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1

Fiber reinforcement of reaction bonded oxide ceramics  

SciTech Connect

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.

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

1995-12-01

2

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

Microsoft Academic Search

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.

Paul Martin Sheedy

2003-01-01

3

Oxidation stability of advanced reaction-bonded Si3N4 materials  

NASA Technical Reports Server (NTRS)

Four slip-cast, injection-molded and isostatically-pressed specimens of reaction-bonded silicon nitride (RBSN) were subjected to static oxidation tests at 900 C for 10 hours. Specimens containing 8-10% interconnected open porosity of size greater than one micron exhibited a 20-30% decrease in average room temperature four-point flexure strength, while those with 10% open porosity of magnitudes much smaller than one micron as well as those with 2-4% interconnected open porosity of about one micron did not decrease in strength after 900 C exposure. It was determined that preoxidation treatment at 1350 C prevents the 20-30% strength degradation due to internal oxidation, and evidence is presented which suggests that surface pit formation in some RBSN may result from contamination by the furnace environment rather than any intrinsic material properties.

Lindberg, L. J.; Richerson, D. W.; Carruthers, W. D.; Gersch, H. M.

1982-01-01

4

Consequences of metal-oxide interconversion for C-H bond activation during CH4 reactions on Pd catalysts.  

PubMed

Mechanistic assessments based on kinetic and isotopic methods combined with density functional theory are used to probe the diverse pathways by which C-H bonds in CH4 react on bare Pd clusters, Pd cluster surfaces saturated with chemisorbed oxygen (O*), and PdO clusters. C-H activation routes change from oxidative addition to H-abstraction and then to ?-bond metathesis with increasing O-content, as active sites evolve from metal atom pairs (*-*) to oxygen atom (O*-O*) pairs and ultimately to Pd cation-lattice oxygen pairs (Pd(2+)-O(2-)) in PdO. The charges in the CH3 and H moieties along the reaction coordinate depend on the accessibility and chemical state of the Pd and O centers involved. Homolytic C-H dissociation prevails on bare (*-*) and O*-covered surfaces (O*-O*), while C-H bonds cleave heterolytically on Pd(2+)-O(2-) pairs at PdO surfaces. On bare surfaces, C-H bonds cleave via oxidative addition, involving Pd atom insertion into the C-H bond with electron backdonation from Pd to C-H antibonding states and the formation of tight three-center (H3C···Pd···H)(‡) transition states. On O*-saturated Pd surfaces, C-H bonds cleave homolytically on O*-O* pairs to form radical-like CH3 species and nearly formed O-H bonds at a transition state (O*···CH3(•)···*OH)(‡) that is looser and higher in enthalpy than on bare Pd surfaces. On PdO surfaces, site pairs consisting of exposed Pd(2+) and vicinal O(2-), Pd(ox)-O(ox), cleave C-H bonds heterolytically via ?-bond metathesis, with Pd(2+) adding to the C-H bond, while O(2-) abstracts the H-atom to form a four-center (H3C(?-)···Pd(ox)···H(?+)···O(ox))(‡) transition state without detectable Pd(ox) reduction. The latter is much more stable than transition states on *-* and O*-O* pairs and give rise to a large increase in CH4 oxidation turnover rates at oxygen chemical potentials leading to Pd to PdO transitions. These distinct mechanistic pathways for C-H bond activation, inferred from theory and experiment, resemble those prevalent on organometallic complexes. Metal centers present on surfaces as well as in homogeneous complexes act as both nucleophile and electrophile in oxidative additions, ligands (e.g., O* on surfaces) abstract H-atoms via reductive deprotonation of C-H bonds, and metal-ligand pairs, with the pair as electrophile and the metal as nucleophile, mediate ?-bond metathesis pathways. PMID:24083571

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

2013-10-16

5

Oxidation effects on the mechanical properties of SiC fiber-reinforced reaction-bonded silicon nitride matrix composites  

NASA Technical Reports Server (NTRS)

The room temperature mechanical properties of SiC fiber reinforced reaction bonded silicon nitride composites were measured after 100 hrs exposure at temperatures to 1400 C in nitrogen and oxygen environments. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The results indicate that composites heat treated in a nitrogen environment at temperatures to 1400 C showed deformation and fracture behavior equivalent to that of the as-fabricated composites. Also, the composites heat treated in an oxidizing environment beyond 400 C yielded significantly lower tensile strength values. Specifically in the temperature range from 600 to 1000 C, composites retained approx. 40 percent of their as-fabricated strength, and those heat treated in the temperatures from 1200 to 1400 C retained 70 percent. Nonetheless, for all oxygen heat treatment conditions, composite specimens displayed strain capability beyond the matrix fracture stress; a typical behavior of a tough composite.

Bhatt, Ramakrishna T.

1989-01-01

6

Sintered-reaction Bonded Silicon Nitride Densified by a Gas Pressure Sintering Process Effects of Rare Earth Oxide Sintering Additives  

SciTech Connect

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, Lu2O3-SiO2 (US), La2O3-MgO (AM) and Y2O3-Al2O3 (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the La2O3-MgO system. Since the Lu2O3-SiO2 system has the highest melting temperature, full densification could not be achieved after sintering at 1950oC. However, the system had a reasonably high bending strength of 527 MPa at 1200oC in air and a high fracture toughness of 9.2 MPa m1/2. The Y2O3-Al2O3 system had the highest room temperature bending strength of 1.2 GPa

Lee, S. H. [Korea Institute of Materials Science; Ko, J. W. [Korea Institute of Materials Science; Park, Y. J. [Korea Institute of Materials Science; Kim, H. D. [Korea Institute of Materials Science; Lin, Hua-Tay [ORNL; Becher, Paul F [ORNL

2012-01-01

7

Reactions of fourth-period metal ions (Ca sup + endash Zn sup + ) with O sub 2 : Metal-oxide ion bond energies  

SciTech Connect

Reactions of Ca{sup +}, Zn{sup +} and all first-row atomic transition metal ions with O{sub 2} are studied using guided ion beam techniques. While reactions of the ground states of Sc{sup +}, Ti{sup +}, and V{sup +} are exothermic, the remaining metal ions react with O{sub 2} in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M{sup +}--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{sup +}, Co{sup +}, Ni{sup +}, and Cu{sup +}. Results (in eV) at 0 K are {ital D}{sup 0}(Ca{sup +}--O)=3.57{plus minus}0.05, {ital D}{sup 0}(Cr{sup +}--O)=3.72{plus minus}0.12, {ital D}{sup 0}(Mn{sup +}--O)=2.95{plus minus}0.13, {ital D}{sup 0}(Fe{sup +}--O)=3.53{plus minus}0.06 (reported previously), {ital D}{sup 0}(Co{sup +}--O)=3.32{plus minus}0.06, {ital D}{sup 0}(Ni{sup +}--O)=2.74{plus minus}0.07, {ital D}{sup 0}(Cu{sup +}--O)=1.62{plus minus}0.15, and {ital D}{sup 0}(Zn{sup +}--O)=1.65{plus minus}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.

Fisher, E.R.; Elkind, J.L.; Clemmer, D.E.; Georgiadis, R.; Loh, S.K.; Aristov, N.; Sunderlin, L.S.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (USA) Department of Chemistry, University of California, Berkeley, CA (USA))

1990-08-15

8

Oxidation effects on the mechanical properties of a SiC-fiber-reinforced reaction-bonded Si3N4 matrix composite  

NASA Technical Reports Server (NTRS)

The room-temperature mechanical properties of SiC fiber reinforced reaction bonded silicon nitride composites were measured after 100 hrs exposure at temperatures to 1400 C in nitrogen and oxygen environments. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The results indicate that composites heat treated in a nitrogen environment at temperatures to 1400 C showed deformation and fracture behavior equivalent to that of the as-fabricated composites. Also, the composites heat treated in an oxidizing environment beyond 400 C yielded significantly lower tensile strength values. Specifically in the temperature range from 600 to 1000 C, composites retained approx. 40 percent of their as-fabricated strength, and those heat treated in the temperatures from 1200 to 1400 C retained 70 percent. Nonetheless, for all oxygen heat treatment conditions, composite specimens displayed strain capability beyond the matrix fracture stress; a typical behavior of a tough composite.

Bhatt, Ramakrishna T.

1992-01-01

9

Sensor/ROIC Integration using Oxide Bonding  

E-print Network

We explore the Ziptronix Direct Bond Interconnect technology for the integration of sensors and readout integrated circuits (ROICs) for high energy physics. The technology utilizes an oxide bond to form a robust mechanical connection between layers which serves to assist with the formation of metallic interlayer connections. We report on testing results of sample sensors bonded to ROICs and thinned to 100 microns.

Zhenyu Ye; for the Fermilab Pixel R&D Group

2009-02-16

10

Sensor/ROIC Integration using Oxide Bonding  

SciTech Connect

We explore the Ziptronix Direct Bond Interconnect (DBI) technology [2] for the integration of sensors and readout integrated circuits (ROICs) for high energy physics. The technology utilizes an oxide bond to form a robust mechanical connection between layers which serves to assist with the formation of metallic interlayer connections. We report on testing results of sample sensors bonded to ROICs and thinned to 100 {micro}m.

Ye, Zhenyu; /Fermilab

2009-02-01

11

Interfacial Bonding Stabilizes Rhodium and Rhodium Oxide Nanoparticles on Layered Nb Oxide and Ta Oxide Supports  

E-print Network

Interfacial Bonding Stabilizes Rhodium and Rhodium Oxide Nanoparticles on Layered Nb Oxide and Ta temperatures. Rhodium oxide and rhodium metal nanoparticles on niobate and tantalate supports are anomalously

12

Effect of processing parameters on reaction bonding of silicon nitride  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

13

Reaction-bonded Si3N4 and SiC matrix composites  

NASA Technical Reports Server (NTRS)

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.

Bhatt, Ramakrishna T.; Behrendt, Donald R.

1992-01-01

14

Palladium nanoparticles bonded to two-dimensional iron oxide graphene nanosheets: a synergistic and highly reusable catalyst for the Tsuji-Trost reaction in water and air.  

PubMed

Low cost, high activity and selectivity, convenient separation, and increased reusability are the main requirements for noble-metal-nanocatalyst-catalyzed reactions. Despite tremendous efforts, developing noble-metal nanocatalysts to meet the above requirements remains a significant challenge. Here we present a general strategy for the preparation of strongly coupled Fe(3)O(4) and palladium nanoparticles (PdNPs) to graphene sheets by employing polyethyleneimine as the coupling linker. Transmission electron microscopic images show that Pd and Fe(3)O(4) nanoparticles are highly dispersed on the graphene surface, and the mean particle size of Pd is around 3?nm. This nanocatalyst exhibits synergistic catalysis by Pd nanoparticles supported on reduced graphene oxide (rGO) and a tertiary amine of polyethyleneimine (Pd/Fe(3)O(4)/PEI/rGO) for the Tsuji-Trost reaction in water and air. For example, the reaction of ethyl acetoacetate with allyl ethyl carbonate afforded the allylated product in more than 99?% isolated yield, and the turnover frequency reached 2200?h(-1). The yield of allylated products was 66?% for Pd/rGO without polyethyleneimine. The catalyst could be readily recycled by a magnet and reused more than 30?times without appreciable loss of activity. In addition, only about 7.5?% of Pd species leached off after 20?cycles, thus rendering this catalyst safer for the environment. PMID:25048270

Liu, Jian; Huo, Xing; Li, Tianrong; Yang, Zhengyin; Xi, Pinxian; Wang, Zhiyi; Wang, Baodui

2014-09-01

15

ChemTeacher Resource: Oxidation Reduction Reactions  

NSDL National Science Digital Library

This computer resource goes over oxidation reduction reactions and how they are broken down into half reactions. It explains which half reaction is the oxidation reaction and which one is the reduction, then has some summary questions at the end.

2012-08-02

16

Boron oxides: Ab initio studies with natural bond orbital analysis  

Microsoft Academic Search

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

A. V. Nemukhin; F. Weinhold

1993-01-01

17

?-Bond maximization of graphene in hydrogen addition reactions  

NASA Astrophysics Data System (ADS)

Thermodynamic stability of graphene hydrides increases in an approximately linear way with the numbers of ?-bonds they contain. Thus, ?-bond maximization is the primary driving force for hydrogen addition reactions of graphene. The previously reported thermal preference of sp2/sp3-phase separation of graphene hydrides is a straightforward effect of ?-bond maximization. Although not well applicable to hydroxylation and epoxidation, the ?-bond maximization principle also holds approximately for the fluorination reactions of graphene. The findings can be used to help locate the lowest-energy structures for graphene hydrides and to estimate the hydrogenation energy without first-principles calculations.Thermodynamic stability of graphene hydrides increases in an approximately linear way with the numbers of ?-bonds they contain. Thus, ?-bond maximization is the primary driving force for hydrogen addition reactions of graphene. The previously reported thermal preference of sp2/sp3-phase separation of graphene hydrides is a straightforward effect of ?-bond maximization. Although not well applicable to hydroxylation and epoxidation, the ?-bond maximization principle also holds approximately for the fluorination reactions of graphene. The findings can be used to help locate the lowest-energy structures for graphene hydrides and to estimate the hydrogenation energy without first-principles calculations. Electronic supplementary information (ESI) available: Computational details, Figures, energy and Cartesian coordinates of graphene hydrides and epoxides. See DOI: 10.1039/c1nr11048a

Gao, Xingfa; Zhao, Yuliang; Liu, Bo; Xiang, Hongjun; Zhang, Shengbai B.

2012-02-01

18

Author's personal copy Bond cleavage reactions in substituted thiophenes  

E-print Network

to decomposition. Insertion into the carbon sulfur bond had been observed with 2,5-dimethyl- thiophene, soAuthor's personal copy Bond cleavage reactions in substituted thiophenes by a rhodium complex of petroleum feedstocks to remove sulfur [1]. Derivatives of thiophenes, benzothiophenes, and dibenzothiophenes

Jones, William D.

19

Silicon wafer direct bonding without hydrophilic native oxides  

NASA Astrophysics Data System (ADS)

Silicon wafer direct bonding was accomplished between two surfaces which had no hydrophilic native oxide layers. Prior to bonding, two wafers were dipped in conv-HF solution (approximately = 49% aq.) to remove the native oxide layers and then immersed in deionized water. It is suggested that the OH groups which substitute the F atoms terminated on the small portion of the surface play an important role in this conv-HF-treated bonding.

Himi, Hiroaki; Matsui, Masaki; Fujino, Seiji; Hattori, Tadashi

1994-01-01

20

Oxidation and Reduction Reactions in Organic Chemistry  

ERIC Educational Resources Information Center

A variety of approaches to the concept of oxidation and reduction appear in organic textbooks. The method proposed here is different than most published approaches. The oxidation state is calculated by totaling the number of heterogeneous atoms, [pi]-bonds, and rings. A comparison of the oxidation states of reactant and product determine what type…

Shibley, Ivan A., Jr.; Amaral, Katie E.; Aurentz, David J.; McCaully, Ronald J.

2010-01-01

21

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

Microsoft Academic Search

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,

Harrell Sellers; Evgeny Shustorovich

1996-01-01

22

Silicon Wafer Direct Bonding without Hydrophilic Native Oxides  

NASA Astrophysics Data System (ADS)

Silicon wafer direct bonding was accomplished between two surfaces which had no hydrophilic native oxide layers. Prior to bonding, two wafers were dipped in conc-HF solution ( ˜49% aq.) to remove the native oxide layers and then immersed in deionized water. The level of bonding was evaluated by X-ray topography, high resolution transmission electron microscopy (HRTEM) and tensile strength measurement. It was found that the bonded wafer pairs were void-free and had good bonding strength. HRTEM observation showed that the crystal lattice was continuous and had only small distortions and precipitates. Spreading resistance (SR) measurement across the interface showed that the electric resistance did not increase at the bonding interface. It is suggested that the OH groups which substitute the F atoms terminated on the small portion of the surface play an important role in this conc-HF-treated bonding.

Himi, Hiroaki; Matsui, Masaki; Fujino, Seiji; Hattori, Tadashi

1994-01-01

23

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...

24

Synthesis of sulfur-containing heterocycles through oxidative carbon-hydrogen bond functionalization.  

PubMed

Vinyl sulfides react rapidly and efficiently with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form ?,?-unsaturated thiocarbenium ions through oxidative carbon-hydrogen bond cleavage. These electrophiles couple with appended ?-nucleophiles to yield sulfur-containing heterocycles through carbon-carbon bond formation. Several nucleophiles are compatible with the procedure, and the reactions generally proceed through readily predictable transition states. PMID:22420412

Cui, Yubo; Floreancig, Paul E

2012-04-01

25

Syntheses of sulfides and selenides through direct oxidative functionalization of C(sp3)-H bond.  

PubMed

A new protocol for C-S and C-Se bond formation by the direct functionalization of the C(sp(3))-H bond of alkanes under metal-free conditions was developed. Using (t)BuOO(t)Bu as the oxidant, the reaction of disulfides or diselenides with alkanes gave sulfides or selenides in moderate to good yields. The method was very simple and atom-economical. PMID:24835082

Du, Bingnan; Jin, Bo; Sun, Peipei

2014-06-01

26

Iodine-catalyzed oxidative coupling reactions utilizing c?h and x?h as nucleophiles.  

PubMed

In recent decades, iodine-catalyzed oxidative coupling reactions utilizing C?H and X?H as nucleophiles have received considerable attention because they represent more efficient, greener, more atom-economical, and milder bond-formation strategies over transition-metal-catalyzed oxidative coupling reactions. This Focus Review gives a brief summary of recent development on iodine-catalyzed oxidative coupling reactions utilizing C?H and X?H as nucleophiles. PMID:25683644

Liu, Dong; Lei, Aiwen

2015-04-01

27

Isotope Effects in C-H Bond Activation Reactions by  

E-print Network

Isotope Effects in C-H Bond Activation Reactions by Transition Metals WILLIAM D. JONES Department, it became common to associate an inverse isotope effect with the intermediacy of a -alkane com- William D. Jones was born in Philadelphia, Pennsylvania, in 1953, and was inspired to work in inorganic chemistry

Jones, William D.

28

Activation of CH Bonds:Stoichiometric Reactions William D. Jones  

E-print Network

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

Jones, William D.

29

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

PubMed

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

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

2014-03-01

30

REACTIONS OF ISOPROPOXY RADICALS WITH NITROGEN OXIDES  

EPA Science Inventory

Information was sought concerning reactions of isopropoxy radicals with nitric oxide and nitrogen dioxide. Isopropyl nitrate was photodissociated in the presence of oxides of nitrogen and an inert gas. The reaction was found to be less important than the alkoxy radical NO reactio...

31

Reactions of a quintuply bonded chromium dimer with alkynes.  

PubMed

Quintuply bonded [(H)L(iPr)Cr](2) reacts with alkynes RC?CR (R = Me, Et, Ph, CF(3)) to form exclusively 1?:?1 adducts [(H)L(iPr)Cr](2)(RCCR). All products feature relatively short Cr-Cr distances (1.919-1.962 Å) and elongated C-C bonds (1.315-1.436 Å), consistent with [2+2] cycloaddition reactions. The hydrocarbon adducts are 4-membered metallacycles, the bridging alkynes of which are progressively skewed with respect to the Cr-Cr axis. In contrast, perfluoroalkyne adds across the metal ligand moiety. PMID:21986955

Shen, Jingmei; Yap, Glenn P A; Werner, Jan-Philipp; Theopold, Klaus H

2011-11-28

32

Alkali metal mediated C-C bond coupling reaction  

NASA Astrophysics Data System (ADS)

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.

Tachikawa, Hiroto

2015-02-01

33

Alkali metal mediated C-C bond coupling reaction.  

PubMed

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. PMID:25681900

Tachikawa, Hiroto

2015-02-14

34

Diffusion bonding of the oxide dispersion strengthened steel PM2000  

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

35

Rhodium catalyzed chelation-assisted C-H bond functionalization reactions  

PubMed Central

Conspectus Over the last several decades, researchers have achieved remarkable progress in the field of organometallic chemistry. The development of metal-catalyzed cross-coupling reactions represents a paradigm shift in chemical synthesis, and today synthetic chemists can readily access carbon-carbon and carbon-heteroatom bonds from a vast array of starting compounds. Although we cannot understate the importance of these methods, the required pre-functionalization to carry out these reactions adds cost and reduces the availability of the starting reagents. The use of C-H bond activation in lieu of pre-functionalization has presented a tantalizing alternative to classical cross-coupling reactions. Researchers have met the challenges of selectivity and reactivity associated with the development of C-H bond functionalization reactions with an explosion of creative advances in substrate and catalyst design. Literature reports on selectivity based on steric effects, acidity, and electronic and directing group effects are now numerous. Our group has developed an array of C-H bond functionalization reactions that take advantage of a chelating directing group, and this Account surveys our progress in this area. The use of chelation control in C-H bond functionalization offers several advantages with respect to substrate scope and application to total synthesis. The predictability and decreased dependence on the inherent stereoelectronics of the substrate generally result in selective and high yielding transformations with broad applicability. The nature of the chelating moiety can be chosen to serve as a functional handle in subsequent elaborations. Our work began with the use of Rh(I) catalysts in intramolecular aromatic C-H annulations, which we further developed to include enantioselective transformations. The application of this chemistry to the simple olefinic C-H bonds found in ?,?-unsaturated imines allowed access to highly substituted olefins, pyridines, and piperidines. We observed complementary reactivity with Rh(III) catalysts and developed an oxidative coupling with unactivated alkenes. Further studies on the Rh(III) catalysts led us to develop methods for the coupling of C-H bonds to polarized ? bonds such as those in imines and isocyanates. In several cases the methods that we have developed for chelation-controlled C-H bond functionalization have been applied to the total synthesis of complex molecules such as natural products, highlighting the utility of these methods in organic synthesis. PMID:22148885

Colby, Denise A.; Tsai, Andy S.; Bergman, Robert G.; Ellman, Jonathan A.

2011-01-01

36

Regio-selectivity of the Oxidative C-S Bond Formation in Ergothioneine and Ovothiol Biosyntheses  

PubMed Central

Ergothioneine (5) and ovothiol (8) are two novel thiol-containing natural products. Their C-S bonds are formed by oxidative coupling reactions catalyzed by EgtB and OvoA enzymes, respectively. In this work, it was discovered that besides catalyzing the oxidative coupling between histidine and cysteine (1 ? 6 conversion), OvoA can also catalyze a direct oxidative coupling between hercynine (2) and cysteine (2 ? 4 conversion), which can shorten the ergothioneine biosynthetic pathway by two steps. PMID:24016264

Song, Heng; Leninger, Maureen; Lee, Norman

2014-01-01

37

Transient liquid phase bonding of ferritic oxide dispersion strengthened alloys  

NASA Astrophysics Data System (ADS)

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.

Krishnardula, Venu Gopal

2006-04-01

38

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

PubMed Central

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

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

2014-01-01

39

Friedel-Crafts reaction of benzyl fluorides: selective activation of C-F bonds as enabled by hydrogen bonding.  

PubMed

A Friedel-Crafts benzylation of arenes with benzyl fluorides has been developed. The reaction produces 1,1-diaryl alkanes in good yield under mild conditions without the need for a transition metal or a strong Lewis acid. A mechanism involving activation of the C-F bond through hydrogen bonding is proposed. This mode of activation enables the selective reaction of benzylic C-F bonds in the presence of other benzylic leaving groups. PMID:25303636

Champagne, Pier Alexandre; Benhassine, Yasmine; Desroches, Justine; Paquin, Jean-François

2014-12-01

40

Copper-catalyzed oxaziridine-mediated oxidation of C-H bonds.  

PubMed

The highly regio- and chemoselective oxidation of activated C-H bonds has been observed via copper-catalyzed reactions of oxaziridines. The oxidation proceeded with a variety of substrates, primarily comprising allylic and benzylic examples, as well as one example of an otherwise unactivated tertiary C-H bond. The mechanism of the reaction is proposed to involve single-electron transfer to the oxaziridines to generate a copper-bound radical anion, followed by hydrogen atom abstraction and collapse to products, with regeneration of the catalyst by a final single-electron transfer event. The involvement of allylic radical intermediates was supported by a radical-trapping experiment with TEMPO. PMID:22830300

Motiwala, Hashim F; Gülgeze, Belgin; Aubé, Jeffrey

2012-08-17

41

Effect of bond coat creep and oxidation on TBC integrity  

NASA Technical Reports Server (NTRS)

The potential of thermal barrier coatings (TBCs) on high-pressure turbine (HPT) nozzles and blades is limited at present by the inability to quantitatively predict TBC life for these components. The goal is to isolate the major TBC failure mechanisms, which is part of the larger program aimed at developing TBC life prediction models. Based on the results of experiments to isolate TBC failure mechanisms, the effects of bond coat oxidation and bond coat creep on TBC integrity is discussed. In bond coat oxidation experiments, Rene prime 80 specimens coated with a NiCrAlY/ZrO2-8 percent Y2O3 TBC received isothermal pre-exposures at 2000 F in static argon, static air, or received no pre-exposure. The effects of oxidation due to the pre-exposures were determined by thermal cycle tests in both static air and static argon at 2000 F. To study the effect of bond coat creep on TBS behavior, four bond coats with different creep properties were evaluated by thermal cycle tests in air at 2000 F. The test results, the relative importance of these two failure mechanisms, and how their effects may be quantified will also be discussed.

Duderstadt, E. C.; Pilsner, B. H.

1985-01-01

42

Bonding of sapphire to sapphire by eutectic mixture of aluminum oxide and zirconium oxide  

NASA Technical Reports Server (NTRS)

An element comprising sapphire, ruby or blue sapphire can be bonded to another element of such material with a eutectic mixture of aluminum oxide and zirconium oxide. The bonding mixture may be applied in the form of a distilled water slurry or by electron beam vapor deposition. In one embodiment the eutectic is formed in situ by applying a layer of zirconium oxide and then heating the assembly to a temperature above the eutectic temperature and below the melting point of the material from which the elements are formed. The formation of a sapphire rubidium maser cell utilizing eutectic bonding is shown.

Deluca, J. J. (inventor)

1979-01-01

43

Bonding of sapphire to sapphire by eutectic mixture of aluminum oxide and zirconium oxide  

NASA Technical Reports Server (NTRS)

Bonding of an element comprising sapphire, ruby or blue sapphire to another element of such material with a eutectic mixture of aluminum oxide and zirconium oxide is discussed. The bonding mixture may be applied in the form of a distilled water slurry or by electron beam vapor deposition. In one embodiment the eutectic is formed in situ by applying a layer of zirconium oxide and then heating the assembly to a temperature above the eutectic temperature and below the melting point of the material from which the elements are formed. The formation of a sapphire rubidium maser cell utilizing eutectic bonding is shown.

Deluca, J. J. (inventor)

1975-01-01

44

Oxidative Reactions with Nonaqueous Enzymes  

SciTech Connect

The objective of this work is to demonstrate a proof-of-concept of enzymatic oxidative processing in nonaqueous media using alkene epoxidation and phenolic polymerization as relevant targets. This project will provide both the fundamental and applied investigations necessary to initiate the implementation of oxidative biocatalysts as commercially relevant alternatives to chemical processing in general, and to phenolic polymerizations and alkene epoxidation specifically. Thus, this work will address the Bioprocessing Solicitation Area to: (1) makes major improvements to phenolic polymerization and alkene epoxidation technologies; (2) is expected to be cost competitive with competing conventional processes; and (3) produces higher yields with less waste.

Jonathan S. Dordick; Douglas Clark; Brian H Davison; Alexander Klibanov

2001-12-30

45

Effects of hydrogen bonding to a bacteriochlorophyll-bacteriopheophytin dimer in reaction centers from Rhodobacter sphaeroides.  

PubMed

The properties of the primary electron donor in reaction centers from Rhodobacter sphaeroides have been investigated in mutants containing a bacteriochlorophyll (BChl)--bacteriopheophytin (BPhe) dimer with and without hydrogen bonds to the conjugated carbonyl groups. The heterodimer mutation His M202 to Leu was combined with each of the following mutations: His L168 to Phe, which should remove an existing hydrogen bond to the BChl molecule; Leu L131 to His, which should add a hydrogen bond to the BChl molecule; and Leu M160 to His and Phe M197 to His, each of which should add a hydrogen bond to the BPhe molecule [Rautter, J., Lendzian, F., Schulz, C., Fetsch, A., Kuhn M., Lin, X., Williams, J. C., Allen J. P., & Lubitz, W. (1995) Biochemistry 34, 8130-8143]. Pigment extractions and Fourier transform Raman spectra confirm that all of the mutants contain a heterodimer. The bands in the resonance Raman spectra arising from the BPhe molecule, which is selectively enhanced, exhibit the shifts expected for the addition of a hydrogen bond to the 9-keto and 2-acetyl carbonyl groups. The oxidation--reduction midpoint potential of the donor is increased by approximately 85 mV by the addition of a hydrogen bond to the BChl molecule but is only increased by approximately 15 mV by the addition of a hydrogen bond to the BPhe molecule. An increase in the rate of charge recombination from the primary quinone is correlated with an increase in the midpoint potential. The yield of electron transfer to the primary quinone is 5-fold reduced for the mutants with a hydrogen bond to the BPhe molecule. Room- and low-temperature optical absorption spectra show small differences from the features that are typical for the heterodimer, except that a large increase in absorption is observed around 860-900 nm for the donor Qy band in the mutant that adds a hydrogen bond to the BChl molecule. The changes in the optical spectra and the yield of electron transfer are consistent with a model in which the addition of a hydrogen bond to the BChl molecule increases the energy of an internal charge transfer state while the addition to the BPhe molecule stabilizes this state. The results show that the properties of the heterodimer are different depending on which side is hydrogen-bonded and suggest that the hydrogen bonds alter the energy of the internal charge transfer state in a well-defined manner. PMID:8639609

Allen, J P; Artz, K; Lin, X; Williams, J C; Ivancich, A; Albouy, D; Mattioli, T A; Fetsch, A; Kuhn, M; Lubitz, W

1996-05-28

46

?-Bond activation of small molecules and reactions catalyzed by transition-metal complexes: theoretical understanding of electronic processes.  

PubMed

?-Bond activations of R1-R2 and R1-X1 (R1, R2 = H, alkyl, aromatics, etc.; X1 = electronegative group) by transition-metal complexes are classified into two main categories: ?-bond activation by a metal (M) center and that by a metal-ligand bond. The former is classified into two subcategories: concerted oxidative addition to M and stepwise oxidative addition via nucleophilic attack of M. The latter is also classified into two subcategories: heterolytic activaton by M-X2 (X2 = anion ligand) and oxidative addition to M-L (L = neutral ligand). In the concerted oxidative addition, charge transfer (CT) occurs from the M d orbital to the ?* antibonding orbital of R1-R2, the clear evidence of which is presented here. The concerted oxidative additions of Ph-CN, Me-CN, and Ph-Cl to a nickel(0) complex are discussed as examples. The stepwise oxidative addition occurs through nucleophilic attack of M to R1-X1 to form an ion-pair intermediate. In the nucleophilic attack, CT occurs from the M d? to either the ?* orbital or empty p? orbital of R1-X1. Solvation plays a crucial role in stabilizing the transition state and ion-pair intermediate. The oxidative addition reactions of Ph-I, CH3-Br, and Br2B(OSiH3) to platinum(0), platinum(II), and palladium(0) complexes are discussed. In the heterolytic activation of R1-R2 by an M-X2 bond, R1 and R2 are bound with M and X2, respectively, indicating that R1 becomes anion-like and R2 becomes cation-like. CT mainly occurs from the X2 ligand to the ?* antibonding orbital of R1-R2 and also from R1 to the M empty d orbital. In the oxidative addition to an M-L moiety, R1 is bound with M, R2 is bound with L, and thus-formed L-R2 is bound with M. The oxidative addition reaction of the Si-H bond of silane to Cp2Zr(C2H4) and that of the H-H bond of H2 to Ni[MesB(o-Ph2PC6H4)2] are discussed as examples. The importance of the ?-bond activation in such catalytic reactions as nickel(0)-catalyzed phenylcyanation of alkyne, nickel(0)-catalyzed carboxylation of phenyl chloride, ruthenium(II)-catalyzed hydrogenation of carbon dioxide, and the Hiyama cross-coupling reaction is discussed based on theoretical studies. PMID:24784994

Guan, Wei; Sayyed, Fareed Bhasha; Zeng, Guixiang; Sakaki, Shigeyoshi

2014-07-01

47

Stereoselective heterocycle synthesis through oxidative carbon-hydrogen bond activation.  

PubMed

Heterocycles are ubiquitous structures in both drugs and natural products, and efficient methods for their construction are being pursued constantly. Carbon-hydrogen bond activation offers numerous advantages for the synthesis of heterocycles with respect to minimizing the length of synthetic routes and reducing waste. As interest in chiral medicinal leads increases, stereoselective methods for heterocycle synthesis must be developed. The use of carbon-hydrogen bond activation reactions for stereoselective heterocycle synthesis has produced a range of creative transformations that provide a wide array of structural motifs, selected examples of which are described in this review. PMID:21061234

Liu, Lei; Floreancig, Paul E

2010-01-01

48

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

PubMed

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

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

2015-02-21

49

Ammonia, oxidation leaching of chalcopyrite —reaction kinetics  

Microsoft Academic Search

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

L. W. Beckstead; J. D. Miller

1977-01-01

50

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

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

Timm, Matthew J; Matta, Chérif F

2014-12-01

51

Direct-Coupling O? Bond Forming Pathway in Cobalt Oxide Water Oxidation Catalysts  

E-print Network

We report a catalytic mechanism for water oxidation in a cobalt oxide cubane model compound, in which the crucial O–O bond formation step takes place by direct coupling between two CoIV(O) metal oxo groups. Our results are ...

Wang, Lee-Ping

52

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

NASA Astrophysics Data System (ADS)

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.

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

2006-11-01

53

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

PubMed Central

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

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

2010-01-01

54

SURFACE REACTIONS OF OXIDES OF SULFUR  

EPA Science Inventory

Surface reactions of several sulfur-containing molecules have been studied in order to understand the mechanism by which sulfate ions are formed on atmospheric aerosols. At 25C the heterogeneous oxidation of SO2 by NO2 to sulfuric acid and sulfate ions occurred on hydrated silica...

55

Metal-Free Oxidative Functionalization of C(sp(3))-H Bond Adjacent to Oxygen and Radical Addition to Olefins.  

PubMed

A DTBP-promoted oxidative functionalization of a C(sp(3))-H bond adjacent to oxygen and intermolecular radical addition to olefins without use of any metal catalyst or photoredox catalysis is reported. The reaction has a wide scope of olefin, alcohol, and cycloether substrates, which provides an easy way for direct preparation of ?,?-amino alcohols. PMID:25692320

Zhou, Wei; Qian, Ping; Zhao, Jincan; Fang, Hong; Han, Jianlin; Pan, Yi

2015-03-01

56

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

PubMed

Reactions of neutral cobalt oxide clusters (Co(m)O(n), m = 3-9, n = 3-13) with CO, NO, C(2)H(2), and C(2)H(4) in a fast flow reactor are investigated by time of flight mass spectrometry employing 118 nm (10.5 eV) single photon ionization. Strong cluster size dependent behavior is observed for all the oxidation reactions; the Co(3)O(4) cluster has the highest reactivity for reactions with CO and NO. Cluster reactivity is also highly correlated with either one or more following factors: cluster size, Co(iii) concentration, the number of the cobalt atoms with high oxidation states, and the presence of an oxygen molecular moiety (an O-O bond) in the Co(m)O(n) clusters. The experimental cluster observations are in good agreement with condensed phase Co(3)O(4) behavior. Density functional theory calculations at the BPW91/TZVP level are carried out to explore the geometric and electronic structures of the Co(3)O(4) cluster, reaction intermediates, transition states, as well as reaction mechanisms. CO, NO, C(2)H(2), and C(2)H(4) are predicted to be adsorbed on the Co(ii) site, and react with one of the parallel bridge oxygen atoms between two Co(iii) atoms in the Co(3)O(4) cluster. Oxidation reactions with CO, NO, and C(2)H(2) on the Co(3)O(4) cluster are estimated as thermodynamically favorable and overall barrierless processes at room temperature. The oxidation reaction with C(2)H(4) is predicted to have a very small overall barrier (<0.23 eV). The oxygen bridge between two Co(iii) sites in the Co(3)O(4) cluster is responsible for the oxidation reactions with CO, NO, C(2)H(2), and C(2)H(4). Based on the gas phase experimental and theoretical cluster studies, a catalytic cycle for these oxidation reactions on a condensed phase cobalt oxide catalyst is proposed. PMID:20066380

Xie, Yan; Dong, Feng; Heinbuch, Scott; Rocca, Jorge J; Bernstein, Elliot R

2010-01-28

57

Mechanical Properties and Chemical Reactions at the Directly Bonded Si-Si Interface  

NASA Astrophysics Data System (ADS)

Directly bonded interfaces of hydrophilic and hydrophobic Si(100) wafers were studied from the viewpoint of bonding energy and chemical products as a function of the annealing temperature. The experimental results indicated that for both hydrophilic and hydrophobic Si/Si bonded wafer pairs, the behavior of the bubbles at the bonding interface and the bonding energy were closely related to the behavior of the hydrogen and oxygen atoms at the bonding interface. The bonding mechanisms for both cases have been discussed on the basis of the chemical reactions induced by the annealing temperature.

Toyoda, Eiji; Sakai, Akira; Isogai, Hiromichi; Senda, Takeshi; Izunome, Koji; Nakatsuka, Osamu; Ogawa, Masaki; Zaima, Shigeaki

2009-01-01

58

Metal-free tandem oxidative aryl migration and C-C bond cleavage: synthesis of ?-ketoamides and esters from acrylic derivatives.  

PubMed

A novel tandem metal-free oxidative aryl migration/C-C bond-cleavage reaction, mediated by hypervalent iodine reagent, has been discovered. The presented transformation provided straightforward access to important ?-ketoamide and ?-ketoester derivatives from readily available acrylic derivatives via a concerted process of 1,2-aryl shift concomitant with C-C bond cleavage. PMID:25343425

Liu, Le; Du, Liang; Zhang-Negrerie, Daisy; Du, Yunfei; Zhao, Kang

2014-11-01

59

Palladium-catalyzed regioselective benzylation-annulation of pyridine N-oxides with toluene derivatives via multiple C-H bond activations: benzylation versus arylation.  

PubMed

A palladium-catalyzed cross-dehydrogenative coupling (CDC) reaction of pyridine N-oxides with toluenes has been developed that operates under mild conditions. 2-Benzylpyridines can be obtained directly by this method via a CDC reaction between unactivated toluenes and pyridine N-oxides. In addition, azafluorene N-oxides, of value for future medicinal chemistry applications, can be obtained successfully by this procedure via four tandem C-H bond activations. PMID:25607468

Kianmehr, Ebrahim; Faghih, Nasser; Khan, Khalid Mohammed

2015-02-01

60

Mullite fiber reinforced reaction bonded Si3N4 composites  

NASA Technical Reports Server (NTRS)

Fracture toughnesses of brittle ceramic materials have been improved by introducing reinforcements and carefully tailored interface layers. Silicon carbide and Si3N4 have been emphasized as matrices of structural composites intended for high temperature service because they combine excellent mechanical, chemical, thermal and physical properties. Both matrices have been successfully toughened with SiC fibers, whiskers and particles for ceramic matrix composite (CMC) parts made by sintering, hot pressing or reaction forming processes. These SiC reinforced CMCs have exhibited significantly improved toughnesses at low and intermediate temperature levels, as well as retention of properties at high temperatures for selected exposures; however, they are vulnerable to attack from elevated temperature dry and wet oxidizing atmospheres after the matrix has cracked. Property degradation results from oxidation of interface layers and/or reinforcements. The problem is particularly acute for small diameter (-20 tim) polymer derived SiC fibers used for weavable toes. This research explored opportunities for reinforcing Si3N4 matrices with fibers having improved environmental stability; the findings should also be applicable to SiC matrix CMCs.

Saleh, T.; Sayir, A.; Lightfoot, A.; Haggerty, J.

1996-01-01

61

Polyorganosilazane preceramic binder development for reaction bonded silicon nitride composites  

SciTech Connect

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.

