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Sample records for complex formation reactions

  1. Formation of Complex Molecules via radiative association reactions

    NASA Astrophysics Data System (ADS)

    Acharyya, Kinsuk; Herbst, Eric

    2016-07-01

    The detection of increasing numbers of complex organic molecules in the various phases of star formation plays a key role since they follow the same chemical rules of carbon-based chemistry that are observed in our planet Earth. Many of these molecules are believed to be formed on the surfaces of grains, and can then be released to the gas phase when these grains are heated. This is evident when we observe a rich chemistry in hot core regions. However, recently complex organic molecules have also been observed in cold clouds. Therefore, it is necessary to re-examine various pathways for the formation of these molecules in the gas phase. In this presentation, I will discuss role of radiative association reactions in the formation of complex molecules in the gas phase and at low temperature. We will compare abundance of assorted molecules with and without new radiative association reactions and will show that the abundance of a few complex molecules such as HCOOCH3, CH3OCH3 etc. can go up due to introduction of these reactions, which can help to explain their observed abundances.

  2. Redox reactions and complex formation of transplutonium elements in solutions

    SciTech Connect

    Krot, N.N.; Myasoedov, B.F.

    1986-01-01

    This paper gives a brief analysis of the kinetics and mechanism of a number of redox processes and the complex formation of transplutonium elements in unusual oxidation states. The composition and strength of complexes of TPE with various addends have been determined. The new experimental data on the oxidation potentials of americium and berkelium ions in solutions are cited in abbreviated form. It follows from the data that in phosphoric acid solutions, when the H/sub 3/PO/sub 4/ concentration is increased from 10 to 15 M, the oxidation potential of the couple Am(IV)-Am(III) decreases. The oxidation potentials of the couples Am(VI)-Am(V), Cm(V)-Cm(IV), and Bk(IV)Bk(III) are also presented.

  3. Rapid-reaction kinetic characterization of the pathway of streptokinase-plasmin catalytic complex formation.

    PubMed

    Verhamme, Ingrid M; Bock, Paul E

    2008-09-19

    Binding of the fibrinolytic proteinase plasmin (Pm) to streptokinase (SK) in a tight stoichiometric complex transforms Pm into a potent proteolytic activator of plasminogen. SK binding to the catalytic domain of Pm, with a dissociation constant of 12 pm, is assisted by SK Lys(414) binding to a Pm kringle, which accounts for a 11-20-fold affinity decrease when Pm lysine binding sites are blocked by 6-aminohexanoic acid (6-AHA) or benzamidine. The pathway of SK.Pm catalytic complex formation was characterized by stopped-flow kinetics of SK and the Lys(414) deletion mutant (SKDeltaK414) binding to Pm labeled at the active site with 5-fluorescein ([5F]FFR-Pm) and the reverse reactions by competitive displacement of [5F]FFR-Pm with active site-blocked Pm. The rate constants for the biexponential fluorescence quenching caused by SK and SKDeltaK414 binding to [5F]FFR-Pm were saturable as a function of SK concentration, reporting encounter complex affinities of 62-110 nm in the absence of lysine analogs and 4900-6500 and 1430-2200 nm in the presence of 6-AHA and benzamidine, respectively. The encounter complex with SKDeltaK414 was approximately 10-fold weaker in the absence of lysine analogs but indistinguishable from that of native SK in the presence of 6-AHA and benzamidine. The studies delineate for the first time the sequence of molecular events in the formation of the SK.Pm catalytic complex and its regulation by kringle ligands. Analysis of the forward and reverse reactions supports a binding mechanism in which SK Lys(414) binding to a Pm kringle accompanies near-diffusion-limited encounter complex formation followed by two slower, tightening conformational changes.

  4. Formation of complex organic molecules in cold objects: the role of gas-phase reactions

    NASA Astrophysics Data System (ADS)

    Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

    2015-04-01

    While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ≳ 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

  5. Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes.

    PubMed

    Perez, Evan; Hanley, Cassandra; Koehler, Stephen; Pestok, Jordan; Polonsky, Nevo; Van Stipdonk, Michael

    2016-12-01

    The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of uranyl cation (U(VI)O2(2+)) coordinated by formate or acetate ligands. Anionic complexes containing U(VI)O2(2+) and formate ligands fragment by decarboxylation and elimination of CH2=O, ultimately to produce an oxo-hydride species [U(VI)O2(O)(H)](-). Cationic species ultimately dissociate to make [U(VI)O2(OH)](+). Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH3CO2•, with associated reduction of uranyl to U(V)O2(+). Subsequent CID steps cause elimination of CO2 and CH4, ultimately to produce [U(V)O2(O)](-). Loss of CH4 occurs by an intra-complex H(+) transfer process that leaves U(V)O2(+) coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH2=C=O to leave [U(V)O2(O)](-). Elimination of CH4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H2O. The reactions of other anionic species with gas-phase H2O create hydroxyl products, presumably through the elimination of H2. Graphical Abstract ᅟ.

  6. Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes

    NASA Astrophysics Data System (ADS)

    Perez, Evan; Hanley, Cassandra; Koehler, Stephen; Pestok, Jordan; Polonsky, Nevo; Van Stipdonk, Michael

    2016-12-01

    The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of uranyl cation (UVIO2 2+) coordinated by formate or acetate ligands. Anionic complexes containing UVIO2 2+ and formate ligands fragment by decarboxylation and elimination of CH2=O, ultimately to produce an oxo-hydride species [UVIO2(O)(H)]-. Cationic species ultimately dissociate to make [UVIO2(OH)]+. Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH3CO2•, with associated reduction of uranyl to UVO2 +. Subsequent CID steps cause elimination of CO2 and CH4, ultimately to produce [UVO2(O)]-. Loss of CH4 occurs by an intra-complex H+ transfer process that leaves UVO2 + coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH2=C=O to leave [UVO2(O)]-. Elimination of CH4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H2O. The reactions of other anionic species with gas-phase H2O create hydroxyl products, presumably through the elimination of H2.

  7. Complex Organic Molecules Formation in Space Through Gas Phase Reactions: A Theoretical Approach

    NASA Astrophysics Data System (ADS)

    Redondo, Pilar; Barrientos, Carmen; Largo, Antonio

    2017-02-01

    Chemistry in the interstellar medium (ISM) is capable of producing complex organic molecules (COMs) of great importance to astrobiology. Gas phase and grain surface chemistry almost certainly both contribute to COM formation. Amino acids as building blocks of proteins are some of the most interesting COMs. The simplest one, glycine, has been characterized in meteorites and comets and, its conclusive detection in the ISM seems to be highly plausible. In this work, we analyze the gas phase reaction of glycine and {{{CH}}5}+ to establish the role of this process in the formation of alanine or other COMs in the ISM. Formation of protonated α- and β-alanine in spite of being exothermic processes is not viable under interstellar conditions because the different paths leading to these isomers present net activation energies. Nevertheless, glycine can evolve to protonated 1-imide-2, 2-propanediol, protonated amino acetone, protonated hydroxyacetone, and protonated propionic acid. However, formation of acetic acid and protonated methylamine is also a favorable process and therefore will be a competitive channel with the evolution of glycine to COMs.

  8. Reactions of a Dinitrogen Complex of Molybdenum: Formation of a Carbon-Nitrogen Bond.

    ERIC Educational Resources Information Center

    Busby, David C.; And Others

    1981-01-01

    Reports a procedure for the formation of alkyldiazenido complexes of molybdenum in the absence of dioxygen, suitable for inclusion in an advanced inorganic chemistry laboratory. Includes background information and experimental procedures for two complexes. (SK)

  9. Organometallic nickel(III) complexes relevant to cross-coupling and carbon-heteroatom bond formation reactions.

    PubMed

    Zheng, Bo; Tang, Fengzhi; Luo, Jia; Schultz, Jason W; Rath, Nigam P; Mirica, Liviu M

    2014-04-30

    Nickel complexes have been widely employed as catalysts in C-C and C-heteroatom bond formation reactions. In addition to Ni(0) and Ni(II) intermediates, several Ni-catalyzed reactions are proposed to also involve odd-electron Ni(I) and Ni(III) oxidation states. We report herein the isolation, structural and spectroscopic characterization, and organometallic reactivity of Ni(III) complexes containing aryl and alkyl ligands. These Ni(III) species undergo transmetalation and/or reductive elimination reactions to form new C-C or C-heteroatom bonds and are also competent catalysts for Kumada and Negishi cross-coupling reactions. Overall, these results provide strong evidence for the direct involvement of organometallic Ni(III) species in cross-coupling reactions and oxidatively induced C-heteroatom bond formation reactions.

  10. Reaction of a copper(II)-nitrosyl complex with hydrogen peroxide: putative formation of a copper(I)-peroxynitrite intermediate.

    PubMed

    Kalita, Apurba; Kumar, Pankaj; Mondal, Biplab

    2012-05-14

    The reaction of a Cu(II)-nitrosyl complex (1) with hydrogen peroxide at -20 °C in acetonitrile results in the formation of the corresponding Cu(I)-peroxynitrite intermediate. The reduction of the Cu(II) center was monitored by UV-visible spectroscopic studies. Formation of the peroxynitrite intermediate has been confirmed by its characteristic phenol ring nitration reaction as well as isolation of corresponding Cu(I)-nitrate (2). On air oxidation, 2 resulted in the corresponding Cu(II)-nitrate (3). Thus, these results demonstrate a possible decomposition pathway for H(2)O(2) and NO through the formation of a peroxynitrite intermediate in biological systems.

  11. Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

    NASA Astrophysics Data System (ADS)

    Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko

    2013-11-01

    Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

  12. Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

    SciTech Connect

    Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko

    2013-11-13

    Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

  13. A Reaction Method for Estimating Gibbs Energy and Enthalpy of Formation of Complex Minerals

    NASA Astrophysics Data System (ADS)

    Li, Ruibing; Zhang, Tingan; Liu, Yan; Kuang, Shibo

    2017-04-01

    New and updated thermodynamic data for simple binary compounds are readily available from both experimental measurements and theoretical calculations. Based on these available data, an approach is proposed to predict Gibbs energies and enthalpies of formation for complex minerals of metallurgical, chemical, and other industrial importance. The approach assumes that complex minerals are formed from binary composite oxides, which in turn, are formed from individual pure oxides. The validity of this approach is examined by comparing the calculated values of Gibbs energies and enthalpies against the experimentally measured ones reported in literature. The results show that for typical complex minerals with available experimental data, the calculated results exhibit an average residual of 0.51 pct for Gibbs energies and 0.52 pct for enthalpies, compared to the experimental results. This new approach thus correlates well with experimental approaches and can be applied to most of the complex minerals.

  14. A Reaction Method for Estimating Gibbs Energy and Enthalpy of Formation of Complex Minerals

    NASA Astrophysics Data System (ADS)

    Li, Ruibing; Zhang, Tingan; Liu, Yan; Kuang, Shibo

    2017-01-01

    Abstract New and updated thermodynamic data for simple binary compounds are readily available from both experimental measurements and theoretical calculations. Based on these available data, an approach is proposed to predict Gibbs energies and enthalpies of formation for complex minerals of metallurgical, chemical, and other industrial importance. The approach assumes that complex minerals are formed from binary composite oxides, which in turn, are formed from individual pure oxides. The validity of this approach is examined by comparing the calculated values of Gibbs energies and enthalpies against the experimentally measured ones reported in literature. The results show that for typical complex minerals with available experimental data, the calculated results exhibit an average residual of 0.51 pct for Gibbs energies and 0.52 pct for enthalpies, compared to the experimental results. This new approach thus correlates well with experimental approaches and can be applied to most of the complex minerals.

  15. Formation of mono(dithiolene)-thiocarboxamido complexes in reactions of thio(dithiocarbamato)-Mo/W complexes and dimethyl acetylenedicarboxylate.

    PubMed

    Lim, Patrick J; Slizys, Damian A; Tiekink, Edward R T; Young, Charles G

    2005-01-10

    Reactions of TpMS(S(2)CNEt(2)) with dimethyl acetylenedicarboxylate in dichloromethane produce olive green/black TpM{S(2)C(2)(CO(2)Me)(2)}(SCNEt(2)-kappa(2)S,C) (M = Mo (1), W (2); Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate). The seven-coordinate complexes exhibit pseudo-octahedral (1) and distorted pentagonal bipyramidal (2) coordination spheres comprised of tridentate fac-Tp, bidentate dithiolene, and thiocarboxamido-kappa(2)S,C ligands. In the solid state, molecules of 1 exhibit pseudo-C(s)() symmetry, with the thiocarboxamide NEt(2) group in a cleft in the Tp ligand. Molecules of 2 have C(1) symmetry in the solid state; here, the thiocarboxamide unit is orientated along one of the W-S(dithiolene) bonds with its NEt(2) group projecting away from the Tp ligand. Both complexes possess effective C(s)() symmetry in solution. Reaction of TpMoI(CO)(3) with AgS(2)CNEt(2) affords olive green TpMo(S(2)CNEt(2))(CO)(2) (3), which reacts with propylene sulfide in a new synthesis for TpMoS(S(2)CNEt(2)), the starting material for 1. Complex 3 exhibits a distorted pentagonal bipyramidal structure, the axial sites being defined by a Tp nitrogen atom and a carbonyl ligand, the pentagonal plane by the remaining nitrogen and carbonyl donors and the two sulfur atoms of the bidentate dithiocarbamate ligand.

  16. Rhodium Complexes Promoting C-O Bond Formation in Reactions with Oxygen: The Role of Superoxo Species.

    PubMed

    Vilella-Arribas, Laia; García-Melchor, Max; Balcells, David; Lledós, Agustí; López, José A; Sancho, Sofía; Villarroya, B Eva; Del Río, M Pilar; Ciriano, Miguel A; Tejel, Cristina

    2017-01-28

    C-O bond formation in reactions of olefins with oxygen is a long standing challenge in chemistry for which the very complicated-sometimes controversial-mechanistic panorama slows down the design of catalysts for oxygenations. In this regard, the mechanistic details of the oxidation of the complex [Rh(cod)(Ph2 N3 )] (1) (cod=1,5-cyclooctadiene) with oxygen to the unique 2-rhodaoxetane compound [{Rh(OC8 H12 )(Ph2 N3 )}2 ] (2) has been investigated by DFT calculations. The results of this study provide evidences for a novel bimetallic mechanism in which two rhodium atoms redistribute the four electrons involved in the cleavage of the O=O bond. Furthermore, both oxygen atoms are used to create two new C-O bonds in a controlled fashion with 100 % atom economy. The key intermediates that we have found in this process are a mononuclear open-shell triplet superoxo compound, an open-shell singlet "μ-(peroxo)" derivative, and a closed-shell singlet "bis(μ-oxo)" complex. Some of the findings are used to predict the reactions of Rh(I) complexes with oxygen, exemplified by that of the complex [Rh(cod)(OnapyMe2 )] (3). Starting from 3, [{Rh(OC8 H12 )(OnapyMe2 )}2 ] (4) has been prepared and characterized, which represents the second example of a 2-rhodaoxetane compound coming from an oxygenation reaction with oxygen.

  17. Reaction of dimethyl ether with hydroxyl radicals: kinetic isotope effect and prereactive complex formation.

    PubMed

    Bänsch, Cornelie; Kiecherer, Johannes; Szöri, Milan; Olzmann, Matthias

    2013-09-05

    The kinetic isotope effect of the reactions OH + CH3OCH3 (DME) and OH + CD3OCD3 (DME-d6) was experimentally and theoretically studied. Experiments were carried out in a slow-flow reactor at pressures between 5 and 21 bar (helium as bath gas) with production of OH by laser flash photolysis of HNO3 and time-resolved detection of OH by laser-induced fluorescence. The temperature dependences of the rate coefficients obtained can be described by the following modified Arrhenius expressions: k(OH+DME) = (4.5 ± 1.3) × 10(-16) (T/K)(1.48) exp(66.6 K/T) cm(3) s(-1) (T = 292-650 K, P = 5.9-20.9 bar) and k(OH+DME-d6) = (7.3 ± 2.2) × 10(-23) (T/K)(3.57) exp(759.8 K/T) cm(3) s(-1) (T = 387-554 K, P = 13.0-20.4 bar). A pressure dependence of the rate coefficients was not observed. The agreement of our experimental results for k(OH+DME) with values from other authors is very good, and from a fit to all available literature data, we derived the following modified Arrhenius expression, which reproduces the values obtained in the temperature range T = 230-1500 K at pressures between 30 mbar and 21 bar to better than within ±20%: k(OH+DME) = 8.45 × 10(-18) (T/K)(2.07) exp(262.2 K/T) cm(3) s(-1). For k(OH+DME-d6), to the best of our knowledge, this is the first experimental study. For the analysis of the reaction pathway and the kinetic isotope effect, potential energy diagrams were calculated by using three different quantum chemical methods: (I) CCSD(T)/cc-pV(T,Q)Z//MP2/6-311G(d,p), (II) CCSD(T)/cc-pV(T,Q)Z//CCSD/cc-pVDZ, and (III) CBS-QB3. In all three cases, the reaction is predicted to proceed via a prereaction OH-ether complex with subsequent intramolecular hydrogen abstraction and dissociation to give the methoxymethyl radical and water. Overall rate coefficients were calculated by assuming a thermal equilibrium between the reactants and the prereaction complex and by calculating the rate coefficients of the hydrogen abstraction step from canonical transition state theory

  18. Kinetics of actinide complexation reactions

    SciTech Connect

    Nash, K.L.; Sullivan, J.C.

    1997-09-01

    Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In light of the central role played by such reactions in actinide process and environmental chemistry, this situation is somewhat surprising. The authors report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Most of the work reported was conducted in acidic media, but a few address reactions in neutral and alkaline solutions. Complex formation reactions tend in general to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions.

  19. Electronic structure and formation of simple ferryloxo complexes: mechanism of the Fenton reaction.

    PubMed

    Petit, Alban S; Pennifold, Robert C R; Harvey, Jeremy N

    2014-07-07

    The Fenton reaction is a famous reaction in inorganic chemistry, with relevance to topics such as bioinorganic oxidation and fundamental redox chemistry of water and oxygen. It is also a reaction concerning which there has been very extensive mechanistic debate, with experimental and computational work leading to extensive evidence concerning its mechanism-not all of which is consistent. Here, we use this reaction as a challenge to modern electronic structure theory methods and show that density functional theory, when validated by accurate ab initio methods, can yield a picture of this reaction that is consistent with experiment. The article also highlights some of the challenges in accurate studies of reaction mechanisms of ionic species in water solution.

  20. Infrared chemiluminescence study of CO + O 2 reaction on Pd(1 1 0): Activated complex of CO 2 formation at high CO coverage

    NASA Astrophysics Data System (ADS)

    Nakao, Kenji; Ito, Shin-ichi; Tomishige, Keiichi; Kunimori, Kimio

    2005-07-01

    The infrared chemiluminescence study of CO 2 formed during steady-state CO + O 2 reaction over Pd(1 1 0) under various CO/O 2 pressure ratios was carried out. Highly excited antisymmetric vibrational mode compared to bending vibrational mode was observed under reaction conditions at high CO coverage. This can be related to the activated complex of CO 2 formation in more linear form.

  1. Reactions of ruthenium complexes having pyridyl-containing ligands, 2-pyridinecarboxylato and 2,2'-bipyridine, with an azide ion: formation of nitrido-bridged diruthenium complexes.

    PubMed

    Matsumura, Sayuri; Shikano, Kazunori; Oi, Takao; Suzuki, Noriyuki; Nagao, Hirotaka

    2008-10-20

    Reactions of ruthenium complexes having 2-pyridinecarboxylato and 2,2'-bipyridine ligands with sodium azide in alcohol afforded nitrido-bridged diruthenium complexes, [{Ru(OR)(pyca)(bpy)}2(mu-N)](+) (R = CH3, C2H5). Diruthenium complexes showed diamagnetic properties, a linear Ru-N-Ru coordination configuration, and two irreversible oxidation waves and two reversible reduction waves.

  2. Mechanistic information from volume profiles for water exchange and complex-formation reactions of aquated Ni(II). pH, buffer and medium effects.

    PubMed

    Gazzaz, Hanaa Asaad; Ember, Erika; Zahl, Achim; van Eldik, Rudi

    2009-11-21

    Rate and activation parameters for the complex-formation reaction of Ni(2+) with 4-(2-pyridylazo)-N,N-dimethyl aniline (PADA) were studied as a function of pH in different buffers in both aqueous and sodium dodecyl sulfate (SDS) micelle solutions. In aqueous Tris buffer solution, the forward and backward rate constants increased with increasing pH, while the complex-formation constant decreased due to a larger increase in the backward rate constant. The activation entropy, DeltaS(#), and activation volume, DeltaV(#), changed with increasing pH from positive to negative values, suggesting an apparent changeover from a dissociative to a more associative mechanism. Complex-formation reactions with 2,2'-bipyridine in Tris buffer showed almost no increase in the forward and backward rate constants on increasing the pH, but the DeltaS(#) and DeltaV(#) values became more negative. N-ethylmorpholine buffer showed no pH effect on the rate constants and activation parameters. Water exchange reactions of aquated Ni(2+) were also studied as a function of pH under the same conditions. The reported rate and activation parameters for water exchange in Tris and N-ethylmorpholine buffers are consistent with those found for the complex-formation reactions of Ni(2+) with PADA. The observed pH and buffer effects for both the complex-formation and water exchange reactions of aquated Ni(2+) can be accounted for in terms of the formation of a Ni(2+)-Tris complex in Tris buffer and general base catalysis by the buffer components. In SDS micelle solution, the complex-formation reaction with PADA was much faster than in aqueous solution, but the increase in rate constant with increasing pH was less significant, while DeltaS(#) and DeltaV(#) became more positive, pointing to a more dissociative mechanism. For SDS micelle solutions there was no effect on the water exchange rate constant or activation volume. Mechanistic interpretations are offered for all observed pH, buffer and medium

  3. Ab initio study on the formation of triiodide CT complex from the reaction of iodine with 2,3-diaminopyridine.

    PubMed

    Al-Hashimi, Nessreen A; Hussein, Yasser H A

    2010-01-01

    The charge transfer (CT) interaction between iodine and 2,3-diaminopyridine (DAPY) has been thoroughly investigated via theoretical calculations. A Hartree-Fock, 3-21G level of theory was used to optimize and calculate the Mullican charge distribution scheme as well as the vibrational frequencies of DAPY alone and both its CT complexes with one and two iodine molecules. A very good agreement was found between experiment and theory. New illustrations were concluded with a deep analysis and description for the vibrational frequencies of the formed CT complexes. The two-step CT complex formation mechanism published earlier was supported.

  4. A STUDY OF FUNDAMENTAL REACTION PATHWAYS FOR TRANSITION METAL ALKYL COMPLEXES. I. THE REACTION OF A NICKEL METHYL COMPLEX WITH ALKYNES. II. THE MECHANISM OF ALDEHYDE FORMATION IN THE REACTION OF A MOLYBDENUM HYDRIDE WITH MOLYBDENUM ALKYLS

    SciTech Connect

    Huggins, John Mitchell

    1980-06-01

    I. This study reports the rapid reaction under mild conditions of internal or terminal alkynes with methyl (acetyl~ acetonato) (triphenylphosphine) nickel (1) in either aromatic or ether solvents. In all cases vinylnickel products 2 are formed by insertion of the alkyne into the nickel=methyl bond. These complexes may be converted into a variety of organic products (e.g. alkenes, esters, vinyl halides) by treatment with appropriate reagents. Unsymmetrical alkynes give selectively the one regioisomer with the sterically largest substituent next to the nickel atom. In order to investigate the stereochemistry of the initial insertion, a x-ray diffraction study of the reaction of 1 with diphenylacetylene was carried out. This showed that the vinylnickel complex formed by overall trans insertion was the product of the reaction. Furthermore, subsequent slow isomerization of this complex, to a mixture of it and the corresponding cis isomer, demonstrated that this trans addition product is the kinetic product of the reaction. In studies with other alkynes, the product of trans addition was not always exclusively (or even predominantly) formed, but the ratio of the stereoisomers formed kinetically was substantially different from the thermodynamic ratio. Isotope labeling, added phosphine, and other experiments have allowed us to conclude that the mechanism of this reaction does involve initial cis addition. However, a coordinatively unsaturated vinylnickel complex is initially formed which can undergo rapid, phosphine-catalyzed cis-trans isomerization in competition with its conversion to the isolable phosphine-substituted kinetic reaction products. II. The reaction of CpMo(CO){sub 3}H (1a) with CpMo(CO){sub 3}R (2, R= CH{sub 3}, C{sub 2}H{sub 5}) at 50{degrees} C in THF gives the aldehyde RCHO and the dimers [CpMo(CO){sub 3}]{sub 2} (3a) and [CpMo(CO){sub 2}]{sub 2} (4a). Labeling one of the reactants with a methylcyclopentadienyl ligand it was possible to show that the

  5. S(H)2 reaction vs hydrogen abstraction/expulsion in methyl radical-methylsilane reactions: effects of prereactive complex formation.

    PubMed

    Norberg, Daniel; Shiotani, Masaru; Lunell, Sten

    2008-02-14

    A quantum chemical study has been undertaken to elucidate the cause of the recently observed S(H)2 reaction between the deuterated methyl radical (*CD3) and methylsilane (SiD3CH3) following the photolysis of CD3I. [Komaguchi, K.; Norberg, D.; Nakazawa, N.; Shiotani, M.; Persson, P.; Lunell, S. Chem. Phys. Lett. 2005, 410, 1-5.] It is found that the backside S(H)2 mechanism may proceed favorably for C-Si-C angles deviating with up to 40 degrees from linearity. The competitive hydrogen abstraction reaction is predicted to be active in the range of 90 degrees reaction paths probably make the frontside mechanism less important for the present S(H)2 reaction. A number of bound SiH3CH3/CH3I complexes have been located with the MP2 method. At the CCSD(T) level, a complex corresponding to the collinear arrangement where the methyl moiety of methyl iodide points toward the silicon, which is the most favorable conformation for the subsequent SH2 reaction with the backside mechanism, is found to be the most stable linear conformer. A complex with similar energy is found where the methyl moiety of methyl iodide points approximately toward an Si-H bond. However, because C-Si-C = 69.4 degrees in this complex, subsequent photolysis of methyl iodide would probably not lead to hydrogen abstraction with full efficiency. These findings could provide an explanation for the observed S(H)2 reaction.

  6. Pressure dependent low temperature kinetics for CN + CH3CN: competition between chemical reaction and van der Waals complex formation.

    PubMed

    Sleiman, Chantal; González, Sergio; Klippenstein, Stephen J; Talbi, Dahbia; El Dib, Gisèle; Canosa, André

    2016-06-01

    The gas phase reaction between the CN radical and acetonitrile CH3CN was investigated experimentally, at low temperatures, with the CRESU apparatus and a slow flow reactor to explore the temperature dependence of its rate coefficient from 354 K down to 23 K. Whereas a standard Arrhenius behavior was found at T > 200 K, indicating the presence of an activation barrier, a dramatic increase in the rate coefficient by a factor of 130 was observed when the temperature was decreased from 168 to 123 K. The reaction was found to be pressure independent at 297 K unlike the experiments carried out at 52 and 132 K. The work was complemented by ab initio transition state theory based master equation calculations using reaction pathways investigated with highly accurate thermochemical protocols. The role of collisional stabilization of a CNCH3CN van der Waals complex and of tunneling induced H atom abstractions were also considered. The experimental pressure dependence at 52 and 132 K is well reproduced by the theoretical calculations provided that an anharmonic state density is considered for the van der Waals complex CH3CNCN and its Lennard-Jones radius is adjusted. Furthermore, these calculations indicate that the experimental observations correspond to the fall-off regime and that tunneling remains small in the low-pressure regime. Hence, the studied reaction is essentially an association process at very low temperature. Implications for the chemistry of interstellar clouds and Titan are discussed.

  7. Statistical Factors in Complexation Reactions.

    ERIC Educational Resources Information Center

    Chung, Chung-Sun

    1985-01-01

    Four cases which illustrate statistical factors in complexation reactions (where two of the reactants are monodentate ligands) are presented. Included are tables showing statistical factors for the reactions of: (1) square-planar complexes; (2) tetrahedral complexes; and (3) octahedral complexes. (JN)

  8. Bacterial formate hydrogenlyase complex

    PubMed Central

    McDowall, Jennifer S.; Murphy, Bonnie J.; Haumann, Michael; Palmer, Tracy; Armstrong, Fraser A.; Sargent, Frank

    2014-01-01

    Under anaerobic conditions, Escherichia coli can carry out a mixed-acid fermentation that ultimately produces molecular hydrogen. The enzyme directly responsible for hydrogen production is the membrane-bound formate hydrogenlyase (FHL) complex, which links formate oxidation to proton reduction and has evolutionary links to Complex I, the NADH:quinone oxidoreductase. Although the genetics, maturation, and some biochemistry of FHL are understood, the protein complex has never been isolated in an intact form to allow biochemical analysis. In this work, genetic tools are reported that allow the facile isolation of FHL in a single chromatographic step. The core complex is shown to comprise HycE (a [NiFe] hydrogenase component termed Hyd-3), FdhF (the molybdenum-dependent formate dehydrogenase-H), and three iron-sulfur proteins: HycB, HycF, and HycG. A proportion of this core complex remains associated with HycC and HycD, which are polytopic integral membrane proteins believed to anchor the core complex to the cytoplasmic side of the membrane. As isolated, the FHL complex retains formate hydrogenlyase activity in vitro. Protein film electrochemistry experiments on Hyd-3 demonstrate that it has a unique ability among [NiFe] hydrogenases to catalyze production of H2 even at high partial pressures of H2. Understanding and harnessing the activity of the FHL complex is critical to advancing future biohydrogen research efforts. PMID:25157147

  9. Hydrogen atom abstraction reactions from tertiary amines by benzyloxyl and cumyloxyl radicals: influence of structure on the rate-determining formation of a hydrogen-bonded prereaction complex.

    PubMed

    Salamone, Michela; DiLabio, Gino A; Bietti, Massimo

    2011-08-05

    A time-resolved kinetic study on the hydrogen atom abstraction reactions from a series of tertiary amines by the cumyloxyl (CumO(•)) and benzyloxyl (BnO(•)) radicals was carried out. With the sterically hindered triisobutylamine, comparable hydrogen atom abstraction rate constants (k(H)) were measured for the two radicals (k(H)(BnO(•))/k(H)(CumO(•)) = 2.8), and the reactions were described as direct hydrogen atom abstractions. With the other amines, increases in k(H)(BnO(•))/k(H)(CumO(•)) ratios of 13 to 2027 times were observed. k(H) approaches the diffusion limit in the reactions between BnO(•) and unhindered cyclic and bicyiclic amines, whereas a decrease in reactivity is observed with acyclic amines and with the hindered cyclic amine 1,2,2,6,6-pentamethylpiperidine. These results provide additional support to our hypothesis that the reaction proceeds through the rate-determining formation of a C-H/N hydrogen-bonded prereaction complex between the benzyloxyl α-C-H and the nitrogen lone pair wherein hydrogen atom abstraction occurs, and demonstrate the important role of amine structure on the overall reaction mechanism. Additional mechanistic information in support of this picture is obtained from the study of the reactions of the amines with a deuterated benzyloxyl radical (PhCD(2)O(•), BnO(•)-d(2)) and the 3,5-di-tert-butylbenzyloxyl radical.

  10. First insertion of NO into a transition-metal cluster-carbon bond: regioselective formation, structure, and reactions of the first alkanenitrile oxide complexes

    SciTech Connect

    Goldhaber, A.; Vollhardt, K.P.C.; Walborsky, E.C.; Wolfgruber, M.

    1986-02-05

    The chemistry of NO in the presence of transition metals is receiving considerable current attention because of its role in air pollution, its potential in organic synthesis by carbon-nitrogen bond formation, and an increasing interest in its basic features. The nitrosyl cation has been reacted with many mono and polynuclear metal systems, leading mainly to substitution and reduction. Insertion into alkyl and aryl metal bonds in mono-metallic complexes is documented. The unprecedented title reaction and some preliminary chemistry of the products are reported here. 27 references, 1 figure.

  11. Energetics and excited state dynamics of the radical pair formation in isolated CP47-reaction center complex of photosystem II at various temperatures

    SciTech Connect

    Groot, Marie-Louise; Paa lsson, Lars-Olof; Pribic, Radmila; Stokkum, Ivo H. van; Dekker, Jan P.; Grondelle, Rienk van

    1996-04-01

    The isolated CP47-reaction center complex of spinach photosystem II has been studied with time resolved picosecond fluorescence spectroscopy between 77 K and 270 K. It was observed that these particles exhibit multi-exponential fluorescence decays of the excited state at all temperatures. The major observations are an energy transfer/trapping time of {approx}40 picoseconds and a long-lived {approx}23 nanosecond component attributed to the recombination of the radical pair. These experimentally obtained parameters were used to estimate the free energy difference for the radical pair formation.

  12. Determination of boron at sub-ppm levels in uranium oxide and aluminum by hyphenated system of complex formation reaction and high-performance liquid chromatography (HPLC).

    PubMed

    Rao, Radhika M; Aggarwal, Suresh K

    2008-04-15

    Boron, at sub-ppm levels, in U3O8 powder and aluminum metal, was determined using complex formation and dynamically modified reversed-phase high-performance liquid chromatography (RP-HPLC). Curcumin was used for complexing boron extracted with 2-ethyl-1,3-hexane diol (EHD). Separation of complex from excess reagent and thereafter its determination using the online diode array detector (DAD) was carried out by HPLC. Calibration curve was found to be linear for boron amounts in the sample ranging from 0.02 microg to 0.5 microg. Precision of about 10% was achieved for B determination in samples containing less than 1 ppmw of boron. The values obtained by HPLC were in good agreement with the data available from other analytical techniques. The precision in the data obtained by HPLC was much better compared to that reported by other techniques. The present hyphenated methodology of HPLC and complex formation reaction is interesting because of cost performance, simplicity, versatility and availability when compared to other spectroscopic techniques like ICP-MS and ICP-AES.

  13. Electrochemiluminescent (ECL) [Ru(bpy)3](2+)/PAMAM dendrimer reactions: coreactant effect and 5-fluorouracil/dendrimer complex formation.

    PubMed

    Jimenez-Ruiz, Aila; Grueso, Elia; Perez-Tejeda, Pilar; Muriel-Delgado, Fernando; Torres-Marquez, Concepcion

    2016-10-01

    Electrogenerated chemiluminescence (ECL) reactions between tris(2,2'-bipyridine)ruthenium(II) and PAMAM dendrimers of the full (G1.0) and half (G1.5) generations were carried out in an aqueous medium at pH 6.1 and 10.0. In the absence of 5-fluoro-1H,3H-pyrimidine-2,4-dione (5-fluorouracil, 5-Fu) (coreactant effect study), the ECL efficiency trends as a function of [G1.0] and [G1.5] at pH 6.1 and 10.0 revealed that PAMAM dendrimers are about 100 (G1.5, pH 6.1), 60 (G1.5, pH 10.0), 26 (G1.0, pH 10.0) and 13 (G1.0, pH 6.1) times more efficient as ECL coreactants than oxalate anion is. Moreover, ECL reactions were done in the presence of several solutions of 5-Fu at a fixed concentration of the G1.0 and G1.5 dendrimers at pH 6.1 and 10.0 (binding study). The ECL efficiency trends as a function of [5-Fu] highlighted a dendrimer/5-Fu binding. Therefore, one of the most remarkable and novel findings of this work is the potential of PAMAM dendrimers to be used as both sensors and biosensors in an aqueous medium in the presence of a suitable sensitizer. Redox potentials of the [Ru(bpy)3](3+/2+) couple were also determined in the absence and presence of 5-Fu at both pHs. In the absence of 5-Fu the positive or negative shift of redox potentials showed the influence of the repulsive or attractive electrostatic long-range and short-range interactions between the charged dendrimer surface and the oxidized and reduced forms of the couple. In the presence of 5-Fu the trends of redox potentials highlighted the existence of a charged dendrimer/5-Fu species. Graphical Abstract ECL emission for the [Ru(bpy)3](2+)/ G1.0 dendrimer reaction in the presence of the 5-Fu at pH 6.1.

  14. Pulse radiolytic study of the oxidation reactions of uric acid in presence of bovine serum albumin. Evidence of possible complex formation in the transient state

    NASA Astrophysics Data System (ADS)

    Adhikari, S.; Joshi, R.; Gopinathan, C.

    1997-01-01

    The pulse radiolytic and spectrophotometric study of uric acid in presence of bovine serum albumin (BSA) has been carried out. In the spectrophotometric study there is no evidence for ground state interaction between BSA and uric acid. The oxidation reactions of uric acid in presence and absence of BSA employing CCl 3OO and Br radicals have been carried out. In a composition of equal concentration of uric acid and BSA, the CCl 3OO and Br radicals produce a transient absorption spectrum which show two peaks at 330 and 360 nm. The peak at 360 nm is ascribed due to weak complex formation between semioxidised BSA and uric acid radicals. The rate constant of CCl 3OO . radical with uric acid increases with the increase in BSA concentration which is explained as protection of BSA by uric acid from radical attack. The Br radical attacks uric acid and BSA in a manner similar to CCl 3OO radical. The bimolecular rate constants for the reaction of Br radical with BSA and uric acid have been found as 2.9 × 10 10 dm 3 mol -1 s -1 and 6.33 × 10 9 dm 3 mol -1 s -, respectively.

  15. Complexity of formation in holography

    NASA Astrophysics Data System (ADS)

    Chapman, Shira; Marrochio, Hugo; Myers, Robert C.

    2017-01-01

    It was recently conjectured that the quantum complexity of a holographic boundary state can be computed by evaluating the gravitational action on a bulk region known as the Wheeler-DeWitt patch. We apply this complexity=action duality to evaluate the `complexity of formation' [1, 2], i.e. the additional complexity arising in preparing the entangled thermofield double state with two copies of the boundary CFT compared to preparing the individual vacuum states of the two copies. We find that for boundary dimensions d > 2, the difference in the complexities grows linearly with the thermal entropy at high temperatures. For the special case d = 2, the complexity of formation is a fixed constant, independent of the temperature. We compare these results to those found using the complexity=volume duality.

  16. A spectrophotometric and thermodynamic study of the sitting-atop complex formation from reaction between free base meso-tetraarylporphyrins and zirconyl nitrate in chloroform solution

    NASA Astrophysics Data System (ADS)

    Dehghani, Hossein; Mansournia, Mohammad Reza

    2009-10-01

    The sitting-atop complexation of meso-tetraarylporphyrins and its para-substituted derivatives (H 2t(4-X)pp, X:H, Br, Cl, CH(CH 3) 2, OCH 3, CH 3), as electron donors, with zirconyl, as an electron acceptor, have been investigated spectrophotometrically in chloroform. The mole ratio studies based on physicochemical techniques were employed clearly and revealed the formation of 1:1 sitting-atop complexes which was confirmed by UV-vis, 1H NMR and IR spectroscopic data. The value of the formation constant was estimated for each complex using a nonlinear optimization of the complex absorbance vs. mole ratio data by package KINFIT. The results showed that the stability of these complexes decreases with the temperature enhancement. Thermodynamic parameters, Δ G°, Δ H° and Δ S°, of the SAT complexes have been determined from the temperature dependence of formation constants by Van't Hoff equation. Also, the influence of the substituents of the aryl rings in H 2t(4-X)pp on the stability of the SAT complexes is discussed.

  17. Unusual Complex Formation and Chemical Reaction of Haloacetate Anion on the Exterior Surface of Cucurbit[6]uril in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Choi, Tae Su; Ko, Jae Yoon; Heo, Sung Woo; Ko, Young Ho; Kim, Kimoon; Kim, Hugh I.

    2012-10-01

    Noncovalent interactions of cucurbit[6]uril (CB[6]) with haloacetate and halide anions are investigated in the gas phase using electrospray ionization ion mobility mass spectrometry. Strong noncovalent interactions of monoiodoacetate, monobromoacetate, monochloroacetate, dichloroacetate, and trichloroacetate on the exterior surface of CB[6] are observed in the negative mode electrospray ionization mass spectra. The strong binding energy of the complex allows intramolecular SN2 reaction of haloacetate, which yields externally bound CB[6]-halide complex, by collisional activation. Utilizing ion mobility technique, structures of exteriorly bound CB[6] complexes of haloacetate and halide anions are confirmed. Theoretically determined low energy structures using density functional theory (DFT) further support results from ion mobility studies. The DFT calculation reveals that the binding energy and conformation of haloacetate on the CB[6] surface affect the efficiency of the intramolecular SN2 reaction of haloacetate, which correlate well with the experimental observation.

  18. Modeling the complex bromate-iodine reaction.

    PubMed

    Machado, Priscilla B; Faria, Roberto B

    2009-05-07

    In this article, it is shown that the FLEK model (ref 5 ) is able to model the experimental results of the bromate-iodine clock reaction. Five different complex chemical systems, the bromate-iodide clock and oscillating reactions, the bromite-iodide clock and oscillating reactions, and now the bromate-iodine clock reaction are adequately accounted for by the FLEK model.

  19. Markovian dynamics on complex reaction networks

    NASA Astrophysics Data System (ADS)

    Goutsias, J.; Jenkinson, G.

    2013-08-01

    Complex networks, comprised of individual elements that interact with each other through reaction channels, are ubiquitous across many scientific and engineering disciplines. Examples include biochemical, pharmacokinetic, epidemiological, ecological, social, neural, and multi-agent networks. A common approach to modeling such networks is by a master equation that governs the dynamic evolution of the joint probability mass function of the underlying population process and naturally leads to Markovian dynamics for such process. Due however to the nonlinear nature of most reactions and the large size of the underlying state-spaces, computation and analysis of the resulting stochastic population dynamics is a difficult task. This review article provides a coherent and comprehensive coverage of recently developed approaches and methods to tackle this problem. After reviewing a general framework for modeling Markovian reaction networks and giving specific examples, the authors present numerical and computational techniques capable of evaluating or approximating the solution of the master equation, discuss a recently developed approach for studying the stationary behavior of Markovian reaction networks using a potential energy landscape perspective, and provide an introduction to the emerging theory of thermodynamic analysis of such networks. Three representative problems of opinion formation, transcription regulation, and neural network dynamics are used as illustrative examples.

  20. Notable effects of the metal salts on the formation and decay reactions of α-tocopheroxyl radical in acetonitrile solution. The complex formation between α-tocopheroxyl and metal cations.

    PubMed

    Kohno, Yutaro; Fujii, Miyabi; Matsuoka, Chihiro; Hashimoto, Haruka; Ouchi, Aya; Nagaoka, Shin-ichi; Mukai, Kazuo

    2011-08-18

    The measurement of the UV-vis absorption spectrum of α-tocopheroxyl (α-Toc(•)) radical was performed by reacting aroxyl (ArO(•)) radical with α-tocopherol (α-TocH) in acetonitrile solution including four kinds of alkali and alkaline earth metal salts (MX or MX(2)) (LiClO(4), LiI, NaClO(4), and Mg(ClO(4))(2)), using stopped-flow spectrophotometry. The maximum wavelength (λ(max)) of the absorption spectrum of the α-Toc(•) at 425.0 nm increased with increasing concentration of metal salts (0-0.500 M) in acetonitrile, and it approached constant values, suggesting an [α-Toc(•)-M(+) (or M(2+))] complex formation. The stability constants (K) were determined to be 9.2, 2.8, and 45 M(-1) for LiClO(4), NaClO(4), and Mg(ClO(4))(2), respectively. By reacting ArO(•) with α-TocH in acetonitrile, the absorption of ArO(•) disappeared rapidly, while that of α-Toc(•) appeared and then decreased gradually as a result of the bimolecular self-reaction of α-Toc(•) after passing through the maximum. The second-order rate constants (k(s)) obtained for the reaction of α-TocH with ArO(•) increased linearly with an increasing concentration of metal salts. The results indicate that the hydrogen transfer reaction of α-TocH proceeds via an electron transfer intermediate from α-TocH to ArO(•) radicals followed by proton transfer. Both the coordination of metal cations to the one-electron reduced anions of ArO(•) (ArO:(-)) and the coordination of counteranions to the one-electron oxidized cations of α-TocH (α-TocH(•)(+)) may stabilize the intermediate, resulting in the acceleration of electron transfer. A remarkable effect of metal salts on the rate of bimolecular self-reaction (2k(d)) of the α-Toc(•) radical was also observed. The rate constant (2k(d)) decreased rapidly with increasing concentrations of the metal salts. The 2k(d) value decreased at the same concentration of the metal salts in the following order: no metal salt > NaClO(4) > LiClO(4) > Mg

  1. In-situ formation of cobalt-phosphate oxygen-evolving complex-anchored reduced graphene oxide nanosheets for oxygen reduction reaction.

    PubMed

    Zhao, Zhi-Gang; Zhang, Jing; Yuan, Yinyin; Lv, Hong; Tian, Yuyu; Wu, Dan; Li, Qing-Wen

    2013-01-01

    Oxygen conversion process between O₂ and H₂O by means of electrochemistry or photochemistry has lately received a great deal of attention. Cobalt-phosphate (Co-Pi) catalyst is a new type of cost-effective artificial oxygen-evolving complex (OEC) with amorphous features during photosynthesis. However, can such Co-Pi OEC also act as oxygen reduction reaction (ORR) catalyst in electrochemical processes? The question remains unanswered. Here for the first time we demonstrate that Co-Pi OEC does be rather active for the ORR. Particularly, Co-Pi OEC anchoring on reduced graphite oxide (rGO) nanosheet is shown to possess dramatically improved electrocatalytic activities. Differing from the generally accepted role of rGO as an "electron reservoir", we suggest that rGO serves as "peroxide cleaner" in enhancing the electrocatalytic behaviors. The present study may bridge the gap between photochemistry and electrochemistry towards oxygen conversion.

  2. Formation of diphenylphosphanylbutadienyl complexes by insertion of two P-coordinated alkynylphosphanes into a PtbondC6F5 bond: detection of intermediate and reaction products.

    PubMed

    Ara, Irene; Forniés, Juan; García, Ana; Gómez, Julio; Lalinde, Elena; Moreno, M Teresa

    2002-08-16

    The reactions between cis-[M(C(6)F(5))(2)(PPh(2)CtriplebondCR)(2)] (M=Pt, Pd; R=Ph, tBu, Tol 2, 3) or cis-[Pt(C(6)F(5))(2)(PPh(2)CtriplebondCR)(PPh(2)CtriplebondCtBu)] (R=Ph 4, Tol 5) and cis-[Pt(C(6)F(5))(2)(thf)(2)] 1 have been investigated. Whereas [M](PPh(2)CtriplebondCtBu)(2) ([M]=cis-M(C(6)F(5))(2)) is inert towards 1, the analogous reactions starting from [M](PPh(2)CtriplebondCR)(2) or [Pt](PPh(2)CtriplebondCR)(PPh(2)CtriplebondCtBu) (R=Ph, Tol) afford unusual binuclear species [Pt(C(6)F(5))(S)mu-[C(R')dbondC(PPh(2))C(PPh(2))doublebondC(R)(C(6)F(5))]M(C(6)F(5))(2)] (R=R'=Ph, Tol, M=Pt 6 a,c, M=Pd 7 a,c; M=Pt, R'=tBu, R=Ph 8, Tol 9) containing a bis(diphenylphosphanyl)butadienyl bridging ligand formed by an unprecedented sequential insertion reaction of two P-coordinated PPh(2)CtriplebondCR ligands into a PtbondC(6)F(5) bond. Although in solution the presence of coordinated solvent S (S=(thf)(x)(H(2)O)(y)) in 6, 7 is suggested by NMR spectroscopy, X-ray diffraction analyses of different crystals of the mixed complex [Pt(C(6)F(5))mu-[C(tBu)doublebondC(PPh(2))C(PPh(2))doublebondC(Tol)(C(6)F(5))]Pt(C(6)F(5))(2)] 9 unequivocally establish that in the solid state the steric crowding of the new diphenylbutadienyl ligand formed stabilizes an unusual coordinatively unsaturated T-shaped 3-coordinated platinum(II) center. Structure determinations of the mononuclear precursors cis-[Pt(C(6)F(5))(2)(PPh(2)CtriplebondCR)(2)] (R=Ph, tBu, Tol) have been carried out to evaluate the factors affecting the insertion processes. The reactions of the platinum complexes 6 towards neutral ligands (L=CO, py, PPh(2)H, CNtBu) in a 1:1 molar ratio afford related diplatinum derivatives 10-13, whereas treatment with CNtBu (1:2 molar ratio) or 2,2'-bipy (1:1 molar ratio) results in the opening of the chelating ring to give cis,cis-[Pt(C(6)F(5))(L)(2)mu-[1-kappaC(1):2-kappaPP'-C(R)doublebondC(PPh(2))C(PPh(2))doublebondC(R)(C(6)F(5))]Pt(C(6)F(5))(2)] (14, 15). The unsaturated or solvento

  3. Reactions of trivacant Wells-Dawson heteropolytungstates. Ionic strength and Jahn-Teller effects on formation in multi-iron complexes.

    PubMed

    Anderson, Travis M; Zhang, Xuan; Hardcastle, Kenneth I; Hill, Craig L

    2002-05-06

    Reaction of alpha-P(2)W(15)O(56)(12-) and Fe(III) in a saturated NaCl solution produces a trisubstituted Wells-Dawson structure with three low-valent metals, alpha-(Fe(III)Cl)(2)(Fe(III)OH(2))P(2)W(15)O(59)(11-) (1). Dissolution of this species into 1 M NaBr (Br(-) is non-coordinating) gives the triaquated species alpha-(Fe(III)OH(2))(3)P(2)W(15)O(59)(9-) (2). Ionic strength values of 1 M or greater are necessary to avoid decomposition of 1 or 2 to the conventional sandwich-type complex, alpha beta beta alpha-(Fe(III)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(12-) (3). If the pH is greater than 5, a new triferric sandwich, alpha alpha beta alpha-(NaOH(2))(Fe(III)OH(2))Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (4), forms rather than 3. Like the previously reported Wells-Dawson-derived sandwich-type structures with three metals in the central unit ([TM(II)Fe(III)(2)(P(2)W(15)O(56))(P(2)TM(II)(2)W(13)O(52))],(16-) TM = Cu, Co), this complex has a central alpha-junction and a central beta-junction. Thermal studies suggest that 4 is more stable than 3 over a wide range of temperatures and pH values. The intrinsic Jahn-Teller distortion of d-electron-containing metal ions incorporated into the external sites of the central multi-metal unit impacts the stoichiometry of their incorporation (with a consequent change in the inter-POM-unit connectivity, where POM = polyoxometalate). Reaction of non-distorting Ni(II) with the diferric lacunary sandwich-type POM alpha alpha alpha alpha-(NaOH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(16-) (5) produces alpha beta beta alpha-(Ni(II)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (6), a Wells-Dawson sandwich-type structure with two Ni(II) and two Fe(III) in the central unit. All structures are characterized by (31)P NMR, IR, UV-vis, magnetic susceptibility, and X-ray crystallography. Complexes 4 and 6 are highly selective and effective catalysts for the H(2)O(2)-based epoxidation of alkenes.

  4. Three-component reaction of tautomeric amidines with 3-ferrocenylmethylidene-2,4-pentanedione. Formation of polymeric coordination complexes of potassium ferrocenyl-(hexahydro)pyrimidoxides.

    PubMed

    Klimova, Elena I; Flores-Alamo, Marcos; Klimova, Tatiana; Maya, Sandra Cortez; Beletskaya, Irina P

    2013-12-20

    Acetamidine hydrochloride and p-aminobenzamidine dihydrochloride interact with 3-ferrocenylmethylidene-2,4-pentanedione at 80-82 °C in the presence of K2CO3 in the water-alcohol medium in two tautomeric forms (the amidoimine and enediamine ones) with formation of mixtures of pyrimidine and piperidone derivatives and polymeric coordination complexes of potassium ferrocenyl(hexahydro)pyrimidoxides. The structure of the resultant compounds is elucidated on the basis of IR, 1H- and 13C-NMR spectroscopy, mass spectrometry and elemental analysis data. The crystal structures of 6-ferrocenyl-4-hydroxy-4-methyl-2-piperidone, potassium 6-ferrocenyl-4-methyl-2-methylidene(hexahydro)pyrimidin-4-oxide and 2-(4-aminophenyl)-4-ferrocenyl-6-methyl-pyrimidine were determined by X-ray analysis of suitable single crystals.

  5. Audience Reactions to Two Visual Formats.

    ERIC Educational Resources Information Center

    Ramsey, Richard David

    One hundred undergraduate business students completed a questionnaire designed to determine their reactions to a traditional and a "flashier" textbook format. Before completing the questionnaire, subjects spent several minutes examining two business textbooks--one an older textbook with black ink on white paper, narrow margins, and few…

  6. Reaction front formation in contaminant plumes.

    PubMed

    Cribbin, Laura B; Winstanley, Henry F; Mitchell, Sarah L; Fowler, Andrew C; Sander, Graham C

    2014-12-15

    The formation of successive fronts in contaminated groundwater plumes by subsoil bacterial action is a commonly accepted feature of their propagation, but it is not obviously clear from a mathematical standpoint quite how such fronts are formed or propagate. In this paper we show that these can be explained by combining classical reaction-diffusion theory involving just two reactants (oxidant and reductant), and a secondary reaction in which a reactant on one side of such a front is (re-)formed on the other side of the front via diffusion of its product across the front. We give approximate asymptotic solutions for the reactant profiles, and the propagation rate of the front.

  7. Pattern Formation and Complexity Emergence

    NASA Astrophysics Data System (ADS)

    Berezin, Alexander A.

    2001-03-01

    Success of nonlinear modelling of pattern formation and self-organization encourages speculations on informational and number theoretical foundations of complexity emergence. Pythagorean "unreasonable effectiveness of integers" in natural processes is perhaps extrapolatable even to universal emergence "out-of-nothing" (Leibniz, Wheeler). Because rational numbers (R = M/N) are everywhere dense on real axis, any digital string (hence any "book" from "Library of Babel" of J.L.Borges) is "recorded" infinitely many times in arbitrary many rationals. Furthermore, within any arbitrary small interval there are infinitely many Rs for which (either or both) integers (Ms and Ns) "carry" any given string of any given length. Because any iterational process (such as generation of fractal features of Mandelbrot Set) is arbitrary closely approximatable with rational numbers, the infinite pattern of integers expresses itself in generation of complexity of the world, as well as in emergence of the world itself. This "tunnelling" from Platonic World ("Platonia" of J.Barbour) to a real (physical) world is modern recast of Leibniz's motto ("for deriving all from nothing there suffices a single principle").

  8. Photosynthetic reaction center complexes from heliobacteria

    NASA Technical Reports Server (NTRS)

    Trost, J. T.; Vermaas, W. F. J.; Blankenship, R. E.

    1991-01-01

    The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus of this project is the family of newly discovered strictly anaerobic photosynthetic organisms known as Heliobacteria. These organisms are the only known photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reaction centers suggest that they might be the decendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes have been isolated from the photosynthetic bacteria Heliobacillus mobilis and Heliobacterium gestii. The absorption and fluorescence properties of membranes and reaction centers are almost identical, suggesting that a single pigment-protein complex serves as both antenna and reaction center. Experiments in progress include sequence determination of the 48,000 Mr reaction center protein, and evolutionary comparisons with other reaction center proteins.

  9. Structural determinants for the formation of sulfhemeprotein complexes

    PubMed Central

    Román-Morales, Elddie; Pietri, Ruth; Ramos-Santana, Brenda; Vinogradov, Serge N.; Lewis-Ballester, Ariel; López-Garriga, Juan

    2010-01-01

    Several hemoglobins were explored by UV-Vis and resonance Raman spectroscopy to define sulfheme complex formation. Evaluation of these proteins upon the reaction with H2O2 or O2 in the presence of H2S suggest: (a) the formation of the sulfheme derivate requires a HisE7 residue in the heme distal site with an adequate orientation to form an active ternary complex; (b) that the ternary complex intermediate involves the HisE7, the peroxo or ferryl species, and the H2S molecule. This moiety precedes and triggers the sulfheme formation. PMID:20732304

  10. Photosynthetic reaction center complexes from heliobacteria

    NASA Technical Reports Server (NTRS)

    Trost, J. T.; Vermaas, W. F. J.; Blankenship, R. E.

    1991-01-01

    Photosynthetic reaction centers are pigment-protein complexes that are responsible for the transduction of light energy into chemical energy. Considerable evidence indicates that photosynthetic organisms were present very early in the evolution of life on Earth. The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus is on the family of newly discovered strictly anaerobic photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reactions centers suggest that they may be the descendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes were isolated from the photosynthetic bacteria, Heliobacillus mobilis and Heliobacterium gestii, by extraction of membranes with Deriphat 160C followed by differential centrifugation and sucrose density gradient centrifugation. Other aspects of this investigation are briefly discussed.

  11. Synthesis, DNA binding and complex formation reactions of 3-amino-5,6-dimethyl-1,2,4-triazine with Pd(II) and some selected biorelevant ligands

    NASA Astrophysics Data System (ADS)

    Shoukry, Azza A.; Alghanmi, Reem M.

    2015-03-01

    With the purpose of studying the binding behavior of Pd(II) complexes with DNA as the main biological target, and their ability to penetrate reasonably into tumour cells and destroy their replication ability, Pd(ADT)Cl2 complex was synthesized and characterized, where ADT is 3-amino-5,6-dimethyl-1,2,4-triazine. Stoichiometry and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(ADT)(H2O)2]2+ were investigated at 25 °C and at constant 0.1 mol dm-3 ionic strength. The concentration distribution diagrams of the various species formed are evaluated. Further investigation of the binding properties of the diaqua complex [Pd(ADT)(H2O)2]2+ with calf thymus DNA (CT-DNA) was investigated by UV-vis spectroscopy. The intrinsic binding constants (Kb) calculated from UV-vis absorption studies was calculated to be 2.00 × 103 mol dm-3. The calculated (Kb) value was found to be of lower magnitude than that of the classical intercalator EB (Ethidium bromide) (Kb = 1.23(±0.07) × 105 mol dm-3) suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA. Thermal denaturation has been systematically studied by spectrophotometric method and the calculated ΔTm was nearly 5 °C, supporting the electrostatic and/or groove binding mode for the interaction between the complex and CT-DNA

  12. Formation of a paramagnetic Al complex and extrusion of Fe during the reaction of (diiminepyridine)Fe with AlR3 (R = Me, Et).

    PubMed

    Scott, Jennifer; Gambarotta, Sandro; Korobkov, Ilia; Knijnenburg, Quinten; de Bruin, Bas; Budzelaar, Peter H M

    2005-12-14

    The reaction of the {2,6-[2,6-(iPr)2PhN=C(CH3)]2(C5H3N)}FeCl2 catalyst precursor with R3Al [R = Me, Et] afforded {2,6-[2,6-(iPr)2PhN=C(CH3)]2(C5H3N)}AlMe2 (1) and [eta4-LAl2Et3(mu-Cl)]Fe-(eta6-C7H8) (2), respectively. These paramagnetic species arises from both transmetalation, during which the strong terdentate ligand loses the Fe center, and reduction. The extent of reduction depends on the nature of the Al alkylating agent. The electrons necessary for the reduction are likely to be provided by cleavage of Fe-C bond of transient low-valent organo-Fe species.

  13. Formation of DEG5 and DEG8 complexes and their involvement in the degradation of photodamaged photosystem II reaction center D1 protein in Arabidopsis.

    PubMed

    Sun, Xuwu; Peng, Lianwei; Guo, Jinkui; Chi, Wei; Ma, Jinfang; Lu, Congming; Zhang, Lixin

    2007-04-01

    The widely distributed DEGP proteases play important roles in the degradation of damaged and misfolded proteins. Arabidopsis thaliana contains 16 DEGP-like proteases, four of which are located in the chloroplast. Here, we show that DEG5 and DEG8 form a hexamer in the thylakoid lumen and that recombinant DEG8 is proteolytically active toward both a model substrate (beta-casein) and photodamaged D1 protein of photosystem II (PSII), producing 16-kD N-terminal and 18-kD C-terminal fragments. Inactivation of DEG5 and DEG8 resulted in increased sensitivity to photoinhibition. Turnover of newly synthesized D1 protein in the deg5 deg8 double mutant was impaired, and the degradation of D1 in the presence of the chloroplast protein synthesis inhibitor lincomycin under high-light treatment was slowed in the mutants. Thus, DEG5 and DEG8 are important for efficient turnover of the D1 protein and for protection against photoinhibition in vivo. The deg5 deg8 double mutant showed increased photosensitivity and reduced rates of D1 degradation compared with single mutants of deg5 and deg8. A 16-kD N-terminal degradation fragment of the D1 protein was detected in wild-type plants but not in the deg5 deg8 mutant following in vivo photoinhibition. Therefore, our results suggest that DEG5 and DEG8 have a synergistic function in the primary cleavage of the CD loop of the PSII reaction center protein D1.

  14. Spray formation with complex fluids

    NASA Astrophysics Data System (ADS)

    Lustig, S.; Rosen, M.

    2011-05-01

    Droplet formation through Faraday excitation has been tested in the low driving frequency limit. Kerosene was used to model liquid fuel with the addition of PIB in different proportions. All fluids were characterized in detail. The mechanisms of ejection were investigated to identify the relative influence of viscosity and surface tension. It was also possible to characterize the type of instability leading to the emission drop process.

  15. Activation of C-O and C-C bonds and formation of novel HAlOH-ether complexes: an EPR study of the reaction of ground-state Al atoms with methylethyl ether and diethyl ether.

    PubMed

    Brunet, François D; Feola, Julie C; Joly, Helen A

    2012-03-15

    Reaction mixtures, containing Al atoms and methylethyl ether (MEE) or diethyl ether (DEE) in an adamantane matrix, were prepared with the aid of a metal-atom reactor known as a rotating cryostat. The EPR spectra of the resulting products were recorded from 77-260 K, at 10 K intervals. Al atoms were found to insert into methyl-O, ethyl-O, and C-C bonds to form CH(3)AlOCH(2)CH(3), CH(3)OAlCH(2)CH(3), and CH(3)OCH(2)AlCH(3), respectively, in the case of MEE while DEE produced CH(3)CH(2)AlOCH(2)CH(3) and CH(3)AlCH(2)OCH(2)CH(3), respectively. From the intensity of the transition lines attributed to the Al atom C-O insertion products of MEE, insertion into the methyl-O bond is preferred. The Al hyperfine interaction (hfi) extracted from the EPR spectra of the C-O insertion products was greater than that of the C-C insertion products, that is, 5.4% greater for the DEE system and 7% greater for the MEE system. The increase in Al hfi is thought to arise from the increased electron-withdrawing ability of the substituents bonded to Al. Besides HAlOH, resulting from the reaction of Al atoms with adventitious water, novel mixed HAlOH:MEE and HAlOH:DEE complexes were identified with the aid of isotopic studies involving H(2)(17)O and D(2)O. The Al and H hfi of HAlOH were found to decrease upon complex formation. These findings are consistent with the nuclear hfi calculated using a density functional theory (DFT) method with close agreement between theory and experiment occurring at the B3LYP level using a 6-311+G(2df,p) basis set.

  16. Knockout driven reactions in complex molecules and their clusters

    NASA Astrophysics Data System (ADS)

    Gatchell, Michael; Zettergren, Henning

    2016-08-01

    Energetic ions lose some of their kinetic energy when interacting with electrons or nuclei in matter. Here, we discuss combined experimental and theoretical studies on such impulse driven reactions in polycyclic aromatic hydrocarbons (PAHs), fullerenes, and pure or mixed clusters of these molecules. These studies show that the nature of excitation is important for how complex molecular systems respond to ion/atom impact. Rutherford-like nuclear scattering processes may lead to prompt atom knockout and formation of highly reactive fragments, while heating of the molecular electron clouds in general lead to formation of more stable and less reactive fragments. In this topical review, we focus on recent studies of knockout driven reactions, and present new calculations of the angular dependent threshold (displacement) energies for such processes in PAHs. The so-formed fragments may efficiently form covalent bonds with neighboring molecules in clusters. These unique molecular growth processes may be important in astrophysical environments such as low velocity shock waves.

  17. Reactions of Dinuclear Platinum(II) Complexes with Peptides.

    PubMed

    Rajković, Snežana; Živković, Marija D; Djuran, Miloš I

    2016-01-01

    The present review article highlights recent findings in the reactions between different dinuclear Pt(II) complexes with peptides containing cysteine, methionine and histidine residues. The reactions of {trans-[Pt(NH3)2Cl]2(μ-X)}(2+) and {trans-[Pt(NH3)2(H2O)]2(μ-X)}(4+) type complexes with different bridging ligands (X) (X = pyrazine, 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane) with the tripeptide glutathione proceeded in two steps. In the first step, one water or chlorido ligand of the dinuclear Pt(II) complex was substituted by the sulfhydryl group of GSH, while in the second step, the remaining water or chlorido ligand from the dinuclear Pt(II)-peptide complex was replaced by the second molecule of glutathione, finally leading to the formation of the {trans-[Pt(NH3)2(GS)]2(μ-X)}(2+) complex. It was shown that the bridging ligand had an important influence on the reactivity of these complexes with glutathione. No hydrolytic cleavage of any amide bond was observed in the reactions between these complexes and glutathione. However, in reactions performed in acidic media (2.0 < pH < 2.5) between dinuclear Pt(II) complexes with the general formulae {[Pt(L)(H2O)]2(μ-diazine)}(4+) (L is different bidentate coordinated diamine ligands and diazine is a pyrazine- or pyridazine-bridging ligand) and Nacetylated peptides containing L-methionine and L-histidine amino acids in the side chains (Ac-L-Met-Gly, Ac-L-His-Gly and Ac-L-Met-Gly-L-His-GlyNH2), regioselective cleavage of these peptides occurred. The mechanism of these hydrolytic reactions was discussed in relation to the structure of the diazine-bridged Pt(II) complex and the investigated peptides. A systematic summary of these results could contribute to the future design of new dinuclear Pt(II) complexes as potential reagents for regioselective cleavage of peptides and proteins.

  18. Speciation studies on the complex formation reactions of [Pd( N, N-diethyl-ethylendiamine)(H 2O) 2] 2+ with some bio-relevant ligands and displacement reaction by mercaptoethylamine

    NASA Astrophysics Data System (ADS)

    Shehata, Mohamed R.; Shoukry, Mohamed M.; Osman, Afaf A.; AbedelKarim, Abeer T.

    2011-09-01

    Pd(deen)Cl 2 and Pd(deen)(CBDCA) complexes, where deen = N, N-diethylethylenediamine and CBDCA = 1,1-cyclobutanedicarboxylate, were synthesized and characterized by elemental analysis and spectroscopic techniques. The stoichiometry and stability of the complexes formed between various biologically relevant ligands (amino acids, peptides, DNA constituents and dicarboxylic acids) and [Pd(deen)(H 2O) 2] 2+ were investigated at 25 °C and 0.1 M ionic strength. The speciation diagrams of the complexes formed in solutions are evaluated. The mode of coordination of glycylglycine is investigated by spectrophotometric measurements. The equilibrium constants for the displacement of coordinated ligands as inosine, glycine or methionine by mercaptoethylamine are calculated. The results are expected to contribute to the chemistry of antitumour agents.

  19. Disulfirm-ethanol reaction: a complex mechanism

    SciTech Connect

    Yourick, J.J.; Faiman, M.D.

    1986-03-01

    Hypothermia has previously been shown to be a component of the disulfiram-ethanol reaction (DER). In rats, hypothermia correlated with the hypotension and tachycardia observed when ethanol was administered 8 hours after disfulfiram treatment. These studies have now been extended, and in addition, the role of diethyldithiocarbamate (DDTC) and diethyldithiocarbamate-methyl ester (DDTC-MF) in the DER have been examined. In rats challenged with ethanol (1g/kg, i.p.) 4 and 24 hours after disulfiram (75 mg/kg, i.p.) no hypothermia was observed, but was found when ethanol was given 8, 12 and 16 hours after disulfiram. Hypotension and tachycardia were found at all time periods studied. Low Km ALDH also was inhibited at the 4, 8, 16 and 24 hour time periods. Although pretreatment with DDTC and DDTC-ME failed to produce hypothermia, hypotension and tachycardia were observed in rats challenged with ethanol. As with disulfiram administration, hypothermia did not correlate with ALDH inhibition in the DDTC and DDTC-ME studies. These studies support the known myriad of effects produced during the DER, and provide additional evidence that difference mechanisms contribute to the complexity of the disulfiram-ethanol reaction.

  20. C-H bond activation of the methyl group of the supporting ligand in an osmium(III) complex upon reaction with H2O2: formation of an organometallic osmium(IV) complex.

    PubMed

    Sugimoto, Hideki; Ashikari, Kenji; Itoh, Shinobu

    2013-01-18

    Oxidation of the hydroxoosmium(III) complex resulted in C-H bond activation of the methyl group of the supporting ligand (N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridinophane). The product was an osmium(IV) complex exhibiting a seven-coordinate structure with an additional Os-CH(2) bond.

  1. STAR FORMATION ACROSS THE W3 COMPLEX

    SciTech Connect

    Román-Zúñiga, Carlos G.; Ybarra, Jason E.; Tapia, Mauricio; Megías, Guillermo D.; Lada, Elizabeth A.; Alves, Joáo F.

    2015-09-15

    We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex and determined their structure and extension. We constructed extinction-limited samples for five principal clusters and constructed K-band luminosity functions that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star-forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and shows small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster-forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.

  2. Star Formation Across the W3 Complex

    NASA Astrophysics Data System (ADS)

    Román-Zúñiga, Carlos G.; Ybarra, Jason E.; Megías, Guillermo D.; Tapia, Mauricio; Lada, Elizabeth A.; Alves, Joáo F.

    2015-09-01

    We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex and determined their structure and extension. We constructed extinction-limited samples for five principal clusters and constructed K-band luminosity functions that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star-forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and shows small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster-forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.

  3. Complex organic molecules and star formation

    NASA Astrophysics Data System (ADS)

    Bacmann, A.; Faure, A.

    2014-12-01

    Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.

