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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. Reversible Formation and Transmetalation of Schiff-Base Complexes in Subcomponent Self-Assembly Reactions.

    PubMed

    Lewing, Dennis; Koppetz, Hannah; Hahn, F Ekkehardt

    2015-08-01

    Dinuclear complexes [Zn2(NS,NS)2] 3 and [Ni2(NS,NS)2] 6 bearing Schiff-base ligands featuring two NS donor groups were obtained in subcomponent self-assembly reactions using nickel or zinc as template metals. Several transmetalation reactions starting from 3 or 6 yielded the complexes [Pd2(NS,NS)2] 4 and [Co2(NS,NS)2] 5, and their molecular structures were determined by X-ray diffraction. Starting from the mononuclear complex [Ni(NS/NOH)2] 9 featuring a coordinated NS Schiff base and a free NOH Schiff base, completely reversible thermodynamically controlled imine bond formation was observed leading to complex [Ni2(NS,NS)2] 6 and the free Schiff -base ligand NOH,NOH 10.

  4. Formation of stable sessile interstitial complexes in reactions between glissile dislocation loops in bcc Fe

    NASA Astrophysics Data System (ADS)

    Terentyev, Dmitry; Malerba, Lorenzo; Klaver, Peter; Olsson, Par

    2008-12-01

    Clusters of self-interstitial atoms (loops) are commonly observed in the microstructure of irradiated metals. These clusters can be formed directly in high-energy displacement cascades or by growth as a result of interaction between individual self interstitials. The majority of these clusters have features of glissile dislocation loops and migrate by fast one-dimensional glide. In this paper, we present results of a systematic molecular dynamics (MD) study of reactions involving glissile interstitial loops. By the example of bcc iron we demonstrate that the reactions can produce a number of specific, stable microstructural features, with different properties compared to the reactants. Namely, the reactions between the most common glissile clusters of <1 1 1> crowdions can result in coarsening or formation of immobile self interstitial complexes. The coarsening leads to a decrease of the total dislocation line length and therefore is favourable. The structure and stability of the junction formed in the reactions has been studied using many-body potentials and density functional theory (DFT) techniques. No evidence of the formation of a <1 0 0> loop from two glissile <1 1 1> clusters was found among the studied reactions. The immobile self interstitial complexes that form as a result of these reaction have, however, high binding energies, of the order of tens of eV, implying that a relatively long life time should be assigned to the resulting configurations and therefore that such objects are expected to contribute to the evolution of the microstructure under irradiation.

  5. Direct observation of unstable reaction intermediates by acid-base complex formation.

    PubMed

    Ohashi, Yuji

    2013-06-01

    The structures of several unstable or metastable reaction intermediates that were photoproduced in crystals were analyzed by using X-ray techniques. The presence of enough void space around the reactive group(s) is an essential factor for the reaction to occur with retention of the single-crystal form. To expand the void space, an acid group (COOH) was substituted onto the reactant molecule and acid-base complex crystals were prepared with several amines, such as dibenzylamine and dicyclohexylamine. Following the formation of such acid-base complexes in crystals, the metastable structures of nitrenes and red species of photochromic salicylideneanilines have been successfully analyzed by using X-ray techniques. Moreover, the structure of a Pt complex anion in the excited state has been analyzed, which formed acid-base complex crystals with various alkylammonium cations. The formation of acid-base complexes will be a powerful tool for directly observing the structure of unstable or metastable reaction intermediates by using X-ray techniques.

  6. Nucleophilicity and P-C Bond Formation Reactions of a Terminal Phosphanido Iridium Complex.

    PubMed

    Serrano, Ángel L; Casado, Miguel A; Ciriano, Miguel A; de Bruin, Bas; López, José A; Tejel, Cristina

    2016-01-19

    The diiridium complex [{Ir(ABPN2)(CO)}2(μ-CO)] (1; [ABPN2](-) = [(allyl)B(Pz)2(CH2PPh2)](-)) reacts with diphenylphosphane affording [Ir(ABPN2)(CO)(H) (PPh2)] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the terminal phosphanido lone pair to the HOMO of 2, indicating nucleophilic character of this ligand, which is evidenced by reactions of 2 with typical electrophiles such as H(+), Me(+), and O2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir(ABPN2)(CO)(H)(PPh2CH2CO2Me)][PF6] ([6]PF6) or [Ir(ABPN2)(CO)(Cl)(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving P-C bond formation, depending on the reaction conditions. New complexes having iridacyclophosphapentenone and iridacyclophosphapentanone moieties result from reactions of 2 with dimethyl acetylenedicarboxylate and dimethyl maleate, respectively, as a consequence of a further incorporation of the carbonyl ligand. In this line, the terminal alkyne methyl propiolate gave a mixture of a similar iridacyclophosphapentanone complex and [Ir(ABPN2){CH═C(CO2Me)-CO}{PPh2-CH═CH(CO2Me)}] (10), which bears the functionalized phosphane PPh2-CH═CH(CO2Me) and an iridacyclobutenone fragment. Related model reactions aimed to confirm mechanistic proposals are also studied.

  7. Kinetic and mechanistic studies on the formation and reactions of early-transition-metal-ketene complexes

    SciTech Connect

    Galante, J.M.; Bruno, J.W.; Hazin, P.N.; Folting, K.; Huffman, J.C.

    1988-05-01

    A series of complexes of vanadocene or molybdenocene with unsymmetrical ketenes were prepared, either by reaction of the various ketenes with vanadocene itself or by reaction with the molybdenocene phosphine complex (C/sub 5/H/sub 5/)/sub 2/Mo(PEt/sub 3/). All of the complexes exhibited the expected ketene C=O bonding mode, and all reactions were very specific in their formation of the facial isomer with metallocene fragment located on the side of the smaller ketene substituent. Kinetic studies were used to assess the sensitivity of the incoming vanadocene to steric and electronic effects, with the latter found to dominate. Kinetic studies and activation parameters for reaction of Cp/sub 2/Mo(PEt/sub 3/) with EtPhC=C=O indicated a second-order associative mechanism, proposed to involve a nucleophilic attack of the metal center on the ketene central carbon in the rate-limiting step. Lastly, reactions of the bound ketenes with nucleophiles (alkyllithiums or Grignard reagents) proceeded readily to either ketone or aldehyde enolates (the latter via transfer of a ..beta..-hydride from the alkyl); the clean production of only Z enolates from the unsymmetrical ketenes is indicate of a metal-mediated internal attack of nucleophile on the bound ketene.

  8. Formation of titanium(IV) transferrin by reaction of human serum apotransferrin with titanium complexes.

    PubMed

    Messori, L; Orioli, P; Banholzer, V; Pais, I; Zatta, P

    1999-01-15

    The reaction of human serum apotransferrin with titanium(IV) citrate under physiological conditions results in the formation of a specific bis-titanium(IV) transferrin adduct (Ti2Tf hereafter) with two titanium(IV) ions loaded at the iron binding sites. The same specific Ti2Tf complex is formed by reacting apotransferrin with titanium(III) chloride and exposing the sample to air. The derivative thus obtained was characterized by spectroscopic techniques, including absorption, UV difference, circular dichroism and 13C NMR spectroscopies, and shown to be stable within the pH range 5.5-9.0. Surprisingly, the reaction of apoTf with titanium(IV) nitrilotriacetate (NTA) does not lead to formation of appreciable amounts of Ti2Tf, even after long incubation times, although some weak interactions of Ti(IV)-NTA with apoTf are spectroscopically detected. Implications of the present results for a role of transferrin in the uptake, transport and delivery of soluble titanium(IV) compounds under physiological conditions are discussed. PMID:9928993

  9. 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)

  10. Formation of Complex Organics by Gas Phase and Intracluster Ion-Molecule Reactions Involving Acetylene and Hydrogen Cyanide

    NASA Astrophysics Data System (ADS)

    El-Shall, S.; Hamed, A.; Soliman, A. R.; Momoh, P. O.

    2011-05-01

    Many complex organics including polycyclic aromatic hydrocarbons are present in flames and combustion processes as well as in interstellar clouds and solar nebulae. Here, we present evidence for the formation of complex covalent organics by gas phase and intracluster reactions of the benzene, phenylium, pyridine, pyrimidine, phenylacetylene and benzonitrile cations with acetylene and hydrogen cyanide molecules. These reactions are studied using mass-selected ion mobility, chemical reactivity, collisional dissociation, and ab initio calculations. Measurements of collision cross sections in helium provide structural information on the adducts and allow probing structural changes at different temperatures (isomerization). We observed multiple additions of five acetylene molecules on the pyridine cation at room temperature. This is a remarkable result considering that only two acetylene molecules were added to the phenyl cation and no addition was observed on the benzene cation at room temperature. The experimental results are in full agreement with the ab initio calculations which predict that the first and second acetylenes add to the pyridine ion in barrierless, highly exothermic reactions. Similar reactions have been observed for the pyrimidine radical cation although the extent of the addition reactions is limited to only two acetylene molecules at room temperature. The results provide the first evidence for the incorporation of nitrogen in the formation cyclic hydrocarbons via the gas phase reactions of pyridine and pyrimidine ions with acetylene molecules. In addition, the formation of covalent adducts in the ionized acetylene/HCN system will be reported for the first time. Sequential reactions leading to the formation of pyridine and pyrimidine radical cations and higher adducts are observed over a wide range of temperature and pressure. The formation of these covalent adducts may represent a general class of addition reactions that can form complex

  11. 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.

  12. The Formation Of Glycerol Monodecanoate By A Dehydration Condensation Reaction: Increasing The Chemical Complexity Of Amphiphiles On The Early Earth

    NASA Astrophysics Data System (ADS)

    Apel, Charles L.; Deamer, David W.

    2005-08-01

    Dehydration/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into primitive cellular organisms. As a model of such reactions and to demonstrate this principle, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate (GMD). This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects of pH, divalent cation binding and osmotic stress. Experimental variables included temperature, water activity and hydrolysis of the resulting ester product, providing insights into the environmental conditions that would favor the formation and stability of this more evolved amphiphile. At temperatures exceeding 50 ∘C, the ester product formed even in the presence of bulk water, suggesting that the reaction occurs at the liquid interface of the two reactants and that the products segregate in the two immiscible layers, thereby reducing hydrolytic back reactions. This implies that esterification reactions were likely to be common in the prebiotic environment as reactants underwent cycles of wetting and drying on rare early landmasses at elevated temperatures

  13. 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.

  14. 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

    2016-09-01

    The gas-phase oxidation of doubly protonated peptides containing neutral basic residues to various products, including [M + H + O]+, [M - H]+, and [M - H - NH3]+, is demonstrated here via ion/ion reactions with periodate. It was previously demonstrated that periodate anions are capable of oxidizing disulfide bonds and methionine, tryptophan, and S-alkyl cysteine residues. However, in the absence of these easily oxidized sites, we show here that systems containing neutral basic residues can undergo oxidation. Furthermore, we show that these neutral basic residues primarily undergo different types of oxidation (e.g., hydrogen abstraction) reactions than those observed previously (i.e., oxygen transfer to yield the [M + H + O]+ species) upon gas-phase ion/ion reactions with periodate anions. This chemistry is illustrated with a variety of systems, including a series of model peptides, a cell-penetrating peptide containing a large number of unprotonated basic sites, and ubiquitin, a roughly 8.6 kDa protein.

  15. G protein activation by G protein coupled receptors: ternary complex formation or catalyzed reaction?

    PubMed

    Roberts, David J; Waelbroeck, Magali

    2004-09-01

    G protein coupled receptors catalyze the GDP/GTP exchange on G proteins, thereby activating them. The ternary complex model, designed to describe agonist binding in the absence of GTP, is often extended to G protein activation. This is logically unsatisfactory as the ternary complex does not accumulate when G proteins are activated by GTP. Extended models taking into account nucleotide binding exist, but fail to explain catalytic G protein activation. This review puts forward an enzymatic model of G protein activation and compares its predictions with the ternary complex model and with observed receptor phenomenon. This alternative model does not merely provide a new set of formulae but leads to a new philosophical outlook and more readily accommodates experimental observations. The ternary complex model implies that, HRG being responsible for efficient G protein activation, it should be as stable as possible. In contrast, the enzyme model suggests that although a limited stabilization of HRG facilitates GDP release, HRG should not be "too stable" as this might trap the G protein in an inactive state and actually hinder G protein activation. The two models also differ completely in the definition of the receptor "active state": the ternary complex model implies that the active state corresponds to a single active receptor conformation (HRG); in contrast, the catalytic model predicts that the active receptor state is mobile, switching smoothly through various conformations with high and low affinities for agonists (HR, HRG, HRGGDP, HRGGTP, etc.).

  16. Theoretical study on the transition-metal oxoboryl complex: M-BO bonding nature, mechanism of the formation reaction, and prediction of a new oxoboryl complex.

    PubMed

    Zeng, Guixiang; Sakaki, Shigeyoshi

    2012-04-16

    The Pt-BO bonding nature and the formation reaction of the experimentally reported platinum(II) oxoboryl complex, simplified to PtBr(BO)(PMe(3))(2), were theoretically investigated with the density functional theory method. The BO(-) ligand was quantitatively demonstrated to have extremely strong σ-donation but very weak d(π)-electron-accepting abilities. Therefore, it exhibits a strong trans influence. The formation reaction occurs through a four-center transition state, in which the B(δ+)-Br(δ-) polarization and the Br → Si and O p(π) → B p(π) charge-transfer interactions play key roles. The Gibbs activation energy (ΔG°(++)) and Gibbs reaction energy (ΔG°) of the formation reaction are 32.2 and -6.1 kcal/mol, respectively. The electron-donating bulky phosphine ligand is found to be favorable for lowering both ΔG°(++) and ΔG°. In addition, the metal effect is examined with the nickel and palladium analogues and MBrCl[BBr(OSiMe(3))](CO)(PR(3))(2) (M = Ir and Rh). By a comparison of the ΔG°(++) and ΔG° values, the M-BO (M = Ni, Pd, Ir, and Rh) bonding nature, and the interaction energy between [MBrCl(CO)(PR(3))(2)](+) and BO(-) with those of the platinum system, MBrCl(BO)(CO)(PR(3))(2) (M = Ir and Rh) is predicted to be a good candidate for a stable oxoboryl complex. PMID:22458310

  17. Complex formation reactions of lanthanum(III), cerium(III), thorium(IV), dioxouranyl(IV) complexes with tricine.

    PubMed

    Mohamed, Mahmoud M A

    2007-08-01

    Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules.

  18. Dinitrosyl iron complexes with cysteine. Kinetics studies of the formation and reactions of DNICs in aqueous solution.

    PubMed

    Pereira, José Clayston Melo; Iretskii, Alexei V; Han, Rui-Min; Ford, Peter C

    2015-01-14

    Kinetics studies provide mechanistic insight regarding the formation of dinitrosyl iron complexes (DNICs) now viewed as playing important roles in the mammalian chemical biology of the ubiquitous bioregulator nitric oxide (NO). Reactions in deaerated aqueous solutions containing FeSO4, cysteine (CysSH), and NO demonstrate that both the rates and the outcomes are markedly pH dependent. The dinuclear DNIC Fe2(μ-CysS)2(NO)4, a Roussin's red salt ester (Cys-RSE), is formed at pH 5.0 as well as at lower concentrations of cysteine in neutral pH solutions. The mononuclear DNIC Fe(NO)2(CysS)2(-) (Cys-DNIC) is produced from the same three components at pH 10.0 and at higher cysteine concentrations at neutral pH. The kinetics studies suggest that both Cys-RSE and Cys-DNIC are formed via a common intermediate Fe(NO)(CysS)2(-). Cys-DNIC and Cys-RSE interconvert, and the rates of this process depend on the cysteine concentration and on the pH. Flash photolysis of the Cys-RSE formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 5.0 solution led to reversible NO dissociation and a rapid, second-order back reaction with a rate constant kNO = 6.9 × 10(7) M(-1) s(-1). In contrast, photolysis of the mononuclear-DNIC species Cys-DNIC formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 10.0 solution did not labilize NO but instead apparently led to release of the CysS(•) radical. These studies illustrate the complicated reaction dynamics interconnecting the DNIC species and offer a mechanistic model for the key steps leading to these non-heme iron nitrosyl complexes.

  19. 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.

  20. 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

  1. 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.

  2. 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. PMID:27199083

  3. 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)

  4. The citric acid-Mn III,IVO 2(birnessite) reaction. Electron transfer, complex formation, and autocatalytic feedback

    NASA Astrophysics Data System (ADS)

    Wang, Yun; Stone, Alan T.

    2006-09-01

    Citrate released by plants, bacteria, and fungi into soils is subject to abiotic oxidation by MnO 2(birnessite), yielding 3-ketoglutarate, acetoacetate, and Mn II. Citrate loss and generation of products as a function of time all yield S-shaped curves, indicating autocatalysis. Increasing the citrate concentration decreases the induction period. The maximum rate ( rmax) along the reaction coordinate follows a Langmuir-Hinshelwood dependence on citrate concentration. Increases in pH decrease rmax and increase the induction time. Adding Mn II, Zn II, orthophosphate, or pyrophosphate at the onset of reaction decreases rmax. Mn II addition eliminates the induction period, while orthophosphate and pyrophosphate addition increase the induction period. These findings indicate that two parallel processes are responsible. The first, relatively slow process involves the oxidation of free citrate by surface-bound Mn III,IV, yielding Mn II and citrate oxidation products. The second process, which is subject to strong positive feedback, involves electron transfer from Mn II-citrate complexes to surface-bound Mn III,IV, generating Mn III-citrate and Mn II. Subsequent intramolecular electron transfer converts Mn III-citrate into Mn II and citrate oxidation products.

  5. Kinetics and thermodynamics of formation and electron-transfer reactions of Cu-O2 and Cu2-O2 complexes

    PubMed Central

    Fukuzumi, Shunichi; Karlin, Kenneth D.

    2012-01-01

    The kinetics and thermodynamics of formation of Cu(II)-superoxo (Cu-O2) complexes by the reaction of Cu(I) complexes with dioxygen (O2) and the reduction of Cu(II)-superoxo complexes to dinuclear Cu-peroxo complexes are discussed. In the former case, electron transfer from a Cu(I) complex to O2 occurs concomitantly with binding of O2•− to the corresponding Cu(II) species. This is defined as an inner-sphere Cu(II) ion-coupled electron transfer process. Electron transfer from another Cu(I) complex to preformed Cu(II)-superoxo complexes also occurs concomitantly with binding of the the Cu(II)-peroxo species with the Cu(II) species to produce the dinuclear Cu-peroxo (Cu2-O2) complexes. The kinetics and thermodynamics of outer-sphere electron-transfer reduction of Cu2-O2 complexes are also been discussed in light of the Marcus theory of outer-sphere electron transfer. PMID:23470920

  6. H-atom addition and abstraction reactions in mixed CO, H2CO and CH3OH ices - an extended view on complex organic molecule formation

    NASA Astrophysics Data System (ADS)

    Chuang, K.-J.; Fedoseev, G.; Ioppolo, S.; van Dishoeck, E. F.; Linnartz, H.

    2016-01-01

    Complex organic molecules (COMs) have been observed not only in the hot cores surrounding low- and high-mass protostars, but also in cold dark clouds. Therefore, it is interesting to understand how such species can be formed without the presence of embedded energy sources. We present new laboratory experiments on the low-temperature solid state formation of three complex molecules - methyl formate (HC(O)OCH3), glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) - through recombination of free radicals formed via H-atom addition and abstraction reactions at different stages in the CO→H2CO→CH3OH hydrogenation network at 15 K. The experiments extend previous CO hydrogenation studies and aim at resembling the physical-chemical conditions typical of the CO freeze-out stage in dark molecular clouds, when H2CO and CH3OH form by recombination of accreting CO molecules and H-atoms on ice grains. We confirm that H2CO, once formed through CO hydrogenation, not only yields CH3OH through ongoing H-atom addition reactions, but is also subject to H-atom-induced abstraction reactions, yielding CO again. In a similar way, H2CO is also formed in abstraction reactions involving CH3OH. The dominant methanol H-atom abstraction product is expected to be CH2OH, while H-atom additions to H2CO should at least partially proceed through CH3O intermediate radicals. The occurrence of H-atom abstraction reactions in ice mantles leads to more reactive intermediates (HCO, CH3O and CH2OH) than previously thought, when assuming sequential H-atom addition reactions only. This enhances the probability to form COMs through radical-radical recombination without the need of UV photolysis or cosmic rays as external triggers.

  7. The formation of glycerol monodecanoate by a dehydration/condensation reaction: increasing the chemical complexity of amphiphiles on the early earth

    NASA Astrophysics Data System (ADS)

    Apel, C. L.; Deamer, D. W.

    Dehydration/condensation reactions between organic molecules in the prebiotic environment increased the inventory and complexity of organic compounds available for self-assembly into protocellular structures. As a model of such reactions, we have investigated the esterification reaction between glycerol and decanoic acid that forms glycerol monodecanoate. This amphiphile enhances robustness of self-assembled membranous structures of carboxylic acids to the potentially disruptive effects of pH, divalent cation binding and osmotic stress. Experimental variables included temperature, water activity and hydrolysis of the resulting ester product, providing insights into the environmental conditions that would favour the formation and stability of this more evolved amphiphile. At temperatures exceeding 500 C, the ester product formed even in the presence of bulk water, suggesting that the reaction occurs at the liquid interface of the two reactants and that the products segregate in the two immiscible layers, thereby reducing the rate of the hydrolytic back reaction. This suggests that esterification reactions were likely to commonly occur in the prebiotic environment as available reactants underwent cycles of wetting and drying on early landmasses at elevated temperatures.

  8. Characterising Complex Enzyme Reaction Data

    PubMed Central

    Rahman, Syed Asad; Thornton, Janet M.

    2016-01-01

    The relationship between enzyme-catalysed reactions and the Enzyme Commission (EC) number, the widely accepted classification scheme used to characterise enzyme activity, is complex and with the rapid increase in our knowledge of the reactions catalysed by enzymes needs revisiting. We present a manual and computational analysis to investigate this complexity and found that almost one-third of all known EC numbers are linked to more than one reaction in the secondary reaction databases (e.g., KEGG). Although this complexity is often resolved by defining generic, alternative and partial reactions, we have also found individual EC numbers with more than one reaction catalysing different types of bond changes. This analysis adds a new dimension to our understanding of enzyme function and might be useful for the accurate annotation of the function of enzymes and to study the changes in enzyme function during evolution. PMID:26840640

  9. Characterising Complex Enzyme Reaction Data.

    PubMed

    Dönertaş, Handan Melike; Martínez Cuesta, Sergio; Rahman, Syed Asad; Thornton, Janet M

    2016-01-01

    The relationship between enzyme-catalysed reactions and the Enzyme Commission (EC) number, the widely accepted classification scheme used to characterise enzyme activity, is complex and with the rapid increase in our knowledge of the reactions catalysed by enzymes needs revisiting. We present a manual and computational analysis to investigate this complexity and found that almost one-third of all known EC numbers are linked to more than one reaction in the secondary reaction databases (e.g., KEGG). Although this complexity is often resolved by defining generic, alternative and partial reactions, we have also found individual EC numbers with more than one reaction catalysing different types of bond changes. This analysis adds a new dimension to our understanding of enzyme function and might be useful for the accurate annotation of the function of enzymes and to study the changes in enzyme function during evolution.

  10. 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.

  11. Cyclopentadienyl nickel(ii) N,C-chelating benzothiazolyl NHC complexes: synthesis, characterization and application in catalytic C-C bond formation reactions.

    PubMed

    Teo, Wei Jie; Wang, Zhe; Xue, Fei; Andy Hor, T S; Zhao, Jin

    2016-04-25

    Cyclopentadienyl (Cp) Ni(ii) complexes [CpNiL][PF6] containing hybrid N,C chelating benzothiazolyl NHC ligands (L1 = 1-(2-benzothiazolyl)-3-methylimidazol-2-ylidene, ; L2 = 1-(2-benzothiazolyl)-3-allylimidazol-2-ylidene, ; L3 = 1-(2-benzothiazolyl)-3-benzylimidazol-2-ylidene, ) have been synthesized and fully characterized. The catalytic activity of in some C-C bond formation reactions has been examined. They are efficient catalysts for the homo-coupling of benzyl bromide in the presence of MeMgCl at r.t. with good functional group tolerance. Complex is active in the catalytic oxidative homo-coupling of Grignard reagents with 1,2-dichloroethane as an oxidant at r.t. PMID:27011227

  12. Mechanisms of Reactions of Dihydrogen Complexes: Formation of trans-[RuH(H(2))(dppe)(2)](+) and Substitution of Coordinated Dihydrogen.

    PubMed

    Basallote, Manuel G.; Durán, Joaquín; Fernández-Trujillo, M. Jesús; Máñez, M. Angeles

    1999-11-01

    The reactions between cis-[RuH(2)(DPPE)(2)] and a number of acids in THF solution (DPPE = Ph(2)PCH(2)CH(2)PPh(2)) show biphasic kinetics, with initial formation of trans-[RuH(H(2))(DPPE)(2)](+) followed by slower substitution of coordinated dihydrogen by the anion of the acid. The formation of the dihydrogen complex is a second-order process that occurs with an inverse kinetic isotope effect and rate constants k(HX) strongly dependent on the nature of the acid. There is a linear correlation between the values of log k(HX) for cis-[RuH(2)(DPPE)(2)] and the related cis-[FeH(2)(PP(3))] [PP(3) = P(CH(2)CH(2)PPh(2))(3)] that leads to two parameters, S and R, that can be used as a measure of the selectivity and intrinsic reactivity of the dihydride toward acids. The possible contributions to the values of these parameters are discussed, especially the role of the isomerization of the starting complex and the basicity of the reacting species. The substitution of coordinated dihydrogen in trans-[RuH(H(2))(DPPE)(2)](+) occurs through a simple dissociative mechanism instead of the more complicated one previously proposed for substitutions in the analogous Fe complex; the mechanistic change is associated with the relative strength of the M-H(2) and M-P(chelate) bonds.

  13. Exhibition of the Brønsted acid-base character of a Schiff base in palladium(II) complex formation: lithium complexation, fluxional properties and catalysis of Suzuki reactions in water.

    PubMed

    Kumar, Rajnish; Mani, Ganesan

    2015-04-21

    The reaction of the dialdehyde N,N-di(α-formylpyrrolyl-α-methyl)-N-methylamine with two equiv. of 2,6-diisopropylaniline yielded two Schiff bases: bis(iminopyrrolylmethyl)amine () and its hydrolyzed monoimino compound () after column separation. The dimeric lithium complex [(HL)Li]2 () containing the monoanionic form of was obtained by treating with (n)BuLi. The presence of both proton donors and acceptors causes the diimino compound to undergo tautomerization to exhibit an amine-azafulvene structure, though the central amine nitrogen competes for a proton. As a result, in the presence of Pd(2+) ions, the cationic complex [Pd(Cl)(H2L)][Cl] () containing one pendant amine-azafulvene arm and the protonated central amine nitrogen was obtained. Its X-ray structure showed that the bond distances are reversed for the imino-pyrrole moiety relative to those in the structure of . However, the reaction of with [Pd(OAc)2] afforded the neutral complex [PdL] () containing the dianionic form of the ligand. The reaction of with [PdCl2(PhCN)2] yielded a zwitterionic complex [PdCl2(H2L')] () owing to the presence of the central amine nitrogen. The formation of these palladium complexes with the features mentioned above can be explained by invoking the Brønsted acid-base character of the Schiff base. Complex is fluxional owing to the up and down movements of the palladium square plane formed by two 5-membered palladacycles, which causes the interconversion of its enantiomers and is studied by the variable temperature (1)H NMR method. Furthermore, both complexes and are precatalysts for the Suzuki-Miyaura cross-coupling reaction in water. Sterically encumbered and electronically different substrates including activated aryl chlorides and benzyl halides gave the coupled products in very good yields. The reaction proceeds even at room temperature and in the presence of a large excess amount of mercury.

  14. 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. PMID:27518715

  15. 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.

  16. Co-formation of hydroperoxides and ultra-fine particles during the reactions of ozone with a complex VOC mixture under simulated indoor conditions

    NASA Astrophysics Data System (ADS)

    Fan, Zhihua; Weschler, Charles J.; Han, In-Kyu; Zhang, Junfeng (Jim)

    In this study we examined the co-formation of hydrogen peroxide and other hydroperoxides (collectively presented as H 2O 2*) as well as submicron particles, including ultra-fine particles (UFP), resulting from the reactions of ozone (O 3) with a complex mixture of volatile organic compounds (VOCs) under simulated indoor conditions. The VOC mixture contained 23 compounds, including two terpenes ( d-limonene and α-pinene), two unsaturated alkenes (1-decene and 1-octene), and 19 other saturated organic compounds. These compounds are commonly found in indoor air but their concentrations were higher than typical indoor levels. When O 3 was added to a 25-m 3 controlled environmental facility (CEF) containing the 23 VOC mixture, both H 2O 2* and submicron particles were formed. The 2-h average concentration of H 2O 2* was 1.89±0.30 ppb, and the average total particle number concentration was 46,000±12,000 particles cm -3. A small increase of UFP (0.02-0.1 μm) occurred 5 min after the O 3 addition (17 min after the VOC addition) and a sharp increase of UFP occurred 13 min after the O 3 addition, suggesting homogeneous nucleation. The delayed onset of this event might reflect the time required to achieve saturated concentrations of the condensable organics. When the 2 terpenes were removed from the O 3/23 VOCs mixture, no H 2O 2* or particles were formed, indicating that the reactions of O 3 with the two terpenes were the key processes contributing to the formation of H 2O 2* and submicron particles in the O 3/23 VOCs system. The present study confirmed the findings of a previous study carried out in a real-world office and generated new findings regarding co-formation of UFP. Through a comparative analysis of H 2O 2* yields under different reaction conditions, this study demonstrates that VOCs co-present with the terpenes and O 3 may play a role in producing H 2O 2*.

  17. 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.

  18. 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

  19. Modeling the complex bromate-iodine reaction.

    PubMed

    Machado, Priscilla B; Faria, Roberto B

    2009-05-01

    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. PMID:19361181

  20. In-Situ Formation of Cobalt-Phosphate Oxygen-Evolving Complex-Anchored Reduced Graphene Oxide Nanosheets for Oxygen Reduction Reaction

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.

  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. PMID:23877331

  2. Formation and interconversion of organo-cobalt complexes in reactions of cobalt(II) porphyrins with cyanoalkyl radicals and vinyl olefins.

    PubMed

    Peng, Chi-How; Li, Shan; Wayland, Bradford B

    2009-06-01

    Observation of the formation and interconversion of organo-cobalt complexes ((TMP)Co-R) is used to reveal mechanistic features in the living radical polymerization (LRP) of methyl acrylate (MA) mediated by cobalt porphyrins. Both dissociative and associative exchange of radicals in solution with organo-cobalt complexes contribute to controlling the radical polymerization. The sequence of organo-cobalt species formed during the induction period for the (TMP)Co-R mediated LRP of MA indicates that homolytic dissociation is a prominent pathway for the interconversion of organo-cobalt complexes which contrasts with the corresponding vinyl acetate (VAc) system where associative radical exchange totally dominates these processes. The dissociation equilibrium constant (K(d(333 K))) for organo-cobalt complexes formed in methyl acrylate polymerization ((TMP)Co-CH(CO(2)CH(3))CH(2)P) was estimated as 1.15 x 10(-10) from analysis of the polymerization kinetics and (1)H NMR. The ratio of the rate constants (333 K) for the cyanoisopropyl radical (*C(CH(3))(2)CN) adding with monomer (k(1)) to the process of transferring a hydrogen atom to (TMP)Co(II)* (k(2)) was evaluated for the methyl acrylate system as 2 x 10(-3) which is larger than that for vinyl acetate LRP (9 x 10(-5)). Kinetic analysis places the rate constant for associative radical interchange (333 K) at approximately 7 x 10(5) M(-1) s(-1). The larger radical stabilization energy and lower energy of the singly occupied molecular orbital (SOMO) for methyl acrylate based radicals (*CH(CO(2)CH(3))CH(2)P) compared to vinyl acetate contribute to the observed prominence of organo-cobalt homolytic dissociation and much smaller chain transfer which result in substantially better control for living radical polymerization of methyl acrylate than that observed for vinyl acetate.

  3. 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

    2013-01-01

    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. PMID:24362624

  4. Reactions of a tungsten-germylyne complex with α,β-unsaturated ketones: complete cleavage of the W≡Ge bond and formation of two types of η3-germoxyallyl tungsten complexes.

    PubMed

    Fukuda, Tetsuya; Hashimoto, Hisako; Tobita, Hiromi

    2014-01-01

    Germylyne complex Cp*(CO)2W≡Ge{C(SiMe3)3} (1) reacted with two molecules of RC(O)CH═CH2 (R = Me, Et) to give η(3)-allyl complexes, in which an oxagermacyclopentene framework was bound to an η(3)-allyl ligand through an oxygen atom. In the reaction with α-Me-substituted MeC(O)C(Me)═CH2, 1 reacted with only one molecule of the substrate to give another type of η(3)-allyl complex, in which a five-membered oxagermacyclopentenyl ring was coordinated to the W center in an η(3) fashion. Both reactions resulted in unprecedented complete cleavage of a W≡Ge triple bond.

  5. 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").

  6. Reaction front formation in contaminant plumes

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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. Unraveling reaction pathways and specifying reaction kinetics for complex systems.

    PubMed

    Vinu, R; Broadbelt, Linda J

    2012-01-01

    Many natural and industrial processes involve a complex set of competing reactions that include several different species. Detailed kinetic modeling of such systems can shed light on the important pathways involved in various transformations and therefore can be used to optimize the process conditions for the desired product composition and properties. This review focuses on elucidating the various components involved in modeling the kinetics of pyrolysis and oxidation of polymers. The elementary free radical steps that constitute the chain reaction mechanism of gas-phase/nonpolar liquid-phase processes are outlined. Specification of the rate coefficients of the various reaction families, which is central to the theme of kinetics, is described. Construction of the reaction network on the basis of the types of end groups and reactive moieties in a polymer chain is discussed. Modeling frameworks based on the method of moments and kinetic Monte Carlo are evaluated using illustrations. Finally, the prospects and challenges in modeling biomass conversion are addressed.

  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. The reactions of SO3 with HO2 radical and H2O...HO2 radical complex. Theoretical study on the atmospheric formation of HSO5 and H2SO4.

    PubMed

    Gonzalez, Javier; Torrent-Sucarrat, Miquel; Anglada, Josep M

    2010-03-01

    The influence of a single water molecule on the gas-phase reactivity of the HO(2) radical has been investigated by studying the reactions of SO(3) with the HO(2) radical and with the H(2)O...HO(2) radical complex. The naked reaction leads to the formation of the HSO(5) radical, with a computed binding energy of 13.81 kcal mol(-1). The reaction with the H(2)O...HO(2) radical complex can give two different products, namely (a) HSO(5) + H(2)O, which has a binding energy that is computed to be 4.76 kcal mol(-1) more stable than the SO(3) + H(2)O...HO(2) reactants (Delta(E + ZPE) at 0K) and an estimated branching ratio of about 34% at 298K and (b) sulfuric acid and the hydroperoxyl radical, which is computed to be 10.51 kcal mol(-1) below the energy of the reactants (Delta(E + ZPE) at 0K), with an estimated branching ratio of about 66% at 298K. The fact that one of the products is H(2)SO(4) may have relevance in the chemistry of the atmosphere. Interestingly, the water molecule acts as a catalyst, [as it occurs in (a)] or as a reactant [as it occurs in (b)]. For a sake of completeness we have also calculated the anharmonic vibrational frequencies for HO(2), HSO(5), the HSO(5)...H(2)O hydrogen bonded complex, H(2)SO(4), and two H(2)SO(4)...H(2)O complexes, in order to help with the possible experimental identification of some of these species. PMID:20165760

  10. Kinetics of rouleau formation. II. Reversible reactions.

    PubMed Central

    Samsel, R W; Perelson, A S

    1984-01-01

    Red blood cells aggregate face-to-face to form long, cylindrical, straight chains and sometimes branched structures called rouleaux. Here we extend a kinetic model developed by R. W. Samsel and A. S. Perelson (1982, Biophys. J. 37:493-514) to include both the formation and dissociation of rouleaux. We examine thermodynamic constraints on the rate constants of the model imposed by the principle of detailed balance. Incorporation of reverse reactions allows us to compute mean sizes of rouleaux and straight chain segments within rouleaux, as functions of time and at equilibrium. Using the Flory - Stockmayer method from polymer chemistry, we obtain a closed-form solution for the size distribution of straight chain segments within rouleaux at any point in the evolution of the reaction. The predictions of our theory compare favorably with data collected by D. Kernick , A.W.L. Jay , S. Rowlands , and L. Skibo (1973, Can. J. Physiol. Pharmacol. 51:690-699) on the kinetics of rouleau formation. When rouleaux grow large, they may contain rings or loops and take on the appearance of a network. We demonstrate the importance of including the kinetics of ring closure in the development of realistic models of rouleaux formation. Images FIGURE 1 FIGURE 13 PMID:6426540

  11. Stereoregularity Drives Precipitation in Polyelectrolyte Complex Formation

    NASA Astrophysics Data System (ADS)

    Tirrell, Matthew; Perry, Sarah; Leon, Lorraine; Kade, Matthew; Priftis, Dimitris; Black, Katie; Hoffman, Kyle; Whitmer, Jonathan; Qin, Jian; de Pablo, Juan

    2014-03-01

    This study investigates the effect of stereoregularity on the formation of polypeptide-based complex formation and assembly into micelles, hydrogels and ordered phases. We demonstrate that fluid complex coacervate formation (rather than solid complex precipitation) between oppositely charged polypeptides requires at least one racemic partner in order to disrupt backbone hydrogen bonding networks and prevent the hydrophobic collapse of the polymers into compact, fibrillar secondary structures. Computer simulations bear this out and enable visualization of the molecular structure of the complexes. The ability to choose between conditions of fluid phase formation and solid phase formation is a useful tool in developing new self-assembled materials based on polyelectrolyte complex formation. Support from the Argonne National Laboratory Laboratory Research and Development Program (2011-217) is gratefully acknowledged.

  12. 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.

  13. 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

  14. 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.

    PubMed

    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 0.1moldm(-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 2.00×10(3)moldm(-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)×10(5)moldm(-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.

  15. Unraveling reaction pathways and specifying reaction kinetics for complex systems.

    PubMed

    Vinu, R; Broadbelt, Linda J

    2012-01-01

    Many natural and industrial processes involve a complex set of competing reactions that include several different species. Detailed kinetic modeling of such systems can shed light on the important pathways involved in various transformations and therefore can be used to optimize the process conditions for the desired product composition and properties. This review focuses on elucidating the various components involved in modeling the kinetics of pyrolysis and oxidation of polymers. The elementary free radical steps that constitute the chain reaction mechanism of gas-phase/nonpolar liquid-phase processes are outlined. Specification of the rate coefficients of the various reaction families, which is central to the theme of kinetics, is described. Construction of the reaction network on the basis of the types of end groups and reactive moieties in a polymer chain is discussed. Modeling frameworks based on the method of moments and kinetic Monte Carlo are evaluated using illustrations. Finally, the prospects and challenges in modeling biomass conversion are addressed. PMID:22468596

  16. Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions

    PubMed Central

    SUZUKI, Toshinori

    2013-01-01

    Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. PMID:23318678

  17. Kinetic analysis of complex reactions using FEMLAB

    SciTech Connect

    Cao, Chunshe; Wang, Yong

    2005-06-07

    A finite element method software FEMALB has been implemented to the kinetic analysis of complex reaction systems. The established protocol provides fast solutions to the coupled differential-algebraic equations. It shows significant advantages over the conventional coding process with the standard implicit Runge-Kutta (IRK) method. The accuracy and high efficiency have been demonstrated in the simulation of the reaction processes such as glucose/fructose hydrogenation and catalytic cracking of gasoil. As model validation, the numerical results showed satisfactory agreement with the exact solutions. With the powerful capability of solving large matrixes of differential equations (both ODE and PDE) with nonlinear algebraic constrains, such an algorithm has greatly reduced the coding labor in reaction mechanistic studies and provided a unique tool in reactor design and optimization.

  18. Coupling reaction and complex formation for the spectrophotometric determination of physiologically active catecholamines in bulk, pharmaceutical preparations and urine samples of schizophrenic patients.

    PubMed

    Nour El-Dien, Faten A; Frag, Eman Y A; Mohamed, Gehad G

    2010-05-01

    A simple and sensitive spectrophotometric method for the determination of three catecholamines namely dopamine hydrochloride (DO.HCl), dobutamine hydrochloride (DOB.HCl) and vanillymandelic acid (VMA), in both pure form or in their commercially available pharmaceutical formulations or urine samples of schizopherinic patients is described. The method is based on the reaction of diazotized 4-aminoantipyrine (4-AAP) with catecholamines in a basic medium (pH = 10-11) to yield pink-coloured products having absorption maxima at 500, 505 and 480 nm for DO.HCl, VMA and DOB.HCl, respectively. Before carrying out Beer's Law, different experimental conditions, such as time, temperature, sequence of addition, and pH are optimized. The coloured species obeyed Beer's Law in the range of 47.4-417.2, 59.45-445.9 and 67.57-405.4 mg/L for DO.HCl, VMA and DOB.HCl, respectively. The molar absorptivity values as obtained from Beer's Law data were found to be 2.979 x 10(4), 4.39 x 10(4) and 1.036 x 10(4) L mol(-1) cm(-1), while Sandell's sensitivity values were observed to be 3 x 10(-3), 4.4 x 10(-3) and 1.3 x 10(-3) microg cm(2-) for DO.HCl, VMA and DOB.HCl, respectively. Common excipients did not interfere with the proposed method. The results of the proposed method compare favourably with those of official methods. The proposed method offers simplicity, reliability, rapidity, and accuracy compared to the existing methods.