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

1992-11-01

62

Polyorganosilazane preceramic binder development for reaction bonded silicon nitride composites  

SciTech Connect

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.

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

1992-11-01

63

Structure and properties of hydrogen bonded complexes of pyridine-N-oxide and its derivatives  

E-print Network

-N-oxides; Hydrogen bond complexes 1. Introduction Heterocyclic compounds containing N-oxide groups have achievedStructure and properties of hydrogen bonded complexes of pyridine-N-oxide and its derivatives V 1998; accepted 18 January 1999 Abstract Molar Kerr constants and electric dipole moments of hydrogen

64

Copper oxide aerosol: reaction with SO 2  

NASA Astrophysics Data System (ADS)

Copper oxide aerosol and SO 2 are emitted concurrently from copper smelters. The reactions between copper oxide aerosol and SO 2 could result in the formation of irritant sulfur oxides on the surface of the particles that could affect smelter workers or residents living near the smelter. In this study, we investigate the reactions of an ultrafine copper oxide aerosol (count median diameter = 0.03 ?m) and SO 2. In a dry furnace, two S(IV) species were formed as determined using x-ray photoelectron spectroscopy. One S(IV) corresponds to ionic S(IV) with a binding energy of 166.8 eV. The other corresponds to adsorbed S(IV) with a binding energy of 168.4eV. Increasing relative humidity (r.h.) in the mixing chamber to 78% promotes the formation of S(VI). Addition of water vapor into the hot zone of the furnace leads to the formation of only S(VI) on the aerosol and this is not affected by the r.h. in the mixing chamber. Sputtering of the sample by an Ar + beam revealed that these sulfur oxides were on the surface of the aerosol. The concentrations of total S on the particles in the exposure chamber as determined using a flame photometric detector system were 0.24, 0.47 and 0.58 ?mole S m-3 for the mixing conditions of dry furnace, dry furnace with high r.h. and water in the furnace with high humidity, respectively.

Chen, L. C.; Peoples, S. M.; McCarthy, J. F.; Amdur, M. O.

65

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

PubMed Central

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

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

2014-01-01

66

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

67

Mechanisms of Reactions Related to Selective Alkane Oxidation by Pt Complexes  

Microsoft Academic Search

Some of the most promising homogeneous systems for the selective activation and functionalization of alkanes are based on platinum. Proposed key reaction steps at Pt(II) and Pt(IV) metal centers have been directly observed and studied using model compounds. Investigations of oxidative addition and reductive elimination reactions of carbon-hydrogen, carbon- carbon and carbon-heteroatom bonds have provided detailed information about the intermediates

Jennifer L. Look; Ulrich Fekl; Karen I. Goldberg

2004-01-01

68

Graphene-hemin hybrid material as effective catalyst for selective oxidation of primary C-H bond in toluene  

PubMed Central

An effective hemin catalyst on graphene support for selective oxidation of primary C-H bond in toluene is reported with an over 50% conversion rate achieved at mild conditions. Significantly this hybrid material shows catalytic efficiency in toluene oxidation with selectivity towards benzoic acid. The role of graphene support is discussed here as providing large contact area between the catalyst and the substrate, maintaining hemin in catalytically active monomer form, attracting electron to promote site isolation, as well as protecting hemin from oxidative degradation during the reaction. Moreover, graphene is suggested to largely alter the final product selectivity, due to the different ?-? interaction strength between the graphene support and the substrate/oxidized products. With longer reaction time, overall conversion rate tends to maintain relatively unchanged while toluene undergoes a series of oxidation to convert mostly to benzoic acid.

Li, Yongjia; Huang, Xiaoqing; Li, Yujing; Xu, Yuxi; Wang, Yang; Zhu, Enbo; Duan, Xiangfeng; Huang, Yu

2013-01-01

69

The Oxyhemoglobin Reaction of Nitric Oxide  

NASA Astrophysics Data System (ADS)

The oxidation of nitric oxide (NO) to nitrate by oxyhemoglobin is a fundamental reaction that shapes our understanding of NO biology. This reaction is considered to be the major pathway for NO elimination from the body; it is the basis for a prevalent NO assay; it is a critical feature in the modeling of NO diffusion in the circulatory system; and it informs a variety of therapeutic applications, including NO-inhalation therapy and blood substitute design. Here we show that, under physiological conditions, this reaction is of little significance. Instead, NO preferentially binds to the minor population of the hemoglobin's vacant hemes in a cooperative manner, nitrosylates hemoglobin thiols, or reacts with liberated superoxide in solution. In the red blood cell, superoxide dismutase eliminates superoxide, increasing the yield of S-nitrosohemoglobin and nitrosylated hemes. Hemoglobin thus serves to regulate the chemistry of NO and maintain it in a bioactive state. These results represent a reversal of the conventional view of hemoglobin in NO biology and motivate a reconsideration of fundamental issues in NO biochemistry and therapy.

Gow, Andrew J.; Luchsinger, Benjamin P.; Pawloski, John R.; Singel, David J.; Stamler, Jonathan S.

1999-08-01

70

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

NASA Technical Reports Server (NTRS)

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.

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

1979-01-01

71

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

PubMed

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

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

2011-10-27

72

Catalytic access to ?-oxo gold carbenes by N-O bond oxidants.  

PubMed

Metal carbenes are highly versatile species that mediate various transformations. Recent advances in gold catalysis have allowed catalytic access to ?-oxo metal carbenes from the alkyne functionality. Compared with traditional methods that rely upon metal-catalyzed decomposition of diazo precursors, the generation of this synthon occurs in an environmentally more appealing fashion by gold-catalyzed alkyne oxygenation. Hydroxylamine derivatives are typically prepared from hydroxylamine salts that are cheap and can be handled without special precaution. In reactions with an alkyne activated by gold, relatively stable nitrones and related reagents undergo efficient O-atom transfer to form putative ?-oxo gold carbenes. The highly reactive nature of these species could be utilized in a variety of cascade transformations. Herein, recent synthetic methods based on this reactivity as well as the currently available mechanistic and structural studies through computational and experimental methods have been discussed. A variety of tandem reactions performed by our laboratory and others have demonstrated the synthetic utility of catalytically generated ?-oxo gold carbenes and enabled access to various heterocycles. For example, a reaction between nitrones and alkynes led to azomethine ylides for the [3 + 2] dipolar cycloaddition. Alternatively, ?-oxo gold carbenes can be transformed into enolate equivalents through a 1,2-pinacol shift. The addition of hydroxylamine derivatives across triple bonds led to oxoamination, providing ?-aminocarbonyl compounds or regioselective Fisher indole-type synthesis. N-O bond cleaving redox chemistry paved the way for intermolecular redox processes, most notably by use of pyridine-N-oxide derivatives with expanding synthetic applications. In closing, other metal-based oxygenations using N-O bond oxidants will be highlighted. One particularly interesting aspect is the process leading to metal vinylidene complexes. Trapping of this intermediate resulted in opposite regioselectivity from gold catalysis in alkyne oxygenation and led to ketene intermediates for use in subsequent cascade transformations. PMID:24517590

Yeom, Hyun-Suk; Shin, Seunghoon

2014-03-18

73

Heterogeneous reaction of ozone with aluminum oxide  

NASA Technical Reports Server (NTRS)

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.

Keyser, L. F.

1976-01-01

74

Understanding Bond Formation in Polar One-Step Reactions. Topological Analyses of the Reaction between Nitrones and Lithium Ynolates.  

PubMed

The mechanism of the reaction between nitrones and lithium ynolates has been studied using DFT methods at the M06-2X/cc-pVTZ/PCM=THF level. After the formation of a starting complex an without energy barrier, in which the lithium atom is coordinated to both nitrone and ynolate, the reaction takes place in one single kinetic step through a single transition structure. However, the formation of C-C and C-O bonds takes place sequentially through a typical two-stage, one-step process. A combined study of noncovalent interactions (NCIs) and electron localization function (ELFs) of selected points along the intrinsic reaction coordinate (IRC) of the reaction confirmed that, in the transition structure, only the C-C bond is being formed to some extent, whereas an electrostatic interaction is present between carbon and oxygen atoms previous to the formation of the C-O bond. Indeed, the formation of the second C-O bond only begins when the first C-C bond is completely formed without formation of any intermediate. Once the C-C bond is formed and before the C-O bond formation starts the RMS gradient norm dips, approaching but not reaching 0, giving rise to a hidden intermediate. PMID:25803829

Roca-López, David; Polo, Victor; Tejero, Tomás; Merino, Pedro

2015-04-17

75

Oxide treatments of Al 2024 for adhesive bonding- surface characterization  

NASA Astrophysics Data System (ADS)

A study was made to characterize the surface of oxides formed on Al 2024 in comparison to those formed on Al 1100, using Auger, ESCA, SIMS, FTIR and SEM/EDAX techniques. The pretreatments studied were chromate conversion coating, chromic acid anodizing and sulfuric acid anodizing. The specimens were evaluated as treated and after exposure to laboratory conditions ( T=25?3°C and relative humidity of 60?10%) for 6 months. In addition, a new surface pretreatment was studied, which was based on McDonnell Douglas P.S. 13201 specification. Adhesive bond strength of silicone rubbers and epoxy adhesives to pretreated Al 2024 was determined, using single lap joint specimens. It was shown that the main difference between the anodic coatings on Al 1100 and Al 2024 was the presence of copper on the surface in the latter. The presence of copper led us to postulate the mechanism of polymerization inhibition of 2 parts polysiloxane adhesive. The most suitable treatments for adhesive joining were found to be chromic acid sealed or unsealed anodizing for both Al 2024 and Al 1100. Our standard chromic acid anodizing gave higher bond strength for aluminum-adhesive joints than the "Douglas" process. as determined with several epoxy adhesives. Correlation between microscopic and macroscopic phenomena was established.

Fin, N.; Dodiuk, H.; Yaniv, A. E.; Drori, L.

1987-03-01

76

Glass wafers bonding via Diels–Alder reaction at mild temperature  

Microsoft Academic Search

In this paper, we introduced a novel bonding method of glass wafers by Diels–Alder reaction at mild temperature. After standard hydroxylization and aminosilylation, two wafers were modified by 2-furaldehyde and maleic anhydride, respectively. Then they were brought into close contact and tightly held with a clamping fixture. A strong bonding could be achieved by annealing for 5h at 200°C. Bonding

Minjie Zhang; Jianying Zhao; Lianxun Gao

2008-01-01

77

Noncovalent Organocatalysis Based on Hydrogen Bonding: Elucidation of Reaction Paths by Computational Methods  

NASA Astrophysics Data System (ADS)

In this article, the functions of hydrogen bonds in organocatalytic reactions are discussed on atomic level by presenting DFT studies of selected examples. Theoretical investigation provides a detailed insight in the mechanism of substrate activation and orientation, and the stabilization of transition states and intermediates by hydrogen bonding (e.g. oxyanion hole). The examples selected comprise stereoselective catalysis by bifunctional thioureas, solvent catalysis by fluorinated alcohols in epoxidation by hydrogen peroxide, and intramolecular cooperative hydrogen bonding in TADDOL-type catalysts.

Etzenbach-Effers, Kerstin; Berkessel, Albrecht

78

Overcoming the "oxidant problem": strategies to use O2 as the oxidant in organometallic C-H oxidation reactions catalyzed by Pd (and Cu).  

PubMed

Oxidation reactions are key transformations in organic chemistry because they can increase chemical complexity and incorporate heteroatom substituents into carbon-based molecules. This principle is manifested in the conversion of petrochemical feedstocks into commodity chemicals and in the synthesis of fine chemicals, pharmaceuticals, and other complex organic molecules. The utility and function of these molecules correlate directly with the presence and specific placement of oxygen and nitrogen heteroatoms and other functional groups within the molecules. Methods for selective oxidation of C-H bonds have expanded significantly over the past decade, and their role in the synthesis of organic chemicals will continue to increase. Our group's contributions to this field are linked to our broader interest in the development and mechanistic understanding of aerobic oxidation reactions. Molecular oxygen (O(2)) is the ideal oxidant. Its low cost and lack of toxic byproducts make it a highly appealing reagent that can address key "green chemistry" priorities in industry. With strong economic and environmental incentives to use O(2), the commmodity chemicals industry often uses aerobic oxidation reactions. In contrast, O(2) is seldom used to prepare more-complex smaller-volume chemicals, a limitation that reflects, in part, the limited synthetic scope and utility of existing aerobic reactions. Pd-catalyzed reactions represent some of the most versatile methods for selective C-H oxidation, but they often require stoichiometric transition-metal or organic oxidants, such as Cu(II), Ag(I), or benzoquinone. This Account describes recent strategies that we have identified to use O(2) as the oxidant in these reactions. In Pd-catalyzed C-H oxidation reactions that form carbon-heteroatom bonds, the stoichiometric oxidant is often needed to promote difficult reductive elimination steps in the catalytic mechanism. To address this challenge, we have identified new ancillary ligands for Pd that promote reductive elimination, or replaced Pd with a Cu catalyst that undergoes facile reductive elimination from a Cu(III) intermediate. Both strategies have enabled O(2) to be used as the sole stoichiometric oxidant in the catalytic reactions. C-H oxidation reactions that form the product via ?-hydride or C-C reductive elimination steps tend to be more amenable to the use of O(2). The use of new ancillary ligands has also overcome some of the limitations in these methods. Mechanistic studies are providing insights into some (but not yet all) of these advances in catalytic reactivity. PMID:22263575

Campbell, Alison N; Stahl, Shannon S

2012-06-19

79

Low-temperature thermal oxide to plasma-enhanced chemical vapor deposition oxide wafer bonding for thin-film transfer application  

NASA Astrophysics Data System (ADS)

Low-temperature direct plasma-enhanced chemical vapor deposition (PECVD) oxide to thermal oxide bonding is described. The PECVD oxide is densified at 350 °C and chemical-mechanically polished to obtain reasonably smooth surface for bonding. The PECVD oxide wafer is bonded to the thermal oxide wafer at room temperature after piranha clean that leaves the wafer surfaces hydrophilic. A postbonding anneal at 300 °C completes the bonding. A void-free bonding interface is observed from infrared imaging and the bonding strength is estimated to be 432 mJ/m2. This bonding method can be used in a variety of applications, including three-dimensional integration.

Tan, C. S.; Fan, A.; Chen, K. N.; Reif, R.

2003-04-01

80

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

E-print Network

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. ...

Strieter, Eric R

2005-01-01

81

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

NASA Technical Reports Server (NTRS)

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.

Sanders, William A.; Mieskowski, Diane M.

1989-01-01

82

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

E-print Network

On the Nature of Carbon-Hydrogen Bond Activation at Rhodium and Related Reactions William D. Jones to cleave C-S bonds. Mechanistic information has been obtained indicating coordination through sulfur prior to cleavage. Relevant examples of nickel-based C-S cleavage will also be given. Introduction The activation

Jones, William D.

83

Proton transfer reactions and hydrogen-bond networks in protein environments  

PubMed Central

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

Ishikita, Hiroshi; Saito, Keisuke

2014-01-01

84

Carbon-oxygen bond strength as a control of reaction kinetics: Phenol on Mo(110)  

NASA Astrophysics Data System (ADS)

The reaction of phenol on Mo(110) has been studied using temperature programmed reaction and X-ray photoelectron spectroscopies. After desorption of multilayers and a weakly bound molecular species, decomposition produces the only reaction products observed: gaseous dihydrogen, surface carbon and surface oxygen. The O?H bond cleaves first at temperatures below 360 K to form surface phenoxide (C 6H 5O-), followed by C?H bond activation commencing at 370 K. C?O bonds are cleaved in the temperature range of 370 to 450 K. After annealing to 300 K, multiple species are detected on the surface by X-ray photoelectron spectroscopy. The cleavage of C?H bonds in the same temperature regime as C?O bonds is thought to lead to selective decomposition of phenol on Mo(110). The reaction of phenol is contrasted to that of a sulfur-containing analogue, benzenethiol, on the Mo(110) surface. The stability of the phenoxide intermediate with respect to carbon-heteroatom bond cleavage is greater than that of the corresponding phenyl thiolate formed from benzenethiol. Comparison of the reaction of phenol and benzenethiol demonstrates the importance of C? X ( X = O, S) bond strength in determining the reactivity and selectivity of these molecules.

Serafin, J. G.; Friend, C. M.

85

Carbon-oxygen bond strength as a control of reaction kinetics: Phenol on Mo(110)  

NASA Astrophysics Data System (ADS)

The reaction of phenol on Mo(110) has been studied using temperature programmed reaction and X-ray photoelectron spectroscopies. After desorption of multilayers and a weakly bound molecular species, decomposition produces the only reaction products observed: gaseous dihydrogen, surface carbon and surface oxygen. The O-H bond cleaves first at temperatures below 360 K to form surface phenoxide (C 6H 5O-), followed by C-H bond activation commencing at 370 K. C-O bonds are cleaved in the temperature range of 370 to 450 K. After annealing to 300 K, multiple species are detected on the surface by X-ray photoelectron spectroscopy. The cleavage of C-H bonds in the same temperature regime as C-O bonds is thought to lead to selective decomposition of phenol on Mo(110). The reaction of phenol is contrasted to that of a sulfur-containing analogue, benzenethiol, on the Mo(110) surface. The stability of the phenoxide intermediate with respect to carbon-heteroatom bond cleavage is greater than that of the corresponding phenyl thiolate formed from benzenethiol. Comparison of the reaction of phenol and benzenethiol demonstrates the importance of C- X ( X = O, S) bond strength in determining the reactivity and selectivity of these molecules.

Serafin, J. G.; Friend, C. M.

1989-03-01

86

Analytic bond-order potential for atomistic simulations of zinc oxide  

E-print Network

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

Nordlund, Kai

87

Competitive oxygen-18 kinetic isotope effects expose OO bond formation in water oxidation  

E-print Network

Competitive oxygen-18 kinetic isotope effects expose O­O bond formation in water oxidation. Roth*a Competitive oxygen kinetic isotope effects (18 O KIEs) on water oxidation initiated by ruthenium during oxygenic photo- synthesis.1 Formation of the O­O bond in molecular oxygen has been proposed

Roth, Justine P.

88

Palladium-Catalyzed Aryl C(sp(2))-H Bond Hydroxylation of 2-Arylpyridine Using TBHP as Oxidant.  

PubMed

An efficient synthesis of phenols via Pd-catalyzed, pyridyl-directed homogeneous hydroxylation of the aryl C-H bond was developed, in which tert-butyl hydroperoxide was used as the sole oxidant. The method had a broad group tolerance and was available for both electron-rich and electron-deficient substrates. The reaction of a series of 2-arylpyridine derivatives gave the ortho-hydroxylation products in moderate to good yields. PMID:25664805

Dong, Jiawei; Liu, Ping; Sun, Peipei

2015-03-01

89

Effects of thermal cycling on thermal expansion and mechanical properties of SiC fiber-reinforced reaction-bonded Si3N4 composites. Technical memo  

SciTech Connect

Thermal expansion curves for SiC fiber-reinforced reaction-bonded Si3N4 matrix composites (SiC/RBSN) and unreinforced RBSN were measured from 25 to 1400 deg 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 were between the measured curves for the strongly and weakly bonded composites, but those normal to the fiber direction for both bonding cases were similar to that of the unreinforced RBSN. Thermal cycling in nitrogen 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 straln 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 maln reasons for the poor mechanical performance of these composites.

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

1994-10-01

90

Effects of thermal cycling on thermal expansion and mechanical properties of SiC fiber-reinforced reaction-bonded Si3N4 composites  

SciTech Connect

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.

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

1994-10-01

91

Concerted O atom–proton transfer in the O—O bond forming step in water oxidation  

PubMed Central

As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H2O ? O2 + 4e- + 4H+) is key, but it imposes a significant mechanistic challenge with requirements for both 4e-/4H+ loss and O—O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as [Ru(Mebimpy)(bpy)(OH2)]2+ [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2?-bipyridine]. When oxidized from to RuV = O3+, these complexes undergo O—O bond formation by O-atom attack on a H2O molecule, which is often the rate-limiting step. Microscopic details of O—O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom–proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation. PMID:20360565

Chen, Zuofeng; Concepcion, Javier J.; Hu, Xiangqian; Yang, Weitao; Hoertz, Paul G.; Meyer, Thomas J.

2010-01-01

92

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

E-print Network

reaction were compared by using Raman spectroscopy, high-resolution photoemission spectroscopy (HRPES oxidation reaction with slightly partial conversion of aniline to nitrobenzene, as determined by the Raman developing graphene surface modifications.4,5 In an effort to obtain functionalized graphene, many research

Kim, Sehun

93

Reaction bonding and mechanical properties of mullite/silicon carbide composites  

SciTech Connect

Based on the RBAO technology, low-shrinkage mullite/SiC/Al[sub 2]O[sub 3]/ZrO[sub 2] composite were fabricated. A powder mixture of 40 vol% Al, 30 vol% Al[sub 2]O[sub 3], and 30 vol% SiC was attrition milled in acetone with TZP balls which introduced a substantial ZrO[sub 2] wear debris into the mixture. The precursor powder was isopressed at 300--900 MPa and heat-treated in air by two different cycles resulting in various phase ratios in the final products. During heating, Al oxidizes to Al[sub 2]O[sub 3] completely, while SiC oxidizes to SiO[sub 2] only on its surface. Fast densification (at > 1300 C) and mullite formation (at 1400 C) prevent further oxidation of the SiC particles. Because of the volume expansion associated with the oxidation of Al (28%), SiC (108%), and the mullitization (4.2%), sintering shrinkage is effectively compensated. The reaction-bonded composites exhibit low linear shrinkages and high strengths: shrinkages of 7.2%, 4.8%, and 3%, and strengths of 610, 580, and 490 MPa, corresponding to compaction pressure of 300, 600, and 900 MPa, respectively, were achieved in samples containing 49--55 vol% mullite. HIPing improved significantly the mechanical properties: a fracture strength of 490 MPa and a toughness of 4.1 MPa[center dot]m[sup 1/2] increased to 890 MPa and 6 MPa[center dot]m[sup 1/2], respectively.

Wu, S. (Lehigh Univ., Bethlehem, PA (United States). Materials Research Center); Claussen, N. (Technische Univ. Hamburg-Harburg, Hamburg (Germany). Advanced Ceramics Group)

1994-11-01

94

Method and reaction pathway for selectively oxidizing organic compounds  

DOEpatents

A method of selectively oxidizing an organic compound in a single vessel comprises: a) combining an organic compound, an acid solution in which the organic compound is soluble, a compound containing two oxygen atoms bonded to one another, and a metal ion reducing agent capable of reducing one of such oxygen atoms, and thereby forming a mixture; b) reducing the compound containing the two oxygen atoms by reducing one of such oxygen atoms with the metal ion reducing agent to, 1) oxidize the metal ion reducing agent to a higher valence state, and 2) produce an oxygen containing intermediate capable of oxidizing the organic compound; c) reacting the oxygen containing intermediate with the organic compound to oxidize the organic compound into an oxidized organic intermediate, the oxidized organic intermediate having an oxidized carbon atom; d) reacting the oxidized organic intermediate with the acid counter ion and higher valence state metal ion to bond the acid counter ion to the oxidized carbon atom and thereby produce a quantity of an ester incorporating the organic intermediate and acid counter ion; and e) reacting the oxidized organic intermediate with the higher valence state metal ion and water to produce a quantity of alcohol which is less than the quantity of ester, the acid counter ion incorporated in the ester rendering the carbon atom bonded to the counter ion less reactive with the oxygen containing intermediate in the mixture than is the alcohol with the oxygen containing intermediate.

Camaioni, Donald M. (Richland, WA); Lilga, Michael A. (Richland, WA)

1998-01-01

95

Carbon-sulfur bond cleavage reactions of dibenzothiophene derivatives mediated by iron and ruthenium carbonyls.  

PubMed

A thermal reaction of 6-(4''-dibenzothienyl)-2,2'-bipyridine (bpyDBT) with [Ru(3)(CO)(12)] produced a sulfur-bridged triruthenium complex via double carbon-sulfur bond cleavage and CO insertion, while a diiron(I,I) complex containing a thiametallacycle was obtained by a photochemical reaction of bpyDBT with [Fe(CO)(5)]. PMID:21109886

Hirotsu, Masakazu; Tsuboi, Chiaki; Nishioka, Takanori; Kinoshita, Isamu

2011-01-28

96

COPPER-CATALYZED CROSS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS  

E-print Network

COPPER-CATALYZED CROSS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS-COUPLING REACTIONS: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS A Dissertation Presented by CRAIG G. BATES: THE FORMATION OF CARBON-CARBON AND CARBON-SULFUR BONDS MAY 2005 CRAIG G BATES, B.S., ROGER WILLIAMS UNIVERISTY

Venkataraman, Dhandapani "DV"

97

Correlation among electronegativity, cation polarizability, optical basicity and single bond strength of simple oxides  

SciTech Connect

A suitable relationship between free-cation polarizability and electronegativity of elements in different valence states and with the most common coordination numbers has been searched on the basis of the similarity in physical nature of both quantities. In general, the cation polarizability increases with decreasing element electronegativity. A systematic periodic change in the polarizability against the electronegativity has been observed in the isoelectronic series. It has been found that generally the optical basicity increases and the single bond strength of simple oxides decreases with decreasing the electronegativity. The observed trends have been discussed on the basis of electron donation ability of the oxide ions and type of chemical bonding in simple oxides. - Graphical abstract: This figure shows the single bond strength of simple oxides as a function of element electronegativity. A remarkable correlation exists between these independently obtained quantities. High values of electronegativity correspond to high values of single bond strength and vice versa. It is obvious that the observed trend in this figure is closely related to the type of chemical bonding in corresponding oxide. Highlights: Black-Right-Pointing-Pointer A suitable relationship between free-cation polarizability and electronegativity of elements was searched. Black-Right-Pointing-Pointer The cation polarizability increases with decreasing element electronegativity. Black-Right-Pointing-Pointer The single bond strength of simple oxides decreases with decreasing the electronegativity. Black-Right-Pointing-Pointer The observed trends were discussed on the basis of type of chemical bonding in simple oxides.

Dimitrov, Vesselin, E-mail: vesselin@uctm.edu [Department of Silicate Technology, University of Chemical Technology and Metallurgy, 8, Kl. Ohridski Blvd., Sofia 1756 (Bulgaria)] [Department of Silicate Technology, University of Chemical Technology and Metallurgy, 8, Kl. Ohridski Blvd., Sofia 1756 (Bulgaria); Komatsu, Takayuki, E-mail: komatsu@mst.nagaokaut.ac.jp [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188 (Japan)] [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka-cho, Nagaoka 940-2188 (Japan)

2012-12-15

98

Decarbonylative c?c bond-forming reactions of saccharins by nickel catalysis: homocoupling and cycloaddition.  

PubMed

Decarbonylation of saccharins by nickel catalysis enables two kinds of C?C bond-forming reactions; homocoupling of saccharins to form biaryls and cycloaddition with alkynes to form benzosultams. The former represents the first reported nickel-catalyzed decarbonylative C?C homocoupling reaction, whereas the latter constitutes a powerful method to pharmaceutically relevant benzosultams. The reactions proceed with good functional-group tolerance and excellent regioselectivity. PMID:25689489

Mi, Pengbing; Liao, Peiqiu; Tu, Tao; Bi, Xihe

2015-03-27

99

Quantum Chemistry in Organic Reactions: Investigations of Mechanism and Stereoselectivity in C-H Bond Functionalizations and Cycloaddition Reactions  

E-print Network

d ‡ (alkane) 2-eq 2-ax 3-eq 3-ax Compound C-H bond oxidationalkane distortion, dioxirane distortion) are in parentheses. The TSs for tertiary axial/equatorial C-H oxidationalkane distortion, dioxirane distortion) are given in parentheses. The TSs for axial and equatorial C-H oxidation

ZOU, LUFENG

2013-01-01

100

Multiple Scattering Calculations of Bonding and X-ray Absorption Spectroscopy of Manganese Oxides  

E-print Network

Multiple Scattering Calculations of Bonding and X-ray Absorption Spectroscopy of Manganese Oxides B edge X-ray absorption spectra of manganese oxides at the Mn L2,3, Mn K, and O K edges to investigate The particularly rich redox chemistry of manganese is evident in its oxides, which are of wide contemporary

Haskel, Daniel

101

Dependence of cryogenic strength of hydroxide catalysis bonded silicon on type of surface oxide  

NASA Astrophysics Data System (ADS)

Hydroxide catalysis bonding is a joining technique used in the construction of highly stable opto-mechanical systems including quasi-monolithic silica suspensions for first and second generation gravitational wave detectors. Future generations of detector are likely to operate at cryogenic temperatures necessitating a change in testmass/suspension material. A promising candidate material is silicon, which requires an oxide surface layer for hydroxide catalysis bonding to be reliable. Here, we present first results showing the influence of the type of oxide layer applied on bond strength, measured at room temperature and 77 K, and identify preferred oxide deposition methods.

Beveridge, N. L.; van Veggel, A. A.; Cunningham, L.; Hough, J.; Martin, I. W.; Nawrodt, R.; Reid, S.; Rowan, S.

2013-01-01

102

REACTION BONDED REFRACTORY METAL CARBIDE\\/CARBON COMPOSITES  

Microsoft Academic Search

A simple chemical process has been developed that allows the rapid conversion of carbon substrates to the refractory metal carbides (MC) of titanium, zirconium, hafnium, vanadium, niobium, tantalum and tungsten. As a demonstration of the technique, graphite rods are infiltrated with an ethanolic solution of various metal oxide-halides, and resistively fired (1350-3000°C) under an argon atmosphere. The final composite produced

ANDREW R. BARRON; JASON J. LI; THOMAS R. GILBERT

103

Bond cleavage, fragment modification and reassembly in enantioselective three-component reactions.  

PubMed

Chemical bond cleavage and reconstruction are common processes in traditional rearrangement reactions. In contrast, the process that involves bond cleavage, fragment modification and then reconstruction of the modified fragment provides an efficient way to build structurally diversified molecules. Here, we report a palladium(II)/chiral phosphoric acid catalysed three-component reaction of aryldiazoacetates, enamines and imines to afford ?-amino-?-oxo pentanoic acid derivatives in good yields with excellent diastereoselectivities and high enantioselectivities. The stereoselective reaction went through a unique process that involves cleavage of a C-N bond, modification of the resulting amino fragment and selective reassembly of the modified fragment. This innovative multi-component process represents a highly efficient way to build structurally diversified polyfunctional molecules in an atom and step economic fashion. A keto-iminium is proposed as a key intermediate and a chiral palladium/phosphate complex is proposed as an active catalyst. PMID:25586817

Zhang, Dan; Zhou, Jun; Xia, Fei; Kang, Zhenghui; Hu, Wenhao

2015-01-01

104

Bond cleavage, fragment modification and reassembly in enantioselective three-component reactions  

PubMed Central

Chemical bond cleavage and reconstruction are common processes in traditional rearrangement reactions. In contrast, the process that involves bond cleavage, fragment modification and then reconstruction of the modified fragment provides an efficient way to build structurally diversified molecules. Here, we report a palladium(II)/chiral phosphoric acid catalysed three-component reaction of aryldiazoacetates, enamines and imines to afford ?-amino-?-oxo pentanoic acid derivatives in good yields with excellent diastereoselectivities and high enantioselectivities. The stereoselective reaction went through a unique process that involves cleavage of a C–N bond, modification of the resulting amino fragment and selective reassembly of the modified fragment. This innovative multi-component process represents a highly efficient way to build structurally diversified polyfunctional molecules in an atom and step economic fashion. A keto-iminium is proposed as a key intermediate and a chiral palladium/phosphate complex is proposed as an active catalyst. PMID:25586817

Zhang, Dan; Zhou, Jun; Xia, Fei; Kang, Zhenghui; Hu, Wenhao

2015-01-01

105

Role of C-H Bond Strength in the Rate and Selectivity of Oxidative Dehydrogenation of Michael Zboray, Alexis T. Bell,* and Enrique Iglesia*  

E-print Network

. The high rate of C2H4 combustion is thus a consequence of its high heat of adsorption. Introduction with VOx-based catalysts have shown that alkane ODH reaction rates are proportional to alkane pressureRole of C-H Bond Strength in the Rate and Selectivity of Oxidative Dehydrogenation of Alkanes

Bell, Alexis T.

106

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

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

107

A new wafer level TSV build-up stacking using oxide bonding  

NASA Astrophysics Data System (ADS)

A new through-silicon via (TSV) build-up stacking method using oxide bonding is proposed and implemented in this work. The proposed method can be applied to the fabrication of a TSV stack chip. Thermal stress analysis was carried out to compare the structural reliability between conventional TSV and the proposed TSV model. The simulation results indicate that the proposed TSV model is more reliable than the conventional model with respect to stress in the stack chip. Experiments were conducted by oxide bonding of chips and the oxide bonding energy was acquired by a four point bending test. The obtained bonding energy sufficiently exceeds the energy criteria of 3D stacking. Thus, two oxide wafers with an 8 inch diameter were bonded by oxide bonding at the wafer level. The 0.6 µm thick oxide layers were located between bonded wafers and the top wafer was thinned down to fabricate blind via at the top of bonded wafer. The thickness of the top and bottom wafer is to 70 and 725 µm, respectively, after the top chemical mechanical polishing (CMP) process. Then blind vias were fabricated by deep reactive ion etching; the diameter and depth of the via is 20 µm and 150 µm, respectively. A through hole was formed by bottom CMP; total thickness of the oxide bonded wafer is 140 µm. The dielectric layer (SiO2), adhesion and diffusion barrier (TiN, Ti) and wetting layer (Cu) were deposited sequentially to improve the wettability of the via wall. Since the molten solder cannot be filled in the via if there is no wetting layer at the via wall. Finally, the vias were successfully filled with molten solder within 10 s.

Kim, Sun-Rak; Song, Jun-Yeob; Lee, Seung S.; Lee, Jae Hak

2013-06-01

108

In situ UV-visible assessment of extent of reduction during oxidation reactions on oxide catalysts  

E-print Network

to increase with increasing VOx domain size and propane/O2 ratio. Oxidative dehydrogenation (ODH) of alkanes the electronic structure of oxide domains commonly used as alkane ODH catalysts.1,2,4,5 Edge energies dependIn situ UV-visible assessment of extent of reduction during oxidation reactions on oxide catalysts

Bell, Alexis T.

109

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

E-print Network

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

Chorover, Jon

110

SiC continuous fiber-reinforced Si3N4 by infiltration and reaction bonding  

SciTech Connect

Difficulties encountered in the production of long-fiber reinforced ceramic-matrix composites via hot pressing and CVI can be circumvented through the use of the infiltration/consolidation of the long-fiber preforms with submicron particle slurries and reaction-bonding the resulting matrix, as is presently demonstrated for the case of SiC fibers and Si/Si3N4 particle slurries. High temperature fiber degradation during reaction bonding is avoided through the use of additives that lower the nitridation temperature and shorten process time. Attention is given to the microstructure and mechanical properties thus obtained; nearly complete impregnation is achieved. 12 refs.

Brandt, J.; Rundgren, K.; Pompe, R.; Swan, H.; O'meara, C.; Lundberg, R.; Pejryd, L.

1992-10-01

111

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

PubMed Central

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

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

2014-01-01

112

Water oxidation reaction in natural and artificial photosynthetic systems  

SciTech Connect

Understanding the structure and mechanism of water oxidation catalysts is an essential component for developing artificial photosynthetic devices. In the natural water oxidation catalyst, the geometric and electronic structure of its inorganic core, the Mn{sub 4}CaO{sub 5} cluster, has been studied by spectroscopic and diffraction measurements. In inorganic systems, metal oxides seem to be good candidates for water oxidation catalysts. Understanding the reaction mechanism in both natural and oxide-based catalysts will helpin further developing efficient and robust water oxidation catalysts.

Yano, Junko; Yachandra, Vittal [Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720 (United States)

2013-12-10

113

Electrochromic reactions in manganese oxides I. Raman analysis  

SciTech Connect

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.

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

114

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

SciTech Connect

A classification of the HF 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 |V(rc)|/G(rc) where |V(rc)| is the magnitude of the local potential energy density and G(rc) is the local kinetic density evaluated at the bond critical points, rc. A calculation of the ratio for the MO bonded interactions comprising a relatively large number of molecules and earth materials, together with the constraints imposed by the values of Ñ2?(rc) and the local electronic energy density H(rc) = G(rc) + V(rc) in the HF study, yielded the same classification for the oxides as found for the fluorides. This is true despite the different trends of the bond critical point and local energy properties with the bond length displayed by the HF and MO bonded interactions. LiO, NaO and MgO bonded interactions classify as closed shell ionic bonds, BeO, AlO, SiO, BO and PO bonded interactions classify as bonds of intermediate character and NO bonded interactions classify as shared covalent bonds. CO and SO bonded interactions classify as both intermediate and covalent bonded interactions. The CO triple bonded interaction classifies as a bond of intermediate character and the CO single bonded interaction classifies as a covalent bond whereas their H(rc) value indicates that they are both covalent bonds. The |V(rc)|/G(rc) ratios for the BeO, AlO and SiO bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between |V(rc)|/G(rc) and the character of the bonded interaction is consistent with trends expected from electronegativity considerations. The connection between the net charges and the experimental SiO bond length evaluated for the Si and O atoms comprising two orthosilicates are examined in terms of the |V(rc)|/G(rc) values.

Gibbs, Gerald V.; Cox, David; Crawford, T Daniel; Rosso, Kevin M.; Ross, Nancy; Downs, R. T.

2006-02-28

115

Report on study of oxidation reaction rates  

Microsoft Academic Search

A series of experiments were conducted to determine the rate of oxidation of scintillation cocktail components, vacuum pump oil and trichloroethylene by Delphi Research, Inc.`s patented MEDETOX catalytic wet oxidation process utilizing iron(III) oxidant. The materials were placed in acid digestion bombs with the catalytic solution and heated to temperatures in the range of 150--225°C in the presence of platinum

Dhooge

1991-01-01

116

Report on study of oxidation reaction rates  

Microsoft Academic Search

A series of experiments were conducted to determine the rate of oxidation of scintillation cocktail components, vacuum pump oil and trichloroethylene by Delphi Research, Inc.'s patented MEDETOX catalytic wet oxidation process utilizing iron(III) oxidant. The materials were placed in acid digestion bombs with the catalytic solution and heated to temperatures in the range of 150--225°C in the presence of platinum

Dhooge

1991-01-01

117

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

NASA Astrophysics Data System (ADS)

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.

Dubner, Walter Sterling

1990-01-01

118

Deamination, oxidation, and C-C bond cleavage reactivity of 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxycytosine.  