  4. Simulations of photochemical smog formation in complex urban areas

    NASA Astrophysics Data System (ADS)

    Muilwijk, C.; Schrijvers, P. J. C.; Wuerz, S.; Kenjereš, S.

    2016-12-01

    In the present study we numerically investigated the dispersion of photochemical reactive pollutants in complex urban areas by applying an integrated Computational Fluid Dynamics (CFD) and Computational Reaction Dynamics (CRD) approach. To model chemical reactions involved in smog generation, the Generic Reaction Set (GRS) approach is used. The GRS model was selected since it does not require detailed modeling of a large set of reactive components. Smog formation is modeled first in the case of an intensive traffic emission, subjected to low to moderate wind conditions in an idealized two-dimensional street canyon with a building aspect ratio (height/width) of one. It is found that Reactive Organic Components (ROC) play an important role in the chemistry of smog formation. In contrast to the NOx/O3 photochemical steady state model that predicts a depletion of the (ground level) ozone, the GRS model predicts generation of ozone. Secondly, the effect of direct sunlight and shadow within the street canyon on the chemical reaction dynamics is investigated for three characteristic solar angles (morning, midday and afternoon). Large differences of up to one order of magnitude are found in the ozone production for different solar angles. As a proof of concept for real urban areas, the integrated CFD/CRD approach is applied for a real scale (1 × 1 km2) complex urban area (a district of the city of Rotterdam, The Netherlands) with high traffic emissions. The predicted pollutant concentration levels give realistic values that correspond to moderate to heavy smog. It is concluded that the integrated CFD/CRD method with the GRS model of chemical reactions is both accurate and numerically robust, and can be used for modeling of smog formation in complex urban areas.

  5. Reactions and mass spectra of complex particles using Aerosol CIMS

    NASA Astrophysics Data System (ADS)

    Hearn, John D.; Smith, Geoffrey D.

    2006-12-01

    Aerosol chemical ionization mass spectrometry (CIMS) is used both on- and off-line for the analysis of complex laboratory-generated and ambient particles. One of the primary advantages of Aerosol CIMS is the low degree of ion fragmentation, making this technique well suited for investigating the reactivity of complex particles. To demonstrate the usefulness of this "soft" ionization, particles generated from meat cooking were reacted with ozone and the composition was monitored as a function of reaction time. Two distinct kinetic regimes were observed with most of the oleic acid in these particles reacting quickly but with 30% appearing to be trapped in the complex mixture. Additionally, detection limits are measured to be sufficiently low (100-200 ng/m3) to detect some of the more abundant constituents in ambient particles, including sulfate, which is measured in real-time at 1.2 [mu]g/m3. To better characterize complex aerosols from a variety of sources, a novel off-line collection method was also developed in which non-volatile and semi-volatile organics are desorbed from particles and concentrated in a cold U-tube. Desorption from the U-tube followed by analysis with Aerosol CIMS revealed significant amounts of nicotine in cigarette smoke and levoglucosan in oak and pine smoke, suggesting that this may be a useful technique for monitoring particle tracer species. Additionally, secondary organic aerosol formed from the reaction of ozone with R-limonene and volatile organics from orange peel were analyzed off-line showing large molecular weight products (m/z > 300 amu) that may indicate the formation of oligomers. Finally, mass spectra of ambient aerosol collected offline reveal a complex mixture of what appears to be highly processed organics, some of which may contain nitrogen.

  6. Complex kinetics of a Landolt-type reaction: the later phase of the thiosulfate-iodate reaction.

    PubMed

    Varga, Dénes; Nagypál, István; Horváth, Attila K

    2010-05-13

    The thiosulfate-iodate reaction has been studied spectrophotometrically in slightly acidic medium at 25.0 +/- 0.1 degrees C in acetate/acetic acid buffer by monitoring the absorbance at 468 nm at the isosbestic point of iodine-triiodide ion system. The formation of iodine after the Landolt time follows a rather complex kinetic behavior depending on the pH and on the concentration of the reactants as well. It is shown that the key intermediate of the reaction is I(2)O(2), its equilibrium formation from the well-known Dushman reaction along with their further reactions followed by subsequent reactions of HOI, HIO(2), S(2)O(3)OH(-), and S(2)O(3)I(-) adequately accounts for all the experimentally measured characteristics of the kinetic curves. A 19-step kinetic model is proposed and discussed with 13 fitted and 7 fixed parameters in detail.

  7. Visualization of complex hydrocarbon reaction systems

    SciTech Connect

    Shinn, J.H.

    1996-10-01

    Many hydrocarbon reactions of interest involve either poorly characterized reactants and products and/or large numbers of simultaneous reactions. An important step in understanding the behavior of such systems is to develop quantitative pictures of the feeds and products and the transformations which connect them. The processes for constructing these reaction visualizations is illustrated by examining the construction of a molecular model for coal liquefaction and subsequent conversion to distillate products, and the construction of a video simulation of catalytic petroleum naphtha reforming. New techniques which are permitting advances in these visualizations are discussed.

  8. Visualization of complex hydrocarbon reaction systems

    SciTech Connect

    Shinn, J.H.

    1996-12-31

    Many hydrocarbon reactions of interest involve either poorly characterized reactants and products and/or large numbers of simultaneous reactions. An important step in understanding the behavior of such systems is to develop quantitative pictures of the feeds and products and the transformations which connect them. The processes for constructing these reaction visualizations is illustrated by examining the construction of a molecular model for coal liquefaction and subsequent conversion to distillate products, and the construction of a video simulation of catalytic petroleum naphtha reforming. New technique which are permitting advances in these visualizations are discussed.

  9. Artificial Force Induced Reaction Method for Systematic Determination of Complex Reaction Mechanisms.

    PubMed

    Sameera, W M C; Kumar Sharma, Akhilesh; Maeda, Satoshi; Morokuma, Keiji

    2016-10-01

    Nowadays, computational studies are very important for the elucidation of reaction mechanisms and selectivity of complex reactions. However, traditional computational methods usually require an estimated reaction path, mainly driven by limited experimental implications, intuition, and assumptions of stationary points. However, the artificial force induced reaction (AFIR) method in the global reaction route mapping (GRRM) strategy can be used for unbiased and automatic reaction path searches for complex reactions. In this account, we highlight applications of the AFIR method to a variety of reactions (organic, organometallic, enzymatic, and photochemical) of complex molecular systems. In addition, the AFIR method has been successfully used to rationalise the origin of stereo- and regioselectivity. The AFIR method can be applied from small to large molecular systems, and will be a very useful tool for the study of complex molecular problems in many areas of chemistry, biology, and material sciences.

  10. Understanding bond formation in polar one-step reactions. Topological analyses of the reaction between nitrones and lithium ynolates.

    PubMed

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

    2015-04-17

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

  11. Steric Control of Complex Chemical Reactions - 1

    DTIC Science & Technology

    2011-12-26

    their contrasting behaviors upon vibrational and translational excitations can serve as benchmark for gaining deeper insights into polyatomic reaction...equipped with a uniquely designed ion velocity map imaging detector capable of measuring the product pair correlation. The ultrafast femtosecond laser...From A + BC to Polyatomic Systems” K. Liu, Adv. in Chem. Phys. 149, (in press). Invited Review Invited talks at Conferences (* denoting

  12. Steric Control of Complex Chemical Reactions

    DTIC Science & Technology

    2014-05-31

    new light onto the mode- and bond-selective chemistry . We envision that the mode- and bond-selectivity are intimately related to the stereo...of a reaction, as demonstrated in our 2012 Nature Chemistry paper. The detailed methodology is described in the 2014 Journal Chemical Physics paper...13). The most significant contributions during this period are the two papers published in Science 331, 900-903 (2011) and Nature Chemistry 4

  13. Interactive formation control in complex environments.

    PubMed

    Henry, Joseph; Shum, Hubert P H; Komura, Taku

    2014-02-01

    The degrees of freedom of a crowd is much higher than that provided by a standard user input device. Typically, crowd-control systems require multiple passes to design crowd movements by specifying waypoints, and then defining character trajectories and crowd formation. Such multi-pass control would spoil the responsiveness and excitement of real-time control systems. In this paper, we propose a single-pass algorithm to control a crowd in complex environments. We observe that low-level details in crowd movement are related to interactions between characters and the environment, such as diverging/merging at cross points, or climbing over obstacles. Therefore, we simplify the problem by representing the crowd with a deformable mesh, and allow the user, via multitouch input, to specify high-level movements and formations that are important for context delivery. To help prevent congestion, our system dynamically reassigns characters in the formation by employing a mass transport solver to minimize their overall movement. The solver uses a cost function to evaluate the impact from the environment, including obstacles and areas affecting movement speed. Experimental results show realistic crowd movement created with minimal high-level user inputs. Our algorithm is particularly useful for real-time applications including strategy games and interactive animation creation.

  14. Interactive Formation Control in Complex Environments.

    PubMed

    Henry, Joseph; Shum, Hubert P H; Komura, Taku

    2013-08-13

    The degrees of freedom of a crowd is much higher than that provided by a standard user input device. Typically, crowd control systems require multiple passes to design crowd movements by specifying waypoints, and then defining character trajectories and crowd formation. Such multi-pass control would spoil the responsiveness and excitement of real-time control systems. In this paper, we propose a single-pass algorithm to control a crowd in complex environments. We observe that low level details in crowd movement are related to interactions between characters and the environment, such as diverging/merging at cross points, or climbing over obstacles. Therefore, we simplify the problem by representing the crowd with a deformable mesh, and allow the user, via multi-touch input, to specify high level movements and formations that are important for context delivery. To help prevent congestion, our system dynamically reassigns characters in the formation by employing a mass transport solver to minimise their overall movement. The solver uses a cost function to evaluate the impact from the environment, including obstacles and areas affecting movement speed. Experimental results show realistic crowd movement created with minimal high-level user inputs. Our algorithm is particularly useful for real-time applications including strategy games and interactive animation creation.

  15. The catalytic role of uranyl in formation of polycatechol complexes

    PubMed Central

    2011-01-01

    To better understand the association of contaminant uranium with natural organic matter (NOM) and the fate of uranium in ground water, spectroscopic studies of uranium complexation with catechol were conducted. Catechol provides a model for ubiquitous functional groups present in NOM. Liquid samples were analyzed using Raman, FTIR, and UV-Vis spectroscopy. Catechol was found to polymerize in presence of uranyl ions. Polymerization in presence of uranyl was compared to reactions in the presence of molybdate, another oxyion, and self polymerization of catechol at high pH. The effect of time and dissolved oxygen were also studied. It was found that oxygen was required for self-polymerization at elevated pH. The potential formation of phenoxy radicals as well as quinones was monitored. The benzene ring was found to be intact after polymerization. No evidence for formation of ether bonds was found, suggesting polymerization was due to formation of C-C bonds between catechol ligands. Uranyl was found to form outer sphere complexes with catechol at initial stages but over time (six months) polycatechol complexes were formed and precipitated from solution (forming humic-like material) while uranyl ions remained in solution. Our studies show that uranyl acts as a catalyst in catechol-polymerization. PMID:21396112

  16. EXFOR SYSTEMS MANUAL NUCLEAR REACTION DATA EXCHANGE FORMAT.

    SciTech Connect

    MCLANE,V.; NUCLEAR DATA CENTER NETWORK

    2000-05-19

    EXFOR is an exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Centers Network. This document has been written for use by the members of the Network and includes matters of procedure and protocol, as well as detailed rules for the compilation of data. Users may prefer to consult EXFOR Basics' for a brief description of the format.

  17. Spectroscopic, radiochemical, and theoretical studies of the Ga3+-N-2-hydroxyethyl piperazine-N'-2-ethanesulfonic acid (HEPES buffer) system: evidence for the formation of Ga3+ - HEPES complexes in (68) Ga labeling reactions.

    PubMed

    Martins, André F; Prata, M I M; Rodrigues, S P J; Geraldes, Carlos F G C; Riss, P J; Amor-Coarasa, A; Burchardt, C; Kroll, C; Roesch, F

    2013-01-01

    Recent reports have claimed a superior performance of HEPES buffer in comparison to alternative buffer systems for (67/68) Ga labeling in aqueous media. In this paper we report spectroscopic ((1) H and (71) Ga NMR), radiochemical, mass spectrometry and theoretical modeling studies on the Ga(3+)/HEPES system (HEPES = N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) performed with the aim of elucidating a potential contribution of HEPES in the (68/67) Ga radiolabeling process. Our results demonstrate that HEPES acts as a weakly but competitive chelator of Ga(3+) and that this interaction depends on the relative Ga(3+): HEPES concentration. A by-product formed in the labeling mixture has been identified as a [(68) Ga]Ga(HEPES) complex via chromatographic comparison with the nonradioactive analog. The formation of this complex was verified to compete with [(68) Ga]Ga(NOTA) complexation at low NOTA concentration. Putative chelation of Ga(3+) by the hydroxyl and adjacent ring nitrogen of HEPES is proposed on the basis of (1)H NMR shifts induced by Ga(3+) and theoretical modeling studies.

  18. Multiantenna artificial photosynthetic reaction center complex.

    PubMed

    Terazono, Yuichi; Kodis, Gerdenis; Liddell, Paul A; Garg, Vikas; Moore, Thomas A; Moore, Ana L; Gust, Devens

    2009-05-21

    In order to ensure efficient utilization of the solar spectrum, photosynthetic organisms use a variety of antenna chromophores to absorb light and transfer excitation to a reaction center, where photoinduced charge separation occurs. Reported here is a synthetic molecular heptad that features two bis(phenylethynyl)anthracene and two borondipyrromethene antennas linked to a hexaphenylbenzene core that also bears two zinc porphyrins. A fullerene electron acceptor self-assembles to both porhyrins via dative bonds. Excitation energy is transferred very efficiently from all four antennas to the porphyrins. Singlet-singlet energy transfer occurs both directly and by a stepwise funnel-like pathway wherein excitation moves down a thermodynamic gradient. The porphyrin excited states donate an electron to the fullerene with a time constant of 3 ps to generate a charge-separated state with a lifetime of 230 ps. The overall quantum yield is close to unity. In the absence of the fullerene, the porphyrin excited singlet state donates an electron to a borondipyrromethene on a slower time scale. This molecule demonstrates that by incorporating antennas, it is possible for a molecular system to harvest efficiently light throughout the visible from ultraviolet wavelengths out to approximately 650 nm.

  19. Fluid pressure and reaction zone formation at a lithological interface

    NASA Astrophysics Data System (ADS)

    Malvoisin, Benjamin; Podladchikov, Yuri

    2014-05-01

    Chemical composition variations in reaction zones between two distinct lithologies are generally interpreted in terms of chemical potential gradients and diffusion process. Concentration profiles can then be used to quantify the species diffusion coefficients or the time scale of geological events. However, chemical potential gradients are also functions of temperature and pressure and local variations of these parameters can thus potentially modify the diffusion process. In northern Corsica, a centimeter scale reaction zone formed under blueschist conditions at a serpentinite - marble contact of sedimentary origin. Three sub-zones having chemical compositions evolving from one rock end-member to another divide the reaction zone along sharp interfaces. At the reaction zone - marble interface, marble decarbonation occurs to form wollastonite and carbonaceous matter. Thermodynamic calculations for this reaction and the respective increase in density of 25 % and 7 % in the bulk rock and in the garnet minerals are interpreted as records of a pressure gradient during reaction zone formation. Moreover, the formation of a volatile-free sub-zone in the reaction zone from reaction between the H2O-bearing serpentinite and the CO2-bearing marble released fluids at the contact. The impact of such a release on the fluid pressure was modelled by considering the effects of both the rock compaction and the transport of fluid by hydraulic diffusion. Modelling results indicates that > 0.5 GPa fluid overpressure can be generated at the contact if devolatilization rates are of the order of the one experimentally measured (> 10-5 kg of fluid/m3 of rock/s). The resulting pressure gradient is of the order of magnitude of the one necessary to counter-balance the effect on chemical potential of the chemical composition variations across the contact. Finally, after the reaction has run to completion, the model predicts that fluid rapidly diffuses away from the interface which thus stops

  20. Effect of inclusion complex on nitrous acid reaction with flavonoids

    NASA Astrophysics Data System (ADS)

    Khalafi, Lida; Rafiee, Mohammad; Sedaghat, Sajjad

    2011-10-01

    The kinetic of the nitrous acid reactions with quercetin and catechin has been studied using spectrophotometric method in aqueous solution. The results show that these antioxidants participate in oxidation reactions with nitrous acid which is derived from protonation of nitrite ion in mild acidic conditions. Corresponding o-quinones as relatively stable products were detected by spectrophotometric techniques. pH dependence of the reactions has been examined and the rate constants of reactions were obtained by non-linear fitting of kinetic profiles. The effect of β-cyclodextrin on the oxidation pathway was another object of this study. It is shown that β-cyclodextrin has an inhibitory effect on the oxidation reaction. The rate constants of oxidation reactions for complexed forms and their stability constants were obtained based on changes in the reaction rates as a function of β-cyclodextrin concentration.

  1. Thermochemistry for silicic acid formation reaction: Prediction of new reaction pathway

    NASA Astrophysics Data System (ADS)

    Mondal, Bhaskar; Ghosh, Deepanwita; Das, Abhijit K.

    2009-08-01

    Reaction between SiO 2 and water has been studied extensively using ab initio methods. The mechanism for formation of metasilicic acid SiO(OH) 2 and orthosilicic acid Si(OH) 4 has been explored and a new pathway for formation of Si(OH) 4 is predicted. Heats of reaction ( ΔrH298∘) and heats of formation ( ΔfH298∘) at 298 K for the related reactions and species calculated at two different theoretical levels G3B3 and G3MP2B3 agree well with the literature values. It is found that when SiO 2 reacts simultaneously with two water molecules, the thermodynamic as well as kinetic feasibility of the process is much greater than that when SiO 2 reacts with one molecule of water.

  2. Secondary organic aerosol formation from reaction of tertiary amines with nitrate radical

    NASA Astrophysics Data System (ADS)

    Erupe, M. E.; Price, D. J.; Silva, P. J.; Malloy, Q. G. J.; Qi, L.; Warren, B.; Cocker, D. R., III

    2008-09-01

    Secondary organic aerosol formation from the reaction of tertiary amines with nitrate radical was investigated in an indoor environmental chamber. Particle chemistry was monitored using a high resolution aerosol mass spectrometer while gas-phase species were detected using a proton transfer reaction mass spectrometer. Trimethylamine, triethylamine and tributylamine were studied. Results indicate that tributylamine forms the most aerosol mass followed by trimethylamine and triethylamine respectively. Spectra from the aerosol mass spectrometer indicate the formation of complex non-salt aerosol products. We propose a reaction mechanism that proceeds via abstraction of a proton by nitrate radical followed by RO2 chemistry. Rearrangement of the aminyl alkoxy radical through hydrogen shift leads to the formation of hydroxylated amides, which explain most of the higher mass ions in the mass spectra. These experiments show that oxidation of tertiary amines by nitrate radical may be an important night-time source of secondary organic aerosol.

  3. Complex Chemical Reaction Networks from Heuristics-Aided Quantum Chemistry.

    PubMed

    Rappoport, Dmitrij; Galvin, Cooper J; Zubarev, Dmitry Yu; Aspuru-Guzik, Alán

    2014-03-11

    While structures and reactivities of many small molecules can be computed efficiently and accurately using quantum chemical methods, heuristic approaches remain essential for modeling complex structures and large-scale chemical systems. Here, we present a heuristics-aided quantum chemical methodology applicable to complex chemical reaction networks such as those arising in cell metabolism and prebiotic chemistry. Chemical heuristics offer an expedient way of traversing high-dimensional reactive potential energy surfaces and are combined here with quantum chemical structure optimizations, which yield the structures and energies of the reaction intermediates and products. Application of heuristics-aided quantum chemical methodology to the formose reaction reproduces the experimentally observed reaction products, major reaction pathways, and autocatalytic cycles.

  4. ReactionPredictor: prediction of complex chemical reactions at the mechanistic level using machine learning.

    PubMed

    Kayala, Matthew A; Baldi, Pierre

    2012-10-22

    Proposing reasonable mechanisms and predicting the course of chemical reactions is important to the practice of organic chemistry. Approaches to reaction prediction have historically used obfuscating representations and manually encoded patterns or rules. Here we present ReactionPredictor, a machine learning approach to reaction prediction that models elementary, mechanistic reactions as interactions between approximate molecular orbitals (MOs). A training data set of productive reactions known to occur at reasonable rates and yields and verified by inclusion in the literature or textbooks is derived from an existing rule-based system and expanded upon with manual curation from graduate level textbooks. Using this training data set of complex polar, hypervalent, radical, and pericyclic reactions, a two-stage machine learning prediction framework is trained and validated. In the first stage, filtering models trained at the level of individual MOs are used to reduce the space of possible reactions to consider. In the second stage, ranking models over the filtered space of possible reactions are used to order the reactions such that the productive reactions are the top ranked. The resulting model, ReactionPredictor, perfectly ranks polar reactions 78.1% of the time and recovers all productive reactions 95.7% of the time when allowing for small numbers of errors. Pericyclic and radical reactions are perfectly ranked 85.8% and 77.0% of the time, respectively, rising to >93% recovery for both reaction types with a small number of allowed errors. Decisions about which of the polar, pericyclic, or radical reaction type ranking models to use can be made with >99% accuracy. Finally, for multistep reaction pathways, we implement the first mechanistic pathway predictor using constrained tree-search to discover a set of reasonable mechanistic steps from given reactants to given products. Webserver implementations of both the single step and pathway versions of Reaction

  5. Coupling and Reactions of 5-Hydroxyconiferyl Alcohol in Lignin Formation.

    PubMed

    Elder, Thomas; Berstis, Laura; Beckham, Gregg T; Crowley, Michael F

    2016-06-15

    The catechol alcohols, caffeyl and 5-hydroxyconiferyl alcohol, may be incorporated into lignin either naturally or through genetic manipulation. Due to the presence of o-OH groups, these compounds form benzodioxanes, a departure from the interunit connections found in lignins derived from the cinnamyl alcohols. In nature, lignins composed of caffeyl and 5-hydroxyconiferyl alcohol are linear homopolymers and, as such, may have properties that make them amenable for use in value-added products, such as lignin-based carbon fibers. In the current work, results from density functional theory calculations for the reactions of 5-hydroxyconiferyl alcohol, taking stereochemistry into account, are reported. Dehydrogenation and quinone methide formation are found to be thermodynamically favored for 5-hydroxyconiferyl alcohol, over coniferyl alcohol. The comparative energetics of the rearomatization reactions suggest that the formation of the benzodioxane linkage is under kinetic control. Ring-opening reactions of the benzodioxane groups show that the bond dissociation enthalpy of the α-O cleavage reaction is lower than that of the β-O reaction. The catechol lignins represent a novel form of the polymer that may offer new opportunities for bioproducts and genetic targets.

  6. Coupling and Reactions of 5-Hydroxyconiferyl Alcohol in Lignin Formation

    SciTech Connect

    Elder, Thomas; Berstis, Laura; Beckham, Gregg T.; Crowley, Michael F.

    2016-05-28

    The catechol alcohols, caffeyl and 5-hydroxyconiferyl alcohol, may be incorporated into lignin either naturally or through genetic manipulation. Due to the presence of o-OH groups, these compounds form benzodioxanes, a departure from the interunit connections found in lignins derived from the cinnamyl alcohols. In nature, lignins composed of caffeyl and 5-hydroxyconiferyl alcohol are linear homopolymers and, as such, may have properties that make them amenable for use in value-added products, such as lignin-based carbon fibers. In the current work, results from density functional theory calculations for the reactions of 5-hydroxyconiferyl alcohol, taking stereochemistry into account, are reported. Dehydrogenation and quinone methide formation are found to be thermodynamically favored for 5-hydroxyconiferyl alcohol, over coniferyl alcohol. The comparative energetics of the rearomatization reactions suggest that the formation of the benzodioxane linkage is under kinetic control. Ring-opening reactions of the benzodioxane groups show that the bond dissociation enthalpy of the $\\alpha$-O cleavage reaction is lower than that of the $\\beta$-O reaction. In conclusion, the catechol lignins represent a novel form of the polymer that may offer new opportunities for bioproducts and genetic targets.

  7. Coupling and Reactions of 5-Hydroxyconiferyl Alcohol in Lignin Formation

    DOE PAGES

    Elder, Thomas; Berstis, Laura; Beckham, Gregg T.; ...

    2016-05-28

    The catechol alcohols, caffeyl and 5-hydroxyconiferyl alcohol, may be incorporated into lignin either naturally or through genetic manipulation. Due to the presence of o-OH groups, these compounds form benzodioxanes, a departure from the interunit connections found in lignins derived from the cinnamyl alcohols. In nature, lignins composed of caffeyl and 5-hydroxyconiferyl alcohol are linear homopolymers and, as such, may have properties that make them amenable for use in value-added products, such as lignin-based carbon fibers. In the current work, results from density functional theory calculations for the reactions of 5-hydroxyconiferyl alcohol, taking stereochemistry into account, are reported. Dehydrogenation and quinone methide formation are found to be thermodynamically favored for 5-hydroxyconiferyl alcohol, over coniferyl alcohol. The comparative energetics of the rearomatization reactions suggest that the formation of the benzodioxane linkage is under kinetic control. Ring-opening reactions of the benzodioxane groups show that the bond dissociation enthalpy of themore » $$\\alpha$$-O cleavage reaction is lower than that of the $$\\beta$$-O reaction. In conclusion, the catechol lignins represent a novel form of the polymer that may offer new opportunities for bioproducts and genetic targets.« less

  8. Structure of soybean serine acetyltransferase and formation of the cysteine regulatory complex as a molecular chaperone

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Serine acetyltransferase (SAT) catalyzes the limiting reaction in plant and microbial biosynthesis of cysteine. In addition to its enzymatic function, SAT forms a macromolecular complex with O-acetylserine sulfhydrylase (OASS). Formation of the cysteine regulatory complex (CRC) is a critical biochem...

  9. EXFOR systems manual: Nuclear reaction data exchange format

    SciTech Connect

    McLane, V.

    1996-07-01

    This document describes EXFOR, the exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Centers Network. In addition to storing the data and its bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. The exchange format, as outlined, is designed to allow a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine).

  10. A new metalation complex for organic synthesis and polymerization reactions

    NASA Technical Reports Server (NTRS)

    Hirshfield, S. M.

    1971-01-01

    Organometallic complex of N,N,N',N' tetramethyl ethylene diamine /TMEDA/ and lithium acts as metalation intermediate for controlled systhesis of aromatic organic compounds and polymer formation. Complex of TMEDA and lithium aids in preparation of various organic lithium compounds.

  11. Formation of Gold(III) Alkyls from Gold Alkoxide Complexes

    PubMed Central

    2017-01-01

    The gold(III) methoxide complex (C∧N∧C)AuOMe (1) reacts with tris(p-tolyl)phosphine in benzene at room temperature under O abstraction to give the methylgold product (C∧N∧C)AuMe (2) together with O=P(p-tol)3 ((C∧N∧C) = [2,6-(C6H3tBu-4)2pyridine]2–). Calculations show that this reaction is energetically favorable (ΔG = −32.3 kcal mol–1). The side products in this reaction, the Au(II) complex [Au(C∧N∧C)]2 (3) and the phosphorane (p-tol)3P(OMe)2, suggest that at least two reaction pathways may operate, including one involving (C∧N∧C)Au• radicals. Attempts to model the reaction by DFT methods showed that PPh3 can approach 1 to give a near-linear Au–O–P arrangement, without phosphine coordination to gold. The analogous reaction of (C∧N∧C)AuOEt, on the other hand, gives exclusively a mixture of 3 and (p-tol)3P(OEt)2. Whereas the reaction of (C∧N∧C)AuOR (R = But, p-C6H4F) with P(p-tol)3 proceeds over a period of hours, compounds with R = CH2CF3, CH(CF3)2 react almost instantaneously, to give 3 and O=P(p-tol)3. In chlorinated solvents, treatment of the alkoxides (C∧N∧C)AuOR with phosphines generates [(C∧N∧C)Au(PR3)]Cl, via Cl abstraction from the solvent. Attempts to extend the synthesis of gold(III) alkoxides to allyl alcohols were unsuccessful; the reaction of (C∧N∧C)AuOH with an excess of CH2=CHCH2OH in toluene led instead to allyl alcohol isomerization to give a mixture of gold alkyls, (C∧N∧C)AuR′ (R′ = −CH2CH2CHO (10), −CH2CH(CH2OH)OCH2CH=CH2 (11)), while 2-methallyl alcohol affords R′ = CH2CH(Me)CHO (12). The crystal structure of 11 was determined. The formation of Au–C instead of the expected Au–O products is in line with the trend in metal–ligand bond dissociation energies for Au(III): M–H > M–C > M–O.

  12. Controlling the assembly of nanoparticle mixtures with two orthogonal polymer complexation reactions.

    PubMed

    Zhang, Dan; Pelton, Robert

    2012-02-14

    Self-assembly from mixed dispersions of three sizes of monodisperse polystyrene nanoparticles, large (L), medium (M), and small (S), was controlled by coating each particle type with either a monofunctional or bifunctional polymer capable of participating in specific complexation reactions. The complexation reactions were (1) complexation between phenolic polymers and polyethylene glycol (PEG) containing polymers and (2) condensation of phenylboronic acid containing polymers with polyols. These complexation reactions function independently and can be "turned off" independently; phenylboronic acid complexation was reversed by lowering the pH, whereas the interactions of phenolic copolymers with PEG copolymers could be reversed by adding excess PEG homopolymer. The specificity and reversibility of the interactions was demonstrated by the formation of simple binary aggregates from mixtures. The bifunctional copolymers were poly(vinyl phenol-co-diallyldimethyl ammonium chloride), Ph-DADMAC, and poly(3-acrylamide phenylboronic acid-co-PEG methacrylate), PBA-PEG. The monofunctional polymer was polyvinylalcohol, PVA. Ph-DADMAC forms complexes with PBA-PEG (H-bonding) and with anionic surfaces or polymers (electrostatic/polyelectrolyte complexation). PBA-PEG complexes with Ph-DADMAC (H-bonding) and with PVA (boronate ester formation). PVA does not interact with Ph-DADMAC; therefore, PVA coated particles do not deposit onto Ph-DADMAC coated particles.

  13. Forward design of a complex enzyme cascade reaction

    PubMed Central

    Hold, Christoph; Billerbeck, Sonja; Panke, Sven

    2016-01-01

    Enzymatic reaction networks are unique in that one can operate a large number of reactions under the same set of conditions concomitantly in one pot, but the nonlinear kinetics of the enzymes and the resulting system complexity have so far defeated rational design processes for the construction of such complex cascade reactions. Here we demonstrate the forward design of an in vitro 10-membered system using enzymes from highly regulated biological processes such as glycolysis. For this, we adapt the characterization of the biochemical system to the needs of classical engineering systems theory: we combine online mass spectrometry and continuous system operation to apply standard system theory input functions and to use the detailed dynamic system responses to parameterize a model of sufficient quality for forward design. This allows the facile optimization of a 10-enzyme cascade reaction for fine chemical production purposes. PMID:27677244

  14. Forward design of a complex enzyme cascade reaction.

    PubMed

    Hold, Christoph; Billerbeck, Sonja; Panke, Sven

    2016-09-28

    Enzymatic reaction networks are unique in that one can operate a large number of reactions under the same set of conditions concomitantly in one pot, but the nonlinear kinetics of the enzymes and the resulting system complexity have so far defeated rational design processes for the construction of such complex cascade reactions. Here we demonstrate the forward design of an in vitro 10-membered system using enzymes from highly regulated biological processes such as glycolysis. For this, we adapt the characterization of the biochemical system to the needs of classical engineering systems theory: we combine online mass spectrometry and continuous system operation to apply standard system theory input functions and to use the detailed dynamic system responses to parameterize a model of sufficient quality for forward design. This allows the facile optimization of a 10-enzyme cascade reaction for fine chemical production purposes.

  15. Forward design of a complex enzyme cascade reaction

    NASA Astrophysics Data System (ADS)

    Hold, Christoph; Billerbeck, Sonja; Panke, Sven

    2016-09-01

    Enzymatic reaction networks are unique in that one can operate a large number of reactions under the same set of conditions concomitantly in one pot, but the nonlinear kinetics of the enzymes and the resulting system complexity have so far defeated rational design processes for the construction of such complex cascade reactions. Here we demonstrate the forward design of an in vitro 10-membered system using enzymes from highly regulated biological processes such as glycolysis. For this, we adapt the characterization of the biochemical system to the needs of classical engineering systems theory: we combine online mass spectrometry and continuous system operation to apply standard system theory input functions and to use the detailed dynamic system responses to parameterize a model of sufficient quality for forward design. This allows the facile optimization of a 10-enzyme cascade reaction for fine chemical production purposes.

  16. Catalysis of Dialanine Formation by Glycine in the Salt-Induced Peptide Formation Reaction.

    NASA Astrophysics Data System (ADS)

    Suwannachot, Yuttana; Rode, Bernd M.

    1998-02-01

    Mutual catalysis of amino acids in the salt-induced peptide formation (SIPF) reaction is demonstrated for the case of glycine/alanine. The presence of glycine enhances dialanine formation by a factor up to 50 and enables dialanine formation at much lower alanine concentrations. The actual amounts of glycine play an important role for this catalytic effect, the optimal glycine concentration is 1/8 of the alanine concentration. The mechanism appears to be based on the formation of the intermediate Gly-Ala-Ala tripeptide, connected to one coordination site of copper(II) ion, and subsequent hydrolysis to dialanine and glycine.

  17. A DFT/B3LYP study of the mechanisms of the O2 formation reaction catalyzed by the [(terpy)(H2O)Mn(III)(O)2Mn(IV)(OH2)(terpy)](NO3)3 complex: A paradigm for photosystem II.

    PubMed

    Sproviero, Eduardo M

    2017-02-20

    We present a theoretical study of the reaction pathway for dioxygen molecular formation catalyzed by the [(terpy)(H2O)Mn(III)(O)2Mn(IV)(OH2) (terpy)](NO3)3 (terpy=2,2':6',2″-terpyridine) complex based on DFT-B3LYP calculations. In the initial state of the reaction, a partial oxido radical (0.44 spins) is formed ligated to Mn. This radical is involved in a nucleophylic attack by bulk water in the OO bond reaction formation step, in which the oxido fractional unpaired electron is delocalized toward the outermost Mn of the μ-oxo bridge, instead of the ligated Mn center. The reaction then follows with a series of proton-coupled electron transfer steps, in which the oxidation state, as well as the bond strength of the OO moiety increase, while the OOMn(1) bond gets weaker until O2 is released. In this model, basic acetate ions from the buffer solution capture protons in the proton-transfer steps. In each step there is reduction of the OOMn(1) binding strength, with concomitant increase of the OO bond strength, which culminates with the release of O2 in the last step. This last step is entropy driven, while formation of hydroperoxide and superoxide moieties is enthalpy driven. According with experiments, the rate-limiting step is the double oxidation of Mn(IV,III) or peroxymonosulfate binding, which occur prior to the OO bond formation step. This supports our findings that the barriers of all intermediate steps are below the experimental barrier of 19-21kcal/mol. The implications of these findings for understanding photosynthetic water-splitting catalysis are also discussed.

  18. Reaction of an Iron(IV) Nitrido Complex with Cyclohexadienes: Cycloaddition and Hydrogen-Atom Abstraction

    PubMed Central

    2015-01-01

    The iron(IV) nitrido complex PhB(MesIm)3Fe≡N reacts with 1,3-cyclohexadiene to yield the iron(II) pyrrolide complex PhB(MesIm)3Fe(η5-C4H4N) in high yield. The mechanism of product formation is proposed to involve sequential [4 + 1] cycloaddition and retro Diels–Alder reactions. Surprisingly, reaction with 1,4-cyclohexadiene yields the same iron-containing product, albeit in substantially lower yield. The proposed reaction mechanism, supported by electronic structure calculations, involves hydrogen-atom abstraction from 1,4-cyclohexadiene to provide the cyclohexadienyl radical. This radical is an intermediate in substrate isomerization to 1,3-cyclohexadiene, leading to formation of the pyrrolide product. PMID:25068927

  19. Complex reaction noise in a molecular quasispecies model

    NASA Astrophysics Data System (ADS)

    Hochberg, David; Zorzano, María-Paz; Morán, Federico

    2006-05-01

    We have derived exact Langevin equations for a model of quasispecies dynamics. The inherent multiplicative reaction noise is complex and its statistical properties are specified completely. The numerical simulation of the complex Langevin equations is carried out using the Cholesky decomposition for the noise covariance matrix. This internal noise, which is due to diffusion-limited reactions, produces unavoidable spatio-temporal density fluctuations about the mean field value. In two dimensions, this noise strictly vanishes only in the perfectly mixed limit, a situation difficult to attain in practice.

  20. Uncertainty quantification for quantum chemical models of complex reaction networks.

    PubMed

    Proppe, Jonny; Husch, Tamara; Simm, Gregor N; Reiher, Markus

    2016-12-22

    For the quantitative understanding of complex chemical reaction mechanisms, it is, in general, necessary to accurately determine the corresponding free energy surface and to solve the resulting continuous-time reaction rate equations for a continuous state space. For a general (complex) reaction network, it is computationally hard to fulfill these two requirements. However, it is possible to approximately address these challenges in a physically consistent way. On the one hand, it may be sufficient to consider approximate free energies if a reliable uncertainty measure can be provided. On the other hand, a highly resolved time evolution may not be necessary to still determine quantitative fluxes in a reaction network if one is interested in specific time scales. In this paper, we present discrete-time kinetic simulations in discrete state space taking free energy uncertainties into account. The method builds upon thermo-chemical data obtained from electronic structure calculations in a condensed-phase model. Our kinetic approach supports the analysis of general reaction networks spanning multiple time scales, which is here demonstrated for the example of the formose reaction. An important application of our approach is the detection of regions in a reaction network which require further investigation, given the uncertainties introduced by both approximate electronic structure methods and kinetic models. Such cases can then be studied in greater detail with more sophisticated first-principles calculations and kinetic simulations.

  1. A quantitative approach to understanding amphibole reaction rims: Texture, mineralogy, and processes of formation

    NASA Astrophysics Data System (ADS)

    De Angelis, S. H.; Larsen, J. F.; Coombs, M. L.; Dunn, A.

    2012-12-01

    Amphibole is an important mineral present in many calc-alkaline volcanic deposits. A hydrous phase, volcanic amphibole is only stable at pressures greater than 100 MPa (approx. 4 km) and in melts containing at least 4 wt % H2O. When removed from their thermal and barometric stability field, amphiboles decompose to form aggregate rims of anhydrous minerals. Reaction rim thicknesses have been used to estimate timescales and rates of magma ascent, important parameters in determining eruptive style. However, the textures and mineralogy of reaction rims are complex; multiple forcing factors, such as heating and decompression, are responsible for their formation. Few studies have performed in-depth, systematic, and quantitative investigations of reaction rim textures and mineralogy: as a result, amphibole reaction rims are poorly understood. Based on natural reaction rims from Augustine Volcano Alaska, we have developed a new crystallization kinetics model for reaction rim formation in which the differences in reaction rim textures represent different degrees of forcing away from equilibrium. We present the results of an experimental study used to test this model. We performed experiments using a sintered high-silica andesite glass from the 2006 eruption of Augustine volcano. The starting powder was seeded with unrimmed amphibole phenocrysts. After at least 24 hours of equilibration at Augustine storage conditions (140 MPa/ 860oC), experiments were heated or decompressed. The experimental series experiments took samples to differing degrees of thermal of barometric instability, over different time scales, ranging from 3 hours to several days. The resulting reaction rims were analyzed using a variety of analytical imaging and X-ray mapping techniques. Reaction rims thickened and became more texturally and mineralogically complex as a result of 1) greater time spent outside of stability and; 2) the magnitude of instability experienced.

  2. Complex Equilibria Changing in Photochemical Reaction: Computerized Evaluation and Simulation.

    ERIC Educational Resources Information Center

    Horvath, Otto; Papp, Sandor

    1988-01-01

    States that if photochemical reactions can be followed spectrophotometrically, reactivities can be estimated by evaluating data from only one curve. Studies such a system using computerized evaluation and simulation. Uses chlorocuprate(II) complexes in acetonitrile solutions for the model systems. (MVL)

  3. Identification of simple reaction coordinates from complex dynamics

    NASA Astrophysics Data System (ADS)

    McGibbon, Robert T.; Husic, Brooke E.; Pande, Vijay S.

    2017-01-01

    Reaction coordinates are widely used throughout chemical physics to model and understand complex chemical transformations. We introduce a definition of the natural reaction coordinate, suitable for condensed phase and biomolecular systems, as a maximally predictive one-dimensional projection. We then show that this criterion is uniquely satisfied by a dominant eigenfunction of an integral operator associated with the ensemble dynamics. We present a new sparse estimator for these eigenfunctions which can search through a large candidate pool of structural order parameters and build simple, interpretable approximations that employ only a small number of these order parameters. Example applications with a small molecule's rotational dynamics and simulations of protein conformational change and folding show that this approach can filter through statistical noise to identify simple reaction coordinates from complex dynamics.

  4. On the Formation of "Hypercoordinated" Uranyl Complexes

    SciTech Connect

    Schoendorff, George E.; De Jong, Wibe A.; van Stipdonk, Michael J.; Gibson, John K.; Rios, Daniel; Gordon, Mark S.; Windus, Theresa L.

    2011-09-05

    Recent gas phase experimental studies suggest the presence of hypercoordinated uranyl complexes. Coordination of acetone (Ace) to uranyl to form hypercoordinated species is examined using density functional theory (DFT) with a range of functionals and second order perturbation theory (MP2). Complexes with up to eight acetones were studied. It is shown that no more than six acetones can bind directly to uranium and that the observed uranyl complexes are not hypercoordinated.

  5. Oxygen evolving reactions catalysed by manganese-oxo-complexes adsorbed on clays.

    PubMed

    Kurz, Philipp

    2009-08-21

    A series of dinuclear manganese-oxo-complexes was prepared and adsorbed on kaolinite and montmorillonite clays. As indicated by UV-Vis spectroscopy, immobilization of the manganese compounds greatly altered the electronic properties due to strong interactions with the clay surfaces. When studied for their ability to catalyze oxygen formation upon reactions with the strong oxygen-transferring oxidants H(2)O(2) and oxone, it was found that surface adsorption yielded catalysts of improved performance for oxygen formation in aqueous media. Both the rates of oxygen evolution and catalyst stabilities were significantly increased for the clay hybrids of most complexes in comparison to homogeneous solutions of the compounds. Additionally, four heterogeneous systems were also found to catalyze the evolution of O(2) in reactions with the non-oxygen transferring, single- electron oxidation agent Ce(IV)--a reaction not observed for any dinuclear manganese complex in homogeneous reaction. Implications of these observations concerning the mechanism of oxygen formation and the development of manganese-based water oxidation catalysts are discussed.

  6. Ionization reactions of ion complexes in mesoscopic water clusters

    NASA Astrophysics Data System (ADS)

    Consta, Styliani; Kapral, Raymond

    1999-12-01

    The free energy and dynamics of the dissociation reactions of the [Na+(Cl-)2] ion complex in mesoscopic water clusters are examined. The free energy surface shows the existence of stable single and double solvent-separated complex species formed from ionization of the stable double-contact ion complex. The reaction occurs on the cluster surface for mesoscale clusters composed of tens of water molecules. Passage between stable species is an activated process but barrier crossing has a large diffusive component so that dynamical corrections to transition state theory are large. The structure of the decay of the time-dependent rate constant reflects the diffusive character of the recrossing dynamics so that a plateau is not established on a 10 ps time scale in contrast to ionization dynamics in bulk fluids.

  7. Formation of superheavy elements in cold fusion reactions

    NASA Astrophysics Data System (ADS)

    Smolańczuk, Robert

    2001-04-01

    We calculate the formation cross sections of transactinides (superheavy elements), as well as heavy actinides (No and Lr), which have been or might be obtained in fusion reactions with the evaporation of only one neutron. We use both more realistic fusion barrier and survival probability of the compound nucleus in comparison with the original phenomenological model [Phys. Rev. C 59, 2634 (1999)] that prompted the Berkeley experiment on the synthesis of a new superheavy element 118 [Phys. Rev. Lett. 83, 1104 (1999)]. Calculations are performed for asymmetric and symmetric target-projectile combinations and for reactions with stable and radioactive-ion beams. The formation cross sections measured at GSI-Darmstadt for transactinides and heavy actinides, as well as that for superheavy element 118 reported by the LBNL-Berkeley group, are reproduced within a factor of 2.4, on average. Based on the obtained relatively large cross sections, we predict that optimal reactions with stable beams for the synthesis of so far unobserved superheavy elements 119, 120, and 121 are 209Bi(86Kr, 1n)294119, 208Pb(88Sr, 1n)295120, and 209Bi(88Sr, 1n)296121, respectively. This is because of the magic of both the target and the projectile that leads to larger Q value and, consequently, lower effective fusion barrier with larger transmission probability. The same effect is responsible for relatively large cross sections predicted for the symmetric reactions 136Xe(124Sn, 1n)259Rf, 136Xe(136Xe, 1n)271Hs,138Ba(136Xe, 1n)273110, and 140Ce(136Xe, 1n)275112. Although shell effects in the magic nuclei 124Sn, 136Xe, 138Ba, and 140Ce are not as strong as in 208Pb and 209Bi, they act on both the target and the projectile and lead to the prediction of measurable cross sections.

  8. Thermodynamics for complex formation between palladium(ii) and oxalate.

    PubMed

    Pilný, Radomír; Lubal, Přemysl; Elding, Lars I

    2014-08-28

    Complex formation between [Pd(H2O)4](2+) and oxalate (ox = C2O4(2-)) has been studied spectrophoto-metrically in aqueous solution at variable temperature, ionic strength and pH. Thermodynamic parameters at 298.2 K and 1.00 mol dm(-3) HClO4 ionic medium for the complex formation [Pd(H2O)4](2+) + H2ox ⇄ [Pd(H2O)2(ox)] + 2H3O(+) with equilibrium constant K1,H (in mol dm(-3)) are log10K1,H = 3.38 ± 0.08, ΔH = -33 ± 3 kJ mol(-1), and ΔS = -48 ± 11 J K(-1) mol(-1), as determined from spectrophotometric equilibrium titrations at 15.0, 20.0, 25.0 and 31.0 °C. Thermodynamic overall stability constants β (in (mol dm(-3))(-n), n = 1,2) for [Pd(H2O)2(ox)] and [Pd(ox)2](2-) at zero ionic strength and 298.2 K, defined as the equilibrium constants for the reaction Pd(2+) + nox(2-) ⇄ [Pd(ox)n](2-2n) (water molecules omitted) are log10β = 9.04 ± 0.06 and log10β = 13.1 ± 0.3, respectively, calculated by use of Specific Ion Interaction Theory from spectrophotometric titrations with initial hydrogen ion concentrations of 1.00, 0.100 and 0.0100 mol dm(-3) and ionic strengths of 1.00, 2.00 or 3.00 mol dm(-3). The values derived together with literature data give estimated overall stability constants for Pd(ii) compounds such as [Pd(en)(ox)] and cis-[Pd(NH3)2Cl2], some of them analogs to Pt(ii) complexes used in cancer treatment. The palladium oxalato complexes are significantly more stable than palladium(ii) complexes with monodentate O-bonding ligands. A comparison between several different palladium complexes shows that different parameters contribute to the stability variations observed. These are discussed together with the so-called chelate effect.

  9. First stage of CoSi{sub 2} formation during a solid-state reaction

    SciTech Connect

    Delattre, R.; Thomas, O.; Perrin-Pellegrino, C.; Rivero, C.; Simola, R.

    2014-12-28

    The kinetics of CoSi{sub 2} formation via a solid-state reaction between CoSi and single crystal Si has been the object of many studies in the past. Because of the importance of nucleation, complex kinetics has been reported. In this work, we investigate CoSi{sub 2} formation kinetics with in-situ diffraction during isothermal annealing of CoSi films on Si (100). In-situ measurements allow capturing the initial stage of CoSi{sub 2} formation. An initial t{sup 3/2} time-dependent evolution is observed and attributed to 3D growth of individual nuclei. This first regime is followed after the coalescence of the nuclei by a classical parabolic t{sup 1/2} one-dimensional film growth. We evidence a marked influence of the initial Co thickness (50 nm vs 10 nm) on the growth kinetics. A significant slowdown of the CoSi{sub 2} formation kinetics is observed for the thinnest film, whereas the activation energy remains the same. These results shine a new light on the complex formation kinetics of CoSi{sub 2} during solid-state reaction between CoSi and single crystal silicon and bring new knowledge about what occurs in the ultra-thin film regime, which is important for nanotechnologies.

  10. Information-Theoretical Complexity Analysis of Selected Elementary Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Molina-Espíritu, M.; Esquivel, R. O.; Dehesa, J. S.

    We investigate the complexity of selected elementary chemical reactions (namely, the hydrogenic-abstraction reaction and the identity SN2 exchange reaction) by means of the following single and composite information-theoretic measures: disequilibrium (D), exponential entropy(L), Fisher information (I), power entropy (J), I-D, D-L and I-J planes and Fisher-Shannon (FS) and Lopez-Mancini-Calbet (LMC) shape complexities. These quantities, which are functionals of the one-particle density, are computed in both position (r) and momentum (p) spaces. The analysis revealed that the chemically significant regions of these reactions can be identified through most of the single information-theoretic measures and the two-component planes, not only the ones which are commonly revealed by the energy, such as the reactant/product (R/P) and the transition state (TS), but also those that are not present in the energy profile such as the bond cleavage energy region (BCER), the bond breaking/forming regions (B-B/F) and the charge transfer process (CT). The analysis of the complexities shows that the energy profile of the abstraction reaction bears the same information-theoretical features of the LMC and FS measures, however for the identity SN2 exchange reaction does not hold a simple behavior with respect to the LMC and FS measures. Most of the chemical features of interest (BCER, B-B/F and CT) are only revealed when particular information-theoretic aspects of localizability (L or J), uniformity (D) and disorder (I) are considered.

  11. Theoretical aspects of product formation from the NCO + NO reaction

    SciTech Connect

    Lin, M.C.; He, Y. ); Melius, C.F. )

    1993-09-09

    The reaction of NCO with NO, an important elementary process involved in the reduction of NO[sub x] by HNCO, has been studied theoretically using the BAC-MP4 technique in conjunction with RRKM calculations. The computed molecular structures and thermochemical data for various intermediates and transition states suggest that the reaction takes place primarily via the singlet, ground electronic state OCNNO molecule according to the following mechanism; (step a) NCO + NO [leftrightarrow] [sup 1]OCNNO [yields] N[sub 2]O + CO; (step b) NCO + NO [leftrightarrow] [sup 1]OCNNO [yields] c-OCNNO[minus] N[sub 2] + CO[sub 2]. The formation of N[sub 2]O + CO occurs by the fragmentation of the singlet OCNNO intermediate step (a), whereas the production of N[sub 2] + CO[sub 2] by cyclization-fragmentation occurs via step b. The tight transition states leading to the formation of these products, coupled with the loose entrance channel, give rise to the experimentally observed strong negative temperature dependence which can be quantitatively accounted for by the results of RRKM calculations based on the BAC-MP4 data. The experimentally measured product branching ratio for channels a and b could be accounted for theoretically by lowering the calculated energy barrier for step a by 3.6 kcal/mol, corresponding to about 15% of the barrier height. 22 refs., 3 figs., 5 tabs.

  12. Formation of molecular oxygen in ultracold O + OH reaction

    SciTech Connect

    Kendrick, Brian Kent; Quemener, Goulven; Balakrishman, Naduvalath

    2008-01-01

    We discuss the formation of molecular oxygen in ultracold collisions between hydroxyl radicals and atomic oxygen. A time-independent quantum formalism based on hyperspherical coordinates is employed for the calculations. Elastic, inelastic and reactive cross sections as well as the vibrational and rotational populations of the product O{sub 2} molecules are reported. A J-shifting approximation is used to compute the rate coefficients. At temperatures T = 10--100 mK for which the OH molecules have been cooled and trapped experimentally, the elastic and reactive rate coefficients are of comparable magnitude, while at colder temperatures, T < 1 mK, the formation of molecular oxygen becomes the dominant pathway. The validity of a classical capture model to describe cold collisions of OH and O is also discussed. While very good agreement is found between classical and quantum results at T = 0.3 K, at higher temperatures, the quantum calculations predict a higher rate coefficient than the classical model, in agreement with experimental data for the O + OH reaction. The zero-temperature limiting value of the rate coefficient is predicted to be about 6 x 10{sup -12} cm{sup 3} s{sup 01}, a value comparable to that of barrierless alkali metal atom-dimer systems and about a factor of five larger than that of the tunneling dominated F + H{sub 2} reaction.

  13. N-Heterocyclic Carbene Complexes in Oxidation Reactions

    NASA Astrophysics Data System (ADS)

    Jurčík, Václav; Cazin, Catherine S. J.

    This chapter describes applications of N-heterocyclic carbenes (NHCs) in oxidation chemistry. The strong σ-donation capabilities of the NHCs allow an efficient stabilisation of metal centres in high oxidation states, while high metal-NHC bond dissociation energies suppress their oxidative decomposition. These properties make NHCs ideal ligands for oxidation processes. The first part of this chapter is dedicated to the reactivity of NHC-metal complexes towards molecular oxygen whilst the second half highlights all oxidation reactions catalysed by such complexes. These include oxidation of alcohols and olefins, oxidative cyclisations, hydrations of alkynes and nitriles, oxidative cleavage of alkenes and the oxidation of methane.

  14. Reactions of OH and Cl with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate

    NASA Astrophysics Data System (ADS)

    Zhang, Y. J.; Liang, P.; Jiang, Z. H.; Cazaunau, M.; Daële, V.; Mu, Y. J.; Mellouki, A.

    2014-05-01

    The rate coefficients for the reactions of OH with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate have been determined using both absolute and relative methods. The relative rate method has been also used to measure the room temperature rate coefficient for the reaction of Cl with the same esters. In addition, a series of runs conducted on the OH-initiated oxidation of isopropyl formate, isobutyl formate and n-propyl isobutyrate showed the formation of acetone from the three reactions. The formation of propanal was also observed for n-propyl isobutyrate.

  15. Guest exchange in an encapsulation complex: A supramolecular substitution reaction

    PubMed Central

    Santamaría, Javier; Martín, Tomás; Hilmersson, Göran; Craig, Stephen L.; Rebek, Julius

    1999-01-01

    Encapsulation complexes are reversibly formed assemblies in which small molecule guests are completely surrounded by large molecule hosts. The assemblies are held together by weak intermolecular forces and are dynamic: they form and dissipate on time scales ranging from milliseconds to days—long enough for many interactions, even reactions, to take place within them. Little information is available on the exchange process, how guests get in and out of these complexes. Here we report that these events can be slow enough for conventional kinetic studies, and reactive intermediates can be detected. Guest exchange has much in common with familiar chemical substitution reactions, but differs in some respects: no covalent bonds are made or broken, the substrate is an assembly rather than a single molecule, and at least four molecules are involved in multiple rate-determining steps. PMID:10411877

  16. Isolable zirconium hydride species in the reaction of amido complexes with amine-boranes.

    PubMed

    Greño, Maider; Mena, Miguel; Pérez-Redondo, Adrián; Yélamos, Carlos

    2017-03-22

    Mono-, di- and trinuclear zirconium hydride species have been isolated in the treatment of amido complexes [Zr(η(5)-C5Me5)(NMe2)nCl3-n] (n = 3, 1) with amine-borane adducts NHR2BH3 (R2 = Me2, HtBu). The reactions involve the formation of amidoborane ligands with ZrH-B interactions which readily undergo β-hydride elimination to give hydride functions.

  17. Aerosol formation yields from the reaction of catechol with ozone

    NASA Astrophysics Data System (ADS)

    Coeur-Tourneur, Cécile; Tomas, Alexandre; Guilloteau, Angélique; Henry, Françoise; Ledoux, Frédéric; Visez, Nicolas; Riffault, Véronique; Wenger, John C.; Bedjanian, Yuri

    The formation of secondary organic aerosol from the gas-phase reaction of catechol (1,2-dihydroxybenzene) with ozone has been studied in two smog chambers. Aerosol production was monitored using a scanning mobility particle sizer and loss of the precursor was determined by gas chromatography and infrared spectroscopy, whilst ozone concentrations were measured using a UV photometric analyzer. The overall organic aerosol yield ( Y) was determined as the ratio of the suspended aerosol mass corrected for wall losses ( Mo) to the total reacted catechol concentrations, assuming a particle density of 1.4 g cm -3. Analysis of the data clearly shows that Y is a strong function of Mo and that secondary organic aerosol formation can be expressed by a one-product gas-particle partitioning absorption model. The aerosol formation is affected by the initial catechol concentration, which leads to aerosol yields ranging from 17% to 86%. The results of this work are compared to similar studies reported in the literature.

  18. Spatial Heterogeneity and Imperfect Mixing in Chemical Reactions: Visualization of Density-Driven Pattern Formation

    DOE PAGES

    Sobel, Sabrina G.; Hastings, Harold M.; Testa, Matthew

    2009-01-01

    Imore » mperfect mixing is a concern in industrial processes, everyday processes (mixing paint, bread machines), and in understanding salt water-fresh water mixing in ecosystems. The effects of imperfect mixing become evident in the unstirred ferroin-catalyzed Belousov-Zhabotinsky reaction, the prototype for chemical pattern formation. Over time, waves of oxidation (high ferriin concentration, blue) propagate into a background of low ferriin concentration (red); their structure reflects in part the history of mixing in the reaction vessel. However, it may be difficult to separate mixing effects from reaction effects. We describe a simpler model system for visualizing density-driven pattern formation in an essentially unmixed chemical system: the reaction of pale yellow Fe 3 + with colorless SCN − to form the blood-red Fe ( SCN ) 2 + complex ion in aqueous solution. Careful addition of one drop of Fe ( NO 3 ) 3 to KSCN yields striped patterns after several minutes. The patterns appear reminiscent of Rayleigh-Taylor instabilities and convection rolls, arguing that pattern formation is caused by density-driven mixing.« less

  19. Evolution of heliobacteria: implications for photosynthetic reaction center complexes

    NASA Technical Reports Server (NTRS)

    Vermaas, W. F.; Blankenship, R. E. (Principal Investigator)

    1994-01-01

    The evolutionary position of the heliobacteria, a group of green photosynthetic bacteria with a photosynthetic apparatus functionally resembling Photosystem I of plants and cyanobacteria, has been investigated with respect to the evolutionary relationship to Gram-positive bacteria and cyanobacteria. On the basis of 16S rRNA sequence analysis, the heliobacteria appear to be most closely related to Gram-positive bacteria, but also an evolutionary link to cyanobacteria is evident. Interestingly, a 46-residue domain including the putative sixth membrane-spanning region of the heliobacterial reaction center protein show rather strong similarity (33% identity and 72% similarity) to a region including the sixth membrane-spanning region of the CP47 protein, a chlorophyll-binding core antenna polypeptide of Photosystem II. The N-terminal half of the heliobacterial reaction center polypeptide shows a moderate sequence similarity (22% identity over 232 residues) with the CP47 protein, which is significantly more than the similarity with the Photosystem I core polypeptides in this region. An evolutionary model for photosynthetic reaction center complexes is discussed, in which an ancestral homodimeric reaction center protein (possibly resembling the heliobacterial reaction center protein) with 11 membrane-spanning regions per polypeptide has diverged to give rise to the core of Photosystem I, Photosystem II, and of the photosynthetic apparatus in green, purple, and heliobacteria.

  20. Time scales for molecule formation by ion-molecule reactions

    NASA Technical Reports Server (NTRS)

    Langer, W. D.; Glassgold, A. E.

    1976-01-01

    Analytical solutions are obtained for nonlinear differential equations governing the time-dependence of molecular abundances in interstellar clouds. Three gas-phase reaction schemes are considered separately for the regions where each dominates. The particular case of CO, and closely related members of the Oh and CH families of molecules, is studied for given values of temperature, density, and the radiation field. Nonlinear effects and couplings with particular ions are found to be important. The time scales for CO formation range from 100,000 to a few million years, depending on the chemistry and regime. The time required for essentially complete conversion of C(+) to CO in the region where the H3(+) chemistry dominates is several million years. Because this time is longer than or comparable to dynamical time scales for dense interstellar clouds, steady-state abundances may not be observed in such clouds.

  1. Reaction of beta-diketiminate copper(II) complexes and Na2S2.

    PubMed

    Inosako, Masayuki; Kunishita, Atsushi; Shimokawa, Chizu; Teraoka, Junji; Kubo, Minoru; Ogura, Takashi; Sugimoto, Hideki; Itoh, Shinobu

    2008-11-28

    Reaction of beta-diketiminate copper(II) complexes and Na2S2 resulted in formation of (mu-eta2:eta2-disulfido)dicopper(II) complexes (adduct formation) or beta-diketiminate copper(I) complexes (reduction of copper(II)) depending on the substituents of the supporting ligands. In the case of sterically less demanding ligands, adduct formation occurred to provide the (mu-eta2:eta2-disulfido)dicopper(II) complexes, whereas reduction of copper(II) took place to give the corresponding copper(I) complexes with sterically more demanding beta-diketiminate ligands. Spectroscopic examinations of the reactions at low temperature using UV-vis and ESR as well as kinetic analysis have suggested that a 1 : 1 adduct LCuII-S-SNa with an end-on binding mode is initially formed as a common intermediate, from which different reaction pathways exist depending on the steric environment of the metal-coordination sphere provided by the ligands. Thus, with the sterically less demanding ligands, rearrangement of the disulfide adduct from end-on to side-on followed by self-dimerisation occurs to give the (mu-eta2:eta2-disulfido)dicopper(II) complexes, whereas such an intramolecular rearrangement of the disulfide co-ligand does not take place with the sterically more demanding ligands. In this case, homolytic cleavage of the CuII-S bond occurs to give the reduced copper(I) product. The steric effects of the supporting ligands have been discussed on the basis of detailed analysis of the crystal structures of the copper(II) starting materials.

  2. From simple to complex reactions: Nuclear collisions near the Coulomb barrier

    SciTech Connect

    Rehm, K.E.

    1992-12-01

    Collisions between two heavy nuclei produce a diverse spectrum of reaction modes which is much wider than that observed in light ion studies. For the latter case, two processes are observed: direct reactions and compound nucleus formation. Heavy ion reaction studies on the other hand have identified additional processes such as deep-inelastic scattering, incomplete fusion and quasi-fission reactions. While the boundaries between the various processes are usually not well defined, it is generally accepted that with increasing overlap of the two nuclei the interaction evolves from distant collisions where only elastic scattering and Coulomb excitation processes occur, through grazing-type collisions associated with quasi-elastic reactions to deep-inelastic and fusion-fission processes requiring a substantial nuclear overlap. Varying the bombarding energy is a convenient way to change the overlap of the two nuclei. Measurements of excitation functions can thus probe the onset and the interplay of the various reaction modes. Experiments at bombarding energies in the vicinity of the Coulomb barrier are particularly suited for comparisons with theoretical predictions since the small number of degrees of freedom involved in the interaction greatly simplifies the calculations. In the first part of this contribution a short overview is given on the status of heavy ion reaction studies at energies in the vicinity of the Coulomb barrier. In the second part two experiments, one involving simple and the other studying complex reactions, are discussed in more detail.

  3. From simple to complex reactions: Nuclear collisions near the Coulomb barrier

    SciTech Connect

    Rehm, K.E.

    1992-01-01

    Collisions between two heavy nuclei produce a diverse spectrum of reaction modes which is much wider than that observed in light ion studies. For the latter case, two processes are observed: direct reactions and compound nucleus formation. Heavy ion reaction studies on the other hand have identified additional processes such as deep-inelastic scattering, incomplete fusion and quasi-fission reactions. While the boundaries between the various processes are usually not well defined, it is generally accepted that with increasing overlap of the two nuclei the interaction evolves from distant collisions where only elastic scattering and Coulomb excitation processes occur, through grazing-type collisions associated with quasi-elastic reactions to deep-inelastic and fusion-fission processes requiring a substantial nuclear overlap. Varying the bombarding energy is a convenient way to change the overlap of the two nuclei. Measurements of excitation functions can thus probe the onset and the interplay of the various reaction modes. Experiments at bombarding energies in the vicinity of the Coulomb barrier are particularly suited for comparisons with theoretical predictions since the small number of degrees of freedom involved in the interaction greatly simplifies the calculations. In the first part of this contribution a short overview is given on the status of heavy ion reaction studies at energies in the vicinity of the Coulomb barrier. In the second part two experiments, one involving simple and the other studying complex reactions, are discussed in more detail.

  4. Radionuclide reactions with groundwater and basalts from Columbia River basalt formations

    SciTech Connect

    Barney, G.S.

    1981-06-01

    Chemical reactions of radionuclides with geologic materials found in Columbia River basalt formations were studied. The objective was to determine the ability of these formations to retard radionuclide migration from a radioactive waste repository located in deep basalt. Reactions that can influence migration are precipitation, ion-exchange, complexation, and oxidation-reduction. These reactions were studied by measuring the effects of groundwater composition and redox potential (Eh) on radionuclide sorption on fresh basalt surfaces, a naturally altered basalt, and a sample of secondary minerals associated with a Columbia River basalt flow. In addition, radionuclide sorption isotherms were measured for these materials and reaction kinetics were determined. The radionuclides studied were /sup 137/Cs, /sup 85/Sr, /sup 75/Se, /sup 95m/Tc, /sup 237/Np, /sup 241/Am, /sup 226/Ra and /sup 237/Pu. The Freundlich equation accurately describes the isotherms when precipitation of radionuclides does not occur. In general, sorption increased in the order: basalt < altered basalt < secondary minerals. This increase in sorption corresponds to increasing surface area and cation exchange capacity. The Eh of the system had a large effect on technetium, plutonium, and neptunium sorption. Technetium(VII), Pu(VI), and Np(V) are reduced to Tc(IV), Pu(IV), and Np(IV), respectively, under Eh conditions expected in deep basalt formations. The kinetics of radionuclide sorption and basalt-groundwater reactions were observed over a period of 18 weeks. Most sorption reactions stabilized after about four weeks. Groundwater composition changed the least in contact with altered basalt. Contact with secondary minerals greatly increased Ca, K, and Mg concentrations in the groundwater.

  5. Secondary organic aerosol formation from ozone reactions with single terpenoids and terpenoid mixtures

    NASA Astrophysics Data System (ADS)

    Waring, Michael S.; Wells, J. Raymond; Siegel, Jeffrey A.

    2011-08-01

    Ozone reacts with indoor-emitted terpenoids to form secondary organic aerosol (SOA). Most SOA research has focused on ozone reactions with single terpenoids or with consumer products, and this paper reports the results from an investigation of SOA formation from ozone reactions with both single terpenoids and mixtures of D-limonene, α-pinene, and α-terpineol. Transient experiments were conducted at low (25 ppb) and high (100 ppb) initial concentrations of ozone. The three terpenoids were tested singly and in combinations in a manner that controlled for their different reaction rates with ozone. The SOA formation was assessed by examining the evolution in time of the resulting number size-distributions and estimates of the mass concentrations. The results suggest that at higher ozone and terpenoid concentrations, SOA number formation follows a linear trend as a function of the initial rate of reaction. This finding was valid for both single terpenoids and mixtures. Generally speaking, higher ozone and terpenoid concentrations also led to larger geometric mean diameters and smaller geometric standard deviations of fitted lognormal distributions of the formed SOA. By assuming a density, mass concentrations were also assessed and did not follow as consistent of a trend. At low ozone concentration conditions, reactions with only D-limonene yielded the largest number concentrations of any experiment, even more than experiments with mixtures containing D-limonene and much higher overall terpenoid concentrations. This finding was not seen for high ozone concentrations. These experiments demonstrate quantifiable trends for SOA forming reactions of ozone and mixtures, and this work provides a framework for expanding these results to more complex mixtures and consumer products.

  6. STEPS: Modeling and Simulating Complex Reaction-Diffusion Systems with Python.

    PubMed

    Wils, Stefan; De Schutter, Erik

    2009-01-01

    We describe how the use of the Python language improved the user interface of the program STEPS. STEPS is a simulation platform for modeling and stochastic simulation of coupled reaction-diffusion systems with complex 3-dimensional boundary conditions. Setting up such models is a complicated process that consists of many phases. Initial versions of STEPS relied on a static input format that did not cleanly separate these phases, limiting modelers in how they could control the simulation and becoming increasingly complex as new features and new simulation algorithms were added. We solved all of these problems by tightly integrating STEPS with Python, using SWIG to expose our existing simulation code.

  7. Transition state ensemble optimization for reactions of arbitrary complexity

    NASA Astrophysics Data System (ADS)

    Zinovjev, Kirill; Tuñón, Iñaki

    2015-10-01

    In the present work, we use Variational Transition State Theory (VTST) to develop a practical method for transition state ensemble optimization by looking for an optimal hyperplanar dividing surface in a space of meaningful trial collective variables. These might be interatomic distances, angles, electrostatic potentials, etc. Restrained molecular dynamics simulations are used to obtain on-the-fly estimates of ensemble averages that guide the variations of the hyperplane maximizing the transmission coefficient. A central result of our work is an expression that quantitatively estimates the importance of the coordinates used for the localization of the transition state ensemble. Starting from an arbitrarily large set of trial coordinates, one can distinguish those that are indeed essential for the advance of the reaction. This facilitates the use of VTST as a practical theory to study reaction mechanisms of complex processes. The technique was applied to the reaction catalyzed by an isochorismate pyruvate lyase. This reaction involves two simultaneous chemical steps and has a shallow transition state region, making it challenging to define a good reaction coordinate. Nevertheless, the hyperplanar transition state optimized in the space of 18 geometrical coordinates provides a transmission coefficient of 0.8 and a committor histogram well-peaked about 0.5, proving the strength of the method. We have also tested the approach with the study of the NaCl dissociation in aqueous solution, a stringest test for a method based on transition state theory. We were able to find essential degrees of freedom consistent with the previous studies and to improve the transmission coefficient with respect to the value obtained using solely the NaCl distance as the reaction coordinate.

