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Sample records for activated bonding sab

  1. A comparison study: Direct wafer bonding of SiC–SiC by standard surface-activated bonding and modified surface-activated bonding with Si-containing Ar ion beam

    NASA Astrophysics Data System (ADS)

    Mu, Fengwen; Iguchi, Kenichi; Nakazawa, Haruo; Takahashi, Yoshikazu; Fujino, Masahisa; He, Ran; Suga, Tadatomo

    2016-08-01

    In this study, the results of direct wafer bonding of SiC–SiC at room temperature by standard surface-activated bonding (SAB) and modified SAB with a Si-containing Ar ion beam were compared, in terms of bonding energy, interface structure and composition, and the effects of rapid thermal annealing (RTA) at 1273 K in Ar gas. Compared with that obtained by the standard SAB, the bonding interface obtained by the modified SAB with a Si-containing Ar ion beam is ∼30% stronger and almost completely recrystallized without oxidation during RTA, which should be due to the in situ Si compensation during surface activation by the Si-containing Ar ion beam.

  2. Silicon carbide wafer bonding by modified surface activated bonding method

    NASA Astrophysics Data System (ADS)

    Suga, Tadatomo; Mu, Fengwen; Fujino, Masahisa; Takahashi, Yoshikazu; Nakazawa, Haruo; Iguchi, Kenichi

    2015-03-01

    4H-SiC wafer bonding has been achieved by the modified surface activated bonding (SAB) method without any chemical-clean treatment and high temperature annealing. Strong bonding between the SiC wafers with tensile strength greater than 32 MPa was demonstrated at room temperature under 5 kN force for 300 s. Almost the entire wafer has been bonded very well except a small peripheral region and few voids. The interface structure was analyzed to verify the bonding mechanism. It was found an amorphous layer existed as an intermediate layer at the interface. After annealing at 1273 K in vacuum for 1 h, the bonding tensile strength was still higher than 32 MPa. The interface changes after annealing were also studied. The results show that the thickness of the amorphous layer was reduced to half after annealing.

  3. 77 FR 65176 - Science Advisory Board (SAB)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-25

    ... National Oceanic and Atmospheric Administration Science Advisory Board (SAB) AGENCY: Office of Oceanic and... (DOC). ACTION: Notice of open meeting. ] SUMMARY: The Science Advisory Board (SAB) was established by a..., education, and application of science to operations and information services. SAB activities and...

  4. 78 FR 16254 - (NOAA) Science Advisory Board (SAB)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-14

    ... National Oceanic and Atmospheric Administration (NOAA) Science Advisory Board (SAB) AGENCY: Office of... of Commerce (DOC). ACTION: Notice of open meeting. SUMMARY: The Science Advisory Board (SAB) was..., education, and application of science to operations and information services. SAB activities and...

  5. Low-temperature hermetic packaging for microsystems using Au-Au surface-activated bonding at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shin-ichi; Higurashi, Eiji; Suga, Tadatomo; Sawada, Renshi

    2012-05-01

    Low-temperature hermetic bonding based on surface activation is useful for optical microsystem packaging because high bonding temperatures may degrade microsystem performance and sensitivity. However, surface-activated bonding (SAB) is usually performed under ultra-high-vacuum conditions, and the bonding environment cannot be chosen freely. In this study, thin Au sealing rings (300-500 nm thick, and 100 μm wide) were used as bonding layers for SAB at atmospheric pressure. A sufficiently high die-shear strength was achieved via surface activation using an argon radio-frequency plasma treatment. On examination of the fracture surfaces of the broken seal after the die-shear test, we observed that the fractures typically occurred at the deposited interface or partially inside the bulk substrates. Hermeticity was evaluated by measuring the resonance characteristics of photothermally excited microcantilevers inside the cavities. The samples bonded at the low temperature of 150 °C under the application of a bonding pressure of 313 MPa for 30 s showed leakage rates of less than 5.0 × 10-9 Pa·m3 s-1, which is the rejection limit defined by the MIL-STD-883G specification.

  6. Effects of annealing on the electrical characteristics of GaAs/GaAs junctions by surface-activated bonding

    NASA Astrophysics Data System (ADS)

    Chai, Li; Liang, Jianbo; Shigekawa, Naoteru

    2016-06-01

    The electrical properties of GaAs/GaAs junctions fabricated by surface-activated bonding (SAB) and annealing were examined on the basis of the charge neutral level model. The potential barrier height, the density of interface states, and the charge neutral level at GaAs/GaAs interfaces were estimated from the measured dependences of the electrical conductance of n-GaAs/n-GaAs and p-GaAs/p-GaAs junctions on ambient temperature. The barrier height and the density of interface states were lowered by increasing the annealing temperature to 400 °C, which suggested that the damage introduced during the SAB process was partly reduced.

  7. 75 FR 38079 - National Oceanic and Atmospheric Administration (NOAA) Science Advisory Board (SAB)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-01

    ...The Science Advisory Board (SAB) was established by a Decision Memorandum dated September 25, 1997, and is the only Federal Advisory Committee with responsibility to advise the Under Secretary of Commerce for Oceans and Atmosphere on strategies for research, education, and application of science to operations and information services. SAB activities and advice provide necessary input to ensure......

  8. Development of Blocked-Impurity-Band-Type Ge Detectors Fabricated with the Surface-Activated Wafer Bonding Method for Far-Infrared Astronomy

    NASA Astrophysics Data System (ADS)

    Hanaoka, M.; Kaneda, H.; Oyabu, S.; Yamagishi, M.; Hattori, Y.; Ukai, S.; Shichi, K.; Wada, T.; Suzuki, T.; Watanabe, K.; Nagase, K.; Baba, S.; Kochi, C.

    2016-07-01

    We report the current status of the development of our new detectors for far-infrared (FIR) astronomy. We develop Blocked-Impurity-Band (BIB)-type Ge detectors to realize large-format compact arrays covering a wide FIR wavelength range up to 200 μm. We fabricated Ge junction devices of different physical parameters with a BIB-type structure, using the room temperature, surface-activated wafer bonding (SAB) method. We measured the absolute responsivity and the spectral response curve of each device at low temperatures, using an internal blackbody source in a cryostat and a Fourier transform spectrometer, respectively. The results show that the SAB Ge junction devices have significantly higher absolute responsivities and longer cut-off wavelengths of the spectral response than the conventional bulk Ge:Ga device. Based upon the results, we discuss the optimum parameters of SAB Ge junction devices for FIR detectors. We conclude that SAB Ge junction devices possess a promising applicability to next-generation FIR detectors covering wavelengths up to ˜ 200 μm with high responsivity. As a next step, we plan to fabricate a BIB-type Ge array device in combination with a low-power cryogenic readout integrated circuit.

  9. Development of Blocked-Impurity-Band-Type Ge Detectors Fabricated with the Surface-Activated Wafer Bonding Method for Far-Infrared Astronomy

    NASA Astrophysics Data System (ADS)

    Hanaoka, M.; Kaneda, H.; Oyabu, S.; Yamagishi, M.; Hattori, Y.; Ukai, S.; Shichi, K.; Wada, T.; Suzuki, T.; Watanabe, K.; Nagase, K.; Baba, S.; Kochi, C.

    2016-01-01

    We report the current status of the development of our new detectors for far-infrared (FIR) astronomy. We develop Blocked-Impurity-Band (BIB)-type Ge detectors to realize large-format compact arrays covering a wide FIR wavelength range up to 200 \\upmu m. We fabricated Ge junction devices of different physical parameters with a BIB-type structure, using the room temperature, surface-activated wafer bonding (SAB) method. We measured the absolute responsivity and the spectral response curve of each device at low temperatures, using an internal blackbody source in a cryostat and a Fourier transform spectrometer, respectively. The results show that the SAB Ge junction devices have significantly higher absolute responsivities and longer cut-off wavelengths of the spectral response than the conventional bulk Ge:Ga device. Based upon the results, we discuss the optimum parameters of SAB Ge junction devices for FIR detectors. We conclude that SAB Ge junction devices possess a promising applicability to next-generation FIR detectors covering wavelengths up to ˜ 200 \\upmu m with high responsivity. As a next step, we plan to fabricate a BIB-type Ge array device in combination with a low-power cryogenic readout integrated circuit.

  10. Development of Blocked-Impurity-Band-Type Ge Detectors Fabricated with the Surface-Activated Wafer Bonding Method for Far-Infrared Astronomy

    NASA Astrophysics Data System (ADS)

    Hanaoka, M.; Kaneda, H.; Oyabu, S.; Yamagishi, M.; Hattori, Y.; Ukai, S.; Shichi, K.; Wada, T.; Suzuki, T.; Watanabe, K.; Nagase, K.; Baba, S.; Kochi, C.

    2016-07-01

    We report the current status of the development of our new detectors for far-infrared (FIR) astronomy. We develop Blocked-Impurity-Band (BIB)-type Ge detectors to realize large-format compact arrays covering a wide FIR wavelength range up to 200 \\upmu m. We fabricated Ge junction devices of different physical parameters with a BIB-type structure, using the room temperature, surface-activated wafer bonding (SAB) method. We measured the absolute responsivity and the spectral response curve of each device at low temperatures, using an internal blackbody source in a cryostat and a Fourier transform spectrometer, respectively. The results show that the SAB Ge junction devices have significantly higher absolute responsivities and longer cut-off wavelengths of the spectral response than the conventional bulk Ge:Ga device. Based upon the results, we discuss the optimum parameters of SAB Ge junction devices for FIR detectors. We conclude that SAB Ge junction devices possess a promising applicability to next-generation FIR detectors covering wavelengths up to ˜ 200 \\upmu m with high responsivity. As a next step, we plan to fabricate a BIB-type Ge array device in combination with a low-power cryogenic readout integrated circuit.

  11. 78 FR 68037 - Science Advisory Board (SAB)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-13

    ... National Oceanic and Atmospheric Administration Science Advisory Board (SAB) AGENCY: Office of Oceanic and... the NOAA Science Advisory Board (SAB) was published in the Federal Register on October 2, 2013.... Cynthia Decker, Executive Director, Science Advisory Board, NOAA, Rm. 11230, 1315 East-West...

  12. Cu-Cu direct bonding achieved by surface method at room temperature

    NASA Astrophysics Data System (ADS)

    Utsumi, Jun; Ichiyanagi, Yuko

    2014-02-01

    The metal bonding is a key technology in the processes for the microelectromechanical systems (MEMS) devices and the semiconductor devices to improve functionality and higher density integration. Strong adhesion between surfaces at the atomic level is crucial; however, it is difficult to achieve close bonding in such a system. Cu films were deposited on Si substrates by vacuum deposition, and then, two Cu films were bonded directly by means of surface activated bonding (SAB) at room temperature. The two Cu films, with the surface roughness Ra about 1.3nm, were bonded by using SAB at room temperature, however, the bonding strength was very weak in this method. In order to improve the bonding strength between the Cu films, samples were annealed at low temperatures, between 323 and 473 K, in air. As the result, the Cu-Cu bonding strength was 10 times higher than that of the original samples without annealing.

  13. Cu-Cu direct bonding achieved by surface method at room temperature

    SciTech Connect

    Utsumi, Jun; Ichiyanagi, Yuko

    2014-02-20

    The metal bonding is a key technology in the processes for the microelectromechanical systems (MEMS) devices and the semiconductor devices to improve functionality and higher density integration. Strong adhesion between surfaces at the atomic level is crucial; however, it is difficult to achieve close bonding in such a system. Cu films were deposited on Si substrates by vacuum deposition, and then, two Cu films were bonded directly by means of surface activated bonding (SAB) at room temperature. The two Cu films, with the surface roughness Ra about 1.3nm, were bonded by using SAB at room temperature, however, the bonding strength was very weak in this method. In order to improve the bonding strength between the Cu films, samples were annealed at low temperatures, between 323 and 473 K, in air. As the result, the Cu-Cu bonding strength was 10 times higher than that of the original samples without annealing.

  14. 76 FR 12364 - Agency Information Collection Activities: Bonded Warehouse Regulations

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-07

    ... SECURITY U.S. Customs and Border Protection Agency Information Collection Activities: Bonded Warehouse... Bonded Warehouse Regulations. This request for comment is being made pursuant to the Paperwork Reduction... concerning the following information collection: Title: Bonded Warehouse Regulations. OMB Number:...

  15. 26 CFR 1.141-2 - Private activity bond tests.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 2 2013-04-01 2013-04-01 false Private activity bond tests. 1.141-2 Section 1.141-2 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) INCOME TAX (CONTINUED) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.141-2 Private activity bond tests. (a) Overview....

  16. 26 CFR 1.141-2 - Private activity bond tests.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 2 2012-04-01 2012-04-01 false Private activity bond tests. 1.141-2 Section 1.141-2 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) INCOME TAX (CONTINUED) INCOME TAXES (CONTINUED) Tax Exemption Requirements for State and Local Bonds § 1.141-2 Private activity bond tests. (a) Overview....

  17. Predicting Promoter-Induced Bond Activation on Solid Catalysts Using Elementary Bond Orders.

    PubMed

    Tsai, Charlie; Latimer, Allegra A; Yoo, Jong Suk; Studt, Felix; Abild-Pedersen, Frank

    2015-09-17

    In this Letter, we examine bond activation induced by nonmetal surface promoters in the context of dehydrogenation reactions. We use C-H bond activation in methane dehydrogenation on transition metals as an example to understand the origin of the promoting or poisoning effect of nonmetals. The electronic structure of the surface and the bond order of the promoter are found to establish all trends in bond activation. On the basis of these results, we develop a predictive model that successfully describes the energetics of C-H, O-H, and N-H bond activation across a range of reactions. For a given reaction step, a single data point determines whether a nonmetal will promote bond activation or poison the surface and by how much. We show how our model leads to general insights that can be directly used to predict bond activation energetics on transition metal sulfides and oxides, which can be perceived as promoted surfaces. These results can then be directly used in studies on full catalytic pathways. PMID:26722740

  18. SAbPred: a structure-based antibody prediction server.

    PubMed

    Dunbar, James; Krawczyk, Konrad; Leem, Jinwoo; Marks, Claire; Nowak, Jaroslaw; Regep, Cristian; Georges, Guy; Kelm, Sebastian; Popovic, Bojana; Deane, Charlotte M

    2016-07-01

    SAbPred is a server that makes predictions of the properties of antibodies focusing on their structures. Antibody informatics tools can help improve our understanding of immune responses to disease and aid in the design and engineering of therapeutic molecules. SAbPred is a single platform containing multiple applications which can: number and align sequences; automatically generate antibody variable fragment homology models; annotate such models with estimated accuracy alongside sequence and structural properties including potential developability issues; predict paratope residues; and predict epitope patches on protein antigens. The server is available at http://opig.stats.ox.ac.uk/webapps/sabpred. PMID:27131379

  19. 76 FR 71561 - Request for Nominations of Candidates to the EPA's Science Advisory Board (SAB) Chemical...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-18

    ... AGENCY Request for Nominations of Candidates to the EPA's Science Advisory Board (SAB) Chemical... appointment to the EPA's Science Advisory Board (SAB) Chemical Assessment Advisory Committee to provide advice... a variety of EPA science and research programs and reviews and approves all SAB subcommittee...

  20. 76 FR 32202 - Science Advisory Board Staff Office Request for Additional Nominations for the SAB Environmental...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-06-03

    ... AGENCY Science Advisory Board Staff Office Request for Additional Nominations for the SAB Environmental...: The EPA Science Advisory Board (SAB) Staff Office is requesting public nominations of additional... . General information concerning the EPA Science Advisory Board can be found at the EPA SAB Web site at...

  1. Combined surface-activated bonding technique for low-temperature hydrophilic direct wafer bonding

    NASA Astrophysics Data System (ADS)

    He, Ran; Fujino, Masahisa; Yamauchi, Akira; Suga, Tadatomo

    2016-04-01

    A combined surface-activated bonding technique is studied for surface activation and water management to improve the hydrophilic SiO2-SiO2 bonding quality. Prebonding treatment involving a Si-containing Ar beam bombardment and prebonding attach-detach is employed prior to wafer bonding in vacuum. The results of bonding strength measurement, Monte Carlo simulation, and surface analysis by Fourier transform infrared spectroscopy are reported. A mechanism is proposed to better understand the nature of the hydrophilic bonding at low temperatures of no more than 200 °C. We suggest that the Si-containing Ar beam modifies the SiO2 surfaces by Si enrichment to make them more reactive for OH adsorption, while the prebonding attach and detach facilitate a further increase in the number of OH and the removal of excess trapped H2O prior to bonding, respectively. As a consequence, SiO2-SiO2 bonding strength close to the Si bulk fracture energy can be achieved after low-temperature annealing.

  2. Recognizing Revenue under SAB 101: A Case Study Approach.

    ERIC Educational Resources Information Center

    Casabona, Patrick; Shoaf, Victoria

    The primary cause of enforcement proceedings by the Securities Exchange Commission against U.S. businesses resulted from inappropriate revenue recognition procedures used to inflate income. The concern with revenue recognition improprieties led the SEC to issue Staff Accounting Bulletin No. 101 (SAB 101) in 1999 to clarify existing Generally…

  3. 75 FR 69920 - (NOAA) Science Advisory Board (SAB)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-16

    ... meeting agenda. Place: The meeting will be held both days at Dupont Hotel, 1500 New Hampshire Ave., NW... SAB Climate Working Group; (2) Strategic Framework for the Climate Service; (3) Report on the Climate... Research; (6) NOAA Response to the Ecosystem Science and Management Working Group Recommendations on...

  4. 76 FR 28801 - Agency Information Collection Activities: Bonded Warehouse Regulations

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-18

    ... Federal Register (76 FR 11254) on March 1, 2011, allowing for a 60-day comment period. This notice allows... SECURITY U.S. Customs and Border Protection Agency Information Collection Activities: Bonded Warehouse... approval in accordance with the Paperwork Reduction Act: Bonded Warehouse Regulations. This is a...

  5. Electrochemical activation of a tetrathiafulvalene halogen bond donor in solution.

    PubMed

    Oliveira, R; Groni, S; Fave, C; Branca, M; Mavré, F; Lorcy, D; Fourmigué, M; Schöllhorn, B

    2016-06-21

    The halogen bond donor properties of iodo-tetrathiafulvalene (I-TTF) can be electrochemically switched and controlled via reversible oxidation in the solution phase. Interestingly the activation of only one single halogen bond yielded already a strong and selective interaction, quantified by cyclic voltammetry. The standard potentials of the redox couples I-TTF(0/1+) and I-TTF(1+/2+) were observed to shift upon the addition of halides. These anions selectively stabilize the cationic I-TTF species through halogen bonding in polar liquid electrolytes. The thermodynamic affinity constants for chloride and bromide binding to the oxidized species have been determined. Competition in halide binding between I-TTF(1+) and other halogen bond donors allowed for comparing the relative donor strength of the respective electrophilic species. Furthermore it has been shown that halogen bonding can prevail over hydrogen bonding in the investigated system. PMID:27231819

  6. Hydrogen bonds and antiviral activity of benzaldehyde derivatives

    NASA Astrophysics Data System (ADS)

    Tolstorozhev, G. B.; Skornyakov, I. V.; Belkov, M. V.; Shadyro, O. I.; Brinkevich, S. D.; Samovich, S. N.

    2012-09-01

    We have obtained the Fourier transform IR spectra of solutions of benzaldehyde derivatives having different antiviral activities against a herpes virus. We observe a correlation between the presence of hydrogen bonds in the benzaldehyde molecules and the appearance of antiviral properties in the compounds. For compounds having antiviral activity, we have obtained spectral data suggesting the existence of hydrogen bonds of the type C=OṡṡṡH-O and O-HṡṡṡO in the molecules. When the hydrogen atom in the hydroxyl groups are replaced by a methyl group, no intramolecular hydrogen bonds are formed and the compounds lose their antiviral activity.

  7. Changes in active site histidine hydrogen bonding trigger cryptochrome activation.

    PubMed

    Ganguly, Abir; Manahan, Craig C; Top, Deniz; Yee, Estella F; Lin, Changfan; Young, Michael W; Thiel, Walter; Crane, Brian R

    2016-09-01

    Cryptochrome (CRY) is the principal light sensor of the insect circadian clock. Photoreduction of the Drosophila CRY (dCRY) flavin cofactor to the anionic semiquinone (ASQ) restructures a C-terminal tail helix (CTT) that otherwise inhibits interactions with targets that include the clock protein Timeless (TIM). All-atom molecular dynamics (MD) simulations indicate that flavin reduction destabilizes the CTT, which undergoes large-scale conformational changes (the CTT release) on short (25 ns) timescales. The CTT release correlates with the conformation and protonation state of conserved His378, which resides between the CTT and the flavin cofactor. Poisson-Boltzmann calculations indicate that flavin reduction substantially increases the His378 pKa Consistent with coupling between ASQ formation and His378 protonation, dCRY displays reduced photoreduction rates with increasing pH; however, His378Asn/Arg variants show no such pH dependence. Replica-exchange MD simulations also support CTT release mediated by changes in His378 hydrogen bonding and verify other responsive regions of the protein previously identified by proteolytic sensitivity assays. His378 dCRY variants show varying abilities to light-activate TIM and undergo self-degradation in cellular assays. Surprisingly, His378Arg/Lys variants do not degrade in light despite maintaining reactivity toward TIM, thereby implicating different conformational responses in these two functions. Thus, the dCRY photosensory mechanism involves flavin photoreduction coupled to protonation of His378, whose perturbed hydrogen-bonding pattern alters the CTT and surrounding regions. PMID:27551082

  8. Carbon [bond] hydrogen bond activation by titanium imido complexes. Computational evidence for the role of alkane adducts in selective C [bond] H activation.

    PubMed

    Cundari, Thomas R; Klinckman, Thomas R; Wolczanski, Peter T

    2002-02-20

    This paper reports calculations that probe the role of R (hydrocarbon) and R' (ligand substituent) effects on the reaction coordinate for C [bond] H activation: Ti(OR')(2)(=NR') + RH --> adduct --> transition state --> (OR')(2)Ti(N(H)R')(R). Compounds with R = H, Me, Et, Vy, cPr, Ph, Cy, Bz, and cubyl are studied using quantum (R' = H, SiH(3), SiMe(3)) and classical (R' = Si(t)Bu(3)) techniques. Calculated geometries are in excellent agreement with data for experimental models. There is little variability in the calculated molecular structure of the reactants, products, and most interestingly, transition states as R and R' are changed. Structural flexibility is greatest in the adducts Ti(OR')(2)(=NR')...HR. Despite the small structural changes observed for Ti(OR')(2)(double bond] NR') with different R', significant changes are manifested in calculated electronic properties (the Mulliken charge on Ti becomes more positive and the Ti [double bond] N bond order decreases with larger R'), changes that should facilitate C [bond] H activation. Substantial steric modification of the alkane complex is expected from R [bond] R' interactions, given the magnitude of Delta G(add) and the conformational flexibility of the adduct. Molecular mechanics simulations of Ti(OSi(t)Bu(3))(2)([double bond] NSi(t)Bu(3))...isopentane adducts yield an energy ordering as a function of the rank of the C [bond] H bond coordinated to Ti that is consistent with experimental selectivity patterns. Calculated elimination barriers compare very favorably with experiment; larger SiH(3) and TMS ligand substituents generally yield better agreement with experiment, evidence that the modeling of the major contributions to the elimination barrier (N [bond] H and C [bond] H bond making) is ostensibly correct. Calculations indicate that weakening the C [bond] H bond of the hydrocarbon yields a more strongly bound adduct. Combining the different conclusions, the present computational research points to the

  9. Activation of the C-H bond by metal complexes

    NASA Astrophysics Data System (ADS)

    Shilov, Aleksandr E.; Shul'pin, Georgiy B.

    1990-09-01

    Reactions involving the cleavage of C-H bonds by metal complexes in saturated and aromatic hydrocarbons and also in other compounds are examined. Some of these processes occur with formation of a carbon-metal bond, whilst in others the interaction of the complexes with the hydrocarbon takes place without direct contact between the metal atom and the C-H bonds. Metal compounds are widely used as initiators of the liquid-phase oxidation of hydrocarbons at relatively low temperatures. There is a prospect of creating new technologies for the chemical processing of petroleum and gas hydrocarbons, whereby they can be converted into valuable products, for example, into alcohols, ketones, and carboxylic acids, on the basis of processes involving metal complexes. The study of the metal complex activation of the C-H bond also makes it possible to understand and model the metalloenzyme-catalysed hydrocarbon oxidation reactions in the living cell. The bibliography includes 340 references.

  10. Hydrogen bonds of anti-HIV active aminophenols

    NASA Astrophysics Data System (ADS)

    Belkov, M. V.; Ksendzova, G. A.; Skornyakov, I. V.; Sorokin, V. L.; Tolstorozhev, G. B.; Shadyro, O. I.

    2011-05-01

    Analysis of IR-Fourier spectra from solutions and crystals of antiviral sulfo-containing aminophenols has shown that various types of intramolecular and intermolecular interactions can occur in molecules of these compounds. Three types of intramolecular hydrogen bonds (O-HṡṡṡN, O-HṡṡṡO=S=O, and N-HṡṡṡO=S=O) are formed in CCl4 solutions of the sulfo-containing aminophenols. The formation of intermolecular H-bonds involving the NH- and OH-groups and the preservation of the intramolecular O-HṡṡṡO=S=O H-bond are characteristic of the anti-HIV active aminophenol crystals. Spectral attributes are determined in order to distinguish between the anti-HIV active and inactive sulfo-containing aminophenols.

  11. 26 CFR 1.141-2 - Private activity bond tests.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... test and private security or payment test of section 141(b) or the private loan financing test of section 141(c). The private business use and private security or payment tests are described in §§ 1.141-3... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Private activity bond tests. 1.141-2 Section...

  12. 26 CFR 1.141-2 - Private activity bond tests.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... test and private security or payment test of section 141(b) or the private loan financing test of section 141(c). The private business use and private security or payment tests are described in §§ 1.141-3... 26 Internal Revenue 2 2011-04-01 2011-04-01 false Private activity bond tests. 1.141-2 Section...

  13. Selenium bond decreases ON resistance of light-activated switch

    NASA Technical Reports Server (NTRS)

    1965-01-01

    Vitrified amorphous selenium bond decreases the ON resistance of a gallium arsenide-silicon light-activated, low-level switch. The switch is used under a pulse condition to prolong switch life and minimize errors due to heating, devitrification, and overdrawing.

  14. 77 FR 6814 - Agency Information Collection Activities: Bonded Warehouse Proprietor's Submission

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-09

    ... SECURITY U.S. Customs and Border Protection Agency Information Collection Activities: Bonded Warehouse... the Bonded Warehouse Proprietor's Submission (CBP Form 300). This request for comment is being made... CBP is soliciting comments concerning the following information collection: Title: Bonded...

  15. C-H bond activation by f-block complexes.

    PubMed

    Arnold, Polly L; McMullon, Max W; Rieb, Julia; Kühn, Fritz E

    2015-01-01

    Most homogeneous catalysis relies on the design of metal complexes to trap and convert substrates or small molecules to value-added products. Organometallic lanthanide compounds first gave a tantalizing glimpse of their potential for catalytic C-H bond transformations with the selective cleavage of one C-H bond in methane by bis(permethylcyclopentadienyl)lanthanide methyl [(η(5) -C5 Me5 )2 Ln(CH3 )] complexes some 25 years ago. Since then, numerous metal complexes from across the periodic table have been shown to selectively activate hydrocarbon C-H bonds, but the challenges of closing catalytic cycles still remain; many f-block complexes show great potential in this important area of chemistry. PMID:25384554

  16. Transition Metals Catalyzed Element-Cyano Bonds Activations

    PubMed Central

    Wang, Rui; Falck, John R.

    2014-01-01

    Cyano group as a versatile functionalized intermediate has been explored for several decades, as it readily transfers to many useful functionalization groups such as amine, amide, acid, etc., which make it possess high popularization and use value in organic synthesis. Reactions involved with element-cyano bond cleavage can provide not only a new cyano group but also a freshly functionalized skeleton in one-pot, consequently making it of high importance. The highlights reviewed herein include H-CN, Si-CN, C-CN, B-CN, Sn-CN, Ge-CN, S-CN, Halo-CN, N-CN, and O-CN bonds cleavages and will summarize progress in such an important research area. This review article will focus on transition metal catalyzed reactions involving element-cyano bond activation. PMID:25558119

  17. 75 FR 80050 - Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-21

    ...The EPA Science Advisory Board (SAB) Staff Office is requesting public nominations of experts to augment the SAB Drinking Water Committee (DWC) to review technical studies examining the effectiveness of partial lead service line...

  18. EPA's 2007 Report on the Environment: Science Report (Sab Review Draft)

    EPA Science Inventory

    The EPA's 2007 Report on the Environment: Science Report (SAB Review Draft), formally known as the EPA's Report on the Environment - Technical Document, was released for public review and comment prior to the Science Advisory Board's (SAB) meeting and review held in July 2007. Co...

  19. 76 FR 17649 - Science Advisory Board Staff Office; Request for Nominations; SAB Mercury Review Panel

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-30

    ...), 5 U.S.C., App. 2. On February 28, 2011 (76 FR 10896-10897) the EPA SAB Staff Office published a..., transport and modeling; bioaccumulation; human exposure; epidemiology; toxicology, including reproductive... AGENCY Science Advisory Board Staff Office; Request for Nominations; SAB Mercury Review Panel...

  20. 75 FR 73080 - Science Advisory Board Staff Office; Request for Nominations of Experts for the SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-29

    ... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts for the SAB.... SUMMARY: The EPA Science Advisory Board (SAB) Staff Office is requesting public nominations of experts to...-M@epa.gov . General information concerning the EPA Science Advisory Board can be found at the...

  1. 77 FR 52330 - Request for Additional Nominations of Candidates for the EPA's Science Advisory Board (SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-29

    ... AGENCY Request for Additional Nominations of Candidates for the EPA's Science Advisory Board (SAB... experts to be considered for appointment to the EPA's Science Advisory Board (SAB) Chemical Assessment... provides strategic advice to the EPA Administrator on a variety of EPA science and research programs...

  2. Structural/aerodynamic Blade Analyzer (SAB) User's Guide, Version 1.0

    NASA Technical Reports Server (NTRS)

    Morel, M. R.

    1994-01-01

    The structural/aerodynamic blade (SAB) analyzer provides an automated tool for the static-deflection analysis of turbomachinery blades with aerodynamic and rotational loads. A structural code calculates a deflected blade shape using aerodynamic loads input. An aerodynamic solver computes aerodynamic loads using deflected blade shape input. The two programs are iterated automatically until deflections converge. Currently, SAB version 1.0 is interfaced with MSC/NASTRAN to perform the structural analysis and PROP3D to perform the aerodynamic analysis. This document serves as a guide for the operation of the SAB system with specific emphasis on its use at NASA Lewis Research Center (LeRC). This guide consists of six chapters: an introduction which gives a summary of SAB; SAB's methodology, component files, links, and interfaces; input/output file structure; setup and execution of the SAB files on the Cray computers; hints and tips to advise the user; and an example problem demonstrating the SAB process. In addition, four appendices are presented to define the different computer programs used within the SAB analyzer and describe the required input decks.

  3. 75 FR 20992 - Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-22

    ... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...: Notice. SUMMARY: The EPA Science Advisory Board (SAB) Staff Office is requesting public nominations of... concerning the EPA Science Advisory Board can be found on the EPA SAB Web site at...

  4. 75 FR 69069 - Science Advisory Board Staff Office Notification of a Public Meeting of the SAB Lead Review Panel

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-10

    ... AGENCY Science Advisory Board Staff Office Notification of a Public Meeting of the SAB Lead Review Panel... (SAB) Staff Office announces a public meeting of the SAB Lead Review Panel to peer review two draft EPA documents entitled Approach for Developing Lead Dust Hazard Standards for Residences and Approach...

  5. 75 FR 31433 - Science Advisory Board Staff Office; Notification of a Public Meeting of the SAB Lead Review Panel

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-03

    ... dated February 5, 2010 (75 FR 6030-6031)] and formed a review panel for Lead. The panel will provide an... AGENCY Science Advisory Board Staff Office; Notification of a Public Meeting of the SAB Lead Review Panel... (SAB) Staff Office announces a public meeting of the SAB Lead Review Panel to provide a consultation...

  6. 75 FR 6030 - EPA Science Advisory Board Staff Office Request for Nominations of Experts for the SAB Lead (Pb...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-05

    ... AGENCY EPA Science Advisory Board Staff Office Request for Nominations of Experts for the SAB Lead (Pb.... SUMMARY: The Science Advisory Board (SAB) Staff Office is requesting public nominations of experts to form... concerning the EPA Science Advisory Board can be found on the EPA SAB Web site at...

  7. 75 FR 42087 - Science Advisory Board Staff Office; Request for Nominations of Experts for the SAB Hydraulic...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-20

    ..., 2010 (75 FR 13125)]. On June 24, 2010 the SAB provided the EPA Administrator with an advisory report... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts for the SAB Hydraulic... an SAB Ad Hoc Panel to review EPA's draft Hydraulic Fracturing Study Plan to investigate...

  8. Activation of C-H and B-H bonds through agostic bonding: an ELF/QTAIM insight.

    PubMed

    Zins, Emilie-Laure; Silvi, Bernard; Alikhani, M Esmaïl

    2015-04-14

    Agostic bonding is of paramount importance in C-H bond activation processes. The reactivity of the σ C-H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X-H bond can indeed be described as "agostic" bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X-H bond is in agostic interaction with a metal center when the protonated X-H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X-Hagostic bond critical point with respect to that of X-Hfree well correlates with the lengthening of the agostic X-H bond distance as well as with the shift of the vibrational frequency associated with the νX-H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes. PMID:25760795

  9. Frequency of sabA Gene in Helicobacter pylori Strains Isolated From Patients in Tehran, Iran

    PubMed Central

    Pakbaz, Zahra; Shirazi, Mohammad Hasan; Ranjbar, Reza; pourmand, Mohammad Reza; Khalifeh Gholi, Mohammad; Aliramezani, Amir; Vaise Malekshahi, Ziba

    2013-01-01

    Background The importance of sialic acid binding adhesin (sabA) as a new outer membrane protein in gastroduodenal diseases has been recognized. The prevalence rate of sabA gene varies in different geographic areas. Objectives The aim of this study was to determine the frequency of sabA gene in Helicobacter pylori (H. pylori) strains isolated from different clinical outcomes in Tehran, Iran. Patients and Methods The study included 120 patients with dyspeptic symptoms admitted to the endoscopy suite of gastroenterology section of Firouzgar University Hospital, Tehran, Iran from March to August 2011. Gastric biopsy specimens were evaluated for the presence of H. pylori using standard microbiological method and polymerase chain reaction (PCR) assay. The sabA genopositive was determined by PCR in H. pylori strains. Results H. pylori isolates were recovered from 82 patients with duodenal ulcer (DU; n = 17), gastric ulcer (GU; n = 15), gastric cancer (GC; n = 13), and gastritis (G; n = 37). The frequency of sabA gene in H. pylori strains was 100% in gastric cancer, 86.7% in gastric ulcer, and 83.3% in both gastritis and duodenal ulcer. Conclusions This is a report on the prevalence of sabA gene in H. pylori isolated from different gastric patients in Iran. The results showed a high prevalence of sabA in our clinical H. pylori isolates. PMID:24616782

  10. Transition metal activation and functionalization of carbon-hydrogen bonds

    SciTech Connect

    Jones, W.D.

    1992-06-01

    We are investigating the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers and the conversion of hydrocarbons into functionalized products of potential use to the chemical industry. Advances have been made in both understanding the interactions of hydrocarbons with metals and in the functionalization of hydrocarbons. We have found that RhCl(PR{sub 3}){sub 2}(CNR) complexes can catalyze the insertion of isonitriles into the C-H bonds or arenes upon photolysis. The mechanism of these reactions was found to proceed by way of initial phosphine dissociation, followed by C-H activation and isonitrile insertion. We have also examined reactions of a series of arenes with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and begun to map out the kinetic and thermodynamic preferences for arene coordination. The effects of resonance, specifically the differences in the Hueckel energies of the bound vs free ligand, are now believed to fully control the C-H activation/{eta}{sup 2}-coordination equilibria. We have begun to examine the reactions of rhodium isonitrile pyrazolylborates for alkane and arene C-H bond activation. A new, labile, carbodiimide precursor has been developed for these studies. We have completed studies of the reactions of (C{sub 5}Me{sub 5})Rh(PMe{sub 3})H{sub 2} with D{sub 2} and PMe{sub 3} that indicate that both {eta}{sup 5} {yields} {eta}{sup 3} ring slippage and metal to ring hydride migration occur more facilely than thermal reductive elimination of H{sub 2}. We have examined the reactions of heterocycles with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and found that pyrrole and furan undergo C-H or N-H activation. Thiophene, however, undergoes C-S bond oxidative addition, and the mechanism of activation has been shown to proceed through sulfur coordination prior to C-S insertion.

  11. Catalytic diamination of olefins via N-N bond activation.

    PubMed

    Zhu, Yingguang; Cornwall, Richard G; Du, Haifeng; Zhao, Baoguo; Shi, Yian

    2014-12-16

    CONSPECTUS: Vicinal diamines are important structural motifs present in various biologically and chemically significant molecules. Direct diamination of olefins provides an effective approach to this class of compounds. Unlike well-established oxidation processes such as epoxidation, dihydroxylation, and aminohydroxylation, direct diamination of olefins had remained a long-standing challenge and had been less well developed. In this Account, we summarize our recent studies on Pd(0)- and Cu(I)-catalyzed diaminations of olefins using di-tert-butyldiaziridinone and its related analogues as nitrogen sources via N-N bond activation. A wide variety of imidazolidinones, cyclic sulfamides, indolines, imidazolinones, and cyclic guanidines can be obtained from conjugated dienes and terminal olefins. For conjugated dienes, the diamination proceeds regioselectively at the internal double bond with the Pd(0) catalyst. Mechanistic studies show that the diamination likely involves a four-membered Pd(II) species resulting from the insertion of Pd(0) into the N-N bond of di-tert-butyldiaziridinone. Interestingly, the Cu(I)-catalyzed process occurs regioselectively at either the terminal or internal double bond depending on the reaction conditions via two mechanistically distinct pathways. The Cu(I) catalyst cleaves the N-N bond of di-tert-butyldiaziridinone to form a Cu(II) nitrogen radical and a four-membered Cu(III) species, which are likely in rapid equilibrium. The Cu(II) nitrogen radical and the four-membered Cu(III) species lead to the terminal and internal diamination, respectively. Terminal olefins are effectively C-H diaminated at the allylic and homoallylic carbons with Pd(0) as catalyst and di-tert-butyldiaziridinone as nitrogen source, likely involving a diene intermediate generated in situ from the terminal olefin via formation of a π-allyl Pd complex and subsequent β-hydride elimination. When di-tert-butylthiadiaziridine 1,1-dioxide is used as nitrogen source

  12. Catalytic Diamination of Olefins via N–N Bond Activation

    PubMed Central

    2015-01-01

    Conspectus Vicinal diamines are important structural motifs present in various biologically and chemically significant molecules. Direct diamination of olefins provides an effective approach to this class of compounds. Unlike well-established oxidation processes such as epoxidation, dihydroxylation, and aminohydroxylation, direct diamination of olefins had remained a long-standing challenge and had been less well developed. In this Account, we summarize our recent studies on Pd(0)- and Cu(I)-catalyzed diaminations of olefins using di-tert-butyldiaziridinone and its related analogues as nitrogen sources via N–N bond activation. A wide variety of imidazolidinones, cyclic sulfamides, indolines, imidazolinones, and cyclic guanidines can be obtained from conjugated dienes and terminal olefins. For conjugated dienes, the diamination proceeds regioselectively at the internal double bond with the Pd(0) catalyst. Mechanistic studies show that the diamination likely involves a four-membered Pd(II) species resulting from the insertion of Pd(0) into the N–N bond of di-tert-butyldiaziridinone. Interestingly, the Cu(I)-catalyzed process occurs regioselectively at either the terminal or internal double bond depending on the reaction conditions via two mechanistically distinct pathways. The Cu(I) catalyst cleaves the N–N bond of di-tert-butyldiaziridinone to form a Cu(II) nitrogen radical and a four-membered Cu(III) species, which are likely in rapid equilibrium. The Cu(II) nitrogen radical and the four-membered Cu(III) species lead to the terminal and internal diamination, respectively. Terminal olefins are effectively C–H diaminated at the allylic and homoallylic carbons with Pd(0) as catalyst and di-tert-butyldiaziridinone as nitrogen source, likely involving a diene intermediate generated in situ from the terminal olefin via formation of a π-allyl Pd complex and subsequent β-hydride elimination. When di-tert-butylthiadiaziridine 1,1-dioxide is used as nitrogen source

  13. 26 CFR 1.145-2 - Application of private activity bond regulations.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... of the private business use test and the private security or payment test mean “5 percent” and “net... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Application of private activity bond regulations... Bonds § 1.145-2 Application of private activity bond regulations. (a) In general. Except as provided...

  14. 26 CFR 1.145-2 - Application of private activity bond regulations.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... of the private business use test and the private security or payment test mean “5 percent” and “net... 26 Internal Revenue 2 2012-04-01 2012-04-01 false Application of private activity bond regulations... Bonds § 1.145-2 Application of private activity bond regulations. (a) In general. Except as provided...

  15. 26 CFR 1.145-2 - Application of private activity bond regulations.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... of the private business use test and the private security or payment test mean “5 percent” and “net... 26 Internal Revenue 2 2011-04-01 2011-04-01 false Application of private activity bond regulations... Bonds § 1.145-2 Application of private activity bond regulations. (a) In general. Except as provided...

  16. 26 CFR 1.145-2 - Application of private activity bond regulations.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... of the private business use test and the private security or payment test mean “5 percent” and “net... 26 Internal Revenue 2 2013-04-01 2013-04-01 false Application of private activity bond regulations... Bonds § 1.145-2 Application of private activity bond regulations. (a) In general. Except as provided...

  17. 26 CFR 1.145-2 - Application of private activity bond regulations.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... of the private business use test and the private security or payment test mean “5 percent” and “net... 26 Internal Revenue 2 2010-04-01 2010-04-01 false Application of private activity bond regulations... Bonds § 1.145-2 Application of private activity bond regulations. (a) In general. Except as provided...

  18. Intramolecular hydrogen bond in biologically active o-carbonyl hydroquinones.

    PubMed

    Martínez-Cifuentes, Maximiliano; Weiss-López, Boris E; Santos, Leonardo S; Araya-Maturana, Ramiro

    2014-01-01

    Intramolecular hydrogen bonds (IHBs) play a central role in the molecular structure, chemical reactivity and interactions of biologically active molecules. Here, we study the IHBs of seven related o-carbonyl hydroquinones and one structurally-related aromatic lactone, some of which have shown anticancer and antioxidant activity. Experimental NMR data were correlated with theoretical calculations at the DFT and ab initio levels. Natural bond orbital (NBO) and molecular electrostatic potential (MEP) calculations were used to study the electronic characteristics of these IHB. As expected, our results show that NBO calculations are better than MEP to describe the strength of the IHBs. NBO energies (∆Eij(2)) show that the main contributions to energy stabilization correspond to LP-->σ* interactions for IHBs, O1…O2-H2 and the delocalization LP-->π* for O2-C2=Cα(β). For the O1…O2-H2 interaction, the values of ∆Eij(2) can be attributed to the difference in the overlap ability between orbitals i and j (Fij), instead of the energy difference between them. The large energy for the LP O2-->π* C2=Cα(β) interaction in the compounds 9-Hydroxy-5-oxo-4,8, 8-trimethyl-l,9(8H)-anthracenecarbolactone (VIII) and 9,10-dihydroxy-4,4-dimethylanthracen-1(4H)-one (VII) (55.49 and 60.70 kcal/mol, respectively) when compared with the remaining molecules (all less than 50 kcal/mol), suggests that the IHBs in VIII and VII are strongly resonance assisted. PMID:24995921

  19. Formation of disulfide bonds in insect prophenoloxidase enhances immunity through improving enzyme activity and stability.

    PubMed

    Lu, Anrui; Peng, Qin; Ling, Erjun

    2014-06-01

    Type 3 copper proteins, including insect prophenoloxidase (PPO), contain two copper atoms in the active site pocket and can oxidize phenols. Insect PPO plays an important role in immunity. Insects and other invertebrates show limited recovery from pathogen invasion and wounds if phenoloxidase (PO) activity is low. In most insect PPOs, two disulfide bonds are present near the C-terminus. However, in Pimpla hypochondriaca (a parasitoid wasp), each PPO contains one disulfide bond. We thus questioned whether the formation of two sulfide bonds in insect PPOs improved protein stability and/or increased insect innate immunity over time. Using Drosophila melanogaster PPO1 as a model, one or two disulfide bonds were deleted to evaluate the importance of disulfide bonds in insect immunity. rPPO1 and mutants lacking disulfide bonds could be expressed and showed PO activity. However, the PO activities of mutants lacking one or two disulfide bonds significantly decreased. Deletion of disulfide bonds also reduced PPO thermostability. Furthermore, antibacterial activities against Escherichia coli and Bacillus subtilis significantly decreased when disulfide bonds were deleted. Therefore, the formation of two disulfide bond(s) in insect PPO enhances antibacterial activity by increasing PO activity and stability. PMID:24480295

  20. Carbon–carbon bond activation of cyclobutenones enabled by the addition of chiral organocatalyst to ketone

    PubMed Central

    Li, Bao-Sheng; Wang, Yuhuang; Jin, Zhichao; Zheng, Pengcheng; Ganguly, Rakesh; Chi, Yonggui Robin

    2015-01-01

    The activation of carbon–carbon (C–C) bonds is an effective strategy in building functional molecules. The C–C bond activation is typically accomplished via metal catalysis, with which high levels of enantioselectivity are difficult to achieve due to high reactivity of metal catalysts and the metal-bound intermediates. It remains largely unexplored to use organocatalysis for C–C bond activation. Here we describe an organocatalytic activation of C–C bonds through the addition of an NHC to a ketone moiety that initiates a C–C single bond cleavage as a key step to generate an NHC-bound intermediate for chemo- and stereo-selective reactions. This reaction constitutes an asymmetric functionalization of cyclobutenones using organocatalysts via a C–C bond activation process. Structurally diverse and multicyclic compounds could be obtained with high optical purities via an atom and redox economic process. PMID:25652912

  1. 75 FR 50772 - Agency Information Collection Activities: Importation Bond Structure

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-17

    ... Structure AGENCY: U.S. Customs and Border Protection, Department of Homeland Security. ] ACTION: 60-Day... concerning the: Importation Bond Structure. This request for comment is being made pursuant to the Paperwork...: Title: Importation Bond Structure. OMB Number: 1651-0050. Form Numbers: 301 and 5297. Abstract:...

  2. 78 FR 75576 - Agency Information Collection Activities: Importation Bond Structure

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-12-12

    ... Structure AGENCY: U.S. Customs and Border Protection (CBP), Department of Homeland Security. ACTION: 60-day... Importation Bond Structure. This request for comment is being made pursuant to the Paperwork Reduction Act of... Structure. OMB Number: 1651-0050. Form Number: CBP Forms 301 and 5297. Abstract: Bonds are used to...

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

    SciTech Connect

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

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

  4. 26 CFR 1.103(n)-3T - Private activity bond limit (temporary).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 2 2010-04-01 2010-04-01 false Private activity bond limit (temporary). 1.103(n)-3T Section 1.103(n)-3T Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY....103(n)-3T Private activity bond limit (temporary). Q-1: What is the “State ceiling”? A-1: In...

  5. 26 CFR 1.103(n)-3T - Private activity bond limit (temporary).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 2 2011-04-01 2011-04-01 false Private activity bond limit (temporary). 1.103(n)-3T Section 1.103(n)-3T Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY....103(n)-3T Private activity bond limit (temporary). Q-1: What is the “State ceiling”? A-1: In...

  6. 26 CFR 1.103(n)-3T - Private activity bond limit (temporary).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 2 2013-04-01 2013-04-01 false Private activity bond limit (temporary). 1.103(n)-3T Section 1.103(n)-3T Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY....103(n)-3T Private activity bond limit (temporary). Q-1: What is the “State ceiling”? A-1: In...

  7. 26 CFR 1.103(n)-3T - Private activity bond limit (temporary).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Private activity bond limit (temporary). 1.103(n)-3T Section 1.103(n)-3T Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY....103(n)-3T Private activity bond limit (temporary). Q-1: What is the “State ceiling”? A-1: In...

  8. 26 CFR 1.103(n)-3T - Private activity bond limit (temporary).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 2 2012-04-01 2012-04-01 false Private activity bond limit (temporary). 1.103(n)-3T Section 1.103(n)-3T Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY....103(n)-3T Private activity bond limit (temporary). Q-1: What is the “State ceiling”? A-1: In...

  9. 75 FR 8700 - Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-25

    ... (74 FR 44632), and some States have established standards of their own. In addition, a number of... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...: Notice. SUMMARY: The EPA Science Advisory Board (SAB) Staff Office is requesting public nominations...

  10. 77 FR 12302 - Request for Public Comments on the List of Candidates for EPA's Science Advisory Board (SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-29

    ... AGENCY Request for Public Comments on the List of Candidates for EPA's Science Advisory Board (SAB... considered for appointment to the EPA's Science Advisory Board (SAB) Chemical Assessment Advisory Committee... telephone at 202-564-2057. Background: The U.S. Environmental Protection Agency (EPA) Science Advisory...

  11. 76 FR 13181 - Science Advisory Board Staff Office; Notification of a Public Meeting of the SAB Drinking Water...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-10

    ...The EPA Science Advisory Board (SAB) Staff Office announces a public meeting of the SAB Drinking Water Committee Augmented for the Review of the Effectiveness of Partial Lead Service Line Replacements to review technical studies examining the effectiveness of partial lead service line...

  12. 76 FR 29746 - Science Advisory Board Staff Office Notification of a Public Meeting of the SAB Mercury Review Panel

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-23

    ... serve on an ad hoc review panel on February 28, 2011 (76 FR 10896-10897) and March 30, 2011 (76 FR 17649... AGENCY Science Advisory Board Staff Office Notification of a Public Meeting of the SAB Mercury Review... SAB Mercury Review Panel. DATES: The meeting will be held on June 15, 2011 and June 16, 2011 from 9...

  13. 75 FR 10481 - Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-08

    ... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts To Augment the SAB...). ACTION: Notice. SUMMARY: The EPA Science Advisory Board (SAB) Staff Office is requesting public....edward @epa.gov. General information concerning the EPA Science Advisory Board can be found at the...

  14. 76 FR 30939 - Science Advisory Board Staff Office; Request for Nominations of Experts for SAB Libby Amphibole...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-27

    ...The EPA Science Advisory Board (SAB) Staff Office is requesting public nominations of technical experts to serve on an Asbestos expert panel under the auspices of the SAB to conduct a peer review of EPA's Draft Toxicological Review of Libby Amphibole...

  15. 75 FR 27554 - Science Advisory Board Staff Office; Request for Nominations of Experts for the SAB Arsenic...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-17

    ... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts for the SAB Arsenic Review...: The Science Advisory Board (SAB) Staff Office is requesting public nominations of experts to form an... Nominations may contact Dr. Sue Shallal, Designated Federal Officer (DFO), EPA Science Advisory Board...

  16. 76 FR 2373 - Science Advisory Board Staff Office; Request for Nominations of Experts to Augment the SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-13

    ... AGENCY Science Advisory Board Staff Office; Request for Nominations of Experts to Augment the SAB...). ACTION: Notice. SUMMARY: The EPA Science Advisory Board (SAB) Staff Office is requesting public...@epa.gov . General information concerning the EPA Science Advisory Board can be found at the EPA...

  17. Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Laufer, A. H.

    1981-01-01

    Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

  18. Effect of Intermediate Agents and Preheated Composites on Repair Bond Strength of Silorane-Based Composites

    PubMed Central

    Shafiei, Fereshteh; Daryadar, Marzieh

    2015-01-01

    Objectives: Repairing composite restorations is a challenging procedure especially when two different types of composites are used. This study aimed to compare the repair strength of silorane-based composite (SC) (Filtek P90) with that of preheated SC, methacrylate composite (MC)(Z250), flowable MC (Filtek Supreme Plus) and different adhesive/composite combinations. Materials and Methods: Eighty-four SC specimens were fabricated and randomly divided into seven groups (G). In the control group (G7), SC was bonded immediately to SC. The other specimens were water-aged for two months and were then roughened, etched and repaired with the following materials: G1) Silorane Adhesive Bond (SAB)/SC; G2) Preheated SC; G3) SAB/MC; G4) Adper Single Bond (SB)/MC; G5) Flowable MC/MC; G6) Preheated MC. After water storage and thermocycling, the repaired specimens were subjected to shear bond strength testing. The data were analyzed using ANOVA and Tukey’s test. Results: Preheated SC and MC, flowable MC and SAB/SC resulted in bond strength comparable to that of the control group. Preheated SC showed significantly higher bond strength when compared to SAB/MC (P=0.04) and SB/MC (P<0.001). Bond strength of SB/MC was significantly lower than that of the other groups (P<0.05), except for SAB/SC and SAB/MC. Conclusion: All repairing materials except for SB/MC resulted in bond strength values comparable to that of the control group. Repair with preheated SC yielded the highest bond strength. PMID:27148378

  19. Surface-Controlled Mono/Diselective ortho C-H Bond Activation.

    PubMed

    Li, Qing; Yang, Biao; Lin, Haiping; Aghdassi, Nabi; Miao, Kangjian; Zhang, Junjie; Zhang, Haiming; Li, Youyong; Duhm, Steffen; Fan, Jian; Chi, Lifeng

    2016-03-01

    One of the most charming and challenging topics in organic chemistry is the selective C-H bond activation. The difficulty arises not only from the relatively large bond-dissociation enthalpy, but also from the poor reaction selectivity. In this work, Au(111) and Ag(111) surfaces were used to address ortho C-H functionalization and ortho-ortho couplings of phenol derivatives. More importantly, the competition between dehydrogenation and deoxygenation drove the diversity of reaction pathways of phenols on surfaces, that is, diselective ortho C-H bond activation on Au(111) surfaces and monoselective ortho C-H bond activation on Ag(111) surfaces. The mechanism of this unprecedented phenomenon was extensively explored by scanning tunneling microscopy, density function theory, and X-ray photoelectron spectroscopy. Our findings provide new pathways for surface-assisted organic synthesis via the mono/diselective C-H bond activation. PMID:26853936

  20. Influence of preheating the bonding agent of a conventional three-step adhesive system and the light activated resin cement on dentin bond strength

    PubMed Central

    Holanda, Daniel Brandão Vilela; França, Fabiana Mantovani Gomes; do Amaral, Flávia Lucisano Botelho; Flório, Flávia Martão; Basting, Roberta Tarkany

    2013-01-01

    Aims: to evaluate the influence of preheating the bonding agent (Scotchbond Multipurpose Adhesive/3M ESPE) and the light-activated resin cement (RelyX Venner/3M ESPE) on dentin microtensile bond strength. Materials and Methods: The exposed flat dentin surface of 40 human third molars were randomly distributed into four groups for cementation (SR Adoro/Ivoclar Vivadent) (n = 10): G1-bond and resin cement, both at room temperature (22°C), G2-bond preheated to 58°C and cement at room temperature (22°C), G3-bond at room temperature (22°C) and the cement preheated to 58°C, G4-bond preheated to 58°C and cement preheated to 58°C. Sticks of dentin/block set measuring approximately 1 mm2 were obtained and used for the microtensile bond strength test. All sticks had their failure mode classified. Statistical analysis used: Factorial analysis of variance was applied, 2 × 2 (bond × cement) (P < 0.05). Results: Preheating the bonding agent (P = 0.8411) or the cement (P = 0.7155), yielded no significant difference. The interaction bond × cement was not significant (P = 0.9389). Conclusions: Preheating the bond and/or the light-activated resin cement did not influence dentin bond strength or fracture failure mode. PMID:24347889

  1. 75 FR 68809 - Agency Information Collection Activities: Importation Bond Structure

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-11-09

    ... information collection was previously published in the Federal Register (75 FR 50772) on August 17, 2010... Structure AGENCY: U.S. Customs and Border Protection, Department of Homeland Security. ACTION: 30-day notice... review and approval in accordance with the Paperwork Reduction Act: Importation Bond Structure. This is...

  2. Repeatable mechanochemical activation of dynamic covalent bonds in thermoplastic elastomers.

    PubMed

    Imato, Keiichi; Kanehara, Takeshi; Nojima, Shiki; Ohishi, Tomoyuki; Higaki, Yuji; Takahara, Atsushi; Otsuka, Hideyuki

    2016-08-18

    Repeated mechanical scission and recombination of dynamic covalent bonds incorporated in segmented polyurethane elastomers are demonstrated by utilizing a diarylbibenzofuranone-based mechanophore and by the design of the segmented polymer structures. The repeated mechanochemical reactions can accompany clear colouration and simultaneous fading. PMID:27424868

  3. Rhodium mediated bond activation: from synthesis to catalysis

    SciTech Connect

    Ho, Hung-An

    2012-01-01

    Recently, our lab has developed monoanionic tridentate ligand, ToR, showing the corresponding coordination chemistry and catalyst reactivity of magnesium, zirconium, zinc and iridium complexes. This thesis details synthetic chemistry, structural study and catalytic reactivity of the ToR-supported rhodium compounds. Tl[ToR] has been proved to be a superior ligand transfer agent for synthesizing rhodium complexes. The salt metathesis route of Tl[ToM] with [Rh(μ-Cl)(CO)]2 and [Rh(μ- Cl)(COE)]2 gives ToMRh(CO)2 (2.2) and ToMRhH(β3-C8H13) (3.1) respectively while Tl[ToM] with [Rh(μ-Cl)(CO)]2 affords ToPRh(CO)2 (2.3). 2.2 reacts with both strong and weak electrophiles, resulting in the oxazoline N-attacked and the metal center-attacked compounds correspondingly. Using one of the metal center-attacked electrophiles, 2.3 was demonstrated to give high diastereoselectivity. Parallel to COE allylic C-H activation complex 3.1, the propene and allylbenzene allylic C-H activation products have also been synthesized. The subsequent functionalization attempts have been examined by treating with Brønsted acids, Lewis acids, electrophiles, nucleophiles, 1,3-dipolar reagents and reagents containing multiple bonds able to be inserted. Various related complexes have been obtained under these conditions, in which one of the azide insertion compounds reductively eliminates to give an allylic functionalization product stoichiometrically. 3.1 reacts with various primary alcohols to give the decarbonylation dihydride complex ToMRh(H)2CO (4.1). 4.1 shows catalytic reactivity for primary alcohol decarbonylation under a photolytic condition. Meanwhile, 2.2 has been found to be more reactive than 4.1 for catalytic alcohol decarbonylation under the same condition. Various complexes and primary

  4. 78 FR 55064 - Solicitation for Members of the NOAA Science Advisory Board (SAB) Gulf Coast Ecosystem...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-09

    ... National Oceanic and Atmospheric Administration Solicitation for Members of the NOAA Science Advisory Board (SAB) Gulf Coast Ecosystem Restoration Science Program Advisory Working Group (RSPAWG) AGENCY: National... Administration is publishing this notice to solicit nominations for the NOAA Science Advisory Board Gulf...

  5. 76 FR 10888 - Science Advisory Board (SAB); Notice of Open Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-28

    ... National Oceanic and Atmospheric Administration (NOAA) Science Advisory Board (SAB); Notice of Open Meeting... (NOAA), Department of Commerce (DOC). ACTION: Notice of open meeting. SUMMARY: The Science Advisory....gov for confirmation of the venue and for directions. STATUS: The meeting will be open to...

  6. 76 FR 8366 - Science Advisory Board Staff Office; Request for Nominations; SAB Environmental Justice Technical...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-14

    ... AGENCY Science Advisory Board Staff Office; Request for Nominations; SAB Environmental Justice Technical Panel AGENCY: Environmental Protection Agency (EPA). ACTION: Notice. SUMMARY: The EPA Science Advisory... shallal.suhair@epa.gov General information concerning the EPA Science Advisory Board can be found at...

  7. IRIS Toxicological Review of Ingested Inorganic Arsenic (2005 Sab External Review Draft)

    EPA Science Inventory

    EPA's Office of Research and Development (ORD), Office of Pesticide Programs (OPP), and Office of Water (OW) requested the SAB to provide advice to the Agency on several issues about the mode of carcinogenic action of various arsenic species and the implications of these issues f...

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

    PubMed

    Yedage, Subhash L; Bhanage, Bhalchandra M

    2016-05-20

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

  9. Merging photoredox catalysis with Lewis acid catalysis: activation of carbon-carbon triple bonds.

    PubMed

    Jin, Ruiwen; Chen, Yiyong; Liu, Wangsheng; Xu, Dawen; Li, Yawei; Ding, Aishun; Guo, Hao

    2016-08-01

    Here, we demonstrate that merging photoredox catalysis with Lewis acid catalysis provides a fundamentally new activation mode of C-C triple bonds, to achieve the bond-forming reaction of alkynes with weak nucleophiles. Using a synergistic merger of Eosin Y and Cu(OTf)2, a highly efficient cyclization reaction of arene-ynes was developed. PMID:27432542

  10. 43 CFR 3214.12 - What activities must my bond cover?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false What activities must my bond cover? 3214.12 Section 3214.12 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) GEOTHERMAL RESOURCE LEASING Personal and Surety Bonds § 3214.12 What...

  11. 77 FR 26024 - Agency Information Collection Activities: Bonded Warehouse Proprietor's Submission

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-02

    ... previously published in the Federal Register (77 FR 6814) on February 9, 2012, allowing for a 60-day comment... SECURITY U.S. Customs and Border Protection Agency Information Collection Activities: Bonded Warehouse... approval in accordance with the Paperwork Reduction Act: Bonded Warehouse Proprietor's Submission (CBP...

  12. 26 CFR 1.103(n)-2T - Private activity bond defined (temporary).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 2 2010-04-01 2010-04-01 false Private activity bond defined (temporary). 1.103....103(n)-2T Private activity bond defined (temporary). Q-1: What is the definition of the term “private activity bond”? A-1: In general, for purposes of §§ 1.103(n)-1T through 1.103(n)-6T, the term...

  13. 26 CFR 1.103(n)-2T - Private activity bond defined (temporary).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Private activity bond defined (temporary). 1.103....103(n)-2T Private activity bond defined (temporary). Q-1: What is the definition of the term “private activity bond”? A-1: In general, for purposes of §§ 1.103(n)-1T through 1.103(n)-6T, the term...