  19. Reaction-diffusion controlled growth of complex structures

    NASA Astrophysics Data System (ADS)

    Noorduin, Willem; Mahadevan, L.; Aizenberg, Joanna

    2013-03-01

    Understanding how the emergence of complex forms and shapes in biominerals came about is both of fundamental and practical interest. Although biomineralization processes and organization strategies to give higher order architectures have been studied extensively, synthetic approaches to mimic these self-assembled structures are highly complex and have been difficult to emulate, let alone replicate. The emergence of solution patterns has been found in reaction-diffusion systems such as Turing patterns and the BZ reaction. Intrigued by this spontaneous formation of complexity we explored if similar processes can lead to patterns in the solid state. We here identify a reaction-diffusion system in which the shape of the solidified products is a direct readout of the environmental conditions. Based on insights in the underlying mechanism, we developed a toolbox of engineering strategies to deterministically sculpt patterns and shapes, and combine different morphologies to create a landscape of hierarchical multi scale-complex tectonic architectures with unprecedented levels of complexity. These findings may hold profound implications for understanding, mimicking and ultimately expanding upon nature's morphogenesis strategies, allowing the synthesis of advanced highly complex microscale materials and devices. WLN acknowledges the Netherlands Organization for Scientific Research for financial support

  20. Chemical reactions of As complexation by glutathione: an XAFS study

    NASA Astrophysics Data System (ADS)

    Franco, M. W.; Vasconcelos, I. F.; Modolo, L. V.; Barbosa, F. A. R.

    2016-05-01

    In this study, the chemical reactions between As(III) and As(V) with glutathione, which is a target compound in As biochemistry due to its primordial role in As immobilization and intracellular reduction, in various molar ratios were investigated using As K-edge XAFS spectroscopy. Results showed a gradual substitution of As-O bonds in the coordination of aqueous As(III) and As(V) for three As-S bonds in the As+GSH complex. Moreover, the data showed reduction of As(V) to As(III) prior or concomitant to the As+GSH complex formation.

  1. New Pathways for the Formation of Complex Organics and Prebiotic Synthesis in the Gas Phase

    NASA Astrophysics Data System (ADS)

    El-Shall, M. S.

    2010-04-01

    We study the formation mechanisms of complex organics that are present in interstellar clouds. The reaction of acetylene ion with water produces vinyl alcohol while the reaction of benzene ion with acetylene produces naphthalene-type ion.

  2. Reactions of tetrakis(dimethylamide)-titanium, -zirconium and -hafnium with silanes: synthesis of unusual amide hydride complexes and mechanistic studies of titanium-silicon-nitride (Ti-Si-N) formation.

    PubMed

    Liu, X; Wu, Z; Cai, H; Yang, Y; Chen, T; Vallet, C E; Zuhr, R A; Beach, D B; Peng, Z H; Wu, Y D; Concolino, T E; Rheingold, A L; Xue, Z

    2001-08-22

    M(NMe(2))(4) (M = Ti, Zr, Hf) were found to react with H(2)SiR'Ph (R' = H, Me, Ph) to yield H(2), aminosilanes, and black solids. Unusual amide hydride complexes [(Me(2)N)(3)M(mu-H)(mu-NMe(2))(2)](2)M (M = Zr, 1; Hf, 2) were observed to be intermediates and characterized by single-crystal X-ray diffraction. [(Me(2)N)(3)M(mu-D)(mu-NMe(2))(2)](2)M (1-d(2), 2-d(2)) were prepared through reactions of M(NMe(2))(4) with D(2)SiPh(2). Reactions of (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) with H(2)SiR'Ph were found to give aminosilanes and (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6). These reactions are reversible through unusual equilibria such as (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) + H(2)SiPh(2) right arrow over left arrow (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6) + HSi(NMe(2))Ph(2). The deuteride ligand in (Me(2)N)(2)Zr(D)Si(SiMe(3))(3) (6-d(1)) undergoes H-D exchange with H(2)SiR'Ph (R' = Me, H) to give 6 and HDSiR'Ph. The reaction of Ti(NMe(2))(4) with SiH(4) in chemical vapor deposition at 450 degrees C yielded thin Ti-Si-N ternary films containing TiN and Si(3)N(4). Ti(NMe(2))(4) reacts with SiH(4) at 23 degrees C to give H(2), HSi(NMe(2))(3), and a black solid. HNMe(2) was not detected in this reaction. The reaction mixture, upon heating, gave TiN and Si(3)N(4) powders. Analyses and reactivities of the black solid revealed that it contained -H and unreacted -NMe(2) ligands but no silicon-containing ligand. Ab initio quantum chemical calculations of the reactions of Ti(NR(2))(4) (R = Me, H) with SiH(4) indicated that the formation of aminosilanes and HTi(NR(2))(3) was favored. These calculations also showed that HTi(NH(2))(3) (3b) reacted with SiH(4) or H(3)Si-NH(2) in the following step to give H(2)Ti(NH(2))(2) (4b) and aminosilanes. The results in the current studies indicated that the role of SiH(4) in its reaction with Ti(NMe(2))(4) was mainly to remove amide ligands as HSi(NMe(2))(3). The removal of amide ligands is incomplete, and the reaction thus yielded "=Ti(H)(NMe(2))" as the black

  3. 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.

  4. 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.

  5. 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.

  6. Quantum chemical mechanism in parasitic reaction of AlGaN alloys formation

    NASA Astrophysics Data System (ADS)

    Makino, Osamu; Nakamura, Koichi; Tachibana, Akitomo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh

    2000-06-01

    The mechanism of parasitic reactions among trimethylaluminum (TMA), trimethylgallium (TMG), and NH 3 in atmospheric pressure (AP) MOVPE for growth of AlGaN is theoretically studied using the quantum chemical method. The calculations show that metal-nitrogen chain growth reaction easily proceeds through the successive reactions of 'complex formation with NH 3' and 'CH 4 elimination by the bimolecular mechanism'. Additionally, a parasitic reaction in APMOVPE using other raw material is also investigated. The calculated result shows that small change of raw material raises activation energy of parasitic reaction, and, thus, the parasitic reaction is suppressed. This result suggests a way to improve APMOVPE by a suitable choice of substituent.

  7. 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.

  8. 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.

  9. 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.

  10. Surface-Guided Formation of an Organocobalt Complex.

    PubMed

    Weber, Peter B; Hellwig, Raphael; Paintner, Tobias; Lattelais, Marie; Paszkiewicz, Mateusz; Casado Aguilar, Pablo; Deimel, Peter S; Guo, Yuanyuan; Zhang, Yi-Qi; Allegretti, Francesco; Papageorgiou, Anthoula C; Reichert, Joachim; Klyatskaya, Svetlana; Ruben, Mario; Barth, Johannes V; Bocquet, Marie-Laure; Klappenberger, Florian

    2016-05-01

    Organocobalt complexes represent a versatile tool in organic synthesis as they are important intermediates in Pauson-Khand, Friedel-Crafts, and Nicholas reactions. Herein, a single-molecule-level investigation addressing the formation of an organocobalt complex at a solid-vacuum interface is reported. Deposition of 4,4'-(ethyne-1,2-diyl)dibenzonitrile and Co atoms on the Ag(111) surface followed by annealing resulted in genuine complexes in which single Co atoms laterally coordinated to two carbonitrile groups undergo organometallic bonding with the internal alkyne moiety of adjacent molecules. Alternative complexation scenarios involving fragmentation of the precursor were ruled out by complementary X-ray photoelectron spectroscopy. According to density functional theory analysis, the complexation with the alkyne moiety follows the Dewar-Chatt-Duncanson model for a two-electron-donor ligand where an alkyne-to-Co donation occurs together with a strong metal-to-alkyne back-donation. PMID:27059261

  11. 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.

  12. Formation of carbyne complexes in reactions of laser-ablated Os atoms with halomethanes: characterization by C-H(X) and Os-H(X) stretching absorptions and computed structures.

    PubMed

    Cho, Han-Gook; Andrews, Lester

    2009-08-14

    Reactions of laser-ablated Os atoms with halomethanes have been investigated. Small carbyne complexes are produced in reactions of Os atoms with fluoromethanes and identified through matrix infrared spectra and vibrational frequencies computed by density functional theory. The preference for the carbon-osmium triple bond is traced to the low energy of the Os carbyne products. The C-H and C-X stretching absorptions of the carbyne complexes are observed on the high frequency sides of the corresponding precursor bands, which result from the high s character in the C-H bond and interaction between the C-X and C-Os stretching modes, respectively. The calculated Os complex structures show a large variation with the ligands and electronic states, similar to the analogous Ru complex structures. The present report also compares previous Fe, Ru, and Os results and supports the general trend that the higher oxidation state complexes become more stable on going down the family group column. PMID:19623385

  13. Formation of carbyne complexes in reactions of laser-ablated Os atoms with halomethanes: characterization by C-H(X) and Os-H(X) stretching absorptions and computed structures.

    PubMed

    Cho, Han-Gook; Andrews, Lester

    2009-08-14

    Reactions of laser-ablated Os atoms with halomethanes have been investigated. Small carbyne complexes are produced in reactions of Os atoms with fluoromethanes and identified through matrix infrared spectra and vibrational frequencies computed by density functional theory. The preference for the carbon-osmium triple bond is traced to the low energy of the Os carbyne products. The C-H and C-X stretching absorptions of the carbyne complexes are observed on the high frequency sides of the corresponding precursor bands, which result from the high s character in the C-H bond and interaction between the C-X and C-Os stretching modes, respectively. The calculated Os complex structures show a large variation with the ligands and electronic states, similar to the analogous Ru complex structures. The present report also compares previous Fe, Ru, and Os results and supports the general trend that the higher oxidation state complexes become more stable on going down the family group column.

  14. Formation of apatite-collagen complexes.

    PubMed

    Doi, Y; Horiguchi, T; Moriwaki, Y; Kitago, H; Kajimoto, T; Iwayama, Y

    1996-05-01

    An apatite-collagen complex was prepared in calcium beta-glycerophosphate solutions at pH 9.0 and 37 degrees C with the purpose of developing new bone substitutes that more closely resemble bone than currently available materials. Reconstituted type I collagen as well as sheet collagen were crosslinked in the presence of alkaline phosphatase and egg-yolk phosvitin. The crosslinked collagens were immersed in daily-renewed calcium beta-glycerophosphate solutions for 2 and 4 weeks to induce the deposition of apatite on the collagen fibers. After 2 weeks of reaction, for example, apatites deposited approximately two times the crosslinked collagen in weight. With reconstituted collagen, the complex showed some elasticity but no apatite was visually observed to detach under deformation with fingers and forceps. The complex, moreover, did not disintegrate when immersed in saline or animal blood. Nevertheless, the complex resorbed with no evidence of cytotoxicity when implanted in muscle tissues. These findings suggest that the apatite-collagen complex prepared would be useful as bone substitutes, especially for periodontal osseous lesion repair and alveolar ridge augmentation. PMID:8731148

  15. Synthesis and reaction of the first 1,2-oxaphosphetane complexes.

    PubMed

    Kyri, Andreas Wolfgang; Nesterov, Vitaly; Schnakenburg, Gregor; Streubel, Rainer

    2014-09-26

    While P(V) 1,2-oxaphosphetanes are well known from the Wittig reaction, their P(III) analogues are still unexplored. Herein, the synthesis and reactions of the first 1,2-oxaphosphetane complexes are presented, which were achieved by reaction of the phosphinidenoid complex [Li(12-crown-4)(solv)][(OC)5W{(Me3Si)2HCPCl}] with different epoxides. The title compounds appeared to be stable in toluene up to 100 °C, before unselective decomposition started. Acid-induced ring expansion with benzonitrile resulted in selective formation of the first complex bearing a 1,3,4-oxazaphosphacyclohex-2-ene ligand.

  16. 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.

  17. 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. PMID:25803829

  18. Hydroxyl radical reactions with adenine: reactant complexes, transition states, and product complexes.

    PubMed

    Cheng, Qianyi; Gu, Jiande; Compaan, Katherine R; Schaefer, Henry F

    2010-10-18

    In order to address problems such as aging, cell death, and cancer, it is important to understand the mechanisms behind reactions causing DNA damage. One specific reaction implicated in DNA oxidative damage is hydroxyl free-radical attack on adenine (A) and other nucleic acid bases. The adenine reaction has been studied experimentally, but there are few theoretical results. In the present study, adenine dehydrogenation at various sites, and the potential-energy surfaces for these reactions, are investigated theoretically. Four reactant complexes [A···OH]* have been found, with binding energies relative to A+OH* of 32.8, 11.4, 10.7, and 10.1 kcal mol(-1). These four reactant complexes lead to six transition states, which in turn lie +4.3, -5.4, (-3.7 and +0.8), and (-2.3 and +0.8) kcal mol(-1) below A+OH*, respectively. Thus the lowest lying [A···OH]* complex faces the highest local barrier to formation of the product (A-H)*+H(2)O. Between the transition states and the products lie six product complexes. Adopting the same order as the reactant complexes, the product complexes [(A-H)···H(2)O]* lie at -10.9, -22.4, (-24.2 and -18.7), and (-20.5 and -17.5) kcal mol(-1), respectively, again relative to separated A+OH*. All six A+OH* → (A-H)*+H(2)O pathways are exothermic, by -0.3, -14.7, (-17.4 and -7.8), and (-13.7 and -7.8) kcal mol(-1), respectively. The transition state for dehydrogenation at N(6) lies at the lowest energy (-5.4 kcal mol(-1) relative to A+OH*), and thus reaction is likely to occur at this site. This theoretical prediction dovetails with the observed high reactivity of OH radicals with the NH(2) group of aromatic amines. However, the high barrier (37.1 kcal mol(-1)) for reaction at the C(8) site makes C(8) dehydrogenation unlikely. This last result is consistent with experimental observation of the imidazole ring opening upon OH radical addition to C(8). In addition, TD-DFT computed electronic transitions of the N(6) product around 420 nm

  19. Formation and characterization of thioglycolic acid-silver cluster complexes.

    PubMed

    Bellina, Bruno; Antoine, Rodolphe; Broyer, Michel; Gell, Lars; Sanader, Željka; Mitrić, Roland; Bonačić-Koutecký, Vlasta; Dugourd, Philippe

    2013-06-21

    Gas phase reactivity observed in an ion trap was used to produce silver clusters protected with thioglycolic acid. Fragmentation pathways as well as optical properties were explored experimentally and theoretically. Sequential losses of SCH2 and CO2 in the ion trap lead to redox reactions with charge transfers between the metal part and the carboxylate and thiolate groups. This allows us to control the number of electrons in the metallic subunit and thus optical properties of the complexes. The presented formation process can be used as a prototype for tuning optical and chemical properties of ligated metal clusters by varying the number of confined electrons within the metallic subunit.

  20. Modelling complex organic molecules in dense regions: Eley-Rideal and complex induced reaction

    NASA Astrophysics Data System (ADS)

    Ruaud, M.; Loison, J. C.; Hickson, K. M.; Gratier, P.; Hersant, F.; Wakelam, V.

    2015-03-01

    Recent observations have revealed the existence of complex organic molecules (COMs) in cold dense cores and pre-stellar cores. The presence of these molecules in such cold conditions is not well understood and remains a matter of debate since the previously proposed `warm-up' scenario cannot explain these observations. In this paper, we study the effect of Eley-Rideal and complex induced reaction mechanisms of gas-phase carbon atoms with the main ice components of dust grains on the formation of COMs in cold and dense regions. Based on recent experiments, we use a low value for the chemical desorption efficiency (which was previously invoked to explain the observed COM abundances). We show that our introduced mechanisms are efficient enough to produce a large amount of COMs in the gas phase at temperatures as low as 10 K.

  1. Formation of a Bridging Phosphinidene Thorium Complex.

    PubMed

    Behrle, Andrew C; Castro, Ludovic; Maron, Laurent; Walensky, Justin R

    2015-12-01

    The synthesis and structural determination of the first thorium phosphinidene complex are reported. The reaction of 2 equiv of (C5Me5)2Th(CH3)2 with H2P(2,4,6-(i)Pr3C6H2) at 95 °C produces [(C5Me5)2Th]2(μ2-P[(2,6-CH2CHCH3)2-4-(i)PrC6H2] as well as 4 equiv of methane, 2 equiv from deprotonation of the phosphine and 2 equiv from C-H bond activation of one methyl group of each of the isopropyl groups at the 2- and 6-positions. Transition state calculations indicate that the steps in the mechanism are P-H, C-H, C-H, and then P-H bond activation to form the phosphinidene. PMID:26575219

  2. Vortex formation in a complex plasma

    NASA Astrophysics Data System (ADS)

    Ishihara, Osamu

    Complex plasma experiments in ground-based laboratories as well as in microgravity conditions have shown the formation of vortex structures in various conditions (e.g., 1,2,3,4). The vortex structures formed in a complex plasma are visible by naked eyes with the help of irradiating laser and the individual dust particles in the structure give us the opportunity to study detailed physics of the commonly observed natural phenomena known such as tornadoes, typhoons, hurricanes and dust devils. Based on the Navier-Stokes equation with proper complex plasma conditions we analyze as much as possible in a universal way the vortex structure and clarifies the role of the controlling parameters like flow velocity and external magnetic field. 1. G. E. Morfill,H. M. Thomas, U. Konopka,H. Rothermel, M. Zuzic, A. Ivlev, and J. Goree, Phys,. Rev. Lett. 83, 1598 (1999). 2. E. Nebbat and R. Annou, Phys. Plasmas 17, 093702 (2010). 3. Y. Saitou and O. Ishihara, Phys. Rev. Lett. 111, 185003 (2013). 4. V. N. Tsytovich and N. G. Gusein-zade, Plasma Phys. Rep. 39, 515 (2013).

  3. Formation of flavour compounds in the Maillard reaction.

    PubMed

    van Boekel, M A J S

    2006-01-01

    This paper discusses the importance of the Maillard reaction for food quality and focuses on flavour compound formation. The most important classes of Maillard flavour compounds are indicated and it is shown where they are formed in the Maillard reaction. Some emphasis is given on the kinetics of formation of flavour compounds. It is concluded that the essential elements for predicting the formation of flavour compounds in the Maillard reaction are now established but much more work needs to be done on specific effects such as the amino acid type, the pH, water content and interactions in the food matrix. It is also concluded that most work is done on free amino acids but hardly anything on peptides and proteins, which could generate peptide- or protein-specific flavour compounds. PMID:16386869

  4. 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

  5. A stunning example for a spontaneous reaction with a complex mechanism: the vinylidene-acetylene cycloaddition reaction

    NASA Astrophysics Data System (ADS)

    Kraka, Elfi; Joo, Hyun; Cremer, Dieter

    2010-10-01

    The chelotropic addition reaction (1): singlet vinylidene + acetylene → methylenecyclopropene (MCP), was investigated using different levels of theory (B3LYP, CASSCF, CCSD(T), G2M) and different basis sets (6-31G(d,p), 6-311G(d,p), 6-311++G(3df,3pd), cc-pVTZ). The concerted reaction is spontaneous at room temperature (activation enthalpy of 3 kcal mol-1) and strongly exothermic (ΔE = -64 kcal mol-1; ΔH(298) = -59 kcal mol-1). Analysis of the reaction mechanism with the help of the Unified Reaction Valley approach reveals a complicated sequence of structural and electronic changes, which can be best described by partitioning the mechanism into seven phases: (1) van der Waals, (2) electrophilic attack, (3) biradical, (4) allene, (5) carbene, (6) ring closure, and (7) MCP formation phase. In the transient regions from one phase to the next, structures are located that possess properties of hidden transition states (TSs) or hidden intermediates, i.e. by variation of the electronic nature or the environment of the reaction complex, real TSs and/or real intermediates can be generated. There is indication that a given sequence of reaction phases is fixed for a wide variation in the electronic nature of the reaction complex and that other than just orbital symmetry principles play a decisive role for the reaction mechanism.

  6. 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.

  7. 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.

  8. A complex reaction time study (Sternberg) in space flight

    NASA Technical Reports Server (NTRS)

    Thornton, W.; Uri, John; Moore, Tom

    1993-01-01

    Simple and complex (Sternberg) reaction time studies were flown on three and seven day Shuttle flights in 1985. Three subjects did selftesting with an onboard handheld calculator without difficulty. There was little change in simple reaction time. One subject demonstrated a decrease in the processing rate during space motion sickness while a second exhibited an increase in complex reaction time without a change in processing rate during a period of high work load. The population was too small to demonstrate significant changes. This study demonstrates the ease and practicality of such measurements and indicates the potential value of such studies in space.

  9. Gas-phase organolanthanide (Ln) chemistry: Formation of Ln{sup +}-[benzene] and Ln{sup +}-[benzyne] complexes by reactions of laser-ablated Ln{sup +} with cyclic hydrocarbons

    SciTech Connect

    Gibson, J.K.

    1996-09-26

    Nascent laser-ablated lanthanide metal ions, Ln{sup +}, were reacted with cyclohexacarbons. C{sub 6}H{sub 6+2n} (n = 0, 1, 2, or 3), and the resulting organometallic complex ions, [Ln{sup +}] - [C{sub p}H{sub q}], were identified by time-of-flight mass spectrometry. Cyclohexane and cyclohexadiene were especially reactive, primarily undergoing one or more dehydrogenations to produce adduct ions. Also identified as minor products were the `sandwich` complexes. Carbon-carbon bond activation was generally an unimportant reaction channel. Significant differences were observed in product yields and distributions, between the several Ln{sup +} studied, providing the following comparative reactivities: Ce{sup +} >= Tb{sup +} >= Gd{sup +} = Pr{sup +} >= Ho{sup +} >= Dy{sup +} >= Lu{sup +} >= [Sm{sup +}/Tm{sup +}/Eu{sup +}/Yb{sup +} unreactive]. These differences are explained by the metal ion ground state electronic configurations and promotion energies (PE) for excitation of a (nonbonding) 4f electron to a valence 5d orbital. The distinctive Ln{sup +} reactivities indicate that most ablated Ln{sup +} were in the ground or a low-lying electronic state. Contrasting the reactivities of two or more Ln{sup +} co-ablated from a multicomponent target circumvented effects of experimental variables and provided especially reliable comparative reactivities. 52 refs., 4 figs., 5 tabs.

  10. Formation of superheavy nuclei in cold fusion reactions

    SciTech Connect

    Feng Zhaoqing; Jin Genming; Li Junqing; Scheid, Werner

    2007-10-15

    Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus, and the de-excitation process are calculated by using an empirical coupled channel model, solving a master equation numerically and applying statistical theory, respectively. Evaporation residue excitation functions in cold fusion reactions are investigated systematically and compared with available experimental data. Maximal production cross sections of superheavy nuclei in cold fusion reactions with stable neutron-rich projectiles are obtained. Isotopic trends in the production of the superheavy elements Z=110, 112, 114, 116, 118, and 120 are analyzed systematically. Optimal combinations and the corresponding excitation energies are proposed.

  11. 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.

  12. Deduction of compound nucleus formation probability from the fragment angular distributions in heavy-ion reactions

    NASA Astrophysics Data System (ADS)

    Yadav, C.; Thomas, R. G.; Mohanty, A. K.; Kapoor, S. S.

    2015-07-01

    The presence of various fissionlike reactions in heavy-ion induced reactions is a major hurdle in the path to laboratory synthesis of heavy and super-heavy nuclei. It is known that the cross section of forming a heavy evaporation residue in fusion reactions depends on the three factors—the capture cross section, probability of compound nucleus formation PCN, and the survival probability of the compound nucleus against fission. As the probability of compound nucleus formation, PCN is difficult to theoretically estimate because of its complex dependence on several parameters; attempts have been made in the past to deduce it from the fission fragment anisotropy data. In the present work, the fragment anisotropy data for a number of heavy-ion reactions are analyzed and it is found that deduction of PCN from the anisotropy data also requires the knowledge of the ratio of relaxation time of the K degree of freedom to pre-equilibrium fission time.

  13. 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...

  14. 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. PMID:27236926

  15. 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.

  16. 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).

  17. 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.

  18. 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

  19. 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

  20. Buffering dissociation/formation reaction of biogenic calcium carbonate.

    PubMed

    Ichikawa, Kazuhiko

    2007-01-01

    The oscillating stability of coral reef seawater pH has been maintained at around physiological pH values over the past 300 years (Pelejero et al., 2005). The stability mechanism of its pH has been interpreted in terms of the buffering dissolution/formation reaction of CaCO(3) as well as the proton consumption/generation reaction in CaCO(3)-saturated water. Here the pH-dependent solubility product [HCO(3)(-)][Ca(2+)] has been derived on the basis of the actual pH-dependent reactions for the atmospheric CO(2)/CO(2 (aq.))/HCO(3)(-)/CO(3)(2-)/Ca(2+)/CaCO(3) system. Overbasic pH peaks appeared between pH approximately 8 and approximately 9.5 during sodium hydroxide titration, as a result of simultaneous CaCO(3) formation and proton generation. The spontaneous and prompt water pH recovery from the acidic to the physiological range has been confirmed by the observation of acid/base time evolution, because of simultaneous CaCO(3) dissolution and proton consumption. The dissolution/formation of CaCO(3) in water at pH 7.5-9 does not take place without a proton consumption/generation reaction, or a buffering chemical reaction of HCO(3)(-)+Ca(2+)right arrow over left arrowCaCO(3)+H(+). SEM images of the CaCO(3) fragments showed that the acid water ate away at the CaCO(3) formed at physiological pH values. Natural coral reefs can thus recover the physiological pH levels of seawater from the acidic range through partial dissolution of their own skeletons.

  1. Direct computer simulation of ferredoxin and FNR complex formation in solution

    NASA Astrophysics Data System (ADS)

    Kovalenko, I. B.; Diakonova, A. N.; Abaturova, A. M.; Riznichenko, G. Yu; Rubin, A. B.

    2010-06-01

    Ferredoxin reduced by Photosystem I in light serves as an electron donor for the reduction of NADP+ to NADPH, and this reaction is catalyzed by enzyme ferredoxin:NADP+-reductase (FNR). Kinetics and mechanisms of this reaction have been extensively studied experimentally by site-specific mutagenesis, laser flash photolysis and stopped-flow methods. We have applied a method of multiparticle computer simulation to study the effects of electrostatic interactions upon the reaction rate of Fd-FNR complex formation. Using the model we calculated rate constants of Fd-FNR complex formation for the wild-type proteins and some mutant forms of FNR at different values of ionic strength. Simulation revealed that electrostatic interactions play an important role in Fd-FNR complex formation and define its specificity.

  2. Efficient stochastic simulations of complex reaction networks on surfaces.

    PubMed

    Barzel, Baruch; Biham, Ofer

    2007-10-14

    Surfaces serve as highly efficient catalysts for a vast variety of chemical reactions. Typically, such surface reactions involve billions of molecules which diffuse and react over macroscopic areas. Therefore, stochastic fluctuations are negligible and the reaction rates can be evaluated using rate equations, which are based on the mean-field approximation. However, in case that the surface is partitioned into a large number of disconnected microscopic domains, the number of reactants in each domain becomes small and it strongly fluctuates. This is, in fact, the situation in the interstellar medium, where some crucial reactions take place on the surfaces of microscopic dust grains. In this case rate equations fail and the simulation of surface reactions requires stochastic methods such as the master equation. However, in the case of complex reaction networks, the master equation becomes infeasible because the number of equations proliferates exponentially. To solve this problem, we introduce a stochastic method based on moment equations. In this method the number of equations is dramatically reduced to just one equation for each reactive species and one equation for each reaction. Moreover, the equations can be easily constructed using a diagrammatic approach. We demonstrate the method for a set of astrophysically relevant networks of increasing complexity. It is expected to be applicable in many other contexts in which problems that exhibit analogous structure appear, such as surface catalysis in nanoscale systems, aerosol chemistry in stratospheric clouds, and genetic networks in cells.

  3. 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.

  4. Effect of reaction time on the formation of disinfection byproducts

    USGS Publications Warehouse

    Rathbun, R.E.

    1997-01-01

    The effect of reaction time on the trihalomethane and nonpurgeable total organic-halide formation potentials was determined by chlorinating water samples from the Mississippi, Missouri, and Ohio Rivers. Samples were collected for three seasons at 12 locations on the Mississippi from Minneapolis, Minnesota, to New Orleans, Louisiana, and on the Missouri and Ohio 1.6 kilometers above their confluences with the Mississippi. Both types of compounds formed rapidly during the initial stages of the reaction-time period, with formation rates decreasing with time. The ratio of the nonpurgeable total organic-halide and trihalomethane concentrations decreased with time, with the nonpurgeable total organic-halide compounds forming faster during the first stages of the time period and the trihalomethane compounds forming faster during the latter stages of the time period. Variation with distance along the Mississippi River of the formation rates approximately paralleled the variation of the dissolved organic carbon concentration, indicating that the rates of formation, as well as the concentrations of the compounds formed, depended on the dissolved organic carbon concentration.

  5. Actinide complexation kinetics: rate and mechanism of dioxoneptunium (V) reaction with chlorophosphonazo III

    SciTech Connect

    Fugate, G.; Feil-Jenkins, J.F.; Sullivan, J.C.; Nash, K.L.

    1996-12-01

    Rates of complex formation and dissociation in NpO{sub 2}{sup +}- Chlorophosphonazo III (2,7-bis(4-chloro-2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studies were made of the rates of reaction of La{sup 3+}, Eu{sup 3+}, Dy{sup 3+}, and Fe{sup 3+} with CLIII. Rate determining step in each system is an intramolecular process, the NpO{sub 2}{sup +}-CLIII reaction proceeding by a first order approach to equilibrium in the acid range from 0.1 to 1.0 M. Complex formation occurs independent of acidity, while both acid dependent and independent dissociation pathways are observed. Activation parameters for the complex formation reaction are {Delta}H=46.2{+-}0.3 kJ/m and {Delta}S=7{+-} J/mK (I=1.0 M); these for the acid dependent and independent dissociation pathways are {Delta}H=38.8{+-}0.6 kJ/m, {Delta}S=-96{+-}18 J/mK, {Delta}H=70.0{+-} kJ/m, and {Delta}S=17{+-}1 J/mK, respectively. An isokinetic relationship is observed between the activation parameters for CLIII complex formation with NpO{sub 2}{sup +}, UO{sub 2}{sup 2+}, Th{sup 4+}, and Zr{sup 4+}. Rates of CLIII complex formation reactions for Fe{sup 3+}, Zr{sup 4+}, NpO{sub 2}{sup +}, UO{sub 2}{sup 2+}, Th{sup 4+}, La{sup 3+}, Eu{sup 3+}, and Dy{sup 3+} correlate with cation radius rather than charge/radius ratio.

  6. Arene complexes of transition metals in reactions with nucleophilic reagents. XVI. Kinetics and mechanism of the reaction of the. pi. -arene complexes of chromium and iron and piperidine

    SciTech Connect

    Oleinik, I.I.; Kun, P.P.; Litvak, V.V.; Shteingarts, V.D.

    1988-05-20

    The kinetics of the reaction of ..pi..-arene complexes of the (/eta/-XC/sub 6/H/sub 4/Cl)ML type (where ML = Cr(CO)/sub 3/ (X = p-Cl), Cr/sup +/(/eta/-C/sub 6/H/sub 5/Cl) (X = H), Fe/sup +/(/eta/-C/sub 5/H/sub 5/) (X = H)) with piperidine in acetone suggest that in the second and third cases the controlling stage is the transformation of the intermediate sigma complex into the reaction products almost entirely by a path with catalysis by the reagent while in the first case it is the formation of the intermediate. The marked increase in the catalytic effect of piperidine in the transition from neutral to cationic ..pi..-arene complexes show that the charge of the metal-complex fragment, coordinated with the arene, has a significant effect on the ratio of the rates of transformation of the intermediate sigma complex into the initial compounds and the final reaction products.

  7. Equilibrium and Kinetic Investigations of the Interaction of Model Platinum(II) Complex with DNA Constituents in Reference to the Antitumour Activity: Complex-Formation Reactions of [Pd(N,N-diethylethylenediamine)(H2O)2]2+ with Ligands of Biological Significance and Displacement Reactions of DNA Constituents

    PubMed Central

    Shoukry, Eman Mohamed

    2009-01-01

    The [Pd(DEEN)Cl2] and [Pt(DEEN)Cl2] complexes were synthesized and characterized where DEEN = N,N-diethylethylenediamine. The stoichiometry and stability of the complexes formed between various biologically relevant ligands (amino acids, peptides, DNA constituents and dicarboxylic acids) and [Pd(DEEN)(H2O)2]2+ were investigated at 37°C and 0.16 M ionic strength. The stability constant of the complexes formed in solution were determined and the binding centres of the ligands were assigned. The concentration distribution diagrams of the complexes were evaluated The equilibrium constants for the displacement of representative coordinated ligands such as inosine, glycine or methionine by cysteine were calculated and the concentration distribution diagrams of the various species were evaluated. The kinetics of base hydrolysis of free and coordinated S-methylcysteine methyl ester was investigated. The mechanism of hydrolysis was discussed. PMID:19696935

  8. 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)

  9. 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.

  10. Chemical reaction and dust formation studies in laboratory hydrocarbon plasmas.

    NASA Astrophysics Data System (ADS)

    Hippler, Rainer; Majumdar, Abhijit; Thejaswini, H. C.

    Plasma chemical reaction studies with relevance to, e.g., Titan's atmosphere have been per-formed in various laboratory plasmas [1,2]. Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH4 /N2 and CH4 /Ar gas mixtures by means of mass spectrometry. The main reaction scheme is production of H2 by fragmenta-tion of CH4 , but also production of larger hydrocarbons like Cn Hm with n up to 10 including formation of different functional CN groups is observed. [1] A. Majumdar and R. Hippler, Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition, Rev. Sci. Instrum. 78, 075103 (2007) [2] H.T. Do, G. Thieme, M. Frühlich, H. Kersten, and R. Hippler, Ion Molecule and Dust Particle Formation in Ar/CH4 , Ar/C2 H2 and Ar/C3 H6 Radio-frequency Plasmas, Contrib. Plasma Phys. 45, No. 5-6, 378-384 (2005)

  11. Pore-scale studies of multiphase flow and reaction involving CO2 sequestration in geologic formations

    NASA Astrophysics Data System (ADS)

    Kang, Q.; Wang, M.; Lichtner, P. C.

    2008-12-01

    In geologic CO2 sequestration, pore-scale interfacial phenomena ultimately govern the key processes of fluid mobility, chemical transport, adsorption, and reaction. However, spatial heterogeneity at the pore scale cannot be resolved at the continuum scale, where averaging occurs over length scales much larger than typical pore sizes. Natural porous media, such as sedimentary rocks and other geological media encountered in subsurface formations, are inherently heterogeneous. This pore-scale heterogeneity can produce variabilities in flow, transport, and reaction processes that take place within a porous medium, and can result in spatial variations in fluid velocity, aqueous concentrations, and reaction rates. Consequently, the unresolved spatial heterogeneity at the pore scale may be important for reactive transport modeling at the larger scale. In addition, current continuum models of surface complexation reactions ignore a fundamental property of physical systems, namely conservation of charge. Therefore, to better understand multiphase flow and reaction involving CO2 sequestration in geologic formations, it is necessary to quantitatively investigate the influence of the pore-scale heterogeneity on the emergent behavior at the field scale. We have applied the lattice Boltzmann method to simulating the injection of CO2 saturated brine or supercritical CO2 into geological formations at the pore scale. Multiple pore-scale processes, including advection, diffusion, homogeneous reactions among multiple aqueous species, heterogeneous reactions between the aqueous solution and minerals, ion exchange and surface complexation, as well as changes in solid and pore geometry are all taken into account. The rich pore scale information will provide a basis for upscaling to the continuum scale.

  12. Reactions of organometallic compounds catalyzed by transition metal complexes. XIII. Comparison of the reactivity of organometallic compounds in aryldemetallation reactions catalyzed by palladium complexes

    SciTech Connect

    Bumagin, N.A.; Ponomarev, A.B.; Beletskaya, I.P.

    1987-12-10

    The effect of the nature of the metal M and the organic group R on the reaction of organometallic compounds RM (R = Ph, PhC triple bond C, C/sub 3/H/sub 7/, Allyl; M = Li, Mg, Zn, Cd, Cu Al), produced in situ from Grignard reagents or organolithium compounds and the respective salts, with p-iodoanisole in the presence of palladium complexes PdCl/sub 2/L/sub 2/ (L = PPh/sub 3/, MeCN, dppf) was studied. The organozinc and organoaluminum compounds react with a high degree of selectivity. In the reactions of C/sub 3/H/sub 7/M with p-MeOC/sub 6/H/sub 4/I the highest yield from cross-coupling is obtained with catalysis by the PdCl/sub 2/ (dppf) complex. The mechanism of the formation of the homocoupling products is discussed.

  13. Star formation regions in galaxies: Star complexes and spiral arms

    NASA Astrophysics Data System (ADS)

    Efremov, Iurii N.

    This book describes observational data on star formation regions (from young star clusters to spiral arms) in the Milky Way and other galaxies. It is concluded that not only high-luminosity stars but also star clusters and associations are forming together in vast complexes. It is claimed that these complexes are the primary, fundamental entities of star formation.

  14. Arylpalladium Phosphonate Complexes as Reactive Intermediates in Phosphorus-Carbon Bond Forming Reactions

    SciTech Connect

    Kohler, Mark C.; Grimes, Thomas V.; Wang, Xiaoping; Cundari, Thomas R.; Stockland, Robert A. Jr.

    2009-01-01

    Phosphorus-carbon bond formation from discrete transition metal complexes have been investigated through a combination of synthetic, spectroscopic, crystallographic, and computational methods. Reactive intermediates of the type (diphosphine)Pd(aryl)(P(O)(OEt)(2)) have been prepared, characterized, and studied as possible intermediates in metal-mediated coupling reactions. Several of the reactive intermediates were characterized crystallographicaliy, and a discussion of the solid state structures is presented. In contrast to other carbon-heteroelement bond forming reactions, palladium complexes containing electron-donating substituents on the aromatic fragment exhibited faster rates of reductive elimination. Large bite angle diphosphine ligands induced rapid rates of elimination, while bipyridine and small bite angle diphosphine ligands resulted in much slower rates of elimination. An investigation of the effect of typical impurities on the elimination reaction was carried out. While excess diphosphine, pyridine, and acetonitrile had little effect on the observed rate, the addition of water slowed the phosphorus-carbon bond forming reaction. Coordination of water to the complex was observed spectroscopically and crystallographically. Computational studies were utilized to probe the reaction pathways for P-C bond formation via Pd catalysis.

  15. Investigation of the complex reaction coordinate of acid catalyzed amide hydrolysis from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Zahn, Dirk

    2004-05-01

    The rate-determining step of acid catalyzed peptide hydrolysis is the nucleophilic attack of a water molecule to the carbon atom of the amide group. Therein the addition of the hydroxyl group to the amide carbon atom involves the association of a water molecule transferring one of its protons to an adjacent water molecule. The protonation of the amide nitrogen atom follows as a separate reaction step. Since the nucleophilic attack involves the breaking and formation of several bonds, the underlying reaction coordinate is rather complex. We investigate this reaction step from path sampling Car-Parrinello molecular dynamics simulations. This approach does not require the predefinition of reaction coordinates and is thus particularly suited for investigating reaction mechanisms. From our simulations the most relevant components of the reaction coordinate are elaborated. Though the C⋯O distance of the oxygen atom of the water molecule performing the nucleophilic attack and the corresponding amide carbon atom is a descriptor of the reaction progress, a complete picture of the reaction coordinate must include all three molecules taking part in the reaction. Moreover, the proton transfer is found to depend on favorable solvent configurations. Thus, also the arrangement of non-reacting, i.e. solvent water molecules needs to be considered in the reaction coordinate.

  16. Complex formation between benzene carboxylic acids and β-cyclodextrin

    NASA Astrophysics Data System (ADS)

    Belyakova, L. A.; Lyashenko, D. Yu.

    2008-05-01

    Complex formation between benzene carboxylic acids and β-cyclodextrin in aqueous solutions at 290 300 K was studied using UV spectroscopy. The formation of 1:1 supramolecular inclusion compounds β-cyclodextrin-benzene and β-cyclodextrin-salicylic acid was found. Stability constants (Ks) of the complexes and thermodynamic parameters for formation of the inclusion compounds (ΔG, ΔH, and ΔS) were calculated.