  8. Studies of complex fragment emission in heavy ion reactions

    SciTech Connect

    Charity, R.J.; Sobotka, L.G.

    1992-01-01

    Our work involves the study of intermediate energy heavy-ion nuclear reactions. This work has two foci. On the one hand, we desire to learn about the properties of nuclear matter under abnormal conditions, in this energy domain, predominately low densities. This purpose runs abreast of the second, which is the study of the relevant reaction mechanisms. The two objectives are inexorably linked because our experimental laboratory for studying nuclear matter properties is a dynamic one. We are forced to ask how nuclear matter properties, such as phase transitions, are reflected in the dynamics of the reactions. It may be that irrefutable information about nuclear matter will not be extracted from the reaction work. Nevertheless, we are compelled to undertake this effort not only because it is the only game in town and as yet we do not know that information cannot be extracted, but also because of our second objective. The process leads to an understanding of the reaction mechanism themselves and therefore to the response characteristics of finite, perhaps non-equilibrium, strongly interacting systems. Our program has been: To study energy, mass, and angular momentum deposition by studying incomplete fusion reactions. To gain confidence that we understand how highly excited systems decompose by studying all emissions from the highly excited systems. To push these kinds of studies into the intermediate energy domain, with excitation function studies. And attempt to learn about the dynamics of the decays using particle-particle correlations. In the last effort, we have decided to focus on simple systems, where we believe, definitive statements are possible. These avenues of research share a common theme, large complex fragment production.

  9. The formation of Kuiper-belt binaries through exchange reactions.

    PubMed

    Funato, Yoko; Makino, Junichiro; Hut, Piet; Kokubo, Eiichiro; Kinoshita, Daisuke

    2004-02-05

    Recent observations have revealed that an unexpectedly high fraction--a few per cent--of the trans-Neptunian objects (TNOs) that inhabit the Kuiper belt are binaries. The components have roughly equal masses, with very eccentric orbits that are wider than a hundred times the radius of the primary. Standard theories of binary asteroid formation tend to produce close binaries with circular orbits, so two models have been proposed to explain the unique characteristics of the TNOs. Both models, however, require extreme assumptions regarding the size distribution of the TNOs. Here we report a mechanism that is capable of producing binary TNOs with the observed properties during the early stages of their formation and growth. The only required assumption is that the TNOs were initially formed through gravitational instabilities in the protoplanetary dust disk. The basis of the mechanism is an exchange reaction in which a binary whose primary component is much more massive than the secondary interacts with a third body, whose mass is comparable to that of the primary. The low-mass secondary component is ejected and replaced by the third body in a wide but eccentric orbit.

  10. Bis-diimidazolylidine complexes of nickel: investigations into nickel catalyzed coupling reactions.

    PubMed

    Paulose, Tressia A P; Wu, Shih-Chang; Olson, Jeremy A; Chau, Tony; Theaker, Nikki; Hassler, Matt; Quail, J Wilson; Foley, Stephen R

    2012-01-07

    Air and moisture stable homoleptic bis(diimidazolylidine)nickel(II) complexes, ([(diNHC)(2)Ni](2+)) 3a,b and their corresponding silver(I) 4a,b and palladium(II) 5a,b complexes were synthesized and characterized by NMR and single crystal X-ray analysis. The catalytic potential of complex 3a was assessed in Mizoroki-Heck and Suzuki-Miyaura coupling reactions. In the Suzuki-Miyaura coupling reaction, nickel precatalyst 3a was active for the coupling of aryl chlorides as well as aryl fluorides. The analogously synthesized Pd(II) complexes resulted in formation of (diNHC)PdCl(2) species which were not active for the coupling of aryl fluorides. For the Mizoroki-Heck reaction, it was found that aryl iodides could be activated in the absence of nickel or palladium precatalysts when using Na(2)CO(3) or NEt(3) as base while aryl iodides and aryl bromides could be activated in the Suzuki-Miyaura reaction sans precatalyst when K(3)PO(4) was used as base.

  11. Direct electronic probing of biological complexes formation

    NASA Astrophysics Data System (ADS)

    Macchia, Eleonora; Magliulo, Maria; Manoli, Kyriaki; Giordano, Francesco; Palazzo, Gerardo; Torsi, Luisa

    2014-10-01

    Functional bio-interlayer organic field - effect transistors (FBI-OFET), embedding streptavidin, avidin and neutravidin as bio-recognition element, have been studied to probe the electronic properties of protein complexes. The threshold voltage control has been achieved modifying the SiO2 gate diaelectric surface by means of the deposition of an interlayer of bio-recognition elements. A threshold voltage shift with respect to the unmodified dielectric surface toward more negative potential values has been found for the three different proteins, in agreement with their isoelectric points. The relative responses in terms of source - drain current, mobility and threshold voltage upon exposure to biotin of the FBI-OFET devices have been compared for the three bio-recognition elements.

  12. Stochastic analysis of complex reaction networks using binomial moment equations.

    PubMed

    Barzel, Baruch; Biham, Ofer

    2012-09-01

    The stochastic analysis of complex reaction networks is a difficult problem because the number of microscopic states in such systems increases exponentially with the number of reactive species. Direct integration of the master equation is thus infeasible and is most often replaced by Monte Carlo simulations. While Monte Carlo simulations are a highly effective tool, equation-based formulations are more amenable to analytical treatment and may provide deeper insight into the dynamics of the network. Here, we present a highly efficient equation-based method for the analysis of stochastic reaction networks. The method is based on the recently introduced binomial moment equations [Barzel and Biham, Phys. Rev. Lett. 106, 150602 (2011)]. The binomial moments are linear combinations of the ordinary moments of the probability distribution function of the population sizes of the interacting species. They capture the essential combinatorics of the reaction processes reflecting their stoichiometric structure. This leads to a simple and transparent form of the equations, and allows a highly efficient and surprisingly simple truncation scheme. Unlike ordinary moment equations, in which the inclusion of high order moments is prohibitively complicated, the binomial moment equations can be easily constructed up to any desired order. The result is a set of equations that enables the stochastic analysis of complex reaction networks under a broad range of conditions. The number of equations is dramatically reduced from the exponential proliferation of the master equation to a polynomial (and often quadratic) dependence on the number of reactive species in the binomial moment equations. The aim of this paper is twofold: to present a complete derivation of the binomial moment equations; to demonstrate the applicability of the moment equations for a representative set of example networks, in which stochastic effects play an important role.

  13. Efficient and selective formation of macrocyclic disubstituted Z alkenes by ring-closing metathesis (RCM) reactions catalyzed by Mo- or W-based monoaryloxide pyrrolide (MAP) complexes: applications to total syntheses of epilachnene, yuzu lactone, ambrettolide, epothilone C, and nakadomarin A.

    PubMed

    Wang, Chenbo; Yu, Miao; Kyle, Andrew F; Jakubec, Pavol; Dixon, Darren J; Schrock, Richard R; Hoveyda, Amir H

    2013-02-18

    The first broadly applicable set of protocols for efficient Z-selective formation of macrocyclic disubstituted alkenes through catalytic ring-closing metathesis (RCM) is described. Cyclizations are performed with 1.2-7.5 mol% of a Mo- or W-based monoaryloxide pyrrolide (MAP) complex at 22 °C and proceed to complete conversion typically within two hours. Utility is demonstrated by synthesis of representative macrocyclic alkenes, such as natural products yuzu lactone (13-membered ring: 73% Z) epilachnene (15-membered ring: 91% Z), ambrettolide (17-membered ring: 91% Z), an advanced precursor to epothilones C and A (16-membered ring: up to 97% Z), and nakadomarin A (15-membered ring: up to 97% Z). We show that catalytic Z-selective cyclizations can be performed efficiently on gram-scale with complex molecule starting materials and catalysts that can be handled in air. We elucidate several critical principles of the catalytic protocol: 1) The complementary nature of the Mo catalysts, which deliver high activity but can be more prone towards engendering post-RCM stereoisomerization, versus W variants, which furnish lower activity but are less inclined to cause loss of kinetic Z selectivity. 2) Reaction time is critical to retaining kinetic Z selectivity not only with MAP species but with the widely used Mo bis(hexafluoro-tert-butoxide) complex as well. 3) Polycyclic structures can be accessed without significant isomerization at the existing Z alkenes within the molecule.

  14. Structure and kinetics of formation of catechol complexes of ferric soybean lipoxygenase-1

    SciTech Connect

    Nelson, M.J.; Brennan, B.A.; Chase, D.B. |

    1995-11-21

    Ferric soybean lipoxygenase forms stable complexes with 4-substituted catechols. The structure of the complex between the enzyme and 3,4-dihydroxybenzonitrile has been studied by resonance Raman, electron paramagnetic resonance, visible, and X-ray spectroscopies. It is a bidentate iron-catecholate complex with at least one water ligand. The kinetics of formation of complexes between lipoxygenase and 3,4-dihydroxybenzonitrile and 3,4-dihydroxyacetophenone have been studied by stopped-flow spectroscopy. The data are consistent with two kinetically distinct, reversible steps. The pH dependence of the first step suggests that the substrate for the reaction is the catechol monoanion. When these results are combined, plausible mechanisms for the complexation reaction are suggested. 51 refs., 12 figs., 2 tabs.

  15. Theoretical predictions of hydrolysis and complex formation of the heaviest elements

    NASA Astrophysics Data System (ADS)

    Pershina, V.

    2000-07-01

    In the presentation, investigations of hydrolysis and complex formation of group 4, 5 and 6 elements, including the transactinide elements 104, 105 and 106 are described. They were carried out on the basis of results of relativistic calculations of the electronic structure of various hydrated, hydrolyzed and complex compounds of these elements using the fully relativistic ab initio density functional method with the GGA approximation for the exchange-correlation potential. Predictions of equilibria of hydrolysis or complex formation reactions have been made using a model which enables determination of free energy changes of the reactions as changes in the ionic and covalent contributions to the binding molecular energy separately. Those contributions were calculated using the Mulliken analysis of the electronic density distribution.

  16. Positronium formation in solid transition metal losartanates complexes

    NASA Astrophysics Data System (ADS)

    de Oliveira, F. C.; Denadai, A. M. L.; Fulgêncio, F.; da Silva, J. G.; Windmöller, D.; Marques-Netto, A.; Machado, J. C.; Magalhães, W. F.

    2013-10-01

    In this Letter, positron annihilation lifetime (PALS) measurements were performed in transition metal losartanates complexes, MT(Los)2, and in potassium losartanate, KLos, in order to built up insights about the positronium formation mechanism in molecular environment. A correlation was obtained between formation probability, I3, and the covalence of complexes, evaluated by molar electrical conductivity in dimethylformamide (DMF). Furthermore, some metallic ion properties, such as reduction potential and pauling electronegativity, were also correlated with I3. These results were analyzed in terms of the spur model and of the recently proposed mechanism, named cybotatic correlated system kinetic mechanism (CCSKM), which involves molecular excited states in positronium formation.

  17. Contribution of the photo-Fenton reaction to hydroxyl radical formation rates in river and rain water samples.

    PubMed

    Nakatani, Nobutake; Ueda, Marina; Shindo, Hirotaka; Takeda, Kazuhiko; Sakugawa, Hiroshi

    2007-09-01

    The hydroxyl radical (OH radical) formation rates from the photo-Fenton reaction in river and rain water samples were determined by using deferoxamine mesylate (DFOM), which makes a stable and strong complex with Fe(III), resulting in a suppression of the photo-Fenton reaction. The difference between the OH radical formation rates with and without added DFOM denotes the rate from the photo-Fenton reaction. The photoformation rates from the photo-Fenton reaction were in the range of 0.7 - 45.8 x 10(-12) and 2.7 - 32.3 x 10(-12) M s(-1) in river and rain water samples, respectively. A strong positive correlation between the OH radical formation rate from the photo-Fenton reaction and the amount of fluorescent matter in river water suggests that fluorescent matter, such as humic substances, plays an important role in the photo-Fenton reaction. In rain water, direct photolysis of hydrogen peroxide was an important source of OH radicals as well as the photo-Fenton reaction. The contributions of the photo-Fenton reaction to the OH radical photoformation rates in river and rain water samples were in the ranges of 2 - 29 and 5 - 38%, respectively. Taking into account the photo-Fenton reaction, 33 - 110 (mean: 80) and 42 - 110 (mean: 84)% of OH radical sources in river and rain water samples, respectively, collected in Hiroshima prefecture were elucidated.

  18. Investigation of cu-BTA complex formation during Cu chemical mechanical planarization process

    NASA Astrophysics Data System (ADS)

    Cho, Byoung-Jun; Shima, Shohei; Hamada, Satomi; Park, Jin-Goo

    2016-10-01

    The effect of Cu surface conditions on Cu-BTA complex formation was investigated using contact angle, electrochemical impedance spectroscopy, spectroscopic ellipsometry and XPS measurements which is of interest to Cu Chemical Mechanical Planarization (CMP) process. During Cu CMP process BTA is widely used as a corrosion inhibitor, reacts with Cu and forms a strong Cu-BTA complex. Thus, it is very essential to remove Cu-BTA complex during post-Cu CMP cleaning process as Cu-BTA complex causes severe problems such as particle contamination and watermark due to its hydrophobic nature. In this report, the Cu-BTA complex formation at various Cu surfaces (as received, pure Cu and Cu oxide) was investigated in order to understand its adsorption reaction and develop effective post-Cu CMP cleaning process.

  19. Electrochemical detection of oligopeptides through the precolumn formation of biuret complexes.

    PubMed

    Tsai, H Y; Weber, S G

    1991-04-12

    The relatively slow kinetics of formation of the electroactive Cu(II)-peptide complexes from larger (greater than 6 amino acids) peptides requires relatively high temperature and long reaction times for a postcolumn reactor. The precolumn incubation of bradykinin, Tyr8-bradykinin and insulin A chain with biuret reagent for 20 min at 60 degrees C leads to the formation of biuret complexes which can be subjected to chromatography in acidic or basic eluents. These complexes are detected electrochemically with a sensitivity similar to the Cu(II)-(ala)3 complex (1 nC/pmol at 1.0 ml/min). The influence of the column-packing material on the electrochemical detector response of the Cu-peptide complexes has also been studied.

  20. Complex molecule formation around massive young stellar objects.

    PubMed

    Oberg, Karin I; Fayolle, Edith C; Reiter, John B; Cyganowski, Claudia

    2014-01-01

    Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T = 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics--CH3CCH, CH3CN, CH3OCH3 and CH3CHO--in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history.

  1. Validated spectrophotometric methods for determination of sodium valproate based on charge transfer complexation reactions

    NASA Astrophysics Data System (ADS)

    Belal, Tarek S.; El-Kafrawy, Dina S.; Mahrous, Mohamed S.; Abdel-Khalek, Magdi M.; Abo-Gharam, Amira H.

    2016-02-01

    This work presents the development, validation and application of four simple and direct spectrophotometric methods for determination of sodium valproate (VP) through charge transfer complexation reactions. The first method is based on the reaction of the drug with p-chloranilic acid (p-CA) in acetone to give a purple colored product with maximum absorbance at 524 nm. The second method depends on the reaction of VP with dichlone (DC) in dimethylformamide forming a reddish orange product measured at 490 nm. The third method is based upon the interaction of VP and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 415 nm. The fourth method involves the formation of a yellow complex peaking at 361 nm upon the reaction of the drug with iodine in chloroform. Experimental conditions affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed spectrophotometric procedures were effectively validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curves of the formed color products with p-CA, DC, PA and iodine showed good linear relationships over the concentration ranges 24-144, 40-200, 2-20 and 1-8 μg/mL respectively. The proposed methods were successfully applied to the assay of sodium valproate in tablets and oral solution dosage forms with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method.

  2. Validated spectrophotometric methods for determination of sodium valproate based on charge transfer complexation reactions.

    PubMed

    Belal, Tarek S; El-Kafrawy, Dina S; Mahrous, Mohamed S; Abdel-Khalek, Magdi M; Abo-Gharam, Amira H

    2016-02-15

    This work presents the development, validation and application of four simple and direct spectrophotometric methods for determination of sodium valproate (VP) through charge transfer complexation reactions. The first method is based on the reaction of the drug with p-chloranilic acid (p-CA) in acetone to give a purple colored product with maximum absorbance at 524nm. The second method depends on the reaction of VP with dichlone (DC) in dimethylformamide forming a reddish orange product measured at 490nm. The third method is based upon the interaction of VP and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 415nm. The fourth method involves the formation of a yellow complex peaking at 361nm upon the reaction of the drug with iodine in chloroform. Experimental conditions affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed spectrophotometric procedures were effectively validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curves of the formed color products with p-CA, DC, PA and iodine showed good linear relationships over the concentration ranges 24-144, 40-200, 2-20 and 1-8μg/mL respectively. The proposed methods were successfully applied to the assay of sodium valproate in tablets and oral solution dosage forms with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method.

  3. Snapshot of a Reaction Intermediate: Analysis of Benzoylformate Decarboxylase in Complex with a Benzoylphosphonate Inhibitor

    SciTech Connect

    Brandt, Gabriel S.; Kneen, Malea M.; Chakraborty, Sumit; Baykal, Ahmet T.; Nemeria, Natalia; Yep, Alejandra; Ruby, David I.; Petsko, Gregory A.; Kenyon, George L.; McLeish, Michael J.; Jordan, Frank; Ringe, Dagmar

    2009-04-22

    Benzoylformate decarboxylase (BFDC) is a thiamin diphosphate- (ThDP-) dependent enzyme acting on aromatic substrates. In addition to its metabolic role in the mandelate pathway, BFDC shows broad substrate specificity coupled with tight stereo control in the carbon-carbon bond-forming reverse reaction, making it a useful biocatalyst for the production of chiral-hydroxy ketones. The reaction of methyl benzoylphosphonate (MBP), an analogue of the natural substrate benzoylformate, with BFDC results in the formation of a stable analogue (C2{alpha}-phosphonomandelyl-ThDP) of the covalent ThDP-substrate adduct C2{alpha}-mandelyl-ThDP. Formation of the stable adduct is confirmed both by formation of a circular dichroism band characteristic of the 1',4'-iminopyrimidine tautomeric form of ThDP (commonly observed when ThDP forms tetrahedral complexes with its substrates) and by high-resolution mass spectrometry of the reaction mixture. In addition, the structure of BFDC with the MBP inhibitor was solved by X-ray crystallography to a spatial resolution of 1.37 {angstrom} (PDB ID 3FSJ). The electron density clearly shows formation of a tetrahedral adduct between the C2 atom of ThDP and the carbonyl carbon atom of the MBP. This adduct resembles the intermediate from the penultimate step of the carboligation reaction between benzaldehyde and acetaldehyde. The combination of real-time kinetic information via stopped-flow circular dichroism with steady-state data from equilibrium circular dichroism measurements and X-ray crystallography reveals details of the first step of the reaction catalyzed by BFDC. The MBP-ThDP adduct on BFDC is compared to the recently solved structure of the same adduct on benzaldehyde lyase, another ThDP-dependent enzyme capable of catalyzing aldehyde condensation with high stereospecificity.

  4. Insight into hydrolytic reaction of N-acetylated L-histidylglycine dipeptide with novel mechlorethamine platinum(II) complex. NMR and DFT study of the hydrolytic reaction.

    PubMed

    Petrović, Zorica D; Petrović, Vladimir P; Simijonović, Dušica; Marković, Svetlana

    2011-09-28

    The reaction of K(2)PtCl(4) with the alkylating agent mechlorethamine hydrochloride, at a molar ratio of 1:2, results in the formation of 2-chloro-N-(2-chloroethyl)-N-methylethylammonium-tetrachloridoplatinate(II) complex. The hydrolytic activity of the novel Pt(II) complex was tested in the reaction with N-acetylated L-histidylglycine dipeptide at a molar ratio 1:1. It was shown that the hydrolytic reaction, performed at 60 °C in acidic medium, leads to the regioselective cleavage of the amide bond involving the carboxylic group of histidine. Density functional theory was used to explore the structures of the proposed participants in the hydrolytic reaction.

  5. Reactions of a Ruthenium Complex with Substituted N-Propargyl Pyrroles.

    PubMed

    Chia, Pi-Yeh; Huang, Shou-Ling; Liu, Yi-Hong; Lin, Ying-Chih

    2016-04-05

    In an investigation into the chemical reactions of N-propargyl pyrroles 1 a-c, containing aldehyde, keto, and ester groups on the pyrrole ring, with [Ru]-Cl ([Ru]=Cp(PPh3 )2 Ru; Cp=C5 H5 ), an aldehyde group in the pyrrole ring is found to play a crucial role in stimulating the cyclization reaction. The reaction of 1 a, containing an aldehyde group, with [Ru]-Cl in the presence of NH4 PF6 yields the vinylidene complex 2 a, which further reacts with allyl amine to give the carbene complex 6 a with a pyrrolizine group. However, if 1 a is first reacted with allyl amine to yield the iminenyne 8 a, then the reaction of 8 a with [Ru]-Cl in the presence of NH4 PF6 yields the ruthenium complex 9 a, containing a cationic pyrrolopyrazinium group, which has been fully characterized by XRD analysis. These results can be adequately explained by coordination of the triple bond of the propargyl group to the ruthenium metal center first, followed by two processes, that is, formation of a vinylidene intermediate or direct nucleophilic attack. Additionally, the deprotonation of 2 a by R4 NOH yields the neutral acetylide complex 3 a. In the presence of NH4 PF6 , the attempted alkylation of 3 a resulted in the formation the Fischer-type amino-carbene complex 5 a as a result of the presence of NH3, which served as a nucleophile. With KPF6, the alkylation of 3 a with ethyl and benzyl bromoacetates afforded the disubstituted vinylidene complexes 10 a and 11 a, containing ester groups, which underwent deprotonation reactions to give the furyl complexes 12 a and 13 a, respectively. For 13 a, containing an O-benzyl group, subsequent 1,3-migration of the benzyl group was observed to yield product 14 a with a lactone unit. Similar reactivity was not observed for the corresponding N-propargyl pyrroles 1 b and 1 c, which contained keto and ester groups, respectively, on the pyrrole ring.

  6. Kinetic study of the complex reaction between copper(II) and 2-(2'-hydroxy-3'-methoxyphenyl)benzothiazole

    NASA Astrophysics Data System (ADS)

    Freinbichler, Wolfhardt; Soliman, Ahmed; Jameson, Reginald F.; Jameson, Guy N. L.; Linert, Wolfgang

    2009-09-01

    2-(2'-Hydroxy-3'-methoxyphenyl)benzothiazole reacts with copper(II) in an ethanol/water mixture to form an O,S chelate which exhibits the remarkable property of changing the chelation site above a pH of ca. 5.0, to the O,N site. The detailed kinetics of this reaction in an ethanol/water mixture (3:1) at a temperature of 25 °C was investigated using a stopped-flow spectrophotometric technique employing a wavelength of 400 nm. The initial complex, Cu(O,S), is formed via a fast, reversible second-order complex formation step whereupon the formation of the Cu (O,N) follows first order kinetics. The Cu(O,N) complex is, however, unstable towards internal electron exchange and after the reaction is complete, a black polymeric material very slowly precipitates out of solution. Rate and equilibrium constants for the postulated reactions are presented and discussed.

  7. Stereospecific formation of dinuclear vanadium(V) tartrato complexes.

    PubMed

    Gáliková, Jana; Schwendt, Peter; Tatiersky, Jozef; Tracey, Alan S; Zák, Zdirad

    2009-09-07

    The first dinuclear nonperoxido tartrato complexes of vanadium(V), (NMe(4))(2)[V(2)O(4)((2R,3R)-H(2)tart)(2)] x 6 H(2)O (1), (NMe(4))(2)[V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)] (2), (NEt(4))(2)[V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)] (3) (tart = tartrato(4-) = C(4)H(2)O(6)(4-)) have been prepared from water-ethanol medium and characterized by X-ray structure analysis and spectral methods. The formation of the complexes has been found to be stereospecific; the composition and structure of anions containing one or both enantiomers of the ligand are profoundly different. The structure of anions in 1-3 also differs significantly from the structure of other dinuclear vanadium(V) alpha-hydroxycarboxylato complexes, but, interestingly, the geometry of the [V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)](2-) ion resembles the structure of the [(VO)(2)((2R,3R)-tart)((2S,3S)-tart)](4-) ion which has a vanadium(IV) center. Using Raman and (51)V NMR spectroscopy the solvent dependent mutual transformations of [V(4)O(8)((2R,3R)-tart)(2)](4-) (V(4)L(2)-RR), [V(4)O(8)((2S,3S)-tart)(2)](4-) (V(4)L(2)-SS), [V(2)O(4)((2R,3R)-H(2)tart)(2)](2-) (V(2)L(2)-RR), [V(2)O(4)((2S,3S)-H(2)tart)(2)](2-) (V(2)L(2)-SS), and [V(2)O(2)((2R,3R)-tart)((2S,3S)-tart)](2-) (V(2)L(2)-rac) have been established. In aqueous solution the following reactions take place; 2 V(2)L(2)-rac --> V(2)L(2)-RR + V(2)L(2)-SS followed by partial decomposition, V(2)L(2)-RR --> V(4)L(2)-RR + 2 L (V(2)L(2)-SS --> V(4)L(2)-SS + 2 L). On the other hand V(2)L(2)-rac is stable in CH(3)CN solution while V(2)L(2)-RR (V(2)L(2)-SS) decomposes into several species.

  8. Enthalpy of hydrogen bond formation in a protein-ligand binding reaction.

    PubMed

    Connelly, P R; Aldape, R A; Bruzzese, F J; Chambers, S P; Fitzgibbon, M J; Fleming, M A; Itoh, S; Livingston, D J; Navia, M A; Thomson, J A

    1994-03-01

    Parallel measurements of the thermodynamics (free-energy, enthalpy, entropy and heat-capacity changes) of ligand binding to FK506 binding protein (FKBP-12) in H2O and D2O have been performed in an effort to probe the energetic contributions of single protein-ligand hydrogen bonds formed in the binding reactions. Changing tyrosine-82 to phenylalanine in FKBP-12 abolishes protein-ligand hydrogen bond interactions in the FKBP-12 complexes with tacrolimus or rapamycin and leads to a large apparent enthalpic stabilization of binding in both H2O and D2O. High-resolution crystallographic analysis reveals that two water molecules bound to the tyrosine-82 hydroxyl group in unliganded FKBP-12 are displaced upon formation of the protein-ligand complexes. A thermodynamic analysis is presented that suggests that the removal of polar atoms from water contributes a highly unfavorable enthalpy change to the formation of C=O...HO hydrogen bonds as they occur in the processes of protein folding and ligand binding. Despite the less favorable enthalpy change, the entropic advantage of displacing two water molecules upon binding leads to a slightly more favorable free-energy change of binding in the reactions with wild-type FKBP-12.

  9. Enthalpy of hydrogen bond formation in a protein-ligand binding reaction.

    PubMed Central

    Connelly, P R; Aldape, R A; Bruzzese, F J; Chambers, S P; Fitzgibbon, M J; Fleming, M A; Itoh, S; Livingston, D J; Navia, M A; Thomson, J A

    1994-01-01

    Parallel measurements of the thermodynamics (free-energy, enthalpy, entropy and heat-capacity changes) of ligand binding to FK506 binding protein (FKBP-12) in H2O and D2O have been performed in an effort to probe the energetic contributions of single protein-ligand hydrogen bonds formed in the binding reactions. Changing tyrosine-82 to phenylalanine in FKBP-12 abolishes protein-ligand hydrogen bond interactions in the FKBP-12 complexes with tacrolimus or rapamycin and leads to a large apparent enthalpic stabilization of binding in both H2O and D2O. High-resolution crystallographic analysis reveals that two water molecules bound to the tyrosine-82 hydroxyl group in unliganded FKBP-12 are displaced upon formation of the protein-ligand complexes. A thermodynamic analysis is presented that suggests that the removal of polar atoms from water contributes a highly unfavorable enthalpy change to the formation of C=O...HO hydrogen bonds as they occur in the processes of protein folding and ligand binding. Despite the less favorable enthalpy change, the entropic advantage of displacing two water molecules upon binding leads to a slightly more favorable free-energy change of binding in the reactions with wild-type FKBP-12. Images PMID:7510408

  10. Electrochemical Formation of Fe(V) (O) and Mechanism of Its Reaction with Water During O-O Bond Formation.

    PubMed

    Pattanayak, Santanu; Chowdhury, Debarati Roy; Garai, Bikash; Singh, Kundan K; Paul, Amit; Dhar, Basab B; Gupta, Sayam Sen

    2017-03-08

    A detailed electrochemical investigation of a series of iron complexes (biuret-modified tetraamido iron macrocycles Fe(III) -bTAML), including the first electrochemical generation of Fe(V) (O), and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium are reported. Spectroelectrochemical and mass spectral studies indicated Fe(V) (O) as the active oxidant, formed due to two redox transitions, which were assigned as Fe(IV) (O)/Fe(III) (OH2 ) and Fe(V) (O)/Fe(IV) (O). The spectral properties of both of these high-valent iron oxo species perfectly match those of their chemically synthesised versions, which were thoroughly characterised by several spectroscopic techniques. The O-O bond-formation step occurs by nucleophilic attack of H2 O on Fe(V) (O). A kinetic isotope effect of 3.2 indicates an atom-proton transfer (APT) mechanism. The reaction of chemically synthesised Fe(V) (O) in CH3 CN and water was directly probed by electrochemistry and was found to be first-order in water. The pKa value of the buffer base plays a critical role in the rate-determining step by increasing the reaction rate several-fold. The electronic effect on redox potential, WO rates, and onset overpotential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework. Changing the substituents from OMe to NO2 resulted in an eightfold increase in reaction rate, while the overpotential increased threefold.

  11. Electron transfer reactions of osmium(II) complexes with phenols and phenolic acids

    NASA Astrophysics Data System (ADS)

    Rajeswari, Angusamy; Ramdass, Arumugam; Muthu Mareeswaran, Paulpandian; Velayudham, Murugesan; Rajagopal, Seenivasan

    2016-07-01

    Three [Os(NN)3]2+ complexes (NN = polypyridine) with ligands of varying hydrophobicity were synthesized and characterized by NMR spectral techniques. The geometry of the molecules are optimized by DFT calculations. The interaction between [Os(NN)3]2+ complexes and phenolate ion in ground state is confirmed by absorption spectral study and the binding constant values are in the range of 3-740 M-1. The photoinduced electron transfer reaction of these [Os(NN)3]2+ complexes with phenols and phenolic acids at pH 12.5 leads to the formation of phenoxyl radical confirmed through transient absorption spectral study. Binding constants and electron transfer rate constants within the [Os(NN)3]2+-phenolate ion adduct account for the change for the overall quenching constant with the change of structure of reactants.

  12. Carbon–heteroatom bond formation catalysed by organometallic complexes

    PubMed Central

    Hartwig, John F.

    2010-01-01

    At one time the synthetic chemist’s last resort, reactions catalysed by transition metals are now the preferred method for synthesizing many types of organic molecule. A recent success in this type of catalysis is the discovery of reactions that form bonds between carbon and heteroatoms (such as nitrogen, oxygen, sulphur, silicon and boron) via complexes of transition metals with amides, alkoxides, thiolates, silyl groups or boryl groups. The development of these catalytic processes has been supported by the discovery of new elementary reactions that occur at metal–heteroatom bonds and by the identification of factors that control these reactions. Together, these findings have led to new synthetic processes that are in daily use and have formed a foundation for the development of processes that are likely to be central to synthetic chemistry in the future. PMID:18800130

  13. Oxygen atom transfer reactions from Mimoun complexes to sulfides and sulfoxides. A bonding evolution theory analysis.

    PubMed

    González-Navarrete, Patricio; Sensato, Fabricio R; Andrés, Juan; Longo, Elson

    2014-08-07

    In this research, a comprehensive theoretical investigation has been conducted on oxygen atom transfer (OAT) reactions from Mimoun complexes to sulfides and sulfoxides. The joint use of the electron localization function (ELF) and Thom's catastrophe theory (CT) provides a powerful tool to analyze the evolution of chemical events along a reaction pathway. The progress of the reaction has been monitored by structural stability domains from ELF topology while the changes between them are controlled by turning points derived from CT which reveal that the reaction mechanism can be separated in several steps: first, a rupture of the peroxo O1-O2 bond, then a rearrangement of lone pairs of the sulfur atom occurs and subsequently the formation of S-O1 bond. The OAT process involving the oxidation of sulfides and sulfoxides is found to be an asynchronous process where O1-O2 bond breaking and S-O1 bond formation processes do not occur simultaneously. Nucleophilic/electrophilic characters of both dimethyl sulfide and dimethyl sulfoxide, respectively, are sufficiently described by our results, which hold the key to unprecedented insight into the mapping of electrons that compose the bonds while the bonds change.

  14. Remarkably high asymmetric amplification in the chiral lanthanide complex-catalyzed hetero-Diels-Alder reaction: first example of the nonlinear effect in ML3 system

    PubMed

    Furuno; Hanamoto; Sugimoto; Inanaga

    2000-01-01

    [reaction: see text] A remarkably high asymmetric amplification was realized in the Yb[(R)-BNP]3-catalyzed hetero-Diels-Alder reaction as the first example in the metal/chiral ligand 1:3 system. The mechanism may be explained by the autogenetic formation of the enantiopure complex as the most active catalyst. The enantiomer-discriminative formation of homochiral ML3 complexes is quite general within the lanthanide metal ions with similar ionic radii to that of the ytterbium ion.

  15. Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

    SciTech Connect

    Soorkia, Satchin; Taatjes, Craig A.; Osborn, David L.; Selby, Talitha M.; Trevitt, Adam J.; Wilson, Kevin R.; Leone, Stephen R.

    2010-03-16

    The reaction of the ground state methylidyne radical CH (X2Pi) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 90 oC (363 K), at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by Helimination. The Photoionization Efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (dpyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as in gas-phase combustion processes, are discussed.

  16. Ozone process insights from field experiments - Part III: extent of reaction and ozone formation

    NASA Astrophysics Data System (ADS)

    Blanchard, Charles L.

    The analysis of ambient data offers a means of developing a qualitative understanding of the sensitivity of ozone formation at specific times and places to changes in VOC and NO x concentrations. The Integrated Empirical Rate (IER) model (Johnson, 1984, Proceedings of the Eighth International Clean Air Conference, Melbourne, Australia, pp. 715-731) and two revisions known as the Smog Production (SP) algorithm (Blanchard et al., 1999, Atmospheric Environment 33, 369-381; Chang et al., 1997, Atmospheric Environment 31, 2787-2794) are reviewed. Applied to ambient data, the algorithm requires measurements of ozone, NO, and either NO x or NO y and computes a quantity known as the extent of reaction. The extent of reaction is shown to be related to photochemical age and serves as an indicator of the sensitivity of instantaneous ozone production to changes in VOC or NO x concentrations. Extent of reaction alone is insufficient as an indicator of the sensitivity of ozone concentration to a complex upwind history of emission changes. Consideration of daily, hourly, and spatial patterns of extent of reaction is needed to interpret applications of the SP algorithm.

  17. Efficient and Selective Formation of Macrocyclic Disubstituted Z Alkenes by Ring-Closing Metathesis (RCM) Reactions Catalyzed by Mo- or W-Based Monoaryloxide Pyrrolide (MAP) Complexes. Applications to Total Syntheses of Epilachnene, Yuzu Lactone, Ambrettolide, Epothilone C and Nakadomarin A

    PubMed Central

    Wang, Chenbo; Yu, Miao; Kyle, Andrew F.; Jakubec, Jakubec; Dixon, Darren J.; Schrock, Richard R.; Hoveyda, Amir H.

    2014-01-01

    The first broadly applicable set of protocols for efficient and highly Z-selective formation of macrocyclic disubstituted alkenes through catalytic ring-closing metathesis (RCM) is described. Cyclizations are performed in the presence of 1.2–7.5 mol % of a Mo- or W-based mono-aryloxide pyrrolide (MAP) complex at 22 °C and typically proceed to complete conversion within two hours. The utility of the catalytic strategy is demonstrated by stereoselective synthesis of representative macrocyclic alkenes, including natural products yuzu lactone (13-membered ring: 73% Z) epilachnene (15-membered ring: 91% Z), ambrettolide (17-membered ring: 91% Z), an advanced precursor to epothilones C and A (16-membered ring: up to 97% Z) and nakadomarin A (polycyclic 15-membered ring: up to 97% Z). We demonstrate the complementary nature of the Mo-based catalysts, which deliver high activity but can be more prone to causing post-RCM stereoisomerization, versus W-based variants, which furnish lower activity but are less inclined towards causing loss of kinetic Z selectivity; a number of catalytic Z-selective cases are provided to elucidate which catalyst class is best suited for which substrate and particular type of alkene RCM process. Mechanistic models that rationalize the origin and the trends in Z selectivity as a function of alterations in the catalyst structure (i.e., Mo vs W and different imido and aryloxide or alkoxide ligands) are provided; we show that reaction time can be critical in retaining the Z selectivity attained not only with MAP complexes but with the original Mo-based bis-alkoxides as well. The W-based catalysts are sufficiently stable to be manipulated in air even with humidity levels of up to 80%; the catalytic Z-selective cyclizations can be performed on gram scale with complex molecule starting materials. PMID:23345004

  18. CARBON DIOXIDE INFLUENCE ON THE THERMAL FORMATION OF COMPLEX ORGANIC MOLECULES IN INTERSTELLAR ICE ANALOGS

    SciTech Connect

    Vinogradoff, V.; Fray, N.; Bouilloud, M.; Cottin, H.; Duvernay, F.; Chiavassa, T.

    2015-08-20

    Interstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complex organic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understand the chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermal evolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde is investigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation of hexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue left after ice sublimation. A better understanding of this result is realized with the study of another ice mixture containing methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, a reaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMT and PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from the warming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed in interstellar ices (H{sub 2}O, NH{sub 3}, CO{sub 2}, H{sub 2}CO). This result strengthens the importance of thermal reactions in the ices’ evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects of our solar system, such as comets and carbonaceous chondrites.

  19. Carbon Dioxide Influence on the Thermal Formation of Complex Organic Molecules in Interstellar Ice Analogs

    NASA Astrophysics Data System (ADS)

    Vinogradoff, V.; Duvernay, F.; Fray, N.; Bouilloud, M.; Chiavassa, T.; Cottin, H.

    2015-08-01

    Interstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complex organic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understand the chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermal evolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde is investigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation of hexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue left after ice sublimation. A better understanding of this result is realized with the study of another ice mixture containing methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, a reaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMT and PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from the warming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed in interstellar ices (H2O, NH3, CO2, H2CO). This result strengthens the importance of thermal reactions in the ices’ evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects of our solar system, such as comets and carbonaceous chondrites.

  20. Geology of the Biwabik Iron Formation and Duluth Complex

    USGS Publications Warehouse

    Jirsa, M.A.; Miller, J.D.; Morey, G.B.

    2008-01-01

    The Biwabik Iron Formation is a ???1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by ???1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. ?? 2007 Elsevier Inc. All rights reserved.

  1. Geology of the Biwabik Iron Formation and Duluth Complex.

    PubMed

    Jirsa, Mark A; Miller, James D; Morey, G B

    2008-10-01

    The Biwabik Iron Formation is a approximately 1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by approximately 1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact.

  2. Photochemical reactions of metal nitrosyl complexes. Mechanisms of NO reactions with biologically relevant metal centers

    DOE PAGES

    Ford, Peter C.

    2001-01-01

    Tmore » he discoveries that nitric oxide (a.k.a. nitrogen monoxide) serves important roles in mammalian bioregulation and immunology have stimulated intense interest in the chemistry and biochemistry of NO and derivatives such as metal nitrosyl complexes. Also of interest are strategies to deliver NO to biological targets on demand. One such strategy would be to employ a precursor which displays relatively low thermal reactivity but is photochemically active to release NO.his proposition led us to investigate laser flash and continuous photolysis kinetics of nitrosyl complexes such as the Roussin's iron-sulfur-nitrosyl cluster anions Fe 2 S 2 ( NO ) 4 2 − and Fe 4 S 3 ( NO ) 7 − and several ruthenium salen and porphyrin nitrosyls.hese include studies using metal-nitrosyl photochemistry as a vehicle for delivering NO to hypoxic cell cultures in order to sensitize γ -radiation damage. Also studied were the rates and mechanisms of NO “on” reactions with model water soluble heme compounds, the ferriheme protein met-myoglobin and various ruthenium complexes using ns laser flash photolysis techniques. An overview of these studies is presented.« less

  3. Reactions in 1,1,1-trifluoroacetone triggered by low energy electrons (0-10 eV): from simple bond cleavages to complex unimolecular reactions.

    PubMed

    Illenberger, Eugen; Meinke, Martina C

    2014-08-21

    The impact of low energy electrons (0-10 eV) to 1,1,1-trifluoroacetone yields a variety of fragment anions which are formed via dissociative electron attachment (DEA) through three pronounced resonances located at 0.8 eV, near 4 eV, and in the energy range 8-9 eV. The fragment ions arise from different reactions ranging from the direct cleavage of one single or double bond (formation of F(-), CF3(-), O(-), (M-H)(-), and M-F)(-)) to remarkably complex unimolecular reactions associated with substantial geometric and electronic rearrangement in the transitory intermediate (formation of OH(-), FHF(-), (M-HF)(-), CCH(-), and HCCO(-). The ion CCH(-), for example, is formed by an excision of unit from the target molecule through the concerted cleavage of four bonds and recombination to H2O within the neutral component of the reaction.

  4. Structure of solvated Fe(CO)5: complex formation during solvation in alcohols.

    PubMed

    Lessing, Joshua; Li, Xiaodi; Lee, Taewoo; Rose-Petruck, Christoph G

    2008-03-20

    The equilibrium structure of iron pentacarbonyl, Fe(CO)5, solvated in various alcohols has been investigated by Fourier transform infrared (FTIR) measurements and density functional theory calculations. This system was studied because it is prototypical of a larger class of monometallic systems, which are electronically saturated but not sterically crowded. Upon solvation, the Fe(CO)5 is not just surrounded by a solvation shell. Instead, solute-solvent complexes are formed with the oxygen of the alcohol oriented toward an axial ligand of the Fe(CO)5 giving a formation energy on the order of -5 kJ/mol. This complexation is not a chemical reaction but rather a "preassembly" of the solute molecules with a single solvent molecule. For instance, at room temperature the interaction between Fe(CO)5 and ethanol results in 87% of all Fe(CO)5 molecules being complexated with a single ethanol molecule. This complexation was found in all the alcohol systems studied in this paper. The stability of these complexes was found to depend on the alcohol chain length and branching. The observed complexation mechanism is accompanied by an electron density shift from the complexed alcohol molecule toward Fe(CO)5 where it induces a dipole moment. The finding that Fe(CO)5 forms a complex with the hydroxyl group of a single solvent molecule might have significant implications for ligand substitution reactions. This implies that ligand substitution reactions do not have to proceed via a dissociative mechanism. Instead, the reaction might proceed through a concerted mechanism with the leaving CO simultaneously being replaced by the incoming alcohol that was complexed to Fe(CO)5 prior to the photoexcitation.

  5. Thermodynamics and kinetics of aqueous ferric phosphate complex formation

    SciTech Connect

    Wilhelmy, R.B.; Patel, R.C.; Matijevic, E.

    1985-09-25

    The equilibria and kinetics of complexation of iron(III) with phosphoric acid (at pH < 2) were studied at 25 and 50/sup 0/C at ionic strength ..mu.. = 2.5 M by using spectrophotometric and stopped-flow techniques. The results are consistent with the formation of two complexes, FeH/sub 2/PO/sub 4//sup 2 +/ and Fe(H/sub 2/PO/sub 4/)/sub 2//sup +/. The second species could only be detected by the analysis of kinetic data. The equilibrium constants, extinction coefficients, rate constants, and activation parameters for the formation of these complexes are given. A mechanism is proposed to account for the observed hydrogen ion dependency of the apparent forward rate constants. 35 references, 8 figures, 6 tables.

  6. Ubisemiquinone is the electron donor for superoxide formation by complex III of heart mitochondria.

    PubMed

    Turrens, J F; Alexandre, A; Lehninger, A L

    1985-03-01

    Much evidence indicates that superoxide is generated from O2 in a cyanide-sensitive reaction involving a reduced component of complex III of the mitochondrial respiratory chain, particularly when antimycin A is present. Although it is generally believed that ubisemiquinone is the electron donor to O2, little experimental evidence supporting this view has been reported. Experiments with succinate as electron donor in the presence of antimycin A in intact rat heart mitochondria, which contain much superoxide dismutase but little catalase, showed that myxothiazol, which inhibits reduction of the Rieske iron-sulfur center, prevented formation of hydrogen peroxide, determined spectrophotometrically as the H2O2-peroxidase complex. Similarly, depletion of the mitochondria of their cytochrome c also inhibited formation of H2O2, which was restored by addition of cytochrome c. These observations indicate that factors preventing the formation of ubisemiquinone also prevent H2O2 formation. They also exclude ubiquinol, which remains reduced under these conditions, as the reductant of O2. Since cytochrome b also remains fully reduced when myxothiazol is added to succinate- and antimycin A-supplemented mitochondria, reduced cytochrome b may also be excluded as the reductant of O2. These observations, which are consistent with the Q-cycle reactions, by exclusion of other possibilities leave ubisemiquinone as the only reduced electron carrier in complex III capable of reducing O2 to O2-.

  7. Asymmetric hollow nanorod formation through a partial galvanic replacement reaction.

    PubMed

    Seo, Daeha; Song, Hyunjoon

    2009-12-30

    An asymmetric single hollow structure was generated from Ag-Au-Ag heterometal nanorods by a partial galvanic replacement reaction for the first time. The C(2)-symmetry breaking took place because of the random generation of a single pit on only one end of the silver domain at an early stage of the reaction. Careful control of the reaction kinetics could also yield a double-hollow structure on both ends of the silver domain. The resulting single- and double-hollow nanorods exhibited characteristic extinctions in the near-IR range.

  8. Reversible dissociation and ligand-glutathione exchange reaction in binuclear cationic tetranitrosyl iron complex with penicillamine.

    PubMed

    Syrtsova, Lidia; Sanina, Natalia; Lyssenko, Konstantin; Kabachkov, Evgeniy; Psikha, Boris; Shkondina, Natal'ja; Pokidova, Olesia; Kotelnikov, Alexander; Aldoshin, Sergey

    2014-01-01

    This paper describes a comparative study of the decomposition of two nitrosyl iron complexes (NICs) with penicillamine thiolic ligands [Fe2(SC5H11NO2)2(NO)4]SO4 ·5H2O (I) and glutathione- (GSH-) ligands [Fe2(SC10H17N3O6)2(NO)4]SO4 ·2H2O (II), which spontaneously evolve to NO in aqueous medium. NO formation was measured by a sensor electrode and by spectrophotometric methods by measuring the formation of a hemoglobin- (Hb-) NO complex. The NO evolution reaction rate from (I)  k 1 = (4.6 ± 0.1)·10(-3) s(-1) and the elimination rate constant of the penicillamine ligand k 2 = (1.8 ± 0.2)·10(-3) s(-1) at 25°C in 0.05 M phosphate buffer,  pH 7.0, was calculated using kinetic modeling based on the experimental data. Both reactions are reversible. Spectrophotometry and mass-spectrometry methods have firmly shown that the penicillamine ligand is exchanged for GS(-) during decomposition of 1.5·10(-4) M (I) in the presence of 10(-3) M GSH, with 76% yield in 24 h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron to GSH in the complex. The discovered reaction may impede S-glutathionylation of the essential enzyme systems in the presence of (I) and is important for metabolism of NIC, connected with its antitumor activity.

  9. Chiral bis(oxazoline) copper(II) complexes: versatile catalysts for enantioselective cycloaddition, Aldol, Michael, and carbonyl ene reactions.

    PubMed

    Johnson, J S; Evans, D A

    2000-06-01

    A bis(oxazoline) (box) copper(II) complex and its hydrated counterpart (1 and 2) function as enantioselective Lewis acid catalysts for carbocyclic and hetero Diels-Alder, aldol, Michael, ene, and amination reactions with substrates capable of chelation through six- and five-membered rings. X-ray crystallography of the chiral complexes reveals a propensity for the formation of distorted square planar or square pyramidal geometries. The sense of asymmetric induction is identical for all the processes catalyzed by [Cu((S,S)-t-Bu-box)](X)(2) complexes 1 and 2 (X = OTf and SbF) resulting from the intervention of a distorted square planar catalyst-substrate binary complex. These catalyzed processes exhibit excellent temperature-selectivity profiles. Reactions catalyzed by [Cu(S,S-Ph-pybox)](SbF(6))(2) and their derived chelation complexes are also discussed.

  10. Thermodynamics and Complexation Reactions of Anionic Silicate Species

    SciTech Connect

    Choppin, Gregory R.; Felmy, Andrew R.

    2001-06-01

    Highly basic tank wastes contain several important radionuclides, including {sup 90}Sr, {sup 99}Tc, and {sup 60}Co as well as actinide elements (isotopes of U, Pu and Am). A fraction of these wastes are known to have leaked into the vadose zone at the Hanford Site. Upon entering the sediments in the vadose zone, such highly basic solutions dissolve concentrations of silica from the silica and aluminosilicate minerals present in subsurface. These dissolution reactions alter the chemical composition of the leaking solutions, transforming them from highly basic (as high as 2 M NaOH) solution into a pore solution with dissolved silica and significantly reduced pH. This moderately basic (pH 9 to 10), high-silica solution has the potential to complex radionuclides and promote migration through the subsurface. This path of radionuclide migration currently is not a recognized transport mode in the factors that are modeled for radionuclide transport through the vadose zone beneath leaking tanks. The goal of this project is to ascertain the free monosilicic acid concentration, and the degree of polymerization as a function of pH and total concentration of silicate ions, and to use this data to measure the interaction of radionuclides of Co(II), Sr(II), Nd(III), Eu(III), Am(III), U(VI) and Th(IV) with the ionic silicate.

  11. Positronium formation studies in crystalline molecular complexes: Triphenylphosphine oxide - Acetanilide

    NASA Astrophysics Data System (ADS)

    Oliveira, F. C.; Denadai, A. M. L.; Guerra, L. D. L.; Fulgêncio, F. H.; Windmöller, D.; Santos, G. C.; Fernandes, N. G.; Yoshida, M. I.; Donnici, C. L.; Magalhães, W. F.; Machado, J. C.

    2013-04-01

    Hydrogen bond formation in the triphenylphosphine oxide (TPPO), acetanilide (ACN) supramolecular heterosynton system, named [TPPO0.5·ACN0.5], has been studied by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques. In toluene solution, Isothermal Titration Calorimetry (ITC) presented a 1:1 stoichiometry and indicated that the complexation process is driven by entropy, with low enthalpy contribution. X-ray structure determination showed the existence of a three-dimensional network of hydrogen bonds, allowing also the confirmation of the existence of a 1:1 crystalline molecular complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complex are relatively weaker than those found in pure precursors, leading to a higher positronium formation probability at [TPPO0.5·ACN0.5]. These weak interactions in the complex enhance the possibility of the n- and π-electrons to interact with positrons and consequently, the probability of positronium formation is higher. Through the present work is shown that PALS is a sensible powerful tool to investigate intermolecular interactions in solid heterosynton supramolecular systems.

  12. Associative and dissociative mechanisms in the formation of phthalazine bridged organodiplatinum(II) complexes.

    PubMed

    Rashidi, Mehdi; Nabavizadeh, S Masoud; Zare, Ahad; Jamali, Sirous; Puddephatt, Richard J

    2010-09-20

    The reaction of phthalazine with the binuclear organoplatinum complexes [Me(2)Pt(μ-SMe(2))(μ-dppm)PtR(2)], R = Me, Ph, 4-tolyl or R(2) = (CH(2))(4), dppm = bis(diphenylphosphino)methane, gives the corresponding complexes [Me(2)Pt(μ-phthalazine)(μ-dppm)PtR(2)] by displacement of the bridging dimethylsulfide ligand. The structures of [Me(2)Pt(μ-SMe(2))(μ-dppm)PtMe(2)] and [Me(2)Pt(μ-phthalazine)(μ-dppm)PtMe(2)] have been determined. Kinetic studies show that the reactions occur mostly by a second order reaction when R = Me or R(2) = (CH(2))(4) but entirely by a first order reaction when R = Ph or 4-tolyl. Evidence is presented that the reactions when R = Me or R(2) = (CH(2))(4) can occur by either associative or dissociative mechanisms but that the reactions when R = Ph or 4-tolyl occur only by an unusual dissociative mechanism involving formation of an intermediate with a donor-acceptor Pt-Pt bond.

  13. Complexation Key to a pH Locked Redox Reaction

    ERIC Educational Resources Information Center

    Rizvi, Masood Ahmad; Dangat, Yuvraj; Shams, Tahir; Khan, Khaliquz Zaman

    2016-01-01

    An unfavorable pH can block a feasible electron transfer for a pH dependent redox reaction. In this experiment, a series of potentiometric titrations demonstrate the sequential loss in feasibility of iron(II) dichromate redox reaction over a pH range of 0-4. The pH at which this reaction failed to occur was termed as a pH locked reaction. The…

  14. Pattern Formation and Reaction Textures during Dunite Carbonation

    NASA Astrophysics Data System (ADS)

    Lisabeth, H. P.; Zhu, W.

    2015-12-01

    Alteration of olivine-bearing rocks by fluids is one of the most pervasive geochemical processes on the surface of the Earth. Serpentinized and/or carbonated ultramafic rocks often exhibit characteristic textures on many scales, from polygonal mesh textures on the grain-scale to onion-skin or kernel patterns on the outcrop scale. Strong disequilibrium between pristine ultramafic rocks and common geological fluids such as water and carbon dioxide leads to rapid reactions and coupled mechanical and chemical feedbacks that manifest as characteristic textures. Textural evolution during metasomatic reactions can control effective reaction rates by modulating dynamic porosity and therefore reactant supply and reactive surface area. We run hydrostatic experiments on thermally cracked dunites saturated with carbon dioxide bearing brine at 15 MPa confining pressure and 150°C to explore the evolution of physical properties and reaction textures as carbon mineralization takes place in the sample. Compaction and permeability reduction are observed throughout experiments. Rates of porosity and permeability changes are sensitive to pore fluid chemistry. After reaction, samples are imaged in 3-dimension (3D) using a dual-beam FIB-SEM. Analysis of the high resolution 3D microstructure shows that permeable, highly porous domains are created by olivine dissolution at a characteristic distance from pre-existing crack surfaces while precipitation of secondary minerals such as serpentine and magnesite is limited largely to the primary void space. The porous dissolution channels provide an avenue for fluid ingress, allow reactions to continue and could lead to progressive hierarchical fracturing. Initial modeling of the system indicates that this texture is the result of coupling between dissolution-precipitation reactions and the local stress state of the sample.

  15. Accelerating procelain formation by incorporating a complex additive

    SciTech Connect

    Maslennikova, G.N.; Dubovitskii, S.A.; Moroz, I.K.

    1986-05-01

    The authors studied the influence of a complex additive consisting of oxides of calcium, zinc, and magnesium on the formaton of porcelain. In order to achieve a more uniform distribution of the complex additive in the porcelain body it was incorporated in the form of water soluble salts-nitrates, which ensured comparability of results and excluded the effect of the different types of anions. The study of the main parameters of sintering (porosity, shrinkage, and mechanical strength) for the test bodies showed that they sinter at lower temperatures and attain zero porosity, maximum shrinkage, and mechanical strength. The most typical bodies indentified in this way were investigated by methods of complex differential thermal analysis and x-ray diffraction. Thus, the introduction of complex additives consisting of calcium, zinc, and magnesium oxides contributes to the earlier formation of porcelain. With the reduction of firing temperatures by 100/sup 0/C the authors observe an improvement in the basic properties of porcelain.

  16. Reaction path and crystallograpy of cobalt silicide formation on silicon(001) by reaction deposition epitaxy

    NASA Astrophysics Data System (ADS)

    Lim, Chong Wee

    CaF2-structure CoSi2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi2 layers obtained by conventional solid phase growth (SPG). In the case of RDE, CoSi 2 formation occurred during Co deposition at elevated temperature while for SPG, Co was deposited at 25°C and silicidation took place during subsequent annealing. My results demonstrate that RDE CoSi2 layers are epitaxial with a cube-on-cube relationship, 001CoSi2 ‖001Si and 100CoSi2 ‖100 Si . In contrast, SPG films are polycrystalline with a mixed 111/002/022/112 orientation. I attribute the striking difference to rapid Co diffusion during RDE for which the high Co/Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. Initial formation of CoSi2(001) follows the Volmer-Weber mode with two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal <110> directions, bounded by four {111} CoSi2/Si interfaces, and grow with a cube-on-cube orientation with respect to Si(001). Platelet-shaped islands are bounded across their long <110> directions by {111} twin planes and their narrow <110> directions by 511CoSi2 ‖111Si interfaces. The top and bottom surfaces are {22¯1}, with 22¯1 CoSi2‖001 Si , and {1¯1¯1}, with 1¯1¯ 1CoSi2‖ 11¯1Si , respectively. The early stages of film growth (tCo ≤ 13 A) are dominated by the twinned platelets due to a combination of higher nucleation rates and rapid elongation along preferred <110> directions. However, at tCo ≥ 13 A, island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. Further island growth becomes dominated by the untwinned islands. I show that high-flux low-energy Ar+ ion irradiation during RDE growth dramatically increases the area fraction of untwinned regions from 0.17 in films grown under standard magnetically balanced

  17. Computational Analyses of Complex Flows with Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Bae, Kang-Sik

    missiles. The comprehensive skeletal mechanism consists of 58 species and 315 reactions including in CPD, Benzene formation process by the theory for polycyclic aromatic hydrocarbons (PAH) and soot formation process on the constant volume combustor, premixed flame characteristics.

  18. Rosette: Understanding Star Formation in Molecular Cloud Complexes

    NASA Astrophysics Data System (ADS)

    Wang, Junfeng

    2010-09-01

    We propose Chandra imaging of three embedded clusters in the Rosette Molecular Cloud (RMC) complex. With complementary existing Spitzer and FLAMINGOS infrared surveys, the Chandra observation is critical for us to: (1) create a complete census of the young stars in the cloud; (2) study the spatial distribution of the young stars in different evolutionary stages within the RMC and the disk frequency in the embedded clusters; (3) construct X-ray Luminosity Function (XLF) and Initial Mass Function (IMF) for the clusters to examine XLF/IMF variations; (4) elucidate star formation history in this complex.

  19. The Copper-nicotinamide complex: sustainable applications in coupling and cycloaddition reactions

    EPA Science Inventory

    Crystalline copper (II)-nicotinamide complex, synthesized via simple mixing of copper chloride and nicotinamide solution at room temperature, catalyzes the C-S, C-N bond forming and cycloaddition reactions under a variety of sustainable reaction conditions.

  20. Gel phase formation in dilute triblock copolyelectrolyte complexes

    NASA Astrophysics Data System (ADS)

    Srivastava, Samanvaya; Andreev, Marat; Levi, Adam E.; Goldfeld, David J.; Mao, Jun; Heller, William T.; Prabhu, Vivek M.; de Pablo, Juan J.; Tirrell, Matthew V.

    2017-02-01

    Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (<1% by mass) has been observed in scattering experiments and molecular dynamics simulations. Here we show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously on solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chain aggregates in early stages of copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Our discoveries contribute to the fundamental understanding of the structure and pathways of complexation-driven assemblies, and raise intriguing prospects for gel formation at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics.

  1. Gel phase formation in dilute triblock copolyelectrolyte complexes

    PubMed Central

    Srivastava, Samanvaya; Andreev, Marat; Levi, Adam E.; Goldfeld, David J.; Mao, Jun; Heller, William T.; Prabhu, Vivek M.; de Pablo, Juan J.; Tirrell, Matthew V.

    2017-01-01

    Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (<1% by mass) has been observed in scattering experiments and molecular dynamics simulations. Here we show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously on solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chain aggregates in early stages of copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Our discoveries contribute to the fundamental understanding of the structure and pathways of complexation-driven assemblies, and raise intriguing prospects for gel formation at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics. PMID:28230046

  2. An Investigation of Model Catalyzed Hydrocarbon Formation Reactions

    SciTech Connect

    Tysoe, W. T.

    2001-05-02

    Work was focused on two areas aimed at understanding the chemistry of realistic catalytic systems: (1) The synthesis and characterization of model supported olefin metathesis catalysts. (2) Understanding the role of the carbonaceous layer present on Pd(111) single crystal model catalysts during reaction.

  3. Reactivity of a Ruthenium–Carbonyl Complex in the Methanol Dehydrogenation Reaction

    PubMed Central

    van de Watering, Fenna F.; Lutz, Martin; Dzik, Wojciech I.; de Bruin, Bas

    2016-01-01

    Abstract Finding new catalysts for the release of molecular hydrogen from methanol is of high relevance in the context of the development of sustainable energy carriers. Herein, we report that the ruthenium complex Ru(salbinapht)(CO)(Pi‐Pr3) {salbinapht=2‐[({2′‐[(2‐hydroxybenzyl)amino]‐[1,1′‐binaphthalen]‐2‐yl}imino)methyl]phenolato} (2) catalyzes the methanol dehydrogenation reaction in the presence of base and water to yield H2, formate, and carbonate. Dihydrogen is the only gas detected and a turnover frequency up to 55 h−1 at 82 °C is reached. Complex 2 bears a carbonyl ligand that is derived from methanol, as is demonstrated by labeling experiments. The carbonyl ligand can be treated with base to form formate (HCOO−) and hydrogen. The nature of the active species is further shown not to contain a CO ligand but likely still possesses a salen‐derived ligand. During catalysis, formation of Ru(CO)2(H)2(P‐iPr3)2 is occasionally observed, which is also an active methanol dehydrogenation catalyst. PMID:27917245

  4. Demixing-stimulated lane formation in binary complex plasma

    SciTech Connect

    Du, C.-R.; Jiang, K.; Suetterlin, K. R.; Ivlev, A. V.; Morfill, G. E.

    2011-11-29

    Recently lane formation and phase separation have been reported for experiments with binary complex plasmas in the PK3-Plus laboratory onboard the International Space Station (ISS). Positive non-additivity of particle interactions is known to stimulate phase separation (demixing), but its effect on lane formation is unknown. In this work, we used Langevin dynamics (LD) simulation to probe the role of non-additivity interactions on lane formation. The competition between laning and demixing leads to thicker lanes. Analysis based on anisotropic scaling indices reveals a crossover from normal laning mode to a demixing-stimulated laning mode. Extensive numerical simulations enabled us to identify a critical value of the non-additivity parameter {Delta} for the crossover.

  5. The Dynamics of Coalition Formation on Complex Networks

    NASA Astrophysics Data System (ADS)

    Auer, S.; Heitzig, J.; Kornek, U.; Schöll, E.; Kurths, J.

    2015-08-01

    Complex networks describe the structure of many socio-economic systems. However, in studies of decision-making processes the evolution of the underlying social relations are disregarded. In this report, we aim to understand the formation of self-organizing domains of cooperation (“coalitions”) on an acquaintance network. We include both the network’s influence on the formation of coalitions and vice versa how the network adapts to the current coalition structure, thus forming a social feedback loop. We increase complexity from simple opinion adaptation processes studied in earlier research to more complex decision-making determined by costs and benefits, and from bilateral to multilateral cooperation. We show how phase transitions emerge from such coevolutionary dynamics, which can be interpreted as processes of great transformations. If the network adaptation rate is high, the social dynamics prevent the formation of a grand coalition and therefore full cooperation. We find some empirical support for our main results: Our model develops a bimodal coalition size distribution over time similar to those found in social structures. Our detection and distinguishing of phase transitions may be exemplary for other models of socio-economic systems with low agent numbers and therefore strong finite-size effects.

  6. Chiral symmetry breaking in complex chemical systems during formation of life on earth

    NASA Astrophysics Data System (ADS)

    Konstantinova, A. F.; Konstantinov, K. K.

    2015-09-01

    The chiral symmetry in complex chemical systems containing many amino acids and characterized by many similar chemical reactions (a situation corresponding to the formation of life on Earth) is considered. It is shown that effective averaging over similar reaction channels may lead to very weak effective enantioselectivity, which does not allow for chiral symmetry breaking in most known models. A class of models with simple and catalytic synthesis of one amino acid, the formation of peptides with a length reaching three, and the precipitation of one insoluble pair of materials is analyzed. It is proven that chiral symmetry breaking may occur in one possible version from an insoluble pair of materials even in the complete absence of catalytic synthesis of amino acid. It is shown that the presence of weakly enantioselective catalytic synthesis in a model significantly increases the number of possible versions in which chiral symmetry breaks.

  7. Synthesis and hydride transfer reactions of cobalt and nickel hydride complexes to BX3 compounds.

    PubMed

    Mock, Michael T; Potter, Robert G; O'Hagan, Molly J; Camaioni, Donald M; Dougherty, William G; Kassel, W Scott; DuBois, Daniel L

    2011-12-05

    Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H(2) gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe)(2) (dmpe = 1,2-bis(dimethylphosphinoethane)) was capable of reducing a variety of BX(3) compounds having a hydride affinity (HA) greater than or equal to the HA of BEt(3). This study examines the reactivity of less expensive cobalt and nickel hydride complexes, HCo(dmpe)(2) and [HNi(dmpe)(2)](+), to form B-H bonds. The hydride donor abilities (ΔG(H(-))°) of HCo(dmpe)(2) and [HNi(dmpe)(2)](+) were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX(3) compounds. The collective data guided our selection of BX(3) compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe)(2) was observed to transfer H(-) to BX(3) compounds with X = H, OC(6)F(5), and SPh. The reaction with B(SPh)(3) is accompanied by the formation of dmpe-(BH(3))(2) and dmpe-(BH(2)(SPh))(2) products that follow from a reduction of multiple B-SPh bonds and a loss of dmpe ligands from cobalt. Reactions between HCo(dmpe)(2) and B(SPh)(3) in the presence of triethylamine result in the formation of Et(3)N-BH(2)SPh and Et(3)N-BH(3) with no loss of a dmpe ligand. Reactions of the cationic complex [HNi(dmpe)(2)](+) with B(SPh)(3) under analogous conditions give Et(3)N-BH(2)SPh as the final product along with the nickel-thiolate complex [Ni(dmpe)(2)(SPh)](+). The synthesis and characterization of HCo(dedpe)(2) (dedpe = Et(2)PCH(2)CH(2)PPh(2)) from H(2) and a base is also discussed, including the formation of an uncommon trans dihydride species, trans-[(H)(2)Co(dedpe)(2)][BF(4)].

  8. Synthesis and Hydride Transfer Reactions of Cobalt and Nickel Hydride Complexes to BX₃ Compounds

    SciTech Connect

    Mock, Michael T.; Potter, Robert G.; O'Hagan, Molly; Camaioni, Donald M.; Dougherty, William G.; Kassel, W. Scott; DuBois, Daniel L.

    2011-10-31

    Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H₂ gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe)₂ (dmpe = 1,2-bis(dimethylphosphinoethane)) was capable of reducing a variety of BX₃ compounds having a hydride affinity (HA) greater than or equal to the HA of BEt₃. This study examines the reactivity of less expensive cobalt and nickel hydride complexes, HCo(dmpe)₂ and [HNi(dmpe)₂]+, to form B–H bonds. The hydride donor abilities (ΔGH °) of HCo(dmpe)₂ and [HNi(dmpe)₂]+ were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX₃ compounds. The collective data guided our selection of BX₃ compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe)₂ was observed to transfer H to BX₃ compounds with X = H, OC₆F₅, and SPh. The reaction with B(SPh)₃ is accompanied by the formation of dmpe-(BH₃)₂ and dmpe-(BH₂(SPh))₂ products that follow from a reduction of multiple B–SPh bonds and a loss of dmpe ligands from cobalt. Reactions between HCo(dmpe)₂ and B(SPh)₃ in the presence of triethylamine result in the formation of Et₃N–BH₂SPh and Et₃N–BH₃ with no loss of a dmpe ligand. Reactions of the cationic complex [HNi(dmpe)₂]+ with B(SPh)₃ under analogous conditions give Et₃N–BH₂SPh as the final product along with the nickel–thiolate complex [Ni(dmpe)₂(SPh)]+. The synthesis and characterization of HCo(dedpe)₂ (dedpe = Et₂PCH₂CH₂PPh₂) from H₂ and a base is also discussed, including the formation of an uncommon trans dihydride species, trans-[(H)₂Co(dedpe)₂][BF₄].

  9. Synthesis and Hydride Transfer Reactions of Cobalt and Nickel Hydride Complexes to BX3 Compounds

    SciTech Connect

    Mock, Michael T.; Potter, Robert G.; O'Hagan, Molly J.; Camaioni, Donald M.; Dougherty, William G.; Kassel, W. S.; DuBois, Daniel L.