PubMed

Three new cytosine derived DNA modifications, 5-hydroxymethyl-2'-deoxycytidine (hmdC), 5-formyl-2'-deoxycytidine (fdC) and 5-carboxy-2'-deoxycytidine (cadC) were recently discovered in mammalian DNA, particularly in stem cell DNA. Their function is currently not clear, but it is assumed that in stem cells they might be intermediates of an active demethylation process. This process may involve base excision repair, C-C bond cleaving reactions or deamination of hmdC to 5-hydroxymethyl-2'-deoxyuridine (hmdU). Here we report chemical studies that enlighten the chemical reactivity of the new cytosine nucleobases. We investigated their sensitivity toward oxidation and deamination and we studied the C-C bond cleaving reactivity of hmdC, fdC, and cadC in the absence and presence of thiols as biologically relevant (organo)catalysts. We show that hmdC is in comparison to mdC rapidly oxidized to fdC already in the presence of air. In contrast, deamination reactions were found to occur only to a minor extent. The C-C bond cleavage reactions require the presence of high concentration of thiols and are acid catalyzed. While hmdC dehydroxymethylates very slowly, fdC and especially cadC react considerably faster to dC. Thiols are active site residues in many DNA modifiying enzymes indicating that such enzymes could play a role in an alternative active DNA demethylation mechanism via deformylation of fdC or decarboxylation of cadC. Quantum-chemical calculations support the catalytic influence of a thiol on the C-C bond cleavage. PMID:23980549

Schiesser, Stefan; Pfaffeneder, Toni; Sadeghian, Keyarash; Hackner, Benjamin; Steigenberger, Barbara; Schröder, Arne S; Steinbacher, Jessica; Kashiwazaki, Gengo; Höfner, Georg; Wanner, Klaus T; Ochsenfeld, Christian; Carell, Thomas

2013-10-01

119

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

Microsoft Academic Search

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,

Ikchoon Lee

2003-01-01

120

The pathophysiology of extracellular hemoglobin associated with enhanced oxidative reactions  

PubMed Central

Hemoglobin (Hb) continuously undergoes autoxidation producing superoxide which dismutates into hydrogen peroxide (H2O2) and is a potential source for subsequent oxidative reactions. Autoxidation is most pronounced under hypoxic conditions in the microcirculation and for unstable dimers formed at reduced Hb concentrations. In the red blood cell (RBC), oxidative reactions are inhibited by an extensive antioxidant system. For extracellular Hb, whether from hemolysis of RBCs and/or the infusion of Hb-based blood substitutes, the oxidative reactions are not completely neutralized by the available antioxidant system. Un-neutralized H2O2 oxidizes ferrous and ferric Hbs to Fe(IV)-ferrylHb and OxyferrylHb, respectively. FerrylHb further reacts with H2O2 producing heme degradation products and free iron. OxyferrylHb, in addition to Fe(IV) contains a free radical that can undergo additional oxidative reactions. Fe(III)Hb produced during Hb autoxidation also readily releases heme, an additional source for oxidative stress. These oxidation products are a potential source for oxidative reactions in the plasma, but to a greater extent when the lower molecular weight Hb dimers are taken up into cells and tissues. Heme and oxyferryl have been shown to have a proinflammatory effect further increasing their potential for oxidative stress. These oxidative reactions contribute to a number of pathological situations including atherosclerosis, kidney malfunction, sickle cell disease, and malaria. The toxic effects of extracellular Hb are of particular concern with hemolytic anemia where there is an increase in hemolysis. Hemolysis is further exacerbated in various diseases and their treatments. Blood transfusions are required whenever there is an appreciable decrease in RBCs due to hemolysis or blood loss. It is, therefore, essential that the transfused blood, whether stored RBCs or the blood obtained by an Autologous Blood Recovery System from the patient, do not further increase extracellular Hb. PMID:25642190

Rifkind, Joseph M.; Mohanty, Joy G.; Nagababu, Enika

2015-01-01

121

The pathophysiology of extracellular hemoglobin associated with enhanced oxidative reactions.  

PubMed

Hemoglobin (Hb) continuously undergoes autoxidation producing superoxide which dismutates into hydrogen peroxide (H2O2) and is a potential source for subsequent oxidative reactions. Autoxidation is most pronounced under hypoxic conditions in the microcirculation and for unstable dimers formed at reduced Hb concentrations. In the red blood cell (RBC), oxidative reactions are inhibited by an extensive antioxidant system. For extracellular Hb, whether from hemolysis of RBCs and/or the infusion of Hb-based blood substitutes, the oxidative reactions are not completely neutralized by the available antioxidant system. Un-neutralized H2O2 oxidizes ferrous and ferric Hbs to Fe(IV)-ferrylHb and OxyferrylHb, respectively. FerrylHb further reacts with H2O2 producing heme degradation products and free iron. OxyferrylHb, in addition to Fe(IV) contains a free radical that can undergo additional oxidative reactions. Fe(III)Hb produced during Hb autoxidation also readily releases heme, an additional source for oxidative stress. These oxidation products are a potential source for oxidative reactions in the plasma, but to a greater extent when the lower molecular weight Hb dimers are taken up into cells and tissues. Heme and oxyferryl have been shown to have a proinflammatory effect further increasing their potential for oxidative stress. These oxidative reactions contribute to a number of pathological situations including atherosclerosis, kidney malfunction, sickle cell disease, and malaria. The toxic effects of extracellular Hb are of particular concern with hemolytic anemia where there is an increase in hemolysis. Hemolysis is further exacerbated in various diseases and their treatments. Blood transfusions are required whenever there is an appreciable decrease in RBCs due to hemolysis or blood loss. It is, therefore, essential that the transfused blood, whether stored RBCs or the blood obtained by an Autologous Blood Recovery System from the patient, do not further increase extracellular Hb. PMID:25642190

Rifkind, Joseph M; Mohanty, Joy G; Nagababu, Enika

2014-01-01

122

Time-resolved IR spectroscopy in liquid rare gases: Direct rate measurement of an intermolecular alkane CH oxidative addition reaction  

Microsoft Academic Search

Since the first demonstration of the intermolecular oxidative addition of alkane C-H bonds to transition-metal centers, there have been many studies of the mechanism of this reaction. While these studies have illuminated many aspects of the C-H activation process, they do not provide direct information about the reactive intermediates or the potential energy surface for the elementary insertion reaction. Flash

B. H. Weiller; E. P. Wasserman; R. G. Bergman; C. B. Moore; G. C. Pimentel

1989-01-01

123

Concerted O Atom-Proton Transfer in the O—O Bond Forming Step in Water Oxidation  

SciTech Connect

As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H{sub 2}O ? O{sub 2 + 4e{sup -} + 4H{sup +}) is key, but it imposes a significant mechanistic challenge with requirements for both 4e{sup -}/4H{sup +} loss and O—O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as [Ru(Mebimpy)(bpy)(OH{sub 2})]{sup 2+} [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2?-bipyridine]. When oxidized from Ru{sup II}-OH{sub 2}{sup 2+} to Ru{sup V} = O{sup 3+}, these complexes undergo O—O bond formation by O-atom attack on a H{sub 2}O molecule, which is often the rate-limiting step. Microscopic details of O—O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom–proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation.

Chen, Zuofeng; Concepcion, Javier C.; Hu, Xiangqian; Yang, Weitao; Hoertz, Paul G.; Meyer, Thomas J

2010-01-01

124

Effects of anodizing conditions on bond strength of anodically oxidized film to titanium substrate  

NASA Astrophysics Data System (ADS)

The bond strength of the oxide film to the titanium substrate and its inherent structural characteristics are very important preconditions for the success of titanium implants. The purpose of this study was to evaluate the micro-morphologies, crystalline structures, and bond strengths of the anodically oxidized films formed on titanium with the variation of electrolytes and applied current densities. In contrast to the specimens produced using sulfuric acid as the electrolyte, those produced using phosphoric acid showed quite different shapes and densities of the pores as the applied current densities were varied. The oxide films anodized in sulfuric acid consisted of anatase and rutile TiO 2, whileTiP 2O 7 was predominantly formed on the Ti surfaces anodized using phosphoric acid as the electrolyte. The oxide films, which did not experience spark deposition showed amorphous shape and their bond strengths were significantly lower than those of the other groups ( p < 0.05). Those specimens which experienced initial spark deposition with a low current condition showed the highest bond strengths (34.2 MPa) within each electrolyte sub-set. The growing rates of the oxide film thicknesses in relation to the electric current changes varied according to the type of electrolyte, and the oxide film thickness influenced the bond strength.

Park, Yeong-Joon; Shin, Kyung-Ha; Song, Ho-Jun

2007-05-01

125

Shock-Induced Reactions in Metal\\/Metal Oxide = Systems  

Microsoft Academic Search

Start your abstract by replacing this line with your text. A recent study of shock induced reactions in metal\\/metal oxide systems has been completed. The systems studied included oxides of Iron, Copper, Molybdenum mixed in a stoichiometric ratio with aluminum. Also add ed was a small amount of Teflon (5 weight percent) to act as a binder. Other materials studied

Fallen J. Lindfors; Philip J. Miller; Jeff J. Davis

1997-01-01

126

The Effect of Metal Oxide on Nanoparticles from Thermite Reactions  

ERIC Educational Resources Information Center

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…

Moore, Lewis Ryan

2006-01-01

127

A new approach to carbon-carbon bond formation: Development of aerobic Pd-catalyzed reductive coupling reactions of organometallic reagents and styrenes  

PubMed Central

Alkenes are attractive starting materials for organic synthesis and the development of new selective functionalization reactions are desired. Previously, our laboratory discovered a unique Pd-catalyzed hydroalkoxylation reaction of styrenes containing a phenol. Based upon deuterium labeling experiments, a mechanism involving an aerobic alcohol oxidation coupled to alkene functionalization was proposed. These results inspired the development of a new Pd-catalyzed reductive coupling reaction of alkenes and organometallic reagents that generates a new carbon-carbon bond. Optimization of the conditions for the coupling of both organostannanes and organoboronic esters is described and the initial scope of the transformation is presented. Additionally, several mechanistic experiments are outlined and support the rationale for the development of the reaction based upon coupling alcohol oxidation to alkene functionalization. PMID:20161306

Gligorich, Keith M.; Iwai, Yasumasa; Cummings, Sarah A.; Sigman, Matthew S.

2009-01-01

128

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...

129

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...

130

Nondestructive Impedance Spectroscopy Evaluation of the Bond Coat Oxidation in Thermal Barrier Coatings  

NASA Astrophysics Data System (ADS)

In this paper, the impedance spectroscopy technique was employed to examine nondestructively the isothermal oxidation of air plasma sprayed (APS) thermal barrier coatings (TBCs) in air at 800°C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also used to characterize the microstructure evolution of TBCs. After oxidation, the thermally grown oxide (TGO), which was mainly composed of alumina as confirmed by EDX, formed at the upper ceramic coat/bond coat interface, the lower bond coat/substrate interface, and the bond coat. Impedance diagrams obtained from impedance measurements at room temperature were analyzed according to the equivalent circuit model proposed for the TBCs. Various observed electrical responses relating to the growth of oxides and the sintering of YSZ were explained by simulating the impedance spectra of the TBCs.

Yang, L.; Zhou, Y. C.; Mao, W. G.; Liu, Q. X.

131

Direct functionalization of M-C (M = Pt(II), Pd(II)) bonds using environmentally benign oxidants, O2 and H2O2.  

PubMed

Atom economy and the use of "green" reagents in organic oxidation, including oxidation of hydrocarbons, remain challenges for organic synthesis. Solutions to this problem would lead to a more sustainable economy because of improved access to energy resources such as natural gas. Although natural gas is still abundant, about a third of methane extracted in distant oil fields currently cannot be used as a chemical feedstock because of a dearth of economically and ecologically viable methodologies for partial methane oxidation. Two readily available "atom-economical" "green" oxidants are dioxygen and hydrogen peroxide, but few methodologies have utilized these oxidants effectively in selective organic transformations. Hydrocarbon oxidation and C-H functionalization reactions rely on Pd(II) and Pt(II) complexes. These reagents have practical advantages because they can tolerate moisture and atmospheric oxygen. But this tolerance for atmospheric oxygen also makes it challenging to develop novel organometallic palladium and platinum-catalyzed C-H oxidation reactions utilizing O(2) or H(2)O(2). This Account focuses on these challenges: the development of M-C bond (M = Pt(II), Pd(II)) functionalization and related selective hydrocarbon C-H oxidations with O(2) or H(2)O(2). Reactions discussed in this Account do not involve mediators, since the latter can impart low reaction selectivity and catalyst instability. As an efficient solution to the problem of direct M-C oxidation and functionalization with O(2) and H(2)O(2), this Account introduces the use of facially chelating semilabile ligands such as di(2-pyridyl)methanesulfonate and the hydrated form of di(2-pyridyl)ketone that enable selective and facile M(II)-C(sp(n)) bond functionalization with O(2) (M = Pt, n = 3; M = Pd, n = 3 (benzylic)) or H(2)O(2) (M = Pd, n = 2). The reactions proceed efficiently in protic solvents such as water, methanol, or acetic acid. With the exception of benzylic Pd(II) complexes, the organometallic substrates studied form isolable high-valent Pt(IV) or Pd(IV) intermediates as a result of an oxidant attack at the M(II) atom. The resulting high-valent M(IV) intermediates undergo C-O reductive elimination, leading to products in high yields. Guidelines for the synthesis of products containing other C-X bonds (X = OAc, Cl, Br) while using O(2) or H(2)O(2) as oxidants are also discussed. Although the M(II)-C bond functionalization reactions including high-valent intermediates are well understood, the mechanism for the aerobic functionalization of benzylic Pd(II) complexes will require a more detailed exploration. Importantly, further optimization of the systems suitable for stoichiometric M(II)-C bond functionalization led to the development of catalytic reactions, including selective acetoxylation of benzylic C-H bonds with O(2) as the oxidant and hydroxylation of aromatic C-H bonds with H(2)O(2) in acetic acid solutions. Both reactions proceed efficiently with substrates that contain a directing heteroatom. This Account also describes catalytic methods for ethylene dioxygenation with H(2)O(2) using M(II) complexes supported by facially chelating ligands. Mechanistic studies of these new oxidation reactions point to important ways to improve their substrate scope and to develop "green" CH functionalization chemistry. PMID:22087633

Vedernikov, Andrei N

2012-06-19

132

Reactions of a uranium (IV) tertiary alkyl bond. Facile ligand-assisted reduction and insertion of ethylene and carbon monoxide  

SciTech Connect

Reaction of (MeC{sub 5}H{sub 4}){sub 3}UX (X = Cl, MeC{sub 5}H{sub 4}) with t-BuLi affords the tertiary alkyl complex (MeC{sub 5}H{sub 4}){sub 3}U(t-Bu). Despite uranium(IV) generally being the preferred oxidation state in organometallic systems, (MeC{sub 5}H{sub 4}){sub 3}U(t-Bu) reacts with Lewis bases (L = PMe{sub 3}, THF, RCN, RNC) to yield the reduced uranium(III) base adducts (MeC{sub 5}H{sub 4}){sub 3}U(L). Carbon monoxide undergoes migratory insertion into the metal tertiary alkyl bond. The resulting acyl derivative decomposes at 90{degree}C to yield insoluble uranium-containing products and a mixture of tert-butyltoluenes by ring expansion of a methylcyclopentadienyl ligand. Ethylene also undergoes migratory insertion into the metal tertiary alkyl bond. No subsequent insertion of ethylene into the metal carbon bond takes place after the first equivalent has inserted. In marked contrast, reaction of various (MeC{sub 5}H{sub 4}){sub 3}ThX (X = Cl, I, MeC{sub 5}H{sub 4}, O-2,6-Me{sub 2}C{sub 6}H{sub 3}, OTs) compounds with t-BuLi gave intractable materials. However, reaction of the cationic species [(RC{sub 5}H{sub 4}){sub 3}Th](BPh{sub 4}) (R = Me{sub 3}Si, t-Bu) with t-BuLi yields the new thorium hydrides (RC{sub 5}H{sub 4}){sub 3}ThH. 40 refs., 2 figs.

Weydert, M.; Brennan, J.G.; Andersen, R.A.; Bergman, R.G. [Lawrence Berkeley Lab., CA (United States)

1995-08-01

133

Studies on the Reactive Species in Fluoride-Mediated Carbon-Carbon Bond-Forming Reactions: Carbanion Formation  

E-print Network

Studies on the Reactive Species in Fluoride-Mediated Carbon-Carbon Bond-Forming ReactionsVed October 27, 2005 The reactive species in fluoride-mediated carbon-carbon bond-forming reactions- methylsilicate (TASF) or crypt[2.1.1]-solvated lithium enolates. The catalytic cycle runs smoothly with the crypt

Reich, Hans J.

134

Hydrogen bonding constrains free radical reaction dynamics at serine and threonine residues in peptides.  

PubMed

Free radical-initiated peptide sequencing (FRIPS) mass spectrometry derives advantage from the introduction of highly selective low-energy dissociation pathways in target peptides. An acetyl radical, formed at the peptide N-terminus via collisional activation and subsequent dissociation of a covalently attached radical precursor, abstracts a hydrogen atom from diverse sites on the peptide, yielding sequence information through backbone cleavage as well as side-chain loss. Unique free-radical-initiated dissociation pathways observed at serine and threonine residues lead to cleavage of the neighboring N-terminal C?-C or N-C? bond rather than the typical C?-C bond cleavage observed with other amino acids. These reactions were investigated by FRIPS of model peptides of the form AARAAAXAA, where X is the amino acid of interest. In combination with density functional theory (DFT) calculations, the experiments indicate the strong influence of hydrogen bonding at serine or threonine on the observed free radical chemistry. Hydrogen bonding of the side-chain hydroxyl group with a backbone carbonyl oxygen aligns the singly occupied ? orbital on the ?-carbon and the N-C? bond, leading to low-barrier ?-cleavage of the N-C? bond. Interaction with the N-terminal carbonyl favors a hydrogen-atom transfer process to yield stable c and z(•) ions, whereas C-terminal interaction leads to effective cleavage of the C?-C bond through rapid loss of isocyanic acid. Dissociation of the C?-C bond may also occur via water loss followed by ?-cleavage from a nitrogen-centered radical. These competitive dissociation pathways from a single residue illustrate the sensitivity of gas-phase free radical chemistry to subtle factors such as hydrogen bonding that affect the potential energy surface for these low-barrier processes. PMID:24605822

Thomas, Daniel A; Sohn, Chang Ho; Gao, Jinshan; Beauchamp, J L

2014-09-18

135

CONTAMINANT ADSORPTION AND OXIDATION VIA FENTON REACTION  

EPA Science Inventory

A ground water treatment process is proposed involving two cgemical processes: adsorption and oxidation. Adsorption of an organic compound onto granulated activated carbon (GAC) containing iron conveniently results in immobilizing and concentrating contaminants from the ground w...

136

Evidence of trigonal dangling bonds at the Ge(111)/oxide interface by electrically detected magnetic resonance.  

PubMed

Despite a renewed interest in Ge as a competitor with Si for a broad range of electronic applications, the microstructure and the electronic properties of the dangling bonds that, in analogy with Si, are expected at the Ge/oxide interface have escaped a firm spectroscopy observation and characterization. Clear evidence based on contactless electrically detected magnetic resonance spectroscopy of a dangling bond at the Ge(111)/GeO(2) interface is reported in this Letter. This result supports the similarity between dangling bonds at the Si(111)/oxide and Ge(111)/oxide interfaces, both showing C(3v) trigonal point symmetry with the main axis oriented along the ?111? direction. In contrast, at the Ge(001)/oxide interface the absence of the trigonal center in favor of a lower symmetry dangling bond marks the difference with the Si(001)/oxide interface, where both centers are present and the one having higher point symmetry prevails. This fact is rationalized in terms of suboxide interface rearrangement and oxide viscoelasticity, which promote the generation of the nonaxial centers at distorted dimers. The unambiguous identification of the centers at the Ge/oxide interfaces yields a deeper insight into the physical properties of the suboxide interface structure and offers a valid indicator for the evaluation of different surface capping and passivation techniques, with the potential to boost the Ge-related technology. PMID:25167431

Paleari, S; Baldovino, S; Molle, A; Fanciulli, M

2013-05-17

137

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

NASA Technical Reports Server (NTRS)

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.

Zaplatynsky, I.

1979-01-01

138

Formation of aromatics in thermally induced reactions of chemically bonded RP-C18 stationary phase.  

PubMed

In continuation of the research on the thermally induced chemical transformation of the silica-based chemically bonded stationary phases (C18), the oxidative cleavage of the silicon-carbon bonds with hydrogen peroxide and potassium fluoride was utilized, followed by the gas chromatography coupled with mass spectrometry (GC-MS) study of the resulting products. These investigations allowed determination of the probable structures of certain thermal modification products as the various different alkyl derivatives of the phenylsilane ligands. Apart from aromatic compounds, the products with unsaturated bonds and carbonyl functionalities were found in the analyzed extracts. The analysis of the GC-MS chromatograms reveals that under the applied working conditions, the investigated process runs with relatively low yields. PMID:24105920

Prus, Wojciech

2014-10-01

139

Unification of catalytic water oxidation and oxygen reduction reactions: amorphous beat crystalline cobalt iron oxides.  

PubMed

Catalytic water splitting to hydrogen and oxygen is considered as one of the convenient routes for the sustainable energy conversion. Bifunctional catalysts for the electrocatalytic oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are pivotal for the energy conversion and storage, and alternatively, the photochemical water oxidation in biomimetic fashion is also considered as the most useful way to convert solar energy into chemical energy. Here we present a facile solvothermal route to control the synthesis of amorphous and crystalline cobalt iron oxides by controlling the crystallinity of the materials with changing solvent and reaction time and further utilize these materials as multifunctional catalysts for the unification of photochemical and electrochemical water oxidation as well as for the oxygen reduction reaction. Notably, the amorphous cobalt iron oxide produces superior catalytic activity over the crystalline one under photochemical and electrochemical water oxidation and oxygen reduction conditions. PMID:25469760

Indra, Arindam; Menezes, Prashanth W; Sahraie, Nastaran Ranjbar; Bergmann, Arno; Das, Chittaranjan; Tallarida, Massimo; Schmeißer, Dieter; Strasser, Peter; Driess, Matthias

2014-12-17

140

Improving the bond strength between steel rebar and concrete by oxidation treatments of the rebar  

SciTech Connect

Oxidation treatments of steel rebar by water immersion (2--5 days) and ozone exposure increased the bond strength between steel rebar and concrete by 14% and 22% respectively. The treatments slightly increased the electrical contact resistivity between rebar and concrete. Increase of the water immersion time to 7 or 10 days caused the bond strength to decrease to values still above that of the case without water treatment. The contact resistivity increased monotonically with the water immersion time.

Fu, X.; Chung, D.D.L. [State Univ. of New York, Buffalo, NY (United States). Composite Materials Research Lab.] [State Univ. of New York, Buffalo, NY (United States). Composite Materials Research Lab.

1996-10-01

141

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

Microsoft Academic Search

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

A. V. Nemukhin; F. Weinhold

1992-01-01

142

Thermal oxidative degradation reactions of perfluoroalklethers  

NASA Technical Reports Server (NTRS)

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.

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

1983-01-01

143

Aqueous Oxidative Heck Reaction as a Protein-Labeling Strategy  

PubMed Central

An increasing number of chemical reactions are being employed for bio-orthogonal ligation of detection labels to protein-bound functional groups. Several of these strategies, however, are limited in their application to pure proteins and are ineffective in complex biological samples such as cell lysates. Here we present the palladium-catalyzed oxidative Heck reaction as a new and robust bio-orthogonal strategy for linking functionalized arylboronic acids to protein-bound alkenes in high yields and with excellent chemoselectivity even in the presence of complex protein mixtures from living cells. Advantageously, this reaction proceeds under aerobic conditions, whereas most other metal-catalyzed reactions require inert atmosphere. PMID:24376051

Ourailidou, Maria Eleni; van der Meer, Jan-Ytzen; Baas, Bert-Jan; Jeronimus-Stratingh, Margot; Gottumukkala, Aditya L; Poelarends, Gerrit J; Minnaard, Adriaan J; Dekker, Frank J

2014-01-01

144

Oxidation of a polycrystalline silver foil by reaction with ozone  

NASA Astrophysics Data System (ADS)

The surface oxidation of a polycrystalline silver foil by reaction with ozone (5 mol% O 3 in O 2) at 300 K and ambient pressure was investigated. The morphology, microstructure and chemical composition of the oxide scale which developed on the foil surface during exposure to ozone was characterised by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface of silver foil was rapidly oxidised upon contact with ozone, initially producing a thick Ag 2O protective film. After 10 min reaction, the oxide film thickness was around 8-10 ?m. SEM analysis revealed that Ag 2O film thickening occurred via a discontinuous film growth mechanism. Growth stresses, resulting from the large lattice volume mismatch between the oxide and the metal, caused the oxide film to crack and flake extensively during development. Spallation of the oxide film exposed fresh silver metal to ozone, which lead to further Ag 2O deposition. The continued recurrence of this process resulted in the formation a thick, discontinuous Ag 2O film on the silver foil. After foil exposure to ozone for 300 min, the oxide film thickness was 17-20 ?m. Furthermore, Ag 2O at the surface of the oxide film was slowly oxidised to AgO with prolonged exposure to ozone. The combined results of our experimental studies were used to develop a better understanding of the oxidation of silver surfaces by O 3.

Waterhouse, G. I. N.; Bowmaker, G. A.; Metson, J. B.

2001-11-01

145

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

SciTech Connect

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.

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

2012-02-04

146

A thermodynamically consistent surface reaction mechanism for CO oxidation on Pt  

SciTech Connect

The thermodynamic inconsistency of catalytic combustion reaction mechanisms has been a long-standing, fundamental, and practical problem. Here, we develop a thermodynamically consistent catalytic reaction mechanism for CO oxidation on Pt. First, we propose a modification of the bond index of the unity bond index-quadratic exponential potential (UBI-QEP) semiempirical framework for calculation of the activation energy of the Langmuir-Hinshelwood-type bimolecular surface reaction between co-adsorbed CO{sup *} and O{sup *}. Thermodynamic consistency is then ensured in the reaction mechanism by combining the semiempirical UBI-QEP theory, statistical mechanics, and constraint-based optimization against experimental data. Atmospheric pressure ignition and ultrahigh vacuum molecular beam experiments are selected as targets for optimization. The optimized mechanism is validated against redundant experiments, including temperature-programmed desorption, temperature-programmed reaction, and molecular beam experiments. Our microkinetic model is able to capture multiple types of data while being thermodynamically consistent over a wide range of conditions.

Mhadeshwar, A.B.; Vlachos, D.G. [Department of Chemical Engineering and Center for Catalytic Science and Technology, University of Delaware, Newark, DE 19716-3110 (United States)

2005-08-01

147

Selective oxidation reactions of natural compounds with hydrogen peroxide mediated by methyltrioxorhenium.  

PubMed

We have investigated the oxidative behaviour of natural compounds such as methyl abietate (1), farnesyl acetate (2), ?-ionone (3), ?-ionone (4), methyl linolelaidate (5), methyl linolenate (6) and bergamottin (7) with the oxidant system methyltrioxo-rhenium/ H2O2/pyridine. The reactions, performed in CH2Cl2/H2O at 25 °C, have shown good regio- and stereoselectivity. The oxidation products were isolated by HPLC or silica gel chromatography and characterized by MS(EI), 1H-, 13C-NMR, APT, gCOSY, HSQC, TOCSY and NOESY measurements. The selectivity seems to be controlled by the nucleophilicity of double bonds and by stereoelectronic and steric effects. PMID:24213654

Amato, Maria E; Ballistreri, Francesco P; Pappalardo, Andrea; Tomaselli, Gaetano A; Toscano, Rosa M; Sfrazzetto, Giuseppe Trusso

2013-01-01

148

Pathways to soot oxidation: reaction of OH with phenanthrene radicals.  

PubMed

Energetics and kinetics of the oxidation of possible soot surface sites by hydroxyl radicals were investigated theoretically. Energetics were calculated by employing density functional theory. Three candidate reactions were selected as suitable prototypes of soot oxidation by OH. The first two, OH + benzene and OH + benzene-phenol complex, did not produce pathways that lead to substantial CO expulsion. The third reaction, OH attack on the phenanthrene radical, had multiple pathways leading to CO elimination. The kinetics of the latter reaction system were determined by solving the master equations with the MultiWell suite of codes. The barrierless reaction rates of this system were computed using the VariFlex program. The computations were carried out over the ranges 1500-2500 K and 0.01-10 atm. At higher temperatures, above 2000 K, the oxidation of phenanthrene radicals by OH followed a chemically activated path. At temperatures lower than 2000 K, chemical activation was not sufficient to drive the reaction to products; reaction progress was impeded by intermediate adducts rapidly de-energizing before reaching products. In such cases, the reaction system was modeled by treating the accumulating adducts as distinct chemical species and computing their kinetics via thermal decomposition. The overall rate coefficient of phenanthrene radical oxidation by OH forming CO was found to be insensitive to pressure and temperature and is approximately 1 × 10(14) cm(3) mol(-1) s(-1). The oxidation of phenanthrene radicals by OH is shown to be controlled by two main processes: H atom migration/elimination and oxyradical decomposition. H atom migration and elimination made possible relatively rapid rearrangement of the aromatic edge to form oxyradicals with favorable decomposition rates. The reaction then continues down the fastest oxyradical pathways, eliminating CO. PMID:24761798

Edwards, David E; Zubarev, Dmitry Yu; Lester, William A; Frenklach, Michael

2014-09-18

149

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

NASA Technical Reports Server (NTRS)

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.

Dias, S.; Wightman, J. P.

1983-01-01

150

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

SciTech Connect

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.

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

2013-07-15

151

Intramolecular Anodic Olefin Coupling Reactions: Using Competition Studies to Probe the Mechanism of Oxidative Cyclization Reactions  

PubMed Central

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

Xu, Hai-Chao; Moeller, Kevin D.

2014-01-01

152

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

PubMed

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

Xu, Hai-Chao; Moeller, Kevin D

2010-04-16

153

A bond-topological approach to theoretical mineralogy: crystal structure, chemical composition and chemical reactions  

NASA Astrophysics Data System (ADS)

Here, I describe a theoretical approach to the structure and chemical composition of minerals based on their bond topology. This approach allows consideration of many aspects of minerals and mineral behaviour that cannot be addressed by current theoretical methods. It consists of combining the bond topology of the structure with aspects of graph theory and bond-valence theory (both long range and short range), and using the moments approach to the electronic energy density-of-states to interpret topological aspects of crystal structures. The structure hierarchy hypothesis states that higher bond-valence polyhedra polymerize to form the (usually anionic) structural unit, the excess charge of which is balanced by the interstitial complex (usually consisting of large low-valence cations and (H2O) groups). This hypothesis may be justified within the framework of bond topology and bond-valence theory, and may be used to hierarchically classify oxysalt minerals. It is the weak interaction between the structural unit and the interstitial complex that controls the stability of the structural arrangement. The principle of correspondence of Lewis acidity-basicity states that stable structures will form when the Lewis-acid strength of the interstitial complex closely matches the Lewis-base strength of the structural unit, and allows us to examine the factors that control the chemical composition and aspects of the structural arrangements of minerals. It also provides a connection between a structure, the speciation of its constituents in aqueous solution and its mechanism of crystallization. The moments approach to the electronic energy density-of-states provides a link between the bond topology of a structure and its thermodynamic properties, as indicated by correlations between average anion coordination number and reduced enthalpy of formation from the oxides for [6]Mg{/m [4]}Si n O( m+2 n) and MgSO4(H2O) n .

Hawthorne, Frank C.

2012-11-01

154

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

NASA Technical Reports Server (NTRS)

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.

Napier, Mary E.; Stair, Peter C.

1992-01-01

155

Final Report: Catalytic Hydrocarbon Reactions over Supported Metal Oxides, August 1, 1995 - July 31, 1999  

SciTech Connect

The research program focused on the catalysis of hydrodesulfurization (HDS) over molybdenum-based catalysts and how catalyst composition, redox ability, structure and neighboring sites control the catalytic properties of metal oxides. We sought to understand the catalytic features/sites that control hydrogenation, hydrogenolysis, and isomerization during HDS. Unprompted silica-supported molybdenum oxides and molybdenum sulfides were studied. Model catalyst systems were prepared from organometallic precursors or cluster compounds to generate supported structures that feature Mo(II) and Mo(IV) cations that are isolated or in ensembles and that have either Mo-O or Mo-S bonds. Conventional MOS{sub 2} catalysts, which contain both edge and rim sites, were be studied. Finally, single-layer MOS{sub 2} structures were also prepared from 2H-MoS{sub 2} powder so that the model systems could be compared against a disulfide catalyst that only involves rim sites. Catalytic reactions for thiophene and tetrahydrothione were studied over the various catalysts. Oxidation states were determined using X-ray photoelectron spectroscopy. X-ray crystallography was used to characterize and follow changes in the MOS{sub 2} structures. The program on metal oxides prepared supported oxides that have a specific structure and oxidation state to serve as model templates for the more complex commercial catalysts and then employed these structures in reaction studies. This focus area examined the relationships between structure and cation redox characteristics in oxidation catalysis. Infrared and Raman spectroscopy were used to characterize the cations and reaction intermediates.

Ekerdt, John G.

1999-07-31

156

Hydroperoxide Oxidation of Difficult-to-Oxidize Substrates: An Unprecedented C–C Bond Cleavage in Alkanes and the Oxidation of Molecular Nitrogen  

Microsoft Academic Search

In the V(V)H2O2\\/AcOH system, C5–C20n-alkanes, isooctane, and neohexane undergo oxidation to ketones and alcohols; the oxidation products of branched alkanes are indicative of a C–C bond cleavage in these substrates. A concept is developed, according to which the peroxo complexes of vanadium(V) are responsible for alkane oxidation. These complexes can transfer the oxygen atom or the O+· radical cation to

A. E. Gekhman; I. P. Stolyarov; N. V. Ershova; N. I. Moiseeva; I. I. Moiseev

2004-01-01

157

Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product  

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

158

Plasma-activated direct bonding of diamond-on-insulator wafers to thermal oxide grown silicon wafers  

E-print Network

Plasma-activated direct bonding of diamond-on-insulator wafers to thermal oxide grown silicon microscopy, profilometer and wafer bow measurements. Plasma-activated direct bonding of DOI wafers to thermal September 2010 Keywords: Diamond-on-insulator Plasma activation Ultrananocrystalline diamond Direct bonding

Akin, Tayfun

159

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

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 ...

Ciccolini, Rocco P

2008-01-01

160

Bonding  

MedlinePLUS

... between teeth Make teeth look longer Change the shape or color of teeth Sometimes, bonding also is used to ... a color that will most closely match the color of the tooth. He or she will shape the tooth with a drill (handpiece) if necessary, ...

161

Regioselective gold-catalyzed oxidative C-N bond formation.  

PubMed

A novel protocol for the regioselective intermolecular amination of various arenes has been developed. By using an I(III) oxidant in the presence of a Au(I) catalyst, a direct and novel route for regioselectively accessing a variety of substituted aniline moieties has been achieved with yields as high as 90%. Mechanistic insight suggests that regioselectivity can be predicted based on electrophilic aromatic metalation patterns. PMID:25539392

Marchetti, Louis; Kantak, Abhishek; Davis, Riley; DeBoef, Brenton

2015-01-16

162

Favorite Demonstration: Demonstrating Indigo Carmine Oxidation-Reduction Reactions--A Choreography for Chemical Reactions  

NSDL National Science Digital Library

The indigo carmine demonstration (Ferguson et al. 1973), also referred to as a traffic-light demonstration (Flinn Scientific 2007a), is an example of a set of oxidation-reduction reactions that occurs within one solution. This type of demonstration can be used to introduce the concept of chemical reaction to undergraduate nonscience majors. Through their observations guided by the instructor, students begin to develop and construct the following concepts: color changes, reaction rates, reversible reactions, energy requirements (endothermic/exothermic), and equilibrium.

David M. Majerich

2008-03-01

163

Oxidation of estrone by permanganate: Reaction kinetics and estrogenicity removal  

Microsoft Academic Search

Permanganate was used as an oxidant to control estrone in the present study. Kinetics was determined at pH 2.5–9.4 and temperature\\u000a 15–40°C for the reaction of estrone with potassium permanganate. It was found that the reaction is second-order overall and\\u000a first-order with respect to both estrone and permanganate. The second-order rate constant for the reaction at pH 5.8 and 25°C

XiaoLing Shao; Jun Ma; Gang Wen; JingJing Yang

2010-01-01

164

Oxidation Control with Chromate Pretreatment of MCrAlY Unmelted Particle and Bond Coat in Thermal Barrier Systems  

NASA Astrophysics Data System (ADS)

MCrAlY alloy bond coat is widely used in thermal barrier coating (TBC) systems to protect substrates from high-temperature oxidizing environments. However, failure of the ceramic topcoat can occur due to a thermally grown oxide (TGO) that grows at the interface between the bond coat and the topcoat. In this study, the effect of chromate treatment was investigated. Prior to topcoat deposition, a thin film of Cr2O3 was formed on the bond coat surface. High-temperature oxidation tests were carried out, and the oxidation rates were determined by inspection of cross sections. Similar oxidation tests were carried out using MCrAlY powder material assumed to be unmelted particles. As a result, the chromate-treated bond coat showed outstanding oxidation resistance. Calculations that take into account the oxidation of particles in the topcoat indicated the generation of internal stress to cause local fracture of the topcoat.

Yamano, Hideaki; Tani, Kazumi; Harada, Yoshio; Teratani, Takema

2008-06-01

165

Method for producing bio-fuel that integrates heat from carbon-carbon bond-forming reactions to drive biomass gasification reactions  

DOEpatents

A low-temperature catalytic process for converting biomass (preferably glycerol recovered from the fabrication of bio-diesel) to synthesis gas (i.e., H.sub.2/CO gas mixture) in an endothermic gasification reaction is described. The synthesis gas is used in exothermic carbon-carbon bond-forming reactions, such as Fischer-Tropsch, methanol, or dimethylether syntheses. The heat from the exothermic carbon-carbon bond-forming reaction is integrated with the endothermic gasification reaction, thus providing an energy-efficient route for producing fuels and chemicals from renewable biomass resources.

Cortright, Randy D.; Dumesic, James A.

2013-04-02

166

Method for producing bio-fuel that integrates heat from carbon-carbon bond-forming reactions to drive biomass gasification reactions  

DOEpatents

A low-temperature catalytic process for converting biomass (preferably glycerol recovered from the fabrication of bio-diesel) to synthesis gas (i.e., H.sub.2/CO gas mixture) in an endothermic gasification reaction is described. The synthesis gas is used in exothermic carbon-carbon bond-forming reactions, such as Fischer-Tropsch, methanol, or dimethylether syntheses. The heat from the exothermic carbon-carbon bond-forming reaction is integrated with the endothermic gasification reaction, thus providing an energy-efficient route for producing fuels and chemicals from renewable biomass resources.

Cortright, Randy D. (Madison, WI); Dumesic, James A. (Verona, WI)

2012-04-10

167

Method for producing bio-fuel that integrates heat from carbon-carbon bond-forming reactions to drive biomass gasification reactions  

DOEpatents

A low-temperature catalytic process for converting biomass (preferably glycerol recovered from the fabrication of bio-diesel) to synthesis gas (i.e., H.sub.2/CO gas mixture) in an endothermic gasification reaction is described. The synthesis gas is used in exothermic carbon-carbon bond-forming reactions, such as Fischer-Tropsch, methanol, or dimethylether syntheses. The heat from the exothermic carbon-carbon bond-forming reaction is integrated with the endothermic gasification reaction, thus providing an energy-efficient route for producing fuels and chemicals from renewable biomass resources.

Cortright, Randy D. (Madison, WI); Dumesic, James A. (Verona, WI)

2011-01-18

168

Copper-mediated synthesis of pyrazolo[1,5-a]pyridines through oxidative linkage of C-C/N-N bonds.  

PubMed

Copper-mediated synthesis of pyrazolo[1,5-a]pyridine-3-carboxylates through oxidative linkage of C-C and N-N bonds under mild reaction conditions is described. This protocol is applicable to a variety of pyridyl esters as well as various benzonitriles including nicotinonitrile, isonicotinonitrile and thiophene-2-carbonitrile. Better yields were observed with electron withdrawing substituted benzonitriles. PMID:25679457

Mohan, Darapaneni Chandra; Ravi, Chitrakar; Rao, Sadu Nageswara; Adimurthy, Subbarayappa

2015-03-11

169

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

E-print Network

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

Jones, William D.

170

Disulfide Bond Formation and Activation of Escherichia coli ?-Galactosidase under Oxidizing Conditions  

PubMed Central

Escherichia coli ?-galactosidase is probably the most widely used reporter enzyme in molecular biology, cell biology, and biotechnology because of the easy detection of its activity. Its large size and tetrameric structure make this bacterial protein an interesting model for crystallographic studies and atomic mapping. In the present study, we investigate a version of Escherichia coli ?-galactosidase produced under oxidizing conditions, in the cytoplasm of an Origami strain. Our data prove the activation of this microbial enzyme under oxidizing conditions and clearly show the occurrence of a disulfide bond in the ?-galactosidase structure. Additionally, the formation of this disulfide bond is supported by the analysis of a homology model of the protein that indicates that two cysteines located in the vicinity of the catalytic center are sufficiently close for disulfide bond formation. PMID:22286993

Seras-Franzoso, Joaquin; Affentranger, Roman; Ferrer-Navarro, Mario; Daura, Xavier; Villaverde, Antonio

2012-01-01

171

Palladium-catalyzed regio-selective oxidative C-H bond acylation of azoxybenzenes with alcohols.  