  17. Formation of β-cyclodextrin complexes in an anhydrous environment.

    PubMed

    Sifaoui, Hocine; Modarressi, Ali; Magri, Pierre; Stachowicz-Kuśnierz, Anna; Korchowiec, Jacek; Rogalski, Marek

    2016-09-01

    The formation of inclusion complexes of β-cyclodextrin was studied at the melting temperature of guest compounds by differential scanning calorimetry. The complexes of long-chain n-alkanes, polyaromatics, and organic acids were investigated by calorimetry and IR spectroscopy. The complexation ratio of β-cyclodextrin was compared with results obtained in an aqueous environment. The stability and structure of inclusion complexes with various stoichiometries were estimated by quantum chemistry and molecular dynamics calculations. Comparison of experimental and theoretical results confirmed the possible formation of multiple inclusion complexes with guest molecules capable of forming hydrogen bonds. This finding gives new insight into the mechanism of formation of host-guest complexes and shows that hydrophobic interactions play a secondary role in this case. Graphical abstract The formation of complexes of β-cyclodextrin with selected n-alkanes, polyaromatics, and organic acids in an anhydrous environment is studied by differential scanning calorimetry, IR spectroscopy, and molecular modeling. The results obtained confirm the possible formation of multiple inclusion complexes with guest molecules capable of forming hydrogen bonds and give a new perspective on the mechanism of formation of host-guest complexes. PMID:27518085

  18. Complex wave patterns in an effective reaction-diffusion model for chemical reactions in microemulsions.

    PubMed

    Alonso, Sergio; John, Karin; Bär, Markus

    2011-03-01

    An effective medium theory is employed to derive a simple qualitative model of a pattern forming chemical reaction in a microemulsion. This spatially heterogeneous system is composed of water nanodroplets randomly distributed in oil. While some steps of the reaction are performed only inside the droplets, the transport through the extended medium occurs by diffusion of intermediate chemical reactants as well as by collisions of the droplets. We start to model the system with heterogeneous reaction-diffusion equations and then derive an equivalent effective spatially homogeneous reaction-diffusion model by using earlier results on homogenization in heterogeneous reaction-diffusion systems [S.Alonso, M.Bär, and R.Kapral, J. Chem. Phys. 134, 214102 (2009)]. We study the linear stability of the spatially homogeneous state in the resulting effective model and obtain a phase diagram of pattern formation, that is qualitatively similar to earlier experimental results for the Belousov-Zhabotinsky reaction in an aerosol OT (AOT)-water-in-oil microemulsion [V.K.Vanag and I.R.Epstein, Phys. Rev. Lett. 87, 228301 (2001)]. Moreover, we reproduce many patterns that have been observed in experiments with the Belousov-Zhabotinsky reaction in an AOT oil-in-water microemulsion by direct numerical simulations.

  19. 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.

  20. 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.

  1. Bow shock formation in a complex plasma.

    PubMed

    Saitou, Y; Nakamura, Y; Kamimura, T; Ishihara, O

    2012-02-10

    A bow shock is observed in a two-dimensional supersonic flow of charged microparticles in a complex plasma. A thin conducting needle is used to make a potential barrier as an obstacle for the particle flow in the complex plasma. The flow is generated and the flow velocity is controlled by changing a tilt angle of the device under the gravitational force. A void, microparticle-free region, is formed around the potential barrier surrounding the obstacle. The flow is bent around the leading edge of the void and forms an arcuate structure when the flow is supersonic. The structure is characterized by the bow shock as confirmed by a polytropic hydrodynamic theory as well as numerical simulation. PMID:22401079

  2. 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.

  3. Photochemistry of group 6 Fischer carbene complexes: beyond the photocarbonylation reaction.

    PubMed

    Fernández, Israel; Cossío, Fernando P; Sierra, Miguel A

    2011-07-19

    The seminal report by Hegedus in 1982, showing that alkoxychromium(0) carbenes reacted with imines under bright Colorado sunlight to yield β-lactams, marked the beginning of a key reaction in organometallic chemistry. Very little was known about the mechanism of this reaction. In fact, Hegedus proposed the reversible generation of a chromium-coordinated ketene, which would react with nucleophiles. This coordinated species would show all the advantages of ketenes without their shortcomings, namely, dimerization, formation of undesired adducts, and so forth. The quest for the detection of these species and the pursuit of the mechanism of the photocarbonylation (a reaction exclusive to Cr(0) and Mo(0) carbene complexes, not W(0) carbene complexes) remained unabated over the next 15 years. In fact, all attempts to experimentally determine the mechanism of this useful reaction have been fruitless. At the same time, the photocarbonylation of Cr(0) carbenes matured into a valuable synthetic reaction, allowing access to several families of organic compounds. Unfortunately, reactions other than photocarbonylation remained elusive. We used a combination of experimental and computational methodologies to study the photocarbonylation of Cr(0) carbene complexes and the subsequent reaction of the photogenerated ketenes with nucleophiles. In parallel, we discovered new photochemical processes and succeeded in making photoreactive the so-called "unreactive" W(0) carbene complexes. In this Account, we discuss the disentangling of the mechanisms of these transformations, thereby shedding some light onto the photochemistry of group 6 metal (Fischer) carbene complexes. The original designation of the electronic transitions of group 6 carbene complexes was reassigned, and the photocarbonylation step was analyzed again, resulting in the sequence S(0)-T(1)-S(0), which is far removed from conventional organic photochemistry. The T(1) species is a chromacyclopropanone; its unpaired

  4. 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.

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

    DOE PAGESBeta

    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

  6. 1H NMR studies of reactions of copper complexes with human blood plasma and urine.

    PubMed

    Bligh, S W; Boyle, H A; McEwen, A B; Sadler, P J; Woodham, R H

    1992-01-22

    Reactions of the copper complexes Cu(II)Cl2, [Cu(II)(EDTA)]2-, [Cu(II)2(DIPS)4] and [Cu(I)(DMP)2]+ (where DIPS is 3,5-diisopropylsalicylate and DMP is 2,9-dimethylphenanthroline) with human blood plasma and urine have been studied by 500 MHz 1H NMR spectroscopy, and CD spectroscopy has been used to monitor the transfer of Cu(II) onto albumin in plasma. The rate of transfer of Cu(II) from [Cu(II)(EDTA)]2- onto albumin as measured by CD (T1/2 26 min, 0.5 mM Cu, 21 degrees), was similar to the rate of Cu(II) binding to amino acids and citrate, and to the rate of formation of [Ca(II)(EDTA)]2- in plasma. Reactions of Cu(II)Cl2 and [Cu(II)2(DIPS)4] in plasma followed a similar course, but were more rapid. The latter complex also appeared to give rise to the displacement of lactate from protein binding. Reactions of copper complexes in plasma therefore involve a range of low Mr ligands as well as albumin, and the ligands play a major role in determining the kinetics of the reactions. These factors, as well as the partitioning of both complexes and displaced ligands into lipoproteins, are likely to play important roles in the molecular pharmacology of copper-containing drugs. In urine, His and formate were involved in EDTA and DIPS displacement from their respective copper complexes, and peaks for free DIPS and [Ca(II)(EDTA)]2- were observed. The complex (Cu(I)(DMP)2]+ appeared to be relatively stable in both plasma and urine. PMID:1739401

  7. [Riboflavin-radical formation by mechanochemical solid-state reaction using stainless steel vessel].

    PubMed

    Kondo, Shin-ichi; Furuta, Youji; Okita, Shintarou; Sasai, Yasushi; Aramaki, Hideki; Kuzuya, Masayuki

    2004-03-01

    The mechanochemical reaction of free riboflavin (FR) due to vibratory ball milling was carried out in a stainless steel vessel at room temperature under anaerobic conditions. The ESR of the fractured sample showed a broad single-line spectrum. It is suggested that the solid-state single-electron transfer (SSET) reaction from the surface of the stainless steel vessel to FR proceeded during the vibratory milling, resulting in the formation of the corresponding anion radicals. When the mechanochemical reaction of FR in the presence of calcium pantothenate (PC) was carried out, the radical concentration increased with the increasing PC content. It was shown that the anion radical in the metal complex was stable for a lengthy period of time even in highly humid air. PMID:15049132

  8. Experimental Astrochemistry: Molecular Formation via Grain-Surface Reactions

    NASA Astrophysics Data System (ADS)

    Congiu, E.

    2007-03-01

    Central to this thesis is the chemistry occurring on dust grain surfaces leading to the formation of molecules in the ISM, and, in particular, the laboratory simulation of formation mechanisms and formation rates. Surface chemistry plays a crucial role in the ISM because it produces key species that are not formed in gas-phase reactions at an efficient rate. Among them, molecular hydrogen (H_2) is by far the most important. In this work (Chapter 3), I shall address the experimental investigation of H_2 formation on diverse samples of amorphous silicates. The experimental work was conducted in the Physics Department laboratories at Syracuse University, New York, as part of the most successful programme of experiments so far to study the processes involved in the formation of molecular hydrogen on a variety of dust analogue materials, also including poly-crystalline olivine, amorphous carbon, and ices. The experiments were carried out through mass spectrometry and TPD techniques and under conditions that come as close as technically feasible to the ones in the most relevant ISM environments, namely, under ultra high vacuum pressures (low 10e-10 torr) and at surface temperatures between 6 and 30 K. Experimental studies of H_2 formation on amorphous olivines are of major concern in grain-surface chemistry because amorphous silicates are believed, together with carbonaceous materials, to be the most realistic analogues of bare cosmic dust surfaces in diffuse clouds. In my doctorate work I carried out numerous experiments on a set of several samples of amorphous olivines of the type (Mg_x,Fe_1-x)_2SiO_4, namely, samples made up of diverse amounts of Mg and Fe. Besides, in Chapter 4, I shall address the project and the construction of a FT-RAIRS facility that is to integrate the existent research apparatus in the laboratory at Syracuse University. I shall first discuss the FT-IR spectroscopy, then I shall focus on a particular technique used in surface science called

  9. 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. PMID:19623245

  10. 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.

  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. 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.

  13. 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.

  14. Dynamics of Lane Formation in Driven Binary Complex Plasmas

    SciTech Connect

    Suetterlin, K. R.; Ivlev, A. V.; Raeth, C.; Thomas, H. M.; Rubin-Zuzic, M.; Morfill, G. E.; Wysocki, A.; Loewen, H.; Goedheer, W. J.; Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.

    2009-02-27

    The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.

  15. Formation of Formaldehyde and Glyoxal From The Toluene + Oh Reaction

    NASA Astrophysics Data System (ADS)

    Volkamer, R.; Wirtz, K.; Platt, U.

    Aromatic hydrocarbons are emitted into the urban atmosphere mostly as part of au- tomobile exhaust. Toluene thereby is the single most abundant aromatic compound emitted into the atmosphere. Despite the importance of aromatic hydrocarbon oxi- dation for the formation of photooxidants from urban plumes the oxidation mech- anism of aromatic hydrocarbons is far from being understood.Considerable progress has been made in recent years concerning our understanding of the ring-retaining path- ways, while major uncertainties remain to be linked with the operative ring-cleavage mechanisms. The representation of the aromatic oxidation in presently used chemical transport models (CTM) is estimated a major uncertainty for these models. This work presents data on formaldehyde (HCHO) and glyoxal, which are two impor- tant ring-cleavage products from the the toluene + OH reaction. While glyoxal was observed to form as a high yield primary product (Volkamer et al., JPC A, 2001, 105, 7865-7874) the formation of HCHO is observed delayed, i.e. as a secondary prod- uct. The temporal behaviour of glyoxal and HCHO concentrations allowed to con- clude that short lived stable intermediate compounds must form upon ring-cleavage of toluene. With an approximate lifetime of the order of ten minutes, these highly reac- tive intermediate compounds are likely to be a significant radical source. Atmospheric implications of the results are adressed.

  16. Ethanol oxidation by imidorhenium(V) complexes: formation of amidorhenium(III) complexes.

    PubMed

    Suing, A L; Dewan, C R; White, P S; Thorp, H H

    2000-12-25

    The reaction of Re(NC6H4R)Cl3(PPh3)2 (R = H, 4-Cl, 4-OMe) with 1,2-bis(diphenylphosphino)ethane (dppe) is investigated in refluxing ethanol. The reaction produces two major products, Re(NC6H4R)Cl(dppe)(2)2+ (R = H, 1-H; R = Cl, 1-Cl; R = OMe, 1-OMe) and the rhenium(III) species Re(NHC6H4R)Cl(dppe)2+ (R = H, 2-H; R = Cl, 2-Cl). Complexes 1-H (orthorhombic, Pcab, a = 22.3075(10) A, b = 23.1271(10) A, c = 23.3584(10) A, Z = 8), 1-Cl (triclinic, P1, a = 11.9403(6) A, b = 14.6673(8) A, c = 17.2664(9) A, alpha = 92.019(1) degrees, beta = 97.379(1) degrees, gamma = 90.134(1) degrees, Z = 2), and 1-OMe (triclinic, P1, a = 11.340(3) A, b = 13.134(4) A, c = 13.3796(25) A, alpha = 102.370(20) degrees, beta = 107.688(17) degrees, gamma = 114.408(20) degrees, Z = 1) are crystallographically characterized and show an average Re-N bond length (1.71 A) typical of imidorhenium(V) complexes. There is a small systematic decrease in the Re-N bond length on going from Cl to H to OMe. Complex 2-Cl (monoclinic, Cc, a = 24.2381(11) A, b = 13.4504(6) A, c = 17.466(8) A, beta = 97.06900(0) degrees, Z = 4) is also crystallographically characterized and shows a Re-N bond length (1.98 A) suggestive of amidorhenium(III). The rhenium(III) complexes exhibit unusual proton NMR spectra where all of the resonances are found at expected locations except those for the amido protons, which are at 37.8 ppm for 2-Cl and 37.3 ppm for 1-H. The phosphorus resonances are also unremarkable, but the 13C spectrum of 2-Cl shows a significantly shifted resonance at 177.3 ppm, which is assigned to the ipso carbon of the phenylamido ligand. The extraordinary shifts of the amido hydrogen and ipso carbon are attributed to second-order magnetism that is strongly focused along the axially compressed amido axis. The reducing equivalents for the formation of the Re(III) product are provided by oxidation of the ethanol solvent, which produces acetal and acetaldehyde in amounts as much as 30 equiv based on the quantity of

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

    NASA Astrophysics Data System (ADS)

    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.PRLTAO0031-900710.1103/PhysRevLett.106.150602 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.

  18. 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. PMID:23030885

  19. 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.

  20. Stable RNA-DNA-RNA polymerase complexes can accompany formation of a single phosphodiester bond.

    PubMed

    Sylvester, J E; Cashel, M

    1980-03-18

    Incubation of RNA polymerase with poly[d(A-T)n] template results in a binary enzyme-DNA complex. Further addition of the dinucleotide UpA and [alpha-32P]UTP results in catalytic formation of the labeled trinucleotide UpApU until substrate exhaustion. In contrast, incubation of binary enzyme-DNA complexes with ApU and [alpha-32P]ATP results in labeled ApUpA formation to an extent that is stoichiometric with the amount of enzyme present despite an excess of substrates. The occurrence of ApUpA in a stable DNA-enzyme-RNA ternary complex is shown by gel exclusion chromatography, Millipore filtration, and the ability of ternary complexes to support subsequent RNA chain elongation. Radioactivity is not bound to Millipore filters when purified, labeled ApUpA is added to enzyme-DNA binary complexes. Hence, phosphodiester bond formation is required for stable ternary complex formation. The absence of the delta subunit of RNA polymerase or the addition of rifampicin to the reaction before ribonucleotide substrates results in catalytic ApUpA formation instead of stable ternary complexes.

  1. Reaction of monovalent gold complex salts with ferrocene thio derivatives

    SciTech Connect

    Perevalova, E.G.; Bavkova, T.V.; Grandberg, K.I.; Sazonenko, M.M.

    1986-02-01

    In a continuation of a study of the reactions of aurous complex salts with ferrocene thio derivatives, the authors studied the auration of 1,1-ferrocenylenedithiol (II). The auration of dithiol (II) by tris(triphenylphosphinegold)oxonium tetrafluoroborate was carried out in an argon atmosphere. Relative to the auration of ethyl cyanoacetate, the aurating capacity of the tris-(triphenylphosphinegold)sulfonium tetrafluorobroate is significantly lower than that of (Dh/sub 3/PAu)/sub 3/>0 +BF-/sub 4/ and (Ph/sub 3/PAu)/sub 4/N /SUP BF/ >-/sub 4/.

  2. Roles of acetone and diacetone alcohol in coordination and dissociation reactions of uranyl complexes.

    PubMed

    Rios, Daniel; Schoendorff, George; Van Stipdonk, Michael J; Gordon, Mark S; Windus, Theresa L; Gibson, John K; de Jong, Wibe A

    2012-12-01

    Combined collision-induced dissociation mass spectrometry experiments with DFT and MP2 calculations were employed to elucidate the molecular structures and energetics of dissociation reactions of uranyl species containing acetone and diacetone alcohol ligands. It is shown that solutions containing diacetone alcohol ligands can produce species with more than five oxygen atoms available for coordination. Calculations confirm that complexes with up to four diacetone alcohol ligands can be energetically stable but that the effective number of atoms coordinating with uranium in the equatorial plane does not exceed five. Water elimination reactions of diacetone alcohol ligands are shown to have two coordination-dependent reaction channels, through formation of mesityl oxide ligands or formation of alkoxide and protonated mesityl oxide species. The present results provide an explanation for the implausible observation of "[UO(2)(ACO)(6,7,8)](2+)" in and observed water-elimination reactions from purportedly uranyl-acetone complexes (Rios, D.; Rutkowski, P. X.; Van Stipdonk, M. J.; Gibson, J. K. Inorg. Chem. 2011, 50, 4781). PMID:23146003

  3. Turing instability in reaction-diffusion models on complex networks

    NASA Astrophysics Data System (ADS)

    Ide, Yusuke; Izuhara, Hirofumi; Machida, Takuya

    2016-09-01

    In this paper, the Turing instability in reaction-diffusion models defined on complex networks is studied. Here, we focus on three types of models which generate complex networks, i.e. the Erdős-Rényi, the Watts-Strogatz, and the threshold network models. From analysis of the Laplacian matrices of graphs generated by these models, we numerically reveal that stable and unstable regions of a homogeneous steady state on the parameter space of two diffusion coefficients completely differ, depending on the network architecture. In addition, we theoretically discuss the stable and unstable regions in the cases of regular enhanced ring lattices which include regular circles, and networks generated by the threshold network model when the number of vertices is large enough.

  4. 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.

  5. 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. PMID:25302375

  6. 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.

  7. Novel mechanistic aspects on the reaction between low spin Fe(II) Schiff base amino acid complexes and hydrogen peroxide-spectrophotometric tracer of intraperoxo intermediate catalyzed reaction.

    PubMed

    Awad, Aida M; Shaker, Ali Mohamad; Zaki, Ahmad Borhan El-Din; Nassr, Lobna Abdel-Mohsen Ebaid

    2008-12-01

    The kinetics and mechanism of the reaction of hydrogen peroxide with some Fe(II) Schiff base complexes were investigated spectrophotometrically in aqueous solution at pH 8 and 35 degrees C under pseudo-first-order conditions. The used ligands were derived from salicylaldehyde or o-hydroxynaphthaldehyde and some amino acids (l-leucine, l-iso-leucine, l-serine, l-methionine and dl-tryptophan). It was found that the formation of the purple interaperoxo complex appears only above pH 7.5. The reaction consists of two steps. The first step involves reversible formation of the intraperoxo intermediate which renders irreversible at pH 8. The second step consists of inner-sphere electron transfer. The suggested scheme illustrated first-order kinetics at low [H(2)O(2)] and zero-order at high [H(2)O(2)]. Moreover, the activation parameters of the reaction were evaluated. PMID:18394952

  8. Complex I Function and Supercomplex Formation Are Preserved in Liver Mitochondria Despite Progressive Complex III Deficiency

    PubMed Central

    Davoudi, Mina; Kotarsky, Heike; Hansson, Eva; Fellman, Vineta

    2014-01-01

    Functional oxidative phosphorylation requires appropriately assembled mitochondrial respiratory complexes and their supercomplexes formed mainly of complexes I, III and IV. BCS1L is the chaperone needed to incorporate the catalytic subunit, Rieske iron-sulfur protein, into complex III at the final stage of its assembly. In cell culture studies, this subunit has been considered necessary for supercomplex formation and for maintaining the stability of complex I. Our aim was to assess the importance of fully assembled complex III for supercomplex formation in intact liver tissue. We used our transgenic mouse model with a homozygous c.232A>G mutation in Bcs1l leading to decreased expression of BCS1L and progressive decrease of Rieske iron-sulfur protein in complex III, resulting in hepatopathy. We studied supercomplex formation at different ages using blue native gel electrophoresis and complex activity using high-resolution respirometry. In isolated liver mitochondria of young and healthy homozygous mutant mice, we found similar supercomplexes as in wild type. In homozygotes aged 27–29 days with liver disorder, complex III was predominantly a pre-complex lacking Rieske iron-sulfur protein. However, the main supercomplex was clearly detected and contained complex III mainly in the pre-complex form. Oxygen consumption of complex IV was similar and that of complex I was twofold compared with controls. These complexes in free form were more abundant in homozygotes than in controls, and the mRNA of complex I subunits were upregulated. In conclusion, when complex III assembly is deficient, the pre-complex without Rieske iron-sulfur protein can participate with available fully assembled complex III in supercomplex formation, complex I function is preserved, and respiratory chain stability is maintained. PMID:24466228

  9. Complex reaction networks in high temperature hydrocarbon chemistry.

    PubMed

    Mutlay, İbrahim; Restrepo, Albeiro

    2015-03-28

    Complex chemical reaction mechanisms of high temperature hydrocarbon decomposition are represented as networks and their underlying graph topologies are analyzed as a dynamic system. As model reactants, 1,3-butadiene, acetylene, benzene, ethane, ethylene, methane, methyl isobutyl ketone (MIBK) and toluene are chosen in view of their importance for the global environment, energy technologies as well as their quantum chemical properties. Accurate kinetic mechanisms are computationally simulated and converted to bipartite graphs for the incremental conversion steps of the main reactant. Topological analysis of the resulting temporal networks reveals novel features unknown to classical chemical kinetics theory. The time-dependent percolation behavior of the chemical reaction networks shows infinite order phase transition and a unique correlation between the percolation thresholds and electron distribution of the reactants. These observations are expected to yield important applications in the development of a new theoretical perspective to chemical reactions and technological processes e.g. inhibition of greenhouse gases, efficient utilization of fossil fuels, and large scale carbon nanomaterial production. PMID:25720589

  10. 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.

  11. Complexes of sulfur-containing ligands. I. Factors influencing complex formation between D-penicillamine and copper (II) ion.

    PubMed

    Gergely, A; Sóvágó, I

    1978-07-01

    Complex formation and redox reactions between copper (II) ion and D-penicillamine were studied in detail as functions of the metal/-ligand ratio and the concentration of halide ions. It was established that a copper (I)- D-penicillamine polymeric complex of amphoteric character is formed when excess D-penicillamine is present. When the D-penicillamine/copper (II) ratio = 1.45 in the starting reaction mixture, a mixed valence complex with an intense red-violet color is formed. The formation of this compound, which contains 44% copper (II) ion, is greatly influenced by the experimental conditions, primarily by the concentration of halide ions. The main chemical and physical characteristics of the mixed valence complex were determined via magnetic and spectroscopic measurements. It was further established that a very intense blue complex is formed when the D-penicillamine/copper (II) ratio = 2 and halide ions are present. On the basis of the nature of the products formed under various conditions it was concluded that the copper (II)-D-penicillamine system may serve as a good model for studying the binding sites of copper-containing proteins. PMID:210846

  12. Exploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex.

    PubMed

    Desnoyer, Addison N; Friese, Florian W; Chiu, Weiling; Drover, Marcus W; Patrick, Brian O; Love, Jennifer A

    2016-03-14

    Recently, esters have received much attention as transmetalation partners for cross-coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}2(μ-η(2):η(2)-C6H6)] (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η(2)-carbonyl complexes. In contrast, acetylthioesters underwent rapid Cacyl-S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross-coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η(2)-carbonyl complex, phenyl esters were found to predominantly undergo Caryl-O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2-naphthyl acetate was also found to undergo clean Caryl-O bond cleavage, and although stoichiometric cross-coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive.

  13. Exploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex.

    PubMed

    Desnoyer, Addison N; Friese, Florian W; Chiu, Weiling; Drover, Marcus W; Patrick, Brian O; Love, Jennifer A

    2016-03-14

    Recently, esters have received much attention as transmetalation partners for cross-coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}2(μ-η(2):η(2)-C6H6)] (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η(2)-carbonyl complexes. In contrast, acetylthioesters underwent rapid Cacyl-S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross-coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η(2)-carbonyl complex, phenyl esters were found to predominantly undergo Caryl-O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2-naphthyl acetate was also found to undergo clean Caryl-O bond cleavage, and although stoichiometric cross-coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive. PMID:26879766

  14. 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.

  15. The SWI/SNF chromatin remodeling complex regulates germinal center formation by repressing Blimp-1 expression.

    PubMed

    Choi, Jinwook; Jeon, Shin; Choi, Seungjin; Park, Kyungsoo; Seong, Rho Hyun

    2015-02-17

    Germinal center (GC) reaction is crucial in adaptive immune responses. The formation of GC is coordinated by the expression of specific genes including Blimp-1 and Bcl-6. Although gene expression is critically influenced by the status of chromatin structure, little is known about the role of chromatin remodeling factors for regulation of GC formation. Here, we show that the SWI/SNF chromatin remodeling complex is required for GC reactions. Mice lacking Srg3/mBaf155, a core component of the SWI/SNF complex, showed impaired differentiation of GC B and follicular helper T cells in response to T cell-dependent antigen challenge. The SWI/SNF complex regulates chromatin structure at the Blimp-1 locus and represses its expression by interacting cooperatively with Bcl-6 and corepressors. The defect in GC reactions in mice lacking Srg3 was due to the derepression of Blimp-1 as supported by genetic studies with Blimp-1-ablated mice. Hence, our study identifies the SWI/SNF complex as a key mediator in GC reactions by modulating Bcl-6-dependent Blimp-1 repression.

  16. Activation of immobilized plasminogen by tissue activator. Multimolecular complex formation

    SciTech Connect

    Silverstein, R.L.; Nachman, R.L.; Leung, L.L.; Harpel, P.C.

    1985-08-25

    Ternary complex formation of tissue plasminogen activator (TPA) and plasminogen (Plg) with thrombospondin (TSP) or histidine-rich glycoprotein (HRGP) has been demonstrated using an enzyme-linked immunosorbent assay, an affinity bead assay, and a rocket immunoelectrophoresis assay. The formation of these complexes was specific, concentration dependent, saturable, lysine binding site-dependent, and inhibitable by fluid phase plasminogen. Apparent Kd values were approximately 12-36 nM for the interaction of TPA with TSP-Plg complexes and 15-31 nM with HRGP-Plg complexes. At saturation the relative molar stoichiometry of Plg:TPA was 3:1 within the TSP-containing complexes and 1:1 within HRGP-containing complexes. The activation of Plg to plasmin by TPA on TSP- and HRGP-coated surfaces was studied using a synthetic fluorometric plasmin substrate (D-Val-Leu-Lys-7-amino-4-trifluoromethyl coumarin). Kinetic analysis demonstrated a marked increase in the affinity of TPA for plasminogen in the presence of surface-associated TSP or HRGP. Complex formation of locally released tissue plasminogen activator with Plg immobilized on TSP or HRGP surfaces may thus play an important role in effecting proteolytic events in nonfibrin-containing microenvironments.

  17. The significance of surface complexation reactions in hydrologic systems: a geochemist's perspective

    NASA Astrophysics Data System (ADS)

    Koretsky, C.

    2000-05-01

    Complexation reactions at the mineral-water interface affect the transport and transformation of metals and organic contaminants, nutrient availability in soils, formation of ore deposits, acidification of watersheds and the global cycling of elements. Such reactions can be understood by quantifying speciation reactions in homogeneous aqueous solutions, characterizing reactive sites at mineral surfaces and developing models of the interactions between aqueous species at solid surfaces. In this paper, the application of thermodynamic principles to quantify aqueous complexation reactions is described. This is followed by a brief overview of a few of the methods that have been used to characterize reactive sites on mineral surfaces. Next, the application of empirical and semi-empirical models of adsorption at the mineral-water interface, including distribution coefficients, simple ion exchange models, and Langmuir and Freundlich isotherms is discussed. Emphasis is placed on the limitations of such models in providing an adequate representation of adsorption in hydrological systems. These limitations arise because isotherms do not account for the structure of adsorbed species, nor do they account for the development of surface charge with adsorption. This is contrasted with more sophisticated models of adsorption, termed 'surface complexation models', which include the constant capacitance model, the diffuse layer model, the triple layer model and the MUSIC model. In these models, speciation reactions between surface functional groups and dissolved species control the variable surface charge build-up and the specific adsorption properties of minerals in aqueous solutions. Next, the influence of mineral surface speciation on the reactivity of adsorbed species and on far from equilibrium dissolution rates of minerals is discussed. Finally, the applicability of microscopic models of surface complexation to field-scale systems is explored and the need to integrate

  18. 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

  19. Molecular Epoxidation Reactions Catalyzed by Rhenium, Molybdenum, and Iron Complexes.

    PubMed

    Kück, Jens W; Reich, Robert M; Kühn, Fritz E

    2016-02-01

    Epoxidations are of high relevance in many organic syntheses, both in industry and academia. In this personal account, the development of rhenium, molybdenum, and iron complexes in molecular epoxidation catalysis is presented. Methyltrioxorhenium (MTO) is the benchmark catalyst for these reactions, with a thoroughly investigated mechanism and reactivity profile. More recently, highly active molecular molybdenum and iron catalysts have emerged, challenging the extraordinary role of MTO in epoxidation catalysis with high turnover frequencies (TOFs). This development is highlighted in its use of cheaper, more readily available metals, and the challenges of using base metals in catalysis are discussed. These results show the promise that relatively cheap and abundant metals, such as molybdenum and iron, hold for the future of epoxidation catalysis. PMID:26776087

  20. 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.

  1. WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H{sub 2}, AT 10 K

    SciTech Connect

    Oba, Y.; Watanabe, N.; Hama, T.; Kuwahata, K.; Hidaka, H.; Kouchi, A.

    2012-04-10

    The present study experimentally demonstrated that solid H{sub 2}O is formed through the surface reaction OH + H{sub 2} at 10 K. This is the first experimental evidence of solid H{sub 2}O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H{sub 2}O formation through the reaction OH + H{sub 2} is about one order of magnitude more effective than HDO formation through the reaction OH + D{sub 2}. This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling.

  2. The formation of bifurcated charge transfer complexes with molecular iodine

    NASA Astrophysics Data System (ADS)

    Kulevsky, Norman; Pierce, Ken

    1993-03-01

    I 2 complexes with triptycene and several di- and triaryl derivatives of methane and ethane were studied. For these complexes the values of λ CT are virtually identical to those reported for the complexes with the analogous monoaryl donors, while the values of λ for their blue shifted I 2 peaks are significantly lower than those for the monoaryl complexes. Both the equilibrium constants and - ΔH 0 values for the formation of complexes from the components lead to the conclusion that the complexes with the di- and triaryl compounds are more stable than those with the monoaryl donors. For the diaryl donors, the Δ S0298 values for complex formation are less favorable than those of the monoaryl donors. The dipole moment for I 2 in diphenylmethane is larger than the moment of I 2 in toluene. All of these observations can be explained by taking into account the transannular effect of one aromatic ring on another and viewing the complexes as bifurcated ones in which the I atom at one end of an I 2 molecule simultaneously interacts with two rings in the donor molecules.

  3. New insights into formation of trivalent actinides complexes with DTPA.

    PubMed

    Leguay, Sébastien; Vercouter, Thomas; Topin, Sylvain; Aupiais, Jean; Guillaumont, Dominique; Miguirditchian, Manuel; Moisy, Philippe; Le Naour, Claire

    2012-12-01

    Complexation of trivalent actinides with DTPA (diethylenetriamine pentaacetic acid) was studied as a function of pcH and temperature in (Na,H)Cl medium of 0.1 M ionic strength. Formation constants of both complexes AnHDTPA(-) and AnDTPA(2-) (where An stands for Am, Cm, and Cf) were determined by TRLFS, CE-ICP-MS, spectrophotometry, and solvent extraction. The values of formation constants obtained from the different techniques are coherent and consistent with reinterpreted literature data, showing a higher stability of Cf complexes than Am and Cm complexes. The effect of temperature indicates that formation constants of protonated and nonprotonated complexes are exothermic with a high positive entropic contribution. DFT calculations were also performed on the An/DTPA system. Geometry optimizations were conducted on AnDTPA(2-) and AnHDTPA(-) considering all possible protonation sites. For both complexes, one and two water molecules in the first coordination sphere of curium were also considered. DFT calculations indicate that the lowest energy structures correspond to protonation on oxygen that is not involved in An-DTPA bonds and that the structures with two water molecules are not stable.

  4. DNA strand exchange stimulated by spontaneous complex formation with cationic comb-type copolymer.

    PubMed

    Kim, Won Jong; Akaike, Toshihiro; Maruyama, Atsushi

    2002-10-30

    Cationic comb-type copolymers (CCCs) composed of a polycation backbone and water-soluble side chains accelerate by 4-5 orders the DNA strand exchange reaction (SER) between double helical DNA and its homologous single-strand DNA. The accelerating effect is considered due to alleviation of counterion association during transitional intermediate formation in sequential displacement pathway. CCCs stabilize not only matured hybrids but also the nucleation complex to accelerate hybridization. PMID:12392411

  5. 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.

  6. 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.

  7. 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.

  8. 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. PMID:17997209

  9. 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.

  10. Multiscale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Reactions.

    PubMed

    Burke, Michael P; Goldsmith, C Franklin; Klippenstein, Stephen J; Welz, Oliver; Huang, Haifeng; Antonov, Ivan O; Savee, John D; Osborn, David L; Zádor, Judit; Taatjes, Craig A; Sheps, Leonid

    2015-07-16

    The present paper describes further development of the multiscale informatics approach to kinetic model formulation of Burke et al. (Burke, M. P.; Klippenstein, S. J.; Harding, L. B. Proc. Combust. Inst. 2013, 34, 547-555) that directly incorporates elementary kinetic theories as a means to provide reliable, physics-based extrapolation of kinetic models to unexplored conditions. Here, we extend and generalize the multiscale informatics strategy to treat systems of considerable complexity-involving multiwell reactions, potentially missing reactions, nonstatistical product branching ratios, and non-Boltzmann (i.e., nonthermal) reactant distributions. The methodology is demonstrated here for a subsystem of low-temperature propane oxidation, as a representative system for low-temperature fuel oxidation. A multiscale model is assembled and informed by a wide variety of targets that include ab initio calculations of molecular properties, rate constant measurements of isolated reactions, and complex systems measurements. Active model parameters are chosen to accommodate both "parametric" and "structural" uncertainties. Theoretical parameters (e.g., barrier heights) are included as active model parameters to account for parametric uncertainties in the theoretical treatment; experimental parameters (e.g., initial temperatures) are included to account for parametric uncertainties in the physical models of the experiments. RMG software is used to assess potential structural uncertainties due to missing reactions. Additionally, branching ratios among product channels are included as active model parameters to account for structural uncertainties related to difficulties in modeling sequences of multiple chemically activated steps. The approach is demonstrated here for interpreting time-resolved measurements of OH, HO2, n-propyl, i-propyl, propene, oxetane, and methyloxirane from photolysis-initiated low-temperature oxidation of propane at pressures from 4 to 60 Torr and

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

    DOE PAGESBeta

    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

  12. Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction

    PubMed Central

    2013-01-01

    Irradiation of CpRh(PMe3)(C2H4) (1; Cp = η5-C5H5) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable η2-C,C-coordinated pentafluoropyridine complex, CpRh(PMe3)(η2-C,C-C5NF4) (2). The molecular structure of 2 was determined by single-crystal X-ray diffraction, showing coordination by C3–C4, unlike previous structures of pentafluoropyridine complexes that show N-coordination. Corresponding experiments with 2,3,5,6-tetrafluoropyridine yield the C–H oxidative addition product CpRh(PMe3)(C5NF4)H (3). In contrast, UV irradiation of 1 in hexane, in the presence of 4-substituted tetrafluoropyridines C5NF4X, where X = NMe2, OMe, results in elimination of C2H4 and HF to form the metallacycles CpRh(PMe3)(κ2-C,C-CH2N(CH3)C5NF3) (4) and CpRh(PMe3)(κ2-C,C-CH2OC5NF3) (5), respectively. The X-ray structure of 4 shows a planar RhCCNC-five-membered ring. Complexes 2–5 may also be formed by thermal reaction of CpRh(PMe3)(Ph)H with the respective pyridines at 50 °C. PMID:24563575

  13. 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.

  14. Pattern formation in oscillatory complex networks consisting of excitable nodes

    NASA Astrophysics Data System (ADS)

    Liao, Xuhong; Xia, Qinzhi; Qian, Yu; Zhang, Lisheng; Hu, Gang; Mi, Yuanyuan

    2011-05-01

    Oscillatory dynamics of complex networks has recently attracted great attention. In this paper we study pattern formation in oscillatory complex networks consisting of excitable nodes. We find that there exist a few center nodes and small skeletons for most oscillations. Complicated and seemingly random oscillatory patterns can be viewed as well-organized target waves propagating from center nodes along the shortest paths, and the shortest loops passing through both the center nodes and their driver nodes play the role of oscillation sources. Analyzing simple skeletons we are able to understand and predict various essential properties of the oscillations and effectively modulate the oscillations. These methods and results will give insights into pattern formation in complex networks and provide suggestive ideas for studying and controlling oscillations in neural networks.

  15. Gas-phase activation and reaction dynamics of chiral ion-dipole complexes.

    PubMed

    Filippi, Antonello; Speranza, Maurizio

    2003-11-01

    A family of enantiomerically pure oxonium ions, that is O-protonated 1-aryl-1-methoxyethanes, has been generated in the gas phase by the (CH(3))(2)Cl(+) methylation of the corresponding 1-arylethanols. Some information on their reaction dynamics was obtained from a detailed kinetic study of their inversion of configuration and dissociation. The activation parameters of the inversion reaction are found to obey two different isokinetic relationships depending upon the nature and the position of the substituents in the oxonium ions. In contrast, the activation parameters of the dissociation reaction obey a single isokinetic relationship. The inversion and dissociation rate constants do not follow simple linear free-energy relationships. This complicated kinetic picture has been rationalized in terms of different activation dynamics in gaseous CH(3)Cl, which, in turn, determine the reaction dynamics of the oxonium ion. When the predominant activation of the oxonium ion involves resonant energy exchange from the 1015 cm(-1) CH(3) rocking mode of unperturbed CH(3)Cl, the inversion reaction proceeds through the dynamically most favored TS, characterized by the unassisted C(alpha)bond;O bond elongation. When, instead, the activation of the oxonium ions requires the formation of an intimate encounter complex with CH(3)Cl, the inversion reaction takes place via the energetically most favored TS, characterized by multiple coordination of the CH(3)OH moiety with the H(alpha) and H(ortho) atoms of the benzylic residue. The activation dynamics operating in the intimate encounter complex with CH(3)Cl is also responsible for the dissociation of most selected oxonium ions.

  16. Oxidation Reactions of Dithiocarbamate Complexes of Ruthenium(II).

    PubMed

    Leung, Wa-Hung; Chim, Joyce L. C.; Hou, Hongwei; Hun, Tom S. M.; Williams, Ian D.; Wong, Wing-Tak

    1997-09-24

    The reaction of Ru(Et(2)dtc)(2)(DMSO)(2) (Et(2)dtc = N,N-diethyldithiocarbamate; DMSO = dimethyl sulfoxide) with t-BuNC gave trans-Ru(Et(2)dtc)(2)(CN-t-Bu)(2), 1. Complex 1 crystallizes in the monoclinic space group P2(1)/n with a = 9.753(2) Å, b = 11.583(2) Å, c = 12.974(2) Å, and beta = 91.8(2) degrees for Z = 2. The crystal structure of 1 shows the trans disposition of the two isocyanides; the mean Ru-S and Ru-C distances are 2.409 and 1.977(2) Å, respectively. Treatment of [Ru(diene)Cl(2)](n)() with Na(Et(2)dtc) afforded Ru(Et(2)dtc)(2)(diene) (diene = bicyclo[2.2.1]hepta-2,5-diene (NBD), 2, 1,5-cyclooctadiene (COD), 3). Complex 2 crystallizes in the triclinic space group P&onemacr; with a = 7.316(1) Å, b = 10.346(1) Å, c = 15.123(2) Å, alpha = 103.69(2) degrees, beta = 93.54(2) degrees, and gamma = 100.61(2) degrees for Z = 2. The mean Ru-S and Ru-C distances in 2 are 2.416 and 2.137 Å, respectively. The reaction of cis-Ru(Et(2)dtc)(2)(CO)(2) with iodine gave the 2:1 molecular iodine complex cis-Ru(Et(2)dtc)(2)(CO)(2).(1)/(2)I(2) 4, which crystallizes in the monoclinic space group P2(1)/c with a = 7.347(2), b = 22.227(2) Å, c = 12.891(2) Å, and beta =95.98 (2) degrees for Z = 4. The mean Ru-S and Ru-C and the I-I distances in complex 4 are 2.427, 1.903, and 2.745(1) Å, respectively. Treatment of Ru(Et(2)dtc)(2)(DMSO)(2) with I(2) gave the linear Ru(II)-Ru(III)-Ru(III) trimer [Ru(3)(Et(2)dtc)(6)(DMSO)(2)](I(3))(2), 5, which crystallizes in the triclinic space group P&onemacr; with a = 14.125(3) Å, b = 20.829(6) Å, c = 13.658(3) Å, alpha = 97.57(2) degrees, beta = 110.01(2) degrees, and gamma = 71.25(2) degrees for Z = 2. The structure of complex 6 can be viewed as consisting of a {Ru(2)(III)(Et(2)dtc)(4)}(2+) core and a {Ru(II)(Et(2)dtc)(2)(DMSO)(2)} moiety, which are linked together via the two dithiocarbamate sulfurs of the latter. While the two Ru(III) centers are connected by a Ru-Ru single bond (Ru-Ru = 2.826(2) Å), there is no direct

  17. Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents

    NASA Astrophysics Data System (ADS)

    Usacheva, T. R.; Lan, Pham Thi; Sharnin, V. A.