    2011-12-05

    Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H{sub 2} gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe){sub 2}, dmpe = 1,2-bis(dimethylphosphinoethane) was capable of reducing a variety of BX{sub 3} compounds having hydride affinity (HA) greater than or equal to HA of BEt{sub 3}. This study examines the reactivity of less expensive cobalt and nickel hydride complexes, (HCo(dmpe){sub 2} and [HNi(dmpe){sub 2}]{sup +}), to form B-H bonds. The hydride donor abilities ({Delta}G{sub H{sup -}}{sup o}) of HCo(dmpe){sub 2} and [HNi(dmpe){sub 2}]{sup +} were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX{sub 3} compounds. The collective data guided our selection of BX{sub 3} compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe){sub 2} was observed to transfer H{sup -} to BX{sub 3} compounds with X = H, OC{sub 6}F{sub 5} and SPh. The reaction with B(SPh){sub 3} is accompanied by formation of (BH{sub 3}){sub 2}-dmpe and (BH{sub 2}SPh){sub 2}-dmpe products that follow from reduction of multiple BSPh bonds and loss of a dmpe ligand from Co. Reactions between HCo(dmpe){sub 2} and B(SPh){sub 3} in the presence of triethylamine result in formation of Et{sub 3}N-BH{sub 2}SPh and Et{sub 3}N-BH{sub 3} with no loss of dmpe ligand. Reactions of the cationic complex [HNi(dmpe){sub 2}]{sup +} with B(SPh){sub 3} under analogous conditions give Et{sub 3}N-BH{sub 2}SPh as the final product along with the nickel-thiolate complex [Ni(dmpe){sub 2}(SPh)]{sup +}. The synthesis and characterization of HCo(dedpe){sub 2} (dedpe = diethyldiphenyl(phosphino)ethane) from H{sub 2} and a base is also discussed; including the formation of an uncommon trans

  10. Heat capacity contributions to the formation of inclusion complexes.

    PubMed

    Olvera, Angeles; Pérez-Casas, Silvia; Costas, Miguel

    2007-10-04

    An analysis scheme for the formation of the inclusion complexes in water is presented. It is exemplified for the case where the host is alpha-cyclodextrin and the guest is a linear alcohol (1-propanol to 1-octanol) or the isomers of 1-pentanol. Eight transfer isobaric heat capacities, DeltatCp, involving different initial and final states are evaluated at infinite dilution of the guest using both data determined in this work and from the literature. Apart from the usual definition for the inclusion heat capacity change, three inclusion transfers are used. The sign of each DeltatCp indicates if the transfer is an order-formation or an order-destruction process. From the DeltatCp data, the main contributions to the heat capacity of cyclodextrin complexation, namely, those due to dehydration of the hydrophobic section of the guest molecule, H-bond formation, formation of hydrophobic interactions, and release of water molecules from the cyclodextrin cavity, are estimated. The relative weight of each of these contributions to the DeltatCp values is discussed, providing a better characterization of the molecular recognition process involved in the inclusion phenomena.

  11. EXFOR BASICS A SHORT GUIDE TO THE NEUTRON REACTION DATA EXCHANGE FORMAT.

    SciTech Connect

    MCLANE,V.; NUCLEAR DATA CENTER NETWORK

    2000-05-19

    This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear reaction data between the Nuclear Reaction Data Centers. In addition to storing the data and its' bibliographic information, experimental information is also compiled. The status (e.g., the source of the data) and history (e.g., date of last update) of the data set is also included. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear reaction data centers. It was originally conceived for the exchange of neutron data and was developed through discussions among personnel from centers situated in Saclay, Vienna, Livermore and Brookhaven. It was accepted as the official exchange format of the neutron data centers at Saclay, Vienna, Brookhaven and Obninsk, at a meeting held in November 1969.3 As a result of two meetings held in 1975 and 1976 and attended by several charged-particle data centers, the format was further developed and adapted to cover all nuclear reaction data. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center's own sphere of responsibility. The EXFOR format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in a format: l that is machine-readable (for checking and indicating possible errors); l that can be read by personnel (for passing judgment on and correcting errors). The data presently included in the EXFOR exchange file include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle-induced reaction data, a selected compilation of photon-induced reaction data.

  12. EXFOR BASICS A SHORT GUIDE TO THE NEUTRON REACTION DATA EXCHANGE FORMAT.

    SciTech Connect

    MCLANE,V.; NUCLEAR DATA CENTER NETWORK

    2000-05-19

    This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear reaction data between the Nuclear Reaction Data Centers. In addition to storing the data and its' bibliographic information, experimental information is also compiled. The status (e.g., the source of the data) and history (e.g., date of last update) of the data set is also included. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear reaction data centers. It was originally conceived for the exchange of neutron data and was developed through discussions among personnel from centers situated in Saclay, Vienna, Livermore and Brookhaven. It was accepted as the official exchange format of the neutron data centers at Saclay, Vienna, Brookhaven and Obninsk, at a meeting held in November 1969. As a result of two meetings held in 1975 and 1976 and attended by several charged-particle data centers, the format was further developed and adapted to cover all nuclear reaction data. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center's own sphere of responsibility. The EXFOR format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in a format: that is machine-readable (for checking and indicating possible errors); that can be read by personnel (for passing judgment on and correcting errors). The data presently included in the EXFOR exchange file include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle-induced reaction data, a selected compilation of photon-induced reaction data.

  13. Segrosome Complex Formation during DNA Trafficking in Bacterial Cell Division.

    PubMed

    Oliva, María A

    2016-01-01

    Bacterial extrachromosomal DNAs often contribute to virulence in pathogenic organisms or facilitate adaptation to particular environments. The transmission of genetic information from one generation to the next requires sufficient partitioning of DNA molecules to ensure that at least one copy reaches each side of the division plane and is inherited by the daughter cells. Segregation of the bacterial chromosome occurs during or after replication and probably involves a strategy in which several protein complexes participate to modify the folding pattern and distribution first of the origin domain and then of the rest of the chromosome. Low-copy number plasmids rely on specialized partitioning systems, which in some cases use a mechanism that show striking similarity to eukaryotic DNA segregation. Overall, there have been multiple systems implicated in the dynamic transport of DNA cargo to a new cellular position during the cell cycle but most seem to share a common initial DNA partitioning step, involving the formation of a nucleoprotein complex called the segrosome. The particular features and complex topologies of individual segrosomes depend on both the nature of the DNA binding protein involved and on the recognized centromeric DNA sequence, both of which vary across systems. The combination of in vivo and in vitro approaches, with structural biology has significantly furthered our understanding of the mechanisms underlying DNA trafficking in bacteria. Here, I discuss recent advances and the molecular details of the DNA segregation machinery, focusing on the formation of the segrosome complex.

  14. Nanoparticle-protein complexes mimicking corona formation in ocular environment.

    PubMed

    Jo, Dong Hyun; Kim, Jin Hyoung; Son, Jin Gyeong; Dan, Ki Soon; Song, Sang Hoon; Lee, Tae Geol; Kim, Jeong Hun

    2016-12-01

    Nanoparticles adsorb biomolecules to form corona upon entering the biological environment. In this study, tissue-specific corona formation is provided as a way of controlling protein interaction with nanoparticles in vivo. In the vitreous, the composition of the corona was determined by the electrostatic and hydrophobic properties of the associated proteins, regardless of the material (gold and silica) or size (20- and 100-nm diameter) of the nanoparticles. To control protein adsorption, we pre-incubate 20-nm gold nanoparticles with 5 selectively enriched proteins from the corona, formed in the vitreous, to produce nanoparticle-protein complexes. Compared to bare nanoparticles, nanoparticle-protein complexes demonstrate improved binding to vascular endothelial growth factor (VEGF) in the vitreous. Furthermore, nanoparticle-protein complexes retain in vitro anti-angiogenic properties of bare nanoparticles. In particular, priming the nanoparticles (gold and silica) with tissue-specific corona proteins allows nanoparticle-protein complexes to exert better in vivo therapeutic effects by higher binding to VEGF than bare nanoparticles. These results suggest that controlled corona formation that mimics in vivo processes may be useful in the therapeutic use of nanomaterials in local environment.

  15. Mercury(II) Penicillamine Complex Formation in Alkaline Aqueous Solution

    SciTech Connect

    Leung, B.O.; Jalilehvand, F.; Mah, V.

    2009-06-01

    The complex formation between mercury(II) and penicillamine (H{sub 2}Pen = 3,3'-dimethyl cysteine) in alkaline aqueous solutions (pH {approx}2) has been investigated with extended X-ray absorption fine structure (EXAFS) and {sup 199}Hg NMR spectroscopy. By varying the penicillamine concentration (C{sub H{sub 2}Pen} = 0.2--1.25 M) in {approx}0.1 M Hg(II) solutions, two coexisting major species [Hg(Pen){sub 2}]{sup 2-} and [Hg(Pen){sub 3}]{sub 4-} were characterized with mean Hg-S bond distances 2.34(2) and 2.44(2) {angstrom}, respectively. The [Hg(Pen){sub 2}]{sup 2-} complex with two deprotonated penicillamine ligands forms an almost linear S-Hg-S entity with two weak chelating Hg-N interactions at the mean Hg-N distance 2.52(2) {angstrom}. The same type of coordination is also found for the corresponding [Hg(Cys){sub 2}]{sup 2-} complex in alkaline aqueous solution with the mean bond distances Hg-S 2.34(2) {angstrom} and Hg-N 2.56(2) {angstrom}. The relative amounts of the [Hg(Pen){sub 2}]{sup 2-} and [Hg(Pen){sub 3}]{sup 4-} complexes were estimated by fitting linear combinations of the EXAFS oscillations to the experimental spectra. Also their {sup 199}Hg NMR chemical shifts were used to evaluate the complex formation, showing that the [Hg(Pen){sub 3}]{sup 4-} complex dominates already at moderate excess of the free ligand ([Pen{sup 2-}] > {approx} 0.1 M).

  16. Protein-Templated Formation of an Inhibitor of the Blood Coagulation Factor Xa through a Background-Free Amidation Reaction.

    PubMed

    Jaegle, Mike; Steinmetzer, Torsten; Rademann, Jörg

    2017-03-20

    Protein-templated reactions enable the target-guided formation of protein ligands from reactive fragments, ideally with no background reaction. Herein, we investigate the templated formation of amides. A nucleophilic fragment that binds to the coagulation factor Xa was incubated with the protein and thirteen differentially activated dipeptides. The protein induced a non-catalytic templated reaction for the phenyl and trifluoroethyl esters; the latter was shown to be a completely background-free reaction. Starting from two fragments with millimolar affinity, a 29 nm superadditive inhibitor of factor Xa was obtained. The fragment ligation reaction was detected with high sensitivity by an enzyme activity assay and by mass spectrometry. The reaction progress and autoinhibition of the templated reaction by the formed ligation product were determined, and the structure of the protein-inhibitor complex was elucidated.

  17. Protein‐Templated Formation of an Inhibitor of the Blood Coagulation Factor Xa through a Background‐Free Amidation Reaction

    PubMed Central

    Jaegle, Mike; Steinmetzer, Torsten

    2017-01-01

    Abstract Protein‐templated reactions enable the target‐guided formation of protein ligands from reactive fragments, ideally with no background reaction. Herein, we investigate the templated formation of amides. A nucleophilic fragment that binds to the coagulation factor Xa was incubated with the protein and thirteen differentially activated dipeptides. The protein induced a non‐catalytic templated reaction for the phenyl and trifluoroethyl esters; the latter was shown to be a completely background‐free reaction. Starting from two fragments with millimolar affinity, a 29 nm superadditive inhibitor of factor Xa was obtained. The fragment ligation reaction was detected with high sensitivity by an enzyme activity assay and by mass spectrometry. The reaction progress and autoinhibition of the templated reaction by the formed ligation product were determined, and the structure of the protein–inhibitor complex was elucidated. PMID:28199769

  18. Formation and Stability of Manganese-Desferrioxamine B Complexes

    NASA Astrophysics Data System (ADS)

    Duckworth, O. W.; Sposito, G.

    2004-12-01

    Recent laboratory and field studies suggest that Mn(III) forms persistent aqueous complexes with high-affinity ligands, particularly those produced by microbes. Aqueous Mn(III) species thus may play a significant, as-yet largely unexplored role in biogeochemical processes. We determined stability constants for both Mn(II) and Mn(III) complexes with the common tri-hydroxamate siderophore, desferrioxamine B (DFOB). We found the thermodynamic stability constants of the species, MHDFOBx-2 [M = Mn(II), x = 2; M = Mn(III), x = 3] to be KMn(II) = 106.8 ± 0.1 and KMn(III) = 1029.2 ± 0.2 at 25° C. The Mn(III)HDFOB+ complex is stable for pH in the range 7.0 - 11.3, but at pH < 7.0, Mn(III)HDFOB+ decays by internal electron transfer, yielding oxidized DFOB products and Mn2+. For pH > 11.3, the complex decays by disproportionation, yielding Mn2+ and solid MnO2. The Mn(III)HDFOB+ complex may be formed by either the oxidation of aqueous Mn(II)-HDFOB complexes or the DFOB-promoted dissolution of solid manganese(III) oxides. The DFOB-promoted Mn(II) air-oxidation rate was found to be proportional to the concentration of Mn(II)-DFOB complexes. At pH > 6.5, the dissolution of manganite (γ -MnOOH) in the presence of DFOB is predominantly a non-reductive ligand-promoted reaction whose rate is proportional to the adsorbed surface concentration of DFOB. At pH < 6.5, Mn2+ is the dominant species resulting from manganite dissolution, thus implicating a reductive dissolution pathway. The results of this study have broad implications for the biogeochemical cycling of manganese, redox-active elements, and siderophores in natural waters and soils.

  19. Apparent anti-Woodward-Hoffmann addition to a nickel bis(dithiolene) complex: the reaction mechanism involves reduced, dimetallic intermediates.

    PubMed

    Dang, Li; Shibl, Mohamed F; Yang, Xinzheng; Harrison, Daniel J; Alak, Aiman; Lough, Alan J; Fekl, Ulrich; Brothers, Edward N; Hall, Michael B

    2013-04-01

    Nickel dithiolene complexes have been proposed as electrocatalysts for alkene purification. Recent studies of the ligand-based reactions of Ni(tfd)2 (tfd = S2C2(CF3)2) and its anion [Ni(tfd)2](-) with alkenes (ethylene and 1-hexene) showed that in the absence of the anion, the reaction proceeds most rapidly to form the intraligand adduct, which decomposes by releasing a substituted dihydrodithiin. However, the presence of the anion increases the rate of formation of the stable cis-interligand adduct, and decreases the rate of dihydrodithiin formation and decomposition. In spite of both computational and experimental studies, the mechanism, especially the role of the anion, remained somewhat elusive. We are now providing a combined experimental and computational study that addresses the mechanism and explains the role of the anion. A kinetic study (global analysis) for the reaction of 1-hexene is reported, which supports the following mechanism: (1) reversible intraligand addition, (2) oxidation of the intraligand addition product prior to decomposition, and (3) interligand adduct formation catalyzed by Ni(tfd)2(-). Density functional theory (DFT) calculations were performed on the Ni(tfd)2/Ni(tfd)2(-)/ethylene system to shed light on the selectivity of adduct formation in the absence of anion and on the mechanism in which Ni(tfd)2(-) shifts the reaction from intraligand addition to interligand addition. Computational results show that in the neutral system the free energy of activation for intraligand addition is lower than that for interligand addition, in agreement with the experimental results. The computations predict that the anion enhances the rate of the cis-interligand adduct formation by forming a dimetallic complex with the neutral complex. The [(Ni(tfd)2)2](-) dimetallic complex then coordinates ethylene and isomerizes to form a Ni,S-bound ethylene complex, which then rapidly isomerizes to the stable interligand adduct but not to the intraligand adduct

  20. Bio-Photoelectrochemical Solar Cells Incorporating Reaction Center and Reaction Center Plus Light Harvesting Complexes

    NASA Astrophysics Data System (ADS)

    Yaghoubi, Houman

    Harvesting solar energy can potentially be a promising solution to the energy crisis now and in the future. However, material and processing costs continue to be the most important limitations for the commercial devices. A key solution to these problems might lie within the development of bio-hybrid solar cells that seeks to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. The bio-photoelectrochemical cell technologies exploit biomimetic means of energy conversion by utilizing plant-derived photosystems which can be inexpensive and ultimately the most sustainable alternative. Plants and photosynthetic bacteria harvest light, through special proteins called reaction centers (RCs), with high efficiency and convert it into electrochemical energy. In theory, photosynthetic RCs can be used in a device to harvest solar energy and generate 1.1 V open circuit voltage and ~1 mA cm-2 short circuit photocurrent. Considering the nearly perfect quantum yield of photo-induced charge separation, efficiency of a protein-based solar cell might exceed 20%. In practice, the efficiency of fabricated devices has been limited mainly due to the challenges in the electron transfer between the protein complex and the device electrodes as well as limited light absorption. The overarching goal of this work is to increase the power conversion efficiency in protein-based solar cells by addressing those issues (i.e. electron transfer and light absorption). This work presents several approaches to increase the charge transfer rate between the photosynthetic RC and underlying electrode as well as increasing the light absorption to eventually enhance the external quantum efficiency (EQE) of bio-hybrid solar cells. The first approach is to decrease the electron transfer distance between one of the redox active sites in the RC and the underlying electrode by direct attachment of the of protein complex

  1. Complex formation with nucleic acids and aptamers alters the antigenic properties of platelet factor 4

    PubMed Central

    Jaax, Miriam E.; Krauel, Krystin; Marschall, Thomas; Brandt, Sven; Gansler, Julia; Fürll, Birgitt; Appel, Bettina; Fischer, Silvia; Block, Stephan; Helm, Christiane A.; Müller, Sabine; Preissner, Klaus T.

    2013-01-01

    The tight electrostatic binding of the chemokine platelet factor 4 (PF4) to polyanions induces heparin-induced thrombocytopenia, a prothrombotic adverse drug reaction caused by immunoglobulin G directed against PF4/polyanion complexes. This study demonstrates that nucleic acids, including aptamers, also bind to PF4 and enhance PF4 binding to platelets. Systematic assessment of RNA and DNA constructs, as well as 4 aptamers of different lengths and secondary structures, revealed that increasing length and double-stranded segments of nucleic acids augment complex formation with PF4, while single nucleotides or single-stranded polyA or polyC constructs do not. Aptamers were shown by circular dichroism spectroscopy to induce structural changes in PF4 that resemble those induced by heparin. Moreover, heparin-induced anti-human–PF4/heparin antibodies cross-reacted with human PF4/nucleic acid and PF4/aptamer complexes, as shown by an enzyme immunoassay and a functional platelet activation assay. Finally, administration of PF4/44mer–DNA protein C aptamer complexes in mice induced anti–PF4/aptamer antibodies, which cross-reacted with murine PF4/heparin complexes. These data indicate that the formation of anti-PF4/heparin antibodies in postoperative patients may be augmented by PF4/nucleic acid complexes. Moreover, administration of therapeutic aptamers has the potential to induce anti-PF4/polyanion antibodies and a prothrombotic diathesis. PMID:23673861

  2. Formation of a Ternary Complex for Selenocysteine Biosynthesis in Bacteria*

    PubMed Central

    Silva, Ivan R.; Serrão, Vitor H. B.; Manzine, Livia R.; Faim, Lívia M.; da Silva, Marco T. A.; Makki, Raphaela; Saidemberg, Daniel M.; Cornélio, Marinônio L.; Palma, Mário S.; Thiemann, Otavio H.

    2015-01-01

    The synthesis of selenocysteine-containing proteins (selenoproteins) involves the interaction of selenocysteine synthase (SelA), tRNA (tRNASec), selenophosphate synthetase (SelD, SPS), a specific elongation factor (SelB), and a specific mRNA sequence known as selenocysteine insertion sequence (SECIS). Because selenium compounds are highly toxic in the cellular environment, the association of selenium with proteins throughout its metabolism is essential for cell survival. In this study, we demonstrate the interaction of SPS with the SelA-tRNASec complex, resulting in a 1.3-MDa ternary complex of 27.0 ± 0.5 nm in diameter and 4.02 ± 0.05 nm in height. To assemble the ternary complex, SPS undergoes a conformational change. We demonstrated that the glycine-rich N-terminal region of SPS is crucial for the SelA-tRNASec-SPS interaction and selenoprotein biosynthesis, as revealed by functional complementation experiments. Taken together, our results provide new insights into selenoprotein biosynthesis, demonstrating for the first time the formation of the functional ternary SelA-tRNASec-SPS complex. We propose that this complex is necessary for proper selenocysteine synthesis and may be involved in avoiding the cellular toxicity of selenium compounds. PMID:26378233

  3. Designing metal hydride complexes for water splitting reactions: a molecular electrostatic potential approach.

    PubMed

    Sandhya, K S; Suresh, Cherumuttathu H

    2014-08-28

    The hydridic character of octahedral metal hydride complexes of groups VI, VII and VIII has been systematically studied using molecular electrostatic potential (MESP) topography. The absolute minimum of MESP at the hydride ligand (Vmin) and the MESP value at the hydride nucleus (VH) are found to be very good measures of the hydridic character of the hydride ligand. The increasing/decreasing electron donating feature of the ligand environment is clearly reflected in the increasing/decreasing negative character of Vmin and VH. The formation of an outer sphere metal hydride-water complex showing the HH dihydrogen interaction is supported by the location and the value of Vmin near the hydride ligand. A higher negative MESP suggested lower activation energy for H2 elimination. Thus, MESP features provided a way to fine-tune the ligand environment of a metal-hydride complex to achieve high hydridicity for the hydride ligand. The applicability of an MESP based hydridic descriptor in designing water splitting reactions is tested for group VI metal hydride model complexes of tungsten.

  4. An Investigation of the Complexity of Maillard Reaction Product Profiles from the Thermal Reaction of Amino Acids with Sucrose Using High Resolution Mass Spectrometry

    PubMed Central

    Golon, Agnieszka; Kropf, Christian; Vockenroth, Inga; Kuhnert, Nikolai

    2014-01-01

    Thermal treatment of food changes its chemical composition drastically with the formation of “so-called” Maillard reaction products, being responsible for the sensory properties of food, along with detrimental and beneficial health effects. In this contribution, we will describe the reactivity of several amino acids, including arginine, lysine, aspartic acid, tyrosine, serine and cysteine, with carbohydrates. The analytical strategy employed involves high and ultra-high resolution mass spectrometry followed by chemometric-type data analysis. The different reactivity of amino acids towards carbohydrates has been observed with cysteine and serine, resulting in complex MS spectra with thousands of detectable reaction products. Several compounds have been tentatively identified, including caramelization reaction products, adducts of amino acids with carbohydrates, their dehydration and hydration products, disproportionation products and aromatic compounds based on molecular formula considerations. PMID:28234331

  5. Supramolecular substitution reactions between hydrazide-based molecular duplex strands: complexation induced nonsymmetry and dynamic behavior.

    PubMed

    Yang, Yong; Xiang, Jun-Feng; Xue, Min; Hu, Hai-Yu; Chen, Chuan-Feng

    2008-08-15

    Supramolecular substitution reactions between hydrazide-based oligomers 1a- c and 2a- c were systematically investigated. Each oligomer existed as hydrogen-bonding mediated molecular duplex strands or a polymeric zipper structure in apolar solvents. But when another oligomer with complementary hydrogen bonding sites was added, a heterodimer structure formed due to supramolecular substitution reaction driven by the formation of more hydrogen bonds, which was evidenced by NMR experiments, sometimes gel-sol transition. When a nonsymmetric oligomer and a symmetric oligomer were involved, complexation-induced nonsymmetry was observed. When two nonsymmetric oligomers were involved, two hydrogen-bonded isomers were observed in solution. Variable-temperature (1)H NMR experiments further revealed unique dynamic behavior for the individual oligomer and the complexes. When diacetyl-terminated oligomer 1c was involved, slides perpendicular to hydrogen bonds between two constituent molecules were observed, which led to complicated (1)H NMR spectra at lower temperature; otherwise, high selectivity was obtained. Combined with the results we reported previously, a detailed picture of the structure-property relationship for our hydrazide-based oligomers was depicted, which would provide guidelines for the design of hydrazide-based fine-tuning functional materials.

  6. Formation and Recondensation of Complex Organic Molecules during Protostellar Luminosity Outbursts

    NASA Astrophysics Data System (ADS)

    Taquet, Vianney; Wirström, Eva S.; Charnley, Steven B.

    2016-04-01

    During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion-molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

  7. FORMATION AND RECONDENSATION OF COMPLEX ORGANIC MOLECULES DURING PROTOSTELLAR LUMINOSITY OUTBURSTS

    SciTech Connect

    Taquet, Vianney; Wirström, Eva S.; Charnley, Steven B.

    2016-04-10

    During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion–molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

  8. Formation and Recondensation of Complex Organic Molecules During Protostellar Luminosity Outbursts

    NASA Technical Reports Server (NTRS)

    Taquet, Vianney; Wirstrom, Eva S.; Charnley, Steven B.

    2016-01-01

    During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion-molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

  9. Novel palladium complex-catalyzed reaction of magnesium amides with allylic electrophiles

    SciTech Connect

    Dzhemilev, U.M.; Ibragimov, A.G.; Minsker, D.L.; Muslukhov, R.R.

    1987-08-20

    In order to develop an efficient method for the synthesis of higher order unsaturated tertiary amines, and also to explore a new method for the formation of C-N bonds, they have investigated the transition metal complex-catalyzed reaction of magnesium amides with electrophiles; the electrophiles selected for study included allyl ethers and esters, as well as sulfones, sulfides and quaternized allylamines. The effects of the nature and structure of the catalyst components, as well as of the reaction conditions, on product yield were examined in the case of the reaction of diethyl (bromomagnesium)amine with diallyl ether, and revealed that the highest yield of diethylallyl-amine (I) was achieved using Pd(acac)/sub 2/ (3-5 mole %) and Ph/sub 3/P (1:2) as catalyst in THF solution at 50/sup 0/C for 5 h. Other transition metal (Ni, Fe, Zr, Ti, Cu) compounds were also examined as catalysts, but the yield of (I) did not exceed 15% with these compounds. Bimetallic catalysts based on Zr (Cp/sub 2/ZrCl, Py/sub 2/ZrCl/sub 6/, (RO)/sub 4/Zr) and Ni (Ni(acac)/sub 2/ and NiCl/sub 2/) were successful in forming (I) from diethyl (bromomagnesium)amine and diallyl ether in 60% yield.

  10. The ribosome-associated complex antagonizes prion formation in yeast.

    PubMed

    Amor, Alvaro J; Castanzo, Dominic T; Delany, Sean P; Selechnik, Daniel M; van Ooy, Alex; Cameron, Dale M

    2015-01-01

    The number of known fungal proteins capable of switching between alternative stable conformations is steadily increasing, suggesting that a prion-like mechanism may be broadly utilized as a means to propagate altered cellular states. To gain insight into the mechanisms by which cells regulate prion formation and toxicity we examined the role of the yeast ribosome-associated complex (RAC) in modulating both the formation of the [PSI(+)] prion - an alternative conformer of Sup35 protein - and the toxicity of aggregation-prone polypeptides. The Hsp40 RAC chaperone Zuo1 anchors the RAC to ribosomes and stimulates the ATPase activity of the Hsp70 chaperone Ssb. We found that cells lacking Zuo1 are sensitive to over-expression of some aggregation-prone proteins, including the Sup35 prion domain, suggesting that co-translational protein misfolding increases in Δzuo1 strains. Consistent with this finding, Δzuo1 cells exhibit higher frequencies of spontaneous and induced prion formation. Cells expressing mutant forms of Zuo1 lacking either a C-terminal charged region required for ribosome association, or the J-domain responsible for Ssb ATPase stimulation, exhibit similarly high frequencies of prion formation. Our findings are consistent with a role for the RAC in chaperoning nascent Sup35 to regulate folding of the N-terminal prion domain as it emerges from the ribosome.

  11. The ribosome-associated complex antagonizes prion formation in yeast

    PubMed Central

    Amor, Alvaro J; Castanzo, Dominic T; Delany, Sean P; Selechnik, Daniel M; van Ooy, Alex; Cameron, Dale M

    2015-01-01

    Abstract The number of known fungal proteins capable of switching between alternative stable conformations is steadily increasing, suggesting that a prion-like mechanism may be broadly utilized as a means to propagate altered cellular states. To gain insight into the mechanisms by which cells regulate prion formation and toxicity we examined the role of the yeast ribosome-associated complex (RAC) in modulating both the formation of the [PSI+] prion – an alternative conformer of Sup35 protein – and the toxicity of aggregation-prone polypeptides. The Hsp40 RAC chaperone Zuo1 anchors the RAC to ribosomes and stimulates the ATPase activity of the Hsp70 chaperone Ssb. We found that cells lacking Zuo1 are sensitive to over-expression of some aggregation-prone proteins, including the Sup35 prion domain, suggesting that co-translational protein misfolding increases in Δzuo1 strains. Consistent with this finding, Δzuo1 cells exhibit higher frequencies of spontaneous and induced prion formation. Cells expressing mutant forms of Zuo1 lacking either a C-terminal charged region required for ribosome association, or the J-domain responsible for Ssb ATPase stimulation, exhibit similarly high frequencies of prion formation. Our findings are consistent with a role for the RAC in chaperoning nascent Sup35 to regulate folding of the N-terminal prion domain as it emerges from the ribosome. PMID:25739058

  12. Formation of N-nitrosodimethylamine (NDMA) from reaction of monochloramine: a new disinfection by-product.

    PubMed

    Choi, Junghoon; Valentine, Richard L

    2002-02-01

    Studies have been conducted specifically to investigate the hypothesis that N-nitrosodimethylamine (NDMA) can be produced by reactions involving monochloramine. Experiments were conducted using dimethylamine (DMA) as a model precursor. NDMA was formed from the reaction between DMA and monochloramine indicating that it should be considered a potential disinfection by-product. The formation of NDMA increased with increased monochloramine concentration and showed maximum in yield when DMA was varied at fixed monochloramine concentrations. The mass spectra of the NDMA formed from DMA and 15N isotope labeled monochloramine (15NH2Cl) showed that the source of one of the nitrogen atoms in the nitroso group in NDMA was from monochloramine. Addition of 0.05 and 0.5 mM of preformed monochloramine to a secondarily treated wastewater at pH 7.2 also resulted in the formation of 3.6 and 111 ng/L of NDMA, respectively, showing that this is indeed an environmentally relevant NDMA formation pathway. The proposed NDMA formation mechanism consists of (i) the formation of 1,1-dimethylhydrazine (UDMH) intermediate from the reaction of DMA with monochloramine followed by, (ii) the oxidation of UDMH by monochloramine to NDMA, and (iii) the reversible chlorine transfer reaction between monochloramine and DMA which is parallel to (i). We conclude that reactions involving monochloramine in addition to classical nitrosation reactions are potentially important pathways for NDMA formation.

  13. Clay surface catalysis of formation of humic substances: potential role of maillard reactions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The mechanisms of the formation of humic substances are poorly understood, especially the condensation of amino acids and reducing sugars products (Maillard reaction) in soil environments. Clay minerals behave as Lewis and Brönsted acids and catalyze several reactions and likely to catalyze the Mai...

  14. Quasifission in heavy and superheavy element formation reactions

    NASA Astrophysics Data System (ADS)

    Hinde, D. J.; Dasgupta, M.; Jeung, D. Y.; Mohanto, G.; Prasad, E.; Simenel, C.; Walshe, J.; Wahkle, A.; Williams, E.; Carter, I. P.; Cook, K. J.; Kalkal, Sunil; Rafferty, D. C.; Rietz, R. du; Simpson, E. C.; David, H. M.; Düllmann, Ch. E.; Khuyagbaatar, J.

    2016-12-01

    Superheavy elements are created in the laboratory by the fusion of two heavy nuclei. The large Coulomb repulsion that makes superheavy elements decay also makes the fusion process that forms them very unlikely. Instead, after sticking together for a short time, the two nuclei usually come apart, in a process called quasifission. Mass-angle distributions give the most direct information on the characteristics and time scales of quasifission. A systematic study of carefully chosen mass-angle distributions has provided information on the global trends of quasifission. Large deviations from these systematics reveal the major role played by the nuclear structure of the two colliding nuclei in determining the reaction outcome, and thus implicitly in hindering or favouring superheavy element production.

  15. Photochemical redox reactions of copper(II)-alanine complexes in aqueous solutions.

    PubMed

    Lin, Chen-Jui; Hsu, Chao-Sheng; Wang, Po-Yen; Lin, Yi-Liang; Lo, Yu-Shiu; Wu, Chien-Hou

    2014-05-19

    The photochemical redox reactions of Cu(II)/alanine complexes have been studied in deaerated solutions over an extensive range of pH, Cu(II) concentration, and alanine concentration. Under irradiation, the ligand-to-metal charge transfer results in the reduction of Cu(II) to Cu(I) and the concomitant oxidation of alanine, which produces ammonia and acetaldehyde. Molar absorptivities and quantum yields of photoproducts for Cu(II)/alanine complexes at 313 nm are characterized mainly with the equilibrium Cu(II) speciation where the presence of simultaneously existing Cu(II) species is taken into account. By applying regression analysis, individual Cu(I) quantum yields are determined to be 0.094 ± 0.014 for the 1:1 complex (CuL) and 0.064 ± 0.012 for the 1:2 complex (CuL2). Individual quantum yields of ammonia are 0.055 ± 0.007 for CuL and 0.036 ± 0.005 for CuL2. Individual quantum yields of acetaldehyde are 0.030 ± 0.007 for CuL and 0.024 ± 0.007 for CuL2. CuL always has larger quantum yields than CuL2, which can be attributed to the Cu(II) stabilizing effect of the second ligand. For both CuL and CuL2, the individual quantum yields of Cu(I), ammonia, and acetaldehyde are in the ratio of 1.8:1:0.7. A reaction mechanism for the formation of the observed photoproducts is proposed.

  16. Modeling the formation and reactions of benzene metabolites.

    PubMed

    Golding, Bernard T; Barnes, Martine L; Bleasdale, Christine; Henderson, Alistair P; Jiang, Dong; Li, Xin; Mutlu, Esra; Petty, Hannah J; Sadeghi, Majid M

    2010-03-19

    One or more of the muconaldehyde isomers is a putative product of benzene metabolism. As muconaldehydes are highly reactive dienals and potentially mutagenic they might be relevant to the carcinogenicity of benzene. Muconaldehydes may be derived through the action of a cytochrome P450 mono-oxygenase on benzene oxide-oxepin, which are established metabolites of benzene. Oxidation of benzene oxide-oxepin either by the one-electron oxidant cerium(IV) ammonium nitrate (CAN) or by iron(III) tris(1,10-phenanthroline) hexafluorophosphate in acetone at -78 degrees C or acetonitrile at -40 degrees C gave (E,Z)-muconaldehyde, which was a single diastereoisomer according to analysis by (1)H NMR spectroscopy. Reaction of toluene-1,2-oxide/2-methyloxepin with CAN gave (2E,4Z)-6-oxo-hepta-2,4-dienal. Similarly, the action of CAN on 1,6-dimethylbenzene oxide-2,7-dimethyloxepin gave (3Z,5E)-octa-3,5-diene-2,7-dione. In vivo, benzene oxide-oxepin could suffer one-electron oxidation by cytochrome P450 mono-oxygenase giving (E,Z)-muconaldehyde. The observations presented may be relevant to the toxicology of benzene oxide-oxepin and other arene oxide-oxepins as we have previously shown that (E,Z)-muconaldehyde, analogously to (Z,Z)-muconaldehyde, affords pyrrole adducts with the exocyclic amino groups of the DNA bases adenine and guanine. Independent of their possible toxicological significance, the experiments described provide preparatively useful routes to (E,Z)-muconaldehyde and its congeners. Methods are also described for the trapping and analysis of reactive benzene metabolites, e.g. using the Diels-Alder reaction with the dienophile 4-phenyl-1,2,4-triazoline-3,5-dione to trap arene oxides and with the diene 1,3-diphenylisobenzofuran to trap enals.

  17. Formation of gold mineralization in ultramafic alkalic magmatic complexes

    NASA Astrophysics Data System (ADS)

    Ryabchikov, I. D.; Kogarko, L. N.; Sazonov, A. M.; Kononkova, N. N.

    2016-06-01

    Study of mineral inclusions within alluvial gold particles of the Guli Complex (East Siberia) and findings of lode gold in rocks of the same intrusion have demonstrated that gold mineralization occurs in interstitions of both early high-magnesium rocks (dunite) and later alkalic and carbonatite rocks. In dunite the native gold occurs in association with Fe-Ni sulfides (monosulfide solid solution, pentlandite, and heazlewoodite). Formation of the gold-bearing alloys took place under a low oxygen potential over a broad range of temperatures: from those close to 600°C down to below 400°C.

  18. Factors Leading to the Formation of Arc Cloud Complexes.

    DTIC Science & Technology

    1985-12-01

    I. M2i .16 MICROCnWY O TEST CHART NATIONAL BUREAU 0F STANDARDS-1963-A ils. ... TEXAS A&M UNIVERSITY DEPARTMENT OF R AOL mMETEOROLOGY FACTORS LEADING...PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASKAFIT STUDENT AT: AREA & WORK UNIT NUMBERS Texas A&M Univ II. CONTROLLING...to an ACC. /0 FACTORS LEADING TO THE FORMATION OF ARC CLOUD COMPLEXES A Thesis by MARK JOHN WELSHINGER Submitted to the Graduate College of Texas A&M

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

    PubMed Central

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

    2014-01-01

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

  20. Automated Discovery of Complex Reaction Networks: Reaction Topology, Thermochemistry and Kinetics

    DTIC Science & Technology

    2015-07-08

    characterization of chemical reaction networks in combustion, minimize human input, and avoid on-the -fly thermochemical estimation. Based on the...transition states of different types of chemical reactions . 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF... chemical reaction networks in combustion, minimize human input, and avoid on-the-fly thermochemical estimation. Based on the enumerated elementary

  1. Mixed amido-/imido-/guanidinato niobium complexes: synthesis and the effect of ligands on insertion reactions.

    PubMed

    Elorriaga, David; Carrillo-Hermosilla, Fernando; Antiñolo, Antonio; López-Solera, Isabel; Fernández-Galán, Rafael; Villaseñor, Elena

    2014-12-14

    The new monoguanidinato complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(NR)(NR')C(NMe2)}] (R = R' = (i)Pr, 2; R = (t)Bu, R' = Et, 3) were obtained by the insertion reaction of either diisopropylcarbodiimide or 1-tert-butyl-3-ethylcarbodiimide with the triamido precursor [Nb(NMe2)3(N-2,6-(i)Pr2C6H3)] (1) bearing a bulky imido moiety. The μ-oxo derivative [{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NMe2)}(NMe2)Nb]2(μ-O) (2a) was formed by an unexpected hydrolysis reaction of the amido niobium compound 2. Alternatively, monoguanidinato complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NHR)}] (R = (i)Pr, 4, (n)Bu, 5) can be obtained by protonolysis of 1 with N,N',N''-alkylguanidines [(NH(i)Pr)2C(NR)] (R = (i)Pr, (n)Bu). Compound also reacts with either tert-butylisocyanide or 2,6-xylylisocyanide to give, by a migratory insertion reaction, the corresponding iminocarbamoyl compounds [Nb(NMe2)2{(NMe2)C=NR}{N(2,6-(i)Pr2C6H3)}] (R = (t)Bu, 6, Xy, 7). Addition of the neutral alkylguanidines to complex 6 results in a facile C-N bond cleavage at room temperature in a process directed by the formation of the stable chelate complex 4 or 5. Complex reacts with heterocumulenic CS2 to produce new imido dithiocarbamato complexes [Nb(NMe2){S2C(NMe2)}2{N(2,6-(i)Pr2C6H3)}] (8) and [Nb{S2C(NMe2)}3{N(2,6-(i)Pr2C6H3)}] (9). These complexes do not react with alkylguanines, although new mixed guanidinato dithiocarbamato complexes [Nb(NMe2){S2C(NMe2)}{(N(i)Pr)2C(NHiPr)}{N(2,6-(i)Pr2C6H3)}] (10) and [Nb{(S2C(NMe2)}2{(N(i)Pr)2C(NH(i)Pr)}{N(2,6-(i)Pr2C6H3)}] (11) can be obtained by reaction of complex 4 with one or two equivalents of CS2, respectively. All of the complexes were characterized spectroscopically and the dynamic behaviour of some of them was studied by variable-temperature NMR. The molecular structures of 2a, 3, 6 and 10 were also established by X-ray diffraction studies.

  2. Cu(II) complex formation with xylitol in alkaline solutions.

    PubMed

    Norkus, Eugenijus; Vaiciūniene, Jūrate; Vuorinen, Tapani; Gaidamauskas, Ernestas; Reklaitis, Jonas; Jääskeläinen, Anna-Stiina; Crans, Debbie C

    2004-02-25

    The formation of four Cu(II)-xylitol complexes was observed in aqueous alkaline solutions (11.0< or =pH< or =14.0, I=1.0, 20 degrees C) by means of direct current polarography and VIS spectrophotometry. Mononuclear hydroxy complexes, CuXyl(OH)- (log beta=17.7 +/- 0.5), CuXyl(OH)2(2-) (log beta=20.2 +/- 0.3) and CuXyl2(OH)2(4-) (log beta=22.4 +/- 0.3), are formed at high ligand-to-metal ratios (L:M> or =10), whereas dinuclear complex Cu2Xyl (log beta=29.2 +/- 0.3) is the predominant species at low ligand-to-metal ratio (L:M=0.5). Diffusion coefficients and molar absorptivities of the complex species were determined. pH variable 13C NMR suggested that pKa values of xylitol are rather similar and equal to 13.8 +/- 0.2, 13.9 +/- 0.1 and 13.9 +/- 0.2 for OH-groups adjacent to (C-1,C-5), (C-3) and (C-2,C-4) carbon atoms, respectively.

  3. Characterization of Hydrogen Complex Formation in III-V Semiconductors

    SciTech Connect

    Williams, Michael D

    2006-09-28

    Atomic hydrogen has been found to react with some impurity species in semiconductors. Hydrogenation is a methodology for the introduction of atomic hydrogen into the semiconductor for the express purpose of forming complexes within the material. Efforts to develop hydrogenation as an isolation technique for AlGaAs and Si based devices failed to demonstrate its commercial viability. This was due in large measure to the low activation energies of the formed complexes. Recent studies of dopant passivation in long wavelength (0.98 - 1.55m) materials suggested that for the appropriate choice of dopants much higher activation energies can be obtained. This effort studied the formation of these complexes in InP, This material is extensively used in optoelectronics, i.e., lasers, modulators and detectors. The experimental techniques were general to the extent that the results can be applied to other areas such as sensor technology, photovoltaics and to other material systems. The activation energies for the complexes have been determined and are reported in the scientific literature. The hydrogenation process has been shown by us to have a profound effect on the electronic structure of the materials and was thoroughly investigated. The information obtained will be useful in assessing the long term reliability of device structures fabricated using this phenomenon and in determining new device functionalities.

  4. Nickel-Catalyzed Reactions Directed toward the Formation of Heterocycles.

    PubMed

    Kurahashi, Takuya; Matsubara, Seijiro

    2015-06-16

    Heterocycles have garnered significant attention because they are important functional building blocks in various useful molecules, such as pharmaceuticals, agricultural chemicals, pesticides, and materials. Several studies have been conducted regarding the preparation of heterocyclic skeletons with an emphasis on selectivity and efficiency. Three strategies are typically employed to construct cyclic molecules, namely, cyclization, cycloaddition, and ring-size alterations. Although each method has certain advantages, cycloaddition may be superior from the viewpoint of divergence. Specifically, cycloadditions enable the construction of rings from several pieces. However, the construction of heterocycles via cycloadditions is more challenging than the construction of carbocycles. For heterocycle construction, simple pericyclic reactions rarely work smoothly because of the large HOMO-LUMO gap unless well-designed combinations, such as electron-rich dienes and aldehydes, are utilized. Thus, a different approach should be employed to prepare heterocycles via cycloadditions. To this end, the use of metallacycles containing heteroatoms is expected to serve as a promising solution. In this study, we focused on the preparation of heteroatom-containing nickelacycles. Because nickel possesses a relatively high redox potential and an affinity for heteroatoms, several methods were developed to synthesize heteronickelacycles from various starting materials. The prepared nickelacycles were demonstrated to be reasonable intermediates in cycloaddition reactions, which were used to prepare various heterocycles. In this Account, we introduce the following four methods to prepare heterocycles via heteronickelacycles. (1) Direct oxidative insertion of Ni(0) to α,β-unsaturated enone derivatives: treatment of 3-ethoxycarbonyl-4-phenyl-3-buten-2-one with Ni(0) afforded an oxa-nickelacycle, which reacted with alkynes to give pyrans. (2) Substitution of a part of a cyclic compound with

  5. Theory of diffusion-influenced reactions in complex geometries

    NASA Astrophysics Data System (ADS)

    Galanti, Marta; Fanelli, Duccio; Traytak, Sergey D.; Piazza, Francesco

    Chemical reactions involving diffusion of reactants and subsequent chemical fixation steps are generally termed "diffusion-influenced" (DI). Virtually all biochemical processes in living media can be counted among them, together with those occurring in an ever-growing number of emerging nano-technologies. The role of the environment's geometry (obstacles, compartmentalization) and distributed reactivity (competitive reactants, traps) is key in modulating the rate constants of DI reactions, and is therefore a prime design parameter. Yet, it is a formidable challenge to build a comprehensive theory able to describe the environment's "reactive geometry". Here we show that such a theory can be built by unfolding this many-body problem through addition theorems for special functions. Our method is powerful and general and allows one to study a given DI reaction occurring in arbitrary "reactive landscapes", made of multiple spherical boundaries of given size and reactivity. Importantly, ready-to-use analytical formulas can be derived easily in most cases.

  6. Proton exchange in acid-base complexes induced by reaction coordinates with heavy atom motions

    NASA Astrophysics Data System (ADS)

    Alavi, Saman; Taghikhani, Mahdi

    2012-06-01

    We extend previous work on nitric acid-ammonia and nitric acid-alkylamine complexes to illustrate that proton exchange reaction coordinates involve the rocking motion of the base moiety in many double hydrogen-bonded gas phase strong acid-strong base complexes. The complexes studied involve the biologically and atmospherically relevant glycine, formic, acetic, propionic, and sulfuric acids with ammonia/alkylamine bases. In these complexes, the magnitude of the imaginary frequencies associated with the proton exchange transition states are <400 cm-1. This contrasts with widely studied proton exchange reactions between symmetric carboxylic acid dimers or asymmetric DNA base pair and their analogs where the reaction coordinate is localized in proton motions and the magnitude of the imaginary frequencies for the transition states are >1100 cm-1. Calculations on complexes of these acids with water are performed for comparison. Variations of normal vibration modes along the reaction coordinate in the complexes are described.

  7. Interference-mediated synaptonemal complex formation with embedded crossover designation

    PubMed Central

    Zhang, Liangran; Espagne, Eric; de Muyt, Arnaud; Zickler, Denise; Kleckner, Nancy E.

    2014-01-01

    Biological systems exhibit complex patterns at length scales ranging from the molecular to the organismic. Along chromosomes, events often occur stochastically at different positions in different nuclei but nonetheless tend to be relatively evenly spaced. Examples include replication origin firings, formation of chromatin loops along chromosome axes and, during meiosis, localization of crossover recombination sites (“crossover interference”). We present evidence in the fungus Sordaria macrospora that crossover interference is part of a broader pattern that includes synaptonemal complex (SC) nucleation. This pattern comprises relatively evenly spaced SC nucleation sites, among which a subset are crossover sites that show a classical interference distribution. This pattern ensures that SC forms regularly along the entire length of the chromosome as required for the maintenance of homolog pairing while concomitantly having crossover interactions locally embedded within the SC structure as required for both DNA recombination and structural events of chiasma formation. This pattern can be explained by a threshold-based designation and spreading interference process. This model can be generalized to give diverse types of related and/or partially overlapping patterns, in two or more dimensions, for any type of object. PMID:25380597

  8. Gel phase formation in dilute triblock copolyelectrolyte complexes

    DOE PAGES

    Srivastava, Samanvaya; Andreev, Marat; Levi, Adam E.; ...

    2017-02-23

    Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (<1% by mass) has been observed in scattering experiments and molecular dynamics simulations. Here we show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously on solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chainmore » aggregates in early stages of copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Finally, our discoveries contribute to the fundamental understanding of the structure and pathways of complexation-driven assemblies, and raise intriguing prospects for gel formation at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics.« less

  9. The formation of illite from nontronite by mesophilic and thermophilic bacterial reaction

    USGS Publications Warehouse

    Jaisi, D.P.; Eberl, D.D.; Dong, H.; Kim, J.

    2011-01-01

    The formation of illite through the smectite-to-illite (S-I) reaction is considered to be one of the most important mineral reactions occurring during diagenesis. In biologically catalyzed systems, however, this transformation has been suggested to be rapid and to bypass the high temperature and long time requirements. To understand the factors that promote the S-I reaction, the present study focused on the effects of pH, temperature, solution chemistry, and aging on the S-I reaction in microbially mediated systems. Fe(III)-reduction experiments were performed in both growth and non-growth media with two types of bacteria: mesophilic (Shewanella putrefaciens CN32) and thermophilic (Thermus scotoductus SA-01). Reductive dissolution of NAu-2 was observed and the formation of illite in treatment with thermophilic SA-01 was indicated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A basic pH (8.4) and high temperature (65??C) were the most favorable conditions forthe formation of illite. A long incubation time was also found to enhance the formation of illite. K-nontronite (non-permanent fixation of K) was also detected and differentiated from the discrete illite in the XRD profiles. These results collectively suggested that the formation of illite associated with the biologically catalyzed smectite-to-illite reaction pathway may bypass the prolonged time and high temperature required for the S-I reaction in the absence of microbial activity.

  10. The C(3P) + NH3 Reaction in Interstellar Chemistry. I. Investigation of the Product Formation Channels

    NASA Astrophysics Data System (ADS)

    Bourgalais, Jérémy; Capron, Michael; Abhinavam Kailasanathan, Ranjith Kumar; Osborn, David L.; Hickson, Kevin M.; Loison, Jean-Christophe; Wakelam, Valentine; Goulay, Fabien; Le Picard, Sébastien D.

    2015-10-01

    The product formation channels of ground state carbon atoms, C(3P), reacting with ammonia, NH3, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C + NH3 reaction. In addition, H-atom formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H2CN production channel represents 100% of the product yield for this reaction. Kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.

  11. The C(3P) + NH3 reaction in interstellar chemistry. I. Investigation of the product formation channels

    DOE PAGES

    Bourgalais, Jeremy; Capron, Michael; Kailasanathan, Ranjith Kumar Abhinavam; ...

    2015-10-13

    The product formation channels of ground state carbon atoms, C(3P), reacting with ammonia, NH3, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C + NH3 reaction. In addition, H-atom formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzlemore » technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H2CN production channel represents 100% of the product yield for this reaction. As a result, kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.« less

  12. Polycyclic aromatic hydrocarbon (PAH) formation from benzyl radicals: a reaction kinetics study.

    PubMed

    Sinha, Sourab; Raj, Abhijeet

    2016-03-21

    The role of resonantly stabilized radicals such as propargyl, cyclopentadienyl and benzyl in the formation of aromatic hydrocarbons such as benzene and naphthalene in the high temperature environments has been long known. In this work, the possibility of benzyl recombination to form three-ring aromatics, phenanthrene and anthracene, is explored. A reaction mechanism for it is developed, where reaction energetics are calculated using density functional theory (B3LYP functional with 6-311++G(d,p) basis set) and CBS-QB3, while temperature-dependent reaction kinetics are evaluated using transition state theory. The mechanism begins with barrierless formation of bibenzyl from two benzyl radicals with the release of 283.2 kJ mol(-1) of reaction energy. The further reactions involve H-abstraction by a H atom, H-desorption, H-migration, and ring closure to gain aromaticity. Through mechanism and rate of production analyses, the important reactions leading to phenanthrene and anthracene formation are determined. Phenanthrene is found to be the major product at high temperatures. Premixed laminar flame simulations are carried out by including the proposed reactions for phenanthrene formation from benzyl radicals and compared to experimentally observed species profiles to understand their effects on species concentrations.

  13. Fluoridonitrosyl complexes of technetium(I) and technetium(II). Synthesis, characterization, reactions, and DFT calculations.

    PubMed

    Balasekaran, Samundeeswari Mariappan; Spandl, Johann; Hagenbach, Adelheid; Köhler, Klaus; Drees, Markus; Abram, Ulrich

    2014-05-19

    A mixture of [Tc(NO)F5](2-) and [Tc(NO)(NH3)4F](+) is formed during the reaction of pertechnetate with acetohydroxamic acid (Haha) in aqueous HF. The blue pentafluoridonitrosyltechnetate(II) has been isolated in crystalline form as potassium and rubidium salts, while the orange-red ammine complex crystallizes as bifluoride or PF6(-) salts. Reactions of [Tc(NO)F5](2-) salts with HCl give the corresponding [Tc(NO)Cl4/5](-/2-) complexes, while reflux in neat pyridine (py) results in the formation of the technetium(I) cation [Tc(NO)(py)4F](+), which can be crystallized as hexafluoridophosphate. The same compound can be synthesized directly from pertechnetate, Haha, HF, and py or by a ligand-exchange procedure starting from [Tc(NO)(NH3)4F](HF2). The technetium(I) cation [Tc(NO)(NH3)4F](+) can be oxidized electrochemically or by the reaction with Ce(SO4)2 to give the corresponding Tc(II) compound [Tc(NO)(NH3)4F](2+). The fluorido ligand in [Tc(NO)(NH3)4F](+) can be replaced by CF3COO(-), leaving the "[Tc(NO)(NH3)4](2+) core" untouched. The experimental results are confirmed by density functional theory calculations on [Tc(NO)F5](2-), [Tc(NO)(py)4F](+), [Tc(NO)(NH3)4F](+), and [Tc(NO)(NH3)4F](2+).

  14. The origin of enantioselectivity for intramolecular Friedel-Crafts reaction catalyzed by supramolecular Cu/DNA catalyst complex

    NASA Astrophysics Data System (ADS)

    Petrova, Galina P.; Ke, Zhuofeng; Park, Soyoung; Sugiyama, Hiroshi; Morokuma, Keiji

    2014-04-01

    The present theoretical investigation aims at understanding the origin of enantioselectivity of intramolecular Friedel-Crafts reaction, catalyzed by supramolecular Cu/DNA catalyst. 28 Conformations of the supramolecular L-Cu(II)-R/d(CAAAAATTTTTG)2 complex were thoroughly modeled to estimate their stability and structural features depending on the metal complex conformation and its intercalation position. The preferred formation of S-product can be rationalized by the higher binding energy of pro-S conformations to DNA. Pro-S conformations are structurally closer to the expected C3-C2‧ bond formation TS and usually not deeply buried into DNA, which would facilitate TS formation by decreasing the energy for conformational changes.

  15. Pattern formation of a reaction-diffusion system with self-consistent flow in the amoeboid organism Physarum plasmodium

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroyasu; Nakagaki, Toshiyuki; Ito, Masami

    1999-01-01

    The amoeboid organism, the plasmodium of Physarum polycephalum, moves by forming a spatiotemporal pattern of contraction oscillators. This biological system can be regarded as a reaction-diffusion system with spatial interaction via active flow of protoplasmic sol in the cell. We present a reaction-diffusion system with self-consistent flow on the basis of the physiological evidence that the flow is determined by contraction patterns in the plasmodium. Such a coupling of reaction, diffusion, and advection is characteristic of biological systems, and is expected to be related to control mechanisms of amoeboid behavior. Using weakly nonlinear analysis, we show that the envelope dynamics obeys the complex Ginzburg-Landau (CGL) equation when a bifurcation occurs at finite wave number. The flow term affects the nonlinear term of the CGL equation through the critical wave number squared. A physiological role of pattern formation with the flow is discussed.

  16. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  17. A complex postnatal mental health intervention: Australian translational formative evaluation.

    PubMed

    Rowe, Heather J; Wynter, Karen H; Burns, Joanna K; Fisher, Jane R W

    2016-01-07

    Reducing the burden of postnatal maternal mental health problems is an international public health priority. We developed What Were We Thinking (WWWT), a psychoeducation programme for primary postnatal health care that addresses known but neglected risks. We then demonstrated evidence of its effects in a before-and-after controlled study in preventing maternal postnatal mental health problems among women without a psychiatric history participating in the intervention compared to usual care (AOR 0.43; 95% CI 0.21, 0.89) when conducted by specialist nurses. Testing its effectiveness when implemented in routine primary care requires changes at practitioner, organizational and health system levels. This paper describes a programme of translational formative evaluation to inform the protocol for a cluster RCT. Following the UK Medical Research Council (MRC) Guidance for evaluating complex interventions, we conducted a translational formative evaluation using mixed methods. Collection and analysis of postnatal health service documents, semi-structured interviews, group discussions and an online survey were used to investigate service provision, consumers' needs and expectations, clinicians' attitudes and clinical practice, and the implications for health service delivery. Participants were expectant parents, health care providers, health service managers and government policy makers. Results documented current clinical practice, staff training needs, necessary service modifications to standardize advice to parents and include fathers, key priorities and drivers of government health policy, and informed a model of costs and expected health and social outcomes. Implementation of WWWT into routine postnatal care requires adjustments to clinical practice. Staff training, modifications to service opening hours and economic implications for the health system also need to be considered. The MRC Guidance for developing and evaluating complex interventions is a useful framework

  18. Spatially Periodic Domain Structure in Coupled Reaction--Diffusion Equations for Segment Formation

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu

    2012-02-01

    Segment formation is an important process of pattern formation in the developing vertebrate embryo. The mechanism of such pattern formation is considered to be different from that of Turing instability. We propose reaction--diffusion equations generating traveling pulses and coupled reaction--diffusion equations for two genes that generate a domain structure. Next, we construct a synthetic model for segment formation by combining the coupled reaction--diffusion equations. A spatially periodic domain structure is found in the numerical simulation of the model equation. It is shown that the wavelength of the spatially periodic pattern and the proportion of the sizes of the anterior and posterior domains in each segment can be controlled by adjusting some system parameters.

  19. Kinetic study of model reactions in the gas phase at the early stage of coke formation

    SciTech Connect

    Nohara, D.; Sakai, T. )

    1992-01-01

    This paper reports that the most probable gas-phase reactions at the early stage of coke formation were elucidated by kinetic study on the model reactions adopted for formation of cyclic compounds and growth of ring. It was revealed that the formation and growth of ring proceeded mainly through cycloaddition of butadiene or allyl radicals to unsaturated hydrocarbons at relatively low temperatures ({approximately}600{degrees}C), i.e., through a Diels-Alder type reaction. On the other hand, such growth of ring as formation of biphenyl accompanying dehydrogenation from benzene can proceed only at the higher temperatures. It was also revealed that in the growth of the ring, cycloaddition of butadiene favors a cyclic olefin molecule that possesses a nonconjugated double bond and a nearly planar structure.

  20. Photoinduced Vesicle Formation via the Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction.

    PubMed

    Konetski, Danielle; Gong, Tao; Bowman, Christopher N

    2016-08-16

    Synthetic vesicles have a wide range of applications from drug and cosmetic delivery to artificial cell and membrane studies, making simple and controlled formation of vesicles a large focus of the field today. Here, we report the use of the photoinitiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using visible light to introduce spatiotemporal control into the formation of vesicles. Upon the establishment of the spatiotemporal control over vesicle formation, it became possible to adjust initiation conditions to modulate vesicle sizes resulting in the formation of controllably small or large vesicles based on light intensity or giant vesicles when the formation was initiated in flow-free conditions. Additionally, this photoinitiated method enables vesicle formation at a density 400-fold higher than initiation using sodium ascorbate as the catalyst. Together, these advances enable the formation of high-density, controlled size vesicles using low-energy wavelengths while producing enhanced control over the formation characteristics of the vesicle.

  1. Investigation of the Composition and Formation Constant of Molecular Complexes

    PubMed Central

    Sahai, R.; Loper, G. L.; Lin, S. H.; Eyring, H.

    1974-01-01

    It has been the purpose of the present paper to investigate and explore the conditions under which the linear relation between Δ/CD0 and Δ in the Hanna-Ashbaugh-Foster-Fyfe equation for the evaluation of equilibrium constants holds, (CD0 is initial concentration of a donor and Δ is the observed chemical shift relative to the chemical shift of the acceptor) to obtain the equation representing the exact linear relation between Δ/CD0 and Δ, when the linear relation between Δ/CD0 and Δ holds, and to discuss how to use the Job method in nuclear magnetic resonance measurements to determine the stoichiometry of molecular complexes. We have found that the conventional belief that CD0 should always be chosen to be much greater than CA0 (initial concentration of acceptor) is not necessarily always true and the exact linear relation between Δ/CD0 and Δ is represented by the equation Δ/CD0 = K1Δ0/(1 + K1CA0) - K1Δ/(1 + K1CA0)2, where K1 is the formation constant of the complex. It is shown that in the Job method of nuclear magnetic resonance measurements one has to plot ΔCA0 against the mole fraction, and the mole fraction at the maximum should give us the composition of the complex. Theoretical results have been verified experimentally on the weak interaction between naphthalene and methyl iodide. PMID:16592155

  2. Protein complexing in a methanogen suggests electron bifurcation and electron delivery from formate to heterodisulfide reductase

    PubMed Central

    Costa, Kyle C.; Wong, Phoebe M.; Wang, Tiansong; Lie, Thomas J.; Dodsworth, Jeremy A.; Swanson, Ingrid; Burn, June A.; Hackett, Murray; Leigh, John A.

    2010-01-01

    In methanogenic Archaea, the final step of methanogenesis generates methane and a heterodisulfide of coenzyme M and coenzyme B (CoM-S-S-CoB). Reduction of this heterodisulfide by heterodisulfide reductase to regenerate HS-CoM and HS-CoB is an exergonic process. Thauer et al. [Thauer, et al. 2008 Nat Rev Microbiol 6:579–591] recently suggested that in hydrogenotrophic methanogens the energy of heterodisulfide reduction powers the most endergonic reaction in the pathway, catalyzed by the formylmethanofuran dehydrogenase, via flavin-based electron bifurcation. Here we present evidence that these two steps in methanogenesis are physically linked. We identify a protein complex from the hydrogenotrophic methanogen, Methanococcus maripaludis, that contains heterodisulfide reductase, formylmethanofuran dehydrogenase, F420-nonreducing hydrogenase, and formate dehydrogenase. In addition to establishing a physical basis for the electron-bifurcation model of energy conservation, the composition of the complex also suggests that either H2 or formate (two alternative electron donors for methanogenesis) can donate electrons to the heterodisulfide-H2 via F420-nonreducing hydrogenase or formate via formate dehydrogenase. Electron flow from formate to the heterodisulfide rather than the use of H2 as an intermediate represents a previously unknown path of electron flow in methanogenesis. We further tested whether this path occurs by constructing a mutant lacking F420-nonreducing hydrogenase. The mutant displayed growth equal to wild-type with formate but markedly slower growth with hydrogen. The results support the model of electron bifurcation and suggest that formate, like H2, is closely integrated into the methanogenic pathway. PMID:20534465

  3. A chromium(III)-superoxo complex in oxygen atom transfer reactions as a chemical model of cysteine dioxygenase.

    PubMed

    Cho, Jaeheung; Woo, Jaeyoung; Nam, Wonwoo

    2012-07-11

    Metal-superoxo species are believed to play key roles in oxygenation reactions by metalloenzymes. One example is cysteine dioxygenase (CDO) that catalyzes the oxidation of cysteine with O(2), and an iron(III)-superoxo species is proposed as an intermediate that effects the sulfoxidation reaction. We now report the first biomimetic example showing that a chromium(III)-superoxo complex bearing a macrocyclic TMC ligand, [Cr(III)(O(2))(TMC)(Cl)](+), is an active oxidant in oxygen atom transfer (OAT) reactions, such as the oxidation of phosphine and sulfides. The electrophilic character of the Cr(III)-superoxo complex is demonstrated unambiguously in the sulfoxidation of para-substituted thioanisoles. A Cr(IV)-oxo complex, [Cr(IV)(O)(TMC)(Cl)](+), formed in the OAT reactions by the chromium(III)-superoxo complex, is characterized by X-ray crystallography and various spectroscopic methods. The present results support the proposed oxidant and mechanism in CDO, such as an iron(III)-superoxo species is an active oxidant that attacks the sulfur atom of the cysteine ligand by the terminal oxygen atom of the superoxo group, followed by the formation of a sulfoxide and an iron(IV)-oxo species via an O-O bond cleavage.

  4. EXFOR basics: A short guide to the nuclear reaction data exchange format

    SciTech Connect

    McLane, V.

    1996-07-01

    This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear data between the Nuclear Reaction Data Centers. In addition to storing the data and its` bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear data compilation centers. This format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center`s own sphere of responsibility. The exchange format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine). The data presently included in the EXFOR exchange include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle induced reaction data, a selected compilation of photon-induced reaction data.

  5. What Is the Overall Stoichiometry of a Complex Reaction?

    NASA Astrophysics Data System (ADS)

    Toby, Sidney; Tobias, Irwin

    2003-05-01

    The overall stoichiometry of a reaction having a multistep mechanism can be derived using methods based on either of the following two approaches: elemental-balance or extent of reaction. The extent of reaction method (ξ method) has been used for many years. We have recently shown (J.Chem. Educ. 2000, 77, 188) that integration of rate equations (the kinetic method) offers an alternative to the ξ method using methods that may be more familiar to many chemists. The two methods are, however, equivalent and give the same results, as pointed out in the Appendix. The elemental-balance method is the simplest of the three methods but, as we shall show, it does not always give as much information about the system being analyzed as do the other two methods. In this paper both elemental-balance and kinetic methods will be used to derive stoichiometric relationships and the results will be compared. We show that each method has its advantages and conclude that both methods are useful in different contexts.

  6. Cadmium(II) complex formation with cysteine and penicillamine.

    PubMed

    Jalilehvand, Farideh; Leung, Bonnie O; Mah, Vicky

    2009-07-06

    The complex formation between cadmium(II) and the ligands cysteine (H(2)Cys) and penicillamine (H(2)Pen = 3,3'-dimethylcysteine) in aqueous solutions, having C(Cd(II)) approximately 0.1 mol dm(-3) and C(H(2)L) = 0.2-2 mol dm(-3), was studied at pH = 7.5 and 11.0 by means of (113)Cd NMR and Cd K- and L(3)-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine molar ratios, the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52-2.54 and 2.27-2.35 A, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50-2.53 A, but with the Cd-(N/O) bond distances in a similar wide range, 2.28-2.33 A. For the molar ratio C(H(2)L)/C(Cd(II)) = 2, the (113)Cd chemical shifts, in the range 509-527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS(2)N(N/O) coordination geometry. With a large excess of cysteine (molar ratios C(H(2)Cys)/C(Cd(II)) >or= 10), complexes with CdS(4) coordination geometry dominate, consistent with the (113)Cd NMR chemical shifts, delta approximately 680 ppm at pH 7.5 and 636-658 ppm at pH 11.0, and their mean Cd-S distances were 2.53 +/- 0.02 A. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)(4)](n-), while at higher pH, the deprotonation of the amine groups promotes chelate formation. At pH 11.0, a minor amount of the [Cd(Cys)(3)](4-) complex with CdS(3)N coordination is formed. For the corresponding penicillamine solutions with molar ratios C(H(2)Pen)/C(Cd(II)) >or= 10, the (113)Cd NMR chemical shifts, delta approximately 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances, Cd-S 2.53 +/- 0.02 A and Cd-(N/O) 2.30-2.33 A, indicate that [Cd(penicillaminate)(3)](n-) complexes with chelating CdS(3)(N/O) coordination dominate already at pH 7.5 and become mixed with CdS(2)N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the

  7. Perfluoroalkyl Cobalt(III) Fluoride and Bis(perfluoroalkyl) Complexes: Catalytic Fluorination and Selective Difluorocarbene Formation.

    PubMed

    Leclerc, Matthew C; Bayne, Julia M; Lee, Graham M; Gorelsky, Serge I; Vasiliu, Monica; Korobkov, Ilia; Harrison, Daniel J; Dixon, David A; Baker, R Tom

    2015-12-30

    Four perfluoroalkyl cobalt(III) fluoride complexes have been synthesized and characterized by elemental analysis, multinuclear NMR spectroscopy, X-ray crystallography, and powder X-ray diffraction. The remarkable cobalt fluoride (19)F NMR chemical shifts (-716 to -759 ppm) were studied computationally, and the contributing paramagnetic and diamagnetic factors were extracted. Additionally, the complexes were shown to be active in the catalytic fluorination of p-toluoyl chloride. Furthermore, two examples of cobalt(III) bis(perfluoroalkyl)complexes were synthesized and their reactivity studied. Interestingly, abstraction of a fluoride ion from these complexes led to selective formation of cobalt difluorocarbene complexes derived from the trifluoromethyl ligand. These electrophilic difluorocarbenes were shown to undergo insertion into the remaining perfluoroalkyl fragment, demonstrating the elongation of a perfluoroalkyl chain arising from a difluorocarbene insertion on a cobalt metal center. The reactions of both the fluoride and bis(perfluoroalkyl) complexes provide insight into the potential catalytic applications of these model systems to form small fluorinated molecules as well as fluoropolymers.

  8. Computational study of peptide bond formation in the gas phase through ion-molecule reactions.

    PubMed

    Redondo, Pilar; Martínez, Henar; Cimas, Alvaro; Barrientos, Carmen; Largo, Antonio

    2013-08-21

    A computational study of peptide bond formation from gas-phase ion-molecule reactions has been carried out. We have considered the reaction between protonated glycine and neutral glycine, as well as the reaction between two neutral glycine molecules for comparison purposes. Two different mechanisms, concerted and stepwise, were studied. Both mechanisms show significant energy barriers for the neutral reaction. The energy requirements for peptide bond formation are considerably reduced upon protonation of one of the glycine molecules. For the reaction between neutral glycine and N-protonated glycine the lowest energy barrier is observed for the concerted mechanism. For the reaction between neutral glycine and protonated glycine at carbonyl oxygen, the preferred mechanism is the stepwise one, with a relatively small energy barrier (23 kJ mol(-1) at 0 K) and leading to the lowest-lying protonated glycylglycine isomer. In the case that the reaction could be initiated by protonated glycine at hydroxyl oxygen the process would be barrier-free and clearly exothermic. In that case peptide bond formation could take place even under interstellar conditions if glycine is present in space.

