11009618

  8. Creep analysis of solid oxide fuel cell with bonded compliant seal design

    NASA Astrophysics Data System (ADS)

    Jiang, Wenchun; Zhang, Yucai; Luo, Yun; Gong, J. M.; Tu, S. T.

    2013-12-01

    Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

  9. Destruction of hydrogen bonds of poly(N-isopropylacrylamide) aqueous solution by trimethylamine N-oxide

    NASA Astrophysics Data System (ADS)

    Reddy, P. Madhusudhana; Taha, Mohamed; Venkatesu, Pannuru; Kumar, Awanish; Lee, Ming-Jer

    2012-06-01

    Trimethylamine N-oxide (TMAO) is a compatible or protective osmolyte that stabilizes the protein native structure through non-bonding mechanism between TMAO and hydration surface of protein. However, we have shown here first time the direct binding mechanism for naturally occurring osmolyte TMAO with hydration structure of poly(N-isopropylacrylamide) (PNIPAM), an isomer of polyleucine, and subsequent aggregation of PNIPAM. The influence of TMAO on lower critical solution temperature (LCST) of PNIPAM was investigated as a function of TMAO concentration at different temperatures by fluorescence spectroscopy, viscosity (?), multi angle dynamic light scattering, zeta potential, and Fourier transform infrared (FTIR) spectroscopy measurements. To address some of the basis for further analysis of FTIR spectra of PNIPAM, we have also measured FTIR spectra for the monomer of N-isopropylacrylamide (NIPAM) in deuterium oxide (D2O) as a function of TMAO concentration. Our experimental results purportedly elucidate that the LCST values decrease with increasing TMAO concentration, which is mainly contributing to the direct hydrogen bonding of TMAO with the water molecules that are bound to the amide (-CONH) functional groups of the PNIPAM. We believed that the present work may act as a ladder to reach the heights of understanding of molecular mechanism between TMAO and macromolecule.

  10. Chemistry of sulfur oxides on transition metal surfaces: a bond order conservation-Morse potential modeling perspective

    NASA Astrophysics Data System (ADS)

    Sellers, Harrell; Shustorovich, Evgeny

    1996-06-01

    We have employed the bond order conservation-Morse potential (BOC-MP) method to analyze the chemistry of sulfur oxides on the copper and nickel group metals. Specifically, we have calculated the reaction energetics (heats of adsorption, reaction enthalpies and intrinsic activation barriers) of the decomposition and oxidation of sulfur dioxide at low coverages on fcc (111) surfaces of Cu, Ag, Au, Ni, Pd and Pt. The accuracy of the BOC-MP heats of adsorption has been corroborated by high quality ab initio calculations of the heats of SO2 adsorption on Ag and Pd surfaces. We have addressed the following issues: (1) the dissociation of SO2; (2) the stability of adsorbed SO and its likelihood of being a product of SO2 decomposition; (3) the oxidation of SO2; and, (4) the nature of adsorbed SO3 and SO4. The major model projections (obtained for low coverages and without considering diffusional effects) are: (1) the dissociation of SO2?SO + O is unfavorable on all the metals considered, but, the dissociation of SO2?S + O + O, showing distinct periodic trends, is feasible on Cu and particularly on Ni; in the presence of carbon monoxide the dissociation, SO2 + CO?S + O + CO2, may occur on all the metals examined; (2) on the Pt, Pd, Ni and Cu surfaces, SO is unstable; (3) the oxidation of SO2 to SO3 may be achieved with O, O2, H2O2 and NO as oxygen sources on Ag, Au, Pd and Pt surfaces. Although adsorbed SO3 may be readily obtained, it may be impossible to desorb SO3 intact at low coverages because SO3 will decompose to SO2 + O before desorption. (4) The most stable oxygen sulfur specie that withstands elevated temperatures should be dianion sulfate. The relevant experimental data have been discussed. Most of the model projections are in agreement with experiment, but, some suggest reconsideration of the reported experimental data or represent predictions to be verified.

  11. Catalysis of Reduction and Oxidation Reactions for Application in Gas Particle Filters

    SciTech Connect

    Udron, L.; Turek, T.

    2002-09-19

    The present study is a first part of an investigation addressing the simultaneous occurrence of oxidation and reduction reactions in catalytic filters. It has the objectives (a) to assess the state of knowledge regarding suitable (types of) catalysts for reduction and oxidation, (b) to collect and analyze published information about reaction rates of both NOx reduction and VOC oxidation, and (c) to adjust a lab-scale screening method to the requirements of an activity test with various oxidation/reduction catalysts.

  12. Quantification of reaction violence and combustion enthalpy of plastic bonded explosive 9501 under strong confinement

    NASA Astrophysics Data System (ADS)

    Perry, W. Lee; Dickson, Peter M.; Parker, Gary R.; Asay, B. W.

    2005-01-01

    The confinement experienced by an explosive during thermal self-initiation can substantially affect performance in terms of deflagration-to-detonation characteristics and explosion/detonation violence. To this end, we have developed an experiment to quantitatively observe enthalpy change and reaction violence in thermally initiated plastic bonded explosive (PBX) 9501. Traditionally, researchers attempt to quantify violence using terminal observations of fragment size, fragment velocity, and through subjective observations. In the work presented here, the explosive was loaded into a heated gun assembly where we subjected a 300 mg charge to a cook-off schedule and a range of static and inertial confinements. Static confinement was controlled using rupture disks calibrated at 34.5 and 138 MPa. The use of 3.15 and 6.3 g projectile masses provided a variation in inertial confinement. This was a regime of strong confinement; a significant fraction of the explosive energy was required to rupture the disk, and the projectile mass was large compared to the charge mass. The state variables pressure and volume were measured in the breech. From these data, we quantified both the reaction enthalpy change and energy release rate of the explosive on a microsecond time scale using a thermodynamic analyisis. We used these values to unambiguously quantify explosion violence as a function of confinement at a fixed cook-off schedule of 190 C for 1 h. P2?, a measure of critical shock energy required for shock ignition of an adjacent explosive was also computed. We found variations in this confinement regime to have a weak effect on enthalpy change, power, violence and shock energy. Violence was approximately 100 times lower than detonating trinitrotoluene, but the measured shock energy approached the critical shock energy for initiating secondary high explosives.

  13. Kinetics and Mechanism of Iodide Oxidation by Iron(III): A Clock Reaction Approach

    ERIC Educational Resources Information Center

    Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.

    2008-01-01

    A simple method for studying the kinetics of a chemical reaction is described and the significance of reaction orders in deducing reaction mechanisms is demonstrated. In this student laboratory experiment, oxidation of iodide by iron(III) ions in an acidic medium is transformed into a clock reaction. By means of the initial rates method, it is…

  14. Effect of composition on the processing and properties of sintered reaction-bonded silicon nitride

    SciTech Connect

    Tiegs, T.N.; Kiggans, J.O.; Montgomery, F.C.; Lin, H.T.; Barker, D.L.; Snodgrass, J.D.; Sabolsky, E.M.; Coffey, D.W.

    1996-04-01

    The type of silicon powder and sintering additive were found to influence the processing and final mechanical properties of sintered reaction bonded silicon nitride. High purity silicon powders produced low {alpha}-Si{sub 3}N{sub 4} content during nitridation. The Si powder type had no apparent effect on densification. More complete nitridation and higher room temperature mechanical properties were observed for the Si powders with higher Fe contents. However, the higher Fe contents resulted in greater high temperature strength degradation and so there was better high temperature strength retention with the higher purity Si. High {alpha}-Si{sub 3}N{sub 4} contents were found after nitridation with {alpha}-Si{sub 3}N{sub 4} seeded materials and with MgO-Y{sub 2}O{sub 3} as the sintering additive. Densification was inhibited by refractory additives, such as Y{sub 2}O{sub 3}-SiO{sub 2}. The highest room temperature strength and fracture toughness values correlated to high nitrided {alpha}-Si{sub 3}N{sub 4} contents. The high temperature strength behavior was similar for all additive types.

  15. Hydrogen oxidation reaction at the Ni/YSZ anode of solid oxide fuel cells from first principles.

    PubMed

    Cucinotta, Clotilde S; Bernasconi, Marco; Parrinello, Michele

    2011-11-11

    By means of ab initio simulations we here provide a comprehensive scenario for hydrogen oxidation reactions at the Ni/zirconia anode of solid oxide fuel cells. The simulations have also revealed that in the presence of water chemisorbed at the oxide surface, the active region for H oxidation actually extends beyond the metal/zirconia interface unraveling the role of water partial pressure in the decrease of the polarization resistance observed experimentally. PMID:22181748

  16. Unified view of oxidative C-H bond cleavage and sulfoxidation by a nonheme iron(IV)-oxo complex via Lewis acid-promoted electron transfer.

    PubMed

    Park, Jiyun; Morimoto, Yuma; Lee, Yong-Min; Nam, Wonwoo; Fukuzumi, Shunichi

    2014-04-01

    Oxidative C-H bond cleavage of toluene derivatives and sulfoxidation of thioanisole derivatives by a nonheme iron(IV)-oxo complex, [(N4Py)Fe(IV)(O)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), were remarkably enhanced by the presence of triflic acid (HOTf) and Sc(OTf)3 in acetonitrile at 298 K. All the logarithms of the observed second-order rate constants of both the oxidative C-H bond cleavage and sulfoxidation reactions exhibit remarkably unified correlations with the driving forces of proton-coupled electron transfer (PCET) and metal ion-coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes between PCET and MCET were taken into account, respectively. Thus, the mechanisms of both the oxidative C-H bond cleavage of toluene derivatives and sulfoxidation of thioanisole derivatives by [(N4Py)Fe(IV)(O)](2+) in the presence of HOTf and Sc(OTf)3 have been unified as the rate-determining electron transfer, which is coupled with binding of [(N4Py)Fe(IV)(O)](2+) by proton (PCET) and Sc(OTf)3 (MCET). There was no deuterium kinetic isotope effect (KIE) on the oxidative C-H bond cleavage of toluene via the PCET pathway, whereas a large KIE value was observed with Sc(OTf)3, which exhibited no acceleration of the oxidative C-H bond cleavage of toluene. When HOTf was replaced by DOTf, an inverse KIE (0.4) was observed for PCET from both toluene and [Ru(II)(bpy)3](2+) (bpy =2,2'-bipyridine) to [(N4Py)Fe(IV)(O)](2+). The PCET and MCET reactivities of [(N4Py)Fe(IV)(O)](2+) with Brønsted acids and various metal triflates have also been unified as a single correlation with a quantitative measure of the Lewis acidity. PMID:24605985

  17. Oxidation Behavior of Thermal Barrier Coatings with a TiAl3 Bond Coat on ?-TiAl Alloy

    NASA Astrophysics Data System (ADS)

    Wang, Jiqiang; Kong, Lingyan; Li, Tiefan; Xiong, Tianying

    2015-02-01

    The thermal barrier coatings investigated in this paper included a TiAl3 bond coat and a yttria partially stabilized zirconia (YSZ) layer. The TiAl3 bond coat was prepared by deposition of aluminum by cold spray, followed by a heat-treatment. The YSZ layer was prepared by air plasma spray. The isothermal and cyclic oxidation tests were conducted at 900 °C for 1000 h and 500 cycles to test the oxidation resistance of the thermal barrier coatings. The microstructure and composition of the ?-TiAl alloy with and without the thermal barrier coatings after oxidation were investigated. The results showed that a dense TGO layer about 5 ?m had grown between the YSZ layer and the TiAl3 bond coat. The TGO had good adhesion to both the YSZ layer and the bond coat even after the TiAl3 bond coat entirely degraded into the TiAl2 phase, which decreased the inward oxygen diffusion. Thus, the thermal barrier coatings improved the oxidation resistance of ?-TiAl alloy effectively.

  18. Simultaneous carbon coating and lithiation of oxides by contact reaction.

    PubMed

    Wächter, Florian; Krumeich, Frank; Nesper, Reinhard

    2014-04-25

    Chemical lithiation and carbon coating of cathode materials can lead to strongly improved electrochemical properties, especially if the active materials have low electronic conductivity. This behavior is quite often the case for new high-capacity materials. A novel synthesis method is presented in which the two processes are performed simultaneously by employing Li2C2 as both the carbon and the lithium source. In this contact reaction, the acetylide anion C2(2-) is oxidized to carbon and deposited directly on the surface of the active material, while lithium is reductively inserted into the oxidant. Two different synthesis routes are demonstrated: a tribochemical approach at room temperature and heat treatments between 150 and 600?°C. The applicability of these new carbon-coating methods are demonstrated on various crystalline and amorphous Li(x)V2O5 phases. The composites obtained were characterized by powder X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. In addition, electrochemical data confirm the chemical lithiation and show that lithiated Li(x)V2O5 with specific phases can be prepared selectively. PMID:24692318

  19. Reaction of superoxide with nitric oxide to form peroxonitrite in alkaline aqueous solution

    Microsoft Academic Search

    Neil V. Blough; Oliver C. Zafiriou

    1985-01-01

    Although aqueous superoxide often acts as a one-electron reductant or less frequently as an oxidant, it rarely undergoes covalent bond formation with simple organic or inorganic compounds in water, perhaps owing to its poor nucleophilicity in this solvent. In this communication it is shown, however, that superoxide can react with nitric oxide to form the peroxionitrite anion in deaerated aqueous

  20. Redox reactions involving hydrocarbons and mineral oxidants: Mechanism for porosity enhancement

    SciTech Connect

    Surdam, R.C.; Jiao, Z.S.; MacGowan, D.B. [Univ. of Wyoming, Laramie, WY (United States)

    1993-12-31

    Hydrocarbon invasion into a sandstone containing mineral oxidants and carbonate or sulphate cements may result in redox reactions that enhanced porosity. When hydrocarbons invade red sandstones, significant bleaching (i.e., iron reduction) occurs. Reactions responsible for the color distribution in the red (oxidized) and white (reduced) zones are reactions of iron oxides ({plus_minus}sulphate) with hydrocarbons. Commonly the red sandstones are tight due to carbonate and sulphate cements, whereas the white zones are more porous. Organic acids are one product of these reactions and are available to dissolve carbonate cements. Volumetric calculations show that significant porosity can be generated in any sandstone by these reactions. These redox reactions may explain why hydrocarbon accumulations appear to have created porosity in some cases and emphasize the importance of redox reactions involving kerogen/hydrocarbons and mineral oxidants as a significant source oxygenated organic compounds in diagenetic systems.

  1. Transition-metal-free tandem oxidative removal of benzylic methylene group by C-C and C-N bond cleavage followed by intramolecular new aryl C-N bond formation under radical conditions.

    PubMed

    Laha, Joydev K; Tummalapalli, K S Satyanarayana; Gupta, Ankur

    2014-09-01

    A novel tandem oxidative conversion of 10,11-dihydro-5H-dibenzo[b,e][1,4]diazepines to phenazines has been achieved under transition-metal-free, mild conditions using K2S2O8 or DDQ as the oxidizing agent. The transformation proceeds through oxidative removal of a benzylic methylene group by C-C and C-N bond cleavage followed by a new aryl C-N bond formation under radical conditions. PMID:25119523

  2. Conduction and Gas–Surface Reaction Modeling in Metal Oxide Gas Sensors

    Microsoft Academic Search

    Brian Chwieroth; Bruce R. Patton; Yunzhi Wang

    2001-01-01

    A phenomenological approach to the operation of metal oxide gas sensors, the Integrated Reaction Conduction (IRC) model, is proposed which integrates the gas-surface reactions with the electrical conduction process in a weakly sintered, porous metal oxide. An effective medium approximation is employed to relate the mesoscopic microstructure and the carrier depletion at the granular surface to the macroscopic electrical conduction.

  3. Reaction mechanism reduction and optimisation for modelling aviation fuel oxidation using standard and hybrid genetic algorithms

    Microsoft Academic Search

    Lionel Elliott; Derek B. Ingham; Adrian G. Kyne; Nicolae S. Mera; Mohamed Pourkashanian; Sean Whittaker

    2006-01-01

    This study describes the development of a new binary encoded genetic algorithm for the combinatorial problem of determining a subset of species and their associated reactions that best represent the full starting point reaction mechanism in modelling aviation fuel oxidation. The genetic algorithm has a dual objective in finding a reduced mechanism that best represents aviation fuel oxidation in both

  4. The interaction of reaction-bonded silicon carbide and inconel 600 with a nickel-based brazing alloy

    Microsoft Academic Search

    J. R. McDermid; M. D. Pugh; R. A. L. Drew

    1989-01-01

    The objective of the present research was to join reaction-bonded silicon carbide (RBSC) to INCONEL 600 (a nickel-based superalloy)\\u000a for use in advanced heat engine applications using either direct brazing or composite interlayer joining. Direct brazing experiments\\u000a employed American Welding Society (AWS) BNi-5, a commercial nickel-based brazing alloy, as a filler material; composite interlayers\\u000a consisted of intimate mixtures of ?-SiC

  5. High-Temperature Thermoelectric Characterization of III-V Semiconductor Thin Films by Oxide Bonding

    NASA Astrophysics Data System (ADS)

    Bahk, Je-Hyeong; Zeng, Gehong; Zide, Joshua M. O.; Lu, Hong; Singh, Rajeev; Liang, Di; Ramu, Ashok T.; Burke, Peter; Bian, Zhixi; Gossard, Arthur C.; Shakouri, Ali; Bowers, John E.

    2010-08-01

    A device fabrication and measurement method utilizing a SiO2-SiO2 covalent bonding technique is presented for high-temperature thermoelectric characterization of thin-film III-V semiconductor materials that suffer from the side-effect of substrate conduction at high temperatures. The proposed method includes complete substrate removal, high-temperature surface passivation, and metallization with a Ti-W-N diffusion barrier. A thermoelectric material, thin-film ErAs:InGaAlAs metal/semiconductor nanocomposite grown on a lattice-matched InP substrate by molecular beam epitaxy, was transferred onto a sapphire substrate using the oxide bonding technique at 300°C, and its original InP substrate, which is conductive at high temperatures, was removed. Electrical conductivities and Seebeck coefficients were measured from room temperature to 840 K for this material on both the InP and sapphire substrates, and the measurement results clearly show that the InP substrate effect was eliminated for the sample on the sapphire substrate. A strain experiment has been conducted to investigate the effect of strain on electrical conductivity.

  6. Instability of Si?F bonds in fluorinated silicon oxide (SiOF) films formed by various techniques

    Microsoft Academic Search

    Tetsuya Homma

    1996-01-01

    Instability of Si?F bonds in fluorinated silicon oxide (SiOF) films is studied. Al wiring corrosion and underlayer SiO2 etching problems are the major issues for the use of SiOF interlayer dielectric films. To clarify the mechanism, three kinds of SiOF films have been used for this study. They are: (i) a fluorinated silicon oxide (SiOF) film prepared by room-temperature chemical

  7. Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Fitting Kourkoutis, L.

    2010-03-01

    Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study buried perovskite oxide heterointerfaces. With the recent addition of 3^rd order and now 5^th order aberration correction, which provides a factor of 100x increase in signal over an uncorrected system, we are now able to record 2D maps of composition and bonding of oxide interfaces at atomic resolution [1]. Here, we present studies of the microscopic structure of oxide/oxide multilayers and heterostructures by STEM in combination with EELS and its effect on the properties of the film. Using atomic-resolution spectroscopic imaging we show that the degradation of the magnetic and transport properties of La0.7Sr0.3MnO3/SrTiO3 multilayers correlates with atomic intermixing at the interfaces and the presence of extended defects in the La0.7Sr0.3MnO3 layers. When these defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in 5 unit cell thick manganite layers, almost 40% thinner than the previously reported critical thickness of 3-5 nm for sustaining metallic ferromagnetism below Tc in La0.7Sr0.3MnO3 thin films grown on SrTiO3.[4pt] [1] D.A. Muller, L. Fitting Kourkoutis, M. Murfitt, J.H. Song, H.Y. Hwang, J. Silcox, N. Dellby, O.L. Krivanek, Science 319, 1073-1076 (2008).

  8. An Effective Hamiltonian Molecular Orbital-Valence Bond (MOVB) Approach for Chemical Reactions Applied to the Nucleophilic Substitution Reaction of Hydrosulfide Ion and Chloromethane

    PubMed Central

    Song, Lingchun; Mo, Yirong; Gao, Jiali

    2009-01-01

    An effective Hamiltonian mixed molecular orbital and valence bond (EH-MOVB) method is described to obtain an accurate potential energy surface for chemical reactions. Building upon previous results on the construction of diabatic and adiabatic potential surfaces using ab initio MOVB theory, we introduce a diabatic-coupling scaling factor to uniformly scale the ab initio off-diagonal matrix element H12 such that the computed energy of reaction from the EH-MOVB method is in agreement with the target value. The scaling factor is very close to unity, resulting in minimal alteration of the potential energy surface of the original MOVB model. Furthermore, the relative energy between the reactant and product diabatic states in the EH-MOVB method can be improved to match the experimental energy of reaction. A key ingredient in the EH-MOVB theory is that the off-diagonal matrix elements are functions of all degrees of freedom of the system and the overlap matrix is explicitly evaluated. The EH-MOVB method has been applied to the nucleophilic substitution reaction between hydrosulfide and chloromethane to illustrate the methodology and the results were matched to reproduce the results from ab initio valence bond self-consistent valence bond (VBSCF) calculations. The diabatic coupling (the off-diagonal matrix element in the generalized secular equation) has small variations along the minimum energy reaction path in the EH-MOVB model, whereas it shows a maximum value at the transition state and has nearly zero values in the regions of the ion-dipole complexes from VBSCF calculations. The difference in the diabatic coupling stabilization is attributed to the large overlap integral in the computationally efficient MOVB method. PMID:20047006

  9. Surface reactions of uranium oxide powder, thin films and single crystals

    NASA Astrophysics Data System (ADS)

    Idriss, H.

    2010-03-01

    The review deals with surface reactions of the complex uranium oxide systems with relevance to catalysis and the environment. After a brief introduction on the properties of uranium oxides, the focus of the review is on surface science studies of defined structures of uranium oxides which are entirely on UO 2 because of the lack of available model on other uranium oxide systems. Powder work is also included as it has given considerable information related to the dynamics between the many phases of uranium oxides. Many chemical reactions are mapped and these include water dissociative adsorption and reaction, CO oxidation and reductive coupling, as well as the reaction of oxygen containing organic compounds such as alcohols, aldehydes, ketones and carboxylic acids in addition to a few examples of sulfur and nitrogen containing compounds.

  10. Nitric oxide in star-forming regions - Further evidence for interstellar N-O bonds

    NASA Technical Reports Server (NTRS)

    Ziurys, L. M.; Mcgonagle, D.; Minh, Y.; Irvine, W. M.

    1991-01-01

    Nitric oxide has been newly detected toward several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2-1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both lambda-doubling components of NO were observed toward all sources. Column densities derived for nitric oxide in these clouds are 10 to the 15th-10 to the 16th/sq cm, corresponding to fractional abundances of 0.5-1.0 x 10 to the -8th, relative to H2. Toward Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude.

  11. Determination of carbon-bonded sulfur in soils by ICP-AES after hydriodic acid reduction and hydrogen peroxide oxidation

    SciTech Connect

    Long-zhu, J. [National Natural Science Foundation of China, Beijing (China); Xiao-quan, S. [Academia Sinica, Beijing (China)

    1994-12-31

    A method has been developed for the determination of carbon-bonded sulfur in soil by ICP-AES after sequential extraction. The operating conditions of ICP-AES for the determination of sulfur was optimized. A subsample of the soil was sequentially treated with HI reduction and H{sub 2}O{sub 2} oxidation. All inorganic sulfur components and ester sulfur were reduced to H{sub 2}S by HI except pyritic sulfur, previously unidentified residue sulfur and carbon-bonded sulfur. The present study indicated that part of carbon-bonded sulfur was dissolved in the HI reducing solution, and another part of carbon-bonded sulfur was removed by H{sub 2}O{sub 2} oxidation. Therefore, carbon-bonded sulfur was the sum of HI-dissolved sulfur and H{sub 2}O{sub 2}-oxidized sulfur for oxic soils. However, pyritic sulfur should be subtracted from the sum of the two sulfur fractions in case of anoxic soils.

  12. Comparative analysis of oxidation methods of reaction-sintered silicon carbide for optimization of oxidation-assisted polishing.

    PubMed

    Shen, Xinmin; Dai, Yifan; Deng, Hui; Guan, Chaoliang; Yamamura, Kazuya

    2013-11-01

    Combination of the oxidation of reaction-sintered silicon carbide (RS-SiC) and the polishing of the oxide is an effective way of machining RS-SiC. In this study, anodic oxidation, thermal oxidation, and plasma oxidation were respectively conducted to obtain oxides on RS-SiC surfaces. By performing scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX) analysis and scanning white light interferometry (SWLI) measurement, the oxidation behavior of these oxidation methods was compared. Through ceria slurry polishing, the polishing properties of the oxides were evaluated. Analysis of the oxygen element on polished surfaces by SEM-EDX was conducted to evaluate the remaining oxide. By analyzing the three oxidation methods with corresponding polishing process on the basis of schematic diagrams, suitable application conditions for these methods were clarified. Anodic oxidation with simultaneous polishing is suitable for the rapid figuring of RS-SiC with a high material removal rate; polishing of a thermally oxidized surface is suitable for machining RS-SiC mirrors with complex shapes; combination of plasma oxidation and polishing is suitable for the fine finishing of RS-SiC with excellent surface roughness. These oxidation methods are expected to improve the machining of RS-SiC substrates and promote the application of RS-SiC products in the fields of optics, molds, and ceramics. PMID:24216836

  13. Temperature evolution of structure and bonding of formic acid and formate on fully oxidized and highly reduced CeO2(111)

    SciTech Connect

    Gordon, Wesley O [ORNL; Xu, Ye [ORNL; Mullins, David R [ORNL; Overbury, Steven {Steve} H [ORNL

    2009-01-01

    Adsorption of formate on oxide surfaces plays a role in water-gas shift (WGS) and other reactions related to H2 production and CO2 utilization. CeO2 is of particular interest because its reducibility affects the redox of organic molecules. In this work, the adsorption and thermal evolution of formic acid and formate on highly ordered films of fully oxidized CeO2(111) and highly reduced CeOx(111) surfaces have been studied using reflection absorption infrared spectroscopy (RAIRS) under ultra-high vacuum conditions, and the experimental results are combined with density functional theory (DFT) calculations to probe the identity, symmetry, and bonding of the surface intermediates. Disordered ice, ordered a-polymorph and molecular formic acid bonded through the carbonyl are observed at low temperatures. By 250 K, desorption and deprotonation lead to formate coexisting with hydroxyl on CeO2(111), identified to be a bridging bidentate formate species that is coordinated to Ce cations in nearly C2v symmetry and interacting strongly with neighboring H. Changes in the spectra at higher temperatures are consistent with additional tilting of the formate, resulting in Cs(2) or lower symmetry. This change in bonding is caused primarily by interaction with oxygen vacancies introduced by water desorption at 300 K. On reduced CeOx, multiple low-symmetry formate states exist likewise due to interactions with oxygen vacancies. Isotopic studies demonstrate that the formyl hydrogen does not contribute to H incorporated in hydroxyl on the surface, and that both formate oxygen atoms may exchange with lattice oxygen at 400 K. The combined experimental and theoretical results thus provide important insights on the surface reaction pathways of formic acid on ceria.

  14. Influence of alumina reaction tube impurities on the oxidation of chemically-vapor-deposited silicon carbide

    Microsoft Academic Search

    Elizabeth Opila

    1995-01-01

    Pure coupons of chemically vapor deposited (CVD) SiC oxidized for 100 h in dry flowing oxygen at 1,300 C. The oxidation kinetics were monitored using thermogravimetry (TGA). The experiments were first performed using high-purity alumina reaction tubes. The experiments were then repeated using fused quartz reaction tubes. Differences in oxidation kinetics, scale composition, and scale morphology were observed. These differences

  15. Nitric oxide interaction with oxy-coboglobin models containing trans-pyridine ligand: two reaction pathways.

    PubMed

    Kurtikyan, Tigran S; Eksuzyan, Shahane R; Goodwin, John A; Hovhannisyan, Gohar Sh

    2013-10-21

    The oxy-cobolglobin models of the general formula (Py)Co(Por)(O2) (Por = meso-tetraphenyl- and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low-temperature interaction of Py and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Similar to the recently studied (NH3)Co(Por)(O2) system (Kurtikyan et al. J. Am. Chem. Soc., 2012, 134, 13671-13680), this interaction leads to the nitric oxide dioxygenation reaction with the formation of thermally unstable nitrato complexes (Py)Co(Por)(?(1)-ONO2). The reaction proceeds through the formation of the six-coordinate peroxynitrite adducts (Py)Co(Por)(OONO), as was demonstrated by FTIR measurements with the use of isotopically labeled (18)O2, (15)NO, N(18)O, and (15)N(18)O species and DFT calculations. In contrast to the ammonia system, however, the binding of dioxygen in (Py)Co(Por)(O2) is weaker and the second reaction pathway takes place due to autoxidation of NO by rebound O2 that in NO excess gives N2O3 and N2O4 species adsorbed in the layer. This leads eventually to partial formation of (Py)Co(Por)(NO) and (Py)Co(Por)(NO2) as a result of NO and NO2 reactions with five-coordinate Co(Por)(Py) complexes that are present in the layer after the O2 has been released. The former is thermally unstable and at room temperature passes to the five-coordinate nitrosyl complex, while the latter is a stable compound. In these experiments at 210 K, the layer consists mostly of six-coordinate nitrato complexes and some minor quantities of six-coordinate nitro and nitrosyl species. Their relative quantities depend on the experimental conditions, and the yield of nitrato species is proportional to the relative quantity of peroxynitrite intermediate. Using differently labeled nitrogen oxide isotopomers in different stages of the process the formation of the caged radical pair after homolytic disruption of the O-O bond in peroxynitrite moiety is clearly shown. The composition of the layers upon farther warming to room temperature depends on the experimental conditions. In vacuo the six-coordinate nitrato complexes decompose to give nitrate anion and oxidized cationic complex Co(III)(Por)(Py)2. In the presence of NO excess, however, the nitro-pyridine complexes (Py)Co(Por)(NO2) are predominantly formed formally indicating the oxo-transfer reactivity of (Py)Co(Por)(?(1)-ONO2) with regard to NO. Using differently labeled nitrogen in nitric oxide and coordinated nitrate a plausible mechanism of this reaction is suggested based on the isotope distribution in the nitro complexes formed. PMID:24090349

  16. Double bond stereochemistry influences the susceptibility of short-chain isoprenoids and polyprenols to decomposition by thermo-oxidation.

    PubMed

    Moli?ska, Ewa; Klimczak, Urszula; Komaszy?o, Joanna; Derewiaka, Dorota; Obiedzi?ski, Mieczys?aw; Kania, Magdalena; Danikiewicz, Witold; Swiezewska, Ewa

    2015-04-01

    Isoprenoid alcohols are common constituents of living cells. They are usually assigned a role in the adaptation of the cell to environmental stimuli, and this process might give rise to their oxidation by reactive oxygen species. Moreover, cellular isoprenoids may also undergo various chemical modifications resulting from the physico-chemical treatment of the tissues, e.g., heating during food processing. Susceptibility of isoprenoid alcohols to heat treatment has not been studied in detail so far. In this study, isoprenoid alcohols differing in the number of isoprene units and geometry of the double bonds, ?-citronellol, geraniol, nerol, farnesol, solanesol and Pren-9, were subjected to thermo-oxidation at 80 °C. Thermo-oxidation resulted in the decomposition of the tested short-chain isoprenoids as well as medium-chain polyprenols with simultaneous formation of oxidized derivatives, such as hydroperoxides, monoepoxides, diepoxides and aldehydes, and possible formation of oligomeric derivatives. Oxidation products were monitored by GC-FID, GC-MS, ESI-MS and spectrophotometric methods. Interestingly, nerol, a short-chain isoprenoid with a double bond in the cis (Z) configuration, was more oxidatively stable than its trans (E) isomer, geraniol. However, the opposite effect was observed for medium-chain polyprenols, since Pren-9 (di-trans-poly-cis-prenol) was more susceptible to thermo-oxidation than its all-trans isomer, solanesol. Taken together, these results experimentally confirm that both short- and long-chain polyisoprenoid alcohols are prone to thermo-oxidation. PMID:25739731

  17. Direct Conversion of Glycerol into Formic Acid via Water Stable Pd(II) Catalyzed Oxidative Carbon-Carbon Bond Cleavage

    PubMed Central

    Pullanikat, Prasanna; Lee, Joo Ho; Yoo, Kyung Soo; Jung, Kyung Woon

    2013-01-01

    Using our tridentate NHC-amidate-alkoxide Pd(II) complex, we developed a catalytic method for oxidative C-C bond cleavage of glycerol. The glycerol was degraded exclusively to formic acid and CO2. Two possible degradation pathways were proposed through 13C labeled studies. PMID:23997315

  18. Metallapyrimidines and Metallapyrimidiniums from Oxidative Addition of Pyrazolate N-N Bonds to Niobium(III), Niobium(IV), and

    E-print Network

    Schlegel, H. Bernhard

    Metallapyrimidines and Metallapyrimidiniums from Oxidative Addition of Pyrazolate N-N Bonds, whereas no hydrogen atom abstraction occurred in 3. These complexes represent rare examples of pyrazolate to the highly aromatic 3,5-di-tert-butylpyrazolate ligands and pyrimidine. Complexes containing pyrazolate

  19. Competition between covalent bonding and charge transfer tendencies at complex-oxides interfaces

    NASA Astrophysics Data System (ADS)

    Salafranca, J.; Tornos, J.; García-Barriocanal, J.; León, C.; Santamaria, J.; Rincón, J.; Álvarez, G.; Pennycook, S. J.; Dagotto, E.; Varela, M.