    2014-06-01

    The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H2O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from log K ∘ = 1.10 to log K ∘ = 2.44, and an increase in the exothermicity of the reaction of its formation, from -5.9 to -16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H2O-DMSO solvents. Analysis of the reagents' solvation characteristics reveals that the increase in the reaction's exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Glysolv + 18C6solv ↔ [3Gly18C6]solv is due to differences in the change in the solvation state of the complex and the peptide (Δtr G ∘([3Gly18C6])-Δtr G ∘(3Gly)).

  18. Complexation of Al(III) with gluconate in alkaline to hyperalkaline solutions: formation, stability and structure.

    PubMed

    Pallagi, Attila; Tasi, Ágost Gyula; Peintler, Gábor; Forgo, Péter; Pálinkó, István; Sipos, Pál

    2013-10-01

    Contrary to suggestions in the literature, it has been proven that Al(III) forms a 1 : 1 complex with gluconate (hereafter Gluc(-)) in strongly alkaline (pH > 12) aqueous solutions. The complex formation was proven via(27)Al and (1)H NMR, freezing-point depression, polarimetric measurements as well as potentiometric and conductometric titrations. This complexation is a pH independent process, i.e., a condensation reaction takes place. The stability constant of the complex formed was derived from (1)H NMR and polarimetric measurements, and was found to be log K = 2.4 ± 0.4. In the complex formed, Al(III) has a tetrahedral geometry, and the Al(OH)4(-) is most probably statistically distributed between the alcoholate groups of the Gluc(-). PMID:23897548

  19. a Model Study of Complex Behavior in the Belousov - Reaction.

    NASA Astrophysics Data System (ADS)

    Lindberg, David Mark

    1988-12-01

    We have studied the complex oscillatory behavior in a model of the Belousov-Zhabotinskii (BZ) reaction in a continuously-fed stirred tank reactor (CSTR). The model consisted of a set of nonlinear ordinary differential equations derived from a reduced mechanism of the chemical system. These equations were integrated numerically on a computer, which yielded the concentrations of the constituent chemicals as functions of time. In addition, solutions were tracked as functions of a single parameter, the stability of the solutions was determined, and bifurcations of the solutions were located and studied. The intent of this study was to use this BZ model to explore further a region of complex oscillatory behavior found in experimental investigations, the most thorough of which revealed an alternating periodic-chaotic (P-C) sequence of states. A P-C sequence was discovered in the model which showed the same qualitative features as the experimental sequence. In order to better understand the P-C sequence, a detailed study was conducted in the vicinity of the P-C sequence, with two experimentally accessible parameters as control variables. This study mapped out the bifurcation sets, and included examination of the dynamics of the stable periodic, unstable periodic, and chaotic oscillatory motion. Observations made from the model results revealed a rough symmetry which suggests a new way of looking at the P-C sequence. Other nonlinear phenomena uncovered in the model were boundary and interior crises, several codimension-two bifurcations, and similarities in the shapes of areas of stability for periodic orbits in two-parameter space. Each earlier model study of this complex region involved only a limited one-parameter scan and had limited success in producing agreement with experiments. In contrast, for those regions of complex behavior that have been studied experimentally, the observations agree qualitatively with our model results. Several new predictions of the model

  20. Parameter estimation in complex flows with chemical reactions

    NASA Astrophysics Data System (ADS)

    Robinson, Daniel J.

    The estimation of unknown parameters in engineering and scientific models continues to be of great importance in order to validate them to available experimental data. These parameters of concern cannot be known beforehand, but must be measured experimentally, variables such as chemical species concentrations, pressures, or temperatures as examples. Particularly, in chemically reacting flows, the estimation of kinetic rate parameters from experimentally determined values is in great demand and not well understood. New parameter optimization algorithms have been developed from a Gauss-Newton formulation for the estimation of reaction rate parameters in several different complex flow applications. A zero-dimensional parameter estimation methodology was used in conjunction with a parameter sensitivity study and then applied to three-dimensional flow models. This new parameter estimation technique was applied to three-dimensional models for chemical vapor deposition of silicon carbide and gallium arsenide semiconductor materials. The parameter estimation for silicon carbide for several different operating points was in close agreement to experiment. The parameter estimation for gallium arsenide proved to be very accurate, being within four percent of the experimental data. New parameter estimation algorithms were likewise created for a three-dimensional multiphase model for methanol spray combustion. The kinetic rate parameters delivered results in close agreement to experiment for profiles of combustion species products. In addition, a new parameter estimation method for the determination of spray droplet sizes and velocities is presented. The results for methanol combustion chemical species profiles are in good agreement to experiment for several different droplet sizes. Lastly, the parameter estimation method was extended to a bio-kinetic application, namely mitochondrial cells, that are cardiac or respiratory cells found in animals and humans. The results for the

  1. Insights into the Halogen Oxidative Addition Reaction to Dinuclear Gold(I) Di(NHC) Complexes.

    PubMed

    Baron, Marco; Tubaro, Cristina; Basato, Marino; Isse, Abdirisak Ahmed; Gennaro, Armando; Cavallo, Luigi; Graiff, Claudia; Dolmella, Alessandro; Falivene, Laura; Caporaso, Lucia

    2016-07-11

    Gold(I) dicarbene complexes [Au2 (MeIm-Y-ImMe)2 ](PF6 )2 (Y=CH2 (1), (CH2 )2 (2), (CH2 )4 (4), MeIm=1-methylimidazol-2-ylidene) react with iodine to give the mixed-valence complex [Au(MeIm-CH2 -ImMe)2 AuI2 ](PF6 )2 (1 a(I) ) and the gold(III) complexes [Au2 I4 (MeIm-Y-ImMe)2 ](PF6 )2 (2 c(I) and 4 c(I) ). Reaction of complexes 1 and 2 with an excess of ICl allows the isolation of the tetrachloro gold(III) complexes [Au2 Cl4 (MeIm-CH2 -ImMe)2 ](PF6 )2 (1 c(Cl) ) and [Au2 Cl4 (MeIm-(CH2 )2 -ImMe)2 ](Cl)2 (2 c(Cl) -Cl) (as main product); remarkably in the case of complex 2, the X-ray molecular structure of the crystals also shows the presence of I-Au-Cl mixed-sphere coordination. The same type of coordination has been observed in the main product of the reaction of complexes 3 or 4 with ICl. The study of the reactivity towards the oxidative addition of halogens to a large series of dinuclear bis(dicarbene) gold(I) complexes has been extended and reviewed. The complexes react with Cl2 , Br2 and I2 to give the successive formation of the mixed-valence gold(I)/gold(III) n a(X) and gold(III) n c(X) (excluding compound 1 c(I) ) complexes. However, complex 3 affords with Cl2 and Br2 the gold(II) complex 3 b(X) [Au2 X2 (MeIm-(CH2 )3 -ImMe)2 ](PF6 )2 (X=Cl, Br), which is the predominant species over compound 3 c(X) even in the presence of free halogen. The observed different relative stabilities of the oxidised complexes of compounds 1 and 3 have also been confirmed by DFT calculations. PMID:27297191

  2. Standard thermodynamic functions of complex formation between Cu2+ and glycine in aqueous solution

    NASA Astrophysics Data System (ADS)

    Gorboletova, G. G.; Metlin, A. A.

    2013-05-01

    Heat effects of the interaction of copper(II) solutions with aminoacetic acid (glycine) are measured by the direct calorimetry at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 against a background of potassium nitrate. Standard enthalpy values for reactions of the formation of aminoacetic acid copper complexes in aqueous solutions are obtained using an equation with a single individual parameter by extrapolating it to zero ionic strength. The standard thermodynamic characteristics of complex formation in the Cu2+-glycine system are calculated. It is shown that glycine-like coordination is most likely in Cu(II) complexes with L-asparagine, L-glutamine, and L-valine.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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…

  8. Reactions of Co(III)–Nitrosyl Complexes with Superoxide and Their Mechanistic Insights

    PubMed Central

    Kumar, Pankaj; Lee, Yong-Min; Park, Young Jun; Siegler, Maxime A.; Karlin, Kenneth D.; Nam, Wonwoo

    2015-01-01

    New CoIII-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(12-TMC)CoIII(NO)]2+ (1) and [(13-TMC)CoIII(NO)]2+ (2), were synthesized via [(TMC)CoII(CH3CN)]2+ plus NO(g) reactions. Spectroscopic and structural characterization shows that these compounds bind the nitrosyl moiety in a bent end-on fashion. The CoIII-nitrosyl complexes, (1) and (2), reacted with KO2/2.2.2-Cryptand and produced [(12-TMC)CoII(NO2)]+ (3) and [(13-TMC)CoII(NO2)]+ (4), respectively; these possess O,O’-chelated nitrito ligands. Mechanistic studies using 18O-labeled superoxide (18O2•−) demonstrate that one oxygen atom in the nitrito ligand derives from superoxide and dioxygen produced comes from the other superoxide oxygen atom. Evidence supporting the formation of a Co-peroxynitrite intermediate is also presented. PMID:25793706

  9. Complex formation of fenchone with α-cyclodextrin: NMR titrations.

    PubMed

    Nowakowski, Michał; Ejchart, Andrzej

    2014-01-01

    (13)C NMR titration studies of inclusion complexes of bicyclic terpenoid, fenchone enantiomers with α-cyclodextrin revealed their 1:2 guest-host stoichiometry. Sequential binding constants were determined indicating a strong binding cooperativity of two α-cyclodextrin to fenchone. The overall association constants were used to calculate the Gibbs free energies of diastereomeric complex formation, which might be used as a measure of chiral recognition of fenchone by α-cyclodextrin. These results were compared with corresponding data derived for camphor, which is an isomeric bicyclic terpenoid.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Hierarchical structure formation of cylindrical brush polymer-surfactant complexes.

    PubMed

    Cong, Yang; Gunari, Nikhil; Zhang, Bin; Janshoff, Andreas; Schmidt, Manfred

    2009-06-01

    The complex formation of cylindrical brush polymers with poly(l-lysine) side chains (PLL) and sodium dodecyl sulfate (SDS) can induce a helical conformation of the cylindrical brush polymer in aqueous solution (Gunari, N.; Cong, Y.; Zhang, B.; Fischer, K.; Janshoff, A.; Schmidt, M. Macromol. Rapid Commun. 2008, 29, 821-825). Herein, we have systematically investigated the influence of surfactant, salt, and pH on the supramolecular structure formation. The cylindrical brush polymers and their complexes with surfactants were directly visualized by atomic force microscopy in air and in aqueous solution. The alkyl chain length (measured by the carbon number, n) of the surfactant plays a key role. While helical structures were formed with n=10, 11, and 12, no helices were observed with n<10 and n>13. Addition of salt destroys the helical structures as do pH conditions below 4 and above 6, most probably because the polymer-surfactant complexes start to disintegrate. Circular dichroism was utilized to monitor the PLL side chain conformation and clearly revealed that beta-sheet formation of the side chains induces the helical conformation of the atactic main chain. PMID:19326944

  16. The Dynamics of Coalition Formation on Complex Networks

    PubMed Central

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

    2015-01-01

    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. PMID:26303622

  17. 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.

  18. Three-Coordinate Terminal Imidoiron(III) Complexes: Structure, Spectroscopy, and Mechanism of Formation

    PubMed Central

    Cowley, Ryan E.; DeYonker, Nathan J.; Eckert, Nathan A.; Cundari, Thomas R.; DeBeer, Serena; Bill, Eckhard; Ottenwaelder, Xavier; Flaschenriem, Christine; Holland, Patrick L.

    2010-01-01

    Reaction of 1-adamantyl azide with iron(I) diketiminate precursors gives metastable but isolable imidoiron(III) complexes LFe=NAd (L = bulky β-diketiminate ligand; Ad = 1-adamantyl). This paper addresses: (1) the spectroscopic and structural characterization of the Fe=N multiple bond in these interesting three-coordinate iron imido complexes, and (2) the mechanism through which the imido complexes form. The iron(III) imido complexes have been examined by 1H NMR and EPR spectroscopies and temperature-dependent magnetic susceptibility (SQUID), and structurally characterized by crystallography and/or X-ray absorption (EXAFS) measurements. These data show that the imido complexes have quartet ground states and short (1.68 ± 0.01 Å) iron-nitrogen bonds. The formation of the imido complexes proceeds through unobserved iron–RN3 intermediates, which are indicated by QM/MM computations to be best described as iron(II) with an RN3 radical anion. The radical character on the organoazide bends its NNN linkage to enable easy N2 loss and imido complex formation. The product distribution between imidoiron(III) products and hexazene-bridged diiron(II) products is solvent-dependent, and the solvent dependence can be explained by coordination of certain solvents to the iron(I) precursor prior to interaction with the organoazide. PMID:20524625

  19. Formation of η{^'(958) meson bound states by the 6Li(γ,d) reaction

    NASA Astrophysics Data System (ADS)

    Miyatani, M.; Ikeno, N.; Nagahiro, H.; Hirenzaki, S.

    2016-07-01

    We have investigated the 6Li( γ, d) reaction theoretically for the formation of the η^'(958) mesic nucleus close to the recoilless kinematics. We have developed the theoretical formula and reported the quantitative results of the formation spectra for various cases in this article. We have found that the formation cross sections are reduced by the effects of the fragile deuteron form factor.

  20. 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

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

    PubMed Central

    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. PMID:27668216

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

    PubMed Central

    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.

  3. 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. PMID:27668216

  4. Complex formation between polyelectrolytes and oppositely charged oligoelectrolytes

    NASA Astrophysics Data System (ADS)

    Zhou, Jiajia; Barz, Matthias; Schmid, Friederike

    2016-04-01

    We study the complex formation between one long polyanion chain and many short oligocation chains by computer simulations. We employ a coarse-grained bead-spring model for the polyelectrolyte chains and model explicitly the small salt ions. We systematically vary the concentration and the length of the oligocation and examine how the oligocations affects the chain conformation, the static structure factor, the radial and axial distribution of various charged species, and the number of bound ions in the complex. At low oligocation concentration, the polyanion has an extended structure. Upon increasing the oligocation concentration, the polyanion chain collapses and forms a compact globule, but the complex still carries a net negative charge. Once the total charge of the oligocations is equal to that of the polyanion, the collapse stops and is replaced by a slow expansion. In this regime, the net charge on the complexes is positive or neutral, depending on the microion concentration in solution. The expansion can be explained by the reduction of the oligocation bridging. We find that the behavior and the structure of the complex are largely independent of the length of oligocations, and very similar to that observed when replacing the oligocations by multivalent salt cations, and conclude that the main driving force keeping the complex together is the release of monovalent counterions and coions. We speculate on the implications of this finding for the problem of controlled oligolyte release and oligolyte substitution.

  5. Electrogenic steps in the redox reactions catalyzed by photosynthetic reaction-centre complex from Rhodopseudomonas viridis.

    PubMed

    Dracheva, S M; Drachev, L A; Konstantinov, A A; Semenov AYu; Skulachev, V P; Arutjunjan, A M; Shuvalov, V A; Zaberezhnaya, S M

    1988-01-15

    Electrogenic and redox events in the reaction-centre complexes from Rhodopseudomonas viridis have been studied. In contrast to the previous points of view it is shown that all the four hemes of the tightly bound cytochrome c have different Em values (-60, +20, +310 and +380 mV). The first three hemes reveal alpha absorption maxima at 554 nm, 552 nm and 556 nm respectively. The 380-mV heme displays a split alpha band with a maximum at 559 nm and a shoulder at 552 nm. Such a splitting is due to non-degenerated Qx and Qy transitions in the iron-porphyrin ring as demonstrated by magnetic circular dichroism spectra. Fast kinetic measurements show that, at redox potentials when only high-potential hemes c-559 and c-556 are reduced, heme c-559 appears to be the electron donor to P-960+ (tau = 0.32 microsecond) whereas heme c-556 serves to rereduce c-559 (tau = 2.5 microsecond). Upon reduction of the third heme (c-552), the P-960+ reduction rate increases twofold (tau = 0.17 microsecond) and all photoinduced redox events within the cytochrome appear to be complete in less than 1 microsecond after the flash. The following sequence of the redox centers is tentatively suggested: c-554, c-556, c-552, c-559, P-960. To study electrogenesis, the reaction-centre complexes from Rps. viridis were incorporated into asolectin liposomes, and fast kinetics of laser flash-induced electric potential difference has been measured in proteoliposomes adsorbed on a phospholipid-impregnated film. The electrical difference induced by a single 15-ns flash was found to be as high as 100 mV. The photoelectric response has been found to involve four electrogenic stages associated with (I) QA reduction by P-960; (II) reduction of P-960+ by heme c-559; (III) reduction of c-559 by c-556 and (IV) protonation of Q2-B. The relative contributions of stages I, II, III and IV are found to be equal to 70%, 15%, 5% and 10%, respectively, of the overall electrogenic process. At the same time, the first three

  6. Terminal phosphanido rhodium complexes mediating catalytic P-P and P-C bond formation.

    PubMed

    Geer, Ana M; Serrano, Ángel L; de Bruin, Bas; Ciriano, Miguel A; Tejel, Cristina

    2015-01-01

    Complexes with terminal phosphanido (M-PR2) functionalities are believed to be crucial intermediates in new catalytic processes involving the formation of P-P and P-C bonds. We showcase here the isolation and characterization of mononuclear phosphanide rhodium complexes ([RhTp(H)(PR2)L]) that result from the oxidative addition of secondary phosphanes, a reaction that was also explored computationally. These compounds are active catalysts for the dehydrocoupling of PHPh2 to Ph2P-PPh2. The hydrophosphination of dimethyl maleate and the unactivated olefin ethylene is also reported. Reliable evidence for the prominent role of mononuclear phosphanido rhodium species in these reactions is also provided.

  7. 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.

  8. 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.

  9. Unified reaction pathways for the prebiotic formation of RNA and DNA nucleobases.

    PubMed

    Jeilani, Yassin Aweis; Williams, Phoenix N; Walton, Sofia; Nguyen, Minh Tho

    2016-07-27

    The reaction pathways for the prebiotic formation of nucleobases are complex and lead to the formation of a mixture of products. In the past 50 years, there has been a concerted effort for identifying a unified mechanism for the abiotic origin of the biomolecules but with little success. In the present theoretical study, we identified two prominent precursors for the building up of RNA and DNA nucleobases under prebiotic conditions: (a) 1,2-diaminomaleonitrile (DAMN), which is a tetramer of hydrogen cyanide (HCN), and (b) formamide, a hydrolysis product of HCN; it is important to emphasize that HCN is the source of both precursors. We find that free radical pathways are potentially appropriate to account for the origin of nucleobases from HCN. The current study unites the formamide pathways with the DAMN pathways. The mechanisms for the formation of the RNA and DNA nucleobases (uracil, adenine, purine, cytosine) were studied by quantum chemical computations using density functional theory at the B3LYP/6-311G(d,p) level. All the routes involved proceed with relatively low energy barriers (within the error margin of DFT methods). We showed that the radical mechanisms for the formation of nucleobases could be unified through common precursors. The results demonstrated that 4-aminoimidazole-5-carbonitrile (AICN), which is a known precursor for nucleobases, is a product of DAMN. The overall mechanisms are internally consistent with the abiotic formation of the nucleobases, namely (a) under a meteoritic impact scenario on the early Earth's surface that generated high internal energy, and/or (b) in the (gas phase) interstellar regions without the presence of catalysts.

  10. Long-lived excited states of zwitterionic copper(I) complexes for photoinduced cross-dehydrogenative coupling reactions.

    PubMed

    Wang, Bin; Shelar, Deepak Prakash; Han, Xian-Zhu; Li, Ting-Ting; Guan, Xiangguo; Lu, Wei; Liu, Kun; Chen, Yong; Fu, Wen-Fu; Che, Chi-Ming

    2015-01-12

    Four heteroleptic copper(I) complexes containing phenanthroline and monoanionic nido-carborane-diphosphine ligands have been prepared and structurally characterized by various spectroscopic techniques and X-ray diffraction. These complexes exhibit intense absorptions in the visible range and excited-state lifetimes on the microsecond scale. Their application in visible-light-induced cross-dehydrogenative coupling reactions was investigated. Preliminary studies showed that one of the four copper(I) complexes is an efficient catalyst for photoinduced oxidative C-H functionalization using oxygen as oxidant. Furthermore, α-functionalized tertiary amines were obtained in good-to-excellent yields by light irradiation (λ>420 nm) of a mixture of our Cu(I) complex, tertiary amines, and a variety of nucleophiles (nitroalkane, acetone, or indoles) under aerobic conditions. Electron paramagnetic resonance measurements provided evidence for the formation of superoxide radical anions (O2(-⋅)) rather than singlet oxygen ((1)O2) during these photocatalytic reactions. PMID:25413572

  11. Formation of antihydrogen by the charge-transfer reaction

    SciTech Connect

    Mitroy, J.

    1995-10-01

    The cross sections for antihydrogen formation in the {ital n}=1, 2, 3, 4, 5, 6, and 7 levels from antiproton-positronium collisions are computed in the unitarized Born approximation (UBA). Twenty-seven physical states of antihydrogen (1{ital s}{r_arrow}7{ital h}) and ten physical states (1{ital s}{r_arrow}4{ital f}) of positronium are included in the UBA basis. The peak cross section for antihydrogen formation from excited positronium targets is much larger than that from a ground-state positronium target at low incident energies. The high-{ital n} antihydrogen levels make a significant contribution to the total antihydrogen formation cross section, especially for incident positronium atoms in the Ps({ital n}=3) and Ps({ital n}=4) levels.

  12. Evaluation of maillard reaction variables and their effect on heterocyclic amine formation in chemical model systems.

    PubMed

    Dennis, Cara; Karim, Faris; Smith, J Scott

    2015-02-01

    Heterocyclic amines (HCAs), highly mutagenic and potentially carcinogenic by-products, form during Maillard browning reactions, specifically in muscle-rich foods. Chemical model systems allow examination of in vitro formation of HCAs while eliminating complex matrices of meat. Limited research has evaluated the effects of Maillard reaction parameters on HCA formation. Therefore, 4 essential Maillard variables (precursors molar concentrations, water amount, sugar type, and sugar amounts) were evaluated to optimize a model system for the study of 4 HCAs: 2-amino-3-methylimidazo-[4,5-f]quinoline, 2-amino-3-methylimidazo[4,5-f]quinoxaline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, and 2-amino-3,4,8-trimethyl-imidazo[4,5-f]quinoxaline. Model systems were dissolved in diethylene glycol, heated at 175 °C for 40 min, and separated using reversed-phase liquid chromatography. To define the model system, precursor amounts (threonine and creatinine) were adjusted in molar increments (0.2/0.2, 0.4/0.4, 0.6/0.6, and 0.8/0.8 mmol) and water amounts by percentage (0%, 5%, 10%, and 15%). Sugars (lactose, glucose, galactose, and fructose) were evaluated in several molar amounts proportional to threonine and creatinine (quarter, half, equi, and double). The precursor levels and amounts of sugar were significantly different (P < 0.05) in regards to total HCA formation, with 0.6/0.6/1.2 mmol producing higher levels. Water concentration and sugar type also had a significant effect (P < 0.05), with 5% water and lactose producing higher total HCA amounts. A model system containing threonine (0.6 mmol), creatinine (0.6 mmol), and glucose (1.2 mmol), with 15% water was determined to be the optimal model system with glucose and 15% water being a better representation of meat systems. PMID:25597341

  13. Evaluation of maillard reaction variables and their effect on heterocyclic amine formation in chemical model systems.

    PubMed

    Dennis, Cara; Karim, Faris; Smith, J Scott

    2015-02-01

    Heterocyclic amines (HCAs), highly mutagenic and potentially carcinogenic by-products, form during Maillard browning reactions, specifically in muscle-rich foods. Chemical model systems allow examination of in vitro formation of HCAs while eliminating complex matrices of meat. Limited research has evaluated the effects of Maillard reaction parameters on HCA formation. Therefore, 4 essential Maillard variables (precursors molar concentrations, water amount, sugar type, and sugar amounts) were evaluated to optimize a model system for the study of 4 HCAs: 2-amino-3-methylimidazo-[4,5-f]quinoline, 2-amino-3-methylimidazo[4,5-f]quinoxaline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, and 2-amino-3,4,8-trimethyl-imidazo[4,5-f]quinoxaline. Model systems were dissolved in diethylene glycol, heated at 175 °C for 40 min, and separated using reversed-phase liquid chromatography. To define the model system, precursor amounts (threonine and creatinine) were adjusted in molar increments (0.2/0.2, 0.4/0.4, 0.6/0.6, and 0.8/0.8 mmol) and water amounts by percentage (0%, 5%, 10%, and 15%). Sugars (lactose, glucose, galactose, and fructose) were evaluated in several molar amounts proportional to threonine and creatinine (quarter, half, equi, and double). The precursor levels and amounts of sugar were significantly different (P < 0.05) in regards to total HCA formation, with 0.6/0.6/1.2 mmol producing higher levels. Water concentration and sugar type also had a significant effect (P < 0.05), with 5% water and lactose producing higher total HCA amounts. A model system containing threonine (0.6 mmol), creatinine (0.6 mmol), and glucose (1.2 mmol), with 15% water was determined to be the optimal model system with glucose and 15% water being a better representation of meat systems.

  14. C-NH2 bond formation mediated by iridium complexes.

    PubMed

    Mena, Inmaculada; Casado, Miguel A; Polo, Víctor; García-Orduña, Pilar; Lahoz, Fernando J; Oro, Luis A

    2014-09-01

    In the presence of phosphanes (PR3 ), the amido-bridged trinuclear complex [{Ir(μ-NH2 )(tfbb)}3 ] (tfbb=tetrafluorobenzobarrelene) transforms into mononuclear discrete compounds [Ir(1,2-η(2) -4-κ-C12 H8 F4 N)(PR3 )3 ], which are the products of the CN coupling between the amido moiety and a vinylic carbon of the diolefin. An alternative synthetic approach to these species involves the reaction of the 18 e(-) complex [Ir(Cl)(tfbb)(PMePh2 )2 ] with gaseous ammonia and additional phosphane. DFT studies show that both transformations occur through nucleophilic attack. In the first case the amido moiety attacks a diolefin coordinated to a neighboring molecule following a bimolecular mechanism induced by the highly basic NH2 moiety; the second pathway involves a direct nucleophilic attack of ammonia to a coordinated tfbb molecule.

  15. Noble reactions for the actinides: safe gold-based access to organouranium and azide complexes

    SciTech Connect

    Thomson, Robert K; Graves, Christopher R; Scott, Brian L; Kiplinger, Jaqueline L

    2008-01-01

    Gold has had a profound impact on organic chemistry; its compounds are spectacular catalysts for many organic transformations involving the formation of C-C, C-O, C-N and CoS bonds, and have enabled unprecedented pathways for the functionalization of C-H and C-C bonds. In general, gold complexes have not been exploited as reagents in organometallic or inorganic chemistry, although a few gold(l) aryl and alkynyl compounds have been reported to undergo transmetalation with transition metal complexes. We have been developing methods for functionalizing uranium complexes and have shown that Cu(l)-X reagents effect the oxidation of uranium with formation of U-X bonds, providing easy chemical control over uranium in oxidation states ranging from U{sup III}{yields}U{sup VI}. Although a logical approach for the direct generation of U-carbon and U-azide bonds, this Cu-based platform is limited in scope as it only works for pure and isolable copper compounds. This is problematic given the instability of organocuprates and copper azides, which can detonate violently as isolated solids. As such, this route has been confined to the synthesis of select uranium phenylacetylide complexes. Over the past few years, a variety of stable gold(l) alkyl, alkenyl, aryl, alkynyl, and azide complexes have been reported, propelling us to investigate their potential as reagents within the oxidative functionalization platform. Unlike the related CU{sup I} systems, Au{sup I} reagents are easily derivatized, and are safe to handle and isolate. Herein, we report that gold(l)-phosphine compounds can undergo a new class of reaction, and are excellent reagents for the oxidative functionalization of uranium with azide and carbon anions.

  16. 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

  17. Formation of a Ternary Complex for Selenocysteine Biosynthesis in Bacteria.

    PubMed

    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

    2015-12-01

    The synthesis of selenocysteine-containing proteins (selenoproteins) involves the interaction of selenocysteine synthase (SelA), tRNA (tRNA(Sec)), 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-tRNA(Sec) 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-tRNA(Sec)-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-tRNA(Sec)-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

  18. Titanium complex formation of organic ligands in titania gels.

    PubMed

    Nishikiori, Hiromasa; Todoroki, Kenta; Setiawan, Rudi Agus; Teshima, Katsuya; Fujii, Tsuneo; Satozono, Hiroshi

    2015-01-27

    Thin films of organic ligand-dispersing titania gels were prepared from titanium alkoxide sols containing ligand molecules by steam treatment without heating. The formation of the ligand-titanium complex and the photoinduced electron transfer process in the systems were investigated by photoelectrochemical measurements. The complex was formed between the 8-hydroxyquinoline (HQ) and titanium species, such as the titanium ion, on the titania nanoparticle surface through the oxygen and nitrogen atoms of the quinolate. A photocurrent was observed in the electrodes containing the complex due to the electron injection from the LUMO of the complex into the titania conduction band. A bidentate ligand, 2,3-dihydroxynaphthalene (DHN), formed the complex on the titania surface through dehydration between its two hydroxyl groups of DHN and two TiOH groups of the titania. The electron injection from the HOMO of DHN to the titania conduction band was observed during light irradiation. This direct electron injection was more effective than the two-step electron injection.

  19. Formation of a Ternary Complex for Selenocysteine Biosynthesis in Bacteria.

    PubMed

    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

    2015-12-01

    The synthesis of selenocysteine-containing proteins (selenoproteins) involves the interaction of selenocysteine synthase (SelA), tRNA (tRNA(Sec)), 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-tRNA(Sec) 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-tRNA(Sec)-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-tRNA(Sec)-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.

  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. The cytoprotective effect of nitrite is based on the formation of dinitrosyl iron complexes.

    PubMed

    Dungel, Peter; Perlinger, Martin; Weidinger, Adelheid; Redl, Heinz; Kozlov, Andrey V

    2015-12-01

    Nitrite protects various organs from ischemia-reperfusion injury by ameliorating mitochondrial dysfunction. Here we provide evidence that this protection is due to the inhibition of iron-mediated oxidative reactions caused by the release of iron ions upon hypoxia. We show in a model of isolated rat liver mitochondria that upon hypoxia, mitochondria reduce nitrite to nitric oxide (NO) in amounts sufficient to inactivate redox-active iron ions by formation of inactive dinitrosyl iron complexes (DNIC). The scavenging of iron ions in turn prevents the oxidative modification of the outer mitochondrial membrane and the release of cytochrome c during reoxygenation. This action of nitrite protects mitochondrial function. The formation of DNIC with nitrite-derived NO could also be confirmed in an ischemia-reperfusion model in liver tissue. Our data suggest that the formation of DNIC is a key mechanism of nitrite-mediated cytoprotection.

  2. The mechanism of haem degradation in vitro. Kinetic evidence for the formation of a haem-oxygen complex.

    PubMed Central

    Brown, S B; Thomas, S E

    1978-01-01

    The rate of haem degradation in aqueous pyridine shows a saturation dependence on O2 concentration. CO competitively inhibits the reaction. This is evidence for formation of an iron-O2 complex and is consistent with an intramolecular pathway for haem degradation. PMID:728112

  3. Accurately Predicting Complex Reaction Kinetics from First Principles

    NASA Astrophysics Data System (ADS)

    Green, William

    Many important systems contain a multitude of reactive chemical species, some of which react on a timescale faster than collisional thermalization, i.e. they never achieve a Boltzmann energy distribution. Usually it is impossible to fully elucidate the processes by experiments alone. Here we report recent progress toward predicting the time-evolving composition of these systems a priori: how unexpected reactions can be discovered on the computer, how reaction rates are computed from first principles, and how the many individual reactions are efficiently combined into a predictive simulation for the whole system. Some experimental tests of the a priori predictions are also presented.

  4. 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.

  5. Star formation in a hierarchical model for Cloud Complexes

    NASA Astrophysics Data System (ADS)

    Sanchez, N.; Parravano, A.

    The effects of the external and initial conditions on the star formation processes in Molecular Cloud Complexes are examined in the context of a schematic model. The model considers a hierarchical system with five predefined phases: warm gas, neutral gas, low density molecular gas, high density molecular gas and protostars. The model follows the mass evolution of each substructure by computing its mass exchange with their parent and children. The parent-child mass exchange depends on the radiation density at the interphase, which is produced by the radiation coming from the stars that form at the end of the hierarchical structure, and by the external radiation field. The system is chaotic in the sense that its temporal evolution is very sensitive to small changes in the initial or external conditions. However, global features such as the star formation efficience and the Initial Mass Function are less affected by those variations.

  6. Formation and Redox Interconversion of Niobium Methylidene and Methylidyne Complexes.

    PubMed

    Searles, Keith; Smith, Kyle T; Kurogi, Takashi; Chen, Chun-Hsing; Carroll, Patrick J; Mindiola, Daniel J

    2016-06-01

    The niobium methylidene [{(Ar'O)2 Nb}2 (μ2 -Cl)2 (μ2 -CH2 )] (2) can be cleanly prepared via thermolysis or photolysis of [(Ar'O)2 Nb(CH3 )2 Cl] (1) (OAr'=2,6-bis(diphenylmethyl)-4-tert-butylphenoxide). Reduction of 2 with two equivalents of KC8 results in formation of the first niobium methylidyne [K][{(Ar'O)2 Nb}2 (μ2 -CH)(μ2 -H)(μ2 -Cl)] (3) via a binuclear α-hydrogen elimination. Oxidation of 3 with two equiv of ClCPh3 reforms 2. In addition to solid state X-ray analysis, all these complexes were elucidated via multinuclear NMR experiments and isotopic labelling studies, including a crossover experiment, support the notion for a radical mechanism as well as a binuclear α-hydrogen abstraction pathway being operative in the formation of 2 from 1. PMID:27110689

  7. The first examples of a meta-benzannulation from the reaction of Fischer carbene complexes with alkynes.

    PubMed

    Wang, Huan; Huang, Jie; Wulff, William D; Rheingold, Arnold L

    2003-07-30

    The intramolecular benzannulations of carbene complexes with alkynes are examined where the alkyne is tethered to the alpha-carbon of the vinyl carbene complex. These reactions are sensitive to the length of the tether and to the nature of the solvent. With a tether length of 16 methylenes, the reaction occurs in the same fashion as the intermolecular reactions to give a p-cyclophane. With intermediate tether lengths (n = 10, 13), the reaction gives an additional p-cyclophane in which the two oxygen substituents are meta on the arene ring. This type of product is unprecedented from the reaction of carbene complexes and alkynes and is quite surprising because the formation of this product requires that the carbon-carbon bond between the alpha- and beta-carbons of the vinyl carbene complex is broken. A mechanism is proposed to account for this process which involves the crossed intramolecular [2 + 2] cycloaddition of the alkene and a ketene in a conjugated dienyl ketene to give a benzvalenone paddalane intermediate.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Resonant-pattern formation induced by additive noise in periodically forced reaction-diffusion systems

    NASA Astrophysics Data System (ADS)

    Wang, Hongli; Zhang, Ke; Ouyang, Qi

    2006-09-01

    We report frequency-locked resonant patterns induced by additive noise in periodically forced reaction-diffusion Brusselator model. In the regime of 2:1 frequency-locking and homogeneous oscillation, the introduction of additive noise, which is colored in time and white in space, generates and sustains resonant patterns of hexagons, stripes, and labyrinths which oscillate at half of the forcing frequency. Both the noise strength and the correlation time control the pattern formation. The system transits from homogeneous to hexagons, stripes, and to labyrinths successively as the noise strength is adjusted. Good frequency-locked patterns are only sustained by the colored noise and a finite time correlation is necessary. At the limit of white noise with zero temporal correlation, irregular patterns which are only nearly resonant come out as the noise strength is adjusted. The phenomenon induced by colored noise in the forced reaction-diffusion system is demonstrated to correspond to noise-induced Turing instability in the corresponding forced complex Ginzburg-Landau equation.

  13. Resonant-pattern formation induced by additive noise in periodically forced reaction-diffusion systems.

    PubMed

    Wang, Hongli; Zhang, Ke; Ouyang, Qi

    2006-09-01

    We report frequency-locked resonant patterns induced by additive noise in periodically forced reaction-diffusion Brusselator model. In the regime of 2:1 frequency-locking and homogeneous oscillation, the introduction of additive noise, which is colored in time and white in space, generates and sustains resonant patterns of hexagons, stripes, and labyrinths which oscillate at half of the forcing frequency. Both the noise strength and the correlation time control the pattern formation. The system transits from homogeneous to hexagons, stripes, and to labyrinths successively as the noise strength is adjusted. Good frequency-locked patterns are only sustained by the colored noise and a finite time correlation is necessary. At the limit of white noise with zero temporal correlation, irregular patterns which are only nearly resonant come out as the noise strength is adjusted. The phenomenon induced by colored noise in the forced reaction-diffusion system is demonstrated to correspond to noise-induced Turing instability in the corresponding forced complex Ginzburg-Landau equation. PMID:17025732

  14. 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...

  15. 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

  16. Resonant Chemical Oscillations: Pattern Formation in Reaction-Diffusion Systems

    NASA Astrophysics Data System (ADS)

    Lin, Anna L.

    2003-03-01

    Using the Belousov-Zhabotinsky (BZ) chemical system we explore the resonant response of spatially-extended oscillatory and excitable media to periodic perturbation. Resonance in excitable media is particularly relevant to biological systems, where excitable dynamics (threshold response to stimulus and refractoriness) are common. Methods to quantify spatio-temporal patterns will be discussed and the resonant patterns in excitable and oscillatory media will be compared. Experimental observations are compared to the results from numerical simulations of the Brusselator and FitzHugh-Nagumo models and from a forced complex Ginzburg-Landau amplitude equation.

  17. 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

  18. 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+).

  19. 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.

  20. 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.

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

    DOE PAGESBeta

    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 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

  2. 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.

  3. Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures.

    PubMed

    Constantinidis, P; Schmitt, H-C; Fischer, I; Yan, B; Rijs, A M

    2015-11-21

    The self-reaction of the phenyl radical is one of the key reactions in combustion chemistry. Here we study this reaction in a high-temperature flow reactor by IR/UV ion dip spectroscopy, using free electron laser radiation as mid-infrared source. We identified several major reaction products based on their infrared spectra, among them indene, 1,2-dihydronaphthalene, naphthalene, biphenyl and para-terphenyl. Due to the structural sensitivity of the method, the reaction products were identified isomer-selectively. The work shows that the formation of indene and naphthalene, which was previously considered to be evidence for the HACA (hydrogen abstraction C2H2 addition) mechanism in the formation of polycyclic aromatic hydrocarbons and soot can also be understood in a phenyl addition model.

  4. Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures.

    PubMed

    Constantinidis, P; Schmitt, H-C; Fischer, I; Yan, B; Rijs, A M

    2015-11-21

    The self-reaction of the phenyl radical is one of the key reactions in combustion chemistry. Here we study this reaction in a high-temperature flow reactor by IR/UV ion dip spectroscopy, using free electron laser radiation as mid-infrared source. We identified several major reaction products based on their infrared spectra, among them indene, 1,2-dihydronaphthalene, naphthalene, biphenyl and para-terphenyl. Due to the structural sensitivity of the method, the reaction products were identified isomer-selectively. The work shows that the formation of indene and naphthalene, which was previously considered to be evidence for the HACA (hydrogen abstraction C2H2 addition) mechanism in the formation of polycyclic aromatic hydrocarbons and soot can also be understood in a phenyl addition model. PMID:26457393

  5. Synthesis, characterisation, and oxygen atom transfer reactions involving the first gold(I)-alkylperoxo complexes.

    PubMed

    Collado, Alba; Gómez-Suárez, Adrián; Oonishi, Yoshihiro; Slawin, Alexandra M Z; Nolan, Steven P

    2013-11-25

    The synthesis of a new class of organogold species containing a peroxo moiety is reported. Complexes [Au(IPr)(OO(t)Bu)] and [Au(SIPr)(OO(t)Bu)] have been synthesised via a straightforward methodology using the parent gold(I) hydroxide complexes as synthons. These complexes have been successfully used in oxygen-transfer reactions to triphenylphosphine.

  6. Evaluation of in vivo immune complex formation and complement activation in patients receiving intravenous streptokinase.

    PubMed Central

    Freysdottir, J; Ormarsdottir, S; Sigfusson, A

    1993-01-01

    The usefulness of several different methods for detecting immune complex formation and complement activation in the circulation were applied to samples from patients receiving intravenous Streptokinase therapy for myocardial infarction. Streptokinase is a foreign antigen and can cause immune reactions. We collected samples from 13 patients, before Streptokinase administration (baseline), at the end of infusion (1 h), 12 h later and on day 7. We measured IgG containing immune complexes (IgG-IC), free C3d and antibodies to Streptokinase by ELISA, and CR1, C3d and C4d on erythrocytes by flow cytometric assay. Antibodies to Streptokinase are common, as all but two of the patients had measurable antibody levels. During Streptokinase treatment there was a drop in antibody levels, most prominent in those patients who had high baseline levels. At the same time increased levels of free C3d and erythrocyte-bound C3d were observed. After 12 h free C3d was usually back to baseline level, but C3d on erythrocytes was still raised. These data indicate the formation of Streptokinase immune complexes in patients with high Streptokinase antibody levels, and show that these complexes are cleared rapidly from the circulation, leaving more persistent signs of complement activation. We conclude that free C3d is a good indicator of ongoing complement activation, whereas C3d on erythrocytes indicates that complement activation has recently taken place. PMID:8222319

  7. Biological pattern formation: from basic mechanisms to complex structures

    NASA Astrophysics Data System (ADS)

    Koch, A. J.; Meinhardt, H.

