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1

Reactions of chloride complexes of ruthenium (IV) with formic acid and sodium formate in aqueous solutions  

SciTech Connect

Study of the reactions of (NH/sub 4/)/sub 2/RuCl/sub 6/ with formic acid and sodium formate showed that, depending on the conditions, chlorocarbonyl, chloroformatocarbonyl, or chloroformato complexes of ruthenium(III) are formed.

Simanova, S.A.; Krylova, G.S.; Maslov, E.I.

1982-04-20

2

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

NASA Astrophysics Data System (ADS)

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.

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

2008-12-01

3

Rapid-reaction Kinetic Characterization of the Pathway of Streptokinase-Plasmin Catalytic Complex Formation*  

PubMed Central

Binding of the fibrinolytic proteinase plasmin (Pm) to streptokinase (SK) in a tight stoichiometric complex transforms Pm into a potent proteolytic activator of plasminogen. SK binding to the catalytic domain of Pm, with a dissociation constant of 12 pm, is assisted by SK Lys414 binding to a Pm kringle, which accounts for a 11-20-fold affinity decrease when Pm lysine binding sites are blocked by 6-aminohexanoic acid (6-AHA) or benzamidine. The pathway of SK·Pm catalytic complex formation was characterized by stopped-flow kinetics of SK and the Lys414 deletion mutant (SK?K414) binding to Pm labeled at the active site with 5-fluorescein ([5F]FFR-Pm) and the reverse reactions by competitive displacement of [5F]FFR-Pm with active site-blocked Pm. The rate constants for the biexponential fluorescence quenching caused by SK and SK?K414 binding to [5F]FFR-Pm were saturable as a function of SK concentration, reporting encounter complex affinities of 62-110 nm in the absence of lysine analogs and 4900-6500 and 1430-2200 nm in the presence of 6-AHA and benzamidine, respectively. The encounter complex with SK?K414 was ?10-fold weaker in the absence of lysine analogs but indistinguishable from that of native SK in the presence of 6-AHA and benzamidine. The studies delineate for the first time the sequence of molecular events in the formation of the SK·Pm catalytic complex and its regulation by kringle ligands. Analysis of the forward and reverse reactions supports a binding mechanism in which SK Lys414 binding to a Pm kringle accompanies near-diffusion-limited encounter complex formation followed by two slower, tightening conformational changes.

Verhamme, Ingrid M.; Bock, Paul E.

2008-01-01

4

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

ERIC Educational Resources Information Center

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)

Busby, David C.; And Others

1981-01-01

5

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

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

6

Formation of water soluble complexes of ?: solid-state reaction between tertiary amines and ?  

NASA Astrophysics Data System (ADS)

Water soluble complexes of 0953-4075/29/21/015/img3 have been prepared on solid-state mechano-chemical reaction between 0953-4075/29/21/015/img3 and tertiary amines (hexamine, DABCO) at room temperature 0953-4075/29/21/015/img5. The product is characterized by x-ray diffraction and FTIR methods. It is presumably due to the charge transfer interactions between electron affinic 0953-4075/29/21/015/img3 and electron rich tertiary amines.

Mohan, H.; Priyadarsini, K. I.; Tyagi, A. K.; Mittal, J. P.

1996-11-01

7

The reaction of platinum(II) complexes with DNA. Kinetics of intrastrand crosslink formation in vitro.  

PubMed Central

The kinetics of the formation of bifunctional DNA platinum(II) adducts (DNA-crosslinks) have been investigated by endonuclease digestion and subsequent HPLC analysis of the soluble nucleotides and nucleotide platinum(II) adducts. The results indicate two waves of crosslinking [rate constants (0.2-0.3) min-1 and (0.015-0.025) min-1] that correlate with changes in ultra violet absorbance and ethidium bromide dependent fluorescence intensity, previously interpreted in terms of two consecutive, local conformational rearrangements of platinum-DNA (Schaller, W., Reisner, H., and Holler, E. (1987) Biochemistry 26, 943-950). The formation of crosslinks at sequences d(GpG) and d(GpNpG) follows identical kinetics. A minimal reaction mechanism is proposed for the binding of cis-diamminedichloroplatinum(II) to DNA under in vitro conditions. The approximately 3-fold higher rate for meso-[1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine]diaquaplatinum(II) in comparison to the rate for cis-diamminediaquaplatinum(II) indicates that crosslink formation is affected by the nature of the non-leaving platinum ligand(s).

Bernges, F; Holler, E

1991-01-01

8

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

PubMed

Reactions of TpMS(S(2)CNEt(2)) with dimethyl acetylenedicarboxylate in dichloromethane produce olive green/black TpM{S(2)C(2)(CO(2)Me)(2)}(SCNEt(2)-kappa(2)S,C) (M = Mo (1), W (2); Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate). The seven-coordinate complexes exhibit pseudo-octahedral (1) and distorted pentagonal bipyramidal (2) coordination spheres comprised of tridentate fac-Tp, bidentate dithiolene, and thiocarboxamido-kappa(2)S,C ligands. In the solid state, molecules of 1 exhibit pseudo-C(s)() symmetry, with the thiocarboxamide NEt(2) group in a cleft in the Tp ligand. Molecules of 2 have C(1) symmetry in the solid state; here, the thiocarboxamide unit is orientated along one of the W-S(dithiolene) bonds with its NEt(2) group projecting away from the Tp ligand. Both complexes possess effective C(s)() symmetry in solution. Reaction of TpMoI(CO)(3) with AgS(2)CNEt(2) affords olive green TpMo(S(2)CNEt(2))(CO)(2) (3), which reacts with propylene sulfide in a new synthesis for TpMoS(S(2)CNEt(2)), the starting material for 1. Complex 3 exhibits a distorted pentagonal bipyramidal structure, the axial sites being defined by a Tp nitrogen atom and a carbonyl ligand, the pentagonal plane by the remaining nitrogen and carbonyl donors and the two sulfur atoms of the bidentate dithiocarbamate ligand. PMID:15627367

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

2005-01-10

9

New reaction model for O-O bond formation and O2 evolution catalyzed by dinuclear manganese complex.  

PubMed

A new mechanism of the oxygen evolving reaction catalyzed by [H(2)O(terpy)Mn(?-O)(2)Mn(terpy)OH(2)](3+) is proposed by using density functional theory. This proton coupled electron transfer (PCET) model shows reasonable barriers. Because in experiments excess oxidants (OCl(-) or HSO(5)(-)) are required to evolve oxygen from water, we considered the Mn(2) complex neutralized by three counterions. Structure optimization made the coordinated OCl(-) withdraw a H(+) from the water ligand and produces the reaction space for H(2)O(2) formation with the deprotonated OH(-) ligand. The reaction barrier for the H(2)O(2) formation from OH(-) and protonated OCl(-) depends significantly on the system charge and is 14.0 kcal/mol when the system is neutralized. The H(2)O(2) decomposes to O(2) during two PCET processes to the Mn(2) complex, both with barriers lower than 12.0 kcal/mol. In both PCET processes the spin moment of transferred electrons prefers to be parallel to that of Mn 3d electrons because of the exchange interaction. This model thus explains how the triplet O(2) molecule is produced. PMID:22672069

Hatakeyama, Makoto; Nakata, Hiroya; Wakabayashi, Masamitsu; Yokojima, Satoshi; Nakamura, Shinichiro

2012-07-01

10

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

PubMed

The kinetic isotope effect of the reactions OH + CH3OCH3 (DME) and OH + CD3OCD3 (DME-d6) was experimentally and theoretically studied. Experiments were carried out in a slow-flow reactor at pressures between 5 and 21 bar (helium as bath gas) with production of OH by laser flash photolysis of HNO3 and time-resolved detection of OH by laser-induced fluorescence. The temperature dependences of the rate coefficients obtained can be described by the following modified Arrhenius expressions: k(OH+DME) = (4.5 ± 1.3) × 10(-16) (T/K)(1.48) exp(66.6 K/T) cm(3) s(-1) (T = 292-650 K, P = 5.9-20.9 bar) and k(OH+DME-d6) = (7.3 ± 2.2) × 10(-23) (T/K)(3.57) exp(759.8 K/T) cm(3) s(-1) (T = 387-554 K, P = 13.0-20.4 bar). A pressure dependence of the rate coefficients was not observed. The agreement of our experimental results for k(OH+DME) with values from other authors is very good, and from a fit to all available literature data, we derived the following modified Arrhenius expression, which reproduces the values obtained in the temperature range T = 230-1500 K at pressures between 30 mbar and 21 bar to better than within ±20%: k(OH+DME) = 8.45 × 10(-18) (T/K)(2.07) exp(262.2 K/T) cm(3) s(-1). For k(OH+DME-d6), to the best of our knowledge, this is the first experimental study. For the analysis of the reaction pathway and the kinetic isotope effect, potential energy diagrams were calculated by using three different quantum chemical methods: (I) CCSD(T)/cc-pV(T,Q)Z//MP2/6-311G(d,p), (II) CCSD(T)/cc-pV(T,Q)Z//CCSD/cc-pVDZ, and (III) CBS-QB3. In all three cases, the reaction is predicted to proceed via a prereaction OH-ether complex with subsequent intramolecular hydrogen abstraction and dissociation to give the methoxymethyl radical and water. Overall rate coefficients were calculated by assuming a thermal equilibrium between the reactants and the prereaction complex and by calculating the rate coefficients of the hydrogen abstraction step from canonical transition state theory. The results based on the molecular data from methods (I) and (II) showed a satisfactory agreement with the experimental values, which indicates that the pre-equilibrium assumption is reasonable under our conditions. In the case of method (III), the isotope effect was significantly underpredicted. The reason for this discrepancy was identified in a fundamentally differing reaction coordinate. Obviously, the B3LYP functional applied in method (III) for geometry and frequency calculations is inadequate to describe such systems, which is in line with earlier findings of other authors. PMID:23914942

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

2013-09-01

11

Formation of complex organics in the gas phase by sequential reactions of acetylene with the phenylium ion.  

PubMed

In this paper, we report a study on the reactivity of the phenylium ion with acetylene, by measuring product yield as a function of pressure and temperature using mass-selected ion mobility mass spectrometry. The reactivity is dominated by a rapid sequential addition of acetylene to form covalently bonded C8H7(+) and C10H9(+) ions with an overall rate coefficient of 7-5 × 10(-10) cm(3) s(-1), indicating a reaction efficiency of nearly 50% at room temperature. The covalent bonding nature of the product ions is confirmed by high temperature studies where enhanced production of these ions is observed at temperatures as high as 660 K. DFT calculations at the UPBEPBE/6-31++G** level identify the C8H7(+) adduct as 2-phenyl-ethenylium ion, the most stable C8H7(+) isomer that maintains the phenylium ion structure. A small barrier of 1.6 kcal/mol is measured and attributed to the formation of the second adduct C10H9(+) containing a four-membered ring connected to the phenylium ion. Evidence for rearrangement of the C10H9(+) adduct to the protonated naphthalene structure at temperatures higher than 600 K is provided and suggests further reactions with acetylene with the elimination of an H atom and an H2 molecule to generate 1-naphthylacetylene or acenaphthylene cations. The high reactivity of the phenylium ion toward acetylene is in sharp contrast to the low reactivity of the benzene radical cation with a reaction efficiency of 10(-4)-10(-5), confirming that the first step in the cation ring growth mechanism is the loss of an aromatic H atom. The observed reactions can explain the formation of complex organics by gas phase ion-molecule reactions involving the phenylium ion and acetylene under a wide range of temperatures and pressures in astrochemical environments. PMID:22889439

Soliman, Abdel-Rahman; Hamid, Ahmed M; Momoh, Paul O; El-Shall, M Samy; Taylor, Danielle; Gallagher, Lauren; Abrash, Samuel A

2012-09-13

12

Complex formation reactions of palladium(II)-1,3-diaminopropane with various biologically relevant ligands. Kinetics of hydrolysis of glycine methyl ester through complex formation  

Microsoft Academic Search

The interaction of [Pd(DAP)(H2O)2]2+ (DAP = 1,3-diaminopropane) with some selected bio-relevant ligands, containing different functional groups, were investigated.\\u000a The ligands used are dicarboxylic acids, amino acids, peptides and DNA constituents. Stoichiometry and stability constants\\u000a of the complexes formed are reported at 25°C and 0.1 M ionic strength. The results show the formation of 1:1 complexes with\\u000a amino acids and dicarboxylic

Ahmed A. El-Sherif; Mohamed M. Shoukry; Ramadan M. El-Bahnasawy; Dalia M. Ahmed

2010-01-01

13

Spatiotemporal Patterns and Nonclassical Kinetics of Competing Elementary Reactions:  Chromium Complex Formation with Xylenol Orange in a Capillary  

Microsoft Academic Search

kinetically different species that react competitively with xylenol orange. The parameters that determine whether pattern formation is observable at the front are the ratios of (1) the microscopic reaction constants of the competing reactions and (2) the concentrations of the competing species. Under the parameter values studied, which allowed clear spatiotemporal separation of the two competing reactions, we find that

Andrew Yen; Anna L. Lin; Yong-Eun Lee Koo; Baruch Vilensky; Haim Taitelbaum; Raoul Kopelman

1997-01-01

14

Complex Formation Reactions of (2,2?-dipyridylamine)copper(II) with Various Biologically Relevant Ligands. The Kinetics of Hydrolysis of Amino Acid Esters  

Microsoft Academic Search

Binary and ternary copper(II) complexes involving 2,2?-dipyridylamine (DPA) and various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA unit constituents. The ternary complexes of amino acids, dicarboxylic acids or peptides are formed by simultaneous reactions. The results showed the formation of 1:1 complexes with amino acids and dicarboxylic

Azza A. Shoukry

2005-01-01

15

Hydride-Meisenheimer Complex Formation and Protonation as Key Reactions of 2,4,6Trinitrophenol Biodegradation by Rhodococcus erythropolis  

Microsoft Academic Search

Biodegradation of 2,4,6-trinitrophenol (picric acid) by Rhodococcus erythropolis HLPM-1 proceeds via initial hydrogenation of the aromatic ring system. Here we present evidence for the formation of a hydride-Meisen- heimer complex (anionic s-complex) of picric acid and its protonated form under physiological conditions. These complexes are key intermediates of denitration and productive microbial degradation of picric acid. For comparative spectroscopic identification

PAUL-GERHARD RIEGER; VOLKER SINNWELL; ANDREA PREUß; WITTKO FRANCKE; HANS-JOACHIM KNACKMUSS

1999-01-01

16

Investigation of A New Catalytic Reaction of Complex Formation of Cobalt (III) With Nitroso-R-Salt for the Determination of Microquantities of Phosphate-Ions  

Microsoft Academic Search

The catalytic action of phosphate-ions on the reaction of complex formation of cobalt (III) with nitroso-R-salt in a weakly acid medium has been found. The dependence of the rate of the catalytic reaction on temperature, concentrations of reagents and catalyst, pH of the medium, as well as on the presence of some anion and non-ion surface-active substances and accompanying inorganic

L. I. Mikhailova; I. V. Pulyaeva; A. B. Blank

2000-01-01

17

Hydride-Meisenheimer Complex Formation and Protonation as Key Reactions of 2,4,6-Trinitrophenol Biodegradation by Rhodococcus erythropolis  

PubMed Central

Biodegradation of 2,4,6-trinitrophenol (picric acid) by Rhodococcus erythropolis HLPM-1 proceeds via initial hydrogenation of the aromatic ring system. Here we present evidence for the formation of a hydride-Meisenheimer complex (anionic ?-complex) of picric acid and its protonated form under physiological conditions. These complexes are key intermediates of denitration and productive microbial degradation of picric acid. For comparative spectroscopic identification of the hydride complex, it was necessary to synthesize this complex for the first time. Spectroscopic data revealed the initial addition of a hydride ion at position 3 of picric acid. This hydride complex readily picks up a proton at position 2, thus forming a reactive species for the elimination of nitrite. Cell extracts of R. erythropolis HLPM-1 transform the chemically synthesized hydride complex into 2,4-dinitrophenol. Picric acid is used as the sole carbon, nitrogen, and energy source by R. erythropolis HLPM-1.

Rieger, Paul-Gerhard; Sinnwell, Volker; Preuss, Andrea; Francke, Wittko; Knackmuss, Hans-Joachim

1999-01-01

18

Hydride-Meisenheimer complex formation and protonation as key reactions of 2,4,6-trinitrophenol biodegradation by Rhodococcus erythropolis.  

PubMed

Biodegradation of 2,4,6-trinitrophenol (picric acid) by Rhodococcus erythropolis HLPM-1 proceeds via initial hydrogenation of the aromatic ring system. Here we present evidence for the formation of a hydride-Meisenheimer complex (anionic sigma-complex) of picric acid and its protonated form under physiological conditions. These complexes are key intermediates of denitration and productive microbial degradation of picric acid. For comparative spectroscopic identification of the hydride complex, it was necessary to synthesize this complex for the first time. Spectroscopic data revealed the initial addition of a hydride ion at position 3 of picric acid. This hydride complex readily picks up a proton at position 2, thus forming a reactive species for the elimination of nitrite. Cell extracts of R. erythropolis HLPM-1 transform the chemically synthesized hydride complex into 2,4-dinitrophenol. Picric acid is used as the sole carbon, nitrogen, and energy source by R. erythropolis HLPM-1. PMID:9973345

Rieger, P G; Sinnwell, V; Preuss, A; Francke, W; Knackmuss, H J

1999-02-01

19

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

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 mixed dimers MeCpMo(CO){sub 3}-(CO){sub 3}MoCp (3b) and MeCpMo(CO){sub 2}{triple_bond}(CO){sub 2}MoCp (4b) are the predominant kinetic products of the reaction. Additionally labeling the carbonyl ligands of 1a with {sup 13}CO led to the conclusion that all three of the carbonyl ligands in 1a end up in the tetracarbonyl dimers 4a if the reaction is carried out under a continuous purge of argon Trapping studies failed to find any evidence for the intermediacy of either [CpMo(CO){sub 3}]{sup -} or [CpMo(CO){sub 3}]{sup +} in this reaction. A mechanism is proposed that involves the initial migration of the alkyl ligand in 2 to CO forming an unsaturated acyl complex which reacts with 1a to give a binuclear complex containing a three center-two electron Mo-H-Mo bond. This complex then selectively looses a carbonyl from the acyl molybdenum, migrates the hydride to that same metal, and forms a metal-metal bond. This binuclear complex with the hydride and acyl ligands on one metal reductively eliminates aldehyde, and migrates a carbonyl ligand, to give 4a directly. The other product 3a is formed by addition of two molecules of free CO to 4a.

Huggins, John Mitchell

1980-06-01

20

Reaction of the RuTp(PR 3)Cl fragment with alkynols: Formation of carbene, vinylidene, allenylidene, and carbyne complexes  

Microsoft Academic Search

The reaction of RuTp(COD)Cl (1) with PR3 (PR3=PPh2iPr, PiPr3, PPh3) and propargylic alcohols HCCCPh2OH, HCCCFc2OH (Fc=ferrocenyl), and HCCC(Ph)MeOH has been studied.In the case of PR3=PPh2iPr, PiPr3 and HCCCPh2OH, the 3-hydroxyvinylidene complexes RuTp(PPh2iPr)(CCHC(Ph)2OH)Cl (2a) and RuTp(PiPr3)(CCHC(Ph2)OH)Cl (2b) were isolated.With PR3=PPh2iPr and HCCCFc2OH as well as with PR3=PPh3 and HCCCPh2OH dehydration takes place affording the allenylidene complexes RuTp(PPh2iPr)(CCCFc2)Cl (3b) and RuTp(PPh3)(CCCPh2)Cl (3c).Similarly,

Sonja Pavlik; Kurt Mereiter; Michael Puchberger; Karl Kirchner

2005-01-01

21

Reactions of a tungsten-germylyne complex with ?,?-unsaturated ketones: complete cleavage of the W?Ge bond and formation of two types of ?3-germoxyallyl tungsten complexes.  

PubMed

Germylyne complex Cp*(CO)2W?Ge{C(SiMe3)3} (1) reacted with two molecules of RC(O)CH?CH2 (R = Me, Et) to give ?(3)-allyl complexes, in which an oxagermacyclopentene framework was bound to an ?(3)-allyl ligand through an oxygen atom. In the reaction with ?-Me-substituted MeC(O)C(Me)?CH2, 1 reacted with only one molecule of the substrate to give another type of ?(3)-allyl complex, in which a five-membered oxagermacyclopentenyl ring was coordinated to the W center in an ?(3) fashion. Both reactions resulted in unprecedented complete cleavage of a W?Ge triple bond. PMID:24328309

Fukuda, Tetsuya; Hashimoto, Hisako; Tobita, Hiromi

2014-01-01

22

Simple, sensitive and selective spectrophotometric methods for the determination of atenolol in pharmaceuticals through charge transfer complex formation reaction.  

PubMed

Three rapid, selective and sensitive spectrophotometric methods have been proposed for the quantitative determination of atenolol (ATN) in pure form as well as in its pharmaceutical formulation. The methods are based on charge transfer complexation reaction of ATN as n-electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (picric acid; PA) as pi-acceptors to give highly colored radical anion species. The colored products were quantified spectrophotometrically at 590 nm with DDQ (method A) and at 420 nm with both DNP (method B) and PA (method C). Under the optimized experimental conditions, Beer's law is obeyed over the concentration ranges of 3-48, 2-24 and 1.5-18 ?g/mL ATN for method A, method B and method C, respectively. The molar absorptivity, Sandell sensitivity, limits of detection and quantification are also reported. The effects of reaction medium, reaction time and reagent concentration on the sensitivity and stability of the complexes formed have been examined. The proposed methods were successfully applied to the determination of ATN in pure form and commercial tablets with good accuracy and precision. Statistical comparison of the results was performed using Student's t-test and F-ratio at 95% confidence level and the results showed no significant difference between the reference and proposed methods with regard to accuracy and precision. Further, the accuracy and reliability of the methods were confirmed by recovery studies via standard addition technique. PMID:22568035

Prashanth, Kudige Nagaraju; Basavaiah, Kanakapura

2012-01-01

23

Reaction Route of GaN Powder Formation via Sintering Gallium Ethylenediamine Tetraacetic Acid Complexes in Ammonia  

NASA Astrophysics Data System (ADS)

The thermal decomposition behaviours of gallium ethylenediamine tetraacetic acid (Ga-EDTA) complex (Ga[(OOCCH2)2-N-CH2-CH2-N-(CH2COO)2]NH4) powders were investigated by thermogravimetric and differential thermal analysis (TG/DTA) under a flow of various ambient gas. It is found that the thermal stability of Ga-EDTA complexes is not much influenced by the ambient gases. In the case of ammonia ambient, with increasing the temperature, the mass loss undergoes four steps due to thermal decomposition and release of organic groups, resulting in Ga-iminodiacetate (IMDA), Ga-glycinate, and other Ga-related compounds, followed by the formation of GaN and carbon elimination. X-ray diffraction (XRD) patterns of the residue revealed that the temperature of GaN crystallization ranged from about 600 to 1100 °C and that the crystal quality improved with temperature. GaN powders of high crystal quality was obtained at 1100 °C.

Liu, Yu-Huai; Koide, Shinya; Miyake, Hideto; Hiramatsu, Kazumasa; Nakamura, Atsushi; Nambu, Nobuyoshi

2007-12-01

24

Reactions of copper(II) chloride in solution: facile formation of tetranuclear copper clusters and other complexes that are relevant in catalytic redox processes.  

PubMed

Mixing CuCl2?2?H2O with benzylamine in alcoholic solutions led to an extremely colorful chemistry caused by the formation of a large number of different complexes. Many of these different species could be structurally characterized. These include relatively simple compounds such as [Cu(L(1))4Cl2] (L(1) = benzylamine) and (HL(1))2[CuCl4]. Most interestingly is the easy formation of two cluster complexes, one based on two cluster units Cu4OCl6(L(1))4 connected through one [Cu(L(1))2Cl2] complex and one based on a cubane-type cluster ([Cu4O4](C11H14)4Cl4). Both clusters proved to be highly reactive in a series of oxidation reactions of organic substrates by using air or peroxides as oxidants. Furthermore, it was possible to isolate and structurally characterize ([Cu(L(1))Cl]3 and [Cu(benz2mpa)2]CuCl2 (benz2mpa = benzyl-(2-benzylimino-1-methyl-propylidene)-amine), two copper(I) complexes that formed in solution, demonstrating the high redox activity of the cluster systems. In addition, it was possible to solve the molecular structures of the compounds Cu4OCl6(MeOH)4, [Cu(MeOH)2Cl2], [Cu(aniline)2Cl2], and an organic side product (HC13 H19 NOCl). In fact all determined structures are of a known type but the chemical relation between these compounds could be explained for the first time. The paper describes these different compounds and their chemical equilibria. Some of these complexes seem to be relevant in catalytic oxidation reactions and their reactivity is discussed in more detail. PMID:23447462

Löw, Sabine; Becker, Jonathan; Würtele, Christian; Miska, Andreas; Kleeberg, Christian; Behrens, Ulrich; Walter, Olaf; Schindler, Siegfried

2013-04-22

25

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

PubMed

Boron, at sub-ppm levels, in U3O8 powder and aluminum metal, was determined using complex formation and dynamically modified reversed-phase high-performance liquid chromatography (RP-HPLC). Curcumin was used for complexing boron extracted with 2-ethyl-1,3-hexane diol (EHD). Separation of complex from excess reagent and thereafter its determination using the online diode array detector (DAD) was carried out by HPLC. Calibration curve was found to be linear for boron amounts in the sample ranging from 0.02 microg to 0.5 microg. Precision of about 10% was achieved for B determination in samples containing less than 1 ppmw of boron. The values obtained by HPLC were in good agreement with the data available from other analytical techniques. The precision in the data obtained by HPLC was much better compared to that reported by other techniques. The present hyphenated methodology of HPLC and complex formation reaction is interesting because of cost performance, simplicity, versatility and availability when compared to other spectroscopic techniques like ICP-MS and ICP-AES. PMID:18371924

Rao, Radhika M; Aggarwal, Suresh K

2008-04-15

26

Complexation reactions in aquatic systems  

Microsoft Academic Search

This book discusses the properties, reactivities, and ecological implications of all chemically ill-defined natural complexants in aquatic systems. Analytical and theoretical aspects are presented simultaneously, covering speciation parameters, nature, and properties of organic and inorganic ligands in natural waters, their reactions with inorganic elements (particularly metals), and methods of measurement of speciation parameters.

J. Buffle; R. A. Chalmers

1988-01-01

27

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

NASA Astrophysics Data System (ADS)

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

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

1997-01-01

28

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)

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 ?-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 ?m) 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*.

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

29

Ab initio study on the mechanism of C2H2++NH3 reaction: Efficient charge transfer and proton transfer processes competing with stable complex formation  

NASA Astrophysics Data System (ADS)

High level ab initio calculations have been performed to investigate the mechanism of the ion-molecule reaction NH3+C2H2+. Three channels, covalent complex formation (CC), proton transfer (PT), and charge transfer (CT) have been studied. Among the two pathways found for the PT channel, one leads the reactants NH3+C2H2+ to NH4++C2H(2?) through a moderately bound complex without any barrier, and the other leads NH3++C2H2 to the H-atom transferred products NH4++C2H(2?+) with a modest barrier. These findings support the fast ``stripping'' mechanism proposed by Anderson et al. As to the CC channel, several isomers of C2H5N+ and the isomerization transition states have been located. No significant barrier relative to the reactants has been found on either the ground or the 2A'' excited state. To rationalize the experimental fact that no CC channel products have been observed, it is argued that the reactants NH3+C2H2+ correlate adiabatically to excited states of covalent C2H5N+ species, whose formation requires significant alternation of the C2H2+ geometry and electronic structure. Therefore, the system is most likely to follow the PT or the CT channel instead of visiting the CC channel. For the CT channel, limited potential energy surface scans of the three electronic states (1,2 2A'+2A'') indicate that CT at different approach angles or between electronic states of different symmetries (A'-->A',A''-->A') may produce final products of different characteristics, and might account for the two pathways proposed by Anderson et al.

Cui, Qiang; Morokuma, Keiji

1998-03-01

30

Seeking a mechanistic analogue of the water-gas shift reaction: carboxamido ligand formation and isocyanate elimination from complexes containing the Tp'PtMe fragment.  

PubMed

A series of stable, isolable Tp'Pt(IV) carboxamido complexes of the type Tp'PtMe(2)(C(O)NHR) (R = Et, (n)Pr, (i)Pr, (t)Bu, Bn, Ph) has been synthesized by addition of amide nucleophiles to the carbonyl ligand in Tp'Pt(Me)(CO) followed by trapping of the Pt(II) intermediate with methyl iodide as the methylating reagent. These compounds mimic elusive intermediates resulting from hydroxide addition to platinum-bound CO in the Water-Gas Shift Reaction (WGSR). Seeking parallels to WGSR chemistry, we find that deprotonation of the carboxamido NH initiates elimination and the isocyanate-derived products form; the resulting platinum fragment can be protonated to reoxidize the metal center and generate Tp'PtMe(2)H, the synthetic precursor to Tp'Pt(Me)(CO). Mechanistic studies on the formation of and elimination from Tp'PtMe(2)(C(O)NHR) suggest a stepwise process with deprotonation from a Pt(IV) species as the key step prompting elimination. PMID:22563841

Frauhiger, Bryan E; Ondisco, Matthew T; White, Peter S; Templeton, Joseph L

2012-05-30

31

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)

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, ? G°, ? H° and ? 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.

Dehghani, Hossein; Mansournia, Mohammad Reza

2009-10-01

32

Unusual complex formation and chemical reaction of haloacetate anion on the exterior surface of cucurbit[6]uril in the gas phase.  

PubMed

Noncovalent interactions of cucurbit[6]uril (CB[6]) with haloacetate and halide anions are investigated in the gas phase using electrospray ionization ion mobility mass spectrometry. Strong noncovalent interactions of monoiodoacetate, monobromoacetate, monochloroacetate, dichloroacetate, and trichloroacetate on the exterior surface of CB[6] are observed in the negative mode electrospray ionization mass spectra. The strong binding energy of the complex allows intramolecular S(N)2 reaction of haloacetate, which yields externally bound CB[6]-halide complex, by collisional activation. Utilizing ion mobility technique, structures of exteriorly bound CB[6] complexes of haloacetate and halide anions are confirmed. Theoretically determined low energy structures using density functional theory (DFT) further support results from ion mobility studies. The DFT calculation reveals that the binding energy and conformation of haloacetate on the CB[6] surface affect the efficiency of the intramolecular S(N)2 reaction of haloacetate, which correlate well with the experimental observation. PMID:22864828

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

2012-10-01

33

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

34

Selective formation of cis-diacyl, cis-PPh(2)R rhodium(III) complexes by the reaction of rhodium(III) cis-diacyl, trans-PPh(2)R complexes with aliphatic diamines.  

PubMed

The cis-diacyl, trans-PPh(2)R complex [RhCl(PPh(2)(o-C(6)H(4)CO))(2)(pyridine)] () reacts with substituted aliphatic diamines to afford selectively cationic cis-diacyl, cis-PPh(2)R, diamine derivatives [Rh(PPh(2)(o-C(6)H(4)CO))(2)(NN')](+) (NN' = 1,2-diphenylethylenediamine, 2; 1,2-propanediamine, 3; N-methylethylenediamine, 4; N,N-dimethylethylenediamine, 5; N,N'-dimethylethylenediamine, 6; N,N,N'-trimethylethylenediamine, 7) with high stereoselectivity depending on the N-donor ligand employed. Complexes 2 and 3 contain a single isomer, while 4 is a mixture of two isomers, 4a and 4b. Formation of 4a occurs first and is followed by isomerisation to 4b until the equilibrium 4a:4b = 1:4 ratio is attained. In contrast, 5 and 6 contain a single isomer. More basic amino groups prefer positions trans to an acyl group while less basic amino groups are trans to a phosphine group. The preferred intramolecular N-H...O hydrogen bond formation between an amino and an acyl coordinated ligands, trans to the phosphorus atoms, appears to be relevant to the selectivity observed. 7 is a mixture of two isomers 7a and 7b in a 7a:7b = 5.7:1 ratio. N,N,N',N'-tetramethylethylenediamine or N,N'-diphenylethylenediamine led to the elimination of the N-donor ligands and the formation of a mixture of isomers of [Rh(2)(mu-Cl)(mu-PPh(2)(o-C(6)H(4)CO))(2)(PPh(2)(o-C(6)H(4)CO))(2)](+) (), where the Rh atoms are triply bridged by two acyl groups in a head-to-tail arrangement and by a chloride. The reaction of [Rh(PPh(2)(o-C(6)H(4)CO))(2)(ndmeen)]ClO(4) (5) with acids led to the displacement of the diamine and the formation of a [8a](+):[8b](+):[8c](+) = 1:1:3 mixture. 8c, containing the weakest sigma-donor oxygen atoms trans to the strongest sigma-donor acyl groups, represents the most electronically favourable geometry for . All the complexes were fully characterized spectroscopically. Single crystal X-ray diffraction analysis was performed on 5, 6, 8a and 8b. PMID:19885535

Garralda, María A; Hernández, Ricardo; Pinilla, Elena; Torres, M Rosario; Zarandona, Malkoa

2009-11-28

35

COMPLEX TRAUMA, COMPLEX REACTIONS: ASSESSMENT AND TREATMENT  

Microsoft Academic Search

Complex trauma occurs repeatedly and escalates over its duration. In families, it is exemplified by domestic violence and child abuse and in other situations by war, prisoner of war or refugee status, and human trafficking. Complex trauma also refers to situations such as acute\\/chronic illness that requires intensive medical intervention or a single traumatic event that is calamitous. Complex trauma

Christine A. Courtois

2004-01-01

36

Getting more out of a Job plot: determination of reactant to product stoichiometry in cases of displacement reactions and n:n complex formation.  

PubMed

The method of continuous variation (often referred to as Job's method) is an easy and common method for the determination of the reactant stoichiometry of chemical equilibria. The traditional interpretation of Job plots has been limited to complex association equilibria of the type nA + mB ? A(n)B(m), while little focus has been placed upon displacement type reactions (e.g., A + B ? C + D), which can give Job plots that look quite similar. We developed a novel method that allows the user to accurately distinguish between 1:1 complex association, 2:2 complex association, and displacement reactions using nothing more than a pocket calculator. This method involves preparing a Job plot of the system under investigation (using regularly spaced mole fractions), normalizing the measured quantities (such as the concentration of A(n)B(m) or C for the above reactions) to their maximum value (i.e., at mole fraction 0.5), and determining the sum of the normalized values. This sum is then compared with theoretically predicted normalized sum values that depend on the nature of the equilibrium. The relationship between, on the one hand, the sum of the normalized values and, on the other hand, the reaction equilibrium constant and the concentration of the stock solutions used for the preparation of the Job plot is also explored. The use of this new technique for the interpretation of Job plots permits users to readily determine information that can be obtained otherwise only with laborious additional experiments, as illustrated by the analysis of four Job plots taken from the literature. PMID:21895009

Olson, Eric J; Bühlmann, Philippe

2011-10-21

37

Markovian dynamics on complex reaction networks  

NASA Astrophysics Data System (ADS)

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

Goutsias, J.; Jenkinson, G.

2013-08-01

38

Reaction rate constant of methane clathrate formation  

Microsoft Academic Search

Particle size distribution measurements were performed during the growth stage of methane hydrate formation in a semi-batch stirred tank crystallizer. Experiments were carried out at temperatures between 275.1 and 279.2K and pressures ranging from 3873 to 5593kPa. The reaction rate constant of methane hydrate formation was determined using the model of Bergeron and Servio (AIChE J 2008;54:2964). The experimental reaction

Sebastien Bergeron; Juan G. Beltrán; Phillip Servio

2010-01-01

39

Complex-formation reactions of dicholoro(S-methyl-L-cysteine)palladium(II) with bio-relevant ligands. Labilization induced by S-donor chelates.  

PubMed

The complex-formation equilibria of [Pd(SMC)(H2O)2]+, where SMC = S-methyl-l-cysteinate, with bio-relevant ligands such as amino acids, peptides, dicarboxylic acids and DNA constituents were studied and their formation constants were determined. The binding mode of the ligands containing various functional groups was studied and the speciation diagrams were evaluated. The kinetics of base hydrolysis of amino acid esters bound to [Pd(SMC)(H2O)2]+ was studied in aqueous solution at 25 degrees C and 0.1 M ionic strength. The effect of solvent polarity and temperature on the hydrolysis of coordinated glycine methyl ester was investigated. The activation parameters are evaluated and discussed. PMID:18239833

Shehata, Mohamed R; Shoukry, Mohamed M; Nasr, Fatma M H; van Eldik, Rudi

2008-02-14

40

Equilibrium investigation of complex formation reactions involving copper(II), nitrilo-tris(methyl phosphonic acid) and amino acids, peptides or DNA constitutents. The kinetics, mechanism and correlation of rates with complex stability for metal ion promoted hydrolysis of glycine methyl ester  

Microsoft Academic Search

The complex formation reactions of [Cu(NTP)(OH2)] (NTP?=?nitrilo-tris(methyl phosphonic acid)) with some selected bio-relevant ligands containing different functional groups, are investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show that the ternary complexes are formed in a stepwise mechanism whereby NTP binds to copper(II), followed by coordination of amino acid, peptide or DNA. Copper(II) is found

Ahmed A. El-Sherif; Mohamed M. Shoukry

2006-01-01

41

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

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

42

Complex formation of metal ions with xylenol orange  

SciTech Connect

The complex formation of metals with xylenol orange, purified by gel filtration on Molselekt G-10, was studied. The spectrophotometric characteristics of the complexes formed were refined. The chemistry of the reaction with xylenol orange was studied. A method was developed for the determination of aluminum in copper alloys.

Tikhonov, V.N.

1987-01-20

43

Formation of complex films with water-soluble CTAB molecules  

NASA Astrophysics Data System (ADS)

This communication reports the formation of complex Langmuir monolayer at the air-water interface with the water-soluble N-cetyl N, N, N-trimethyl ammonium bromide (CTAB) molecules when interacted with the stearic acid (SA) molecules. The reaction kinetics of the formation of the CTAB-SA complex was monitored by observing the surface pressure versus time graph. Multilayered LB films of this complex doped with Congo red was successfully formed onto a quartz substrate. UV-Vis absorption and steady-state fluorescence spectroscopic characteristics of this doped LB films confirms the successful incorporation of Congo red molecules in to the CTAB-SA complex films.

Biswas, S.; Hussain, S. A.; Deb, S.; Nath, R. K.; Bhattacharjee, D.

2006-11-01

44

Complex Formation between Dimethyl Methylphosphonate and Hexafluoroisopropanol.  

National Technical Information Service (NTIS)

A solvent/water partitioning method was used to measure the complex formation between dimethyl methylphosphonate (DMMP) and hexafluoroisopropanol (HFIP). The highest formation constant was obtained when n-hexane was used as the partitioning solvent. Other...

D. C. Leggett

1990-01-01

45

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

PubMed

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

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

2010-03-01

46

Photosynthetic reaction center complexes from heliobacteria  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

47

Reactions of Ph3Sb=S with Copper(I) Complexes Supported by N-Donor Ligands: Formation of Stable Adducts and S-Transfer Reactivity  

PubMed Central

In the exploration of sulfur-delivery reagents useful for synthesizing models of the tetracopper-sulfide cluster of nitrous oxide reductase, reactions of Ph3Sb=S with Cu(I) complexes of N,N,N’,N’-tetramethyl-2R,3R-cyclohexanediamine (TMCHD) and 1,4,7-trialkyltriazacyclononanes (R3tacn; R = Me, Et, iPr) were studied. Treatment of [(R3tacn)Cu(NCCH3)]SbF6 (R = Me, Et, or iPr) with one equivalent of S=SbPh3 in CH2Cl2 yielded adducts [(R3tacn)Cu(S=SbPh3)]SbF6 (1–3), which were fully characterized, including by X-ray crystallography. The adducts slowly decayed to [(R3tacn)2Cu2(µ-?2: ?2-S2)]2+ species (4–6) and SbPh3, or more quickly in the presence of additional [(R3tacn)Cu(NCCH3)]SbF6 to 4–6 and [(R3tacn)Cu(SbPh3)]SbF6 (7–9). The results of mechanistic studies of the latter process were consistent with rapid intermolecular exchange of S=SbPh3 between 1–3 and added [(R3tacn)Cu(NCCH3)]SbF6, followed by conversion to product via a dicopper intermediate formed in a rapid pre-equilibrium step. Key evidence supporting this step came from the observation of saturation behavior in a plot of the initial rate of loss of 1 versus the initial concentration of [(Me3tacn)Cu(NCCH3)]SbF6. Also, treatment of [(TMCHD)Cu(CH3CN)]PF6 with S=SbPh3 led to the known tricopper cluster [(TMCHD)3Cu3(µ3-S)2](PF6)3 in good yield (79%), a synthetic procedure superior to that previously reported (Brown, E. C.; York, J. T.; Antholine, W. E.; Ruiz, E.; Alvarez, S.; Tolman, W. B. J. Am. Chem. Soc. 2005, 127, 13752–13753).

Yang, Lei; Tehranchi, Jacqui; Tolman, William B.

2011-01-01

48

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

NASA Astrophysics Data System (ADS)

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.

El-Shall, M. S.

2010-04-01

49

Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions  

PubMed Central

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.

SUZUKI, Toshinori

2013-01-01

50

In vacuo formation of peptide-metal coordination complexes  

PubMed Central

Here we report on the reaction of rhenate anions (ReO3?) with multiply protonated peptide cations in a quadrupole linear ion trap mass spectrometer. These reactions effect the formation of an anion–cation complex that, upon collisional activation, dissociates along the peptide backbone rather than by displacement of the anion. Cleavage of the peptide backbone, with anion retention, leads us to conclude the anion–cationcomplexmust be tightly bound, most probably through coordination chemistry. We describe this chemistry and detail the possible application of such ion attachment reactions to the characterization of intact proteins.

McAlister, Graeme C.; Kiessel, Sharon E.B.; Coon, Joshua J.

2009-01-01

51

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

Microsoft Academic Search

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

C. Koretsky

2000-01-01

52

Complex-anisotropy-induced pattern formation in bistable media.  

PubMed

A construct of anisotropy in bistable media is adopted to characterize the effects of anisotropy on pattern formation by means of anisotropic line tension. A velocity curvature relation is further derived to account for the anisotropic wave propagations. Stability analysis of transverse perturbations indicates that a sufficiently strong complex anisotropy can induce dynamical instabilities and even lead to a breakup of the wave patterns. Numerical simulations show that complex anisotropy can induce rich spatiotemporal behaviors in bistable media. The results of analysis and simulations demonstrate that this method successfully incorporates complex anisotropy into the reaction diffusion model and has general significance. PMID:19391804

He, Zhi Zhu; Liu, Jing

2009-02-01

53

The platinum hydrido-methyl complex: A frozen reaction intermediate?  

SciTech Connect

Methane activation by transition metals has been a topic of growing interest during the past decade, due to economic interest in methane conversion and chemistry. Reactions of platinum-argon complexes Pt{sup +}Ar{sub m}, m = 1--6, with methane (CH{sub 4}) and methane-d{sub 4} (CD{sub 4}) were investigated by means of FT-ICR mass spectrometry and DFT calculations. Ligand exchange reactions are observed for Pt{sup +}Ar{sub m}, m = 2--6, in which up to four argon ligands are replaced by methane. In contrast, the bare platinum ion and platinum solvated with one argon ligand lead to the formation of a platinum-carbene complex. Gibbs free enthalpies from ligand exchange reactions of Pt{sup +}CH{sub 4} with CD{sub 4} and H{sub 2}O provide evidence for the inserted hydrido-methyl complex HPt{sup +}CH{sub 4} with CD{sub 4} (and the reverse reaction). This is attributed to the inability of the platinum cation to form more than three covalent bonds.

Achatz, U.; Beyer, M.; Joos, S.; Fox, B.S.; Niedner-Schatteburg, G.; Bondybey, V.E.

1999-10-14

54

Reaction Dynamics of the Bromine-Bromoform Complex in Solution  

NASA Astrophysics Data System (ADS)

We have followed the evolution of the bromine species that arise from the photolysis of bromoform in the condensed phase. Solvent caging promotes the formation of iso-bromoform (CHBr_2-Br), which can then release a Br atom by breaking the newly formed Br-Br bond. This ejected Br can form a van der Waals complex (Br-CHBr_3) with a nearby un-photolyzed bromoform molecule, which is stable during our 1 ns time-window. Using the van der Waals complex as a reservoir for Br atoms, we now proceed to drive hydrogen abstraction from CHBr_3 by Br. Estimates indicate that the barrier to this reaction is a few thousand wavenumbers. Our goal is to introduce excitation into the C-H stretching motion of a nearby solvent CHBr_3 to access the activated complex region of the bimolecular potential energy surface.