  14. Thermally-Activated Metal-to-Glass Bonding

    NASA Technical Reports Server (NTRS)

    Gallagher, B. D.

    1986-01-01

    Hermetic seals formed easily by use of metallo-organic film. Metallo-organic film thermally bonded to glass and soldered or welded to form hermetic seal. Film applied as ink consisting of silver neodecanoate in xylene. Relative amounts of ingredients selected to obtain desired viscosity. Material applied by printing or even by scribing with pen. Sealing technique useful in making solar-cell modules, microelectronic packages, and other hermetic silicon devices.

  15. Quantification of primary versus secondary C-H bond cleavage in alkane activation: Propane on Pt

    SciTech Connect

    Weinberg, W.H.; Sun, Yongkui )

    1991-08-02

    The trapping-mediated dissociative chemisorption of three isotopes of propane (C{sub 3}H{sub 8}, CH{sub 3}, CD{sub 2}CH{sub 3}, and C{sub 3}D{sub 8}) has been investigated on the Pt(110)-(1 {times} 2) surface, and both the apparent activation energies and the preexponential factors of the surface reaction rate coefficients have been measured. In addition, the probabilities of primary and secondary C-H bond cleavage for alkane activation on a surface were evaluated. The activation energy for primary C-H bond cleavage was 425 calories per mole greater than that of secondary C-H bond cleavage, and the two true activation energies that embody the single measured activation energy were determined for each of the three isotopes. Secondary C-H bond cleavage is also preferred on entropic grounds, and the magnitude of the effect was quantified.

  16. SabR enhances nikkomycin production via regulating the transcriptional level of sanG, a pathway-specific regulatory gene in Streptomyces ansochromogenes

    PubMed Central

    2011-01-01

    Background sabR is a pleiotropic regulatory gene which has been shown to positively regulate the nikkomycin biosynthesis and negatively affect the sporulation of Streptomyces ansochromogenes. In this study, we investigate the mechanism of SabR on modulating nikkomycin production in Streptomyces ansochromogenes. Results The transcription start point of sabR was determined by high-resolution S1 nuclease mapping and localized at the nucleotide T at position 37 bp upstream of the potential sabR translation start codon (GTG). Disruption of sabR enhanced its own transcription, but retarded the nikkomycin production. Over-expression of sabR enhanced nikkomycin biosynthesis in Streptomyces ansochromogenes. EMSA analysis showed that SabR bound to the upstream region of sanG, but it did not bind to the upstream region of its encoding gene (sabR), sanF and the intergenic region between sanN and sanO. DNase 1 footprinting assays showed that the SabR-binding site upstream of sanG was 5'-CTTTAAGTCACCTGGCTCATTCGCGTTCGCCCAGCT-3' which was designated as SARE. Deletion of SARE resulted in the delay of nikkomycin production that was similar to that of sabR disruption mutant. Conclusions These results indicated that SabR modulated nikkomycin biosynthesis as an enhancer via interaction with the promoter region of sanG, and expanded our understanding about regulatory cascade in nikkomycin biosynthesis. PMID:21771341

  17. Iridium-Catalyzed Branch-Selective Hydroarylation of Vinyl Ethers via C-H Bond Activation.

    PubMed

    Ebe, Yusuke; Nishimura, Takahiro

    2015-05-13

    Iridium-catalyzed hydroarylation of vinyl ethers via a directed C-H bond activation of aromatic compounds gave high yields of the corresponding addition products with high branch selectivity. PMID:25928127

  18. Surface-Bonded Antimicrobial Activity of an Organosilicon Quaternary Ammonium Chloride

    PubMed Central

    Isquith, A. J.; Abbott, E. A.; Walters, P. A.

    1972-01-01

    The hydrolysis product of 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride exhibited antimicrobial activity against a broad range of microorganisms while chemically bonded to a variety of surfaces. The chemical was not removed from surfaces by repeated washing with water, and its antimicrobial activity could not be attributed to a slow release of the chemical, but rather to the surface-bonded chemical. Images PMID:4650597

  19. Quantum delocalization of protons in the hydrogen-bond network of an enzyme active site

    PubMed Central

    Wang, Lu; Fried, Stephen D.; Boxer, Steven G.; Markland, Thomas E.

    2014-01-01

    Enzymes use protein architectures to create highly specialized structural motifs that can greatly enhance the rates of complex chemical transformations. Here, we use experiments, combined with ab initio simulations that exactly include nuclear quantum effects, to show that a triad of strongly hydrogen-bonded tyrosine residues within the active site of the enzyme ketosteroid isomerase (KSI) facilitates quantum proton delocalization. This delocalization dramatically stabilizes the deprotonation of an active-site tyrosine residue, resulting in a very large isotope effect on its acidity. When an intermediate analog is docked, it is incorporated into the hydrogen-bond network, giving rise to extended quantum proton delocalization in the active site. These results shed light on the role of nuclear quantum effects in the hydrogen-bond network that stabilizes the reactive intermediate of KSI, and the behavior of protons in biological systems containing strong hydrogen bonds. PMID:25503367

  20. Quantification of Electrophilic Activation by Hydrogen-Bonding Organocatalysts

    PubMed Central

    2015-01-01

    A spectrophotometric sensor is described that provides a useful assessment of the LUMO-lowering provided by catalysts in Diels–Alder and Friedel–Crafts reactions. A broad range of 33 hydrogen-bonding catalysts was assessed with the sensor, and the relative rates in the above reactions spanned 5 orders of magnitude as determined via 1H- and 2H NMR spectroscopic measurements, respectively. The differences between the maximum wavelength shift of the sensor with and without catalyst (Δλmax–1) were found to correlate linearly with ln(krel) values for both reactions, even though the substrate feature that interacts with the catalyst differs significantly (ketone vs nitro). The sensor provides an assessment of both the inherent reactivity of a catalyst architecture as well as the sensitivity of the reaction to changes within an architecture. In contrast, catalyst pKa values are a poor measure of reactivity, although correlations have been identified within catalyst classes. PMID:25325850

  1. Time resolved studies of bond activation by organometallic complexes

    SciTech Connect

    Wilkens, M J

    1998-05-01

    In 1971, Jetz and Graham discovered that the silicon-hydrogen bond in silanes could be broken under mild photochemical conditions in the presence of certain transition metal carbonyls. Such reactions fall within the class of oxidative addition. A decade later, similar reactivity was discovered in alkanes. In these cases a C-H bond in non-functionalized alkanes was broken through the oxidative addition of Cp*Ir(H){sub 2}L (Cp* = (CH{sub 3}){sub 5}C{sub 5}, L = PPh{sub 3}, Ph = C{sub 6}H{sub 5}) to form Cp*ML(R)(H) or of Cp*Ir(CO){sub 2} to form Cp*Ir(CO)(R)(H). These discoveries opened an entirely new field of research, one which naturally included mechanistic studies aimed at elucidating the various paths involved in these and related reactions. Much was learned from these experiments but they shared the disadvantage of studying under highly non-standard conditions a system which is of interest largely because of its characteristics under standard conditions. Ultrafast time-resolved IR spectroscopy provides an ideal solution to this problem; because it allows the resolution of chemical events taking place on the femto-through picosecond time scale, it is possible to study this important class of reactions under the ambient conditions which are most of interest to the practicing synthetic chemist. Certain of the molecules in question are particularly well-suited to study using the ultrafast IR spectrophotometer described in the experimental section because they contain one or more carbonyl ligands.

  2. 77 FR 31847 - Notification of a Public Meeting and Public Teleconference of the Science Advisory Board (SAB...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-30

    ... Perchlorate Advisory Panel under the auspices of the SAB in the Federal Register on December 16, 2011 (76 FR... maximum contaminant level goal (MCLG) for perchlorate. DATES: The Perchlorate Advisory Panel...

  3. 26 CFR 1.103(n)-4T - Elective carryforward of unused private activity bond limit (temporary).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... unused private activity bond limit in order to provide a sports facility described in section 103(b)(4)(B... carry forward its unused private activity bond limit in order to issue an exempt small issue of... bond limit (temporary). 1.103(n)-4T Section 1.103(n)-4T Internal Revenue INTERNAL REVENUE...

  4. 26 CFR 1.103(n)-4T - Elective carryforward of unused private activity bond limit (temporary).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... unused private activity bond limit in order to provide a sports facility described in section 103(b)(4)(B... carry forward its unused private activity bond limit in order to issue an exempt small issue of... bond limit (temporary). 1.103(n)-4T Section 1.103(n)-4T Internal Revenue INTERNAL REVENUE...

  5. 26 CFR 1.103(n)-4T - Elective carryforward of unused private activity bond limit (temporary).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... unused private activity bond limit in order to provide a sports facility described in section 103(b)(4)(B... carry forward its unused private activity bond limit in order to issue an exempt small issue of... bond limit (temporary). 1.103(n)-4T Section 1.103(n)-4T Internal Revenue INTERNAL REVENUE...

  6. Low-cost bump bonding activities at CERN

    NASA Astrophysics Data System (ADS)

    Vähänen, S.; Tick, T.; Campbell, M.

    2010-11-01

    Conventional bumping processes used in the fabrication of hybrid pixel detectors for High Energy Physics (HEP) experiments use electroplating for Under Bump Metallization (UBM) and solder bump deposition. This process is laborious, involves time consuming photolithography and can only be performed using whole wafers. Electroplating has been found to be expensive when used for the low volumes which are typical of HEP experiments. In the low-cost bump bonding development work, electroless deposition technology of UBM is studied as an alternative to the electroplating process in the bump size / pitch window beginning from 20 μm / 50 μm. Electroless UBM deposition used in combination with solder transfer techniques has the potential to significantly lower the cost of wafer bumping without requiring increased wafer volumes. A test vehicle design of sensor and readout chip, having daisy chains and Kelvin bump structures, was created to characterize the flip chip process with electroless UBM. Two batches of test vehicle wafers were manufactured with different bump pad metallization. Batch #1 had AlSi(1%) metallization, which is similar to the one used on sensor wafers, and Batch #2 had AlSi(2%)Cu(1%) metallization, which is very similar to the one used on readout wafers. Electroless UBMs were deposited on both wafer batches. In addition, electroplated Ni UBM and SnPb solder bumps were grown on the test sensor wafers. Test assemblies were made by flip chip bonding the solder-bumped test sensors against the test readout chips with electroless UBMs. Electrical yields and individual joint resistances were measured from assemblies, and the results were compared to a well known reference technique based on electroplated solder bumps structures on both chips. The electroless UBMs deposited on AlSi(2%)Cu(1%) metallization showed excellent electrical yields and small tolerances in individual joint resistance. The results from the UBMs deposited on AlSi(1%) metallization were non

  7. An intramolecular disulfide bond designed in myoglobin fine-tunes both protein structure and peroxidase activity.

    PubMed

    Wu, Lei-Bin; Yuan, Hong; Zhou, Hu; Gao, Shu-Qin; Nie, Chang-Ming; Tan, Xiangshi; Wen, Ge-Bo; Lin, Ying-Wu

    2016-06-15

    Disulfide bond plays crucial roles in stabilization of protein structure and in fine-tuning protein functions. To explore an approach for rational heme protein design, we herein rationally introduced a pair of cysteines (F46C/M55C) into the scaffold of myoglobin (Mb), mimicking those in native neuroglobin. Molecular modeling suggested that it is possible for Cys46 and Cys55 to form an intramolecular disulfide bond, which was confirmed experimentally by ESI-MS analysis, DTNB reaction and CD spectrum. Moreover, it was shown that the spontaneously formed disulfide bond of Cys46-Cys55 fine-tunes not only the heme active site structure, but also the protein functions. The substitution of Phe46 with Ser46 in F46S Mb destabilizes the protein while facilitates H2O2 activation. Remarkably, the formation of an intramolecular disulfide bond of Cys46-Cys55 in F46C/M55C Mb improves the protein stability and regulates the heme site to be more favorable for substrate binding, resulting in enhanced peroxidase activity. This study provides valuable information of structure-function relationship for heme proteins regulated by an intramolecular disulfide bond, and also suggests that construction of such a covalent bond is useful for design of functional heme proteins. PMID:27117233

  8. Room temperature bonding of SiO2 and SiO2 by surface activated bonding method using Si ultrathin films

    NASA Astrophysics Data System (ADS)

    Utsumi, Jun; Ide, Kensuke; Ichiyanagi, Yuko

    2016-02-01

    The bonding of metal electrodes and insulator hybrid interfaces is one of the key techniques in three-dimensional integration technology. Metal materials such as Cu or Al are easily directly bonded by surface activated bonding at room temperature, but insulator materials such as SiO2 or SiN are not. Using only Si ultrathin films, we propose a new bonding technique for SiO2/SiO2 bonding at room temperature. Two SiO2 surfaces, on which Si thin films were deposited, were contacted in vacuum. We confirmed that the thickness of the layer was about 7 nm by transmission electron microscopy observation and that the layer was non crystalline by electron energy loss spectroscopy analysis. No metal material was found in the bonding interface by energy-dispersive X-ray spectroscopy analysis. The surface energy was about 1 J/m2, and the bonding strength was more than 25 MPa. This bonding technique was successfully realized to enable SiO2/SiO2 bonding without a metal adhesion layer.

  9. Effect of water-ageing on dentine bond strength and anti-biofilm activity of bonding agent containing new monomer dimethylaminododecyl methacrylate

    PubMed Central

    Zhang, Ke; Cheng, Lei; Wu, Eric J.; Weir, Michael D.; Bai, Yuxing; Xu, Hockin H. K.

    2013-01-01

    Objectives The objectives of this study were to develop bonding agent containing a new antibacterial monomer dimethylaminododecyl methacrylate (DMADDM) as well as nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP), and to investigate the effects of water-ageing for 6 months on dentine bond strength and anti-biofilm properties for the first time. Methods Four bonding agents were tested: Scotchbond Multi-Purpose (SBMP) Primer and Adhesive control; SBMP + 5% DMADDM; SBMP + 5% DMADDM + 0.1% NAg; and SBMP + 5% DMADDM + 0.1% NAg with 20% NACP in adhesive. Specimens were water-aged for 1 d and 6 months at 37 °C. Then the dentine shear bond strengths were measured. A dental plaque microcosm biofilm model was used to inoculate bacteria on water-aged specimens and to measure metabolic activity, colony-forming units (CFUs), and lactic acid production. Results Dentine bond strength showed a 35% loss in 6 months of water-ageing for SBMP control (mean ± sd; n = 10); in contrast, the new antibacterial bonding agents showed no strength loss. The DMADDM–NAg–NACP containing bonding agent imparted a strong antibacterial effect by greatly reducing biofilm viability, metabolic activity and acid production. The biofilm CFU was reduced by more than two orders of magnitude, compared to SBMP control. Furthermore, the DMADDM–NAg–NACP bonding agent exhibited a long-term antibacterial performance, with no significant difference between 1 d and 6 months (p > 0.1). Conclusions Incorporating DMADDM–NAg–NACP in bonding agent yielded potent and long-lasting antibacterial properties, and much stronger bond strength after 6 months of water-ageing than a commercial control. The new antibacterial bonding agent is promising to inhibit biofilms and caries at the margins. The method of DMADDM–NAg–NACP incorporation may have a wide applicability to other adhesives, cements and composites. PMID:23583528

  10. Activation of C-H bonds and functionalization of hydrocarbons of the adamantane series. Review

    SciTech Connect

    Bagrii, Ye.I.; Karaulova, Ye.N.

    1993-12-31

    The highly symmetrical compact structure of an adamantane molecule gives its derivatives unusual properties. This governs the use of compounds with an adamantane fragment both for scientific research and in industry, and in particular in medicine. Importants ways of producing functional derivatives of adamantane without changing its carbon skeleton are processes occurring via the activation of the C-H bond. Detailed information concerning these reactions was given in an earlier monograph, which dealt with research published mainly before 1986. In the present review an examination is made of later investigations of C-H bond activation in adamantane, including research using biological and biomimetic methods of activation.

  11. Hormonal changes and couple bonding in consensual sadomasochistic activity.

    PubMed

    Sagarin, Brad J; Cutler, Bert; Cutler, Nadine; Lawler-Sagarin, Kimberly A; Matuszewich, Leslie

    2009-04-01

    In two studies, 58 sadomasochistic (SM) practitioners provided physiological measures of salivary cortisol and testosterone (hormones associated with stress and dominance, respectively) and psychological measures of relationship closeness before and after participating in SM activities. Observed activities included bondage, sensory deprivation, a variety of painful and pleasurable stimulation, verbal and non-verbal communication, and expressions of caring and affection. During the scenes, cortisol rose significantly for participants who were bound, receiving stimulation, and following orders, but not for participants who were providing stimulation, orders, or structure. Female participants who were bound, receiving stimulation, and following orders also showed increases in testosterone during the scenes. Thereafter, participants who reported that their SM activities went well showed reductions in physiological stress (cortisol) and increases in relationship closeness. Among participants who reported that their SM activities went poorly, some showed decreases in relationship closeness whereas others showed increases. The increases in relationship closeness combined with the displays of caring and affection observed as part of the SM activities offer support for the modern view that SM, when performed consensually, has the potential to increase intimacy between participants. PMID:18563549

  12. C-ON Bond Homolysis of Alkoxyamines, Part 11: Activation of the Nitroxyl Fragment.

    PubMed

    Audran, Gérard; Brémond, Paul; Marque, Sylvain R A; Yamasaki, Toshihide

    2016-03-01

    A few years ago, Bagryanskaya and colleagues (J. Org. Chem. 2011) showed that protonation of the nitroxyl fragment deactivated the alkoxyamine C-ON bond. Conversely, our group showed that protonation (Chem. Commun. 2011), as well as other chemical reactions such as oxidation or amine quaternization (Org. Lett. 2012), of the pyridyl moiety carried by the alkyl fragment was suitable to activate the homolysis of the C-ON bond. To pursue our goal of applying alkoxyamines as theranostic agents (Org. Biomol. Chem. 2014 and Mol. Pharmaceutics 2014) by activation of the C-ON bond homolysis, we turned our interest to the chemical activation of the nitroxyl fragment by oxidation/reduction of selected functions. Conversion of a hydroxyl group located close to the nitroxyl moiety successively into aldehyde, then acid, and eventually into ester, led to a successive decrease in kd. PMID:26878593

  13. Shear bond strength to enamel after power bleaching activated by different sources.

    PubMed

    Can-Karabulut, Deniz C; Karabulut, Baris

    2010-01-01

    The purpose of the present study was to evaluate enamel bond strength of a composite resin material after hydrogen peroxide bleaching, activated by a diode laser (LaserSmile), an ozone device (HealOzone), a light-emitting diode (BT Cool whitening system), and a quartz-Plus. Fifty extracted caries-free permanent incisors were used in this study. Thirty-eight percent hydrogen peroxidegel was applied to sound, flattened labial enamel surfaces and activated by different sources. Enamel surfaces that had received no treatment were used as control samples. Bonding agent was applied according to the manufacturer's instructions and the adhesion test was performed according to ISO/TS 11405. Statistical analysis showed significant influence of the different activation technique of hydrogen peroxide on shear bond strength to enamel (ANOVA, LSD, P < 0.05). The data in this vitro explorative study suggest the activation of hydrogen peroxide by different sources may further affect the shear bond strength of subsequent composite resin restoration to enamel. Within the limitations of this in vitro study, further studies examining the structural changes of activated hydrogen peroxide-treated enamel are needed. Due to the different activation methods; duration of light irradiation effects, longer time periods may be needed before application of adhesive restorations to enamel, compared with non-activated bleaching. PMID:21069109

  14. Covalent Bond between Ligand and Receptor Required for Efficient Activation in Rhodopsin*

    PubMed Central

    Matsuyama, Take; Yamashita, Takahiro; Imai, Hiroo; Shichida, Yoshinori

    2010-01-01

    Rhodopsin is an extensively studied member of the G protein-coupled receptors (GPCRs). Although rhodopsin shares many features with the other GPCRs, it exhibits unique features as a photoreceptor molecule. A hallmark in the molecular structure of rhodopsin is the covalently bound chromophore that regulates the activity of the receptor acting as an agonist or inverse agonist. Here we show the pivotal role of the covalent bond between the retinal chromophore and the lysine residue at position 296 in the activation pathway of bovine rhodopsin, by use of a rhodopsin mutant K296G reconstituted with retinylidene Schiff bases. Our results show that photoreceptive functions of rhodopsin, such as regiospecific photoisomerization of the ligand, and its quantum yield were not affected by the absence of the covalent bond, whereas the activation mechanism triggered by photoisomerization of the retinal was severely affected. Furthermore, our results show that an active state similar to the Meta-II intermediate of wild-type rhodopsin did not form in the bleaching process of this mutant, although it exhibited relatively weak G protein activity after light irradiation because of an increased basal activity of the receptor. We propose that the covalent bond is required for transmitting structural changes from the photoisomerized agonist to the receptor and that the covalent bond forcibly keeps the low affinity agonist in the receptor, resulting in a more efficient G protein activation. PMID:20042594

  15. 29 CFR 2580.412-8 - The nature of the duties or activities to which the bonding requirement relates.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 9 2011-07-01 2011-07-01 false The nature of the duties or activities to which the bonding requirement relates. 2580.412-8 Section 2580.412-8 Labor Regulations Relating to Labor (Continued) EMPLOYEE... INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-8 The nature...

  16. 29 CFR 2580.412-8 - The nature of the duties or activities to which the bonding requirement relates.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 9 2014-07-01 2014-07-01 false The nature of the duties or activities to which the bonding requirement relates. 2580.412-8 Section 2580.412-8 Labor Regulations Relating to Labor (Continued) EMPLOYEE... INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-8 The nature...

  17. 29 CFR 2580.412-8 - The nature of the duties or activities to which the bonding requirement relates.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 9 2012-07-01 2012-07-01 false The nature of the duties or activities to which the bonding requirement relates. 2580.412-8 Section 2580.412-8 Labor Regulations Relating to Labor (Continued) EMPLOYEE... INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-8 The nature...

  18. 29 CFR 2580.412-8 - The nature of the duties or activities to which the bonding requirement relates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 9 2010-07-01 2010-07-01 false The nature of the duties or activities to which the bonding requirement relates. 2580.412-8 Section 2580.412-8 Labor Regulations Relating to Labor (Continued) EMPLOYEE... INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-8 The nature...

  19. 29 CFR 2580.412-8 - The nature of the duties or activities to which the bonding requirement relates.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 9 2013-07-01 2013-07-01 false The nature of the duties or activities to which the bonding requirement relates. 2580.412-8 Section 2580.412-8 Labor Regulations Relating to Labor (Continued) EMPLOYEE... INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES Scope and Form of the Bond § 2580.412-8 The nature...

  20. Nickel-Catalyzed Decarbonylative Borylation of Amides: Evidence for Acyl C-N Bond Activation.

    PubMed

    Hu, Jiefeng; Zhao, Yue; Liu, Jingjing; Zhang, Yemin; Shi, Zhuangzhi

    2016-07-18

    A nickel/N-heterocyclic carbene catalytic system has been established for decarbonylative borylation of amides with B2 nep2 by C-N bond activation. This transformation shows good functional-group compatibility and can serve as a powerful synthetic tool for late-stage borylation of amide groups in complex compounds. More importantly, as a key intermediate, the structure of an acyl nickel complex was first confirmed by X-ray analysis. Furthermore, the decarbonylative process was also observed. These findings confirm the key mechanistic features of the acyl C-N bond activation process. PMID:27258597

  1. Active-Metal Template Synthesis of a Halogen-Bonding Rotaxane for Anion Recognition.

    PubMed

    Langton, Matthew J; Xiong, Yaoyao; Beer, Paul D

    2015-12-21

    The synthesis of an all-halogen-bonding rotaxane for anion recognition is achieved by using active-metal templation. A flexible bis-iodotriazole-containing macrocycle is exploited for the metal-directed rotaxane synthesis. Endotopic binding of a Cu(I) template facilitates an active-metal CuAAC iodotriazole axle formation reaction that captures the interlocked rotaxane product. Following copper-template removal, exotopic coordination of a more sterically demanding rhenium(I) complex induces an inversion in the conformation of the macrocycle component, directing the iodotriazole halogen-bond donors into the rotaxane's interlocked binding cavity to facilitate anion recognition. PMID:26500150

  2. [Hydrogen induced C-C, C-N, and C-S bond activities on Pi and Ni surfaces]: Summary

    SciTech Connect

    Gland, J.L.

    1994-12-31

    This document summarizes research applied to chemical bond activation studies. Topics summarized include: Carbon nitrogen bonds experimentation with aniline on Ni(111), Mi(100), and Pt(111) surfaces; carbon sulfur bonds experimentation with methanethiol, phenylthiol, and dimethyl disulfide on Pt(111) and Ni(111) surfaces; carbon-carbon bonds experimentation on Ni(100), Ni(111) and Pt(111) surfaces; and in-situ fluorescence yield near edge spectroscopy.

  3. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

    SciTech Connect

    Lichtenberger, D.L.

    1992-01-01

    Purpose of this research program is to obtain experimental information on the different fundamental ways metals bond and activate organic molecules. Our approach has been to directly probe the electronic interactions between metals and molecules through a wide variety of ionization spectroscopies and other techniques, and to investigate the relationships with bonding modes, structures, and chemical behavior. During this period, we have (1) characterized the electronic features of diphosphines and monophosphines in their coordination to metals, (2) carried out theoretical and experimental investigations of the bonding capabilities of C[sub 60] to transition metals, (3) developed techniques for the imaging of single molecules on gold substrates that emphasizes the electronic backbonding from the metal to the molecule, (4) obtained the high resolution photoelectron spectrum of pure C[sub 70] in the gas phase, (5) compared the bonding of [eta][sup 3]- acetylide ligands to the bonding of other small organic molecules with metals, and (6) reported the photoelectron spectra and bonding of [eta][sup 3]-cyclopropenyl groups to metals.

  4. Effect of bonding on the performance of a piezoactuator-based active control system

    NASA Technical Reports Server (NTRS)

    Baz, A.; Poh, S.

    1987-01-01

    The utilization of piezoelectric actuators in controlling the structural vibrations of flexible beams is studied. A Modified Independent Modal Space Control (MIMSC) method is devised to select the optimal location, control gains and excitation voltage of the piezoelectric actuators in a way that would minimize the amplitudes of vibrations of beams to which these actuators are bonded, as well as the input control energy necessary to suppress these vibrations. The presented method accounts for the effects that the piezoelectric actuators and the bonding layers have on changing the elastic and inertial properties of the flexible beams. Numerical examples are presented to illustrate the application of the MIMSC method and to demonstrate the effect of the physical and geometrical properties of the bonding layer on the dynamic performance of the actively controlled beams. The obtained results emphasize the importance of the devised method in designing more realistic active control systems for flexible beams, in particular, and large flexible structures in general.

  5. Effect of different irrigant activation protocols on push-out bond strength.

    PubMed

    Akyuz Ekim, Sefika Nur; Erdemir, Ali

    2015-11-01

    The study aimed to evaluate the effect of various final irrigant activation protocols on push-out bond strength of fiber post. Thirty-two single-rooted human maxillar central teeth were sectioned below the cementoenamel junction, instrumented and obturated. Post-space preparation was performed, and roots were randomly divided into eight groups (n = 4) according to the final irrigant activation protocols; distilled water was used as an irrigant in group 1. The other groups were treated with 2.5% NaOCl and 17% EDTA. Conventional syringe irrigation (CSI, no activation) was used in group 2. Irrigation solutions were activated using passive ultrasonic irrigation (PUI, group 3), EndoVac apical negative pressure (ANP, group 4), diode laser (group 5), neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (group 6), erbium:yttrium-aluminum-garnet (Er:YAG) laser (group 7), and Er:YAG laser using with photon-induced photoacoustic streaming (PIPS™) technique (group 8). In all groups, fiber posts (White Post DC, FGM) were luted using Panavia F 2.0 (Kuraray, Osaka, Japan). The specimens were transversally sectioned, and all slices from coronal and apical regions were subjected to push-out tests. The data were calculated as megapascals and analyzed by using two-way analysis of variance followed by post hoc Tukey honestly significant difference (HSD) tests. Removing the smear layer increased the bond strength to dentine when compared with the control group (p < 0.05). The highest bond strength was obtained in the PIPS laser-activated irrigation group (p < 0.05). Coronal root region presented significantly higher bond strength than the apical region (p < 0.05). PIPS laser-activated irrigation showed higher efficiency as a final irrigant activation protocol on push-out bond strength of fiber post. PMID:26022731

  6. Diffusion Bonding Beryllium to Reduced Activation Ferritic Martensitic Steel: Development of Processes and Techniques

    NASA Astrophysics Data System (ADS)

    Hunt, Ryan Matthew

    Only a few materials are suitable to act as armor layers against the thermal and particle loads produced by magnetically confined fusion. These candidates include beryllium, tungsten, and carbon fiber composites. The armor layers must be joined to the plasma facing components with high strength bonds that can withstand the thermal stresses resulting from differential thermal expansion. While specific joints have been developed for use in ITER (an experimental reactor in France), including beryllium to CuCrZr as well as tungsten to stainless steel interfaces, joints specific to commercially relevant fusion reactors are not as well established. Commercial first wall components will likely be constructed front Reduced Activation Ferritic Martensitic (RAFM) steel, which will need to be coating with one of the three candidate materials. Of the candidates, beryllium is particularly difficult to bond, because it reacts during bonding with most elements to form brittle intermetallic compounds. This brittleness is unacceptable, as it can lead to interface crack propagation and delamination of the armor layer. I have attempted to overcome the brittle behavior of beryllium bonds by developing a diffusion bonding process of beryllium to RAFM steel that achieves a higher degree of ductility. This process utilized two bonding aids to achieve a robust bond: a. copper interlayer to add ductility to the joint, and a titanium interlayer to prevent beryllium from forming unwanted Be-Cu intermetallics. In addition, I conducted a series of numerical simulations to predict the effect of these bonding aids on the residual stress in the interface. Lastly, I fabricated and characterized beryllium to ferritic steel diffusion bonds using various bonding parameters and bonding aids. Through the above research, I developed a process to diffusion bond beryllium to ferritic steel with a 150 M Pa tensile strength and 168 M Pa shear strength. This strength was achieved using a Hot Isostatic

  7. Peroxide bond strength of antimalarial drugs containing an endoperoxide cycle. Relation with biological activity.

    PubMed

    Fernández, Israel; Robert, Anne

    2011-06-01

    Several endoperoxide compounds are very efficient antimalarial analogues of the natural drug artemisinin. Quantum chemical calculations have been used to correlate the computed free energies of the O-O bond with respect to the total number of oxygen atoms contained in the cycle, and with the size/strain of the cycle (5- or 6-membered cycles). The gas-phase homolysis of the O-O bond has been studied for five- and six-membered oxygenated cycles which are models of the "real" drugs. Our results indicate that, in 6-membered cycles, the stability order is the following: 1,2-dioxane > 1,2,4-trioxane > 1,2,4,5-tetraoxane. In cycles containing 3 oxygen atoms, the 5-membered cycle 1,2,4-trioxolane was found much less stable than its 6-membered counterpart 1,2,4-trioxane. This feature indicates the possible role of the cycle strain for the O-O bond stability, and may also explain the high antimalarial activity of some trioxolane derivatives. Similar trends in the O-O bond strength have been found for the real antimalarial drugs. However, the O-O bond stability is not in itself a decisive argument to anticipate the antimalarial activity of drugs. PMID:21487624

  8. 26 CFR 1.103(n)-1T - Limitation on aggregrate amount of private activity bonds (temporary).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... section 103(n) since the aggregate amount of private activity bonds issued by City M in 1986 exceeded its... activity bonds (temporary). 1.103(n)-1T Section 1.103(n)-1T Internal Revenue INTERNAL REVENUE SERVICE... Excluded from Gross Income § 1.103(n)-1T Limitation on aggregrate amount of private activity...

  9. 26 CFR 1.103(n)-1T - Limitation on aggregrate amount of private activity bonds (temporary).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... section 103(n) since the aggregate amount of private activity bonds issued by City M in 1986 exceeded its... activity bonds (temporary). 1.103(n)-1T Section 1.103(n)-1T Internal Revenue INTERNAL REVENUE SERVICE... Excluded from Gross Income § 1.103(n)-1T Limitation on aggregrate amount of private activity...

  10. The value of spontaneous alternation behavior (SAB) as a test of retention in pharmacological investigations of memory.

    PubMed

    Hughes, Robert N

    2004-09-01

    Because of its reliance on memory, the tendency for rats, mice and other animals to alternate successive choices of T- or Y-maze arms has assumed considerable popularity in pharmacological studies of spatial memory as a quick and simple measure of retention that avoids the need for extensive training and the use of conventional reinforcers. Two forms of this tendency have been utilized, namely two-trial and continuous spontaneous alternation behavior (SAB). However, as the behavior can also reflect drug-related changes in sensory/attentional, motivational and performance processes, SAB should not be unquestionably accepted as a measure of memory alone. While assessments of post-acquisition drug effects on longer term memory may be possible through the appropriate timing of drug administration, this is more problematic if SAB is used as a measure of shorter term memory. Even though SAB can be a useful index of responsiveness to novelty, its value as a measure of retention is less certain. In this latter respect, a possible alternative to SAB testing might be the recently developed form of the related procedure, responsiveness to change. PMID:15465137

  11. Direct 2-acetoxylation of quinoline N-oxides via copper catalyzed C-H bond activation.

    PubMed

    Chen, Xuan; Zhu, Chongwei; Cui, Xiuling; Wu, Yangjie

    2013-08-01

    An efficient and direct 2-acetoxylation of quinoline N-oxides via copper(I) catalyzed C-H bond activation has been developed. This transformation was achieved using TBHP as an oxidant in the cross-dehydrogenative coupling (CDC) reaction of quinoline N-oxides with aldehydes, and provided a practical pathway to 2-acyloxyl quinolines. PMID:23793162

  12. Effects of metal ions and disulfide bonds on the activity of phosphodiesterase from Trimeresurus stejnegeri venom.

    PubMed

    Peng, Lili; Xu, Xiaolong; Guo, Mingchun; Yan, Xincheng; Wang, Shasha; Gao, Shang; Zhu, Shanshan

    2013-06-01

    Obviously different from the other known phosphodiesterases, the phosphodiesterase from Trimeresurus stejnegeri venom (TS-PDE) consists of two different chains linked with disulfide bonds and contains both endogenous Cu(2+) and Zn(2+). Cu(2+) and Zn(2+) are important for its phosphodiesterase activity. In this study, the effects of metal ions and small-molecule reductants on its structure and activity have been investigated by polyacrylamide gel electrophoresis, high performance liquid chromatography, fluorescence and electron paramagnetic resonance spectroscopy. The results show that TS-PDE has one class of Zn(2+) binding site and two classes of Cu(2+) binding site, including the high affinity activator sites and the low affinity sites. Cu(2+) ions function as a switch for its phosphodiesterase activity. The catalytic activity of TS-PDE does not have an absolute requirement for Cu(2+) and Zn(2+). Mg(2+), Mn(2+), Ni(2+), Co(2+) and Ca(2+) are all effective for its phosphodiesterase activity. TS-PDE has seven disulfide bonds and ten free cysteine residues. l-Ascorbate inhibits the phosphodiesterase activity of TS-PDE through reduction of the Cu(2+), while dithiothreitol, glutathione and tris(2-carboxyethyl)phosphine inhibit the phosphodiesterase activity of TS-PDE by reducing both the Cu(2+) and disulfide bonds. The catalytic activity of TS-PDE relies on its disulfide bonds and bimetallic cluster. In addition, biologically-relevant reductants, glutathione and l-ascorbate, have been found to be endogenous inhibitors to the phosphodiesterase activity of TS-PDE. PMID:23775423

  13. Titanium-Thiolate-Aluminum-Carbide Complexes by Multiple C-H Bond Activation.

    PubMed

    Guérin; Stephan

    1999-12-16

    All three C-H bonds of a methyl group are activated in the reaction of [Cp(iPr(3)PN)Ti(SR)(2)] with AlMe(3) [Eq. (1)]. The Ti-Al-carbide clusters formed contain a severely distorted tetrahedral carbide carbon atom with a relatively short bond to Ti, which is attributed to a relative increase in the Lewis acidity of the Ti center as a result of the interaction of the S and N donors with Al. PMID:10649329

  14. Repetitive Sequence Variations in the Promoter Region of the Adhesin-Encoding Gene sabA of Helicobacter pylori Affect Transcription

    PubMed Central

    Harvey, Vivian C.; Acio, Catherine R.; Bredehoft, Amy K.; Zhu, Laurence; Hallinger, Daniel R.; Quinlivan-Repasi, Vanessa; Harvey, Samuel E.

    2014-01-01

    The pathogenesis of diseases elicited by the gastric pathogen Helicobacter pylori is partially determined by the effectiveness of adaptation to the variably acidic environment of the host stomach. Adaptation includes appropriate adherence to the gastric epithelium via outer membrane protein adhesins such as SabA. The expression of sabA is subject to regulation via phase variation in the promoter and coding regions as well as repression by the two-component system ArsRS. In this study, we investigated the role of a homopolymeric thymine [poly(T)] tract −50 to −33 relative to the sabA transcriptional start site in H. pylori strain J99. We quantified sabA expression in H. pylori J99 by quantitative reverse transcription-PCR (RT-PCR), demonstrating significant changes in sabA expression associated with experimental manipulations of poly(T) tract length. Mimicking the length increase of this tract by adding adenines instead of thymines had similar effects, while the addition of other nucleotides failed to affect sabA expression in the same manner. We hypothesize that modification of the poly(T) tract changes DNA topology, affecting regulatory protein interaction(s) or RNA polymerase binding efficiency. Additionally, we characterized the interaction between the sabA promoter region and ArsR, a response regulator affecting sabA expression. Using recombinant ArsR in electrophoretic mobility shift assays (EMSA), we localized binding to a sequence with partial dyad symmetry −20 and +38 relative to the sabA +1 site. The control of sabA expression by both ArsRS and phase variation at two distinct repeat regions suggests the control of sabA expression is both complex and vital to H. pylori infection. PMID:25022855

  15. Bond activation with an apparently benign ethynyl dithiocarbamate Ar-C≡C-S-C(S)NR2.

    PubMed

    Ung, Gaël; Frey, Guido D; Schoeller, Wolfgang W; Bertrand, Guy

    2011-10-10

    The hedgehog molecule: A simple ethynyl dithiocarbamate [Ar-C≡C-S-C(S)NR(2)] is able to cleave a broad range of enthalpically strong σ bonds and to activate carbon dioxide and elemental sulfur. Depending on the substrate, the bond activation process involves either the existence of an equilibrium with the nonobservable mesoionic carbene isomer or the cooperation of the nucleophilic carbon-carbon triple bond and the electrophilic CS carbon atom. PMID:23210141

  16. Bond slip detection of concrete-encased composite structure using shear wave based active sensing approach

    NASA Astrophysics Data System (ADS)

    Zeng, Lei; Parvasi, Seyed Mohammad; Kong, Qingzhao; Huo, Linsheng; Lim, Ing; Li, Mo; Song, Gangbing

    2015-12-01

    Concrete-encased composite structure exhibits improved strength, ductility and fire resistance compared to traditional reinforced concrete, by incorporating the advantages of both steel and concrete materials. A major drawback of this type of structure is the bond slip introduced between steel and concrete, which directly reduces the load capacity of the structure. In this paper, an active sensing approach using shear waves to provide monitoring and early warning of the development of bond slip in the concrete-encased composite structure is proposed. A specimen of concrete-encased composite structure was investigated. In this active sensing approach, shear mode smart aggregates (SAs) embedded in the concrete act as actuators and generate desired shear stress waves. Distributed piezoceramic transducers installed in the cavities of steel plates act as sensors and detect the wave response from shear mode SAs. Bond slip acts as a form of stress relief and attenuates the wave propagation energy. Experimental results from the time domain analysis clearly indicate that the amplitudes of received signal by lead zirconate titanate sensors decreased when bond slip occurred. In addition, a wavelet packet-based analysis was developed to compute the received signal energy values, which can be used to determine the initiation and development of bond slip in concrete-encased composite structure. In order to establish the validity of the proposed method, a 3D finite element analysis of the concrete-steel bond model is further performed with the aid of the commercial finite element package, Abaqus, and the numerical results are compared with the results obtained in experimental study.

  17. Antibacterial activity and ion release of bonding agent containing amorphous calcium phosphate nanoparticles

    PubMed Central

    Chen, Chen; Weir, Michael D.; Cheng, Lei; Lin, Nancy; Lin-Gibson, Sheng; Chow, Laurence C.; Zhou, Xuedong; Xu, Hockin H. K.

    2015-01-01

    Objectives Recurrent caries at the margins is a primary reason for restoration failure. The objectives of this study were to develop bonding agent with the double benefits of antibacterial and remineralizing capabilities, to investigate the effects of NACP filler level and solution pH on Ca and P ion release from adhesive, and to examine the antibacterial and dentin bond properties. Methods Nanoparticles of amorphous calcium phosphate (NACP) and a quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM) were synthesized. Scotchbond Multi-Purpose (SBMP) primer and adhesive served as control. DMADDM was incorporated into primer and adhesive at 5% by mass. NACP was incorporated into adhesive at filler mass fractions of 10%, 20%, 30% and 40%. A dental plaque microcosm biofilm model was used to test the antibacterial bonding agents. Calcium (Ca) and phosphate (P) ion releases from the cured adhesive samples were measured vs. filler level and solution pH of 7, 5.5 and 4. Results Adding 5% DMADDM and 10–40% NACP into bonding agent, and water-aging for 28 days, did not affect dentin bond strength, compared to SBMP control at 1 day (p > 0.1). Adding DMADDM into bonding agent substantially decreased the biofilm metabolic activity and lactic acid production. Total microorganisms, total streptococci, and mutans streptococci were greatly reduced for bonding agents containing DMADDM. Increasing NACP filler level from 10% to 40% in adhesive increased the Ca and P ion release by an order of magnitude. Decreasing solution pH from 7 to 4 increased the ion release from adhesive by 6–10 folds. Significance Bonding agents containing antibacterial DMADDM and remineralizer NACP were formulated to have Ca and P ion release, which increased with NACP filler level from 10% to 40% in adhesive. NACP adhesive was “smart” and dramatically increased the ion release at cariogenic pH 4, when these ions would be most-needed to inhibit caries. Therefore, bonding agent

  18. Silver(I) NHC mediated C-C bond activation of alkyl nitriles and catalytic efficiency in oxazoline synthesis.

    PubMed

    Heath, Rachael; Müller-Bunz, Helge; Albrecht, Martin

    2015-05-21

    Preparation of silver triazolylidene (trz) species from triazolium salts and Ag2O in refluxing MeCN leads to a selective C-C bond cleavage and the formation of complexes of general formula [(trz)Ag(CN)] from Calkyl-CN bond activation. Moreover, these silver carbene complexes are precursors of highly active catalysts for oxazoline formation via aldol condensation. PMID:25913007

  19. Highly dispersed buckybowls as model carbocatalysts for C–H bond activation

    DOE PAGESBeta

    Soykal, I. Ilgaz; Wang, Hui; Park, Jewook; Li, An-Ping; Liang, Chengdu; Schwartz, Viviane

    2015-03-19

    Buckybowl fractions dispersed on mesoporous silica constitute an ideal model for studying the catalysis of graphitic forms of carbon since the dispersed carbon nanostructures contain a high ratio of edge defects and curvature induced by non-six-membered rings. Dispersion of the active centers on an easily accessible high surface area material allowed for high density of surface active sites associated with oxygenated structures. This report illustrates a facile method of creating model polycyclic aromatic nano-structures that are not only active for alkane C-H bond activation and oxidative dehydrogenation but also can be practical catalysts to be eventually used in industry.

  20. The active site of hen egg-white lysozyme: flexibility and chemical bonding

    SciTech Connect

    Held, Jeanette Smaalen, Sander van

    2014-04-01

    Chemical bonding at the active site of lysozyme is analyzed on the basis of a multipole model employing transferable multipole parameters from a database. Large B factors at low temperatures reflect frozen-in disorder, but therefore prevent a meaningful free refinement of multipole parameters. Chemical bonding at the active site of hen egg-white lysozyme (HEWL) is analyzed on the basis of Bader’s quantum theory of atoms in molecules [QTAIM; Bader (1994 ▶), Atoms in Molecules: A Quantum Theory. Oxford University Press] applied to electron-density maps derived from a multipole model. The observation is made that the atomic displacement parameters (ADPs) of HEWL at a temperature of 100 K are larger than ADPs in crystals of small biological molecules at 298 K. This feature shows that the ADPs in the cold crystals of HEWL reflect frozen-in disorder rather than thermal vibrations of the atoms. Directly generalizing the results of multipole studies on small-molecule crystals, the important consequence for electron-density analysis of protein crystals is that multipole parameters cannot be independently varied in a meaningful way in structure refinements. Instead, a multipole model for HEWL has been developed by refinement of atomic coordinates and ADPs against the X-ray diffraction data of Wang and coworkers [Wang et al. (2007), Acta Cryst. D63, 1254–1268], while multipole parameters were fixed to the values for transferable multipole parameters from the ELMAM2 database [Domagala et al. (2012), Acta Cryst. A68, 337–351] . Static and dynamic electron densities based on this multipole model are presented. Analysis of their topological properties according to the QTAIM shows that the covalent bonds possess similar properties to the covalent bonds of small molecules. Hydrogen bonds of intermediate strength are identified for the Glu35 and Asp52 residues, which are considered to be essential parts of the active site of HEWL. Furthermore, a series of weak C

  1. Chromoselective Photocatalysis: Controlled Bond Activation through Light-Color Regulation of Redox Potentials.

    PubMed

    Ghosh, Indrajit; König, Burkhard

    2016-06-27

    Catalysts that can be regulated in terms of activity and selectivity by external stimuli may allow the efficient multistep synthesis of complex molecules and pharmaceuticals. Herein, we report the light-color regulation of the redox potential of a photocatalyst to control the activation of chemical bonds. Light-color control of the redox power of a photocatalyst introduces a new selectivity parameter to photoredox catalysis: Instead of changing the catalyst or ligand, alteration of the color of the visible-light irradiation adjusts the selectivity in catalytic transformations. By using this principle, the selective activation of aryl-halide bonds for C-H arylation and the sequential conversion of functional groups with different reduction potentials is possible by simply applying different colors of light for excitation of the photocatalyst. PMID:27198967

  2. Quantitative dissection of hydrogen bond-mediated proton transfer in the ketosteroid isomerase active site

    PubMed Central

    Sigala, Paul A.; Fafarman, Aaron T.; Schwans, Jason P.; Fried, Stephen D.; Fenn, Timothy D.; Caaveiro, Jose M. M.; Pybus, Brandon; Ringe, Dagmar; Petsko, Gregory A.; Boxer, Steven G.; Herschlag, Daniel

    2013-01-01

    Hydrogen bond networks are key elements of protein structure and function but have been challenging to study within the complex protein environment. We have carried out in-depth interrogations of the proton transfer equilibrium within a hydrogen bond network formed to bound phenols in the active site of ketosteroid isomerase. We systematically varied the proton affinity of the phenol using differing electron-withdrawing substituents and incorporated site-specific NMR and IR probes to quantitatively map the proton and charge rearrangements within the network that accompany incremental increases in phenol proton affinity. The observed ionization changes were accurately described by a simple equilibrium proton transfer model that strongly suggests the intrinsic proton affinity of one of the Tyr residues in the network, Tyr16, does not remain constant but rather systematically increases due to weakening of the phenol–Tyr16 anion hydrogen bond with increasing phenol proton affinity. Using vibrational Stark spectroscopy, we quantified the electrostatic field changes within the surrounding active site that accompany these rearrangements within the network. We were able to model these changes accurately using continuum electrostatic calculations, suggesting a high degree of conformational restriction within the protein matrix. Our study affords direct insight into the physical and energetic properties of a hydrogen bond network within a protein interior and provides an example of a highly controlled system with minimal conformational rearrangements in which the observed physical changes can be accurately modeled by theoretical calculations. PMID:23798390

  3. Merging allylic carbon-hydrogen and selective carbon-carbon bond activation

    NASA Astrophysics Data System (ADS)

    Masarwa, Ahmad; Didier, Dorian; Zabrodski, Tamar; Schinkel, Marvin; Ackermann, Lutz; Marek, Ilan

    2014-01-01

    Since the nineteenth century, many synthetic organic chemists have focused on developing new strategies to regio-, diastereo- and enantioselectively build carbon-carbon and carbon-heteroatom bonds in a predictable and efficient manner. Ideal syntheses should use the least number of synthetic steps, with few or no functional group transformations and by-products, and maximum atom efficiency. One potentially attractive method for the synthesis of molecular skeletons that are difficult to prepare would be through the selective activation of C-H and C-C bonds, instead of the conventional construction of new C-C bonds. Here we present an approach that exploits the multifold reactivity of easily accessible substrates with a single organometallic species to furnish complex molecular scaffolds through the merging of otherwise difficult transformations: allylic C-H and selective C-C bond activations. The resulting bifunctional nucleophilic species, all of which have an all-carbon quaternary stereogenic centre, can then be selectively derivatized by the addition of two different electrophiles to obtain more complex molecular architecture from these easily available starting materials.

  4. Room temperature GaN-GaAs direct bonding by argon-beam surface activation

    NASA Astrophysics Data System (ADS)

    Higurashi, Eiji; Tokuda, Yuichiro; Akaike, Masatake; Suga, Tadatomo

    2007-10-01

    A room temperature direct bonding using surface activation by argon (Ar)-beam sputtering was applied to the bonding between gallium nitride (GaN) and gallium arsenide (GaAs). The silicon doped n-type GaN films used in this experiment were grown by metal organic chemical vapor deposition on (0001) sapphire substrates. The GaN film thickness is 3 μm with a surface roughness of approximately 0.22 nm (R a) as measured by atomic force microscopy. The silicon doped n-type GaAs (100) wafers with a surface roughness of approximately 0.34 nm (R a) were used as GaAs substrates. The GaN and GaAs samples were cleaned by sputtering with a 1.5 keV Ar-fast atom beam with 15 mA in the vacuum chamber (background pressure: 1.3×10 -5~4.0×10 -4 Pa). Then, the samples were brought into contact as quickly as possible with a load of 735 N at room temperature. After this process, GaN films were successfully bonded to GaAs substrates without any heat treatment. Cross-sectional scanning electron microscopy showed that most of the interface area was well bonded. The bonding strength was evaluated by die-shear tests. Although all samples were visibly separated from the interface rather than in the bulk region after die-shear tests, the estimated die-shear strength of GaN/GaAs structures was 1.5 -7 MPa. The advantage of our process is free from the various problems caused by the large thermal expansion mismatch during heat treatment in the conventional fusion bonding.

  5. Non-coordinating-Anion-Directed Reversal of Activation Site: Selective C-H Bond Activation of N-Aryl Rings.

    PubMed

    Wang, Dawei; Yu, Xiaoli; Xu, Xiang; Ge, Bingyang; Wang, Xiaoli; Zhang, Yaxuan

    2016-06-13

    An Rh-catalyzed selective C-H bond activation of diaryl-substituted anilides is described. In an attempt to achieve C-H activation of C-aryl rings, we unexpectedly obtained an N-aryl ring product under non-coordinating anion conditions, whereas the C-aryl ring product was obtained in the absence of a non-coordinating anion. This methodology has proved to be an excellent means of tuning and adjusting selective C-H bond activation of C-aryl and N-aryl rings. The approach has been rationalized by mechanistic studies and theoretical calculations. In addition, it has been found and verified that the catalytic activity of the rhodium catalyst is obviously improved by non-coordinating anions, which provides an efficient strategy for obtaining a highly chemoselective catalyst. Mechanistic experiments also unequivocally ruled out the possibility of a so-called "silver effect" in this transformation involving silver. PMID:27159169

  6. Pd/Norbornene: A Winning Combination for Selective Aromatic Functionalization via C-H Bond Activation.

    PubMed

    Della Ca', Nicola; Fontana, Marco; Motti, Elena; Catellani, Marta

    2016-07-19

    Direct C-H bond activation is an important reaction in synthetic organic chemistry. This methodology has the potential to simplify reactions by avoiding the use of prefunctionalized reagents. However, selectivity, especially site selectivity, remains challenging. Sequential reactions, in which different molecules or groups are combined in an ordered sequence, represent a powerful tool for the construction of complex molecules in a single operation. We have discovered and developed a synthetic methodology that combines selective C-H bond activation with sequential reactions. This procedure, which is now known as the "Catellani reaction", enables the selective functionalization of both the ortho and ipso positions of aryl halides. The desired molecules are obtained with high selectivity from a pool of simple precursors. These molecules are assembled under the control of a palladacycle, which is formed through the joint action of a metal (Pd) and an olefin such as norbornene. These two species act cooperatively with an aryl halide to construct the palladacycle, which is formed through ortho-C-H activation of the original aryl halide. The resulting complex acts as a scaffold to direct the reaction (via Pd(IV)) of other species, such as alkyl or aryl halides and amination or acylation agents, toward the sp(2) C-Pd bond. At the end of this process, because of steric hindrance, the scaffold is dismantled by norbornene extrusion. Pd(0) is cleaved from the organic product through C-C, C-H, C-N, C-O, or C-B coupling, in agreement with the well-known reactivity of aryl-Pd complexes. The cycle involves Pd(0), Pd(II), and Pd(IV) species. In particular, our discovery relates to alkylation and arylation reactions. Recently, remarkable progress has been made in the following areas: (a) the installation of an amino or an acyl group at the ortho position of aryl halides, (b) the formation of a C-B bond at the ipso position, (c) the achievement of meta-C-H bond activation of aryl

  7. Aromatic C-H bond activation revealed by infrared multiphoton dissociation spectroscopy.

    PubMed

    Jašíková, Lucie; Hanikýřová, Eva; Schröder, Detlef; Roithová, Jana

    2012-04-01

    Metal-oxide cations are models of catalyst mediating the C-H bond activation of organic substrates. One of the most powerful reagents suggested in the gas phase is based on CuO(+) . Here, we describe the activation of the aromatic C-H bonds of phenanthroline in its complex with CuO(+) . The reaction sequence starts with a hydrogen atom abstraction by the oxygen atom from the 2-position of the phenanthroline ring, followed by OH migration to the ring. Using infrared multiphoton spectroscopy, it is shown that the reaction can be energetically facilitated by additional coordination of a water ligand to the copper ion. As the reaction is intramolecular, a spectroscopic characterization of the product is mandatory in order to unambiguously address the reaction mechanism. PMID:22689621

  8. Carbon-carbon bond cleavage in activation of the prodrug nabumetone.

    PubMed

    Varfaj, Fatbardha; Zulkifli, Siti N A; Park, Hyoung-Goo; Challinor, Victoria L; De Voss, James J; Ortiz de Montellano, Paul R

    2014-05-01

    Carbon-carbon bond cleavage reactions are catalyzed by, among others, lanosterol 14-demethylase (CYP51), cholesterol side-chain cleavage enzyme (CYP11), sterol 17β-lyase (CYP17), and aromatase (CYP19). Because of the high substrate specificities of these enzymes and the complex nature of their substrates, these reactions have been difficult to characterize. A CYP1A2-catalyzed carbon-carbon bond cleavage reaction is required for conversion of the prodrug nabumetone to its active form, 6-methoxy-2-naphthylacetic acid (6-MNA). Despite worldwide use of nabumetone as an anti-inflammatory agent, the mechanism of its carbon-carbon bond cleavage reaction remains obscure. With the help of authentic synthetic standards, we report here that the reaction involves 3-hydroxylation, carbon-carbon cleavage to the aldehyde, and oxidation of the aldehyde to the acid, all catalyzed by CYP1A2 or, less effectively, by other P450 enzymes. The data indicate that the carbon-carbon bond cleavage is mediated by the ferric peroxo anion rather than the ferryl species in the P450 catalytic cycle. CYP1A2 also catalyzes O-demethylation and alcohol to ketone transformations of nabumetone and its analogs. PMID:24584631

  9. Carbon-Carbon Bond Cleavage in Activation of the Prodrug Nabumetone

    PubMed Central

    Varfaj, Fatbardha; Zulkifli, Siti N. A.; Park, Hyoung-Goo; Challinor, Victoria L.; De Voss, James J.

    2014-01-01

    Carbon-carbon bond cleavage reactions are catalyzed by, among others, lanosterol 14-demethylase (CYP51), cholesterol side-chain cleavage enzyme (CYP11), sterol 17β-lyase (CYP17), and aromatase (CYP19). Because of the high substrate specificities of these enzymes and the complex nature of their substrates, these reactions have been difficult to characterize. A CYP1A2-catalyzed carbon-carbon bond cleavage reaction is required for conversion of the prodrug nabumetone to its active form, 6-methoxy-2-naphthylacetic acid (6-MNA). Despite worldwide use of nabumetone as an anti-inflammatory agent, the mechanism of its carbon-carbon bond cleavage reaction remains obscure. With the help of authentic synthetic standards, we report here that the reaction involves 3-hydroxylation, carbon-carbon cleavage to the aldehyde, and oxidation of the aldehyde to the acid, all catalyzed by CYP1A2 or, less effectively, by other P450 enzymes. The data indicate that the carbon-carbon bond cleavage is mediated by the ferric peroxo anion rather than the ferryl species in the P450 catalytic cycle. CYP1A2 also catalyzes O-demethylation and alcohol to ketone transformations of nabumetone and its analogs. PMID:24584631

  10. Nickel-catalyzed Csp2-Csp3 bond formation by carbon-fluorine activation.

    PubMed

    Sun, Alex D; Leung, Kaylyn; Restivo, Anita D; LaBerge, Nicole A; Takasaki, Harumi; Love, Jennifer A

    2014-03-10

    We report herein a general catalytic method for Csp(2)-Csp(3) bond formation through C-F activation. The process uses an inexpensive nickel complex with either diorganozinc or alkylzinc halide reagents, including those with β-hydrogen atoms. A variety of fluorine substitution patterns and functional groups can be readily incorporated. Sequential reactions involving different precatalysts and coupling partners permit the synthesis of densely functionalized fluorinated building blocks. PMID:24522982

  11. Asymmetric Intramolecular Alkylation of Chiral Aromatic Imines via Catalytic C-H Bond Activation

    SciTech Connect

    Watzke, Anja; Wilson, Rebecca; O'Malley, Steven; Bergman, Robert; Ellman, Jonathan

    2007-04-16

    The asymmetric intramolecular alkylation of chiral aromatic aldimines, in which differentially substituted alkenes are tethered meta to the imine, was investigated. High enantioselectivities were obtained for imines prepared from aminoindane derivatives, which function as directing groups for the rhodium-catalyzed C-H bond activation. Initial demonstration of catalytic asymmetric intramolecular alkylation also was achieved by employing a sterically hindered achiral imine substrate and catalytic amounts of a chiral amine.

  12. Intermonomer disulfide bonds impair the fusion activity of influenza virus hemagglutinin.

    PubMed Central

    Kemble, G W; Bodian, D L; Rosé, J; Wilson, I A; White, J M

    1992-01-01

    At a low pH, the influenza virus hemagglutinin (HA) undergoes conformational changes that promote membrane fusion. While the critical role of fusion peptide release from the trimer interface has been demonstrated previously, the role of globular head dissociation in the overall fusion mechanism remains unclear. To investigate this question, we have analyzed in detail the fusion activity and low pH-induced conformational changes of a mutant, Cys-HA, in which the globular head domains are locked together by engineered intermonomer disulfide bonds (L. Godley, J. Pfeifer, D. Steinhauer, B. Ely, G. Shaw, R. Kaufmann, E. Suchanek, C. Pabo, J. J. Skehel, D. C. Wiley, and S. Wharton, Cell 68:635-645, 1992). In this paper, we show that Cys-HA expressed on the cell surface is predominantly a disulfide-bonded trimer. Cell surface Cys-HA is impaired in its membrane fusion activity, as demonstrated by both content-mixing and lipid-mixing fusion assays. It is also impaired in its ability to change conformation at a low pH, as assessed by proteinase K sensitivity. The fusion activity and low pH-induced conformational changes of cell surface Cys-HA are, however, restored to nearly wild-type levels upon reduction of the intermonomer disulfide bonds. By using a set of conformation-specific monoclonal and anti-peptide antibodies, we found that purified Cys-HA trimers are impaired in changes that occur in the globular head domain interface. In addition, changes that occur at a great distance from the engineered intermonomer disulfide bonds, notably release of the fusion peptides, are also impaired. Our results are discussed with respect to current views of the fusion-active conformation of the HA trimer. Images PMID:1629960

  13. Silylations of Arenes with Hydrosilanes: From Transition-Metal-Catalyzed C¢X Bond Cleavage to Environmentally Benign Transition-Metal-Free C¢H Bond Activation.

    PubMed

    Xu, Zheng; Xu, Li-Wen

    2015-07-01

    The construction of carbon-silicon bonds is highlighted as an exciting achievement in the field of organosilicon chemistry and green chemistry. Recent developments in this area will enable the sustainable chemical conversion of silicon resources into synthetically useful compounds. Especially, the catalytic silylation through C¢H bond activation without directing groups and hydrogen acceptors is one of the most challenging topics in organic chemistry and green chemistry. These remarkable findings on catalytic silylation can pave the way to a more environmentally benign utilization of earth-abundant silicon-based resources in synthetic chemistry. PMID:26073645

  14. 76 FR 23587 - Science Advisory Board Staff Office Request for Nominations of Candidates for a SAB Panel on...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-27

    ... V permitting requirements to biogenic CO 2 emissions (proposed March 21, 2011, 76 FR 15249), and a... the Prevention of Significant Deterioration (PSD) and Title V Programs'' (76 FR 15249). The four broad... AGENCY Science Advisory Board Staff Office Request for Nominations of Candidates for a SAB Panel...

  15. 77 FR 25479 - Notification of a Public Meeting of the Science Advisory Board (SAB); Exposure and Human Health...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-30

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  16. 76 FR 39102 - Science Advisory Board Staff Office; Notification of a Public Teleconference of the SAB Mercury...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-05

    ... Mercury Review Panel met on June 15-17, 2011 (76 FR 29746-29747) to review the draft Technical Support... AGENCY Science Advisory Board Staff Office; Notification of a Public Teleconference of the SAB Mercury... of the Mercury Review Panel. DATES: The teleconference will be held on July 20, 2011, from 1 to 4...

  17. 77 FR 6795 - Notification of a Public Meeting of the Science Advisory Board (SAB) Animal Feeding Operations...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-09

    ... and Basins at Swine and Dairy Animal Feeding Operations'' (February 2012 draft). DATES: The SAB Panel... at Swine and Dairy Animal Feeding Operations'' (February 2012 draft). EPA's Office of Air and... agreement signed in 2005 between EPA and nearly 14,000 broiler, dairy, egg layer, and swine animal...