    1994-10-01

    The reliable development of highly complex organisms is an intriguing and fascinating problem. The genetic material is, as a rule, the same in each cell of an organism. How then do cells, under the influence of their common genes, produce spatial patterns? Simple models are discussed that describe the generation of patterns out of an initially nearly homogeneous state. They are based on nonlinear interactions of at least two chemicals and on their diffusion. The concepts of local autocatalysis and of long-range inhibition play a fundamental role. Numerical simulations show that the models account for many basic biological observations such as the regeneration of a pattern after excision of tissue or the production of regular (or nearly regular) arrays of organs during (or after) completion of growth. Very complex patterns can be generated in a reproducible way by hierarchical coupling of several such elementary reactions. Applications to animal coats and to the generation of polygonally shaped patterns are provided. It is further shown how to generate a strictly periodic pattern of units that themselves exhibit a complex and polar fine structure. This is illustrated by two examples: the assembly of photoreceptor cells in the eye of Drosophila and the positioning of leaves and axillary buds in a growing shoot. In both cases, the substructures have to achieve an internal polarity under the influence of some primary pattern-forming system existing in the fly's eye or in the plant. The fact that similar models can describe essential steps in organisms as distantly related as animals and plants suggests that they reveal some universal mechanisms.

  8. Biological pattern formation: from basic mechanisms to complex structures

    SciTech Connect

    Koch, A.J.; Meinhardt, H. )

    1994-10-01

    The reliable development of highly complex organisms is an intriguing and fascinating problem. The genetic material is, as a rule, the same in each cell of an organism. How then do cells, under the influence of their common genes, produce spatial patterns Simple models are discussed that describe the generation of patterns out of an initially nearly homogeneous state. They are based on nonlinear interactions of at least two chemicals and on their diffusion. The concepts of local autocatalysis and of long-range inhibition play a fundamental role. Numerical simulations show that the models account for many basic biological observations such as the regeneration of a pattern after excision of tissue or the production of regular (or nearly regular) arrays of organs during (or after) completion of growth. Very complex patterns can be generated in a reproducible way by hierarchical coupling of several such elementary reactions. Applications to animal coats and to the generation of polygonally shaped patterns are provided. It is further shown how to generate a strictly periodic pattern of units that themselves exhibit a complex and polar fine structure. This is illustrated by two examples: the assembly of photoreceptor cells in the eye of [ital Drosophila] and the positioning of leaves and axillary buds in a growing shoot. In both cases, the substructures have to achieve an internal polarity under the influence of some primary pattern-forming system existing in the fly's eye or in the plant. The fact that similar models can describe essential steps in organisms as distantly related as animals and plants suggests that they reveal some universal mechanisms.

  9. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects.

    PubMed

    Awasthi, Neha; Hub, Jochen S

    2016-07-12

    Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation.

  10. 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.

  11. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects.

    PubMed

    Awasthi, Neha; Hub, Jochen S

    2016-07-12

    Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation. PMID:27254744

  12. Reaction mechanism of Ru(II) piano-stool complexes: umbrella sampling QM/MM MD study.

    PubMed

    Futera, Zdeněk; Burda, Jaroslav V

    2014-07-15

    Biologically relevant interactions of piano-stool ruthenium(II) complexes with ds-DNA are studied in this article by hybrid quantum mechanics-molecular mechanics (QM/MM) computational technique. The whole reaction mechanism is divided into three phases: (i) hydration of the [Ru(II) (η(6) -benzene)(en)Cl](+) complex, (ii) monoadduct formation between the resulting aqua-Ru(II) complex and N7 position of one of the guanines in the ds-DNA oligomer, and (iii) formation of the intrastrand Ru(II) bridge (cross-link) between two adjacent guanines. Free energy profiles of all the reactions are explored by QM/MM MD umbrella sampling approach where the Ru(II) complex and two guanines represent a quantum core, which is described by density functional theory methods. The combined QM/MM scheme is realized by our own software, which was developed to couple several quantum chemical programs (in this study Gaussian 09) and Amber 11 package. Calculated free energy barriers of the both ruthenium hydration and Ru(II)-N7(G) DNA binding process are in good agreement with experimentally measured rate constants. Then, this method was used to study the possibility of cross-link formation. One feasible pathway leading to Ru(II) guanine-guanine cross-link with synchronous releasing of the benzene ligand is predicted. The cross-linking is an exergonic process with the energy barrier lower than for the monoadduct reaction of Ru(II) complex with ds-DNA.

  13. Reaction mechanism of Ru(II) piano-stool complexes: umbrella sampling QM/MM MD study.

    PubMed

    Futera, Zdeněk; Burda, Jaroslav V

    2014-07-15

    Biologically relevant interactions of piano-stool ruthenium(II) complexes with ds-DNA are studied in this article by hybrid quantum mechanics-molecular mechanics (QM/MM) computational technique. The whole reaction mechanism is divided into three phases: (i) hydration of the [Ru(II) (η(6) -benzene)(en)Cl](+) complex, (ii) monoadduct formation between the resulting aqua-Ru(II) complex and N7 position of one of the guanines in the ds-DNA oligomer, and (iii) formation of the intrastrand Ru(II) bridge (cross-link) between two adjacent guanines. Free energy profiles of all the reactions are explored by QM/MM MD umbrella sampling approach where the Ru(II) complex and two guanines represent a quantum core, which is described by density functional theory methods. The combined QM/MM scheme is realized by our own software, which was developed to couple several quantum chemical programs (in this study Gaussian 09) and Amber 11 package. Calculated free energy barriers of the both ruthenium hydration and Ru(II)-N7(G) DNA binding process are in good agreement with experimentally measured rate constants. Then, this method was used to study the possibility of cross-link formation. One feasible pathway leading to Ru(II) guanine-guanine cross-link with synchronous releasing of the benzene ligand is predicted. The cross-linking is an exergonic process with the energy barrier lower than for the monoadduct reaction of Ru(II) complex with ds-DNA. PMID:24865949

  14. 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

  15. Reactions of nitric oxide with mitochondrial cytochrome c: a novel mechanism for the formation of nitroxyl anion and peroxynitrite.

    PubMed Central

    Sharpe, M A; Cooper, C E

    1998-01-01

    The aerobic reactions of nitric oxide with cytochrome c were analysed. Nitric oxide (NO) reacts with ferrocytochrome c at a rate of 200 M-1 s-1 to form ferricytochrome c and nitroxyl anion (NO-). Ferricytochrome c was detected by optical spectroscopy; NO- was detected by trapping with metmyoglobin (Mb3+) to form the EPR-detectable Mb-nitrosyl complex, and by the formation of dimers in yeast ferrocytochrome c via cross-linking of the free cysteine residue. The NO- formed subsequently reacted with oxygen to form peroxynitrite, as measured by the oxidation of dihydrorhodamine 123. NO binds to ferricytochrome c to form the ferricytochrome c-NO complex. The on-rate for this reaction is 1.3+/-0.4x10(3) M-1.s-1, and the off-rate is 0.087+/-0.054 s-1. The dissociation constant (Kd) of the complex is 22+/-7 microM. These reactions of NO with cytochrome c are likely to be relevant to mitochondrial metabolism of NO. Ferricytochrome c can act as a reversible sink for excess NO in the mitochondria. The reduction of NO to NO- by ferrocytochrome c may play a role in the irreversible inhibition of mitochondrial oxygen consumption by peroxynitrite. It is generally assumed that peroxynitrite would be formed in mitochondria via the reaction of NO with superoxide. The finding that NO- is formed from the reaction of NO and ferrocytochrome c provides a means of producing peroxynitrite in the absence of superoxide, via the reaction of NO- with oxygen. PMID:9576846

  16. 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.

  17. 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.

  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. 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. PMID:27241805

  20. Image formation in the eye: very specified complexity

    NASA Astrophysics Data System (ADS)

    Stoltzmann, David E.

    2005-08-01

    The formation of an image, and its correct interpretation by sighted living creatures, is a unique example of specified complexity unlike anything else in nature. While many of the functional aspects of living organisms are extremely complex, only an image requires a unique mapping process by the eye-brain system to be useful to the organism. The transfer of light from an object scene to a visual detection system (eye + brain) conveys an enormous amount of information. But unless that information is correctly organized into a useful image, the exchange of information is degraded and of questionable use. This paper examines the "connections" necessary for images to be interpreted correctly, as well as addressing the additional complexity requirement of dual-image mapping for stereovision capabilities. Statistics are presented for "simple eyes" consisting of a few pixels to illustrate the daunting task that random chance has to produce any form of a functional eye. For example, a 12-pixel eye (or camera) has 12! (479,001,600) possible pixel-to-brain (computer) wiring combinations, which can then be compared to the 126 million rods/cones of the actual human eye. If one tries to "connect the wires" (correctly interpret the information contained) in a 12-pixel image by random processes, by the time 6 pixels become correctly connected, over 99.9% of all the trials are incorrect, producing "noise" rather than a recognizable image. Higher numbers of pixels quickly make the problem astronomically worse for achieving any kind of useful image. This paper concludes that random-chance purposeless undirected processes cannot account for how images are perceived by living organisms.

  1. 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. PMID:26686054

  2. Iron nitrosyl hemoglobin formation from the reaction of hydroxylamine and hemoglobin under physiological conditions.

    PubMed

    Lockamy, Virginia L; Shields, Howard; Kim-Shapiro, Daniel B; King, S Bruce

    2004-11-01

    Sickle cell disease patients receiving hydroxyurea (HU) therapy have shown increases in the production of nitric oxide (NO) metabolites, which include iron nitrosyl hemoglobin (HbNO), nitrite, and nitrate. However, the exact mechanism by which HU forms HbNO in vivo is not understood. Previous studies indicate that the reaction of oxyhemoglobin (oxyHb) or deoxyhemoglobin (deoxyHb) with HU are too slow to account for in vivo HbNO production. In this study, we show that the reaction of methemoglobin (metHb) with HU to form HbNO could potentially be fast enough to account for in vivo HbNO formation but competing reactions of either excess oxyHb or deoxyHb during the reaction reduces the likelihood that HbNO will be produced from the metHb-HU reaction. Using electron paramagnetic resonance (EPR) spectroscopy we have detected measurable amounts of HbNO and metHb during the reactions of oxyHb, deoxyHb, and metHb with excess hydroxylamine (HA). We also demonstrate HbNO and metHb formation from the reactions of excess oxyHb, deoxyHb, or metHb and HA, conditions that are more likely to mimic those in vivo. These results indicate that the reaction of hydroxylamine with hemoglobin produces HbNO and lend chemical support for a potential role for hydroxylamine in the in vivo metabolism of hydroxyurea.

  3. In Situ Catalyst Modification in Atom Transfer Radical Reactions with Ruthenium Benzylidene Complexes.

    PubMed

    Lee, Juneyoung; Grandner, Jessica M; Engle, Keary M; Houk, K N; Grubbs, Robert H

    2016-06-01

    Ruthenium benzylidene complexes are well-known as olefin metathesis catalysts. Several reports have demonstrated the ability of these catalysts to also facilitate atom transfer radical (ATR) reactions, such as atom transfer radical addition (ATRA) and atom transfer radical polymerization (ATRP). However, while the mechanism of olefin metathesis with ruthenium benzylidenes has been well-studied, the mechanism by which ruthenium benzylidenes promote ATR reactions remains unknown. To probe this question, we have analyzed seven different ruthenium benzylidene complexes for ATR reactivity. Kinetic studies by (1)H NMR revealed that ruthenium benzylidene complexes are rapidly converted into new ATRA-active, metathesis-inactive species under typical ATRA conditions. When ruthenium benzylidene complexes were activated prior to substrate addition, the resulting activated species exhibited enhanced kinetic reactivity in ATRA with no significant difference in overall product yield compared to the original complexes. Even at low temperature, where the original intact complexes did not catalyze the reaction, preactivated catalysts successfully reacted. Only the ruthenium benzylidene complexes that could be rapidly transformed into ATRA-active species could successfully catalyze ATRP, whereas other complexes preferred redox-initiated free radical polymerization. Kinetic measurements along with additional mechanistic and computational studies show that a metathesis-inactive ruthenium species, generated in situ from the ruthenium benzylidene complexes, is the active catalyst in ATR reactions. Based on data from (1) H, (13)C, and (31)P NMR spectroscopy and X-ray crystallography, we suspect that this ATRA-active species is a RuxCly(PCy3)z complex.

  4. Mechanism for the uncatalyzed cyclic acetone-peroxide formation reaction: an experimental and computational study.

    PubMed

    Espinosa-Fuentes, Eduardo A; Pacheco-Londoño, Leonardo C; Hidalgo-Santiago, Migdalia; Moreno, Martha; Vivas-Reyes, Ricardo; Hernández-Rivera, Samuel P

    2013-10-17

    In this study, a mechanism for the uncatalyzed reaction between acetone and hydrogen peroxide is postulated. The reaction leads to the formation of the important homemade explosives collectively known as cyclic acetone peroxides (CAP). The proposed mechanistic scheme is based on Raman, GC-MS, and nuclear magnetic resonance measurements, and it is supported by ab initio density functional theory (DFT) calculations. The results demonstrate that the proposed mechanism for the uncatalyzed formation reaction of CAP occurs in three steps: monomer formation, polymerization of the 2-hydroperoxipropan-2-ol monomer, and cyclization. The temporal decay of the intensities of important assigned-bands is in excellent agreement with the proposed mechanism. Previous reports also confirm that the polymerization step is favored in comparison to other possible pathways.

  5. The colorants, antioxidants, and toxicants from nonenzymatic browning reactions and the impacts of dietary polyphenols on their thermal formation.

    PubMed

    Zhang, Xinchen; Tao, Ningping; Wang, Xichang; Chen, Feng; Wang, Mingfu

    2015-02-01

    Nonenzymatic browning reactions proceed with the starting reactants of sugar and/or protein during thermal processing and storage of food. In addition to food color formation, the process also contributes to the loss of essential nutrients, generation of beneficial antioxidants, and production of toxicants, including 5-hydroxymethylfurfural (5-HMF), reactive carbonyl species, advanced glycation end products (AGEs), and heterocyclic amines (HAs). Recent research has demonstrated that dietary polyphenols can actively participate in nonenzymatic browning reactions, contributing to the generation of new colorants and antioxidants. More importantly, polyphenol addition has been found to be an effective approach to mitigate heat-induced formation of toxicants, mainly through inhibiting oxidative pathways and trapping reactive intermediates. In the matrix of polyphenol-fortified foods, a complex array of chemical interactions happen among polyphenols, traditional nutritional components, and neo-formed compounds they are thermally converted to. These reactions play a significant role in the colorants, antioxidants as well as toxicants production. Our findings support the potential of dietary polyphenols for increasing the antioxidant content and for reducing the level of toxicants when they participate in nonenzymatic browning reactions in fortified food products. PMID:25468403

  6. The colorants, antioxidants, and toxicants from nonenzymatic browning reactions and the impacts of dietary polyphenols on their thermal formation.

    PubMed

    Zhang, Xinchen; Tao, Ningping; Wang, Xichang; Chen, Feng; Wang, Mingfu

    2015-02-01

    Nonenzymatic browning reactions proceed with the starting reactants of sugar and/or protein during thermal processing and storage of food. In addition to food color formation, the process also contributes to the loss of essential nutrients, generation of beneficial antioxidants, and production of toxicants, including 5-hydroxymethylfurfural (5-HMF), reactive carbonyl species, advanced glycation end products (AGEs), and heterocyclic amines (HAs). Recent research has demonstrated that dietary polyphenols can actively participate in nonenzymatic browning reactions, contributing to the generation of new colorants and antioxidants. More importantly, polyphenol addition has been found to be an effective approach to mitigate heat-induced formation of toxicants, mainly through inhibiting oxidative pathways and trapping reactive intermediates. In the matrix of polyphenol-fortified foods, a complex array of chemical interactions happen among polyphenols, traditional nutritional components, and neo-formed compounds they are thermally converted to. These reactions play a significant role in the colorants, antioxidants as well as toxicants production. Our findings support the potential of dietary polyphenols for increasing the antioxidant content and for reducing the level of toxicants when they participate in nonenzymatic browning reactions in fortified food products.

  7. 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...

  8. 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

    2016-08-01

    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.

  9. Reactions of cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ with GaCp*: novel gallium complexes of iron, cobalt, copper and silver.

    PubMed

    Bollermann, Timo; Puls, Arik; Gemel, Christian; Cadenbach, Thomas; Fischer, Roland A

    2009-02-28

    The reactions of the cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ (m = 2: M = Fe, Co and m = 1: M = Cu, Ag) with GaCp* were investigated. The reaction of [Fe(CH3CN)6][BArF]2 (BAr(F) = [B{C6H3(CF3)2}4) with GaCp* leads to [Cp*Fe(GaCp*)3][BAr(F)] (1) via a redox neutral Cp* transfer and [Ga2Cp*][BAr(F)] as a by-product while the formation of [Cp*Co(GaCp*)3][BAr(F)]2 (2) from [Co(CH3CN)6][BAr(F)]2 is accompanied by oxidation of Co(II) to Co(III) with GaCp* as the oxidant. The reactions of [Cu(CH3CN)4][BAr(F)] and Ag[BPh4] with GaCp* lead to the formation of the homoleptic compounds [Cu(GaCp*)4][BAr(F)] (4) and [Ag(GaCp*)4][BPh4] (5), while treatment of Ag[CF3SO3] with GaCp* leads to the dimeric complex [Ag2(GaCp*)3(micro-GaCp*)2][CF3SO3]2 (6). All compounds were characterized by NMR spectroscopy, single crystal X-ray diffraction and elemental analysis. PMID:19462658

  10. Orbitally selective chemical reaction in Hg-H2 van der Waals complexes

    NASA Astrophysics Data System (ADS)

    Breckenridge, W. H.; Jouvet, Christophe; Soep, Benoit

    1986-02-01

    A new technique is described for probing the reaction dynamics of ``half-collisions'' in systems where ``full-collision'' chemical dynamics can also be studied. By selective laser excitation of an atom-molecule van der Waals complex, an electronically excited atom can be created at a known distance from, and with a known orbital symmetry with respect to, the reactive molecule. From spectra of the complex and from detection of nascent products in a state-resolved fashion, not only can a great deal be learned about the dynamics of the half-collision, but comparison can also be made with analogous full-collision dynamical information. Reported here are initial results involving the HgṡH2 van der Waals complex. When the Hg (6s 1S0)ṡH2 ground-state complex is excited to the Hg(6p 3P1)ṡH2 complex with frequencies near that of the Hg(6 1S0-6 3P1) free atom transition, the molecular product HgH(X 2Σ+) is readily detected. No fluorescence of the Hg(6p 3P1)ṡH2 complex is observed, nor is Hg(6p 3P0) detected as a major product. The two electronic configurations of the excited Hg(6p 3P1)ṡH2 complex, 3Σ and 3Π (which correspond approximately to axial and perpendicular orientation, respectively, of the p orbital with respect to the freely rotating H2 molecule) exhibit different behavior. The reaction to form HgH (X 2Σ+) via the 3Π complex is ``direct,'' i.e., occurs within 0.1 ps, since the HgH(X 2Σ+) action spectrum for 3Π excitation is continuous. In contrast, there is rovibrational structure in the HgH (X2 Σ+) action spectrum for 3Σ excitation, showing that HgH(X 2Σ+) formation in this case is ``indirect,'' i.e., occurs on a time scale between 2 ps and 1 ns. Furthermore, the HgH (X 2Σ+, v=0) rotational quantum-state distribution from 3Σ complex excitation is bimodal, with a major component quite similar to that resulting from excitation of the 3Π complex, but with a minor component present at low N. Possible explanations of these results, which

  11. 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.

  12. 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. PMID:27228310

  13. Anion Effects in Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions of Cu(II) Chlorodiketonate Complexes.

    PubMed

    Saraf, Sushma L; Miłaczewska, Anna; Borowski, Tomasz; James, Christopher D; Tierney, David L; Popova, Marina; Arif, Atta M; Berreau, Lisa M

    2016-07-18

    Aliphatic oxidative carbon-carbon bond cleavage reactions involving Cu(II) catalysts and O2 as the terminal oxidant are of significant current interest. However, little is currently known regarding how the nature of the Cu(II) catalyst, including the anions present, influence the reaction with O2. In previous work, we found that exposure of the Cu(II) chlorodiketonate complex [(6-Ph2TPA)Cu(PhC(O)CClC(O)Ph)]ClO4 (1) to O2 results in oxidative aliphatic carbon-carbon bond cleavage within the diketonate unit, leading to the formation of benzoic acid, benzoic anhydride, benzil, and 1,3-diphenylpropanedione as organic products. Kinetic studies of this reaction revealed a slow induction phase followed by a rapid decay of the absorption features of 1. Notably, the induction phase is not present when the reaction is performed in the presence of a catalytic amount of chloride anion. In the studies presented herein, a combination of spectroscopic (UV-vis, EPR) and density functional theory (DFT) methods have been used to examine the chloride and benzoate ion binding properties of 1 under anaerobic conditions. These studies provide evidence that each anion coordinates in an axial position of the Cu(II) center. DFT studies reveal that the presence of the anion in the Cu(II) coordination sphere decreases the barrier for O2 activation and the formation of a Cu(II)-peroxo species. Notably, the chloride anion more effectively lowers the barrier associated with O-O bond cleavage. Thus, the nature of the anion plays an important role in determining the rate of reaction of the diketonate complex with O2. The same type of anion effects were observed in the O2 reactivity of the simple Cu(II)-bipyridine complex [(bpy)Cu(PhC(O)C(Cl)C(O)Ph)ClO4] (3). PMID:27377103

  14. 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.

  15. [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. PMID:27434951

  16. Molecular Complexity via C–H Activation: A Dehydrogenative Diels-Alder Reaction

    PubMed Central

    Stang, Erik M.; White, M. Christina

    2011-01-01

    Traditionally, C–H oxidation reactions install oxidized functionality onto a preformed molecular skeleton, resulting in a local molecular change. The use of C–H activation chemistry to construct complex molecular scaffolds is a new area with tremendous potential in synthesis. We report a Pd(II)/bis-sulfoxide catalyzed dehydrogenative Diels-Alder reaction that converts simple terminal olefins into complex cycloadducts in a single operation. PMID:21842902

  17. Molecular complexity via C-H activation: a dehydrogenative Diels-Alder reaction.

    PubMed

    Stang, Erik M; White, M Christina

    2011-09-28

    Traditionally, C-H oxidation reactions install oxidized functionality onto a preformed molecular skeleton, resulting in a local molecular change. The use of C-H activation chemistry to construct complex molecular scaffolds is a new area with tremendous potential in synthesis. We report a Pd(II)/bis-sulfoxide-catalyzed dehydrogenative Diels-Alder reaction that converts simple terminal olefins into complex cycloadducts in a single operation.

  18. The elimination of fast variables in complex chemical reactions. I. Macroscopic level

    NASA Astrophysics Data System (ADS)

    Janssen, J. A. M.

    1989-10-01

    The kinetics of complex chemical reactions is considered. Different time scales exist if one or more of the rate constants of the individual reaction steps is much larger than the others. Examples of specific reactions are given in which the intermediates vary on the fast time scale. They can be eliminated according to a standard scheme, the lowest order of which coincides with the steady-state approximation usually employed in textbooks on chemical kinetics.

  19. Zebra reaction or the recipe for the synthesis of heterodimeric zinc complexes.

    PubMed

    Jędrzkiewicz, D; Ejfler, J; John, Ł; Szafert, S

    2016-02-21

    A series of asymmetric heterodimeric zinc complexes have been synthesized in a direct reaction between conformationally flexible chiral/achiral homodimers. The cooperative activity of steric factors and coordination codes resulted in an intriguing chiral self-sorting process. Herein, we are reporting our recent exploration of the first example of such a type of reaction. PMID:26658768

  20. Zebra reaction or the recipe for the synthesis of heterodimeric zinc complexes.

    PubMed

    Jędrzkiewicz, D; Ejfler, J; John, Ł; Szafert, S

    2016-02-21

    A series of asymmetric heterodimeric zinc complexes have been synthesized in a direct reaction between conformationally flexible chiral/achiral homodimers. The cooperative activity of steric factors and coordination codes resulted in an intriguing chiral self-sorting process. Herein, we are reporting our recent exploration of the first example of such a type of reaction.

  1. Formation of degradation compounds from lignocellulosic biomass in the biorefinery: sugar reaction mechanisms.

    PubMed

    Rasmussen, Helena; Sørensen, Hanne R; Meyer, Anne S

    2014-02-19

    The degradation compounds formed during pretreatment when lignocellulosic biomass is processed to ethanol or other biorefinery products include furans, phenolics, organic acids, as well as mono- and oligomeric pentoses and hexoses. Depending on the reaction conditions glucose can be converted to 5-(hydroxymethyl)-2-furaldehyde (HMF) and/or levulinic acid, formic acid and different phenolics at elevated temperatures. Correspondingly, xylose can follow different reaction mechanisms resulting in the formation of furan-2-carbaldehyde (furfural) and/or various C-1 and C-4 compounds. At least four routes for the formation of HMF from glucose and three routes for furfural formation from xylose are possible. In addition, new findings show that biomass monosaccharides themselves can react further to form pseudo-lignin and humins as well as a wide array of other compounds when exposed to high temperatures. Hence, several aldehydes and ketones and many different organic acids and aromatic compounds may be generated during hydrothermal treatment of lignocellulosic biomass. The reaction mechanisms are of interest because the very same compounds that are possible inhibitors for biomass processing enzymes and microorganisms may be valuable biobased chemicals. Hence a new potential for industrial scale synthesis of chemicals has emerged. A better understanding of the reaction mechanisms and the impact of the reaction conditions on the product formation is thus a prerequisite for designing better biomass processing strategies and forms an important basis for the development of new biorefinery products from lignocellulosic biomass as well. PMID:24412507

  2. Formation and reaction of hydroxycarbonyls from the reaction of OH radicals with 1,3-butadiene and isoprene.

    PubMed

    Baker, Jillian; Arey, Janet; Atkinson, Roger

    2005-06-01

    1,3-Butadiene and isoprene (2-methyl-1,3-butadiene) are emitted into the atmosphere in vehicle exhaust and, in the case of isoprene, from vegetation. We have investigated the formation and further reaction of products of their hydroxyl radical-initiated reactions using atmospheric pressure ionization mass spectrometry (API-MS) and solid-phase microextraction fibers precoated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for on-fiber derivatization of carbonyl compounds, with subsequent analysis by thermal desorption and gas chromatography with flame ionization detection (SPME/GC-FID) or MS detection. Products attributed as HOCH2CH=CHCHO and HOCH2CH=CHCH2ONO2 (and isomers) from 1,3-butadiene; HOCD2CD=CDCDO and HOCD2CD=CDCD2ONO2 (and isomers) from 1,3-butadiene-d6; HOCH2C(CH3)=CHCHO and/or HOCH2CH=C(CH3)CHO, and HOCH2C(CH3)=CHCH2ONO2 (and isomers) from isoprene; and HOCD2C(CD3)=CDCDO and/or HOCD2CD=C(CD3)CDO, and HOCD2C(CD3)=CDCD2ONO2 (and isomers) from isoprene-d8 were observed as their NO2- adducts in the API-MS analyses. The hydroxycarbonyls were observed from SPME/GC-FID analyses of the 1,3-butadiene and isoprene reactions as their oximes, together with acrolein, glycolaldehyde, and glyoxal from the 1,3-butadiene reaction. A rate constant for the reaction of OH radicals with 4-hydroxy-2-butenal of (5.7 +/- 1.4) x 10(-11) cm3 molecule(-1) s(-1) at 298 +/- 2 K was derived, and formation yields of acrolein and 4-hydroxy-2-butenal from the 1,3-butadiene reaction of 58 +/- 10% and 25 (+15/-10)%, respectively, were determined. Analogous experiments showed that the two C5-hydroxycarbonyls formed from isoprene have rate constants for their reactions with OH radicals of (1.0 +/- 0.3) x 10(-10) cm3 molecule(-1) s(-1) and (4 +/- 2) x 10(-11) cm3 molecule(-1) s(-1) and a combined yield of approximately 15%, although isomer-specific identification of the hydroxycarbonyls was not achieved.

  3. Modeling of the formation of complex molecules in protostellar objects

    NASA Astrophysics Data System (ADS)

    Kochina, O. V.; Wiebe, D. S.; Kalenskii, S. V.; Vasyunin, A. I.

    2013-11-01

    The results of molecular composition modeling are presented for the well studied low-mass star-forming region TMC-1 and the massive star-forming region DR21(OH), which is poorly studied from a chemical point of view. The column densities of dozens of molecules, ranging from simple diatomic to complex organic molecules, are reproduced to within an order of magnitude using a one-dimensional model for the physical and chemical structure of these regions. The chemical ages of the regions are approximately 105 years in both cases. The main desorption mechanisms that are usually included in chemical models (photodesorption, thermal desorption, and cosmic-ray-induced desorption) do not provide sufficient gasphase abundances of molecules that are synthesized in surface reactions; however, this shortcoming can be removed by introducing small amount of reactive desorption into the model. It is possible to reproduce the properties of the TMC-1 chemical composition in a standard model, without requiring additional assumptions about an anomalous C/O ratio or the recent accretion of matter enriched with atomic carbon, as has been proposed by some researchers.

  4. Fluorimetric determination of sulphathiazole in honey by means the formation of CDs inclusion complexes.

    PubMed

    Lucas-Abellán, C; Guillén, I; Mercader-Ros, M T; Serrano-Martínez, A; Núñez-Delicado, E; Gabaldón, J A

    2014-03-15

    The inclusion complex of sulphathiazole in β-cyclodextrin has been investigated. A 1:2 stoichiometry of the complex was established and formation constants K2 (42.83 ± 3.27 M(-1)) and K1 (4.98 ± 0.36 M(-1)) were calculated by using the changes produced on the native fluorescence of the drug, when included on the hydrophobic cyclodextrin cavity. An enhancement in the fluorescence emission of sulphathiazole and protection of the drug against photochemical reactions has been attained upon inclusion. In solutions of β-CD dual emission (458 nm) was noticed in STZ. Formation of the inclusion complex of STZ should result in dual emission, which is due to a twisted intramolecular charge transfer band (TICT). A fluorimetric method for the determination of sulphathiazole has been proposed and applied in honey without sample treatment. The optimized fluorimetric method showed detection and quantitation limits of 9.74 ng/g and 32.48 ng/g, respectively. Selectivity is high, showing no cross-reactivity to other chemically related antibiotics. The results obtained for blind honey samples (mean recovery 97%), were in good agreement with those obtained by liquid chromatography separation and mass spectrometry detection (LC-MS) (mean recovery 102%), showing that the proposed method might be used for the determination of sulphathiazole residues without expensive equipment.

  5. Direct Formation of Oxocarbenium Ions under Weakly Acidic Conditions: Catalytic Enantioselective Oxa-Pictet-Spengler Reactions.

    PubMed

    Zhao, Chenfei; Chen, Shawn B; Seidel, Daniel

    2016-07-27

    Two catalysts, an amine HCl salt and a bisthiourea, work in concert to enable the generation of oxocarbenium ions under mild conditions. The amine catalyst generates an iminium ion of sufficient electrophilicity to enable 1,2-attack by an alcohol. Catalyst turnover is achieved by amine elimination with concomitant formation of an oxocarbenium intermediate. The bisthiourea catalyst accelerates all of the steps of the reaction and controls the stereoselectivity via anion binding/ion pair formation. This new concept was applied to direct catalytic enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes. PMID:27396413

  6. Direct Formation of Oxocarbenium Ions under Weakly Acidic Conditions: Catalytic Enantioselective Oxa-Pictet-Spengler Reactions.

    PubMed

    Zhao, Chenfei; Chen, Shawn B; Seidel, Daniel

    2016-07-27

    Two catalysts, an amine HCl salt and a bisthiourea, work in concert to enable the generation of oxocarbenium ions under mild conditions. The amine catalyst generates an iminium ion of sufficient electrophilicity to enable 1,2-attack by an alcohol. Catalyst turnover is achieved by amine elimination with concomitant formation of an oxocarbenium intermediate. The bisthiourea catalyst accelerates all of the steps of the reaction and controls the stereoselectivity via anion binding/ion pair formation. This new concept was applied to direct catalytic enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes.

  7. [Characteristics of the formation of conditioned defense reactions in monkeys in a primatological chair].

    PubMed

    Karamian, A I; Sollertinskaia, T N; Iliukha, V A

    1987-01-01

    Rate of reactions in motor conditioned electro-defensive reflexes and different kinds of internal inhibition, such as acute extinction, differentiation and delay with different retardations, were studied on monkeys in primatological chair. Specificity in formation of conditioned reactions was studied with simultaneous recording of vegetative (respiration and heart rate) and motor conditioned reactions. It has been established, that forming of vegetative and motor components of defensive reflex does not proceed synchronously. At first (2-4 trials) vegetative reactions appear, such as increase of heart and respiration rates. Conditioned motor reactions (legs' jerks) appear later, after 4-9 trials. It has been shown that in monkeys in the primatological chair we have a possibility to form all kinds of negative conditioned defensive reactions: acute extinction, differentiation, delay. Formation of delay inhibition with retardation of 90 s leads to neurotic disorders. But they last only for short periods and disappear after breaks in work. The obtained data are discussed from evolutionary point of view, with a comparative study of specificity of higher nervous activity formation among lower organized vertebrates and with consideration of processes of excitation and inhibition in evolution.

  8. Kinetics of acrylamide formation/elimination reactions as affected by water activity.

    PubMed

    De Vleeschouwer, Kristel; Van der Plancken, Iesel; Van Loey, Ann; Hendrickx, Marc E

    2007-01-01

    The influence of water activity on the kinetics of acrylamide formation and elimination reaction was investigated using low-moisture equimolar asparagine-glucose model systems, which were heated at temperatures between 120 and 200 degrees C for variable heating times. To determine the water content corresponding to the water activities tested, a sorption moisture isotherm was constructed experimentally. The acrylamide concentrations measured at different water activities could be modeled on the basis of a reaction scheme including not only acrylamide formation and elimination reactions but also an alternative Maillard reaction between both reactants. The corresponding rate constants and activation energies were estimated using nonlinear regression analysis. Whereas the rate constant for acrylamide formation varied only slightly with the initial water activity of the model system, the elimination rate constant showed a clear minimum around a water activity of 0.82. The opposite trend, namely, a maximum at a water activity of 0.82, was found for the Maillard reaction rate constant as a function of water activity, which confirms data from literature. The activation energies for the different reactions changed in a comparable way as the corresponding rate constant with water activity. PMID:17503764

  9. 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.

  10. 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.

  11. How can macromolecular crowding inhibit biological reactions? The enhanced formation of DNA nanoparticles

    PubMed Central

    Hou, Sen; Trochimczyk, Piotr; Sun, Lili; Wisniewska, Agnieszka; Kalwarczyk, Tomasz; Zhang, Xuzhu; Wielgus-Kutrowska, Beata; Bzowska, Agnieszka; Holyst, Robert

    2016-01-01

    In contrast to the already known effect that macromolecular crowding usually promotes biological reactions, solutions of PEG 6k at high concentrations stop the cleavage of DNA by HindIII enzyme, due to the formation of DNA nanoparticles. We characterized the DNA nanoparticles and probed the prerequisites for their formation using multiple techniques such as fluorescence correlation spectroscopy, dynamic light scattering, fluorescence analytical ultracentrifugation etc. In >25% PEG 6k solution, macromolecular crowding promotes the formation of DNA nanoparticles with dimensions of several hundreds of nanometers. The formation of DNA nanoparticles is a fast and reversible process. Both plasmid DNA (2686 bp) and double-stranded/single-stranded DNA fragment (66bp/nt) can form nanoparticles. We attribute the enhanced nanoparticle formation to the depletion effect of macromolecular crowding. This study presents our idea to enhance the formation of DNA nanoparticles by macromolecular crowding, providing the first step towards a final solution to efficient gene therapy. PMID:26903405

  12. Formation and stability of carbocations and carbanions in water and intrinsic barriers to their reactions.

    PubMed

    Richard, J P; Amyes, T L; Toteva, M M

    2001-12-01

    Lifetimes in water as short as 10(-11) s have been determined for carbocations and carbanions by referencing the rate of their reaction with solvent species to that for the appropriate "clock" reaction, and equilibrium constants have been determined as the ratio of rate constants for their formation and breakdown. Rate-equilibrium correlations for these organic ions are often poor and sometimes even defy the simple generalization that reactivity increases with decreasing stability. This seemingly confusing body of data can be understood through consideration of the both the Marcus intrinsic barrier and the thermodynamic driving force to reaction of these organic ions.

  13. Reaction Rates for the Formation of Deuterium Tritide from Deuterium and Tritium

    SciTech Connect

    McConville, G. T.; Menke, D. A.; Ellefson, R. E.

    1985-04-01

    The rates of formation of DT in a mixture of D2 and T2 have been measured as a function of initial T2 concentration, pressure, temperature,and methane concentration in a stainless steel reaction container which had been treated to inhibit protium ingrowth. An attempt has been made to explain the experimental resuts on the basis of ion-molecule chain reactions. Some of the observations are consistent with a gas-phase ion, ground-state molecule reaction, but some of the more interesting observations require more complicated models. The addition of excited state molecules or heterogeneous catalytic effects are possibilities that will need further experiments for confirmation.

  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. Water formation at low temperatures by surface O2 hydrogenation II: The reaction network.

    PubMed

    Cuppen, H M; Ioppolo, S; Romanzin, C; Linnartz, H

    2010-10-14

    Water is abundantly present in the Universe. It is the main component of interstellar ice mantles and a key ingredient for life. Water in space is mainly formed through surface reactions. Three formation routes have been proposed in the past: hydrogenation of surface O, O(2), and O(3). In a previous paper [Ioppolo et al., Astrophys. J., 2008, 686, 1474] we discussed an unexpected non-standard zeroth-order H(2)O(2) production behaviour in O(2) hydrogenation experiments, which suggests that the proposed reaction network is not complete, and that the reaction channels are probably more interconnected than previously thought. In this paper we aim to derive the full reaction scheme for O(2) surface hydrogenation and to constrain the rates of the individual reactions. This is achieved through simultaneous H-atom and O(2) deposition under ultra-high vacuum conditions for astronomically relevant temperatures. Different H/O(2) ratios are used to trace different stages in the hydrogenation network. The chemical changes in the forming ice are followed by means of reflection absorption infrared spectroscopy (RAIRS). New reaction paths are revealed as compared to previous experiments. Several reaction steps prove to be much more efficient (H + O(2)) or less efficient (H + OH and H(2) + OH) than originally thought. These are the main conclusions of this work and the extended network concluded here will have profound implications for models that describe the formation of water in space.

  16. Reactions of Complex Phenols on Aerosols with Gaseous Ozone

    NASA Astrophysics Data System (ADS)

    Hoffmann, M. R.; Enami, S.; Colussi, A. J.

    2009-12-01

    We report that α-tocopherol (α-TOH/α-TO-), as a model of substituted phenols in atmosphere, reacts with closed shell O3(g) on the surface of inert solvent microdroplets within 1 ms to produce persistent (n = 1 - 4) adducts detectable by online electrospray ionization mass spectrometry. The prototype phenolate PhO- undergoes electron transfer under identical conditions. These reactions occur at the gas/liquid interface since their rates: (1) depend on pH, (2) are several orders of magnitude faster than those in the bulk of O33-saturated microdroplets, and (3) approach O3(g) mass accommodation rates. Furthermore, they fail to incorporate solvent into the products: the same species are formed on acetonitrile or nucleophilic methanol microdroplets. Signals initially evolve with the concentration of ozone as expected from first-generation species. However, α-TO- reacts further with ozone via a collision-induced dissociation into a C19H40 fragment (vs. C19H38 from α-TO-, carrying the phytyl side-chain, whereas the higher homologues (α-TO-On ≥ 2-) are not reactive with O3(g). On this basis, α-TO- is assigned to a chroman-6-ol (4a, 8a)-ene oxide (an epoxide), α-TO-O2- to an endoperoxide, and α-TO-O3- to a secondary ozonide. These products are previous unreported. The atmospheric degradation of the substituted phenols detected in forest fires and combustion emissions is therefore expected to produce related oxidants on aerosol particles.

  17. 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).

  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. PMID:15330667

  19. 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.

  20. In vivo analysis of synaptonemal complex formation during yeast meiosis.

    PubMed Central

    White, Eric J; Cowan, Carrie; Cande, W Zacheus; Kaback, David B

    2004-01-01

    During meiotic prophase a synaptonemal complex (SC) forms between each pair of homologous chromosomes and is believed to be involved in regulating recombination. Studies on SCs usually destroy nuclear architecture, making it impossible to examine the relationship of these structures to the rest of the nucleus. In Saccharomyces cerevisiae the meiosis-specific Zip1 protein is found throughout the entire length of each SC. To analyze the formation and structure of SCs in living cells, a functional ZIP1::GFP fusion was constructed and introduced into yeast. The ZIP1::GFP fusion produced fluorescent SCs and rescued the spore lethality phenotype of zip1 mutants. Optical sectioning and fluorescence deconvolution light microscopy revealed that, at zygotene, SC assembly was initiated at foci that appeared uniformly distributed throughout the nuclear volume. At early pachytene, the full-length SCs were more likely to be localized to the nuclear periphery while at later stages the SCs appeared to redistribute throughout the nuclear volume. These results suggest that SCs undergo dramatic rearrangements during meiotic prophase and that pachytene can be divided into two morphologically distinct substages: pachytene A, when SCs are perinuclear, and pachytene B, when SCs are uniformly distributed throughout the nucleus. ZIP1::GFP also facilitated the enrichment of fluorescent SC and the identification of meiosis-specific proteins by MALDI-TOF mass spectroscopy. PMID:15166136

  1. Structural basis of complement membrane attack complex formation

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

  2. 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.