    2013-03-01

    Interfaces alter the subtle balance among different degrees of freedom responsible for exotic phenomena in complex oxides, such as cuprate-manganite interfaces. We study these interfaces by means of scanning transmission electron microscopy and theoretical calculations. Microscopy and EEL spectroscopy indicate that the interfaces are sharp, and the chemical profile is symmetric with two equivalent interfaces. Spectroscopy also allows us to establish an oxidation state profile with sub-nanometer resolution. We find an anomalous charge redistribution: a non-monotonic behavior of the occupancy of d orbitals in the manganite layers as a function of distance to the interface. Relying on model calculations, we establish that this profile is a result of the competition between standard charge transfer tendencies involving materials with different chemical potentials and strong bonding effects across the interface. The competition can be tuned by different factors (temperature, doping, magnetic fields...). As examples, we report different charge distributions as a function of doping of the manganite layers. ACKNOWLEDGEMENTS ORNL:U.S. DOE-BES, Material Sciences and Engineering Division & ORNL's ShaRE. UCM:Juan de la Cierva, Ramon y Cajal, & ERC Starting Investigator Award programs.

  20. Structure Sensitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces

    E-print Network

    Rohrer, Gregory S.

    Structure Sensitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces) on the surface. Mi- croscopic analysis has been used to relate the rates of these two reactions to the structure and the composition of the termination layer does not influence this reaction. On the polar (111) surface

  1. Coordinate Contribution of Lipid Oxidation and Maillard Reaction to the Nonenzymatic Food Browning

    Microsoft Academic Search

    ROSARIO ZAMORA; FRANCISCO J. HIDALGO

    2005-01-01

    Lipid oxidation and the Maillard reaction are probably the two most important reactions in Food Science. Both include a whole network of different reactions in which an extraordinary complex mixture of compounds are obtained in very different amounts and produce important changes in food flavor, color, texture, and nutritional value, with positive and negative consequences. This article analyzes the interactions

  2. Coordination-Resolved Spectrometrics of Local Bonding and Electronic Dynamics of Au Atomic Clusters, Solid Skins, and Oxidized Foils.

    PubMed

    Yu, Wang; Bo, Maolin; Huang, Yongli; Wang, Yan; Li, Can; Sun, Chang Q

    2015-07-20

    By using combination of bond-order-length-strength (BOLS) correlation, the tight-binding (TB) approach, and zone-selective photoelectron spectroscopy (ZPS), we were able to resolve local bond relaxation and the associated 4f7/2 core-level shift of Au atomic clusters, Au(100, 110, 111) skins, and Au foils exposed to ozone for different lengths of time. In addition to quantitative information, such as local bond length, bond energy, binding-energy density, and atomic cohesive energy, the results confirm our predictions that bond-order deficiency shortens and stiffens the bond between undercoordinated atoms, which results in local densification and quantum entrapment of bonding electrons. The entrapment perturbs the Hamiltonian, and hence, shifts the core-level energy accordingly. ZPS also confirms that oxidation enhances the effect of atomic undercoordination on the positive 4f7/2 energy shift, with the associated valence electron polarization contributing to the catalytic ability of undercoordinated Au atoms. PMID:25916877

  3. Activation energy of tantalum-tungsten oxide thermite reactions

    SciTech Connect

    Cervantes, Octavio G.; Munir, Zuhair A. [Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, CA (United States); Chemical Engineering and Materials Science, University of California, Davis, CA (United States); Kuntz, Joshua D.; Gash, Alexander E. [Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, CA (United States)

    2011-01-15

    The activation energy of a sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the high-pressure spark plasma sintering (HPSPS) technique at 300 and 400 C. The ignition temperatures were investigated under high heating rates (500-2000 C min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Samples consolidated at 300 C exhibit an abrupt change in temperature response prior to the main ignition temperature. This change in temperature response is attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465 to 670 C. The activation energies of the SG derived Ta-WO{sub 3} thermite composite consolidated at 300 and 400 C were determined to be 38{+-} 2 kJ mol{sup -1} and 57 {+-} 2 kJ mol{sup -1}, respectively. (author)

  4. Reaction of Unsaturated Esters with the Oxidative System Aluminum Tri-tert-Butoxide-tert-Butyl Hydroperoxide

    Microsoft Academic Search

    L. P. Stepovik; I. M. Martynova; V. A. Dodonov

    2002-01-01

    Unsaturated esters containing double bonds in the acyl (methyl acrylate) or in the alcohol (vinyl and allyl acetates) fragments are cleaved under mild conditions (20°C) by the system aluminum tri-tert-butoxide-tert-butyl hydroperoxide to give tert-butyl esters of peroxycarboxylic acids and unsymmetrical aluminum alkoxides. The double bond in the acyl fragment is inert to this oxidation system. Vinyloxy- and allyloxy derivatives are

  5. Rhenium-catalyzed synthesis of 2H-1,2-oxaphosphorin 2-oxides via the regio- and stereoselective addition reaction of ?-keto phosphonates with alkynes.

    PubMed

    Murai, Masahito; Nakamura, Masahiro; Takai, Kazuhiko

    2014-11-01

    Treatment of ?-keto phosphonates (Horner-Wadsworth-Emmons reagents) with terminal alkynes in the presence of a rhenium catalyst gave 2H-1,2-oxaphosphorin 2-oxides with various substitution patterns. The reaction proceeds via two consecutive processes: cleavage of a carbon-carbon ?-bond of the ?-keto phosphonate with insertion of the alkyne in a regio- and stereoselective manner, followed by cyclization of the resulting ?-phosphonyl ?,?-unsaturated ketone yielding the 2H-1,2-oxaphosphorin 2-oxide. Horner-Wadsworth-Emmons reagents were found to add to nonpolar unsaturated compounds under neutral conditions. PMID:25341380

  6. Oxydehydrogenation of propane over Mg-V-Sb-oxide catalysts. II. Reaction kinetics and mechanism

    Microsoft Academic Search

    James N. Michaels; David L. Stern; Robert K. Grasselli

    1996-01-01

    Recently we reported that Mg4V2Sb2Ox is selective for propane andn-butane Oxydehydrogenation at low hydrocarbon conversion, and that propane is oxidized in parallel reactions to propylene and COx. We report now on the kinetics of propane and propylene oxidations over this catalyst. The partial oxidations of propane and propylene and zero-order in oxygen, whereas deep oxidations of both hydrocarbons are half-order.

  7. Preparation of leady oxide for lead–acid battery by cementation reaction

    Microsoft Academic Search

    Joon-Ho Shin; Ki-Won Kim; Hyo-Jun Ahn

    2000-01-01

    The aim of this research is to prepare leady oxide with high specific area for lead–acid batteries by a new production process. Leady oxide is produced by a cementation reaction in 1.0 wt% HCl solution using a pure aluminum or a magnesium rod as the reductant. Leady oxide prepared in this process is much superior to Barton-pot or ball-mill oxide

  8. Reaction of sp/sup 2/ C-H bonds in unactivated alkenes with bis(diphosphine) complexes of iron

    SciTech Connect

    Baker, M.V.; Field, L.D.

    1986-11-12

    Over the last 10 years, there has been much interest in the chemistry of coordinatively unsaturated transition-metal complexes, particularly in the activation of alkyl C-H bonds by complexes of Ir, Rh, Re, and W. Some early fundamental work in the area of C-H bond activation involved Fe(DMPE)/sub 2/ (1) (DMPE = 1,2-bis(dimethylphosphino)ethane), a reactive intermediate generated by reductive elimination of naphthalene from cis-FeH(Np)DMPE)/sub 2/ (Np = 2-naphthyl); however, this system was limited in that only substrates with a reactivity greater than (or comparable to) that of the naphthalene byproduct could be examined. In addition, this route to 1 necessarily required reaction temperatures close to room temperature, where any thermally labile products may not have been sufficiently stable to be observed or characterized. An alternative, more versatile route to 1 is by photolysis of the dihydride FeH/sub 2/(DMPE)/sub 2/ (2). The authors have examined the reactions of 1, generated photochemically at low temperature, with hydrocarbons, and report here the formation of products arising from Fe insertion into sp/sup 2/ C-H bonds of unactivated alkenes.

  9. A quantum chemical topological analysis of the C-C bond formation in organic reactions involving cationic species.

    PubMed

    Domingo, Luis R; Pérez, Patricia

    2014-07-21

    ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P(k)(o) Parr functions of the iminium cation, and the nucleophilic P(k)(-) Parr functions of Cp makes the characterisation of the most favourable two-center interaction along the formation of the C-C single bond possible. PMID:24901220

  10. Reaction of SC+, Ti+, and V+ with CO. MC+ and MO+ bond energies D. E. Clemmer, J. L. Elkind,") N. Aristov,b) and P. B. Armentrout")

    E-print Network

    Clemmer, David E.

    Reaction of SC+, Ti+, and V+ with CO. MC+ and MO+ bond energies D. E. Clemmer, J. L. Elkind,") N (Received 16April 1991;accepted28 May 1991) The reactionsof SC+ , Ti + , and V + with CO are studiedasa.Thresholdsof the reaction crosssectionsare interpreted to give the 0 K bond energies(in eV) DO(ScC+ ) = 3.34f 0.06,D'(Ti

  11. Effect of oxidation heat treatment on the bond strength between a ceramic and cast and milled cobalt-chromium alloys.

    PubMed

    Li, Jieyin; Ye, Xiuhua; Li, Bohua; Liao, Juankun; Zhuang, Peilin; Ye, Jiantao

    2015-08-01

    There is a dearth of dental scientific literature on the effect of different oxidation heat treatments (OHTs) (as surface pretreatments) on the bonding performance of cast and milled cobalt-chromium (CoCr) alloys. The objective of this study was to evaluate the effect of different OHTs on the bond strength between a ceramic and cast and milled CoCr alloys. Cobalt-chromium metallic specimens were prepared using either a cast or a milled method. Specimens were subjected to four different OHT methods: without OHT; OHT under normal atmospheric pressure; OHT under vacuum; and OHT under vacuum followed by sandblasting. The metal-ceramic bond strength was evaluated using a three-point bending test according to ISO9693. Scanning electron microscopy and energy-dispersive spectroscopy were used to study the specimens' microstructure and elemental composition. The bond strength was not affected by the CoCr manufacturing method. Oxidation heat treatment performed under normal atmospheric pressure resulted in the highest bond strength. The concentration of oxygen on the alloy surfaces varied with the different pretreatment methods in the following order: OHT under normal atmospheric pressure > OHT under vacuum > without OHT ? OHT under vacuum followed by sandblasting. PMID:26104804

  12. Effect of Cyclic Oxidation Exposure on Tensile Properties of a Pt-Aluminide Bond-Coated Ni-Base Superalloy

    NASA Astrophysics Data System (ADS)

    Zafir Alam, Md.; Hazari, N.; Varma, Vijay K.; Das, Dipak K.

    2011-12-01

    The tensile behavior of a directionally solidified (DS) Ni-base superalloy, namely, CM-247LC, was evaluated in the presence of a Pt-aluminide bond coat. The effect of the thermal cycling exposure of the coated alloy at 1373 K (1100 °C) on its tensile properties was examined. The tensile properties were evaluated at a temperature of 1143 K (870 °C). The presence of the bond coating caused an approximately 8 pct drop in the strength of the alloy in the as-coated condition. However, the coating did not appreciably affect the tensile ductility of the substrate alloy. The bond coat prevented oxidation-related surface damage to the superalloy during thermal cycling exposure in air at 1373 K (1100 °C). Such cyclic oxidation exposure (up to 750 hours) did not cause any further reduction in yield strength (YS) of the coated alloy. There was a marginal decrease in the ultimate tensile strength (UTS) with increased exposure duration. Because of the oxidation protection provided by the bond coat, the drastic loss in ductility of the alloy, which would have happened in the absence of the coating, was prevented.

  13. NITROGEN OXIDES REACTIONS WITHIN URBAN PLUMES TRANSPORTED OVER THE OCEAN

    EPA Science Inventory

    The report describes an airborne measurements program in the downwind urban plume of Boston. The variables measured included ozone, nitric oxide, oxides of nitrogen, nitric acid, peroxyacetylnitrate, carbon monoxide, nonmethane hydrocarbon, freon-11, C1-C5 hydrocarbons, condensat...

  14. Behaviour of oxide at diffusion?bonded interfaces in Al?Mg?Si series 6063 alloy: Study of diffusion?bonding mechanism of aluminium alloys by transmission electron microscopy (1st Report)

    Microsoft Academic Search

    K. Ikeuchi; F. Matsuda; K. Kotani

    1996-01-01

    The behaviour of the surface oxide film during the diffusion?bonding of Al?Mg?Si series 6063 alloy and its influence on the bond strength have been investigated mainly by TEM observations in order to explain the effect of alloying elements on the bondability of aluminium alloys. When faying surfaces were finished by electro?polishing, crystalline oxide particles smaller than a few 10 ?m

  15. Interfacial Reactions between Oxide Films and Refractory Metal Substrates

    E-print Network

    Goodman, Wayne

    in an ultrahigh vacuum (UHV) chamber with a base pressure of j1 × 10-9 Torr. The chamber was equipped. The thermal stabilities of the oxide films are considerably less than the corresponding bulk oxides. NiO films difficulties related to poor thermal and electrical conduc- tivity typically experienced with bulk oxides.4

  16. Influence of Alumina Reaction Tube Impurities on the Oxidation of Chemically-Vapor-Deposited Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth

    1995-01-01

    Pure coupons of chemically vapor deposited (CVD) SiC were oxidized for 100 h in dry flowing oxygen at 1300 C. The oxidation kinetics were monitored using thermogravimetry (TGA). The experiments were first performed using high-purity alumina reaction tubes. The experiments were then repeated using fused quartz reaction tubes. Differences in oxidation kinetics, scale composition, and scale morphology were observed. These differences were attributed to impurities in the alumina tubes. Investigators interested in high-temperature oxidation of silica formers should be aware that high-purity alumina can have significant effects on experiment results.

  17. Infrared Spectroscopy of OH··CH3OH: Hydrogen-Bonded Intermediate Along the Hydrogen Abstraction Reaction Path.

    PubMed

    Hernandez, Federico J; Brice, Joseph T; Leavitt, Christopher M; Pino, Gustavo A; Douberly, Gary E

    2015-07-23

    Substantial non-Arrhenius behavior has been previously observed in the low temperature reaction between the hydroxyl radical and methanol. This behavior can be rationalized assuming the stabilization of an association adduct in the entrance channel of the reaction, from which barrier penetration via quantum mechanical tunneling produces the CH3O radical and H2O. Helium nanodroplet isolation and a serial pick-up technique are used to stabilize the hydrogen bonded prereactive OH··CH3OH complex. Mass spectrometry and infrared spectroscopy are used to confirm its production and probe the OH stretch vibrations. Stark spectroscopy reveals the magnitude of the permanent electric dipole moment, which is compared to ab initio calculations that account for wide-amplitude motion in the complex. The vibrationally averaged structure has Cs symmetry with the OH moiety hydrogen bonded to the hydroxyl group of methanol. Nevertheless, the zero-point level of the complex exhibits a wave function significantly delocalized over a bending coordinate leading to the transition state of the CH3O producing reaction. PMID:26135615

  18. Reactions of dioxygen difluoride with neptunium oxides and fluorides

    Microsoft Academic Search

    P. Gary Eller; Larned B. Asprey; Scott A. Kinkead; Basil I. Swanson; Richard J. Kissane

    1998-01-01

    Neptunium dioxide and tetrafluoride are converted in essentially quantitative yield to volatile neptunium hexafluoride by dioxygen difluoride (O2F2), both in gas–solid reactions at ambient temperatures and in liquid anhydrous hydrogen fluoride at ?78°C. Neptunium dioxydifluoride was identified by Raman spectroscopy as a dominant reaction intermediate in the neptunium dioxide reaction. Direct reaction of NpF4 with liquid O2F2 resulted in violent

  19. Identification and cleavage of breakable single bonds by selective oxidation, reduction, and hydrolysis

    SciTech Connect

    Hirschon, A.S.; Zevely, J.; Mayo, F.R.

    1982-05-25

    The objective of this project is to determine the proportions of the various kinds of connecting links in coal and how they can best be broken - in other words, to determine the structure of bituminous coal, with emphasis on the cross-links and breakable single bonds. An extraction of Illinois No. 6 coal, some swelling experiments on Illinois No. 6 coal products, and some extractions of other recently acquired coal samples are described. The results show that on long heating at a high solvent-to-coal ratio ethanolamine does not extract as much material from whole coal as either BnNH/sub 2/ or EDA, yet the swelling ratio of the extracted coal is greater than with the other amines. BnNH/sub 2/ swells both EDA/DMSO- and pyridine-extracted coals better than other amine solvents tested, including ethanolamine. The EDA/DMSO-extracted coal is swollen more by all the solvents tested than pyridine-extracted coal. Preliminary results show that solvents swell EDA/DMSO-extracted coal more when either t-BuOK or tetraalkylammonium hydroxides are added to the solvents than when the pure solvents are used but are not conclusive. Results from pyridine extractions of several coals of varying ranks show that less coal is extracted by pyridine as the coal rank increases. A series of oxidations with nitric acid and sodium hypochlorite are described. Model compounds are being oxidized to determine the best way to distinguish between single and multiple methylene groups. Results from ESR measurements on a pyridine extraction of Illinois No. 6 coal are reported. Most of the free spins remain in the insoluble fractions and 38 +- 7% of the spins are lost during the extraction.

  20. Influence of interfacial shear strength on the mechanical properties of SiC fiber reinforced reaction-bonded silicon nitride matrix composites

    NASA Technical Reports Server (NTRS)

    Bhatt, Ramakrishna T.

    1990-01-01

    The influence of fiber/matrix interface microstructure and interfacial shear strength on the mechanical properties of a fiber-reinforced ceramic composite was evaluated. The composite consisted of approximately 30 vol percent uniaxially aligned 142 microns diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix (SiC/RBSN). The interface microstructure was varied by controlling the composite fabrication conditions and by heat treating the composite in an oxidizing environment. Interfacial shear strength was determined by the matrix crack spacing method. The results of microstructural examination indicate that the carbon-rich coating provided with the as-produced SiC fibers was stable in composites fabricated at 1200 C in a nitrogen or in a nitrogen plus 4 percent hydrogen mixture for 40 hr. However this coating degraded in composites fabricated at 1350 C in N2 + 4 percent H2 for 40 and 72 hr and also in composites heat treated in an oxidizing environment at 600 C for 100 hr after fabrication at 1200 C in a nitrogen. It was determined that degradation occurred by carbon removal which in turn had a strong influence on interfacial shear strength and other mechanical properties. Specifically, as the carbon coating was removed, the composite interfacial shear strength, primary elastic modulus, first matrix cracking stress, and ultimate tensile strength decreased, but the first matrix cracking strain remained nearly the same.

  1. Properties of a reaction-bonded ?-SiAlON ceramic doped with an FeMo alloy for application to molten aluminum environments

    NASA Astrophysics Data System (ADS)

    Li, Yan-jun; Yu, Hai-liang; Jin, Hai-yun; Shi, Zhong-qi; Qiao, Guan-jun; Jin, Zhi-hao

    2015-05-01

    An FeMo-alloy-doped ?-SiAlON (FeMo/?-SiAlON) composite was fabricated via a reaction-bonding method using raw materials of Si, Al2O3, AlN, FeMo, and Sm2O3. The effects of FeMo on the microstructure and mechanical properties of the composite were investigated. Some properties of the composite, including its bending strength at 700°C and after oxidization at 700°C for 24 h in air, thermal shock resistance and corrosion resistance to molten aluminum, were also evaluated. The results show that the density, toughness, bending strength, and thermal shock resistance of the composite are obviously improved with the addition of an FeMo alloy. In addition, other properties of the composite such as its high-temperature strength and oxidized strength are also improved by the addition of FeMo alloy, and its corrosion resistance to molten aluminum is maintained. These findings indicate that the developed FeMo/?-SiAlON composite exhibits strong potential for application to molten aluminum environments.

  2. Visible Light Driven Nanosecond Bromide Oxidation by a Ru Complex with Subsequent Br-Br Bond Formation.

    PubMed

    Li, Guocan; Ward, William M; Meyer, Gerald J

    2015-07-01

    Visible light excitation of [Ru(deeb)(bpz)2](2+) (deeb = 4,4'-diethylester-2,2'-bipyridine; bpz = 2,2'-bipyrazine), in Br(-) acetone solutions, led to the formation of Br-Br bonds in the form of dibromide, Br2(•-). This light reactivity stores ?1.65 eV of free energy for milliseconds. Combined (1)H NMR, UV-vis and photoluminescence measurements revealed two distinct mechanisms. The first involves diffusional quenching of the excited state by Br(-) with a rate constant of (8.1 ± 0.1) × 10(10) M(-1) s(-1). At high Br(-) concentrations, an inner-sphere pathway is dominant that involves the association of Br(-), most likely with the 3,3'-H atoms of a bpz ligand, before electron transfer from Br(-) to the excited state, ket = (2.5 ± 0.3) × 10(7) s(-1). In both mechanisms, the direct photoproduct Br(•) subsequently reacts with Br(-) to yield dibromide, Br(•) + Br(-) ? Br2(•-). Under pseudo-first-order conditions, this occurs with a rate constant of (1.1 ± 0.4) × 10(10) M(-1) s(-1) that was, within experimental error, the same as that measured when Br(•) were generated with ultraviolet light. Application of Marcus theory to the sensitized reaction provided an estimate of the Br(•) formal reduction potential E(Br(•)/Br(-)) = 1.22 V vs SCE in acetone, which is about 460 mV less positive than the accepted value in H2O. The results demonstrate that Br(-) oxidation by molecular excited states can be rapid and useful for solar energy conversion. PMID:26085129

  3. Tensile creep behavior of a vitreous-bonded aluminum oxide under static and cyclic loading

    SciTech Connect

    Dey, N.; Socie, D.F.; Hsia, K.J. [Univ. of Illinois at Urbana-Champaign, IL (United States)

    1996-09-01

    Creep deformation and rupture behavior of a vitreous-bonded aluminum oxide was investigated under uniaxial static and cyclic tensile loadings at 1000, 1100, and 1175 C. The material was more creep resistant, i.e., having lower creep strain rates, under cyclic loading compared to that under static loading. For the same maximum applied stress, the ratio of steady-state creep rate under static loading to that under cyclic loading at 1100 C was approximately 100. However, the value of this ratio decreased to about 10 when the testing temperature was raised to 1175 C or lowered to 1000 C. Under static loading the material had more propensity to develop creep damage in the form of micro- and macrocracks, leading to early failure, whereas under cyclic loading the creep damage was more uniformly distributed in the form of cavities confined to the multigrain junctions. Viscous bridging by the grain boundary second phase may be the primary contributor to the lower creep deformation rate and improved lifetime under cyclic loading.

  4. Role of van der Waals bonding in layered oxide: Bulk vanadium pentoxide

    E-print Network

    Elisa Londero; Elsebeth Schroder

    2010-06-12

    Sparse matter is characterized by regions with low electron density and its understanding calls for methods to accurately calculate both the van der Waals (vdW) interactions and other bonding. Here we present a first-principles density functional theory (DFT) study of a layered oxide (V2O5) bulk structure which shows charge voids in between the layers and we highlight the role of the vdW forces in building up material cohesion. The result of previous first-principles studies involving semilocal approximations to the exchange-correlation functional in DFT gave results in good agreement with experiments for the two in-plane lattice parameters of the unit cell but overestimated the parameter for the stacking direction. To recover the third parameter we include the nonlocal (dispersive) vdW interactions through the vdW-DF method [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] testing also various choices of exchange flavors. We find that the transferable first-principle vdW-DF calculations stabilizes the bulk structure. The vdW-DF method gives results in fairly good agreement with experiments for all three lattice parameters.

  5. Turning regioselectivity into stereoselectivity: efficient dual resolution of P-stereogenic phosphine oxides through bifurcation of the reaction pathway of a common intermediate.

    PubMed

    Nikitin, Kirill; Rajendran, Kamalraj V; Müller-Bunz, Helge; Gilheany, Declan G

    2014-02-10

    Synthetic routes that provide facile access to either enantiomeric form of a target compound are particularly valuable. The crystallization-free dual resolution of phosphine oxides that gives highly enantioenriched materials (up to 94?% ee) in excellent yields is reported. Both enantiomeric oxides have been prepared from a single intermediate, (RP )-alkoxyphosphonium chloride, which is formed in the course of a selective dynamic kinetic resolution using a single enantiomer of menthol as the chiral auxiliary. The origin of the dual stereoselectivity lies in bifurcation of the reaction pathway of this intermediate, which works as a stereochemical railroad switch. Under controlled conditions, Arbuzov-type collapse of this intermediate proceeds through C?O bond fission with retention of the configuration at the phosphorus center. Conversely, alkaline hydrolysis of the P?O bond leads to the opposite SP ?enantiomer. PMID:24474623

  6. Carbon-coated magnetic palladium: applications in partial oxidation of alcohols and coupling reactions.

    EPA Science Inventory

    Magnetic carbon supported Pd catalyst has been synthesized via in situ generation of nanoferrites and incorporation of carbon from renewable cellulose via calcination; catalyst can be used for oxidation of alcohols, amination reaction and arylation of aryl halides (cross coupli...

  7. Palladium and gold nanotubes as oxygen reduction reaction and alcohol oxidation reaction catalysts in base.

    PubMed

    Alia, Shaun M; Duong, Kathlynne; Liu, Toby; Jensen, Kurt; Yan, Yushan

    2014-06-01

    Palladium (PdNTs) and gold nanotubes (AuNTs) were synthesized by the galvanic displacement of silver nanowires. PdNTs and AuNTs have wall thicknesses of 6?nm, outer diameters of 60?nm, and lengths of 5-10 and 5-20??m, respectively. Rotating disk electrode experiments showed that the PdNTs and AuNTs have higher area normalized activities for the oxygen reduction reaction (ORR) than conventional nanoparticle catalysts. The PdNTs produced an ORR area activity that was 3.4, 2.2, and 3.7?times greater than that on carbon-supported palladium nanoparticles (Pd/C), bulk polycrystalline palladium, and carbon-supported platinum nanoparticles (Pt/C), respectively. The AuNTs produced an ORR area activity that was 2.3, 9.0, and 2.0?times greater than that on carbon-supported gold nanoparticles (Au/C), bulk polycrystalline gold, and Pt/C, respectively. The PdNTs also had lower onset potentials than Pd/C and Pt/C for the oxidation of methanol (0.236?V), ethanol (0.215?V), and ethylene glycol (0.251?V). In comparison to Pt/C, the PdNTs and AuNTs further demonstrated improved alcohol tolerance during the ORR. PMID:24757078

  8. Ultrasonic and micromechanical study of damage and elastic properties of SiC/RBSN ceramic composites. [Reaction Bonded Silicon Nitride

    NASA Technical Reports Server (NTRS)

    Chu, Y. C.; Hefetz, M.; Rokhlin, S. I.; Baaklini, G. Y.

    1992-01-01

    Ultrasonic techniques are employed to develop methods for nondestructive evaluation of elastic properties and damage in SiC/RBSN composites. To incorporate imperfect boundary conditions between fibers and matrix into a micromechanical model, a model of fibers having effective anisotropic properties is introduced. By inverting Hashin's (1979) microstructural model for a composite material with microscopic constituents the effective fiber properties were found from ultrasonic measurements. Ultrasonic measurements indicate that damage due to thermal shock is located near the surface, so the surface wave is most appropriate for estimation of the ultimate strength reduction and critical temperature of thermal shock. It is concluded that bonding between laminates of SiC/RBSN composites is severely weakened by thermal oxidation. Generally, nondestructive evaluation of thermal oxidation effects and thermal shock shows good correlation with measurements previously performed by destructive methods.

  9. Rheological kinetics of thermo-sensitive supramolecular assemblies from poly( N-isopropyl acrylamide) and adenine-functionalized poly(ethylene oxide) stabilized by complementary multiple hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Cui, Hui-Wang; Kuo, Shiao-Wei

    2014-05-01

    In this study, we synthesized a poly( N-isopropylacrylamide) (PNIPAm) through the polymerization of N-isopropylacrylamide in distilled water with azodiisobutyronitrile as the initiator and a bisadenine-functionalized poly(ethylene oxide) (A-PEO-A) from the reaction of adenine with a difunctionalized toluenesulfonyl-PEO. When blended together in distilled water, PNIPAm and A-PEO-A formed supramolecular aggregates stabilized through complementary multiple hydrogen bonds between the amide groups of PNIPAm and the adenine units of A-PEO-A. Agrawal integral equation and rheometry revealed the rheological kinetics of supramolecular assemblies, which were influenced significantly by the spherical micelles, large associated aggregates of spherical micelles, network structures, and toroid structures formed in aqueous solutions.

  10. Reactions of lanthanide atoms with oxygen difluoride and the role of the Ln oxidation state.

    PubMed

    Mikulas, Tanya; Chen, Mingyang; Dixon, David A; Peterson, Kirk A; Gong, Yu; Andrews, Lester

    2014-01-01

    Laser-ablated lanthanide metal atoms were condensed with OF2 in excess argon or neon at 4 K. New infrared absorption bands were observed and assigned to the oxidative addition products OLnF2 and OLnF on the basis of (18)O isotopic substitution and electronic structure calculations of the vibrational frequencies. The dominant absorptions in the 500 cm(-1) region are identified as Ln-F stretching modes, which follow the lanthanide contraction. The Ln-O stretching frequency is an important measure of the oxidation states of the Ln and oxygen and the spin state of the complex. The OCeF2, OPrF2, and OTbF2 molecules have higher frequency Ln-O stretching modes. The Ce is assigned to the IV oxidation state and the Pr and Tb are assigned to a mixed III/IV oxidation state. The remaining OLnF2 compounds have lower Ln-O stretches, and the Ln is in the III oxidation state and the O is in the -1 oxidation state. For all of the OLnF compounds, the metal is in the III oxidation state, and the Ln-F bonds are ionic. In OCeF2, OLaF, and OLuF, the bonding between the Ln and O is best described as a highly polarized ? bond and two pseudo ? bonds formed by donation from the two 2p lone pairs on the O to the Ln. Bonding for the OLnF2 compounds in the III oxidation state is predicted to be fully ionic. The bonding in OLnF2 and OLnF is dominated by the oxidation state on the lanthanide and the spin state of the molecule. The observation of larger neon to argon matrix shifts for Ln-O modes in several OLnF molecules as compared to their OLnF2 analogues is indicative of more ionic character in the OLnF species, consistent with the more formal negative charge on the oxygen in OLnF. PMID:24344827

  11. Oxidative condensation reactions of (diethylenetriamine)cobalt(III) complexes with substituted bis(pyridin-2-yl)methane ligands

    NASA Astrophysics Data System (ADS)

    Zhou, Xiangting; Hockless, David C. R.; Willis, Anthony C.; Jackson, W. Gregory

    2005-04-01

    The synthesis and characterisation of Co(III) complexes derived from a condensation reaction with a central or terminal nitrogen of a dien ligand and the ?-carbon of a range of substituted bis(pyridin-2-yl)methane ligands are described. Aerial oxidation of bpm {bis(pyridin-2-yl)methane with Co(II)/dien or direct reaction with Co(dien)Cl 3 provided in low yield a single C-N condensation product 1 (at the primary terminal NH 2) after the pyridyl -CH 2- is formally oxidised to -CH +-. The methyl substituted ligand bpe {1,1-bis(pyridin-2-yl)ethane} behaves likewise, except both terminal (prim) and central (sec) amines condense to yield isomeric products 2 and 3. Two of these three materials have been characterised by single crystal X-ray crystallography. The corresponding reactions for the bis(pyridyl) ligand bpk {bis(pyridin-2-yl)ketone} provided C-N condensation products without the requirement for oxidation at the ?-C center; two carbinolamine complexes in different geometrical configurations resulted, mer-anti-[Co(dienbpc)Cl]ZnCl 4, 5, and unsym- fac-[Co(dienbpc)Cl]ZnCl 4, 6, {dienbpc=[2-(2-aminoethylamino)-ethylamino]-di-pyridin-2-yl-methanol}. In addition, a novel complex, [Co(bpk)(bpd-OH)Cl]ZnCl 4, 4, in which one bidentate N, N-bonded bpk ligand and one tridentate N, O, N-bonded bpd (the diol from bpk+OH -) were coordinated, was obtained via the Co(II)/O 2 synthetic route. When the bpc ligand (bpc=bis(pyridin-2-yl)methanol) was employed directly as a reagent along with dien, no condensation reactions were observed, but rather a single isomeric complex [Co(dien)(bpc)]Cl.ZnCl 4, 7, in which the ligand bpc acted as a N,N,O-bonded tridentate ligand rather than as a N,N-bidentate ligand was isolated. 13C, 1D and 2D 1H NMR studies are reported for all the complexes; they establish the structures unambiguously.

  12. Stable gold(III) catalysts by oxidative addition of a carbon-carbon bond.

    PubMed

    Wu, Chung-Yeh; Horibe, Takahiro; Jacobsen, Christian Borch; Toste, F Dean

    2015-01-22

    Low-valent late transition-metal catalysis has become indispensable to chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of high-valent transition-metal complexes and the challenges associated with synthesizing them. Here we report a carbon-carbon bond cleavage at ambient conditions by a Au(i) complex that generates a stable Au(iii) cationic complex. In contrast to the well-established soft and carbophilic Au(i) catalyst, this Au(iii) complex exhibits hard, oxophilic Lewis acidity. For example, we observed catalytic activation of ?,?-unsaturated aldehydes towards selective conjugate additions as well as activation of an unsaturated aldehyde-allene for a [2 + 2] cycloaddition reaction. The origin of the regioselectivity and catalytic activity was elucidated by X-ray crystallographic analysis of an isolated Au(iii)-activated cinnamaldehyde intermediate. The concepts revealed suggest a strategy for accessing high-valent transition-metal catalysis from readily available precursors. PMID:25612049

  13. Method to Improve Indium Bump Bonding via Indium Oxide Removal Using a Multi-Step Plasma Process

    NASA Technical Reports Server (NTRS)

    Greer, H. Frank (Inventor); Jones, Todd J. (Inventor); Vasquez, Richard P. (Inventor); Hoenk, Michael E. (Inventor); Dickie, Matthew R. (Inventor); Nikzad, Shouleh (Inventor)

    2012-01-01

    A process for removing indium oxide from indium bumps in a flip-chip structure to reduce contact resistance, by a multi-step plasma treatment. A first plasma treatment of the indium bumps with an argon, methane and hydrogen plasma reduces indium oxide, and a second plasma treatment with an argon and hydrogen plasma removes residual organics. The multi-step plasma process for removing indium oxide from the indium bumps is more effective in reducing the oxide, and yet does not require the use of halogens, does not change the bump morphology, does not attack the bond pad material or under-bump metallization layers, and creates no new mechanisms for open circuits.