  18. 77 FR 50505 - Science Advisory Board Staff Office Request for Nominations of Experts for the SAB Hydraulic...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-21

    ... AGENCY Science Advisory Board Staff Office Request for Nominations of Experts for the SAB Hydraulic... hydraulic fracturing. DATES: Nominations should be submitted by September 11, 2012 per instructions below... and environmental protection issues that may be associated with hydraulic fracturing should...

  19. Time resolved infrared studies of C-H bond activation by organometallics

    SciTech Connect

    Asplund, M.C. |

    1998-06-01

    This work describes how step-scan Fourier Transform Infrared spectroscopy and visible and near infrared ultrafast lasers have been applied to the study of the photochemical activation of C-H bonds in organometallic systems, which allow for the selective breaking of C-H bonds in alkanes. The author has established the photochemical mechanism of C-H activation by Tp{sup *}Rh(CO){sub 2}(Tp{sup *} = HB-Pz{sup *}{sub 3}, Pz = 3,5-dimethylpyrazolyl) in alkane solution. The initially formed monocarbonyl forms a weak solvent complex, which undergoes a change in Tp{sup *} ligand connectivity. The final C-H bond breaking step occurs at different time scales depending on the structure of the alkane. In linear solvents, the time scale is <50 ns and cyclic alkanes is {approximately}200 ps. The reactivity of the Tp{sup *}Rh(CO){sub 2} system has also been studied in aromatic solvents. Here the reaction proceeds through two different pathways, with very different time scales. The first proceeds in a manner analogous to alkanes and takes <50 ns. The second proceeds through a Rh-C-C complex, and takes place on a time scale of 1.8 {micro}s.

  20. Key amino acids of arabidopsis VKOR in the activity of phylloquinone reduction and disulfide bond formation.

    PubMed

    Yang, Xiao-Jian; Cui, Hao-Ran; Yu, Zhi-Bo; Du, Jia-Jia; Xu, Jia-Ning; Wang, Xiao-Yun

    2015-01-01

    Many proteins in chloroplast are regulated through the disulfide bond/thiol transformation to realize their activities. A homologue of VKOR (Vitamin K epoxide reductase) in Arabidopsis chloroplast is found to catalyze the disulfide bond formation in vivo and to mediate the specific phylloquinone reduction in vitro. It is also called LTO1 (Lumen Thiol Oxidoreductase 1). Investigations about functions and essential amino acid residues of AtVKOR have important theoretical significance to clarify the chloroplast redox regulation mechanism. In this study, several amino acids in the VKOR domain of AtVKOR were identified to be involved in binding of phylloquinone. Site-directed mutagenesis was used to study the function of these positions. The results suggested that residues Ser77, Leu87, Phe137 and Leu141 were quite important in the binding and catalyzing the reduction of phylloquinone. These residues were also involved in the electron transferring and disulfide bond formation of substrate proteins by motility assays in vivo, suggesting that the binding of phylloquinone not only affected the delivery of electrons to phylloquinone but also affected the whole electron transfer process. The conserved cysteines in the AtVKOR domain also played critical roles in phylloquinone reduction. When each of the four conserved cysteines was mutated to alanine, the mutants lost reduction activity entirely, suggesting that the four conserved cysteines played crucial roles in the electron transfer process. PMID:25267254

  1. Binuclear Aromatic C-H Bond Activation at a Dirhenium Site.

    PubMed

    Adams, Richard D; Rassolov, Vitaly; Wong, Yuen Onn

    2016-01-22

    The electronically unsaturated dirhenium complex [Re2(CO)8(μ-H)(μ-Ph)] (1) has been found to exhibit aromatic C-H activation upon reaction with N,N-diethylaniline, naphthalene, and even [D6]benzene to yield the compounds [Re2(CO)8(μ-H)(μ-η(1)-NEt2C6H4)] (2), [Re2(CO)8(μ-H)(μ-η(2)-1,2-C10H7)] (3), and [D6]-1, respectively, in good yields. The mechanism has been elucidated by using DFT computational analyses, and involves a binuclear C-H bond-activation process. PMID:26643854

  2. Thermally activated delayed fluorescence evidence in non-bonding transition electron donor-acceptor molecules

    NASA Astrophysics Data System (ADS)

    Marghad, Ikbal; Clochard, M. C.; Ollier, N.; Wade, Travis L.; Aymes-Chodur, C.; Renaud, C.; Zissis, G.

    2015-09-01

    The exhibition of thermally activated delayed fluorescence on triazine derivative by the introduction of a nonbonding part is demonstrated. Two molecules containing triazine core as acceptor and carbazole part as donor has been synthesized and characterized. One of these molecules bears an additional nonbonding part by the means of a phenoxy group. The results indicated that the molecule bearing the nonbonding molecular part (phenoxy) exhibit thermally activated delayed fluorescence while not on molecule free of non-bonding group. The results are supported by, photoluminescence, spectral analysis time-resolved fluorescence and time-dependent density functional estimation

  3. Sphalerite is a geochemical catalyst for carbon−hydrogen bond activation

    PubMed Central

    Shipp, Jessie A.; Gould, Ian R.; Shock, Everett L.; Williams, Lynda B.; Hartnett, Hilairy E.

    2014-01-01

    Reactions among minerals and organic compounds in hydrothermal systems are critical components of the Earth’s deep carbon cycle, provide energy for the deep biosphere, and may have implications for the origins of life. However, there is limited information as to how specific minerals influence the reactivity of organic compounds. Here we demonstrate mineral catalysis of the most fundamental component of an organic reaction: the breaking and making of a covalent bond. In the absence of mineral, hydrothermal reaction of cis- and trans-1,2-dimethylcyclohexane is extremely slow and generates many products. In the presence of sphalerite (ZnS), however, the reaction rate increases dramatically and one major product is formed: the corresponding stereoisomer. Isotope studies show that the sphalerite acts as a highly specific heterogeneous catalyst for activation of a single carbon−hydrogen bond in the dimethylcyclohexanes. PMID:25071186

  4. Mercury Detoxification by Bacteria: Simulations of Transcription Activation and Mercury-Carbon Bond Cleavage

    SciTech Connect

    Guo, Hao-Bo; Parks, Jerry M; Johs, Alexander; Smith, Jeremy C

    2011-01-01

    In this chapter, we summarize recent work from our laboratory and provide new perspective on two important aspects of bacterial mercury resistance: the molecular mechanism of transcriptional regulation by MerR, and the enzymatic cleavage of the Hg-C bond in methylmercury by the organomercurial lyase, MerB. Molecular dynamics (MD) simulations of MerR reveal an opening-and-closing dynamics, which may be involved in initiating transcription of mercury resistance genes upon Hg(II) binding. Density functional theory (DFT) calculations on an active-site model of the enzyme reveal how MerB catalyzes the Hg-C bond cleavage using cysteine coordination and acid-base chemistry. These studies provide insight into the detailed mechanisms of microbial gene regulation and defense against mercury toxicity.

  5. Regulation of the activity of Escherichia coli quinolinate synthase by reversible disulfide-bond formation.

    PubMed

    Saunders, Allison H; Booker, Squire J

    2008-08-19

    Quinolinate synthase (NadA) catalyzes a unique condensation reaction between dihydroxyacetone phosphate and iminoaspartate, yielding inorganic phosphate, 2 mol of water, and quinolinic acid, a central intermediate in the biosynthesis of nicotinamide adenine dinucleotide and its derivatives. The enzyme from Escherichia coli contains a C (291)XXC (294)XXC (297) motif in its primary structure. Bioinformatics analysis indicates that only Cys297 serves as a ligand to a [4Fe-4S] cluster that is required for turnover. In this report, we show that the two remaining cysteines, Cys291 and Cys294, undergo reversible disulfide-bond formation, which regulates the activity of the enzyme. This mode of redox regulation of NadA appears physiologically relevant, since disulfide-bond formation and reduction are effected by oxidized and reduced forms of E. coli thioredoxin. A midpoint potential of -264 +/- 1.77 mV is approximated for the redox couple. PMID:18651751

  6. BORON CATALYSIS. Metal-free catalytic C-H bond activation and borylation of heteroarenes.

    PubMed

    Légaré, Marc-André; Courtemanche, Marc-André; Rochette, Étienne; Fontaine, Frédéric-Georges

    2015-07-31

    Transition metal complexes are efficient catalysts for the C-H bond functionalization of heteroarenes to generate useful products for the pharmaceutical and agricultural industries. However, the costly need to remove potentially toxic trace metals from the end products has prompted great interest in developing metal-free catalysts that can mimic metallic systems. We demonstrated that the borane (1-TMP-2-BH2-C6H4)2 (TMP, 2,2,6,6-tetramethylpiperidine) can activate the C-H bonds of heteroarenes and catalyze the borylation of furans, pyrroles, and electron-rich thiophenes. The selectivities complement those observed with most transition metal catalysts reported for this transformation. PMID:26228143

  7. Hydrogen induced C-C, C-N, and C-S bond activation on Pt and Ni surfaces

    SciTech Connect

    Gland, J.L.

    1992-01-01

    The work has focussed on hydrogen induced bond activation in adsorbed organic molecules and intermediates containin C-S and C-N and C-C bonds on Ni(100), Ni(111), and Pt(111) surfaces. Fluorescence Yield Near Edge Spectroscopy (FYNES) above the carbon K edge was used for adsorbed organic reactants and in-situ kinetic studies of bond activation. Results indicate that the activation is enhanced on Ni relative to Pt. Methylthiolate and methylamine adsorbed on Pt(111) were studied.

  8. Hydrogen induced C-C, C-N, and C-S bond activation on Pt and Ni surfaces

    SciTech Connect

    Gland, J.L.

    1992-12-01

    The work has focussed on hydrogen induced bond activation in adsorbed organic molecules and intermediates containin C-S and C-N and C-C bonds on Ni(100), Ni(111), and Pt(111) surfaces. Fluorescence Yield Near Edge Spectroscopy (FYNES) above the carbon K edge was used for adsorbed organic reactants and in-situ kinetic studies of bond activation. Results indicate that the activation is enhanced on Ni relative to Pt. Methylthiolate and methylamine adsorbed on Pt(111) were studied.

  9. Bile salt–induced intermolecular disulfide bond formation activates Vibrio cholerae virulence

    PubMed Central

    Yang, Menghua; Liu, Zhi; Hughes, Chambers; Stern, Andrew M.; Wang, Hui; Zhong, Zengtao; Kan, Biao; Fenical, William; Zhu, Jun

    2013-01-01

    To be successful pathogens, bacteria must often restrict the expression of virulence genes to host environments. This requires a physical or chemical marker of the host environment as well as a cognate bacterial system for sensing the presence of a host to appropriately time the activation of virulence. However, there have been remarkably few such signal–sensor pairs identified, and the molecular mechanisms for host-sensing are virtually unknown. By directly applying a reporter strain of Vibrio cholerae, the causative agent of cholera, to a thin layer chromatography (TLC) plate containing mouse intestinal extracts, we found two host signals that activate virulence gene transcription. One of these was revealed to be the bile salt taurocholate. We then show that a set of bile salts cause dimerization of the transmembrane transcription factor TcpP by inducing intermolecular disulfide bonds between cysteine (C)-207 residues in its periplasmic domain. Various genetic and biochemical analyses led us to propose a model in which the other cysteine in the periplasmic domain, C218, forms an inhibitory intramolecular disulfide bond with C207 that must be isomerized to form the active C207–C207 intermolecular bond. We then found bile salt–dependent effects of these cysteine mutations on survival in vivo, correlating to our in vitro model. Our results are a demonstration of a mechanism for direct activation of the V. cholerae virulence cascade by a host signal molecule. They further provide a paradigm for recognition of the host environment in pathogenic bacteria through periplasmic cysteine oxidation. PMID:23341592

  10. Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution

    SciTech Connect

    Bromberg, S.E.

    1998-05-01

    When certain organometallic compounds are photoexcited in room temperature alkane solution, they are able to break or activate the C-H bonds of the solvent. Understanding this potentially practical reaction requires a detailed knowledge of the entire reaction mechanism. Because of the dynamic nature of chemical reactions, time-resolved spectroscopy is commonly employed to follow the important events that take place as reactants are converted to products. For the organometallic reactions examined here, the electronic/structural characteristics of the chemical systems along with the time scales for the key steps in the reaction make ultrafast UV/Vis and IR spectroscopy along with nanosecond Step-Scan FTIR spectroscopy the ideal techniques to use for this study. An initial study of the photophysics of (non-activating) model metal carbonyls centering on the photodissociation of M(CO){sub 6} (M = Cr, W, Mo) was carried out in alkane solutions using ultrafast IR spectroscopy. Next, picosecond UV/vis studies of the C-H bond activation reaction of Cp{sup *}M(CO){sub 2} (M = Rh, Ir), conducted in room temperature alkane solution, are described in an effort to investigate the origin of the low quantum yield for bond cleavage ({approximately}1%). To monitor the chemistry that takes place in the reaction after CO is lost, a system with higher quantum yield is required. The reaction of Tp{sup *}Rh(CO){sub 2} (Tp{sup *} = HB-Pz{sub 3}{sup *}, Pz{sup *} = 3,5-dimethylpyrazolyl) in alkanes has a quantum yield of {approximately}30%, making time resolved spectroscopic measurements possible. From ultrafast IR experiments, two subsequently formed intermediates were observed. The nature of these intermediates are discussed and the first comprehensive reaction mechanism for a photochemical C-H activating organometallic complex is presented.

  11. Water-containing hydrogen-bonding network in the active center of channelrhodopsin.

    PubMed

    Ito, Shota; Kato, Hideaki E; Taniguchi, Reiya; Iwata, Tatsuya; Nureki, Osamu; Kandori, Hideki

    2014-03-01

    Channelrhodopsin (ChR) functions as a light-gated ion channel in Chlamydomonas reinhardtii. Passive transport of cations by ChR is fundamentally different from the active transport by light-driven ion pumps such as archaerhodopsin, bacteriorhodopsin, and halorhodopsin. These microbial rhodopsins are important tools for optogenetics, where ChR is used to activate neurons by light, while the ion pumps are used for neural silencing. Ion-transport functions by these rhodopsins strongly depend on the specific hydrogen-bonding networks containing water near the retinal chromophore. In this work, we measured protein-bound water molecules in a chimeric ChR protein of ChR1 (helices A to E) and ChR2 (helices F and G) of Chlamydomonas reinhardtii using low-temperature FTIR spectroscopy at 77 K. We found that the active center of ChR possesses more water molecules (9 water vibrations) than those of other microbial (2-6 water vibrations) and animal (6-8 water vibrations) rhodopsins. We conclude that the protonated retinal Schiff base interacts with the counterion (Glu162) directly, without the intervening water molecule found in proton-pumping microbial rhodopsins. The present FTIR results and the recent X-ray structure of ChR reveal a unique hydrogen-bonding network around the active center of this light-gated ion channel. PMID:24512107

  12. C-H Bond Activation by Early Transition Metal Carbide Cluster Anion MoC3 (-).

    PubMed

    Li, Zi-Yu; Hu, Lianrui; Liu, Qing-Yu; Ning, Chuan-Gang; Chen, Hui; He, Sheng-Gui; Yao, Jiannian

    2015-12-01

    Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC3 (-) ) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC3 (-) with C2 H6 . The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC3 (-) anion and C2 H6 is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt(+) +C2 H6 ) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different. PMID:26490554

  13. Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry.

    PubMed

    Ruscic, Branko

    2015-07-16

    Active Thermochemical Tables (ATcT) thermochemistry for the sequential bond dissociations of methane, ethane, and methanol systems were obtained by analyzing and solving a very large thermochemical network (TN). Values for all possible C-H, C-C, C-O, and O-H bond dissociation enthalpies at 298.15 K (BDE298) and bond dissociation energies at 0 K (D0) are presented. The corresponding ATcT standard gas-phase enthalpies of formation of the resulting CHn, n = 4-0 species (methane, methyl, methylene, methylidyne, and carbon atom), C2Hn, n = 6-0 species (ethane, ethyl, ethylene, ethylidene, vinyl, ethylidyne, acetylene, vinylidene, ethynyl, and ethynylene), and COHn, n = 4-0 species (methanol, hydroxymethyl, methoxy, formaldehyde, hydroxymethylene, formyl, isoformyl, and carbon monoxide) are also presented. The ATcT thermochemistry of carbon dioxide, water, hydroxyl, and carbon, oxygen, and hydrogen atoms is also included, together with the sequential BDEs of CO2 and H2O. The provenances of the ATcT enthalpies of formation, which are quite distributed and involve a large number of relevant determinations, are analyzed by variance decomposition and discussed in terms of principal contributions. The underlying reasons for periodic appearances of remarkably low and/or unusually high BDEs, alternating along the dissociation sequences, are analyzed and quantitatively rationalized. The present ATcT results are the most accurate thermochemical values currently available for these species. PMID:25760799

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

    PubMed

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

    2016-01-13

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

  15. Annulation of Aromatic Imines via Directed C-H BondActivation

    SciTech Connect

    Thalji, Reema K.; Ahrendt, Kateri A.; Bergman, Robert G.; Ellman,Jonathan A.

    2005-04-14

    A directed C-H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh{sub 3}){sub 3}RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good regioselectivity. Different ring sizes and substitution patterns can be accessed through the coupling of monosubstituted, 1,1- or 1,2-disubstituted, and trisubstituted alkenes bearing both electron-rich and electron-deficient functionality.

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

    PubMed

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

    2015-01-01

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

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

    PubMed Central

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

    2015-01-01

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

  18. Annulation of aromatic imines via directed C-H bond activation.

    PubMed

    Thalji, Reema K; Ahrendt, Kateri A; Bergman, Robert G; Ellman, Jonathan A

    2005-08-19

    A directed C-H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh3)3RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good regioselectivity. Different ring sizes and substitution patterns can be accessed through the coupling of monosubstituted, 1,1- or 1,2-disubstituted, and trisubstituted alkenes bearing both electron-rich and electron-deficient functionality. PMID:16095296

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

    SciTech Connect

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

    2004-11-27

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  1. A theoretical view on CrO2+-mediated C-H bond activation in ethane

    NASA Astrophysics Data System (ADS)

    Tong, YongChun; Zhang, XiaoYong; Wang, QingYun; Xu, XinJian; Wang, YongCheng

    2015-06-01

    The gas-phase reaction of C-H bond activation in ethane by CrO2+ has been investigated using density functional theory (DFT) at the UB3LYP/6-311G(2d,p) level. Our results reveal that the activation process is actually a spin-forbidden reaction. The involved crossing point between the doublet and quartet potential energy surfaces (PES) has been discussed by two well-known methods, i.e., intrinsic reaction coordinate (IRC) approach for crossing point (CP) and Harvey's algorithm for minimum energy crossing point (MECP). The obtained single ( P1ISC = 2.48 × 10-3) and double ( P1ISC = 4.95 × 10-3) passes estimated at MECP show that the intersystem crossing (ISC) occurs with a little probability. The C-H bond activation processes should proceed to be endothermic by 73.16 kJ/mol on the doublet surface without any spin change.

  2. Activation of carbon-hydrogen bonds in alkanes and other organic molecules using organotransition metal complexes

    SciTech Connect

    Bergman, R.G.

    1991-10-01

    We have recently begun to investigate the interaction of C-H activating iridium and rhodium complexes with functionalized organic molecules, to determine the effect of functional groups on the process, as well as to investigate the propensity of Ir and Rh to insert into C-H versus other types of X-H bonds. Recent experiments have demonstrated that xenon liquefied at -70{degrees}C and 10 atm pressure serves as an inert solvent for the C-H oxidative addition reaction. We have been able to prepare and isolate, for the first time, C-H oxidative addition products formed from high-melting solid substrates such as naphthalene, adamantane, and even cubane; the latter case represents the first observation of C-H oxidative addition at a tertiary C-H bond. Liquid xenon has also allowed us to carry out more conveniently the C-H oxidative addition reactions of low-boiling gases that are difficult to liquefy, such as methane. Recently we have also been able to carry out analogous studies in the gas phase. Under these conditions, ``naked`` rather than solvated Cp*Rh(CO) is formed, and this species reacts with cyclohexane at nearly gas-kinetic rates. Under the conditions, collision between Cp*Rh(CO) and cyclohexane is the slowest step in the overall C-H activation process. In contrast, in solution association of solvent with free Cp*Rh(CO) is so rapid that the step involving C-H bond cleavage in the coordinated alkane complex becomes rate-determining. 3 refs., 5 figs.

  3. Activation of carbon-hydrogen bonds in alkanes and other organic molecules using organotransition metal complexes

    SciTech Connect

    Bergman, R.G.

    1991-10-01

    We have recently begun to investigate the interaction of C-H activating iridium and rhodium complexes with functionalized organic molecules, to determine the effect of functional groups on the process, as well as to investigate the propensity of Ir and Rh to insert into C-H versus other types of X-H bonds. Recent experiments have demonstrated that xenon liquefied at -70{degrees}C and 10 atm pressure serves as an inert solvent for the C-H oxidative addition reaction. We have been able to prepare and isolate, for the first time, C-H oxidative addition products formed from high-melting solid substrates such as naphthalene, adamantane, and even cubane; the latter case represents the first observation of C-H oxidative addition at a tertiary C-H bond. Liquid xenon has also allowed us to carry out more conveniently the C-H oxidative addition reactions of low-boiling gases that are difficult to liquefy, such as methane. Recently we have also been able to carry out analogous studies in the gas phase. Under these conditions, naked'' rather than solvated Cp*Rh(CO) is formed, and this species reacts with cyclohexane at nearly gas-kinetic rates. Under the conditions, collision between Cp*Rh(CO) and cyclohexane is the slowest step in the overall C-H activation process. In contrast, in solution association of solvent with free Cp*Rh(CO) is so rapid that the step involving C-H bond cleavage in the coordinated alkane complex becomes rate-determining. 3 refs., 5 figs.

  4. CH Bond Activation of Methane by a Transient η(2)-Cyclopropene/Metallabicyclobutane Complex of Niobium.

    PubMed

    Li, Chen; Dinoi, Chiara; Coppel, Yannick; Etienne, Michel

    2015-10-01

    This study challenges the problem of the activation of a CH bond of methane by soluble transition metal complexes. High pressure solution NMR, isotopic labeling studies, and kinetic analyses of the degenerate exchange of methane in the methyl complex [Tp(Me2)NbCH3(c-C3H5)(MeCCMe)] (1) are reported. Stoichiometric methane activation by the mesitylene complex [Tp(Me2)Nb(CH2-3,5-C6H3Me2)(c-C3H5) (MeCCMe)] (2) giving 1 is also realized. Evidence is provided that these reactions proceed via an intramolecular abstraction of a β-H of the cyclopropyl group to form either methane or mesitylene from 1 or 2, respectively, yielding the transient unsaturated η(2)-cyclopropene/metallabicyclobutane intermediate [Tp(Me2)Nb(η(2)-c-C3H4) (MeCCMe)] A. This is followed by its mechanistic reverse 1,3-CH bond addition of methane yielding the product. PMID:26374390

  5. Metal-Oxygen Bond Ionicity as an Efficient Descriptor for Doped NiOOH Photocatalytic Activity.

    PubMed

    Zaffran, Jeremie; Toroker, Maytal Caspary

    2016-06-01

    The computational design of solid catalysts has become a very "hot" field during the last decades, especially with the recent increase in computational tool performance. However, theoretical techniques are still very time demanding because they require the consideration of many adsorption configurations of the reaction intermediates on the surface. Herein, we propose to use the metal-oxygen (M-O) bond ionicity as a descriptor for the photocatalytic activity of one of the best catalysts for the oxygen evolution reaction (OER). Ionicity is a bulk property and thus carries the advantage of being easily obtainable from a simple Bader charge analysis by using density functional theory (DFT). We will show that this criterion can be used successfully to design efficient dopants for NiOOH material. This catalyst is known to exhibit interesting photoelectrochemical properties for OER if it is doped with specific transition metals. Finally, we demonstrate that other electronic properties that relate to bulk calculation, such as oxidation states and density of states, are not alone sufficient to explain the photocatalytic activity of the material. Thus, M-O bond ionicity attracts significant interest compared with other bulk observables obtained by using DFT computations. PMID:26945687

  6. Electrical properties of Si/Si interfaces by using surface-activated bonding

    SciTech Connect

    Liang, J.; Miyazaki, T.; Morimoto, M.; Nishida, S.; Shigekawa, N.

    2013-11-14

    Electrical properties of n-Si/n-Si, p-Si/n-Si, and p{sup −}-Si/n{sup +}-Si junctions fabricated by using surface-activated-bonding are investigated. The transmission electron microscopy/energy dispersive X-ray spectroscopy of the n-Si/n-Si interfaces reveals no evidence of oxide layers at the interfaces. From the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics of the p-Si/n-Si and p{sup −}-Si/n{sup +}-Si junctions, it is found that the interface states, likely to have formed due to the surface activation process using Ar plasma, have a more marked impact on the electrical properties of the p-Si/n-Si junctions. An analysis of the temperature dependence of the I-V characteristics indicates that the properties of carrier transport across the bonding interfaces for reverse-bias voltages in the p-Si/n-Si and p{sup −}-Si/n{sup +}-Si junctions can be explained using the trap-assisted-tunneling and Frenkel-Poole models, respectively.

  7. An ABC Transporter System of Yersinia pestis Allows Utilization of Chelated Iron by Escherichia coli SAB11

    PubMed Central

    Bearden, Scott W.; Staggs, Teanna M.; Perry, Robert D.

    1998-01-01

    The acquisition of iron is an essential component in the pathogenesis of Yersinia pestis, the agent of bubonic and pneumonic plague. A cosmid library derived from the genomic DNA of Y. pestis KIM6+ was used for transduction of an Escherichia coli mutant (SAB11) defective in the biosynthesis of the siderophore enterobactin. Recombinant plasmids which had a common 13-kb BamHI fragment were isolated from SAB11 transductants in which growth but not enterobactin synthesis was restored on media containing the iron chelator EDDA [ethylenediamine-di(o-hydroxyphenyl acetic acid)]. Subcloning and transposon mutagenesis revealed a 5.6-kb region, designated yfe, essential for SAB11 growth stimulation. In vitro transcription-translation analysis identified polypeptides of 18, 29.5, 32, and 33 kDa encoded by the yfe locus. Sequence analysis shows this locus to be comprised of five genes in two separate operons which have potential Fur-binding sequences in both promoters. A putative polycistronic operon, yfeABCD, is Fur regulated and responds to iron and manganese. A functional Fur protein is required for the observed manganese repression of this operon. This operon encodes polypeptides which have strong similarity to the ATP-binding cassette (ABC) family of transporters and include a periplasmic binding protein (YfeA), an ATP-binding protein (YfeB), and two integral membrane proteins (YfeC and -D), which likely function in the acquisition of inorganic iron and possibly other ions. The ∼21-kDa protein encoded by the separately transcribed yfeE gene may be located in the cell envelope, since a yfeE::TnphoA fusion is PhoA+. Mutations in this gene abrogate growth of SAB11 on iron-chelated media. PMID:9495751

  8. Peel resistance characterization of localized polymer film bonding via thin film adhesive thermally activated by scanned CO2 laser

    NASA Astrophysics Data System (ADS)

    Dowding, Colin; Dowding, Robert; Griffiths, Jonathan; Lawrence, Jonathan

    2013-06-01

    Thermal laser polymer bonding is a non-contact process for the joining of polymer laminates using thermally activated adhesives. Conventional, contact based bonding techniques suffer from mechanical wear, geometric inflexibility and poor energy efficiency. The application of lasers offers the potential for highly localized delivery of energy and increased process flexibility whilst achieving controlled and repeatable bonding of polymer laminates in a contact free process. Unlike previously reported techniques, here it is reported that laser based non-contact bonding is both viable and highly desirable due to the increased levels of control it affords the user. In this work, laser polymer bonding of 75 μm thick linear low density polyethylene (LLDPE) film backed with a thermally activated adhesive to a 640 μm thick polypropylene (PP) substrate was conducted using continuous wave 10.6 μm laser radiation and scanning galvanometric optics. The effect of laser power and scanning traverse speed on the peel resistance properties of the bonded polymer laminates is presented, with a threshold specific energy density for successful adhesive activation determined.

  9. The road to the first, fully active and more stable human insulin variant with an additional disulfide bond.

    PubMed

    Vinther, Tine N; Kjeldsen, Thomas B; Jensen, Knud J; Hubálek, František

    2015-11-01

    Insulin, a small peptide hormone, is crucial in maintaining blood glucose homeostasis. The stability and activity of the protein is directed by an intricate system involving disulfide bonds to stabilize the active monomeric species and by their non-covalent oligomerization. All known insulin variants in vertebrates consist of two peptide chains and have six cysteine residues, which form three disulfide bonds, two of them link the two chains and a third is an intra-chain bond in the A-chain. This classical insulin fold appears to have been conserved over half a billion years of evolution. We addressed the question whether a human insulin variant with four disulfide bonds could exist and be fully functional. In this review, we give an overview of the road to engineering four-disulfide bonded insulin analogs. During our journey, we discovered several active four disulfide bonded insulin analogs with markedly improved stability and gained insights into the instability of analogs with seven cysteine residues, importance of dimerization for stability, insulin fibril formation process, and the conformation of insulin binding to its receptor. Our results also open the way for new strategies in the development of insulin biopharmaceuticals. PMID:26382042

  10. 75 FR 47608 - Agency Information Collection Activities: Application for Exportation of Articles under Special Bond

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-06

    ... Exportation of Articles under Special Bond AGENCY: U.S. Customs and Border Protection, Department of Homeland... requirement concerning the: Application for Exportation of Articles under Special Bond. This request for...: Title: Application for Exportation of Articles under Special Bond. OMB Number: 1651-0004. Form...

  11. 75 FR 61162 - Agency Information Collection Activities: Application for Exportation of Articles Under Special Bond

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-04

    ... Exportation of Articles Under Special Bond AGENCY: U.S. Customs and Border Protection, Department of Homeland... Exportation of Articles under Special Bond (CBP Form 3495). This is a proposed extension of an information... Exportation of Articles under Special Bond. OMB Number: 1651-0004. Form Number: Form 3495. Abstract:...

  12. 78 FR 49761 - Agency Information Collection Activities: Application for Exportation of Articles Under Special Bond

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-15

    ... Exportation of Articles Under Special Bond AGENCY: U.S. Customs and Border Protection, Department of Homeland... information collection requirement concerning the Application for Exportation of Articles under Special Bond... Articles Under Special Bond. OMB Number: 1651-0004. Form Number: CBP Form 3495. Abstract: CBP Form...

  13. 78 FR 66038 - Agency Information Collection Activities: Application for Exportation of Articles Under Special Bond

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-04

    ... Exportation of Articles Under Special Bond AGENCY: U.S. Customs and Border Protection, Department of Homeland... Exportation of Articles under Special Bond (CBP Form 3495). This is a proposed extension of an information.... Title: Application for Exportation of Articles under Special Bond. OMB Number: 1651-0004. Form...

  14. Disulfide Bond Oxidoreductase DsbA2 of Legionella pneumophila Exhibits Protein Disulfide Isomerase Activity

    PubMed Central

    Kpadeh, Zegbeh Z.; Jameson-Lee, Max; Yeh, Anthony J.; Chertihin, Olga; Shumilin, Igor A.; Dey, Rafik; Day, Shandra R.

    2013-01-01

    The extracytoplasmic assembly of the Dot/Icm type IVb secretion system (T4SS) of Legionella pneumophila is dependent on correct disulfide bond (DSB) formation catalyzed by a novel and essential disulfide bond oxidoreductase DsbA2 and not by DsbA1, a second nonessential DSB oxidoreductase. DsbA2, which is widely distributed in the microbial world, is phylogenetically distinct from the canonical DsbA oxidase and the DsbC protein disulfide isomerase (PDI)/reductase of Escherichia coli. Here we show that the extended N-terminal amino acid sequence of DsbA2 (relative to DsbA proteins) contains a highly conserved 27-amino-acid dimerization domain enabling the protein to form a homodimer. Complementation tests with E. coli mutants established that L. pneumophila dsbA1, but not the dsbA2 strain, restored motility to a dsbA mutant. In a protein-folding PDI detector assay, the dsbA2 strain, but not the dsbA1 strain, complemented a dsbC mutant of E. coli. Deletion of the dimerization domain sequences from DsbA2 produced the monomer (DsbA2N), which no longer exhibited PDI activity but complemented the E. coli dsbA mutant. PDI activity was demonstrated in vitro for DsbA2 but not DsbA1 in a nitrocefin-based mutant TEM β-lactamase folding assay. In an insulin reduction assay, DsbA2N activity was intermediate between those of DsbA2 and DsbA1. In L. pneumophila, DsbA2 was maintained as a mixture of thiol and disulfide forms, while in E. coli, DsbA2 was present as the reduced thiol. Our studies suggest that DsbA2 is a naturally occurring bifunctional disulfide bond oxidoreductase that may be uniquely suited to the majority of intracellular bacterial pathogens expressing T4SSs as well as in many slow-growing soil and aquatic bacteria. PMID:23435972

  15. C-H bond activation with actinides: The first example of intramolecular ring bite of a pentamethylcyclopentadienyl methyl group

    SciTech Connect

    Peters, R.G.; Warner, B.P.; Scott, B.L.; Burns, C.J.

    1999-07-05

    Thermolysis of (C{sub 5}Me{sub 5}){sub 2}U({double_bond}NAd){sub 2}, 1 (Ad = 1-adamantyl), in benzene or hexane results in the intramolecular C-H bond activation of a methyl group on a pentamethylcyclopentadienyl ligand across the two imido functional groups. The product of this reaction has been spectroscopically and structurally characterized. The activation product is a reduced U(IV) metallocene bis(amide) complex with an N-bound methylene unit derived from the methyl group attached to one amide group. The activation parameters for this process have been determined; the results are consistent with a simple unimolecular process. This is the first example of intramolecular activation of a (C{sub 5}Me{sub 5}) methyl C-H bond in an actinide complex.

  16. Activation of CO and CO2 on homonuclear boron bonds of fullerene-like BN cages: first principles study

    NASA Astrophysics Data System (ADS)

    Sinthika, S.; Kumar, E. Mathan; Surya, V. J.; Kawazoe, Y.; Park, Noejung; Iyakutti, K.; Thapa, Ranjit

    2015-12-01

    Using density functional theory we investigate the electronic and atomic structure of fullerene-like boron nitride cage structures. The pentagonal ring leads to the formation of homonuclear bonds. The homonuclear bonds are also found in other BN structures having pentagon line defect. The calculated thermodynamics and vibrational spectra indicated that, among various stable configurations of BN-60 cages, the higher number of homonuclear N-N bonds and lower B:N ratio can result in the more stable structure. The homonuclear bonds bestow the system with salient catalytic properties that can be tuned by modifying the B atom bonding environment. We show that homonuclear B-B (B2) bonds can anchor both oxygen and CO molecules making the cage to be potential candidates as catalyst for CO oxidation via Langmuir-Hinshelwood (LH) mechanism. Moreover, the B-B-B (B3) bonds are reactive enough to capture, activate and hydrogenate CO2 molecules to formic acid. The observed trend in reactivity, viz B3 > B2 > B1 is explained in terms of the position of the boron defect state relative to the Fermi level.

  17. Activation of CO and CO2 on homonuclear boron bonds of fullerene-like BN cages: first principles study

    PubMed Central

    Sinthika, S.; Kumar, E. Mathan; Surya, V. J.; Kawazoe, Y.; Park, Noejung; Iyakutti, K.; Thapa, Ranjit

    2015-01-01

    Using density functional theory we investigate the electronic and atomic structure of fullerene-like boron nitride cage structures. The pentagonal ring leads to the formation of homonuclear bonds. The homonuclear bonds are also found in other BN structures having pentagon line defect. The calculated thermodynamics and vibrational spectra indicated that, among various stable configurations of BN-60 cages, the higher number of homonuclear N-N bonds and lower B:N ratio can result in the more stable structure. The homonuclear bonds bestow the system with salient catalytic properties that can be tuned by modifying the B atom bonding environment. We show that homonuclear B-B (B2) bonds can anchor both oxygen and CO molecules making the cage to be potential candidates as catalyst for CO oxidation via Langmuir–Hinshelwood (LH) mechanism. Moreover, the B-B-B (B3) bonds are reactive enough to capture, activate and hydrogenate CO2 molecules to formic acid. The observed trend in reactivity, viz B3 > B2 > B1 is explained in terms of the position of the boron defect state relative to the Fermi level. PMID:26626147

  18. Activation of CO and CO2 on homonuclear boron bonds of fullerene-like BN cages: first principles study.

    PubMed

    Sinthika, S; Kumar, E Mathan; Surya, V J; Kawazoe, Y; Park, Noejung; Iyakutti, K; Thapa, Ranjit

    2015-01-01

    Using density functional theory we investigate the electronic and atomic structure of fullerene-like boron nitride cage structures. The pentagonal ring leads to the formation of homonuclear bonds. The homonuclear bonds are also found in other BN structures having pentagon line defect. The calculated thermodynamics and vibrational spectra indicated that, among various stable configurations of BN-60 cages, the higher number of homonuclear N-N bonds and lower B:N ratio can result in the more stable structure. The homonuclear bonds bestow the system with salient catalytic properties that can be tuned by modifying the B atom bonding environment. We show that homonuclear B-B (B2) bonds can anchor both oxygen and CO molecules making the cage to be potential candidates as catalyst for CO oxidation via Langmuir-Hinshelwood (LH) mechanism. Moreover, the B-B-B (B3) bonds are reactive enough to capture, activate and hydrogenate CO2 molecules to formic acid. The observed trend in reactivity, viz B3 > B2 > B1 is explained in terms of the position of the boron defect state relative to the Fermi level. PMID:26626147

  19. Oxygen activation and intramolecular C-H bond activation by an amidate-bridged diiron(II) complex.

    PubMed

    Jones, Matthew B; Hardcastle, Kenneth I; Hagen, Karl S; MacBeth, Cora E

    2011-07-18

    A diiron(II) complex containing two μ-1,3-(κN:κO)-amidate linkages has been synthesized using the 2,2',2''-tris(isobutyrylamido)triphenylamine (H(3)L(iPr)) ligand. The resulting diiron complex, 1, reacts with dioxygen (or iodosylbenzene) to effect intramolecular C-H bond activation at the methine position of the ligand isopropyl group. The ligand-activated product, 2, has been isolated and characterized by a variety of methods including X-ray crystallography. Electrospray ionization mass spectroscopy of 2 prepared from(18)O(2) was used to confirm that the oxygen atom incorporated into the ligand framework is derived from molecular oxygen. PMID:21667986

  20. Polyhydrides of Platinum Group Metals: Nonclassical Interactions and σ-Bond Activation Reactions.

    PubMed

    Esteruelas, Miguel A; López, Ana M; Oliván, Montserrat

    2016-08-10

    The preparation, structure, dynamic behavior in solution, and reactivity of polyhydride complexes of platinum group metals, described during the last three decades, are contextualized from both organometallic and coordination chemistry points of view. These compounds, which contain dihydrogen, elongated dihydrogen, compressed dihydride, and classical dihydride ligands promote the activation of B-H, C-H, Si-H, N-H, O-H, C-C, C-N, and C-F, among other σ-bonds. In this review, it is shown that, unlike other more mature areas, the chemistry of polyhydrides offers new exciting conceptual challenges and at the same time the possibility of interacting with other fields including the conversion and storage of regenerative energy, organic synthetic chemistry, drug design, and material science. This wide range of possible interactions foresees promising advances in the near future. PMID:27268136

  1. Annealing effects on recombinative activity of nickel at direct silicon bonded interface

    SciTech Connect

    Kojima, Takuto Ohshita, Yoshio; Yamaguchi, Masafumi

    2015-09-15

    By performing capacitance transient analyses, the recombination activity at a (110)/(100) direct silicon bonded (DSB) interface contaminated with nickel diffused at different temperatures, as a model of grain boundaries in multicrystalline silicon, was studied. The trap level depth from the valence band, trap density of states, and hole capture cross section peaked at an annealing temperature of 300 °C. At temperatures ⩾400 °C, the hole capture cross section increased with temperature, but the density of states remained unchanged. Further, synchrotron-based X-ray analyses, microprobe X-ray fluorescence (μ-XRF), and X-ray absorption near edge structure (XANES) analyses were performed. The analysis results indicated that the chemical phase after the sample was annealed at 200 °C was a mixture of NiO and NiSi{sub 2}.

  2. Metal Nanoparticles Catalyzed Selective Carbon-Carbon Bond Activation in the Liquid Phase.

    PubMed

    Ye, Rong; Yuan, Bing; Zhao, Jie; Ralston, Walter T; Wu, Chung-Yeh; Unel Barin, Ebru; Toste, F Dean; Somorjai, Gabor A

    2016-07-13

    Understanding the C-C bond activation mechanism is essential for developing the selective production of hydrocarbons in the petroleum industry and for selective polymer decomposition. In this work, ring-opening reactions of cyclopropane derivatives under hydrogen catalyzed by metal nanoparticles (NPs) in the liquid phase were studied. 40-atom rhodium (Rh) NPs, encapsulated by dendrimer molecules and supported in mesoporous silica, catalyzed the ring opening of cyclopropylbenzene at room temperature under hydrogen in benzene, and the turnover frequency (TOF) was higher than other metals or the Rh homogeneous catalyst counterparts. Comparison of reactants with various substitution groups showed that electron donation on the three-membered ring boosted the TOF of ring opening. The linear products formed with 100% selectivity for ring opening of all reactants catalyzed by the Rh NP. Surface Rh(0) acted as the active site in the NP. The capping agent played an important role in the ring-opening reaction kinetics. Larger particle size tended to show higher TOF and smaller reaction activation energy for Rh NPs encapsulated in either dendrimer or poly(vinylpyrrolidone). The generation/size of dendrimer and surface group also affected the reaction rate and activation energy. PMID:27322570

  3. Human Defensin 5 Disulfide Array Mutants: Disulfide Bond Deletion Attenuates Antibacterial Activity Against Staphylococcus aureus

    PubMed Central

    Wanniarachchi, Yoshitha A.; Kaczmarek, Piotr; Wan, Andrea; Nolan, Elizabeth M.

    2011-01-01

    Human α-defensin 5 (HD5, HD5ox to specify the oxidized and disulfide linked form) is a 32-residue cysteine-rich host-defense peptide, expressed and released by small intestinal Paneth cells, that exhibits antibacterial activity against a number of Gram-negative and –positive bacterial strains. To ascertain the contributions of its disulfide array to structure, antimicrobial activity, and proteolytic stability, a series of HD5 double mutant peptides where pairs of cysteine residues corresponding to native disulfide linkages (Cys3—Cys31, Cys5—Cys20, Cys10—Cys30) were mutated to Ser or Ala residues were overexpressed in E. coli, purified and characterized. A hexa mutant peptide, HD5[Serhexa], where all six native Cys residues are replaced by Ser residues was also evaluated. Removal of a single native S—S linkage influences oxidative folding and regioisomerization, antibacterial activity, Gram-negative bacterial membrane permeabilization, and proteolytic stability. Whereas the majority of the HD5 mutant peptides show low-micromolar activity against Gram-negative E. coli ATCC 25922 in colony counting assays, the wild-type disulfide array is essential for low-micromolar activity against Gram-positive S. aureus ATCC 25923. Removal of a single disulfide bond attenuates the activity observed for HD5ox against this Gram-positive bacterial strain. This observation supports the notion that the HD5ox mechanism of antibacterial action differs for Gram-negative and Gram-positive species (Wei, G.; de Leeuw, E., Pazgier, M., Yuan, W., Zou, G., Wang, J., Ericksen, B., Lu, W.-Y.; Lehrer, R. I.; Lu, W. (2009) J. Biol. Chem. 284, 29180-29192), and that the native disulfide array is a requirement for its activity against S. aureus. PMID:21861459

  4. Cross-Couplings Using Aryl Ethers via C-O Bond Activation Enabled by Nickel Catalysts.

    PubMed

    Tobisu, Mamoru; Chatani, Naoto

    2015-06-16

    Arene synthesis has been revolutionized by the invention of catalytic cross-coupling reactions, wherein aryl halides can be coupled with organometallic and organic nucleophiles. Although the replacement of aryl halides with phenol derivatives would lead to more economical and ecological methods, success has been primarily limited to activated phenol derivatives such as triflates. Aryl ethers arguably represent one of the most ideal substrates in terms of availability, cost, safety, and atom efficiency. However, the robust nature of the C(aryl)-O bonds of aryl ethers renders it extremely difficult to use them in catalytic reactions among the phenol derivatives. In 1979, Wenkert reported a seminal work on the nickel-catalyzed cross-coupling of aryl ethers with Grignard reagents. However, it was not until 2004 that the unique ability of a low-valent nickel species to activate otherwise unreactive C(aryl)-O bonds was appreciated with Dankwardt's identification of the Ni(0)/PCy3 system, which significantly expanded the efficiency of the Wenkert reaction. Application of the nickel catalyst to cross-couplings with other nucleophiles was first accomplished in 2008 by our group using organoboron reagents. Later on, several other nucleophiles, including organozinc reagents, amines, hydrosilane, and hydrogen were shown to be coupled with aryl ethers under nickel catalysis. Despite these advances, progress in this field is relatively slow because of the low reactivity of benzene derivatives (e.g., anisole) compared with polyaromatic substrates (e.g., methoxynaphthalene), particularly when less reactive and synthetically useful nucleophiles are used. The "naphthalene problem" has been overcome by the use of N-heterocyclic carbene (NHC) ligands bearing bulky N-alkyl substituents, which enables a wide range of aryl ethers to be coupled with organoboron nucleophiles. Moreover, the use of N-alkyl-substituted NHC ligands allows the use of alkynylmagnesium reagents, thereby realizing

  5. Antimicrobial activities of amphiphilic peptides covalently bonded to a water-insoluble resin.

    PubMed Central

    Haynie, S L; Crum, G A; Doele, B A

    1995-01-01

    A series of polymer-bound antimicrobial peptides was prepared, and the peptides were tested for their antimicrobial activities. The immobilized peptides were prepared by a strategy that used solid-phase peptide synthesis that linked the carboxy-terminal amino acid with an ethylenediamine-modified polyamide resin (PepsynK). The acid-stable, permanent amide bond between the support and the nascent peptide renders the peptide resistant to cleavage from the support during the final acid-catalyzed deprotection step in the synthesis. Select immobilized peptides containing amino acid sequences that ranged from the naturally occurring magainin to simpler synthetic sequences with idealized secondary structures were excellent antimicrobial agents against several organisms. The immobilized peptides typically reduced the number of viable cells by > or = 5 log units. We show that the reduction in cell numbers cannot be explained by the action of a soluble component. We observed no leached or hydrolyzed peptide from the resin, nor did we observe any antimicrobial activity in soluble extracts from the immobilized peptide. The immobilized peptides were washed and reused for repeated microbial contact and killing. These results suggest that the surface actions by magainins and structurally related antimicrobial peptides are sufficient for their lethal activities. PMID:7726486

  6. C-H Bond activation and C-C bond formation in the reaction of 2,5-dimethylthiophene with TpMe2Ir compounds.

    PubMed

    Paneque, Margarita; Poveda, Manuel L; Carmona, Ernesto; Salazar, Verónica

    2005-04-21

    The bulky 2,5-dimethylthiophene (2,5-Me2T) reacts at 60 degrees C with TpMe2Ir(C2H4)2 to give a mixture of two TpMe2Ir(III) hydride products, 3 and 4, that contain in addition a thienyl (3) or a thienyl-derived ligand (4). For the generation of 3 only sp2 C-H activation is needed, but the formation of 4 requires also the activation of an sp3 C-H bond and the formation of a new C-C bond (between vinyl and thienyl fragments). In the presence of 2,5-Me2T, compound 4 reacts further to produce a complex thiophenic structure (5, characterized by X-ray methods) that derives formally from two molecules of 2,5-Me2T and a vinyl fragment. Compounds 3-5 can be readily protonated by [H(OEt2)2][BAr'4](Ar'= 3,5-C6H3(CF3)2), with initial generation of carbene ligands (in the case of 3 and 5) as a consequence of H+ attack at the beta-carbon of the Ir-thienyl unit. Free, substituted thiophenes, derived from the original 2,5-Me2T, may be isolated in this way. PMID:15824780

  7. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    PubMed Central

    Lewis, Jared C.; Bergman, Robert G.; Ellman, Jonathan A.

    2008-01-01

    Conspectus Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct functionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes our work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. We initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. We then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, we discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. We then synthesized analogous Rh–NHC complexes directly by treating precursors to the intermediate [RhCl(PCy3)2] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazoline, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy3)2 fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, we developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including

  8. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    SciTech Connect

    Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-02-04

    Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of

  9. Thermochronology and geochemistry of the Pan-African basement below the Sab'atayn Basin, Yemen

    NASA Astrophysics Data System (ADS)

    Veeningen, Resi; Rice, A. Hugh N.; Schneider, David A.; Grasemann, Bernhard

    2015-02-01

    Three important lithologies occur in two drill wells from the Pan-African basement underlying the Mesozoic Sab'atayn Basin, in a previously undocumented area of the Pan-African, 83 and 90 km NE of known exposures in Yemen. Cores from well 1 include amphibolite, with basaltic to andesitic compositions, affected by crustal contamination during emplacement into a thickened crust. Deeper in the well, an unfoliated dark red monzogranite has a U-Pb zircon age of 628.8 ± 3.1 Ma and a Rb-Sr biotite cooling age of 591.6 ± 5.8 Ma (∼300 °C). Regional constraints suggest emplacement in a transitional tectonic setting with compressional terrane amalgamation followed by extensional collapse. Sm-Nd isotope analysis yields a TDM model age of 1.24 Ga with negative εNd values, suggesting the monzogranite is part of the Al Bayda island arc terrane. Cores from well 2 contains a weakly deformed, massive (unbedded) medium grey meta-arkose exhibiting essentially no geochemical signature of weathering and with an almost pure dacitic composition. This rock may have been directly derived from an (extrusive) granitoid that was emplaced prior to, or during terrane amalgamation. A (U-Th-Sm)/He zircon age of 156 ± 14 Ma constrains the time of basement cooling to ∼180 °C, synchronous with basin formation. These lithologies provide new insights in the development of the Pan-African basement of Yemen, extending our knowledge of the nearby surface geology to the subsurface.

  10. Active Metal Brazing and Adhesive Bonding of Titanium to C/C Composites for Heat Rejection System

    NASA Technical Reports Server (NTRS)

    Singh, M.; Shpargel, Tarah; Cerny, Jennifer

    2006-01-01

    Robust assembly and integration technologies are critically needed for the manufacturing of heat rejection system (HRS) components for current and future space exploration missions. Active metal brazing and adhesive bonding technologies are being assessed for the bonding of titanium to high conductivity Carbon-Carbon composite sub components in various shapes and sizes. Currently a number of different silver and copper based active metal brazes and adhesive compositions are being evaluated. The joint microstructures were examined using optical microscopy, and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). Several mechanical tests have been employed to ascertain the effectiveness of different brazing and adhesive approaches in tension and in shear that are both simple and representative of the actual system and relatively straightforward in analysis. The results of these mechanical tests along with the fractographic analysis will be discussed. In addition, advantages, technical issues and concerns in using different bonding approaches will also be presented.

  11. The effect of methyl-donated hydrogen bonding on active site conformations of hyaluronate lyase

    NASA Astrophysics Data System (ADS)

    Migues, Angela N.; Vergenz, Robert A.; Moore, Kevin B.

    2010-03-01

    Geometric evidence shows a val-A252 methyl-donated (MD) hydrogen bond (HB) in hyaluronate lyase (Streptococcus pneumoniae) interacts with nearby NH--O and OH--O HBs, distorting active-site helical structure. Results for model fragment A248-254 are based on experimental heavy atom positions with ab initio hydrogen atoms. The MDHB, with (H-O distance, donor-H-O angle) = (2.3å; 174^o), exhibits more favorable geometry than thr-A253 OH--O HB (1.8å; 170^o) to the same ala-249 C=O. Consequently, thr-253 N-H--O interaction is forced closer to lys-250 C=O than ala-249 C=O(2.6 versus 2.7å). A novel method has been developed to quantify the effects of atomic diplacements on motions of neighboring helices. A coordinate system was established to track the movement of specific residues and to ascertain the effect of such motions on active site conformations.

  12. The role of short-range Cys171-Cys178 disulfide bond in maintaining cutinase active site integrity: A molecular dynamics simulation

    SciTech Connect

    Matak, Mehdi Youssefi; Moghaddam, Majid Erfani

    2009-12-11

    Understanding structural determinants in enzyme active site integrity can provide a good knowledge to design efficient novel catalytic machineries. Fusarium solani pisi cutinase with classic triad Ser-His-Asp is a promising enzyme to scrutinize these structural determinants. We performed two MD simulations: one, with the native structure, and the other with the broken Cys171-Cys178 disulfide bond. This disulfide bond stabilizes a turn in active site on which catalytic Asp175 is located. Functionally important H-bonds and atomic fluctuations in catalytic pocket have been changed. We proposed that this disulfide bond within active site can be considered as an important determinant of cutinase active site structural integrity.

  13. The study of a light-activated albumin protein solder to bond layers of porcine small intestinal submucosa.

    PubMed

    Ware, Mark H; Buckley, Christine A

    2003-01-01

    This study investigated the feasibility of bonding layers of porcine small intestinal submucosa (SIS, Cook Biotech, Inc.) with a light-activated protein solder. SIS is an acellular, collagen-based extracellular matrix material that is approximately 100 microns thick. The solder consists of bovine serum albumin and indocyanine green dye (ICG) in deionized water. The solder is activated by an 808 nm diode laser, which denatures the albumin, causing the albumin to bond with the collagen of the tissue. The predictable absorption and thermal energy diffusion rates of ICG increase the chances of reproducible results. To determine the optimal condition for laser soldering SIS, the following parameters were varied: albumin concentration (from 30-45% (w/v) in increments of 5%), the concentration of ICG (from 0.5-2.0 mg/ml H2O) and the irradiance of the laser (10-64 W/cm2). While many of the solder compositions and laser irradiance combinations resulted in no bonding, a solder composition of 45% albumin, ICG concentration of 0.5 mg/ml H2O, and a laser irradiance of 21 W/cm2 did produce a bond between two pieces of SIS. The average shear strength of this bond was 29.5 +/- 17.1 kPa (n = 14). This compares favorably to our previous work using fibrin glue as an adhesive, in which the average shear strength was 27 +/- 15.8 kPa (n = 40). PMID:12724859

  14. Approach to In- Situ Producing Reinforcing Phase Within an Active-Transient Liquid Phase Bond Seam for Aluminum Matrix Composite

    NASA Astrophysics Data System (ADS)

    Zhang, Guifeng; Liao, Xianjin; Chen, Bo; Zhang, Linjie; Zhang, Jianxun

    2015-06-01

    To optimize the braze composition design route for aluminum matrix composite, the feasibility of in situ producing reinforcing phase within the transient liquid phase bond seam matrix, by adding active melting point increaser (MPI, e.g., Ti) together with general melting point depressant (MPD, e.g., Cu) into the interlayer, was demonstrated. For SiC p /A356 composite, by comparing the wettability, joint microstructure, joint shear strength, and fracture path for the developed Al-19Cu-1Ti, Al-19Cu, Al-33Cu-1Ti, Al-33Cu (wt pct), and commercial Cu foils as interlayer, the feasibility of in situ producing reinforcing phase within the bond seam by adding Ti was demonstrated. Especially for Al-19Cu-1Ti active braze, small and dispersed ternary aluminide of Al-Si-Ti phase was obtained within the bond seam as in situ reinforcement, leading to a favorable fracture path within SiC p /A356, not along the initial interface or within the bond seam. For the formation mechanism of the in situ reinforcing phase of MPI-containing intermetallic compound within the bond seam, a model of repeating concentration-precipitation-termination-engulfment during isothermal solidification is proposed.

  15. 77 FR 6136 - Agency Information Collection Activities: Application for Extension of Bond for Temporary...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-07

    ... Extension of Bond for Temporary Importation AGENCY: U.S. Customs and Border Protection (CBP), Department of... requirement concerning the Application for Extension of Bond for Temporary Importation (CBP Form 3173). This...: Direct all written comments to U.S. Customs and Border Protection, Attn: Tracey Denning, Regulations...

  16. 77 FR 21578 - Agency Information Collection Activities: Application for Extension of Bond for Temporary...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-10

    ... information collection was previously published in the Federal Register (77 FR 6136) on February 7, 2012... Extension of Bond for Temporary Importation AGENCY: U.S. Customs and Border Protection, Department of... review and approval in accordance with the Paperwork Reduction Act: Application for Extension of Bond...

  17. Palladium-Catalyzed Synthesis of Phenanthridine/Benzoxazine-Fused Quinazolinones by Intramolecular C-H Bond Activation.

    PubMed

    Gupta, Puneet K; Yadav, Nisha; Jaiswal, Subodh; Asad, Mohd; Kant, Ruchir; Hajela, Kanchan

    2015-09-14

    A highly efficient synthesis of phenanthridine/benzoxazine-fused quinazolinones by ligand-free palladium-catalyzed intramolecular C-H bond activation under mild conditions has been developed. The C-C coupling provides the corresponding N-fused polycyclic heterocycles in good to excellent yields and with wide functional group tolerance. PMID:26230355

  18. Palladium-catalyzed oxidative arylalkylation of activated alkenes: dual C-H bond cleavage of an arene and acetonitrile.

    PubMed

    Wu, Tao; Mu, Xin; Liu, Guosheng

    2011-12-23

    Not one but two: The title reaction proceeds through the dual C-H bond cleavage of both aniline and acetonitrile. The reaction affords a variety of cyano-bearing indolinones in excellent yield. Mechanistic studies demonstrate that this reaction involves a fast arylation of the olefin and a rate-determining C-H activation of the acetonitrile. PMID:22076660

  19. 26 CFR 1.103(n)-1T - Limitation on aggregrate amount of private activity bonds (temporary).

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 2 2014-04-01 2014-04-01 false Limitation on aggregrate amount of private activity bonds (temporary). 1.103(n)-1T Section 1.103(n)-1T Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) INCOME TAX (CONTINUED) INCOME TAXES (CONTINUED) Items Specifically Excluded from Gross Income §...

  20. 26 CFR 1.103(n)-1T - Limitation on aggregrate amount of private activity bonds (temporary).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... authority has elected to carry forward to a future year, does not exceed the issuing authority's private... 1986 is $200 million. City M, within the State, and State Z itself are authorized to issue private activity bonds. Under the allocation formula provided by the Governor of State Z, City M has a...

  1. 26 CFR 1.103(n)-1T - Limitation on aggregrate amount of private activity bonds (temporary).

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... authority has elected to carry forward to a future year, does not exceed the issuing authority's private... 1986 is $200 million. City M, within the State, and State Z itself are authorized to issue private activity bonds. Under the allocation formula provided by the Governor of State Z, City M has a...

  2. Reactions of 4-nitro-1,2,3-triazole with alkylating agents and compounds with activated multiple bonds

    SciTech Connect

    Vereshchagin, L.I.; Kuznetsova, N.I.; Kirillova, L.P.; Shcherbakov, V.V.; Sukhanov, G.T.; Gareev, G.A.

    1987-01-01

    When 4-nitro-1,2,3-triazole is alkylated, a mixture of N1- and N2-isomers is formed, with the latter usually predominating. The same behavior is also observed in addition reactions of 4-nitrotriazole to activated multiple bonds.

  3. Consequences of Metal–Oxide Interconversion for C–H Bond Activation during CH₄ Reactions on Pd Catalysts

    SciTech Connect

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

    2013-10-01

    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 Habstraction and then to σ-bond metathesis with increasing O-content, as active sites evolve from metal atom pairs (*-*) to oxygen atom (O*-O*) pairs and ultimately to Pd cationlattice oxygen pairs (Pd2+-O2-) 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 Pd2+-O2- 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 Pd2+ and vicinal O2-, Pdox-Oox, cleave C-H bonds heterolytically via σ-bond metathesis, with Pd2+ adding to the C-H bond, while O2- abstracts the H-atom to form a four-center (H3Cδ-···Pdox···Hδ+···Oox) transition state without detectable Pdox 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

  4. CHEMICAL ACTIVATION OF MOLECULES BY METALS: EXPERIMENTAL STUDIES OF ELECTRON DISTRIBUTIONS AND BONDING

    SciTech Connect

    LICHTENBERGER, DENNIS L.

    2002-03-26

    This research program is directed at obtaining detailed experimental information on the electronic interactions between metals and organic molecules. These interactions provide low energy pathways for many important chemical and catalytic processes. A major feature of the program is the continued development and application of our special high-resolution valence photoelectron spectroscopy (UPS), and high-precision X-ray core photoelectron spectroscopy (XPS) instrumentation for study of organometallic molecules in the gas phase. The study involves a systematic approach towards understanding the interactions and activation of bound carbonyls, C-H bonds, methylenes, vinylidenes, acetylides, alkenes, alkynes, carbenes, carbynes, alkylidenes, alkylidynes, and others with various monometal, dimetal, and cluster metal species. Supporting ligands include -aryls, alkoxides, oxides, and phosphines. We are expanding our studies of both early and late transition metal species and electron-rich and electron-poor environments in order to more completely understand the electronic factors that serve to stabilize particular organic fragments and intermediates on metals. Additional new directions for this program are being taken in ultra-high vacuum surface UPS, XPS, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) experiments on both physisorbed and chemisorbed organometallic thin films. The combination of these methods provides additional electronic structure information on surface-molecule and molecule-molecule interactions. A very important general result emerging from this program is the identification of a close relationship between the ionization energies of the species and the thermodynamics of the chemical and catalytic reactions of these systems.

  5. Coordination and activation of Al-H and Ga-H bonds.

    PubMed

    Abdalla, Joseph A B; Riddlestone, Ian M; Turner, Joshua; Kaufman, Paul A; Tirfoin, Remi; Phillips, Nicholas; Aldridge, Simon

    2014-12-22

    The modes of interaction of donor-stabilized Group 13 hydrides (E=Al, Ga) were investigated towards 14- and 16-electron transition-metal fragments. More electron-rich N-heterocyclic carbene-stabilized alanes/gallanes of the type NHC⋅EH3 (E=Al or Ga) exclusively generate κ(2) complexes of the type [M(CO)4 (κ(2)-H3 E⋅NHC)] with [M(CO)4 (COD)] (M=Cr, Mo), including the first κ(2) σ-gallane complexes. β-Diketiminato ('nacnac')-stabilized systems, {HC(MeCNDipp)2 }EH2 , show more diverse reactivity towards Group 6 carbonyl reagents. For {HC(MeCNDipp)2 }AlH2, both κ(1) and κ(2) complexes were isolated, while [Cr(CO)4 (κ(2)-H2 Ga{(NDippCMe)2 CH})] is the only simple κ(2) adduct of the nacnac-stabilized gallane which can be trapped, albeit as a co-crystallite with the (dehydrogenated) gallylene system [Cr(CO)5 (Ga{(NDippCMe)2 CH})]. Reaction of [Co2 (CO)8] with {HC(MeCDippN)2 }AlH2 generates [(OC)3 Co(μ-H)2 Al{(NdippCme)2 CH}][Co(CO)4] (12), which while retaining direct AlH interactions, features a hitherto unprecedented degree of bond activation in a σ-alane complex. PMID:25358970

  6. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

    NASA Astrophysics Data System (ADS)

    Lichtenberger, D. L.