Preston, Thomas J.; Dutta, Maitreya; Crim, F. Fleming

2010-06-01

55

Disulfirm-ethanol reaction: a complex mechanism  

SciTech Connect

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.

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

1986-03-01

56

Molecular Matchmakers. [Formation of stable DNA-protein complexes  

SciTech Connect

Molecular matchmakers are a class of proteins that use the energy released from the hydrolysis of adenosine triphosphate to cause a conformational change in one or both components of a DNA binding protein pair to promote formation of a metastable DNA-protein complex. After matchmaking the matchmaker dissociates from the complex, permitting the matched protein to engage in other protein-protein interactions to bring about the effector function. Matchmaking is most commonly used under circumstances that require targeted, high-avidity DNA binding without relying solely on sequence specificity. Molecular matchmaking is an extensively used mechanism in repair, replication, and transcription and most likely in recombination and transposition reactions, too.

Sancar, A. (Univ. of North Carolina School of Medicine, Chapel Hill (United States)); Hearst, J.E. (Lawrence Berkely Lab., CA (United States))

1993-03-05

57

Reactions and mass spectra of complex particles using Aerosol CIMS  

NASA Astrophysics Data System (ADS)

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.

Hearn, John D.; Smith, Geoffrey D.

2006-12-01

58

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

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

Cho, Han-Gook; Andrews, Lester

2009-08-14

59

Complex formation between polyelectrolytes and ionic surfactants  

NASA Astrophysics Data System (ADS)

The interaction between polyelectrolyte and ionic surfactant is of great importance in different areas of chemistry and biology. In this Letter we present a theory of polyelectrolyte-ionic-surfactant solutions. The new theory successfully explains the cooperative transition observed experimentally, in which the condensed counterions are replaced by ionic surfactants. The transition is found to occur at surfactant densities much lower than those for a similar transition in non-ionic polymer-surfactant solutions. Possible application of DNA surfactant complex formation to polynucleotide delivery systems is also mentioned.

Kuhn, Paulo S.; Levin, Yan; Barbosa, Marcia C.

1998-12-01

60

Formation and characterization of thioglycolic acid-silver cluster complexes.  

PubMed

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. PMID:23609144

Bellina, Bruno; Antoine, Rodolphe; Broyer, Michel; Gell, Lars; Sanader, Željka; Mitri?, Roland; Bona?i?-Koutecký, Vlasta; Dugourd, Philippe

2013-06-21

61

Assessing Child and Adolescent Complex Traumatic Stress Reactions  

Microsoft Academic Search

Children and adolescents exposed to traumatic stressors may develop severe and persistent complex traumatic stress reactions. A framework for conceptualizing and assessing children's and adolescents' complex traumatic stress reactions as forms of impaired self-regulation is described. Psychometric measures for the assessment of posttraumatic dysregulation of emotion, cognition, behavior, and bodily functioning are also described. The question of whether children and

Julian D. Ford

2011-01-01

62

Reaction Kinetics of Fuel Formation for In-Situ Combustion  

Microsoft Academic Search

Chemical reactions believed to cause fuel formation for in-situ combustion have been studied and modeled. A thin, packed bed of sand\\/oil mixture is heated under nitrogen flow at linearly increasing temperatures, simulating the approach of a combustion front. Analysis of gases produced from the reaction cell revealed that pyrolysis of crude oil in porous media goes through three overlapping stages:

Sidqi Abu-Khamsin; William Brigham; Henry Ramey Jr.

1988-01-01

63

Interactive formation control in complex environments.  

PubMed

The degrees of freedom of a crowd is much higher than that provided by a standard user input device. Typically, crowd-control systems require multiple passes to design crowd movements by specifying waypoints, and then defining character trajectories and crowd formation. Such multi-pass control would spoil the responsiveness and excitement of real-time control systems. In this paper, we propose a single-pass algorithm to control a crowd in complex environments. We observe that low-level details in crowd movement are related to interactions between characters and the environment, such as diverging/merging at cross points, or climbing over obstacles. Therefore, we simplify the problem by representing the crowd with a deformable mesh, and allow the user, via multitouch input, to specify high-level movements and formations that are important for context delivery. To help prevent congestion, our system dynamically reassigns characters in the formation by employing a mass transport solver to minimize their overall movement. The solver uses a cost function to evaluate the impact from the environment, including obstacles and areas affecting movement speed. Experimental results show realistic crowd movement created with minimal high-level user inputs. Our algorithm is particularly useful for real-time applications including strategy games and interactive animation creation. PMID:24356364

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

2014-02-01

64

C?H Bond Activation during and after the Reactions of a Metallacyclic Amide with Silanes: Formation of a ?-Alkylidene Hydride Complex, Its H-D Exchange, and ?-H Abstraction by a Hydride Ligand.  

PubMed

Metallacyclic complex [(Me2 N)3 Ta(?(2) -CH2 SiMe2 NSiMe3 )] (3) undergoes C?H activation in its reaction with H3 SiPh to afford a Ta/?-alkylidene/hydride complex, [(Me2 N)2 {(Me3 Si)2 N}Ta(?-H)2 (?-C-?(2) -CHSiMe2 NSiMe3 )Ta(NMe2 )2 ] (4). Deuterium-labeling studies with [D3 ]SiPh show H-D exchange between the Ta?D?Ta unit and all methyl groups in [(Me2 N)2 {(Me3 Si)2 N}Ta(?-D)2 (?-C-?(2) -CHSiMe2 NSiMe3 )Ta(NMe2 )2 ] ([D2 ]-4) to give the partially deuterated complex [Dn ]-4. In addition, 4 undergoes ?-H abstraction between a hydride and an NMe2 ligand and forms a new complex [(Me2 N){(Me3 Si)2 N}Ta(?-H)(?-N-?(2) -C,N-CH2 NMe)(?-C-?(2) -C,N-CHSiMe2 NSiMe3 )Ta(NMe2 )2 ] (5) with a cyclometalated, ?(2) -imine ligand. These results indicate that there are two simultaneous processes in [Dn ]-4: 1)?H-D exchange through ?-bond metathesis, and 2)?H?D elimination through ?-H abstraction (to give [Dn ]-5). Both 4 and 5 have been characterized by single-crystal X-ray diffraction studies. PMID:24682935

Wang, Li; Hunter, Seth C; Song, Zhimin; Steren, Carlos A; Chen, Tianniu; Wei, Zhenhong; Cai, Hu; Xue, Zi-Ling

2014-05-12

65

Ferrous complexes in the catalase reaction  

Microsoft Academic Search

Résumé L'auteur critique l'idée que la polarographie démontra l'existence de complexes d'hématine ferreuse avec le peroxide, actifs dans la catalyse. D'autres expériences montrent que les dérivés de l'hématine et du peroxyde sont instables et provoquent la dégradation de la porphyrine. Les complexes de la catalase et du peroxyde ne sont pas actifs polarographiquement et contiennent probablement le fer à l'état

P. Nicholls

1963-01-01

66

Star formation activities in Sharpless 311 complex  

NASA Astrophysics Data System (ADS)

The H II region NGC 2467, also known as Sharpless 311, is located at a distance of 4.1 kpc. This region is dominated by one O6 Vn star, HD 64315. There are also two stellar clusters in the area, Haffner 19 (H19) and Haffner 18ab (H18ab). Hubble Space Telescope (HST) Advanced Camera for Survey (ACS) data shows a large number of brightened ridges and cloud fragments in NGC 2467 (De Macro et al. 2006). Recently, Sinder et al. (2009) found several YSO candidates at the edge of the H II region, indicating a possible site of induced star formation. We present the results of optical and near-infrared (NIR) observations with the KISO and CTIO telescope, to search for very low mass young stellar objects in this region. We construct JHK color-color and J - H /J to identify very low luminosity young stellar objects and to estimate their masses. Based on these color-color and color-magnitude diagrams, we identified a population of embedded YSO candidates with infrared excesses (Class I and Class II), associated with the region. Based on these observations, we will present the nature of these YSO candidates and associated cluster properties. We will also try to interpret the possible star formation scenario in this complex.

Yadav, R. K.; Pandey, A. K.; Sharma, Saurabh

67

Reaction synthesis and formation mechanism of barium hexaboride  

Microsoft Academic Search

The synthesis and formation mechanism of BaB6 powder by the reaction of BaCO3 with B4C and carbon was investigated systematically in the present study. The influences of heating temperature and holding time on the reaction products were studied by X-ray diffractometry, and the morphologies of BaB6 were investigated by scanning electron microscopy. The interaction in the BaCO3–B4C–C system by which

Guanghui Min; Shuqi Zheng; Zengda Zou; Huashun Yu; Jiande Han

2003-01-01

68

Modeling of solid–liquid equilibria for systems with solid-complex phase formation  

Microsoft Academic Search

The Perturbed-Chain SAFT (PC-SAFT) equation of state (EOS) is applied to model the solid–liquid equilibria (SLE) of binary and ternary systems showing a solid-complex phase formation. Modeling results for mixtures composed of associating components, e.g. water, alcohols, phenol, bisphenol A (BPA), as well as acetamide are presented. The solid-complex phase formation is modeled as a chemical reaction between species in

Feelly Tumakaka; Igor V. Prikhodko; Gabriele Sadowski

2007-01-01

69

Intermolecular dynamics and exciplex formation of the 1-cyanonaphthalene\\/triethylamine van der Waals complex  

Microsoft Academic Search

The exciplex formation dynamics of the 1-cyanonaphthalene\\/triethylamine van der Waals complex upon excitation has been examined under collision free conditions. Mode-specificity has been found in the excitation of a combination band between intra- and intermolecular vibrational modes in the S1 state of the vdW complex to promote the exciplex formation reaction. The specificity is lost at higher excess energies since

Hiroyuki Saigusa; Michiya Itoh; Masaaki Baba; Ichiro Hanazaki

1987-01-01

70

Reaction of (mu-oxo)diiron(III) core with CO2 in N-methylimidazole: formation of mono(mu-carboxylato)(mu-oxo)diiron(III) complexes with N-methylimidazole as ligands.  

PubMed

Several iron(III) complexes with N-methylimidazole (N-MeIm) as the ligand have been synthesized by using N-MeIm as the solvent. Under anaerobic conditions, [Fe(N-MeIm)(6)](ClO(4))(3) (1) reacts with stoichiometric amounts of water in N-MeIm to afford the (mu-oxo)diiron(III) complex, [Fe(2)(mu-O)(N-MeIm)(10)](ClO(4))(4) (3). Exposure of a solution of 3 in N-MeIm to stoichiometric and excess CO(2) gives rise to the (mu-oxo)(mu-carboxylato)diiron(III) species [Fe(2)(mu-O)(mu-HCO(2))(N-MeIm)(8)](ClO(4))(3) (4) and the methyl carbonate complex [Fe(2)(mu-O)(mu-CH(3)OCO(2))(N-MeIm)(8)](ClO(4))(3) (5), respectively. Formation of the formato-bridged complex 4 upon fixation of CO(2) by 3 in N-MeIm is unprecedentated. Methyl transfer from N-MeIm to a bicarbonato-bridged (mu-oxo)diiron(III) intermediate appears to give rise to 5. Complex 3 is a good starting material for the synthesis of (mu-oxo)mono(mu-carboxylato)diiron(III) species [Fe(2)(mu-O)(mu-RCO(2))(N-MeIm)(8)](ClO(4))(3) (where R = H (4), CH(3) (6), or C(6)H(5) (7)); addition of the respective carboxylate ligand in stoichiometric amount to a solution of 3 in N-MeIm affords these complexes in high yields. Attempts to add a third bridge to complexes 4, 6, and 7 to form the (mu-oxo)bis(mu-carboxylato)diiron(III) species result in the isolation of the previously known triiron(III) mu-eta(3)-oxo clusters [[Fe(mu-RCO(2))(2)(N-MeIm)](3)O](ClO(4)) (8). The structures of 3, 4, 6, and 7 allow one, for the first time, to inspect the various features of the [Fe(2)(mu-O)(mu-RCO(2))](3+) moiety with no strain from the ligand framework. PMID:12611539

Marlin, Dana S; Olmstead, Marilyn M; Mascharak, Pradip K

2003-03-10

71

Formation of superheavy elements in cold fusion reactions  

Microsoft Academic Search

The process of the synthesis of superheavy elements (SHEs) is not yet understood completely. In the presented work we make an attempt to describe the cold fusion reactions of the type X+(Pb,Bi)-->SHE+1n at subbarrier energies. The process of the formation of SHEs is subdivided into three steps. (1) The capture of two spherical nuclei and the formation of a common

V. Yu. Denisov; S. Hofmann

2000-01-01

72

EXFOR SYSTEMS MANUAL NUCLEAR REACTION DATA EXCHANGE FORMAT.  

SciTech Connect

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.

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

73

Effect of inclusion complex on nitrous acid reaction with flavonoids  

NASA Astrophysics Data System (ADS)

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

Khalafi, Lida; Rafiee, Mohammad; Sedaghat, Sajjad

2011-10-01

74

Diffusion impregnation of alloys under conditions of complex formation  

SciTech Connect

In most cases, diffusion impregnation of alloys with elements for the purpose of improving their service properties occurs with chemical interaction with the constituents of the base. Such processes are described within the limits of the model of reaction diffusion, assuming the formation and growth of new continuous layers by the Fick equation. At the same time, instantaneous reaction of the elements is assumed, as the result of which the rate of the whole process is limited by diffusion. Together with this, diffusion processes and chemical transformations occur simultaneously, as the result of which continuous phases are not formed (internal oxidation, nitriding, etc.). The purpose of this work was an analytical investigation of diffusion impregnation by element A from a constant source of a flat specimen initially uniformly alloyed with a mobile impurity B. The model presented makes it possible to investigate the initial stage of homogeneous formation of complexes and to reveal their influence on the kinetics of redistribution of the diffusing elements.

Pavlina, V.S.; Matychak, Y.S.

1985-05-01

75

Bimolecular chemical reactions on weighted complex networks.  

PubMed

We investigate the kinetics of bimolecular chemical reactions A+A?0 and A+B?0 on weighted scale-free networks (WSFNs) with degree distribution P(k)?k^{-?} . On WSFNs, a weight w{ij} is assigned to the link between node i and j . We consider the symmetric weight given as w{ij}=(k{i}k{j})^{?} , where k{i} and k{j} are the degree of node i and j . The hopping probability T{ij} of a particle from node i to j is then given as T{ij}?(k{i}k{j})^{?} . From a mean-field analysis, we analytically show in the thermodynamic limit that the kinetics of A+A?0 and A+B?0 are identical and there exist two crossover ? values, ?{1c}=?-2 and ?{2c}=(?-3)/2 . The density of particles ?(t) algebraically decays in time t as t^{-?} with ?=1 for ?

Kwon, Sungchul; Choi, Woosik; Kim, Yup

2010-08-01

76

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

PubMed

Self-assembly from mixed dispersions of three sizes of monodisperse polystyrene nanoparticles, large (L), medium (M), and small (S), was controlled by coating each particle type with either a monofunctional or bifunctional polymer capable of participating in specific complexation reactions. The complexation reactions were (1) complexation between phenolic polymers and polyethylene glycol (PEG) containing polymers and (2) condensation of phenylboronic acid containing polymers with polyols. These complexation reactions function independently and can be "turned off" independently; phenylboronic acid complexation was reversed by lowering the pH, whereas the interactions of phenolic copolymers with PEG copolymers could be reversed by adding excess PEG homopolymer. The specificity and reversibility of the interactions was demonstrated by the formation of simple binary aggregates from mixtures. The bifunctional copolymers were poly(vinyl phenol-co-diallyldimethyl ammonium chloride), Ph-DADMAC, and poly(3-acrylamide phenylboronic acid-co-PEG methacrylate), PBA-PEG. The monofunctional polymer was polyvinylalcohol, PVA. Ph-DADMAC forms complexes with PBA-PEG (H-bonding) and with anionic surfaces or polymers (electrostatic/polyelectrolyte complexation). PBA-PEG complexes with Ph-DADMAC (H-bonding) and with PVA (boronate ester formation). PVA does not interact with Ph-DADMAC; therefore, PVA coated particles do not deposit onto Ph-DADMAC coated particles. PMID:22251456

Zhang, Dan; Pelton, Robert

2012-02-14

77

Spectrophotometric study of molecular complex formation between o-chloranil and a series of methylated pyridines  

NASA Astrophysics Data System (ADS)

o-Chloranil has been shown to form 1:1 molecular complexes with pyridine and 2-, 3- and 4-picolines in CCl 4 medium. Isosbestic points have been found but charge-transfer bands could not be detected. The formation constants of the complexes exhibit a very good linear free energy relationship from which the Hammett ? parameter for the complexation reaction is found to be -3.67.

Ray, Asim Kumar; Bhattacharya, Sumanta; Banerjee, Manas; Mukherjee, Asok K.

2002-05-01

78

Reactions of sulfur dioxide with pentaaquoorganochromium(III) complexes and trispolypyridinechromium(II) complexes  

Microsoft Academic Search

Chapter I describes the kinetics and mechanism of the reaction between sulfur dioxide and (HâO)âCrR\\/sup 2 +\\/ complexes. Parallels between this reaction and other electrophilic reactions of the (HâO)âCrR\\/sup 2 +\\/ complexes are drawn. The occurrence of two types of inorganic products is explained. Chapter II describes the production of *Cr(NN)â\\/sup 3 +\\/ via photochemical methods, the reductive quenching of

1988-01-01

79

Complex formation between copper. beta. -diketonates and polyoxypropylene glycols  

SciTech Connect

The complex formation between copper (II) dipivaloylmethanate Cu(dpm)/sub 2/ and copper (II) hexafluoroacetylacetonate Cu(hfacac)/sub 2/ and polyoxypropylene glycols (PPG) with molecular masses of 200 and 1050 was studied by spectrophotometry in the visible region and by ESR. The compositions of the complexes (1:1) and the thermodynamic parameters of complex formation were determined. In complexing power Cu(dpm)/sub 2/ is inferior to Cu(hfacac)/sub 2/. Complex formation between Cu(hfacac)/sub 2/ and PPG is accompanied by structural changes in the ..beta..-diketonate.

Nizel'skii, Y.N.; Ishchenko, S.S.

1987-06-01

80

Lamellar reaction phenomena: from intercalation to nanomaterials formation  

NASA Astrophysics Data System (ADS)

Lamellar reaction processes govern the formation and properties of a wide range of materials of fundamental and technological interest, offering the potential to control the structure, composition and dimension of materials down to the nanoscale. Environmental transmission electron microscopy, complementary investigations, and atomistic modeling have been combined to explore the mechanisms that control these processes. Model transition metal disulfide (e.g. TS2, T=Ti,Ta) intercalation/deintercalation and lamellar hydroxide (e.g. Mg(OH)2) dehydroxylation/rehydroxylation reaction processes are compared to probe the effect of relatively strong and weak/transitory intralayer bonding on lamellar reaction processes. Intriguing similarities are observed even though the hydroxide lamella are destroyed and reform during dehydroxylation and rehydroxylation processes, respectively. Deintercalation and dehydroxylation occur via analogous empty gallery and oxide layer formation. Both processes generally progress via lamellar nucleation and growth, with growth progressing away from the lamellar nucleation site. Similarities extend to stage formation, with random/‘stage-2-like’ oxide and hydroxide layer ordering occurring in the lamellar oxyhydroxide regions that form. In contrast to stable host layers associated with intercalation processes, relatively weak/transitory intralayer bonding associated with lamellar dehydroxylation/rehydroxylation processes facilitates layer delamination, shearing, cracking, and nanoreconstruction during dehydroxylation, and, nanocrystal formation, intergrowth and the rapid ‘annealing out’ of lamellar defects that form during rehydroxylation.

McKelvy, Michael J.; Sharma, Renu; Chizmeshya, Andrew V. G.

2006-05-01

81

EXFOR systems manual: Nuclear reaction data exchange format  

SciTech Connect

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).

McLane, V. [ed.

1996-07-01

82

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

PubMed

Complex formation between [Pd(H2O)4](2+) and oxalate (ox = C2O4(2-)) has been studied spectrophoto-metrically in aqueous solution at variable temperature, ionic strength and pH. Thermodynamic parameters at 298.2 K and 1.00 mol dm(-3) HClO4 ionic medium for the complex formation [Pd(H2O)4](2+) + H2ox ? [Pd(H2O)2(ox)] + 2H3O(+) with equilibrium constant K1,H (in mol dm(-3)) are log10K1,H = 3.38 ± 0.08, ?H = -33 ± 3 kJ mol(-1), and ?S = -48 ± 11 J K(-1) mol(-1), as determined from spectrophotometric equilibrium titrations at 15.0, 20.0, 25.0 and 31.0 °C. Thermodynamic overall stability constants ? (in (mol dm(-3))(-n), n = 1,2) for [Pd(H2O)2(ox)] and [Pd(ox)2](2-) at zero ionic strength and 298.2 K, defined as the equilibrium constants for the reaction Pd(2+) + nox(2-) ? [Pd(ox)n](2-2n) (water molecules omitted) are log10? = 9.04 ± 0.06 and log10? = 13.1 ± 0.3, respectively, calculated by use of Specific Ion Interaction Theory from spectrophotometric titrations with initial hydrogen ion concentrations of 1.00, 0.100 and 0.0100 mol dm(-3) and ionic strengths of 1.00, 2.00 or 3.00 mol dm(-3). The values derived together with literature data give estimated overall stability constants for Pd(ii) compounds such as [Pd(en)(ox)] and cis-[Pd(NH3)2Cl2], some of them analogs to Pt(ii) complexes used in cancer treatment. The palladium oxalato complexes are significantly more stable than palladium(ii) complexes with monodentate O-bonding ligands. A comparison between several different palladium complexes shows that different parameters contribute to the stability variations observed. These are discussed together with the so-called chelate effect. PMID:24912768

Pilný, Radomír; Lubal, P?emysl; Elding, Lars I

2014-07-22

83

The reaction pathway for the formation of Tl2223  

Microsoft Academic Search

The reaction pathway for the formation of Tl2Ba2Ca2Cu3Oz (Tl-2223), a promising compound for applications in passive microwave devices, has been investigated by in situ neutron powder diffraction. The experiments were carried out in an initially evacuated closed system on two samples with compositions Tl1.7Ba2Ca2Cu3Oz and Tl2.3Ba2Ca2Cu3Oz. We find that, under the conditions specified above, the formation path implies Tl2BaO4, Tl6Ba4O13

Ph. Galez; Th. Hopfinger; J. L Soubeyroux; M. Lomello-Tafin; Ch. Opagiste; Ch. Bertrand; J. L Jorda

2002-01-01

84

Experimental steady pattern formation in reaction-diffusion-advection systems  

NASA Astrophysics Data System (ADS)

We present here experimental evidence of a mechanism of a steady-chemical pattern formation called “flow-and-diffusion structures” (FDS). Experiments were performed using the photosensitive chlorine dioxide-iodine-malonic acid reaction, where the differential diffusion can be chemically controlled. Using the analogy between an advection boundary and a moving boundary, we obtain the formation of spatially periodic steady patterns, which matches all the previously theoretical predictions for FDS patterns. Numerical simulations are also reported in agreement with the experimental results.

Míguez, David G.; Satnoianu, Razvan A.; Muñuzuri, Alberto P.

2006-02-01

85

Light induced electron transfer reactions of metal complexes  

SciTech Connect

Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed.

Sutin, N; Creutz, C

1980-01-01

86

Atmospheric Formation of Hydroxynitrofluoranthene from Photochemical Reactions of 2-Nitrofluoranthene  

Microsoft Academic Search

The formation of hydroxynitrofluoranthene (OHNF) via photochemical reactions of 2-nitrofluoranthene (2-NF) was demonstrated using a UV irradiation system. The photoreaction of 2-NF in acetonitrile\\/water (3\\/1, v\\/v) gave a product that was hydroxynitro-substituted. Moreover, we detected an OHNF isomer, which was found in the 2-NF photoreaction products, in soluble organic fractions of ambient airborne particles collected in Kanazawa, Japan. The atmospheric

TAKAYUKI KAMEDA; AYUKO AKIYAMA; AKIRA TORIBA; NING TANG; KAZUICHI HAYAKAWA

2012-01-01

87

Kinetics and mechanism of the formation of (1,8) bis (2-hydroxybenzamido)3,6-diazaoctaneiron(III) and its reactions with thiocyanate, azide, acetate, sulfur(IV) and ascorbic acid in solution, and the synthesis and characterization of a novel oxo bridged diiron(III) complex. The role of phenol–amide–amine coordination  

Microsoft Academic Search

The interaction of (1,8)bis(2-hydroxybenzamido)3,6-diazaoctane (LH2) with iron(III) in acidic medium resulted in the formation of a mononuclear complex, Fe(LH3)4+ which further yielded, [Fe(LH2)]3+, [Fe(LH)]2+, and [FeL]+ due to protolytic equilibria. The formation of [Fe(LH3)]4+ was investigated under varying [H+]T (0.01–0.10 mol dm?3) and [Fe3+]T (1.00 10?3–1.70 10?2, [L]T = 1.0 10?4 mol dm?3) (I = 0.3 mol dm?3, 10% MeOH + H2O, 25.0 C). The reaction was

Suprava Nayak; Anadi C. Dash

2006-01-01

88

Microkinetics of oxygenate formation in the Fischer-Tropsch reaction.  

PubMed

Microkinetics simulations are presented on the intrinsic activity and selectivity of the Fischer-Tropsch reaction with respect to the formation of long chain oxygenated hydrocarbons. Two different chain growth mechanisms are compared: the carbide chain growth mechanism and the CO insertion chain growth mechanism. The microkinetics simulations are based on quantum-chemical data on reaction rate parameters of the elementary reaction steps of the Fischer-Tropsch reaction available in the literature. Because the overall rate constant of chain growth remains too low the CO insertion chain growth mechanism is not found to produce higher hydrocarbons, except for ethylene and acetaldehyde or the corresponding hydrogenated products. According to the carbide mechanism available quantum-chemical data are consistent with high selectivity to long chain oxygenated hydrocarbon production at low temperature. The anomalous initial increase with temperature of the chain growth parameter observed under such conditions is reproduced. It arises from the competition between the apparent rate of C-O bond activation to produce "CHx" monomers to be inserted into the growing hydrocarbon chain and the rate of chain growth termination. The microkinetics simulations data enable analysis of selectivity changes as a function of critical elementary reaction rates such as the rate of activation of the C-O bond of CO, the insertion rate of CO into the growing hydrocarbon chain or the rate constant of methane formation. Simulations show that changes in catalyst site reactivity affect elementary reaction steps differently. This has opposing consequences for oxygenate production selectivity, so an optimizing compromise has to be found. The simulation results are found to be consistent with most experimental data available today. It is concluded that Fischer-Tropsch type catalysis has limited scope to produce long chain oxygenates with high yield, but there is an opportunity to improve the yield of C2 oxygenates. PMID:24509610

van Santen, Rutger A; Ghouri, Minhaj; Hensen, Emiel M J

2014-06-01

89

Effect of reaction time on the formation of disinfection byproducts  

USGS Publications Warehouse

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.

Rathbun, R. E.

1997-01-01

90

Reaction network governing diphosphine-protected gold nanocluster formation from nascent cationic platforms.  

PubMed

We identify the reaction network governing gold monolayer protected cluster (MPC) formation during the reduction of Au(PPh(3))Cl and L(5) (L(5) = 1,5-bis(diphenylphosphino)pentane) in solutions. UV-vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS) monitored the formation of ligated Au(x): 6 ? x ? 12 clusters, which comprise the reaction intermediates and final products. Initially, predominantly [Au(2)L(5)(2)](2+) complexes form through dissolution of Au(PPh(3))Cl. These complexes control the reduction and nucleation reactions that form nascent phosphine-ligated Au(8) and Au(10) ionic clusters. [Au(10)L(5)(4)](2+) is an observed growth platform for ligated Au(11) and Au(12) clusters. The data for syntheses of Au : L(5) systems evidence that the nascent reaction products (t < 3 days) are less dependent on the chosen reducing agent (borane tert-butylamine complex or NaBH(4)); instead, after reduction ceases, subsequent solution phase processing provides greater control for tuning cluster nuclearity. PMID:22337143

Pettibone, John M; Hudgens, Jeffrey W

2012-03-28

91

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

The [Pd(DEEN)Cl(2)] and [Pt(DEEN)Cl(2)] 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)(H(2)O)(2)](2+) were investigated at 37 degrees 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

Shoukry, Eman Mohamed

2009-01-01

92

Acid-catalyzed Heterogeneous Reactions in SOA Formation  

NASA Astrophysics Data System (ADS)

The importance of heterogeneous reactions in secondary organic aerosol (SOA) formation has recently excited a great deal of interest in the aerosol community. Jang and Kamens (2001) showed enhanced aerosol yield from aldehydes, which can be produced by atmospheric photochemical reactions, in the presence of acidic seed. They suggest that the carbonyl functional groups of the aldehydes further react in the aerosol phase via hydration, polymerization, and hemiacetal/acetal formation with alcohols at an accelerated rate in the presence of acid. Jang et al. (2003) demonstrated similar results using a flow reactor and Czoschke et al. (in press) qualitatively showed increased yields for isoprene and alpha-pinene ozonolysis in the presence of acidic seed. While these findings are intriguing and important, the conditions under which the experiments were carried out were atmospherically unrealistic. A series of SOA formation experiments have been carried out in the Caltech Indoor Chamber Facility, which is comprised of dual 28 m3 FEP Teflon chambers, with the flexibility to carry out both dark ozonolysis and photochemical OH oxidation reactions. Cycloheptene and alpha-pinene were oxidized in the presence of neutral seed under dry (<10% RH) and humid (50% RH) conditions and in the presence of acidic seed under humid (50% RH) conditions. The SOA yields for these experiments will be presented, and the extent of the influence of acid-catalyzed reactions on SOA yield will be discussed. Reference List 1. Cocker, D. R. III. and R. C. Flagan and J. H. Seinfeld, State-of-the-art chamber facility for studying atmospheric aerosol chemistry, Environmental Science and Technology, 35, 2594-2601, 2001. 2. Czoschke, N. M., M. Jang, and R. M. Kamens, Effect of acid seed on biogenic sceondary organic aerosol growth, Atmospheric Environment, In press. 3. Jang, M., S. Lee, and R. M. Kamens, Organic aerosol growth by acid-catalyzed heterogeneous reactions of octanal in a flow reactor, Atmospheric Environment, 37, 2125-2138, 2003. 4. Jang, M. S. and R. M Kamens, Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst. Environmental Science and Technology, 35, 4758-4766,2001.

Ng, N.; Keywood, M.; Varutbangkul, V.; Gao, S.; Loewer, E.; Surratt, J.; Richard, F. C.; John, S. H.

2003-12-01

93

Light Induced Electron Transfer Reactions of Metal Complexes.  

National Technical Information Service (NTIS)

Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excite...

N. Sutin C. Creutz

1980-01-01

94

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

SciTech Connect

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.

Kohler, Mark C. [Bucknell University; Grimes, Thomas V. [University of North Texas; Wang, Xiaoping [ORNL; Cundari, Thomas R. [University of North Texas; Stockland, Robert A. Jr. [Bucknell University

2009-01-01

95

Formation of self-inhibiting copper(II) nanoparticles in an autocatalytic Fenton-like reaction.  

PubMed

Cu(II)-catalysed decomposition of hydrogen peroxide at alkaline pH in the presence of etidronic acid (HEDP) showed a sigmoid kinetic profile typical of autocatalytic reactions. However, the reaction abruptly stopped well before all hydrogen peroxide had decomposed, and further addition of Cu(II) and HEDP did not restart the reaction. Results of a mechanistic study suggest that the reaction involves the formation of an active catalyst which decomposes hydrogen peroxide and oxidizes HEDP. Once all HEDP has been consumed, the active complex triggers Cu(II) aggregation to form remarkably stable but catalytically inactive nanoparticles. The nanoparticles were found to be basic Cu(II) phosphate/carbonate. They exhibit self-poisoning behaviour in the hydrogen peroxide decomposition and undergo seed-mediated growth upon addition of further Cu(II). PMID:24472897

Naqvi, Kazim R; Marsh, Jennifer; Chechik, Victor

2014-03-28

96

Formation of micelles with complex coacervate cores  

Microsoft Academic Search

Micelles are commonly regarded as colloidal structures spontaneously formed by amphiphilic molecules, that is, molecules consisting of two distinct parts of which one is soluble and the other is insoluble. This definition is too restrictive: other kinds of molecules can also form micelles. We report on the formation of micelles from a mixture of a (water-soluble) polyanion and a diblock

M. A. Cohen Stuart; N. A. M. Besseling; R. G. Fokkink

1998-01-01

97

Methyl-transfer reaction to alkylthiol catalyzed by a simple vitamin B 12 model complex using zinc powder  

Microsoft Academic Search

The catalytic methyl-transfer reaction from methyl tosylate to 1-octanethiol was carried out in the presence of a simple vitamin B12 model complex, [Co(III){(C2C3)(DO)(DOH)pn}Br2], with zinc powder as the reducing reagent at 50°C. Such a catalytic reaction proceeded via the formation and dissociation of a cobalt–carbon bond in the simple vitamin B12 model complex under non-enzymatic conditions. The mechanism for the

Ling Pan; Keishiro Tahara; Takahiro Masuko; Yoshio Hisaeda

2011-01-01

98

Tungsten oxo salicylate complexes from tungsten hexachloride reactions systems.  

PubMed

Tungsten hexachloride is a potent halogen-transfer agent, capable of reacting directly with salicylic acid to generate a tungsten oxo fragment and salicoyl chloride. As a result, oxo complexes dominate the chemistry of tungsten(VI) salicylates. Both mono- and disalicylate substituted tungsten oxo complexes are accessible. The Brønsted free acid W(=O)Cl(Hsal)(sal) complex is a sparingly soluble, presumably polymeric material that can be dissolved in THF. The THF adduct has been characterized by NMR spectroscopy, although an X-ray crystallographic study indicates that the product cocrystallizes with a structurally analogous d(1) WCl(2)(Hsal.THF)(sal) byproduct. The remaining chloride ligand in W(=O)Cl(Hsal)(sal) is replaced by a bridging oxo unit when the reaction contains a significant excess of salicylic acid. The product "linear" oxo bridged ditungsten complex, [W(=O)(Hsal)(sal)](2)O, forms intramolecular hydrogen bonds, accounting for its high solubility in noncoordinating solvents. An X-ray study shows that the intramolecular Hsal.sal hydrogen bonding in this complex accommodates a more linear W-O-W arrangement than does a previously observed class of isostructural diolate derivatives. Tungsten oxo tetrachloride, formed in the initial reaction between salicylic acid and WCl(6), also reacts with the salicoyl chloride byproduct to generate tungsten salicoylate (OAr-2-COCl) complexes. PMID:11531451

Kolesnichenko, V; Mason, M H; Botts, J B; Botts, A M; Baroni, T E; Heppert, J A; Rheingold, A L; Liable-Sands, L; Yap, G P

2001-09-10

99

Information-Theoretical Complexity Analysis of Selected Elementary Chemical Reactions  

NASA Astrophysics Data System (ADS)

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

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

100

Formation of superheavy elements in cold fusion reactions  

NASA Astrophysics Data System (ADS)

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

Smola?czuk, Robert

2001-04-01

101

Pattern formation in three-dimensional reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

Existing group theoretic analysis of pattern formation in three dimensions [T.K. Callahan, E. Knobloch, Symmetry-breaking bifurcations on cubic lattices, Nonlinearity 10 (1997) 1179-1216] is used to make specific predictions about the formation of three-dimensional patterns in two models of the Turing instability, the Brusselator model and the Lengyel-Epstein model. Spatially periodic patterns having the periodicity of the simple cubic (SC), face-centered cubic (FCC) or body-centered cubic (BCC) lattices are considered. An efficient center manifold reduction is described and used to identify parameter regimes permitting stable lamellæ, SC, FCC, double-diamond, hexagonal prism, BCC and BCCI states. Both models possess a special wavenumber k* at which the normal form coefficients take on fixed model-independent ratios and both are described by identical bifurcation diagrams. This property is generic for two-species chemical reaction-diffusion models with a single activator and inhibitor.

Callahan, T. K.; Knobloch, E.

1999-08-01

102

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

SciTech Connect

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

Nelson, M.J.; Brennan, B.A.; Chase, D.B. [E.I. du Pont de Nemours & Co., Wilmington, DE (United States)]|[Haverford College, PA (United States)] [and others

1995-11-21

103

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

104

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

PubMed

The seminal report by Hegedus in 1982, showing that alkoxychromium(0) carbenes reacted with imines under bright Colorado sunlight to yield ?-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 electrons are primarily localized in the metal fragment and in the former carbene carbon atom. The T(1)-S(0) intersystem crossing occurs with the participation of the solvent through an unusual loose-bolt radiationless mechanism. The photogenerated S(0) species reacts with imines to form the final ?-lactams in a mechanism that resembles the organic Staudinger reaction, but here the metal is present during the entire reaction coordinate. The selectivity of these reactions is defined by the nucleophilic attack on the O-bonded metallaketene instead of the subsequent conrotatory ring closure, a distinct departure from the organic reaction. Appropriate modification of the substituents of the carbene ligand or in the coordination sphere of the complex results in new photoprocesses; these include 1,2-metalladyotropic rearrangements as well as ?-fragmentations in which W(0) carbene complexes become photoreactive. Moreover, the inclusion of additional metal centers usually results in new reactions, such as the formation of fulvenes by ?(5)? ?(3) photoslippage, or in the complete inhibition of the photoreactivity. The photochemistry of group 6 metal-carbene complexes thus offers unexplored territory for pursuing new reactions and reaction mechanisms. PMID:21517052

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

2011-07-19

105

Lead(II) Complex Formation with Glutathione  

PubMed Central

A structural investigation of complexes formed between the Pb2+ ion and glutathione (GSH, denoted AH3 in its triprotonated form) the most abundant non2protein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and CPb2+ = 10 mM, and in the solid state. The Pb LIII-edge EXAFS oscillation for a solid compound with the empirical formula [Pb(AH2)]ClO4 was modeled with one Pb-S and two short Pb-O bond distances at 2.64 ± 0.04 Å and 2.28 ± 0.04 Å, respectively. In addition Pb···Pb interactions at 4.15 ± 0.05 Å indicate dimeric species in a network where the thiolate group forms an asymmetrical bridge between two Pb2+ ions. In aqueous solution at the mole ratio GSH / Pb(II) = 2.0 (CPb2+ = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge transfer band (LMCT) S- ? Pb2+ at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 ± 0.04 Å and 2.51 ± 0.04 Å, respectively, from a Pb LIII-edge EXAFS spectrum. For solutions with higher mole ratios, GSH / Pb(II) ? 3.0, ESI-MS spectra identified a trisglutathionyl lead(II) complex, for which Pb LIII-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 ± 0.04 Å in PbS3 coordination, 207Pb NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum an S- ? Pb2+ LMCT band appears at 335 nm. The complex persists at high excess of glutathione, and also at ~25 K in frozen glycerol (33%) / water glasses for GSH / Pb(II) mole ratios from 4.0 to 10 (CPb2+ = 10 mM) measured by Pb LIII-edge EXAFS spectroscopy.

Mah, Vicky

2012-01-01

106

Lead(II) complex formation with glutathione.  

PubMed

A structural investigation of complexes formed between the Pb(2+) ion and glutathione (GSH, denoted AH(3) in its triprotonated form), the most abundant nonprotein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and C(Pb(2+)) = 10 mM and in the solid state. The Pb L(III)-edge extended X-ray absorption fine structure (EXAFS) oscillation for a solid compound with the empirical formula [Pb(AH(2))]ClO(4) was modeled with one Pb-S and two short Pb-O bond distances at 2.64 ± 0.04 and 2.28 ± 0.04 Å, respectively. In addition, Pb···Pb interactions at 4.15 ± 0.05 Å indicate dimeric species in a network where the thiolate group forms an asymmetrical bridge between two Pb(2+) ions. In aqueous solution at the mole ratio GSH/Pb(II) = 2.0 (C(Pb(2+)) = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge-transfer band (LMCT) S(-) ? Pb(2+) at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 ± 0.04 and 2.51 ± 0.04 Å, respectively, from a Pb L(III)-edge EXAFS spectrum. For solutions with higher mole ratios, GSH/Pb(II) ? 3.0, electrospray ionization mass spectroscopy spectra identified a triglutathionyllead(II) complex, for which Pb L(III)-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 ± 0.04 Å in PbS(3) coordination, (207)Pb NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum, an S(-) ? Pb(2+) LMCT band appears at 335 nm. The complex persists at high excess of GSH and also at ?25 K in frozen glycerol (33%)/water glasses for GSH/Pb(II) mole ratios from 4.0 to 10 (C(Pb(2+)) = 10 mM) measured by Pb L(III)-edge EXAFS spectroscopy. PMID:22594853

Mah, Vicky; Jalilehvand, Farideh

2012-06-01

107

Formation of complex bacterial colonies via self-generated vortices  

Microsoft Academic Search

Depending on the environmental conditions bacterial colonies growing on agar surfaces can exhibit complex colony formation and various types of collective motion. Experimental results are presented concerning the hydrodynamics (vortices, migration of bacteria in clusters) and colony formation of a morphotype of Bacillus subtilis. Some of these features are not specific to this morphotype but also have been observed in

András Czirók; Eshel Ben-Jacob; Inon Cohen; Tamás Vicsek

1996-01-01

108

?-Complexation in nickel-catalyzed cross-coupling reactions.  

PubMed

The kinetic isotope effect (KIE) is used to experimentally elucidate the first irreversible step in oxidative addition reactions of a zerovalent nickel catalyst to a set of haloarene substrates. Halogenated o-methylbenzene, dimethoxybenzene, and thiophene derivatives undergo intramolecular oxidative addition through irreversible ?-complexation. Density functional theory computations at the B3LYP-D3/TZ2P-LANL2TZ(f)-LANL08d level predict ?(2)-bound ?-complexes are generally stable relative to a solvated catalyst plus free substrate and that ring-walking of the Ni(0) catalyst and intramolecular oxidative addition are facile in these intermediates. PMID:24490934

Sontag, S Kyle; Bilbrey, Jenna A; Huddleston, N Eric; Sheppard, Gareth R; Allen, Wesley D; Locklin, Jason

2014-02-21

109

Formation of crystalline complexes between amylomaize dextrin and ceramide.  

PubMed

Complexes between amylomaize dextrin (average DP 311) and ceramide were prepared by using two different blending systems: an aqueous batch system containing ethanol and a two-phase system of isopropyl ether and water. The organic solvents and complex formation temperature (50-90°C) were important in determining the level of complex formation and its crystalline structure. Under X-ray diffraction analysis, the solvents as well as ceramide could form complexes with dextrin as weak V6I type crystals. However, the crystallinity of complexes was much higher in the presence of ceramide, which would enhance complex formation by forming ternary co-inclusion complexes of dextrin-solvent-ceramide. Compared to the two-phase system, the batch system yielded much higher crystallinity of complexes. With a minor use of ethanol (0.5 mL) in the batch system, aqueous blending of dextrin and ceramide at 50°C for 2 days followed by a storage at 25°C for 1 day produced well-defined V6I crystal particles as precipitates. The isolated particles had rectangular shapes with a size of 1 ?m or less, and contained about half of the ceramide initially added. The ceramide-dextrin complex exhibited enhanced water dispersibility, up to 45% based on the ceramide content in complex. PMID:24299790

Kim, Hee-Young; Lim, Jae Kag; Kim, Doun; Lim, Seung-Taik

2014-01-30

110

Calculations on the complex mechanism of the HCNO + OH reaction  

NASA Astrophysics Data System (ADS)

Complex reaction mechanism of HCNO + OH were investigated at the CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p) level. The results show that this reaction has four main entrance channels. From initial adducts sixteen different pathways lead to products. The most favorable channel involves the barrierless entrance isomer (HC(OH)CNO) which is formed by OH adding to C atom. Products of (CO + NHOH) and (CHO + HNO) are the most favorable, (H2O + NO), (H2 + OCNO), (H2 + CO + NO), (CO + NH2O) are minor pathways. Heats of reaction are predicted at the CCSD(T)/CBS level. Our results are in good agreement with available experiment.