  14. Multilayered thermal insulation formed of zirconia bonded layers of zirconia fibers and metal oxide fibers and method for making same

    DOEpatents

    Wrenn, G.E. Jr.; Holcombe, C.E. Jr.

    1988-09-13

    A multilayered thermal insulating composite is formed of a first layer of zirconia-bonded zirconia fibers for utilization near the hot phase or surface of a furnace or the like. A second layer of zirconia-bonded metal oxide fibers is attached to the zirconia fiber layer by a transition layer formed of intermingled zirconia fibers and metal oxide fibers. The thermal insulation is fabricated by vacuum molding with the layers being sequentially applied from aqueous solutions containing the fibers to a configured mandrel. A portion of the solution containing the fibers forming the first layer is intermixed with the solution containing the fibers of the second layer for forming the layer of mixed fibers. The two layers of fibers joined together by the transition layer are saturated with a solution of zirconium oxynitrate which provides a zirconia matrix for the composite when the fibers are sintered together at their nexi.

  15. Multilayered thermal insulation formed of zirconia bonded layers of zirconia fibers and metal oxide fibers and method for making same

    DOEpatents

    Wrenn, Jr., George E. (Clinton, TN); Holcombe, Jr., Cressie E. (Farragut, TN)

    1988-01-01

    A multilayered thermal insulating composite is formed of a first layer of zirconia-bonded zirconia fibers for utilization near the hot phase or surface of a furnace or the like. A second layer of zirconia-bonded metal oxide fibers is attached to the zirconia fiber layer by a transition layer formed of intermingled zirconia fibers and metal oxide fibers. The thermal insulation is fabricated by vacuum molding with the layers being sequentially applied from aqueous solutions containing the fibers to a configured mandrel. A portion of the solution containing the fibers forming the first layer is intermixed with the solution containing the fibers of the second layer for forming the layer of mixed fibers. The two layers of fibers joined together by the transition layer are saturated with a solution of zirconium oxynitrate which provides a zirconia matrix for the composite when the fibers are sintered together at their nexi.

  16. Catalytic asymmetric carbon-carbon bond-forming reaction utilizing rare earth metal complexes

    Microsoft Academic Search

    Masakatsu Shibasaki; Hiroaki Sasai

    1996-01-01

    Novel optically active rare earth complexes have made possible a catalytic asymmetric nitroaldol reaction for the first time. Structural elucidation reveals that the complexes consist of one rare earth metal, three lithium atoms, and three BINOL units. Applications of the catalytic asymmetric nitroaldol reaction to syntheses of several p-blockers and erythro-AYA have been also achieved. Although the lithium containing rare

  17. Visible Light Mediated Oxidative C-N Bond Formation/Aromatization Cascade: A New Photocatalytic Entry to N-Arylindoles

    PubMed Central

    Maity, Soumitra

    2012-01-01

    Indoles: A joint effort of light and air We have developed a mild aerobic oxidation protocol using visible light photocatalysis to synthesize structurally diverse N-arylindoles. The procedure employs 4 mol% [Ru(bpz)3](PF6)2, 18W LED light, and is performed open to the atmosphere. Readily prepared o-stryryl anilines are converted to a variety of indoles via a cascade sequence composed of oxidation of anilines, C-N bond formation, and aromatization. A 1,2-carbon shift can be also incorporated into this cascade event to further extend the substrate scope of the method. bpz = 2, 2?-Bipyrazine PMID:22915489

  18. Controlled oxidation of aliphatic CH bonds in metallo-monooxygenases: mechanistic insights derived from studies on deuterated and fluorinated hydrocarbons.

    PubMed

    Chen, Yao-Sheng; Luo, Wen-I; Yang, Chung-Ling; Tu, Yi-Jung; Chang, Chun-Wei; Chiang, Chih-Hsiang; Chang, Chi-Yao; Chan, Sunney I; Yu, Steve S-F

    2014-05-01

    The control over the regio- and/or stereo-selective aliphatic CH oxidation by metalloenzymes is of great interest to scientists. Typically, these enzymes invoke host-guest chemistry to sequester the substrates within the protein pockets, exploiting sizes, shapes and specific interactions such as hydrogen-bonding, electrostatic forces and/or van der Waals interactions to control the substrate specificity, regio-specificity and stereo-selectivity. Over the years, we have developed a series of deuterated and fluorinated variants of these hydrocarbon substrates as probes to gain insights into the controlled CH oxidations of hydrocarbons facilitated by these enzymes. In this review, we illustrate the application of these designed probes in the study of three monooxygenases: (i) the particulate methane monooxygenase (pMMO) from Methylococcus capsulatus (Bath), which oxidizes straight-chain C1-C5 alkanes and alkenes to form their corresponding 2-alcohols and epoxides, respectively; (ii) the recombinant alkane hydroxylase (AlkB) from Pseudomonas putida GPo1, which oxidizes the primary CH bonds of C5-C12 linear alkanes; and (iii) the recombinant cytochrome P450 from Bacillus megaterium, which oxidizes C12-C20 fatty acids at the ?-1, ?-2 or ?-3 CH positions. PMID:24629413

  19. Kinetics of reactions at an interface: functionalisation of silicate glass with porphyrins via covalent bonds.

    PubMed

    Fujimoto, Takahiro; Furuta, Nao; Mizutani, Tadashi

    2015-03-21

    Porphyrins carrying either a primary alcohol, a tertiary alcohol or a primary bromide linker group were allowed to react with the surface silanol groups on silicate glass thermally at 80-240 °C to obtain a monolayer film. The kinetics of the reaction was analysed based on the pseudo-second order equation. The tertiary alcohol and the primary bromide reacted much slower than the primary alcohol. Arrhenius plots indicated that higher activation energies can account for the slower reaction of both tertiary alcohol and primary bromide linkers. The introduction of six dodecyl chains into hydroxyporphyrin accelerated the anchoring reaction by a factor of 50 owing to the larger frequency factor of the reaction, demonstrating that the dynamics of the interface is one of the dominant factors regulating the reaction kinetics. PMID:25658579

  20. Putative Hydrogen Bond to Tyrosine M208 in Photosynthetic Reaction Centers from Rhodobacter capsulatus Significantly Slows Primary Charge Separation

    PubMed Central

    2015-01-01

    Slow, ?50 ps, P* ? P+HA– electron transfer is observed in Rhodobacter capsulatus reaction centers (RCs) bearing the native Tyr residue at M208 and the single amino acid change of isoleucine at M204 to glutamic acid. The P* decay kinetics are unusually homogeneous (single exponential) at room temperature. Comparative solid-state NMR of [4?-13C]Tyr labeled wild-type and M204E RCs show that the chemical shift of Tyr M208 is significantly altered in the M204E mutant and in a manner consistent with formation of a hydrogen bond to the Tyr M208 hydroxyl group. Models based on RC crystal structure coordinates indicate that if such a hydrogen bond is formed between the Glu at M204 and the M208 Tyr hydroxyl group, the ?OH would be oriented in a fashion expected (based on the calculations by Alden et al., J. Phys. Chem.1996, 100, 16761–16770) to destabilize P+BA– in free energy. Alteration of the environment of Tyr M208 and BA by Glu M204 via this putative hydrogen bond has a powerful influence on primary charge separation. PMID:24902471

  1. EFFECTS OF SOLAR RADIATION ON MANGANESE OXIDE REACTIONS WITH SELECTED ORGANIC COMPOUNDS

    EPA Science Inventory

    The effects of sunlight on aqueous redox reactions between manganese oxides (MnOx) and selected organic substances are reported. o sunlight-induced rate enhancement was observed for the MnOx oxidation of substituted phenols, anisole, o-dichlorobenzene, or p-chloroaniline. n the o...

  2. Ceramic oxide reactions with V2O5 and SO3

    NASA Technical Reports Server (NTRS)

    Jones, R. L.; Williams, C. E.

    1985-01-01

    Ceramic oxides are not inert in combustion environments, but can react with, inter alia, SO3, and Na2SO4 to yield low melting mixed sulfate eutectics, and with vanadium compounds to produce vanadates. Assuming ceramic degradation to become severe only when molten phases are generated in the surface salt (as found for metallic hot corrosion), the reactivity of ceramic oxides can be quantified by determining the SO3 partial pressure necessary for molten mixed sulfate formation with Na2SO3. Vanadium pentoxide is an acidic oxide that reacts with Na2O, SO3, and the different ceramic oxides in a series of Lux-Flood type of acid-base displacement reactions. To elucidate the various possible vanadium compound-ceramic oxide interactions, a study was made of the reactions of a matrix involving, on the one axis, ceramix oxides of increasing acidity, and on the other axis, vanadium compounds of increasing acidity. Resistance to vanadium compound reaction increased as the oxide acidity increased. Oxides more acidic than ZrO2 displaced V2O5. Examination of Y2O3- and CeO2-stabilized ZrO2 sintered ceramics which were degraded in 700 C NaVO3 has shown good agreement with the reactions predicted above, except that the CeO2-ZrO2 ceramic appears to be inexplicably degraded by NaVO3.

  3. Adsorption and redox reactions of heavy metals on synthesized Mn oxide minerals

    Microsoft Academic Search

    Xiong Han Feng; Li Mei Zhai; Wen Feng Tan; Fan Liu; Ji Zheng He

    2007-01-01

    Several Mn oxide minerals commonly occurring in soils were synthesized by modified or optimized methods. The morphologies, structures, compositions and surface properties of the synthesized Mn oxide minerals were characterized. Adsorption and redox reactions of heavy metals on these minerals in relation to the mineral structures and surface properties were also investigated. The synthesized birnessite, todorokite, cryptomelane, and hausmannite were

  4. Chemical modification of carbon fiber surfaces by nitric acid oxidation followed by reaction with tetraethylenepentamine

    Microsoft Academic Search

    C. U. Pittman; G.-R. He; B. Wu; S. D. Gardner

    1997-01-01

    Amino groups react rapidly with both isocyanates and epoxides. Thus, to prepare carbon fibers which might exhibit enhanced adhesion to both polyurethanes and epoxy resin matrices, attempts were made to introduce a high surface amine concentration onto high-strength carbon fibers (derived from PAN) by nitric acid oxidation followed by reaction with excess tetraethylenepentamine (TEPA). Fibers were oxidized with concentrated (70%)

  5. Ubiquinol oxidation in the cytochrome bc1 complex: Reaction mechanism and prevention of short-circuiting

    E-print Network

    Steinhoff, Heinz-Jürgen

    Review Ubiquinol oxidation in the cytochrome bc1 complex: Reaction mechanism and prevention This review is focused on the mechanism of ubiquinol oxidation by the cytochrome bc1 complex (bc1­sulfur Rieske protein (FeS protein) and the other goes to cytochrome b. The nature of intermediates

  6. Basic character of rare earth metal alkoxides. Utilization in catalytic CC bond-forming reactions and catalytic asymmetric nitroaldol reactions

    Microsoft Academic Search

    Hiroaki Sasai; Takeyuki Suzuki; Shigeru Arai; Takayoshi Arai; Masakatsu Shibasaki

    1992-01-01

    In a recent paper, the authors reported that Zr(O-t-Bu)â was an efficient and convenient basic reagent in organic synthesis. However, all reactions examined were performed with stoichiometric quantities of the reagent. The authors envisioned that rare earth metal alkoxides would be stronger bases than group 4 metal alkoxides due to the lower ionization potential (ca. 5.4-6.4 eV) and the lower

  7. On the nature of the hydrogen bonds to neutral ubiquinone in the QA binding site in purple bacterial photosynthetic reaction centers.

    PubMed

    Zhao, Nan; Hastings, Gary

    2013-07-25

    The nature of hydrogen bonding to pigments in protein complexes is currently a topic of some debate. The debate centers on whether hydrogen bonds can be understood on purely electrostatic grounds or whether they need to be considered quantum mechanically. This distinction is of current relevance primarily because of the application of QM/MM computational methods to the study of biological problems. To address this problem we have used QM/MM methods to study the neutral state of the hydrogen bonded ubiquinone molecule termed QA that functions as an electron transfer cofactor in purple bacterial photosynthetic reaction centers. In these calculations we have treated the hydrogen bonding amino acids either quantum mechanically or using molecular mechanics methods. As a specific metric for comparing the different computational methods isotope edited FTIR difference spectra are calculated. The calculated spectra are in remarkable agreement with experimental spectra, and it is found that the calculated spectra are very similar when hydrogen bonding amino acids are treated using either QM or MM methods. The latter result suggests that hydrogen bonding to neutral ubiquinone in purple bacterial reaction centers can be considered in purely electrostatic terms, which is contrary to the widely held belief that the hydrogen bonding amino acids should be treated quantum mechanically. Natural bond orbital analysis is used to further verify that the hydrogen bonds are predominantly electrostatic in nature. Calculated bond lengths and vibrational frequencies of the N-H groups involved in hydrogen bonding are used to estimate the relative strengths of the hydrogen bonds to either ubiquinone carbonyl group. PMID:23822580

  8. Design and synthesis of chiral Zn2+ complexes mimicking natural aldolases for catalytic C-C bond forming reactions in aqueous solution.

    PubMed

    Itoh, Susumu; Sonoike, Shotaro; Kitamura, Masanori; Aoki, Shin

    2014-01-01

    Extending carbon frameworks via a series of C-C bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective C-C bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn2+ ions as a catalytic factor that mimic aldolases in stereoselective C-C bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented. PMID:24481060

  9. Study on the mechanism of the reaction of NO 2 with aluminium oxide

    Microsoft Academic Search

    N Apostolescu; T Schröder; S Kureti

    2004-01-01

    In this study, the reaction of NO2 with aluminium oxide is examined. Aluminium oxide is an important component of NOx storage catalysts (NSC) that are used for the removal of nitrogen oxides from the exhaust gas of lean burn engines. Temperature-programmed desorption (TPD), diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) and continuous analysis of gas-phase products are used in order

  10. Overall rate constant measurements of the reactions of alkene-derived hydroxyalkylperoxy radicals with nitric oxide

    E-print Network

    Elrod, Matthew J.

    with nitric oxide Angela M. Miller, Laurence Y. Yeung, Annastassja C. Kiep and Matthew J. Elrod* Department ! R CHðOHÞ CHðO2Þ R0 ð2Þ which is generally followed by reaction with nitric oxide: R CHðOHÞ CHðO2Þ R0 derived from the OH-initiated oxidation of several atmospherically abundant alkenes--ethene, propene, 1

  11. Thermal oxidative degradation reactions of linear perfluoroalkyl ethers

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Paclorek, K. J. L.; Ito, T. I.; Kratzer, R. H.

    1983-01-01

    Thermal and thermal oxidative stability studies were performed on linear perfluoroalkyl ether fluids. The effect on degradation by metal catalysts and degradation inhibitors is reported. The linear perfluoroalkyl ethers are inherently unstable at 316 C in an oxidizing atmosphere. The metal catalysts greatly increased the rate of degradation in oxidizing atmospheres. In the presence of these metals in an oxidizing atmosphere, the degradation inhibitors were highly effective in arresting degradation at 288 C. However, the inhibitors had only limited effectiveness at 316 C. The metals promote degradation by chain scission. Based on elemental analysis and oxygen consumption data, the linear perfluoroalkyl ether fluids have a structural arrangement based on difluoroformyl and tetrafluoroethylene oxide units, with the former predominating. Previously announced in STAR as N82-26468

  12. Thermal oxidative degradation reactions of linear perfluoroalky lethers

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Paciorek, K. J. L.; Ito, T. I.; Kratzer, R. H.

    1982-01-01

    Thermal and thermal oxidative stability studies were performed on linear perfluoro alkyl ether fluids. The effect on degradation by metal catalysts and degradation inhibitors are reported. The liner perfluoro alkylethers are inherently unstable at 316 C in an oxidizing atmosphere. The metal catalysts greatly increased the rate of degradation in oxidizing atmospheres. In the presence of these metals in an oxidizing atmosphere, the degradation inhibitors were highly effective in arresting degradation at 288 C. However, the inhibitors had only limited effectiveness at 316 C. The metals promote degradation by chain scission. Based on elemental analysis and oxygen consumption data, the linear perfluoro alkylether fluids have a structural arrangement based on difluoroformyl and tetrafluoroethylene oxide units, with the former predominating.

  13. Microwave induced reactions of sulfur dioxide and nitrogen oxides in char and anthracite bed

    Microsoft Academic Search

    Chang Yul Cha; Dong Sik Kim

    2001-01-01

    Microwaves applied to a pyrolytic carbon matrix enhance the chemical reactions of nitric oxide (NO) and sulfur dioxide (SO2) with carbon to produce nitrogen, sulfur, and carbon dioxide. These microwave-induced reactions were investigated to find the feasibility of applying microwaves to directly destroy NO and SO2 in the combustion product gases or to minimize the formation of these pollutants during

  14. Access to aryl mellitic acid esters through a surprising oxidative esterification reaction.

    PubMed

    Geraskina, Margarita R; Juetten, Mark J; Winter, Arthur H

    2014-06-01

    A serendipitously discovered oxidative esterification reaction of cyclohexane hexacarboxylic acid with phosphorus pentachloride and phenols provides one-pot access to previously unknown aryl mellitic acid esters. The reaction features a solvent-free digestion and chromatography-free purifications and demonstrates the possibility of cyclohexane-to-benzene conversions under relatively mild, metal-free conditions. PMID:24815576

  15. Reaction of catalytic oxidation by liquid water and its application to waste water purification

    SciTech Connect

    Ioffe, I.I. [All-Union Inst. of Pulp and Paper Industry, Leningrad (Russian Federation)] [All-Union Inst. of Pulp and Paper Industry, Leningrad (Russian Federation); Rubinskaya, E.V. [All-Union Inst. of Petrochemical Processes, Leningrad (Russian Federation)] [All-Union Inst. of Petrochemical Processes, Leningrad (Russian Federation)

    1997-06-01

    In this paper the results of experiments and some considerations of theoretical and practical problems devoted to a new type of chemical reaction--oxidation of organic substances by liquid water with the aid of noble metal catalyst--are given. Some problems of application such as reaction to self-purification of industrial waste waters are also considered.

  16. Molecular description of active sites in oxidation reactions: Acidbase and redox properties, and role of water

    Microsoft Academic Search

    Jacques C. Vedrine; Jean Marc M. Millet; Jean-Claude Volta

    1996-01-01

    Oxidation reactions in heterogeneous catalysis usually involve a Mars and van Krevelen mechanism which includes activation of the substrate on a metallic cation, insertion of oxygen from lattice oxygen ions, a redox mechanism on the catalyst surface, and the transfer of several electrons. It follows that such a reaction necessitates both acid-base and redox properties of a catalyst the acid

  17. Spectroscopic Characterization of Mixed Fe-Ni Oxide Electrocatalysts for the Oxygen Evolution Reaction in Alkaline

    E-print Network

    Frenkel, Anatoly

    of producing hydrogen is from water electrolysis which enables H2 production from renewable energy sources Reaction in Alkaline Electrolytes James Landon, Ethan Demeter, Nilay Inoglu, Chris Keturakis,§ Israel E Information ABSTRACT: Mixed Fe-Ni oxide electrocatalysts for the oxygen evolution reaction in alkaline

  18. The Adsorption and Reactions of Halogenated Volatile Organic Compounds (VOCs) on Metal Oxides - Final Report

    Microsoft Academic Search

    Lunsford

    2000-01-01

    The purpose of this research was to provide a fundamental understanding of the adsorption and catalytic reactions of CClâ on metal oxide surfaces with a view to developing strategies for its remediation. The scientific knowledge generated by this project should enable environmental engineers to evaluate the potential of destructive adsorption of CClâ and the catalytic reaction of CClâ with HâO

  19. The relationship between the amount of oxidation and activation energy on the steam oxidation reaction of Zircaloy-4 cladding

    NASA Astrophysics Data System (ADS)

    Amaya, Masaki; Nagase, Fumihisa

    2013-09-01

    Zirconium-based alloys are widely used as cladding material for light-water reactors, and in the case of a loss-of-coolant accident (LOCA), oxidation of the cladding by high temperature steam plays important roles in fuel rod failure and hydrogen generation during the accident. In this study, considering that the oxidation rate is related to the activation energy of the oxidation reaction, the relationship between the amount of oxidation and the activation energy of cladding oxidation by steam was investigated by thermogravimetry. The oxidation rate of the specimen decreased with increasing heating rate. The activation energy of oxidation was evaluated based on a non-isothermal kinetics theory. It was found that the activation energy of oxidation depends on the specimen weight gain. The activation energies showed constant values of ˜300 and ˜180 kJ/mol in the oxidation range between 30 and 120 g/m2 and above 120 g/m2, respectively. A master curve which expresses the amount of steam oxidation of Zircaloy-4 cladding was formulated based on the activation energies obtained.

  20. The aniline-to-azobenzene oxidation reaction on monolayer graphene or graphene oxide surfaces fabricated by benzoic acid

    PubMed Central

    2013-01-01

    The oxidation of aniline to azobenzene was conducted in the presence of either monolayer graphene (EG) or graphene-oxide-like surface, such as GOx, under ultra-high vacuum conditions maintaining a 365-nm UV light exposure to enhance the oxidation reaction. The surface-bound products were investigated using micro Raman spectroscopy, high-resolution photoemission spectroscopy, and work function measurements. The oxygen carriers present on the GOx surfaces, but not on the EG surfaces, acted as reaction reagents to facilitate the oxidation reaction from aniline to azobenzene. Increasing the aniline concentration at 300 K confirmed that the exchange ratio from the aniline to the azobenzene was enhanced, as determined by the intensity ratio between the aniline- and azobenzene-induced N 1 s core-level spectra. The work function changed dramatically as the aniline concentration increased, indicating that the aniline on the GOx surface conveyed n-type doping characteristics at a low coverage level. A higher aniline concentration increased the p-type doping character by increasing the azobenzene concentration on the GOx surface. A comparison of the oxidation reactivity of aniline molecules on the EG or GOx surfaces revealed the role of the oxygen carriers on the GOx surfaces in the context of catalytic oxidation. PMID:24229051

  1. Strong Bond Activation with Late Transition-Metal Pincer Complexes as a Foundation for Potential Catalysis 

    E-print Network

    Zhu, Yanjun

    2012-07-16

    cleavage of B-H and B-B bonds across the N-Pd bond in a cationic (PNP)Pd fragment, the C-H oxidative addition to a (PNP)Ir center and the recent results on the C-H and C-O oxidative addition in reactions of aryl carboxylates with the (PNP)Rh fragment...

  2. Strong Bond Activation with Late Transition-Metal Pincer Complexes as a Foundation for Potential Catalysis

    E-print Network

    Zhu, Yanjun

    2012-07-16

    cleavage of B-H and B-B bonds across the N-Pd bond in a cationic (PNP)Pd fragment, the C-H oxidative addition to a (PNP)Ir center and the recent results on the C-H and C-O oxidative addition in reactions of aryl carboxylates with the (PNP)Rh fragment...

  3. Formation of oxidized products from the reaction of gaseous phenanthrene with the OH radical in a reaction chamber

    NASA Astrophysics Data System (ADS)

    Lee, JiYi; Lane, Douglas A.

    2010-07-01

    The reaction of gas phase phenanthrene (Phen) with the OH radical in the presence of NO x was studied in a reaction chamber. A number of oxidation products were identified by two dimensional gas chromatography-time of flight mass spectrometry (GC × GC-TOFMS). Identified products included 9-fluorenone, 1,2-naphthalic anhydride, 2,2'-diformylbiphenyl, dibenzopyranone, 1, 2, 3, 4 and 9-phenanthrols, 2, 3, 4 and 9-nitrophenanthrenes, 1,4-phenanthrenequinone, 9,10-phenanthrenequinone, and 2- and 4-nitrodibenzopyranones. This is the first study to identify 1,2-naphthalic anhydride and 1,4-phenanthrenequinone as products of the gas phase reaction of Phen with the OH radical. Eight more products were tentatively identified by their mass spectral fragmentation patterns and based on the typical OH radical initiated photochemical reaction mechanisms of simple aromatic compounds and naphthalene. In the reaction chamber, particle formation of products as a function of irradiation time was measured. Phenanthrenequinones, phenanthrol, nitrophenanthrene and nitrobenzopyranone were observed predominantly in the particle phase. This implies that these oxidized products formed from the reaction of Phen with the OH radical in the chamber would be associated with particles in the atmosphere and may, therefore, have an impact on human health. Possible pathways for the formation of these products are suggested and discussed.

  4. Valence-bond study of the /H2, D2/ exchange reaction mechanism.

    NASA Technical Reports Server (NTRS)

    Freihaut, B.; Raff, L. M.

    1973-01-01

    The exchange reaction of H2 with D2 to form 2 HD is important in that it is fundamentally the simplest four-body exchange reaction and should therefore represent a model system on which various theories of reactions dynamics might be tested. A number of theoretical and experimental investigations carried out on this system are reviewed. It is concluded that a Y yields T yields Y mechanism for the (H2, D2) exchange is not a low energy pathway that would make theory compatible with the shock-tube experiments of Bauer and Ossa (1966) and of Burcat and Lifshits (1967).

  5. Chemoselective quantum control of carbonyl bonds in Grignard reactions using shaped laser pulses.

    PubMed

    Gollub, Caroline; Kowalewski, Markus; Thallmair, Sebastian; de Vivie-Riedle, Regina

    2010-12-28

    Grignard reactants like methylmagnesium chloride are not selective with respect to different carbonyl bonds. We present a theoretical study where shaped laser pulses are utilized to prefer specific bonds in a mixture of more than one carbonyl reactant. A mixture of cyclohexanone and cyclopentanone has been chosen as a representative example. The light pulse is supposed to provide the activation energy and to adopt the function of a protecting group. The control aim is to stretch exclusively the C-O bond of one compound to the length required in the Grignard transition state. To guarantee an experimentally realizable bandwidth for the unshaped pulse, we use our recently developed optimal control theory algorithm, which allows the simultaneous optimization of the light field in the time and frequency domain. Highly selective picosecond control pulses could be optimized in the infrared regime suggesting that laser assisted chemoselectivity is possible to a large extent. To obtain control not only on the final product but also on the excitation mechanism, various initial conditions and frequency restrictions were investigated. PMID:21082089

  6. Bond length and radii variations in fluoride and oxide molecules and crystals

    Microsoft Academic Search

    J. S. Nicoll; G. V. Gibbs; M. B. Boisen; R. T. Downs; K. L. Bartelmehs

    1994-01-01

    Molecular orbital calculations completed on fluoride molecules containing first and second row cations have generated bond lengths, R, that match those observed for coordinated polyhedra in crystals to within ~0.04 Å, on average. The calculated bond lengths and those observed for fluoride crystals can be ranked with the expression R=Kp-0.22, where p=s\\/r, s is the Pauling strength of the bond,

  7. Rapid and effective oxidative pretreatment of woody biomass at mild reaction conditions and low oxidant loadings

    PubMed Central

    2013-01-01

    Background One route for producing cellulosic biofuels is by the fermentation of lignocellulose-derived sugars generated from a pretreatment that can be effectively coupled with an enzymatic hydrolysis of the plant cell wall. While woody biomass exhibits a number of positive agronomic and logistical attributes, these feedstocks are significantly more recalcitrant to chemical pretreatments than herbaceous feedstocks, requiring higher chemical and energy inputs to achieve high sugar yields from enzymatic hydrolysis. We previously discovered that alkaline hydrogen peroxide (AHP) pretreatment catalyzed by copper(II) 2,2?-bipyridine complexes significantly improves subsequent enzymatic glucose and xylose release from hybrid poplar heartwood and sapwood relative to uncatalyzed AHP pretreatment at modest reaction conditions (room temperature and atmospheric pressure). In the present work, the reaction conditions for this catalyzed AHP pretreatment were investigated in more detail with the aim of better characterizing the relationship between pretreatment conditions and subsequent enzymatic sugar release. Results We found that for a wide range of pretreatment conditions, the catalyzed pretreatment resulted in significantly higher glucose and xylose enzymatic hydrolysis yields (as high as 80% for both glucose and xylose) relative to uncatalyzed pretreatment (up to 40% for glucose and 50% for xylose). We identified that the extent of improvement in glucan and xylan yield using this catalyzed pretreatment approach was a function of pretreatment conditions that included H2O2 loading on biomass, catalyst concentration, solids concentration, and pretreatment duration. Based on these results, several important improvements in pretreatment and hydrolysis conditions were identified that may have a positive economic impact for a process employing a catalyzed oxidative pretreatment. These improvements include identifying that: (1) substantially lower H2O2 loadings can be used that may result in up to a 50-65% decrease in H2O2 application (from 100 mg H2O2/g biomass to 35–50 mg/g) with only minor losses in glucose and xylose yield, (2) a 60% decrease in the catalyst concentration from 5.0 mM to 2.0 mM (corresponding to a catalyst loading of 25 ?mol/g biomass to 10 ?mol/g biomass) can be achieved without a subsequent loss in glucose yield, (3) an order of magnitude improvement in the time required for pretreatment (minutes versus hours or days) can be realized using the catalyzed pretreatment approach, and (4) enzyme dosage can be reduced to less than 30 mg protein/g glucan and potentially further with only minor losses in glucose and xylose yields. In addition, we established that the reaction rate is improved in both catalyzed and uncatalyzed AHP pretreatment by increased solids concentrations. Conclusions This work explored the relationship between reaction conditions impacting a catalyzed oxidative pretreatment of woody biomass and identified that significant decreases in the H2O2, catalyst, and enzyme loading on the biomass as well as decreases in the pretreatment time could be realized with only minor losses in the subsequent sugar released enzymatically. Together these changes would have positive implications for the economics of a process based on this pretreatment approach. PMID:23971902

  8. Selective, nickel-catalyzed carbon-carbon bond-forming reactions of alkynes

    E-print Network

    Miller, Karen M. (Karen Marie)

    2005-01-01

    Catalytic addition reactions to alkynes are among the most useful and efficient methods for preparing diverse types of substituted olefins. Controlling both regioselectivity and (EIZ)- selectivity in such transformations ...

  9. Oxidation kinetics of reaction products formed in uranium metal corrosion.

    SciTech Connect

    Totemeier, T. C.

    1998-04-22

    The oxidation behavior of uranium metal ZPPR fuel corrosion products in environments of Ar-4%O{sub 2} and Ar-20%O{sub 2} were studied using thermo-gravimetric analysis (TGA). These tests were performed to extend earlier work in this area specifically, to assess plate-to-plate variations in corrosion product properties and the effect of oxygen concentration on oxidation behavior. The corrosion products from two relatively severely corroded plates were similar, while the products from a relatively intact plate were not reactive. Oxygen concentration strongly affected the burning rate of reactive products, but had little effect on low-temperature oxidation rates.

  10. High responsivity in integrated optically controlled metal-oxide semiconductor field-effect transistor using directly bonded SiO2InP

    Microsoft Academic Search

    T. Yamagata; K. Shimomura

    1997-01-01

    For the first time, high responsivity was obtained from an integrated optically controlled metal-oxide semiconductor field-effect transistor using the direct wafer bonding technique. The integrated structure of the device was composed of an absorption p-i-n photodiode region and a MOSFET. These two regions were bonded using the SiO2-InP direct wafer bonding technique. When a laser light with a wavelength of

  11. Oxidation Reactions of Ethane over Ba-Ce-O Based Perovskites

    SciTech Connect

    Miller, James E.; Sault, Allen G.; Trudell, Daniel E.; Nenoff, Tina M.; Thoma, Steven G.; Jackson, Nancy B.

    1999-08-18

    Ethane oxidation reactions were studied over pure and Ca-, Mg-, Sr-, La-, Nd-, and Y-substituted BaCeO{sub 3} perovskites under oxygen limited conditions. Several of the materials, notably the Ca- and Y-substituted materials, show activity for complete oxidation of the hydrocarbon to CO{sub 2} at temperatures below 650 C. At higher temperatures, the oxidative dehydrogenation (ODH) to ethylene becomes significant. Conversions and ethylene yields are enhanced by the perovskites above the thermal reaction in our system in some cases. The perovskite structure is not retained in the high temperature reaction environment. Rather, a mixture of carbonates and oxides is formed. Loss of the perovskite structure correlates with a loss of activity and selectivity to ethylene.

  12. Self-sustaining oxidation initiated by rapid formation reactions in multilayer foils

    NASA Astrophysics Data System (ADS)

    Joress, H.; Barron, S. C.; Livi, K. J. T.; Aronhime, N.; Weihs, T. P.

    2012-09-01

    Here we report that a self-sustaining oxidation of a multilayer foil can be ignited by an intermetallic formation reaction, releasing ˜4× the energy of the formation reaction. We examine foils with overall chemistries of 3Al:2Ni, 3Al:Zr, and Al:Zr and find that only the latter experiences significant oxidation. The Al:Zr samples initially react to form intermetallics and reach ˜1500 K in <10 ms. The samples then oxidize in air, absorbing ˜30 at. % O and remaining at ˜1400 K for >2.0 s. The phases within the Al:Zr foils are characterized and temperature-time profiles are examined to predict the heat generated by the oxidation reaction.

  13. In vitro evaluation of shear bond strengths of resin to densely-sintered high-purity zirconium-oxide ceramic after long-term storage and thermal cycling

    Microsoft Academic Search

    Markus B Blatz; Avishai Sadan; Javier Martin; Brien Lang

    2004-01-01

    Statement of problemThe few available studies on the resin bond to zirconium-oxide ceramic recommend airborne-particle abrasion and modified resin luting agents containing adhesive monomers for superior and long-term durable bond strengths. It is unknown whether this regimen can also be successfully applied to the intaglio surface of a commercial zirconia-based all-ceramic system.