    1991-10-01

    The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies has been developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. This relationship has been used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. We have been able to obtain a direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal. The ionization energies have also been used to correlate the rates of carbonyl substitution reactions of (eta sup 5-C5H4)Rh(CO)2 complexes, and to reveal the electronic factors that control the stability of the transition state. The extent that the electronic features of these bonding interactions transfer to other chemical systems is being investigated in terms of the principle of additivity of ligand electronic effects. Specific examples under study include metal- phosphines, metal-halides, and metallocenes. Especially interesting has been the recent application of these techniques to the characterization of the soccer-ball shaped C60 molecule, buckminsterfullerene, and its interaction with a metal surface. The high resolution valence ionizations in the gas phase reveal the high symmetry of the molecule, and studies of thin films of C60 reveal weak intermolecular interactions. Scanning tunneling and atomic force microscopy reveal the arrangement of spherical molecules on gold substrates, with significant delocalization of charge from the metal surface.

  7. Locking covalent organic frameworks with hydrogen bonds: general and remarkable effects on crystalline structure, physical properties, and photochemical activity.

    PubMed

    Chen, Xiong; Addicoat, Matthew; Jin, Enquan; Zhai, Lipeng; Xu, Hong; Huang, Ning; Guo, Zhaoqi; Liu, Lili; Irle, Stephan; Jiang, Donglin

    2015-03-11

    A series of two-dimensional covalent organic frameworks (2D COFs) locked with intralayer hydrogen-bonding (H-bonding) interactions were synthesized. The H-bonding interaction sites were located on the edge units of the imine-linked tetragonal porphyrin COFs, and the contents of the H-bonding sites in the COFs were synthetically tuned using a three-component condensation system. The intralayer H-bonding interactions suppress the torsion of the edge units and lock the tetragonal sheets in a planar conformation. This planarization enhances the interlayer interactions and triggers extended π-cloud delocalization over the 2D sheets. Upon AA stacking, the resulting COFs with layered 2D sheets amplify these effects and strongly affect the physical properties of the material, including improving their crystallinity, enhancing their porosity, increasing their light-harvesting capability, reducing their band gap, and enhancing their photocatalytic activity toward the generation of singlet oxygen. These remarkable effects on the structure and properties of the material were observed for both freebase and metalloporphyin COFs. These results imply that exploration of supramolecular ensembles would open a new approach to the structural and functional design of COFs. PMID:25706112

  8. The Three-dimensional Structure of the Extracellular Adhesion Domain of the Sialic Acid-binding Adhesin SabA from Helicobacter pylori

    PubMed Central

    Pang, Siew Siew; Nguyen, Stanley Thai Son; Perry, Andrew J.; Day, Christopher J.; Panjikar, Santosh; Tiralongo, Joe; Whisstock, James C.; Kwok, Terry

    2014-01-01

    The gastric pathogen Helicobacter pylori is a major cause of acute chronic gastritis and the development of stomach and duodenal ulcers. Chronic infection furthermore predisposes to the development of gastric cancer. Crucial to H. pylori survival within the hostile environment of the digestive system are the adhesins SabA and BabA; these molecules belong to the same protein family and permit the bacteria to bind tightly to sugar moieties LewisB and sialyl-LewisX, respectively, on the surface of epithelial cells lining the stomach and duodenum. To date, no representative SabA/BabA structure has been determined, hampering the development of strategies to eliminate persistent H. pylori infections that fail to respond to conventional therapy. Here, using x-ray crystallography, we show that the soluble extracellular adhesin domain of SabA shares distant similarity to the tetratricopeptide repeat fold family. The molecule broadly resembles a golf putter in shape, with the head region featuring a large cavity surrounded by loops that vary in sequence between different H. pylori strains. The N-terminal and C-terminal helices protrude at right angles from the head domain and together form a shaft that connects to a predicted outer membrane protein-like β-barrel trans-membrane domain. Using surface plasmon resonance, we were able to detect binding of the SabA adhesin domain to sialyl-LewisX and LewisX but not to LewisA, LewisB, or LewisY. Substitution of the highly conserved glutamine residue 159 in the predicted ligand-binding pocket abrogates the binding of the SabA adhesin domain to sialyl-LewisX and LewisX. Taken together, these data suggest that the adhesin domain of SabA is sufficient in isolation for specific ligand binding. PMID:24375407

  9. Bond Activation by Metal-Carbene Complexes in the Gas Phase.

    PubMed

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-03-15

    "Bare" metal-carbene complexes, when generated in the gas phase and exposed to thermal reactions under (near) single-collision conditions, exhibit rather unique reactivities in addition to the well-known metathesis and cyclopropanation processes. For example, at room temperature the unligated [AuCH2](+) complex brings about efficient C-C coupling with methane to produce C2Hx (x = 4, 6), and the couple [TaCH2](+)/CO2 gives rise to the generation of the acetic acid equivalent CH2═C═O. Entirely unprecedented is the thermal extrusion of a carbon atom from halobenzenes (X = F, Cl, Br, I) by [MCH2](+) (M = La, Hf, Ta, W, Re, Os) and its coupling with the methylene ligand to deliver C2H2 and [M(X)(C5H5)](+). Among the many noteworthy C-N bond-forming processes, the formation of CH3NH2 from [RhCH2](+)/NH3, the generation of CH2═NH2(+) from [MCH2](+)/NH3 (M = Pt, Au), and the production of [PtCH═NH2](+) from [PtCH2](+)/NH3 are of particular interest. The latter species are likely to be involved as intermediates in the platinum-mediated large-scale production of HCN from CH4/NH3 (the DEGUSSA process). In this context, a few examples are presented that point to the operation of co-operative effects even at a molecular level. For instance, in the coupling of CH4 with NH3 by the heteronuclear clusters [MPt](+) (M = coinage metal), platinum is crucial for the activation of methane, while the coinage metal M controls the branching ratio between the C-N bond-forming step and unwanted soot formation. For most of the gas-phase reactions described in this Account, detailed mechanistic insight has been derived from extensive computational work in conjunction with time-honored labeling and advanced mass-spectrometry-based experiments, and often a coherent description of the experimental findings has been achieved. As for some transition metals, in particular those from the third row, the metal-carbene complexes can be formed directly from methane, coupling of the so

  10. Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.

    PubMed

    Becker, Julia; Modl, Tanja; Gessner, Viktoria H

    2014-09-01

    The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. PMID:25047390

  11. The Nature of Activated Non-classical Hydrogen Bonds: A Case Study on Acetylcholinesterase-Ligand Complexes.

    PubMed

    Berg, Lotta; Mishra, Brijesh Kumar; Andersson, C David; Ekström, Fredrik; Linusson, Anna

    2016-02-18

    Molecular recognition events in biological systems are driven by non-covalent interactions between interacting species. Here, we have studied hydrogen bonds of the CH⋅⋅⋅Y type involving electron-deficient CH donors using dispersion-corrected density functional theory (DFT) calculations applied to acetylcholinesterase-ligand complexes. The strengths of CH⋅⋅⋅Y interactions activated by a proximal cation were considerably strong; comparable to or greater than those of classical hydrogen bonds. Significant differences in the energetic components compared to classical hydrogen bonds and non-activated CH⋅⋅⋅Y interactions were observed. Comparison between DFT and molecular mechanics calculations showed that common force fields could not reproduce the interaction energy values of the studied hydrogen bonds. The presented results highlight the importance of considering CH⋅⋅⋅Y interactions when analysing protein-ligand complexes, call for a review of current force fields, and opens up possibilities for the development of improved design tools for drug discovery. PMID:26751405

  12. Transition metal activation and functionalization of C-H bonds: Progress report, December 1, 1987-November 30, 1988

    SciTech Connect

    Jones, W.D.

    1988-08-01

    This project is directed towards the continued investigation of the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers. The project is also directed towards the conversion of hydrocarbons into functionalized products of potential use to chemical industry. Goals will be 1) to identify new transition metal complexes capable of activating arene and alkane C-H bonds, 2) to quantitatively evaluate the kinetic and thermodynamic stability of these complexes, and 3) to examine routes for functionalization of the activated hydrocarbons. Specific complexes involved are derivatives of the formulation (C/sub 5/Me/sub 5/)Rh(PR/sub 3/)(R)H, Fe(PMe/sub 3/)/sub 2/(CNR)/sub 3/, Ru(PR/sub 3/)/sub 4/(R)H, and Rh(CNR)/sub 3/H. Functionalization will focus upon isocyanide and acetylene insertion reactions. New compounds that activate hydrocarbon C-H bonds include HRe(PR/sub 3/)/sub 5/, HRe(PR/sub 3/)/sub 2/(CNR)/sub 3/, CpRe(PR/sub 3/)H/sub 4/, CpRe(PR/sub 3/)/sub 2/H/sub 2/, (/eta//sup 6/-C/sub 6/H/sub 6/)Re(PPh/sub 3/)/sub 2/H, and MnH/sub 3/(dmpe)/sub 2/. The latter complex is found to be an /eta//sup 2/-dihydrogen complex. The new complexes RhCl(P(i-Pr)/sub 3/)/sub 2/(CNCH/sub 2/CMe/sub 3/) and (trispyrazolylborate)Rh(CNR)/sub 2/ are shown to be active for the activation and functionalization of aromatic C-H bonds. 10 figs., 1 tab.

  13. C-O and O-H Bond Activation of Methanole by Lanthanum

    NASA Astrophysics Data System (ADS)

    Silva, Ruchira; Hewage, Dilrukshi; Yang, Dong-Sheng

    2012-06-01

    The interaction between methanol (CH_3OH) molecules and laser-vaporized La atoms resulted in the cleavage of C-O and O-H bonds and the formation of three major products, LaH_2O_2, LaCH_4O_2 and LaC_2H_6O_2, in a supersonic molecular beam. These products were identified by time-of-flight mass spectrometry, and their electronic spectra were obtained using mass-analyzed threshold ionization (MATI) spectroscopy. From the MATI spectra, adiabatic ionization energies of the three complexes were measured to be 40136 (5), 39366 (5) and 38685 (5) cm-1 for LaH_2O_2, LaCH_4O_2 and LaC_2H_6O_2, respectively. The ionization energies of these complexes decrease as the size of the coordinated organic fragments increases. The most active vibrational transitions of all three complexes were observed to be the M-O stretches in the ionic state. A metal-ligand bending mode with a frequency of 127 cm-1 was also observed for [LaH_2O_2]^+. However, the spectra of the other two complexes were less resolved, due to the existence of a large number of low frequency modes, which could be thermally excited even in the supersonic molecular beams, and of multiple rotational isomers formed by the free rotation of the methyl group in these systems. The electronic transitions responsible for the observed spectra were identified as ^1A_1 (C2v) ← ^2A_1 (C2v) for LaH_2O_2 and ^1A (C_1) ← ^2A (C_1) for LaCH_4O_2 and LaC_2H_6O_2.

  14. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

    SciTech Connect

    Lichtenberger, D.L.

    1991-10-01

    The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies has been developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. This relationship has been used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. We have been able to obtain a direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal. The ionization energies have also been used to correlate the rates of carbonyl substitution reactions of ({eta}{sup 5}-C{sub 5}H{sub 4}X)Rh(CO){sub 2} complexes, and to reveal the electronic factors that control the stability of the transition state. The extent that the electronic features of these bonding interactions transfer to other chemical systems is being investigated in terms of the principle of additivity of ligand electronic effects. Specific examples under study include metal- phosphines, metal-halides, and metallocenes. Especially interesting has been the recent application of these techniques to the characterization of the soccer-ball shaped C{sub 60} molecule, buckminsterfullerene, and its interaction with a metal surface. The high-resolution valence ionizations in the gas phase reveal the high symmetry of the molecule, and studies of thin films of C{sub 60} reveal weak intermolecular interactions. Scanning tunneling and atomic force microscopy reveal the arrangement of spherical molecules on gold substrates, with significant delocalization of charge from the metal surface. 21 refs.

  15. H-bonding networks of the distal residues and water molecules in the active site of Thermobifida fusca hemoglobin.

    PubMed

    Nicoletti, Francesco P; Droghetti, Enrica; Howes, Barry D; Bustamante, Juan P; Bonamore, Alessandra; Sciamanna, Natascia; Estrin, Darío A; Feis, Alessandro; Boffi, Alberto; Smulevich, Giulietta

    2013-09-01

    The ferric form of truncated hemoglobin II from Thermobifida fusca (Tf-trHb) and its triple mutant WG8F-YB10F-YCD1F at neutral and alkaline pH, and in the presence of CN(-) have been characterized by resonance Raman spectroscopy, electron paramagnetic resonance spectroscopy, and molecular dynamics simulations. Tf-trHb contains three polar residues in the distal site, namely TrpG8, TyrCD1 and TyrB10. Whereas TrpG8 can act as a potential hydrogen-bond donor, the tyrosines can act as donors or acceptors. Ligand binding in heme-containing proteins is determined by a number of factors, including the nature and conformation of the distal residues and their capability to stabilize the heme-bound ligand via hydrogen-bonding and electrostatic interactions. Since both the RR Fe-OH(-) and Fe-CN(-) frequencies are very sensitive to the distal environment, detailed information on structural variations has been obtained. The hydroxyl ligand binds only the WT protein giving rise to two different conformers. In form 1 the anion is stabilized by H-bonds with TrpG8, TyrCD1 and a water molecule, in turn H-bonded to TyrB10. In form 2, H-bonding with TyrCD1 is mediated by a water molecule. Unlike the OH(-) ligand, CN(-) binds both WT and the triple mutant giving rise to two forms with similar spectroscopic characteristics. The overall results clearly indicate that H-bonding interactions both with distal residues and water molecules are important structural determinants in the active site of Tf-trHb. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins. PMID:23467007

  16. 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

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

    2010-10-29

    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 (d8, d6, d4, and d0), 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, σ-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 d6 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*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in

  17. 77 FR 75419 - Agency Information Collection Activities; Comment Request; School Attendance Boundary Survey...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-20

    ..., Acting Director, Information Collection Clearance Division, Privacy, Information and Records Management... Director of the Information Collection Clearance Division, U.S. Department of Education, 400 Maryland... Agency Information Collection Activities; Comment Request; School Attendance Boundary Survey (SABS)...

  18. Quantitative evaluation on activated property-tunable bulk liquid water with reduced hydrogen bonds using deconvoluted Raman spectroscopy.

    PubMed

    Chen, Hsiao-Chien; Mai, Fu-Der; Yang, Kuang-Hsuan; Chen, Liang-Yih; Yang, Chih-Ping; Liu, Yu-Chuan

    2015-01-01

    Interesting properties of water with distinguishable hydrogen-bonding structure on interfacial phase or in confined environment have drawn wide attentions. However, these unique properties of water are only found within the interfacial phase and confined environment, thus, their applications are limited. In addition, quantitative evaluation on these unique properties associating with the enhancement of water's physical and chemical activities represents a notable challenge. Here we report a practicable production of free-standing liquid water at room temperature with weak hydrogen-bonded structure naming Au nanoparticles (NPs)-treated (AuNT) water via treating by plasmon-induced hot electron transfer occurred on resonantly illuminated gold NPs (AuNPs). Compared to well-known untreated bulk water (deionized water), the prepared AuNT water exhibits many distinct activities in generally physical and chemical reactions, such as high solubilities to NaCl and O2. Also, reducing interaction energy within water molecules provides lower overpotential and higher efficiency in electrolytic hydrogen production. In addition, these enhanced catalytic activities of AuNT water are tunable by mixing with deionized water. Also, most of these tunable activities are linearly proportional to its degree of nonhydrogen-bonded structure (DNHBS), which is derived from the O-H stretching in deconvoluted Raman spectrum. PMID:25471522

  19. Tautomerization lowers the activation barriers for N-glycosidic bond cleavage of protonated uridine and 2'-deoxyuridine.

    PubMed

    Wu, R R; Rodgers, M T

    2016-09-21

    The gas-phase conformations of protonated uridine, [Urd+H](+), and its 2'-deoxy form, protonated 2'-deoxyuridine, [dUrd+H](+), have been examined in detail previously by infrared multiple photon dissociation action spectroscopy techniques. Both 2,4-dihydroxy tautomers and O4 protonated conformers of [Urd+H](+) and [dUrd+H](+) were found to coexist in the experiments with the 2,4-dihydroxy tautomers dominating the population. In the present study, the kinetic energy dependence of the collision-induced dissociation behavior of [Urd+H](+) and [dUrd+H](+) are examined using a guided ion beam tandem mass spectrometer to probe the mechanisms and energetics for activated dissociation of these protonated nucleosides. The primary dissociation pathways observed involve N-glycosidic bond cleavage leading to competitive elimination of protonated or neutral uracil. The potential energy surfaces (PESs) for these N-glycosidic bond cleavage pathways are mapped out via electronic structure calculations for the mixture of 2,4-dihydroxy tautomers and O4 protonated conformers of [Urd+H](+) and [dUrd+H](+) populated in the experiments. The calculated activation energies (AEs) and heats of reaction (ΔHrxns) for N-glycosidic bond cleavage at both the B3LYP and MP2(full) levels of theory are compared to the measured values. The agreement between experiment and theory indicates that B3LYP provides better estimates of the energetics of the species along the PESs for N-glycosidic bond cleavage than MP2, and that the 2,4-dihydroxy tautomers, which are stabilized by strong hydrogen-bonding interactions, predominantly influence the observed threshold dissociation behavior of [Urd+H](+) and [dUrd+H](+). PMID:27536972

  20. Insulin analog with additional disulfide bond has increased stability and preserved activity.

    PubMed

    Vinther, Tine N; Norrman, Mathias; Ribel, Ulla; Huus, Kasper; Schlein, Morten; Steensgaard, Dorte B; Pedersen, Thomas Å; Pettersson, Ingrid; Ludvigsen, Svend; Kjeldsen, Thomas; Jensen, Knud J; Hubálek, František

    2013-03-01

    Insulin is a key hormone controlling glucose homeostasis. All known vertebrate insulin analogs have a classical structure with three 100% conserved disulfide bonds that are essential for structural stability and thus the function of insulin. It might be hypothesized that an additional disulfide bond may enhance insulin structural stability which would be highly desirable in a pharmaceutical use. To address this hypothesis, we designed insulin with an additional interchain disulfide bond in positions A10/B4 based on Cα-Cα distances, solvent exposure, and side-chain orientation in human insulin (HI) structure. This insulin analog had increased affinity for the insulin receptor and apparently augmented glucodynamic potency in a normal rat model compared with HI. Addition of the disulfide bond also resulted in a 34.6°C increase in melting temperature and prevented insulin fibril formation under high physical stress even though the C-terminus of the B-chain thought to be directly involved in fibril formation was not modified. Importantly, this analog was capable of forming hexamer upon Zn addition as typical for wild-type insulin and its crystal structure showed only minor deviations from the classical insulin structure. Furthermore, the additional disulfide bond prevented this insulin analog from adopting the R-state conformation and thus showing that the R-state conformation is not a prerequisite for binding to insulin receptor as previously suggested. In summary, this is the first example of an insulin analog featuring a fourth disulfide bond with increased structural stability and retained function. PMID:23281053

  1. Chemically Non-Innocent Cyclic (Alkyl)(Amino)Carbenes: Ligand Rearrangement, C-H and C-F Bond Activation.

    PubMed

    Turner, Zoë R

    2016-08-01

    A cyclic (alkyl)(amino)carbene (CAAC) was found to undergo unprecedented rearrangements and transformations of its core structure in the presence of Group 1 and 2 metals. Although the carbene was also found to be prone to intramolecular C-H activation, it was competent for intermolecular activation of a variety of sp-, sp(2) -, and sp(3) -hybridized C-H bonds. Double C-F activation of hexafluorobenzene was also observed in this work. These processes all hold relevance to the role of these carbenes in catalysis, as well as to their use in the synthesis of new and unusual main group or transition metal complexes. PMID:27363588

  2. Rhodium-catalysed C(sp(2))-C(sp(2)) bond formation via C-H/C-F activation.

    PubMed

    Tian, Panpan; Feng, Chao; Loh, Teck-Peng

    2015-01-01

    Fluoroalkenes represent a class of privileged structural motifs, which found widespread use in medicinal chemistry. However, the synthetic access to fluoroalkenes was much underdeveloped with previous reported methods suffering from either low step economy or harsh reaction conditions. Here we present a Rh(III)-catalysed tandem C-H/C-F activation for the synthesis of (hetero)arylated monofluoroalkenes. The use of readily available gem-difluoroalkenes as electrophiles provides a highly efficient and operationally simple method for the introduction of α-fluoroalkenyl motifs onto (hetero)arenes under oxidant-free conditions. Furthermore, the employment of alcoholic solvent and the in-situ generated hydrogen fluoride are found to be beneficial in this transformation, indicating the possibility of the involvement of hydrogen bond activation mode with regards to the C-F bond cleavage step. PMID:26081837

  3. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

    Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

  4. Conversion of amides to esters by the nickel-catalysed activation of amide C-N bonds

    NASA Astrophysics Data System (ADS)

    Hie, Liana; Fine Nathel, Noah F.; Shah, Tejas K.; Baker, Emma L.; Hong, Xin; Yang, Yun-Fang; Liu, Peng; Houk, K. N.; Garg, Neil K.

    2015-08-01

    Amides are common functional groups that have been studied for more than a century. They are the key building blocks of proteins and are present in a broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to the resonance stability of the amide bond. Although amides can readily be cleaved by enzymes such as proteases, it is difficult to selectively break the carbon-nitrogen bond of an amide using synthetic chemistry. Here we demonstrate that amide carbon-nitrogen bonds can be activated and cleaved using nickel catalysts. We use this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory calculations provide insight into the thermodynamics and catalytic cycle of the amide-to-ester transformation. Our results provide a way to harness amide functional groups as synthetic building blocks and are expected to lead to the further use of amides in the construction of carbon-heteroatom or carbon-carbon bonds using non-precious-metal catalysis.

  5. High heat flux test of a HIP-bonded first wall panel of reduced activation ferritic steel F-82H

    NASA Astrophysics Data System (ADS)

    Hatano, T.; Suzuki, S.; Yokoyama, K.; Kuroda, T.; Enoeda, M.

    2000-12-01

    Reduced activation ferritic steel F-82H is a primary candidate structural material of DEMO fusion reactors. In fabrication technology, development of the DEMO blanket in JAERI, a hot isostatic pressing (HIP) bonding method, especially for the first wall structure with built-in cooling tubes has been proposed. A HIP-bonded F-82H first wall panel was successfully fabricated with selected manufacturing parameters. A high heat flux test of the HIP-bonded F-82H first wall panel has been performed to examine the thermo-mechanical performance of the panel including the integrity of the HIP-bonded interfaces and the fatigue behavior. A maximum heat flux of 2.7 MW/m2 was applied to accelerate the fatigue test up to 5000 cycles in test blanket inserted ITER. The maximum temperature of the panel was ∼450°C under this heat flux. Through this test campaign, no damage such as cracks was observed on the surface of the panel, and no degradation in heat removal performance was observed either from the temperature responses. The thermal fatigue lifetime of the panel was found to be longer than the fatigue data obtained by mechanical testing.

  6. Conversion of Amides to Esters by the Nickel-Catalyzed Activation of Amide C–N Bonds

    PubMed Central

    Hie, Liana; Fine Nathel, Noah F.; Shah, Tejas K.; Baker, Emma L.; Hong, Xin; Yang, Yun-Fang; Liu, Peng; Houk, K. N.; Garg, Neil K.

    2015-01-01

    Amides are common functional groups that have been well studied for more than a century.1 They serve as the key building blocks of proteins and are present in an broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to resonance stability of the amide bond.1,2 Whereas Nature can easily cleave amides through the action of enzymes, such as proteases,3 the ability to selectively break the C–N bond of an amide using synthetic chemistry is quite difficult. In this manuscript, we demonstrate that amide C–N bonds can be activated and cleaved using nickel catalysts. We have used this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory (DFT) calculations provide insight into the thermodynamics and catalytic cycle of this unusual transformation. Our results provide a new strategy to harness amide functional groups as synthons and are expected fuel the further use of amides for the construction of carbon–heteroatom or carbon–carbon bonds using non-precious metal catalysis. PMID:26200342

  7. Enantioselective Aminomethylamination of Conjugated Dienes with Aminals Enabled by Chiral Palladium Complex-Catalyzed C-N Bond Activation.

    PubMed

    Liu, Yang; Xie, Yinjun; Wang, Hongli; Huang, Hanmin

    2016-04-01

    A novel highly enantioselective aminomethylamination of conjugated dienes with aminals catalyzed by a chiral palladium complex ligated with BINOL-derived chiral diphosphinite has been successfully developed. This reaction proceeds via a Pd-catalyzed cascade C-N bond activation, aminomethylation, and asymmetric allylic amination reaction under mild reaction conditions, providing a unique and efficient strategy for the synthesis of enantiomerically pure allylic 1,3-diamines. PMID:26998813

  8. 77 FR 15378 - Agency Information Collection Activities: Application for Withdrawal of Bonded Stores for Fishing...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-15

    ...U.S. Customs and Border Protection (CBP) of the Department of Homeland Security will be submitting the following information collection request to the Office of Management and Budget (OMB) for review and approval in accordance with the Paperwork Reduction Act: Application for Withdrawal of Bonded Stores for Fishing Vessels and Certificate of Use (CBP Form 5125). This is a proposed extension of......

  9. Diffusion bonding aeroengine components

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, G. A.; Broughton, T.

    1988-10-01

    The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

  10. Sacrificial adhesive bonding: a powerful method for fabrication of glass microchips

    PubMed Central

    Lima, Renato S.; Leão, Paulo A. G. C.; Piazzetta, Maria H. O.; Monteiro, Alessandra M.; Shiroma, Leandro Y.; Gobbi, Angelo L.; Carrilho, Emanuel

    2015-01-01

    A new protocol for fabrication of glass microchips is addressed in this research paper. Initially, the method involves the use of an uncured SU-8 intermediate to seal two glass slides irreversibly as in conventional adhesive bonding-based approaches. Subsequently, an additional step removes the adhesive layer from the channels. This step relies on a selective development to remove the SU-8 only inside the microchannel, generating glass-like surface properties as demonstrated by specific tests. Named sacrificial adhesive layer (SAB), the protocol meets the requirements of an ideal microfabrication technique such as throughput, relatively low cost, feasibility for ultra large-scale integration (ULSI), and high adhesion strength, supporting pressures on the order of 5 MPa. Furthermore, SAB eliminates the use of high temperature, pressure, or potential, enabling the deposition of thin films for electrical or electrochemical experiments. Finally, the SAB protocol is an improvement on SU-8-based bondings described in the literature. Aspects such as substrate/resist adherence, formation of bubbles, and thermal stress were effectively solved by using simple and inexpensive alternatives. PMID:26293346

  11. Sacrificial adhesive bonding: a powerful method for fabrication of glass microchips

    NASA Astrophysics Data System (ADS)

    Lima, Renato S.; Leão, Paulo A. G. C.; Piazzetta, Maria H. O.; Monteiro, Alessandra M.; Shiroma, Leandro Y.; Gobbi, Angelo L.; Carrilho, Emanuel

    2015-08-01

    A new protocol for fabrication of glass microchips is addressed in this research paper. Initially, the method involves the use of an uncured SU-8 intermediate to seal two glass slides irreversibly as in conventional adhesive bonding-based approaches. Subsequently, an additional step removes the adhesive layer from the channels. This step relies on a selective development to remove the SU-8 only inside the microchannel, generating glass-like surface properties as demonstrated by specific tests. Named sacrificial adhesive layer (SAB), the protocol meets the requirements of an ideal microfabrication technique such as throughput, relatively low cost, feasibility for ultra large-scale integration (ULSI), and high adhesion strength, supporting pressures on the order of 5 MPa. Furthermore, SAB eliminates the use of high temperature, pressure, or potential, enabling the deposition of thin films for electrical or electrochemical experiments. Finally, the SAB protocol is an improvement on SU-8-based bondings described in the literature. Aspects such as substrate/resist adherence, formation of bubbles, and thermal stress were effectively solved by using simple and inexpensive alternatives.

  12. Comparative evaluation of cyanide removal by adsorption, biodegradation, and simultaneous adsorption and biodegradation (SAB) process using Bacillus cereus and almond shell.

    PubMed

    Dwivedi, Naveen; Balomajumder, Chandrajit; Mondal, Prasenji

    2016-07-01

    The present study aimed to investigate the removal efficiency of cyanide from contaminated water by adsorption, biodegradation and simultaneous adsorption and biodegradation (SAB) process individually in a batch reactor. Adsorption was achieved by using almond shell granules and biodegradation was conducted with suspended cultures of Bacillus cereus, whereas SAB process was carried out using Bacillus cereus and almond shell in a batch reactor. The effect of agitation time, pH, and initial cyanide concentration on the % removal of cyanide has been discussed. Under experimental conditions, optimum removal was obtained at pH 7 with agitation time of 48 hrs and temperature of 35 degrees C. Cyanide was utilized by bacteria as sole source of nitrogen for growth. The removal efficiencies of cyanide by adsorption, biodegradation, and SAB were found to be 91.38%, 95.87%, and 99.63%, respectively, at initial cyanide concentration of 100 mg l(-1). The removal efficiency of SAB was found to be better as compared to that of biodegradation and adsorption alone. PMID:27498500

  13. Nonnative Disulfide Bond Formation Activates the σ32-Dependent Heat Shock Response in Escherichia coli

    PubMed Central

    Müller, Alexandra; Hoffmann, Jörg H.; Meyer, Helmut E.; Narberhaus, Franz; Jakob, Ursula

    2013-01-01

    Formation of nonnative disulfide bonds in the cytoplasm, so-called disulfide stress, is an integral component of oxidative stress. Quantification of the extent of disulfide bond formation in the cytoplasm of Escherichia coli revealed that disulfide stress is associated with oxidative stress caused by hydrogen peroxide, paraquat, and cadmium. To separate the impact of disulfide bond formation from unrelated effects of these oxidative stressors in subsequent experiments, we worked with two complementary approaches. We triggered disulfide stress either chemically by diamide treatment of cells or genetically in a mutant strain lacking the major disulfide-reducing systems TrxB and Gor. Studying the proteomic response of E. coli exposed to disulfide stress, we found that intracellular disulfide bond formation is a particularly strong inducer of the heat shock response. Real-time quantitative PCR experiments showed that disulfide stress induces the heat shock response in E. coli σ32 dependently. However, unlike heat shock treatment, which induces these genes transiently, transcripts of σ32-dependent genes accumulated over time in disulfide stress-treated cells. Analyzing the stability of σ32, we found that this constant induction can be attributed to an increase of the half-life of σ32 upon disulfide stress. This is concomitant with aggregation of E. coli proteins treated with diamide. We conclude that oxidative stress triggers the heat shock response in E. coli σ32 dependently. The component of oxidative stress responsible for the induction of heat shock genes is disulfide stress. Nonnative disulfide bond formation in the cytoplasm causes protein unfolding. This stabilizes σ32 by preventing its DnaK- and FtsH-dependent degradation. PMID:23585533

  14. Catalytic carbon-carbon bond activation and functionalization by nickel complexes

    SciTech Connect

    Edelback, B.L.; Lachicotte, R.J.; Jones, W.D.

    1999-09-27

    The nickel alkyne complexes (dippe)Ni(PhC{triple{underscore}bond}CPh), 2, (dippe) Ni(MeO{sub 2}CC{triple{underscore}bond}CCO{sub 2}Me), 3, (dippe)Ni(CH{sub 3}OCH{sub 2}C{triple{underscore}bond}CCH{sub 2}OCH{sub 3}), 4, and (dippe)Ni(CF{sub 3}C{triple{underscore}bond}CCF{sub 3}), 5, were synthesized (dippe = bis(diisopropylphosphino)ethane) and characterized by {sup 1}H, {sup 31}P, and {sup 13}C{l{underscore}brace}{sup 1}H{r{underscore}brace} NMR spectroscopy. Complexes 1, 2, and 3 were characterized by X-ray crystallography. The thermolysis of complex 1 or 2 (120 C) in the presence of excess biphenylene and excess alkyne results in very slow catalytic formation of the corresponding 9,10-disubstituted phenanthrene. However, addition of {approximately}6 mol % O{sub 2} (based on the metal complex) to the reaction mixture results in an acceleration in catalysis at lower temperatures ({approximately}70--80 C). The thermolysis of complexes 3 or 4 with excess biphenylene and excess alkyne leads to the alkyne cyclotrimerization product as the major organic species formed in the reaction. Fluorenone was catalytically produced by heating (dippe)Ni(CO){sub 2}, biphenylene, and CO. Catalytic insertion of 2,6-xylylisocyanide into the strained C-C bond of biphenylene was also achieved by heating (dippe)Ni(2,6-xylylisocyanide){sub 2}, excess biphenylene, and 2,6-xylylisocyanide. Mechanistic schemes are proposed for these reactions.

  15. Bond strength of Epiphany™ Sealer combined with different adhesive systems photo-activated with LED and QTH

    NASA Astrophysics Data System (ADS)

    Minto, A. M. P.; Bandéca, M. C.; Borges, A. H.; Nadalin, M. R.; Thomé, L. H. C.

    2009-08-01

    The Epiphany™ Sealer is a new dual-curing resin-based sealer and has been introduced as an alternative to gutta-percha and traditional root canal sealers. The canal filling is claimed to create a seal with the dentinal tubules within the root canal system producing a ‘monoblock’ effect between the sealer and dentinal tubules. Therefore, considering the possibility to incorporate the others adhesive systems, it is important to study the bond strength of the resulting cement. Forty-eight root mandibular canines were sectioned 8-mm below CEJ. The dentine discs were prepared using a tapered diamond bur and irrigated with 1% NaOCl and 17% EDTA. Previous the application Epiphany™ Sealer, the Epiphany™ Primer, AdheSE, and One Up Bond F were applied to the root canal walls. The LED and QTH (Quartz Tungsten Halogen) were used to photo-activation during 45 s with power density of 400 and 720 mW/cm2, respectively. The specimens were performed on a universal testing machine at a cross-head speed of 1 mm/min until bond failure occurred. The force was recorded and the debonding values were used to calculate Push-out bond strength. The analysis of variance (ANOVA) and Tukey’s post-hoc tests showed significant statistical differences ( P < 0.05) to Epiphany™ Sealer/Epiphany™ Primer/QTH and EpiphanyTM Sealer/AdheSE/QTH, which had the highest mean values of bond strength. The efficiency of resin-based filling materials are dependent the type of light curing unit used including the power density, the polymerization characteristics of these resin-based filling materials, depending on the primer/adhesive used.

  16. Low-valent niobium-mediated double activation of C-F/C-H bonds: fluorene synthesis from o-arylated alpha,alpha,alpha-trifluorotoluene derivatives.

    PubMed

    Fuchibe, Kohei; Akiyama, Takahiko

    2006-02-01

    By the treatment of 0.3 molar amount of NbCl5 and LiAlH4, o-arylated alpha,alpha,alpha-trifluorotoluenes afforded fluorene derivatives in good yields. C-F bonds of the CF3 group and the neighboring ortho C-H bond were doubly activated to give the coupling products. PMID:16448098

  17. Foster Mother-Infant Bonding: Associations Between Foster Mothers’ Oxytocin Production, Electrophysiological Brain Activity, Feelings of Commitment, and Caregiving Quality

    PubMed Central

    Bick, Johanna; Dozier, Mary; Bernard, Kristin; Simons, Robert; Grasso, Damion

    2012-01-01

    This study examined the biological processes associated with foster mother-infant bonding. In an examination of foster mother-infant dyads (N = 41, mean infant age = 8.5 months), foster mothers’ oxytocin production was associated with their expressions of behavioral delight toward their foster infant and their average P3 response to images of all infant faces in the first two months of the relationship. Three months later, foster mothers’ oxytocin production was still associated with delight toward their foster infant and was also specifically associated with their P3 response to an image of their foster infant. Similar to biologically-related mothers and infants, oxytocin appears to be associated with foster mothers’ brain activity and caregiving behavior, with patterns suggestive of bond formation. PMID:23163703

  18. E-H (E = B, Si, Ge) bond activation of pinacolborane, silanes, and germanes by nucleophilic palladium carbene complexes.

    PubMed

    Comanescu, Cezar C; Iluc, Vlad M

    2016-07-12

    The reactivity of two nucleophilic palladium carbenes, [PC(sp(2))P]Pd(PMe3) and [PC(sp(2))P]Pd(PPh3), where [PC(sp(2))P] = bis[2-(di-iso-propylphosphino)phenyl]methylene, toward the E-H bond activation of Ph4-nEHn (E = Si, Ge; n = 1-3) and pinacolborane (HBpin) is discussed. Unlike previous reports, both types of isomer species, hydride [PC(EHn-1Ph4-n)P]PdH or [PC(Bpin)P]PdH and silyl/germyl [PC(H)P]Pd(EHn-1Ph4-n), were observed depending on the substrate and the phosphine ligand, showing that the polarity of the Pd-C bond can be tuned by the phosphine substituents. PMID:26830660

  19. Aniline hydrogenolysis on the Pt(111) single crystal surface: Mechanisms for C-N bond activation

    SciTech Connect

    Huang, S.X.; Gland, J.L.; Fischer, D.A. |

    1993-12-31

    Hydrogenolysis of C-N bond on transition metals is a crucial step in hydrodenitrogenation (HDN) reactions. Despite the overall complexity of HDN processes, the details of important surface reactions can be characterized using model reactions of organonitrogen compounds on single crystal model catalysts. The structure and reactivity of well characterized aniline monolayers on the Pt(111) surface both in vacuum and in the presence of hydrogen is discussed here. Adsorption and reactions of aniline were studied by Gland and Somorjai on the Pt(111) and Pt(100) surfaces, and more recently by Benziger`s group on the Ni(111) and Ni(100) surfaces. On both Pt and Ni surfaces, aniline {pi} bonds through the aromatic ring with its ring parallel to the substrate surface.

  20. Halogen-Bonding-Assisted Iodosylbenzene Activation by a Homogenous Iron Catalyst.

    PubMed

    de Sousa, David P; Wegeberg, Christina; Vad, Mads Sørensen; Mørup, Steen; Frandsen, Cathrine; Donald, William A; McKenzie, Christine J

    2016-03-01

    The iron(III) complex of hexadentate N,N,N'-tris(2-pyridylmethyl)ethylendiamine-N'-acetate (tpena(-) ) is a more effective homogenous catalyst for selective sulfoxidation and epoxidation with insoluble iodosylbenzene, [PhIO]n , compared with soluble methyl-morpholine-N-oxide (NMO). We propose that two molecules of [Fe(tpena)](2+) cooperate to solubilize PhIO, extracting two equivalents to form the halogen-bonded dimeric {[Fe(tpena)OIPh]2 }(4+) . The closest intradimeric I⋅⋅⋅O distance, 2.56 Å, is nearly 1 Å less than the sum of the van de Waals radii of these atoms. A correlation of the rates of the reaction of {[Fe(tpena)OIPh]2 }(4+) with para-substituted thioanisoles indicate that this species is a direct metal-based oxidant rather than a derived ferryl or perferryl complex. A study of gas-phase reactions indicate that an ion at m/z=231.06100 originates from solution-state {[Fe(tpena)OIPh]2 }(4+) and is ascribed to [Fe(III) (tpenaO)](2+) , derived from an intramolecular O atom insertion into an Fe-tpena donor bond. Proposed ion pairs, {[Fe(tpena)OIPh]Cl}(+) and {[Fe(tpena)OIPh]ClO4 }(+) , are more stable than native [Fe(tpena)OIPh](2+) ions, suggesting that halogen-bonding, as for the solution and solid states, operates also in the gas phase. PMID:26598789

  1. Transition metal activation and functionalization of carbon-hydrogen bonds. Progress report, December 1, 1989--November 30, 1992

    SciTech Connect

    Jones, W.D.

    1992-06-01

    We are investigating the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers and the conversion of hydrocarbons into functionalized products of potential use to the chemical industry. Advances have been made in both understanding the interactions of hydrocarbons with metals and in the functionalization of hydrocarbons. We have found that RhCl(PR{sub 3}){sub 2}(CNR) complexes can catalyze the insertion of isonitriles into the C-H bonds or arenes upon photolysis. The mechanism of these reactions was found to proceed by way of initial phosphine dissociation, followed by C-H activation and isonitrile insertion. We have also examined reactions of a series of arenes with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and begun to map out the kinetic and thermodynamic preferences for arene coordination. The effects of resonance, specifically the differences in the Hueckel energies of the bound vs free ligand, are now believed to fully control the C-H activation/{eta}{sup 2}-coordination equilibria. We have begun to examine the reactions of rhodium isonitrile pyrazolylborates for alkane and arene C-H bond activation. A new, labile, carbodiimide precursor has been developed for these studies. We have completed studies of the reactions of (C{sub 5}Me{sub 5})Rh(PMe{sub 3})H{sub 2} with D{sub 2} and PMe{sub 3} that indicate that both {eta}{sup 5} {yields} {eta}{sup 3} ring slippage and metal to ring hydride migration occur more facilely than thermal reductive elimination of H{sub 2}. We have examined the reactions of heterocycles with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and found that pyrrole and furan undergo C-H or N-H activation. Thiophene, however, undergoes C-S bond oxidative addition, and the mechanism of activation has been shown to proceed through sulfur coordination prior to C-S insertion.

  2. C-H bond activation enables the rapid construction and late-stage diversification of functional molecules

    NASA Astrophysics Data System (ADS)

    Wencel-Delord, Joanna; Glorius, Frank

    2013-05-01

    The beginning of the twenty-first century has witnessed significant advances in the field of C-H bond activation, and this transformation is now an established piece in the synthetic chemists' toolbox. This methodology has the potential to be used in many different areas of chemistry, for example it provides a perfect opportunity for the late-stage diversification of various kinds of organic scaffolds, ranging from relatively small molecules like drug candidates, to complex polydisperse organic compounds such as polymers. In this way, C-H activation approaches enable relatively straightforward access to a plethora of analogues or can help to streamline the lead-optimization phase. Furthermore, synthetic pathways for the construction of complex organic materials can now be designed that are more atom- and step-economical than previous methods and, in some cases, can be based on synthetic disconnections that are just not possible without C-H activation. This Perspective highlights the potential of metal-catalysed C-H bond activation reactions, which now extend beyond the field of traditional synthetic organic chemistry.

  3. Structure-activity relationships of the intramolecular disulfide bonds in coprisin, a defensin from the dung beetle

    PubMed Central

    Lee, Daeun; Choi, Hyemin; Kim, Ha Hyung; Kim, Ho; Hwang, Jae Sam; Lee, Dong Gun; Kim, Jae Il

    2014-01-01

    Defensins, which are small cationic molecules produced by organisms as part of their innate immune response, share a common structural scaffold that is stabilized by three disulfide bridges. Coprisin is a 43-amino acid defensin-like peptide from Copris tripartitus. Here, we report the intramolecular disulfide connectivity of cysteine-rich coprisin, and show that it is the same as in other insect defensins. The disulfide bond pairings of coprisin were determined by combining the enzymatic cleavage and mass analysis. We found that the loss of any single disulfide bond in coprisin eliminated all antibacterial, but not antifungal, activity. Circular dichroism (CD) analysis showed that two disulfide bonds, Cys20-Cys39 and Cys24-Cys41, stabilize coprisin’s α-helical region. Moreover, a BLAST search against UniProtKB database revealed that coprisin’s α-helical region is highly homologous to those of other insect defensins. [BMB Reports 2014; 47(11): 625-630] PMID:24393527

  4. The Stereoselective Formation of Bicyclic Enamines with Bridgehead Unsaturation via Tandem C-H Bond Activation/Alkenylation/Electrocyclization

    SciTech Connect

    Ellman, Jonathan A.; Yotphan, Sirilata; Bergman, Robert

    2007-12-10

    Rhodium-catalyzed intermolecular C-H activation of {alpha}, {beta}-unsaturated imines in the presence of alkynes leads to a tandem process in which coupling to the alkyne occurs at the {beta}-C-H bond of the imine, followed by electrocyclization of the resulting azatriene intermediates to give dihydropyridines (eq 1). Consideration of the intramolecular version of this overall transformation (Scheme 1) raises interesting regiochemical issues. For example in a compound such as 1, where the nitrogen and alkyne are connected by a 4-carbon tether, the presumed first-formed hydrido(vinyl)rhodium function can add to the triple bond in a 1,2-fashion, producing complex 2 with a new endocyclic double bond. Alternatively, addition might occur in a 2,1-fashion, leading to product 4 with an exocyclic double bond. We now wish to report that this intramolecular cyclization occurs smoothly at 100 C, and the exocyclic double bond route is exclusively followed. Remarkably, products such as 4 do not resist further cyclization. Even though both the transition state for this process and the resulting product are presumably strained, the overall transformation leads to good yields of unusual bridgehead doubly-bonded enamines such as 5. The unique chemistry of conjugated enamine 5 is consistent with the increased strain of this molecule as well as with inhibited conjugation between the nitrogen lone pair and the adjacent double bond (vida infra). We began our investigation into the C-H activation/cyclization of alkyne-tethered imine 1 by extensive screening of transition metal catalysts for this process. Rhodium-based catalysts were found to be the most efficient (Table 1), leading exclusively to the bridgehead dienamine; none of the catalysts that were employed in the screening led to quinolizidine 3 or to the product of intramolecular Diels-Alder reaction. The optimized reaction conditions employ the electron-rich monophosphine ligand (p-NMe{sub 2})PhPEt{sub 2} in 1:1 ratio relative

  5. Transition metal activation and functionalization of carbon-hydrogen bonds: Progress report, December 1, 1988--November 30, 1989

    SciTech Connect

    Jones, W.D.

    1989-06-01

    This project is directed toward the continued investigation of the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers. The project is also directed toward the conversion of hydrocarbons into functionalized products of potential use to chemical industry. Our goals during the grant period will be (1) to identify new transition metal complexes capable of activating arene and alkane C-H bonds, (2) to quantitatively evaluate the kinetic and thermodynamic stability of these complexes, and (3) to examine routes for functionalization of the activated hydrocarbons. These studies will also contribute toward the formulation of a unified theory of C-H bond activation that applies to other transition metal complexes. The specific complexes involved in these studies are derivatives of the formulation (C/sub 5/Me/sub 5/)Rh(PR/sub 3/)(R)H, Fe(PMe/sub 3/)/sub 2/(CNR)/sub 3/, Ru(PR/sub 3/)/sub 4/(R)H, and Rh(CNR)/sub 3/H. Functionalization will focus upon isocyanide and acetylene insertion reactions. New compounds that activate hydrocarbon C-H bonds include HRe(PR/sub 3/)/sub 5/, HRe(PR/sub 3/)/sub 2/(CNR)/sub 3/, CpRe(PR/sub 3/)H/sub 4/, CpRe(PR/sub 3/)/sub 2/H/sub 2/, (/eta//sup 6/-C/sub 6/H/sub 6/)Re(PPh/sub 3/)/sub 2/H, and MnH/sub 3/(dmpe)/sub 2/. In the third year of this project, significant advances have been made in the observation of /eta//sup 2/-arene complexes of ((C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)). The complex (C/sub 5/Me/sub 5/)Rh(PMe/sub 3/)(/eta//sup 2/-phenanthrene) has been structurally characterized. Several other /eta//sup 2/-complexes have also been prepared. 17 refs., 4 tabs.

  6. Bonding thermoplastic polymers

    DOEpatents

    Wallow, Thomas I.; Hunter, Marion C.; Krafcik, Karen Lee; Morales, Alfredo M.; Simmons, Blake A.; Domeier, Linda A.

    2008-06-24

    We demonstrate a new method for joining patterned thermoplastic parts into layered structures. The method takes advantage of case-II permeant diffusion to generate dimensionally controlled, activated bonding layers at the surfaces being joined. It is capable of producing bonds characterized by cohesive failure while preserving the fidelity of patterned features in the bonding surfaces. This approach is uniquely suited to production of microfluidic multilayer structures, as it allows the bond-forming interface between plastic parts to be precisely manipulated at micrometer length scales. The bond enhancing procedure is easily integrated in standard process flows and requires no specialized equipment.

  7. A Highly Reactive Mononuclear Non-Heme Manganese(IV)-Oxo Complex That Can Activate the Strong C-H Bonds of Alkanes

    SciTech Connect

    Wu, Xiujuan; Seo, Mi Sook; Davis, Katherine M; Lee, Yong-Min; Chen, Junying; Cho, Kyung-Bin; Pushkar, Yulia N; Nam, Wonwoo

    2012-03-15

    A mononuclear non-heme manganese(IV)-oxo complex has been synthesized and characterized using various spectroscopic methods. The Mn(IV)-oxo complex shows high reactivity in oxidation reactions, such as C-H bond activation, oxidations of olefins, alcohols, sulfides, and aromatic compounds, and N-dealkylation. In C-H bond activation, the Mn(IV)-oxo complex can activate C-H bonds as strong as those in cyclohexane. It is proposed that C-H bond activation by the non-heme Mn(IV)-oxo complex does not occur via an oxygen-rebound mechanism. The electrophilic character of the non-heme Mn(IV)-oxo complex is demonstrated by a large negative ρ value of ~4.4 in the oxidation of para-substituted thioanisoles.

  8. Computational study on the mechanism and selectivity of C-H bond activation and dehydrogenative functionalization in the synthesis of rhazinilam.

    PubMed

    Ellis, Corey S; Ess, Daniel H

    2011-09-01

    The key platinum mediated C-H bond activation and functionalization steps in the synthesis of (-)-rhazinilam (Johnson, J. A.; Li, N.; Sames, D. J. Am. Chem. Soc. 2002, 124, 6900) were investigated using the M06 and B3LYP density functional approximation methods. This computational study reveals that ethyl group dehydrogenation begins with activation of a primary C-H bond in preference to a secondary C-H bond in an insertion/methane elimination pathway. The C-H activation step is found to be reversible while the methane elimination (reductive elimination) transition state controls rate and diastereoselectivity. The chiral oxazolinyl ligand induces ethyl group selectivity through stabilizing weak interactions between its phenyl group (or cyclohexyl group) and the carboxylate group. After C-H activation and methane elimination steps, Pt-C bond functionalization occurs through β-hydride elimination to give the alkene platinum hydride complex. PMID:21812492

  9. Activation of Si-Si Bonds for Copper(I)-Catalyzed Conjugate Silylation.

    PubMed

    Iannazzo, Laura; Molander, Gary A

    2012-09-01

    Several alkyl- and vinylsilanes were prepared through the copper(I)-catalyzed conjugate silylation of α,β-unsaturated compounds. Optimal reaction conditions were first investigated to realize the conjugate addition of a nucleophilic silicon species to poorly electrophilic acceptors such as phenylvinyl sulfone by cleavage of the Si-Si bond of a disilane reagent. The scope of this reaction was extended to various electrophiles bearing different electron-withdrawing groups and afforded the desired substituted alkyl- and vinylsilanes. Among the wide range of commercially available disilanes, the reactivities of alkyl-, aryl-, and ethoxydisilane were also examined. PMID:23204924

  10. Activation of Si–Si Bonds for Copper(I)-Catalyzed Conjugate Silylation

    PubMed Central

    Iannazzo, Laura; Molander, Gary A.

    2012-01-01

    Several alkyl- and vinylsilanes were prepared through the copper(I)-catalyzed conjugate silylation of α,β-unsaturated compounds. Optimal reaction conditions were first investigated to realize the conjugate addition of a nucleophilic silicon species to poorly electrophilic acceptors such as phenylvinyl sulfone by cleavage of the Si–Si bond of a disilane reagent. The scope of this reaction was extended to various electrophiles bearing different electron-withdrawing groups and afforded the desired substituted alkyl- and vinylsilanes. Among the wide range of commercially available disilanes, the reactivities of alkyl-, aryl-, and ethoxydisilane were also examined. PMID:23204924

  11. Dehydrogenative Coupling Reactions with Oxidized Guanidino-Functionalized Aromatic Compounds: Novel Options for σ-Bond Activation.

    PubMed

    Wild, Ute; Federle, Stefanie; Wagner, Arne; Kaifer, Elisabeth; Himmel, Hans-Jörg

    2016-08-16

    We present a new option for metal-free σ-bond activation, making use of oxidized, guanidino-functionalized aromatic compounds (GFAs). We demonstrate this new option by the homocoupling reactions of thiols and phosphines. The kinetics and the reaction pathway were studied by a number of experiments (including heterocoupling of thiols and phosphines), supported by quantum-chemical computations. Reaction of the oxidized GFA with p-dihydrobenzoquinone to give p-benzoquinone shows that typical proton-coupled electron-transfer reactions are also possible. PMID:27430589

  12. The significance of disulfide bonding in biological activity of HB-EGF, a mutagenesis approach

    SciTech Connect

    Hoskins, J.T.; Zhou, Z.; Harding, P.A.

    2008-10-31

    A site-directed mutagenesis approach was taken to disrupt each of 3 disulfide bonds within human HB-EGF by substituting serine for both cysteine residues that contribute to disulfide bonding. Each HB-EGF disulfide analogue (HB-EGF-Cys/Ser{sub 108/121}, HB-EGF-Cys/Ser{sub 116/132}, and HB-EGF-Cys/Ser{sub 134/143}) was cloned under the regulation of the mouse metallothionein (MT) promoter and stably expressed in mouse fibroblasts. HB-EGF immunoreactive proteins with M{sub r} of 6.5, 21 and 24 kDa were observed from lysates of HB-EGF and each HB-EGF disulfide analogue. HB-EGF immunohistochemical analyses of each HB-EGF stable cell line demonstrated ubiquitous protein expression except HB-EGF-Cys/Ser{sub 108/121} and HB-EGF-Cys/Ser{sub 116/132} stable cell lines which exhibited accumulated expression immediately outside the nucleus. rHB-EGF, HB-EGF, and HB-EGF{sub 134/143} proteins competed with {sup 125}I-EGF in an A431 competitive binding assay, whereas HB-EGF-Cys/Ser{sub 108/121} and HB-EGF-Cys/Ser{sub 116/132} failed to compete. Each HB-EGF disulfide analogue lacked the ability to stimulate tyrosine phosphorylation of the 170 kDa EGFR. These results suggest that HB-EGF-Cys/Ser{sub 134/143} antagonizes EGFRs.

  13. Simple Bond Cleavage

    SciTech Connect

    Gary S. Groenewold

    2005-08-01

    Simple bond cleavage is a class of fragmentation reactions in which a single bond is broken, without formation of new bonds between previously unconnected atoms. Because no bond making is involved, simple bond cleavages are endothermic, and activation energies are generally higher than for rearrangement eliminations. The rate of simple bond cleavage reactions is a strong function of the internal energy of the molecular ion, which reflects a loose transition state that resembles reaction products, and has a high density of accessible states. For this reason, simple bond cleavages tend to dominate fragmentation reactions for highly energized molecular ions. Simple bond cleavages have negligible reverse activation energy, and hence they are used as valuable probes of ion thermochemistry, since the energy dependence of the reactions can be related to the bond energy. In organic mass spectrometry, simple bond cleavages of odd electron ions can be either homolytic or heterolytic, depending on whether the fragmentation is driven by the radical site or the charge site. Simple bond cleavages of even electron ions tend to be heterolytic, producing even electron product ions and neutrals.

  14. Rationale of the effects from dopants on C-H bond activation for sp2 hybridized nanostructured carbon catalysts

    NASA Astrophysics Data System (ADS)

    Mao, Shanjun; Sun, Xiaoying; Li, Bo; Su, Dang Sheng

    2015-10-01

    Doping has become an effective way to tune the catalytic properties of nanostructured carbon catalysts. Taking C-H activation as an example, first-principles calculations propose that the relative energy level and the BEP rule might be applicable to explain the observed doping effects. Moreover, boron doping is proposed as an effective way to enhance the catalytic performance.Doping has become an effective way to tune the catalytic properties of nanostructured carbon catalysts. Taking C-H activation as an example, first-principles calculations propose that the relative energy level and the BEP rule might be applicable to explain the observed doping effects. Moreover, boron doping is proposed as an effective way to enhance the catalytic performance. Electronic supplementary information (ESI) available: The computational setup, the doping positions for B, N and S doping, the definition of the binding energy and dissociation energy for C2H5 and C2H6 respectively, the transition state and dissociation state structures for the C-H bond activation of C2H6 in the undoped case, and the lengths of the C-H bond of C2H6 at the transition states for both the undoped and doped cases. See DOI: 10.1039/c5nr05759k

  15. Comparison of carbon-sulfur and carbon-amine bond in therapeutic drug: 4β-S-aromatic heterocyclic podophyllum derivatives display antitumor activity

    PubMed Central

    Li, Jian-Long; Zhao, Wei; Zhou, Chen; Zhang, Ya-Xuan; Li, Hong-Mei; Tang, Ya-Ling; Liang, Xin-Hua; Chen, Tao; Tang, Ya-Jie

    2015-01-01

    Herein is a first effort to systematically study the significance of carbon-sulfur (C-S) and carbon-amine (C-NH) bonds on the antitumor proliferation activity of podophyllum derivatives and their precise mechanism of apoptosis. Compared with the derivative modified by a C-NH bond, the derivative modified by a C-S bond exhibited superior antitumor activity, the inhibition activity of target proteins tubulin or Topo II, cell cycle arrest, and apoptosis induction. Antitumor mechanistic studies showed that the death receptor and the mitochondrial apoptotic pathways were simultaneously activated by the C-S bond modified aromatic heterocyclic podophyllum derivatives with a higher cellular uptake percentage of 60–90% and induction of a higher level of reactive oxygen species (ROS). Only the mitochondrial apoptotic pathway was activated by the C-NH bond modified aromatic heterocyclic podophyllum derivatives, with a lower cellular uptake percentage of 40–50%. This study provided insight into effects of the C-S and C-NH bond modification on the improvement of the antitumor activity of Podophyllum derivatives. PMID:26443888

  16. Effect of active hydroxyl groups on the interfacial bond strength of titanium with segmented polyurethane through gamma-mercapto propyl trimethoxysilane.

    PubMed

    Sakamoto, Harumi; Hirohashi, Yohei; Saito, Haruka; Doi, Hisashi; Tsutsumi, Yusuke; Suzuki, Yoshiaki; Noda, Kazuhiko; Hanawa, Takao

    2008-01-01

    The objective of this study was to investigate the effect of active hydroxyl groups on a titanium (Ti) surface on the bond strength between Ti and segmented polyurethane (SPU) composite through gamma-mercapto propyl trimethoxysilane (gamma-MPS). Active hydroxyl groups on Ti surface oxide were controlled by immersion in hydrogen peroxide (H2O2) with different lengths of immersion time, and the resulting concentrations of active hydroxyl groups were evaluated using a zinc-complex substitution technique. For the H2O2-treated Ti, it was characterized using X-ray photoelectron spectroscopy and scanning electron spectroscopy. For the bond strength of Ti/ gamma-MPS/SPU interface, it was determined using a shear bond test. Results showed that the bond strength increased with increase in the concentration of active hydroxyl groups. In terms of durability after immersion in water at 310 K for 30 days, it was found that bond strength was improved with increase in active hydroxyl groups. Based on the results obtained, active hydroxyl groups on the surface oxide film were clearly one of the causes governing the interfacial bond strength. PMID:18309616

  17. SU-C-BRA-07: Virtual Bronchoscopy-Guided IMRT Planning for Mapping and Avoiding Radiation Injury to the Airway Tree in Lung SAbR

    SciTech Connect

    Sawant, A; Modiri, A; Bland, R; Yan, Y; Ahn, C; Timmerman, R

    2015-06-15

    Purpose: Post-treatment radiation injury to central and peripheral airways is a potentially important, yet under-investigated determinant of toxicity in lung stereotactic ablative radiotherapy (SAbR). We integrate virtual bronchoscopy technology into the radiotherapy planning process to spatially map and quantify the radiosensitivity of bronchial segments, and propose novel IMRT planning that limits airway dose through non-isotropic intermediate- and low-dose spillage. Methods: Pre- and ∼8.5 months post-SAbR diagnostic-quality CT scans were retrospectively collected from six NSCLC patients (50–60Gy in 3–5 fractions). From each scan, ∼5 branching levels of the bronchial tree were segmented using LungPoint, a virtual bronchoscopic navigation system. The pre-SAbR CT and the segmented bronchial tree were imported into the Eclipse treatment planning system and deformably registered to the planning CT. The five-fraction equivalent dose from the clinically-delivered plan was calculated for each segment using the Universal Survival Curve model. The pre- and post-SAbR CTs were used to evaluate radiation-induced segmental collapse. Two of six patients exhibited significant segmental collapse with associated atelectasis and fibrosis, and were re-planned using IMRT. Results: Multivariate stepwise logistic regression over six patients (81 segments) showed that D0.01cc (minimum point dose within the 0.01cc receiving highest dose) was a significant independent factor associated with collapse (odds-ratio=1.17, p=0.010). The D0.01cc threshold for collapse was 57Gy, above which, collapse rate was 45%. In the two patients exhibiting segmental collapse, 22 out of 32 segments showed D0.01cc >57Gy. IMRT re-planning reduced D0.01cc below 57Gy in 15 of the 22 segments (68%) while simultaneously achieving the original clinical plan objectives for PTV coverage and OAR-sparing. Conclusion: Our results indicate that the administration of lung SAbR can Result in significant injury to

  18. Biomass Oxidation: Formyl C-H Bond Activation by the Surface Lattice Oxygen of Regenerative CuO Nanoleaves.

    PubMed

    Amaniampong, Prince N; Trinh, Quang Thang; Wang, Bo; Borgna, Armando; Yang, Yanhui; Mushrif, Samir H

    2015-07-27

    An integrated experimental and computational investigation reveals that surface lattice oxygen of copper oxide (CuO) nanoleaves activates the formyl C-H bond in glucose and incorporates itself into the glucose molecule to oxidize it to gluconic acid. The reduced CuO catalyst regains its structure, morphology, and activity upon reoxidation. The activity of lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface and the hydrogen abstraction ability of the catalyst is correlated with the adsorption energy. Based on the present investigation, it is suggested that surface lattice oxygen is critical for the oxidation of glucose to gluconic acid, without further breaking down the glucose molecule into smaller fragments, because of C-C cleavage. Using CuO nanoleaves as catalyst, an excellent yield of gluconic acid is also obtained for the direct oxidation of cellobiose and polymeric cellulose, as biomass substrates. PMID:26119659

  19. Metal-ligand cooperation by aromatization-dearomatization: a new paradigm in bond activation and "green" catalysis.

    PubMed

    Gunanathan, Chidambaram; Milstein, David

    2011-08-16

    In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on "cooperating" ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation. We have discovered a new mode of metal-ligand cooperation, involving aromatization-dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H-H, C-H (sp(2) and sp(3)), O-H, and N-H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H(2) and light-induced liberation of O(2), using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique "long-range" metal-ligand cooperation in the activation of H(2) and in reaction with ammonia. In this Account, we begin by providing an overview of the metal-ligand cooperation based on aromatization-dearomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal-ligand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcohols to ketones, (2) acceptorless dehydrogenative coupling of alcohols to esters, (3) acylation of secondary alcohols by esters with dihydrogen liberation, (4) direct coupling of alcohols and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides

  20. Activating mutations in the extracellular domain of the fibroblast growth factor receptor 2 function by disruption of the disulfide bond in the third immunoglobulin-like domain.