Nguyen, Hue Minh Thi; Nguyen, Trong Nghia

2014-04-01

111

Complex signal amplitude analysis for complete fusion nuclear reaction products  

NASA Astrophysics Data System (ADS)

A complex analysis has been performed on the energy amplitude signals corresponding to events of Z = 117 element measured in the 249Bk + 48Ca complete fusion nuclear reaction. These signals were detected with PIPS position sensitive detector. The significant values of pulse height defect both for recoils (ER) and for fission fragments2 were measured. Comparison with the computer simulations and empirical formulae has been performed both for ER and FF signals.

Tsyganov, Yu.

2011-01-01

112

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

PubMed

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 rhenium starting material. Equal amounts of hydrogen gas are produced, suggesting that the catalyzed reaction is the dehydrogenation of ethanol to produce acetaldehyde and hydrogen gas. Metal hydrides are detected in the reaction solution, suggesting a mechanism involving beta-elimination of ethanol at the metal center. Formation of the amidorhenium(III) product possibly arises from migration of a metal hydride in the imidorhenium(V) complex. PMID:11151507

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

2000-12-25

113

Formation and reactions of hydronium species in silica  

NASA Astrophysics Data System (ADS)

Water-related impurities in silica-based glasses are known to affect the properties of the network and corresponding devices in many types of ways. Here, we use first-principles calculations to highlight the special role of one of these species, hydronium (H3O). We elucidate the atomic-scale details of formation and reactions of H3O molecules in amorphous SiO2. We find that the attachment of a migrating H^+ on a water molecule is an exothermic reaction with an energy gain of 0.4 eV and activation energy of only 0.6 eV. We present results on pertinent features in the vibrational spectra of silica that support the presence of H3O, and we describe the role of H3O as a passivant of oxide defects, like oxygen vacancies and non-bridging oxygen atoms, and the atomic-scale details of H3O-mediated diffusion of H species in SiO2. The results bear on the formation and dynamics of defects in electronic devices and the physical properties of hygroscopic silica-based glasses. This work was supported in part by the AFOSR and the US Navy.

Batyrev, I. G.; Tsetseris, L.; Pantelides, S. T.

2008-03-01

114

Formation of molecular oxygen in ultracold O + OH reaction  

SciTech Connect

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.

Kendrick, Brian Kent [Los Alamos National Laboratory; Quemener, Goulven [UNLV; Balakrishman, Naduvalath [UNLV

2008-01-01

115

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

PubMed Central

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.

Wils, Stefan; Schutter, Erik De

2008-01-01

116

Formation of Maillard reaction products during heat treatment of carrots.  

PubMed

As indicators of the early stage of the Maillard reaction in carrots, N-(furoylmethyl) amino acids (FMAAs) formed during acid hydrolysis of the corresponding Amadori products were analyzed using RP-HPLC with UV detection. N(?)-FM-Lys (furosine), FM-Gly, FM-Ala, FM-Val, FM-Ile, FM-Leu, and FM-GABA were identified using synthesized standard material by means of mass spectrometry. Furthermore, N(?)-carboxymethyllysine (CML) and pyrraline were analyzed as indicators for advanced stages of glycation. For commercial samples with high water content, the formation of Amadori compounds predominates, whereas the advanced stage of Maillard reaction plays only a minor part. Carrot juices, baby food, and tinned carrots showed quite low rates of amino acid modification up to 5%. For dehydrated carrots, significantly higher values for Amadori products were measured, corresponding to a lysine derivatization of up to 58% and nearly 100% derivatization of GABA. Drying experiments revealed great differences in reactivity between the amino acids studied. Whereas furosine reached constant values quite quickly, some FMAAs showed a continuous increase with heating time, indicating that selected FMAAs can be used as a hallmark for the early Maillard reaction to control processing conditions. PMID:21682346

Wellner, Anne; Huettl, Christine; Henle, Thomas

2011-07-27

117

Formation constants of mercury(II) with some buffer/masking agents and the formation of mixed-ligand complexes.  

PubMed

Values are given for the formation constants of complexes of mercury(II) with some buffer/masking agents. The mixed-ligand complex formation of mercury(II)-chelates with other complexing agents has also been studied. PMID:18961624

Van der Linden, W E; Beers, C

1975-01-01

118

Reactions of the ‘ferrole’ complex [Fe 2(CO) 6(C 2Et 2) 2] with group 15 donor ligands and with alkynes. Stepwise formation and disengagement of tropones. Crystal and molecular structure of [Fe 2(CO) 5{(CEt) 2 CO(CEt) 2 CHCPh}  

Microsoft Academic Search

The reactions of [Fe2(CO)6(C2Et2)2] (complex A) with phosphorus donors in the presence of Me3NO results in an unexpected CO insertion to give ‘flyover-bridged’ dinuclear compounds. The same reaction also takes place with nitriles giving similar, though less stable, complexes. The reactions of A with terminal alkynes give rise again to CO insertion into the ferrole ring and, in addition, the

Roberto Giordano; Enrico Sappa; Daniele Cauzzi; Giovanni Predieri; Antonio Tiripicchio

1996-01-01

119

A Two-step Process Controls the Formation of the Bienzyme Cysteine Synthase Complex*  

PubMed Central

The regulation of enzyme activity through the transient formation of multiprotein assemblies plays an important role in the control of biosynthetic pathways. One of the first regulatory complexes to be discovered was cysteine synthase (CS), formed by the pyridoxal 5?-phosphate-dependent enzyme O-acetylserine sulfhydrylase (OASS) and serine acetyltransferase (SAT). These enzymes are at the branch point of the sulfur, carbon, and nitrogen assimilation pathways. Understanding the mechanism of complex formation helps to clarify the role played by CS in the regulation of sulfur assimilation in bacteria and plants. To this goal, stopped-flow fluorescence spectroscopy was used to characterize the interaction of SAT with OASS, at different temperatures and pH values, and in the presence of the physiological regulators cysteine and bisulfide. Results shed light on the mechanism of complex formation and regulation, so far poorly understood. Cysteine synthase assembly occurs via a two-step mechanism involving rapid formation of an encounter complex between the two enzymes, followed by a slow conformational change. The conformational change likely results from the closure of the active site of OASS upon binding of the SAT C-terminal peptide. Bisulfide, the second substrate and a feedback inhibitor of OASS, stabilizes the CS complex mainly by decreasing the back rate of the isomerization step. Cysteine, the product of the OASS reaction and a SAT inhibitor, slightly affects the kinetics of CS formation leading to destabilization of the complex.

Salsi, Enea; Campanini, Barbara; Bettati, Stefano; Raboni, Samanta; Roderick, Steven L.; Cook, Paul F.; Mozzarelli, Andrea

2010-01-01

120

Particle formation during oxidation catalysis with Cp* iridium complexes.  

PubMed

Real-time monitoring of light scattering and UV-vis profiles of four different Cp*Ir(III) precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO(4) as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*(2)Ir(2)(?-OH)(3)]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-vis data with light scattering profiles revealed that the formation of a deep purple-blue color (~580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously. PMID:22594951

Hintermair, Ulrich; Hashmi, Sara M; Elimelech, Menachem; Crabtree, Robert H

2012-06-13

121

Background defining during the imine formation reaction in FT-IR liquid cell.  

PubMed

Imine formation is a very important chemical reaction because of its relevance to biological process. Therefore, it is crucial to follow whole reaction process in detail. The current work performed to monitor the whole imination reaction in real time in liquid cell by FT-IR spectroscopy. The complex spectral futures due to solvent, unreacted reagents, acid catalysis and other additives are eliminated by defining a background at the beginning or at any time during the reaction. This procedure also makes it possible to monitor the changes in the concentration of each component in the liquid cell. The consumption of the functional groups of the reagents results in absorbance due to the direct difference spectra while the appearance of functional groups is monitored as percentage transmittance. The concentration changes in the cell arising from the reaction gives the product spectra without having to isolate it from the mixture. It is also possible to see the intermediates appearing and disappearing during the reaction. This report also illustrates a brief application of the technique by time dependence of the peak highs in absorption (ABS) mode. PMID:16095956

Namli, Hilmi; Turhan, Onur

2006-05-01

122

Studies of complex fragment emission in heavy ion reactions  

SciTech Connect

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.

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

1992-01-01

123

Crossed beam investigation of elementary reactions relevant to the formation of polycyclic aromatic hydrocarbon (PAH)-like molecules in extraterrestrial environments  

Microsoft Academic Search

The reactions of ground state carbon atoms, C(3Pj), with benzene, C6H6, and phenyl radicals, C6H5, with methylacetylene, CH3CCH, were investigated in crossed beam experiments at collision energies of 21.8 and 140 kJ mol?1 to investigate elementary reactions relevant to the formation and chemistry of polycyclic aromatic hydrocarbons (PAHs) in extraterrestrial environments. The C(3Pj) reaction proceeds via complex formation and gives a

R. I. Kaiser; O. Asvany; Y. T. Lee

2000-01-01

124

Studies of reductive elimination reactions to form carbon-oxygen bonds from Pt(IV) complexes.  

PubMed

The platinum(IV) complexes fac-L(2)PtMe(3)(OR) (L(2) = bis(diphenylphosphino)ethane, o-bis(diphenylphosphino)benzene, R = carboxyl, aryl; L = PMe(3), R = aryl) undergo reductive elimination reactions to form carbon-oxygen bonds and/or carbon-carbon bonds. The carbon-oxygen reductive elimination reaction produces either methyl esters or methyl aryl ethers (anisoles) and L(2)PtMe(2), while the carbon-carbon reductive elimination reaction affords ethane and L(2)PtMe(OR). Choice of reaction conditions allows the selection of either type of coupling over the other. A detailed mechanistic study of the reductive elimination reactions supports dissociation of the OR(-) ligand as the initial step for the C-O bond formation reaction. This is followed by a nucleophilic attack of OR(-) upon a methyl group bound to the Pt(IV) cation to produce the products MeOR and L(2)PtMe(2). C-C reductive elimination proceeds from L(2)PtMe(3)(OR) by initial L (L = PMe(3)) or OR(-) (L(2) = dppe, dppbz) dissociation, followed by C-C coupling from the resulting five-coordinate intermediate. Our studies demonstrate that both C-C and C-O reductive elimination reactions from Pt(IV) are more facile in polar solvents, in the presence of Lewis acids, and for OR(-) groups that contain electron withdrawing substituents. PMID:11456927

Williams, B S; Goldberg, K I

2001-03-21

125

The formation of Kuiper-belt binaries through exchange reactions  

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

126

Mechanisms Underlying Methamphetamine-Induced Dopamine Transporter Complex Formation  

PubMed Central

Repeated, high-dose methamphetamine (METH) administrations cause persistent dopaminergic deficits in rodents, nonhuman primates, and humans. In rats, this treatment also causes the formation of high-molecular mass (greater than approximately 120 kDa) dopamine transporter (DAT)-associated complexes, the loss of DAT monomer immunoreactivity, and a decrease in DAT function, as assessed in striatal synaptosomes prepared 24 h after METH treatment. The present study extends these findings by demonstrating the regional selectivity of DAT complex formation and monomer loss because these changes in DAT immunoreactivity were not observed in the nucleus accumbens. Furthermore, DAT complex formation was not a consequence limited to METH treatment because it was also caused by intrastriatal administration of 6-hydroxydopamine. Pretreatment with the D2 receptor antagonist, eticlopride [S-(-)-3-chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2-methoxybenzamide hydrochloride], but not the D1 receptor antagonist, SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], attenuated METH-induced DAT complex formation. Eticlopride pretreatment also attenuated METH-induced DAT monomer loss and decreases in DAT function; however, the attenuation was much less pronounced than the effect on DAT complex formation. Finally, results also revealed a negative correlation between METH-induced DAT complex formation and DAT activity. Taken together, these data further elucidate the underlying mechanisms and the functional consequences of repeated administrations of METH on the DAT protein. Furthermore, these data suggest a multifaceted role for D2 receptors in mediating METH-induced alterations of the DAT and its function.

Hadlock, Gregory C.; Baucum, Anthony J.; King, Jill L.; Horner, Kristen A.; Cook, Glen A.; Gibb, James W.; Wilkins, Diana G.; Hanson, Glen R.; Fleckenstein, Annette E.

2009-01-01

127

Mechanisms underlying methamphetamine-induced dopamine transporter complex formation.  

PubMed

Repeated, high-dose methamphetamine (METH) administrations cause persistent dopaminergic deficits in rodents, nonhuman primates, and humans. In rats, this treatment also causes the formation of high-molecular mass (greater than approximately 120 kDa) dopamine transporter (DAT)-associated complexes, the loss of DAT monomer immunoreactivity, and a decrease in DAT function, as assessed in striatal synaptosomes prepared 24 h after METH treatment. The present study extends these findings by demonstrating the regional selectivity of DAT complex formation and monomer loss because these changes in DAT immunoreactivity were not observed in the nucleus accumbens. Furthermore, DAT complex formation was not a consequence limited to METH treatment because it was also caused by intrastriatal administration of 6-hydroxydopamine. Pretreatment with the D2 receptor antagonist, eticlopride [S-(-)-3-chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2-methoxybenzamide hydrochloride], but not the D1 receptor antagonist, SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], attenuated METH-induced DAT complex formation. Eticlopride pretreatment also attenuated METH-induced DAT monomer loss and decreases in DAT function; however, the attenuation was much less pronounced than the effect on DAT complex formation. Finally, results also revealed a negative correlation between METH-induced DAT complex formation and DAT activity. Taken together, these data further elucidate the underlying mechanisms and the functional consequences of repeated administrations of METH on the DAT protein. Furthermore, these data suggest a multifaceted role for D2 receptors in mediating METH-induced alterations of the DAT and its function. PMID:19141713

Hadlock, Gregory C; Baucum, Anthony J; King, Jill L; Horner, Kristen A; Cook, Glen A; Gibb, James W; Wilkins, Diana G; Hanson, Glen R; Fleckenstein, Annette E

2009-04-01

128

Synthesis of coordinatively unsaturated mesityliron thiolate complexes and their reactions with elemental sulfur.  

PubMed

The reactions of Fe(2)Mes(4) (1; Mes = mesityl) with bulky thiols, namely, HSDmp (Dmp = 2,6-dimesitylphenyl), HSDxp (Dxp = 2,6-dixylylphenyl), and HSBtip [Btip = 2,6-(2,4,6-(i)Pr(3)C(6)H(2))(2)C(6)H(3)], provided a series of iron(II) mesityl complexes bearing bulky thiolate ligands. These iron complexes are the thiolate-bridged dinuclear complexes Fe(2)Mes(2)(mu-SAr)(mu-Mes) (2a, Ar = Dmp; 2b, Ar = Dxp), the 1,2-dimethoxyethane (DME) adducts (DME)Fe(SAr)(Mes) (3a, Ar = Dmp; 3b, Ar = Dxp), the mixed-valence Fe(I)-Fe(II) dinuclear complexes (Mes)Fe(mu-SAr)(mu-S Ar) Fe (4a, Ar = Dmp; 4b, Ar = Dxp), and a low-coordinate mononuclear complex (B tipS) Fe(Mes) (5). An [Fe(8)S(7)] cluster [Fe(4)S(3)(SDmp)](2)(mu-SDmp)(2)(mu-SMes)(mu(6)-S) (6), the core structure of which is topologically relevant to that of the FeMo-cofactor of nitrogenase, was obtained from the reaction of 3a or 4a with S(8). The mu-SMes ligand in 6 is formed via insertion of a sulfur atom into the Fe-C(Mes) bond. The formation of cluster 6 from 3a or 4a demonstrates that organoiron complexes are applicable as precursors for iron-sulfur clusters. PMID:20527790

Hashimoto, Takayoshi; Ohki, Yasuhiro; Tatsumi, Kazuyuki

2010-07-01

129

Kinetics and Equilibria for Complex Formation between Palladium(II) and Chloroacetate  

Microsoft Academic Search

Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol$$\\\\cdot {\\\\rm dm}^{-3}$$ HClO4 at 298.2 K. The equilibrium constant, K, of the reaction\\u000a$$ {\\\\rm Pd}^{2 + } + {\\\\rm HL}^{K} {\\\\rm PdL}^+ +{\\\\rm H}^+ $$\\u000awas determined from multi-wavelength absorbance measurements of equilibrated solutions at variable temperatures

P?emysl Lubal; Lars I. Elding

2006-01-01

130

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

SciTech Connect

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.

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; (Michigan); (Rutgers); (Brandeis)

2009-04-22

131

An artificial photosynthetic antenna-reaction center complex  

SciTech Connect

A model photosynthetic antenna consisting of four covalently linked zinc tetraarylporphyrins, (P{sub ZP}){sub 3}-P{sub ZP}, has been joined to a free base porphyrin-fullerene artificial photosynthetic reaction center, P-C{sub 60}, to form a (P{sub ZP}){sub 3}-P{sub ZC}-PC{sub 60} hexad. As revealed by time-resolved absorption and emissions studies, excitation of any peripheral zinc porphyrin moiety (P{sub ZP}) in 2-methyltetrahydrofuran solution is followed by singlet-singlet energy transfer to the central zinc porphyrin to give (P{sub ZP}){sub 3}-{sup 1}P{sub ZC}-P-C{sub 60} with a time constant of {approximately}50 ps. The excitation is passed on to the free base porphyrin in 240 ps to produce (P{sub ZP}){sub 3}-P{sub ZC}-{sup 1}P-C{sub 60}, which decays by electron transfer to the fullerene with a time constant of 3 ps. The (P{sub ZP}){sub 3}-P{sub ZC}-P{sup {center{underscore}dot}{plus}}-C{sub 60}{sup {center{underscore}dot}{minus}} charge-separated state thus formed has a lifetime of 1,330 ps, and is generated with a quantum yield of 0.70 based on light absorbed by the zinc porphyrin antenna. The complex thus mimics the basic functions of natural photosynthetic antenna systems and reaction center complexes.

Kuciauskas, D.; Liddell, P.A.; Lin, S.; Johnson, T.E.; Weghorn, S.J.; Lindsey, J.S.; Moore, A.L.; Moore, T.A.; Gust, D.

1999-09-22

132

Hierarchical star formation in M 51: star/cluster complexes  

NASA Astrophysics Data System (ADS)

We report on a study of young star cluster complexes in the spiral galaxy M 51. Recent studies have confirmed that star clusters do not form in isolation, but instead tend to form in larger groupings or complexes. We use HST broad and narrow band images (from both WFPC2 and ACS), along with BIMA-CO observations to study the properties and investigate the origin of these complexes. We find that the complexes are all young (<10 Myr), have sizes between ~85 and ~240 pc, and have masses between 3-30 × 104~ M?. Unlike that found for isolated young star clusters, we find a strong correlation between the complex mass and radius, namely M? R2.33 ± 0.19. This is similar to that found for giant molecular clouds (GMCs). By comparing the mass-radius relation of GMCs in M 51 to that of the complexes we can estimate the star formation efficiency within the complexes, although this value is heavily dependent on the assumed CO-to-H2 conversion factor. The complexes studied here have the same surface density distribution as individual young star clusters and GMCs. If star formation within the complexes is proportional to the gas density at that point, then the shared mass-radius relation of GMCs and complexes is a natural consequence of their shared density profiles. We briefly discuss possibilities for the lack of a mass-radius relation for young star clusters. We note that many of the complexes show evidence of merging of star clusters in their centres, suggesting that larger star clusters can be produced through the build up of smaller clusters.

Bastian, N.; Gieles, M.; Efremov, Yu. N.; Lamers, H. J. G. L. M.

2005-11-01

133

Ordered complexes of cytochrome c fragments. Kinetics of formation of the reduced (ferrous) forms.  

PubMed

The kinetics of formation of noncovalently bound ferrous complexes derived from fragments of horse heart cytochrome c have been investigated. When the reactions are initiated by combining ferrous heme fragments with an appropriate apofragment, in the presence of 50 mM imidazole, second order rate processes are observed with rate constants essentially the same as those reported with ferric heme fragments (Parr, G. R., and Taniuchi, H. (1979) J. Biol. Chem. 254, 4836-4842). An additional, probably consecutive, kinetic process is also demonstrated. If imidazole is not present in the reaction buffer, the kinetic profiles are dramatically altered. While this is partially due to aggregation (dimerization) of the ferrous heme fragments, it can nevertheless be demonstrated that the complementation reactions with apofragments are much faster than those observed with the corresponding ferric heme fragments (in the absence of imidazole). These results reflect the effect of the oxidation state of the heme iron on the folding mechanism and, thus, the manifold nature of protein folding pathways. The rate of reduction of productive ferric complexes by sodium ascorbate was investigated and biphasic reactions were found in all cases. The data indicate an equilibrium between two forms of the ferric complexes. The results of an experiment in which the complementation of ferric (1-25)H and (23-104) was carried out in the presence of sodium ascorbate indicate that the intermediate complex (Parr, G. R., and Taniuchi, H. (1980) J. Biol. Chem. 255, 8914-8918) is not reducible by ascorbate. Thus, the increase in oxidation-reduction potential occurring on formation of the productive complex from the unbound heme fragment occurs at a late stage of the overall reaction, possibly coinciding with ligation of methionine 80 to the heme iron. PMID:6256341

Parr, G R; Taniuchi, H

1981-01-10

134

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

NASA Astrophysics Data System (ADS)

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 sophisticated surface chemical and hydrological modeling approaches is stressed.

Koretsky, C.

2000-05-01

135

Mössbauer study of peroxynitrito complex formation with FeIII-chelates  

NASA Astrophysics Data System (ADS)

The reaction of the ?-oxo-diiron(III)-L complex (L = EDTA, ethylene diamine tetraacetate, HEDTA, hydroxyethyl ethylene diamine triacetate, and CyDTA, cyclohexane diamine tetraacetate) with peroxynitrite in alkaline solution was studied by Mössbauer spectroscopy using rapid-freezing technique. These complexes yield an (L)FeIII( ? 2-O2)^{3-} complex ion when they react with hydrogen peroxide and the formation of the peroxide adduct results in a deep purple coloration of the solution. The same color appears when the reaction occurs with peroxinitrite. Although spectrophotometry indicated some difference between the molar extinction coefficients of the peroxo and the peroxinitrito adducts, the Mössbauer parameters proved to be the same within experimental error. It is concluded that the peroxynitrite ion decomposes when reacting with FeIII(L) and the peroxo adduct forms.

Homonnay, Zoltan; Buszlai, Peter; Nádor, Judit; Sharma, Virender K.; Kuzmann, Erno; Vértes, Attila

2012-03-01

136

Molecular Dynamics Simulations of DNA-Polycation Complex Formation  

PubMed Central

Abstract Complexes formed from DNA and polycations are of interest because of their potential use in gene therapy; however, there remains a lack of understanding of the structure and formation of DNA-polycation complexes at atomic scale. In this work, molecular dynamics simulations of the DNA duplex d(CGCGAATTCGCG) in the presence of polycation chains are carried out to shed light on the specific atomic interaction that result in complex formation. The structures of complexes formed from DNA with polyethylenimine, which is considered one of the most promising DNA vector candidates, and a second polycation, poly-L-lysine, are compared. After an initial separation of ?50 Å, the DNA and polycation come together and form a stable complex within 10 ns. The DNA does not undergo any major structural changes on complexation and remains in the B-form. In the formed complex, the charged amine groups of the polycation mainly interact with DNA phosphate groups, with polycation intrusion into the major and minor grooves dependent on the identity and charge state of the polycation. The ability of the polycation to effectively neutralize the charge of the DNA phosphate groups and the resulting influence on the DNA helix interaction are discussed.

Ziebarth, Jesse; Wang, Yongmei

2009-01-01

137

Monte Carlo simulation on complex formation of proteins and polysaccharides.  

PubMed

In protein-polysaccharide complex systems, how nonspecific interactions such as electrostatic and van der Waals interactions affect complex formation has not been clearly understood. On the basis of a coarse-grained model with the specificity of a target system, we have applied Monte Carlo (MC) simulation to illustrate the process of complex coacervate formation from the association of proteins and polysaccharides. The coarse-grained model is based on serum albumin and a polycation system, and the MC simulation of pH impact on complex coacervation has been carried out. We found that complex coacervates could form three ways, but the conventional association through electrostatic attraction between the protein and polysaccharide still dominated the complex coacervation in such systems. We also observed that the depletion potential always participated in protein crowding and was weakened in the presence of strong electrostatic interactions. Furthermore, we observed that the sizes of polysaccharide chains nonmonotonically increased with the number of bound proteins. Our approach provides a new way to understand the details during protein-polysaccharide complex coacervation at multiple length scales, from interaction and conformation to aggregation. PMID:22280485

Li, Yunqi; Shi, Tongfei; An, Lijia; Huang, Qingrong

2012-03-15

138

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

PubMed

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

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

2013-10-01

139

Geology of the Biwabik Iron Formation and Duluth Complex.  

PubMed

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

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

2008-10-01

140

Effect of ternary complex formation on chromatographic selectivity using in situ complexation chromatography  

SciTech Connect

In situ complexation chromatography is a relatively novel form of reversed-phase chromatography. A method for controlling selectivity via ternary complex formation is discussed. This method is potentially useful, not only for controlling separations but also for enhancing detection of metal species. Limitations of the methods are discussed. 30 references, 5 figures, 4 tables.

O'Riordan, K.P.; Heneghan, G.; Wallace, G.G.

1985-06-01

141

Chemical Behaviour of Pu and Am: Hydrolysis Reaction in Brine Solutions, Carbonate Complexation, alpha -Radiolysis, Humate Complexation and Speciation.  

National Technical Information Service (NTIS)

The chemical behaviour of transuranic elements (Pu and Am) has been investigated in saline solution of different NaCl concentrations in the near neutral pH range. Important reactions considered are hydrolysis, carbonate complexation, redox reaction, alpha...

J. I. Kim G. Buckau K. Bueppelmann R. Klenze C. Lierse

1986-01-01

142

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

NASA Astrophysics Data System (ADS)

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 (?tr G ?([3Gly18C6])-?tr G ?(3Gly)).

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

2014-06-01

143

Electronic effects in oxo transfer reactions catalysed by salan molybdenum(VI) cis-dioxo complexes.  

PubMed

A series of molybdenum(vi) cis-dioxo complexes containing tetradentate salan ligands with different para-substitutions on the phenoxy group have been prepared. These complexes catalyse the oxygen atom transfer reaction between dimethylsulfoxide and triphenylphosphine. During oxo transfer catalysis, the complexes are resistant to formation of catalytically inactive oxo-bridged dimeric Mo(v) complexes. Electronic effects influence the rate of the oxo transfer reaction and the fastest rates are achieved when the para-phenoxy substituent is an electron withdrawing nitro substituent. Hammett correlations have shown that the rate-determining step involves nucleophillic attack of the phosphine on one of the oxo ligands. Electrochemical measurements have shown that all complexes containing tertiary amine ligands exhibit quasi-reversible behaviour and that the para-substituent has a considerable effect on the half potentials (E(1/2)). A linear correlation between the E(1/2) values and the Hammett sigma(p) parameter is observed. PMID:19290366

Whiteoak, Christopher J; Britovsek, George J P; Gibson, Vernon C; White, Andrew J P

2009-04-01

144

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

NASA Astrophysics Data System (ADS)

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.

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

2013-05-01

145

Potentiometric studies of complex formation between methylmercury(II) and EDTA.  

PubMed

The protonation of EDTA (ethylenediaminetetra-acetic acid) and its complex formation with methylmercury(II) ions was studied by a potentiometric method at 25 degrees in 1.0M NaNO(3). The protonation constants of EDTA and the equilibrium constants for the complexation reactions between methylmercuric ions and EDTA were evaluated by analysing the experimental data with the ETITR version of the general error-minimizing program LETAGROP. The results were used to develop an analytical method, based on complexometric titration and ion-exchange separation, for the determination of inorganic and organic mercury in the presence of one another. PMID:18962242

Jawaid, M

1978-04-01

146

Formation of cation-anion complexes in the photochemical reaction of molybdenocene dihydrode with iron pentacarbonyl. Crystal structures of (Cp/sub 2/Mo(CO)H)/sup +/(Fe/sub 3/(CO)/sub 11/H)/sup -/ and (Cp/sub 2/Mo(CO)H)/sup +/(CoMo(CO)/sub 3/)/sup -/ (triclinic modification)  

SciTech Connect

The reaction of Cp/sub 2/MoH/sub 2/ with Fe(CO)/sub 5/ in boiling benzene under UV irradiation gives the ionic complexes (Cp/sub 2/Mo(CO)H)/sup +/(Fe/sub 3/(CO)/sub 11/H)/sup -/ (I) and (Cp/sub 2/Mo(CO)H)/sup +/(CpMo(CO)/sub 3/)/sup -/ (II), whose structures were established by x-ray diffraction analysis (Syntex P2/sub 1/ automatic diffractometer, lambda Mo K/sub ..cap alpha../, graphite monochromator, theta/2theta scan technique, full-matrix least-squares method, isotropic variant for I on the basis of 2112 reflections to % = 0.11 and anisotropic variant for II on the basis of 3770 values of hkl to R = 0.052). In complexes I and II the (CpMo(CO)H)/sup +/ fragment is a tapered sandwich with an eclipsed conformation of the rings. In complex I the angle between the rings is 33.9/sup 0/, the mean Mo-C(C/sub 5/H/sub 5/) distance is 2.28(3) A, the mean Mo-C(CO) distance is 2.03(3) A, and the mean Mo-H distance is 1.78(10) A. The corresponding parameters in complex II are: 32.4/sup 0/, 2.296(7), 2.020(6), and 1.87(7) A. The anion in complex I is based on a triangular cluster of Fe atoms, in which one Fe-Fe distance is significantly shorter (2.488(5) A) than the other two (2.702(5) and 2.697(5) A). The Fe atoms forming the short bond are joined additionally by hydride (Fe-H = 2.14 A) and carbonyl (Fe-C = 1.90(3) and 1.93(3) A) Bridges. The remaining groups are terminal. A probable scheme for the process of the formation of complexes I and II has been discussed.

Antsyshkina, A.S.; Dikareva, L.M.; Porai-Koshits, M.A.; Ostrikova, V.N.; Skripkin, Yu.V.; Volkov, O.G.; Pasynskii, A.A.; Kalinnikov, V.T.

1985-11-01

147

Catalytic asymmetric Michael reactions promoted by a lithium-free lanthanum-BINOL complex  

SciTech Connect

In this communication, we report about a new lithium-free BINOL-lanthanum complex, which is quite effective in catalytic asymmetric Michael reaction. We have succeeded in developing effective asymmetric base catalysts, in particular, asymmetric ester enolate catalysts for asymmetric Michael reactions. Two asymmetric lanthanum complexes are now available, namely, BINOL-lanthanum-lithium complex, which is quite effective in catalytic asymmetric nitrosaldol reactions, and a new lithium-free BINOL-lanthanum ester enolate complex, that is very effective in catalytic asymmetric Michael reactions. The two complexes complement each other in their ability to catalyze asymmetric nitroaldol and asymmetric Michael reactions. 14 refs., 1 fig., 2 tabs.

Sasai, Hiroaki; Arai, Takayoshi; Shibasaki, Masakatsu (Univ. of Tokyo (Japan))

1994-02-23

148

Cation-induced formation of a macro-glucan synthase complex  

SciTech Connect

Incubation of Chaps or digitonin-solubilized membrane proteins from cotton fiber with Ca{sup 2+} in combination with Mg{sup 2+}, leads to formation of a complex which can be sedimented within 15 min at 15,000 g. The complex is enriched >10-fold in callose synthase activity and possesses a characteristic pattern of enriched polypeptides when analyzed by SDS-PAGE. Although cation dependent, formation of the complex is not dependent upon the presence of the callose synthase substrate, UDP-glc, indicating that complex formation is not due to entrapment of the enzyme by association with glucan product. The enriched polypeptides include: >200, 50, and 46 kD, all of which have been shown by direct photo-labeling to interact with {sup 92}P-UDP-glc in a Ca{sup 2+} or beta-glucoside dependent reaction are considered likely subunits of callose synthase; a 60-62 kD doublet which is recognized by our MAb 2-1 which can form an immune complex with callose synthase; 74 and 34 kD polypeptides which also interact with UDP-glc, but do not associate with callose synthase in the presence of EDTA. A similar phenomenon is also observed with solubilized membrane proteins from mung beans. Possible functions of each of the enriched polypeptides, the catalytic properties, and ultra-structure of this macro-glucan synthase complex are currently under investigation.

Delmer, D.; Solomon, M.; Andrawis, A.; Amor, Y. (Hebrew Univ., Jerusalem (Israel))

1990-05-01

149

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

SciTech Connect

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.

Oba, Y.; Watanabe, N.; Hama, T.; Kuwahata, K.; Hidaka, H.; Kouchi, A., E-mail: oba@lowtem.hokudai.ac.jp [Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819 (Japan)

2012-04-10

150

An efficient, nonlinear stability analysis for detecting pattern formation in reaction diffusion systems.  

PubMed

Reaction diffusion systems are often used to study pattern formation in biological systems. However, most methods for understanding their behavior are challenging and can rarely be applied to complex systems common in biological applications. I present a relatively simple and efficient, nonlinear stability technique that greatly aids such analysis when rates of diffusion are substantially different. This technique reduces a system of reaction diffusion equations to a system of ordinary differential equations tracking the evolution of a large amplitude, spatially localized perturbation of a homogeneous steady state. Stability properties of this system, determined using standard bifurcation techniques and software, describe both linear and nonlinear patterning regimes of the reaction diffusion system. I describe the class of systems this method can be applied to and demonstrate its application. Analysis of Schnakenberg and substrate inhibition models is performed to demonstrate the methods capabilities in simplified settings and show that even these simple models have nonlinear patterning regimes not previously detected. The real power of this technique, however, is its simplicity and applicability to larger complex systems where other nonlinear methods become intractable. This is demonstrated through analysis of a chemotaxis regulatory network comprised of interacting proteins and phospholipids. In each case, predictions of this method are verified against results of numerical simulation, linear stability, asymptotic, and/or full PDE bifurcation analyses. PMID:24158538

Holmes, William R

2014-01-01

151

Alcohol, self-focus and complex reaction-time performance.  

PubMed

The effects of alcohol, expectancy and state-trait varieties of public self-focus on complex reaction-time performance were evaluated. The procedure crossed a 2 (expectancy) X 2 (dose) modified balanced-placebo design with two levels of public self-awareness (normal versus high). A median split procedure performed on public and private self-consciousness scale scores served to evaluate trait effects. Results indicated that subject's task performance was best understood as an interaction between his subjective experience of intoxication-sobriety, his beliefs concerning what he had drunk and the salience of situational standards toward effortful performance. Public self-consciousness proved to mediate the behavioral expression of conventional expectancies concerning drunken comportment. Interactions between alcohol, expectancy and self-focus are discussed in terms of an interactive model of drunken comportment. PMID:3361903

Ross, D F; Pihl, R O

1988-03-01

152

Reinvestigation of the formation of a mononuclear Fe(III) hydroperoxido complex using high pressure kinetics.  

PubMed

Previous stopped flow kinetic experiments suggested an interchange associative mechanism for the ligand substitution reaction, [Fe(bztpen)(OMe)](2+) + H(2)O(2)--> {[Fe(bztpen)(OMe)(HOOH)](2+)}(++)--> [Fe(bztpen)(OOH)](2+) + MeOH (bztpen = N-benzyl-N, N',N'tris(2-methylpyridyl)-ethylenediamine). Thus a seven-coordinate transition state containing both the leaving methoxide and the incoming hydrogen peroxide ligands was proposed. On the basis of high pressure kinetic data we can now conclude that this is not the case since the rate of the reaction is independent of pressure for the formation of the purple low spin transient hydroperoxido complex, [Fe(bztpen)(OOH)](2+). [Fe(bztpen)(OOH)](2+) has so far proved to be too short-lived for solid state isolation. As part of our ongoing pursuit of this elusive species we have structurally characterised the nitrosyl and acetate iron(II) complexes, [Fe(bztpen)(NO)](OTf)(2) and [Fe(bztpen)(OAc)](BPh(4)), as well as the air stable Co(II) complexes [Co(bztpen)Cl)]BF(4), [Co(metpen)Cl]SbF(6) and [Co(bztpen)(OAc)]BPh(4). We did not realise our aim of accessing stable Co(III) hydroperoxido or peroxido complexes by reaction of the cobalt complexes with H(2)O(2). PMID:20648392

Nebe, Thomas; Beitat, Alexander; Würtele, Christian; Dücker-Benfer, Carlos; van Eldik, Rudi; McKenzie, Christine J; Schindler, Siegfried

2010-09-01

153

Trialkylphosphine-stabilized copper-phenyltellurolate complexes: from small molecules to nanoclusters via condensation reactions.  

PubMed

Reactions of CuCl with Te(Ph)SiMe3 and solublizing trialkylphosphine ligands afford a series of polynuclear copper-phenyltellurolate complexes that has been structurally characterized. The formation of the complexes is found to be highly dependent on the ancillary phosphine ligand used. The synthesis and structures of [Cu2(mu-TePh)2(PMe3)4] 1, [Cu4(mu3-TePh)4(PPr(i)3)3] 2, [Cu5(mu-TePh)3(mu3-TePh)3(PEt3)3][PEt3Ph] 3, and [Cu12Te3(mu3-TePh)6(PEt3)6] 4 are described. The telluride (Te(2-)) ligands in 4 arise from the generation of TePh2 in the reaction mixtures. The subsequent co-condensation of clusters 3 and 4 leads to the generation of the nanometer sized complex [Cu29Te9(mu3-TePh)10(mu4-TePh)2(PEt3)8][PEt3Ph] 5 in good yield, in addition to small amounts of [Cu39(mu3-TePh)10(mu4-TePh)Te16(PEt3)13] 6. These complexes are formed via the photo elimination of TePh2. The cyclic voltammogram of 5 in THF solution exhibits two oxidation waves, assigned to the oxidation of the Cu(I) centers. PMID:11511215

DeGroot, M W; Cockburn, M W; Workentin, M S; Corrigan, J F

2001-08-27

154

Versatile reactivity of a four-coordinate scandium phosphinidene complex: reduction, addition, and CO activation reactions.  

PubMed

The four-coordinate scandium phosphinidene complex, [LSc(?-PAr)]2 (L = (MeC(NDIPP)CHC(Me)(NCH2CH2N((i)Pr)2)), DIPP = 2,6-((i)Pr)2C6H3; Ar = 2,6-Me2C6H3) (1), has been synthesized in good yield, and its reactivity has been investigated. Although 1 has a bis(?-phosphinidene)discandium structural unit, this coordinatively unsaturated complex shows high and versatile reactivity toward a variety of substrates. First, two-electron reduction occurs when substrates as 2,2'-bipyridine, elemental selenium, elemental tellurium, Me3P?S, or Ph3P?E (E = S, Se) is used, resulting in the oxidative coupling of two phosphinidene ligands 2[PAr](2-) into a diphosphene ligand [ArP-PAr](2-). Complex 1 easily undergoes nucleophilic addition reactions with unsaturated substrates, such as benzylallene, benzonitrile, tert-butyl isocyanide, and CS2. This complex also shows a peculiar reactivity to CO and Mo(CO)6, that includes C-P bond formation, C-C coupling and C-O bond cleavage of CO, to afford novel phosphorus-containing products. In the last two types of reactivity, reaction profiles have been computed (for the insertion of (t)BuNC and the CO activation by 1) at the DFT level. The unexpected/surprising sequence of steps in the latter case is also revealed. PMID:24004243

Lv, Yingdong; Kefalidis, Christos E; Zhou, Jiliang; Maron, Laurent; Leng, Xuebing; Chen, Yaofeng

2013-10-01

155

Reactions of alkynes with [RuCl(cyclopentadienyl)] complexes: the important first steps.  

PubMed

Cyclopentadienyl-ruthenium half-sandwich complexes with eta(2)-bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru-catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp--)(eta(2)-RC[triple bond]CR')] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp-- (Cp--=eta(5)-1-methoxy-2,4-tert-butyl-3-neopentyl-cyclopentadienyl). Furthermore we demonstrate that [RuCl(2)(Cp==)](2) is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(eta(2)-alkyne) complexes containing {RuCl(Cp*)} (Cp*=eta(5)-C(5)Me(5)) and {RuCl(Cp--)} fragments with alkynes were investigated by DFT calculations at the M06/6-31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp-- ligand increases the activation energy required for the formation of the corresponding di(eta(2)-alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne. PMID:20583066

Dutta, Barnali; Curchod, Basile F E; Campomanes, Pablo; Solari, Euro; Scopelliti, Rosario; Rothlisberger, Ursula; Severin, Kay

2010-07-26

156

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

PubMed Central

Reaction of 1-adamantyl azide with iron(I) diketiminate precursors gives metastable but isolable imidoiron(III) complexes LFe=NAd (L = bulky ?-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.

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

157

Massive Star Formation in the LMC HII Complex N44  

NASA Astrophysics Data System (ADS)

The star formation process can be characterized microscopically by the initial mass function (IMF) and macroscopically by the intensity of the activity as a function of space and time. To study the star formation process in a mild starburst environment, I have analyzed N44, one of the three top-ranking HII complexes in the Large Magellanic Cloud, using the most comprehensive inventory of resolved massive stars and young stellar objects (YSOs) derived from CTIO 4-m MOSAIC UBVI and ISPI JK images, supplemented by 0.9-m UBV images, and Spitzer Space Telescope IRAC and MIPS observations. The N44 complex can be divided into three regions that are coincident with three concentrations of giant molecular clouds but exhibiting different evolutionary states and intensities of star formation. The central concentration is associated with a prominent superbubble and bright HII regions along its periphery; the south concentration is associated with a group of bright HII regions; and the north concentration has only two faint little HII regions. I have defined and examined regions with contrasting star formation properties to determine their present-day mass functions (PDMFs). I find that comparisons of slopes of the IMF between star forming regions and the "field" is highly dependent on the definition of the regions. I have also used the Spitzer mid-IR observations to identify massive YSOs in order to study the current, on-going star formation. I have also used ground-based high-resolution UBVIJK observations to confirm their nature as YSOs and to model their spectral energy distributions for mass estimates. I find that the more massive YSOs are preferentially formed near sites previous active star formation has taken place. The stellar energy feedback may play some role in the formation of massive stars.

Chen, C. H. Rosie

2007-12-01

158

Star Formation in Giant Complexes: the Cat's Paw Nebula  

NASA Astrophysics Data System (ADS)

NGC 6334, the Cat's Paw Nebula, is a 106 M? molecular cloud, one of the most massive known clouds in the Galaxy. It hosts the youngest massive cluster complex within 2 kpc of the Sun, and is therefore an ideal laboratory to investigate the onset and early evolution of star formation in an environment comparable to that of massive, extra-galactic complexes. Using multi-wavelength data, we are conducting the most sensitive and most complete characterization of this unique region to date.

Ascenso, Joana; Wolk, Scott; Lombardi, Marco; Alves, João; Rathborne, Jill; Forbrich, Jan; Leibundgut, Bruno; Hilker, Michael

2013-07-01

159

A new dynamical layout algorithm for complex biochemical reaction networks  

PubMed Central

Background To study complex biochemical reaction networks in living cells researchers more and more rely on databases and computational methods. In order to facilitate computational approaches, visualisation techniques are highly important. Biochemical reaction networks, e.g. metabolic pathways are often depicted as graphs and these graphs should be drawn dynamically to provide flexibility in the context of different data. Conventional layout algorithms are not sufficient for every kind of pathway in biochemical research. This is mainly due to certain conventions to which biochemists/biologists are used to and which are not in accordance to conventional layout algorithms. A number of approaches has been developed to improve this situation. Some of these are used in the context of biochemical databases and make more or less use of the information in these databases to aid the layout process. However, visualisation becomes also more and more important in modelling and simulation tools which mostly do not offer additional connections to databases. Therefore, layout algorithms used in these tools have to work independently of any databases. In addition, all of the existing algorithms face some limitations with respect to the number of edge crossings when it comes to larger biochemical systems due to the interconnectivity of these. Last but not least, in some cases, biochemical conventions are not met properly. Results Out of these reasons we have developed a new algorithm which tackles these problems by reducing the number of edge crossings in complex systems, taking further biological conventions into account to identify and visualise cycles. Furthermore the algorithm is independent from database information in order to be easily adopted in any application. It can also be tested as part of the SimWiz package (free to download for academic users at [1]). Conclusion The new algorithm reduces the complexity of pathways, as well as edge crossings and edge length in the resulting graphical representation. It also considers existing and further biological conventions to create a drawing most biochemists are familiar with. A lot of examples can be found on [2].