  14. Oxides reactions with a high-chrome sesquioxide refractory

    SciTech Connect

    Rawers, James C.; Collins, W. Keith; Peck, M.

    2001-10-01

    In slagging coal-gasifier systems, the combination of oxides present as impurities in coal and combustion temperatures that can exceed 1650 degrees C restrict the use of liner materials in the coal combustion chambers to refractories. In this study, the slag-refractory interactions of a new high chrome sesquioxide refractory was characterized. High-temperature cup tests showed that the molten oxides infused into the refractory and that the sesquioxide refractory reacts with the oxides in a manner similar to spinel phase refractories. Studies of the coal slag’s individual oxide components showed CaO reacts with the chrome refractory to form a low melting Ca(CrO2)2. FeO reacts with the sesquioxide to form a interface layer of (Cr,Fe)3O4 spinel phase. Results of this study now make it possible to design studies for improving corrosion resistance to increase refractory life.

  15. Low interface defect density of atomic layer deposition BeO with self-cleaning reaction for InGaAs metal oxide semiconductor field effect transistors

    SciTech Connect

    Shin, H. S. [Department of Electronics Engineering, Chungnam National University, Daejeon (Korea, Republic of) [Department of Electronics Engineering, Chungnam National University, Daejeon (Korea, Republic of); SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States); The University of Texas, Austin, Texas 78758 (United States); Yum, J. H. [SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States) [SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States); The University of Texas, Austin, Texas 78758 (United States); Johnson, D. W. [SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States) [SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States); Texas A and M University College Station, Texas 77843 (United States); Harris, H. R. [Texas A and M University College Station, Texas 77843 (United States)] [Texas A and M University College Station, Texas 77843 (United States); Hudnall, Todd W. [Texas State University, 601 University Drive, San Marcos, Texas 78666 (United States)] [Texas State University, 601 University Drive, San Marcos, Texas 78666 (United States); Oh, J. [Yonsei University, Incheon, 406-840 (Korea, Republic of)] [Yonsei University, Incheon, 406-840 (Korea, Republic of); Kirsch, P.; Wang, W.-E. [SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States)] [SEMATECH, 2706 Montopolis Dr., Austin, Texas 78741 (United States); Bielawski, C. W.; Banerjee, S. K.; Lee, J. C. [The University of Texas, Austin, Texas 78758 (United States)] [The University of Texas, Austin, Texas 78758 (United States); Lee, H. D. [Department of Electronics Engineering, Chungnam National University, Daejeon (Korea, Republic of)] [Department of Electronics Engineering, Chungnam National University, Daejeon (Korea, Republic of)

    2013-11-25

    In this paper, we discuss atomic configuration of atomic layer deposition (ALD) beryllium oxide (BeO) using the quantum chemistry to understand the theoretical origin. BeO has shorter bond length, higher reaction enthalpy, and larger bandgap energy compared with those of ALD aluminum oxide. It is shown that the excellent material properties of ALD BeO can reduce interface defect density due to the self-cleaning reaction and this contributes to the improvement of device performance of InGaAs MOSFETs. The low interface defect density and low leakage current of InGaAs MOSFET were demonstrated using X-ray photoelectron spectroscopy and the corresponding electrical results.

  16. Oxidative catalysis using the stoichiometric oxidant as a reagent: an efficient strategy for single-electron-transfer-induced tandem anion-radical reactions.

    PubMed

    Kafka, František; Holan, Martin; Hidasová, Denisa; Pohl, Radek; Císa?ová, Ivana; Klepetá?ová, Blanka; Jahn, Ullrich

    2014-09-01

    Oxidative single-electron transfer-catalyzed tandem reactions consisting of a conjugate addition and a radical cyclization are reported, which incorporate the mandatory terminal oxidant as a functionality into the product. PMID:25070407

  17. SPECTROSCOPIC STUDY OF SURFACE REDOX REACTIONS WITH MANGANESE OXIDES

    EPA Science Inventory

    Redox reactions involving soil minerals and materials are important processes in environmental chemistry, but unfortunately they only have been characterized in the solution phase. he lack of a suitable method has prevented investigations of the mineral surface component of redox...

  18. Tailoring the composition of ultrathin, ternary alloy PtRuFe nanowires for the methanol oxidation reaction and formic acid oxidation reaction

    DOE PAGESBeta

    Scofield, Megan E.; Koenigsmann, Christopher; Wang, Lei; Lui, Haiqing; Wong, Stanislaus S.

    2015-01-01

    In the search for alternatives to conventional Pt electrocatalysts, we have synthesized ultrathin, ternary PtRuFe nanowires (NW), possessing different chemical compositions in order to probe their CO tolerance as well as electrochemical activity as a function of composition for both (i) the methanol oxidation reaction (MOR) and (ii) the formic acid oxidation reaction (FAOR). As-prepared ‘multifunctional’ ternary NW catalysts exhibited both higher MOR and FAOR activity as compared with binary Pt?Ru? NW, monometallic Pt NW, and commercial catalyst control samples. In terms of synthetic novelty, we utilized a sustainably mild, ambient wet-synthesis method never previously applied to the fabrication ofmore »crystalline, pure ternary systems in order to fabricate ultrathin, homogeneous alloy PtRuFe NWs with a range of controlled compositions. These NWs were subsequently characterized using a suite of techniques including XRD, TEM, SAED, and EDAX in order to verify not only the incorporation of Ru and Fe into the Pt lattice but also their chemical homogeneity, morphology, as well as physical structure and integrity. Lastly, these NWs were electrochemically tested in order to deduce the appropriateness of conventional explanations such as (i) the bi-functional mechanism as well as (ii) the ligand effect to account for our MOR and FAOR reaction data. Specifically, methanol oxidation appears to be predominantly influenced by the Ru content, whereas formic acid oxidation is primarily impacted by the corresponding Fe content within the ternary metal alloy catalyst itself.« less

  19. Tailoring the composition of ultrathin, ternary alloy PtRuFe nanowires for the methanol oxidation reaction and formic acid oxidation reaction

    DOE PAGESBeta

    Scofield, Megan E. [State Univ. of New York at Stony Brook, Stony Brook, NY (United States); Koenigsmann, Christopher [State Univ. of New York at Stony Brook, Stony Brook, NY (United States); Wang, Lei [State Univ. of New York at Stony Brook, Stony Brook, NY (United States); Lui, Haiqing [State Univ. of New York at Stony Brook, Stony Brook, NY (United States); Wong, Stanislaus S. [State Univ. of New York at Stony Brook, Stony Brook, NY (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)

    2015-01-01

    In the search for alternatives to conventional Pt electrocatalysts, we have synthesized ultrathin, ternary PtRuFe nanowires (NW), possessing different chemical compositions in order to probe their CO tolerance as well as electrochemical activity as a function of composition for both (i) the methanol oxidation reaction (MOR) and (ii) the formic acid oxidation reaction (FAOR). As-prepared ‘multifunctional’ ternary NW catalysts exhibited both higher MOR and FAOR activity as compared with binary Pt?Ru? NW, monometallic Pt NW, and commercial catalyst control samples. In terms of synthetic novelty, we utilized a sustainably mild, ambient wet-synthesis method never previously applied to the fabrication of crystalline, pure ternary systems in order to fabricate ultrathin, homogeneous alloy PtRuFe NWs with a range of controlled compositions. These NWs were subsequently characterized using a suite of techniques including XRD, TEM, SAED, and EDAX in order to verify not only the incorporation of Ru and Fe into the Pt lattice but also their chemical homogeneity, morphology, as well as physical structure and integrity. Lastly, these NWs were electrochemically tested in order to deduce the appropriateness of conventional explanations such as (i) the bi-functional mechanism as well as (ii) the ligand effect to account for our MOR and FAOR reaction data. Specifically, methanol oxidation appears to be predominantly influenced by the Ru content, whereas formic acid oxidation is primarily impacted by the corresponding Fe content within the ternary metal alloy catalyst itself.

  20. Intramolecular C-N bond activation and ring-expansion reactions of N-heterocyclic carbenes.

    PubMed

    Hemberger, Patrick; Bodi, Andras; Berthel, Johannes H J; Radius, Udo

    2015-01-19

    Intramolecular ring-expansion reactions (RER) of the N-heterocyclic carbene 1,3-dimethylimidazolin-2-ylidene were observed upon vacuum ultraviolet (VUV) photoexcitation. Similarly to RERs reported in the solvent phase, for the reaction of NHCs with main-group-element hydrides, hydrogen transfer to the NHC carbon atom is the crucial initial step. In an ionization-mediated protonation, 1,3-dimethylimidazolin-2-ylidene forms an imidazolium ion, which is the rate-limiting step on the pathway to two six-membered ring products, namely, methylpyrimidinium and -pyrazinium ions. To unravel the reaction path, we have used imaging photoelectron photoion coincidence spectroscopy with VUV synchrotron radiation, as well as high-level composite method calculations. Similarities and differences between the mechanism in the gas phase and in the condensed phase are discussed. PMID:25430962

  1. C?N and N?H Bond Metathesis Reactions Mediated by Carbon Dioxide.

    PubMed

    Wang, Yehong; Zhang, Jian; Liu, Jing; Zhang, Chaofeng; Zhang, Zhixin; Xu, Jie; Xu, Shutao; Wang, Fangjun; Wang, Feng

    2015-06-22

    Herein, we report CO2 -mediated metathesis reactions between amines and DMF to synthesize formamides. More than 20?amines, including primary, secondary, aromatic, and heterocyclic amines, diamines, and amino acids, are converted to the corresponding formamides with good-to-excellent conversions and selectivities under mild conditions. This strategy employs CO2 as a mediator to activate the amine under metal-free conditions. The experimental data and in?situ NMR and attenuated total reflectance IR spectroscopy measurements support the formation of the N-carbamic acid as an intermediate through the weak acid-base interaction between CO2 and the amine. The metathesis reaction is driven by the formation of a stable carbamate, and a reaction mechanism is proposed. PMID:26043443

  2. Identification of nitriding mechanisms in high purity reaction bonded silicon nitride

    SciTech Connect

    Haggerty, J.S.

    1993-03-01

    The rapid, low-temperature nitriding results from surface effects on the Si particles beginning with loss of chemisorbed H and sequential formation of thin amorphous Si nitride layers. Rapid complete conversion to Si{sub 3}N{sub 4} during the fast reaction can be inhibited when either too few or too many nuclei form on Si particels. Optimally, {approximately} 10 Si{sub 3}N{sub 4} nuclei form per Si particles under rapid, complete nitridation conditions. Nitridation during the slow reaction period appears to progress by both continued reaction of nonpreferred Si{sub 3}N{sub 4} growth interfaces and direct nitridation of the remaining Si/vapor interfaces.

  3. Identification of nitriding mechanisms in high purity reaction bonded silicon nitride

    SciTech Connect

    Haggerty, J.S.

    1993-03-01

    The rapid, low-temperature nitriding results from surface effects on the Si particles beginning with loss of chemisorbed H and sequential formation of thin amorphous Si nitride layers. Rapid complete conversion to Si[sub 3]N[sub 4] during the fast reaction can be inhibited when either too few or too many nuclei form on Si particels. Optimally, [approximately] 10 Si[sub 3]N[sub 4] nuclei form per Si particles under rapid, complete nitridation conditions. Nitridation during the slow reaction period appears to progress by both continued reaction of nonpreferred Si[sub 3]N[sub 4] growth interfaces and direct nitridation of the remaining Si/vapor interfaces.

  4. The oxidative dechlorination reaction of 2,4,6-trichlorophenol in dilute aqueous suspensions of manganese oxides

    SciTech Connect

    Ukrainczyk, L.; McBride, M.B. (Cornell Univ., Ithaca, NY (United States). Dept. of Soil, Crop and Atmospheric Sciences)

    1993-11-01

    Oxidation of 2,4,6-trichlorophenol (TCP) by layered manganese oxides (Na and Co-buserite) in dilute acidified aqueous suspension gives 2,6-dichloro-p-benzoquinone as a major product. This compound is likely to further polymerize and become incorporated into humus like materials. The oxidation rate was higher at lower pH and higher on Na-buserite compared to Co-buserite. TCP reacted at a faster rate than unsubstituted phenol at pH3 and 5.5, which is explained by (a) the lower half-wave potential of TCP compared to phenol; (b) a stronger bond dipole associated with the electronegative halogen, favoring an addition step in nucleophilic substitution; and (c) easier depronation of TCP at the manganese oxide-water interface due to its lower pK[sub a]. IR spectroscopy shows that TCP adsorbs in deprotonated form on the surface of manganese oxide, and it cannot be washed from the surface by water. Nucleophilic attack by addition-elimination is suggested as a mechanism of TCP dechlorination and oxidation.

  5. Reaction of SO2 with pure and metal-doped MgO: Basic principles for the cleavage of S-O bonds

    NASA Astrophysics Data System (ADS)

    Rodriguez, J. A.; Jirsak, T.; González, L.; Evans, J.; Pérez, M.; Maiti, A.

    2001-12-01

    Synchrotron-based high-resolution photoemission, x-ray absorption near-edge spectroscopy, and first-principles density-functional calculations are used to examine the interaction of SO2 with pure and modified surfaces of magnesium oxide. On a MgO(100) single crystal, SO2 reacts with O centers to form SO3 and SO4 species. The bonding interactions with the Mg cations are weak and do not lead to cleavage of S-O bonds. An identical result is found after adsorbing SO2 on pure stoichiometric powders of MgO and other oxides (TiO2, Cr2O3, Fe2O3, NiO, CuO, ZnO, V2O5, CeO2, BaO). In these systems, the occupied cations bands are too stable for effective bonding interactions with the LUMO of SO2. To activate an oxide for S-O bond cleavage, one has to create occupied metal states above the valence band of the oxide. DF calculations predict that in the presence of these "extra" electronic states the adsorption energy of SO2 should increase, and there should be a significant oxide?SO2(LUMO) charge transfer that facilitates the cleavage of the S-O bonds. In this article, we explore three different approaches (formation of O vacancies, promotion with alkali metals, and doping with transition metals) that lead to the activation of SO2 and S-O bond breaking on MgO and oxides in general. Basic principles for a rational design of catalysts with a high efficiency for the destruction of SO2 are presented.

  6. Electric-field control of magnetism by reversible surface reduction and oxidation reactions

    NASA Astrophysics Data System (ADS)

    Leistner, K.; Wunderwald, J.; Lange, N.; Oswald, S.; Richter, M.; Zhang, H.; Schultz, L.; Fähler, S.

    2013-06-01

    Electric control of magnetism is a vision which drives intense research on magnetic semiconductors and multiferroics. Recently, ultrathin metallic films were also reported to show magnetoelectric effects at room temperature. Here we demonstrate much stronger effects by exploiting reduction/oxidation reactions in a naturally grown oxide layer exchange coupled to an underlying ferromagnet. For the exemplarily studied FePt/iron oxide composite in an electrolyte, a large and reversible change of magnetization and anisotropy is obtained. The principle can be transferred to various metal/oxide combinations. It represents an approach towards multifunctionality.

  7. Theoretical study of reactions of HO{sub 2} in low-temperature oxidation of benzene

    SciTech Connect

    Altarawneh, Mohammednoor [Chemical Engineering Department, Al-Hussein Bin Talal University, Ma'an (Jordan); Dlugogorski, Bogdan Z.; Kennedy, Eric M.; Mackie, John C. [Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308 (Australia)

    2010-07-15

    We have generated a set of thermodynamic and kinetic parameters for the reactions involving HO{sub 2} in the very early stages of benzene oxidation at low temperatures using density functional theory (DFT). In particular, we report the rate constants for the reactions of HO{sub 2} with benzene and phenyl. The calculated reaction rate constant for the abstraction of H-C{sub 6}H{sub 5} by HO{sub 2} is found to be in good agreement with the limited experimental values. HO{sub 2} addition to benzene is found to be more important than direct abstraction. We show that the reactions of HO{sub 2} with the phenyl radical generate the propagating radical OH in a highly exoergic reaction. The results presented herein should be useful in modeling the oxidation of aromatic compounds at low temperatures. (author)

  8. Adaptation of a Small-Molecule Hydrogen-Bond Donor Catalyst to an Enantioselective Hetero-Diels–Alder Reaction Hypothesized for Brevianamide Biosynthesis

    PubMed Central

    2015-01-01

    Chiral diamine-derived hydrogen-bond donors were evaluated for their ability to effect stereocontrol in an intramolecular hetero-Diels–Alder (HDA) reaction hypothesized in the biosynthesis of brevianamides A and B. Collectively, these results provide proof of principle that small-molecule hydrogen-bond catalysis, if even based on a hypothetical biosynthesis construct, holds significant potential within enantioselective natural product synthesis. PMID:25697748

  9. Adaptation of a small-molecule hydrogen-bond donor catalyst to an enantioselective hetero-Diels-Alder reaction hypothesized for brevianamide biosynthesis.

    PubMed

    Sprague, Daniel J; Nugent, Benjamin M; Yoder, Ryan A; Vara, Brandon A; Johnston, Jeffrey N

    2015-02-20

    Chiral diamine-derived hydrogen-bond donors were evaluated for their ability to effect stereocontrol in an intramolecular hetero-Diels-Alder (HDA) reaction hypothesized in the biosynthesis of brevianamides A and B. Collectively, these results provide proof of principle that small-molecule hydrogen-bond catalysis, if even based on a hypothetical biosynthesis construct, holds significant potential within enantioselective natural product synthesis. PMID:25697748

  10. Adsorption and Reaction of NO on Oxidized and Reduced SrTiO{sub 3} (100) Surfaces

    SciTech Connect

    Azad, Samina; Szanyi, Janos; Peden, Charles HF.; Wang, Li Q.

    2003-07-01

    Adsorption and reaction of NO on oxidized and reduced SrTiO{sub 3}(100) surfaces have been studied using temperature programmed desorption (TPD). Major desorption peaks for NO from the fully oxidized surface as found at 140 and 260 K, along with a long tail that continues up to 500 K. The desorption features at 140 and 260 K correspond to activation energies of 36 and 66 kJ/mol, respectively, using a simple Redhead analysis. NO reacts non-dissociatively on the fully oxidized surface. Reactivity of reduced SrTiO{sub 3}(100) is relatively higher than that of the fully oxidized surface and is influenced by the adsorption temperature of the NO molecules on the surface. NO and N{sub 2}O are the major desorption products following adsorption of NO on the reduced surface at 110 K. Desorption of N{sub 2}O from significantly reduced SrTiO{sub 3}(100) indicates that the oxygen atoms of the adsorbed NO molecules are preferentially extracted by the surface oxygen vacancy sites whereas the surface oxidizes as a result of the de-oxygenation of the adsorbates. Adsorption of NO on the reduced surface at 297 K is followed by breakage of the N-O bond producing adsorbed N and O atoms and recombination of these ad-species results in desorption of NO and N{sub 2} from this surface. Adsorption of NO on the significantly reduced surface at 200 K is followed by desorption of NO, N{sub 2} and N{sub 2}O as TPD products and the reactivity of this surface at 200 K presumable is a composite of the behavior observed for NO adsorption at 110 and 297 K.

  11. Adsorption and reaction of NO on oxidized and reduced SrTiO3(100) surfaces

    NASA Astrophysics Data System (ADS)

    Azad, S.; Szanyi, J.; Peden, C. H. F.; Wang, L.-Q.

    2003-07-01

    Adsorption and reaction of NO on oxidized and reduced SrTiO3(100) surfaces have been studied using temperature programmed desorption (TPD). Major desorption peaks for NO from the fully oxidized surface are found at 140 and 260 K, along with a long tail that continues up to 500 K. The desorption features at 140 and 260 K correspond to activation energies of 36 and 66 kJ/mol, respectively, using a simple Redhead analysis. NO reacts nondissociatively on the fully oxidized surface. Reactivity of reduced SrTiO3(100) is relatively higher than that of the fully oxidized surface and is influenced by the adsorption temperature of the NO molecules on the surface. NO and N2O are the major desorption products following adsorption of NO on the reduced surface at 110 K. Desorption of N2O from significantly reduced SrTiO3(100) indicates that the oxygen atoms of the adsorbed NO molecules are preferentially extracted by the surface oxygen vacancy sites, whereas the surface oxidizes as a result of the deoxygenation of the adsorbates. Adsorption of NO on the reduced surface at 297 K is followed by breakage of the N-O bond producing adsorbed N and O atoms and recombination of these adspecies results in desorption of NO and N2 from this surface. Adsorption of NO on the significantly reduced surface at 200 K is followed by desorption of NO, N2, and N2O as TPD products and the reactivity of this surface at 200 K presumably is a composite of the behavior observed for NO adsorption at 110 and 297 K.

  12. Chemically bonded TiO2-bronze nanosheet/reduced graphene oxide hybrid for high-power lithium ion batteries.

    PubMed

    Etacheri, Vinodkumar; Yourey, Joseph E; Bartlett, Bart M

    2014-02-25

    Although Li-ion batteries have attracted significant interest due to their higher energy density, lack of high rate performance electrode materials and intrinsic safety issues challenge their commercial applications. Herein, we demonstrate a simple photocatalytic reduction method that simultaneously reduces graphene oxide (GO) and anchors (010)-faceted mesoporous bronze-phase titania (TiO2-B) nanosheets to reduced graphene oxide (RGO) through Ti(3+)-C bonds. Formation of Ti(3+)-C bonds during the photocatalytic reduction process was identified using electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) techniques. When cycled between 1-3 V (vs Li(+/0)), these chemically bonded TiO2-B/RGO hybrid nanostructures show significantly higher Li-ion storage capacities and rate capability compared to bare TiO2-B nanosheets and a physically mixed TiO2-B/RGO composite. In addition, 80% of the initial specific (gravimetric) capacity was retained even after 1000 charge-discharge cycles at a high rate of 40C. The improved electrochemical performance of TiO2-B/RGO nanoarchitectures is attributed to the presence of exposed (010) facets, mesoporosity, and efficient interfacial charge transfer between RGO monolayers and TiO2-B nanosheets. PMID:24446910

  13. REACTION OF BENZENE OXIDE WITH THIOLS INCLUDING GLUTATHIONE

    EPA Science Inventory

    This study accounts for the observations that the metabolism of benzene is dominated by the formation of phenol. As demonstrated here, the pathway leading to S-phenylmercapturic acid is necessarily minor on account of the low efficiency of benzene oxide capture by glutathione at ...

  14. Effect of grain size on microstructure, properties, and surface roughness of reaction bonded SiC ceramics

    NASA Astrophysics Data System (ADS)

    Aghajanian, Michael; Emmons, Craig; Rummel, Steve; Barber, Paul; Robb, Chris; Hibbard, Doug

    2013-09-01

    Silicon carbide (SiC) based ceramics have received significant study for optical applications due to high specific stiffness, high thermal conductivity, and low coefficient of thermal expansion (CTE). Reaction bonded SiC ceramics, which are composites of SiC and Si, are of particular interest due to large size and complex shape capability. The behavior of these ceramics is very much affected by the grain size of the SiC phase. The present work examines SiC grain sizes ranging from 6 to 50 ?m, with the goal of optimizing properties and finishing capability for optical uses. Microstructures are reviewed; physical, mechanical and thermal properties are presented; and post-polishing surface roughness data are provided. In particular, results demonstrate that properties can be tailored by SiC particle size selection, and that measureable enhancement in surface roughness can be achieved by moving to smaller SiC grain size.

  15. The Effect of Si contents on the reaction-bonded Si3N4/SiC composite ceramics

    NASA Astrophysics Data System (ADS)

    Li, J.; Yuan, W. J.; Deng, C. J.; Zhu, H. X.

    2013-12-01

    Effect of Si contents on reaction-bonded Si3N4/SiC composite ceramics under pressureless was investigated. Si3N4/SiC composite ceramics were sintered at 1600 °C under nitrogen atmosphere by using SiC powders (1.5?m), Si powders (74?m) with different contents 37~55wt% and sintering additives Y2O3 as raw materials. The phases, microstructure and mechanical property were characterized by XRD, SEM, and compressive strength tests. The results demonstrated that when the content of Si powders was 37wt%, the more dense samples with the bulk density of 2.41 g/cm3 and the higher compressive strength of 319 MPa could be obtained under pressureless.

  16. Identification and cleavage of breakable single bonds by selective oxidation, reduction, and hydrolysis. Quarterly report No. 13, October 1-December 31, 1981

    SciTech Connect

    Hirschon, A.S.; Zevely, J.; Mayo, F.R.

    1982-02-26

    Bituminous coal is assumed to consist mostly of aggregates of condensed aromatic and aliphatic rings which are connected and made soluble by crosslinks containing single bonds. The objective of this project is to determine the structure of bituminous coal with emphasis on the crosslinks and breakable single bonds. During this past quarter the following studies were conducted on Illinois No. 6 coal: extraction with benzylamine (BnH/sub 2/), ethanolamine, ethylenediamine (EDA), pyridine; saponification of some toluene-insoluble, pyridine-soluble (TIPS) fraction; cleavages by amines; oxidation with aqueous NaOCl of butylated and methylated pyridine-extracted coal; decarboxylation on black acids. The investigations dealt with two kinds of connecting links in coal, which are designated as ester and ether groups. The ester groups are cleaved by strongly basic amines (to give amides) at 25/sup 0/C and by alcoholic KOH at 100/sup 0/C (to give salts and alcohols or phenols). Both esters and ethers are cleaved by HI or ZnCL/sub 2/ in pyridine at or below 50/sup 0/C. The ethers are also cleaved by BnNH/sub 2/, EDA, and EDA/DMSO to nearly the same extent on several days heating at 100/sup 0/C. Although a cleavage of model ethers by amines were not established, the parallel easy reactions of HI and ZnCl/sub 2/ and the slow 100/sup 0/C reactions of amines on coal lead the authors to designate the non-ester cleavages as ether cleavages. (ATT)

  17. Iron oxide mineral-water interface reactions studied by AFM

    SciTech Connect

    Hawley, M.E.; Rogers, P.S.Z.

    1994-07-01

    Natural iron mineral surfaces have been examined in air by atomic force (AFM) and scanning tunneling (STM) microscopies. A number of different surface features were found to be characteristic of the native surface. Even surfaces freshly exposed by crushing larger crystals were found to have a pebbly surface texture caused by the presence of thin coatings of what might be surface precipitates. This finding is interpreted as evidence for previous exposure to water, probably through an extensive network of microfractures. Surface reactions on the goethite crystals were studied by AFM at size resolutions ranging from microns to atomic resolution before, during, and after reaction with distilled water and 0.lN HCl. Immediate and extensive surface reconfiguration occurred on contact with water. In one case, after equilibration with water for 3 days, surface reprecipitation, etching and pitting were observed. Atomic resolution images taken under water were found to be disordered. The result of surface reaction was generally to increase the surface area substantially through the extension of surface platelet arrays, present prior to reaction. This work is being done in support of the site characterization project at Yucca Mountain.

  18. Influence of aluminum oxide film on thermocompression bonding of gold wire to evaporated aluminum film

    NASA Technical Reports Server (NTRS)

    Iwata, S.; Ishizaka, A.; Yamamoto, H.

    1984-01-01

    The influence of Al surface condition on the thermocompression bonding of Au wires to Al electrodes for integrated electric circuits was studied. Au wires were connected to Al electrodes by nail-head bonding after various Al surface treatments. Bonding was evaluated by measuring the wire pull strength and fraction of the number of failures at Au-Al bonds to the total number of failures. Dependence of the fraction on applied load was derived theoretically with a parameter named critical load to take into consideration the differences in Al surface condition. The relation also held explicately for various surface treatments. Characterization of the Al surface was carried out by electron microscopy for chemical analysis.

  19. Effects of anode material and fuel on anodic reaction of solid oxide fuel cells

    Microsoft Academic Search

    Toshihiko Setoguchi; K. Okamoto; K. Eguchi; H. Arai

    1992-01-01

    In this paper, anodic properties of solid oxide fuel cells are evaluated for several anode\\/electrolyte systems. Anodic over-voltage of metal\\/yttria-stabilized zirconia (YSZ) interface was related with metal-oxygen bonding strength and was the smallest for the Ni anode in the present study. The anodic polarization conductivity of Ni-YSZ cermet\\/YSZ electrolyte interface strongly depended on oxygen partial pressure P[sub 02], in fuel,

  20. Bond length and radii variations in fluoride and oxide molecules and crystals

    Microsoft Academic Search

    J. S. Nicoll; G. V. Gibbs; M. B. Boisen; R. T. Downs; K. L. Bartelmehs

    1994-01-01

    Molecular orbital calculations completed on fluoride molecules containing first and second row cations have generated bond lengths, R, that match those observed for coordinated polyhedra in crystals to within ˜0.04 Å, on average. The calculated bond lengths and those observed for fluoride crystals can be ranked with the expression R=Kp -0.22, where p=s\\/r, s is the Pauling strength of the

  1. 40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721...Hydroxypropyl methacrylate, reaction products with propylene...reporting. (1) The chemical substance identified...hydroxypropyl methacrylate, reaction products with...

  2. 40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721...Hydroxypropyl methacrylate, reaction products with propylene...reporting. (1) The chemical substance identified...hydroxypropyl methacrylate, reaction products with...

  3. 40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances § 721...Hydroxypropyl methacrylate, reaction products with propylene...reporting. (1) The chemical substance identified...hydroxypropyl methacrylate, reaction products with...

  4. Activation of Noble Metals on Metal-Carbide Surfaces: Novel Catalysts for CO Oxidation, Desulfurization and Hydrogenation Reactions

    SciTech Connect

    Rodriguez J. A.; Illas, F.

    2012-01-01

    This perspective article focuses on the physical and chemical properties of highly active catalysts for CO oxidation, desulfurization and hydrogenation reactions generated by depositing noble metals on metal-carbide surfaces. To rationalize structure-reactivity relationships for these novel catalysts, well-defined systems are required. High-resolution photoemission, scanning tunneling microscopy (STM) and first-principles periodic density-functional (DF) calculations have been used to study the interaction of metals of Groups 9, 10 and 11 with MC(001) (M = Ti, Zr, V, Mo) surfaces. DF calculations give adsorption energies that range from 2 eV (Cu, Ag, Au) to 6 eV (Co, Rh, Ir). STM images show that Au, Cu, Ni and Pt grow on the carbide substrates forming two-dimensional islands at very low coverage, and three-dimensional islands at medium and large coverages. In many systems, the results of DF calculations point to the preferential formation of admetal-C bonds with significant electronic perturbations in the admetal. TiC(001) and ZrC(001) transfer some electron density to the admetals facilitating bonding of the adatom with electron-acceptor molecules (CO, O{sub 2}, C{sub 2}H{sub 4}, SO{sub 2}, thiophene, etc.). For example, the Cu/TiC(001) and Au/TiC(001) systems are able to cleave both S-O bonds of SO{sub 2} at a temperature as low as 150 K, displaying a reactivity much larger than that of TiC(001) or extended surfaces of bulk copper and gold. At temperatures below 200 K, Au/TiC is able to dissociate O{sub 2} and perform the 2CO + O{sub 2} {yields} 2CO{sub 2} reaction. Furthermore, in spite of the very poor hydrodesulfurization performance of TiC(001) or Au(111), a Au/TiC(001) surface displays an activity for the hydrodesulfurization of thiophene higher than that of conventional Ni/MoS{sub x} catalysts. In general, the Au/TiC system is more chemically active than systems generated by depositing Au nanoparticles on oxide surfaces. Thus, metal carbides are excellent supports for enhancing the chemical reactivity of noble metals.

  5. Heme-protein covalent bonds in peroxidases and resistance to heme modification during halide oxidation

    Microsoft Academic Search

    Liusheng Huang; Paul R. Ortiz de Montellano

    2006-01-01

    Plant peroxidases, as typified by horseradish peroxidase (HRP), primarily catalyze the one-electron oxidation of phenols and other low oxidation potential substrates. In contrast, the mammalian homologues such as lactoperoxidase (LPO) and myeloperoxidase primarily oxidize halides and pseudohalides to the corresponding hypohalides (e.g., Br? to HOBr, Cl? to HOCl). A further feature that distinguishes the mammalian from the plant and fungal

  6. Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies

    NASA Technical Reports Server (NTRS)

    Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

    1988-01-01

    The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.

  7. Process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers

    SciTech Connect

    Swallow, K.C.; Killilea, W.R.; Hong, G.T.; Bourhis, A.L.

    1993-08-03

    A method is described for substantially completely oxidizing combustible materials in which an aqueous stream bearing the combustible materials is reacted in the presence of an oxidant comprising diatomic oxygen and at a temperature greater than the critical temperature of water and at a pressure greater than about 25 bar, within a reactor for a period of less than about 5 minutes to produce a reaction product stream, wherein the reaction is initiated in the presence of a rate enhancer comprising at least one oxidizing agent in addition to said oxidant selected from the group consisting of ozone, hydrogen peroxide, salts containing persulfate, salts containing permanganate, nitric acid, salts containing nitrate, oxyacids of chlorine and their corresponding salts, hypochlorous acid, salts containing hypochlorite, chlorous acid, salts containing chlorite, chloric acid, salts containing chlorate, perchloric acid, and salts containing perchlorate.

  8. Ultra-stable Molecule-Surface Architectures at Metal Oxides: Structure, Bonding, and Electron-transfer Processes

    SciTech Connect

    Hamers, Robert John

    2013-12-07

    Research funded by this project focused on the development of improved strategies for functionalization of metal oxides to enhance charge?transfer processes relevant to solar energy conversion. Initial studies included Fe2O3, WO3, TiO2, SnO2, and ZnO as model oxide systems; these systems were chosen due to differences in metal oxidation state and chemical bonding types in these oxides. Later studies focused largely on SnO2 and ZnO, as these materials show particularly promising surface chemistry, have high electron mobility, and can be readily grown in both spherical nanoparticles and as elongated nanorods. New molecules were synthesized that allowed the direct chemical assembly of novel nanoparticle ?dyadic? structures in which two different oxide materials are chemically joined, leading to an interface that enhances the separation of of charge upon illumination. We demonstrated that such junctions enhance photocatalytic efficiency using model organic compounds. A separate effort focused on novel approaches to linking dye molecules to SnO2 and ZnO as a way to enhance solar conversion efficiency. A novel type of surface binding through

  9. Kinetics of the hydrogen oxidation reaction on nanostructured rhodium electrodes in alkaline solution

    NASA Astrophysics Data System (ADS)

    Montero, María A.; Gennero de Chialvo, María R.; Chialvo, Abel C.