PubMed

A palladium-catalyzed regio-selective acylation of C-H bonds of azoxybenzenes with alcohols was developed using tert-butyl hydroperoxide (TBHP) as an oxidant. Alcohol derivatives can act as effective acyl precursors in situ, which are less toxic, inexpensive, stable, and commercially available. These transformations proceeded smoothly and could tolerate a variety of functional groups. PMID:25723965

Hou, Lekai; Chen, Xiangxiang; Li, Shuang; Cai, Suxian; Zhao, Yanxia; Sun, Meng; Yang, Xiao-Juan

2015-04-14

172

CH Bond Activation at Pt(II): A Route to Selective Alkane Oxidation?  

Microsoft Academic Search

A hypothetical catalytic cycle for the selective oxidation of alkanes to alcohols by dioxygen may be based on the activation to C-H bonds at Pt(II) centers, coupled with additional known organoplatinum chemistry. Mechanistic studies on the C-H activation process offer guides for designing potential for catalytic species.

Alan F. Heyduk; H. Annita Zhong; Jay A. Labinger; John E. Bercaw

2004-01-01

173

Oxide treatments of Al 1100 for adhesive bonding-surface characterization  

NASA Astrophysics Data System (ADS)

A study was made to characterize by spectroscopic methods the surface of oxides formed on Al 1100 by chromate conversion coating, chromic acid anodizing and sulfuric acid anodizing. Adhesive bond strength to silicone rubber was determined using single lap joint specimens, and correlation between the microscopic structure and macroscopic values was found. It was observed that the layer formed in chromate conversion coating was essentially hydrated chromia, and it yielded the lowest bond strength. Sulfuric acid anodizing produced hydrated alumina, incorporating sulfate ions in its matrix; an intermediate bond strength was found with this pretreatment. Chromic acid anodizing gave rise to a compact, almost anhydrous alumina film, and the highest bond strength was attained.

Yaniv, A. E.; Fin, N.; Dodiuk, H.; Klein, I. E.

1985-02-01

174

New approach for kinetic parameters determination for hydrothermal oxidation reaction  

E-print Network

1 New approach for kinetic parameters determination for hydrothermal oxidation reaction David different methods, namely pseudo first order kinetics, multiple linear regression and Runge-Kutta algorithm for industrial or agricultural applications. In order to scale up reactors for HOT of industrial wastewaters

Paris-Sud XI, Université de

175

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

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

Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

2014-05-01

176

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

PubMed

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

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

2014-10-01

177

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

PubMed Central

?-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

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

2012-01-01

178

Biotransformations utilizing ?-oxidation cycle reactions in the synthesis of natural compounds and medicines.  

PubMed

?-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

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

2012-01-01

179

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

SciTech Connect

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.

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

2011-01-01

180

Gold supported on well-ordered ceria films: nucleation, growth and morphology in CO oxidation reaction  

E-print Network

are found to be stable in O2 ambient up to 10 mbar, meanwhile gold sintering emerges at CO pressures above oxidation reaction. KEY WORDS: gold; ceria; CO oxidation; thin films; scanning tunneling microscopy. 1 oxidation, selective oxidation of propene to propene oxide, water gas shift reaction, NO reduction

Gao, Hongjun

181

Theoretical study of the reaction formalhydrazone with singlet oxygen. Fragmentation of the C=N bond, ene reaction and other processes.  

PubMed

Photobiologic and synthetic versatility of hydrazones has not yet been established with (1)O2 as a route to commonly encountered nitrosamines. Thus, to determine whether the "parent" reaction of formalhydrazone and (1)O2 leads to facile C=N bond cleavage and resulting nitrosamine formation, we have carried out CCSD(T)//DFT calculations and analyzed the energetics of the oxidation pathways. A [2 + 2] pathway occurs via diradicals and formation of 3-amino-1,2,3-dioxazetidine in a 16 kcal/mol(-1) process. Reversible addition or physical quenching of (1)O2 occurs either on the formalhydrazone carbon for triplet diradicals at 2-3 kcal mol(-1), or on the nitrogen (N(3)) atom forming zwitterions at ~15 kcal/mol(-1), although the quenching channel by charge-transfer interaction was not computed. The computations also predict a facile conversion of formalhydrazone and (1)O2 to hydroperoxymethyl diazene in a low-barrier 'ene' process, but no 2-amino-oxaziridine-O-oxide (perepoxide-like) intermediate was found. A Benson-like analysis (group increment calculations) on the closed-shell species are in accord with the quantum chemical results. PMID:24354600

Rudshteyn, Benjamin; Castillo, Alvaro; Ghogare, Ashwini A; Liebman, Joel F; Greer, Alexander

2014-01-01

182

Theoretical Study of the Reaction Formalhydrazone with Singlet Oxygen. Fragmentation of the C=N Bond, Ene Reaction, and Other Processes†  

PubMed Central

Photobiologic and synthetic versatility of hydrazones has not yet been established with 1O2 as a route to commonly encountered nitrosamines. Thus, to determine whether the “parent” reaction of formalhydrazone and 1O2 leads to facile C=N bond cleavage and resulting nitrosamine formation, we have carried out CCSD(T)//DFT calculations and analyzed the energetics of the oxidation pathways. A [2 + 2] pathway occurs via diradicals and formation of 3-amino-1,2,3-dioxazetidine in a 16 kcal/mol process. Reversible addition or physical quenching of 1O2 occurs either on the formalhydrazone carbon for triplet diradicals at 2–3 kcal/mol, or on the nitrogen (N(3)) atom forming zwitterions at ~15 kcal/mol, although the quenching channel by charge-transfer interaction was not computed. The computations also predict a facile conversion of formalhydrazone and 1O2 to hydroperoxymethyl diazene in a low-barrier ‘ene’ process, but no 2-amino-oxaziridine-O-oxide (perepoxide-like) intermediate was found. A Benson-like analysis (group increment calculations) on the closed shell species are in accord with the quantum chemical results. PMID:24354600

Rudshteyn, Benjamin; Castillo, Álvaro; Ghogare, Ashwini A.; Liebman, Joel F.; Greer, Alexander

2013-01-01

183

Mode- and bond-selected reactions of vibrationally excited methane and monodeuterated methane with chlorine atoms  

NASA Astrophysics Data System (ADS)

Direct infrared absorption prepares CH4 in two nearly isoenergetic vibrationally excited states, the symmetric stretch-bend combination (nu 1 + nu4) and the antisymmetric stretch-bend combination (nu3 + nu4), for a study of the effect of stretching vibrations of CH4 on the reaction, CH4 + Cl( 2P3/2) ? CH3 + HCl. Comparison of intensities in the action spectra with those in the simulated absorption spectra shows that vibrational excitation of methane to the nu1 + nu4 state promotes the reaction more efficiently than excitation to the nu3 + nu4 state by a factor of 1.9 +/- 0.5. The reduced symmetry of CH3D allows us to explore the relative reactivity of the fundamental symmetric and the antisymmetric C-H stretches. We excite three vibrational eigenstates of CH3D near 3000 cm -1 that contain different amounts of symmetric C-H stretch (nu 1), antisymmetric C-H stretch (nu4), and two quanta of bend (2nu5). Analyzing the action spectra with the simulation and the composition of the eigenstates reveals that the nu1 vibration is 6 +/- 1 times more reactive than the nu4 vibration. Ab initio calculations of the vibrational eigenfunctions along the reaction coordinate show that as the Cl atom approaches, the nu1 vibration of CH3D is transformed into localized vibrational excitation in the C-H bond pointing toward the Cl atom, promoting the reaction, and the nu 4 vibrational energy flows into the distal C-H bonds that remain unaffected during the reaction, consistent with our experimental results. Selective vibrational excitation permits control of the outcome of a reaction with two competing channels. Vibrational excitation of the first overtone of C-D stretch (2nu2) of CH3D at ˜4300 cm-1 exclusively increases the probability of breaking the C-D bond, yielding CH3 but no CH2D. By contrast, excitation of the nu1 vibration, the nu4 vibration, or the combination vibration of C-H stretch and CH3 umbrella bend (nu4 + nu3) preferentially promotes the H-atom abstraction to produce CH2D over CH3. The vibrational action spectra for the two products permit the separation of the two sets of interleaved transitions to give band origins and rotational constants of the 2nu 2 state and the nu4 + nu3 state of CH 3D.

Yoon, Sangwoon

184

Oxidative Degradation of Decabromodiphenyl Ether (BDE 209) by Potassium Permanganate: Reaction Pathways, Kinetics, and Mechanisms Assisted by Density Functional Theory Calculations.  

PubMed

This study found that decabromodiphenyl ether (BDE 209) could be oxidized effectively by potassium permanganate (KMnO4) in sulfuric acid medium. A total of 15 intermediate oxidative products were detected. The reaction pathways were proposed, which primarily included cleavage of the ether bond to form pentabromophenol. Direct oxidation on the benzene ring also played an important role because hydroxylated polybrominated diphenyl ethers (PBDEs) were produced during the oxidation process. The degradation occurred dramatically in the first few minutes and fitted pseudo-first-order kinetics. Increasing the water content decelerated the reaction rate, whereas increasing the temperature facilitated the reaction. In addition, density functional theory (DFT) was employed to determine the frontier molecular orbital (FMO) and frontier electron density (FED) of BDE 209 and the oxidative products. The theoretical calculation results confirmed the proposed reaction pathways. PMID:25751737

Shi, Jiaqi; Qu, Ruijuan; Feng, Mingbao; Wang, Xinghao; Wang, Liansheng; Yang, Shaogui; Wang, Zunyao

2015-04-01

185

Relationships between toughness and microstructure of reaction bonded Si3N4  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

186

Bend strengths of reaction bonded silicon nitride prepared from dry attrition milled silicon powder  

NASA Technical Reports Server (NTRS)

Dry attrition milled silicon powder was compacted, sintered in helium, and reaction bonded in nitrogen-4 volume percent hydrogen. Bend strengths of bars with as-nitrided surfaces averaged as high as 210 MPa at room temperature and 220 MPa at 1400 C. Bars prepared from the milled powder were stronger than those prepared from as-received powder at both room temperature and at 1400 C. Room temperature strength decreased with increased milling time and 1400 C strength increased with increased milling time.

Herbell, T. P.; Glasgow, T. K.

1979-01-01

187

Te-Te and Te-C bond cleavage reactions using a monovalent gallanediyl.  

PubMed

LGa (L = [(2,6-i-Pr2-C6H3)NC(Me)]2CH) reacts with elemental tellurium with formation of the Te-bridged compound [LGa-?-Te]2, whereas the reactions with Ph2Te2 and i-Pr2Te occurred with cleavage of the Te-Te and Te-C bond, respectively, and subsequent formation of LGa(TePh)2 and LGa(i-Pr)Tei-Pr . were characterized by heteronuclear NMR ((1)H, (13)C, (125)Te) and IR spectroscopy and their solid state structures were determined by single crystal X-ray analyses. PMID:25680084

Ganesamoorthy, Chelladurai; Bendt, Georg; Bläser, Dieter; Wölper, Christoph; Schulz, Stephan

2015-03-01

188

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

SciTech Connect

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.

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

2004-11-27

189

Method for facilitating catalyzed oxidation reactions, device for facilitating catalyzed oxidation reactions  

DOEpatents

A catalytic process for the oxidation of organic. Oxygen is loaded into a metal foil by heating the foil while in contact with an oxygen-containing fluid. After cooling the oxygen-activated foil to room temperature, oxygen diffuses through the foil and oxidizes reactants exposed to the other side of the foil.

Beuhler, Robert J. (East Moriches, NY); White, Michael G. (Blue Point, NY); Hrbek, Jan (Rocky Point, NY)

2006-08-15

190

The oxidative burst reaction in mammalian cells depends on gravity.  

PubMed

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

Adrian, Astrid; Schoppmann, Kathrin; Sromicki, Juri; Brungs, Sonja; von der Wiesche, Melanie; Hock, Bertold; Kolanus, Waldemar; Hemmersbach, Ruth; Ullrich, Oliver

2013-01-01

191

The oxidative burst reaction in mammalian cells depends on gravity  

PubMed Central

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

2013-01-01

192

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

SciTech Connect

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.

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

1981-11-12

193

Sintered reaction bonded Si3N4 for the AGT 101 turbine rotor  

NASA Technical Reports Server (NTRS)

The sintered reaction reaction bonded Si3N4 (SRBSN) process, with Y2O3 as a sintering aid, was selected for the fabrication of the AGT 101 turbine rotor. Experiments to determine the optimum Y2O3 composition of this system are discussed. The room temperature strength of the optimum material (RM-1) exceeds 700 MPa while the 1200 C strength exceeds 550 MPa. The slip casting fabrication technique employed for the AGT 101 simulated rotor is described. Rotors have been cast, nitrided and sintered. Densities exceeding 97% of theoretical (3.26 g/cc) have been obtained. Problems relating to sintering reproducibility, and the overall quality of the simulated rotors have been identified.

Mangels, J. A.

1980-01-01

194

Synthesis, molecular and electronic structure, and reactions of a Zn-Hg-Zn bonded complex.  

PubMed

Reaction of ((Ar')NacNac)ZnI with potassium/mercury amalgam gave the trimetallic compound {((Ar')NacNac)Zn}2Hg () containing a Zn-Hg-Zn unit and the first example of a bond between two different Group 12 metals; DFT and QTAIM analyses suggest that 1 is best described as two formally Zn(i) atoms with a Hg(0) atom positioned between them; reactions of with stoichiometric I2, FpI or Fp2 gave addition products of the type ((Ar')NacNac)ZnX (X = I, Fp) and Hg. (Ar')NacNac = HC{C(Me)N(2,6-C6H3(i)Pr2)}2; Fp = CpFe(CO)2. PMID:25720674

Blake, Matthew P; Kaltsoyannis, Nikolas; Mountford, Philip

2015-03-17

195

Raman spectroscopic characterization of the core-rim structure in reaction bonded boron carbide ceramics  

NASA Astrophysics Data System (ADS)

Raman spectroscopy was used to characterize the microstructure of reaction bonded boron carbide ceramics. Compositional and structural gradation in the silicon-doped boron carbide phase (rim), which develops around the parent boron carbide region (core) due to the reaction between silicon and boron carbide, was evaluated using changes in Raman peak position and intensity. Peak shifting and intensity variation from the core to the rim region was attributed to changes in the boron carbide crystal structure based on experimental Raman observations and ab initio calculations reported in literature. The results were consistent with compositional analysis determined by energy dispersive spectroscopy. The Raman analysis revealed the substitution of silicon atoms first into the linear 3-atom chain, and then into icosahedral units of the boron carbide structure. Thus, micro-Raman spectroscopy provided a non-destructive means of identifying the preferential positions of Si atoms in the boron carbide lattice.

Jannotti, Phillip; Subhash, Ghatu; Zheng, James Q.; Halls, Virginia; Karandikar, Prashant G.; Salamone, S.; Aghajanian, Michael K.

2015-01-01

196

Homogeneous and heterogeneous reactions of anthracene with selected atmospheric oxidants.  

PubMed

The reactions of gas-phase anthracene and suspended anthracene particles with O3 and O3-NO were conducted in a 200-L reaction chamber, respectively. The secondary organic aerosol (SOA) formations from gas-phase reactions of anthracene with O3 and O3-NO were observed. Meanwhile, the size distributions and mass concentrations of SOA were monitored with a scanning mobility particle sizer (SMPS) during the formation processes. The rapid exponential growths of SOA reveal that the atmospheric lifetimes of gas-phase anthracene towards O3 and O3-NO are less than 20.5 and 4.34 hr, respectively. The particulate oxidation products from homogeneous and heterogeneous reactions were analyzed with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). Gas chromatograph/mass spectrometer (GC/MS) analyses of oxidation products of anthracene were carried out for assigning the time-of-flight (TOF) mass spectra of products from homogeneous and heterogeneous reactions. Anthrone, anthraquinone, 9,10-dihydroxyanthracene, and 1,9,10-trihydroxyanthracene were the ozonation products of anthracene, while anthrone, anthraquinone, 9-nitroanthracene, and 1,8-dihydroxyanthraquinone were the main products of anthracene with O3-NO. PMID:24520724

Zhang, Yang; Shu, Jinian; Zhang, Yuanxun; Yang, Bo

2013-09-01

197

Photocatalytic reaction centers in two-dimensional titanium oxide crystals.  

PubMed

Co-catalysts play an important role in photocatalytic water splitting. The co-catalyst is generally deposited in the form of nanoparticles on the catalyst surface, and is believed to provide water oxidation and reduction sites. However, the minimum size of a co-catalyst that can function as a reaction site and the detailed local environment of the photocatalytic reaction centers are not yet fully understood. Here, we show that even isolated single-atom Rh dopants in two-dimensional titanium oxide crystals can effectively act as co-catalysts for the water-splitting reaction. At an optimal doping concentration, the hydrogen production rate is increased substantially in comparison to that found with the undoped crystals. We also present first-principles simulations based on density functional theory to provide insights into the atomic-scale mechanism by which the isolated Rh dopants induce changes to the dissociation reaction energy landscape. These results provide new insights for better understanding the role of the co-catalyst in the photocatalytic reaction. PMID:25479408

Ida, Shintaro; Kim, Namhoon; Ertekin, Elif; Takenaka, Sakae; Ishihara, Tatsumi

2015-01-14

198

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

NASA Astrophysics Data System (ADS)

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.

Rustad, James R.; Casey, William H.

2012-03-01

199

Electronic effects in the reaction of diphenylcarbonyl oxide with aldehydes  

Microsoft Academic Search

The reactivity of 14 aldehydes with diphenylcarbonyl oxide Ph2COO was characterized by thek\\u000a 33\\/k\\u000a 31 ratio. The values ofk\\u000a 33\\/k\\u000a 31 vary from 1.310?2 (C6F5CHO) to 1.0 (p-Me2N-PhCHO), 70 C, acetonitrile as the solvent. A charge transfer complex (CTC) was suggested to be primarily formed during\\u000a the reaction. The electronic effects of substituents in the reaction were analyzed using the

A. M. Nazarov; S. L. Khursan; G. A. Yamilova; V. D. Komissarov

1999-01-01

200

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

E-print Network

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2 Hans a factor of 10. Reactions with CH2D2 prepared in a local mode containing two quanta in one C­H oscillator 2000 or in a local mode containing one quantum each in two C­H oscillators 1100 lead to products

Zare, Richard N.

201

Hydrolysis of Surfactants Containing Ester Bonds: Modulation of Reaction Kinetics and Important Aspects of Surfactant Self-Assembly  

ERIC Educational Resources Information Center

The effects of self-assembly on the hydrolysis kinetics of surfactants that contain ester bonds are discussed. A number of examples on how reaction rates and apparent reaction orders can be modulated by changes in the conditions, including an instance of apparent zero-order kinetics, are presented. Furthermore, it is shown that the examples on…

Lundberg, Dan; Stjerndahl, Maria

2011-01-01

202

Condensed-Phase, Halogen-Bonded CF3 I and C2 F5 I Adducts for Perfluoroalkylation Reactions.  

PubMed

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 CF3 I and CF3 CF2 I. 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

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

2015-03-16

203

Fabrication and characterization of reaction bonded silicon carbide/carbon nanotube composites  

NASA Astrophysics Data System (ADS)

Carbon nanotubes have generated considerable excitement in the scientific and engineering communities because of their exceptional mechanical and physical properties observed at the nanoscale. Carbon nanotubes possess exceptionally high stiffness and strength combined with high electrical and thermal conductivities. These novel material properties have stimulated considerable research in the development of nanotube-reinforced composites (Thostenson et al 2001 Compos. Sci. Technol. 61 1899, Thostenson et al 2005 Compos. Sci. Technol. 65 491). In this research, novel reaction bonded silicon carbide nanocomposites were fabricated using melt infiltration of silicon. A series of multi-walled carbon nanotube-reinforced ceramic matrix composites (NT-CMCs) were fabricated and the structure and properties were characterized. Here we show that carbon nanotubes are present in the as-fabricated NT-CMCs after reaction bonding at temperatures above 1400 °C. Characterization results reveal that a very small volume content of carbon nanotubes, as low as 0.3 volume %, results in a 75% reduction in electrical resistivity of the ceramic composites. A 96% decrease in electrical resistivity was observed for the ceramics with the highest nanotube volume fraction of 2.1%.

Thostenson, Erik T.; Karandikar, Prashant G.; Chou, Tsu-Wei

2005-11-01

204

Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures  

NASA Astrophysics Data System (ADS)

Roasting of enargite (Cu3AsS4) in the temperature range of 648 K to 898 K (375 °C to 625 °C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diffraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:

Padilla, Rafael; Aracena, Alvaro; Ruiz, Maria C.

2012-10-01

205

Oxidative reactions of tetrahydrobenzimidazole derivatives with N-sulfonyloxaziridines  

PubMed Central

An investigation of the utility of N-sulfonyloxaziridines to effect the oxidative rearrangement of tetrahydrobenzimidazoles to spiro fused 5-imidazolones is reported. In addition to the anticipated rearrangement manifold, it was found that 2-amino substituted derivatives afford products resulting from rearrangement, or alternatively from addition of methanol or water depending on the nature of the N-substituents and reaction conditions. PMID:20016755

Sivappa, Rasapalli; Koswatta, Panduka; Lovely, Carl J.

2009-01-01

206

Photovoltaic-driven organic electrosynthesis and efforts toward more sustainable oxidation reactions  

PubMed Central

Summary The combination of visible light, photovoltaics, and electrochemistry provides a convenient, inexpensive platform for conducting a wide variety of sustainable oxidation reactions. The approach presented in this article is compatible with both direct and indirect oxidation reactions, avoids the need for a stoichiometric oxidant, and leads to hydrogen gas as the only byproduct from the corresponding reduction reaction.

Nguyen, Bichlien H; Perkins, Robert J; Smith, Jake A

2015-01-01

207

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

PubMed Central

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

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

2009-01-01

208

Electrophilic, Ambiphilic, and Nucleophilic C-H bond Activation: Understanding the electronic continuum of C-H bond activation through transition-state and reaction pathway interaction energy decompositions  

SciTech Connect

The potential energy and interaction energy profiles for metal- and metal?ligand-mediated alkane C?H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7?9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d{sup 8}, d{sup 6}, d{sup 4}, and d{sup 0}), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal?ligand fragment and the coordinated C?H bond in the transition state for cleavage of the C?H bond allows classification of C?H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, ?-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C?H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C?H bond. Transition states and reaction profiles for d{sup 6} Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe{sub 3})Ir(Me). Nucleophilic character, where the metal to C?H bond charge-transfer interaction is most stabilizing, was found in metathesis reactions with W(II) and Sc(III) metal center complexes in reactions as well as late transition metal Ir(I) and Rh(I) pincer complexes that undergo C?H bond insertion. Comparison of pincer ligands shows that the PCP ligand imparts more nucleophilic character to an Ir metal center than a deprotonated PNP ligand. The PCP and POCOP ligands do not show a substantial difference in the electronics of C?H activation. It was also found that Rh(I) is substantially more nucleophilic than Ir(I). Lastly, as a qualitative approximation, investigation of transition-state fragment orbital energies showed that relative frontier orbital energy gaps correctly reflect electrophilic, ambiphilic, or nucleophilic charge-transfer stabilization patterns.

Ess, Daniel H; Goddard, William A; Periana, Roy A

2010-01-01

209

Synthesis and oxidation behavior of nanocrystalline MCrAlY bond coatings  

Microsoft Academic Search

Thermal barrier coating systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a\\u000a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO2\\/Y2O3). In this work, the oxidation behavior of conventional and nanostructured high-velocity oxyfuel (HVOF) NiCrAlY coatings has\\u000a been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a

Leonardo Ajdelsztajn; Feng Tang; J. M. Schoenung; G. E. Kim; V. Provenzano

2005-01-01

210

Manganese chlorins immobilized on silica as oxidation reaction catalysts.  

PubMed

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

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

211

Transformation of acetaminophen using manganese dioxide-mediated oxidative processes: reaction rates and pathways.  

PubMed

This study investigates the oxidative transformation kinetics of acetaminophen (APAP) by ?-MnO2 under different conditions. APAP was rapidly oxidized by ?-MnO2 with the generation of Mn(2+). The measured APAP reaction rate considerably increased with an increase in initial ?-MnO2 and APAP concentration, but decreased as pH increased. The APAP reaction rate also increased with an increase in temperature. The addition of inorganic ions (Mn(2+), Ca(2+), and Fe(3+)) and substituted phenols (guaiacol, caffeic acid, and p-coumaric acid) as co-solutes remarkably decreased the transformation rate of APAP. The UV-Vis absorption spectra exhibited the ? ? ?* transition, typical for aromatic rings. In addition, the intensity of the absorption peak gradually improved with increasing reaction time, suggesting that APAP can polymerize to form oligomers. Moreover, the secondary mass spectra of the dimers elucidated that the dimers were formed by the covalent bonding of phenol aromatic rings. Moreover, the higher-degree oligomers were formed by the coupling polymerization of phenolic and anilidic groups of dimers. These results are useful in understanding the fate of APAP in natural systems. PMID:23434488

Xiao, Hong; Song, Haiyan; Xie, Hongqin; Huang, Wei; Tan, Jun; Wu, Jianzhong

2013-04-15

212

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

PubMed Central

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

Jatania, Archana; Shivalinga, B. M.

2014-01-01

213

Elementary reaction modeling of solid oxide electrolysis cells: Main zones for heterogeneous chemical/electrochemical reactions  

NASA Astrophysics Data System (ADS)

A theoretical model of solid oxide electrolysis cells considering the heterogeneous elementary reactions, electrochemical reactions and the transport process of mass and charge is applied to study the relative performance of H2O electrolysis, CO2 electrolysis and CO2/H2O co-electrolysis and the competitive behavior of heterogeneous chemical and electrochemical reactions. In cathode, heterogeneous chemical reactions exist near the outside surface and the electrochemical reactions occur near the electrolyte. According to the mathematical analysis, the mass transfer flux D ?c determines the main zone size of heterogeneous chemical reactions, while the charge transfer flux ? ?V determines the other one. When the zone size of heterogeneous chemistry is enlarged, more CO2 could react through heterogeneous chemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to H2O electrolysis. Meanwhile, when the zone size of electrochemistry is enlarged, more CO2 could react through electrochemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to CO2 electrolysis. The relative polarization curves, the ratio of CO2 participating in electrolysis and heterogeneous chemical reactions, the mass and charge transfer flux and heterogeneous chemical/electrochemical reaction main zones are simulated to study the effects of cathode material characteristics (porosity, particle diameter and ionic conductivity) and operating conditions (gas composition and temperature).

Li, Wenying; Shi, Yixiang; Luo, Yu; Cai, Ningsheng

2015-01-01

214

Reaction rate oscillations during catalytic CO oxidation: A brief overview  

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

215

Reaction between nitric oxide and ozone in solid nitrogen  

NASA Technical Reports Server (NTRS)

Nitrogen dioxide, NO2, is produced when nitric oxide, NO, and ozone, O3, are suspended in a nitrogen matrix at 11-20 K. The NO2 is formed with first-order kinetics, a 12 K rate constant of (1.4 + or - 0.2) x 0.00001/sec, and an apparent activation energy of 106 + or - 10 cal/mol. Isotopic labeling, variation of concentrations, and cold shield experiments show that the growth of NO2 is due to reaction between ozone molecules and NO monomers, and that the reaction is neither infrared-induced nor does it seem to be a heavy atom tunneling process. Reaction is attributed to nearest-neighbor NO.O3 pairs probably held in a specific orientational relationship that affects the kinetic behavior. When the temperature is raised, more such reactive pairs are generated, presumably by local diffusion. Possible mechanisms are discussed.

Lucas, D.; Pimentel, G. C.

1979-01-01

216

Metal-catalyzed nitrogen-atom transfer methods for the oxidation of aliphatic C-H bonds.  

PubMed

For more than a century, chemists have endeavored to discover and develop reaction processes that enable the selective oxidation of hydrocarbons. In the 1970s, Abramovitch and Yamada described the synthesis and electrophilic reactivity of sulfonyliminoiodinanes (RSO(2)N?IPh), demonstrating the utility of this new class of reagents to function as nitrene equivalents. Subsequent investigations by Breslow, Mansuy, and Müller would show such oxidants to be competent for alkene and saturated hydrocarbon functionalization when combined with transition metal salts or metal complexes, namely those of Mn, Fe, and Rh. Here, we trace our own studies to develop N-atom transfer technologies for C-H and ?-bond oxidation. This Account discusses advances in both intra- and intermolecular amination processes mediated by dirhodium and diruthenium complexes, as well as the mechanistic foundations of catalyst reactivity and arrest. Explicit reference is given to questions that remain unanswered and to problem areas that are rich for discovery. A fundamental advance in amination technology has been the recognition that iminoiodinane oxidants can be generated in situ in the presence of a metal catalyst that elicits subsequent N-atom transfer. Under these conditions, both dirhodium and diruthenium lantern complexes function as competent catalysts for C-H bond oxidation with a range of nitrogen sources (e.g., carbamates, sulfamates, sulfamides, etc.), many of which will not form isolable iminoiodinane equivalents. Practical synthetic methods and applications thereof have evolved in parallel with inquiries into the operative reaction mechanism(s). For the intramolecular dirhodium-catalyzed process, the body of experimental and computational data is consistent with a concerted asynchronous C-H insertion pathway, analogous to the consensus mechanism for Rh-carbene transfer. Other studies reveal that the bridging tetracarboxylate ligand groups, which shroud the dirhodium core, are labile to exchange under standard reaction conditions. This information has led to the generation of chelating dicarboxylate dinuclear rhodium complexes, exemplified by Rh(2)(esp)(2). The performance of this catalyst system is unmatched by other dirhodium complexes in both intra- and intermolecular C-H amination reactions. Tetra-bridged, mixed-valent diruthenium complexes function as effective promoters of sulfamate ester oxidative cyclization. These catalysts can be crafted with ligand sets other than carboxylates and are more resistant to oxidation than their dirhodium counterparts. A range of experimental and computational mechanistic data amassed with the tetra-2-oxypyridinate diruthenium chloride complex, [Ru(2)(hp)(4)Cl], has established the insertion event as a stepwise pathway involving a discrete radical intermediate. These data contrast dirhodium-catalyzed C-H amination and offer a cogent model for understanding the divergent chemoselectivity trends observed between the two catalyst types. This work constitutes an important step toward the ultimate goal of achieving predictable, reagent-level control over product selectivity. PMID:22546004

Roizen, Jennifer L; Harvey, Mark Edwin; Du Bois, J

2012-06-19

217

Copper-catalyzed oxidative N-s bond formation for the synthesis of N-sulfenylimines.  

PubMed

Despite the remarkable success of the copper-catalyzed oxidative coupling reaction, direct cross-coupling of amines and thiols for the synthesis of N-sulfenylimines has not been previously reported. Using commercially available copper catalysts (CuI) and oxygen as an environmentally benign oxidant, synthetically useful N-sulfenylimines were prepared from amines and thiols in good yields without overoxidation of sulfur atoms. PMID:25685885

Lee, Chan; Wang, Xi; Jang, Hye-Young

2015-03-01

218

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon-carbon bond forming reactions.  

PubMed

The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki-Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon-carbon bond forming reactions both in terms of activity and selectivity. For example, when used as ligands in the rhodium-catalysed hydroformylation of styrene, they lead to both high isoselectivity and high enantioselectivity. In the study dealing with the Mizoroki-Heck reactions, comparative tests were carried out with WIDEPHOS, a diphosphine analogue of HUGPHOS-2. PMID:25383109

Jouffroy, Matthieu; Gramage-Doria, Rafael; Sémeril, David; Armspach, Dominique; Matt, Dominique; Oberhauser, Werner; Toupet, Loïc

2014-01-01

219

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions  

PubMed Central

Summary The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki–Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon–carbon bond forming reactions both in terms of activity and selectivity. For example, when used as ligands in the rhodium-catalysed hydroformylation of styrene, they lead to both high isoselectivity and high enantioselectivity. In the study dealing with the Mizoroki–Heck reactions, comparative tests were carried out with WIDEPHOS, a diphosphine analogue of HUGPHOS-2. PMID:25383109

Jouffroy, Matthieu; Gramage-Doria, Rafael; Sémeril, David; Oberhauser, Werner; Toupet, Loïc

2014-01-01

220

Understanding Selectivity in the Oxidative Addition of the Carbon-Sulfur Bonds of 2-Cyanothiophene to Pt(0)  

E-print Network

Understanding Selectivity in the Oxidative Addition of the Carbon-Sulfur Bonds of 2-Cyanothiophene the cleavage of the substituted and unsubstituted C--S bonds. While cleavage away from the cyano group is preferred kinetically, cleavage adjacent to the cyano group is preferred thermodynamically. Density

Jones, William D.

221

Development of a classical force field for the oxidized Si surface: Application to hydrophilic wafer bonding  

NASA Astrophysics Data System (ADS)

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidized Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO2 polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress, and interactions with single water molecules of a natively oxidized Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidized and amorphous silica surfaces of 97 and 90mJ /m2, respectively, at a water adsorption coverage of approximately 1 ML. The difference arises from the stronger interaction of the natively oxidized surface with liquid water, resulting in a higher heat of immersion (203 vs 166mJ/m2), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller densities with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account.

Cole, Daniel J.; Payne, Mike C.; Csányi, Gábor; Mark Spearing, S.; Colombi Ciacchi, Lucio

2007-11-01

222

Development of a classical force field for the oxidized Si surface: application to hydrophilic wafer bonding.  

PubMed

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidized Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO(2) polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress, and interactions with single water molecules of a natively oxidized Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidized and amorphous silica surfaces of 97 and 90 mJm(2), respectively, at a water adsorption coverage of approximately 1 ML. The difference arises from the stronger interaction of the natively oxidized surface with liquid water, resulting in a higher heat of immersion (203 vs 166 mJm(2)), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller densities with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account. PMID:18052443

Cole, Daniel J; Payne, Mike C; Csányi, Gábor; Spearing, S Mark; Colombi Ciacchi, Lucio

2007-11-28

223

Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction  

Microsoft Academic Search

This study was undertaken in order to assess the potential for oxidizing NO to NOâ in flue gas environments, with the aim of promoting the so-called fast SCR reaction. In principle this can result in improved SCR kinetics and reduced SCR catalyst volumes. Prior to commencing experimental work, a literature study was undertaken to identify candidate catalysts for screening. Selection

Mark Crocker

2005-01-01

224

Bond strength of selected composite resin-cements to zirconium-oxide ceramic  

PubMed Central

Objectives: The aim of this study was to evaluate bond strengths of zirconium-oxide (zirconia) ceramic and a selection of different composite resin cements. Study Design: 130 Lava TM cylinders were fabricated. The cylinders were sandblasted with 80 µm aluminium oxide or silica coated with CoJet Sand. Silane, and bonding agent and/or Clearfil Ceramic Primer were applied. One hundred thirty composite cement cylinders, comprising two dual-polymerizing (Variolink II and Panavia F) and two autopolymerizing (Rely X and Multilink) resins were bonded to the ceramic samples. A shear test was conducted, followed by an optical microscopy study to identify the location and type of failure, an electron microscopy study (SEM and TEM) and statistical analysis using the Kruskal-Wallis test for more than two independent samples and Mann-Whitney for two independent samples. Given the large number of combinations, Bonferroni correction was applied (?=0.001). Results: Dual-polymerizing cements provided better adhesion values (11.7 MPa) than the autopolymerizing (7.47 MPa) (p-value M-W<0.001). The worst techniques were Lava TM + sandblasting + Silane + Rely X; Lava TM + sandblasting + Silane + Multilink and Lava TM + CoJet + silane + Multilink. Adhesive failure (separation of cement and ceramic) was produced at a lesser force than cohesive failure (fracture of cement) (p-value M-W<0.001). Electron microscopy confirmed that the surface treatments modified the zirconium-oxide ceramic, creating a more rough and retentive surface, thus providing an improved micromechanical interlocking between the cement and the ceramic. Key words:Shear bond strength, silica coating, surface treatment, zirconia ceramics, phosphate monomer. PMID:22926485

Fons-Font, Antonio; Amigó-Borrás, Vicente; Granell-Ruiz, María; Busquets-Mataix, David; Panadero, Rubén A.; Solá-Ruiz, Maria F.

2013-01-01

225

Time-resolved spectroscopic characterization of a novel photodecarboxylation reaction mediated by homolysis of a carbon ?-bond in flurbiprofen.  

PubMed

Flurbiprofen (Fp), a nonsteroidal anti-inflammatory drug (NSAID) currently in use for arthritis pain relief and in clinical trials for metastatic prostate cancer, can induce photosensitization and phototoxicity upon exposure to sunlight. The mechanisms responsible for Fp phototoxicity are poorly understood and deserve investigation. In this study, the photodecarboxylation reaction of Fp, which has been assumed to underpin its photoinduced side effects, was explored by femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopic techniques in pure acetonitrile (MeCN) solvent. Density functional theory (DFT) calculations were also performed to facilitate the assignments of transient species. The resonance Raman and DFT calculation results reveal that the neutral form of Fp was the predominant species present in MeCN. Analysis of the ultraviolet/visible absorption spectrum and results from TD-DFT calculations indicate that the second excited singlet (S2) can be excited by 266 nm light. Due to its intrinsic instability, S2 rapidly underwent internal conversion (IC) to decay to the lowest lying excited singlet (S1), which was observed in the fs-TA spectra at very early delay times. Intriguingly, three distinct pathways for S1 decay seem to coexist. Specifically, other than fluorescence emission back to the ground state and transformation to the lowest triplet state T1 through intersystem crossing (ISC), the homolysis of the carbon ?-bond decarboxylation reaction proceeded simultaneously to give rise to two radical species, one being carboxyl and another being the residual, denoted as FpR. The coexistence of the triplet Fp (T1) and FpR species was verified by means of TR(3) spectra along with ns-TA spectra. As a consequence of its apparent high reactivity, the FpR intermediate was observed to undergo oxidation under oxygen-saturated conditions to yield another radical species, denoted as FOR, which subsequently underwent intramolecular hydrogen transfer (IHT) and dehydroxylation (DHO) to form a final product, which could react with the carboxyl from the decarboxylation reaction to generate a minor final product. TD-DFT and transient state (TS) calculations for predicting the absorption bands and activation energies of the transient species produced in the photodecarboxylation reaction have provided valuable mechanistic insights for the assignment of the intermediate species observed in the time-resolved spectroscopy experiments reported here. The results of the time-resolved spectroscopy experiments and DFT calculations were used to elucidate the reaction mechanisms and intermediates involved in the photochemistry of Fp. PMID:23750456

Su, Tao; Ma, Jiani; Wong, Naikei; Phillips, David Lee

2013-07-18

226

Strength and fracture toughness of reaction-bonded Si3N4  

NASA Technical Reports Server (NTRS)

Fracture strength and fracture toughness measurements were made on reaction-bonded Si3N4 materials with a range of alpha/beta ratios. The results do not indicate any clear relation between the modulus of rupture and the alpha/beta ratio over the range 1.5-9. Values for the modulus of rupture range from 219 to 290 MN per sq m, with an overall average of 238 MN per sq m. The notched beam fracture toughness is found to be constant over the range of microstructures produced, indicating that of the various microstructural features (e.g., alpha/beta ratio and pore size and distribution) no single element has a controlling influence over fracture toughness and the fracture surface energy.

Danforth, S. C.; Richman, M. H.

1983-01-01

227

SiC fiber reinforced reaction-bonded Si3N4 composites  

NASA Technical Reports Server (NTRS)

A technique for fabricating strong and tough SiC fiber reinforced reaction bonded Si3N4 matrix composites (SiC/RBSN) was developed. Using this technique, composites containing approximately 23, 30, and 40 volume fractions of aligned 140 micron diameter, chemically vapor deposited SiC fibers were fabricated. The room temperature physical and mechanical properties were evaluated. The results for composite tensile strength, bend strength, and fracture strain indicate that the composite displays excellent properties when compared with the unreinforced matrix of comparable porosity. The composite stress at which the matrix first cracks and the ultimate composite fracture strength increase with increasing volume fraction of fibers, and the composite fails gracefully. The mechanical property data of this ceramic composite are compared with similar data for unreinforced commercially available Si3N4 materials and for SEP SiC/SiC composites.