Wegner, Katja; Kummer, Ursula

2005-01-01

160

Electron Transfer Reactions in Colloidal Quantum Dot-Ligand Complexes  

NASA Astrophysics Data System (ADS)

This thesis describes a quantitative analysis of the chemical composition of colloidal II-VI quantum dot (QD)-ligand complexes and transient absorption experiments analyzing the rates of electron transfer reactions in these complexes functionalized with redox active ligands. Chemical analysis reveals that phosphonate impurities in the surfactants used to synthesize CdSe QDs are the dominant ligands on the surface of the QDs, and these phosphonate impurities cause size-dependent Cd-enrichment of the QD surface. A study of the adsorption equilibrium of solution-phase CdS quantum dots and acid-derivatized viologen ligands (V2+) reveals that the structure of the surfaces of the QDs depends on the concentration of the QDs. A new model based on the Langmuir isotherm that treats both the number of adsorbed ligands per QD and the number of available binding sites per QD as binomially-distributed quantities is described. Transient absorption spectroscopy of solution-phase mixtures of colloidal CdS QDs and V2+ indicates electron transfer occurs from the conduction band of the QD to the LUMO of V2+. The rate constant for photoinduced electron transfer (PET) is independent of the number of methylene groups in the alkyl chain on the acid-derivatized viologen. The insensitivity of the electron transfer rate constant to the length of the functional groups on the viologen suggests a van der Waals (vdW) pathway for PET, where the electron bypasses the alkylcarboxylate and tunnels through the orbitals of the QD and of the bipyridinium core. The rate of PET from colloidal CdSe quantum dots (QDs) to oxo-centered triruthenium clusters (Ru 3O) depends on the structure of the chemical headgroup by which the Ru3O clusters adsorb to the QDs. Complexes comprising QDs and Ru 3O clusters adsorbed through a pyridine-4-carboxylic acid ligand have a PET rate constant of (4.9 ± 0.9)×109 s -1 whereas complexes comprising QDs and Ru3O clusters adsorbed through a 4-mercaptopyridine ligand have an intrinsic PET rate constant of (36 ± 7)×109 s-1. The difference in the observed rates of PET for the two complexes is attributed to a difference in donor-acceptor electronic coupling.

Morris-Cohen, Adam Joshua

161

Quantitation of Ligand Effect in oxo-transfer reactions from dioxo-Mo(VI) trispyrazolyl borate complexes  

PubMed Central

The oxygen atom transfer reactivity (OAT) from dioxo-Mo(VI) complexes of hydrotrispyrazolyl borate (hydrotris(3,5-dimethylpyrazolyl)borate, TpMe2; hydrotris(3-isopropylpyrazol-1-yl)borate, TpiPr) to tertiary phosphines (PMe3, PMe2Ph, PEt3, PEt2Ph, PBun3, PMePh2, or PEtPh2) has been investigated. In acetonitrile, these reactions proceed via the formation of a phosphoryl intermediate complex that undergoes a solvolysis reaction. We report the synthesis and characterization of several phosphoryl complexes. The rates of formation of phosphoryl complexes and their solvation were determined by spectrophotometry. The rates of the reactions and the properties of the phosphoryl species were investigated using the Quantitative Analysis of Ligand Effect (QALE) methodology. The results show that, at least in this system, the first step of the reaction is controlled primarily by the steric factor, and in the second step, both electronic and steric factors are important. We also analyzed the effect of ligands on the reaction rate e.g., TpMe2 vs. TpiPr.

Kail, Brian W.; Adams, Andrew K.; Nemykin, Victor N.

2012-01-01

162

Mechanistic insights into the formation of N2O by a nickel nitrosyl complex.  

PubMed

Reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with 1 equiv of nitric oxide (NO) in CH2Cl2 results in the formation of N2O and [{(Me2phen)Ni(NO)}2(?-?(1)-N:?(1)-O)-NO2)][PF6] (3), along with the known complex, [Ni(bipy)3][PF6]2 (4). The isolation of complex 3, which contains a nitrite ligand, demonstrates that the reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with exogenous NO results in NO disproportionation and not NO reduction. Complex 3 could also be accessed by reaction of [Ni(NO)(Me2phen)][PF6] (5) with (Me2phen)Ni(NO)(NO2) (7) in good yield. Complexes 3, 5, and 7 were fully characterized, including analysis by X-ray crystallography in the case of 3 and 7. Furthermore, addition of 0.5 equiv of bipy to [Ni(NO)(bipy)][PF6] results in formation of the hyponitrite complex, [{(bipy)Ni(?(2)-O2N2)}?(1):?(1)-N,N-{Ni(NO)(bipy)}2][PF6]2 (9), in modest yield. Importantly, the hyponitrite ligand in 9 is thought to form via coupling of two NO(-) ligands and not by coupling of a nucleophilic nitrosyl ligand (NO(-)) with an electrophilic nitrosyl ligand (NO(+)). X-ray crystallography reveals that complex 9 features a new binding mode of the cis-hyponitrite ligand. PMID:24597563

Wright, Ashley M; Zaman, Homaira T; Wu, Guang; Hayton, Trevor W

2014-03-17

163

Processive Ubiquitin Chain Formation by the Anaphase-Promoting Complex  

PubMed Central

Progression through mitosis requires the sequential ubiquitination of cell cycle regulators by the anaphase-promoting complex, resulting in their proteasomal degradation. Although several mechanisms contribute to APC/C regulation during mitosis, the APC/C is able to discriminate between its many substrates by exploiting differences in the processivity of ubiquitin chain assembly. Here, we discuss how the APC/C achieves processive ubiquitin chain formation to trigger the sequential degradation of cell cycle regulators during mitosis.

Meyer, Hermann-Josef; Rape, Michael

2011-01-01

164

Reversible Dissociation and Ligand-Glutathione Exchange Reaction in Binuclear Cationic Tetranitrosyl Iron Complex with Penicillamine  

PubMed Central

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)??k1 = (4.6 ± 0.1)·10?3?s?1 and the elimination rate constant of the penicillamine ligand k2 = (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.

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

2014-01-01

165

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

PubMed

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. PMID:24790592

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

2014-01-01

166

Correlations between Community Structure and Link Formation in Complex Networks  

PubMed Central

Background Links in complex networks commonly represent specific ties between pairs of nodes, such as protein-protein interactions in biological networks or friendships in social networks. However, understanding the mechanism of link formation in complex networks is a long standing challenge for network analysis and data mining. Methodology/Principal Findings Links in complex networks have a tendency to cluster locally and form so-called communities. This widely existed phenomenon reflects some underlying mechanism of link formation. To study the correlations between community structure and link formation, we present a general computational framework including a theory for network partitioning and link probability estimation. Our approach enables us to accurately identify missing links in partially observed networks in an efficient way. The links having high connection likelihoods in the communities reveal that links are formed preferentially to create cliques and accordingly promote the clustering level of the communities. The experimental results verify that such a mechanism can be well captured by our approach. Conclusions/Significance Our findings provide a new insight into understanding how links are created in the communities. The computational framework opens a wide range of possibilities to develop new approaches and applications, such as community detection and missing link prediction.

Liu, Zhen; He, Jia-Lin; Kapoor, Komal; Srivastava, Jaideep

2013-01-01

167

A spectroscopic study on the formation of Cm(III) acetate complexes at elevated temperatures.  

PubMed

The complexation of Cm(III) with acetate is studied by time resolved laser fluorescence spectroscopy (TRLFS) as a function of ionic strength, ligand concentration, temperature and background electrolyte (NaClO4, NaCl and CaCl2 solution). The speciation of Cm(III) is determined by peak deconvolution of the emission spectra. To obtain the thermodynamic stability constants (log K) for the formation of [Cm(Ac)n](3-n) (n = 1-3), the experimental data are extrapolated to zero ionic strength according to the specific ion interaction theory (SIT). The results show a continuous increase of the stability constants with increasing temperature (20-90 °C). The standard reaction enthalpies and entropies (?rH, ?rS) of the respective reactions are derived from the integrated Van't Hoff equation. The results show that all complexation steps are endothermic and thus entropy driven (?rH and ?rS > 0). PMID:24448229

Fröhlich, Daniel R; Skerencak-Frech, Andrej; Panak, Petra J

2014-03-14

168

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

PubMed Central

Irradiation of CpRh(PMe3)(C2H4) (1; Cp = ?5-C5H5) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable ?2-C,C-coordinated pentafluoropyridine complex, CpRh(PMe3)(?2-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)(?2-C,C-CH2N(CH3)C5NF3) (4) and CpRh(PMe3)(?2-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.

2013-01-01

169

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

PubMed Central

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.

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

2013-01-01

170

Parameter estimation in complex flows with chemical reactions  

NASA Astrophysics Data System (ADS)

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 electrochemical parameters examined again show very close agreement to the experimental values. The usual method of determining chemical reaction rates by measurement is lengthy and time consuming, especially where the chemistry and chemical processes are of a more complex nature. This computational method and associated algorithms has shown to deliver accurate correlations to the experimental data for three-dimensional models, demonstrated in these new unique applications of the technique.

Robinson, Daniel J.

171

New fluorescence reactions in DNA cytochemistry. 2. Microscopic and spectroscopic studies on fluorescent aluminum complexes  

SciTech Connect

Metal-dye complexes are widely applied in light microscopic techniques for chromatin staining (e.g., hematoxylin and carmine), but fluorescent complexes between phosphate-binding cations and suitable ligands have been little used. Preformed and postformed Al complexes with different anionic dyes induced strong and selective fluorescence reactions in nuclei from chicken blood smears, frozen sections, paraffin-embedded sections and Epon-embedded sections of mouse and rat tissues, mitotic chromosomes, meiotic chromosomes and kinetoplasts of Trypanosoma cruzi epimastigotes. The DNA-dependent fluorescence of these structures showed a very low fading rate. The emission colors were related to the ligand. The most suitable compounds for forming fluorescent Al chelates were 8-hydroxyquinoline, morin, nuclear fast red and purpurin. Staining with diluted carmine solutions and InCl3 mordanting, followed by 8-hydroxyquinoline, also induced chromatin fluorescence. After treating isolated mouse chromosomes with the preformed complex Al-nuclear fast red, x-ray microanalysis indicated a P:Al:dye binding ratio of about 40:15:1. The selectivity, stability and easy formation of these fluorescent Al complexes are obvious advantages for their use as new cytochemical probes in cytologic studies.

Del Castillo, P.; Llorente, A.R.; Gomez, A.; Gosalvez, J.; Goyanes, V.J.; Stockert, J.C. (Autonomous Univ., Madrid (Spain))

1990-02-01

172

Synthesis and reactions of Cp-linked phosphine complexes of rhodium  

SciTech Connect

The linked Cp ligand [C{sub 5}H{sub 4}SiMe{sub 2}CH{sub 2}PPh{sub 2}]{sup {minus}} has been used to synthesize several rhodium derivatives. Reaction with [RhClL{sub 2}]{sub 2} where L = C{sub 2}H{sub 4}, C{sub 8}H{sub 14}, or CO, gives ({eta}{sup 5}:{eta}{sup 1}-C{sub 5}H{sub 4}SiMe{sub 2}-CH{sub 2}PPh{sub 2})Rh(L) complexes, which have been characterized by single-crystal X-ray diffraction. Reaction of the ethylene complex with CO or PMe{sub 3} gives the carbonyl- and phosphine-substituted derivatives, respectively. Irradiation of the ethylene complex in the presence of hydrogen gives a new binuclear polyhydride, also structurally characterized, in which the chelating ligand spans the two metal centers. Reaction of the ethylene complex with iodine leads to the formation of the diiodide ({eta}{sup 5}:{eta}{sup 1}-C{sub 5}H{sub 4}SiMe{sub 2}CH{sub 2}PPh{sub 2})RhI{sub 2}, which in turn can be converted to the dihydride ({eta}{sup 5}:{eta}{sup 1}-C{sub 5}H{sub 4}SiMe{sub 2}CH{sub 2}PPh{sub 2})RhH{sub 2} by reaction with NaAl(OCH{sub 2}CH{sub 2}OCH{sub 3}){sub 2}H{sub 2}. The reactivity of the dihydride toward C-H bond activation has been investigated. While benzene does not give a stable oxidative addition adduct, pentafluorobenzene yields ({eta}{sup 5}:{eta}{sup 1}-C{sub 5}H{sub 4}SiMe{sub 2}CH{sub 2}PPh{sub 2})Rh(C{sub 6}F{sub 5})H, which was structurally characterized as its chloro derivative. Reaction of the dihydride with C{sub 6}F{sub 6} gives the {eta}{sup 2} complex ({eta}{sup 5}:{eta}{sup 1}-C{sub 5}H{sub 4}SiMe{sub 2}CH{sub 2}PPh{sub 2})Rh({eta}{sup 2}-C{sub 6}F{sub 6}), also structurally characterized.

Lefort, L.; Crane, T.W.; Farwell, M.D.; Baruch, D.M.; Kaeuper, J.A.; Lachicotte, R.J.; Jones, W.D. [Univ. of Rochester, NY (United States). Dept. of Chemistry] [Univ. of Rochester, NY (United States). Dept. of Chemistry

1998-08-31

173

A calorimetric comparison of trypsin and its anhydro modification in complex formation with Kunitz soybean inhibitor.  

PubMed

The heat of complex formation between native trypsin or its anhydro modification (Ako, H., Foster, R. J., and Ryan, C. J. (1972) Biochem. Biophys. Res Commun. 47, 1402--1407) with native or cleaved Kunitz soybean inhibitor (Finkenstadt, W. R., and Laskowski, M., Jr. (1965) J. Biol. Chem. 240, 962--963) has been observed from pH 3.5 to 7.5. Steep dependence of reaction heat upon pH between pH 3.5 and 4.25 is observed with native inhibitor in reaction with both trypsin and anhydrotrypsin. The character of this heat-pH relationship is consistent with a cooperative process involving three to four ionizable groups. Above pH 4.25, trypsin and anhydrotrypsin in reaction with native inhibitor have quite different pH dependencies. Native trypsin shows an apparent pK near pH 5, whereas anhydrotrypsin + inhibitor reaction heat remains nearly constant from pH 4.5 to 6, and shows an apparent pK near pH 7.0. Above pH 4, the reaction heat-pH relations for native or cleaved inhibitor in reaction with trypsin are only slightly different (Barnhill, M. T., Jr., and Trowbridge, C. G. (1975) J. Biol. Chem. 250, 5501--5507). On the other hand, substitution of cleaved for native inhibitor in reaction with anhydrotrypsin causes a greatly reduced reaction heat, with no clearly developed pH dependence from pH 5.5 to 7.5. The reaction heat-pH relationships are analyzed thermodynamically in terms of the temperature coefficient of a pH-dependent equilibrium constant. It is clear that conversion of the active site serine side chain of trypsin to dehydroalanine changes the pH dependence of its reaction heat with soybean inhibitor, and that the complex formed is sensitive to the state of the scissile inhibitor bond. These differences provide a comparison of a protein-protein association with and without covalent bond formation between reactants. PMID:7191852

Yung, B Y; Trowbridge, C G

1980-10-25

174

Protonation and bromination of an osmabenzyne: reactions leading to the formation of new metallabenzynes.  

PubMed

The reactivities of benzynes and metal-carbyne complexes are normally associated with the triple bond units. However, we have now found that electrophiles do not attack the formal osmium-carbon triple bond of osmabenzyne complex 1. Instead, 1 undergoes electrophilic substitution reactions-the typical reactions of aromatic systems. PMID:12537483

Wen, Ting Bin; Ng, Sze Ming; Hung, Wai Yiu; Zhou, Zhong Yuan; Lo, Man Fung; Shek, Lai-Yung; Williams, Ian D; Lin, Zhenyang; Jia, Guochen

2003-01-29

175

Synthesis of heterometal cluster complexes by the reaction of cobaltadichalcogenolato complexes with groups 6 and 8 metal carbonyls.  

PubMed

Metalladichalcogenolate cluster complexes [{CpCo(S2C6H4)}2Mo(CO)2] (Cp = eta(5)-C5H5) (3), [{CpCo(S2C6H4)}2W(CO)2] (4), [CpCo(S2C6H4)Fe(CO)3] (5), [CpCo(S2C6H4)Ru(CO)2(P(t)Bu3)] (6), [{CpCo(Se2C6H4)}2Mo(CO)2] (7), and [{CpCo(Se2C6H4)}(Se2C6H4)W(CO)2] (8) were synthesized by the reaction of [CpCo(E2C6H4)] (E = S, Se) with [M(CO)3(py)3] (M = Mo, W), [Fe(CO)5], or [Ru(CO)3(P(t)Bu3)2], and their crystal structures and physical properties were investigated. In the series of trinuclear group 6 metal-Co complexes, 3, 4, and 7 have similar structures, but the W-Se complex, 8, eliminates one cobalt atom and one cyclopentadienyl group from the sulfur analogue, 4, and does not satisfy the 18-electron rule. 1H NMR observation suggested that the CoW dinuclear complex 8 was generated via a trinuclear Co2W complex, with a structure comparable to 7. The trinuclear cluster complexes, 3, 4, and 7, undergo quasi-reversible two-step one-electron reduction, indicating the formation of mixed-valence complexes Co(III)M(0)Co(II) (M = Mo, W). The thermodynamic stability of the mixed-valence state increases in the order 4 < 3 < 7. In the dinuclear group 8 metal-Co complexes, 5 and 6, the CpCo(S2C6H4) moiety and the metal carbonyl moiety act as a Lewis acid character and a base character, respectively, as determined by their spectrochemical and redox properties. Complex 5 undergoes reversible two-step one-electron reduction, and an electron paramagnetic resonance (EPR) study indicates the stepwise reduction process from Co(III)Fe(0) to form Co(III)Fe(-I) and Co(II)Fe(-I). PMID:16441120

Murata, Masaki; Habe, Satoru; Araki, Shingo; Namiki, Kosuke; Yamada, Teppei; Nakagawa, Norikiyo; Nankawa, Takuya; Nihei, Masayuki; Mizutani, Jun; Kurihara, Masato; Nishihara, Hiroshi

2006-02-01

176

Reaction of iminopropadienones with amines: mechanistic explanations of zwitterionic intermediate, ketene and ketenimine formation.  

PubMed

The complex reaction of thermally generated iminopropadienones with amines in the gas phase and upon matrix deposition and its varying product composition is investigated using density functional theory. In the high energy gas phase addition a single amine molecule reacts readily with iminopropadienone with the decisive step being a 1,3-hydrogen shift and activation barriers of at least 100 kJ/mol. In accordance with the experiment, the formation of ketenes is favored. In the condensed phase of an amine matrix, the utilization of amine dimers both as reagents and as explicit solvents lowers the activation energy required to a feasible 20-30 kJ/mol and predicts ketenimines as the main products, as observed experimentally. PMID:18759423

Koch, Rainer; Finnerty, Justin J; Bruhn, Torsten; Borget, Fabien; Wentrup, Curt

2008-09-25

177

Computational Analyses of Complex Flows with Chemical Reactions  

NASA Astrophysics Data System (ADS)

The heat and mass transfer phenomena in micro-scale for the mass transfer phenomena on drug in cylindrical matrix system, the simulation of oxygen/drug diffusion in a three dimensional capillary network, and a reduced chemical kinetic modeling of gas turbine combustion for Jet propellant-10 have been studied numerically. For the numerical analysis of the mass transfer phenomena on drug in cylindrical matrix system, the governing equations are derived from the cylindrical matrix systems, Krogh cylinder model, which modeling system is comprised of a capillary to a surrounding cylinder tissue along with the arterial distance to veins. ADI (Alternative Direction Implicit) scheme and Thomas algorithm are applied to solve the nonlinear partial differential equations (PDEs). This study shows that the important factors which have an effect on the drug penetration depth to the tissue are the mass diffusivity and the consumption of relevant species during the time allowed for diffusion to the brain tissue. Also, a computational fluid dynamics (CFD) model has been developed to simulate the blood flow and oxygen/drug diffusion in a three dimensional capillary network, which are satisfied in the physiological range of a typical capillary. A three dimensional geometry has been constructed to replicate the one studied by Secomb et al. (2000), and the computational framework features a non-Newtonian viscosity model for blood, the oxygen transport model including in oxygen-hemoglobin dissociation and wall flux due to tissue absorption, as well as an ability to study the diffusion of drugs and other materials in the capillary streams. Finally, a chemical kinetic mechanism of JP-10 has been compiled and validated for a wide range of combustion regimes, covering pressures of 1atm to 40atm with temperature ranges of 1,200 K--1,700 K, which is being studied as a possible Jet propellant for the Pulse Detonation Engine (PDE) and other high-speed flight applications such as hypersonic 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.

Bae, Kang-Sik

178

Redox Reactions of the ?-Synuclein-Cu2+ Complex and Their Effects on Neuronal Cell Viability  

PubMed Central

?-Synuclein (?-syn), a presynaptic protein believed to play an important role in neuropathology in Parkinson’s disease (PD), is known to bind Cu2+. Cu2+ has been shown to accelerate the aggregation of ?-syn to form various toxic aggregates in vitro. Copper is also a redox active metal whose complexes with amyloidogenic proteins/peptides have been linked to oxidative stress in major neurodegenerative diseases. In this work, the formation of Cu2+ complex with ?-syn or with an N-terminus peptide, ?-syn(1–19), was confirmed with electrospray-mass spectrometry (ES–MS). The redox potentials of Cu2+ complex with ?-syn (?-syn-Cu2+) and ?-syn(1–19) were determined to be 0.018 and 0.053 V, respectively. Furthermore, the Cu2+ center(s) can be readily reduced to Cu+ and possible reactions of ?-syn-Cu2+ with cellular species (e.g., O2, ascorbic acid, and dopamine) were investigated. The occurrence of a redox reaction can be rationalized by comparing the redox potential of the ?-syn-Cu2+ complex to that of the specific cellular species. For example, ascorbic acid can directly reduce ?-syn-Cu2+ to ?-syn-Cu+, setting up a redox cycle in which O2 is reduced to H2O2 and cellular redox species is continuously exhausted. In addition, the H2O2 generated was demonstrated to reduce viability of the neuroblastoma SY-HY5Y cells. Although our results ruled out the direct oxidation of dopamine by ?-syn-Cu2+, the H2O2 generated in the presence of ?-syn-Cu2+ can oxidize dopamine. Our results suggest that oxidative stress is at least partially responsible for the loss of dopaminergic cells in PD brain and reveal the multifaceted role of the ?-syn-Cu2+ complex in oxidative stress associated with PD symptoms.

Wang, Chengshan; Liu, Lin; Zhang, Lin; Peng, Yong; Zhou, Feimeng

2010-01-01

179

Complex Interactions between Formative Assessment, Technology, and Classroom Practices  

NSDL National Science Digital Library

Interactive engagement (IE) methods provide instructors with evidence of student thinking that can guide instructional decisions across a range of timescales: facilitating an activity, determining the flow of activities, or modifying the curriculum. Thus, from the instructor's perspective, IE activities can function as formative assessments. As a practical matter, the ability to utilize this potential depends on how the activities are implemented. This paper describes different tools for small group problem solving, including whiteboards, Tablet PCs, digital cameras, and photo-sharing websites. These tools provide the instructor with varying levels of access to student work during and after class, and therefore provide a range of support for formative assessment. Furthermore, the tools differ in physical size, ease of use, and the roles for students and instructor. These differences lead to complex, often surprising interactions with classroom practices.

Price, Edward

2012-05-15

180

Focus Formation by a Murine Sarcoma-Leukemia Virus Complex  

PubMed Central

The transformation of cells in culture by a murine sarcoma-leukemia virus complex leads to the formation of identifiable foci. Titration patterns of focus counts vs. virus dilutions have been explained as being due to the interactions of three virions: leukemia, defective sarcoma, and competent hybrid. This interaction is analyzed quantitatively and equations are derived which permit determination of the composition of a sarcoma virus pseudotype as well as use of the technique for the assay of exogeneous leukemia virus. The analysis is based on the statistical distribution of virions in the culture cells and assumes that all virions have equal probability of infecting a cell and that transformation of any one cell will lead to focus formation. Limitations of the assumptions and expected measurement accuracy are discussed.

Hahn, G. M.; Decleve, A.; Lieberman, M.; Kaplan, H. S.

1970-01-01

181

Complex interactions between formative assessment, technology, and classroom practices  

NASA Astrophysics Data System (ADS)

Interactive engagement (IE) methods provide instructors with evidence of student thinking that can guide instructional decisions across a range of timescales: facilitating an activity, determining the flow of activities, or modifying the curriculum. Thus, from the instructor's perspective, IE activities can function as formative assessments. As a practical matter, the ability to utilize this potential depends on how the activities are implemented. This paper describes different tools for small group problem solving, including whiteboards, Tablet PCs, digital cameras, and photo-sharing websites. These tools provide the instructor with varying levels of access to student work during and after class, and therefore provide a range of support for formative assessment. Furthermore, the tools differ in physical size, ease of use, and the roles for students and instructor. These differences lead to complex, often surprising interactions with classroom practices.

Price, Edward

2012-02-01

182

Model experiment for studying lane formation in binary complex plasmas  

NASA Astrophysics Data System (ADS)

We present the first experimental realisation on lane formation in binary complex plasmas under gravity conditions. The amount of penetrating particles can be controlled. The experiment can be operated with stable conditions continuously, which allows to study steady state. The driving force is independent of time and position and the background density is homogeneous and isotropic. This provides an ideal model system for comparison with numerical experiments and observations in colloidal suspensions. The experiment setup is based on PK-3 Plus laboratory operated on the International Space Station. Gravitation is compensated by thermophoretic force and penetrating particles are controlled via a toroidal vortex with poloidal flow. The evolution of lane formation along the penetration direction is illustrated by lane order parameter.

Du, C.-R.; Sütterlin, K. R.; Ivlev, A. V.; Thomas, H. M.; Morfill, G. E.

2012-08-01

183

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

SciTech Connect

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.

Thomson, Robert K [Los Alamos National Laboratory; Graves, Christopher R [Los Alamos National Laboratory; Scott, Brian L [Los Alamos National Laboratory; Kiplinger, Jaqueline L [Los Alamos National Laboratory

2008-01-01

184

Characterization of Hydrogen Complex Formation in III-V Semiconductors  

SciTech Connect

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 - 1.55?m) 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.

Williams, Michael D.

2006-09-28

185

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

SciTech Connect

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.

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

186

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

SciTech Connect

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.

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

187

Factors Affecting DBP Formation During Ozone-Bromide Reactions  

Microsoft Academic Search

Ozonation of waters containing bromide ion leads to the formation of organic and inorganic by-products. By-product formation is influenced by bromide ion concentration, the source and concentration of organic precursors, pH, ozone dosage, temperature, and alkalinity. Both organic and inorganic by-products increased when bromide ion concentration increased but decreased with an increase in alkalinity. Organic by-products were found to increase

Mohamed S. Siddiqui; Gary L. Amy

1993-01-01

188

Translation initiation complex formation in the crenarchaeon Sulfolobus solfataricus  

PubMed Central

The function of initiation factors in and the sequence of events during translation initiation have been intensively studied in Bacteria and Eukaryotes, whereas in Archaea knowledge on these functions/processes is limited. By employing chemical probing, we show that translation initiation factor aIF1 of the model crenarchaeon Sulfolobus solfataricus binds to the same area on the ribosome as the bacterial and eukaryal orthologs. Fluorescence energy transfer assays (FRET) showed that aIF1, like its eukaryotic and bacterial orthologs, has a fidelity function in translation initiation complex formation, and that both aIF1 and aIF1A exert a synergistic effect in stimulating ribosomal association of the Met-tRNAiMet binding factor a/eIF2. However, as in Eukaryotes their effect on a/eIF2 binding appears to be indirect. Moreover, FRET was used to analyze for the first time the sequence of events toward translation initiation complex formation in an archaeal model system. These studies suggested that a/eIF2-GTP binds first to the ribosome and then recruits Met-tRNAiMet, which appears to comply with the operational mode of bacterial IF2, and deviates from the shuttle function of the eukaryotic counterpart eIF2. Thus, despite the resemblance of eIF2 and a/eIF2, recruitment of initiator tRNA to the ribosome is mechanistically different in Pro- and Eukaryotes.

Hasenohrl, David; Fabbretti, Attilio; Londei, Paola; Gualerzi, Claudio O.; Blasi, Udo

2009-01-01

189

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

PubMed

In methanogenic Archaea, the final step of methanogenesis generates methane and a heterodisulfide of coenzyme M and coenzyme B (CoM-S-S-CoB). Reduction of this heterodisulfide by heterodisulfide reductase to regenerate HS-CoM and HS-CoB is an exergonic process. Thauer et al. [Thauer, et al. 2008 Nat Rev Microbiol 6:579-591] recently suggested that in hydrogenotrophic methanogens the energy of heterodisulfide reduction powers the most endergonic reaction in the pathway, catalyzed by the formylmethanofuran dehydrogenase, via flavin-based electron bifurcation. Here we present evidence that these two steps in methanogenesis are physically linked. We identify a protein complex from the hydrogenotrophic methanogen, Methanococcus maripaludis, that contains heterodisulfide reductase, formylmethanofuran dehydrogenase, F(420)-nonreducing hydrogenase, and formate dehydrogenase. In addition to establishing a physical basis for the electron-bifurcation model of energy conservation, the composition of the complex also suggests that either H(2) or formate (two alternative electron donors for methanogenesis) can donate electrons to the heterodisulfide-H(2) via F(420)-nonreducing hydrogenase or formate via formate dehydrogenase. Electron flow from formate to the heterodisulfide rather than the use of H(2) as an intermediate represents a previously unknown path of electron flow in methanogenesis. We further tested whether this path occurs by constructing a mutant lacking F(420)-nonreducing hydrogenase. The mutant displayed growth equal to wild-type with formate but markedly slower growth with hydrogen. The results support the model of electron bifurcation and suggest that formate, like H(2), is closely integrated into the methanogenic pathway. PMID:20534465

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

2010-06-15

190

"Extreme" Ugi reactions with some complex ?-amino acids.  

PubMed

The Ti(IV)-catalyzed Ugi condensation of ?-amino acids with electron-rich aromatic aldehydes performs adequately even with sterically demanding ?-amino carboxylate salts. The reaction occurs diastereoselectively, in some cases with virtually complete diastereoselectivity. A stereochemical rationale for the reaction is proposed. PMID:22954286

Turner, Charles Dylan; Ciufolini, Marco A

2012-09-21

191

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

Microsoft Academic Search

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

Masakatsu Shibasaki; Hiroaki Sasai

1996-01-01

192

Sodium ferric gluconate complex in hemodialysis patients: Adverse reactions compared to placebo and iron dextran  

Microsoft Academic Search

Sodium ferric gluconate complex in hemodialysis patients: Adverse reactions compared to placebo and iron dextran.BackgroundParenteral iron is often required by hemodialysis patients to maintain adequate iron stores. Until recently, the only available form of intravenous iron was iron dextran, which is associated with significant adverse reactions, including anaphylaxis and death. Sodium ferric gluconate complex (SFGC) was recently approved for use

Beckie Michael; Daniel W. Coyne; Steven Fishbane; Vaughn Folkert; Robert Lynn; Allen R. Nissenson; Rajiv Agarwal; Joseph W. Eschbach; Stephen Z. Fadem; J. Richard Trout; Jur Strobos; David G. Warnock

2002-01-01

193

Complex formation of yeast Rev1 with DNA polymerase eta.  

PubMed

In Saccharomyces cerevisiae, Rev1 functions in translesion DNA synthesis (TLS) together with polymerase zeta (Pol zeta), comprised of the Rev3 catalytic and Rev7 accessory subunits. Rev1 plays an indispensable structural role in promoting Pol zeta function, and deletion of the Rev1-C terminal region that is involved in physical interactions with Rev3 inactivates Pol zeta function in TLS. In humans, however, Rev1 has been shown to physically interact with the Y-family polymerases Pol eta, Pol iota, and Pol kappa, and the Rev1 C terminus mediates these interactions. Since all the available genetic and biochemical evidence in yeast support the requirement of Rev1 as a structural element for Pol zeta and not for Pol eta, these observations have raised the possibility that in its structural role, Rev1 has diverged between yeast and humans. Here we show that although in yeast a stable Rev1-Pol eta complex can be formed, this complex formation involves the polymerase-associated domain of Rev1 and not the Rev1 C terminus as in humans. We also found that the DNA synthesis activity of Rev1 is enhanced in this complex. We discuss the implications of these and other observations for the possible divergence of Rev1's structural role between yeast and humans. PMID:17875922

Acharya, Narottam; Haracska, Lajos; Prakash, Satya; Prakash, Louise

2007-12-01

194

In vivo Formation of Halogenated Reaction Products Following Peroral Sodium Hypochlorite.  

National Technical Information Service (NTIS)

To date the principal concern of the disinfection of potable water has centered on the formation of halogenated organic reaction products and the adverse health effects that these products may have. However, an additional area for concern relating to wate...

F. L. Mink W. E. Coleman J. W. Munch W. H. Kaylor H. P. Ringhand

1983-01-01

195

Preventing Alkali-Silica Reaction and Delayed Ettringite Formation in New Concrete.  

National Technical Information Service (NTIS)

The state of Texas has been widely impacted by materials-related distress in various transportation structures. This distress has been mainly attributed to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) and has been commonly referred ...

B. Bournier J. Ideker K. J. Folliard L. Du M. Juenger M. D. A. Thomas R. Barborak S. Garber S. Williams T. Drimalas T. Ley

2006-01-01

196

Alkali-Silica Reaction and Delayed Ettringite Formation in Concrete: A Literature Review.  

National Technical Information Service (NTIS)

Recently in Texas, there has been significant damage of field structures resulting from concrete durability problems. Alkali-silica reaction (ASR) and delayed ettringite formation (DEF), or combinations of the two, have been found to be the main causes of...

S. Bauer B. Cornell D. Figurski T. Ley J. Miralles K. Folliard

2006-01-01

197

Formation of methyl nitrite in the surface reaction of nitrogen dioxide and methanol. 1. Dark reaction  

SciTech Connect

The reaction of nitrogen dioxide and methanol which has been known in the gas phase to proceed thermally as CH/sub 3/OH + 2NO/sub 2/ ..-->.. CH/sub 3/ONO + HNO/sub 3/, was found to proceed heterogeneously on various surfaces as well, in an 11-L Pyrex cell and a 6065-L evacuable smog chamber. An FTIR study has revealed that the reaction products are the same as in the homogeneous reaction, i.e., methyl nitrite and nitric acid. Neither methyl nitrate nor nitrous acid was observed. Among the surfaces studied, uncoated stainless steel, pyrex, and the smog chamber wall surfaces were found to be the most active to induce the surface reaction. The apparent activation energy of the surface reaction in the smog chamber was determined to be -11.9 +/- 3.3 kJ mol/sup -1/. 25 references, 5 figures, 4 tables.

Takagi, H.; Hatakeyama, S.; Akimoto, H.; Koda, S.

1986-04-01

198

Ligand exchange reactions in Cu(III) complexes: mechanistic insights by combined NMR and DFT studies.  

PubMed

NMR studies of (13)C/(12)C isotopic patterns in Cu(iii) intermediates and reaction products together with DFT calculations of possible reaction pathways indicate an intermolecular S(N)2 like substitution mechanism for ligand exchange reactions in square planar Cu(iii) complexes, which is proposed to be slow compared to reductive elimination at synthetic conditions. PMID:20461240

Gärtner, Tobias; Yoshikai, Naohiko; Neumeier, Maria; Nakamura, Eiichi; Gschwind, Ruth M

2010-07-01

199

Formation and Reactions of Bis(trimethylphosphine)-Methyldiborane(4).  

National Technical Information Service (NTIS)

Reaction of CH3B5H8 with P(CH3)3 methylpentaborane, 1-CH3B5H8 or 2-CH3B5H8, reacted with excess trimethylphosphine. The product, CH3B2H3.2P(CH3)3 separated in a good yield from the triborane adduct by sublimation. Its purity, however, was only about 90%, ...

M. Kameda J. A. Driscoll G. Kodama

1990-01-01

200

Pd II square planar complexes of the type [IL] 2[PdX 4] as catalyst precursors for the Suzuki–Miyaura cross-coupling reaction. The first in situ ESI-MS evidence of [(IL) x Pd 3] clusters formation  

Microsoft Academic Search

PdII anionic, square planar complexes of the type [IL]2[PdX4], where IL=imidazolium cations, X=Cl, Br, have been applied for the first time as catalyst precursors for the Suzuki–Miyaura (S–M) reaction carried out in alcohols at 40°C. Depending on the structure of the catalyst precursor used, different yields of 2-methylbiphenyl (2-MePh–Ph) were obtained in a test reaction of 2-bromotoluene (2-MePhBr) with phenyl

W. Zawartka; A. Gniewek; A. M. Trzeciak; J. J. Zió?kowski; J. Pernak

2009-01-01

201

Reaction of nitrosonium cation with resorc[4]arenes activated by supramolecular control: covalent bond formation.  

PubMed

Resorc[4]arenes 1 and 2, which previously proved to entrap NO(+) cation within their cavities under conditions of host-to-guest excess, were treated with a 10-fold excess of NOBF4 salt in chloroform. Kinetic and spectral UV-visible analyses revealed the formation of isomeric 1:2 complexes as a direct evolution of the previously observed event. Accordingly, three-body 1-(NO(+))2 and 2-(NO(+))2 adducts were built by MM and fully optimized by DFT calculations at the B3LYP/6-31G(d) level of theory. Notably, covalent nitration products 4, 5 and 6, 7 were obtained by reaction of NOBF4 salt with host 1 and 2, respectively, involving macrocycle ring-opening and insertion of a nitro group in one of the four aromatic rings. In particular, compounds 4 and 6, both containing a trans-double bond in the place of the methine bridge, were oxidized to aldehydes 5 and 7, respectively, after addition of water to the reaction mixture. Calculation of the charge and frontier orbitals of the aromatic donor (HOMO) and the NO(+) acceptor (LUMO) clearly suggests an ipso electrophilic attack by a first NO(+) unit on the resorcinol ring, mediated by the second NO(+) unit. PMID:23786237

Ghirga, Francesca; D'Acquarica, Ilaria; Delle Monache, Giuliano; Mannina, Luisa; Molinaro, Carmela; Nevola, Laura; Sobolev, Anatoly P; Pierini, Marco; Botta, Bruno

2013-07-19

202

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

203

Carbon-chalcogen bond cleavage reactions characterized for dinuclear sulfur-bridged cyclopentadienyl molybdenum complexes  

Microsoft Academic Search

The types of carbon-chalcogen bond cleavage reactions which have been characterized for dinuclear cyclopentadienylmolybdenum complexes are reviewed. The reactions include both the homolytic cleavage and the protonolysis of carbon-chalcogen bonds in neutral ?-thiolate derivatives of MoIII, nucleophilic cleavage of carbon-chalcogen bonds in certain cationic derivatives of MoIII or MoIV, and the reactions of certain dinuclear complexes with molecular hydrogen. Unique

1997-01-01

204

Cadmium(II) Complex Formation with Cysteine and Penicillamine  

PubMed Central

The complex formation between cadmium(II) and the ligands cysteine (H2Cys) or penicillamine (H2Pen = 3, 3?-dimethylcysteine) in aqueous solutions, containing CCd(II) ? 0.1 mol dm-3 and CH2L = 0.2 – 2 mol dm-3, was studied at pH = 7.5 and 11.0 by means of 113Cd-NMR and Cd K- and L3-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine mole ratios the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52 – 2.54 Å and 2.27 – 2.35 Å, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50 – 2.53 Å, but with the Cd-(N/O) bond distances in a similar wide range, 2.28 – 2.33 Å. For the mole ratio CH2L / CCd(II) = 2, the 113Cd chemical shifts, in the range 509 – 527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS2N(N/O) coordination geometry. With a large excess of cysteine (mole ratios CH2Cys / CCd(II) ? 10) complexes with CdS4 coordination geometry dominate, consistent with the 113Cd NMR chemical shifts, ? ? 680 ppm at pH 7.5 and 636 - 658 ppm at pH 11.0, and their mean Cd-S distances of 2.53 ± 0.02 Å. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)4]n-, while at higher pH the deprotonation of the amine groups promotes chelate formation, and at pH 11.0 a minor amount of the [Cd(Cys)3]4- complex with CdS3N coordination is formed. For the corresponding penicillamine solutions with mole ratios CH2Pen / CCd(II) ? 10, the 113Cd-NMR chemical shifts, ? ? 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances Cd-S 2.53 ± 0.02 Å and Cd-O 2.30 – 2.33 Å, indicate that [Cd(penicillaminate)3]n- complexes with chelating CdS3(N/O) coordination dominate already at pH 7.5, and become mixed with CdS2N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the cadmium(II) ion that can explain why cysteine-rich metallothionines are capable of capturing cadmium(II) ions, while penicillamine, clinically useful for treating the toxic effects of mercury(II) and lead(II) exposure, is not efficient against cadmium(II) poisoning.

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

2009-01-01

205

Mechanism of primary and secondary ion-radical pair formation in photosystem I complexes.  

PubMed

The mechanisms of the ultrafast charge separation in reaction centers of photosystem I (PS I) complexes are discussed. A kinetic model of the primary reactions in PS I complexes is presented. The model takes into account previously calculated values of redox potentials of cofactors, reorganization energies of the primary P700(+)A0(-) and secondary P700(+)A1(-) ion-radical pairs formation, and the possibility of electron transfer via both symmetric branches A and B of redox-cofactors. The model assumes that the primary electron acceptor A0 in PS I is represented by a dimer of chlorophyll molecules Chl2A/Chl3A and Chl2B/Chl3B in branches A and B of the cofactors. The characteristic times of formation of P700(+)A0(-) and P700(+)A1(-) calculated on the basis of the model are close to the experimental values obtained by pump-probe femtosecond absorption spectroscopy. It is demonstrated that a small difference in the values of redox potentials between the primary electron acceptors A0A and A0B in branches A and B leads to asymmetry of the electron transfer in a ratio of 70 : 30 in favor of branch A. The secondary charge separation is thermodynamically irreversible in the submicrosecond range and is accompanied by additional increase in asymmetry between the branches of cofactors of PS I. PMID:24821448

Milanovsky, G E; Ptushenko, V V; Cherepanov, D A; Semenov, A Yu

2014-03-01

206

Role of water complexes in the reaction of propionaldehyde with OH radicals.  

PubMed

There has been considerable debate and speculation about the role of weakly bound complexes in radical-molecule reactions in the gas phase, especially in atmospheric chemistry. Among the significant number of potentially important molecular aggregates in chemical reactions, water complexes are of particular interest. Beyond the well-known energy transfer role of water in complex-forming reactions, it has been shown that water may also have a catalytic effect on the kinetics of radical-molecule reactions because of reduced reaction barrier heights for the complexes. Here we report studies of the reaction of OH radicals and propionaldehyde in the presence and absence of water vapor between 300 and 60 K in Laval nozzle expansions. Water accelerates the overall reaction at low temperatures but much less pronounced than for the reaction of OH with acetaldehyde reported recently. Quantum chemical calculations help us to understand this behavior, which can be rationalized in terms of the stability of intermediate reaction complexes and the effect of water aggregation on the barrier separating prereactive complexes and products. PMID:20507131

Vöhringer-Martinez, E; Tellbach, E; Liessmann, M; Abel, B

2010-09-16

207

Formation of an iron phosphine-borane complex by formal insertion of BH? into the Fe-P bond.  

PubMed

A unique hydrido phosphine-borane iron(II) complex [(dppa)(Ph?P-N-P(BH?)Ph?)Fe(H)] (1) was obtained by the reaction of iron(II) chloride and two equivalents of bis(diphenylphosphino)amine (dppa) with an excess of sodium borohydride in acetonitrile-ethanol mixtures. Detailed investigations of the reaction revealed that a mixture of cis- and trans-[(dppa)?Fe(NCMe)?]²? is formed prior to the reduction by sodium borohydride. Depending on the solvent, different products were obtained by the reduction: in acetonitrile-ethanol mixtures the hydrido phosphine-borane complex 1 is formed by formal insertion of BH?, while the reduction in pure acetonitrile results in the formation of the cationic complex trans-[(dppa)?Fe(H)(NCMe)](BH?) (4). Complex 4 is remarkably stable in ethanol and does not undergo phosphine-borane formation, even in the presence of excess sodium borohydride. This observation suggests that the phosphine-borane complex is generated by the reaction with the first equivalent of sodium borohydride with the participation of ethanol, followed by deprotonation or dihydrogen elimination. Experiments with similar diphosphine ligands, such as bis(diphenylphosphino)methane, did not yield a phosphine-borane complex, indicating the crucial role of the amine group in the observed reactivity. PMID:23811820

Frank, Nicolas; Hanau, Katharina; Flosdorf, Kimon; Langer, Robert

2013-08-21

208

Direct detection of key reaction intermediates in photochemical CO2 reduction sensitized by a rhenium bipyridine complex.  