  9. Formation of HCN+ in Heterogeneous Reactions of N2+ and N+ with Surface Hydrocarbons

    PubMed Central

    2013-01-01

    A significant increase of the ion yield at m/z 27 in collisions of low-energy ions of N2+ and N+ with hydrocarbon-covered room-temperature or heated surfaces of tungsten, carbon-fiber composite, and beryllium, not observed in analogous collisions of Ar+, is ascribed to the formation of HCN+ in heterogeneous reactions between N2+ or N+ and surface hydrocarbons. The formation of HCN+ in the reaction with N+ indicated an exothermic reaction with no activation barrier, likely to occur even at very low collision energies. In the reaction with N2+, the formation of HCN+ was observed to a different degree on these room-temperature and heated (150 and 300 °C) surfaces at incident energies above about 50 eV. This finding suggested an activation barrier or reaction endothermicity of the heterogeneous reaction of about 3–3.5 eV. The main process in N2+ or N+ interaction with the surfaces is ion neutralization; the probability of forming the reaction product HCN+ was very roughly estimated for both N2+ and N+ ions to about one in 104 collisions with the surfaces. PMID:23614645

  10. Orientation dependence for Br formation in the reaction of oriented OH radical with HBr molecule.

    PubMed

    Tsai, Po-Yu; Che, Dock-Chil; Nakamura, Masaaki; Lin, King-Chuen; Kasai, Toshio

    2011-01-28

    The orientation dependence of Br-atom formation in the reaction of the oriented OH radical with the HBr molecule using the hexapole electrostatic field was studied. Experimental results for the orientation dependence in the reaction were analyzed using a Legendre polynomial fit. The results show two reactive sites. It was found that O-end attack is most favored for this reaction, and that H-end attack also shows a pronounced reactivity. The reactivity of the side-ways attack was found to be small. By comparing the results of the orientation dependence in the reaction with studies of inelastic collisions and theoretical calculations, two reaction pathways are proposed. Reaction by O-end attack is followed by a direct abstraction of the H-atom from the HBr molecule. The mechanism for H-end attack may have H-atom migration from HBr to form the water molecule.

  11. Reaction layer formation at the graphite/copper-chromium alloy interface

    NASA Technical Reports Server (NTRS)

    Devincent, Sandra M.; Michal, Gary M.

    1993-01-01

    Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

  12. Reaction layer formation at the graphite/copper-chromium alloy interface

    NASA Technical Reports Server (NTRS)

    Devincent, Sandra M.; Michal, Gary M.

    1992-01-01

    Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, auger electron spectroscopy, and x ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

  13. Module Based Complexity Formation: Periodic Patterning in Feathers and Hairs

    PubMed Central

    Chuong, Cheng-Ming; Yeh, Chao-Yuan; Jiang, Ting-Xin; Widelitz, Randall

    2012-01-01

    Patterns describe order which emerges from homogeneity. Complex patterns on the integument are striking because of their visibility throughout an organism's lifespan. Periodic patterning is an effective design because the ensemble of hair or feather follicles (modules) allows the generation of complexity, including regional variations and cyclic regeneration, giving the skin appendages a new lease on life. Spatial patterns include the arrangements of feathers and hairs in specified number, size, and spacing. We explore how a field of equivalent progenitor cells can generate periodically arranged modules based on genetic information, physical-chemical rules and developmental timing. Reconstitution experiments suggest a competitive equilibrium regulated by activators / inhibitors involving Turing reaction-diffusion. Temporal patterns result from oscillating stem cell activities within each module (micro-environment regulation), reflected as growth (anagen) and resting (telogen) phases during the cycling of feather and hair follicles. Stimulating modules with activators initiates the spread of regenerative hair waves, while global inhibitors outside each module (macro-environment) prevent this. Different wave patterns can be simulated by Cellular Automata principles. Hormonal status and seasonal changes can modulate appendage phenotypes, leading to “organ metamorphosis”, with multiple ectodermal organ phenotypes generated from the same precursors. We discuss potential evolutionary novel steps using this module based complexity in several amniote integument organs, exemplified by the spectacular peacock feather pattern. We thus explore the application of the acquired knowledge of patterning in tissue engineering. New hair follicles can be generated after wounding. Hairs and feathers can be reconstituted through self-organization of dissociated progenitor cells. PMID:23539312

  14. Theoretical studies on N-O or N-N bond formation from aryl azide catalyzed by iron(II) bromide complex.

    PubMed

    Li, Juan; Zhang, Qi; Zhou, Lixin

    2012-03-02

    DFT calculations have been carried out to study the reaction mechanism on N-O or N-N bond formation from aryl azide catalyzed by iron(II) bromide complex. A favorable reaction pathway is proposed to account for the construction of the core structure of 2H-indazoles or 2,1-benzisoxazoles.

  15. Dynamical complexity in the perception-based network formation model

    NASA Astrophysics Data System (ADS)

    Jo, Hang-Hyun; Moon, Eunyoung

    2016-12-01

    Many link formation mechanisms for the evolution of social networks have been successful to reproduce various empirical findings in social networks. However, they have largely ignored the fact that individuals make decisions on whether to create links to other individuals based on cost and benefit of linking, and the fact that individuals may use perception of the network in their decision making. In this paper, we study the evolution of social networks in terms of perception-based strategic link formation. Here each individual has her own perception of the actual network, and uses it to decide whether to create a link to another individual. An individual with the least perception accuracy can benefit from updating her perception using that of the most accurate individual via a new link. This benefit is compared to the cost of linking in decision making. Once a new link is created, it affects the accuracies of other individuals' perceptions, leading to a further evolution of the actual network. As for initial actual networks, we consider both homogeneous and heterogeneous cases. The homogeneous initial actual network is modeled by Erdős-Rényi (ER) random networks, while we take a star network for the heterogeneous case. In any cases, individual perceptions of the actual network are modeled by ER random networks with controllable linking probability. Then the stable link density of the actual network is found to show discontinuous transitions or jumps according to the cost of linking. As the number of jumps is the consequence of the dynamical complexity, we discuss the effect of initial conditions on the number of jumps to find that the dynamical complexity strongly depends on how much individuals initially overestimate or underestimate the link density of the actual network. For the heterogeneous case, the role of the highly connected individual as an information spreader is also discussed.

  16. Binuclear metallohydrolases: complex mechanistic strategies for a simple chemical reaction.

    PubMed

    Schenk, Gerhard; Mitić, Nataša; Gahan, Lawrence R; Ollis, David L; McGeary, Ross P; Guddat, Luke W

    2012-09-18

    Binuclear metallohydrolases are a large family of enzymes that require two closely spaced transition metal ions to carry out a plethora of hydrolytic reactions. Representatives include purple acid phosphatases (PAPs), enzymes that play a role in bone metabolism and are the only member of this family with a heterovalent binuclear center in the active form (Fe(3+)-M(2+), M = Fe, Zn, Mn). Other members of this family are urease, which contains a di-Ni(2+) center and catalyzes the breakdown of urea, arginase, which contains a di-Mn(2+) center and catalyzes the final step in the urea cycle, and the metallo-β-lactamases, which contain a di-Zn(2+) center and are virulence factors contributing to the spread of antibiotic-resistant pathogens. Binuclear metallohydrolases catalyze numerous vital reactions and are potential targets of drugs against a wide variety of human disorders including osteoporosis, various cancers, antibiotic resistance, and erectile dysfunctions. These enzymes also tend to catalyze more than one reaction. An example is an organophosphate (OP)-degrading enzyme from Enterobacter aerogenes (GpdQ). Although GpdQ is part of a pathway that is used by bacteria to degrade glycerolphosphoesters, it hydrolyzes a variety of other phosphodiesters and displays low levels of activity against phosphomono- and triesters. Such a promiscuous nature may have assisted the apparent recent evolution of some binuclear metallohydrolases to deal with situations created by human intervention such as OP pesticides in the environment. OP pesticides were first used approximately 70 years ago, and therefore the enzymes that bacteria use to degrade them must have evolved very quickly on the evolutionary time scale. The promiscuous nature of enzymes such as GpdQ makes them ideal candidates for the application of directed evolution to produce new enzymes that can be used in bioremediation and against chemical warfare. In this Account, we review the mechanisms employed by binuclear

  17. Secondary Organic Aerosol Formation by Molecular-Weight Building Reactions of Biogenic Oxidation Products

    NASA Astrophysics Data System (ADS)

    Barsanti, K.; Guenther, A.; Matsunaga, S.; Smith, J.

    2006-12-01

    Understanding the chemical composition of atmospheric organic aerosols (OA) remains one of the significant challenges to accurately representing OA in air quality and climate models. Meeting this challenge will require further understanding of secondary organic aerosols (SOA), of which biogenic emissions are thought to be major precursors. Of recent interest is the significance of higher-molecular weight (MW) compounds (i.e., "oligomers"). Theoretical, laboratory, and field study results suggest that relatively volatile oxidation products may contribute to SOA formation through multi-phase MW- building reactions. The significance of such reactions for biogenic SOA formation, including for newly considered precursors such as isoprene, is explored in this work. Theoretical and field studies are employed to: 1) identify MW-building reactions that may contribute to SOA formation in the atmosphere, 2) identify MW-building reaction products in ambient samples, and 3) parameterize atmospheric SOA formation by MW-building reactions of biogenic oxidation products. Likely reactions of biogenic oxidation products include ester, amide, and peroxyhemiacetal formation. Each of the proposed reactions involves known oxidation productions of biogenic precursors (e.g., carboxylic acids and aldehydes) reacting with one another and/or other atmospheric constituents (e.g., sulfuric acid and ammonia) to form higher-MW/lower-volatility products that can condense to form SOA. It has been suggested that products of MW-building reactions can revert to the parent reactants during sampling and analysis. Thus, relatively volatile compounds detected in ambient particle samples in fact may be decomposition products of higher-MW products. The contribution of relatively volatile biogenic oxidation products to SOA via ester, amide, and peroxyhemiacetal formation, as determined by studies based on fundamental thermodynamics and gas/particle partitioning theory, will be discussed; in addition to

  18. Theory of diffusion-influenced reactions in complex geometries.

    PubMed

    Galanti, Marta; Fanelli, Duccio; Traytak, Sergey D; Piazza, Francesco

    2016-06-21

    Chemical transformations involving the diffusion of reactants and subsequent chemical fixation steps are generally termed "diffusion-influenced reactions" (DIR). Virtually all biochemical processes in living media can be counted among them, together with those occurring in an ever-growing number of emerging nano-technologies. The role of the environment's geometry (obstacles, compartmentalization) and distributed reactivity (competitive reactants, traps) is key in modulating the rate constants of DIRs, and is therefore a prime design parameter. Yet, it is a formidable challenge to build a comprehensive theory that is able to describe the environment's "reactive geometry". Here we show that such a theory can be built by unfolding this many-body problem through addition theorems for special functions. Our method is powerful and general and allows one to study a given DIR reaction occurring in arbitrary "reactive landscapes", made of multiple spherical boundaries of given size and reactivity. Importantly, ready-to-use analytical formulas can be derived easily in most cases.

  19. Complex formation dynamics in a single-molecule electronic device

    PubMed Central

    Wen, Huimin; Li, Wengang; Chen, Jiewei; He, Gen; Li, Longhua; Olson, Mark A.; Sue, Andrew C.-H.; Stoddart, J. Fraser; Guo, Xuefeng

    2016-01-01

    Single-molecule electronic devices offer unique opportunities to investigate the properties of individual molecules that are not accessible in conventional ensemble experiments. However, these investigations remain challenging because they require (i) highly precise device fabrication to incorporate single molecules and (ii) sufficient time resolution to be able to make fast molecular dynamic measurements. We demonstrate a graphene-molecule single-molecule junction that is capable of probing the thermodynamic and kinetic parameters of a host-guest complex. By covalently integrating a conjugated molecular wire with a pendent crown ether into graphene point contacts, we can transduce the physical [2]pseudorotaxane (de)formation processes between the electron-rich crown ether and a dicationic guest into real-time electrical signals. The conductance of the single-molecule junction reveals two-level fluctuations that are highly dependent on temperature and solvent environments, affording a nondestructive means of quantitatively determining the binding and rate constants, as well as the activation energies, for host-guest complexes. The thermodynamic processes reveal the host-guest binding to be enthalpy-driven and are consistent with conventional 1H nuclear magnetic resonance titration experiments. This electronic device opens up a new route to developing single-molecule dynamics investigations with microsecond resolution for a broad range of chemical and biochemical applications. PMID:28138528

  20. Formation of Cluster Complexes by Cluster-Cluster-Collisions

    NASA Astrophysics Data System (ADS)

    Ichihashi, Masahiko; Odaka, Hideho

    2015-03-01

    Multi-element clusters are interested in their chemical and physical properties, and it is expected that they are utilized as catalysts, for example. Their properties critically depend on the size, composition and atomic ordering, and it should be important to adjust the above parameters for their functionality. One of the ways to form a multi-element cluster is to employ a low-energy collision between clusters. Here, we show characteristic results obtained in the collision between a neutral Ar cluster and a size-selected Co cluster ion. Low-energy collision experiment was accomplished by using a newly developed merging-beam apparatus. Cobalt cluster ions were produced by laser ablation, and mass-selected. On the other hand, argon clusters were prepared by the supersonic expansion of Ar gas. Both cluster beams were merged together in an ion guide, and ionic cluster complexes were mass-analyzed. In the collision of Co2+ and ArN, Co2Arn+ (n = 1 - 30) were observed, and the total intensity of Co2Arn+ (n >= 1) is inversely proportional to the relative velocity between Co2+ and ArN. This suggests that the charge-induced dipole interaction between Co2+ and a neutral Ar cluster is dominant in the formation of the cluster complex, Co2+Arn.

  1. Optimized Reaction Conditions for Amide Bond Formation in DNA-Encoded Combinatorial Libraries.

    PubMed

    Li, Yizhou; Gabriele, Elena; Samain, Florent; Favalli, Nicholas; Sladojevich, Filippo; Scheuermann, Jörg; Neri, Dario

    2016-08-08

    DNA-encoded combinatorial libraries are increasingly being used as tools for the discovery of small organic binding molecules to proteins of biological or pharmaceutical interest. In the majority of cases, synthetic procedures for the formation of DNA-encoded combinatorial libraries incorporate at least one step of amide bond formation between amino-modified DNA and a carboxylic acid. We investigated reaction conditions and established a methodology by using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide, 1-hydroxy-7-azabenzotriazole and N,N'-diisopropylethylamine (EDC/HOAt/DIPEA) in combination, which provided conversions greater than 75% for 423/543 (78%) of the carboxylic acids tested. These reaction conditions were efficient with a variety of primary and secondary amines, as well as with various types of amino-modified oligonucleotides. The reaction conditions, which also worked efficiently over a broad range of DNA concentrations and reaction scales, should facilitate the synthesis of novel DNA-encoded combinatorial libraries.

  2. Interaction between the antibiotic spiramycin and a ribosomal complex active in peptide bond formation.

    PubMed

    Dinos, G; Synetos, D; Coutsogeorgopoulos, C

    1993-10-12

    The inhibition of peptide bond formation by spiramycin was studied in an in vitro system derived from Escherichia coli. Peptide bonds are formed between puromycin (S) and Ac-Phe-tRNA, which is a component of complex C, i.e., of the [Ac-Phe-tRNA-70S ribosome-poly(U)] complex, according to the puromycin reaction: C+S (Ks)<==>CS (k3)==>C'+P [Synetos, D., & Coutsogeorgopoulos, C. (1987) Biochim. Biophys. Acta 923, 275-285]. It is shown that spiramycin (A) reacts with complex C and forms the spiramycin complex C*A, which is inactive toward puromycin. C*A is the tightest complex formed between complex C and any of a number of antibiotics, such as chloramphenicol, blasticidin S, lincomycin, or sparsomycin. C*A remains stable following gel chromatography on Sephadex G-200 and sucrose gradient ultracentrifugation. Detailed kinetic study suggests that C*A is formed in a variation of a two-step mechanism in which the initial encounter complex CA is kinetically insignificant and C*A is the product of a conformational change of complex CA according to the equation, C+A (kassoc)<==>(kdissoc) C*A. The rate constants of this reaction (spiramycin reaction) are kassoc = 3.0 x 10(4) M-1 s-1 and kdissoc = 5.0 x 10(-5) s-1. Such values allow the classification of spiramycin as a slow-binding, slowly reversible inhibitor; they also lead to the calculation of an apparent overall dissociation constant equal to 1.8 nM for the C*A complex. Furthermore, they render spiramycin a useful tool in the study of antibiotic action on protein synthesis in vitro. Thus, the spiramycin reaction, in conjunction with the puromycin reaction, is applied (i) to detect a strong preincubation effect exerted by chloramphenicol and lincomycin (this effect constitutes further evidence that these two antibiotics combine with complex C as slow-binding inhibitors) and (ii) to determine the rate constant for the regeneration (k7 = 2.0 x 10(-3) s-1) of complex C from the sparsomycin complex C*I [Theocharis, D. A

  3. [THE THROMBUS FORMATION IN THE PROSTHESIS AS A REACTION OF ORGANISM ON ITS MATERIAL].

    PubMed

    Alekseyeva, T A; Gupalo, Yu M; Kolomoets, A M; Lazarenko, O N; Lazarenko, G O; Litvin, P M; Lohs, I V; Smorzhevskiy, V J; Stepkin, V I

    2016-04-01

    Abstract Vascular prostheses, excised because of their functional properties loss, were studied. Using different methods there was established, that this complication is caused by the thrombus formation as a reaction of organism on the prosthesis material. The testing procedure on compatibility was proposed, using atomic-power microscope. Components of a patient immunity may identify the prosthesis material and start the rejection mechanisms in case of negative reaction.

  4. Numerical study on the impacts of heterogeneous reactions on ozone formation in the Beijing urban area

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Zhang, Yuanhang; Wang, Wei

    2006-12-01

    The air quality model CMAQ-MADRID (Community Multiscale Air Quality-Model of Aerosol Dynamics, Reaction, Ionization and Dissolution) was employed to simulate summer O3 formation in Beijing China, in order to explore the impacts of four heterogeneous reactions on O3 formation in an urban area. The results showed that the impacts were obvious and exhibited the characteristics of a typical response of a VOC-limited regime in the urban area. For the four heterogeneous reactions considered, the NO2 and HO2 heterogeneous reactions have the most severe impacts on O3 formation. During the O3 formation period, the NO2 heterogeneous reaction increased new radical creation by 30%, raising the atmospheric activity as more NO→NO2 conversion occurred, thus causing the O3 to rise. The increase of O3 peak concentration reached a maximum value of 67 ppb in the urban area. In the morning hours, high NO titration reduced the effect of the photolysis of HONO, which was produced heterogeneously at night in the surface layer. The NO2 heterogeneous reaction in the daytime is likely one of the major reasons causing the O3 increase in the Beijing urban area. The HO2 heterogeneous reaction accelerated radical termination, resulting in a decrease of the radical concentration by 44% at the most. O3 peak concentration decreased by a maximum amount of 24 ppb in the urban area. The simulation results were improved when the heterogeneous reactions were included, with the O3 and HONO model results close to the observations.

  5. Uncertainty quantification: Making predictions of complex reaction systems reliable

    NASA Astrophysics Data System (ADS)

    Russi, Trent; Packard, Andy; Frenklach, Michael

    2010-10-01

    There is increasing need to make chemical reaction models and modeling more predictive. We examine the modeling methodology from the perspective of propagation of uncertainties, those in assumed model parameters along with those in experimental observations. Accepting the length of the uncertainty interval in the predicted property as a measure of model predictiveness, we examine methodological factors affecting it. Employing the recently introduced technique of Data Collaboration, we show that even 'harmless' assumptions, invoked explicitly or implicitly to alleviate a burden of numerical procedures, could lead to substantial differences in model predictiveness. We also demonstrate that the direct, one-step methodology, such as Data Collaboration, necessarily makes modeling more predictive and thus more reliable than a two-step approach typical of most current methods.

  6. Calibration of Complex Subsurface Reaction Models Using a Surrogate-Model Approach

    EPA Science Inventory

    Application of model assessment techniques to complex subsurface reaction models involves numerous difficulties, including non-trivial model selection, parameter non-uniqueness, and excessive computational burden. To overcome these difficulties, this study introduces SAMM (Simult...

  7. Cyclodextrins in pharmaceutical formulations I: structure and physicochemical properties, formation of complexes, and types of complex.

    PubMed

    Jambhekar, Sunil S; Breen, Philip

    2016-02-01

    Cyclodextrins are cyclic oligosaccharides that have been recognized as pharmaceutical adjuvants for the past 20 years. The molecular structure of these glucose derivatives, which approximates a truncated cone, bucket, or torus, generates a hydrophilic exterior surface and a nonpolar interior cavity. Cyclodextrins can interact with appropriately sized drug molecules to yield an inclusion complex. These noncovalent inclusion complexes offer a variety of advantages over the noncomplexed form of a drug. Cyclodextrins are primarily used to enhance the aqueous solubility, physical chemical stability, and bioavailability of drugs. Their other applications include preventing drug-drug interactions, converting liquid drugs into microcrystalline powders, minimizing gastrointestinal and ocular irritation, and reducing or eliminating unpleasant taste and smell. Here, we discuss the physical chemical properties of various cyclodextrins, including the effects of substitutions on these properties. Additionally, we report on the regulatory status of their use, commercial products containing cyclodextrins, toxicological considerations, and the forces involved in complex formation. We also highlight the types of complex formed and discuss the methods used to determine the types of complex present.

  8. Transient kinetics of electron transfer reactions of flavodoxin: ionic strength dependence of semiquinone oxidation by cytochrome c, ferricyanide, and ferric ethylenediaminetetraacetic acid and computer modeling of reaction complexes.

    PubMed

    Simondsen, R P; Weber, P C; Salemme, F R; Tollin, G

    1982-12-07

    Electron transfer reactions between Clostridum pasteurianum flavodoxin semiquinone and various oxidants [horse heart cytochrome c, ferricyanide, and ferric ethylenediaminetetraacetic [horse heart cytochrome c, ferricyanide, and ferric ethylenediaminetetraacetic acid (EDTA)] have been studied as a function of ionic strength by using stopped-flow spectrophotometry. The cytochrome c reaction is complicated by the existence of two cytochrome species which react at different rates and whose relative concentrations are ionic strength dependent. Only the faster of these two reactions is considered here. At low ionic strength, complex formation between cytochrome c and flavodoxin is indicated by a leveling off of the pseudo-first-order rate constant at high cytochrome c concentration. This is not observed for either ferricyanide or ferric EDTA. For cytochrome c, the rate and association constants for complex formation were found to increase with decreasing ionic strength, consistent with negative charges on flavodoxin interacting with the positively charged cytochrome electron transfer site. Both ferricyanide and ferric EDTA are negatively charged oxidants, and the rate data respond to ionic strength changes as would be predicted for reactants of the same charge sign. These results demonstrate that electrostatic interactions involving negatively charged groups are important in orienting flavodoxin with respect to oxidants during electron transfer. We have also carried out computer modeling studies of putative complexes of flavodoxin with cytochrome c and ferricyanide, which relate their structural properties to both the observed kinetic behavior and some more general features of physiological electron transfer processes. The results of this study are consistent with the ionic strength behavior described above.

  9. Neutral and Cationic Alkyl Tantalum Imido Complexes: Synthesis and Migratory Insertion Reactions

    PubMed Central

    Anderson, Laura L.; Schmidt, Joseph A. R.; Arnold, John; Bergman, Robert G.

    2008-01-01

    The synthesis and reactivity of dibenzyl cationic tantalum imido complexes is described. The trialkyl tantalum imido compounds Bn3Ta=NCMe3 (1) and Np3Ta=NCMe3 (2) were synthesized as starting materials for the study of dialkyl cationic tantalum imido complexes. Compound 1 undergoes insertion reactions with diisopropylcarbodiimide and 2,6-dimethylphenylisocyanide to give (bisamidinate)imido complex 5 and (bisimino-acyl)imido complex 6, respectively. Treatment of compound 1 with B(C6F5)3 gives the zwitterionic tantalum complex [Bn2Ta=NCMe3][BnB(C6F5)3] (7) which is stabilized by η6-coordination of the benzyl triaryl borate anion. Coordination of the aryl anion can be displaced by three equivalents of pyridine to give the Lewis base complex 8. Treatment of compound 1 with [Ph3C][B(C6F5)4] gives the cationic tantalum imido complex [Bn2Ta=NCMe3][B(C6F5)4] (3). This salt forms insoluble aggregates unless trapped by THF coordination or an insertion reaction with an alkyne or an alkene. Cation 3 undergoes migratory insertion reactions with diphenylacetylene, phenylacetylene, norbornene, and cis-cyclooctene to give the corresponding alkenyl or modified alkyl imido complexes. The characterization of these products and the significance of these insertion reactions with respect to Ziegler-Natta polymerizations and hydroamination reactions are described. PMID:19079787

  10. Analysis of the Pressure and Temperature Dependence of the Complex-Forming Bimolecular Reaction CH3OCH3 + Fe(.).

    PubMed

    Ard, Shaun G; Johnson, Ryan S; Martinez, Oscar; Shuman, Nicholas S; Guo, Hua; Troe, Jürgen; Viggiano, Albert

    2016-07-14

    The kinetics of the reaction CH3OCH3 + Fe(+) has been studied between 250 and 600 K in the buffer gas He at pressures between 0.4 and 1.6 Torr. Total rate constants and branching ratios for the formation of Fe(+)O(CH3)2 adducts and of Fe(+)OCH2 + CH4 products were determined. Quantum-chemical calculations provided the parameters required for an analysis in terms of statistical unimolecular rate theory. The analysis employed a recently developed simplified representation of the rates of complex-forming bimolecular reactions, separating association and chemical activation contributions. Satisfactory agreement between experimental results and kinetic modeling was obtained that allows for an extrapolation of the data over wide ranges of conditions. Possible reaction pathways with or without spin-inversion are discussed in relation to the kinetic modeling results.

  11. Secondary organic aerosol formation from ozone-initiated reactions with nicotine and secondhand tobacco smoke

    NASA Astrophysics Data System (ADS)

    Sleiman, Mohamad; Destaillats, Hugo; Smith, Jared D.; Liu, Chen-Lin; Ahmed, Musahid; Wilson, Kevin R.; Gundel, Lara A.

    2010-11-01

    We used controlled laboratory experiments to evaluate the aerosol-forming potential of ozone reactions with nicotine and secondhand smoke. Special attention was devoted to real-time monitoring of the particle size distribution and chemical composition of SOA as they are believed to be key factors determining the toxicity of SOA. The experimental approach was based on using a vacuum ultraviolet photon ionization time-of-flight aerosol mass spectrometer (VUV-AMS), a scanning mobility particle sizer (SMPS) and off-line thermal desorption coupled to mass spectrometry (TD-GC-MS) for gas-phase byproducts analysis. Results showed that exposure of SHS to ozone induced the formation of ultrafine particles (<100 nm) that contained high molecular weight nitrogenated species ( m/ z 400-500), which can be due to accretion/acid-base reactions and formation of oligomers. In addition, nicotine was found to contribute significantly (with yields 4-9%) to the formation of secondary organic aerosol through reaction with ozone. The main constituents of the resulting SOA were tentatively identified and a reaction mechanism was proposed to elucidate their formation. These findings identify a new component of thirdhand smoke that is associated with the formation of ultrafine particles (UFP) through oxidative aging of secondhand smoke. The significance of this chemistry for indoor exposure and health effects is highlighted.

  12. Incorporation of polyoxotungstate complexes in silica spheres and in situ formation of tungsten trioxide nanoparticles.

    PubMed

    Zhao, Yuanyuan; Fan, Haimei; Li, Wen; Bi, Lihua; Wang, Dejun; Wu, Lixin

    2010-09-21

    In this paper, we demonstrated a new convenient route for in situ fabrication of well separated small sized WO(3) nanoparticles in silica spheres, through a predeposition of surfactant encapsulated polyoxotungates as tungsten source, and followed by a calcination process. In a typical procedure, selected polyoxotungates with different charges were enwrapped with dioctadecyldimethylammonium cations through electrostatic interaction. Elemental analysis, thermogravimetric analysis, and spectral characterization confirmed the formation of prepared complexes with the anticipated chemical structure. The complexes were then phase-transferred into aqueous solution that predissolved surfactant cetyltrimethylammonium bromide, and finally incorporated into silica spheres through a joint sol-gel reaction with tetraethyl orthosilicate in a well dispersed state under the protection of organic layer for polyoxotungates from the alkaline reaction condition. Transmission electron microscopic images illustrated the well dispersed WO(3) nanoparticles in the size range of ca. 2.2 nm in the silica spheres after the calcination at 465 °C. The sizes of both the silica spheres and WO(3) nanoparticles could be adjusted independently through changing the doping content to a large extent. Meanwhile, the doped polyoxotungate complexes acted as the template for the mesoporous structure in silica spheres after the calcination. Along with the increase of doping content and surfactant, the mesopore size changed little (2.0-2.9 nm), but the specific surface areas increased quite a lot. Importantly, the WO(3)-nanoparticle-doped silica spheres displayed an interesting photovoltaic property, which is favorable for the funtionalization of these nanomaterials.

  13. Calcium l-tartrate complex formation in neutral and in hyperalkaline aqueous solutions.

    PubMed

    Gácsi, Attila; Kutus, Bence; Csendes, Zita; Faragó, Tünde; Peintler, Gábor; Pálinkó, István; Sipos, Pál

    2016-11-01

    The complex formation reaction between the l-tartrate (Tar(2-)) and calcium ions taking place in neutral and in hyperalkaline (pH > 13) aqueous solutions has been investigated. It was demonstrated that upon NaOH addition the solubility of the CaTar(s) precipitate significantly increases. Conductometric and freezing point depression measurements further confirmed that in this process water soluble species are formed as a result of a reaction between the CaTar(s) and the hydroxide ion (or, conversely, between Ca(OH)2(s) and the Tar(2-) ion). (13)C NMR spectroscopic measurements yielded the value of pK3 = 15.4 ± 0.2 for the proton dissociation of one of the alcoholic OH groups of Tar(2-) (at 25.0 °C and 4 M Na(Cl) ionic strength). Upon addition of calcium ions to an alkaline Tar(2-) solution, the (1)H NMR signal gradually broadened and the (13)C-satellite peaks split to two components, which also indicate complexation. From H2/Pt potentiometric titrations performed with solutions in the 13.6 ≤ pH ≤ 14.4 range, it was observed, that this complex formation is accompanied by a hydroxide ion consuming process. The titration curves can be best described via assuming the formation of the CaTarH-1(-)(aq) (lg β11-1 = -11.2 ± 0.1) and CaTarH-2(2-)(aq) (lg β11-2 = -25.3 ± 0.1) complexes. In hyperalkaline solutions, these two species account for more than 90-99% of the calcium ions present and the contribution of the other reasonable and well-established calcium-containing solution species is rather small. The possible structures of the above complexes have been modeled via ab initio calculations. The stoichiometries are consistent both with species containing coordinated alcoholate group(s) and with mixed Ca(ii)-hydroxo-tartrato complexes. From the data available at present, both types of structures can be considered as chemically reasonable.

  14. Substrate decomposition in galvanic displacement reaction: Contrast between gold and silver nanoparticle formation

    SciTech Connect

    Ghosh, Tapas; Satpati, Biswarup

    2015-06-24

    We have investigated substrate decomposition during formation of silver and gold nanoparticles in galvanic displacement reaction on germanium surfaces. Silver and gold nanoparticles were synthesized by electroless deposition on sputter coated germanium thin film (∼ 200 nm) grown initially on silicon substrate. The nanoparticles formation and the substrate corrosion were studied using scanning transmission electron microscopy (STEM) and the energy dispersive X-ray (EDX) spectroscopy.

  15. Paternò-Büchi reaction between furan and heterocyclic aldehydes: oxetane formation vs. metathesis.

    PubMed

    D'Auria, Maurizio; Racioppi, Rocco; Viggiani, Licia

    2010-08-01

    The photochemical reaction of 2-substituted heterocyclic aldehydes with furan gave the corresponding exo oxetane derivatives through the excited triplet state. However, in situ the oxetane derivatives were converted through a metathesis reaction into the corresponding Z,E-butadienyl formate derivatives. On the contrary, 3-substituted heterocyclic aldehydes gave the corresponding exo oxetane derivatives. The effect of 2-substituted heterocyclic ring in order to facilitate the metathesis reaction is explained considering the possible participation of the pi aromatic orbitals in the oxetane C-O bond cleavage.

  16. EXFOR systems manual: Nuclear reaction data exchange format. Revision 97/1

    SciTech Connect

    McLane, V.

    1997-07-01

    This document describes EXFOR, the exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Center Network. In addition to storing the data and its` bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. EXFOR is designed for flexibility rather than optimization of data processing in order to meet the diverse needs of the nuclear reaction data centers. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center`s own sphere of responsibility. The exchange format, as outlined, is designed to allow a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine).

  17. Reaction of a copper(II)-nitrosyl complex with hydrogen peroxide: phenol ring nitration through a putative peroxynitrite intermediate.

    PubMed

    Kalita, Apurba; Deka, Ramesh C; Mondal, Biplab

    2013-10-07

    Copper(II) complex, 1, with the histidine-derived ligand L (L = methyl 2-(2-hydroxybenzylamino)-3-(1H-imidazol-5-yl)propanoate) has been synthesized and characterized. Single-crystal structure determination reveals a diphenolato-bridged dicopper(II) core in 1. Addition of (•)NO to an acetonitrile solution of 1 affords the corresponding mononuclear copper(II)-nitrosyl complex, 2. In the presence of H2O2, 2 results in formation of the corresponding copper(I)-peroxynitrite. Formation of peroxynitrite ((-)OONO) intermediate is evident from its characteristic phenol ring nitration reaction which resembles the tyrosine nitration in biological systems. Further, isolation of nitrate (NO3(-)) as the decomposition product from 2 at room temperature also supports the involvement of (-)OONO intermediate.

  18. Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction.

    PubMed

    Yao, Qingwei; Kinney, Elizabeth P; Zheng, Chong

    2004-08-19

    Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.

  19. Changes in protein structure at the interface accompanying complex formation

    PubMed Central

    Chakravarty, Devlina; Janin, Joël; Robert, Charles H.; Chakrabarti, Pinak

    2015-01-01

    Protein interactions are essential in all biological processes. The changes brought about in the structure when a free component forms a complex with another molecule need to be characterized for a proper understanding of molecular recognition as well as for the successful implementation of docking algorithms. Here, unbound (U) and bound (B) forms of protein structures from the Protein–Protein Interaction Affinity Database are compared in order to enumerate the changes that occur at the interface atoms/residues in terms of the solvent-accessible surface area (ASA), secondary structure, temperature factors (B factors) and disorder-to-order transitions. It is found that the interface atoms optimize contacts with the atoms in the partner protein, which leads to an increase in their ASA in the bound interface in the majority (69%) of the proteins when compared with the unbound interface, and this is independent of the root-mean-square deviation between the U and B forms. Changes in secondary structure during the transition indicate a likely extension of helices and strands at the expense of turns and coils. A reduction in flexibility during complex formation is reflected in the decrease in B factors of the interface residues on going from the U form to the B form. There is, however, no distinction in flexibility between the interface and the surface in the monomeric structure, thereby highlighting the potential problem of using B factors for the prediction of binding sites in the unbound form for docking another protein. 16% of the proteins have missing (disordered) residues in the U form which are observed (ordered) in the B form, mostly with an irregular conformation; the data set also shows differences in the composition of interface and non-interface residues in the disordered polypeptide segments as well as differences in their surface burial. PMID:26594372

  20. Changes in protein structure at the interface accompanying complex formation.

    PubMed

    Chakravarty, Devlina; Janin, Joël; Robert, Charles H; Chakrabarti, Pinak

    2015-11-01

    Protein interactions are essential in all biological processes. The changes brought about in the structure when a free component forms a complex with another molecule need to be characterized for a proper understanding of molecular recognition as well as for the successful implementation of docking algorithms. Here, unbound (U) and bound (B) forms of protein structures from the Protein-Protein Interaction Affinity Database are compared in order to enumerate the changes that occur at the interface atoms/residues in terms of the solvent-accessible surface area (ASA), secondary structure, temperature factors (B factors) and disorder-to-order transitions. It is found that the interface atoms optimize contacts with the atoms in the partner protein, which leads to an increase in their ASA in the bound interface in the majority (69%) of the proteins when compared with the unbound interface, and this is independent of the root-mean-square deviation between the U and B forms. Changes in secondary structure during the transition indicate a likely extension of helices and strands at the expense of turns and coils. A reduction in flexibility during complex formation is reflected in the decrease in B factors of the interface residues on going from the U form to the B form. There is, however, no distinction in flexibility between the interface and the surface in the monomeric structure, thereby highlighting the potential problem of using B factors for the prediction of binding sites in the unbound form for docking another protein. 16% of the proteins have missing (disordered) residues in the U form which are observed (ordered) in the B form, mostly with an irregular conformation; the data set also shows differences in the composition of interface and non-interface residues in the disordered polypeptide segments as well as differences in their surface burial.

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

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; KAMALUDDIN

    1989-01-01

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

  2. Modeling dichloroacetic acid formation from the reaction of monochloramine with natural organic matter.

    PubMed

    Duirk, Stephen E; Valentine, Richard L

    2006-08-01

    A kinetic model was developed to predict dichloroacetic acid (DCAA) formation in chloraminated systems. Equations describing DCAA formation were incorporated into an established comprehensive monochloramine-natural organic matter (NOM) reaction model. DCAA formation was theorized to be proportional to the amount of NOM oxidized by monochloramine and described by a single dimensionless DCAA formation coefficient, theta(DCAA) (M(DCAA)/M(DOC(ox)). The applicability of the model to describe DCAA formation in the presence of six different NOM sources was evaluated. DCAA formation could be described by considering a single NOM source-specific value for theta(DCAA) over a wide range of experimental conditions (i.e., pH, NOM, free ammonia, and monochloramine concentrations). DCAA formation appears to be directly proportional to the amount of active chlorine (monochloramine and free chlorine) that reacted with the NOM under these experimental conditions. Values of theta(DCAA) for all six NOM sources, determined by nonlinear regression analysis, varied from 6.51 x 10(-3) to 1.15 x 10(-2) and were linearly correlated with specific ultraviolet absorbance at 280 nm (SUVA(280)). The ability to model monochloramine loss and DCAA formation in the presence of NOM provides insight into disinfection by-product (DBP) formation pathways under chloramination conditions. The subsequent model and correlations to SUVA has the potential to aid the water treatment industry as a tool in developing strategies that minimize DBP formation while maintaining the microbial integrity of the water distribution system.

  3. Effects of formate binding on the quinone-iron electron acceptor complex of photosystem II.

    PubMed

    Sedoud, Arezki; Kastner, Lisa; Cox, Nicholas; El-Alaoui, Sabah; Kirilovsky, Diana; Rutherford, A William

    2011-02-01

    EPR was used to study the influence of formate on the electron acceptor side of photosystem II (PSII) from Thermosynechococcus elongatus. Two new EPR signals were found and characterized. The first is assigned to the semiquinone form of Q(B) interacting magnetically with a high spin, non-heme-iron (Fe²(+), S=2) when the native bicarbonate/carbonate ligand is replaced by formate. This assignment is based on several experimental observations, the most important of which were: (i) its presence in the dark in a significant fraction of centers, and (ii) the period-of-two variations in the concentration expected for Q(B)(•-) when PSII underwent a series of single-electron turnovers. This signal is similar but not identical to the well-know formate-modified EPR signal observed for the Q(A)(•-)Fe²(+) complex (W.F.J. Vermaas and A.W. Rutherford, FEBS Lett. 175 (1984) 243-248). The formate-modified signals from Q(A)(•-)Fe²(+) and Q(B)(•-)Fe²(+) are also similar to native semiquinone-iron signals (Q(A)(•-)Fe²(+)/Q(B)(•-)Fe²(+)) seen in purple bacterial reaction centers where a glutamate provides the carboxylate ligand to the iron. The second new signal was formed when Q(A)(•-) was generated in formate-inhibited PSII when the secondary acceptor was reduced by two electrons. While the signal is reminiscent of the formate-modified semiquinone-iron signals, it is broader and its main turning point has a major sub-peak at higher field. This new signal is attributed to the Q(A)(•-)Fe²(+) with formate bound but which is perturbed when Q(B) is fully reduced, most likely as Q(B)H₂ (or possibly Q(B)H(•-) or Q(B)(²•-)). Flash experiments on formate-inhibited PSII monitoring these new EPR signals indicate that the outcome of charge separation on the first two flashes is not greatly modified by formate. However on the third flash and subsequent flashes, the modified Q(A)(•-)Fe²(+)Q(B)H₂ signal is trapped in the EPR experiment and there is a marked

  4. Formation of Secondary Particulate Matter by Reactions of Gas Phase Hexanal with Sulfate Aerosol Particles

    NASA Astrophysics Data System (ADS)

    Zhang, J.

    2003-12-01

    The formation of secondary particulate matter from the atmospheric oxidation of organic compounds can significantly contribute to the particulate burden, but the formation of organic secondary particulate matter is poorly understood. One way of producing organic secondary particulate matter is the oxidation of hydrocarbons with seven or more carbon atoms to get products with low vapor pressure. However, several recent reports suggest that relatively low molecular weight carbonyls can enter the particle phase by undergoing heterogeneous reactions. This may be a very important mechanism for the formation of organic secondary particulate matter. Atmospheric aldehydes are important carbonyls in the gas phase, which form via the oxidation of hydrocarbons emitted from anthropogenic and biogenic sources. In this poster, we report the results on particle growth by the heterogeneous reactions of hexanal. A 5 L Continuous Stirred Tank Reactor (CSTR) is set up to conduct the reactions in the presence of seed aerosol particles of deliquesced ammonia bisulfate. Hexanal is added into CSTR by syringe pump, meanwhile the concentrations of hexanal are monitored with High Pressure Liquid Chromatograph (HPLC 1050). A differential Mobility Analyzer (TSI 3071) set to an appropriate voltage is employed to obtain monodisperse aerosols, and another DMA associated with a Condensation Nuclear Counter (TSI 7610) is used to measure the secondary particle size distribution by the reaction in CSTR. This permits the sensitive determination of particle growth due to the heterogeneous reaction, very little growth occurs when hexanal added alone. Results for the simultaneous addition of hexanal and alcohols will also be presented.

  5. The effects of phytic acid on the Maillard reaction and the formation of acrylamide.

    PubMed

    Wang, Huan; Zhou, Yamin; Ma, Jimei; Zhou, Yuanyuan; Jiang, Hong

    2013-11-01

    Phytic acid, myo-inositol hexaphosphoric acid, exists in substantial (1-5%) amounts in edible plant seeds. In this study the effects of phytic acid on the Maillard reaction and the formation of acrylamide were investigated. Both phytic acid and phosphate enhanced browning in glucose/β-alanine system, but phytic acid was less effective than phosphate. Higher pH favoured the catalytic activities for both of them. The influence of the types of sugar and amino acid on the reaction was also examined. Browning was suppressed by the addition of calcium and magnesium ions, but an additive effect was observed for ferrous ions and phytic acid in glucose/β-alanine solution at pH 8.0. Both phytic acid and phosphate promoted the polymerisation of the reaction intermediates. The kinetics of Maillard reaction was first-ordered reaction in the presence of phytic acid. Phytic acid was less effective than phosphate in the formation of acrylamide. When potato slices were treated with sodium phytate and calcium chloride successively, the formation of acrylamide was greatly suppressed.

  6. THE OZONE REACTION WITH BUTADIENE: FORMATION OF TOXIC PRODUCTS. (R826236)

    EPA Science Inventory

    Abstract

    The formation yields of acrolein, 1,2-epoxy-3-butene and OH radicals have been measured from reaction of ozone with 1,3-butadiene at room temperature and atmosphere pressure. 1,3,5-Trimethyl benzene was added to scavenge OH radicals in measurements of product ...

  7. Exposing the hidden complexity of stoichiometric and catalytic metathesis reactions by elucidation of Mg-Zn hybrids

    PubMed Central

    Hevia, Eva; Chua, Jonathan Z.; García-Álvarez, Pablo; Kennedy, Alan R.; McCall, Matthew D.

    2010-01-01

    Studying seemingly simple metathesis reactions between ZnCl2 and tBuMgCl has, surprisingly, revealed a much more complex chemistry involving mixed magnesium-zinc compounds that could be regarded as Mg-Zn hybrids. Thus, the reaction of equimolar amounts of ZnCl2 and tBuMgCl reveals the formation of the unprecedented mixed Mg-Zn complex [(THF)4Mg(μ-Cl)2Zn(tBu)(Cl)] (1), as a result of the co-complexation of the two anticipated exchange products of the metathesis. This magnesium zincate adopts a contacted ion-pair structure, closely related to Knochel’s pioneering “Turbo” Grignard reagents. Furthermore, a second coproduct identified in this reaction is the solvent-separated mixed magnesium-zinc chloride complex [{Mg(THF)6}2+{Zn2Cl6}2-] (3) that critically diminishes the amount of ZnCl2 available for the intended metathesis reaction to take place. In another surprising result, when the reaction is carried out by using an excess of 3 M equivalents of the Grignard reagent (closer to the catalytic conditions employed by synthetic chemists), solvent-separated magnesium trialkyl zincate [{Mg2Cl3(THF)6}+{Zn(tBu)3}-] (4) is obtained that can be viewed as a model for the active species involved in the increasingly important organic transformations of Grignard reagents catalysed by ZnCl2. Furthermore, preliminary reactivity studies reveal that complex 4 can be used as an effective new reagent for direct Zn-I exchange reactions that allow the preparation and structural identification of the magnesium tris(aryl) zincate [{Mg2Cl3(THF)6}+{Zn(p-Tol)3}-] (5) that represents the first example of complete 3-fold activation of a zincate in a Zn-I exchange reaction which, in turn, can efficiently be used as a precursor for Negishi cross-coupling reactions. PMID:20212145

  8. Adhesion and formation of microbial biofilms in complex microfluidic devices

    SciTech Connect

    Kumar, Aloke; Karig, David K; Neethirajan, Suresh; Suresh, Anil K; Srijanto, Bernadeta R; Mukherjee, Partha P; Retterer, Scott T; Doktycz, Mitchel John

    2012-01-01

    Shewanella oneidensis is a metal reducing bacterium, which is of interest for bioremediation and clean energy applications. S. oneidensis biofilms play a critical role in several situations such as in microbial energy harvesting devices. Here, we use a microfluidic device to quantify the effects of hydrodynamics on the biofilm morphology of S. oneidensis. For different rates of fluid flow through a complex microfluidic device, we studied the spatiotemporal dynamics of biofilms, and we quantified several morphological features such as spatial distribution, cluster formation and surface coverage. We found that hydrodynamics resulted in significant differences in biofilm dynamics. The baffles in the device created regions of low and high flow in the same device. At higher flow rates, a nonuniform biofilm develops, due to unequal advection in different regions of the microchannel. However, at lower flow rates, a more uniform biofilm evolved. This depicts competition between adhesion events, growth and fluid advection. Atomic force microscopy (AFM) revealed that higher production of extra-cellular polymeric substances (EPS) occurred at higher flow velocities.

  9. Structural basis of complement membrane attack complex formation

    PubMed Central

    Serna, Marina; Giles, Joanna L.; Morgan, B. Paul; Bubeck, Doryen

    2016-01-01

    In response to complement activation, the membrane attack complex (MAC) assembles from fluid-phase proteins to form pores in lipid bilayers. MAC directly lyses pathogens by a ‘multi-hit' mechanism; however, sublytic MAC pores on host cells activate signalling pathways. Previous studies have described the structures of individual MAC components and subcomplexes; however, the molecular details of its assembly and mechanism of action remain unresolved. Here we report the electron cryo-microscopy structure of human MAC at subnanometre resolution. Structural analyses define the stoichiometry of the complete pore and identify a network of interaction interfaces that determine its assembly mechanism. MAC adopts a ‘split-washer' configuration, in contrast to the predicted closed ring observed for perforin and cholesterol-dependent cytolysins. Assembly precursors partially penetrate the lipid bilayer, resulting in an irregular β-barrel pore. Our results demonstrate how differences in symmetric and asymmetric components of the MAC underpin a molecular basis for pore formation and suggest a mechanism of action that extends beyond membrane penetration. PMID:26841837

  10. Structural basis of complement membrane attack complex formation.

    PubMed

    Serna, Marina; Giles, Joanna L; Morgan, B Paul; Bubeck, Doryen

    2016-02-04

    In response to complement activation, the membrane attack complex (MAC) assembles from fluid-phase proteins to form pores in lipid bilayers. MAC directly lyses pathogens by a 'multi-hit' mechanism; however, sublytic MAC pores on host cells activate signalling pathways. Previous studies have described the structures of individual MAC components and subcomplexes; however, the molecular details of its assembly and mechanism of action remain unresolved. Here we report the electron cryo-microscopy structure of human MAC at subnanometre resolution. Structural analyses define the stoichiometry of the complete pore and identify a network of interaction interfaces that determine its assembly mechanism. MAC adopts a 'split-washer' configuration, in contrast to the predicted closed ring observed for perforin and cholesterol-dependent cytolysins. Assembly precursors partially penetrate the lipid bilayer, resulting in an irregular β-barrel pore. Our results demonstrate how differences in symmetric and asymmetric components of the MAC underpin a molecular basis for pore formation and suggest a mechanism of action that extends beyond membrane penetration.

  11. Integrin activation and focal complex formation in cardiac hypertrophy

    NASA Technical Reports Server (NTRS)

    Laser, M.; Willey, C. D.; Jiang, W.; Cooper, G. 4th; Menick, D. R.; Zile, M. R.; Kuppuswamy, D.

    2000-01-01

    Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.

  12. Secondary organic aerosol formation initiated from reactions between ozone and surface-sorbed squalene

    NASA Astrophysics Data System (ADS)

    Wang, Chunyi; Waring, Michael S.

    2014-02-01

    Previous research has shown that ozone reactions on surface-sorbed D-limonene can promote gas phase secondary organic aerosol (SOA) formation indoors. In this work, we conducted 13 steady state chamber experiments to measure the SOA formation entirely initiated by ozone reactions with squalene sorbed to glass, at chamber ozone of 57-500 ppb for two relative humidity (RH) conditions of 21% and 51%, in the absence of seed particles. Squalene is a nonvolatile compound that is a component of human skin oil and prevalent on indoor surfaces and in settled dust due to desquamation. The size distributions, mass and number secondary emission rates (SER), aerosol mass fractions (AMF), and aerosol number fractions (ANF) of formed SOA were quantified. The surface AMF and ANF are defined as the change in SOA mass or number formed, respectively, per ozone mass consumed by ozone-squalene reactions. All experiments but one exhibited nucleation and mass formation. Mass formation was relatively small in magnitude and increased with ozone, most notably for the RH = 51% experiments. The surface AMF was a function of the chamber aerosol concentration, and a multi-product model was fit using the 'volatility basis set' framework. Number formation was relatively strong at low ozone and low RH conditions. Though we cannot extrapolate our results because experiments were conducted at high air exchange rates, we speculate that this process may enhance particle number more than mass concentrations indoors.

  13. The effects of a complexing agent on the transverse stability of cubic autocatalytic reaction fronts

    NASA Astrophysics Data System (ADS)

    Merkin, J. H.

    2009-07-01

    The effects of adding a complexing agent on the propagation and transverse stability of reaction fronts in a system based on cubic autocatalysis is considered. Adding the complexing agent is seen to reduce the propagation speed, alter the reaction dynamics and the concentration of the final reaction product of the propagating reaction fronts. A linear stability analysis (LSA) is considered to determine how the complexing agent affects the stability of planar reaction fronts through the numerical calculation of dispersion curves, plots of the growth rate σ against wavenumber k. These dispersion curves show that adding the complexing agent can make the system unstable when it would otherwise be stable and, when the system is diffusionally unstable without the complexing agent, weaken this instability. An analysis valid for small values of k is undertaken, which confirms the results from the LSA and indicates how the critical value Dc of the diffusion coefficient ratio D for the onset of an instability is changed by the addition of the complexing agent.

  14. The first chiral diene-based metal-organic frameworks for highly enantioselective carbon-carbon bond formation reactions

    SciTech Connect

    Sawano, Takahiro; Ji, Pengfei; McIsaac, Alexandra R.; Lin, Zekai; Abney, Carter W.; Lin, Wenbin

    2016-02-01

    We have designed the first chiral diene-based metal–organic framework (MOF), E₂-MOF, and postsynthetically metalated E₂-MOF with Rh(I) complexes to afford highly active and enantioselective single-site solid catalysts for C–C bond formation reactions. Treatment of E₂-MOF with [RhCl(C₂H₄)₂]₂ led to a highly enantioselective catalyst for 1,4-additions of arylboronic acids to α,β-unsaturated ketones, whereas treatment of E₂-MOF with Rh(acac)(C₂H₄)₂ afforded a highly efficient catalyst for the asymmetric 1,2-additions of arylboronic acids to aldimines. Interestingly, E₂-MOF·Rh(acac) showed higher activity and enantioselectivity than the homogeneous control catalyst, likely due to the formation of a true single-site catalyst in the MOF. E₂-MOF·Rh(acac) was also successfully recycled and reused at least seven times without loss of yield and enantioselectivity.

  15. Reactions of Lithiated Diphosphanes R2P-P(SiMe3)Li (R = tBu and iPr) with [(Me)NacnacTiCl2·THF] and [(Me)NacnacTiCl3]. Formation and Structure of Titanium(III) and Titanium(IV) β-Diketiminato Complexes Bearing the Side-on Phosphanylphosphido and Phosphanylphosphinidene Functionalities.

    PubMed

    Ponikiewski, Ł; Ziółkowska, A; Pikies, J

    2017-02-06

    β-Diketiminate complexes of Ti(III)-containing phosphanylphosphido ligands [(Me)NacnacTi(Cl){η(2)-P(SiMe3)-PR2}] ((Me)Nacnac(-) = [Ar]NC(Me)CHC(Me)N[Ar]; Ar = 2,6-iPr2C6H3) were prepared by reactions of [(Me)NacnacTiCl2·THF] with lithium derivatives of diphosphanes R2P-P(SiMe3)Li (R = tBu, iPr) in toluene solutions. Surprisingly, reactions of [(Me)NacnacTiCl2·THF] with R2P-P(SiMe3)Li in THF solutions led to Ti(IV) complexes containing phosphanylphosphinidene ligands [(Me)NacnacTi(Cl)(η(2)-P-PtBu2)] via an autoredox path involving a migration of a nitrene NAr from the Nacnac skeleton to the Ti centers. Solid-state structures of [(Me)NacnacTi(Cl){η(2)-P(SiMe3)-PtBu2}] (1a) and [(Me)NacnacTi(Cl)(η(2)-P-PtBu2)] (two isomers 2a1, 2a2) together with [(Me)NacnacTi(Cl){η(2)-P(SiMe3)-PiPr2}] (1b) and [(Me)NacnacTi(Cl)(η(2)-P-PiPr2)] (2b) were established by the single-crystal X-ray diffraction and display clearly side-on geometry of the (Me3Si)P-PR2 and P-PR2 moieties in the solid state. Phosphanylphosphinidene complexes [(Me)NacnacTi(Cl)(η(2)-P-PR2)] indicate that the (31)P NMR resonances of phosphinidene P atoms appear at a very low field in solution and in the solid state.

  16. Use of an osmium complex as a universal luminescent probe for enzymatic reactions.

    PubMed

    Virel, Ana; Sanchez-Lopez, Jose; Saa, Laura; García, Ana Carla; Pavlov, Valeri

    2009-06-15

    The water-soluble bis(bipyridine)chloro(4-picolinic acid) osmium complex, [Os(III)(bpy)2Cl(PyCOOH)]2+ (bpy=2,2'-bipyridine, Py=pyridine), is fluorescent in aqueous solution, whereas the reduced form of the complex, [Os(II)(bpy)2Cl(PyCOOH)]+, shows no significant fluorescence under the same conditions. Such reversible redox control of the fluorescence of the complex can be easily adapted to follow any enzymatic reaction to yield oxidising or reducing products that are capable of interacting with [Os(III)(bpy)2Cl(PyCOOH)]2+ or [Os(II)(bpy)2Cl(PyCOOH)]+. Based on the redox reaction between products of biocatalytic reactions and the osmium complex, we have designed a simple bioanalytical assay for the detection of nerve gases, alpha-ketoglutarate, hydrogen peroxide and glucose.

  17. Highly active and selective catalysis of copper diphosphine complexes for the transformation of carbon dioxide into silyl formate.

    PubMed

    Motokura, Ken; Kashiwame, Daiki; Takahashi, Naoki; Miyaji, Akimitsu; Baba, Toshihide

    2013-07-22

    Copper diphosphine complexes have been found to be highly active and selective homogeneous catalysts for the hydrosilylation of CO2. The structure of the phosphine ligands strongly affects their catalytic activity. Turnover number (TON) reaches 70,000 after 24 hours with 1,2-bis(diisopropylphosphino)benzene as a ligand under 1 atmosphere of CO2. (1)H and (13)C NMR spectra, carried out under the reaction conditions, showed the reaction mechanism through insertion of CO2 into Cu-H to afford Cu/formate species.

  18. Joint catalytic activation of CO/sub 2/ and NH/sub 3/ in reaction with butadiene under the action of palladium complexes

    SciTech Connect

    Dzhemilev, U.M.; Kunakova, R.V.; Sidorova, V.V.

    1987-08-20

    In a continuation of the study of catalytic reactions in which small molecules participate they have examined the reaction of butadiene simultaneously with CO/sub 2/ and NH/sub 3/ in the presence of homogeneous Pd-containing catalyst complexes with the object of developing a single-step method for the synthesis of unsaturated higher formamides. The possibility of joint catalytic activation of small molecules (CO/sub 2/ and NH/sub 3/) has been demonstrated in their reaction with butadiene with the participation of palladium complexes, the products being mono- and bis-(2,7-octadienyl)formamides. It has been found that 2-pyrrolidone can take part in a telomerization reaction with butadiene in solutions containing palladium complexes, ammonia and carbon dioxide with the formation of N-2,7-octadienylpyrrolidone.

  19. Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II

    SciTech Connect

    Fedorenko, S. G.; Burshtein, A. I.

    2014-09-21

    Creation of exciplexes from the charged products of photoionization is considered by means of Integral Encounter Theory. The general kinetic equations of such a reaction following the Weller scheme II are developed. The special attention is given to the particular case of irreversible remote ionization of primary excited electron donor. Kinetics of exciplex formation is considered at fast biexponential geminate transformation of exciplexes in cage that gives way to subsequent bulk reaction of equilibrated reaction products controlled by power law recombination of ions. It is shown that the initial geminate stage of exciplex kinetics is observed only in diffusion controlled regime of the reaction and disappears with increasing mobility of ions in passing to kinetic regime. The quantum yield of exciplexes is studied along with their kinetics.

  20. Silver(I) complex formation with cysteine, penicillamine, and glutathione.

    PubMed

    Leung, Bonnie O; Jalilehvand, Farideh; Mah, Vicky; Parvez, Masood; Wu, Qiao

    2013-04-15

    The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen), and glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and (109)Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol dm(-3) Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10-11) a mean Ag-S bond distance of 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and (109)Ag NMR spectra of a concentrated Ag(I)-cysteine solution (C(Ag(I)) = 0.8 mol dm(-3), L/Ag = 2.2) showed a mean Ag-S bond distance of 2.47 ± 0.02 Å and δ((109)Ag) 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (C(Ag(I)) = 0.5 mol dm(-3), L/Ag = 2.0) the mean Ag-S bond distance of 2.40 ± 0.02 Å and δ((109)Ag) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C(Ag(I)) = 0.01 mol dm(-3), pH ∼11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ∼10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N), and AgS3 coordination environments was used, together with a survey of (109)Ag NMR chemical shifts, to assist assignments of the Ag

  1. Aza-crown ether complex cation ionic liquids: preparation and applications in organic reactions.

    PubMed

    Song, Yingying; Cheng, Chen; Jing, Huanwang

    2014-09-26

    Aza-crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG-DTA), elemental analysis and physical properties. These new and room-temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO2 to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel-Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza-[18-C-6HK][HSO4]2 was the best acidic catalyst in the reactions of esterification and Friedel-Crafts alkylation under mild reaction conditions.

  2. To address surface reaction network complexity using scaling relations machine learning and DFT calculations.

    PubMed

    Ulissi, Zachary W; Medford, Andrew J; Bligaard, Thomas; Nørskov, Jens K

    2017-03-06

    Surface reaction networks involving hydrocarbons exhibit enormous complexity with thousands of species and reactions for all but the very simplest of chemistries. We present a framework for optimization under uncertainty for heterogeneous catalysis reaction networks using surrogate models that are trained on the fly. The surrogate model is constructed by teaching a Gaussian process adsorption energies based on group additivity fingerprints, combined with transition-state scaling relations and a simple classifier for determining the rate-limiting step. The surrogate model is iteratively used to predict the most important reaction step to be calculated explicitly with computationally demanding electronic structure theory. Applying these methods to the reaction of syngas on rhodium(111), we identify the most likely reaction mechanism. Propagating uncertainty throughout this process yields the likelihood that the final mechanism is complete given measurements on only a subset of the entire network and uncertainty in the underlying density functional theory calculations.

  3. To address surface reaction network complexity using scaling relations machine learning and DFT calculations

    PubMed Central

    Ulissi, Zachary W.; Medford, Andrew J.; Bligaard, Thomas; Nørskov, Jens K.

    2017-01-01

    Surface reaction networks involving hydrocarbons exhibit enormous complexity with thousands of species and reactions for all but the very simplest of chemistries. We present a framework for optimization under uncertainty for heterogeneous catalysis reaction networks using surrogate models that are trained on the fly. The surrogate model is constructed by teaching a Gaussian process adsorption energies based on group additivity fingerprints, combined with transition-state scaling relations and a simple classifier for determining the rate-limiting step. The surrogate model is iteratively used to predict the most important reaction step to be calculated explicitly with computationally demanding electronic structure theory. Applying these methods to the reaction of syngas on rhodium(111), we identify the most likely reaction mechanism. Propagating uncertainty throughout this process yields the likelihood that the final mechanism is complete given measurements on only a subset of the entire network and uncertainty in the underlying density functional theory calculations. PMID:28262694

  4. To address surface reaction network complexity using scaling relations machine learning and DFT calculations

    NASA Astrophysics Data System (ADS)

    Ulissi, Zachary W.; Medford, Andrew J.; Bligaard, Thomas; Nørskov, Jens K.

    2017-03-01

    Surface reaction networks involving hydrocarbons exhibit enormous complexity with thousands of species and reactions for all but the very simplest of chemistries. We present a framework for optimization under uncertainty for heterogeneous catalysis reaction networks using surrogate models that are trained on the fly. The surrogate model is constructed by teaching a Gaussian process adsorption energies based on group additivity fingerprints, combined with transition-state scaling relations and a simple classifier for determining the rate-limiting step. The surrogate model is iteratively used to predict the most important reaction step to be calculated explicitly with computationally demanding electronic structure theory. Applying these methods to the reaction of syngas on rhodium(111), we identify the most likely reaction mechanism. Propagating uncertainty throughout this process yields the likelihood that the final mechanism is complete given measurements on only a subset of the entire network and uncertainty in the underlying density functional theory calculations.

  5. N-Heterocyclic Carbene Complexes in other Transition Metal Mediated Reactions

    NASA Astrophysics Data System (ADS)

    Nixon, Tracy D.; Williams, Jonathan M. J.

    This chapter describes reactions involving NHC-transition metal complexes that have not been considered in previous chapters. The reactions are treated in six sections, presenting borrowing hydrogen reactions where C-C and C-N bonds are formed from alcohols in the first section. Then dehydration reactions either with or without coupling are discussed. The dynamic kinetic resolution of alcohols using a combination of NHC-TM catalysed racemisation coupled with enzyme-catalysed resolution is described. The next section considers the emerging area of dehydrogenation reactions, followed by a section discussing the isomerisation of alkene-containing substrates. The final section details hydrogen/deuterium exchange reactions within aryl and alkyl substrates.

  6. Interaction of ortho-Phospho-l-serine with Hydroxyapatite: Formation of a Surface Complex

    PubMed

    Misra

    1997-10-01

    ortho-Phospho-l-serine (H2Psi, where Psi represents the serinephosphato ion), a constituent of salivary proteins, seems to play an important role in the mineralization of teeth. To understand the basic mechanism of this interaction, the uptake of o-phospho-l-serine from relatively concentrated aqueous solutions (up to 100 mmol/L) onto synthetic hydroxyapatite was studied. Previous studies have shown that in the dilute concentration range (<12.5 mmol/L) the uptake followed a regular Langmuirian adsorption plot. At higher concentrations the uptake curve increased steeply, but no formation of a separate phase in the reacted apatite was discernible, either by optical or by scanning electron microscopy. The dissolution of apatite released phosphate and calcium ions into the solution in amounts linearly related to the uptake of serine with P/Psi = 1 and Ca/Psi = 2. The charge and mass balance of the reaction can be reconciled with the formation of the surface complex (shown within brackets):Ca10(OH)2(PO4)6 + 6H2Psi --> [Ca6(HPsi)2(HPO4)2(PO4)2] + 4Ca2+ + 2HPsi1- + 2Psi2- + 2H2PO1-4 + 2H2O.The formation of two other surface complexes is possible; however, the complex shown above probably disrupts the apatite lattice the least. Traces of CaPsi·H2O precipitate out from the filtrates of highly concentrated solutions after 6 days. Copyright 1997 Academic Press. Copyright 1997Academic Press

  7. Formation of orthopyroxenite by reaction between peridotite and hydrous basaltic melt: an experimental study

    NASA Astrophysics Data System (ADS)

    Wang, Chunguang; Liang, Yan; Dygert, Nick; Xu, Wenliang

    2016-09-01

    The consequences of hydrous basaltic melts and peridotite interaction were examined experimentally in Au-Pd, Pt, and graphite capsules using the reaction couple method. Reactions between a hydrous basaltic andesite (4 wt% H2O) and dunite or lherzolite in an Au-Pd capsule at 1 GPa and 1200 °C produce a melt-bearing orthopyroxenite-dunite sequence. Reactions between a hydrous ferro-basalt and lherzolite in Pt or Au-Pd capsules at 0.8-2 GPa and 1250-1385 °C produce a melt-bearing orthopyroxenite-harzburgite sequence. Reactions between the ferro-basalt and lherzolite in graphite capsules (not designed to retain water) result in a melt-bearing dunite-harzburgite sequence at 1 GPa and a melt-bearing harzburgite-lherzolite sequence at 2 GPa. The orthopyroxenite from the hydrous reaction experiments has a high porosity, and it is separated by a sharp lithological interface from the dunite or harzburgite. Orthopyroxenes in the orthopyroxenite are large in size with resorbed olivine inclusions. Formation of the high-porosity orthopyroxenite in the hydrous melt-rock reaction experiments is determined by the liquidus phase relation of the interface reacting melt and reaction kinetics. Reaction between orthopyroxene-saturated hydrous melt and olivine at melt-rock interface produces orthopyroxenite. Water infiltration induces hydrous melting of the lherzolite, producing a dunite or an orthopyroxene-depleted harzburgite. Efficient diffusive exchange between the partial melt and the hydrous reacting melt promotes orthopyroxene-oversaturation around the melt-rock interfacial region. The simplified experiments reveal end-member processes for understanding the formation of orthopyroxenite in the upper mantle. The presence of orthopyroxenites in mantle samples is a strong indication of hydrous melt and peridotite interaction.

  8. Formation of {beta}-hydroxycarbonyls from the OH radical-initiated reactions of selected alkenes

    SciTech Connect

    Aschmann, S.M.; Arey, J.; Atkinson, R.

    2000-05-01

    {beta}-Hydroxycarbonyls can be formed from the gas-phase reactions of alkenes with the OH radical, both in the presence and in the absence of NO. To date, because of analytical difficulties, few data have been reported for the formation of this class of compound from the reactions of the OH radical with alkenes. The authors have determined that {beta}-hydroxy-ketones can be readily analyzed by gas chromatography, and in this work they have shown that in 1 atm of air the {beta}-hydroxyalkoxy radicals formed in the reactions of the OH radical with trans-2-butene, trans-3-hexene, 1-butene, and {alpha}-pinene in the presence of NO primarily decompose rather than react with O{sub 2}. Rate constant ratios k{sub d}/k{sub 0{sub 2}} (or lower limits thereof), where k{sub d} and k{sub 0{sub 2}} are respectively the rate constants for the decomposition and the reaction with 0{sub 2} of the intermediate {beta}-hydroxyalkoxy radicals, have been obtained for the reactions of the CH{sub 3}CH(O)CH-(OH)CH{sub 3}, CH{sub 3}CH{sub 2}CH(O)CH{sub 2}OH, and CH{sub 3}CH{sub 2}CH(O)CH(OH)CH{sub 2}-CH{sub 3} radicals at 296 {+-} 2 K and atmospheric pressure. Using the O{sub 3} reactions with the alkenes to generate OH radicals, the reactions of the OH radical to generate OH radicals, the reactions of the OH radical with trans-2-butene, trans-3-hexene, and {alpha}-pinene in the absence of NO lead to the formation of the expected {beta}-hydroxycarbonyls and (at least for trans-2-butene) the {alpha},{beta}-diol.

  9. Mechanism of Formation of Copper(II) Chloro Complexes Revealed by Transient Absorption Spectroscopy and DFT/TDDFT Calculations.

    PubMed

    Mereshchenko, Andrey S; Olshin, Pavel K; Karabaeva, Kanykey E; Panov, Maxim S; Wilson, R Marshall; Kochemirovsky, Vladimir A; Skripkin, Mikhail Yu; Tveryanovich, Yury S; Tarnovsky, Alexander N

    2015-07-16

    Copper(II) complexes are extremely labile with typical ligand exchange rate constants on the order of 10(6)-10(9) M(-1) s(-1). As a result, it is often difficult to identify the actual formation mechanism of these complexes. In this work, using UV-vis transient absorption when probing in a broad time range (20 ps to 8 μs) in conjunction with DFT/TDDFT calculations, we studied the dynamics and underlying reaction mechanisms of the formation of extremely labile copper(II) CuCl4(2-) chloro complexes from copper(II) CuCl3(-) trichloro complexes and chloride ions. These two species, produced via photochemical dissociation of CuCl4(2-) upon 420 nm excitation into the ligand-to-metal-charge-transfer electronic state, are found to recombine into parent complexes with bimolecular rate constants of (9.0 ± 0.1) × 10(7) and (5.3 ± 0.4) × 10(8) M(-1) s(-1) in acetonitrile and dichloromethane, respectively. In dichloromethane, recombination occurs via a simple one-step addition. In acetonitrile, where [CuCl3](-) reacts with the solvent to form a [CuCl3CH3CN](-) complex in less than 20 ps, recombination takes place via ligand exchange described by the associative interchange mechanism that involves a [CuCl4CH3CN](2-) intermediate. In both solvents, the recombination reaction is potential energy controlled.