    PubMed

    Robertson, S C; Meyer, A N; Hart, K C; Galvin, B D; Webster, M K; Donoghue, D J

    1998-04-14

    Multiple human skeletal and craniosynostosis disorders, including Crouzon, Pfeiffer, Jackson-Weiss, and Apert syndromes, result from numerous point mutations in the extracellular region of fibroblast growth factor receptor 2 (FGFR2). Many of these mutations create a free cysteine residue that potentially leads to abnormal disulfide bond formation and receptor activation; however, for noncysteine mutations, the mechanism of receptor activation remains unclear. We examined the effect of two of these mutations, W290G and T341P, on receptor dimerization and activation. These mutations resulted in cellular transformation when expressed as FGFR2/Neu chimeric receptors. Additionally, in full-length FGFR2, the mutations induced receptor dimerization and elevated levels of tyrosine kinase activity. Interestingly, transformation by the chimeric receptors, dimerization, and enhanced kinase activity were all abolished if either the W290G or the T341P mutation was expressed in conjunction with mutations that eliminate the disulfide bond in the third immunoglobulin-like domain (Ig-3). These results demonstrate a requirement for the Ig-3 cysteine residues in the activation of FGFR2 by noncysteine mutations. Molecular modeling also reveals that noncysteine mutations may activate FGFR2 by altering the conformation of the Ig-3 domain near the disulfide bond, preventing the formation of an intramolecular bond. This allows the unbonded cysteine residues to participate in intermolecular disulfide bonding, resulting in constitutive activation of the receptor. PMID:9539778

  1. An activated triple bond linker enables ‘click’ attachment of peptides to oligonucleotides on solid support

    PubMed Central

    Wenska, Malgorzata; Alvira, Margarita; Steunenberg, Peter; Stenberg, Åsa; Murtola, Merita; Strömberg, Roger

    2011-01-01

    A general procedure, based on a new activated alkyne linker, for the preparation of peptide–oligonucleotide conjugates (POCs) on solid support has been developed. With this linker, conjugation is effective at room temperature (RT) in millimolar concentration and submicromolar amounts. This is made possible since the use of a readily attachable activated triple bond linker enhances the Cu(I) catalyzed 1,3-dipolar cycloaddition (‘click’ reaction). The preferred scheme for conjugate preparation involves sequential conjugation to oligonucleotides on solid support of (i) an H-phosphonate-based aminolinker; (ii) the triple bond donor p-(N-propynoylamino)toluic acid (PATA); and (iii) azido-functionalized peptides. The method gives conversion of oligonucleotide to the POC on solid support, and only involves a single purification step after complete assembly. The synthesis is flexible and can be carried out without the need for specific automated synthesizers since it has been designed to utilize commercially available oligonucleotide and peptide derivatives on solid support or in solution. Methodology for the ready conversion of peptides into ‘clickable’ azidopeptides with the possibility of selecting either N-terminus or C-terminus connection also adds to the flexibility and usability of the method. Examples of synthesis of POCs include conjugates of oligonucleotides with peptides known to be membrane penetrating and nuclear localization signals. PMID:21795380

  2. Palladium-Catalyzed Carbonylative Cyclization of Arenes by C-H Bond Activation with DMF as the Carbonyl Source.

    PubMed

    Chen, Jianbin; Feng, Jian-Bo; Natte, Kishore; Wu, Xiao-Feng

    2015-11-01

    A novel palladium-catalyzed CO-gas- and autoclave-free protocol for the synthesis of 11H-pyrido[2,1-b]quinazolin-11-ones has been developed. Quinazolinones, which are omnipresent motif in many pharmaceuticals and agrochemicals, were prepared in good yields by C-H bond activation and annulation using DMF as the CO surrogate. A (13) CO-labelled DMF control experiment demonstrated that CO gas was released from the carbonyl of DMF with acid as the promotor. The kinetic isotope effect (KIE) value indicated that the C-H activation step may not be involved in the rate-determining step. This methodology is operationally simple and showed a broad substrate scope with good to excellent yields. PMID:26406903

  3. The Comparative Studies of Binding Activity of Curcumin and Didemethylated Curcumin with Selenite: Hydrogen Bonding vs Acid-Base Interactions.

    PubMed

    Liao, Jiahn-Haur; Wu, Tzu-Hua; Chen, Ming-Yi; Chen, Wei-Ting; Lu, Shou-Yun; Wang, Yi-Hsuan; Wang, Shao-Pin; Hsu, Yen-Min; Huang, Yi-Shiang; Huang, Zih-You; Lin, Yu-Ching; Chang, Ching-Ming; Huang, Fu-Yung; Wu, Shih-Hsiung

    2015-01-01

    In this report, the in vitro relative capabilities of curcumin (CCM) and didemethylated curcumin (DCCM) in preventing the selenite-induced crystallin aggregation were investigated by turbidity tests and isothermal titration calorimetry (ITC). DCCM showed better activity than CCM. The conformers of CCM/SeO3(2-) and DCCM/SeO3(2-) complexes were optimized by molecular orbital calculations. Results reveal that the selenite anion surrounded by CCM through the H-bonding between CCM and selenite, which is also observed via IR and NMR studied. For DCCM, the primary driving force is the formation of an acid-base adduct with selenite showing that the phenolic OH group of DCCM was responsible for forming major conformer of DCCM. The formation mechanisms of selenite complexes with CCM or DCCM explain why DCCM has greater activity than CCM in extenuating the toxicity of selenite as to prevent selenite-induced lens protein aggregation. PMID:26635113

  4. The Comparative Studies of Binding Activity of Curcumin and Didemethylated Curcumin with Selenite: Hydrogen Bonding vs Acid-Base Interactions

    NASA Astrophysics Data System (ADS)

    Liao, Jiahn-Haur; Wu, Tzu-Hua; Chen, Ming-Yi; Chen, Wei-Ting; Lu, Shou-Yun; Wang, Yi-Hsuan; Wang, Shao-Pin; Hsu, Yen-Min; Huang, Yi-Shiang; Huang, Zih-You; Lin, Yu-Ching; Chang, Ching-Ming; Huang, Fu-Yung; Wu, Shih-Hsiung

    2015-12-01

    In this report, the in vitro relative capabilities of curcumin (CCM) and didemethylated curcumin (DCCM) in preventing the selenite-induced crystallin aggregation were investigated by turbidity tests and isothermal titration calorimetry (ITC). DCCM showed better activity than CCM. The conformers of CCM/SeO32- and DCCM/SeO32- complexes were optimized by molecular orbital calculations. Results reveal that the selenite anion surrounded by CCM through the H-bonding between CCM and selenite, which is also observed via IR and NMR studied. For DCCM, the primary driving force is the formation of an acid-base adduct with selenite showing that the phenolic OH group of DCCM was responsible for forming major conformer of DCCM. The formation mechanisms of selenite complexes with CCM or DCCM explain why DCCM has greater activity than CCM in extenuating the toxicity of selenite as to prevent selenite-induced lens protein aggregation.

  5. The Comparative Studies of Binding Activity of Curcumin and Didemethylated Curcumin with Selenite: Hydrogen Bonding vs Acid-Base Interactions

    PubMed Central

    Liao, Jiahn-Haur; Wu, Tzu-Hua; Chen, Ming-Yi; Chen, Wei-Ting; Lu, Shou-Yun; Wang, Yi-Hsuan; Wang, Shao-Pin; Hsu, Yen-Min; Huang, Yi-Shiang; Huang, Zih-You; Lin, Yu-Ching; Chang, Ching-Ming; Huang, Fu-Yung; Wu, Shih-Hsiung

    2015-01-01

    In this report, the in vitro relative capabilities of curcumin (CCM) and didemethylated curcumin (DCCM) in preventing the selenite-induced crystallin aggregation were investigated by turbidity tests and isothermal titration calorimetry (ITC). DCCM showed better activity than CCM. The conformers of CCM/SeO32− and DCCM/SeO32− complexes were optimized by molecular orbital calculations. Results reveal that the selenite anion surrounded by CCM through the H-bonding between CCM and selenite, which is also observed via IR and NMR studied. For DCCM, the primary driving force is the formation of an acid-base adduct with selenite showing that the phenolic OH group of DCCM was responsible for forming major conformer of DCCM. The formation mechanisms of selenite complexes with CCM or DCCM explain why DCCM has greater activity than CCM in extenuating the toxicity of selenite as to prevent selenite-induced lens protein aggregation. PMID:26635113

  6. Defluorination of perfluoroolefins by divalent lanthanoid reagents: Activating C-F bonds

    SciTech Connect

    Watson, P.L.; Tulip, T.H.; Williams, I. )

    1990-07-01

    Divalent lanthanoid complexes MCp*{sub 2} {times} L (M = Yb, Eu, Sm; L = diethyl ether or THF; Cp* = {eta}{sup 5}-pentamethylcyclopetadienyl) and YbCp{prime}{sub 2} {times} L (Cp{prime} = {eta}{sup 5}-methylcyclopentadienyl; L = tetrahydrofuran) rapidly abstract fluorine atoms from a variety of perfluoroolefins including perfluoro-2,4-dimethyl-3-ethylpent-2-ene, perfluoro-2,3-dimethylpent-2-ene, and perfluorocyclohexene. Qualitative observation shows that the relative fluorine abstraction reactivity of the four lanthanoid complexes increases with increasingly negative reduction potential for reasonably unhindered fluoroolefin substrates. The Yb(III)/Yb(II) reduction potential of YbCp{prime}{sub 2} solvated in acetonitrile is determined here to be {minus}1.65 V (relative to ferrocene) by cyclic voltammetry. The fully characterized organometallic products from the fluorine atom abstraction reactions are solvated trivalent lanthanoid fluorides MCp*{sub 2}F {times} L (M = Yb, Eu, Sm; L = diethyl ether or THF) and YbCp{prime}{sub 2}F {times} THF. The molecular structures of YbCp*{sub 2}F {times} OEt{sub 2} and YbCp*{sub 2}F {times} THF determined by X-ray crystallography reveal the first terminal lanthanoid-fluoride bonds.

  7. Electronic and hydrogen bonding effects on the chain-breaking activity of sulfur-containing phenolic antioxidants.

    PubMed

    Amorati, Riccardo; Fumo, Maria Grazia; Menichetti, Stefano; Mugnaini, Veronica; Pedulli, Gian Franco

    2006-08-18

    A kinetic and thermodynamic investigation of phenols para-substituted with thiyl (SR), sulfinyl (SOR), and sulfonyl (SO(2)R) groups and ortho-substituted with thiyl groups is reported. The effect of the sulfur substituents on the O-H bond dissociation enthalpy values, BDE(O-H), was measured by means of the EPR radical equilibration technique and the reactivity toward peroxyl radicals, k(inh), of these phenolic antioxidants was determined by inhibited autoxidation studies. An inverse correlation between these two parameters was found. A p-SMe substituent decreased the BDE(O-H) value to a lesser extent than a p-OMe group (-3.6 vs -4.4 kcal/mol), whereas the effect of the same groups in an ortho position showed an opposite trend (-0.85 vs -0.2 kcal/mol). The latter result is explained in terms of the different strength of the intramolecular hydrogen bond between the OH proton and the sulfur or oxygen substituents in ortho derivatives. ESI-MS analysis of the products formed by reacting the sulfides with peroxyl radicals from the azoinitiator AIBN revealed the formation of a complex mixture of products, which may play an important role in determining the overall antioxidant activity of the parent compounds. PMID:16901112

  8. Carbon-hydrogen and carbon-carbon bond activation of cyclopropane by a hydridotris(pyrazolyl)borate rhodium complex

    SciTech Connect

    Wick, D.D.; Northcutt, T.O.; Lachicotte, R.J.; Jones, W.D.

    1998-09-28

    Generation of the 16-electron fragment {l_brace}[HB(3,5-dimethylpyrazolyl){sub 3}]Rh(CNCH{sub 2}CMe{sub 3}){r_brace} (Tp{prime}RhL) in the presence of cyclopropane results in C-H activation of the hydrocarbon. The cyclopropyl hydride complex rearranges in benzene solvent to the metallacyclobutane complex Tp{prime}Rh(CNCH{sub 2}CMe{sub 3})(CH{sub 2}CH{sub 2}CH{sub 2}). Thermolysis of the rhodacyclobutane complex produces an {eta}{sup 2}-propylene complex. The related complex Tp{prime}Rh(CN-2,6-xylyl)(C{sub 2}H{sub 4}) has been structurally characterized and displays {eta}{sup 3}-Tp{prime} coordination, both in the solid state and in solution. Thermolysis of the rhodacyclobutane complex in the presence of neopentyl isocyanide leads to insertion of isocyanide into both Rh-C bonds of the metallacycle. Cyclobutane undergoes C-H but not C-C bond cleavage.

  9. Cooperativity between Al Sites Promotes Hydrogen Transfer and Carbon–Carbon Bond Formation upon Dimethyl Ether Activation on Alumina

    PubMed Central

    2015-01-01

    The methanol-to-olefin (MTO) process allows the conversion of methanol/dimethyl ether into olefins on acidic zeolites via the so-called hydrocarbon pool mechanism. However, the site and mechanism of formation of the first carbon–carbon bond are still a matter of debate. Here, we show that the Lewis acidic Al sites on the 110 facet of γ-Al2O3 can readily activate dimethyl ether to yield CH4, alkenes, and surface formate species according to spectroscopic studies combined with a computational approach. The carbon–carbon forming step as well as the formation of methane and surface formate involves a transient oxonium ion intermediate, generated by a hydrogen transfer between surface methoxy species and coordinated methanol on adjacent Al sites. These results indicate that extra framework Al centers in acidic zeolites, which are associated with alumina, can play a key role in the formation of the first carbon–carbon bond, the initiation step of the industrial MTO process. PMID:27162986

  10. Cooperativity between Al Sites Promotes Hydrogen Transfer and Carbon-Carbon Bond Formation upon Dimethyl Ether Activation on Alumina.

    PubMed

    Comas-Vives, Aleix; Valla, Maxence; Copéret, Christophe; Sautet, Philippe

    2015-09-23

    The methanol-to-olefin (MTO) process allows the conversion of methanol/dimethyl ether into olefins on acidic zeolites via the so-called hydrocarbon pool mechanism. However, the site and mechanism of formation of the first carbon-carbon bond are still a matter of debate. Here, we show that the Lewis acidic Al sites on the 110 facet of γ-Al2O3 can readily activate dimethyl ether to yield CH4, alkenes, and surface formate species according to spectroscopic studies combined with a computational approach. The carbon-carbon forming step as well as the formation of methane and surface formate involves a transient oxonium ion intermediate, generated by a hydrogen transfer between surface methoxy species and coordinated methanol on adjacent Al sites. These results indicate that extra framework Al centers in acidic zeolites, which are associated with alumina, can play a key role in the formation of the first carbon-carbon bond, the initiation step of the industrial MTO process. PMID:27162986

  11. Synthesis of aza-fused polycyclic quinolines via double C-H bond activation.

    PubMed

    Huang, Ji-Rong; Dong, Lin; Han, Bo; Peng, Cheng; Chen, Ying-Chun

    2012-07-16

    Simple but efficient: Aza-fused polycyclic quinolines were efficiently assembled through rhodium(III)-based direct double C-H activation of N-aryl azoles followed by cyclization with alkynes without heteroatom-assisted chelation. Copper(II) acetate, aside from acting as an oxidant, could also play an important role in the C-H activation process. PMID:22715023

  12. Bond Issues.

    ERIC Educational Resources Information Center

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of…

  13. Efficient Amide Bond Formation through a Rapid and Strong Activation of Carboxylic Acids in a Microflow Reactor**

    PubMed Central

    Fuse, Shinichiro; Mifune, Yuto; Takahashi, Takashi

    2014-01-01

    The development of highly efficient amide bond forming methods which are devoid of side reactions, including epimerization, is important, and such a method is described herein and is based on the concept of rapid and strong activation of carboxylic acids. Various carboxylic acids are rapidly (0.5 s) converted into highly active species, derived from the inexpensive and less-toxic solid triphosgene, and then rapidly (4.3 s) reacted with various amines to afford the desired peptides in high yields (74 %–quant.) without significant epimerization (≤3 %). Our process can be carried out at ambient temperature, and only CO2 and HCl salts of diisopropylethyl amine are generated. In the long history of peptide synthesis, a significant number of active coupling reagents have been abandoned because the highly active electrophilic species generated are usually susceptible to side reactions such as epimerization. The concept presented herein should renew interest in the use of these reagents. PMID:24402801

  14. Modifications on the hydrogen bond network by mutations of Escherichia coli copper efflux oxidase affect the process of proton transfer to dioxygen leading to alterations of enzymatic activities

    SciTech Connect

    Kajikawa, Takao; Kataoka, Kunishige; Sakurai, Takeshi

    2012-05-25

    Highlights: Black-Right-Pointing-Pointer Proton transfer pathway to dioxygen in CueO was identified. Black-Right-Pointing-Pointer Glu506 is the key amino acid to transport proton. Black-Right-Pointing-Pointer The Ala mutation at Glu506 formed a compensatory proton transfer pathway. Black-Right-Pointing-Pointer The Ile mutation at Glu506 shut down the hydrogen bond network. -- Abstract: CueO has a branched hydrogen bond network leading from the exterior of the protein molecule to the trinuclear copper center. This network transports protons in the four-electron reduction of dioxygen. We replaced the acidic Glu506 and Asp507 residues with the charged and uncharged amino acid residues. Peculiar changes in the enzyme activity of the mutants relative to the native enzyme indicate that an acidic amino acid residue at position 506 is essential for effective proton transport. The Ala mutation resulted in the formation of a compensatory hydrogen bond network with one or two extra water molecules. On the other hand, the Ile mutation resulted in the complete shutdown of the hydrogen bond network leading to loss of enzymatic activities of CueO. In contrast, the hydrogen bond network without the proton transport function was constructed by the Gln mutation. These results exerted on the hydrogen bond network in CueO are discussed in comparison with proton transfers in cytochrome oxidase.

  15. Athermal fracture of covalent bonds

    SciTech Connect

    Gilman, J.J.

    1999-08-01

    Most fracture is athermal. Either because it occurs at low temperatures or because it occurs too fast for thermal activation to be effective. Thus it must be directly activated by applied stresses. This can occur via quantum tunneling when the chemical bonding of a solid resides in localized (covalent) bonds. Then applied stresses can cause the bonding electrons to become delocalized (anti-bonded) through quantum tunneling. That is, the bonds become broken. The process is related to the Zener tunneling process that is thought to be responsible for dielectric breakdown in semiconductors. Under a driving force, bonding electrons tunnel at constant energy from their bonding states into anti-bonding states through the forbidden gap in the bonding energy spectrum.

  16. Bonding, Bridging, and Boundary Breaking: The Civic Lessons of High School Student Activities

    ERIC Educational Resources Information Center

    Shelly, Bryan

    2011-01-01

    This article presents evidence designed to expand scholarly knowledge of how high school co-curricular activities generate the positive effects previous scholarship has found. Studies of empowerment across various fields identify a sense of autonomy, self-belief, self-expression, the ability to work together with diverse others, and a critical…

  17. Constitutive Activation of the N-Methyl-d-aspartate Receptor via Cleft-spanning Disulfide Bonds*

    PubMed Central

    Blanke, Marie L.; VanDongen, Antonius M. J.

    2008-01-01

    Although the N-methyl-d-aspartate (NMDA) receptor plays a critical role in the central nervous system, many questions remain regarding the relationship between its structure and functional properties. In particular, the involvement of ligand-binding domain closure in determining agonist efficacy, which has been reported in other glutamate receptor subtypes, remains unresolved. To address this question, we designed dual cysteine point mutations spanning the NR1 and NR2 ligand-binding clefts, aiming to stabilize these domains in closed cleft conformations. Two mutants, E522C/I691C in NR1 (EI) and K487C/N687C in NR2 (KN) were found to exhibit significant glycine- and glutamate-independent activation, respectively, and co-expression of the two subunits produced a constitutively active channel. However, both individual mutants could be activated above constitutive levels in a concentration-dependent manner, indicating that cleft closure does not completely prevent agonist association. Interestingly, whereas the NR2 KN disulfide was found to potentiate channel gating and M3 accessibility, NR1 EI exhibited the opposite phenotype, suggesting that the EI disulfide may trap the NR1 ligand-binding domain in a lower efficacy conformation. Furthermore, both mutants affected agonist sensitivity at the opposing subunit, suggesting that closed cleft stabilization may contribute to coupling between the subunits. These results support a correlation between cleft stability and receptor activation, providing compelling evidence for the Venus flytrap mechanism of glutamate receptor domain closure. PMID:18450751

  18. Carbon–Hydrogen Bond Activation, C–N Bond Coupling, and Cycloaddition Reactivity of a Three-Coordinate Nickel Complex Featuring a Terminal Imido Ligand

    PubMed Central

    2015-01-01

    The three-coordinate imidos (dtbpe)Ni=NR (dtbpe = tBu2PCH2CH2PtBu2, R = 2,6-iPr2C6H3, 2,4,6-Me3C6H2 (Mes), and 1-adamantyl (Ad)), which contain a legitimate Ni–N double bond as well as basic imido nitrogen based on theoretical analysis, readily deprotonate HC≡CPh to form the amide acetylide species (dtbpe)Ni{NH(Ar)}(C≡CPh). In the case of R = 2,6-iPr2C6H3, reductive carbonylation results in formation of the (dtbpe)Ni(CO)2 along with the N–C coupled product keteneimine PhCH=C=N(2,6- iPr2C6H3). Given the ability of the Ni=N bond to have biradical character as suggested by theoretical analysis, H atom abstraction can also occur in (dtbpe)Ni=N{2,6-iPr2C6H3} when this species is treated with HSn(nBu)3. Likewise, the microscopic reverse reaction—conversion of the Ni(I) anilide (dtbpe)Ni{NH(2,6-iPr2C6H3)} to the imido (dtbpe)Ni=N{2,6-iPr2C6H3}—is promoted when using the radical Mes*O• (Mes* = 2,4,6-tBu3C6H2). Reactivity studies involving the imido complexes, in particular (dtbpe)Ni=N{2,6-iPr2C6H3}, are also reported with small, unsaturated molecules such as diphenylketene, benzylisocyanate, benzaldehyde, and carbon dioxide, including the formation of C–N and N–N bonds by coupling reactions. In addition to NMR spectroscopic data and combustion analysis, we also report structural studies for all the cycloaddition reactions involving the imido (dtbpe)Ni=N{2,6-iPr2C6H3}. PMID:25437507

  19. Computational evaluations of charge coupling and hydrogen bonding in the active site of a family 7 cellobiohydrolase.

    PubMed

    Granum, David M; Vyas, Shubham; Sambasivarao, Somisetti V; Maupin, C Mark

    2014-01-16

    Solution pH and the pKa values of ionizable residues are critical factors known to influence enzyme catalysis, structural stability, and dynamical fluctuations. Presented here is an exhaustive computational study utilizing long time constant pH molecular dynamics, pH replica exchange simulations, and kinetic modeling to evaluate pH-dependent conformations, charge dynamics, residue pKa values, and the catalytic activity-pH profile for cellobiohydrolase Cel7B from Melanocarpus albomyces . The predicted pKa values support the role of Glu212 as the catalytic nucleophile and Glu217 as the acid-base residue. The presence of a charge-correlated active site and an extensive hydrogen bonding network is found to be critical in enabling favorable residue orientations for catalysis and shuttling excess protons around the active site. Clusters of amino acids are identified that act in concert to effectively modulate the optimal pH for catalysis while elevating the overall catalytic rate with respect to a noncoupled system. The work presented here demonstrates the complex and critical role of coupled ionizable residues to the proper functioning of cellobiohydrolase Cel7B, functionally related glycosyl hydrolases, and enzymes in general. The simulations also support the use of the CpHMD for the accurate prediction of residue pKa values and to evaluate the impact of pH on protein structure and charge dynamics. PMID:24359013

  20. 26 CFR 1.103(n)-2T - Private activity bond defined (temporary).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... in section 103(b)(4) (C) or (D) apply? A-4: Section 103(n)(7)(C) provides that the term “private... activity bond”? A-1: In general, for purposes of §§ 1.103(n)-1T through 1.103(n)-6T, the term “private... from tax under section 103(a) (without application of section 103(n)). See § 1.103-7(b) for...

  1. Organo- and Organometallic-Catalytic Intramolecular [1,5]-Hydride Transfer/Cyclization Process through C(sp(3) )-H Bond Activation.

    PubMed

    Kwon, Su Jin; Kim, Dae Young

    2016-06-01

    The direct functionalization of C(sp(3) )-H bonds is one of the most synthetically powerful research areas in current organic synthesis. Organocatalytic C(sp(3) )-H bond activation reactions have recently been developed in addition to the traditional metal-catalyzed C(sp(3) )-H activation reactions. In this review, we aim to give a brief overview of organo- and organometallic internal redox cascade reactions with respect to the mechanism, the reactivity of hydrogen donors and acceptors, and the migration modes of hydrogen. PMID:27062480

  2. Catalysis of hydrolysis and nucleophilic substitution at the P-N bond of phosphoimidazolide-activated nucleotides in phosphate buffers

    NASA Technical Reports Server (NTRS)

    Kanavarioti, A.; Rosenbach, M. T.

    1991-01-01

    Phosphoimidazolide-activated derivatives of guanosine and cytidine 5'-monophosphates, henceforth called ImpN's, exhibit enhanced rates of degradation in the presence of aqueous inorganic phosphate in the range 4.0 < or = pH < or = 8.6. This degradation is been attributed to (i) nucleophilic substitution of the imidazolide and (ii) catalysis of the P-N bond hydrolysis by phosphate. The first reaction results in the formation of nucleoside 5'-diphosphate and the second in nucleoside 5'-monophosphate. Analysis of the observed rates as well as the product ratios as a function of pH and phosphate concentration allow distinction between various mechanistic possibilities. The results show that both H2PO4- and HPO4(2-) participate in both hydrolysis and nucleophilic substitution. Statistically corrected biomolecular rate constants indicate that the dianion is 4 times more effective as a general base than the monoanion, and 8 times more effective as nucleophile. The low Bronsted value beta = 0.15 calculated for these phosphate species, presumed to act as general bases in facilitating water attack, is consistent with the fact that catalysis of the hydrolysis of the P-N bond in ImpN's has not been detected before. The beta nuc = 0.35 calculated for water, H2PO4-, HPO4(2-), and hydroxide acting as nucleophiles indicates a more associative transition state for nucleotidyl (O2POR- with R = nucleoside) transfers than that observed for phosphoryl (PO3(2-)) transfers (beta nuc = 0.25). With respect to the stability/reactivity of ImpN's under prebiotic conditions, our study shows that these materials would not suffer additional degradation due to inorganic phosphate, assuming the concentrations of phosphate, Pi, on prebiotic Earth were similar to those in the present oceans ([Pi] approximately 2.25 micromoles).

  3. Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation

    SciTech Connect

    Bergman, Roberg G.; Gribble, Jr., Michael W.; Ellman, Jonathan A.

    2008-01-30

    The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy{sub 3}){sub 2} fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benzodiazepines and related pharmacophores via C-H functionalization are discussed.

  4. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding. Progress report, March 1, 1992--September 30, 1992

    SciTech Connect

    Lichtenberger, D.L.

    1992-11-01

    Purpose of this research program is to obtain experimental information on the different fundamental ways metals bond and activate organic molecules. Our approach has been to directly probe the electronic interactions between metals and molecules through a wide variety of ionization spectroscopies and other techniques, and to investigate the relationships with bonding modes, structures, and chemical behavior. During this period, we have (1) characterized the electronic features of diphosphines and monophosphines in their coordination to metals, (2) carried out theoretical and experimental investigations of the bonding capabilities of C{sub 60} to transition metals, (3) developed techniques for the imaging of single molecules on gold substrates that emphasizes the electronic backbonding from the metal to the molecule, (4) obtained the high resolution photoelectron spectrum of pure C{sub 70} in the gas phase, (5) compared the bonding of {eta}{sup 3}- acetylide ligands to the bonding of other small organic molecules with metals, and (6) reported the photoelectron spectra and bonding of {eta}{sup 3}-cyclopropenyl groups to metals.

  5. A Systematic Study of Structure and E-H Bond Activation Chemistry by Sterically Encumbered Germylene Complexes.

    PubMed

    Usher, Matthew; Protchenko, Andrey V; Rit, Arnab; Campos, Jesús; Kolychev, Eugene L; Tirfoin, Rémi; Aldridge, Simon

    2016-08-01

    A series of new germylene compounds has been synthesized offering systematic variation in the σ- and π-capabilities of the α-substituent and differing levels of reactivity towards E-H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn )] (1-6: ERn =NHDipp, CH(SiMe3 )2 , P(SiMe3 )2 , Si(SiMe3 )3 or B(NDippCH)2 ; terphenyl=C6 H3 Mes2 -2,6=Ar(Mes) or C6 H3 Dipp2 -2,6=Ar(Dipp) ; Dipp=C6 H3 iPr2 -2,6, Mes=C6 H2 Me3 -2,4,6), while the related complex [{(Me3 Si)2 N}Ge{B(NDippCH)2 }] (8) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X-ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ-donating boryl or silyl ancillary donors. HOMO-LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)-germylene system [Ar(Mes) Ge{B(NDippCH)2 }] (6-Mes), which features a wide C-Ge-B angle (110.4(1)°) and (albeit relatively weak) ancillary π-acceptor capabilities, has the smallest HOMO-LUMO gap (119 kJ mol(-1) ). These features result in 6-Mes being remarkably reactive, undergoing facile intramolecular C-H activation involving one of the mesityl ortho-methyl groups. The related aryl(silyl)-germylene system, [Ar(Mes) Ge{Si(SiMe3 )3 }] (5-Mes) has a marginally wider HOMO-LUMO gap (134 kJ mol(-1) ), rendering it less labile towards decomposition, yet reactive enough to oxidatively cleave H2 and NH3 to give the corresponding dihydride and (amido)hydride. Mixed aryl/alkyl, aryl/amido and aryl/phosphido complexes are unreactive, but amido/boryl complex 8 is competent for the activation of E-H bonds (E=H, B, Si) to give hydrido, boryl and silyl products. The results of these reactivity studies

  6. 26 CFR 1.142-1 - Exempt facility bonds.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... bonds. (a) Overview. Interest on a private activity bond is not excludable from gross income under section 103(a) unless the bond is a qualified bond. Under section 141(e)(1)(A), an exempt facility bond issued under section 142 may be a qualified bond. Under section 142(a), an exempt facility bond is...

  7. 26 CFR 1.142-1 - Exempt facility bonds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... bonds. (a) Overview. Interest on a private activity bond is not excludable from gross income under section 103(a) unless the bond is a qualified bond. Under section 141(e)(1)(A), an exempt facility bond issued under section 142 may be a qualified bond. Under section 142(a), an exempt facility bond is...

  8. One-Pot Amide Bond Formation from Aldehydes and Amines via a Photoorganocatalytic Activation of Aldehydes.

    PubMed

    Papadopoulos, Giorgos N; Kokotos, Christoforos G

    2016-08-19

    A mild, one-pot, and environmentally friendly synthesis of amides from aldehydes and amines is described. Initially, a photoorganocatalytic reaction of aldehydes with di-isopropyl azodicarboxylate leads to an intermediate carbonyl imide, which can react with a variety of amines to afford the desired amides. The initial visible light-mediated activation of a variety of monosubstituted or disubstituted aldehydes is usually fast, occurring in a few hours. Following the photocatalytic reaction, addition of the primary amine at room temperature or the secondary amine at elevated temperatures leads to the corresponding amide from moderate to excellent yields without epimerization. This methodology was applied in the synthesis of Moclobemide, a drug against depression and social anxiety. PMID:27227271

  9. Asymmetric Desymmetrization via Metal-Free C-F Bond Activation: Synthesis of 3,5-Diaryl-5-fluoromethyloxazolidin-2-ones with Quaternary Carbon Centers.

    PubMed

    Tanaka, Junki; Suzuki, Satoru; Tokunaga, Etsuko; Haufe, Günter; Shibata, Norio

    2016-08-01

    We disclose the first asymmetric activation of a non-activated aliphatic C-F bond in which a conceptually new desymmetrization of 1,3-difluorides by silicon-induced selective C-F bond scission is a key step. The combination of a cinchona alkaloid based chiral ammonium bifluoride catalyst and N,O-bis(trimethylsilyl)acetoamide (BSA) as the silicon reagent enabled the efficient catalytic cycle of asymmetric Csp3 -F bond cleavage under mild conditions with high enantioselectivities. The ortho effect of the aryl group at the prostereogenic center is remarkable. This concept was applied for the asymmetric synthesis of promising agrochemical compounds, 3,5-diaryl-5-fluoromethyloxazolidin-2-ones bearing a quaternary carbon center. PMID:27332650

  10. Synthesis of hybrid cellulose nanocomposite bonded with dopamine SiO2/TiO2 and its antimicrobial activity

    NASA Astrophysics Data System (ADS)

    Ramesh, Sivalingam; Kim, Gwang-Hoon; Kim, Jaehwan; Kim, Joo-Hyung

    2015-04-01

    Organic-inorganic hybrid material based cellulose was synthesized by the sol-gel approach. The explosion of activity in this area in the past decade has made tremendous progress in industry or academic both fundamental understanding of sol-gel process and applications of new functionalized hybrid materials. In this present research work, we focused on cellulose-dopamine functionalized SiO2/TiO2 hybrid nanocomposite by sol-gel process. The cellulose-dopamine hybrid nanocomposite was synthesized via γ-aminopropyltriethoxysilane (γ-APTES) coupling agent by in-situ sol-gel process. The chemical structure of cellulose-amine functionalized dopamine bonding to cellulose structure with covalent cross linking hybrids was confirmed by FTIR spectral analysis. The morphological analysis of cellulose-dopamine nanoSiO2/TiO2 hybrid nanocomposite materials was characterized by XRD, SEM and TEM. From this different analysis results indicate that the optical transparency, thermal stability, control morphology of cellulose-dopamine-SiO2/TiO2 hybrid nanocomposite. Furthermore cellulose-dopamine-SiO2/TiO2 hybrid nanocomposite was tested against pathogenic bacteria for antimicrobial activity.

  11. Active vibration reduction of a flexible structure bonded with optimised piezoelectric pairs using half and quarter chromosomes in genetic algorithms

    NASA Astrophysics Data System (ADS)

    Daraji, A. H.; Hale, J. M.

    2012-08-01

    The optimal placement of sensors and actuators in active vibration control is limited by the number of candidates in the search space. The search space of a small structure discretized to one hundred elements for optimising the location of ten actuators gives 1.73 × 1013 possible solutions, one of which is the global optimum. In this work, a new quarter and half chromosome technique based on symmetry is developed, by which the search space for optimisation of sensor/actuator locations in active vibration control of flexible structures may be greatly reduced. The technique is applied to the optimisation for eight and ten actuators located on a 500×500mm square plate, in which the search space is reduced by up to 99.99%. This technique helps for updating genetic algorithm program by updating natural frequencies and mode shapes in each generation to find the global optimal solution in a greatly reduced number of generations. An isotropic plate with piezoelectric sensor/actuator pairs bonded to its surface was investigated using the finite element method and Hamilton's principle based on first order shear deformation theory. The placement and feedback gain of ten and eight sensor/actuator pairs was optimised for a cantilever and clamped-clamped plate to attenuate the first six modes of vibration, using minimization of linear quadratic index as an objective function.

  12. Polymerization of ethylene by silica-supported dinuclear Cr(III) sites through an initiation step involving C-H bond activation.

    PubMed

    Conley, Matthew P; Delley, Murielle F; Siddiqi, Georges; Lapadula, Giuseppe; Norsic, Sébastien; Monteil, Vincent; Safonova, Olga V; Copéret, Christophe

    2014-02-10

    The insertion of an olefin into a preformed metal-carbon bond is a common mechanism for transition-metal-catalyzed olefin polymerization. However, in one important industrial catalyst, the Phillips catalyst, a metal-carbon bond is not present in the precatalyst. The Phillips catalyst, CrO3 dispersed on silica, polymerizes ethylene without an activator. Despite 60 years of intensive research, the active sites and the way the first CrC bond is formed remain unknown. We synthesized well-defined dinuclear Cr(II) and Cr(III) sites on silica. Whereas the Cr(II) material was a poor polymerization catalyst, the Cr(III) material was active. Poisoning studies showed that about 65 % of the Cr(III) sites were active, a far higher proportion than typically observed for the Phillips catalyst. Examination of the spent catalyst and isotope labeling experiments showed the formation of a Si-(μ-OH)-Cr(III) species, consistent with an initiation mechanism involving the heterolytic activation of ethylene at Cr(III) O bonds. PMID:24505006

  13. Active-site amino acid residues in γ-glutamyltransferase and the nature of the γ-glutamyl-enzyme bond

    PubMed Central

    Elce, John S.

    1980-01-01

    Active-site residues in rat kidney γ-glutamyltransferase (EC 2.3.2.2) were investigated by means of chemical modification. 1. In the presence of maleate, the activity was inhibited by phenylmethanesulphonyl fluoride, and the inhibition was not reversed by β-mercaptoethanol, suggesting that a serine residue is close to the active site, but is shielded except in the presence of maleate. 2. Treatment of the enzyme with N-acetylimidazole modified an amino group, exposed a previously inaccessible cysteine residue and inhibited hydrolysis of the γ-glutamyl-enzyme intermediate, but not its formation. 3. After reaction of the enzyme successively with N-acetylimidazole and with non-radioactive iodoacetamide/serine/borate, two active-site residues reacted with iodo[14C]acetamide. One of these possessed a carboxy group, which formed a [14C]glycollamide ester, and the other was cysteine, shown by isolation of S-[14C]carboxymethylcysteine after acid hydrolysis. When N-acetylimidazole treatment was omitted, only the carboxy group reacted with iodo[14C]acetamide. 4. Isolation of the γ-[14C]glutamyl-enzyme intermediate was made easier by prior treatment of the enzyme with N-acetylimidazole. The γ-glutamyl-enzyme bond was stable to performic acid, and to hydroxylamine/urea at pH10, but was hydrolysed slowly at pH12, indicating attachment of the γ-[14C]glutamyl group in amide linkage to an amino group on the enzyme. Proteolysis of the γ-[14C]glutamyl-enzyme after performic acid oxidation gave rise to a small acidic radioactive peptide that was resistant to further proteolysis and was not identical with γ-glutamyl-ε-lysine. 5. A scheme for the catalytic mechanism is proposed. PMID:6104953

  14. C-H Bond Activation by Pd-substituted CeO2: Substituted Ions versus Reduced Species

    SciTech Connect

    Misch, Lauren M; Kurzman, Joshua A; Derk, Alan R; Kim, Young-Il; Seshadri, Ram; Metiu, Horia; McFarland, Eric W; Stucky, Galen D

    2012-02-07

    Substituted metal oxides containing ionic species have been attracting a great deal of attention because of their potential ability to reduce the usage of precious metals in heterogeneous catalysts. We investigate Pd-substituted CeO2 for C-H bond activation reactions including the partial oxidation and dry reforming of CH4. This catalyst has been previously studied for CO oxidation, NOx reduction, and the water-gas shift reaction. Pd-substituted CeO2, Ce1-xPdxO2-δ, was prepared as a powder with high surface area and a hollow sphere morphology using ultrasonic spray pyrolysis. The catalysts were extensively characterized using synchrotron X-ray diffraction and other techniques, confirming phase pure samples up to 10 mol % Pd substitution. Ce0.95Pd0.05O2-δ was found to be active for partial oxidation of CH4 around 500 °C and higher. Our studies, including postcatalytic synchrotron diffraction, suggest that the single-phase Ce1-xPdxO2-δ material is not the active species and that catalysis occurs instead over the reduced two-phase Pd0/CeO2. This observation has been further confirmed by verifying the activity of the reduced Pd0/CeO2 catalysts for ethylene hydrogenation, a reaction that is known to require Pd0.

  15. Hydrodesulfurization on Transition Metal Catalysts: Elementary Steps of C-S Bond Activation and Consequences of Bifunctional Synergies

    NASA Astrophysics Data System (ADS)

    Yik, Edwin Shyn-Lo

    convergence to a single phase is expected and predictable from thermodynamics at a given temperature and sulfur chemical potential, metastability of two phases can exist. We demonstrate, through extensive characterization and kinetic evidence, such behaviors exist in Re, where structural disparities between its phases lead to kinetic hurdles that prevent interconversions between layered ReSx nanostructures and sulfur-covered Re metal clusters. Such features allowed, for the first time, direct comparisons of reaction rates at identical conditions on two disparate phases of the same transition metal identity. Rigorous assessments of kinetic and selectivity data indicated that more universal mechanistic features persist across all catalysts studied, suggesting that differences in their catalytic activity were the result of different densities of HDS sites, which appeared to correlate with their respective metal-sulfur bond energies. Kinetic responses and product distributions indicated that the consumption of thiophene proceeds by the formation of a partially-hydrogenated surface intermediate, which subsequently produces tetrahydrothiophene (THT) and butene/butane (C4) via primary routes on similar types of sites. These sites are formed from desorption of weakly-bound sulfur adatoms on sulfur-covered metal surfaces, which can occur when the heat of sulfur adsorption is sufficiently low at high sulfur coverage as a result of increased sulfur-sulfur repulsive interactions. Relative stabilities and differences in the molecularity of the respective transition states that form THT and C4 dictate product distributions. THT desulfurization to form C4 occurs via readsorption and subsequent dehydrogenation, evidenced by secondary rates that exhibited negative H2 dependences. These behaviors suggest that C-S bond activation occurs on a partially (un)saturated intermediate, analogous to behaviors observed in C-C bond scission reactions of linear and cycloalkanes on hydrogen-covered metal

  16. Palladium-catalyzed Suzuki-Miyaura coupling of amides by carbon-nitrogen cleavage: general strategy for amide N-C bond activation.

    PubMed

    Meng, Guangrong; Szostak, Michal

    2016-06-15

    The first palladium-catalyzed Suzuki-Miyaura cross-coupling of amides with boronic acids for the synthesis of ketones by sterically-controlled N-C bond activation is reported. The transformation is characterized by operational simplicity using bench-stable, commercial reagents and catalysts, and a broad substrate scope, including substrates with electron-donating and withdrawing groups on both coupling partners, steric-hindrance, heterocycles, halides, esters and ketones. The scope and limitations are presented in the synthesis of >60 functionalized ketones. Mechanistic studies provide insight into the catalytic cycle of the cross-coupling, including the first experimental evidence for Pd insertion into the amide N-C bond. The synthetic utility is showcased by a gram-scale cross-coupling and cross-coupling at room temperature. Most importantly, this process provides a blueprint for the development of a plethora of metal catalyzed reactions of typically inert amide bonds via acyl-metal intermediates. A unified strategy for amide bond activation to enable metal insertion into N-C amide bond is outlined (). PMID:26864384

  17. Propane σ-Complexes on PdO(101): Spectroscopic Evidence of the Selective Coordination and Activation of Primary C-H Bonds.

    PubMed

    Zhang, Feng; Pan, Li; Choi, Juhee; Mehar, Vikram; Diulus, John T; Asthagiri, Aravind; Weaver, Jason F

    2015-11-16

    Achieving selective C-H bond cleavage is critical for developing catalytic processes that transform small alkanes to value-added products. The present study clarifies the molecular-level origin for an exceptionally strong preference for propane to dissociate on the crystalline PdO(101) surface via primary C-H bond cleavage. Using reflection absorption infrared spectroscopy (RAIRS) and density functional theory (DFT) calculations, we show that adsorbed propane σ-complexes preferentially adopt geometries on PdO(101) in which only primary C-H bonds datively interact with the surface Pd atoms at low propane coverages and are thus activated under typical catalytic reaction conditions. We show that a propane molecule achieves maximum stability on PdO(101) by adopting a bidentate geometry in which a H-Pd dative bond forms at each CH3 group. These results demonstrate that structural registry between the molecule and surface can strongly influence the selectivity of a metal oxide surface in activating alkane C-H bonds. PMID:26420576

  18. TECHNICAL NOTE: A real-time active smart patch system for monitoring the integrity of bonded repair on an aircraft structure

    NASA Astrophysics Data System (ADS)

    Qing, Xinlin P.; Beard, Shawn J.; Kumar, Amrita; Hannum, Robert

    2006-06-01

    There currently exists a need to develop a cost-effective, in-service structural health monitoring (SHM) system for determining the initial quality of a bonded repair and assessing the long-term durability of the bonded repair on an aircraft structure. In this paper, a real-time active smart patch system (SPS) based on SMART layer technology is introduced for monitoring the integrity of bonded repairs. First, an overview of the SPS is given for typical metal and composite repairs. To illustrate the capability of the SPS, three applications are presented: (1) monitoring of the cure progress of the bonded repair adhesive, (2) detection of the initial artificial disbond between the composite patch and the metal structure, and (3) monitoring of damage in and around a bonded repair during fatigue cycling. The results show that, through the use of a real-time active SPS approach of using sensors placed in, on or around the repair, the initial quality and long-term durability of the repair can be evaluated and monitored.

  19. Effect of addition of chitosan to self-etching primer: antibacterial activity and push-out bond strength to radicular dentin

    PubMed Central

    Elsaka, Shaymaa; Elnaghy, Amr

    2012-01-01

    The purpose of this study was to evaluate the antibacterial activity of a modified self-etching primer incorporating chitosan and whether this modification affected the bond strength to radicular dentin. A modified self-etching primer was prepared by adding chitosan solutions at 0.03%, 0.06%, 0.12% and 0.25% (W/W) to RealSeal selfe-tching primer. RealSeal primer without chitosan was used as the control. The antibacterial activity of the modified self-etching primer was evaluated using the direct contact test against Enterococcus faecalis. The bonding ability of the RealSeal system to radicular dentin was evaluated using the push-out bond strength test. The modes of failure were examined under a stereomicroscope. Data were analyzed using analysis of variance (ANOVA) and Tukey's test, with a P-value < 0.05 indicating statistical significance. The results showed that the antibacterial properties of the freshly prepared and aged modified self-etching primer incorporating chitosan exhibited potent antibacterial effect against Enterococcus faecalis compared with the unmodified primer. The RealSeal system with the aged modified self-etching primer incorporating chitosan showed no significant differences in the bond strength as compared with the control (P = 0.99). The findings suggest that modified self-etching primer incorporating chitosan is a promising antibacterial primer which does not adversely affect the bond strength of the RealSeal system to radicular dentin. PMID:23554762

  20. Structure, bonding, and catalytic activity of monodisperse, transition-metal-substituted CeO2 nanoparticles.

    PubMed

    Elias, Joseph S; Risch, Marcel; Giordano, Livia; Mansour, Azzam N; Shao-Horn, Yang

    2014-12-10

    We present a simple and generalizable synthetic route toward phase-pure, monodisperse transition-metal-substituted ceria nanoparticles (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni, Cu). The solution-based pyrolysis of a series of heterobimetallic Schiff base complexes ensures a rigorous control of the size, morphology and composition of 3 nm M0.1Ce0.9O2-x crystallites for CO oxidation catalysis and other applications. X-ray absorption spectroscopy confirms the dispersion of aliovalent (M(3+) and M(2+)) transition metal ions into the ceria matrix without the formation of any bulk transition metal oxide phases, while steady-state CO oxidation catalysis reveals an order of magnitude increase in catalytic activity with copper substitution. Density functional calculations of model slabs of these compounds confirm the stabilization of M(3+) and M(2+) in the lattice of CeO2. These results highlight the role of the host CeO2 lattice in stabilizing high oxidation states of aliovalent transition metal dopants that ordinarily would be intractable, such as Cu(3+), as well as demonstrating a rational approach to catalyst design. The current work demonstrates, for the first time, a generalizable approach for the preparation of transition-metal-substituted CeO2 for a broad range of transition metals with unparalleled synthetic control and illustrates that Cu(3+) is implicated in the mechanism for CO oxidation on CuO-CeO2 catalysts. PMID:25406101

  1. Ultraviolet Signposts of Resonant Dynamics in the Starburst-ringed SAB Galaxy M94 (NGC 4736)

    NASA Astrophysics Data System (ADS)

    Waller, William H.; Fanelli, Michael N.; Keel, William C.; Bohlin, Ralph; Collins, Nicholas R.; Madore, Barry F.; Marcum, Pamela M.; Neff, Susan G.; O'Connell, Robert W.; Offenberg, Joel D.; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

    2001-03-01

    The dynamic orchestration of star-birth activity in the starburst-ringed galaxy M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging Telescope (UIT; far-ultraviolet [FUV] band), Hubble Space Telescope (HST; near-ultraviolet [NUV] band), Kitt Peak 0.9 m telescope (Hα, R, and I bands), and Palomar 5 m telescope (B band), along with spectra from the International Ultraviolet Explorer (IUE) and the Lick 1 m telescope. The wide-field UIT image shows FUV emission from (1) an elongated nucleus, (2) a diffuse inner disk, where Hα is observed in absorption, (3) a bright inner ring of H II regions at the perimeter of the inner disk (R=48"=1.1 kpc), and (4) two 500 pc size knots of hot stars exterior to the ring on diametrically opposite sides of the nucleus (R=130"=2.9 kpc). The HST Faint Object Camera image resolves the NUV emission from the nuclear region into a bright core and a faint 20" long ``minibar'' at a position angle of 30°. Optical and IUE spectroscopy of the nucleus and diffuse inner disk indicates a ~107-108 yr old stellar population from low-level star-birth activity blended with some LINER activity. Analysis of the Hα-, FUV-, NUV-, B-, R-, and I-band emissions, along with other observed tracers of stars and gas in M94, indicates that most of the star formation is being orchestrated via ring-bar dynamics, involving the nuclear minibar, inner ring, oval disk, and outer ring. The inner starburst ring and bisymmetric knots at intermediate radius, in particular, argue for bar-mediated resonances as the primary drivers of evolution in M94 at the present epoch. Similar processes may be governing the evolution of the ``core-dominated'' galaxies that have been observed at high redshift. The gravitationally lensed ``Pretzel Galaxy'' (0024+1654) at a redshift of ~1.5 provides an important precedent in this regard.

  2. Ultrasonically bonded value assembly

    NASA Technical Reports Server (NTRS)

    Salvinski, R. J. (Inventor)

    1975-01-01

    A valve apparatus capable of maintaining a fluid-tight seal over a relatively long period of time by releasably bonding a valve member to its seat is described. The valve member is bonded or welded to the seat and then released by the application of the same energy to the bond joint. The valve member is held in place during the bonding by a clamping device. An appropriate force device can activate the opening and closing of the valve member. Various combinations of material for the valve member and valve seat can be utilized to provide an adequate sealing bond. Aluminum oxide, stainless steel, inconel, tungsten carbide as hard materials and copper, aluminum, titanium, silver, and gold as soft materials are suggested.

  3. Institutional Bonding.

    ERIC Educational Resources Information Center

    Allard, M. June

    Institutional bonding was examined at a public, urban commuter college with exceptionally high attrition and visibly low morale. Changes in bonding and attrition were measured 6 years after a 2-year effort to develop school identity and student feelings of membership. It was found that a simple index of campus morale is provided by level of…

  4. Contributions of a disulfide bond and a reduced cysteine side chain to the intrinsic activity of the high-density lipoprotein receptor SR-BI.

    PubMed

    Yu, Miao; Lau, Thomas Y; Carr, Steven A; Krieger, Monty

    2012-12-18

    The high-density lipoprotein (HDL) receptor scavenger receptor class B, type I (SR-BI), binds HDL and mediates selective cholesteryl ester uptake. SR-BI's structure and mechanism are poorly understood. We used mass spectrometry to assign the two disulfide bonds in SR-BI that connect cysteines within the conserved Cys(321)-Pro(322)-Cys(323) (CPC) motif and connect Cys(280) to Cys(334). We used site-specific mutagenesis to evaluate the contributions of the CPC motif and the side chain of extracellular Cys(384) to HDL binding and lipid uptake. The effects of CPC mutations on activity were context-dependent. Full wild-type (WT) activity required Pro(322) and Cys(323) only when Cys(321) was present. Reduced intrinsic activities were observed for CXC and CPX, but not XXC, XPX, or XXX mutants (X ≠ WT residue). Apparently, a free thiol side chain at position 321 that cannot form an intra-CPC disulfide bond with Cys(323) is deleterious, perhaps because of aberrant disulfide bond formation. Pro(322) may stabilize an otherwise strained CPC disulfide bond, thus supporting WT activity, but this disulfide bond is not absolutely required for normal activity. C(384)X (X = S, T, L, Y, G, or A) mutants exhibited altered activities that varied with the side chain's size: larger side chains phenocopied WT SR-BI treated with its thiosemicarbazone inhibitor BLT-1 (enhanced binding, weakened uptake); smaller side chains produced almost inverse effects (increased uptake:binding ratio). C(384)X mutants were BLT-1-resistant, supporting the proposal that Cys(384)'s thiol interacts with BLT-1. We discuss the implications of our findings on the functions of the extracellular loop cysteines in SR-BI and compare our results to those presented by other laboratories. PMID:23205738

  5. Contributions of a disulfide bond and a reduced cysteine side chain to the intrinsic activity of the HDL receptor SR-BI

    PubMed Central

    Yu, Miao; Lau, Thomas Y.; Carr, Steven A.; Krieger, Monty

    2013-01-01

    The high density lipoprotein (HDL) receptor, scavenger receptor class B, type I (SR-BI), binds HDL and mediates selective cholesteryl ester uptake. SR-BI's structure and mechanism are poorly understood. We used mass spectrometry to assign the two disulfide bonds in SR-BI that connect cysteines within the conserved Cys321-Pro322-Cys323 (CPC) motif and connect Cys280 to Cys334. We used site-specific mutagenesis to evaluate the contributions of the CPC motif and the side chain of extracellular Cys384 to HDL binding and lipid uptake. The effects of CPC mutations on activity were context dependent. Full wild-type (WT) activity required Pro322 and Cys323 only when Cys321 was present. Reduced intrinsic activities were observed for CXC and CPX, but not XXC, XPX or XXX mutants (X≠WT residue). Apparently, a free thiol side chain at position 321 that cannot form an intra-CPC disulfide bond with Cys323 is deleterious, perhaps because of aberrant disulfide bond formation. Pro322 may stabilize an otherwise strained CPC disulfide bond, thus supporting WT activity, but this disulfide bond is not absolutely required for activity. C384X (X=S,T,L,Y,G,A) mutants exhibited altered activities that varied with the side chain's size: larger side chains phenocopied WT SR-BI treated with its thiosemicarbazone inhibitor BLT-1 (increased binding, decreased uptake); smaller side chains produced almost inverse effects (increased uptake:binding ratio). C384X mutants were BLT-1 resistant, supporting the proposal that Cys384's thiol interacts with BLT-1. We discuss the implications of our findings on the functions of the extracellular loop cysteines in SR-BI and compare our results to those presented by other laboratories. PMID:23205738

  6. Implementation and Evaluation of Web-Based Learning Activities on Bonding and the Structure of Matter for 10-th Grade Chemistry

    NASA Astrophysics Data System (ADS)

    Frailich, Marcel

    This study deals with the development, implementation, and evaluation of web-based activities associated with the topic of chemical bonding , as taught in 10th grade chemistry. A website was developed entitled: "Chemistry and the Chemical Industry in the Service of Mankind", its URL is: http://stwww.weizmann.ac.il/g-chem/learnchem (Kesner, Frailich, & Hofstein, 2003). The main goal of this study was to assess the educational effectiveness of website activities dealing with the chemical bonding concept. These activities include visualization tools, as well as topics relevant to daily life and industrial applications. The study investigated the effectiveness of a web-based learning environment regarding the understanding of chemical bonding concepts, students' perceptions of the classroom learning environment, their attitudes regarding the relevance of learning chemistry to everyday life, and their interest in chemistry studies. As mentioned before, in the present study we focused on activities (from the website), all of which deal with chemical bonding concept. The following are the reasons for the decision to focus on this topic: (1) Chemical bonding is a key concept that is taught in 10th grade chemistry in high school. It provides the basis for many other chemistry topics that are taught later, and (2) Chemical bonding is a difficult for students using existing tools (e. g., static models in books, ball-and- stick models), which are insufficient to demonstrate the abstract nature phenomena associated with this topic. The four activities developed for this study are (1) models of the atomic structure, (2) metals -- structure and properties, (3) ionic substances in everyday life and in industry, and (4) molecular substances -- structure, properties, and uses. The study analyzed both quantitative and qualitative research. The quantitative tools of the study included: A Semantic Differential questionnaire and a Chemistry Classroom Web-Based Learning Environment

  7. Spectroscopic and Crystallographic Evidence for the Role of a Water-Containing H-Bond Network in Oxidase Activity of an Engineered Myoglobin.

    PubMed

    Petrik, Igor D; Davydov, Roman; Ross, Matthew; Zhao, Xuan; Hoffman, Brian; Lu, Yi

    2016-02-01

    Heme-copper oxidases (HCOs) catalyze efficient reduction of oxygen to water in biological respiration. Despite progress in studying native enzymes and their models, the roles of non-covalent interactions in promoting this activity are still not well understood. Here we report EPR spectroscopic studies of cryoreduced oxy-F33Y-CuBMb, a functional model of HCOs engineered in myoglobin (Mb). We find that cryoreduction at 77 K of the O2-bound form, trapped in the conformation of the parent oxyferrous form, displays a ferric-hydroperoxo EPR signal, in contrast to the cryoreduced oxy-wild-type (WT) Mb, which is unable to deliver a proton and shows a signal from the peroxo-ferric state. Crystallography of oxy-F33Y-CuBMb reveals an extensive H-bond network involving H2O molecules, which is absent from oxy-WTMb. This H-bonding proton-delivery network is the key structural feature that transforms the reversible oxygen-binding protein, WTMb, into F33Y-CuBMb, an oxygen-activating enzyme that reduces O2 to H2O. These results provide direct evidence of the importance of H-bond networks involving H2O in conferring enzymatic activity to a designed protein. Incorporating such extended H-bond networks in designing other metalloenzymes may allow us to confer and fine-tune their enzymatic activities. PMID:26716352

  8. Mechanistic insight into conjugated N-N bond cleavage by Rh(III)-catalyzed redox-neutral C-H activation of pyrazolones.

    PubMed

    Wu, Weirong; Liu, Yuxia; Bi, Siwei

    2015-08-14

    Density functional theory (DFT) calculations have been performed to investigate the detailed mechanism of Rh(III)-catalyzed redox-neutral C-H activation of pyrazolones with PhC≡CPh. It is found that (1) the methylene C-H activation is prior to the phenyl C-H activation, (2) the N-N bond cleavage is realized via Rh(III) → Rh(I) → Rh(III) rather than via Rh(III) → Rh(V) → Rh(III). The zwitterionic Rh(I) complex is identified to be a key intermediate in promoting the N-N bond cleavage. (3) Different from the Rh(III)-catalyzed hydrazine-directed C-H activation for indole synthesis, the rate-determining step of the reaction studied in this work is the Rh(III) → Rh(I) → Rh(III) process resulting in the N-N bond cleavage rather than the alkyne insertion step. The present theoretical study provides new insight into the mechanism of the conjugated N-N bond cleavage. PMID:26138233

  9. A Selective Rh(I) -Catalyzed Substrate-Controlled C-C Bond Activation of Benzyl Sulfonamide/Alcohol-Tethered Alkylidenecyclopropanes.

    PubMed

    Chen, Kai; Liu, Jia-Xin; Tang, Xiang-Ying; Shi, Min

    2016-08-01

    Benzyl sulfonamide/alcohol-tethered alkylidenecyclopropanes undergo a rhodium-catalyzed and substrate-controlled selective C-C bond activation, producing three types of common organic structural units: benzo[c]azepine/oxepines, dihydronaphthalen-1-amines, and conjugated dienes. Epoxidation and aromatization of these products to construct two useful compounds have also been achieved. PMID:27305281

  10. Discovery of molluscicidal and cercaricidal activities of 3-substituted quinazolinone derivatives by a scaffold hopping approach using a pseudo-ring based on the intramolecular hydrogen bond formation.

    PubMed

    Guo, Wei; Zheng, Lv-Yin; Li, Yong-Dong; Wu, Ren-Miao; Chen, Qiang; Yang, Ding-Qiao; Fan, Xiao-Lin

    2016-06-10

    Discovery of novel topological agents against Oncomelania hupensis snails and cercariae remains a significant challenge in current Schistosomiasis control. A pseudo-ring formed from salicylanilide by an intramolecular hydrogen bond led to the discovery of 3-substituted quinazolinone derivatives which showed a potent molluscicidal and cercaricidal activities. PMID:27017555

  11. Iridium-mediated Bond Activation and Water Oxidation as an Exemplary Case of CARISMA, A European Network for the Development of Catalytic Routines for Small Molecule Activation.