PubMed

Photochemical CO2 reduction sensitized by rhenium-bipyridyl complexes has been studied through multiple approaches during the past several decades. However, a key reaction intermediate, the CO2-coordinated Re-bipyridyl complex, which should govern the activity of CO2 reduction in the photocatalytic cycle, has never been detected in a direct way. In this study on photoreduction of CO2 catalyzed by the 4,4'-dimethyl-2,2'-bipyridine (dmbpy) complex, [Re(dmbpy)(CO)3Cl] (1), we successfully detect the solvent-coordinated Re complex [Re(dmbpy)(CO)3DMF] (2) as the light-absorbing species to drive photoreduction of CO2. The key intermediate, the CO2-coordinated Re-bipyridyl complex, [Re(dmbpy)(CO)3(COOH)], is also successfully detected for the first time by means of cold-spray ionization spectrometry (CSI-MS). Mass spectra for a reaction mixture with isotopically labeled (13)CO2 provide clear evidence for the incorporation of CO2 into the Re-bipyridyl complex. It is revealed that the starting chloride complex 1 was rapidly transformed into the DMF-coordinated Re complex 2 through the initial cycle of photoreduction of CO2. The observed induction period in the time profile of the CSI-MS signals can well explain the subsequent formation of the CO2-coordinated intermediate from the solvent-coordinated Re-bipyridyl complex. An FTIR study of the reaction mixture in dimethyl sulfoxide clearly shows the appearance of a signal at 1682 cm(-1), which shifts to 1647 cm(-1) for the (13)CO2-labeled counterpart; this is assigned as the CO2-coordinated intermediate, Re(II)-COOH. Thus, a detailed understanding has now been obtained for the mechanism of the archetypical photochemical CO2 reduction sensitized by a Re-bipyridyl complex. PMID:24689747

Kou, Youki; Nabetani, Yu; Masui, Dai; Shimada, Tetsuya; Takagi, Shinsuke; Tachibana, Hiroshi; Inoue, Haruo

2014-04-23

209

Insights from reconstitution reactions of COPII vesicle formation using pure components and low mechanical perturbation.  

PubMed

Abstract As shape transformations of membranes are vital for intracellular trafficking, it is crucial to understand both the mechanics and the biochemistry of these processes. The interplay of these two factors constitutes an experimental challenge, however, because biochemical experiments are not tailored to the investigation of mechanical processes, and biophysical studies using model membranes are not capable of emulating native biological complexity. Reconstituted liposome-based model systems have been widely used for investigating the formation of transport vesicles by the COPII complex that naturally occurs at the endoplasmic reticulum. Here we have revisited these model systems, to address the influence of lipid composition, GTP hydrolyzing conditions and mechanical perturbation on the experimental outcome. We observed that the lipid-dependence of COPII-induced membrane remodeling differs from that predicted based on the lipid-dependence of COPII membrane binding. Under GTP non-hydrolyzing conditions, a structured coat was seen while GTP-hydrolyzing conditions yielded uncoated membranes as well as membranes coated by a thick protein coat of rather unstructured appearance. Detailed up-to-date protocols for purifications of Saccharomyces cerevisiae COPII proteins and for reconstituted reactions using these proteins with giant liposomes are also provided. PMID:25003385

Daum, Sebastian; Krüger, Daniela; Meister, Annette; Auerswald, Jan; Prinz, Simone; Briggs, John A G; Bacia, Kirsten

2014-07-01

210

Formation of bubbles, blobs, and surface cusps in complex plasmas.  

PubMed

Investigations of the dynamical evolution of a complex plasma, in which a vertical temperature gradient compensates gravity, were carried out. At low power the formation of microparticle bubbles, blobs, and spraying cusps was observed. This activity can be turned on and off by changing control parameters, such as the rf power and the gas pressure. Several observational effects indicate the presence of surface tension, even at small "nanoscales" of a few 100's of particles. By tracing the individual microparticle motion the detailed (atomistic) dynamics can be studied as well as the pressure dependence of the forces. A possible mechanism that could drive the observed phenomena is analogous to the Rayleigh-Taylor instability. PMID:19659088

Schwabe, M; Rubin-Zuzic, M; Zhdanov, S; Ivlev, A V; Thomas, H M; Morfill, G E

2009-06-26

211

Physical volcanology of the Gubisa Formation, Kone Volcanic Complex, Ethiopia  

NASA Astrophysics Data System (ADS)

Despite their significance for understanding the potential environmental factors involved in hominin evolution in Ethiopia, very few modern volcanologic studies have been carried out on the Quaternary calderas and associated silicic tephra deposits of the Ethiopian Rift. We present here the second of a set of papers reporting the findings of fieldwork and laboratory analyses of one of the largest of these structures, Kone Caldera, located within the Kone Volcanic Complex in the northern Main Ethiopian Rift. The most recent major episode of explosive eruptive activity at Kone Caldera was apparently associated with formation of part of the overall 8-km-diameter collapse area, and deposited a widely-dispersed alkali rhyolite tephra that reaches a thickness of up to 60 m in vent-proximal deposits. We report here the physical characteristics of this unit in order to constrain eruptive conditions. The pumice fall deposit suggests that an abrupt decrease in magma discharge rate occurred part way through the eruption.

Rampey, Michael L.; Oppenheimer, Clive; Pyle, David M.; Yirgu, Gezahegn

2014-08-01

212

An effective method for refining predicted protein complexes based on protein activity and the mechanism of protein complex formation  

PubMed Central

Background Identifying protein complexes from protein-protein interaction network is fundamental for understanding the mechanism of cellular component and protein function. At present, many methods to identify protein complexes are mainly based on the topological characteristics or the functional similarity features, neglecting the fact that proteins must be in their active forms to interact with others and the formation of protein complex is following a just-in-time mechanism. Results This paper firstly presents a protein complex formation model based on the just-in-time mechanism. By investigating known protein complexes combined with gene expression data, we find that most protein complexes can be formed in continuous time points, and the average overlapping rate of the known complexes during the formation is large. A method is proposed to refine the protein complexes predicted by clustering algorithms based on the protein complex formation model and the properties of known protein complexes. After refinement, the number of known complexes that are matched by predicted complexes, Sensitivity, Specificity, and f-measure are significantly improved, when compared with those of the original predicted complexes. Conclusion The refining method can discard the spurious proteins by protein activity and generate new complexes by just-in-time assemble mechanism, which can enhance the ability to predict complex.

2013-01-01

213

Scope and Mechanism of Formal SN2? Substitution Reactions of a Monomeric Imidozirconium Complex with Allylic Electrophiles  

PubMed Central

The zirconium imido complex Cp2(THF)Zr = NSi(t-Bu)Me2 (1) reacts with allylic ethers, chlorides, and bromides to give exclusively the products of the SN2? reaction; i.e., attack at the allylic position remote from the leaving group with migration of the double bond. The primary amine products can be isolated in excellent yields, after in situ Cbz protection, in the presence of variety of functional groups. Good diastereoselectivity and complete stereoselectivity allowed the formation of enantioenriched allylic amines from enantioenriched allylic ethers. Regiospecific substitution with 1 has also been achieved with allylic fluorides, which are notoriously poor substrates in other substitution reactions. On the basis of rate and kinetic isotope effect studies, we propose a general mechanism for the allylic substitution reactions with 1 which involves dissociation of THF and binding of the substrate, followed by the substitution step. In a DFT study of the substitution reaction, we identified a six-membered closed transition state for the substitution step and other relevant stationary points along the reaction coordinate. This study shows that the substitution reaction can be described as a concerted asynchronous [3,3]-sigmatropic rearrangement. This detailed knowledge of the reaction mechanism provides a rationale for the origins of the observed regio-, diastereo-, and stereoselectivity and of the unusual reactivity profile observed in the reaction.

Lalic, Gojko; Krinsky, Jamin L.; Bergman, Robert G.

2008-01-01

214

Biological pattern formation: from basic mechanisms to complex structures  

NASA Astrophysics Data System (ADS)

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.

Koch, A. J.; Meinhardt, H.

1994-10-01

215

Module Based Complexity Formation: Periodic Patterning in Feathers and Hairs  

PubMed Central

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

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

2012-01-01

216

Dual specificity and the formation of stable autoimmune complexes.  

PubMed

Since dual specificity at the antibody active-site level involves new principles relative to monospecific antigen-antibody interactions and may be a general property of autoantibodies, it was important to further characterize such antibodies. Four lupus derived autoantibodies were studied to understand parameters and mechanisms involved in the participation of dual-specific antibody molecules in the formation of highly stable immune complexes. Because the dual-specific binding properties of selected lupus-related murine autoantibodies had been previously described using a solid-phase polystyrene-based ELISA, a conformational sensitive membrane based assay (CSI) was used on a comparative basis to further characterize NZB/NZW F1 murine monoclonal anti-DNA autoantibodies BV 04-01 (anti-ssDNA), BV 16-19 (anti-ssDNA), BV 17-45 (anti-dsDNA), and BV 16-13 (anti-dsDNA). All four monoclonal autoantibodies exhibited anti-IgG binding in the solid-phase ELISA. However in the CSI assay, only anti-dsDNA monoclonal autoantibodies BV 17-45 and BV 16-13 demonstrated anti-IgG binding, while anti-ssDNA autoantibodies BV 04-01 and BV 16-19 did not. Upon subjection to time-dependent thermal denaturation, with and without thiol reduction at 100 degrees C in the CSI, the self-binding activities of BV 17-45 and BV 16-13 were abrogated demonstrating that the recognized IgG autoepitope(s) possessed conformational or discontinuous three-dimensional properties. The immunological implications of dual specificity are discussed on a structure-function basis and its correlation with formation of pathogenic immune complexes. PMID:9587872

Workman, C J; Pfund, W P; Voss, E W

1997-01-01

217

Complex behavior of self-propagating reaction waves in heterogeneous media.  

PubMed

Self-propagating high temperature reaction waves, leading to the synthesis of advanced materials, are investigated in a variety of heterogeneous reaction systems by using a digital high-speed microscopic video recording technique. It is shown that, although on the macroscopic length and time scales, the reaction appears to move in a steady mode, on the microscopic level it has a complex character that is related to the reaction mechanism. PMID:9736688

Varma, A; Rogachev, A S; Mukasyan, A S; Hwang, S

1998-09-15

218

Complex behavior of self-propagating reaction waves in heterogeneous media  

PubMed Central

Self-propagating high temperature reaction waves, leading to the synthesis of advanced materials, are investigated in a variety of heterogeneous reaction systems by using a digital high-speed microscopic video recording technique. It is shown that, although on the macroscopic length and time scales, the reaction appears to move in a steady mode, on the microscopic level it has a complex character that is related to the reaction mechanism.

Varma, Arvind; Rogachev, Alexander S.; Mukasyan, Alexander S.; Hwang, Stephen

1998-01-01

219

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

NASA Astrophysics Data System (ADS)

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

Yamada, Hiroyasu; Nakagaki, Toshiyuki; Ito, Masami

1999-01-01

220

Kinetics and mechanism of reactions of the drug tiopronin with platinum(IV) complexes.  

PubMed

Tiopronin, a synthetic thiol-containing drug being used in treatments of cystinuria and certain types of rare arthritis, is also a hepatoprotective and a detoxifying agent. Many analytical methods have been developed based on its redox chemistry with metal ions/complexes, but the kinetic and mechanistic aspects are poorly understood. In this work, the oxidation of tiopronin by cisplatin prodrug and a model compound, cis-[Pt(NH3)2Cl4] and trans-[PtCl2(CN)4](2-), was investigated. The oxidation kinetics was followed by a stopped-flow spectrophotometer over a wide pH range under the pseudo first-order conditions of [Tiopronin]?[Pt(IV)]. Time-resolved spectra were also recorded for both Pt(IV) complexes, enabling to establish an overall second-order rate law: -d[Pt(IV)]/dt=k'[Tiopronin][Pt(IV)], where k' pertains to observed second-order rate constants. Under the kinetic conditions, tiopronin was oxidized to form the tiopronin-disulfide exclusively as identified by mass spectrometry. A reaction mechanism was proposed, involving parallel reductions of the Pt(IV) complexes by the three protolytic tiopronin species as rate-determining steps. The rate constants for the rate-determining steps were derived. The fully deprotonated tiopronin is about 4×10(4) more reactive than its corresponding thiol form for both Pt(IV) complexes; the huge reactivity difference orchestrates closely with the fact that the nucleophilicity of thiolate is much higher than the corresponding thiol. Hence, the attack of the sulfur atom in thiol/thiolate of tiopronin on the axially-coordinated chloride in the Pt(IV) complexes is nucleophilic in nature in the rate-determining steps, resulting in a bridge formation and a subsequent bridged electron-transfer. PMID:23665090

Huo, Shuying; Shi, Hongmei; Liu, Dongzhi; Shen, Shigang; Zhang, Jiong; Song, Changying; Shi, Tiesheng

2013-08-01

221

Colorimetric method for enzymatic screening assay of ATP using Fe(III)-xylenol orange complex formation.  

PubMed

In hygiene management, recently there has been a significant need for screening methods for microbial contamination by visual observation or with commonly used colorimetric apparatus. The amount of adenosine triphosphate (ATP) can serve as the index of a microorganism. This paper describes the development of a colorimetric method for the assay of ATP, using enzymatic cycling and Fe(III)-xylenol orange (XO) complex formation. The color characteristics of the Fe(III)-XO complexes, which show a distinct color change from yellow to purple, assist the visual observation in screening work. In this method, a trace amount of ATP was converted to pyruvate, which was further amplified exponentially with coupled enzymatic reactions. Eventually, pyruvate was converted to the Fe(III)-XO complexes through pyruvate oxidase reaction and Fe(II) oxidation. As the assay result, yellow or purple color was observed: A yellow color indicates that the ATP concentration is lower than the criterion of the test, and a purple color indicates that the ATP concentration is higher than the criterion. The method was applied to the assay of ATP extracted from Escherichia coli cells added to cow milk. PMID:18726586

Ishida, Akihiko; Yamada, Yasuko; Kamidate, Tamio

2008-11-01

222

Reversible C-C bond formation between redox-active pyridine ligands in iron complexes.  

PubMed

This manuscript describes the formally iron(I) complexes L(Me)Fe(Py-R)(2) (L(Me) = bulky ?-diketiminate; R = H, 4-tBu), in which the basal pyridine ligands preferentially accept significant unpaired spin density. Structural, spectroscopic, and computational studies on the complex with 4-tert-butylpyridine ((tBu)py) indicate that the S = 3/2 species is a resonance hybrid between descriptions as (a) high-spin iron(II) with antiferromagnetic coupling to a pyridine anion radical and (b) high-spin iron(I). When the pyridine lacks the protection of the tert-butyl group, it rapidly and reversibly undergoes radical coupling reactions that form new C-C bonds. In one reaction, the coordinated pyridine couples to triphenylmethyl radical, and in another, it dimerizes to give a pyridine-derived dianion that bridges two iron(II) ions. The rapid, reversible C-C bond formation in the dimer stores electrons from the formally reduced metal as a C-C bond in the ligands, as demonstrated by using the coupled diiron(II) complex to generate products that are known to come from iron(I) precursors. PMID:23181620

Dugan, Thomas R; Bill, Eckhard; MacLeod, K Cory; Christian, Gemma J; Cowley, Ryan E; Brennessel, William W; Ye, Shengfa; Neese, Frank; Holland, Patrick L

2012-12-19

223

Dioxygen activation by an organometallic Pd(II) precursor: formation of a Pd(IV)-OH complex and its C-O bond formation reactivity.  

PubMed

The complex (Me3tacn)Pd(II)(CH2CMe2C6H4) is readily oxidized by O2 or H2O2 to yield the Pd(IV)-OH complex [(Me3tacn)Pd(IV)(OH)(CH2CMe2C6H4)](+). Thermolysis of this product leads to the selective C(sp(2))-O reductive elimination of 2-tert-butylphenol, no C(sp(3))-O elimination product being detected. This system represents a rare example of selective C(sp(2))-O bond formation that is relevant to Pd-catalyzed aerobic C-H hydroxylation reactions. PMID:24509780

Qu, Fengrui; Khusnutdinova, Julia R; Rath, Nigam P; Mirica, Liviu M

2014-03-21

224

Evidence that covalent complex formation between BCNU-treated oligonucleotides and E. coli alkyltransferases requires the O6-alkylguanine function.  

PubMed Central

Chloroethylnitrosoureas (CENUs) are thought to induce cytotoxic DNA interstrand cross-links via an initial reaction at O6-position of guanine, yielding a rearranged intermediate, O6,N1-ethanoguanine. Repair of these adducts by mammalian and bacterial DNA alkyltransferases blocks the formation of cross-links. Human alkyltransferase can form a covalent complex with DNA containing BCNU-induced cross-link precursors, but the nature of the DNA-protein linkage remains unknown. Using E. coli alkyltransferases expressed by the ada and ogt genes, we now demonstrate that both enzymes can form such complexes with CENU-treated DNA. We attribute this reaction to the O6-alkylguanine repair function, because an N-terminal fragment of the ada protein, which has only alkylphosphotriester repair activity, failed to form a similar complex. This result is consistent with the idea that complex formation requires an alkyltransferase reaction with a guanine adduct, such as O6,N1-ethanoguanine. It tends to exclude the possibility that such reactions simply involve alkylation of the enzyme by reactive DNA adducts such as chloroethylphosphate or chloroethylguanine. Images

Gonzaga, P E; Harris, L; Margison, G P; Brent, T P

1990-01-01

225

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

PubMed

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) (?(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. © 2014 Wiley Periodicals, Inc. PMID:24865949

Futera, Zden?k; Burda, Jaroslav V

2014-07-15

226

Modelling formation of complex topography by the seagrass Posidonia oceanica  

NASA Astrophysics Data System (ADS)

Posidonia oceanica is a slow growing seagrass species that extends via growing rhizomes that grow only centimetres both horizontally and vertically each year. Posidonia oceanica forms topographically complex biogenic reefs of dead rhizome and sediments that are up to 4 m in height that are called "matte". This study investigates the role of slow horizontal and vertical growth of rhizomes in the formation of topographic complexity in P. oceanica matte using agent-based modelling. The simulated infilling of landscapes by P. oceanica was run over 600 iterations (years) for 10 random starts of 150 agents each. Initial infilling rates were very slow and P. oceanica had limited cover after a century of growth. Growth accelerated after 100 years but plateaued after 400 years such that after 600 years only two-thirds of the landscape was occupied by P. oceanica. The pattern of spread of agents was initially random in direction but after larger patches were formed spread was radial from these patches. The seagrass landscape was initially highly fragmented with many small separate patches made up of a few agents each, with a Landscape Division index close to 1. Between 300 and 600 years Landscape Division declined sharply to 0.42, indicating patches had coalesced into larger more continuous meadows forming a less fragmented landscape. Perimeter to area ratio of seagrass patches declined exponentially from >1 to approximately 0.2 over 600 years of simulation. The matte developed from growth of patches and its greatest height occurred in more continuously occupied cells of the grid. The topography of the reef that occupied two-thirds of the landscape after six centuries of growth could be described as a pattern of channels between reef plateaus elevated 1-2 m above channels. These results demonstrate that development in P. oceanica meadows of three-dimensional structure, in the formation of biogenic reefs, can be explained by, and is an emergent property of, slow horizontal and vertical rhizome growth rates combined with the time it takes for the accumulation of rhizomes in any region of the landscape. As such, the model provides a parsimonious explanation for the development of complex matte topography.

Kendrick, Gary A.; Marbà, Núria; Duarte, Carlos M.

2005-12-01

227

Impact of high-intensity ultrasound on the formation of lactulose and Maillard reaction glycoconjugates.  

PubMed

The impact of high-intensity ultrasound (US) on the formation of lactulose during lactose isomerization and on the obtention of lysine-glucose glycoconjugates during Maillard reaction (MR) has been studied, respectively, in basic and neutral media. As compared to equivalent conventional heat treatments, a higher formation of furosine, as indicator of initial steps of MR, was observed together with more advance of the reaction in US treated samples, this effect being more pronounced with the increase of US amplitude (50-70%) and temperature (25-40 °C). Regarding the influence of US on lactulose formation, in general, in a buffered system (pH 10.0), US at 70% of amplitude and 60 °C increased the rate of lactose isomerization, higher values of lactulose, epilactose and galactose being observed in comparison to conventional heating. The results of this work showed an acceleration of both reactions by US, indicating its usefulness to promote the formation of functional ingredients. PMID:24679769

Corzo-Martínez, Marta; Montilla, Antonia; Megías-Pérez, Roberto; Olano, Agustín; Moreno, F Javier; Villamiel, Mar

2014-08-15

228

Hrs regulates early endosome fusion by inhibiting formation of an endosomal SNARE complex  

PubMed Central

Movement through the endocytic pathway occurs principally via a series of membrane fusion and fission reactions that allow sorting of molecules to be recycled from those to be degraded. Endosome fusion is dependent on SNARE proteins, although the nature of the proteins involved and their regulation has not been fully elucidated. We found that the endosome-associated hepatocyte responsive serum phosphoprotein (Hrs) inhibited the homotypic fusion of early endosomes. A region of Hrs predicted to form a coiled coil required for binding the Q-SNARE, SNAP-25, mimicked the inhibition of endosome fusion produced by full-length Hrs, and was sufficient for endosome binding. SNAP-25, syntaxin 13, and VAMP2 were bound from rat brain membranes to the Hrs coiled-coil domain. Syntaxin 13 inhibited early endosomal fusion and botulinum toxin/E inhibition of early endosomal fusion was reversed by addition of SNAP-25(150–206), confirming a role for syntaxin 13, and establishing a role for SNAP-25 in endosomal fusion. Hrs inhibited formation of the syntaxin 13–SNAP-25–VAMP2 complex by displacing VAMP2 from the complex. These data suggest that SNAP-25 is a receptor for Hrs on early endosomal membranes and that the binding of Hrs to SNAP-25 on endosomal membranes inhibits formation of a SNARE complex required for homotypic endosome fusion.

Sun, Wei; Yan, Qing; Vida, Thomas A.; Bean, Andrew J.

2003-01-01

229

A new mechanism for the control of phenoloxidase activity: inhibition and complex formation with quinone isomerase.  

PubMed

Insect phenoloxidases participate in three physiologically important processes, viz., cuticular hardening (sclerotization), defense reactions (immune reaction), and wound healing. Arrest or even delay of any of these processes compromises the survival of insects. Since the products of phenoloxidase action, viz., quinones, are cytotoxic, uncontrolled phenoloxidase action is deleterious to the insects. Therefore, the activity of this important enzyme has to be finely controlled. A novel inhibition of insect phenoloxidases, which serves as a new regulatory mechanism for control of its activity, is described. The activity of phenoloxidases isolated from both Sarcophaga bullata and Manduca sexta is drastically inhibited by quinone isomerase (isolated from Calliphora), an enzyme that utilizes the phenoloxidase-generated 4-alkylquinones. In turn, phenoloxidase reciprocated the inhibition of isomerase. By forming a complex and controlling each other's activity, these two enzymes seem to regulate the levels of endogenously quinones. In support of this contention, an endogenous complex consisting of phenoloxidase, quinone isomerase, and quinone methide isomerase was characterized from the insect, Calliphora. This sclerotinogenic complex was isolated and purified by borate extraction of the larval cuticle, ammonium sulfate precipitation, and Sepharose 6B column chromatography. The complex exhibited a molecular mass of about 620-680 kDa, as judged by size-exclusion chromatography on Sepharose 6B and HPLC and did not even enter 3% polyacrylamide gel during electrophoresis. The phenoloxidase activity of the complex exhibited a wide substrate specificity. Incubation of the complex with N-acetyldopamine rapidly generated N-acetylnorepinephrine, dehydro-N-acetyldopamine, and its dimers. In addition, transient accumulation of N-acetyldopamine quinone was also observed. These results confirm the presence of phenoloxidase, quinone isomerase, and quinone methide isomerase in the complex. Attempts to dissociate the complex with even trace amounts of SDS ended in the total loss of quinone isomerase activity. The complex does not seems to be made up of stoichiometric amounts of individual enzymes as the ratio of phenoloxidase to quinone isomerase varied from preparation to preparation. It is proposed that the complex formation between sequential enzymes of sclerotinogenic pathway is advantageous for the organism to effectively channel various reactive intermediates during cuticular hardening. PMID:10898942

Sugumaran, M; Nellaiappan, K; Valivittan, K

2000-07-15

230

Unsaturated selenacrown ethers: synthesis, structure, and formation of silver complexes.  

PubMed

The unsaturated selenacrown ethers, (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) (2), (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6) (3), (Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19-heptaselenacycloheneicosa-2,5,8,11,14,17,20-heptaene (21-US-7) (4), (Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22-octaselenacyclotetracosa-2,5,8,11,14,17,20,23-octaene (24-US-8) (5), and (Z,Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22,25-nonaselenacycloheptacosa-2,5,8,11,14,17,20,23,26-nonaene (27-US-9) (6), were obtained together with 1,4-diselenin (1) by reacting sodium selenide with cis-dichloroethene in the presence of a phase-transfer catalyst. The crystal structures of 2-5 were determined by X-ray crystallographic analysis. The UV spectra of the selenacrown ethers showed absorption maximums in the range of 251-262 nm, which were assigned to n-->pi transitions. The cyclic voltammograms indicated that the large unsaturated selenacrown ethers were oxidized more easily than the small ones. The thermal reactions of the unsaturated selenacrown ethers afforded 1,4-diselenin (1) along with polymeric materials, whereas 1 was thermally stable even at 100 degrees C. The reactions of 1 or unsaturated selenacrown ethers 2-5 with silver ion yielded various novel silver complexes, Ag(C(4)H(4)Se(2))(CF(3)COO) (7), Ag(C(4)H(4)Se(2))(2)(CF(3)COO) (8), Ag(15-US-5)(CF(3)COO) (9), Ag(5)(18-US-6)(3)(CF(3)COO)(5) (10), Ag(7)(21-US-7)(CF(3)COO)(5) (11), Ag(24-US-8)(2)(CF(3)COO) (12), Ag(2)(24-US-8)(CF(3)COO)(2) (13), Ag(3)(24-US-8)(2)(CF(3)COO)(3) (14), Ag(15-US-5)NO(3) (15), and Ag(21-US-7)BF(4) (16). The stoichiometry for the complexation with silver trifluoroacetate in solution was examined by (1)H NMR measurement. The titration plots of 2 and 5 under the dilution conditions showed a distinct inflection point at the 1/1 metal/macrocycle ratio, whereas the plots of 1 and 3 showed gradual change. PMID:15960503

Shimizu, Toshio; Kawaguchi, Mari; Tsuchiya, Takahiro; Hirabayashi, Kazunori; Kamigata, Nobumasa

2005-06-24

231

Reactions of Transition Metal Complexes with Cyclic Ethers.  

National Technical Information Service (NTIS)

Three novel reactions of epoxides with homogeneous transition-metal catalysts have been explored: (a) the selective rearrangement of internal epoxides to ketones; (b) the cleavage of C-C bond in epoxides having electron-attracting substituents; (c) the tr...

D. Milstein

1977-01-01

232

Silver(I) Complex formation with Cysteine, Penicillamine and Glutathione  

PubMed Central

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

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

2013-01-01

233

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

SciTech Connect

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.

McLane, V.

1996-07-01

234

Stepwise formation of iridium(III) complexes with monocyclometalating and dicyclometalating phosphorus chelates.  

PubMed

With the motivation of assembling cyclometalated complexes without nitrogen-containing heterocycle, we report here the design and systematic synthesis of a class of Ir(III) metal complexes functionalized with facially coordinated phosphite (or phosphonite) dicyclometalate tripod, together with a variety of phosphine, chelating diphosphine, or even monocyclometalate phosphite ancillaries. Thus, treatment of [IrCl(3)(tht)(3)] with stoichiometric amount of triphenylphosphite (or diphenyl phenylphosphonite), two equiv of PPh(3), and in presence of NaOAc as cyclometalation promoter, gives formation of respective tripodal dicyclometalating complexes [Ir(tpit)(PPh(3))(2)Cl] (2a), [Ir(dppit)(PPh(3))(2)Cl] (2b), and [Ir(dppit)(PMe(2)Ph)(2)Cl] (2c) in high yields, where tpitH(2) = triphenylphosphite and dppitH(2) = diphenyl phenylphosphonite. The reaction sequence that afforded these complexes is established. Of particular interest is isolation of an intermediate [Ir(tpitH)(PPh(3))(2)Cl(2)] (1a) with monocyclometalated phosphite, together with the formation of [Ir(tpit)(tpitH)(PPh(3))] (3a) with all tripodal, bidentate, and monodentate phosphorus donors coexisting on the coordination sphere, upon treatment of 2a with a second equiv of triphenylphosphite. Spectroscopic studies were performed to explore the photophysical properties. For all titled Ir(III) complexes, virtually no emission can be observed in either solution at room temperature or 77 K CH(2)Cl(2) matrix. Time-dependent DFT calculation indicates that the lowest energy triplet manifold involves substantial amount of metal centered (3)MC dd contribution. Due to its repulsive potential energy surface (PES) that touches the PES of ground state, the (3)MC dd state executes predominant nonradiative deactivation process. PMID:22272818

Lin, Cheng-Huei; Lin, Chih-Yuan; Hung, Jui-Yi; Chang, Yao-Yuan; Chi, Yun; Chung, Min-Wen; Chang, Yuh-Chia; Liu, Chun; Pan, Hsiao-An; Lee, Gene-Hsiang; Chou, Pi-Tai

2012-02-01

235

Structural and configurational relationships 'metal complex-substrate-product' in asymmetric catalytic hydrogenation, hydrosilylation and cross-coupling reactions  

NASA Astrophysics Data System (ADS)

The present-day published data on the relationships between the structures of rhodium, iridium, ruthenium, nickel and cobalt catalytic complexes and substrates in homogeneous asymmetric hydrogenation, hydrosilylation and cross-coupling reactions are systematised. The optimum ratio between the number of coordination vacancies in the complex and the number of functional groups of the substrate has been characterised in terms of a criterion of maximum enantioselectivity of the catalytic complex. The relationships between the configurations of the complexes and the products formed in the reactions are analysed. In the case of C2-symmetrical chiral diphosphine complexes as catalysts (some structural elements of their ligands represent an incomplete turn of a helix surrounding the central metal atoms), substrates of the same kind form the products having definite configurations characteristic of the particular orientation of the helix. For example, rhodium complexes with ligands that form an incomplete P-helical turn around metal atoms catalyse the formation of (R)-amino acids from the corresponding precursors. If the ligands contain fragments of M-helices around rhodium atoms, it is (S)-amino acids that are formed. The bibliography includes 234 references.

Pavlov, Valerii A.

2001-12-01

236

Polyelectrolyte complexes of chitosan: formation, properties and applications  

Microsoft Academic Search

The results of studies of polyelectrolyte complexes of chitosan are summarised and described systematically. Chitosan complexes with biopolyelectrolytes, with modified natural polyelectrolytes and with synthetic polyanions are considered. Medical and biotechnological applications of chitosan complexes are discussed.

M. A. Krayukhina; N. A. Samoilova; I. A. Yamskov

2008-01-01

237

Parahydrogen derived illumination of pyridine based coordination products obtained from reactions involving rhodium phosphine complexes.  

PubMed

The reactions of RhCl(PBz3)3 with H2 and pyridine or 4-methylpyridine yield RhCl(H)2(PBz3)2(py) and RhCl(H)2(PBz3)2(4-Me-py), respectively. These species undergo hydride site exchange via the loss of the pyridyl donor and formation of RhCl(H)2(PBz3)2 which contains equivalent hydride ligands; for the py system the activation free energy, deltaG++300, is 57.4 +/- 0.1 kJ mol(-1) while for 4-Me-py the value is 59.6 +/- 0.3 kJ mol(-1). These products only showed parahydrogen enhancement in the corresponding hydride resonances when a sacrificial substrate was added to promote hydrogen cycling. When RhCl(PPh3)3 was used as the precursor similar observations were made, while when RhCl(PCy3)2(C2H4) was examined, H2 addition led to the formation of the binuclear complex (H)2Rh(PCy3)2(micro-Cl)2Rh(H)2(PCy3)2 which was differentiated from RhCl(H)2(PCy3)2 on the basis of the similarity in diffusion coefficient (5.5 x 10(-9) m2 s(-1)) to that of (H)2Rh(PPh3)2(micro-Cl)2Rh(PPh3)2 (5.3 x 10(-9) m2 s(-1)). The detection of RhCl(H)2(PCy3)2(py) was facilitated when pyridine was added to a solution of RhCl(PCy3)2(C2H4) before the introduction of H2. During these reactions trace amounts of the double substitution products, RhCl(H)2(phosphine)(py)2, were also detected. PMID:16471059

Zhou, Rongrong; Aguilar, Juan A; Charlton, Adrian; Duckett, Simon B; Elliott, Paul I P; Kandiah, Rathika

2005-12-01

238

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

NASA Astrophysics Data System (ADS)

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

Harnisch, Martina; Keim, Alan; Scheier, Paul; Herman, Zdenek

2013-10-01

239

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

PubMed Central

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

2013-01-01

240

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

NASA Technical Reports Server (NTRS)

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.

Devincent, Sandra M.; Michal, Gary M.

1992-01-01

241

Alkoxy/halogen exchange reaction of molybdenum complexes containing phosphite with boron trihalides  

SciTech Connect

The ability of boron trihalides, BX/sub 3/, to extract an OR group or halogens on a carbon atom has been applied to the preparation of transition-metal carbyne complexes from Fischer-type carbyne complexes and to the halogen exchange of transition-metal perfluoroalkyl carbonyl complexes. The specific reaction studied was that of fac-(Mo(bpy)-(CO)/sub 3/(P(OR)/sub 3/)) where bpy = 2,2'-bipyridine with BF/sub 3//center dot/OEt/sub 2/ and BCl/sub 3/. Reaction with the former resulted in replacement of one OR group by F, while in the latter reaction, two OR groups were replaced with two Cl atoms. In the first reaction, geometrical retention around the Mo atom was retained; but in the latter reaction, a change in geometry around the Mo atom was noted. 9 refs.

Nakazawa, H.; Ohta, M.; Yoneda, H.

1988-03-23

242

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...

243

Efficient and enantioselective nitroaldol reaction catalyzed by copper Schiff-base complexes  

Microsoft Academic Search

Mild and efficient enantioselective nitroaldol reactions of nitromethane with various aldehydes were catalyzed by chiral copper Schiff-base complexes, which can be readily prepared from amino acid, yielding the corresponding adducts with high yields and good enantiometric excess (ee).

Changsheng Gan; Guoyin Lai; Zuhui Zhang; Zhiyong Wang; Ming-Ming Zhou

2006-01-01

244

Addition reaction of dialkyl disulfides to terminal alkynes catalyzed by a rhodium complex and trifluoromethanesulfonic acid.  

PubMed

[reaction: see text]. Addition of dialkyl disulfides to terminal alkynes is catalyzed by a rhodium-phosphine complex and trifluoromethanesulfonic acid giving (Z)-bis(alkylthio)olefins stereoselectively. PMID:11259056

Arisawa, M; Yamaguchi, M

2001-03-01

245

Integrin activation and focal complex formation in cardiac hypertrophy  

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

246

A heteroleptic cyclometalated iridium(III) fluorophenylpyridine complex from partial defluorohydrogenation reaction: synthesis, photophysical properties and mechanistic insights.  

PubMed

In this paper, a C-F bond activation reaction of a chloro-bridged iridium(III) dimer (dfppy)(2)Ir(?-Cl)(2)Ir(dfppy)(2) (1) (dfppy denotes 2-(4,6-difluorophenyl)pyridyl) in the presence of sodium methoxide has been reported, leading to the formation of a heteroleptic cyclometalated iridium(III) fluorophenylpyridine complex 2. HPLC-mass analysis confirmed the release of formaldehyde in the product mixture. When sodium benzyloxide was used as the base, complex 2 was also generated with the release of a benzaldehyde derivative. Complex 2 has been fully characterized by (1)H-NMR, (19)F-NMR and X-ray crystallographic methods, confirming the partial loss of one of the fluorine atoms on one of the cyclometalated phenylpyridyl ligands. Photophysical studies of complex 2 show that it has a similar absorption spectrum to that of Ir(III)(dfppy)(3). However, the emission spectrum shows a red shift maximum emission band at 478 nm due to the loss of a single fluorine atom, highlighting the critical effect of fluorine on the photoluminescence of these Ir(III) complexes. Finally, intensive mechanistic studies including HPLC-mass analysis, (1)H-NMR, and (19)F-NMR studies demonstrate that the formation of complex 2 should involve a critical ?-hydride elimination of Ir(III)-alkoxide intermediate and the participation of Ir-hydride and/or Ir-fluoride intermediates. PMID:23348919

Li, Liang; Wu, Feng; Zhang, Songlin; Wang, Dawei; Ding, Yuqiang; Zhu, Zhenzhong

2013-04-01

247

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

PubMed Central

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 (NO2?) complex and 0.5 mol equiv O2. 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.

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

2010-01-01

248

Formation of cation-anion complexes in the photochemical reaction of molybdenocene dihydrode with iron pentacarbonyl. Crystal structures of (CpâMo(CO)H)\\/sup +\\/(Feâ(CO)ââH)⁻ and (CpâMo(CO)H)\\/sup +\\/(CoMo(CO)â)⁻ (triclinic modification)  

Microsoft Academic Search

The reaction of CpâMoHâ with Fe(CO)â in boiling benzene under UV irradiation gives the ionic complexes (CpâMo(CO)H)\\/sup +\\/(Feâ(CO)ââH)⁻ (I) and (CpâMo(CO)H)\\/sup +\\/(CpMo(CO)â)⁻ (II), whose structures were established by x-ray diffraction analysis (Syntex P2⁠automatic diffractometer, lambda Mo K\\/sub ..cap alpha..\\/, graphite monochromator, theta\\/2theta scan technique, full-matrix least-squares method, isotropic variant for I on the basis of 2112 reflections to %

A. S. Antsyshkina; L. M. Dikareva; M. A. Porai-Koshits; V. N. Ostrikova; Yu. V. Skripkin; O. G. Volkov; A. A. Pasynskii; V. T. Kalinnikov

1985-01-01

249

Stereoselective [4 + 1] annulation reactions with silyl vinylketenes derived from Fischer carbene complexes.  

PubMed

Stable silyl vinylketenes were prepared via the thermal reaction of Fischer carbene complexes with triisopropylsilyl- or tert-butyldimethylsilyl-substituted alkynes. The ability of these silyl vinylketenes to participate with carbenoid reagents in [4 + 1] annulation reactions was investigated. The best results were obtained with diazomethane and substituted diazomethane reagents, which provided cyclopentenone products in excellent yields and essentially complete stereoselectivity. PMID:16901142

Moser, William H; Feltes, Laura A; Sun, Liangdong; Giese, Matthew W; Farrell, Ryan W

2006-08-18

250

Selective arylation reactions of bismuth-transition metal salicylate complexes.  

PubMed

Heterometallic bismuth-niobium or -tantalum salicylate complexes react with sodium tetraphenylborate to produce complexes in which one or more aryl groups have been transferred from boron to bismuth with the concomitant displacement of a eta(2)-salicylato ligand. When the previously reported Bi(2)Ta(2)(sal)(4)(Hsal)(4)(OEt)(4) (1) and BiTa(4)(mu-O)(4)(sal)(4)(Hsal)(3)(O(i)Pr)(4) (2) are treated with an alcoholic solution of NaBPh(4), the compounds [PhBi(Hsal)Ta(sal)(2)(OEt)(2) x EtOH](2) (3) and PhBiTa(4)(mu-O)(4)(Hsal)(2)(sal)(4)(OEt)(4) x CH(2)Cl(2) (4) are produced (sal = O(2)CC(6)H(4)-2-O(2-), Hsal = O(2)CC(6)H(4)-2-OH(-)). The core geometries of the heterometallic complexes are retained. However, if preparations of compound 1 are treated with NaBPh(4) without prior isolation of 1, [Ph(2)BiNb(sal)(2)(OMe)(2)](infinity) (5) is produced instead. This compound was characterized both as a solvent-free crystalline form and as one containing a lattice diethyl ether. The compound exhibits a polymeric chain structure that can be viewed as alternating [Ph(2)Bi](+) and [Nb(sal)(2)(OMe)(2)](-) units connected via bridging carboxylate groups. The arylation of the bismuth(III) center proceeds smoothly under mild conditions at room temperature, affording a new means for the mild functionalization of bismuth-transition metal heterometallic complexes. PMID:19537724

Stavila, Vitalie; Thurston, John H; Whitmire, Kenton H

2009-07-20

251

Formation of Flavor Components by the Reaction of Amino Acid and Carbonyl Compounds in Mild Conditions  

Microsoft Academic Search

This work describe products of reactions between four R-dicarbonyl compounds (diacetyl, pentan- 2,3-dione, glyoxal, and methylglyoxal) or two R-hydroxy ketones, (acetoine and acetol) and amino acids present in wines. The results shows the formation of odorous products or strong-smelling additives resulting from the Maillard and Strecker reaction in a primarily aqueous medium, at low temperature and low pH (pH 3.5)

Laura Pripis-Nicolau; Gilles de Revel; Alain Bertrand; Alain Maujean

2000-01-01

252

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

NASA Astrophysics Data System (ADS)

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.

Xu, Jun; Zhang, Yuanhang; Wang, Wei

2006-12-01

253

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

NASA Astrophysics Data System (ADS)

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

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

254

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

PubMed

Four new complexes, [M(Salpyr)] where Salpyr=N,N'-bis(Salicylidene)-2,3- and 3,4-diiminopyridine and M=Co, Cu, Mn, Ni and Zn were synthesized and characterized by (1)H NMR, IR spectroscopy, elemental analysis and UV-vis spectrophotometry. UV-vis spectrophotometric study of the adduct formation of the zinc(II) complexes, [Zn(2,3-Salpyr)] and [Zn(3,4-Salpyr)], as donor with R(2)SnCl(2) (R=methyl, phenyl, n-butyl), PhSnCl(3) and Bu(3)SnCl as acceptors has been investigated in methanol, as solvent. The formation constants and the thermodynamic free energies were measured using UV-vis spectrophotometry. Titration of the organotin chlorides with Zn(II) complexes at various temperatures (T=283-313K) leads to 1:1 adduct formation. The results show that the formation constants were decreased by increasing the temperature. The trend of the reaction of R(n)SnCl(4-n) as acceptors toward given zinc complexes was as follows: PhSnCl3 > Me2SnCl2 > Ph2SnCl2 > Bu2SnCl2 > Bu3SnCl. By considering the formation constants and the ?G° of the complex formation for the Schiff base as donor and the M(II) as acceptor, the following conclusion was drawn: the formation constant for a given Schiff base changes according to the following trend: Ni > Cu > Co > Zn > Mn. PMID:22626922

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

2012-08-01

255

Reaction-induced pore formation and superconductivity in in situ processed MgB2 superconductors  

NASA Astrophysics Data System (ADS)

The pore formation in in situ processed MgB2 bulk superconductors was systematically examined in terms of a reaction temperature and time. Powder compacts of magnesium (Mg) and boron (B) were heat-treated at a temperature below or above the melt point (m. p., 649 °C) of Mg for various time periods. As the reaction time increased at each reaction temperatures, the size of the powder compacts increased and the compact weight was decreased. The de-densification (so-called the pellet expansion) phenomena at the temperature above the m. p. of Mg was more remarkable. The density decrease was attributed to the three main factors of the pore formation, the out-growth of MgB2 plates and the Mg evaporation during the formation reaction of MgB2. The microstructure investigation for the initial formation stage of MgB2 at the temperature below the m. p. showed that the pores begun to form at the Mg/matrix interfaces and the spaces that the Mg powders occupied turned into open space (pores) gradually as a reaction time increased. This result indicates that the pores formation at the solid state (temperatures below the m. p.) is attributed to the large difference in diffusivity between Mg and B. In comparison to the solid state, the pore formation at the liquid state (temperatures above the m. p.) was attributed to the melting of Mg powders and the subsequent rapid movement of the melt due to the capillary force. Due to the faster mass transfer through the liquid, the pore formation at temperatures above the m. p. was much faster than that below the m. p. The critical current density of the MgB2 superconductor prepared at 600 °C was higher than that at 900 °C owing the higher pellet density and the smaller grain size.