    2015-06-01

    The hydrogen oxidation reaction was studied on a nanostructured rhodium electrode at different rotation rates in alkaline solution. The electrode was prepared via sputtering on a glassy carbon disc support and it was characterized by atomic force microscopy and cyclic voltammetry. The real surface area was evaluated by CO stripping voltammetry. Experimental current density (j) - overpotential (?) curves of the hydrogen oxidation reaction were obtained in the range -0.015 ? ?/V ? 0.40 at different rotation rates (900 ? ?/rpm ? 4900). The resulting curves were correlated by kinetic expressions derived from the Tafel-Heyrovsky-Volmer mechanism with a Frumkin type adsorption of the reaction intermediate and the kinetic parameters were evaluated. It was verified that over this overpotential region the reaction in alkaline solution proceeds mainly through the Tafel-Volmer route. These results were compared with those previously obtained in acid solutions.

  10. Measurements of hydrogen in metal-oxide-semiconductor structures using nuclear reaction profiling

    Microsoft Academic Search

    A. D. Marwick; D. R. Young

    1988-01-01

    We report depth profiles of the hydrogen concentrations in metal-oxide-semiconductor structures measured using the nuclear reaction profiling technique with a 6.4-MeV 15N beam. In both conventionally grown and ultra-dry thermal oxide samples with aluminum or gold gate metal, a peak of hydrogen concentration is observed at the metal\\/SiO2 interface. The amount of hydrogen at this interface varied from sample to

  11. Acidbase reactions of tungsten and uranium oxide fluorides in anhydrous hydrogen fluoride

    Microsoft Academic Search

    Yasushi Katayama; Rika Hagiwara; Yasuhiko Ito

    1995-01-01

    The acid-base reactions of tungsten oxide tetrafluoride, WOF4. and uranium dioxide difluoride, UO2F2, have been examined in anhydrous hydrogen fluoride (HF). WOF4 reacts with silver(I and II) fluorides, AgF and AgF2, to form complex salts, AgWOF5, AgW2O2F9 and AgFW2O2F9. AgFW2O2F9, which is also prepared by the reaction of AgW2O2F9 and F2 in HF, oxidizes elemental xenon to XeII in HF

  12. Bond cleavage reactions in the tripeptide trialanine upon free electron capture

    NASA Astrophysics Data System (ADS)

    Puschnigg, Benjamin; Huber, Stefan E.; Scheier, Paul; Probst, Michael; Denifl, Stephan

    2014-05-01

    In the present study we performed dissociative electron attachment (DEA) measurements with the tripeptide trialanine, C9H17N3O4, utilizing a crossed electron-molecular beam experiment with high electron energy resolution (~100 meV). Anion efficiency yields as a function of the incident electron energy are obtained for the most abundant anions up to electron energies of ~4 eV. Quantum chemical calculations are performed to determine the thermochemical thresholds for the anions observed in the measurements. There is no evidence of a molecular anion with lifetime of mass spectrometric timescales. The dehydrogenated closed shell anion (M-H)- is one of the fragment anions observed for which the calculations show that H-loss is energetically possible from carboxyl, as well as amide groups. In contrast to the dipeptide dialanine and monomer alanine the cleavage of the N-C? bond in the peptide chain is already possible by attachment of electrons at ~0 eV. Contribution to the Topical Issue "Nano-scale Insights into Ion-beam Cancer Therapy", edited by Andrey V. Solov'yov, Nigel Mason, Paulo Limão-Vieira and Malgorzata Smialek-Telega.

  13. Transient FTIR studies of the reaction pathway for n-butane selective oxidation over vanadyl pyrophosphate

    SciTech Connect

    Xue, Z.Y.; Schrader, G.L. [Ames Lab., IA (United States)] [Ames Lab., IA (United States); [Iowa State Univ., Ames, IA (United States). Dept. of Chemical Engineering

    1999-05-15

    New information has been provided about the reaction pathway for n-butane partial oxidation to maleic anhydride over vanadyl pyrophosphate (VPO) catalysts using FTIR spectroscopy under transient conditions. Adsorption studies of n-butane, 1,3-butadiene, and related oxygenates were performed to gain information about reaction intermediates. n-Butane was found to adsorb on the VPO catalyst to form olefinic species at low temperatures. Unsaturated, noncyclic carbonyl species were determined to be precursors to maleic anhydride.

  14. Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces

    Microsoft Academic Search

    Jaime M. Ferreira; Stephen Marcinko; Richard Sheardy; Alexander Y. Fadeev

    2005-01-01

    The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy\\/energy analysis showed that the net enthalpy of the formation of

  15. Compounds producing the kreis color reaction with particular reference to oxidized milk fat

    Microsoft Academic Search

    Stuart Patton; Mark Keeney; George W. Kurtz

    1951-01-01

    Summary  Evidence is presented which suggests that epihydrin aldehyde and its derivatives are not necessarily solely responsible for\\u000a the Kreis color reaction of oxidized fats. Malonic dialdehyde has been shown to give a positive reaction in the Kreis test\\u000a and the resulting color demonstrated to be spectrally similar to the Kreis colors obtained with epihydrin aldehyde diethyl\\u000a acetal, acrolein treated with

  16. A quantum molecular-dynamics study of proton-transfer reactions along asymmetrical H bonds in solution

    NASA Astrophysics Data System (ADS)

    Azzouz, H.; Borgis, D.

    1993-05-01

    A molecular-dynamics study of a model for AH-B?A--H+B reactions in liquid chloromethane is presented. The parameters of the model are fitted to those of typical OH-N proton-transfer complexes. The rate constant is computed at a quantum level for complexes of various H-bond strength and A-B equilibrium distance. The influence of the properties of the complex on the proton-transfer mechanism is outlined. Also the static and dynamical role of the solvent, the tunneling contribution to the rate, and the associated kinetic isotope effect are discussed. The rate calculations are based on two independent methods. First a curve-crossing, transition-state rate formula which, although related to standard charge-transfer theories, presents some original features and allows the determination of the rate at very low computational cost is developed. The curve-crossing results are compared to those of a path-integral, quantum transition-state calculation. The overall agreement between the two methods is satisfactory, although there is a discrepancy in the adiabatic reaction regime; a rigorous estimation of the transmission coefficients would be needed then. Finally, it is shown that zero-point energy and parabolic barrier tunneling factors added to the classical transition-state-theory rate constant are unable to describe properly the quantum effects in the present case.

  17. The interaction of reaction-bonded silicon carbide and inconel 600 with a nickel-based brazing alloy

    NASA Astrophysics Data System (ADS)

    McDermid, J. R.; Pugh, M. D.; Drew, R. A. L.

    1989-09-01

    The objective of the present research was to join reaction-bonded silicon carbide (RBSC) to INCONEL 600 (a nickel-based superalloy) for use in advanced heat engine applications using either direct brazing or composite interlayer joining. Direct brazing experiments employed American Welding Society (AWS) BNi-5, a commercial nickel-based brazing alloy, as a filler material; composite interlayers consisted of intimate mixtures of ?-SiC and BNi-5 powders. Both methods resulted in the liquid filler metal forming a Ni-Si liquid with the free Si in the RBSC, which, in turn, reacted vigorously with the SiC component of the RBSC to form low melting point constituents in both starting materials and Cr carbides at the metal-ceramic interface. Using solution thermodynamics, it was shown that a Ni-Si liquid of greater than 60 at. pct Ni will decompose a-SiC at the experimental brazing temperature of 1200 ‡C; these calculations are consistent with the experimentally observed composition profiles and reaction morphology within the ceramic. It was concluded that the joining of RBSC to INCONEL 600 using a nickel-based brazing alloy is not feasible due to the inevitability of the filler metal reacting with the ceramic, degrading the high-temperature properties of the base materials.

  18. Catalytic constructive deoxygenation of lignin-derived phenols: new C-C bond formation processes from imidazole-sulfonates and ether cleavage reactions.

    PubMed

    Leckie, Stuart M; Harkness, Gavin J; Clarke, Matthew L

    2014-10-01

    As part of a programme aimed at exploiting lignin as a chemical feedstock for less oxygenated fine chemicals, several catalytic C-C bond forming reactions utilising guaiacol imidazole sulfonate are demonstrated. These include the cross-coupling of a Grignard, a non-toxic cyanide source, a benzoxazole, and nitromethane. A modified Meyers reaction is used to accomplish a second constructive deoxygenation on a benzoxazole functionalised anisole. PMID:25130565

  19. Elementary Steps of Syngas Reactions on Mo2C(001): Adsorption Thermochemistry and Bond Dissociation

    SciTech Connect

    Medford, Andrew

    2012-02-16

    Density functional theory (DFT) and ab initio thermodynamics are applied in order to investigate the most stable surface and subsurface terminations of Mo{sub 2}C(001) as a function of chemical potential and in the presence of syngas. The Mo-terminated (001) surface is then used as a model surface to evaluate the thermochemistry and energetic barriers for key elementary steps in syngas reactions. Adsorption energy scaling relations and Broensted-Evans-Polanyi relationships are established and used to place Mo{sub 2}C into the context of transition metal surfaces. The results indicate that the surface termination is a complex function of reaction conditions and kinetics. It is predicted that the surface will be covered by either C{sub 2}H{sub 2} or O depending on conditions. Comparisons to transition metals indicate that the Mo-terminated Mo{sub 2}C(001) surface exhibits carbon reactivity similar to transition metals such as Ru and Ir, but is significantly more reactive towards oxygen.

  20. ADVANCED CHEMICAL OXIDATION OF 2,4,6 TRICHLOROPHENOL IN AQUEOUS PHASE BY FENTON'S REAGENT-PART II: EFFECTS OF VARIOUS REACTION PARAMETERS ON THE TREATMENT REACTION

    Microsoft Academic Search

    SOMNATH BASU; IRVINE W. WEI

    1998-01-01

    Part I of this paper examined the effects of the amounts of oxidant and catalyst on the rates and extents of oxidation of 2,4,6-Trichlorophenol (TCP), in aqueous phase, by Fenton's Reagent. In this part the effects of various reaction parameters, e.g. temperature, pH, oxidation state of catalyst (ferrous versus ferric), mode of addition of oxidant to the reactor (single batch

  1. Doubly bonded e13?p and b?e15 molecules and their reactions with h2, acetonitrile, benzophenone, and 2,3-dimethylbutadiene.

    PubMed

    Shih, Tsung-Wei; Li, Ming-Chung; Su, Ming-Der

    2015-06-01

    The bonding properties and the potential energy surfaces for the chemical reactions of doubly bonded compounds that have the >E13?E15< pattern are studied using density functional theory (M06-2X/Def2-SVPD). Nine molecules, >E13?P< (E13 = B, Al, Ga, In, and Tl) and >B?E15< (E15 = N, P, As, Sb, and Bi), are used as model reactants in this work. Four types of chemical reactions, H2 addition, acetonitrile, benzophenone [2 + 2] cycloadditions, and dimethylbutadiene [4 + 2] cycloaddition, are used to study the chemical reactivity of these inorganic, ethylene-like molecules. The results of these theoretical analyses show that only the >B?P< molecule has a weak B?P double bond, while the >Al?P< , >Ga?P< , >In?P< , >Tl?P< , >B?N< , >B?As<, >B?Sb<, and >B?Bi< compounds are best described as having a strong single ? bond, instead of a traditional p-p ? bond. The theoretical results also show that the singlet-triplet energy gap can be used to determine the relative reactivity of these doubly bonded molecules. According to these theoretical investigations, it is predicted that the order of reactivity is as follows: B?P > Al?P > Ga?P > In?P > Tl?P and B?N ? B?P < B?As < B?Sb < B?Bi. The conclusions drawn are consistent with the available experimental observations. PMID:25954984

  2. Catalytic migratory oxidative coupling of nitrones.

    PubMed

    Hashizume, Shogo; Oisaki, Kounosuke; Kanai, Motomu

    2011-08-19

    A Cu(I)-catalyzed migratory oxidative coupling between nitrones and heterocycles or a methylamine is described. Selective C-C bond-formation proceeds through cleavage of two C(sp(3))-H bonds concomitant with C?N double bond-migration. The reaction provides an alternating nitrone moiety, allowing for further synthetically useful transformations. Radical clock studies suggest that the nucleophilic addition of nitrones to an oxidatively generated carbocation is a key step. PMID:21766802

  3. Yttrium oxide/gadolinium oxide-modified platinum nanoparticles as cathodes for the oxygen reduction reaction.

    PubMed

    Luo, Yun; Habrioux, Aurélien; Calvillo, Laura; Granozzi, Gaetano; Alonso-Vante, Nicolas

    2014-07-21

    Rare-earth-element (Y, Gd) modified Pt nanoparticles (NPs) supported on a carbon substrate (Vulcan XC-72) are synthesized via a water-in-oil chemical route. In both cases, X-ray diffraction (XRD) measurements show the non-formation of an alloyed material. Photoemission spectroscopy (XPS) results reveal that Y and Gd are oxidized. Additionally, no evidence of an electronic modification of Pt can be brought to light. Transmission electron microscopy (TEM) studies indicate that Pt-Y(2)O(3) and Pt-Gd(2)O(3) particles are well dispersed on the substrate-and that their average particle sizes are smaller than the Pt-NP sizes. The catalytic activity of the Pt-Y(2)O(3)/C and Pt-Gd(2)O(3)/C catalysts towards the oxygen reduction reaction (ORR) is studied in a 0.5?M H(2)SO(4) electrolyte. The surface and mass specific activities of the Pt-Y(2)O(3)/C catalyst towards the ORR at 0.9 V (vs. the reversible hydrogen electrode, RHE) are (54.3±1.2) ?A?cm(-2)(Pt) and MA=(23.1±0.5) mA?mg(-1)(Pt), respectively. These values are 1.3-, and 1.6-fold higher than the values obtained with a Pt/C catalyst. Although the as-prepared Pt-Gd(2)O(3)/C catalyst has a lower catalytic activity for the ORR compared to Pt/C, the heat-treated sample shows a surface specific activity of about (53.0±0.7) ?A?cm(-2) Pt , and a mass specific activity (MA) of about (18.2±0.5) mA?mg(-1) Pt at 0.9 V (vs. RHE). The enhancement of the ORR kinetics on the Pt-Y(2)O(3)/C and heat-treated Pt-Gd(2)O(3)/C catalysts could be associated with the formation of platinum NPs presenting modified surface properties. PMID:24819164

  4. Chemiluminescence spectra of the reaction products of gallium, indium and thallium vapors with nitrous oxide

    SciTech Connect

    Eliseev, M.V.; Koryazhkin, V.A.; Mal'tsev, A.A.; Popov, A.D.

    1983-03-01

    The search for active media for chemical lasers generating in the visible range has led to numerous investigations of the chemiluminescence of oxidation reactions of metals in the gas phase. In the present work, the chemiluminescence spectra of flames of gallium, indium, and thallium vapors in nitrous oxide in an argon flux are investigated. The chemiluminescence intensity was studied as a function of the total pressure in the reactor, the rate of admission of the nitrous oxide, the rate of admission of argon and the cell temperature. The oxide molecules formed are in vibrational levels of the electronic ground state that are close to the dissociational limit. As a result of collisions with argon atoms, the oxide molecule passes to the excited electronic state. The thermal effects of the above reaction and the equal dissociational energies of the oxide molecules are sufficient for excitation of the vibrational levels 10 and 2 of the excited electronic states of the GaO and InO molecules, respectively. Atomic chemiluminescence is evidently a consequence of collision of metal oxide molecules with metal atoms in the electronic ground states.

  5. N-B dative bond-induced [3.3.0] bicyclic boronate-tethered exo-selective intramolecular Diels-Alder reaction.

    PubMed

    Feng, Chao; Wang, Hong; Xu, Liang; Li, Pengfei

    2015-07-14

    We report herein a highly exo-selective intramolecular Diels-Alder reaction of alkenyl boronates which employs an N-B dative bond-involved bicyclic rigid tether. Complex C(sp(3))-rich polycyclic molecules containing up to 8 stereocenters can be readily formed via an operationally simple two-step procedure. PMID:26055829

  6. Designed synthesis of size-tunable Ag2S nanoclusters via distinguishable C-S bond cleavage reaction of alkyl- and aryl-thiolates.

    PubMed

    Chen, Hang-Qing; He, Xin; Guo, Hui; Fu, Nan-Yan; Zhao, Liang

    2015-03-01

    We report herein the synthesis of two different silver clusters of aryl- and alkyl-thiolates. These two cluster complexes exhibited biased C-S bond cleavage reaction rates upon removing protective hexamethylazacalix[6]pyridine (Py[6]) ligands, which was applied in the fabrication of silver sulfide nanoclusters with variable and controllable sizes. PMID:25652650

  7. Ozonolysis of methyl oleate monolayers at the air-water interface: oxidation kinetics, reaction products and atmospheric implications.

    PubMed

    Pfrang, Christian; Sebastiani, Federica; Lucas, Claire O M; King, Martin D; Hoare, Ioan D; Chang, Debby; Campbell, Richard A

    2014-07-14

    Ozonolysis of methyl oleate monolayers at the air-water interface results in surprisingly rapid loss of material through cleavage of the C=C bond and evaporation/dissolution of reaction products. We determine using neutron reflectometry a rate coefficient of (5.7 ± 0.9) × 10(-10) cm(2) molecule(-1) s(-1) and an uptake coefficient of ?3 × 10(-5) for the oxidation of a methyl ester monolayer: the atmospheric lifetime is ?10 min. We obtained direct experimental evidence that <2% of organic material remains at the surface on atmospheric timescales. Therefore known long atmospheric residence times of unsaturated fatty acids suggest that these molecules cannot be present at the interface throughout their ageing cycle, i.e. the reported atmospheric longevity is likely to be attributed to presence in the bulk and viscosity-limited reactive loss. Possible reaction products were characterized by ellipsometry and uncertainties in the atmospheric fate of organic surfactants such as oleic acid and its methyl ester are discussed. Our results suggest that a minor change to the structure of the molecule (fatty acid vs. its methyl ester) considerably impacts on reactivity and fate of the organic film. PMID:24870051

  8. Kinetics and dynamics of oxidation reactions involving an adsorbed CO species

    SciTech Connect

    Harold, M.P.; Conner, C.W.

    1992-07-01

    Objectives were to formulate kinetic models/mechanistic sequences, and to develop bifunctional catalysts for selective oxidation of hdyrocarbons. Efforts are reported this year on 3 items: development of Fourier transform infrared emission spectroscopy to monitor near infrared (ir) under reaction conditions (ethylene oxidation on V{sub 2}O{sub 5}); kinetics study of methanol oxidation on supported Pt catalysts (methanol-rich feed the CO{sub 2} yield exhibits a maximum at an intermediate temperature); and comparative kinetics study of CO oxidation on Pt, Pd, and Rh. The ir spectra of V{sub 2}O{sub 5} show a correlation between the ir features and the degree of surface oxidation. 4 figs. (DLC)

  9. Low temperature wafer direct bonding

    Microsoft Academic Search

    Qin-Yi Tong; Giho Cha; Roman Gafiteanu; Ulrich Gosele

    1994-01-01

    A pronounced increase of interface energy of room temperature bonded hydrophilic Si\\/Si, Si\\/SiO2, and SiO2\\/SiO 2 wafers after storage in air at room temperature, 150°C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and\\/or silicon at the interface at temperatures below 110°C and the formation of

  10. A new reaction between common compounds: lead oxide reacts with formaldehyde.

    PubMed

    Zou, Shihui; Liu, Juanjuan; Kobayashi, Hisayoshi; Hu, Xiurong; Xiao, Liping; Fan, Jie

    2014-06-18

    We show here a new reaction between lead(II) oxide and formaldehyde aqueous solution, which has been overlooked all along. The special structure of the new substance (PbCH2O2) and the DFT calculations suggest a diol-mechanism, which not only informs people about the corrosive nature of HCHO toward Pb and PbO, but also leads us to discover some new reactions between a variety of vicinal diol-type molecules and PbO. The reaction is further highlighted because of its potential application in detection and treatment of formaldehyde-containing wastewaters. PMID:24600686

  11. Effect of acidic pretreatment combined with a silane coupling agent on bonding durability to silicon oxide ceramic.

    PubMed

    Foxton, Richard M; Nakajima, Masatoshi; Tagami, Junji; Miura, Hiroyuki

    2005-04-01

    This study examined the effect of different acidic treatments and the role of a phosphate monomer in a silane coupling agent on the durability of the dual-cure resin cement/silicon oxide bond. Ceramic blocks (Vita Celay Blanks) were cut into multiple 3 mm-thick slices and polished using 600 grit SiC paper. Two pairs were left untreated [controls (CTRL)], two pairs were treated with 40% phosphoric acid and rinsed with water for 30 s (PA), and another two pairs treated with 20% hydrofluoric acid followed by 30 s water rinsing (HF). Half the specimens were silanated with Tokuso Ceramics Primer (TCP) (Tokuyama) and the other half with TCP formulated without phosphate monomer (TCP-NoPM). All the pairs were bonded with Bistite II dual-cure resin cement (Tokuyama) and light cured. After 24 h water storage at 37 degrees C, 0.7 mm-thick slabs were serially sectioned. Immediately, after 6 months and after 1 year of water storage, two slabs were randomly selected from each subgroup, and sliced into beams (6 x 0.7 x 0.7 mm) for the microtensile bond strength (muTBS) test. The muTBS data were statistically analyzed using multiple Wilcoxon Signed Rank tests (p < 0.05). Failure modes were determined using a confocal laser-scanning microscope. Ceramic surface morphology after the different acidic treatments was examined using an SEM. After 1 day, in the case of silane treatment with TCP, there were no significant differences in muTBS between the control and acid-treated groups (p > 0.05), whereas with TCP-NoPM, the muTBS of the control was significantly lower than the acid-treated groups (p < 0.05). All the TCP and acid-treated TCP-NoPM groups exhibited significant reductions in muTBS after 6 months (p < 0.05). After 1 year, the muTBS of the acid-treated TCP groups were not significantly different from the control TCP group (p > 0.05). There was also no significant difference between the HF-treated TCP and TCP-NoPM groups (p > 0.05) after 1 year, all exhibiting greater than 10 MPa tensile bond strength. It is suggested that acidic pretreatment of the ceramic surface does not improve the durability of the dual-cure resin cement/silicon oxide ceramic bond when an acidic phosphate monomer is present as an activator in a ceramic primer. PMID:15625674

  12. Toluene removal by oxidation reaction in spray wet scrubber: experimental, modeling and optimization

    Microsoft Academic Search

    Juntima Chungsiriporn; Charun Bunyakan

    Toluene, an important volatile organic compound (VOC), is used in many kinds of industries, such as painting, printing, coating, and petrochemical industries. The emission of toluene causes serious air pollution, odor problem, flammability problem and affects human health. This paper proposes the removal of toluene from waste air using a spray wet scrubber combining the absorption and oxidation reaction. Aqueous

  13. FTIR Spectroscopic Analysis of Surface Oxidation Reactions During Ozonation of Fossil Resin and Coal

    Microsoft Academic Search

    Q. YU; K. BUKKA; Y. YE; J. D. MILLER

    1992-01-01

    Diffuse and specular reflectance FTIR analysis both fossil resin (resinite) and coal has been carried out to study surface oxidation reactions which occur during the selective flotation of fossil resin from coal by ozone conditioning. It was found from the FTIR spectra that ozonation of both fossil resin and coal causes an increase in the peak intensity associated with stretching

  14. Synthesis of biaryls via AlCl3 catalyzed domino reaction involving cyclization, dehydration, and oxidation.

    PubMed

    Narender, Tadigoppula; Sarkar, Satinath; Rajendar, Kandikonda; Tiwari, Sriniwas

    2011-12-01

    A new chemical access has been developed to synthesize biaryls from substituted acetophenones, phenylacetones, dihydrochalcone, and 2-acetylnaphthalene in reasonably good yields at room temperature via a domino reaction sequence of AlCl(3) catalyzed cyclization, dehydration, and then oxidation. PMID:22040063

  15. A Tentative Modeling Study of the Effect of Wall Reactions on Oxidation Phenomena

    E-print Network

    Paris-Sud XI, Université de

    temperature diagram of oxidation phenomena in the case of n-butane. Reactions which depend on the type-Ta ignition diagrams for equimolar n-butane/oxygen in an untreated silica vessel, a vessel internally coated Figure 1. Experimental p-Ta ignition diagrams for equimolar n-butane + oxygen mixtures (50 % n- butane

  16. Oxidative reactions in the tear fluid of patients suffering from dry eyes

    Microsoft Academic Search

    Albert J. Augustin; Manfred Spitznas; Nahid Kaviani; Daniel Meller; Frank H. J. Koch; Franz Grus; Martin J. Göbbels

    1995-01-01

    • Purpose: To evaluate whether products of oxidative and inflammatory reactions are detectable in the tear fluid of patients suffering from dry eyes. • Methods: The tear fluid of 217 patients (397 eyes) was sampled. Criteria for grouping of the patients were (1) basic secretion test (“sicca l”: BST = 0–5 mm, n = 78 eyes; “sicca 2”: BST =

  17. Bond cleavage reactions in oxygen and nitrogen heterocycles by a rhodium phosphine complex

    SciTech Connect

    Jones, W.D.; Dong, L.; Myers, A.W. (Univ. of Rochester, NY (United States))

    1995-02-01

    The reactions of (C[sub 5]Me[sub 5])Rh(PMe[sub 3])PhH with furan, 2,5-dimethylfuran, 2,3-dihydrofuran, dibenzofuran, pyrrole, 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, carbazole, 9-methylcarbazole, pyrrolidine, pyridine, 3,5-lutidine, 2,4,6-collidine, pyrazole, 3-methylpyrazole, and piperidine have been investigated. While the oxygen heterocycles give only C-H activation, the nitrogen heterocycles yield C-H and N-H insertion products. The chloro derivative (C[sub 5]Me[sub 5])Rh(PMe[sub 3])[2-(1-methylpyrrole)]Cl was found to crystallize in the monoclinic space group C2/c with a = 13.753 (6) A, b = 9.665 (5) A, c = 30.14 (2) A, [beta] = 99.77 (5)-[degree], Z = 8, and V = 3949 (4.1) A[sup 3] while (C[sub 5]Me[sub 5])Rh(PMe[sub 5])[2-(3,5-lutidine)]Cl was found to crystallize in the monoclinic space group P2[sub 1]/c with a = 14.976 (8) A, b = 8.613 (5) A, c = 17.12 (2) A, [beta] = 101.90 (6)[degree], Z = 4, and V = 2160 (5.2) A[sup 3]. 30 refs., 2 figs., 3 tabs.

  18. Storage stability of cauliflower soup powder: The effect of lipid oxidation and protein degradation reactions.

    PubMed

    Raitio, Riikka; Orlien, Vibeke; Skibsted, Leif H

    2011-09-15

    Soups based on cauliflower soup powders, prepared by dry mixing of ingredients and rapeseed oil, showed a decrease in quality, as evaluated by a sensory panel, during the storage of the soup powder in the dark for up to 12weeks under mildly accelerated conditions of 40°C and 75% relative humidity. Antioxidant, shown to be effective in protecting the rapeseed bulk oil, used for the powder preparation, had no effect on storage stability of the soup powder. The freshly prepared soup powder had a relatively high concentration of free radicals, as measured by electron spin resonance spectroscopy, which decreased during storage, and most remarkably during the first two weeks of storage, with only marginal increase in lipid hydroperoxides as primary lipid oxidation products, and without any increase in secondary lipid oxidation products. Analyses of volatiles by SPME-GC-MS revealed a significant increase in concentrations of 2-methyl- and 3-methyl butanals, related to Maillard reactions, together with an increase in 2-acetylpyrrole concentration. The soup powders became more brown during storage, as indicated by a decreasing Hunter L-value, in accord with non-enzymatic browning reactions. A significant increase in the concentrations of dimethyl disulfide in soup powder headspace indicated free radical-initiated protein oxidation. Protein degradation, including Maillard reactions and protein oxidation, is concluded to be more important than lipid oxidation in determining the shelf-life of dry cauliflower soup powder. PMID:25212144

  19. On the biologic role of the reaction of NO with oxidized cytochrome c oxidase.

    PubMed

    Antunes, Fernando; Boveris, Alberto; Cadenas, Enrique

    2007-10-01

    The inhibition of cytochrome c oxidase (CcOX) by nitric oxide (NO) is analyzed with a mathematical model that simulates the metabolism in vivo. The main results were the following: (a) We derived novel equations for the catalysis of CcOX that can be used to predict CcOX inhibition in any tissue for any [NO] or [O(2)]; (b) Competitive inhibition (resulting from the reversible binding of NO to reduced CcOX) emerges has the sole relevant component of CcOX inhibition under state 3 in vivo; (c) In state 4, contribution of uncompetitive inhibition (resulting from the reaction of oxidized CcOX with NO) represents a significant nonmajority fraction of inhibition, being favored by high [O(2)]; and (d) The main biologic role of the reaction between NO and oxidized CcOX is to consume NO. By reducing [NO], this reaction stimulates, rather than inhibits, respiration. Finally, we propose that the biologic role of NO as an inhibitor of CcOX is twofold: in state 4, it avoids an excessive buildup of mitochondrial membrane potential that triggers rapid production of oxidants, and in state 3, increases the efficiency of oxidative phosphorylation by increasing the ADP/O ratio, supporting the therapeutic use of NO in situations in which mitochondria are dysfunctional. PMID:17665969

  20. Easy oxidative addition of the carbon-halogen bond by dimethylplatinum(II) complexes containing a related series of diimine ligands: Synthesis, spectral characterization and crystal structure

    NASA Astrophysics Data System (ADS)

    Momeni, Badri Z.; Fathi, Nastaran; Mohagheghi, Arezoo

    2015-01-01

    Dimethylplatinum(II) complexes [PtMe2(NN)] {NN = 4,4?-Me2bpy (4,4?-dimethyl-2,2?-bipyridine); 5,5?-Me2bpy (5,5?-dimethyl-2,2?-bipyridine)} were reacted with alkyl halides (RX = EtI, EtBr) to yield the organoplatinum(IV) complexes [PtMe2RX(NN)]. On the basis of NMR data, the platinum(IV) product of each reaction contains almost exclusively the trans isomer but small traces of the cis isomers are also observed. On the other hand, the reaction of [PtMe2(NN)] {NN = bu2bpy (4,4?-di-tert-butyl-2,2?-bipyridine); 4,4?-Me2bpy; 5,5?-Me2bpy} with CH2Br2 gave a mixture of cis and trans-[PtMe2(CH2Br)Br(NN)] formed by the oxidative addition of one of the C-Br bonds. The formation of the cis isomer increases in the order of 5,5?-Me2bpy > bu2bpy > 4,4?-Me2bpy. The reaction of [PtMe2(NN)] {NN = bpy (2,2?-bipyridine), phen (1,10-phenanthroline)} with 1,8-dibromooctane or 1,9-dibromononane afforded the mononuclear complexes [PtMe2{(CH2)nBr}Br(NN)] (n = 8-9). The products were fully characterized by elemental analysis, 1H, 13C, HH COSY, HMQC, DEPT and DEPTQ-135 NMR spectroscopy. The crystal structure of [PtMe2EtI(4,4?-Me2bpy)] reveals that Pt(IV) atom is six-coordinated in a slightly distorted octahedral geometry with the ethyl group trans to iodide.

  1. Failure of gold and copper ball bonds due to intermetallic oxidation and corrosion

    Microsoft Academic Search

    C. D. Breach; Ng Hun Shen; Teck Kheng Lee; R. Holliday

    2011-01-01

    Strong interest in the replacement of gold bonding wire by copper in microelectronics packaging has highlighted poor performance of copper wire under moist conditions. Attempts have been made to address this problem by coating copper wire with palladium, which may be a solution for some applications but ignores the fundamental reasons for the poor performance of copper wire. Gold and

  2. Spatially-resolved modeling of electric double layers and surface chemistry for the hydrogen oxidation reaction in

    E-print Network

    Litster, Shawn

    HOR with the three elementary steps for hydrogen oxidation reaction on Pt surface: ( )2H +2Pt 2 HSpatially-resolved modeling of electric double layers and surface chemistry for the hydrogen oxidation reaction in water-filled platinum-carbon electrodes Iryna V. Zenyuk and Shawn Litster Department

  3. Experimental and theoretical studies of reactions of neutral vanadium and tantalum oxide clusters with NO and NH3

    E-print Network

    Rocca, Jorge J.

    Experimental and theoretical studies of reactions of neutral vanadium and tantalum oxide clusters; accepted 16 September 2010; published online 3 November 2010 Reactions of neutral vanadium and tantalum, a vanadium oxide catalyst is loaded on an anatase support as a monolayer, and the active VOx species

  4. Water-gas shift reaction on oxide/Cu(111): Rational catalyst screening from density functional theory

    NASA Astrophysics Data System (ADS)

    Liu, Ping

    2010-11-01

    Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO2/Cu(111), ZrO2/Cu(111) < MoO3/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.

  5. Water-gas Shift Reaction on oxide/Cu(111): Rational Catalyst Screening from Density Functional Theory

    SciTech Connect

    Liu, P.

    2010-11-28

    Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO{sub 2}/Cu(111), ZrO{sub 2}/Cu(111) < MoO{sub 3}/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.

  6. Ferrate(VI) oxidation of ?-lactam antibiotics: reaction kinetics, antibacterial activity changes, and transformation products.