Bhatt, Ramakrishna T.

1986-01-01

228

Experimental investigation on material migration phenomena in micro-EDM of reaction-bonded silicon carbide  

NASA Astrophysics Data System (ADS)

Material migration between tool electrode and workpiece material in micro electrical discharge machining of reaction-bonded silicon carbide was experimentally investigated. The microstructural changes of workpiece and tungsten tool electrode were examined using scanning electron microscopy, cross sectional transmission electron microscopy and energy dispersive X-ray under various voltage, capacitance and carbon nanofibre concentration in the dielectric fluid. Results show that tungsten is deposited intensively inside the discharge-induced craters on the RB-SiC surface as amorphous structure forming micro particles, and on flat surface region as a thin interdiffusion layer of poly-crystalline structure. Deposition of carbon element on tool electrode was detected, indicating possible material migration to the tool electrode from workpiece material, carbon nanofibres and dielectric oil. Material deposition rate was found to be strongly affected by workpiece surface roughness, voltage and capacitance of the electrical discharge circuit. Carbon nanofibre addition in the dielectric at a suitable concentration significantly reduced the material deposition rate.

Liew, Pay Jun; Yan, Jiwang; Kuriyagawa, Tsunemoto

2013-07-01

229

Effect of loading rate on dynamic fracture of reaction bonded silicon nitride  

NASA Technical Reports Server (NTRS)

Wedge-loaded, modified tapered double cantilever beam (WL-MTDCB) specimens under impact loading were used to determine the room temperature dynamic fracture response of reaction bonded silicon nitride (RBSN). The crack extension history, with the exception of the terminal phase, was similar to that obtained under static loading. Like its static counterpart, a distinct crack acceleration phase, which was not observed in dynamic fracture of steel and brittle polymers, was noted. Unlike its static counterpart, the crack continued to propagate at nearly its terminal velocity under a low dynamic stress intensity factor during the terminal phase of crack propagation. These and previously obtained results for glass and RBSN show that dynamic crack arrest under a positive dynamic stress intensity factor is unlikely in static and impact loaded structural ceramics.

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

1986-01-01

230

Electrochemical behaviour of Teflon-bonded iron oxide electrodes in alkaline solutions  

NASA Astrophysics Data System (ADS)

The electrochemical behaviour af Teflon-bonded iron oxide electrodes in 5.35 M KOH +0.65 M LiOH solution that contains various additives (such as thiourea, ethylenediaminetetraacetic acid (EDTA), hexamine and sodium sulfide) is examined by cyclic voltammetry. chronopotentiometry, open-circuit potential (OCP) decay and charge/discharge studies. The incorporation of Na2S in the alkaline electrolyte improves the performance of iron oxide electrodes by increasing the value of the OCP and decreasing the transient time. Moreover, the addition of Na 2S gives maximum capacity for the iron oxide electrode and a value of zero for {dE }/{dt }. The addition of thiourea lowers the performance of pressed iron electrodes. Thus, the incorporation of Na 2S in the alkaline electrolyte is essential for improving the performance of these electrodes.

Periasamy, P.; Ramesh Babu, B.; Venkatakrishna Iyer, S.

231

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

PubMed

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

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

2015-02-23

232

A half-reaction alternative to water oxidation: chloride oxidation to chlorine catalyzed by silver ion.  

PubMed

Chloride oxidation to chlorine is a potential alternative to water oxidation to oxygen as a solar fuels half-reaction. Ag(I) is potentially an oxidative catalyst but is inhibited by the high potentials for accessing the Ag(II/I) and Ag(III/II) couples. We report here that the complex ions AgCl2(-) and AgCl3(2-) form in concentrated Cl(-) solutions, avoiding AgCl precipitation and providing access to the higher oxidation states by delocalizing the oxidative charge over the Cl(-) ligands. Catalysis is homogeneous and occurs at high rates and low overpotentials (10 mV at the onset) with ?M Ag(I). Catalysis is enhanced in D2O as solvent, with a significant H2O/D2O inverse kinetic isotope effect of 0.25. The results of computational studies suggest that Cl(-) oxidation occurs by 1e(-) oxidation of AgCl3(2-) to AgCl3(-) at a decreased potential, followed by Cl(-) coordination, presumably to form AgCl4(2-) as an intermediate. Adding a second Cl(-) results in "redox potential leveling", with further oxidation to {AgCl2(Cl2)}(-) followed by Cl2 release. PMID:25700124

Du, Jialei; Chen, Zuofeng; Chen, Chuncheng; Meyer, Thomas J

2015-03-11

233

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

SciTech Connect

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{sub 2} (An: U, Pu) to form non-stoichiometric species described as AnO{sub 2+x}. Environmental studies have shown the value of utilizing the chemical signatures of these actinide oxide materials to understand transport following release into the environment. Chemical speciation of actinide-oxide samples may also provide clues as to the age, source, or process history of the material. The scientific challenge is to identify, measure and understand those aspects of speciation of actinide analytes that carry information about material origin and history most relevant to forensics. Here, we will describe our efforts in material synthesis and analytical methods development that we will use to provide the fundamental science to characterize actinide oxide molecular structures for forensic science. Structural properties and initial results to measure structural variability of uranium oxide samples using synchrotron-based X-ray Absorption Fine Structure will be discussed.

Wilkerson, Marianne Perry [Los Alamos National Laboratory

2010-01-01

234

Chemical bonds and vibrational properties of ordered (U, Np, Pu) mixed oxides  

NASA Astrophysics Data System (ADS)

We use density functional theory +U to investigate the chemical bonding characters and vibrational properties of the ordered (U, Np, Pu) mixed oxides (MOXs), UNpO4,NpPuO4, and UPuO4. It is found that the 5f electronic states of different actinide elements keep their localized characters in all three MOXs. The occupied 5f electronic states of different actinide elements do not overlap with each other and tend to distribute over the energy band gap of the other actinide element's 5f states. As a result, the three ordered MOXs all show smaller band gaps than those of the component dioxides, with values of 0.91, 1.47, and 0.19 eV for UNpO4,NpPuO4, and UPuO4, respectively. Through careful charge density analysis, we further show that the U-O and Pu-O bonds in MOXs show more ionic character than in UO2 and PuO2, while the Np-O bonds show more covalent character than in NpO2. The change in covalencies in the chemical bonds leads to vibrational frequencies of oxygen atoms that are different in MOXs.

Yang, Yu; Zhang, Ping

2013-01-01

235

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

PubMed

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

Biswas, Abhijit; Banerjee, Arindam

2014-12-01

236

Role of asparagine 510 in the relative timing of substrate bond cleavages in the reaction catalyzed by choline oxidase.  

PubMed

The flavoprotein choline oxidase catalyzes the oxidation of choline to glycine betaine with transient formation of an aldehyde intermediate and molecular oxygen as final electron acceptor. The enzyme has been grouped in the glucose-methanol-choline oxidoreductase enzyme superfamily, which shares a highly conserved His-Asn catalytic pair in the active site. In this study, the conserved asparagine residue at position 510 in choline oxidase was replaced with alanine, aspartate, histidine, or leucine by site-directed mutagenesis, and the resulting mutant enzymes were purified and characterized in their biochemical and mechanistic properties. All of the substitutions resulted in low incorporation of FAD into the protein. The Asn510Asp enzyme was not catalytically active with choline and had 75% of the flavin associated noncovalently. The most notable changes in the catalytic parameters with respect to wild-type choline oxidase were seen in the Asn510Ala enzyme, with decreases of 4300-fold in the k(cat)/K(choline), 600-fold in the k(red), 660-fold in the k(cat), and 50-fold in the k(cat)/K(oxygen) values. Smaller, but nonetheless similar, changes were seen also in the Asn510His enzyme. Both the K(d) and K(m) values for choline changed < or = 7-fold. These data are consistent with Asn510 participating in both the reductive and oxidative half-reactions but having a minimal role in substrate binding. Substrate, solvent, and multiple kinetic isotope effects on the k(red) values indicated that the substitution of Asn510 with alanine, but not with histidine, resulted in a change from stepwise to concerted mechanisms for the cleavages of the OH and CH bonds of choline catalyzed by the enzyme. PMID:20163155

Rungsrisuriyachai, Kunchala; Gadda, Giovanni

2010-03-23

237

Fly Ash and Mercury Oxidation/Chlorination Reactions  

SciTech Connect

Mercury is a known pollutant that has detrimental effect on human health and environment. The anthropogenic emissions of mercury account for 10 to 30% of worldwide mercury emissions. There is a need to control/reduce anthropogenic mercury emissions. Many mercury control technologies are available but their effectiveness is dependent on the chemical form of mercury, because different chemical forms of mercury have different physical and chemical properties. Mercury leaves the boiler in its elemental form but goes through various transformations in the post-combustion zone. There is a need to understand how fly ash and flue gas composition affect speciation, partitioning, and reactions of mercury under the full range of post-combustion zone conditions. This knowledge can then be used to predict the chemical transformation of mercury (elemental, oxidized or particulate) in the post combustion zone and thus help with the control of mercury emissions from coal-burning power plants. To accomplish this goal present study was conducted using five coal fly ashes. These ashes were characterized and their catalytic activity was compared under selected reaction conditions in a fixed bed reactor. Based on the results from these fly ash experiments, three key components (carbon, iron oxide and calcium oxide) were chosen. These three components were then used to prepare model fly ashes. Silica/alumina was used as a base for these model fly ashes. One, two or three component model fly ashes were then prepared to investigate mercury transformation reactions. The third set of experiments was performed with CuO and CuCl2 catalysts to further understand the mercury oxidation process. Based on the results of these three studies the key components were predicted for different fly ash compositions under variety of flue gas conditions. A fixed bed reactor system was used to conduct this study. In all the experiments, the inlet concentration of Hg0(g) was maintained at 35 {micro}g/m3 using a diffusion tube as the source of Hg0(g). All experiments were conducted using 4% O2 in nitrogen mix as a reaction gas, and other reactants (HCl, H2O and SO2, NO2, Br2) were added as required. The fixed bed reactor was operated over a temperature range of 200 to 400 C. In each experiment, the reactor effluent was analyzed using the modified Ontario-Hydro method. After each experiment, fly ash particles were also analyzed for mercury. The results show that the ability of fly ash to adsorb and/or oxidize mercury is primarily dependent on its carbon, iron and calcium content. There can be either one or more than one key component at a particular temperature and flue gas condition. Surface area played a secondary role in effecting the mercury transformations when compared to the concentration of the key component in the fly ash. Amount of carbon and surface area played a key important role in the adsorption of mercury. Increased concentration of gases in the flue gas other than oxygen and nitrogen caused decreased the amount of mercury adsorbed on carbon surface. Mercury adsorption by iron oxide primarily depended on the crystalline structure of iron oxide. {alpha}-Iron oxide had no effect on mercury adsorption or oxidation under most of the flue gas conditions, but ?-iron oxide adsorbed mercury under most of the flue gas conditions. Bromine is a very good oxidizing agent for mercury. But in the presence of calcium oxide containing fly ashes, all the oxidized mercury would be reduced to elemental form. Among the catalysts, it was observed that presence of free lattice chlorine in the catalyst was very important for the oxidation of mercury. But instead of using the catalyst alone, using it along with carbon may better serve the purpose by providing the adsorption surface for mercury and also some extra surface area for the reaction to occur (especially for fly ashes with low surface area).

Sukh Sidhu; Patanjali Varanasi

2008-12-31

238

CO oxidation as a prototypical reaction for heterogeneous processes.  

PubMed

CO oxidation, although seemingly a simple chemical reaction, provides us with a panacea that reveals the richness and beauty of heterogeneous catalysis. The Fritz Haber Institute is a place where a multidisciplinary approach to study the course of such a heterogeneous reaction can be generated in house. Research at the institute is primarily curiosity driven, which is reflected in the five sections comprising this Review. We use an approach based on microscopic concepts to study the interaction of simple molecules with well-defined materials, such as clusters in the gas phase or solid surfaces. This approach often asks for the development of new methods, tools, and materials to prove them, and it is exactly this aspect, both, with respect to experiment and theory, that is a trade mark of our institute. PMID:21960461

Freund, Hans-Joachim; Meijer, Gerard; Scheffler, Matthias; Schlögl, Robert; Wolf, Martin

2011-10-17

239

Oxidation reactions of thymol: a pulse radiolysis and theoretical study.  

PubMed

The reactions of (•)OH and O(•-), with thymol, a monoterpene phenol and an antioxidant, were studied by pulse radiolysis technique and DFT calculations at B3LYP/6-31+G(d,p) level of theory. Thymol was found to efficiently scavenge OH radicals (k = 8.1 × 10(9) dm(3) mol(-1) s(-1)) to produce reducing adduct radicals, with an absorption maximum at 330 nm and oxidizing phenoxyl radicals, with absorption maxima at 390 and 410 nm. A major part of these adduct radicals was found to undergo water elimination, leading to phenoxyl radicals, and the process was catalyzed by OH(-) (or Na(2)HPO(4)). The rate of reaction of O(•-) with thymol was found to be comparatively low (k = 1.1 × 10(9) dm(3) mol(-1) s(-1)), producing H abstracted species of thymol as well as phenoxyl radicals. Further, these phenoxyl radicals of thymol were found to be repaired by ascorbate (k = 2.1 × 10(8) dm(3) mol(-1) s(-1)). To support the interpretation of the experimental results, DFT calculations were carried out. The transients (both adducts and H abstracted species) have been optimized in gas phase at B3LYP/6-31+G(d,p) level of calculation. The relative energy values and thermodynamic stability suggests that the ortho adduct (C6_OH adduct) to be most stable in the reaction of thymol with OH radicals, which favors the water elimination. However, theoretical calculations showed that C4 atom in thymol (para position) can also be the reaction center as it is the main contributor of HOMO. The absorption maxima (?(max)) calculated from time-dependent density functional theory (TDDFT) for these transient species were close to those obtained experimentally. Finally, the redox potential value of thymol(•)/thymol couple (0.98 V vs NHE) obtained by cyclic voltammetry is less than those of physiologically important oxidants, which reveals the antioxidant capacity of thymol, by scavenging these oxidants. The repair of the phenoxyl radicals of thymol with ascorbate together with the redox potential value makes it a potent antioxidant with minimum pro-oxidant effects. PMID:23240914

Venu, S; Naik, D B; Sarkar, S K; Aravind, Usha K; Nijamudheen, A; Aravindakumar, C T

2013-01-17

240

Kinetics and dynamics of oxidation reactions involving an adsorbed CO species on bulk and supported platinum and copper-oxide  

SciTech Connect

The proposed research is an integrated experimental and modeling study of oxidation reactions involving CO as a key player -- be it a reactant, adsorbed intermediate, and/or partial oxidation product -- in the catalytic sequence and chemistry. The reaction systems of interest in the project include CO, formaldehyde, and methanol oxidation by O{sub 2} and CO oxidation by NO, on both Pt and copper oxide catalysts. These reactions are of importance in automobile exhaust catalysis. There is a paucity of rate data in the literature for these important environmental control reactions. The goal of this research is to better understand the catalytic chemistry and kinetics of oxidations reactions involving CO as an adsorbed intermediate. Successfully meeting this goal requires an integration of basic kinetic measurements, in situ catalyst surface monitoring, kinetic modeling, and nonlinear mathematical tools.

Harold, M.P.

1991-07-01

241

Bis(trifluoromethyl)methylene Addition to Vinyl-Terminated SAMs: A Gas-Phase C–C Bond-Forming Reaction on a Surface  

PubMed Central

Vinyl-terminated self-assembled monolayers (SAMs) on silicon oxide substrates were chemically modified by the addition of a bis(trifluoromethyl)methylene group in a rare gas-phase C–C bond-forming reaction to directly generate films carrying terminal CF3 groups. The vinyl-terminated films were treated with hexafluoroacetone azine (HFAA) for modification. The films were characterized with ellipsometry, contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In this study, we find that for optimized conditions clean reactions occur on a surface between SAMs with terminal olefins and HFAA, and the product is consistent with bis(trifluoromethyl)cyclopropanation formation after nitrogen extrusion. PMID:24806554

2014-01-01

242

C-H activation and C=C double bond formation reactions in iridium ortho-methyl arylphosphane complexes.  

PubMed

The Vaska-type iridium(I) complex [IrCl(CO){PPh(2)(2-MeC(6)H(4))}(2)] (1), characterized by an X-ray diffraction study, was obtained from iridium(III) chloride hydrate and PPh(2)(2,6-MeRC(6)H(3)) with R=H in DMF, whereas for R=Me, activation of two ortho-methyl groups resulted in the biscyclometalated iridium(III) compound [IrCl(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}(2)] (2). Conversely, for R=Me the iridium(I) compound [IrCl(CO){PPh(2)(2,6-Me(2)C(6)H(3))}(2)] (3) can be obtained by treatment of [IrCl(COE)(2)](2) (COE=cyclooctene) with carbon monoxide and the phosphane in acetonitrile. Compound 3 in CH(2)Cl(2) undergoes intramolecular C-H oxidative addition, affording the cyclometalated hydride iridium(III) species [IrHCl(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}{PPh(2)(2,6-Me(2)C(6)H(3))}] (4). Treatment of 2 with Na[BAr(f) (4)] (Ar(f)=3,5-C(6)H(3)(CF(3))(2)) gives the fluxional cationic 16-electron complex [Ir(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}(2)][BAr(f) (4)] (5), which reversibly reacts with dihydrogen to afford the delta-agostic complex [IrH(CO){PPh(2)(2,6-CH(2)MeC(6)H(3))}{PPh(2)(2,6-Me(2)C(6)H(3))}][BAr(f)(4)] (6), through cleavage of an Ir-C bond. This species can also be formed by treatment of 4 with Na[BAr(f)(4)] or of 2 with Na[BAr(f)(4)] through C-H oxidative addition of one ortho-methyl group, via a transient 14-electron iridium(I) complex. Heating of the coordinatively unsaturated biscyclometalated species 5 in toluene gives the trans-dihydride iridium(III) complex [IrH(2)(CO){PPh(2)(2,6-MeC(6)H(3)CH=CHC(6)H(3)Me-2,6)PPh(2)}][BAr(f) (4)] (7), containing a trans-stilbene-type terdentate ligand, as result of a dehydrogenative carbon-carbon double bond coupling reaction, possibly through an iridium carbene species. PMID:17535000

Baratta, Walter; Ballico, Maurizio; Del Zotto, Alessandro; Zangrando, Ennio; Rigo, Pierluigi

2007-01-01

243

Gas-phase reaction of CeVO5(+) cluster ions with C2H4: the reactivity of cluster bonded peroxides.  

PubMed

Cerium-vanadium oxide cluster cations CeVO5(+) were generated by laser ablation, mass-selected using a quadrupole mass filter, thermalized through collisions with helium atoms, and then reacted with ethene molecules in a linear ion trap reactor. The cluster reactions have been characterized by time-of-flight mass spectrometry and density functional theory calculations. The CeVO5(+) cluster has a closed-shell electronic structure and contains a peroxide (O2(2-)) unit. The cluster bonded O2(2-) species is reactive enough to oxidize a C2H4 molecule to generate C2H4O2 that can be an acetic acid molecule. Atomic oxygen radicals (O(-)?), superoxide radicals (O2(-)?), and peroxides are the three common reactive oxygen species. The reactivity of cluster bonded O(-)? and O2(-)? radicals has been widely studied while the O2(2-) species were generally thought to be much less reactive or inert toward small molecules under thermal collision conditions. This work is among the first to report the reactivity of the peroxide unit on transition metal oxide clusters with hydrocarbon molecules, to the best of our knowledge. PMID:25573178

Ma, Jia-Bi; Meng, Jing-Heng; He, Sheng-Gui

2015-02-01

244

Designing a Cu(II)-ArCu(II)-ArCu(III)-Cu(I) catalytic cycle: Cu(II)-catalyzed oxidative arene C-H bond azidation with air as an oxidant under ambient conditions.  

PubMed

On the basis of our recent discovery of high valent organocopper compounds, we have designed and achieved efficient copper(II)-catalyzed oxidative arene C-H bond azidation under very mild aerobic conditions by using NaN3 as an azide source. In the presence of a Cu(II) catalyst, a number of azacalix[1]arene[3]pyridines underwent direct arene C-H bond cupration through an electrophilic aromatic metalation pathway to form an arylcopper(II) intermediate. Oxidized by a free copper(II) ion, the arylcopper(II) intermediate was transformed into an arylcopper(III) species that subsequently cross-coupled with azide to furnish the formation of aryl azide products with the release of a copper(I) ion. Under ambient catalytic reaction conditions, the copper(I) species generated was oxidized by air into copper(II), which entered into the next catalytic cycle. Application of the method was demonstrated by the synthesis of functional azacalix[1]arene[3]pyridines by means of simple and practical functional group transformations of azide. The showcase of the Cu(II)-ArCu(II)-ArCu(III)-Cu(I) catalytic cycle would provide a new strategy for the design of copper(II)-catalyzed aerobic oxidative arene C-H bond activation and transformations. PMID:25350606

Yao, Bo; Liu, Yang; Zhao, Liang; Wang, De-Xian; Wang, Mei-Xiang

2014-11-21

245

Oxidative Addition of Carbon–Carbon Bonds with a Redox-Active Bis(imino)pyridine Iron Complex  

PubMed Central

Addition of biphenylene to the bis(imino)pyridine iron dinitrogen complexes, (iPrPDI)Fe(N2)2 and [(MePDI)Fe(N2)]2(?2-N2) (RPDI = 2,6-(2,6-R2—C6H3— N=CMe)2C5H3N; R = Me, iPr), resulted in oxidative addition of a C—C bond at ambient temperature to yield the corresponding iron biphenyl compounds, (RPDI)Fe-(biphenyl). The molecular structures of the resulting bis-(imino)pyridine iron metallacycles were established by X-ray diffraction and revealed idealized square pyramidal geometries. The electronic structures of the compounds were studied by Mössbauer spectroscopy, NMR spectroscopy, magnetochemistry, and X-ray absorption and X-ray emission spectroscopies. The experimental data, in combination with broken-symmetry density functional theory calculations, established spin crossover (low to intermediate spin) ferric compounds antiferromagnetically coupled to bis(imino)pyridine radical anions. Thus, the overall oxidation reaction involves cooperative electron loss from both the iron center and the redox-active bis(imino)pyridine ligand. PMID:23043331

Darmon, Jonathan M.; Stieber, S. Chantal E.; Sylvester, Kevin T.; Fernández, Ignacio; Lobkovsky, Emil; Semproni, Scott P.; Bill, Eckhard; Wieghardt, Karl; DeBeer, Serena; Chirik, Paul J.

2013-01-01

246

Mixed valency in cerium oxide crystallographic phases: Valence of different cerium sites by the bond valence method  

Microsoft Academic Search

We have applied the bond valence method to cerium oxides to determine the oxidation states of the Ce ion at the various site symmetries of the crystals. The crystals studied include cerium dioxide and the two sesquioxides along with some selected intermediate phases which are crystallographically well characterized. Our results indicate that cerium dioxide has a mixed-valence ground state with

E. Shoko; M. F. Smith; Ross H. McKenzie

2009-01-01

247

Tuning reactivity and mechanism in oxidation reactions by mononuclear nonheme iron(IV)-oxo complexes.  

PubMed

Mononuclear nonheme iron enzymes generate high-valent iron(IV)-oxo intermediates that effect metabolically important oxidative transformations in the catalytic cycle of dioxygen activation. In 2003, researchers first spectroscopically characterized a mononuclear nonheme iron(IV)-oxo intermediate in the reaction of taurine: ?-ketogultarate dioxygenase (TauD). This nonheme iron enzyme with an iron active center was coordinated to a 2-His-1- carboxylate facial triad motif. In the same year, researchers obtained the first crystal structure of a mononuclear nonheme iron(IV)-oxo complex bearing a macrocyclic supporting ligand, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecene), in studies that mimicked the biological enzymes. With these breakthrough results, many other studies have examined mononuclear nonheme iron(IV)-oxo intermediates trapped in enzymatic reactions or synthesized in biomimetic reactions. Over the past decade, researchers in the fields of biological, bioinorganic, and oxidation chemistry have extensively investigated the structure, spectroscopy, and reactivity of nonheme iron(IV)-oxo species, leading to a wealth of information from these enzymatic and biomimetic studies. This Account summarizes the reactivity and mechanisms of synthetic mononuclear nonheme iron(IV)-oxo complexes in oxidation reactions and examines factors that modulate their reactivities and change their reaction mechanisms. We focus on several reactions including the oxidation of organic and inorganic compounds, electron transfer, and oxygen atom exchange with water by synthetic mononuclear nonheme iron(IV)-oxo complexes. In addition, we recently observed that the C-H bond activation by nonheme iron(IV)-oxo and other nonheme metal(IV)-oxo complexes does not follow the H-atom abstraction/oxygen-rebound mechanism, which has been well-established in heme systems. The structural and electronic effects of supporting ligands on the oxidizing power of iron(IV)-oxo complexes are significant in these reactions. However, the difference in spin states between nonheme iron(IV)-oxo complexes with an octahedral geometry (with an S = 1 intermediate-spin state) or a trigonal bipyramidal (TBP) geometry (with an S = 2 high-spin state) does not lead to a significant change in reactivity in biomimetic systems. Thus, the importance of the high-spin state of iron(IV)-oxo species in nonheme iron enzymes remains unexplained. We also discuss how the axial and equatorial ligands and binding of redox-inactive metal ions and protons to the iron-oxo moiety influence the reactivities of the nonheme iron(IV)-oxo complexes. We emphasize how these changes can enhance the oxidizing power of nonheme metal(IV)-oxo complexes in oxygen atom transfer and electron-transfer reactions remarkably. This Account demonstrates great advancements in the understanding of the chemistry of mononuclear nonheme iron(IV)-oxo intermediates within the last 10 years. PMID:24524675

Nam, Wonwoo; Lee, Yong-Min; Fukuzumi, Shunichi

2014-04-15

248

Oxidation Numbers, Oxidants, and Redox Reactions: Variants of the Electrophilic Bromination of Alkenes and Variants of the Application of Oxone  

ERIC Educational Resources Information Center

Oxidation-state and donor-acceptor concepts are important areas in the chemical education. Student worksheets containing problems that emphasize oxidation numbers, redox reactions of organic compounds, and stoichiometric reaction equations are presented. All of the examples are incorporated under one unifying topic: the production of vicinal…

Eissen, Marco; Strudthoff, Merle; Backhaus, Solveig; Eismann, Carolin; Oetken, Gesa; Kaling, Soren; Lenoir, Dieter

2011-01-01

249

Electrodepositing Pt on a Nafion-bonded carbon electrode as a catalyzed electrode for oxygen reduction reaction  

Microsoft Academic Search

The research aims to increase the utilization of platinum (Pt) catalysts and thus to lower the catalyst loadings in the electrode for oxygen reduction reaction (ORR). The electrodeposition of Pt was performed on a rotation disk electrode (RDE) of glass carbon (GC), on which a layer of Nafion-bonded carbon of Vulcan XC 72R was dispersed in advance. The behaviors of

Z. D. Wei; S. H. Chan; L. L. Li; H. F. Cai; Z. T. Xia; C. X. Sun

2005-01-01

250

From ketones to esters by a Cu-catalyzed highly selective C(CO)-C(alkyl) bond cleavage: aerobic oxidation and oxygenation with air.  

PubMed

The Cu-catalyzed aerobic oxidative esterification of simple ketones via C-C bond cleavage has been developed. Varieties of common ketones, even inactive aryl long-chain alkyl ketones, are selectively converted into esters. The reaction tolerates a wide range of alcohols, including primary and secondary alcohols, chiral alcohols with retention of the configuration, electron-deficient phenols, as well as various natural alcohols. The usage of inexpensive copper catalyst, broad substrate scope, and neutral and open air conditions make this protocol very practical. (18)O labeling experiments reveal that oxygenation occurs during this transformation. Preliminary mechanism studies indicate that two novel pathways are mainly involved in this process. PMID:25251943

Huang, Xiaoqiang; Li, Xinyao; Zou, Miancheng; Song, Song; Tang, Conghui; Yuan, Yizhi; Jiao, Ning

2014-10-22

251

Laminate behavior for SiC fiber-reinforced reaction-bonded silicon nitride matrix composites  

NASA Technical Reports Server (NTRS)

The room temperature mechanical properties of SiC fiber reinforced reaction-bonded silicon nitride matrix composite laminates (SiC/RBSN) have been measured. The laminates contained approx 30 volume fraction of aligned 142-micron diameter SiC fiber in a porous RBSN matrix. Three types of laminate studied were unidirectional: (1) (0) sub 8, (2) (10) sub 8, and (3) (45) sub 8, and (90) sub 8; cross plied laminates (0 sub 2/90 sub 2); and angle plied laminates: (+45 sub 2/-45 sub 2). Each laminate contained eight fiber plies. Results of the unidirectionally reinforced composites tested at various angles to the reinforcement direction indicate large anisotropy in in-plane properties. In addition, strength properties of these composites along the fiber direction were independent of specimen gage length and were unaffected by notches normal to the fiber direction. Splitting parallel to the fiber at the notch tip appears to be the dominant crack blunting mechanism responsible for notch insensitive behavior of these composites. In-plane properties of the composites can be improved by 2-D laminate construction. Mechanical property results for (0 sub 2/90 sub 2)sub s and (+45/-45 sub 2) sub s laminates showed that their matrix failure strains were similar to that for (0) sub 8 laminates, but their primary elastic moduli, matrix cracking strengths, and ultimate composite strengths were lower. The elastic properties of unidirectional, cross-ply, and angle-ply composites can be predicted from modified constitutive equations and laminate theory. Further improvements in laminate properties may be achieved by reducing the matrix porosity and by optimizing the bond strength between the SiC fiber and RBSN matrix.

Rhatt, R. T.; Phillips, R. E.

1988-01-01

252

Recent advances in catalytic C-N bond formation: a comparison of cascade hydroaminomethylation and reductive amination reactions with the corresponding hydroamidomethylation and reductive amidation reactions.  

PubMed

The design and catalytic implementation of tandem reactions to selectively create nitrogen-containing products under mild conditions has encountered numerous challenges in synthetic chemistry. Several known classes of homogeneously catalyzed carbon-nitrogen bond formation including hydroamination, hydroamidation, hydroaminoalkylation, hydroaminomethylation and reductive amination were reported in the literature. More recently, a new class of C-N bond formation consisting of hydroamidomethylation and reductive amidation extended the applicability of these synthetic methodologies. The tandem reactions do considerably impact on the selectivity and efficiency of synthetic strategies. This review highlights and compares selected examples of the hydroaminomethylation, reductive amination, hydroamidomethylation and reductive amidation reactions, and thus consequently reveals their potential applications in synthetic chemistry as well as chemical industries. PMID:25098332

Raoufmoghaddam, Saeed

2014-10-01

253

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

PubMed

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

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

2006-11-01

254

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

PubMed Central

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

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

2012-01-01

255

Using Reduced Catalysts for Oxidation Reactions: Mechanistic Studies of the "Periana-Catalytica" System for CH4 Oxidation  

E-print Network

could help to guide the design of new catalysts for alkane oxidation that operate by CH activationUsing Reduced Catalysts for Oxidation Reactions: Mechanistic Studies of the "Periana-Catalytica" System for CH4 Oxidation Oleg A. Mironov, Steven M. Bischof, Michael M. Konnick, Brian G. Hashiguchi

Goddard III, William A.

256

A study on thermal barrier coatings including thermal expansion mismatch and bond coat oxidation  

NASA Technical Reports Server (NTRS)

The present investigation deals with a plasma-sprayed thermal barrier coating (TBC) intended for high temperature applications to advanced gas turbine blades. Typically, this type of coating system consists of a zirconia-yttria ceramic layer with a nickel-chromium-aluminum bond coat on a superalloy substrate. The problem on hand is a complex one due to the fact that bond coat oxidation and thermal mismatch occur in the TBC. Cracking in the TBC has also been experimentally illustrated. A clearer understanding of the mechanical behavior of the TBC is investigated. The stress states in a model thermal barrier coating as it cools down in air is studied. The powerful finite element method was utilized to model a coating cylindrical specimen. Four successively refined finite element models were developed. Some results obtained using the first two models have been reported previously. The major accomplishment is the successful development of an elastic TBC finite element model known as TBCG with interface geometry between the ceramic layer and the bond coat. An equally important milestone is the near-completion of the new elastic-plastic TBC finite element model called TBCGEP which yielded initial results. Representative results are presented.

Chang, George C.; Phucharoen, Woraphat; Miller, Robert A.

1986-01-01

257

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

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.

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

2011-10-06

258

Ligand-based carbon-nitrogen bond forming reactions of metal dinitrosyl complexes with alkenes and their application to C-H bond functionalization.  

PubMed

Over the past few decades, researchers have made substantial progress in the development of transition metal complexes that activate and functionalize C-H bonds. For the most part, chemists have focused on aliphatic and aromatic C-H bonds and have put less effort into complexes that activate and functionalize vinylic C-H bonds. Our groups have recently developed a novel method to functionalize vinylic C-H bonds that takes advantage of the unique ligand-based reactivity of a rare class of metal dinitrosyl complexes. In this Account, we compare and discuss the chemistry of cobalt and ruthenium dinitrosyl complexes, emphasizing alkene binding, C-H functionalization, and catalysis. Initially discovered in the early 1970s by Brunner and studied more extensively in the 1980s by the Bergman group, the cyclopentadienylcobalt dinitrosyl complex CpCo(NO)2 reacts reversibly with alkenes to give, in many cases, stable and isolable cobalt dinitrosoalkane complexes. More recently, we found that treatment with strong bases, such as lithium hexamethyldisilazide, Verkade's base, and phosphazene bases, deprotonates these complexes and renders them nucleophilic at the carbon ? to the nitroso group. This conjugate anion of metal dinitrosoalkanes can participate in conjugate addition to Michael acceptors to form new carbon-carbon bonds. These functionalized cobalt complexes can further react through alkene exchange to furnish the overall vinylic C-H functionalized organic product. This stepwise sequence of alkene binding, functionalization, and retrocycloaddition represents an overall vinylic C-H functionalization reaction of simple alkenes and does not require directing groups. We have also developed an asymmetric variant of this reaction sequence and have used this method to synthesize C1- and C2-symmetric diene ligands with high enantioinduction. Building upon these stepwise reactions, we eventually developed a simple one-pot procedure that uses stoichiometric amounts of a cobalt dinitrosoalkane complex for both inter- and intramolecular C-H functionalization. We can achieve catalysis in one-pot intramolecular reactions with a limited range of substrates. Our groups have also reported an analogous ruthenium dinitrosyl complex. In analogy to the cobalt complex, this ruthenium complex reacts with alkenes in the presence of neutral bidentate ligands, such as TMEDA, to give octahedral dinitrosoalkane complexes. Intramolecular functionalization or cyclization of numerous ruthenium dinitrosoalkane complexes proceeds under mild reaction conditions to give the functionalized organic products in excellent yields. However, despite extensive efforts, so far we have not been able to carry out intermolecular reactions of these complexes with a variety of electrophiles or C-H functionalization reactions. Although additional work is necessary to further boost the catalytic capabilities of both cobalt and ruthenium dinitrosyl complexes for vinylic C-H functionalization of simple alkenes, we believe this ligand-based vinylic C-H functionalization reaction has provided chemists with a useful set of tools for organic synthesis. PMID:24359109

Zhao, Chen; Crimmin, Mark R; Toste, F Dean; Bergman, Robert G

2014-02-18

259

Low-index nanopatterned barrier for hybrid oxide-free III-V silicon conductive bonding.  

PubMed

Oxide-free bonding of a III-V active stack emitting at 1300-1600 nm to a silicon-on-insulator wafer offers the capability to electrically inject lasers from the silicon side. However, a typical 500-nm-thick silicon layer notably attracts the fundamental guided mode of the silicon + III-V stack, a detrimental feature compared to established III-V Separate-Confinement Heterostructure (SCH) stacks. We experimentally probe with photoluminescence as an internal light source the guiding behavior for oxide-free bonding to a nanopatterned silicon wafer that acts as a low-index barrier. We use a sub-wavelength square array of small holes as an effective "low-index silicon" medium. It is weakly modulated along one dimension (superperiodic array) to outcouple the resulting guided modes to free space, where we use an angle-resolved spectroscopy study. Analysis of experimental branches confirms the capability to operate with a fundamental mode well localized in the III-V heterostructures. PMID:25321802

Bougot-Robin, Kristelle; Talneau, Anne; Benisty, Henri

2014-09-22

260

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

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

261

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

NASA Astrophysics Data System (ADS)

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.

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

2005-01-01

262

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

SciTech Connect

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.

Udron, L.; Turek, T.

2002-09-19

263

Lubricating Properties of Some Bonded Fluoride and Oxide Coatings for Temperature to 1500 F  

NASA Technical Reports Server (NTRS)

The lubricating properties of some experimental ceramic coatings, diffusion-bonded fluoride coatings, and ceramic-bonded fluoride coatings were determined. The experiments were conducted in an air atmosphere at a sliding velocity of 430 feet per minute and at temperatures from 75 to 1500 F. Several ceramic coatings provided substantial reductions in friction coefficient and rider wear (compared with the unlubricated metals). For example, a cobaltous oxide (CoO) base coating gave friction coefficients of 0.24 to 0.36 within the temperature range of 75 to 1400 F; serious galling and welding of the metal surfaces were prevented. The friction coefficients were higher than the arbitrary maximum (0.2) usually considered for effective boundary lubrication. However, when a moderately high friction coefficient can be tolerated, this type of coating may be a useful antiwear composition. Diffusion-bonded calcium fluoride (CaF2) on Haynes Stellite 21 and on Inconel X gave friction coefficients of 0.1 to 0.2 at 1500 F. Endurance life was dependent on the thermal history of the coating; life improved with increased exposure time at elevated temperatures prior to running. Promising results were obtained with ceramic-bonded CaF2 on Inconel X. Effective lubrication and good adherence were obtained with a 3 to 1 ratio of CaF2 to ceramic. A very thin sintered and burnished film of CaF2 applied to the surface of this coating further improved lubrication, particularly above 1350 F. The friction coefficient was 0.2 at 500 F and decreased with increasing temperature to 0.06-at 1500 F. It was 0.25 at 75 F and 0.22 at 250 F.

Sliney, Harold E.

1960-01-01

264

A study of bond-length fluctuations in transition metal oxides  

NASA Astrophysics Data System (ADS)

Bond-length fluctuations with different origins have been investigated by thermal conductivity measurement performed on La1.60-xNd 0.40SrxCuO4, RCoO3, and RVO3 single crystals grown by floating zone method. Thermal conductivity has been proved to be a sensitive probe to bond-length fluctuations in strongly-correlated transition-metal oxides. Superconductivity in cuprates occurs at a crossover from localized to itinerant electronic behavior. The segregation of localized spins and delocalized holes into hole-poor and hole-rich regions in La2-xSr xCuO4 induces bond-length fluctuations via a strong electron-lattice coupling. This bond-length fluctuation suppresses in-plane thermal conductivity due to charge fluctuations in this quasi-2D system. In the La1.60-x Nd0.40SrxCuO4 system, the low-temperature orthorhombic (LTO) phase transforms into a low-temperature-tetragonal (LTT) phase with decreasing temperature. The hole-rich regions order into static stripes in the LTT phase of La2-x-yNdySr xCuO4; this charge order revives the phonon contribution to the thermal conductivity. The phonon thermal conductivity in the normal state of LTT phase and the LTO phase of some underdoped compositions of LSCO calls for reconsideration of the role of bond-length fluctuations on superconducting pairing in different structures. Suppression of the phonon thermal conductivity in the Mott-Hubbard insulator RCoO3 is interpreted to be caused by the spin-state transition from the low-spin t6e0 ground state to a higher spin-state, either intermediate-spin t 5e1 or high-spin t4e2, with increasing temperature. RVO3 offers us a unique chance to study the bond-length fluctuations caused by strong spin-orbital-lattice coupling. An unusually strong orbital-lattice and spin-lattice coupling has been clearly demonstrated.