  3. 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.

  4. Star Formation in the Northern Cloud Complex of NGC 2264

    NASA Astrophysics Data System (ADS)

    Hedden, Abigail S.; Walker, Christopher K.; Groppi, Christopher E.; Butner, Harold M.

    2006-07-01

    We have made continuum and spectral line observations of several outflow sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope (HHT) and ARO 12 m millimeter-wave telescope. This study explores the kinematics and outflow energetics of the young stellar systems observed and assesses the impact star formation is having on the surrounding cloud environment. Our data set incorporates 12CO (3-2),13CO (3-2), and 12CO (1-0) observations of outflows associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS 25 and 27, respectively, in the northern cloud complex. Complementary 870 μm continuum maps were made with the HHT 19 channel bolometer array. Our results indicate there is a weak <=0.5% coupling between outflow kinetic energy and turbulent energy of the cloud. An analysis of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining their dynamical integrity except where outflowing material directly interacts with the core, such as along the outflow axes.

  5. Reactivity of the uranium(IV) carbene complex [U(BIPM(TMS))(Cl)(μ-Cl)₂Li(THF)₂] (BIPM(TMS) = {C(PPh₂NSiMe₃)₂}) towards carbonyl and heteroallene substrates: metallo-Wittig, adduct formation, C-F bond activation, and [2 + 2]-cycloaddition reactions.

    PubMed

    Cooper, Oliver J; Mills, David P; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2014-10-14

    The reactivity of the uranium(IV) carbene complex [U(BIPM(TMS))(Cl)(μ-Cl)2Li(THF)2] (1, BIPM(TMS) = {C(PPh2NSiMe3)2}) towards carbonyl and heteroallene substrates is reported. Reaction of 1 with benzophenone proceeds to give the metallo-Wittig terminal alkene product Ph2C=C(PPh2NSiMe3)2 (2); the likely "UOCl2" byproduct could not be isolated. Addition of the bulky ketone PhCOBu(t) to 1 resulted in loss of LiCl, coordination of the ketone, and dimerisation to give [U(BIPM(TMS))(Cl)(μ-Cl){OC(Ph)(Bu(t))}]2 (3). The reaction of 1 with coumarin resulted in ring opening of the cyclic ester and a metallo-Wittig-type reaction to afford [U{BIPM(TMS)[C(O)(CHCHC6H4O-2)]-κ(3)-N,O,O'}(Cl)2(THF)] (4) where the enolate product remains coordinated to uranium. The reaction of PhCOF with 1 resulted in C-F bond activation and oxidation resulting in isolation of [U(O)2(Cl)2(μ-Cl)2{(μ-LiDME)OC(Ph)=C(PPh2NSiMe3)(PPh2NHSiMe3)}2] (5) along with [U(Cl)2(F)2(py)4] (6). The reactions of 1 with tert-butylisocyanate or dicyclohexylcarbodiimide resulted in the isolation of the [2 + 2]-cycloaddition products [U{BIPM(TMS)[C(NBu(t)){OLi(THF)2(μ-Cl)Li(THF)3}]-κ(4)-C,N,N',N''}(Cl)3] (7) and [U{BIPM(TMS)[C(NCy)2]-κ(4)-C,N,N',N''}(Cl)(μ-Cl)2Li(THF)2] (8). Complexes 2-8 have been variously characterised by single crystal X-ray diffraction, multi-nuclear NMR and FTIR spectroscopies, Evans method solution magnetic moments, variable temperature SQUID magnetometry, and elemental analyses.

  6. 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.

  7. 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.

  8. 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. PMID:23768320

  9. On the dynamics of a forced reaction-diffusion model for biological pattern formation.

    PubMed Central

    Tsonis, A A; Elsner, J B; Tsonis, P A

    1989-01-01

    Ideas from the theory of dynamical systems are applied in biological pattern formation. By considering a simple reaction-diffusion model subjected to an external excitation, we find that the system can give rise to a great variety of periodic, quasiperiodic, and chaotic evolutions. PMID:2740333

  10. 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 ...

  11. Computer analysis of the binding reactions leading to a transmembrane receptor-linked multiprotein complex involved in bacterial chemotaxis.

    PubMed Central

    Bray, D; Bourret, R B

    1995-01-01

    The chemotactic response of bacteria is mediated by complexes containing two molecules each of a transmembrane receptor and the intracellular signaling proteins CheA and CheW. Mutants in which one or the other of the proteins of this complex are absent, inactive, or expressed at elevated amounts show altered chemotactic behavior and the phenotypes are difficult to interpret for some overexpression mutants. We have examined the possibility that these unexpected phenotypes might arise from the binding steps that lead to active complex formation. A limited genetic algorithm was used to search for sets of binding reactions and associated binding constants expected to give mutant phenotypes in accord with experimental data. Different sets of binding equilibria and different assumptions about the activity of particular receptor complexes were tried. Computer analysis demonstrated that it is possible to obtain sets of binding equilibria consistent with the observed phenotypes and provided a simple explanation for these phenotypes in terms of the distribution of active and inactive complexes formed under various conditions. Optimization methods of this kind offer a unique way to analyze reactions taking place inside living cells based on behavioral data. PMID:8573792

  12. 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.

  13. An isoelectronic NO dioxygenase reaction using a nonheme iron(III)-peroxo complex and nitrosonium ion.

    PubMed

    Yokoyama, Atsutoshi; Han, Jung Eun; Karlin, Kenneth D; Nam, Wonwoo

    2014-02-18

    Reaction of a nonheme iron(III)-peroxo complex, [Fe(III)(14-TMC)(O2)](+), with NO(+), a transformation which is essentially isoelectronic with that for nitric oxide dioxygenases [Fe(III)(O2˙(-)) + NO], affords an iron(IV)-oxo complex, [Fe(IV)(14-TMC)(O)](2+), and nitrogen dioxide (NO2), followed by conversion to an iron(III)-nitrato complex, [Fe(III)(14-TMC)(NO3)(F)](+).

  14. anti-Selective Asymmetric Henry Reaction Catalyzed by a Heterobimetallic Cu-Sm-Aminophenol Sulfonamide Complex.

    PubMed

    Li, Yang; Deng, Ping; Zeng, Youmao; Xiong, Yan; Zhou, Hui

    2016-04-01

    A novel heterobimetallic Cu/Sm/aminophenol sulfonamide complex has been developed by a convenient one-pot method for the anti-selective asymmetric Henry reaction. The corresponding anti-β-nitro alcohols are obtained in up to 99% yield, >30:1 dr, and 98% ee. The results of control experiments and ESI-MS analysis of the complex indicate that the monomeric bimetallic Cu/Sm/1 complex would be the active species.

  15. Evidence for the intermediacy of Wheland-Meisenheimer complexes in SEAr reactions of aminothiazoles with 4,6-dinitrobenzofuroxan.

    PubMed

    Boga, Carla; Del Vecchio, Erminia; Forlani, Luciano; Goumont, Régis; Terrier, François; Tozzi, Silvia

    2007-01-01

    Reactions of DNBF with a series of 2-aminothiazoles (1 a-f) to afford thermodynamically stable C-bonded sigma-adducts have been investigated in acetonitrile. A most significant finding emerged on recording NMR spectra immediately after mixing of equimolar amounts of DNBF and the unsubstituted 2-aminothiazole (1 a) in Me2SO: namely, that the formation of 9 a is preceded by that of a short-lived intermediate species X. From the 1H NMR parameters characterizing this intermediate, as well as the dependence of its lifetime on the experimental conditions-the presence of excess DNBF over 1 a increases the lifetime of X while an excess of base (1 a) accelerates its conversion into 9 a--it is convincingly demonstrated that the structure of X combines the presence of a positively charged Wheland complex moiety (with regard to the thiazole ring) with that of a negatively charged Meisenheimer complex moiety (with regard to the benzofuroxan system). So far, only one intermediate of this type (noted WM) has been successfully characterized, in the reactions of DNBF with 1,3,5-tris(N,N-dialkylamino)benzenes. Among the key features supporting the intermediacy of X along the reaction coordinate leading to 9 a is the fact that the reactions of DNBF with 1 a in the presence of an alcohol (MeOH, EtOH, nPrOH) produce new adducts arising from the addition of an alcohol molecule to the thiazole moiety of WM-1 a. Reflecting the presence of three chiral centres, these species are formed as mixtures of several diastereomers that could all be characterized in their racemic forms in ethanol. These findings generalize the previous report on the formation of Wheland-Meisenheimer carbon-carbon complexes in homocyclic series.

  16. Formation Of Vinyl Chloride And Vinylidene Fluoride By UV-Laser Induced Chain Reactions

    NASA Astrophysics Data System (ADS)

    Wolfrum, J.; Schneider, M.

    1984-05-01

    Thermal elimination of hydrogen chloride from 1,2-dichloroethane and 1,1,1-chlorodifluoroethane is a main industrial route to some important monomer compounds. Two reaction paths are possible - unimolecular four-center-elimination and a radical chain mechanism. The latter is started by the endothermic C-Cl bond rupture, followed by the chain consisting of an abstraction reaction and a monomolecular decomposition step. Inducing the chain by photo-initiation offers the advantage that the monomolecular process becomes the rate determining step leading to a lower activation energy for the total reaction. This allows lower process temperatures, therefore decreasing energy expense and avoiding the high temperature formation of byproducts. In our investigation we used as photolysis source several lines of an UV-Exciplex-Laser which provide short pulses of monochromatic UV-radiation with high energy. It was possible to study the effects of initial radical concentration on the quantum yield 0 as function of the temperature. Long reaction chains and a decrease of 0 inversely proportional to the square root of irradiation intensity were observed. The formation of the monomers was detected by a time-resolved UV-absorption technique. Experimental results were analysed in order to yield information about the temperature and pressure dependence of the rate determining reaction. By application of our data in computer simulations wP were able to extrapolate the reaction behaviour to various technical conditions.

  17. 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.

  18. Influence of ions on the antigen-antibody complex formation as measured by radioimmunoassay.

    PubMed

    Vader, H L; Geuskens, L M; Vink, C L

    1977-10-15

    In this study, using radioimmunoassay techniques, we found that ions at concentrations in the order of 0.1 molar influence the antigen-antibody complex formation. The angiotensin I/anti-angiotensin I reaction was studied in detail. Particularly bivalent cations and anions with a strong chaotropic effect (SCN-, I- and ClO4-) were found to influence strongly the specific immunological reaction. However, NO3- had also a remarkably strong influence. We found that the equilibrium constant, rather than the number of binding sites of the antibody, is influenced by the ions. It should be borne in mind that relatively high concentrations of electrolyte (as compared with the concentrations of antigen and antibody) show this effect. Consequently, this effect is of less practical importance for routine radioimmunoassay than is, for example, the effect of pH. However, this phenomenon shows that the radioimmunoassay technique might be valuable not only for quantization of very low hormone concentrations in biological fluids, but has also important potential applications in physical and protein chemistry. Particularly, the high sensitivity of this technique and the possibility of studying a homogeneous reaction system might give it advantages over other techniques.

  19. 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. PMID:25154312

  20. 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.

  1. 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. PMID:26079181

  2. 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. PMID:19662443

  3. 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.

  4. Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.

    PubMed

    Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

    2014-08-18

    The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures.

  5. Redox-Active-Ligand-Mediated Formation of an Acyclic Trinuclear Ruthenium Complex with Bridging Nitrido Ligands.

    PubMed

    Bagh, Bidraha; Broere, Daniël L J; Siegler, Maxime A; van der Vlugt, Jarl Ivar

    2016-07-11

    Coordination of a redox-active pyridine aminophenol ligand to Ru(II) followed by aerobic oxidation generates two diamagnetic Ru(III) species [1 a (cis) and 1 b (trans)] with ligand-centered radicals. The reaction of 1 a/1 b with excess NaN3 under inert atmosphere resulted in the formation of a rare bis(nitrido)-bridged trinuclear ruthenium complex with two nonlinear asymmetrical Ru-N-Ru fragments. The spontaneous reduction of the ligand centered radical in the parent 1 a/1 b supports the oxidation of a nitride (N(3-) ) to half an equivalent of N2 . The trinuclear omplex is reactive toward TEMPO-H, tin hydrides, thiols, and dihydrogen. PMID:27321547

  6. Formation of impeller-like helical DNA–silica complexes by polyamines induced chiral packing

    PubMed Central

    Liu, Ben; Han, Lu; Che, Shunai

    2012-01-01

    The helicity of DNA and its long-range chiral packing are widespread phenomena; however, the packing mechanism remains poorly understood both in vivo and in vitro. Here, we report the extraordinary DNA chiral self-assembly by silica mineralization, together with circular dichroism measurements and electron microscopy studies on the structure and morphology of the products. Mg2+ ion and diethylenetriamine were found to induce right- and left-handed chiral DNA packing with two-dimensional-square p4mm mesostructures, respectively, to give corresponding enantiomeric impeller-like helical DNA–silica complexes. Moreover, formation of macroscopic impeller-like helical architectures depends on the types of polyamines and co-structure-directing agents and pH values of reaction solution. It has been suggested that interaction strength between negatively charged DNA phosphate strands and positively charged counterions may be the key factor for the induction of DNA packing handedness. PMID:24098845

  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. N,O-Chelating Four-Membered Metallacyclic Titanium(IV) Complexes for Atom-Economic Catalytic Reactions.

    PubMed

    Ryken, Scott A; Schafer, Laurel L

    2015-09-15

    Titanium, as the second most abundant transition metal in the earth's crust, lends itself as a sustainable and inexpensive resource in catalysis. Its nontoxicity and biocompatibility are also attractive features for handling and disposal. Titanium has excelled as a catalyst for a broad range of transformations, including ethylene and α-olefin polymerizations. However, many reactions relevant to fine chemical synthesis have preferrentially employed late transition metals, and reactive, inexpensive early transition metals have been largely overlooked. In addition to promising reactivity, titanium complexes feature more robust character compared with some other highly Lewis-acidic metals such as those found in the lanthanide series. Since the advent of modulating ligand scaffolds, titanium has found use in a growing variety of reactions as a versatile homogeneous catalyst. These catalytic transformations include hydrofunctionalization reactions (adding an element-hydrogen (E-H) bond across a C-C multiple bond), as well as the ring-opening polymerization of cyclic esters, all of which are atom-economic transformations. Our investigations have focused on tight bite angle monoanionic N,O-chelating ligands, forming four-membered metallacycles. These ligand sets, including amidates, ureates, pyridonates, and sulfonamidates, have flexible binding modes offering a range of stable and reactive intermediates necessary for catalytic activity. Additionally, the simple form of these ligands leads to easily prepared proligands, along with facile tuning of steric and electronic factors. A sterically bulky titanium amidate complex has proven to be a leading catalyst for the selective formation of anti-Markovnikov addition products via intermolecular hydroamination of terminal alkynes, while sterically less demanding titanium pyridonates have opened the path to the selective formation of amine substituted cycloalkanes via the intramolecular hydroaminoalkylation of aminoalkenes over

  9. Statistical considerations on the formation of circular photosynthetic light-harvesting complexes from Rhodopseudomonas palustris.

    PubMed

    Taniguchi, Masahiko; Henry, Sarah; Cogdell, Richard J; Lindsey, Jonathan S

    2014-07-01

    Depending on growth conditions, some species of purple photosynthetic bacteria contain peripheral light-harvesting (LH2) complexes that are heterogeneous owing to the presence of different protomers (containing different αβ-apoproteins). Recent spectroscopic studies of Rhodopseudomonas palustris grown under low-light conditions suggest the presence of a C 3-symmetric LH2 nonamer comprised of two distinct protomers. The software program Cyclaplex, which enables generation and data-mining of virtual libraries of molecular rings formed upon combinatorial reactions, has been used to delineate the possible number and type of distinct nonamers as a function of numbers of distinct protomers. The yield of the C 3-symmetric nonamer from two protomers (A and B in varying ratios) has been studied under the following conditions: (1) statistical, (2) enriched (preclusion of the B-B sequence), and (3) seeded (pre-formation of an A-B-A block). The yield of C 3-symmetric nonamer is at most 0.98 % under statistical conditions versus 5.6 % under enriched conditions, and can be dominant under conditions of pre-seeding with an A-B-A block. In summary, the formation of any one specific nonamer even from only two protomers is unlikely on statistical grounds but must stem from enhanced free energy of formation or a directed assembly process by as-yet unknown factors.

  10. 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.

  11. In Situ Catalyst Modification in Atom Transfer Radical Reactions with Ruthenium Benzylidene Complexes.

    PubMed

    Lee, Juneyoung; Grandner, Jessica M; Engle, Keary M; Houk, K N; Grubbs, Robert H

    2016-06-01

    Ruthenium benzylidene complexes are well-known as olefin metathesis catalysts. Several reports have demonstrated the ability of these catalysts to also facilitate atom transfer radical (ATR) reactions, such as atom transfer radical addition (ATRA) and atom transfer radical polymerization (ATRP). However, while the mechanism of olefin metathesis with ruthenium benzylidenes has been well-studied, the mechanism by which ruthenium benzylidenes promote ATR reactions remains unknown. To probe this question, we have analyzed seven different ruthenium benzylidene complexes for ATR reactivity. Kinetic studies by (1)H NMR revealed that ruthenium benzylidene complexes are rapidly converted into new ATRA-active, metathesis-inactive species under typical ATRA conditions. When ruthenium benzylidene complexes were activated prior to substrate addition, the resulting activated species exhibited enhanced kinetic reactivity in ATRA with no significant difference in overall product yield compared to the original complexes. Even at low temperature, where the original intact complexes did not catalyze the reaction, preactivated catalysts successfully reacted. Only the ruthenium benzylidene complexes that could be rapidly transformed into ATRA-active species could successfully catalyze ATRP, whereas other complexes preferred redox-initiated free radical polymerization. Kinetic measurements along with additional mechanistic and computational studies show that a metathesis-inactive ruthenium species, generated in situ from the ruthenium benzylidene complexes, is the active catalyst in ATR reactions. Based on data from (1) H, (13)C, and (31)P NMR spectroscopy and X-ray crystallography, we suspect that this ATRA-active species is a RuxCly(PCy3)z complex. PMID:27186790

  12. Effect of gel network on pattern formation in the ferrocyanide-iodate-sulfite reaction.

    PubMed

    Ueno, Tomonaga; Yoshida, Ryo

    2011-06-01

    Stationary patterns have been researched experimentally since the discovery of the Turing pattern in the chlorite-iodide-malonic acid (CIMA) reaction and the self-replicating spot pattern in the ferrocyanide-iodate-sulfite (FIS) reaction. In this study, we reproduced the pattern formation in the FIS reaction by using poly(acrylamide) gels. Gels with different swelling ratios were prepared to use as a medium. The effect of the swelling ratio was compared with the effect of thickness. It was found that the swelling ratio greatly influenced pattern formation. Oscillating spot patterns appeared at high swelling ratios, and lamellar patterns appeared at a low swelling ratio. Self-replicating spot patterns appeared in between the two areas. The front velocities, which were observed in the initial stage of pattern formation, depended on the swelling ratio. Furthermore, this dependence obeys the free volume theory of diffusion. These results provide evidence that the change in front velocities is caused by a change in diffusion. Pattern formation can be controlled not only by thickness but also by swelling ratio, which may be useful for creating novel pattern templates. PMID:21557556

  13. Pattern formation on networks with reactions: A continuous-time random-walk approach

    NASA Astrophysics Data System (ADS)

    Angstmann, C. N.; Donnelly, I. C.; Henry, B. I.

    2013-03-01

    We derive the generalized master equation for reaction-diffusion on networks from an underlying stochastic process, the continuous time random walk (CTRW). The nontrivial incorporation of the reaction process into the CTRW is achieved by splitting the derivation into two stages. The reactions are treated as birth-death processes and the first stage of the derivation is at the single particle level, taking into account the death process, while the second stage considers an ensemble of these particles including the birth process. Using this model we have investigated different types of pattern formation across the vertices on a range of networks. Importantly, the CTRW defines the Laplacian operator on the network in a non-ad hoc manner and the pattern formation depends on the structure of this Laplacian. Here we focus attention on CTRWs with exponential waiting times for two cases: one in which the rate parameter is constant for all vertices and the other where the rate parameter is proportional to the vertex degree. This results in nonsymmetric and symmetric CTRW Laplacians, respectively. In the case of symmetric Laplacians, pattern formation follows from the Turing instability. However in nonsymmetric Laplacians, pattern formation may be possible with or without a Turing instability.

  14. Evidence for oligomer formation in clouds: reactions of isoprene oxidation products.

    PubMed

    Altieri, Katye E; Carlton, Annmarie G; Lim, Ho-Jin; Turpin, Barbara J; Seitzinger, Sybil P

    2006-08-15

    Electrospray ionization mass spectrometry (ESI-MS) was used to investigate product formation in laboratory experiments designed to study secondary organic aerosol (SOA) formation in clouds. It has been proposed that water soluble aldehydes derived from aromatics and alkenes, including isoprene, oxidize further in cloud droplets forming organic acids and, upon droplet evaporation, SOA. Pyruvic acid is an important aqueous-phase intermediate. Time series samples from photochemical batch aqueous phase reactions of pyruvic acid and hydrogen peroxide were analyzed for product formation. In addition to the monomers predicted by the reaction scheme, products consistent with an oligomer system were found when pyruvic acid and OH radical were both present. No evidence of oligomer formation was found in a standard mix composed of pyruvic, glyoxylic, and oxalic acids prepared in the same matrix as the samples analyzed using the same instrument conditions. The distribution of high molecular weight products is consistent with oligomers composed of the mono-, oxo-, and di-carboxylic acids expected from the proposed reaction scheme.

  15. Early stages of particle formation in precipitation reactions-quinacridone and boehmite as generic examples.

    PubMed

    Haberkorn, H; Franke, D; Frechen, Th; Goesele, W; Rieger, J

    2003-03-01

    For many products, such as nanoparticulate systems, particle formation by precipitation is an essential procedural step. To learn more about the processes involved in precipitation, we investigated particle formation during precipitation reactions by means of online and offline methods. As model systems we chose the catalyst boehmite and the organic pigment quinacridone. The reactants were mixed in a mixing device and led into a reaction tube. At the end of the tube, a free jet of the suspension was produced. By varying the length of the reaction tube the time between mixing the reactants and the moment of observation was varied. Thus a time resolution down to 10 ms from the beginning of the reaction was obtained. Small-angle X-ray scattering on the free jet yielded online information about the structural inhomogeneities within the reacting systems. Transmission electron microscopy patterns obtained from quenched samples, which were taken by shooting copper grids through the free jet into liquid nitrogen, provided complementary information about structural features. Immediately after mixture an emulsion-like structure develops indicating that classical nucleation theory does not apply in the present systems. This finding can be explained by assuming instantaneous reaction at the interfaces of the two reactants that meet in the mixing device. From this preliminary state primary particles form with a size in the nanometer range. The observations can be rationalized by considering the underlying hydrodynamics of turbulent mixing of the reactants.

  16. 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.

  17. 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. PMID:27443396

  18. Multicomponent One-pot Reactions Towards the Synthesis of Stereoisomers of Dipicolylamine Complexes.

    PubMed

    Raje, Sakthi; Gurusamy, Sureshbabu; Koner, Abhishek; Mehrotra, Sonam; Jennifer, Samson Jegan; Vasudev, Prema G; Butcher, Ray J; Angamuthu, Raja

    2016-01-01

    Reported are multi-component one-pot syntheses of chiral complexes [M(L(R) OR')Cl2 ] or [M(L(R) SR')Cl2 ] from the mixture of an N-substituted ethylenediamine, pyridine-2-carboxaldehyde, a primary alcohol or thiol and MCl2 utilizing in-situ formed cyclized Schiff bases where a C-O bond, two stereocenters, and three C-N bonds are formed (M=Zn, Cu, Ni, Cd; R=Et, Ph; R'=Me, Et, nPr, nBu). Tridentate ligands L(R) OR' and L(R) SR' comprise two chiral centers and a hemiaminal ether or hemiaminal thioether moiety on the dipicolylamine skeleton. Syn-[Zn(L(Ph) OMe)Cl2 ] precipitates out readily from the reaction mixture as a major product whereas anti-[Zn(L(Ph) OMe)Cl2 ] stays in solution as minor product. Both syn-[Zn(L(Ph) OMe)Cl2 ] and anti-[Zn(L(Ph) OMe)Cl2 ] were characterized using NMR spectroscopy and mass spectrometry. Solid-state structures revealed that syn-[Zn(L(Ph) OMe)Cl2 ] adopted a square pyramidal geometry while anti-[Zn(L(Ph) OMe)Cl2 ] possesses a trigonal bipyramidal geometry around the Zn centers. The scope of this method was shown to be wide by varying the components of the dynamic coordination assembly, and the structures of the complexes isolated were confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. Syn complexes were isolated as major products with Zn(II) and Cu(II) , and anti complexes were found to be major products with Ni(II) and Cd(II) . Hemiaminals and hemiaminal ethers are known to be unstable and are seldom observed as part of cyclic organic compounds or as coordinated ligands assembled around metals. It is now shown, with the support of experimental results, that linear hemiaminal ethers or thioethers can be assembled without the assistance of Lewis acidic metals in the multi-component assembly, and a possible pathway of the formation of hemiaminal ethers has been proposed.

  19. Quantum-mechanical calculations on termolecular association reactions XY+Z+M-->XYZ+M: Application to ozone formation

    NASA Astrophysics Data System (ADS)

    Charlo, David; Clary, David C.

    2002-07-01

    We present a quantum-mechanical model for termolecular association reactions XY+Z+M→XYZ+M involving the formation of a long-lived complex XYZ*. The rotation of the molecule XYZ is treated in the infinite order sudden approximation (IOS) and its vibrations are treated by the coupled-channel method (VCC). Resonances featuring the XYZ* long-lived complex formation are first computed by means of the stabilization method and are then included in the vibrational basis functions used for the inelastic VCC-IOS scattering calculation. The method yields rate constants for the association process selected in resonance and bound states of XYZ. We apply the method to the formation of ozone and investigate isotope effects. Calculations of energy transfer and collision-induced recombination of O+O2 in collision with Ar are reported for a range of ozone isotopomers. The bending mode of O3 is not treated explicitly in these computations. The results establish a strong selectivity in vibrational state-to-state cross sections for the deactivation of O3 during the collisional energy transfer process with Ar. The present calculations also account for the high sensitivity of rate constants with respect to the isotopic composition of ozone molecules but not in the same proportion as experiments. The energy transfer from selected initial vibrational states is also calculated as a function of the initial relative kinetic energy.

  20. Formation of high-molecular-weight angiotensinogen during pregnancy is a result of competing redox reactions with the proform of eosinophil major basic protein.

    PubMed

    Kløverpris, Søren; Skov, Louise L; Glerup, Simon; Pihl, Kasper; Christiansen, Michael; Oxvig, Claus

    2013-01-01

    The plasma concentration of the placentally derived proMBP (proform of eosinophil major basic protein) increases in pregnancy, and three different complexes containing proMBP have been isolated from pregnancy plasma and serum: a 2:2 complex with the metalloproteinase, PAPP-A (pregnancy-associated plasma protein-A), a 2:2 complex with AGT (angiotensinogen) and a 2:2:2 complex with AGT and complement C3dg. In the present study we show that during human pregnancy, all of the circulating proMBP exists in covalent complexes, bound to either PAPP-A or AGT. We also show that the proMBP-AGT complex constitutes the major fraction of circulating HMW (high-molecular weight) AGT in late pregnancy, and that this complex is able to further associate with complement C3 derivatives post-sampling. Clearance experiments in mice suggest that complement C3-based complexes are removed faster from the circulation compared to monomeric AGT and the proMBP-AGT complex. Furthermore, we have used recombinant proteins to analyse the formation of the proMBP-PAPP-A and the proMBP-AGT complexes, and we demonstrate that they are competing reactions, depending on the same cysteine residue of proMBP, but differentially on the redox potential, potentially important for the relative amounts of the complexes in vivo. These findings may be important physiologically, since the biochemical properties of the proteins change as a consequence of complex formation.

  1. Revisiting the Passerini reaction mechanism: existence of the nitrilium, organocatalysis of its formation, and solvent effect.

    PubMed

    Ramozzi, Romain; Morokuma, Keiji

    2015-06-01

    The Passerini reaction mechanism is revisited using high-level DFT calculations. Contrary to the common belief, the nitrilium intermediate is found to be stable in solution and its formation is rate-determining. The present results point out that this step is catalyzed by a second carboxylic acid molecule, as the subsequent Mumm rearrangement is. The solvent effect on the reaction rate was investigated. In a protic solvent like methanol, hydrogen bonds are responsible of the increasing barrier of the rate-determining step, compared to the commonly used solvent, the dichloromethane.

  2. Theoretical study of the formation reaction of the methyl vinyl ketone: A conformational approach

    NASA Astrophysics Data System (ADS)

    Ramírez-Ramírez, Víctor M.; Nebot-Gil, Ignacio

    The formation reaction of both isomers of the methyl vinyl ketone (MVK) from the corresponding alkoxy radicals was investigated by means of theoretical methods based on quantum chemistry. Perturbative unrestricted Möller-Plesset (UMP2) and density functional methods B3LYP and BH and HLYP were used to obtain the stationary points on the potential energy surface. In addition to this, the interconversion reaction between both isomers of the MVK was studied, characterizing the corresponding transition state. A conformational study was done, and the energy and geometry of the stationary points located were analyzed by means of ab initio calculations.

  3. Formation of HO2/+/ by reaction of metastable O2/+/ ions with H2

    NASA Technical Reports Server (NTRS)

    Ajello, J. M.; Huntress, W. T.; Lane, A. L.; Lebreton, P. R.; Williamson, A. D.

    1974-01-01

    The photoionization efficiency curves of H2(+), O2(+), and HO2(+) have been studied in a mixture of hydrogen and oxygen over the wavelength range from 650 to 810 A. The HO2(+) ion appears at 804 A, the threshold for ionization of H2, by the reaction H2(+) + O2 yields HO2(+) + H. The relative photoionization efficiency curves of H2(+) and HO2(+) are the same from 804 to 764 A. Below 764 A production of the 4 Pi u metastable electronic state of O2(+) leads to the formation of HO2(+) by the reaction O2(+)(a 4 Pi u) + H2 yields HO2(+) + H.

  4. Formations of Bacteria-like Textures by dynamic reactions in Meteorite and Syntheses

    NASA Astrophysics Data System (ADS)

    Miura, Y.

    2009-05-01

    1. Introduction Spherule texture can be formed in dynamic reaction during meteoritic impact in air. However, there are no reports on nano-bacteria-like (i.e. spherule-chained) textures with iron (and Nickel) oxides (with chlorine) in composition and micro-texture with 100nm order [1] in meteorite and synthetic experiment. The purpose of the present study is to elucidate spherule-chained texture with micro-texture of 100nm in order found in the Kuga iron meteorite, Iwakuni, Yamaguchi, Japan, and its first artificial synthesis in laboratory. 2. Two textures in the Kuga meteorite: The Kuga iron meteorite found in Kuga, Iwakuni, Yamaguchi, Japan reveals spherule-chained texture with Fe, Ni-rich composition with 10μm in size, where each spherule contained "long micro-texture in 100nm in size"[1,2]. The complex texture of flow and chained shapes can be found only in the fusion crust of the meteorite formed by quenched and random processes with vapor-melting process in air of the Earth. The FE-ASEM with EDX analyses by an in-situ observation indicate that the matrix of the spherule-chained texture with Fe, Ni, O-rich (with minor Cl) composition is carbon-rich composition formed by impact reactions in air. 3. Comparison with Martian meteorite Remnant of life in ocean can be found by mineralized fossil, which can be found in the Martian meteorite ALH84001 as bacteria-like chained texture of magnetite in composition (in 100nm order) around carbonate spherules [3]. Similarity of bacteria-like texture of the ALH84001 compared with the Kuga meteorites in this study are composition of Fe-rich, C-bearing, and chained texture of small size replaced by Fe and O-rich composition in air. Major difference of these textures is no carbonates minerals in the Kuga meteorite at dynamic reaction in air [1, 2, 3]. 4. First synthesis of bacteria- like akaganeite: A bacteria-like texture with Fe oxides (with minor chlorine as akaganeite-like compositions) is synthesized by chlorine and water

  5. Reaction-diffusion processes and epidemic metapopulation models in complex networks

    NASA Astrophysics Data System (ADS)

    Vespignani, A.

    2008-08-01

    The correct description of reaction-diffusion phenomena requires a detailed knowledge of the contact networks defining the interactions between individuals and groups of individuals. For this reason, the study of reaction-diffusion processes has been recently widened with opportune models and methods dealing with the heterogeneity and large scale fluctuations observed in many real world networks. Here we present a brief overview of some recent results on reaction-diffusion processes in complex networks which provide useful insights into the dynamic behavior of epidemic metapopulation models.

  6. 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

    2016-09-01

    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.

  7. Intermediate colloidal formation and the varying width of periodic precipitation bands in reaction-diffusion systems.

    PubMed

    George, Jacob; Varghese, George

    2005-02-15

    The mechanism of rhythmic pattern formation in reaction-diffusion systems is investigated theoretically by introducing a new concept. The boundary that separates the two reacting species virtually migrates as the diffusion proceeds into the gelatinous medium. Based on this boundary migration scenario, all the well-established relations on Liesegang patterns could be proved, in a rather modified way. The idea of formation of intermediate colloidal haze prior to patterning along with the moving boundary model proved to be efficient in predicting the concentration dependence of the width of the spatiotemporal patterns. The experimental observations support the width law relation developed.

  8. 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. PMID:24351110

  9. 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.

  10. C-Cl bond activation and catalytic hydrodechlorination of hexachlorobenzene by cobalt and nickel complexes with sodium formate as a reducing agent.

    PubMed

    Li, Junye; Li, Xiaoyan; Wang, Lin; Hu, Qingping; Sun, Hongjian

    2014-05-14

    A benzyne cobalt complex, Co(η(2)-C6Cl4)(PMe3)3 (2), was generated from the reaction of hexachlorobenzene with 2 equiv. of Co(PMe3)4 through selective activation of two C-Cl bonds of hexachlorobenzene. Meanwhile, the byproduct CoCl2(PMe3)3 was also confirmed by IR spectra. The cobalt(II) complex, CoCl(C6Cl5)(PMe3)3 (1), as an intermediate in the formation of aryne complex 2, was also isolated by the reaction of hexachlorobenzene with the stoichiometric amount of Co(PMe3)4. Complex 2 could be obtained by the reaction of 1 with Co(PMe3)4. Under similar reaction conditions, the reaction of Ni(PMe3)4 with hexachlorobenzene afforded only a mono-(C-Cl) bond activation nickel(II) complex, NiCl(C6H5)(PMe3)2 (5). The expected benzyne nickel complex was not formed. The structures of complexes 2 and 5 were determined by X-ray single crystal diffraction. Successful selective hydrodechlorinations of hexachlorobenzene were studied and in the presence of Co(PMe3)4 or Ni(PMe3)4 as catalysts and sodium formate as a reducing agent pentachlorobenzene and 1,2,4,5-tetrachlorobenzene were obtained. The catalytic hydrodechlorination mechanism is proposed and discussed.

  11. 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.

  12. Formation of O3/+/ by the reaction of metastable O2/+/ ions with O2

    NASA Technical Reports Server (NTRS)

    Ajello, J. M.; Pang, K. D.; Monahan, K. M.

    1974-01-01

    The high resolution of the photoionization mass spectrophotometer was utilized to resolve some doubts about the participating species in the reaction of metastable oxygen molecular ions with oxygen molecules to yield ozone ions and oxygen radicals. It is found from inspection of the appearance potential of the ozone ion that an a4 Pi-excited state is responsible for the formation of ozone near the appearance potential of these lines.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. The Combination of Salt Induced Peptide Formation Reaction and Clay Catalysis: A Way to Higher Peptides under Primitive Earth Conditions

    NASA Astrophysics Data System (ADS)

    Rode, Bernd M.; Son, Hoang L.; Suwannachot, Yuttana; Bujdak, Juraj

    1999-05-01

    Two reactions with suggested prebiotic relevance for peptide evolution, the saltinduced peptide formation reaction and the peptide chain elongation/stabilization on clay minerals have been combined in experimental series starting from dipeptides and dipeptide/amino acid mixtures. The results show that both reactions can take place simultaneously in the same reaction environment and that the presence of mineral catalysts favours the formation of higher oligopeptides. These findings lend further support to the relevance of these reactions for peptide evolution on the primitive earth. The detailed effects of the specific clay mineral depend both on the nature of the mineral and the reactants in solution.

  19. Pressure dependence of butyl nitrate formation in the reaction of butylperoxy radicals with nitrogen oxide.

    PubMed

    Butkovskaya, N I; Kukui, A; Le Bras, G; Rayez, M-T; Rayez, J-C

    2015-05-14

    The yield of 1- and 2-butyl nitrates in the gas-phase reactions of NO with n-C4H9O2 and sec-C4H9O2, obtained from the reaction of F atoms with n-butane in the presence of O2, was determined over the pressure range of 100-600 Torr at 298 K using a high-pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass spectrometer. The yield of butyl nitrates was found to increase linearly with pressure from about 3% at 100 Torr to about 8% at 600 Torr. The results obtained are compared with the available data concerning nitrate formation from NO reaction with other small alkylperoxy radicals. These results are also discussed through the topology of the lowest potential energy surface mainly obtained from DFT(B3LYP/aug-cc-pVDZ) calculations of the RO2 + NO reaction paths. The formation of alkyl nitrates, due essentially to collision processes, is analyzed through a model that points out the pertinent physical parameters of this system. PMID:25380343

  20. 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.

  1. 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. PMID:27490239

  2. 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.

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

    PubMed

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

    2015-07-01

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

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

    PubMed

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

    2015-07-01

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

  5. Complex formation between the hepatitis C virus serine protease and a synthetic NS4A cofactor peptide.

    PubMed

    Bianchi, E; Urbani, A; Biasiol, G; Brunetti, M; Pessi, A; De Francesco, R; Steinkühler, C

    1997-06-24

    The NS3 protein of the hepatitis C virus contains a serine protease that, upon binding to its cofactor, NS4A, is responsible for maturational cleavages that occur in the nonstructural region of the viral polyprotein. We have studied in vitro complex formation between the NS3 protease domain expressed in Escherichia coli and a synthetic peptide spanning the minimal domain of the NS4A cofactor. Complex dissociation constants in the low micromolar range were measured using different techniques such as activity titration, fluorescence titration, and pre-equilibrium analysis of complex formation. Cofactor binding was strictly dependent on the glycerol content of buffer solutions and was not significantly influenced by substrate saturation of the enzyme. NS4A peptide binding to NS3 was accompanied by changes in the circular dichroism spectrum in the region between 270 and 290 nm, as well as by an enhancement of tryptophan fluorescence. Conversely, no changes in the far UV region of the circular dichroism spectrum were detectable. These data are indicative of induced tertiary structure changes and suggest that the secondary structure content of the uncomplexed enzyme does not differ significantly from that of the NS3-cofactor complex. Pre-equilibrium measurements of complex formation showed very low values for k(on), suggesting conformational transitions to be rate limiting for the association reaction.

  6. Troglitazone quinone formation catalyzed by human and rat CYP3A: an atypical CYP oxidation reaction.

    PubMed

    He, K; Woolf, T F; Kindt, E K; Fielder, A E; Talaat, R E

    2001-07-15

    Oxidative ring opening of troglitazone (TGZ)(1) a thiazolidine 2,4-dione derivative used for the treatment of type II diabetes mellitus, leads to the formation of a quinone metabolite. The formation of TGZ quinone was shown to be NADPH dependent and to require active microsomal enzymes. Quinone formation was not affected by co-incubation with catalase or sodium azide and was partially inhibited (25%) by superoxide dismutase (SOD). Kinetic analysis of TGZ quinone formation in human liver microsomes implied single enzyme involvement. CYP3A isoforms were characterized as the primary enzymes involved in quinone formation by several lines of evidence including: (a) troleandomycin and ketoconazole almost completely inhibited microsomal quinone formation when SOD was present, whereas other CYP inhibitors had minimal effects (<20%); (b) TGZ quinone formation was highly correlated with regard to both contents (r(2): 0.9374) and activities (r(2): 0.7951) of CYP3A4 in human liver microsomes (HLM); (c) baculovirus insect cell-expressed human CYP3A4 was able to catalyze TGZ quinone formation at a higher capacity (V(max)/K(m)) than other human CYPs with the relative contribution of CYP3A4 in HLM estimated to be 20-fold higher than that of other CYPs; (d) TGZ quinone formation was increased by 350% in liver microsomes from rats pretreated with dexamethasone (DEX); and (e) plasma concentrations of TGZ quinone were increased by 260-680% in rats pretreated with DEX. The chemical nature of the quinone metabolite suggests an atypical CYP reaction consistent with a one-electron oxidation mechanism where an intermediate phenoxy radical combines with ferryl oxygen to subsequently form the quinone metabolite.