    PubMed

    Karlesa, Anggita; De Vera, Glen Andrew D; Dodd, Michael C; Park, Jihye; Espino, Maria Pythias B; Lee, Yunho

    2014-09-01

    Oxidation of ?-lactam antibiotics by aqueous ferrate(VI) was investigated to determine reaction kinetics, reaction sites, antibacterial activity changes, and transformation products. Apparent second-order rate constants (kapp) were determined in the pH range 6.0-9.5 for the reaction of ferrate(VI) with penicillins (amoxicillin, ampicillin, cloxacillin, and penicillin G), a cephalosporin (cephalexin), and several model compounds. Ferrate(VI) shows an appreciable reactivity toward the selected ?-lactams (kapp for pH 7 = 110-770 M(-1) s(-1)). The pH-dependent kapp could be well explained by considering species-specific reactions between ferrate(VI) and the ?-lactams (with reactions occurring at thioether, amine, and/or phenol groups). On the basis of the kinetic results, the thioether is the main reaction site for cloxacillin and penicillin G. In addition to the thioether, the amine is a reaction site for ampicillin and cephalexin, and amine and phenol are reaction sites for amoxicillin. HPLC/MS analysis showed that the thioether of ?-lactams was transformed to stereoisomeric (R)- and (S)-sulfoxides and then to a sulfone. Quantitative microbiological assay of ferrate(VI)-treated ?-lactam solutions indicated that transformation products resulting from the oxidation of cephalexin exhibited diminished, but non-negligible residual activity (i.e., ?24% as potent as the parent compound). For the other ?-lactams, the transformation products showed much lower (<5%) antibacterial potencies compared to the parent compounds. Overall, ferrate(VI) oxidation appears to be effective as a means of lowering the antibacterial activities of ?-lactams, although alternative approaches may be necessary to achieve complete elimination of cephalosporin activities. PMID:25073066

  7. The reactions of O(ID) and OH with CH3OH, oxidation of the HCO radial, and the photochemical oxidation of formaldehyde. [photochemical reactions in stratosphere

    NASA Technical Reports Server (NTRS)

    Osif, T. L.

    1976-01-01

    An experimental, laboratory study of the various photochemical reactions that can occur in the mesosphere and stratosphere is presented. N2O was photolyzed at 2139 A in the presence of CH3OH and CO. The O(id) produced in the photolysis reacted with CH3OH to produce OH radicals, and thus the reactions of both O(id) and OH were able to be studied. Also considered was the oxidation of the HCO radical. Mixtures of Cl2, O2, H2CO, and sometimes N2 or He were irradiated at 3660 A at several temperatures to photodecompose the Cl2. The photochemical oxidation of formaldehyde was studied as follows: formaldehyde in the presence of N2 and/or O2 (usually dry air) was photolyzed with a medium pressure Hg lamp used in conjunction with various filters which transmit different relative amounts of Hg lines from 2894 A to 3660 A. Results are presented and discussed, along with a description of experimental procedures and apparatus, and chemical reaction kinetics.

  8. Experimental and ab initio investigations of H2S-assisted propane oxidative dehydrogenation reactions.

    PubMed

    Premji, Zahra A; Lo, John M H; Clark, Peter D

    2014-03-01

    The oxidative dehydrogenation (ODH) reaction of propane was investigated at temperatures between 923 and 1023 K using either O2 or O2/H2S mixture as oxidant. GC analysis of the product mixtures showed that ethylene was the major olefin product in the conventional ODH reaction whereas propylene became dominant when H2S was included in the feed gas. With an oxygen-rich feed (4:2:2 C3H8:O2:H2S), ? 70% propane conversion, and ? 50% propylene selectivity could be achieved at 1023 K, a level of performance comparable to that for the ODH reaction employing reducible solid oxide catalysts. Theoretical calculations utilizing CBS-QB3 method were also conducted to explore the causes of the enhanced propylene yield and selectivity of the H2S-assisted ODH reaction. It was found that the increased propane conversion was due to a large enthalpy gain from the in situ formation of S2 that compensated for the high energy cost of hydrogen abstraction by SH and S2H. Also, the promoted propylene selectivity was attributed to the instability of the sulfur-containing products, which made the reaction route to propylene the most thermodynamically favored. PMID:24524187

  9. Electrocatalysis of hydrogen peroxide reactions on perovskite oxides: experiment versus kinetic modeling.

    PubMed

    Poux, T; Bonnefont, A; Ryabova, A; Kéranguéven, G; Tsirlina, G A; Savinova, E R

    2014-07-21

    Hydrogen peroxide has been identified as a stable intermediate of the electrochemical oxygen reduction reaction on various electrodes including metal, metal oxide and carbon materials. In this article we study the hydrogen peroxide oxidation and reduction reactions in alkaline medium using a rotating disc electrode (RDE) method on oxides of the perovskite family (LaCoO3, LaMnO3 and La0.8Sr0.2MnO3) which are considered as promising electrocatalytic materials for the cathode of liquid and solid alkaline fuel cells. The experimental findings, such as the higher activity of Mn-compared to that of Co-perovskites, the shape of RDE curves, and the influence of the H2O2 concentration, are rationalized with the help of a microkinetic model. PMID:24643772

  10. Modelling of silicon oxynitridation by nitrous oxide using the reaction rate approach

    NASA Astrophysics Data System (ADS)

    Dominique Krzeminski, Christophe

    2013-12-01

    Large technological progress in oxynitridation processing leads to the introduction of silicon oxynitride as ultra-thin gate oxide. On the theoretical side, few studies have been dedicated to the process modelling of oxynitridation. Such an objective is a considerable challenge regarding the various atomistic mechanisms occurring during this fabrication step. In this article, some progress performed to adapt the reaction rate approach for the modelling of oxynitride growth by a nitrous ambient are reported. The Ellis and Buhrman's approach is used for the gas phase decomposition modelling. Taking into account the mass balance of the species at the interface between the oxynitride and silicon, a minimal kinetic model describing the oxide growth has been calibrated and implemented. The influence of nitrogen on the reaction rate has been introduced in an empirical way. The oxidation kinetics predicted with this minimal model compares well with several experiments.

  11. Chemoselective Oxidation of Benzyl, Amino, and Propargyl Alcohols to Aldehydes and Ketones under Mild Reaction Conditions.

    PubMed

    Reddy, C B Rajashekar; Reddy, Sabbasani Rajasekhara; Naidu, Shivaji

    2015-04-01

    Catalytic oxidation reactions often suffer from drawbacks such as low yields and poor selectivity. Particularly, selective oxidation of alcohols becomes more difficult when a compound contains more than one oxidizable functional group. In order to deliver a methodology that addresses these issues, herein we report an efficient, aerobic, chemoselective and simplified approach to oxidize a broad range of benzyl and propargyl alcohols containing diverse functional groups to their corresponding aldehydes and ketones in excellent yields under mild reaction conditions. Optimal yields were obtained at room temperature using 1?mmol substrate, 10?mol?% copper(I) iodide, 10?mol?% 4-dimethylaminopyridine (DMAP), and 1?mol?% 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) in acetonitrile, under an oxygen balloon. The catalytic system can be applied even when sensitive and oxidizable groups such as alkynes, amines, and phenols are present; starting materials and products containing such groups were found to be stable under the developed conditions. PMID:25969806

  12. Elucidation of the reaction mechanism during the removal of copper oxide by halogen surfactant at the surface of copper plate

    NASA Astrophysics Data System (ADS)

    Yokoyama, Shun; Takahashi, Hideyuki; Itoh, Takashi; Motomiya, Kenichi; Tohji, Kazuyuki

    2013-01-01

    Although copper nanoparticles have various attractive properties, electrical applications of these was not achieved because of its surface oxide layer which prohibited electrical conduction. Thus, it can be considered that a new elimination method of the oxide on Cu surface, which simultaneously provide the resistance to re-oxidized, should be developed. In this study, the reaction between the metal oxide on Cu plate surface and halogen surfactant was introduced into development as a new elimination method of surface oxide layer. Since electrochemical and surface analysis are effective for analyzing the reaction mechanism which expected to be the reduction reaction of the oxide on metal surface, Cu electrode, which represented material of Cu nanoparticles surface, was used for the reaction mechanism analysis. The oxide is removed by controlling the temperature and selecting the optimal combination of solvents and the halogen surfactant (TIC). Results of electrochemical measurements strongly suggest that the chemical reaction between the oxides on the surface with the halogen surfactant is a substitution reaction which converts Cu oxide to Cu bromide, and continuously formed Cu bromide was dissolved into solvent. Totally, the oxide on the Cu surface was successfully eliminated.

  13. In vitro comparative bond strength of contemporary self-adhesive resin cements to zirconium oxide ceramic with and without air-particle abrasion

    Microsoft Academic Search

    Markus B. Blatz; Jin-Ho Phark; Fusun Ozer; Francis K. Mante; Najeed Saleh; Michael Bergler; Avishai Sadan

    2010-01-01

    This study compared shear bond strengths of six self-adhesive resin cements to zirconium oxide ceramic with and without air-particle\\u000a abrasion. One hundred twenty zirconia samples were air-abraded (group SB; n?=?60) or left untreated (group NO). Composite cylinders were bonded to the zirconia samples with either BisCem (BC), Maxcem\\u000a (MC), G-Cem (GC), RelyX Unicem Clicker (RUC), RelyX Unicem Applicator (RUA), or

  14. Reusable ionic liquid-catalyzed oxidative coupling of azoles and benzylic compounds via sp(3) C-N bond formation under metal-free conditions.

    PubMed

    Liu, Wenbo; Liu, Chenjiang; Zhang, Yonghong; Sun, Yadong; Abdukadera, Ablimit; Wang, Bin; Li, He; Ma, Xuecheng; Zhang, Zengpeng

    2015-07-14

    The heterocyclic ionic liquid-catalyzed direct oxidative amination of benzylic sp(3) C-H bonds via intermolecular sp(3) C-N bond formation for the synthesis of N-alkylated azoles under metal-free conditions is reported for the first time. The catalyst 1-butylpyridinium iodide can be recycled and reused with similar efficacies for at least eight cycles. PMID:26060993

  15. Neocarzinostatin-based hybrid biocatalysts for oxidation reactions.

    PubMed

    Sansiaume-Dagousset, Elodie; Urvoas, Agathe; Chelly, Kaouthar; Ghattas, Wadih; Maréchal, Jean-Didier; Mahy, Jean-Pierre; Ricoux, Rémy

    2014-06-14

    An anionic iron(III)-porphyrin-testosterone conjugate 1-Fe has been synthesized and fully characterized. It has been further associated with a neocarzinostatin variant, NCS-3.24, to generate a new artificial metalloenzyme following the so-called 'Trojan Horse' strategy. This new 1-Fe-NCS-3.24 biocatalyst showed an interesting catalytic activity as it was found able to catalyze the chemoselective and slightly enantioselective (ee = 13%) sulfoxidation of thioanisole by H2O2. Molecular modelling studies show that a synergy between the binding of the steroid moiety and that of the porphyrin macrocycle into the protein binding site can explain the experimental results, indicating a better affinity of 1-Fe for the NCS-3.24 variant than testosterone and testosterone-hemisuccinate themselves. They also show that the Fe-porphyrin complex is sandwiched between the two subdomains of the protein providing with good complementarities. However, the artificial cofactor entirely fills the cavity and its metal ion remains widely exposed to the solvent which explains the moderate enantioselectivity observed. Some possible improvements in the "Trojan Horse" strategy for obtaining better catalysts of selective oxidations are presented. PMID:24728274

  16. Reaction of Acylated Homoserine Lactone Bacterial Signaling Molecules with Oxidized Halogen Antimicrobials

    PubMed Central

    Borchardt, S. A.; Allain, E. J.; Michels, J. J.; Stearns, G. W.; Kelly, R. F.; McCoy, W. F.

    2001-01-01

    Oxidized halogen antimicrobials, such as hypochlorous and hypobromous acids, have been used extensively for microbial control in industrial systems. Recent discoveries have shown that acylated homoserine lactone cell-to-cell signaling molecules are important for biofilm formation in Pseudomonas aeruginosa, suggesting that biofouling can be controlled by interfering with bacterial cell-to-cell communication. This study was conducted to investigate the potential for oxidized halogens to react with acylated homoserine lactone-based signaling molecules. Acylated homoserine lactones containing a 3-oxo group were found to rapidly react with oxidized halogens, while acylated homoserine lactones lacking the 3-oxo functionality did not react. The Chromobacterium violaceum CV026 bioassay was used to determine the effects of such reactions on acylated homoserine lactone activity. The results demonstrated that 3-oxo acyl homoserine lactone activity was rapidly lost upon exposure to oxidized halogens; however, acylated homoserine lactones lacking the 3-oxo group retained activity. Experiments with the marine alga Laminaria digitata demonstrated that natural haloperoxidase systems are capable of mediating the deactivation of acylated homoserine lactones. This may illustrate a natural defense mechanism to prevent biofouling on the surface of this marine alga. The Chromobacterium violaceum activity assay illustrates that reactions between 3-oxo acylated homoserine lactone molecules and oxidized halogens do occur despite the presence of biofilm components at much greater concentrations. This work suggests that oxidized halogens may control biofilm not only via a cidal mechanism, but also by possibly interfering with 3-oxo acylated homoserine lactone-based cell signaling. PMID:11425738

  17. Chemical oxidation of anthracite with hydrogen peroxide via the Fenton reaction

    USGS Publications Warehouse

    Heard, I.; Senftle, F.E.

    1984-01-01

    Solutions of 30% H2O2 ranging from pH = 0 to pH = 11.5 have been used to oxidize anthracite at room temperature. The inorganic impurities, primarily pyrite, catalysed the oxidation and reduction of H2O2 (the Fenton reaction) to form the hydroxyl radical; the oxidation of the organic matter was minimal and was observed only in strong acidic solutions (pH < 1.5). After acid demineralization, samples of the same anthracite underwent a significant enhancement of oxidation in both acid and alkaline solutions (pH = 0.4-11.5). As all the iron had been removed from the surface and the reactions were completed in a much shorter time, the oxidation mechanism must have been of a different nature than that for the untreated anthracite. A qualitative model based on the catalytic decomposition of H2O2 by activated carbon sites in the coal surface is used to explain the oxidation of the demineralized anthracite. ?? 1984.

  18. Structure and Reaction of Oxametallacycles Derived from Styrene Oxide on Ag(110).

    SciTech Connect

    Lukaski, Adrienne C.; Enever, Michael C.; Barteau, Mark A.

    2007-08-15

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Styrene oxide forms a strongly bound oxametallacycle intermediate via activated adsorption on the Ag(110) surface. The oxametallacycle species derived from styrene oxide on Ag(110) fits well with the family of oxametallacycles identified previously in studies of nonallylic epoxides with unsaturated substituent groups on silver. Temperature-programmed reaction experiments demonstrate that styrene oxide ring opens at the substituted carbon, and Density Functional Theory calculations indicate that the phenyl ring of the resulting oxametallacycle is oriented nearly parallel to the Ag(110) surface. Interaction of the phenyl group with the silver surface stabilizes this intermediate relative to that derived from the mono-olefin epoxide, ethylene oxide. During temperature-programmed reaction, the oxametallacycle undergoes ring-closure to reform styrene oxide and isomerization to phenylacetaldehyde at 505 K on Ag(11 0). Styrene oxide-derived oxametallacycles exhibit similar ring-closure behavior on the Ag(111) surface.

  19. Mass transfer model for two-layer TBP oxidation reactions: Revision 1

    SciTech Connect

    Laurinat, J.E.

    1994-11-04

    To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the Canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. Bubbles containing reaction products enhance the rate of transfer of water from the aqueous layer to the organic layer. These bubbles are generated by the oxidation of TBP and its reaction products in the organic layer and by the oxidation of butanol in the aqueous layer. Butanol is formed by the hydrolysis of TBP in the organic layer. For aqueous-layer bubbling to occur, butanol must transfer into the aqueous layer. Consequently, the rate of oxidation and bubble generation in the aqueous layer strongly depends on the rate of transfer of butanol from the organic to the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments.

  20. A new mechanism for DMS oxidation - reaction with stabilized Criegee radicals

    NASA Astrophysics Data System (ADS)

    Mauldin, L.; Berndt, T.; Sipilä, M.; Jokinen, T.; Stratmann, F.; Petäjä, T.; Kulmala, M. T.

    2012-12-01

    Oxidation is a key atmospheric process and impacts such issues as climate change, air quality, and acid rain. Current belief is that reactions involving OH and NO3 are the predominate mechanism in initiating removal processes. This outlook could change with the recent discovery that stabilized Criegee radicals (sCI) also have a significant capacity to oxidize compounds such as NO2 and SO2. Formed from the ozonolysis of alkenes, sCIs represent a new link between the biosphere and atmospheric oxidation chemistry. To determine the importance this newly discovered oxidant to the overall oxidizing capacity of the atmosphere, more information is required as to its reactivity with other compounds. Here we present results that show that sCIs also react with dimethyl sulfide, DMS. sCIs produced from tetra-methyl ethene, TME, were reacted with DMS. Unlike oxidation via OH, methane sulfonic acid, MSA, was found to be the dominate oxidation product. The formation of dimethyl sulfoxide, DMSO was also observed. These results represent an additional route of DMS atmospheric oxidation and can possibly explain anomalous observations made in the Pacific boundary layer.

  1. New solid state routes to lithium transition metal oxides via reactions with lithium oxide

    Microsoft Academic Search

    Marco D. Aguas; Graham C. Coombe; Ivan P. Parkin

    1998-01-01

    Thermolysis of a mixture of lithium oxide and transition metal halides MXn (M = Ti, Zr, Hf, V, Nb, Ta, Mo, W, Fe, Mn) at 800°C for 2–12 h produces crystalline lithium transition metal oxides Li2MO3 (M = Ti, Zr, Hf, Mn), Li3MO4 (M = V, Nb, Ta), Li2MnO3 Li2Fe3O4 and Li2MO4 (M = Mo, W). For M = Cr,

  2. Tamao-Fleming Oxidations in Organic Synthesis: Carbon-Silicon Bonds as Functional Group Masks

    E-print Network

    Stoltz, Brian M.

    Tamao Oxidations can be carried out under a variety of pH's when H2O2 is the oxidant Acidic Conditions: R SiLn 30% H2O2, Ac2O, KHF2 DMF, r.t. R OH Neutral Conditions: 30% H2O2, KHF2 DMF, r.t. to 60°CR SiLn R OH Basic: R SiLn R OH30% H2O2 , KHCO3 MeOH / THF, 60°C -mCPBA is also a commonly employed oxidant

  3. Oxidation and dechlorination of chlorophenols in dilute aqueous suspensions of manganese oxides: Reaction products

    SciTech Connect

    Ukrainczyk, L.; McBride, M.B. (Cornell Univ., Ithaca, NY (United States). Dept.of Soil, Crop, and Atmospheric Sciences)

    1993-11-01

    Some monomeric and dimeric oxidation products of para- and/or ortho-chlorinated phenols in dilute (1 mmol/L phenol), acidified, aqueous suspensions of manganese oxide (Na-buserite) were identified by MS, Fourier-transform IR spectroscopy and UV/visible spectroscopy. The para-chlorinated phenols (4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 4-chloro-2-methylphenol) gave corresponding p-benzoquionones (benzoquinone, 2-chlorobenzoquinone, 2,6-dichlorobenzoquinone, 2-methylbenzoquinone) as the detectable water-soluble oxidation products. Dimeric products were present in the extracts obtained by washing the oxide with methylene chloride. Michael addition of phenolate to quinone seems to be the predominant mode of coupling. Chlorinated phenols without chlorine in the para-position (2-chlorophenol, 2,6-dichlorophenol) were more difficult to oxidize and afforded diphenoquinones as the only detectable water-soluble products. For all studied phenols, with the exception of 2,4,6-trichlorophenol, the amount of water-soluble products accounts only for a small fraction of oxidized phenol. The quinone and diphenoquinone products readily couple with phenols into humus like materials.

  4. Bonding, Ion Mobility, and Rate-Limiting Steps in Deintercalation Reactions with ThCr[subscript 2]Si[subscript 2]-type KNi[subscript 2]Se[subscript 2

    SciTech Connect

    Neilson, James R.; McQueen, Tyrel M. (JHU)

    2012-06-28

    Here, we study the nature of metal-metal bonding in the ThCr{sub 2}Si{sub 2} structure type by probing the rate-limiting steps in the oxidative deintercalation of KNi{sub 2}Se{sub 2}. For low extents of oxidation, alkali ions are removed exclusively to form K{sub 1-x}Ni{sub 2}Se{sub 2}. For greater extents of oxidation, the rate of the reaction decreases dramatically, concomitant with the extraction of both potassium and nickel to form K{sub 1-x}Ni{sub 2-y}Se{sub 2}. The appreciable mobility of transition metal ions is unexpected, but illustrates the relative energy scales of different defects in the ThCr{sub 2}Si{sub 2} structure type. Furthermore, the fully oxidized compounds, K{sub 0.25}Ni{sub 1.5}Se{sub 2}, spontaneously convert from the tetrahedral [NiSe{sub 4}]-containing ThCr{sub 2}Si{sub 2} structure to a vacancy-ordered NiAs structure with [NiSe{sub 6}] octahedra. From analysis of the atom positions and kinetic data, we have determined that this transformation occurs by a continuous, low-energy pathway via subtle displacements of Ni atoms and buckling of the Se sublattice. These results have profound implications for our understanding of the stability, mobility, and reactivity of ions in materials.

  5. Hydrocarbon reaction with HF-cleaned Si(lOQ) and effects on metal-oxide-semiconductor device quality

    E-print Network

    Rubloff, Gary W.

    Hydrocarbon reaction with HF-cleaned Si(lOQ) and effects on metal-oxide-semiconductor device Sic, Metal-oxide-semiconductor devices fabricated on contaminated surfaces are degraded then loaded through a load lock into an UHV sample-transfer chamber for analysis. Metal-oxide- semiconductor

  6. Phase transformation and bond coat oxidation behavior of EB-PVD thermal barrier coating

    Microsoft Academic Search

    M. H. Li; X. F. Sun; S. K. Gong; Z. Y. Zhang; H. R. Guan; Z. Q. Hu

    2004-01-01

    Thermal barrier coating, consisting of an electron beam physical vapor deposited partially stabilized zirconia (PSZ, 7 wt.%Y2O3) and a sputtered NiCrAlY bond coat, was investigated by thermal cycling at 1050 °C in air. Experimental characterization was conducted using X-ray diffraction analysis and scanning electron microscopy equipped with energy dispersive analytical X-ray spectroscopy. The lattice parameters of the tetragonal phase were

  7. Densification of Reaction Bonded Silicon Nitride with the Addition of Fine Si Powder Effects on the Sinterability and Mechanical Properties

    SciTech Connect

    Lee, Sea-Hoon [Korea Institute of Materials Science; Cho, Chun-Rae [Korea Institute of Materials Science; Park, Young-Jo [Korea Institute of Materials Science; Ko, Jae-Woong [Korea Institute of Materials Science; Kim, Hai-Doo [Korea Institute of Materials Science; Lin, Hua-Tay [ORNL; Becher, Paul F [ORNL

    2013-01-01

    The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain Lu2O3-SiO2 additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at 1850oC through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at 1950oC. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine Si3N4 particles after nitridation and sintering at and above 1600oC. The amount of residual SiO2 within the specimens was not strongly affected by adding fine Si powder because most of the SiO2 layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and 8.0 MPa m1/2, respectively.

  8. Sigma-bond metathesis reactions of Sc(OCD3)2 with water, ethanol, and 1-propanol: measurements of equilibrium constants,

    E-print Network

    Goddard III, William A.

    for the reaction Sc(OCD3)2 ROH º CD3OScOR CD3OH with R H, ethyl, and n-propyl are 0.013 0.004, 0.5 0.15, and 0.7 0, methyl, ethyl, and n-propyl. The relative bond strengths, D298 o (CD3OSc ­OR)­D298 o (CD3OSc ­OCD3 bond strengths for HOSc ­OCD3, CD3OSc ­OCD3, CD3OSc ­OC2H5, CD3OSc ­OCH2CH2CH3, and H5C2OSc ­OC2H5

  9. Understanding the role of gold nanoparticles in enhancing the catalytic activity of manganese oxides in water oxidation reactions.

    PubMed

    Kuo, Chung-Hao; Li, Weikun; Pahalagedara, Lakshitha; El-Sawy, Abdelhamid M; Kriz, David; Genz, Nina; Guild, Curtis; Ressler, Thorsten; Suib, Steven L; He, Jie

    2015-02-16

    The Earth-abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn(3+) species, a small amount of AuNPs (<5%) in ?-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure ?-MnO2. PMID:25284796

  10. Structures and hydrogen bonding in the 1:1 and 1:2 complexes of trimethylamine N oxide with pentachlorophenol

    NASA Astrophysics Data System (ADS)

    Tykarska, Ewa; Dega-Szafran, Zofia; Szafran, Miros?aw

    1999-03-01

    The following crystalline complexes of trimethylamine N-oxide (TMAO) with pentachlorophenol (PCP): TMAO·PCP, TMAO·PCP·H 2O and TMAO·2PCP have been prepared and characterized by FTIR spectroscopy, quantum-mechanical calculations with DFT and semiempirical methods and X-ray diffraction (two complexes). The crystals of TMAO·PCP are orthorombic, space group Pccn with a=27.621(6), b=13.642(3), c=7.191(1) Å, V=2709.6(9) Å 3, Z=8. The proton is transferred from PCP to TMAO and both residues are linked by an O-H⋯O hydrogen bond of length 2.464(3) Å and an angle of 168(4)°. The crystals of TMAO·PCP·H 2O are monoclinic, space group C2/c with a=20.388(3), b=10.314(2), c=14.300(2) Å, ?=105.43(2)°, V=2898.6(8) Å 3, Z=8. The proton is transferred from PCP to TMAO. Two pentachlorophenolates are bridged by two water molecules to form an eight membered ring with four O-H·O hydrogen bonds of 2.663(3) and 2.647(3) Å, respectively. Each water molecule, in turn, additionally forms a hydrogen bond of 2.497(3) Å to protonated TMAO. BLYP, SAM1 and PM3 calculations have been carried out of the most stable structures. In the case of TMAO·PCP and TMAO·PCP·H 2O a good agreement between the calculated and X-ray data are obtained. FTIR spectra of the investigated complexes are consistent with the O⋯O distances. TMAO·2PCP in acetonitrile solution exists as a mixture of TMAO·PCP and solvated PCP. The observed shifts of the centre of gravity of the broad absorption in TMAO·PCP toward higher wavenumbers relative to those in complexes of pyridine N-oxides with comparable ?pK a can be explained by the resonance interaction between the N-oxide group and aromatic ring.

  11. Spatial Separation of Photochemical Oxidation and Reduction Reactions on the Surface of Ferroelectric BaTiO3

    E-print Network

    Rohrer, Gregory S.

    LETTERS Spatial Separation of Photochemical Oxidation and Reduction Reactions on the Surface reaction products are deposited on the surface in patterns that correspond to the underlying ferroelectric and holes migrate to the solid surface, where they can participate in reactions with adsorbed species. One

  12. Photoelectron spectroscopic and electronic structure studies of CH(2)O bonding and reactivity on ZnO surfaces: steps in the methanol synthesis reaction.

    PubMed

    Jones, P M; May, J A; Reitz, J B; Solomon, Edward I

    2004-05-31

    Adsorption of CH(2)O on ZnO(0001) has been investigated using XPS, NEXAFS, variable-energy photoelectron spectroscopy (PES), and density functional theory (DFT) calculations. CH(2)O is chemisorbed on the (0001) surface at 130 K. Its C1s XPS peak position at 292.7 eV and NEXAFS sigma shape resonance at 302.6 eV are consistent with an eta(1) bound surface geometry. Geometry optimized DFT calculations also indicate that CH(2)O is bound to the Zn(II) site in an eta(1) configuration through its oxygen atom. The variable-energy PES of the eta(1) bound CH(2)O/ZnO(0001) complex exhibits four valence band features at 21.2, 16.4, 13.8, and 10.7 eV below the vacuum level providing an experimental and theoretical description of this surface interaction. Annealing the ZnO(0001)/CH(2)O surface complex to 220 K decomposes the chemisorbed CH(2)O, producing formyl (291.5 eV), methoxide (290.2 eV), and formate (293.6 eV) intermediates. Thus this reaction coordinate involves the conversion of an oxygen bound formaldehyde to a carbon bound formyl species on ZnO(0001). Only formate is formed on the ZnO(100) surface. DFT is used to explore surface intermediates and the transition state in the methanol synthesis reaction (MSR). The bonding interactions of H(2), CO, CH(3)O(-), HCO(-), and trans-HCOH to the ZnO(0001) surface are elucidated using geometry optimization. H(2) was found to be heterolytically cleaved on the ZnO(0001) surface, and carbon monoxide, formyl, and methoxide are calculated to be eta(1) bound. These results are consistent with observed metal oxide surface reactivity where heterolytic bond cleavage is dominant. The oxygen atom in the bound formyl was found to be activated for attack by a proton. This results in the planar eta(1) bound trans-HCOH surface species. The transition state in the gas phase rearrangement of trans-HCOH to formaldehyde was calculated to have a barrier of 31 kcal/mol. The correlation diagram for this rearrangement in the gas phase indicates that configuration interaction at the crossing of two levels helps to lower the barrier. A transition state calculation was also performed for this rearrangement on the ZnO(0001) surface. The surface transition state geometry is significantly different than the gas phase. The surface geometry is no longer planar (23 degrees dihedral angle) and is displaced parallel to the surface. Interaction with the Zn(II) site at the crossing of surface bound CH(2)O and trans-HCOH levels further lowers the barrier to rearrangement relative to gas phase by 9 kcal/mol. The rearrangement of trans-HCOH (carbon bound) to CH(2)O (oxygen bound) on ZnO(0001) was calculated to be the overall barrier of the MSR reaction. PMID:15154797

  13. One-electron oxidation reactions of purine and pyrimidine bases in cellular DNA

    PubMed Central

    Cadet, Jean; Wagner, J. Richard; Shafirovich, Vladimir; Geacintov, Nicholas E.

    2014-01-01

    Purpose The aim of this survey is to critically review the available information on one-electron oxidation reactions of nucleobases in cellular DNA with emphasis on damage induced through the transient generation of purine and pyrimidine radical cations. Since the indirect effect of ionizing radiation mediated by hydroxyl radical is predominant in cells, efforts have been made to selectively ionize bases using suitable one-electron oxidants that consist among others of high intensity UVC laser pulses. Thus, the main oxidation product in cellular DNA was found to be 8-oxo-7,8-dihydroguanine as a result of direct bi-photonic ionization of guanine bases and indirect formation of guanine radical cations through hole transfer reactions from other base radical cations. The formation of 8-oxo-7,8-dihydroguanine and other purine and pyrimidine degradation products was rationalized in terms of the initial generation of related radical cations followed by either hydration or deprotonation reactions in agreement with mechanistic pathways inferred from detailed mechanistic studies. The guanine radical cation has been shown to be implicated in three other nucleophilic additions that give rise to DNA-protein and DNA-DNA cross-links in model systems. Evidence was recently provided for the occurrence of these three reactions in cellular DNA. Conclusion There is growing evidence that one-electron oxidation reactions of nucleobases whose mechanisms have been characterized in model studies involving aqueous solutions take place in a similar way in cells. It may also be pointed out that the above cross-linked lesions are only produced from the guanine radical cation and may be considered as diagnostic products of the direct effect of ionizing radiation. PMID:24369822

  14. Reactions of the cumyloxyl and benzyloxyl radicals with tertiary amides. Hydrogen abstraction selectivity and the role of specific substrate-radical hydrogen bonding.

    PubMed

    Salamone, Michela; Milan, Michela; DiLabio, Gino A; Bietti, Massimo

    2013-06-21

    A time-resolved kinetic study in acetonitrile and a theoretical investigation of hydrogen abstraction reactions from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) by the cumyloxyl (CumO(•)) and benzyloxyl (BnO(•)) radicals was carried out. CumO(•) reacts with both substrates by direct hydrogen abstraction. With DMF, abstraction occurs from the formyl and N-methyl C-H bonds, with the formyl being the preferred abstraction site, as indicated by the measured kH/kD ratios and by theory. With DMA, abstraction preferentially occurs from the N-methyl groups, whereas abstraction from the acetyl group represents a minor pathway, in line with the computed C-H BDEs and the kH/kD ratios. The reactions of BnO(•) with both substrates were best described by the rate-limiting formation of hydrogen-bonded prereaction complexes between the BnO(•) ?-C-H and the amide oxygen, followed by intramolecular hydrogen abstraction. This mechanism is consistent with the very large increases in reactivity measured on going from CumO(•) to BnO(•) and with the observation of kH/kD ratios close to unity in the reactions of BnO(•). Our modeling supports the different mechanisms proposed for the reactions of CumO(•) and BnO(•) and the importance of specific substrate/radical hydrogen bond interactions, moreover providing information on the hydrogen abstraction selectivity. PMID:23713448

  15. Formation of carriers in Ti-oxide thin films by substitution reactions

    SciTech Connect

    Liu, Y. S.; Lin, Y. H.; Wei, Y. S.; Liu, C. Y. [Department of Chemical and Materials Engineering, National Central University, Jhong-Li, Taiwan (China)

    2012-02-15

    Conductive Ti-oxide thin films are produced using a reactive sputtering and post-annealing process. The lowest resistivity of Ti-oxide thin films (2.30 x 10{sup -2}{Omega}-cm) can be achieved after annealing for 1 h at 400 deg. C in ambient O{sub 2}. Additionally, the Hall measurement results indicate that the carrier concentration increases during the initial 1-h annealing process before decreasing during subsequent annealing. By curve fitting the O{sub ls} core-level peaks in the x ray photoelectron spectroscopy (XPS) spectrum of the annealed Ti-oxide thin films, we found that the oxygen (O) vacancy concentration monotonically increases with annealing time, which differs from the behavior of the carrier concentration regarding annealing time. This means that the O-vacancy mechanism alone cannot explain the formation of carriers in Ti-oxide thin films. By curve-fitting core-level Ti peaks in the XPS spectrum of annealed Ti-oxide thin films, a Ti{sup 3+}-to-Ti{sup 4+} substitution reaction in the TiO{sub 2} phase of the Ti-oxide thin film after annealing plays the dominant role in the formation of conduction carriers. Instead of the O-vacancy mechanism, the Ti{sup 3+}-to-Ti{sup 4+} substitution mechanism can explain the concentration of carriers in Ti-oxide thin films following annealing.