    PubMed

    Licini, Giulia; Albrecht, Martin

    2015-01-01

    CARISMA is a currently running COST Action that pools leading European experts in computational and experimental chemistry to foster synergies for developing new catalytic processes for the transformation of abundant small molecules such as water, carbon dioxide, or ammonia into high-value chemicals and energy-relevant products. CARISMA promotes new collaborations, exchange of knowledge and skills, frontier training to young as well as established researchers, and a platform for the advancement of theoretical and experimental research in an iterative process, comprised of expertise in various connate domains including synthesis, catalysis, spectroscopy, kinetics, and computational chemistry. These interactions stimulate the discovery of new and efficient catalytic processes, illustrated in the second part of this contribution with the collaborative development of powerful iridium-based complexes for bond activation and water oxidation catalysis. PMID:26507475

  12. The role of group 14 element hydrides in the activation of C-H bonds in cyclic olefins.

    PubMed

    Summerscales, Owen T; Caputo, Christine A; Knapp, Caroline E; Fettinger, James C; Power, Philip P

    2012-09-01

    Formally, triple-bonded dimetallynes ArEEAr [E = Ge (1), Sn (2); Ar = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)] have been previously shown to activate aliphatic, allylic C-H bonds in cyclic olefins, cyclopentadiene (CpH), cyclopentene (c-C(5)H(8)) and 1,4-cyclohexadiene, with intriguing selectivity. In the case of the five-membered carbocycles, cyclopentadienyl species ArECp [E = Ge (3), Sn (4)] are formed. In this study, we examine the mechanisms for activation of CpH and c-C(5)H(8) using experimental methods and describe a new product found from the reaction between 1 and c-C(5)H(8), an asymmetrically substituted digermene ArGe(H)Ge(c-C(5)H(9))Ar (5), crystallized in 46% yield. This compound contains a hydrogenated cyclopentyl moiety and is found to be produced in a 3:2 ratio with 3, explaining the fate of the liberated H atoms following triple C-H activation. We show that when these C-H activation reactions are carried out in the presence of tert-butyl ethylene (excess), compounds {ArE(CH(2)CH(2)tBu)}(2) [E = Ge(8), Sn(9)] are obtained in addition to ArECp; in the case of CpH, the neohexyl complexes replace the production of H(2) gas, and for c-C(5)H(8) they displace cyclopentyl product 5 and account for all the hydrogen removed in the dehydroaromatization reactions. To confirm the source of 8 and 9, it was demonstrated that these molecules are formed cleanly between the reaction of (ArEH)(2) [E = Ge(6), Sn(7)] and tert-butyl ethylene, new examples of noncatalyzed hydro-germylation and -stannylation. Therefore, the presence of transient hydrides of the type 6 and 7 can be surmised to be reactive intermediates in the production of 3 and 4, along with H(2), from 1 and 2 and CpH (respectively), or the formation of 3 and 5 from 1. The reaction of 6 or 7 with CpH gave 3 or 4, respectively, with concomitant H(2) evolution, demonstrating the basic nature of these low-valent group 14 element hydrides and their key role in the 'cascade' of C-H activation steps

  13. Accelerated Bonding of Magnesium and Aluminum with a CuNi/Ag/CuNi Sandwich Interlayer by Plasma-Activated Sintering

    NASA Astrophysics Data System (ADS)

    Wang, Yiyu; Rao, Mei; Li, Leijun; Luo, Guoqiang; Shen, Qiang; Zhang, Lianmeng

    2016-02-01

    Plasma-activated sintering (PAS) has been applied, for the first time, to join magnesium and aluminum using a CuNi/Ag/CuNi sandwich structural interlayer. A cleaning effect and high efficient plasma heating mode in PAS have contributed to forming a strong interfacial diffusion bond under low temperature 673 K (400 °C) and short dwell time (0.6 ks). The designed interlayer provides a diffusion barrier effect and an enhanced physical contact between the interfaces. Strong bonding has been achieved without forming the brittle Mg-Al intermetallics.

  14. The Effect of Artificial Aging on The Bond Strength of Heat-activated Acrylic Resin to Surface-treated Nickel-chromium-beryllium Alloy

    PubMed Central

    Al Jabbari, Youssef S.; Zinelis, Spiros; Al Taweel, Sara M.; Nagy, William W.

    2016-01-01

    Purpose The debonding load of heat-activated polymethylmethacrylate (PMMA) denture base resin material to a nickel-chromium-beryllium (Ni-Cr-Be) alloy conditioned by three different surface treatments and utilizing two different commercial bonding systems was investigated. Materials and Methods Denture resin (Lucitone-199) was bonded to Ni-Cr-Be alloy specimens treated with Metal Primer II, the Rocatec system with opaquer and the Rocatec system without opaquer. Denture base resin specimens bonded to non-treated sandblasted Ni-Cr-Be alloy were used as controls. Twenty samples for each treatment condition (80 specimens) were tested. The 80 specimens were divided into two categories, thermocycled and non-thermocycled, containing four groups of ten specimens each. The non-thermocycled specimens were tested after 48 hours’ storage in room temperature water. The thermocycled specimens were tested after 2,000 cycles in 4°C and 55°C water baths. The debonding load was calculated in Newtons (N), and collected data were subjected by non parametric test Kruskal-Wallis One Way Analysis of Variance on Ranks and Dunn’s post hoc test at the α = 0.05. Results The Metal Primer II and Rocatec system without opaquer groups produced significantly higher bond strengths (119.9 and 67.6 N), respectively, than did the sandblasted and Rocatec system with opaquer groups, where the bond strengths were 2.6 N and 0 N, respectively. The Metal Primer II was significantly different from all other groups (P<0.05). The bond strengths of all groups were significantly decreased (P<0.05) after thermocycling. Conclusions Although thermocycling had a detrimental effect on the debonding load of all surface treatments tested, the Metal Primer II system provided higher values among all bonding systems tested, before and after thermocycling. PMID:27335613

  15. Supramolecular hydrogen-bonding patterns of co-crystals containing the active pharmaceutical ingredient (API) phloroglucinol and N-heterocycles.

    PubMed

    Cvetkovski, Aleksandar; Bertolasi, Valerio; Ferretti, Valeria

    2016-06-01

    The active pharmaceutical ingredient phloroglucinol (PHL) has been taken as an illustrative molecule to explore the intermolecular interactions which can be established with other molecular entities to build PHL pharmaceutical co-crystals. The crystal structures of five newly synthesized co-crystals are reported, where PHL is crystallized with N-heterocycles, namely 2-hydroxy-6-methylpyridine (1), 2,4-dimethyl-6-hydroxypyrimidine (2), 4-phenylpyridine (3), 2-hydroxypyridine (4) and 2,3,5,6-tetramethylpyrazine (5). The structural characteristics of these co-crystals, as far as the hydrogen-bonding networks and the crystalline architectures are concerned, are strongly dependent on the chemical features of the coformer molecules, as well as on their size and shape. A detailed analysis of the intermolecular interactions established in all the PHL co-crystals of known structures has allowed the recognition of some regularities in the packing modes that can be useful in the design of new supramolecular adducts forming predictable structural motifs. PMID:27240764

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

    PubMed Central

    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

    Addition of biphenylene to the bis(imino)pyridine iron dinitrogen complexes, (iPrPDI)Fe(N2)2 and [(MePDI)Fe(N2)]2(μ2-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

  17. Geometric and Electronic Structure of [{Cu(MeAN)}2(μ-η2:η2(O22−))]2+ with an Unusually Long O–O Bond: O–O Bond Weakening vs Activation for Reductive Cleavage

    PubMed Central

    Park, Ga Young; Qayyum, Munzarin F.; Woertink, Julia; Hodgson, Keith O.; Hedman, Britt; Narducci Sarjeant, Amy A.; Solomon, Edward I.; Karlin, Kenneth D.

    2012-01-01

    Certain side-on peroxo dicopper(II) species with particularly low υO–O (710–730 cm−1) have been found in equilibrium with their bis-μ-oxo dicopper(III) isomer. An issue is whether such side-on peroxo bridges are further activated for O–O cleavage. In a previous study (Liang, H.-C., et al., J. Am. Chem. Soc. 2002, 124, 4170–4171), we showed that oxygenation of the three-coordinate complex [CuI(MeAN)]+ (MeAN=N-methyl-N,N-bis[3-(dimethylamino)propyl]amine) leads to a low-temperature stable [{CuII(MeAN)}2(μ-η2:η2-O22−)]2+ peroxo species with low υO–O (721 cm−1), as characterized by UV-Vis absorption and resonance Raman (rR) spectroscopies. Here, this complex has been crystallized as its SbF6− salt and an X-ray structure indicates the presence of an unusually long O–O bond (1.540(5) Å) consistent with the low υO–O. EXAFS and rR spectroscopic and reactivity studies indicate the exclusive formation of [{CuII(MeAN)}2(μ-η2:η2-O22−)]2+ without any bis-μ-oxo-dicopper(III) isomer present. This is the first structure of a side-on peroxo dicopper(II) species with a significantly long and weak O–O bond. DFT calculations show that the weak O–O bond results from strong σ donation from the MeAN ligand to Cu that is compensated by a decrease in the extent of peroxo to Cu charge transfer. Importantly, the weak O–O bond does not reflect an increase in backbonding into the σ* orbital of the peroxide. Thus, although the O–O bond is unusually weak, this structure is not further activated for reductive cleavage to form a reactive bis-μ-oxo-dicopper(III) species. These results highlight the necessity of understanding electronic structure changes associated with spectral changes for correlations to reactivity. PMID:22571744

  18. Iron-Carbonyl-Catalyzed Redox-Neutral [4+2] Annulation of N-H Imines and Internal Alkynes by C-H Bond Activation.

    PubMed

    Jia, Teng; Zhao, Chongyang; He, Ruoyu; Chen, Hui; Wang, Congyang

    2016-04-18

    Stoichiometric C-H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C-H transformations have not been developed. Herein, an iron-catalyzed annulation of N-H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C-H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C-H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C-H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step. PMID:27002210

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

    PubMed

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

    2007-01-01

    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

  20. Density function theoretical study on the complex involved in Th atom-activated C–C bond in C2H6

    NASA Astrophysics Data System (ADS)

    Qing-Qing, Wang; Peng, Li; Tao, Gao; Hong-Yan, Wang; Bing-Yun, Ao

    2016-06-01

    Density functional theory (DFT) calculations are performed to investigate the reactivity of Th atom toward ethane C–C bond activation. A comprehensive description of the reaction mechanisms leading to two different reaction products is presented. We report a complete exploration of the potential energy surfaces by taking into consideration different spin states. In addition, the intermediate and transition states along the reaction paths are characterized. Total, partial, and overlap population density of state diagrams and analyses are also presented. Furthermore, the natures of the chemical bonding of intermediate and transition states are studied by using topological method combined with electron localization function (ELF) and Mayer bond order. Infrared spectrum (IR) is obtained and further discussed based on the optimized geometries. Project supported by the National Natural Science Foundation of China (Grant Nos. 21371160, 21401173, and 11364023).

  1. Activation of carbon dioxide by a terminal uranium-nitrogen bond in the gas-phase: a demonstration of the principle of microscopic reversibility.

    PubMed

    Dau, Phuong D; Armentrout, P B; Michelini, Maria C; Gibson, John K

    2016-03-14

    Activation of CO2 is demonstrated by its spontaneous dissociative reaction with the gas-phase anion complex NUOCl2(-), which can be considered as NUO(+) coordinated by two chloride anion ligands. This reaction was previously predicted by density functional theory to occur exothermically, without barriers above the reactant energy. The present results demonstrate the validity of the prediction of microscopic reversibility, and provide a rare case of spontaneous dissociative addition of CO2 to a gas-phase complex. The activation of CO2 by NUOCl2(-) proceeds by conversion of a U[triple bond, length as m-dash]N bond to a U[double bond, length as m-dash]O bond and creation of an isocyanate ligand to yield the complex UO2(NCO)Cl2(-), in which uranyl, UO2(2+), is coordinated by one isocyanate and two chloride anion ligands. This activation of CO2 by a uranium(vi) nitride complex is distinctive from previous reports of oxidative insertion of CO2 into lower oxidation state U(iii) or U(iv) solid complexes, during which both C-O bonds remain intact. This unusual observation of spontaneous addition and activation of CO2 by NUOCl2(-) is a result of the high oxophilicity of uranium. If the computed Gibbs free energy of the reaction pathway, rather than the energy, is considered, there are barriers above the reactant asymptotes such that the observed reaction should not proceed under thermal conditions. This result provides a demonstration that energy rather than Gibbs free energy determines reactivity under low-pressure bimolecular conditions. PMID:26898535

  2. Active-Transient Liquid Phase (A-TLP) Bonding of Pure Aluminum Matrix Composite Reinforced with Short Alumina Fiber Using Al-12Si-xTi Foils as Active Interlayer

    NASA Astrophysics Data System (ADS)

    Zhang, Guifeng; Su, Wei; Suzumura, Akio

    2016-02-01

    To optimize both the interlayer composition design route and pressure for joining aluminum matrix composite reinforced with short alumina fiber (as-cast 30 vol pct Al2O3sf/Al), traditional transient liquid phase (TLP) bonding using Al-12Si and Cu interlayer and active-TLP (A-TLP) bonding using an active Ti-containing interlayer (Al-12Si-xTi, x = 0.1, 0.5, and 1 wt pct) under the same condition [883 K (610 °C) × 30 minutes × 1 or 0.015 MPa in flowing argon] were compared in terms of interfacial wettability, bond seam microstructure, shear strength, and fracture path. It was found that not only the Ti content but also the pressure are critical factors affecting interfacial wettability and bond seam microstructure. The improvement in wettability by adding Ti as an active element were confirmed by reduction of expulsion of liquid interlayer, elimination of interfacial gap, higher shear strength and favorable fracture path (partially through bond seam and the composite). Because of the incubation period for wetting, reducing the pressure after melting of the interlayer could further increase joint shear strength by thickening the remaining bond seam of solid-solution matrix and decreasing fraction of the in situ newly formed Al-Si-Ti IMC phase (short bar shape) within the bond seam. The maximum shear strength of 88.6 MPa (99 pct of the as-cast composite) was obtained by adding trace Ti content (0.5 Ti wt pct) addition and using low pressure (0.015 MPa). The results showed that suitable combination of Ti content and pressure pattern is required for improving both wettability and bond seam microstructure.

  3. Active-Transient Liquid Phase (A-TLP) Bonding of Pure Aluminum Matrix Composite Reinforced with Short Alumina Fiber Using Al-12Si- xTi Foils as Active Interlayer

    NASA Astrophysics Data System (ADS)

    Zhang, Guifeng; Su, Wei; Suzumura, Akio

    2016-06-01

    To optimize both the interlayer composition design route and pressure for joining aluminum matrix composite reinforced with short alumina fiber (as-cast 30 vol pct Al2O3sf/Al), traditional transient liquid phase (TLP) bonding using Al-12Si and Cu interlayer and active-TLP (A-TLP) bonding using an active Ti-containing interlayer (Al-12Si- xTi, x = 0.1, 0.5, and 1 wt pct) under the same condition [883 K (610 °C) × 30 minutes × 1 or 0.015 MPa in flowing argon] were compared in terms of interfacial wettability, bond seam microstructure, shear strength, and fracture path. It was found that not only the Ti content but also the pressure are critical factors affecting interfacial wettability and bond seam microstructure. The improvement in wettability by adding Ti as an active element were confirmed by reduction of expulsion of liquid interlayer, elimination of interfacial gap, higher shear strength and favorable fracture path (partially through bond seam and the composite). Because of the incubation period for wetting, reducing the pressure after melting of the interlayer could further increase joint shear strength by thickening the remaining bond seam of solid-solution matrix and decreasing fraction of the in situ newly formed Al-Si-Ti IMC phase (short bar shape) within the bond seam. The maximum shear strength of 88.6 MPa (99 pct of the as-cast composite) was obtained by adding trace Ti content (0.5 Ti wt pct) addition and using low pressure (0.015 MPa). The results showed that suitable combination of Ti content and pressure pattern is required for improving both wettability and bond seam microstructure.

  4. Hydrodesulfurization on Transition Metal Catalysts: Elementary Steps of C-S Bond Activation and Consequences of Bifunctional Synergies

    NASA Astrophysics Data System (ADS)

    Yik, Edwin Shyn-Lo

    convergence to a single phase is expected and predictable from thermodynamics at a given temperature and sulfur chemical potential, metastability of two phases can exist. We demonstrate, through extensive characterization and kinetic evidence, such behaviors exist in Re, where structural disparities between its phases lead to kinetic hurdles that prevent interconversions between layered ReSx nanostructures and sulfur-covered Re metal clusters. Such features allowed, for the first time, direct comparisons of reaction rates at identical conditions on two disparate phases of the same transition metal identity. Rigorous assessments of kinetic and selectivity data indicated that more universal mechanistic features persist across all catalysts studied, suggesting that differences in their catalytic activity were the result of different densities of HDS sites, which appeared to correlate with their respective metal-sulfur bond energies. Kinetic responses and product distributions indicated that the consumption of thiophene proceeds by the formation of a partially-hydrogenated surface intermediate, which subsequently produces tetrahydrothiophene (THT) and butene/butane (C4) via primary routes on similar types of sites. These sites are formed from desorption of weakly-bound sulfur adatoms on sulfur-covered metal surfaces, which can occur when the heat of sulfur adsorption is sufficiently low at high sulfur coverage as a result of increased sulfur-sulfur repulsive interactions. Relative stabilities and differences in the molecularity of the respective transition states that form THT and C4 dictate product distributions. THT desulfurization to form C4 occurs via readsorption and subsequent dehydrogenation, evidenced by secondary rates that exhibited negative H2 dependences. These behaviors suggest that C-S bond activation occurs on a partially (un)saturated intermediate, analogous to behaviors observed in C-C bond scission reactions of linear and cycloalkanes on hydrogen-covered metal

  5. 15N NMR spectroscopy of hydrogen-bonding interactions in the active site of serine proteases: evidence for a moving histidine mechanism.

    PubMed

    Bachovchin, W W

    1986-11-18

    Nitrogen-15 NMR spectroscopy has been used to study the hydrogen-bonding interactions involving the histidyl residue in the catalytic triad of alpha-lytic protease in the resting enzyme and in the transition-state or tetrahedral intermediate analogue complexes formed with phenylmethanesulfonyl fluoride and diisopropyl fluorophosphate. The 15N shifts indicate that a strong hydrogen bond links the active site histidine and serine residues in the resting enzyme in solution. This result is at odds with interpretations of the X-ray diffraction data of alpha-lytic protease and of other serine proteases, which indicate that the serine and histidine residues are too far apart and not properly aligned for the formation of a hydrogen bond. In addition, the nitrogen-15 shifts demonstrate that protonation of the histidine imidazole ring at low pH in the transition-state or tetrahedral intermediate analogue complexes formed with phenylmethanesulfonyl fluoride and diisopropyl fluorophosphate triggers the disruption of the aspartate-histidine hydrogen bond. These results suggest a catalytic mechanism involving directed movement of the imidazole ring of the active site histidyl residue. PMID:3542033

  6. GaInAsP/silicon-on-insulator hybrid laser with ring-resonator-type reflector fabricated by N2 plasma-activated bonding

    NASA Astrophysics Data System (ADS)

    Hayashi, Yusuke; Suzuki, Junichi; Inoue, Satoshi; Tanvir Hasan, Shovon Muhammad; Kuno, Yuki; Itoh, Kazuto; Amemiya, Tomohiro; Nishiyama, Nobuhiko; Arai, Shigehisa

    2016-08-01

    III–V/Si hybrid integration with direct bonding is an attractive method of realizing an electrophotonic convergence router with a small size and a low power consumption. Plasma-activated bonding (PAB) is an effective approach for reducing thermal stress during the bonding process because PAB achieves a high bonding strength with low-temperature annealing. This time, the fabrication of a GaInAsP/silicon-on-insulator (SOI) hybrid laser with Si ring-resonator-type reflectors was demonstrated by N2 PAB. By measuring the lasing spectra, we confirmed the reflective characteristics resulting from the cascaded Si ring resonators. We also investigated kink characteristics, which occur around the threshold current, of the current–light output (I–L) characteristics, and successfully approximated the kink characteristics by considering saturable absorption occurring at the III–V/Si taper tip. The taper structure was investigated in terms of a passive device as well as an active device, and a structure for eliminating saturable absorption was proposed.

  7. Conjugation-Driven "Reverse Mars-van Krevelen"-Type Radical Mechanism for Low-Temperature C-O Bond Activation.

    PubMed

    Mironenko, Alexander V; Vlachos, Dionisios G

    2016-07-01

    C-O bond activation on monofunctional catalysts (metals, carbides, and oxides) is challenging due to activity constraints imposed by energy scaling relationships. Yet, contrary to predictions, recently discovered multifunctional metal/metal oxide catalysts (e.g., Rh/ReOx, Rh/MoOx, Ir/VOx) demonstrate unusually high C-O scission activity at moderate temperatures. Herein, we use extensive density functional theory calculations, first-principles microkinetic modeling, and electronic structure analysis to elucidate the metal/metal oxide synergy in the Ru/RuO2 catalyst, which enables up to 76% yield of the C-O scission product (2-methyl furan) in catalytic transfer hydrogenolysis of furfural at low temperatures. Our key mechanistic finding is a facile radical-mediated C-O bond activation on RuO2 oxygen vacancies, which directly leads to a weakly bound final product. This is the first time the radical reduction mechanism is reported in heterogeneous catalysis at temperatures <200 °C. We attribute the unique catalytic properties to the formation of a conjugation-stabilized furfuryl radical upon C-O bond scission, the strong hydroxyl affinity of oxygen vacancies due to the metallic character of RuO2, and the acid-base heterogeneity of the oxide surface. The conjugation-driven radical-assisted C-O bond scission applies to any catalytic surface that preserves the π-electron system of the reactant and leads to C-O selectivity enhancement, with notable examples including Cu, H-covered Pd, self-assembled monolayers on Pd, and oxygen-covered Mo2C. Furthermore, we reveal the cooperativity of active sites in multifunctional catalysts. The mechanism is fully consistent with kinetic studies and isotopic labeling experiments, and the insights gained might prove useful more broadly in overcoming activity constraints induced by energy scaling relationships. PMID:27281043

  8. A Substrate-Assisted Mechanism of Nucleophile Activation in a Ser-His-Asp Containing C-C Bond Hydrolase

    SciTech Connect

    Ruzzini, Antonio C.; Bhowmik, Shiva; Ghosh, Subhangi; Yam, Katherine C.; Bolin, Jeffrey T.; Eltis, Lindsay D.

    2013-11-12

    The meta-cleavage product (MCP) hydrolases utilize a Ser–His–Asp triad to hydrolyze a carbon–carbon bond. Hydrolysis of the MCP substrate has been proposed to proceed via an enol-to-keto tautomerization followed by a nucleophilic mechanism of catalysis. Ketonization involves an intermediate, ESred, which possesses a remarkable bathochromically shifted absorption spectrum. We investigated the catalytic mechanism of the MCP hydrolases using DxnB2 from Sphingomonas wittichii RW1. Pre-steady-state kinetic and LC ESI/MS evaluation of the DxnB2-mediated hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid to 2-hydroxy-2,4-pentadienoic acid and benzoate support a nucleophilic mechanism catalysis. In DxnB2, the rate of ESred decay and product formation showed a solvent kinetic isotope effect of 2.5, indicating that a proton transfer reaction, assigned here to substrate ketonization, limits the rate of acylation. For a series of substituted MCPs, this rate was linearly dependent on MCP pKa2nuc ~ 1). Structural characterization of DxnB2 S105A:MCP complexes revealed that the catalytic histidine is displaced upon substrate-binding. The results provide evidence for enzyme-catalyzed ketonization in which the catalytic His–Asp pair does not play an essential role. The data further suggest that ESred represents a dianionic intermediate that acts as a general base to activate the serine nucleophile. This substrate-assisted mechanism of nucleophilic catalysis distinguishes MCP hydrolases from other serine hydrolases.

  9. Transition metal activation and functionalization of C-H (carbon-hydrogen) bonds: Progress report for period June 1, 1986-November 30, 1987

    SciTech Connect

    Jones, W.D.

    1987-08-01

    The fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers were investigated. The project was also directed towards the conversion of hydrocarbons into functionalized products of potential use to chemical industry. Goals during the grant period were (1) to identify new transition metal complexes capable of activating arene and alkane C-H bonds, (2) to quantitatively evaluate the kinetic and thermodynamic stability of these complexes, and (3) to examine routes for functionalization of the activated hydrocarbons. The specific complexes involved in these studies were derivatives of the formulation (C/sub 2/Me/sub 5/)Rh(PR/sub 3/)(R)H, Fe(PMe/sub 3/)/sub 2/(CNR)/sub 3/, Ru(PR/sub 3/)/sub 4/(R)H, and Rh(CNR)/sub 3/H. Functionalization focused upon isocyanide and acetylene insertion reactions. New compounds that activated hydrocarbon C-H bonds include HRe(PR/sub 3/)/sub 5/, HRe(PR/sub 3/)/sub 2/(CNR)/sub 3/, CpRe(Pr/sub 3/)H/sub 4/, CpRe(PR/sub 3/)/sub 2/H/sub 2/, and (eta/sup 6/-C/sub 6/H/sub 6/)Re(PPh/sub 3/)/sub 2/H. 7 figs., 1 tab.

  10. Distinguishing Bonds.

    PubMed

    Rahm, Martin; Hoffmann, Roald

    2016-03-23

    The energy change per electron in a chemical or physical transformation, ΔE/n, may be expressed as Δχ̅ + Δ(VNN + ω)/n, where Δχ̅ is the average electron binding energy, a generalized electronegativity, ΔVNN is the change in nuclear repulsions, and Δω is the change in multielectron interactions in the process considered. The last term can be obtained by the difference from experimental or theoretical estimates of the first terms. Previously obtained consequences of this energy partitioning are extended here to a different analysis of bonding in a great variety of diatomics, including more or less polar ones. Arguments are presented for associating the average change in electron binding energy with covalence, and the change in multielectron interactions with electron transfer, either to, out, or within a molecule. A new descriptor Q, essentially the scaled difference between the Δχ̅ and Δ(VNN + ω)/n terms, when plotted versus the bond energy, separates nicely a wide variety of bonding types, covalent, covalent but more correlated, polar and increasingly ionic, metallogenic, electrostatic, charge-shift bonds, and dispersion interactions. Also, Q itself shows a set of interesting relations with the correlation energy of a bond. PMID:26910496

  11. Strained Si-O-Si bonds in amorphous SiO2 materials: A family member of active centers in radio, photo, and chemical responses

    NASA Astrophysics Data System (ADS)

    Awazu, Koichi; Kawazoe, Hiroshi

    2003-11-01

    Amorphous SiO2 (a-SiO2), such as bulk silica glasses and thin films has been one of the key materials in modern optoelectronic industries. These materials are currently used in communication technologies as optical fibers, thin films for electrical insulation in dynamic random access memories (DRAM), and optical lenses for excimer laser lithography, for example. The property essential for these applications is the wide band gap amounting to ˜9 eV. However, bulk silica glasses commercially available and silica thin films show photoresponses to subband gap lights in the vicinity of 5 eV and unexpected trapping of charges, and the behavior has a strong dependency on the preparation history. A number of studies were carried out to clarify the relationship between the properties and structural imperfections in the materials and the formation mechanisms of the defects. There are two categories of the imperfections: one is dopant- or impurity-related imperfections and the other is nonstoichiometry related defects. These defects constitute gap states in a-SiO2. The structural identification was usually performed by absorption and emission spectroscopy in the visible-ultraviolet (UV) region and electron spin resonance (ESR). The experimentally proposed models were compared with the predictions by theoretical calculations of energy levels. Recent development of the excimer laser lithography technique led us to recognize that a latent member, which has been unnoticed because of no response to the optical absorption or emission in the visible-UV range and ESR absorption, exists in the family of active centers in a-SiO2, that is a strained Si-O-Si bond originating from the planar three membered ring. In contrast, the puckered four membered ring is unstrained. Although it has been pointed out that there was a wide distribution in Si-O-Si bond angle from 90° to 180° by x-ray analysis or 29Si solid state nuclear magnetic resonance, the physical, and chemical responses of the Si

  12. Rhodium-catalysed C(sp2)–C(sp2) bond formation via C–H/C–F activation

    PubMed Central

    Tian, Panpan; Feng, Chao; Loh, Teck-Peng

    2015-01-01

    Fluoroalkenes represent a class of privileged structural motifs, which found widespread use in medicinal chemistry. However, the synthetic access to fluoroalkenes was much underdeveloped with previous reported methods suffering from either low step economy or harsh reaction conditions. Here we present a RhIII-catalysed tandem C–H/C–F activation for the synthesis of (hetero)arylated monofluoroalkenes. The use of readily available gem-difluoroalkenes as electrophiles provides a highly efficient and operationally simple method for the introduction of α-fluoroalkenyl motifs onto (hetero)arenes under oxidant-free conditions. Furthermore, the employment of alcoholic solvent and the in-situ generated hydrogen fluoride are found to be beneficial in this transformation, indicating the possibility of the involvement of hydrogen bond activation mode with regards to the C–F bond cleavage step. PMID:26081837

  13. Comparison of the kinetics of S-S bond, secondary structure, and active site formation during refolding of reduced denatured hen egg white lysozyme.

    PubMed Central

    Roux, P.; Ruoppolo, M.; Chaffotte, A. F.; Goldberg, M. E.

    1999-01-01

    To investigate the role of some tertiary interactions, the disulfide bonds, in the early stages of refolding of hen lysozyme, we report the kinetics of reoxidation of denatured and reduced lysozyme under the same refolding conditions as those previously used to investigate the kinetics of regain of its circular dichroism (CD), fluorescence, and activity. At different stages of the refolding, the oxidation of the protein was blocked by alkylation of the free cysteines with iodoacetamide and the various oxidation states present in the samples were identified by electrospray-mass spectrometry. Thus, it was possible to monitor the appearance and/or disappearance of the species with 0 to 4 disulfide bonds. Using a simulation program, these kinetics were compared with those of regain of far-UV CD, fluorescence, and enzymatic activity and were discussed in terms of a refined model for the refolding of reduced hen egg white lysozyme. PMID:10631992

  14. Theoretical study of optical activity of 1:1 hydrogen bond complexes of water with S-warfarin.

    PubMed

    Dadsetani, Mehrdad; Abdolmaleki, Ahmad; Zabardasti, Abedin

    2016-11-01

    The molecular interaction between S-warfarin (SW) and a single water molecule was investigated using the B3LYP method at 6-311++G(d,p) basis set. The vibrational spectra of the optimized complexes have been investigated for stabilization checking. Quantum theories of atoms in molecules, natural bond orbitals, molecular electrostatic potentials and energy decomposition analysis methods have been applied to analyze the intermolecular interactions. The intermolecular charge transfer in the most stable complex is in the opposite direction from those in the other complexes. The optical spectra and the hyperpolarizabilities of SW-water hydrogen bond complexes have been computed. PMID:27294546

  15. The Comparative Evaluation of Antibacterial Activity of Methacryloxydodecyl Pyridinium Bromide and Non-methacryloxydodecyl Pyridinium Bromide Dentin Bonding Systems Using Two Different Techniques: An In vitro Study

    PubMed Central

    Deshpande, Prashanth; Nainan, Mohan Thomas; Metta, Kiran Kumar; Shivanna, Vasundhara; Ravi, Ramkrishna; Prashanth, B R

    2014-01-01

    Background: Adhesive systems have enabled clinicians to preserve more tooth structure by changing cavity designs. However, because of the polymerization shrinkage adhesive systems are not capable of totally prohibiting the gap formation between the cavity and restorative material of composite resin leading to colonization of oral microorganisms from saliva. One possible solution for this serious problem is to use dental materials with antibacterial properties. So the development of such agents has initiated for successful restorations. Hence, the purpose of this study was to compare the antibacterial activities of two dentin bonding systems: Clearfil protect bond (CPB) and prime & bond NT using agar well technique and tooth cavity model. Materials and Methods: CPB and prime and bond NT (PBNT) were evaluated in this study using agar well technique and tooth cavity model. In the agar well technique, the materials were filled in the wells of Muller-Hinton agar plates inoculated with Streptococcus mutans NCTC 10449M and the diameter of inhibition zones produced around the materials were measured after 24 h of incubation. For the tooth cavity model test, 3 cavities (of diameter - 1 mm and depth - 2 mm) were prepared in the flat occlusal dentin of human extracted molar. After sterilization, the teeth were left in the culture of broth of S. mutans at 37°C for 72 h for allowing bacteria to invade the cavity for 72 h. The dentin bonding systems were applied separately to each of the two infected cavities, and the third cavity was not applied and used as control. After sealing the occlusal surfaces, the teeth were kept in sterile physiological saline at 37°C for 72 h. The standardized amounts of dentin chips (120 + 5 mg) were obtained from the cavity walls, and the numbers of bacteria recovered were determined. The results were analyzed using one-way ANOVA, Kruskal–Wallis and Mann–Whitney’s U-tests. Results: The primer of CPB and PBNT produced similar inhibition

  16. Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin

    NASA Astrophysics Data System (ADS)

    Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T.

    2013-01-01

    In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the σ* and π* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis.

  17. Cu(II)-mediated C-S/N-S bond formation via C-H activation: access to benzoisothiazolones using elemental sulfur.

    PubMed

    Chen, Fa-Jie; Liao, Gang; Li, Xin; Wu, Jun; Shi, Bing-Feng

    2014-11-01

    A copper-mediated C-S/N-S bond-forming reaction via C-H activation that uses elemental sulfur has been developed. The addition of TBAI was found to be crucial for the success of this transformation. The method is scalable, shows excellent functional group tolerance, and is compatible with heterocycle substrates, providing efficient and practical access to benzoisothiazolones. The direct diversification of the benzoisothiazolone products into a variety of sulfur-containing compounds is also demonstrated. PMID:25325568

  18. Rhodium(III)-Catalyzed C-H Activation/Alkyne Annulation by Weak Coordination of Peresters with O-O Bond as an Internal Oxidant.

    PubMed

    Mo, Jiayu; Wang, Lianhui; Cui, Xiuling

    2015-10-16

    A redox-economic strategy has been developed, involved in an efficient Rh(III)-catalyzed oxidative C-H activation and alkyne annulation with perester as the oxidizing directing group. In this process, the cleavage of an oxidizing O-O bond as an internal oxidant is described for the first time. This reaction could be carried out under mild conditions and exhibits excellent regioselectivity and wide functional groups tolerance. PMID:26414431

  19. Activation of C-F bonds in fluoroarenes by N-heterocyclic carbenes as an effective route to synthesize abnormal NHC complexes.

    PubMed

    Kim, Youngsuk; Lee, Eunsung

    2016-09-18

    IPr (1a) reacts with octafluorotoluene by an unexpected sequential substitution of fluorides in two separate rings. The resulting tetrasubstituted imidazolium salt was isolated and elaborated into Ag(i) and Au(i) complexes with a novel abnormal NHC ligand. Both IPr (1a) and IMes (1b) were also found to be moderately reactive by nucleophilic substitution of the aromatic C-F bond in a weakly-activated fluoroarene, 1-fluoro-4-trifluoromethylbenzene (5). PMID:27533338

  20. Total Synthesis of cis-Clavicipitic Acid from Asparagine via Ir-Catalyzed C-H bond Activation as a Key Step.

    PubMed

    Tahara, Yu-ki; Ito, Mamoru; Kanyiva, Kyalo Stephen; Shibata, Takanori

    2015-08-01

    4-Substituted tryptophan derivatives and the total synthesis of cis-clavicipitic acid were achieved in reactions in which Ir-catalyzed C-H bond activation was a key step. The starting material for these reactions is asparagine, which is a cheap natural amino acid. The reductive amination step from the 4-substituted tryptophan derivative gave cis-clavicipitic acid with perfect diastereoselectivity. PMID:26178075

  1. Synthesis of Ketones through Microwave Irradiation Promoted Metal-Free Alkylation of Aldehydes by Activation of C(sp(3))-H Bond.

    PubMed

    Zhang, Xinying; Wang, Zhangxin; Fan, Xuesen; Wang, Jianji

    2015-11-01

    In this paper, a novel methodology for the synthesis of ketones via microwave irradiation promoted direct alkylation of aldehydes by activation of the inert C(sp(3))-H bond has been developed. Notably, the reactions were accomplished under metal-free conditions and used commercially available aldehydes and cycloalkanes as substrates without prefunctionalization. By using this novel method, an alternative synthetic approach toward the key intermediates for the preparation of the pharmaceutically valuable oxaspiroketone derivatives was successfully established. PMID:26457376

  2. Studies on pharmacological activation of human serum immunoglobulin G by chemical modification and active subfragments. IV. Induction of anti-inflammatory activity by chemical cleavage of interchain disulfide bonds in human immunoglobulin G and pharmacological activity of alkylated subfragments.

    PubMed

    Mimura, T; Tsujikawa, K; Nakajima, H; Okabe, M; Kohama, Y; Iwai, M; Yokoyama, K

    1986-01-01

    Commercially available human serum immunoglobulin G (IgG, native IgG) was separated into two fractions (Fr.I and II) using a diethylaminoethyl cellulose column. Heavy and light chains containing fractions were obtained from these two fractions after carboxamide-methylation. Thus, these fractions were subjected to an anti-inflammatory screening procedure and were shown to have a potent inhibitory activity against rat carrageenin induced paw edema, while no effect was observed in native IgG, Fr.I or II. The reduction and alkylation of the interchain disulfide bonds were essential to induce the anti-inflammatory activity. The anti-inflammatory activity of alkylated heavy and light chains of Fr.I (Fr.I-H and I-L) was also noted in subacute inflammation caused by the felt pellet and croton oil granuloma methods. Moreover, strong membrane stabilizing activities of Fr.I-H and I-L were demonstrated in vitro using rat red blood cell membrane and liver lysosomal membrane. PMID:3712209

  3. Activation of C-H Bonds in Pt(+) + x CH4 Reactions, where x = 1-4: Identification of the Platinum Dimethyl Cation.

    PubMed

    Wheeler, Oscar W; Salem, Michelle; Gao, Amanda; Bakker, Joost M; Armentrout, P B

    2016-08-11

    Activation of C-H bonds in the sequential reactions of Pt(+) + x(CH4/CD4), where x = 1-4, have been investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theoretical calculations. Pt(+) cations are formed by laser ablation and exposed to controlled amounts of CH4/CD4 leading to [Pt,xC,(4x-2)H/D](+) dehydrogenation products. Irradiation of these products in the 400-2100 cm(-1) range leads to CH4/CD4 loss from the x = 3 and 4 products, whereas PtCH2(+)/PtCD2(+) products do not decompose at all, and x = 2 products dissociate only when formed from a higher order product. The structures of these complexes were explored theoretically at several levels of theory with three different basis sets. Comparison of the experimental and theoretical results indicate that the species formed have a Pt(CH3)2(+)(CH4)x-2/Pt(CD3)2(+)(CD4)x-2 binding motif for x = 2-4. Thus, reaction of Pt(+) with methane occurs by C-H bond activation to form PtCH2(+), which reacts with an additional methane molecule by C-H bond activation to form the platinum dimethyl cation. This proposed reaction mechanism is consistent with theoretical explorations of the potential energy surface for reactions of Pt(+) with one and two methane molecules. PMID:27438025

  4. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    SciTech Connect

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  5. Foster Mother-Infant Bonding: Associations between Foster Mothers' Oxytocin Production, Electrophysiological Brain Activity, Feelings of Commitment, and Caregiving Quality

    ERIC Educational Resources Information Center

    Bick, Johanna; Dozier, Mary; Bernard, Kristin; Grasso, Damion; Simons, Robert

    2013-01-01

    This study examined the biological processes associated with foster mother-infant bonding. In an examination of foster mother-infant dyads ("N" = 41, mean infant age = 8.5 months), foster mothers' oxytocin production was associated with their expressions of behavioral delight toward their foster infant and their average P3 response to images of…

  6. Enhancing Students' Understanding of the Concept of "Chemical Bonding" by Using Activities Provided on an Interactive Website

    ERIC Educational Resources Information Center

    Frailich, Marcel; Kesner, Miri; Hofstein, Avi

    2009-01-01

    This study investigated the effectiveness of a web-based learning environment in enhancing 10th grade high-school students' understanding of the concept of "chemical bonding". Two groups participated in this study: an experimental group (N = 161) and a comparison one (N = 93). The teachers in the experimental group were asked to implement four…

  7. Comparison of insect kinin analogs with cis-peptide bond motif 4-aminopyroglutamate identifies optimal stereochemistry for diuretic activity.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The insect kinins are present in a wide variety of insects and function as potent diuretic peptides, though they are subject to rapid degradation by internal peptidases. Insect kinin analogs incorporating stereochemical variants of (2S,4S)-4-aminopyroglutamate (APy), a cis-peptide bond motif, demon...

  8. The Chemical Bond in C2.

    PubMed

    Hermann, Markus; Frenking, Gernot

    2016-03-14

    Quantum chemical calculations using the complete active space of the valence orbitals have been carried out for Hn CCHn (n=0-3) and N2 . The quadratic force constants and the stretching potentials of Hn CCHn have been calculated at the CASSCF/cc-pVTZ level. The bond dissociation energies of the C-C bonds of C2 and HC≡CH were computed using explicitly correlated CASPT2-F12/cc-pVTZ-F12 wave functions. The bond dissociation energies and the force constants suggest that C2 has a weaker C-C bond than acetylene. The analysis of the CASSCF wavefunctions in conjunction with the effective bond orders of the multiple bonds shows that there are four bonding components in C2 , while there are only three in acetylene and in N2 . The bonding components in C2 consist of two weakly bonding σ bonds and two electron-sharing π bonds. The bonding situation in C2 can be described with the σ bonds in Be2 that are enforced by two π bonds. There is no single Lewis structure that adequately depicts the bonding situation in C2 . The assignment of quadruple bonding in C2 is misleading, because the bond is weaker than the triple bond in HC≡CH. PMID:26756311

  9. Yankee bonds

    SciTech Connect

    Delaney, P. )

    1993-10-01

    Yankee and Euromarket bonds may soon find their way into the financing of power projects in Latin America. For developers seeking long-term commitments under build, own, operate, and transfer (BOOT) power projects in Latin America, the benefits are substantial.

  10. Effects of hydrogen peroxide pretreatment and heat activation of silane on the shear bond strength of fiber-reinforced composite posts to resin cement

    PubMed Central

    Shin, Tae-Bong; Lee, Joo-Hee; Ahn, Kang-Min; Kim, Tae-Hyung

    2016-01-01

    PURPOSE To evaluate the effects of hydrogen peroxide pretreatment and heat activation of silane on the shear bond strength of fiber-reinforced composite posts to resin cement. MATERIALS AND METHODS The specimens were prepared to evaluate the bond strength of epoxy resin-based fiber posts (D.T. Light-Post) to dual-curing resin cement (RelyX U200). The specimens were divided into four groups (n=18) according to different surface treatments: group 1, no treatment; group 2, silanization; group 3, silanization after hydrogen peroxide etching; group 4, silanization with warm drying at 80℃ after hydrogen peroxide etching. After storage of the specimens in distilled water at 37℃ for 24 hours, the shear bond strength (in MPa) between the fiber post and resin cement was measured using a universal testing machine. The fractured surface of the fiber post was examined using scanning electron microscopy. Data were analyzed using one-way ANOVA and post-hoc analysis with Tukey's HSD test (α=0.05). RESULTS Silanization of the fiber post (Group 2) significantly increased the bond strength in comparison with the non treated control (Group 1) (P<.05). Heat drying after silanization also significantly increased the bond strength (Group 3 and 4) (P<.05). However, no effect was determined for hydrogen peroxide etching before applying silane agent (Group 2 and 3) (P>.05). CONCLUSION Fiber post silanization and subsequent heat treatment (80℃) with warm air blower can be beneficial in clinical post cementation. However, hydrogen peroxide etching prior to silanization was not effective in this study. PMID:27141252

  11. Promotional effects of chemisorbed oxygen and hydroxide in the activation of C-H and O-H bonds over transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Hibbitts, David; Neurock, Matthew

    2016-08-01

    Electronegative coadsorbates such as atomic oxygen (O*) and hydroxide (OH*) can act as Brønsted bases when bound to Group 11 as well as particular Group 8-10 metal surfaces and aid in the activation of X-H bonds. First-principle density functional theory calculations were carried out to systematically explore the reactivity of the C-H bonds of methane and surface methyl intermediates as well as the O-H bond of methanol directly and with the assistance of coadsorbed O* and OH* intermediates over Group 11 (Cu, Ag, and Au) and Group 8-10 transition metal (Ru, Rh, Pd, Os, Ir, and Pt) surfaces. C-H as well as O-H bond activation over the metal proceeds via a classic oxidative addition type mechanism involving the insertion of the metal center into the C-H or O-H bond. O* and OH* assist C-H and O-H activation over particular Group 11 and Group 8-10 metal surfaces via a σ-bond metathesis type mechanism involving the oxidative addition of the C-H or O-H bond to the metal along with a reductive deprotonation of the acidic C-H and O-H bond over the M-O* or M-OH* site pair. The O*- and OH*-assisted C-H activation paths are energetically preferred over the direct metal catalyzed C-H scission for all Group 11 metals (Cu, Ag, and Au) with barriers that are 0.4-1.5 eV lower than those for the unassisted routes. The barriers for O*- and OH*-assisted C-H activation of CH4 on the Group 8-10 transition metals, however, are higher than those over the bare transition metal surfaces by as much as 1.4 eV. The C-H activation of adsorbed methyl species show very similar trends to those for CH4 despite the differences in structure between the weakly bound methane and the covalently adsorbed methyl intermediates. The activation of the O-H bond of methanol is significantly promoted by O* as well as OH* intermediates over both the Group 11 metals (Cu, Ag, and Au) as well as on all Group 8-10 metals studied (Ru, Rh, Pd, Os, Ir, and Pt). The O*- and OH*-assisted CH3O-H barriers are 0.6 to 2

  12. STC-SAB program users manual for the turbulent boundary layer and turbulent separation prediction methods employed in the NASA Langley streamtube curvature computer program

    NASA Technical Reports Server (NTRS)

    Ferguson, D. R.

    1972-01-01

    The streamtube curvature program (STC) has been developed to predict the inviscid flow field and the pressure distribution about nacelles at transonic speeds. The effects of boundary layer are to displace the inviscid flow and effectively change the body shape. Thus, the body shape must be corrected by the displacement thickness in order to calculate the correct pressure distribution. This report describes the coupling of the Stratford and Beavers boundary layer solution with the inviscid STC analysis so that all nacelle pressure forces, friction drag, and incipient separation may be predicted. The usage of the coupled STC-SAB computer program is outlined and the program input and output are defined. Included in this manual are descriptions of the principal boundary layer tables and other revisions to the STC program. The use of the viscous option is controlled by the engineer during program input definition.

  13. Fabrication of Si/SiO2/GaN structure by surface-activated bonding for monolithic integration of optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Tsuchiyama, Kazuaki; Yamane, Keisuke; Sekiguchi, Hiroto; Okada, Hiroshi; Wakahara, Akihiro

    2016-05-01

    A Si/SiO2/GaN-light-emitting-diode (LED) wafer is proposed as a new structure for the monolithic integration of both Si circuits and GaN-based optical devices. Surface-activated bonding was performed to transfer a Si layer from a silicon-on-insulator substrate to a SiO2/GaN-LED substrate. Transmission electron microscopy observation revealed that a defect-free Si layer was formed on the SiO2/GaN-LED substrate without interfacial voids. The crystalline quality of the Si layer, which is characterized by an X-ray rocking curve, was markedly improved by flattening the SiO2/GaN-LED substrate before bonding. Finally, a micro-LED array was successfully fabricated on the Si/SiO2/GaN-LED wafer without the delamination of the Si layer.

  14. Computational SN 2-Type Mechanism for the Difluoromethylation of Lithium Enolate with Fluoroform through Bimetallic C-F Bond Dual Activation.

    PubMed

    Honda, Kazuya; Harris, Travis V; Hatanaka, Miho; Morokuma, Keiji; Mikami, Koichi

    2016-06-20

    The reaction mechanism for difluoromethylation of lithium enolates with fluoroform was analyzed computationally (DFT calculations with the artificial force induced reaction (AFIR) method and solvation model based on density (SMD) solvation model (THF)), showing an SN 2-type carbon-carbon bond formation; the "bimetallic" lithium enolate and lithium trifluoromethyl carbenoid exert the C-F bond "dual" activation, in contrast to the monometallic butterfly-shaped carbenoid in the Simmons-Smith reaction. Lithium enolates, generated by the reaction of 2 equiv. of lithium hexamethyldisilazide (rather than 1 or 3 equiv.) with the cheap difluoromethylating species fluoroform, are the most useful alkali metal intermediates for the synthesis of pharmaceutically important α-difluoromethylated carbonyl products. PMID:26992061

  15. Metal-catalyzed activation of ethers via C-O bond cleavage: a new strategy for molecular diversity.

    PubMed

    Cornella, Josep; Zarate, Cayetana; Martin, Ruben

    2014-12-01

    In 1979, the seminal work of Wenkert set the standards for the utilization of aryl and vinyl ethers as coupling partners via C-O bond-cleavage. Although the topic remained dormant for almost three decades, the last few years have witnessed a renaissance in this area of expertise, experiencing an exponential growth and becoming a significant discipline within the cross-coupling arena. The means to utilize readily accessible aryl or vinyl ethers as counterparts does not only represent a practical, powerful and straightforward alternative to organic halides, but also constitutes an excellent opportunity to improve our chemical knowledge about a relatively unexplored area of expertise. This review summarizes the most significant developments in the area of C-O bond-cleavage when employing aryl or vinyl ethers, providing a detailed overview of the current state of the art and including future aspects, when applicable. PMID:25157613

  16. Bismuth Undecahydro-closo-dodecaborane: A Retainable Intermediate of B-H Bond Activation by Bismuth(III) Cations.

    PubMed

    Zimmermann, Lucas W; Van, Nguyen-Duc; Gudat, Dietrich; Schleid, Thomas

    2016-01-26

    The [B12 H12](2-) anion shows an extensive substitutional chemistry based on its three-dimensional aromaticity. The replacement of functional groups can be attained by electrophilically induced substitution caused by Brønsted or Lewis acidic electrophiles (e.g. Pt(2+)). Until now, it was impossible to structurally characterize a metal-substituted [B12 H12](2-) cage. When an aqueous solution containing both Bi(3+) cations and [B12 H12](2-) anions was heated, the charge-neutral bismuth undecahydro-closo-dodecaborane BiB12 H11 was obtained, representing a new class of metalated [B12 H12](2-) clusters. The title compound was characterized by single-crystal X-ray diffraction and NMR spectroscopic methods. Compared to the typical B-H bond, the short B-Bi single bond (230 pm) exhibits inverted polarity. PMID:26676462

  17. 26 CFR 1.103(n)-4T - Elective carryforward of unused private activity bond limit (temporary).

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... carryforward for any one or more projects described in A-5 of this § 1.103(n)-4T (carryforward projects). Q-2... titled “Carryforward election under section 103(n)”. (ii) The statement required by (i) of this A-2 shall... bond limit (temporary). 1.103(n)-4T Section 1.103(n)-4T Internal Revenue INTERNAL REVENUE...

  18. 26 CFR 1.103(n)-4T - Elective carryforward of unused private activity bond limit (temporary).

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... carryforward for any one or more projects described in A-5 of this § 1.103(n)-4T (carryforward projects). Q-2... titled “Carryforward election under section 103(n)”. (ii) The statement required by (i) of this A-2 shall... bond limit (temporary). 1.103(n)-4T Section 1.103(n)-4T Internal Revenue INTERNAL REVENUE...

  19. Diffusion bonding

    DOEpatents

    Anderson, Robert C.

    1976-06-22

    1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

  20. The thermodynamics and kinetics of phosphoester bond formation, use, and dissociation in biology, with the example of polyphosphate in platelet activation, trasience, and mineralization.

    NASA Astrophysics Data System (ADS)

    Omelon, S. J.

    2014-12-01

    Mitochondria condense orthophosphates (Pi), forming phosphoester bonds for ATP production that is important to life. This represents an exchange of energy from dissociated carbohydrate bonds to phosophoester bonds. These bonds are available to phosphorylate organic compounds or hydrolyze to Pi, driving many biochemical processes. The benthic bacteria T. namibiensis 1 and Beggiatoa 2 condense Pi into phosphate polymers in oxygenated environments. These polyphosphates (polyPs) are stored until the environment becomes anoxic, when these bacteria retrieve the energy from polyP dissociation into Pi3. Dissociated Pi is released outside of the bacteria, where it precipitates as apatite.The Gibbs free energy of polyP phosphoester bond hydrolysis is negative, however, the kinetics are slow4. Diatoms contain a polyP pool that is stable until after death, after which the polyPs hydrolyze and form apatite5. The roles of polyP in eukaryotic organism biochemistry continue to be discovered. PolyPs have a range of biochemical roles, such as bioavailable P-storage, stress adaptation, and blood clotting6. PolyP-containing granules are released from anuclear platelets to activate factor V7 and factor XII in the blood clotting process due to their polyanionic charge8. Platelets have a lifespan of approximately 8 days, after which they undergo apoptosis9. Data will be presented that demonstrate the bioactive, thermodynamically unstable polyP pool within older platelets in vitro can spontaneously hydrolyze and form phosphate minerals. This process is likely avoided by platelet digestion in the spleen and liver, possibly recycling platelet polyPs with their phosphoester bond energy for other biochemical roles. 1 Schulz HN et al. Science (2005) 307: 416-4182 Brüchert V et al. Geochim Cosmochim Acta (2003) 67: 4505-45183 Goldhammer T et al. Nat Geosci (2010) 3: 557-5614 de Jager H-J et al. J Phys Chem A (1988) 102: 2838-28415 Diaz, J et al. Science (2008) 320: 652-6556 Mason KD et al

  1. A catalytic diad involved in substrate-assisted catalysis: NMR study of hydrogen bonding and dynamics at the active site of phosphatidylinositol-specific phospholipase C.

    PubMed

    Ryan, M; Liu, T; Dahlquist, F W; Griffith, O H

    2001-08-14

    Phosphatidylinositol-specific phospholipase Cs (PI-PLCs, EC 3.1.4.10) are ubiquitous enzymes that cleave phosphatidylinositol or phosphorylated derivatives, generating second messengers in eukaryotic cells. A catalytic diad at the active site of Bacillus cereus PI-PLC composed of aspartate-274 and histidine-32 was postulated from the crystal structure to form a catalytic triad with the 2-OH group of the substrate [Heinz, D. W., et al. (1995) EMBO J. 14, 3855-3863]. This catalytic diad has been observed directly by proton NMR. The single low-field line in the 1H NMR spectrum is assigned by site-directed mutagenesis: The peak is present in the wild type but absent in the mutants H32A and D274A, and arises from the histidine Hdelta1 forming the Asp274-His32 hydrogen bond. This hydrogen is solvent-accessible, and exchanges slowly with H2O on the NMR time scale. The position of the low-field peak shifts from 16.3 to 13.8 ppm as the pH is varied from 4 to 9, reflecting a pKa of 8.0 at 6 degrees C, which is identified with the pKa of His32. The Hdelta1 signal is modulated by rapid exchange of the Hepsilon2 with the solvent. Estimates of the exchange rate as a function of pH and protection factors are derived from a line shape analysis. The NMR behavior is remarkably similar to that of the serine proteases. The postulated function of the Asp274-His32 diad is to hydrogen-bond with the 2-OH of phosphatidylinositol (PI) substrate to form a catalytic triad analogous to Asp-His-Ser of serine proteases. This is an example of substrate-assisted catalysis where the substrate provides the catalytic nucleophile of the triad. This hydrogen bond becomes shorter as the imidazole is protonated, suggesting it is stronger in the transition state, contributing further to the catalytic efficiency. The hydrogen bond fits the NMR criteria for a short, strong hydrogen bond, i.e., a highly deshielded proton resonance, bond length of 2.64 +/- 0.04 A at pH 6 measured by NMR, a D/H fractionation

  2. The conserved His8 of the Moloney murine leukemia virus Env SU subunit directs the activity of the SU-TM disulphide bond isomerase

    SciTech Connect

    Li Kejun; Zhang, Shujing; Kronqvist, Malin; Ekstroem, Maria; Wallin, Michael; Garoff, Henrik . E-mail: henrik.garoff@cbt.ki.se

    2007-04-25

    Murine leukemia virus (MLV) fusion is controlled by isomerization of the disulphide bond between the receptor-binding surface (SU) and fusion-active transmembrane subunits of the Env-complex. The bond is in SU linked to a CXXC motif. This carries a free thiol that upon receptor binding can be activated (ionized) to attack the disulphide and rearrange it into a disulphide isomer within the motif. To find out whether His8 in the conserved SPHQ sequence of Env directs thiol activation, we analyzed its ionization in MLV vectors with wtEnv and Env with His8 deleted or substituted for Tyr or Arg, which partially or completely arrests fusion. The ionization was monitored by following the pH effect on isomerization in vitro by Ca{sup 2+} depletion or in vivo by receptor binding. We found that wtEnv isomerized optimally at slightly basic pH whereas the partially active mutant required higher and the inactive mutants still higher pH. This suggests that His8 directs the ionization of the CXXC thiol.

  3. Role for the disulfide-bonded region of human immunodeficiency virus type 1 gp41 in receptor-triggered activation of membrane fusion function

    SciTech Connect

    Bellamy-McIntyre, Anna K.; Baer, Severine; Ludlow, Louise; Drummer, Heidi E.; Poumbourios, Pantelis

    2010-04-16

    The conserved disulfide-bonded region (DSR) of the human immunodeficiency virus type 1 (HIV-1) fusion glycoprotein, gp41, mediates association with the receptor-binding glycoprotein, gp120. Interactions between gp120, CD4 and chemokine receptors activate the fusion activity of gp41. The introduction of W596L and W610F mutations to the DSR of HIV-1{sub QH1549.13} blocked viral entry and hemifusion without affecting gp120-gp41 association. The fusion defect correlated with inhibition of CD4-triggered gp41 pre-hairpin formation, consistent with the DSR mutations having decoupled receptor-induced conformational changes in gp120 from gp41 activation. Our data implicate the DSR in sensing conformational changes in the gp120-gp41 complex that lead to fusion activation.

  4. Substrate-Triggered Activation of a Synthetic [Fe2(μ-O)2] Diamond Core for C–H Bond Cleavage

    PubMed Central

    Xue, Genqiang; Pokutsa, Alexander; Que, Lawrence

    2011-01-01

    An [FeIV2(μ-O)2] diamond core structure has been postulated for intermediate Q of soluble methane monooxygenase (sMMO-Q), the oxidant responsible for cleaving the strong C–H bond of methane and its hydroxylation. By extension, analogous species may be involved in the mechanisms of related diiron hydroxylases and desaturases. Due to the paucity of well-defined synthetic examples, there are few, if any, mechanistic studies on the oxidation of hydrocarbon substrates by complexes with high-valent [Fe2(μ-O)2] cores. We report here that water or alcohol substrates can activate synthetic [FeIIIFeIV(μ-O)2] complexes supported by tetradentate tris(pyridyl-2-methyl)amine ligands (1 and 2) by several orders of magnitude for C–H bond oxidation. On the basis of detailed kinetic studies, it is postulated that the activation results from Lewis base attack on the [FeIIIFeIV(μ-O)2] core, resulting in the formation of a more reactive species with a [X–FeIII–O–FeIV=O] ring-opened structure (1-X, 2-X, X = OH− or OR−). Treatment of 2 with methoxide at −80 °C forms the 2-methoxide adduct in high yield, which is characterized by an S = 1/2 EPR signal indicative of an antiferromagnetically coupled [S = 5/2 FeIII/S = 2 FeIV] pair. Even at this low temperature, the complex undergoes facile intramolecular C–H bond cleavage to generate formaldehyde, showing that the terminal high-spin FeIV=O unit is capable of oxidizing a C–H bond as strong as 96 kcal mol−1. This intramolecular oxidation of the methoxide ligand can in fact be competitive with intermolecular oxidation of triphenylmethane, which has a much weaker C–H bond (DC-H 81 kcal mol−1). The activation of the [FeIIIFeIV(μ-O)2] core is dramatically illustrated by the oxidation of 9,10-dihydroanthracene by 2-methoxide, which has a second order rate constant that is 3.6 x 107-fold larger than that for the parent diamond core complex 2. These observations provide strong support for the DFT-based notion that an

  5. Driving Forces for Covalent Assembly of Porphyrins by Selective C-H Bond Activation and Intermolecular Coupling on a Copper Surface.

    PubMed

    Floris, Andrea; Haq, Sam; In't Veld, Mendel; Amabilino, David B; Raval, Rasmita; Kantorovich, Lev

    2016-05-11

    Recent synthesis of covalent organic assemblies at surfaces has opened the promise of producing robust nanostructures for functional interfaces. To uncover how this new chemistry works at surfaces and understand the underlying mechanisms that control bond-breaking and bond-making processes at specific positions of the participating molecules, we study here the coupling reaction of tetra(mesityl)porphyrin molecules, which creates covalently connected networks on the Cu(110) surface by utilizing the 4-methyl groups as unique connection points. Using scanning tunneling microscopy (STM), state-of-the-art density functional theory (DFT), and Nudged Elastic Band (NEB) calculations, we show that the unique directionality of the covalent bonding is found to stem from a chain of highly selective C-H activation and dehydrogenation processes, followed by specific intermolecular C-C coupling reactions that are facilitated by the surface, by steric constraints, and by anisotropic molecular diffusion. These insights provide the first steps toward developing synthetic rules for complex two-dimensional covalent organic chemistry that can be enacted directly at a surface to deliver specific macromolecular structures designed for specific functions. PMID:27097295

  6. Strain shielding from mechanically activated covalent bond formation during nanoindentation of graphene delays the onset of failure.

    PubMed

    Kumar, Sandeep; Parks, David M

    2015-03-11

    Mechanical failure of an ideal crystal is dictated either by an elastic instability or a soft-mode instability. Previous interpretations of nanoindentation experiments on suspended graphene sheets,1,2 however, indicate an anomaly: the inferred strain in the graphene sheet directly beneath the diamond indenter at the measured failure load is anomalously large compared to the fracture strains predicted by both soft-mode and acoustic analyses. Through multiscale modeling combining the results of continuum, atomistic, and quantum calculations, and analysis of experiments, we identify a strain-shielding effect initiated by mechanochemical interactions at the graphene-indenter interface as the operative mechanism responsible for this anomaly. Transmission electron micrographs and a molecular model of the diamond indenter's tip suggest that the tip surface contains facets comprising crystallographic {111} and {100} planes. Ab initio and molecular dynamics (MD) simulations confirm that a covalent bond (weld) formation between graphene and the crystallographic {111} and {100} facets on the indenter's surface can be induced by compressive contact stresses of the order achieved in nanoindentation tests. Finite element analysis (FEA) and MD simulations of nanoindentation reveal that the shear stiction provided by the induced covalent bonding restricts relative slip of the graphene sheet at its contact with the indenter, thus initiating a local strain-shielding effect. As a result, subsequent to stress-induced bonding at the graphene-indenter interface, the spatial variation of continuing incremental strain is substantially redistributed, locally shielding the region directly beneath the indenter by limiting the buildup of strain while imparting deformation to the surrounding regions. The extent of strain shielding is governed by the strength of the shear stiction, which depends upon the level of hydrogen saturation at the indenter's surface. We show that at intermediate levels

  7. Pi Bond Orders and Bond Lengths

    ERIC Educational Resources Information Center

    Herndon, William C.; Parkanyi, Cyril

    1976-01-01

    Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

  8. New Insights into Mechanism of Molybdenum(VI)-Dioxo Complex Catalyzed Hydrosilylation of Carbonyls: An Alternative Model for Activating Si-H Bond.