Yan, Jiaqiang

265

Mullite fiber reinforced reaction bonded Si{sub 3}N{sub 4} composites  

SciTech Connect

Fracture toughnesses of brittle ceramic materials have been improved by introducing reinforcements and carefully tailored interface layers. Silicon carbide and Si{sub 3}N{sub 4} have been emphasized as matrices of structural composites intended for high temperature service because they combine excellent mechanical, chemical, thermal and physical properties. Both matrices have been successfully toughened with SiC fibers, whiskers and particles for ceramic matrix composite (CMC) parts made by sintering, hot pressing or reaction forming processes. These SiC reinforced CMCs have exhibited significantly improved toughnesses at low and intermediate temperature levels, as well as retention of properties at high temperatures for selected exposures; however, they are vulnerable to attack from elevated temperature dry and wet oxidizing atmospheres after the matrix has cracked. Property degradation results from oxidation of interface layers and/or reinforcements. The problem is particularly acute for small diameter ({approximately}20 {mu}m) polymer derived SiC fibers used for weavable toes. This research explored opportunities for reinforcing Si{sub 3}N{sub 4} matrices with fibers having improved environmental stability; the finding should also be applicable to SiC matrix CMCs.

Saleh, T.; Lightfoot, A.; Haggerty, J. [Massachusetts Institute of Technology, Cambridge, MA (United States); Sayir, A. [NASA Lewis Research Center, Cleveland, OH (United States)

1996-12-31

266

Pre-treatments applied to oxidized aluminum surfaces to modify the interfacial bonding with bis-1,2-(triethoxysilyl)ethane (BTSE). Part I. High-purity Al with native oxide  

NASA Astrophysics Data System (ADS)

A remote microwave-generated H 2 plasma and heating to 250 °C were separately used to modify high-purity oxidized aluminum surfaces and to assess whether these treatments can help enhance adhesion with bis-1,2-(triethoxysilyl)ethane (BTSE) coatings. Different initial oxide surfaces were considered, corresponding to the native oxide and to surfaces formed by the Forest Products Laboratory (FPL) treatment applied for either 15 or 60 min. BTSE is applied from solution at pH 4, and competing processes of etching, protonation (to form OH groups) and coupling (to form Al sbnd O sbnd Si interfacial bonds) occur at the solid-liquid interface. Scanning electron microscopy (SEM) was used to determine how the topographies of the modified Al surfaces changed with the different pre-treatments and with exposure to a buffer solution of pH 4. Secondary-ion mass spectrometry (SIMS) was used to determine the direct amount of Al sbnd O sbnd Si interfacial bonds by measuring the ratio of peak intensities 71-70 amu, while X-ray photoelectron spectroscopy (XPS) was used to determine the overall strength of the silane coating adhesion by measuring the Si 2p signals before and after application of an ultrasonic rinse to the coated sample. Measured Al 2p and O 1s spectra helped assess how the different pre-treatments modified the various Al oxidized surfaces prior to BTSE coating. Pre-treated samples that showed increased Al sbnd O sbnd Si bonding after BTSE coating corresponded to surfaces, which did not show evidence of significant etching after exposure to a pH 4 environment. This suggests that such surfaces are more receptive to the coupling reaction during exposure to the BTSE coating solution. These surfaces include all H 2 plasma-treated samples, the heated native oxide and the sample that only received the 15 min FPL treatment. In contrast, other surfaces that show evidence of etching in pH 4 environments are samples that received lower amounts of Al sbnd O sbnd Si interfacial bonding. Overall, heating improved the BTSE adhesive bonding for the native Al oxide, while H 2 plasma treatment improved the BTSE bonding for surfaces that had initially been FPL-treated for 15 and 60 min.

Teo, M.; Kim, J.; Wong, P. C.; Wong, K. C.; Mitchell, K. A. R.

2005-12-01

267

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

SciTech Connect

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.

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

268

Reaction progress kinetic analysis of a copper-catalyzed aerobic oxidative coupling reaction with N-phenyl tetrahydroisoquinoline.  

PubMed

The results from a kinetic investigation of a Cu-catalyzed oxidative coupling reaction between N-phenyl tetrahydroisoquinoline and a silyl enol ether using elemental oxygen as oxidant are presented. By using reaction progress kinetic analysis as an evaluation method for the obtained data, we discovered information regarding the reaction order of the substrates and catalysts. Based on this information and some additional experiments, a refined model for the initial oxidative activation of the amine substrate and the activation of the nucleophile by the catalyst was developed. The mechanistic information also helped to understand why silyl nucleophiles have previously failed in a related Cu-catalyzed reaction using tert-butyl hydroperoxide as oxidant and how to overcome this limitation. PMID:25203932

Scott, Martin; Sud, Abhishek; Boess, Esther; Klussmann, Martin

2014-12-19

269

Transition-State Charge Transfer Reveals Electrophilic, Ambiphilic, and Nucleophilic Carbon-Hydrogen Bond Activation  

E-print Network

functionalized products.1 For alkane oxidation reactions, Pt, Pd, Hg, and Au metal catalysts have been exploited and magni- tude of charge transfer (CT) bonding between metal/ligand com- plexes and alkane C-H bonds of insertion and substitution C-H activation TSs that were analyzed, including oxidative addition, -bond

Goddard III, William A.

270

Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of benzotriazoles.  

PubMed

Benzotriazoles (BTs) are high production volume chemicals with broad application in various industrial processes and in households, and have been found to be omnipresent in aquatic environments. We investigated oxidation of five benzotriazoles (BT: 1H-benzotriazole; 5MBT: 5-methyl-1H-benzotriazole; DMBT: 5,6-dimethyl-1H-benzotriazole hydrate; 5CBT: 5-chloro-1H-benzotriazole; HBT: 1-hydroxybenzotriazole) by aqueous ferrate (Fe(VI)) to determine reaction kinetics as a function of pH (6.0-10.0), and interpreted the reaction mechanism of Fe(VI) with BTs by using a linear free-energy relationship. The pK(a) values of BT and DMBT were also determined using UV-Visible spectroscopic method in order to calculate the species-specific rate constants, and they were 8.37 ± 0.0 and 8.98 ± 0.08 respectively. Each of BTs reacted moderately with Fe(VI) with the k(app) ranged from 7.2 to 103.8 M(-1)s(-1) at pH 7.0 and 24 ± 1 °C. When the molar ratio of Fe(VI) and BTs increased up to 30:1, the removal rate of BTs reached about >95% in buffered milli-Q water or secondary wastewater effluent. The electrophilic oxidation mechanism of the above reaction was illustrated by using a linear free-energy relationship between pH-dependence of species-specific rate constants and substituent effects (?(p)). Fe(VI) reacts initially with BTs by electrophilic attack at the 1,2,3-triazole moiety of BT, 5MBT, DMBT and 5CBT, and at the N-OH bond of HBT. Moreover, for BT, 5MBT, DMBT and 5CBT, the reactions with the species HFeO(4)(-) predominantly controled the reaction rates. For HBT, the species H(2)FeO(4) with dissociated HBT played a major role in the reaction. The results showed that Fe(VI) has the ability to degrade benzotriazoles in water. PMID:21334710

Yang, Bin; Ying, Guang-Guo; Zhang, Li-Juan; Zhou, Li-Jun; Liu, Shan; Fang, Yi-Xiang

2011-03-01

271

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

ERIC Educational Resources Information Center

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…

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

2008-01-01

272

Simultaneous carbon coating and lithiation of oxides by contact reaction.  

PubMed

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

Wächter, Florian; Krumeich, Frank; Nesper, Reinhard

2014-04-25

273

Uraninite oxidation and dissolution induced by manganese oxide: A redox reaction between two insoluble minerals  

NASA Astrophysics Data System (ADS)

The longevity of subsurface U(IV) produced by reduction of U(VI) during in situ bioremediation can be limited by reoxidation to more mobile U(VI) species. Coupling of the biogeochemical cycles of U and Mn may affect the fate and transport of uranium. Manganese oxides can act as a powerful oxidant that accelerates the oxidative dissolution of UO2. This study investigated the physical and chemical factors controlling the interaction between UO2 and MnO2, which are both poorly soluble minerals. A multi-chamber reactor with a permeable membrane was used to eliminate direct contact of the two minerals while still allowing transport of aqueous species. The oxidation of UO2 was not significantly enhanced by MnO2 if the two solids were physically separated. Complete mixing of MnO2 with UO2 led to a much greater extent and rate of U oxidation. When direct contact is not possible, the reaction slowly progresses through release of soluble U(IV) with its adsorption and oxidation on MnO2. Continuously-stirred tank reactors (CSTRs) were used to quantify the steady-state rates of UO2 dissolution induced by MnO2. MnO2 dramatically promoted UO2 dissolution, but the degree of promotion leveled off once the MnO2:UO2 ratio exceeded a critical value. Substantial amounts of U(VI) and Mn(II) were retained on MnO2 surfaces. The total production of Mn(II) was less than that of U(VI), indicating that the fate of Mn products and their impact on UO2-MnO2 reaction kinetics were complicated and may involve formation of Mn(III) phases. At higher dissolved inorganic carbon concentrations, UO2 oxidation by MnO2 was faster and less U(VI) was adsorbed to MnO2. Such an inverse relationship suggested that U(VI) may passivate MnO2 surfaces. A conceptual model was developed to describe the oxidation rate of UO2 by MnO2. This model is potentially applicable to a broad range of water chemistry conditions and is relevant to other environmental redox processes involving two poorly soluble minerals.

Wang, Zimeng; Lee, Sung-Woo; Kapoor, Pratyul; Tebo, Bradley M.; Giammar, Daniel E.

2013-01-01

274

Influence of a reaction medium on the oxidation of aromatic nitrogen-containing compounds by peroxyacids  

NASA Astrophysics Data System (ADS)

The influence of different solvents on the oxidation reaction rate of pyridine (Py), quinoline (QN), acridine (AN), ?-oxyquinoline (OQN) and ?-picolinic acid (APA) by peroxydecanoic acid (PDA) was studied. It was found that the oxidation rate grows in the series Py < QN < AN, and the rate of the oxidation reaction of compounds containing a substituent in the ? position from a reactive center is significantly lower than for unsubstituted analogues. The effective energies of activation of the oxidation reaction were found. It was shown that in the first stage, the reaction mechanism includes the rapid formation of an intermediate complex nitrogen-containing compound, peroxyacid, which forms products upon decomposing in the second stage. A kinetic equation that describes the studied process is offered. The constants of equilibrium of the intermediate complex formation ( K eq) and its decomposition constant ( k 2) in acetone and benzene were calculated. It was shown that the nature of the solvent influences the numerical values of both K p and k 2. It was established that introduction of acetic acid (which is able to form compounds with Py) into the reaction medium slows the rate of the oxidation process drastically. Correlation equations linking the polarity, polarizability, electrophilicity, and basicity of solvents with the constant of the PDA oxidation reaction rate for Py were found. It was concluded that the basicity and polarity of the solvent have a decisive influence on the oxidation reaction rate, while the polarizability and electrophilicity of the reaction medium do not influence the oxidation reaction rate.

Dutka, V. S.; Matsyuk, N. V.; Dutka, Yu. V.

2011-01-01

275

N-Heterocyclic Carbene Complexes of Rh: Reaction With Dioxygen Without Oxidation  

SciTech Connect

The reaction of oxygen with rhodium complexes containing N-heterocyclic carbenes was found to give dioxygen complexes with rare square planar geometries and unusually short O-O bond lengths. Analysis of the bonding in these complexes by Rh L-edge X-ray absorption spectroscopy (XAS), Raman spectroscopy, and DFT calculations provides evidence for a bonding model in which singlet oxygen is bound to a Rh(I) d{sup 8} metal complex, rather than the more common Rh(III) d{sup 6} peroxo species with octahedral geometry and O-O bond lengths in the 1.4-1.5 {angstrom} range.

Praetorius, J.M.; Allen, D.P.; Wang, R.; Webb, J.D.; Grein, F.; Kennepohl, P.; Crudden, C.M.

2009-05-21

276

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

277

Energetic and topological analyses of the oxidation reaction between Mo(n) (n = 1, 2) and N2O.  

PubMed

The interaction between molybdenum, atom, and dimer, with nitrous oxide has been investigated using density functional theory. The analysis of the potential energy surfaces for both reactions has revealed that a single molybdenum atom can activate the N--O bond of N2O requiring a small activation energy. However, the presence of several intersystem crossings between three different spin states, namely, septet, quintet and triplet states, seems to be the major constraint to the Mo + N2O reaction. Contrarily, the low-lying excited states (triplet and quintet) do not participate in the reaction between the molybdenum dimer and N2O. The latter reaction fully evolves on the singlet spin surface. Three different regions have been distinguished along the pathway: formation of an adduct complex, formation of an inserted compound, and the N2 detachment. The connection between the two first regions has been characterized by the formation of a special complex in which the N--O bond is so weakened that it could be considered as a first step in the insertion process. It has been shown that the topological changes along the pathways provide a clear explanation for the geometrical changes that occur along the reaction pathway. In summary, the detachment of the N2 molecule is found to be kinetically an effective process for both reactions, owing to the high exothermicity and consequently to the high internal energy of the insertion intermediates. However, in the case of Mo atom, the reaction should be a slow process due to the presence of spin-forbidden transitions. These results fully agree with previous experimental works. PMID:15981256

Michelini, Maria Del Carmen; Russo, Nino; Alikhani, Mohammad Esmaïl; Silvi, Bernard

2005-09-01

278

Anti-oxidant enzyme activities and expression and oxidative damage in patients with non-immediate reactions to drugs  

PubMed Central

Adverse drug reactions with an immunological basis (ADRIB) may involve activation of other concomitant, non-specific mechanisms, amplifying the specific response and contributing to the severity and duration. One concomitant mechanism could be the generation of reactive oxygen species (ROS) and/or their detoxification by anti-oxidants, including anti-oxidant enzymes. We analysed the activity of the anti-oxidant enzymes Cu/Zn-superoxide dismutase (SOD), catalase (CAT) and cellular glutathione peroxidase (GPX), as well as certain markers of oxidative damage (thiobarbituric acid reactive substances (TBARS) and carbonyl content) in peripheral blood mononuclear cells from patients with non-immediate ADRIB using spectrophotometric methods and the anti-oxidant enzymes expression by quantitative real-time reverse transcription–polymerase chain reaction. SOD activity and expression were increased in all types of non-immediate reactions (urticaria, maculopapular exanthema and toxic epidermal necrolysis). Regarding oxidative damage, TBARS were increased in urticaria and maculopapular exanthema, and carbonyl groups in all types of reactions. Our observations indicate that oxidative damage occurs in non-immediate reactions. Carbonyl stress and the inadequacy of the anti-oxidant defences are probable causes. PMID:16879248

Cornejo-Garcia, J A; Mayorga, C; Torres, M J; Fernandez, T D; R-Pena, R; Bravo, I; Mates, J M; Blanca, M

2006-01-01

279

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

E-print Network

Overall Rate Constant Measurements of the Reaction of Chloroalkylperoxy Radicals with Nitric Oxide, Oberlin, Ohio 44074 ReceiVed: January 21, 2005; In Final Form: March 22, 2005 The overall rate constants of the NO reaction with chloroalkylperoxy radicals derived from the Cl-initiated oxidation of several atmospherically

Elrod, Matthew J.

280

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

E-print Network

with nitric oxide Angela M. Miller, Laurence Y. Yeung, Annastassja C. Kiep and Matthew J. Elrod* Department derived from the OH-initiated oxidation of several atmospherically abundant alkenes--ethene, propene, 1 for the reactions of several alkane-derived peroxy radicals with NO. Introduction The reactions involved

Elrod, Matthew J.

281

Modeling the bacterial photosynthetic reaction center. 4. The structural, electrochemical, and hydrogen-bonding properties of 22 mutants of Rhodobacter sphaeroides.  

PubMed

Site-directed mutagenesis has been employed by a number of groups to produce mutants of bacterial photosynthetic reaction centers, with the aim of tuning their operation by modifying hydrogen-bond patterns in the close vicinity of the "special pair" of bacteriochlorophylls P identical with P(L)P(M). Direct X-ray structural measurements of the consequences of mutation are rare. Attention has mostly focused on effects on properties such as carbonyl stretching frequencies and midpoint potentials to infer indirectly the induced structural modifications. In this work, the structures of 22 mutants of Rhodobacter sphaeroides have been calculated using a mixed quantum-mechanical molecular-mechanical method by modifying the known structure of the wild type. We determine (i) the orientation of the 2a-acetyl groups in the wild type, FY(M197), and FH(M197) series mutants of the neutral and oxidized reaction center, (ii) the structure of the FY(M197) mutant and possible water penetration near the special pair, (iii) that significant protein chain distortions are required to assemble some M160 series mutants (LS(M160), LN(M160), LQ(M160), and LH(M160) are considered), (iv) that there is competition for hydrogen-bonding between the 9-keto and 10a-ester groups for the introduced histidine in LH(L131) mutants, (v) that the observed midpoint potential of P for HL(M202) heterodimer mutants, including one involving also LH(M160), can be correlated with the change of electrostatic potential experienced at P(L), (vi) that hydrogen-bond cleavage may sometimes be induced by oxidation of the special pair, (vii) that the OH group of tyrosine M210 points away from P(M), and (viii) that competitive hydrogen-bonding effects determine the change in properties of NL(L166) and NH(L166) mutants. A new technique is introduced for the determination of ionization energies at the Koopmans level from QM/MM calculations, and protein-induced Stark effects on vibrational frequencies are considered. PMID:11525663

Hughes, J M; Hutter, M C; Reimers, J R; Hush, N S

2001-09-01

282

Wollastonite based-Chemically Bonded Phosphate Ceramics with lead oxide contents under gamma irradiation  

NASA Astrophysics Data System (ADS)

The shielding properties to gamma rays as well as the effect of lead concentration incorporated into Chemically Bonded Phosphate Ceramics (CBPCs) composites are presented. The Wollastonite-based CBPC was fabricated by mixing a patented aqueous phosphoric acid formulation with Wollastonite powder. CBPC has been proved to be good structural material, with excellent thermal resistant properties, and research already showed their potential for radiation shielding applications. Wollastonite-based CBPC is a composite material itself with several crystalline and amorphous phases. Irradiation experiments were conducted on different Wollastonite-based CBPCs with lead oxide. Radiation shielding potential, attenuation coefficients in a broad range of energies pertinent to engineering applications and density experiments showing the effect of the PbO additions (to improve gamma shielding capabilities) are also presented. Microstructure was identified by using scanning electron microscopy and X-ray diffraction.

Colorado, H. A.; Pleitt, J.; Hiel, C.; Yang, J. M.; Hahn, H. T.; Castano, C. H.

2012-06-01

283

Chemical Bonding, Interfaces and Defects in Hafnium Oxide/Germanium Oxynitride Gate Stacks on Ge (100)  

SciTech Connect

Correlations among interface properties and chemical bonding characteristics in HfO{sub 2}/GeO{sub x}N{sub y}/Ge MIS stacks were investigated using in-situ remote nitridation of the Ge (100) surface prior to HfO{sub 2} atomic layer deposition (ALD). Ultra thin ({approx}1.1 nm), thermally stable and aqueous etch-resistant GeO{sub x}N{sub y} interfaces layers that exhibited Ge core level photoelectron spectra (PES) similar to stoichiometric Ge{sub 3}N{sub 4} were synthesized. To evaluate GeO{sub x}N{sub y}/Ge interface defects, the density of interface states (D{sub it}) was extracted by the conductance method across the band gap. Forming gas annealed (FGA) samples exhibited substantially lower D{sub it} ({approx} 1 x 10{sup 12} cm{sup -2} eV{sup -1}) than did high vacuum annealed (HVA) and inert gas anneal (IGA) samples ({approx} 1x 10{sup 13} cm{sup -2} eV{sup -1}). Germanium core level photoelectron spectra from similar FGA-treated samples detected out-diffusion of germanium oxide to the HfO{sub 2} film surface and apparent modification of chemical bonding at the GeO{sub x}N{sub y}/Ge interface, which is related to the reduced D{sub it}.

Oshima, Yasuhiro; /Stanford U., Materials Sci. Dept.; Sun, Yun; /SLAC, SSRL; Kuzum, Duygu; /Stanford U.; Sugawara, Takuya; Saraswat, Krishna C.; Pianetta, Piero; /SLAC, SSRL; McIntyre, Paul C.; /Stanford U., Materials Sci. Dept.

2008-10-31

284

Observation of the bond-dependent Doppler broadening of the p( 15N, ??) 12C nuclear reaction  

NASA Astrophysics Data System (ADS)

Excitation curves for the p( 15N, ??) 12C nuclear reaction have been measured on a number of hydrogen-bearing gases to investigate the bond-dependent Doppler broadening resulting from the motion of the target hydrogen atoms. Contributions to the resonance width due to the intrinsic width of the resonance, gas-induced beam energy loss and energy straggle, accelerator beam energy spread, and Doppler broadening are considered. Calculations of Doppler broadening based on molecular spectroscopy data are presented.

Horn, K. M.; Lanford, W. A.

1988-01-01

285

Material removal and micro-roughness in fluid-assisted smoothing of reaction-bonded silicon carbide surfaces  

Microsoft Academic Search

The magnetic fluid-assisted polishing for fuse silica and other optical materials with a high degree of success, and a super-smooth surface (Ra<1nm) and subsurface-damage-free layer can be produced. However, the fundamental mechanisms of the process for polishing reaction-bonded silicon carbide (RB-SiC) have not yet been studied in detail. This paper is concerned with the fabrication processability aspect of the RB-SiC

H. B. Cheng; Y. P. Feng; L. Q. Ren; Suet To; Y. T. Wang

2009-01-01

286

Hydrogen bonds in 1:2 complexes of substituted pyridine N-oxides with pentachlorophenol  

NASA Astrophysics Data System (ADS)

Pyridine N-oxides form two types of crystalline complexes with phentachlorophenol, with 1:1 and 1:2 base-to-acid ratios. The 1:2 complex of 2,6-dimethylpyridine N-oxide with pentachlorophenol crystallizes in space group P1¯ with a = 7.335(1) Å, b = 11.324(2) Å, c = 15.824(2) Å, ? = 100.38(1)°, ? = 94.63(1)°, ? = 106.60(1)°, V = 1226.7(6) Å3 and Z = 2. The structure has been refined to R = 0.046 for 3408 observed Mo K? reflections. The oxygen atom of the N-oxide group accepts hydrogen bonds from two molecules of pentachlorophenol, with Otctdot;O distances of 2.639(5) and 2.642(5) Å and OHO angles of 141.2° and 157.6°, respectively. Both N?Otctdot;H?O bridges are formed in, or near, the directions of the electron lone-pairs of the N-oxygen atom. The two pentachlorophenol rings (A and B) are nearly parallel to each other and they are almost perpendicular to the pyridine ring. FTIR spectra of eleven 1:2 complexes in the solid state are similar and independent of the proton acceptor properties of the N-oxides. Five lines in the 35Cl NQR spectra of the 1:2 complexes provide evidence that both molecules of pentachlorophenol are equivalent. In CHCl 3 solution, all the 1:2 complexes exist as a mixture of the 1:1 complex and pentachlorophenol.

Dega-Szafran, Zofia; Kosturkiewicz, Zofia; Tykarska, Ewa; Szafran, Miroslaw; Lema?ski, Dariusz; Nogaj, Boles?aw

1997-02-01

287

Chemical bonding, optical constants, and electrical resistivity of sputter-deposited gallium oxide thin films  

NASA Astrophysics Data System (ADS)

Gallium oxide (Ga2O3) thin films were made by sputter deposition employing a Ga2O3 ceramic target for sputtering. The depositions were made over a wide range of substrate temperatures (Ts), from 25 to 600 °C. The effect of Ts on the chemical bonding, surface morphological characteristics, optical constants, and electrical properties of the grown films was evaluated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and four-point probe measurements. XPS analyses indicate the binding energies (BE) of the Ga 2p doublet, i.e., the Ga 2p3/2 and Ga 2p1/2 peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga3+) in the grown films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE ˜ 531 eV, which is also characteristic of Ga-O bonds in the Ga2O3 phase. The granular morphology of the nanocrystalline Ga2O3 films was evident from AFM measurements, which also indicate that the surface roughness of the films increases from 0.5 nm to 3.0 nm with increasing Ts. The SE analyses indicate that the index of refraction (n) of Ga2O3 films increases with increasing Ts due to improved structural quality and packing density of the films. The n(?) of all the Ga2O3 films follows the Cauchy's dispersion relation. The room temperature electrical resistivity was high (˜200 ?-cm) for amorphous Ga2O3 films grown at Ts = RT-300 °C and decreased to ˜1 ?-cm for nanocrystalline Ga2O3 films grown at Ts ? 500-600 °C. A correlation between growth conditions, microstructure, optical constants, and electrical properties of Ga2O3 films is derived.

Ramana, C. V.; Rubio, E. J.; Barraza, C. D.; Miranda Gallardo, A.; McPeak, Samantha; Kotru, Sushma; Grant, J. T.

2014-01-01

288

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

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

Song, Lingchun; Mo, Yirong; Gao, Jiali

2009-01-01

289

Gold-Aluminum Intermetallics: Ball Bond Shear Testing and Thin Film Reaction Couples  

Microsoft Academic Search

The gold-aluminum intermetallic phases are known to contribute to the long term degradation of gold wire ball bonds to aluminum metallization on semiconductor devices. The properties of these intermetallics were investigated through two techniques: 1) ball bond shear testing and 2) preparation of known intermetallic compositions by using thin film Au-Al diffusion couples. The influence of thermal aging on gold

GUY V. CLATTERBAUGH; JOEL A. WEINER; HARRY K. CHARLES

1984-01-01

290

A Novel Reaction of Peroxiredoxin 4 towards Substrates in Oxidative Protein Folding  

PubMed Central

Peroxiredoxin 4 (Prx4) is the only endoplasmic reticulum localized peroxiredoxin. It functions not only to eliminate peroxide but also to promote oxidative protein folding via oxidizing protein disulfide isomerase (PDI). In Prx4-mediated oxidative protein folding we discovered a new reaction that the sulfenic acid form of Prx4 can directly react with thiols in folding substrates, resulting in non-native disulfide cross-linking and aggregation. We also found that PDI can inhibit this reaction by exerting its reductase and chaperone activities. This discovery discloses an off-pathway reaction in the Prx4-mediated oxidative protein folding and the quality control role of PDI. PMID:25137134

Wang, Xi’e; Wang, Xi; Wang, Chih-chen

2014-01-01

291

Formation of Active Sites for Selective Toluene Oxidation during Catalyst Synthesis via Solid-State Reaction of V 2O 5 with TiO 2  

Microsoft Academic Search

Interaction of V2O5 with TiO2 during the preparation of V\\/Ti-oxide catalysts via solid-state reaction has been studied by means of in situ FT-Raman spectroscopy, HRTEM and XPS. This interaction results in the formation of monomeric vanadia species with vanadium in tetrahedral coordination. The bridging oxygen in the V–O–Ti bond is suggested to be responsible for the catalytic activity during the

Dmitri A. Bulushev; Lioubov Kiwi-Minsker; Vladimir I. Zaikovskii; Albert Renken

2000-01-01

292

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

293

Do synthetic Fe-zeolites mimic biological Fe-porphyrins in reactions with nitric oxide?  

Microsoft Academic Search

Iron containing ZSM-5 zeolites is extremely active in nitrous oxide decomposition. This reaction involves atomic oxygen species known as “alpha oxygen” on iron sites. Despite the multiple techniques devoted to its characterization, the active sites’ structure remains nevertheless unknown. Herein, these centers are quantified via surface titration by nitrous oxide followed by temperature programmed desorption and characterized via nitric oxide

Mickaël Rivallan; Bryan Bromley; Lioubov Kiwi-Minsker

2010-01-01

294

Pyroprocessing of oxidized sodium-bonded fast reactor fuel - An experimental study of treatment options for degraded EBR-II fuel  

SciTech Connect

An experimental study was conducted to assess pyrochemical treatment options for degraded EBR-II fuel. As oxidized material, the degraded fuel would need to be converted back to metal to enable electrorefining within an existing electro-metallurgical treatment process. A lithium-based electrolytic reduction process was studied to assess the efficacy of converting oxide materials to metal with a particular focus on the impact of zirconium oxide and sodium oxide on this process. Bench-scale electrolytic reduction experiments were performed in LiCl-Li{sub 2}O at 650 C. degrees with combinations of manganese oxide (used as a surrogate for uranium oxide), zirconium oxide, and sodium oxide. In the absence of zirconium or sodium oxide, the electrolytic reduction of MnO showed nearly complete conversion to metal. The electrolytic reduction of a blend of MnO-ZrO{sub 2} in LiCl - 1 wt% Li{sub 2}O showed substantial reduction of manganese, but only 8.5% of the zirconium was found in the metal phase. The electrolytic reduction of the same blend of MnO-ZrO{sub 2} in LiCl - 1 wt% Li{sub 2}O - 6.2 wt% Na{sub 2}O showed substantial reduction of manganese, but zirconium reduction was even less at 2.4%. This study concluded that ZrO{sub 2} cannot be substantially reduced to metal in an electrolytic reduction system with LiCl - 1 wt% Li{sub 2}O at 650 C. degrees due to the perceived preferential formation of lithium zirconate. This study also identified a possible interference that sodium oxide may have on the same system by introducing a parasitic and cyclic reaction of dissolved sodium metal between oxidation at the anode and reduction at the cathode. When applied to oxidized sodium-bonded EBR-II fuel (e.g., U-10Zr), the prescribed electrolytic reduction system would not be expected to substantially reduce zirconium oxide, and the accumulation of sodium in the electrolyte could interfere with the reduction of uranium oxide, or at least render it less efficient.

Hermann, S.D.; Gese, N.J. [Separations Department, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 (United States); Wurth, L.A. [Zinc Air Inc., 5314-A US Hwy 2 West, Columbia Falls, MT 59912 (United States)

2013-07-01

295

Oxidation and reduction characteristics of oxygen carrier particles and reaction kinetics by unreacted core model  

Microsoft Academic Search

The reaction kinetics of the oxygen carrier particles, which are used as bed material for a fluidized bed chemical looping\\u000a combustor (CLC), has been studied experimentally by a conventional thermal gravimetrical analysis technique. The weight percent of nickel\\u000a and nickel oxide in oxygen carrier particles and reaction temperature were considered as experimental variables. After oxidation\\u000a reaction, the pure nickel particle

Ho-Jung Ryu; Dal-Hee Bae; Keun-Hee Han; Seung-Yong Lee; Gyoung-Tae Jin; Jeong-Hoo Choi

2001-01-01

296

Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction  

SciTech Connect

This study was undertaken in order to assess the potential for oxidizing NO to NO{sub 2} in flue gas environments, with the aim of promoting the so-called fast SCR reaction. In principle this can result in improved SCR kinetics and reduced SCR catalyst volumes. Prior to commencing experimental work, a literature study was undertaken to identify candidate catalysts for screening. Selection criteria comprised (1) proven (or likely) activity for NO oxidation, (2) low activity for SO2 oxidation (where data were available), and (3) inexpensive component materials. Catalysts identified included supported base metal oxides, supported and unsupported mixed metal oxides, and metal ion exchanged ZSM-5 (Fe, Co, Cu). For comparison purposes, several low loaded Pt catalysts (0.5 wt% Pt) were also included in the study. Screening experiments were conducted using a synthetic feed gas representative of flue gas from coal-fired utility boilers: [NO] = 250 ppm, [SO{sub 2}] = 0 or 2800 ppm, [H{sub 2}O] = 7%, [CO{sub 2}] = 12%, [O{sub 2}] = 3.5%, balance = N{sub 2}; T = 275-375 C. Studies conducted in the absence of SO{sub 2} revealed a number of supported and unsupported metal oxides to be extremely active for NO oxidation to NO{sub 2}. These included known catalysts (Co{sub 3}O{sub 4}/SiO{sub 2}, FeMnO{sub 3}, Cr{sub 2}O{sub 3}/TiO{sub 2}), as well as a new one identified in this work, CrFeO{sub x}/SiO{sub 2}. However, in the presence of SO{sub 2}, all the catalysts tested were found to be severely deactivated with respect to NO oxidation. Of these, Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/ZSM-5 and Pt/CeO{sub 2} showed the highest activity for NO oxidation in the presence of SO{sub 2} (based on peak NO conversions to NO{sub 2}), although in no cases did the NO conversion exceed 7%. Reactor studies indicate there are two components to SO{sub 2}-induced deactivation of Co{sub 3}O{sub 4}/SiO{sub 2}, corresponding to an irreversible deactivation due to sulfation of the surface of the Co{sub 3}O{sub 4} phase, together with a reversible inhibition due to competitive adsorption of SO{sub 2} with NO on the catalyst. In an effort to minimize the deactivating effect of SO{sub 2} on Co{sub 3}O{sub 4}/SiO{sub 2}, two synthetic approaches were briefly examined. These consisted of (1) the incorporation of highly dispersed Co(II) ions in silica, as a non-sulfating matrix, via the sol-gel preparation of CoO-SiO{sub 2}; and (2) the sol-gel preparation of a mixed metal oxide, CoO-Nb{sub 2}O{sub 5}-SiO{sub 2}, with the aim of exploiting the acidity of the niobium oxide to minimize SO2 adsorption. While both catalysts showed almost no activity for NO oxidation in the absence of SO{sub 2}, when SO{sub 2} was present low activity was observed, indicating that SO{sub 2} acts as a promoter for NO oxidation over these materials. The kinetics of NO oxidation over Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/SiO{sub 2} and Pt/CeO{sub 2} were also examined. Co{sub 3}O{sub 4}/SiO{sub 2} was found to exhibit a higher apparent activation energy for NO oxidation than the Pt catalysts, while the combined reaction order in NO and O{sub 2} for the three catalysts was very close to one. CO{sub 2} was found to have no effect on the kinetics of NO oxidation over these catalysts. The presence of H{sub 2}O caused a decrease in NO conversion for both Co{sub 3}O{sub 4}/SiO{sub 2} and Pt/CeO{sub 2} catalysts, while no effect was observed for Pt/SiO{sub 2}. The inhibiting effect of water was reversible and is attributed to competitive adsorption with the reactants. In sum, this study has shown that a variety of base metal catalysts are very active for NO oxidation. However, all of the catalysts studied are strongly deactivated in the presence of 2800 ppm SO{sub 2} at typical flue gas temperatures; consequently improving catalyst resistance to SO{sub x} will be a pre-requisite if the fast SCR concept is to be applied to coal-fired flue gas conditions.

Mark Crocker

2005-09-30

297

Reaction pathways of glucose oxidation by ozone under acidic conditions.  

PubMed

The ozonation of d-glucose-1-(13)C, 2-(13)C, and 6-(13)C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and (13)C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For the first time, a pentaric acid was identified and its formation quantitatively correlated to the loss of C-6 of glucose in the form of carbon dioxide. Potential mechanisms for the formation of this pentaric acid are discussed. The well-accepted pathway involving the anomeric position in glucose, gluconic acid, arabinose, and carbon dioxide is reinvestigated. The origin of small molecules such as tartaric, erythronic, and oxalic acids is clarified. Finally, new reaction pathways and tentative mechanisms consistent with the formation of ketoaldonic acids and smaller acids are proposed. PMID:19524217

Marcq, Olivier; Barbe, Jean-Michel; Trichet, Alain; Guilard, Roger

2009-07-27

298

Activation Energy of Tantalum-Tungsten Oxide Thermite Reaction  

SciTech Connect

The activation energy of a high melting temperature sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the High Pressure Spark Plasma Sintering (HPSPS) technique to 300 and 400 C to produce pellets with dimensions of 5 mm diameter by 1.5 mm height. A custom built ignition setup was developed to measure ignition temperatures at high heating rates (500-2000 C {center_dot} min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Unlike the 400 C samples, results show that the samples consolidated to 300 C undergo an abrupt change in temperature response prior to ignition. This change in temperature response has been attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465-670 C. The activation energy of the SG derived Ta-WO{sup 3} thermite composite consolidated to 300 and 400 C were determined to be 37.787 {+-} 1.58 kJ {center_dot} mol{sup -1} and 57.381 {+-} 2.26 kJ {center_dot} mol{sup -1}, respectively.

Cervantes, O; Kuntz, J; Gash, A; Munir, Z

2010-02-25

299

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

PubMed

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

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

2015-04-01

300

Exploring Oxidation of Half-Sandwich Rhodium Complexes: Oxygen Atom Insertion into the Rhodium-Carbon Bond of 2  

E-print Network

Exploring Oxidation of Half-Sandwich Rhodium Complexes: Oxygen Atom Insertion into the Rhodium into the rhodium-carbon bond of coordinated phpy was observed. This resulted in the formation of a 2 2-(2-pyridyl as a neutral, two-electron donor ligand, coordinated to the rhodium center through the iodosyl oxygen. Over

Jones, William D.

301

Effect of Layer-Graded Bond Coats on Edge Stress Concentration and Oxidation Behavior of Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

Thermal barrier coating (TBC) durability is closely related to design, processing and microstructure of the coating Z, tn systems. Two important issues that must be considered during the design of a thermal barrier coating are thermal expansion and modulus mismatch between the substrate and the ceramic layer, and substrate oxidation. In many cases, both of these issues may be best addressed through the selection of an appropriate bond coat system. In this study, a low thermal expansion and layer-graded bond coat system, that consists of plasma-sprayed FeCoNiCrAl and FeCrAlY coatings, and a high velocity oxyfuel (HVOF) sprayed FeCrAlY coating, is developed to minimize the thermal stresses and provide oxidation resistance. The thermal expansion and oxidation behavior of the coating system are also characterized, and the strain isolation effect of the bond coat system is analyzed using the finite element method (FEM). Experiments and finite element results show that the layer-graded bond coat system possesses lower interfacial stresses. better strain isolation and excellent oxidation resistance. thus significantly improving the coating performance and durability.

Zhu, Dongming; Ghosn, Louis J.; Miller, Robert A.

1998-01-01

302

Simplified Reaction Mechanisms for the Oxidation of Hydrocarbon Fuels in Flames  

Microsoft Academic Search

Simplified reaction mechanisms for the oxidation of hydrocarbon fuels have been examined using a numerical laminar flame model. The types of mechanisms studied include one and two global reaction steps as well as quasi-global mechanisms. Reaction rate parameters were varied in order to provide the best agreement between computed and experimentally observed flame speeds in selected mixtures of fuel and

CHARLES K. WESTBROOK; FREDERICK L DRYER

1981-01-01

303

Kinetics of COCO2 reaction with iron oxide containing slags  

Microsoft Academic Search

The reaction between CO-CO2 gases and metallurgical slags is one of the most crucial reactions in metal production and refining processes. However, a full understanding of the reaction kinetics has not been achieved due to the complex effect of different variables. The aim of the present study was to obtain a consistent and comprehensive picture of the reaction kinetics. ^

Mansoor Barati Sedeh

2006-01-01

304

Direct evidence of multiple vibrational excitation for the SiSingle_BondH/D bond breaking in metal-oxide-semiconductor transistors  

NASA Astrophysics Data System (ADS)

Experiments based on substrate hot-electron generation due to impact ionization are designed to reveal whether the hydrogen/deuterium (H/D) isotope effect is caused by the density of electrons or their energy. It is found that the H/D isotope effect for hot-electron degradation is strongly dependent on the density of hot electrons presented at the interface. This suggests that the multiple vibrational excitation (heating) plays a major role in hot-carrier degradation of metal-oxide-semiconductor (MOS) transistors. Because of the unique nature of multiple vibrational excitation (heating), low-energy electrons are able to break SiSingle_BondH/D bonds in MOS devices. This implies that hot-electron degradation is still an important reliability issue even if the drain voltage is scaled down to below 1 V.

Chen, Zhi; Ong, Pangling; Mylin, Alicia Kay; Singh, Vijay; Chetlur, Sundar

2002-10-01

305

ENDOR studies of the primary donor cation radical in mutant reaction centers of Rhodobacter sphaeroides with altered hydrogen-bond interactions.  