  16. Reaction between Hydrosulfide and Iron\\/cerium (hydr)oxide: Hydrosulfide Oxidation and Iron Dissolution Kinetics

    Microsoft Academic Search

    Catalin F. Petre; Faïçal Larachi

    2006-01-01

    Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N2) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide\\u000a initial concentration (0.90–3.30 mmol\\/L), oxide initial surface area (16–143 m2\\/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by\\u000a means of capillary electrophoresis, while iron dissolution was monitored

  17. Thalassaemic erythrocytes: cellular suicide arising from iron and glutathione-dependent oxidation reactions?

    PubMed

    Scott, M D; Eaton, J W

    1995-12-01

    Both beta-thalassaemic red blood cells and normal red blood cells (RBC) artificially loaded with unpaired alpha-haemoglobin chains exhibit increased amounts of membrane-bound haem and iron. In the model beta-thalassaemic RBC the amount of free haem and iron was as much as 20 times that which could have been contributed by the entrapped alpha-haemoglobin chains alone. This excess haem/iron arises from destabilization of haemoglobin via reactions between ferric iron (Fe3+), initially contributed by the unpaired alpha chains, and cytoplasmic constituents, primarily reduced glutathione (GSH). Indeed, in the presence of Fe3+ (100 microM) addition of even small amounts of GSH (0.5 mM) to dilute RBC haemolysates (0.15 mg haemoglobin/dl) greatly accelerated methaemoglobin formation. In contrast, lysates from GSH-depleted RBC demonstrated a significantly reduced rate of iron-mediated haemoglobin oxidation which was reversible by addition of GSH. The initiation, and subsequent propagation, of Fe(3+)-mediated haemoglobin oxidation was significantly inhibited by iron chelators. Finally, Fe(3+)-driven haemoglobin oxidation was synergized by low amounts of H2O2, an oxidant spontaneously generated in thalassaemic RBC. To summarize, the release of small amounts of free iron from unpaired alpha-haemoglobin chains in the beta-thalassaemic RBC can initiate self-amplifying redox reactions which simultaneously deplete cellular reducing potential (e.g. GSH), oxidize additional haemoglobin, and accelerate the red cell destruction. PMID:8547123

  18. Oxidative Degradation of Nadic-End-Capped Polyimides. 2; Evidence for Reactions Occurring at High Temperatures

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Johnston, J. Christopher; Cavano, Paul J.; Frimer, Aryeh A.

    1997-01-01

    The oxidative degradation of PMR (for polymerization of monomeric reactants) polyimides at elevated temperatures was followed by cross-polarized magic angle spinning (Cp-MAS) NMR. C-13 labeling of selected sites in the polymers allowed for direct observation of the transformations arising from oxidation processes. As opposed to model compound studies, the reactions were followed directly in the polymer. The labeling experiments confirm the previously reported oxidation of the methylene carbon to ketone in the methylenedianiline portion of the polymer chain. They also show the formation of two other oxidized species, acid and ester, from this same carbon. In addition, the technique provides the first evidence of the kind of degradation reactions that are occurring in the nadic end caps. Several PMR formulations containing moieties determined to be present after oxidation, as suggested by the labeling study, were synthesized. Weight loss, FTIR, and natural abundance NMR of these derivatives were followed during aging. In this way, weight loss could be related to the observed transformations.

  19. Nitric oxide-forming reactions of the water-soluble nitric oxide spin-trapping agent, MGD.

    PubMed

    Tsuchiya, K; Jiang, J J; Yoshizumi, M; Tamaki, T; Houchi, H; Minakuchi, K; Fukuzawa, K; Mason, R P

    1999-08-01

    The objective of this study was to elucidate the nitric oxide-forming reactions of the iron-N-methyl-D-glucamine dithiocarbamate (Fe-MGD) complex from the nitrogen-containing compound hydroxyurea. The Fe2+(MGD)2 complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. The reaction of Fe2+(MGD)2 with NO yields the resultant NO-Fe2+(DETC)2 complex, which has a characteristic triplet EPR signal. It is widely believed that only NO reacts with Fe2+(MGD)2 to form the NO-Fe2+(MGD)2 complex. In this report, the mechanism leading to the formation of NO-Fe2+(MGD)2 was investigated using oxygen-uptake studies in conjunction with the EPR spin-trapping technique. We found that the air oxidation of Fe2+(MGD)2 complex results in the formation of the Fe3+(MGD)3 complex, presumably concomitantly with superoxide (O3*-). Dismutation of superoxide forms hydrogen peroxide, which can subsequently reduce Fe3+(MGD)3 back to Fe2+(MGD)2. The addition of NO to the Fe3+(MGD)3 complex resulted in the formation of the NO-Fe2+(MGD)2 complex. Hydroxyurea is not considered to be a spontaneous NO donor, but has to be oxidized in order to form NO. We present data showing that in the presence of oxygen, Fe2+(MGD)2 can oxidize hydroxyurea to yield the stable NO-Fe2+(MGD)2 complex. These results imply that hydroxyurea can be oxidized by reactive oxygen species that are formed from the air oxidation of the Fe2+(MGD)2 complex. Formation of the NO-Fe2+(MGD)2 complex in this case could erroneously be interpreted as spontaneous formation of NO from hydroxyurea. The chemistry of the Fe2+(MGD)2 complexes in aerobic conditions must be taken into account in order to avoid erroneous conclusions. In addition, the use of these complexes may contribute to the overall oxidative stress of the system under investigation. PMID:10468208

  20. Direct gas-phase epoxidation of propylene to propylene oxide through radical reactions: A theoretical study

    NASA Astrophysics Data System (ADS)

    Kizilkaya, Ali Can; Fellah, Mehmet Ferdi; Onal, Isik

    2010-03-01

    The gas-phase radical chain reactions which utilize O 2 as the oxidant to produce propylene oxide (PO) are investigated through theoretical calculations. The transition states and energy profiles were obtained for each path. The rate constants were also calculated. The energetics for the competing pathways indicate that PO can be formed selectively due to its relatively low activation barrier (9.3 kcal/mol) which is in a good agreement with the experimental value (11 kcal/mol) of gas-phase propylene epoxidation. The formation of the acrolein and combustion products have relatively high activation barriers and are not favored. These results also support the recent experimental findings.

  1. Partially Fluorinated Metal Oxide Catalysts for a Friedel–Crafts-type Reaction of Dichlorofluoromethane with Tetrafluoroethylene

    Microsoft Academic Search

    T. Tanuma; H. Okamoto; K. Ohnishi; S. Morikawa; T. Suzuki

    2010-01-01

    Partially fluorinated metal oxides were studied for manufacturing dichloropentafluoropropanes (CF3CF2CHCl2 and CCl2FCF2CHClF) and controlling the selectivity of their isomers. When activated by elemental fluorine or dichlorodifluoromethane,\\u000a metal oxides such as TiO2, HfO2, Al2O3, and ZrO2, exhibited catalytic activity in the reaction of dichlorofluoromethane with tetrafluoroethylene. In the case of the TiO2 catalyst, the more fluorine incorporated, the higher the selectivity

  2. Low temperature synthesis of LnOF rare-earth oxyfluorides through reaction of the oxides with PTFE

    SciTech Connect

    Dutton, S.E., E-mail: sdutton@princeton.edu [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States); Hirai, D.; Cava, R.J. [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States)] [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States)

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer Low temperature synthesis of LnOF rare-earth oxyfluorides from Ln{sub 2}O{sub 3} and PTFE (CF{sub 2}). Black-Right-Pointing-Pointer Rhombohedral LnOF is the major phase and forms as nanocrystals, 29-103 nm. Black-Right-Pointing-Pointer Expected lanthanide contraction observed in lattice parameters and bond lengths. Black-Right-Pointing-Pointer TbOF orders antiferromagnetically at 10 K and has a metamagnetic transition at 1.8 T. Black-Right-Pointing-Pointer GdOF orders antiferromagnetically at 5 K, other LnOF are paramagnetic. -- Abstract: A low temperature solid-state synthesis route, employing polytetrafluoroethylene (PTFE) and the rare-earth oxides, for the formation of the LnOF rare-earth oxyfluorides (Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er), is reported. With the exception of LaOF, which forms in a tetragonal variant, rhomobohedral LnOF is found to be the major product of the reaction. In the case of PrOF, a transition from the rhombohedral to the cubic fluorite phase is observed on heating in air to 500 Degree-Sign C. X-ray diffraction shows the expected lanthanide contraction in the lattice parameters and bond lengths. Magnetic susceptibility measurements show antiferromagnetic-like ordering in TbOF, T{sub m} = 10 K, with a metamagnetic transition at a field {mu}{sub 0}H{sub t} = 1.8 T at 2 K. An antiferromagnetic transition, T{sub N} = 4 K, is observed in GdOF. Paramagnetic behavior is observed above 2 K in PrOF, NdOF, DyOF, HoOF and ErOF. The magnetic susceptibility of EuOF is characteristic of Van Vleck paramagnetism.

  3. Stepwise ligand transformations through [2+2] photodimerization and hydrothermal in situ oxidation reactions.

    PubMed

    Liu, Dong; Lang, Jian-Ping; Abrahams, Brendan F

    2013-04-01

    The SCSC transformation of a 1D polymer [Cd(1,3-bdc)(4-spy)2]n produced a 2D polymer [Cd(1,3-bdc)(4-spy)(HT-ppcb)0.5]n through the [2+2] photodimerization reaction. Hydrothermal reactions of HT-ppcb with CdCl2, 1,3-H2bdc and H2O2 afforded another 2D polymer {[Cd(H2O)(1,3-bdc)(bpbpf)]·H2O}n in which HT-ppcb underwent in situ oxidation to form a unique furan-based ligand bpbpf. PMID:23435695

  4. Effect of temperature towards lipid oxidation and non-enzymatic browning reactions in krill oil upon storage.

    PubMed

    Lu, F S H; Bruheim, I; Haugsgjerd, B O; Jacobsen, C

    2014-08-15

    The main objective of this study was to investigate the effect of temperature towards lipid oxidation and non-enzymatic browning reactions in krill oil upon storage. Krill oil was incubated at two different temperatures (20 and 40 °C) for 28 or 42 days. The oxidative stability of krill oil was assessed by peroxide value and anisidine value, measurement of lipid derived volatiles, lipid classes and antioxidants. The non-enzymatic browning reactions were assessed through the measurement of pyrroles, free amino acids content and Strecker-derived volatiles. The increase of incubation temperature firstly increased the lipid oxidation in krill oil and subsequently the non-enzymatic browning reactions. The occurrence of these reactions was most likely due to the reaction between ?-dicarbonyl or carbonyl compounds with amino acids or ammonia. In addition to tocopherol and astaxanthin esters, the formation of pyrroles might help to protect the krill oil against lipid oxidation. PMID:24679797

  5. Oxidative cyclization reaction of 2-aryl-substituted cinnamates to form phenanthrene carboxylates by using MoCl5.

    PubMed

    Wehming, Kathrin; Schubert, Moritz; Schnakenburg, Gregor; Waldvogel, Siegfried R

    2014-09-22

    The oxidative cyclization reaction of 2-aryl cinnamates and derivatives thereof can be easily performed with MoCl5 as the oxidant. This powerful reagent allows oxidative coupling reactions for which other reagents fail. The best results are obtained when the 2-phenyl substituent of the cinnamate is equipped with two methoxy groups. Even iodo moieties in the bay region of phenanthrene are tolerated under the reaction conditions. If naphthalene moieties are involved, a rearrangement of the skeleton occurs, providing an elegant route to highly functionalized angular arenes. The cyclization is demonstrated for 15 example substrates with isolated yields of up to 99?% for the phenanthrene derivative. The broad scope of the reaction underlines the usefulness of MoCl5 and MoCl5 /TiCl4 in the oxidative coupling reaction. PMID:25043751

  6. Diffuse reflectance Fourier transform infrared spectroscopic study of chemical bonding and hydrothermal stability of an amino silane on metal oxide surfaces. Technical report

    Microsoft Academic Search

    S. Naviroj; J. L. Koenig; H. Ishida

    1982-01-01

    Fourier transform infrared spectroscopy is used to study the metal oxide\\/silane interface. Structures of gamma-aminopropyldimethylethoxysilane (gamma-APDMES) coupling agent on the surface of metal oxide powders are proposed. The structure depends on the surface characteristics of the substrate. The amine group of the silane molecule forms a hydrogen bond with the silica surface. The enhanced intensity of the amine band around

  7. Copper-catalyzed aerobic oxidative amination of C(sp(3))-H bonds: synthesis of imidazo[1,5-a]pyridines.

    PubMed

    Chandra Mohan, Darapaneni; Nageswara Rao, Sadu; Ravi, Chitrakar; Adimurthy, Subbarayappa

    2015-05-28

    Copper-catalyzed synthesis of imidazo[1,5-a]pyridine-1-carboxylates through oxidative amination of C(sp(3))-H bonds under mild aerobic conditions with broad substrate scope is described. Use of naturally abundant air as the sole oxidant was found to be efficient and selective. The present protocol is also applicable for direct synthesis of functionalized imidazo[1,5-a]pyridines from amino acid derivatives. PMID:25917053

  8. Direct ?-acyloxylation of enamines via PhIO-mediated intermolecular oxidative C-O bond formation and its application to the synthesis of oxazoles.

    PubMed

    Liu, Xin; Cheng, Ran; Zhao, Feifei; Zhang-Negrerie, Daisy; Du, Yunfei; Zhao, Kang

    2012-11-01

    A direct ?-acyloxylation of enamine compounds has been achieved by using iodosobenzene (PhIO) as an oxidant to realize the intermolecular oxidative C(sp(2))-O bond formation between enamines and various carboxylic acids, including N-protected amino acids. The transformation tolerates a wide range of functional groups and furnishes a variety of ?-acyloxy enamines that can be conveniently converted to oxazole compounds via cyclodehydration. PMID:23098266

  9. Synthesis and Oxidation Behavior of Platinum-Enriched ?+?' Bond Coatings on Ni-Based Superalloys

    SciTech Connect

    Zhang, Ying [Tennessee Technological University; Ballard, D A [Tennessee Technological University; Stacy, J P [Tennessee Technological University; Pint, Bruce A [ORNL; Haynes, James A [ORNL

    2006-01-01

    Simple Pt-enriched {gamma}+{gamma}{prime} coatings were synthesized on Rene 142 and Rene N5 Ni-based superalloys by electroplating a thin layer of Pt followed by a diffusion treatment at 1150-1175 C. The Al content in the resulting {gamma}+{gamma}{prime} coating was in the range of 16-19 at.% on superalloys with 13-14 at.% Al. After oxidation testing, alumina scale adherence to these {gamma}+{gamma}{prime} coatings was not as uniform as to the {beta}-(Ni,Pt)Al coatings on the same superalloy substrates. To better understand the effect of Al, Pt and Hf concentrations on coating oxidation resistance, a number of Ni-Pt-Al cast alloys with {gamma}+{gamma}{prime} or {beta} phase were cyclically oxidized at 1100 C. The Hf-containing {gamma}+{gamma}{prime} alloys with 22 at.% Al and 10-30 at.% Pt exhibited similar oxidation resistance to the {beta} alloys with 50 at.% Al. An initial effort was made to increase the Al content in the Pt-enriched {gamma}+{gamma}{prime} coatings by introducing a short-term aluminizing process via chemical vapor deposition or pack cementation. However, too much Al was deposited, leading to the formation of {beta} or martensitic phase on the coating surface.

  10. High temperature thermoelectric characterization of III-V semiconductor thin films by oxide bonding

    E-print Network

    Bowers, John

    material characterization of semiconductor thin films for thermoelectric power generation, photovoltaicAs:InGa(Al)As materials have been used to build thermoelectric power generator modules to generate output power densityPage 1 High temperature thermoelectric characterization of III-V semiconductor thin films by oxide

  11. Hydrogen bonding between the QB site ubisemiquinone and Ser-L223 in the bacterial reaction centre – a combined spectroscopic and computational perspective^

    PubMed Central

    Martin, Erik; Baldansuren, Amgalanbaatar; Lin, Tzu-Jen; Samoilova, Rimma I.; Wraight, Colin A.; Dikanov, Sergei A.; O’Malley, Patrick J.

    2012-01-01

    In the QB site of the Rba. sphaeroides photosynthetic reaction centre the donation of a hydrogen bond from the hydroxyl group of Ser-L223 to the ubisemiquinone formed after the first flash is debatable. In this study we use a combination of spectroscopy and quantum mechanics/molecular mechanics (QM/MM) calculations to comprehensively explore this topic. We show that ENDOR, ESEEM and HYSCORE spectroscopic differences between the mutant L223SA and the wild type sample (WT) are negligible, indicating only minor perturbations in the ubisemiquinone spin density for the mutant sample. Qualitatively this suggests that a strong hydrogen bond does not exist in the WT between the Ser-L223 hydroxyl group and the semiquinone O1 atom, as removal of this hydrogen bond in the mutant should cause a significant redistribution of spin density in the semiquinone. We show quantitatively, using QM/MM calculations, that a WT model in which the Ser-L223 hydroxyl group is rotated to prevent hydrogen bond formation with the O1 atom of the semiquinone predicts negligible change for the L223SA mutant. This, together with the better agreement between key QM/MM calculated and experimental hyperfine couplings for the non-hydrogen bonded model, leads us to conclude that no strong hydrogen bond is formed between the Ser-L223 hydroxyl group and the semiquinone O1 atom after the first flash. The implications of this finding for quinone reduction in photosynthetic reaction centres are discussed. PMID:23016832

  12. Guanine Oxidation in Double-stranded DNA by MnTMPyP/KHSO5: At Least Three Independent Reaction Pathways

    PubMed Central

    Lapi, Andrea; Pratviel, Geneviève

    2001-01-01

    In order to better define the mechanism and the products of guanine oxidation within DNA, we investigated the details of the mechanism of guanine oxidation by a metalloporphyrin, Mn-TMPyP, associated to KHSO5 on oligonucleotides. We found that the three major products of guanine oxidation are formed by independent reaction routes. The oxidized guanidinohydantoin (1) and the proposed spiro compound 3 derivatives are not precursors of imidazolone lesion (Iz). These guanine lesions as well as their degradation products, may account for non-detected guanine oxidation products on oxidatively damaged DNA. PMID:18475975

  13. Initial reactions in the anaerobic oxidation of toluene and m-xylene by denitrifying bacteria

    SciTech Connect

    Seyfried, B.; Glod, G.; Schocher, R.; Tschech, A.; Zeyer, J. [Institute of Terrestrial Ecology, Schlieren (Switzerland)

    1994-11-01

    Anaerobic degradation of toluene has been observed under different redox conditions, and several pure cultures of bacteria which grow anaerobically with toluene have been isolated. Both denitrifying Pseufomonas sp. strain T and denitrifying Pseudomonas sp. strain K172 grow anaerobically with toluene, benzaldehyde, and benzoate, but only strain K172 also grows with benzlyalchohol. Carboxylation of toluene to yield phenylacetate or methylbenzoate does not occur in strains K172 and T. Utilization of benzylalcohol might be considered a prerequisite for initial activation of toluene via methyl group oxidation. This paper describes studies examining the initial reaction in anaerobic toluene degradation by strains T and K172. The initial reaction in anaerobic degradation of m-xylene by strain T. was also examined. The results indicate that initial direct oxidation of the methyl groups of toluene and m-xylene occurs. 21 refs., 3 figs., 3 tabs.

  14. The Many Paths of Hypervalent Iodine Reactions

    E-print Network

    Stoltz, Brian M.

    The Many Paths of Hypervalent Iodine Reactions Ryan McFadden Stoltz Literature Group Meeting June! In Outline I. What is Hypervalency? A. The Martin-Arduengo Notation B. Bonding in Hypervalent Iodine Compounds C. A Brief History of IBX and DMP II. Oxidation Chemistry of Hypervalent Iodine A. Oxidations

  15. Bronsted-Evans-Polanyi 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, Rajeev S.; Broadbelt, Linda J; Curtiss, Larry A

    2011-04-27

    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 Brønsted-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.

  16. 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. (Center for Nanoscale Materials); ( MSD); (Northwestern Univ.)

    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.

  17. Theoretical study of the Diels-Alder reaction of C{sub 60}. Transition-state structures and reactivities of C-C bonds

    SciTech Connect

    Chikama, Akirou; Fueno, Hiroyuki; Fujimoto, Hiroshi [Kyoto Univ. (Japan)

    1995-05-25

    Chemical interactions between large species are not easy to look at by means of accurate MO calculations and by the usual orbital interaction scheme based on perturbation theory. By transforming the MO`s of the reagent and reactant parts into paired interacting orbitals, we have studied the Diels-Alder reaction of C{sub 60} with butadiene. The interaction involved in this system has been demonstrated to be almost completely localized on a C-C bond at the transition state, bearing a close resemblance to the orbital interactions between dienes and small dienophiles. The addition of butadiene to a C-C bond of C{sub 60} that is common to two annulated six-membered rings has been calculated to have a much lower activation energy than the addition to a C-C bond shared by a six-membered ring and a five-membered ring. The difference in reactivities has been shown to be related qualitatively to the local electron-donating potential and the electron-accepting capacitance of those bonds. The double addition of butadiene has been suggested to be not highly regioselective, both from these local reactivity scales and from the calculated heat of reactions. The possibility of C{sub 60} serving as a diene has also been studied. 98 refs., 6 figs., 9 tabs.

  18. Oxidation of elemental mercury by chlorine: Gas phase, Surface,and Photo-induced reaction pathways

    SciTech Connect

    Yan, Nai-Qiang; Liu, Shou-Heng; Chang, Shih-Ger

    2004-10-22

    Accurate oxidation rate constants of mercury gas are needed for determining its dispersion and lifetime in the atmosphere. They would also help in developing a technology for the control of mercury emissions from coal-fired power plants. However, it is difficult to establish the accurate rate constants primarily due to the fact that mercury easily adsorbs on solid surface and its reactions can be catalyzed by the surface. We have demonstrated a procedure that allows the determination of gas phase, surface-induced, and photo-induced contributions in the kinetic study of the oxidation of mercury by chlorine gas. The kinetics was studied using reactors with various surface to volume ratios. The effect of the surface and the photo irradiation on the reaction was taken into consideration. The pressure dependent study revealed that the gas phase oxidation was a three-body collision process. The third order rate constant was determined to be 7.5({+-}0.2) x 10{sup -39} mL{sup 2} molecules{sup -2}s{sup -1} with N{sub 2} as the third body at 297 {+-} 1 K. The surface induced reaction on quartz window was second order and the rate constant was 2.7 x 10{sup -17} mL{sup 2} molecules{sup -1} cm{sup -2} sec. Meanwhile, the 253.7 nm photon employed for mercury detection was found to accelerate the reaction. The utilization efficiency of 253.7 nm photon for Hg{sup 0} oxidation was 6.7 x 10{sup -4} molecules photon{sup -1} under the conditions employed in this study.

  19. Calorimetric study of vanadium pentoxide catalysts used in the reaction of ethane oxidative dehydrogenation

    Microsoft Academic Search

    J. Le Bars; J. C. Vedrine; A. Auroux; B. Pommier; G. M. Pajonk

    1992-01-01

    Vanadium pentoxide catalysts have been studied in the partial oxidation reaction of ethane in the 723-843 K temperature range. The relationship between the acid-base properties and the catalytic behavior was investigated. The number and character of acidic sites of VâOâ catalysts were determined by studying the adsorption of a basic molecule using microcalorimetry. The reducibility level and the evolution of

  20. Structures and reaction rates of the gaseous oxidation of SO2 by an O-

    E-print Network

    Meskhidze, Nicholas

    Structures and reaction rates of the gaseous oxidation of SO2 by an O- 3 (H2O)0-5 cluster - an ab initio study N. Bork, T. Kurt´en, M.B. Enghoff, J.O.P. Pedersen, K.V. Mikkelsen, and H. Svensmark shown in Fig. 7 in the main article. Sulfur (yellow), oxygen (red), hydrogen (white). #12;Table SI-2: T1

  1. Mechanism of the Heck reaction: nature of oxidative addition and alkene insertion 

    E-print Network

    Evans, Anthony Steven

    2004-11-15

    molecules differing only by isotopic substitution at a particular atom (isotopomers). The zero point energies (ZPE) of isotopomers will necessarily differ. ZPEs are a quantum mechanical value representing the lowest vibration state of a normal mode... fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2004 Major Subject: Chemistry MECHANISM OF THE HECK REACTION: NATURE OF OXIDATIVE ADDITION AND ALKENE INSERTION A Thesis...

  2. Visible-Light-Driven Oxidation of Primary C–H Bonds over CdS with Dual Co-catalysts Graphene and TiO2

    PubMed Central

    Yang, Min-Quan; Zhang, Yanhui; Zhang, Nan; Tang, Zi-Rong; Xu, Yi-Jun

    2013-01-01

    Selective activation of primary C–H bonds for fine chemicals synthesis is of crucial importance for the sustainable exploitation of available feedstocks. Here, we report a viable strategy to synthesize ternary GR-CdS-TiO2 composites with an intimate spatial integration and sheet-like structure, which is afforded by assembling two co-catalysts, graphene and TiO2, into the semiconductor CdS matrix with specific morphology as a visible light harvester. The GR-CdS-TiO2 composites are able to serve as a highly selective visible-light-driven photocatalyst for oxidation of saturated primary C–H bonds using benign oxygen as oxidant under ambient conditions. This work demonstrates a wide, promising scope of adopting co-catalyst strategy to design more efficient semiconductor-based photocatalyst toward selective activation of C–H bonds using solar light and molecular oxygen. PMID:24264835

  3. Stable platinum nanoclusters on genomic DNA-graphene oxide with a high oxygen reduction reaction activity.

    PubMed

    Tiwari, Jitendra N; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N; Kemp, K Christian; Le, Nhien H; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S

    2013-01-01

    Nanosize platinum clusters with small diameters of 2-4?nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2?nm). Here we report the synthesis of platinum clusters (diameter ?1.4?nm) deposited on genomic double-stranded DNA-graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA-graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA-graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456

  4. The synthetic substance hypoxanthine 3-N-oxide elicits alarm reactions in zebrafish (Danio rerio)

    PubMed Central

    Parra, Kevin V.; Adrian, James C.; Gerlai, Robert

    2009-01-01

    Zebrafish, one of the preferred study species of geneticists, is gaining increasing popularity in behavioral neuroscience. This small and prolific species may be an excellent tool with which the biological mechanisms of vertebrate brain function and behavior are investigated. Zebrafish has been proposed as a model organism in the analysis of fear responses and human anxiety disorders. Species-specific cues signaling the presence of predators have been successfully utilized in such research. Zebrafish has been shown to respond to its natural alarm substance with species-typical fear reactions. However, the extraction of this alarm substance and ascertaining its consistent dosing has been problematic. A synthetic substance with a known chemical identity and molecular weight would allow precise dosing and experimental control. Previously, the chemical component, hypoxanthine 3-N-oxide, common to several fish alarm substances has been identified and has been shown to elicit alarm reactions in fish species belonging to the Osteriophysan superorder. In the current study we investigate the effect of hypoxanthine 3-N-oxide by exposing zebrafish to three different concentrations of this synthetic substance. Our results show that the substance efficaciously induces species-typical fear reactions increasing the number of erratic movement episodes and jumps in zebrafish. We discuss the translational relevance of our findings and conclude that hypoxanthine 3-N-oxide will have utility to elicit fear responses in the laboratory in a precisely controlled manner in zebrafish. PMID:19583985

  5. Stable platinum nanoclusters on genomic DNA–graphene oxide with a high oxygen reduction reaction activity

    PubMed Central

    Tiwari, Jitendra N.; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N.; Kemp, K. Christian; Le, Nhien H.; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S.

    2013-01-01

    Nanosize platinum clusters with small diameters of 2–4?nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2?nm). Here we report the synthesis of platinum clusters (diameter ?1.4?nm) deposited on genomic double-stranded DNA–graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA–graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA–graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456

  6. Construction materials for reaction unit in the liquid-phase synthesis of propylene oxide

    SciTech Connect

    Zaritskii, V.I.D.

    1987-09-01

    The main components of the reaction medium in equipment for the synthesis of propylene oxide by liquid-phase oxidation of gaseous propylene with peracetic acid are propylene, peracetic acid, ethyl acetate, acetic acid, propylene oxide, carbon dioxide, oxygen, methane, and propylene glycol acetates. The operating conditions of the equipment and content of the main components of the medium are shown. Results are given for the investigation of the corrosion behavior of 12Kh18N10T, 10Kh17N13M2T, 08Kh22N6T, and 08Kh21N6M2T steels, AD0 and AD1 aluminum, and VT1-0 titanium. VSt3 carbon steel was tested for comparison.

  7. Iron Oxides from Volcanic Soils as Potential Catalysts in the Water Gas Shift Reaction

    SciTech Connect

    Pizarro, C.; Escudey, M.; Moya, S.A. [Facultad de Quimica y Biologia, USACH, Av. L. B. O'Higgins 3363, Santiago 7254758 (Chile); Fabris, J.D. [Departamento de Quimica, ICEx-UFMG, Pampulha, 31270-901 Belo Horizonte, MG (Brazil)

    2005-04-26

    This study was focused on changes of the iron oxide mineralogy with temperature of two Chilean soils (Andisol and Ultisol) derived from volcanic materials and their use as iron-based catalysts in the water gas shift reaction (WGSR). Ultisol materials produced about twice as much hydrogen than did those from Andisol upon WGSR, but in both cases hydrogen yielding increased as the heating temperature of the soil materials increased from 124 deg. C to 500 deg. C. The room temperature Moessbauer spectra showed an increase of the relative proportion of the magnetically ordered components as temperature increased. Higher heating temperature produced a negative effect on the catalytic activity, whereas the organic matter destruction led to a positive effect, due to an increasing exposition of the iron oxide surfaces; heating the soil sample at 600 deg. C induced changes on the iron oxide mineralogy with a significant decrease of the catalytic activity.

  8. Destabilization of the hydrogen-bond structure of water by the osmolyte trimethylamine N-oxide

    Microsoft Academic Search

    Y. L. A. Rezus; H. J. Bakker

    2009-01-01

    We use femtosecond mid-infrared pump?probe spectroscopy to investigate the effects of the osmolyte trimethylamine N-oxide (TMAO) on the structural dynamics of water. As a comparison, we also investigate the effects of other amphiphilic molecules: tetramethylurea (TMU), urea, proline, and N-methylacetamide (NMA). Our measurements show that TMAO has the unique property of increasing the orientational mobility of part of the water

  9. Kinetics and thermodynamics of atmospherically relevant aqueous phase reactions of ?-pinene oxide.

    PubMed

    Bleier, Dylan B; Elrod, Matthew J

    2013-05-23

    Recent work has demonstrated that isoprene-derived epoxide intermediates are responsible for a wide variety of chemical species found in ambient secondary organic aerosol (SOA). Since the second most abundant biogenic hydrocarbon, ?-pinene, is also known to form an epoxide intermediate, nuclear magnetic resonance techniques were used to study products, kinetics, and equilibria of the aqueous phase reactions of that epoxide, ?-pinene oxide. The present results indicate that ?-pinene oxide will react very quickly with aqueous atmospheric particles, even under low acidity conditions. Depending on the acid concentration of the aqueous solutions, a number of new products are observed from the reaction of ?-pinene oxide, some of which are expected to partition back to the gas phase. In contrast to some previous results, no long-lived organosulfate or organonitrate species are observed, and no species which retain the ?-pinene bicyclic carbon backbone are observed. Rather, the overall product distribution can be explained by various rearrangements of the initial carbocation intermediate formed in the ring opening of ?-pinene oxide, all of which can be rationalized by the thermodynamically driven relief of the bicyclic ring strain in the ?-pinene carbon backbone. PMID:23614856

  10. Site-selective surface reactions: nitric oxide reduction on Mo(110).

    PubMed

    Queeney, K; Friend, C M

    2000-11-01

    The catalytic reduction of NO(x) compounds formed in combustion processes is a critical factor in maintaining a clean environment. The introduction of the "catalytic converter" has been extremely effective in reducing these pollutants in automobile exhaust over the last two decades. Nevertheless, new environmental regulations have necessitated the development of processes that operate over a wider range of conditions and that are more efficient, so that NOx emissions can be reduced further. The need for new catalysts and processes has motivated a considerable number of studies of NO reduction using metal oxides as catalysts. In order to better understand the mechanisms for NO reduction on oxides, we have systematically studied the reactions of NO on thin-film oxides grown on Mo(110). By using a thin-film oxide, we are able to change the type of coordination sites that are available for NO binding and to use surface-sensitive spectroscopies to identify intermediates on the surface. We specifically explore the role of low-temperature NO coupling to a dinitrosyl species in our work and contrast this reaction to the higher temperature process, NO dissociation followed by nitrogen atom coupling. PMID:23696302

  11. Insight into the Mechanism of Graphene Oxide Degradation via the Photo-Fenton Reaction

    PubMed Central

    2015-01-01

    Graphene represents an attractive two-dimensional carbon-based nanomaterial that holds great promise for applications such as electronics, batteries, sensors, and composite materials. Recent work has demonstrated that carbon-based nanomaterials are degradable/biodegradable, but little work has been expended to identify products formed during the degradation process. As these products may have toxicological implications that could leach into the environment or the human body, insight into the mechanism and structural elucidation remain important as carbon-based nanomaterials become commercialized. We provide insight into a potential mechanism of graphene oxide degradation via the photo-Fenton reaction. We have determined that after 1 day of treatment intermediate oxidation products (with MW 150–1000 Da) were generated. Upon longer reaction times (i.e., days 2 and 3), these products were no longer present in high abundance, and the system was dominated by graphene quantum dots (GQDs). On the basis of FTIR, MS, and NMR data, potential structures for these oxidation products, which consist of oxidized polycyclic aromatic hydrocarbons, are proposed. PMID:24860637

  12. Detection of intermediates in the oxidative half-reaction of the FAD-dependent thymidylate synthase from Thermotoga maritima: carbon transfer without covalent pyrimidine activation.