  10. Cationic lanthanide complexes of neutral tripodal N,O ligands: enthalpy versus entropy-driven podate formation in water.

    PubMed

    Bravard, Florence; Rosset, Caroline; Delangle, Pascale

    2004-07-07

    The cationic lanthanide complexes of two neutral tripodal N,O ligands, tpa (tris[(2-pyridyl)methyl]amine) and tpaam (tris[6-((2-N,N-diethylcarbamoyl)pyridyl)methyl]amine) are studied in water. The analysis of the proton lanthanide induced NMR shifts indicate that there is no abrupt structural change in the middle of the rare-earth series. Unexpectedly, the formation constant values of the lanthanide podates of tpaam and tpa in D2O at 298 K are similar, suggesting that the addition of the three amide groups to the ligand tpa does not lead to any increase in stability of the lanthanide complexes of tpaam in respect to tpa, even though the amide groups are coordinated to the metal in aqueous solution. The measurement of the enthalpy and entropy changes of the complexation reactions shows that the two similar ligands tpa and tpaam have different driving forces for lanthanide complexation. Indeed, the formation of tpa podates benefits from an exothermic enthalpy change associated with a small entropy change, whereas the complexation reaction with tpaam is clearly entropy-driven though opposed by a positive enthalpy change. The hydration states of the europium complexes were measured by luminescence and show the coordination of 4-5 water ligands in [Eu(tpa)]3+ whereas there are only 2 in [Eu(tpaam)]3+. Therefore the heptadentate ligand tpaam releases the translational entropy of more water molecules than does the tetradentate ligand tpa.

  11. Mechanistic investigation of the reaction of epoxides with heterocumulenes catalysed by a bimetallic aluminium salen complex.

    PubMed

    Beattie, Christopher; North, Michael

    2014-06-23

    The bimetallic aluminium(salen) complex [(Al(salen))2O] is known to catalyse the reaction between epoxides and heterocumulenes (carbon dioxide, carbon disulfide and isocyanates) leading to five-membered ring heterocycles. Despite their apparent similarities, these three reactions have very different mechanistic features, and a kinetic study of oxazolidinone synthesis combined with previous kinetic work on cyclic carbonate and cyclic dithiocarbonate synthesis showed that all three reactions follow different rate equations. An NMR study of [Al(salen)]2O and phenylisocyanate provided evidence for an interaction between them, consistent with the rate equation data. A variable-temperature kinetics study on all three reactions showed that cyclic carbonate synthesis had a lower enthalpy of activation and a more negative entropy of activation than the other two heterocycle syntheses. The kinetic study was extended to oxazolidinone synthesis catalysed by the monometallic complex Al(salen)Cl, and this reaction was found to have a much less negative entropy of activation than any reaction catalysed by [Al(salen)]2O, a result that can be explained by the partial dissociation of an oligomeric Al(salen)Cl complex. A mechanistic rationale for all of the results is presented in terms of [Al(salen)]2O being able to function as a Lewis acid and/or a Lewis base, depending upon the susceptibility of the heterocumulene to reaction with nucleophiles.

  12. A peroxynitrite complex of copper: formation from a copper-nitrosyl complex, transformation to nitrite and exogenous phenol oxidative coupling or nitration.

    PubMed

    Park, Ga Young; Deepalatha, Subramanian; Puiu, Simona C; Lee, Dong-Heon; Mondal, Biplab; Narducci Sarjeant, Amy A; del Rio, Diego; Pau, Monita Y M; Solomon, Edward I; Karlin, Kenneth D

    2009-11-01

    Reaction of nitrogen monoxide with a copper(I) complex possessing a tridentate alkylamine ligand gives a Cu(I)-(*NO) adduct, which when exposed to dioxygen generates a peroxynitrite (O=NOO(-))-Cu(II) species. This undergoes thermal transformation to produce a copper(II) nitrito (NO(2) (-)) complex and 0.5 mol equiv O(2). In the presence of a substituted phenol, the peroxynitrite complex effects oxidative coupling, whereas addition of chloride ion to dissociate the peroxynitrite moiety instead leads to phenol ortho nitration. Discussions include the structures (including electronic description) of the copper-nitrosyl and copper-peroxynitrite complexes and the formation of the latter, based on density functional theory calculations and accompanying spectroscopic data.

  13. Chemistry of polycyclic aromatic hydrocarbons formation from phenyl radical pyrolysis and reaction of phenyl and acetylene.

    PubMed

    Comandini, A; Malewicki, T; Brezinsky, K

    2012-03-15

    An experimental investigation of phenyl radical pyrolysis and the phenyl radical + acetylene reaction has been performed to clarify the role of different reaction mechanisms involved in the formation and growth of polycyclic aromatic hydrocarbons (PAHs) serving as precursors for soot formation. Experiments were conducted using GC/GC-MS diagnostics coupled to the high-pressure single-pulse shock tube present at the University of Illinois at Chicago. For the first time, comprehensive speciation of the major stable products, including small hydrocarbons and large PAH intermediates, was obtained over a wide range of pressures (25-60 atm) and temperatures (900-1800 K) which encompass the typical conditions in modern combustion devices. The experimental results were used to validate a comprehensive chemical kinetic model which provides relevant information on the chemistry associated with the formation of PAH compounds. In particular, the modeling results indicate that the o-benzyne chemistry is a key factor in the formation of multi-ring intermediates in phenyl radical pyrolysis. On the other hand, the PAHs from the phenyl + acetylene reaction are formed mainly through recombination between single-ring aromatics and through the hydrogen abstraction/acetylene addition mechanism. Polymerization is the common dominant process at high temperature conditions.

  14. Contrasting reactions of hydrated electron and formate radical with 2-thio analogues of cytosine and uracil.

    PubMed

    Prasanthkumar, Kavanal P; Alvarez-Idaboy, Juan R; Kumar, Pavitra V; Singh, Beena G; Priyadarsini, K Indira

    2016-10-19

    2-Thiocytosine (TC) and 2-thiouracil (TU) were subjected to hydrated electron (eaq(-)), formate radical (CO2˙(-)) and 2-hydroxypropan-2-yl radical ((CH3)2˙COH) reactions in aqueous medium. Transients were characterized by absorption spectroscopy and the experimental findings were rationalized by DFT calculations at LC-ωPBE and M06-2X levels using a 6-311+G(d,p) basis set and SMD solvation. In eaq(-) reactions, a ring N-atom protonated radical of TC and an exocyclic O-atom protonated radical of TU were observed via addition of eaq(-) and subsequent protonation by solvent molecules. However, two competing but simultaneous mechanisms are operative in CO2˙(-) reactions with TC and TU. The first one corresponds to formations of N(O)-atom protonated radicals (similar to eaq(-) reactions); the second mechanism led to 2 center-3 electron, sulfur-sulfur bonded neutral dimer radicals, TCdim˙ and TUdim˙. DFT calculations demonstrated that H-abstraction by CO2˙(-) from TC(TU) results in S-centered radical which upon combination with TC(TU) provide the dimer radical. In some cases, DFT energy profiles were further validated by CBS-QB3//M06-2X calculations. This is the first time report for a contradictory behavior in the mechanisms of eaq(-) and CO2˙(-) reactions with any pyrimidines or their thio analogues.

  15. Quantifying the ionic reaction channels in the Secondary Organic Aerosol formation from glyoxal

    NASA Astrophysics Data System (ADS)

    Maxut, Aurelia; Nozière, Barbara; Rossignol, Stéphanie; George, Christian; Waxman, Eleanor Marie; Laskin, Alexander; Slowik, Jay; Dommen, Josef; Prévôt, André; Baltensperger, Urs; Volkamer, Rainer

    2014-05-01

    Glyoxal, a common organic gas in the atmosphere, has been identified in recent years as an important Secondary Organic Aerosol (SOA) precursor (Volkamer et al., 2007). But, unlike with other precursors, the SOA is largely produced by particle-phase reactions (Volkamer et al., 2009) and equilibria (Kampf et al. 2013) that are still not entirely characterized. Since 2009 series of smog chamber experiments have been performed within the Eurochamp program at the Paul Scherrer Institute, Switzerland, to investigate SOA formation from glyoxal. In these experiments, glyoxal was produced by the gas-phase oxidation of acetylene in the presence of seeds, the seed composition and other conditions being varied. The 2011 campaign resulted in the identification of salting processes controlling the glyoxal partitioning in the seeds (Kampf et al. 2013). This presentation will report results of the 2013 campaign focusing on the identification of the various reactions (ionic or photo-induced) contributing to the SOA mass. In particular, the contribution of the ionic reactions, i.e. mediated by NH4+, were investigated by quantifying the formation of imidazoles (imidazole, imidazole-2-carboxaldehyde, 2,2'-biimidazole) from the small condensation channel of glyoxal with ammonia. For this, the SOA produced were collected on quartz filters and analyzed by Orbitrap LC/MS (Q-Exactive Thermo Fisher). The formation of other products such as organic acids was also investigated to determine potential competing reactions. Time-resolved MOUDI sampling coupled with nano-DESY/ESI-MS/MS analysis was also used to identify nitrogen- and sulphur-containing products from all the reactions. The results obtained for a range of conditions will be presented and compared with recent mechanistic information on the ionic reaction channels (Nozière et al., in preparation, 2013). The implementation of all this new information into a glyoxal-SOA model will be discussed.

  16. Synthesis, characterization and thermodynamics of complex formation of some new Schiff base ligands with some transition metal ions and the adduct formation of zinc Schiff base complexes with some organotin chlorides

    NASA Astrophysics Data System (ADS)

    Asadi, Mozaffar; Asadi, Zahra; Torabi, Susan; Lotfi, Najmeh

    Four new complexes, [M(Salpyr)] where Salpyr = N,N'-bis(Salicylidene)-2,3- and 3,4-diiminopyridine and M = Co, Cu, Mn, Ni and Zn were synthesized and characterized by 1H NMR, IR spectroscopy, elemental analysis and UV-vis spectrophotometry. UV-vis spectrophotometric study of the adduct formation of the zinc(II) complexes, [Zn(2,3-Salpyr)] and [Zn(3,4-Salpyr)], as donor with R2SnCl2 (R = methyl, phenyl, n-butyl), PhSnCl3 and Bu3SnCl as acceptors has been investigated in methanol, as solvent. The formation constants and the thermodynamic free energies were measured using UV-vis spectrophotometry. Titration of the organotin chlorides with Zn(II) complexes at various temperatures (T = 283-313 K) leads to 1:1 adduct formation. The results show that the formation constants were decreased by increasing the temperature. The trend of the reaction of RnSnCl4-n as acceptors toward given zinc complexes was as follows: PhSnCl3 > Me2SnCl2 > Ph2SnCl2 > Bu2SnCl2 > Bu3SnCl By considering the formation constants and the ΔG° of the complex formation for the Schiff base as donor and the M(II) as acceptor, the following conclusion was drawn: the formation constant for a given Schiff base changes according to the following trend: Ni > Cu > Co > Zn > Mn

  17. Complex Cure Kinetics of the Hydroxyl-Epoxide Reaction in DGEBA Epoxy Hardened with Diethanolamine

    NASA Astrophysics Data System (ADS)

    Ancipink, Windy; McCoy, John; Kropka, Jamie; Celina, Mathias

    The curing of a diglycidyl ether of bisphenol-A Epoxy (Epon 828) with diethanolamine (DEA) involves a fast amine-epoxide reaction followed by a slower hydroxyl-epoxide reaction. At curing temperatures below 100°C, the time scales of these two reactions are well separated, and the hydroxyl addition can be studied as an ''isolated'' reaction. The hydroxyl-epoxide reaction is of great interest due to the complex kinetics involved, which are brought about by competing reactions. The reaction kinetics are believed to be tertiary amine catalyzed and are well fit to a modified form of the Kamal-type equation. Here we study the complex long term reaction kinetics at various temperatures, by using isothermal modulated differential scanning calorimetry, micro calorimetry, and infrared spectroscopy. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  18. Chiral glycine formation on cold interstellar grains by quantum tunneling hydrogen-deuterium substitution reactions

    NASA Astrophysics Data System (ADS)

    Oba, Yasuhiro; Watanabe, Naoki; Osamura, Yoshihiro; Kouchi, Akira

    2015-08-01

    We report experimental evidence that chiral glycine (NH2CHDCOOH) is formed by the surface reaction of normal glycine (NH2CH2COOH) solid with deuterium (D) atom at 12 K under the simulative conditions of interstellar molecular clouds. Chiral glycine formation is most likely initiated by the tunneling abstraction reaction of H atom by D atom followed by the addition of D atom to the glycine radical (NH2CHCOOH). Given that chiral glycine can form in such a primordial low-temperature environment, it might source molecular chirality as molecular clouds evolve into planetary systems.

  19. Diffusion and reaction of pollutants in stratus clouds: application to nocturnal acid formation in plumes

    SciTech Connect

    Seigneur, C.; Saxena, P.; Mirabella, V.A.

    1985-09-01

    A mathematical model is presented that describes the transport, turbulent diffusion, and chemical reactions of air pollutants in stratus clouds. The chemical kinetic mechanism treats 97 gaseous, heterogeneous, and aqueous reactions between 54 species. The dispersion and night-time chemistry of a power plant plume in a stratus cloud is simulated. The contributions of various chemical pathways to the formation of sulfate and nitrate, the differences between plume and background concentrations, and the effect of reduced primary emissions on secondary pollutants are discussed. Calculated sulfate and nitrate concentrations are commensurate with measured atmospheric concentrations.

  20. Macroscopically structured polymer formation governed by spatial patterns in the Belousov Zhabotinsky reaction

    NASA Astrophysics Data System (ADS)

    Kalishyn, Yevhen Yu.; Khavrus, Vyacheslav O.; Strizhak, Peter E.; Seipel, Michael; Münster, Arno F.

    2002-09-01

    We report the formation of macroscopically structured cross-linked polyacrylamide hydrogel in the Belousov-Zhabotinsky (BZ) system (oxidation of malonic acid by bromate catalyzed by ferroin). Here, acrylamide, the cross-linker bis-acrylamide, and polymerization initiator are added into the BZ system. We show that the formation of waves and ripples in the polymer is governed by spatial structures emerging in the BZ system. Without any spatial structures in the BZ system only the formation of a spatially uniform polymer is observed. Without cross-linker, a spatially uniform polymer was observed as well. Structured polymer formation is caused by the interaction of chemical reactions in the BZ system and the polymerization process including gelation and cross-linking of the monomer units.

  1. Formation of nitrogen-containing polycyclic cations by gas-phase and intracluster reactions of acetylene with the pyridinium and pyrimidinium ions.

    PubMed

    Soliman, Abdel-Rahman; Hamid, Ahmed M; Attah, Isaac; Momoh, Paul; El-Shall, M Samy

    2013-01-09

    Here, we present evidence from laboratory experiments for the formation of nitrogen-containing complex organic ions by sequential reactions of acetylene with the pyridinium and pyrimidinium ions in the gas phase and within ionized pyridine-acetylene binary clusters. Additions of five and two acetylene molecules onto the pyridinium and pyrimidinium ions, respectively, at room temperature are observed. Second-order rate coefficients of the overall reaction of acetylene with the pyridinium and pyrimidinium ions are measured as 9.0 × 10(-11) and 1.4 × 10(-9) cm(3) s(-1), respectively, indicating reaction efficiencies of about 6% and 100%, respectively, at room temperature. At high temperatures, only two acetylene molecules are added to the pyridinium and pyrimidinium ions, suggesting covalent bond formation. A combination of ion dissociation and ion mobility experiments with DFT calculations reveals that the addition of acetylene into the pyridinium ion occurs through the N-atom of the pyridinium ion. The relatively high reaction efficiency is consistent with the absence of a barrier in the exothermic N-C bond forming reaction leading to the formation of the C(7)H(7)N(•+) covalent adduct. An exothermic addition/H-elimination reaction of acetylene with the C(7)H(7)N(•+) adduct is observed leading to the formation of a bicyclic quinolizinium cation (C(9)H(8)N(+)). Similar chemistry is observed in the sequential reactions of acetylene with the pyrimidinium ion. The second acetylene addition onto the pyrimidinium ion involves an exclusive addition/H-elimination reaction at room temperature leading to the formation of a bicyclic pyrimidinium cation (C(8)H(7)N(2)(+)). The high reactivity of the pyridinium and pyrimidinium ions toward acetylene is in sharp contrast to the very low reactivity of the benzene cation, which has a reaction efficiency of 10(-4)-10(-5). This indicates that the presence of a nitrogen atom within the aromatic ring enhances the ring growth

  2. Charge-transfer complex formation between o-chloranil and a series of polynuclear aromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Chakraborty, Biswanath; Mukherjee, Asok K.; Seal, Bejoy K.

    2001-02-01

    The equilibrium constants, enthalpies and entropies of formation of molecular electron donor-acceptor (EDA) complexes of o-chloranil with a series of aromatic hydrocarbons have been determined spectrophotometrically. Spectroscopic and thermodynamic aspects of these complexes have been analysed.

  3. Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes.

    PubMed

    Camasso, Nicole M; Sanford, Melanie S

    2015-03-13

    Homogeneous nickel catalysis is used for the synthesis of pharmaceuticals, natural products, and polymers. These reactions generally proceed via nickel intermediates in the Ni(0), Ni(I), Ni(II), and/or Ni(III) oxidation states. In contrast, Ni(IV) intermediates are rarely accessible. We report herein the design, synthesis, and characterization of a series of organometallic Ni(IV) complexes, accessed by the reaction of Ni(II) precursors with the widely used oxidant S-(trifluoromethyl)dibenzothiophenium triflate. These Ni(IV) complexes undergo highly selective carbon(sp(3))-oxygen, carbon(sp(3))-nitrogen, and carbon(sp(3))-sulfur coupling reactions with exogenous nucleophiles. The observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions.

  4. SN2-like reaction in hydrogen-bonded complexes: a theoretical study.

    PubMed

    Wang, Weizhou; Zhang, Yu; Huang, Kaixun

    2005-10-20

    S(N)2-like reactions in hydrogen-bonded complexes have been investigated in this paper at a correlated MP2(full)/6-311++G(3df,3pd) level, employing FH...NH(3)...HF and ClH...NH(3)...HCl as model systems. The unconventional F(Cl)-H...N noncovalent bond and the conventional F(Cl)-H...N hydrogen bond can coexist in one complex which is taken as the reactant of the S(N)2-like reaction. The S(N)2-like reaction occurs along with the inversion of NH(3) and the interconversion of the unconventional F(Cl)-H...N noncovalent bond and the conventional F(Cl)-H...N hydrogen bond. In comparison with that of the isolated NH(3), the inversion barriers of the two complexes both are significantly reduced. The effect of carbon nanotube confinement on the inversion barrier is also discussed.

  5. Formation of coronene:water complexes: FTIR study in argon matrices and theoretical characterisation.

    PubMed

    Simon, A; Noble, J A; Rouaut, G; Moudens, A; Aupetit, C; Iftner, C; Mascetti, J

    2017-03-13

    In this paper, we report a combined theoretical and experimental study of coronene:water interactions in low temperature argon matrices. The theoretical calculations were performed using the mixed density functional-based tight binding/force field approach. The results are discussed in the light of experimental matrix isolation FTIR spectroscopic data. We show that, in the solid phase, (C24H12)(H2O)n (n ≤ 6) σ-type complexes, i.e. with water molecules coordinated on the edge of coronene, are formed, whereas in the gas phase, π-interaction is preferred. These σ-complexes are characterised by small shifts in water absorption bands and a larger blue shift of the out-of-plane γ(CH) deformation of coronene, with the shift increasing with the number of complexed water molecules. Such σ interaction is expected to favour photochemical reaction between water and coronene at the edges of the coronene molecule, leading to the formation of oxidation products at low temperature, even in the presence of only a few water molecules and at radiation energies below the ionisation potential of coronene.

  6. Stoichiometric Reactions of Acylnickel(II) Complexes with Electrophiles and the Catalytic Synthesis of Ketones

    PubMed Central

    2015-01-01

    Acylnickel(II) complexes feature prominently in cross-electrophile coupling (XEC) reactions that form ketones, yet their reactivity has not been systematically investigated. We present here our studies on the reactivity of acylnickel(II) complexes with a series of carbon electrophiles. Bromobenzene, α-chloroethylbenzene, bromooctane, and iodooctane were reacted with (dtbbpy)NiII(C(O)C5H11)(Br) (1b) and (dtbbpy)NiII(C(O)tolyl)(Br) (1c) to form a variety of organic products. While reactions with bromobenzene formed complex mixtures of ketones, reactions with α-chloroethylbenzene were highly selective for the cross-ketone product. Reactions with iodooctane and bromooctane also produced the cross-ketone product, but in intermediate yield and selectivity. In most cases the presence or absence of a chemical reductant (zinc) had only a small effect on the selectivity of the reaction. The coupling of 1c with iodooctane (60% yield) was translated into a catalytic reaction, the carbonylative coupling of bromoarenes with primary bromoalkanes (six examples, 60% average yield). PMID:25364092

  7. Brown carbon formation by aqueous-phase carbonyl compound reactions with amines and ammonium sulfate.

    PubMed

    Powelson, Michelle H; Espelien, Brenna M; Hawkins, Lelia N; Galloway, Melissa M; De Haan, David O

    2014-01-21

    Reactions between small water-soluble carbonyl compounds, ammonium sulfate (AS), and/or amines were evaluated for their ability to form light-absorbing species in aqueous aerosol. Aerosol chemistry was simulated with bulk phase reactions at pH 4, 275 K, initial concentrations of 0.05 to 0.25 M, and UV-vis and fluorescence spectroscopy monitoring. Glycolaldehyde-glycine mixtures produced the most intense absorbance. In carbonyl compound reactions with AS, methylamine, or AS/glycine mixtures, product absorbance followed the order methylglyoxal > glyoxal > glycolaldehyde > hydroxyacetone. Absorbance extended into the visible, with a wavelength dependence fit by absorption Ångstrom coefficients (Å(abs)) of 2 to 11, overlapping the Å(abs) range of atmospheric, water-soluble brown carbon. Many reaction products absorbing between 300 and 400 nm were strongly fluorescent. On a per mole basis, amines are much more effective than AS at producing brown carbon. In addition, methylglyoxal and glyoxal produced more light-absorbing products in reactions with a 5:1 AS-glycine mixture than with AS or glycine alone, illustrating the importance of both organic and inorganic nitrogen in brown carbon formation. Through comparison to biomass burning aerosol, we place an upper limit on the contribution of these aqueous carbonyl-AS-amine reactions of ≤ 10% of global light absorption by brown carbon.

  8. Formaldehyde Reactions with Amines and Ammonia: Particle Formation and Product Identification

    NASA Astrophysics Data System (ADS)

    Galloway, M. M.; Millage, K. D.; Rodriguez, A.; Sedehi, N.; Powelson, M. H.; De Haan, D. O.

    2012-12-01

    Aqueous phase reactions between carbonyls and amines or ammonium salts have recently been implicated in secondary organic aerosol and brown carbon formation processes. Formaldehyde is ubiquitous in the atmosphere, and is present in both the gas and aqueous phases. However, the reactions of formaldehyde in the aqueous phase have not been completely characterized. This study aims to determine the interactions between formaldehyde and amines or ammonium salts present in atmospheric droplets. Bulk phase reactions of formaldehyde with these reactive nitrogen-containing compounds were monitored with ESI-MS and NMR to determine reaction kinetics and for product characterization, while UV-Vis spectroscopy was used to monitor changes in light absorption over time. Hexamethylenetetramine was found to be a major product of the formaldehyde/ammonium sulfate reaction, appearing within minutes of mixing. No products were formed that absorbed light beyond 225 nm. Mono-disperse particles containing mixtures of formaldehyde and ammonium sulfate or an amine were dried and analyzed via SMPS to determine the non-volatile fraction of the reaction products. Similarly, aqueous droplets were dried in a humid atmosphere to determine residual aerosol sizes over time as a function of formaldehyde concentration. This work indicates that formaldehyde plays a key role in aqueous-phase organic processing, as it has been observed to contribute to both an increase and reduction in the diameter and volume of residual aerosol particles.

  9. Aluminium coordination complexes in copolymerization reactions of carbon dioxide and epoxides.

    PubMed

    Ikpo, Nduka; Flogeras, Jenna C; Kerton, Francesca M

    2013-07-07

    Al complexes are widely used in a range of polymerization reactions (ROP of cyclic esters and cationic polymerization of alkenes). Since the discovery in 1978 that an Al porphyrin complex could copolymerize propylene oxide with carbon dioxide, Al coordination compounds have been studied extensively as catalysts for epoxide-carbon dioxide copolymerizations. The most widely studied catalysts are Al porphyrin and Al salen derivatives. This is partially due to their ability to act as mechanistic models for more reactive, paramagnetic Cr catalysts. However, this in depth mechanistic understanding could be employed to design more active Al catalysts themselves, which would be beneficial given the wide availability of this metal. Polymerization data (% CO3 linkages, M(n), M(w)/M(n) and TON) for these complexes are presented and mechanisms discussed. In most cases, especially those employing square-based pyramidal Al complexes, co-catalysts are required to obtain high levels of carbon dioxide incorporation. However, in some cases, the use of co-catalysts inhibits the copolymerization reaction. Lewis acidic Al phenolate complexes have been used as activators in CHO-carbon dioxide copolymerizations to increase TOF and this has recently led to the development of asymmetric copolymerization reactions. Given the ready availability of Al, the robustness of many complexes (e.g. use in immortal polymerizations) and opportunity to prepare block copolymers and other designer materials, Al complexes for copolymerization of carbon dioxide are surely worth a second look.

  10. Selective covalent bond formation in polypeptide ions via gas-phase ion/ion reaction chemistry.

    PubMed

    Han, Hongling; McLuckey, Scott A

    2009-09-16

    Primary amines present in protonated polypeptides can be covalently modified via gas-phase ion/ion reactions using bifunctional reagent ions. The use of reagent anions with a charge-bearing site that leads to strong interactions with the polypeptide, such as sulfonic acid, gives rise to the formation of a long-lived adduct. A distinct reactive functional group, an aldehyde in the present case, can then undergo reaction with the peptide. Collisional activation of the adduct ion formed from a reagent with an aldehyde group and a peptide ion with a primary amine gives rise to water loss in conjunction with imine (Schiff base) formation. The covalently bound modification is retained upon subsequent collisional activation. This work demonstrates the ability to selectively modify polypeptide ions in the gas phase within the context of a multistage mass spectrometry experiment.

  11. Lattice based Kinetic Monte Carlo Simulations of a complex chemical reaction network

    NASA Astrophysics Data System (ADS)

    Danielson, Thomas; Savara, Aditya; Hin, Celine

    Lattice Kinetic Monte Carlo (KMC) simulations offer a powerful alternative to using ordinary differential equations for the simulation of complex chemical reaction networks. Lattice KMC provides the ability to account for local spatial configurations of species in the reaction network, resulting in a more detailed description of the reaction pathway. In KMC simulations with a large number of reactions, the range of transition probabilities can span many orders of magnitude, creating subsets of processes that occur more frequently or more rarely. Consequently, processes that have a high probability of occurring may be selected repeatedly without actually progressing the system (i.e. the forward and reverse process for the same reaction). In order to avoid the repeated occurrence of fast frivolous processes, it is necessary to throttle the transition probabilities in such a way that avoids altering the overall selectivity. Likewise, as the reaction progresses, new frequently occurring species and reactions may be introduced, making a dynamic throttling algorithm a necessity. We present a dynamic steady-state detection scheme with the goal of accurately throttling rate constants in order to optimize the KMC run time without compromising the selectivity of the reaction network. The algorithm has been applied to a large catalytic chemical reaction network, specifically that of methanol oxidative dehydrogenation, as well as additional pathways on CeO2(111) resulting in formaldehyde, CO, methanol, CO2, H2 and H2O as gas products.

  12. Towards a density functional treatment of chemical reactions in complex media

    SciTech Connect

    Berard, D.R.; Wei, D.; Salahub, D.R. |

    1996-12-31

    We discuss two techniques involving density functional theory (i.e., ab initio molecular dynamics simulations and frozen density functional theory) which show promise for applications directed towards understanding reactions in complex media. Preliminary results for the simulation of the conformational dynamics of an isolated analogue of alanine dipeptide and for the interaction between F{sup -} and H{sub 2}O are included. These results represent the first steps towards a combined theoretical approach of reactions in complex media. 23 refs., 4 figs.

  13. Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

    PubMed

    Barman, Prasenjit; Upadhyay, Pranav; Faponle, Abayomi S; Kumar, Jitendra; Nag, Sayanta Sekhar; Kumar, Devesh; Sastri, Chivukula V; de Visser, Sam P

    2016-09-05

    Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction. Evidence of the mechanism comes from experiments which identify a primary kinetic isotope effect of 5.4 for the deformylation reaction. Computational modeling supports the established mechanism and identifies the origin of the reactivity preference of hydrogen-atom abstraction over nucleophilic addition.

  14. New reaction of elementary sulfur with botadiene proceeding under the action of palladium complex catalysts

    SciTech Connect

    Dzhemilev, U.M.; Baibulatova, N.Z.; Kunakova, R.V.; Tolstikov, G.A.

    1986-07-01

    This paper discusses the use of elementary sulfur for the synthesis of organosulfur compounds using homogeneous metallocomplex catalysis. An attempt is made to use low-valence complexes of palladium for the activation of S /SUB alpha/ -cyclooctasulfane in reactions with conjugated dienes. The authors demonstrate the possibility of catalytic generation of mono- and diatomic sulfur from cyclooctasulfane in the reaction with butadiene in the presence of a three-component palladium catalyst. It is shown that this reaction can serve as a new and effective method of synthesizing thiacyclanes of various structures.

  15. Denatured proteins facilitate the formation of the football-shaped GroEL-(GroES)2 complex.

    PubMed

    Sameshima, Tomoya; Iizuka, Ryo; Ueno, Taro; Funatsu, Takashi

    2010-03-29

    Controversy exists over whether the chaperonin GroEL forms a GroEL-(GroES)2 complex (football-shaped complex) during its reaction cycle. We have revealed previously the existence of the football-shaped complex in the chaperonin reaction cycle using a FRET (fluorescence resonance energy transfer) assay [Sameshima, Ueno, Iizuka, Ishii, Terada, Okabe and Funatsu (2008) J. Biol. Chem. 283, 23765-23773]. Although denatured proteins alter the ATPase activity of GroEL and the dynamics of the GroEL-GroES interaction, the effect of denatured proteins on the formation of the football-shaped complex has not been characterized. In the present study, a FRET assay was used to demonstrate that denatured proteins facilitate the formation of the football-shaped complex. The presence of denatured proteins was also found to increase the rate of association of GroES to the trans-ring of GroEL. Furthermore, denatured proteins decrease the inhibitory influence of ADP on ATP-induced association of GroES to the trans-ring of GroEL. From these findings we conclude that denatured proteins facilitate the dissociation of ADP from the trans-ring of GroEL and the concomitant association of ATP and the second GroES.

  16. Thermochemistry and reaction barriers for the formation of levoglucosenone from cellobiose.

    SciTech Connect

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

    2012-02-06

    Cellobiose jumps the barrier: High-level quantum mechanical studies show that the ether bond cleavage in cellobiose occurs through internal hydrogen transfer in the gas phase and that the activation energy required is similar to that required for activating cellulose. The reaction barriers are computed for various pathways for the formation of levoglucosenone from levoglucosan, and the most likely pathway requires a relatively low activation barrier compared to that for the activation of cellobiose.

  17. Thermochemistry and Reaction Barriers for the Formation of Levoglucosenone from Cellobiose

    SciTech Connect

    Assary, Rajeev S.; Curtiss, Larry A.

    2012-02-06

    Cellobiose jumps the barrier: High-level quantum mechanical studies show that the ether bond cleavage in cellobiose occurs through internal hydrogen transfer in the gas phase and that the activation energy required is similar to that required for activating cellulose. The reaction barriers are computed for various pathways for the formation of levoglucosenone from levoglucosan, and the most likely pathway requires a relatively low activation barrier compared to that for the activation of cellobiose.

  18. Thermochemistry and Reaction Barriers for the Formation of Levoglucosenone from Cellobiose

    SciTech Connect

    Assary, Rajeev S.; Curtiss, Larry A.

    2011-10-19

    Cellobiose jumps the barrier: High-level quantum mechanical studies show that the ether bond cleavage in cellobiose occurs through internal hydrogen transfer in the gas phase and that the activation energy required is similar to that required for activating cellulose. The reaction barriers are computed for various pathways for the formation of levoglucosenone from levoglucosan, and the most likely pathway requires a relatively low activation barrier compared to that for the activation of cellobiose.

  19. Negative collision energy dependence of Br formation in the OH + HBr reaction.

    PubMed

    Che, Dock-Chil; Matsuo, Takashi; Yano, Yuya; Bonnet, Laurent; Kasai, Toshio

    2008-03-14

    The reaction between HBr and OH leading to H(2)O and Br in its ground state is studied by means of a crossed molecular beam experiment for a collision energy varying from 0.05 to 0.26 eV, the initial OH being selected in the state |JOmega> = |3/2 3/2> by an electrostatic hexapole field. The reaction cross-section is found to decrease with increasing collision energy. This negative dependence suggests that there is no barrier on the potential energy surface for the formation pathway considered. The experimental results are compared with the previously reported quantum scattering calculations of Clary et al. (D. C. Clary, G. Nyman and R. Hernandez, J. Phys. Chem., 1994, 101, 3704), and briefly discussed in the light of skewed potential energy surfaces associated with heavy-light-heavy type reactions.

  20. Proton Mobility in b2 Ion Formation and Fragmentation Reactions of Histidine-Containing Peptides

    NASA Astrophysics Data System (ADS)

    Nelson, Carissa R.; Abutokaikah, Maha T.; Harrison, Alex G.; Bythell, Benjamin J.

    2016-03-01

    A detailed energy-resolved study of the fragmentation reactions of protonated histidine-containing peptides and their b2 ions has been undertaken. Density functional theory calculations were utilized to predict how the fragmentation reactions occur so that we might discern why the mass spectra demonstrated particular energy dependencies. We compare our results to the current literature and to synthetic b2 ion standards. We show that the position of the His residue does affect the identity of the subsequent b2 ion (diketopiperazine versus oxazolone versus lactam) and that energy-resolved CID can distinguish these isomeric products based on their fragmentation energetics. The histidine side chain facilitates every major transformation except trans-cis isomerization of the first amide bond, a necessary prerequisite to diketopiperazine b2 ion formation. Despite this lack of catalyzation, trans-cis isomerization is predicted to be facile. Concomitantly, the subsequent amide bond cleavage reaction is rate-limiting.

  1. Self-organized nanostructured spherulitic crystal pattern formation in Belousov-Zhabotinsky type reaction system

    NASA Astrophysics Data System (ADS)

    Srivastava, Rohit; Srivastava, P. K.

    2013-11-01

    We report the formation of self-organized nanostructured spherulitic crystal pattern in a modified Belousov-Zhabotinsky (BZ) type system. In liquid phase, we observed the reaction system to exhibit well distinguishable spatial patterns including stripe and hexagonal structures. The solid phase nucleation was found to occur in the colloidal phase and nanostructured spherulitic crystal patterns were obtained as one of the final products. Transmission electron microscopy, scanning electron microscopy, optical microscopy, powder X-ray diffraction and Fourier transform infrared spectroscopy were used to characterize the spherulitic crystal pattern. The average diameter of the grown crystals was found to be ˜30-100 nm. In situ UV-Visible spectroscopic measurement exhibited damped oscillatory nature corresponding to ferroin in the reaction system. This oscillation was found to be well conjugated to the spherulitic structures. The paper elucidates the roles of the various possible factors behind such phase-transformation along with the plausible explanation of the corresponding reaction pathways.

  2. Reaction pathways towards the formation of dolomite-analogues at ambient conditions

    NASA Astrophysics Data System (ADS)

    Pimentel, Carlos; Pina, Carlos M.

    2016-04-01

    In this paper we present results of a study of the crystallisation behaviour of the dolomite-analogues norsethite and PbMg(CO3)2 at room temperature and atmospheric pressure. Whereas precipitation of norsethite was previously obtained by mixing solutions (Hood et al., 1974; Pimentel and Pina, 2014a,b), we report, for the first time, the synthesis of PbMg(CO3)2 by using the same method. The formation of both phases was promoted by ageing slurries for periods of time ranging from a few days (norsethite) up to 6 months (PbMg(CO3)2). The crystallisation of both norsethite and PbMg(CO3)2 occurs by sequences of dissolution-precipitation reactions involving several amorphous and crystalline precursor phases, which were identified and characterised by X-ray diffraction and scanning electron microscopy. Depending on the initial composition and Ba:Mg and Pb:Mg ratios in the slurries, different precursors and reaction kinetics were observed. This demonstrates the existence of different reaction pathways towards the formation of the investigated dolomite-analogues. Our experimental results provide new insights into the possible mechanisms of formation of dolomite and other double carbonates in nature.

  3. Photochemical formation of complexed HNO in low temperature matrices

    NASA Astrophysics Data System (ADS)

    Müller, R. P.; Murata, S.; Huber, J. Robert

    1982-04-01

    The molecule HNO complexed to N-methylenemethylamine (H 2CNCH 3) was prepared by photolyzing N,N-dimethylnitrosamine [(CH 3) 2NNO] in low temperature matrices. The infrared absorptions of six isotopic such complexed HNO species were measured and assigned. Based on these results a complex between HNO and the amine involving a hydrogen bond is proposed. The bands associated with the hydrogen bond, NH out-of-plane bend and N…HN stretch, were assigned. The NH stretch vibrational band of HNO is blue-shifted by complexation and has a linewidth < 1 cm -1.

  4. SOA formation from partitioning and heterogeneous reactions: model study in the presence of inorganic species.

    PubMed

    Jang, Myoseon; Czoschke, Nadine M; Northcross, Amanda L; Cao, Gang; Shaof, David

    2006-05-01

    A predictive model for secondary organic aerosol (SOA) formation by both partitioning and heterogeneous reactions was developed for SOA created from ozonolysis of alpha-pinene in the presence of preexisting inorganic seed aerosols. SOA was created in a 2 m3 polytetrafluoroethylene film indoor chamber under darkness. Extensive sets of SOA experiments were conducted varying humidity, inorganic seed compositions comprising of ammonium sulfate and sulfuric acid, and amounts of inorganic seed mass. SOA mass was decoupled into partitioning (OM(P)) and heterogeneous aerosol production (OM(H)). The reaction rate constant for OM(H) production was subdivided into three categories (fast, medium, and slow) to consider different reactivity of organic products for the particle phase heterogeneous reactions. The influence of particle acidity on reaction rates was treated in a previous semiempirical model. Model OM(H) was developed with medium and strong acidic seed aerosols, and then extrapolated to OM(H) in weak acidic conditions, which are more relevant to atmospheric aerosols. To demonstrate the effects of preexisting glyoxal derivatives (e.g., glyoxal hydrate and dimer) on OM(H), SOA was created with a seed mixture comprising of aqueous glyoxal and inorganic species. Our results show that heterogeneous SOA formation was also influenced by preexisting reactive glyoxal derivatives.

  5. Cycloaddition reactivity studies of first-row transition metal-azide complexes and alkynes: an inorganic click reaction for metalloenzyme inhibitor synthesis.

    PubMed

    Evangelio, Emi; Rath, Nigam P; Mirica, Liviu M

    2012-07-14

    The studies described herein focus on the 1,3-dipolar cycloaddition reaction between first-row transition metal-azide complexes and alkyne reagents, i.e. an inorganic variant of the extensively used "click reaction". The reaction between the azide complexes of biologically-relevant metals (e.g., Fe, Co and Ni) found in metalloenzyme active sites and alkyne reagents has been investigated as a proof-of-principle for a novel method of developing metalloenzyme triazole-based inhibitors. Six Fe, Co and Ni mono-azide complexes employing salen- and cyclam-type ligands have been synthesized and characterized. The scope of the targeted inorganic azide-alkyne click reaction was investigated using the electron-deficient alkyne dimethyl acetylenedicarboxylate. Of the six metal-azide complexes tested, the Co and Ni complexes of the 1,4,8,11-tetrametyl-1,4,8,11-tetraazacyclotetradecane (Me(4)cyclam) ligand showed a successful cycloaddition reaction and formation of the corresponding metal-triazolate products, which were crystallographically characterized. Moreover, use of less electron deficient alkynes resulted in a loss of cycloaddition reactivity. Analysis of the structural parameters of the investigated metal-azide complexes suggests that a more symmetric structure and charge distribution within the azide moiety is needed for the formation of a metal-triazolate product. Overall, these results suggest that a successful cycloaddition reaction between a metal-azide complex and an alkyne substrate is dependent both on the ligand and metal oxidation state, that determine the electronic properties of the bound azide, as well as the electron deficient nature of the alkyne employed.

  6. Light saturation curves show competence of the water splitting complex in inactive Photosystem II reaction centers.

    PubMed

    Nedbal, L; Gibas, C; Whitmarsh, J

    1991-12-01

    Photosystem II complexes of higher plants are structurally and functionally heterogeneous. While the only clearly defined structural difference is that Photosystem II reaction centers are served by two distinct antenna sizes, several types of functional heterogeneity have been demonstrated. Among these is the observation that in dark-adapted leaves of spinach and pea, over 30% of the Photosystem II reaction centers are unable to reduce plastoquinone to plastoquinol at physiologically meaningful rates. Several lines of evidence show that the impaired reaction centers are effectively inactive, because the rate of oxidation of the primary quinone acceptor, QA, is 1000 times slower than in normally active reaction centers. However, there are conflicting opinions and data over whether inactive Photosystem II complexes are capable of oxidizing water in the presence of certain artificial electron acceptors. In the present study we investigated whether inactive Photosystem II complexes have a functional water oxidizing system in spinach thylakoid membranes by measuring the flash yield of water oxidation products as a function of flash intensity. At low flash energies (less that 10% saturation), selected to minimize double turnovers of reaction centers, we found that in the presence of the artificial quinone acceptor, dichlorobenzoquinone (DCBQ), the yield of proton release was enhanced 20±2% over that observed in the presence of dimethylbenzoquinone (DMBQ). We argue that the extra proton release is from the normally inactive Photosystem II reaction centers that have been activated in the presence of DCBQ, demonstrating their capacity to oxidize water in repetitive flashes, as concluded by Graan and Ort (Biochim Biophys Acta (1986) 852: 320-330). The light saturation curves indicate that the effective antenna size of inactive reaction centers is 55±12% the size of active Photosystem II centers. Comparison of the light saturation dependence of steady state oxygen evolution

  7. Rates and Mechanisms of Complexation Reactions of Cations with Crown Ethers and Related Macrocycles

    DTIC Science & Technology

    1989-01-23

    as stability constants and entropies of solvation t, be of paramount importance. Complexation rate constants alone seldom disclose a great deal more...sample equilibrium to assure detectability of the reaction. Disadvantages include 1) the need for high solute concentrations in order to detect small...ultrasonic techniques. In principle, the stability constants of macrocycles complexing various cations can be deduced from the amplitudes of the experimental

  8. Double layer formation at the interface of complex plasmas

    SciTech Connect

    Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E.

    2008-08-15

    Necessary conditions are formulated for the generation of a double layer at the interface of a complex plasma and a particle-free electron-ion plasma in a weakly collisional discharge. Examples are calculated for realistic observed complex plasmas, and it is shown that situations of both ''smooth'' transitions and 'sharp' transitions can exist. The model can explain the abrupt boundaries observed.

  9. Enantioconvergent Nucleophilic Substitution Reaction of Racemic Alkyne-Dicobalt Complex (Nicholas Reaction) Catalyzed by Chiral Brønsted Acid.

    PubMed

    Terada, Masahiro; Ota, Yusuke; Li, Feng; Toda, Yasunori; Kondoh, Azusa

    2016-08-31

    Catalytic enantioselective syntheses enable a practical approach to enantioenriched molecules. While most of these syntheses have been accomplished by reaction at the prochiral sp(2)-hybridized carbon atom, little attention has been paid to enantioselective nucleophilic substitution at the sp(3)-hybridized carbon atom. In particular, substitution at the chiral sp(3)-hybridized carbon atom of racemic electrophiles has been rarely exploited. To establish an unprecedented enantioselective substitution reaction of racemic electrophiles, enantioconvergent Nicholas reaction of an alkyne-dicobalt complex derived from racemic propargylic alcohol was developed using a chiral phosphoric acid catalyst. In the present enantioconvergent process, both enantiomers of the racemic alcohol were transformed efficiently to a variety of thioethers with high enantioselectivity. The key to achieving success is dynamic kinetic asymmetric transformation (DYKAT) of enantiomeric cationic intermediates generated via dehydroxylation of the starting racemic alcohol under the influence of the chiral phosphoric acid catalyst. The present fascinating DYKAT involves the efficient racemization of these enantiomeric intermediates and effective resolution of these enantiomers through utilization of the chiral conjugate base of the phosphoric acid.

  10. Formation of Chlorotriophenoxy Radicals from Complete Series Reactions of Chlorotriophenols with H and OH Radicals

    PubMed Central

    Xu, Fei; Shi, Xiangli; Zhang, Qingzhu; Wang, Wenxing

    2015-01-01

    The chlorothiophenoxy radicals (CTPRs) are key intermediate species in the formation of polychlorinated dibenzothiophenes/thianthrenes (PCDT/TAs). In this work, the formation of CTPRs from the complete series reactions of 19 chlorothiophenol (CTP) congeners with H and OH radicals were investigated theoretically by using the density functional theory (DFT) method. The profiles of the potential energy surface were constructed at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution at 600–1200 K. The present study indicates that the structural parameters, thermal data, and rate constants as well as the formation potential of CTPRs from CTPs are strongly dominated by the chlorine substitution at the ortho-position of CTPs. Comparison with the study of formation of chlorophenoxy radicals (CPRs) from chlorophenols (CPs) clearly shows that the thiophenoxyl-hydrogen abstraction from CTPs by H is more efficient than the phenoxyl-hydrogen abstraction from CPs by H, whereas the thiophenoxyl-hydrogen abstraction from CTPs by OH is less impactful than the phenoxyl-hydrogen abstraction from CPs by OH. Reactions of CTPs with H can occur more readily than that of CTPs with OH, which is opposite to the reactivity comparison of CPs with H and OH. PMID:26270566

  11. Synthesis, Characterization, and Reactions of Isolable (β-Diketiminato)Nb(III) Imido Complexes*

    PubMed Central

    Tomson, Neil C.; Arnold, John; Bergman, Robert G.

    2010-01-01

    mesityl azide by (BDI)Nb(NtBu)(py) and diphenylsulfoxide by (BDI)Nb(NtBu)(CO)2 led to the monomeric bis(imido) and dimeric oxo complexes (BDI)Nb(NtBu)(NMes)(py) and [(BDI)Nb(NtBu)]2(μ2-O)2, respectively. MeLi addition to (BDI)Nb(NtBu)(CO)2(py) resulted in the formation of a Nb-acylate via methide addition to one of the carbonyl carbons. The acylate product was revealed to have a short Nb–Cacylate bond distance (2.059(4) Å), consistent with multiple Nb–C bond character resulting from Nb(III) back-bonding into the acylate carbon. The interaction of (BDI)Nb(NtBu)(CO)2 with two equivalents of 4,4′-dichlorobenzophenone resulted in the clean, quantitative formation of the corresponding pinacol coupling product, but introduction of the ketone in 1: 1 molar ratios resulted in mixtures of the pinacol product and the starting material, suggesting that ketone coordination to the Nb(III) complex may be reversible. Relatedly, addition of 1-phenyl-1-propyne to (BDI)Nb(NtBu)(CO)2 formed a thermally unstable 1: 1 Nb/alkyne complex, as characterized by NMR and IR spectroscopies; reaction of this species with HCl/MeOH yielded a 2: 1 mixture of 1-phenyl-1-propene and the free alkyne, suggesting a high degree of covalency in the Nb–C bonds. PMID:21116450

  12. Infrared spectroscopic studies on reaction induced conformational changes in the NADH ubiquinone oxidoreductase (complex I).

    PubMed

    Hellwig, Petra; Kriegel, Sébastien; Friedrich, Thorsten

    2016-07-01

    Redox-dependent conformational changes are currently discussed to be a crucial part of the reaction mechanism of the respiratory complex I. Specialized difference Fourier transform infrared techniques allow the detection of side-chain movements and minute secondary structure changes. For complex I, (1)H/(2)H exchange kinetics of the amide modes revealed a better accessibility of the backbone in the presence of NADH and quinone. Interestingly, the presence of phospholipids, that is crucial for the catalytic activity of the isolated enzyme complex, changes the overall conformation. When comparing complex I samples from different species, very similar electrochemically induced FTIR difference spectra and very similar rearrangements are reported. Finally, the information obtained with variants and from Zn(2+) inhibited samples for the conformational reorganization of complex I upon electron transfer are discussed in this review. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.

  13. Chemistry of high-oxidation-state groups V and VI complexes: Novel silyl and imido complexes and the reactions of silyl and alkyl alkylidyne complexes with oxygen

    NASA Astrophysics Data System (ADS)

    Chen, Tianniu

    This dissertation describes the synthesis and characterization of the novel early transition metal (especially group VI metals) complexes free of anionic pi-ligands such as cyclopentadienyl (Cp) and studies of their reactions with oxygen and silanes. Our study of Cp-free tungsten silyl chemistry is reported. A novel d 0 tungsten silyl complex 2 [(ButCH 2)W(=CHBut)2(SiButPh2 ) (2a) ⇌ (ButCH2)2W(≡CBu t)(SiButPh2) (2b)] and an equilibrium between 2a and 2b are described in Chapter 2. The thermodynamics of this equilibrium [DeltaH° = -0.9(0.2) kcal/mol, DeltaS° = -0.6(0.8) eu] was investigated by 1H NMR. The studies of the alpha-hydrogen exchange between 2a and 2b by 2-D EXSY experiments gave kinetic parameters of the exchange: DeltaH≠ = 17.9(1.1) kcal/mol, DeltaS≠ = 1.9(5.7) eu for the forward reaction (2a → 2b) and Delta H≠ = 18.6 (1.1) kcal/mol, DeltaS ≠ = 1.9(5.7) eu for the back reaction (2b → 2a). The reaction of O2 with silyl alkylidyne 2b [(Bu tCH2)W(=CHBut)2(SiBut Ph2) (2a) ⇌ (ButCH2)2W(≡CBu t)(SiButPh2) (2b)] is described in Chapter 3. A silyl migration product (ButCH2) 2W(=O)[=C(But)(SiButPh2)] ( 5) was characterized. A siloxy analog of 2b, (Bu tCH2)2W≡CBut(OSiBu tPh2) (6), was prepared and excluded as a possible intermediate in the formation of 5. Ab initio calculations suggested a pathway involving silyl migration in 2b to give a tungsten (IV) intermediate (ButCH 2)2W=C(But)(SiButPh2) (7) prior to the reaction with O2. A crystal structure of (Me3SiCH2)2W(=O)(=CHSiMe3)(O=PMe 3)•(Me3SiCH2)3W≡CSiMe 3 (12) was obtained from the reaction of alkyl alkylidyne (Me3SiCH2)3W≡CSiMe3 with O2 in the presence of PMe3. In Chapter 4, preparation and characterization of bis(2,6-diisopropylphenylimido)molybdenum(VI) amide and silyl complexes (ArN=)2Mo(NMe2)2 (14), (ArN=)2Mo(NMe2)[Si(SiMe3) 3] (15), (ArN=)2MoCl[N(SiMe3) 2] (16), (ArN=)2Mo(NMe2)[N(SiMe 3)2] (17), and (ArN=)2Mo(NHAr) 2 (18) are reported. In addition, new bis

  14. The catalytic effect of water, water dimers and water trimers on H2S + (3)O2 formation by the HO2 + HS reaction under tropospheric conditions.

    PubMed

    Zhang, Tianlei; Yang, Chen; Feng, Xukai; Kang, Jiaxin; Song, Liang; Lu, Yousong; Wang, Zhiyin; Xu, Qiong; Wang, Wenliang; Wang, Zhuqing

    2016-06-29

    In this article, the reaction mechanisms of H2S + (3)O2 formation by the HO2 + HS reaction without and with catalyst X (X = H2O, (H2O)2 and (H2O)3) have been investigated theoretically at the CCSD(T)/6-311++G(3df,2pd)//B3LYP/6-311+G(2df,2p) level of theory, coupled with rate constant calculations by using conventional transition state theory. Our results show that in the presence of catalyst X (X = H2O, (H2O)2 and (H2O)3) into the channel of H2S + (3)O2 formation, the reactions between the SH radical and HO2(H2O)n (n = 1-3) complexes are more favorable than the corresponding reactions of the HO2 radical with HS(H2O)n (n = 1-3) complexes due to the lower barrier of the former reactions and the higher concentrations of HO2(H2O)n (n = 1-3) complexes. Meanwhile, the catalytic effect of water, water dimers and water trimers is mainly taken from the contribution of a single water vapor molecule, since the total effective rate constant of HO2H2O + HS and H2OHO2 + HS reactions was, respectively, larger by 7-9 and 9-12 orders of magnitude than that of SH + HO2(H2O)2 and SH + HO2(H2O)3 reactions. Besides, the enhancement factor of water vapor is only 0.37% at 240 K, while at high temperatures, such as 425 K, the positive water vapor effect is enhanced up to 38.00%, indicating that at high temperatures the positive water effect is obvious under atmospheric conditions. Overall, these results show how water and water clusters catalyze the gas phase reactions under atmospheric conditions.

  15. Formation of diverse polycyclic spirooxindoles via three-component reaction of isoquinolinium salts, isatins and malononitrile

    NASA Astrophysics Data System (ADS)

    Sun, Jing; Shen, Guo-Liang; Huang, Ying; Yan, Chao-Guo

    2017-01-01

    The triethylamine promoted three-component reaction of N-(4-nitrobenzyl), N-ethoxycarbonylmethylisoquinolinium bromide, isatins and malononitrile in ethanol afforded spiro[indoline-3,2‧-pyrrolo[2,1-a]isoquinolines] in good yields and with high diastereoselectivity. The similar reaction of N-cyanomethylisoquinolinium chloride mainly gave complex indolo[2″,3″:2‧,3‧]pyrrolo[3‧,4‧:4,5]pyrrolo[2,1-a]isoquinoline derivatives. However, the three-component reaction of N-cyanomethylisoquinolinium chloride, isatins and ethyl cyanoacetate mainly resulted in functionalized spiro[indoline-3,8‧-pyrido[2‧,3‧:4,5]pyrrolo[2,1-a]isoquinolines].

  16. Formation of diverse polycyclic spirooxindoles via three-component reaction of isoquinolinium salts, isatins and malononitrile

    PubMed Central

    Sun, Jing; Shen, Guo-liang; Huang, Ying; Yan, Chao-Guo

    2017-01-01

    The triethylamine promoted three-component reaction of N-(4-nitrobenzyl), N-ethoxycarbonylmethylisoquinolinium bromide, isatins and malononitrile in ethanol afforded spiro[indoline-3,2′-pyrrolo[2,1-a]isoquinolines] in good yields and with high diastereoselectivity. The similar reaction of N-cyanomethylisoquinolinium chloride mainly gave complex indolo[2″,3″:2′,3′]pyrrolo[3′,4′:4,5]pyrrolo[2,1-a]isoquinoline derivatives. However, the three-component reaction of N-cyanomethylisoquinolinium chloride, isatins and ethyl cyanoacetate mainly resulted in functionalized spiro[indoline-3,8′-pyrido[2′,3′:4,5]pyrrolo[2,1-a]isoquinolines]. PMID:28106130

  17. Neutrophil extracellular trap formation as innate immune reactions against the apicomplexan parasite Eimeria bovis.

    PubMed

    Behrendt, Jan Hillern; Ruiz, Antonio; Zahner, Horst; Taubert, Anja; Hermosilla, Carlos

    2010-01-15

    Eimeria bovis infections are under immunological control and recent studies have emphasized the role of early PMN-mediated innate immune responses in infected calves. Neutrophil extracellular traps (NETs) have recently been demonstrated to act as a killing mechanism of PMN against several pathogens. In the present study, the interactions of bovine PMN with sporozoites of E. bovis were investigated in this respect in vitro. For demonstration and quantification of NET formation, extracellular DNA was stained by Sytox Orange. Fluorescence images after Sytox Orange staining as well as scanning electron microscopy (SEM) showed NET formation to occur upon contact with E. bovis sporozoites. Exposure of PMN to viable sporozoites induced stronger NET formation than to dead or homogenized parasites. NET formation was abolished by treatment with DNase and could be reduced by diphenylene iodonium, which is described as a potent inhibitor of NADPH oxidase. After sporozoite and PMN co-culture, extracellular fibres were found attached to sporozoites and seemed to trap them, strongly suggesting that NETs immobilize E. bovis sporozoites and thereby prevent them from infecting host cells. Thus, transfer of sporozoites, previously being confronted with PMN, to adequate host cells resulted in clearly reduced infection rates when compared to PMN-free controls. NET formation by PMN may therefore represent an effector mechanism in early innate immune reactions against E. bovis. This is the first report indicating Eimeria-induced NET formation.

  18. On the formation of aliphatic polycarbonates from epoxides with chromium(III) and aluminum(III) metal-salen complexes.

    PubMed

    Luinstra, Gerrit A; Haas, Gerhard R; Molnar, Ferenc; Bernhart, Volker; Eberhardt, Robert; Rieger, Bernhard

    2005-10-21

    A DFT-based description is given of the CO2/epoxide copolymerization with a catalyst system consisting of metal (chromium, iron, titanium, aluminum)-salen complexes (salen = N,N'-bis(3,5-di-tert-butylsalicyliden-1,6-diaminophenyl) in combination with either chloride, acetate, or dimethylamino pyridine (DMAP) as external nucleophile. Calculations indicate that initiation proceeds through nucleophilic attack at a metal-coordinated epoxide, and the most likely propagation reaction is a bimolecular process in which a metal-bound nucleophile attacks a metal-bound epoxide. Carbon dioxide insertion occurs at a single metal center and is most likely the rate-determining step at low pressure. The prevalent chain terminating/degradation-the so-called backbiting, a reaction leading to formation of cyclic carbonate from the polymer chain-would involve attack of a carbonate nucleophile rather than an alkoxide at the last unit of the growing chain. The backbiting of a free carbonato chain end is particularly efficient. Anion dissociation from six-coordinate aluminum is appreciably easier than from chromium-salen complexes, indicating the reason why in the former case cyclic carbonate is the sole product. Experimental data were gathered for a series of chromium-, aluminum-, iron-, and zinc-salen complexes, which were used in combination with external nucleophiles like DMAP and mainly (tetraalkyl ammonium) chloride/acetate. Aluminum complexes transform PO (propylene oxide) and CO2 to give exclusively propylene carbonate. This is explained by rapid carbonate anion dissociation from a six-coordinate complex and cyclic formation. CO2 insertion or nucleophilic attack of an external nucleophile at a coordinated epoxide (at higher CO2 pressure) are the rate-determining steps. Catalysis with [Cr(salen)(acetate/chloride)] complexes leads to the formation of both cyclic carbonate and polypropylene carbonate with various quantities of ether linkages. The dependence of the activity and

  19. Characterizing Pyroxene Reaction Space in Calcium-Aluminum Rich Inclusions: Oxidation During CAI Rim Formation

    NASA Astrophysics Data System (ADS)

    Dyl, K. A.; Young, E. D.

    2009-12-01

    We define the reaction space that controls changes in pyroxene composition in CAIs and Wark-Lovering (WL) rims in an oxidizing solar nebula. Ti-rich pyroxenes in CAIs record a sub-solar oxygen fugacity (Ti3+/Ti4+~1.5). WL rim pyroxenes in the CAI Leoville 144A have a distinctly lower oxidation state.This difference supports WL rim condensation in an environment of increasing O2(g) and Mg(g) (Simon et al. 2005). We used the following phase components to identify four linearly independent reactions (Thompson 1982): diopside, CaTs (Al2Mg-1Si-1), T3 (Ti3+AlMg-1Si-1), T4 (Ti4+Al2Mg-1Si-2), En (MgCa-1), perovskite, O(g), Mg(g), SiO(g), and Ca(g). Compositional variation in this system is dominated by two reactions. The first is oxidation of Ti3+ via reaction with O and Mg in the gas phase: 1.5 O(g) + Mg(g) → ¼ Di + [Ti4+Mg3/4Ti3+-1Ca-1/4Si-1/2] (1). Pyroxene is produced and En is introduced. The second reaction (2) is perovskite formation. It is observed in the WL rim of Leoville 144A, and experiments confirm that an elevated Ti component converts pyroxene to perovskite(Gupta et al. 1973). MgCa-1 is the third linearly independent reaction (3). They combine to give: ½ Di + x Ca(g)→ x Mg(g)+ Pv + [Mg1/2-xSiTi4+-1Ca-1/2+x](2,3). Unlike (1), pyroxene is consumed in this reaction. The parameter x defines the extent of Mg-Ca exchange. When x > 0.5, WL rim formation occurs in an environment where Mg is volatile and Ca condenses. The reaction space defined by reactions (1) and (2,3) describes the transition from CAI interior to WL rims. WL rim pyroxene Ti contents, [CaTs], and Ca < 1 pfu are all explained in this space. The fourth linearly independent reaction is SiO(g):1/8 Di + ¼ Mg(g)→ ¾ SiO(g) + [Mg3/8Ca1/8Ti4+Ti3+-1Si-1/2](4). Silica reduction forms Ti4+, releasing SiO(g). (4) does not describe the oxidation of Ti3+ in WL rim pyroxene, but (1) - (4) results in En formation directly from the gas phase. This may explain WL rim analyses that have Si contents in excess

  20. Formation of hydrocarbons on Titan: Impact of rapid association reactions at low pressure

    NASA Astrophysics Data System (ADS)

    Vuitton, V.; Yelle, R. V.; Lavvas, P.; Klippenstein, S. J.

    2011-10-01

    In the 1980's, Voyager revealed that complex organic molecules were present in Titan's atmosphere but the actual mechanisms leading to this rich chemistry were largely unknown. The recent Cassini results indicate that the chemistry ocurring in Titan's upper atmosphere is far more complex than anticipated. The detection of heavy positive and negative ions [13] reveals that much of the molecular growth occurs in the upper atmosphere rather than at lower altitudes [5, 12]. Photochemical models predict that three-body association reactions (A + B + M!AB + M) are the main production route for several hydrocarbons, including alkanes [2, 3]. The kinetic parameters of these reactions strongly depend on density and are therefore extremely difficult to constrain by experimental measurements as the low pressure of Titan's upper atmosphere cannot be reproduced in the laboratory. As a consequence, they have to be extrapolated outside the range of measurements, leading to high uncertainties. According to these extrapolations, three-body association reactions are only efficient in Titan's lower atmosphere. However, radiative association reactions (A + B ! AB + h) do not depend on pressure and can therefore still be efficient in the upper atmosphere. Unfortunately, they are largely uncharacterized and have consequently been neglected in photochemical models so far. Because of their potential importance at higher altitude, association reactions can have an important contribution to our understanding of molecular growth and better constraints for them are required. In the recent years, theoretical calculations of kinetics parameters have become more and more reliable [7]. We therefore performed ab initio transition state theory based master equation calculations for several radical-radical and radical-molecule association reactions. The computed kinetics parameters were included in our photochemical model of Titan. We present here the main results and discuss their impact for the

  1. Transient protection of strained alkynes from click reaction via complexation with copper.

    PubMed

    Yoshida, Suguru; Hatakeyama, Yasutomo; Johmoto, Kohei; Uekusa, Hidehiro; Hosoya, Takamitsu

    2014-10-01

    A transient protection method of cyclooctynes from a click reaction with an azide through 1:1 complexation with a cationic copper(I) salt is reported. The application of the method to a cyclooctyne bearing a terminal alkyne enabled the selective copper-catalyzed click conjugation with an azide at the terminal alkyne moiety, which made cyclooctyne derivatives readily accessible.

  2. Placebo Effect upon Complex Reaction Time When Hypnotic Suggestibility is Controlled.

    ERIC Educational Resources Information Center

    Eskridge, Veronica L.

    This study was designed to investigate the effect of a placebo (sugar pill) accompanied by suggestions that the pill would either (1) improve performance as a stimulant or (2) cause a deterioration in performance as a depressant when the performance in question was the subjects' complex reaction time to a light stimulus. The Harvard Group Scale of…

  3. Chiral holmium complex-catalyzed Diels-Alder reaction of silyloxyvinylindoles: stereoselective synthesis of hydrocarbazoles.

    PubMed

    Harada, Shinji; Morikawa, Takahiro; Nishida, Atsushi

    2013-10-18

    The catalytic and asymmetric cycloaddition between 3-[1-(silyloxy)vinyl]indoles and electron-deficient olefins gave substituted hydrocarbazoles in up to 99% yield and 94% ee. This reaction was catalyzed by a novel chiral holmium(III) complex. Alkylation of the cycloadduct gave a tricyclic compound with four continuous chiral centers, one of which was a quaternary carbon.

  4. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  5. Protein complex formation by acetylcholinesterase and the neurotoxin fasciculin-2 appears to involve an induced-fit mechanism

    PubMed Central

    Bui, Jennifer M.; McCammon, J. Andrew

    2006-01-01

    Specific, rapid association of protein complexes is essential for all forms of cellular existence. The initial association of two molecules in diffusion-controlled reactions is often influenced by the electrostatic potential. Yet, the detailed binding mechanisms of proteins highly depend on the particular system. A complete protein complex formation pathway has been delineated by using structural information sampled over the course of the transformation reaction. The pathway begins at an encounter complex that is formed by one of the apo forms of neurotoxin fasciculin-2 (FAS2) and its high-affinity binding protein, acetylcholinesterase (AChE), followed by rapid conformational rearrangements into an intermediate complex that subsequently converts to the final complex as observed in crystal structures. Formation of the intermediate complex has also been independently captured in a separate 20-ns molecular dynamics simulation of the encounter complex. Conformational transitions between the apo and liganded states of FAS2 in the presence and absence of AChE are described in terms of their relative free energy profiles that link these two states. The transitions of FAS2 after binding to AChE are significantly faster than in the absence of AChE; the energy barrier between the two conformational states is reduced by half. Conformational rearrangements of FAS2 to the final liganded form not only bring the FAS2/AChE complex to lower energy states, but by controlling transient motions that lead to opening or closing one of the alternative passages to the active site of the enzyme also maximize the ligand's inhibition of the enzyme. PMID:17021015

  6. Recent aspects of the proton transfer reaction in H-bonded complexes

    NASA Astrophysics Data System (ADS)

    Szafran, Mirosław

    1996-07-01

    Proton transfer processes cover a very wide range of situations and time scales and they are of great interest from the viewpoint of chemical reactions in solution. These processes can occur via thermally activated crossing or tunneling. This review considers various aspects of this many-faceted field. Spectroscopic, dielectric, colligative and energetic properties and structures of various species with H-bonds are examined. Proton transfer reactions in water and organic solvents, and the contribution of various H-bonded species and ions to these processes are discussed. Among other topics, this survey includes the effects of solvent, acid-base stoichiometry, concentration, temperature and impurity on proton transfer reactions in complexes of phenols and carboxylic acids with amines, pyridines and pyridine N-oxides. The contribution of the nonstoichiometric acid-base complexes and ionic species to the reversible proton transfer mechanism is discussed.

  7. Photo-initiated thiol-ene click reactions as a potential strategy for incorporation of [M(I)(CO)3]+ (M = Re, (99m)Tc) complexes.

    PubMed

    Hayes, Thomas R; Lyon, Patrice A; Silva-Lopez, Elsa; Twamley, Brendan; Benny, Paul D

    2013-03-18

    Click reactions offer a rapid technique to covalently assemble two molecules. In radiopharmaceutical construction, these reactions can be utilized to combine a radioactive metal complex with a biological targeting molecule to yield a potent tool for imaging or therapy applications. The photo-initiated radical thiol-ene click reaction between a thiol and an alkene was examined for the incorporation of [M(I)(CO)3](+) (M = Re, (99m)Tc) systems for conjugating biologically active targeting molecules containing a thiol. In this strategy, a potent chelate system, 2,2'-dipicolylamine (DPA), for [M(I)(CO)3](+) was functionalized at the central amine with a terminal alkene linker that was explored with two synthetic approaches, click then chelate and chelate then click, to determine the flexibility and applicability of the thiol-ene click reaction to specifically incorporate ligand systems and metal complexes with a thiol containing molecule. In the click then chelate approach, the thiol-ene click reaction was carried out with the DPA chelate followed by complexation with [M(I)(CO)3](+). In the chelate then click approach, the alkene functionalized DPA chelate was first complexed with [M(I)(CO)3](+) followed by the conduction of the thiol-ene click reaction. Initial studies utilized benzyl mercaptan as a model thiol for both strategies to generate the identical product from either route to provide information on reactivity and product formation. DPA ligands functionalized with two unique linker systems (allyl and propyl allyl ether) were prepared to examine the effect of the proximity of the chelate or complex on the thiol-ene click reaction. Both the thiol-ene click and coordination reactions with Re, (99m)Tc were performed in moderate to high yields demonstrating the potential of the thiol-ene click reaction for [M(I)(CO)3](+) incorporation into thiol containing biomolecules.

  8. Co-complexes Derived from Alkene Insertion to Alkyne-dicobaltpentacarbonyl complexes: Insight into the Regioselectivity of Pauson-Khand Reactions of Cyclopropenes

    PubMed Central

    Pallerla, Mahesh K.; Yap, Glenn P. A.; Fox, Joseph M.