PubMed

The electronic structure of the cation radical of the primary electron donor was investigated in genetically modified reaction centers of Rhodobacter sphaeroides. The site-directed mutations were designed to add or remove hydrogen bonds between the conjugated carbonyl groups of the primary donor, a bacteriochlorophyll dimer, and histidine residues of the protein and were introduced at the symmetry-related sites L168 His-->Phe, HF(L168), and M197 Phe-->His, FH(M197), near the 2-acetyl groups of the dimer and at sites M160 Leu-->His, LH(M160), and L131 Leu-->His, LH(L131), in the vicinity of the 9-keto carbonyls of the dimer. The single mutants and a complete set of double mutants were studied using EPR, ENDOR, and TRIPLE resonance spectroscopy. The changes in the hydrogen bond situation of the primary donor were accompanied by changes in the dimer oxidation midpoint potential, ranging from 410 to 710 mV in the investigated mutants [Lin, X., Murchison, H. A., Nagarajan, V., Parson, W. W., Williams, J. C. & Allen, J. P. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 10265-10269]. It was found that the addition or removal of a hydrogen bond causes large shifts of the spin density between the two halves of the dimer. Measurements on double mutants showed that the unpaired electron can be gradually shifted from a localization on the L-half of the dimer to a localization on the M-half, depending on the hydrogen bond situation. As a control, the effects of the different hydrogen bonds on P.+ in the mutant HL(M202), which contains a BChlL-BPheM heterodimer as the primary donor with localized spin on the BChl aL [Bylina, E. J., & Youvan, D. C. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7226-7230; Schenck, C. C., Gaul, D., Steffen M., Boxer S. G., McDowell L., Kirmaier C., & Holten D. (1990) in Reaction Centers of Photosynthetic Bacteria (Michel-Beyerle M. E., Ed.) pp 229-238, Springer, Berlin] were studied. In this mutant only small local changes of the spin densities (< or = 10%) in the vicinity of the hydrogen bonds were observed. The effects of the introduced hydrogen bonds on the spin density distribution of the dimer in the mutants are discussed in terms of different orbital energies of the two BChl a moieties which are directly influenced by hydrogen bond formation. The observed changes of the spin density distribution for the double mutants are additive with respect to the single mutations.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:7794927

Rautter, J; Lendzian, F; Schulz, C; Fetsch, A; Kuhn, M; Lin, X; Williams, J C; Allen, J P; Lubitz, W

1995-06-27

306

Advances in the Stille reaction and new methods for continuous flow Pd-catalyzed C-N bond forming reactions  

E-print Network

Chapter 1: A highly active catalyst system based upon a biaryl monophosphine ligand, XPhos, for the palladium-catalyzed Stille reaction has been developed. This method allows for the coupling of aryl chlorides with a range ...

Naber, John R. (John Robert)

2010-01-01

307

High-temperature oxidation behavior of reaction-formed silicon carbide ceramics  

NASA Technical Reports Server (NTRS)

The oxidation behavior of reaction-formed silicon carbide (RFSC) ceramics was investigated in the temperature range of 1100 to 1400 C. The oxidation weight change was recorded by TGA; the oxidized materials were examined by light and electron microscopy, and the oxidation product by x-ray diffraction analysis (XRD). The materials exhibited initial weight loss, followed by passive weight gain (with enhanced parabolic rates, k(sub p)), and ending with a negative (logarithmic) deviation from the parabolic law. The weight loss arose from the oxidation of residual carbon, and the enhanced k(sub p) values from internal oxidation and the oxidation of residual silicon, while the logarithmic kinetics is thought to have resulted from crystallization of the oxide. The presence of a small amount of MoSi, in the RFSC material caused a further increase in the oxidation rate. The only solid oxidation product for all temperatures studied was silica.

Ogbuji, Linus U. J. T.; Singh, M.

1995-01-01

308

Evaluation of antioxidants using oxidation reaction rate constants  

Microsoft Academic Search

An evaluation method for the capacity of antioxidants to protect drugs against oxidation is presented. As a new viewpoint,\\u000a to determine the priority of the competitive oxidations between the antioxidant and the protected drug, and to compare the\\u000a drug-protection capacity of antioxidants, it is important to determine their oxidation rate constants using chemical kinetics\\u000a instead of standard oxidation (or reduction)

Yan Shi; Xiancheng Zhan; Lie Ma; Linli Li; Chengrong Li

2007-01-01

309

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

PubMed

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

Murai, Masahito; Nakamura, Masahiro; Takai, Kazuhiko

2014-11-01

310

HYDROTHERMAL OXIDATION TREATMENT AND REACTION CONTROL BY OXYGEN INJECTION  

Microsoft Academic Search

for oral communication Hydrothermal Oxidation Treatment (HOT) of organic and inorganic compounds needs operating conditions up to 22.1 MPa for the pressure and temperature between 200°C to 600°C. These conditions permit a total solubility of both organic matter and oxidant, which is very interesting to avoid mass transfer limitations. Furthermore, high temperature ensures rapid rates of oxidation. HOT appears to

David MATEOS; Juan PORTELA; Christine MARRAUD; François CANSELL

311

Bonding principles of the Passivation Mechanism at III-V -- oxide Interfaces  

NASA Astrophysics Data System (ADS)

It has always been much more difficult to make FETs from GaAs than Si, because of `Fermi level pinning' and the difficulty of passivating its surfaces and interfaces. These issues have been discussed from the early days of PCSI by Spicer et al [1] with their ``unified defect model.'' Hasegawa [2] introduced the idea of ``Disorder Induced Gap states'' (DIGS). Since 1997 it has been possible to make inverted MOSFETs on GaAs using the epitaxial Gadolinium gallium oxide [3], but the main impetuous has been since 2003 to use atomic layer dpeosition to make scalable FETs, as recently acheived by Intel [4]. The obvious question is why GaAs is so much more difficult to passivate than Si. The early answer was that the native oxide was poor. But since the advent of good deposited ALD oxides on Si such as HfO2 or Al2O3, this answer is no good, as they should also work on GaAs. They do to an extent, but the interfacial density of states is still too large and the CV p lots are distorted. The cause of the defects is cannot be due to stress. The reason must be some underlying chemical reason. I show that the reason is the polar nature of bonding in GaAa and other III-Vs, and the driving force to keep the Fermi level in a gap. The electron counting rule of Pashley [5] that describes surface reconstruction is shown to be a variant of auto-compensation, and it is proposed to work more generally, at each layer deposition or growth on GaAs [6]. This leads to a continuous generation of defects if it is not satisfied. So the answer is to deposit oxide layers that meet this rule, and also break up any surface reconstructions that would lead to As-As dimers [6]. [4pt] [1] W E Spicer, Phys Rev Lett 44 420 (1980)[0pt] [2] H Hasegawa, J Vac Sci Technol B 5 1097 (1987)[0pt] [3] M Hong et al, Science 283 1897 (1997)[0pt] [4] M Radosavljevic, et al, IEDM (2009) p13.1[0pt] [5] M D Pashley, Phys Rev B 40 10481 (1989)[0pt] [6] J Robertson, L Lin, App Phys Letts (submitted), App Phys Lett 98 082903 (2011)

Robertson, John

2012-02-01

312

Chemical bonding, optical constants, and electrical resistivity of sputter-deposited gallium oxide thin films  

SciTech Connect

Gallium oxide (Ga{sub 2}O{sub 3}) thin films were made by sputter deposition employing a Ga{sub 2}O{sub 3} ceramic target for sputtering. The depositions were made over a wide range of substrate temperatures (T{sub s}), from 25 to 600?°C. The effect of T{sub s} on the chemical bonding, surface morphological characteristics, optical constants, and electrical properties of the grown films was evaluated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and four-point probe measurements. XPS analyses indicate the binding energies (BE) of the Ga 2p doublet, i.e., the Ga 2p{sub 3/2} and Ga 2p{sub 1/2} peaks, are located at 1118.0 and 1145.0?eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga{sup 3+}) in the grown films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE???531?eV, which is also characteristic of Ga-O bonds in the Ga{sub 2}O{sub 3} phase. The granular morphology of the nanocrystalline Ga{sub 2}O{sub 3} films was evident from AFM measurements, which also indicate that the surface roughness of the films increases from 0.5?nm to 3.0?nm with increasing T{sub s}. The SE analyses indicate that the index of refraction (n) of Ga{sub 2}O{sub 3} films increases with increasing T{sub s} due to improved structural quality and packing density of the films. The n(?) of all the Ga{sub 2}O{sub 3} films follows the Cauchy's dispersion relation. The room temperature electrical resistivity was high (?200 ?-cm) for amorphous Ga{sub 2}O{sub 3} films grown at T{sub s}?=?RT-300?°C and decreased to ?1 ?-cm for nanocrystalline Ga{sub 2}O{sub 3} films grown at T{sub s}???500–600?°C. A correlation between growth conditions, microstructure, optical constants, and electrical properties of Ga{sub 2}O{sub 3} films is derived.

Ramana, C. V., E-mail: rvchintalapalle@utep.edu; Rubio, E. J.; Barraza, C. D.; Miranda Gallardo, A. [Department of Mechanical Engineering, University of Texas at El Paso, El Paso, Texas 79968 (United States); McPeak, Samantha [Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, Alabama 35487 (United States); Kotru, Sushma [Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, Alabama 35487 (United States); Materials for Information and Technology, The University of Alabama, Tuscaloosa, Alabama 35487 (United States); Grant, J. T. [Research Institute, University of Dayton, Dayton, Ohio 45469 (United States)

2014-01-28

313

Molecular Recognition in Mn-Catalyzed C-H Oxidation. Reaction Mechanism and Origin of Selectivity from a DFT Perspective  

PubMed Central

Experimental studies have shown that the C-H oxidation of ibuprofen and methylcyclohexane acetic acid can be carried out with high selectivies using [(terpy’)Mn(OH2)(?-O)2Mn(OH2)(terpy’)]3+ as catalyst, where terpy’ is a terpyridine ligand functionalized with a phenylene linker and a Kemp’s triacid serving to recognize the reactant via H-bonding. Experiments, described here, suggest that the sulfate counter anion, present in stochiometric amounts, coordinates to manganese in place of water. DFT calculations have been carried out using [(terpy’)Mn(O)(?-O)2Mn(SO4)(terpy’)]+ as model catalyst, to analyze the origin of selectivity and its relation to molecular recognition, as well as the mechanism of catalyst inhibition by tert-butyl benzoic acid. The calculations show that a number of spin states, all having radical oxygen character, are energetically accessible. All these spin states promote C-H oxidation via a rebound mechanism. The catalyst recognizes the substrate by a double H bond. This interaction orients the substrate inducing highly selective C-H oxidation. The double hydrogen bond stabilizes the reactant, the transition state and the product to the same extent. Consequently, the reaction occurs at lower energy than without molecular recognition. The association of the catalyst with tert-butyl benzoic acid is shown to shield the access of unbound substrate to the reactive oxo site, hence preventing non-selective hydroxylation. It is shown that the two recognition sites of the catalyst can be used in a cooperative manner to control the access to the reactive centre. PMID:19623399

Balcells, David; Moles, Pamela; Blakemore, James; Raynaud, Christophe; Brudvig, Gary W.; Crabtree, Robert H.

2010-01-01

314

Aminomethylation reaction of ortho-pyridyl C-H bonds catalyzed by group 3 metal triamido complexes.  

PubMed

Tris[N,N-bis(trimethylsilyl)amido] complexes of group 3 metals, especially yttrium and gadolinium, served as catalysts for ortho-C-H bond addition of pyridine derivatives and N-heteroaromatics into the C?N double bond of nonactivated imines to afford the corresponding aminomethylated products. Addition of catalytic amounts of secondary amines, such as dibenzylamine, dramatically improved the catalytic activity through the formation of a mixed ligated complex such as [(Me3Si)2N]2Y(NBn2)(THF) (4). Furthermore, kinetic studies using the isolated complex 4 provided a plausible reaction mechanism by which coordination of two pyridine derivatives afforded a penta-coordinated species as a key step. PMID:25543453

Nagae, Haruki; Shibata, Yu; Tsurugi, Hayato; Mashima, Kazushi

2015-01-21

315

The Crystal Structure of Arabidopsis thaliana Allene Oxide Cyclase: Insights into the Oxylipin Cyclization Reaction[W  

PubMed Central

We describe the crystallization and structure elucidation of Arabidopsis thaliana allene oxide cyclase 2 (AOC2), a key enzyme in the biosynthesis of jasmonates. In a coupled reaction with allene oxide synthase, AOC2 releases the first cyclic and biologically active metabolite, 12-oxo-phytodienoic acid (OPDA). AOC2 (AT3G25770) folds into an eight-stranded antiparallel ?-barrel with a C-terminal partial helical extension. The protein forms a hydrophobic binding cavity with two distinct polar patches. AOC2 is trimeric in crystals, in vitro and in planta. Based on the observed folding pattern, we assigned AOC2 as a low molecular weight member of the lipocalin family with enzymatic activity in plants. We determined the binding position of the competitive inhibitor vernolic acid (a substrate analog) in the binding pocket. Based on models for bound substrate 12,13-epoxy-9,11,15-octadecatrienoic acid and product OPDA, we propose a reaction scheme that explains the influence of the C15 double bond on reactivity. Reaction is promoted by anchimeric assistance through a conserved Glu residue. The transition state with a pentadienyl carbocation and an oxyanion is stabilized by a strongly bound water molecule and favorable ?–? interactions with aromatic residues in the cavity. Stereoselectivity results from steric restrictions to the necessary substrate isomerizations imposed by the protein. PMID:17085685

Hofmann, Eckhard; Zerbe, Philipp; Schaller, Florian

2006-01-01

316

Investigation of the reactions of small neutral iron oxide clusters with methanol.  

PubMed

Reactions of neutral iron oxide clusters (Fe(m)O(n), m=1-2, n=0-5) with methanol (CH(3)OH) in a fast flow reactor are investigated by time of flight mass spectrometry. Detection of the neutral iron oxide cluster distribution and reaction intermediates and products is accomplished through single photon ionization by a 118 nm (10.5 eV) VUV laser. Partially deuterated methanol (CD(3)OH) is employed to distinguish reaction products and reaction mechanisms. Three major reactions are identified experimentally: CH(3)OH association with FeO; methanol dehydrogenation on FeO(1,2) and Fe(2)O(2-5); and (CH(2)O)Fe formation. Density functional theory calculations are carried out to identify reaction products, and to explore the geometric and electronic structures of the iron oxide clusters, reaction intermediates, and transition states, and to evaluate reaction pathways. Neutral formaldehyde is calculated to be formed on FeO(1,2) and Fe(2)O(2-5) clusters. Hydrogen transfer from methanol to iron oxide clusters occurs first from the O-H moiety of methanol, and is followed by a hydrogen transfer from the C-H moiety of methanol. Computational results are in good agreement with experimental observations and reveal reaction mechanisms for neutral iron oxide clusters taking methanol to formaldehyde through various reaction intermediates. Based on the experimental results and the calculated reaction mechanisms and pathways, complete catalytic cycles are suggested for the heterogeneous reaction of CH(3)OH to CH(2)O facilitated by an iron oxide catalyst. PMID:19317538

Xie, Yan; Dong, Feng; Heinbuch, Scott; Rocca, Jorge J; Bernstein, Elliot R

2009-03-21

317

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

NASA Technical Reports Server (NTRS)

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.

Opila, Elizabeth

1995-01-01

318

Fundamental kinetics and mechanistic pathways for oxidation reactions in supercritical water  

NASA Technical Reports Server (NTRS)

Oxidation of the products of human metabolism in supercritical water has been shown to be an efficient way to accomplish the on-board water/waste recycling in future long-term space flights. Studies of the oxidation kinetics of methane to carbon dioxide in supercritical water are presented in this paper in order to enhance the fundamental understanding of the oxidation of human waste compounds in supercritical water. It is concluded that, although the elementary reaction models remain the best hope for simulating oxidation in supercritical water, several modifications to existing mechanisms need to be made to account for the role of water in the reaction mechanism.

Webley, Paul A.; Tester, Jefferson W.

1988-01-01

319

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

E-print Network

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.

Elisa Londero; Elsebeth Schroder

2010-06-12

320

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

E-print Network

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 s...

Londero, Elisa

2010-01-01

321

Comparison of properties of sintered and sintered reaction-bonded silicon nitride fabricated by microwave and conventional heating  

SciTech Connect

A comparison of microwave and conventional processing of silicon nitride-based ceramics was performed to identify any differences between the two, such as improved fabrication parameters or increased mechanical properties. Two areas of thermal processing were examined: (1) sintered silicon nitride (SSN) and (2) sintered reaction-bonded silicon nitride (SRBSN). The SSN powder compacts showed improved densification and enhanced grain growth. SRBSN materials were fabricated in the microwave with a one-step process using cost-effective raw materials. The SRBSN materials had properties appropriate for structural applications. Observed increases in fracture toughness for the microwave processed SRBSN materials were attributable to enhanced elongated grain growth.

Tiegs, T.N.; Kiggans, J.O. Jr.; Lin, H.T. [Oak Ridge National Lab., TN (United States); Willkens, C.A. [St. Gobain/Norton Industrial Ceramics, Northboro, MA (United States)

1994-10-01

322

Comparison of properties of sintered and sintered reaction-bonded silicon nitride fabricated by microwave and conventional heating  

SciTech Connect

A comparison of microwave and conventional processing of silicon nitride-based ceramics was performed to identify any differences between the two, such as improved fabrication parameters or increased mechanical properties. Two areas of thermal processing were examined: sintered silicon nitride (SSN) and sintered reaction-bonded silicon nitride (SRBSN). The SSN powder compacts showed improved densification and enhanced grain growth. SRBSN materials were fabricated in the microwave with a one-step process using cost-effective raw materials. The SRBSN materials had properties appropriate for structural applications. Observed increases in fracture toughness for the microwave processed SRBSN materials were attributable to enhanced elongated grain growth.

Tiegs, T.N.; Kiggans, J.O. Jr.; Lin, H.T. [and others

1995-10-01

323

Pulp Tissue Reactions to a Dentin Bonding Agent as a Direct Capping Agent  

Microsoft Academic Search

The aim of this study was to investigate the response of human pulp tissue to a dentin bonding agent, Scotchbond Multi-Purpose Plus (SMPP), in exposed class V cavities. Sixteen human premolar teeth were mechanically exposed. Ten pulps were capped with SMPP and six teeth were capped with Dycal. The cavities were filled with a composite. After 40 days, the teeth

Rüstem Kemal Sübay; Mustafa Demirci

2005-01-01

324

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...

325

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

PubMed

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

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

2015-01-22

326

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

327

Oxidative reactions and their impact on the properties of asphalt as a pavement binder  

E-print Network

of MASTER OF SCIENCE December 1991 Major Subject: Chemical Engineering OXIDATIVE REACTIONS AND THEIR IMPACT ON THE PROPERTIES OF ASPHALT AS A PAVEMENT BINDER A Thesis by CHEE KEUNG LAU Approved as to style and content by: Charles J. over (Chair... of Committee) Rich d R. Davison (Member) i ( Alan Letton (Member) Raymond W. umerfelt (Head of Department) December, 1991 111 Oxidative Reactions and Their Impact on the Properties of Asphalt as a Pavement Binder. (December 1991) Chee Keung Lau, B...

Lau, Chee Keung

1991-01-01

328

Influence of the Reaction Temperature on the Oscillatory Behavior during Partial Oxidation of Methane  

Microsoft Academic Search

The oscillatory behavior during partial oxidation of methane was studied by the Monte Carlo simulation with Langmuir-Hinshelwood mechanism and oxide formation and removal. The well-developed reaction rate oscillations can be observed when the CH4 adsorption probability varies in a small window. The oscillation window is very sensitive to the variation of reaction temperature. When the temperature increases, the window for

Xiu-Bin Ren; Xiang-Yun Guo

2008-01-01

329

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

Microsoft Academic Search

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

Masakatsu Shibasaki; Hiroaki Sasai

1996-01-01

330

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

PubMed

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

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

2014-02-10

331

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

Microsoft Academic Search

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

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

1992-01-01

332

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)

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.

Cui, Hui-Wang; Kuo, Shiao-Wei

2014-05-01

333

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

PubMed

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

Fujimoto, Takahiro; Furuta, Nao; Mizutani, Tadashi

2015-03-01

334

Rim region growth and its composition in reaction bonded boron carbide composites with core-rim structure  

NASA Astrophysics Data System (ADS)

Aluminum was detected in reaction-bonded boron carbide that had been prepared by pressureless infiltration of boron carbide preforms with molten silicon in a graphite furnace under vacuum. The presence of Al2O3 in the heated zone, even though not in contact with the boron carbide preform, stands behind the presence of aluminium in the rim region that interconnects the initial boron carbide particles. The composition of the rim corresponds to the Bx(C,Si,Al)y quaternary carbide phase. The reaction of alumina with graphite and the formation of a gaseous aluminum suboxide (Al2O) accounts for the transfer of aluminum in the melt and, subsequently in the rim regions. The presence of Al increases the solubility of boron in liquid silicon, but with increasing aluminum content the activity of boron decreases. These features dominate the structural evolution of the rim-core in the presence of aluminum in the melt.

Hayun, S.; Weizmann, A.; Dilman, H.; Dariel, M. P.; Frage, N.

2009-06-01

335

Applied reaction dynamics: Efficient synthesis gas production via single collision partial oxidation of methane to CO on Rh(111)  

NASA Astrophysics Data System (ADS)

Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh(111) catalytic substrate, CH4+(1/2)O2?CO +2H2, as a function of beam kinetic energy. These experiments were done under ultrahigh vacuum conditions with concurrent molecular beams of O2 and CH4, ensuring that there was only a single collision for the CH4 to react with the surface. The fraction of CH4 converted is strongly dependent on the normal component of the incident beam's translational energy, and approaches unity for energies greater than ˜1.3eV. Comparison with a simplified model of the methane-Rh(111) reactive potential gives insight into the barrier for methane dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO +2H2, are of interest in hydrogen generation, and have the optimal stoichiometry for subsequent utilization in synthetic fuel production (Fischer-Tropsch or methanol synthesis). Moreover, under the reaction conditions explored, no CO2 was detected, i.e., the reaction proceeded with the production of very little, if any, unwanted greenhouse gas by-products. These findings demonstrate the efficacy of overcoming the limitations of purely thermal reaction mechanisms by coupling nonthermal mechanistic steps, leading to efficient C-H bond activation with subsequent thermal heterogeneous reactions.

Gibson, K. D.; Viste, M.; Sibener, S. J.

2006-10-01

336

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

NASA Technical Reports Server (NTRS)

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.

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

337

Understanding selectivity in the oxidative addition of the carbon-sulfur bonds of 2-cyanothiophene to Pt(0).  

PubMed

The reaction of 2-cyanothiophene with a zerovalent platinum bisalkylphosphine fragment yields two thiaplatinacycles derived from the cleavage of the substituted and unsubstituted C-S bonds. While cleavage away from the cyano group is preferred kinetically, cleavage adjacent to the cyano group is preferred thermodynamically. Density functional theory using B3LYP level of theory on a model of this system is consistent with experimental results in that the transition state energy leading to the formation of the kinetically favored C-S bond cleavage product is lower by 5.3 kcal mol(-1) than the barrier leading to the thermodynamically favored product. There is a 6.7 kcal mol(-1) difference between these two products. The cyano substituent at the 2- position of thiophene did not substantially change the mechanism involved in the C-S bond cleavage of thiophene previously reported. PMID:18447341

Ate?in, Tülay A; Ate?in, Abdurrahman C; Skugrud, Karlyn; Jones, William D

2008-06-01

338

Reaction of tungsten carbide with oxides of refractory metals in a vacuum  

Microsoft Academic Search

An investigation was made into the kinetics of the reaction of tungsten carbide with niobium, tantalum, vanadium, titanium, chromium, and zirconium oxides. Low-carbon alloys of tungsten with niobium, tantalum, chromium, and vanadium were produced. A method of preparing refractory alloys, using an oxide-carbide mixture as an intermediate product, has been proposed.

G. P. Shveikin

1962-01-01

339

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

Microsoft Academic Search

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%)

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

1997-01-01

340

AQUEOUS-PHASE OXIDATION OF SLUDGE USING THE VERTICAL REACTION VESSEL SYSTEM  

EPA Science Inventory

The overall objective of the study was to provide plant-scale operating data on the wet-oxidation of municipal wastewater sludge utilizing the Vertical Reaction Vessel System and the effect of the return flow from the wet-oxidation process on the operation of the wastewater treat...

341

Ceramic oxide reactions with V2O5 and SO3  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

342

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

E-print Network

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 (bc1: (i) the formed semiquinone anion remains bound to the reduced FeS domain and impedes its undocking

Steinhoff, Heinz-Jürgen

343

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...

344

Mixed valency in cerium oxide crystallographic phases: Determination of valence of the different cerium sites by the bond valence method  

Microsoft Academic Search

We have applied the bond valence method to cerium oxides to determine the\\u000aoxidation states of the Ce ion at the various site symmetries of the crystals.\\u000aThe crystals studied include cerium dioxide and the two sesquioxides along with\\u000asome selected intermediate phases which are crystallographically well\\u000acharacterized. Our results indicate that cerium dioxide has a mixed-valence\\u000aground state with

E. Shoko; M. F. Smith; Ross H. McKenzie

2008-01-01

345

Recent advances in the synthetic and mechanistic aspects of the ruthenium-catalyzed carbon-heteroatom bond forming reactions of alkenes and alkynes*  

PubMed Central

The group’s recent advances in catalytic carbon-to-heteroatom bond forming reactions of alkenes and alkynes are described. For the C–O bond formation reaction, a well-defined bifunctional ruthenium-amido catalyst has been successfully employed for the conjugate addition of alcohols to acrylic compounds. The ruthenium-hydride complex (PCy3)2(CO)RuHCl was found to be a highly effective catalyst for the regioselective alkyne-to-carboxylic acid coupling reaction in yielding synthetically useful enol ester products. Cationic ruthenium-hydride catalyst generated in-situ from (PCy3)2(CO)RuHCl/HBF4·OEt2 was successfully utilized for both the hydroamination and related C–N bond forming reactions of alkenes. For the C–Si bond formation reaction, regio- and stereoselective dehydrosilylation of alkenes and hydrosilylation of alkynes have been developed by using a well-defined ruthenium-hydride catalyst. Scope and mechanistic aspects of these carbon-to-heteroatom bond-forming reactions are discussed. PMID:21278832

Yi, Chae S.

2010-01-01

346

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

NASA Technical Reports Server (NTRS)

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).

Freihaut, B.; Raff, L. M.

1973-01-01

347

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

Microsoft Academic Search

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

James P. Ferris; Kamaluddin

1989-01-01

348

Sigma-bond metathesis reactions of Sc(OCD3)2 with water, ethanol, and 1-propanol: measurements of equilibrium constants,  

E-print Network

Sigma-bond metathesis reactions of Sc(OCD3)2 with water, ethanol, and 1-propanol: measurements the reactions of Sc(OCD3)2 with water, ethanol, and 1-propanol. Sigma-bond metathesis resulting 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

Goddard III, William A.

349

Development of a redox-free Mitsunobu reaction exploiting phosphine oxides as precursors to dioxyphosphoranes.  

PubMed

The development of the first redox-free protocol for the Mitsunobu reaction is described. This has been achieved by exploiting triphenylphosphine oxide--the unwanted by-product in the conventional Mitsunobu reaction--as the precursor to the active P(V) coupling reagent. Multinuclear NMR studies are consistent with hydroxyl activation via an alkoxyphosphonium salt. PMID:24871529

Tang, Xiaoping; Chapman, Charlotte; Whiting, Matthew; Denton, Ross

2014-07-14

350

Journal of Power Sources 167 (2007) 265271 Simultaneous oxygen-reduction and methanol-oxidation reactions  

E-print Network

Journal of Power Sources 167 (2007) 265­271 Simultaneous oxygen-reduction and methanol-reduction reaction (ORR) and methanol- oxidation reaction (MOR) at the cathode of a DMFC. Good agreements between a significant poisoning effect on the ORR by the presence of methanol at the cathode. The results also indicated

Zhao, Tianshou

351

Reactions of Polycarbonate with Cyclohexene Oxide and Phosphites: A Density Functional Study  

E-print Network

Reactions of Polycarbonate with Cyclohexene Oxide and Phosphites: A Density Functional Study J bisphenol A polycarbonate (BPA-PC). We describe density functional (DF) calculations of the reactions to organic molecules and polymers, focusing on bisphenol A polycarbonate (BPA-PC). BPA-PC is an important

352

Design and Synthesis of Chiral Zn2+ Complexes Mimicking Natural Aldolases for Catalytic C–C Bond Forming Reactions in Aqueous Solution  

PubMed Central

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

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

2014-01-01

353

Process of forming catalytic surfaces for wet oxidation reactions  

NASA Technical Reports Server (NTRS)

A wet oxidation process was developed for oxidizing waste materials, comprising dissolved ruthenium salt in a reactant feed stream containing the waste materials. The feed stream is introduced into a reactor, and the reactor contents are then raised to an elevated temperature to effect deposition of a catalytic surface of ruthenium black on the interior walls of the reactor. The feed stream is then maintained in the reactor for a period of time sufficient to effect at least partial oxidation of the waste materials.

Jagow, R. B. (inventor)

1977-01-01

354

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

PubMed Central

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

2013-01-01

355

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

E-print Network

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 ...

Miller, Karen M. (Karen Marie)

2005-01-01

356

In?situ observation of surface species on iridium oxide nanoparticles during the oxygen evolution reaction.  

PubMed

An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in?situ by ambient-pressure X-ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from Ir(IV) to Ir(V) that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH-mediated deprotonation mechanism. PMID:24889896

Sanchez Casalongue, Hernan G; Ng, May Ling; Kaya, Sarp; Friebel, Daniel; Ogasawara, Hirohito; Nilsson, Anders

2014-07-01

357

Hydroxyl radical recycling in isoprene oxidation driven by hydrogen bonding and hydrogen tunneling: the upgraded LIM1 mechanism.  

PubMed

The Leuven isoprene mechanism, proposed earlier to aid in rationalizing the unexpectedly high hydroxyl radical (OH) concentrations in isoprene-rich, low-nitric-oxide (NO) regions ( Peeters ; et al. Phys. Chem. Chem. Phys . 2009 , 11 , 5935 ), is presented in an upgraded and extended version, LIM1. The kinetics of the crucial reactions in the proposed isoprene-peroxy radical interconversion and isomerization pathways are re-evaluated theoretically, on the basis of energy barriers computed at the much higher CCSD(T)/aug-cc-pVTZ//QCISD/6-311G(d,p) level of theory, and using multiconformer partition functions obtained at the M06-2X/6-311++G(3df,2p) level that, different from the B3LYP level used in our earlier work, accounts for the crucial London dispersion effects in the H-bonded systems involved. The steady-state fraction of the specific Z-?-OH-peroxy radical isomers/conformers that can isomerize by a 1,6-H shift is shown to be largely governed by hydrogen-bond strengths, whereas their isomerization itself is found to occur quasi-exclusively by hydrogen atom tunneling. The isomer-specific Z-?-OH-peroxy 1,6-H-shift rate coefficients are predicted to be of the order of 1 s(-1) at 298 K, but the experimentally accessible bulk rate coefficients, which have to be clearly distinguished from the former, are 2 orders of magnitude lower due to the very low Z-?-OH-peroxy steady-state fractions that are only around or below 0.01 at low to moderate NO and depend on the peroxy lifetime. Two pathways subsequent to the peroxy radical 1,6-H shift are identified, the earlier predicted route yielding the photolabile hydroperoxy-methylbutenals (HPALDs), and a second, about equally important path, to dihydroperoxy-carbonyl peroxy radicals (di-HPCARP). Taking this into account, our predicted bulk peroxy isomerization rate coefficients are about a factor 1.8 higher than the available experimental results for HPALD production ( Crounse ; et al. Phys. Chem. Chem. Phys. 2011 , 13 , 13607 ), which is within the respective uncertainty margins. We also show that the experimental temperature dependence of the HPALD production rates as well as the observed kinetic isotope effect for per-deuterated isoprene support quantitatively our theoretical peroxy interconversion rates. Global modeling implementing LIM1 indicates that on average about 28% of the isoprene peroxys react via the 1,6-H-shift isomerization route, representing 100-150 Tg carbon per year. The fast photolysis of HPALDs we proposed earlier as primary OH regeneration mechanism ( Peeters and Muller . Phys. Chem. Chem. Phys . 2010 , 12 , 14227 ) found already experimental confirmation ( Wolfe ; et al. Phys. Chem. Chem. Phys. 2012 , 14 , 7276 ); based on further theoretical work in progress, reaction schemes are presented of the oxy coproduct radicals from HPALD photolysis and of the di-HPCARP radicals from the second pathway following peroxy isomerization that are both expected to initiate considerable additional OH recycling. PMID:25010574

Peeters, Jozef; Müller, Jean-François; Stavrakou, Trissevgeni; Nguyen, Vinh Son

2014-09-25

358

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...

359

Water-medium and solvent-free organic reactions over a bifunctional catalyst with Au nanoparticles covalently bonded to HS/SO3H functionalized periodic mesoporous organosilica.  

PubMed

An operationally simple approach for the preparation of a new class of bifunctional Au nanoparticle-acid catalysts has been developed. In situ reduction of Au(3+) with HS-functionalized periodic mesoporous organosilicas (PMOs) creates robust, fine Au nanoparticles and concomitantly produces a sulfonic acid moiety strongly bonded to PMOs. Characterizations of the nanostructures reveal that Au nanoparticles are formed with uniformed, narrow size distribution around 1-2 nm, which is very critical for essential catalytic activities. Moreover, the Au nanoparticles are mainly attached onto the pore surface rather than onto the outer surface with ordered mesoporous channels, allowing for maximal exposure to reaction substrates while minimizing Au nanoparticle leaching. Their higher S(BET), V(P), and D(P) than either the Au-HS-PMO(Et) or the Au/SO(3)H-PMO(Et) render the catalyst with comparably even higher catalytic efficiency than its homogeneous counterparts. Furthermore, the unique amphiphilic compartment of the Au-HS/SO(3)H-PMO(Et) nanostructures enables organic reactions to proceed efficiently in a pure aqueous solution without using any organic solvents or even without water. As demonstrated experimentally, remarkably, the unique bifunctional Au-HS/SO(3)H-PMO(Et) catalyst displays higher efficiencies in promoting water-medium alkyne hydration, intramolecular hydroamination, styrene oxidation, and three-component coupling reactions and even the solvent-free alkyne hydration process than its homogeneous catalysts. The robust catalyst can be easily recycled and used repetitively at least 10 times without loss of catalytic efficiency. These features render the catalyst particularly attractive in the practice of organic synthesis in an environmentally friendly manner. PMID:21707062

Zhu, Feng-Xia; Wang, Wei; Li, He-Xing

2011-08-01

360

Reaction of oleic acid particles with NO3 radicals: Products, mechanism, and implications for radical-initiated organic aerosol oxidation.  

PubMed

The heterogeneous reaction of liquid oleic acid aerosol particles with NO3 radicals in the presence of NO2, N2O5, and O2 was investigated in an environmental chamber using a combination of on-line and off-line mass spectrometric techniques. The results indicate that the major reaction products, which are all carboxylic acids, consist of hydroxy nitrates, carbonyl nitrates, dinitrates, hydroxydinitrates, and possibly more highly nitrated products. The key intermediate in the reaction is the nitrooxyalkylperoxy radical, which is formed by the addition of NO3 to the carbon-carbon double bond and subsequent addition of O2. The nitrooxyalkylperoxy radicals undergo self-reactions to form hydroxy nitrates and carbonyl nitrates, and may also react with NO2 to form nitrooxy peroxynitrates. The latter compounds are unstable and decompose to carbonyl nitrates and dinitrates. It is noteworthy that in this reaction nitrooxyalkoxy radicals appear not to be formed, as indicated by the absence of the expected products of decomposition or isomerization of these species. This is different from gas-phase alkene-NO3 reactions, in which a large fraction of the products are formed through these pathways. The results may indicate that, for liquid organic aerosol particles in low NOx environments, the major products of the radical-initiated oxidation (including by OH radicals) of unsaturated and saturated organic compounds will be substituted forms of the parent compound rather than smaller decomposition products. These compounds will remain in the particle and can potentially enhance particle hygroscopicity and the ability of particles to act as cloud condensation nuclei. PMID:16526637

Docherty, Kenneth S; Ziemann, Paul J

2006-03-16

361

Reaction network and kinetics for the catalytic oxidation of toluene over V sub 2 O sub 5  

SciTech Connect

The oxidation of three methyl-diphenylmethane isomers and of bibenzyl, benzyl alcohol, and benzaldehyde, which are intermediates in the catalytic oxidation of toluene over V{sub 2}O{sub 5}, has been studied to elucidate the reaction network and relative importance of various reactions. Selectivity dependences reveal that the network is composed mainly of three parallel reaction routes: (1) side-chain oxidation with consecutive reactions, (2) oxidative coupling with both parallel and consecutive reactions, and (3) carbon oxide formation. Coupling products are not negligible, with an initial selectivity of 29% (400{degree}C). Anthraquinone is produced mainly from o-methyl-diphenylmethane conditions and catalyst used. Selectivity dependences suggested product lumping and a simplified network. Kinetic analysis of this reaction network indicates that higher temperatures favor route 2 over route 1. The same initial intermediates for route 1 of side-chain oxidation and for route 2 of oxidative coupling are suggested.

Zhu, J.; Andersson, L.T. (Univ. of Lund (Sweden))

1990-11-01

362

Identification of nitriding mechanisms in high purity reaction bonded silicon nitride  

SciTech Connect

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.

Haggerty, J.S.

1993-03-01

363

Identification of nitriding mechanisms in high purity reaction bonded silicon nitride  

SciTech Connect

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.

Haggerty, J.S.

1993-03-01

364

Intramolecular c?n bond activation and ring-expansion reactions of N-heterocyclic carbenes.  

PubMed

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

Hemberger, Patrick; Bodi, Andras; Berthel, Johannes H J; Radius, Udo

2015-01-19

365

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

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.

Markus B Blatz; Avishai Sadan; Javier Martin; Brien Lang

2004-01-01

366

The carbon monoxide oxidation reaction over controlled catalyst structures based on gold\\/cerium dioxide thin films  

Microsoft Academic Search

Gold-based catalysts have attracted significant research interest due to their remarkably high activity for many important reactions, including the low-temperature CO oxidation reaction. Despite extensive studies, several fundamental issues in the understanding of CO oxidation over supported gold catalysts are unresolved. The locus and nature of active sites, including the role of the metal, metal oxide support, and their interface,

Zheng Zhou

2010-01-01

367

Determination of carbon by the oxidation reduction reaction with chromium  

NASA Technical Reports Server (NTRS)

Free carbon was determined in silicon and boron carbides in ash, oxides, and other materials by oxidation to carbon dioxide with a mixture of K2Cr2O7 + H2SO4. The determination was made from the amount of CR(6) consumed, by adding excess Mohr's salt and titrating with a standard solution of KMnO4. The amount of Cr(6) self reduced was determined in a blank test. Optimum oxidation and conditions were achieved when the volumes of 5% k2Cr2Oz and H2SO4 were equal. The mixture was boiled for 1-2 hours using a reflex condenser. The volume should not be reduced, in order to avoid an increase in the sulfuric acid concentration. The relative error was 4-7% for 0.005-0.04 g C and less than or equal to 3.5% for 0.1 g C.

Mashkovich, L.; Kuteynikov, A. F.

1978-01-01

368

Low interface defect density of atomic layer deposition BeO with self-cleaning reaction for InGaAs metal oxide semiconductor field effect transistors  

SciTech Connect

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.

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

369

Two-site Model for Aluminum Oxide with Mass Balanced Competitive pH+Salt/Salt Dependent Reactions1  

E-print Network

Two-site Model for Aluminum Oxide with Mass Balanced Competitive pH+Salt/Salt Dependent Reactions1 surface sites, (ii)pH+salt-dependent reactions (H+ andCl~, 2OH~, or Na+ and OH"),(iii)competitive salt-site model for alu- minum oxide with mass balanced competitive pH+salt/salt depen- dent reactions. Soil Sci

Sparks, Donald L.