    PubMed

    Conrad, John A; Ortiz-Maldonado, Mariliz; Hoppe, Samuel W; Palfey, Bruce A

    2014-08-19

    Thymidylate, a vital DNA precursor, is synthesized by thymidylate synthases (TSs). A second class of TSs, encoded by the thyX gene, is found in bacteria and a few other microbes and is especially widespread in anaerobes. TS encoded by thyX requires a flavin adenine dinucleotide prosthetic group for activity. In the oxidative half-reaction, the reduced flavin is oxidized by 2'-deoxyuridine 5'-monophosphate (dUMP) and (6R)-N5,N10-methylene-5,6,7,8-tetrahydrofolate (CH2THF), synthesizing 2'-deoxythymidine 5'-monophosphate (dTMP). dTMP synthesis is a complex process, requiring the enzyme to promote carbon transfer, probably by increasing the nucleophilicity of dUMP and the electrophilicity of CH2THF, and reduction of the transferred carbon. The mechanism of the oxidative half-reaction was investigated by transient kinetics. Two intermediates were detected, the first by a change in the flavin absorbance spectrum in stopped-flow experiments and the second by the transient disappearance of deoxynucleotide in acid quenching experiments. The effects of substrate analogues and the behavior of mutated enzymes on these reactions lead to the conclusion that activation of dUMP does not occur through a Michael-like addition, the mechanism for the activation analogous with that of the flavin-independent TS. Rather, we propose that the nucleophilicity of dUMP is enhanced by electrostatic polarization upon binding to the active site. This conclusion rationalizes many of our observations, for instance, the markedly slower reactions when two arginine residues that hydrogen bond with the uracil moiety of dUMP were mutated to alanine. The activation of dUMP by polarization is consistent with the majority of the published data on ThyX and provides a testable mechanistic hypothesis. PMID:25068636

  13. An Iodine-Catalyzed Hofmann-Löffler Reaction.

    PubMed

    Martínez, Claudio; Muñiz, Kilian

    2015-07-01

    Iodine reagents have been identified as economically and ecologically benign alternatives to transition metals, although their application as molecular catalysts in challenging C?H oxidation reactions has remained elusive. An attractive iodine oxidation catalysis is now shown to promote the convenient conversion of carbon-hydrogen bonds into carbon-nitrogen bonds with unprecedented complete selectivity. The reaction proceeds by two interlocked catalytic cycles comprising a radical chain reaction, which is initiated by visible light as energy source. This unorthodox synthetic strategy for the direct oxidative amination of alkyl groups has no biosynthetic precedence and provides an efficient and straightforward access to a general class of saturated nitrogenated heterocycles. PMID:26016458

  14. Enhanced methanol electro-oxidation reaction on Pt-CoOx/MWCNTs hybrid electro-catalyst

    NASA Astrophysics Data System (ADS)

    Nouralishahi, Amideddin; Rashidi, Ali Morad; Mortazavi, Yadollah; Khodadadi, Abbas Ali; Choolaei, Mohammadmehdi

    2015-04-01

    The electro-catalytic behavior of Pt-CoOx/MWCNTs in methanol electro-oxidation reaction (MOR) is investigated and compared to that of Pt/MWCNTs. The electro-catalysts were synthesized by an impregnation method using NaBH4 as the reducing agent. The morphological and physical characteristics of samples are examined by XRD, TEM, ICP and EDS techniques. In the presence of CoOx, Pt nanoparticles were highly distributed on the support with an average particle size of 2 nm, an obvious decrease from 5.1 nm for Pt/MWCNTs. Cyclic voltammetry, CO-stripping, Chronoamperometry, and electrochemical impedance spectroscopy (EIS) measurements are used to study the electrochemical behavior of the electro-catalysts. The results revealed a considerable enhancement in the oxidation kinetics of COads on Pt active sites by the participation of CoOx. Compared to Pt/MWCNTs, Pt-CoOx/MWCNTs sample has a larger electrochemical active surface area (ECSA) and higher electro-catalytic activity and stability toward methanol electro-oxidation. According to the results of cyclic voltammetry, the forward anodic peak current density enhances more than 89% at the optimum atomic ratio of Pt:Co = 2:1. Furthermore, inclusion of cobalt oxide species causes the onset potential of methanol electro-oxidation reaction to shift 84 mV to negative values compared to that on Pt/MWCNTs. Based on EIS data, dehydrogenation of methanol is the rate-determining step of MOR on both Pt/MWCNTs and Pt-CoOx/MWCNTs, at small overpotentials. However, at higher overpotentials, the oxidation of adsorbed oxygen-containing groups controls the total rate of MOR process.

  15. Multiscale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Reactions.

    PubMed

    Burke, Michael P; Goldsmith, C Franklin; Klippenstein, Stephen J; Welz, Oliver; Huang, Haifeng; Antonov, Ivan O; Savee, John D; Osborn, David L; Zádor, Judit; Taatjes, Craig A; Sheps, Leonid

    2015-07-16

    The present paper describes further development of the multiscale informatics approach to kinetic model formulation of Burke et al. (Burke, M. P.; Klippenstein, S. J.; Harding, L. B. Proc. Combust. Inst. 2013, 34, 547-555) that directly incorporates elementary kinetic theories as a means to provide reliable, physics-based extrapolation of kinetic models to unexplored conditions. Here, we extend and generalize the multiscale informatics strategy to treat systems of considerable complexity-involving multiwell reactions, potentially missing reactions, nonstatistical product branching ratios, and non-Boltzmann (i.e., nonthermal) reactant distributions. The methodology is demonstrated here for a subsystem of low-temperature propane oxidation, as a representative system for low-temperature fuel oxidation. A multiscale model is assembled and informed by a wide variety of targets that include ab initio calculations of molecular properties, rate constant measurements of isolated reactions, and complex systems measurements. Active model parameters are chosen to accommodate both "parametric" and "structural" uncertainties. Theoretical parameters (e.g., barrier heights) are included as active model parameters to account for parametric uncertainties in the theoretical treatment; experimental parameters (e.g., initial temperatures) are included to account for parametric uncertainties in the physical models of the experiments. RMG software is used to assess potential structural uncertainties due to missing reactions. Additionally, branching ratios among product channels are included as active model parameters to account for structural uncertainties related to difficulties in modeling sequences of multiple chemically activated steps. The approach is demonstrated here for interpreting time-resolved measurements of OH, HO2, n-propyl, i-propyl, propene, oxetane, and methyloxirane from photolysis-initiated low-temperature oxidation of propane at pressures from 4 to 60 Torr and temperatures from 300 to 700 K. In particular, the multiscale informed model provides a consistent quantitative explanation of both ab initio calculations and time-resolved species measurements. The present results show that interpretations of OH measurements are significantly more complicated than previously thought-in addition to barrier heights for key transition states considered previously, OH profiles also depend on additional theoretical parameters for R + O2 reactions, secondary reactions, QOOH + O2 reactions, and treatment of non-Boltzmann reaction sequences. Extraction of physically rigorous information from those measurements may require more sophisticated treatment of all of those model aspects, as well as additional experimental data under more conditions, to discriminate among possible interpretations and ensure model reliability. PMID:25946172

  16. Citric acid-modified Fenton's reaction for the oxidation of chlorinated ethylenes in soil solution systems.

    PubMed

    Seol, Yongkoo; Javandel, Iraj

    2008-06-01

    Fenton's reagent, a solution of hydrogen peroxide and ferrous iron catalyst, is used for an in situ chemical oxidation of organic contaminants. Sulfuric acid is commonly used to create an acidic condition needed for catalytic oxidation. Fenton's reaction often involves pressure buildup and precipitation of reaction products, which can cause safety hazards and diminish efficiency. We selected citric acid, a food-grade substance, as an acidifying agent to evaluate its efficiencies for organic contaminant removal in Fenton's reaction, and examined the impacts of using citric acid on the unwanted reaction products. A series of batch and column experiments were performed with varying H2O2 concentrations to decompose selected chlorinated ethylenes. Either dissolved iron from soil or iron sulfate salt was added to provide the iron catalyst in the batch tests. Batch experiments revealed that both citric and sulfuric acid systems achieved over 90% contaminant removal rates, and the presence of iron catalyst was essential for effective decontamination. Batch tests with citric acid showed no signs of pressure accumulation and solid precipitations, however the results suggested that an excessive usage of H2O2 relative to iron catalysts (Fe2+/H2O2<1/330) would result in lowering the efficiency of contaminant removal by iron chelation in the citric acid system. Column tests confirmed that citric acid could provide suitable acidic conditions to achieve higher than 55% contaminant removal rates. PMID:18472129

  17. Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides

    NASA Technical Reports Server (NTRS)

    Collins, J.; Rosner, D. E.; Castillo, J.

    1992-01-01

    A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

  18. Mechanism of 1,1-D/sub 2/-propene oxidation over oxide catalysts

    SciTech Connect

    Figueras, M.; Forrissier, F.; Portefaix, J.L.

    1980-06-01

    The mechanism of C-C bond cleavage, which is responsible for loss of selectivty in the oxidation of propylene to acrolein, was studied in the oxidation of CD/sub 2/=CH-CH/sub 3/ on bismuth molybdate, tin/antimony mixed oxides, silica-supported molybdenum oxide and silica- or alumina-supported vanadium oxides. Of the produced ethanal (acetaldehyde), only 0-15% contained deuterium, depending on the catalyst, which suggested that the partial oxidation of propylene to acrolein and bond rupture yielding ethanal are paralled reactions via different intermediates. The mechanisms are discussed.

  19. Oxidation and crack nucleation\\/growth in an air-plasma-sprayed thermal barrier coating with NiCrAlY bond coat

    Microsoft Academic Search

    W. R. Chen; X. Wu; B. R. Marple; P. C. Patnaik

    2005-01-01

    The oxidation behavior of an air-plasma-sprayed thermal barrier coating (APS-TBC) system was investigated in both air and low-pressure oxygen environments. It was found that mixed oxides, in the form of (Cr,Al)2O3·Ni(Cr,Al)2O4·NiO, formed heterogeneously at a very early stage during oxidation in air, and in the meantime, a layer of predominantly Al2O3 grew rather uniformly along the rest of the ceramic\\/bond

  20. Peroxynitrite reaction with carbon dioxide/bicarbonate: kinetics and influence on peroxynitrite-mediated oxidations.

    PubMed

    Denicola, A; Freeman, B A; Trujillo, M; Radi, R

    1996-09-01

    Peroxynitrite is a strong oxidant produced in vivo as the reaction product of superoxide anion and nitric oxide (k approximately 5 x 10(9) M-1 s-1) and can be formed and mediate reactions in the extracellular environment. It has recently been reported that peroxynitrite and carbon dioxide react in a second-order process (S. V. Lymar and K. Hurst (1995) J. Am. Chem. Soc. 117, 8867-8868). Since one of the most abundant constituents of the extracellular milieu is bicarbonate anion (25 mM in plasma) which is in equilibrium with carbon dioxide (1.3 mM in plasma) we have further studied the kinetics of the reaction between peroxynitrite and carbon dioxide/ bicarbonate and the effect of bicarbonate on different peroxynitrite-mediated oxidations. The apparent second-order rate constant for the reaction is (2.3 +/- 0.1) x 10(3) M-1 s-1 at 37 degrees C and pH 7.4 and a pH-independent second-order rate constant of (5.8 +/- 0.2) x 10(4) M-1 s-1 at 37 degrees C was obtained considering peroxynitrite anion and carbon dioxide as the reacting species. The enthalpy and entropy of activation are delta H* = +10.7 +/- 0.8 kcal mol-1 and delta S* = -6.5 +/- 0.5 cal mol-1 K-1, respectively. The presence of bicarbonate had variable influence on peroxynitrite-mediated oxidations. While bicarbonate significantly enhanced peroxynitrite-mediated nitration of aromatics, it partially inhibited the oxidation of thiols, dimethylsulfoxide, oxyhemoglobin, and cytochrome c+2 and totally inhibited the hydroxylation of benzoate. Spontaneous chemiluminescence studies suggest the formation of bicarbonate radicals during the interactions of peroxynitrite with carbon dioxide/ bicarbonate. Our results support that peroxynitrite anion rapidly reacts with carbon dioxide to yield an adduct (ONOOCO2-) which can participate in oxidation and nitration processes, thus redirecting the primary reactivity of peroxynitrite. PMID:8806753

  1. Reaction of tributyl phosphite with oxidized iron: surface and tribological chemistry.

    PubMed

    Gao, Feng; Furlong, Octavio; Kotvis, Peter V; Tysoe, Wilfred T

    2004-08-31

    The surface chemistry of a model lubricant additive, tributyl phosphite (TBPi), is investigated on Fe3O4 in ultrahigh vacuum. A portion of the TBPi desorbs molecularly following adsorption at approximately 200 K, the remainder decomposing either by C-O bond scission to form 1-butyl species or by P-O bond cleavage to form butoxy species. Adsorbed butyl species either undergo beta-hydride elimination to desorb 1-butene or decompose to deposit carbon and hydrogen on the surface. The resulting adsorbed hydrogen reacts with the oxide to desorb water or with the butoxy species to form 1-butanol. Butoxy species are stable up to approximately 600 K at which temperature they also undergo beta-hydride elimination to form butanal and the released hydrogen reacts with other butoxy species to form 1-butanol. Only a small amount of carbon is deposited onto the surface following adsorption at approximately 200 K, which then desorbs as CO above approximately 750 K. Adsorbing TBPi at 300 K results in the deposition of more carbon and an Auger depth profile reveals that the carbon is located predominantly on the surface, while the phosphorus is rather uniformly distributed throughout the oxide film. This result is in accord with previous near-edge X-ray absorption fine structure measurements, which show the formation of phosphates and polyphosphate glasses. The resulting tribological film appears to be composed of a relatively hard polyphosphate glass formed by rapid diffusion of POx species into the oxide, covered by a low shear strength graphitic layer. PMID:15323502

  2. Mechanisms and reaction pathways for simultaneous oxidation of NOx and SO? by ozone determined by in situ IR measurements.

    PubMed

    Sun, Chenglang; Zhao, Nan; Zhuang, Zhuokai; Wang, Haiqiang; Liu, Yue; Weng, Xiaole; Wu, Zhongbiao

    2014-06-15

    Ozone (O3) oxidation combined with wet scrubbing is a promising method for the simultaneous removal of SO2 and NOx in flue gas. In this study, the O3 oxidation processes of NO and SO2, as well as their coexistence, were investigated using an in situ IR spectrometer. Experimental results showed that the O3 concentration and the reaction temperature played critical roles in the O3 oxidation process of NO. Around 80°C, when inlet molar ratio of O3/NO was less than 1, NO was mainly oxidized to NO2, while when the ratio was greater than 1, NO would be further oxidized to NO3, N2O5, and HNO3. NO3 was the key intermediate product for the formation of N2O5 and HNO3. However, the subsequent reactions of NO3 were temperature dependence. With the increase of reaction temperature above 100°C, the concentration of NO2 increased whereas the concentrations of N2O5 and HNO3 decreased. The oxidation of SO2 by O3 was negligible and SO2 had little influence on the oxidation of NO in the simultaneous oxidation of NO and SO2. Finally, based on the in situ IR results, the oxidation mechanism is discussed and the reaction pathways are proposed. PMID:24801895

  3. Photo-redox reactions of dicarboxylates and ?-hydroxydicarboxylates at the surface of Fe(III)(hydr)oxides followed with in situ ATR-FTIR spectroscopy.

    PubMed

    Borer, Paul; Hug, Stephan J

    2014-02-15

    Colloidal mineral-phases play an important role in the adsorption, transport and transformation of organic and inorganic compounds in the atmosphere and in aqueous environments. Artificial UV-light and sunlight can induce electron transfer reactions between metal ions of the solid phases and adsorbed compounds, leading to their transformation and degradation. To investigate different possible photo-induced oxidation pathways of dicarboxylates adsorbed on iron(III)(hydr)oxide surfaces, we followed UV-A induced photoreactions of oxalate, malonate, succinate and their corresponding ?-hydroxy analogues tartronate and malate with in situ ATR-FTIR spectroscopy in immersed particle layers of lepidocrocite, goethite, maghemite and hematite at pH 4. UV-A light (365 ± 5 nm) lead to fast degradation of oxalate, tartronate and malate, while malonate and succinate were photo-degraded at much slower rates. Efficient generation of OH-radicals can be excluded, as this would lead to fast and indiscriminate degradation of all tested compounds. Rapid photo-degradation of adsorbed oxalate and the ?-hydroxydicarboxylates must be induced by direct ligand-to-metal charge transfer (LMCT) or by selectively oxidizing valence band holes, both processes requiring inner-sphere coordination with direct ligand-to-metal bonds to enable efficient electron-transfer. The slow photo-degradation of malonate and succinate can be explained by low-yield production of OH-radicals at the surface of the iron(III)(hydr)oxides. PMID:24370400

  4. Mechanism of atmospheric photooxidation of organic compounds. Reactions of alkoxy radicals in oxidation of n-butane and simple ketones

    Microsoft Academic Search

    Richard A. Cox; Kenneth F. Patrick; Susan A. Chant

    1981-01-01

    The OH-initiated photo-oxidation of n-butane was used as a source of 1- and 2-butoxy radicals. Reactions producing ketones and other organic compounds are explained. Rates of photolysis were determined and are discussed.

  5. The Photochemical Oxidation of Siderite That Drove Hydrogen Based Microbial Redox Reactions in The Archean Biosphere

    NASA Astrophysics Data System (ADS)

    Kim, J. D.; Yee, N.; Falkowski, P. G.

    2012-12-01

    Hydrogen is the most abundant element in the universe and molecular hydrogen (H2) is a rich source of electron in a mildly reducing environment for microbial redox reactions, such as anoxygenic photosynthesis and methanogenesis. Subaerial volcanoes, ocean crust serpentinization and mid-ocean ridge volcanoes have been believed to be the major source of the hydrogen flux to the atmosphere. Although ferrous ion (Fe2+) photooxidation has been proposed as an alternative mechanism by which hydrogen gas was produced, ferruginous water in contact with a CO2-bearing atmosphere is supersaturated with respect to FeCO3 (siderite), thus the precipitation of siderite would have been thermodynamically favored in the Archean environment. Siderite is the critical mineral component of the oldest fossilized microbial mat. It has also been inferred as a component of chemical sedimentary protolith in the >3750 Ma Nuvvuagittuq supracrustal belt, Canada and the presence of siderite in the protolith suggests the occurrence of siderite extends to Hadean time. Analyses of photooxidation of siderite suggest a significant flux of hydrogen in the early atmosphere. Our estimate of the hydrogen production rate under Archean solar flux is approximately 50 times greater than the estimated hydrogen production rate by the volcanic activity based on a previous report (Tian et al. Science 2005). Our analyses on siderite photooxidation also suggest a mechanism by which banded iron formation (BIF) was formed. The photooxidation transforms siderite to magnetite/maghemite (spinnel iron oxide), while oxygenic oxidation of siderite leads to goethite, and subsequently to hematite (Fe3+2O3) upon dehydration. We will discuss the photochemical reaction, which was once one of the most ubiquitous photochemical reactions before the rise of oxygen in the atmosphere. Photooxidation of siderite over time by UV light From left to right: UV oxidized siderite, pristine siderite, oxidized siderite by oxygen

  6. Modelling and Ni/Yttria-Stabilized-Zirconia pattern anode experimental validation of a new charge transfer reactions mechanism for hydrogen electrochemical oxidation on solid oxide fuel cell anodes

    NASA Astrophysics Data System (ADS)

    Yao, Weifang; Croiset, Eric

    2014-02-01

    Good understanding of the H2 electrochemical reaction mechanism helps optimize SOFC anode design and improve its performance. Controversies still exist regarding H2 oxidation mechanism despite extensive studies performed. In this work, a new charge transfer reactions mechanism proposed by Shishkin and Ziegler (2010) based on Density Functional Theory (DFT) study was investigated through kinetic modelling and pattern anode experimental validation. The new charge transfer reactions mechanism considers hydrogen oxidation at the interface of Ni and YSZ. It involves a hydrogen atom reacting with the oxygen ions bound to both Ni and YSZ to produce hydroxyl (Charge transfer reaction 1), the latter reacting with the other hydrogen atom to form water (Charge transfer reaction 2). The predictive capability of this reaction mechanism to represent our experimental results was evaluated. The simulated Tafel plots were compared with our experimental data for a wide range of H2 and H2O partial pressures and at different temperatures. Good agreements between simulation and experimental results were obtained. Charge transfer reaction 1 was found to dominate the overall charge transfer reaction under cathodic polarization. Under anodic polarization, a change in the dominating charge transfer reaction from charge transfer reaction 1 to charge transfer reaction 2 was found when increasing the H2O partial pressure.

  7. Oxidative Tryptophan Modification by Terpene- and Squalene-Hydroperoxides and a Possible Link to Cross-Reactions in Diagnostic Tests.

    PubMed

    Natsch, Andreas; Emter, Roger; Badertscher, Remo P; Brunner, Gerhard; Granier, Thierry; Kern, Susanne; Ellis, Graham

    2015-06-15

    Hydroperoxides can act as specific haptens and oxidatively modify proteins. Terpene hydroperoxides trigger unusually high frequencies of positive skin reactions in human patients if tested at high concentrations. It is unknown whether this is due to specific hapten formation. Here, we show that both terpene hydroperoxides and the endogenous hydroperoxide formed from squalene can oxidatively modify tryptophan. Oxidative modifications of Trp were recently postulated to explain cross-sensitization between unrelated photosensitizers. Current observations may extend this hypothesis: Oxidative events triggered by endogenous hydroperoxides and hydroperoxides/oxidants derived from xenobiotics might lead to a sensitized state detected by patch tests with high concentrations of hydroperoxides. PMID:25942677

  8. Minerals as molecules--use of aqueous oxide and hydroxide clusters to understand geochemical reactions.

    PubMed

    Casey, William H; Rustad, James R; Spiccia, Leone

    2009-01-01

    Large aqueous oxide ions as minerals! Minerals dissolve by repeated ligand exchange reactions and geochemists use polyoxometalate ions to establish structure-reactivity relations for environmentally important functional groups. Here, for example, are plotted the dissolution rates of two classes of minerals against rates of solvent exchanges around the corresponding aquo ions.Geochemists and environmental chemists make predictions about the fate of chemicals in the shallow earth over enormously long times. Key to these predictions is an understanding of the hydrolytic and complexation reactions at oxide mineral surfaces that are difficult to probe spectroscopically. These minerals are usually oxides with repeated structural motifs, like silicate or aluminosilicate polymers, and they expose a relatively simple set of functional groups to solution. The geochemical community is at the forefront of efforts to describe the surface reactivities of these interfacial functional groups and some insights are being acquired by using small oligomeric oxide molecules as experimental models. These small nanometer-size clusters are not minerals, but their solution structures and properties are better resolved than for minerals and calculations are relatively well constrained. The primary experimental data are simple rates of steady oxygen-isotope exchanges into the structures as a function of solution composition that can be related to theoretical results. There are only a few classes of large oxide ions for which data have been acquired and here we review examples and illustrate the general approach, which also derives directly from the use of model clusters to understand for the active core of metalloenzymes in biochemistry. PMID:19347896

  9. Reaction mechanism of melatonin oxidation by reactive oxygen species in vitro.

    PubMed

    Bonnefont-Rousselot, Dominique; Collin, Fabrice; Jore, Daniel; Gardès-Albert, Monique

    2011-04-01

    Melatonin (N-acetyl-5-hydroxytryptamine) is a pineal hormone widely known for its antioxidant properties, both in vivo and by direct capture of free radicals in vitro. Although some metabolites and oxidation products of melatonin have been identified, the molecular mechanism by which melatonin exerts its antioxidant properties has not been totally unravelled. This study investigated the reaction mechanism of oxidation of melatonin by radio-induced reactive oxygen species, generated by gamma radiolysis of water for aqueous solutions of melatonin (from 20 to 200 ?m), in the presence or absence of molecular oxygen. The hydroxyl radical was found to be the unique species able to initiate the oxidation process, leading to three main products, e.g. N(1)-acetyl-N(2)-formyl-5-methoxykynurenin (AFMK), N(1)-acetyl-5-methoxykynurenin (AMK) and hydroxymelatonin (HO-MLT). The generation of AFMK and HO-MLT strongly depended on the presence of molecular oxygen in solution: AFMK was the major product in aerated solutions (84%), whereas HO-MLT was favoured in the absence of oxygen (86%). Concentrations of AMK remained quite low, and AMK was proposed to result from a chemical hydrolysis of AFMK in solution. A K-value of 1.1 × 10(-4) was calculated for this equilibrium. Both hydrogen peroxide and superoxide dismutase had no effect on the radio-induced oxidation of melatonin, in good accordance for the second case with the poor reactivity of the superoxide anion towards melatonin. Finally, a reaction mechanism was proposed for the oxidation of melatonin in vitro. PMID:21244479

  10. Reversible swelling-shrinking behavior of hydrogen-bonded free-standing thin film stabilized by catechol reaction.

    PubMed

    Sun, Jiaxing; Su, Chao; Zhang, Xuejian; Yin, Wenjing; Xu, Jian; Yang, Shuguang

    2015-05-12

    Dopamine-modified poly(acrylic acid) (PAA-dopa) and poly(vinylpyrrolidone) (PVPON) was layer-by-layer (LbL) assembled to prepare thin film based on hydrogen bonding. The carboxylic group of acrylic acid and the phenolic hydroxyl group of dopamine can both act as hydrogen bond donors. The critical assembly and the critical disintegration pH values of PVPON/PAA-dopa film are enhanced compared with PVPON/PAA film. The hydrogen-bonded PVPON/PAA-dopa thin film can be cross-linked via catechol chemistry of dopamine. After cross-linking, the film can be exfoliated from the substrate in alkaline solution to get a free-standing film. Moreover, by tuning the pH value, deprotonation and protonation of PAA will make the hydrogen bond in the film break and reconstruct, which induces that the free-standing film has a reversible swelling-shrinking behavior. PMID:25899235

  11. Synthesis gas production by zinc oxide reaction with methane: elimination of greenhouse gas emission from a metallurgical plant

    Microsoft Academic Search

    H. Ale Ebrahim; E. Jamshidi

    2004-01-01

    Most natural gas based petrochemical processes consist of catalytic reforming or partial oxidation units for producing synthesis gas. This research shows that it is possible to replace these units by the reaction of zinc oxide with methane, which produces metallic zinc and synthesis gas (CO+2H2) simultaneously. Therefore, by combination of the metallurgical and petrochemical units, it is possible to eliminate

  12. Kinetic stabilization against the oxidation reaction induced by a silaalkane cage in a thiophene-bridged molecular gyroscope.

    PubMed

    Setaka, Wataru; Ohmizu, Soichiro; Kira, Mitsuo

    2014-02-01

    Macrocage molecules with a bridged rotor have been synthesized as molecular gyroscopes. The kinetics of the oxidation reaction of the thiophene-bridged molecular gyroscope, whose thiophene ring was bridged inside a silaalkane cage, was investigated. A remarkable kinetic stabilization against the oxidation of the thiophene moiety induced by the molecular cage framework was observed. PMID:24317303

  13. Redox activity of surface oxygen anions in oxygen-deficient perovskite oxides during electrochemical reactions.

    PubMed

    Mueller, David N; Machala, Michael L; Bluhm, Hendrik; Chueh, William C

    2015-01-01

    Surface redox-active centres in transition-metal oxides play a key role in determining the efficacy of electrocatalysts. The extreme sensitivity of surface redox states to temperatures, to gas pressures and to electrochemical reaction conditions renders them difficult to investigate by conventional surface-science techniques. Here we report the direct observation of surface redox processes by surface-sensitive, operando X-ray absorption spectroscopy using thin-film iron and cobalt perovskite oxides as model electrodes for elevated-temperature oxygen incorporation and evolution reactions. In contrast to the conventional view that the transition metal cations are the dominant redox-active centres, we find that the oxygen anions near the surface are a significant redox partner to molecular oxygen due to the strong hybridization between oxygen 2p and transition metal 3d electronic states. We propose that a narrow electronic state of significant oxygen 2p character near the Fermi level exchanges electrons with the oxygen adsorbates. This result highlights the importance of surface anion-redox chemistry in oxygen-deficient transition-metal oxides. PMID:25598003

  14. The analysis of magnesium oxide hydration in three-phase reaction system

    SciTech Connect

    Tang, Xiaojia; Guo, Lin; Chen, Chen; Liu, Quan; Li, Tie; Zhu, Yimin, E-mail: ntp@dlmu.edu.cn

    2014-05-01

    In order to investigate the magnesium oxide hydration process in gas–liquid–solid (three-phase) reaction system, magnesium hydroxide was prepared by magnesium oxide hydration in liquid–solid (two-phase) and three-phase reaction systems. A semi-empirical model and the classical shrinking core model were used to fit the experimental data. The fitting result shows that both models describe well the hydration process of three-phase system, while only the semi-empirical model right for the hydration process of two-phase system. The characterization of the hydration product using X-Ray diffraction (XRD) and scanning electron microscope (SEM) was performed. The XRD and SEM show hydration process in the two-phase system follows common dissolution/precipitation mechanism. While in the three-phase system, the hydration process undergo MgO dissolution, Mg(OH){sub 2} precipitation, Mg(OH){sub 2} peeling off from MgO particle and leaving behind fresh MgO surface. - Graphical abstract: There was existence of a peeling-off process in the gas–liquid–solid (three-phase) MgO hydration system. - Highlights: • Magnesium oxide hydration in gas–liquid–solid system was investigated. • The experimental data in three-phase system could be fitted well by two models. • The morphology analysis suggested that there was existence of a peel-off process.

  15. No evidence found for Diels-Alder reaction products in soybean oil oxidized at the frying temperature by NMR study

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been generally accepted that the Diels-Alder reaction mechanism is one of the major reaction mechanisms to produce dimers and polymers during heating process of vegetable oil. Soybean oil oxidized at 180 °C for 24 hrs with 1.45 surface area-to-volume ratio showed 36.1% polymer peak area in g...

  16. Spatially Resolved Modeling of Electric Double Layers and Surface Chemistry for the Hydrogen Oxidation Reaction in Water-Filled

    E-print Network

    Litster, Shawn

    ); surface charging due to functional groups; and multistep, multipathway electrochemical reactionsSpatially Resolved Modeling of Electric Double Layers and Surface Chemistry for the Hydrogen Oxidation Reaction in Water-Filled Platinum-Carbon Electrodes Iryna V. Zenyuk and Shawn Litster* Department

  17. The Mechanism of the Catalytic Oxidation of Ethylene. II. Reactions between Ethylene, Etc. and Chemisorbed Oxygen Monolayers

    Microsoft Academic Search

    G. H. Twigg

    1946-01-01

    Experiments have been carried out at temperatures of 263 degrees C and higher between oxygen adsorbed as atoms on the silver catalyst, and ethylene, ethylene oxide and acetaldehyde. The course of reaction was followed by measuring the change in pressure, and analyses of the products were made by micro-fractionation of the gases at low temperatures. In the reaction of ethylene

  18. Effects of oxidation on reaction front instabilities and average propagation speed in Ni/Ti multilayer foils

    NASA Astrophysics Data System (ADS)

    McDonald, Joel P.; Reeves, Robert V.; Jones, Eric D.; Chinn, Kathryn A.; Adams, David P.

    2013-03-01

    Vapor-deposited, equiatomic Ni/Ti multilayer foils exhibit low-speed, self-propagating formation reactions that are characterized by a spin-like reaction front instability. In addition to the intermetallic reaction between Ni and Ti, reactions performed in air can also exhibit a discrete combustion wave associated with the oxidation of Ti. In general, the oxidation wave trails the complex intermetallic reaction front. Multilayers that have a large reactant layer periodicity (?200 nm) exhibit a decrease in net reaction speed as air pressure is reduced. Oxidation has a much smaller effect on the net propagation speed of multilayers with small layer periodicity (<100 nm). The net propagation speed of the multilayers is increased when air is present, due to the added energy release of Ti oxidation. High-speed optical microscopy shows that the increased front speed is associated with an increased nucleation rate of the reaction bands that typify the spinning reaction instability of the Ni/Ti system.

  19. Pro-oxidative versus antioxidative reactions between Trolox and Cr(VI): The role of H 2O 2

    Microsoft Academic Search

    Borut Poljšak; Zoltán Gazdag; Miklós Pesti; Špela Jenko-Brinovec; Joseph Belagyi; Stojan Plesni?ar; Peter Raspor

    2006-01-01

    The effect of the Vitamin E model compound Trolox in reactions with Cr(VI) in the presence or absence of hydrogen peroxide was investigated. The aim of this study was to establish and discuss potential Trolox-mediated pro-oxidative reactions. The importance of the Trolox:Cr(VI) ratio in the Cr(VI) reduction process was determined from the EPR spectra and DNA cleavage reactions. In the

  20. Reaction of Antimony-Uranium Composite Oxide in the Chlorination Treatment of Waste Catalyst - 13521

    SciTech Connect

    Sawada, Kayo [EcoTopia Science Institute (Japan)] [EcoTopia Science Institute (Japan); Hirabayashi, Daisuke; Enokida, Youichi [Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan)] [Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan)

    2013-07-01

    The effect of oxygen gas concentration on the chlorination treatment of antimony-uranium composite oxide catalyst waste was investigated by adding different concentrations of oxygen at 0-6 vol% to its chlorination agent of 0.6 or 6 vol% hydrogen chloride gas at 1173 K. The addition of oxygen tended to prevent the chlorination of antimony in the oxide. When 6 vol% hydrogen chloride gas was used, the addition of oxygen up to 0.1 vol% could convert the uranium contained in the catalyst to U{sub 3}O{sub 8} without any significant decrease in the reaction rate compared to that of the treatment without oxygen. (authors)