Kim, C.-J.; Yi, J. H.; Jun, B.-H.; You, B. Y.; Park, S.-D.; Choo, K.-N.

2014-07-01

256

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

PubMed

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

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

2014-02-19

257

A Multiphysics Model of In Vitro Transcription Coupling Enzymatic Reaction and Precipitation Formation  

PubMed Central

Multiphysics modeling, which integrates the models studied in different disciplines so far, is an indispensable approach toward a comprehensive understanding of biological systems composed of diverse phenomena. However, the variety of the models is narrower than the actual diverse phenomena because of the difficulty in coupling independent models separately studied in different disciplines for the actual coupled phenomena. In this study, we develop a mathematical model coupling an enzymatic reaction and mineralization formation. As a test case, we selected an in vitro transcription system where a transcription reaction occurs along with the precipitation formation of magnesium pyrophosphate (Mg2PPi). To begin, we experimentally elucidated how the transcription reaction and the precipitation formation are coupled. In the analysis, we applied a Michaelis-Menten-type equation to the transcription reaction and a semiempirical equation describing the correlation between the induction period and the supersaturation ratio to the precipitation formation, respectively. Based on the experimental results, we then integrated these two models. These models were connected by supersaturation that increases as the transcription reaction proceeds and becomes the driving force of the precipitation. We believe that our modeling approach could significantly contribute to the development of newer multiphysics models in systems biology such as bone metabolic networks.

Akama, Satoru; Yamamura, Masayuki; Kigawa, Takanori

2012-01-01

258

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

PubMed

The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen), and glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and (109)Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol dm(-3) Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10-11) a mean Ag-S bond distance of 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and (109)Ag NMR spectra of a concentrated Ag(I)-cysteine solution (C(Ag(I)) = 0.8 mol dm(-3), L/Ag = 2.2) showed a mean Ag-S bond distance of 2.47 ± 0.02 Å and ?((109)Ag) 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (C(Ag(I)) = 0.5 mol dm(-3), L/Ag = 2.0) the mean Ag-S bond distance of 2.40 ± 0.02 Å and ?((109)Ag) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C(Ag(I)) = 0.01 mol dm(-3), pH ?11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ?10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N), and AgS3 coordination environments was used, together with a survey of (109)Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution. PMID:23556419

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

2013-04-15

259

Phase formation sequence for the reaction of multilayer thin films of Nb/Al  

SciTech Connect

We have investigated the phase formation sequence for the reaction of Nb and Al in multilayer films using cross-sectional transmission electron microscopy and x-ray diffraction. NbAl{sub 3} is the first intermetallic phase to form. Contrary to previous reports, we find evidence from cross-sectional transmission electron microscopy that the sigma phase, Nb{sub 2}Al, is not bypassed in the reaction sequence. Instead, its formation is concurrent with the formation of the superconducting {ital A}15 phase, Nb{sub 3}Al. However, depending on the periodicity and the composition of the film, the Nb{sub 2}Al phase can be consumed by the Nb{sub 3}Al phase for long annealing times. The significance of this phase formation sequence to powder metallurgically processed magnet wire is discussed.

Barmak, K.; Coffey, K.R.; Rudman, D.A. (Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA (USA)); Foner, S. (Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA (USA) Department of Physics, Massachusetts Institute of Technology, Cambridge, MA (USA))

1990-06-15

260

The CO formation reaction pathway in steam methane reforming by rhodium.  

PubMed

Three different pathways toward CO formation from adsorbed CH and O are compared by quantum-chemical density functional theory (DFT) calculations for planar and stepped Rh surfaces. The conventional pathway competes with the pathway involving a formyl (CHO) species. This holds for both types of surfaces. The barrier for carbon-oxygen bond formation for the planar surface (180 kJ/mol) is substantially higher than that for the stepped surface (90 kJ/mol). The reaction path through intermediate formyl formation competes with direct formation of CO from recombination via adsorbed C and O atoms. Calculations are used as a basis for the analysis of the overall kinetics of the methane steam reforming reaction as a function of the particle size and the metal. PMID:20919687

van Grootel, Pieter W; Hensen, Emiel J M; van Santen, Rutger A

2010-11-01

261

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

PubMed

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

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

2007-01-01

262

EUV resist simulation based on process parameters of pattern formation reaction  

NASA Astrophysics Data System (ADS)

We simulated the process parameters of a pattern formation reaction that included during-the-exposure and post exposure bake (PEB) processes using an originally developed simulator. From the simulation results, the relationship between process parameters of pattern formation reaction and quencher concentration has been clarified. Moreover, we simulated the present target process parameters of extreme ultraviolet (EUV) resist for breaking the RLS trade-off. In this simulation, the process parameters were calculated from lithographic results (sensitivity, LWR, and CD) using real SEM images. This methodology was used to determine the process parameters required to break the RLS trade-off to obtain the required lithographic target of the EUV resist. We simulated the present lithography performance target using the process parameters of pattern formation reactions. These simulation results showed that a large reaction radius is necessary to break the RLS trade-off. Furthermore, we confirmed that increasing the PEB temperature leads to an improvement in the reaction radius. However, there is a discrepancy between the target radius and the controllable range of reaction radius that can be obtained by varying the PEB temperature.

Sugie, Norihiko; Itani, Toshiro; Kozawa, Takahiro

2014-04-01

263

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

NASA Astrophysics Data System (ADS)

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.

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

2010-11-01

264

Experimental and computational investigation on the gas phase reaction of ethyl formate with cl atoms.  

PubMed

The rate coefficient for the gas-phase reaction of Cl atoms with ethyl formate was measured over the temperature range of 268-343 K using relative rate methods, with ethyl chloride as a reference compound. The temperature dependent relative rate coefficients for the ethyl formate + Cl reaction were measured, and the modified Arrhenius expression kethyl formate(268-343) = (2.54 ± 0.57) × 10(-23) T(4.1) exp {-(981 ± 102)/T} cm(3) molecule(-1) s(-1) was obtained with 2? error limits. The room temperature rate coefficient for the title reaction is (9.84 ± 0.79) × 10(-12) cm(3) molecule(-1) s(-1), which is in good agreement with reported values. To complement the experimental measurement, computational methods were used to calculate the rate coefficient for the ethyl formate + Cl reaction atoms using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) and the CCSD (T)/cc-pVDZ//M062X/6-31+g(d,p) level of theory. The temperature dependent Arrhenius expression was obtained to be 2.97 × 10(-18) T(2.4) exp[-(390/T)] cm(3) molecule(-1) s(-1) over the temperature range of 200-400 K. The thermodynamic parameters and branching ratio were calculated. Also, the atmospheric lifetime and global warming potentials (GWPs) were calculated for ethyl formate. PMID:24945822

Balaganesh, M; Dash, Manas Ranjan; Rajakumar, B

2014-07-17

265

Kinetic Lability, Structural Diversity, and Oxidation Reactions of New Oligomeric, Anionic Carboxylate-Pyridine Complexes.  

PubMed

The dimeric [M(2)(OAc)(5)(py)(2)&mgr;-(OH(2))]Et(4)N complexes, I (M = Mn, Fe, Co), have been isolated from pyridine solutions of M(II)(OAc)(2).xH(2)O and Et(4)N(OAc).4H(2)O. The X-ray structures of I (M = Mn, Fe, Co) have been determined and show the metal ions asymmetrically bridged by two acetate ligands and a water molecule. One of the metal ions is bound by a pyridine ligand and two monodentate acetate ligands that are hydrogen bonded to the bridging water molecule. The second metal ion is bound to a bidentate acetate ligand and a pyridine ligand. Recrystallization of I from acetonitrile leads to the reorganization of I and isolation of the M(3)(OAc)(8)(Et(4)N)(2) complexes, II (M = Mn, Fe, Co). The X-ray structure of II (M = Mn, Co) has been determined and shows the three metal ions connected by four bridging acetate ligands in a &mgr;(1), &mgr;(2) mode and two acetate ligands in the &mgr;(1),eta(1) mode, with a bidentate acetate ligand on each of the external metal ions completing the distorted octahedral geometry. Air oxidation of I-Fe in propionitrile leads to the formation of the mixed-valence [Fe(3)&mgr;(3)-(O)(OAc)(7)(OH(2))]Et(4)N(III). The X-ray structure of III has been determined and resembles the core of the basic acetate complexes; however, it has five bridging acetate ligands. The Mössbauer spectrum of III shows two quadrupole doublets in a 1:2 ratio with delta(Fe) = 1.29(1) and 0.48 mm/s; DeltaE(q) = 1.89 and 0.71 mm/s. The oxidation of I-Fe by H(2)O(2)/O(2) in pyridine solution in the presence of Cl(-) ligands affords Fe(4)&mgr;(3)-(O)(2)(OAc)(6)(py)(4)Cl(2) (IV). The X-ray structure of IV shows a rhombic {Fe(III)(4)(&mgr;(3)-O)(2)} core previously found in iron and manganese chemistry. The reaction of ferrocenium ion with I-Fe under basic conditions in dichloromethane solution led to the formation of the familiar mixed-valence Fe(3)&mgr;(3)-(O)(OAc)(6)(py)(3) complex (V) with the basic acetate structure. Complexes I-Fe, II-Fe, III, and IV catalyze the reaction of O(2) with adamantane under GiF conditions to give adamantanols and adamantanone. The similarity of the results in comparison to similar studies previously reported for iron/carboxylate complexes are noted and discussed. PMID:11670328

Reynolds III, R. A.; Dunham, W. R.; Coucouvanis, D.

1998-03-23

266

On the formation of iron(III) hydroxo acetate complexes.  

PubMed

The formation of hydroxo acetate complexes of iron (III) ion has been studied at 25 degrees C in 3 M (Na)ClO4 ionic medium by measuring with a glass electrode the hydrogen ion concentration in Fe(ClO4)3-HClO4-NaAc mixtures (Ac = acetate ion). The acetate/metal ratio ranged from 0 to 6, the metal concentration varied from 0.005 to 0.06 M, whereas [H+] was stepwise decreased from 0.1 M to initial precipitation of hydroxo-acetates. This occurred, depending on the acetate/metal ratio, in the -log[H+] range 1.85-2.7. The potentiometric data are consistent with the presence of Fe3(OH)3Ac3(3+), Fe2(OH)2(4+), Fe3(OH)4(5+), Fe3(OH)5(4+) and, as minor species, of Fe3(OH)2Ac6+, FeAc2+, FeAc2+, FeOH2+ and Fe(OH)2+. Previously published EMF measurements with redox and glass half-cells were recalculated to refine the stability constants of FeAc2+, FeAc2+ and Fe3(OH)2Ac6+. Formation constants *beta pqr for pFe(3+)+(q-r)H2O + rHAc reversible Fep(OH)(q-r)(Ac)r3p-q + qH+ (in parenthesis the infinite dilution value): log*beta 111 = -1.85 +/- 0.02 (-0.67 +/- 0.15), log*beta 122 = -3.43 +/- 0.02 (-1.45 +/- 0.15); log*beta 363 = -5.66 +/- 0.03 (-2.85 +/- 0.40), log*beta 386 = -8.016 +/- 0.006 (-4.06 +/- 0.15), log*beta 220 = -2.88 +/- 0.02 (-2.84 +/- 0.05), log*beta 340 = -6.14 +/- 0.18 (-6.9 +/- 0.4), log*beta 350 = -8.44 +/- 0.09 (-7.65 +/- 0.15). PMID:11507828

Ciavatta, L; De Tommaso, G; Iuliano, M

2001-01-01

267

Cleavage of Ni-(?2-S)-Ni Bridges in Dinuclear Nickel(II) Dithiolate Pincer Complexes and Related Reactions  

PubMed Central

Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble NiII pincer complexes formulated as [Ni(pdmt)]2 and [Ni(pdtc)]2, respectively, with two Ni-(?2-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)]2 + 2L0,? ? 2[Ni(pdtc)L]0,? with an extensive set of nucleophiles to afford planar mononuclear products with L? = halide, CN, Me3SiO?, RS? and L0 = Et3P and a N-heterocyclic carbene. [Ni(pdmt)]2 is considerably less reactive toward bridge disruption. Cleavage products support several reactions of interest leading to other mononuclear species and to di- and trinuclear complexes. [Ni(pdtc)(OSiMe3)]1? deprotonates acetonitrile and acetone to form [Ni(pdtc)(CH2R)]1? (R = CN, COMe). Reaction of [Ni(pdtc)SEt]1? with FeII yields the thiolate-bridged dimer {[Ni(pdtc)]2(SEt)}1?. Refluxing an acetonitrile solution of [Ni(pdtc)SH]1? in air results in formation of trinuclear {[Ni(pdtc)]3S]2? containing the rare unsupported Ni3(?3-S) bridge core. Reaction of [Ni(pdtc)CN]1? with [Fe(Me6tren)(OTf)]1+ forms the complex [Ni(pdtc)CNFe(Me6tren)]1+, the only example of a single Ni-C?N-Fe bridge within a molecule. Structures of the various types of reaction products are presented. This work demonstrates the potential utility of bridge cleavage of polynuclear NiII thiolates, an extensive family of compounds, to produce mononuclear products.

Huang, Deguang; Deng, Liang; Sun, Jibin; Holm, R. H.

2009-01-01

268

Effect of antioxidants on elimination and formation of acrylamide in model reaction systems.  

PubMed

Antioxidants, including tert-butyl hydroquinone (TBHQ), butylated hydroxy anisole (BHA), butylated hydroxytoluene (BHT), ferulic acid, epigallocatechin gallate (EGCG) and vitamin C (V(C)), and their corresponding oxidation products, were tested for their influence on elimination of acrylamide and inhibition of acrylamide formation. Our experimental results showed that the antioxidants could neither effectively destruct acrylamide nor inhibit (or even promote) its formation, but their corresponding oxidation products were able to directly destruct acrylamide and its precursor, asparagine, thus inhibit acrylamide formation. Moreover, a positive correlation between the carbonyl value and acrylamide formation was observed in a frying oil-asparagine reaction model system, suggesting that antioxidants can inhibit acrylamide formation by inhibiting oil carbonyl compounds formation. PMID:20667655

Ou, Shiyi; Shi, Jianjun; Huang, Caihuan; Zhang, Guangwen; Teng, Jiuwei; Jiang, Yue; Yang, Baoru

2010-10-15

269

Study of the dynamic complex formation of pentanoic acid with ?-cyclodextrin by using an ultrasonic relaxation method  

NASA Astrophysics Data System (ADS)

This study examined the effects of pentanoic acid as a guest molecule on the inclusion complex formation with ?-cyclodextrin ( ?-CD). Ultrasonic absorption measurements were carried out for ?-CD solutions with pentanoic acid over the frequency range from 0.2 to 45 MHz. A single relaxational absorption resulting from the perturbation of chemical equilibrium was observed for the inclusion of pentanoic acid into the ?-CD cavity. The undissociated form of pentanoic acid produced a more stable complex with ?-CD than its dissociated form. An ultrasonic relaxation associated with a protontransfer reaction was also observed when no additive was present in the solution.

Bae, Jong-Rim

2013-07-01

270

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

PubMed

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. Mg(2+) 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

Liu, Ben; Han, Lu; Che, Shunai

2012-10-01

271

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

PubMed Central

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.

Liu, Ben; Han, Lu; Che, Shunai

2012-01-01

272

Pattern formation in reaction-diffusion models with nonuniform domain growth  

Microsoft Academic Search

Recent examples of biological pattern formation where a pattern changes qualitatively as the underlying domain grows have\\u000a given rise to renewed interest in the reaction-diffusion (Turing) model for pattern formation. Several authors have now reported\\u000a studies showing that with the addition of domain growth the Turing model can generate sequences of patterns consistent with\\u000a experimental observations. These studies demonstrate the

E. J. Crampin; W. W. Hackborn; P. K. Maini

2002-01-01

273

Reaction sequence of nickel(II) with kaolinite: Mineral dissolution and surface complexation and precipitation  

SciTech Connect

The dissolution kinetics of Ni(II) sorbed to kaolinite at pH 7 were examined as a function of initial aqueous Ni(II) concentrations; the local molecular structure of the Ni surface complexes were determined using extended x-ray absorption fine structure (EXAFS) spectroscopy. The dissolution of kaolinite was nonstoichiometric with a preferential release of Si over Al. The dissolution rate, R{sub Si}, increased with an increase in the aqueous concentration of Ni. A rate law was developed representing a fractional-order dissolution reaction with respect to the surface concentration of Ni. Absorption spectra were obtained from kaolinite samples washed with 0.10 M NaNO{sub 3} adjusted to pH 3.4 to remove amorphous Al-hydroxide surface deposits or adsorbed Al and from kaolinite that was untreated. For all samples, EXAFS results revealed the presence of multinuclear Ni surface complexes wit h a similar, but not identical, local structural environment to pure crystalline Ni(OH){sub 2}. The Ni-Ni bond distances were shorter (3.06--3.11 {angstrom}) than in Ni(OH){sub 2}(s) (3.13 {angstrom}) and increased with an increase in surface coverage. Additionally, Al was present in all but the highest surface coverage as a second neighbor backscatterer. At the lower surface coverages, Al is present at 2.69 {angstrom}, indicating the formation of a bidentate Ni surface complex. With increased surface coverage, the d(Ni-Al) increases to 2.96 {angstrom}, which is believed to result from a Ni,Al-hydroxide precipitate. No significant structural differences were found between kaolinite pretreatments. Based on these results, a hypothesized mechanism for Ni sorption on kaolinite is proposed.

Eick, M.J. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Crop and Soil Environmental Sciences; Fendorf, S.E. [Univ. of Idaho, Moscow, ID (United States). Soil Science Div.

1998-09-01

274

Rhodium complex-catalyzed Pauson-Khand-type reaction with aldehydes as a CO source.  

PubMed

With aldehydes as a CO source under solvent-free conditions, rhodium complex efficiently catalyzed an intramolecular carbonylative alkene-alkyne coupling (Pauson-Khand-type reaction) and various bicyclic enones were obtained in high yield. Experiments under argon flow and a 13C-labeling experiment suggested that almost no free carbon monoxide was generated in this reaction. When noncationic rhodium complex with chiral phosphine was used as a chiral catalyst, the reaction proceeded enantioselectively to give various chiral cyclopentenones in up to 90% ee under solvent-free conditions. PMID:12375978

Shibata, Takanori; Toshida, Natsuko; Takagi, Kentaro

2002-10-18

275

Spectroscopic studies on charge-transfer complexes formed in the reaction of ferric(III) acetylacetonate with ?- and ?-acceptors  

NASA Astrophysics Data System (ADS)

The reaction of ferric(III) acetylacetonate (donor), Fe(acac) 3, with iodine as a ?-acceptor and with other different ?-acceptors have been studied spectrophotometrically at room temperature in chloroform. The ?-acceptors used in this investigation are 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil and 7,7',8,8'-tetracyanoquinodimethane (TCNQ). The results indicate the formation of 1:1 charge-transfer complexes with a general formula, [Fe(acac) 3 (acceptors)]. The iodine complex was shown to contain the triiodide species, [Fe(acac) 3] 2I +I 3-, based on the electronic absorptions as well as on the Far-infrared absorption bands characteristic for the non-linear triiodide species, I 3-, with C 2v symmetry. The proposed structure of this complex is further supported by thermal and middle infrared measurements.

Teleb, S. M.; Refat, M. S.

2004-06-01

276

Neutral-neutral reactions for the formation of C3O and C3S  

NASA Astrophysics Data System (ADS)

We investigate, neutral-neutral radiative association reactions (C2+CO) and (C2+CS) for the formation of C3O and C3S respectively by DFT. Both the reactions are spin allowed and found to be exothermic and barrierless in nature. The product of these reactions are perfectly linear and the calculated rotational transitions are in good agreement with earlier published data. At the DFT/TZ2P level, the difference between the calculated rotational constant and experimental one is 0.064 % for C3O and 0.16 % for C3S. We also discussed the intrinsic and relative stability of these molecules.

Abbas, Haider

2014-05-01

277

Temperature dependence of pentyl nitrate formation from the reaction of pentyl peroxy radicals with NO.  

PubMed

Alkyl nitrate yields from the reaction of 1-pentyl, 2-pentyl and 2-methyl-2-butyl peroxy radicals with NO have been determined over the temperature range (261-305 K) and at 1 bar pressure from the photo-oxidation of the iodoalkane precursors in air-NO mixtures. Yields were observed to increase with decreasing temperature and, contrary to previous observations, along the series primary < secondary congruent with tertiary. Our results suggests a significant temperature dependence for the formation of nitrates from the reaction of pentyl peroxy radicals with NO and represent an extension in the temperature range over which this reaction has been studied experimentally in the past. PMID:17687480

Cassanelli, Paola; Fox, David J; Cox, R Anthony

2007-08-21

278

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

SciTech Connect

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).

McLane, V. [ed.] [comp.

1997-07-01

279

Substituent-induced switch of the role of charge-transfer complexes in the Diels-Alder reactions of o-chloranil and styrenes.  

PubMed

Addition of p-substituted styrenes, XSty (X = H, Me, MeO, or Cl) to the solutions of o-chloranil, oCA, in dichloromethane resulted in the transient formation of the charge-transfer complexes, [XSty, oCA], followed by the Diels-Alder reaction. At low temperatures, these reactions led to formation of essentially pure endocycloadducts. As expected for the inverse-electron-demand Diels-Alder reaction, the rate constants of the cycloaddition rose with the increase of the donor strength. However, while facile cycloaddition took place in the neat mixtures of the o-chloranil with p-methyl, p-chloro-, or unsubstituted styrenes at low temperatures, a similar system involving the strongest MeOSty donor was surprisingly persistent. X-ray structural measurements and quantum-mechanical computations indicated that this anomaly is related to the fact that the diene/dienophile orientation in the charge-transfer [MeOSty, oCA] complex is opposite to that in the endocycloadduct and in the lowest-energy transition state leading to this isomer. Thus, the proceeding of the cycloaddition requires dissociation of the (dead-end) complex. For the systems involving the oCA diene and either the HSty, ClSty, or MeSty dienophile, the donor/acceptor arrangements in the charge-transfer complexes apparently are consistent with that in the corresponding products, and the formation of these complexes does not hinder the Diels-Alder reaction. PMID:22712804

Rosokha, Sergiy V; Korotchenko, Vasiliy; Stern, Charlotte L; Zaitsev, Vladimir; Ritzert, Jeremy T

2012-07-20

280

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

PubMed

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 ??-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. PMID:24510549

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

2014-07-01

281

Reactivity of radical complexes Zr(IV) (O 2 ? ) in electron transfer reactions  

Microsoft Academic Search

Rate constants of the reactions of the radical complex Zr(IV) (O2?) with Fe(II), Ti(III), resorcinol, guaiacol and ascorbic acid in aqueous solutions have been measured by the ESR flow method. They are similar to the values obtained for the radical complex Ti(IV) (O2?).

L. S. Ryvkina; V. M. Berdnikov

1982-01-01

282

Functional LH1 antenna complexes influence electron transfer in bacterial photosynthetic reaction centers  

Microsoft Academic Search

The effect of the light harvesting 1 (LH1) antenna complex on the driving force for light-driven electron transfer in the Rhodobacter sphaeroidesreaction center has been examined. Equilibrium redox titrations show that the presence of the LH1 antenna complex influences the free energy change for the primary electron transfer reaction through an effect on the reduction potential of the primary donor.

Ronald W. Visschers; Simone I. E. Vulto; Michael R. Jones; Rienk van Grondelle; Ruud Kraayenhof

1999-01-01

283

Hydrosilylation reactions catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts  

Microsoft Academic Search

Hydrosilylation reactions of styrene with triethoxysilane catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts are reported. In comparison with Wilkinson’s catalyst, Rh(PPh3)3Cl, all of the present rhodium complexes with phosphines functionalized with imidazolium salts exhibit higher catalytic activity and selectivity.

Jiayun Li; Jiajian Peng; Diliang Wang; Ying Bai; Jianxiong Jiang; Guoqiao Lai

2011-01-01

284

Secondary organic aerosol (SOA) formation from reaction of isoprene with nitrate radicals (NO3)  

NASA Astrophysics Data System (ADS)

Secondary organic aerosol (SOA) formation from the reaction of isoprene with nitrate radicals (NO3) is investigated in the Caltech indoor chambers. Experiments are performed in the dark and under dry conditions (RH<10%) using N2O5 as a source of NO3 radicals. For an initial isoprene concentration of 18.4 to 101.6 ppb, the SOA yield (defined as the ratio of the mass of organic aerosol formed to the mass of parent hydrocarbon reacted) ranges from 4.3% to 23.8%. By examining the time evolutions of gas-phase intermediate products and aerosol volume in real time, we are able to constrain the chemistry that leads to the formation of low-volatility products. Although the formation of ROOR from the reaction of two peroxy radicals (RO2) has generally been considered as a minor channel, based on the gas-phase and aerosol-phase data it appears that RO2+RO2 reaction (self reaction or cross-reaction) in the gas phase yielding ROOR products is a dominant SOA formation pathway. A wide array of organic nitrates and peroxides are identified in the aerosol formed and mechanisms for SOA formation are proposed. Using a uniform SOA yield of 10% (corresponding to Mo≅10 ?g m-3), it is estimated that ~2 to 3 Tg yr-1 of SOA results from isoprene + NO3. The extent to which the results from this study can be applied to conditions in the atmosphere depends on the fate of peroxy radicals (i.e. the relative importance of RO2+RO2 versus RO2+NO3 reactions) in the nighttime troposphere.

Ng, N. L.; Kwan, A. J.; Surratt, J. D.; Chan, A. W. H.; Chhabra, P. S.; Sorooshian, A.; Pye, H. O. T.; Crounse, J. D.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H.

2008-02-01

285

Gas phase reactions of trimethyl borate with phosphates and their non-covalent complexes.  

PubMed

Using a quadrupole ion trap mass spectrometer, trimethyl borate was allowed to react with dihydrogen phosphate, deprotonated O-phosphoserine, and a set of hydrogen bonded complexes involving dihydrogen phosphate and neutral acids (phosphoric acid, acetic acid, serine, and O-phosphoserine). The reactions show a consistent pattern in which the initial attack leads to addition with the loss of one or two CH3OH molecules. Collision-activated dissociation (CAD) experiments on the reaction products generally lead to the loss of an additional CH3OH molecule. In no case is a partner from the original hydrogen-bonded complex lost. The results indicate that the reactions lead to structures where the phosphate and its complex partner are covalently bound to the boron. For each of the reactions, rate constants were determined. In the course of CAD experiments (up to MS5), several novel borophosphate structures were identified. The work is supported by ab initio calculations on selected species. PMID:12322956

Gronert, Scott; O'Hair, Richard A J

2002-09-01

286

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

NASA Astrophysics Data System (ADS)

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

Merkin, J. H.

2009-07-01

287

Reactions of Complex Phenols on Aerosols with Gaseous Ozone  

NASA Astrophysics Data System (ADS)

We report that ?-tocopherol (?-TOH/?-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, ?-TO- reacts further with ozone via a collision-induced dissociation into a C19H40 fragment (vs. C19H38 from ?-TO-, carrying the phytyl side-chain, whereas the higher homologues (?-TO-On ? 2-) are not reactive with O3(g). On this basis, ?-TO- is assigned to a chroman-6-ol (4a, 8a)-ene oxide (an epoxide), ?-TO-O2- to an endoperoxide, and ?-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.

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

2009-12-01

288

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

PubMed

A benzyne cobalt complex, Co(?(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. PMID:24626376

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

2014-05-14

289

Reaction of thiols with N-bonded sulfenamide complexes of cobalt(III): steric effect and reaction pathway.  

PubMed

The products and kinetics of the reaction of several thiols (RSH = 2-aminoethanethiol, cysteine, penicillamine, cysteine ethyl ester) with N-bonded sulfenamide complexes ([Co(en)(2)(NH(2)S(CH(2))(2)NH(2)](3+) (IA), [Co(en)(2)(NH(2)SCH(2)CH(CO(2)H)NH(2)](3+) (IC), [Co(en)(2)(NH(2)SC(CH(3))(2)CH(CO(2)H)NH(2)](3+) (IP)) have been studied. The reaction proceeds by nucleophilic attack at sulfur with cleavage of the N-S bond to form a disulfide and leave a coordinated NH(3) ligand. The kinetics (pH 4-10) reveal that the deprotonated thiol, RS(-), is the reactive nucleophile and that the N-deprotonated sulfenamide complex is unreactive. The reactions of IP are approximately 10(4) times slower than those of IA or IC, and the reasons and consequences of this large steric effect are discussed. It is concluded, on the basis of these and other observations from the literature, that there will be substantial steric retardation to nucleophilic attack at two-coordinate sulfur in a R-C(CH(3))(2)-S-X-R' unit because of the regiospecificity of the reaction. The acid dissociation constants of IP and the X-ray structure of its bromide salt also are reported. PMID:15651875

Sisley, Margaret J; Ferguson, Michael J; Jordan, Robert B

2005-01-24

290

Reaction path study of helix formation in tetrapeptides: Effect of side chains  

Microsoft Academic Search

A computational protocol to calculate steepest descent paths in flexible molecules is discussed in detail. The algorithm does not use second derivatives and related matrices, and is therefore suitable for large systems. The shortest reaction coordinate from the helix to the extended chain conformation is calculated for a series of different tetrapeptides. The formation of a helical turn is investigated

Chyung Choi; Ron Elber

1991-01-01

291

Colorimetric determination of the reaction capacity of cellulose for viscose formation  

Microsoft Academic Search

A comparative analysis of methods of determining the reaction capacity (RC) of cellulose for viscose formation and the correlation between the results and the production indices [i] showed that the Fock method [2; 3, p. 804] was the most acceptable one. This method too, however, has its faults. The indicator 'insoluble part of the cellulose' used by Fock represents the

M. A. Korkina; V. N. Parshikova; S. A. Mikhailova; K. A. Malyshevskaya

1976-01-01

292

IN VIVO FORMATION OF HALOGENATED REACTION PRODUCTS FOLLOWING PERORAL SODIUM HYPOCHLORITE  

EPA Science Inventory

To date the principal concern of the disinfection of potable water has centered on the formation of halogenated organic reaction products and the adverse health effects that these products may have. However, an additional area for concern relating to water disinfection is the pot...

293

Assessment of the potential for ammonium nitrate formation and reaction in Tank 241-SY-101.  

National Technical Information Service (NTIS)

Two principal scenarios by which ammonium nitrate may be formed were considered: (a) precipitation of ammonium nitrate in the waste, and (b) ammonium nitrate formation via the gas phase reaction of ammonia and nitrogen dioxide. The first of these can be d...

L. R. Pederson S. A. Bryan

1994-01-01

294

An experimental clarification of the association of delayed ettringite formation with alkali-aggregate reaction  

Microsoft Academic Search

The issue of determining the primary cause of damage to concrete elements in the presence of a combination of delayed ettringite formation (DEF) and alkali-aggregate reaction (AAR) is very controversial. Some authors believe that DEF has been the cause of serious damage (cracking) to concrete elements cured at elevated temperatures, and some others attribute the damage to AAR, with a

A. Shayan; I. Ivanusec

1996-01-01

295

The formation of H_2 by H-atom reaction with grain surfaces  

NASA Astrophysics Data System (ADS)

A model for H_2 formation by reaction of H-atoms with the surface of carbonaceous grains is developed. Such reactions, which involve interstitial H-atoms at low grain temperature and H-atoms bonded to -CH, -CH_2 and -CH_3 groups at higher temperature, occur promptly on the collision of an H-atom with a grain surface. The rate of hydrogen formation and the efficiency of reaction depend on both gas kinetic and dust temperature. The rate coefficient R (cm^3 s^-1) for H_2 formation using this prompt-reaction model (PRM) can be calculated from laboratory data and is consistent with measured values of R. The dependence of R on ambient conditions in interstellar clouds can be easily estimated from this prompt-reaction model. R is found to be strongly dependent on gas kinetic temperature T_k and can exceed 10^-17 cm^3 s^-1, even for warm dust, when T_k>~300 K.

Duley, W. W.

1996-03-01

296

Calculated formation and reaction energies of 3d transition metal oxides using a hierachy of exchange-correlation functionals  

NASA Astrophysics Data System (ADS)

The formation and oxidation reaction energies of 16 transition metal oxides (TMOs) are benchmarked against experiments with an increasing complexity of the exchange-correlation (xc) functionals: PBE, PBE + U with a single U for each transition metal element, PBE0 (25% exact exchange included), EXX (100% exact exchange), and EXX + RPA (random phase approximation for the correlation energy). Although rather challenging on standard CPU computing facilities, the RPA calculations were performed efficiently on graphic processing units (GPUs). For the formation energies, the PBE + U, PBE0, EXX + RPA improves significantly over PBE with mean absolute errors (MAE) of 0.83 (PBE), 0.39 (PBE + U), 0.34 (PBE0), and 0.39 (EXX + RPA) eV per oxygen. In addition, EXX + RPA improves over the other xc functionals on the oxidation reaction energies, with MAE of 0.27 (PBE), 0.28 (PBE + U), 0.30 (PBE0), to 0.13 (EXX + RPA) eV per oxygen. The distinct trend observed for the calculated oxidation reaction energies compared to the formation energies is due to that the errors in formation energies for PBE and EXX + RPA are systematic; while for PBE + U and PBE0 the deviations have both signs, so that the error cancellations between different valence states work better for PBE and EXX + RPA. Finally, we compared the performance of the EXX + RPA for total energies and G0W0, which uses the random phase approximation in constructing the W kernel, for band gaps, and discuss a few challenges for the EXX + RPA method on TMOs.

Yan, Jun; Nørskov, Jens K.

2013-12-01

297

Uncovering the fundamental chemistry of alkyl + O2 reactions via measurements of product formation.  

PubMed

The reactions of alkyl radicals (R) with molecular oxygen (O(2)) are critical components in chemical models of tropospheric chemistry, hydrocarbon flames, and autoignition phenomena. The fundamental kinetics of the R + O(2) reactions is governed by a rich interplay of elementary physical chemistry processes. At low temperatures and moderate pressures, the reactions form stabilized alkylperoxy radicals (RO(2)), which are key chain carriers in the atmospheric oxidation of hydrocarbons. At higher temperatures, thermal dissociation of the alkylperoxy radicals becomes more rapid and the formation of hydroperoxyl radicals (HO(2)) and the conjugate alkenes begins to dominate the reaction. Internal isomerization of the RO(2) radicals to produce hydroperoxyalkyl radicals, often denoted by QOOH, leads to the production of OH and cyclic ether products. More crucially for combustion chemistry, reactions of the ephemeral QOOH species are also thought to be the key to chain branching in autoignition chemistry. Over the past decade, the understanding of these important reactions has changed greatly. A recognition, arising from classical kinetics experiments but firmly established by recent high-level theoretical studies, that HO(2) elimination occurs directly from an alkylperoxy radical without intervening isomerization has helped resolve tenacious controversies regarding HO(2) formation in these reactions. Second, the importance of including formally direct chemical activation pathways, especially for the formation of products but also for the formation of the QOOH species, in kinetic modeling of R + O(2) chemistry has been demonstrated. In addition, it appears that the crucial rate coefficient for the isomerization of RO(2) radicals to QOOH may be significantly larger than previously thought. These reinterpretations of this class of reactions have been supported by comparison of detailed theoretical calculations to new experimental results that monitor the formation of products of hydrocarbon radical oxidation following a pulsed-photolytic initiation. In this article, these recent experiments are discussed and their contributions to improving general models of alkyl + O(2) reactions are highlighted. Finally, several prospects are discussed for extending the experimental investigations to the pivotal questions of QOOH radical chemistry. PMID:16571032

Taatjes, Craig A

2006-04-01

298

Self-sustaining oxidation initiated by rapid formation reactions in multilayer foils  

NASA Astrophysics Data System (ADS)

Here we report that a self-sustaining oxidation of a multilayer foil can be ignited by an intermetallic formation reaction, releasing ~4× the energy of the formation reaction. We examine foils with overall chemistries of 3Al:2Ni, 3Al:Zr, and Al:Zr and find that only the latter experiences significant oxidation. The Al:Zr samples initially react to form intermetallics and reach ~1500 K in <10 ms. The samples then oxidize in air, absorbing ~30 at. % O and remaining at ~1400 K for >2.0 s. The phases within the Al:Zr foils are characterized and temperature-time profiles are examined to predict the heat generated by the oxidation reaction.

Joress, H.; Barron, S. C.; Livi, K. J. T.; Aronhime, N.; Weihs, T. P.

2012-09-01

299

Theoretical investigation of the thermodynamic structures and kinetic water-exchange reactions of aqueous Al(III)-salicylate complexes  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) calculations were performed on the structures and water-exchange reactions of aqueous Al(III)-salicylate complexes. Based on the four models (gas phase (GP); polarizable continuum model (PCM), which estimates the bulk solvent effect; supermolecule model (SM), which considers the explicit solvent effect, and supermolecule-polarizable continuum model (SM-PCM), which accounts for both types of solvent effects), we systematically conducted this study by examining three different properties of the complexes. (1) The microscopic properties of the aqueous Al(III)-salicylate complexes were studied by optimizing their various structures (including the possible 1:1 mono- and bidentate complexes, cis and trans isomers of the 1:2 bidentate complexes and 1:3 bidentate complexes) at the B3LYP/6-311+G(d, p) level. (2) The 27Al and 13C NMR chemical shifts were calculated using the GIAO method at the HF/6-311+G(d, p) level. The calculation results show that the values obtained with the SM-PCM models are in good agreement with the experimental data available in the literature, indicating that the models we employed are appropriate for Al(III)-salicylate complexes. (3) The water-exchange reactions of 1:1 mono- and bidentate Al(III)-salicylate complexes were simulated using supermolecule models at the B3LYP/6-311+G(d, p) level. The logarithm of the water-exchange rate constant (log kex) of the 1:1 bidentate complex predicted using the "log kex-dAl-OH2" correlation is 4.0, which is in good agreement with the experimental value of 3.7, whereas the calculated range of log kex of the 1:1 monodentate complexes is 1.3-1.9. By effectively combining the results for the thermodynamic static structures with the simulations of the kinetic water-exchange reactions, this work promotes further understanding of the configurations and formation mechanism of Al(III)-salicylate complexes.

Shi, Wenjing; Jin, Xiaoyan; Dong, Shaonan; Bi, Shuping

2013-11-01

300

In Vitro Formation of the Endoplasmic Reticulum Occurs Independently of Microtubules by a Controlled Fusion Reaction  

PubMed Central

We have established an in vitro system for the formation of the endoplasmic reticulum (ER). Starting from small membrane vesicles prepared from Xenopus laevis eggs, an elaborate network of membrane tubules is formed in the presence of cytosol. In the absence of cytosol, the vesicles only fuse to form large spheres. Network formation requires a ubiquitous cytosolic protein and nucleoside triphosphates, is sensitive to N-ethylmaleimide and high cytosolic Ca2+ concentrations, and proceeds via an intermediate stage in which vesicles appear to be clustered. Microtubules are not required for membrane tubule and network formation. Formation of the ER network shares significant similarities with formation of the nuclear envelope. Our results suggest that the ER network forms in a process in which cytosolic factors modify and regulate a basic reaction of membrane vesicle fusion.

Dreier, Lars; Rapoport, Tom A.

2000-01-01

301

Influence of Ge Substrate Crystallinity on Co Germanide Formation in Solid-State Reactions  

SciTech Connect

A strong influence of substrate crystallinity is observed for thin-film Co/Ge reactions. For the detected phases (CoGe, Co{sub 5}Ge{sub 7}, and CoGe{sub 2}), the formation temperatures on amorphous Ge (a-Ge) are found to be the lowest, while the highest are on single-crystalline Ge(100). Moreover, while the phase sequence on Ge(100) and polycrystalline Ge (poly-Ge) was unaltered, the formation of intermediate Co{sub 5}Ge{sub 7} was not observed on a-Ge. It is likely that this is due to a promoted CoGe{sub 2} formation on a-Ge, resulting in a {approx}200 {sup o}C decrease in formation temperature (depending on the ramp rate). These observations suggest a strong competition among the formation of these Ge-rich phases.

Opsomer,K.; Deduytsche, D.; Detaveriner, C.; Van Meirhaeghe, R.; Lauwers , A.; Maex, K.; Lavoie, C.

2007-01-01

302

Implementation of the NCN pathway of prompt-NO formation in the detailed reaction mechanism  

SciTech Connect

This work presents revised detailed reaction mechanism for small hydrocarbons combustion with possibly full implementation of available kinetic data related to the prompt NO route via NCN. It was demonstrated that model predictions with the rate constant of reaction CH + N{sub 2} = NCN + H measured by Vasudevan and co-workers are much higher than experimental concentrations of NO in rich premixed flames at atmospheric pressure. Analysis of the correlations of NO formation with calculated concentrations of C{sub 2}O radicals strongly supports the inclusion of reaction between C{sub 2}O and N{sub 2} and reduction of the rate constant of reaction between CH and N{sub 2}. Rate constants of the reactions of NCN consumption were mostly taken from the works of Lin and co-workers. Some of these reactions affect calculated profiles of NCN in flames. Proposed modifications allow accurate prediction of NO formation in lean and rich flames of methane, ethylene, ethane and propane. Agreement of the experiments and the modeling was much improved as compared to the previous Release 0.5 of the Konnov mechanism. Satisfactory agreement with available measurements of NCN radicals in low pressure flames was also demonstrated. (author)

Konnov, A.A. [Department of Mechanical Engineering, Technische Universiteit Eindhoven, P.O. Box 513, 5600 MB Eindhoven (Netherlands)

2009-11-15

303

Lattice Boltzmann study of pattern formation in reaction-diffusion systems.  

PubMed

Pattern formation in reaction-diffusion systems is of great importance in surface micropatterning [Grzybowski et al., Soft Matter 1, 114 (2005)], self-organization of cellular micro-organisms [Schulz et al., Annu. Rev. Microbiol. 55, 105 (2001)], and in developmental biology [Barkai et al., FEBS Journal 276, 1196 (2009)]. In this work, we apply the lattice Boltzmann method to study pattern formation in reaction-diffusion systems. As a first methodological step, we consider the case of a single species undergoing transformation reaction and diffusion. In this case, we perform a third-order Chapman-Enskog multiscale expansion and study the dependence of the lattice Boltzmann truncation error on the diffusion coefficient and the reaction rate. These findings are in good agreement with numerical simulations. Furthermore, taking the Gray-Scott model as a prominent example, we provide evidence for the maturity of the lattice Boltzmann method in studying pattern formation in nonlinear reaction-diffusion systems. For this purpose, we perform linear stability analysis of the Gray-Scott model and determine the relevant parameter range for pattern formation. Lattice Boltzmann simulations allow us not only to test the validity of the linear stability phase diagram including Turing and Hopf instabilities, but also permit going beyond the linear stability regime, where large perturbations give rise to interesting dynamical behavior such as the so-called self-replicating spots. We also show that the length scale of the patterns may be tuned by rescaling all relevant diffusion coefficients in the system with the same factor while leaving all the reaction constants unchanged. PMID:21405790

Ayodele, S G; Varnik, F; Raabe, D

2011-01-01

304

Lattice Boltzmann study of pattern formation in reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

Pattern formation in reaction-diffusion systems is of great importance in surface micropatterning [Grzybowski , Soft Matter1744-683X10.1039/B501769F 1, 114 (2005)], self-organization of cellular micro-organisms [Schulz , Annu. Rev. Microbiol.ARMIAZ0066-422710.1146/annurev.micro.55.1.105 55, 105 (2001)], and in developmental biology [Barkai , FEBS Journal1742-464X10.1111/j.1742-4658.2008.06854.x 276, 1196 (2009)]. In this work, we apply the lattice Boltzmann method to study pattern formation in reaction-diffusion systems. As a first methodological step, we consider the case of a single species undergoing transformation reaction and diffusion. In this case, we perform a third-order Chapman-Enskog multiscale expansion and study the dependence of the lattice Boltzmann truncation error on the diffusion coefficient and the reaction rate. These findings are in good agreement with numerical simulations. Furthermore, taking the Gray-Scott model as a prominent example, we provide evidence for the maturity of the lattice Boltzmann method in studying pattern formation in nonlinear reaction-diffusion systems. For this purpose, we perform linear stability analysis of the Gray-Scott model and determine the relevant parameter range for pattern formation. Lattice Boltzmann simulations allow us not only to test the validity of the linear stability phase diagram including Turing and Hopf instabilities, but also permit going beyond the linear stability regime, where large perturbations give rise to interesting dynamical behavior such as the so-called self-replicating spots. We also show that the length scale of the patterns may be tuned by rescaling all relevant diffusion coefficients in the system with the same factor while leaving all the reaction constants unchanged.