    PubMed

    Ning, Xiaoshuang; Wang, Jiandi; Wei, Haiyan

    2016-06-23

    Recently, a series of oxo/nitrido-Re(V)/Mo(VI)/Ru(VI)/Mn(V) complexes were demonstrated to be efficient catalysts in activating silanes and catalyzing hydrosilylations of unsaturated organic substrates. In the present study, the high-valent molybdenum(VI)-dioxo complex MoO2Cl2 catalyzed hydrosilylations of carbonyls was reinvestigated using density functional theory method. Previous experimental and theoretical investigations suggested a [2 + 2] addition pathway for MoO2Cl2 catalyzed hydrosilylations of ketones. In the present study, we propose an ionic outer-sphere mechanistic pathway to be the most favorable pathway. The key step in the ionic outer-sphere pathway is oxygen atom of C═O bonds nucleophilically attacking the silicon atom in an η(1)-silane molybdenum adduct. The Si-H bond is then cleaved heterolytically. This process features a novel SN2@Si transition state, which then generates a loosely bound ion pair: anionic molybdenum hydride paired with silylcarbenium ion ([MoO2Cl2H](-) [SiR3(OCR'R″)](+)) in solvent. The last step is silylcarbenium ion abstracting the hydride on molybdenum hydride to yield silyl ether. The calculated activation free energy barrier of the rate-determing step was 24.1 kcal/mol for diphenylketone (PhC═OPh) and silane of PhMe2SiH. Furthermore, the ionic outer-sphere pathway is calculated to be ∼10.0 kcal/mol lower than the previously proposed [2 + 2] addition pathway for a variety of silanes and aldehyde/ketone substrates. This preference arises from stronger electrophilicity of the high-valent molybdenum(VI) metal center toward a hydride. Here, we emphasize MoO2Cl2 behaves similar to Lewis acidic trispentafluorophenyl borane B(C6F5)3 in activating Si-H bond. PMID:27243271

  9. Rh-Catalyzed Decarbonylation of Conjugated Ynones via Carbon–Alkyne Bond Activation: Reaction Scope and Mechanistic Exploration via DFT Calculations

    PubMed Central

    Dermenci, Alpay; Whittaker, Rachel E.; Gao, Yang; Cruz, Faben A.; Yu, Zhi-Xiang; Dong, Guangbin

    2015-01-01

    In this full article, detailed development of a catalytic decarbonylation of conjugated monoynones to synthesize disubstituted alkynes is described. The reaction scope and limitation has been thoroughly investigated, and a broad range of functional groups including heterocycles were compatible under the catalytic conditions. Mechanistic exploration via DFT calculations has also been executed. Through the computational study, a proposed catalytic mechanism has been carefully evaluated. These efforts are expected to serve as an important exploratory study for developing catalytic alkyne-transfer reactions via carbon−alkyne bond activation. PMID:26229587

  10. Transesterification of PHA to Oligomers Covalently Bonded with (Bio)Active Compounds Containing Either Carboxyl or Hydroxyl Functionalities

    PubMed Central

    Kwiecień, Iwona; Radecka, Iza; Kowalczuk, Marek; Adamus, Grażyna

    2015-01-01

    This manuscript presents the synthesis and structural characterisation of novel biodegradable polymeric controlled-release systems of pesticides with potentially higher resistance to weather conditions in comparison to conventional forms of pesticides. Two methods for the preparation of pesticide-oligomer conjugates using the transesterification reaction were developed. The first method of obtaining conjugates, which consist of bioactive compounds with the carboxyl group and polyhydroxyalkanoates (PHAs) oligomers, is "one-pot" transesterification. In the second method, conjugates of bioactive compounds with hydroxyl group and polyhydroxyalkanoates oligomers were obtained in two-step method, through cyclic poly(3-hydroxybutyrate) oligomers. The obtained pesticide-PHA conjugates were comprehensively characterised using GPC, 1H NMR and mass spectrometry techniques. The structural characterisation of the obtained products at the molecular level with the aid of mass spectrometry confirmed that both of the synthetic strategies employed led to the formation of conjugates in which selected pesticides were covalently bonded to PHA oligomers via a hydrolysable ester bond. PMID:25781908

  11. Structural insights into the role of iron–histidine bond cleavage in nitric oxide-induced activation of H-NOX gas sensor proteins

    PubMed Central

    Herzik, Mark A.; Jonnalagadda, Rohan; Kuriyan, John; Marletta, Michael A.

    2014-01-01

    Heme-nitric oxide/oxygen (H-NOX) binding domains are a recently discovered family of heme-based gas sensor proteins that are conserved across eukaryotes and bacteria. Nitric oxide (NO) binding to the heme cofactor of H-NOX proteins has been implicated as a regulatory mechanism for processes ranging from vasodilation in mammals to communal behavior in bacteria. A key molecular event during NO-dependent activation of H-NOX proteins is rupture of the heme–histidine bond and formation of a five-coordinate nitrosyl complex. Although extensive biochemical studies have provided insight into the NO activation mechanism, precise molecular-level details have remained elusive. In the present study, high-resolution crystal structures of the H-NOX protein from Shewanella oneidensis in the unligated, intermediate six-coordinate and activated five-coordinate, NO-bound states are reported. From these structures, it is evident that several structural features in the heme pocket of the unligated protein function to maintain the heme distorted from planarity. NO-induced scission of the iron–histidine bond triggers structural rearrangements in the heme pocket that permit the heme to relax toward planarity, yielding the signaling-competent NO-bound conformation. Here, we also provide characterization of a nonheme metal coordination site occupied by zinc in an H-NOX protein. PMID:25253889

  12. Bonded Lubricants

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Another spinoff to the food processing industry involves a dry lubricant developed by General Magnaplate Corp. of Linden, N.J. Used in such spacecraft as Apollo, Skylab and Viking, the lubricant is a coating bonded to metal surfaces providing permanent lubrication and corrosion resistance. The coating lengthens equipment life and permits machinery to be operated at greater speed, thus increasing productivity and reducing costs. Bonded lubricants are used in scores of commercia1 applications. They have proved particularly valuable to food processing firms because, while increasing production efficiency, they also help meet the stringent USDA sanitation codes for food-handling equipment. For example, a cookie manufacturer plagued production interruptions because sticky batter was clogging the cookie molds had the brass molds coated to solve the problem. Similarly, a pasta producer faced USDA action on a sanitation violation because dough was clinging to an automatic ravioli-forming machine; use of the anti-stick coating on the steel forming plates solved the dual problem of sanitation deficiency and production line downtime.

  13. Dehydrofluorination of Hydrofluorocarbons by Titanium Alkylidynes via Sequential C-H/C-F Bond Activation Reactions. A Synthetic, Structural, and Mechanistic Study of 1,2-CH Bond Addition and [beta]-Fluoride Elimination

    SciTech Connect

    Fout, A.R.; Scott, J.; Miller, D.L.; Bailey, B.C.; Pink, M.; Mindiola, D.J.

    2009-01-07

    The neopentylidene-neopentyl complex (PNP)Ti=CH{sup t}Bu(CH{sub 2}{sup t}Bu) (1); (PNP{sup -} = N[2-P(CHMe{sub 2}){sub 2}-4-methylphenyl]{sub 2}) extrudes neopentane in neat fluorobenzene under mild conditions (25 C) to generate the transient titanium alkylidyne (PNP)Ti-C{sup t}Bu (A), which subsequently undergoes regioselective 1,2-CH bond addition of a fluorobenzene across the Ti-C linkage to generate (PNP)Ti=CH{sup t}Bu(o-FC{sub 6}H{sub 4}) (2). Kinetic and mechanistic studies suggest that the C-H activation process is pseudo-first-order in titanium, with the {alpha}-hydrogen abstraction being the rate-determining step and the post-rate-determining step being the C-H bond activation of fluorobenzene. At 100 C complex 2 does not equilibrate back to A and the preference for C-H activation in benzene versus fluorobenzene is 2:3, respectively. Compound 1 also reacts readily, and in most cases cleanly, with a series of hydrofluoroarenes (HAr{sub F}), to form a family of alkylidene-arylfluoride derivatives of the type (PNP)Ti=CH{sup t}Bu(Ar{sub F}). Thermolysis of the latter compounds generates the titanium alkylidene-fluoride (PNP)Ti=CH{sup t}Bu(F) (14) by a {beta}-fluoride elimination, concurrent with formation of o-benzyne. {beta}-Fluoride elimination to yield 14 occurs from 2 under elevated temperatures with k{sub average} = 4.96(16) x 10{sup -5} s{sup -1} and with activation parameters {Delta}H{sub {-+}} = 29(1) kcal/mol and {Delta}S{sub {-+}} = -3(4) cal/mol {center_dot}K. It was found that {beta}-fluoride elimination is accelerated when electron-rich groups are adjacent to the fluoride group, thus implying that a positive charge buildup at the arylfluoride ring occurs in the activated complex of 2. The alkylidene derivative (PNP)Ti=CHSiMe{sub 3}(CH{sub 2}SiMe{sub 3}) (15) also undergoes {alpha}-hydrogen abstraction to form the putative (PNP)Ti'-CSiMe{sub 3} (B) at higher temperatures (>70 C) and dehydrofluorinates the same series of HArF when the reaction

  14. Basics of Fidelity Bonding.

    ERIC Educational Resources Information Center

    Kahn, Steven P.

    Fidelity bonds are important for an agency to hold to protect itself against any financial loss that can result from dishonest acts by its employees. Three types of fidelity bonds are available to an agency: (1) public official bonds; (2) dishonesty bonds; and (3) faithful performance bonds. Public official bonds are required by state law to be…

  15. The Reductive Activation of CO2 Across a Ti=Ti Double Bond: Synthetic, Structural, and Mechanistic Studies

    PubMed Central

    2015-01-01

    The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti2Pn†2 (1) (Pn† = 1,4-{SiiPr3}2C8H4) with CO2 is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO2 reaction is performed at −78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO2 molecule bound symmetrically to the two Ti centers in a μ:η2,η2 binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO2 is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a μ-O dimer in which the Ti–Ti bond has been cleaved and one pentalene ligand binds in an η8 fashion to each of the formally TiIII centers. The molecular structure of 7 shows a “side-on” bound carbonyl ligand. Bonding of the double-sandwich species Ti2Pn2 (Pn = C8H6) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO2 reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-TiIII species to yield di-TiII and di-TiIV products. 1 forms a structurally characterized, thermally stable CS2 adduct 8 that shows symmetrical binding to the Ti2 unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(μ-S) mono(CO) species 10. Ph3PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(μ-S) complex 11 with a double-sandwich structure and bis(μ-S) dimer 12 in which the Ti

  16. Disiloxane Synthesis Based on Silicon-Hydrogen Bond Activation using Gold and Platinum on Carbon in Water or Heavy Water.

    PubMed

    Sawama, Yoshinari; Masuda, Masahiro; Yasukawa, Naoki; Nakatani, Ryosuke; Nishimura, Shumma; Shibata, Kyoshiro; Yamada, Tsuyoshi; Monguchi, Yasunari; Suzuka, Hiroyasu; Takagi, Yukio; Sajiki, Hironao

    2016-05-20

    Disiloxanes possessing a silicon-oxygen linkage are important as frameworks for functional materials and coupling partners for Hiyama-type cross coupling. We found that disiloxanes were effectively constructed of hydrosilanes catalyzed by gold on carbon in water as the solvent and oxidant in association with the emission of hydrogen gas at room temperature. The present oxidation could proceed via various reaction pathways, such as the hydration of hydrosilane into silanol, dehydrogenative coupling of hydrosilane into disilane, and the subsequent corresponding reactions to disiloxane. Additionally, the platinum on carbon catalyzed hydrogen-deuterium exchange reaction of arylhydrosilanes as substrates in heavy water proceeded on the aromatic nuclei at 80 °C with high deuterium efficiency and high regioselectivity at the only meta and para positions of the aromatic-silicon bond to give the deuterium-labeled disiloxanes. PMID:27129497

  17. Pair-bonding in birds and the active role of females: a critical review of the empirical evidence.

    PubMed

    Cézilly; Préault; Dubois; Faivre; Patris

    2000-10-01

    Over the recent years the role of females in maintaining or breaking the pair-bond in socially monogamous birds has received growing attention. Here, we review the overall evidence for a direct and predominant role of female behaviour in initiating or preventing divorce and its relevance for the understanding of both interspecific and intraspecific variation in divorce rate in monogamous bird species. The evidence is so far limited to a few species. We discuss the relevance of some alternative explanations and confounding factors. We conclude that the possible predominance of females in both initiating divorce or limiting its occurrence deserves further consideration. Future studies should favour experimental approaches, such as mate-removal experiments. PMID:11074313

  18. Selectivity of Chemisorbed Oxygen in C–H Bond Activation and CO Oxidation and Kinetic Consequences for CH₄–O₂ Catalysis on Pt and Rh Clusters

    SciTech Connect

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

    2011-10-06

    Rate measurements, density functional theory (DFT) within the framework of transition state theory, and ensemble-averaging methods are used to probe oxygen selectivities, defined as the reaction probability ratios for O* reactions with CO and CH₄, during CH₄–O₂ catalysis on Pt and Rh clusters. CO₂ and H₂O 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–¹³CH₄–O₂ reactants, increase with O₂/ 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 CH₄, causing any CO that forms and desorbs from metal cluster surfaces to react along the reactor bed with other O* to produce CO₂ at any residence time required for detectable extents of CH₄ conversion. O* selectivities were also calculated by averaging DFTderived activation barriers for CO and CH₄ 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 O₂ 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). CH₄ 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 CH₄, forming a three-centered HC₃–Pt–H transition state. C–H bond activation barriers reflect the strength of Pt–CH₃ and Pt–H interactions at the transition state, which correlates, in turn, with the Pt coordination and with CH₃ * binding energies. Ensemble-averaged O* selectivities increase linearly with O₂/CO ratios, which define the O* coverages, via a proportionality constant. The proportionality constant is given by the ratio of rate

  19. 30 CFR 282.40 - Bonds.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... BUREAU OF OCEAN ENERGY MANAGEMENT, REGULATION, AND ENFORCEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE... Bonds. (a) Pursuant to the requirements for a bond in § 281.33 of this title, prior to the commencement of any activity on a lease, the lessee shall submit a surety or personal bond to cover the...

  20. CQ-397 and CQ-414: antimicrobial activity and spectrum of two fluoroquinolone---cephalosporin, dual-action compounds with carboxamido bonds.

    PubMed

    Johnson, David M.; Jones, Ronald N.

    1997-06-01

    OBJECTIVE: To evaluate the potential spectrum of activity of two novel dual-action compounds with carboxamido bonds (CQ-397 and CQ-414; Laboratorios Aranda, San Rafael, Mexico) against human pathogens. METHODS: Approximately 800 Gram-positive and Gram-negative aerobic clinical bacteria were tested in vitro using the Mueller-Hinton broth microdilution method of the National Committee of Clinical Laboratory Standards. RESULTS: CQ-397 (cefamandole+enrofloxacin) and CQ-414 (cefamandole+norfloxacin) were equally potent against Enterobacteriaceae (MIC90 range, 0.06--0.5 microg/mL and 0.06--1 microg/mL, respectively). Citrobacter freundii (MIC90, 4 microg/mL) and Providencia spp. (MIC90, >32 microg/mL) exhibited elevated study drug MICs. Enterobacteriaceae resistant to fluoroquinolones generally remained resistant. CQ-397 and CQ-414 were active against Stenotrophomonas maltophilia (MIC90, 4 microg/mL) and oxacillin-susceptible staphylococci (MIC90, 0.25 microg/mL), but not oxacillin-resistant Staphylococcus aureus (MIC90, >32 microg/mL), Staphylococcus epidermidis (MIC90, 8 microg/mL), and enterococci (MIC90s, 8 to >32 microg/mL). There was no difference in the dual-action drug activity (MIC90, 2 microg/mL) between penicillin-susceptible and -resistant pneumococci. Haemophilus influenzae and Moraxella catarrhalis were very susceptible (MIC range, less-than-or-equal0.015--0.06 microg/mL) to both compounds. CONCLUSIONS: The activity of these novel dual-action compounds, formed from the bonding of older antimicrobials, warrants further investigation for potential human and/or animal health use, including toxicology and pharmacokinetics. PMID:11864130

  1. Identification of glycoprotein receptors within the human salivary proteome for the lectin-like BabA and SabA adhesins of Helicobacter pylori by fluorescence-based 2-D bacterial overlay.

    PubMed

    Walz, Anke; Odenbreit, Stefan; Stühler, Kai; Wattenberg, Andreas; Meyer, Helmut E; Mahdavi, Jafar; Borén, Thomas; Ruhl, Stefan

    2009-03-01

    Because gastric infection by Helicobacter pylori takes place via the oral route, possible interactions of this bacterium with human salivary proteins could occur. By using modified 1- and 2-D bacterial overlay, binding of H. pylori adhesins BabA and SabA to the whole range of salivary proteins was explored. Bound salivary receptor molecules were identified by MALDI-MS and by comparison to previously established proteome maps of whole and glandular salivas. By use of adhesin-deficient mutants, binding of H. pylori to MUC7 and gp-340 could be linked to the SabA and BabA adhesins, respectively, whereas binding to MUC5B was associated with both adhesins. Binding of H. pylori to the proline-rich glycoprotein was newly detected and assigned to BabA adhesin whereas the SabA adhesin was found to mediate binding to newly detected receptor molecules, including carbonic anhydrase VI, secretory component, heavy chain of secretory IgA1, parotid secretory protein and zinc-alpha(2)-glycoprotein. Some of these salivary glycoproteins are known to act as scavenger molecules or are involved in innate immunity whereas others might come to modify the pathogenetic properties of this organism. In general, this 2-D bacterial overlay technique represents a useful supplement in adhesion studies of bacteria with complex protein mixtures. PMID:19253298

  2. Subsurface defect detection in first layer of pavement structure and reinforced civil engineering structure by FRP bonding using active infrared thermography

    NASA Astrophysics Data System (ADS)

    Dumoulin, Jean; Ibos, Laurent

    2010-05-01

    In many countries road network ages while road traffic and maintenance costs increase. Nowadays, thousand and thousand kilometers of roads are each year submitted to surface distress survey. They generally lean on pavement surface imaging measurement techniques, mainly in the visible spectrum, coupled with visual inspection or image processing detection of emergent distresses. Nevertheless, optimisation of maintenance works and costs requires an early detection of defects within the pavement structure when they still are hidden from surface. Accordingly, alternative measurement techniques for pavement monitoring are currently under investigation (seismic methods, step frequency radar). On the other hand, strengthening or retrofitting of reinforced concrete structures by externally bonded Fiber Reinforced Polymer (FRP) systems is now a commonly accepted and widespread technique. However, the use of bonding techniques always implies following rigorous installing procedures. To ensure the durability and long-term performance of the FRP reinforcements, conformance checking through an in situ auscultation of the bonded FRP systems is then highly suitable. The quality-control program should involve a set of adequate inspections and tests. Visual inspection and acoustic sounding (hammer tap) are commonly used to detect delaminations (disbonds) but are unable to provide sufficient information about the depth (in case of multilayered composite) and width of debonded areas. Consequently, rapid and efficient inspection methods are also required. Among the non destructive methods under study, active infrared thermography was investigated both for pavement and civil engineering structures through experiments in laboratory and numerical simulations, because of its ability to be also used on field. Pulse Thermography (PT), Pulse Phase Thermography (PPT) and Principal Component Thermography (PCT) approaches have been tested onto pavement samples and CFRP bonding on concrete

  3. A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C−X (X=Cl, Br) Bond Activation

    PubMed Central

    Samigullin, Kamil; Georg, Isabelle; Bolte, Michael; Lerner, Hans‐Wolfram

    2016-01-01

    Abstract The geminal frustrated Lewis pair tBu2PCH2B(Fxyl)2 (1; Fxyl=3,5‐(CF3)2C6H3) is accessible in 65 % yield from tBu2PCH2Li and (Fxyl)2BF. According to NMR spectroscopy and X‐ray crystallography, 1 is monomeric both in solution and in the solid state. The intramolecular P⋅⋅⋅B distance of 2.900(5) Å and the full planarity of the borane site exclude any significant P/B interaction. Compound 1 readily activates a broad variety of substrates including H2, EtMe2SiH, CO2/CS2, Ph2CO, and H3CCN. Terminal alkynes react with heterolysis of the C−H bond. Haloboranes give cyclic adducts with strong P−BX3 and weak R3B−X bonds. Unprecedented transformations leading to zwitterionic XP/BCX3 adducts occur on treatment of 1 with CCl4 or CBr4 in Et2O. In less polar solvents (C6H6, n‐pentane), XP/BCX3 adduct formation is accompanied by the generation of significant amounts of XP/BX adducts. FLP 1 catalyzes the hydrogenation of PhCH=NtBu and the hydrosilylation of Ph2CO with EtMe2SiH. PMID:26833900

  4. Managing bond tension in spreading macromolecules.

    NASA Astrophysics Data System (ADS)

    Sheyko, Sergey; Park, Insun; Nese, Alper; Matyjaszewski, Krzysztof; Shirvaniants, David; Rubinstein, Michael

    2009-03-01

    Mechanical activation of chemical bonds plays a vital role in biology, chemistry, and engineering. Unlike other activation stimuli, such as light and temperature, mechanical activation is site and direction specific. However, in a typical experiment, macroscopic stress is distributed over myriads of different molecules. This results in significant and ill-defined variation of both the magnitude and direction of forces at individual chemical bonds. Here, we show how to achieve a great degree of control over bond tension in flowing polymer films. The distinctive feature of this finding is that the mechanical tension is controlled on three different length scales. First, chemical bonds are activated within a narrowly defined area of a macroscopic film. Second, only certain molecules are activated within a mixture of molecules. Third, the tension can be focused to a specific bond within a flowing macromolecule. It is demonstrated that the focused tension breaks covalent bonds with a molecular-scale precision.

  5. N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd-NHC complexes: synthesis, characterization and catalytic activity in carbon-carbon bond-forming reactions.

    PubMed

    Akkoç, Senem; Gök, Yetkin; İlhan, İlhan Özer; Kayser, Veysel

    2016-01-01

    A series of novel benzimidazolium salts (1-4) and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI) themed palladium N-heterocyclic carbene complexes [PdCl2(NHC)(Py)] (5-8), where NHC = 1-(N-methylphthalimide)-3-alkylbenzimidazolin-2-ylidene and Py = 3-chloropyridine, were synthesized and characterized by means of (1)H and (13)C{(1)H} NMR, UV-vis (for 5-8), ESI-FTICR-MS (for 2, 4, 6-8) and FTIR spectroscopic methods and elemental analysis. The synthesized compounds were tested in Suzuki-Miyaura cross-coupling (for 1-8) and arylation (for 5-8) reactions. As catalysts, they demonstrated a highly efficient route for the formation of asymmetric biaryl compounds even though they were used in very low loading. For example, all compounds displayed good catalytic activity for the C-C bond formation of 4-tert-butylphenylboronic acid with 4-chlorotoluene. PMID:26877810

  6. N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd–NHC complexes: synthesis, characterization and catalytic activity in carbon–carbon bond-forming reactions

    PubMed Central

    Gök, Yetkin; İlhan, İlhan Özer

    2016-01-01

    Summary A series of novel benzimidazolium salts (1–4) and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI) themed palladium N-heterocyclic carbene complexes [PdCl2(NHC)(Py)] (5–8), where NHC = 1-(N-methylphthalimide)-3-alkylbenzimidazolin-2-ylidene and Py = 3-chloropyridine, were synthesized and characterized by means of 1H and 13C{1H} NMR, UV–vis (for 5–8), ESI-FTICR-MS (for 2, 4, 6–8) and FTIR spectroscopic methods and elemental analysis. The synthesized compounds were tested in Suzuki–Miyaura cross-coupling (for 1–8) and arylation (for 5–8) reactions. As catalysts, they demonstrated a highly efficient route for the formation of asymmetric biaryl compounds even though they were used in very low loading. For example, all compounds displayed good catalytic activity for the C–C bond formation of 4-tert-butylphenylboronic acid with 4-chlorotoluene. PMID:26877810

  7. Access to novel fluorovinylidene ligands via exploitation of outer-sphere electrophilic fluorination: new insights into C-F bond formation and activation.

    PubMed

    Milner, Lucy M; Hall, Lewis M; Pridmore, Natalie E; Skeats, Matthew K; Whitwood, Adrian C; Lynam, Jason M; Slattery, John M

    2016-01-28

    Metal vinylidene complexes are widely encountered, or postulated, as intermediates in a range of important metal-mediated transformations of alkynes. However, fluorovinylidene complexes have rarely been described and their reactivity is largely unexplored. By making use of the novel outer-sphere electrophilic fluorination (OSEF) strategy we have developed a rapid, robust and convenient method for the preparation of fluorovinylidene and trifluoromethylvinylidene ruthenium complexes from non-fluorinated alkynes. Spectroscopic investigations (NMR and UV/Vis), coupled with TD-DFT studies, show that fluorine incorporation results in significant changes to the electronic structure of the vinylidene ligand. The reactivity of fluorovinylidene complexes shows many similarities to non-fluorinated analogues, but also some interesting differences, including a propensity to undergo unexpected C-F bond cleavage reactions. Heating fluorovinylidene complex [Ru(η(5)-C5H5)(PPh3)2(C[double bond, length as m-dash]C{F}R)][BF4] led to C-H activation of a PPh3 ligand to form an orthometallated fluorovinylphosphonium ligand. Reaction with pyridine led to nucleophilic attack at the metal-bound carbon atom of the vinylidene to form a vinyl pyridinium species, which undergoes both C-H and C-F activation to give a novel pyridylidene complex. Addition of water, in the presence of chloride, leads to anti-Markovnikov hydration of a fluorovinylidene complex to form an α-fluoroaldehyde, which slowly rearranges to its acyl fluoride isomer. Therefore, fluorovinylidenes ligands may be viewed as synthetic equivalents of 1-fluoroalkynes providing access to reactivity not possible by other routes. PMID:26701305

  8. Chemical Bonds II

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    The continuation of a paper discussing chemical bonding from a bond energy viewpoint, with a number of examples of single and multiple bonds. (Part I appeared in volume 1 number 3, pages 16-23, February 1972.) (AL)

  9. What Determines Bond Costs. Municipal Bonds Series.

    ERIC Educational Resources Information Center

    Young, Douglas; And Others

    Public officials in small towns who participate infrequently in the bond market need information about bond financing. This publication, one in a series of booklets published by the Western Rural Development Center using research gathered between 1967-77, discusses factors influencing the marketability and cost of bond financing for towns and…

  10. Direct Synthesis of Protoberberine Alkaloids by Rh-Catalyzed C-H Bond Activation as the Key Step.

    PubMed

    Jayakumar, Jayachandran; Cheng, Chien-Hong

    2016-01-26

    A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant. PMID:26689172

  11. Selection of two optional covalent bonds by electric stimuli: dual catalytic switching of redox-active copper.

    PubMed

    Kamamoto, Yu; Nitta, Yuya; Kubo, Kazuyuki; Mizuta, Tsutomu; Kume, Shoko

    2016-08-18

    Two types of redox functionality were selected for covalent immobilization on a carbon electrode, using an electric potential as the sole stimulus. A redox-active copper catalyst transformed a terminal alkyne in two ways with and without an oxidation process, to form a triazole or butadiyne. PMID:27435917

  12. The Molybdenum Active Site of Formate Dehydrogenase Is Capable of Catalyzing C-H Bond Cleavage and Oxygen Atom Transfer Reactions.

    PubMed

    Hartmann, Tobias; Schrapers, Peer; Utesch, Tillmann; Nimtz, Manfred; Rippers, Yvonne; Dau, Holger; Mroginski, Maria Andrea; Haumann, Michael; Leimkühler, Silke

    2016-04-26

    Formate dehydrogenases (FDHs) are capable of performing the reversible oxidation of formate and are enzymes of great interest for fuel cell applications and for the production of reduced carbon compounds as energy sources from CO2. Metal-containing FDHs in general contain a highly conserved active site, comprising a molybdenum (or tungsten) center coordinated by two molybdopterin guanine dinucleotide molecules, a sulfido and a (seleno-)cysteine ligand, in addition to a histidine and arginine residue in the second coordination sphere. So far, the role of these amino acids in catalysis has not been studied in detail, because of the lack of suitable expression systems and the lability or oxygen sensitivity of the enzymes. Here, the roles of these active site residues is revealed using the Mo-containing FDH from Rhodobacter capsulatus. Our results show that the cysteine ligand at the Mo ion is displaced by the formate substrate during the reaction, the arginine has a direct role in substrate binding and stabilization, and the histidine elevates the pKa of the active site cysteine. We further found that in addition to reversible formate oxidation, the enzyme is further capable of reducing nitrate to nitrite. We propose a mechanistic scheme that combines both functionalities and provides important insights into the distinct mechanisms of C-H bond cleavage and oxygen atom transfer catalyzed by formate dehydrogenase. PMID:27054466

  13. The C-H bond activation in 1-ethyl-3-methylimidazolium acetate-copper(II) acetate-water-air (dioxygen) systems.

    PubMed

    Shtyrlin, Valery G; Serov, Nikita Yu; Islamov, Daut R; Konkin, Alexander L; Bukharov, Mikhail S; Gnezdilov, Oleg I; Krivolapov, Dmitry B; Kataeva, Ol'ga N; Nazmutdinova, Gulnara A; Wendler, Frank

    2014-01-14

    Ionic liquid (1-ethyl-3-methylimidazolium acetate, [C2C1im][AcO])-copper(ii) diacetate monohydrate-water-air (O2) systems have been investigated by (13)C NMR, EPR, spectrophotometry, HPLC, and synthetic chemistry methods at different temperatures. The C-H bond activation of [C2C1im](+) with the formation of the unusual dication 1,1'-diethyl-3,3'-dimethyl-2,2'-biimidazolium ([(C2C1im)2](2+)) at 50 °C and 1-ethyl-3-methyl-1H-imidazol-2(3H)-one (C2C1imO) at 50-85 °C was revealed. Two new complexes with the above compounds, [(C2C1im)2][Cu(AcO)4] and Cu2(AcO)4(C2C1imO)2, were isolated from the systems and characterized by X-ray structural analysis. Catalytic cycles with the participation of copper(ii) acetate and dioxygen and the production of [(C2C1im)2](2+) and C2C1imO have been proposed. The catalysis presumably includes the formation of the Cu(II)(O2)Cu(II) active centre with μ-η(2):η(2)-peroxide bridging in analogy with tyrosinase and catechol oxidase activity. PMID:24154681

  14. Two-step C-H, C-P bond activation at an α-diimine iron dinitrogen complex.

    PubMed

    Ghosh, Chandrani; Groy, Thomas L; Bowman, Amanda C; Trovitch, Ryan J

    2016-03-15

    Reduction of 6-coordinate under N2 results in formation of the terminal dinitrogen complex, ((Ph2PPr)DI)FeN2. Heating this product to 75 °C allows for C-H and C-P activation of the chelate to generate the cisoid and transoid isomers of [(μ-PrPPh-κ(5)-P,N,N,Cγ,P-(Ph2PPr)DI(PrPPh))Fe]2. Mechanistic possibilities for this transformation are discussed. PMID:26939725

  15. A study of hydrogen bond effects on the oxygen, nitrogen, and hydrogen electric field gradient tensors in the active site of human dehydroepiandrosterone sulphotransferase: A density-functional theory based treatment

    NASA Astrophysics Data System (ADS)

    Astani, Elahe; Heshmati, Emran; Chen, Chun-Jung; Hadipour, Nasser L.; Shekarsaraei, Setareh

    2016-06-01

    An investigation of the density functional theory (DFT) was carried out to study the effects of the hydrogen bond (HB) interactions on 2H, 14N, and 17O electric field gradient (EFG) tensors in the active site of human dehydroepiandrosterone sulphotransferase (SULT2A1/DHEA). Natural Bonding Orbital (NBO) analysis was also performed on this active site. The results revealed that the magnitude of the quadrupole coupling constant (QCC) change at each nucleus directly depends on its contribution amount to the HB interaction.

  16. Effect of light activation mode on the incompatibility between one-bottle adhesives and light-cured composites: an in vitro shear bond strength study.

    PubMed

    Shafiei, Fereshteh; Saffarpour, Aida; Safarpoor, Ida; Moradmand, Masoud; Alavi, Ali Asghar

    2009-01-01

    This study examined the effect of different light activation modes for light-cured resin-based composites on the shear bond strength to dentin of two one-bottle adhesives with differing acidity. In this experimental study, a flat middle dentin surface was prepared on 110 extracted sound molars using a 600-grit polish paper. The teeth were then randomly divided into 10 equal groups (n = 11). One-Step Plus (OS) and Prime & Bond NT (P&B NT) were used according to the manufacturer's instruction with their respective composite (Aelite, Spectrum TPH) applied and cured using five different light-activation modes: 1. Conventional (CO): 600 mW/cm2 (40 seconds) 2. Soft-Start I (SSI): 100 mW/cm2 (10 seconds) 600 mW/cm2 (30 seconds) 3. Soft-Start II (SSII): 200 mW/cm2 (10 seconds), 600 mW/cm2 (30 seconds) 4. Pulse-Delay I (PDI): 100 mW/cm2 (3 seconds), 3-minute delay, 600 mW/cm2 (37 seconds) 5. Pulse-Delay II (PDII): 200 mW/cm2 (3 seconds), 3-minute delay, 600 mW/cm2 (37 seconds) After 24 hours storage in distilled water at room temperature, a shear bond strength (SBS) test was performed using an Instron machine at 1 mm/minute and the results were recorded in MPa. Statistical analysis included two-way ANOVA and Tukey HSD (p < 0.05). The highest SBS (MPa) was shown in the OS conventional group (19.62 +/- 2.21) and the lowest SBS was shown in P&B NT, PDII (5.93 +/- 1.79). In each group of five curing modes, the mean SBS for P&B NT was significantly lower than OS: conventional mode--P&B NT (17.27 +/- 1.98) vs OS (19.62 +/- 2.21); SSI-P&B NT (10.84 +/- 2.82) vs OS (13.09 +/- 1.24); SSII - P&B NT (14.78 +/- 1.63) vs OS (18.79 +/- 1.57); PDI-P&B NT (5.93 +/- 1.79) vs OS (11.97 +/- 2.59) and PDII-P&B NT (11.82 +/- 1.24) vs OS (16.00 +/- 1.62) (p < 0.001 for all comparisons). For each of the adhesives, the ranking of SBS was as follows: CO > SSII > PDII > SSI > PDI, with the two-paired comparisons of curing modes being significantly different (p < 0.05). The results of the current

  17. A high-performance liquid chromatography assay with a triazole-bonded column for evaluation of d-amino acid oxidase activity.

    PubMed

    Iwasaki, Megumi; Kashiwaguma, Yoshiyuki; Nagashima, Chihiro; Izumi, Mao; Uekusa, Ayano; Iwasa, Sumiko; Onozato, Mayu; Ichiba, Hideaki; Fukushima, Takeshi

    2016-03-01

    Elution profiles of kynurenic acid (KYNA) and 7-chlorokynurenic acid (Cl-KYNA) were examined by high-performance liquid chromatography (HPLC) using a triazole-bonded stationary phase column (Cosmosil® HILIC) under isocratic elution of a mobile phase consisting of CH3 CN-aqueous 10 mm ammonium formate between pH 3.0 and 6.0. The capacity factors of KYNA and Cl-KYNA varied with both the CH3 CN content and the pH of the mobile phase. The elution order of KYNA and Cl-KYNA was reversed between the CH3 CN- and H2 O-rich mobile phases, suggesting that hydrophilic interactions and anion-exchange interactions caused retention of KYNA and Cl-KYNA in the CH3 CN- and H2 O-rich mobile phases, respectively. The present HPLC method using a triazole-bonded column and fluorescence detection (excitation 250 nm, emission 398 nm) was applied to monitor in vitro production of KYNA from d-kynurenine (d-KYN) by d-amino acid oxidase (DAO) using Cl-KYNA as an internal standard. A single KYNA peak was clearly observed after enzymatic reaction of d-KYN with DAO. Production of KYNA from d-KYN was suppressed by the addition of commercial DAO inhibitors. The present HPLC method can be used to evaluate DAO activity and DAO inhibitory effects in candidate drugs for the treatment of schizophrenia. PMID:26174062

  18. Reactions of [Cu(X)(BPEP-Ph)] (X = PF6, SbF6) with silyl compounds. Cooperative bond activation involving non-coordinating anions.

    PubMed

    Nakajima, Yumiko; Tsuchimoto, Takahiro; Chang, Yung-Hung; Takeuchi, Katsuhiko; Ozawa, Fumiyuki

    2016-02-01

    Bond activation of silyl compounds, assisted by the cooperative action of non-coordinating anions, is achieved using Cu(I) complexes coordinated with a PNP-pincer type phosphaalkene ligand, [Cu(X)(BPEP-Ph)] (X = PF6 (1a), SbF6 (1b); BPEP-Ph = 2,6-bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine). Complexes 1a and 1b react with Me3SiCN to form Me3SiF and Cu(i) cyanide complexes of the formula [Cu(CN-EF5)(BPEP-Ph)] (E = P (2a), Sb (2b)), in which the CN ligand is associated with the EF5 group arising from EF6(-). Formation of the intermediary isonitrile complex [Cu(CNSiMe3)(BPEP-Ph)](+)SbF6(-) (3b) is confirmed by its isolation. Thus, a two-step reaction process involving coordination of Me3SiCN, followed by nucleophilic attack of SbF6(-) on the silicon atom of 3b is established for the conversion of 1b to 2b. Complex 1b cleaves the H-Si bond of PhMe2SiH as well. The isolation and structural identification of [Cu(BPEP-Ph)](+)BAr(F)4(-) (1c) (BAr(F)4 = B{3,5-(CF3)2C6H3}4) as a rare example of a T-shaped, three-coordinated Cu(i) complex is reported. PMID:26455594

  19. Unraveling the contributions of hydrogen-bonding interactions to the activity of native and non-native ligands in the quorum-sensing receptor LasR

    PubMed Central

    Gerdt, Joseph P.; McInnis, Christine E.; Schell, Trevor L.; Blackwell, Helen E.

    2014-01-01

    Quorum sensing (QS) via the synthesis and detection of N-acyl L-homoserine lactone (AHL) signals regulates important pathogenic and mutualistic phenotypes in many bacteria. Over the past two decades, the development of non-native molecules that modulate this cell-cell signaling process has become an active area of research. The majority of these compounds were designed for block binding of the native AHL signal to its cognate LuxR-type receptor, and much effort has focused on LasR in the opportunistic pathogen Pseudomonas aeruginosa. Despite a small set of reported LasR structural data, it remains unclear which polar interactions are most important for either (i) activation of the LasR receptor by its native AHL signal, N-(3-oxo)-dodecanoyl L-homoserine lactone (OdDHL), or (ii) activation or inhibition of LasR by related AHL analogs. Herein, we report our investigations into the activity of OdDHL and five synthetic analogs in wild-type LasR and in nine LasR mutants with modifications to key polar residues in their ligand binding sites. Our results allowed us to rank, for the first time, the relative importance of each LasR:OdDHL hydrogen bond for LasR activation and provide strong evidence for the five synthetic ligands binding LasR in a very similar orientation as OdDHL. By delineating the specific molecular interactions that are important for LasR modulation by AHLs, these findings should aid in the design of new synthetic modulators of LasR (and homologous LuxR-type receptors) with improved potencies and selectivities. PMID:25474181

  20. Comparative anti-inflammatory activities of curcumin and tetrahydrocurcumin based on the phenolic O-H bond dissociation enthalpy, ionization potential and quantum chemical descriptor.

    PubMed

    Murakami, Yukio; Ishii, Hiroaki; Takada, Naoki; Tanaka, Shoji; Machino, Mamoru; Ito, Shigeru; Fujisawa, Seiichiro

    2008-01-01

    Curcumin and its reduced derivative tetrahydrocurcumin have been shown to exhibit chemopreventive activity. Cyclooxygenase-2 (COX-2) inhibition in lipopolysaccharide (LPS)- or Porphyromonas gingivalis fimbria-stimulated RAW 264.7 cells was investigated using Northern blot analysis. The fimbria-stimulated expression of the COX-2 gene was inhibited by curcumin but not by tetrahydrocurcumin. LPS-stimulated COX-2 gene expression was completely inhibited by curcumin, but an increase in the concentration of tetrahydrocurcumin did not cause complete inhibition of COX-2 expression. The inhibitory effect of curcumin on nuclear factor kappa B (NF-kappaB) activation in the cells was clearly observed, but that of tetrahydrocurcumin was incomplete even at a concentration of 20 microM. To explain the difference in effect between the two compounds, analysis of the frontier orbital was performed using ab initio 6-31G* wave function. The calculated chemical hardness (eta) for curcumin was clearly smaller, whereas its electronegativity (chi) and electrophilicity (omega) were clearly greater than the corresponding values for the curcumin-related compounds tetrahydrocurcumin, isoeugenol and eugenol. This suggested that the anti-inflammatory activities of curcumin may be related to eta-, chi- and/or omega-controlled enzymes. In addition, the bond dissociation enthalpy (BDE) of the phenolic OH was calculated using the density function theory (DFT)/B3LY. The total BDE values of curcumin and tetrahydrocurcumin were almost identical, but the BDE of one-electron oxidation and ionization potential (IP) for curcumin were lower than those for tetrahydrocurcumin, suggesting the highly pro-oxidative activity of curcumin. Curcumin has both oxidant and antioxidant properties. A causal link between the anti-inflammatory activities and molecular properties of phenolic antioxidants is suggested. PMID:18507010

  1. Ethylene C-H Bond Activation by Neutral Mn2O5 Clusters under Visible Light Irradiation.

    PubMed

    Yin, Shi; Bernstein, Elliot R

    2016-05-01

    A photo excitation fast flow reactor coupled with a single-photon ionization (118 nm, 10.5 eV) time-of-flight mass spectrometry (TOFMS) instrument is used to investigate reactions of neutral MnmOn clusters with C2H4 under visible (532 nm) light irradiation. Association products Mn2O5(C2H4) and Mn3O6,7(C2H4) are observed without irradiation. Under light irradiation, the Mn2O5(C2H4) TOFMS feature decreases, and a new species, Mn2O5H2, is observed. This light-activated reaction suggests that the visible radiation can induce the chemistry, Mn2O5 + C2H4 + hv(532 nm) → Mn2O5*(C2H4) → Mn2O5H2 + C2H2. High barriers (0.67 and 0.59 eV) are obtained on the ground-state potential energy surface (PES); the reaction is barrierless and thermodynamically favorable on the first excited-state PES, as performed by time-dependent density functional theory calculations. The calculational and experimental results suggest that Mn2O5-like structures on manganese oxide surfaces are the appropriate active catalytic sites for visible light photocatalysis of ethylene dehydrogenation. PMID:27099985

  2. Rhodium(I)-catalyzed regiospecific dimerization of aromatic acids: two direct C-H bond activations in water.

    PubMed

    Gong, Hang; Zeng, Huiying; Zhou, Feng; Li, Chao-Jun

    2015-05-01

    2,2'-Diaryl acids are key building blocks for some of the most important and high-performance polymers such as polyesters and polyamides (imides), as well as structural motifs of MOFs (metal-organic frameworks) and biological compounds. In this study, a direct, regiospecific and practical dimerization of simple aromatic acids to generate 2,2'-diaryl acids has been discovered, which proceeds through two rhodium-catalyzed C-H activations in water. This reaction can be easily scaled up to gram level by using only 0.4-0.6 mol % of the rhodium catalyst. As a proof-of-concept, the natural product ellagic acid was synthesized in two steps by this method. PMID:25765625

  3. The amide C-N bond of isatins as the directing group and the internal oxidant in Ru-catalyzed C-H activation and annulation reactions: access to 8-amido isocoumarins.

    PubMed

    Kaishap, Partha Pratim; Sarma, Bipul; Gogoi, Sanjib

    2016-07-28

    The N-O, N-N and O-O bonds are the frequently used internally oxidative directing groups used in various redox-neutral coupling reactions. The sole use of the C-N bond as the oxidizing directing group was reported recently by Li X. and co-workers for the Rh(iii)-catalyzed C-H activation of phenacyl ammonium salts. Herein, we report the use of the amide C-N bond of isatins as the oxidizing directing group for the Ru(ii)-catalyzed redox-neutral C-H activation and annulation reactions with alkynes which afford 8-amido isocoumarins. The reaction also features excellent regioselectivity with alkyl aryl substituted alkynes. PMID:27417438

  4. Positioning a Carbon-Fluorine Bond over the π Cloud of an Aromatic Ring: A Different Type of Arene Activation.

    PubMed

    Holl, Maxwell Gargiulo; Struble, Mark D; Singal, Prakhar; Siegler, Maxime A; Lectka, Thomas

    2016-07-11

    It is known that the fluoro group has only a small effect on the rates of electrophilic aromatic substitutions. Imagine instead a carbon-fluorine (C-F) bond positioned tightly over the π cloud of an aryl ring-such an orthogonal, noncovalent arrangement could instead stabilize a positively charged arene intermediate or transition state, giving rise to novel electrophilic aromatic substitution chemistry. Herein, we report the synthesis and study of molecule 1, containing a rigid C-F⋅⋅⋅Ar interaction that plays a prominent role in both its reaction chemistry and spectroscopy. For example, we established that the C-F⋅⋅⋅Ar interaction can bring about a >1500 fold increase in the relative rate of an aromatic nitration reaction, affording functionalization on the activated ring exclusively. Overall, these results establish fluoro as a through-space directing/activating group that complements the traditional role of fluorine as a slightly deactivating aryl substituent in nitrations. PMID:27145463

  5. Using Multiple Bonding Strategies.

    PubMed

    Larson, Thomas D

    2015-01-01

    There are many ways to bond to tooth structure, some micro-mechanical some chemical, some a combination. Different dentin bonding materials have different bonding strengths to differently prepared surfaces, and because of differences in their nature, different areas of tooth structure present peculiar bonding challenges. This paper will review a variety of material types, elucidating their particular bonding strengths and commenting on improved bonding strategies to increase durability, strength, and favorable pulpal response. In this discussion, resin dentin bonding systems, glass ionomers, Gluma, resin cements, and newer combined products will br reviewed. PMID:26485903

  6. Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

    SciTech Connect

    Lewis, Jared; Berman, Ashley; Bergman, Robert; Ellman, Jonathan

    2007-07-18

    A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active yet thermally stable arylation catalyst, is essential to the success of this method. By using the tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a glove box without purification of reagents or solvent. The reactions are also conducted in THF or dioxane, which greatly simplifies product isolation relative to most other methods for direct arylation of azoles employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor to obtain excellent product yields in two hours.

  7. Nitric oxide activates intradomain disulfide bond formation in the kinase loop of Akt1/PKBα after burn injury.

    PubMed

    Lu, X-M; Tompkins, R G; Fischman, A J

    2013-03-01

    Severe burn injury is an acute inflammatory state with massive alterations in gene expression and levels of growth factors, cytokines and free radicals. During the catabolic processes, changes in insulin sensitivity and skeletal muscle wasting (unintended loss of 5-15% of lean body mass) are observed clinically. Here, we reveal a novel molecular mechanism of Akt1/protein kinase Bα (Akt1/PKBα) regulated via cross-talking between dephosphorylation of Thr308 and S-nitrosylation of Cys296 post severe burn injury, which were characterized using nano-LC interfaced with tandem quadrupole time-of-fight mass spectrometry (Q-TOF)micro tandem mass spectrometry in both in vitro and in vivo studies. For the in vitro studies, Akt1/PKBα was S-nitrosylated with S-nitrosoglutathione and derivatized by three methods. The derivatives were isolated by SDS-PAGE, trypsinized and analyzed by the tandem MS. For the in vivo studies, Akt1/PKBα in muscle lysates from burned rats was immunoprecipitated, derivatized with HPDP-Biotin and analyzed as above. The studies demonstrated that the NO free radical reacts with the free thiol of Cys296 to produce a Cys296-SNO intermediate which accelerates interaction with Cys310 to form Cys296-Cys310 in the kinase loop. MS/MS sequence analysis indicated that the dipeptide, linked via Cys296-Cys310, underwent dephosphorylation at Thr308. These effects were not observed in lysates from sham animals. As a result of this dual effect of burn injury, the loose conformation that is slightly stabilized by the Lys297-Thr308 salt bridge may be replaced by a more rigid structure which may block substrate access. Together with the findings of our previous report concerning mild IRS-1 integrity changes post burn, it is reasonable to conclude that the impaired Akt1/PKBα has a major impact on FOXO3 subcellular distribution and activities. PMID:23314241

  8. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 9 2010-07-01 2010-07-01 false Use of existing bonds, separate bonds and additional..., separate bonds and additional bonding. (a) Additional bonding. Section 13 neither prevents additional... or separate bond. (b) Use of existing bonds. Insofar as a bond currently in use is adequate to...

  9. Hydroxide-catalyzed bonding

    NASA Technical Reports Server (NTRS)

    Gwo, Dz-Hung (Inventor)

    2003-01-01

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

  10. Activation of X-H and X-D bonds (X = O, N, C) by alkaline-earth metal monoxide cations: experiment and theory.

    PubMed

    Bozović, Andrea; Bohme, Diethard K

    2009-07-28

    Experimental investigations are reported for reactions of MO (+) (M = Ca, Sr, and Ba) with elemental hydrides water, ammonia and methane proceeding in the gas phase at 295 +/- 3 K in helium buffer gas at a pressure of 0.35 +/- 0.01 Torr. Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer and a novel electrospray ion source/ion selection quadrupole/selected-ion flow tube/triple quadrupole (ESI/qQ/SIFT/QqQ) mass spectrometer. All three alkaline-earth metal oxide ions exclusively abstract a H-atom from the three hydrides with rate coefficients > 1 x 10(-11) cm(3) molecule(-1) s(-1). Formation of metal hydroxide ion was followed by sequential addition of water or ammonia, but not methane. Density functional calculations have provided potential energy surfaces for the X-H bond activations leading to H-atom abstraction as well as those for O-atom transfer and H(2)O elimination (with ammonia and methane). A comparison of experimental and theoretical isotope effects points toward a mechanism involving the direct atom transfer from XH and XD to O in MO (+)via a three-centered transition structure. PMID:19588017

  11. Acetaldehyde partial oxidation on the Au(111) model catalyst surface: C-C bond activation and formation of methyl acetate as an oxidative coupling product

    NASA Astrophysics Data System (ADS)

    Karatok, Mustafa; Vovk, Evgeny I.; Shah, Asad A.; Turksoy, Abdurrahman; Ozensoy, Emrah

    2015-11-01

    Partial oxidation of acetaldehyde (CH3CHO) on the oxygen pre-covered Au(111) single crystal model catalyst was investigated via Temperature Programmed Desorption (TPD) and Temperature Programmed Reaction Spectroscopy (TPRS) techniques, where ozone (O3) was utilized as the oxygen delivery agent providing atomic oxygen to the reacting surface. We show that for low exposures of O3 and small surface oxygen coverages, two partial oxidation products namely, methyl acetate (CH3COOCH3) and acetic acid (CH3COOH) can be generated without the formation of significant quantities of carbon dioxide. The formation of methyl acetate as the oxidative coupling reaction product implies that oxygen pre-covered Au(111) single crystal model catalyst surface can activate C-C bonds. In addition to the generation of these products; indications of the polymerization of acetaldehyde on the gold surface were also observed as an additional reaction route competing with the partial and total oxidation pathways. The interplay between the partial oxidation, total oxidation and polymerization pathways reveals the complex catalytic chemistry associated with the interaction between the acetaldehyde and atomic oxygen on catalytic gold surfaces.

  12. Molecular Dynamics Study of Twister Ribozyme: Role of Mg(2+) Ions and the Hydrogen-Bonding Network in the Active Site.

    PubMed

    Ucisik, Melek N; Bevilacqua, Philip C; Hammes-Schiffer, Sharon

    2016-07-12

    The recently discovered twister ribozyme is thought to utilize general acid-base catalysis in its self-cleavage mechanism, but the roles of nucleobases and metal ions in the mechanism are unclear. Herein, molecular dynamics simulations of the env22 twister ribozyme are performed to elucidate the structural and equilibrium dynamical properties, as well as to examine the role of Mg(2+) ions and possible candidates for the general base and acid in the self-cleavage mechanism. The active site region and the ends of the pseudoknots were found to be less mobile than other regions of the ribozyme, most likely providing structural stability and possibly facilitating catalysis. A purported catalytic Mg(2+) ion and the closest neighboring Mg(2+) ion remained chelated and relatively immobile throughout the microsecond trajectories, although removal of these Mg(2+) ions did not lead to any significant changes in the structure or equilibrium motions of the ribozyme on the microsecond time scale. In addition, a third metal ion, a Na(+) ion remained close to A1(O5'), the leaving group atom, during the majority of the microsecond trajectories, suggesting that it might stabilize the negative charge on A1(O5') during self-cleavage. The locations of these cations and their interactions with key nucleotides in the active site suggest that they may be catalytically relevant. The P1 stem is partially melted at its top and bottom in the crystal structure and further unwinds in the trajectories. The simulations also revealed an interconnected network comprised of hydrogen-bonding and π-stacking interactions that create a relatively rigid network around the self-cleavage site. The nucleotides involved in this network are among the highly conserved nucleotides in twister ribozymes, suggesting that this interaction network may be important to structure and function. PMID:27295275

  13. Probing the importance of hydrogen bonds in the active site of the subtilisin nattokinase by site-directed mutagenesis and molecular dynamics simulation.

    PubMed

    Zheng, Zhong-liang; Ye, Mao-qing; Zuo, Zhen-yu; Liu, Zhi-gang; Tai, Keng-chang; Zou, Guo-lin

    2006-05-01

    Hydrogen bonds occurring in the catalytic triad (Asp32, His64 and Ser221) and the oxyanion hole (Asn155) are very important to the catalysis of peptide bond hydrolysis by serine proteases. For the subtilisin NK (nattokinase), a bacterial serine protease, construction and analysis of a three-dimensional structural model suggested that several hydrogen bonds formed by four residues function to stabilize the transition state of the hydrolysis reaction. These four residues are Ser33, Asp60, Ser62 and Thr220. In order to remove the effect of these hydrogen bonds, four mutants (Ser33-->Ala33, Asp60-->Ala60, Ser62-->Ala62, and Thr220-->Ala220) were constructed by site-directed mutagenesis. The results of enzyme kinetics indicated that removal of these hydrogen bonds increases the free-energy of the transition state (DeltaDeltaG(T)). We concluded that these hydrogen bonds are more important for catalysis than for binding the substrate, because removal of these bonds mainly affects the kcat but not the K(m) values. A substrate, SUB1 (succinyl-Ala-Ala-Pro-Phe-p-nitroanilide), was used during enzyme kinetics experiments. In the present study we have also shown the results of FEP (free-energy perturbation) calculations with regard to the binding and catalysis reactions for these mutant subtilisins. The calculated difference in FEP also suggested that these four residues are more important for catalysis than binding of the substrate, and the simulated values compared well with the experimental values from enzyme kinetics. The results of MD (molecular dynamics) simulations further demonstrated that removal of these hydrogen bonds partially releases Asp32, His64 and Asn155 so that the stability of the transition state decreases. Another substrate, SUB2 (H-D-Val-Leu-Lys-p-nitroanilide), was used for FEP calculations and MD simulations. PMID:16411898

  14. Probing the importance of hydrogen bonds in the active site of the subtilisin nattokinase by site-directed mutagenesis and molecular dynamics simulation

    PubMed Central

    Zheng, Zhong-liang; Ye, Mao-qing; Zuo, Zhen-yu; Liu, Zhi-gang; Tai, Keng-chang; Zou, Guo-lin

    2006-01-01

    Hydrogen bonds occurring in the catalytic triad (Asp32, His64 and Ser221) and the oxyanion hole (Asn155) are very important to the catalysis of peptide bond hydrolysis by serine proteases. For the subtilisin NK (nattokinase), a bacterial serine protease, construction and analysis of a three-dimensional structural model suggested that several hydrogen bonds formed by four residues function to stabilize the transition state of the hydrolysis reaction. These four residues are Ser33, Asp60, Ser62 and Thr220. In order to remove the effect of these hydrogen bonds, four mutants (Ser33→Ala33, Asp60→Ala60, Ser62→Ala62, and Thr220→Ala220) were constructed by site-directed mutagenesis. The results of enzyme kinetics indicated that removal of these hydrogen bonds increases the free-energy of the transition state (ΔΔGT). We concluded that these hydrogen bonds are more important for catalysis than for binding the substrate, because removal of these bonds mainly affects the kcat but not the Km values. A substrate, SUB1 (succinyl-Ala-Ala-Pro-Phe-p-nitroanilide), was used during enzyme kinetics experiments. In the present study we have also shown the results of FEP (free-energy perturbation) calculations with regard to the binding and catalysis reactions for these mutant subtilisins. The calculated difference in FEP also suggested that these four residues are more important for catalysis than binding of the substrate, and the simulated values compared well with the experimental values from enzyme kinetics. The results of MD (molecular dynamics) simulations further demonstrated that removal of these hydrogen bonds partially releases Asp32, His64 and Asn155 so that the stability of the transition state decreases. Another substrate, SUB2 (H-D-Val-Leu-Lys-p-nitroanilide), was used for FEP calculations and MD simulations. PMID:16411898

  15. Rapid adhesive bonding concepts

    NASA Technical Reports Server (NTRS)

    Stein, B. A.; Tyeryar, J. R.; Hodges, W. T.

    1984-01-01

    Adhesive bonding in the aerospace industry typically utilizes autoclaves or presses which have considerable thermal mass. As a consequence, the rates of heatup and cooldown of the bonded parts are limited and the total time and cost of the bonding process is often relatively high. Many of the adhesives themselves do not inherently require long processing times. Bonding could be performed rapidly if the heat was concentrated in the bond lines or at least in the adherends. Rapid adhesive bonding concepts were developed to utilize induction heating techniques to provide heat directly to the bond line and/or adherends without heating the entire structure, supports, and fixtures of a bonding assembly. Bonding times for specimens are cut by a factor of 10 to 100 compared to standard press bonding. The development of rapid adhesive bonding for lap shear specimens (per ASTM D1003 and D3163), for aerospace panel bonding, and for field repair needs of metallic and advanced fiber reinforced polymeric matrix composite structures are reviewed.

  16. A Series of Diamagnetic Pyridine Monoimine Rhenium Complexes with Different Degrees of Metal-to-Ligand Charge Transfer: Correlating (13) C NMR Chemical Shifts with Bond Lengths in Redox-Active Ligands.

    PubMed

    Sieh, Daniel; Kubiak, Clifford P

    2016-07-18

    A set of pyridine monoimine (PMI) rhenium(I) tricarbonyl chlorido complexes with substituents of different steric and electronic properties was synthesized and fully characterized. Spectroscopic (NMR and IR) and single-crystal X-ray diffraction analyses of these complexes showed that the redox-active PMI ligands are neutral and that the overall electronic structure is little affected by the choices of the substituent at the ligand backbone. One- and two-electron reduction products were prepared from selected starting compounds and could also be characterized by multiple spectroscopic methods and X-ray diffraction. The final product of a one-electron reduction in THF is a diamagnetic metal-metal-bonded dimer after loss of the chlorido ligand. Bond lengths in and NMR chemical shifts of the PMI ligand backbone indicate partial electron transfer to the ligand. Two-electron reduction in THF also leads to the loss of the chlorido ligand and a pentacoordinate complex is obtained. The comparison with reported bond lengths and (13) C NMR chemical shifts of doubly reduced free pyridine monoaldimine ligands indicates that both redox equivalents in the doubly reduced rhenium complex investigated here are located in the PMI ligand. With diamagnetic complexes varying over three formal reduction stages at the PMI ligand we were, for the first time, able to establish correlations of the (13) C NMR chemical shifts with the relevant bond lengths in redox-active ligands over a full redox series. PMID:27319753

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

    PubMed

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

    2014-11-24

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

  18. Second sphere control of spin state: Differential tuning of axial ligand bonds in ferric porphyrin complexes by hydrogen bonding.

    PubMed

    Mittra, Kaustuv; Sengupta, Kushal; Singha, Asmita; Bandyopadhyay, Sabyasachi; Chatterjee, Sudipta; Rana, Atanu; Samanta, Subhra; Dey, Abhishek

    2016-02-01

    An iron porphyrin with a pre-organized hydrogen bonding (H-Bonding) distal architecture is utilized to avoid the inherent loss of entropy associated with H-Bonding from solvent (water) and mimic the behavior of metallo-enzyme active sites attributed to H-Bonding interactions of active site with the 2nd sphere residues. Resonance Raman (rR) data on these iron porphyrin complexes indicate that H-Bonding to an axial ligand like hydroxide can result in both stronger or weaker Fe(III)-OH bond relative to iron porphyrin complexes. The 6-coordinate (6C) complexes bearing water derived axial ligands, trans to imidazole or thiolate axial ligand with H-Bonding stabilize a low spin (LS) ground state (GS) when a complex without H-Bonding stabilizes a high spin (HS) ground state. DFT calculations reproduce the trend in the experimental data and provide a mechanism of how H-Bonding can indeed lead to stronger metal ligand bonds when the axial ligand donates an H-Bond and lead to weaker metal ligand bonds when the axial ligand accepts an H-Bond. The experimental and computational results explain how a weak Fe(III)-OH bond (due to H-Bonding) can lead to the stabilization of low spin ground state in synthetic mimics and in enzymes containing iron porphyrin active sites. H-Bonding to a water ligand bound to a reduced ferrous active site can only strengthen the Fe(II)-OH2 bond and thus exclusion of water and hydrophilic residues from distal sites of O2 binding/activating heme proteins is necessary to avoid inhibition of O2 binding by water. These results help demonstrate the predominant role played by H-Bonding and subtle changes in its orientation in determining the geometric and electronic structure of iron porphyrin based active sites in nature. PMID:26638009

  19. Formation, Characterization, and O-O Bond Activation of a Peroxomanganese(III) Complex Supported by a Cross-Clamped Cyclam Ligand.