  7. 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.

  8. Spectroscopic investigation on the inclusion complex formation between amisulpride and γ-cyclodextrin.

    PubMed

    Negi, Jeetendra Singh; Singh, Shivpal

    2013-02-15

    The purpose of this research was to investigate inclusion complex formation between poorly soluble drug amisulpride (AMI) and γ-cyclodextrin (γ-CD). The solubility of AMI was enhanced by formation of inclusion complex of AMI with nano-hydrophobic cavity of γ-CD. The stoichiometry of inclusion complex was studied by continuous variation Job's plot method and found 1:1. The binding constant was found 1166.65 M(-1) by Benesi-Hildebrand plot. The molecular docking of AMI and γ-CD was done to investigate complexation. The inclusion complex formation was further confirmed by (1)H NMR and FT-IR, DSC and XRD analysis. The solubility of AMI was increased 3.74 times after inclusion complex formation with γ-CD.

  9. 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.

  10. 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.

  11. TraML—A Standard Format for Exchange of Selected Reaction Monitoring Transition Lists*

    PubMed Central

    Deutsch, Eric W.; Chambers, Matthew; Neumann, Steffen; Levander, Fredrik; Binz, Pierre-Alain; Shofstahl, Jim; Campbell, David S.; Mendoza, Luis; Ovelleiro, David; Helsens, Kenny; Martens, Lennart; Aebersold, Ruedi; Moritz, Robert L.; Brusniak, Mi-Youn

    2012-01-01

    Targeted proteomics via selected reaction monitoring is a powerful mass spectrometric technique affording higher dynamic range, increased specificity and lower limits of detection than other shotgun mass spectrometry methods when applied to proteome analyses. However, it involves selective measurement of predetermined analytes, which requires more preparation in the form of selecting appropriate signatures for the proteins and peptides that are to be targeted. There is a growing number of software programs and resources for selecting optimal transitions and the instrument settings used for the detection and quantification of the targeted peptides, but the exchange of this information is hindered by a lack of a standard format. We have developed a new standardized format, called TraML, for encoding transition lists and associated metadata. In addition to introducing the TraML format, we demonstrate several implementations across the community, and provide semantic validators, extensive documentation, and multiple example instances to demonstrate correctly written documents. Widespread use of TraML will facilitate the exchange of transitions, reduce time spent handling incompatible list formats, increase the reusability of previously optimized transitions, and thus accelerate the widespread adoption of targeted proteomics via selected reaction monitoring. PMID:22159873

  12. Inhibitory mechanism of naringenin against carcinogenic acrylamide formation and nonenzymatic browning in Maillard model reactions.

    PubMed

    Cheng, Ka-Wing; Zeng, Xiaohui; Tang, Yun Sang; Wu, Jia-Jun; Liu, Zhiwei; Sze, Kong-Hung; Chu, Ivan K; Chen, Feng; Wang, Mingfu

    2009-08-01

    Chemical model reactions were carried out to investigate the effect of a citrus flavonoid, naringenin, on the formation of acrylamide under mild heating conditions. Results showed that naringenin significantly and dose dependently inhibited the formation of acrylamide (20-50% relative to the control), although not in a linear manner. Moreover, the presence of naringenin in acrylamide-producing models effectively reduced the extent of browning. Careful comparison of the HPLC chromatograms of samples from the chemical model reactions revealed that naringenin likely reacted with Maillard intermediates, giving rise to new derivatives. Subsequent LC-MS analyses suggested that the proposed derivatives have a predicted molecular mass of 341 Da. Eventually, two derivatives were purified and characterized with LC-MS/MS and NMR spectroscopy as 8-C-(E-propenamide)naringenin and 6-C-(E-propenamide)naringenin, respectively. In other words, naringenin, a rather weak antioxidant, strongly inhibited acrylamide formation probably by directly reacting with acrylamide precursors, thus diverting them from the pathways that lead to acrylamide formation. PMID:19639978

  13. 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

  14. 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

  15. 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.

  16. Intimations of neck formation in heavy-ion subbarrier fusion reactions

    SciTech Connect

    Stelson, P.H.

    1990-07-01

    Since the observed fusion cross sections for collisions between heavy ions at subbarrier energies are orders of magnitude larger than would be expected for barrier tunnelling, one is faced with the task of identifying the basic force which is strong enough to overcome the strong Coulomb force and bring about fusion. The two possibilities seem to be excursions of the nuclear surface (and strong nuclear force) due to collective motions of the colliding nuclei and formation of a neck of nuclear matter. The first possibility has received the most attention. However, the systematics of fusion cross sections suggest neck formation is playing an important role. Neck formation can also result in a reseparation of the composite system and we review the experimental information on these reactions at barrier and subbarrier energies. 15 refs., 18 figs.

  17. Zwitterion formation in titan ice analogs: reaction between HC3N and NH3.

    PubMed

    Couturier-Tamburelli, Isabelle; Sessouma, Bintou; Chiavassa, Thierry; Piétri, Nathalie

    2012-11-01

    A zwitterion is formed in the laboratory at low temperatures in the solid phase from the thermal reaction of HC(3)N and NH(3). We report for the first time its infrared spectrum. We study its reaction using Fourier transform infrared spectroscopy. Its reaction rate is estimated to be k(T) = 2.9 × 10(5) exp(-2.3 ± 0.1 (kJ mol(-1))/RT). Calculations using density functional theory (B3LYP/6-31g**) are used to characterize all the species (complexes, zwitterions, and transition states) and are in good agreement with the infrared spectra. The structure of the zwitterion is determined planar and it is characterized by a N-C bond around 1.5 Å.

  18. Reaction of benzophenone UV filters in the presence of aqueous chlorine: kinetics and chloroform formation.

    PubMed

    Duirk, Stephen E; Bridenstine, David R; Leslie, Daniel C

    2013-02-01

    The transformation of two benzophenone UV filters (Oxybenzone and Dioxybenzone) was examined over the pH range 6-11 in the presence of excess aqueous chlorine. Under these conditions, both UV filters were rapidly transformed by aqueous chlorine just above circumneutral pH while transformation rates were significantly lower near the extremes of the pH range investigated. Observed first-order rate coefficients (k(obs)) were obtained at each pH for aqueous chlorine concentrations ranging from 10 to 75 μM. The k(obs) were used to determine the apparent second-order rate coefficient (k(app)) at each pH investigated as well as determine the reaction order of aqueous chlorine with each UV filter. The reaction of aqueous chlorine with either UV filter was found to be an overall second-order reaction, first-order with respect to each reactant. Assuming elemental stoichiometry described the reaction between aqueous chlorine and each UV filter, models were developed to determine intrinsic rate coefficients (k(int)) from the k(app) as a function of pH for both UV filters. The rate coefficients for the reaction of HOCl with 3-methoxyphenol moieties of oxybenzone (OXY) and dioxybenzone (DiOXY) were k(1,OxY) = 306 ± 81 M⁻¹s⁻¹ and k(1,DiOxY) = 154 ± 76 M⁻¹s⁻¹, respectively. The k(int) for the reaction of aqueous chlorine with the 3-methoxyphenolate forms were orders of magnitude greater than the un-ionized species, k(2,OxY) = 1.03(±0.52) × 10⁶ M⁻¹s⁻¹ and k(2_1,DiOxY) = 4.14(±0.68) × 10⁵ M⁻¹s⁻¹. Also, k(int) for the reaction of aqueous chlorine with the DiOXY ortho-substituted phenolate moiety was k(2_2,DiOxY) = 2.17(±0.30) × 10³ M⁻¹s⁻¹. Finally, chloroform formation potential for OXY and DiOXY was assessed over the pH range 6-10. While chloroform formation decreased as pH increased for OXY, chloroform formation increased as pH increased from 6 to 10 for DiOXY. Ultimate molar yields of chloroform per mole of UV filter were pH dependent

  19. Unexpected formation of π-expanded isoquinoline from anthracene possessing four electron-donating groups via the Duff reaction.

    PubMed

    Węcławski, Marek K; Deperasińska, Irena; Leniak, Arkadiusz; Banasiewicz, Marzena; Kozankiewicz, Bolesław; Gryko, Daniel T

    2016-08-01

    New synthetic methods leading towards π-expanded heterocycles are sought after mainly due to their promising opto-electronic properties. Subjecting 1,5,9,10-tetramethoxyanthracene to the modern Duff reaction conditions led to the formation of a compound possessing the 2-azabenzoanthrone (dibenzo[de,h]isoquinolin-7-on) skeleton instead of the expected dialdehyde. This non-typical course of reaction can be rationalized by the double electrophilic aromatic substitution at two neighboring electron-rich positions of anthracene followed by oxidation of the resulting intermediate to form a pyridine ring. Optical studies supported by the quantum chemistry calculations indicated the lack of excited-state intramolecular proton transfer (ESIPT); for energy reasons, only one tautomeric form, with a hydrogen atom bonded to one of the two nearby oxygen atoms, was populated in the electronic ground S0 and in the excited S1 states. Nonradiative depopulation of the S1 state proceeded via internal conversion stimulated by the presence of the low frequency vibrational modes. Our serendipitous discovery represents the most complex case of rearrangement of aromatic compounds under Duff reaction conditions and could help to design analogous processes. At the same time this is the simplest method for the synthesis of derivatives of 2-azabenzoanthrone. PMID:27367169

  20. Introduction to Homogeneous Catalysis: Carbon-Carbon Bond Formation Catalyzed by a Defined Palladium Complex

    NASA Astrophysics Data System (ADS)

    Herrmann, Wolfgang A.; Böhm, Volker P. W.; Reisinger, Claus-Peter

    2000-01-01

    In this laboratory experiment students synthesize a phosphine ligand, P(o-tol)3, and with it the corresponding cyclometallated Pd(II) complex. This complex is an extremely active (pre)catalyst for C-C-bond-forming reactions (e.g. the Heck vinylation or the Grignard cross-coupling reaction). Students test the complex for activation in the catalysis of these two reactions using especially economical bromoaromatic compounds. The catalytic mechanisms of these reactions involve basic reaction types in organometallic chemistry such as ligand exchange, cyclometallation, oxidative addition, transmetallation, olefin insertion, reductive elimination and ß-hydride elimination. This experimental sequence combines synthetic organometallic and synthetic organic chemistry to introduce students to the field of catalysis as it appears in daily scientific research laboratory work.

  1. 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

  2. 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).

  3. Imaging Proton Transfer and Dihalide Formation Pathways in Reactions of F(-) + CH3I.

    PubMed

    Carrascosa, Eduardo; Michaelsen, Tim; Stei, Martin; Bastian, Björn; Meyer, Jennifer; Mikosch, Jochen; Wester, Roland

    2016-07-14

    Ion-molecule reactions of the type X(-) + CH3Y are commonly assumed to produce Y(-) through bimolecular nucleophilic substitution (SN2). Beyond this reaction, additional reaction products have been observed throughout the last decades and have been ascribed to different entrance channel geometries differing from the commonly assumed collinear approach. We have performed a crossed beam velocity map imaging experiment on the F(-) + CH3I reaction at different relative collision energies between 0.4 and 2.9 eV. We find three additional channels competing with nucleophilic substitution at high energies. Experimental branching ratios and angle- and energy differential cross sections are presented for each product channel. The proton transfer product CH2I(-) is the main reaction channel, which competes with nucleophilic substitution up to 2.9 eV relative collision energy. At this level, the second additional channel, the formation of IF(-) via halogen abstraction, becomes more efficient. In addition, we present the first evidence for an [FHI](-) product ion. This [FHI](-) product ion is present only for a narrow range of collision energies, indicating possible dissociation at high energies. All three products show a similar trend with respect to their velocity- and scattering angle distributions, with isotropic scattering and forward scattering of the product ions occurring at low and high energies, respectively. Reactions leading to all three reaction channels present a considerable amount of energy partitioning in product internal excitation. The internally excited fraction shows a collision energy dependence only for CH2I(-). A similar trend is observed for the isoelectronic OH(-) + CH3I system. The comparison of our experimental data at 1.55 eV collision energy with a recent theoretical calculation for the same system shows a slightly higher fraction of internal excitation than predicted, which is, however, compatible within the experimental accuracy. PMID:26799548

  4. Imaging Proton Transfer and Dihalide Formation Pathways in Reactions of F– + CH3I

    PubMed Central

    2016-01-01

    Ion–molecule reactions of the type X– + CH3Y are commonly assumed to produce Y– through bimolecular nucleophilic substitution (SN2). Beyond this reaction, additional reaction products have been observed throughout the last decades and have been ascribed to different entrance channel geometries differing from the commonly assumed collinear approach. We have performed a crossed beam velocity map imaging experiment on the F– + CH3I reaction at different relative collision energies between 0.4 and 2.9 eV. We find three additional channels competing with nucleophilic substitution at high energies. Experimental branching ratios and angle- and energy differential cross sections are presented for each product channel. The proton transfer product CH2I– is the main reaction channel, which competes with nucleophilic substitution up to 2.9 eV relative collision energy. At this level, the second additional channel, the formation of IF– via halogen abstraction, becomes more efficient. In addition, we present the first evidence for an [FHI]− product ion. This [FHI]− product ion is present only for a narrow range of collision energies, indicating possible dissociation at high energies. All three products show a similar trend with respect to their velocity- and scattering angle distributions, with isotropic scattering and forward scattering of the product ions occurring at low and high energies, respectively. Reactions leading to all three reaction channels present a considerable amount of energy partitioning in product internal excitation. The internally excited fraction shows a collision energy dependence only for CH2I–. A similar trend is observed for the isoelectronic OH– + CH3I system. The comparison of our experimental data at 1.55 eV collision energy with a recent theoretical calculation for the same system shows a slightly higher fraction of internal excitation than predicted, which is, however, compatible within the experimental accuracy. PMID:26799548

  5. Mesotidal barrier complex, Sundance Formation, north-central Wyoming

    SciTech Connect

    Uhlir, D.M.; Vondra, C.F.; Akers, A.; Elliott, T.

    1986-08-01

    The sandstones and coquinas of the upper 20 m of the Sundance Formation are a tidal inlet, back-barrier shoal, and sandy tidal-flat sequence deposited at the close of marine Jurassic sedimentation in north-central Wyoming. The lateral migration of these interbarrier tidal inlets along the regressive shoreline of the late Sundance sea caused the coquinas and sandstones of the uppermost Sundance Formation to be deposited as tabular, laterally extensive units. Earlier models, which attach an offshore environment of deposition to this sequence, fail to explain the tabular gross geometry of the unit and its conformable stratigraphic relationship with the overlying nonmarine sediments of the Morrison Formation. Within the sandstone of the uppermost Sundance Formation, tidal bundles, sigmoidal reactivation surfaces, herringbone cross-lamination, and abundant mud drapes present considerable evidence for tidal influence during the deposition of the unit. The neap-spring cyclicity of the tidal bundles implies they were developed in a diurnal tidal setting. A meso-paleotidal range along the Late Jurassic shoreline is estimated, based on calculations of sediment transport rates during the tidal bundle development.

  6. 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. PMID:27664602

  7. 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.

  8. Crystal structures of complexes of NAD+-dependent formate dehydrogenase from methylotrophic bacterium Pseudomonas sp. 101 with formate

    NASA Astrophysics Data System (ADS)

    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.

    2006-07-01

    Formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 catalyzes oxidation of formate to NI2 with the coupled reduction of nicotinamide adenine dinucleotide (NAD+). The three-dimensional structures of the apo form (the free enzyme) and the holo form (the ternary FDH-NAD+-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 Å 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.

  9. 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.

  10. Serpentinization of Ocean Core Complex in the Central Indian Ridge: Reactions and Hydrogen Production

    NASA Astrophysics Data System (ADS)

    Omori, S.; Yoshizaki, M.; Shibuya, T.; Suzuki, K.; Yamamoto, S.; Morishita, T.; Kumagai, H.; Maruyama, S.

    2012-12-01

    The submarine hydrothermal system has been considered as a birthplace of life, and it is suggested that hydrothermal alteration of the ocean-floor rocks could influence metabolic system of the early life. The present submarine hydrothermal systems are possible analogs for the early ecosystem, and the serpentinite-hosted system is a candidate for the earliest one. In this study, we report a petrogenetic analysis of a serpentinite sampled from 25 ° S Ocean Core Complex (OCC) near the Rodriguez triple junction, based on textures and compositions of serpentine and other minerals. Phase diagrams for the serpentinite including redox and hydrogen-forming reactions are constructed to interpret the observations. Rodriguez triple junction 25 ° S OCC is located along the Indian Central Ridge (25.5 ° S, 70 ° E), near the Rodriguez triple junction that is formed by three ridges (the Southeast Indian Ridge, Central Indian Ridge, and Southwest Indian Ridge) and located where three plate boundaries (Africa Plate, Indo-Australian Plate, Antarctic Plate) meet. The studied samples are strongly serpentinized, however some relict minerals are preserved (~2%). The alteration minerals are mainly serpentine and magnetite. Most of the serpentine minerals were identified as chrysotile by laser Raman analyses. The relict minerals are orthopyroxene (opx), olivine, clinopyroxene, and spinel. Serpentine shows two types of texture; the one is bustite and the other is mesh texture. Magnetite is found in the mesh texture, and is not present in the bustite. The relict olivine and orthopyroxene were rarely preserved in the center of mesh texture and/or bustite. Size of spinel is 1-2mm, and color of the spinel is brownish-red. Brucite, which is a common product of the abyssal serpentinization, is not observed by optical, SEM, and FE-EPMA analyses. Serpentine minerals were classified into two groups by their chemical compositions; the one is the low-Mg#(90-94) type, which has comparable Mg# with

  11. 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

  12. 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)

  13. Complex mineral zoning patterns caused by ultra-local equilibrium at reaction interfaces

    NASA Astrophysics Data System (ADS)

    Pearce, Mark; Liu, Weihua; Borg, Stacey; Cleverley, James

    2014-05-01

    Chemical compositions of zoned minerals record a time-series of conditions experienced by the rock. They are a function of the prevailing pressure, temperature and effective bulk chemical composition as well as any post-growth modification processes e.g. volume diffusion and deformation. In fluid-buffered systems, zoned mineral compositions should be expected to reflect directly the evolution of fluid composition. Here we show that during rapid fluid-rock reactions, ultra-local equilibrium can form complex mineral zoning patterns, even when the overall system is highly fluid buffered. We reacted calcite single crystals with arsenate-phosphate solutions with molar ratios of As/(As+P) between 0.011 - 0.145 at 250°C and water-saturated pressure with fluid-rock mass ratios in excess of 2500%. Porous, fine-grained apatite polycrystals with varying arsenic contents replaced the calcite by an interface-coupled dissolution reprecipitation mechanism. During the first few hours of the reaction, complex zoning patterns of arsenic content within the apatite formed. The scale of the arsenic variations corresponds with the scale of corrugations of the reaction interface. The variations in arsenic content of the apatite result from spatially and temporally varying increases in the arsenic content of the reaction interface fluid. Since phosphate diffusion cannot keep pace with the reaction rate arsenic becomes enriched in the reaction interface fluid as phosphate is preferentially used in the reaction. The most arsenic rich parts of the apatite crystal show an 8-fold enrichment in arsenic with respect to the bulk fluid composition but only at an ultra-local scale. Once the calcite is completely consumed, the porous crystal equilibrates with the bulk fluid over a few days because the grain size is much finer and diffusion can keep pace with the equilibration reaction. This study highlights the complexity that can arise from ultra-local fluid composition variations due to rapid

  14. Structural investigation of trifuoromethyl substituted bis(β-diketonato)-dichlorotitanium(IV) complexes displaying a mono-dinuclear equilibrium hydrolysis reaction

    NASA Astrophysics Data System (ADS)

    Kuhn, Annemarie; Conradie, Jeanet

    2015-10-01

    Mononuclear Ti(β-diketonato)2Cl2 complexes with CF3-containing β-diketonato ligands, exhibit a monomer-hydrolysed dinuclear complex equilibrium when dissolved in CDCl3 containing trace amounts of water. This result is in contrast to the more electron rich derivatives with non CF3-containing β-diketonato ligands, for example, Ti(acac)2Cl2, which exsists only as the monomer in CDCl3 solution. The X-ray structure of the μ-oxo bridged hydrolysed dinuclear complex {Ti(CF3COCHCOCH3)2Cl}2(μ-O) reveals that the two mononuclear Ti units forming the dinuclear structure, both adopt a cis-trans-cis configuration with the CF3 groups of the trifluoroacetylacetonate ligands in trans positions. In solution both mononuclear Ti(β-diketonato)2Cl2 and hydrolysed dinuclear {Ti(β-diketonato)2Cl}2(μ-O) complexes exist as equilibrium mixtures of isomers. DFT calculations, used to determine the stability of the isomers, showed that for monomeric bis(β-diketonato)-titanium(IV) complexes, there is agreement with experimental solid state structures, in that the most stable DFT calculated isomer, of a specific complex, formed in the solid state. However for the dinuclear {Ti(CF3COCHCOCH3)2Cl}2(μ-O) complex, DFT calculations revealed that although most of the 10 isomers are experimentally possible due to the small energy difference obtained between the isomers, an isomer of higher energy formed in the solid state, suggesting that the equilibrium reaction between the monomer and hydrolysed dinuclear complex may contribute to the formation of the less stable dinuclear isomer {Ti(CF3COCHCOCH3)2Cl}2(μ-O) (1111).

  15. A cobalt-phosphine complex as mediator in the formation of carbon-carbon bonds

    SciTech Connect

    Orsini, F.; Pelizzoni, F.; Pulici, M.

    1994-01-14

    The complex, [Co(P(CH{sub 3}){sub 3}){sub 4}], is found to mediate the Reformatsky-type reaction of halogenated esters, lactones, or amides with carbonyl compounds (ketones, aldehydes). The products of these reactions are alcohols. 15 refs., 1 tab.

  16. 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.

  17. Reactions of the OOH radical with guanine: Mechanisms of formation of 8-oxoguanine and other products

    NASA Astrophysics Data System (ADS)

    Kumar, Nagendra; Shukla, P. K.; Mishra, P. C.

    2010-09-01

    The mutagenic product 8-oxoguanine (8-oxoGua) is formed due to intermediacy of peroxyl (OOR) radicals in lipid peroxidation and protein oxidation-induced DNA damage. The mechanisms of these reactions are not yet understood properly. Therefore, in the present study, the mechanisms of formation of 8-oxoGua and other related products due to the reaction of the guanine base of DNA with the hydroperoxyl radical (OOH) were investigated theoretically employing the B3LYP and BHandHLYP hybrid functionals of density functional theory and the polarizable continuum model for solvation. It is found that the reaction of the OOH radical with guanine can occur following seven different mechanisms leading to the formation of various products including 8-oxoGua, its radicals, 5-hydroxy-8-oxoguanine and CO 2. The mechanism that yields 8-oxoGua as an intermediate and 5-hydroxy-8-oxoGua as the final product was found to be energetically most favorable.

  18. 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…

  19. 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

    2014-10-01

    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.

  20. 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.

  1. The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change† †Electronic supplementary information (ESI) available: Sample preparation, signal enhancements and raw data. CCDC 1026865. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt03088e Click here for additional data file. Click here for additional data file.

    PubMed Central

    Holmes, Arthur J.; Rayner, Peter J.; Cowley, Michael J.; Green, Gary G. R.; Whitwood, Adrian C.

    2015-01-01

    The short lived pincer complex [(C5H3N(CH2P(tBu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange. This catalyst formulation enables the efficient transfer of polarization from parahydrogen to be placed into just a single molecule of the hyperpolarisation target, pyridine. When the catalysts 1H nuclei are replaced by 2H, increased levels of substrate hyperpolarization result and when the reverse situation is examined the catalyst itself is clearly visible through hyperpolarised signals. The ligand exchange pathways of [(C5H3N(CH2P(tBu)2)2)Ir(H)2(py)]BF4 that are associated with this process are shown to involve the formation of 16-electron [(C5H3N(CH2P(tBu)2)2)Ir(H)2]BF4 and the 18-electron H2 addition product [(C5H3N(CH2P(tBu)2)2)Ir(H)2(H2)]BF4. PMID:25410259

  2. 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.

  3. The formation of glycine and other complex organic molecules in exploding ice mantles.

    PubMed

    Rawlings, J M C; Williams, D A; Viti, S; Cecchi-Pestellini, C; Duley, W W

    2014-01-01

    Complex Organic Molecules (COMs), such as propylene (CH3CHCH2) and the isomers of C2H4O2 are detected in cold molecular clouds (such as TMC-1) with high fractional abundances (Marcelino et al., Astrophys. J., 2007, 665, L127). The formation mechanism for these species is the subject of intense speculation, as is the possibility of the formation of simple amino acids such as glycine (NH2CH2COOH). At typical dark cloud densities, normal interstellar gas-phase chemistries are inefficient, whilst surface chemistry is at best ill defined and does not easily reproduce the abundance ratios observed in the gas phase. Whatever mechanism(s) is/are operating, it/they must be both efficient at converting a significant fraction of the available carbon budget into COMs, and capable of efficiently returning the COMs to the gas phase. In our previous studies we proposed a complementary, alternative mechanism, in which medium- and large-sized molecules are formed by three-body gas kinetic reactions in the warm high density gas phase. This environment exists, for a very short period of time, after the total sublimation of grain ice mantles in transient co-desorption events. In order to drive the process, rapid and efficient mantle sublimation is required and we have proposed that ice mantle 'explosions' can be driven by the catastrophic recombination of trapped hydrogen atoms, and other radicals, in the ice. Repeated cycles of freeze-out and explosion can thus lead to a cumulative molecular enrichment of the interstellar medium. Using existing studies we based our chemical network on simple radical addition, subject to enthalpy and valency restrictions. In this work we have extended the chemistry to include the formation pathways of glycine and other large molecular species that are detected in molecular clouds. We find that the mechanism is capable of explaining the observed molecular abundances and complexity in these sources. We find that the proposed mechanism is easily capable

  4. Hydrogen release from dialkylamine-boranes promoted by Mg and Ca complexes: a DFT analysis of the reaction mechanism.

    PubMed

    Butera, Valeria; Russo, Nino; Sicilia, Emilia

    2014-05-12

    Mg and Ca β-diketiminato silylamides [HC{(Me)CN(2,6-iPr2C6H3)}2M(THF)n{N(SiMe3)2}] (M = Mg, n = 0; M = Ca, n = 1) were studied as precatalysts for the dehydrogenation/dehydrocoupling of secondary amine-boranes R2HNBH3 . By reaction with equimolar quantities of amine-boranes, the corresponding amidoborane derivatives are formed, which further react to yield dehydrogenation products such as the cyclic dimer [BH2-NMe2]2. DFT was used here to explore the mechanistic alternatives proposed on the basis of the experimental findings for both Mg and Ca amidoboranes. The influence of the steric demand of amine-boranes on the course of the reaction was examined by performing calculations on the dehydrogenation of dimethylamine-borane (DMAB), pyrrolidine-borane (PB), and diisopropylamine-borane. In spite of the analogies in the catalytic activity of Mg- and Ca-based complexes in the dehydrocoupling of amine-boranes, our theoretical analysis confirmed the experimentally observed lower reactivity of Ca complexes. Differences in catalytic activity of Mg- and Ca-based complexes were examined and rationalized. As a consequence of the increase in ionic radius on going from Mg(2+) to Ca(2+), the dehydrogenation mechanism changes and formation of a key metal hydride intermediate becomes inaccessible. Dimerization is likely to occur off-metal in solution for DMAB and PB, whereas steric hindrance of iPr2NHBH3 hampers formation of the cyclic dimer. The reported results are of particular interest because, although amine-borane dehydrogenation is now well established, mechanistic insight is still lacking for many systems. PMID:24700384

  5. Secondary organic aerosol formation by self-reactions of methylglyoxal and glyoxal in evaporating droplets.

    PubMed

    De Haan, David O; Corrigan, Ashley L; Tolbert, Margaret A; Jimenez, Jose L; Wood, Stephanie E; Turley, Jacob J

    2009-11-01

    Glyoxal and methylglyoxal are scavenged by clouds, where a fraction of these compounds are oxidized during the lifetime of the droplet. As a cloud droplet evaporates, the remaining glyoxal and methylglyoxal must either form low-volatility compounds such as oligomers and remain in the aerosol phase, or transfer back to the gas phase. A series of experiments on evaporating aqueous aerosol droplets indicates that over the atmospherically relevant concentration range for clouds and fog (4-1000 microM), 33 +/- 11% of glyoxal and 19 +/- 13% of methylglyoxal remains in the aerosol phase while the remainder evaporates. Measurements of aerosol density and time-dependent AMS signal changes are consistent with the formation of oligomers by each compound during the drying process. Unlike glyoxal, which forms acetal oligomers, exact mass AMS data indicates that the majority of methylglyoxal oligomers are formed by aldol condensation reactions, likely catalyzed by pyruvic acid, formed from methylglyoxal disproportionation. Our measurements of evaporation fractions can be used to estimate the global aerosol formation potential of glyoxal and methylglyoxal via self-reactions at 1 and 1.6 Tg C yr(-1), respectively. This is a factor of 4 less than the SOA formed by these compounds if their uptake is assumed to be irreversible. However, these estimates are likely lower limits for their total aerosol formation potential because oxidants and amines will also react with glyoxal and methylglyoxal to form additional low-volatility products.

  6. Yttrium (amidate) complexes for catalytic C-N bond formation. Rapid, room temperature amidation of aldehydes.

    PubMed

    Thomson, Jaclyn A; Schafer, Laurel L

    2012-07-14

    Yttrium (amidate) precatalysts are highly active for the mild amidation of aldehydes with amines. Reactions occur at room temperature within 5 min in up to 98% isolated yield. These rare-earth systems are effective for this transformation in the absence of supplementary heat, light, base, or oxidants. The reaction proceeds with functionalized amines and/or aldehydes. A comparison of various amidate precatalysts in combination with reaction monitoring suggests that the targeted amide products formed during the reaction promote the formation of alternative catalytically active amidate species in situ.

  7. Processing of complex sintered reaction bonded silicon nitride parts by microwave heating

    SciTech Connect

    Kiggans, J.O.; Tiegs, T.N.; Kimrey, H.D. ); Holcombe, C.E. )

    1993-01-01

    Several studies have been conducted over the last several years assessing the use of microwave heating for processing reaction-bonded silicon nitride (RBSN) and sintered reaction-bonded silicon nitride (SRBSN). Although SRBSN test specimens up to 500g have been processed by using microwave heating, samples have been limited to simple shapes such as tiles. In this study, microwave packaging techniques were developed to process complex SRBSN parts and multiple samples within a single cycle. Physical and mechanical properties of test samples were measured. Comparison studies were performed using conventional furnace processing to establish baseline values and expected statistical variation.

  8. Processing of complex sintered reaction bonded silicon nitride parts by microwave heating

    SciTech Connect

    Kiggans, J.O.; Tiegs, T.N.; Kimrey, H.D.; Holcombe, C.E.

    1993-06-01

    Several studies have been conducted over the last several years assessing the use of microwave heating for processing reaction-bonded silicon nitride (RBSN) and sintered reaction-bonded silicon nitride (SRBSN). Although SRBSN test specimens up to 500g have been processed by using microwave heating, samples have been limited to simple shapes such as tiles. In this study, microwave packaging techniques were developed to process complex SRBSN parts and multiple samples within a single cycle. Physical and mechanical properties of test samples were measured. Comparison studies were performed using conventional furnace processing to establish baseline values and expected statistical variation.

  9. 'Super Silyl' Group for Diastereoselective Sequential Reactions: Access to Complex Chiral Architecture in One Pot

    SciTech Connect

    Boxer, Matthew B.; Yamamoto, Hisashi

    2008-04-02

    We have shown that the tris(trimethylsilyl)silyl (TTMSS) silyl enol ether of acetaldehyde undergoes aldehyde cross-aldol reactions with high selectivity and the extremely low catalyst loading (0.05 mol % of HNTf{sub 2}) allows for one-pot sequential reactions where acidic or basic nucleophiles can be subsequently added. Various ketone-derived silyl enol ethers, Grignard reagents, and dienes succeeded, generating relatively complex molecular architectures in a single step. This represents the first case where, in a single pot, highly acidic conditions followed by very basic conditions were tolerated to give products with high diastereoselectivities and good yields.

  10. Investigation of the influence of different moisture levels on acrylamide formation/elimination reactions using multiresponse analysis.

    PubMed

    De Vleeschouwer, Kristel; Van der Plancken, Iesel; Van Loey, Ann; Hendrickx, Marc E

    2008-08-13

    The influence of water activity on the formation and elimination reactions of acrylamide was examined by means of multiresponse modeling on two different levels of complexity: basic equimolar asparagine-glucose systems and equimolar potato-based asparagine-glucose systems. To this end, model systems were first equilibrated to initial water activities in the range of 0.88-0.99 (corresponding roughly to the moisture gradient observed in French fries) and then heated at temperatures between 120 and 200 degrees C during different reaction times. For each sample, the concentration of acrylamide, glucose, asparagine, and aspartic acid was measured, as well as the extent of browning. A mechanistic model was proposed to model the five measured responses simultaneously. For both types of model systems, the model prediction was quite adequate, with the exception of the extent of browning, especially in the case of the potato-based model system. Moreover, the corresponding estimated kinetic parameters for acrylamide formation and elimination did not change significantly (based on a 95% confidence level) within the range of water activities tested, nor between the systems in the absence or presence of the potato matrix. The only remarkable difference was observed for the activation energy of acrylamide elimination, which was lower in the presence of the potato matrix, although not always significant. In general, these results confirm the generic nature of the model proposed and show that the influence of different moisture levels on acrylamide formation and elimination is minimal and that the addition of a potato matrix has little or no influence on the kinetic model and corresponding kinetic parameters. PMID:18597471

  11. 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.

  12. Structural Basis of Clostridium perfringens Toxin Complex Formation

    SciTech Connect

    Adams,J.; Gregg, K.; Bayer, E.; Boraston, A.; Smith, S.

    2008-01-01

    The virulent properties of the common human and livestock pathogen Clostridium perfringens are attributable to a formidable battery of toxins. Among these are a number of large and highly modular carbohydrate-active enzymes, including the {mu}-toxin and sialidases, whose catalytic properties are consistent with degradation of the mucosal layer of the human gut, glycosaminoglycans, and other cellular glycans found throughout the body. The conservation of noncatalytic ancillary modules among these enzymes suggests they make significant contributions to the overall functionality of the toxins. Here, we describe the structural basis of an ultra-tight interaction (Ka = 1.44 x 1011 M-1) between the X82 and dockerin modules, which are found throughout numerous C. perfringens carbohydrate-active enzymes. Extensive hydrogen-bonding and van der Waals contacts between the X82 and dockerin modules give rise to the observed high affinity. The {mu}-toxin dockerin module in this complex is positioned {approx}180 relative to the orientation of the dockerin modules on the cohesin module surface within cellulolytic complexes. These observations represent a unique property of these clostridial toxins whereby they can associate into large, noncovalent multitoxin complexes that allow potentiation of the activities of the individual toxins by combining complementary toxin specificities.

  13. Urea-acetylene dicarboxylic acid reaction: A likely pathway for prebiotic uracil formation

    NASA Astrophysics Data System (ADS)

    Subbaraman, A. S.; Kazi, Z. A.; Choughuley, A. S. U.; Chadha, M. S.

    1980-12-01

    A number of routes have been suggested for the prebiotic synthesis of uracil involving the reaction of urea with malic acid, propiolic acid, cyanoacetylene and others. Cyanoacetylene has been detected in the interstellar medium as well as simulated prebiotic experiments. It is therefore plausible that dicyanoacetylene and its hydrolytic product acetylene dicarboxylic acid, (ADCA) may have played a role in chemical evolution. This aspect has been examined in the present work for the synthesis of uracil from ADCA and urea reaction. It was found that when ADCA reacted with urea, uracil was formed only in the presence of phosphoric acid and phosphates. Ammonium phosphates gave higher yields of uracil than other phosphates. In the absence of phosphoric acid or phosphates no uracil formation took place. This type of synthesis could have taken place in prebiotic oceans which contained ammonium phosphates and other salts.

  14. Chemo-Marangoni convection driven by an interfacial reaction: Pattern formation and kinetics

    NASA Astrophysics Data System (ADS)

    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.

  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. 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.

  17. 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

  18. Complex networks: Patterns of complexity

    NASA Astrophysics Data System (ADS)

    Pastor-Satorras, Romualdo; Vespignani, Alessandro

    2010-07-01

    The Turing mechanism provides a paradigm for the spontaneous generation of patterns in reaction-diffusion systems. A framework that describes Turing-pattern formation in the context of complex networks should provide a new basis for studying the phenomenon.

  19. Characterization of self-propagating formation reactions in Ni/Zr multilayered foils using reaction heats, velocities, and temperature-time profiles

    DOE PAGESBeta

    Barron, S. C.; Knepper, R.; Walker, N.; Weihs, T. P.

    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

  20. 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

  1. 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.

  2. 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. PMID:23957215

  3. 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.

  4. 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.

  5. Role of specific residues in coenzyme binding, charge-transfer complex formation, and catalysis in Anabaena ferredoxin NADP+-reductase.

    PubMed

    Peregrina, José Ramón; Sánchez-Azqueta, Ana; Herguedas, Beatriz; Martínez-Júlvez, Marta; Medina, Milagros

    2010-09-01

    Two transient charge-transfer complexes (CTC) form prior and upon hydride transfer (HT) in the reversible reaction of the FAD-dependent ferredoxin-NADP+ reductase (FNR) with NADP+/H, FNR(ox)-NADPH (CTC-1), and FNR(rd)-NADP+ (CTC-2). Spectral properties of both CTCs, as well as the corresponding interconversion HT rates, are here reported for several Anabaena FNR site-directed mutants. The need for an adequate initial interaction between the 2'P-AMP portion of NADP+/H and FNR that provides subsequent conformational changes leading to CTC formation is further confirmed. Stronger interactions between the isoalloxazine and nicotinamide rings might relate with faster HT processes, but exceptions are found upon distortion of the active centre. Thus, within the analyzed FNR variants, there is no strict correlation between the stability of the transient CTCs formation and the rate of the subsequent HT. Kinetic isotope effects suggest that, while in the WT, vibrational enhanced modulation of the active site contributes to the tunnel probability of HT; complexes of some of the active site mutants with the coenzyme hardly allow the relative movement of isoalloxazine and nicotinamide rings along the HT reaction. The architecture of the WT FNR active site precisely contributes to reduce the stacking probability between the isoalloxazine and nicotinamide rings in the catalytically competent complex, modulating the angle and distance between the N5 of the FAD isoalloxazine and the C4 of the coenzyme nicotinamide to values that ensure efficient HT processes.

  6. Reaction between CH2 and HCCN: a theoretical approach to acrylonitrile formation in the interstellar medium.

    PubMed

    Shivani; Misra, Alka; Tandon, Poonam

    2014-04-01

    Acrylonitrile (CH2CHCN) was first detected in dense molecular cloud SgrB2. The synthesis of this interstellar molecule is reported to be quite difficult. Therefore, in the present work an attempt has been made to explore the possibility of formation of acrylonitrile from some simple molecules and radicals detected in interstellar space by radical-radical interaction scheme, both in the gas phase and in the icy grains. All calculations are performed using quantum chemical methods with density functional theory (DFT) at the B3LYP/6-311G (d,p) level and Møller-Plesset perturbation theory at the MP2/6-311G (d,p) level. In the discussed chemical pathway, the reaction is found to be totally exothermic and barrier less giving rise to a high probability of acrylonitrile formation in Interstellar space. PMID:25416678

  7. 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.

  8. Ganymede and Callisto - Complex crater formation and planetary crusts

    NASA Technical Reports Server (NTRS)

    Schenk, Paul M.

    1991-01-01

    Results are presented on measurements of crater depths and other morphological parameters (such as central peak and terrace frequency) of fresh craters on Ganymede and Callisto, two geophysically very similar but geologically divergent large icy satellites of Jupiter. These data were used to investigate the crater mechanics on icy satellites and the intersatellite crater scaling and crustal properties. The morphological transition diameters of and complex crater depths on Ganymede and Callisto were found to be similar, indicating that the crusts of both satellites are dominated by water ice with only a minor rocky component.

  9. 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.

  10. 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

  11. 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

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

    SciTech Connect

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

    1986-11-12

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

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

    PubMed

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

    2014-04-15

    Mononuclear nonheme iron enzymes generate high-valent iron(IV)-oxo intermediates that effect metabolically important oxidative transformations in the catalytic cycle of dioxygen activation. In 2003, researchers first spectroscopically characterized a mononuclear nonheme iron(IV)-oxo intermediate in the reaction of taurine: α-ketogultarate dioxygenase (TauD). This nonheme iron enzyme with an iron active center was coordinated to a 2-His-1- carboxylate facial triad motif. In the same year, researchers obtained the first crystal structure of a mononuclear nonheme iron(IV)-oxo complex bearing a macrocyclic supporting ligand, [(TMC)Fe(IV)(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecene), in studies that mimicked the biological enzymes. With these breakthrough results, many other studies have examined mononuclear nonheme iron(IV)-oxo intermediates trapped in enzymatic reactions or synthesized in biomimetic reactions. Over the past decade, researchers in the fields of biological, bioinorganic, and oxidation chemistry have extensively investigated the structure, spectroscopy, and reactivity of nonheme iron(IV)-oxo species, leading to a wealth of information from these enzymatic and biomimetic studies. This Account summarizes the reactivity and mechanisms of synthetic mononuclear nonheme iron(IV)-oxo complexes in oxidation reactions and examines factors that modulate their reactivities and change their reaction mechanisms. We focus on several reactions including the oxidation of organic and inorganic compounds, electron transfer, and oxygen atom exchange with water by synthetic mononuclear nonheme iron(IV)-oxo complexes. In addition, we recently observed that the C-H bond activation by nonheme iron(IV)-oxo and other nonheme metal(IV)-oxo complexes does not follow the H-atom abstraction/oxygen-rebound mechanism, which has been well-established in heme systems. The structural and electronic effects of supporting ligands on the oxidizing power of iron

  14. 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.