Ayodele, S. G.; Varnik, F.; Raabe, D.

2011-01-01

305

Secondary organic aerosol (SOA) formation from reaction of isoprene with nitrate radicals (NO3)  

NASA Astrophysics Data System (ADS)

Secondary organic aerosol (SOA) formation from the reaction of isoprene with nitrate radicals (NO3) is investigated in the Caltech indoor chambers. Experiments are performed in the dark and under dry conditions (RH<10%) using N2O5 as a source of NO3 radicals. For an initial isoprene concentration of 18.4 to 101.6 ppb, the SOA yield (defined as the ratio of the mass of organic aerosol formed to the mass of parent hydrocarbon reacted) ranges from 4.3% to 23.8%. By examining the time evolutions of gas-phase intermediate products and aerosol volume in real time, we are able to constrain the chemistry that leads to the formation of low-volatility products. Although the formation of ROOR from the reaction of two peroxy radicals (RO2) has generally been considered as a minor channel, based on the gas-phase and aerosol-phase data it appears that RO2+RO2 reaction (self reaction or cross-reaction) in the gas phase yielding ROOR products is a dominant SOA formation pathway. A wide array of organic nitrates and peroxides are identified in the aerosol formed and mechanisms for SOA formation are proposed. Using a uniform SOA yield of 10% (corresponding to Mo?10 ?g m-3), it is estimated that ~2 to 3 Tg yr-1 of SOA results from isoprene+NO3. The extent to which the results from this study can be applied to conditions in the atmosphere depends on the fate of peroxy radicals in the nighttime troposphere.

Ng, N. L.; Kwan, A. J.; Surratt, J. D.; Chan, A. W. H.; Chhabra, P. S.; Sorooshian, A.; Pye, H. O. T.; Crounse, J. D.; Wennberg, P. O.; Flagan, R. C.; Seinfeld, J. H.

2008-08-01

306

Mononuclear Phenolate Diamine Zinc Hydride Complexes and Their Reactions With CO2  

PubMed Central

The synthesis, characterization, and zinc coordination chemistry of the three proligands 2-tert-butyl-4-[tert-butyl (1)/methoxy (2)/nitro (3)]-6-{[(2?-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes 4–6; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes 7–9. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes 10–12. The new complexes 4–12 have been fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of the zinc hydride complexes have been probed using VT-NMR spectroscopy and X-ray diffraction experiments. These data indicate that the complexes exhibit mononuclear structures at 298 K, both in the solid state and in solution (d8-toluene). At 203 K, the NMR signals broaden, consistent with an equilibrium between the mononuclear and dinuclear bis(?-hydrido) complexes. All three zinc hydride complexes react rapidly and quantitatively with carbon dioxide, at 298 K and 1 bar of pressure over 20 min, to form the new zinc formate complexes 13–15. The zinc formate complexes have been analyzed by NMR spectroscopy and VT-NMR studies, which reveal a temperature-dependent monomer–dimer equilibrium that is dominated by the mononuclear species at 298 K.

2014-01-01

307

On the formation of aliphatic polycarbonates from epoxides with chromium(III) and aluminum(III) metal-salen complexes.  

PubMed

A DFT-based description is given of the CO2/epoxide copolymerization with a catalyst system consisting of metal (chromium, iron, titanium, aluminum)-salen complexes (salen = N,N'-bis(3,5-di-tert-butylsalicyliden-1,6-diaminophenyl) in combination with either chloride, acetate, or dimethylamino pyridine (DMAP) as external nucleophile. Calculations indicate that initiation proceeds through nucleophilic attack at a metal-coordinated epoxide, and the most likely propagation reaction is a bimolecular process in which a metal-bound nucleophile attacks a metal-bound epoxide. Carbon dioxide insertion occurs at a single metal center and is most likely the rate-determining step at low pressure. The prevalent chain terminating/degradation-the so-called backbiting, a reaction leading to formation of cyclic carbonate from the polymer chain-would involve attack of a carbonate nucleophile rather than an alkoxide at the last unit of the growing chain. The backbiting of a free carbonato chain end is particularly efficient. Anion dissociation from six-coordinate aluminum is appreciably easier than from chromium-salen complexes, indicating the reason why in the former case cyclic carbonate is the sole product. Experimental data were gathered for a series of chromium-, aluminum-, iron-, and zinc-salen complexes, which were used in combination with external nucleophiles like DMAP and mainly (tetraalkyl ammonium) chloride/acetate. Aluminum complexes transform PO (propylene oxide) and CO2 to give exclusively propylene carbonate. This is explained by rapid carbonate anion dissociation from a six-coordinate complex and cyclic formation. CO2 insertion or nucleophilic attack of an external nucleophile at a coordinated epoxide (at higher CO2 pressure) are the rate-determining steps. Catalysis with [Cr(salen)(acetate/chloride)] complexes leads to the formation of both cyclic carbonate and polypropylene carbonate with various quantities of ether linkages. The dependence of the activity and selectivity on the CO2 pressure, added nucleophile, reaction temperature, and catalyst concentration is complex. A mechanistic description for the chromium-salen catalysis is proposed comprising a multistep and multicenter reaction cycle. PO and CO2 were also treated with mixtures of aluminum- and chromium-salen complexes to yield unexpected ratios of polypropylene carbonate and cyclic propylene carbonate. PMID:16106457

Luinstra, Gerrit A; Haas, Gerhard R; Molnar, Ferenc; Bernhart, Volker; Eberhardt, Robert; Rieger, Bernhard

2005-10-21

308

Arsenite binding to natural organic matter: spectroscopic evidence for ligand exchange and ternary complex formation.  

PubMed

The speciation of As in wetlands is often controlled by natural organic matter (NOM), which can form strong complexes with Fe(III). Here, we elucidated the molecular-scale interaction of arsenite (As(III)) with Fe(III)-NOM complexes under reducing conditions. We reacted peat (40-250 ?m size fraction, 1.0 g Fe/kg) with 0-15 g Fe/kg at pH <2, removed nonreacted Fe, and subsequently equilibrated the Fe(III) complexes formed with 900 mg As/kg peat at pH 7.0, 8.4, and 8.8. The solid-phase speciation of Fe and As was studied by electron paramagnetic resonance (Fe) and X-ray absorption spectroscopy (As, Fe). Our results show that the majority of Fe in the peat was present as mononuclear Fe(III) species (RFe-C = 2.82-2.88 Å), probably accompanied by small Fe(III) clusters of low nuclearity (RFe-Fe = 3.25-3.46 Å) at high pH and elevated Fe contents. The amount of As(III) retained by the original peat was 161 mg As/kg, which increased by up to 250% at pH 8.8 and an Fe loading of 7.3 g/kg. With increasing Fe content of peat, As(III) increasingly formed bidentate mononuclear (RAs-Fe = 2.88-2.94 Å) and monodentate binuclear (RAs-Fe = 3.35-3.41 Å) complexes with Fe, thus yielding direct evidence of ternary complex formation. The ternary complex formation went along with a ligand exchange reaction between As(III) and hydroxylic/phenolic groups of the peat (RAs-C = 2.70-2.77 Å). Our findings thus provide spectroscopic evidence for two yet unconfirmed As(III)-NOM interaction mechanisms, which may play a vital role in the cycling of As in sub- and anoxic NOM-rich environments such as peatlands, peaty sediments, swamps, or rice paddies. PMID:24088046

Hoffmann, Martin; Mikutta, Christian; Kretzschmar, Ruben

2013-11-01

309

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

PubMed

The bimetallic aluminium(salen) complex [(Al(salen))2 O] is known to catalyse the reaction between epoxides and heterocumulenes (carbon dioxide, carbon disulfide and isocyanates) leading to five-membered ring heterocycles. Despite their apparent similarities, these three reactions have very different mechanistic features, and a kinetic study of oxazolidinone synthesis combined with previous kinetic work on cyclic carbonate and cyclic dithiocarbonate synthesis showed that all three reactions follow different rate equations. An NMR study of [Al(salen)]2 O and phenylisocyanate provided evidence for an interaction between them, consistent with the rate equation data. A variable-temperature kinetics study on all three reactions showed that cyclic carbonate synthesis had a lower enthalpy of activation and a more negative entropy of activation than the other two heterocycle syntheses. The kinetic study was extended to oxazolidinone synthesis catalysed by the monometallic complex Al(salen)Cl, and this reaction was found to have a much less negative entropy of activation than any reaction catalysed by [Al(salen)]2 O, a result that can be explained by the partial dissociation of an oligomeric Al(salen)Cl complex. A mechanistic rationale for all of the results is presented in terms of [Al(salen)]2 O being able to function as a Lewis acid and/or a Lewis base, depending upon the susceptibility of the heterocumulene to reaction with nucleophiles. PMID:24824615

Beattie, Christopher; North, Michael

2014-06-23

310

First-Principles Studies of Phase Stability and Reaction Dynamics in Complex Metal Hydrides  

NASA Astrophysics Data System (ADS)

Complex metal hydrides are believed to be one of the promising materials for developing hydrogen storage systems that can operate under desirable conditions. At the same time, these are also a class of materials that exhibit intriguing properties. We have applied state-of-the-art computational techniques to study the structural, dynamic, and electronic properties of these materials. This talk will focus on the critical role played by the Ti catalyst in helping hydrogen cycling in the alanates, which remains a challenging topic for this hydrogen storage material. We have performed a series of calculations to address the hydrogen interaction on the aluminum surface in the presence of the Ti ``dopant,'' focusing on the effect of near-surface alloying on the Al(100) surface. It is found that Ti occupies subsurface sites near the Al surface. This subsurface Ti arrangement not only enhances H binding with the Al surface layer, but also improves H mobility on the surface. Based on existing experimental data and our preliminary results, we propose a model in which the catalyst does not enter the bulk, but facilitates hydrogen dissociation-recombination near the surface. In the dehydrogenation cycle, the catalyst kinetically facilitates the release and decomposition of AlH3 from the solid-state alanate. In the hydrogenation cycle, the catalyst helps the adsorption of hydrogen and the formation of AlH3 oligomers on Al surfaces. The implication of Ti as a catalyst for the hydrogenation reactions will be discussed.

Chou, Mei-Yin

2009-03-01

311

Formation of acetone from the OH radical- and O3-initiated reactions of a series of monoterpenes  

NASA Astrophysics Data System (ADS)

The formation yields of acetone from the gas-phase reactions of the OH radical (in the presence of NO) and O3 with a series of monoterpenes have been measured at room temperature and atmospheric pressure of air. The acetone formation yields ranged from <2-3% for the OH radical reaction with limonene and the O3 reactions with limonene and ?-phellandrene to 50% for the O3 reaction with terpinolene. Combining these acetone formation yields with literature estimates of emission rates of monoterpenes from vegetation leads to an estimate of acetone formation from the atmospheric photooxidation of monoterpenes of ˜10-11 Tg yr-1 globally, a significant fraction of the global acetone source strength of 40-60 Tg yr-1. Reaction mechanisms leading to acetone formation from these monoterpene reactions are discussed.

Reissell, Anni; Harry, Cheryl; Aschmann, Sara M.; Atkinson, Roger; Arey, Janet

1999-06-01

312

Microscopic approach to nonlinear reaction-diffusion: the case of morphogen gradient formation.  

PubMed

We develop a microscopic theory for reaction-diffusion (RD) processes based on a generalization of Einstein's master equation [Ann. Phys. 17, 549 (1905)] with a reactive term and show how the mean-field formulation leads to a generalized RD equation with nonclassical solutions. For the nth-order annihilation reaction A+A+A+···+A?0, we obtain a nonlinear reaction-diffusion equation for which we discuss scaling and nonscaling formulations. We find steady states with solutions either exhibiting long-range power-law behavior showing the relative dominance of subdiffusion over reaction effects in constrained systems or, conversely, solutions that go to zero a finite distance from the source, i.e., having finite support of the concentration distribution, describing situations in which diffusion is slow and extinction is fast. Theoretical results are compared with experimental data for morphogen gradient formation. PMID:22463171

Boon, Jean Pierre; Lutsko, James F; Lutsko, Christopher

2012-02-01

313

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

PubMed

The purpose of this research was to investigate inclusion complex formation between poorly soluble drug amisulpride (AMI) and ?-cyclodextrin (?-CD). The solubility of AMI was enhanced by formation of inclusion complex of AMI with nano-hydrophobic cavity of ?-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 ?-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 ?-CD. PMID:23399226

Negi, Jeetendra Singh; Singh, Shivpal

2013-02-15

314

Thermodynamic characteristics of the formation of Cd2+ ion-L-serine complexes in aqueous KNO3 solutions at 288-308 K  

NASA Astrophysics Data System (ADS)

The heats of formation of complexes of L-serine and doubly charged cadmium ions are determined by calorimetry. The heat effects of the reaction between an amino acid solution and a cadmium(II) solution and the respective heats of dilution of cadmium nitrate solution are measured at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 against the background of KNO3. The standard thermodynamic characteristics of complexation are calculated. Standard enthalpies of formation of mono-, bis-, and tris-coordinated complexes of cadmium(II) in an aqueous solution are found.

Kochergina, L. A.; Khokhlova, E. A.; Drobilova, O. M.

2014-06-01

315

Hierarchical star formation in M 51: star\\/cluster complexes  

Microsoft Academic Search

We report on a study of young star cluster complexes in the spiral galaxy M 51. Recent studies have confirmed that star clusters do not form in isolation, but instead tend to form in larger groupings or complexes. We use HST broad and narrow band images (from both WFPC2 and ACS), along with BIMA-CO observations to study the properties and

N. Bastian; M. Gieles; Yu. N. Efremov

2005-01-01

316

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

SciTech Connect

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

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

2000-05-01

317

Synthesis and reactions of platinum(IV) complexes with sodium ascorbate  

Microsoft Academic Search

The platinum(IV) complexes [PtCl2(OH)2(N?N)] (N?N=en, N,N-dmen, N,N?-dmen) were prepared by oxidation of [PtCl2(N?N)] with hydrogen peroxide. The complexes were characterized by multinuclear NMR and infrared spectroscopy, as well as microanalysis. The reactions of these compounds with sodium ascorbate were monitored spectroscopically. Reduction of the platinum(IV) complexes by sodium ascorbate occurred only slowly. An oxalatoplatinum(IV) complex [Pt(C2O4)Cl(OH)(N,N-dmen)]·H2O was isolated from the

Malcolm J Arendse; Gordon K Anderson; Raquel N Majola; Nigam P Rath

2002-01-01

318

Dynamics of Research Team Formation in Complex Networks  

Microsoft Academic Search

Most organizations encourage the formation of teams to accomplish complicated tasks, and vice verse, effective teams could\\u000a bring lots benefits and profits for organizations. Network structure plays an important role in forming teams. In this paper,\\u000a we specifically study the dynamics of team formation in large research communities in which knowledge of individuals plays\\u000a an important role on team performance

Caihong Sun; Yuzi Wan; Yu Chen

2009-01-01

319

Time-dependent-S-matrix Hartree-Fock theory of complex reactions  

Microsoft Academic Search

Some limitations of the conventional time-dependent Hartree-Fock method for describing complex reactions are noted, and one particular ubiquitous defect is discussed in detail: the post-breakup spurious cross channel correlations which arise whenever several asymptotic reaction channels must be simultaneously described by a single determinant. A reformulated time-dependent-S-matrix Hartree-Fock theory is proposed, which obviates this difficulty. Axiomatic requirements minimal to assure

James J. Griffin; Peter C. Lichtner; Maria Dworzecka

1980-01-01

320

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

PubMed

Al complexes are widely used in a range of polymerization reactions (ROP of cyclic esters and cationic polymerization of alkenes). Since the discovery in 1978 that an Al porphyrin complex could copolymerize propylene oxide with carbon dioxide, Al coordination compounds have been studied extensively as catalysts for epoxide-carbon dioxide copolymerizations. The most widely studied catalysts are Al porphyrin and Al salen derivatives. This is partially due to their ability to act as mechanistic models for more reactive, paramagnetic Cr catalysts. However, this in depth mechanistic understanding could be employed to design more active Al catalysts themselves, which would be beneficial given the wide availability of this metal. Polymerization data (% CO3 linkages, M(n), M(w)/M(n) and TON) for these complexes are presented and mechanisms discussed. In most cases, especially those employing square-based pyramidal Al complexes, co-catalysts are required to obtain high levels of carbon dioxide incorporation. However, in some cases, the use of co-catalysts inhibits the copolymerization reaction. Lewis acidic Al phenolate complexes have been used as activators in CHO-carbon dioxide copolymerizations to increase TOF and this has recently led to the development of asymmetric copolymerization reactions. Given the ready availability of Al, the robustness of many complexes (e.g. use in immortal polymerizations) and opportunity to prepare block copolymers and other designer materials, Al complexes for copolymerization of carbon dioxide are surely worth a second look. PMID:23450228

Ikpo, Nduka; Flogeras, Jenna C; Kerton, Francesca M

2013-07-01

321

Triple-Color Coincidence Analysis: One Step Further in Following Higher Order Molecular Complex Formation  

PubMed Central

Confocal fluorescence spectroscopy is a versatile method for studying dynamics and interactions of biomolecules in their native environment with minimal interference with the observed system. Analyzing coincident fluctuations induced by single molecule movement in spectrally distinct detection channels, dual-color fluorescence cross-correlation, and coincidence analysis have proven most powerful for probing the formation or cleavage of molecular bonds in real time. The similarity of the optical setup with those used for laser scanning microscopy, as well as the non-invasiveness of the methods, make them easily adaptive for intracellular measurements, to observe the association and dissociation of biomolecules in situ. However, in contrast to standard fluorescence microscopy, where multiple fluorophores can be spectrally resolved, single molecule detection has so far been limited to dual-color detection systems due to the harsh requirements on detection sensitivity. In this study, we show that under certain experimental conditions, employing simultaneous two-photon excitation of three distinct dye species, their successful discrimination indeed becomes possible even on a single molecule level. This enables the direct observation of higher order molecular complex formation in the confocal volume. The theoretical concept of triple-color coincidence analysis is outlined in detail, along with an experimental demonstration of its principles utilizing a simple nucleic acid reaction system.

Heinze, Katrin G.; Jahnz, Michael; Schwille, Petra

2004-01-01

322

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

NASA Astrophysics Data System (ADS)

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.

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

323

Formation of a Dynamic Kinetochore Microtubule Interface through Assembly of the Dam1 Ring Complex  

Microsoft Academic Search

How kinetochore proteins form a dynamic interface with microtubules is largely unknown. In budding yeast, the 10-protein Dam1 complex is an Aurora kinase target that plays essential roles maintaining the integrity of the mitotic spindle and regulating interactions with the kinetochore. Here, we investigated the biochemical properties of purified Dam1 complex. The complex oligomerized into rings around microtubules. Ring formation

Stefan Westermann; Agustin Avila-Sakar; Hong-Wei Wang; Hanspeter Niederstrasser; Jonathan Wong; David G. Drubin; Eva Nogales; Georjana Barnes

2005-01-01

324

Investigation of S-nitrosothiol formation in complex I and model compounds by FTIR spectroscopy  

Microsoft Academic Search

In addition to its role as a regulator of vascular tone, synaptic signalling and cellular defence, nitric oxide (NO) has been shown to inhibit complex I and cytochrome c oxidase of the respiratory electron transfer chain. It has been suggested that the mechanism by which NO inhibits complex I involves the formation of S-nitrosothiols on the complex which are deleterious

Doug Marshall

325

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

NASA Astrophysics Data System (ADS)

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 10?m 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 fixings on iron plates at author's laboratory [4]. 5. Summary 1) Spherule- chained texture with Fe, Ni and Cl has been obtained at the fusion crust of the Kuga iron meteorite found in Japan. 2) As the Kuga iron meteorite is different with the Martian meteorite ALH84001 with composition and formation steps, bacteria-like texture of the Kuga meteorite is first significant example to form fossil-like texture by dynamic reaction of materials in the Solar System. Acknowledgements Author thanks to Dr. T. Kato, Yamaguchi University, for interpretation on bacteria-like texture. References: [1] Miura Y.(2008) 5th AOGS (Asia- Oceania Geosciences Society) Annual Meet. (Busan, Korea), CD#PS07- ST31-A22. [2] Miura Y.(2008). Meteoritics & Planetary Science (USA), 43-7, #5203. [3] McKay D.S. et al. (1996): Science, 273, 924-930. [4]Miura Y. (2009): 6th AGOS (submitted )

Miura, Y.

2009-05-01

326

Photoinduced reaction in the ion-molecule complex Mg +-C 6H 5OCF 3  

NASA Astrophysics Data System (ADS)

The metal cation-molecule complex of Mg + cation with C 6H 5OCF 3 molecule was produced in a laser-ablation supersonic expansion nozzle source. The intra-complex reaction in Mg +-C 6H 5OCF 3 by photons in the spectral region of 230-440 nm has been studied. The formation of Mg + was found to be the predominant dissociation path way, and at the same time, the other products MgF, CH5+, and CHOCF3+ were also observed. We monitored all of the photodissociation products as a function of the excitation wavelength in the 230-440 nm spectral region. The action spectra of the all products except the dissociative charge-transfer product CHOCF3+ are very similar. They consist of two pronounced bands, one of which is on the red side and the other is on the blue side of the Mg + 3 2P ? 3 2S atomic transition. The two peaks of these products are all located at about 243 nm and 332 nm, respectively. The calculated results at the B3LYP/6-31+G ?? level show that there are three isomers: one is with Mg + attached to the O atom, while it also partially interacts with one of F atoms ( 4), the next is with Mg + simultaneously to the two F atoms ( 4'), and the last is with Mg + sitting above the aromatic ring ( 4?). The isomer 4 is more stable than 4' and 4? by ˜3-5 kcal/mol. Although the three isomers are comparable in energy, on the basis of the formation channels of the products and their action spectra, the photoreaction products in our experiment are deduced to originate from 4. The branching fraction ratios for the all product except CHOCF3+ were nearly constant. A photoreaction mechanism is proposed that the conical intersection opens an efficient pathway for the nonadiabatic transition from the excited state to the ground state, producing an intermediate, which yields the photoproducts with a constant branching ratio. The charge-transfer product ion CHOCF3+ is ascribed to a predissociative charge transfer process.

Hu, Yihua; Liu, Haichuan; Yang, Shihe

2007-01-01

327

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

SciTech Connect

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.

Filippova, E. V., E-mail: kostya@eimb.relarn.ru; Polyakov, K. M. [Russian Academy of Sciences, Engelhardt Institute of Molecular Biology (Russian Federation); Tikhonova, T. V.; Stekhanova, T. N.; Boiko, K. M.; Sadykhov, I. G. [Russian Academy of Sciences, Bach Institute of Biochemistry (Russian Federation); Tishkov, V. I. [Moscow State University (Russian Federation); Popov, V. O. [Russian Academy of Sciences, Bach Institute of Biochemistry (Russian Federation); Labru, N. [Agricultural University (Greece)

2006-07-15

328

REACTIVE DESORPTION AND RADIATIVE ASSOCIATION AS POSSIBLE DRIVERS OF COMPLEX MOLECULE FORMATION IN THE COLD INTERSTELLAR MEDIUM  

SciTech Connect

The recent discovery of terrestrial-type organic species such as methyl formate and dimethyl ether in the cold interstellar gas has proved that the formation of organic matter in the Galaxy begins at a much earlier stage of star formation than was previously thought. This discovery represents a challenge for astrochemical modelers. The abundances of these molecules cannot be explained by the previously developed ''warm-up'' scenario, in which organic molecules are formed via diffusive chemistry on surfaces of interstellar grains starting at 30 K, and then released to the gas at higher temperatures during later stages of star formation. In this article, we investigate an alternative scenario in which complex organic species are formed via a sequence of gas-phase reactions between precursor species formed on grain surfaces and then ejected into the gas via efficient reactive desorption, a process in which non-thermal desorption occurs as a result of conversion of the exothermicity of chemical reactions into the ejection of products from the surface. The proposed scenario leads to reasonable if somewhat mixed results at temperatures as low as 10 K and may be considered as a step toward the explanation of abundances of terrestrial-like organic species observed during the earliest stages of star formation.

Vasyunin, A. I. [Department of Chemistry, University of Virginia, Charlottesville, VA (United States); Herbst, Eric, E-mail: anton.vasyunin@gmail.com, E-mail: eh2ef@virginia.edu [Departments of Chemistry, Astronomy, and Physics, University of Virginia, Charlottesville, VA (United States)

2013-05-20

329

C-Terminal Membrane Spanning Region of Human Heme Oxygenase-1 Mediates a Time Dependent Complex Formation with Cytochrome P450 Reductase  

PubMed Central

Heme oxygenase-1 (HO-1) catalyzes the oxidative degradation of heme to biliverdin, carbon monoxide, and free iron in a reaction requiring the interaction of HO-1 with NADPH-cytochrome P450 reductase (CPR). HO-1 is bound to the endoplasmic reticulum by 23 C-terminal amino acids; however, a soluble HO-1 (sHO-1) lacking this membrane spanning region has been extensively studied. The goal of this project was to characterize the effect of the C-terminal hydrophobic domain on formation of the HO-1/CPR complex. Full-length HO-1 was shown to exhibit higher reaction rates than sHO-1, particularly at subsaturating CPR; indicating that the C-terminal region influences HO-1 binding to CPR. The increased activity of HO-1 was attributable to a time dependent formation of a low Km HO-1/CPR complex that was not seen with sHO1. Gel filtration analysis confirmed the formation of multiple high molecular weight complexes in the presence and absence of the synthetic lipid dilauroylphosphatidylcholine (DLPC). However, the largest complex appeared following a two hour incubation of HO-1 and CPR in DLPC, suggesting that C-terminal region was required for the high affinity HO-1/CPR complex formation and membrane incorporation. These data demonstrate that the C-terminal region of HO-1 influenced complex formation and ultimately its affinity for CPR.

Huber, Warren J.; Scruggs, Brittni A.; Backes, Wayne L.

2009-01-01

330

Phase Formation and Kinetics in Thin Film Reactions of Aluminum with Platinum and Palladium.  

NASA Astrophysics Data System (ADS)

The solid state reaction of aluminum with platinum and palladium are investigated in a thin film geometry. In particular, the phase formation, the phase sequence and stability of the reaction phases are analyzed. The results of these experiments serve to explore the validity of the current understanding of metastable phase formation and the phase sequence in thin film reactions. In the introduction, a short review is given of characteristic observations made on bulk diffusion couples and thin film diffusion experiments. We have found that the first phase to form in the solid state reaction between aluminum and platinum is an amorphous Al-Pt phase. The amorphization reaction is monitored during in-situ TEM annealing of Al-Pt multilayer samples. It is shown that the dominant diffusing species is Al and that the amorphous alloy transforms through a growth and nucleation process to the equilibrium Al _2Pt. The occurrence of a solid state amorphization reaction in the Al-Pt system is discussed in relation to the criteria previously proposed for this phenomenon. In chapter 3, the solid state reaction between Al and Pd is studied in lateral and conventional thin film Al-Pd diffusion couples. The first reaction phase for both diffusion couple geometries is the crystalline Al _3Pd_2 phase. For Al-rich samples, we show that the second growth phase is the metastable quasicrystalline decagonal Al_3 Pd phase. The lateral diffusion geometry is used in chapter 4 to measure the growth kinetics of the solid state reaction between Al and Pd. The transition between single phase growth and multiple phase growth is studied by comparing the growth data with different growth models. Excellent agreement between the data and a recently developed model of kinetic suppression was found and the relevance of this result for the metastable phase formation is pointed out. In the last chapter we assess the stability of co-evaporated Al-Pt thin films on GaAs substrates for self -aligned gate metallization applications. We show that Al-Pt alloys ranging between 33 and 50 at.% of Pt fulfill the thermal stability requirements imposed by current GaAs MESFET technology.

Blanpain, Bart Jan

1990-01-01

331

Dependence of the enthalpies of formation of glycylglycinate complexes of nickel(II) on the composition of a mixed water-dimethylsulfoxide solvent  

NASA Astrophysics Data System (ADS)

The heat effects of the complexation reactions of nickel(II) with a glycylglycinate ion in a water-dimethylsulfoxide solvent in a range of compositions of 0.00-0.60 molar parts of dimethylsulfoxide (DMSO) (an ionic strength of 0.1 was maintained using sodium perchlorate) were determined by means of calorimetry at 298.15 K. It is established that the exothermicity of complexation reactions rises by the first two steps and falls upon the addition of a third glycylglycinate anion with an increase in the concentration of DMSO. It is shown that the formation of mono- and bis-glycylglycinate complexes of nickel(II) in a water-DMSO solvent is determined mostly by the enthalpic contribution. It is concluded that the formation of tris-ligand complexes is more associated with the entropic contribution.

Naumov, V. V.; Kovaleva, Yu. A.; Isaeva, V. A.; Usacheva, T. R.; Sharnin, V. A.

2014-06-01

332

Chemistry of high-oxidation-state groups V and VI complexes: Novel silyl and imido complexes and the reactions of silyl and alkyl alkylidyne complexes with oxygen  

NASA Astrophysics Data System (ADS)

This dissertation describes the synthesis and characterization of the novel early transition metal (especially group VI metals) complexes free of anionic pi-ligands such as cyclopentadienyl (Cp) and studies of their reactions with oxygen and silanes. Our study of Cp-free tungsten silyl chemistry is reported. A novel d 0 tungsten silyl complex 2 [(ButCH 2)W(=CHBut)2(SiButPh2 ) (2a) ? (ButCH2)2W(?CBu t)(SiButPh2) (2b)] and an equilibrium between 2a and 2b are described in Chapter 2. The thermodynamics of this equilibrium [DeltaH° = -0.9(0.2) kcal/mol, DeltaS° = -0.6(0.8) eu] was investigated by 1H NMR. The studies of the alpha-hydrogen exchange between 2a and 2b by 2-D EXSY experiments gave kinetic parameters of the exchange: DeltaH? = 17.9(1.1) kcal/mol, DeltaS? = 1.9(5.7) eu for the forward reaction (2a ? 2b) and Delta H? = 18.6 (1.1) kcal/mol, DeltaS ? = 1.9(5.7) eu for the back reaction (2b ? 2a). The reaction of O2 with silyl alkylidyne 2b [(Bu tCH2)W(=CHBut)2(SiBut Ph2) (2a) ? (ButCH2)2W(?CBu t)(SiButPh2) (2b)] is described in Chapter 3. A silyl migration product (ButCH2) 2W(=O)[=C(But)(SiButPh2)] ( 5) was characterized. A siloxy analog of 2b, (Bu tCH2)2W?CBut(OSiBu tPh2) (6), was prepared and excluded as a possible intermediate in the formation of 5. Ab initio calculations suggested a pathway involving silyl migration in 2b to give a tungsten (IV) intermediate (ButCH 2)2W=C(But)(SiButPh2) (7) prior to the reaction with O2. A crystal structure of (Me3SiCH2)2W(=O)(=CHSiMe3)(O=PMe 3)•(Me3SiCH2)3W?CSiMe 3 (12) was obtained from the reaction of alkyl alkylidyne (Me3SiCH2)3W?CSiMe3 with O2 in the presence of PMe3. In Chapter 4, preparation and characterization of bis(2,6-diisopropylphenylimido)molybdenum(VI) amide and silyl complexes (ArN=)2Mo(NMe2)2 (14), (ArN=)2Mo(NMe2)[Si(SiMe3) 3] (15), (ArN=)2MoCl[N(SiMe3) 2] (16), (ArN=)2Mo(NMe2)[N(SiMe 3)2] (17), and (ArN=)2Mo(NHAr) 2 (18) are reported. In addition, new bis(imido)molybdenum(VI) amine adducts (ArN=)2MoCl2(NHMe2) ( 19), (ArN=)2MoCl2(NHEt2) (20 ), (ArN=)2MoCl2(NHMe2)2 (21), and (ArN=)2MoCl2(NHMe2)•(ArN=) 2MoCl2(DME) (22) and their X-ray structures are reported. Preparation and characterization of Cp-free tantalum(V) amide silyl complexes have been investigated, as reported in Chapter 5. Thermodynamics of interesting equilibria (Me2N)3Ta[Si(SiMe3)3] 2 (25) ? (Me2N)3Ta(SiButPh2)[Si(SiMe 3)3] (27) ? (Me2N)3Ta(SiButPh2) 2 (26) was studied. In the equilibrium 25 + Li(THF)3SiButPh2 ? 27 + Li(THF)3Si(SiMe3)3, Delta H° = -0.54(0.17) kcal/mol and DeltaS° = -0.79(0.65) eu, and in the equilibrium 27 + Li(THF) 3SiButPh2 ? 26 + Li(THF)3Si(SiMe3)3, Delta H° = - 0.56(0.17) kcal/mol and DeltaS° = -1.52(0.65) eu.

Chen, Tianniu

333

Indoor secondary organic aerosol formation initiated from reactions between ozone and surface-sorbed D-limonene.  

PubMed

Reactions between ozone and terpenoids produce numerous products, some of which may form secondary organic aerosol (SOA). This work investigated the contribution to gas-phase SOA formation of ozone reactions with surface-sorbed D-limonene, which is common indoors. A model framework was developed to predict SOA mass formation because of ozone/terpenoid surface reactions, and it was used with steady state experiments in a 283 L chamber to determine the aerosol mass fraction of SOA resulting from surface reactions, ?s (the ratio of mass of SOA formed and mass of ozone consumed by ozone/terpenoid surface reactions), for ozone/D-limonene reactions on stainless steel. The ?s = 0.70-0.91, with lower relative humidity leading to both higher mass and number formation. Also, surface reactions promoted nucleation more than gas-phase reactions, and number formation due to surface reactions and gas-phase reactions were 126-339 and 51.1-60.2 no./cm(3) per ?g/m(3) of formed SOA, respectively. We also used the model framework to predict that indoor spaces in which ozone/D-limonene surface reactions would likely lead to meaningful gas-phase SOA formation are those with surfaces that have low original reactivity with ozone, such as glass, sealed materials, or smooth metals. PMID:23724989

Waring, Michael S; Siegel, Jeffrey A

2013-06-18

334

Reactions of vitamin A with acceptors of electrons. Interactions with iodine and the formation of iodide  

PubMed Central

1. The reactions of retinol and retinoic acid with iodine were investigated since knowledge of the chemical reactions of vitamin A with acceptors of electrons may shed light on its biochemical mode of action. 2. Colloidal retinol, but not retinoic acid, reacts with iodine to yield a blue–green complex that rapidly decomposes, giving iodide and an unknown species with ?max. at 870m?. 3. In addition, both retinol and retinoic acid reduce iodine to iodide by a reaction that does not involve an intermediate coloured complex; this reaction appears to yield unstable carbonium ion derivatives of the vitamin. 4. The presence of water greatly facilitates the production of iodide from vitamin A and iodine. 5. Possible chemical pathways involved in these reactions are discussed. 6. It is suggested that the chemical properties of retinol and retinoic acid that underlie their biochemical behaviour might be apparent only when the molecules are at a lipid–water interface, and that vitamin A might be expected to react with a number of different electron acceptors in vivo.

Lucy, J. A.; Lichti, F. Ulrike

1969-01-01

335

Formation of deeply bound kaonic atoms in (K-,N) reactions  

NASA Astrophysics Data System (ADS)

We study theoretically the (K-,N) reactions for the formation of the deeply bound kaonic atoms, which were predicted to be quasistable with narrow widths, using the Green's function method. We systematically consider various cases with different target nuclei and energies and find clear signals in the theoretical spectra for all cases considered in this article. The signals show very interesting structures, such as a RESONANCE DIP instead of a resonance peak. We discuss the origins of the interesting structures and the possibilities of obtaining new information on the existence of kaonic nuclei from the spectra of atomic state formations.

Yamagata, J.; Nagahiro, H.; Kimura, R.; Hirenzaki, S.

2007-10-01

336

Changes in the redox potential and catalase activity of Mn2+ ions during formation of Mn-bicarbonate complexes.  

PubMed

Changes in the redox potentials of Mn2+ ions and Mn-bicarbonate complexes were studied due to their possible participation in the photosynthetic oxidation of water in plant photosystem 2 and in H2O2 decomposition. Electrochemical oxidation of Mn2+ ions was demonstrated by voltammetry on a platinum electrode in 0.1 M LiClO4 solution at a potential of 1.19 V (vs NHE). When NaHCO3 was added, the oxidation peak of Mn2+ ions disappeared. New oxidation peaks appeared at 0.92 V and 0.63 V which corresponded to the oxidation of Mn(HCO3)+ and Mn(HCO3)2, respectively, generated by complex formation between Mn2+ and HCO3- ions. The effect of the Mn(2+)-bicarbonate complex on H2O2 redox decomposition was studied. It was shown that the addition of MnSO4 to the H2O2 solution did not affect the H2O2 oxidation peak height thereby indicating the absence of H2O2 decomposition by Mn2+ ions. At the same time, subsequent addition of NaHCO3 resulted in the disappearance of the oxidation peaks of both H2O2 and Mn2+. As at pH 7 the thermodynamic potential of H2O2 reduction is 1.1 V and the Mn2+ oxidation potential is 1.19 V, the redox reaction between them is hampered. Formation of the Mn(2+)-bicarbonate complex shifted the Mn2+ oxidation potential to 0.63 V, thereby inducing the decomposition of H2O2. It is suggested that the decrease in the Mn2+ oxidation potential resulting from the formation of the bicarbonate complex determines the bicarbonate capability to enhance the Mn2+ ability to donate electrons for PS 2 reaction centres. PMID:9257286

Kozlov YuN; Kazakova, A A; Klimov, V V

1997-01-01

337

N-Heterocyclic Carbene Complexes in Polymerisation, Oligomerisation and Telomerisation Reactions  

NASA Astrophysics Data System (ADS)

Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in ?-olefin polymerisation and oligomerisation, CO/olefin copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discussed in subsequent sections.

McGuinness, David S.; Cavell, Kingsley J.

338

Dinuclear formation, oxygen atom transfer, and intramolecular coordination isomerization in oxotechnetium complexes  

SciTech Connect

Dinuclear, asymmetric and dissymmetric, mixed-valent (III-IV), {mu}-oxo complexes of technetium spontaneously form in both neat pyridine and pyridine solutions in dichlorobenzene from higher valent, mononuclear species, with which they reach an equilibrium. When (OX{sub 4}Tc{sup V}){sup {minus}} is used as the starting material and only the neat pyridine ligand is present, the formation of the dinuclear species is second-order in Tc{sup V} and occurs with concomitant production of pyridine N-oxide, indicating that oxygen atom transfer occurs in the technetium reduction process. K{sub eq} for the formation of the dinuclear species in picoline solution is 193 {plus minus} 8 M{sup {minus}1} with k = (1.46 {plus minus} 0.1) {times} 10{sup {minus}2} M{sup {minus}1} s{sup {minus}1}. The asymmetric and dissymmetric dinuclear species spontaneously interconvert. In o-dichlorobenzene, this process is first-order in chloride ion and requires a minimum concentration ({approximately}0.1 M) of the pyridine ligand to prevent decomposition of the dinuclear starting material. With picoline as the ligand, at 140{degree}C the reaction proceeds with a specific rate of (3.12 {plus minus} 0.08) {times} 10{sup {minus}3} M{sup {minus}1} s{sup {minus}1} to approach an equilibrium between the asymmetric and dissymmetric complexes with K{sub eq} = 2.83 {plus minus} 0.12. Activation parameters are {Delta}H* = 144 {plus minus} 2 kJ/mol and {Delta}S* = 53.5 {plus minus} 1 J/(mol K). Minor changes in the ligands generate marked differences in K{sub eq} and K{sub iso}.

Lu, Jun; Clarke, M.J. (Boston College, Chestnut Hill, MA (USA))

1988-12-28

339

Synthesis, Characterization, and Reactions of Isolable (?-Diketiminato)Nb(III) Imido Complexes*  

PubMed Central

We have investigated both the chemical reduction of (BDI)Nb(V) imido complexes (BDI = HC[C(Me)NAr]2; Ar = 2,6-iPr2-C6H3) to the formal Nb(III) oxidation state and the ability of these Nb(III) complexes to behave as two-electron reductants. The reduction of the Nb(V) species was found to depend heavily on the nature of available supporting ligands, but the chemistry of the reduced compounds proceeded cleanly with a number of unsaturated organic reagents. Accordingly, the novel Nb(V) bis(imido) complexes supported by the monoazabutadiene (mad) ligand (mad)Nb(NtBu)(NAr)(L?) (L? = py, thf) were formed by either KC8 reduction of (BDI)Nb(NtBu)Cl2(py) in the absence of strong ?-acids or by H2 reduction of the Nb(V) dimethyl complex (BDI)Nb(NtBu)Me2 in THF. These products are likely formed though an intramolecular, 2 e? reductive C–N bond cleavage, as has been observed previously for related Group 4 systems, suggesting that transient Nb(III) intermediates were present in both cases. In the presence of 1,2-bis(dimethylphosphino)ethane (dmpe), KC8 reduction of (BDI)Nb(NtBu)Cl2(py) was arrested at the Nb(IV) oxidation state to give (BDI)Nb(NtBu)Cl(dmpe), which was characterized by solution-state EPR spectroscopy as a Nb-centered paramagnet with strong coupling to the two equivalent phosphorus nuclei (Aiso{93Nb} = 120.5×10?4 cm?1, Aiso{31P} = 31.0×10?4 cm?1, giso = 1.9815). When strong ?-acids were used to intercept the thermally unstable Nb(III) complex (BDI)Nb(NtBu)(py) prior to reductive cleavage of the ligand C–N bond, the thermally stable Nb(III) species (BDI)Nb(NtBu)(CX)2(L?) (X = O, L? = py; X = NXyl, L? = CNXyl; Xyl = 2,6-Me2-C6H3) were obtained in good yields. The Nb(III) complexes (BDI)Nb(NtBu)py, (BDI)Nb(NtBu)(CO)2(py) and (BDI)Nb(NtBu)(CO)2 were subsequently investigated for their ability to serve as two-electron reducing reagents for both metal-ligand multiple bond formation and for the reduction of organic ?-systems. The reduction of mesityl azide by (BDI)Nb(NtBu)(py) and diphenylsulfoxide by (BDI)Nb(NtBu)(CO)2 led to the monomeric bis(imido) and dimeric oxo complexes (BDI)Nb(NtBu)(NMes)(py) and [(BDI)Nb(NtBu)]2(?2-O)2, respectively. MeLi addition to (BDI)Nb(NtBu)(CO)2(py) resulted in the formation of a Nb-acylate via methide addition to one of the carbonyl carbons. The acylate product was revealed to have a short Nb–Cacylate bond distance (2.059(4) Å), consistent with multiple Nb–C bond character resulting from Nb(III) back-bonding into the acylate carbon. The interaction of (BDI)Nb(NtBu)(CO)2 with two equivalents of 4,4?-dichlorobenzophenone resulted in the clean, quantitative formation of the corresponding pinacol coupling product, but introduction of the ketone in 1: 1 molar ratios resulted in mixtures of the pinacol product and the starting material, suggesting that ketone coordination to the Nb(III) complex may be reversible. Relatedly, addition of 1-phenyl-1-propyne to (BDI)Nb(NtBu)(CO)2 formed a thermally unstable 1: 1 Nb/alkyne complex, as characterized by NMR and IR spectroscopies; reaction of this species with HCl/MeOH yielded a 2: 1 mixture of 1-phenyl-1-propene and the free alkyne, suggesting a high degree of covalency in the Nb–C bonds.

Tomson, Neil C.; Arnold, John; Bergman, Robert G.