    PubMed

    Colmer, Hannah E; Howcroft, Anthony W; Jackson, Timothy A

    2016-03-01

    Although there have been reports describing the nucleophilic reactivity of peroxomanganese(III) intermediates, as well as their conversion to high-valent oxo-bridged dimers, it remains a challenge to activate peroxomanganese(III) species for conversion to high-valent, mononuclear manganese complexes. Herein, we report the generation, characterization, and activation of a peroxomanganese(III) adduct supported by the cross-clamped, macrocyclic Me2EBC ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). This ligand is known to support high-valent, mononuclear Mn(IV) species with well-defined spectroscopic properties, which provides an opportunity to identify mononuclear Mn(IV) products from O-O bond activation of the corresponding Mn(III)-peroxo adduct. The peroxomanganese(III) intermediate, [Mn(III)(O2)(Me2EBC)](+), was prepared at low-temperature by the addition of KO2 to [Mn(II)(Cl)2(Me2EBC)] in CH2Cl2, and this complex was characterized by electronic absorption, electron paramagnetic resonance (EPR), and Mn K-edge X-ray absorption (XAS) spectroscopies. The electronic structure of the [Mn(III)(O2)(Me2EBC)](+) intermediate was examined by density functional theory (DFT) and time-dependent (TD) DFT calculations. Detailed spectroscopic investigations of the decay products of [Mn(III)(O2)(Me2EBC)](+) revealed the presence of mononuclear Mn(III)-hydroxo species or a mixture of mononuclear Mn(IV) and Mn(III)-hydroxo species. The nature of the observed decay products depended on the amount of KO2 used to generate [Mn(III)(O2)(Me2EBC)](+). The Mn(III)-hydroxo product was characterized by Mn K-edge XAS, and shifts in the pre-edge transition energies and intensities relative to [Mn(III)(O2)(Me2EBC)](+) provide a marker for differences in covalency between peroxo and nonperoxo ligands. To the best of our knowledge, this work represents the first observation of a mononuclear Mn(IV) center upon decay of a nonporphyrinoid Mn(III)-peroxo center. PMID:26908013

  20. Prospective bonding applications

    NASA Astrophysics Data System (ADS)

    Ancenay, H.; Benazet, D.

    1981-07-01

    Adhesive bonding in industry and in the laboratory is surveyed and prospects for its wider utilization are assessed. The economic impact of bonding technology on industry is discussed. Research is reviewed, centering on the development of nondestructive testing and inspection techniques. Traditional (wood) as well as new materials susceptible to bonding are considered. Applications in construction and civil engineering, in aeronautics, and in the automobile industry are covered. The use of glues in mechanical constructions, in assembling cylindrical parts, and in metal-metal bonding are examined. Hybrid assembling and bonding of composite materials are included.

  1. Weak bond screening system

    NASA Astrophysics Data System (ADS)

    Chuang, S. Y.; Chang, F. H.; Bell, J. R.

    Consideration is given to the development of a weak bond screening system which is based on the utilization of a high power ultrasonic (HPU) technique. The instrumentation of the prototype bond strength screening system is described, and the adhesively bonded specimens used in the system developmental effort are detailed. Test results obtained from these specimens are presented in terms of bond strength and level of high power ultrasound irradiation. The following observations were made: (1) for Al/Al specimens, 2.6 sec of HPU irradiation will screen weak bond conditions due to improper preparation of bonding surfaces; (2) for composite/composite specimens, 2.0 sec of HPU irradiation will disrupt weak bonds due to under-cured conditions; (3) for Al honeycomb core with composite skin structure, 3.5 sec of HPU irradiation will disrupt weak bonds due to bad adhesive or oils contamination of bonding surfaces; and (4) for Nomex honeycomb with Al skin structure, 1.3 sec of HPU irradiation will disrupt weak bonds due to bad adhesive.

  2. On divorcing isomers, dissecting reactivity, and resolving mechanisms of propane Csbnd H and aryl Csbnd X (X = halogen) bond activations mediated by a ligated copper(III) oxo complex

    NASA Astrophysics Data System (ADS)

    Rijs, Nicole J.; Weiske, Thomas; Schlangen, Maria; Schwarz, Helmut

    2014-07-01

    The long suspected presence of two isomeric copper complexes (A and B), proportionally dependent on ESI cone voltage, was confirmed by their isolation, separation and characterization in a travelling wave ion mobility spectrometry-mass spectrometer (TWIMS-MS) with modifications to allow for ion/molecule reactions to be performed. Despite their small difference in cross-sectional area (∼1%) the isomers were well resolved, in part due to a strong interaction of isomer B with the N2 buffer gas. The reactivity of each TWIMS-separated isomer was probed: propane reacted with isomer A via Csbnd H bond activation and O-atom transfer, while no such reactions were observed for isomer B; the aryl halides PhX (X = F, Cl, Br, I) also reacted solely with A, via either concerted oxidation and halide transfer, or O-atom transfer. DFT calculations reveal that the aryl Csbnd X bond activation of PhX by isomer A involves several mechanistic pathways. Are the suspected structural isomers of the copper species resolvable via TWIMS-MS? If so, what type of reactivity does each isomer have toward hydrocarbons? Further, the ability to selectively activate aryl halides is highly sought-after in order to carry out selective functionalizations. The halogen exchange of X is a desirable reaction and can be mediated by copper catalysts [56-58]. As well known, the Csbnd F and Csbnd Cl bonds are more stable than the Csbnd Br and Csbnd I bonds, the latter being more reactive and thus used more often in organic transformations. An understanding of the underlying mechanisms is thus key to using these underutilized substrates in catalytic reactions.Thus we also address the question: Can any isomer-separated reactive copper oxo species also activate other strong bonds, such as the Csbnd X bonds in aryl halides (PhX)? In addition, we carry out careful electronic structure calculations in order to gain additional mechanistic insight into the mechanism(s) of halogen-atom and O-atom transfer reactions

  3. Theoretical aspects of the biological catch bond.

    PubMed

    Prezhdo, Oleg V; Pereverzev, Yuriy V

    2009-06-16

    bond properties on weak protein-water interactions may provide universal activation mechanisms in many biological systems and create new types of catch binding. Molecular dynamics simulations provide atomistic insights: the molecular view of bond dissociation gives a foundation for theoretical models and differentiates between alternative interpretations of experimental data. The number of known catch bonds is growing; analogs are found in enzyme catalysis, peptide translocation through nanopores, DNA unwinding, photoinduced dissociation of chemical bonds, and negative thermal expansion of bulk materials, for example. Finer force resolution will likely provide many more. Understanding the properties of catch bonds offers insight into the behavior of biological systems subjected to external perturbations in general. PMID:19331389

  4. Bonded semiconductor substrate

    DOEpatents

    Atwater, Jr.; Harry A. , Zahler; James M.

    2010-07-13

    Ge/Si and other nonsilicon film heterostructures are formed by hydrogen-induced exfoliation of the Ge film which is wafer bonded to a cheaper substrate, such as Si. A thin, single-crystal layer of Ge is transferred to Si substrate. The bond at the interface of the Ge/Si heterostructures is covalent to ensure good thermal contact, mechanical strength, and to enable the formation of an ohmic contact between the Si substrate and Ge layers. To accomplish this type of bond, hydrophobic wafer bonding is used, because as the invention demonstrates the hydrogen-surface-terminating species that facilitate van der Waals bonding evolves at temperatures above 600.degree. C. into covalent bonding in hydrophobically bound Ge/Si layer transferred systems.

  5. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding. Technical progress report, March 1, 1992--February 28, 1995

    SciTech Connect

    Lichtenberger, D.L.

    1997-06-01

    During this period of the project we have (1) accomplished the high-resolution gas phase photoelectron spectra of C{sub 60} and C{sub 70}, (2) characterized the electronic features of imaging C{sub 60} on gold by STM, (3) evaluated the orbital distributions of C{sub 60} and the bonding interactions with metals, (4) revealed details of the bonding of phosphines to metals, including the subtleties of a geometrical twist in sterically crowded situations, (5) determined the formal electron distribution in the bonding of {eta}{sup 3} -cyclopropenyl with metals, (6) related gas-phase ionization energies to electron transfer kinetics and ion salvation thermochemistry of metallocenes, (7) correlated lone-pair ionization energies with proton affinities for a variety of amino acids and related compounds, (8) examined sigma-pi interactions in non-conjugated polyalkynes, (9) characterized extensive metal-ligand {pi} interactions in metal-acetylide compounds, and (10) continued to develop the experimental and theoretical methods for these studies. All of these studies have contributed significantly to expanding our understanding of the electronic structure and bonding of organic molecules and the ways this electronic structure is altered by interaction with metals. Further developments in the instrumentation and methods of gas phase and surface photoelectron spectroscopy are underway. Most notable is the progress on the new gas phase photoelectron spectrometer that combines improved capabilities for He I/He II UPS, XPS, and Auger investigations of organometallic molecules.

  6. Activation of wood surfaces for glue bonds by mechanical pre-treatment and its effects on some properties of veneer surfaces and plywood panels

    NASA Astrophysics Data System (ADS)

    Aydin, İsmail

    2004-06-01

    Some chemical pre-treatments with chemical reagents are widely applied to wood surfaces in order to improve bonding ability, wettability and reactivate wood surfaces for glue-wood bonds. Besides these chemical treatments, some mechanical pre-treatments such as sanding and planing can be applied to get a fresh surface which eliminates bonding problems and improves glue bonding of wood. In this study, 2 mm thick rotary cut veneers obtained from steamed beech ( Fagus orientalis) logs were used as material. Both air-drying and oven-drying methods were used for drying veneer. After drying, the surfaces of some veneers were sanded with 100 and 180 grit sandpapers. Three-layer-plywood panels were produced from sanded and non-sanded veneers by using urea formaldehyde and phenol formaldehyde glue resins to evaluate the effects of sanding some mechanical properties of plywood. Changes in pH, surface roughness and adhesive wettability of veneers were evaluated. Wettability of veneers was assessed with contact angle measurements according to the sessile drop method. Both veneer and plywood properties investigated in this study improved clearly after the sanding process. Shear and bending strength values of plywood panels manufactured from sanded and non-sanded veneers were vary depending on glue types and veneer drying methods.

  7. Energy pulse bonding

    NASA Technical Reports Server (NTRS)

    Smith, G. C.

    1972-01-01

    To eliminate many of the present termination problems a technique called energy pulse bonding (EPB) was developed. The process demonstrated the capability of: (1) joining conductors without prior removal of insulations, (2) joining conductors without danger of brittle intermetallics, (3) increased joint temperature capability, (4) simultaneous formation of several bonds, (5) capability of higher joint density, and (6) a production oriented process. The following metals were successfully bonded in the solid state: copper, beryllium copper, phosphor bronze, aluminum, brass, and Kovar.

  8. BONDING ALUMINUM METALS

    DOEpatents

    Noland, R.A.; Walker, D.E.

    1961-06-13

    A process is given for bonding aluminum to aluminum. Silicon powder is applied to at least one of the two surfaces of the two elements to be bonded, the two elements are assembled and rubbed against each other at room temperature whereby any oxide film is ruptured by the silicon crystals in the interface; thereafter heat and pressure are applied whereby an aluminum-silicon alloy is formed, squeezed out from the interface together with any oxide film, and the elements are bonded.

  9. Chemical bonding technology

    NASA Technical Reports Server (NTRS)

    Plueddemann, E.

    1986-01-01

    Primers employed in bonding together the various material interfaces in a photovoltaic module are being developed. The approach develops interfacial adhesion by generating actual chemical bonds between the various materials bonded together. The current status of the program is described along with the progress toward developing two general purpose primers for ethylene vinyl acetate (EVA), one for glass and metals, and another for plastic films.

  10. Valence bond entanglement entropy.

    PubMed

    Alet, Fabien; Capponi, Sylvain; Laflorencie, Nicolas; Mambrini, Matthieu

    2007-09-14

    We introduce for SU(2) quantum spin systems the valence bond entanglement entropy as a counting of valence bond spin singlets shared by two subsystems. For a large class of antiferromagnetic systems, it can be calculated in all dimensions with quantum Monte Carlo simulations in the valence bond basis. We show numerically that this quantity displays all features of the von Neumann entanglement entropy for several one-dimensional systems. For two-dimensional Heisenberg models, we find a strict area law for a valence bond solid state and multiplicative logarithmic corrections for the Néel phase. PMID:17930468

  11. Dichotomous Hydrogen Atom Transfer vs. Proton Coupled Electron Transfer During Activation of X-H Bonds (X = C, N, O) by Nonheme Iron-Oxo Complexes of Variable Basicity

    PubMed Central

    Usharani, Dandamudi; Lacy, David C.; Borovik, A. S.; Shaik, Sason

    2013-01-01

    We describe herein the hydrogen-atom transfer (HAT)/ proton-coupled electron-transfer (PCET) reactivity for FeIV-oxo and FeIII-oxo complexes (1–4) that activate C-H, N-H, and O-H bonds in 9,10 dihydroanthracene (S1), dimethylformamide (S2), 1,2 diphenylhydrazine (S3), p-methoxyphenol (S4), and 1,4-cyclohexadiene (S5). In 1–3, the iron is pentacoordinated by tris[N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) or its derivatives. These complexes are basic, in the order 3 >> 1 > 2. Oxidant 4, [FeIVN4Py(O)]2+ (N4Py: N,N-bis(2-pyridylmethyl)-bis(2-pyridyl) methylamine), is the least basic oxidant. The DFT results match experimental trends and exhibit a mechanistic spectrum ranging from concerted HAT and PCET reactions to concerted-asynchronous proton transfer (PT) / electron transfer (ET) mechanisms, all the way to PT. The singly occupied orbital along the O---H---X (X= C, N, O) moiety in the TS shows clearly that in the PCET cases, the electron is transferred separately from the proton. The Bell-Evans-Polanyi principle does not account for the observed reactivity pattern, as evidenced by the scatter in the plot of calculated barrier vs. reactions driving forces. However, a plot of the deformation energy in the TS vs. the respective barrier provides a clear signature of the HAT/PCET dichotomy. Thus, in all C-H bond activations, the barrier derives from the deformation energy required to create the TS, whereas in N-H/O-H bond activations, the deformation energy is much larger than the corresponding barrier, indicating the presence of stabilizing interaction between the TS fragments. A valence bond model is used to link the observed results with the basicity/acidity of the reactants. PMID:24124906

  12. Enhancement of laccase activity through the construction and breakdown of a hydrogen bond at the type I copper center in Escherichia coli CueO and the deletion mutant Δα5-7 CueO.

    PubMed

    Kataoka, Kunishige; Hirota, Shun; Maeda, Yasuo; Kogi, Hiroki; Shinohara, Naoya; Sekimoto, Madoka; Sakurai, Takeshi

    2011-02-01

    CueO is a multicopper oxidase involved in a copper efflux system of Escherichia coli and has high cuprous oxidase activity but little or no oxidizing activity toward various organic substances. However, its activity toward oxidization of organic substrates was found to be considerably increased by the removal of the methionine-rich helical segment that covers the substrate-binding site (Δα5-7 CueO) [Kataoka, K., et al. (2007) J. Mol. Biol. 373, 141]. In the study presented here, mutations at Pro444 to construct a second NH-S hydrogen bond between the backbone amide and coordinating Cys500 thiolate of the type I copper are shown to result in positive shifts in the redox potential of this copper center and enhanced oxidase activity in CueO. Analogous enhancement of the activity of Δα5-7 CueO has been identified only in the Pro444Gly mutant because Pro444 mutants limit the incorporation of copper ions into the trinuclear copper center. The activities of both CueO and Δα5-7 CueO were also enhanced by mutations to break down the hydrogen bond between the imidazole group of His443 that is coordinated to the type I copper and the β-carboxy group of Asp439 that is located in the outer sphere of the type I copper center. A synergetic effect of the positive shift in the redox potential of the type I copper center and the increase in enzyme activity has been achieved by the double mutation of Pro444 and Asp439 of CueO. Absorption, circular dichroism, and resonance Raman spectra indicate that the characteristics of the Cu(II)-S(Cys) bond were only minimally perturbed by mutations involving formation or disruption of a hydrogen bond from the coordinating groups to the type I copper. This study provides widely applicable strategies for tuning the activities of multicopper oxidases. PMID:21142169

  13. Do Social Bonds Matter for Emerging Adults?

    PubMed Central

    Salvatore, Christopher; Taniguchi, Travis A.

    2013-01-01

    The extent to which social bonds and turning points influence criminal activity has been the focus of much empirical research. However, there have been few empirical studies exploring social bonds and turning points and offending for those who have experienced emerging adulthood, a recently identified stage of the life course. Using data from the National Longitudinal Study of Adolescent Health we examined if indicators of social bonds and turning points were predictors of criminal offending. Several of the turning points and social bonds included in these analyses were found to influence decreases in criminal offending for a cohort of emerging adults. We extend previous research by examining the influence of social bonds and turning points on patterns of criminal offending during emerging adulthood. PMID:23487587

  14. Interfacial bonding stability

    NASA Technical Reports Server (NTRS)

    Boerio, J.

    1984-01-01

    Interfacial bonding stability by in situ ellipsometry was investigated. It is found that: (1) gamma MPS is an effective primer for bonding ethylene vinyl acetate (EVA) to aluminum; (2) ellipsometry is an effective in situ technique for monitoring the stability of polymer/metal interfaces; (3) the aluminized back surface of silicon wafers contain significant amounts of silicon and may have glass like properties.

  15. The dissociative bond.

    PubMed

    Gordon, Nirit

    2013-01-01

    Dissociation leaves a psychic void and a lingering sense of psychic absence. How do 2 people bond while they are both suffering from dissociation? The author explores the notion of a dissociative bond that occurs in the aftermath of trauma--a bond that holds at its core an understanding and shared detachment from the self. Such a bond is confined to unspoken terms that are established in the relational unconscious. The author proposes understanding the dissociative bond as a transitional space that may not lead to full integration of dissociated knowledge yet offers some healing. This is exemplified by R. Prince's (2009) clinical case study. A relational perspective is adopted, focusing on the intersubjective aspects of a dyadic relationship. In the dissociative bond, recognition of the need to experience mutual dissociation can accommodate a psychic state that yearns for relationship when the psyche cannot fully confront past wounds. Such a bond speaks to the need to reestablish a sense of human relatedness and connection when both parties in the relationship suffer from disconnection. This bond is bound to a silence that becomes both a means of protection against the horror of traumatic memory and a way to convey unspoken gestures toward the other. PMID:23282044

  16. Chemical Bonds I

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

  17. Earth-Bonding.

    ERIC Educational Resources Information Center

    Norgaard, Jim

    1988-01-01

    Defines "earth bonding" as dynamic interaction between individual and physical environment. Examines methods and goals of traditional environmental education. Describes development of five-day camping workshop for 11 outdoor education teachers. Describes how workshop facilitated earth bonding for teachers. Calls for further research in "bonding…

  18. Incorporation of an Intramolecular Hydrogen-bonding Motif in the Side-Chain of 4-Aminoquinolines Enhances Activity against Drug-Resistant P. falciparum

    PubMed Central

    Madrid, Peter B.; Liou, Ally P.; DeRisi, Joseph L.; Guy, R. Kiplin

    2006-01-01

    Previous data showing that several chloroquine analogs containing an intramolecular hydrogen bonding motif were potent against multidrug-resistant P. falciparum, led to the exploration of the importance of this motif. A series of 116 compounds containing four different alkyl linkers and various aromatic substitutions with hydrogen bond accepting capability was synthesized. The series showed broad potency against the drug-resistant W2 strain of P. falciparum. In particular, a novel series containing variations of the α-aminocresol motif gave 8 compounds with IC50's more potent than 5 nM against the W2 strain. Such simple modifications, significantly altering the pKa and sterics of the basic side chain in chloroquine analogs, may prove to be part of a strategy for overcoming the problem of worldwide resistance to affordable antimalarial drugs. PMID:16854059

  19. Synthesis, characterization and molecular modelling of a novel dipyridamole supramolecule - X-ray structure, quantum mechanics and molecular dynamics study to comprehend the hydrogen bond structure-activity relationship

    NASA Astrophysics Data System (ADS)

    Vepuri, Suresh B.; Devarajegowda, H. C.; Soliman, Mahmoud E.

    2016-02-01

    Hydrochloride salt formation for Active Pharmaceutical Ingredients (APIs) is the primary choice to impart aqueous solubility and to promote dissolution. Dipyridamole (DIP) is a cardiovascular drug which is practically insoluble in water. We discovered a new form of DIP called as dipyridamole hydrochloride trihydrate (DIPHT), which was prepared by an unusual method of reacting the DIP with hydrated hydrochloric acid (HCl) that was liberated in situ by the reaction of ferric chloride with water. The liberated HCl was consumed as reagent in situ by the scavenger (API) and was converted to a hydrochloride trihydrate. The product was characterized by FTIR, mass spectroscopy, PXRD and DSC. Supramolecular structure of this novel DIPHT was revealed by single crystal XRD. A sustained intramolecular hydrogen bond alliance was found in DIP and the DIPHT. Stability of this hydrogen bond was further evaluated by means of molecular modelling studies. We performed electron calculations using quantum mechanics (QM) on both the base and salt structures to compare their geometry and molecular orbital energy levels. Molecular Dynamics (MD) simulations were also conducted in explicit solvent models to provide more insights into the hydrogen bond strength and conformational preferences of the base and salt structure. Together with QM and MD, we were able to explain the influence of hydrogen bonds on proton uptake activity of DIP and stability of DIP and DIPHT. DIPHT which can dissolve faster than DIP in water may enhance the dissolution and bioavailability of the drug. As the current drug development research is shifting to repurpose the existing drugs in order to subside the untoward risks in new drug development, we believe that DIPHT with its intrinsic aqueous solubility could bring more application for DIP and generate interest within the pharmaceutical industry.

  20. Influence of Water Storage and Bonding Material on Bond Strength of Metallic Brackets to Ceramic.

    PubMed

    Costa, Ana Rosa; Correr, Américo Bortolazzo; Consani, Simonides; Giorgi, Maria Cecília Caldas; Vedovello, Silvia Amélia; Vedovello Filho, Mário; Santos, Eduardo Cesar Almada; Correr-Sobrinho, Lourenço

    2015-10-01

    This study investigated the influence of water storage (24 h and 6 months), and Transbond XT and Fuji Ortho LC bonding materials on the bond strength of metallic brackets bonded to feldspathic ceramic. Four cylinders of feldspathic ceramic were etched with 10% hydrofluoric acid for 60 s. Each cylinder received two layers of silane. Metallic brackets were bonded to the cylinders using Transbond XT or Fuji Ortho LC. Light-activation was carried out with 40 s total exposure time using Bluephase G2. Half the specimens for each bonding materials (n=20) were stored in distilled water at 37 °C for 24 h and the other half for 6 months. Shear bond strength testing was performed after storage times at a crosshead speed of 1 mm/min. The adhesive remnant index (ARI) was used to evaluate the amount of adhesive remaining on the ceramic surface at ×8 magnification. Data were subjected to two-way ANOVA and Tukey's test (p<0.05). Transbond XT showed significantly higher bond strength (p<0.05) than Fuji Ortho LC. Significant differences in bond strength (p<0.05) were found when 24 h and 6 months storage times were compared between materials. ARI showed a predominance of score 0 for all groups, and higher scores at 1, 2 and 3 for 24 h storage time. In conclusion, storage time and bonding materials showed significant influence on the bond strength of brackets to ceramic. PMID:26647936

  1. Direct C-C Coupling of CO2 and the Methyl Group from CH4 Activation through Facile Insertion of CO2 into Zn-CH3 σ-Bond.

    PubMed

    Zhao, Yuntao; Cui, Chaonan; Han, Jinyu; Wang, Hua; Zhu, Xinli; Ge, Qingfeng

    2016-08-17

    Conversion of CO2 and CH4 to value-added products will contribute to alleviating the green-house gas effect but is a challenge both scientifically and practically. Stabilization of the methyl group through CH4 activation and facile CO2 insertion ensure the realization of C-C coupling. In the present study, we demonstrate the ready C-C coupling reaction on a Zn-doped ceria catalyst. The detailed mechanism of this direct C-C coupling reaction was examined based on the results from density functional theory calculations. The results show that the Zn dopant stabilizes the methyl group by forming a Zn-C bond, thus hindering subsequent dehydrogenation of CH4. CO2 can be inserted into the Zn-C bond in an activated bent configuration, with the transition state in the form of a three-centered Zn-C-C moiety and an activation barrier of 0.51 eV. The C-C coupling reaction resulted in the acetate species, which could desorb as acetic acid by combining with a surface proton. The formation of acetic acid from CO2 and CH4 is a reaction with 100% atom economy, and the implementation of the reaction on a heterogeneous catalyst is of great importance to the utilization of the greenhouse gases. We tested other possible dopants including Al, Ga, Cd, In, and Ni and found a positive correlation between the activation barrier of C-C coupling and the electronegativity of the dopant, although C-H bond activation is likely the dominant reaction on the Ni-doped ceria catalyst. PMID:27452233

  2. Dicobalt-μ-oxo polyoxometalate compound, [(α(2)-P2W17O61Co)2O](14-): a potent species for water oxidation, C-H bond activation, and oxygen transfer.

    PubMed

    Barats-Damatov, Delina; Shimon, Linda J W; Weiner, Lev; Schreiber, Roy E; Jiménez-Lozano, Pablo; Poblet, Josep M; de Graaf, Coen; Neumann, Ronny

    2014-02-01

    High-valent oxo compounds of transition metals are often implicated as active species in oxygenation of hydrocarbons through carbon-hydrogen bond activation or oxygen transfer and also in water oxidation. Recently, several examples of cobalt-catalyzed water oxidation have been reported, and cobalt(IV) species have been suggested as active intermediates. A reactive species, formally a dicobalt(IV)-μ-oxo polyoxometalate compound [(α2-P2W17O61Co)2O](14-), [(POMCo)2O], has now been isolated and characterized by the oxidation of a monomeric [α2-P2W17O61Co(II)(H2O)](8-), [POMCo(II)H2O], with ozone in water. The crystal structure shows a nearly linear Co-O-Co moiety with a Co-O bond length of ∼1.77 Å. In aqueous solution [(POMCo)2O] was identified by (31)P NMR, Raman, and UV-vis spectroscopy. Reactivity studies showed that [(POMCo)2O]2O] is an active compound for the oxidation of H2O to O2, direct oxygen transfer to water-soluble sulfoxides and phosphines, indirect epoxidation of alkenes via a Mn porphyrin, and the selective oxidation of alcohols by carbon-hydrogen bond activation. The latter appears to occur via a hydrogen atom transfer mechanism. Density functional and CASSCF calculations strongly indicate that the electronic structure of [(POMCo)2O]2O] is best defined as a compound having two cobalt(III) atoms with two oxidized oxygen atoms. PMID:24437566

  3. Intermolecular C-H bond activation of benzene and pyridines by a vanadium(III) alkylidene including a stepwise conversion of benzene to a vanadium-benzyne complex

    SciTech Connect

    Andino, José G; Kilgore, Uriah J; Pink, Maren; Ozarowski, Andrew; Krzystek, J; Telser, Joshua; Baik, Mu-Hyun; Mindiola, Daniel J

    2012-01-20

    Breaking of the carbon-hydrogen bond of benzene and pyridine is observed with (PNP)V(CH2tBu)2 (1), and in the case of benzene, the formation of an intermediate benzyne complex (C) is proposed, and indirect proof of its intermediacy is provided by identification of (PNP)V=O(η2-C6H4) in combination with DFT calculations.

  4. Role of Active Site Residues in Promoting Cobalt-Carbon Bond Homolysis in Adenosylcobalamin-Dependent Mutases Revealed Through Experiment and Computation

    PubMed Central

    Román-Meléndez, Gabriel D.; von Glehn, Patrick; Harvey, Jeremy N.; Mulholland, Adrian J.; Marsh, E. Neil G.

    2014-01-01

    Adenosylcobalamin serves as a source of reactive free radicals that are generated by homolytic scission of the coenzyme’s cobalt-carbon bond. AdoCbl-dependent enzymes accelerate AdoCbl homolysis by ~1012-fold, but the mechanism by which this is accomplished remains unclear. We have combined experimental and computational approaches to gain molecular-level insight into this process for glutamate mutase. Two residues, glutamate-330 and lysine-326, form hydrogen bonds with the adenosyl group of the coenzyme. A series of mutations were introduced at these positions that impair the enzyme’s ability to catalyze coenzyme homolysis and tritium exchange with the substrate by 2 – 4 orders of magnitude. These mutations, together with the wild-type enzyme, were also characterized in silico by molecular dynamics simulations of the enzyme:AdoCbl:substrate with AdoCbl modeled in either the associated (Co-C bond formed) or the dissociated (adenosyl radical + CblII) state. The simulations reveal that the number of hydrogen bonds between the adenosyl group and the protein side-chains increases in the homolytically-dissociated state, with respect to the associated state, for both the wild-type and mutant enzymes. The mutations also cause a progressive increase in the mean distance between the 5′-carbon of the adenosyl radical and the abstractable hydrogen of the substrate. Interestingly, the distance between the 5′-carbon and substrate hydrogen, determined computationally, was found to inversely correlate with the logk for tritium exchange (r = 0.93) determined experimentally. Taken together, these results point to a dual role for these residues: they both stabilize the homolytic state through electrostatic interactions between the protein and the dissociated coenzyme, and correctly position the adenosyl radical to facilitate hydrogen abstraction from the substrate. PMID:24341954

  5. Shape Bonding method

    NASA Technical Reports Server (NTRS)

    Pontius, James T. (Inventor)

    2010-01-01

    The present invention is directed to a method of bonding at least two surfaces together. The methods step of the present invention include applying a strip of adhesive to a first surface along a predefined outer boundary of a bond area and thereby defining a remaining open area there within. A second surface, or gusset plate, is affixed onto the adhesive before the adhesive cures. The strip of adhesive is allowed to cure and then a second amount of adhesive is applied to cover the remaining open area and substantially fill a void between said first and second surfaces about said bond area. A stencil may be used to precisely apply the strip of adhesive. When the strip cures, it acts as a dam to prevent overflow of the subsequent application of adhesive to undesired areas. The method results in a precise bond area free of undesired shapes and of a preferred profile which eliminate the drawbacks of the prior art bonds.

  6. Halogen bonding anion recognition.

    PubMed

    Brown, Asha; Beer, Paul D

    2016-07-01

    A halogen bond is an attractive non-covalent interaction between an electrophilic region in a covalently bonded halogen atom and a Lewis base. While these interactions have long been exploited as a tool in crystal engineering their powerful ability to direct supramolecular self-assembly and molecular recognition processes in solution has, until recently, been overlooked. During the last decade however an ever-increasing number of studies on solution-phase halogen-bond-mediated anion recognition processes has emerged. This Feature Article summarises advancements which have been made thus far in this rapidly developing research area. We survey the use of iodoperfluoroarene, haloimidazolium and halotriazole/triazolium halogen-bond-donor motifs in anion receptor design, before providing an account of our research into the application of mechanically interlocked rotaxane and catenane frameworks as halogen bonding anion host systems. PMID:27273600

  7. Wood Bond Testing

    NASA Technical Reports Server (NTRS)

    1989-01-01

    A joint development program between Hartford Steam Boiler Inspection Technologies and The Weyerhaeuser Company resulted in an internal bond analyzer (IBA), a device which combines ultrasonics with acoustic emission testing techniques. It is actually a spinoff from a spinoff, stemming from a NASA Lewis invented acousto-ultrasonic technique that became a system for testing bond strength of composite materials. Hartford's parent company, Acoustic Emission Technology Corporation (AET) refined and commercialized the technology. The IBA builds on the original system and incorporates on-line process control systems. The IBA determines bond strength by measuring changes in pulsar ultrasonic waves injected into a board. Analysis of the wave determines the average internal bond strength for the panel. Results are displayed immediately. Using the system, a mill operator can adjust resin/wood proportion, reduce setup time and waste, produce internal bonds of a consistent quality and automatically mark deficient products.

  8. Chemical Bonding Technology: Direct Investigation of Interfacial Bonds

    NASA Technical Reports Server (NTRS)

    Koenig, J. L.; Boerio, F. J.; Plueddemann, E. P.; Miller, J.; Willis, P. B.; Cuddihy, E. F.

    1986-01-01

    This is the third Flat-Plate Solar Array (FSA) Project document reporting on chemical bonding technology for terrestrial photovoltaic (PV) modules. The impetus for this work originated in the late 1970s when PV modules employing silicone encapsulation materials were undergoing delamination during outdoor exposure. At that time, manufacturers were not employing adhesion promoters and, hence, module interfaces in common with the silicone materials were only in physical contact and therefore easily prone to separation if, for example, water were to penetrate to the interfaces. Delamination with silicone materials virtually vanished when adhesion promoters, recommended by silicone manufacturers, were used. The activities related to the direct investigation of chemically bonded interfaces are described.

  9. Nature of the Xe(VI)-N Bonds in F6 XeNCCH3 and F6 Xe(NCCH3)2 and the Stereochemical Activity of Their Xenon Valence Electron Lone Pairs.

    PubMed

    Haner, Jamie; Matsumoto, Kazuhiko; Mercier, Hélène P A; Schrobilgen, Gary J

    2016-03-24

    The recently reported syntheses and X-ray crystal structures of the highly endothermic compounds F6XeNCCH3 and F6Xe(NCCH3)2 ⋅CH3CN provide the first, albeit weakly covalent, Xe(VI)-N bonds. The XeF6 unit of F6 XeNCCH3 possesses distorted octahedral (C3v ) symmetry similar to gas-phase XeF6 , whereas the XeF6 unit of F6 Xe(NCCH3)2 ⋅CH3CN possesses C2v symmetry. Herein, the natural bond orbital (NBO), atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses show that the Xe valence electron lone pairs (VELPs) of both compounds are stereochemically active. The Xe VELPS are diffuse and ineffectively screen their Xe cores so that the Xe VELP positions correspond to the most electrophilic regions of the MEPS, which enables the opposing N VELP of CH3CN to coordinate to this region. These bonds are predominantly electrostatic in nature and are interpreted as σ-hole interactions. PMID:26918266

  10. The Halogen Bond

    PubMed Central

    2016-01-01

    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design. PMID:26812185

  11. The Halogen Bond.

    PubMed

    Cavallo, Gabriella; Metrangolo, Pierangelo; Milani, Roberto; Pilati, Tullio; Priimagi, Arri; Resnati, Giuseppe; Terraneo, Giancarlo

    2016-02-24

    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design. PMID:26812185

  12. Activation of Homolytic Si-Zn and Si-Hg Bond Cleavage, Mediated by a Pt(0) Complex, via Novel Pt-Zn and Pt-Hg Compounds.

    PubMed

    Kratish, Yosi; Molev, Gregory; Kostenko, Arseni; Sheberla, Dennis; Tumanskii, Boris; Botoshansky, Mark; Shimada, Shigeru; Bravo-Zhivotovskii, Dmitry; Apeloig, Yitzhak

    2015-09-28

    The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized. Mild warming or photolysis of 2 or 3 lead to homolytic dissociation of the Pt-MSiR3 bond generating silyl radicals and novel unstable pentacoordinate platinum paramagnetic complexes (M=Zn (5), Hg (6)) whose structures were determined by EPR spectroscopy and DFT calculations. PMID:26288342

  13. Novel enzymatic activity of cell free extract from thermophilic Geobacillus sp. UZO 3 catalyzes reductive cleavage of diaryl ether bonds of 2,7-dichlorodibenzo-p-dioxin.

    PubMed

    Suzuki, Yuzoh; Nakamura, Masaya; Otsuka, Yuichiro; Suzuki, Nao; Ohyama, Keisuke; Kawakami, Takeshi; Sato, Kanna; Kajita, Shinya; Hishiyama, Shojiro; Fujii, Takeo; Takahashi, Atsushi; Katayama, Yoshihiro

    2011-04-01

    We characterized the ability of the cell free extract from polychlorinated dibenzo-p-dioxins degrading bacterium Geobacillus sp. UZO 3 to reduce even highly chlorinated dibenzo-p-dioxins such as octachlorodibenzo-p-dioxins in incineration fly ash. The degradation of 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD) as a model dioxin catalyzed by the cell free extract from this strain implicates that the ether bonds of 2,7-DCDD molecule undergo reductive cleavage, since 4',5-dichloro-2-hydroxydiphenyl ether and 4-chlorophenol were detected as intermediate products of 2,7-DCDD degradation. PMID:21435685

  14. Bonding aerogels with polyurethanes

    SciTech Connect

    Matthews, F.M.; Hoffman, D.M.

    1989-11-01

    Aerogels, porous silica glasses with ultra-fine cell size (30nm), are made by a solution gelation (sol-gel) process. The resulting gel is critical point dried to densities from 0.15--0.60 g/cc. This material is machinable, homogeneous, transparent, coatable and bondable. To bond aerogel an adhesive should have long cure time, no attack on the aerogel structure, and high strength. Several epoxies and urethanes were examined to determine if they satisfied these conditions. Bond strengths above 13 psi were found with double bubble and DP-110 epoxies and XI-208/ODA-1000 and Castall U-2630 urethanes. Hardman Kalex Tough Stuff'' A-85 hardness urethane gave 18 psi bond strength. Hardman A-85, Tuff-Stuff'' was selected for further evaluation because it produced bond strengths comparable to the adherend cohesive strength. 5 refs., 2 figs.

  15. Junk-Bond Colleges.

    ERIC Educational Resources Information Center

    Van Der Werf, Martin

    2003-01-01

    Describes how a long-predicted decline in the fortunes of small private colleges is beginning to show up in the bond market, as the number of colleges now rated in the junk category has nearly doubled. (EV)

  16. Detecting Defective Solder Bonds

    NASA Technical Reports Server (NTRS)

    Paulson, R.; Barney, J.; Decker, H. J.

    1984-01-01

    Method is noncontact and nondestructive. Technique detects solder bonds in solar array of other large circuit board, using thermal-imaging camera. Board placed between heat lamp and camera. Poor joints indiated by "cold" spots on the infrared image.

  17. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay - The effect of mononucleotide structure, phosphate activation and montmorillonite composition on phosphodiester bond formation

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; KAMALUDDIN; Ertem, Gozen

    1990-01-01

    The 2(prime)-d-5(prime)-GMP and 2(prime)-d-5(prime)-AMP bind 2 times more strongly to montmorillonite 22A than do 2(prime)-d-5(prime)-CMP and 5(prime)-TMP. The dinucleotide d(pG)2 forms in 9.2 percent yield and the cyclic dinucleotide c(dpG)2 in 5.4 percent yield in the reaction of 2(prime)-d-5(prime)-GMP with EDAC in the presence of montmorillonite 22A. The yield of dimers which contain the phosphodiester bond decreases as the reaction medium is changed from 0.2 M NaCl to a mixture of 0.2 M NaCl and 0.075 M MgCl2. A low yield of d(pA)2 was observed in the condensation reaction of 5(prime)-ImdpA on montmorillonite 22A. The yield of d(pA)2 obtained when EDAC is used as the condensing agent increases with increasing iron content of the Na(+)-montmorillonite used as catalyst. Evidence is presented which shows that the acidity of the Na(+)-montmorillonite is a necessary but not sufficient factor for the montmorillonite catalysis of phosphodiester bond formation.

  18. H2O2/DMSO-Promoted Regioselective Synthesis of 3,3'-Bisimidazopyridinylmethanes via Intermolecular Oxidative C(sp(2))-H Bond Activation of Imidazoheterocycles.

    PubMed

    Patel, Om P S; Anand, Devireddy; Maurya, Rahul K; Yadav, Prem P

    2016-09-01

    In the past decade, metal-free approaches for C-C bond formation have attracted a great deal of attention due to their ease of use and low cost. This report represents a novel and metal-free synthesis of 3,3'-bisimidazopyridinylmethanes via intermolecular oxidative C(sp(2))-H bond functionalization of imidazo[1,2-a]pyridines with dimethyl sulfoxide as the carbon synthon (CH2) using H2O2 as a mild oxidant under air. A library of 3,3'-bis(2-arylimidazo[1,2-a]pyridin-3-yl)methanes has been achieved in good to excellent yields. The present methodology has been successfully applied to imidazo[2,1-b]thiazoles and imidazo[2,1-b]benzothiazoles. Furthermore, the current approach was also extended for the synthesis of unsymmetrical 3,3'-bisimidazopyridinylmethanes under optimized reaction conditions. A mechanistic pathway is proposed on the basis of experiments with radical scavengers and DMSO-d6 and ESI-MS observations. PMID:27487477

  19. Neural mechanisms of mother-infant bonding and pair bonding: Similarities, differences, and broader implications.

    PubMed

    Numan, Michael; Young, Larry J

    2016-01-01

    This article is part of a Special Issue "Parental Care". Mother-infant bonding is a characteristic of virtually all mammals. The maternal neural system may have provided the scaffold upon which other types of social bonds in mammals have been built. For example, most mammals exhibit a polygamous mating system, but monogamy and pair bonding between mating partners occur in ~5% of mammalian species. In mammals, it is plausible that the neural mechanisms that promote mother-infant bonding have been modified by natural selection to establish the capacity to develop a selective bond with a mate during the evolution of monogamous mating strategies. Here we compare the details of the neural mechanisms that promote mother-infant bonding in rats and other mammals with those that underpin pair bond formation in the monogamous prairie vole. Although details remain to be resolved, remarkable similarities and a few differences between the mechanisms underlying these two types of bond formation are revealed. For example, amygdala and nucleus accumbens-ventral pallidum (NA-VP) circuits are involved in both types of bond formation, and dopamine and oxytocin actions within NA appear to promote the synaptic plasticity that allows either infant or mating partner stimuli to persistently activate NA-VP attraction circuits, leading to an enduring social attraction and bonding. Further, although the medial preoptic area is essential for maternal behavior, its role in pair bonding remains to be determined. Our review concludes by examining the broader implications of this comparative analysis, and evidence is provided that the maternal care system may have also provided the basic neural foundation for other types of strong social relationships, beyond pair bonding, in mammals, including humans. PMID:26062432

  20. Template Catalysis by Metal-Ligand Cooperation. C-C Bond Formation via Conjugate Addition of Non-activated Nitriles under Mild, Base-free Conditions Catalyzed by a Manganese Pincer Complex.

    PubMed

    Nerush, Alexander; Vogt, Matthias; Gellrich, Urs; Leitus, Gregory; Ben-David, Yehoshoa; Milstein, David

    2016-06-01

    The first example of a catalytic Michael addition reaction of non-activated aliphatic nitriles to α,β-unsaturated carbonyl compounds under mild, neutral conditions is reported. A new de-aromatized pyridine-based PNP pincer complex of the Earth-abundant, first-row transition metal manganese serves as the catalyst. The reaction tolerates a variety of nitriles and Michael acceptors with different steric features and acceptor strengths. Mechanistic investigations including temperature-dependent NMR spectroscopy and DFT calculations reveal that the cooperative activation of alkyl nitriles, which leads to the generation of metalated nitrile nucleophile species (α-cyano carbanion analogues), is a key step of the mechanism. The metal center is not directly involved in the catalytic bond formation but rather serves, cooperatively with the ligand, as a template for the substrate activation. This approach of "template catalysis" expands the scope of potential donors for conjugate addition reactions. PMID:27164437

  1. Canonical-ensemble state-averaged complete active space self-consistent field (SA-CASSCF) strategy for problems with more diabatic than adiabatic states: Charge-bond resonance in monomethine cyanines

    SciTech Connect

    Olsen, Seth

    2015-01-28

    This paper reviews basic results from a theory of the a priori classical probabilities (weights) in state-averaged complete active space self-consistent field (SA-CASSCF) models. It addresses how the classical probabilities limit the invariance of the self-consistency condition to transformations of the complete active space configuration interaction (CAS-CI) problem. Such transformations are of interest for choosing representations of the SA-CASSCF solution that are diabatic with respect to some interaction. I achieve the known result that a SA-CASSCF can be self-consistently transformed only within degenerate subspaces of the CAS-CI ensemble density matrix. For uniformly distributed (“microcanonical”) SA-CASSCF ensembles, self-consistency is invariant to any unitary CAS-CI transformation that acts locally on the ensemble support. Most SA-CASSCF applications in current literature are microcanonical. A problem with microcanonical SA-CASSCF models for problems with “more diabatic than adiabatic” states is described. The problem is that not all diabatic energies and couplings are self-consistently resolvable. A canonical-ensemble SA-CASSCF strategy is proposed to solve the problem. For canonical-ensemble SA-CASSCF, the equilibrated ensemble is a Boltzmann density matrix parametrized by its own CAS-CI Hamiltonian and a Lagrange multiplier acting as an inverse “temperature,” unrelated to the physical temperature. Like the convergence criterion for microcanonical-ensemble SA-CASSCF, the equilibration condition for canonical-ensemble SA-CASSCF is invariant to transformations that act locally on the ensemble CAS-CI density matrix. The advantage of a canonical-ensemble description is that more adiabatic states can be included in the support of the ensemble without running into convergence problems. The constraint on the dimensionality of the problem is relieved by the introduction of an energy constraint. The method is illustrated with a complete active space

  2. The electronic structure and chemical bonding of vitamin B12

    NASA Astrophysics Data System (ADS)

    Kurmaev, E. Z.; Moewes, A.; Ouyang, L.; Randaccio, L.; Rulis, P.; Ching, W. Y.; Bach, M.; Neumann, M.

    2003-05-01

    The electronic structure and chemical bonding of vitamin B12 (cyanocobalamin) and B12-derivative (methylcobalamin) are studied by means of X-ray emission (XES) and photoelectron (XPS) spectroscopy. The obtained results are compared with ab initio electronic structure calculations using the orthogonalized linear combination of the atomic orbital method (OLCAO). We show that the chemical bonding in vitamin B12 is characterized by the strong Co-C bond and relatively weak axial Co-N bond. It is further confirmed that the Co-C bond in cyanocobalamin is stronger than that of methylcobalamin resulting in their different biological activity.

  3. 27 CFR 24.147 - Operations bond or unit bond.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Operations bond or unit bond. 24.147 Section 24.147 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS WINE Establishment and Operations Bonds and Consents of Surety § 24.147 Operations bond or unit...

  4. Magnesium ion catalyzed P-N bond hydrolysis in imidazolide-activated nucleotides - Relevance to template-directed synthesis of polynucleotides

    NASA Technical Reports Server (NTRS)

    Kanavarioti, Anastassia; Bernasconi, Claude F.; Doodokyan, Donald L.; Alberas, Diann J.

    1989-01-01

    Results are presented from a detailed study of the P-N bond hydrolysis in guanosine 5-prime-monophosphate 2-methylimidazolide (2-MeImpG) and in guanosine 5-prime-imidazolide (ImpG) in the presence of 0-0.50 M Mg(2+). Pseudo-first-order rate constants of these compounds were obtained as a function of Mg(2+) concentration, for pH values between 6 and 10 and 37 C. It was found that Mg(2+) catalysis was most effective at pH 10, where a 15-fold increase in hydrolysis was achieved in 0.02 M Mg; at 0.2 M, a 115-fold increase was observed. Implication of these results for the mechanism of template-directed oligomerization is discussed.

  5. Neutron Diffraction Reveals Hydrogen Bonds Critical for cGMP-Selective Activation: Insights for cGMP-Dependent Protein Kinase Agonist Design

    PubMed Central

    2015-01-01

    High selectivity of cyclic-nucleotide binding (CNB) domains for cAMP and cGMP are required for segregating signaling pathways; however, the mechanism of selectivity remains unclear. To investigate the mechanism of high selectivity in cGMP-dependent protein kinase (PKG), we determined a room-temperature joint X-ray/neutron (XN) structure of PKG Iβ CNB-B, a domain 200-fold selective for cGMP over cAMP, bound to cGMP (2.2 Å), and a low-temperature X-ray structure of CNB-B with cAMP (1.3 Å). The XN structure directly describes the hydrogen bonding interactions that modulate high selectivity for cGMP, while the structure with cAMP reveals that all these contacts are disrupted, explaining its low affinity for cAMP. PMID:25271401

  6. Neutron diffraction reveals hydrogen bonds critical for cGMP-selective activation: insights for cGMP-dependent protein kinase agonist design.

    PubMed

    Huang, Gilbert Y; Gerlits, Oksana O; Blakeley, Matthew P; Sankaran, Banumathi; Kovalevsky, Andrey Y; Kim, Choel

    2014-11-01

    High selectivity of cyclic-nucleotide binding (CNB) domains for cAMP and cGMP are required for segregating signaling pathways; however, the mechanism of selectivity remains unclear. To investigate the mechanism of high selectivity in cGMP-dependent protein kinase (PKG), we determined a room-temperature joint X-ray/neutron (XN) structure of PKG Iβ CNB-B, a domain 200-fold selective for cGMP over cAMP, bound to cGMP (2.2 Å), and a low-temperature X-ray structure of CNB-B with cAMP (1.3 Å). The XN structure directly describes the hydrogen bonding interactions that modulate high selectivity for cGMP, while the structure with cAMP reveals that all these contacts are disrupted, explaining its low affinity for cAMP. PMID:25271401

  7. A Tale of Copper Coordination Frameworks: Controlled Single-Crystal-to-Single-Crystal Transformations and Their Catalytic C-H Bond Activation Properties.

    PubMed

    Chen, Yifa; Feng, Xiao; Huang, Xianqiang; Lin, Zhengguo; Pei, Xiaokun; Li, Siqing; Li, Jikun; Wang, Shan; Li, Rui; Wang, Bo

    2015-09-28

    Metal-organic frameworks (MOFs), as a class of microporous materials with well-defined channels and rich functionalities, hold great promise for various applications. Yet the formation and crystallization processes of various MOFs with distinct topology, connectivity, and properties remain largely unclear, and the control of such processes is rather challenging. Starting from a 0D Cu coordination polyhedron, MOP-1, we successfully unfolded it to give a new 1D-MOF by a single-crystal-to-single-crystal (SCSC) transformation process at room temperature as confirmed by SXRD. We also monitored the continuous transformation states by FTIR and PXRD. Cu MOFs with 2D and 3D networks were also obtained from this 1D-MOF by SCSC transformations. Furthermore, Cu MOFs with 0D, 1D, and 3D networks, MOP-1, 1D-MOF, and HKUST-1, show unique performances in the kinetics of the C-H bond catalytic oxidation reaction. PMID:26296038

  8. Formation and High Reactivity of the anti-Dioxo Form of High-Spin μ-Oxodioxodiiron(IV) as the Active Species That Cleaves Strong C-H Bonds.

    PubMed

    Kodera, Masahito; Ishiga, Shin; Tsuji, Tomokazu; Sakurai, Katsutoshi; Hitomi, Yutaka; Shiota, Yoshihito; Sajith, P K; Yoshizawa, Kazunari; Mieda, Kaoru; Ogura, Takashi

    2016-04-18

    Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is toluenebond cleavage of ethylbenzene than the most reactive diiron system reported so far. The KIE for the reaction with toluene/[D8 ]toluene is 95 at -30 °C, which the largest in diiron systems reported so far. The present diiron complex efficiently catalyzes the oxidation of various alkanes with H2 O2 . PMID:26970337

  9. Strength of Chemical Bonds

    NASA Technical Reports Server (NTRS)

    Christian, Jerry D.

    1973-01-01

    Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

  10. Asymmetric bifurcated halogen bonds.

    PubMed

    Novák, Martin; Foroutan-Nejad, Cina; Marek, Radek

    2015-03-01

    Halogen bonding (XB) is being extensively explored for its potential use in advanced materials and drug design. Despite significant progress in describing this interaction by theoretical and experimental methods, the chemical nature remains somewhat elusive, and it seems to vary with the selected system. In this work we present a detailed DFT analysis of three-center asymmetric halogen bond (XB) formed between dihalogen molecules and variously 4-substituted 1,2-dimethoxybenzene. The energy decomposition, orbital, and electron density analyses suggest that the contribution of electrostatic stabilization is comparable with that of non-electrostatic factors. Both terms increase parallel with increasing negative charge of the electron donor molecule in our model systems. Depending on the orientation of the dihalogen molecules, this bifurcated interaction may be classified as 'σ-hole - lone pair' or 'σ-hole - π' halogen bonds. Arrangement of the XB investigated here deviates significantly from a recent IUPAC definition of XB and, in analogy to the hydrogen bonding, the term bifurcated halogen bond (BXB) seems to be appropriate for this type of interaction. PMID:25656525

  11. Surface analysis in composite bonding

    NASA Technical Reports Server (NTRS)

    Messick, D. L.; Wightman, J. P.

    1982-01-01

    The role of the interfacial region in determining the bond strength and durability of composite bonds is discussed. The characterization of a variety of carbon fibers including Celion 6000 using both scanning electron microscopy and X-ray photoelectron spectroscopy is discussed. The emphasis is on composite bonding, that is, the adhesive bonding between composites in contrast to fiber-matrix interaction. The primary objective of the research is the characterization of composite surfaces before adhesive bonding and after fracture of bonded specimens. Work done on the analysis of composite samples pretreated in a number of ways prior to bonding is detailed.

  12. Insulation bonding test system

    NASA Technical Reports Server (NTRS)

    Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (Inventor)

    1984-01-01

    A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

  13. Metallic Adhesion and Bonding

    NASA Technical Reports Server (NTRS)

    Ferrante, J.; Smith, J. R.; Rose, J. H.

    1984-01-01

    Although metallic adhesion has played a central part in much tribological speculation, few quantitative theoretical calculations are available. This is in part because of the difficulties involved in such calculations and in part because the theoretical physics community is not particularly involved with tribology. The calculations currently involved in metallic adhesion are summarized and shown that these can be generalized into a scaled universal relationship. Relationships exist to other types of covalent bonding, such as cohesive, chemisorptive, and molecular bonding. A simple relationship between surface energy and cohesive energy is offered.

  14. Modeling the Active Sites in Metalloenzymes 5. The Heterolytic Bond Cleavage of H2 in the [NiFe] Hydrogenase of DesulfoWibrio gigas by a Nucleophilic Addition Mechanism

    SciTech Connect

    Niu, Shuqiang; Hall, Michael B.

    2001-11-19

    The H2 activation catalyzed by an Fe(II)-Ni(III) model of the [NiFe] hydrogenase of DesulfoVibrio gigas has been investigated by density functional theory (DFT/B3LYP) calculations on the neutral and anionic active site complexes, [(CO)(CN)2Fe(Mu-SH)2Ni(SH)(SH2)]0 and [(CO)(CN)2Fe(Mu-SH)2Ni(SH)2]-. The results suggest that the reaction proceeds by a nucleophilic addition mechanism that cleaves the H-H bond heterolytically. The terminal cysteine residue Cys530 in the [NiFe] hydrogenase active site of the D. gigas enzyme plays a crucial role in the catalytic process by accepting the proton. The active site is constructed to provide access by this cysteine residue, and this role explains the change in activity observed when this cysteine is replaced by a selenocysteine. Furthermore, the optimized geometry of the transition state in the model bears a striking resemblance to the geometry of the active site as determined by X-ray crystallography.

  15. 29 CFR 2580.412-20 - Use of existing bonds, separate bonds and additional bonding.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... bonding. 2580.412-20 Section 2580.412-20 Labor Regulations Relating to Labor (Continued) EMPLOYEE BENEFITS SECURITY ADMINISTRATION, DEPARTMENT OF LABOR TEMPORARY BONDING RULES UNDER THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 TEMPORARY BONDING RULES General Bond Rules § 2580.412-20 Use of existing...

  16. Bonds that strengthen under force

    NASA Astrophysics Data System (ADS)

    Vogel, Viola

    2006-03-01

    While the adhesive strength of most receptor-ligand interactions is exponentially reduced if strained, some receptor-ligand complexes exist that strengthen under force which is the hallmark of catch bonds. Although the existence of catch bonds was theoretically predicted, the first experimental demonstrations of their existence were given only recently, i.e. for the bacterial adhesin FimH that is located at the tip of type I fimbriae of E. coli and for p-selectin. In a major collaborative effort, we studied the structural origin by which the FimH-mannose bond is switched by force to a high binding state. Mutational studies were thereby combined with steered molecular dynamic simulations to decipher how force might affect protein conformation. Force-activation of FimH leads to a complex `stick-and-roll' bacterial adhesion behavior in which E. coli preferentially rolls over mannosylated surfaces at low shear but increasingly sticks firmly as the shear is increased. Interesting similarities are further seen if comparing the structural mechanisms by which liganded FimH and liganded integrins are switched to a high binding state. This comparison was made possible by docking fibronectin's 10^th type III module (fnIII10) to αVβ3 integrin. αVβ3 can switch from the ``closed'' αVβ3 integrin headpiece to the ``open'' conformation by opening the hinge angle between the βA domain and the hybrid domain of the β-integrin. The ``open'' state has been implicated by many experimental laboratories to correspond to the activated state of integrins. W. E. Thomas, E. Trintchina, M. Forero, V. Vogel, E. Sokurenko, Bacterial adhesion to target cells enhanced by shear-force, Cell, 109 (2002) 913. W. E. Thomas, L. M. Nilsson, M. Forero, E. V. Sokurenko, V. Vogel, Shear-dependent `stick-and-roll' adhesion of type 1 fimbriated Escherichia coli, Molecular Microbiology 53 (2004) 1545. W. Thomas, M. Forero, O. Yakovenko, L. Nilsson, P. Vicini, E. Sokurenko, V. Vogel, Catch Bond Model

  17. Metal-Metal Bonds in Biology

    PubMed Central

    Lindahl, Paul A.

    2011-01-01

    Nickel-containing carbon monoxide dehydrogenases, acetyl-CoA synthases, nickel-iron hydrogenases, and diron hydrogenases are distinct metalloenzymes yet they share a number of important characteristics. All are O2-sensitive, with active-sites composed of iron and/or nickel ions coordinated primarily by sulfur ligands. In each case, two metals are juxtaposed at the “heart” of the active site, within range of forming metal-metal bonds. These active-site clusters exhibit multielectron redox abilities and must be reductively activated for catalysis. Reduction potentials are milder than expected based on formal oxidation state changes. When reductively activated, each cluster attacks an electrophilic substrate via an oxidative addition reaction. This affords a two-electron-reduced substrate bound to one or both metals of an oxidized cluster. M-M bonds have been established in hydrogenases where they serve to initiate the oxidative addition of protons and perhaps stabilize active sites in multiple redox states. The same may be true of the CODH and ACS active sites – Ni-Fe and Ni-Ni bonds in these sites may play critical roles in catalysis, stabilizing low-valence states and initiating oxidative addition of CO2 and methyl group cations, respectively. In this article, the structural and functional commonalities of these metalloenzyme active sites are described, and the case is made for the formation and use of metal-metal bonds in each enzyme mentioned. As a post-script, the importance of Fe-Fe bonds in the nitrogenase FeMoco active site is discussed. PMID:22119810

  18. Reactions of titanocene bis(trimethylsilyl)acetylene complexes with carbodiimides: an experimental and theoretical study of complexation versus C-N bond activation.

    PubMed

    Haehnel, Martin; Ruhmann, Martin; Theilmann, Oliver; Roy, Subhendu; Beweries, Torsten; Arndt, Perdita; Spannenberg, Anke; Villinger, Alexander; Jemmis, Eluvathingal D; Schulz, Axel; Rosenthal, Uwe

    2012-09-26

    The reaction of the low valent metallocene(II) sources Cp'(2)Ti(η(2)-Me(3)SiC(2)SiMe(3)) (Cp' = η(5)-cyclopentadienyl, 1a or η(5)-pentamethylcyclopentadienyl, 1b) with different carbodiimide substrates RN═C═NR' 2-R-R' (R = t-Bu; R' = Et; R = R' = i-Pr; t-Bu; SiMe(3); 2,4,6-Me-C(6)H(2) and 2,6-i-Pr-C(6)H(3)) was investigated to explore the frontiers of ring strained, unusual four-membered heterometallacycles 5-R. The product complexes show dismantlement, isomerization, or C-C coupling of the applied carbodiimide substrates, respectively, to form unusual mono-, di-, and tetranuclear titanium(III) complexes. A detailed theoretical study revealed that the formation of the unusual complexes can be attributed to the biradicaloid nature of the unusual four-membered heterometallacycles 5-R, which presents an intriguing situation of M-C bonding. The combined experimental and theoretical study highlights the delicate interplay of electronic and steric effects in the stabilization of strained four-membered heterometallacycles, accounting for the isolation of the obtained complexes. PMID:22891968

  19. Nucleophile-catalyzed additions to activated triple bonds. Protection of lactams, imides, and nucleosides with MocVinyl and related groups.

    PubMed

    Mola, Laura; Font, Joan; Bosch, Lluís; Caner, Joaquim; Costa, Anna M; Etxebarría-Jardí, Gorka; Pineda, Oriol; de Vicente, David; Vilarrasa, Jaume

    2013-06-21

    Additions of lactams, imides, (S)-4-benzyl-1,3-oxazolidin-2-one, 2-pyridone, pyrimidine-2,4-diones (AZT derivatives), or inosines to the electron-deficient triple bonds of methyl propynoate, tert-butyl propynoate, 3-butyn-2-one, N-propynoylmorpholine, or N-methoxy-N-methylpropynamide in the presence of many potential catalysts were examined. DABCO and, second, DMAP appeared to be the best (highest reaction rates and E/Z ratios), while RuCl3, RuClCp*(PPh3)2, AuCl, AuCl(PPh3), CuI, and Cu2(OTf)2 were incapable of catalyzing such additions. The groups incorporated (for example, the 2-(methoxycarbonyl)ethenyl group that we name MocVinyl) serve as protecting groups for the above-mentioned heterocyclic CONH or CONHCO moieties. Deprotections were accomplished via exchange with good nucleophiles: the 1-dodecanethiolate anion turned out to be the most general and efficient reagent, but in some particular cases other nucleophiles also worked (e.g., MocVinyl-inosines can be cleaved with succinimide anion). Some structural and mechanistic details have been accounted for with the help of DFT and MP2 calculations. PMID:23713491

  20. Bonding without Tears.

    ERIC Educational Resources Information Center

    Akeroyd, F. Michael

    1982-01-01

    Discusses merits of using sigma-pi model of ethylene as a teaching aid in introductory organic chemistry. The nonmathematical treatment of sigma-pi bonding is then extended to such phenomena as conjugation, hyperconjugation, Markovnikoff addition, aromaticity, and aromatic substitution. (SK)