    2009-01-01

    Described are the X-ray crystallographic and spectral properties of Co-complexes that were isolated from two Pauson-Khand reactions of chiral cyclopropenes. These are the first examples of isolated Co-complexes derived from the putative alkene-insertion intermediates of Pauson-Khand reactions. The binuclear Co-complexes are coordinated to μ-bonded, five-carbon “flyover” carbene ligands. It is proposed that the complexes result from cyclopropane fragmentation subsequent to alkene insertion. The observation of these metal complexes provides a rationale for the origin of regioselectivity in Pauson-Khand reactions of cyclopropenes. PMID:18637694

  9. Aqueous-Phase Reactions of Isoprene with Sulfoxy Radical Anions as a way of Wet Aerosol Formation in the Atmosphere

    NASA Astrophysics Data System (ADS)

    Kuznietsova, I.; Rudzinski, K. J.; Szmigielski, R.; Laboratory of the Environmental Chemistry

    2011-12-01

    Atmospheric aerosols exhibit an important role in the environment. They have implications on human health and life, and - in the larger scale - on climate, the Earth's radiative balance and the cloud's formation. Organic matter makes up a significant fraction of atmospheric aerosols (~35% to ~90%) and may originate from direct emissions (primary organic aerosol, POA) or result from complex physico-chemical processes of volatile organic compounds (secondary organic aerosol, SOA). Isoprene (2-methyl-buta-1,3-diene) is one of the relevant volatile precursor of ambient SOA in the atmosphere. It is the most abundant non-methane hydrocarbon emitted to the atmosphere as a result of living vegetation. According to the recent data, the isoprene emission rate is estimated to be at the level of 500 TgC per year. While heterogeneous transformations of isoprene have been well documented, aqueous-phase reactions of this hydrocarbon with radical species that lead to the production of new class of wet SOA components such as polyols and their sulfate esters (organosulfates), are still poorly recognized. The chain reactions of isoprene with sulfoxy radical-anions (SRA) are one of the recently researched route leading to the formation of organosulfates in the aqueous phase. The letter radical species originate from the auto-oxidation of sulfur dioxide in the aqueous phase and are behind the phenomenon of atmospheric acid rain formation. This is a complicated chain reaction that is catalyzed by transition metal ions, such as manganese(II), iron(III) and propagated by sulfoxy radical anions . The presented work addresses the chemical interaction of isoprene with sulfoxy radical-anions in the water solution in the presence of nitrite ions and nitrous acid, which are important trace components of the atmosphere. We showed that nitrite ions and nitrous acid significantly altered the kinetics of the auto-oxidation of SO2 in the presence of isoprene at different solution acidity from 2 to 8

  10. Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine: Formation of Complexes With Bound Amines

    SciTech Connect

    Zhang, Shaoguang; Bullock, R. Morris

    2015-07-06

    CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature 1H and 31P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis and trans-isomers. Both cis-CpMo(CO)(PEtNMePEt)H and trans-CpMo(CO)(PPhNMePPh)H were analyzed by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(PEtNMePEt)H and CpMo(CO)(PPhNMePPh)H in CH3CN are both irreversible at slow scan rates and quasi-reversible at higher scan rates, with E1/2 = -0.36 V (vs. Cp2Fe+/0) for CpMo(CO)(PEtNMePEt)H and E1/2 = -0.18 V for CpMo(CO)(PPhNMePPh)H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C]+[A]- (A = B(C6F5)4 or BArF4; [ArF = 3,5-bis(trifluoromethyl)phenyl]) afforded “tuck-in” [CpMo(CO)(κ3-PNP)]+ complexes that feature the amine bound to the metal. Displacement of the κ3 Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)]+. The kinetics of this reaction were studied by NMR spectroscopy, providing the activation parameters ΔH‡ = 22.1 kcal/mol, ΔS‡ = 1.89 cal/(mol·K), Ea = 22.7 kcal/mol. Protonation of CpMo(CO)(PEtNMePEt)H affords [CpMo(CO)(κ2-PEtNMePEt)(H)2]+ as a Mo dihydride complex, which loses H2 to generate [CpMo(CO)(κ3-PEtNMePEt)]+ at room temperature. CpMo(CO)(dppp)H (dppp = 1,2-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2]+. Our results show that the pendant amine has a strong driving force to form stable “tuck-in” [CpMo(CO)(κ3-PNP)]+ complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2]+ complexes by formation of Mo-N dative bond. We thank the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences for support. Pacific Northwest National Laboratory is operated by

  11. Role of weakly bound complexes in temperature-dependence and relative rates of MxOy- + H2O (M = Mo, W) reactions

    NASA Astrophysics Data System (ADS)

    Kafader, Jared O.; Ray, Manisha; Raghavachari, Krishnan; Jarrold, Caroline Chick

    2016-02-01

    Results of a systematic comparison of the MoxOy- + H2O and WxOy- + H2O reaction rate coefficients are reported and compared to previous experimental and computational studies on these reactions. WxOy- clusters undergo more direct oxidation by water to yield WxOy+1- + H2, while for MoxOy- clusters, production of MoxOyH2- (trapped intermediates in the oxidation reaction) is comparatively more prevalent. However, MoxOy- clusters generally have higher rate coefficients than analogous WxOy- clusters if MoxOy+1H2- formation is included. Results of calculations on the M2Oy- + H2O (M = Mo, W; y = 4, 5) reaction entrance channel are reported. They include charge-dipole complexes formed from long-range interactions, and the requisite conversion to a Lewis acid-base complex that leads to MxOy+1H2- formation. The results predict that the Lewis acid-base complex is more strongly bound for MoxOy- clusters than for WxOy- clusters. The calculated free energies along this portion of the reaction path are also consistent with the modest anti-Arrhenius temperature dependence measured for most MoxOy- + H2O reactions, and the WxOy- + H2O reaction rate coefficients generally being constant over the temperature range sampled in this study. For clusters that exhibit evidence of both water addition and oxidation reactions, increasing the temperature increases the branching ratio toward oxidation for both species. A more direct reaction path to H2 production may therefore become accessible at modest temperatures for certain cluster stoichiometries and structures.

  12. Numerical simulation and analysis of complex patterns in a two-layer coupled reaction diffusion system

    NASA Astrophysics Data System (ADS)

    Li, Xin-Zheng; Bai, Zhan-Guo; Li, Yan; He, Ya-Feng; Zhao, Kun

    2015-04-01

    The resonance interaction between two modes is investigated using a two-layer coupled Brusselator model. When two different wavelength modes satisfy resonance conditions, new modes will appear, and a variety of superlattice patterns can be obtained in a short wavelength mode subsystem. We find that even though the wavenumbers of two Turing modes are fixed, the parameter changes have influences on wave intensity and pattern selection. When a hexagon pattern occurs in the short wavelength mode layer and a stripe pattern appears in the long wavelength mode layer, the Hopf instability may happen in a nonlinearly coupled model, and twinkling-eye hexagon and travelling hexagon patterns will be obtained. The symmetries of patterns resulting from the coupled modes may be different from those of their parents, such as the cluster hexagon pattern and square pattern. With the increase of perturbation and coupling intensity, the nonlinear system will convert between a static pattern and a dynamic pattern when the Turing instability and Hopf instability happen in the nonlinear system. Besides the wavenumber ratio and intensity ratio of the two different wavelength Turing modes, perturbation and coupling intensity play an important role in the pattern formation and selection. According to the simulation results, we find that two modes with different symmetries can also be in the spatial resonance under certain conditions, and complex patterns appear in the two-layer coupled reaction diffusion systems. Project supported by the National Natural Science Foundation of China (Grant No. 11247242), the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 51201057), and the Natural Science Foundation of Hebei Province, China (Grant No. A2014208171).

  13. Developing mononuclear copper-active-oxygen complexes relevant to reactive intermediates of biological oxidation reactions.

    PubMed

    Itoh, Shinobu

    2015-07-21

    Active-oxygen species generated on a copper complex play vital roles in several biological and chemical oxidation reactions. Recent attention has been focused on the reactive intermediates generated at the mononuclear copper active sites of copper monooxygenases such as dopamine β-monooxygenase (DβM), tyramine β-monooxygenase (TβM), peptidylglycine-α-hydroxylating monooxygenase (PHM), and polysaccharide monooxygenases (PMO). In a simple model system, reaction of O2 and a reduced copper(I) complex affords a mononuclear copper(II)-superoxide complex or a copper(III)-peroxide complex, and subsequent H(•) or e(-)/H(+) transfer, which gives a copper(II)-hydroperoxide complex. A more reactive species such as a copper(II)-oxyl radical type species could be generated via O-O bond cleavage of the peroxide complex. However, little had been explored about the chemical properties and reactivity of the mononuclear copper-active-oxygen complexes due to the lack of appropriate model compounds. Thus, a great deal of effort has recently been made to develop efficient ligands that can stabilize such reactive active-oxygen complexes in synthetic modeling studies. In this Account, I describe our recent achievements of the development of a mononuclear copper(II)-(end-on)superoxide complex using a simple tridentate ligand consisting of an eight-membered cyclic diamine with a pyridylethyl donor group. The superoxide complex exhibits a similar structure (four-coordinate tetrahedral geometry) and reactivity (aliphatic hydroxylation) to those of a proposed reactive intermediate of copper monooxygenases. Systematic studies based on the crystal structures of copper(I) and copper(II) complexes of the related tridentate supporting ligands have indicated that the rigid eight-membered cyclic diamine framework is crucial for controlling the geometry and the redox potential, which are prerequisites for the generation of such a unique mononuclear copper(II)-(end-on)superoxide complex

  14. Complex Type 2 Reactions in Three Patients with Hansen's Disease from a Southern United States Clinic.

    PubMed

    Leon, Kristoffer E; Salinas, Jorge L; McDonald, Robert W; Sheth, Anandi N; Fairley, Jessica K

    2015-11-01

    In non-endemic countries, leprosy, or Hansen's disease (HD), remains rare and is often underrecognized. Consequently, the literature is currently lacking in clinical descriptions of leprosy complications in the United States. Immune-mediated inflammatory states known as reactions are common complications of HD. Type 1 reactions are typical of borderline cases and occur in 30% of patients and present as swelling and inflammation of existing skin lesions, neuritis, and nerve dysfunction. Type 2 reactions are systemic events that occur at the lepromatous end of the disease spectrum, and typical symptoms include fever, arthralgias, neuritis, and classic painful erythematous skin nodules known as erythema nodosum leprosum. We report three patients with lepromatous leprosy seen at a U.S. HD clinic with complicated type 2 reactions. The differences in presentations and clinical courses highlight the complexity of the disease and the need for increased awareness of unique manifestations of lepromatous leprosy in non-endemic areas.

  15. Complex Type 2 Reactions in Three Patients with Hansen's Disease from a Southern United States Clinic

    PubMed Central

    Leon, Kristoffer E.; Salinas, Jorge L.; McDonald, Robert W.; Sheth, Anandi N.; Fairley, Jessica K.

    2015-01-01

    In non-endemic countries, leprosy, or Hansen's disease (HD), remains rare and is often underrecognized. Consequently, the literature is currently lacking in clinical descriptions of leprosy complications in the United States. Immune-mediated inflammatory states known as reactions are common complications of HD. Type 1 reactions are typical of borderline cases and occur in 30% of patients and present as swelling and inflammation of existing skin lesions, neuritis, and nerve dysfunction. Type 2 reactions are systemic events that occur at the lepromatous end of the disease spectrum, and typical symptoms include fever, arthralgias, neuritis, and classic painful erythematous skin nodules known as erythema nodosum leprosum. We report three patients with lepromatous leprosy seen at a U.S. HD clinic with complicated type 2 reactions. The differences in presentations and clinical courses highlight the complexity of the disease and the need for increased awareness of unique manifestations of lepromatous leprosy in non-endemic areas. PMID:26304919

  16. Complex spatiotemporal behavior in the photosensitive ferroin-bromate-4-nitrophenol reaction.

    PubMed

    Bell, Jeffrey G; Wang, Jichang

    2015-04-09

    Investigation illustrates that the bromate-4-nitrophenol reaction in a stirred batch reactor undergoes spontaneous oscillations under very broad initial reactant concentrations. The addition of ferroin has subtle influences on the nonlinear behavior, in which the frequency and total number of oscillations were greatly reduced at a low or high ferroin concentration, as opposed to the significant increase at a moderate ferroin concentration. Temporal oscillations with a modulating frequency were also observed in the ferroin-bromate-4-nitrophenol system. In a capillary tube the ferroin-bromate-4-nitrophenol reaction generated propagating wave trains with various complex behaviors such as period-doubled intermittent propagation failure. Illumination was found to have a profound effect on the temporal oscillations in the bromate-4-nitrophenol reaction and on those long lasting wave activities. Spectroscopic studies were able to identify 1,4-benzoquinone, 2-bromo-1,4-benzoquinone, and 2-bromo-4-nitrophenol as major components during the reaction.

  17. Dearomatization Reactions of N-Heterocycles Mediated by Group 3 Complexes

    SciTech Connect

    Miller, Kevin L; Williams, Bryan N; Benitez, Diego; Carver, Colin T; Ogilby, Kevin R; Tkatchouk, Ekaterina; Goddard, William A; Diaconescu, Paula L

    2010-01-13

    Group 3 (Sc, Y, Lu, La) benzyl complexes supported by a ferrocene diamide ligand are reactive toward aromatic N-heterocycles by mediating their coupling and, in a few cases, the cleavage of their C-N bonds. When these complexes reacted with 2,2'-bipyridine or isoquinoline, they facilitated the alkyl migration of the benzyl ligand onto the pyridine ring, a process accompanied by the dearomatization of the N-heterocycle. The products of the alkyl-transfer reactions act as hydrogen donors in the presence of aromatic N-heterocycles, ketones, and azobenzene. Experimental and computational studies suggest that the hydrogen transfer takes place through a concerted mechanism. An interesting disproportionation reaction of the dearomatized, alkyl-substituted isoquinoline complexes is also reported.

  18. A new reaction mode of germanium-silicon bond formation: insertion reactions of H₂GeLiF with SiH₃X (X = F, Cl, Br).

    PubMed

    Yan, Bingfei; Li, Wenzuo; Xiao, Cuiping; Li, Qingzhong; Cheng, Jianbo

    2013-10-01

    A combined density functional and ab initio quantum chemical study of the insertion reactions of the germylenoid H2GeLiF with SiH3X (X = F, Cl, Br) was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connected the reactants and the products. The calculated barrier heights relative to the respective precursors are 102.26 (X = F), 95.28 (X = Cl), and 84.42 (X = Br) kJ mol(-1) for the three different insertion reactions, respectively, indicating the insertion reactions should occur easily according to the following order: SiH3-Br > SiH3-Cl > SiH3-F under the same situation. The solvent effects on the insertion reactions were also calculated and it was found that the larger the dielectric constant, the easier the insertion reactions. The elucidations of the mechanism of these insertion reactions provided a new reaction model of germanium-silicon bond formation.

  19. Crystal structures of complexes of NAD{sup +}-dependent formate dehydrogenase from methylotrophic bacterium Pseudomonas sp. 101 with formate

    SciTech Connect

    Filippova, E. V. Polyakov, K. M.; Tikhonova, T. V.; Stekhanova, T. N.; Boiko, K. M.; Sadykhov, I. G.; Tishkov, V. I.; Popov, V. O.; Labru, N.

    2006-07-15

    Formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 catalyzes oxidation of formate to NI{sub 2} with the coupled reduction of nicotinamide adenine dinucleotide (NAD{sup +}). The three-dimensional structures of the apo form (the free enzyme) and the holo form (the ternary FDH-NAD{sup +}-azide complex) of FDH have been established earlier. In the present study, the structures of FDH complexes with formate are solved at 2.19 and 2.28 A resolution by the molecular replacement method and refined to the R factors of 22.3 and 20.5%, respectively. Both crystal structures contain four protein molecules per asymmetric unit. These molecules form two dimers identical to the dimer of the apo form of FDH. Two possible formatebinding sites are found in the active site of the FDH structure. In the complexes the sulfur atom of residue Cys354 exists in the oxidized state.

  20. Universal reaction mechanism of boronic acids with diols in aqueous solution: kinetics and the basic concept of a conditional formation constant.

    PubMed

    Furikado, Yuki; Nagahata, Tomomi; Okamoto, Takuya; Sugaya, Tomoaki; Iwatsuki, Satoshi; Inamo, Masahiko; Takagi, Hideo D; Odani, Akira; Ishihara, Koji

    2014-10-06

    To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (Ka(BL)) of boronic acid diol esters (HBLs) were determined based on the well-established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4-difluorophenylboronic acid and chromotropic acid, 3-nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K', based on the main reaction: RB(OH)2 + H2L (K1)⇌ RB(L)(OH)(-) + H3O(+) instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B') with uncomplexed diol species (L') to form boronic acid diol complex species (esters, BL') in aqueous solution at pH 5-11: B' + L' (K')⇌ BL'. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution.

  1. Monitoring benzene formation from benzoate in model systems by proton transfer reaction-mass spectrometry

    NASA Astrophysics Data System (ADS)

    Aprea, Eugenio; Biasioli, Franco; Carlin, Silvia; Märk, Tilmann D.; Gasperi, Flavia

    2008-08-01

    The presence of benzene in food and in particular in soft drinks has been reported in several studies and should be considered in fundamental investigations about formation of this carcinogen compound as well as in quality control. Proton transfer reaction-mass spectrometry (PTR-MS) has been used here for rapid, direct quantification of benzene and to monitor its formation in model systems related to the use of benzoate, a common preservative, in presence of ascorbic acid: a widespread situation that yields benzene in, e.g., soft drinks and fruit juices. Firstly, we demonstrate here that PTR-MS allows a rapid determination of benzene that is in quantitative agreement with independent solid phase micro-extraction/gas chromatography (SPME/GC) analysis. Secondly, as a case study, the effect of different sugars (sucrose, fructose and glucose) on benzene formation is investigated indicating that they inhibit its formation and that this effect is enhanced for reducing sugars. The sugar-induced inhibition of benzene formation depends on several parameters (type and concentration of sugar, temperature, time) but can be more than 80% in situations that can be expected in the storage of commercial soft drinks. This is consistent with the reported observations of higher benzene concentrations in sugar-free soft drinks.

  2. Effects of chemical and enzymatic modifications on starch-linoleic acid complex formation.

    PubMed

    Arijaje, Emily Oluwaseun; Wang, Ya-Jane

    2017-02-15

    This study investigated the complexation yield and physicochemical properties of soluble and insoluble starch complexes with linoleic acid when a β-amylase treatment was applied to acetylated and debranched potato starch. The degree of acetylation was generally higher in the soluble complexes than in the insoluble ones. The insoluble complexes from the acetylated starch displayed the V-type pattern, whereas, the soluble complexes displayed a mixture of either the A-/V-type or the B-/V-type pattern. Acetylation decreased onset and peak melting temperatures for the insoluble complexes, whereas no melting endotherm was observed in the soluble complexes. Acetylation substantially increased the amount of complexed linoleic acid in the insoluble complexes, but had little positive effect on the formation of the soluble complexes. The β-amylase treatment significantly increased the complexed linoleic content in both soluble and insoluble complexes for the low acetylated starch, but not for the high acetylated starch.

  3. Hybrid NS ligands supported Cu(I)/(II) complexes for azide-alkyne cycloaddition reactions.

    PubMed

    Bai, Shi-Qiang; Jiang, Lu; Zuo, Jing-Lin; Hor, T S Andy

    2013-08-21

    Three copper complexes of nitrogen-sulfur donor ligands, [CuBr₂(L1)] (1), [CuCl₂(L2)₂] (2) and [Cu₂I₂(L3)]n (3) (L1 = bis(2-cyclohexylsulfanylethyl)amine, L2 = 2-(benzylsulfanylmethyl)pyridine and L3 = 2-(4-pyridylsulfanylmethyl)pyridine), have been synthesized and characterized by single-crystal X-ray diffraction (XRD), powder XRD and TGA analysis. Complexes 1 and 2 are mononuclear Cu(II) complexes and are EPR active with distorted square-pyramidal and octahedral geometry, respectively. Complex 3 is a two-dimensional tetrahedral Cu(I) coordination polymer with 16- and 20-membered metallocycles. These complexes show good catalytic activities for one-pot azide-alkyne cycloaddition reactions in CH₃OH-H₂O.

  4. Formation, dynamic behavior, and chemical transformation of Pt complexes with a rotaxane-like structure.

    PubMed

    Suzaki, Yuji; Osakada, Kohtaro

    2006-09-18

    The reaction of [Pt(CH2COMe)(Ph)(cod)] (cod = 1,5-cyclooctadiene) with (ArCH2NH2CH2-C6H4COOH)+ (PF6)- (Ar = 4-tBuC6H4 or 9-anthryl) in the presence of cyclic oligoethers such as dibenzo[24]crown-8 (DB24C8) and dicyclohexano[24]crown-8 (DC24C8) produces {(ce)[ArCH2NH2CH2C6H4COOPt(Ph)(cod)]}+ (PF6)- (ce = DB24C8 or DC24C8, Ar = 4-tBuC6H4 or 9-anthryl) with interlocked structures. FABMS and NMR spectra of a solution of these compounds indicate that the Pt complexes with a secondary ammonium group and DB24C8 (or DC24C8) make up the axis and cyclic components, respectively. Temperature-dependent 1H NMR spectra of a solution of {(DB24C8)[4-tBuC6H4CH2NH2CH2-C6H4COOPt(Ph)(cod)]}+ (PF6)- ({(DB24C8)[4-H]}+ (PF6)-) show equilibration with free DB24C8 and the axis component. The addition of DB24C8 to a solution of {(DC24C8)[4-H]}+ (PF6)- causes partial exchange of the macrocyclic component of the interlocked molecules, giving a mixture of {(DC24C8)[4-H]}+ (PF6)-, {(DB24C8)[4-H]}+ (PF6)-, and free macrocyclic compounds. The reaction of 3,5-Me2C6H3COCl with {(DB24C8)[4-H]}+ (PF6)- affords the organic rotaxane {(DB24C8)(4-tBuC6H4CH2NH2CH2-C6H4COOCOC6H3Me2-3,5)}+ (PF6)- through C-O bond formation between the aroyl group and the carboxylate ligand of the axis component. The addition of 2,2'-bipyridine (bpy) to a solution of {(DB24C8)[4-H]}+ (PF6)- induces the degradation of the interlocked structure to form a complex with trigonal bipyramidal coordination, [Pt(Ph)(bpy)(cod)]+ (PF6)-, whereas the reaction of bpy with [Pt(OCOC6H4Me-4)(Ph)(cod)] produces the square-planar complex [Pt(OCOC6H4Me-4)(Ph)(bpy)].

  5. Reactions Between Water Soluble Organic Acids and Nitrates in Atmospheric Aerosols: Recycling of Nitric Acid and Formation of Organic Salts

    SciTech Connect

    Wang, Bingbing; Laskin, Alexander

    2014-03-25

    Atmospheric particles often include a complex mixture of nitrate and secondary organic materials accumulated within the same individual particles. Nitrate as an important inorganic component can be chemically formed in the atmosphere. For instance, formation of sodium nitrate (NaNO3) and calcium nitrate Ca(NO3)2 when nitrogen oxide and nitric acid (HNO3) species react with sea salt and calcite, respectively. Organic acids contribute a significant fraction of photochemically formed secondary organics that can condense on the preexisting nitrate-containing particles. Here, we present a systematic microanalysis study on chemical composition of laboratory generated particles composed of water soluble organic acids and nitrates (i.e. NaNO3 and Ca(NO3)2) investigated using computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and Fourier transform infrared micro-spectroscopy (micro-FTIR). The results show that water-soluble organic acids can react with nitrates releasing gaseous HNO3 during dehydration process. These reactions are attributed to acid displacement of nitrate with weak organic acids driven by the evaporation of HNO3 into gas phase due to its relatively high volatility. The reactions result in significant nitrate depletion and formation of organic salts in mixed organic acids/nitrate particles that in turn may affect their physical and chemical properties relevant to atmospheric environment and climate. Airborne nitrate concentrations are estimated by thermodynamic calculations corresponding to various nitrate depletions in selected organic acids of atmospheric relevance. The results indicate a potential mechanism of HNO3 recycling, which may further affect concentrations of gas- and aerosol-phase species in the atmosphere and the heterogeneous reaction chemistry between them.

  6. The Effect of Complex Formation upon the Redox Potentials of Metallic Ions. Cyclic Voltammetry Experiments.

    ERIC Educational Resources Information Center

    Ibanez, Jorge G.; And Others

    1988-01-01

    Describes experiments in which students prepare in situ soluble complexes of metal ions with different ligands and observe and estimate the change in formal potential that the ion undergoes upon complexation. Discusses student formation and analysis of soluble complexes of two different metal ions with the same ligand. (CW)

  7. Radiative capture reaction for 17Ne formation within a full three-body model

    NASA Astrophysics Data System (ADS)

    Casal, J.; Garrido, E.; de Diego, R.; Arias, J. M.; Rodríguez-Gallardo, M.

    2016-11-01

    Background: The breakout from the hot Carbon-Nitrogen-Oxigen (CNO) cycles can trigger the rp-process in type I x-ray bursts. In this environment, a competition between 15O(α ,γ )19Ne and the two-proton capture reaction 15O(2 p ,γ )17Ne is expected. Purpose: Determine the three-body radiative capture reaction rate for 17Ne formation including sequential and direct, resonant and nonresonant contributions on an equal footing. Method: Two different discretization methods have been applied to generate 17Ne states in a full three-body model: the analytical transformed harmonic oscillator method and the hyperspherical adiabatic expansion method. The binary p -15O interaction has been adjusted to reproduce the known spectrum of the unbound 16F nucleus. The dominant E 1 contributions to the 15O(2 p ,γ )17Ne reaction rate have been calculated from the inverse photodissociation process. Results: Three-body calculations provide a reliable description of 17Ne states. The agreement with the available experimental data on 17Ne is discussed. It is shown that the 15O(2 p ,γ )17Ne reaction rates computed within the two methods agree in a broad range of temperatures. The present calculations are compared with a previous theoretical estimation of the reaction rate. Conclusions: It is found that the full three-body model provides a reaction rate several orders of magnitude larger than the only previous estimation. The implications for the rp-process in type I x-ray bursts should be investigated.

  8. Fission and quasifission modes in heavy-ion-induced reactions leading to the formation of Hs{sup *}

    SciTech Connect

    Itkis, I. M.; Kozulin, E. M.; Itkis, M. G.; Knyazheva, G. N.; Bogachev, A. A.; Chernysheva, E. V.; Krupa, L.; Oganessian, Yu. Ts.; Zagrebaev, V. I.; Rusanov, A. Ya.; Goennenwein, F.; Dorvaux, O.; Stuttge, L.; Hanappe, F.; Vardaci, E.; Goes Brennand, E. de

    2011-06-15

    Mass and energy distributions of binary reaction products obtained in the reactions {sup 22}Ne+{sup 249}Cf,{sup 26}Mg+{sup 248}Cm, {sup 36}S+{sup 238}U, and {sup 58}Fe+{sup 208}Pb have been measured. All reactions lead to Hs isotopes. At energies below the Coulomb barrier the bimodal fission of Hs{sup *}, formed in the reaction {sup 26}Mg+{sup 248}Cm, is observed. In the reaction {sup 36}S+{sup 238}U, leading to the formation of a similar compound nucleus, the main part of the symmetric fragments arises from the quasifission process. At energies above the Coulomb barrier fusion-fission is the main process leading to the formation of symmetric fragments for both reactions with Mg and S ions. In the case of the {sup 58}Fe+{sup 208}Pb reaction the quasifission process dominates at all measured energies.

  9. Asymmetric 1,3-Dipolar Cycloaddition Reactions Catalyzed by Heterocycle-Based Metal Complexes

    NASA Astrophysics Data System (ADS)

    Suga, Hiroyuki

    Highly enantioselective 1,3-dipolar cycloaddition reactions of several 1,3-dipoles, such as nitrones, nitrile oxides, nitrile imines, diazoalkanes, azomethine imines and carbonyl ylides, catalyzed by heterocyclic supramolecular type of metal complexes consisting of chiral heterocyclic compounds and metal salts were described in terms of their ability of asymmetric induction and enantioface differentiation. The scope and limitations of each cycloaddition reactions were also briefly described. Of the chiral hererocycle-based ligands, chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction. The combination of the bisoxazoline ligand derived from (1S,2R)-cis-1-amino-2-indanol and metal salts was especially efficient for asymmetric cycloaddition reactions of a number of 1,3-dipoles, such as nitrones, nitrile oxide, nitrile imines, diazoacetates and azomethine imines. The metals utilized for the heterocycle-based complexes show a crucial role for degree of asymmetric induction depending upon the 1,3-dipole used. High levels of enantioselectivity were achieved in 1,3-dipolar cycloaddition reactions of unstable carbonyl ylides with benzyloxyacetaldehyde derivatives, α-keto esters, 3-(2-alkenoyl)-2-oxazolidinones, and even vinyl ethers, which were catalyzed by Pybox-lanthanoid metal complexes.

  10. Spectrophotometric Determination of 6-Propyl-2-Thiouracil in Pharmaceutical Formulations Based on Prussian Blue Complex Formation: An Undergraduate Instrumental Analysis Laboratory Experiment

    ERIC Educational Resources Information Center

    Zakrzewski, Robert; Skowron, Monika; Ciesielski, Witold; Rembisz, Zaneta

    2016-01-01

    The laboratory experiment challenges students to determine 6-propyl-2-thiouracil (PTU) based on Prussian blue complex formation. Prussian blue is formed by ferricyanide and Fe(II) ions which are generated in situ from Fe(III) ions reduced by PTU. The absorbance of this product was measured at a wavelength of 840 nm, after a reaction time of 30…

  11. Formation of flavor components by the reaction of amino acid and carbonyl compounds in mild conditions.

    PubMed

    Pripis-Nicolau, L; de Revel, G; Bertrand, A; Maujean, A

    2000-09-01

    This work describe products of reactions between four alpha-dicarbonyl compounds (diacetyl, pentan-2,3-dione, glyoxal, and methylglyoxal) or two alpha-hydroxy ketones, (acetoine and acetol) and amino acids present in wines. The results shows the formation of odorous products or strong-smelling additives resulting from the Maillard and Strecker reaction in a primarily aqueous medium, at low temperature and low pH ( approximately pH 3.5) of the wine. GC/FID, GC/FPD, GC/NPD and GC/MS techniques were used. The olfactive characteristics of the products are described. In the presence of sulfur amino acids and in particular cysteine, many products were formed with a heterocycle production such as pyrazines and methylpyrazines, methylthiazoles, acetylthiazoles, acetylthiazolines, acetylthiazolidines, trimethyloxazole, and dimethylethyloxazoles. These various compounds present odors of sulfur, cornlike, pungent, nut, popcorn, roasted hazelnut, toasted, roasted, and ripe fruits. The chemical conditions of the model reactions are specified. The influence of temperature and pH on the reactions in the presence of cysteine were also studied.

  12. B-H bond activation using an electrophilic metal complex: insights into the reaction pathway.

    PubMed

    Kumar, Rahul; Jagirdar, Balaji R

    2013-01-07

    A highly electrophilic ruthenium center in the [RuCl(dppe)(2)][OTf] complex brings about the activation of the B-H bond in ammonia borane (H(3)N·BH(3), AB) and dimethylamine borane (Me(2)HN·BH(3), DMAB). At room temperature, the reaction between [RuCl(dppe)(2)][OTf] and AB or DMAB results in trans-[RuH(η(2)-H(2))(dppe)(2)][OTf], trans-[RuCl(η(2)-H(2))(dppe)(2)][OTf], and trans-[RuH(Cl)(dppe)(2)], as noted in the NMR spectra. Mixing the ruthenium complex and AB or DMAB at low temperature (198/193 K) followed by NMR spectral measurements as the reaction mixture was warmed up to room temperature allowed the observation of various species formed enroute to the final products that were obtained at room temperature. On the basis of the variable-temperature multinuclear NMR spectroscopic studies of these two reactions, the mechanistic insights for B-H bond activation were obtained. In both cases, the reaction proceeds via an η(1)-B-H moiety bound to the metal center. The detailed mechanistic pathways of these two reactions as studied by NMR spectroscopy are described.

  13. Synthesis of complex pyridine bases in the reaction of. cap alpha. ,omega-nitrileacetylenes with acetylene, catalyzed by cobalt complexes

    SciTech Connect

    Dzhemilev, U.M.; Selimov, F.A.; Khafizov, V.R.

    1987-01-20

    It has been shown that ..cap alpha..,omega-nitrileacetylenes under the action of homogeneous cobalt-containing catalysts undergo transformations into pyridine derivatives. In order to expand the scope of this method for synthesis of complex pyridine bases, for investigation of the reactivity of nitrileacetylenes of various structure in the reaction of cooligomerization with acetylene, as well as for the introduction to these reactions of new types of ..cap alpha..,omega-nitrileacetylenes, containing in their molecules an oxygen atom, they studied the homo- and codimerization of ..cap alpha..,omega-nitrileacetylenes with acetylene under the action of a Co(2-ethyl hexanoate)/sub 2/-AIR/sub 3/ catalyst in a toluene solution. Cyclodimerization of acetylene with ..cap alpha..,omega-nitrileacetylenes, catalyzed by a Co(2-ethyl hexanoate)/sub 2/-AlEt/sub 3/ system gives new types of mono- and bicyclic pyridines.

  14. Dichotomous-noise-induced pattern formation in a reaction-diffusion system

    NASA Astrophysics Data System (ADS)

    Das, Debojyoti; Ray, Deb Shankar

    2013-06-01

    We consider a generic reaction-diffusion system in which one of the parameters is subjected to dichotomous noise by controlling the flow of one of the reacting species in a continuous-flow-stirred-tank reactor (CSTR) -membrane reactor. The linear stability analysis in an extended phase space is carried out by invoking Furutzu-Novikov procedure for exponentially correlated multiplicative noise to derive the instability condition in the plane of the noise parameters (correlation time and strength of the noise). We demonstrate that depending on the correlation time an optimal strength of noise governs the self-organization. Our theoretical analysis is corroborated by numerical simulations on pattern formation in a chlorine-dioxide-iodine-malonic acid reaction-diffusion system.

  15. Chemo-Marangoni convection driven by an interfacial reaction: pattern formation and kinetics.

    PubMed

    Eckert, K; Acker, M; Tadmouri, R; Pimienta, V

    2012-09-01

    A combined study devoted to chemo-Marangoni convection and the underlying kinetics is presented for a biphasic system in which surfactants are produced in situ by an interfacial reaction. The pattern formation studied in a Hele-Shaw cell in both microgravity and terrestrial environments initially shows an ensemble of chemo-Marangoni cells along a nearly planar interface. Soon, a crossover occurs to periodic large-scale interfacial deformations which coexist with the Marangoni cells. This crossover can be correlated with the autocatalytic nature of the interfacial reaction identified in the kinetic studies. The drastic increase in the product concentration is associated with an enhanced aggregate-assisted transfer after the critical micellar concentration is approached. In this context, it was possible to conclusively explain the changes in the periodicity of the interfacial deformations depending on the reactant concentration ratio.

  16. Redirection of the Reaction Specificity of a Thermophilic Acetolactate Synthase toward Acetaldehyde Formation

    PubMed Central

    Cheng, Maria; Yoshiyasu, Hayato; Okano, Kenji; Ohtake, Hisao; Honda, Kohsuke

    2016-01-01

    Acetolactate synthase and pyruvate decarboxylase are thiamine pyrophosphate-dependent enzymes that convert pyruvate into acetolactate and acetaldehyde, respectively. Although the former are encoded in the genomes of many thermophiles and hyperthermophiles, the latter has been found only in mesophilic organisms. In this study, the reaction specificity of acetolactate synthase from Thermus thermophilus was redirected to catalyze acetaldehyde formation to develop a thermophilic pyruvate decarboxylase. Error-prone PCR and mutant library screening led to the identification of a quadruple mutant with 3.1-fold higher acetaldehyde-forming activity than the wild-type. Site-directed mutagenesis experiments revealed that the increased activity of the mutant was due to H474R amino acid substitution, which likely generated two new hydrogen bonds near the thiamine pyrophosphate-binding site. These hydrogen bonds might result in the better accessibility of H+ to the substrate-cofactor-enzyme intermediate and a shift in the reaction specificity of the enzyme. PMID:26731734

  17. Redirection of the Reaction Specificity of a Thermophilic Acetolactate Synthase toward Acetaldehyde Formation.

    PubMed

    Cheng, Maria; Yoshiyasu, Hayato; Okano, Kenji; Ohtake, Hisao; Honda, Kohsuke

    2016-01-01

    Acetolactate synthase and pyruvate decarboxylase are thiamine pyrophosphate-dependent enzymes that convert pyruvate into acetolactate and acetaldehyde, respectively. Although the former are encoded in the genomes of many thermophiles and hyperthermophiles, the latter has been found only in mesophilic organisms. In this study, the reaction specificity of acetolactate synthase from Thermus thermophilus was redirected to catalyze acetaldehyde formation to develop a thermophilic pyruvate decarboxylase. Error-prone PCR and mutant library screening led to the identification of a quadruple mutant with 3.1-fold higher acetaldehyde-forming activity than the wild-type. Site-directed mutagenesis experiments revealed that the increased activity of the mutant was due to H474R amino acid substitution, which likely generated two new hydrogen bonds near the thiamine pyrophosphate-binding site. These hydrogen bonds might result in the better accessibility of H+ to the substrate-cofactor-enzyme intermediate and a shift in the reaction specificity of the enzyme.

  18. The Formation and Thermochemical Properties of Multiligand Complexes

    DTIC Science & Technology

    1987-08-25

    complexes, binary solvent systems, mass spectrometry, chemi- , .. luminescence, thermochemistry , kinetics V BSTRACT (Continue on reverse if necessary and...Involving Sulfides and Phosphonates ...... I Thermochemistry of Multiligand Cluster Ions*..................... 6 II. BIBLIOGRAPHY...and to explore relationships with the thermochemistry of binary soutions in the condensed phase. The results of this research have formed the basis

  19. Ligand substitution reactions of a phenolic quinolyl hydrazone; oxidovanadium (IV) complexes

    PubMed Central

    2011-01-01

    Background Quinoline ring has therapeutic and biological activities. Quinolyl hydrazones constitute a class of excellent chelating agents. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have aimed to study the competency effect of a phenolic quinolyl hydrazone (H2L; primary ligand) with some auxiliary ligands (Tmen, Phen or Oxine; secondary ligands) towards oxidovanadium (IV) ions. Results Mono- and binuclear oxidovanadium (IV) - complexes were obtained from the reaction of a phenolic quinolyl hydrazone with oxidovanadium (IV)- ion in absence and presence of N,N,N',N'- tetramethylethylenediamine (Tmen), 1,10-phenanthroline (Phen) or 8-hydroxyquinoline (Oxine). The phenolic quinolyl hydrazone ligand behaves as monobasic bidentate (NO- donor with O- bridging). All the obtained complexes have the preferable octahedral geometry except the oxinato complex (2) which has a square pyramid geometry with no axial interaction; the only homoleptic complex in this study. Conclusion The ligand exchange (substitution/replacement) reactions reflect the strong competency power of the auxiliary aromatic ligands (Phen/Oxine) compared to the phenolic quinolyl hydrazone (H2L) towards oxidovanadium (IV) ion; (complexes 2 and 3). By contrast, in case of the more flexible aliphatic competitor (Tmen), an adduct was obtained (4). The obtained complexes reflect the strength of the ligand field towards the oxidovanadium (IV)- ion; Oxine or Phen >> phenolic hydrazone (H2L) > Tmen. PMID:21846387

  20. Structural analysis of the homodimeric reaction center complex from the photosynthetic green sulfur bacterium Chlorobaculum tepidum.

    PubMed

    He, Guannan; Zhang, Hao; King, Jeremy D; Blankenship, Robert E

    2014-08-05

    The reaction center (RC) complex of the green sulfur bacterium Chlorobaculum tepidum is composed of the Fenna-Matthews-Olson antenna protein (FMO) and the reaction center core (RCC) complex. The RCC complex has four subunits: PscA, PscB, PscC, and PscD. We studied the FMO/RCC complex by chemically cross-linking the purified sample followed by biochemical and spectroscopic analysis. Blue-native gels showed that there were two types of FMO/RCC complexes, which are consistent with complexes with one copy of FMO per RCC and two copies of FMO per RCC. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the samples after cross-linking showed that all five subunits of the RC can be linked by three different cross-linkers: bissulfosuccinimidyl suberate, disuccinimidyl suberate, and 3,3-dithiobis-sulfosuccinimidyl propionate. The interaction sites of the cross-linked complex were also studied using liquid chromatography coupled to tandem mass spectrometry. The results indicated that FMO, PscB, PscD, and part of PscA are exposed on the cytoplasmic side of the membrane. PscD helps stabilize FMO to the reaction center and may facilitate transfer of the electron from the RC to ferredoxin. The soluble domain of the heme-containing cytochrome subunit PscC and part of the core subunit PscA are located on the periplasmic side of the membrane. There is a close relationship between the periplasmic portions of PscA and PscC, which is needed for the efficient transfer of the electron between PscC and P840.

  1. Dynamics of Research Team Formation in Complex Networks

    NASA Astrophysics Data System (ADS)

    Sun, Caihong; Wan, Yuzi; Chen, Yu

    Most organizations encourage the formation of teams to accomplish complicated tasks, and vice verse, effective teams could bring lots benefits and profits for organizations. Network structure plays an important role in forming teams. In this paper, we specifically study the dynamics of team formation in large research communities in which knowledge of individuals plays an important role on team performance and individual utility. An agent-based model is proposed, in which heterogeneous agents from research communities are described and empirically tested. Each agent has a knowledge endowment and a preference for both income and leisure. Agents provide a variable input (‘effort’) and their knowledge endowments to production. They could learn from others in their team and those who are not in their team but have private connections in community to adjust their own knowledge endowment. They are allowed to join other teams or work alone when it is welfare maximizing to do so. Various simulation experiments are conducted to examine the impacts of network topology, knowledge diffusion among community network, and team output sharing mechanisms on the dynamics of team formation.

  2. Assessment of the potential for ammonium nitrate formation and reaction in Tank 241-SY-101

    SciTech Connect

    Pederson, L.R.; Bryan, S.A.

    1994-08-01

    Two principal scenarios by which ammonium nitrate may be formed were considered: (a) precipitation of ammonium nitrate in the waste, and (b) ammonium nitrate formation via the gas phase reaction of ammonia and nitrogen dioxide. The first of these can be dismissed because ammonium ions, which are necessary for ammonium nitrate precipitation, can exist only in negligibly small concentrations in strongly alkaline solutions. Gas phase reactions between ammonia, nitrogen dioxide, and water vapor in the gas phase represent the most likely means by which ammonium nitrate aerosols could be formed in Tank 241-SY-101. Predicted ammonium nitrate formation rates are largely controlled by the concentration of nitrogen dioxide. This gas has not been detected among those gases vented from the wastes using Fourier Transform Infrared Spectrometry (FTIR) or mass spectrometry. While detection limits for nitrogen dioxide have not been established experimentally, the maximum concentration of nitrogen dioxide in the gas phase in Tank 241-SY-101 was estimated at 0.1 ppm based on calculations using the HITRAN data base and on FTIR spectra of gases vented from the wastes. At 50 C and with 100 ppm ammonia also present, less than one gram of ammonium nitrate per year is estimated to be formed in the tank. To date, ammonium nitrate has not been detected on HEPA filters in the ventilation system, so any quantity that has been formed in the tank must be quite small, in good agreement with rate calculations. The potential for runaway exothermic reactions involving ammonium nitrate in Tank 241-SY-101 is minimal. Dilution by non-reacting waste components, particularly water, would prevent hazardous exothermic reactions from occurring within the waste slurry, even if ammonium nitrate were present. 41 refs.

  3. Characterization of self-propagating formation reactions in Ni/Zr multilayered foils using reaction heats, velocities, and temperature-time profiles

    DOE PAGES

    Barron, S. C.; Knepper, R.; Walker, N.; ...

    2011-01-11

    We report on intermetallic formation reactions in vapor-deposited multilayered foils of Ni/Zr with 70 nm bilayers and overall atomic ratios of Ni:Zr, 2 Ni:Zr, and 7 Ni:2 Zr. The sequence of alloy phase formation and the stored energy is evaluated at slow heating rates (~1 K/s) using differential scanning calorimetry (DSC) traces to 725ºC. All three chemistries initially form a Ni-Zr amorphous phase which crystallizes first to the intermetallic NiZr. The heat of reaction to the final phase is 34-36 kJ/mol atom for all chemistries. Intermetallic formation reactions are also studied at rapid heating rates (greater than 105 K/s) inmore » high temperature, self-propagating reactions which can be ignited in these foils by an electric spark. We find that reaction velocities and maximum reaction temperatures (Tmax) are largely independent of foil chemistry at 0.6 ± 0.1 m/s and 1220 ± 50 K, respectively, and that the measured Tmax is more than 200 K lower than predicted adiabatic temperatures (Tad). The difference between Tmax and Tad is explained by the prediction that transformation to the final intermetallic phases occurs after Tmax and results in the release of 20-30 % of the total heat of reaction and a delay in rapid cooling.« less

  4. Spectrophotometric sequential injection determination of D-penicillamine based on a complexation reaction with nickel ion.

    PubMed

    Martinović-Bevanda, Anita; Radić, Njegomir

    2013-01-01

    A simple and sensitive spectrophotometric method, based on reaction between Ni(II) ion and D-penicillamine (PEN), was developed. The proposed SIA system enhanced the analytical applicability of the reaction of complexation, and allowed the determination of PEN in the concentration range of 3.0 × 10(-6) - 2.0 × 10(-4) mol L(-1) with a sampling rate of 200 h(-1). With the proposed SIA system, PEN could be accurately determinated up to 0.9 nmol quantity. The method was successfully applied to the determination of PEN in laboratory samples and pharmaceuticals.

  5. Kinetics and activation thermodynamics of methane monooxygenase compound Q formation and reaction with substrates.

    PubMed

    Brazeau, B J; Lipscomb, J D

    2000-11-07

    The transient kinetics of formation and decay of the reaction cycle intermediates of the Methylosinus trichosporium OB3b methane monooxygenase (MMO) catalytic cycle are studied as a function of temperature and substrate type and deuteration. Kinetic evidence is presented for the existence of three intermediates termed compounds O, P, and P forming after the addition of O(2) to diferrous MMO hydroxylase (H(r)) and before the formation of the reactive intermediate compound Q. The Arrhenius plots for these reactions are linear and independent of substrate concentration and type, showing that substrate does not participate directly in the oxygen activation phase of the catalytic cycle. Analysis of the transient kinetic data revealed only small changes relative to the weak optical spectrum of H(r) for any of these intermediates. In contrast, large changes in the 430 nm spectral region are associated with the formation of Q. The decay reaction of Q exhibits an apparent first-order concentration dependence for all substrates tested, and the observed rate constant depends on the substrate type. The kinetics of the decay reaction of Q yield a nonlinear Arrhenius plot when methane is the substrate, and the rates in both segments of the plot increase linearly with methane concentration. Together these observations suggest that at least two reactions with a methane concentration dependence, and perhaps two methane molecules, are involved in the decay process. When CD(4) is used as the substrate, a large isotope effect and a linear Arrhenius plot are observed. Analogous plots for all other MMO substrates tested (e.g., ethane) are linear, and no isotope effect for deuterated analogues is observed. This demonstrates that a step other than C-H bond breaking is rate limiting for alternative MMO substrates. A two step Q decay mechanism is proposed that provides an explanation for the lack of an isotope effect for alternative MMO substrates and the fact that rate of oxidation of

  6. In vitro surface reaction layer formation and dissolution of calcium phosphate cement-bioactive glass composites.

    PubMed

    Liu, Changsheng; Chen, Chien-Wen; Ducheyne, Paul

    2008-09-01

    Composites of hydrated calcium phosphate cement (CPC) and bioactive glass (BG) containing Si were immersed in vitro to study the effect of chemical composition on surface reaction layer formation and dissolution/precipitation behavior. The solutions used were 0.05 M tris hydroxymethyl aminomethane/HCl (tris buffer), tris buffer supplemented with plasma electrolyte (TE) with pH 7.4 at 37 degrees C, and this solution complemented with 10% newborn bovine serum (TES). The post-immersion solutions were analyzed for changes in Ca, PO(4) and Si concentrations. The reacted surfaces were analyzed using Fourier transform infrared (FTIR), and scanning electron microscopy with energy dispersive x-ray analysis. The sample weight variations after immersion were also determined. The results showed that the composition of the bioactive composite CPCs greatly affected their behavior in solution and the formation of apatite bioactive surface reaction layers. After immersion in the TE solution, Ca ions were taken up by all samples during the entire immersion duration. Initially, the P ion concentration increased sharply, and then decreased. This reaction pattern reveals the formation of an amorphous calcium phosphate layer on the surface of these composite CPCs. FTIR revealed that the layer was, in fact, poorly crystallized Ca-deficient carbonate apatite. The thickness of the layer was 12-14 microm and it was composed of rod-like apatite with directional arrangement. For immersion in the TES solution, the Ca and Si ion concentrations showed a similar behavior to that in TE, but the release rate of Si ions was higher. FTIR revealed that after TES immersion, not only did the typical, poorly crystallized, Ca-deficient carbonated apatite form, as it did in TE, but also the serum proteins co-adsorbed on the surface and thereby affected the surface reaction layer formation. A thinner apatite layer was formed and was composed of a micro-porous layer comprising rounded particles in a glue

  7. Oligomer Formation Reactions of Criegee Intermediates in the Ozonolysis of Small Unsaturated Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Sakamoto, Y.; Inomata, S.; Hirokawa, J.

    2013-12-01

    Secondary organic aerosol (SOA) constitutes a substantial fraction of atmospheric fine particulate matters and has an effect on visibility, climate and human health. One of the major oxidizing processes leading to SOA formation is an ozonolysis of unsaturated hydrocarbons (UHCs).[1] Despite of its importance, the contribution of the ozonolysis of UHCs to the SOA formation in the troposphere is not sufficiently understood due to a lack of information on reaction pathways to produce low volatile compounds. While many studies have previously been focused on SOA formation from the ozonolysis of large UHCs, SOA formation from the ozonolysis of UHCs with less than six carbon atoms have been rarely investigated because their products are expected to be too volatile to contribute to the SOA formation. Very recently, a few studies have reported the SOA formation from the ozonolysis of such small UHCs but chemical mechanisms are still unclear. [2-4] In order to understand SOA formation from the ozonolysis of the small UHCs, this study investigated gas- and particle-phase products in laboratory experiments with a Teflon bag using a negative ion chemical ionization mass spectrometry (NI-CIMS) with chloride ion transfer for chemical ionization. This technique is suitable for analysis of compounds such as carboxylic acids and hydroperoxides expected to be produced in the ozonolysis of UHCs with less fragmentation, high selectivity, and high sensitivity. In the particle-phase analysis, SOAs collected on a PTFE filter were heated, and thermally desorbed compounds were analyzed. In the gas-phase analysis, series of peaks with an interval of a mass-to-charge ratio equal to the molecular weight of a Criegee intermediate formed in their ozonolysis were observed. These peaks were attributed to oligomeric hydroperoxides composed of Criegee intermediates as a chain unit. These oligomeric hydroperoxides were also observed in the particle-phase analysis, indicating that the oligomeric

  8. Search for reaction conditions and catalyst for selective prebiotic formation of Aldopentoses from Glycolaldehyde and Formaldehyde

    NASA Astrophysics Data System (ADS)

    Delidovich, Irina; Taran, Oxana; Parmon, Valentin; Gromov, Nikolay

    2012-07-01

    Formation of organic compounds from simple precursors appears to have been one of the first steps from geochemistry towards modern biochemistry. The Earth lagoons, hydrothermal springs, cosmic dust, meteorites, protoplanetary disk, etc. has been considered as the possible ``reactors'' in which the prebiotic synthesis could have taken place. The finding of reactions and reaction conditions which allow to produce the high yields of the biologically relevant substances from simple compounds could help us to verify different hypothesis of plausible prebotic conditions. In this work we have studied the formation of vitally important sugars, namely aldopentoses (ribose, xylose, lyxose and arabinose), from glycolaldehyde and formaldehyde over catalysts. Aldopentoses nowadays play the important roles as the components of polysaccharides, glycosides, nucleic acids and ATP. Glycolaldehyde is the simplest monosaccharide, which was found in the interstellar space [1], where it could be generated as a result of several processes, for instance, condensation of formaldehyde under UV-radiation [2]. In this work the peculiarities of interaction between glycolaldehyde and formaldehyde in the presence of soluble (phosphate and borate buffers) and solid (minerals apatite and montmorillonites) catalysts were studied. The dependences of composition of the reaction products on the catalyst nature, molar ratio of substrates, pH value of reaction mixture were revealed. The yields of aldopentoses amount to ca. 60-65% in the presence of borate catalyst under optimized reaction conditions. Borate acts not only as a catalyst, but also as the stabilizer of active intermediates and aldopentoses from side reactions [3]. Borates are present in some mineral and clays (serpentine, montmorillonite etc.) and in water of Cityhot springs (Geyser valley, placeKamchatka) in rather high concentrations. Therefore catalysis by borates could be considered as plausible prebotic condition. Acknowledgements. We

  9. Reactivity of Ir(III) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation.

    PubMed

    Elliott, Paul I P; Haak, Susanne; Meijer, Anthony J H M; Sunley, Glenn J; Haynes, Anthony

    2013-12-21

    The reactions of water with a number of iridium(III) complexes relevant to the mechanism for catalytic methanol carbonylation are reported. The iridium acetyl, [Ir(CO)2I3(COMe)](-), reacts with water under mild conditions to release CO2 and CH4, rather than the expected acetic acid. Isotopic labeling and kinetic experiments are consistent with a mechanism involving nucleophilic attack by water on a terminal CO ligand of [Ir(CO)2I3(COMe)](-) to give an (undetected) hydroxycarbonyl species. Subsequent decarboxylation and elimination of methane gives [Ir(CO)2I2](-). Similar reactions with water are observed for [Ir(CO)2I3Me](-), [Ir(CO)2(NCMe)I2(COMe)] and [Ir(CO)3I2Me] with the neutral complexes exhibiting markedly higher rates. The results demonstrate that CO2 formation during methanol carbonylation is not restricted to the conventional water gas shift mechanism mediated by [Ir(CO)2I4](-) or [Ir(CO)3I3], but can arise directly from key organo-iridium(III) intermediates in the carbonylation cycle. An alternative pathway for methane formation not involving the intermediacy of H2 is also suggested. A mechanism is proposed for the conversion MeOH + CO → CO2 + CH4, which may account for the similar rates of formation of the two gaseous by-products during iridium-catalysed methanol carbonylation.

  10. Evaluation of Multi-tRNA Synthetase Complex by Multiple Reaction Monitoring Mass Spectrometry Coupled with Size Exclusion Chromatography

    PubMed Central

    Kim, Jun Seok; Lee, Cheolju

    2015-01-01

    Eight aminoacyl-tRNA synthetases (M, K, Q, D, R, I, EP and LARS) and three auxiliary proteins (AIMP1, 2 and 3) are known to form a multi-tRNA synthetase complex (MSC) in mammalian cells. We combined size exclusion chromatography (SEC) with reversed-phase liquid chromatography multiple reaction monitoring mass spectrometry (RPLC-MRM-MS) to characterize MSC components and free ARS proteins in human embryonic kidney (HEK 293T) cells. Crude cell extract and affinity-purified proteins were fractionated by SEC in non-denaturing state and ARSs were monitored in each fraction by MRM-MS. The eleven MSC components appeared mostly in earlier SEC fractions demonstrating their participation in complex formation. TARSL2 and AIMP2-DX2, despite their low abundance, were co-purified with KARS and detected in the SEC fractions, where MSC appeared. Moreover, other large complex-forming ARS proteins, such as VARS and FARS, were detected in earlier fractions. The MRM-MS results were further confirmed by western blot analysis. Our study demonstrates usefulness of combined SEC-MRM analysis for the characterization of protein complexes and in understanding the behavior of minor isoforms or variant proteins. PMID:26544075

  11. Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

    PubMed Central

    Apps, Michael G.; Johnson, Ben W.; Sutcliffe, Oliver B.; Brown, Sarah D.; Wheate, Nial J.

    2014-01-01

    Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand. PMID:24893964

  12. [Studies by means of 1H NMR spectroscopy of complex formation of aromatic biologically active compounds with antibiotic topotecan].

    PubMed

    Mosunov, A A; Kostiukov, V V; Evstigneev, M P

    2012-01-01

    The analysis of heteroassociation of antibiotic topotecan (TPT) with aromatic biologically active compounds (BAC): caffeine, mutagens ethidium bromide and proflavine, antibiotic daunomycin, vitamins flavin-mononucleotide and nicotinamide, has been carried out in the work using 1H NMR spectroscopy data. The equilibrium constants of heteroassociation and induced chemical shifts of the protons have been obtained in the complexes with BAC. It is found that the complex formation TPT-BAC has the nature of stacking of the chromophores, additionally stabilized in the case of proflavine by intermolecular hydrogen bond. Calculation of the basic components of the Gibbs free energy of the complexation reactions is carried out, and the factors which stabilize and destabilize the heterocomplexes of molecules are revealed.

  13. Secondary Reaction Zone Formations in coated Ni-base Single Crystal Superalloys

    NASA Astrophysics Data System (ADS)

    Suzuki, A.; Rae, C. M. F.

    2009-05-01

    Ruthenium (Ru) has been added to the latest 4th Generation Ni-base superalloys to improve phase stability and modify creep life. Various coatings are routinely applied to these advanced alloys to protect the turbine blade at elevated temperature, however, this creates several problems such as the precipitation of brittle Topologically Close-Packed (TCP) phases and the formation of Secondary Reaction Zones (SRZ). The SRZ forms under the plat-aluminized coating of turbine blades and consists of γ, γ and TCP phases growing into substrate by the migration of high-angle grain boundaries. Surface residual stress and chemical super-saturation of alloying elements are associated to SRZ formation. In the thin sections of high-pressure turbine blades this is critical in determining blade performance and longevity. It is essential to know how Ru additions affect coating and SRZ morphologies during exposure. In this study, we focus on the effects of three variables on the SRZ formation: Ru concentration, alloy composition in Ru-containing alloys and surface finish. A series of Platinum-Aluminised superalloys containing 2-5wt% Ru and having various surface finishes was studied after isothermal exposure at 1100°C for up to 500h. The alloys were classified into two groups by their distinctive SRZ morphology. At the lowest Ru levels sporadic formation of SRZ was observed, whilst a continuous SRZ was formed in the higher Ru alloys. EBSD analysis revealed that the latter group have a higher nucleation rate of individual SRZ grains and also showed more rapid SRZ growth. The precipitation of TCPs in the substrate also inhibited the growth of the SRZ towards the end of the exposure further reducing the penetration of the SRZ into the substrate. It is concluded that Ru-additions to Ni-base superalloys are effective in impeding TCP phase formation in the substrate, but increase both the extent and the rate of SRZ formation beneath coating.

  14. Elementary steps in the reaction of the pyruvate dehydrogenase complex from pig heart. Kinetics of thiamine diphosphate binding to the complex.

    PubMed

    Sümegi, B; Alkonyi, I

    1983-11-02

    In the progress curve of the reaction of the pyruvate dehydrogenase complex, a lag phase was observed when the concentration of thiamin diphosphate was lower than usual (about 0.2-1 mM) in the enzyme assay. The length of the lag phase was dependent on thiamin diphosphate concentration, ranging from 0.2 min to 2 min as the thiamin diphosphate concentration varied from 800 nM to 22 nM. The lag phase was also observed in the elementary steps catalyzed by the pyruvate dehydrogenase component. A Km value of 107 nM was found for thiamin diphosphate with respect to the steady-state reaction rate following the lag phase. The pre-steady-state kinetic data indicate that the resulting lag phase was the consequence of a slow holoenzyme formation from apoenzyme and thiamin diphosphate. The thiamin diphosphate can bind to the pyruvate dehydrogenase complex in the absence of pyruvate, but the presence of 2 mM pyruvate increases the rate constant of binding from 1.4 X 10(4) M-1 S-1 to 1.3 X 10(5) M-1 S-1 and decreases the rate constant of dissociation from 2.3 X 10(-2) S-1 to 4.1 X 10(-3) S-1. On the other hand, the effect of pyruvate on the thiamin diphosphate binding revealed the existence of a thiamin-diphosphate-independent pyruvate-binding site in the pyruvate dehydrogenase complex. Direct evidence was also obtained with fluorescence techniques for the existence of this binding site and the dissociation constant of pyruvate was found to be 0.38 mM. On the basis of these data we have proposed a random mechanism for the binding of pyruvate and thiamin diphosphate to the complex. Binding of substrates to the enzyme complex caused an increase in the fluorescence of the dansylaziridine-labelled pyruvate dehydrogenase complex, showing that binding of substrates to the complex is accompanied by structural changes.

  15. Complexation facilitated reduction of aromatic N-oxides by aqueous Fe(II)-tiron complex: reaction kinetics and mechanisms.

    PubMed

    Chen, Yiling; Zhang, Huichun

    2013-10-01

    Rapid reduction of carbadox (CDX), olaquindox and several other aromatic N-oxides were investigated in aqueous solution containing Fe(II) and tiron. Consistent with previous work, the 1:2 Fe(II)-tiron complex, FeL2(6-), is the dominant reactive species as its concentration linearly correlates with the observed rate constant kobs under various conditions. The N-oxides without any side chains were much less reactive, suggesting direct reduction of the N-oxides is slow. UV-vis spectra suggest FeL2(6-) likely forms 5- or 7-membered rings with CDX and olaquindox through the N and O atoms on the side chain. The formed inner-sphere complexes significantly facilitated electron transfer from FeL2(6-) to the N-oxides. Reduction products of the N-oxides were identified by HPLC/QToF-MS to be the deoxygenated analogs. QSAR analysis indicated neither the first electron transfer nor N-O bond cleavage is the rate-limiting step. Calculations of the atomic spin densities of the anionic N-oxides confirmed the extensive delocalization between the aromatic ring and the side chain, suggesting complex formation can significantly affect the reduction kinetics. Our results suggest the complexation facilitated N-oxide reduction by Fe(II)-tiron involves a free radical mechanism, and the subsequent deoxygenation might also benefit from the weak complexation of Fe(II) with the N-oxide O atom.

  16. FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS AND THEIR GROWTH TO SOOT -A REVIEW OF CHEMICAL REACTION PATHWAYS. (R824970)

    EPA Science Inventory

    The generation by combustion processes of airborne species of current health concern such as polycyclic aromatic hydrocarbons (PAH) and soot particles necessitates a detailed understanding of chemical reaction pathways responsible for their formation. The present review discus...

  17. Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

    2013-03-15

    Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on the temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.

  18. Peculiarities in the formation of complex organic compounds in a nitrogen-methane atmosphere during hypervelocity impacts

    NASA Astrophysics Data System (ADS)

    Zaitsev, M. A.; Gerasimov, M. V.; Safonova, E. N.; Vasiljeva, A. S.

    2016-03-01

    Results of the experiments on model impact vaporization of peridotite, a mineral analogue of stony asteroids, in a nitrogen-methane atmosphere are presented. Nd-glass laser (γ = 1.06 µm) was used for simulation. Pulse energy was ~600-700 J, pulse duration ~10-3 s, vaporization tempereature ~4000-5000 K. The gaseous medium (96% vol. of N2 and 4% vol. of CH4, P = 1 atm) was a possible analogue of early atmospheres of terrestrial planets and corresponded to the present-day atmosphere composition of Titan, a satellite of Saturn. By means of pyrolytic gas chromatography/mass spectrometry, it is shown that solid condensates obtained in laser experiments contain relatively complex lowand high-molecular weight (kerogen-like) organic compounds. The main products of condensate pyrolysis were benzene and alkyl benzenes (including long-chain ones), unbranched aliphatic hydrocarbons, and various nitrogen-containing compounds (aliphatic and aromatic nitriles and pyrrol). It is shown that the nitrogen-methane atmosphere favors the formation of complex organic compounds upon hypervelocity impacts with the participation of stony bodies even with a small methane content in it. In this process, falling bodies may not contain carbon, hydrogen, and other chemical elements necessary for the formation of the organic matter. In such conditions, a noticeable contribution to the impact-induced synthesis of complex organic substances is probably made by heterogeneous catalytic reactions, in particular, Fischer-Tropsch type reactions.

  19. Chemical complexity and star-formation in merging galaxies

    NASA Astrophysics Data System (ADS)

    Davis, T. A.; Heiderman, A.; Iono, D.; VIXENS Team

    2013-03-01

    When galaxies merge the resulting conditions are some of the most extreme found anywhere in nature. Large gas flows, shocks and active black holes all can affect the ISM. Nearby merging galaxies with strong starbursts are the only places where we can conduct detailed study of star formation in conditions that mimic those under which the majority of stars in the universe formed. Here we study molecular gas tracers in 8 galaxies selected from the VIRUS-P Investigation of the eXtreme ENvironments of Starbursts (VIXENS) survey. Each galaxy has also been observed using the integral field unit spectrograph VIRUS-P, allowing us to investigate the relation between the chemical state of the gas, star formation and total gas content. Full details can be found in Heiderman et al. (2011). Here we report on new results obtained from IRAM-30m/NRO-45m 3mm line surveys towards 14 positions in these 8 merging galaxies. We detect ≈ 25 different molecular transitions towards these objects, many which have never been observed in these galaxies before. Our measurements show that the mean fraction of dense gas increases in later-stage mergers (Fig. 1, left), as does the average optical depth of the gas. Molecular diagnostic diagrams (Fig. 1, right) show that molecular regions we probe are, in general, UV photon dominated. Triggered AGN activity, and/or cosmic ray ionisation (from SNe II in the starburst) are not yet energetically important in determining the state of the gas.

  20. Protein-free parallel triple-stranded DNA complex formation

    PubMed Central

    Shchyolkina, A. K.; Timofeev, E. N.; Lysov, Yu. P.; Florentiev, V. L.; Jovin, T. M.; Arndt-Jovin, D. J.

    2001-01-01

    A 14 nt DNA sequence 5′-AGAATGTGGCAAAG-3′ from the zinc finger repeat of the human KRAB zinc finger protein gene ZNF91 bearing the intercalator 2-methoxy,6-chloro,9-amino acridine (Acr) attached to the sugar–phosphate backbone in various positions has been shown to form a specific triple helix (triplex) with a 16 bp hairpin (intramolecular) or a two-stranded (intermolecular) duplex having the identical sequence in the same (parallel) orientation. Intramolecular targets with the identical sequence in the antiparallel orientation and a non-specific target sequence were tested as controls. Apparent binding constants for formation of the triplex were determined by quantitating electrophoretic band shifts. Binding of the single-stranded oligonucleotide probe sequence to the target led to an increase in the fluorescence anisotropy of acridine. The parallel orientation of the two identical sequence segments was confirmed by measurement of fluorescence resonance energy transfer between the acridine on the 5′-end of the probe strand as donor and BODIPY-Texas Red on the 3′-amino group of either strand of the target duplex as acceptor. There was full protection from OsO4-bipyridine modification of thymines in the probe strand of the triplex, in accordance with the presumed triplex formation, which excluded displacement of the homologous duplex strand by the probe–intercalator conjugate. The implications of these results for the existence of protein-independent parallel triplexes are discussed. PMID:11160932

  1. Organosulfate Formation through the Heterogeneous Reaction of Sulfur Dioxide with Unsaturated Fatty Acids and Long-Chain Alkenes.

    PubMed

    Passananti, Monica; Kong, Lingdong; Shang, Jing; Dupart, Yoan; Perrier, Sébastien; Chen, Jianmin; Donaldson, D James; George, Christian

    2016-08-22

    The heterogeneous reaction between SO2 and unsaturated compounds results in the efficient production of organosulfates for several fatty acids and long-chain alkenes. The presence of an acid group, the physical state of the reactants (solid or liquid), the nature of the double bond (cis, trans, terminal), and the use of light irradiation all have an impact on the reaction rate. The reaction was investigated using different set-ups (coated flow tube, aerosol flow tube, and diffuse reflectance infrared Fourier transform cell). The reaction products were identified by high-resolution mass spectrometry and the impact of this reaction on organosulfate formation in the atmosphere is discussed.

  2. Steric effect for proton, hydrogen-atom, and hydride transfer reactions with geometric isomers of NADH-model ruthenium complexes.

    PubMed

    Cohen, Brian W; Polyansky, Dmitry E; Achord, Patrick; Cabelli, Diane; Muckerman, James T; Tanaka, Koji; Thummel, Randolph P; Zong, Ruifa; Fujita, Etsuko

    2012-01-01

    Two isomers, [Ru(1)]2+ (Ru = Ru(bpy)2, bpy = 2,2'-bipyridine, 1 = 2-(pyrid-2'-yl)-1-azaacridine) and [Ru(2)]2+ (2 = 3-(pyrid-2'-yl)-4-azaacridine), are bioinspired model compounds containing the nicotinamide functionality and can serve as precursors for the photogeneration of C-H hydrides for studying reactions pertinent to the photochemical reduction of metal-C1 complexes and/or carbon dioxide. While it has been shown that the structural differences between the azaacridine ligands of [Ru(1)]2+ and [Ru(2)]2+ have a significant effect on the mechanism of formation of the hydride donors, [Ru(1HH)]2+ and [Ru(2HH)]2+, in aqueous solution, we describe the steric implications for proton, net-hydrogen-atom and net-hydride transfer reactions in this work. Protonation of [Ru(2*-)] in aprotic and even protic media is slow compared to that of [Ru(1*-)]+. The net hydrogen-atom transfer between *[Ru(1)]2+ and hydroquinone (H2Q) proceeds by one-step EPT, rather than stepwise electron-proton transfer. Such a reaction was not observed for *[Ru(2)]2+ because the non-coordinated N atom is not easily available for an interaction with H2Q. Finally, the rate of the net hydride ion transfer from [Ru(1HH)]2+ to [Ph3C]+ is significantly slower than that of [Ru (2HH)]2+ owing to steric congestion at the donor site.