  15. 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.

  16. 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.

  17. Heterogeneous reactions of glyoxal on mineral particles: A new avenue for oligomers and organosulfate formation

    NASA Astrophysics Data System (ADS)

    Shen, Xiaoli; Wu, Huihui; Zhao, Yue; Huang, Dao; Huang, Liubin; Chen, Zhongming

    2016-04-01

    Glyoxal (GL) plays a crucial role in the formation of secondary organic aerosols (SOA), because it is highly water soluble and capable of oligomerization. This is the first study to describe irreversible heterogeneous reactions of GL on clean and acidic gas-aged SiO2, α-Al2O3, and CaCO3 particles, as models of real mineral particles, at various relative humidity and without irradiation and gas phase oxidants. A series of products, including oligomers, organosulfates, and organic acids, which contribute to SOA formation, were produced. GL uptake on SO2-aged α-Al2O3 enabled the oxidation of surface S(IV) to S(VI). The presence of adsorbed water on particles favored GL uptake and the formation of oligomers and organosulfate, but it suppressed organic acid formation. In addition, the aging process enhanced the positive effect of adsorbed water on GL uptake. These findings will further our understanding of the GL sink and SOA sources in the atmosphere.

  18. The complex interplay between semantics and grammar in impression formation.

    PubMed

    Shreves, Wyley B; Hart, William; Adams, John M; Guadagno, Rosanna E; Eno, Cassie A

    2014-09-01

    We sought to bridge findings showing that (a) describing a person's behavior with the perfective verb aspect (did), compared to the imperfective aspect (was doing), increases processing of semantic knowledge unrelated to the target's action such as stereotypes and (b) an increased recognition of stereotypical thoughts often promotes a judgment correction for the stereotypes. We hypothesized an interplay between grammar (verb conjugation) and semantic information (gender) in impression-formation. Participants read a resume, attributed to a male or female, for a traditionally masculine job. When the resume was written in the imperfective, people rated a male (vs. female) more positively. When the resume was in the perfective, this pattern reversed. Only these latter effects of gender were influenced by cognitive load. Further, people more quickly indicated the applicant's gender in the perfective condition, suggesting an enhanced focus on gender during processing.

  19. 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

  20. Simplicity in complexity: the photosynthetic reaction center performs as a simple 0.2 V battery.

    PubMed

    van Rotterdam, Bart J; Crielaard, Wim; van Stokkum, Ivo H M; Hellingwerf, Klaas J; Westerhoff, Hans V

    2002-01-01

    The photosynthetic reaction center is one of the most complicated molecular complexes. Transducing photon energy to a transmembrane electrochemical potential difference for protons, it is the direct or indirect energy source for virtually all life. We show here that it operates in a simple, battery-like manner, with a maximum potential of 0.20 V. Intriguingly this is only one fifth of the energy of the absorbed photon.

  1. Halogenated catechols from cycloaddition reactions of η-(2-ethoxyvinylketene)iron(0) complexes with 1-haloalkynes.

    PubMed

    Truong, Jimmy; Caze, Vioela; Akhani, Ravish K; Joshi, Gayatribahen K; Kakalis, Lazaros; Matsunaga, Nikita; Schnatter, Wayne F K

    2010-02-10

    1-chloroalkynes and 1-bromohexyne undergo cycloaddition reactions with ethoxyvinylketeneiron(0) complexes to form chloro and bromocatechols. With most substituents, the halogen is incorporated ortho to the phenolic hydroxyl group regioselectively. With chloroethyne, chlorohexyne, and methyl chloropropiolate, the reverse regioselection is observed. Ab initio calculations reveal that the products are, in most cases, nearly isoenergetic, which indicates that the intermediate ketene-alkyne adduct geometry must be important in determining the product distribution.

  2. Nitrene transfer reactions catalysed by copper(I) complexes in ionic liquid using chloramine-T.

    PubMed

    Cano, Israel; Nicasio, M Carmen; Pérez, Pedro J

    2009-01-28

    The complex [Tpm(*,Br)Cu(NCMe)]BF4 (Tpm(*,Br) = HC(3,5-Me2-4-Br-pyrazolyl)3) catalyses the aziridination of alkenes and the amidation of cyclic ethers with chloramine-T as the nitrene source and the ionic liquid [bmim]PF6 as the reaction medium (bmim = 1-n-butyl-3-methylimidazolium). High conversions have been obtained over several cycles of catalyst recovery and reuse.

  3. EXPERIMENTAL STUDY OF CO{sub 2} FORMATION BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES

    SciTech Connect

    Oba, Yasuhiro; Watanabe, Naoki; Kouchi, Akira; Hama, Tetsuya; Pirronello, Valerio

    2010-04-01

    Surface reactions between carbon monoxide and non-energetic hydroxyl radicals were carried out at 10 K and 20 K in order to investigate possible reaction pathways to yield carbon dioxide in dense molecular clouds. Hydroxyl radicals, produced by dissociating water molecules in microwave-induced plasma, were cooled down to 100 K prior to the introduction of CO. The abundances of species were monitored in situ using a Fourier transform infrared spectrometer. Formation of CO{sub 2} was clearly observed, even at 10 K, suggesting that reactions of CO with OH proceed with little or no activation barrier. The present results indicate that CO{sub 2} formation, due to reactions between CO and OH, occurs in tandem with H{sub 2}O formation, and this may lead to the formation of CO{sub 2} ice in polar environments, as typically observed in molecular clouds.

  4. 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...

  5. 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.

  6. 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.

  7. 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. PMID:27458109

  8. Heterogeneous photocatalytic effect of zinc oxide on photochemical smog formation reaction of C 4H 8-NO 2-air

    NASA Astrophysics Data System (ADS)

    Takeuchi, Koji; Yazawa, Takenori; Ibusuki, Takashi

    As a model of heterogeneous photochemical smog formation reaction, butene-NO 2-air systems in the presence of zinc oxide were experimentally studied using a flowing reaction system. Zinc oxide revealed a remarkable photocatalytic action which involved the production of hitherto unreported species such as cyano-compounds (HCN and CH 3CN) as well as a striking change in the distribution of the reaction products (aldehydes, ketones, epoxides, alkyl nitrates, HNO 3, CO, CO 2, etc.). It is confirmed that ZnO little affected the initial process of gas-phase photochemical reactions but interacted photocatalytically with the gas-phase reaction products.

  9. 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.

  10. 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

    2008-05-01

    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.

  11. Removal of boron from wastewater by the hydroxyapatite formation reaction using acceleration effect of ammonia.

    PubMed

    Yoshikawa, Eishi; Sasaki, Atsushi; Endo, Masatoshi

    2012-10-30

    The mechanism was discussed for the removal of boron by the hydroxyapatite (HAp) formation reaction using Ca(OH)(2) and (NH(4))(2)HPO(4) in room temperature. Time required to remove boron was 20 min by adding Ca(OH)(2) and (NH(4))(2)HPO(4) for the remaining boron to below 1mg/L. The removal rate of boron was controlled by the HAp precipitate formation and the presence of ammonia. From the XRD patterns and SEM images, HAp could be confirmed in the precipitate product. The reaction between borate ions and calcium hydroxide was accelerated by dehydration with ammonia; the borate-calcium hydroxide compound coprecipitated with resulting HAp. Although the removal of boron decreased in the presence of sulfate, phosphate, and aluminum, these effects could be prevented by adding excess Ca(OH)(2). Interference of fluoride ions was eliminated by adding Al(3+). Sodium alpha-olefin sulfonate was the most effective coagulant for HAp precipitation. The proposed boron removal method has several advantages about treating time and ability of boron removal. The method was successfully applied to the real hot spring wastewater.

  12. Reaction of Thin Ni Films with Ge: Phase Formation and Texture

    SciTech Connect

    Gaudet,S.; Detavernier, C.; Lavoie, C.; Desjardins, P.

    2006-01-01

    The solid-state reaction between a 30-nm-thick Ni film and Ge substrates was investigated using in situ x-ray diffraction, diffuse light scattering, and four-point probe electrical measurements. Our results reveal that Ni{sub 5}Ge{sub 3} and NiGe appear consecutively on Ge(111) while they grow simultaneously on amorphous Ge ({alpha}-Ge) and Ge(001). Furthermore, phase formation temperatures depend strongly on the nature of the substrate being the lowest on {alpha}-Ge and the highest on Ge(111). X-ray pole figure measurements of the NiGe phase obtained from the reaction with an amorphous substrate indicate a completely random texture while several epitaxial and axiotaxial texture components are observed on both Ge(001) and Ge(111). The texturing for the NiGe film on Ge(111), which showed a sequential phase formation, is an order of magnitude more pronounced than for the film on Ge(001) which showed a simultaneous growth.

  13. Removal of boron from wastewater by the hydroxyapatite formation reaction using acceleration effect of ammonia.

    PubMed

    Yoshikawa, Eishi; Sasaki, Atsushi; Endo, Masatoshi

    2012-10-30

    The mechanism was discussed for the removal of boron by the hydroxyapatite (HAp) formation reaction using Ca(OH)(2) and (NH(4))(2)HPO(4) in room temperature. Time required to remove boron was 20 min by adding Ca(OH)(2) and (NH(4))(2)HPO(4) for the remaining boron to below 1mg/L. The removal rate of boron was controlled by the HAp precipitate formation and the presence of ammonia. From the XRD patterns and SEM images, HAp could be confirmed in the precipitate product. The reaction between borate ions and calcium hydroxide was accelerated by dehydration with ammonia; the borate-calcium hydroxide compound coprecipitated with resulting HAp. Although the removal of boron decreased in the presence of sulfate, phosphate, and aluminum, these effects could be prevented by adding excess Ca(OH)(2). Interference of fluoride ions was eliminated by adding Al(3+). Sodium alpha-olefin sulfonate was the most effective coagulant for HAp precipitation. The proposed boron removal method has several advantages about treating time and ability of boron removal. The method was successfully applied to the real hot spring wastewater. PMID:22981286

  14. Formation, Migration, and Reactivity of Au CO Complexes on Gold Surfaces

    DOE PAGESBeta

    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 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

  15. Formation, Migration, and Reactivity of Au-CO Complexes on Gold Surfaces.

    PubMed

    Wang, Jun; McEntee, Monica; Tang, Wenjie; Neurock, Matthew; Baddorf, Arthur P; Maksymovych, Petro; Yates, John T

    2016-02-10

    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(δ+)) on Au. Our 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. PMID:26754257

  16. Theoretical influence of third molecule on reaction channels of weakly bound complex CO2? HF systems

    NASA Astrophysics Data System (ADS)

    Chen, Shyh-Jong; Chen, Cheng; Hong, Yaw-Shun

    In this investigation, reaction channels of weakly bound complexes CO2?HF, CO2?HF?NH3, CO2?HF?H2O and CO2?HF?CH3OH systems were established at the B3LYP/6-311++G(3df,2pd) level, using the Gaussian 98 program. The conformers of syn-fluoroformic acid or syn-fluoroformic acid plus a third molecule (NH3, H2O, or CH3OH) were found to be more stable than the conformers of the related anti-fluoroformic acid or anti-fluoroformic acid plus a third molecule (NH3, H2O, or CH3OH). However, the weakly bound complexes were found to be more stable than either the related syn- and anti-type fluoroformic acid or the acid plus third molecule (NH3, H2O, or CH3OH) conformers. They decomposed into CO2 + HF, CO2 + NH4F, CO2 + H3OF or CO2 + (CH3)OH2F combined molecular systems. The weakly bound complexes have four reaction channels, each of which includes weakly bound complexes and related systems. Moreover, each reaction channel includes two transition state structures. The transition state between the weakly bound complex and anti-fluoroformic acid type structure (T13) is significantly larger than that of internal rotation (T23) between the syn- and anti-FCO2H (or FCO2H?NH3, FCO2H?H2O, or FCO2H?CH3OH) structures. However, adding the third molecule NH3, H2O, or CH3OH can significantly reduce the activation energy of T13. The catalytic strengths of the third molecules are predicted to follow the order H2O < NH3 < CH3OH.

  17. Metal-mediated reaction modeled on nature: the activation of isothiocyanates initiated by zinc thiolate complexes.

    PubMed

    Eger, Wilhelm A; Presselt, Martin; Jahn, Burkhard O; Schmitt, Michael; Popp, Jürgen; Anders, Ernst

    2011-04-18

    On the basis of detailed theoretical studies of the mode of action of carbonic anhydrase (CA) and models resembling only its reactive core, a complete computational pathway analysis of the reaction between several isothiocyanates and methyl mercaptan activated by a thiolate-bearing model complex [Zn(NH(3))(3)SMe](+) was performed at a high level of density functional theory (DFT). Furthermore, model reactions have been studied in the experiment using relatively stable zinc complexes and have been investigated by gas chromatography/mass spectrometry and Raman spectroscopy. The model complexes used in the experiment are based upon the well-known azamacrocyclic ligand family ([12]aneN(4), [14]aneN(4), i-[14]aneN(4), and [15]aneN(4)) and are commonly formulated as ([Zn([X]aneN(4))(SBn)]ClO(4). As predicted by our DFT calculations, all of these complexes are capable of insertion into the heterocumulene system. Raman spectroscopic investigations indicate that aryl-substituted isothiocyanates predominantly add to the C═N bond and that the size of the ring-shaped ligands of the zinc complex also has a very significant influence on the selectivity and on the reactivity as well. Unfortunately, the activated isothiocyanate is not able to add to the thiolate-corresponding mercaptan to invoke a CA analogous catalytic cycle. However, more reactive compounds such as methyl iodide can be incorporated. This work gives new insight into the mode of action and reaction path variants derived from the CA principles. Further, aspects of the reliability of DFT calculations concerning the prediction of the selectivity and reactivity are discussed. In addition, the presented synthetic pathways can offer a completely new access to a variety of dithiocarbamates. PMID:21405064

  18. 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.

  19. 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

  20. Tandem buildup of complexity of aromatic molecules through multiple successive electrophile generation in one pot, controlled by varying the reaction temperature.

    PubMed

    Sumita, Akinari; Otani, Yuko; Ohwada, Tomohiko

    2016-02-01

    While some sequential electrophilic aromatic substitution reactions, known as tandem/domino/cascade reactions, have been reported for the construction of aromatic single skeletons, one of the most interesting and challenging possibilities remains the one-pot build-up of a complex aromatic molecule from multiple starting components, i.e., ultimately multi-component electrophilic aromatic substitution reactions. In this work, we show how tuning of the leaving group ability of phenolate derivatives from carbamates and esters provides a way to successively generate multiple unmasked electrophiles in a controlled manner in one pot, simply by varying the temperature. Here, we demonstrate the autonomous formation of up to three bonds in one pot and formation of two bonds arising from a three-component electrophilic aromatic substitution reaction. This result provides a proof-of-concept of our strategy applicable for the self-directed construction of complex aromatic structures from multiple simple molecules, which can be a potential avenue to realize multi-component electrophilic aromatic substitution reactions.

  1. 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

  2. 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.

  3. Impacts of diffusive transport on carbonate mineral formation from magnesium silicate-CO2-water reactions.

    PubMed

    Giammar, Daniel E; Wang, Fei; Guo, Bin; Surface, J Andrew; Peters, Catherine A; Conradi, Mark S; Hayes, Sophia E

    2014-12-16

    Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, (13)C NMR spectroscopy tracked the inorganic carbon transport and speciation in situ. The data were compared with the output of reactive transport simulations that accounted for diffusive transport processes, aqueous speciation, and the forsterite dissolution rate. All three approaches found that the onset of magnesium carbonate precipitation was spatially localized about 1 cm from the opening of the forsterite bed. Magnesite was the dominant reaction product. Geochemical gradients that developed in the diffusion-limited zones led to locally supersaturated conditions at specific locations even while the volume-averaged properties of the system remained undersaturated.

  4. 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.

  5. 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

  6. Prompt HO2 formation following the reaction of OH with aromatic compounds under atmospheric conditions.

    PubMed

    Nehr, Sascha; Bohn, Birger; Wahner, Andreas

    2012-06-21

    The secondary formation of HO(2) radicals following OH + aromatic hydrocarbon reactions in synthetic air under normal pressure and temperature was investigated in the absence of NO after pulsed production of OH radicals. OH and HO(x) (=OH + HO(2)) decay curves were recorded using laser-induced fluorescence after gas-expansion. The prompt HO(2) yields (HO(2) formed without preceding NO reactions) were determined by comparison to results obtained with CO as a reference compound. This approach was recently introduced and applied to the OH + benzene reaction and was extended here for a number of monocyclic aromatic hydrocarbons. The measured HO(2) formation yields are as follows: toluene, 0.42 ± 0.11; ethylbenzene, 0.53 ± 0.10; o-xylene, 0.41 ± 0.08; m-xylene, 0.27 ± 0.06; p-xylene, 0.40 ± 0.09; 1,2,3-trimethylbenzene, 0.31 ± 0.06; 1,2,4-trimethylbenzene, 0.37 ± 0.09; 1,3,5-trimethylbenzene, 0.29 ± 0.08; hexamethylbenzene, 0.32 ± 0.08; phenol, 0.89 ± 0.29; o-cresol, 0.87 ± 0.29; 2,5-dimethylphenol, 0.72 ± 0.12; 2,4,6-trimethylphenol, 0.45 ± 0.13. For the alkylbenzenes HO(2) is the proposed coproduct of phenols, epoxides, and possibly oxepins formed in secondary reactions with O(2). In most product studies the only quantified coproducts were phenols whereas only a few studies reported yields of epoxides. Oxepins have not been observed so far. Together with the yields of phenols from other studies, the HO(2) yields determined in this work set an upper limit to the combined yields of epoxides and oxepins that was found to be significant (≤0.3) for all investigated alkylbenzenes except m-xylene. For the hydroxybenzenes the currently proposed HO(2) coproducts are dihydroxybenzenes. For phenol and o-cresol the determined HO(2) yields are matching the previously reported dihydroxybenzene yields, indicating that these are the only HO(2) forming reaction channels. For 2,5-dimethylphenol and 2,4,6-trimethylphenol no complementary product studies are available.

  7. Effect of heterogeneous aqueous reactions on the secondary formation of inorganic aerosols during haze events

    DOE PAGESBeta

    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) 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

  8. 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

  9. Asymmetric catalytic cascade reactions for constructing diverse scaffolds and complex molecules.

    PubMed

    Wang, Yao; Lu, Hong; Xu, Peng-Fei

    2015-07-21

    With the increasing concerns about chemical pollution and sustainability of resources, among the significant challenges facing synthetic chemists are the development and application of elegant and efficient methods that enable the concise synthesis of natural products, drugs, and related compounds in a step-, atom- and redox-economic manner. One of the most effective ways to reach this goal is to implement reaction cascades that allow multiple bond-forming events to occur in a single vessel. This Account documents our progress on the rational design and strategic application of asymmetric catalytic cascade reactions in constructing diverse scaffolds and synthesizing complex chiral molecules. Our research is aimed at developing robust cascade reactions for the systematic synthesis of a range of interesting molecules that contain structural motifs prevalent in natural products, pharmaceuticals, and biological probes. The strategies employed to achieve this goal can be classified into three categories: bifunctional base/Brønsted acid catalysis, covalent aminocatalysis/N-heterocyclic carbene catalysis, and asymmetric organocatalytic relay cascades. By the use of rationally designed substrates with properly reactive sites, chiral oxindole, chroman, tetrahydroquinoline, tetrahydrothiophene, and cyclohexane scaffolds were successfully assembled under bifunctional base/Brønsted acid catalysis from simple and readily available substances such as imines and nitroolefins. We found that some of these reactions are highly efficient since catalyst loadings as low as 1 mol % can promote the multistep sequences affording complex architectures with high stereoselectivities and yields. Furthermore, one of the bifunctional base/Brønsted acid-catalyzed cascade reactions for the synthesis of chiral cyclohexanes has been used as a key step in the construction of the tetracyclic core of lycorine-type alkaloids and the formal synthesis of α-lycorane. Guided by the principles of

  10. 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.

  11. Visible-light induced isoindoles formation to trigger intermolecular Diels-Alder reactions in the presence of air.

    PubMed

    Lin, Chao; Zhen, Le; Cheng, Yong; Du, Hong-Jin; Zhao, Hui; Wen, Xiaoan; Kong, Ling-Yi; Xu, Qing-Long; Sun, Hongbin

    2015-06-01

    Visible-light induced isoindole formation triggered an intermolecular Diels-Alder reaction with dienophiles such as acetylenedicarboxylate and maleimides in the presence of air. The reaction resulted in excellent diastereoselctivity and high yields under mild reaction conditions. This protocol provides an atom-economical, transition-metal-free (TM-free) and straightforward approach to structurally diverse bridged-ring heterocycles from easily accessible molecules.

  12. 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.

  13. 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.

  14. 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.

  15. A cyclo‐P6 Ligand Complex for the Formation of Planar 2D Layers

    PubMed Central

    Heindl, Claudia; Peresypkina, Eugenia V.; Lüdeker, David; Brunklaus, Gunther; Virovets, Alexander V.

    2016-01-01

    Abstract The all‐phosphorus analogue of benzene, stabilized as middle deck in triple‐decker complexes, is a promising building block for the formation of graphene‐like sheet structures. The reaction of [(CpMo)2(μ,η6:η6‐P6)] (1) with CuX (X=Br, I) leads to self‐assembly into unprecedented 2D networks of [{(CpMo)2P6}(CuBr)4]n (2) and [{(CpMo)2P6}(CuI)2]n (3). X‐ray structural analyses show a unique deformation of the previously planar cyclo‐P6 ligand. This includes bending of one P atom in an envelope conformation as well as a bisallylic distortion. Despite this, 2 and 3 form planar layers. Both polymers were furthermore analyzed by 31P{1H} magic angle spinning (MAS) NMR spectroscopy, revealing signals corresponding to six non‐equivalent phosphorus sites. A peak assignment is achieved by 2D correlation spectra as well as by DFT chemical shift computations. PMID:26711699

  16. 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).

  17. Formation and Self-assembly of Gold Nanoplates through an Interfacial Reaction for Surface-Enhanced Raman Scattering.

    PubMed

    Ma, Ying; Yung, Lin-Yue Lanry

    2016-06-22

    3D hierarchical architectures assembled from individual particles have attracted great interest because they displayed novel properties from the individual building blocks as well as their complex structures. Here we present a new strategy to form 3D hierarchical gold (Au) nanostructures via an interfacial reduction reaction. An aniline (ANI) derivative, N-(3-amidino)-aniline (NAAN), and HAuCl4 were separately dissolved in toluene and water to form an organic/water interface. Au nanoplates formed at the interface and subsequently moved to the aqueous phase. As a capping agent for the nanoplate formation, the oxidized NAAN, i.e., poly(N-(3-amidino)-aniline) (PNAAN), also facilitated the self-assembly of Au nanoplates into 3D hierarchical Au nanoflowers (AuNFs) through π-π stacking. The individual AuNF exhibited good surface-enhanced Raman scattering (SERS) response both in enhancement factor and reproducibility because it integrates the SERS enhancement effects of individual Au nanoplates and their hierarchical structures. This is the first report depicting the one-pot formation and self-assembly of Au nanoplates into 3D organized hierarchical nanostructures through the molecular interaction of conducting polymer. PMID:27276116

  18. Effect of helix stability on the formation of loop-loop complexes.

    PubMed

    Sehdev, Preeti; Crews, Gordon; Soto, Ana Maria

    2012-12-01

    Kissing loop complexes are loop-loop complexes where two RNA hairpins interact through their complementary loops. In this work, we have investigated the role of the helical stems on the ability of hairpins derived from the ColE1 plasmid to associate as kissing loop complexes in the presence and absence of divalent cations. Our results show that although kissing loop complexes form more readily in the presence of Mg(2+), they are able to form in the presence of 850 mM NaCl, as long as their stems contain at least six base-pairs. Formation of the Na(+) loop-loop complexes is facilitated by changing the sequence at the stem-loop interface to include less stable AU base pairs. We suggest that the conformation at the stem-loop interface is critical in the formation of kissing loop complexes and that in the absence of Mg(2+) the conformation at the stem-loop interface is packed more loosely than with Mg(2+), to allow for a lower charge density. Consistent with this hypothesis, shortening the stems to five base pairs results in unfolding of the hairpins and formation of an extended duplex rather than a kissing loop complex because the short stems are not stable enough to tolerate the necessary conformation at the stem-loop interface to allow the formation of a kissing loop complex. PMID:23094588

  19. 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

  20. 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.

  1. 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.

  2. Levoglucosan formation from crystalline cellulose: importance of a hydrogen bonding network in the reaction.

    PubMed

    Hosoya, Takashi; Sakaki, Shigeyoshi

    2013-12-01

    Levoglucosan (1,6-anhydro-β-D-glucopyranose) formation by the thermal degradation of native cellulose was investigated by MP4(SDQ)//DFT(B3LYP) and DFT(M06-2X)//DFT(B3LYP) level computations. The computational results of dimer models lead to the conclusion that the degradation occurs by a concerted mechanism similar to the degradation of methyl β-D-glucoside reported in our previous study. One-chain models of glucose hexamer, in which the interchain hydrogen bonds of real cellulose crystals are absent, do not exhibit the correct reaction behavior of levoglucosan formation; for instance, the activation enthalpy (Ea =≈38 kcal mol(-1) ) is considerably underestimated compared to the experimental value (48-60 kcal mol(-1) ). This problem is solved with the use of two-chain models that contain interchain hydrogen bonds. The theoretical study of this model clearly shows that the degradation of the internal glucosyl residue leads to the formation of a levoglucosan precursor at the chain end and levoglucosan is selectively formed from this levoglucosan end. The calculated Ea (56-62 kcal mol(-1) ) agrees well with the experimental value. The computational results of three-chain models indicate that this degradation occurs selectively on the crystalline surface. All these computational results provide a comprehensive understanding of several experimental facts, the mechanisms of which have not yet been elucidated.

  3. 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).

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

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    An effort was undertaken to determine if the formation of the generally observed layer of large porosity adjacent to the as-nitride surfaces of reaction bonded silicon nitrides could be prevented during processing. Isostatically pressed test bars were prepared from wet vibratory milled Si powder. Sintering and nitriding were each done under three different conditions:(1) bars directly exposed to the furnance atmosphere; (2) bars packed in Si powder; (3) bars packed in Si3N4 powder. Packing the bars in either Si of Si3N4 powder during sintering retarded formation of the layer of large porosity. Only packing the bars in Si prevented formation of the layer during nitridation. The strongest bars (316 MPa) were those sintered in Si and nitrided in Si3N4 despite their having a layer of large surface porosity; failure initiated at very large pores and inclusions. The alpha/beta ratio was found to be directly proportional to the oxygen content; a possible explanation for this relationship is discussed.

  5. Synthesis and reactions of the first room temperature stable Li/Cl phosphinidenoid complex.

    PubMed

    Nesterov, Vitaly; Schnakenburg, Gregor; Espinosa, Arturo; Streubel, Rainer

    2012-11-19

    P-Trityl substituted Li/Cl phosphinidenoid tungsten(0) complex (OC)5W{Ph3CP(Li/12-crown-4)Cl} (3) was prepared via chlorine/lithium exchange in complex (OC)5W{Ph3CPCl2} (2) using (t)BuLi in the presence of 12-crown-4 in tetrahydrofuran (THF) at low temperature; complex 3 possesses significantly increased thermal stability in contrast to previously reported analogue derivatives. Terminal phosphinidene-like reactivity of 3 was used in reactions with benzaldehyde and isopropyl alcohol as oxaphosphirane complex (OC)5W{Ph3CPC(Ph)O} (5) and phosphinite complex (OC)5W{Ph3CP(H)O(i)Pr} (6) were obtained selectively. Reaction of 3 with phosgene allowed to obtain the first kinetically stabilized chloroformylphosphane complex (OC)5W{Ph3CP(Cl)C(O)Cl} (4). Density functional theory (DFT) calculations revealed remarkable differences in the degree of P-Li bond dissociation 3a-d: using a continuum model 3 displays a covalent character of P-Li bond (COSMO (THF)) (a), which becomes elongated if 12-crown-4 is coordinated to lithium (b) and is cleaved if a dimethylether unit is additionally coordinated to lithium (c). A similar result was obtained for the case of 3(thf)4 in which also a solvent-separated ion pair structure is present (d). All products were unambiguously characterized by various spectroscopic means and, in the case of 2 and 4-6, by single-crystal X-ray diffraction analysis. In all structures very long P-C bonds were determined being in the range from 1.896 to 1.955 Å.

  6. O2 reduction reaction by biologically relevant anionic ligand bound iron porphyrin complexes.

    PubMed

    Samanta, Subhra; Das, Pradip Kumar; Chatterjee, Sudipta; Sengupta, Kushal; Mondal, Biswajit; Dey, Abhishek

    2013-11-18

    Iron porphyrin complex with a covalently attached thiolate ligand and another with a covalently attached phenolate ligand has been synthesized. The thiolate bound complex shows spectroscopic features characteristic of P450, including the hallmark absorption spectrum of the CO adduct. Electrocatalytic O2 reduction by this complex, which bears a terminal alkyne group, is investigated by both physiabsorbing on graphite surfaces (fast electron transfer rates) and covalent attachment to azide terminated self-assembled monolayer (physiologically relevant electron transfer rates) using the terminal alkyne group. Analysis of the steady state electrochemical kinetics reveals that this catalyst can selectively reduce O2 to H2O with a second-order k(cat.) ~10(7) M(-1 )s(-1) at pH 7. The analogous phenolate bound iron porphyrin complex reduces O2 with a second-order rate constant of 10(5) M(-1) s(-1) under the same conditions. The anionic ligand bound iron porphyrin complexes catalyze oxygen reduction reactions faster than any known synthetic heme porphyrin analogues. The kinetic parameters of O2 reduction of the synthetic thiolate bound complex, which is devoid of any second sphere effects present in protein active sites, provide fundamental insight into the role of the protein environment in tuning the reactivity of thiolate bound iron porphyrin containing metalloenzymes. PMID:24171513

  7. 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.

    2016-08-01

    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.

  8. 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. PMID:26986849

  9. 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

  10. Cellular consequences of copper complexes used to catalyze bioorthogonal click reactions.

    PubMed

    Kennedy, David C; McKay, Craig S; Legault, Marc C B; Danielson, Dana C; Blake, Jessie A; Pegoraro, Adrian F; Stolow, Albert; Mester, Zoltan; Pezacki, John Paul

    2011-11-01

    Copper toxicity is a critical issue in the development of copper-based catalysts for copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions for applications in living systems. The effects and related toxicity of copper on mammalian cells are dependent on the ligand environment. Copper complexes can be highly toxic, can induce changes in cellular metabolism, and can be rapidly taken up by cells, all of which can affect their ability to function as catalysts for CuAAC in living systems. Herein, we have evaluated the effects of a number of copper complexes that are typically used to catalyze CuAAC reactions on four human cell lines by measuring mitochondrial activity based on the metabolism of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to study toxicity, inductively coupled plasma mass spectrometry to study cellular uptake, and coherent anti-Stokes Raman scattering (CARS) microscopy to study effects on lipid metabolism. We find that ligand environment around copper influences all three parameters. Interestingly, for the Cu(II)-bis-L-histidine complex (Cu(his)(2)), cellular uptake and metabolic changes are observed with no toxicity after 72 h at micromolar concentrations. Furthermore, we show that under conditions where other copper complexes kill human hepatoma cells, Cu(I)-L-histidine is an effective catalyst for CuAAC labeling of live cells following metabolic incorporation of an alkyne-labeled sugar (Ac(4)ManNAl) into glycosylated proteins expressed on the cell surface. This result suggests that Cu(his)(2) or derivatives thereof have potential for in vivo applications where toxicity as well as catalytic activity are critical factors for successful bioconjugation reactions. PMID:21970470

  11. Positronium formation studies in solid molecular complexes: Triphenylphosphine oxide-triphenylmethanol

    NASA Astrophysics Data System (ADS)

    Oliveira, F. C.; Denadai, A. M. L.; Fulgêncio, F. H.; Magalhães, W. F.; Alcântara, A. F. C.; Windmöller, D.; Machado, J. C.

    2012-06-01

    Positronium formation in triphenylphosphine oxide (TPPO), triphenylmethanol (TPM), and systems [TPPO(1-X)ṡTPMX] has been studied. The low probability of positronium formation in complex [TPPO0.5ṡTPM0.5] was attributed to strong hydrogen bond and sixfold phenyl embrace interactions. These strong interactions in complex reduce the possibility of the n- and π-electrons to interact with positrons on the spur and consequently, the probability of positronium formation is lower. The τ3 parameter and free volume (correlated to τ3) were also sensitive to the formation of hydrogen bonds and sixfold phenyl embrace interactions within the complex. For physical mixture the positron annihilation parameters remained unchanged throughout the composition range.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Coke formation on HFAU and HEMT zeolites. Influence of the reaction temperature and propene pressure

    NASA Astrophysics Data System (ADS)

    Doka Nassionou, G. A.; Magnoux, P.; Guisnet, M.

    1999-02-01

    The formation of coke from propene (Pp = 1.3 kPa and 13 kPa) was investigated on HFAU and HEMT zeolites in a microbalance for temperatures ranging from 120 °C to 450 °C. For both zeolites, the greater the propene pressure and the lower the temperature the faster the initial coke formation. However for high propene pressure, initial coke formation is faster with HEMT zeolite. This can be related to the stronger acidity of the HEMT sample. For low propene pressure and after 420 minutes of coking, a minimum in coke is observed for T = 350 ^circC, which can be related to the difference between the rate of formation and the rate of retention of coke molecules. At low temperature, due to their low volatility, oligomers are easily formed and retained in the zeolite pores. These molecules can be totally eliminated by an adequate thermal treatment in vacuum. At higher temperature, only aromatic or polyaromatic compounds which present a size larger than the pore apertures can be retained in the cavities of the zeolites. The greater the reaction time, the faster the retention. Whatever the reaction temperature, coke molecules are more homogeneously distributed in the HEMT crystallites than in those of HFAU samples. For this latter zeolite coke molecules are preferentially formed in the cavities located near the outer surface of the crystallites (shell coking). La formation de coke à partir du propène (Pp = 1,3 et 13 kPa) a été étudiée en microbalance sur zéolithes HFAU et HEMT dans une gamme de température variant de 120 à 450°C. La vitesse initiale de formation de coke dépend de la pression du propène, de la température et également de la zéolithe. Ainsi, pour une forte pression en propène, la vitesse initiale de formation de coke est toujours plus importante sur HEMT que sur HFAU. Ceci est à relier à la plus grande acidité et à la présence de sites acides plus forts sur HEMT. Après 420 minutes de réaction, et pour une faible pression en propène le

  17. Synthesis, structural characterization, and ligand replacement reactions of gem-dithiolato-bridged rhodium and iridium complexes.

    PubMed

    Rivas, Angel B; Gascón, José M; Lahoz, Fernando J; Balana, Ana I; Pardey, Alvaro J; Oro, Luis A; Pérez-Torrente, Jesús J

    2008-07-01

    The reaction of gem-dithiol compounds R 2C(SH) 2 (R = Bn (benzyl), (i) Pr; R 2 = -(CH 2) 4-) with dinuclear rhodium or iridium complexes containing basic ligands such as [M(mu-OH)(cod)] 2 and [M(mu-OMe)(cod)] 2, or the mononuclear [M(acac)(cod)] (M = Rh, Ir, cod = 1,5-cyclooctadiene) in the presence of a external base, afforded the dinuclear complexes [M 2(mu-S 2CR 2)(cod) 2] ( 1- 4). The monodeprotonation of 1,1-dimercaptocyclopentane gave the mononuclear complex [Rh(HS 2Cptn)(cod)] ( 5) that is a precursor for the dinuclear compound [Rh 2(mu-S 2Cptn)(cod) 2] ( 6). Carbonylation of the diolefin compounds gave the complexes [Rh 2(mu-S 2CR 2)(CO) 4] ( 7- 9), which reacted with P-donor ligands to stereoselectively produce the trans isomer of the disubstituted complexes [Rh 2(mu-S 2CR 2)(CO) 2(PR' 3) 2] (R' = Ph, Cy (cyclohexyl)) ( 10- 13) and [Rh 2(mu-S 2CBn 2)(CO) 2{P(OR') 3} 2] (R' = Me, Ph) ( 14- 15). The substitution process in [Rh 2(mu-S 2CBn 2)(CO) 4] ( 7) by P(OMe) 3 has been studied by spectroscopic means and the full series of substituted complexes [Rh 2(mu-S 2CBn 2)(CO) 4- n {P(OR) 3} n ] ( n = 1, 4) has been identified in solution. The cis complex [Rh 2(mu-S 2CBn 2)(CO) 2(mu-dppb)] ( 16) was obtained by reaction of 7 with the diphosphine dppb (1,4-bis(diphenylphosphino)butane). The molecular structures of the diolefinic dinuclear complexes [Rh 2(mu-S 2CR 2)(cod) 2] (R = Bn ( 1), (i) Pr ( 2); R 2 = -(CH 2) 4- ( 6)) and that of the cis complex 16 have been studied by X-ray diffraction. PMID:18507456

  18. Short relaxation times but long transient times in both simple and complex reaction networks

    PubMed Central

    Henry, Adrien; Martin, Olivier C.

    2016-01-01

    When relaxation towards an equilibrium or steady state is exponential at large times, one usually considers that the associated relaxation time τ, i.e. the inverse of the decay rate, is the longest characteristic time in the system. However, that need not be true, other times such as the lifetime of an infinitesimal perturbation can be much longer. In the present work, we demonstrate that this paradoxical property can arise even in quite simple systems such as a linear chain of reactions obeying mass action (MA) kinetics. By mathematical analysis of simple reaction networks, we pin-point the reason why the standard relaxation time does not provide relevant information on the potentially long transient times of typical infinitesimal perturbations. Overall, we consider four characteristic times and study their behaviour in both simple linear chains and in more complex reaction networks taken from the publicly available database ‘Biomodels’. In all these systems, whether involving MA rates, Michaelis–Menten reversible kinetics, or phenomenological laws for reaction rates, we find that the characteristic times corresponding to lifetimes of tracers and of concentration perturbations can be significantly longer than τ. PMID:27411726

  19. Carbon-carbon bond cleavage and formation reactions in drug metabolism and the role of metabolic enzymes.

    PubMed

    Bolleddula, Jayaprakasam; Chowdhury, Swapan K

    2015-01-01

    Elimination of xenobiotics from the human body is often facilitated by a transformation to highly water soluble and more ionizable molecules. In general, oxidation-reduction, hydrolysis, and conjugation reactions are common biotransformation reactions that are catalyzed by various metabolic enzymes including cytochrome P450s (CYPs), non-CYPs, and conjugative enzymes. Although carbon-carbon (C-C) bond formation and cleavage reactions are known to exist in plant secondary metabolism, these reactions are relatively rare in mammalian metabolism and are considered exceptions. However, various reactions such as demethylation, dealkylation, dearylation, reduction of alkyl chain, ring expansion, ring contraction, oxidative elimination of a nitrile through C-C bond cleavage, and dimerization, and glucuronidation through C-C bond formation have been reported for drug molecules. Carbon-carbon bond cleavage reactions for drug molecules are primarily catalyzed by CYP enzymes, dimerization is mediated by peroxidases, and C-glucuronidation is catalyzed by UGT1A9. This review provides an overview of C-C bond cleavage and formation reactions in drug metabolism and the metabolic enzymes associated with these reactions.

  20. Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2'-bipyridine

    PubMed Central

    Lichtenthaler, Martin R.; Stahl, Florian; Kratzert, Daniel; Heidinger, Lorenz; Schleicher, Erik; Hamann, Julian; Himmel, Daniel; Weber, Stefan; Krossing, Ingo

    2015-01-01

    Group 13 MI compounds often disproportionate into M0 and MIII. Here, however, we show that the reaction of the MI salt of the weakly coordinating alkoxyaluminate [GaI(C6H5F)2]+[Al(ORF)4]− (RF=C(CF3)3) with 2,2'-bipyridine (bipy) yields the paramagnetic and distorted octahedral [Ga(bipy)3]2+•{[Al(ORF)4]−}2 complex salt. While the latter appears to be a GaII compound, both, EPR and DFT investigations assign a ligand-centred [GaIII{(bipy)3}•]2+ radical dication. Surprisingly, the application of the heavier homologue [InI(C6H5F)2]+[Al(ORF)4]− leads to aggregation and formation of the homonuclear cationic triangular and rhombic [In3(bipy)6]3+, [In3(bipy)5]3+ and [In4(bipy)6]4+ metal atom clusters. Typically, such clusters are formed under strongly reductive conditions. Analysing the unexpected redox-neutral cationic cluster formation, DFT studies suggest a stepwise formation of the clusters, possibly via their triplet state and further investigations attribute the overall driving force of the reactions to the strong In−In bonds and the high lattice enthalpies of the resultant ligand stabilized [M3]3+{[Al(ORF)4]−}3 and [M4]4+{[Al(ORF)4]−}4 salts. PMID:26478464