2010-01-01

340

Secondary sup 15 N isotope effects on the reactions catalyzed by alcohol and formate dehydrogenases  

SciTech Connect

Secondary {sup 15}N isotope effects at the N-1 position of 3-acetylpyridine adenine dinucleotide have been determined, by using the internal competition technique, for horse liver alcohol dehydrogenase (LADH) with cyclohexanol as a substrate and yeast formate dehydrogenase (FDH) with formate as a substrate. On the basis of less precise previous measurements of these {sup 15}N isotope effects, the nicotinamide ring of NAD has been suggested to adopt a boat conformation with carbonium ion character at C-4 during hydride transfer. If this mechanism were valid, as N-1 becomes pyramidal an {sup 15}N isotope effect for the reaction catalyzed by LADH was measured. These values suggest that a significant {sup 15}N kinetic isotope effect is not associated with hydride transfer for LADH and FDH. Thus, in contrast with the deformation mechanism previously postulated, the pyridine ring of the nucleotide apparently remains planar during these dehydrogenase reactions.

Rotberg, N.S.; Cleland, W.W. (Univ. of Wisconsin, Madison (USA))

1991-04-23

341

Reaction-diffusion scheme for the clock and wavefront mechanism of pattern formation  

NASA Astrophysics Data System (ADS)

We present a model of pattern formation in reaction-diffusion systems that is based on coupling between a propagating wave front and temporal oscillations. To study effects of internal fluctuations on the spatial structure development we use a chemical master equation for our reaction-diffusion model. First, a model with local, uncoupled oscillators is studied. Based on it we show that synchronization of oscillations in neighboring cells is necessary for the formation of regular patterns. We introduce synchronization through diffusion, but then, to get a stable pattern, it is necessary to add an additional species that represents the local state of the system. Numerical simulations of the master equation show that this extended model is resistant to fluctuations.

Dziekan, Piotr; Nowakowski, Bogdan; Lemarchand, Annie

2014-04-01

342

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

PubMed

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

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

2014-01-21

343

Swellings due to alkali-silica reaction and delayed ettringite formation: Characterisation of expansion isotropy and effect of moisture conditions  

Microsoft Academic Search

This paper investigates the effect of different conditions on the development of concrete expansions due to alkali-silica reaction (ASR), delayed ettringite formation (DEF) and their combination. The presence of products of the two reactions has been observed during structure diagnosis. The aim of this research is to study the two reactions in concretes with close mix designs but with various

Hassina Bouzabata; Stéphane Multon; Alain Sellier; Hacène Houari

344

Equilibrium and 1 H NMR Kinetic Study of the Reactions of Dichlorido [S-Methyl-L-Cysteine(N,S)]Platinum(II) Complex with Some Relevant Biomolecules  

Microsoft Academic Search

The formation equilibria of the [Pt(SMC)(H2O)2]+ complex with some biologically relevant ligands such as L-methionine (L-met) and glutathione (GSH) were studied. The stoichiometry\\u000a and stability constants of the formed complexes are reported, and the concentration distribution of the various complex species\\u000a has been evaluated as a function of pH. The reaction between [PtCl2(SMC)] and guanosine-5?-monophosphate (5?-GMP) was studied by 1H

Tanja Soldatovi?; Predrag ?anovi?; Radivoje Nikoli?; Ratomir Jeli?; Živadin D. Bugar?i?

2009-01-01

345

Enthalpies of formation of Zr–Au compounds determined by direct reaction calorimetry  

Microsoft Academic Search

The enthalpies of formation of Zr(1?x)Aux compounds, (x =1\\/4, 1\\/3, 4\\/9, 1\\/2, 10\\/17, 2\\/3, 3\\/4, 4\\/5) have been measured by direct reaction calorimetry with reference to pure metals taken in their solid states. Mixing calorimetry, solid Zr in liquid Au, was performed at 1473 K. The results are compared to earlier experimental data and values predicted from Miedema's model.

M. Lomello-Tafin; P. Galez; P. Feschotte; J. J. Kuntz; J. L. Jorda; J. C. Gachon

1998-01-01

346

In vitro surface reaction layer formation and dissolution of calcium phosphate cement–bioactive glass composites  

Microsoft Academic Search

Composites of hydrated calcium phosphate cement (CPC) and bioactive glass (BG) containing Si were immersed in vitro to study the effect of chemical composition on surface reaction layer formation and dissolution\\/precipitation behavior. The solutions used were 0.05 M tris hydroxymethyl aminomethane\\/HCl (tris buffer), tris buffer supplemented with plasma electrolyte (TE) with pH 7.4 at 37 °C, and this solution complemented

Changsheng Liu; Chien-Wen Chen; Paul Ducheyne

2008-01-01

347

H 2S-producing reactions in deep carbonate gas reservoirs: Khuff Formation, Abu Dhabi  

Microsoft Academic Search

The economic viability of gas production from deep reservoirs is often limited by the presence of hydrogen sulphide (H2S) thought to be the result of thermochemical sulphate reduction (TSR). This study constrains the reactions responsible for the origin of H2S-rich gas in a classic sour gas province: the Permian Khuff Formation of Abu Dhabi. In reservoirs hotter than 140°C, anhydrite

R. H. Worden; P. C. Smalley

1996-01-01

348

Some factors influencing the formation of reaction-bonded silicon nitride  

Microsoft Academic Search

Several salient factors influencing the formation of reaction-bonded silicon nitride (RBSN) compacts have been studied. These include the effects of mullite and alumina furnace tubes typically employed during “high-purity” nitridation studies, pre-sintering of green silicon compacts, free powder versus compact nitridation, and the influence of metal\\/metal oxide additions. The latter studies have provided experimental evidence for enhancement due to dissociated

R. G. Pigeon; A. Varma; A. E. Miller

1993-01-01

349

Nitrous oxide formation during the reaction of simulated exhaust streams over rhodium, platinum and palladium catalysts  

Microsoft Academic Search

The formation of nitrous oxide during the reaction of a mixture of CO, NO, C3H6, C3H8, H2 and O2 over supported rhodium, platinum and palladium catalysts has been investigated under near-stoichiometric conditions. Rhodium gives the highest amount of N2O with a peak selectivity near 70% at 250°C followed by a steady decline to low levels by 400°C. With Pt N2O

Noel W. Cant; Dennys E. Angove; Dean C. Chambers

1998-01-01

350

Thermochemistry and reaction barriers for the formation of levoglucosenone from cellobiose.  

SciTech Connect

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.

Assary, R. S.; Curtiss, L. A. (Center for Nanoscale Materials); ( MSD); (Northwestern Univ.)

2012-02-06

351

Thermochemistry and Reaction Barriers for the Formation of Levoglucosenone from Cellobiose  

SciTech Connect

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.

Assary, Rajeev S.; Curtiss, Larry A.

2012-02-06

352

Some new reaction pathways for the formation of cytosine in interstellar space - A quantum chemical study  

NASA Astrophysics Data System (ADS)

The detection of nucleic acid bases in carbonaceous meteorites suggests that their formation and survival is possible outside of the Earth. Small N-heterocycles, including pyrimidine, purines and nucleobases, have been extensively sought in the interstellar medium. It has been suggested theoretically that reactions between some interstellar molecules may lead to the formation of cytosine, uracil and thymine though these processes involve significantly high potential barriers. We attempted therefore to use quantum chemical techniques to explore if cytosine can possibly form in the interstellar space by radical-radical and radical-molecule interaction schemes, both in the gas phase and in the grains, through barrier-less or low barrier pathways. Results of DFT calculations for the formation of cytosine starting from some of the simple molecules and radicals detected in the interstellar space are being reported. Global and local descriptors such as molecular hardness, softness and electrophilicity, and condensed Fukui functions and local philicity indices were used to understand the mechanistic aspects of chemical reaction. The presence and nature of weak bonds in the molecules and transition states formed during the reaction process have been ascertained using Bader's quantum theory of atoms in molecules (QTAIMs). Two exothermic reaction pathways starting from propynylidyne (CCCH) and cyanoacetylene (HCCCN), respectively, have been identified. While the first reaction path is found to be totally exothermic, it involves a barrier of 12.5 kcal/mol in the gas phase against the lowest value of about 32 kcal/mol reported in the literature. The second path is both exothermic and barrier-less. The later has, therefore, a greater probability of occurrence in the cold interstellar clouds (10-50 K).

Gupta, V. P.; Tandon, Poonam; Mishra, Priti

2013-03-01

353

Extraction-spectrophotometric determination of iron(II) by ternary complex formation with pyrocatechol violet and cetyltrimethylammonium bromide.  

PubMed

A method for iron(II) determination based on reaction with Pyrocatechol Violet to form a 1:2 binary complex at pH 5-7 is described and has been extended to an extraction-spectrophotometric procedure for the determination of iron(II) by formation of the 1:2:2 iron(II)-Pyrocatechol Violet-cetyltrimethylammonium bromide ternary complex. The molar absorptivities of the binary and ternary complexes at 595 and 605 nm are 6.55 x 10(4) and 1.35 x 10(5)1.mole(-1).cm(-1), respectively. The method has been successfully applied to the determination of iron in felspar, Portland cement and sodium hydroxide. PMID:18964508

Tarek, M; Zaki, M; Mahmoud, W H; El-Sayed, A Y

1988-04-01

354

Pattern formation in the iodate-sulfite-thiosulfate reaction-diffusion system.  

PubMed

Sodium polyacrylate-induced pH pattern formation and starch-induced iodine pattern formation were investigated in the iodate-sulfite-thiosulfate (IST) reaction in a one-side fed disc gel reactor (OSFR). As binding agents of the autocatalyst of hydrogen ions or iodide ions, different content of sodium polyacrylate or starch has induced various types of pattern formation. We observed pH pulses, striped patterns, mixed spots and stripes, and hexagonal spots upon increasing the content of sodium polyacrylate and observed iodine pulses, branched patterns, and labyrinthine patterns upon increasing the starch content in the system. Coexistence of a pH front and an iodine front was also studied in a batch IST reaction-diffusion system. Both pH and iodine front instabilities were observed in the presence of sodium polyacrylate, i.e., cellular fronts and transient Turing structures resulting from the decrease in diffusion coefficients of activators. The mechanism of multiple feedback may explain the different patterns in the IST reaction-diffusion system. PMID:22068976

Liu, Haimiao; Pojman, John A; Zhao, Yuemin; Pan, Changwei; Zheng, Juhua; Yuan, Ling; Horváth, Attila K; Gao, Qingyu

2012-01-01

355

Reactivity of Ir(III) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation.  

PubMed

The reactions of water with a number of iridium(III) complexes relevant to the mechanism for catalytic methanol carbonylation are reported. The iridium acetyl, [Ir(CO)2I3(COMe)](-), reacts with water under mild conditions to release CO2 and CH4, rather than the expected acetic acid. Isotopic labeling and kinetic experiments are consistent with a mechanism involving nucleophilic attack by water on a terminal CO ligand of [Ir(CO)2I3(COMe)](-) to give an (undetected) hydroxycarbonyl species. Subsequent decarboxylation and elimination of methane gives [Ir(CO)2I2](-). Similar reactions with water are observed for [Ir(CO)2I3Me](-), [Ir(CO)2(NCMe)I2(COMe)] and [Ir(CO)3I2Me] with the neutral complexes exhibiting markedly higher rates. The results demonstrate that CO2 formation during methanol carbonylation is not restricted to the conventional water gas shift mechanism mediated by [Ir(CO)2I4](-) or [Ir(CO)3I3], but can arise directly from key organo-iridium(III) intermediates in the carbonylation cycle. An alternative pathway for methane formation not involving the intermediacy of H2 is also suggested. A mechanism is proposed for the conversion MeOH + CO ? CO2 + CH4, which may account for the similar rates of formation of the two gaseous by-products during iridium-catalysed methanol carbonylation. PMID:24071892

Elliott, Paul I P; Haak, Susanne; Meijer, Anthony J H M; Sunley, Glenn J; Haynes, Anthony

2013-12-21

356

Formation of a novel colored product during the Maillard reaction of D-glucose.  

PubMed

Reactions between reducing sugars and proteins or amino acids (Maillard reaction) lead to the formation of yellow to brown products (melanoidins) that are important for food preparation and processing, such as baking, roasting, or malt production. Thus far, the structures of the melanoidins have not been elucidated, although some structural insights have been gained from model reactions. In this study, D-glucose was heated with an amine and two colored compounds were detected by HPLC/UV--vis. After purification, the main product was identified as [(4aS,6R,7S,8R,8aR)-4,4a,6,7,8,8a-hexahydro-7,8-dihydroxy-6-hydroxymethyl-1,4-dipropyl-1H-pyrano[2,3-b]pyrazine-2-yl]-1-hydroxy-3-buten-2-one (1a). For the minor compound (2a), some spectral data were obtained, but the structure was not fully characterized. 1a and 2a are the main colored compounds when the reaction is performed in alcoholic solution or on a cellulose surface. Thus, it was concluded that products with an analogous structure are important for the color formation of foodstuffs with low water activity. PMID:11308354

Knerr, T; Lerche, H; Pischetsrieder, M; Severin, T

2001-04-01

357

Formation of - Complexes between Phenanthrene and Model Acceptor Humic Subunits  

Microsoft Academic Search

aromatic hydrocarbons (PAHs), an important class of pollutants that can act as strong donors. Although - Interactions may play a role in association of aromatic com- desolvation of apolar organic compounds or their parts pounds with natural organic substances. Complexation in aqueous solvents was studied between the donor, phenanthrene (PHEN), (i.e., the \\

Hotze Wijnja; Joseph J. Pignatello; Kalumbu Malekani

358

Interferogram formation in the presence of complex and large deformation  

Microsoft Academic Search

Sierra Negra volcano in Isabela island, Galápagos, 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

Sang-Ho Yun; Howard Zebker; Paul Segall; Andrew Hooper; Michael Poland

2007-01-01

359

Search Graph Formation for Minimizing the Complexity of Planning  

Microsoft Academic Search

A large number of path planning problems are solved by the use of graph based search algorithms. There are a variety of techniques available to optimize the search within these graphs as well as thorough studies of the complexity involved in searching through them. However, little eort has been dedicated to construct- ing the graphs so that the results of

Alberto Lacaze; Stephen Balakirsky

360

Placebo Effect upon Complex Reaction Time When Hypnotic Suggestibility is Controlled.  

ERIC Educational Resources Information Center

This study was designed to investigate the effect of a placebo (sugar pill) accompanied by suggestions that the pill would either (1) improve performance as a stimulant or (2) cause a deterioration in performance as a depressant when the performance in question was the subjects' complex reaction time to a light stimulus. The Harvard Group Scale of…

Eskridge, Veronica L.

361

Kinetics and mechanism of the reactions of Au(III) complexes with some biologically relevant molecules.  

PubMed

The kinetics of the substitution reactions between the mono-functional Au(III) complexes, [Au(dien)Cl](2+) and [Au(terpy)Cl](2+) (dien = 3-azapentane-1,5-diamine, terpy = 2,2';6',2''-terpyridine) and bi-functional Au(III) complexes, [Au(bipy)Cl(2)](+) and [Au(dach)Cl(2)](+) (bipy = 2.2'-bipyridine, dach = (1R,2R)-1,2-diaminocyclohexane) and biologically relevant ligands such as l-histidine (l-His), inosine (Ino), inosine-5'-monophosphate (5'-IMP) and guanosine-5'-monophosphate (5'-GMP), were studied in detail. All kinetic studies were performed in 25 mM Hepes buffer (pH = 7.2) in the presence of NaCl to prevent the spontaneous hydrolysis of the chloride complexes. The reactions were followed under pseudo-first order conditions as a function of ligand concentration and temperature using stopped-flow UV-vis spectrophotometry. The results showed that the mono-functional complexes react faster than the bi-functional complexes in all studied reactions. The [Au(terpy)Cl](2+) complex is more reactive than the [Au(dien)Cl](2+) complex, which was confirmed by quantum chemical (DFT) calculations. A more than 50% lower activation energy for the terpy than for the dien based complex was found. The bi-functional [Au(bipy)Cl(2)](+) complex is more reactive than the [Au(dach)Cl(2)](+) complex. The reactivity of the studied nucleophiles follows the same order for all studied systems, viz. l-His > 5'-GMP > 5'-IMP > Ino. According to the measured activation parameters, all studied reactions follow an associative substitution mechanism. Quantum chemical calculations (B3LYP/LANL2DZp) suggest that ligand substitution in [Au(terpy)Cl](2+) and [Au(dien)Cl](2+) by imidazole follows an interchange mechanism with a significant degree of associative character. The results demonstrate the strong connection between the reactivity of the complexes toward biologically relevant ligands and their structural and electronic characteristics. Therefore, the binding of gold(III) complexes to 5'-GMP, constituent of DNA, is of particular interest since this interaction is thought to be responsible for their anti-tumour activity. PMID:22318647

Djekovi?, Ana; Petrovi?, Biljana; Bugar?i?, Zivadin D; Puchta, Ralph; van Eldik, Rudi

2012-04-01

362

Computational insights into carbon-carbon homocoupling reactions mediated by organolanthanide(III) complexes.  

PubMed

Homocoupling of terminal alkynes into trienediyl complexes by alkyl samarocenes is known experimentally. By means of computational techniques, we investigated the mechanism of this reaction in detail. The overall reaction sequence is: ?-bond metathesis, dimerisation of metallocenes, and homocoupling of two acetylides into trienediyl. We show that the rate-determining step corresponds to the homocoupling of two anionic acetylides. This coupling takes place at a bis-samarocene dimer complex in which the bridging mode of the two acetylide moieties is critical for the reaction to proceed. The limited energy barrier for the homocoupling of the carbanions originates from a synergistic effect of the two samarium centres within the dimer. Variation of the steric demand of both substrates and lanthanocenes allowed rationalising all the experimental data available for these systems. PMID:24429590

Kefalidis, Christos E; Perrin, Lionel; Maron, Laurent

2014-03-21

363

Guerbet reaction of primary alcohols leading to beta-alkylated dimer alcohols catalyzed by iridium complexes.  

PubMed

[IrCl(cod)]2 and [Cp*IrCl2]2 complexes catalyzed efficiently the Guerbet reaction of primary alcohols to beta-alkylated dimer alcohols in good yields. For instance, the reaction of 1-butanol in the presence of [Cp*IrCl2]2 (1 mol %), t-BuOK (40 mol %), and 1,7-octadiene (10 mol %) produced 2-ethyl-1-hexanol in 93% yield. Various primary alcohols undergo the Guerbet reaction under the influence of Ir complexes to give the corresponding dimer alcohols in good yields. This method provides an alternative direct route to beta-alkylated primary alcohols which are prepared by aldol condensation of aldehydes followed by hydrogenation. PMID:17025333

Matsu-ura, Toyomi; Sakaguchi, Satoshi; Obora, Yasushi; Ishii, Yasutaka

2006-10-13

364

TraML--A Standard Format for Exchange of Selected Reaction Monitoring Transition Lists*  

PubMed Central

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.

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

365

Mono(pentamethylcyclopentadienyl)thorium chemistry. Formation and structural characterization of a novel triflate-bridged dimeric thorium complex  

SciTech Connect

We have shown that the reaction of an actinide amide complex, such as Th[N(SiMe{sub 3}){sub 2}]{sub 3}(OTf) (2), with Cp{sup *}H can provide an alternative to the traditional halide metathesis routes to mono(pentamethylcyclopentadienyl)actinide species. As reported recently for the Group IV metals, this synthetic method can offer distinct advantages over halide metathesis procedures, most notably by eliminating the problem of salt retention by the actinide product. The X-ray crystal structure of the dinuclear actinide complex Cp{sup *}[(Me{sub 3}Si){sub 2}N]Th({mu}{sub 2}-OSO{sub 2}CF{sub 3}) [N(SiMe{sub 3})(SiMe{sub 2}CH{sub 2})]Cp{sup *} (4), formed from reaction of 2 with Cp{sup *}H, has been determined and reveals an unusual molecular geometry in which three {eta}{sup 2}-triflate ligands bridge the two thorium metal centers. We have proposed a mechanism to explain the formation of 4 and have shown that several of the proposed mechanistic steps may be verified in independent reactions. Further studies of the reactivity and catalytic properties of mono-Cp{sup *} thorium complexes with alkoxide and alkyl supporting ligands are currently underway. 17 refs., 1 fig., 3 tabs.

Butcher, R.J.; Clark, D.L.; Grumbine, S.K.; Watkin, J.G. [Los Alamos National Lab., NM (United States)

1995-06-01

366

Intermediate species possessing bent DNA are present along the pathway to formation of a final TBP-TATA complex.  

PubMed

Binding of the TATA-binding protein (TBP) to the "TATA" sequences present in the promoters of eukaryotic class II genes is the first step in the sequential assembly of transcription pre-initiation complexes. Myriad structural changes, including severe bending of the DNA, accompany TBP-TATA complex formation. A detailed kinetic study has been conducted to elucidate the mechanistic details of TBP binding and DNA bending. The binding of Saccharomyces cerevisiae TBP to the adenovirus major late promoter (AdMLP) was followed in real-time through a range of temperatures and TBP concentrations using fluorescence resonance energy transfer (FRET) and stopped-flow mixing. The results of association and relaxation kinetics and equilibrium binding experiments were analyzed globally to obtain the complete kinetic and energetic profile of the reaction. This analysis reveals a complex mechanism with two intermediate species, with the DNA in the intermediates apparently bent similarly to the DNA in the final complex. TBP binding and DNA bending occur simultaneously through the multiple steps of the reaction. The first and third steps in this sequential process show nearly identical large increases in both enthalpy and entropy, whereas the middle step is highly exothermic and proceeds with a large decrease in entropy. The first intermediate is significantly populated at equilibrium and resembles the final complex both structurally and energetically. It is postulated that both this intermediate and the final complex bind transcription factor IIB in the second step of pol II pre-initiation complex assembly. A consequence of such a reactive intermediate is that the rate of assembly of transcriptionally competent pre-initiation complexes from bi-directionally bound TBP is greatly increased. PMID:10373370

Parkhurst, K M; Richards, R M; Brenowitz, M; Parkhurst, L J

1999-06-25

367

Controlling Elastic Instabilities: From Complex Pattern Formation to Functionality  

NASA Astrophysics Data System (ADS)

Exploiting elastic instability in thin films has proven a robust method for creating complex patterns and structures across a wide range of lengthscales. Even the simplest of systems, an elastic membrane with a lattice of pores, under stress, generates a plethora of complex patterns featuring long-range orientational order. Harnessing the underlying elastic instability allows for the rational design of materials with highly desirable properties: from a film with a switchable photonic bandgap to a material with a negative Poisson ratio. Within the framework of linear elasticity, we model the system as a lattice of interacting deformation elements, or ``dislocation dipoles,'' which captures the configuration and orientational order present in any conceivable deformation of the system. In addition, when we promote this system to a curved surface, a novel set of features, patterns and broken symmetries appears.

Matsumoto, Elisabetta; Kamien, Randall

2010-03-01

368

Hydrophobic core formation in protein complex of cathepsin.  

PubMed

The "fuzzy oil drop" model assumes that the idealized hydrophobic core in a protein body can be described by a 3D Gauss function. The structure of the 1ICF protein (cathepsin), which participates in the proteolysis process and has cysteine-type peptidase activity, has been analyzed on the basis of the "fuzzy oil drop" model. The authors have determined the contribution of individual exon fragments to the creation of a common hydrophobic core and assessed the involvement of each chain in this process, depending on the number of complexed chains. Quantitative assessment of exons, chains, dimers, and the whole complex suggest that each of these units plays a different role in shaping the protein's hydrophobic core. PMID:23826628

Piwowar, Monika; Banach, Mateusz; Konieczny, Leszek; Roterman, Irena

2014-07-01

369

Contributions to the Sudbury Igneous Complex and the Depth of Excavation: Evidence from Onaping Formation Zircon  

NASA Astrophysics Data System (ADS)

U-Pb data for zircon preserved in the crater-fill sequence (Onaping Formation) of the Sudbury impact structure reveal a previously unrecognized but significant contributor to the Sudbury Igneous Complex.

Petrus, J. A.; Ayer, J. A.; Long, D. G. F.; Lightfoot, P. C.; Kamber, B. S.

2013-08-01

370

Formation of ruthenium thiolates via complexes of molecular hydrogen  

SciTech Connect

RuH[sub 2](DMPE)[sub 2][DMPE = 1,2-bis(dimethylphosphino)ethane] was synthesized by reduction of trans-RuCl[sub 2](DMPE)[sub 2] with sodium/2-propanol. Protonation of RuH[sub 2](DMPE)[sub 2] with weak organic acids such as methanol, ethanol, and thiols affords the molecular hydrogen complex trans-[RuH([eta][sup 2]-H[sub 2])(DMPE)[sub 2

Field, L.D.; Hambley, T.W.; Yau, B.C.K. (Univ. of Sydney, Sydney (Australia))

1994-04-27

371

New silane-induced CO activation in [({eta}{sup 5}-H{sub 3}CC{sub 5}H{sub 4})Mn(CO){sub 2}{lg_bullet}THF]: Formation of the cyclic bis({mu}-carbyne) complex ({eta}{sup 5}-H{sub 3}CC{sub 5}H{sub 4})(CO)Mn({mu}-COSiH(t-Bu){sub 2}){sub 2}Mn(CO)({eta}{sup 5}-H{sub 3}CC{sub 5}H{sub 4}) and the CC-coupling reaction of the siloxy-carbyne ligands  

SciTech Connect

The labile complex [({eta}{sup 5}-H{sub 3}CC{sub 5}H{sub 4})Mn(CO){sub 2}{lg_bullet}THF] (6) is generated by photolysis of ({eta}{sup 5}-H{sub 3}CC{sub 5}H{sub 4})Mn(CO){sub 3} (5) and subjected to oxidative addition reactions with various silanes. With (t-Bu){sub 2}SiHCl (7) the cyclic bis({mu}-carbyne) complex ({eta}{sup 5}-H{sub 3}CC{sub 5}H{sub 4})(CO)Mn({mu}-COSiH(t-Bu){sub 2}){sub 2}Mn(CO)({eta}{sup 5}H{sub 4}) (8) is formed in 15% yield. A systematic investigation of the product distribution in these reactions shows that the formation of bis({mu}-carbyne) complexes versus silylmetal hydrides is a strong function of the substituents at the silane. A single-crystal X-ray structure determination of 8 shows a cyclic four-membered ring structure with a bond distance Mn-C15 (carbyne C) of 1.857 (2) A. The metallacycle is folded along the Mn-Mn bond (2.565 (1) A) which is in accordance with an all-trans geometry of the ring substituents. This ring geometry opens up a reaction pathway for 1,3-cis elimination reaction of bis(siloxy)ethyne [(t-Bu){sub 2}HSiOC{triple_bond}]{sub 2} (9) via a CC-coupling reaction of both carbyne units as C2/c, {alpha} = 31.283 (3) A, B = 8.350 (1) A, c = 16.312 (2) A, {Beta} =126.63 (1){degrees}, Z = 8. 28 refs., 3 figs., 6 tabs.

Handwerker, H.; Beruda, H.; Kleine, M.; Zybill, C. [Technische Universitaet Muncheen (Germany)

1992-11-01

372

Hybrid NS ligands supported Cu(I)/(II) complexes for azide-alkyne cycloaddition reactions.  

PubMed

Three copper complexes of nitrogen-sulfur donor ligands, [CuBr?(L1)] (1), [CuCl?(L2)?] (2) and [Cu?I?(L3)]n (3) (L1 = bis(2-cyclohexylsulfanylethyl)amine, L2 = 2-(benzylsulfanylmethyl)pyridine and L3 = 2-(4-pyridylsulfanylmethyl)pyridine), have been synthesized and characterized by single-crystal X-ray diffraction (XRD), powder XRD and TGA analysis. Complexes 1 and 2 are mononuclear Cu(II) complexes and are EPR active with distorted square-pyramidal and octahedral geometry, respectively. Complex 3 is a two-dimensional tetrahedral Cu(I) coordination polymer with 16- and 20-membered metallocycles. These complexes show good catalytic activities for one-pot azide-alkyne cycloaddition reactions in CH?OH-H?O. PMID:23817835

Bai, Shi-Qiang; Jiang, Lu; Zuo, Jing-Lin; Hor, T S Andy

2013-08-21

373

Decay of activity complexes and the formation of coronal holes  

NASA Astrophysics Data System (ADS)

Analysis of long-term measurements of solar magnetic fields and the flux of UV radiation from the Sun indicates a cause-effect relationship between activity complexs, their residual magnetic fields, and coronal holes. A comparison of the background magnetic fields of the Sun and the evolution of former activity complexes reveals unipolar magnetic regions that form after the decay of these complexes. The latitude and time evolution of unipolar magnetic regions in solar cycles 21-24 is studied. A North-South asymmetry in solar activity is manifest in the distribution of unipolar regions migrating toward higher latitudes. It is shown that, when residual magnetic fields of the opposite polarity reach the polar regions, this leads to a sign change of the polar magnetic field and a decrease in the area of polar coronal holes, or even their complete disappearance. These interactions can explain the triple sign change of the polar magnetic field of the Sun in cycle 21 and the short-term polarity reversals observed in 2010 and 2011.

Mordvinov, A. V.; Yazev, S. A.

2013-06-01

374

Cu(II) complex formation by ACES buffer.  

PubMed

ACES (N-(2-Acetamido)-2-aminoethanesulfonic acid), a popular Good's buffer, binds Cu(II) ions with a moderate affinity. Although this interaction was the subject of previous studies, no consensus in the literature was found. We used potentiometry to establish binding constants, and controlled the potentiometric model selection and binding constant calculations by UV-vis spectroscopy. As a result, we obtained a consistent set of complex stoichiometries and binding constants in this system, which contains Cu(2+), CuL(+), CuL2, CuH-1L2(-1) and CuH(-)2L2(-2) complexes. The negative indexes at H atoms in these formulae denote the Cu(II) assisted deprotonation of the amide nitrogen present in the ACES molecule. The affinity of ACES for Cu(II) strongly depends on the concentration and ACES:Cu(II) ratio, reaching submicromolar apparent affinities at ratios higher than 100. These results will enable more accurate determinations of biologically relevant stability constants of Cu(II) complexes using ACES buffer. PMID:24077022

Zawisza, Izabela; Rózga, Ma?gorzata; Pozna?ski, Jaros?aw; Bal, Wojciech

2013-12-01

375

Structural Basis of Clostridium perfringens Toxin Complex Formation  

SciTech Connect

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.

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

2008-01-01

376

Grain boundary diffusion induced reaction layer formation in Fe/Pt thin films  

NASA Astrophysics Data System (ADS)

The solid-state reaction in Pt(15 nm)/Fe(15 nm) and Pt(15 nm)/Ag(10 nm)/Fe(15 nm) thin films after post-annealing at 593 K and 613 K for different annealing times has been studied. The structural properties of these samples were investigated by various methods including depth profiling with secondary neutral mass spectrometry, transmission electron microscopy, and X-ray diffraction. It is shown that after annealing at the above temperatures where the bulk diffusion processes are still frozen, homogeneous reaction layers of FePt and FePt with about 10 at.% Ag, respectively, have been formed. Corresponding depth profiles of the element concentrations revealed strong evidence that the formation mechanism is based on a grain boundary diffusion induced solid-state reaction in which the reaction interfaces sweep perpendicularly to the original grain boundary. Interestingly, X-ray diffraction indicated that in both thin-film systems after the solid-state reaction the ordered L10 FePt phase, which is the requested phase for future magnetic data storage applications, is also present.

Katona, G. L.; Vladymyrskyi, I. A.; Makogon, I. M.; Sidorenko, S. I.; Kristály, F.; Daróczi, L.; Csik, A.; Liebig, A.; Beddies, G.; Albrecht, M.; Beke, D. L.

2014-04-01

377

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

NASA Astrophysics Data System (ADS)

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 the relict minerals, and the other is the high-Mg#(96-98) type, which shows distinctly higher-Mg# than the relict minerals. The low-Mg# type occurs around the relicts and in bustite, while the high-Mg# type composed the most part of the mesh texture. Phase diagrams for serpentinite in the model system MgO-FeO-SiO2-O-H are calculated using internally consistent thermodynamic-dataset for the rock forming minerals and fluid. The diagrams show multistage formation of serpentinite, and yield constraints for equilibrium fH2 in each stage from the mineral compositions and corresponding reactions.

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

2012-12-01

378

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

PubMed

Mg and Ca ?-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

Butera, Valeria; Russo, Nino; Sicilia, Emilia

2014-05-12

379

Tube formation by complex cellular processes in Ciona intestinalis notochord  

PubMed Central

In the course of embryogenesis multicellular structures and organs are assembled from constituent cells. One structural component common to many organs is the tube, which consists most simply of a luminal space surrounded by a single layer of epithelial cells. The notochord of ascidian Ciona forms a tube consisting of only 40 cells, and serves as a hydrostatic “skeleton” essential for swimming. While the early processes of convergent extension in ascidian notochord development have been extensively studied, the later phases of development, which include lumen formation, have not been well characterized. Here we used molecular markers and confocal imaging to describe tubulogenesis in the developing Ciona notochord. We found that during tubulogenesis each notochord cell established de novo apical domains, and underwent a mesenchymal-epithelial transition to become an unusual epithelial cell with two opposing apical domains. Concomitantly, extracellular luminal matrix was produced and deposited between notochord cells. Subsequently, each notochord cell simultaneously executed two types of crawling movements bi-directionally along the anterior/posterior axis on the inner surface of notochordal sheath. Lamellipodia-like protrusions resulted in cell lengthening along the anterior/posterior axis, while the retraction of trailing edges of the same cell led to the merging of the two apical domains. As a result, the notochord cells acquired endothelial-like shape and formed the wall of the central lumen. Inhibition of actin polymerization prevented the cell movement and tube formation. Ciona notochord tube formation utilized an assortment of common and fundamental cellular processes including cell shape change, apical membrane biogenesis, cell/cell adhesion remodeling, dynamic cell crawling, and lumen matrix secretion.

Dong, Bo; Horie, Takeo; Denker, Elsa; Kusakabe, Takehiro; Tsuda, Motoyuki; Smith, William C.; Jiang, Di

2009-01-01

380

Thermodynamics of Cationic Lipid-DNA Complex Formation as Studied by Isothermal Titration Calorimetry  

Microsoft Academic Search

The detailed analysis of the cationic lipid-DNA complex formation by means of isothermal titration calorimetry is presented. Most experiments were done using 1,2-dioleyl-sn-glycero-3-ethylphosphocholine (EDOPC), but basic titrations were also done using DOTAP, DOTAP:DOPC, and DOTAP:DOPE mixtures. Complex formation was endothermic with less than 1kcal absorbed per mole of lipid or DNA charge. This enthalpy change was attributed to DNA-DNA mutual

Edwin Pozharski; Robert C. MacDonald

2002-01-01

381

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

NASA Astrophysics Data System (ADS)

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 fluid-rock interaction in a short-lived fluid flow event, such as that can occur during a seismic cycle. Subsequent interpretation of the complex zoning patterns to reflect the evolution of bulk fluid would not only be extremely complex but also erroneous.

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

2014-05-01

382

A reaction-diffusion mechanism influences cell lineage progression as a basis for formation, regeneration, and stability of intestinal crypts  

PubMed Central

Background Colon crypts, a single sheet of epithelia cells, consist of a periodic pattern of stem cells, transit-amplifying cells, and terminally differentiated cells that constantly renew and turnover. Experimental evidence suggests that Wnt signaling promotes and regulates stem cell division, differentiation, and possible cell migrations while intestinal BMP signaling inhibits stem cell self-renewal and repression in crypt formation. As more molecular details on Wnt and BMP in crypts are being discovered, little is still known about how complex interactions among Wnt, BMP, and different types of cells, and surrounding environments may lead to de novo formation of multiple crypts or how such interactions affect regeneration and stability of crypts. Results We present a mathematical model that contains Wnt and BMP, a cell lineage, and their feedback regulations to study formation, regeneration, and stability of multiple crypts. The computational explorations and linear stability analysis of the model suggest a reaction–diffusion mechanism, which exhibits a short-range activation of Wnt plus a long-range inhibition with modulation of BMP signals in a growing tissue of cell lineage, can account for spontaneous formation of multiple crypts with the spatial and temporal pattern observed in experiments. Through this mechanism, the model can recapitulate some distinctive and important experimental findings such as crypt regeneration and crypt multiplication. BMP is important in maintaining stability of crypts and loss of BMP usually leads to crypt multiplication with a fingering pattern. Conclusions The study provides a mechanism for de novo formation of multiple intestinal crypts and demonstrates a synergetic role of Wnt and BMP in regeneration and stability of intestinal crypts. The proposed model presents a robust framework for studying spatial and temporal dynamics of cell lineages in growing tissues driven by multiple signaling molecules.

2012-01-01

383

Indene formation from alkylated aromatics: kinetics and products of the fulvenallene + acetylene reaction.  

PubMed

A novel reaction is described for formation of the polyaromatic hydrocarbon (PAH) indene in aromatic flames, via the reaction of fulvenallene with acetylene (C2H2). Fulvenallene has been recently identified as the major decomposition product of the benzyl radical, the dominant intermediate in the oxidation of alkylated aromatic hydrocarbons, yet it is not presently included in kinetic models for aromatic oxidation or PAH/soot formation. Ab initio calculations with the G3B3 theoretical method show that acetylene adds to fulvenallene with a barrier of around 27 kcal mol(-1). This forms an activated C9H8 adduct that can rearrange to indene and dissociate to 1-indenyl + H with energy barriers below that of the entrance channel. Master equation simulations across a range of temperature and pressure conditions demonstrate that for temperatures relevant to combustion indene is the dominant product at high pressures while 1-indenyl + H dominate at lower pressures. At low to moderate temperatures, the production of collision stabilized cyclopentadiene-fulvene intermediates is also significant. The results presented in this study provide a new pathway to cyclopenta-fused PAHs in aromatic combustion and are expected to improve modeling of PAH and soot formation. The formation of cyclopenta-fused C5-C6 structures is required to describe the flame synthesis of carbon nanoparticles like fullerenes and buckybowls (corannulene). Improved rate expressions are also reported for the 1-indenyl + H --> indene association reaction, and for the reverse dissociation, from variational transition state theory calculations. The new rate constants are significantly different than current estimates, primarily due to a re-evaluation of the indene C-H bond dissociation energy. PMID:19603772

da Silva, Gabriel; Bozzelli, Joseph W

2009-08-01

384

Synthesis and stability of new hexaazamacrocyclic dinuclear cobalt complexes and its oxidation reactions  

Microsoft Academic Search

Homodinuclear cobalt complexes with a new 26-membered unsymmetric macrocyclic ligand: 3,6,10,18,22,25,-hexaaza-31,32-dihydroxy-14,29-dimethyl-tricyclo[25,3,1,111,17] dotriaconta-l(30),12,14,16(32),27,28-hexaene (L or BTBP), have been synthesized and characterized with elemental analysis, FAB-MS and X-ray. The ligand maintains preorganized dinuclear integrity for cobalt(II) complexes, while facilitating the formation of non-bridged dicobalt centers. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear complexes are formed with Co(II)

Deyuan Kong; Jianggao Mao; Arthur E Martell; Abraham Clearfield

2002-01-01

385

Chemical complexity and star-formation in merging galaxies  

NASA Astrophysics Data System (ADS)

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.

Davis, T. A.; Heiderman, A.; Iono, D.; VIXENS Team

2013-03-01

386

Regioselective Intermolecular Coupling Reaction of Arylketones and Alkenes Involving C-H Bond Activation Catalyzed by an In-Situ Formed Cationic Ruthenium-Hydride Complex  

PubMed Central

The cationic ruthenium-hydride complex, formed in-situ from the treatment of the tetranuclear ruthenium-hydride complex {[(PCy3)(CO)RuH]4(?4-O)(?3-OH)(?2-OH)} with HBF4·OEt2, was found to be a highly effective catalyst for the intermolecular coupling reaction of arylketones and 1-alkenes to give the substituted indene and ortho-C–H insertion products. The formation of the indene products was resulted from the initial alkene isomerization followed by regioselective ortho-C–H insertion of 2-alkene and the dehydrative cyclization. The preliminary mechanistic studies revealed a rapid and reversible ortho-C–H bond activation followed by the rate-limiting C–C bond formation step for the coupling reaction.

Yi, Chae S.; Lee, Do W.

2009-01-01

387

Genesis of coordinatively unsaturated palladium complexes dissolved from solid precursors during Heck coupling reactions and their role as catalytically active species.  

PubMed

The Forum Article critically summarizes investigations and discussions on the nature and role of potential active species in C-C coupling reactions of the Heck type using catalyst systems with "ligand-free" inorganic salts, simple inorganic complexes, and supported and nonsupported (colloidal) Pd particles. From a series of experiments and reports, it can be concluded that the "active species" is generated in situ in catalytic systems at higher temperature conditions (>100 degrees C). In all heterogeneous systems with solid Pd catalysts, Pd is dissolved from the solid catalyst surface under reaction conditions by a chemical reaction (complex formation and/or oxidative addition of the aryl halide), forming extremely active coordinatively unsaturated Pd species. Pd is partially or completely redeposited onto the support at the end of the reaction when the aryl halide is used up. The Pd dissolution-redeposition processes correlate with the reaction rate and are strongly influenced by the reaction conditions. Skilled preparation of the catalyst and careful adjustment of the reaction conditions allowed the development of highly active heterogeneous catalysts (Pd/C, Pd/metal oxide, and Pd/zeolite), converting aryl bromides and aryl chlorides in high yields and short reaction times. Reaction conditions have been developed allowing the conversion of bromobenzene with turnover numbers (TONs) of 10(7) and even of unreactive aryl chlorides (chlorobenzene and chlorotoluene) in high yields with simple "ligand-free" Pd catalyst systems like PdCl2 or Pd(OH)2 in the absence of any organic ligand. Simple coordinatively unsaturated anionic palladium halide (in particular, bromo) complexes [PdXn](m-) play a crucial role as precursor and active species in all ligand-free and heterogeneous catalyst systems and possibly in Heck reactions at all. PMID:17348718

Köhler, Klaus; Kleist, Wolfgang; Pröckl, Sandra S

2007-03-19

388

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

PubMed

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

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

2008-08-13

389

Landscape complexity influences route-memory formation in navigating pigeons.  

PubMed

Observations of the flight paths of pigeons navigating from familiar locations have shown that these birds are able to learn and subsequently follow habitual routes home. It has been suggested that navigation along these routes is based on the recognition of memorized visual landmarks. Previous research has identified the effect of landmarks on flight path structure, and thus the locations of potentially salient sites. Pigeons have also been observed to be particularly attracted to strong linear features in the landscape, such as roads and rivers. However, a more general understanding of the specific characteristics of the landscape that facilitate route learning has remained out of reach. In this study, we identify landscape complexity as a key predictor of the fidelity to the habitual route, and thus conclude that pigeons form route memories most strongly in regions where the landscape complexity is neither too great nor too low. Our results imply that pigeons process their visual environment on a characteristic spatial scale while navigating and can explain the different degrees of success in reproducing route learning in different geographical locations. PMID:24451267

Mann, Richard P; Armstrong, Chris; Meade, Jessica; Freeman, Robin; Biro, Dora; Guilford, Tim

2014-01-01

390

B-H bond activation using an electrophilic metal complex: insights into the reaction pathway.  

PubMed

A highly electrophilic ruthenium center in the [RuCl(dppe)(2)][OTf] complex brings about the activation of the B-H bond in ammonia borane (H(3)N·BH(3), AB) and dimethylamine borane (Me(2)HN·BH(3), DMAB). At room temperature, the reaction between [RuCl(dppe)(2)][OTf] and AB or DMAB results in trans-[RuH(?(2)-H(2))(dppe)(2)][OTf], trans-[RuCl(?(2)-H(2))(dppe)(2)][OTf], and trans-[RuH(Cl)(dppe)(2)], as noted in the NMR spectra. Mixing the ruthenium complex and AB or DMAB at low temperature (198/193 K) followed by NMR spectral measurements as the reaction mixture was warmed up to room temperature allowed the observation of various species formed enroute to the final products that were obtained at room temperature. On the basis of the variable-temperature multinuclear NMR spectroscopic studies of these two reactions, the mechanistic insights for B-H bond activation were obtained. In both cases, the reaction proceeds via an ?(1)-B-H moiety bound to the metal center. The detailed mechanistic pathways of these two reactions as studied by NMR spectroscopy are described. PMID:23244598

Kumar, Rahul; Jagirdar, Balaji R

2013-01-01

391

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

NASA Astrophysics Data System (ADS)

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.

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

2010-09-01

392

Monitoring benzene formation from benzoate in model systems by proton transfer reaction-mass spectrometry  

NASA Astrophysics Data System (ADS)

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