370

The high-temperature oxidation, reduction, and volatilization reactions of silicon and silicon carbide  

Microsoft Academic Search

A thermochemical analysis was made of the oxidation, reduction, and volatilization reactions which occur in the Si-O-C system. One characteristic feature is the high SiO(g) and SiO(g) + CO(g) pressures at the Si(s)-SiO2 and SiC(s)-SiO2(s) interfaces. Active oxidation with weight losses and passive oxidation with weight gains were found on oxidizing Si(s) and SiC(s) in low oxygen pressures above 1000°C.

Earl A. Gulbransen; Sven A. Jansson

1972-01-01

371

The Shono-type electroorganic oxidation of unfunctionalised amides. Carbon–carbon bond formation via electrogenerated N-acyliminium ions  

PubMed Central

Summary N-acyliminium ions are useful reactive synthetic intermediates in a variety of important carbon–carbon bond forming and cyclisation strategies in organic chemistry. The advent of an electrochemical anodic oxidation of unfunctionalised amides, more commonly known as the Shono oxidation, has provided a complementary route to the C–H activation of low reactivity intermediates. In this article, containing over 100 references, we highlight the development of the Shono-type oxidations from the original direct electrolysis methods, to the use of electroauxiliaries before arriving at indirect electrolysis methodologies. We also highlight new technologies and techniques applied to this area of electrosynthesis. We conclude with the use of this electrosynthetic approach to challenging syntheses of natural products and other complex structures for biological evaluation discussing recent technological developments in electroorganic techniques and future directions. PMID:25670975

2014-01-01

372

In Pursuit of an Ideal C-C Bond-Forming Reaction  

PubMed Central

Attempts to introduce the highly versatile vinyl group into other organic molecules in a chemo-, regio- and stereoselective fashion via catalytic activation of ethylene provided challenging opportunities to explore new ligand and salt effects in homogeneous catalysis. This review provides a personal account of the development of enantioselective reactions involving ethylene. PMID:19606231

RajanBabu, T. V.

2009-01-01

373

Liquid-phase reaction-bonding of silicon carbide using alloyed silicon-molybdenum melts  

Microsoft Academic Search

The authors have investigated reaction-forming of silicon carbide by the infiltration of carbonaceous preforms using alloyed silicon melts, in order to synthesize composite materials free of the residual silicon phase that has previously limited mechanical properties and upper use temperatures. In this approach, rejection of the alloying component(s) from the primary silicon carbide phase into the remaining melt results in

Robert P. Messner; Yet-Ming Chiang

1990-01-01

374

Theoretical study of reactions of HO{sub 2} in low-temperature oxidation of benzene  

SciTech Connect

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)

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

375

Oxidative degradation of sulfathiazole by Fenton and photo-Fenton reactions.  

PubMed

This article presents experimental results on 47 ?mol L(-1) sulfathiazole (STZ) degradation by Fenton and photo-Fenton reactions using multivariate analysis. The optimal experimental conditions for reactions were obtained by Response Surface Methodology (RSM). In the case of the Fenton reactions there were 192 ?mol L(-1) ferrous ions (Fe(II)) and 1856 ?mol L(-1) hydrogen peroxide (H2O2), as compared with 157 ?mol L(-1) (Fe(II)) and 1219 ?mol L(-1) (H2O2) for photo-Fenton reactions. Under these conditions, around 90% of STZ degradation were achieved after 8 minutes treatment by Fenton and photo-Fenton reactions, respectively. Moreover, a marked difference was observed in the total organic carbon (TOC) removal after 60-min treatment, achieving 30% and 75% for the Fenton and photo-Fenton reactions, respectively. Acetic, maleic, succinic and oxamic acids could be identified as main Fenton oxidation intermediates. A similar pattern was found in the case of photo-Fenton reaction, including the presence of oxalic acid and ammonia at short periods of irradiation with UV-A. The calculated values of Average Oxidation State (AOS) corroborate the formation of oxidized products from the initial steps of the reaction. PMID:24521411

Velásquez, Marizú; Santander, I Paola; Contreras, David R; Yáñez, Jorge; Zaror, Claudio; Salazar, Ricardo A; Pérez-Moya, Montserrat; Mansilla, Héctor D

2014-01-01

376

Kinetic mechanism of reaction between TT-phfase niobium oxide and carbon tetrachloride (CCI{sub 4})  

SciTech Connect

The kinetic mechanism of reaction between TT-phase niobium oxide and carbon tetrachloride (CC1{sub 4}) at low (453 K) and high (above 573 K) temperatures was investigated. The reaction of the TT-phase niobium oxide with CC1{sub 4} at 453 K was controlled by the diffusion of CC1{sub 4} through the outer layer of the reaction product, NbOC1{sub 3}, formed around the surface. For the reaction at temperatures above 573 K, the chemical reaction on the surface of the niobium oxide controls the total reaction rate due to the disappearance of the layer of NbOCl{sub 3}.

Ebitani, Kohki; Hirano, Yoshiaki; Morikawa, Akira [Tokyo Institute of Tetchnology (Japan)

1995-07-01

377

Effects of thermal cycling on thermal expansion and mechanical properties of SiC fiber-reinforced reaction-bonded Si3N4 composites  

Microsoft Academic Search

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.

R. T. Bhatt; A. R. Palczer

1994-01-01

378

Effects of thermal cycling on thermal expansion and mechanical properties of SiC fiber-reinforced reaction-bonded Si3N4 composites. Technical memo  

Microsoft Academic Search

Thermal expansion curves for SiC fiber-reinforced reaction-bonded Si3N4 matrix composites (SiC\\/RBSN) and unreinforced RBSN were measured from 25 to 1400 deg 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

R. T. Bhatt; A. R. Palczer

1994-01-01

379

The dehalogenation reaction of organic halides by tributyltin radical: The energy of activation vs. the BDE of the C?X bond  

Microsoft Academic Search

The energy of activation (Ea) of the dehalogenation reaction induced by Bu3Sn was measured for some aryl, alkyl and benzyl halides. BDE values of the C?X bond undergoing homolysis were obtained from thermochemical cycles, and correlated with the Ea values. No major effect due to the polarity of the C?X bond was found. Durene derivatives showed a buttressing effect. A

Carlo Galli; Tullia Pau

1998-01-01

380

Adaptation of a Small-Molecule Hydrogen-Bond Donor Catalyst to an Enantioselective Hetero-Diels–Alder Reaction Hypothesized for Brevianamide Biosynthesis  

PubMed Central

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

2015-01-01

381

Metal catalyzed carbonylation and oxidation- reduct ion reactions  

Microsoft Academic Search

By the use of rhodium, rhenium, or palladium complexes as cata- lysts, and cyclodextrins or polyethylene glycols as phase transfer cata- lysts, the s elective reduction or oxidation o f carbonyl compounds, as well as t he s ynthesis of t he latter from olefins, occurs under remarkably mild conditions. olefins, epoxides and thiiranes to acids, esters, and lactones are

Howard Alper

1988-01-01

382

Adsorption and reaction of NO on oxidized and reduced SrTiO3(100) surfaces  

NASA Astrophysics Data System (ADS)

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.

Azad, S.; Szanyi, J.; Peden, C. H. F.; Wang, L.-Q.

2003-07-01

383

Adsorption and Reaction of NO on Oxidized and Reduced SrTiO{sub 3} (100) Surfaces  

SciTech Connect

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.

Azad, Samina; Szanyi, Janos; Peden, Charles HF.; Wang, Li Q.

2003-07-01

384

Iron oxide mineral-water interface reactions studied by AFM  

SciTech Connect

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.

Hawley, M.E.; Rogers, P.S.Z.

1994-07-01

385

Processing and properties of SiC whisker- and particulate-reinforced reaction bonded Si3N4  

SciTech Connect

The microstructure and mechanical properties of reaction bonded Si3N4 (RBSN) reinforced with SiC whiskers of particles were investigated using RBSN composites made from colloidally pressed octanol dispersions of high-purity Si powders mixed with either SiC whiskers or alpha-SiC particles. Results of investigations, revealing high conversions of Si to Si3N4, specific surface areas, and constant relative densities and strengths, showed that the uniform microstructure and small flaw size of the matrix were maintained in the composites and that no degradation of the reinforcements was taking place. Neither the monolithic nor the composite materials exhibited R-curve behavior. A modest increase in fracture toughness was observed only in the RBSN containing 33 vol pct SiC(p). 37 refs.

Lightfoot, A.; Ewart, L.; Haggerty, J.; Cai, Z.Q.; Ritter, J.; Nair, S.

1991-08-01

386

Processing and properties of SiC whisker- and particulate-reinforced reaction bonded Si3N4  

NASA Technical Reports Server (NTRS)

The microstructure and mechanical properties of reaction bonded Si3N4 (RBSN) reinforced with SiC whiskers of particles were investigated using RBSN composites made from colloidally pressed octanol dispersions of high-purity Si powders mixed with either SiC whiskers or alpha-SiC particles. Results of investigations, revealing high conversions of Si to Si3N4, specific surface areas, and constant relative densities and strengths, showed that the uniform microstructure and small flaw size of the matrix were maintained in the composites and that no degradation of the reinforcements was taking place. Neither the monolithic nor the composite materials exhibited R-curve behavior. A modest increase in fracture toughness was observed only in the RBSN containing 33 vol pct SiC(p).

Lightfoot, A.; Ewart, L.; Haggerty, J.; Cai, Z. Q.; Ritter, J.; Nair, S.

1991-01-01

387

Mechanical properties of SiC fiber-reinforced reaction-bonded Si3N4 composites  

NASA Technical Reports Server (NTRS)

The room temperature mechanical and physical properties of silicon carbide fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) have been evaluated. The composites contained 23 and 40 volume fraction of aligned 140 micro m diameter chemically vapor deposited SiC fibers. Preliminary results for composite tensile and bend strengths and fracture strain indicate that the composites displayed excellent properties when compared with unreinforced RBSN of comparable porosity. Fiber volume fraction showed little influence on matrix first cracking strain but did influence the stressed required for matrix first cracking and for ultimate composite fracture strength. It is suggested that by reducing matrix porosity and by increasing the volume fraction of the large diameter SiC fiber, it should be possible to further improve the composite stress at which the matrix first cracks.

Bhatt, Ramakrishna T.

1986-01-01

388

Syntheses and reactions of rhenium vinylidene and acetylide complexes. Unprecedented chirality transfer through a C identical with C triple bond  

SciTech Connect

Communication we describes (a) the facile synthesis of chiral rhenium vinylidene and acetylide complexes ((eta-C/sub 5/H/sub 5/)Re(NO)(PPh/sub 3/)(==C identical with CRR'))/sup +/X/sup -/ (1) and (eta-C/sub 5/H/sub 5/)Re(NO)(PPh/sub 3/)(C identical with CR) (2) R,R' = H, CH/sub 3/, C/sub 6/H/sub 5/), (b) unique observation of geometric isomerism in vinylidene complexes, (c) the thermal and photochemical interconversion of these isomers, (d) energy barriers associated with these isomerizations, and (e) sterospecific reactions of acetylide complexes 2 that entail transfer of the metal chirality through a C==C triple bond of formal cylindrical symmetry.

Wong, A.; Gladysz, J.A.

1982-09-08

389

Influence of prebonding cleaning on the electrical properties of the buried oxide of bond-and-etchback silicon-on-insulator materials  

NASA Astrophysics Data System (ADS)

Three different groups of metal-oxide-semiconductor devices were manufactured of bond-and-etchback silicon-on-insulator wafers where the buried oxide functioned as the gate dielectric. The groups differed in the procedure used to clean the surfaces prior to bonding and in the location of the bonded interface. The surfaces were cleaned using either the standard RCA cleaning procedure without HF dip or by rinsing in de-ionized water only. The location of the bonded interface was in the buried oxide or at its interface toward a silicon wafer. The RCA-cleaned devices with the bonded interface within the buried oxide were found to degrade severely under bias temperature stress. This degradation was evident from both oxide charging and an increase in the density of states at the Si/SiO2 interface for negative gate biases. For positive biases the most prominent effect was lateral nonuniform charging of the oxide. The lateral nonuniformities might be connected to voids formed by ammonia desorption during postbonding annealing. Devices rinsed in de-ionized water prior to bonding and devices with a homogeneous oxide showed only slight degradation after bias temperature stress. Electron injection by internal photoemission showed that the buried oxides contained electron traps with capture cross sections corresponding to Coulomb attractive traps. The different processing conditions did not affect the trap cross section but influenced the trap density Nt. Devices with the bonded interface within the buried oxide had Nt?1×1011 cm-2 in the case of RCA cleaning and Nt?4×1010 cm-2 for de-ionized water rinsing. The devices with a homogeneous oxide had Nt?4×109 cm-2. Electron trapping in the Coulomb attractive traps was accompanied by a corresponding increase in the density of states at the thermally grown Si/SiO2 interface for devices with a bonded buried oxide. SIMS investigations revealed a correlation between the degradation upon stress and hydrogen concentration in the devices with bonded oxides.

Ericsson, Per; Bengtsson, Stefan; Södervall, Ulf

1995-09-01

390

40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...  

Code of Federal Regulations, 2012 CFR

...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...

2012-07-01

391

40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...  

Code of Federal Regulations, 2013 CFR

...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...

2013-07-01

392

40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...  

Code of Federal Regulations, 2014 CFR

...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...

2014-07-01

393

Synthesis of Morphology Controlled Aluminum Oxide by Hydrothermal Reaction  

NASA Astrophysics Data System (ADS)

Plate-like and wire-like aluminum oxides were successfully synthesized by hydrothermal method without any template additives. Al(NO3)3·9H2O aqueous solution and precipitator were mixed and introduced to a Teflon lined autoclave, followed by heat treatment at 200°C for 24 h. By controlling the concentration of starting material and precipitator, the products with different morphologies were selectively obtained, i.e., the 2-dimensional platelike particles with a diameter of about 8?m were synthesized at low aluminum concentration (0.1 mol/L), while 1-dimensional wire-like products of about 10?m in length were synthesized at high aluminum concentration (0.2 mol/L). The plate-like particles and wire-like particles consisted of single phase of aluminum oxide hydroxide (boehmite, AlOOH) and the sodium aluminate, respectively.

Yang, L.; Yin, S.; Sato, T.

2011-10-01

394

biochemical reaction mechanisms in sulfur oxidation by chemosynthetic bacteria  

Microsoft Academic Search

Summary  Aspects of the biochemistry of the oxidation of inorganic sulfur compounds are discussed in thiobacilli but chiefly inThiobacillus denitrificans. Almost all of the thiobacilli (e.g. T. denitrificans, T. neapolitanus, T. novellus, andThiobacillus A\\u000a 2) were capable of producing approximately 7.5 moles of sulfuric acid aerobically from 3.75 moles of thiosulfate per gram of\\u000a cellular protein per hr. By far the

M. I. H. Aleem

1975-01-01

395

Characterization of transparent zinc oxide films prepared by electrochemical reaction  

Microsoft Academic Search

Transparent zinc oxide (ZnO) films have been grown by galvanostatic cathodic deposition onto conductive glasses from a simple aqueous zinc nitrate electrolyte maintained at 335 K. The as-deposited ZnO films were characterized with Fourier transform infrared absorption spectroscopy, x-ray diffraction, scanning electron microscopy, optical transmission and absorption studies, and measurement of sheet resistivity as a function of cathodic current density.

Masanobu Izaki; Takashi Omi

1997-01-01

396

Cyclic Voltammetric Preparation of Palladium Nanoparticles for Ethanol Oxidation Reaction  

E-print Network

to the limited resources of Pt,3 non-Pt-based catalysts used in the oxidation of small organic moleculesO-coated glassy carbon (GC) electrode for a few cycles with the potential swept from -1.0 to -1.2 V versus.4,5 Among those developed non-Pt-based catalysts, palladium (Pd) is thought to be the main Pt

Guo, John Zhanhu

397

Microstructures of brazed and solid-state diffusion bonded joints of tungsten with oxide dispersion strengthened steel  

NASA Astrophysics Data System (ADS)

The brazed and solid-state diffusion bonded (SSDB) joints of tungsten with oxide dispersion strengthened (ODS) steel were fabricated to use ODS steels as a structure component of first wall with tungsten as a plasma facing material in fusion blankets. Particular attention was paid to changes in the microstructure and chemical compositions in the bonding region. W was found to diffuse significantly into ODS steel, whereas there was only a limited diffusion of Fe and Cr from the ODS steel into W; these results are consistent with the diffusivity of each element. Interdiffusion multi-layer containing a layer with high concentration of B and of C was produced in the brazed joint and the SSDB joint, respectively.

Oono, Naoko; Noh, Sanghoon; Iwata, Noriyuki; Nagasaka, Takuya; Kasada, Ryuta; Kimura, Akihiko

2011-10-01

398

Bonding of nitride based LEDs on tin oxide templates for advanced optoelectronic devices  

SciTech Connect

A process for fabrication of flip chip LEDs based on SnO{sub 2}-GaN wafer bonding is reported. Typical LED characteristics have been measured and no detrimental effect of the bonding interface has been observed. The forward voltage at 20 mA is 3.96 V and differential resistance at 100 mA is as low as 16 ?.

Simeonov, D.; Tsai, M. Y.; Chen, H. T.; Weisbuch, C.; Speck, J. S.

2011-01-01

399

Oxidation of glycine by Phaseolus leghaemoglobin with associated catabolic reactions at the haem.  

PubMed Central

Leghaemoglobin from the root nodules of kidney bean (Phaseolus vulgaris) reacts in alkaline glycine solutions as a glycine oxidase in a reaction that may also be regarded as a coupled oxidation. Leghaemoglobin is reduced to the ferrous form by glycinate, the oxygen complex is formed, and finally the haem is attacked to yield a green reaction product. Glycine is simultaneously oxidized to glyoxylate, and hydrogen peroxide is generated. The initial velocity of the formation of the green product is proportional to the concentrations of leghaemoglobin and glycine, and the optimum pH for the reaction is 10.2. The green product is not formed if carbon monoxide, azide of imidazole is bound to the haem, whereas oxidation of glycine to glyoxylate is not inhibited by azide and not essentially by carbon monoxide. Haem breakdown is activated by digestion of leghaemoglobin by carboxypeptidase, and partly inhibited by catalase and superoxide dismutase. PMID:743243

Lehtovaara, P

1978-01-01

400

Oxidation of glycine by Phaseolus leghaemoglobin with associated catabolic reactions at the haem.  

PubMed

Leghaemoglobin from the root nodules of kidney bean (Phaseolus vulgaris) reacts in alkaline glycine solutions as a glycine oxidase in a reaction that may also be regarded as a coupled oxidation. Leghaemoglobin is reduced to the ferrous form by glycinate, the oxygen complex is formed, and finally the haem is attacked to yield a green reaction product. Glycine is simultaneously oxidized to glyoxylate, and hydrogen peroxide is generated. The initial velocity of the formation of the green product is proportional to the concentrations of leghaemoglobin and glycine, and the optimum pH for the reaction is 10.2. The green product is not formed if carbon monoxide, azide of imidazole is bound to the haem, whereas oxidation of glycine to glyoxylate is not inhibited by azide and not essentially by carbon monoxide. Haem breakdown is activated by digestion of leghaemoglobin by carboxypeptidase, and partly inhibited by catalase and superoxide dismutase. PMID:743243

Lehtovaara, P

1978-11-15

401

Process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers  

SciTech Connect

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.

Swallow, K.C.; Killilea, W.R.; Hong, G.T.; Bourhis, A.L.

1993-08-03

402

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

PubMed

Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000?h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue. PMID:25302630

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

2014-11-24

403

Metal-free oxidative C(sp(3))-H bond functionalization of alkanes and alkylation-initiated radical 1,2-aryl migration in ?,?-diaryl allylic alcohols.  

PubMed

An oxidative C(sp(3))-H bond functionalization of alkanes and alkylation-initiated radical 1,2-aryl migration in ?,?-diaryl allylic alcohols using di-tert-butyl peroxide (DTBP) as the oxidant was established, which tolerates a wide range of simple alkane substrates and ?,?-diaryl allylic alcohols for direct preparation of ?-aryl-?-alkylated carbonyl ketones. PMID:25415337

Zhao, Jincan; Fang, Hong; Song, Ruichun; Zhou, Jie; Han, Jianlin; Pan, Yi

2015-01-11

404

Elementary Steps of Syngas Reactions on Mo2C(001): Adsorption Thermochemistry and Bond Dissociation  

SciTech Connect

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.

Medford, Andrew

2012-02-16

405

Ultra-stable Molecule-Surface Architectures at Metal Oxides: Structure, Bonding, and Electron-transfer Processes  

SciTech Connect

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

Hamers, Robert John

2013-12-07

406

Copper(II)-coordinated organic nanotube: A novel heterogeneous catalyst for various oxidation reactions  

Microsoft Academic Search

Copper(II)-coordinated organic nanotube can function as a heterogeneous catalyst for oxidation of a variety of organic compounds in the presence of hydrogen peroxide and tert-butyl hydroperoxide. The morphology of this catalyst remained same before and after the oxidation reactions. The catalyst can be reused for several times. In the presence of hydrogen peroxide, Copper(II)-coordinated organic nanotube formed a stable brown

Tanmay Chattopadhyay; Masaki Kogiso; Masumi Asakawa; Toshimi Shimizu; Masaru Aoyagi

2010-01-01

407

Total synthesis of (+)-cis-sylvaticin: double oxidative cyclization reactions catalyzed by osmium.  

PubMed

The double oxidative cyclization of dienes is a viable procedure for making complex natural products containing cis-THF units. A double deprotection/double oxidative cyclization strategy using catalytic osmium tetroxide was used to construct the bisheterocyclic core of cis-sylvaticin and ultimately confirm its structure. The natural product was then prepared by a short sequence of reactions that is exceptionally concise: the final route being just 13 linear steps and 19 chemical operations in total. PMID:17044695

Donohoe, Timothy J; Harris, Robert M; Burrows, Jeremy; Parker, Jeremy

2006-10-25

408

The rapid and enhanced reduction of graphene oxide by microwave assisted acid catalyzed reaction.  

PubMed

We report a novel synthetic route to fabricate reduced graphene oxide (rGO) from graphene oxide (GO) using a microwave assisted acid catalyzed reaction in organic solvent. The obtained rGO in this study exhibited 4 times higher electrical conductivity, less oxygen content and better ordered structure than that of conventional solvothermally fabricated ones. By using microwave irradiation, high quality rGO can be obtained in several minutes. PMID:24245202

Tien, Huynh Ngoc; Luan, Van Hoang; Hoa, Le Thuy; Lee, Tae Kyu; Kong, Byung-Seon; Chung, Jin Suk; Kim, Eui Jung; Hur, Seung Hyun

2013-10-01

409

Hydrogen production reaction with a metal oxide catalyst in high pressure high temperature water  

Microsoft Academic Search

Hydrogen production from biomass was attempted in high pressure high temperature water at 573 K by adopting partial oxidation to increase the yield of H2 via CO production in the presence of ZnO. The results revealed that an addition of H2O2 as an oxidant to the reaction of glucose and sugarcane bagasse brought about the trend of increasing the yields

M. Watanabe; M. Takahashi; H. Inomata

2008-01-01

410

Fluorine hot atom oxidation of bismuth vapor. A comment on the evaluation of the BiF bond energy  

NASA Astrophysics Data System (ADS)

The energetics of the chemiluminescent reaction between bismuth dimers and fluorine atoms (T.C. Devore et al., Chem. Phys. 155 (1991) 423; 156 (1991) 156) has been evaluated to better refine a determination of the bismuth fluoride dissociation energy. By directly examining the spectrum of the SF 6 discharge used to generate the F atoms to establish the significant energy imparted to these dissociation products and by exploring F atom chemiluminescent reactions with known energetics, the F atom beam is established to have contributed a maximum of 0.8-0.9 eV to the chemiluminescent process. Based upon the observed population of the ?'=4 level of the BiF A0 + state resulting from the Bi 2 + F reaction, a BiF bond energy of 3.9 ± 0.2 eV is established. This value is slightly higher than a very recent evaluation of the BiF bond energy (Yoo et al., Chem. Phys. 166 (1992) 215) but disagrees with previous determinations in the literature. Many of the previous evaluations of the group 15 halide dissociation energies have been based on Birge—Sponer extrapolations. The data now available for BiF permits an evaluation of the nature of these extrapolations for this molecule. The limitations of these extrapolations and possible corrections for these shortcomings are presented.

Devore, T. C.; Gole, J. L.

1993-08-01

411

Direct formation of element chlorides from the corresponding element oxides through microwave-assisted carbohydrochlorination reactions.  

PubMed

A series of technically and economically important element chlorides-such as SiCl4, BCl3, AlCl3, FeCl2, PCl3 and TiCl4-was synthesized through reactions between hydrogen chloride and the corresponding element oxides in the presence of different carbon sources with microwave assistance. This process route was optimized for demonstration purposes for tetrachlorosilane formation and successfully demonstrates the broad applicability of various silicon oxide-containing minerals and materials for carbohydrochlorination. The chlorination reaction occurs at lower temperatures than with conventional heating in a tubular oven, with substantially shorter reaction times and in better yields: quantitatively in the case of tetrachlorosilane, based on the silicon content of the starting material. The experimental procedure is very simple and provides basic information about the suitability of element compounds, especially element oxides, for carbohydrochlorination. According to the general reaction sequence element oxide-->element-->element chloride used in today's technology, this one-step carbohydrochlorination with hydrogen chloride is considerably more efficient, particularly in terms of energy input and reaction times, avoiding the isolation of the pure elements required for chlorination to give the element chlorides with use of the more corrosive and toxic chlorine gas. PMID:18324655

Nordschild, Simon; Auner, Norbert

2008-01-01

412

Effect of surface treatment on the initial bond strength of different luting cements to zirconium oxide ceramic  

Microsoft Academic Search

The objective of this study was to compare the shear bond strength to zirconium oxide ceramic of adhesive-phosphate-monomer-containing\\u000a (APM) and non-APM-containing (nAPM) luting cements after different surface treatments. nAPM cements: Bifix QM, Dual Cement,\\u000a Duo Cement Plus, Multilink Automix, ParaCem Universal DC, PermaCem Smartmix, RelyX ARC, Variolink Ultra, and Variolink II;\\u000a APM cements: Panavia EX, Panavia F2.0, and RelyX UniCem.

F. P. Nothdurft; P. J. Motter; P. R. Pospiech

2009-01-01

413

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

NASA Astrophysics Data System (ADS)

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.

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

1989-09-01

414

Compounds producing the kreis color reaction with particular reference to oxidized milk fat  

Microsoft Academic Search

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

Stuart Patton; Mark Keeney; George W. Kurtz

1951-01-01

415

Kinetic and photochemical data for atmospheric chemistry reactions of the nitrogen oxides  

NASA Technical Reports Server (NTRS)

Data sheets for thermal and photochemical reactions of importance in the atmospheric chemistry of the nitrogen oxides are presented. For each reaction the available experimental data are summarized and critically evaluated, and a preferred value of the rate coefficient is given. The selection of the preferred value is discussed and an estimate of its accuracy is given. For the photochemical process, the data are summarized, and preferred for the photoabsorption cross section and primary quantum yields are given.

Hampson, R. F., Jr.

1980-01-01

416

Role of nitric oxide in brain regions related to defensive reactions  

Microsoft Academic Search

Nitric oxide synthase (NOS) positive neurons are located in most brain areas related to defensive reactions, including the dorsolateral periaqueductal grey (dlPAG). NOS inhibitors injected into this structure induce anxiolytic-like responses whereas NO donors promote flight reactions. Intra-dlPAG administration of carboxy-PTIO, a NO scavenger, or ODQ, a soluble guanylate cyclase inhibitor, produced anxiolytic-like effects on rats exposed to the elevated

F. S. Guimarães; V. Beijamini; F. A. Moreira; D. C. Aguiar; A. C. B. de Lucca

2005-01-01

417

Secondary Organic Aerosol Formation by Molecular-Weight Building Reactions of Biogenic Oxidation Products  

NASA Astrophysics Data System (ADS)

Understanding the chemical composition of atmospheric organic aerosols (OA) remains one of the significant challenges to accurately representing OA in air quality and climate models. Meeting this challenge will require further understanding of secondary organic aerosols (SOA), of which biogenic emissions are thought to be major precursors. Of recent interest is the significance of higher-molecular weight (MW) compounds (i.e., "oligomers"). Theoretical, laboratory, and field study results suggest that relatively volatile oxidation products may contribute to SOA formation through multi-phase MW- building reactions. The significance of such reactions for biogenic SOA formation, including for newly considered precursors such as isoprene, is explored in this work. Theoretical and field studies are employed to: 1) identify MW-building reactions that may contribute to SOA formation in the atmosphere, 2) identify MW-building reaction products in ambient samples, and 3) parameterize atmospheric SOA formation by MW-building reactions of biogenic oxidation products. Likely reactions of biogenic oxidation products include ester, amide, and peroxyhemiacetal formation. Each of the proposed reactions involves known oxidation productions of biogenic precursors (e.g., carboxylic acids and aldehydes) reacting with one another and/or other atmospheric constituents (e.g., sulfuric acid and ammonia) to form higher-MW/lower-volatility products that can condense to form SOA. It has been suggested that products of MW-building reactions can revert to the parent reactants during sampling and analysis. Thus, relatively volatile compounds detected in ambient particle samples in fact may be decomposition products of higher-MW products. The contribution of relatively volatile biogenic oxidation products to SOA via ester, amide, and peroxyhemiacetal formation, as determined by studies based on fundamental thermodynamics and gas/particle partitioning theory, will be discussed; in addition to evidence for such reactions based on field measurements. Finally, while the role of MW-building reactions in contributing to existing SOA has been considered previously, the role of such reactions in OA nucleation events also will be addressed.

Barsanti, K.; Guenther, A.; Matsunaga, S.; Smith, J.

2006-12-01

418

Stabilization and Characterization of a Heme-Oxy Reaction Intermediate in Inducible Nitric-oxide Synthase*S?  

PubMed Central

Nitric-oxide synthases (NOS) are heme-thiolate enzymes that N-hydroxylate l-arginine (l-Arg) to make NO. NOS contain a unique Trp residue whose side chain stacks with the heme and hydrogen bonds with the heme thiolate. To understand its importance we substituted His for Trp188 in the inducible NOS oxygenase domain (iNOSoxy) and characterized enzyme spectral, thermodynamic, structural, kinetic, and catalytic properties. The W188H mutation had relatively small effects on l-Arg binding and on enzyme heme-CO and heme-NO absorbance spectra, but increased the heme midpoint potential by 88 mV relative to wild-type iNOSoxy, indicating it decreased heme-thiolate electronegativity. The protein crystal structure showed that the His188 imidazole still stacked with the heme and was positioned to hydrogen bond with the heme thiolate. Analysis of a single turnover l-Arg hydroxylation reaction revealed that a new heme species formed during the reaction. Its build up coincided kinetically with the disappearance of the enzyme heme-dioxy species and with the formation of a tetrahydrobiopterin (H4B) radical in the enzyme, whereas its subsequent disappearance coincided with the rate of l-Arg hydroxylation and formation of ferric enzyme. We conclude: (i) W188H iNOSoxy stabilizes a heme-oxy species that forms upon reduction of the heme-dioxy species by H4B. (ii) The W188H mutation hinders either the processing or reactivity of the heme-oxy species and makes these steps become rate-limiting for l-Arg hydroxylation. Thus, the conserved Trp residue in NOS may facilitate formation and/or reactivity of the ultimate hydroxylating species by tuning heme-thiolate electronegativity. PMID:18815130

Tejero, Jesús; Biswas, Ashis; Wang, Zhi-Qiang; Page, Richard C.; Haque, Mohammad Mahfuzul; Hemann, Craig; Zweier, Jay L.; Misra, Saurav; Stuehr, Dennis J.

2008-01-01

419

Heterobifunctional PEG Ligands for Bioconjugation Reactions on Iron Oxide Nanoparticles  

PubMed Central

Ever since iron oxide nanoparticles have been recognized as promising scaffolds for biomedical applications, their surface functionalization has become even more important. We report the synthesis of a novel polyethylene glycol-based ligand that combines multiple advantageous properties for these applications. The ligand is covalently bound to the surface via a siloxane group, while its polyethylene glycol backbone significantly improves the colloidal stability of the particle in complex environments. End-capping the molecule with a carboxylic acid introduces a variety of coupling chemistry possibilities. In this study an antibody targeting plasminogen activator inhibitor-1 was coupled to the surface and its presence and binding activity was assessed by enzyme-linked immunosorbent assay and surface plasmon resonance experiments. The results indicate that the ligand has high potential towards biomedical applications where colloidal stability and advanced functionality is crucial. PMID:25275378

Bloemen, Maarten; Van Stappen, Thomas; Willot, Pieter; Lammertyn, Jeroen; Koeckelberghs, Guy; Geukens, Nick; Gils, Ann; Verbiest, Thierry

2014-01-01

420

Oxidation of thiocyanate by hydrogen peroxide - a reaction kinetic study by capillary electrophoresis.  

PubMed

The oxidation reaction kinetics of thiocyanate by excess hydrogen peroxide has been studied by using capillary electrophoresis. The paper illustrates for the first time the use of capillary electrophoresis in studying reaction kinetics and provides a non-laborious way to determine the rate law and the rate constant for the above reaction in the pH range 6-8. Standard solutions of thiocyanate were mixed with buffer solutions of different pHs (6-8) and the reactions were initiated by adding appropriate volumes of hydrogen peroxide in capillary electrophoresis vials. Each reaction mixture was sampled at regular time intervals using an automatic injection programme to follow the progress of the reaction and identify the reaction products. The peak areas, representing the products, were integrated and their concentrations were quantified using calibration plots. The concentration profiles obtained from a series of experiments at a particular pH were then used to determine the rate law and the rate constant for the reaction. Furthermore, the rate of decomposition of hypothiocyanite formed during the reaction is determined for the first time. The rate law is zero order with respect to hypothiocyanite and first order with respect to hydrogen peroxide. The results indicate that the rate law for the oxidation reaction is zero order with respect to thiocyanate and first order with respect to hydrogen peroxide. The rate constant for the reaction at 25 degrees C and at zero ionic strength is 3.6(+/-0.2)x10((-4)) min(-1). PMID:18967936

Christy, A A; Egeberg, P K

2000-05-01

421

Chemiluminescence spectra of the reaction products of gallium, indium and thallium vapors with nitrous oxide  

SciTech Connect

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.

Eliseev, M.V.; Koryazhkin, V.A.; Mal'tsev, A.A.; Popov, A.D.

1983-03-01

422

Oil as reaction medium for glycation, oxidation, denaturation, and aggregation of whey protein systems of low water activity.  

PubMed

Whey protein isolate (WPI)-oil (75:25) and WPI-oil-(glucose-fructose) (45:15:40) as models of high-protein systems containing either olive (OO) or sunflower oil (SO) were stored at 20 or 40 °C to investigate component interactions. The indicators of protein oxidation (carbonyl content) and aggregation (total sulfhydryl content) and heats of protein denaturation and aggregation were investigated. Highest levels of disulfide bonding and carbonyls in WPI-OO formed during the first 2 weeks of storage concomitantly with enhanced protein aggregation. WPI-OO and WPI-SO systems (prestorage) showed increased protein denaturation temperature. The WPI proteins showed higher heat sensitivity with OO or SO at 40 °C, and the system with OO showed preaggregated protein as found from decreased heats of protein aggregation. OO or SO in WPI-oil-(glucose-fructose) systems reduced heats of protein aggregation. Lipid oxidation products and nonenzymatic browning reactions in glucose-fructose-containing systems decreased the solubility of solids and increased protein aggregation, hydrophobicity, and hardening of structure. PMID:23517062

Potes, Naritchaya; Kerry, Joseph P; Roos, Yrjö H

2013-04-17

423

Structural and functional investigation of graphene oxide–Fe3O4 nanocomposites for the heterogeneous Fenton-like reaction  

PubMed Central

Graphene oxide–iron oxide (GO–Fe3O4) nanocomposites were synthesised by co-precipitating iron salts onto GO sheets in basic solution. The results showed that formation of two distinct structures was dependent upon the GO loading. The first structure corresponds to a low GO loading up to 10?wt%, associated with the beneficial intercalation of GO within Fe3O4 nanoparticles and resulting in higher surface area up to 409?m2 g?1. High GO loading beyond 10?wt% led to the aggregation of Fe3O4 nanoparticles and the undesirable stacking of GO sheets. The presence of strong interfacial interactions (Fe-O-C bonds) between both components at low GO loading lead to 20% higher degradation of Acid Orange 7 than the Fe3O4 nanoparticles in heterogeneous Fenton-like reaction. This behaviour was attributed to synergistic structural and functional effect of the combined GO and Fe3O4 nanoparticles. PMID:24699690

Zubir, Nor Aida; Yacou, Christelle; Motuzas, Julius; Zhang, Xiwang; Diniz da Costa, João C.

2014-01-01

424

Short-step synthesis of tamoxifen and its derivatives via the three-component coupling reaction and migration of the double bond  

Microsoft Academic Search

The anti-tumor agent, tamoxifen, is easily synthesized by the successive allylation of benzaldehyde and the Friedel–Crafts alkylation reaction of anisole with the intermediary homoallyl silyl ethers, followed by the migration of the double bond to form the desired tetra-substituted ethylenes. Several derivatives of tamoxifen are also produced according to a similar synthetic strategy.

Isamu Shiina; Masahiko Suzuki; Kazutoshi Yokoyama

2004-01-01

425

Kinetics, Thermodynamics, and Effect of BPh3 on Competitive C-C and C-H Bond Activation Reactions in the  

E-print Network

Kinetics, Thermodynamics, and Effect of BPh3 on Competitive C-C and C-H Bond Activation Reactions-H cleavage steps (larger Hq and positive Sq ). Addition of the Lewis acid BPh3 to 1 at low temperature yields exclusively the C-CN activation product (dippe)Ni(3 -allyl)(CNBPh3) (4). Independently prepared (dippe)Ni(crotononitrile-BPh

Jones, William D.

426

A cascade of acid-promoted C-O bond cleavage and redox reactions: from oxa-bridged benzazepines to benzazepinones.  

PubMed

A sequence of C-O bond cleavage and redox reactions in oxa-bridged azepines was realized under acid promoted conditions. This protocol provides an atom-economical and straightforward approach to access benzo[b]azepin-5(2H)-ones in high yields. The formal synthesis of tolvaptan was achieved by exploiting this new transformation. PMID:25397583

Zhang, Yuewei; Yang, Fengzhi; Zheng, Lianyou; Dang, Qun; Bai, Xu

2014-12-01

427

Bond cleavage reactions in oxygen and nitrogen heterocycles by a rhodium phosphine complex  

SciTech Connect

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.

Jones, W.D.; Dong, L.; Myers, A.W. (Univ. of Rochester, NY (United States))

1995-02-01

428

Influence of "Island-Like" Oxides in the Bond-Coat on the Stress and Failure Patterns of the Thermal-Barrier Coatings Fabricated by Atmospheric Plasma Spraying During Long-Term High Temperature Oxidation  

NASA Astrophysics Data System (ADS)

Thermal-barrier coatings (TBCs) are very important ceramic-coating materials due to their excellent performance at high temperature. The inner zone of the bond-coat is often easily endured oxidized (internal oxidation) in the process of thermal spraying and the long-time exposure to the high temperature, and the "island-like" oxides can be formed. Especially, when the bond-coat was fabricated by atmospheric plasma spraying (APS), this trend is more evident. In this paper, the stress distribution around the thermally grown oxide (TGO) has been calculated by the finite element method when the "island-like" oxides have been considered. The simulation results indicate that the maximum tensile stress and compressive stress existed in the TGO, and the existence of the "island-like" oxides will further decrease the maximum tensile stress level in the TGO. While the "island-like" oxides in the bond-coat will decrease the effective thickness of the TGO at the metallic layer/ceramic layer interface due to the oxidation of the metallic elements in the bond-coat. The crack propagation equation has been established and the failure mechanism of the TBC due to the formation and growth of the TGO has also been discussed in detail. The lifetime of the TBCs which have experienced high temperature oxidation has been predicted and the theoretical results agreed well with the experimental data.

Wang, L.; Zhao, Y. X.; Zhong, X. H.; Tao, S. Y.; Zhang, W.; Wang, Y.

2014-02-01

429