  3. CuAAC click reactions for the design of multifunctional luminescent ruthenium complexes.

    PubMed

    Zabarska, Natalia; Stumper, Anne; Rau, Sven

    2016-02-14

    CuAAC (Cu(i) catalyzed azide-alkyne cycloaddition) click chemistry has emerged as a versatile tool in the development of photoactive ruthenium complexes with multilateral potential applicability. In this contribution we discuss possible synthetic approaches towards CuAAC reactions with ruthenium(ii) polypyridine complexes and their differences with respect to possible applications. We focus on two main application possibilities of the click-coupled ruthenium assemblies. New results within the development of ruthenium based photosensitizers for the field of renewable energy supply, i.e. DSSCs (dye-sensitized solar cells) and artificial photocatalysis for the production of hydrogen, or for anticancer photodynamic therapeutic applications are reviewed.

  4. Boron-selective reactions as powerful tools for modular synthesis of diverse complex molecules.

    PubMed

    Xu, Liang; Zhang, Shuai; Li, Pengfei

    2015-12-21

    In the context of modular and rapid construction of molecular diversity and complexity for applications in organic synthesis, biomedical and materials sciences, a generally useful strategy has emerged based on boron-selective chemical transformations. In the last decade, these types of reactions have evolved from proof-of-concept to some advanced applications in the efficient preparation of complex natural products and even automated precise manufacturing on the molecular level. These advances have shown the great potential of boron-selective reactions in simplifying synthetic design and experimental operations, and should inspire new developments in related chemical and technological areas. This tutorial review will highlight the original contributions and representative advances in this emerging field.

  5. Roles of Acetone and Diacetone Alcohol in Coordination and Dissociation Reactions of Uranyl Complexes

    SciTech Connect

    Rios, Daniel; Schoendorff, George E.; Van Stipdonk, Michael J.; Gordon, Mark S.; Windus, Theresa L.; Gibson, John K.; De Jong, Wibe A.

    2012-12-03

    Combined collision-induced dissociation mass-spectrometry experiments and DFT calculations were employed to elucidate the molecular structure of "hypercoordinated" species and the energetics of water-elimination reactions of uranyl acetone complexes observed in earlier work (Rios, D.; Rutkowski, P. X.; Van Stipdonk, M. J.; Gibson, J. K. Inorg. Chem. 2011, 50, 4781). It is shown that the "hypercoordinated" species contain diacetone alcohol ligands bonded in either bidentate or monodentate fashion, which are indistinguishable from (acetone)2 in mass spectrometry. Calculations confirm that four diacetone ligands can form stable complexes, but that the effective number of atoms coordinating with uranium in the equatorial plane does not exceed five. Diacetone alcohol ligands are shown to form mesityl oxide ligands and alkoxide species through the elimination of water, providing an explanation for the observed water-elimination reactions.

  6. New qualitative colour reaction for the identification of copper(I) compounds and complexes.

    PubMed

    Johar, G S; Majumdar, G; Dwivedi, R C

    1974-06-01

    The colour reaction of copper(I) salts and complexes, in sulphuric acid medium, with ferricyanide and ammonia, has been used for the general identification of cuprous compounds. A sulphuric acid solution of Cu(I) compound, when treated with a dilute ferricyanide solution in the presence of ammonia, gives a salmon-pink, red-pink, pink-purple or purple colour or precipitate, characteristic of copper(I). Copper(II) compounds fail to give a positive response. The reaction also forms the basis of a test for ammonium ion and differentiation between ferrocyanide and ferricyanide. The preparation of the copper(I) complex of 1-allyl-2-tetrazoline-5-thione is described.

  7. Sharper Graph-Theoretical Conditions for the Stabilization of Complex Reaction Networks

    PubMed Central

    Knight, Daniel; Shinar, Guy; Feinberg, Martin

    2015-01-01

    Across the landscape of all possible chemical reaction networks there is a surprising degree of stable behavior, despite what might be substantial complexity and nonlinearity in the governing differential equations. At the same time there are reaction networks, in particular those that arise in biology, for which richer behavior is exhibited. Thus, it is of interest to understand network-structural features whose presence enforces dull, stable behavior and whose absence permits the dynamical richness that might be necessary for life. We present conditions on a network’s Species-Reaction Graph that ensure a high degree of stable behavior, so long as the kinetic rate functions satisfy certain weak and natural constraints. These graph-theoretical conditions are considerably more incisive than those reported earlier. PMID:25600138

  8. Synthetic and Mechanistic Studies of Strained Heterocycle Opening Reactions Mediated by Zirconium(IV) Imido Complexes

    PubMed Central

    Blum, Suzanne A.; Rivera, Vicki A.; Ruck, Rebecca T.; Michael, Forrest E.; Bergman, Robert G.

    2005-01-01

    The reactions of the bis(cyclopentadienyl)(tert-butylimido)zirconium complex (Cp2Zr=N-t-Bu)(THF) (1) with epoxides, aziridines, and episulfides were investigated. Heterocycles without accessible β-hydrogens undergo insertion/protonation of the C–X bond to produce 1,2-amino alcohols (X = O) and 1,2-diamines (X = NR), whereas heterocycles with accessible β-hydrogens undergo elimination/protonation to produce allylic alcohols (X = O) and allylic sulfides (X = S). Mechanistic investigations support a stepwise pathway with zwitterionic intermediates for the first reaction class and a concerted pathway for the second reaction class. Additionally, the feasibility of chirality transfer from the planar-chiral ebthi (ebthi = ethylenebis(tetrahydroindenyl)) ligand was demonstrated with a chiral analogue, (ebthi)-Zr=NAr(THF) (Ar = 2,6-dimethylphenyl), 2, through the diastereoselective ring opening of meso epoxides. PMID:16508693

  9. EFFECT OF PHYSICAL FACTORS ON REACTIONS OF HORSE-RADISH PEROXIDASE COMPLEXES WITH REDUCED CYTOCHROME C.

    PubMed

    FARWELL, R W; ACKERMAN, E

    1963-11-01

    This investigation concerns the effect of certain physical factors-viscosity, dielectric constant, ionic strength, and temperature of the medium-on the reaction of hydrogen peroxide and ferrocytochrome c in the presence of the enzyme horse-radish peroxidase. From study of the effects of viscosity and dielectric constant, it was concluded that the reaction between the secondary complex of hydrogen peroxide and enzyme on the one hand and ferrocytochrome c on the other is controlled by diffusion in media of high viscosity and by electrostatic effects at low viscosities. With respect to ionic strength, the data at pH 4.7 indicated a dipole-dipole interreaction. The temperature dependence of the over-all reaction had a Q(10) of 1.25.

  10. Effect of pH on complex formation between debranched waxy rice starch and fatty acids.

    PubMed

    Yotsawimonwat, Songwut; Sriroth, Klanarong; Kaewvichit, Sayam; Piyachomkwan, Kaukoon; Jane, Jay-Lin; Sirithunyalug, Jakkapan

    2008-08-15

    Complex formations between debranched waxy rice starch (DBS) and fatty acids (FA) of different hydrocarbon chain lengths (8:0, 10:0, 12:0, 14:0, 16:0, and 18:0) were studied in an aqueous solution by measuring the blue colour stained with iodine. The objective of this study was to understand the effects of the solubility and hydrophobicity of guest molecules (FA) on the complex formation with DBS. Lauric acid (12:0) displayed the greatest complex forming ability with DBS by showing the least blue colour developed with iodine. The effect of pH (3-7) on the DBS/FA complex formation was evaluated by measuring the iodine-scanning spectra of the mixture. Short-chain FA (8:0) displayed less complex formation at pH>or=5, above the pK(a) of fatty acid (approximately 4.8), which suggested that the charge formation of the short-chain FA caused a lower partitioning of the FA into the hydrophobic cavity of the DBS single helix. On the contrary, FA of 10:0-18:0 displayed an increased complex formation at pH>5, which could be attributed to increased solubility of these longer-chain FA at a dissociated and ionized form. The hydrocarbon chain length of the FA had an important impact on the extent of the complex formation. A FA that had a shorter hydrocarbon chain was more soluble in an aqueous solution and more readily formed a complex with DBS. At pH 6 and 7 (above the pK(a)), 10:0 formed less inclusion complexes with DBS than did 12:0. Iodine-scanning spectra showed that the absorbances of all iodine-stained DBS/FA solutions at higher wavelength were substantially lower than that of the iodine-stained DBS alone, suggesting that FA preferentially formed inclusion complexes with DBS of longer chains.

  11. The sound of a mobile phone ringing affects the complex reaction time of its owner

    PubMed Central

    Zajdel, Justyna; Zwolińska, Anna; Śmigielski, Janusz; Beling, Piotr; Cegliński, Tomasz; Nowak, Dariusz

    2012-01-01

    Introduction Mobile phone conversation decreases the ability to concentrate and impairs the attention necessary to perform complex activities, such as driving a car. Does the ringing sound of a mobile phone affect the driver's ability to perform complex sensory-motor activities? We compared a subject's reaction time while performing a test either with a mobile phone ringing or without. Material and methods The examination was performed on a PC-based reaction time self-constructed system Reactor. The study group consisted of 42 healthy students. The protocol included instruction, control without phone and a proper session with subject's mobile phone ringing. The terms of the study were standardised. Results There were significant differences (p < 0.001) in reaction time in control (597 ms), mobile (633 ms) and instruction session (673 ms). The differences in female subpopulation were also significant (p < 0.01). Women revealed the longest reaction time in instruction session (707 ms), were significantly quicker in mobile (657 ms, p < 0.01) and in control session (612 ms, p < 0.001). In men, the significant difference was recorded only between instruction (622 ms) and control session (573 ms, p < 0.01). The other differences were not significant (p > 0.08). Men proofed to complete significantly quicker than women in instruction (p < 0.01) and in mobile session (p < 0.05). Differences amongst the genders in control session was not significant (p > 0.05). Conclusions The results obtained proofed the ringing of a phone exerts a significant influence on complex reaction time and quality of performed task. PMID:23185201

  12. The formation and study of titanium, zirconium, and hafnium complexes

    NASA Technical Reports Server (NTRS)

    Wilson, Bobby; Sarin, Sam; Smith, Laverne; Wilson, Melanie

    1989-01-01

    Research involves the preparation and characterization of a series of Ti, Zr, Hf, TiO, and HfO complexes using the poly(pyrazole) borates as ligands. The study will provide increased understanding of the decomposition of these coordination compounds which may lead to the production of molecular oxygen on the Moon from lunar materials such as ilmenite and rutile. The model compounds are investigated under reducing conditions of molecular hydrogen by use of a high temperature/pressure stainless steel autoclave reactor and by thermogravimetric analysis.

  13. Temperature perturbations evolution as a possible mechanism of exothermal reaction kernels formation in shock tubes

    NASA Astrophysics Data System (ADS)

    Drakon, A. V.; Kiverin, A. D.; Yakovenko, I. S.

    2016-11-01

    The basic question raised in the paper concerns the origins of exothermal reaction kernels and the mechanisms of detonation onset behind the reflected shock wave in shock-tube experiments. Using the conventional experimental technique, it is obtained that in the certain diapason of conditions behind the reflected shocks a so-called “mild ignition” arises which is characterized by the detonation formation from the kernel distant from the end-wall. The results of 2-D and 3-D simulations of the flow evolution behind the incident and reflected shocks allow formulation of the following scenario of ignition kernels formation. Initial stage during and after the diaphragm rupture is characterized by a set of non-steady gasdynamical processes. As a result, the flow behind the incident shock occurs to be saturated with temperature perturbations. Further evolution of these perturbations provides generating of the shear stresses in the flow accompanied with intensification of velocity and temperature perturbations. After reflection the shock wave interacts with the formed kernels of higher temperature and more pronounced kernels arise on the background of reactivity profile determined by moving reflected shock. Exothermal reaction starts inside such kernels and propagates into the ambient medium as a spontaneous ignition wave with minimum initial speed equal to the reflected shock wave speed.

  14. Heterocycles as key substrates in multicomponent reactions: the fast lane towards molecular complexity.

    PubMed

    Isambert, Nicolas; Lavilla, Rodolfo

    2008-01-01

    Heterocycles display an intrinsic reactivity which enables rich, versatile and productive transformations. Taking into account their ubiquitous presence in natural products and drugs, the development of new, fast and efficient preparative protocols for these structures remains an urgent task in Organic Synthesis. Multicomponent reactions using heterocyclic chemistry offer new possibilities to exploit this exclusive reactivity. Recent results show relevant examples of such transformations. Several approaches which allow the construction of complex heterocyclic compounds from simple starting materials using this principle have been analyzed.

  15. Peptide bond formation through gas-phase reactions in the interstellar medium: formamide and acetamide as prototypes

    SciTech Connect

    Redondo, Pilar; Barrientos, Carmen; Largo, Antonio

    2014-09-20

    A theoretical study of the reactions of NH{sub 4}{sup +} with formaldehyde and CH{sub 5}{sup +} with formamide is carried out. The viability of these gas-phase ion-molecule reactions as possible sources of formamide and acetamide under the conditions of interstellar medium is evaluated. We report a theoretical estimation of the reaction enthalpies and an analysis of their potential energy surfaces. Formation of protonated formamide from the reaction between ammonium cation and formaldehyde is an exothermic process, but all the channels located on the potential energy surface leading to this product present net activation energies. For the reaction between methanium and formamide, different products are possible from a thermodynamic point of view. An analysis of its potential energy surface showed that formation of protonated acetamide and amino acetaldehyde takes place through barrier-free paths. Therefore, this reaction could be a feasible source of acetamide and amino acetaldehyde in space.

  16. Peptide Bond Formation through Gas-phase Reactions in the Interstellar Medium: Formamide and Acetamide as Prototypes

    NASA Astrophysics Data System (ADS)

    Redondo, Pilar; Barrientos, Carmen; Largo, Antonio

    2014-09-01

    A theoretical study of the reactions of NH_4+ with formaldehyde and CH_5+ with formamide is carried out. The viability of these gas-phase ion-molecule reactions as possible sources of formamide and acetamide under the conditions of interstellar medium is evaluated. We report a theoretical estimation of the reaction enthalpies and an analysis of their potential energy surfaces. Formation of protonated formamide from the reaction between ammonium cation and formaldehyde is an exothermic process, but all the channels located on the potential energy surface leading to this product present net activation energies. For the reaction between methanium and formamide, different products are possible from a thermodynamic point of view. An analysis of its potential energy surface showed that formation of protonated acetamide and amino acetaldehyde takes place through barrier-free paths. Therefore, this reaction could be a feasible source of acetamide and amino acetaldehyde in space.

  17. Double-Ended Surface Walking Method for Pathway Building and Transition State Location of Complex Reactions.

    PubMed

    Zhang, Xiao-Jie; Shang, Cheng; Liu, Zhi-Pan

    2013-12-10

    Toward the activity prediction with large-scale computations, here a double-ended surface walking (DESW) method is developed for connecting two minima on a potential energy surface (PES) and locating the associated transition state (TS) using only the first derivatives. The method operates two images starting from the initial and the final states, respectively, to walk in a stepwise manner toward each other. The surface walking involves repeated bias potential addition and local relaxation with the constrained Broyden dimer method to correct the walking direction. We apply the method to a model PES, a large set of gas phase Baker reactions, and complex surface catalytic reactions, which demonstrates that the DESW method can establish a low energy pathway linking two minima even without iterative optimization of the pathway, from which the TS can be located readily. By comparing the efficiency of the new method with the existing methods, we show that the DESW method is much less computationally demanding and is applicable for reactions with complex PESs. We hope that the DESW method may be integrated with the PES sampling methods for automated reaction prediction.

  18. Formation of Au and tetrapyridyl porphyrin complexes in superfluid helium.

    PubMed

    Feng, Cheng; Latimer, Elspeth; Spence, Daniel; Al Hindawi, Aula M A A; Bullen, Shem; Boatwright, Adrian; Ellis, Andrew M; Yang, Shengfu

    2015-07-14

    Binary clusters containing a large organic molecule and metal atoms have been formed by the co-addition of 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) molecules and gold atoms to superfluid helium nanodroplets, and the resulting complexes were then investigated by electron impact mass spectrometry. In addition to the parent ion H2TPyP yields fragments mainly from pyrrole, pyridine and methylpyridine ions because of the stability of their ring structures. When Au is co-added to the droplets the mass spectra are dominated by H2TPyP fragment ions with one or more Au atoms attached. We also show that by switching the order in which Au and H2TPyP are added to the helium droplets, different types of H2TPyP-Au complexes are clearly evident from the mass spectra. This study suggests a new route for the control over the growth of metal-organic compounds inside superfluid helium nanodroplets.

  19. Flow induced streamer formation in particle laden complex flows

    NASA Astrophysics Data System (ADS)

    Debnath, Nandini; Hassanpourfard, Mahtab; Ghosh, Ranajay; Trivedi, Japan; Thundat, Thomas; Kumar, Aloke

    2016-11-01

    We study the combined flow of a polyacrylamide (PAM)solution with polystyrene (PS) nanoparticles, through a microfluidic device containing an array of micropillars. The flow is characterized by a very low Reynolds number (Re<<1). We find that for exceeding a critical Weissenberg number (Wi >= 20), PS nanoparticles localize near pillar walls to form thin slender string-like structures, which we call 'streamers' due to their morphology. Post-formation, these streamers show significant viscous behavior for short observational time-scales, and at longer observational time scales elastic response dominates. Our abiotic streamers could provide a framework for understanding similar structures that often form in biological systems. PhD student, Department of Mechanical Engineering.

  20. Coke formation and carbon atom economy of methanol-to-olefins reaction.

    PubMed

    Wei, Yingxu; Yuan, Cuiyu; Li, Jinzhe; Xu, Shutao; Zhou, You; Chen, Jingrun; Wang, Quanyi; Xu, Lei; Qi, Yue; Zhang, Qing; Liu, Zhongmin

    2012-05-01

    The methanol-to-olefins (MTO) process is becoming the most important non-petrochemical route for the production of light olefins from coal or natural gas. Maximizing the generation of the target products, ethene and propene, and minimizing the production of byproducts and coke, are major considerations in the efficient utilization of the carbon resource of methanol. In the present work, the heterogeneous catalytic conversion of methanol was evaluated by performing simultaneous measurements of the volatile products generated in the gas phase and the confined coke deposition in the catalyst phase. Real-time and complete reaction profiles were plotted to allow the comparison of carbon atom economy of methanol conversion over the catalyst SAPO-34 at varied reaction temperatures. The difference in carbon atom economy was closely related with the coke formation in the SAPO-34 catalyst. The confined coke compounds were determined. A new type of confined organics was found, and these accounted for the quick deactivation and low carbon atom economy under low-reaction-temperature conditions. Based on the carbon atom economy evaluation and coke species determination, optimized operating conditions for the MTO process are suggested; these conditions guarantee high conversion efficiency of methanol.

  1. Reaction between drug substances and pharmaceutical excipients: formation of esters between cetirizine and polyols.

    PubMed

    Yu, He; Cornett, Claus; Larsen, Jesper; Hansen, Steen Honoré

    2010-11-02

    Reactions between active drug substances and excipients are of interest in the drug formulation process and should also be considered in the following storage of final preparations. Some excipients react more readily with certain chemical groups in drug substances and in the present paper the ester formation between a drug substance having a carboxylic acid moiety and some polyols are described. The drug substance cetirizine was chosen as the model substance as it is already marketed and used as a common drug for treatment of allergic reactions. Among the marketed products are oral solutions and oral drops containing excipients like sorbitol and glycerol. It was found that the carboxylic acid cetirizine readily reacts with sorbitol and glycerol to form monoesters. At a temperature as low as 40 degrees C, more than 1% of the cetirizine content was transformed into a monoester within 1 week using concentrations similar to those used in marketed preparations. The kinetic studies of the reaction performed at 40, 60 and 80 degrees C also revealed that the esters were unstable and they degraded especially at higher temperatures. Analysis of two marketed preparations having expiry dates in 2011 showed content of the cetirizine esters corresponding to a range from 0.1 to 0.3% of the declared cetirizine content.

  2. Carbon Isotopic Fractionation During Formation of Macromolecular Organic Grain Coatings via FTT Reactions

    NASA Technical Reports Server (NTRS)

    Nuth, J. A.; Johnson, N. M.; Elsila-Cook, J.; Kopstein, M.

    2011-01-01

    Observations of carbon isotopic fractionation of various organic compounds found in meteorites may provide useful diagnostic information concerning the environments and mechanisms that were responsible for their formation. Unfortunately, carbon has only two stable isotopes, making interpretation of such observations quite problematic. Chemical reactions can increase or decrease the C-13/C-12 ratio by various amounts, but the final ratio will depend on the total reaction pathway followed from the source carbon to the final product, a path not readily discernable after 4.5 billion years. In 1970 Libby showed that the C-13/C-12 ratios of terrestrial and meteoritic carbon were similar by comparing carbon from the Murchison meteorite to that of terrestrial sediments. More recent studies have shown that the C-13/C-12 ratio of the Earth and meteorites may be considerably enriched in C-13 compared to the ratio observed in the solar wind [2], possibly suggesting that carbon produced via ion-molecule reactions in cold dark clouds could be an important source of terrestrial and meteoritic carbon. However, meteoritic carbon has been subjected to parent body processing that could have resulted in significant changes to the C-13/C-12 ratio originally present while significant variation has been observed in the C-13/C-12 ratio of the same molecule extracted from different terrestrial sources. Again we must conclude that understanding the ratio found in meteorites may be difficult.

  3. Effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events

    NASA Astrophysics Data System (ADS)

    Quan, Jiannong; Liu, Quan; Li, Xia; Gao, Yang; Jia, Xingcan; Sheng, Jiujiang; Liu, Yangang

    2015-12-01

    The effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events was investigated by analysis of comprehensive measurements of aerosol composition and concentrations [e.g., particular matters (PM2.5), nitrate (NO3), sulfate (SO4), ammonium (NH4)], gas-phase precursors [e.g., nitrogen oxides (NOx), sulfur dioxide (SO2), and ozone (O3)], and relevant meteorological parameters [e.g., visibility and relative humidity (RH)]. The measurements were conducted in Beijing, China from Sep. 07, 2012 to Jan. 16, 2013. The results show that the conversion ratios of N from NOx to nitrate (Nratio) and S from SO2 to sulfate (Sratio) both significantly increased in haze events, suggesting enhanced conversions from NOx and SO2 to their corresponding particle phases in the late haze period. Further analysis shows that Nratio and Sratio increased with increasing RH, with Nratio and Sratio being only 0.04 and 0.03, respectively, when RH < 40%, and increasing up to 0.16 and 0.12 when RH reached 60-80%, respectively. The enhanced conversion ratios of N and S in the late haze period is likely due to heterogeneous aqueous reactions, because solar radiation and thus the photochemical capacity are reduced by the increases in aerosols and RH. This point was further affirmed by the relationships of Nratio and Sratio to O3: the conversion ratios increase with decreasing O3 concentration when O3 concentration is lower than <15 ppb but increased with increasing O3 when O3 concentration is higher than 15 ppb. The results suggest that heterogeneous aqueous reactions likely changed aerosols and their precursors during the haze events: in the beginning of haze events, the precursor gases accumulated quickly due to high emission and low reaction rate; the occurrence of heterogeneous aqueous reactions in the late haze period, together with the accumulated high concentrations of precursor gases such as SO2 and NOx, accelerated the formation of secondary

  4. Effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events

    SciTech Connect

    Quan, Jiannong; Liu, Yangang; Liu, Quan; Li, Xia; Gao, Yang; Jia, Xingcan; Sheng, Jiujiang

    2015-09-30

    In this study, the effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events was investigated by analysis of comprehensive measurements of aerosol composition and concentrations [e.g., particular matters (PM2.5), nitrate (NO3), sulfate (SO4), ammonium (NH4)], gas-phase precursors [e.g., nitrogen oxides (NOx), sulfur dioxide (SO2), and ozone (O3)], and relevant meteorological parameters [e.g., visibility and relative humidity (RH)]. The measurements were conducted in Beijing, China from Sep. 07, 2012 to Jan. 16, 2013. The results show that the conversion ratios of N from NOx to nitrate (Nratio) and S from SO2 to sulfate (Sratio) both significantly increased in haze events, suggesting enhanced conversions from NOx and SO2 to their corresponding particle phases in the late haze period. Further analysis shows that Nratio and Sratio increased with increasing RH, with Nratio and Sratio being only 0.04 and 0.03, respectively, when RH < 40%, and increasing up to 0.16 and 0.12 when RH reached 60–80%, respectively. The enhanced conversion ratios of N and S in the late haze period is likely due to heterogeneous aqueous reactions, because solar radiation and thus the photochemical capacity are reduced by the increases in aerosols and RH. This point was further affirmed by the relationships of Nratio and Sratio to O3: the conversion ratios increase with decreasing O3 concentration when O3 concentration is lower than <15 ppb but increased with increasing O3 when O3 concentration is higher than 15 ppb. The results suggest that heterogeneous aqueous reactions likely changed aerosols and their precursors during the haze events: in the beginning of haze events, the precursor gases accumulated quickly

  5. Effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events

    DOE PAGES

    Quan, Jiannong; Liu, Yangang; Liu, Quan; ...

    2015-09-30

    In this study, the effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events was investigated by analysis of comprehensive measurements of aerosol composition and concentrations [e.g., particular matters (PM2.5), nitrate (NO3), sulfate (SO4), ammonium (NH4)], gas-phase precursors [e.g., nitrogen oxides (NOx), sulfur dioxide (SO2), and ozone (O3)], and relevant meteorological parameters [e.g., visibility and relative humidity (RH)]. The measurements were conducted in Beijing, China from Sep. 07, 2012 to Jan. 16, 2013. The results show that the conversion ratios of N from NOx to nitrate (Nratio) and S from SO2 to sulfate (Sratio) bothmore » significantly increased in haze events, suggesting enhanced conversions from NOx and SO2 to their corresponding particle phases in the late haze period. Further analysis shows that Nratio and Sratio increased with increasing RH, with Nratio and Sratio being only 0.04 and 0.03, respectively, when RH < 40%, and increasing up to 0.16 and 0.12 when RH reached 60–80%, respectively. The enhanced conversion ratios of N and S in the late haze period is likely due to heterogeneous aqueous reactions, because solar radiation and thus the photochemical capacity are reduced by the increases in aerosols and RH. This point was further affirmed by the relationships of Nratio and Sratio to O3: the conversion ratios increase with decreasing O3 concentration when O3 concentration is lower than <15 ppb but increased with increasing O3 when O3 concentration is higher than 15 ppb. The results suggest that heterogeneous aqueous reactions likely changed aerosols and their precursors during the haze events: in the beginning of haze events, the precursor gases accumulated quickly due to high emission and low reaction rate; the occurrence of heterogeneous aqueous reactions in the late haze period, together with the accumulated high concentrations of precursor gases such as SO2 and NOx, accelerated the

  6. Chemically activated formation of organic acids in reactions of the Criegee intermediate with aldehydes and ketones.

    PubMed

    Jalan, Amrit; Allen, Joshua W; Green, William H

    2013-10-21

    Reactions of the Criegee intermediate (CI, ˙CH2OO˙) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between ˙CH2OO˙ and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48-51 kcal mol(-1) lower in energy, formed via 1,3-cycloaddition of ˙CH2OO˙ across the C=O bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O-O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO < CH3CHO < CH3COCH3 (the highest yield being 10(-4) times lower than the initial ˙CH2OO˙ concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.

  7. Chemically Activated Formation of Organic Acids in Reactions of the Criegee Intermediate with Aldehydes and Ketones

    SciTech Connect

    Jalan, Amrit; Allen, Joshua W.; Green, William H.

    2013-08-08

    Reactions of the Criegee intermediate (CI, .CH2OO.) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between .CH2OO. and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48–51 kcal mol-1 lower in energy, formed via 1,3- cycloaddition of .CH2OO. across the CQO bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O–O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO o CH3CHO o CH3COCH3 (the highest yield being 10-4 times lower than the initial .CH2OO. concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.

  8. Kinetics and mechanism for formation of enols in reaction of hydroxide radical with propene.

    PubMed

    Zhou, Chong-Wen; Li, Ze-Rong; Li, Xiang-Yuan

    2009-03-19

    Recently, enols have been found to be the common intermediates in hydrocarbon combustion flames (Taatjes et al. Science 2005, 308, 1887), but the knowledge of kinetic properties for such species in combustion flames is rare. Therefore in this work, particular attention is paid to the formation of enols in combustion flames. Starting with HO and propene (CH(3)CH=CH(2)), the reaction mechanism involving eight product channels has been investigated systematically. It is revealed that the electrophilic addition of OH to the double bond of CH(3)CH=CH(2) is unselective and the chemically activated adducts, CH(3)CHOH=CH(2) and CH(3)CH=CH(2)OH, may undergo dissociation in competition with H-abstractions. The kinetics and product branching ratios of the HO and propene reaction have been evaluated in the temperature range of 200-3000 K by Variflex code, based on the weak collision master equation/microcanonical variational RRKM theory. Available experimental kinetic data can be quantitatively reproduced by this study, with a minor adjustment (1.0 kcal/mol) of the OH central addition barrier. From the theoretical calculations with multiple reflection correction included, the total rate constant is fitted to k(t) = 6.07 x 10(-5)T(-2.54) exp(108/T) cm(3) x molecule(-1) x s(-1) in the range of 200-800 K and k(t) = 7.11 x 10(-23)T(3.38) exp(-1097/T) cm(3) x molecule(-1) x s(-1) in the range of 800-3000 K, which are in close agreement with experimental data. The branching ratios of enol channels are consistent with the observation in low-pressure flames and hence the reaction mechanisms presented here provide valuable descriptions of enol formations in hydrocarbon combustion chemistry.

  9. Is a proposed reaction mechanism free from unnecessary assumptions? Occam's razor applied in a mathematical way to complex first-order reaction systems.

    PubMed

    Bergson, Göran; Linderberg, Jan

    2008-05-08

    Following Occam's principle, a proposed reaction mechanism should not contain assumptions about the existence of reactive intermediates and reaction paths that are unnecessary for a full description and interpretation of the available facts. A mechanism refers, in this paper, to a proposed reaction scheme or network that represents the reactions supposed to be going on in a complex reaction system with observable species as well as unobservable reactive intermediates. The scope is limited here to (pseudo) first-order reactions and the steady-state approximation is invoked in order to relate unknown mechanistic rate constants to experimentally determined ones, and, when available, theoretically calculated quantities. When the resulting, nonlinear system of equations admits a unique solution within a physically reasonable domain, it is concluded that the reaction mechanism fulfills Occam's principle. Otherwise, there are many or no solutions. No subjective or qualitative arguments enter the procedure and the outcome is not negotiable.

  10. Subcellular location for the formation of the retinol/retinol-binding protein complex in rat liver

    SciTech Connect

    Crumbaugh, L.M.; Green, E.L.; Smith, J.E.

    1986-03-01

    Retinol complexes with retinol-binding protein (RBP) within the hepatocyte, however the subcellular location where complex formation occurs has not previously been identified. A model similar to that of lipoproteins formation has been hypothesized. The authors have identified the initial site of retinol/RBP complex formation. Furthermore, the authors have elucidated the progression of the complex through the subcellular organelles. Intravenous injections of /sup 3/H-retinol suspended in Tween 40 were administered to vitamin A depleted rats. After intervals of 2, 3, 4, 5, 10, 15, 20, and 30 minutes the rat livers were removed and fractions enriched in rough and smooth microsomes and Golgi apparatus were prepared. Extracts of these subcellular fractions were chromatographed on Sephadex G-100. Simultaneous elution of /sup 3/H-retinol and immunoreactive RBP indicated the presence of the complex. The retinol/RBP complex was observed in rough microsomes 2 minute after the injection of /sup 3/H-retinal. The complex appeared subsequently in smooth microsomes and Golgi apparatus. The complex was first detected serum around 10 minutes after injection. Based on the data, they believe that the retinol/RBP complex formation occurs in rough microsomes.

  11. Histidinyl radical formation in the self-peroxidation reaction of bovine copper-zinc superoxide dismutase.

    PubMed

    Gunther, Michael R; Peters, J Andrew; Sivaneri, Meena K

    2002-03-15

    In the absence of suitable oxidizable substrates, the peroxidase reaction of copper-zinc superoxide dismutase (SOD) oxidizes SOD itself, ultimately resulting in its inactivation. A SOD-centered free radical adduct of 2-methyl-2-nitrosopropane (MNP) was detected upon incubation of SOD with the spin trap and a hydroperoxide (either H(2)O(2) or peracetic acid). Proteolysis by Pronase converted the anisotropic electron paramagnetic resonance (EPR) spectrum of MNP/(center dot)SOD to a nearly isotropic spectrum with resolved hyperfine couplings to several atoms with non-zero nuclear spin. Authentic histidinyl radical (from histidine + HO(center dot)) formed a MNP adduct with a very similar EPR spectrum to that of the Pronase-treated MNP/(center dot)SOD, suggesting that the latter was centered on a histidine residue. An additional hyperfine coupling was detected when histidine specifically (13)C-labeled at C-2 of the imidazole ring was used, providing evidence for trapping at that atom. All of the experimental spectra were convincingly simulated assuming hyperfine couplings to 2 nearly equivalent nitrogen atoms and 2 different protons, also consistent with trapping at C-2 of the imidazole ring. Free histidinyl radical consumed oxygen, implying peroxyl radical formation. MNP-inhibitable oxygen consumption was also observed when cuprous SOD but not cupric SOD was added to a H(2)O(2) solution. Formation of 2-oxohistidine, the stable product of the SOD-hydroperoxide reaction, required oxygen and was inhibited by MNP. These results support formation of a transient SOD-peroxyl radical.

  12. Formation, Migration, and Reactivity of Au CO Complexes on Gold Surfaces

    DOE PAGES

    Wang, Jun; McEntee, Monica; Tang, Wenjie; ...

    2016-01-12

    Here, we report experimental as well as theoretical evidence that suggests Au CO complex formation upon the exposure of CO to active sites (step edges and threading dislocations) on a Au(111) surface. Room-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, transmission infrared spectroscopy, and density functional theory calculations point to Au CO complex formation and migration. Room-temperature STM of the Au(111) surface at CO pressures in the range from 10^ 8 to 10^ 4 Torr (dosage up to 10^6 langmuir) indicates Au atom extraction from dislocation sites of the herringbone reconstruction, mobile Au CO complex formation and diffusion, and Aumore » adatom cluster formation on both elbows and step edges on the Au surface. The formation and mobility of the Au CO complex result from the reduced Au Au bonding at elbows and step edges leading to stronger Au CO bonding and to the formation of a more positively charged CO (CO +) on Au. These studies indicate that the mobile Au CO complex is involved in the Au nanoparticle formation and reactivity, and that the positive charge on CO increases due to the stronger adsorption of CO at Au sites with lower coordination numbers.« less

  13. Formation, Migration, and Reactivity of Au CO Complexes on Gold Surfaces

    SciTech Connect

    Wang, Jun; McEntee, Monica; Tang, Wenjie; Neurock, Matthew; Baddorf, Arthur P.; Maksymovych, Petro; Yates, Jr, John T.

    2016-01-12

    Here, we report experimental as well as theoretical evidence that suggests Au CO complex formation upon the exposure of CO to active sites (step edges and threading dislocations) on a Au(111) surface. Room-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, transmission infrared spectroscopy, and density functional theory calculations point to Au CO complex formation and migration. Room-temperature STM of the Au(111) surface at CO pressures in the range from 10^ 8 to 10^ 4 Torr (dosage up to 10^6 langmuir) indicates Au atom extraction from dislocation sites of the herringbone reconstruction, mobile Au CO complex formation and diffusion, and Au adatom cluster formation on both elbows and step edges on the Au surface. The formation and mobility of the Au CO complex result from the reduced Au Au bonding at elbows and step edges leading to stronger Au CO bonding and to the formation of a more positively charged CO (CO +) on Au. These studies indicate that the mobile Au CO complex is involved in the Au nanoparticle formation and reactivity, and that the positive charge on CO increases due to the stronger adsorption of CO at Au sites with lower coordination numbers.

  14. HSO2+ formation from ion-molecule reactions of SO2.+ with water and methane: two fast reactions with reverse temperature-dependent kinetic trend.

    PubMed

    Cartoni, Antonella; Catone, Daniele; Bolognesi, Paola; Satta, Mauro; Markus, Pal; Avaldi, Lorenzo

    2017-02-08

    In this work an experimental and theoretical study on the formation of HSO2+ ion from the SO2.+ + CH4 and SO2.+ + H2O ion-molecule reactions at different temperatures is reported. Tunable synchrotron radiation has been used to produce the SO2.+ ion in excited ro-vibrational levels of the ionic ground state X2A1 and mass spectrometry has been employed to identify the product ions. Calculations in the frame of the density functional theory and variational transtition state theory have been combined to explore the dynamics of the reactions. The experimental results show that HSO2+ is the only product in both reactions. Its yield decreases monotonically with photon energy in the SO2.+ + H2O reaction, while it decreases at first and then increases in the SO2.+ + CH4 reaction. Theory confirms this trend by calculating the rate constants at different temperatures and explains the results by means of the polar, spin and charge effects as well as structural reorganization occuring in the reaction coordinate. The dynamic behavior observed in these two reactions is of general and fundamental interest. It can also provide some insights in the role of these reactions in astrochemistry as well as in their use as models for bond-activation reactions.

  15. Thermodynamics of electron transfer in oxygenic photosynthetic reaction centers: volume change, enthalpy, and entropy of electron-transfer reactions in manganese-depleted photosystem II core complexes.

    PubMed

    Hou, J M; Boichenko, V A; Diner, B A; Mauzerall, D

    2001-06-19

    We have previously reported the thermodynamic data of electron transfer in photosystem I using pulsed time-resolved photoacoustics [Hou et al. (2001) Biochemistry 40, 7109-7116]. In the present work, using preparations of purified manganese-depleted photosystem II (PS II) core complexes from Synechocystis sp. PCC 6803, we have measured the DeltaV, DeltaH, and estimated TDeltaS of electron transfer on the time scale of 1 micros. At pH 6.0, the volume contraction of PS II was determined to be -9 +/- 1 A3. The thermal efficiency was found to be 52 +/- 5%, which corresponds to an enthalpy change of -0.9 +/- 0.1 eV for the formation of the state P680+Q(A-) from P680*. An unexpected volume expansion on pulse saturation of PS II was observed, which is reversible in the dark. At pH 9.0, the volume contraction, the thermal efficiency, and the enthalpy change were -3.4 +/- 0.5 A3, 37 +/- 7%, and -1.15 +/- 0.13 eV, respectively. The DeltaV of PS II, smaller than that of PS I and bacterial centers, is assigned to electrostriction and analyzed using the Drude-Nernst equation. To explain the small DeltaV for the formation of P680+Q(A-) or Y(Z*)Q(A-), we propose that fast proton transfer into a polar region is involved in this reaction. Taking the free energy of charge separation of PS II as the difference between the energy of the excited-state P680* and the difference in the redox potentials of the donor and acceptor, the apparent entropy change (TDeltaS) for charge separation of PS II is calculated to be negative, -0.1 +/- 0.1 eV at pH 6.0 (P680+Q(A-)) and -0.2 +/- 0.15 eV at pH 9.0 (Y(Z*)Q(A-)). The thermodynamic properties of electron transfer in PS II core reaction centers thus differ considerably from those of bacterial and PS I reaction centers, which have DeltaV of approximately -27 A3, DeltaH of approximately -0.4 eV, and TDeltaS of approximately +0.4 eV.

  16. Kinetics and Thermochemistry of ClCO Formation from the Cl + CO Association Reaction

    NASA Technical Reports Server (NTRS)

    Nicovich, J. M.; Kreutter, K. D.; Wine, P. H.

    1997-01-01

    Laser flash photolysis of Cl2/CO/M mixtures (M = N2, CO, Ar, CO2) has been employed in conjunction with Cl((sup 2)P(sub J)) detection by time-resolved resonance fluorescence spectroscopy to investigate equilibration kinetics in the reactions Cl((sup 2)P(sub J)) + CO ClCO as a function of temperature (185-260 K) and pressure (14-200 Torr). The association and dissociation reactions are found to be in the low-pressure limit over the range of experimental conditions investigated. In N2 and/or CO buffer gases, the temperature dependences of the ClCO formation and dissociation reaction rate constants are described by the Arrhenius expressions k(sub 1) = (1.05 +/- 0.36) x 10(exp -34) exp[(810 +/- 70)/T] cm(exp 6)/molecules(exp 2).s and k(sub -1) = (4.1 +/- 3.1) x 10(exp -10) exp[(-2960 +/- 60)/T]cu cm/(molecule.s) (errors are 2 sigma). Second- and third-law analyses of the temperature dependence of the equilbrium constant (k/k-1) lead to the following thermodynamic parameters for the association reaction: Delta-H(sub 298) = -7.7 +/- 0.6 kcal/mol, Delta-H(sub 0) = -6.9 +/- 0.7 kcal/mol, Delta-S(sub 298) = -23.8 +/- 2.0 cal/mole.K, Delta-H(sub f,298)(ClCO) = 5.2 +/- 0.6 kcal/mol (errors are 2 sigma). The results repported in this study significantly reduce the uncertainties in all reported kinetic and thermodynamic parameters.

  17. Complex Formation History of Highly Evolved Basaltic Shergottite, Zagami

    NASA Technical Reports Server (NTRS)

    Niihara, T.; Misawa, K.; Mikouchi, T.; Nyquist, L. E.; Park, J.; Hirata, D.

    2012-01-01

    Zagami, a basaltic shergottite, contains several kinds of lithologies such as Normal Zagami consisting of Fine-grained (FG) and Coarse-grained (CG), Dark Mottled lithology (DML), and Olivine-rich late-stage melt pocket (DN). Treiman and Sutton concluded that Zagami (Normal Zagami) is a fractional crystallization product from a single magma. It has been suggested that there were two igneous stages (deep magma chamber and shallow magma chamber or surface lava flow) on the basis of chemical zoning features of pyroxenes which have homogeneous Mg-rich cores and FeO, CaO zoning at the rims. Nyquist et al. reported that FG has a different initial Sr isotopic ratio than CG and DML, and suggested the possibility of magma mixing on Mars. Here we report new results of petrology and mineralogy for DML and the Olivine-rich lithology (we do not use DN here), the most evolved lithology in this rock, to understand the relationship among lithologies and reveal Zagami s formation history

  18. Secondary Organic Aerosol formation from the gas-phase reaction of catechol with ozone

    NASA Astrophysics Data System (ADS)

    Coeur-Tourneur, C.; Tomas, A.; Guilloteau, A.; Henry, F.; Ledoux, F.; Visez, N.; Riffault, V.; Wenger, J. C.; Bedjanian, Y.; Foulon, V.

    2009-04-01

    The formation of secondary organic aerosol from the gas-phase reaction of catechol (1,2-dihydroxybenzene) with ozone has been studied in two smog chambers (at the LPCA in France and at the CRAC in Ireland). Aerosol production was monitored using a scanning mobility particle sizer. The overall organic aerosol yield (Y) was determined as the ratio of the suspended aerosol mass corrected for wall losses (Mo) to the total reacted catechol concentrations, assuming a particle density of 1.4 g cm-3. Analysis of the data clearly shows that Y is a strong function of Mo and that secondary organic aerosol formation can be expressed by a one-product gas/particle partitioning absorption model. The aerosol formation is affected by the initial catechol concentration, which leads to aerosol yields ranging from 17% to 86%. The aerosol yields determined in the LPCA and CRAC smog chambers were comparable and were also in accordance with those determined in a previous study performed in EUPHORE (EUropean PHOto REactor, Spain).

  19. Microbanded manganese formations; protoliths in the Franciscan Complex, California

    USGS Publications Warehouse

    Huebner, J. Stephen; Flohr, Marta J.

    1990-01-01

    The Buckeye manganese deposit, 93 km southeast of San Francisco in the California Coast Ranges, preserves a geologic history that provides clues to the origin of numerous lenses of manganese carbonate, oxides, and silicates that occur with interbedded radiolarian chert and metashale of the Franciscan Complex. Compositionally and mineralogically laminated Mn-rich protoliths were deformed and dismembered, in a manner that mimics in smaller scale the deformation of the host complex, and then were incipiently metamorphosed at blueschistfacies conditions. Eight phases occur as almost monomineralic protoliths and mixtures: rhodochrosite, caryopilite, chlorite, gageite, taneyamalite, braunite, hausmannite, and laminated chert (quartz). Braunite, gageite, and some chlorite and caryopilite layers were deposited as gel-like materials; rhodochrosite, most caryopilite, and at least some hausmannite layers as lutites; and the chert as turbidites of radiolarian sand. Some gel-like materials are now preserved as transparent, sensibly isotropic relics of materials that fractured or shattered when deformed, creating curved surfaces. In contrast, the micrites flowed between the fragments of gel-like materials. The orebody and most of its constituent minerals have unusually Mn-rich compositions that are described by the system MnO-SiO2-O2-CO2-H2O. High values of Mn/Fe and U/Th, and low concentrations of Co, Cu, and Ni, distinguish the Buckeye deposit from many high-temperature hydrothermal deposits and hydrogenous or diagenetic manganese and ferromanganese nodules and pavements. This chemical signature suggests that ore deposition was related to fluids from the sediment column and seawater. Tungsten is associated exclusively with gageite, in concentrations as high as 80 parts per million. The source of the manganese is unknown; because basalts do not occur near the deposit, it was probably manganese leached from the sediment column by reducing solutions. Low concentrations of calcium

  20. Photo-induced reactions in the ion-molecule complex Mg+-OCNC2H5

    NASA Astrophysics Data System (ADS)

    Sun, Ju-Long; Liu, Haichuan; Han, Ke-Li; Yang, Shihe

    2003-06-01

    Ion-molecule complexes of magnesium cation with ethyl isocyanate were produced in a laser-ablation supersonic expansion nozzle source. Photo-induced reactions in the 1:1 complexes have been studied in the spectral range of 230-410 nm. Photodissociation mass spectrometry revealed the persistent product Mg+ from nonreactive quenching throughout the entire wavelength range. As for the reactive channels, the photoproducts, Mg+OCN and C2H5+, were produced only in the blue absorption band of the complex with low yields. The action spectrum of Mg+(OCNC2H5) consists of two pronounced peaks on the red and blue sides of the Mg+ 32P←32S atomic transition. The ground state geometry of Mg+-OCNC2H5 was fully optimized at B3LYP/6-31+G** level by using GAUSSIAN 98 package. The calculated absorption spectrum of the complex using the optimized structure of its ground state agrees well with the observed action spectrum. Photofragment branching fractions of the products are almost independent of the photolysis photon energy for the 3Px,y,z excitations. The very low branching ratio of reactive products to nonreactive fragment suggests that evaporation is the main relaxation pathway in the photo-induced reactions of Mg+(OCNC2H5).

  1. FLUID EVOLUTION AND MINERAL REACTIONS DURING SHEAR ZONE FORMATION AT NUSFJORD, LOFOTEN, NORWAY (Invited)

    NASA Astrophysics Data System (ADS)

    Kullerud, K.

    2009-12-01

    At Nusfjord in Lofoten, Norway, three 0.3 - 3 m thick shear zones occur in a gabbro-anorthosite. During deformation, the shear zones were infiltrated by a hydrous fluid enriched in Cl. In the central parts of the shear zones, fluid-rock interaction resulted in complete break-down of the primary mafic silicates. Complete hydration of these minerals to Cl-free amphibole and biotite suggests that the hydrous fluid was present in excess during deformation in these parts of the shear zones. Along the margins of the shear zones, however, the igneous mafic silicates (Cpx, Bt, Opx) were only partly overgrown by hydrous minerals. Here, Cl-enriched minerals (Amph, Bt, Scp, Ap) can be observed. Amphibole shows compositions covering the range 0.1 - 4.0 wt % Cl within single thin sections. Mineral textures and extreme compositional variations of the Cl-bearing minerals indicate large chemical gradients of the fluid phase. Relics of primary mafic silicates and compositionally zoned reaction coronas around primary mafic silicates suggest that the free fluid was totally consumed before the alteration of the primary phases were completed. The extreme variations in the Cl-content of amphibole are inferred to monitor a gradual desiccation of the Cl-bearing grain-boundary fluid during fluid-mineral reactions accordingly: 1) The first amphibole that formed during the reactions principally extracted water from the fluid, resulting in a slight increase in the Cl content of the fluid. 2) Continued amphibole-forming reactions resulted in gradual consumption of the free fluid phase, principally by extracting water from the fluid, resulting in an increase in its Cl-content. Higher Cl-content of the fluid resulted in higher Cl-content of the equilibrium amphibole. 3) The most Cl-enriched amphibole (4 wt % Cl) formed in equilibrium with the last volumes of the grain-boundary fluid, which had evolved to a highly saline solution. Mineral reactions within a 1-2 thick zone of the host rock along

  2. An illustration of the complexity of continent formation

    NASA Technical Reports Server (NTRS)

    Burke, Kevin

    1988-01-01

    It was pointed out that a consensus may be emerging in crustal growth models, considering the clustering of most growth curves and their uncertainties. Curves most distant from this clustering represent models involving extensive recycling of continental material back into the mantle, but the author wondered if geochemical signatures for this would be recognizable considering the lack of evidence from seismic tomography for discrete mantle reservoirs, and the likelihood of core-mantle interaction based on recent high pressure experiments. Unreactivated Archean rocks represent only 2 percent of present continental area, and the author was uncomfortable about basing inferences on what the early Earth was like on such a small amount of information. He feels that the hypothesis of continental assembly that needs testing is that of banging together of island arcs, such as in Indonesia today. As an example of how complex this process can be, the author described the geology of the Caribbean arc system, which shows evidence for reversals of subduction polarity, numerous collisional events, and substantial strike-slip movements. It seemed unlikely to the author that Archean examples would have been less complicated.

  3. Factors leading to the formation of arc cloud complexes

    NASA Technical Reports Server (NTRS)

    Welshinger, Mark John; Brundidge, Kenneth C.

    1987-01-01

    A total of 12 mesoscale convective systems (MCSs) were investigated. The duration of the gust front, produced by each MCS, was used to classify the MCSs. Category 1 MCSs were defined as ones that produced a gust front and the gust front lasted for more than 6 h. There were 7 category 1 MCSs in the sample. Category 2 MCSs were defined as ones that produced a gust front and the gust front lasted for 6 h or less. There were 4 category 2 MCSs. The MCS of Case 12 was not categorized because the precipitation characteristics were similar to a squall line, rather than an MCS. All of the category 1 MCSs produced arc cloud complexes (ACCs), while only one of the category 2 MCSs produced an ACC. To determine if there were any differences in the characteristics between the MCSs of the two categories, composite analyses were accomplished. The analyses showed that there were significant differences in the characteristics of category 1 and 2 MCSs. Category 1 MCSs, on average, had higher thunderstorm heights, greater precipitation intensities, colder cloud top temperatures and produced larger magnitudes of surface divergence than category 2 MCSs.

  4. Oxidative peptide /and amide/ formation from Schiff base complexes

    NASA Technical Reports Server (NTRS)

    Strehler, B. L.; Li, M. P.; Martin, K.; Fliss, H.; Schmid, P.

    1982-01-01

    One hypothesis of the origin of pre-modern forms of life is that the original replicating molecules were specific polypeptides which acted as templates for the assembly of poly-Schiff bases complementary to the template, and that these polymers were then oxidized to peptide linkages, probably by photo-produced oxidants. A double cycle of such anti-parallel complementary replication would yield the original peptide polymer. If this model were valid, the Schiff base between an N-acyl alpha mino aldehyde and an amino acid should yield a dipeptide in aqueous solution in the presence of an appropriate oxidant. In the present study it is shown that the substituted dipeptide, N-acetyl-tyrosyl-tyrosine, is produced in high yield in aqueous solution at pH 9 through the action of H2O2 on the Schiff-base complex between N-acetyl-tyrosinal and tyrosine and that a great variety of N-acyl amino acids are formed from amino acids and aliphatic aldehydes under similar conditions.

  5. Interferogram formation in the presence of complex and large deformation

    USGS Publications Warehouse

    Yun, S.-H.; Zebker, H.; Segall, P.; Hooper, A.; Poland, M.

    2007-01-01

    Sierra Negra volcano in Isabela island, Gala??pagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a "rubber-sheeting" SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra. Copyright 2007 by the American Geophysical Union.

  6. DHA- Rich Fish Oil Improves Complex Reaction Time in Female Elite Soccer Players

    PubMed Central

    Guzmán, José F.; Esteve, Hector; Pablos, Carlos; Pablos, Ana; Blasco, Cristina; Villegas, José A.

    2011-01-01

    Omega-3 fatty acids (n-3) has shown to improve neuromotor function. This study examined the effects of docosahexaenoic acid (DHA) on complex reaction time, precision and efficiency, in female elite soccer players. 24 players from two Spanish female soccer Super League teams were randomly selected and assigned to two experimental groups, then administered, in a double-blind manner, 3.5 g·day-1 of either DHA-rich fish oil (FO =12) or olive oil (OO = 12) over 4 weeks of training. Two measurements (pre- and post-treatment) of complex reaction time and precision were taken. Participants had to press different buttons and pedals with left and right hands and feet, or stop responding, according to visual and auditory stimuli. Multivariate analysis of variance displayed an interaction between supplement administration (pre/post) and experimental group (FO/OO) on complex reaction time (FO pre = 0.713 ± 0.142 ms, FO post = 0.623 ± 0.109 ms, OO pre = 0.682 ± 1.132 ms, OO post = 0.715 ± 0.159 ms; p = 0.004) and efficiency (FO pre = 40.88 ± 17.41, FO post = 57.12 ± 11.05, OO pre = 49.52 ± 14.63, OO post = 49. 50 ± 11.01; p = 0.003). It was concluded that after 4 weeks of supplementation with FO, there was a significant improvement in the neuromotor function of female elite soccer players. Key points The results obtained from the study suggest that supplementation with DHA produced perceptual-motor benefits in female elite athletes. DHA could be a beneficial supplement in sports where decision making and reaction time efficiency are of importance. PMID:24149875

  7. Ligand Exchange Reaction of Au(I) R-N-Heterocyclic Carbene Complexes with Cysteine.

    PubMed

    Dos Santos, H F; Vieira, M A; Sánchez Delgado, G Y; Paschoal, D

    2016-04-14

    The chemotherapy with gold complexes has been attempted since the 90s after the clinical success of auranofin, a gold(I) coordination complex. Currently, the organometallics compounds have shown promise in cancer therapy, mainly in those complexes containing N-heterocylic carbenes (NHC) as a ligand. The present study shows a kinetic analysis of the reaction of six alkyl-substituted NHC with cysteine (Cys), which is taken as an important bionucleophile representative. The first and second ligand exchange processes were analyzed with the complete description of the mechanism and energy profiles. For the first reaction step, which is the rate-limiting step of the whole substitution reaction, the activation enthalpy follows the order 1/Me2 < 2/Me,Et < 4/n-Bu2 < 3/i-Pr2 < 6/Cy2 < 5/t-Bu2, which is fully explained by steric and electronic features. From a steric point of view, the previous reactivity order is correlated with the r(Au-S) calculated for the transition state structures where S is the sulfur ligand from the Cys entering group. This means that longer r(Au-S) leads to higher activation enthalpy and is consistent with the effectiveness of gold shielding from nucleophile attack by bulkier alkyl-substituted NHC ligand. When electronic effect was addressed we found that higher activation barrier was predicted for strongly electron-donating NHC ligand, represented by the eigenvalue of σ-HOMO orbital of the free ligands. The molecular interpretation of the electronic effects is that strong donating NHC forms strong metal-ligand bond. For the second reaction step, similar structure-reactivity relationships were obtained, however the activation energies are less sensitive to the structure.

  8. Lewis acid-water/alcohol complexes as hydrogen atom donors in radical reactions.

    PubMed

    Povie, Guillaume; Renaud, Philippe

    2013-01-01

    Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative.

  9. Copper complexes as catalyst precursors in the electrochemical hydrogen evolution reaction.

    PubMed

    Kügler, Merle; Scholz, Julius; Kronz, Andreas; Siewert, Inke

    2016-04-28

    Herein, we report the synthesis and species distribution of copper(ii) complexes based on two different ligand scaffolds and the application of the two complexes in the electrochemical proton reduction catalysis. The ligands bind to one or two copper(II) ions and the pH-dependent mono/dinuclear equilibrium depends on the steric bulk of the ligands. The two water soluble copper(II) complexes were investigated for their activities in the electrochemical hydrogen evolution reaction (HER). In both complexes the copper(ii) ions have a N4-coordination environment composed of N-heterocycles, although in different coordination geometries (SPY-5 and TBPY-5). The solutions of the complexes were highly active catalysts in water at acidic pH but the complexes decompose under catalytic conditions. They act as precursors for highly active copper(0) and Cu2O deposits at the electrode surface, which are in turn the active catalysts. The absence or presence of the ligands has neither an influence on the catalytic activity of the solutions nor an influence on the activity of the deposit formed during controlled potential electrolysis. Finally, we can draw some conclusions on the stability of copper catalysts in the aqueous electrochemical HER.

  10. Native Mass Spectrometry Characterizes the Photosynthetic Reaction Center Complex from the Purple Bacterium Rhodobacter sphaeroides

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Harrington, Lucas B.; Lu, Yue; Prado, Mindy; Saer, Rafael; Rempel, Don; Blankenship, Robert E.; Gross, Michael L.

    2017-01-01

    Native mass spectrometry (MS) is an emerging approach to study protein complexes in their near-native states and to elucidate their stoichiometry and topology. Here, we report a native MS study of the membrane-embedded reaction center (RC) protein complex from the purple photosynthetic bacterium Rhodobacter sphaeroides. The membrane-embedded RC protein complex is stabilized by detergent micelles in aqueous solution, directly introduced into a mass spectrometer by nano-electrospray (nESI), and freed of detergents and dissociated in the gas phase by collisional activation. As the collision energy is increased, the chlorophyll pigments are gradually released from the RC complex, suggesting that native MS introduces a near-native structure that continues to bind pigments. Two bacteriochlorophyll a pigments remain tightly bound to the RC protein at the highest collision energy. The order of pigment release and their resistance to release by gas-phase activation indicates the strength of pigment interaction in the RC complex. This investigation sets the stage for future native MS studies of membrane-embedded photosynthetic pigment-protein and related complexes.

  11. The C(3P) + NH3 reaction in interstellar chemistry. I. Investigation of the product formation channels

    SciTech Connect

    Bourgalais, Jeremy; Capron, Michael; Kailasanathan, Ranjith Kumar Abhinavam; Osborn, David L.; Hickson, Kevin M.; Loison, Jean -Christophe; Wakelam, Valentine; Goulay, Fabien; Picard, Sebastien D. Le

    2015-10-13

    The product formation channels of ground state carbon atoms, C(3P), reacting with ammonia, NH3, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C + NH3 reaction. In addition, H-atom formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H2CN production channel represents 100% of the product yield for this reaction. As a result, kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.

  12. THE C({sup 3}P) + NH{sub 3} REACTION IN INTERSTELLAR CHEMISTRY. I. INVESTIGATION OF THE PRODUCT FORMATION CHANNELS

    SciTech Connect

    Bourgalais, Jérémy; Capron, Michael; Picard, Sébastien D. Le; Kailasanathan, Ranjith Kumar Abhinavam; Goulay, Fabien; Osborn, David L.; Hickson, Kevin M.; Loison, Jean-Christophe; Wakelam, Valentine E-mail: fabien.goulay@mail.wvu.edu

    2015-10-20

    The product formation channels of ground state carbon atoms, C({sup 3}P), reacting with ammonia, NH{sub 3}, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C + NH{sub 3} reaction. In addition, H-atom formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H{sub 2}CN production channel represents 100% of the product yield for this reaction. Kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.

  13. Monopropionate analogues of DOTA4- and DTPA5-: kinetics of formation and dissociation of their lanthanide(III) complexes.

    PubMed

    Balogh, Edina; Tripier, Raphaël; Fousková, Petra; Reviriego, Felipe; Handel, Henri; Tóth, Eva

    2007-08-28

    The replacement of an acetate function of the macrocyclic DOTA4-(DO3A-Nprop4-) or the acyclic DTPA5- in terminal position (DTTA-Nprop5-) has been recently shown to result in a significant increase of the water exchange rate on the Gd3+ complexes, which makes these chelates potential contrast agents for MRI applications. Here, two novel and straightforward synthetic routes to H4DO3A-Nprop are described. Protonation constants of DO3A-Nprop4- and stability constants with several alkaline earth and transition metal ions have been determined by potentiometry. For each metal, the thermodynamic stability constant is decreased in comparison to the DOTA chelates. The formation reaction of LnDO3A-Nprop- complexes (Ln=Ce, Gd and Yb) proceeds via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH- catalyzed process. The stability of the LnH2DO3A-Nprop* intermediates is similar to those reported for the corresponding DOTA analogues. The rate constants of the OH- catalyzed deprotonation step increase with decreasing lanthanide ion size, and are slightly higher than for DOTA complexes. The kinetic inertness of GdDTTA-Nprop2- was characterized by the rates of its exchange reactions with Zn2+ and Eu3+. The rate of the reaction between GdDTTA-Nprop2- and Zn2+ increases with Zn2+ concentration, while it is independent of pH, implying that the exchange takes place predominantly via direct attack of the metal ion on the complex. In the Eu3+ exchange, the rate decreases with increasing concentration of the exchanging ion which is accounted for by the transitional formation of a dinuclear GdDTTA-NpropEu+ species. The kinetic inertness of the monopropionate GdDTTA-Nprop2- is decreased in comparison to GdDTPA2-: all rate constants, characterizing the dissociation reaction via either proton- or metal-catalyzed pathways being higher by 1-2 orders of magnitude. Similarly, a study of the acid-catalyzed dissociation of the

  14. Relativistic effect on enthalpy of formation for transition-metal complexes

    NASA Astrophysics Data System (ADS)

    Nakajima, Yuya; Seino, Junji; Nakai, Hiromi

    2017-04-01

    This Letter examines the enthalpy of formation for 12 transition metal diatomic molecules and 23 transition metal complexes from the viewpoint of effect of the relativistic effect by using the infinite-order Douglas-Kroll-Hess method with the local unitary transformation and three types of pseudopotentials for several levels of theory. The spin-orbit effect contribution to the enthalpy of formation is more than 10 kcal/mol for third transition metal complexes. Frozen orbital approximation at the outermost orbitals in pseudopotential methods shows a contribution to the enthalpy of formation that is more than two times larger than those of inner core orbitals.

  15. Complex dynamic behavior in the bromate-oxalic acid-acetone-Mn(II) oscillating reaction in a continuous stirred tank reactor (CSTR)

    NASA Astrophysics Data System (ADS)

    Silva, Lucyane C.; Faria, Roberto B.

    2007-05-01

    The oscillating reaction bromate-oxalic acid-acetone-Mn(II)-sulfuric acid was observed for the first time in a CSTR at 20 °C. Depending on the bromate concentrations and flow rate, the system showed large amplitude oscillations, two kinds of mixed mode oscillations, quasiperiodicity and bursts of large amplitude oscillations, all mapped in a phase diagram. More complex behavior was favored at low bromate concentrations. The system without acetone was discovered to oscillate too, but the more complex patterns were not seen, indicating that acetone is implied in their formation.

  16. Time-dependent insulin oligomer reaction pathway prior to fibril formation: cooling and seeding.

    PubMed

    Sorci, Mirco; Grassucci, Robert A; Hahn, Ingrid; Frank, Joachim; Belfort, Georges

    2009-10-01

    The difficulty in identifying the toxic agents in all amyloid-related diseases is likely due to the complicated kinetics and thermodynamics of the nucleation process and subsequent fibril formation. The slow progression of these diseases suggests that the formation, incorporation, and/or action of toxic agents are possibly rate limiting. Candidate toxic agents include precursors (some at very low concentrations), also called oligomers and protofibrils, and the fibrils. Here, we investigate the kinetic and thermodynamic behavior of human insulin oligomers (imaged by cryo-EM) under fibril-forming conditions (pH 1.6 and 65 degrees C) by probing the reaction pathway to insulin fibril formation using two different types of experiments-cooling and seeding-and confirm the validity of the nucleation model and its effect on fibril growth. The results from both the cooling and seeding studies confirm the existence of a time-changing oligomer reaction process prior to fibril formation that likely involves a rate-limiting nucleation process followed by structural rearrangements of intermediates (into beta-sheet rich entities) to form oligomers that then form fibrils. The latter structural rearrangement step occurs even in the absence of nuclei (i.e., with added heterologous seeds). Nuclei are formed at the fibrillation conditions (pH 1.6 and 65 degrees C) but are also continuously formed during cooling at pH 1.6 and 25 degrees C. Within the time-scale of the experiments, only after increasing the temperature to 65 degrees C are the trapped insulin nuclei and resultant structures able to induce the structural rearrangement step and overcome the energy barrier to form fibrils. This delay in fibrillation and accumulation of nuclei at low temperature (25 degrees C) result in a decrease in the mean length of the fibers when placed at 65 degrees C. Fits of an empirical model to the data provide quantitative measures of the delay in the lag-time during the nucleation process and

  17. Time-dependent insulin oligomer reaction pathway prior to fibril formation: Cooling and seeding

    PubMed Central

    Sorci, Mirco; Grassucci, Robert A.; Hahn, Ingrid; Frank, Joachim; Belfort, Georges

    2009-01-01

    The difficulty in identifying the toxic agents in all amyloid-related diseases is likely due to the complicated kinetics and thermodynamics of the nucleation process and subsequent fibril formation. The slow progression of these diseases suggests that the formation, incorporation and/or action of toxic agents is possibly rate limiting. Candidate toxic agents include precursors (some at very low concentrations), also called oligomers and protofibrils, and the fibrils. Here, we investigate the kinetic and thermodynamic behavior of human insulin oligomers (imaged by cryo-EM) under fibril forming conditions (pH 1.6 and 65°C) by probing the reaction pathway to insulin fibril formation using two different types of experiments – cooling and seeding – and confirm the validity of the nucleation model and its effect on fibril growth. The results from both the cooling and seeding studies confirm the existence of a time-changing oligomer reaction process prior to fibril formation that likely involves a rate-limiting nucleation process followed by structural rearrangements of intermediates (into β-sheet rich entities) to form oligomers that then form fibrils. The latter structural rearrangement step occurs even in the absence of nuclei (i.e. with added heterologous seeds). Nuclei are formed at the fibrillation conditions (pH 1.6 and 65°C) but are also continuously formed during cooling at pH 1.6 and 25°C. Within the time-scale of the experiments, only after increasing the temperature to 65°C are the trapped insulin nuclei and resultant structures able to induce the structural rearrangement step and overcome the energy barrier to form fibrils. This delay in fibrillation and accumulation of nuclei at low temperature (25°C), result in a decrease in the mean length of the fibers when placed at 65°C. Fits of an empirical model to the data provide quantitative measures of the delay in the lag-time during the nucleation process and subsequent reduction in fibril growth rate

  18. The α-Effect and Competing Mechanisms: The Gas-Phase Reactions of Microsolvated Anions with Methyl Formate

    NASA Astrophysics Data System (ADS)

    Thomsen, Ditte L.; Nichols, Charles M.; Reece, Jennifer N.; Hammerum, Steen; Bierbaum, Veronica M.

    2013-12-01

    The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase SN2 reactions of the microsolvated HOO-(H2O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the α-effect as we compare the gas-phase reactivity of the microsolvated α-nucleophile HOO-(H2O) with that of microsolvated normal alkoxy nucleophiles, RO-(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO-(H2O) towards methyl formate, and clearly demonstrate the presence of an overall α-effect for the reactions of the microsolvated α-nucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the SN2 and BAC2 reactivity compared with the unsolvated analogs. HOO-(H2O) reacts with methyl formate exclusively via the BAC2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the BAC2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the BAC2 reaction in a way that continuously stabilizes the negative charge throughout the reaction.

  19. Reactions between vanadium ions and biogenic reductants of tunicates: Spectroscopic probing for complexation and redox products in vitro

    SciTech Connect

    Ryan, D.E.; Grant, K.B.; Nakanishi, K.

    1996-07-02

    Several species of marine tunicates store oxygen-sensitive V{sup III} in blood cells. A sensitive colorimetric V{sup III} assay was used t survey the leading candidates for the native reducing agent of vanadate in tunicates (i.e., An-type tunichromes, glutathione, NADPH, and H{sub 2}S) in reactions with V{sup V} or V{sup IV} ions under anaerobic, aqueous conditions at acidic or neutral pH. Except for the case of An-1 and V{sup V} ions in pH 7 buffer, the assay results for the biogenic reducing agents clearly showed that appreciable quantities of V{sup III} products were not generated under the conditions tested. Therefore, the assay results place new limits on hypothetical mechanisms of V{sup III} formation in vivo. For reactions between An-1 and V{sup V} ions in pH 7 buffer, low levels of V{sup III} products could not be ruled out because of an interfering peak in the colorimetric assays. For similar reactions between V{sup V} ions and An-1, or an An-1,2 mixture, in mildly to moderately basic media, the product mixtures precipitated as greenish black solids. Analyses of the precipitated V/An mixtures using vanadium K-edge X-ray absorption spectroscopy (XAS) showed that the major products were tris(catecholate)-type V{sup IV} complexes (65 {plus_minus} 6%) and bis(catecholate)-type V{sup IV}O complexes (20 {plus_minus} 4%). XAS analysis of the V/An-1 product mixture also provided evidence of a minor V{sup III} component (9 {plus_minus} 5% of total V), notable for possible relevance to tunicate biochemistry. The combined results of XAS studies, spectrophotometric studies, and EPR studies consistently establish that reactions between tunichromes (Mm-1 or An-1) and V{sup V} ions generate predominantly V{sup IV}-tunichrome complexes in neutral to moderately basic aqueous media. 53 refs., 4 figs., 3 tabs.

  20. Rotational effects in complex-forming bimolecular substitution reactions: A quantum-mechanical approach

    NASA Astrophysics Data System (ADS)

    Hennig, Carsten; Schmatz, Stefan

    2009-12-01

    The quantum dynamics of the complex-forming SN2 reaction Cl-+CH3Br→ClCH3+Br- is studied with emphasis on rotational effects. The pseudotriatomic system Cl-Me-Br is treated with a correspond